Lithium secondary battery

Abstract

A lithium secondary battery (1) comprises: a positive electrode (200); a negative electrode (100); a porous separator (300) disposed between the positive electrode (200) and the negative electrode (100); a spacer (400) disposed between the positive electrode (200) and / or the negative electrode (100), and the separator (300); and a non-aqueous electrolyte having lithium ion conductivity. At the negative electrode (100), lithium metal is deposited during charging, and the lithium metal is dissolved during discharging. The region of the negative electrode (100) facing the positive electrode (200) includes a first region (R1) which faces the spacer (400), and a second region (R2) which does not face the spacer (400). The spacer (400) is non-porous or porous, and the height (t) of the spacer (400) is 20 μm or more. When the spacer (400) is porous, the porosity Psp of the spacer (400) is no more than the porosity Pse of the separator (300).

Description

[Technical Field]

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

[0002] Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Higher capacities of lithium-ion batteries can be achieved by using, for example, graphite in combination with an alloy active material such as a silicon compound as the negative electrode active material. However, the capacity of lithium-ion batteries is reaching its limit.

[0003] Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with higher capacities than lithium ion batteries. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and during discharging, the lithium metal dissolves and is released as lithium ions into the non-aqueous electrolyte.

[0004] Patent Document 1 proposes a separator for a non-aqueous electrolyte battery, which includes a substrate made of a porous film and a porous surface layer formed on at least one surface of the substrate, which contains particles and a resin material and has an irregular shape with an arithmetic mean roughness Sa of 1.0 μm or more and 4.0 μm or less.

[0005] Patent Document 2 proposes an electrode group for a non-aqueous secondary battery, which is formed by stacking a positive electrode plate, formed by applying a positive electrode mixture paint, which is made by kneading and dispersing an active material made of at least a lithium-containing composite oxide, a conductive material, and a binder in a dispersion medium, onto a positive electrode current collector to form a positive electrode mixture layer, and a negative electrode plate, formed by applying a negative electrode mixture paint, which is made by kneading and dispersing an active material made of at least a material capable of retaining lithium, and a binder in a dispersion medium, onto a negative electrode current collector to form a negative electrode mixture layer, with a porous insulator between them, and which is characterized in that a spacer made of resin that softens with the non-aqueous electrolyte and relieves stress due to expansion and contraction of the electrode plate during charging and discharging is disposed at least either between the positive electrode plate and the porous insulator or between the negative electrode plate and the porous insulator. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-137984 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-8929 Summary of the Invention

[0007] In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging and dissolves during discharging, causing significant volume changes in the negative electrode, which can easily cause electrode breakage or buckling.

[0008] In contrast, when the proposal in Patent Document 1 was adopted for a lithium secondary battery, as the charge-discharge cycle progressed, lithium metal precipitated more at the protruding parts, damaging the negative or positive electrode and resulting in a significant decrease in capacity.

[0009] Furthermore, when the proposal in Patent Document 2 was adopted for a lithium secondary battery, as the charge-discharge cycle progressed, it became difficult for the resin spacer to alleviate expansion and contraction, causing strain to concentrate near the spacer, damaging the negative electrode or positive electrode and resulting in a significant decrease in capacity.

[0010] One aspect of the present disclosure relates to a lithium secondary battery including a positive electrode, a negative electrode, a porous separator disposed between the positive electrode and the negative electrode, a spacer disposed between the separator and at least one of the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, wherein lithium metal precipitates in the negative electrode during charging and dissolves during discharging, and a region of the negative electrode facing the positive electrode has a first region facing the spacer and a second region not facing the spacer, the spacer is non-porous or porous, the height of the spacer is 20 μm or more, and when the spacer is porous, the porosity Psp of the spacer is equal to or less than the porosity Pse of the separator.

[0011] According to the present disclosure, electrode breakage and electrode buckling are suppressed in a lithium secondary battery, thereby improving cycle characteristics. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a main part of an electrode group of a lithium secondary battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a longitudinal sectional view schematically showing a lithium secondary battery according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is an enlarged view schematically showing a main part of the lithium secondary battery of FIG. [Figure 4] FIG. 4 is a plan view schematically showing spacers arranged on the surface of a separator. [Figure 5] FIG. 5 is a plan view schematically showing another spacer disposed on the surface of the separator. [Figure 6] FIG. 6 is a plan view schematically showing still another spacer disposed on the surface of the separator. [Figure 7] FIG. 7 is a plan view schematically showing still another spacer disposed on the surface of the separator. [Figure 8] FIG. 8 is a plan view schematically showing still another spacer disposed on the surface of the separator. DETAILED DESCRIPTION OF THE INVENTION

