Lithium secondary battery

Abstract

This lithium secondary battery is provided with an electrode group obtained by winding a positive electrode, a negative electrode that precipitates Li during charging, and a separator. The separator includes a first separator (second separator) 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 convex portion (second convex portion). The positive electrode has a region PL on the L-th circumference from the end of the positive electrode on the winding start side. XL (YL) is the ratio of the area ALt (BLt) of the portion of the region S1L (S2L) that overlaps the first protrusion (second protrusion) to the area AL (BL) of the region S1L (S2L) of the first substrate (second substrate) that faces the inner peripheral side (outer peripheral side) of the region PL. When the value of XL (YL) corresponding to regions P1-Pn in which L = 1-n (n is an integer of 3 or more) is represented by X1-Xn (Y1-Yn), X1 (Y1) is less than at least one of X2-Xn (Y2-Yn).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a lithium secondary battery. BACKGROUND

[0002] As a high-capacity nonaqueous electrolyte secondary battery, a lithium ion battery is known. As a high-capacity nonaqueous electrolyte secondary battery exceeding the lithium ion battery, a lithium secondary battery (lithium metal secondary battery) is expected. In the lithium secondary battery, lithium metal is deposited at a negative electrode at the time of charging, and the lithium metal dissolves at the time of discharging, and is released as lithium ions into a nonaqueous electrolyte.

[0003] In the lithium secondary battery, lithium metal is deposited at a negative electrode at the time of charging, and therefore a spacer needs to be provided between a positive electrode and the negative electrode to secure a space for deposition of lithium.

[0004] Patent Literature 1 proposes: “A lithium secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte having lithium ion conductivity, lithium metal is deposited at the negative electrode at the time of charging, the lithium metal dissolves from the negative electrode at the time of discharging, a spacer is provided between at least one of the positive electrode and the negative electrode and the separator, a first length in a first direction D1 of the separator is smaller than a second length in a second direction D2 intersecting the first direction D1, in a cross section of the spacer cut in a thickness direction of the separator and the first direction D1, at least one of an angle of the separator on a separator side of the spacer and an angle of an electrode in contact with the spacer on the separator side of the spacer is larger than 90°”.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: International Publication No. 2021 / 192645 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] In a wound-type electrode group, stress generated by deposition of Li in the negative electrode is locally concentrated in the innermost peripheral portion of the positive electrode, and thus the base material is damaged, and sometimes internal short circuit occurs.

[0010] SOLUTION TO THE PROBLEM

[0011] One aspect of the present disclosure relates to a lithium secondary battery including: 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 nonaqueous electrolyte, wherein lithium metal is deposited in the negative electrode at the time of charging, the lithium metal is dissolved at the time of discharging, the separator includes 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 includes a first base material in a sheet shape and a first spacer disposed on a main surface of the first base material, the first spacer includes a first protrusion, the second separator includes a second base material in a sheet shape and a second spacer disposed on a main surface of the second base material, the second spacer includes a second protrusion, the positive electrode has a region PL of the Lth circumferential position from an end portion on a winding start side of the positive electrode, a ratio ALt / AL of an area ALt of a portion of the region S1L overlapping with the first protrusion with respect to an area AL of the region S1L of the first base material opposite to an inner circumferential side of the region PL is set to XL, a ratio BLt / BL of an area BLt of a portion of the region S2L overlapping with the second protrusion with respect to an area BL of the region S2L of the second base material opposite to an outer circumferential side of the region PL is set to YL, and when values of XL and YL corresponding to regions P1 to Pn for L = 1 to n (n is an integer of 3 or more) are set to X1 to Xn and Y1 to Yn, respectively, X1 is smaller than at least one of X2 to Xn, and Y1 is smaller than at least one of Y2 to Xn.

[0012] Effects of the Invention

[0013] According to the present disclosure, it is possible to suppress occurrence of internal short circuit of a lithium secondary battery.

[0014] The novel features of the application are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present application will be obtained by reference to the following detailed description that sets forth illustrative BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 FIG. 1 is a longitudinal sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0016] Figure 2 FIG. 2 is a sectional view schematically showing a main part of the lithium secondary battery shown in FIG. 1. Figure 1

[0017] Figure 3 FIG. 4 is a schematic plan view showing the positive electrode in the electrode group when viewed from the direction of the winding axis.

[0018] Figure 4 FIG. 6 is a plan view showing an example of a spacer.

[0019] Figure 5 ​is a plan view showing another example of a separator.

[0020] Figure 6 is a plan view showing still another example of a separator.

[0021] Figure 7 is a plan view of a separator provided in a conventional lithium secondary battery. DETAILED DESCRIPTION

[0022] Hereinafter, examples will be given to describe embodiments of the present disclosure, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials are sometimes shown as examples, but other numerical values and materials can also be used as long as the effects of the present disclosure are obtained. In the present specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be replaced with "numerical value A or more and numerical value B or less". In the following description, in the case where a lower limit and an upper limit are shown as examples with respect to a specific property, condition, or the like, any one of the lower limits shown as examples can be combined with any one of the upper limits shown as examples as long as the lower limit is not equal to or higher than the upper limit. In the case where a plurality of materials are shown as examples, one of the materials can be selected and used alone, or two or more of the materials can be used in combination.

[0023] The lithium secondary battery of the embodiment of the present disclosure includes an electrode group and a nonaqueous electrolyte. The electrode group is wound by a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. In the negative electrode, lithium metal is deposited at the time of charging and dissolved at the time of discharging. Specifically, the negative electrode includes at least a negative electrode current collector, and lithium metal is deposited on the negative electrode current collector at the time of charging. The nonaqueous electrolyte has lithium ion conductivity. The lithium secondary battery is also referred to as a lithium metal secondary battery.

[0024] In the lithium secondary battery, for example, 70% or more of the rated capacity is embodied by deposition and dissolution of lithium metal. Migration of electrons in the negative electrode at the time of charging and at the time of discharging is mainly dependent on deposition and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100%, 90 to 100%) of migration of electrons in the negative electrode at the time of charging and at the time of discharging (in other aspects, current) is dependent on deposition and dissolution of lithium metal. That is, the movement of electrons in the negative electrode at the time of charging and at the time of discharging of the negative electrode of the lithium secondary battery is different from the negative electrode in which lithium ions are mainly absorbed and released by the negative electrode active material (graphite or the like).

[0025] An electrode group is configured by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator (a strip-shaped base material) interposed therebetween. In the electrode group, the positive electrode and the negative electrode are wound in a manner that the negative electrode is disposed with the separator interposed therebetween on both sides (an inner peripheral side and an outer peripheral side) of the positive electrode in the entire region (regions P1 to Pn described later) of the positive electrode. The separator includes a first separator disposed on the inner peripheral side of the positive electrode and a second separator disposed on the outer peripheral side of the positive electrode. The first separator has a first base material in a sheet shape and a first spacer disposed on a main surface of the first base material, and the first spacer includes a first protrusion. The second separator has a second base material in a sheet shape and a second spacer disposed on a main surface of the second base material, and the second spacer includes a second protrusion. Hereinafter, for matters common to the first separator and the second separator, the separator, the base material, the spacer, and the protrusion are sometimes referred to simply as "separator", "base material", "spacer", and "protrusion".

