JP2010205547A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which has an excellent electrode structure and is improved greatly in cycle characteristics by suppressing decomposition of the electrolyte solution in a negative electrode. <P>SOLUTION: The nonaqueous electrolyte secondary battery is provided with a positive electrode 33, a negative electrode 34, and an nonaqueous electrolyte, and the negative electrode 34 has a negative electrode current collector 34A and a negative electrode active material layer 34B provided in the negative electrode current collector 34A. The negative electrode active material layer 34B contains graphite, and the volume density of the negative electrode active material layer is 1.4-1.6 g/cm<SP>3</SP>, and the nonaqueous electrolyte contains nonaqueous electrolyte solution. The nonaqueous electrolyte solution contains succinic anhydride and propylene carbonate as a nonaqueous solvent, and the content of the succinic anhydride is 0.2-0.6 wt.% in the electrolyte solution. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. More specifically, the present invention relates to a nonaqueous electrolyte secondary battery using graphite as an active material of a negative electrode and a nonaqueous electrolyte containing propylene carbonate as a nonaqueous solvent.

  2. Description of the Related Art Conventionally, portable electronic devices typified by a camera-integrated VTR (videotape recorder), a mobile phone device, or a laptop computer have been widely used, and their miniaturization, weight reduction, and continuous driving for a long time have been strongly demanded. Along with this, development of batteries, particularly secondary batteries, as power sources has been actively promoted. Especially, a lithium ion secondary battery is anticipated as a thing which can implement | achieve a big energy density compared with the lead battery and nickel cadmium battery which are the conventional nonaqueous electrolyte secondary batteries.

  A high dielectric constant propylene carbonate is used as a non-aqueous solvent for the electrolyte of the lithium ion secondary battery. However, propylene carbonate is easily decomposed in the negative electrode using a carbonaceous material as an active material, thereby reducing the discharge capacity of the battery. Thus, several methods have been proposed in the past to improve battery characteristics such as cycle characteristics.

  As a first example, Patent Document 1 includes a positive electrode, a negative electrode using a carbon material as a negative electrode material, and a non-aqueous electrolyte, and contains propylene carbonate in a non-aqueous solvent and vinylene carbonate as a film forming agent. A lithium secondary battery is disclosed.

  As a second example, Patent Document 2 contains 90% by weight or more of one or more solvents selected from non-aqueous solvents having a relative dielectric constant of 25 or more, and the flash point of the non-aqueous solvent is 70 ° C. In addition, a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte in which at least one cyclic acid anhydride is added to the non-aqueous solvent is disclosed.

  As a third example, Patent Document 3 discloses a nonaqueous electrolyte battery in which an acid anhydride is added as a film forming agent to the electrolyte of a nonaqueous electrolyte secondary battery using a graphite-based negative electrode. Yes.

  As a fourth example, Patent Document 4 includes an electrolyte layer having a non-fluidic electrolyte, the electrolyte layer contains an acid anhydride, and the amount of acid anhydride used is 0.001 with respect to the total amount of the electrolyte. A lithium secondary battery in the range of ˜20% by weight is disclosed.

  In the batteries shown in the first to fourth examples, an acid anhydride represented by vinylene carbonate or succinic anhydride is added as a film forming agent in a non-aqueous solvent, and a film is formed on the surface of the negative electrode. It suppresses the decomposition of propylene carbonate and improves battery characteristics. In particular, the acid anhydride has a higher effect of suppressing the decomposition of propylene carbonate in the negative electrode than vinylene carbonate.

JP 2001-167797 A JP 2001-126762 A Japanese Patent No. 3658517 Japanese Patent No. 4026288

  However, when a film was formed on the negative electrode surface by the acid anhydride, the film resistance increased. Therefore, for example, when succinic anhydride is added to a non-aqueous solvent as a film-forming agent, the initial charge / discharge efficiency is improved, but the discharge capacity tends to decrease when charge / discharge is repeated, so the cycle characteristics are improved. There was room for.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that significantly improves cycle characteristics while suppressing decomposition of the electrolytic solution.

In order to solve the problems described above, the present invention provides:
A positive electrode and a negative electrode, and a non-aqueous electrolyte,
The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer contains graphite, and the negative electrode active material layer has a volume density of 1.4 to 1.6 g / cm ³ ,
The non-aqueous electrolyte contains a non-aqueous electrolyte, and the non-aqueous electrolyte contains succinic anhydride and propylene carbonate as a non-aqueous solvent,
It is a nonaqueous electrolyte secondary battery whose content in the nonaqueous electrolyte of the said succinic anhydride is 0.2-0.6 mass%.

