Nonaqueous electrolyte secondary battery

Abstract

To provide a nonaqueous electrolyte secondary battery that can achieve both higher capacity and quick charging property.SOLUTION: A nonaqueous electrolyte secondary battery includes an electrode body and a nonaqueous electrolyte solution. The electrode body includes a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate includes a positive electrode base material and a positive electrode active material layer. The negative electrode plate includes a negative electrode base material and a negative electrode active material layer. The separator is disposed while being bent in a zigzag way. The positive electrode plate and the negative electrode plate are disposed by being held alternately between the folded separators. In at least one of the positive electrode active material layer and the negative electrode active material layer, when the porosity of a 50% region from a surface on the positive electrode base material side or the negative electrode base material side is VB and the porosity of a 50% region from a surface, which is opposite to the positive electrode base material side or the negative electrode base material side is VA in the thickness direction, the ratio (VA / VB) of VA to VB satisfies 1<VA / VB≤1.4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] The negative electrode for a non-aqueous electrolyte secondary battery disclosed in International Publication No. 2020 / 110589 (Patent Document 1) discloses that two types of styrene butadiene rubber with different glass transition temperatures (Tg) are used in the thickness direction of the negative electrode active material layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 110589 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to achieve high capacity, prismatic lithium-ion batteries have increased the planar area of ​​the electrodes and the density of the active material in the electrodes. As a result, uneven lithium (Li) ion concentration due to the extrusion of the nonaqueous electrolyte solution out of the system can occur both within the electrode plane and in the thickness direction (stacking direction). As a result, rapid charging performance tends to deteriorate.

[0005] An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery that can achieve both high capacity and rapid chargeability. [Means for solving the problem]

[0006] The present disclosure provides the following nonaqueous electrolyte secondary battery. [1] A non-aqueous electrolyte secondary battery including an electrode assembly and a non-aqueous electrolyte solution, the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator; the positive electrode plate includes a positive electrode substrate and a positive electrode active material layer, the negative electrode plate includes a negative electrode substrate and a negative electrode active material layer, The separator is folded back in a zigzag pattern, the positive electrode plates and the negative electrode plates are alternately sandwiched between the folded separators, In at least one of the positive electrode active material layer and the negative electrode active material layer, when a porosity of a 50% region from the surface on the positive electrode substrate side or the negative electrode substrate side in the thickness direction is VB, and a 50% region from the surface on the opposite side to the positive electrode substrate side or the negative electrode substrate side is VA, the ratio of VA to VB (VA / VB) satisfies the following formula (1): (1) 1 <VA / VB≦1.4 A non-aqueous electrolyte secondary battery that satisfies the above requirements. [2] In the electrode assembly, one folded portion of the separator is in contact with the excess liquid of the nonaqueous electrolyte, the positive electrode plate or the negative electrode plate is disposed between adjacent folded portions that are in contact with the excess liquid; The positive electrode plate or the negative electrode plate disposed between adjacent folded portions in contact with the excess liquid includes the positive electrode active material layer or the negative electrode active material layer that satisfies formula (1). [3] In at least one of the positive electrode active material layer and the negative electrode active material layer, when a porosity of an 80% region from the surface on the positive electrode substrate or the negative electrode substrate side in the thickness direction is VD and a porosity of a 20% region from the surface on the opposite side to the positive electrode substrate or the negative electrode substrate side is VC, the ratio of VC to VD (VC / VD) satisfies the following formula (2): (twenty one <VC / VD≦1.5 The nonaqueous electrolyte secondary battery according to [1] or [2], which satisfies the above condition. [4] The nonaqueous electrolyte secondary battery according to any one of [1] to [3], wherein the negative electrode active material layer satisfies the formula (1). [5] The device further includes an exterior housing that accommodates the electrode assembly and the nonaqueous electrolyte solution, the exterior body has a bottom, an upper part facing the bottom, a pair of first side walls standing upright from the edge of the bottom and facing each other, and a pair of second side walls standing upright from the edge of the bottom and facing each other, connecting the first side walls; When the longer of the width dimension in the direction in which the pair of first side walls face each other and the width dimension in the direction in which the pair of second side walls face each other is defined as W, and the height dimension from the bottom to the top is defined as H, The width dimension W is greater than 150 mm and less than or equal to 500 mm, The nonaqueous electrolyte secondary battery according to any one of [1] to [4], wherein the ratio (H / W) of the height dimension H to the width dimension W is 0.5 or less. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery that can achieve both high capacity and rapid chargeability. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. [Figure 2] FIG. 2 is a cross-sectional view of the battery as seen from the Y-axis direction. [Figure 3] FIG. 2 is a schematic diagram showing an example of the configuration of an electrode body. [Figure 4] FIG. 2 is a schematic diagram illustrating an example of a layer configuration of a positive electrode. [Figure 5] FIG. 2 is a schematic diagram illustrating an example of a layer structure of a negative electrode. [Figure 6] FIG. 2 is a schematic diagram showing an example of the positional relationship of electrode bodies in a battery. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all of the drawings, the scales of the components are appropriately adjusted to make them easier to understand, and the scales of the components shown in the drawings do not necessarily match the scales of the actual components.

