Lithium secondary battery

Abstract

This lithium secondary battery is provided with an electrode group that is obtained by winging a positive electrode, a negative electrode at which Li precipitates during charging, and a separator. The separator includes a first separator (second separator) which is disposed on the inner peripheral side (outer peripheral side) of the positive electrode. The first separator (second separator) includes a first base material (second base material) and a first projection (second projection). The positive electrode has a region PL which is in the L-th wind from the end of the positive electrode on the winding start side. XL (YL) is the ratio of an area ALt (BLt) of a portion overlapping with a first projection (a second projection) of a region S1L (S2L) to an area AL (BL) of the region S1L (S2L) of a first base material (a second base material) facing the inner peripheral side (the outer peripheral side). When X1 to Xn (Y1 to Yn) are values of XL (YL) corresponding to regions P1 to Pn where L is 1 to n (n is an integer of 3 or more), X1 (Y1) is smaller than the value of at least one of X2 to Xn (Y2 to Yn).

Description

Lithium secondary battery

[0001] The present disclosure relates to lithium secondary batteries.

[0002] Lithium ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with capacities even higher than lithium ion batteries. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and dissolves during discharging, releasing lithium ions into the non-aqueous electrolyte.

[0003] In a lithium secondary battery, lithium metal is deposited on the negative electrode during charging, so it is necessary to provide a space between the positive electrode and the negative electrode to ensure a space for lithium to deposit.

[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 in a cross section of the spacer taken along the thickness direction of the separator and the first direction D1, 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°.

[0005] International Publication No. 2021 / 192645

[0006] In a wound electrode group, stress caused by Li deposition on the negative electrode is concentrated locally at the innermost periphery of the positive electrode, which can damage the substrate and cause an internal short circuit.

[0007] One aspect of the present disclosure provides an electrode assembly including a wound positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein lithium metal precipitates in the negative electrode during charging and dissolves during discharging, the separator including a first separator disposed on an inner circumferential side of the positive electrode and a second separator disposed on an outer circumferential side of the positive electrode, the first separator including a sheet-like first substrate and a first spacer disposed on a main surface of the first substrate, the first spacer including a first convex portion, the second separator including a sheet-like second substrate and a second spacer disposed on a main surface of the second substrate, the second spacer including a second convex portion, and the positive electrode including a non-aqueous electrolyte, the ratio ALt / AL of an area ALt of a portion of the region S1L of the first substrate facing the inner periphery of the region PL to an area AL of the region S1L of the first substrate facing the inner periphery of the region PL is defined as XL; the ratio BLt / BL of an area BLt of a portion of the region S2L of the second substrate facing the outer periphery of the region PL to an area BL of the region S2L of the second substrate facing the outer periphery of the region PL is defined as YL; and the values ​​of XL and YL corresponding to regions P1 to Pn, where L=1 to n (n is an integer of 3 or more), are defined as X1 to Xn and Y1 to Yn, respectively; X1 is smaller than at least one value of X2 to Xn, and Y1 is smaller than at least one value of Y2 to Xn.

[0008] According to the present disclosure, it is possible to suppress the occurrence of an internal short circuit in a lithium secondary battery.

[0009] 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.

[0010] Fig. 2 is a longitudinal sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure; Fig. 3 is a sectional view schematically showing a main part of the lithium secondary battery shown in Fig. 1; Fig. 4 is a schematic top view of a positive electrode in an electrode group when viewed from the direction of the winding axis; Fig. 5 is a top view showing an example of a spacer; Fig. 6 is a top view showing another example of a spacer; Fig. 7 is a top view showing yet another example of a spacer; Fig. 8 is a top view of a spacer provided in a conventional lithium secondary battery;

[0011] 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.

[0012] A lithium secondary battery according to an embodiment of the present disclosure includes an electrode group formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Lithium metal precipitates in the negative electrode during charging and dissolves during discharging. Specifically, 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 lithium ion conductivity. The lithium secondary battery is also referred to as a lithium metal secondary battery.

[0013] 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).

