JP2009164052A - battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of obtaining high energy density, and excellent cycle characteristics. <P>SOLUTION: At a negative electrode 22, a thickness of one face of a negative electrode active material layer 22B containing a carbon material as a negative electrode active material is to be ≥70 μm and ≤120 μm. Electrolyte solution contains chloroethylene carbonate as a solvent. With this arrangement , energy density of the negative electrode 22 is improved, and at the same time, diffusion and acceptance properties of lithium ions are improved at the negative electrode 22. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a battery using a carbon material as a negative electrode active material.

  In recent years, portable electronic devices such as mobile phones, PDAs (Personal Digital Assistants) and notebook computers have been actively reduced in size and weight, and as part of these efforts, Improvement of the energy density of a battery as a driving power source, particularly a secondary battery is strongly desired.

  As a secondary battery capable of obtaining a high energy density, for example, a secondary battery using lithium (Li) as an electrode reactant is known. Among these, lithium ion secondary batteries using a carbon material capable of inserting and extracting lithium into and from the negative electrode have been widely put into practical use.

  However, since lithium ion secondary batteries using a carbon material for the negative electrode have already advanced in technology to near the theoretical capacity, as a means for further improving the energy density, the thickness of the active material layer is increased in the battery. It has been studied to increase the ratio of the active material layer and decrease the ratio of the current collector and the separator (for example, see Patent Document 1).

JP-A-9-204936

  However, if the thickness of the active material layer is increased without changing the battery volume, the area of the current collector is relatively reduced, so that the current density applied to the negative electrode during charging increases, and lithium ion diffusion and lithium in the negative electrode are increased. There was a problem that the electrochemical acceptance of ions could not catch up and metal lithium was likely to precipitate. As described above, the lithium metal deposited on the negative electrode is easily deactivated. As a result, the cycle characteristics are remarkably deteriorated, so that it is difficult to increase the thickness of the active material layer.

  The present invention has been made in view of such problems, and an object thereof is to provide a battery that can obtain a high energy density and an excellent cycle characteristic.

  The battery of the present invention includes an electrolyte solution together with a positive electrode and a negative electrode, and the negative electrode includes a carbon material and has a negative electrode active material layer having a thickness of 70 μm to 120 μm per side. The electrolytic solution contains a solvent containing chloroethylene carbonate (ClEC).

  In the battery of the present invention, a high energy density is obtained by increasing the thickness of the negative electrode active material layer, and a film is formed on the surface of the active material layer when the solvent in the electrolytic solution contains chloroethylene carbonate. The diffusibility and acceptability of the electrolyte are increased, and decomposition of the electrolytic solution accompanying charge / discharge is suppressed.

  According to the battery of the present invention, since the thickness of the negative electrode active material layer is increased and the electrolyte contains chloroethylene carbonate, the energy density can be improved and excellent cycle characteristics can be obtained. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 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 11, a pair of insulating plates 12 and 13 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 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14, and a heat sensitive resistance element (PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 24 is inserted in the center of the wound electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

  The positive electrode active material layer 21B includes, for example, one or more positive electrode materials capable of inserting and extracting lithium as an electrode reactant as a positive electrode active material.

Examples of the positive electrode material capable of inserting and extracting lithium include lithium-containing compounds such as lithium oxide, lithium sulfide, an intercalation compound containing lithium, and a lithium phosphate compound. Among them, a composite oxide containing lithium and a transition metal element, or a phosphoric acid compound containing lithium and a transition metal element is preferable. In particular, cobalt (Co), nickel, manganese (Mn), iron, aluminum, Those containing at least one of vanadium (V) and titanium (Ti) are preferred. The chemical formula is represented by, for example, Li _x MIO ₂ and Li _y MIIPO ₄ . In the formula, MI and MII contain one or more kinds of transition metal elements, and the values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1. .10.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), lithium nickel cobalt composite oxide [Li _x Ni _1-z Co _z O ₂ (z <1)], lithium nickel cobalt manganese composite oxide [Li _x Ni _(1-vw) Co _v Mn _w O ₂ (v + w <1)] and a spinel structure And lithium manganese composite oxide (LiMn ₂ O ₄ ). Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound [LiFe _1-u Mn _u PO ₄ (u <1)]. Is mentioned.

