JP2008288112A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

A non-aqueous electrolyte secondary battery having a large charge / discharge capacity and capable of suppressing deterioration of cycle characteristics is provided.
A battery can 1 has a wound electrode body 20 in which a strip-like positive electrode 2 and a negative electrode 3 are wound via a separator 4. In this non-aqueous electrolyte secondary battery, the open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is in the range of 4.30 V to 4.45 V, and at least one of the positive electrode 2 and the electrolyte, It contains calcium salts.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, a non-aqueous electrolyte secondary battery in which a positive electrode and a negative electrode are opposed to each other via a separator, and an open circuit voltage in a fully charged state per pair of the positive electrode and the negative electrode is 4.30 V or more. About.

  In recent years, with the widespread use of portable information electronic devices such as mobile phones, video cameras, and notebook personal computers, the performance, size, and weight of the devices are rapidly developing. A disposable primary battery or a rechargeable secondary battery is used as a power source used for portable information electronic devices.

  Among them, as a power source used for portable information electronic devices, demand for secondary batteries, particularly lithium ion secondary batteries, is increasing due to a good balance of economy, high performance, small size and light weight. In portable information electronic devices, higher performance and smaller size are being promoted, and higher energy density is also required for lithium ion secondary batteries.

  By the way, in the conventional lithium ion secondary battery, a lithium cobaltate is used for a positive electrode, a carbon material is used for a negative electrode, and a charge end voltage is 4.10V to 4.20V. In the lithium ion secondary battery designed with the end-of-charge voltage in this way, the positive electrode active material such as lithium cobaltate used for the positive electrode utilizes a capacity of about 50% to 60% with respect to its theoretical capacity. Not too much.

  Therefore, in principle, it is possible to utilize the remaining capacity by further increasing the charging voltage. In fact, it is possible to increase the energy density by setting the upper limit voltage during charging to 4.30 V or higher. It is known (see, for example, Patent Document 1).

International Publication No. 03/0197131 Pamphlet

  Further, when the area density is increased for increasing the energy density, there is a concern about cycle deterioration. This is presumably because the lithium diffusibility at the negative electrode deteriorates, so that metal Li is deposited on the surface of the negative electrode, and the deposited Li promotes the decomposition reaction of the electrolytic solution and the like.

  Therefore, it has been studied to suppress the reaction by adding various additives to the electrolytic solution. For example, Patent Document 2 proposes to use an electrolytic solution to which 4-fluoroethylene carbonate (FEC) is added.

JP 2001-313075 A

  However, in a battery in which the end-of-charge voltage of the battery is higher than the conventional 4.20 V, there is a problem that the internal resistance of the battery increases during the charge / discharge cycle test, particularly during a high temperature cycle or high temperature continuous charge. This is because, for example, free fluorine generated in the discharge reaction due to decomposition of the binder containing fluorine contained in the positive electrode, electrolyte salt, and electrolytic solution is generated in the electrolytic solution by being exposed to high temperature, and Li This is considered to be because the positive electrode active material that has become unstable due to extraction of hydrogen is decomposed and eluted, and a large amount of decomposition film such as LiF is formed on the negative electrode lithium.

  In particular, batteries using an electrolyte containing at least one of 4-fluoroethylene carbonate (FEC) and difluoroethylene carbonate tend to improve the cycle characteristics at room temperature. There was a tendency for the deterioration to be large.

  Accordingly, an object of the present invention is a nonaqueous electrolyte secondary battery in which the open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is in the range of 4.30V to 4.45V, and the charge / discharge capacity is large, And it is providing the nonaqueous electrolyte secondary battery which can suppress deterioration of cycling characteristics.

In order to solve the above-described problems, the present invention provides:
A positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolyte;
The open circuit voltage in a fully charged state per pair of positive and negative electrodes is in the range of 4.30V to 4.45V,
A nonaqueous electrolyte secondary battery characterized in that a calcium salt is contained in at least one of a positive electrode and an electrolyte.

  In the present invention, the calcium salt contained in at least one of the positive electrode and the electrolyte captures free fluorine, reduces the decomposition and elution of excess positive electrode active material by the free fluorine, and decomposes LiF and the like on the negative electrode lithium. It is thought that the formation of the film can be suppressed.

  According to the present invention, in a nonaqueous electrolyte secondary battery in which an open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is in a range of 4.30 V to 4.45 V, the charge / discharge capacity is large and the cycle is Deterioration of characteristics can be suppressed.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows the structure of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. This nonaqueous electrolyte secondary battery is, for example, a lithium ion secondary battery that uses lithium (Li) as an electrode reactant.

  As shown in FIG. 1, the non-aqueous electrolyte secondary battery is a so-called cylindrical type, and a pair of strip-shaped positive electrode 2, strip-shaped negative electrode 3 and separator are formed inside a substantially hollow cylindrical battery can 1. 4, and the positive electrode 2 and the negative electrode 3 are disposed to face each other with the separator 4 interposed therebetween.

  Here, the width of each of the positive electrode 2, the negative electrode 3, and the separator 4 is, for example, in a relation of separator width> negative electrode width> positive electrode width. It effectively prevents lithium in the positive electrode 2 from flowing into the negative electrode 3 during charging and causing crystal growth in a dendrite shape in the negative electrode 3 and reaching the positive electrode 2 and causing an internal short circuit. Because it can.

  The battery can 1 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 1, a pair of insulating plates 5 and 6 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 1, a battery lid 7, a safety valve mechanism 8 and a thermal resistance element (PTC element) 9 provided inside the battery lid 7 are interposed via a gasket 10. It is attached by caulking, and the inside of the battery can 1 is sealed.

  The battery lid 7 is made of, for example, the same material as the battery can 1. The safety valve mechanism 8 is electrically connected to the battery lid 7 via the heat sensitive resistance element 9, and the disk plate 11 is reversed when the internal pressure of the battery becomes a certain level or more due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 7 and the wound electrode body 20 is cut off.

  When the temperature rises, the heat sensitive resistance element 9 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 10 is made of, for example, an insulating material, and asphalt is applied to the surface.

  A center pin 12 is inserted in the center of the wound electrode body 20. A positive electrode lead 13 made of, for example, aluminum (Al) or the like is connected to the positive electrode 2 of the spirally wound electrode body 20, and a negative electrode lead 14 made of, for example, nickel (Ni) or the like is connected to the negative electrode 3. The positive electrode lead 13 is electrically connected to the battery cover 7 by being welded to the safety valve mechanism 8, and the negative electrode lead 14 is welded and electrically connected to the battery can 1.

  FIG. 2 is an enlarged view of a part of the spirally wound electrode body 20 shown in FIG. As shown in FIG. 2, the positive electrode 2 has a structure in which, for example, a positive electrode active material layer 2B is provided on both surfaces of a positive electrode current collector 2A having a pair of opposed surfaces. Although not shown, a region where the positive electrode active material layer 2B is provided on only one surface of the positive electrode current collector 2A may be provided. The positive electrode current collector 2A is made of, for example, a metal foil such as an aluminum foil. The positive electrode active material layer 2B includes, for example, a positive electrode material capable of inserting and extracting lithium (Li) as a positive electrode active material.

  The negative electrode 3 has, for example, a structure in which a negative electrode active material layer 3B is provided on both surfaces of a negative electrode current collector 3A having a pair of opposed surfaces. Although not shown, a region where the negative electrode active material layer 3B is provided on only one surface of the negative electrode current collector 3A may be provided. The negative electrode current collector 3A is made of, for example, a metal foil such as a copper foil. The negative electrode active material layer 3B includes one or more negative electrode materials capable of inserting and extracting lithium (Li) as a negative electrode active material.

  In this secondary battery, the electrochemical equivalent of the negative electrode material capable of inserting and extracting lithium (Li) is larger than the electrochemical equivalent of the positive electrode 2, and the negative electrode 3 is charged with lithium during the charging. The metal is not deposited.

  The secondary battery is designed so that the open circuit voltage (that is, the battery voltage) at the time of full charge is in the range of 4.30V to 4.45V. Therefore, even if the positive electrode active material is the same as that of the battery having an open circuit voltage of 4.20 V at the time of full charge, the amount of lithium released per unit mass is increased. Accordingly, the positive electrode active material and the negative electrode active material are increased accordingly. The amount is adjusted so that a high energy density can be obtained. In particular, when the open circuit voltage at the time of full charge is in the range of 4.30 V or more and 4.45 V or less, the effect that can be practically used is high.

[Positive electrode]
The positive electrode 2 can be obtained by applying a positive electrode mixture containing a positive electrode active material, a conductive agent and a binder, and a calcium salt to the surface of the positive electrode current collector 2A. Specifically, the positive electrode 2 is made of a positive electrode active material, a conductive agent, a calcium salt, a binder, and a positive electrode current collector slurry such as an aluminum foil. It can be obtained by coating, drying and press rolling the body 2A to form the positive electrode active material layer 2B on the positive electrode current collector 2A.