[0014] The electrode group is constructed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator (strip-shaped substrate) interposed therebetween. In the electrode group, the positive electrode and the negative electrode are wound so that the negative electrode is disposed on both sides (inner and outer circumferential sides) of the positive electrode in all regions (regions P1 to Pn described below) of the positive electrode with the separator interposed therebetween. The separators include a first separator disposed on the inner circumferential side of the positive electrode and a second separator disposed on the outer circumferential side of the positive electrode. The first separator includes a sheet-shaped first substrate and a first spacer disposed on a main surface of the first substrate, the first spacer including a first convex portion. The second separator includes a sheet-shaped second substrate and a second spacer disposed on a main surface of the second substrate, the second spacer including a second convex portion. Hereinafter, matters common to the first separator and the second separator may be simply referred to as "separator," "substrate," "spacer," and "convex portion."

[0015] In the electrode group, the first convex portions and the second convex portions may be arranged so as to overlap with each other via the positive electrode, or may be arranged so as to be entirely or partially offset from each other via the positive electrode. The arrangement patterns of the first spacers and the second spacers may be the same or different. For example, one of the first spacers and the second spacers may be striped, and the other of the first spacers and the second spacers may be honeycomb-shaped.

[0016] The positive electrode has a region PL that is L turns from the end of the winding start side of the positive electrode. XL is the ratio of the area ALt of the portion of region S1L that overlaps with the first convex portion to the area AL of region S1L of the first substrate facing the inner periphery of region PL: ALt / AL. YL is the ratio of the area BLt of the portion of region S2L that overlaps with the second convex portion to the area BL of region S2L of the second substrate facing the outer periphery of region PL: BLt / BL. The values ​​of XL and YL corresponding to regions P1 to Pn, where L = 1 to n (n is an integer of 3 or greater), are X1 to Xn and Y1 to Yn, respectively. In this case, X1 is smaller than at least one value of X2 to Xn. Y1 is smaller than at least one value of Y2 to Xn. In other words, X1 and Y1 are not the maximum values ​​of X1 to Xn and Y1 to Yn, respectively. Region P1 is the innermost portion of the positive electrode, and region Pn is the outermost portion of the positive electrode. XL and YL may be substantially the same or different. For example, X1 and Y1 may be substantially the same or different.

[0017] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer supported on both sides of the positive electrode current collector. In this case, region S1L (S2L) is a region of the first substrate (second substrate) facing the positive electrode mixture layer on the inner circumferential side (outer circumferential side) of region PL. For connection with the positive electrode lead, the positive electrode may have a region (current collector exposed region) in the center in the winding direction (length direction) where the positive electrode mixture layer is not supported. When a part of the inner circumferential side (outer circumferential side) of region PL other than region P1 has a current collector exposed region, region S1L (S2L) is a region facing the positive electrode mixture layer excluding the current collector exposed region.

[0018] When the above configuration is satisfied, local concentration of stress caused by Li deposition on the negative electrode at the innermost periphery of the positive electrode is suppressed, and damage to the substrate due to the stress concentration is suppressed, thereby suppressing the occurrence of internal short circuits due to damage to the substrate.

[0019] In a wound electrode assembly, the expansion of the negative electrode has a large effect on the inner periphery, easily creating a step at the boundary of the expanded region. Therefore, the load on the separator is large at the end of the positive electrode at the start of winding. Furthermore, near the protrusions, Li may precipitate from the positive electrode mixture layer covered by the protrusions, resulting in a localized increase in the thickness of the deposited Li. Due to the combination of these factors, the stress generated by the expansion of the electrode assembly tends to be locally large near the area where the innermost periphery of the positive electrode (particularly the edge of the innermost periphery at the start of winding) overlaps with the protrusions. In response to this, in the present disclosure, the first protrusions (second protrusions) are positioned so that X1 (Y1) is not the largest among X1 to Xn (Y1 to Yn). This prevents the above-mentioned stress from becoming locally large.

[0020] From the viewpoint of suppressing damage to the substrate due to the above-mentioned stress concentration, it is preferable to arrange the first convex portion (second convex portion) with X1 (Y1) as small as possible relative to X2 to Xn (Y2 to Yn). X1 (Y1) is preferably smaller than half or more of the values ​​of X2 to Xn (Y2 to Yn). It is particularly preferable that X1 (Y1) is smaller than any of the values ​​of X2 to Xn (Y2 to Yn), that is, smaller than the smallest value of X2 to Xn (Y2 to Yn).

