JP6098885B2 - Nonaqueous electrolyte secondary battery - Google Patents

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 having an anode with amorphous carbon-coated graphite.

  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.

  As one of negative electrode active materials used for this non-aqueous electrolyte secondary battery, a carbonaceous material made of graphite or the like having an amorphous structure introduced on the surface is known. For example, Patent Document 1 discloses a negative electrode active material including an amorphous structure obtained from natural graphite and a carbonized precursor. And it is described that the lithium ion secondary battery constructed | assembled using this negative electrode active material is excellent in a quick charge / discharge characteristic. By adopting such a negative electrode active material, for example, a further improvement in input / output characteristics is expected for non-aqueous electrolyte secondary batteries (for example, batteries for in-vehicle use) that are used for repeated high-rate charge / discharge (rapid charge / discharge). it can.

JP 2012-033376 A JP 2011-018588 A

However, since amorphous carbon has a high reactivity due to exposure of many edge surfaces on the particle surface, a side reaction (reductive decomposition reaction) with the electrolytic solution is likely to occur, and the leakage current at the negative electrode is increased. The leakage current at the edge surface is locally generated and the amount of leakage current increases as the temperature is higher. There is concern that it may cause fever. Furthermore, the occurrence of such a leakage current is not preferable from the viewpoint that the safety of the battery at the time of overcharging, particularly after the shutdown by the separator can be lowered. Such a non-aqueous electrolyte secondary battery in consideration of safety during overcharge is disclosed in, for example, Patent Document 2.
The present invention has been made in view of such circumstances, and a purpose thereof is a non-aqueous electrolyte secondary battery that exhibits sufficient rapid charge / discharge characteristics due to amorphous carbon-coated graphite and is also excellent in safety. Is to provide.

  In order to solve the above problems, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. In such a non-aqueous electrolyte secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes natural graphite (hereinafter referred to as amorphous carbon) having amorphous carbon disposed on the surface. , Which is also simply referred to as “amorphous carbon-coated graphite”). Between the positive electrode and the negative electrode, a porous insulating layer having heat resistance (hereinafter sometimes simply referred to as “HRL” (Heat Resistance Layer)) is provided. The HRL is characterized in that the average thickness is 2 μm or more and 10 μm or less. The negative electrode has a capacitance of 0.12 F / g or more and 0.192 F / g or less.

The capacitance of the negative electrode is an index that can suitably reflect various characteristics typified by the resistance characteristics and capacity retention rate of the nonaqueous electrolyte secondary battery including the negative electrode based on the essential characteristics of the negative electrode. possible. For example, the form of the negative electrode active material layer formed on the negative electrode and the amount of leakage current generated in the negative electrode can be indirectly evaluated by the capacitance of the negative electrode. From this, when the negative electrode was 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, a negative electrode active material layer having a small number of defects was provided. In addition, it can be evaluated that a non-aqueous electrolyte secondary battery in which generation of leakage current at the negative electrode is suppressed is realized.
In the present specification, the capacitance (F / g) of the negative electrode is described in detail below, but a symmetry cell composed of the same two negative electrodes of interest is measured by a general AC impedance method. This is a value obtained by converting the real component of the electric double layer capacity at a frequency of 0.1 Hz per unit mass of the negative electrode active material.
In addition, amorphous carbon-coated graphite has high reactivity, and can increase the leakage current of the negative electrode, for example. Even in such a case, when the thickness of the HRL arranged between the positive electrode and the negative electrode is in the above range, an increase in leakage current or the like can be preferentially suppressed without excessively increasing the charging resistance. Thus, it is possible to realize a high-quality nonaqueous electrolyte secondary battery that also has safety while maintaining the above.

In the suitable one aspect | mode of the nonaqueous electrolyte secondary battery disclosed here, the porous separator which has insulation is further provided between the positive electrode and the negative electrode. The HRL is arranged between the separator and the negative electrode.
In the nonaqueous electrolyte secondary battery, a configuration in which a separator is provided between a positive electrode and a negative electrode is widely adopted. In the nonaqueous electrolyte secondary battery having such a configuration, by providing HRL between the separator and the negative electrode, for example, a metal (locally) is formed on the negative electrode surface due to the high reactivity of amorphous carbon-coated graphite. For example, even when lithium dendrite is deposited in the case of a lithium secondary battery, it is possible to suitably suppress the occurrence of a micro short circuit due to the deposited metal. As a result, for example, even when the separator is shut down due to heat generated when the battery is overcharged (the fine holes are blocked by melting and the permeability of the charge carrier is lost), the leakage current is suppressed, The electrochemical reaction at can be stopped more quickly. That is, a non-aqueous electrolyte secondary battery with high safety against abnormal battery operation is realized.

