Lithium secondary battery

Abstract

A lithium secondary battery is provided with a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, a separator disposed between the separator and at least one of the positive electrode and the negative electrode, a separator having a plurality of linear portions, and a non-aqueous electrolyte, the separator being disposed between the separator and the positive electrode and / or the negative electrode, and the separator having a plurality of linear portions. The diaphragm has a long shape having a length L1 in a first direction and a length L2 (L1 > L2) in a second direction perpendicular to the first direction, and an angle theta (theta < = pi / 2) of each of the plurality of linear portions with respect to the first direction satisfies theta > = tan-1 (L2 / L1).

Description

[0001] Cross-references between related applications

[0002] This disclosure claims the benefit of priority from Japanese Patent Application No. 2023-030106 filed in the Japan Patent Office on February 28, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a lithium secondary battery. Background Art

[0004] Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Lithium secondary batteries (lithium metal secondary batteries) are highly anticipated as non-aqueous electrolyte secondary batteries with higher capacities than lithium-ion batteries. In lithium secondary batteries, lithium metal is deposited on the negative electrode during charging and dissolves during discharge, releasing lithium ions into the non-aqueous electrolyte.

[0005] In lithium secondary batteries, lithium metal is deposited on the negative electrode during charging, so a separator needs to be provided between the separator and the electrode to ensure space for lithium deposition.

[0006] Patent document 1 proposes "a lithium secondary battery comprising an electrode group formed by winding a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, and a non-aqueous electrolyte with lithium ion conductivity, the negative electrode comprising a negative electrode collector, the negative electrode collector comprising a layer having a first surface facing the outer side of the winding of the electrode group and a second surface facing the inner side of the winding of the electrode group, a plurality of first protrusions protruding from the first surface, and a plurality of second protrusions protruding from the second surface, on the first surface and the second surface, lithium metal is deposited by charging, and a second average height of the plurality of second protrusions is higher than the first average height of the plurality of first protrusions."

[0007] Patent document 2 proposes "a lithium secondary battery comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte with lithium ion conductivity that fills the space between the positive electrode and the negative electrode, the positive electrode comprising a positive electrode active material containing lithium, the negative electrode comprising a negative electrode collector having a surface on which lithium metal is precipitated in a charged state, the negative electrode collector comprising a plurality of protrusions protruding from the surface toward the separator, no protrusions existing on a predetermined line on the surface of the negative electrode collector, the predetermined line extending from a first end through an area extending between the plurality of protrusions to a second end opposite to the first end".

[0008] Prior art literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2019-160776

[0010] Patent Document 2: Japanese Patent Application Publication No. 2018-195572 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] Lithium secondary batteries (lithium metal secondary batteries) in which lithium metal is deposited in spaces formed by separators during charge and dissolved during discharge have high energy density. Therefore, it is desirable to design separators from the perspective of sufficiently improving safety.

[0013] Means for solving problems

[0014] One aspect of the present disclosure relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, a spacer, and a non-aqueous electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode, and the spacer is disposed between at least one of the positive electrode and the negative electrode and the separator. At the negative electrode, lithium metal is deposited during charging and dissolved in the non-aqueous electrolyte during discharge. The spacer has a plurality of linear portions. The separator is in an elongated shape having a length L1 in a first direction and a length L2 in a second direction perpendicular to the first direction (L1>L2). The angle θ (θ≤π / 2) of each of the plurality of linear portions relative to the first direction satisfies θ≥tan -1 (L2 / L1).

[0015] Effects of the Invention

[0016] According to the above structure, the safety of the lithium secondary battery can be improved.

[0017] While the novel features of the present invention are described in the appended claims, the present invention, both in structure and content, together with other objects and features of the invention, will be better understood from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The diaphragm has a long length L1 in the first direction D1 and a length L2 in the second direction D2 (L1>L2), and the angles θ of the plurality of linear portions with respect to the first direction D1, and tan -1 Plot of the correlation between (L2 / L1).

[0019] Figure 2 It is a longitudinal cross-sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0020] Figure 3 It is schematically represented Figure 2 A cross-sectional view of a portion of a lithium secondary battery is shown.

[0021] Figure 4It is composed Figure 2 FIG. 1 is a top view of multiple linear portions of a separator of a lithium secondary battery.

[0022] Figure 5 It is a top view of a plurality of linear portions constituting another spacer.

[0023] Figure 6 It is a top view of a plurality of linear portions constituting another spacer. DETAILED DESCRIPTION

[0024] Hereinafter, the embodiments of the present disclosure will be described with reference to examples, but the embodiments of the present disclosure are not limited to the examples described below. In the following description, specific numerical values ​​or materials are sometimes exemplified, but other numerical values ​​or other materials may also be applied as long as the invention of the present disclosure can be implemented. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, which can be replaced by "above numerical value A and below numerical value B". In the following description, when a lower limit and an upper limit are exemplified for a numerical value of a specific physical property or condition, any one of the exemplified lower limits and any one of the exemplified upper limits may be arbitrarily combined as long as the lower limit is not above the upper limit.

[0025] The present disclosure includes combinations of matters described in two or more claims arbitrarily selected from the plurality of claims recited in the appended claims. In other words, matters described in two or more claims arbitrarily selected from the plurality of claims recited in the appended claims may be combined as long as no technical contradiction arises.

[0026] (Lithium secondary battery)

[0027] A lithium secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator, a spacer, and a non-aqueous electrolyte. The separator is disposed between the positive electrode and the negative electrode. The spacer is disposed between the separator and at least one of the positive electrode and the negative electrode. The non-aqueous electrolyte has lithium ion conductivity.

[0028] Lithium metal precipitates in the negative electrode during charging and dissolves in the non-aqueous electrolyte during discharge. Specifically, the negative electrode comprises at least a negative electrode current collector, on which the lithium metal precipitates. Such lithium secondary batteries are also called lithium metal secondary batteries.

[0029] In a lithium secondary battery, more than 70% of the rated capacity, for example, is realized by the precipitation and dissolution of lithium metal. The movement of electrons in the negative electrode during charging and discharging is mainly due to the precipitation and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100% or 90 to 100%) of the movement of electrons in the negative electrode during charging and discharging (current in other viewpoints) is caused by the precipitation and dissolution of lithium metal. That is, the negative electrode of a lithium secondary battery is different from the negative electrode in which the movement of electrons in the negative electrode during charging and discharging is mainly caused by the absorption and release of lithium ions by the negative electrode active material (graphite, etc.).

