Secondary battery

Abstract

A secondary battery comprises: a positive electrode; a negative electrode; a separator that is disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector, and a positive electrode mixture layer that is supported by the positive electrode current collector. The separator includes a first region that faces an end portion of the positive electrode mixture layer, and a second region that faces a central portion of the positive electrode mixture layer. At least part of the first region is a first thick film region in which the thickness of the separator is greater than in the second region.

Description

secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-147900, filed on August 29, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to secondary batteries.

[0003] 2. Description of the Related Art Known high-capacity non-aqueous electrolyte secondary batteries include lithium ion batteries and lithium secondary batteries (lithium metal secondary batteries). Various studies have been conducted on non-aqueous electrolyte secondary batteries.

[0004] 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 is dissolved from the negative electrode during discharging; a spacer is provided between the separator and at least one of the positive electrode and the negative electrode; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting with the first direction D1; and at least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between the spacer and an electrode in contact with the spacer is greater than 90° in a cross section of the spacer taken along the thickness direction of the separator and the first direction D1.

[0005] International Publication No. 2021 / 192645

[0006] In recent years, there has been a demand for improved reliability of secondary batteries.

[0007] One aspect of the present disclosure relates to a secondary battery including: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector, and the separator includes a first region facing an end of the positive electrode composite layer and a second region facing a central portion of the positive electrode composite layer, and at least a portion of the first region is a first thick film region in which the separator is thicker than the second region.

[0008] According to the present disclosure, the reliability of secondary batteries can be improved. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0009] FIG. 1 is a top view schematically showing an example of a positive electrode; FIG. 2 is a top view schematically showing an example of a separator; FIG. 3 is a top view schematically showing another example of a separator; FIG. 4 is a longitudinal sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; FIG. 5 is a sectional view schematically showing a main part of an electrode group; FIG. 6 is a top view schematically showing an example of a spacer; and FIG. 7 is a top view schematically showing another example of a spacer.

[0010] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0011] A secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector. The separator includes a first region facing an end of the positive electrode mixture layer and a second region facing a central portion of the positive electrode mixture layer. At least a portion of the first region is a first thick film region in which the separator is thicker than the second region.

[0012] As the electrodes expand and contract during charging and discharging, stress is likely to occur in the separator at the portion facing the end of the positive electrode (positive electrode composite layer), which can damage the separator and cause an internal short circuit. Factors that may lead to stress occurring at the portion of the separator facing the positive electrode end include the fact that the area of ​​the positive electrode (composite layer) is usually smaller than the area of ​​the negative electrode in a plan view, and the fact that some negative electrodes have a high expansion coefficient. Examples of negative electrodes with a high expansion coefficient include electrodes containing a negative electrode active material (e.g., a Si-containing material) that expands and contracts to a large extent, and electrodes in which lithium metal precipitates during charging.

[0013] In contrast, in the present disclosure, in a separator including a first region facing an end of a positive electrode composite layer and a second region facing a central portion of the positive electrode composite layer, at least a portion of the first region is a first thick film region having a separator thickness greater than that of the second region. The formation of the first thick film region suppresses damage to the separator due to stress generated in the first region, suppresses the occurrence of internal short circuits due to such damage, and improves reliability.

[0014] The end of the positive electrode mixture layer is an end along a side that constitutes the outer shape of the positive electrode mixture layer in a plan view of the positive electrode. When the dimension D0 in the D direction (one direction) of the positive electrode is 600 mm or less, the width of the end of the positive electrode mixture layer in the D direction may be, for example, 0.05 × D0 mm or less. When the dimension D0 in the D direction (one direction) of the positive electrode is greater than 600 mm, the width of the end of the positive electrode mixture layer in the D direction may be, for example, 30 mm or less. For example, the D direction of the positive electrode may be the length direction (LD direction) of an elongated or strip-shaped positive electrode, and the width of the end of the positive electrode mixture layer in the LD direction may be the width of the winding start end 1e (or the winding end end 2e) of the positive electrode mixture layer.

[0015] The central portion of the positive electrode mixture layer is the portion other than the end portions of the positive electrode mixture layer.

[0016] In a plan view, the positive electrode has, for example, a rectangular outer shape, and the positive electrode composite layer has, for example, a rectangular outer shape. In this case, the ends of the positive electrode composite layer have first to fourth ends (e.g., ends 1e to 4e in FIGS. 2 and 3) corresponding to the four sides of the rectangle, respectively. The first thick film region faces, for example, at least one of the first to fourth ends. The first thick film region may face any one of the first to fourth ends, or may face all of the first to fourth ends. When the first thick film region faces the nth end (n is an integer from 1 to 4), it preferably faces 80% or more or 90% or more of the length of the nth end along the nth end, and more preferably faces the entire nth end.

[0017] When the first thick film region is disposed along the edge of the positive electrode composite layer, the first thick film region may be further extended from the edge of the positive electrode composite layer to a side not facing the positive electrode composite layer (excluding the third region described below), for example, by a width approximately equal to that of the edge. For example, when the first thick film region is disposed along the nth edge, the first thick film region may be further extended from the nth edge to a side not facing the positive electrode composite layer (excluding the third region described below), for example, by a width approximately equal to that of the edge. In this case, the first thick film region is more likely to have the effect of suppressing damage to the separator.

[0018] The first region may have a region other than the first thick film region. In this case, it is preferable that the region of the first region other than the first thick film region has the same thickness as the second region.

[0019] From the viewpoint of ensuring a sufficient area of ​​thin separator thickness and facilitating reduction of internal resistance, the ratio of the area of ​​the first thick film region to the total area of ​​the separator may be, for example, 20% or less, or may be 10% or less. Furthermore, from the viewpoint of facilitating obtaining the effects of the first thick film region, the ratio of the area of ​​the first thick film region to the total area of ​​the separator may be, for example, 1% or more, or may be 5% or more. The ratio of the area of ​​the first thick film region to the total area of ​​the separator is the area ratio of the second separator to the first separator, which will be described later. The ratio of the area of ​​the first thick film region to the total area of ​​the separator may be, for example, 1% or more and 20% or less, 1% or more and 10% or less, or 5% or more and 20% or less.

[0020] The positive electrode, the negative electrode, and the separator may be wound together. A wound electrode group may be configured in this manner. In the case of a wound electrode group, the first thick film region preferably faces the end of the positive electrode composite layer on the winding start side of the positive electrode (hereinafter also referred to as the "winding start end of the positive electrode composite layer"). Since stress is likely to be applied to the separator at the portion facing the winding start end of the positive electrode composite layer, facing the first thick film region with the winding start end of the positive electrode composite layer significantly reduces damage to the separator.

