JP2018113167A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which is superior in storability and charge and discharge cycle characteristics.SOLUTION: A lithium ion secondary battery comprises a negative electrode, a positive electrode, a separator and a nonaqueous electrolyte solution which are encased in an outer packaging body. In the lithium ion secondary battery, a negative electrode mixture layer includes a Si-containing material S as a negative electrode active material. The negative electrode mixture layer includes a particular copolymer as a binder. In the negative electrode mixture layer, the content of the copolymer is 2-15 mass%. To the nonaqueous electrolyte solution, at least a fluorine-containing compound and a compound of a particular composition are added.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a lithium ion secondary battery excellent in storability and cycle characteristics.

  Lithium ion secondary batteries, which are one type of electrochemical element, are considered to be applied to portable devices, automobiles, electric tools, electric chairs, household and commercial power storage systems because of their high energy density. Yes. In particular, as a portable device, it is widely used as a power source for a mobile phone, a smartphone, or a tablet PC.

  In addition, lithium ion secondary batteries are required to improve various battery characteristics as well as to increase the capacity in accordance with the spread of applied devices. Since it is a secondary battery especially, the improvement of a charge / discharge cycle characteristic is calculated | required strongly.

Usually, a carbon material such as graphite capable of inserting and removing lithium (Li) ions is widely used as a negative electrode active material of a lithium ion secondary battery. On the other hand, Si or Sn as a material capable of inserting and desorbing more Li ions, or a material containing these elements has been studied, and especially SiO _x having a structure in which Si fine particles are dispersed in SiO ₂ has attracted attention. Yes. Further, since these materials have low conductivity, a structure in which the surface of particles is covered with a conductor such as carbon has been proposed (Patent Documents 1 and 2).

  In Patent Document 3, a copolymer of vinyl alcohol and an alkali metal neutralized ethylenically unsaturated carboxylic acid is used as a binder for the negative electrode mixture layer, so that the negative electrode active material is removed and the negative electrode mixture layer is collected. A technique for suppressing peeling from an electric body has been proposed.

  Patent Document 4 proposes a lithium secondary battery in which the outer package is a rectangular can and includes a compound represented by the following general formula (3).

Japanese Patent Laying-Open No. 2015-65163 Japanese Patent Laid-Open No. 2006-46151 JP 2006-170945 A Japanese Patent Laid-Open No. 2006-72119

  In the above lithium ion secondary battery, there is still room for improvement in improving storage characteristics and cycle characteristics. In particular, there is room for improvement particularly in a laminate-type lithium ion secondary battery that has been widely used as an exterior body in recent years.

  This invention is made | formed in view of the said situation, and is providing the lithium ion secondary battery excellent in the storage characteristic and cycling characteristics.

  The present invention is a lithium ion secondary battery in which a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a positive electrode, a separator, and a nonaqueous electrolyte solution are contained in an outer package, and the negative electrode mixture layer includes Contains a material S containing Si as a negative electrode active material, and the negative electrode mixture layer includes a copolymer having a unit represented by the following formula (1) and a unit represented by the following formula (2). The content of the copolymer in the negative electrode mixture layer is 2 to 15% by mass, and the non-aqueous electrolyte is a fluorine-containing compound and a compound represented by the following general formula (3) A lithium ion secondary battery characterized in that at least is added.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery excellent in the storage characteristic and cycling characteristics can be provided.

It is a top view showing an example of the positive electrode of this invention. It is a top view showing an example of the negative electrode of this invention. It is a perspective view which represents typically an example of the laminated electrode body of this invention. It is a perspective view showing an example of the 3rd electrode of the present invention. It is the perspective view which assembled FIG. 3 and FIG. It is a top view showing an example of the lithium ion secondary battery of this invention. It is II sectional drawing of FIG.

  As the negative electrode according to the lithium ion secondary battery of the present invention, one having a structure in which a negative electrode mixture layer containing a negative electrode active material, a binder or the like is provided on one side or both sides of a current collector is used.

  The negative electrode active material in the present invention contains a material S that is a negative electrode material containing Si. It is known that Si is introduced into Li ions by alloying with Li, but at the same time, it is also known that the volume expansion upon introduction of Li is large.

  The material S containing Si exhibits a capacity of 1000 mAh / g or more, and is characterized by significantly exceeding 372 mAh / g, which is called the theoretical capacity of graphite. On the other hand, compared with the charge / discharge efficiency (90% or more) of general graphite, the material S containing Si often has an initial charge / discharge efficiency of less than 80%, and the irreversible capacity increases, so there is a problem in cycle characteristics. It was. Therefore, it is desired to introduce a Li source into the negative electrode in advance.

  In the material S, the volume change of the negative electrode mixture layer occurs due to the expansion and contraction of the particles due to repeated charge and discharge, thereby causing the separator to move, and the adhesion between the positive electrode and the negative electrode is lowered, resulting in capacity deterioration for each cycle. There was a twist. In particular, when the above-described Li source was introduced into the negative electrode in advance, the tendency was prominent.

  Therefore, the inventor has found that the cycle characteristics are improved by adding the compound represented by the general formula (3) described above to the non-aqueous electrolyte. The compound represented by the general formula (3) described above reacts with hydrogen fluoride (HF), which is an inevitable impurity derived from a fluorine-containing compound that is also added to the non-aqueous electrolyte, and undergoes a polymerization reaction in the first charge / discharge. Has the effect of gelling the non-aqueous electrolyte. It is presumed that the adhesion between the positive electrode and the negative electrode and the separator is improved and the cycle characteristics are improved by the non-aqueous electrolyte becoming a gel.

The material S is a negative electrode material containing Si. For example, a material in which Si powder and carbon are combined, a material further coated with a carbon material, a material in which Si powder is sandwiched between graphene or scaly graphite, SiO _x containing Si and O as constituent elements (however, for Si The atomic ratio x of O is 0.5 ≦ x ≦ 1.5. Among these, it is preferable to use a material containing SiO _x .

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, the SiO _x to SiO ₂ matrix of amorphous Si (e.g., microcrystalline Si) is include the dispersed structure, the SiO ₂ of the amorphous, dispersed therein It is only necessary that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

The material S containing Si is preferably a composite that is combined with a carbon material. For example, the surface of SiO _x is preferably covered with the carbon material. Usually, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. If complexes complexed with carbon material SiO _x, for example, simply than with a material obtained by mixing a conductive material such as SiO _x and the carbon material, good conductive network in the negative electrode Formed.

That is, the specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, whereas the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm, and SiO _x and carbon By combining the material, the conductivity of SiO _x can be improved.

The complex with the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, granulated material or the like between the SiO _x and the carbon material can be cited.

Preferred examples of the carbon material that can be used for forming a composite with the SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

Details of the carbon material include at least selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. One material is preferred. A fibrous or coiled carbon material is preferable in that it easily forms a conductive network and has a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and the SiO _x particles expand and contract. However, it is preferable in that it has a property of easily maintaining contact with the particles.

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable as a material used when the composite with SiO _x is a granulated body. The fibrous carbon material has a thin thread shape and high flexibility so that it can follow the expansion and contraction of SiO _x that accompanies charging / discharging of the battery, and because of its large bulk density, it has a large amount of SiO _x particles. It is because it can have the following junction point. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is SiO _x : 100 parts by weight from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. On the other hand, the carbon material is preferably 5 parts by weight or more, and more preferably 10 parts by weight or more. In the composite, if the ratio of the carbon material to be composited with SiO _x is too large, the amount of SiO _x in the negative electrode mixture layer may be reduced, and the effect of increasing the capacity may be reduced. The carbon material is preferably 50 parts by weight or less and more preferably 40 parts by weight or less with respect to SiO _x : 100 parts by weight.

The composite of the above SiO _x and carbon material can be obtained by, for example, the following method.

When the surface of SiO _x is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon gas are heated in the gas phase, and are generated by thermal decomposition of the hydrocarbon gas. Carbon is deposited on the surface of the particles. Thus, according to the vapor deposition (CVD) method, a hydrocarbon-based gas spreads to every corner of the SiO _x particle, and a thin and uniform film (carbon material) containing a conductive carbon material on the surface of the particle. Since the coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with the carbon material, the processing temperature (atmosphere temperature) of the CVD method varies depending on the type of hydrocarbon-based gas, but usually 600 to 1200 ° C. is suitable. It is preferable that it is higher than ℃, and more preferable that it is higher than 800 ℃. This is because the higher the treatment temperature, the fewer impurities remain and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

Further, when a granulated body of SiO _x and a carbon material is prepared, a dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, sprayed and dried to obtain a granulated body including a plurality of particles. Make it. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. In addition to the above method, a granulated body of SiO _x and a carbon material can be produced also by a granulating method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

  If the average particle size of the material S is too small, the dispersibility of the material S may be reduced, and the effects of the present invention may not be sufficiently obtained, and the material S has a large volume change associated with charging / discharging of the battery. If the average particle diameter is too large, the material S is likely to collapse due to expansion / contraction (this phenomenon leads to capacity degradation of the material S), and therefore it is preferably 0.1 μm or more and 10 μm or less.

