JP2016024987A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery having both of a high energy density and a high-rate cycle characteristics by preventing the outflow of a nonaqueous electrolyte from an electrode body.SOLUTION: The present invention provides a nonaqueous secondary battery which comprises an electrode body having positive and negative electrode opposed to each other, provided that the positive electrode has a positive electrode active material layer and the negative electrode has a negative electrode active material layer. One of the positive and negative electrode active material layers is larger than the other electrode active material layer in area. The active material layer of each of the positive and negative electrodes has an opposing portion which is opposed to that of the active material layer of the other electrode. The active material layer larger in area has a non-opposing portion which is not opposed to the active material layer of the other electrode. As to the opposing portions, the apparent volume of the positive electrode active material layer is substantially equal to that of the negative electrode active material layer. In a range of SOC which is supposed in normal use of the battery, the porosity Pp (vol.%) of the positive electrode active material layer and the porosity Pn (vol.%) of the negative electrode active material layer satisfy the following condition: |Pp-Pn|≤4.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a secondary battery (non-aqueous secondary battery) provided with a non-aqueous electrolyte.

  In a typical configuration of a nonaqueous secondary battery, an active material layer mainly composed of a material (active material) capable of reversibly occluding and releasing charge carriers is provided on a positive electrode and a negative electrode. Voids are formed in the active material layer, and charge and discharge are performed by the charge carriers moving between the positive and negative electrodes through the nonaqueous electrolytic solution impregnated in the gaps.

By the way, depending on the use of the non-aqueous secondary battery, for example, charging / discharging in which a large current is instantaneously supplied at a high rate of 2C (particularly 5C) or more may be repeated. In such a battery, the load of the active material layer accompanying charge / discharge (transfer of charge carriers) is large, and the nonaqueous electrolyte solution may be pushed out of the electrode body due to, for example, a pump effect accompanying expansion and contraction of the active material. If the use in such a mode is repeated, so-called liquid withering may occur on one electrode side, or the concentration of charge carriers in the non-aqueous electrolyte may become uneven. As a result, the load accompanying the movement of the charge carriers increases, and the internal resistance of the battery may increase.
As a technique for coping with this, for example, Patent Document 1 discloses that the non-aqueous electrolyte is used at the electrode during high-rate discharge by setting the porosity of the positive electrode to 30 to 50% and the porosity of the negative electrode to 20 to 30%. It is described that the shortage is suppressed and high rate deterioration is prevented. In addition, Patent Documents 2 and 3 are other prior art documents related to the volume change of the active material and the porosity of the separator.

JP 2010-225366 A JP 2012-123968 A JP2013-016523A

However, when the above technique is applied to a battery (for example, a vehicle-mounted battery) that requires both high energy density and high input / output density, there is room for further improvement. That is, since the active material repeatedly expands and contracts with charge and discharge, the porosity of the active material layer can vary greatly depending on the state of charge of the battery. For this reason, even if the porosity of the active material layer is defined without considering the state of charge (SOC) of the battery, the outflow of the nonaqueous electrolyte from the electrode body may not be sufficiently prevented. For example, if the porosity of one of the active material layers is too large, the balance between the positive and negative electrode capacities may be lost and the energy density may be reduced.
The present invention has been made in view of the above points, and an object of the present invention is to prevent the outflow of the nonaqueous electrolyte from the electrode body accurately, and to combine the high energy density and the high rate cycle characteristics with a nonaqueous secondary battery. Is to provide.

In order to solve the above-mentioned problems, the present inventor has studied to maintain the small difference in the pore volume between the positive electrode active material layer and the negative electrode active material layer over the SOC range in which the battery is used. I came to the conclusion. Then, after further intensive studies, the present invention was completed.
That is, according to the present invention, there is provided a non-aqueous secondary battery comprising an electrode body formed by opposing a positive electrode having a positive electrode active material layer and a negative electrode having a negative electrode active material layer, and a non-aqueous electrolyte. Provided. Either one of the positive electrode active material layer and the negative electrode active material layer has a larger area than the other, and each of the active material layers of the positive and negative electrodes has a facing portion facing the counterpart active material layer, and has a larger area. The other active material layer has a non-opposing portion that does not face the other active material layer. Moreover, in the said opposing part, the apparent volume of the said positive electrode active material layer and the apparent volume of the said negative electrode active material layer are substantially equal. Further, in the SOC range assumed in normal use of the battery, the porosity Pp (volume%) of the positive electrode active material layer and the porosity Pn (volume%) of the negative electrode active material layer are expressed by the following relational expression. : | Pp−Pn | ≦ 4 is satisfied.

  By adopting the above configuration, the difference between the positive and negative electrode pore volumes (the product of the apparent volume and the porosity, that is, the pore volume = apparent volume × porosity) during charge / discharge can be kept small while securing a high capacity. And the outflow of the non-aqueous electrolyte from the positive and negative electrode active material layers accompanying the expansion of the active material can be prevented. As a result, a non-aqueous secondary battery having both a high energy density and high rate cycle characteristics can be realized with little increase in resistance even when high rate charge / discharge is repeated.

The “apparent volume of the active material layer” can be calculated by the product of the area (cm ² ) and the thickness (cm) in plan view. Specifically, first, a battery adjusted to a SOC of 0% (complete discharge) is disassembled, an electrode is taken out, and cut into a square or a rectangle with a punching machine or a cutter. Next, about the active material layer part of the cut-out electrode, the area (cm < ² >) in planar view is measured. Next, the thickness (cm) of the active material layer portion is measured with a micrometer or a thickness meter. Then, by multiplying these values, the “apparent volume of the active material layer” can be calculated.
In addition, the “porosity” in a state where the SOC of the battery is 0% (for example, when the battery is built or in a completely discharged state) It can be calculated by determining the volume and dividing this by the apparent volume and multiplying by 100. In addition, “porosity” in other SOCs (charged state) is the volume increase rate (change rate) from the SOC 0% state (reference) using X-ray crystal structure analysis (XRD; X-ray diffraction). Can be calculated and grasped. Specific measurement / calculation methods will be described in detail in Examples.
In addition, in this specification, “SOC range assumed in normal use of a battery” (hereinafter, simply referred to as “used SOC range”) means that the initial charge capacity of the battery is 100% (that is, full charge). State), typically the SOC (charge rate) range of the battery does not fall below 0% SOC (for example, does not fall below 10% SOC) or does not exceed 100% SOC (eg, does not exceed 90% SOC). ) The range is appropriately determined according to the intended use. As an example, in an application of a power source for driving a vehicle such as a plug-in hybrid vehicle (PHV), the used SOC range may be, for example, SOC 15% to 85%.