  Examples of the positive electrode material capable of inserting and extracting lithium include other metal compounds and polymer materials. Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide and manganese dioxide, and disulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include polyaniline and polythiophene.

  The positive electrode active material layer 21B may include a conductive material and a binder as necessary. Examples of the conductive material include carbon materials such as graphite, carbon black, and ketjen black, and one kind or a mixture of two or more kinds is used. In addition to the carbon material, a metal material, a conductive polymer material, or the like may be used as long as it is a conductive material. Examples of the binder include synthetic rubbers such as styrene butadiene rubber, fluorine rubber and ethylene propylene diene rubber, and polymer materials such as polyvinylidene fluoride. One or two or more kinds are used in combination. It is done.

  The negative electrode 22 has, for example, a configuration in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 22B includes, for example, one or more negative electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as a negative electrode active material. Accordingly, for example, the binder similar to that of the positive electrode active material layer 21B may be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. These carbon materials are preferable because the change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good charge / discharge cycle characteristics can be obtained. In particular, graphite is preferable because it has a large electrochemical equivalent and can provide a high energy density. The graphite may be natural graphite or artificial graphite.

The graphite preferably has a lattice spacing d ₀₀₂ in the C-axis direction of X-ray diffraction of 0.335 nm or more and less than 0.338 nm. This is because a higher energy density can be obtained by setting the lattice spacing d ₀₀₂ within this range. Also, if the lattice spacing d ₀₀₂ is less than 0.335, it cannot be theoretically manufactured. Note that the lattice spacing d ₀₀₂ is, for example, an X-ray diffraction method using CuKα rays as X-rays and high-purity silicon as a standard material (“Otani Sugirou, Carbon Fiber, p. 733-742 (1986), Modern Edit ").

Furthermore, the bulk density of graphite is preferably 1.2 g / cm ³ or more, for example, and the fracture strength is preferably 50 MPa or more, for example. This is because even if the negative electrode active material layer 22B is pressed to increase the volume density, the layered structure of graphite can be maintained, and lithium occlusion and release reactions can be maintained smoothly.

Note that the fracture strength of the graphite particles can be obtained from Equation 1, for example.
(Equation 1)
St (Sx) = 2.8P / (π × d × d)
St (Sx) represents the fracture strength (Pa), P represents the force (N) during the test, and d represents the average particle diameter (mm) of the particles. The average particle diameter d can be measured by, for example, a laser diffraction particle size distribution measuring device.

As the non-graphitizable carbon, for example, the lattice spacing d ₀₀₂ is 0.37 nm or more, the true density is less than 1.70 g / cm ³ , and in differential thermal analysis (DTA) in air, What does not show an exothermic peak at 700 ° C. or higher is preferable.

  In this secondary battery, the positive electrode active material layer 21B and the negative electrode active material layer 22B are made thick so that the volumes of the positive electrode current collector 21A, the negative electrode current collector 22A, and the separator 23 in the battery are relatively increased. Can be reduced and energy density can be improved. On the other hand, if it is too thick, the acceptability of lithium ions may be reduced, leading to deterioration of battery characteristics such as heavy load characteristics and cycle characteristics.

  For these reasons, the thickness of the negative electrode active material layer 22B is set to 70 μm or more and 120 μm or less for one surface of the negative electrode current collector 22A, and the total of both surfaces is 140 μm or more and 240 μm or less. The thickness of the positive electrode active material layer 21B is preferably, for example, 70 μm or more and 120 μm or less on one surface of the positive electrode current collector 21A, and the total of both surfaces is 140 μm or more and 240 μm or less.

Furthermore, when the negative electrode active material layer 22B is formed using graphite having a lattice spacing d ₀₀₂ of 0.335 nm or more and less than 0.338 nm as the negative electrode active material, the volume density of the negative electrode active material layer 22B is, for example, 1 .0g / cm ³ or more 1.9 g / cm ³ or less is preferably. By forming the above-described negative electrode active material layer 22B containing graphite at such a volume density, the amount of active material that can be filled in the battery is sufficiently secured, high energy density is secured, and lithium ions are received. This is because the nature increases.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is made of, for example, a porous material made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, and a porous material made of ceramic, and a porous material obtained by mixing or laminating two or more of these. It may be a film structure.