  The content ratio of the material S in the negative electrode mixture layer with respect to the total negative electrode active material is preferably 5% by mass or more, more preferably 10% by mass or more, and most preferably 50% by mass or more. As described above, the material S is a material that can realize a dramatic increase in capacity compared to graphite. Therefore, if the material S is contained even in a small amount in the negative electrode active material, an effect of improving the capacity of the battery can be obtained. On the other hand, the material S is preferably 10% by mass or more with respect to the front negative electrode active material in order to achieve a dramatic increase in battery capacity. The content of the material S may be adjusted in accordance with various battery uses and required characteristics. In addition, although the content ratio of the material S with respect to all the negative electrode active materials can also be made into 100 mass% (that is, all negative electrode active materials are material S), content of the material S in the case of using together with negative electrode active materials other than the material S is included. The ratio is 99% by mass or less, preferably 90% by mass or less, more preferably 80% by mass or less.

  In addition to the material S described above, the negative electrode of the present invention may be used in combination with a carbon material capable of electrochemical storage and release of Li, such as graphite. In the case of using graphite for the negative electrode, in order to suppress the reactivity with propylene carbonate, for example, graphite in which the surface of natural graphite is coated with resin, or graphite in which the surface of graphite particles is coated with amorphous carbon Etc. are suitable.

Specifically, the graphite in which the surface of the graphite particles is coated with amorphous carbon is a peak intensity ratio appearing at 1340 to 1370 cm ⁻¹ with respect to a peak intensity appearing at 1570 to 1590 cm ⁻¹ in an argon ion laser Raman spectrum. It is graphite with a certain R value of 0.1 to 0.7. The R value is more preferably 0.3 or more in order to ensure a sufficient coating amount of amorphous carbon. Moreover, since an irreversible capacity | capacitance will increase if there is too much coating amount of amorphous carbon, R value is 0.6 or less. Such graphite B uses, for example, natural graphite having d ₀₀₂ of 0.338 nm or less or graphite obtained by spherically shaping artificial graphite as a base material (base particle), and the surface thereof is coated with an organic compound. It can be obtained by calcining at 0 ° C., pulverizing, and sizing through a sieve. The organic compound covering the base material includes aromatic hydrocarbons; tars or pitches obtained by polycondensation of aromatic hydrocarbons under heat and pressure; tars mainly composed of a mixture of aromatic hydrocarbons. , Pitch or asphalt; In order to coat the base material with the organic compound, a method of impregnating and kneading the base material into the organic compound can be employed. It can also be produced by a vapor phase method in which a hydrocarbon gas such as propane or acetylene is carbonized by pyrolysis and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less.

  Furthermore, the graphite has high Li ion acceptability (for example, it can be quantified by the ratio of the constant current charge capacity to the total charge capacity). Therefore, the lithium ion secondary battery when graphite is used in combination has good acceptability of Li ions and good charge / discharge cycle characteristics. As described above, when the Li source is introduced into the negative electrode containing the material S by electrochemical contact (short circuit), if the graphite is used in combination, non-uniformity of Li introduction can be suppressed and battery characteristics can be suppressed. It is thought that this can be improved.

  In addition, when the particle diameter of the graphite is too small, the specific surface area is excessively increased (the irreversible capacity is increased). Therefore, it is preferable that the particle diameter is not so small. Therefore, it is preferable to use graphite having an average particle diameter of 8 μm or more.

The average particle size of graphite is determined by, for example, dispersing the graphite in a medium that does not dissolve or swell the graphite using a laser scattering particle size distribution analyzer (for example, Microtrack particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd.). The 50% diameter value (D _50% ) median diameter in the volume-based integrated fraction when the integrated volume is determined from particles having a small particle size distribution measured in the above.

The specific surface area of graphite (according to the BET method, such as “Bellethorpe mini” manufactured by Nippon Bell Co., Ltd.) is preferably 1.0 m ² / g or more, and is 5.0 m ² / g or less. It is preferable.

  Moreover, negative electrode active materials other than the above-described material S and graphite can also be used as the negative electrode active material to the extent that the effects of the present invention are not impaired.

  For the binder of the negative electrode mixture layer, a copolymer having a unit represented by the formula (1) and a unit represented by the formula (2) [hereinafter referred to as “copolymer (A)”] is used. To do.

When the copolymer (A) is used as a binder, the load characteristics of the battery are improved even when the density of the negative electrode mixture layer is set to a high value as described later and the thickness is set to a large value as described later. be able to. The reason is not clear, but in the negative electrode mixture layer using the binder, it is thought that even if the density is increased, a structure that allows the nonaqueous electrolyte to permeate well is formed. Yes. In addition, since the copolymer (A) is excellent in flexibility and adhesiveness, even if a composite of SiO _x and a carbon material having a large expansion / contraction amount due to charging / discharging of the battery is used as the negative electrode active material, Detachment of the composite from the negative electrode mixture layer and separation between the negative electrode mixture layer and the current collector can be satisfactorily suppressed, and for example, charge / discharge cycle characteristics of the battery can be improved. Furthermore, by using the copolymer (A) as a binder, it is possible to highly suppress the precipitation of Li on the negative electrode surface that may occur with the use of the battery.

While the copolymer (A) is excellent in flexibility and adhesiveness, it has a high water absorption and is a compound containing moisture contained in the copolymer (A) and fluorine added to the non-aqueous electrolyte (for example, LiPF ₆ ), which is an electrolyte salt described later, reacts to generate HF. This HF has a problem of causing gas generation at a high temperature or reacting with the material S containing Si to significantly reduce the characteristics of the material S as a negative electrode active material. However, as described above, HF is consumed when the compound represented by the general formula (3) used in the present invention is polymerized, so that the characteristics of the material S containing Si as a negative electrode active material are suppressed from being reduced. I found that there is an effect.

  A copolymer (A) having vinyl alcohol and an alkali metal neutralized ethylenically unsaturated carboxylic acid is obtained by polymerizing vinyl ester and at least one of acrylic acid ester and methacrylic acid ester as monomers. The copolymer can be obtained by saponification.

  Examples of the vinyl ester for obtaining the copolymer (A) include vinyl acetate, vinyl propionate, and vinyl pivalate, and one or more of them can be used. Among these vinyl esters, vinyl acetate is more preferable.

  The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester for obtaining copolymer (A) is a unit derived from monomers other than vinyl ester, acrylic acid ester and methacrylic acid ester. You may have.

  The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester is a suspension in which polymerization is performed in a state where these monomers are suspended in an aqueous solution containing a polymerization catalyst and a dispersant, for example. Polymerization can be performed by a turbid polymerization method. As the polymerization catalyst at this time, organic peroxides such as benzoyl peroxide and lauryl peroxide; azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile; and the like can be used. In addition, the dispersant used in the suspension polymerization includes water-soluble polymers (polyvinyl alcohol, poly (meth) acrylic acid or a salt thereof, polyvinyl pyrrolidone, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), inorganic compounds (Calcium phosphate, magnesium silicate, etc.) can be used.

  The temperature at which the suspension polymerization is performed may be about -20 to + 20 ° C with respect to the 10-hour half-life temperature of the polymerization catalyst, and the polymerization time may be several hours to several tens of hours.

  Saponification of a copolymer of vinyl ester with at least one of acrylic acid ester and methacrylic acid ester uses an alkali (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.) containing an alkali metal, and is aqueous. It can be performed in a mixed solvent of an organic solvent and water. By this saponification, the unit derived from the vinyl ester becomes a unit in which a hydroxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the above formula (1)]. The unit derived from at least one monomer is a unit in which an alkali metal salt (group) of a carboxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the formula (2)]. Therefore, examples of M in the formula (2) include sodium, potassium, and lithium.

  Examples of the aqueous organic solvent used for saponification include lower alcohols (such as methanol and ethanol) and ketones (such as acetone and methyl ethyl ketone). The use ratio of the aqueous organic solvent and water is preferably 3/7 to 8/2 in terms of mass ratio.

  The temperature at the time of saponification should just be 20-60 degreeC, and the time in that case should just be about several hours.

  The saponified copolymer may be taken out from the reaction solution, washed, and then dried.

  The unit represented by the formula (1) of the copolymer (A) obtained through the saponification has a structure in which an unsaturated bond of vinyl alcohol is opened and polymerized, The unit represented by (2) is an acrylate or methacrylate (hereinafter referred to as “(meth) acrylate” collectively, and acrylic acid and methacrylic acid are collectively referred to as “(meth) A structure in which an unsaturated bond of “acrylic acid” is polymerized by opening. Therefore, the copolymer (A) uses vinyl alcohol or (meth) acrylate as a monomer and is not obtained by copolymerizing these, but for convenience, “vinyl alcohol and (meth) It may also be referred to as an acrylate salt [a copolymer of (meth) acrylic acid alkali metal neutralized product].

  In the copolymer (A), the composition ratio of the unit represented by the formula (1) and the unit represented by the formula (2) is the formula (1) when the total of these units is 100 mol%. Is preferably 5 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, and preferably 95 mol% or less, and 90 mol%. The following is more preferable. That is, when the total of the unit represented by the formula (1) and the unit represented by the formula (2) is 100 mol%, the ratio of the unit represented by the formula (2) is 5 mol% or more. Is preferably 10 mol% or more, more preferably 95 mol% or less, more preferably 50 mol% or less, and still more preferably 40 mol% or less.