[0026] In the electrode group, the first protrusion and the second protrusion can be disposed in a manner of overlapping with the positive electrode interposed therebetween, or can be disposed with positions shifted in whole or in part with the positive electrode interposed therebetween. The disposition pattern of the first spacer and the second spacer can be the same or different. For example, one of the first spacer and the second spacer can be in a strip shape, and the other of the first spacer and the second spacer can be in a honeycomb shape.

[0027] The positive electrode has a region PL of the Lth turn from an end portion on a winding start side of the positive electrode. A ratio of an area ALt of a portion of the region S1L overlapping with the first protrusion with respect to an area AL of the region S1L of the first base material opposite to the inner peripheral side of the region PL: ALt / AL is set as XL. A ratio of an area BLt of a portion of the region S2L overlapping with the second protrusion with respect to an area BL of the region S2L of the second base material opposite to the outer peripheral side of the region PL: BLt / BL is set as YL. Values of XL and YL corresponding to the regions P1 to Pn for L = 1 to n (n is an integer of 3 or more) are set as X1 to Xn and Y1 to Yn, respectively. At this time, X1 is smaller than at least one of X2 to Xn. Y1 is smaller than at least one of Y2 to Xn. That is, X1 and Y1 are not the maximum values of X1 to Xn and Y1 to Yn, respectively. The region P1 is the innermost peripheral portion of the positive electrode, and the region Pn is the outermost peripheral portion of the positive electrode. XL can be substantially the same as YL, or can be different. For example, X1 can be substantially the same as Y1, or can be different.

[0028] The positive electrode can have a positive electrode current collector and a positive electrode mixture layer loaded on both faces of the positive electrode current collector. In this case, the region S1L (S2L) is a region of the 1st substrate (2nd substrate) opposed to the positive electrode mixture layer on the inner (outer) circumferential side of the region PL. In order to be connected to the positive electrode lead, the positive electrode can have a region (current collector exposed region) in which the positive electrode mixture layer is not loaded in the central portion in the winding direction (lengthwise direction). In the case where a portion of the inner (outer) circumferential side of the region PL other than the region P1 has the current collector exposed region, the region S1L (S2L) is a region opposed to the positive electrode mixture layer other than the current collector exposed region.

[0029] In the case where the above constitution is satisfied, the stress generated due to the precipitation of Li from the negative electrode can be inhibited from being locally concentrated in the innermost circumferential portion of the positive electrode, and damage to the substrate caused by the concentration of the stress can be inhibited. As a result, the occurrence of internal short circuit caused by the damage to the substrate can be inhibited.

[0030] In the electrode group of the winding type, the influence of the expansion of the negative electrode on the inner circumferential side is large, and a step is easily generated at the boundary of the expanded region. Therefore, the load applied to the separator becomes large at the end portion of the winding start side of the positive electrode. Furthermore, near the convex portion, Li is sometimes precipitated in a manner of encircling the positive electrode mixture layer covered by the convex portion, and thus the thickness of the precipitated Li becomes locally large. Due to the superposition of these main causes, the stress generated along with the expansion of the electrode group is easily locally increased near the portion where the innermost circumferential portion of the positive electrode (particularly, the end edge portion of the winding start side of the innermost circumferential portion) overlaps with the convex portion.

[0031] On the contrary, in the present disclosure, the 1st convex portion (2nd convex portion) is arranged in a manner that X1 (Y1) does not become the largest among X1 to Xn (Y1 to Yn). Thereby, the above stress can be inhibited from being locally increased.

[0032] From the viewpoint of inhibiting the damage to the substrate caused by the concentration of the above stress, it is preferable that the 1st convex portion (2nd convex portion) is arranged with X1 (Y1) being as small as possible with respect to X2 to Xn (Y2 to Yn). X1 (Y1) is preferably smaller than more than half of the values among X2 to Xn (Y2 to Yn). X1 (Y1) is particularly preferably smaller than any value among X2 to Xn (Y2 to Yn), that is, smaller than the minimum value of X2 to Xn (Y2 to Yn).

[0033] From the viewpoint of suppressing the damage to the substrate caused by the stress concentration described above, X1(Y1) can be 0.5 or less, can be 0.35 or less, can be 0.2 or less, or can be 0. Since the partition has the spacer, in the case where X1(Y1) is 0, X1(Y1) cannot become the maximum value of X1 to Xn. Assuming the case where X1 becomes the maximum among X1 to Xn, even if X1(Y1) is 0.5 or less, the stress concentration described above sometimes occurs, and the substrate is damaged. In the case where X1(Y1) is 0, the 1st protrusion (2nd protrusion) is not disposed on the 1st substrate (2nd substrate) on the inner circumferential side (outer circumferential side) opposite to the region P1, but the region P1 is very small compared to the regions P2 to Pn, and thus the expansion of the electrode group caused by the precipitation of Li can be sufficiently suppressed by the disposition of the 1st spacer (2nd spacer).

[0034] From the viewpoint that a space is also easily formed between the regions P2 to Pn and the negative electrode and between the region P1 and the negative electrode, and the expansion of the electrode group caused by the precipitation of Li is more easily suppressed, X1(Y1) can be 0.01 or more, can be 0.025 or more, or can be 0.05 or more. The range of X1(Y1) can be, for example, 0 or more and 0.5 or less, can be 0.01 or more and 0.5 or less, can be 0.01 or more and 0.4 or less, can be 0.01 or more (or 0.025 or more) and 0.35 or less, or can be 0.05 or more and 0.2 or less.

[0035] From the viewpoint that the space in which Li is precipitated is easily and stably formed, X2 to Xn(Y2 to Yn) can be 0.02 or more, or can be 0.05 or more. From the viewpoint that the space in which Li is precipitated is easily ensured, X2 to Xn(Y2 to Yn) can be 0.6 or less, can be 0.45 or less, or can be 0.25 or less. The range of X2 to Xn(Y2 to Yn) can be, for example, 0.02 or more and 0.6 or less, can be 0.05 or more and 0.45 or less, or can be 0.08 or more and 0.25 or less.

[0036] In the innermost circumferential portion of the positive electrode, stress is easily concentrated particularly in the vicinity of the end edge portion of the winding start side of the positive electrode (positive electrode mixture layer), and thus the 1st protrusion (2nd protrusion) is preferably disposed in such a manner that the proportion of overlap with the end edge portion of the winding start side of the positive electrode (positive electrode mixture layer) is reduced, and is more preferably disposed in such a manner that the end edge portion of the winding start side of the positive electrode (positive electrode mixture layer) is not overlapped.

[0037] The 1st protrusion (2nd protrusion) is preferably not disposed on the inner circumferential side (for example, on the outer circumferential side) than the end edge portion of the winding start side of the positive electrode, for example, than the end edge portion of the winding start side of the positive electrode mixture layer. Figures 5-6In this case, since the convex portion does not interfere with the sliding of the end portion of the winding start side of the positive electrode, stress generated due to the expansion of the electrode group toward the inner circumferential side can be mitigated by the sliding of the end portion of the winding start side of the positive electrode. In this case, it is easy to arrange the first convex portion (the second convex portion) so as not to overlap with the end edge portion of the winding start side of the positive electrode. In the case of the strip-shaped spacer, it is easy to arrange the first convex portion (the second convex portion) so as not to cross the edge corresponding to the end edge portion E1 of the winding start side of the positive electrode.

[0038] (Separator)

[0039] The separator has a sheet-shaped base material and a spacer arranged on a main surface of the base material.