In order to maintain the above relational expression in the SOC range in which the energy density is used, that is, to maintain a high energy density and to keep the difference in porosity between the positive and negative electrode active material layers smaller, the absolute value of the porosity and the charge / discharge It is important to adjust both the rate of change of porosity. From this point of view,
In a preferred embodiment, the ratio (Cn / Cp) of the initial charge capacity Cn (Ah) of the negative electrode to the initial charge capacity Cp (Ah) of the positive electrode is 1.25 or more and 1.3 or less.
In another preferred aspect, the difference between the maximum value and the minimum value of Pn when the SOC is changed from the lowest SOC state to the highest SOC state is 3% by volume or less.
In another preferred embodiment, when the SOC of the non-aqueous secondary battery is 0% (for example, before charge and discharge), the Pp and the Pn have the following relationship: | Pp−Pn | ≦ 1; Satisfies.
By satisfying one or more of these, it is possible to more stably suppress the difference in positive and negative electrode pore volumes in the SOC range used.

The “positive charge capacity Cp (Ah) of the positive electrode” is the mass (g) of the positive electrode active material (used for producing the positive electrode) contained in the battery and the theoretical capacity per unit mass of the positive electrode active material. It can be calculated by the product of (Ah / g). The theoretical capacity per unit mass of the positive electrode active material can be measured, for example, as follows. First, a positive electrode (working electrode) is prepared using a positive electrode active material to be measured, placed in a test cell so as to face a metal lithium foil (counter electrode), and a nonaqueous electrolytic solution is injected therein. Build a bipolar cell. Next, under a temperature environment of 25 ° C., after performing constant current (CC) charging at a rate of 0.1 C until the voltage between the working electrode and the counter electrode becomes 4.2 V, the voltage is charged for 15 hours or charging rate. The constant voltage (CV) charging is performed until one of the conditions until the temperature reaches 0.01 C is satisfied. The CCCV charge capacity (Ah) at this time is divided by the mass (g) of the positive electrode active material (used for producing the positive electrode) contained in the cell, and the theoretical capacity per unit mass of the positive electrode active material (Ah / g) can be determined. As an example, the theoretical capacity per unit mass of LiNi _0.33 Co _0.33 Mn _0.33 O ₂ is approximately 170 mAh / g.
“Initial charge capacity Cn (Ah) of the negative electrode” is the same as in the case of the positive electrode described above. The mass (g) of the negative electrode active material (used for producing the negative electrode) contained in the battery and the negative electrode active material It can be calculated by the product of the theoretical capacity per unit mass (Ah / g). The theoretical capacity per unit mass of the negative electrode active material can be measured, for example, as follows. First, a negative electrode (working electrode) is prepared using a negative electrode active material to be measured, placed in a test cell so as to face a metal lithium foil (counter electrode), and a non-aqueous electrolyte is injected therein. Build a bipolar cell. Next, under a temperature environment of 25 ° C., constant current (CC) charging was performed at a rate of 0.1 C until the voltage between the working electrode and the counter electrode reached 0.01 V (10 mV), and then the voltage was applied for 15 hours. Alternatively, constant voltage (CV) charging is performed until one of the conditions until the charging rate reaches 0.01 C is satisfied. The CCCV charge capacity (Ah) at this time is divided by the mass (g) of the negative electrode active material (used for production of the negative electrode) contained in the cell, and the theoretical capacity per unit mass of the negative electrode active material (Ah / g) can be determined. As an example, the theoretical capacity per unit mass of the graphite-based carbon material is approximately 360 mAh / g.

It is a conceptual diagram for demonstrating the mode in the electrode body at the time of charge. It is a longitudinal cross-sectional view which shows typically the non-aqueous secondary battery which concerns on one Embodiment. It is a graph which shows the relationship between the charge condition (SOC) of a battery based on Example 1, and the porosity of a positive / negative electrode. It is a graph which shows the relationship between the charge condition (SOC) of a battery and the porosity of positive and negative electrodes according to Comparative Example 1. It is a graph which shows the relationship between the absolute value (| Pp-Pn |) of the maximum difference of the porosity of positive and negative electrodes, and the resistance increase rate after 10,000 cycles.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than the matters specifically mentioned in the present specification (for example, properties of the active material layer) and matters necessary for the implementation of the present invention (for example, battery components and general features that do not characterize the present invention) A simple manufacturing process) can be grasped as a design matter of a person skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

≪Non-aqueous secondary battery≫
The non-aqueous secondary battery disclosed herein is an electrode body in which a positive electrode having a positive electrode active material layer and a negative electrode having a negative electrode active material layer are opposed to each other (typically via a separator). And a non-aqueous electrolyte. Hereinafter, each component will be described in order.

<Positive electrode>
The positive electrode typically includes a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. As the positive electrode current collector, a conductive member made of a highly conductive metal (for example, aluminum, nickel, etc.) is suitable. A large number of fine pores are formed in the positive electrode active material layer. The pores are impregnated with a non-aqueous electrolyte containing a supporting salt (solvated charge carrier).

The positive electrode active material layer contains at least a positive electrode active material. As the positive electrode active material, one kind or two or more kinds of various materials that are known to be usable as the positive electrode active material of the non-aqueous secondary battery can be adopted. Preferable examples include layered and spinel lithium composite metal oxides (for example, LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _{0. 5} Mn _1.5 O ₄ etc.). Among them, from the viewpoint of thermal stability and energy density, lithium having a layered structure (typically a layered rock salt structure) represented by the following general formula: Li _{1 + α} Ni _x Co _y Mn _z M _β O ₂ Nickel cobalt manganese composite oxide (hereinafter sometimes referred to as “LNCM oxide”) is preferable. Here, α, x, y, z, and β are −0.05 ≦ α ≦ 0.2, x + y + z + β≈1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.4, 0 A real number satisfying 1 ≦ z ≦ 0.4 and 0 ≦ β ≦ 0.02. When β> 0, M is sodium (Na), magnesium (Mg), aluminum (Al), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium One or more elements selected from (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W).