  The content of the copolymer (A) in the negative electrode mixture layer suppresses the effects of its use (the effect of enhancing the load characteristics of the battery, the falling off of the negative electrode active material, and the peeling between the negative electrode mixture layer and the current collector). From the viewpoint of ensuring a good effect), it is 2% by mass or more, and preferably 5% by mass or more. However, if the amount of the copolymer (A) in the negative electrode mixture layer is too large, it becomes difficult to adjust the density of the negative electrode mixture layer to a value described later, and the capacity and load characteristics of the battery are reduced. There is a fear. Therefore, content of the copolymer (A) in a negative mix layer is 15 mass% or less, and it is preferable that it is 10 mass% or less.

  The content of the copolymer (A) in the negative electrode mixture layer suppresses the effects of its use (the effect of enhancing the load characteristics of the battery, the falling off of the negative electrode active material, and the peeling between the negative electrode mixture layer and the current collector). From the viewpoint of ensuring a good effect), it is 2% by mass or more, and preferably 5% by mass or more. However, if the amount of the copolymer (A) in the negative electrode mixture layer is too large, it becomes difficult to adjust the density of the negative electrode mixture layer to a value described later, and the capacity and load characteristics of the battery are reduced. There is a fear. Therefore, content of the copolymer (A) in a negative mix layer is 15 mass% or less, and it is preferable that it is 10 mass% or less.

  In the negative electrode mixture layer, together with the copolymer (A), a binder used in the negative electrode mixture layer of the negative electrode of the conventional lithium ion secondary battery, for example, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC) ), Polyvinylidene fluoride (PVDF), and the like can also be used. However, the content of the binder other than the copolymer (A) in the total amount of binder contained in the negative electrode mixture layer is preferably 50% by mass or less.

  A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon It is possible to use one or more materials such as fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (described in JP-A-59-20971). it can. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

  The negative electrode is prepared, for example, by preparing a negative electrode mixture-containing composition in which a negative electrode active material and a binder and, if necessary, a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. (However, the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per side of the current collector, and the density of the negative electrode mixture layer (from the mass and thickness of the negative electrode mixture layer per unit area laminated on the current collector) (Calculated) is preferably 1.0 g / cm ³ or more, more preferably 1.2 g / cm ³ or more in order to increase the capacity of the battery. In addition, if the density of the negative electrode mixture layer is too high, adverse effects such as a decrease in the permeability of the non-aqueous electrolyte solution occur, so 1.6 g / cm ³ or less is desirable. Moreover, as a composition of a negative mix layer, it is preferable that the quantity of a negative electrode active material is 80-99 mass%, for example, it is preferable that the quantity of a binder is 0.5-10 mass%, and a conductive support agent. When using, it is preferable that the quantity is 1-10 mass%.

  As a support (negative electrode current collector) for supporting the current collector of the negative electrode and the negative electrode mixture layer, for example, a foil made of copper or nickel can be used. Alternatively, a copper or nickel foil having a through hole penetrating from one surface of the negative electrode current collector to the other surface, a punching metal, a net, or an expanded metal may be used. The upper limit of the thickness of the negative electrode current collector is preferably 30 μm, and the lower limit is preferably 4 μm in order to ensure mechanical strength. If the current collector uses a foil having no through-holes, the contact area between the negative electrode mixture layer and the negative electrode current collector can be ensured. This is preferable because it can ensure sufficient strength.

  In the lithium ion secondary battery of the present invention, the surface of the negative electrode mixture layer is insulated without reacting with Li for the purpose of extending the cycle life or preventing Li from being deposited on the surface of the negative electrode mixture layer. A porous layer containing a functional material may be formed.

  As the insulating material that does not react with Li, there are no particular limitations on inorganic materials and organic materials, and inorganic materials such as alumina, silica, boehmite, titania and the like are preferable. In particular, if the plate-like material has an aspect ratio of 5 or more, the insulating material can be suitably oriented on the surface of the negative electrode mixture layer, and an appropriate curved path can be provided in the porous layer. A short circuit phenomenon can be suitably prevented, which is desirable.

  The porous layer only needs to contain an insulating material that does not react with the above-described Li. For example, the insulating material, a binder (for example, the above-described negative electrode binder), a dispersant, A thickener dispersed in a solvent can be applied to the negative electrode mixture layer and dried. The thickness of the porous layer is preferably 2 to 10 μm.

  For the positive electrode according to the lithium ion secondary battery of the present invention, for example, a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder is used on one or both sides of the positive electrode current collector. be able to.

The positive electrode active material used for the positive electrode is not particularly limited, and a generally usable active material such as a lithium-containing transition metal oxide may be used. Specific examples of the lithium-containing transition metal oxide include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _2. , etc. _{Li x Ni 1-y M y} O 2, Li x Mn y Ni z Co 1-y-z O 2, Li x Mn 2 O 4, Li x Mn 2-y M y O 4 are exemplified. However, in each structural formula above, M is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, Ti, Ge, and Cr, and 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 <z <1.0.

  The material S containing Si used as the negative electrode active material in the present invention is characterized in that it has a capacity of 1000 mAh / g or more and greatly exceeds 372 mAh / g, which is called the theoretical capacity of graphite. In addition, it is also known that the material S containing Si has a lower Li insertion potential during charging than the Li insertion potential during general graphite charging.

  In general, most lithium ion secondary batteries are charged by a constant current constant voltage charging (CC-CV) method. At the beginning of charging of a lithium ion secondary battery, charging is performed at a constant current (CC charging), and when the battery reaches a charging upper limit voltage, charging is performed so as to maintain a constant voltage (CV charging). In this CV charging, charging is performed with a current value much lower than the current value during CC charging. In recent lithium-ion secondary batteries, the charging upper limit voltage is often set between 4.2V and 4.7V.

  When the ratio of the material S containing Si in the negative electrode active material is increased by 5% by mass or more, Li is liable to precipitate during charging, which may be caused by battery swelling or capacity deterioration during high-temperature storage. there were. This is presumed to be as follows. When a lithium-ion secondary battery is charged with CC-CV, the Li ion is desorbed from the positive electrode and the battery voltage rises when charging in the CC mode, and the Li ion is inserted into the material S without any problem at the initial stage of charging. It will be done. When the charging in the CC mode progresses and the battery voltage approaches the charging upper limit voltage (CC mode end stage), the potential of the negative electrode approaches 0 V, and Li ions are accepted at the same time as accepting Li ions. It is considered that this deposited Li becomes a reaction active surface with the electrolytic solution, and particularly when stored at a high temperature, the electrolytic solution reacts to generate gas and causes the battery to swell.

  Therefore, it has been found that it is preferable to increase the resistance of the positive electrode during charging. As a result, the positive electrode potential in the CC mode becomes high and the battery voltage can be raised relatively. Therefore, the CC mode is switched from the end of the CC mode where Li deposition easily occurs to the CV mode, and the charge current is attenuated for polarization. It is considered that Li can be made difficult to precipitate at the negative electrode.

In particular, lithium cobalt oxide (Li _x CoO ₂ ) is used as a positive electrode active material, and the surface thereof is formed of an Al-containing oxide, and by increasing the resistance at the positive electrode during charging, the deposition of Li at the negative electrode is reduced. Even if the ratio of the material S containing SiOx is increased, it is possible to provide a lithium ion secondary battery that can suppress battery swelling and capacity deterioration during high-temperature storage.

The Al-containing oxide that coats the surface of lithium cobaltate inhibits the entry and exit of lithium ions in the positive electrode active material, and thus has, for example, an effect of reducing the load characteristics of the battery. By setting the average coating thickness of the battery to a specific value, it is possible to suppress the deterioration of the battery characteristics due to the coating with the Al-containing oxide. The lithium cobalt oxide in the positive electrode material acts as a positive electrode active material in the lithium ion secondary battery of the present invention. Lithium cobaltate is represented by the composition formula LiM ¹ O ₂ when Co and other elements that may be contained are grouped into an element group M ¹ .

In the lithium cobalt oxide, the element M ¹ has an effect of increasing the stability of the lithium cobalt oxide in the high voltage region and suppressing the elution of Co ions, and an effect of increasing the thermal stability of the lithium cobalt oxide. Also have.

In the lithium cobaltate, the amount of the element M ¹ is preferably such that the atomic ratio M ¹ / Co with Co is 0.003 or more from the viewpoint of more effectively exerting the above action, and is 0.008 or more. More preferably.

However, when the amount of the element M ¹ in the lithium cobalt oxide is too large, too small amounts of Co, there is a possibility can not be sufficient action by these. Therefore, in the lithium cobalt oxide, the amount of the element M ¹ is such that the atomic ratio M ¹ / Co with Co is preferably 0.06 or less, and more preferably 0.03 or less.

In lithium cobaltate, Zr has an action of adsorbing hydrogen fluoride that may be generated due to LiPF ₆ contained in the non-aqueous electrolyte and suppressing deterioration of lithium cobaltate.