[0021] In the case of a wound electrode group, the first thick film region preferably faces an end of the positive electrode composite layer on the winding end side of the positive electrode (hereinafter also referred to as the "winding end end of the positive electrode composite layer"). Because stress is likely to be applied to the separator at the portion facing the winding end end of the positive electrode composite layer, having the first thick film region face the winding end end of the positive electrode composite layer significantly reduces damage to the separator.

[0022] The first thick film region may face each of the winding start end and the winding end of the positive electrode composite material layer.

[0023] The positive electrode may have a current collector exposed portion where the positive electrode composite layer is not supported on the positive electrode current collector. A positive electrode lead may be connected to the current collector exposed portion. The first thick film region preferably faces an end of the positive electrode composite layer adjacent to the current collector exposed portion. In the case of a wound electrode group, the current collector exposed portion may be formed in the center in the winding direction (longitudinal direction), or may be formed at the winding start end or winding end end of the positive electrode.

[0024] When the positive electrode has a current collector exposed portion, the separator includes a third region facing the current collector exposed portion. In this case, the third region may have the same thickness as the second region, but is preferably a second thick film region having a separator thickness greater than that of the second region. The separator is prone to stress at the portion facing the current collector exposed portion to which the positive electrode lead is connected, and this stress can damage the separator, resulting in an internal short circuit. By configuring the third region as the second thick film region, damage to the separator due to stress generated in the third region is suppressed, and the occurrence of an internal short circuit due to this damage is suppressed.

[0025] Although it is preferable that the entire third region is the second thick film region, a part of the third region may be the second thick film region. The area ratio of the second thick film region to the third region may be, for example, 50% or more, or 80% or more.

[0026] The second thick film region may be formed to extend further from the third region to the side not facing the positive electrode, in which case the entire exposed portion of the current collector is likely to be covered with the second thick film region.

[0027] The separator may include a first separator and a second separator. The second separator is used to form a thick film region. The first separator may be disposed in the first region and the second region, and the second separator may be disposed in at least a portion of the first region, and the region where the first separator and the second separator overlap may be the first thick film region. A plurality of second separators may be used to form a plurality of first thick film regions.

[0028] When the separator has a third region, the first separator is arranged in a region that combines the first region, the second region, and the third region, the second separator is arranged in a region that combines at least a portion of the first region and the third region, and the region where the first separator and the second separator overlap may be a first thick film region and a second thick film region.

[0029] The second separator may be disposed between the first separator and the negative electrode, but is preferably disposed between the first separator and the positive electrode. When the second separator is disposed between the first separator and the positive electrode, damage to the first separator due to stress applied to the portion of the first separator facing the end of the positive electrode mixture layer is likely to be suppressed.

[0030] The first separator and the second separator may be made of the same or different substrate material, may have the same or different thickness, and may be integrated by thermal bonding or the like.

[0031] From the viewpoint of suppressing damage to the separator, the ratio T / T1 of the total thickness T (= T1 + T2) of the first separator to the thickness T1 of the first separator may be, for example, 1.1 or more, or 1.2 or more, or 1.3 or more, or 1.5 or more. From the viewpoint of reducing internal resistance, T / T1 may be, for example, 2.0 or less, or 1.5 or less, or 1.2 or less. T / T1 may be, for example, 1.1 or more and 3.0 or less, or 1.2 or more and 2.0 or less. T / T1 is the thickness ratio of the first thick film region to the second region. When a second thick film region is provided, T / T1 is the thickness ratio of the second thick film region to the second region.

[0032] In the separator, the thickness of the first thick film region may be T, and the thickness of the region other than the first thick film region may be T1. When the separator has a second thick film region, the thicknesses of the first thick film region and the second thick film region may be T, and the thickness of the region other than the first thick film region and the second thick film region may be T1.

[0033] In a secondary battery, the area of ​​the negative electrode facing the positive electrode is usually larger than the area of ​​the positive electrode, and the negative electrode is disposed so as to face the entirety of one or both main surfaces of the positive electrode (the positive electrode composite layer formed on one or both main surfaces of the positive electrode) via a separator.

[0034] The negative electrode and separator may be disposed on both sides of the positive electrode. That is, the negative electrode may be disposed so as to face both main surfaces of the positive electrode (positive electrode composite layers formed on both main surfaces of the positive electrode) via the separator. In the case of a wound electrode assembly, the negative electrode and separator are disposed on both sides (outer and inner sides) of the positive electrode. In this case, it is sufficient that a separator having a first thick film region is disposed on at least one side of the positive electrode, and it is preferable to dispose separators having a first thick film region on both sides of the positive electrode. The first thick film regions disposed on both sides (outer and inner sides) of the positive electrode may be disposed so as to overlap with each other via the positive electrode, or may be disposed so as to be totally or partially offset from each other.

[0035] Alternatively, the negative electrode and the separator may be disposed on one side of the positive electrode. That is, the negative electrode may be disposed so as to face one main surface of the positive electrode (the positive electrode composite layer formed on one main surface of the positive electrode) via the separator. In this case, the separator disposed on one side of the positive electrode has the first thick film region.

[0036] A spacer may be placed between the positive electrode or negative electrode and the separator. In secondary batteries, the volume of the electrode group changes significantly during charge and discharge. By placing a spacer between the separator and the electrode, the volume change of the electrode group can be suppressed. The spacer serves to form a space to absorb the expansion of the electrode.

[0037] When a spacer is disposed, Li ions released from the positive electrode during charging migrate around the spacer (protrusion) to the negative electrode, causing Li deposition (Li ion absorption) and resulting in expansion of the negative electrode. The end of the positive electrode composite layer faces the end of the Li deposition region (Li ion absorption region) of the negative electrode. As a result, stress caused by the expansion of the negative electrode may concentrate locally near the overlapping portion between the end of the positive electrode composite layer and the spacer, potentially damaging the separator. In particular, in lithium secondary batteries, the edge of the precipitated Li is likely to be thick near the overlapping portion, causing stress caused by Li deposition to concentrate locally. In response to this, using a separator having the first thick film region can significantly reduce damage to the separator near the overlapping portion when a spacer is disposed.

[0038] The ratio of the length of the overlapping portion between one end of the positive electrode composite layer and a spacer (e.g., linear protrusion 53 a in FIG. 6 ) to the length of one end of the positive electrode composite layer (e.g., winding start end 1 e of the positive electrode composite layer in FIG. 6 ) is, for example, 5% or more and 25% or less.