In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the HRL is disposed on the surface of the separator. Moreover, it is more preferable that this HRL contains an inorganic filler.
By adopting such a configuration, it is possible to achieve excellent productivity and to more effectively suppress leakage current in a limited space in the battery case. Further, it becomes possible to more suitably manufacture an HRL that is excellent in heat resistance in addition to insulation and ion permeability.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the negative electrode active material layer includes a binder made of a rubber-based resin at a ratio of 0.5% by mass or more and 0.9% by mass or less. It is a feature. 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. Moreover, the resistance of the negative electrode can be further reduced by setting the addition amount of the binder to 0.9 mass% or less. Thereby, a higher quality nonaqueous electrolyte secondary battery can be provided.

  The nonaqueous electrolyte secondary battery described above can be provided as a battery that is particularly excellent in battery characteristics such as high-rate charge / discharge (rapid charge / discharge) characteristics and that has high safety. Therefore, taking advantage of such characteristics, it can be suitably used as a power source (driving power source) for a hybrid vehicle or a plug-in hybrid vehicle.

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 at the time of measuring the capacitance of a negative electrode. It is a figure which shows the relationship between the capacitance which concerns on one Embodiment, and the number of faults. It is a figure which shows the relationship between the capacitance which concerns on one Embodiment, and a kneading NV value. It is a figure which shows the relationship between the capacitance which concerns on one Embodiment, and a leakage current. It is a figure which shows the relationship between the capacitance which concerns on one Embodiment, and charging resistance ratio. It is a figure which shows the relationship between the kind of negative electrode active material which concerns on one Embodiment, and leakage current.

Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification (for example, characteristics of the negative electrode active material, HRL configuration, etc.) and matters necessary for carrying out the present invention (for example, a battery that does not characterize the present invention) The structure, the general manufacturing process of the battery, etc.) can be grasped as the 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 “nonaqueous electrolyte secondary battery” refers to a general battery that can be repeatedly charged and discharged using a nonaqueous electrolyte as an electrolyte. For example, a secondary battery that uses lithium ions (Li ions) or sodium ions (Na ions) as electrolyte ions and can be charged and discharged by movement of charges accompanying Li ions and Na ions between positive and negative electrodes is included. . A battery generally called a lithium ion battery or a lithium secondary battery is a typical example included in the nonaqueous electrolyte secondary battery in this specification.

[Nonaqueous electrolyte secondary battery]
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.

<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. The negative electrode active material does not prevent this type of negative electrode active material other than amorphous carbon-coated graphite from being contained (for example, at a ratio of less than 50% by mass of the negative electrode active material).

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. When a binder is used, the proportion of the binder in the negative electrode active material layer 54 can be set to, for example, 1 part by mass to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material, and usually about 1 part by mass to 5 parts by mass is appropriate.
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 0.192 F / g or less. When a negative electrode is produced using amorphous carbon-coated graphite as the negative electrode active material, by setting the negative electrode capacitance within the above range, for example, a negative electrode active material layer having a good shape with few defects is provided. Thus, it is possible to realize a nonaqueous electrolyte secondary battery in which generation of leakage current at the negative electrode is suppressed. In addition, a defect means morphological defects, such as coating nonuniformity of a negative electrode active material layer, coating skein, and a coating stripe, and can cause a fall of an electrode characteristic. Such defects tend to occur more often when the conditions for forming the negative electrode active material layer are not appropriate. Examples of the formation conditions include, for example, the solid content concentration (NV value) in the negative electrode paste used for forming the negative electrode active material layer, the negative electrode active material and the binder in the negative electrode active material layer (or the negative electrode paste). The dispersion state and the bonding state, the form of the negative electrode active material, and the like. The criteria for determining the quality of the form of the negative electrode active material layer can be set according to, for example, the use of the battery. Here, when the capacitance of the negative electrode is 0.12 F / g or more, it can be determined that there are few defects (that is, non-defective products) for batteries for all applications. The capacitance of the negative electrode is preferably 0.13 F / g or more, more preferably 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 0.192 F / g or less. The capacitance of the negative electrode is preferably 0.19 F / g or less, more preferably 0.18 F / g or less.