If some moisture is inevitably mixed in the non-aqueous electrolyte used in the lithium ion secondary battery or if moisture is adsorbed to other battery materials, the LiPF ₆ contained in the non-aqueous electrolyte and Reaction produces hydrogen fluoride. When hydrogen fluoride is generated in the battery, the action causes deterioration of the positive electrode active material.

  However, when lithium cobaltate is synthesized so as to also contain Zr, Zr oxide is deposited on the surface of the particles, and this Zr oxide adsorbs hydrogen fluoride. Therefore, deterioration of lithium cobalt oxide due to hydrogen fluoride can be suppressed.

  In addition, when Zr is included in the positive electrode active material, the load characteristics of the battery are improved. When the lithium cobalt oxide contained in the positive electrode material is two materials having different average particle diameters, the larger average particle diameter is lithium cobaltate (A), and the smaller average particle diameter is lithium cobalt oxide (B). To do. In general, when a positive electrode active material having a large particle size is used, the load characteristics of the battery tend to deteriorate. Therefore, among the positive electrode active materials constituting the positive electrode material according to the present invention, it is preferable that lithium cobaltate (A) having a larger average particle diameter contains Zr. On the other hand, lithium cobaltate (B) may contain Zr or may not contain it.

  In the lithium cobaltate, the amount of Zr is preferably such that the atomic ratio Zr / Co with Co is 0.0002 or more and 0.0003 or more from the viewpoint of better exerting the above-described action. More preferred. However, if the amount of Zr in the lithium cobaltate is too large, the amount of other elements decreases, and there is a possibility that the effects of these elements cannot be ensured sufficiently. Therefore, the amount of Zr in the lithium cobaltate is preferably such that the atomic ratio Zr / Co with Co is 0.005 or less, and more preferably 0.001 or less.

Lithium cobaltate includes Li-containing compounds (such as lithium hydroxide and lithium carbonate), Co-containing compounds (such as cobalt oxide and cobalt sulfate), Mg-containing compounds (such as magnesium sulfate), Zr-containing compounds (such as zirconium oxide), and element M It can be synthesized by mixing a compound containing ¹ (oxide, hydroxide, sulfate, etc.) and firing this raw material mixture. Note that in order to synthesize lithium cobalt oxide at a higher purity, the composite compound containing Co and the element M ¹ (hydroxides, oxides, etc.) were mixed with such a Li-containing compound, firing the raw material mixture Is preferred.

  The firing condition of the raw material mixture for synthesizing lithium cobaltate can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once heated to a temperature lower than the firing temperature (for example, 250 to 850 ° C.). Then, it is preferable to carry out preliminary heating by holding at that temperature, and then to raise the temperature to the firing temperature to advance the reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

Examples of the Al-containing oxide that covers the surface of the lithium cobalt oxide particles include Al ₂ O ₃ , AlOOH, LiAlO ₂ , and LiCo _1-w Al _w O ₂ (where 0.5 <w <1). Only 1 type may be used and 2 or more types may be used together. For example, when the surface of lithium cobalt oxide is coated with Al ₂ O ₃ by a method described later, an Al-containing oxide containing elements such as Co, Li, and Al that migrate from lithium cobalt oxide is contained in Al ₂ O _3. Although a partially mixed film is formed, the film formed of an Al-containing oxide covering the surface of lithium cobaltate relating to the positive electrode material constituting the positive electrode material according to the present invention is a film containing such a component. There may be.

  The average coating thickness of the Al-containing oxide in the particles constituting the positive electrode material increases the resistance due to the inhibition of the lithium ion in and out of the positive electrode active material during charging and discharging of the battery related to the positive electrode material. From the viewpoint of improving the charge / discharge cycle characteristics of the battery by suppressing Li deposition on the negative electrode, and from the viewpoint of satisfactorily suppressing the reaction between the positive electrode active material and the nonaqueous electrolytic solution relating to the positive electrode material, the thickness is 5 nm or more. Yes, it is preferably 15 nm or more. In addition, from the viewpoint of suppressing deterioration in load characteristics of the battery due to the Al-containing oxide inhibiting lithium ions from entering and exiting the positive electrode active material during charge and discharge of the battery, Al in the particles constituting the positive electrode material according to the present invention The average coating thickness of the contained oxide is 50 nm or less, and more preferably 35 nm or less.

The “average coating thickness of the Al-containing oxide in the particles constituting the positive electrode material according to the present invention” as used herein refers to the cross section of the positive electrode material obtained by processing by the focused ion beam method using a transmission electron microscope. Using the positive electrode material particles observed at a magnification of 400,000 times and having a field of view of 500 × 500 nm, particles having a cross-sectional size within the average particle diameter (d ₅₀ ) ± 5 μm of the positive electrode material are equivalent to 10 fields of view. Arbitrarily selected, for each field of view, the thickness of the Al-containing oxide film was measured at any 10 locations, and the average value (number average) calculated for all thicknesses obtained at all fields (100 locations) Value).

The positive electrode material has a specific surface area (specific surface area of the whole positive electrode material) of preferably 0.1 m ² / g or more, more preferably 0.2 m ² / g or more, and preferably 0.4 m ² / g or less. More preferably, it is 0.3 m ² / g or less. The positive electrode material according to the present invention can increase the resistance during charging / discharging of the battery according to the positive electrode material by taking the specific surface area within the above range, and further suppress the occurrence of Li precipitation. This also can suppress battery swelling and capacity deterioration during high-temperature storage.

  When the surface of the positive electrode active material particles constituting the positive electrode material is coated with an Al-containing oxide or the Zr oxide is deposited on the surface of the positive electrode active material particles, the surface of the positive electrode material is usually used. Becomes rough and the specific surface area increases. Therefore, the positive electrode material is likely to have a small specific surface area as described above if the properties of the Al-containing oxide film covering the surface of the positive electrode active material particles are good in addition to a relatively large particle size. ,preferable.

The lithium cobalt oxide contained in the positive electrode material may be one type, two materials having different average particle diameters as described above, or three or more materials having different average particle diameters. There may be.
In order to adjust to the above specific surface area (specific surface area of the whole positive electrode material), when one kind of lithium cobaltate is used, it is preferable to use a positive electrode material having an average particle diameter of 10 to 35 μm. .

  When two materials having different average particle diameters are used for the lithium cobalt oxide contained in the positive electrode material, the surface of the lithium cobalt oxide (A) particles is coated with an Al-containing oxide, and the average particle diameter is 1 to 40 μm. The surface of the positive electrode material (a) and the lithium cobalt oxide (B) particles are coated with an Al-containing oxide, the average particle diameter is 1 to 40 μm, and the average is larger than the positive electrode material (a). It is preferable that at least the positive electrode material (b) having a small particle size is included. More preferably, it is composed of large particles [positive electrode material (a)] having an average particle diameter of 24 to 30 μm and small particles [positive electrode material (b)] having an average particle diameter of 4 to 8 μm. The ratio of the large particles in the total amount of the positive electrode material is preferably 75 to 90% by mass.

  As a result, not only can the specific surface area be adjusted, but also when the positive electrode mixture layer is pressed, the positive electrode material having a small particle size enters the gap between the positive electrode materials having a large particle size, so that the stress applied to the positive electrode mixture layer is entirely reduced. It is possible to disperse and to suppress the cracking of the positive electrode material particles satisfactorily, so that the action by the coating with the Al-containing oxide can be exhibited better.

  As described above, the positive electrode active material used for the positive electrode in the present invention is not particularly limited, and an active material that can be generally used, such as a lithium-containing transition metal oxide, may be used. You may use lithium cobaltate other than what was formed with the containing oxide. However, when using lithium cobalt oxide other than the one in which the surface of lithium cobalt oxide is formed of an Al-containing oxide for the purpose of increasing the resistance at the positive electrode during charging, for example, Al-containing oxidation such as alumina, boehmite, etc. Preferably, the product is contained in the positive electrode mixture layer.

  As a conductive support agent used for the said positive electrode, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metal powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives, etc. You may use independently and may use 2 or more types together. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

  Moreover, PVdF, P (VDF-CTFE), polytetrafluoroethylene (PTFE), SBR, etc. can be used for the binder which concerns on a positive mix layer.

The positive electrode is prepared, for example, as a paste-like or slurry-like positive electrode mixture-containing composition in which the above-described positive electrode active material, conductive additive and binder are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). (However, the binder may be dissolved in a solvent.) After applying this to one or both sides of the current collector and drying, it can be produced through a process of calendering if necessary. . The manufacturing method of a positive electrode is not necessarily restricted to said method, It can also manufacture with another manufacturing method.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 65-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass. Moreover, you may form the porous layer containing the insulating material which does not react with Li on the surface of a positive mix layer for the purpose of improving battery performance, such as a cycle, similarly to the case of a negative electrode.