  Among these, a porous film made of polyolefin is preferable because it is excellent in the effect of preventing short circuit and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained within a range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and other resins having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The separator 23 is impregnated with an electrolytic solution. The electrolytic solution includes, for example, a solvent and an electrolyte salt.

  The solvent contains chloroethylene carbonate, and may further contain other one or more materials. By using chloroethylene carbonate, a good film can be formed on the negative electrode 22, and even if the thickness of the negative electrode active material layer 22B is increased as described above, diffusion of lithium ions and electrochemical acceptance in the negative electrode 22 are achieved. This is because the performance can be improved. In addition, since the film formed by chloroethylene carbonate is thin and dense, the amount of lithium used for film formation is small, charging / discharging efficiency is improved, and excellent heavy load characteristics can be obtained. .

  The content of chloroethylene carbonate in the solvent is preferably 0.1% by mass or more and 20% by mass or less. This is because a higher effect can be obtained within these ranges.

  Moreover, it is preferable that the solvent contains propylene carbonate or vinylene carbonate. This is because excellent charge / discharge capacity characteristics and charge / discharge cycle characteristics can be obtained. Even if propylene carbonate is contained, by using chloroethylene carbonate, a good film can be formed on the negative electrode 22, and decomposition of propylene carbonate on the graphite surface can be prevented.

  Examples of other solvents include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2- Methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, ethyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, ethylene sulfite and vinyl Room temperature molten salts such as trifluoromethylsulfonylimide trimethylhexylammonium.

Examples of the electrolyte salt include lithium hexafluorophosphate (LiPF ₆ ), lithium bis (pentafluoroethanesulfonyl) imide [Li (C ₂ F ₅ SO ₂ ) ₂ N], lithium perchlorate (LiClO ₄ ), Lithium hexafluoroarsenate (LiAsF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiSO ₃ CF ₃ ), lithium bis (trifluoromethanesulfonyl) imide [Li (CF ₃ SO ₂ ) ₂ N], lithium salts such as tris (trifluoromethanesulfonyl) methyllithium [LiC (SO ₂ CF ₃ ) ₃ ], lithium chloride (LiCl) and lithium bromide (LiBr). Any one electrolyte salt may be used alone, or two or more electrolyte salts may be mixed and used. Among them, preferably contains lithium hexafluorophosphate (LiPF _6).

  For example, the secondary battery can be manufactured as follows.

  First, for example, the positive electrode active material layer 21B is formed on the positive electrode current collector 21A to produce the positive electrode 21. A positive electrode active material, a conductive material, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste-like positive electrode mixture slurry And Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like. Further, the positive electrode active material layer 21B may be formed by attaching a positive electrode mixture to the positive electrode current collector 21A.

  Further, for example, in the same manner as the positive electrode 21, the negative electrode active material layer 22 </ b> B is formed on the negative electrode current collector 22 </ b> A to produce the negative electrode 22. A carbon material, which is a negative electrode active material, and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry And Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured. The negative electrode active material layer 22B may be formed by sticking a negative electrode mixture to the negative electrode current collector 22A.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through the gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode active material layer 21B and inserted into the negative electrode active material layer 22B through the electrolytic solution. In addition, when discharging is performed, for example, lithium ions are released from the negative electrode active material layer 22B and inserted into the positive electrode active material layer 21B through the electrolytic solution. At this time, in the present embodiment, since the thickness of the positive electrode active material layer 21B and the negative electrode active material layer 22B is increased, the areas of the positive electrode current collector 21A and the negative electrode current collector 22A are relatively reduced, and charging is performed. Sometimes the current density across the negative electrode 22 increases.

  However, in this embodiment, since chloroethylene carbonate is contained in the electrolytic solution, a favorable coating is formed on the negative electrode 22, and even if the current density applied to the negative electrode 22 is high, the diffusion of lithium ions in the negative electrode 22 and Electrochemical acceptability is improved, and precipitation of metallic lithium on the negative electrode 22 is suppressed. Furthermore, decomposition of the electrolytic solution accompanying charging / discharging is also suppressed by the effect of this coating.