  According to the study of the present inventor, the type and composition ratio of the positive electrode active material (for example, the ratio of x, y, z) is the amount of change (rate of change) during the charge / discharge of the porosity Pp of the positive electrode active material layer Can affect. From this point of view, an LNCM oxide in which the above x, y, and z are approximately the same (for example, the difference between x, y, and z is 0.1 or less) can be preferably used.

Such a positive electrode active material is typically particulate. The properties of the positive electrode active material particles are not particularly limited, but the average particle size is generally about 20 μm or less, typically 0.1 to 20 μm, for example 1 to 10 μm.
The shape of the particles is preferably a substantially spherical shape or a slightly distorted spherical shape. Specifically, the average aspect ratio can be approximately 0.5 to 1.0, typically 0.7 to 1.0, such as 0.9 ± 0.1.
According to the study of the present inventor, the properties (average particle diameter, average aspect ratio) of such a positive electrode active material have an influence on the amount of change (change rate) during charge / discharge of the porosity Pp of the positive electrode active material layer. Can give. In other words, the positive electrode active material satisfying one or two of the above properties has a small change in porosity in an arbitrary SOC range (typically SOC 0% to 100%, for example, SOC 15% to 85%). The above relational expression can be preferably satisfied.

In the present specification, the “average particle size” means a particle corresponding to a cumulative 50% from the fine particle side in a volume-based particle size distribution measured by a particle size distribution measurement based on a general laser diffraction / light scattering method. diameter _{(D 50} particle size, also called median diameter.) refers to. In the present specification, the “average aspect ratio” means that at least 30 particles (for example, 30 to 100 particles) are observed using an electron microscope, and a minimum rectangle circumscribing each particle image is drawn. The arithmetic mean value of the value obtained by dividing the short side length by the long side length.

  In addition to the positive electrode active material, the positive electrode active material layer may contain one or more materials that can be used as a constituent component of the positive electrode active material layer in a general non-aqueous secondary battery as necessary. . Examples of such a material include a conductive material and a binder. As the conductive material, for example, carbon materials such as various carbon blacks (for example, acetylene black and ketjen black), activated carbon, graphite, and carbon fiber can be suitably used. As the binder, for example, a halogenated vinyl resin such as polyvinylidene fluoride (PVdF), or a polyalkylene oxide such as polyethylene oxide (PEO) can be preferably used. In addition, various additives (for example, an inorganic compound that generates gas during overcharge, a dispersant, a thickener, and the like) can be included as long as the effects of the present invention are not significantly impaired.

  The proportion of the positive electrode active material in the entire positive electrode active material layer is suitably about 60% by mass or more from the viewpoint of realizing a high energy density, and is usually about 80% by mass or more, for example, 85 to 95% by mass. It is good to be. Moreover, when using a electrically conductive material, the ratio of the electrically conductive material to the whole positive electrode active material layer is good normally about 1-20 mass%, for example, about 3-10 mass%. Thereby, a favorable conductive path can be maintained in the positive electrode active material layer, and a battery having both high energy density and high input / output density can be realized. Moreover, when using a binder, the ratio of the binder to the whole positive electrode active material layer is generally about 0.5 to 10% by mass, for example, about 1 to 5% from the viewpoint of ensuring mechanical strength (shape retention). % Is good.

In a preferred embodiment, the mass (weight per unit area) of the positive electrode active material layer provided per unit area of the positive electrode current collector is 5 mg / cm ² or more, preferably 20 mg / cm ² or more, on both sides of the positive electrode current collector. More preferably, it is 30 mg / cm ² or more and 100 mg / cm ² or less, typically 50 mg / cm ² or less, for example, 40 mg / cm ² or less.
In another preferable embodiment, the average thickness of the positive electrode active material layer is 20 μm or more per side, typically 40 μm or more, and 100 μm or less, typically 80 μm or less.
In another preferable embodiment, the density of the positive electrode active material layer is 1.0 g / cm ³ or more, preferably 1.5 g / cm ³ or more, more preferably 2.0 g / cm ³ or more, 4.5 g / cm ³ or less, typically 4.0 g / cm ³ or less, for example 3.0 g / cm ³ or less.
According to the study by the present inventors, the proportions of constituent materials of the positive electrode active material layer, properties such as basis weight, average thickness, density, etc. can greatly affect the absolute value of the porosity Pp of the positive electrode active material layer. In other words, the relational expression can be stably satisfied by satisfying one or more of the preferable properties.

  In a preferred embodiment, when the SOC of the battery is 0% (for example, when the battery is constructed), the volume ratio (porosity Pp) of pores in the positive electrode active material layer is 25% by volume or more, preferably 30% by volume. As mentioned above, More preferably, it is 35 volume% or more. Thereby, the non-aqueous electrolyte can be sufficiently infiltrated into the positive electrode active material layer, and a wide reaction field with the charge carrier can be secured. From the viewpoint of realizing a higher energy density, the porosity Pp when the SOC of the battery is 0% is typically 40% by volume or less, for example, 38% by volume or less. Thereby, high energy density and high power density can be made compatible at a higher level.

  In another preferred embodiment, the difference between the maximum value and the minimum value of the porosity Pp when the SOC range is changed from the lowest SOC state to the highest SOC state is 2% by volume or less, preferably 1 .5% by volume or less, more preferably 1% by volume or less. This makes it possible to reduce the rate of change of porosity with respect to time (for example, the slope of a straight line in the graph with SOC on the horizontal axis and porosity on the vertical axis), and the movement of the nonaqueous electrolyte due to a sudden change in porosity. Can be suppressed. As a result, the above relational expression can be satisfied more suitably, and higher high-rate cycle characteristics can be realized.

<Negative electrode>
The negative electrode typically includes a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. As the negative electrode current collector, a conductive member made of a metal having good conductivity (for example, copper, nickel, etc.) is suitable. A large number of fine holes are formed in the negative electrode active material layer in the same manner as the positive electrode active material layer. The pores are impregnated with a non-aqueous electrolyte containing a supporting salt (solvated charge carrier).

  The negative electrode active material layer contains at least a negative electrode active material. As the negative electrode active material, one kind or two or more kinds of various materials known to be usable as a negative electrode active material of a non-aqueous secondary battery can be adopted. Preferred examples include carbon materials composed of graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotubes, and combinations thereof. Among these, a graphite-based carbon material is preferable from the viewpoint of realizing a high energy density battery. The “graphite-based carbon material” refers to a carbon material composed of only graphite, and a carbon material in which graphite accounts for 50 mass% or more (typically 80 mass% or more, for example, 90 mass% or more) of the entire material. Is a general term.