[0010] <Nonaqueous electrolyte secondary battery> FIG. 1 is a perspective view showing an example of a nonaqueous electrolyte secondary battery (hereinafter also referred to as a battery) according to this embodiment. The battery 100 shown in FIG. 1 can be used for any purpose. For example, the battery 100 may be used as a main power source or a power source for power assist in an electric vehicle. A plurality of batteries 100 may be connected to form a battery module or a battery pack. The battery 100 may be a lithium-ion battery.

[0011] 1, the battery 100 has a rectangular shape. The battery 100 has electrode terminals 110 and an exterior body 120 (exterior can). In other words, the battery 100 is a rectangular secondary battery cell. The exterior body 120 may be made of, for example, an aluminum (Al) alloy.

[0012] The electrode terminal 110 may be formed on the exterior body 120. The electrode terminal 110 has a positive electrode terminal 111 and a negative electrode terminal 112 that are aligned along an X-axis direction (second direction) that is perpendicular to a Y-axis direction (first direction). The positive electrode terminal 111 and the negative electrode terminal 112 are spaced apart from each other in the X-axis direction.

[0013] The exterior body 120 has a rectangular parallelepiped shape and forms the outer appearance of the battery 100. The exterior body 120 includes a main body 120A and a sealing plate 120B that seals the opening of the main body 120A. The sealing plate 120B is joined to the main body 120A by welding.

[0014] The exterior body 120 has a bottom 122, an upper part 121 facing the bottom 122, a pair of first side walls 123 standing upright from the edge of the bottom 122 and facing each other, and a pair of second side walls 124 standing upright from the edge of the bottom 122 and facing each other, connecting the first side walls 123 to each other.

[0015] The upper portion 121 has a plane perpendicular to a Z-axis direction (third direction) that is perpendicular to the Y-axis direction and the X-axis direction. The electrode terminal 110 is disposed on the upper portion 121. The bottom portion 122 faces the upper portion 121 along the Z-axis direction. A gas exhaust valve 126 may be provided on the upper portion 121.

[0016] The first side wall 123 has a plane perpendicular to the Y-axis direction. The plane of the first side wall 123 may have the largest area among the multiple planes of the exterior body 120. The first side wall 123 has a rectangular shape when viewed in the Y-axis direction. When viewed in the Y-axis direction, the first side wall 123 has a rectangular shape with the X-axis direction as the longitudinal direction and the Z-axis direction as the lateral direction.

[0017] When the longer of the width dimension W1 in the direction in which the pair of first side walls 123 face each other and the width dimension W2 in the direction in which the pair of second side walls 124 face each other is defined as W, and the height dimension from the bottom 122 to the top 121 is defined as H, the width dimension W may be, for example, more than 150 mm and not more than 500 mm. The width dimension W may be the length of the long side of the flat surface of the one having the larger flat surface out of the first side wall 123 and the second side wall 124. The height dimension H may be, for example, not less than 50 mm and not more than 200 mm. The ratio of the height dimension H to the width dimension W (H / W) may be, for example, not more than 0.5, and may be not less than 0.1 and not more than 0.5.

[0018] Fig. 2 is a schematic diagram showing an example of the configuration of an electrode assembly. As shown in Fig. 2, in a battery 100, an exterior housing 120 contains an electrode assembly 130, a current collecting member 140, and a non-aqueous electrolyte (not shown). The current collecting member 140 includes a positive electrode current collecting member 141 and a negative electrode current collecting member 142. The electrode assembly 130 is connected to a positive electrode terminal 111 by the positive electrode current collecting member 141. The electrode assembly 130 is connected to a negative electrode terminal 112 by the negative electrode current collecting member 142.

[0019] The electrode body 130 may have a rectangular planar shape when viewed in the thickness direction (Y direction). The electrode body 130 may have, for example, a rectangular parallelepiped outer shape. The electrode body 130 may have, for example, a flat rectangular parallelepiped shape.

[0020] When the electrode assembly 130 has a rectangular planar shape when viewed in the thickness direction, the dimension of the long side may be, for example, 140 mm or more and 490 mm or less, and the dimension of the short side may be, for example, 50 mm or more and 240 mm or less. When the electrode assembly 130 has a rectangular shape when viewed in the thickness direction, the ratio of the length of the short side to the long side may be, for example, 0.1 or more and 0.5 or less. The thickness of the electrode assembly 130 may be, for example, 5 mm or more and 50 mm or less.

[0021] FIG. 3 is a schematic cross-sectional view showing an example of an electrode assembly 130. The electrode assembly 130 is a laminated type. The electrode assembly 130 includes a positive electrode plate 10, a negative electrode plate 20, and a separator 30. The electrode assembly 130 may include one or more positive electrode plates 10. The electrode assembly 130 may include one or more negative electrode plates 20. The electrode assembly 130 may include one or more separators 30. The separator 30 may be strip-shaped. The separator 30 is arranged by being folded back in a zigzag pattern. The positive electrode plates 10 and the negative electrode plates 20 are arranged by being alternately sandwiched between the separators 30 that are arranged by being folded back in a zigzag pattern.

