JP2009032682A - Lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To constitute a lithium ion secondary battery used for such application that the charging/discharging of a large current is repeated by a power tool or the like, whose cycle life is improved and reliability is enhanced. <P>SOLUTION: The lithium ion secondary battery comprises a negative electrode comprising a negative electrode mixture layer containing a negative electrode active material, a positive electrode comprising a positive electrode mixture layer containing a positive electrode active material, a separator, and a nonaqueous electrolyte. As the negative electrode active material such as a carbon material is used as an R value of a Raman spectrum when excited by an argon laser of a wavelength 514.5 nm is 0.3 to 0.8, with a surface interval d<SB>002</SB>of 002 surface being 0.34 nm or shorter. The density of the negative electrode mixture layer is 1.4-1.6 g/cm<SP>3</SP>. Such a laminate which comprises a porous resin layer whose melting point is 120-140°C and a porous resin layer whose melting point is 150°C or higher or a porous layer whose main material is an inorganic particle whose a heatproof temperature is 150°C or higher is used as a separator. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery used for various electric devices.

  A lithium ion secondary battery, which is a type of nonaqueous electrolyte battery, is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density. In addition, due to consideration of environmental issues, the importance of rechargeable secondary batteries is increasing, and in addition to portable devices, they can be applied to automobiles, power tools, electric chairs, household and commercial power storage systems. Is being considered.

  As described above, the characteristics required of batteries vary widely, and various measures are required depending on the application, but in applications that require use at high currents such as power tools, Further improvements in input / output characteristics are required for higher energy density and shorter charging time, that is, for adaptation to high load equipment.

  In order to meet such demands, it has been studied to make an electrode active material suitable for a large current load. For example, a carbon material usually used as a negative electrode active material is made amorphous on the surface of graphite particles. It has been proposed to use a composite material having a low crystalline carbon coating layer (see Patent Documents 1 to 4).

JP-A-6-267531 Japanese Patent Laid-Open No. 10-162858 JP 2002-42887 A JP 2003-168429 A

  However, in applications where both charging and discharging are performed with a large current, such as power tools, the reaction at the electrode tends to become non-uniform, and as the heat is repeatedly used, the large amount of heat generated during charging and discharging causes local localized in the electrode. Therefore, it is a problem that the deterioration of the characteristics becomes large as compared with the case where the mobile phone is used in an application where a large current is not required.

  In addition, the heat generated during the charge / discharge may affect battery members other than the electrodes and cause problems. Usually, an electric power tool is used in a pack of several unit cells. Therefore, when the temperature inside the unit cell rises due to charging / discharging, heat is accumulated inside the pack, and the temperature of the unit cell further rises. As a result, the internal temperature of the battery rises to near the melting point of the separator, the separator gradually clogs, and it becomes impossible to charge and discharge with a large current, and a battery that can maintain reliability over a long period is necessary. It was said.

  The present invention has been made in order to solve the above-described problems, and is a lithium ion secondary battery used for a purpose of repeatedly charging and discharging with a large current such as an electric tool, improving the cycle life and having a high reliability. It aims at constructing.

The lithium ion secondary battery of the present invention includes a negative electrode having a negative electrode mixture layer containing a negative electrode active material, a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a separator, and a lithium ion secondary having a non-aqueous electrolyte. In the battery, the R value of the Raman spectrum when excited by an argon laser having a wavelength of 514.5 nm as the negative electrode active material is 0.3 or more and 0.8 or less, and the interplanar spacing d ₀₀₂ of 0 is 0. .34 nm or less of carbon material, the ratio of the carbon material in the negative electrode active material is 60 wt% or more, the density of the negative electrode mixture layer is 1.4 to 1.6 g / cm ³ , and the separator Is a laminate comprising a porous resin layer having a melting point of 120 to 140 ° C. and a porous resin layer having a melting point of 150 ° C. or higher or a porous layer mainly composed of inorganic particles having a heat resistant temperature of 150 ° C. or higher. And features.

  It is possible to obtain a lithium ion secondary battery that has little deterioration in characteristics due to charging and discharging at a large current and maintains stable characteristics over a long period of time.

