JP2015210891A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which enables the achievement of the balance between high output and input characteristics and safety.SOLUTION: A nonaqueous electrolyte secondary battery comprises: a positive electrode and a negative electrode. The positive electrode has: a positive electrode collector; and a positive electrode active material layer including a positive electrode active material. The positive electrode active material includes a lithium transition metal complex oxide including at least one transition metal element selected from nickel, cobalt and manganese, and tungsten. The percentage of the tungsten to the at least one transition metal element is 0.3-0.7 mol%. The negative electrode has: a negative electrode current collector; and a negative electrode active material layer including a negative electrode active material. The negative electrode active material includes natural graphite with amorphous carbon arranged on its surface. The negative electrode has a capacitance 0.12-0.2 F/g. In the nonaqueous electrolyte secondary battery, the negative electrode active material includes 0.4-1 mass% of a binder including a rubber-based resin.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery including a lithium transition metal oxide containing tungsten on a positive electrode.

  A non-aqueous electrolyte secondary battery represented by a lithium ion battery is preferably used as a portable power source, a high-output power source for mounting on a vehicle, and the like because it is lightweight and has a high energy density. A non-aqueous electrolyte secondary battery used as a power source for driving a vehicle is particularly required to have excellent high rate charge / discharge (rapid charge / discharge) characteristics.

  As one of positive electrode active materials used for such non-aqueous electrolyte secondary batteries, lithium transition metal oxides are widely known. And it is disclosed by including tungsten (W) in this lithium transition metal oxide that it is effective in the further improvement of charging / discharging efficiency and reduction of reaction resistance (for example, refer patent document 1).

JP 2013-235653 A International Publication No. 2012/164693 JP 2009-158099 A JP 2013-247035 A

By the way, since a nonaqueous electrolyte secondary battery has a high output and a high energy density, higher safety is required compared to other batteries. Therefore, for example, when the battery is overcharged, a shutdown function such as a separator or a current interruption mechanism is developed, and it is required to quickly stop the electrochemical reaction in the battery. However, in the non-aqueous electrolyte secondary battery using the lithium transition metal oxide containing tungsten as the positive electrode active material, there is a possibility that leakage current continues to flow even after the shutdown and excessive heat generation of the battery is caused.
The present invention has been made in view of such circumstances, and its purpose is to exhibit excellent charge / discharge characteristics due to the tungsten-containing lithium transition metal oxide sufficiently, and to suppress a leakage current after shutdown to be safe. It is providing the nonaqueous electrolyte secondary battery also provided with property.

  In order to solve the above problems, the present invention provides a non-aqueous electrolyte secondary battery (hereinafter sometimes simply referred to as a battery or the like) including a positive electrode, a negative electrode, and a non-aqueous electrolyte. Here, the positive electrode has a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material includes at least one transition metal element selected from nickel, cobalt, and manganese, and tungsten. And a lithium transition metal composite oxide. More preferably, the positive electrode active material is a lithium transition metal composite oxide containing nickel, cobalt, and manganese together with tungsten. And the ratio of the said tungsten with respect to the said transition metal element is 0.3 mol% or more and 0.7 mol% or less, It is characterized by the above-mentioned. The negative electrode includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material, and the negative electrode active material includes natural graphite having amorphous carbon disposed on a surface thereof. The negative electrode has a capacitance of 0.12 F / g or more and 0.2 F / g or less.

  According to such a configuration, not only lithium transition metal composite oxide containing tungsten (hereinafter also referred to as W-containing lithium transition metal composite oxide) is used, but also natural graphite (hereinafter referred to as amorphous carbon) having amorphous carbon disposed on the surface. In some cases, the charge / discharge characteristics (which may be input / output characteristics) of the battery are sufficiently enhanced by using the amorphous carbon-coated graphite in some cases. Furthermore, by identifying the properties of the W-containing lithium transition metal composite oxide and the amorphous carbon-coated graphite, and controlling and combining these properties more appropriately, not only the battery input / output characteristics can be improved, but also the shutdown can be performed. The later leakage current is also suppressed. Thereby, a non-aqueous electrolyte secondary battery having both high input / output characteristics and safety is provided.

In Patent Document 2, LiNi _1/3 Co _1/3 Mn _1/3 W _1/200 O ₂ can be used as the positive electrode active material, and the ratio of the theoretical capacity of the positive electrode to the negative electrode (Ca / Cc) is 1. .2 or more and 1.5 or less. Patent Document 3 discloses that the capacity of the negative electrode on one side per unit area is 0.8 mAh / cm ² or more and 1.2 mAh / h from the relationship with the coating amount of the negative electrode for controlling the reaction resistance and diffusion resistance of the electrode. It is disclosed that it is preferable to make it cm ² or less. However, these patent documents have not been studied from the viewpoint of safety to reduce the leakage current after the battery is shut down, and the leakage current actually cannot be controlled. On the other hand, in the present invention, high input / output characteristics and safety are realized by a combination of positive and negative active materials and control of their properties.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the ratio of the tungsten to the transition metal element is 0.3 mol% or more and 0.6 mol% or less. According to such a configuration, a leakage current can be more reliably suppressed, and a battery with further improved safety is provided.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode and the negative electrode constitute a wound electrode body that is laminated and wound via a separator. . A battery including a wound electrode body has a tendency to easily generate heat during overcharge because it has a relatively low heat dissipation and can realize a higher capacity and a higher energy density. Therefore, it is preferable to apply the technique disclosed herein to a battery including such a wound electrode body because the effect can be sufficiently exhibited. As a result, a battery that achieves a high capacity and a high energy density and is further improved in safety is provided.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the negative electrode active material layer includes a binder made of a rubber-based resin at a ratio of 0.4 mass% to 1 mass%. By setting it as this structure, a highly reliable nonaqueous electrolyte secondary battery provided with the negative electrode active material layer excellent in mechanical strength and durability is realizable. Further, the resistance of the negative electrode can be further reduced.

  The above non-aqueous electrolyte secondary battery is provided as being particularly excellent in charge / discharge characteristics (input / output characteristics) and having high safety. Therefore, taking advantage of this feature, for example, it can be particularly preferably used as a non-aqueous electrolyte secondary battery used as, for example, a power source (drive power source) for driving a motor mounted on various vehicles.