  In the present invention, since the volume density of the negative electrode active material layer containing graphite as the active material is set in a specific range, the electrode structure is good. Furthermore, since a specific amount of succinic anhydride is contained in the electrolytic solution, it is possible to suppress the decomposition of propylene carbonate in the electrolytic solution on the negative electrode surface having a good electrode structure, not only the initial charge and discharge efficiency, The battery capacity can be maintained even after repeated charging and discharging, and the cycle characteristics can be greatly improved.

  According to the present invention, it has a good electrode structure and can suppress decomposition of the negative electrode surface of propylene carbonate in the electrolytic solution while suppressing an increase in film resistance. The battery capacity can be maintained even after charging / discharging, and the cycle characteristics can be greatly improved.

It is sectional drawing showing the structure of the battery by 1st Embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the battery shown in FIG. It is sectional drawing showing the structure of the battery by 2nd Embodiment of this invention. It is sectional drawing along the II line | wire of the winding electrode body shown in FIG.

  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 battery according to the first embodiment of the present invention. This battery is, for example, a nonaqueous electrolyte secondary battery. For example, lithium (Li) is used as an electrode reactant, and the capacity of the negative electrode is expressed by a capacity component due to insertion and extraction of lithium (Li). It is an ion secondary battery.

  This battery is called a so-called cylindrical type, and is a wound electrode in which a pair of strip-like positive electrode 21 and strip-like negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. It has a body 20. 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 (Ni) 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 to and electrically connected to the battery can 11.

  FIG. 2 is an enlarged cross-sectional view showing a 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, a region where the positive electrode active material layer 21B exists 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. The positive electrode active material layer 21B includes, for example, one or more positive electrode materials capable of inserting and extracting lithium (Li) as a positive electrode active material, and a conductive agent such as graphite as necessary. And a binder such as polyvinylidene fluoride.

As a positive electrode material capable of inserting and extracting lithium (Li), for example, a lithium composite oxide represented by an average composition shown in Chemical Formula I, more specifically, shown in Chemical Formulas II to IV Preferable examples include lithium composite oxides having a layered rock salt type structure represented by an average composition. When such a lithium composite oxide is used, the energy density can be increased. Specific examples of such lithium composite oxides include Li _a CoO ₂ (a≈1), Li _c1 Ni _c2 Co _1-c2 O ₂ (c1≈1, 0 <c2 ≦ 0.5), etc. There is.

(Chemical I)
_{Li p Ni (1-q-} r) Mn q M1 r O (2-y) X z
(M1 represents at least one element selected from Group 2 to Group 15 excluding nickel (Ni) and manganese (Mn). X represents at least one of Group 16 elements and Group 17 elements 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 (It is a value within the range of ≦ z ≦ 0.2.)

(Chemical II)
Li _r Co _(1-s) M3 _s O _{(2-t) Fu}
(In the formula, M3 represents nickel (Ni), manganese (Mn), 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), at least one kind. s, t, and u are values within the ranges of 0.8 ≦ r ≦ 1.2, 0 ≦ s <0.5, −0.1 ≦ t ≦ 0.2, and 0 ≦ u ≦ 0.1. (Note that the composition of lithium (Li) varies depending on the state of charge and discharge, and the value of r represents the value in a fully discharged state.)

(Chemical III)
Li _f Mn _(1-g-h) Ni _g M1 _h O _(2-j) F _k
(In the formula, M1 is cobalt (Co), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu ), Zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). g, h, j and k are 0.8 ≦ f ≦ 1.2, 0 <g <0.5, 0 ≦ h ≦ 0.5, g + h <1, −0.1 ≦ j ≦ 0.2, (The value is in the range of 0 ≦ k ≦ 0.1. Note that the composition of lithium varies depending on the state of charge and discharge, and the value of f represents a value in a fully discharged state.)

(Chemical IV)
Li _m Ni _(1-n) M2 _n O _(2-p) F _q
(In the formula, M2 represents cobalt (Co), manganese (Mn), 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), at least one selected from the group consisting of m, n, p and q are values within the range of 0.8 ≦ m ≦ 1.2, 0.005 ≦ n ≦ 0.5, −0.1 ≦ p ≦ 0.2, 0 ≦ q ≦ 0.1. Note that the composition of lithium varies depending on the state of charge and discharge, and the value of m represents a value in a fully discharged state.)