  As described above, according to the present embodiment, since an appropriate thickness is secured in the positive electrode active material layer 21B and the negative electrode active material layer 22B, good heavy load characteristics and cycle characteristics can be obtained while improving energy density. Obtainable. Furthermore, since the electrolytic solution contains chloroethylene carbonate as a solvent, even if a good coating is formed on the negative electrode 22 and the thickness of the negative electrode active material layer 22B is increased, the diffusion and acceptance of lithium ions in the negative electrode 22 In addition, the decomposition of the electrolyte accompanying charging / discharging can be suppressed.

  Therefore, precipitation of metallic lithium in the negative electrode 22 can be suppressed, and the cycle characteristics can be further improved. In particular, it is more effective when the content of chloroethylene carbonate in the solvent is 0.1% by mass or more and 20% by mass or less.

Furthermore, as the carbon material contained in the negative electrode active material layer 22B, graphite having a lattice plane distance d ₀₀₂ in the C-axis direction of X-ray diffraction of 0.335 nm or more and less than 0.338 nm can be used to achieve higher energy density. can get. Here, since the electrolyte solution contains chloroethylene carbonate, even with such a graphite having a small lattice spacing _d002 , intercalation of lithium ions at the edge of the graphite crystal is performed smoothly. Battery characteristics such as cycle characteristics are not deteriorated. That is, the acceptability of lithium ions substantially equal to that of a carbon material having a lattice spacing of 0.338 nm or more is ensured. This is thought to be due to the fact that lithium ions move quickly in the edge portion, and as a result, the speed of incorporation as lithium into the interlayer is improved.

Furthermore, when the negative electrode active material layer 22B is formed using graphite having a lattice spacing d ₀₀₂ of 0.335 nm or more and less than 0.338 nm as the negative electrode active material, the negative electrode active material layer 22B has a volume density of 1.0 g. If it is / cm ³ or more and 1.9 g / cm ³ or less, the amount of active material that can be filled in the battery is sufficiently secured, high energy density is secured, and the acceptability of lithium ions is improved. In this case, in particular, due to the coating effect of chloroethylene carbonate, high energy density is obtained and excellent cycle characteristics are obtained.

  Although the present invention has been described with reference to the embodiment, the present invention is not limited to the embodiment, and various modifications can be made. For example, in the above embodiment, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium (Na) and potassium (K), alkaline earth metals such as magnesium and calcium (Ca), In addition, the present invention can be applied to the case of using other light metals such as aluminum. At that time, the positive electrode active material capable of inserting and extracting the electrode reactant is selected according to the electrode reactant.

  In the above embodiment, a cylindrical secondary battery including a battery element having a winding structure has been specifically described. However, the present invention is an elliptical or polygonal type having a winding structure. The present invention can be similarly applied to a secondary battery including a battery element, or a secondary battery including a battery element having another structure in which a positive electrode and a negative electrode are folded or stacked. In addition, the present invention can be similarly applied to secondary batteries having other exterior shapes such as a coin shape, a button shape, a square shape, and a laminate film shape.

  In the above embodiment, the thickness of the positive electrode active material layer is made larger than usual along with the thickness of the negative electrode active material layer. However, the thickness of the positive electrode active material layer is, for example, 55 μm to 70 μm on one side, In total, the thickness may be reduced to about 110 μm to 140 μm.

  In the above embodiment, the case where a liquid electrolytic solution is used as the electrolyte has been described. However, a gel electrolyte in which the electrolytic solution is held by a holding body such as a polymer compound may be used.

  Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene and polycarbonate. In particular, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene and polyethylene oxide are preferable from the viewpoint of electrochemical stability. Although the ratio of the polymer compound to the electrolytic solution varies depending on the compatibility thereof, it is usually preferable to add a polymer compound corresponding to 5% by mass or more and 50% by mass or less of the electrolytic solution.

