Secondary battery and separator

Abstract

This secondary battery comprises an electrode group and a nonaqueous electrolyte. The electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode. The separator comprises a base material and a spacer disposed on a main surface of the base material. The spacer includes linear protrusions, and when the linear protrusions are viewed from the thickness direction of the linear protrusions in a plan view of the separator, each linear protrusion has end sections formed along the edge of a positioning region where the linear protrusion is positioned, and a main section other than the end section. Each linear protrusion has a thick-walled portion at the end sections, the thick-walled portions being thicker than the main section.

Description

Secondary batteries and separators Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2024-192158, filed with the Japan Patent Office on 31 October 2024, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to a secondary battery and a separator used in a secondary battery.

[0003] A secondary battery comprises an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes. Examples of secondary batteries include lithium-ion batteries and lithium secondary batteries (lithium metal secondary batteries). In the negative electrode of a lithium secondary battery, lithium metal is deposited during charging, and the lithium metal dissolves into the non-aqueous electrolyte during discharge.

[0004] To suppress volume changes in the electrode group during charging and discharging, it is conceivable to place a spacer between the separator substrate and the positive or negative electrode. In lithium secondary batteries, the spacer creates a space for accommodating the lithium metal deposited on the negative electrode during charging.

[0005] Patent Document 1 proposes a lithium secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, wherein lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves from the negative electrode during discharge, and a spacer is provided between at least one of the positive electrode and the negative electrode and the separator, the first length of the separator in a first direction D1 is smaller than the second length in a second direction D2 intersecting the first direction D1, and at least one of the angle on the spacer side formed by the separator and the spacer, and the angle on the spacer side formed by the electrode in contact with the spacer and the spacer, is greater than 90° in the cross section of the spacer cut along the thickness direction of the separator and the first direction D1.

[0006] International Publication No. 2021 / 192645

[0007] In recent years, there has been a growing need to suppress the degradation of cycle characteristics in secondary batteries equipped with spacers.

[0008] One aspect of the present disclosure relates to a secondary battery comprising an electrode group and a non-aqueous electrolyte, wherein the electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, the separator comprises a substrate and a spacer disposed on the main surface of the substrate, the spacer includes a linear projection, and in a plan view of the separator, when the linear projection is viewed from the thickness direction of the linear projection, the linear projection has an end portion formed along the edge of the arrangement region where the linear projection is located and a main portion other than the end portion, and the linear projection has a thicker portion at the end portion that is thicker than the main portion.

[0009] Another aspect of the present disclosure relates to a separator for a secondary battery, comprising a base material and a spacer disposed on the main surface of the base material, wherein the spacer includes a linear projection, and in a plan view of the separator, when the linear projection is viewed from the thickness direction of the linear projection, the linear projection has an end portion formed along the edge of the arrangement region where the linear projection is disposed, and a main portion other than the end portion, and the linear projection has a thicker portion at the end portion that is thicker than the main portion.

[0010] According to this disclosure, the degradation of the cycle characteristics of a secondary battery equipped with a spacer can be suppressed. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0011] This is a schematic top view showing an example of a separator. This is an enlarged top view of a part of the spacer in Figure 1. This is a schematic front view showing an example of a linear protrusion. This is a schematic front view showing another example of a linear protrusion. This is a schematic front view showing yet another example of a linear protrusion. This is a schematic longitudinal cross-sectional view showing an example of a secondary battery. This is a schematic cross-sectional view showing the main part of the electrode group.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits are given as examples for numerical values ​​of specific physical properties or conditions, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0013] This disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0014] A secondary battery according to the embodiment of this disclosure comprises an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode. The separator comprises a substrate and a spacer disposed on the main surface of the substrate. The spacer includes a linear projection, and in a plan view of the separator, when the linear projection is viewed from the thickness direction of the linear projection (normal direction to the main surface of the substrate), the linear projection has an end portion (hereinafter also referred to as end portion E) formed along the edge of the arrangement region where the linear projection is located, and a main portion other than end portion E. The linear projection has a thicker portion at end portion E that is thicker than the main portion.

[0015] In this disclosure, by providing a spacer, a space is formed between the electrode and the separator substrate, thereby suppressing volume changes of the electrode group due to expansion and contraction of the electrodes during charging and discharging, and suppressing deterioration of cycle characteristics due to electrode buckling, etc., when the volume change of the electrode group is large.

[0016] When the spacer is constructed using linear protrusions, a stable space is formed between the positive and negative electrodes in the opposing regions of the positive and negative electrodes, making it easier to ensure a uniform distance between the positive and negative electrodes and to stably obtain an electrode group of a predetermined shape.

[0017] On the other hand, near the linear protrusions within the electrode group, Li ions released from the positive electrode during charging move around the linear protrusions and reach the negative electrode. As a result, the amount of Li deposited (or the amount of Li ions absorbed) increases near the edges of the linear protrusions, causing localized stress concentration, which can lead to the edges of the linear protrusions collapsing. Consequently, the stability of space formation by the spacers decreases, the volume change of the electrode group increases, and the cycle characteristics may deteriorate.

[0018] In contrast, in this disclosure, the strength of the end portion E is increased by providing a thicker portion than the main portion at the end portion E formed along the edge of the arrangement region where the linear protrusions are arranged. As a result, crushing of the end portion E during repeated charging and discharging is suppressed, the space formed by the spacer is stably maintained, and the shape of the electrode group is stably maintained. In addition, a large space is formed near the thicker portion, and stress concentration due to increased Li deposition near the edge of the linear protrusions is alleviated. As a result, the cycle characteristics are greatly improved.

[0019] The linear projection may have a thickened portion throughout the entire end E, or a thickened portion in part of the end E. The end E includes both ends in the longitudinal direction of the linear projection and both ends in the width direction of the linear projection. The linear projection may have a thickened portion at at least one end of both ends in the longitudinal direction of the linear projection. The linear projection may have a thickened portion at at least one end of both ends in the width direction of the linear projection. The linear projection may have a thickened portion at both ends in the longitudinal direction and / or at both ends in the width direction of the linear projection.

[0020] The main part may have a constant thickness T1, and the end part E may have a constant thickness T2 (T1 < T2). Also, the end part E (the end part E near the defect region) may have the following first region, second region, and third region from the side closer to the main part. In the first region, as the distance from the main part increases, the thickness of the linear convex part continuously increases from T1 or more and less than T2 to T2. In the second region, the linear convex part has a constant thickness T2. In the third region, as the distance from the main part increases, the thickness of the linear convex part continuously decreases from T2 to T3. When T1 ≤ T3, a thick part is formed over the entire end part E. When T3 < T1, a thin part is formed in a part of the third region (the region continuously decreasing from T1 to T3 on the defect region side of the third region).

[0021] In the linear convex part, the ratio of the thickness T2 of the thick part to the thickness T1 of the main part: T2 / T1 may be 1.05 or more and 1.5 or less, may be 1.1 or more and 1.5 or less, or may be 1.1 or more and 1.4 or less. The thickness T1 of the main part may be, for example, 15 μm or more and 70 μm or less.