[0022] The positive electrode plates 10 and negative electrode plates 20, which are alternately sandwiched between the separators 30 folded in a zigzag pattern, may have a rectangular shape in plan view (the shape when viewed from the stacking direction), such as a square or a rectangle. When the positive electrode plates 10 and negative electrode plates 20 have a rectangular shape in plan view, the dimensions of the positive electrode plates 10 in the direction perpendicular to the stacking direction (the dimensions of all four sides) may all be smaller than those of the negative electrode plates 20. The positive electrode plates 10 can be arranged so as not to protrude beyond the negative electrode plates 20 when the electrode body 130 is viewed from the stacking direction.

[0023] The separator 30 includes folded portions 32. The folded portions 32 are arranged on both end portions in a direction perpendicular to the stacking direction (Z direction). The electrode body 130 is arranged so that the folded portions 32 are on the top 121 side and bottom 122 side of the battery 100. The positive electrode plate 10 and the negative electrode plate 20 are each arranged between two adjacent folded portions 32 at one end. The positive electrode plate 10 is arranged between two adjacent folded portions 32 at one end, and the negative electrode plate 20 is arranged between two adjacent folded portions 32 at the other end. As a result, the positive electrode plates 10 and the negative electrode plates 20 are arranged alternately sandwiched between the separators 30 arranged by being folded in a zigzag pattern.

[0024] When the separator 30 is folded in a zigzag shape, the diffusion direction of the non-aqueous electrolyte in the electrode body 130 becomes three-way, which makes it easier to eliminate unevenness in the Li ion concentration on the electrode plane, and tends to make it easier to achieve both rapid charging performance and high capacity.

[0025] The separator 30 separates the positive electrode plate 10 from the negative electrode plate 20. The separator 30 may be, for example, two or more sheets. The separator 30 has electrical insulation properties. The separator 30 is permeable to the electrolyte. The separator 30 may be porous. The separator 30 may be made of, for example, polyolefin. The thickness of the separator 30 may be, for example, 5 to 50 μm.

[0026] FIG. 4 is a schematic cross-sectional view of a positive electrode plate in the thickness direction (Y direction). The positive electrode plate 10 includes a positive electrode substrate 12 and a positive electrode active material layer 11. The positive electrode active material layer 11 may be formed on both sides of the positive electrode substrate 12. The positive electrode active material layer 11 is formed on the surface of the positive electrode substrate 12. The positive electrode active material layer 11 may be formed directly on the surface of the positive electrode substrate 12. For example, an intervening layer may be formed between the positive electrode active material layer 11 and the positive electrode substrate 12. In this embodiment, even when an intervening layer is formed, the positive electrode active material layer 11 is considered to be formed on the surface of the positive electrode substrate 12. The intervening layer may have a smaller thickness than the positive electrode active material layer 11. The intervening layer may contain, for example, a conductive material, an insulating material, etc. The positive electrode active material layer 11 may be formed on only one surface of the positive electrode substrate 12. The positive electrode active material layer 11 may be formed on both the front and back surfaces of the positive electrode substrate 12.

[0027] The positive electrode active material layer 11 includes a positive electrode active material 13. The positive electrode active material 13 may be particles. The positive electrode active material layer 11 includes a plurality of positive electrode active materials 13. The positive electrode active material layer 11 may include two or more types of positive electrode active material particles having different particle sizes.

[0028] The positive electrode active material 13 may be a lithium nickel cobalt manganese composite oxide. The positive electrode active material 13 may have a molar ratio of Ni to metals other than lithium (hereinafter also referred to as Ni content) of 0.7 to 1.0. When the Ni content in the positive electrode active material 13 is within the above range, the battery tends to have a higher capacity.

[0029] The positive electrode active material 13 may include, for example, a layered metal oxide. The layered metal oxide is represented by the formula (i): Li 1-a1 Ni x1 Me 1 1-x1 O2(i) In formula (i), "a1" satisfies the relationship "-0.3≦a1≦0.3". "x1" satisfies the relationship 0.1≦x1≦0.9. "Me 1" includes at least one selected from the group consisting of Co, Mn, Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr and Ge.

[0030] Positive electrode active material 13 may contain at least one selected from the group consisting of, for example, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. Here, for example, a notation such as "(NiCoMn)" in a composition formula such as "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. When positive electrode active material layer 11 contains multiple types of positive electrode active materials, the multiple positive electrode active materials can have any chemical composition independently of one another.

[0031] The positive electrode active material layer 11 may further contain a conductive material, a binder, and the like in addition to the positive electrode active material 13. The conductive material may contain any component. The conductive material may include, for example, acetylene black. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The binder may include, for example, polyvinylidene fluoride (PVdF). The amount of the binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material.

[0032] The positive electrode substrate 12 is a conductive sheet. The positive electrode substrate 12 may have a thickness of, for example, 10 μm to 30 μm. The positive electrode substrate 12 may include, for example, an Al alloy foil, a pure Al foil, or the like. The positive electrode substrate 12 may be made of, for example, an Al alloy foil.