[0030] The positive electrode, negative electrode, and separator are sometimes collectively referred to as an "electrode group." The positive electrode and negative electrode can be wound with a separator and a spacer to form a wound electrode group. When forming a wound electrode group, a positive electrode, a negative electrode, and a separator are each in the form of a long strip. Alternatively, the positive electrode, negative electrode, separator, and separator can be stacked. In other words, the electrode group can be either a wound type or a stacked type. The following description focuses on the wound electrode group.

[0031] (Spacer)

[0032] The separator is disposed between at least one of the positive electrode and the negative electrode and the separator. The separator has a plurality of linear portions. Typically, a pair of the plurality of linear portions faces each other, sandwiching the positive electrode or the negative electrode.

[0033] The separator may be formed on at least one of the surface of the positive electrode, the surface of the negative electrode, and the surface of the separator. The separator may be formed on one or both surfaces of the negative electrode, or on one or both surfaces of the positive electrode.

[0034] From the perspective of manufacturing processes (particularly wound electrode assembly manufacturing processes), it is preferred that the separator be formed on the surface of the separator. The separator may be formed on both surfaces of the separator or only on one surface (i.e., the surface on the negative electrode side or the positive electrode side).

[0035] The separator is in an elongated shape, having a length L1 in a first direction D1 and a length (width) L2 in a second direction D2 perpendicular to the first direction (L1>L2). The separator constituting the wound electrode assembly may be in a strip shape, with the first direction D1 being the longitudinal direction.

[0036] In lithium secondary batteries, the main function of the separator is to create a space for lithium metal to precipitate. By accommodating the lithium metal in the space created by the separator between the separator and the electrode, the negative electrode's expansion during charging is suppressed.

[0037] On the other hand, it's understood that separators also play a role in controlling the heat transfer path within the battery. For example, if thermal runaway occurs due to improper battery usage, exothermic reactions may occur within the battery, generating gas and raising internal pressure. In such cases, it's desirable to minimize the rate of heat release and gas generation. To this end, suppressing the propagation of the exothermic reaction in the first direction (D1) of the elongated separator is effective.

[0038] In order to suppress the propagation of the exothermic reaction in the first direction (D1) of the elongated separator, it is effective to tilt the extending direction of the plurality of linear portions constituting the separator at a sufficient angle relative to the first direction (D1) of the separator. Specifically, the angle θ (θ≤π / 2) of each of the plurality of linear portions relative to the first direction (D1) satisfies θ≥tan -1 When the ratio (L2 / L1) is set, the propagation of the exothermic reaction in the first direction (D1) is hindered. As a result, the rate of heat release and gas generation decreases. Furthermore, because the gas generated within the battery easily migrates in the short-side direction (D2), the safety valve activates quickly, suppressing heat accumulation within the battery and ensuring high safety.

[0039] Figure 1 The invention shows a long separator having a length L1 in a first direction D1 and a length (width) L2 in a second direction D2 perpendicular to the first direction (L1>L2), a plurality of linear portions (in Figure 1 (only one is shown) the angle θ (θ≤π / 2) with respect to the first direction (D1), and tan -1 (L2 / L1) correlation.

[0040] The angle θ (θ≤π / 2) of each of the plurality of linear portions with respect to the first direction (D1) may satisfy θ≥tan -1 (1.4×L2 / L1), θ≥tan -1 (3×L2 / L1). Furthermore, the angle θ may satisfy θ≥π / 4. In other words, the angle θ (θ≤π / 2) of each of the plurality of linear portions relative to the first direction (D1) may be 45° or greater, for example, 60° or greater. However, from the perspective of ensuring sufficient space for lithium metal precipitation, the angle θ is preferably less than 90°, and may be 80° or less. By adopting such an angle θ, the phenomenon of spacers being embedded in the space between each other can be suppressed, making it easier to maintain sufficient space between the separator and the electrode.

[0041] The larger the length L1 of the diaphragm relative to the width L2, the easier it is for the exothermic reaction to propagate in the first direction (D1). In other words, as L1 / L2 increases (i.e., tan -1 (L2 / L1) is larger), by satisfying θ≥tan -1Specifically, L1 / L2 satisfies, for example, L1 / L2 ≥ 1.4.

[0042] In one embodiment, the plurality of linear portions are formed in a straight line shape (more specifically, a line segment shape) along a direction defined by the angle θ.

[0043] The plurality of linear portions are preferably formed along a plurality of independent, non-intersecting straight lines (line segments). The plurality of independent, non-intersecting straight lines include "imaginary line segments" defined on the surface of the separator or electrode. The imaginary line segments are predetermined lines that form the basis of the linear portions and are parallel to each other.

[0044] The length L of the imaginary line segment can satisfy L × sinθ ≥ 0.8 × L2. In this case, the multiple linear portions can extend along most of the distance from one end to the other end of the separator in the short-side direction (D2). This makes it easier to ensure the space between the separator and the electrode formed by the multiple linear portions.

[0045] The plurality of straight lines (virtual line segments) may be parallel to each other (ie, in a stripe shape). Such a plurality of linear portions can be easily and evenly arranged between the separator and the electrode.

[0046] At least a portion of the plurality of linear portions can be intermittently formed along the imaginary line segments. That is, the linear portions can be partially missing. These partially missing linear portions can, for example, appear striped when viewed as a whole and can be evenly distributed between the separator and the electrode. The missing portions improve the flowability of the non-aqueous electrolyte in the first direction (D1), thereby enhancing lithium ion conductivity. This can reduce reaction resistance.

[0047] Even when at least a portion of the linear portions are intermittently formed, when the number of the plurality of imaginary line segments is N, it is preferable that any straight line in the first direction (D1) be drawn so as to intersect the number of linear portions that is at least an integer closest to 0.2×N. From the perspective of more uniformly arranging the plurality of linear portions between the separator and the electrode and from the perspective of inhibiting the propagation of the exothermic reaction in the first direction (D1), it is more preferable that any straight line in the first direction (D1) be drawn so as to intersect the number of linear portions that is at least an integer closest to 0.5×N.