[0022] The linear convex part is preferably formed along a predetermined pattern. In this case, the stability of space formation by the spacer is further improved over the entire opposing region of the positive and negative electrodes, and the stability of the shape of the electrode group is further improved.

[0023] The predetermined pattern preferably has an arrangement region where the linear convex part is arranged and a defect region where the linear convex part is not arranged in a part of the length direction in which the linear convex part extends. By providing the defect region, the liquid circulation property of the electrode group is improved. The defect part (the gap formed between adjacent linear convex parts) formed by the defect region serves as a flow path for the non-aqueous electrolyte. In this case, the linear convex part has an end part E near the defect region. In this case, the linear convex part preferably has a thick part with a thickness larger than that of the main part at the end part E near the defect region.

[0024] When the linear convex portion has a thick portion with a greater thickness than the main portion at the end E near the defect region, the strength of the end E near the defect region is increased. As a result, the end E near the defect region is prevented from being crushed, the decrease in the liquid circulation property of the electrode group due to the occlusion of the defect portion is suppressed, and the decrease in the cycle characteristics due to the decrease in the liquid circulation property of the electrode group is suppressed. Since stress is likely to be applied to the linear convex portion at the end near the defect region due to the expansion and contraction of the electrode during charge and discharge, the effect of forming the thick portion is significantly obtained.

[0025] The defect regions may be formed on both sides in the length direction of the arrangement region, and the linear convex portion may have ends E near the defect regions on both sides in the length direction of the main portion. That is, both ends E1 and E2 in the length direction of the linear convex portion may be the ends E near the defect regions. The linear convex portion may have an end E1 near the defect region on one side in the length direction of the main portion and an end E2 near the defect region on the other side in the length direction of the main portion. It is sufficient that at least one of the ends E1 and E2 on both sides in the length direction of the main portion has a thick portion.

[0026] The linear protrusion preferably has thickened sections at the ends E near the defect region, which are formed on both sides in the longitudinal direction of the main part. That is, the linear protrusion preferably has a thickened section P1 at end E1 and a thickened section P2 at end E2. From the viewpoint of easily obtaining the effects of the thickened section, the ratio of the total length LE of the thickened sections P1 and P2 to the length L0 of the linear protrusion, LE / L0, is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.4 or more. Furthermore, from the viewpoint of improving energy density and reducing internal resistance, LE / L0 is preferably 0.55 or less, and more preferably 0.50 or less. When LE / L0 is 0.55 or less (or 0.50 or less), the main part, which is thinner than the thickened section, is sufficiently formed, which makes it easier to suppress the increase in the size of the electrode group (diameter of the electrode group in the case of a wound type) and the resulting decrease in energy density. Furthermore, in this case, the main portion is sufficiently formed, which helps to suppress the increase in the distance between the positive and negative electrodes of the electrode group and the resulting increase in internal resistance. LE can also be said to be the total length of the ends E1 and E2. The length L1 of the thickened portion P1 may be approximately the same as (LE / 2) or different from the length L2 of the thickened portion P2.

[0027] Note that the length L0 of the linear protrusion is the length dimension of the linear protrusion. The length of the thickened portion is the dimension of the thickened portion in the length direction of the linear protrusion. The total length of the thickened portion is the sum of the length of the thickened portion P1 formed on one side of the main portion in the length direction (one end E1 of the linear protrusion in the length direction) and the length of the thickened portion P2 formed on the other side of the main portion in the length direction (the other end E2 of the linear protrusion in the length direction).

[0028] If the spacer includes multiple linear protrusions, then 1 / 2 or more (or 4 / 5 or more) of the total number of linear protrusions may have a thickened portion at their end E. Each of the multiple linear protrusions may also have a thickened portion at its end E. The larger the proportion of linear protrusions that have a thickened portion at their end E, the easier it is to obtain the effect of forming the thickened portion.

[0029] The spacer preferably includes linear protrusions formed along a predetermined pattern. The predetermined repeating pattern may be, for example, a mesh pattern or a stripe pattern. The mesh pattern may be an aggregate of polygons. Examples of mesh patterns include shapes in which polygons are combined so that they share sides. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may be combined. Examples of mesh patterns include honeycomb shapes where the mesh shape is hexagonal, and grid shapes where the mesh shape is quadrilateral, etc.

[0030] The linear protrusions may be straight or curved. When the arrangement pattern is honeycomb, stripe, etc., the spacer is composed of straight linear protrusions. The linear protrusions may be arranged continuously or intermittently. The linear protrusions may be arranged continuously or intermittently along a predetermined pattern. Defects may be formed by the intermittent arrangement of the linear protrusions.

[0031] The predetermined pattern may include only the placement area, or it may include both the placement area and the defect area. If it includes only the placement area, the linear protrusions are arranged continuously. If it includes the defect area, a defect is formed where the linear protrusions are not arranged along the predetermined pattern. The placement area (linear protrusions) and the defect area (defect) may be formed alternately. The linear protrusions may be arranged intermittently in the longitudinal direction. For example, if the placement pattern is stripe-shaped, multiple linear protrusions are arranged parallel to each other and spaced apart. Each of the multiple linear protrusions may be arranged intermittently. In the case of a stripe pattern, the length of one defect (defect area) may be, for example, 0.1 mm or more and 2.0 mm or less.

[0032] Furthermore, if the arrangement pattern is honeycomb (or grid), line-shaped protrusions (arrangement areas) may be formed in the center of each side forming the honeycomb hexagon (or grid-like quadrilateral), and defects (defect areas) may be formed at both ends of each side.

[0033] Secondary batteries include lithium secondary batteries (lithium metal secondary batteries) and lithium-ion batteries. For example, the negative electrode of a lithium secondary battery is an electrode in which lithium metal is deposited during charging and dissolves in a non-aqueous electrolyte during discharge. The negative electrode of a lithium-ion battery is an electrode in which lithium ions are absorbed into the negative electrode active material during charging and released from the negative electrode active material during discharge.

[0034] An electrode group may be constructed, for example, by laminating or winding a positive electrode, a negative electrode, and a separator (a substrate on which a spacer is placed). An electrode group may also be constructed by laminating a positive electrode, a negative electrode, and a separator in a zigzag pattern. The outer shape of a wound electrode group may be cylindrical or elliptical. Typically, a wound electrode group uses a strip-shaped positive electrode, a negative electrode, and a separator, and the length direction of the positive electrode, negative electrode, and separator is the winding direction.

[0035] Here, Figure 1 is a schematic top view showing an example of a separator, and is a top view of the separator (base material) in a plan view. Figure 2 is an enlarged top view of a part of the honeycomb-shaped spacer in Figure 1, and is a top view showing a part of the honeycomb-shaped spacer when the spacer (line-shaped protrusion) is viewed from the direction normal to the main surface of the base material in a plan view of the separator (base material). The LS direction in Figure 2 is the length direction of the line-shaped protrusion (arrangement area) arranged along the dashed line in Figure 2. Figure 3 is a schematic front view showing an example of a line-shaped protrusion, and is a front view of the side of the line-shaped protrusion in Figure 2 when viewed from the width direction of the line-shaped protrusion (direction of arrow X in Figure 2). Note that each figure is a schematic diagram, and the aspect ratio of the length and width of each component does not necessarily reflect the actual dimensions.