  In addition, as the positive electrode material, for example, a lithium composite oxide having a spinel structure represented by the average composition shown in Chemical Formula V, for example, the average shown in Chemical Formula VI, more specifically, Chemical Formula VII Examples thereof include lithium composite phosphates having an olivine structure represented by the composition, sulfides such as iron disulfide, titanium disulfide, and molybdenum sulfide, and oxides such as titanium oxide, vanadium oxide, and manganese dioxide.

(Chemical V)
Li _v Mn _2-w M4 _w O _x F _y
(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), at least one selected from the group consisting of v, w, x, and y are values within the range of 0.9 ≦ v ≦ 1.1, 0 ≦ w ≦ 0.6, 3.7 ≦ x ≦ 4.1, and 0 ≦ y ≦ 0.1. Note that the composition of lithium (Li) varies depending on the state of charge and discharge, and the value of v represents the value in the complete discharge state.)

(Chemical VI)
Li _a M2 _b PO ₄
(M2 represents at least one element selected from Group 2 to Group 15. a and b are values within the range of 0 ≦ a ≦ 2.0 and 0.5 ≦ b ≦ 2.0. .)

(Chemical VII)
Li _z M5PO ₄
(Wherein M5 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) Z is a value within a range of 0.9 ≦ z ≦ 1.1, wherein the composition of lithium (Li) varies depending on the state of charge and discharge, and the value of z represents a value in a fully discharged state. ing.

  In these composite oxides, for the purpose of stabilizing the structure, part of the transition metal is replaced with Al, Mg or other transition metal elements or included in the grain boundaries, and part of oxygen is contained. The thing substituted with fluorine etc. can also be mentioned. Further, at least a part of the surface of the positive electrode active material may be coated with another positive electrode active material. Moreover, you may use a positive electrode active material in mixture of multiple types.

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. 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 anode current collector 22A is made of, for example, a metal foil such as a copper foil.

The volume density of the negative electrode active material layer 22B is 1.4 to 1.6 g / cm ³ , preferably 1.45 to 1.55 g / cm ³ .
When the volume density of the negative electrode active material layer is less than 1.4 g / cm ³ , the negative electrode active material is insufficiently bonded. Therefore, it is estimated that repeated charge / discharge increases the deterioration of the electrode, which is not preferable.
Moreover, when the volume density of a negative electrode active material layer exceeds 1.6 mg / cm < ³ >, since the amount of electrolyte solution inside an electrode runs short, it is unpreferable.

The specific surface area of the active material constituting the negative electrode active material layer 22B, 0.4~1.2m ² / g, it is preferred that preferably 0.5~0.9m ² / g.
An active material means what contains the negative electrode material which can occlude and discharge | release lithium at least among the negative electrode materials shown below.
The specific surface area is a value calculated by the BET (Brunauer, Emmett, Teller) equation based on the N ₂ gas adsorption method, and can be measured using, for example, a specific surface area measuring device (manufactured by Shimadzu Corporation).
It is preferable for the specific surface area of the active material to be in the above-mentioned range since the increase in film resistance is suppressed, the ion diffusibility of lithium ions in the negative electrode is improved, and the cycle characteristics can be improved.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of inserting and extracting lithium (Li) as a negative electrode active material. An agent and a binder may be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon. These graphites are preferable because of their large capacity and high energy density. These may be used individually by 1 type, may be used in mixture of 2 or more types, and may mix and use 2 or more types from which an average particle diameter differs.

  The negative electrode active material layer 12 may also contain other materials such as a conductive agent, a binder, or a viscosity modifier. Examples of the conductive agent include graphite fiber, metal fiber, and metal powder. Examples of the binder include a fluorine-based polymer compound such as polyvinylidene fluoride, or a synthetic rubber such as styrene butadiene rubber or ethylene propylene diene rubber. Examples of the viscosity modifier include carboxymethylcellulose.