[0048] Furthermore, it is preferred that at least a portion of the defective portions of adjacent linear portions in the first direction (D1) do not overlap in the first direction (D1). In this case, the absence of overlap between the defective portions improves the flowability of the non-aqueous electrolyte, enhances lithium ion conductivity, and inhibits the propagation of the exothermic reaction in the first direction (D1).

[0049] When at least a portion of the plurality of linear portions is intermittently formed along an imaginary line segment, the total length of the plurality of linear portions may be at least 80% of the total length of the plurality of imaginary line segments defined on the surface of the separator or electrode. In this case, the plurality of linear portions are more evenly distributed between the separator and the electrode, making it easier to ensure a space between the separator and the electrode.

[0050] The plurality of straight lines may have a periodic pattern. The periodic pattern is not necessarily striped. Such a plurality of linear portions can be easily and evenly arranged between the separator and the electrode.

[0051] To more evenly arrange the plurality of linear portions between the separator and the electrode, the interval between any pair of adjacent linear portions in the first direction may be equal to or less than L1 / 15 of the length of the separator in the first direction (longitudinal direction) (D1). Furthermore, in an elongated separator where L1 is greater than L2, the plurality of linear portions can be more evenly arranged by setting the interval between any pair of adjacent linear portions in the first direction to be equal to or less than L1 / 25.

[0052] Likewise, from the viewpoint of evenly arranging the plurality of linear portions, it is preferable that at least a portion of the other linear portions be included in a circle of radius Lx centered at the end of any linear portion of length Lx.

[0053] The average thickness of each of the plurality of linear portions may be 20 μm or greater. The thickness of a linear portion refers to the maximum dimension (maximum thickness) perpendicular to the longitudinal direction of the linear portion and parallel to the thickness direction of the separator. The average thickness of the linear portion can be calculated by measuring the maximum thickness at at least five locations along the linear portion and calculating the arithmetic mean of these five or more measured values.

[0054] The average width of each of the plurality of linear portions may be 50 μm or greater and 1000 μm or less. The width of a linear portion refers to the dimension perpendicular to the longitudinal direction of the linear portion and parallel to the main surface of the separator. The average width of a linear portion can be calculated by measuring the width at at least five locations along the linear portion and calculating the arithmetic mean of these five or more measured values.

[0055] The maximum thickness and width of the linear portion can be measured by photographing a cross section of the linear portion parallel to the thickness direction of the separator and the upper surface of the linear portion using a scanning electron microscope (SEM).

[0056] On each side of the separator, there is a region A facing the spacer and a region B not facing the spacer. On each side, the area ratio of region A to the combined area of ​​regions A and B can be, for example, 20% or less, 10% or less, or 5% or less. In this case, the internal resistance can be kept within a small range. On each side, the area ratio (coverage) of region A to the combined area of ​​regions A and B can be 2% or more.

[0057] The spacer can be formed by, for example, applying a dispersion containing a spacer material to the surface of the separator or the surface of the electrode and drying it. In this case, the linear portion constituting the spacer can be bonded to the surface of the separator or the surface of the electrode with sufficient strength.

[0058] The linear portion may contain an inorganic filler. The inorganic filler may be insulating particles. The linear portion may comprise a resin material. The resin material may comprise a binder resin and a tackifier. The binder resin is a resin that bonds the inorganic fillers to each other and to the surface of the separator or electrode. Resin materials have excellent insulating properties and moldability. The tackifier is a resin that imparts viscosity to the dispersion used to form the linear portion. The linear portion may comprise a resin material and an inorganic filler.

[0059] The spacers (linear portions) are formed using, for example, a dispersion containing insulating particles, a binder resin, and a tackifier. The spacers formed from the dispersion contain insulating particles, a binder resin, and a tackifier.

[0060] The dispersion medium of the dispersion liquid is not particularly limited, and for example, water, an organic solvent, or a mixture of water and an organic solvent can be used. As the organic solvent, for example, N-methyl-2-pyrrolidone (NMP) can be used. Of these, water is preferably used from the perspective of reducing environmental impact.

[0061] The volume resistivity of the insulating particles may be, for example, 1.0×10 8 Ω·cm or more. Since the insulating particles have sufficient insulation, lithium metal is hardly deposited on the separator, and the deposition of lithium metal in the desired space is promoted. The volume resistivity of the insulating particles can also be higher, for example, 1.0×10 10 Ω·cm or more.

[0062] Volume resistivity can be measured by the four-probe method. For example, 204Kgf / cm 2 The insulating particles are pressurized and measured using a powder resistivity measuring device (for example, Loresta SP manufactured by Nitto Seiko Analytical Science Co., Ltd.).

[0063] Examples of insulating particles include inorganic particles of metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Examples of metal oxides include aluminum oxide (aluminum oxide, boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silicon dioxide). 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, aluminum oxide, silicon dioxide, and titanium dioxide are preferred.

[0064] The content of insulating particles in the spacer is, for example, less than 80% by volume, preferably 50 to 70% by volume. The content (volume ratio) of insulating particles in the spacer can be calculated by observing a cross section of the spacer with a transmission electron microscope (TEM), taking a TEM image, and calculating the value of the TEM image at any 10 μm. 2 The volume ratio is calculated by taking the total area surrounded by the outline of the insulating particles in the field of view as the ratio of the calculated total area to the field of view area. In this case, the volume ratio is preferably obtained in three or more fields of view and their average value is calculated.

[0065] Examples of the binder resin include fluororesins, fluororubbers, styrene-butadiene copolymers or hydrogenated products thereof (hydrogenated products), acrylonitrile-butadiene copolymers or hydrogenated products thereof, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene-propylene rubber, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid), polyimides, polyamideimides, polyacrylonitrile, polyethers, polyolefins, and alkyd resins.

[0066] The amount of the binder resin can be, for example, 20 to 80 parts by volume, 20 to 70 parts by volume, 20 to 50 parts by volume, or 25 to 40 parts by volume relative to 100 parts by volume of the insulating particles. Within this range, the mechanical strength of the separator is easily improved, and the bonding strength between the separator and the surface of the diaphragm or electrode is easily improved.