The capacitance of the negative electrode is the impedance Z (f) of a specific frequency region measured by a general AC impedance method for the symmetry cell 100 configured by preparing two target negative electrodes 50 in an uncharged state. The quantitative value is converted into the electric double layer capacity C (f) for the frequency, and the value obtained as the real part component C ′ (f) of the electric double layer capacity at the frequency of 0.1 Hz is obtained as the unit mass of the negative electrode active material. It can be calculated by converting to per. More specifically, the capacitance of the negative electrode can be determined by the following procedure, for example. 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 target negative electrodes 50 of 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: [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: 0.95 g / cm ^{3 to} 1.02 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 electric double layer capacitance at a sufficiently low frequency of 0.1 Hz is defined as “capacitance of the negative electrode active material”. Specifically, the capacitance of the negative electrode active material can be obtained, for example, as follows. 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 amount of charge generated in the entire symmetry cell 100, this is converted to the amount of charge per unit mass 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.

<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 is not particularly limited, and various types of materials that can be used as the positive electrode active material of the nonaqueous electrolyte secondary battery can be used singly or in combination of two or more. Can be used. Preferable examples include layered and spinel-based lithium composite metal oxides (for example, LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO _4, etc. ). Among these, lithium nickel cobalt manganese composite oxide having a layered structure (typically a layered rock salt structure belonging to a hexagonal system) containing Li, Ni, Co, and Mn as constituent elements can be preferably used. For example, specifically, so-called ternary lithium transition metal composite oxides such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are excellent in thermal stability and can realize a high energy density. Preferred as a positive electrode active material.

  Here, the lithium nickel cobalt manganese composite oxide is an oxide containing only Li, Ni, Co and Mn as constituent metal elements, and at least one other metal element in addition to Li, Ni, Co and Mn ( That is, it is meant to include oxides containing transition metal elements and / or typical metal elements other than Li, Ni, Co and Mn. Such metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), Tungsten (W), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga), It may be one or more elements of indium (In), tin (Sn), lanthanum (La), and cerium (Ce). The amount (mixing amount) of these metal elements is not particularly limited, but is usually 0.01% by mass to 5% by mass (typically 0.05% by mass to 2% by mass, for example, 0.1% by mass to 0.00%). 8% by weight).

  As the conductive material, for example, carbon materials such as carbon black (typically acetylene black and ketjen black), activated carbon, graphite, and carbon fiber can be suitably used. As the binder, for example, a vinyl halide resin such as polyvinylidene fluoride (PVdF) or a polymer material typified by polyalkylene oxide such as polyethylene oxide (PEO) can be preferably used.

The proportion of the positive electrode active material in the entire positive electrode active material layer 34 is suitably about 50% by mass or more, typically 50% by mass to 95% by mass, and usually about 70% by mass to 95% by mass. % Or less is preferable. The proportion of the conductive material in the positive electrode active material layer 34 can be, for example, approximately 0.1 parts by mass to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material, and is usually approximately 1 part by mass to 15 parts by mass. For example, it is preferable to set it as 2 mass parts-10 mass parts, typically 3 mass parts-7 mass parts. The proportion of the binder in the positive electrode active material layer can be, for example, about 0.5 parts by mass to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material, and usually about 1 part by mass to 8 parts by mass, for example, It is preferable to be 2 to 7 parts by mass, typically 2 to 5 parts by mass.
The thickness of the positive electrode active material layer 34 is, for example, 20 μm or more, typically 50 μm or more, and can be 200 μm or less, typically 100 μm or less. The density of the positive electrode active material layer 34 is not particularly limited, but 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. The positive electrode active material layer satisfying the above range can achieve high battery performance (for example, high energy density and output density).

<Capacitance ratio between positive electrode and negative electrode>
It is preferable that the capacity ratio of the positive electrode 30 and the negative electrode 50 is adjusted due to a difference in charge carrier receiving characteristics. Specifically, the ratio (C _a / C _c ) between the positive electrode capacity C _c (mAh) and the negative electrode capacity C _a (mAh) is suitably 1.0 to 2.0, and 1.5 It is preferable to set it to -1.9 (for example, 1.7-1.9). Here, the positive electrode capacity C _c (mAh) is defined as the product of the theoretical capacity (mAh / g) per unit mass of the positive electrode active material and the mass (g) of the positive electrode active material. The negative electrode capacity C _a (mAh) is defined as the product of the theoretical capacity (mAh / g) per unit mass of the negative electrode active material and the mass (g) of the negative electrode active material. As described above, by adjusting the capacity ratio between the positive and negative electrodes facing each other, it is possible to adjust the charge balance between the positive and negative electrodes while maintaining good battery characteristics such as battery capacity and energy density. As a result, it is possible to suitably suppress the deposition of charge carriers on the negative electrode surface.