  In one embodiment of the present invention, by including a calcium salt in the positive electrode, charge / discharge cycle characteristics can be improved in a battery in which the end-of-charge voltage of the battery is increased to 4.30 V or more and 4.45 V or less. In particular, it is possible to improve the high temperature cycle characteristics and the cycle maintenance rate during high temperature continuous charging.

  The mechanism is not completely clear, but is considered as follows. When the end-of-charge voltage of the battery is higher than 4.25 V, the decomposition of the electrolyte salt on the surface of the positive electrode, which has become unstable due to the extraction of Li, is promoted, so that free fluorine generated along with the discharge reaction is reduced. Increase. The calcium salt reacts with the free fluorine to form a compound with calcium such as calcium fluoride, thereby capturing the free fluorine. Thereby, since free fluorine can be reduced, it is thought that generation | occurrence | production of the decomposition | disassembly and elution of the excess positive electrode active material by free fluorine, and LiF etc. on negative electrode lithium can be suppressed.

  The calcium salt in the positive electrode 2 can be confirmed by taking out the positive electrode 2 from the used battery and analyzing the state of the calcium salt compound in the positive electrode 2. As the analysis method, for example, powder X-ray diffraction (XRD), time of flight secondary ion mass spectrometry (TOF-SIMS), or the like can be used.

Examples of calcium salts that can be used include calcium oxide salts, carbonate salts, sulfide salts, phosphate salts, nitrate salts, hydroxide salts, and organic salt salts. Specifically, calcium oxide (CaO), calcium carbonate (CaCO ₃ ), calcium phosphate (CaPO ₄ ), calcium nitrate (Ca (NO ₃ ) ₂ ), calcium acetate (Ca (CH ₃ COO) ₂ ), calcium hydroxide (Ca (OH) ₂ ), calcium sulfate (CaSO ₄ ), or the like can be used.

  The amount of calcium salt added is preferably 0.1 wt% or more and 2.0 wt% or less with respect to the positive electrode active material. This is because high cycle characteristics can be obtained without affecting the discharge capacity of the battery. If it is less than 0.1 wt%, the amount of free fluorine may not be sufficient. Moreover, when larger than 2.0 wt%, there exists a possibility that discharge capacity may fall.

  As the positive electrode active material, a positive electrode material capable of inserting and extracting lithium can be used. Specifically, as the positive electrode material, for example, a lithium-containing compound such as lithium oxide, lithium phosphorus oxide, lithium sulfide, or an intercalation compound containing lithium is suitable, and a mixture of two or more of these is used. Also good. In order to increase the energy density, a lithium-containing compound containing lithium (Li), a transition metal element, and oxygen (O) is preferable. Among them, as the transition metal element, cobalt (Co), nickel (Ni), manganese (Mn And at least one selected from the group consisting of iron (Fe).

  Examples of such a lithium-containing compound include a lithium composite oxide having an average composition represented by chemical formula I, more specifically chemical formula II, and a lithium composite oxide having an average composition represented by chemical formula III. be able to.

(Chemical I)
_{Li p Ni (1-qr)} Mn q M1 r O (2-y) X z
(In the formula, M1 represents at least one element selected from Group 2 to Group 15 excluding nickel (Ni) and manganese (Mn). X represents Group 16 element and Group 17 element other than oxygen (O). P, q, y, and z are 0 ≦ p ≦ 1.5, 0 ≦ q ≦ 1.0, 0 ≦ r ≦ 1.0, −0.10 ≦ y ≦ 0. (20, 0 ≦ z ≦ 0.2)
(Chemical II)
Li _a Co _1-b M2 _b O _2-c
(Wherein M2 is vanadium (V), copper (Cu), zirconium (Zr), zinc (Zn), magnesium (Mg), aluminum (Al), gallium (Ga), yttrium (Y) and iron (Fe). Represents at least one of the group consisting of: values of a, b and c are 0.9 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.3, −0.1 ≦ c ≦ 0.1 Note that the composition of lithium varies depending on the state of charge and discharge, and the value of a represents the value in a fully discharged state.)
(Chemical III)
Li _w Ni _x Co _y Mn _z M3 _1-xyz O _2-v
(Wherein M3 is vanadium (V), copper (Cu), zirconium (Zr), zinc (Zn), magnesium (Mg), aluminum (Al), gallium (Ga), yttrium (Y) and iron (Fe). It represents at least one of the group consisting of: v, w, x, y and z have values of −0.1 ≦ v ≦ 0.1, 0.9 ≦ w ≦ 1.1, 0 <x <. 1, 0 <y <1, 0 <z <0.5, 0 ≦ 1-xyz The composition of lithium varies depending on the state of charge and discharge, and the value of w is a complete discharge. Represents the value in the state.)

Furthermore, examples of the lithium-containing compound include a lithium composite oxide having a spinel structure represented by Formula IV, more specifically, Li _d Mn ₂ O ₄ (d≈1). .
(Chemical IV)
_{Li p Mn 2-q M4 q} O r F s
(In the formula, M4 is cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe ), Copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). q, r, and s are values within the range of 0.9 ≦ p ≦ 1.1, 0 ≦ q ≦ 0.6, 3.7 ≦ r ≦ 4.1, and 0 ≦ s ≦ 0.1. Note that the composition of lithium varies depending on the state of charge and discharge, and the value of p represents a value in a fully discharged state.

Furthermore, examples of the lithium-containing compound may include, for example, a chemical compound V, more specifically, a lithium composite phosphate having an olivine type structure represented by chemical compound VI. _e FePO ₄ (e≈1).
(Chemical V)
Li _a M5 _b PO ₄
(In the formula, M5 represents at least one element selected from Group 2 to Group 15. a and b are in the range of 0 ≦ a ≦ 2.0 and 0.5 ≦ b ≦ 2.0. Value.)
(Chemical VI)
Li _t M6PO ₄
(In the formula, M6 is cobalt (Co), manganese (Mn), iron (Fe), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V ), Niobium (Nb), copper (Cu), zinc (Zn), molybdenum (Mo), calcium (Ca), strontium (Sr), tungsten (W) and zirconium (Zr) T is a value within a range of 0.9 ≦ t ≦ 1.1, wherein the composition of lithium varies depending on the state of charge and discharge, and the value of t represents a value in a fully discharged state. )

In addition to the positive electrode materials described above, examples of positive electrode materials that can occlude and release lithium (Li) include inorganic materials such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS that do not contain lithium. A compound can be mentioned.

  As the positive electrode material, a positive electrode material having a stable structure even at a high charging voltage is preferable. Such a positive electrode material is a high voltage having a charging voltage of 4.30 V or more and 4.45 V or less, in which a positive electrode using this as a positive electrode active material and a negative electrode using, for example, a carbon material as a negative electrode active material are combined. Suitable for non-aqueous electrolyte secondary batteries that can be charged with

  As such a positive electrode material, for example, a positive electrode material designed to improve the structural stability in a high charging pressure range described in the following (a) to (c) can be given.

(A) First, as described in, for example, JP-A-62-90863 and JP-A-4-319260, aluminum (Al), tin (Sn), indium (In), magnesium (Mg) , And positive electrode materials in which different elements such as zirconium (Zr) and titanium (Ti) are dissolved.

(B) Further, for example, as described in JP-A-2002-1003007, there is a positive electrode material in which a small amount of lithium nickel manganese composite oxide or the like is mixed with lithium cobalt composite oxide.

(C) Further, for example, at least part of the lithium composite oxide particles is provided with a coating layer made of an oxide containing lithium (Li), nickel (Ni), and manganese (Mn). It is done.

  Here, a coating layer is a layer which has a composition element or composition ratio different from the inner side of positive electrode material, and coat | covers at least one part of the inner surface. As described above, when the coating layer is provided by an oxide containing lithium (Li), nickel (Ni), and manganese (Mn), nickel (Ni) and manganese (Mn) in the coating layer The concentration varies in the depth direction, and the manganese (Mn) concentration is preferably higher in the outer layer portion on the opposite side than in the inner layer portion on the composite oxide particle side. This is because the charge / discharge efficiency can be further improved by making the manganese concentration in the outer layer portion higher than the average composition of the coating layer.

  Note that the coating layer refers to a region until the concentration change is substantially not observed when the concentration change of the constituent element is examined from the surface to the inside of the lithium composite oxide particles provided with the coating layer. Say. Concentration change from the surface of nickel and manganese in the lithium composite oxide particles provided with the coating layer to the inside, for example, by cutting the lithium composite oxide particles provided with the coating layer by sputtering etc. It can be measured by analysis (Auger Electron Spectroscopy; AES) or SIMS (Secondary Ion Mass Spectrometry). It is also possible to slowly dissolve lithium composite oxide particles with a coating layer in an acidic solution, etc., and measure the change over time of the elution by inductively coupled plasma (ICP) spectroscopy. It is.