Furthermore, in the above embodiment, the thickness of the negative electrode active material layer in the battery of the present invention, the lattice spacing d ₀₀₂ in the C-axis direction calculated by X-ray diffraction of the carbon material, the chloroethylene carbonate contained in the electrolytic solution, Regarding the content rate, the appropriate range derived from the results of the examples has been described. However, the description does not completely deny the possibility that parameters such as thickness are outside the above-described range. That is, the appropriate range described above is a particularly preferable range for obtaining the effects of the present invention, and parameters such as thickness may slightly deviate from the above ranges as long as the effects of the present invention are obtained.

  Furthermore, specific examples of the present invention will be described in detail, but the scope of the present invention is not limited to these examples.

(Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-10)
The cylindrical secondary battery shown in FIGS. First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a molar ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 and fired at 900 ° C. in air for 5 hours. Thus, lithium-cobalt composite oxide (LiCoO ₂ ) was obtained. When the obtained LiCoO ₂ was subjected to X-ray diffraction, it was in good agreement with the LiCoO ₂ peak registered in the JCPDS (Joint Committee of Powder Diffraction Standard) file. Next, the lithium-cobalt composite oxide was pulverized to form a powder having a cumulative 50% particle size of 15 μm obtained by a laser diffraction method as a positive electrode active material.

Subsequently, 95% by mass of this lithium / cobalt composite oxide powder and 5% by mass of lithium carbonate powder (Li ₂ CO ₃ ) powder were mixed, and 94% by mass of this mixture and 3% by mass of ketjen black as a conductive material. Then, 3% by mass of polyvinylidene fluoride as a binder was mixed and dispersed in N-methyl-2-pyrrolidone as a solvent to obtain a positive electrode mixture slurry.

Next, the positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression-molded to form a positive electrode active material layer 21B to produce a positive electrode 21. . At that time, the thickness of one surface of the positive electrode active material layer 21B was 88 μm, and the volume density was 3.55 g / cm ³ . After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

Further, 90% by mass of granular graphite powder having an average particle diameter of 25 μm as a negative electrode active material and 10% by mass of polyvinylidene fluoride as a binder are mixed and dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode. A mixture slurry was obtained. Regarding the physical properties of the graphite used as the negative electrode active material, the lattice spacing d ₀₀₂ in the C-axis direction calculated by X-ray diffraction was 0.3363 nm.

Next, this negative electrode mixture slurry was uniformly applied to both surfaces of a negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 15 μm, dried, and compression-molded to form a negative electrode active material layer 22B, thereby producing a negative electrode 22. At that time, the thickness of one surface of the negative electrode active material layer 22B was 90 μm, and the volume density was 1.80 g / cm ³ . Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22A.

  After producing the positive electrode 21 and the negative electrode 22, respectively, the positive electrode 21 and the negative electrode 22 are laminated in the order of the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 with a separator 23 made of a microporous polyethylene stretched film having a thickness of 25 μm. The jelly roll type wound electrode body 20 was produced by winding a large number of turns. Next, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. 11 was stored inside. Subsequently, an electrolytic solution was injected into the battery can 11, and the battery lid 14 was caulked to the battery can 11 through the gasket 17 to produce a cylindrical secondary battery.

  At that time, chloroethylene carbonate (ClEC), ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) were mixed in the electrolyte solution in the ratio shown in Table 1 below. A solvent in which lithium hexafluorophosphate as an electrolyte salt was dissolved at a rate of 1 mol / kg was used in the solvent. In addition, content of the chloroethylene carbonate in a solvent was changed within the range of 0.05 mass% to 25 mass%.

  As a comparative example for Examples 1-1 to 1-8, Comparative Example 1-1 and Example 1-1 were the same as Examples 1-1 to 1-8 except that chloroethylene carbonate was not mixed in the electrolyte. A secondary battery of 1-2 was produced. In addition, as Comparative Example 1-3, the thickness of one side of the negative electrode active material layer 22B was set to 60 μm, and other than Examples 1-1 to 1-7, except that the electrolyte solution was not mixed with chloroethylene carbonate. A secondary battery was fabricated in the same manner as described above. Further, as Comparative Examples 1-4 to 1-10, secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-7, except that the thickness of one surface of the negative electrode active material layer 22B was 60 μm. did.