  Such a negative electrode active material is typically particulate. The properties of the negative electrode active material particles are not particularly limited, but the average particle size is preferably about 50 μm or less, typically 1 to 30 μm, for example 5 to 20 μm.

The shape of the particles is preferably a substantially spherical shape or a slightly distorted spherical shape. Specifically, the average aspect ratio can be approximately 0.5 to 1.0, typically 0.7 to 1.0, such as 0.7 ± 0.1. If the average aspect ratio deviates significantly from the above range, for example, anisotropy may occur in the expansion direction of the negative electrode active material layer during high-rate charging, and it may expand greatly in the stacking direction (the direction facing the positive electrode). In such a case, the discharge amount of the non-aqueous electrolyte may increase.
One suitable example of the material having a substantially spherical particle shape is so-called spheroidized graphite. Spherical graphite is produced by applying stress to scaly graphite so that the edge surface of the graphite crystal is folded or bent concentrically. For this reason, such spheroidized graphite may be one in which the orientation of the hexagonal network structure is homogenized as compared with so-called scaly graphite. For this reason, it can suppress that it expand | swells largely only in the direction facing a positive electrode at the time of charge. Furthermore, the conductivity in the thickness direction of the negative electrode active material layer can be improved.

  According to the study of the present inventor, the properties (average particle diameter, average aspect ratio) of such a negative electrode active material have a great influence on the amount of change (change rate) during charge / discharge of the porosity Pn of the negative electrode active material layer. Can give. In other words, a negative electrode active material satisfying one or two of the above properties has a small change in porosity in any SOC range (typically SOC 0% to 100%, for example, SOC 15% to 85%). The above relational expression can be preferably satisfied.

  In addition to the negative electrode active material, the negative electrode active material layer can contain one or more materials that can be used as a component of the negative electrode active material layer in a general non-aqueous secondary battery as necessary. . Examples of such materials include binders and various additives. As the binder, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), or the like can be suitably used. In addition, various additives such as a thickener, a dispersant, and a conductive material can be appropriately used. For example, celluloses such as carboxymethyl cellulose (CMC) and methyl cellulose (MC) can be suitably used as the thickener.

  The proportion of the negative electrode active material in the entire negative electrode active material layer is suitably about 60% by mass or more from the viewpoint of realizing a high energy density, and is usually about 90 to 98% by mass, for example, 95 to 99% by mass. % Is good. Moreover, when using a binder, the ratio of the binder to the whole negative electrode active material layer is usually about 1 to 10% by mass, for example, about 1 to 5% by mass, from the viewpoint of ensuring mechanical strength (shape retention). There should be. Moreover, when using a thickener, it is good that the ratio of the thickener to the whole negative electrode active material layer is about 1-10 mass% normally, for example, about 1-5 mass%.

In a preferred embodiment, the negative electrode active material layer contains a graphite-based carbon material, and the peak intensity ratio (I ₁₁₀ / I ₀₀₄ ) between the peak intensity I ₁₁₀ and the peak intensity I ₀₀₄ of the negative electrode active material layer is 0.00. 1 or more, for example, 0.1 or more and 0.15 or less. In general, it can be said that the smaller the peak strength ratio, the higher the orientation of the negative electrode active material layer. If I ₁₁₀ / I ₀₀₄ is significantly less than 0.1, anisotropy may occur in the expansion direction during charging, and the film may expand and contract significantly in the stacking direction (the direction facing the positive electrode). In such a case, the discharge amount of the non-aqueous electrolyte may increase, and the liquid may wither or the concentration of the supporting salt may be uneven in the negative electrode active material layer. By setting the peak intensity ratio within the above range, such inconvenience can be prevented at a higher level.
Note that the peak intensity (I ₁₁₀ , I ₀₀₄ ) of the negative electrode active material layer can be measured by an X-ray diffractometer (XRD) using CuKα rays. Specifically, the battery is first disassembled and a negative electrode sheet provided with a negative electrode active material layer is cut out. Next, XRD measurement is performed on the negative electrode sheet, and a diffraction peak intensity I ₁₁₀ on the ( ₁₁₀ ) plane and a diffraction peak intensity I _{004 on} the (004) plane are obtained from the obtained XRD chart. Then, the peak intensity ratio (I ₁₁₀ / I ₀₀₄ ) can be calculated by dividing I ₁₁₀ by I ₀₀₄ .

In a preferred embodiment, the mass (weight per unit area) of the negative electrode active material layer provided per unit area of the negative electrode current collector is 5 mg / cm ² or more, preferably 10 mg / cm ² or more, on both sides of the negative electrode current collector, More preferably, it is 15 mg / cm ² or more, and typically 30 mg / cm ² or less, for example, 20 mg / cm ² or less.
In another preferable embodiment, the average thickness of the negative electrode active material layer is 40 μm or more, typically 50 μm or more, and 100 μm or less, typically 80 μm or less, per side.
In another preferable embodiment, the density of the negative electrode active material layer is 0.5 g / cm ³ or more, preferably 1.0 g / cm ³ or more and 2.0 g / cm ³ or less, for example, 1. 5 g / cm ³ or less.
According to the study by the present inventors, the proportion of the constituent material of the negative electrode active material layer, the properties such as the basis weight, the average thickness, and the density can greatly affect the absolute value of the porosity Pn of the negative electrode active material layer. In other words, the relational expression can be stably satisfied by satisfying one or more of the preferable properties.

In a preferred embodiment, in a state where the SOC of the battery is 0% (for example, when the battery is constructed), the volume ratio (porosity Pn) of pores in the negative electrode active material layer is 30% by volume or more, preferably 35% by volume. That's it. As a result, the non-aqueous electrolyte can be sufficiently infiltrated into the negative electrode active material layer, and it is possible to suppress the occurrence of liquid withering and local uneven support salt concentration of the charge carrier in the negative electrode active material layer. . Furthermore, a wide reaction field with the charge carrier can be secured, and excellent output characteristics can be realized.
In another preferred embodiment, when the SOC of the battery is 0%, the porosity Pn is 45% by volume or less, for example, 40% by volume or less. Thereby, the battery capacity (energy density) per unit volume can be increased. Furthermore, it is possible to highly prevent the conductive path from being cut off in the negative electrode active material layer to increase the resistance or the mechanical strength (shape retention) to be insufficient.