  The composition ratio of nickel (Ni) and manganese (Mn) in the coating layer is preferably a molar ratio of nickel (Ni): manganese (Mn) in the range of 95: 5 to 20:80, 90: More preferably, it is within the range of 10 to 30:70. When the amount of manganese (Mn) is large, the amount of occlusion of lithium (Li) in the coating layer decreases, the capacity decreases, and the electrical resistance increases. When the amount of manganese (Mn) is small, charge / discharge This is because the efficiency cannot be sufficiently improved.

  The oxide of the coating layer further includes magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), From copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca) and strontium (Sr) At least one of the group may be included as a constituent element. This is because the stability of the positive electrode material can be further improved and the diffusibility of lithium ions can be further improved.

  For example, as a positive electrode material in which a coating layer is provided on at least a part of a lithium composite oxide, as described in JP 2000-164214 A and JP 2000-195517 A, lithium cobalt oxide or the like can be used. Examples include composite particles in which the surface of core particles made of lithium composite oxide particles is coated with fine particles made of lithium composite oxide particles such as lithium manganate having a spinel structure or nickel cobalt composite oxide.

Specifically, for _{example, Li x CoO 2, Li x} NiO 2, Li x Mn 2 O 4, Li x Co 1-y M y O 2, Li x Ni 1-y M y O 2, L x Mn 1 _-y M _y O ₂ (where, M is titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), aluminum (Al), cobalt (Co), nickel (Ni ), Copper (Cu), zinc (Zn), molybdenum (Mo), bismuth (Bi), boron (B), x represents 0 <x ≦ 1.2, and y represents 0 <Y <1), which is a composite particle obtained by coating the surface of a core particle made of any one of the lithium-containing compounds with fine particles made of any of these lithium-containing compounds.

  Examples of the method of coating the surface of the core particle made of the lithium composite oxide particles with the lithium composite oxide fine particles include a high-speed air impact method. In the high-speed airflow impact method, a mixture of powder and fine particles uniformly mixed in a high-speed airflow is dispersed, and the impact operation is repeated to give mechanical and thermal energy to the powder. Is. By this action, fine particles are uniformly attached to the powder surface, and the surface of the powder is modified.

  The positive electrode active material layer 2B may contain a conductive agent as necessary. As the conductive agent, for example, a carbon-based material such as acetylene black, graphite, or ketjen black can be used.

  Examples of the binder contained in the positive electrode active material layer 2B include polyvinylidene fluoride or a copolymer of vinylidene fluoride or a modified product thereof, polytetrafluoroethylene or a copolymer, polyacrylonitrile, polyacrylic acid ester, and the like. An acrylic resin or the like mainly composed of is used. In particular, polyvinylidene fluoride is preferable because it is excellent in durability, particularly swelling resistance.

  More specifically, examples of the vinylidene fluoride copolymer include a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, and a vinylidene fluoride-chlorotrifluoroethylene copolymer. , Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, or a copolymer obtained by further copolymerizing another ethylenically unsaturated monomer with the above exemplified copolymer. More specific examples of the copolymerizable ethylenically unsaturated monomer include, for example, acrylic ester, methacrylic ester, vinyl acetate, acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, butadiene, styrene, N- Examples include vinyl pyrrolidone, N-vinyl pyridine, glycidyl methacrylate, hydroxyethyl methacrylate, and methyl vinyl ether.

  One type of polymer may be used alone, or a plurality of types may be used in combination. Further, a polymer or other binder outside the range of such intrinsic viscosity may be mixed. It may be used.

  The content of the polymer in the positive electrode active material layer 2B is preferably in the range of 0.5 wt% to 7.0 wt%, more preferably in the range of 1.2 wt% to 4.0 wt%. It is. This is because if the content of the polymer is small, the binding property is not sufficient, and it becomes difficult to bind the positive electrode active material or the like to the positive electrode current collector 2A. Moreover, when there is much content of a polymer, it is because a polymer with low electron conductivity and ion conductivity will coat | cover a positive electrode active material, and charge / discharge efficiency will fall.

[Negative electrode]
The negative electrode 3 can be obtained by applying a negative electrode mixture obtained by mixing a negative electrode active material, a conductive agent, a binder, and the like to the surface of the negative electrode current collector 3A and providing the negative electrode active material layer 3B. .

[Negative electrode active material]
As the negative electrode active material, a negative electrode material capable of inserting and extracting lithium (Li) can be used. Examples of the negative electrode material capable of inserting and extracting lithium (Li) include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, and organic polymers. Examples thereof include carbon materials such as compound fired bodies, carbon fibers, and activated carbon. Among these, examples of the coke include pitch coke, needle coke, and petroleum coke. Here, the organic polymer compound fired body refers to a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature. Some are classified as carbonizable carbon. Examples of the polymer material include polyacetylene and polypyrrole. These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent characteristics can be obtained. Furthermore, a battery having a low charge / discharge potential, specifically, a battery having a charge / discharge potential close to that of lithium metal is preferable because a high energy density of the battery can be easily realized.

  When a carbon material is used as the negative electrode material, the mixture area density ratio of the positive electrode 2 to the negative electrode 3 (positive electrode mixture area density / negative electrode mixture area density) is in the range of 1.90 to 2.15. preferable. This is because when the mixture area density ratio is larger than 2.15, metallic lithium is deposited on the surface of the negative electrode 3 and charge / discharge efficiency or safety is lowered. Moreover, when the mixture area density ratio is smaller than 1.90, the negative electrode material not involved in the reaction with lithium (Li) as the electrode reactant increases, and the energy density decreases.

  Furthermore, as a negative electrode material capable of inserting and extracting lithium (Li), it is possible to insert and extract lithium (Li), and at least one of a metal element and a metalloid element is a constituent element. Can be included. This is because a high energy density can be obtained by using such a material. In particular, the use with a carbon material is more preferable because a high energy density can be obtained and excellent cycle characteristics can be obtained.

  This negative electrode material may be a single element or an alloy or a compound of a metal element or a metalloid element, or may have at least a part of one or more of these phases. Note that alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. Some of the structures include a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a mixture of two or more of them.

  Examples of the metal element or metalloid element constituting the negative electrode material include magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), and germanium (Ge). ), Tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium, yttrium (Y), palladium (Pd) or platinum (Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or a semimetal element in the short-period type periodic table as a constituent element is preferable, and at least one of silicon (Si) and tin (Sn) is particularly preferable. It is included as an element. This is because silicon (Si) and tin (Sn) have a large ability to occlude and release lithium (Li), and a high energy density can be obtained.

  As an alloy of tin (Sn), for example, as a second constituent element other than tin (Sn), silicon (Si), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr) The thing containing at least 1 sort can be mentioned. As an alloy of silicon (Si), for example, as a second constituent element other than silicon (Si), tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr). The thing containing 1 type can be mentioned.

  Examples of the compound of tin (Sn) or the compound of silicon (Si) include those containing oxygen (O) or carbon (C), and in addition to tin (Sn) or silicon (Si), The second constituent element may be included.

Further, examples of the negative electrode material capable of inserting and extracting lithium (Li) include other metal compounds or polymer materials. Examples of other metal compounds include oxides such as MnO ₂ , V ₂ O ₅ , and V ₆ O ₁₃ , sulfides such as NiS and MoS, and lithium nitrides such as LiN ₃ . Examples of other polymer materials include polyacetylene, polyaniline, and polypyrrole.

  The negative electrode active material layer 3B may contain a conductive agent and a binder as necessary. As the binder, any of a thermoplastic resin and a thermosetting resin may be used, but a thermoplastic resin is preferable. Examples of the thermoplastic resin that can be used as the binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). , Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer Examples thereof include a copolymer, an ethylene-methyl acrylate copolymer, and an ethylene-methyl methacrylate copolymer. These may be used alone or in combination of two or more. Moreover, these may be a crosslinked body by Na ions or the like.

  The conductive agent may be any electron conductive material that is chemically stable in the battery. For example, graphite such as natural graphite (flaky graphite, etc.), graphite such as artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and conductive such as carbon fiber and metal fiber For example, conductive fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be used. These may be used alone or in combination of two or more. Although the addition amount of a electrically conductive agent is not specifically limited, 1 wt%-30 wt% are preferable with respect to the active material particle contained in a negative electrode mixture, and 1 wt%-10 wt% are more preferable.

[Separator]
The separator 4 has, for example, a base material layer and a surface layer. The surface layer is provided on at least a part of the surface facing the positive electrode 2, more preferably on the entire surface facing the positive electrode 2, and more preferably on both surfaces. As a base material layer, it is comprised by the porous film made from synthetic resins, such as a polypropylene or polyethylene, for example, It may be set as the structure which laminated | stacked these 2 or more types of porous films.

  Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit prevention effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the base material layer because it can obtain a shutdown effect within a range of 100 ° C. or higher and 160 ° C. or lower and is excellent in electrochemical stability. Polypropylene is also preferred, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The surface layer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, aramid, and polypropylene. Thereby, chemical stability improves and the fall of charging / discharging efficiency by generation | occurrence | production of a micro short circuit is suppressed. In addition, when forming a surface layer with a polypropylene, it is good also considering a base material layer as a single layer by forming with a polypropylene.