[0040] (Base material)

[0041] The base material uses a porous sheet having ion permeability and insulation. The porous sheet can be exemplified by, for example, a microporous film, a woven fabric, a nonwoven fabric, and the like. The material of the porous sheet is not particularly limited and can be a high molecular material. As the high molecular material, an olefin resin, a polyamide resin, cellulose, and the like can be exemplified. As the olefin resin, polyethylene, polypropylene, a copolymer of ethylene and propylene, and the like can be exemplified. The base material can include an additive as needed. As the additive, an inorganic filler and the like can be exemplified.

[0042] The thickness of the base material is not particularly limited and is, for example, 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0043] The base material can include a porous sheet and a composite layer (heat-resistant layer). The composite layer can be formed on one main surface of the porous sheet or on both main surfaces. The composite layer is a layer through which lithium ions permeate. The composite layer includes inorganic particles. The composite layer can include a resin material as needed. The thickness of the composite layer can be 5% to 50% of the total thickness of the base material.

[0044] The composite layer can be arranged on the side of the porous sheet opposite to the positive electrode or on the side of the porous sheet opposite to the negative electrode. In the case where the composite layer is arranged on the positive electrode side, the deterioration of the porous sheet due to oxidation reaction can be suppressed. In the case where the composite layer is arranged on the negative electrode side, the deterioration of the porous sheet due to reduction reaction can be suppressed. The spacer can be arranged on the composite layer. In this case, the effect of suppressing the thermal contraction of the base material becomes particularly high.

[0045] The inorganic particles are preferably particles of an inorganic compound having thermal stability and insulation properties that are not likely to melt and decompose at the time of abnormal heat generation caused by a short circuit of the battery or the like. Examples of the material of the inorganic particles include oxides, hydroxides, nitrides, carbides, sulfides, and the like. Examples of the oxides include alumina, boehmite, magnesia, titania, zirconia, silica, yttria, zinc oxide, and the like. Examples of the nitrides include silicon nitride, aluminum nitride, boron nitride, titanium nitride, and the like. Examples of the carbides include silicon carbide, boron carbide, and the like. Examples of the sulfides include barium sulfate, and the like. Examples of the hydroxides include aluminum hydroxide, and the like. The median particle diameter in the particle size distribution on a volume basis of the inorganic particles can be 0.2 to 2.0 μm.

[0046] The median particle diameter in the particle size distribution on a volume basis of the inorganic particles can be measured, for example, using a laser diffraction / scattering type particle size distribution measuring device (e.g., Microtrac manufactured by Nikkiso Co., Ltd.). Alternatively, the cross section of the base material can be observed using a transmission electron microscope (TEM), a TEM image can be taken, the area surrounded by the outlines of 100 inorganic particles can be calculated, the diameter of an equivalent circle (a perfect circle) having the same area as the calculated area can be found, and the average of the diameters of the 100 equivalent circles can be found.

[0047] As the resin material contained in the composite layer (heat-resistant layer), for example, polyvinylidene fluoride (PVdF), fluorine-containing resins such as polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or hydrogenated product thereof, acrylonitrile-butadiene copolymer or hydrogenated product thereof, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, and the like, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, acrylic resins such as acrylic acid-methacrylic acid copolymer, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid), polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin can be listed.

[0048] The resin material contained in the composite layer (heat-resistant layer) preferably uses a high molecular material having higher heat resistance than the material of the porous sheet. Such a high molecular material preferably contains at least one selected from the group consisting of aromatic polyamide, aromatic polyimide, and aromatic polyamideimide. These are known as high molecular materials having high heat resistance. From the viewpoint of heat resistance, aramid, i.e., meta-aramid (meta-aramid wholly aromatic polyamide) and para-aramid (para-aramid wholly aromatic polyamide) are preferable.

[0049] The content of the inorganic particles in the composite layer can be in the range of 50 mass% to 99 mass% (e.g., in the range of 85 mass% to 99 mass%).

[0050] The composite layer is formed, for example, by applying a coating liquid containing the inorganic particles, the resin material, and a liquid component (dispersion medium) to a porous sheet and drying the coating film. Examples of the liquid component include N-methyl-2-pyrrolidone and the like.

[0051] (Spacer)

[0052] The spacer is formed on the main surface of the substrate. From the viewpoint of easy production of the electrode group or the like, the substrate is preferably integrated with the spacer. The spacer can be provided on the main surface of the substrate (the main surface of the substrate on the positive electrode side) facing the positive electrode, on the main surface of the substrate (the main surface of the substrate on the negative electrode side) facing the negative electrode, or on both main surfaces. In the case where the spacer is provided on the main surface of the substrate facing the positive electrode, Li is precipitated between the spacers in a manner that the substrate is extended toward the positive electrode, and thus compression stress is generated in the precipitation of Li, and Li is easily precipitated densely. From the viewpoint of improving the discharge efficiency and the cycle characteristics, the spacer is preferably provided on the main surface of the substrate facing the positive electrode. On the other hand, in the case where the spacer is provided on the main surface of the substrate facing the negative electrode, since a space is formed in advance between the substrate and the negative electrode, the tension load on the substrate due to the precipitation of Li is reduced. That is, it is advantageous in terms of easy maintenance of the insulation of the substrate or easy maintenance of the short-circuit resistance of the substrate.

[0053] In the lithium secondary battery, the main role of the spacer is to form a space in which lithium metal is precipitated. By accommodating the lithium metal in the space ensured by the spacer, the expansion of the negative electrode at the time of charging can be suppressed.

[0054] The spacer can contain a resin material (e.g., an insulating resin), or can contain a resin material and particles. The proportion of the resin material in the spacer can be 10% by volume or more, 30% by volume or more, or 50% by volume or more, or can be 100% by volume or less or 80% by volume or less.

[0055] As the resin material contained in the spacer, for example, polyvinylidene fluoride (PVdF), fluorine-containing resins such as polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or hydrogenated product thereof, acrylonitrile-butadiene copolymer or hydrogenated product thereof, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, and the like rubber-based materials, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and the like cellulose derivatives, acrylic resins such as acrylic acid-methacrylic acid copolymer, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid), polyamide-imide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin can be listed.

[0056] Among the above-mentioned resin materials, as a material through which lithium ions do not pass, polyimide, polyvinylidene fluoride, acrylonitrile-acrylate copolymer, and the like are preferable, and polyimide can also be used. A non-porous spacer of a certain height or more formed of these resin materials is a layer through which lithium ions do not pass. From the viewpoint of suppressing the increase in the gas generation reaction rate at the time of internal short circuit, it is preferable to provide such a spacer.

[0057] The particles can be inorganic particles or organic particles. Among them, inorganic particles such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides can be listed. As the metal oxides, aluminum oxide (alumina, boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, silicon oxide (silica), and the like are preferable. As the metal hydroxides, aluminum hydroxide and the like can be listed. As the metal nitrides, silicon nitride, aluminum nitride, boron nitride, titanium nitride, and the like can be listed. As the metal carbides, silicon carbide, boron carbide, and the like can be listed. As the metal sulfides, barium sulfate and the like can be listed. In addition, minerals such as aluminosilicate, phyllosilicate, barium titanate, strontium titanate, and the like can also be used. Among them, it is preferable to use alumina, silica, titania, and the like.