  In another preferred embodiment, the difference between the maximum value and the minimum value of the porosity Pn is 3% by volume or less, preferably 2.5% by volume or less in the SOC range used. Thereby, the above relational expression can be satisfied more suitably, and higher high-rate cycle characteristics can be realized.

<Configuration of electrode body>
In the technique disclosed here, the appearance of the positive electrode active material layer in the region where the positive electrode active material layer and the negative electrode active material layer face each other in a state where the SOC of the battery is 0% (for example, when the battery is constructed or in a completely discharged state). The volume Vp and the apparent volume Vn of the negative electrode active material layer are substantially equal. More specifically, Vn / Vp is about 0.95 or more, for example 0.98 or more, and satisfies about 1.15 or less, typically 1.1 or less, for example 1.05 or less. . When Vn / Vp is less than 0.95, Vn is too small with respect to Vp. For example, the capacity on the positive electrode side decreases and the energy density tends to decrease, or the liquid retention property of the positive electrode active material layer is low. It may decrease. On the other hand, if Vn / Vp exceeds 1.15, Vn is too large with respect to Vp. For example, the negative electrode capacity decreases or the positive / negative electrode capacity balance (Cn / Cp) collapses. As a result, the energy density may tend to decrease. By making the apparent volume substantially equal between the active material layers of the positive and negative electrodes, a high energy density can be stably realized.
The apparent volume of the active material layer can be suitably controlled, for example, by adjusting the mass (weight per unit area) of the active material layer applied on the current collector or adjusting the press conditions of the active material layer.

In a preferred embodiment, the ratio of the initial charge capacity Cn of the negative electrode to the initial charge capacity Cp of the positive electrode (Cn / Cp) is 1.2 or more (preferably 1.25 or more), and is 1.35 or less. (Preferably 1.3 or less). As a result, the difference in pore volume between the positive and negative electrodes can be more stably suppressed and the battery configuration disclosed herein can be suitably realized.
In addition, by setting the positive / negative electrode capacity ratio (Cn / Cp) to 1.2 or more, for example, even when high-rate charge / discharge is repeated, the charge carrier is highly prevented from being deposited on the negative electrode as a metal. The durability and reliability of the battery can be further improved. Further, by setting the positive / negative electrode capacity ratio (Cn / Cp) to 1.35 or less, the capacity balance between the positive and negative electrodes can be maintained, and a high energy density can be stably realized.

In the technology disclosed herein, the difference between the porosity Pp (volume%) of the positive electrode active material layer and the porosity Pn (volume%) of the negative electrode active material layer is kept small in the SOC range of the battery. Yes. Specifically, the absolute value of Pp-Pn satisfies 4% by volume or less, typically 0 to 4% by volume, for example, 3% by volume or less. In other words, at least the above relational expression is satisfied.
This effect will be described in detail below.

  FIG. 1 shows the inside of the electrode body 30 during charging. That is, as shown in FIG. 1A, a large amount of charge carriers (here, lithium ions) move from the positive electrode 10 (through the separator 40) to the negative electrode 20 during charging. As the charge carriers move, the positive electrode active material 16 contracts, and conversely, the negative electrode active material 26 expands. As shown in FIG. 1B, the non-aqueous electrolyte is pushed out from the pores of the negative electrode active material layer 24 by the expansion of the negative electrode active material 26. At this time, if the porosity of the positive electrode active material layer 14 is small, the non-aqueous electrolyte extruded from the negative electrode active material layer 24 cannot be accommodated and overflows from the electrode body 30. On the other hand, at the time of discharging, if the porosity of the negative electrode active material layer 24 is small, the non-aqueous electrolyte overflows from the positive electrode active material layer 14. By repeating such charging / discharging, for example, liquid erosion may occur in one active material layer, or local unevenness may gradually occur in the concentration of the supporting salt in the non-aqueous electrolyte.

  Therefore, in the technique disclosed herein, the difference in the pore volume between the positive and negative electrodes is kept small in the SOC range (used SOC range) in which charging / discharging is performed. According to the knowledge newly obtained by the present inventors, it is possible to balance the expansion and contraction of the active material layer in the electrode body. That is, the nonaqueous electrolytic solution extruded from the negative electrode active material layer 24 during charging can be suitably stored in the positive electrode active material layer 14. In addition, the nonaqueous electrolytic solution extruded from the positive electrode active material layer 14 during discharge can be suitably stored in the negative electrode active material layer 24. Therefore, for example, even when charging or discharging is performed at a stretch with a large current, it is possible to highly prevent the nonaqueous electrolyte from flowing out of the electrode body 30. As a result, when the battery is used, it is possible to suitably maintain a state in which the pores of the positive electrode active material layer 14 and the negative electrode active material layer 24 are impregnated with the nonaqueous electrolytic solution. Moreover, it can suppress highly that a nonuniformity arises in the support salt density | concentration of a non-aqueous electrolyte. Since the technology disclosed herein may have such a mechanism, the above | Pp-Pn | may be 4% by volume or less (0 to 4% by volume), for example, 0 to 3% by volume. Also good.

  In a preferred embodiment, when the SOC of the battery is 0% (for example, when the battery is constructed), the Pp (volume%) and the Pn (volume%) have the following relationship: | Pp−Pn | ≦ 1; Meet. During charging, charge carriers are released from the positive electrode active material, and the positive electrode active material contracts. For this reason, the porosity Pp of the positive electrode tends to increase as the SOC value increases. On the other hand, in the negative electrode, charge carriers are occluded in the negative electrode active material, and the negative electrode active material expands. For this reason, the porosity Pn of the negative electrode tends to decrease as the SOC value increases. Therefore, the above relational expression can be satisfied more stably by keeping the porosity of the positive and negative electrodes substantially equal in the complete discharge state.

<Separator>
The separator interposed between the positive and negative electrodes may be any separator that insulates the positive electrode active material layer and the negative electrode active material layer and has a function of holding a non-aqueous electrolyte and a shutdown function. Preferable examples include porous resin sheets (films) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among these, polyolefin-based porous resin sheets (for example, PE and PP) are preferable.
The properties of the separator are not particularly limited. For example, the air permeability (Gurley value) is a value measured by the method defined in JIS P8117 (2009), usually 250 seconds / 100 mL or less, for example, 100 to 250 seconds / 100 mL. It is good to be. As a result, the charge carriers can move smoothly in the separator. For example, even when high-rate charge / discharge is repeated, an increase in resistance can be suppressed at a higher level.