  The thickness of the surface layer facing the positive electrode 2 is preferably in the range of 0.1 μm or more and 10 μm or less. This is because if the thickness is small, the effect of suppressing the occurrence of micro-shorts is low, and if the thickness is large, the ion conductivity decreases and the volume capacity decreases.

  The pore diameter of the separator 4 is preferably in a range in which the eluate from the positive electrode 2 or the negative electrode 3 does not permeate, and specifically in the range of 0.01 μm or more and 1 μm or less. Moreover, the thickness of the separator 4 is preferably in the range of 10 μm or more and 300 μm or less, and more preferably in the range of 15 μm or more and 30 μm or less. This is because if the separator 4 is thin, a short circuit may occur. If the separator 4 is thick, the filling amount of the positive electrode material decreases. The porosity of the separator 4 is determined by electron and ion permeability, material, or thickness, but is generally in the range of 30% to 80%, more preferably in the range of 35% to 50%. Is within. This is because if the porosity is low, the ion conductivity is lowered, and if the porosity is high, a short circuit may occur.

[Electrolytes]
The electrolyte is an electrolytic solution containing a liquid solvent and an electrolyte salt dissolved in the solvent. As the solvent, cyclic carbonates such as ethylene carbonate or propylene carbonate can be used, and it is preferable to use one of ethylene carbonate and propylene carbonate, particularly a mixture of both. This is because the cycle characteristics can be improved.

  As the solvent, in addition to these cyclic carbonates, it is preferable to use a mixture of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, or methyl propyl carbonate. This is because high ionic conductivity can be obtained.

  Further, the solvent preferably contains a fluorine-substituted cyclic carbonate. This is because a thin and uniform film can be formed on the negative electrode 3 and the cycle characteristics can be further improved. In addition, if the electrolyte contains a cyclic carbonate substituted with fluorine, there is a concern about deterioration of high-temperature cycle characteristics due to an increase in free fluorine in the nonaqueous electrolyte secondary battery in which the end-of-charge voltage is increased to 4.30 V or more. However, in one embodiment, it is considered that the calcium salt that is included in the positive electrode 2 acts to capture free fluorine and the free fluorine can be reduced, so that deterioration of high-temperature cycle characteristics can be suppressed. That is, when the positive electrode 2 contains a calcium salt and the electrolytic solution contains a fluorine-substituted cyclic carbonate, a synergistic effect of improving the cycle characteristics at room temperature and high temperature can be obtained.

  Examples of the fluorine-substituted cyclic carbonate include a compound obtained by substituting at least one of hydrogen of ethylene carbonate with fluorine. For example, 4-fluoroethylene carbonate (FEC), difluoroethylene carbonate [for example, 4,5 -Difluoroethylene carbonate (DFEC), 4,4-difluoroethylene carbonate] is preferable. Among these, 4-fluoroethylene carbonate (FEC) is more preferable because it can form a thin and uniform film on the negative electrode 3 and can further improve the cycle characteristics.

  The content of the fluorine-substituted cyclic carbonate is preferably 0.5 wt% or more and 25 wt% or less in the electrolytic solution. This is because if it is less than 0.5 wt%, the effect of improving the cycle characteristics may be reduced, and if it exceeds 25 wt%, it may be excessively decomposed on the negative electrode and the charge / discharge efficiency may be reduced.

  Furthermore, it is preferable that vinylene carbonate is contained as the solvent. The content is preferably 0.1 wt% or more and 10 wt% or less in the electrolytic solution. This is because if it is less than 0.1 wt%, the effect of improving the cycle characteristics may be reduced, and if it exceeds 10 wt%, it may be excessively decomposed on the negative electrode and the charge / discharge efficiency may be reduced.

  Further, as the solvent, butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate Methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, Nitromethane, nitroethane, sulfolane, dimethyl sulfoxide or trimethyl phosphate may be included.

The electrolyte salt contains LiPF ₆ . This is because the ion conductivity of the electrolyte can be increased by using LiPF ₆ . The concentration of LiPF ₆ is preferably in the range of 0.1 mol / kg or more and 2.0 mol / kg or less in the electrolytic solution. This is because the ion conductivity can be further increased within this range.

As the electrolyte salt, in addition to these electrolyte salts, other electrolyte salts may be mixed and used. Examples of other electrolyte salts include LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F _{5) 2, LiN (SO 2} CF 3) (SO 2 C 2 F 5), LiN (SO 2 CF 3) (SO 2 C 3 F 7), LiN (SO 2 CF 3) (SO 2 C 4 F 9 ), LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, or LiBr. Other electrolyte salts may be used alone or in combination of two or more.

  Further, the electrolyte salt may contain an organic lithium salt in which an electron-withdrawing organic substituent which is a carbonyl group or a sulfonyl group is bonded to a B (boron) atom serving as an anion center via an oxygen atom. .

  Specific examples of the organic lithium salt in which an electron-withdrawing organic substituent which is a carbonyl group or a sulfonyl group is bonded to a B (boron) atom serving as an anion center via an oxygen atom are as follows.

  The group III b to V group b atoms that are the anion centers may be any of B (boron), N (nitrogen), P (phosphorus), Ga (gallium), Al (aluminum), Si (silicon), and the like. In view of the number of bonds, the group IIIb to group IVb atoms are preferable, and the group IIIb atom is particularly preferable. B (boron) is most suitable as the atom serving as the anion center.

  That is, boron (B) has an atomic weight as small as 10.8, and more than four oxygen (O) and nitrogen (N) can be bonded as an element contained in organic matter. This is because it has the ability to bond to many organic substituents having electron withdrawing properties.

  An oxygen atom is interposed between the anion-centered atom and the electron-withdrawing organic substituent directly, and the oxygen atom has a high electronegativity. In addition, since only two bonds are present for stabilization, an electron-withdrawing organic substituent can be bound in a state with little steric hindrance. And the electron-withdrawing organic substituent attracts electrons to the anion-centered atom through an oxygen atom, lowers the electron density of the anion-centered atom, and makes it difficult to take out the electron from the anion-center. Prevents the anion from being oxidized.

  Examples of the electron withdrawing organic substituent include a carbonyl group, a sulfonyl group, an amino group, a cyano group, and a halogenated alkyl group. Among these, a carbonyl group and a sulfonyl group are suitable because they can be easily synthesized.

  Specific examples of the organic lithium salt as described above include, for example, LiBXX ′ and LiBF2X [where X and X ′ are electron-withdrawing organic substituents having oxygen bonded to B (boron) atoms, for example, , X, X ′ = — O—C (═O) — (CRR ′) n—C (═O) —O—, —O—S (═O) —O— (CRR ′) n—O—S (= O) —O—, n is an integer from 0 to 5, and R and R ′ are alkyl groups or halogen atoms such as H (hydrogen) atom, fluorine (F), chlorine (Cl), etc.] . Among these, lithium bisoxalate borate represented by Chemical Formula 1 and lithium difluorooxalate borate represented by Chemical Formula 2 are preferable.

  This non-aqueous electrolyte secondary battery can be manufactured as described below, for example. First, for example, a positive electrode active material, a conductive agent, a calcium salt, and a polymer containing vinylidene fluoride as components are mixed to prepare a positive electrode mixture, and this positive electrode mixture is mixed with N-methyl-2- A paste-like positive electrode mixture slurry is prepared by dispersing in a solvent such as pyrrolidone. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 2 </ b> A, the solvent is dried, and the positive electrode active material layer 2 </ b> B is formed by compression molding with a roll press or the like, thereby forming the positive electrode 2.

  Next, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste-like negative electrode mixture Make a slurry. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 3A, the solvent is dried, and the negative electrode active material layer 3B is formed by compression molding with a roll press machine or the like, and the negative electrode 3 is manufactured.

  Next, the positive electrode lead 13 is attached to the positive electrode current collector 2A by welding or the like, and the negative electrode lead 14 is attached to the negative electrode current collector 3A by welding or the like. Thereafter, the positive electrode 2 and the negative electrode 3 were wound through the separator 4, and the tip of the positive electrode lead 13 was welded to the safety valve mechanism 8, and the tip of the negative electrode lead 14 was welded to the battery can 1 and wound. The positive electrode 2 and the negative electrode 3 are sandwiched between a pair of insulating plates 5 and 6 and stored in the battery can 1.

  After the positive electrode 2 and the negative electrode 3 are housed in the battery can 1, the electrolyte is injected into the battery can 1 and impregnated in the separator 4. Thereafter, the battery lid 7, the safety valve mechanism 8 and the heat sensitive resistance element 9 are fixed to the opening end of the battery can 1 by caulking through the gasket 10. As described above, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention shown in FIG. 1 is manufactured.