[0058] The average particle diameter of the particles is not particularly limited and can be 0.1 μm or more or 0.5 μm or more, or can be 10 μm or less, 5 μm or less, or 2 μm or less. The average particle diameter can be measured by the following method. First, a cross section of the spacers in the thickness direction of the separator is photographed with an electron microscope to obtain an image of the cross section. Next, the image is subjected to image processing such as binarization to determine the portions of the particles. Next, the diameter of a circle having the same area as the area of the cross section of each particle (equivalent circle diameter) is found, and the arithmetic mean of the found equivalent circle diameters can be taken as the average particle diameter. The arithmetic mean can be found, for example, from 100 or more particles. Note that the average particle diameter of other particles contained in the electrode plate and the separator can also be found by the same method.

[0059] In the case where the spacers contain a resin material and particles, the content ratio of the particles in the spacers is preferably 50 vol% or less. Thereby, sufficient strength of the spacers is easily ensured.

[0060] The spacers can include linear protrusions and / or point-like protrusions. The linear protrusions are ridge-like protrusions from one viewpoint. The linear protrusions can be arranged intermittently or continuously. The linear protrusions can be straight or curved.

[0061] The width of the linear protrusions can be 100 μm or more or 200 μm or more, or can be 2000 μm or less or 1000 μm or less.

[0062] The spacers preferably have a prescribed repeating pattern. That is, the protrusions are preferably arranged in a prescribed repeating pattern. The linear protrusions can be arranged in a strip-like pattern or in a grid-like pattern. The grid-like pattern can also be a collection of polygons. In one example of the grid-like pattern, shapes in which polygons are combined in a manner sharing a side are included. The polygons include triangles, quadrilaterals, hexagons, and the like. Different kinds of polygons can also be combined. The grid-like pattern can also be a honeycomb shape. In addition, the point-like protrusions can also be arranged in a prescribed repeating pattern.

[0063] In the case where the arrangement pattern of the first spacers (second spacers) is dot-like, the maximum diameter, number (interval), or the like of the convex portions can be changed depending on the region S1L (S2L) of the first substrate (second substrate), whereby the above-described XL (YL) can be adjusted. In the case where the arrangement pattern of the first spacers (second spacers) is line-like, the number (interval), or the like of the first convex portions (second convex portions) can be changed depending on the region S1L (S2L) of the first substrate (second substrate), whereby the above-described XL (YL) can be adjusted. In the case where the first spacers (second spacers) (first convex portions (second convex portions)) are arranged intermittently (in the case where the defect portions are locally provided), the number, size (length), or the like of the defect portions can be changed depending on the region S1L (S2L) of the first substrate (second substrate), whereby the above-described XL (YL) can be adjusted.

[0064] The height H of the spacers (convex portions) can be greater than the thickness T of the substrate. The ratio of the height H to the thickness T: H / T is greater than 1, and can be 1.5 or greater, 2 or greater, or 3 or greater. H / T can also be 10 or less, 8 or less, 5 or less, or 4 or less. By setting H / T to be 1.5 or greater, the expansion of the electrode group can be particularly suppressed.

[0065] The height H can be measured by the following method. First, a cross section in the thickness direction of the separator (substrate) is photographed with an electron microscope, and an image of the cross section is obtained. Next, in the image, the height of the spacer at any 20 points in the spacer is measured. Next, the heights of the 20 points that were measured are arithmetically averaged, and the average value obtained is taken as the height H. The thickness T can also be measured by the same procedure.

[0066] The spacers are formed, for example, by applying a coating liquid containing a component of the spacers and a liquid component to a prescribed position of the substrate and drying the coating film. Examples of the liquid component include N-methyl-2-pyrrolidone and the like. The application can be performed using a dispenser or the like, or a known printing method such as gravure printing, inkjet printing, and screen printing. In addition, the drying can be performed by a known method such as drying using heating, natural drying, or the like.

[0067] (Negative electrode)

[0068] The negative electrode has a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode due to charging. More specifically, lithium ions contained in a nonaqueous electrolyte become lithium metal by accepting electrons on the negative electrode due to charging, and are 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 nonaqueous electrolyte due to discharging.

[0069] The negative electrode can include a lithium ion occluding layer (a layer that exhibits capacity by occlusion and release of lithium ions by a negative electrode active material (graphite, etc.)) supported on a negative electrode current collector. In this case, the open circuit potential of the negative electrode at full charge can be 70 mV or less with respect to lithium metal (the dissolution potential of lithium). In the case where the open circuit potential of the negative electrode at full charge is 70 mV or less with respect to lithium metal, lithium metal is present on the surface of the lithium ion occluding layer at full charge. That is, the negative electrode exhibits capacity by precipitation and dissolution of lithium metal.

[0070] Here, full charge refers to a state in which the battery is charged to a state in which the state of charge reaches, for example, 0.98xC or more when the rated capacity of the battery is set to C. The open circuit potential of the negative electrode at full charge can be measured by disassembling the battery at full charge state in an argon atmosphere, taking out the negative electrode, assembling a battery cell with lithium metal as a counter electrode, and performing the measurement. The nonaqueous electrolyte of the battery cell can be the same composition as the nonaqueous electrolyte in the disassembled battery.

[0071] The lithium ion occluding layer is formed by forming a negative electrode mixture including a negative electrode active material in a layer shape. The negative electrode mixture can include, in addition to the negative electrode active material, a binder, a thickening agent, a conductive agent, and the like.

[0072] As the negative electrode active material, a carbonaceous material, a Si-containing material, a Sn-containing material, and the like can be given. The negative electrode can include one kind of negative electrode active material, or two or more kinds in combination. As the carbonaceous material, for example, graphite, easy graphitizable carbon (soft carbon), and hard graphitizable carbon (hard carbon) can be given.

[0073] The conductive material is, for example, a carbon material. As the carbon material, carbon black, acetylene black, ketjen black, carbon nanotube, and graphite can be given.

[0074] As the binder material, for example, a fluorine resin, a polyacrylonitrile, a polyimide resin, an acrylic resin, a polyolefin resin, a rubber-like polymer, and the like can be given. As the fluorine resin, polytetrafluoroethylene, polyvinylidene fluoride, and the like can be given.

[0075] The negative electrode current collector can be any conductive sheet. As the conductive sheet, a foil, a thin film, and the like can be used.

[0076] The material of the negative electrode current collector (conductive sheet) can be any conductive material other than lithium metal and lithium alloy. The conductive material can be a metal material such as a metal or an alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form any of an alloy and an intermetallic compound with lithium is preferred. Such a conductive material can be, for example, copper (Cu), nickel (Ni), iron (Fe), an alloy including these metal elements, or graphite that preferentially exposes a basal plane. As the alloy, a copper alloy, stainless steel (SUS), and the like can be given. Among them, copper and / or a copper alloy having high conductivity is preferred.

[0077] The thickness of the negative current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0078] (Positive electrode)

[0079] The positive electrode, for example, has a positive current collector and a positive electrode mixture layer supported on the positive current collector. The positive electrode mixture layer, for example, contains a positive electrode active material, a conductive material, and a binding material. The positive electrode mixture layer can be formed on only one surface of the positive current collector or on both surfaces. The positive electrode, for example, is obtained by coating the positive electrode mixture paste containing the positive electrode active material, the conductive material, and the binding material on both surfaces of the positive current collector, drying the coated film, and then performing calendering.