[0036] The separator 100 in Figure 1 comprises a sheet-like base material 50 and a spacer 53 arranged on one main surface of the base material 50. The base material 50 is strip-shaped, and LD in Figure 1 indicates the longitudinal direction of the base material 50. The spacer 53 is composed of line-shaped protrusions 53a, and the line-shaped protrusions 53a form a space 14s. The line-shaped protrusions 53a have a width W. The width W may be, for example, 0.1 mm or more and 2 mm or less, or 0.2 mm or more and 1.5 mm or less.

[0037] The spacer 53 includes linear protrusions 53a formed along a honeycomb pattern (dashed line in Figure 2). The honeycomb pattern has an arrangement region 60 where the linear protrusions 53a are arranged, and a defect region 70 in which the linear protrusions 53a are not arranged in a part of the length direction in which the linear protrusions 53a extend (length direction of the dashed line in Figure 2). The linear protrusions 53a have ends 61 and 62 near the defect region 70, and a main portion 63 other than the ends 61 and 62. The ends of the main portion 63 in the width direction do not include thickened portions and are therefore considered to be part of the main portion.

[0038] As shown in Figures 1 and 2, a line-shaped protrusion 53a (arrangement area 60) is formed in the center of each side forming the honeycomb hexagon, and a defect 53b (defect area 70) is formed at both ends of each side. One hexagonal mesh is formed by arranging six line-shaped protrusions 53a at predetermined intervals.

[0039] The defect regions 70 are located on both sides of the length of the arrangement region 60. The linear protrusion 53a has an end 61 on one side of the length of the main portion 63 and an end 62 on the other side of the length of the main portion 63. The defect regions 70 form a defect portion 53b where the linear protrusion 53a is not located. Defect portions 53b are formed on both sides of the length of the linear protrusion 53a.

[0040] In Figure 2, L0 represents the length of one linear protrusion 53a (arrangement area 60). Ld represents the length of one defect 53b (defect area 70). The ratio of the length Ld of the defect 53b to the length L0 of the linear protrusion 53a, Ld / L0, may be, for example, 1 / 20 or more and 1 / 4 or less, 1 / 20 or more and 1 / 5 or less, or 1 / 10 or more and 1 / 4 or less (or 1 / 5 or less).

[0041] The length L0 of the linear protrusion 53a may be, for example, 0.5 mm or more and 5 mm or less. From the viewpoint of improving the fluidity of the non-aqueous electrolyte, the length Ld of the defect 53b may be 0.025 mm or more, 0.1 mm or more, or 0.2 mm or more. From the viewpoint of ensuring the stability of space formation by the spacer, the length Ld of the defect 53b may be 1.25 mm or less, 1.0 mm or less, or 0.8 mm or less. The length Ld of the defect 53b may be, for example, 0.025 mm or more and 1.25 mm or less, 0.1 mm or more and 1.0 mm or less, or 0.2 mm or more and 0.8 mm or less.

[0042] The linear projection 53a has thicker sections P1 and P2 at its ends 61 and 62, which are thicker than the main section 63. The entirety of the ends 61 and 62 of the linear projection 53a is composed of the thicker sections P1 and P2.

[0043] The ratio of the total length of the thickened portion P1 (end 61) L1 and the thickened portion P2 (end 62) L2 to the length L0 of the linear protrusion 53a, (L1 + L2) / L0, may be within the range of LE / L0 as illustrated above, and may be, for example, 0.1 or more (or 0.4 or more). Note that LE = L1 + L2. The length L1 of the thickened portion P1 (end 61) may be approximately the same as the length L2 of the thickened portion P2 (end 62) (LE / 2), or it may be different.

[0044] The main portion 63 has a thickness T1, and the thick-walled portions P1 and P2 each have a thickness T2. The ratio of the thickness T2 of the thick-walled portions P1 and P2 to the thickness T1 of the main portion 63, T2 / T1, may be within the range exemplified above, for example, 1.1 or more and 1.5 or less. The thickness of the thick-walled portion P1 is approximately the same as the thickness of the thick-walled portion P2, but may be different. The thickness T1 of the main portion 63 may be, for example, 15 μm or more and 70 μm or less.

[0045] In Figure 3, the ends 61 and 62 of the linear protrusion 53a have a rectangular shape that protrudes in the thickness direction from the main part 63, and the entirety of the ends 61 and 62 is composed of thickened parts P1 and P2 having a constant thickness T2.

[0046] The linear projection 53a in Figure 3 has thickened portions P1 and P2 throughout its entirety at the ends 61 and 62, but may also have thickened portions P1 and P2 only in a portion of the ends 61 and 62 (for example, a portion of the ends 61 and 62 on the main portion 63 side). In the longitudinal direction (LS direction) of the linear projection 63, the ratio of the length of the thickened portions P1 and P2 to the length of the ends 61 and 62 may be 50% or more, or it may be 70% or more or 80% or more.

[0047] Note that the linear projection is not limited to the linear projection 53a shown in Figure 3. For example, it may be the linear projection (ends 61, 62) shown in Figure 4 or Figure 5.

[0048] In Figure 4, the ends 61 and 62 of the linear protrusion 53a have a shape that is more rounded in the thickness direction than the main part 63. The entirety of the ends 61 and 62 is composed of thickened portions P1 and P2. The thickened portions P1 and P2 (ends 61 and 62) have a maximum thickness T2 at the center in the LS direction.

[0049] In Figure 5, a portion of the ends 61 and 62 of the linear protrusion 53a on the main portion 63 side has a shape that protrudes more in the thickness direction than the main portion 63 and is composed of thickened portions P1 and P2. The thickened portions P1 and P2 have a maximum thickness T2 at the center in the LS direction. A portion of the ends 61 and 62 on the defect region 70 side is composed of thinned portions P3 and P4 that are thinner than the main portion 63. The outer shape of the ends 61 and 62 has the shape of a part of a trapezoid. The three corners formed on the ends 61 and 62 may be rounded. In the case of Figure 5, the ratio of the lengths L1 and L2 of the thickened portions P1 and P2 in the LS direction to the length of the ends 61 and 62 in the LS direction may be, for example, 60 to 90%, or 70 to 90%.

[0050] From the viewpoint of suppressing stress concentration at the tip (rectangular corner) when the tip of end E is rectangular, the tips of ends 61 and 62 may be the line-shaped protrusions shown in Figure 4, which have a rounded shape. Similarly, from the viewpoint of suppressing stress concentration at the tip (rectangular corner) when the tip of end E is rectangular, the line-shaped protrusions shown in Figure 5 may be formed with thin-walled portions P3 and P4 at the tips of ends 61 and 62.

[0051] In this embodiment, the defective portion (defect region) is formed on both sides in the longitudinal direction of the linear protrusion (placement region), but it may also be formed on either one side in the longitudinal direction of the linear protrusion (placement region). In this embodiment, the end E near the defective region is formed on both sides in the longitudinal direction of the main portion, but it may also be formed on either one side in the longitudinal direction of the main portion. In this embodiment, a thickened portion is formed at one end E1 (end 61) of the main portion and at the other end E2 (end 62) of the main portion, but a thickened portion may also be formed at either end E1 or end E2.