[0067] The thickener may include, for example, at least one selected from carboxymethyl cellulose and a carboxymethyl cellulose salt (hereinafter, at least one selected from carboxymethyl cellulose and a carboxymethyl cellulose salt is referred to as "CMC"). When a carboxymethyl cellulose salt is used as CMC, sodium salts, lithium salts, potassium salts, ammonium salts, etc. may be used. Among them, the carboxymethyl cellulose salt preferably contains a sodium salt.

[0068] In order to fully exert the effect of CMC, the dispersion medium of the spacer material dispersion preferably contains water. 50% or more of the dispersion medium may be water, and 70% or more, 80% or more, or 90% or more of the dispersion medium may be water.

[0069] The amount of CMC can be, for example, 0.5 to 5 parts by volume, or 1 to 3 parts by volume relative to 100 parts by volume of the insulating particles. By using CMC within this range, a sufficient thickening effect of CMC can be exhibited.

[0070] <Diaphragm>

[0071] The separator uses a porous sheet having ion permeability and insulating properties. Examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. The material of the porous sheet is not particularly limited and may be a polymer material. Examples of the polymer material include olefin resins, polyamide resins, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and copolymers of ethylene and propylene. The porous sheet may contain additives as needed. Examples of the additives include inorganic fillers and the like.

[0072] The thickness of the separator 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.

[0073] The separator can include a porous sheet and a composite material layer. The composite material layer can be formed on one or both main surfaces of the porous sheet. The composite material layer is a layer that allows lithium ions to pass through. The thickness of the composite material layer can be 5% to 50% of the total thickness of the separator.

[0074] The composite material layer includes a resin material and inorganic particles. The inorganic particles may include first particles and / or second particles. The first particles are particles containing lithium phosphate. The first particles have the effect of suppressing abnormal battery heat generation. The second particles are particles other than the first particles.

[0075] When the composite material layer is formed only on one principal surface of the porous sheet, it is preferably disposed on the principal surface of the porous sheet opposite the positive electrode. By disposing the composite material layer on the positive electrode side, degradation of the porous sheet due to oxidation reactions can be suppressed. On the other hand, when the composite material layer is disposed on the negative electrode side, degradation of the porous sheet due to reduction reactions can be suppressed.

[0076] The phosphate constituting the first particles may be at least one selected from lithium phosphate (Li3PO4), dilithium hydrogen phosphate (Li2HPO4), and lithium dihydrogen phosphate (LiH2PO4). Lithium phosphate is preferred because it effectively suppresses abnormal battery heat generation. The median diameter of the volume-based particle size distribution of the first particles may be 0.1 μm to 1.0 μm.

[0077] A preferred example of the second particle is a particle composed of an insulating inorganic compound that does not melt or decompose during abnormal heating of the battery. Examples of the material of the second particle include oxides, hydroxides, nitrides, carbides, sulfides, and the like. Examples of oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, zinc oxide, and the like. Examples of nitrides include silicon nitride, aluminum nitride, boron nitride, titanium nitride, and the like. Examples of carbides include silicon carbide and boron carbide. Examples of sulfides include barium sulfate, and the like. Examples of hydroxides include aluminum hydroxide, and the like. The median particle size in the volume-based particle size distribution of the second particle can be 0.2 to 2.0 μm.

[0078] The median diameter in the volume-based particle size distribution of the particles can be measured, for example, using a laser diffraction and scattering particle size distribution measuring apparatus (e.g., Microtrack manufactured by Nikkiso Co., Ltd.). Alternatively, the median diameter can be determined by observing a cross section of the separator using a transmission electron microscope (TEM), capturing a TEM image, and calculating the area enclosed by the outlines of 100 arbitrary first particles or second particles. The diameter of an equivalent circle (a perfect circle) having the same area as the calculated area can be determined as the average value of the diameters of the 100 equivalent circles.

[0079] The resin material is preferably a polymer material having higher heat resistance than the material of the porous sheet. Such a polymer material preferably contains at least one selected from aromatic polyamides, aromatic polyimides, and aromatic polyamide-imides. These are known as highly heat-resistant polymers. From the perspective of heat resistance, aramid, namely meta-aramid (meta-type wholly aromatic polyamide) and para-aramid (para-type wholly aromatic polyamide), are preferred.

[0080] The content of the inorganic particles in the composite material layer may be in the range of 50% by mass to 99% by mass (eg, in the range of 85% by mass to 99% by mass).

[0081] (negative electrode)

[0082] The negative electrode includes a negative electrode current collector. In lithium secondary batteries, lithium metal is deposited on the surface of the negative electrode during charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons at the negative electrode during charging, becoming lithium metal, which is then deposited on the negative electrode surface. The lithium metal deposited on the negative electrode surface dissolves as lithium ions in the non-aqueous electrolyte during discharge.

[0083] The negative electrode may include a lithium ion absorption layer (a layer whose capacity is achieved by the absorption and release of lithium ions by the negative electrode active material (graphite, etc.)) supported on the negative electrode current collector. In this case, the open circuit potential of the negative electrode when fully charged can be 70 mV or less relative to lithium metal (lithium dissolution potential). When 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 absorption layer when fully charged. In other words, the negative electrode's capacity is achieved by the precipitation and dissolution of lithium metal.

[0084] Here, "fully charged" refers to a state in which the battery is charged to, for example, 0.98×C or higher, with the rated capacity of the battery being C. The open-circuit potential of the negative electrode at full charge can be measured by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell using lithium metal as the counter electrode. The non-aqueous electrolyte in the cell can have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0085] The lithium ion storage layer is formed by layering a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive agent, and the like in addition to the negative electrode active material.

[0086] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain a single negative electrode active material or a combination of two or more. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon).

[0087] The conductive material is, for example, a carbon material, and examples of the carbon material include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0088] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of the fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0089] The negative electrode current collector may be any conductive sheet, and foil, film, or the like may be used as the conductive sheet.

[0090] The negative electrode current collector (conductive sheet) can be made of any conductive material other than lithium metal and lithium alloys. The conductive material can be a metal material such as a metal or alloy. The conductive material is preferably one that does not react with lithium. More specifically, it is preferably one that does not form an alloy or an intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite with the base surface preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys having high conductivity are preferred.

[0091] 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.