[0080] The positive electrode active material is a material that absorbs and releases lithium ions. As the positive electrode active material, for example, a lithium-containing transition metal oxide, a transition metal fluoride, a polyanion, a fluorinated polyanion, a transition metal sulfide, or the like can be listed. Among them, from the aspects of inexpensive manufacturing cost and high average discharge voltage, a lithium-containing transition metal oxide is preferable.

[0081] Lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions at the time of charging and is deposited as lithium metal on the negative electrode or the negative current collector. At the time of discharging, the lithium metal dissolves from the negative electrode to release lithium ions, which are absorbed by the composite oxide of the positive electrode. That is, the lithium ions involved in charging and discharging are derived substantially from the solutes in the nonaqueous electrolyte and the positive electrode active material.

[0082] As the transition metal element contained in the lithium-containing transition metal oxide, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, or the like can be listed. The lithium-containing transition metal oxide can contain one kind of transition metal element or two or more kinds. The transition metal element can be Ni, Co, and / or Mn. The lithium-containing transition metal oxide can contain one or more typical elements as needed. As the typical element, Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, or the like can be listed. The typical element can be Al or the like.

[0083] In the lithium-containing transition metal oxide, Ni, Co, and / or Mn are contained as the transition metal element and Al is contained as an arbitrary component, and from the viewpoint of obtaining a high capacity, a composite oxide having a rock salt type crystal structure having a layered structure is preferable. In this case, in the lithium secondary battery, the molar ratio of the total amount of lithium mLi possessed by the positive electrode and the negative electrode to the amount mM of the metal M other than lithium possessed by the positive electrode: mLi / mM is, for example, set to 1.1 or less.

[0084] As the binder material, the conductive material, and the like, for example, the substances exemplified in the negative electrode can be used. The shape and the thickness of the positive electrode current collector can be selected from the shapes and the ranges of the positive electrode current collector, respectively.

[0085] As the material of the positive electrode current collector (conductive sheet), for example, a metal material containing Al, Ti, Fe, or the like can be listed. The metal material can be Al, Al alloy, Ti, Ti alloy, Fe alloy, or the like. The Fe alloy can also be stainless steel (SUS).

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

[0087] (non-aqueous electrolyte)

[0088] The non-aqueous electrolyte having lithium ion conductivity can be a liquid electrolyte (electrolytic solution), can be a gel-like electrolyte, or can be 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 can contain a publicly known additive.

[0089] The gel-like electrolyte contains a lithium salt and a base polymer, or contains a lithium salt, a non-aqueous solvent, and a base polymer. As the base polymer, for example, a polymer material that absorbs a non-aqueous solvent to be gelled can be used. As the polymer material, a fluorine resin, an acrylic resin, a polyether resin, polyethylene oxide, or the like can be listed.

[0090] As the solid electrolyte, for example, a publicly known material (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halide-based solid electrolyte, or the like) in a full solid-state lithium ion secondary battery or the like can be used.

[0091] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. By dissolving the lithium salt in the non-aqueous solvent, lithium ions and anions are generated.

[0092] As the anion, BF4 - , ClO4 - , PF6 - , CF3SO3 - , CF3CO2 - , an anion of an imide, an anion of an oxalate complex, or the like can be listed. As the anion of the imide, N(SO2CF3)2 - , N(C m F 2m+1 SO2) x (C n F 2n+ 1SO2) y -(m and n are each independently an integer of 1 or more, x and y are each independently 0, 1, or 2, and x + y = 2) and the like. The anion of the oxalate complex salt can contain boron and / or phosphorus. As the anion of the oxalate complex salt, there can be mentioned a bis-oxalate borate anion, a difluoro-oxalate borate anion (BF2(C2O4) - ), PF4(C2O4) - , PF2(C2O4)2 - , and the like. The nonaqueous electrolyte can contain these anions alone or two or more kinds of them.

[0093] From the viewpoint of suppressing the dendritic precipitation of lithium metal, the nonaqueous electrolyte preferably contains at least the anion of the oxalate complex salt, and it is preferable to contain the anion of the oxalate complex salt having fluorine. By the interaction of the anion of the oxalate complex salt having fluorine with lithium, the lithium metal is easily precipitated uniformly in fine particles. Thus, the local precipitation of lithium metal is easily suppressed. The anion of the oxalate complex salt having fluorine can also be combined with other anions. The other anions can be PF6 - and / or an anion of an imide.

[0094] As the nonaqueous solvent, there can be mentioned, for example, an ester, an ether, a nitrile, an amide, or a halogen-substituted product thereof. The nonaqueous electrolyte can contain these nonaqueous solvents alone or two or more kinds of them. As the halogen-substituted product, there can be mentioned a fluoride or the like.

[0095] As the ester, there can be mentioned, for example, a carbonate, a carboxylate, or the like. As the cyclic carbonate, there can be mentioned ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), or the like. As the chain carbonate, there can be mentioned dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, or the like. As the cyclic carboxylate, there can be mentioned γ-butyrolactone, γ-valerolactone, or the like. As the chain carboxylate, there can be mentioned ethyl acetate, methyl propionate, fluoro methyl propionate, or the like.

[0096] As the ether, there can be mentioned a cyclic ether and a chain ether. As the cyclic ether, there can be mentioned 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, or the like. As the chain ether, there can be mentioned 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diethylene glycol dimethyl ether, or the like.

[0097] The concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the nonaqueous electrolyte can be set to 0.5 mol / L or more and 3.5 mol / L or less. In addition, the concentration of the anion of the oxalate complex salt in the nonaqueous electrolyte can be 0.05 mol / L or more and 1 mol / L or less.

[0098] The nonaqueous electrolyte can contain an additive. The additive can form a coating film on the negative electrode. By forming a coating film derived from the additive on the negative electrode, generation of dendrites is easily suppressed. As such an additive, for example, vinylene carbonate, FEC, vinyl ethylene carbonate (VEC), and the like can be cited.

[0099] Hereinafter, an example of a lithium secondary battery according to the present embodiment will be described with reference to the drawings. The constituent elements of the lithium secondary battery according to the example described hereinafter can apply the constituent elements described above. In addition, the constituent elements according to the example described hereinafter can be changed based on the description above. In addition, the matters to be described hereinafter can apply to the above-described embodiments. In addition, in the lithium secondary battery described hereinafter, the constituent elements not necessary for the lithium secondary battery to which the present disclosure relates can be omitted. Note that in the drawings hereinafter, the scale of the constituent elements is changed for easy understanding.

[0100] (Embodiment 1)

[0101] Figure 1 is a longitudinal sectional view schematically showing an example of the lithium secondary battery according to Embodiment 1. Note that in Figure 1 , the illustration of the spacer and the space formed by the spacer is omitted. Figure 1 The cylindrical lithium secondary battery 10 shown in the figure includes a cylindrical battery case and a jelly-roll type electrode group 14 and a nonaqueous electrolyte (not shown) housed in the battery case. The battery case includes a bottomed cylindrical metal container case main body 15 and a seal 16 that seals the opening of the case main body 15. A gasket 27 is disposed between the case main body 15 and the seal 16. The gasket 27 ensures the airtightness of the battery case. In the case main body 15, insulating plates 17, 18 are disposed at both ends in the winding axis direction of the electrode group 14, respectively.