<HRL>
In the present invention, HRL (not shown) is essentially included between the positive electrode 30 and the negative electrode 50 described above. Such HRL is a porous insulating layer having heat resistance. HRL has a heat resistance against a shutdown temperature (typically 80 ° C. to 140 ° C.) that stops the electrochemical reaction of the battery when the battery generates heat, and is a porous material that can ensure the permeability of the charge carrier. If it has a quality structure, there is no restriction | limiting in particular in the structure, material, etc. For example, it can be made of a material having heat resistance sufficient to maintain a porous structure without being softened or melted at a temperature of 150 ° C. or higher, typically 200 ° C. or higher. Specifically, it can be composed of a resin material, an inorganic material, a glass material, a composite material thereof, and the like having the above heat resistance and insulation. A suitable example of such an HRL is typically a layer composed of an inorganic filler and a binder. As the inorganic filler, typically, granular or fibrous inorganic oxides such as alumina (Al ₂ O ₃ ), magnesia (MgO), silica (SiO ₂ ), titania (TiO ₂ ), aluminum nitride, nitriding Examples thereof include nitrides such as silicon, metal hydroxides such as calcium hydroxide, magnesium hydroxide and aluminum hydroxide, clay minerals such as mica, talc, boehmite, zeolite, apatite and kaolin, and glass fibers. As such an inorganic filler, it is more preferable to use alumina (Al ₂ O ₃ ), boehmite (Al ₂ O ₃ .H ₂ O), etc. which are stable in quality and inexpensive and easily available. The average particle diameter (D50) of the inorganic filler can be, for example, about 0.1 μm to 5.0 μm, and more preferably about 0.2 μm to 2.0 μm. The specific surface area of such inorganic filler, the specific surface area based on BET ^method, can be used about 2.8m ² / g~100m 2 / g as a rough guide.
Moreover, as a binder, it can be set as the various polymer materials used, for example to comprise the said positive electrode and negative electrode.
When the HRL contains an inorganic filler, the proportion of the inorganic filler in the entire HRL is suitably about 50% by mass or more, and usually 85% by mass to 99.8% by mass (for example, 90% by mass to 99%). Mass%) is preferred. When using a binder, the ratio of the binder to the whole HRL can be, for example, approximately 1% by mass to 10% by mass, and is preferably approximately 1% by mass to 5% by mass.

  In the invention disclosed herein, it is important that the average thickness of the HRL is 2 μm or more and 10 μm or less. The average thickness of HRL is more preferably 3 μm or more, and further preferably 4 μm or more. The amorphous carbon-coated graphite used as the negative electrode active material for the nonaqueous electrolyte secondary battery disclosed herein has high reactivity, and can cause, for example, an increase in the leakage current of the negative electrode. When the average thickness of the HRL is 2 μm or more, it is difficult for a fine short circuit to occur even when charging and discharging are repeated, and the amount of leakage current generated can be kept low. Thereby, for example, after the battery generates heat and shuts down, the electrochemical reaction of the battery can be quickly stopped to suppress further heat generation. The average thickness of the HRL is preferably 9 μm or less, more preferably 8 μm or less. With this configuration, the internal resistance can be kept low, and high input / output characteristics can be realized over a long period of time.

<Separator>
The separator 70 is a constituent material that insulates the positive electrode active material layer 34 and the negative electrode active material layer 54 and has charge carrier permeability, and is typically disposed between the positive electrode 30 and the negative electrode 50. . The separator 70 may have a nonaqueous electrolyte holding function and a shutdown function. 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.
In a preferred embodiment of the present invention, the HRL may be disposed on at least one surface (for example, one side or both sides) of the separator 70. Such a separator 70 is, for example, a paste formed by dispersing the material constituting the above-mentioned HRL layer (typically, an inorganic filler and a binder used as necessary) in an appropriate solvent (for example, water). Alternatively, it can be produced by supplying a slurry-like composition to the surface of the separator 70 and then drying to remove the solvent.

  The average thickness of the separator 70 (thickness excluding HRL for the separator with HRL) 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 of the substrate 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 density and safety can be achieved at a high level.