[0039] When spacers are disposed on both sides (outer and inner sides) of the positive electrode, the spacers may be disposed so as to overlap with each other through the positive electrode, or may be disposed so as to be totally or partially offset from each other. The spacers disposed on both sides (outer and inner sides) of the positive electrode may have the same arrangement pattern or different arrangement patterns.

[0040] When the separator is composed of a first separator and a second separator, a spacer may be disposed on the main surface of the first separator facing the second separator, or on the second separator. A spacer may be disposed on the main surface of the first separator opposite the second separator. A spacer may be formed on one main surface of the first separator to integrate the first separator and the spacer, and then the second separator may be disposed on the main surface of the first separator opposite the spacer. A separator may be constructed by stacking the first separator and the second separator, and then a spacer may be disposed on one main surface of the separator.

[0041] Secondary batteries include lithium secondary batteries (lithium metal secondary batteries), lithium ion batteries, etc. For example, the negative electrode of a lithium secondary battery is an electrode in which lithium metal precipitates during charging and dissolves in a non-aqueous electrolyte during discharging. The negative electrode of a lithium ion battery is an electrode in which lithium ions are absorbed into a negative electrode active material during charging and released from the negative electrode active material during discharging. In lithium secondary batteries, the expansion rate of the negative electrode due to Li precipitation during charging is large, so the formation of the first thick film region as described above significantly suppresses damage to the separator.

[0042] Here, FIG. 1 is a top view schematically showing an example of a positive electrode in a plan view. FIG. 2 is a top view schematically showing an example of a separator in a plan view. FIG. 3 is a top view schematically showing another example of a separator in a plan view. The positive electrode of FIG. 1 and the separator of FIG. 2 (or FIG. 3) are used in a wound electrode group. In FIGS. 2 and 3, the positive electrode facing the separator is represented by a dashed line. In FIG. 1, the LD direction indicates the length direction of the strip-shaped positive electrode. In FIGS. 2 and 3, the LD direction indicates the length direction of the strip-shaped separator. Note that each figure is a schematic view, and the aspect ratios of each member, etc., do not necessarily reflect the actual ones.

[0043] The strip-shaped positive electrode 11 includes a positive electrode current collector 11a and a positive electrode composite layer 11b supported on the positive electrode current collector 11a. The positive electrode 11 has a current collector exposed portion 70 where the positive electrode composite layer 11b is not supported on the positive electrode current collector 11a, on the end E2 side of the positive electrode 11. A positive electrode lead 19 is connected to the current collector exposed portion 70.

[0044] Positive electrode 11 is strip-shaped and has opposite ends E1 and E2 in the length direction and opposite ends E3 and E4 in the width direction. One of ends E1 and E2 is the winding start end of positive electrode 11, and the other of ends E1 and E2 is the winding end end of positive electrode 11. Positive electrode composite layer 11b has ends 1e, 3e, and 4e at ends E1, E3, and E4 of positive electrode 11. Positive electrode composite layer 11b has end 2e on the side of end E2 of positive electrode 11.

[0045] Separator 50 includes a first region P1 (hatched region) facing ends 1e to 4e of positive electrode composite layer 11b, a second region P2 facing a central portion of positive electrode composite layer 11b (a region inside ends 1e to 4e), and a third region P3 facing current collector exposed portion 70. At least a portion of first region P1 is a first thick film region 60 in which separator 50 is thicker than second region P2. First region P1 may include a region other than first thick film region 60, or may include a region having the same thickness as second region P2.

[0046] 2 faces end 1e of positive electrode composite material layer 11b on the winding start side of positive electrode 11. First thick film region 60 is disposed so as to extend further from first region P1 facing end 1e of positive electrode composite material layer 11b to the side not facing positive electrode composite material layer 11b, by, for example, approximately the same width as the end.

[0047] 3 faces end 2 e of positive electrode composite material layer 11 b adjacent to current collector exposed portion 70. First thick film region 60 is disposed to extend further from the first region facing end 2 e of positive electrode composite material layer 11 b to the side not facing positive electrode composite material layer 11 b (excluding third region P3), by a width approximately equal to that of the end.

[0048] 3 is a second thick film region 80 in which the thickness of the separator is greater than that of the second region P2. The second thick film region 80 is formed by extending further from the third region P3 to the side not facing the positive electrode 11.

[0049] In FIG. 3, the first thick film region 60 and the second thick film region 80 are combined to form one thick film region 90 .

[0050] 2 and 3, the first thick film region does not face ends 3 e and 4 e of positive electrode composite material layer 11 b, but it may face ends 3 e and 4 e of positive electrode composite material layer 11 b. The first thick film region may face all of ends 1 e to 4 e of positive electrode composite material layer 11 b.

[0051] The secondary battery will be described in detail below.

[0052] (Lithium secondary battery) A lithium secondary battery includes a positive electrode, a negative electrode on which lithium metal precipitates during charging and dissolves in a non-aqueous electrolyte during discharging, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode includes at least a negative electrode current collector, and lithium metal precipitates on the negative electrode current collector during charging. The non-aqueous electrolyte has ion conductivity.

[0053] In a lithium secondary battery, for example, 70% or more of the rated capacity is achieved by the deposition and dissolution of lithium metal. The movement of electrons at the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal at the negative electrode. Specifically, 70 to 100% (e.g., 80 to 100% or 90 to 100%) of the movement of electrons (or current from another perspective) at the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal. In other words, the negative electrode of a lithium secondary battery differs from a negative electrode in which the movement of electrons at the negative electrode during charging and discharging is mainly due to the absorption and release of lithium ions by the negative electrode active material (e.g., graphite).

[0054] (Separator) A porous sheet having ion permeability and insulating properties is used as the substrate of the separator. Examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The material of the porous sheet is not particularly limited, but may be a polymer material. Examples of the polymer material include an olefin resin, a polyamide resin, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The substrate may contain an additive, if necessary. Examples of the additive include an inorganic filler.

[0055] 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.

[0056] The substrate may include a porous sheet and a composite material layer (heat-resistant layer). The composite material layer may be formed on one or both main surfaces of the porous sheet. The composite material layer is a layer that allows lithium ions to permeate. The composite material layer contains inorganic particles. The composite material layer may contain a resin material as needed. The thickness of the composite material layer may be 5% to 50% of the total thickness of the substrate.