[0092] (positive electrode)

[0093] The positive electrode, for example, comprises a positive electrode current collector and a positive electrode mixture layer supported by the positive electrode current collector. The positive electrode mixture layer, for example, comprises 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 on both sides. The positive electrode can be obtained, for example, by coating a positive electrode mixture slurry containing a positive electrode active material, a conductive material, and a binder on both sides of the positive electrode current collector, drying the coating, and then rolling the coating.

[0094] 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 due to their low manufacturing cost and high average discharge voltage.

[0095] During charging, the lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharge, the lithium metal dissolves from the negative electrode, releasing lithium ions that are then absorbed by the composite oxide at the positive electrode. In other words, the lithium ions involved in charging and discharging primarily originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0096] 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, etc. can be mentioned. The lithium-containing transition metal oxide can contain one transition metal element, or it can contain two or more. The transition metal element can be Co, Ni and / or Mn. The lithium-containing transition metal oxide can contain one or more typical elements as needed. As typical elements, Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc. can be mentioned. Typical elements can be Al, etc.

[0097] Among lithium-containing transition metal oxides, composite oxides having a layered structure and a rock-salt-type crystal structure containing Co, Ni, and / or Mn as transition metal elements, and sometimes containing Al as an optional component, are preferred for achieving high capacity. In this case, in a lithium secondary battery, the molar ratio mLi / mM of the total amount of lithium mLi in the positive and negative electrodes to the amount mM of metal M other than lithium in the positive electrode is set to, for example, 1.1 or less.

[0098] As the binder, the conductive agent, etc., for example, the substances 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.

[0099] Examples of materials for the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0100] 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.

[0101] (non-aqueous electrolyte)

[0102] The non-aqueous electrolyte with lithium ion conductivity can be a liquid electrolyte (electrolyte), a gel electrolyte, or a solid electrolyte. For example, the liquid electrolyte is an electrolyte solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte solution is, for example, 0.5 mol / L or higher and 2 mol / L or lower. The electrolyte solution may contain known additives.

[0103] The gel electrolyte comprises a lithium salt and a matrix polymer, or alternatively, a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that gels by absorbing the non-aqueous solvent. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, and polyethylene oxide.

[0104] As the solid electrolyte, for example, a material known in all-solid-state lithium-ion secondary batteries and the like (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halide-based solid electrolyte, etc.) is used.

[0105] Liquid non-aqueous electrolytes are prepared by dissolving a salt in a non-aqueous solvent. Examples of the salt include lithium salts and oxalates. Dissolving the salt in the non-aqueous solvent generates cations such as lithium ions and anions.

[0106] As anion, BF4 can be mentioned. - 、ClO4 - PF6 - CF3SO3- CF3CO2 - , anions of imides, anions of oxalate complexes, etc. As anions of imides, N(SO2CF3)2 can be cited. - 、N(C m F 2m+1 SO2) x (C n F 2n+ 1SO2) y - (m and n are each independently an integer of 0 or greater than 1, x and y are each independently 0, 1 or 2, and x + y = 2) etc. The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalatoborate anion, difluorooxalatoborate anion (BF2(C2O4) - )、PF4(C2O4) - PF2(C2O4)2 - The non-aqueous electrolyte may contain these anions alone or in combination of two or more.

[0107] From the perspective of suppressing the precipitation of lithium metal in the form of dendrites, the non-aqueous electrolyte preferably contains at least an oxalate complex anion, wherein the non-aqueous electrolyte preferably contains an oxalate complex anion having fluorine. Through the interaction between the oxalate complex anion having fluorine and lithium, lithium metal is easily precipitated uniformly in the form of fine particles. Therefore, it is easy to suppress the local precipitation of lithium metal. It is also possible to combine the oxalate complex anion having fluorine with other anions. Other anions can be PF6 - and / or imide anions.

[0108] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, or halogen-substituted products thereof. The non-aqueous electrolyte may contain any of these non-aqueous solvents alone or in combination. Examples of the halogen-substituted product include fluorides and the like.

[0109] Examples of esters include carbonates and carboxylic acid esters. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonates 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.

[0110] Examples of ethers include cyclic ethers and chain ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of 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 diglyme.

[0111] 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 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 in the non-aqueous electrolyte can be set to 0.05 mol / L or more and 1 mol / L or less. Among oxalates, lithium difluorooxalatoborate is preferred.

[0112] The non-aqueous electrolyte may contain additives. These additives may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode can help suppress dendrite formation. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0113] Hereinafter, description will be given with reference to the accompanying drawings. Figure 2 : is a longitudinal cross-sectional view schematically showing an example of a lithium secondary battery. In the components of the lithium secondary battery described below, the above components can be applied. The components described below can be changed based on the above description. In the lithium secondary battery described below, non-essential components of the lithium secondary battery involved in the present disclosure can be omitted. In the following figures, the proportions of the components are changed for ease of understanding.

[0114] Figure 2 : is a longitudinal sectional view schematically showing an example of a lithium secondary battery according to one embodiment. Figure 2 In the figure, illustration of the spacer and the space formed by the spacer is omitted. Figure 2 The cylindrical lithium secondary battery 10 shown includes a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte (not shown). Figure 2 This corresponds to a longitudinal cross-section of the electrode assembly 14, including the winding axis. The battery case includes a case body 15, a bottomed cylindrical metal container, 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. Gasket 27 ensures the airtightness of the battery case. Insulating plates 17 and 18 are disposed within the case body 15 at both ends of the electrode assembly 14 in the winding axis direction (first direction).

[0115] The housing body 15 has a stepped portion 21 formed, for example, by partially punching the side wall of the housing body 15 from the outside. The stepped portion 21 can be formed in an annular shape along the circumference of the housing body 15 on the side wall of the housing body 15. The sealing member 16 is supported by the surface of the stepped portion 21 on the opening side.

[0116] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating component 24, an upper valve body 25 and a cover 26. In the sealing body 16, these components are stacked in this order. The sealing body 16 is installed at the opening of the shell body 15 in such a way that the cover 26 is located on the outside of the shell body 15 and the filter 22 is located on the inside of the shell body 15. The above-mentioned components constituting the sealing body 16 are, for example, in the shape of a circular plate or a ring. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and an insulating component 24 is sandwiched between their respective peripheral portions. The filter 22 and the lower valve body 23 are connected to each other at their respective peripheral portions. The upper valve body 25 and the cover 26 are connected to each other at their respective peripheral portions. That is, the components other than the insulating component 24 are electrically connected to each other.