[0021] From the viewpoint of suppressing damage to the substrate due to the above-mentioned stress concentration, X1 (Y1) may be 0.5 or less, 0.35 or less, 0.2 or less, or even 0. Because the separator includes a spacer, when X1 (Y1) is 0, X1 (Y1) cannot be the maximum value of X1 to Xn. If X1 is the maximum value among X1 to Xn, even if X1 (Y1) is 0.5 or less, the above-mentioned stress concentration may occur, and the substrate may be damaged. When X1 (Y1) is 0, the first convex portion (second convex portion) is not disposed on the first substrate (second substrate) facing the inner circumferential side (outer circumferential side) of region P1. However, since region P1 is much smaller than regions P2 to Pn, the disposition of the first spacer (second spacer) can sufficiently suppress expansion of the electrode group due to Li deposition.

[0022] From the viewpoint that spaces are easily formed between the regions P2 to Pn and the negative electrode as well as between the region P1 and the negative electrode, and that expansion of the electrode group due to Li deposition is more easily suppressed, X1 (Y1) may be 0.01 or more, 0.025 or more, or 0.05 or more. The range of X1 (Y1) may be, for example, 0 or more and 0.5 or less, 0.01 or more and 0.5 or less, 0.01 or more and 0.4 or less, 0.01 or more (or 0.025 or more) and 0.35 or less, or 0.05 or more and 0.2 or less.

[0023] From the viewpoint of easily and stably forming spaces for precipitated Li, X2 to Xn (Y2 to Yn) may be 0.02 or more, or may be 0.05 or more. From the viewpoint of easily securing spaces for precipitated Li, X2 to Xn (Y2 to Yn) may be 0.6 or less, 0.45 or less, or 0.25 or less. The range of X2 to Xn (Y2 to Yn) may be, for example, 0.02 or more and 0.6 or less, 0.05 or more and 0.45 or less, or 0.08 or more and 0.25 or less.

[0024] Since stress is likely to concentrate in the innermost circumferential portion of the positive electrode, particularly near the edge portion on the winding start side of the positive electrode (positive electrode mixture layer), it is preferable to arrange the first convex portion (second convex portion) so that the proportion of overlap with the edge portion on the winding start side of the positive electrode (positive electrode mixture layer) is small, and it is more preferable to arrange the first convex portion (second convex portion) so that it does not overlap with the edge portion on the winding start side of the positive electrode (positive electrode mixture layer).

[0025] The first convex portion (second convex portion) is preferably not disposed more inward than the edge portion of the positive electrode at the winding start side (for example, in the region to the left of the side corresponding to edge E1 in Figures 5 and 6). In this case, the sliding of the end portion of the positive electrode at the winding start side is not hindered by the convex portion, and the stress generated by the expansion of the electrode group toward the inner periphery can be alleviated by the sliding of the end portion of the positive electrode at the winding start side. In this case, it is easy to arrange the first convex portion (second convex portion) so that it does not overlap with the edge portion of the positive electrode at the winding start side. In the case of a striped spacer, it is easy to arrange the linear first convex portion (second convex portion) so that it does not intersect with the side corresponding to edge E1 of the positive electrode at the winding start side.

[0026] (Separator) The separator includes a sheet-like substrate and a spacer disposed on the main surface of the substrate.

[0027] (Substrate) A porous sheet having ion permeability and insulating properties is used as the substrate. 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] (Spacer) The spacer is formed on the main surface of the substrate. From the viewpoint of ease of preparation of the electrode group, it is preferable that the substrate and the spacer are integrated. The spacer may be provided on the main surface of the substrate facing the positive electrode (the main surface on the positive electrode side of the substrate), or on the main surface of the substrate facing the negative electrode (the main surface on the negative electrode side of the substrate), or on both main surfaces. When the spacer is provided on the main surface of the substrate facing the positive electrode, Li precipitates between the spacers so as to stretch the substrate toward the positive electrode, compared to when the spacer is provided on the main surface of the substrate facing the negative electrode, so compressive stress is generated in the precipitated Li, making it easier for Li 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 generated by the precipitation of Li is reduced. That is, it is advantageous in that the insulating properties of the substrate can be easily maintained, or the short-circuit resistance of the substrate can be easily maintained.