  Below, an example of the lithium ion secondary battery of this invention is demonstrated.

The negative electrode is formed by applying a negative electrode active material, a conductive powder serving as a conductive additive and a binder containing a binder on a current collector such as a copper foil, and drying to form a negative electrode mixture layer, followed by pressure molding. Can be obtained. At that time, in order to increase the energy density of the negative electrode mixture layer, pressing may be performed so that the density of the mixture layer is 1.4 g / cm ³ or more. On the other hand, in order to make the infiltration of the electrolyte solution into the mixture layer uniform and to make the reaction inside the mixture layer uniform in charge and discharge, the density of the mixture layer may be 1.6 g / cm ³ or less.

The negative electrode active material, the ratio of the Raman intensity _{I 1580} near Raman intensity _{I 1350} and 1580 cm ^-1 in the vicinity of the Raman spectrum of the R value (1350 cm ^-1 when excited with an argon laser with a wavelength of 514.5nm values: I ₁₃₅₀ / I ₁₅₈₀ ) is 0.3 or more and 0.8 or less, and a carbon material having a ₀₀₂ plane spacing d ₀₀₂ of 0.34 nm or less is used. Such a carbon material has a large capacity, can easily insert and desorb lithium ions on the particle surface, can be used for charging / discharging with a large current, suppresses reaction with the electrolyte, and generates heat during charging / discharging. Since decomposition of the electrolytic solution can be prevented, excellent characteristics can be maintained for a long period of time even if charging and discharging with a large current are repeated. In particular, a BET specific surface area of 1.5 to 3.6 m ² / g is preferable because the above-described effect is easily exhibited.

  The carbon material may be used only as a negative electrode active material, but other carbon materials or other materials may coexist with the carbon material in order to improve the conductivity or increase the capacity of the negative electrode mixture layer. Good. In this case, in order to easily produce the carbon effect, the ratio of the carbon material in the whole negative electrode active material may be 60 wt% or more.

Further, as the other carbon material for use with carbon materials, R value and a high carbon material of less than 0.3 crystallinity, that d ₀₀₂ is illustrated like low carbon material 0.34nm greater crystallinity it can. Further, as materials other than carbon materials, elements such as Si and Sn that alloy with Li, alloys of these elements with metal elements such as Co, Ni, Mn, and Ti, oxides of elements that alloy with Li such as SiO, and the like Examples thereof include oxides having a spinel structure typified by Li ₄ Ti ₅ O ₁₂ and LiMn ₂ O ₄ .

  The conductive auxiliary agent may be added as necessary for the purpose of improving the conductivity of the negative electrode mixture layer, and as a conductive powder to be a conductive auxiliary agent, carbon black, ketjen black, acetylene black, fibrous carbon, Carbon powder such as graphite and metal powder such as nickel powder can be used.

  Examples of the binder include, but are not limited to, cellulose ether compounds and rubber binders. Specific examples of the cellulose ether compound include carboxymethyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose, alkali metal salts such as lithium salts, sodium salts, and potassium salts, ammonium salts, and the like. Specific examples of rubber binders include, for example, styrene / conjugated diene copolymers such as styrene / butadiene copolymer rubber (SBR), and nitrile / conjugated diene copolymers such as nitrile / butadiene copolymer rubber (NBR). Rubber, silicone rubber such as polyorganosiloxane, polymer of alkyl acrylate, acrylic rubber obtained by copolymerization of alkyl acrylate and ethylenically unsaturated carboxylic acid and / or other ethylenically unsaturated monomers And fluororubber such as vinylidene fluoride copolymer rubber.

  The positive electrode is formed by applying a positive electrode active material, a conductive powder serving as a conductive additive and a binder containing a binder on a current collector such as an aluminum foil, and then drying to form a positive electrode mixture layer, followed by pressure molding Can be obtained.