  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 includes, for example, polyethylene and at least one selected from the group consisting of polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, Al ₂ O ₃ , SiO ₂ , aramid, and polyacrylonitrile in addition to polyethylene. It is comprised by the porous film made from the synthetic resin made in the above, or the porous film made from a ceramic. Among them, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve battery safety by a shutdown effect. More specifically, for example, several kinds of polyethylene, polypropylene, and polytetrafluoroethylene may be mixed to form a porous film. A porous film of polyethylene, polypropylene, and polytetrafluoroethylene may include Al ₂ O ₃ , A structure in which at least one of polyvinylidene fluoride, SiO ₂ , aramid, and polyacrylonitrile is applied to the surface may be employed. Further, a structure in which two or more porous films of polyethylene, polypropylene, and polytetrafluoroethylene are laminated may be employed.

The separator 23 is impregnated with a non-aqueous electrolyte that is a liquid non-aqueous electrolyte (hereinafter also simply referred to as “electrolyte”). The electrolytic solution contains propylene carbonate, which is a nonaqueous solvent, succinic anhydride, which is an additive, and an electrolyte salt.
The content of succinic anhydride in the electrolytic solution is 0.2 to 0.6% by mass, preferably 0.3 to 0.5% by mass.
When 0.2 to 0.6% by mass of succinic anhydride is contained in the electrolytic solution, a film having good ion diffusibility can be formed on the negative electrode surface while suppressing film resistance, and propylene on the negative electrode surface. The decomposition of carbonate can be suppressed. Therefore, battery characteristics are improved, and the initial charge / discharge efficiency and cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.
When the content of succinic anhydride in the electrolytic solution is less than 0.2% by mass, the effect of suppressing the decomposition of propylene carbonate on the negative electrode surface is not preferable. Moreover, since film resistance will raise when it exceeds 0.6 mass%, it is not preferable.

The non-aqueous solvent contains propylene carbonate.
Propylene carbonate has a high dielectric constant and its freezing point is lower than that of ethylene carbonate, vinyl carbonate, and the like, and therefore can be suitably used as a nonaqueous solvent for an electrolytic solution.

The content of propylene carbonate in the non-aqueous solvent is preferably 30 to 80% by mass, more preferably 50 to 70% by mass.
When the content of propylene carbonate in the non-aqueous solvent is within the above range, decomposition of propylene carbonate on the negative electrode surface is suppressed due to the film-forming effect of succinic anhydride, and the discharge capacity is maintained even after repeated charge and discharge. And cycle characteristics can be greatly improved.

  Non-aqueous solvents include propylene carbonate, carbonate solvents such as ethylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, Ether solvents such as 1,2-diethoxymethane, tetrahydrofuran, 2-methyltetrahydrofuran, lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, nitrile solvents such as acetonitrile, Non-aqueous solvents such as sulfolane-based solvents, phosphoric acids, phosphate ester solvents, pyrrolidones and the like can be mentioned. Among these, you may use together 1 type, or 2 or more types with propylene carbonate.

The electrolyte salt, for example _{LiPF 6, LiClO 4, LiBF 4} , Li (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, preferably comprises a lithium salt such as LiAsF _6. Any one of these lithium salts may be used, or two or more thereof may be mixed and used.

  This secondary battery can be manufactured, for example, as described below. First, for example, a positive electrode mixture is prepared by mixing the above-described positive electrode active material, a conductive agent, and a binder, and this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste. A positive electrode mixture slurry is prepared. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, the solvent is dried, and the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured.

  Further, for example, 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 Is made. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, the solvent is dried, and the negative electrode active material layer 22B is formed by compression molding with a roll press machine or the like, and the negative electrode 22 is manufactured.

  Subsequently, 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 formed.

  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.

  As described above, in the first embodiment, the volume density of the negative electrode active material layer containing graphite as the active material is set in a specific range, so that the electrode structure is good. Furthermore, since a specific amount of succinic anhydride is contained in the electrolytic solution, it is possible to suppress the decomposition of propylene carbonate in the electrolytic solution on the negative electrode surface having a good electrode structure, not only the initial charge and discharge efficiency, The battery capacity can be maintained even after repeated charging and discharging, and the cycle characteristics can be greatly improved.

(Second Embodiment)
FIG. 3 shows the configuration of the secondary battery according to the second embodiment. This secondary battery is a so-called laminate film type, and has a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached accommodated in a film-shaped exterior member 40.