[0117] 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 heating, for example, the upper valve body 25 expands toward the lid 26 and moves away 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 rises further, the upper valve body 25 ruptures, allowing gas to escape through the opening formed in the lid 26.

[0118] Figure 3 It is schematically represented Figure 2 A cross-sectional view of a portion of a lithium secondary battery is shown. Figure 3 This is an enlarged view of a portion of the longitudinal section of the electrode group 14 including the winding axis. Figure 3 include Figure 2 The part near the positive electrode surrounded by region II and Figure 2 The portion near the negative electrode is surrounded by region III.

[0119] The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, a separator 50, and a spacer 60. The separator 60 is composed of a plurality of linear portions 53 having a thickness (height) h. The positive electrode 11, the negative electrode 12, and the separator 50 are all in the form of elongated strips (ribbons). The positive electrode 11, the negative electrode 12, and the separator 50 are wound with the separator 50 disposed between the positive electrode 11 and the negative electrode 12, thereby forming the electrode assembly 14 having multiple windings.

[0120] The positive electrode 11 includes a positive electrode current collector 11 a and positive electrode mixture layers 11 b formed on both surfaces thereof. The positive electrode current collector 11 a is electrically connected to a lid 26 serving as a positive electrode terminal via a positive electrode lead 19 .

[0121] exist Figure 3, a negative electrode (negative electrode current collector) in a state where no lithium metal is deposited is shown as the negative electrode 12. The negative electrode 12 is electrically connected to the case body 15, which functions as a negative electrode terminal, via a negative electrode lead 20.

[0122] Here, the separator 50 includes a porous sheet 51 and a composite material layer 52. The composite material layer 52 is formed on one of the two main surfaces of the porous sheet 51, facing the negative electrode 12. Separators 60 (multiple linear portions 53) are formed on the composite material layer 52 of the separator 50, in contact with the negative electrode 12. The separator 60 creates a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the separator 50). The presence of the space 14s reduces the volume change of the electrode assembly 14 associated with the precipitation of lithium metal during charging, thereby improving cycle performance.

[0123] Figure 4 It is composed Figure 2 FIG. 1 is a top view of a plurality of linear portions 53 of a separator 60 of a lithium secondary battery. Figure 4 In the embodiment, the plurality of linear portions 53 are formed linearly along a plurality of straight lines (line segments). The plurality of linear portions 53 are arranged parallel to each other in a periodic pattern in a stripe-like pattern. The angle θ of each of the plurality of linear portions 53 with respect to the first direction (D1) is θ<π / 4 (=45°).

[0124] Figure 5 : is a top view of a plurality of linear portions 53 constituting another spacer. Figure 5 In FIG, an angle θ of each of the plurality of linear portions 53 with respect to the first direction ( D1 ) is θ<π / 3 (=60°).

[0125] Figure 6 : is a top view of a plurality of linear portions 53 constituting another spacer. Figure 6 In the example, multiple linear portions are intermittently formed along imaginary line segments. That is, although the linear portions are partially missing, they appear striped overall and are uniformly distributed across the surface of the separator 50. The missing portions 53d of adjacent linear portions 53 in the first direction (D1) do not overlap. This improves the flowability of the non-aqueous electrolyte while hindering the propagation of the exothermic reaction in the first direction (D1).

[0126] In addition, the intervals between the linear portions 53 do not need to be strictly uniform. In the manufacturing process, it is sometimes not possible to arrange the spacers in a uniform pattern. Even in this case, as shown in the example in the figure, as long as the intervals and the angle θ are roughly the same (uniform), there is no particular problem.

[0127] In the above embodiment, a cylindrical lithium secondary battery with a wound electrode group is described. However, the lithium secondary battery of this embodiment is not limited to the method of embodiment 1, and can also be applied to other methods. The shape of the lithium secondary battery can be appropriately selected from various shapes such as cylindrical, square, sheet, flat, etc. according to its application. The shape of the electrode group is not particularly limited, and can also be a stacked type.

[0128] (Note)

[0129] Based on the description of the above embodiments, the following technical solutions are disclosed.

[0130] (Technical Solution 1)

[0131] A lithium secondary battery comprises a positive electrode, a negative electrode, a separator, a spacer and a non-aqueous electrolyte.

[0132] The separator is disposed between the positive electrode and the negative electrode.

[0133] The separator is disposed between at least one of the positive electrode and the negative electrode and the separator.

[0134] In the negative electrode, lithium metal is deposited during charging and dissolved in the non-aqueous electrolyte during discharging.

[0135] The spacer has a plurality of linear portions,

[0136] The diaphragm is in an elongated shape having a length L1 in a first direction and a length L2 in a second direction perpendicular to the first direction (L1>L2).

[0137] The angle θ (θ≤π / 2) of each of the plurality of linear portions relative to the first direction satisfies θ≥tan -1 (L2 / L1).

[0138] (Technical Solution 2)

[0139] According to the lithium secondary battery described in technical solution 1, L1 / L2≥1.4.

[0140] (Technical Solution 3)

[0141] The lithium secondary battery according to technical solution 1 or 2 satisfies θ≥tan -1 (1.4×L2 / L1).

[0142] (Technical Solution 4)

[0143] The lithium secondary battery according to any one of technical solutions 1 to 3 satisfies θ≥tan -1 (3×L2 / L1).

[0144] (Technical Solution 5)

[0145] According to the lithium secondary battery of any one of technical solutions 1 to 4, the angle θ satisfies θ≥π / 4.

[0146] (Technical Solution 6)

[0147] According to the lithium secondary battery of any one of technical solutions 1 to 5, the plurality of linear portions are formed along a plurality of independent line segments that do not intersect with each other.

[0148] (Technical Solution 7)

[0149] According to the lithium secondary battery of any one of technical solutions 1 to 6, the length L of the line segment satisfies L×sinθ≥0.8×L2.

[0150] (Technical Solution 8)

[0151] According to the lithium secondary battery of any one of technical solutions 1 to 7, the multiple line segments are parallel to each other.