The positive electrode active material is not particularly limited, but a lithium-containing composite oxide having a spinel structure [a lithium manganese oxide represented by a general formula LiMn ₂ O ₄ (some of constituent elements are Co, Ni, Al , Including complex oxides substituted with elements such as Mg, Zr, and Ti), and lithium titanium oxides represented by the general formula Li ₄ Ti ₅ O ₁₂ (some of the constituent elements are Co, Ni, Al, A complex oxide substituted with an element such as Mg, Zr, or Ti), and a lithium-containing composite oxide having a layered structure (lithium cobalt oxide represented by the general formula LiCoO ₂ (of constituent elements) Some include complex oxides substituted with elements such as Ni, Mn, Al, Mg, Zr, and Ti), and lithium nickel oxide represented by the general formula LiNiO ₂ (some of the constituent elements are Co , Mn, Al, Mg, Zr, and Ti, including complex oxides substituted with a substitution element containing at least one element)), and the like is represented by the general formula LiM ₁ PO ₄ A lithium composite compound having an olivine structure (wherein M ₁ is at least one selected from Ni, Co, Fe and Mn) can be preferably used.

In particular, lithium having a layered structure represented by the general formula LiNi _1-xy Co _x M _2y O _{2 in} which a part of Ni in the spinel structure lithium manganese oxide or lithium nickel oxide is substituted with Co and the element M ₂ Nickel-cobalt composite oxide (wherein M ₂ is a substitution element containing at least one element selected from Mn, Al, Mg, Zr and Ti, and 0.05 ≦ x ≦ 0.4, 0 ≦ y ≦ 0.5, more preferably 0.1 ≦ x ≦ 0.4, 0.02 ≦ y ≦ 0.5) and lithium composite compounds having an olivine structure are more preferably used because of their high stability at high temperatures. It is done. As the lithium manganese oxide having the spinel structure, Li _{1 + x} Mn _2-xy M _3y O ₄ (where M ₃ is at least one element selected from Co, Ni, Al, Mg, Zr and Ti). -0.05 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.3), Li _{1 + x} Mn _1.5 Ni _0.5 O ₄ (−0.05 ≦ x ≦ 0.1) ) And the like are specifically exemplified, and the lithium nickel cobalt oxide having the layered structure may be Li _{1 + x} Ni _1/3 Co _1/3 Mn _1/3 O ₂ (−0.05 ≦ x ≦ 0.1). ), Li _{1 + x} Ni _0.7 Co _0.25 Al _0.05 O ₂ (−0.05 ≦ x ≦ 0.1) and the like are specifically exemplified.

  In order to cope with charge / discharge with a large current, a lithium cobalt oxide having a layered structure (more preferably, some of the constituent elements are Ni, Mn, Al, Mg, Zr, Ti) as a positive electrode active material. Composite oxide substituted with an element such as) or lithium nickel oxide (more preferably, lithium nickel cobalt composite oxide), and the ratio is desirably 50 to 80 wt% of the whole positive electrode active material. As other active materials, it is desirable to contain a spinel-structure lithium manganese oxide.

  The conductive auxiliary agent may be added as necessary for the purpose of improving the conductivity of the positive electrode mixture layer, and as a conductive powder to be a conductive auxiliary agent, carbon black, ketjen black, acetylene black, fibrous carbon, Carbon powder such as graphite and metal powder such as nickel powder can be used.

  Examples of the binder include, but are not limited to, polyvinylidene fluoride and polytetrafluoroethylene.

  Ratio of the weight P of the positive electrode active material to the weight N of the negative electrode active material: The preferred range of P / N varies depending on the type of the positive electrode active material, but is mainly composed of a lithium-containing composite oxide having a layered structure. Is preferably 2.05 to 2.30 on the surface where the positive electrode mixture layer and the negative electrode mixture layer face each other. By setting the P / N ratio within this range, the capacity ratio between the positive electrode and the negative electrode can be optimized, and excellent cycle characteristics can be obtained.

  A porous film constituted by laminating a plurality of thermoplastic resin films having different melting points is used as a separator between the negative electrode and the positive electrode. In general, a single porous film of polyolefin used in lithium ion secondary batteries is made of a resin having a melting point near the shutdown temperature so as to cause shutdown at around 135 ° C while maintaining a certain degree of heat resistance. It has been. However, due to the large distortion of the film, when it is used for power tools, etc., it does not lead to shutdown, but the film heat generation tends to cause shrinkage or clogging of the film, which may cause short circuit or deterioration of characteristics. . Further, if the melting point of the resin is increased in consideration of heat resistance, it is difficult to cause a shutdown, which causes a problem in terms of safety.