  The positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the exterior member 40 to the outside, for example, in the same direction. The positive electrode lead 31 and the negative electrode lead 32 are made of, for example, a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 40 is disposed so that the polyethylene film side and the wound electrode body 30 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 4 shows a cross-sectional structure taken along line II of the spirally wound electrode body 30 shown in FIG. The electrode winding body 30 is obtained by laminating a positive electrode 33 and a negative electrode 34 via a separator 35 and an electrolyte layer 36 and winding them, and the outermost periphery is protected by a protective tape 37.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on one or both surfaces of a positive electrode current collector 33A. The negative electrode 34 has a structure in which a negative electrode active material layer 34B is provided on one surface or both surfaces of a negative electrode current collector 34A, and the negative electrode active material layer 34B and the positive electrode active material layer 33B are arranged to face each other. Yes. The configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are the same as those of the positive electrode current collector 21A and the positive electrode active material layer 21B in the first embodiment described above. This is the same as the anode current collector 22A, the anode active material layer 22B, and the separator 23.

  The electrolyte layer 36 includes an electrolytic solution according to the present embodiment and a polymer compound that serves as a holding body that holds the electrolytic solution, and has a so-called gel shape. A gel electrolyte is preferable because high ion conductivity can be obtained and battery leakage can be prevented. Examples of the polymer material include, for example, ether polymer compounds such as polyethylene oxide or a crosslinked product containing polyethylene oxide, ester polymer compounds such as polymethacrylate or polyacrylate, or polyvinylidene fluoride or vinylidene fluoride and hexafluoropropylene. Polymers of vinylidene fluoride, such as a copolymer thereof, are used, and any one or two or more of these are used in combination. In particular, from the viewpoint of redox stability, it is desirable to use a fluorine-based polymer compound such as a vinylidene fluoride polymer.

  For example, the secondary battery can be manufactured as follows. First, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 33 and the negative electrode 34, and the mixed solvent is volatilized to form the electrolyte layer 36. After that, the positive electrode lead 31 is attached to the end of the positive electrode current collector 33A by welding, and the negative electrode lead 32 is attached to the end of the negative electrode current collector 34A by welding. Next, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are laminated via a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion. Thus, the wound electrode body 30 is formed. Finally, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by heat fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 33 and the negative electrode 34 are prepared as described above, and after the positive electrode lead 31 and the negative electrode lead 32 are attached to the positive electrode 33 and the negative electrode 34, the positive electrode 33 and the negative electrode 34 are stacked via the separator 35 and wound. Rotate and adhere the protective tape 37 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 30. Next, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 40. Subsequently, an electrolyte composition including an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 40 Inject.

  After injecting the electrolyte composition, the opening of the exterior member 40 is heat-sealed and sealed in a vacuum atmosphere. Next, heat is applied to polymerize the monomer to obtain a polymer compound, thereby forming a gel electrolyte layer 36, and assembling the secondary battery shown in FIGS.

  The operation and effect of the secondary battery are the same as those in the first embodiment described above. That is, the volume density of the negative electrode active material layer containing graphite as an active material is set in a specific range, and a specific amount of succinic anhydride is contained in the electrolytic solution, so that the electrode structure is improved and propylene carbonate in the electrolytic solution is obtained. Decomposition of the negative electrode surface can be suppressed, and the cycle characteristics can be greatly improved.

  Further, specific embodiments of the present invention will be described in detail. However, the present invention is not limited only to these examples.

[Examples 1 to 9, Comparative Examples 1 to 21]
<Preparation of positive electrode>
A positive electrode mixture was prepared by mixing LiCoO ₂ powder, graphite as a conductive agent, and polyvinylidene fluoride as a binder at a mass ratio of LiCoO ₂ powder: graphite, polyvinylidene fluoride = 90: 5: 5. Next, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which was uniformly applied to the surface of a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 20 μm.

  Next, after forming a positive electrode active material layer compression-molded with a roll press through a drying process, the positive electrode was produced by cutting out to be 50 mm × 350 mm. An aluminum positive electrode lead was connected to one end of the positive electrode current collector.

<Production of negative electrode>
A negative electrode mixture was prepared by mixing mesocarbon microbeads (MCMB) having a specific surface area of 0.8 m ² / g as a negative electrode active material and polyvinylidene fluoride (PVdF) as a binder. Next, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, which was uniformly applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 15 μm.

Next, it is compression-molded by a roll press machine through a drying step, and the volume density is 1.3 g / cm ³ , 1.4 g / cm ³ , 1.5 g / cm ³ , 1.6 g / cm ³ , 1.7 g. After forming each negative electrode active material layer to be / cm ³ , each negative electrode was produced by cutting out to be 52 mm × 370 mm. Thereafter, a negative electrode lead made of nickel was connected to one end of the negative electrode current collector.