[0057] The composite material layer may be disposed 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 disposed on the positive electrode side, deterioration of the porous sheet due to oxidation reactions can be suppressed. When the composite material layer is disposed on the negative electrode side, deterioration of the porous sheet due to reduction reactions can be suppressed. A spacer may be disposed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is particularly enhanced.

[0058] The inorganic particles are preferably particles of an inorganic compound that is thermally stable and insulating, and thus unlikely to melt or decompose during abnormal heat generation due to a short circuit in the battery, etc. Examples of inorganic particle materials include oxides, hydroxides, nitrides, carbides, sulfides, etc. Examples of oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, zinc oxide, etc. Examples of nitrides include silicon nitride, aluminum nitride, boron nitride, titanium nitride, etc. Examples of carbides include silicon carbide and boron carbide, etc. Examples of sulfides include barium sulfate, etc. Examples of hydroxides include aluminum hydroxide, etc. The median diameter in the volume-based particle size distribution of the inorganic particles may be 0.2 to 2.0 μm.

[0059] 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 measuring device (for example, Microtrac manufactured by Nikkiso Co., Ltd.) Alternatively, the cross section of the substrate may be observed with a transmission electron microscope (TEM), a TEM image may be taken, the area surrounded by the outlines of any 100 inorganic particles may be calculated, the diameter of an equivalent circle (perfect circle) having the same area as the calculated area may be determined, and the average diameter of the 100 equivalent circles may be calculated.

[0060] Examples of resin materials contained in the composite material layer (heat-resistant 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 hydrogenated product thereof, acrylonitrile-butadiene copolymer or hydrogenated product thereof, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, and rubbers such as polyvinyl acetate. Examples of the resin include cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; acrylic resins such as acrylic acid-methacrylic acid copolymers; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid); polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0061] The resin material contained in the composite material layer (heat-resistant layer) is preferably a polymeric material having higher heat resistance than the material of the porous sheet. Such a polymeric material preferably includes at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides. These are known to have high heat resistance. From the viewpoint of heat resistance, aramids, i.e., meta-aramids (meta-type wholly aromatic polyamides) and para-aramids (para-type wholly aromatic polyamides), are preferred.

[0062] The content of the inorganic particles in the composite material layer may be in the range of 50% by weight to 99% by weight (for example, in the range of 85% by weight to 99% by weight).

[0063] The composite material layer is formed, for example, by applying a coating liquid containing inorganic particles, a resin material, and a liquid component (dispersion medium) to a porous sheet and then drying the coating film. Examples of the liquid component include N-methyl-2-pyrrolidone.

[0064] (Spacer) A spacer may be disposed between the positive electrode or negative electrode and the separator. The ratio of the area of ​​the spacer disposed on the main surface of the separator (first separator) to the area of ​​the main surface of the separator is, for example, 5 to 25%.

[0065] From the viewpoint of ease of fabrication of the electrode assembly, the separator and the spacer may be integrated by forming a spacer on the main surface of the separator. The electrode and the spacer may be integrated by forming a spacer on the main surface of the electrode. It is sufficient that the spacer is disposed on the main surface of the separator when constructing the electrode assembly.

[0066] The spacer may be disposed on the main surface of the separator facing the positive electrode (the main surface of the separator on the positive electrode side) or on the main surface of the separator facing the negative electrode (the main surface of the separator on the negative electrode side). When the spacer is disposed on the main surface of the separator facing the positive electrode, Li is deposited so as to stretch the separator toward the positive electrode, compared to when the spacer is disposed on the main surface of the first separator facing the negative electrode, which generates compressive stress in the deposited Li and makes it easier for Li to deposit densely. From the viewpoint of improving discharge efficiency and cycle characteristics, it is preferable to dispose the spacer on the main surface of the separator facing the positive electrode. On the other hand, when the spacer is disposed on the main surface of the separator facing the negative electrode, a space is formed in advance between the separator and the negative electrode, so the tensile load on the separator that occurs due to Li deposition is reduced. In other words, it is advantageous in that it is easier to maintain the insulating properties of the separator or the short-circuit resistance of the separator.

[0067] In lithium secondary batteries, the main role of the spacer is to form a space for lithium metal to deposit in. By accommodating lithium metal in the space formed by the spacer, volumetric changes in the electrode group during charge and discharge are suppressed, and cycle characteristics are likely to be improved.

[0068] The spacer may include a resin material (e.g., an insulating resin) or may include a resin material and particles. The proportion of the resin material in the spacer may be 10% by volume or more, 30% by volume or more, or 50% by volume or more, or may be 100% by volume or less, or 80% by volume or less.

[0069] Examples of resin materials contained 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 hydrogenated product, acrylonitrile-butadiene copolymer or its hydrogenated product, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate, Examples of the resin include cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; acrylic resins such as acrylic acid-methacrylic acid copolymers; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid); polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0070] Among the above resin materials, preferred materials that are impermeable to lithium ions include polyimide, polyvinylidene fluoride, and acrylonitrile-acrylic acid ester copolymers, and polyimide may also be used. A non-porous spacer of a certain height or greater made of these resin materials is a layer that is impermeable to lithium ions and has a non-porous structure that does not allow lithium ions to pass through. The placement of such a spacer is preferred from the viewpoint of suppressing an increase in the gas generation reaction rate during an internal short circuit.

[0071] The particles may be inorganic or organic. Examples of inorganic particles include insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Examples of 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 preferred.

[0072] The average particle size of the particles is not particularly limited, but may be 0.1 μm or more, 0.5 μm or more, or 10 μm or less, 5 μm or less, or 2 μm or less. 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 using an electron microscope to obtain an image of the cross-section. Next, the image is subjected to image processing such as binarization to identify the particle portion. Next, the diameter of a circle having the same area as the cross-section area of ​​each particle (equivalent circle diameter) is determined, and the arithmetic mean of the determined equivalent circle diameters can be used as the average particle size. The arithmetic mean can be determined, for example, from 100 or more particles. The average particle size of other particles contained in the electrode plate and separator can also be determined by a similar method.

[0073] When the spacer contains a resin material and particles, the particle content in the spacer is preferably 50% by volume or less, which makes it easier to ensure sufficient strength of the spacer.

[0074] The spacer includes a protrusion. The spacer may include a linear protrusion and / or a dot-shaped protrusion. From one viewpoint, the linear protrusion is a ridge-shaped protrusion. The linear protrusion may be arranged continuously or intermittently. The linear protrusion may be straight or curved.