[0038] In lithium secondary batteries, the main role of the spacer is to form a space for lithium metal to deposit, which prevents the negative electrode from expanding during charging.

[0039] 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.

[0040] 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.

[0041] Among the above resin materials, polyimide, polyvinylidene fluoride, acrylonitrile-acrylic acid ester copolymer, etc. are preferred as materials that do not allow lithium ions to pass through, 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 pass through. The placement of such a spacer is preferable from the viewpoint of suppressing an increase in the gas generation reaction rate during an internal short circuit.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] The spacer may include linear protrusions and / or dot-shaped protrusions. From one viewpoint, the linear protrusions are ridge-shaped protrusions. The linear protrusions may be arranged intermittently or continuously. The linear protrusions may be straight or curved.

[0046] 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.

[0047] The spacer preferably has a predetermined repeating pattern. That is, it is preferable that the convex portions are 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.

[0048] When the arrangement pattern of the first spacers (second spacers) is dot-shaped, the above XL (YL) may be adjusted by changing the maximum diameter and number (spacing) of the convex portions according to the region S1L (S2L) of the first substrate (second substrate). When the arrangement pattern of the first spacers (second spacers) is stripe-shaped, the above XL (YL) may be adjusted by changing the number (spacing) of the linear first convex portions (second convex portions) according to the region S1L (S2L) of the first substrate (second substrate). When the first spacers (second spacers) (first convex portions (second convex portions)) are arranged intermittently (when defective portions are partially provided), the above XL (YL) may be adjusted by changing the number and size (length) of the defective portions according to the region S1L (S2L) of the first substrate (second substrate).

[0049] The height H of the spacer (protrusion) may be greater than the thickness T of the substrate. The ratio of the height H to the thickness T, H / T, may be greater than 1, 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. By making H / T 1.5 or greater, expansion of the electrode group can be particularly suppressed.

[0050] The height H can be measured by the following method. First, a cross section of the separator (substrate) in the thickness direction is photographed using an electron microscope to obtain an image of the cross section. Next, 20 arbitrary locations among the spacers are selected in the image, and the heights of the spacers at those locations are measured. Next, the heights measured at the 20 locations are arithmetically averaged, and the obtained average value is defined as the height H. The thickness T can also be measured using a similar procedure.

[0051] The spacers are formed, for example, by applying a coating liquid containing spacer components and a liquid component to a predetermined location on a substrate and drying the coating. Examples of the liquid component include N-methyl-2-pyrrolidone. The coating may be performed using a dispenser or by a known printing method such as gravure printing, inkjet printing, or screen printing. The drying may be performed by a known method such as drying by heating or natural drying.

[0052] (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.

[0053] The negative electrode may include a lithium ion occlusion layer (a layer that develops capacity by occlusion and release of lithium ions by a negative electrode active material (such as graphite)) supported on a negative electrode current collector. In this case, the open circuit potential of the negative electrode when fully charged 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 when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion occlusion layer when fully charged. In other words, the negative electrode develops capacity by deposition and dissolution of lithium metal.

[0054] Here, "fully charged" refers to a state in which the battery is charged to a state of charge of, for example, 0.98 x C or more, 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 a fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The nonaqueous electrolyte of the cell may have the same composition as the nonaqueous electrolyte in the disassembled battery.

[0055] 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.

[0056] 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 or more negative electrode active materials. Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0057] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0058] 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.

[0059] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0060] 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. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form an alloy or an intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, as well as graphite with a preferentially exposed basal plane. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0061] 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.

[0062] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode mixture 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 mixture 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Among lithium-containing transition metal oxides, composite oxides containing Ni, Co, and / or Mn as transition metal elements, and which may contain Al as an optional component, and which have a layered rock-salt crystal structure are preferred in terms of obtaining high capacity. 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 to the amount mM of metal M other than lithium contained in the positive electrode is set to, for example, 1.1 or less.