[0033] As shown in FIG. 4, the positive electrode active material layer 11 may have a laminated structure in which a second positive electrode active material layer 11B and a first positive electrode active material layer 11A are laminated in this order from the positive electrode substrate 12 side. The positive electrode active material layer 11 may be a single layer, or may be composed of two or more layers. The layer structure of the positive electrode active material layer 11 can be confirmed by observing a cross section of the positive electrode active material layer 11 with a transmission electron microscope. When the positive electrode active material layer 11 is composed of two or more layers, the thickness and density of the layers, and the types and contents of the positive electrode active material, binder, and conductive material may differ from one layer to another.

[0034] The positive electrode active material layer 11 may have a thickness of, for example, 10 μm to 200 μm. The positive electrode active material layer 11 may have a high density. The density of the positive electrode active material layer 11 is, for example, 3.5 g / cm. 3 It may have a density of 3.6 g / cm or more. 3 It may have a density of 3.7 g / cm or more. 3 The upper limit of the density is arbitrary. The positive electrode active material layer 11 may have a density of, for example, 3.8 g / cm 3 It may have the following density: When the positive electrode active material layer 11 is composed of two or more layers, the density is the average density of all the layers.

[0035] The positive electrode plate 10 is manufactured by applying a positive electrode slurry to the surface of a positive electrode substrate 12 to form a positive electrode active material layer 11, then rolling the positive electrode active material layer 11 and the positive electrode substrate 12 to produce a raw sheet, and cutting the sheet to a predetermined planar size according to the specifications of the battery 100. The positive electrode slurry is prepared by mixing the positive electrode active material with additional components. When the positive electrode active material layer 11 is composed of a second positive electrode active material layer 11B and a first positive electrode active material layer 11A, the positive electrode active material layer 11 can be formed by first applying a positive electrode slurry for forming the second positive electrode active material layer 11B onto the positive electrode substrate 12 to form the second positive electrode active material layer 11B, and then applying a positive electrode slurry for forming the first positive electrode active material layer 11A onto the second positive electrode active material layer 11B to form the first positive electrode active material layer 11A.

[0036] FIG. 5 is a schematic cross-sectional view of the negative electrode plate 20 in the thickness direction (Y direction). The negative electrode plate 20 includes a negative electrode active material layer 21 and a negative electrode substrate 22. The negative electrode active material layer 21 may be formed on both sides of the negative electrode substrate 22. The negative electrode substrate 22 may include, for example, copper foil. The negative electrode active material layer 21 is formed on the surface of the negative electrode substrate 22. The negative electrode active material layer 21 includes a negative electrode active material 23. The negative electrode active material 23 may be particles. The negative electrode active material layer 21 includes a plurality of negative electrode active materials 23. The negative electrode active material 23 may include any component. The negative electrode active material 23 may be, for example, graphite, soft carbon, hard carbon, Si, SiO, a Si-based alloy, Sn, SnO, a Sn-based alloy, and Li4Ti5O 12 The negative electrode active material layer 21 may further contain a binder or the like in addition to the negative electrode active material 23. The binder may contain, for example, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like.

[0037] As shown in FIG. 5, the anode active material layer 21 may have a laminated structure in which a second anode active material layer 21B and a first anode active material layer 21A are laminated in this order from the anode substrate 22 side. The anode active material layer 21 may be a single layer, or may be composed of two or more layers. The layer structure of the anode active material layer 21 can be confirmed by observing a cross section of the anode active material layer 21 with a transmission electron microscope. When the anode active material layer 21 is composed of two or more layers, the thickness and density of the layers, and the types and contents of the anode active material and binder may differ from one layer to another.

[0038] The negative electrode plate 20 is manufactured by applying a negative electrode slurry to the surface of the negative electrode substrate 22 to form the negative electrode active material layer 21, and then rolling the negative electrode active material layer 21 and the negative electrode substrate 22 to produce a raw sheet, which is then cut to a predetermined planar size according to the specifications of the battery 100. The negative electrode slurry is prepared by mixing the negative electrode active material with other components. When the negative electrode active material layer 21 is composed of a second negative electrode active material layer 21B and a first negative electrode active material layer 21A, the negative electrode active material layer 21 can be formed by a method in which the negative electrode slurry for forming the second negative electrode active material layer 21B is first applied to the negative electrode substrate 22 to form the second negative electrode active material layer 21B, and then the negative electrode slurry for forming the first negative electrode active material layer 21A is applied to the second negative electrode active material layer 21B to form the first negative electrode active material layer 21A.

[0039] The negative electrode active material layer 21 may have a thickness of, for example, 10 μm to 200 μm. The negative electrode active material layer 21 may have a high density. For example, the negative electrode active material layer 21 may have a density of 1.0 g / cm. 3 to 2.0 g / cm 3 The negative electrode active material layer 21 may have a density of, for example, 1.3 g / cm 3 to 1.7 g / cm 3 The negative electrode active material layer 21 may have a density of, for example, 1.3 g / cm 3 to 1.6 g / cm 3 When the negative electrode active material layer 21 is composed of two or more layers, the density is the average density of all the layers.