[0075] The width of the linear convex portion may be 100 μm or more, or 200 μm or more, and may be 2000 μm or less, or 1000 μm or less.

[0076] The spacer preferably includes convex portions arranged in a predetermined repeating pattern. The linear convex portions may be arranged in a striped pattern or a mesh pattern. The mesh pattern may be a collection of polygons. An example of a mesh pattern includes a shape in which polygons are combined so as to share a side. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may be combined. The mesh pattern may be a honeycomb pattern. Furthermore, dot-shaped convex portions may be arranged in a predetermined repeating pattern.

[0077] The thickness of the spacer (height of the convex portion) TC may be greater than the thickness T1 of the first separator. TC / T1 may be 1.5 or greater or 2 or greater. TC / T1 may be 5 or less, 4 or less, or 3 or less. From the viewpoint of suppressing expansion of the electrode group, TC / T1 may be, for example, greater than 1 (or 1.5 or greater) or 5 or less. The thickness of the spacer (height of the convex portion) TC may be greater than the thickness T2 of the second separator. TC / T2 may be 1.5 or greater or 2 or greater. TC / T2 may be 5 or less, 4 or less, or 3 or less.

[0078] The spacers are formed, for example, by applying a coating liquid containing spacer components and a liquid component to a predetermined location on the separator (or electrode) and drying the coating. Examples of the liquid component include N-methyl-2-pyrrolidone. The coating may be performed using a dispenser or by known printing methods such as gravure printing, inkjet printing, and screen printing. The drying may be performed by known methods such as heating or natural drying. The thickness of the spacers can be adjusted by changing the amount applied or the viscosity of the coating liquid.

[0079] (Negative electrode) The negative electrode includes a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode upon charging, becoming lithium metal, which is then 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 upon discharging. The negative electrode may be composed of only the negative electrode current collector, or may include a thin lithium metal foil previously pressed onto the negative electrode current collector.

[0080] The negative electrode may also include a lithium ion occlusion layer (a layer that develops capacity by occlusion 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 lithium metal (dissolution and deposition potential of lithium). If the open circuit potential of the negative electrode at full charge is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion occlusion layer at full charge. In other words, the negative electrode develops capacity by deposition and dissolution of lithium metal.

[0081] The lithium ion occlusion layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0082] Examples of the negative electrode active material include a carbonaceous material, a Si-containing material, and a Sn-containing material. The negative electrode may contain one type of negative electrode active material, or a combination of two or more types. When the negative electrode contains a Si-containing material as the negative electrode active material, the expansion rate of the negative electrode during charging is large, and therefore the effect of the separator having the first thick film region is significantly obtained. Examples of the carbonaceous material include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Examples of the Si-containing material include simple Si, an alloy containing Si, and a composite material containing a lithium silicate phase and a Si phase dispersed within the lithium silicate phase.

[0083] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0084] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0085] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0086] 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. A conductive material that does not react with lithium is preferred. More specifically, a material that does not form an alloy or intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), alloys containing these metal elements, and graphite with a preferentially exposed basal surface. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys, which have high conductivity, are preferred. Alternatively, a laminate sheet in which a metal or alloy such as stainless steel, nickel, nickel alloy, copper, or copper alloy is laminated on the surface of a resin film may be used as the negative electrode current collector. The resin material of the resin film is not particularly limited, but examples include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, polyamide, and polyimide.

[0087] The thickness of the negative electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0088] (Positive Electrode) The positive electrode includes, for example, 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 may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode composite slurry including the positive electrode active material, the conductive material, and the binder to both sides of the positive electrode current collector, drying the coating, and then rolling.

[0089] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material 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 of their low production cost and high average discharge voltage.

[0090] The lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions during charging and precipitates as lithium metal on the negative electrode or negative electrode current collector. During discharging, 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 are generally derived from the solute in the nonaqueous electrolyte and the positive electrode active material.

[0091] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Ni, Co, and / or Mn. The lithium-containing transition metal oxide may contain one or more typical elements as needed. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al, etc.

[0092] The positive electrode composite layer preferably contains a lithium-containing composite oxide having a layered rock salt structure as a positive electrode active material (lithium-containing transition metal oxide). From the viewpoint of increasing capacity, the lithium-containing composite oxide having a layered rock salt structure preferably contains Ni, Co, and / or Mn as a transition metal element, and may contain Al as an optional component. In this case, in the lithium secondary battery, the molar ratio mLi / mM of the total amount of lithium contained in the positive electrode and negative electrode mLi to the amount mM of metal M other than lithium contained in the positive electrode is set to, for example, 1.1 or less.

[0093] As the binder, conductive material, etc., for example, those exemplified for the negative electrode can be used. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0094] Examples of materials for the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS). Alternatively, a laminate sheet in which a metal or alloy such as stainless steel, aluminum, aluminum alloy, or titanium is laminated on the surface of a resin film may be used as the positive electrode current collector. The resin material for the resin film is not particularly limited, and examples include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, polyamide, and polyimide.

[0095] The thickness of the positive electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0096] (Non-aqueous electrolyte) The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte. The liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolytic solution may contain known additives.

[0097] The gel electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and polyethylene oxide.

[0098] As the solid electrolyte, for example, a material known in all-solid-state lithium ion secondary batteries (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) can be used.

[0099] In a liquid (gel) non-aqueous electrolyte, lithium salt dissolves in a non-aqueous solvent to generate lithium ions and anions.

[0100] The anion is BF ４ － , ClO ４ － , P.F. ６ － , C.F. ３ SO ３ － , C.F. 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 － (m and n are each independently an integer of 0 or 1 or more, and x and y are each independently 0, 1, or 2, satisfying the relationship x+y=2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), P.F. ４ (C ２ O ４ ) － , P.F. ２ (C ２ O ４ ) ２ － The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0101] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains an anion of an oxalate complex, and more preferably contains an oxalate complex anion having fluorine. The interaction between the oxalate complex anion having fluorine and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This makes it easier to suppress local deposition of lithium metal. The oxalate complex anion having fluorine may be combined with another anion. The other anion may be PF ６ － and / or an anion of an imide.

[0102] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted products thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted products include fluorides. From the viewpoint of suppressing decomposition of the non-aqueous electrolyte due to contact with lithium metal, the non-aqueous electrolyte preferably contains an ether-based solvent, which has excellent resistance to reduction.