[0067] 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.

[0068] Examples of the material of the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0069] 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.

[0070] (Non-aqueous electrolyte) The non-aqueous electrolyte having lithium ion conductivity 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.

[0071] 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.

[0072] 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.

[0073] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0074] 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.

[0075] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains at least 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.

[0076] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted derivatives include fluorides.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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).

[0081] 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.

[0082] (Embodiment 1) FIG. 1 is a longitudinal cross-sectional view schematically illustrating an example of a lithium secondary battery according to Embodiment 1. Note that FIG. 1 does not illustrate spacers and spaces formed by the spacers. The cylindrical lithium secondary battery 10 shown in FIG. 1 includes a cylindrical battery case and a wound electrode group 14 and a nonaqueous electrolyte (not shown) housed within 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 2 is an enlarged view of a portion of the electrode group 14. FIG. 2 includes a portion near the positive electrode surrounded by region II in FIG. 1 and a portion near the negative electrode surrounded by region III in FIG.

[0087] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator (a substrate 50 and a spacer 53). The positive electrode 11, the negative electrode 12, and the separator substrate 50 are all strip-shaped. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator (substrate 50) so that the separator is disposed between the positive electrode 11 and the negative electrode 12.

[0088] The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode mixture 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. 2, the negative electrode 12 is shown as a negative electrode (negative electrode current collector) on 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.

[0089] The substrate 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The substrate 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, the main surface facing the negative electrode 12. In embodiment 1, a 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 negative electrode 12 and the substrate 50). FIG. 2 shows the height h of the spacer 53.

[0090] 2, the spacer 53 is disposed on the main surface 50a of the substrate 50 on the positive electrode 11 side, but may also be disposed on the main surface 50b of the substrate 50 on the negative electrode 12 side. 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 substrate 50 is disposed on the positive electrode 11 side, but may also be disposed on the negative electrode 12 side.

[0091] 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.

[0092] Fig. 3 is a schematic top view showing an example of a positive electrode when the electrode group is viewed from the direction of the winding axis. Fig. 3 shows a state in which the positive electrode is wound within the electrode group. In Fig. 3, the negative electrode and separator are not shown.

[0093] The strip-shaped positive electrode 11 has an edge E1 on the winding start side and an edge E2 on the winding end side. The positive electrode 11 has a region PL (P1 to Pn) of L turns (L = 1 to n) from the edge E1 on the winding start side of the positive electrode 11. In FIG. 3, n = 5, and the positive electrode 11 has regions P1 to P5 of the first to fifth turns. The positive electrode 11 has a main surface PS1 (PS2) on the inner circumferential side (outer circumferential side). Although FIG. 3 shows the case where n = 5, the value of n is not limited to this. In FIG. 3, the region P5 arranged on the outermost periphery of the positive electrode is one turn around the outermost periphery of the positive electrode, but the region Pn may be smaller than one turn around the outermost periphery of the positive electrode.

[0094] 4 to 6 show examples of the planar shape of the spacer 53. In plan view, the spacer 53 (linear convex portion 53a) is disposed on one main surface of the substrate 50. In each figure, the positive electrode 11 facing the substrate 50 is represented by a dashed line. The substrate 50 on which the spacer 53 (convex portion 53a) is disposed is disposed on the inner circumferential side and the outer circumferential side of the positive electrode 11. The substrate 50 on which the spacer 53 (convex portion 53a) is disposed is disposed on the inner circumferential side (main surface PS1 side) and the outer circumferential side (main surface PS2 side) of the positive electrode 11. Note that each figure is a schematic diagram, and the aspect ratios of each component, the area ratios of each component, etc. do not necessarily reflect actual values.

[0095] The spacers 53 in Figures 4 to 6 include a plurality of linear protrusions 53a arranged in a stripe pattern. The plurality of linear protrusions 53a are arranged parallel to and spaced apart from one another along the length direction (LD direction) of the band-shaped substrate 50. The regions where the spacers 53 are not formed form spaces 14s. Although six linear protrusions 53a are arranged in Figures 4 to 6, the number of linear protrusions 53a is not limited to this. The linear protrusions 53a are arranged continuously, but may also be arranged intermittently.