[0040] At least one of the positive electrode active material layer 11 and the negative electrode active material layer 21 has voids within the layer. When the porosity of a 50% region from the surface on the positive electrode substrate 12 side or the negative electrode substrate 22 side in the thickness direction of at least one of the positive electrode active material layer 11 and the negative electrode active material layer 21 is VB, and the porosity of a 50% region from the surface opposite to the positive electrode substrate 12 side or the negative electrode substrate 22 side is VA, the ratio of VA to VB (VA / VB) satisfies the following formula (1): (1) 1 <VA / VB≦1.4 Meet the following.

[0041] When at least one of the positive electrode active material layer 11 and the negative electrode active material layer 21 satisfies the above formula (1), the upper layer (opposite the substrate) of the active material layer has more voids and the lower layer (on the substrate side) has fewer voids. This makes it easier to eliminate unevenness in the Li-ion concentration in the thickness direction in the stacking direction, and tends to make it easier to achieve both rapid charge performance and high capacity. The ratio of VA to VB (VA / VB) is preferably 1.3 or less. Both the positive electrode active material layer 11 and the negative electrode active material layer 21 may satisfy formula (1). From the viewpoint of high capacity and rapid charge performance, it is preferable that the negative electrode active material layer 21 satisfies formula (1).

[0042] The porosity may vary stepwise or in a gradational manner in the thickness direction. For example, at least one of the positive electrode active material layer 11 and the negative electrode active material layer 21 may be composed of two or more layers with different porosities. The interior of the layer may have a higher porosity than the outermost surface portion.

[0043] When the positive electrode active material layer 11 is composed of a first positive electrode active material layer 11A and a second positive electrode active material layer 11B, and they have the same thickness (thickness ratio 1:1), the porosity VA may be the porosity of the first positive electrode active material layer 11A, and the porosity VB may be the porosity of the second positive electrode active material layer 11B. When the negative electrode active material layer 21 is composed of a first negative electrode active material layer 21A and a second negative electrode active material layer 21B, and they have the same thickness (thickness ratio 1:1), the porosity VA may be the porosity of the first negative electrode active material layer 21A, and the porosity VB may be the porosity of the second negative electrode active material layer 21B.

[0044] The porosity is the percentage (%) of void volume per unit volume of the positive electrode active material layer and the negative electrode active material layer (hereinafter collectively referred to as the active material layer). The porosity can be calculated according to the formula: V = (DE - d) / DE. In the formula, V is the porosity, DE is the apparent density of the active material layer, and d is the true density. DE can be calculated from the measured thickness and mass of the active material layer formed on the substrate. d can be measured by using a true density measuring device (e.g., BELPycno manufactured by MicrotracBEL) to measure the active material layer separated from the substrate. The porosities VA and VB of the positive electrode plate and the negative electrode plate (hereinafter collectively referred to as the electrode plate) can be measured, for example, by the following procedure. First, the thickness of the electrode plate is calculated, and then the thickness of the substrate is subtracted to calculate the thickness of the active material layer. Half of this thickness is defined as the thickness of the first active material layer and the second active material layer, respectively. Next, the mass of the active material layer is measured from a region that is 50% of the thickness direction from the surface opposite the substrate, and the density DE1 is calculated from the thickness and mass of half of the active material layer.The mass of the active material layer in the remaining region is then measured, and the density DE2 is calculated from the thickness and mass of half of the active material layer.The true density d1 of the active material layer sampled from a region that is 50% of the thickness direction is measured, and the true density d2 of the active material layer in the remaining region is similarly measured, and the porosities VA and VB can be calculated according to the formula VA = (DE1 - d1) / DE1 or the formula VB = (DE2 - d2)DE2.

[0045] The porosity VA is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. The porosity VA is preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less. The porosity VB is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. The porosity VB is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less.

[0046] The porosity can be adjusted by selecting the type of binder, for example, the type of particle shape or elasticity after compression, changing the amount of binder in the upper and lower layers when the layer structure is multilayered, or compressing the lower layer and then forming an upper layer coating and compressing it. For example, when forming a negative electrode active material layer that satisfies formula (1), formula (1) can be satisfied by using different types and amounts of SBR in the first and second negative electrode active material layers.

[0047] In at least one of the positive electrode active material layer 11 and the negative electrode active material layer 21, when the porosity of an 80% region from the surface on the positive electrode substrate 12 or negative electrode substrate 22 side in the thickness direction is VD and the porosity of a 20% region from the surface opposite to the positive electrode substrate 12 or negative electrode substrate 22 side is VC, the ratio of VC to VD (VC / VD) satisfies the following formula (2): (twenty one <VC / VD≦1.5 When at least one of the positive electrode active material layer 11 and the negative electrode active material layer 21 satisfies the above formula (1), the upper layer side (opposite the substrate) of the active material layer has many voids and the lower layer (on the substrate side) has few voids, which makes it easier to eliminate unevenness in the Li ion concentration in the thickness direction in the stacking direction, and tends to make it easier to achieve both rapid charging performance and high capacity.