  In the invention disclosed herein, the HRL is preferably arranged so as to be in contact with the negative electrode 50. For example, HRL may be formed on the surface of the negative electrode 50. For example, when the HRL is disposed on one side or both sides of the separator 70, it is preferable that the HRL separator 70 is disposed so that the HRL is in contact with the negative electrode 50. Since the nonaqueous electrolyte secondary battery 10 disclosed here uses amorphous carbon-coated graphite as the negative electrode active material, due to its high local reactivity, it can be repeatedly charged and discharged, overcharged, and the like. There is a tendency for charge carriers to be easily deposited on the surface of the negative electrode. According to such a configuration, for example, even when lithium dendrite or the like can be deposited on the surface of the negative electrode, an internal short circuit can be effectively suppressed. Therefore, the leakage current can be reduced, and the battery 10 excellent in safety and reliability can be realized.

<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, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones that are used as electrolytes in general non-aqueous electrolyte secondary batteries should be used without particular limitation. Can do. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Such a non-aqueous solvent can be used alone or in combination of two or more.
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. As such an additive, a gas generating agent, a film forming agent, etc. can be used for one or more purposes among improvement of input / output characteristics of a battery, improvement of cycle characteristics, improvement of initial charge / discharge efficiency and the like. Specific examples of such additives include fluorophosphate (preferably difluorophosphate. For example, lithium difluorophosphate represented by LiPO ₂ F ₂ ), lithium bis (oxalato) borate (LiBOB), and the like. An oxalato complex compound is mentioned. The concentration of these additives relative to the entire nonaqueous electrolyte is usually 0.1 mol / L or less (typically 0.005 mol / L to 0.1 mol / L).

  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 with HRL. 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 in a flat shape corresponding to the battery case 80 or is molded. In the positive electrode 30, the positive electrode active material layer 34 is exposed on at least one surface (typically both surfaces) of the long positive electrode current collector 32 so that the positive electrode current collector 32 is exposed along the end in the longitudinal direction. 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.

[Preparation of negative electrode]
The pitch as an amorphous carbon source was blended at a ratio of 4% by mass with respect to 96% by mass of natural graphite, and the pitch was impregnated into natural graphite by mixing. This natural graphite with pitch was fired at 800 ° C. to 1300 ° C. for 10 hours in an inert atmosphere to obtain a negative electrode active material made of graphite (amorphous carbon-coated graphite) having amorphous carbon disposed on the surface. . The obtained negative electrode active material was sieved and adjusted so that the average particle size (D50) was 5 μm to 20 μm and the BET specific surface area was in the range of 1.8 to 5.6 m ² / g.
Mass ratio of these natural graphite (C), styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a dispersant is C: SBR: CMC = 98.6: 0. 7: A negative electrode paste was prepared by adding ion-exchanged water so as to be 0.7 and kneading. Here, by adjusting the amount of water when kneading the paste, the solid content concentration during the seven kneading (hereinafter referred to as “paste viscosity” in the range of 1000 mPa · s to 2000 mPa · s (25 ° C., 1 rpm)) Negative pastes (a) to (g) having a kneaded NV value) were prepared.

[Evaluation of coating stability]
Here, stripe coating was carried out to the negative electrode collector using said negative electrode paste (a)-(g), and the negative electrode sheets (a)-(g) were prepared by carrying out rolling press. Specifically, each negative electrode paste, a copper foil having a thickness of 10μm as a negative electrode collector, subjected coated as single side coating amount is ^{3.5mg / cm 2 ~3.8mg / cm 2} , the resulting dried, by negative electrode active material layer density is rolled pressed to the ^{0.95g / cm 3 ~1.02g / cm 3} , a negative electrode sheet having a negative electrode active material layer on an anode current collector It was.
Then, the relationship between the capacitance of the negative electrode thus prepared, the NV value of the negative electrode paste, and the coating stability was examined.
<Measurement of number of defects>
With respect to each of the negative electrodes (a) to (g) thus prepared, the coating stability of each electrode was examined by examining the number of defects of the coating scale. An image inspection apparatus was used to measure the number of defects (coating scale). After the negative electrode paste was applied to the current collector, the state in which coating unevenness occurred and the current collector was transparent in the region of φ1 mm was defined as “coating scale”, and the number of occurrences of the coating scale was measured. The results are shown in Table 1 below.

<Measurement of capacitance>
Moreover, the capacitance of the prepared negative electrodes (a) to (g) was measured using an AC impedance method. Specifically, first, two negative electrodes were cut out from the negative electrode sheets (a) to (g) to a size of 4.5 cm × 4.7 cm (negative electrode active material layer area: about 21.15 cm ² ), The film was dried in vacuum at 80 ° C. for 12 hours. The two negative electrodes are overlapped with a separator made of a microporous membrane (without HRL) made of polypropylene so that the negative electrode active material layers face each other, and 1 ml of nonaqueous electrolyte is vacuum impregnated and laminated bag Housed and constructed symmetry cells (a)-(g). 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.