  In this nonaqueous electrolyte secondary battery, for example, when charged, lithium ions are released from the positive electrode active material layer 2B, and lithium contained in the negative electrode active material layer 3B can be occluded and released through the electrolytic solution. Occluded in possible negative electrode materials. Next, when discharge is performed, lithium ions occluded in the negative electrode material capable of inserting and extracting lithium in the negative electrode active material layer 3B are released and inserted in the positive electrode active material layer 2B through the electrolytic solution. The

  In the nonaqueous electrolyte secondary battery according to one embodiment of the present invention, the open circuit voltage at the time of full charge is set in the range of 4.30 V to 4.45, so that a high energy density can be obtained. In addition, it is preferable that the amount of the electrolytic solution is appropriately adjusted with respect to the space volume of the wound electrode body 20 including the positive electrode 2, the negative electrode 3, and the separator 4, and vinylene carbonate is included in the electrolytic solution. This is because deterioration of charge / discharge cycle characteristics can be further suppressed. Furthermore, it is preferable that the widths of the positive electrode 2, the negative electrode 3, and the separator 4 of the spirally wound electrode body 20 have a relationship of separator width> negative electrode width> positive electrode width, and thereby obtain better charge / discharge cycle characteristics. Can do.

  In the above-described embodiment, the positive electrode 2 is made to contain a calcium salt. However, the present invention is not limited to this. For example, a calcium salt may be included in the electrolyte, or a calcium salt may be included in both the positive electrode and the electrolyte.

  As described below, non-aqueous electrolyte secondary batteries of Sample 1-1 to Sample 8-4 were fabricated and their characteristics were evaluated. The nonaqueous electrolyte secondary battery shown in FIGS. 1 and 2 was produced.

<Sample 1-1 to Sample 1-20>
<Sample 1-1>
(Preparation of positive electrode active material I)
First, the preparation method of the positive electrode active material I used for the nonaqueous electrolyte secondary battery of Sample 1-1 will be described. The positive electrode active material I was prepared by mixing two types of lithium-cobalt composite oxides [LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ] having different particle diameters as described below.

First, a coprecipitated hydroxide represented by LiOH and Co _0.98 Al _0.01 Mg _0.01 (OH) ₂ was mixed in a mortar so that the molar ratio of Li: transition metals was 1: 1. The mixture was heat treated at 800 ° C. for 12 hours in an air atmosphere and then pulverized, and a lithium-cobalt composite oxide having a specific surface area of 0.44 m ² / g and an average particle size of 6.2 μm (BET (Brunauer Emmitt Teller) method) A) [LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ] and a lithium-cobalt composite oxide (B) having a specific surface area of 0.20 m ² / g and an average particle diameter of 16.7 μm by the BET method [LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ] was obtained. The positive electrode active material I was obtained by mixing (A) and (B) at a mass ratio of 85:15. When the positive electrode active material I was subjected to X-ray diffraction analysis using CuKα, it was found to be an R-3 rhombohedral layered rock salt structure.

(Preparation of positive electrode)
First, a positive electrode mixture was prepared by mixing positive electrode active material I, ketjen black as a conductive agent, polyvinylidene fluoride as a binder, and calcium oxide (CaO) as a calcium salt. The ratio of ketjen black and polyvinylidene fluoride in the positive electrode mixture was the same. In Sample 1-1, the amount of calcium oxide (CaO) added is 1 wt%.

  Next, the positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is applied to both sides of a positive electrode current collector 2A made of a strip-shaped aluminum foil having a thickness of 15 μm, and dried. The positive electrode active material layer 2B was formed by compression molding with a roll press machine, and the positive electrode 2 was produced. Next, a positive electrode lead 25 made of nickel was attached to the positive electrode current collector 21A.

(Preparation of negative electrode)
As a negative electrode material, 96 wt% of graphite powder having a specific surface area of 3.0 m ² / g by BET method, 2 wt% of vapor grown carbon fiber as a conductive agent, and 1 wt% of carboxymethyl cellulose (CMC) as a thickener / binder Then, 1 wt% of styrene butadiene rubber (SBR) was mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is dispersed in ion-exchanged water as a solvent to form a negative electrode mixture slurry, which is applied to both sides of the negative electrode current collector 3A made of a strip-shaped copper foil having a thickness of 8 μm and dried. The negative electrode active material layer 3B was formed by compression molding to produce the negative electrode 3.

Here, when the volume density of the negative electrode active material layer 3B was examined, it was 1.70 g / cm ³ . Next, a negative electrode lead 14 made of nickel was attached to the negative electrode current collector 3A. At that time, the amounts of the positive electrode material and the negative electrode material were adjusted so that the open circuit voltage at the time of full charge was 4.20 V, and the capacity of the negative electrode 3 was expressed by the capacity component due to insertion and extraction of lithium.

(Preparation of electrolyte)
The electrolyte solution, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), and vinylene carbonate (VC), and LiPF ₆ as an electrolyte salt, a 18.2: 56.6 : 5.0: 1.0: 19.2 (EC: DMC: EMC: VC: LiPF ₆ ) prepared by mixing at a mass ratio.

(Production of wound electrode body)
The wound electrode body 20 was produced by winding the positive electrode 2, the negative electrode 3, and the separator 4 having a thickness of 20 μm in a cylindrical shape. Specifically, it was produced as described below.

  After each of the positive electrode 2 and the negative electrode 3 was prepared, a microporous membrane separator 4 was prepared, and the negative electrode 3, the separator 4, the positive electrode 2, and the separator 4 were laminated in this order, and this laminate was wound many times in a spiral shape. A jelly roll type wound electrode body 20 was produced. The separator 4 has a thickness of 20 μm and has a three-layer structure in which a polypropylene layer is provided on both sides of a polyethylene layer.

  The strip-shaped separator 4, the negative electrode 3, and the positive electrode 2 were wound so that the width of the separator was greater than the negative electrode width> the positive electrode width. The reason for this winding is that lithium in the positive electrode 2 wraps around the negative electrode 3 during charging and crystal grows in a dendrite shape in the negative electrode 3, or the dendritic crystal reaches the positive electrode 2. This is because it is possible to more effectively prevent the internal short circuit, so that even better charge / discharge cycle characteristics can be obtained. The electrode lengths of the positive electrode 2 and the negative electrode 3 were adjusted so as to have an element diameter of 17.40 mm using a 3.5φ winding core.

(Battery assembly)
The produced wound electrode body 20 is sandwiched between a pair of insulating plates 5 and 6, the negative electrode lead 14 is welded to the battery can 11, the positive electrode lead 13 is welded to the safety valve mechanism 8, and the wound electrode body 20 is attached to the battery can. 1 was stored inside. After that, the above electrolyte solution was injected into the battery can 1 and the battery lid 7 was caulked to the battery can 1 via the gasket 10. As described above, a cylindrical nonaqueous electrolyte secondary battery having an outer diameter of 18 mm and a height of 65 mm was obtained.

<Sample 1-2>
A nonaqueous electrolyte secondary battery of Sample 1-2 was fabricated in the same manner as Sample 1-1, except that the open circuit voltage during full charge was designed to be 4.30V.

<Sample 1-3>
A nonaqueous electrolyte secondary battery of Sample 1-3 was produced in the same manner as Sample 1-1, except that the open circuit voltage during full charge was designed to be 4.35V.

<Sample 1-4>
A nonaqueous electrolyte secondary battery of Sample 1-4 was fabricated in the same manner as Sample 1-1, except that the open circuit voltage during full charge was designed to be 4.45V.

<Sample 1-5>
A nonaqueous electrolyte secondary battery of Sample 1-5 was fabricated in the same manner as Sample 1-1, except that the open circuit voltage at the time of full charge was designed to be 4.50V.

<Sample 1-6>
A nonaqueous electrolyte secondary battery of Sample 1-6 was produced in the same manner as Sample 1-1, except that CaO was not added to the positive electrode mixture.

<Sample 1-7>
A nonaqueous electrolyte secondary battery of Sample 1-7 was fabricated in the same manner as Sample 1-6, except that the open circuit voltage during full charge was designed to be 4.30V.

<Sample 1-8>
A non-aqueous electrolyte secondary battery of Sample 1-8 was fabricated in the same manner as Sample 1-6, except that the open circuit voltage during full charge was designed to be 4.35V.

<Sample 1-9>
A non-aqueous electrolyte secondary battery of Sample 1-9 was fabricated in the same manner as Sample 1-6 except that the open circuit voltage during full charge was designed to be 4.45V.

<Sample 1-10>
A non-aqueous electrolyte secondary battery of Sample 1-10 was fabricated in the same manner as Sample 1-6 except that the open circuit voltage during full charge was designed to be 4.50V.

<Sample 1-11>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 51.6: 5.0: 1.0: 5.0: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) -A nonaqueous electrolyte secondary battery of Sample 1-11 was produced in the same manner as Sample 1-1, except that an electrolytic solution containing 5 wt% of fluoroethylene (FEC) was used.

<Sample 1-12>
A nonaqueous electrolyte secondary battery of Sample 1-12 was fabricated in the same manner as Sample 1-11 except that the open circuit voltage during full charge was designed to be 4.30V.