[0052] The honeycomb-shaped spacer 53 includes a plurality of linear protrusions 53a and a plurality of defective portions 53b. In Figure 1, linear protrusions 53a (placement areas) are formed in the center of each side forming the honeycomb hexagon, and defective portions 53b (defect areas) are formed at both ends of each side, but the honeycomb pattern having defective areas is not limited to this. Linear protrusions 53a (placement areas) may be formed at both ends of each side forming the honeycomb hexagon, and defective portions 53b (defect areas) may be formed in the center of each side.

[0053] It is preferable that 1 / 2 or more (or 4 / 5 or more) of the total number of multiple linear protrusions are linear protrusions 53a having thickened portions P1 and P2 at their ends 61 and 62. It is even more preferable that all of the multiple linear protrusions are linear protrusions 53a having thickened portions P1 and P2 at their ends 61 and 62.

[0054] (Separator) The separator comprises a sheet-like substrate and a spacer placed on the main surface of the substrate. The substrate is placed between the positive electrode and the negative electrode. The spacer is placed between the electrode and the substrate. In a plan view of the substrate, the ratio of the area of ​​the region where the spacer is placed on the main surface of the substrate to the area of ​​the substrate may be, for example, 5% or more and 25% or less.

[0055] (Substrate) A porous sheet having ion permeability and insulating properties is used as the substrate. Examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the porous sheet is not particularly limited, but it may be a polymer material. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate may contain additives as needed. Examples of additives include inorganic fillers.

[0056] The thickness of the substrate is not particularly limited, but is, for example, 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0057] The substrate may include a porous sheet and a composite material layer (heat-resistant layer). The composite material layer may be formed on one main surface of the porous sheet or on both main surfaces. The composite material layer is a layer that allows lithium ions to pass through. The composite material layer contains inorganic particles. The composite material layer may optionally contain a resin material. The thickness of the composite material layer may be 5% to 50% of the total thickness of the substrate.

[0058] The composite material layer may be positioned on the side of the porous sheet facing the positive electrode, or on the side of the porous sheet facing the negative electrode. When the composite material layer is positioned on the positive electrode side, degradation of the porous sheet due to oxidation can be suppressed. When the composite material layer is positioned on the negative electrode side, degradation of the porous sheet due to reduction can be suppressed. A spacer may be placed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is particularly enhanced.

[0059] The inorganic particles are preferably inorganic compound particles that have thermal stability and insulating properties, and are less likely to melt and decompose when abnormal heat is generated due to a short circuit in the battery, etc. Examples of inorganic particle materials include oxides, hydroxides, nitrides, carbides, and sulfides. Examples of oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, and zinc oxide. Examples of nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of carbides include silicon carbide and boron carbide. Examples of sulfides include barium sulfate. Examples of hydroxides include aluminum hydroxide. The median diameter in the volume-based particle size distribution of the inorganic particles may be 0.2 to 2.0 μm.

[0060] The median diameter in the volume-based particle size distribution of inorganic particles can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer (e.g., Microtrac manufactured by Nikkiso Co., Ltd.). Alternatively, the cross-section of the substrate can be observed with a transmission electron microscope (TEM), a TEM image can be taken, the area enclosed by the contours of 100 arbitrary inorganic particles can be calculated, the diameter of an equivalent circle (true circle) having the same area as the calculated area can be determined, and the median diameter can be calculated as the average of the diameters of the 100 equivalent circles.

[0061] Examples of resin materials included in the composite material layer include fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, and other rubbers. Examples include cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; acrylic resins such as acrylic acid-metharyl acid copolymers; polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, and fully aromatic polyamides (aramids); polyamideimide; polyacrylonitrile; polyvinyl alcohol; polyether; polyacrylic acid; polymetharyl acid; polyester; polyolefin; silicone resin; urethane resin; melamine resin; urea resin; and epoxy resin.

[0062] It is desirable to use a polymer material with higher heat resistance than the material of the porous sheet for the resin material contained in the composite material layer (heat-resistant layer). Such a polymer material preferably includes at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamide-imides. These are known as polymer materials with high heat resistance. From the viewpoint of heat resistance, aramid, specifically meta-aramid (meta-total aromatic polyamide) and para-aramid (para-total aromatic polyamide), is preferred.

[0063] The inorganic particle content in the composite material layer may be in the range of 50% to 99% by mass (for example, in the range of 85% to 99% by mass).

[0064] The composite material layer is formed, for example, by applying a coating solution containing inorganic particles, a resin material, and a liquid component (dispersion medium) to a porous sheet and drying the coating film. Examples of liquid components include N-methyl-2-pyrrolidone.

[0065] (Spacer) The spacer is formed on the main surface of the substrate. From the viewpoint of facilitating the fabrication of the electrode group, it is preferable that the spacer is integrated with the substrate. The spacer may be provided on the main surface of the substrate facing the positive electrode (the main surface of the substrate on the positive electrode side), on the main surface of the substrate facing the negative electrode (the main surface of the substrate on the negative electrode side), or on both main surfaces. When the spacer is provided on the main surface of the substrate facing the positive electrode, compared to when the spacer is provided on the main surface of the substrate facing the negative electrode, Li precipitates between the spacers in a way that stretches the substrate toward the positive electrode, so compressive stress is generated in the precipitated Li, and Li tends to precipitate densely. From the viewpoint of improving discharge efficiency and cycle characteristics, it is preferable that the spacer is provided on the main surface of the substrate facing the positive electrode. On the other hand, when the spacer is provided on the main surface of the substrate facing the negative electrode, a space is formed in advance between the substrate and the negative electrode, so the tensile load on the substrate that follows the deposition of Li is reduced. In other words, it is advantageous in that it is easier to maintain the insulating properties of the substrate or the short-circuit resistance of the substrate.

[0066] In lithium-ion batteries, the main role of spacers is to create a space for the deposition of lithium metal. The lithium metal is contained within the space provided by the spacers, thereby suppressing volume changes in the electrode group.

[0067] The spacer may contain a resin material (e.g., an insulating resin), or it may contain a resin material and particles. The proportion of resin material in the spacer may be 10% by volume or more, 30% by volume or more, or 50% by volume or more, or it may be 100% by volume or less, or 80% by volume or less.

[0068] Examples of resin materials included in the spacer include fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, and other rubbers. Examples include cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; acrylic resins such as acrylic acid-metharyl acid copolymers; polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, and fully aromatic polyamides (aramids); polyamideimide; polyacrylonitrile; polyvinyl alcohol; polyether; polyacrylic acid; polymetharyl acid; polyester; polyolefin; silicone resin; urethane resin; melamine resin; urea resin; and epoxy resin.