[0096] The substrate 50 has a region S1L (S2L) facing the inner periphery (outer periphery) of the region PL of the positive electrode 11 (L = 1 to n). The ratio of the area ALt (BLt) of the portion of the region S1L (S2L) overlapping with the protrusion 53a to the area AL (BL) of the region S1L (S2L): ALt / AL (BLt / BL) is defined as XL (YL). The values ​​of XL (YL) corresponding to regions P1 to Pn where L = 1 to n (n is an integer of 3 or greater) are defined as X1 to Xn (Y1 to Yn), respectively. Here, X1 (Y1) is smaller than any of the values ​​of X2 to Xn (Y2 to Yn). In the cases of FIGS. 4 and 5, X1 (Y1) is 1 / 2 of X2 to Xn (Y2 to Yn). In the case of FIG. 6, X1 (Y1) is 0. In Fig. 4, the lengths of some of the linear protrusions are adjusted on the region P1 side, whereas in Figs. 5 and 6, the lengths of all of the linear protrusions are adjusted on the region P1 side.

[0097] The spacers of Figures 5 and 6 are preferable in that none of the multiple linear protrusions 53a are positioned more inward than the edge E1 on the winding start side of the positive electrode 11, and are positioned so as not to overlap with the edge E1 on the winding start side of the positive electrode 11.

[0098] Some of the linear protrusions 53a constituting the striped spacer 53 in FIG. 4 have a portion 54 located more inward than the edge E1 at the winding start side of the positive electrode 11. The portion 54 protrudes from the edge E1 of the positive electrode 11. The linear protrusions 53a having the portion 54 intersect with the side corresponding to the edge E1 and have a portion overlapping with the edge E1, and stress caused by Li deposition tends to increase near the overlapping portion. On the other hand, in the striped spacer 53 in FIGS. 5 and 6, none of the linear protrusions 53a have the portion 54, which further suppresses stress concentration in the region P1 of the positive electrode 11.

[0099] From the viewpoint of forming a space in the region P1, the spacer 53 shown in FIG. 5 in which the convex portion 53a is arranged in a part of the region S1 of the substrate 50 facing the region P1 is more preferable.

[0100] 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.

[0101] <<Appendix>> The above embodiments disclose the following technology: (Technology 1) A battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte; in the negative electrode, lithium metal precipitates during charging and dissolves during discharging; the separator comprises a first separator disposed on the inner circumferential side of the positive electrode and a second separator disposed on the outer circumferential side of the positive electrode; the first separator comprises a sheet-like first substrate and a first spacer disposed on a main surface of the first substrate, the first spacer including a first convex portion; the second separator comprises a sheet-like second substrate and a second spacer disposed on a main surface of the second substrate, the second spacer including a second convex portion; the positive electrode has a region PL of L turns from an end of the positive electrode on the winding start side; A lithium secondary battery in which XL is a ratio of an area ALt of a portion of region S1L overlapping with the first convex portion to an area AL of region S1L of the first substrate facing the inner periphery of region PL: ALt / AL, and YL is a ratio of an area BLt of a portion of region S2L overlapping with the second convex portion to an area BL of region S2L of the second substrate facing the outer periphery of region PL: BLt / BL, and where X1 to Xn and Y1 to Yn are the values ​​of XL and YL corresponding to regions P1 to Pn where L = 1 to n (n is an integer of 3 or more), respectively, X1 is smaller than at least one value of X2 to Xn, and Y1 is smaller than at least one value of Y2 to Xn. (Technology 2) The lithium secondary battery according to Technology 1, in which X1 is smaller than any of X2 to Xn, and Y1 is smaller than any of Y2 to Yn. (Technology 3) The lithium secondary battery according to Technology 1 or 2, wherein X1 is 0 or more and 0.5 or less, and Y1 is 0 or more and 0.5 or less. (Technology 4) The lithium secondary battery according to any one of Technology 1 to 3, wherein the first convex portion and the second convex portion are each arranged so as not to overlap with an edge portion on the winding start side of the positive electrode. (Technology 5) The lithium secondary battery according to any one of Technology 1 to 4, wherein the first convex portion and the second convex portion are each not arranged on the inner peripheral side of the edge portion on the winding start side of the positive electrode.(Technology 6) The lithium secondary battery according to any one of Technologies 1 to 5, wherein the first spacer and the second spacer are disposed on the main surfaces of the first substrate and the second substrate on the positive electrode side, respectively. (Technology 7) The lithium secondary battery according to any one of Technologies 1 to 6, wherein the first spacer and the second spacer each include the first convex portion and the second convex portion arranged in a predetermined repeating pattern, respectively. (Technology 8) The lithium secondary battery according to any one of Technologies 1 to 7, wherein a plurality of linear first convex portions and a plurality of linear second convex portions are arranged parallel to and spaced apart from each other along the length directions of the first substrate and the second substrate, respectively. (Technology 9) The lithium secondary battery according to any one of Technologies 1 to 8, wherein the first spacer and the second spacer each include a resin material. (Technology 10) The lithium secondary battery according to any one of Technologies 1 to 9, wherein the first spacer and the second spacer each include a non-porous structure that is impermeable to lithium ions. (Technology 11) The lithium secondary battery according to any one of Technologies 1 to 10, wherein the first substrate and the second substrate each comprise a porous sheet containing a polymer material. (Technology 12) The lithium secondary battery according to any one of Technologies 1 to 11, wherein the first substrate and the second substrate each further comprise a composite material layer containing a resin material and inorganic particles.