[0103] 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 chain 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 chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0104] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0105] The concentration of the 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 the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Furthermore, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0106] The non-aqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode makes it easier to suppress the formation of dendrites. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0107] (Lithium-ion battery) A lithium-ion battery includes a positive electrode, a negative electrode containing a negative electrode active material that absorbs and releases lithium ions, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode and non-aqueous electrolyte may be the same as those exemplified for lithium secondary batteries. The positive electrode composite and positive electrode current collector contained in the positive electrode may be appropriately selected from those exemplified above. The non-aqueous solvent and lithium salt (anion) contained in the non-aqueous electrolyte may be appropriately selected from those exemplified above.

[0108] The negative electrode includes, for example, a negative electrode current collector and a negative electrode composite layer (the above-mentioned lithium ion occlusion layer) supported on a main surface of the negative electrode current collector. The negative electrode composite layer may be supported on one main surface of the negative electrode current collector, or may be supported on both main surfaces of the negative electrode current collector. The negative electrode composite and negative electrode current collector included in the negative electrode can be appropriately selected from those exemplified above.

[0109] The substrate and spacer included in the separator can be the same as those used in lithium secondary batteries. The substrate may include a porous sheet containing a polymer material. The substrate may further include a composite material layer containing a resin material and inorganic particles. The spacer may include a resin material.

[0110] In the case of a lithium-ion battery, for example, the spacer may be disposed at a location where stress is likely to increase when the negative electrode expands, such as the innermost periphery of a wound electrode assembly, or at a location of a flat electrode assembly with a small radius of curvature.

[0111] An example of a lithium secondary battery according to the present embodiment will be described in detail below with reference to the drawings. The components described above can be applied to the components of the lithium secondary battery of the example described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the lithium secondary battery described below, components that are not essential for the lithium secondary battery according to the present disclosure may be omitted. Note that the scale of the components has been changed in the following drawings to facilitate understanding.

[0112] (Embodiment 1) Fig. 4 is a longitudinal cross-sectional view schematically illustrating an example of a lithium secondary battery according to Embodiment 1. Note that Fig. 4 does not illustrate the spacers and the spaces formed by the spacers. The cylindrical lithium secondary battery 10 shown in Fig. 4 includes a cylindrical battery case and a wound electrode group 14 and a nonaqueous electrolyte (not shown) housed in the battery case. The battery case includes a case body 15, which is a cylindrical metal container with a bottom, and a sealing member 16 that seals the opening of the case body 15. A gasket 27 is disposed between the case body 15 and the sealing member 16. The gasket 27 ensures the hermeticity of the battery case. Within the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the direction of the winding axis.

[0113] Case body 15 has a step 21 formed, for example, by pressing a portion of the side wall of case body 15 from the outside. Step 21 may be formed in an annular shape along the circumferential direction of case body 15 on the side wall of case body 15. In this case, sealing body 16 is supported by the surface of step 21 on the opening side.

[0114] 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. These components are stacked in this order in the sealing body 16. The sealing body 16 is attached to the opening of the case body 15 so that the cap 26 is located outside the case body 15 and the filter 22 is located inside the case body 15. The above-mentioned components constituting the sealing body 16 are, for example, disk-shaped or ring-shaped. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and an insulating member 24 is interposed between their respective peripheral edges. 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, all components except the insulating member 24 are electrically connected to each other.

[0115] A vent hole (not shown) is formed in the lower valve body 23. Therefore, if the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This cuts off the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged from an opening (not shown) formed in the cap 26.

[0116] Fig. 5 is an enlarged view of a portion of the electrode group 14. Fig. 5 includes a portion near the positive electrode surrounded by region II in Fig. 4 and a portion near the negative electrode surrounded by region III in Fig. 4. Separator 50 in Fig. 5 indicates the second region (first separator).

[0117] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 50. The positive electrode 11, the negative electrode 12, and the separator 50 are all strip-shaped. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 50 such that the separator 50 is disposed between the positive electrode 11 and the negative electrode 12.

[0118] 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 FIG. 5, the negative electrode 12 is shown as a negative electrode in a state in which no lithium metal is 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.

[0119] The separator 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The separator 50 of embodiment 1 includes a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on one of the two main surfaces of the porous sheet 51 that faces the negative electrode 12.

[0120] The electrode group 14 includes a spacer 53 disposed between the positive electrode 11 and the separator 50. In the first embodiment, 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 forms a space 14s between the positive electrode 11 and the negative electrode 12 (between the positive electrode 11 and the separator 50). FIG. 5 shows the height h of the spacer 53.

[0121] 5, the spacer 53 is disposed on the main surface 50a of the separator 50 facing the positive electrode 11, but may also be disposed on the main surface 50b of the separator 50 facing the negative electrode 12. The spacer 53 is formed on the composite material layer 52, but may also be formed on the porous sheet 51. The composite material layer 52 of the separator 50 is disposed on the positive electrode 11 side, but may also be disposed on the negative electrode 12 side.

[0122] During charging of the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12. Because a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 that accompanies the deposition of lithium metal is reduced, improving the cycle characteristics.

[0123] Here, FIG. 6 shows an example of the planar shape of the spacer 53. In plan view, the spacer 53 (linear convex portion 53a) is arranged on one main surface of the separator 50. The separator 50 on which the spacer 53 (convex portion 53a) is arranged is arranged on the inner and outer circumferential sides of the positive electrode 11. In each figure, the positive electrode 11 facing the separator 50 is represented by a dashed line. As an example, the separator 50 is shown having the first thick film region 60 of FIG. 2. Note that each figure is a schematic diagram, and the aspect ratio of each member does not necessarily reflect the actual size.

[0124] The spacer 53 in Fig. 6 includes a plurality of linear protrusions 53a arranged in a stripe pattern. The regions where the spacers 53 are not formed form spaces 14s. The linear protrusions 53a are arranged parallel to one another along the length direction (LD direction) of the strip-shaped separator 50. The linear protrusions 53a are arranged spaced apart from one another. The linear protrusions 53a are arranged intermittently and each have a defect portion 53b.

[0125] In Fig. 6, six linear protrusions 53a are arranged, but the number of linear protrusions 53a is not limited to this. The defects in Fig. 6 may be arranged randomly or at regular intervals. In Fig. 6, the positive electrode edge portions E3 and E4 do not overlap with the linear protrusions 53a, but the positive electrode edge portions E3 and E4 may overlap with the linear protrusions 53a. In this case, the first thick film region may face the ends E3 and E4.

[0126] The arrangement pattern of the spacers is not limited to the stripe pattern shown in FIG. 6, but may be, for example, a honeycomb pattern shown in FIG.