[0102] The case main body 15 has, for example, a stepped portion 21 formed by partially pressing the side wall of the case main body 15 from the outside. The stepped portion 21 can also be formed in a ring shape along the circumferential direction of the case main body 15 in the side wall of the case main body 15. In this case, the seal 16 is supported by the face of the stepped portion 21 on the opening side.

[0103] The closure 16 includes a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a lid 26. These members are stacked in this order in the closure 16. The closure 16 is attached to the opening portion of the case main body 15 in such a manner that the lid 26 is located on the outside of the case main body 15 and the perforated metal plate 22 is located on the inside of the case main body 15. Each of the above-described members constituting the closure 16 is, for example, a circular plate shape or a ring shape. The lower valve body 23 and the upper valve body 25 are connected to each other at central portions thereof, and the insulating member 24 is interposed between peripheral edge portions thereof. The perforated metal plate 22 and the lower valve body 23 are connected to each other at central portions thereof. The upper valve body 25 and the lid 26 are connected to each other at central portions thereof. That is, each of the members other than the insulating member 24 is electrically connected to each other.

[0104] A vent hole, not shown, is formed in the lower valve body 23. Therefore, when the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 expands toward the lid 26 side and separates from the lower valve body 23. Thus, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure further rises, the upper valve body 25 breaks and gas is discharged from an opening portion, not shown, formed in the lid 26.

[0105] Figure 2 is an enlarged view of a portion of the electrode group 14. Figure 2 includes a portion near the positive electrode surrounded by Figure 1 Region II, and a portion near the negative electrode surrounded by Figure 1 Region III.

[0106] The electrode group 14 includes the positive electrode 11, the negative electrode 12, and a separator (the base material 50 and the spacer 53). The positive electrode 11, the negative electrode 12, and the base material 50 of the separator are each in a strip shape. The positive electrode 11, the negative electrode 12, and the separator (the base material 50) are wound in such a manner that the separator is disposed between the positive electrode 11 and the negative electrode 12, thereby forming the electrode group 14.

[0107] 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 the lid 26 functioning as a positive electrode terminal via a positive electrode lead 19. Figure 2 In the drawing, as the negative electrode 12, a negative electrode (a negative electrode current collector) in a state in which lithium metal is not deposited is shown. The negative electrode 12 is electrically connected to the case main body 15 functioning as a negative electrode terminal via a negative electrode lead 20.

[0108] The substrate 50 has a main surface 50a opposite to the positive electrode 11 and a main surface 50b opposite to the negative electrode 12. In Embodiment 1, the substrate 50 includes a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on the main surface of the porous sheet 51 on the side facing the negative electrode 12. In Embodiment 1, a spacer 53 is formed on the main surface 50a opposite to the positive electrode 11. The spacer 53 is formed on the composite material layer 52 and is in contact with the positive electrode 11. A space 14s is formed between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the substrate 50) through the spacer 53. Figure 2 The height h represents the height of the spacer 53.

[0109] exist Figure 2 In this structure, the spacer 53 is disposed on the main surface 50a of the positive electrode 11 side of the substrate 50, but it can also be disposed on the main surface 50b of the negative electrode 12 side of the substrate 50. The spacer 53 is formed on the composite material layer 52, but it can 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 it can also be disposed on the negative electrode 12 side.

[0110] In the lithium secondary battery 10, lithium metal is deposited on the negative electrode 12 during charging. Since there is a space 14s between the positive electrode 11 and the negative electrode 12, the volume change of the electrode assembly 14 accompanying the lithium metal deposition is reduced, and the cycle characteristics are improved.

[0111] Figure 3 This is a schematic top view showing an example of the positive electrode when viewed from the direction of the winding shaft. Figure 3 This indicates a state where a positive electrode is wound within the electrode assembly. Figure 3 The diagrams of the negative electrode and the separator are omitted.

[0112] The strip-shaped positive electrode 11 has an end edge E1 on the winding start side and an end edge E2 on the winding end side. The positive electrode 11 has a region PL (P1 to Pn) extending L times (L = 1 to n) from the end edge E1 on the winding start side of the positive electrode 11. Figure 3 In this configuration, n=5, and the positive electrode 11 has regions P1 to P5 in cycles 1 to 5. The positive electrode 11 has a principal surface PS1 (PS2) on its inner peripheral side (outer peripheral side). Figure 3 The example shown illustrates the case where n=5, but the value of n is not limited to this. Figure 3 In the process, region P5, located at the outermost periphery of the positive electrode, has the amount of the outermost periphery of the positive electrode, but region Pn can also be smaller than the amount of the outermost periphery of the positive electrode.

[0113] Figures 4-6Examples of the planar shape of the spacer 53. The spacer 53 (linear protrusions 53a) is arranged on one main surface of the substrate 50 when viewed from above. In each drawing, the positive electrode 11 opposite to the substrate 50 is indicated by a broken line. The substrate 50 on which the spacer 53 (protrusions 53a) is arranged is arranged on the inner circumferential side and the outer circumferential side of the positive electrode 11, respectively. The substrate 50 on which the spacer 53 (protrusions 53a) is arranged is arranged on the inner circumferential side (the main surface PS1 side) and the outer circumferential side (the main surface PS2 side) of the positive electrode 11. Note that each drawing is a schematic view, and the aspect ratio of each member, the area ratio of each member, and the like do not necessarily reflect the actual situation.

[0114] Figures 4-6 The spacer 53 of Example 1 includes a plurality of linear protrusions 53a arranged in a strip shape. The plurality of linear protrusions 53a are arranged in parallel to each other apart along the length direction (the LD direction) of the belt-shaped substrate 50. The region in which the spacer 53 is not formed constitutes the space 14s. In Figures 4-6 Example 1, six linear protrusions 53a are arranged, but the number of linear protrusions 53a is not limited to this. The linear protrusions 53a are arranged continuously, but can be arranged intermittently.

[0115] The substrate 50 has regions S1L (S2L) (L = 1 to n) opposite to the inner circumferential side (the outer circumferential side) of the region PL of the positive electrode 11. 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) is set to XL (YL). The values of XL (YL) corresponding to the regions P1 to Pn for L = 1 to n (n is an integer of 3 or more) are set to X1 to Xn (Y1 to Yn), respectively. At this time, X1 (Y1) is smaller than any of X2 to Xn (Y2 to Yn). In Figure 4 and Figure 5 , X1 (Y1) is 1 / 2 of X2 to Xn (Y2 to Yn). In Figure 6 , X1 (Y1) is 0. In Figure 4 , the length of a part of the plurality of linear protrusions is adjusted on the region P1 side. In Figure 5 and Figure 6 , the length of all of the plurality of linear protrusions is adjusted on the region P1 side.

[0116] The plurality of linear protrusions 53a are not arranged at a position more on the inner circumferential side than the end edge portion E1 of the winding start side of the positive electrode 11, but are arranged so as not to overlap with the end edge portion E1 of the winding start side of the positive electrode 11, and in this regard, the spacer of Figure 5 and Figure 6 is preferable.