[0102] [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.

[0103] Batteries A1-A2, B1 (Preparation of Positive Electrodes) 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 of 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 having the positive electrode mixture layers formed on both sides was cut to a predetermined size to obtain a positive electrode.

[0104] (Preparation of Negative Electrode Current Collector) A strip of electrolytic copper foil (thickness: 12 μm) was prepared as a negative electrode current collector.

[0105] (Preparation of Substrate) 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 solution containing 5.8% by mass of dissolved calcium chloride, and the concentration was adjusted to 2 wt% of aromatic polyamide and 4 wt% of 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, NMP and calcium chloride in the coating film were removed by water washing. The coating film was dried at 60°C for 5 minutes to form a composite material layer (heat-resistant layer). In this way, a substrate comprising a microporous thin film and a composite material layer was obtained.

[0106] (Formation of spacers on the main surface of the substrate) A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to the microporous thin film surface of the substrate, and the coating was dried to form spacers in the pattern (striped) shown in Fig. 5, 6, or 7. In this way, a separator having the substrate and spacers was obtained.

[0107] (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 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).

[0108] (Battery Assembly) An electrode assembly was prepared by spirally winding a positive electrode and a negative electrode current collector with a separator interposed therebetween in an inert gas atmosphere. In this way, a wound electrode assembly with the structure shown in FIG. 2 was obtained. The electrode assembly was constructed so that the separators (substrates with spacers arranged thereon) shown in FIG. 5, FIG. 6, or FIG. 7 were arranged on the inner and outer periphery of the positive electrode, respectively. The separator was arranged so that the main surface of the substrate on which the spacers were formed faced the positive electrode. The linear protrusions arranged on the inner and outer periphery of the positive electrode were positioned relative to the positive electrode as shown in FIG. 5, FIG. 6, or FIG. 7. The electrode assembly was housed in a cylindrical case body with a bottom, and a nonaqueous electrolyte was poured into it. A sealing member was placed in the opening of the case body via a gasket, sealing the electrode assembly and nonaqueous electrolyte within the battery case. In this way, a lithium secondary battery with the structure shown in FIG. 1 was completed. In Table 1, A1 and A2 are examples, and B1 is a comparative example.

[0109] The positive electrode in the electrode group had regions P1 to P5 (n = 5). To connect the positive electrode to the positive electrode lead, a current collector exposure portion was formed along the width direction of a portion of the longitudinal direction of any of regions P2 to P4. In Battery A1 (FIG. 5), X1 (Y1) was 0.06, and each of X2 to X5 (Y2 to Y5) was 0.12. In Battery A2 (FIG. 6), X1 (Y1) was 0, and each of X2 to X5 (Y2 to Y5) was 0.12. In Battery B1 (FIG. 7), X1 to X5 (Y1 to Y5) were the same, each 0.12.