It is a figure which shows typically the cross-sectional structure of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a cross-sectional schematic diagram which shows the structure of the symmetry cell for measuring the capacitance of a negative electrode. It is a figure which shows the relationship between the capacitance of the negative electrode which concerns on the battery of each example, and charging resistance ratio. It is a figure which shows the relationship between W ratio of the positive electrode which concerns on the battery of each example, and discharge resistance ratio. It is a figure which shows the relationship between the capacitance of the negative electrode which concerns on the battery of each example, and leakage current.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification (for example, the characteristics of the positive electrode active material and the negative electrode active material, etc.), and matters necessary for the implementation of the present invention (for example, the present invention is not characterized). The battery structure, the general manufacturing process of the battery, etc.) can be grasped as design matters of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, dimensional relationships (length, width, thickness, etc.) in the drawings shown below do not necessarily reflect actual dimensional relationships.

  In the present specification, the “non-aqueous electrolyte secondary battery” refers to a secondary battery containing a charge carrier in a non-aqueous electrolyte. “Secondary batteries” are used in the same industrial fields as chemical batteries (for example, lithium secondary batteries) in addition to so-called chemical batteries such as lithium secondary batteries, nickel hydride batteries, nickel cadmium batteries, and lead storage batteries. It is a term including a storage element (for example, a pseudo-capacitance capacitor, a redox capacitor) that can be obtained, a hybrid capacitor that combines these, a lithium ion capacitor, and the like. The “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery, a lithium polymer battery, or the like is a typical example included in the lithium secondary battery in this specification. In the present specification, the “active material” refers to a substance (compound) capable of reversibly occluding and releasing chemical species (lithium ions in a lithium secondary battery) serving as a charge carrier on the positive electrode side or the negative electrode side.

[Nonaqueous electrolyte secondary battery]
Hereinafter, the nonaqueous electrolyte secondary battery disclosed herein will be described by taking a preferred embodiment as an example. FIG. 1 is a schematic cross-sectional view showing a configuration of a nonaqueous electrolyte secondary battery 10 disclosed herein. This non-aqueous electrolyte secondary battery 10 essentially includes a positive electrode 30, a negative electrode 50, and a non-aqueous electrolyte (not shown). Each component will be described below.

[Positive electrode]
The positive electrode 30 is typically configured by including a positive electrode active material layer 34 on a positive electrode current collector 32. The positive electrode active material layer 34 is not particularly limited as long as it includes a positive electrode active material. Typically, the positive electrode active material is bonded together with a conductive material together with a binder (binder), and the positive electrode current collector 32. It may be in a form joined to the substrate. Such a positive electrode 30 includes, for example, a positive electrode current collector 32 made of a positive electrode paste in which a positive electrode active material, a conductive material, and a binder (binder) are dispersed in an appropriate solvent (for example, N-methyl-2-pyrrolidone). It can be manufactured by supplying to the surface of the substrate and drying to remove the solvent. As the positive electrode current collector 32, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) can be suitably used.

The positive electrode active material includes a lithium transition metal composite oxide containing at least one transition metal element selected from nickel (Ni), cobalt (Co), and manganese (Mn), and tungsten (W). Among these, lithium nickel cobalt manganese composite oxide having a layered structure (typically a layered rock salt structure belonging to a hexagonal system) containing W, Li, Ni, Co and Mn as constituent elements can be preferably used. Specifically, for example, so-called ternary lithium transition metal composite oxides such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ containing W have excellent thermal stability and high energy density. Is preferable as a positive electrode active material capable of realizing the above. Here, the lithium transition metal composite oxide serving as the basis of the W-containing lithium transition metal composite oxide may contain a transition metal element other than Ci, Co, and Mn. As such transition metal elements, elements existing in Group 3 to Group 11 of the Periodic Table of Elements can be considered without particular limitation. Preferably, it is an element belonging to the fourth period, such as titanium (Ti), vanadium (V), chromium (Cr), iron (Fe) and the like.

  And the ratio of W with respect to the sum total of these transition metal elements is prescribed | regulated to 0.3 mol% or more and 0.7 mol% or less. The ratio of W to the total of transition metal elements is within this range, so that the charge / discharge efficiency of the battery is improved by changing the valence of W, and in particular, the discharge resistance of the battery is kept low and the occurrence of leakage current is suppressed. Can do. In this respect, the above effect can be obtained when the ratio of W to the total of transition metal elements exceeds 0.2 mol%, typically 0.3 mol% or more, preferably 0.4 mol%. % Or more, for example, 0.5 mol% or more. The above effect can be obtained when the ratio of W is less than 0.8 mol%, and typically 0.7 mol% or less, preferably 0.65 mol% or less, for example 0.6 mol% or less. can do. In addition, it is preferable that W exists (is unevenly distributed) on the surface (including the particle interface) of the primary particles of the positive electrode active material (W-containing lithium transition metal composite oxide) particles. Such a W-containing lithium transition metal composite oxide can be suitably manufactured based on the disclosure of Patent Document 1, for example. In addition, the W-containing lithium transition metal composite oxide is allowed to contain an optional element other than lithium, a transition metal element, W, and oxygen as long as the object of the present invention is not impaired. Examples of such optional elements include Al, Mo, Cu, Zn, Ga, In, Sn, La, Ce, Ca, and Na.

The positive electrode active material includes this kind of positive electrode active material other than the W-containing lithium transition metal composite oxide (for example, LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO _{4, and the} like, such as layered or spinel-based lithium composite metal oxides, for example, is less than 50% by mass of the positive electrode active material (typically 30% by mass or less, for example, 10% (Mass% or less) is not prevented from being included.
As the positive electrode active material, a particulate material can be preferably used. The average particle diameter of the positive electrode active material is not particularly limited, and can be appropriately adjusted depending on the configuration and use of the battery. For example, the average particle diameter of the positive electrode active material can be 1 μm to 25 μm (typically 2 μm to 20 μm, for example, 6 μm to 15 μm). In the present specification, the “average particle size” means a particle size (D ₅₀ ) corresponding to a cumulative 50% in a volume-based particle size distribution measured by a particle size distribution measurement based on a general laser diffraction / light scattering method. Indicates.