<Preparation of electrolyte>
Next, LiPF ₆ is dissolved in a mixed solvent in which ethylene carbonate (EC) and propylene carbonate (PC) are mixed at a volume ratio (EC: PC) = 40: 60 so as to be 0.7 mol / kg. Succinic acid is added in the electrolyte so that it becomes 0.1 mass%, 0.2 mass%, 0.4 mass%, 0.6 mass%, 0.7 mass%, and 1.0 mass%. Each electrolyte was prepared.

<Production of electrolyte>
Next, each electrolyte solution was held in a copolymer of vinylidene fluoride and hexafluoropropylene to obtain a gel electrolyte. The ratio of hexafluoropropylene in the copolymer was 6.9% by mass.

<Preparation of nonaqueous electrolyte secondary battery>
A gel electrolyte was formed on both surfaces of the prepared positive electrode and negative electrode, and was laminated and wound through a separator made of a polyethylene microporous film to obtain a wound electrode body. Next, this wound electrode body was covered with a laminate film, and the periphery of the wound electrode body was sealed. Thus, the nonaqueous electrolyte secondary battery of the second embodiment shown in FIGS. 3 and 4 was produced.

[Comparative Examples 22 to 26]
As an electrolytic solution, in the same manner as Comparative Examples 1 to 5, except that an electrolytic solution in which glutaric anhydride was added to 0.4% by mass in the electrolytic solution instead of succinic anhydride was used. A non-aqueous electrolyte secondary battery was produced.

(Evaluation of cycle characteristics)
The cycle characteristics were evaluated as described below. First, 1 C constant current constant voltage charge was performed up to 4.2 V with a total charge time of 2.0 hours, and then 1 C constant current discharge was performed up to a balance voltage of 3.0 V to perform charge and discharge. Moreover, this charging / discharging operation was repeated 300 times. The capacity retention rate was determined by the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle from the following formula (I).
(Formula I)
Capacity maintenance rate (%) = (“Discharge capacity at 300th cycle” / “Discharge capacity at 1st cycle”) × 100 (%)

  Table 1 shows the measurement results of the capacity retention rate (%) of the nonaqueous electrolyte secondary batteries of Examples 1 to 9 and Comparative Examples 1 to 21. Table 2 shows the measurement results of the capacity retention rate (%) of the nonaqueous electrolyte secondary batteries of Comparative Examples 22 to 26.

As shown in Tables 1 and 2, the volume density of the negative electrode active material layer is 1.4 to 1.6 g / cm ³ , and the succinic anhydride content is 0.2 to 0.6 mass%. The non-aqueous electrolyte secondary batteries 1 to 9 had excellent cycle characteristics as compared with Comparative Examples 1 to 26.
According to this result, when the volume density of the negative electrode active material layer is 1.4 to 1.6 g / cm ³ and the content of succinic anhydride in the electrolytic solution is 0.2 to 0.6% by mass, It was found that the effect of improving the characteristics was great.

[Examples 10 to 33, Comparative Examples 27 to 50]
As the negative electrode, a negative electrode having a negative electrode active material layer having a volume density of 1.6 g / cm ³ was produced. As an electrolytic solution, volume ratio (PC: EC) of ethylene carbonate (EC) and propylene carbonate (PC) = 20: 80, 30:70, 40:60, 50:50, 60:40, 70:30, 80 LiPF ₆ was dissolved in a mixed solvent mixed at 20:90:10 so as to be 0.7 mol / kg, and succinic anhydride was further added in an electrolytic solution in an amount of 0.1% by mass, 0.2% by mass, It added so that it might become 0.4 mass%, 0.6 mass%, 0.7 mass%, and 1.0 mass%, and produced each electrolyte solution. Nonaqueous electrolyte secondary batteries were produced in the same manner as in Examples 1 to 9 except that the negative electrode and the electrolytic solution were used.

  The cycle characteristics of the nonaqueous electrolyte secondary batteries of Examples 10 to 33 and Comparative Examples 27 to 50 were evaluated in the same manner as in Examples 1 to 9. Table 3 shows the measurement results of the capacity retention ratio (%) of the nonaqueous electrolyte secondary batteries of Examples 10 to 33 and Comparative Examples 27 to 50.