[0110] [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.

[0111] (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.

[0112] (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.

[0113] The above charge and discharge constitute one cycle, and charge and discharge were repeated. 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 and discharge test was terminated. The number of cycles at this time, m, was determined as the number of cycles at which abnormality occurred. Charge and discharge were repeated until the discharge capacity reached 90% of the discharge capacity at the first cycle, and if no abnormal charging occurred, it was determined that there was no abnormality.

[0114] The evaluation results are shown in Table 1.

[0115]

[0116] In Batteries A1 and A2, the cycle of abnormality occurrence was delayed and the occurrence of small internal short circuits was suppressed compared to Battery B1. In particular, Battery A1 showed no abnormalities and exhibited a significant effect of suppressing the occurrence of internal short circuits.

[0117] The lithium 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.

[0118] 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.

[0119] 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: Convex portion

Claims

1. An electrochemical cell comprising: an electrode group in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are wound; and a non-aqueous electrolyte; in the negative electrode, lithium metal precipitates during charging and dissolves during discharging; the separator comprises a first separator disposed on the inner circumferential side of the positive electrode and a second separator disposed on the outer circumferential side of the positive electrode; the first separator comprises a first sheet-like substrate and a first spacer disposed on a main surface of the first substrate, the first spacer comprising a first convex portion; the second separator comprises a second sheet-like substrate and a second spacer disposed on a main surface of the second substrate, the second spacer comprising a second convex portion; the positive electrode has a region PL of L turns from the end of the positive electrode on the winding start side; a ratio ALt / AL of an area ALt of a portion of the region S1L overlapping with the first convex portion to an area AL of the region S1L of the first substrate facing the inner periphery of the region PL, and a ratio BLt / BL of an area BLt of a portion of the region S2L overlapping with the second convex portion to an area BL of the region S2L of the second substrate facing the outer periphery of the region PL, wherein X1 to Xn and Y1 to Yn are the values ​​of XL and YL corresponding to regions P1 to Pn, where L = 1 to n (n is an integer of 3 or more), respectively; X1 is smaller than at least one value of X2 to Xn, and Y1 is smaller than at least one value of Y2 to Xn.

2. The lithium secondary battery according to claim 1, wherein X1 is smaller than any of X2 to Xn, and Y1 is smaller than any of Y2 to Yn.

3. The lithium secondary battery according to claim 1, wherein X1 is 0 or more and 0.5 or less, and Y1 is 0 or more and 0.5 or less.

4. The lithium secondary battery according to claim 1, wherein the first convex portion and the second convex portion are arranged so as not to overlap with the edge portion of the positive electrode on the winding start side.

5. A lithium secondary battery according to any one of claims 1 to 4, wherein the first convex portion and the second convex portion are not positioned further inward than the edge portion on the winding start side of the positive electrode.

6. A lithium secondary battery according to any one of claims 1 to 4, wherein the first spacer and the second spacer are disposed on the main surfaces of the first substrate and the second substrate on the positive electrode side, respectively.

7. A lithium secondary battery according to any one of claims 1 to 4, wherein the first spacer and the second spacer respectively include the first convex portion and the second convex portion arranged in a predetermined repeating pattern.

8. A lithium secondary battery according to any one of claims 1 to 4, wherein the plurality of linear first protrusions and the plurality of linear second protrusions are arranged parallel to and spaced apart from each other along the longitudinal directions of the first substrate and the second substrate, respectively.

9. The lithium secondary battery according to any one of claims 1 to 4, wherein the first spacer and the second spacer each contain a resin material.

10. The lithium secondary battery according to any one of claims 1 to 4, wherein the first spacer and the second spacer each include a non-porous structure that is impermeable to lithium ions.

11. The lithium secondary battery according to any one of claims 1 to 4, wherein the first substrate and the second substrate each comprise a porous sheet containing a polymeric material.

12. The lithium secondary battery according to claim 11, wherein each of the first substrate and the second substrate further comprises a composite layer including a resin material and inorganic particles.

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