  Examples of the positive electrode current collector include an aluminum foil. Alternatively, an aluminum foil having a through hole penetrating from one surface of the positive electrode current collector to the other surface, a punching metal, a net, or an expanded metal may be used. The upper limit of the thickness of the positive electrode current collector is preferably 30 μm, and the lower limit is preferably 4 μm in order to ensure mechanical strength.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a positive electrode as needed.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator has a melting point, that is, a thermoplastic resin having a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121 as a component. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, a solvent extraction method, a dry type Alternatively, an ion-permeable porous film manufactured by a wet stretching method or the like can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

Moreover, as a characteristic of the separator, a Gurley value represented by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  As the separator, a laminated separator having a porous layer (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher may be used. . The separator has both shutdown characteristics, heat resistance (heat shrinkage resistance), and high mechanical strength. It is expected that the high mechanical strength of this separator shows high resistance to expansion and contraction of the negative electrode accompanying the charge / discharge cycle, and the adhesion between the negative electrode, the separator and the positive electrode is maintained by suppressing the kinking of the separator. .

  In this specification, “heat-resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

  The porous layer (I) according to the separator is mainly for ensuring a shutdown function, and when the battery has reached the melting point of the thermoplastic resin that is the main component of the porous layer (I), The thermoplastic resin related to the porous layer (I) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

  The thermoplastic resin that is the main component of the porous layer (I) is a resin having a melting point, that is, a melting temperature of 140 ° C. or less measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. Specific examples include polyethylene. As the form of the porous layer (I), a microporous membrane usually used as a battery separator or a dispersion containing polyethylene particles is applied to a base material such as a nonwoven fabric and dried. Examples thereof include sheet-like materials such as those obtained. Here, in the total volume of the constituent components of the porous layer (I) [total volume excluding pores. The same applies to the volume content of the constituent components of the porous layer (I) and the porous layer (II) relating to the separator. ], The volume content of the thermoplastic resin as a main component is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous layer (I) is formed of the polyethylene microporous film, the volume content of the thermoplastic resin is 100% by volume.

  The porous layer (II) according to the separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the battery rises, and has a heat resistance temperature of 150 ° C. or higher. The function is secured by. That is, when the battery becomes high temperature, even if the porous layer (I) contracts, the porous layer (II) which does not easily contract can directly generate positive and negative electrodes that can be generated when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact of. Moreover, since this heat-resistant porous layer (II) acts as a skeleton of the separator, the thermal contraction of the porous layer (I), that is, the thermal contraction of the entire separator itself can be suppressed.

  The filler related to the porous layer (II) has a heat resistant temperature of 150 ° C. or higher, is stable with respect to the electrolyte of the battery, and is electrochemically stable that is not easily oxidized and reduced in the battery operating voltage range. If present, inorganic particles or organic particles may be used, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic oxide particles, more specifically, alumina, silica, and boehmite are preferable. Alumina, silica, and boehmite have high oxidation resistance, and the particle size and shape can be adjusted to the desired numerical values, making it easy to control the porosity of the porous layer (II) with high accuracy. It becomes. In addition, the filler whose heat-resistant temperature is 150 degreeC or more may use the thing of the said illustration individually by 1 type, and may use 2 or more types together, for example.

  The non-aqueous electrolyte of the lithium ion secondary battery of the present invention uses a compound of the following general formula (3) in addition to the lithium salt and organic solvent described later.

（ただし、nは１８００＜n＜３０００を満たし、mは３５０＜ｍ＜６００を満たす。）

(However, n satisfies 1800 <n <3000, and m satisfies 350 <m <600.)

The compound represented by the general formula (3) reacts with a Lewis acid to cause a polymerization reaction. In the lithium ion secondary battery, moisture is inevitably mixed in the battery in the manufacturing process. This moisture reacts with a fluorine-containing compound such as LiPF ₆ in the electrolytic solution to generate hydrogen fluoride (HF) which is a kind of Lewis acid. HF is a major factor in gas generation at high temperatures. HF also degrades cycle characteristics by elution of transition metals such as Co and Mn in the positive electrode active material or by eroding Si of the material S in the negative electrode active material. In the present invention, the compound represented by the general formula (3) uses this HF to cause a polymerization reaction. As a result, the HF in the battery is reduced, and the storage characteristics and cycle characteristics are improved.

  The electrolytic solution to which the compound represented by the general formula (3) is added is in a liquid state until it is charged and discharged for the first time in a lithium ion secondary battery, reacts with a Lewis acid, and gels. Is good. Furthermore, when the liquid is injected, the separator infiltrates well, and after the infiltration, gelation starts and the electrode and the separator strongly adhere to each other due to the anchor effect. Thereby, the sway of the separator accompanying charging / discharging can be suppressed.

  In order to exhibit the above-described effect more preferably, the compound represented by the general formula (3) is preferably added in an amount of 0.5% by mass or more with respect to the nonaqueous electrolytic solution, more preferably 1.0%. It is at least mass%. Moreover, it is preferable to add 10.0 mass% or less, More preferably, it is 8.0 mass%.

The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate; fluorine-substituted cyclic carbonates such as 4-fluoro-1,3-dioxolan-2-one (FEC); dimethyl carbonate (DMC), diethyl carbonate (DEC) ), Chain carbonates such as methyl ethyl carbonate (MEC); chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, tetraglyme, etc. A chain ether of dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, etc .; nitriles such as acetonitrile, propionitrile, methoxypropionitrile, etc .; ethylene glycol Sulfite esters such as Rufaito and the like, which can also be used as a mixture of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF _{6 and} other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. be able to.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  In addition, in the non-aqueous electrolyte, vinylene carbonate, vinyl ethylene carbonate, acid anhydride, sulfonic acid ester, for the purpose of improving the safety such as further improvement of charge / discharge cycle characteristics and high temperature storage property and prevention of overcharge, Additives (including these derivatives) such as dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene, phosphonoacetate compounds, 1,3-dioxane as appropriate It can also be added.

  Further, as the non-aqueous electrolyte, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer can be used.

  When the lithium ion secondary battery of the present invention is discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, all the positive electrode materials and positive electrode active materials Li included in the positive electrode described above, and metals other than Li The molar ratio with M (Li / M) is preferably 0.8 to 1.05. When a negative electrode active material having a high irreversible capacity such as SiOx is used for the negative electrode, Li ions desorbed from the positive electrode by charging move to the negative electrode side, and then Li ions returning to the positive electrode side are reduced even after discharging. A phenomenon occurs. Therefore, as described above, if Li is introduced into the negative electrode in advance, the capacity of the positive electrode can be used up when the battery is discharged, and the capacity of the battery can be increased. The (Li / M) of 0.8 to 1.05 can be realized by introducing Li into the negative electrode mixture layer containing the material S described above.

  In addition, the composition analysis of the positive electrode material when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V can be performed as follows using an ICP (Inductively Coupled Plasma) method. First, 0.2 g of the positive electrode material to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition is analyzed by a calibration curve method. The composition amount can be derived from the obtained results.

As for Li / M, Example 1 described later will be described as an example. In Example 1, the surface of LiCo _0.9795 Mg _0.011 Zr _0.0005 Al _0.009 O ₂ lithium cobalt oxide (A1) contains Al. Positive electrode material (a1) having an oxide film formed thereon and positive electrode material having an Al-containing oxide film formed on the surface of lithium cobaltate (B1) of LiCo _0.97 Mg _0.012 Al _0.009 O ₂ ( b1), and the metal M other than Li in this case refers to Co, Mg, Zr, and Al. That is, after making a lithium ion secondary battery, the battery after a predetermined charge / discharge is disassembled, and the positive electrode material (mixture in this Example 1) is collected and analyzed from the positive electrode mixture layer to derive Li / M.

  In order to introduce Li into the negative electrode mixture layer, a method of bringing the negative electrode into contact with a Li source, for example, sticking a Li foil to the negative electrode mixture layer, including particulate Li in the negative electrode mixture layer, In a state where the Li source and the negative electrode are brought into contact with each other by various methods such as depositing Li on the surface, charging and discharging with a nonaqueous electrolyte solution, and so as not to contact the negative electrode and the Li source Examples of the method include arranging, filling with a non-aqueous electrolyte, and charging and discharging by external connection.

  In a conventional lithium ion secondary battery, a negative electrode and a positive electrode are formed by stacking a laminated body (laminated electrode body) with a separator interposed therebetween, or a wound body (winding electrode body) obtained by further winding this laminated body in a spiral shape. ) Is used. In the case of a laminated electrode body, even if the volume of the negative electrode changes due to charging / discharging of the battery, the battery characteristics are more favorably maintained because it is easier to maintain the distance from the positive electrode. . For these reasons, it is desirable to use a laminated electrode body in the lithium ion secondary battery of the present invention.

  When the electrode body is composed of a laminated electrode body, if a Li source is arranged on the end face of the laminated electrode body and Li ions are introduced into the negative electrode, many Li ions are locally introduced into one negative electrode. Therefore, the negative electrode mixture layer can be prevented from falling off from the negative electrode current collector, the distance between the Li source and each negative electrode is the same, and there is no negative electrode that is extremely damaged by expansion, so the charge / discharge cycle It is preferable because deterioration of characteristics can be suppressed.

  Hereinafter, an example of a lithium ion secondary battery using a laminated electrode body and having a Li source will be shown. For example, Li is disposed on an end surface that does not face a mixture layer of a laminated electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and a third electrode that is electrically connected to the negative electrode is provided. Li of the third electrode is a Li source for introducing Li into the negative electrode mixture layer.