  On the other hand, in the laminate as a separator in the present invention, a porous resin layer (high melting point resin) having a melting point of 150 ° C. or higher, in addition to a porous resin layer (low melting point resin layer) having a melting point of 120 to 140 ° C. Layer) or a porous layer (heat-resistant inorganic particle layer) mainly composed of inorganic particles having a heat-resistant temperature of 150 ° C. or higher, so that the separator can be used even when the battery internal temperature is likely to rise, such as a power tool. The heat shrinkage of the separator is suppressed, clogging hardly occurs, and the characteristics of the separator are stably maintained. For this reason, the characteristic which the negative electrode active material mentioned above and a positive electrode active material have can be exhibited effectively, and it can be set as a battery with few characteristic deterioration by charging / discharging by a large current. The separator may be a high-melting resin layer or two layers of a heat-resistant inorganic particle layer and a low-melting resin layer, but in particular, a laminate of three or more layers in which both surfaces are a high-melting resin layer and a low-melting resin layer is disposed inside. A laminate of three or more layers including a high-melting resin layer, a heat-resistant inorganic particle layer, and a low-melting resin layer is suitable for the above purpose, and more preferably used.

  For the low melting point resin layer, a porous film such as polyethylene, polybutene, ethylene propylene copolymer or the like is used, and high density polyethylene is particularly preferably used. For the high melting point resin layer, a porous film such as polypropylene, poly-4-methylpentene-1, poly-3-methylbutene-1 is used, and polypropylene is particularly preferably used.

  As a porous film constituted by laminating a plurality of thermoplastic resin films having different melting points, a porous resin layer having a melting point of 120 to 140 ° C. formed by a stretching method or an extraction method, A method in which a porous resin layer having a melting point of 150 ° C. or higher formed by an extraction method or the like is overlapped and bonded by stretching, pressure bonding, adhesive, or the like, or a resin layer having a melting point of 120 to 140 ° C. and a melting point However, a commercially available laminated film manufactured by a method of thermocompression bonding with a resin layer having a temperature of 150 ° C. or higher and making it porous by a stretching method or the like can be used.

In addition, the inorganic particles constituting the heat-resistant inorganic particle layer have heat resistance of 150 ° C. or higher, that is, particles having heat resistance that do not show deformation such as softening at least at 150 ° C., and have electrical insulation properties. Electrochemically stable particles that are difficult to be oxidized and reduced in the operating voltage range of the battery are preferably used. More specifically, inorganic oxides such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , ZrO ₂ ; inorganic nitrides such as aluminum nitride and silicon nitride; calcium fluoride, barium fluoride, Examples include slightly soluble ionic crystals such as barium sulfate; covalent bonds such as silicon and diamond; clays such as montmorillonite. Here, the inorganic oxide may be a mineral resource-derived substance such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or an artificial product thereof. Among the above inorganic particles, Al ₂ O ₃ , SiO ₂ and boehmite are particularly preferably used.

The shape of the inorganic particles may be, for example, a shape close to a sphere or a plate shape, but is preferably a plate-like particle from the viewpoint of preventing a short circuit. Typical examples of the plate-like particles include plate-like Al ₂ O ₃ and plate-like boehmite. Moreover, the thing of the secondary particle shape which the primary particle aggregated can also be used suitably. By using particles having a secondary particle shape, adhesion between particles can be prevented to some extent, and voids between particles can be appropriately maintained. Thereby, the path | route which ion permeate | transmits can be ensured, high ion permeability can be maintained, and it can be set as the structure suitable for charging / discharging by a large current.

  The average particle size of the inorganic particles is preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, more preferably 5 μm or less. In addition, the average particle diameter of the particle | grains as used in this specification uses these particle | grains in the medium (for example, water) which does not melt | dissolve these, for example using a laser scattering particle size distribution analyzer (for example, "LA-920" by HORIBA). It can be defined as the number average particle size measured by dispersion.