[0069] From the viewpoint of suppressing the increase in the gas generation reaction rate during internal short circuits, it is preferable that the spacer has a non-porous structure that does not allow lithium ions to permeate. Among the above resin materials, polyimide, polyvinylidene fluoride, and acrylonitrile-acrylic acid ester copolymers are preferred as materials that do not allow lithium ions to permeate, and polyimide may also be used. A non-porous spacer of a certain height or more formed from these resin materials is a layer that does not allow lithium ions to permeate.

[0070] The particles may be inorganic or organic. Among these, inorganic particles such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides are particularly suitable. Preferred metal oxides include aluminum oxide (alumina and boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silica). Examples of metal hydroxides include aluminum hydroxide. Examples of metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of metal carbides include silicon carbide and boron carbide. Examples of metal sulfides include barium sulfate. Minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate may also be used. Among these, alumina, silica, and titania are particularly preferred.

[0071] The average particle size is not particularly limited, but may be 0.1 μm or larger, 0.5 μm or larger, 10 μm or smaller, 5 μm or smaller, or 2 μm or smaller. The average particle size can be measured by the following method. First, a cross-section of the spacer in the thickness direction of the separator is photographed with an electron microscope to obtain an image of the cross-section. Next, image processing such as binarization is performed on the image to identify the parts of the particles. Next, the diameter of a circle having the same area as the cross-sectional area of ​​each particle (equivalent circle diameter) is determined, and the arithmetic mean of the obtained equivalent circle diameters can be taken as the average particle size. The arithmetic mean can be calculated from, for example, 100 or more particles. The average particle size of other particles contained in the electrode plate and separator can also be determined by the same method.

[0072] When the spacer contains resin material and particles, it is preferable that the particle content in the spacer be 50% by volume or less. This makes it easier to ensure sufficient strength of the spacer.

[0073] The spacer includes a protrusion. The protrusion includes at least a linear protrusion having a thickened portion at its end E, and may further include other protrusions other than the linear protrusion having a thickened portion at its end E (for example, a linear protrusion without a thickened portion at its end E, a dot-shaped protrusion, etc.).

[0074] The height H of the spacer (protrusion) may be greater than the thickness T of the base material. The ratio of the height H of the spacer (protrusion) to the thickness T of the base material, H / T, may be greater than 1 and be 1.5 or greater, 2 or greater, or 3 or greater. H / T may be 10 or less, 8 or less, 5 or less, or 4 or less. When H / T is 1.5 or greater, volume changes of the electrode group are easily suppressed. In the case of a line-shaped protrusion with a thickened portion, the height H of the spacer (protrusion) refers to the thickness T1 of the main portion as described above.

[0075] Spacers are formed, for example, by applying a coating solution containing spacer components and liquid components to a predetermined location on a substrate and drying the coating film. Examples of liquid components include N-methyl-2-pyrrolidone. Coating may be done using a dispenser or other known printing methods such as gravure printing, inkjet printing, and screen printing. Drying may be done by known methods such as heating or natural drying.

[0076] The following provides a detailed explanation of the positive electrode, negative electrode, and non-aqueous electrolyte of a secondary battery.

[0077] (Lithium secondary battery) (Negative electrode) The negative electrode is equipped with a negative electrode current collector. The negative electrode may consist only of the negative electrode current collector, or it may include a thin lithium metal foil that has been pre-pressed onto the negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode during charging and become lithium metal, which is deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte during discharge. The lithium ions contained in the non-aqueous electrolyte may originate from lithium salts added to the non-aqueous electrolyte, or they may be supplied from the positive electrode active material during charging, or both.

[0078] The negative electrode may include a lithium ion storage layer (a layer that exhibits capacity through the absorption and release of lithium ions by the negative electrode active material) supported on the negative electrode current collector. In this case, the open-circuit potential of the negative electrode at full charge may be 70 mV or less relative to the lithium metal (lithium dissolution potential). When the open-circuit potential of the negative electrode at full charge is 70 mV or less relative to the lithium metal, lithium metal is present on the surface of the lithium ion storage layer at full charge. That is, the negative electrode exhibits capacity through the deposition and dissolution of lithium metal.

[0079] Here, "fully charged" refers to the state in which the battery has been charged to a charge level of, for example, 0.98 × C or higher, where C is the rated capacity of the battery. The open-circuit potential of the negative electrode at full charge can be measured by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The non-aqueous electrolyte of the cell may have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0080] The lithium-ion storage layer is formed by creating layers of a negative electrode composite material containing a negative electrode active material. In addition to the negative electrode active material, the negative electrode composite material may also contain binders, conductive materials, thickeners, etc.

[0081] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material, or a combination of two or more types. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0082] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, and carbon nanotubes.

[0083] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride. Examples of thickeners include carboxymethylcellulose and its sodium salts.

[0084] The negative electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film.

[0085] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloys. The conductive material may be a metallic material such as a metal or alloy. Preferably, the conductive material is one that does not react with lithium. More specifically, it is preferable that the conductive material does not form any alloys or intermetallic compounds with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite in which the basal surface is preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0086] The thickness of the negative electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0087] (Positive electrode) The positive electrode comprises a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode composite layer may be formed on only one side of the positive electrode current collector or on both sides. The positive electrode can be obtained, for example, by applying a positive electrode composite slurry containing the positive electrode active material, a conductive material, and a binder to both sides of the positive electrode current collector, drying the coating, and then rolling it.

[0088] The positive electrode active material is a material that intercepts and releases lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred because they have low manufacturing costs and a high average discharge voltage.

[0089] During charging, lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharge, the lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed into the composite oxide of the positive electrode. In other words, the lithium ions involved in charging and discharging generally originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0090] Examples of transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one transition metal element or two or more. The transition metal elements may be Ni, Co, and / or Mn. Lithium-containing transition metal oxides may optionally contain one or more main group elements. Examples of main group elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The main group elements may also be Al, etc.

[0091] Among lithium-containing transition metal oxides, composite oxides containing Ni, Co, and / or Mn as transition metal elements, and possibly Al as an optional component, and having a layered rock salt-type crystalline structure, are preferred for obtaining high capacity. In this case, in a lithium secondary battery, the molar ratio of the total amount of lithium (mLi) in the positive and negative electrodes to the amount of metal M other than lithium (mM) in the positive electrode (mLi / mM) is set to, for example, 1.1 or less.

[0092] For example, the binder and conductive materials exemplified for the negative electrode can be used. For the positive electrode, graphite can be used as the conductive material. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0093] Examples of materials for the positive electrode current collector (conductive sheet) include metallic materials containing Al, Ti, Fe, etc. The metallic material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0094] The thickness of the positive electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0095] (Non-aqueous electrolyte) A non-aqueous electrolyte having lithium ion conductivity includes a liquid electrolyte (electrolyte solution), and may include a gel electrolyte or a solid electrolyte. The liquid electrolyte is, for example, an electrolyte solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte solution may contain known additives.

[0096] The gel electrolyte includes a lithium salt and a matrix polymer, or includes a lithium salt, a non-aqueous solvent, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, polyethylene oxide, etc.

[0097] As the solid electrolyte, for example, materials known in all-solid-state lithium ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0098] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. When the lithium salt dissolves in the non-aqueous solvent, lithium ions and anions are generated.