About said symmetry cell (a)-(g), 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)”. The input voltage is 5 mV at 25 ° C. and the frequency depends on the frequency range from 10,000 Hz to 0.1 Hz. 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 of the negative electrode was obtained by converting the electric double layer capacity at 0.1 Hz to a value per unit mass (g) of the negative electrode active material. The capacitances of the negative electrodes (a) to (g) thus obtained are shown in Table 1 below. The relationship between the capacitance, the NV value, and the number of defects is shown in FIGS. 3 and 4, respectively.

  As is clear from Table 1 and FIGS. 3 to 4, the preparation of the negative electrode paste was performed despite using the same material and forming the negative electrode in the same form (formulation of negative electrode active material layer, coating amount, density, etc.). It can be seen that the capacitance of the negative electrode reflects the change in the kneading NV value over time. And when capacitance falls below 0.12 F / g, it turns out that the number of faults of a negative electrode active material layer increases rapidly. This is because as the NV value of the negative electrode paste increases, the amount of water in the negative electrode paste is insufficient, and CMC is not sufficiently dissolved and dispersed. As a result, the coatability of the negative electrode paste is not stable. It is considered that a defect occurred in the negative electrode active material layer. From this, the state at the time of negative electrode formation (coating stability) can also be evaluated by the capacitance of the negative electrode, and it has been confirmed that the capacitance of the negative electrode is suitably 0.12 F / g or more.

(Sample Nos. 1-28)
[Construction of evaluation lithium-ion battery]
<Negative electrode>
Using the negative electrode pastes (a) to (g) prepared above, apply the negative electrode paste to a copper foil having a thickness of 10 μm similar to the above so that the weight per unit area is 7.3 mg / cm ^2. after drying, by negative electrode active material layer density is rolled pressed so as to ^{0.9g / cm 3 ~1.3g / cm 3} , a negative electrode sheet having a negative electrode active material layer on an anode current collector Prepared. This negative electrode sheet was slit to a predetermined size, and a negative electrode having a negative electrode active material layer width of 102 mm and a length of 3200 mm was cut out to form negative electrodes 1 to 7.

<Positive electrode>
Li _1.14 Ni _0.34 Co _0.33 Mn _0.33 O ₂ was prepared as a positive electrode active material. Specifically, nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), and manganese sulfate (MnSO ₄ ) as raw material compounds have a molar ratio of Ni: Co: Mn of approximately 1: 1: 1. A mixed solution containing Ni ions, Co ions, and Mn ions was prepared by weighing and dissolving in water. This mixed solution is neutralized with a 25% by mass aqueous sodium hydroxide solution to form a composite hydroxide (precursor hydroxide) having Ni _0.34 Co _0.33 Mn _0.33 (OH) ₂ as a basic component. Got. Then, this precursor hydroxide and lithium carbonate (Li ₂ CO ₃ ) as a lithium source are mixed so that the molar ratio of (Ni + Co + Mn): Li is 1.14: 1. Calcination was performed at 950 to 950 ° C. for 5 to 15 hours. Thereafter, the fired product was cooled, crushed and sieved. This _gave a positive electrode active material having an average composition represented by _{Li 1.14 Ni 0.34 Co 0.33 Mn 0.33} O 2 (LNCM). Examination of the properties of the obtained positive electrode active material, the average particle diameter D50 is 3 to 8 [mu] m, BET specific surface area of 0.5m ² /g~1.9m ² / g. The constituent elements of the positive electrode active material were analyzed using a general inductively coupled plasma mass spectrometer. In addition to Li, Ni, Co, and Mn, trace amounts of transition metal elements, alkali metal elements, and alkalis were analyzed. An earth metal element was detected.

The positive electrode active material (LNCM) 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 was applied to a long aluminum foil having a thickness of 15 μm as a positive electrode current collector so that the total weight of both surfaces was 11.2 mg / cm ² and dried, and then a positive electrode active material layer density of by rolling press so that the ^{1.8g / cm 3 ~2.4g / cm 3} , was prepared positive electrode sheet having a positive electrode active material layer on the positive electrode current collector. 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 the positive electrode.