  Here, the laminated electrode body will be described. An example of the positive electrode 10 and the negative electrode 20 is shown in FIGS. The positive electrode 10 has a positive electrode mixture layer 11 applied to both surfaces of an aluminum metal foil which is a positive electrode current collector. The positive electrode 10 has a positive electrode tab portion 13, and the negative electrode 20 has a negative electrode mixture layer 21 applied to both surfaces of a copper metal foil that is a negative electrode current collector.

  FIG. 3 shows an example of the laminated electrode body 50. The laminated electrode body is formed by laminating the negative electrode 20, the separator 40, the positive electrode 10, the separator 40, the negative electrode 20..., And the positive electrode and the negative electrode through the separator. At this time, a plane parallel to the stacking direction of the stacked electrode body is referred to as an end face of the stacked electrode body (for example, indicated by a dotted virtual surface 210 in FIG. 3), and a plane perpendicular to the stacking direction of the stacked electrode body Called the plane of the body (denoted 211 in FIG. 3). In FIG. 3, the separators of the laminated electrode body 50 are arranged one by one between the positive electrode and the negative electrode. However, the long separator is bent in a Z-shape, and the positive electrode and the negative electrode are arranged therebetween. Also good. Further, the number of electrodes is not limited to three as shown in FIG. Further, the plurality of positive electrode tab portions and negative electrode tab portions may be connected to the positive electrode external terminal and the negative electrode external terminal, respectively, but are omitted in FIGS. 3 and 5.

  In FIG. 3, only one end face and one plane of the laminated electrode body are shown. However, the present invention is not limited to this. For example, the end face of the laminated electrode body is also present on the opposite surface of the virtual dotted line in FIG. The plane is also a matter of course. The end surface of the laminated electrode body is a plane in FIG. 3, but may be a curved surface depending on the shape of the electrode. One side of the positive electrode, the negative electrode, or the separator corresponds to the plane of the laminated electrode body.

In FIG. 4, the 3rd electrode 30 used as Li source is shown. The third electrode 30 includes a third electrode current collector 32 and a Li source 33. In FIG. 4, the third electrode current collector 32 has a third electrode tab portion 31.
FIG. 5 shows a state in which the third electrode 30 is combined with the laminated electrode body 50. The third electrode current collector 32 is bent into an alphabet C shape so as to cover two opposing end surfaces of the laminated electrode body 50. At this time, the Li source 33 is attached to the third electrode current collector 32 so as to be disposed on the end face of the laminated electrode body 50. 4 and 5, the Li source 33 is disposed on both end faces of the third electrode current collector 32, but it may be only on one side, and the upper side of the laminated electrode body 50 (upper side in the drawing). Or you may arrange | position to the end surface of the lower side (paper surface lower side).

  Further, when a metal foil without a through hole is used for the positive and negative electrode current collectors, the strength is improved as compared with the case where the through holes are provided. Since the adhesion area increases, it contributes to the suppression of falling off of the negative electrode mixture layer.

  The third electrode has a current collector made of, for example, a metal foil such as copper or nickel (including one having a through hole penetrating from one surface to the other), punching metal, net, expanded metal, etc. It can be produced by pressure bonding a predetermined amount of Li foil to the electrode current collector. Of course, the third electrode current collector may be cut out so that a predetermined amount of Li is obtained after the Li foil is pressure-bonded to the third electrode current collector.

  The third electrode obtained by pressure-bonding Li to the third electrode current collector is laminated by, for example, welding the tab portion of the third electrode current collector of the third electrode and the tab portion of the negative electrode of the multilayer electrode body. It can be electrically connected to the negative electrode of the mold electrode body. As long as the third electrode is electrically connected to the negative electrode of the multilayer electrode body, the method and form thereof are not limited, and electrical conduction may be ensured by a method other than welding.

  It is preferable to use a metal laminate film outer package for the outer package according to the lithium ion secondary battery of the present invention. Since the metal laminate film outer package is easier to deform than, for example, a metal outer can, the negative electrode mixture layer and the negative electrode current collector are hardly broken even if the negative electrode expands due to battery charging. It is. Further, the lithium ion secondary battery of the present invention is a metal having a low leakage resistance as compared with a metal outer can because the non-aqueous electrolyte is gelled by the compound represented by the general formula (3). Safety can be secured even if a laminate film exterior is used.

  As the metal laminate film constituting the metal laminate film exterior body, for example, a metal laminate film having a three-layer structure composed of exterior resin layer / metal layer / interior resin layer is used.

  The metal layer in the metal laminate film is an aluminum film, a stainless steel film or the like, and the interior resin layer is a heat-sealing resin (for example, a modified polyolefin ionomer that develops heat-fusibility at a temperature of about 110 to 165 ° C.). A structured film is mentioned. Examples of the exterior resin layer of the metal laminate film include a nylon film (such as nylon 66 film) and a polyester film (such as polyethylene terephthalate film).

  In the metal laminate film, the thickness of the metal layer is preferably 10 to 150 μm, the thickness of the interior resin layer is preferably 20 to 100 μm, and the thickness of the exterior resin layer is preferably 20 to 100 μm.

  The shape of the exterior body is not particularly limited. For example, the shape of the exterior body may be a polygon such as a triangle, a quadrangle, a pentagon, a hexagon, a heptagon, and an octagon in plan view. A square (rectangular or square) is common. The size of the exterior body is not particularly limited, and can be various sizes such as a so-called thin shape and large size.

  The metal laminate film exterior body may be configured by folding a single metal laminate film in two, or may be configured by stacking two metal laminate films.

  When the planar shape of the exterior body is a polygon, the side from which the positive external terminal is drawn out and the side from which the negative external terminal is drawn out may be the same side or different sides.

  The width of the heat fusion part in the outer package is preferably 5 to 20 mm.

  The lithium-ion secondary battery of the present invention exhibits stable and excellent characteristics even when used repeatedly over a long period of time while increasing the capacity by using the upper limit voltage of charging as 4.35 V or more. Can do. It is also possible to set the upper limit voltage for charging to 4.4 V or higher, which is higher than this. In addition, it is preferable that the upper limit voltage of charge of a lithium ion secondary battery is 4.7 V or less.

  The lithium ion secondary battery of the present invention can be applied to the same applications as conventionally known lithium ion secondary batteries.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
Li ₂ CO ₃ that is a Li-containing compound, Co ₃ O ₄ that is a Co-containing compound, Mg (OH) ₂ that is a Mg-containing compound, ZrO ₂ that is a Zr compound, and Al (OH that is an Al-containing compound ₃ ) was mixed in a mortar at an appropriate mixing ratio, then solidified into a pellet, and baked in an air atmosphere (under atmospheric pressure) at 950 ° C. for 24 hours using an muffle furnace, and ICP (Inductive Coupled) Lithium cobaltate (A1) having a composition formula determined by the Plasma) method of LiCo _0.9795 Mg _0.011 Zr _0.0005 Al _0.009 O ₂ was synthesized.

Next, 10 g of the lithium cobaltate (A1) is added to 200 g of a lithium hydroxide aqueous solution having a pH of 10 and a temperature of 70 ° C., and the mixture is stirred and dispersed. Then, Al (NO ₃ ) is added thereto. ) ₃ · _9H 2 O: and 0.0154G, and ammonia water to suppress variation in pH, was added dropwise over 5 hours, to produce a Al _{(OH) 3} coprecipitate, the lithium cobalt oxide (A1 ). Thereafter, the lithium cobalt oxide (A1) to which the Al (OH) ₃ coprecipitate is adhered is taken out from the reaction solution, washed, dried, and then heat-treated at 400 ° C. for 10 hours in an air atmosphere. Thus, an Al-containing oxide film was formed on the surface of the lithium cobalt oxide (A1) to obtain a positive electrode material (a1).

  With respect to the positive electrode material (a1) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 27 μm.

Li ₂ CO ₃ that is a Li-containing compound, Co ₃ O ₄ that is a Co-containing compound, Mg (OH) ₂ that is an Mg-containing compound, and Al (OH) ₃ that is an Al-containing compound are appropriately mixed. After mixing in a mortar, the mixture was hardened into pellets, baked at 950 ° C. for 4 hours in an atmospheric atmosphere (under atmospheric pressure) using a muffle furnace, and the composition formula obtained by ICP method was LiCo _0.97. Mg _0.012 Al _0.009 O ₂ lithium cobaltate (B1) was synthesized.

Next, 10 g of the lithium cobalt oxide (B1) is added to 200 g of lithium hydroxide aqueous solution: 200 having a pH of 10 and a temperature of 70 ° C., and dispersed by stirring. _{3) 3} · _9H 2 O: and 0.077 g, and ammonia water to suppress variation in pH, was added dropwise over 5 hours, to produce a Al _{(OH) 3} coprecipitate, the lithium cobaltate ( It was made to adhere to the surface of B1). Thereafter, the lithium cobaltate (B1) to which the Al (OH) ₃ coprecipitate is adhered is taken out from the reaction solution, washed, dried, and then heat-treated at 400 ° C. for 10 hours in an air atmosphere. Then, an Al-containing oxide film was formed on the surface of the lithium cobalt oxide (B1) to obtain a positive electrode material (b1). With respect to the positive electrode material (b1) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 7 μm.