[0127] The spacer 53 in Fig. 7 includes linear protrusions 53a arranged in a honeycomb pattern. Areas where the spacers 53 are not formed form spaces 14s. The linear protrusions 53a are arranged intermittently and have defects 53b. In Fig. 7, the linear protrusion corresponding to one side of the hexagon has defects at both ends, but it may also have a defect in the center.

[0128] In the first embodiment, a cylindrical lithium secondary battery having a wound electrode group has been described. However, the lithium secondary battery of this embodiment is not limited to the form of the first embodiment, and can be applied to other forms. The shape of the lithium secondary battery can be appropriately selected from various shapes such as a cylindrical shape, a coin shape, a rectangular shape, a sheet shape, and a flat shape depending on the application. The shape of the electrode group is also not particularly limited, and may be a stacked type.

[0129] <<Supplementary Notes>> The above embodiments disclose the following techniques. (Technology 1) A 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, wherein the positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector, and the separator includes a first region facing an end of the positive electrode mixture layer and a second region facing a central portion of the positive electrode mixture layer, and at least a portion of the first region is a first thick film region in which the separator is thicker than the second region. (Technology 2) The secondary battery according to Technology 1, wherein the positive electrode, the negative electrode, and the separator are wound together, and the first thick film region faces an end of the positive electrode mixture layer at a winding start side of the positive electrode. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the positive electrode, the negative electrode, and the separator are wound together, and the first thick film region faces an end of the positive electrode mixture layer on the winding end side of the positive electrode. (Technology 4) The secondary battery according to any one of Technology 1 to 3, wherein the positive electrode has a current collector exposed portion where the positive electrode mixture layer is not supported on the positive electrode current collector, a positive electrode lead is connected to the current collector exposed portion, and the first thick film region faces an end of the positive electrode mixture layer adjacent to the current collector exposed portion. (Technology 5) The secondary battery according to Technology 4, wherein the separator includes a third region facing the current collector exposed portion, and the third region is a second thick film region in which the thickness of the separator is greater than that of the second region. (Technology 6) The secondary battery according to any one of Technologies 1 to 3, wherein the separator includes a first separator and a second separator, the first separator is disposed in the first region and the second region, the second separator is disposed in at least a part of the first region, and an area where the first separator and the second separator overlap is the first thick film region.(Technology 7) The secondary battery according to Technology 5, wherein the separator includes a first separator and a second separator, the first separator being disposed in a region where the first region, the second region, and the third region are combined, the second separator being disposed in a region where at least a portion of the first region and the third region are combined, and an overlapping region between the first separator and the second separator is the first thick film region and the second thick film region. (Technology 8) The secondary battery according to Technology 6 or 7, wherein the second separator is disposed between the first separator and the positive electrode. (Technology 9) The secondary battery according to any one of Technology 1 to 8, wherein a spacer is disposed between the positive electrode or the negative electrode and the separator, the spacer including protrusions arranged in a predetermined repeating pattern. (Technology 10) The secondary battery according to Technology 9, wherein the spacer includes linear protrusions arranged intermittently. (Technology 11) The secondary battery according to any one of Technologies 1 to 10, wherein the negative electrode is an electrode on which lithium metal precipitates during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging. (Technology 12) The secondary battery according to any one of Technologies 1 to 11, wherein the positive electrode mixture layer contains, as a positive electrode active material, a lithium-containing composite oxide having a layered rock salt structure.

[0130] [Examples] The lithium secondary battery according to the present disclosure will be described in more detail below based on examples and comparative examples, although the present disclosure is not limited to the following examples.

[0131] Battery A1 (Preparation of Positive Electrode) A positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a positive electrode mixture slurry. The positive electrode active material was a rock-salt lithium-containing transition metal oxide (NCA; positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al was 1.0) and having a layered structure. The mass ratio of NCA:AB:PVdF in the positive electrode mixture slurry was 95:2.5:2.5. The positive electrode mixture slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector), and the coating was dried and rolled to form a positive electrode mixture layer. The positive electrode current collector with the positive electrode composite layer formed on both sides was cut to a predetermined size to obtain a positive electrode. An exposed current collector portion without the positive electrode composite layer was formed on one longitudinal end (winding end) of the positive electrode. A positive electrode lead was connected to the exposed current collector portion. In this way, a positive electrode (FIG. 1) was obtained.

[0132] (Preparation of negative electrode current collector) A strip of electrolytic copper foil (thickness: 12 μm) was prepared as a negative electrode current collector. A negative electrode lead was connected to the negative electrode current collector.

[0133] (Preparation of First Separator) A 10 μm-thick polyethylene microporous thin film was prepared. One main surface of the microporous thin film was coated with a coating liquid containing paraphenylene terephthalamide, an aromatic polyamide, as the resin material and alumina as inorganic particles. The coating liquid was an N-methyl-2-pyrrolidone (NMP) solution containing 5.8% by mass of dissolved calcium chloride, and the concentration was adjusted to 2 wt% aromatic polyamide and 4 wt% alumina. The microporous thin film on which the coating film was formed was left for 1 hour in an atmosphere at 25°C and 70% relative humidity to precipitate the aromatic polyamide. Next, the NMP and calcium chloride in the coating film were removed by water washing. The coating film was then dried at 60°C for 5 minutes to form a 2 μm-thick composite material layer (heat-resistant layer). In this way, a substrate (12 μm thick) having a microporous thin film and a composite material layer was obtained as the first separator.

[0134] (Formation of spacers on the main surface of the first separator) A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to one main surface of the first separator (the main surface on the microporous thin film side), and the coating was dried to form spacers in the pattern (striped) shown in FIG. 6 . The spacers were composed of multiple linear protrusions. The multiple linear protrusions were each arranged intermittently. The linear protrusions had a width of 0.25 mm and a height of 30 μm.

[0135] (Arrangement of a second separator on a first separator having a spacer) A separator having a spacer on one main surface was obtained by placing a second separator on the other main surface of a first separator having a spacer on one main surface. That is, a (second separator / first separator / spacer) configuration was used. The same substrate (thickness: 12 μm) as above was used for the second separator. The ratio of the area of ​​the second separator to the area of ​​the first separator was 10%. The separator was formed by overlapping the main surface of the second separator facing the microporous thin film and the main surface of the first separator facing the composite material layer. The second separator was arranged in a position where the first separator faced the end of the positive electrode composite layer at the winding start side of the positive electrode when constructing the electrode group.