  The fabricated secondary batteries of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-10 were charged and discharged, and the battery capacity, initial charge and discharge efficiency, and cycle characteristics were examined. At that time, charging was performed at a constant current of 1 C until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V until the total charging time reached 4 hours. Discharge was performed at a constant current of 1 C until the battery voltage reached 3.0V.

  1 C is a current value at which the theoretical capacity can be discharged in one hour. The battery capacity is the initial discharge capacity (discharge capacity at the first cycle), and the cycle characteristics are the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity (discharge capacity at the first cycle), that is, (discharge at the 100th cycle). Capacity / discharge capacity at the first cycle) × 100 (%). The results are shown in Tables 1 and 2. The battery capacity is expressed as a relative value with the value of Comparative Example 1-1 as 100. In Tables 1 and 2, chloroethylene carbonate is simply indicated as ClEC.

  As shown in Table 1, in Examples 1-1 to 1-8 and Comparative Examples 1-1 and 1-2 in which the thickness of the negative electrode active material layer 22B was increased, Example 1-1 in which chloroethylene carbonate was added The cycle characteristics of ˜1-8 were significantly improved as compared with Comparative Examples 1-1 and 1-2 in which ˜1-8 was not added.

  Further, from the results of Table 1 and Table 2, if the negative electrode active material layer 22B is made of the same carbon material and has the same volume density, a larger battery capacity can be obtained by increasing the thickness of the negative electrode active material layer 22B. confirmed.

  In addition, as shown in Table 2, in Comparative Examples 1-3 to 1-10 in which the thickness of the negative electrode active material layer 22B was reduced, the cycle characteristics were comparatively higher in Comparative Example 1-3 in which chloroethylene carbonate was not added. Since it was favorable, it was found that when the thickness of the negative electrode active material layer 22B was reduced, no significant improvement effect due to the addition of chloroethylene carbonate was observed.

  That is, it was possible to realize excellent cycle characteristics by adding chloroethylene carbonate to the electrolytic solution while ensuring a high battery capacity by increasing the thickness of the negative electrode active material layer 22B.

  Moreover, by comparing Example 1-3 and Example 1-8, it was found that by adding propylene carbonate to the electrolytic solution, more excellent cycle characteristics were exhibited.

  Regarding the cycle characteristics, when the content of chloroethylene carbonate in the solvent was increased in Examples 1-3 to 1-7, there was a tendency to gradually improve and then decrease. From this, it was found that, particularly when the content of chloroethylene carbonate in the solvent is 0.1% by mass or more and 20% by mass or less, better cycle characteristics are exhibited.

(Examples 2-1 to 2-3, Comparative Examples 2-1 to 2-5)
A secondary battery was fabricated in the same manner as in Example 1-4, except that the thickness on one side of the negative electrode active material layer 22B was changed in the range of 70 μm to 120 μm as shown in Table 3 below. . Specifically, in Example 2-1, the thickness on one side of the negative electrode active material layer 22B was set to 70 μm, and in Example 2-2, the thickness on one side of the negative electrode active material layer 22B was set to 100 μm. Then, the thickness on one side of the negative electrode active material layer 22B was 120 μm.

  As Comparative Example 2-1 with respect to Examples 2-1 to 2-3, a secondary battery was fabricated in the same manner as in Example 1-4, except that the thickness on one side of the negative electrode active material layer was 130 μm. . In Comparative Examples 2-2 to 2-4, secondary batteries were fabricated in the same manner as in Examples 2-1 to 2-3 except that chloroethylene carbonate was not added to the electrolytic solution. In Comparative Example 2-5, a secondary battery was fabricated in the same manner as Comparative Example 2-1, except that chloroethylene carbonate was not added to the electrolytic solution.

  For the fabricated secondary batteries of Examples 2-1 to 2-3 and Comparative examples 2-1 to 2-5, the battery capacity, the initial charge / discharge efficiency, and the cycle characteristics were examined in the same manner as in Example 1-4. . The results are shown in Table 3 together with the results of Example 1-4, Comparative Examples 1-1, 1-2 and 1-7. The battery capacity is expressed as a relative value with the value of Comparative Example 1-1 as 100.