  As the binder, one or more kinds of substances having adhesive ability that are conventionally used in nonaqueous electrolyte secondary batteries can be used without any particular limitation. For example, when the positive electrode active material layer is formed in the form of a positive electrode paste, a compound that can be dissolved or dispersed homogeneously in a solvent described later can be used. For example, when the positive electrode active material layer is formed using an organic solvent-based paste, a polymer material that is dispersed or dissolved in an organic solvent can be preferably used. Examples of such a polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyethylene oxide. Alternatively, when the positive electrode active material layer is formed using an aqueous paste, a polymer material that is dissolved or dispersed in water can be preferably used. Examples of such polymer materials include cellulose polymers, fluorine resins, vinyl acetate copolymers, rubbers, and the like. More specifically, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, polyvinyl alcohol, polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), tetrafluoroethylene-hexafluoropropylene copolymer, acrylic acid-modified SBR resin (SBR latex). Although it does not specifically limit, the ratio of the binder to the whole positive electrode active material layer can be 0.5 mass% or more and 10 mass% or less (preferably 1 mass% or more and 5 mass% or less), for example. In addition, the binder disclosed here can also play the role of a thickener etc. other than the effect | action as a binder.

  As the conductive material, one or more kinds of substances conventionally used in secondary batteries can be used without any particular limitation. For example, carbon materials such as carbon black (for example, acetylene black, furnace black, ketjen black, etc.), coke, graphite (natural graphite and modified products thereof, artificial graphite), and the like can be used. Among these, carbon black (typically acetylene black) having a small particle size and a large specific surface area can be preferably used. Although it does not specifically limit, the ratio of the electrically-conductive material to the whole positive electrode active material layer can be 1 mass% or more and 15 mass% or less (typically 5 mass% or more and 10 mass% or less), for example.

  In addition, the solvent used for preparation of the positive electrode 30 is divided roughly into an aqueous solvent and an organic solvent (non-aqueous solvent) as mentioned above. Specific examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide, 2-propanol, cyclohexanone, methyl acetate, ethyl acetate, and methyl acrylate. In addition, the aqueous solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be homogeneously mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the aqueous solvent is water. A particularly preferable example is an aqueous solvent (for example, water) substantially consisting of water.

In the production method disclosed herein, for example, after the positive electrode paste or the granulated body is applied on the positive electrode current collector, the solvent contained in the paste (or the granulated body) is removed by an appropriate drying means. Then, after removing the solvent, the thickness and density of the positive electrode active material layer can be adjusted by appropriately pressing the positive electrode. For the press treatment, various conventionally known press methods such as a roll press method and a flat plate press method can be employed. The density of the positive electrode active material layer is, for example, 1.5 g / cm ³ or more, typically 2 g / cm ³ or more, and 4.5 g / cm ³ or less, typically 4.2 g / cm ³ or less. It is preferable to do.

[Negative electrode]
The negative electrode 50 is configured by including a negative electrode active material layer 54 on a negative electrode current collector 52. The negative electrode active material layer 54 includes a negative electrode active material. Typically, the negative electrode active materials may be bonded to each other by a binder (binder) and bonded to the negative electrode current collector 52. And in the nonaqueous electrolyte secondary battery 10 of this invention, the natural graphite (amorphous carbon covering graphite) by which the amorphous carbon is arrange | positioned on the surface is included as a negative electrode active material. In such a negative electrode 50, for example, a negative electrode paste obtained by dispersing a negative electrode active material and a binder in a suitable solvent (for example, water or N-methyl-2-pyrrolidone, preferably water) is used. It can be manufactured by supplying to the surface of the substrate and drying to remove the solvent. As the negative electrode current collector, a conductive member made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) can be suitably used.

  The amorphous carbon-coated graphite is not particularly limited as long as amorphous carbon is disposed on at least a part of the surface of the granular graphite. Preferably, almost all of the surface of the granular carbon is covered with an amorphous carbon film. From this viewpoint, in the present specification, the amorphous carbon-coated graphite is not necessarily limited to a form in which the entire outer surface of the graphite is covered with amorphous carbon. Note that amorphous carbon has a large number of edge surfaces exposed on its surface, and has a high charge carrier acceptability (that is, the charge carrier is occluded / released quickly). Graphite has a large theoretical capacity and is excellent in energy density. Therefore, by using amorphous carbon-coated graphite as the negative electrode active material, it is possible to realize a non-aqueous electrolyte secondary battery having a large capacity, high energy density, and excellent input / output characteristics.

  Such amorphous carbon-coated graphite can be produced by various conventionally known methods. For example, first, graphite and an amorphous carbon source (for example, an inorganic carbon material such as graphitizable carbon or an organic polymer material) are prepared as raw materials. Then, an amorphous carbon source is attached to the surface of the graphite by a vapor phase method such as a CVD method (Chemical Vapor Deposition), a liquid phase method, a solid phase method, or the like. As graphite, natural graphite such as massive graphite and flake graphite, artificial graphite obtained by firing a carbon precursor, or those obtained by subjecting the above graphite to processing such as pulverization, sieving, pressing, etc. Can do. In addition, the amorphous carbon source cannot be generally described because it depends on the method for producing the amorphous carbon-coated graphite employed. For example, in the CVD method, unsaturated aliphatic carbonization such as ethylene, acetylene, and propylene is used. Hydrogen: saturated aliphatic hydrocarbons such as methane, ethane, propane, etc .; aromatic hydrocarbons such as benzene, toluene, naphthalene, etc .; It can be a compound (gas) that can form a film. Alternatively, in the liquid phase method and the solid phase method, aromatic hydrocarbons such as naphthalene and anthracene, pitches such as coal tar pitch, petroleum pitch, and wood tar pitch can be used. Then, the graphite material to which the amorphous carbon source is attached is fired and carbonized at a high temperature (for example, 500 ° C. to 1500 ° C.). Next, the obtained carbide is appropriately pulverized and sieved to produce amorphous carbon-coated graphite having the properties disclosed herein.

The properties of amorphous carbon-coated graphite (for example, D50 value, BET specific surface area, etc.) include, for example, the type and properties of raw materials used (particularly the average particle size), firing / carbonization temperature, pulverization and sieve after carbonization. It can be adjusted by dividing. For example, those having an average particle diameter (D50) of about 5 to 20 μm and a specific surface area by the BET method of about 1.8 to 5.6 m ² / g can be preferably used. As the negative electrode active material, this kind of negative electrode active material other than amorphous carbon-coated graphite (for example, graphite such as natural graphite and artificial graphite; carbon material such as non-graphitizable carbon, graphitizable carbon, and carbon nanotube) Metal oxide such as lithium-titanium composite oxide; metal that can form an alloy with lithium such as tin and silicon) is, for example, less than 50% by mass of the negative electrode active material (typically 30% by mass or less, for example, 10 (Mass% or less) is not prevented from being included.