[0048] Both the positive electrode active material layer 11 and the negative electrode active material layer 21 may satisfy formula (2). From the viewpoint of increasing capacity and rapid chargeability, it is preferable that the negative electrode active material layer 21 satisfy formula (2). When the positive electrode active material layer 11 is composed of a first positive electrode active material layer 11A and a second positive electrode active material layer 11B, the porosity V C may be the porosity of the first positive electrode active material layer 11A, and the porosity V D may be the porosity of the second positive electrode active material layer 11B. When the negative electrode active material layer 21 is composed of a first negative electrode active material layer 21A and a second negative electrode active material layer 21B, the porosity V C may be the porosity of the first negative electrode active material layer 21A, and the porosity V D may be the porosity of the second negative electrode active material layer 21B.

[0049] As shown in FIG. 6 , in the electrode assembly 130, the folded portion 32 on one side of the separator 30 may be in contact with excess nonaqueous electrolyte 40. The excess liquid 40 is nonaqueous electrolyte that is not impregnated in the electrode assembly 130 and is present on the bottom 122 side of the exterior body 120. In the electrode assembly 130, all of the folded portions 32 on one side of the separator 30 may be in contact with excess nonaqueous electrolyte 40. When the folded portions 32 on one side of the separator 30 are in contact with excess nonaqueous electrolyte 40, the positive electrode plate 10 or the negative electrode plate 20 can be disposed between adjacent folded portions 32 that are in contact with excess liquid 40. In FIG. 6 , the negative electrode plate 20 is disposed between adjacent folded portions 32 that are in contact with excess liquid 40. The positive electrode plate 10 or the negative electrode plate 20 disposed between adjacent folded portions 32 in contact with the excess liquid 40 preferably includes a positive electrode active material layer 11 or a negative electrode active material layer 21 that satisfies formula (1) from the viewpoints of rapid charge performance and high capacity. The negative electrode plate 20 including the negative electrode active material layer 21 that satisfies formula (1) is preferably disposed between adjacent folded portions 32 in contact with the excess liquid 40 from the viewpoints of rapid charge performance and high capacity. At least one of the positive electrode plate 10 and the negative electrode plate 20 may be in contact with the excess liquid 40. The positive electrode plate 10 including the positive electrode active material layer 11 that satisfies formula (1) may be in contact with the excess liquid 40. The negative electrode plate 20 including the negative electrode active material layer 21 that satisfies formula (1) may be in contact with the excess liquid 40.

[0050] (Non-aqueous electrolyte) The electrolyte solution includes a solvent and a supporting electrolyte. The solvent is aprotic. The solvent may include any component. For example, the solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL).

[0051] The supporting electrolyte is dissolved in a solvent. The supporting electrolyte may include, for example, at least one selected from the group consisting of LiPF, LiBF, and LiN(FSO). The supporting electrolyte may have, for example, a molar concentration of 0.5 mol / L to 2.0 mol / L. The supporting electrolyte may have, for example, a molar concentration of 0.8 mol / L to 1.2 mol / L.

[0052] The electrolyte may further contain an optional additive. For example, the electrolyte may contain 0.01% to 5% by mass of the additive. The additive may include, for example, at least one selected from the group consisting of vinylene carbonate (VC), lithium difluorophosphate (LiPOF), lithium fluorosulfonate (FSOLi), and lithium bis(oxalato)borate (LiBOB).

[0053] <Battery manufacturing method> The method for manufacturing a battery in this embodiment includes a step (A) of inserting the electrode assembly 130 into the exterior body 120, and a step (B) of injecting a non-aqueous electrolyte solution.

[0054] In step (A) of inserting the electrode body into the exterior body, the electrode body 130 is housed in the exterior body 120. The electrode body 130 can be connected to the positive electrode terminal 111 by a positive electrode current collecting member 141. The electrode body 130 can be connected to the negative electrode terminal 112 by, for example, a negative electrode current collecting member 142.

[0055] In step (B) of injecting a non-aqueous electrolyte, the non-aqueous electrolyte is injected into the exterior body 120. The non-aqueous electrolyte is impregnated into the electrode assembly 130. After the non-aqueous electrolyte is injected, the exterior body 120 is sealed. After the non-aqueous electrolyte is impregnated into the electrode assembly 130, excess liquid may be generated.

[0056] This completes the manufacturing process of the battery 100. The battery 100 can be a battery that can achieve both high capacity and rapid chargeability. [Example]

[0057] The present invention will be described in more detail below with reference to examples.

[0058] [Measurement of void ratio] (Preparation of negative electrode plate A) The negative electrode paste A used in the examples was applied to both sides of a copper (Cu) foil having a thickness of 8 μm, dried, and then pressed to a predetermined thickness to prepare a negative electrode plate A. The total coating weight on both sides of the negative electrode plate A was 200 m 2 / g, the total thickness was 133 μm, and the packing density was 1.50 g / cc. The packing density was Z [g / cc], and the coating weight of the active material layer was X [m 2 / g] and thickness Y [μm], it was calculated according to the formula: Z=X / Y.