  As shown in Table 3, in Examples 1-4 and 2-1 to 2-3 in which the thickness of the negative electrode active material layer 22B is set to 70 μm or more and 120 μm or less and includes chloroethylene carbonate, the thickness of the negative electrode active material layer 22B As compared with Comparative Examples 1-1, 2-2 to 2-4, which have the same range and do not contain chloroethylene carbonate, the cycle characteristics could be greatly improved.

  In addition, compared with Comparative Example 1-6 in which the thickness of the negative electrode active material layer 22B was 60 μm, Examples 1-4 and 2-1 to 2-3 showed a high battery capacity, although a decrease in cycle characteristics was observed. It was. Further, when compared with Comparative Example 2-1, in which the thickness of the negative electrode active material layer 22B was 130 μm, in Examples 1-4 and 2-1 to 2-3, the battery capacity was slightly reduced, but the cycle characteristics were significantly increased. Improvement was seen. In Comparative Example 2-1, it is considered that the cycle characteristics slightly higher than those of Comparative Example 2-5 were exhibited due to the coating effect of chloroethylene carbonate.

  From the above results, it was found that when the thickness of the negative electrode active material layer 22B is 70 μm or more and 120 μm or less and the electrolytic solution contains chloroethylene carbonate, high battery capacity and excellent cycle characteristics can be obtained. It has been found that the effect of adding chloroethylene carbonate to the electrolytic solution appears more remarkably in improving the cycle characteristics as the battery capacity increases.

(Examples 3-1, 3-2, Comparative examples 3-1, 3-2)
As Example 3-1 and 3-2, the secondary battery was the same as Example 1-4 except that graphite having a different lattice spacing _d002 was used for the carbon material contained in the anode active material layer 22B. Was made. Specifically, in Example 3-1, graphite having a lattice spacing d ₀₀₂ of 0.3380 nm was used, and in Example 3-2, graphite having a lattice spacing d ₀₀₂ of 0.3385 nm was used. .

  As Comparative Examples 3-1 and 3-2 with respect to Examples 3-1 and 3-2, except that chloroethylene carbonate was not added to the electrolytic solution, the rest was the same as in Examples 3-1 and 3-2. A secondary battery was manufactured.

  For the secondary batteries of Examples 3-1 and 3-2 and Comparative Examples 3-1 and 3-2, the cycle characteristics were examined in the same manner as in Example 1-4. The results are shown in Table 4 together with the results of Example 1-4 and Comparative example 1-1. The volume density of the negative electrode active material layer 22B included in the negative electrode 22 of the fabricated secondary battery was also measured and is shown in Table 4 together. The battery capacity is expressed as a relative value with the value of Comparative Example 1-1 as 100.

  As shown in Table 4, Examples 1-4, 3-1 and 3-2 containing chloroethylene carbonate in the electrolytic solution, and Comparative Examples 1-1 and 3-1, which do not contain chloroethylene carbonate in the electrolytic solution, When 3-2 was compared with each other, it was found that Examples 1-4, 3-1, and 3-2 exhibited higher cycle characteristics.

Here, paying attention to the lattice spacing d _002, in accordance with the lattice spacing d ₀₀₂ is widened, reduces the volume density of the negative electrode active material layer 22B, the battery capacity along with it also decreased. Further, as the lattice spacing d ₀₀₂ becomes wider, the cycle characteristics become higher, but a significant improvement effect by adding chloroethylene carbonate was not observed. However, when the lattice spacing d ₀₀₂ was less than 0.3380, a high battery capacity was ensured, and the cycle characteristics were significantly improved due to the coating effect of chloroethylene carbonate.

Although not shown in this example, the thickness of the negative electrode active material layer 22B is 70 μm in each of the secondary batteries of Examples 3-1 and 3-2 using graphite having different lattice spacing d _002. When the thickness is 120 μm or less and the electrolytic solution contains chloroethylene carbonate, a high battery capacity and excellent cycle characteristics can be obtained.