[0136] (Preparation of non-aqueous electrolyte) 1,2-dimethoxyethane and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF ２ CF ２ OCH ２ CF ３ An ether-based mixed solvent containing lithium bis(sulfonylimide) (LiFSI) at 1 mol / L and LiBF at a volume ratio of 1:2 was prepared. ２ (C ２ O ４ ) was dissolved in the ethanol to a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte (ether-based electrolyte solution).

[0137] (Battery Assembly) A positive electrode and a negative electrode (negative electrode current collector) were spirally wound with a separator interposed therebetween in an inert gas atmosphere to prepare an electrode assembly. A negative electrode, a separator, and a spacer were arranged on both sides (inner and outer periphery) of the positive electrode.

[0138] The electrode assembly was configured as (negative electrode / spacer / first separator / second separator / positive electrode). That is, the second separator was disposed between the first separator and the positive electrode. A spacer was disposed between the first separator and the negative electrode. The second separator was disposed in the region where the end of the positive electrode composite layer on the winding start side of the positive electrode and the first separator faced each other. In this way, a separator having a first thick film region (FIG. 2) was obtained.

[0139] The first thick film region was disposed along the winding-start end of the positive electrode composite layer and faced the entire winding-start end of the positive electrode composite layer, and the ratio of the length of the overlapping portion between the winding-start end and the spacer (linear protrusion) to the length of the winding-start end of the positive electrode composite layer was within a range of 10% to 20%.

[0140] The electrode group was housed in a cylindrical case body with a bottom, and a nonaqueous electrolyte was poured into it. A sealing member was placed over the opening of the case body via a gasket. In this way, a cylindrical lithium secondary battery (Battery A1) was completed.

[0141] Battery A2: A second separator was placed in the region where the first separator faced the end of the positive electrode composite layer (the end adjacent to the exposed current collector portion) at the end of the winding of the positive electrode and the exposed current collector portion. In this manner, a separator having a first thick film region and a second thick film region (FIG. 3) was obtained. Battery A2 was fabricated in the same manner as Battery A1, except for the above. The ratio of the area of ​​the second separator to the area of ​​the first separator was 10%.

[0142] The first thick film region was disposed along the winding end of the positive electrode composite layer and faced the entire winding end of the positive electrode composite layer. The second thick film region faced the entire current collector exposed portion. The ratio of the length of the overlapping portion between the winding end of the positive electrode composite layer and the spacer (linear convex portion) to the length of the winding end of the positive electrode composite layer was within a range of 10% to 20%.

[0143] Battery B1 Battery B1 was fabricated in the same manner as Battery A1, except that the separator was composed of only the first separator without using the second separator.

[0144] [Evaluation] (Charge / Discharge Test) A charge / discharge test was performed on each of the obtained batteries. In the charge / discharge test, the battery was charged in a thermostatic chamber at 25° C. under the following conditions, then rested for 20 minutes, and discharged under the following conditions.

[0145] (Charging) The battery was charged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 4.1 V. Thereafter, the battery was charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 1 mA.

[0146] (Discharge) The battery was discharged at a constant current of 10 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 3.0 V.

[0147] The above charge and discharge cycle was repeated, and when the charge capacity at the mth cycle was 1% or more higher than the charge capacity at the previous (m-1)th cycle, it was determined that abnormal charging had occurred due to the occurrence of a small internal short circuit, and the charge-discharge test was terminated. The number of cycles at this time, m, was calculated as the number of cycles at which abnormality occurred.

[0148] The evaluation results are shown in Table 1. In Table 1, A1 and A2 are examples, and B1 is a comparative example.

[0149]

[0150] In Batteries A1 and A2, the cycle of abnormality occurrence was delayed and the occurrence of minute internal short circuits was suppressed compared to Battery B1. In particular, Battery A2 further delayed the cycle of abnormality occurrence.

[0151] The secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrids and plug-in hybrids, and home storage batteries combined with solar cells.

[0152] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0153] 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: Separator, 51: Porous sheet, 52: Composite material layer, 53: Spacer, 53a: Convex portion, 53b: Defective portion, 60: First thick film region, 70: Current collector exposed portion, 80: Second thick film region

Claims

1. A 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; wherein the positive electrode includes a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector; the separator includes a first region facing an end of the positive electrode composite layer and a second region facing a central portion of the positive electrode composite layer; and at least a portion of the first region is a first thick film region in which the separator is thicker than the second region.

2. The secondary battery according to claim 1, wherein the positive electrode, the negative electrode, and the separator are wound together, and the first thick film region faces an end of the positive electrode mixture layer on the winding start side of the positive electrode.

3. The secondary battery according to claim 1, wherein the positive electrode, the negative electrode, and the separator are wound together, and the first thick film region faces an end of the positive electrode mixture layer on the winding end side of the positive electrode.

4. The secondary battery according to claim 1, wherein the positive electrode has a current collector exposed portion where the positive electrode mixture layer is not supported on the positive electrode current collector, a positive electrode lead is connected to the current collector exposed portion, and the first thick film region faces an end of the positive electrode mixture layer adjacent to the current collector exposed portion.

5. The secondary battery according to claim 4, wherein the separator includes a third region facing the current collector exposed portion, and the third region is a second thick film region in which the thickness of the separator is greater than that of the second region.

6. The secondary battery according to claim 1, wherein the separator includes a first separator and a second separator, the first separator is disposed in the first region and the second region, the second separator is disposed in at least a portion of the first region, and the region where the first separator and the second separator overlap is the first thick film region.

7. The secondary battery described in claim 5, wherein the separator includes a first separator and a second separator, the first separator is disposed in a region that combines the first region, the second region, and the third region, the second separator is disposed in a region that combines at least a portion of the first region and the third region, and the region where the first separator and the second separator overlap is the first thick film region and the second thick film region.

8. The secondary battery according to claim 6 or 7, wherein the second separator is disposed between the first separator and the positive electrode.

9. The secondary battery according to claim 1, wherein a spacer is disposed between the positive electrode or the negative electrode and the separator, and the spacer includes protrusions arranged in a predetermined repeating pattern.

10. The secondary battery according to claim 9, wherein the spacer includes linear protrusions arranged at intervals.

11. The secondary battery according to claim 1, wherein the negative electrode is an electrode on which lithium metal precipitates during charging and from which the lithium metal dissolves in the non-aqueous electrolyte during discharging.

12. The secondary battery according to claim 1, wherein the positive electrode mixture layer contains, as a positive electrode active material, a lithium-containing composite oxide having a layered rock salt structure.

Images