  The separator may have a single-layer structure or a structure in which two or more porous resin sheets having different materials and properties are laminated. As the multilayer structure, for example, a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer (that is, a three-layer structure of PP / PE / PP) is suitable. In addition, for the purpose of preventing an internal short circuit or the like, a porous heat-resistant layer containing inorganic compound particles (inorganic filler) may be provided on one side or both sides of the porous resin sheet.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution typically contains at least a supporting salt in a nonaqueous solvent. The non-aqueous electrolyte is in a liquid state at normal temperature (for example, 25 ° C.), and in a preferred embodiment, the non-aqueous electrolyte is always in a liquid state in a battery use environment (for example, in a temperature environment of −30 to 60 ° C.).
As the non-aqueous solvent, various organic solvents used for non-aqueous electrolytes of general non-aqueous secondary batteries, for example, carbonates, ethers, esters, nitriles, sulfones, lactones, etc. should be used. 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 individually by 1 type or in combination of 2 or more types as appropriate.
In a preferred embodiment, a high dielectric constant solvent and a low viscosity solvent are mixed and used. By using such a mixed solvent, high electric conductivity and use in a wide temperature range are possible. Examples of the high dielectric constant solvent include EC, and examples of the low viscosity solvent include DMC and EMC. As an example, it includes one or more carbonates, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, and further preferably 90% by volume or more) of the total volume of the nonaqueous solvent. A non-aqueous solvent occupying substantially 100% by volume) is preferred.

The supporting salt is the same as a general non-aqueous secondary battery as long as it contains a charge carrier (for example, lithium ion, sodium ion, magnesium ion, etc., lithium ion in a lithium ion secondary battery). One or more types can be selected and used. For example, when the charge carrier is lithium ion, lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ are exemplified. Such a supporting salt can be used singly or in combination of two or more. LiPF ₆ may be mentioned as particularly preferred support salt. Moreover, it is preferable that the density | concentration of supporting salt shall be 0.7-1.3 mol / L with respect to the whole nonaqueous electrolyte.

In addition, in addition to the said component, various additives can be further included in the non-aqueous electrolyte as necessary, as long as the effects of the present invention are not significantly impaired. Such additives are used for one or more purposes such as, for example, improvement of battery cycle characteristics, improvement of high-temperature storage characteristics, improvement of initial charge / discharge efficiency, improvement of input / output performance, and improvement of overcharge resistance. obtain. As specific examples, film forming agents such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), lithium bis (oxalato) borate (Li [B (C ₂ O ₄ ) ₂ ]); biphenyl (BP), cyclohexylbenzene ( Gas generating agents such as CHB); dispersants; thickeners; and the like.

<< One Embodiment of Nonaqueous Secondary Battery >>
Although not intended to be particularly limited, as a schematic configuration of one embodiment of the present invention, a nonaqueous secondary battery (unit cell) schematically shown in FIG. 2 will be described as an example. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not necessarily reflect the actual dimensional relationship.

  FIG. 2 is a vertical cross-sectional view schematically showing a cross-sectional structure of the non-aqueous secondary battery 100. In this embodiment, an electrode body (winding electrode body) 80 in which the long positive electrode sheet 10 and the long negative electrode sheet 20 are wound flatly via the long separator sheet 40, It is housed in a flat box-shaped battery case 50 together with a non-aqueous electrolyte (not shown).

  The battery case 50 includes a flat rectangular parallelepiped (box-shaped) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. As the material of the battery case, a relatively light metal (for example, aluminum or aluminum alloy) can be preferably used for the purpose of improving heat dissipation and increasing energy density. On the upper surface of the battery case 50 (that is, the lid 54), a positive terminal 70 for external connection that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode that is electrically connected to the negative electrode of the wound electrode body 80. A terminal 72 is provided. The lid 54 is also provided with a safety valve 55 for discharging the gas generated inside the battery case 50 to the outside of the case 50, as in the case of the battery case of the conventional non-aqueous secondary battery.

  Inside the battery case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte solution (not shown). The wound electrode body 80 includes a long sheet-like positive electrode (positive electrode sheet) 10 and a long sheet-like negative electrode (negative electrode sheet) 20. The positive electrode sheet 10 includes a long positive electrode current collector and a positive electrode active material layer 14 formed on at least one surface (typically both surfaces) along the longitudinal direction. The negative electrode sheet 20 includes a long negative electrode current collector and a negative electrode active material layer 24 formed on at least one surface (typically both surfaces) along the longitudinal direction. Between the positive electrode active material layer 14 and the negative electrode active material layer 24, two long sheet-like separators 40 are disposed as an insulating layer that prevents direct contact between the two.

  A positive electrode formed on the surface of the positive electrode current collector in the width direction defined as a direction from one end portion of the wound electrode body 80 toward the other end portion in the winding axis direction. A wound core portion is formed in which the active material layer 14 and the negative electrode active material layer 24 formed on the surface of the negative electrode current collector overlap and are densely stacked. Further, at both ends of the wound electrode body 80 in the winding axis direction, the positive electrode active material layer non-formed portion of the positive electrode sheet 10 and the negative electrode active material layer non-formed portion of the negative electrode sheet 20 are respectively outward from the wound core portion. It sticks out. A positive electrode current collector plate is attached to the positive electrode side protruding portion, and a negative electrode current collector plate is attached to the negative electrode side protruding portion, and is electrically connected to the positive electrode terminal 70 and the negative electrode terminal 72, respectively.

≪Uses of non-aqueous secondary batteries≫
In the battery disclosed herein, the non-aqueous electrolyte can be stably held in the electrode body, and even when charging and discharging are repeated with a large current, liquid drainage and uneven concentration of the supporting salt occur. Can be highly suppressed. Therefore, when the effect of the pumping effect due to the expansion and contraction of the active material can be large (for example, when a material with a large expansion and contraction is used as the active material, or when the active material layer is formed relatively thick, it is charged with a large current. The application of the technique disclosed herein is particularly effective when the discharge is repeated. That is, as a preferable application target of the technology disclosed herein, a large capacity type battery having a theoretical capacity of 5 Ah or more, for example, 10 Ah or more, particularly 20 Ah or more; a theoretical capacity per unit volume of 10 Ah / L or more, for example, 20 Ah / A battery having a high energy density of L or more, particularly 100 Ah / L or more; 2C or more (for example, 2 to 50 C), 5 C or more, further 10 C or more, particularly 20 C or more (for example, 20 to 50 C) are repeatedly repeated at a high rate. Examples of batteries that can be used in applications.