<Sample 1-13>
A non-aqueous electrolyte secondary battery of Sample 1-13 was fabricated in the same manner as Sample 1-11 except that the open circuit voltage during full charge was designed to be 4.35V.

<Sample 1-14>
A nonaqueous electrolyte secondary battery of Sample 1-14 was fabricated in the same manner as Sample 1-11 except that the open circuit voltage during full charge was designed to be 4.45 V.

<Sample 1-15>
A nonaqueous electrolyte secondary battery of Sample 1-15 was fabricated in the same manner as Sample 1-11 except that the open circuit voltage during full charge was 4.50V.

<Sample 1-16>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 51.6: 5.0: 1.0: 5.0: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) -A nonaqueous electrolyte secondary battery of Sample 1-16 was produced in the same manner as Sample 1-6, except that an electrolytic solution containing 5 wt% of fluoroethylene (FEC) was used.

<Sample 1-17>
A nonaqueous electrolyte secondary battery of Sample 1-17 was fabricated in the same manner as Sample 1-16, except that the open circuit voltage during full charge was designed to be 4.30V.

<Sample 1-18>
A nonaqueous electrolyte secondary battery of Sample 1-17 was fabricated in the same manner as Sample 1-16, except that the open circuit voltage during full charge was designed to be 4.35V.

<Sample 1-19>
A nonaqueous electrolyte secondary battery of Sample 1-19 was fabricated in the same manner as Sample 1-16, except that the open circuit voltage during full charge was designed to be 4.45V.

<Sample 1-20>
A non-aqueous electrolyte secondary battery of Sample 1-20 was fabricated in the same manner as Sample 1-16 except that the open circuit voltage at the time of full charge was designed to be 4.50V.

<Sample 2-1 to Sample 2-10>
<Sample 2-1>
Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), and vinylene carbonate (VC), and LiPF ₆ as an electrolyte _salt, a 18.2: 56.6: 5.0: Sample 2 in the same manner as Sample 1-13 except that an electrolyte prepared by mixing at a mass ratio of 1.0: 19.2 (EC: DMC: EMC: VC: LiPF ₆ ) was used. A non-aqueous electrolyte secondary battery of -1 was produced.

<Sample 2-2>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 56.55: 5.0: 1.0: 0.05: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) -A non-aqueous electrolyte secondary battery of Sample 2-2 was fabricated in the same manner as Sample 1-13, except that an electrolytic solution containing 0.05 wt% of fluoroethylene (FEC) was used.

<Sample 2-3>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 51.6: 5.0: 1.0: 0.50: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) -A nonaqueous electrolyte secondary battery of Sample 2-3 was produced in the same manner as Sample 1-13, except that an electrolyte solution containing 0.50 wt% of fluoroethylene (FEC) was used.

<Sample 2-4>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 55.6: 5.0: 1.0: 1.0: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) -A nonaqueous electrolyte secondary battery of Sample 2-4 was produced in the same manner as Sample 1-13, except that an electrolytic solution containing 1 wt% of fluoroethylene (FEC) was used.

<Sample 2-5>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 53.6: 5.0: 1.0: 3: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ), an electrolyte prepared by mixing at a mass ratio, that is, 4-fluoro A nonaqueous electrolyte secondary battery of Sample 2-5 was produced in the same manner as Sample 1-13, except that an electrolyte solution containing 3 wt% of ethylene (FEC) was used.

<Sample 2-6>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 46.6: 5.0: 1.0: 10: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) electrolyte solution prepared by mixing at a mass ratio, that is, 4-fluoro A nonaqueous electrolyte secondary battery of Sample 2-6 was produced in the same manner as Sample 1-13, except that an electrolyte solution containing 10 wt% of ethylene (FEC) was used.

<Sample 2-7>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 31.6: 5.0: 1.0: 25: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ), an electrolyte prepared by mixing at a mass ratio, that is, 4-fluoro A nonaqueous electrolyte secondary battery of Sample 2-7 was produced in the same manner as Sample 1-13, except that an electrolyte solution containing 25 wt% ethylene (FEC) was used.

<Sample 2-8>
18.2 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4-fluoroethylene (FEC), and LiPF ₆ as an electrolyte salt. : 26.6: 5.0: 1.0: 30: 19.2 (EC: DMC: EMC: VC: FEC: LiPF ₆ ) electrolyte solution prepared by mixing at a mass ratio, that is, 4-fluoro A nonaqueous electrolyte secondary battery of Sample 2-8 was produced in the same manner as Sample 1-13, except that an electrolyte solution containing 30 wt% of ethylene (FEC) was used.

<Sample 2-9>
Ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4,5-difluoroethylene carbonate (DFEC), and LiPF ₆ as an electrolyte salt. Electrolyte prepared by mixing at a mass ratio of 18.2: 55.6: 5.0: 1.0: 1.0: 19.2 (EC: DMC: EMC: VC: DFEC: LiPF ₆ ) That is, a nonaqueous electrolyte secondary battery of Sample 2-9 was produced in the same manner as Sample 1-13 except that an electrolyte solution containing 1.0 wt% of 4,5-difluoroethylene carbonate (DFEC) was used. .

<Sample 2-10>
Ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 4,5-difluoroethylene carbonate (DFEC), and LiPF ₆ as an electrolyte salt. Electrolyte prepared by mixing at a mass ratio of 18.2: 53.6: 5.0: 1.0: 3.0: 19.2 (EC: DMC: EMC: VC: DFEC: LiPF ₆ ) That is, a nonaqueous electrolyte secondary battery of Sample 2-10 was produced in the same manner as Sample 1-13, except that an electrolyte solution containing 3 wt% of 4,5-difluoroethylene carbonate (DFEC) was used.

(Sample 3-1 to Sample 3-11)
<Sample 3-1>
A nonaqueous electrolyte secondary battery of Sample 3-1 was produced in the same manner as Sample 1-8, except that 0.05 wt% of CaO was added to the positive electrode mixture.

<Sample 3-2>
A nonaqueous electrolyte secondary battery of Sample 3-2 was fabricated in the same manner as Sample 1-8, except that 0.1 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-3>
A nonaqueous electrolyte secondary battery of Sample 3-3 was fabricated in the same manner as Sample 1-8, except that 0.5 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-4>
A nonaqueous electrolyte secondary battery of Sample 3-4 was fabricated in the same manner as Sample 1-8, except that 2 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-5>
A nonaqueous electrolyte secondary battery of Sample 3-5 was produced in the same manner as Sample 1-8, except that 3 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-6>
A nonaqueous electrolyte secondary battery of Sample 3-6 was fabricated in the same manner as Sample 1-18, except that 0.05 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-7>
A nonaqueous electrolyte secondary battery of Sample 3-7 was produced in the same manner as Sample 1-18, except that 0.1 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-8>
A nonaqueous electrolyte secondary battery of Sample 3-8 was produced in the same manner as Sample 1-18, except that 0.5 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-9>
A nonaqueous electrolyte secondary battery of Sample 3-9 was produced in the same manner as Sample 1-18, except that 2 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 3-10>
A nonaqueous electrolyte secondary battery of Sample 3-10 was produced in the same manner as Sample 1-18, except that 3 wt% of calcium oxide (CaO) was added to the positive electrode mixture.

<Sample 4-1 to Sample 4-5>
<Sample 4-1>
A nonaqueous electrolyte secondary battery of Sample 4-1 was produced in the same manner as Sample 1-18, except that 1 wt% of calcium carbonate (CaCO ₃ ) was added to the positive electrode mixture.

<Sample 4-2>
A non-aqueous electrolyte secondary battery of Sample 4-2 was produced in the same manner as Sample 1-18, except that 1 wt% of calcium phosphate (CaPO ₄ ) was added to the positive electrode mixture.

<Sample 4-3>
A nonaqueous electrolyte secondary battery of Sample 4-3 was fabricated in the same manner as Sample 1-18, except that 1 wt% of calcium nitrate [Ca (NO ₃ ) ₂ ] was added to the positive electrode mixture.

<Sample 4-4>
A nonaqueous electrolyte secondary battery of Sample 4-4 was produced in the same manner as Sample 1-18, except that 1 wt% of calcium acetate [Ca (CH ₃ COO) ₂ ] was added to the positive electrode mixture.

<Sample 4-5>
A nonaqueous electrolyte secondary battery of Sample 4-5 was produced in the same manner as Sample 1-18, except that 1 wt% of calcium hydroxide [Ca (OH) ₂ ] was added to the positive electrode mixture.

<Sample 5-1 to Sample 5-3>
<Sample 5-1>
A nonaqueous electrolyte secondary battery of Sample 5-1 was produced in the same manner as Sample 1-13, except that polyethylene (PE) was used as the separator.

<Sample 5-2>
Sample 1-13, except that a three-layer laminated separator (PVDF / PE / PVDF) in which polyvinylidene fluoride (PVDF), polyethylene (PE), and polyvinylidene fluoride (PVDF) were sequentially laminated was used as the separator. In the same manner as described above, a non-aqueous electrolyte secondary battery of Sample 5-2 was produced.