  As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for the positive electrode active material layer. For example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) and the like are exemplified. In particular, a binder made of a rubber-based resin typified by styrene butadiene rubber (SBR) can realize a highly reliable nonaqueous electrolyte secondary battery including a negative electrode active material layer having excellent mechanical strength and durability. preferable. The ratio of the binder in the entire negative electrode active material layer is not particularly limited, but can be adjusted, for example, in the range of about 0.1% by mass to 10% by mass. In particular, the resistance of the negative electrode can be further reduced by setting the binder amount to a ratio of 0.4% by mass or more and 1% by mass or less. Thereby, a higher quality nonaqueous electrolyte secondary battery can be provided.

The proportion of the negative electrode active material in the entire negative electrode active material layer 54 is suitably about 50% by mass or more, and preferably 90% by mass to 99% by mass, for example, 95% by mass to 99% by mass. Then, the thickness and density of the negative electrode active material layer can be adjusted by appropriately pressing the negative electrode. The thickness of the negative electrode active material layer after the press treatment is, for example, 20 μm or more, typically 50 μm or more, and can be 200 μm or less, typically 100 μm or less. Further, the density of the negative electrode active material layer is not particularly limited, but is, for example, 0.8 g / cm ³ or more, typically 1.0 g / cm ³ or more, and 1.6 g / cm ³ or less, typically It can be 1.5 g / cm ³ or less, for example 1.4 g / cm ³ or less.

(Negative capacitance)
In the nonaqueous electrolyte secondary battery of the present invention, the negative electrode has a capacitance in the range of 0.12 F / g or more and 0.2 F / g or less. When a negative electrode is produced using amorphous carbon-coated graphite as the negative electrode active material, by setting the capacitance of the negative electrode within the above range, for example, the charging resistance can be kept low, and a non-aqueous electrolyte with excellent input characteristics can be obtained. A secondary battery can be realized. Further, in combination with a positive electrode using a specific positive electrode active material, a leakage current after shutdown can be reduced, and a non-aqueous electrolyte secondary battery excellent in safety can be realized. Here, when the capacitance of the negative electrode is 0.12 F / g or more, it can be determined that the input characteristics are good for the batteries for almost all uses. The capacitance of the negative electrode is preferably 0.13 F / g or more, more preferably 0.14 F / g or more, for example, 0.15 F / g or more. Further, it is determined that the leakage current can be sufficiently suppressed when the capacitance of the negative electrode is 0.2 F / g or less. The capacitance of the negative electrode is preferably 0.192 F / g or less, more preferably 0.19 F / g or less, for example 0.18 F / g or less.

Note that the capacitance of the negative electrode can be obtained by the following procedure. That is, for a symmetry cell 100 configured by preparing two target negative electrodes 50 in an uncharged state, an impedance Z (f) in a specific frequency region measured by a general AC impedance method is measured. Then, the quantitative value of the impedance Z (f) is converted into the electric double layer capacitance C (f) for the frequency, and the capacitance of the negative electrode is calculated based on the maximum convergence value. In the present invention, such a maximum convergence value is obtained as the real component C ′ (f) of the electric double layer capacity at a frequency of 0.1 Hz. And the capacitance of a negative electrode is computed by converting this value per unit weight of a negative electrode active material.
FIG. 2 illustrates the configuration of a symmetry cell 100 used to measure the negative electrode capacitance. The symmetry cell 100 can be configured by preparing two negative electrodes 50 to be measured with the following sizes and arranging them so that the negative electrode active material layers 54 face each other with the separators 70 interposed therebetween. it can. For example, the negative electrode 50 can have any configuration as long as it is within the following range.

<Basic configuration of symmetry cell>
Negative electrode active material layer: [binder + thickener] (mass ratio) = 98: 2-99: 1
Weight per unit area: 3.5 to 3.8 mg / cm ² (one side)
Active material layer density: 0.90 g / cm ^{3 to} 1.40 g / cm ³
Negative electrode size: 4.5cm x 4.7cm
Electrolyte solution: EC containing 1.1 mol / L LiPF ₆ : DMC: EMC = 3: 4: 3 (volume ratio)

  As the negative electrode current collector 52 constituting the negative electrode 50, various conductive metal foils and the like can be used as described above. Although not particularly limited, a copper foil having a thickness of about 10 μm is preferable. In the structure of the mixed solution of the electrolytic solution, EC represents ethylene carbonate, DMC represents dimethyl carbonate, and EMC represents ethyl methyl carbonate. The separator is not particularly limited as long as it has both insulating properties and ion permeability, and various conventionally known separators can be used. The symmetry cell is accommodated in the battery case 80 such as a laminate bag in which the negative electrode 50 and the electrolytic solution that are opposed to each other as described above can be applied with a voltage between the two negative electrodes 50 from the outside. 100 can be built.

  AC impedance is measured for the symmetry cell 100 configured as described above. The AC impedance measurement method is not particularly limited. For example, the FFT method using a general-purpose Fast Fourier Transform (FFT) analyzer, or a frequency response analyzer (FRA: Frequency Response) that sweeps and measures a single sine wave. Various methods such as (Analyzer) can be adopted as appropriate. For example, it can be measured as follows. First, a direct current is passed between the electrodes 50, and then the impedance is calculated by measuring the response voltage at each frequency when a small alternating current is superimposed, and the frequency characteristic of the impedance is obtained by Fourier transform. . Alternatively, the frequency characteristics of the impedance may be obtained by applying an AC signal from an oscillator between the electrodes 50 and measuring the sample voltage (V) with a voltmeter and the sample current (I) with an ammeter. In the measurement, typically, the frequency of the AC voltage is changed from a high frequency of about 100,000 Hz to a low frequency of about 0.1 Hz. The amplitude of the AC voltage is not particularly limited, but can be set to about 1 to 10 mV, for example, about 5 mV.