[0152] (Technical Solution 9)

[0153] According to the lithium secondary battery of any one of claims 1 to 8, at least a portion of the plurality of linear portions are intermittently formed along the line segment.

[0154] (Technical Solution 10)

[0155] According to the lithium secondary battery of claim 9, when the number of the plurality of line segments is N, any straight line in the first direction can be drawn so as to cross the linear portions equal to or greater than an integer closest to 0.2×N.

[0156] (Technical Solution 11)

[0157] In the lithium secondary battery according to claim 9 or 10, at least a portion of the missing portions of the linear portions adjacent to each other in the first direction do not overlap in the first direction.

[0158] (Technical Solution 12)

[0159] According to the lithium secondary battery of any one of technical solutions 9 to 11, the total length of the plurality of linear portions is greater than or equal to 80% of the total length of the plurality of line segments.

[0160] (Technical Solution 13)

[0161] The lithium secondary battery according to any one of technical solutions 1 to 12,

[0162] The plurality of line segments have a periodic pattern,

[0163] The plurality of linear portions are uniformly arranged on the surface of the diaphragm.

[0164] (Technical Solution 14)

[0165] According to any one of claims 1 to 13, the lithium secondary battery is configured such that a distance between any pair of the linear portions adjacent to each other in the first direction is L1 / 15 or less.

[0166] (Technical Solution 15)

[0167] According to any one of claims 1 to 14, the lithium secondary battery includes at least a portion of the other linear portions within a circle having a radius Lx centered at the end of any of the linear portions having a length Lx.

[0168] (Technical Solution 16)

[0169] According to any one of technical solutions 1 to 15, the linear portion includes a resin material.

[0170] (Technical Solution 17)

[0171] According to any one of technical solutions 1 to 16, the linear portion contains an inorganic filler.

[0172] (Technical Solution 18)

[0173] According to any one of technical solutions 1 to 17, the non-aqueous electrolyte contains oxalate.

[0174] (Technical Solution 19)

[0175] According to the lithium secondary battery described in Technical Solution 18, the oxalate is lithium difluorooxalatoborate.

[0176] (Technical Solution 20)

[0177] According to the lithium secondary battery according to any one of claims 1 to 19, the positive electrode and the negative electrode are wound with the separator and the separator interposed therebetween to form an electrode group.

[0178] [Example]

[0179] Hereinafter, the lithium secondary battery according to the present disclosure will be described in more detail based on Examples and Comparative Examples. However, the present disclosure is not limited to the following Examples.

[0180] Examples 1-3

[0181] (1) Preparation of positive electrode

[0182] A layered, rock-salt-type lithium-containing transition metal oxide (NCA; the positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al being 1.0), acetylene black (AB; the conductive material), and polyvinylidene fluoride (PVdF; the binder) were mixed at a mass ratio of NCA:AB:PVdF = 95:2.5:2.5. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was then added and stirred to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry was applied to both sides of a strip of Al foil (the positive electrode current collector), dried, and the resulting positive electrode mixture film was rolled using rollers. Finally, the resulting stack of positive electrode current collector and positive electrode mixture was cut into the desired electrode size, yielding a positive electrode having positive electrode mixture layers on both sides of the positive electrode current collector.

[0183] (2) Preparation of negative electrode

[0184] A strip-shaped electrolytic copper foil (thickness 15 μm) was prepared as a negative electrode current collector.

[0185] (3) Diaphragm

[0186] A polyethylene microporous film with a thickness of 20 μm was prepared as a separator. Since the ratio L2 / L1 of the length (width) L2 in the second direction D2 to the length L1 in the first direction D1 is 1 / 9, and tan -1 (L2 / L1) is 0.1107, so any embodiment satisfies θ≥tan -1 (3×L2 / L1), and satisfy θ≥π / 4.

[0187] (4) Forming a spacer on the main surface of the diaphragm

[0188] 60 parts by volume of insulating particles (median particle size of 3 μm, volume resistivity of 10 14 Ω·cm), 39 parts by volume of an alkyd resin as a binder resin, 1 part by volume of CMC (sodium salt), and water as a dispersion medium were mixed to prepare a dispersion of the spacer material.

[0189] Next, a dispersion of the building material was sprayed onto one surface of each of the pair of microporous films using a dispenser in a predetermined pattern. The coated film was then vacuum dried to form linear portions in the pattern shown in Table 1. The linear portions had a uniform average thickness of 30 μm and an average width of 250 μm.

[0190] The angle θ (θ ≤ π / 2) of each of the multiple linear portions relative to the first direction (D1) was varied as shown in Table 1 (45°, 60°, and 90°). In all examples, the multiple linear portions were uniformly formed in a periodic pattern along multiple parallel imaginary line segments (length L = L × sinθ ≥ L2). The area ratio (coverage) of the region A facing the spacer on each surface of the separator was uniformly set at 9% relative to the combined area of ​​the region A and the region B not facing the spacer.

[0191] (5) Preparation of non-aqueous electrolyte

[0192] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of EC:DMC=30:70, and LiPF6 and LiBF2(C2O4) were dissolved at a concentration of 1 mol / L and 0.1 mol / L in the resulting mixed solvent to prepare a liquid non-aqueous electrolyte.

[0193] (6) Battery assembly

[0194] In an inert gas atmosphere, the positive and negative electrode current collectors were spirally wound with the separators mentioned above interposed therebetween to produce an electrode assembly. The separators were arranged so that the separators formed on one side of each pair of separators faced the negative electrode. The electrode assembly was housed in a bag-shaped outer casing made of a laminate sheet with an Al layer. After injecting a nonaqueous electrolyte, the outer casing was sealed to complete Batteries A1 to A3 of Examples 1 to 3.

[0195] Example 4

[0196] Battery A4 of Example 4 was completed in the same manner as Example 3 with an angle θ (θ≤π / 2) = 60°, except that a 0.25 mm notch was provided every 2.65 mm of the linear portion length. Adjacent notches were arranged so as not to overlap in the first direction D1.

[0197] Comparative Example 1

[0198] Battery B1 of Comparative Example 1 was completed in the same manner as in the above-described Examples except that the plurality of linear portions were formed at θ=0°.