<Sample 5-3>
Sample 5-3 was prepared in the same manner as Sample 1-13, except that a three-layer laminated separator (aramid / PE / aramid) in which aramid, polyethylene (PE), and aramid were sequentially laminated was used as the separator. A non-aqueous electrolyte secondary battery was produced.

<Sample 6-1 to Sample 6-2>
<Sample 6-1>
A nonaqueous electrolyte secondary battery of Sample 6-1 was produced in the same manner as Sample 1-13, except that the open circuit voltage during full charge was designed to be 4.45V.

<Sample 6-2>
A nonaqueous electrolyte secondary battery of Sample 6-2 was produced in the same manner as Sample 1-13, except that the positive electrode active material II produced as described below was used as the positive electrode active material.

(Preparation of positive electrode active material II)
A positive electrode active material and nickel oxide and manganese oxide having an average particle diameter of 1 μm are mixed at a mass ratio of 96: 2: 2, and dry mixing is performed using a mechanofusion system manufactured by Hosokawa Micron. The positive electrode active material I was coated with nickel oxide and manganese oxide. Next, this was baked in air at 950 ° C. for 10 hours. Thus, a positive electrode active material II having a structure in which the surface of the positive electrode active material was covered with nickel oxide and manganese oxide was obtained. In addition, when the average particle diameter of the produced positive electrode active material II was measured, a big difference with the average particle diameter of the positive electrode active material I was not seen.

<Sample 6-3>
A nonaqueous electrolyte secondary battery of Sample 6-3 was fabricated in the same manner as Sample 6-2, except that the open circuit voltage during full charge was designed to be 4.45V.

<Sample 7-1>
Sample 1-13, except that calcium oxide (CaO) was not added to the positive electrode mixture, but was added to the electrolyte solution, and the open circuit voltage at the time of full charge was designed to be 4.45V. In the same manner as described above, a non-aqueous electrolyte secondary battery of Sample 7-1 was produced. In addition, the addition amount of calcium oxide was added so that it might become the same as 0.5 wt% in the positive electrode 2 as the amount of calcium oxide added inside a battery.

<Sample 8-1 to Sample 8-4>
<Sample 8-1>
A nonaqueous electrolyte secondary battery of Sample 8-1 was produced in the same manner as Sample 1-13, except that the area density ratio was adjusted to 1.90.

<Sample 8-2>
A nonaqueous electrolyte secondary battery of Sample 8-2 was fabricated in the same manner as Sample 1-13, except that the area density ratio was adjusted to 2.06.

<Sample 8-3>
A nonaqueous electrolyte secondary battery of Sample 8-3 was produced in the same manner as Sample 1-13, except that the area density ratio was adjusted to 2.15.

<Sample 8-4>
A nonaqueous electrolyte secondary battery of Sample 8-4 was produced in the same manner as Sample 1-13, except that the area density ratio was adjusted to 2.20.

  As described below, the prepared non-aqueous electrolyte secondary batteries of Sample 1-1 to Sample 8-4 were subjected to an initial charge / discharge test and a cycle evaluation test.

(Initial charge / discharge)
About the non-aqueous electrolyte secondary batteries of Sample 1-1 to Sample 8-4, constant current-constant voltage charging (at the upper limit voltage shown in Tables 1 to 8 at 25 ° C. and a current corresponding to 0.1 C) (CCCV charging), the battery was stored at 45 ° C. for 2 days, and then discharged at a current corresponding to 0.2 C until 3.0 V was reached.

  Next, charging / discharging was repeated 5 times within the range of the charging upper limit voltage and 3.0 V shown in Tables 1 to 8. As a charging condition, a current equivalent to 0.5 C was used in CCCV charging. Discharging was performed at a constant current (CC discharge) corresponding to 0.2 C until 3.0 V was reached. And the average discharge capacity of these 5 cycles was made into the rated discharge capacity.

(Cycle evaluation test)
The nonaqueous electrolyte secondary batteries of Sample 1-1 to Sample 8-4 were charged and discharged, and the discharge capacity at the fifth cycle and the discharge capacity retention ratio at the 300th cycle were measured. At that time, after charging at a constant voltage and constant current at 0.7 C up to the upper limit voltage shown in Tables 1 to 8, the charging current is reduced to 50 mA at the upper limit voltage shown in Tables 1 to 8, and discharging is performed. The test was performed at a constant current of 0.5 C until the terminal voltage reached 3.0V.

  The capacity retention rate at the 300th cycle was determined as the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the 3rd cycle (discharge capacity at the 300th cycle / discharge capacity at the 3rd cycle) × 100 (%). The room temperature cycle test was performed in a constant temperature bath at 25 ° C. The high temperature cycle was performed in a constant temperature bath at 45 ° C.

  Table 1 shows the test results of Sample 1-1 to Sample 1-20. The area density ratio shown in Table 1 was determined as described below.

First, an electrode (positive electrode or negative electrode) was punched out in a 15φ circular shape with the mixture and current collector integrated, and the mass A was measured. Next, separately, only the current collector was punched out in a circular shape of 15φ, and its mass B was measured. From the above, the area density ratio was determined for the measured mass A and mass B using the following formulas (1) and (formula 2).
Formula (1)
Electrode mixture area density = (mass A−mass B) / (7.5 × 7.5 × 3.14)
Formula (2)
Area density ratio = (positive electrode mixture area density) / (negative electrode mixture area density)
(Same for Sample 2-1 to Sample 8-4)

  As shown in Table 1, according to a comparison between Sample 1-1 designed to have an open circuit voltage of 4.20 V during full charge and Sample 1-6, the room temperature cycle is performed regardless of the presence or absence of calcium oxide (CaO). In the high temperature cycle, no significant change in capacity retention rate was observed.

  However, according to the comparison between Sample 1-2 to Sample 1-4 and Sample 1-7 to Sample 1-9, in which the open circuit voltage during full charge is designed to be 4.30V to 4.45V, the room temperature cycle The capacity retention ratio and the high-temperature cycle capacity retention ratio were larger in Samples 1-2 to 1-4 using the positive electrode to which calcium oxide (CaO) was added than in Samples 1-7 to 1-9. That is, it was found that higher cycle characteristics can be obtained by adding calcium oxide (CaO) to the positive electrode.

  Moreover, according to the comparison between Sample 1-5 and Sample 1-10, no clear difference was observed in the room temperature cycle capacity retention rate and the high temperature cycle capacity retention rate, and both exhibited low capacity retention rates. This result is because when the charging upper limit voltage is set to 4.50 V or more, the positive electrode active material is largely deteriorated, so that the effect of including calcium oxide (CaO) in the positive electrode could not be obtained. I guess.

  Furthermore, according to the comparison between Sample 1-1 to Sample 1-10 and Sample 1-11 to Sample 1-20, room temperature cycle characteristics are obtained by including 4-fluoroethylene carbonate (FEC) in the electrolyte. , Found to tend to improve.

  Further, in Samples 1-12 to 1-14, by including calcium oxide (CaO) in the positive electrode, high temperature cycle characteristics were improved while maintaining high room temperature cycle characteristics. That is, the open circuit voltage at the time of full charge is in the range of 4.30V to 4.45V so that the positive electrode contains calcium oxide (CaO) and the electrolyte contains 4-fluoroethylene carbonate (FEC). It was found that the most excellent room temperature cycle characteristics and high temperature cycle characteristics can be obtained.

  Table 2 shows the test results of Sample 2-1 to Sample 2-10 and Sample 1-13.

  As shown in Table 2, according to Sample 2-1 to Sample 2-8 and Sample 1-13, Sample 2-3 to Sample 2- in which the addition amount of 4-fluoroethylene carbonate (FEC) is 0.50 wt% or more. 7. Sample 1-13 showed a high room temperature cycle capacity retention rate. In addition, a sufficiently high room temperature cycle capacity retention rate was obtained in Samples 2-1 to 2-7 and Sample 1-13 in which the amount of 4-fluoroethylene carbonate (FEC) added was 3 wt% or more.

  Also, according to Sample 2-1 to Sample 2-8 and Sample 1-13, in Sample 2-2 to Sample 2-7 and Sample 1-13, the high temperature cycle capacity retention rate increases as the amount of addition increases. However, in Sample 2-8 in which the amount of 4-fluoroethylene carbonate (FEC) added exceeded 25 wt%, the high-temperature cycle capacity retention rate decreased. From the above, it was found that the amount of 4-fluoroethylene carbonate (FEC) in the electrolytic solution is preferably 0.5 wt% or more and 25 wt% or less in consideration of the room temperature cycle capacity maintenance rate and the high temperature cycle capacity maintenance rate.

  Furthermore, according to Sample 2-9 to Sample 2-10, even when 4,5-difluoroethylene carbonate (DFEC) is added, a high room temperature cycle capacity retention rate and a high temperature cycle capacity retention rate can be obtained similarly. I understood it. Further, although not shown in Table 2, 0.5 wt% to 25 wt% of 4,5-difluoroethylene carbonate (DFEC) tends to be preferable as in 4-fluoroethylene carbonate (FEC).