[0117] The spacer 53 of Example 1 includes a plurality of linear protrusions 53a arranged in a strip shape. The plurality of linear protrusions 53a are arranged in parallel to each other apart along the length direction (the LD direction) of the belt-shaped substrate 50. The region in which the spacer 53 is not formed constitutes the space 14s. In Figure 4A portion of the linear protrusion 53a of the strip-shaped spacer 53 has a portion 54 disposed inward of the end edge portion E1 of the winding start side of the positive electrode 11. The portion 54 is a portion protruding from the end edge portion E1 of the positive electrode 11. The linear protrusion 53a having the portion 54 intersects with the side corresponding to the end edge portion E1, has a portion overlapping the end edge portion E1, and stress generated due to precipitation of Li in the vicinity of the overlapping portion tends to increase. On the other hand, Figure 5 and Figure 6 The strip-shaped spacer 53 of the present embodiment does not have the portion 54 in the entire linear protrusion 53a, and thus stress concentration in the region P1 of the positive electrode 11 is further suppressed.

[0118] From the viewpoint of forming a space in the region P1, it is more preferable that the protrusion 53a be disposed in a portion of a region S1 of the substrate 50 opposite the region P1. Figure 5 The spacer 53 of the present embodiment.

[0119] In Embodiment 1, a cylindrical lithium secondary battery provided with a wound electrode group was described. However, the lithium secondary battery of the present embodiment is not limited to the mode of Embodiment 1, and can be applied to other modes. The shape of the lithium secondary battery can be appropriately selected from various shapes such as a cylindrical shape, a coin shape, a square shape, a sheet shape, a flat shape, and the like, according to the use or the like thereof.

[0120] APPENDIX

[0121] The following technology is disclosed by the above description of the embodiments.

[0122] (Technology 1)

[0123] A lithium secondary battery includes 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 nonaqueous electrolyte,

[0124] In the negative electrode, lithium metal is precipitated at the time of charging, and the lithium metal is dissolved at the time of discharging,

[0125] The separator includes a first separator disposed on an inner periphery side of the positive electrode and a second separator disposed on an outer periphery side of the positive electrode,

[0126] The first separator includes a first substrate in a sheet shape and a first spacer disposed on a main surface of the first substrate, and the first spacer includes a first protrusion,

[0127] The second separator includes a second substrate in a sheet shape and a second spacer disposed on a main surface of the second substrate, and the second spacer includes a second protrusion,

[0128] The positive electrode has a region PL at the Lth periphery from an end portion of a winding start side of the positive electrode,

[0129] The ratio of the area ALt of the portion of the aforementioned region S1L overlapping the aforementioned first protrusion to the area AL of the region S1L of the aforementioned first base material opposite the inner circumferential side of the aforementioned region PL is set to XL,

[0130] The ratio of the area BLt of the portion of the aforementioned region S2L overlapping the aforementioned second protrusion to the area BL of the region S2L of the aforementioned second base material opposite the outer circumferential side of the aforementioned region PL is set to YL,

[0131] When the values of XL and YL corresponding to the regions P1 to Pn of L = 1 to n (n is an integer of 3 or more) are set to X1 to Xn and Y1 to Yn, respectively,

[0132] X1 is smaller than at least one of X2 to Xn,

[0133] Y1 is smaller than at least one of Y2 to Xn.

[0134] (Technology 2)

[0135] The lithium secondary battery according to Technology 1, wherein X1 is smaller than any of X2 to Xn, and Y1 is smaller than any of Y2 to Yn.

[0136] (Technology 3)

[0137] 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.

[0138] (Technology 4)

[0139] The lithium secondary battery according to any one of Technologies 1 to 3, wherein the aforementioned first protrusion and the aforementioned second protrusion are each disposed so as not to overlap the end edge portion of the winding start side of the aforementioned positive electrode.

[0140] (Technology 5)

[0141] The lithium secondary battery according to any one of Technologies 1 to 4, wherein neither the aforementioned first protrusion nor the aforementioned second protrusion is disposed at a position more toward the inner circumferential side than the end edge portion of the winding start side of the aforementioned positive electrode.

[0142] (Technology 6)

[0143] The lithium secondary battery according to any one of Technologies 1 to 5, wherein the aforementioned first spacer and the aforementioned second spacer are each disposed at the positive electrode side main surface of the aforementioned first base material and the aforementioned second base material.

[0144] (Technology 7)

[0145] The lithium secondary battery according to any one of techniques 1 to 6, wherein the first spacer and the second spacer each include the first protrusions and the second protrusions, respectively, arranged in a prescribed repeating pattern.

[0146] (TECHNIQUE 8)

[0147] The lithium secondary battery according to any one of techniques 1 to 7, wherein the plurality of linear first protrusions and the plurality of linear second protrusions are each arranged in parallel to each other along a length direction of the first substrate and the second substrate, respectively, separated from each other.

[0148] (TECHNIQUE 9)

[0149] The lithium secondary battery according to any one of techniques 1 to 8, wherein the first spacer and the second spacer each include a resin material.

[0150] (TECHNIQUE 10)

[0151] The lithium secondary battery according to any one of techniques 1 to 9, wherein the first spacer and the second spacer each include a non-porous structure that is impermeable to lithium ions.

[0152] (TECHNIQUE 11)

[0153] The lithium secondary battery according to any one of techniques 1 to 10, wherein the first substrate and the second substrate each include a porous sheet including a polymer material.

[0154] (TECHNIQUE 12)

[0155] The lithium secondary battery according to any one of techniques 1 to 11, wherein the first substrate and the second substrate each further include a composite layer including a resin material and inorganic particles.

[0156] [EMBODIMENT]

[0157] Hereinafter, the lithium secondary battery of the present disclosure will be described more specifically based on an embodiment and a comparative example. However, the present disclosure is not limited to the following embodiment.

[0158] 《Batteries A1 to A2, B1》

[0159] (Production of the positive electrode)

[0160] A positive electrode slurry is prepared by mixing a positive electrode active material, acetylene black (AB; conductive material), polyvinylidene fluoride (PVdF; binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP). The positive electrode active material is a rock-salt type lithium-containing transition metal oxide (NCA: positive electrode active material) with a layered structure, containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0). The mass ratio of NCA:AB:PVdF in the positive electrode slurry is set at 95:2.5:2.5. The positive electrode slurry is coated on both sides of a strip of Al foil (positive electrode current collector), and the coating is dried and calendered to form a positive electrode slurry layer. The positive electrode current collector with positive electrode slurry layers formed on both sides is cut to a specified size to obtain the positive electrode.

[0161] (Preparation of the negative current collector)

[0162] Prepare a strip of electrolytic copper foil (12μm thick) as the negative electrode current collector.

[0163] (Making of the substrate)

[0164] A 10 μm thick polyethylene microporous film was prepared. A coating solution containing an aromatic polyamide (p-phenylene terephthalamide) as the resin material and alumina as inorganic particles was coated onto one main surface of the microporous film. The coating solution was prepared using an N-methyl-2-pyrrolidone solution containing 5.8% by mass calcium chloride, adjusted to a concentration of 2 wt% aromatic polyamide and 4 wt% alumina. The microporous film with the coating was placed at 25°C and 70% relative humidity for 1 hour to allow the aromatic polyamide to precipitate. Then, NMP and calcium chloride were removed from the coating by washing with water. The coating was dried at 60°C for 5 minutes to form a composite material layer (heat-resistant layer). This process was repeated to obtain a substrate having a microporous film and a composite material layer.

[0165] (Form spacers on the main surface of the substrate)

[0166] A coating solution containing polyvinylidene fluoride and alumina particles (inorganic filler) is applied to the microporous film surface of the above-mentioned substrate, and the coating is dried to form... Figure 5 , Figure 6 or Figure 7 The spacers are arranged in the pattern shown (stripes). This process is repeated to obtain a separator having a substrate and spacers.