  The heat-resistant inorganic particle layer is a porous layer formed by binding the inorganic particles to each other with a resin or a binder used for the high-melting resin layer, and the low-melting resin layer or the high-melting resin layer Formed on. The ratio of the inorganic particles in the heat-resistant inorganic particle layer may be 50% by volume or more in terms of solid content so that the inorganic particles are mainly contained. On the other hand, the solid content ratio of the inorganic particles is preferably 99% by volume or less in order to improve the binding property due to the binder.

  Examples of the binder include highly flexible resins such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, fluorine rubber, and styrene-butadiene rubber, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, and polyvinyl butyral. Polyvinyl pyrrolidone, cross-linked acrylic resin, polyurethane, epoxy resin and the like are used. In particular, a heat-resistant binder capable of maintaining excellent binding properties up to a temperature of 150 ° C. or higher and maintaining the shape of the heat-resistant inorganic particle layer is preferably used. The heat-resistant inorganic particle layer may be formed by applying a composition containing the inorganic particles and the binder and the like dispersed in a solvent to the high-melting resin layer or the low-melting resin layer and drying. it can.

  The thickness of the high-melting point resin layer or the heat-resistant inorganic particle layer is preferably 1 μm or more, more preferably 3 μm or more, in order to suppress the thermal shrinkage of the separator. 15 μm or less, more preferably 10 μm or less. In addition, the thickness of the low melting point resin layer is preferably 3 μm or more in order to ensure shutdown, more preferably 5 μm or more. On the other hand, in order to reduce the thickness of the entire separator, the thickness is 20 μm or less. It is preferable that the thickness is 15 μm or less.

  The non-aqueous electrolyte in the present invention is not particularly limited, and a general-purpose non-aqueous electrolyte obtained by dissolving an electrolyte salt such as a lithium salt in a non-aqueous solvent such as an organic solvent is generally used.

  Examples of the non-aqueous solvent include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3- Solvents such as dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether and the like can be used singly or as a mixed solvent in which several kinds are mixed.

As the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF 3 SO 2 ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like. The concentration of the electrolyte salt in the electrolytic solution is preferably 0.3 to 1.7 mol / l, particularly 0.5 to 1.5 mol / l.

  In order to improve the charge / discharge cycle characteristics and storage characteristics of the above electrolyte, vinylene carbonate or its derivatives, alkylbenzenes such as cyclohexylbenzene and tertiary butylbenzene, cyclic sultones such as biphenyl and propane sultone, and sulfides such as diphenyl disulfide Additives such as may be included. The addition amount may be 0.1 to 10 wt% in the electrolytic solution, more preferably 0.5 wt% or more, and more preferably 5 wt% or less.

Example 1
As the negative electrode active material, the R value of the Raman spectrum when excited with an argon laser having a wavelength of 514.5 nm is 0.65, the interplanar spacing d ₀₀₂ of the 002 plane is 0.335 nm, and the BET specific surface area is 2.2 m ² / A mixture of 80% of graphite powder of 20 g and 20% of graphite powder having an R value of 0.15, carboxymethyl cellulose and styrene-butadiene copolymer rubber as a binder, and a weight ratio of 98 with water as a solvent: The mixture was mixed at a ratio of 1: 1 to prepare a slurry-like negative electrode mixture-containing paste. The obtained negative electrode mixture-containing paste was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried to form a negative electrode mixture layer, and the density of the negative electrode mixture layer was 1. After being pressure-molded to 5 g / cm ³ , it was cut to a predetermined width and length to produce a negative electrode.

66.5 parts by weight of LiCoO ₂ as a positive electrode active material, 28.5 parts by weight of LiMn ₂ O ₄ , 2.5 parts by weight of ketjen black as a conductive additive, 2.5 parts by weight of polyvinylidene fluoride as a binder, -Methyl-2-pyrrolidone was mixed uniformly as a solvent to prepare a positive electrode mixture-containing paste. After applying the paste on both sides of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, drying to form a positive electrode mixture layer, and pressing the positive electrode mixture layer to a predetermined thickness with a roller. Then, a positive electrode was produced by cutting to a predetermined width and length.