[0199] [evaluate]

[0200] (Charge and discharge efficiency)

[0201] After the test charge and discharge, each battery was subjected to a charge and discharge test in a thermostatic chamber at 25°C under the following conditions. The pause time between charge and discharge was 20 minutes. The ratio of the discharge capacity to the charge capacity was calculated as the initial charge and discharge efficiency.

[0202] Charging

[0203] The battery was charged at a constant current of 0.5 mA per unit area (cm2) of the electrode until the battery voltage reached 4.2 V. Then, the battery was charged at a constant voltage of 4.2 V until the current value per unit area of ​​the electrode reached 0.05 mA.

[0204] Discharge

[0205] The battery was discharged at a constant current of 0.5 mA per unit area of ​​the electrode until the battery voltage reached 3.0 V.

[0206] (heat release rate)

[0207] Batteries A1-A4 and B1 were charged to 4.2V at a constant current of 0.5 mA per unit area (square centimeter) of the electrode. The batteries were then placed in cylindrical SUS304 sample containers and heated to 300°C using an ARC tester manufactured by NETZSTH in heat-wait-search mode. The temperature rise from 110°C due to self-heating was measured, and the heat release rates of batteries A1-A4 and B1 at 190°C, 200°C, 210°C, and 220°C were calculated. Temperature sensors were placed on the surface of the cylindrical sample containers.

[0208] (Maximum pressure velocity)

[0209] Connect a capillary tube to the cylindrical sample container. Connect a pressure sensor to the end of the capillary tube to measure the pressure inside the sample container and the capillary tube during the test. Calculate the differential of the measured pressures, and use the maximum value as the maximum pressure velocity.

[0210] The evaluation results are shown in Table 1 together with the structure of the separator.

[0211] Table 1

[0212]

[0213] As can be seen from Table 1, the angle θ of the linear portion (spacer) relative to the longitudinal direction of the diaphragm, that is, the first direction (D1), satisfies θ≥tan -1 In the case of (L2 / L1) (specifically, θ≥45°(π / 4)), the heat release rate and the maximum pressure rate at a temperature exceeding 200°C are significantly suppressed.

[0214] Industrial availability

[0215] 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 hybrid and plug-in hybrid electric vehicles, and household storage batteries combined with solar cells.

[0216] The present invention has been described in conjunction with presently preferred embodiments, but this disclosure should not be construed as limiting. Upon reading the above disclosure, a person of ordinary skill in the art will become aware of various changes and modifications. Therefore, the appended claims should be construed to include all changes and modifications that do not depart from the spirit and scope of the present invention.

[0217] Description of Reference Numerals

[0218] 10: Lithium secondary battery

[0219] 11: Positive electrode

[0220] 12: Negative electrode

[0221] 14: Electrode group

[0222] 14s: Space

[0223] 15: Shell body

[0224] 16: Sealing body

[0225] 17, 18: Insulation board

[0226] 21: Step

[0227] 22: Filter

[0228] 23: Lower valve body

[0229] 24: Insulation parts

[0230] 25: Upper valve body

[0231] 26: Cover

[0232] 27: Gasket

[0233] 50: Diaphragm

[0234] 51: Porous sheet

[0235] 52: Composite material layer

[0236] 53: Pars linearis

[0237] 60: Spacer

Claims

1. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, a spacer and a non-aqueous electrolyte, The separator is disposed between the positive electrode and the negative electrode. The separator is disposed between at least one of the positive electrode and the negative electrode and the separator. In the negative electrode, lithium metal is deposited during charging and dissolved in the non-aqueous electrolyte during discharging. The spacer has a plurality of linear portions, The diaphragm is in an elongated shape having a length L1 in a first direction and a length L2 in a second direction perpendicular to the first direction, and L1>L2. The angle θ of each of the plurality of linear portions relative to the first direction is ≤π / 2, and satisfies θ≥tan -1 (L2 / L1).

2. The lithium secondary battery according to claim 1, L1 / L2≥1.

4.

3. The lithium secondary battery according to claim 1, Satisfying θ≥tan -1 (1.4×L2 / L1).

4. The lithium secondary battery according to claim 1, Satisfying θ≥tan -1 (3×L2 / L1).

5. The lithium secondary battery according to claim 1, The angle θ satisfies θ≥π / 4.

6. The lithium secondary battery according to claim 1, The plurality of linear portions are formed along a plurality of independent line segments that do not intersect with each other.

7. The lithium secondary battery according to claim 6, The length L of the line segment satisfies L×sinθ≥0.8×L2.

8. The lithium secondary battery according to claim 6, The plurality of line segments are parallel to each other.

9. The lithium secondary battery according to claim 6, At least a portion of the plurality of linear portions is intermittently formed along the line segment.

10. The lithium secondary battery according to claim 9, When the number of the plurality of line segments is N, any straight line in the first direction can be drawn so as to cross the linear portions equal to or greater than an integer closest to 0.2×N.

11. The lithium secondary battery according to claim 9, At least a portion of the missing portions of the linear portions adjacent to each other in the first direction do not overlap in the first direction.

12. The lithium secondary battery according to claim 9, The total length of the plurality of linear portions is greater than or equal to 80% of the total length of the plurality of line segments.

13. The lithium secondary battery according to any one of claims 1 to 12, The plurality of line segments have a periodic pattern, The plurality of linear portions are uniformly arranged on the surface of the diaphragm.

14. The lithium secondary battery according to claim 13, The interval between any pair of the linear portions adjacent to each other in the first direction is L1 / 15 or less.

15. The lithium secondary battery according to any one of claims 1 to 12, A circle of radius Lx centered at the distal end of any of the linear portions of length Lx includes at least a portion of the other linear portions.

16. The lithium secondary battery according to any one of claims 1 to 12, The linear portion includes a resin material.

17. The lithium secondary battery according to claim 16, The linear portion contains an inorganic filler.

18. The lithium secondary battery according to any one of claims 1 to 12, The nonaqueous electrolyte includes oxalate.

19. The lithium secondary battery according to claim 18, The oxalate salt is lithium difluorooxalatoborate.

20. The lithium secondary battery according to any one of claims 1 to 12, The positive electrode and the negative electrode are wound with the separator and the separator interposed therebetween to form an electrode group.

Images