[0167] (Preparation of non-aqueous electrolytes)

[0168] Prepare a mixed solvent containing 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF2(CF2OCH2)CF3) in a 1:2 volume ratio. Dissolve 1 mol / L lithium bis(sulfonyl)imide (LiFSI) and 0.1 mol / L LiBF2 (C2O4) in the mixed solvent to prepare a liquid non-aqueous electrolyte (ether-based electrolyte).

[0169] (Battery assembly)

[0170] In an inert gas atmosphere, the positive and negative current collectors are wound into a spiral shape with a separator between them to fabricate an electrode assembly. This process yields... Figure 2 The structure shown is a wound-type electrode assembly. At this time, with... Figure 5 , Figure 6 or Figure 7 The electrode assembly is formed by distributing spacers (substrate with spacers) on the inner and outer peripheral sides of the positive electrode. The spacers are positioned so that the main surface of the substrate with the spacers faces the positive electrode. The positional relationship between the linear protrusions on the inner and outer peripheral sides of the positive electrode and the positive electrode is defined as follows: Figure 5 , Figure 6 or Figure 7 The positional relationship is shown. The electrode assembly is housed within a bottomed cylindrical casing, and a non-aqueous electrolyte is injected. A sealing element is placed at the opening of the casing, separated by a gasket, to seal the electrode assembly and non-aqueous electrolyte within the battery casing. This process completes the battery assembly. Figure 1 The lithium secondary battery with the structure shown is illustrated. A1 to A2 in Table 1 are examples, and B1 is a comparative example.

[0171] It should be noted that the positive electrode within the electrode assembly has regions P1 to P5 (n=5). For the connection between the positive electrode and the positive electrode lead, a portion of the current collector is formed along the width direction from the length direction of any region P2 to P4. In battery A1 ( Figure 5 In the battery A2, X1(Y1) is 0.06, and X2 to X5(Y2 to Y5) are 0.12 respectively. Figure 6 In the given information, X1(Y1) is 0, and X2 to X5(Y2 to Y5) are 0.12 respectively. In battery B1 (… Figure 7 In ), X1~X5 (Y1~Y5) are the same as 0.12.

[0172] [evaluate]

[0173] (Charge / Discharge Test)

[0174] Charge-discharge tests were conducted on the obtained batteries. During the charge-discharge tests, the batteries were charged in a constant temperature bath at 25°C under the following conditions, paused for 20 minutes, and then discharged under the following conditions.

[0175] (Charging)

[0176] Constant current charging was performed at a current of 10 mA per unit area (cm2) of the electrode until the battery voltage reached 4.1 V. Then, constant voltage charging was performed at a voltage of 4.1 V until the current value per unit area of the electrode reached 1 mA.

[0177] (Discharging)

[0178] Constant current discharging was performed at a current of 10 mA per unit area (cm2) of the electrode until the battery voltage reached 3.0 V.

[0179] The above charging and discharging were repeated as one cycle, and when the charge capacity of the mth cycle was increased by 1% or more with respect to the charge capacity of the (m-1)th cycle of the previous 1 cycle, it was determined that abnormal charging had occurred due to the occurrence of a slight internal short circuit, and the charging and discharging test was ended. The cycle number m at this time was obtained as the abnormal occurrence cycle number. The charging and discharging were repeated until the discharge capacity reached 90% of the discharge capacity of the 1st cycle, and in the case where abnormal charging did not occur, it was determined that there was no abnormality.

[0180] The evaluation results are shown in Table 1.

[0181] [Table 1]

[0182]

[0183] In the batteries A1 to A2, the cycle at which abnormality occurred was delayed, and the occurrence of a slight internal short circuit was suppressed, as compared with the battery B1. In particular, in the battery A1, there was no abnormality, and the effect of suppressing the occurrence of an internal short circuit was significantly obtained.

[0184] Industrial Applicability

[0185] The lithium secondary battery of the present disclosure can be used for electronic devices such as mobile phones, smartphones, tablet terminals, electric vehicles including hybrid vehicles and plug-in hybrid vehicles, household storage batteries combined with solar cells, and the like.

[0186] The present application has been described with respect to the currently preferred embodiments, but such disclosures are not to be taken as limiting the present application. Various modifications and changes can be made by those of ordinary skill in the art having the benefit of this disclosure, without departing from the true spirit and scope of the application. Therefore, the appended claims should be construed to include all such modifications and changes as falling within the true spirit and scope of the present application.

[0187] Explanation of Reference Numerals

[0188] 10: lithium secondary battery, 11: positive electrode, 12: negative electrode, 14: electrode group, 14s: space, 15: case main body, 16: sealing body, 23: lower valve body, 25: upper valve body, 50: base material, 51: porous sheet, 52: composite layer, 53: spacer, 53a: protrusion

Claims

1. A lithium secondary battery 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 nonaqueous electrolyte, lithium metal is deposited in the negative electrode upon charging, and the lithium metal dissolves upon discharging, the separator includes 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 includes a first base material in a sheet shape and a first spacer disposed on a main surface of the first base material, the first spacer including a first protrusion, the second separator includes a second base material in a sheet shape and a second spacer disposed on a main surface of the second base material, the second spacer including a second protrusion, the positive electrode has a region PL at the Lth turn from an end portion on a winding start side of the positive electrode, a ratio ALt / AL of an area ALt of a portion of the region S1L overlapping the first protrusion with respect to an area AL of the region S1L of the first base material on an inner circumferential side of the region PL is set as XL, a ratio BLt / BL of an area BLt of a portion of the region S2L overlapping the second protrusion with respect to an area BL of the region S2L of the second base material on an outer circumferential side of the region PL is set as YL, When the values of XL and YL corresponding to the regions P1 to Pn of L = 1 to n are set as X1 to Xn and Y1 to Yn, respectively, wherein n is an integer of 3 or more, X1 is less than at least one of X2 to Xn, Y1 is less than at least one of Y2 to Yn.

2. The lithium secondary battery according to claim 1, wherein X1 is less than any one of X2 to Xn, and Y1 is less than any one 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 protrusion and the second protrusion are each disposed so as not to overlap an end edge portion on the winding start side of the positive electrode.

5. The lithium secondary battery according to any one of claims 1 to 4, wherein Neither the first protrusion nor the second protrusion is disposed at a position closer to the inner circumferential side than the end edge portion on the winding start side of the positive electrode.

6. The lithium secondary battery according to any one of claims 1 to 4, wherein The first spacer and the second spacer are each disposed on the positive electrode side of the main surface of the first base material and the second base material.

7. The lithium secondary battery according to any one of claims 1 to 4, wherein The first spacer and the second spacer each include the first protrusion and the second protrusion disposed in a prescribed repeating pattern.

8. The lithium secondary battery according to any one of claims 1 to 4, wherein A plurality of the first protrusions and a plurality of the second protrusions are each parallelly disposed so as to be separated from each other along a length direction of the first base material and the second base material.

9. The lithium secondary battery according to any one of claims 1 to 4, wherein The first spacer and the second spacer each include 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 through which lithium ions do not pass.

11. The lithium secondary battery according to any one of claims 1 to 4, wherein The first base material and the second base material each include a porous sheet including a high molecular material.

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

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