As shown in Table 3, in the nonaqueous electrolyte secondary battery of Examples 10 to 33 in which the content of succinic anhydride is 0.2 to 0.6 mass%, the content of propylene carbonate (PC) is 30 to 30%. The nonaqueous electrolyte secondary batteries of Examples 11 to 16, 19 to 24, and 27 to 32 that are 80% by mass had better cycle characteristics than others. Among them, the nonaqueous electrolyte secondary batteries of Examples 13 to 15, 21 to 23, and 29 to 31, which are 50 to 70% by mass of propylene carbonate (PC), were particularly excellent in cycle characteristics.
From this result, it was found that the cycle characteristics can be further improved significantly when the content of propylene carbonate (PC) in the non-aqueous solvent is preferably 30 to 80% by mass, more preferably 50 to 70% by mass. .

[Examples 34 to 38]
As an anode active material, the mesocarbon microbeads having a specific surface area is ^{0.35m 2 /g,0.4m 2 /g,0.8m 2 /g,1.2m 2} /g,1.3m 2 / g ( MCMB) was used to prepare a negative electrode having each negative electrode active material layer having a volume density of 1.5 g / cm ³ .
Moreover, succinic anhydride was added as electrolyte solution so that it might become 0.4 mass% in electrolyte solution, and electrolyte solution was produced. Nonaqueous electrolyte secondary batteries were produced in the same manner as in Examples 1 to 9 except that the negative electrode and the electrolytic solution were used.

  The cycle characteristics of the nonaqueous electrolyte secondary batteries of Examples 34 to 38 were evaluated in the same manner as in Examples 1 to 9. Table 4 shows the measurement results of the capacity retention rate (%) of the nonaqueous electrolyte secondary batteries of Examples 34 to 38.

As shown in Table 4, the non-aqueous electrolyte secondary batteries (Examples 35 to 37) using an active material having a specific surface area of 0.4 to 1.2 m ² / g were particularly excellent in cycle characteristics.
As a result, when the specific surface area of the negative electrode active material is in the range of 0.4 to 1.2 m ² / g, the electrode structure is improved, the ion diffusibility in the negative electrode is improved, and the cycle characteristics are greatly improved. I understood that I could do it.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made. For example, in the above-described embodiments, the non-aqueous electrolyte secondary battery having a gel electrolyte has been described, but the present invention is not limited to this. For example, the present invention can also be applied to a liquid nonaqueous electrolyte secondary battery. The shape is not particularly limited, and may be a cylindrical shape, a square shape, a coin shape, a button shape, or the like.

  Furthermore, in the embodiments and examples described above, 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.

  Furthermore, for example, the method for manufacturing the positive electrode and the negative electrode is not limited to the above-described example. For example, a method in which a known binder or the like is added to the material and heated to apply, the material alone, or a conductive material, and further mixed with the binder and subjected to a treatment such as molding, on the current collector However, it is not limited to these methods. More specifically, it can be prepared by forming a slurry mixed with a binder, an organic solvent, and the like, and then applying and drying on a current collector. Or it is also possible to produce the electrode which has hardness by pressure-molding with applying heat, regardless of the presence or absence of a binder. Furthermore, for example, the active material layer provided on the current collector may be composed of a plurality of layers.

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, 30, ... Winding electrode body 21, 33 ... Positive electrode 21A, 33A ... Positive electrode current collector 21B, 33B ... Positive electrode active material layer 22, 34 ... Negative electrode 22A, 34A ... Negative electrode current collector 22B 34B ... Negative electrode active material layer 23, 35 ... Separator 24 ... Center pin 25, 31 ... Positive electrode lead 26, 32 ... Negative electrode lead 36 ... Electrolyte layer 37 ... Protective tape 40 ... exterior member 41 ... adhesion film

Claims (3)

A positive electrode and a negative electrode, and a non-aqueous electrolyte,
The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer contains graphite, and the negative electrode active material layer has a volume density of 1.4 to 1.6 g / cm ³ ,
The non-aqueous electrolyte contains a non-aqueous electrolyte, and the non-aqueous electrolyte contains succinic anhydride and propylene carbonate as a non-aqueous solvent,
The non-aqueous electrolyte secondary battery whose content in the non-aqueous electrolyte of the said succinic anhydride is 0.2-0.6 mass%. The nonaqueous electrolyte secondary battery according to claim 1, wherein a specific surface area of the active material constituting the negative electrode active material layer is 0.4 to 1.2 m ² / g.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a content of the propylene carbonate in a nonaqueous solvent is 30 to 80% by mass.

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