  Total thickness of polypropylene film (melting point: 165 ° C.) with a thickness of about 7 μm / polyethylene film (melting point: 125 ° C.) with a thickness of about 7 μm / polypropylene film (melting point: 165 ° C.) with a thickness of about 7 μm between the negative electrode and the positive electrode. A porous laminated film having a diameter of about 20 μm and an opening ratio of 46% was placed as a separator, wound in a spiral shape, and inserted into a cylindrical outer can. On the surface where the positive electrode mixture layer and the negative electrode mixture layer face each other, the ratio P / N between the weight P of the positive electrode active material and the weight N of the negative electrode active material was 2.17.

The non-aqueous electrolyte is prepared by dissolving LiPF ₆ at a ratio of 1.2 mol / liter in a solvent in which ethylene carbonate and methyl ethyl carbonate are mixed at a volume ratio of 1: 2, and further adding 2 wt% of vinylene carbonate. Using this solution, a cylindrical lithium ion secondary battery having a diameter of 18 mm and a height of 65 mm was obtained.

Example 2
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the density of the negative electrode mixture layer was 1.58 g / cm ³ and the PN ratio was 2.22.

Example 3
As the negative electrode active material, the R value of the Raman spectrum when excited with an argon laser having a wavelength of 514.5 nm is 0.65, the interplanar spacing d ₀₀₂ of the 002 plane is 0.335 nm, and the BET specific surface area is 2.2 m ² / A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that the ratio of g graphite powder was 100%, and acetylene black was used instead of ketjen black as the positive electrode conductive assistant.

Example 4
Example except that LiNi _0.82 Co _0.10 Al _0.03 O ₂ was used instead of LiCoO ₂ of the positive electrode active material, and acetylene black was used instead of ketjen black as the conductive assistant for the positive electrode. In the same manner as in Example 1, a lithium ion secondary battery was produced.

Example 5
1 kg of boehmite secondary particles (average particle size: 2 μm) is dispersed in 1 kg of water, and further 120 g of styrene-butadiene rubber latex (solid content ratio 40%) is added and dispersed uniformly to form a heat resistant inorganic particle layer forming composition. Was prepared. This composition was applied to one side of a microporous membrane (thickness 16 μm, porosity 45%) made of polyethylene having a melting point of 135 ° C. and dried, and a heat-resistant inorganic particle layer having a thickness of 5 μm and a low melting point resin layer The laminated body which consists of was produced. A lithium ion secondary battery was produced in the same manner as in Example 1 except that this laminate was used as a separator.

Comparative Example 1
A lithium ion secondary battery was produced in the same manner as in Example 1 except that only graphite powder having an R value of 0.25 was used as the negative electrode active material.

Comparative Example 2
A lithium ion secondary battery was produced in the same manner as in Example 1 except that a single-layer porous film made of polyethylene having a thickness of 25 μm and an aperture ratio of 42% was used as a separator.

Comparative Example 3
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the density of the negative electrode mixture layer was 1.67 g / cm ³ .

Comparative Example 4
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the density of the negative electrode mixture layer was 1.35 g / cm ³ .

Comparative Example 5
A lithium ion secondary battery was produced in the same manner as in Example 1 except that a porous laminated film composed of polypropylene film / polyethylene film (melting point: 105 ° C.) / Polypropylene film was used as the separator.

  The prepared battery was subjected to constant current-constant voltage charging (total charging time: 2.5 hours) with a constant current of 0.75 A and a constant voltage of 4.2 V, and then a constant current discharge at 1.5 A ( Discharge final voltage: 2.5V), and the initial discharge capacity was measured. Next, after the constant current-constant voltage charge, a constant current discharge (discharge end voltage: 2.0 V) is performed at 25 A (discharge rate is about 16 C) to measure a capacity in a large current discharge, and the initial discharge The ratio to the capacity was evaluated as a large current characteristic. Furthermore, charging / discharging was performed under the same conditions as the measurement of the initial discharge capacity, and the ratio of the capacity at this time to the initial discharge capacity was evaluated as a capacity recovery rate. The results are shown in Table 1.