[0013] The lithium secondary battery according to the present disclosure comprises a positive electrode, a negative electrode, a porous separator disposed between the positive electrode and the negative electrode, a spacer disposed between the separator and at least one of the positive electrode and the negative electrode (hereinafter sometimes collectively referred to as an electrode), and a non-aqueous electrolyte having lithium ion conductivity. Lithium metal precipitates in the negative electrode during charging and dissolves during discharging. Specifically, the negative electrode has at least a negative electrode current collector, and lithium metal precipitates on the negative electrode current collector. The lithium secondary battery according to the present disclosure is also referred to as a lithium metal secondary battery.

[0014] In a lithium (metal) secondary battery, for example, 70% or more of the rated capacity is manifested by the deposition and dissolution of lithium metal. The movement of electrons in the negative electrode during charging and discharging is mainly due to the deposition 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 (current from another perspective) in the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal. That is, the negative electrode according to this embodiment is different from a negative electrode in which the movement of electrons in the negative electrode during charging and discharging is mainly due to the insertion and extraction of lithium ions by a negative electrode active material (such as graphite).

[0015] The region of the negative electrode facing the positive electrode has a first region facing the spacer and a second region not facing the spacer. The spacer is non-porous or porous. When the spacer is porous, the porosity Psp of the spacer is not more than the porosity Pse of the separator. Therefore, during charging, lithium metal preferentially deposits in the second region of the negative electrode that does not face the spacer. On the other hand, in the first region of the negative electrode facing the spacer, the deposition of lithium metal is suppressed. As a result, stress does not concentrate in the first region, and electrode breakage and electrode buckling are suppressed. Therefore, the cycle characteristics are improved.

[0016] In other words, when the spacer is porous, the ratio R (that is, Psp / Pse) of the porosity Psp of the spacer to the porosity Pse of the separator satisfies 0 < R < 1. When the spacer is non-porous, R = 0.

[0017] R (Psp / Pse ratio) may satisfy 0 < R < 0.75 or 0 < R < 0.3. The spacer is preferably formed of a porous material that allows lithium ions to permeate rather than a material that does not allow lithium ions to permeate completely. This makes it easier to suppress the depletion of the electrolyte in the positive electrode portion facing the separator. Also, the porous material has flexibility and elasticity and has the effect of contracting and relaxing stress when the volume of the negative electrode expands during charging. This can more effectively prevent damage and buckling of the electrode. However, if the height of the spacer is low, not only is the room for stress relaxation reduced, but also the ratio of the amount of contraction per unit height becomes large, so the height of the spacer may be difficult to recover.

[0018] The height of the spacer is 20 μm or more, may be 25 μm or more, and may be 30 μm or more. The height of the spacer is the maximum dimension of the spacer in the thickness direction of the separator (hereinafter also referred to as direction T). The height of the spacer is obtained by taking a photograph of the cross-section of the spacer in direction T using a scanning electron microscope (SEM), measuring the height at any 10 locations, and taking the average value. The upper limit of the height of the spacer is not particularly limited, but for example, it is 100 μm or less, may be 80 μm or less, and may be 60 μm or less. These upper and lower limits can be arbitrarily combined.

[0019] Conventionally, it has been considered difficult to control the deposition state of lithium metal well when increasing the height of the spacer as described above (for example, to 20 μm or more). This is because the larger the height of the spacer, the smaller the restriction on the growth direction of lithium ions, and dendritic lithium metal is likely to be generated.

[0020] However, in reality, if the spacer height is small, the lithium metal storage space becomes small, resulting in considerable lithium metal deposition near the spacer. In particular, lithium metal deposition is likely to be significant at the boundary between the second region, which does not face the spacer, and the first region, which faces the spacer. As a result, stress caused by volumetric changes in the negative electrode is concentrated near the spacer, making the electrode more susceptible to breakage, buckling, and other problems. When the Psp / Pse ratio R is less than 1 (or even less than 0.75, particularly less than 0.3), and the spacer is impermeable to electrolyte, increasing the spacer height can actually suppress lithium metal deposition at the boundary between the first and second regions. It is believed that if the spacer height is sufficiently large, sufficient lithium metal storage space is secured in the second region, thereby suppressing lithium metal deposition at the boundary between the first and second regions.