[0099] Examples of the anion include BF ４ － , ClO ４ － , PF ６ － , CF ３ SO ３ － , CF ３ CO ２ － , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides include N(SO ２ CF ３ ) ２ － , N(C ｍ F ２ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１ SO ２ )ｙ － Examples include (where m and n are independently 0 or an integer greater than or equal to 1, and x and y are independently 0, 1 or 2, satisfying x + y = 2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of anions of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), PF ４ (C ２ O ４ ) － , PF ２ (C ２ O ４ ) ２ － Examples include these. Non-aqueous electrolytes may contain these anions individually or in combination of two or more.

[0100] From the viewpoint of suppressing the dendritic deposition of lithium metal, the non-aqueous electrolyte preferably contains at least an oxalate complex anion, and more preferably an oxalate complex anion containing fluorine. The interaction between the fluorine-containing oxalate complex anion and lithium makes it easier for lithium metal to precipitate uniformly in fine particulate form. Therefore, it is easier to suppress localized deposition of lithium metal. The fluorine-containing oxalate complex anion may be combined with other anions. Other anions include PF ６ － And / or imide anions.

[0101] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or halogen-substituted versions thereof. The non-aqueous electrolyte may contain one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted versions include fluorides.

[0102] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of linear carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of linear carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0103] Examples of ethers include cyclic ethers and linear ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0104] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Alternatively, the concentration of anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0105] The non-aqueous electrolyte may contain additives. The additives may form a film on the negative electrode. The formation of a film derived from the additive on the negative electrode makes it easier to suppress dendrite formation. Examples of such additives include vinylene carbonate, FEC, vinyl ethyl carbonate (VEC), and the like.

[0106] (Lithium-ion battery) The negative electrode of a lithium-ion battery contains a negative electrode active material capable of intercalating and releasing lithium ions. The positive electrode and non-aqueous electrolyte of a lithium-ion battery can be those exemplified in lithium secondary batteries.

[0107] The negative electrode comprises, for example, a negative electrode current collector and a negative electrode composite material layer (the lithium ion storage layer described above) supported on the negative electrode current collector. The negative electrode composite material layer may be supported on one main surface of the negative electrode current collector, or on both main surfaces of the negative electrode current collector. The negative electrode composite material and the negative electrode current collector can be appropriately selected from those exemplified above.

[0108] In the following, an example of a secondary battery according to this embodiment will be specifically described with reference to the drawings. The components of the secondary battery example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Furthermore, in the secondary battery described below, components that are not essential to the secondary battery according to this disclosure may be omitted. Note that the scale of the components in the following figures has been changed to facilitate understanding.

[0109] Here, Figure 6 is a schematic longitudinal cross-sectional view showing an example of a secondary battery according to the embodiment of this disclosure. In Figure 6, a cylindrical lithium secondary battery is shown as an example of a secondary battery. Note that in Figure 6, the spacers and the spaces formed by the spacers are not shown.

[0110] The cylindrical lithium secondary battery 10 includes a cylindrical battery case and a wound electrode group 14 and a non-aqueous electrolyte (not shown) housed within the battery case. The battery case includes a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is placed between the case body 15 and the sealing body 16. The gasket 27 ensures that the battery case is airtight. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the direction of the winding axis, respectively.

[0111] The case body 15 has a stepped portion 21 formed, for example, by partially pressing the side wall of the case body 15 from the outside. The stepped portion 21 may be formed in an annular shape on the side wall of the case body 15 along the circumferential direction of the case body 15. In this case, the sealing body 16 is supported on the opening side surface of the stepped portion 21.

[0112] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. In the sealing body 16, these members are stacked in this order. The sealing body 16 is fitted into the opening of the case body 15 such that the cap 26 is located on the outside of the case body 15 and the filter 22 is located on the inside of the case body 15. Each of the above-mentioned members constituting the sealing body 16 is, for example, disc-shaped or ring-shaped. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. The filter 22 and the lower valve body 23 are connected to each other at their respective centers. The upper valve body 25 and the cap 26 are connected to each other at their respective centers. In other words, each member except the insulating member 24 is electrically connected to each other.

[0113] The lower valve body 23 has a ventilation hole (not shown) formed therein. Therefore, if the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 bulges towards the cap 26 and separates from the lower valve body 23. This disconnects the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is discharged through an opening (not shown) formed in the cap 26.

[0114] Figure 7 is an enlarged view of a part of the electrode group 14. Figure 7 includes the portion near the positive electrode enclosed by region II in Figure 6 and the portion near the negative electrode enclosed by region III in Figure 6.

[0115] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator (a base material 50 and a spacer 53). The base material 50 of the positive electrode 11, the negative electrode 12, and the separator are all in the shape of a strip. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator so that the separator is positioned between the positive electrode 11 and the negative electrode 12. The separator is the separator of this disclosure (for example, the separator in Figure 1).

[0116] The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode composite layer 11b. The positive electrode current collector 11a is electrically connected to a cap 26, which functions as a positive electrode terminal, via a positive electrode lead 19. In Figure 7, the negative electrode 12 is shown as a negative electrode (negative electrode current collector) in a state where lithium metal has not been deposited. The negative electrode 12 is electrically connected to a case body 15, which functions as a negative electrode terminal, via a negative electrode lead 20.

[0117] The base material 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The base material 50 of Embodiment 1 comprises a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on the main surface of the porous sheet 51 that faces the positive electrode 11. In Embodiment 1, the spacer 53 is formed on the main surface 50a facing the positive electrode 11. The spacer 53 is formed on the composite material layer 52 and is in contact with the positive electrode 11. The spacer 53 creates a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the base material 50). Figure 7 shows the height h of the spacer 53.

[0118] In Figure 7, the spacer 53 is positioned on the main surface 50a of the base material 50 on the positive electrode 11 side, but it may also be positioned on the main surface 50b of the base material 50 on the negative electrode 12 side. The spacer 53 is formed on the composite material layer 52, but it may also be formed on the porous sheet 51. The composite material layer 52 of the base material 50 is positioned on the positive electrode 11 side, but it may also be positioned on the negative electrode 12 side.

[0119] In the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12 during charging. Since a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 due to the deposition of lithium metal is reduced, and the cycle characteristics are improved.

[0120] The secondary battery according to the embodiments of this disclosure is not limited to a cylindrical secondary battery equipped with a wound electrode group. The shape of the secondary battery can be appropriately selected from various shapes such as cylindrical, coin-shaped, prismatic, sheet-shaped, and flattened, depending on its application. The form of the electrode group is also not particularly limited and may be stacked.