  Table 3 shows the test results of Sample 3-1 to Sample 3-10, Sample 1-8, Sample 1-3, Sample 1-18, and Sample 1-13.

  As shown in Table 3, according to sample 1-8, sample 3-1 to sample 3-5, and sample 1-3, by adding calcium oxide (CaO), room temperature cycle capacity maintenance rate and high temperature cycle capacity maintenance It was found that the rate could be improved. It was also found that a higher high-temperature cycle capacity retention rate could be obtained when the amount of calcium oxide salt added was 0.1 wt% or more.

  In addition, it was found that when the amount of calcium oxide added is 3.0 wt% or more, the rated capacity is significantly reduced. In order to maintain a high rated capacity, it is considered that the smaller the amount of calcium salt added, the better. From the above, it was found that the amount of calcium salt added is preferably 0.1 wt% or more and 2.0 wt% or less in consideration of the rated capacity, the room temperature cycle capacity maintenance ratio, and the high temperature cycle capacity maintenance ratio.

  Furthermore, according to Sample 1-18, Sample 4-1 to Sample 4-5, and Sample 1-13, when an electrolyte containing 4-fluoroethylene carbonate (FEC) is used, the amount of calcium salt added is the rated capacity. In view of the room temperature cycle capacity maintenance rate and the high temperature cycle capacity maintenance rate, it was found that 0.1 wt% or more and 2.0 wt% or less is preferable.

  Table 4 shows the test results of Sample 4-1 to Sample 4-5, Sample 1-18, and Sample 1-13.

  As shown in Table 4, according to the comparison between sample 1-18, sample 1-13, and sample 4-1 to sample 4-5, in sample 1-13, sample 4-1 to sample 4-5, calcium Compared with sample 1-18 to which no salt was added, the maintenance rate of the high temperature cycle was maintained while maintaining the maintenance rate of the room temperature cycle. That is, it was found that the effect of improving the room temperature cycle capacity maintenance rate and the high temperature cycle capacity maintenance rate can be obtained regardless of the type of calcium salt.

  Table 5 shows the test results of Samples 5-1 to 5-3 and Sample 1-13.

  As shown in Table 5, according to sample 5-1 to sample 5-3 and sample 1-13, sample 1-13 using (polypropylene / polyethylene / polypropylene), (polyvinylidene fluoride (PVDF) / polyethylene (PE ) / PVDF) sample 5-2 and (aramid / polyethylene (PE) / aramid) sample 5-3, compared with 5-1 using a polyethylene separator, room temperature cycle capacity retention rate and high temperature The cycle capacity maintenance rate increased. Although not shown in the table, in Sample 5-1 using a polyethylene (PE) separator, cycle deterioration was observed from around 280 cycles, and in particular, high temperature cycle characteristics tended to be greatly deteriorated. .

  Table 6 shows the test results of Sample 6-1 to Sample 6-3 and Sample 1-13.

  As shown in Table 6, according to Samples 6-1 to 6-3 and Samples 1-13, in the battery designed to be 4.35V open circuit battery at the time of full charge, using PP / PE / PP separator, When the positive electrode active material II is used in a battery in which 5 wt% of 4-fluoroethylene carbonate (FEC) is added to the electrolytic solution, the room temperature cycle capacity maintenance rate and the high temperature cycle capacity maintenance rate are higher than those of the positive electrode active material I. There was a trend.

  In addition, even when the positive electrode active material II is used in a battery designed at 4.45 V, a high room temperature cycle capacity retention ratio and a high temperature cycle capacity retention ratio can be obtained due to the presence of calcium salt and 4-fluoroethylene carbonate (FEC). It turns out that it is obtained.

  Table 7 shows the test results of Sample 7-1 and Sample 1-13.

  As shown in Table 7, according to Samples 1-13 and 7-1, even when a calcium salt is added to the electrolyte, high cycle characteristics are obtained in the same manner, and when mixed in the positive electrode, It was confirmed that a similar effect was obtained.

  Table 8 shows the test results of Samples 8-1 to 8-4 and Sample 1-13.

  As shown in Table 8, according to Samples 8-1 to 8-4 and Sample 1-13, when the open circuit voltage at the time of full charge is fixed at 4.35 V, the area density ratio (area density of positive electrode mixture) When the ratio / area density ratio of the negative electrode mixture is low, the rated capacity tends to be low. This is because an unused negative electrode active material increases. Further, when the surface precision ratio was 2.20 or more, the cycle characteristics tended to be remarkably deteriorated. That is, it was found that a preferable surface density ratio is 1.90 or more and 2.15 or less.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above-described embodiments and examples, and various modifications and applications can be made without departing from the gist of the present invention. Is possible. For example, in the above-described embodiments and examples, the nonaqueous electrolyte secondary battery having a winding structure has been described. However, the present invention relates to a nonaqueous electrolyte secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. The same applies to. In addition, the present invention can also be applied to non-aqueous electrolyte secondary batteries such as a so-called coin type, button type, square type, and laminated film type.

  Further, in the above-described embodiments and examples, the case where the electrolytic solution in which the electrolyte salt is dissolved in the liquid solvent has been described. However, the present invention can be applied to the case where another electrolyte is used. it can. Examples of other electrolytes include so-called gel electrolytes in which an electrolytic solution is held in a polymer compound.

  Further, in the above-described embodiments and examples, a so-called lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium has been described. The capacity of the negative electrode used is a so-called lithium metal secondary battery whose capacity is represented by the deposition and dissolution of lithium, or the negative electrode material capable of occluding and releasing lithium is more charged than the positive electrode. The same applies to a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof, by reducing the capacity. be able to.

It is a schematic sectional drawing of the nonaqueous electrolyte secondary battery by one Embodiment of this invention. FIG. 2 is an enlarged sectional view of a part of a wound electrode body shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery can 2 ... Positive electrode 2A ... Positive electrode collector 2B ... Positive electrode active material layer 3A ... Negative electrode collector 3B ... Negative electrode active material layer 3 ... Negative electrode 4. ··· Separator 5, 6 ··· Insulating plate 7 ··· Battery cover 8 · · · Safety valve mechanism 9 · · · Thermal resistance element 10 · · · Gasket 11 · · · Disk plate 12 · · · Center pin 13 · · · ..Positive electrode lead 14 ... Negative electrode lead 20 ... Wound electrode body

Claims (11)

A positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolyte;
An open circuit voltage in a fully charged state per pair of the positive electrode and the negative electrode is in the range of 4.30V to 4.45V,
A non-aqueous electrolyte secondary battery, wherein a calcium salt is contained in at least one of the positive electrode and the electrolyte. The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte includes a compound in which at least one of hydrogen of ethylene carbonate is substituted with fluorine. The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte contains at least one of 4-fluoroethylene carbonate and difluoroethylene carbonate. The area density ratio (a mixture area density of the positive electrode / a mixture area density of the negative electrode) of the mixture area density of the positive electrode and the mixture area density of the negative electrode is 1.90 or more and 2.15 or less. The nonaqueous electrolyte secondary battery according to claim 1. 2. The non-aqueous electrolyte according to claim 1, wherein at least one of the 4-fluoroethylene carbonate and difluoroethylene carbonate is contained in an amount of 0.5 wt% to 25 wt%. Next battery. The nonaqueous electrolyte secondary battery according to claim 1, wherein the calcium salt is contained in an amount of 0.1 wt% to 2.0 wt% with respect to the positive electrode active material. The calcium salts include calcium oxide (CaO), calcium carbonate (CaCO ₃ ), calcium sulfate (CaSO ₄ ), calcium nitrate (Ca (NO ₃ ) ₂ ), calcium phosphate (CaPO ₄ ), calcium acetate (Ca (CH ₃ COO). ₂ ) The nonaqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of ₂ ) and calcium hydroxide (Ca (OH) ₂ ). The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte contains 0.1 wt% or more and 10 wt% or less of vinylene carbonate. The nonaqueous electrolyte secondary battery according to claim 1, wherein at least a part of the positive electrode side of the separator includes at least one of polyvinylidene fluoride, polypropylene, and aramid. The positive electrode active material is a composite particle in which the surface of the core particle of the first lithium-containing compound is coated with the fine particles of the second lithium-containing compound,
Each of the first lithium-containing compound and the second lithium-containing compound is Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x Co _{1- y My} O ₂ , or Li _x Ni _{1. -y M y O 2, L x} Mn 1-y M y nonaqueous electrolyte secondary battery according to claim 1, wherein a is any one of O ₂ in the lithium-containing compound represented.
[Wherein M is titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), aluminum (Al), cobalt (Co), nickel (Ni), copper (Cu ), Zinc (Zn), molybdenum (Mo), bismuth (Bi), and boron (B), where x is 0 <x ≦ 1.2 and y is 0 <y <1 is there〕 The electrolyte is non-aqueous electrolyte secondary battery according to claim 1, wherein a is intended to include LiPF _6.

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