  The frequency characteristics of the impedance obtained by the measurement can be typically obtained, for example, by creating a Cole-Cole plot (Nyquist plot) and fitting it into an equivalent circuit for analysis. . In the present invention, a so-called electric double layer capacitance component is extracted from the frequency characteristics of impedance, and the “capacitance of the negative electrode active material” is defined based on the electric double layer capacitance at a sufficiently low frequency of 0.1 Hz. Specifically, the capacitance of the negative electrode active material can be calculated as follows, for example. First, the impedance characteristic regarding the frequency f obtained by the measurement can be expressed by the following formula (1). The relationship of the impedance Z (f) is converted into an equation (2) indicating the relationship with the electric double layer capacitance C (f). Here, the electric double layer capacitance C (f) can be expressed by Expression (3), and its real part component C ′ (f) and imaginary part component C ″ (f) are expressed by Expression (4) and Expression (5), respectively. Therefore, the electric double layer capacitance C ′ value when the frequency is 0.1 Hz may be calculated from the equation (4).

Since the electric double layer capacity C ′ obtained at 0.1 Hz obtained above is the total charge amount generated in the entire symmetry cell 100, it is converted into the charge amount per unit weight of the negative electrode active material. Thus, the capacitance of the negative electrode active material is used. In this calculation, the capacitance C ₁ ′ of _one electrode 50 represented by the equation (7) is calculated from the relationship of the following equation (6). Then, the capacitance value of the active material may be obtained by dividing the capacitance C ₁ ′ of the single electrode 50 by the mass of the total active material contained in the active material layer of the single electrode. More specifically, the capacitance of the negative electrode can be measured with reference to Patent Document 4, for example.

[Separator]
The separator 70 is a constituent material that insulates the positive electrode 30 (the positive electrode active material layer 34) from the negative electrode 50 (the negative electrode active material layer 54) and has a charge carrier permeability. 50. The separator 70 may have a non-aqueous electrolyte holding function and a shutdown function that softens or melts at a predetermined temperature or higher to prevent charge carrier movement. As such a separator, a microporous resin sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide can be suitably used. Among these, a microporous sheet made of a polyolefin resin such as PE or PP is preferably set with a shutdown temperature in the range of 80 ° C to 140 ° C (typically 110 ° C to 140 ° C, for example, 120 ° C to 135 ° C). It is preferable because it is possible. Such a separator may have a single layer structure composed of a single material, and two or more kinds of microporous resin sheets having different materials and properties (for example, average thickness, porosity, etc.) are laminated. A structure (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer) may be used. The average thickness of the separator 70 is not particularly limited, but is usually 10 μm or more, typically 15 μm or more, for example, 17 μm or more. The upper limit may be 40 μm or less, typically 30 μm or less, for example, 25 μm or less. When the average thickness is within the above range, the charge carrier permeability can be kept good, and a minute short circuit (leakage current) is less likely to occur. For this reason, input / output characteristics and safety can be achieved at a higher level.

[Nonaqueous electrolyte]
As the non-aqueous electrolyte, typically, a non-aqueous solvent in which a supporting salt (for example, a lithium salt, a sodium salt, a magnesium salt, etc., or a lithium salt in a lithium ion secondary battery) is dissolved or dispersed is used. Can be adopted. Alternatively, a so-called solid electrolyte in which a polymer is added to a liquid non-aqueous electrolyte to form a gel may be used.
As the non-aqueous solvent, one of various organic solvents used as an electrolytic solution in a general non-aqueous electrolyte secondary battery can be used alone or in combination of two or more. For example, specifically, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), methyl 2,2,2-trifluoroethyl carbonate (MTFEC), etc. Fluorinated cyclic carbonates such as fluorinated chain carbonates, monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC) and the like can be suitably employed.
As the supporting salt, various kinds of salts used for general nonaqueous electrolyte secondary batteries can be appropriately selected and employed. For example, the use of lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ is exemplified. Such supporting salts may be used singly or in combination of two or more. Such a supporting salt is preferably prepared so that the concentration in the non-aqueous electrolyte is within the range of 0.7 mol / L to 1.3 mol / L.

  In addition, the nonaqueous electrolyte may contain various additives and the like as long as the characteristics of the nonaqueous electrolyte secondary battery of the present invention are not impaired. Examples of such additives include film forming agents such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), and gas generating additives such as biphenyl (BP) and cyclohexylbenzene (CHB).

  Hereinafter, although not intended to be particularly limited, the configuration of the nonaqueous electrolyte secondary battery 10 according to an embodiment of the present invention is appropriately referred to with reference to an example of a typical prismatic battery shown in FIG. This will be described in more detail. A nonaqueous electrolyte secondary battery 10 shown in FIG. 1 has a configuration in which an electrode body 20 including a positive electrode 30 and a negative electrode 50 is housed in a flat box-shaped battery case 80 together with a nonaqueous electrolyte (not shown). Yes. The battery case 80 includes a case body 84 having a shape in which one surface (upper surface in the drawing) of a flat rectangular parallelepiped is opened, and a lid body 82 that closes the opening surface. A positive electrode terminal 40 for external connection and a negative electrode terminal 60 for external connection are disposed on the upper surface (typically, the lid 82) of the battery case 80 in a state of being insulated from the battery case 80. ing. Further, in the same manner as the battery case of the conventional nonaqueous electrolyte secondary battery, the gas generated inside the battery case 80 is discharged to the upper surface (typically, the lid 82) of the battery case 80 to the outside. And a liquid injection port 86 for injecting an electrolytic solution. The non-aqueous electrolyte secondary battery 10 having such a configuration includes, for example, the electrode body 20 attached to the lid 82, and then the electrode body 20 is accommodated therein from the opening surface of the case body 84 while the opening surface of the case body 84 is accommodated. Is sealed with a lid 82 to assemble the battery 10. Next, a nonaqueous electrolyte is injected from a liquid injection port 86 provided in the lid 82, and the liquid injection port 86 can be sealed by welding or the like.

  Specifically, the electrode body 20 is configured by superposing the positive electrode 30 and the negative electrode 50 via, for example, a separator. In the electrode body 20 shown in FIG. 1, a long sheet-like positive electrode (positive electrode sheet) 30 and a long sheet-like negative electrode (negative electrode sheet) 50 are insulated from each other via two separators 70. The wound electrode body 20 is overlapped and wound. The wound electrode body 20 is wound into a flat shape corresponding to the battery case 80, or is shaped into a flat shape after winding. In such a wound electrode body, since a plurality of facings of the positive electrode 30 and the negative electrode 50 are laminated, a laminated electrode body in which a plurality of plate electrodes are further laminated as compared with a non-stacking type battery. Compared with, heat generation due to battery reaction is less likely to be released. Therefore, it may be a preferable aspect to apply the technology disclosed herein to such a battery.