  The non-aqueous secondary battery disclosed herein can be suitably used as a power source for a driving source such as a motor for driving a vehicle, utilizing the above-described properties. Although the kind of vehicle is not specifically limited, For example, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), an electric vehicle (EV), an electric truck, an electric scooter, an electric assist bicycle, an electric wheelchair, an electric railway etc. are mentioned.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

[Positive electrode sheet]
As the positive electrode active material, LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCM oxide) having an average particle diameter of 6 μm and an aspect ratio of 0.9 was prepared. Next, this LNCM oxide, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder have a mass ratio of these materials of LNCM oxide: AB: PVdF = 90: 8: The positive electrode slurry was prepared by charging into a kneader so as to be 2, and kneading with a small amount of N-methylpyrrolidone (NMP) while adjusting the viscosity. This slurry was applied to both surfaces of a 15 μm thick aluminum foil (positive electrode current collector) so that the basis weight per surface was the value shown in Table 1, and the solvent component was removed by drying. A positive electrode sheet having a positive electrode active material layer on a positive electrode current collector (Examples 1 and 2 and Comparative Example), which is rolled and controlled by controlling the press conditions (set pressure and press time) so that the active material layer density shown in FIG. 1-3) were produced.

The porosity (volume%) of the produced positive electrode sheet was calculated. Specifically, the pore volume is obtained by subtracting the volume V2 of the constituent material of the active material layer from the apparent volume V1 of the active material layer, and this is divided by the apparent volume V1 and multiplied by 100, that is, ( The porosity before charging / discharging (in a state where the SOC is 0%) was calculated from V1-V2) / V1 × 100. The apparent volume V1 was calculated from the product of the area (cm ² ) and the thickness (cm) in plan view. The volume V2 of the constituent material is expressed by the following formula: positive electrode active material volume + conductive material volume + binder volume = (mass of LNCM oxide (g) / true specific gravity of LNCM oxide (g / cm ³ )) + (Mass of AB (g) / true specific gravity of AB (g / cm ³ )) + (mass of PVdF (g) / true specific gravity of PVdF (g / cm ³ )); The true specific gravity of each material was measured by a general constant volume expansion method (gas displacement pycnometer method). The results are shown in the corresponding column of Table 1.

[Negative electrode sheet]
Spherical graphite (C) having an average particle diameter of 20 μm and an aspect ratio of 0.7 was prepared as a negative electrode active material. Next, this spheroidized graphite (C), styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener have a mass ratio of these materials of C: SBR: CMC = 98: The mixture was put into a kneader so as to be 1: 1, and kneaded while adjusting the viscosity with a small amount of ion-exchanged water to prepare a negative electrode slurry. This slurry was applied to both surfaces of a long copper foil (negative electrode current collector) having a thickness of 10 μm so that the basis weight per both surfaces became the value shown in Table 1, and water was removed by drying. A negative electrode sheet (Examples 1, 2 and Comparative Examples) having a negative electrode active material layer on a negative electrode current collector that is rolled and pressed under controlled press conditions (set pressure and press time) so that the active material layer density shown in FIG. 1-3) were produced.

The porosity (volume%) of the prepared negative electrode sheet was calculated. Specifically, the volume V2 of the constituent material is expressed by the following formula: negative electrode active material volume + binder volume + thickening agent volume = (mass of spheroidized graphite (g) / true specific gravity of spheroidized graphite (g / cm ³ )) + (SBR mass (g) / SBR true specific gravity (g / cm ³ )) + (CMC mass (g) / CMC true specific gravity (g / cm ³ )) As in the case of the positive electrode, the porosity before charging / discharging (in a state where the SOC is 0%) was calculated. The results are shown in the corresponding column of Table 1.

[Non-aqueous secondary battery]
The positive electrode sheet and the negative electrode sheet prepared above were cut out so as to have a facing capacity ratio (Cn / Cp) shown in Table 2, and wound together with two separator sheets to produce a flat wound electrode body. As the separator sheet, a commercial product having a three-layer structure in which polypropylene (PP) was laminated on both sides of polyethylene (PE) was used. In addition, in the area | region where the positive electrode active material layer and negative electrode active material layer of this electrode body oppose, the apparent volume of an active material layer is substantially equal. Table 2 shows the ratio (Vn / Vp) of the apparent volume Vn of the negative electrode active material layer to the apparent volume Vp of the positive electrode active material layer.

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 connected to the lid was housed inside the rectangular battery case provided with the CID, and the opening and the lid were welded. And the non-aqueous electrolyte solution was inject | poured from the electrolyte solution injection hole provided in the cover body. As a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 30: 40: 30 is used as a supporting salt. LiPF ₆ was dissolved at a concentration of 1.1 mol / L, and further, 4% by mass of cyclohexylbenzene (CHB) as a gas generating agent and 1% by mass of biphenyl (BP) were used.
In this way, non-aqueous secondary batteries (rated capacity: 24 Ah, Examples 1 and 2 and Comparative Examples 1 to 3) having different electrode properties were constructed.

[activation]
In an environment of 25 ° C., the battery obtained above was subjected to constant current charging (CC charging) at a constant current of 1/3 C until the voltage between the positive and negative terminals reached 3.95 V, and then the current value was 0.02 C. Constant voltage charging (CV charging) was performed until The battery after such a charging treatment was left in a thermostatic bath at a temperature of 60 ° C. for 24 hours for aging.

[Square wave test]
Under the environment of 25 ° C., the battery after aging was adjusted to a state of SOC 60%, and the battery was discharged at a constant current of 0.6 C for 10 seconds, and the amount of voltage drop was measured. The initial IV resistance was calculated by dividing the voltage drop (V) by the corresponding current value (A).
Next, the battery was adjusted to an SOC of 80%, and high-rate pulse charge / discharge for 10 seconds was repeated 10,000 times with a constant current of 5C. Then, the IV resistance after the pulse charge / discharge test was calculated in the same manner as the initial IV resistance. From the IV resistance after the pulse charge / discharge test and the initial IV resistance, the following formula: resistance increase rate (%) = (IV resistance after the pulse charge / discharge test−initial IV resistance) / initial IV resistance × 100; The resistance increase rate was calculated. The results are shown in the corresponding column of Table 2. FIG. 5 shows the relationship between the absolute value (| Pp−Pn |) of the maximum difference in porosity between the positive and negative electrodes and the resistance increase rate.