[0121] 《Note》 The above description of embodiments discloses the following technologies. (Technology 1) A secondary battery comprising an electrode group and a non-aqueous electrolyte, wherein the electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator comprises a substrate and a spacer disposed on the main surface of the substrate, wherein the spacer includes a linear protrusion, and in a plan view of the separator, when the linear protrusion is viewed from the thickness direction of the linear protrusion, the linear protrusion has an end portion formed along the edge of the arrangement region where the linear protrusion is disposed, and a main portion other than the end portion, and the linear protrusion has a thickened portion at the end portion that is thicker than the main portion. (Technology 2) The secondary battery according to Technology 1, wherein the ratio of the thickness T2 of the thickened portion to the thickness T1 of the main portion: T2 / T1 is 1.1 or more and 1.5 or less. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the linear protrusion is formed along a predetermined pattern, the predetermined pattern has an arrangement area and a defect area in which the linear protrusion is not arranged in a part of the length direction in which the linear protrusion extends, the linear protrusion has an end near the defect area, and the linear protrusion has a thickened portion at the end near the defect area that is thicker than the main portion. (Technology 4) The secondary battery according to Technology 3, wherein the defect area is arranged on both sides in the length direction of the arrangement area, the linear protrusion has an end near the defect area on both sides in the length direction of the main portion, and the ratio of the total length LE of the thickened portion to the length L0 of the linear protrusion: LE / L0 is 0.1 or more. (Technology 5) The secondary battery according to Technology 4, wherein LE / L0 is 0.4 or more. (Technology 6) The secondary battery according to any one of Technologies 1 to 5, wherein the spacer includes a plurality of linear protrusions, and at least half of the total number of the plurality of linear protrusions have the thickened portion at their ends. (Technology 7) The secondary battery according to Technology 6, wherein at least four-fifths of the total number of the plurality of linear protrusions have the thickened portion at their ends. (Technology 8) The secondary battery according to any one of Technologies 1 to 7, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge.(Technical 9) A separator for a secondary battery, wherein the separator comprises a base material and a spacer disposed on the main surface of the base material, the spacer includes a linear projection, and in a plan view of the separator, when the linear projection is viewed from the thickness direction of the linear projection, the linear projection has an end portion formed along the edge of the arrangement region where the linear projection is disposed, and a main portion other than the end portion, and the linear projection has a thickened portion at the end portion that is thicker than the main portion. (Technical 10) The separator according to Technical 9, wherein the ratio of the thickness T2 of the thickened portion to the thickness T1 of the main portion: T2 / T1 is 1.1 or more and 1.5 or less. (Technical 11) The separator according to Technical 9 or 10, wherein the linear protrusion is formed along a predetermined pattern, the predetermined pattern has an arrangement area and a defect area in which the linear protrusion is not arranged in a part of the length direction in which the linear protrusion extends, the linear protrusion has an end near the defect area, and the linear protrusion has a thickened portion at the end near the defect area that is thicker than the main portion. (Technical 12) The separator according to Technical 10 or 11, wherein the defect area is arranged on both sides in the length direction of the arrangement area, the linear protrusion has an end near the defect area on both sides in the length direction of the main portion, and the ratio of the total length LE of the thickened portion to the length L0 of the linear protrusion: LE / L0 is 0.1 or more. (Technical 13) The separator according to Technical 12, wherein LE / L0 is 0.4 or more. (Technical 14) The separator according to any one of Technical 9 to 13, wherein the spacer includes a plurality of linear protrusions, and at least half of the total number of the plurality of linear protrusions have the thickened portion at their ends. (Technical 15) The separator according to Technical 14, wherein at least four-fifths of the total number of the plurality of linear protrusions have the thickened portion at their ends.

[0122] [Examples] The secondary battery relating to this disclosure will be described in more detail below based on examples and comparative examples. However, this disclosure is not limited to the following examples.

[0123] 《Batteries A1-A5》 (Preparation of positive electrode) A positive electrode slurry was prepared by mixing the positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP). The positive electrode active material used was a rock salt type lithium-containing transition metal oxide (NCA: positive electrode active material) having a layered structure and containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0). In the positive electrode slurry, the mass ratio of NCA:AB:PVdF was set to 95:2.5:2.5. The positive electrode slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector), the coating was dried, and the material was rolled to form a positive electrode layer. A positive electrode current collector, having positive electrode composite material layers formed on both sides, was cut to a predetermined size to obtain a strip-shaped positive electrode.

[0124] (Preparation of the negative electrode current collector) A strip of electrolytic copper foil (12 μm thick) was prepared as the negative electrode current collector.

[0125] (Preparation of Substrate) A 10 μm thick microporous thin film made of polyethylene was prepared. A coating solution containing paraphenylene terephthalamide, an aromatic polyamide, as a resin material, and alumina as inorganic particles, was applied to one main surface of the microporous thin film. The coating solution was an N-methyl-2-pyrrolidone solution containing 5.8% by mass of calcium chloride, adjusted to a concentration of 2 wt% aromatic polyamide and 4 wt% alumina. The microporous thin film with the coating was left for 1 hour at a temperature of 25°C and a relative humidity of 70% to precipitate the aromatic polyamide. Next, NMP and calcium chloride in the coating were removed by washing with water. A 5 μm thick composite material layer (heat-resistant layer) was formed by drying the coating at 60°C for 5 minutes. In this way, a substrate (15 μm thick) having a microporous thin film and a composite material layer was obtained.

[0126] (Formation of spacers on the main surface of the substrate) A coating solution containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to the microporous thin film of the substrate described above, and the coating film was dried to form spacers.

[0127] The spacer arrangement pattern was an intermittent honeycomb shape as shown in Figure 1. The linear protrusions constituting the spacers were linear protrusions having a thickened portion at the end E (linear protrusions 53a in Figure 4 or Figure 5). The linear protrusions 53a had a length L0 of 2.5 mm, a width W of 0.5 mm, and a main portion thickness T1 of 40 μm. The length Ld of the defect portion 53b (defect region 70) was 0.5 mm. T2 / T1 was 1.2. The thickened portions P1 and P2 had the same thickness. LE / L0 was the value shown in Table 1. The length L1 of the thickened portion P1 and the length L2 of the thickened portion P2 were the same length (LE / 2).

[0128] If necessary, in addition to the line-shaped protrusions 53a described above, line-shaped protrusions without a thickened portion at the end E (line-shaped protrusions whose thickness at the end E is the same as the thickness T1 of the main portion) were used. The ratio N1 of the number of line-shaped protrusions 53a having thickened portions P1 and P2 at the ends 61 and 62 to the total number N0 of multiple line-shaped protrusions constituting the spacer (N1 / N0 × 100) was set to the values ​​shown in Table 1.

[0129] (Preparation of non-aqueous electrolyte) 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF ２ CF ２ OCH ２ CF ３ A mixed ether solvent containing ) and in a volume ratio of 1:2 was prepared. Lithium bissulfonylimide (LiFSI) was added to the mixed solvent at a concentration of 1 mol / L, and LiBF ２ (C ２ O ４ A liquid non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 0.1 mol / L.

[0130] (Battery Assembly) In an inert gas atmosphere, the positive electrode and the negative electrode current collector were wound in a spiral shape with separators in between to create an electrode group. In this way, a wound-type electrode group with the structure shown in Figure 7 was obtained. At this time, the electrode group was configured such that separators with spacers were placed on the inner and outer circumference sides of the positive electrode, respectively. The separators were positioned so that the main surface of the base material on the side where the spacers were formed faced the positive electrode.