  In such a wound electrode body, the positive electrode 30 is exposed on at least one surface (typically both surfaces) of the elongated positive electrode current collector 32 along the end in the longitudinal direction. Thus, the positive electrode active material layer 34 is formed. In the negative electrode 50, the negative electrode active material layer 54 is exposed on at least one surface (typically, both surfaces) of the long negative electrode current collector 52 along the end in the longitudinal direction. Is formed. By winding the positive electrode 30 and the negative electrode 50 in such a manner so that the exposed portions of the current collectors 32 and 52 protrude from opposite ends, the winding electrode body 20 can also be wound. The exposed portion protrudes at both ends in the direction. The positive electrode current collector 32 and the negative electrode current collector 52 are electrically connected to the positive electrode terminal 40 and the negative electrode terminal 60, respectively. As a result, the charge accumulated in the electrode body 20 is output (discharged) to the outside via these terminals 40 and 60, or the charge is input (charged) to the electrode body 20 from the outside via these terminals 40 and 60. You can do it.

  The non-aqueous electrolyte secondary battery disclosed herein can be used for various applications. For example, the non-aqueous electrolyte secondary battery can have both excellent input / output characteristics and high safety compared to conventional products. In addition, these excellent battery performance and reliability (including safety such as thermal stability during overcharge) can be compatible at a high level. Therefore, taking advantage of such characteristics, it can be preferably used in applications requiring high energy density and high input / output density and applications requiring high reliability. Examples of such applications include drive power supplies mounted on vehicles such as plug-in hybrid vehicles, hybrid vehicles, and electric vehicles. Such secondary batteries can typically be used in the form of an assembled battery in which a plurality are connected in series and / or in parallel.

  Hereinafter, the nonaqueous electrolyte secondary battery disclosed here was produced as a specific example. It should be noted that the present invention is not intended to be limited to those shown in the specific examples.

[Production of negative electrode]
Seven kinds of natural graphite powders having different average particle diameters and pitches as amorphous carbon were prepared, and the pitches were impregnated into the natural graphite powders by mixing so that the mass ratio of these raw materials was 96: 4. . This natural graphite with pitch was fired at 800 ° C. to 1300 ° C. for 10 hours under an inert atmosphere to obtain graphite having amorphous carbon disposed on the surface (amorphous carbon-coated graphite). Five types of negative electrode active materials a to e having different properties were obtained by changing the grinding and sieving conditions for the amorphous carbon-coated graphite. These negative electrode active materials had an average particle diameter (D ₅₀ ) of _{5 to} 20 μm and a BET specific surface area of 1.8 to 5.6 m ² / g.

The negative electrode active materials a to e, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener have a mass ratio of these materials of 98.6: 0.7: 0.7. A negative electrode paste was prepared by adding ion-exchanged water and kneading. Then, this negative electrode paste was applied to a copper foil having a thickness of 10 μm as a negative electrode current collector so that the basis weight on both sides was 7.3 mg / cm ² and dried, whereby the negative electrode active material layer was formed. Formed. Next, the negative electrode active material layer was rolled and pressed so that the density was 0.9 to 1.3 g / cm ³ to obtain a negative electrode sheet. And this sheet | seat was cut out so that the width | variety of a negative electrode active material layer might be 102 mm and length might be 3200 mm, and negative electrode ae was obtained.

[Measurement of capacitance]
The capacitances of the five types of prepared negative electrodes a to e were measured by an AC impedance method. Specifically, first, ^two negative electrodes each having a size of 4.5 cm × 4.7 cm (the area of the negative electrode active material layer: about 21.15 cm ² ) were cut out from the above negative electrode sheet, and each of the negative electrodes was 80 in vacuum. Drying was carried out at 12 ° C. for 12 hours. The two negative electrodes are overlapped with a separator made of microporous polypropylene so that the negative electrode active material layers face each other, and 1 ml of nonaqueous electrolyte is vacuum impregnated and accommodated in a laminate bag. Built. As a non-aqueous electrolyte, 1.1 mol in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of EC: DMC: EMC = 3: 4: 3. / L LiPF ₆ dissolved was used.

  And about the symmetry cell, the alternating current impedance was measured and the capacitance of each negative electrode was computed. AC impedance is measured using Solartron's “1287 type potentio / galvanostat” and “1255B type frequency response analyzer (FRA)”. Sex impedance was measured. In the analysis of the capacitance, using the analysis software “ZPlot / Corware” manufactured by Solartron, the impedance measurement result is converted into the relationship of the electric double layer capacitance component to the frequency, and from the relationship between this frequency and the electric double layer capacitance component, The capacitance (F / g) of the negative electrode was obtained by converting the electric double layer capacity (F) at 0.1 Hz into a value per unit weight (g) of the negative electrode active material. Table 1 below shows the relationship between the negative electrode and the capacitance thus obtained.

[Production of positive electrode]
A positive electrode active material made of a lithium transition metal composite oxide containing tungsten (W) at five ratios was prepared by the following procedure. That is, first, nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), and manganese sulfate (MnSO ₄ ) are dissolved in water, and the molar ratio of Ni: Co: Mn is 1: 1: 1, and An aqueous solution A having a total concentration of Ni, Co and Mn of 1.8 mol / L was prepared.
Further, ammonium paratungstate (5 (NH ₄ ) ₂ O · 12WO ₃ ) was dissolved in water to prepare a W aqueous solution B having a W concentration of 0.05 mol / L.

Next, about half of the capacity of water was placed in a reaction vessel equipped with a stirrer and a nitrogen introduction tube, and heated to 40 ° C. while stirring. After the atmosphere in the reaction vessel was replaced with nitrogen, 25% (mass basis) sodium hydroxide aqueous solution and 25% (mass basis) were maintained in a non-oxidizing atmosphere with an oxygen concentration of 2.0% under a nitrogen stream. Standard) Aqueous aqueous solution C (NH ₃ · NaOH aqueous solution) having a pH of 12.0 based on a liquid temperature of 25 ° C. and a liquid phase ammonia concentration of 20 g / L was added by adding appropriate amounts of ammonia water. Prepared.