[0059] (Preparation of negative electrode plate B) The negative electrode paste B used in the examples was applied to both sides of a copper (Cu) foil having a thickness of 8 μm, dried, and then pressed to a predetermined thickness to prepare a negative electrode plate B. The total coating weight on both sides of the negative electrode plate B was 200 m 2 / g, total thickness 152 μm, and packing density 1.32 g / cc.

[0060] (Porosity measurement) Negative electrode plate A and negative electrode plate B were punched out to specified planar dimensions, and their thickness and mass were measured. The density DE of the active material layer was calculated by subtracting the mass of the Cu foil, which was measured previously. The sampled active material layer was placed in a cell of a true density measuring device (BELPycno, manufactured by MicrotracBEL) to measure the true density d. When the porosity was V, the porosity was calculated according to the formula: V = (DE - d) / DE. When the porosity of negative electrode plate A was VA and the porosity of negative electrode plate B was VB, the porosity ratio (VA / VB) was 1.3.

[0061] [Resistant increase rate evaluation] The IV resistance value of the battery adjusted to 50% SOC at 25°C for 10 seconds was measured as the pre-cycle IV resistance value according to the measurement method described below. Next, the following rapid charge cycle was performed. After that, the battery was adjusted to 50% SOC again, and the IV resistance value at 25°C for 10 seconds was measured as the post-cycle IV resistance value according to the measurement method described below. The rate of increase in the post-cycle IV resistance value relative to the pre-cycle IV resistance value was calculated as the resistance increase rate. (IV resistance measurement method for 10 seconds at 25°C) After adjusting the battery to 50% SOC at 25°C, a constant current (I) of 200A to 600A was applied for 10 seconds, and the difference (=V0-V10) between the voltage before application (V0) and the voltage after 10 seconds of application (V10) was obtained. The voltage difference divided by the current value I [=(V0-V10) / I] was used as the IV resistance at 25°C for 10 seconds. (Fast charging cycle test) After adjusting the SOC to 15%, the battery was charged at 3C, charged to 78% SOC, and then discharged at 1C to 15% SOC. This cycle was repeated 45 times.

[0062] Example 1 [Preparation of negative electrode plate] (Preparation of negative electrode paste) Water was used as a solvent, and graphite particles (D50 = 17 μm, BET specific surface area = 2.2 m) were used as the negative electrode active material. 2The graphite and CMC were mixed and kneaded using a mixing granulator (Planetary Disper, manufactured by Asada Iron Works) with carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders in a mass ratio of 98.3% by mass to 1% by mass to prepare a negative electrode paste. SBR-A and SBR-B were used for negative electrode plates A and B, respectively. SBR-A has a higher single-film Young's modulus than SBR-B. The mixing and kneading process was carried out as follows: First, the graphite and CMC were dry-mixed, and then water was added and kneaded to prepare a kneaded mixture. This mixture was then divided into two portions. SBR-A and SBR-B were then added to each portion and mixed to prepare negative electrode paste A containing SBR-A and negative electrode paste B containing SBR-B.

[0063] (Preparation of negative electrode plate D) Negative electrode paste A was applied to both sides of a Cu foil with a thickness of 8 μm and dried, and then negative electrode paste B was applied to the dried coating film of negative electrode paste A formed on both sides of the Cu foil, respectively, and after drying, the resulting mixture was pressed to a predetermined thickness to produce negative electrode plate D.

[0064] Based on the density obtained when checking the gap difference described above, negative electrode paste A and negative electrode paste B were applied to the Cu foil so that the layer thickness after compression would be 1:1. Negative electrode plate D had a coating weight of 53.2 m on both sides of negative electrode paste A and negative electrode paste B. 2 / g and 46.8m 2 The active material layer of negative electrode plate D had a total thickness of 142 μm on both sides of negative electrode plate D and a packing density of 1.41 g / cc.

[0065] [Preparation of positive electrode plate] A positive electrode paste was prepared by mixing and kneading lithium nickel cobalt manganese composite oxide (NCM) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder in a mass ratio of NCM / AB / PVDF = 97.5 / 1.5 / 1 (mass%) in N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode paste was applied to a 15 μm thick aluminum (Al) foil, dried, pressed to the specified thickness, and processed to the specified dimensions to prepare a positive electrode plate.

[0066] [Preparation of test battery] Negative electrode plate D and positive electrode plate were each cut into single plates. A strip-shaped separator was folded back at equal intervals in a zigzag pattern. Negative electrode plate D and positive electrode plate were alternately sandwiched between adjacent folded portions of the folded separator to prepare a stacked electrode assembly TD with a zigzag separator. The prepared electrode assembly TD was inserted into an outer casing, nonaqueous electrolyte was poured into it, and the opening of the outer casing was sealed to prepare a test cell (prismatic cell). The nonaqueous electrolyte used was 1M LiPF6 as the Li salt, with a solvent of EC / EMC / DMC = 20 / 40 / 40 (volume%). After the electrode assembly TD was impregnated with the nonaqueous electrolyte, the electrode assembly TD was observed using an X-ray fluoroscopy device. All of the folded portions on one side of the separator were in contact with the excess nonaqueous electrolyte, and negative electrode plate D was placed between the adjacent folded portions in contact with the excess liquid. The results are shown in Table 1.