[0131] An electrode group was housed in a bottomed cylindrical case body, and a non-aqueous electrolyte was injected. A sealing body was placed at the opening of the case body via a gasket, sealing the electrode group and non-aqueous electrolyte inside the battery case. In this way, a lithium secondary battery with the structure shown in Figure 6 was completed.

[0132] Battery B1 was manufactured in the same manner as Battery A1, except that all of the linear protrusions constituting the spacer were linear protrusions that did not have thickened sections at the end E. In the linear protrusions that did not have thickened sections at the end E, the thickness of the end E was the same as the thickness T1 of the main part.

[0133] [Evaluation] Each obtained battery underwent a charge-discharge test in a constant temperature chamber at 25°C under the following conditions. The rest period between charging and discharging was 20 minutes.

[0134] (Charging) Constant current charging was performed at a current of 2.15 mA per unit area (square centimeter) of the electrodes until the battery voltage reached 4.1 V. Then, constant voltage charging was performed at a voltage of 4.1 V until the current value per unit area of ​​the electrodes reached 0.54 mA.

[0135] (Discharge) A constant current discharge was performed at a current of 2.15 mA per unit area of ​​the electrodes until the battery voltage reached 3.75 V.

[0136] (Expansion Rate of Electrode Group) The above charging and discharging process constituted one cycle, and the fabricated battery was charged up to the 50th cycle. The battery before charging and discharging, and the battery after the 50th cycle of charging, were disassembled, and the positive electrode, negative electrode, and the laminate of the two separators on either side of the negative electrode were removed. Disassembly was performed in an inert gas atmosphere. The removed positive electrode, negative electrode, and separator laminate were washed with dimethyl carbonate, dried, and the thickness of the laminate was measured. The thickness of the laminate was measured using a Peacock digital thickness gauge G2-205M. The thickness was measured at five arbitrary points within the laminate, and the arithmetic mean of the five measurements was taken as the average thickness of the laminate. Next, the average thickness X obtained by subtracting the thicknesses of the two substrates from this average thickness was calculated. The ratio (%) of the average thickness X at the 50th cycle to the average thickness X before charging and discharging was calculated as the expansion rate of the electrode group.

[0137] (Capacity Retention Rate) The above charging and discharging process was considered one cycle, and charging and discharging was performed up to 50 cycles. The ratio (%) of the discharge capacity at cycle 50 to the discharge capacity at cycle 1 was calculated as the capacity retention rate.

[0138] The evaluation results are shown in Table 1. In Table 1, A1 to A5 are the batteries of the examples, and B1 is the battery of the comparative example. In Table 1, the expansion rate of the electrode group is expressed as a relative value with the expansion rate of battery B1 set to 100.

[0139]

[0140] Batteries A1 to A5 showed a smaller electrode group expansion rate and higher capacity retention rate compared to battery B1.

[0141] The secondary battery of this disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet devices, electric vehicles including hybrid and plug-in hybrid vehicles, and home battery storage systems combined with solar cells.

[0142] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0143] 10: Lithium secondary battery, 11: Positive electrode, 12: Negative electrode, 14: Electrode group, 14s: Space, 15: Case body, 16: Sealing body, 23: Lower valve body, 25: Upper valve body, 50: Substrate, 51: Porous sheet, 52: Composite material layer, 53: Spacer, 53a: Linear protrusion, 60: Placement area, 70: Defect area, 61, 62: Edges near the defect area, 63: Main part

Claims

It comprises an electrode group and a non-aqueous electrolyte, The electrode group includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode. The separator comprises a base material and a spacer disposed on the main surface of the base material. The spacer includes a linear protrusion, In a plan view of the separator, when the linear projection is viewed from the thickness direction of the linear projection, the linear projection has an end portion formed along the edge of the arrangement region where the linear projection is placed, and a main portion other than the end portion. A secondary battery wherein the linear protrusion has a thicker portion at its end than the main portion. 　 The secondary battery according to claim 1, wherein the ratio of the thickness T2 of the thickened portion to the thickness T1 of the main portion, T2 / T1, is 1.1 or more and 1.5 or less. 　 The aforementioned line-shaped protrusions are formed along a predetermined pattern, The predetermined pattern comprises the arrangement region and a defect region in which the line-shaped protrusion is not arranged in a part of the length direction in which the line-shaped protrusion extends. The line-shaped protrusion has the end portion near the defect region, The secondary battery according to claim 1, wherein the line-shaped protrusion has the thickened portion at the end near the defect region. 　 The defect regions are arranged on both sides in the longitudinal direction of the arrangement region. The linear protrusion has the ends near the defect region on both sides in the longitudinal direction of the main portion, The line-shaped protrusion is formed on both sides in the longitudinal direction of the main portion, and has the thickened portion at the end near the defect region. The secondary battery according to claim 3, wherein the ratio of the total length LE of the thickened portion to the length L0 of the linear protrusion, LE / L0, is 0.1 or more. 　 The secondary battery according to claim 4, wherein the LE / L0 is 0.4 or greater. 　 The spacer includes a plurality of linear protrusions, The secondary battery according to any one of claims 1 to 4, wherein at least half of the total number of the plurality of linear protrusions have the thickened portion at their ends. 　 The secondary battery according to claim 6, wherein 4 / 5 or more of the total number of the plurality of linear protrusions have the thickened portion at their ends. 　 The secondary battery according to any one of claims 1 to 4, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge. 　 A separator for secondary batteries, The separator comprises a base material and a spacer disposed on the main surface of the base material. The spacer includes a linear protrusion, In a plan view of the separator, when the linear projection is viewed from the thickness direction of the linear projection, the linear projection has an end portion formed along the edge of the arrangement region where the linear projection is placed, and a main portion other than the end portion. The aforementioned linear protrusion has a thicker portion at its end than the main portion, forming a separator. 　 The separator according to claim 9, wherein the ratio of the thickness T2 of the thickened portion to the thickness T1 of the main portion, T2 / T1, is 1.1 or more and 1.5 or less. 　 The aforementioned line-shaped protrusions are formed along a predetermined pattern, The predetermined pattern comprises the arrangement region and a defect region in which the line-shaped protrusion is not arranged in a part of the length direction in which the line-shaped protrusion extends. The line-shaped protrusion has the end portion near the defect region, The separator according to claim 9, wherein the line-shaped protrusion has the thickened portion at the end near the defect region. 　 The defect regions are arranged on both sides in the longitudinal direction of the arrangement region. The linear protrusion has the ends near the defect region on both sides in the longitudinal direction of the main portion, The line-shaped protrusion is formed on both sides in the longitudinal direction of the main portion, and has the thickened portion at the end near the defect region. The separator according to claim 11, wherein the ratio of the total length LE of the thickened portion to the length L0 of the line-shaped protrusion, LE / L0, is 0.1 or more. 　 The separator according to claim 12, wherein the LE / L0 is 0.4 or greater. 　 The spacer includes a plurality of linear protrusions, The separator according to any one of claims 9 to 12, wherein at least half of the total number of the plurality of line-shaped protrusions have the thickened portion at their ends. 　 The separator according to claim 14, wherein 4 / 5 or more of the total number of the plurality of line-shaped protrusions have the thickened portion at their ends.

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