  Next, by supplying the aqueous solutions A and B prepared above, 25% aqueous sodium hydroxide, and 25% aqueous ammonia at a constant rate to the alkaline aqueous solution C in the reaction vessel, Hydroxides were crystallized from the reaction solution while maintaining the pH at 12.0 or higher (specifically, pH 12.0 to 14.0) and an ammonia concentration of 20 g / L (nucleation stage). In the alkaline aqueous solution A and the aqueous solution B, the ratio X of W to the total of transition metals (Ni, Co, Mn) is (a) 0.2 mol%, (b) 0.3 mol%, (c) 0. It was made to add in 5 ratios so that it might become 6 mol%, (d) 0.8 mol%, and (e) 1 mol%.

And the supply rate of each liquid to the said reaction tank is adjusted, pH of reaction liquid is less than 12.0 (specifically, it adjusts to pH10.5-11.9, and the ammonia concentration of a liquid phase is 1-10 g / The particle growth reaction of the nuclei generated above was performed while controlling the concentration to a predetermined concentration in the range of L. (Particle growth stage) The product was removed from the reaction vessel, washed with water, and dried (Ni _1/3 Co _1/3 Mn _1/3 ) _1-X W _X (OH) ₂ to obtain a composite hydroxide (precursor hydroxide) having a basic composition of 150% in the atmospheric air, 150 Heat treatment was carried out at 12 ° C. for 12 hours.

Thereafter, the precursor hydroxide and Li ₂ CO ₃ (lithium source) were mixed so that the molar ratio of (Ni + Co + Mn): Li was 1.16: 1 (mixing step). This unfired mixture was subjected to a first firing stage in which the maximum firing temperature was maintained at 900 ° C. for 3 hours in an air atmosphere, and then to a second firing stage in which the maximum firing temperature was maintained at 730 ° C. for 8 hours. Thereafter, the fired product was cooled, crushed and sieved. Accordingly, Li _1.15 (Ni _1/3 Co _1/3 Mn _1/3 ) _1-X W _X O ₂ (where X = (a) 0.2, (b) 0.3, (c ) 0.6, (d) 0.8 or (e) 1) positive electrode active material particles having an average composition were obtained.

The five positive electrode active materials prepared above, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder so that the mass ratio of these materials is 90: 8: 2. A positive electrode paste was prepared by mixing with N-methylpyrrolidone (NMP). This positive electrode paste is applied to a long aluminum foil having a thickness of 15 μm as a positive electrode current collector so that the weight per unit area is 11.2 mg / cm ^2, and is dried. Formed. Next, the positive electrode active material layer was rolled and pressed so that the density of the positive electrode active material layer was 1.8 to 2.4 g / cm ³ to obtain a positive electrode sheet. And this sheet | seat was cut out so that the width | variety of a positive electrode active material layer might be 98 mm and length might be 3000 mm, and it was set as positive electrode ae.

[Preparation of lithium ion secondary battery for evaluation]
In the present embodiment, a total of 25 types of lithium ion secondary batteries were constructed using the negative electrodes a to e and the positive electrodes a to e prepared above. Specifically, any one of the positive electrode and the negative electrode was superposed via a separator. The negative electrode and the positive electrode were laminated so that the exposed portion of the current collector was positioned on the opposite side, and the negative electrode active material layer covered the positive electrode active material layer in the width direction. As the separator, a microporous sheet having a three-layer structure of polyethylene (PE) / polypropylene (PP) / polyethylene (PE) was used. And after winding this laminated body to the elongate direction, by forming in a flat shape, the winding electrode body (Charge capacity ratio of positive / negative electrode: 1.5-2.0, the frequency | count of winding: 29 turns) Produced.
Next, a positive electrode terminal and a negative electrode terminal were attached to the lid of the battery case, and these terminals were welded to the positive electrode current collector and the negative electrode current collector exposed at the ends of the wound electrode body, respectively. The wound electrode body thus connected to the lid body was accommodated in the battery case from the opening of the battery case, and the opening and the lid were welded (sealed).

And the non-aqueous electrolyte was inject | poured from the injection hole provided in the cover body of the said battery case, and the lithium ion secondary batteries 1-25 for evaluation were obtained. As a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 3: 4 is used as a supporting salt. In which LiPF ₆ was dissolved at a concentration of 1.1 mol / L was used.

[Evaluation of input characteristics]
About the prepared lithium ion batteries 6-15 and 21-25 constructed by combining the positive electrodes b, c, e and the negative electrodes a to e, after performing appropriate initial conditioning treatment, the input resistance is measured by measuring the charging resistance. Evaluated. Specifically, first, as an initial conditioning process, under a temperature condition of 25 ° C., an operation of constant current charging at a charging rate of 0.2 C until the voltage between the positive and negative terminals becomes 4.1 V, and positive and negative terminals The operation of constant current discharge at a discharge rate of 0.2 C until the voltage between them was 3.0 V was set as one cycle, and this was repeated three cycles. Next, each battery was adjusted to a SOC (State of Charge) 60% (60% of the rated capacity) state of charge, and the charging resistance (reaction resistance) was measured by an AC impedance method in a temperature environment of −30 ° C. AC impedance was measured under the conditions of amplitude: 5 mV and measurement frequency range: 10000 Hz to 0.1 Hz, and the reaction resistance (mΩ) was calculated by fitting the obtained Cole-Cole plot to an equivalent circuit.

The following equipment was used for the measurement and analysis of AC impedance.
Measuring devices: “1287 type potentio / galvanostat” and “1255B type frequency response analyzer (FRA)” manufactured by Solartron
Analysis software: ZPlot / Corware
The charging resistance thus obtained is expressed as “charging resistance ratio” which is a relative value with the charging resistance value of the lithium ion secondary battery 22 being 100 (reference), and is shown in Table 1. FIG. 3 shows the relationship between the charging resistance ratio and the negative electrode capacitance.

  As can be seen from FIG. 3, when the negative electrode capacitance increases, the charge resistance ratio of the battery tends to decrease. This is considered due to the fact that the capacitance increases as the reaction area of the negative electrode increases. And about this tendency, the significant difference by the kind of positive electrode, ie, the ratio of W of a positive electrode active material, was not seen. This charge resistance ratio was found to increase sharply when the negative electrode capacitance was less than about 0.12 F / g. Therefore, it was found that in order to keep the input characteristics of the battery in a good state, it is preferable to use a negative electrode having a capacitance of about 0.12 F / g or more (for example, negative electrodes b to e).