In other words, regardless of the lattice spacing d ₀₀₂ of graphite used as the carbon material, a high battery capacity and excellent performance can be obtained when the thickness of the negative electrode active material layer 22B is 70 μm or more and 120 μm or less and the electrolyte contains chloroethylene carbonate. In particular, it was found that when graphite having a lattice spacing d ₀₀₂ of less than 0.3380 nm is used as the carbon material, a higher battery capacity can be secured and excellent cycle characteristics can be obtained.

(Examples 4-1 to 4-4, Comparative Examples 4-1 to 4-4)
Except that it varies between 0.95 g / cm ³ of 1.95 g / cm ³ as shown in Table 5, infra the volume density of the negative electrode active material layer 22B, another embodiment 1-4,3 A secondary battery was produced in the same manner as in Example-2. Specifically, in Example 4-1, the negative electrode active material layer 22B has a volume density of 1.90 g / cm ^3, and in Example 4-2, the negative electrode active material layer 22B has a volume density of 1.95 g / cm 3. ^In Example 4-3, the volume density of the negative electrode active material layer 22B was set to 1.00 g / cm ^3, and in Example 4-4, the volume density of the negative electrode active material layer 22B was set to 0.95 g / cm ³ . did.

  In Comparative Examples 4-1 to 4-4, secondary batteries were fabricated in the same manner as in Examples 4-1 to 4-4, except that chloroethylene carbonate was not added to the electrolytic solution.

  For the fabricated secondary batteries of Examples 4-1 to 4-4 and Comparative examples 4-1 to 4-4, the battery capacity, the initial charge / discharge efficiency, and the cycle characteristics were examined in the same manner as in Example 1-4. . The results are shown in Table 5 together with the results of Examples 1-4 and 3-2 and Comparative Examples 1-1 and 3-2. The battery capacity is expressed as a relative value with the value of Comparative Example 1-1 as 100.

  As shown in Table 5, Examples 1-4, 3-2, 4-1 to 4-4 containing chloroethylene carbonate in the electrolytic solution, and Comparative Examples 1-4 not containing chloroethylene carbonate in the electrolytic solution, When comparing 3-2 and 4-1 to 4-4, it was found that Examples 1-4, 3-2, and 4-1 to 4-4 exhibited higher cycle characteristics.

Here, paying attention to the volume density of the negative electrode active material layer 22B, in Example 4-2 in which the volume density is 1.9 g / cm ³ or more, the cycle characteristics are low, and a significant improvement effect by adding chloroethylene carbonate. Was not seen. In Example 4-4 in which the volume density was 1.0 g / cm ³ or less, high cycle characteristics were obtained, but a significant improvement effect by adding chloroethylene carbonate was not observed. On the other hand, in Examples 1-4, 3-2, and 4-1 to 4-3 in which the volume density is 1.0 g / cm ³ or more and 1.9 g / cm ³ or less, a high battery capacity is secured, and chloroethylene is obtained. Significant improvement in cycle characteristics due to the coating effect of carbonate was observed.

That is, it was found that when the volume density of the negative electrode active material layer 22B is 1.0 g / cm ³ or more and 1.9 g / cm ³ or less, a high battery capacity and excellent cycle characteristics can be obtained.

It is sectional drawing showing the structure of the secondary battery which concerns on embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding electrode body, 21 ... Positive electrode, 21A DESCRIPTION OF SYMBOLS ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active material layer, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead.

Claims (5)

A battery comprising an electrolyte solution together with a positive electrode and a negative electrode,
The negative electrode includes a carbon material and has a negative electrode active material layer having a thickness of 70 μm to 120 μm per side,
The electrolytic solution contains a solvent containing chloroethylene carbonate. 2. The battery according to claim 1, wherein the carbon material has graphite having a lattice plane distance d ₀₀₂ in the C-axis direction of 0.335 nm or more and less than 0.338 nm in X-ray diffraction.   The battery according to claim 1, wherein the content of chloroethylene carbonate in the solvent is 0.1 mass% or more and 20 mass% or less. The battery according to claim 1, wherein the negative electrode active material layer has a volume density of 1.0 g / cm ³ or more and 1.9 g / cm ³ or less.   The battery according to claim 1, wherein the solvent includes propylene carbonate.

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