Then, the positive electrode material (a1) and the positive electrode material (b1) were mixed at a mass ratio of 85:15 to obtain a positive electrode material (1) for battery preparation. When the average coating thickness of the Al-containing oxide on the surface of the obtained positive electrode material (1) was measured by the above method, it was 30 nm. Moreover, when the composition of the film was confirmed by element mapping when measuring the average coating thickness, the main component was Al ₂ O ₃ . Furthermore, when the volume-based particle size distribution of the positive electrode material (1) was confirmed by the above method, the average particle diameter was 25 μm, and peak tops were observed at the respective average particle diameters of the positive electrode material (a1) and the positive electrode material (b1). Two peaks were observed with Moreover, it was 0.25 m < ² > / g when the BET specific surface area of positive electrode material (1) was measured using the specific surface area measuring apparatus by a nitrogen adsorption method.

  Positive electrode material (1): 96.5 parts by mass, NMP solution containing P (VDF-CTFE) as a binder at a concentration of 10% by mass: 20 parts by mass, and acetylene black as a conductive auxiliary agent: 1.5 parts by mass Part was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste. This paste is applied to both sides of an aluminum foil having a thickness of 15 μm, vacuum-dried at 120 ° C. for 12 hours, a positive electrode mixture layer is formed on both sides of the aluminum foil, press treatment is performed, and a predetermined size is obtained. This was cut to obtain a strip-like positive electrode. In addition, when applying the positive electrode mixture-containing paste to the aluminum foil, a part of the aluminum foil is exposed, and the positive electrode mixture-containing paste is applied to both sides of the aluminum foil. The applied part was also made into the application part. The thickness of the positive electrode mixture layer of the obtained positive electrode (the thickness per one side when the positive electrode mixture layer was formed on both surfaces of the aluminum foil) was 55 μm.

  Forming the positive electrode mixture layer so that a part of the exposed portion of the aluminum foil (positive electrode current collector) protrudes so that the strip-like positive electrode having the positive electrode mixture layer formed on both surfaces of the aluminum foil becomes a tab portion. The part was punched out with a Thomson blade so as to have a substantially quadrangular shape with four corners being curved, and a positive electrode for a battery having a positive electrode mixture layer on both surfaces of the positive electrode current collector was obtained. FIG. 1 is a plan view schematically showing the battery positive electrode (however, in order to facilitate understanding of the structure of the positive electrode, the size of the positive electrode shown in FIG. 1 does not necessarily match the actual one). Not) The positive electrode 10 has a shape having a tab portion 13 punched out so that a part of the exposed portion of the positive electrode current collector 12 protrudes, and the shape of the formation portion of the positive electrode mixture layer 11 is a substantially rectangular shape with four corners curved. In the figure, the lengths a, b and c were 8 mm, 37 mm and 2 mm, respectively.

<Production of negative electrode>
Graphite A-1 (graphite whose surface is not coated with amorphous carbon): 25% by mass and graphite B-1 (surface of mother particles made of graphite is coated with amorphous carbon using pitch as a carbon source) Graphite): 25% by mass, and a composite Si-1 having an SiO surface coated with a carbon material (average particle size is 5 μm, specific surface area is 8.8 m ² / g, and the amount of carbon material in the composite is SiO 2 : 10 parts by mass with respect to 100 parts by mass): 50% by mass was mixed with a V-type blender for 12 hours to obtain a negative electrode active material.

  A unit represented by the above formula (1) and a unit represented by the above formula (2), wherein R is hydrogen and M 'is potassium in the above formula (2). A copolymer (A) having a molar ratio of 6/4 to the unit represented by the formula (2) is dissolved in ion-exchanged water, and an aqueous solution having a copolymer (A) concentration of 8% by mass is obtained. Prepared. The negative electrode active material and carbon black were added to this aqueous solution and mixed by stirring to obtain a negative electrode mixture-containing paste. The composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in this paste was 90: 2: 8.

The negative electrode mixture paste is applied to one side of a copper foil having a thickness of 10 μm and dried, a negative electrode mixture layer is formed on one side and both sides of the copper foil, and press treatment is performed to form the negative electrode mixture layer. The density was adjusted to 1.2 g / cm ³ and then cut at a predetermined size to obtain a strip-shaped negative electrode. In addition, when applying the negative electrode mixture-containing paste to the copper foil, a part of the copper foil was exposed, and the negative electrode mixture layer formed on both sides is the back side where the coating part is the application part Was also applied.

  In order to make the strip-shaped negative electrode into a tab portion, a part of the exposed portion of the copper foil (negative electrode current collector) protrudes, and the negative electrode mixture layer forming portion has a substantially square shape with four corners curved. Thus, a negative electrode for a battery having a negative electrode mixture layer on both surfaces and one surface of the negative electrode current collector was obtained. FIG. 2 is a plan view schematically showing the battery negative electrode (however, in order to facilitate understanding of the structure of the negative electrode, the size of the negative electrode shown in FIG. 2 does not necessarily match the actual size). Not) The negative electrode 20 has a shape having a tab portion 23 punched out so that a part of the exposed portion of the negative electrode current collector 22 protrudes, and the shape of the formation portion of the negative electrode mixture layer 21 is a substantially rectangular shape with four corners curved. In the figure, the lengths of d, e, and f were 9 mm, 38 mm, and 2 mm, respectively.

<Preparation of separator>
Modified polybutyl acrylate resin binder: 3 parts by mass, boehmite powder (average particle size: 1 μm): 97 parts by mass, and water: 100 parts by mass were mixed to prepare an insulating layer forming slurry. This slurry was applied on one side of a polyethylene microporous membrane for lithium ion batteries having a thickness of 12 μm; the porous layer (I) and dried. A separator in which a porous layer (II) mainly composed of boehmite was formed on one surface of the porous layer (I) was obtained. The thickness of the porous layer (II) was 3 μm.

  Two negative electrodes for a battery with a negative electrode mixture layer formed on one side of the negative electrode current collector, 16 negative electrodes for a battery with a negative electrode mixture layer formed on both sides of the negative electrode current collector, and a positive electrode mixture on both sides of the positive electrode current collector Seventeen positive electrodes for a battery on which an agent layer was formed were prepared. Further, a negative electrode for a battery in which a negative electrode mixture layer is formed on one side of the negative electrode current collector, a positive electrode for a battery 10 in which a positive electrode mixture layer is formed on both sides of the positive electrode current collector, and a battery in which a negative electrode mixture layer is formed on both sides. The negative electrodes 20 are alternately arranged, and the separator 40 is laminated between each positive electrode and each negative electrode so that the porous layer (II) faces the positive electrode, and is shown in FIG. A laminated electrode body 50 was obtained.

<Production of third electrode>
As shown in FIG. 4, the 3rd electrode 30 was produced as follows. A copper foil having a through hole penetrating from one surface to the other surface (thickness 10 μm, diameter of the through hole 0.1 mm, porosity 47%) is cut into a size of 45 × 25 mm, and 2 × A third electrode current collector 32 having a 3 mm square third electrode tab portion 31 was produced. In addition, two Li foils 33 each having a thickness of 200 μm and a mass of 20 mg per sheet were bonded to the both end surfaces of the third electrode current collector 32 one by one and folded into a C-shape of the alphabet. A third electrode 30 was obtained.

<Adjustment of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7, and a compound represented by the general formula (3) (n in the general formula (1) at this time, m was n = 2620 and m = 420, respectively, in an amount of 2.0% by mass, and vinylene carbonate was further added in an amount of 3% by mass to prepare a non-aqueous electrolyte.

<Battery assembly>
The tab portion between the positive electrodes, the tab portion between the negative electrodes, and the tab portion of the third electrode produced as described above are welded, respectively, and the laminated electrode body 50 and the third electrode 30 are combined to form the electrode shown in FIG. A body 102 was produced. And the said laminated electrode body is inserted in the said hollow of the aluminum laminate film of thickness: 0.15mm, width: 34mm, and height: 50mm which formed the hollow so that the said laminated electrode body 50 might be accommodated, and the said The aluminum laminate film of the same size as the above was placed, and three sides of both aluminum laminate films were heat-welded. And the said non-aqueous electrolyte was inject | poured from the remaining 1 side of both aluminum laminate films. Thereafter, the remaining one side of both aluminum laminate films was vacuum-sealed to produce a lithium ion secondary battery having the appearance shown in FIG. 6 and the cross-sectional structure shown in FIG.

  Here, FIG. 6 and FIG. 7 will be described. FIG. 6 is a plan view schematically showing a lithium ion secondary battery, and FIG. 7 is a cross-sectional view taken along the line II in FIG. The lithium ion secondary battery 100 contains an electrode body 102 and a non-aqueous electrolyte (not shown) in an aluminum laminate film exterior body 101 composed of two aluminum laminate films. The body 101 is sealed at its outer periphery by heat-sealing upper and lower aluminum laminate films. In FIG. 7, in order to avoid the drawing from being complicated, each layer constituting the aluminum laminate film outer package 101 and the positive electrode, the negative electrode, and the separator constituting the electrode body are not distinguished.