  In addition, the charge / discharge cycle was repeated with a large current, and the ratio of the capacity at the elapse of 100 cycles, 200 cycles and 500 cycles with respect to the capacity of the first cycle was measured to evaluate the cycle characteristics. The results are shown in Table 2. Charging was constant current-constant voltage charging with a constant current of 4 A and a constant voltage of 4.2 V, and discharging was a constant current discharge of 3 A (discharge end voltage: 2.0 V).

  Further, the same separator as used in Example 1, Comparative Example 2 and Comparative Example 5 was cut into a predetermined size, sandwiched between glass plates from both sides, left in a thermostatic bath at 130 ° C. for 1 hour, and then taken out. The change in length and the change in Gurley value were measured. Table 3 shows the result of calculating the relative value of the Gurley value with the ratio of the change amount with respect to the length before the test as the shrinkage and the Gurley value before the test as 100.

  Since the lithium ion secondary batteries of Examples 1 to 5 have a battery configuration in which the reactions at the electrodes are made uniform and can cope with the temperature rise inside the battery due to charge and discharge, it has excellent large current characteristics, and discharge exceeding 10 C Even so, the battery had good cycle characteristics with little deterioration in characteristics after capacity. On the other hand, in Comparative Example 1, since the R value of the negative electrode active material was small, it was difficult to insert and desorb lithium ions on the particle surface, and it was impossible to handle charge / discharge with a large current, resulting in a decrease in capacity. In Comparative Example 2 using a single-layer porous film, as shown by the increase in the Gurley value at high temperature, the clogging of the separator gradually proceeds and the cycle characteristics deteriorate, and the heat shrinkage of the separator There was also the danger of a short circuit. In Comparative Examples 3 and 4, since the density of the negative electrode mixture layer was not appropriate, the reaction inside the mixture layer during charge and discharge became non-uniform and the cycle characteristics deteriorated. Further, in Comparative Example 5, although the separator was not contracted, the melting point of the low melting point resin layer was too low, so that when the discharge exceeding 10 C was performed, the characteristics of the separator changed and capacity was deteriorated.

Claims (5)

A negative electrode having a negative electrode mixture layer containing a negative electrode active material, a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a separator, and a lithium ion secondary battery having a non-aqueous electrolyte,
When the negative electrode active material is excited with an argon laser having a wavelength of 514.5 nm, the R value of the Raman spectrum is 0.3 or more and 0.8 or less, and the surface spacing d ₀₀₂ of the 002 plane is 0.34 nm or less. Containing carbon materials,
The ratio of the carbon material in the negative electrode active material is 60 wt% or more,
The negative electrode mixture layer has a density of 1.4 to 1.6 g / cm ³ ,
The separator is a laminate including a porous resin layer having a melting point of 120 to 140 ° C and a porous resin layer having a melting point of 150 ° C or higher or a porous layer mainly composed of inorganic particles having a heat resistant temperature of 150 ° C or higher. A lithium ion secondary battery characterized by being. The lithium ion secondary battery according to claim 1, wherein the negative electrode active material has a BET specific surface area of 1.5 to 3.6 m ² / g.   3. The lithium ion according to claim 1, wherein the positive electrode active material includes at least one compound selected from a spinel structure lithium manganese oxide, a layered structure lithium nickel cobalt composite oxide, and an olivine structure lithium composite compound. Secondary battery.   4. The positive electrode active material includes a spinel-structure lithium manganese oxide and a layered lithium-nickel-cobalt composite oxide, and the proportion of the lithium-nickel-cobalt composite oxide is 50 to 80 wt% of the total positive electrode active material. The lithium ion secondary battery described in 1.   The ratio P / N between the weight P of the positive electrode active material and the weight N of the negative electrode active material is set to 2.05 to 2.30 on the surface where the positive electrode mixture layer and the negative electrode mixture layer face each other. Item 5. The lithium ion secondary battery according to Item 3 or 4.