<Construction of lithium ion battery>
The negative electrodes 1 to 7 prepared above and the positive electrode were overlapped with a separator interposed therebetween. As the separator, a microporous film made of polyethylene having an average thickness of 20 μm is used as a base material, and one having a HRL containing alumina fine particles on one side of the base material is used so that the HRL faces the negative electrode active material. Arranged in layers. In addition, as shown in the following Table 2, the thickness of HRL prepared the thickness of 4 types of 1.2 micrometers-15 micrometers. In addition, the negative electrode and the positive electrode were laminated so that the exposed portions of the current collectors were located on the opposite side, and the negative electrode active material layer covered the positive electrode active material layer in the width direction. 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 through the opening thereof, and the opening and the lid body were welded.

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 was used as a supporting salt. LiPF ₆ dissolved at a concentration of 1.1 mol / L was used. 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 battery (theoretical capacity | capacitance 3.8Ah) was constructed | assembled. In this embodiment, by combining four types of separators for each of the negative electrodes 1 to 7, lithium ion batteries (lithium ion batteries 1 to 28) having a total of 28 configurations having the configurations shown in Table 2 are provided. Prepared.

[Evaluation of safety (leakage current) 1]
With respect to the lithium ion batteries for evaluation 1 to 14 constructed as described above, the thermal stability was examined under the following conditions, and the safety was evaluated. That is, the batteries 1 to 14 that have been subjected to appropriate initial conditioning were forcibly shut down by continuously charging, and the magnitude of the subsequent leakage current was evaluated. Specifically, first, as a conditioning process, under a temperature condition of 25 ° C., an operation of charging at a constant current at a charge rate of 0.2 C until the voltage between the positive and negative terminals becomes 4.1 V, and between the positive and negative terminals The operation of discharging at a constant current at a discharge rate of 0.2 C until the voltage becomes 3.0 V was taken as one cycle, and this was repeated three cycles. Subsequently, each battery was adjusted to a state of 30% SOC (State of Charge), and charged with a constant current of 40 A until the maximum voltage reached 40 V. In such an overcharged state, the current value (leakage current value) for 10 minutes after the battery was shut down was measured, and the maximum current value in the 10 minutes was defined as “leakage current”. The measurement results of the leakage current are shown in Table 2, and the relationship (part) between the leakage current and the capacitance is shown in FIG.

  As is clear from FIG. 5, when the separator has the same HRL thickness, the leakage current tends to increase as the negative electrode capacitance increases, and the negative electrode capacitance and the battery leakage current have a certain correlation. I understand. And it is confirmed that the leakage current value can be sufficiently suppressed by increasing the thickness of the HRL to 2.0 μm, whereas the leakage current value is extremely high when using a thin separator with a thickness of 1.2 μm. did it. However, even when the thickness of the HRL is 2.0 μm, if the capacitance of the negative electrode exceeds 0.192 F / g, the leakage current increases remarkably, and the effect of increasing the thickness of the HRL can be obtained. I understand that there is not. From this, it can be seen that it is effective to set the HRL thickness of the separator to 2 μm or more in order to keep the leakage current of the battery low when the capacitance is in the range of about 0.12 F / g to 0.25 F / g. It was.

[Evaluation of charging resistance 1]
The lithium ion batteries for evaluation 8 to 28 produced as described above were subjected to appropriate initial conditioning treatment, and then the charging resistance was measured. 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 60% charge state, and under 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. The reaction resistance (mΩ) was calculated by fitting the 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 reaction resistance thus obtained was a relative value using a negative electrode produced using the negative electrode paste (c) and a reaction resistance value of the lithium ion battery 17 having a HRL thickness of 10.0 μm as 100 (reference). It is expressed as “Charging Resistance Ratio” and is shown in Table 2. Further, the relationship (part) between the charging resistance ratio and the capacitance is shown in FIG.

  As is clear from FIG. 6, when the negative electrode capacitance decreases, the charging resistance ratio of the battery tends to increase, and it has been confirmed that the negative electrode capacitance and the charging resistance ratio of the battery have a certain correlation. It can also be seen that the charging resistance ratio increases as the HRL thickness of the separator increases with the negative electrode capacitance in the range of about 0.12 F / g to 0.25 F / g. The increase in the charging resistance ratio is remarkably increased particularly when the thickness of the HRL exceeds 10 μm. Therefore, in order to keep the internal resistance when charging the battery low when the negative electrode capacitance is in the range of about 0.12 F / g to 0.25 F / g, the thickness of the HRL of the separator is preferably 10 μm or less. I understood that.