  Each positive electrode of the electrode body 102 is integrated by welding the tab portions, and the integrated product of the welded tab portions is connected to the positive electrode external terminal 103 in the battery 100. Each negative electrode and the third electrode of the electrode body 102 are also integrated by welding the tab portions, and the integrated product of the welded tab portions is connected to the negative electrode external terminal 104 in the battery 100. The positive electrode external terminal 103 and the negative electrode external terminal 104 are drawn out to the outside of the aluminum laminate film exterior body 101 so that they can be connected to an external device or the like.

The lithium ion secondary battery produced as described above was stored in a constant temperature bath at 45 ° C. for 1 week.

(Example 2)
A negative electrode was produced in the same manner as in Example 1 except that the composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture-containing paste was 92: 6: 2. . The lithium ion secondary was the same as in Example 1 except that two Li foils 33 each having a mass of 20.5 mg were bonded to both end faces of the third electrode current collector 32 one by one. A battery was produced.

(Example 3)
A negative electrode was prepared in the same manner as in Example 1 except that the composition ratio (mass ratio) of the negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture-containing paste was 90: 4: 6. A lithium ion secondary battery was produced.

Example 4
A negative electrode was produced in the same manner as in Example 1 except that the composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture-containing paste was 88: 2: 10. . The lithium ion secondary was the same as in Example 1 except that two Li foils 33 each having a mass of 19.5 mg and one each were bonded to both end faces of the third electrode current collector 32. A battery was produced.

(Example 5)
A negative electrode was produced in the same manner as in Example 1 except that the composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture-containing paste was 81: 4: 15. . A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that two Li foils 33 each having a mass of 18 mg and one Li foil 33 were bonded to both end faces of the third electrode current collector 32, respectively. Produced.

(Example 6)
Graphite A-1: 15% by mass, graphite B-1: 15% by mass, and composite Si-1: 70% by mass were mixed for 12 hours with a V-type blender to obtain a negative electrode active material. Except that this was used as the negative electrode active material, and two Li foils 33 each having a mass of 28 mg were bonded to both end faces of the third electrode current collector 32 one by one. Similarly, a lithium ion secondary battery was produced.

(Example 7)
Composite Si-1: 100% by mass was used as the negative electrode active material, and two Li foils 33 each having a mass of 40 mg were bonded to both end surfaces of the third electrode current collector 32, one by one. Except for this, a lithium ion secondary battery was fabricated in the same manner as in Example 1.

(Example 8)
Graphite A-1: 40% by mass, graphite B-1: 40% by mass, and composite Si-1: 20% by mass were mixed in a V-type blender for 12 hours to obtain a negative electrode active material. Except that this was used as the negative electrode active material, two Li foils 33 each having a mass of 8 mg, and two sheets of each of the third electrode current collectors 32 were bonded to each end surface of the third electrode current collector 32. Similarly, a lithium ion secondary battery was produced.

Example 9
<Composite of negative electrode active material>
The non-graphitic carbon material 3 parts by mass is mixed with 100 parts by mass of the mixture A obtained by mixing 97 parts by mass of the flaky graphite powder and 3 parts by mass of the silicon powder by a mixing method involving compressive force and shear force. Mixing was performed by the accompanying mixing method to prepare mixture B.
The mixture B was heated in an inert atmosphere at 1000 ° C. for 1 hour, then crushed, and the composite particles Si— in which the silicon sandwiched between the flaky graphite particles was fixed by amorphous carbon 2 was obtained. Si-2: 100% by mass was used as the negative electrode active material.
A negative electrode was produced in the same manner as in Example 1 except that the composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture-containing paste was 95: 1: 4. A lithium ion secondary battery was produced.

(Example 10)
LiCoO _{2 as a} positive electrode active material: 96.5 parts by mass, NMP solution containing P (VDF-CTFE) as a binder at a concentration of 10% by mass: 17 parts by mass, and acetylene black as a conductive auxiliary agent: 1. 3 parts by mass and alumina filler having an average particle diameter of 0.7 μm: 0.5 parts by mass are kneaded using a biaxial kneader, and NMP is further added to adjust the viscosity to obtain a positive electrode mixture-containing paste. A positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing paste was used, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Comparative Example 1)
Composite Si-1 (negative electrode active material): 90 parts by mass, carbon black: 2 parts by mass, CMC: 1.5 parts by mass, and SBR: 6.5 parts by mass were mixed with ion-exchanged water, and Example In the same manner as in Example 1, a negative electrode mixture-containing paste was obtained. A negative electrode was produced in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used, and a lithium ion secondary battery was produced.

(Comparative Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode produced in the same manner as in Example 1 was used and the electrolyte solution did not contain the compound represented by the general formula (3). .

(Comparative Example 3)
A negative electrode was prepared in the same manner as in Example 1 except that the composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture paste was 93: 6: 1. did. The lithium ion secondary was the same as in Example 1 except that two Li foils 33 each having a mass of 20.5 mg were bonded to both end faces of the third electrode current collector 32 one by one. A battery was produced.

(Comparative Example 4)
A negative electrode was produced in the same manner as in Example 1 except that the composition ratio (mass ratio) of the negative electrode active material: carbon black: copolymer (A) in the negative electrode mixture paste was 75: 5: 20. did. A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that two Li foils 33 each having a mass of 18 mg and one Li foil 33 were bonded to both end faces of the third electrode current collector 32, respectively. Produced.

The following evaluation was performed about each lithium ion secondary battery of an Example and a comparative example.
<60 ° C storage characteristics evaluation>
Lithium ion secondary batteries (5 each) were charged at a constant current of up to 4.4 V at a current value of 0.5 C, and then charged at a constant voltage of 4.4 V until the current value reached 0.02 C. After charging, the thickness of the battery (the vertical thickness in FIG. 7) was measured with a thickness gauge, and this was taken as the thickness before storage.
After being stored in a thermostat adjusted to 60 ° C. for 7 days, it was taken out from the thermostat, cooled at room temperature for 3 hours, measured with a thickness gauge, and this was taken as the thickness after storage. The thickness change rate before and after storage was calculated from the following formula. Table 1 shows the average value for five.
Thickness change rate (%) = (Thickness after storage−Thickness before storage) / Thickness before storage × 100

<Charge / discharge cycle characteristics evaluation>
Lithium ion secondary batteries (5 each) were charged at a constant current of up to 4.4 V at a current value of 0.5 C, and then charged at a constant voltage of 4.4 V until the current value reached 0.02 C. Then, it discharged to 2.0V with the constant current of 0.2C, and calculated | required the initial discharge capacity. Next, each battery was charged with a constant current up to 4.4 V at a current value of 1 C, subsequently charged with a constant voltage of 4.4 V until the current value reached 0.05 C, and then 2. with a current value of 1 C. A series of operations for discharging to 0 V was taken as one cycle, and this was cycled 300 times. And about each battery, the constant current-constant voltage charge and the constant current discharge were performed on the same conditions as the time of the said first time discharge capacity measurement, and the discharge capacity was calculated | required. The values obtained by dividing these discharge capacities by the initial discharge capacities are expressed as percentages to calculate the cycle capacity maintenance ratio, and the average value of five is shown in Table 1.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Positive electrode mixture layer 12 Positive electrode collector 13 Tab part 20 Negative electrode 21 Negative electrode mixture layer 22 Negative electrode collector 23 Tab part 30 3rd electrode 31 3rd electrode tab part 32 3rd electrode collector 33 Li foil 40 Separator 50 Multilayer Electrode Body 100 Lithium Ion Secondary Battery 101 Metal Laminate Film Outer Body 102 Electrode Body 103 Positive External Terminal 104 Negative Negative External Terminal

Claims (4)

A negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a positive electrode, a separator, and a non-aqueous electrolyte solution are housed in a lithium ion secondary battery,
The negative electrode mixture layer contains a material S containing Si as a negative electrode active material,
The negative electrode mixture layer contains a copolymer having a unit represented by the following formula (1) and a unit represented by the following formula (2) as the binder, and the copolymer in the negative electrode mixture layer. The content of the polymer is 2 to 15% by mass,
The lithium ion secondary battery, wherein the non-aqueous electrolyte solution is added with at least a fluorine-containing compound and a compound represented by the following general formula (3).

  The said negative electrode active material contains the material S which is negative electrode material containing Si, and when the sum total of all the negative electrode active materials contained in the said negative electrode is 100 mass%, the content rate of the material S in the said negative electrode active material The lithium ion secondary battery according to claim 1, wherein is at least 5% by mass or more.   The lithium according to claim 1, wherein the material S includes a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5). Ion secondary battery. The positive electrode includes a positive electrode material in which the surface of positive electrode active material particles is coated with an Al-containing oxide, and the positive electrode active material contained in the positive electrode material includes Co, Mg, Zr, Ni, Mn, Ti, and The lithium ion secondary battery according to any one of claims 1 to 3, which is lithium cobaltate containing at least ^one element M1 selected from the group consisting of Al.

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