[Measurement of porosity]
Six laminate cells were prepared for each example with the same configuration as the prismatic battery, and the relationship between the SOC (charge rate) of the battery and the porosity of the active material layer was confirmed. Specifically, first, by using a charging / discharging device, the six batteries were adjusted to SOC states of 0%, 15%, 40%, 60%, 85%, and 100%. This battery was disassembled, and the electrode body was carefully taken out so as not to short-circuit, and a part of the positive electrode sheet and the negative electrode sheet was cut out. And orientation was measured under the following conditions using an X-ray diffractometer (Model “Ultima IV” manufactured by Rigaku Corporation).
・ Target: Cu (Kα ray) graphite monochromator ・ Slit: Diverging slit = 1 °, Receiving slit = 0.1 mm, Scattering slit = 1 °
In the LNCM oxide used as the positive electrode active material in this test example, the a-axis length and the c-axis length are changed (expanded / contracted) by charging. Therefore, the surface index of the (003) plane and (101) plane for the positive electrode sheet ( Calculate the a-axis length and c-axis length from the peak position), calculate the a-axis length x c-axis length, compare with the SOC 0% state, and calculate the volume increase rate (change rate) Px (%) in each SOC did. And, based on the porosity (Pp shown in Table 1 above) in the SOC 0% state, the following formula:
The porosity of the SOC x% (%) = 100 − {(100−Pp) × (100 + volume increase rate Px) / 100}; The porosity of the positive electrode in each SOC was determined.
Further, the graphite-based carbon material used as the negative electrode active material in this test example changes the interlayer distance d (002) by charging, and therefore the negative electrode sheet has a (002) plane spacing (peak position) of SOC 0%. The volume increase rate (rate of change) Py (%) in each SOC was calculated. And based on the porosity (Pn shown in Table 1 above) in the SOC 0% state, the following formula:
The porosity of the SOC y% (%) = 100 − {(100−Pn) × (100 + volume increase rate Py) / 100}; The porosity of the negative electrode in each SOC was determined.
As an example, the measurement result according to Example 1 is shown in FIG. 3, and the measurement result according to Comparative Example 1 is shown in FIG. Further, the absolute value (| Pp−Pn |) of the maximum difference in porosity in the SOC range of 15% to 85% as the used SOC range of the vehicle driving battery is shown in the corresponding column of Table 2.

As shown in Table 2 and FIG. 5, in Comparative Examples 1 to 3, the resistance increase rate was large, while in Examples 1 and 2, almost no increase in resistance was observed after 10,000 cycles of high-rate charge / discharge. . The reason for this is that the volume difference between the positive and negative electrodes during charge and discharge is alleviated by setting the absolute value of the maximum difference in porosity between the positive and negative electrodes to 4% by volume or less (eg 3% by volume or less) in the SOC range of the battery. It is possible that the non-aqueous electrolyte was prevented from flowing out of the electrode body.
As described above, by satisfying the above relational expression, it is possible to suppress a difference in the pore volume of the positive and negative electrodes during charging and discharging, and to prevent the nonaqueous electrolyte from flowing out from the electrode body. That is, at the time of charging, the nonaqueous electrolytic solution pushed out from the negative electrode along with the expansion of the negative electrode active material can be accurately stored in the pores (voids) of the positive electrode. On the other hand, at the time of discharge, the nonaqueous electrolytic solution pushed out from the positive electrode with the expansion of the positive electrode active material can be accurately stored in the pores of the negative electrode. As a result, the amount of the non-aqueous electrolyte pushed out from one electrode does not exceed the capacity that the other electrode can receive, and the outflow of the non-aqueous electrolyte outside the electrode body can be highly prevented. Furthermore, the amount of the non-aqueous electrolyte present in the positive and negative electrodes in the SOC range used can be made substantially equal, and the absolute amount of movement of the non-aqueous electrolyte can be reduced. Therefore, a non-aqueous secondary battery having both high energy density and high rate cycle characteristics can be realized. Such results indicate the technical significance of the present invention.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

10 Positive electrode sheet (positive electrode)
14 Positive electrode active material layer 16 Positive electrode active material 20 Negative electrode sheet (negative electrode)
24 Negative electrode active material layer 26 Negative electrode active material 30 Electrode body 40 Separator sheet (separator)
DESCRIPTION OF SYMBOLS 50 Battery case 52 Battery case main body 54 Cover body 55 Safety valve 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Non-aqueous secondary battery

Claims (5)

An electrode body formed by opposing a positive electrode having a positive electrode active material layer and a negative electrode having a negative electrode active material layer in an insulated state;
A non-aqueous electrolyte,
A non-aqueous secondary battery comprising:
Either one of the positive electrode active material layer and the negative electrode active material layer has a larger area than the other,
Each of the positive and negative electrode active material layers has a facing portion that faces the counterpart active material layer, and the active material layer having a larger area has a non-facing portion that does not face the counterpart active material layer,
In the facing portion, the apparent volume of the positive electrode active material layer and the apparent volume of the negative electrode active material layer are substantially equal,
In the range of SOC assumed in normal use of the battery, the porosity Pp (volume%) of the positive electrode active material layer and the porosity Pn (volume%) of the negative electrode active material layer are expressed by the following relational expression:
Non-aqueous secondary battery satisfying | Pp−Pn | ≦ 4;   2. The non-aqueous secondary according to claim 1, wherein a ratio (Cn / Cp) of an initial charge capacity Cn (Ah) of the negative electrode to an initial charge capacity Cp (Ah) of the positive electrode is 1.25 or more and 1.3 or less. battery.   The difference between the maximum value and the minimum value of Pn when the SOC is changed from the lowest SOC state to the highest SOC state in the SOC range assumed in normal use of the battery is 3% by volume or less. The non-aqueous secondary battery according to claim 1 or 2.   4. The state according to claim 1, wherein the Pp and the Pn satisfy the following relationship: | Pp−Pn | ≦ 1 in a state where the SOC of the non-aqueous secondary battery is 0%. Non-aqueous secondary battery.   The non-aqueous secondary battery according to any one of claims 1 to 4, wherein a range of SOC assumed in normal use of the battery is SOC 15% to 85%.

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