(Sample No. 29-38)
[Evaluation of safety (leakage current) 2]
Next, a lithium ion battery for evaluation (theoretical capacity 3.8 Ah) was constructed in the same manner as described above, using a separator having an HRL thickness of 10 μm. However, as the negative electrode active material, the amorphous carbon-coated graphite prepared above is used by adjusting the particle size of A to E in five different ways, and by directing the separator's HRL to either the positive electrode or the negative electrode side, Lithium ion batteries 29 to 38 having the configurations shown in Table 3 below were used.
The lithium ion batteries 29 to 38 were evaluated for safety by measuring the leakage current after shutdown in the same manner as described above. That is, the batteries 1 to 14 that have been subjected to appropriate initial conditioning were forcibly shut down by continuously charging, and the magnitude of the subsequent leakage current was evaluated. Specifically, first, as a conditioning process, under a temperature condition of 25 ° C., an operation of charging at a constant current at a charge rate of 0.2 C until the voltage between the positive and negative terminals becomes 4.1 V, and between the positive and negative terminals The operation of discharging at a constant current at a discharge rate of 0.2 C until the voltage becomes 3.0 V was taken as one cycle, and this was repeated three cycles. Next, each battery was prepared in a state of 30% SOC (State of Charge), and charged with a constant current of 40 A until the highest voltage reached 40 V. In such an overcharged state, the current value (leakage current value) for 10 minutes after the battery was shut down was measured, and the maximum current value in the 10 minutes was defined as “leakage current”. The measurement results of the leakage current are shown together in Table 3, and the relationship (part) between the leakage current and the type of the negative electrode active material is shown in FIG.

  As shown in Table 3 and FIG. 7, it was confirmed that the leakage current can be further reduced by arranging the HRL so as to face the negative electrode. In general, in a lithium ion battery, when it is overcharged, lithium dendrite is deposited on the surface of the negative electrode, and this dendrite can break through the separator and cause a short circuit. It has been found that by making the HRL opposite the negative electrode, it is possible to effectively suppress a micro short circuit and to build a highly safe battery during overcharge.

(Sample No. 39-43)
[Evaluation of charging resistance ratio 2]
Using the negative electrode active material B prepared above, a separator having an HRL thickness of 10 μm was arranged so that the HRL faced the negative electrode, and the same evaluation lithium ion battery (theoretical capacity 3.8 Ah) was constructed. . However, by changing the ratio of the binder (herein, SBR) in the negative electrode active material layer in five ways, lithium ion batteries 39 to 43 having configurations shown in Table 4 below were obtained.
For the lithium ion batteries 39 to 43, the charge resistance ratio was measured under the same conditions as in the charge resistance ratio evaluation 1 described above. The results are shown in Table 4. Moreover, the adhesiveness with respect to the electrical power collector of the negative electrode at the time of electrode formation was evaluated, and the result was collectively shown in Table 4. In Table 4, for the evaluation in the column of electrode adhesion, ○ indicates that the negative electrode was successfully manufactured, and x indicates that the electrode active material layer was collected when the negative electrode was slit (cut out) after the negative electrode active material layer was formed. Indicates peeling from the body.

As shown in Table 4, it can be seen that the charging resistance ratio increases as the blending amount of the binder increases. In particular, for the battery 43 in which the binder amount was 1.1% by mass, the charging resistance ratio was significantly increased. This is presumably because the surface of the negative electrode active material was covered with a binder and the acceptability of lithium ions was impaired. From the viewpoint of adhesion between the current collector and the negative electrode active material layer, it is understood that the amount of binder added is preferably 0.5% by mass or more. For these reasons, the amount of binder added is 0.4% by mass or more and 1% by mass or less, more preferably 0.5% by mass or more and 0.9% by mass or less. It was confirmed that both were compatible.
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 negative electrode includes a negative electrode current collector and a negative electrode active material layer,
The negative active material layer, Ri Do from natural graphite amorphous carbon is disposed on the surface, an average particle diameter of 5 to 20 [mu] m, BET specific surface area is 1.8~5.6m ² / g includes a negative electrode active material Ru der,
Wherein between the positive electrode and the negative electrode, a porous and insulation layers are provided that have a heat resistance for maintaining the porous structure without the softening and melting at a temperature of 200 ° C.,
The insulating layer has an average thickness of 2 μm to 10 μm,
The negative electrode is a non-aqueous electrolyte secondary battery in which a capacitance per unit mass of the negative electrode active material in a state of constituting the negative electrode is 0.12 F / g or more and 0.192 F / g or less. Between the positive electrode and the negative electrode, further comprising a porous separator having insulating properties,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating layer is disposed between the separator and the negative electrode.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the insulating layer is disposed on a surface of the separator.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material layer includes a binder made of a rubber-based resin at a ratio of 0.5 mass% to 0.9 mass%. .   The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating layer includes an inorganic filler.

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