[0067] <Comparative Example 1> A negative electrode paste was prepared by mixing CMC and SBR-C binders in a mass ratio of 53.2:46.8 (mass%), and the paste was applied to both sides of a Cu foil, dried, and then pressed to a predetermined thickness to prepare a negative electrode plate S. A test battery was prepared in the same manner as in Example 1, except that the negative electrode plate S had a total coating weight of 200 m on both sides. 2 / g, the total thickness of the active material layers on both sides was 142 μm, and the packing density was 1.41 g / cc. After the electrode body TS was impregnated with the nonaqueous electrolyte, the electrode body TS was observed using an X-ray fluoroscopy device. All of the folded portions on one side of the separator were in contact with the excess nonaqueous electrolyte, and the negative electrode plate S was placed between the adjacent folded portions in contact with the excess liquid. The results are shown in Table 1.

[0068] <Comparative Example 2> A test battery was fabricated in the same manner as in Example 1, except that a laminate formed by stacking negative electrode plate D, a separator, a positive electrode plate, and a separator in this order was wound to fabricate a wound electrode body WD. The results are shown in Table 1.

[0069] <Comparative Example 3> A test battery was fabricated in the same manner as in Example 1, except that a laminate formed by stacking a negative electrode plate S, a separator, a positive electrode plate, and a separator in this order was wound to fabricate a wound electrode body WS. The results are shown in Table 1.

[0070] [Table 1]

[0071] In Example 1, the resistance increase rate was lower than in Comparative Examples 1 to 3. It is clear that the nonaqueous electrolyte secondary battery according to the present disclosure has excellent rapid charging properties despite having a high capacity. [Explanation of symbols]

[0072] 10 positive electrode plate, 11 positive electrode active material layer, 11A first positive electrode active material layer, 11B second positive electrode active material layer, 12 positive electrode substrate, 13 positive electrode active material, 20 negative electrode plate, 21 negative electrode active material layer, 21A first negative electrode active material layer, 21B second negative electrode active material layer, 22 negative electrode substrate, 23 negative electrode active material, 30 separator, 32 folded portion, 40 excess liquid, 100 battery, 110 electrode terminal, 111 positive electrode terminal, 112 negative electrode terminal, 120 outer casing, 120A main body, 120B sealing plate, 121 upper portion, 122 bottom portion, 123 first side wall, 124 second side wall, 126 gas release valve, 130 electrode body, 140 current collecting member, 141 positive electrode current collecting member, 142 Negative electrode current collecting member, H height dimension, W1 width dimension, W2 width dimension.

Claims

1. A non-aqueous electrolyte secondary battery including an electrode assembly and a non-aqueous electrolyte solution, the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator; the positive electrode plate includes a positive electrode substrate and a positive electrode active material layer, the negative electrode plate includes a negative electrode substrate and a negative electrode active material layer, The separator is folded back in a zigzag pattern, the positive electrode plates and the negative electrode plates are alternately sandwiched between the folded separators, In at least one of the positive electrode active material layer and the negative electrode active material layer, when a porosity of a 50% region from the surface on the positive electrode substrate side or the negative electrode substrate side in the thickness direction is VB and a 50% region from the surface on the positive electrode substrate side or the opposite side to the negative electrode substrate side is VA, the ratio of VA to VB (VA / VB) satisfies the following formula (1): (1) 1<VA / VB≦1.4 A non-aqueous electrolyte secondary battery that satisfies the above requirements.

2. In the electrode assembly, a folded portion on one side of the separator is in contact with the excess liquid of the nonaqueous electrolyte, the positive electrode plate or the negative electrode plate is disposed between adjacent folded portions that are in contact with the excess liquid; 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode plate or the negative electrode plate disposed between adjacent folded portions in contact with the excess liquid includes the positive electrode active material layer or the negative electrode active material layer that satisfies the formula (1).

3. In at least one of the positive electrode active material layer and the negative electrode active material layer, when a porosity of an 80% region from the surface on the positive electrode substrate or the negative electrode substrate side in the thickness direction is VD and a porosity of a 20% region from the surface on the opposite side to the positive electrode substrate or the negative electrode substrate side is VC, the ratio of VC to VD (VC / VD) satisfies the following formula (2): (2) 1<VC / VD≦1.5 The nonaqueous electrolyte secondary battery according to claim 1 , which satisfies the above.

4. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the negative electrode active material layer satisfies the formula (1).

5. The electrode assembly further includes an outer casing that accommodates the electrode assembly and the nonaqueous electrolyte solution. the exterior body has a bottom, an upper part facing the bottom, a pair of first side walls standing upright from the edge of the bottom and facing each other, and a pair of second side walls standing upright from the edge of the bottom and facing each other, connecting the first side walls, When the longer of the width dimension in the direction in which the pair of first side walls face each other and the width dimension in the direction in which the pair of second side walls face each other is defined as W, and the height dimension from the bottom to the top is defined as H, The width dimension W is greater than 150 mm and less than or equal to 500 mm, 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio (H / W) of said height dimension H to said width dimension W is 0.5 or less.

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