[Evaluation of output characteristics]
About the lithium ion battery constructed | assembled combining the negative electrode a, b, d and the positive electrodes ad, output characteristics were evaluated by measuring discharge resistance. Specifically, first, as an initial conditioning process, under a temperature condition of 25 ° C., an operation of constant current charging at a charging rate of 0.2 C until the voltage between the positive and negative terminals becomes 4.1 V, and positive and negative terminals The operation of constant current discharge at a discharge rate of 0.2 C until the voltage between them was 3.0 V was set as one cycle, and this was repeated three cycles. Next, under a temperature condition of 25 ° C., CC charging was performed at a constant current of 1 C until the battery voltage reached 3.7 V, and then CV charging was performed at the voltage until the charging current reached 1/10 C. Thereafter, high-rate discharge was performed at a constant current of 10 C for 10 seconds, and the discharge resistance (IV resistance) was calculated from the voltage drop at this time using the following equation.
Discharge resistance = (voltage immediately before discharge−voltage after 10 seconds of discharge) / (discharge current)
The discharge resistance thus obtained is expressed as “discharge resistance ratio” which is a relative value with the charge resistance value of the lithium ion secondary battery 22 as 100 (reference), and is shown in Table 1. FIG. 4 shows the relationship between the discharge resistance ratio and the W ratio of the positive electrode.

  As apparent from FIG. 4, when the proportion of W contained in the positive electrode active material is a certain amount or more, a tendency that the discharge resistance ratio of the battery can be kept low was recognized. And regarding this tendency, there was no significant difference due to the type of negative electrode, that is, the difference in capacitance of the negative electrode. This discharge resistance ratio was found to be kept low when the ratio of W to the transition metal element contained in the positive electrode active material was greater than 0.2 mol%. Therefore, in order to keep the output characteristics of the battery in a good state, a battery is constructed using a positive electrode active material (for example, positive electrodes b to e) having a W ratio of less than 0.2 mol%, for example, 0.3 mol% or more. It turned out to be preferable.

[Safety evaluation]
The lithium ion batteries 6 to 25 constructed by combining the positive electrodes b to e determined to have excellent output characteristics and the negative electrodes a to e were evaluated for safety after shutdown due to overcharge. Specifically, first, for each battery, at 25 ° C., the operation of constant current charging at a charging rate of 0.2 C until the voltage between the positive and negative terminals becomes 4.1 V, and the voltage between the positive and negative terminals is The operation of constant current discharge at a discharge rate of 0.2 C until 3.0 V was taken as one cycle, and a conditioning treatment was repeated for 3 cycles. Next, each battery was adjusted to SOC 30%, and then charged with a constant current of 40 A until the maximum voltage reached by the battery reached 40V. The battery was forcibly shut down by such overcharge. Then, the current value for 10 minutes after the shutdown was measured, and the maximum current value measured during the 10 minutes was defined as “leakage current”. The measurement results of the leakage current are shown in Table 1, and the relationship between the leakage current and the capacitance is shown in FIG.

  As apparent from FIG. 5, the leakage current tends to increase as the negative electrode capacitance increases. This is thought to be due to an increase in capacitance due to an increase in the reaction area of the negative electrode and an increase in heat generation due to an increase in contact between the negative electrode active material and the electrolyte due to an increase in the reaction area of the negative electrode. It is done. However, it has been found that this tendency varies greatly depending on the type of positive electrode, that is, the proportion of W in the positive electrode active material.

  That is, when the positive electrodes d and e are used, it can be said that the leakage current is small in combination with the negative electrode a, and the safety at the time of shutdown due to overcharge is high. However, the leakage current significantly increased in combination with the negative electrodes b to e. That is, it has been found that even after a shutdown due to overcharge, current continues to flow in the battery, which may cause a further overcharge state, resulting in poor safety. Here, the battery using the negative electrode a has extremely poor input characteristics regardless of the type of the positive electrode. Therefore, it can be said that it is difficult for a battery including positive electrodes d and e using a positive electrode active material having a high W ratio to satisfy all of input / output characteristics and safety.

  On the other hand, when the positive electrodes b and c are used, it can be said that the leakage current is small in the combination with the negative electrodes a to d, and the safety at the time of shutdown due to overcharge is high. However, in combination with the negative electrode e, it has been found that the leakage current increases remarkably, the current flows even after shutdown due to overcharge, and a further overcharge state can be caused. Therefore, as the negative electrode combined with the positive electrodes b and c, one having a capacitance smaller than about 0.264 F / g (for example, 0.25 F / g or less, more preferably 0.2 F / g or less) may be used. I understand that. In order to construct a battery with excellent safety, it is preferable to use a positive electrode using a positive electrode active material in which the W ratio is suppressed to about 0.7 mol% or less (for example, 0.6 mol% or less). I understand.

  From the above, in order to obtain a battery having both input / output characteristics and safety, the capacitance is about 0.12 F / g or more and 0.25 F / g or less (for example, 0.12 F / g or more and 0.2 F / g or less). ) And a positive electrode containing a positive electrode active material in which the ratio of W to the transition metal element is approximately 0.2 mol% and 0.7 mol% or less (eg, 0.3 mol% or more and 0.6 mol% or less). It was confirmed that it was good.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

10 battery 20 electrode body 30 positive electrode (positive electrode sheet)
32 Positive electrode current collector 34 Positive electrode active material layer 40 Positive electrode terminal 50 Negative electrode (negative electrode sheet)
52 Negative electrode current collector 54 Negative electrode active material layer 60 Negative electrode terminal 70 Separator 80 Battery case 82 Lid 84 Case body 86 Injection port 88 Safety valve 100 Symmetry cell

Claims (5)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode has a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material,
The positive electrode active material includes a lithium transition metal composite oxide containing at least one transition metal element selected from nickel, cobalt and manganese and tungsten,
The ratio of the tungsten to the transition metal element is 0.3 mol% or more and 0.7 mol% or less,
The negative electrode has a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material,
The negative electrode active material includes natural graphite having amorphous carbon disposed on the surface,
The negative electrode has a capacitance of 0.12 F / g or more and 0.2 F / g or less.
Non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the tungsten to the transition metal element is 0.3 mol% or more and 0.6 mol% or less.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode and the negative electrode constitute a wound electrode body that is laminated and wound via a separator.   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material layer includes a binder made of a rubber-based resin at a ratio of 0.4% by mass to 1% by mass.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a lithium transition metal composite oxide containing nickel, cobalt, and manganese together with tungsten.

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