[0021] Furthermore, the starting points of lithium metal deposition are less likely to form in the first region facing the spacer, and are preferentially formed in greater numbers in the second region. Therefore, the deposition locations of lithium metal are more limited than when lithium metal is deposited throughout the entire first and second regions, making it less likely that the lithium metal will become partially isolated. In this case, it is desirable to increase the height of the spacer to ensure sufficient space in direction T for lithium metal deposition. This promotes the deposition of lithium metal in direction T, making it even less likely that the lithium metal will become isolated.

[0022] However, if the spacer is porous, the greater the height of the spacer, the higher the probability that lithium ions will penetrate the pores inside the spacer, and the greater the amount of lithium ions that can precipitate in the first region. If a significant amount of lithium metal precipitates in the first region, stress caused by volume changes in the negative electrode will eventually concentrate in the first region, making the electrode more susceptible to breakage, buckling, and other problems. Therefore, the greater the height of the spacer, the smaller the Psp / Pse ratio R should be, and the greater the resistance to lithium ion penetration into the spacer.

[0023] As described above, in order to suppress electrode breakage and buckling and improve cycle characteristics in lithium secondary batteries, it is important to control the Psp / Pse ratio R and the spacer height in a well-balanced manner.

[0024] The ratio of the area of ​​the first region to the total area of ​​the first and second regions is not particularly limited, but may be, for example, 5% to 30% or 5% to 20% in consideration of the balance between cycle characteristics and internal resistance. The larger the area ratio of the first region, the more likely it is that the amount of lithium metal deposited per unit area in the second region will be. This promotes the deposition of lithium metal in direction T, making it easier to reduce isolated lithium metal. Furthermore, by controlling the area ratio of the first region within the above range, a more uniform pressing force can be applied from the separator to the entire deposited lithium metal. Furthermore, resistance to the electrode reaction can be reduced.

[0025] It is desirable that the first region facing the spacer be arranged on the negative electrode in as uniform and dispersed a manner as possible. This suppresses an increase in internal resistance, reduces the number of areas where lithium metal can be locally deposited in large amounts, and makes it easier to limit the amount of isolated lithium metal to as small an amount as possible. Typically, positive and negative electrodes are strip-shaped with long and short sides. When the length (width) of the short side of the strip-shaped negative electrode is L, and a circular region with a diameter of L / 3 is set on the surface of the negative electrode, it is desirable that the first and second regions always coexist in such a circular region.

[0026] The spacer may be a composite containing a resin material and particles. In this case, a porous spacer can be easily formed. Furthermore, the porosity of the spacer can be easily controlled. The particles may be inorganic or organic.

[0027] <Measurement of spacer porosity Psp> The porosity Psp of the spacer can be determined by photographing a cross section of the spacer in direction T with a scanning electron microscope (SEM), performing image processing such as binarization of the photographed image in a field of view of, for example, 2000 μm × 100 μm, distinguishing between pore portions A and other portions B, and determining the area ratio of portion A to the total area of ​​portions A and B. It is desirable to measure the photographed image at any 10 points, and determine the porosity Psp (volume %) of the spacer as the average of the area ratios of portion A obtained at the 10 points.

[0028] <Measurement of separator porosity Pse> The porosity Pse of a separator is determined, for example, by cutting the separator to a certain area and then measuring its mass. The volume is calculated by multiplying the area by the thickness. The apparent density (Va) is calculated by dividing the mass by the volume. The porosity is calculated from the apparent density and the true density of the separator's constituent materials (density when porosity is 0%: Vr) (Pse = 100 × (1 - Va / Vr)). If the separator has a multilayer structure, the volume fraction of each layer is calculated by measuring the thickness of each layer using a scanning electron microscope (SEM), and the average true density Vre is calculated from the true density and volume fraction of the constituent materials of each layer. The porosity is similarly calculated from the apparent density and the average true density Vre (Pse = 100 × (1 - Va / Vre)).

[0029] The thickness of the separator is determined as the average value of measurements taken at 10 arbitrary points on the sample without any load being applied to the separator in direction T.

[0030] The porosity Pse of the separator is preferably 25% or more and 70% or less, and more preferably 40% or more and 50% or less, from the viewpoint of ensuring sufficient ion permeability and mechanical strength.

[0031] FIG. 1 shows a schematic diagram of a main portion of an electrode group of a lithium secondary battery according to one embodiment. The electrode group 1 includes a first electrode 100, a second electrode 200, a separator 300 disposed between the first electrode 100 and the second electrode 200, and a spacer 400 disposed between the first electrode 100 and the separator 300. One of the first electrode 100 and the second electrode 200 is a positive electrode, and the other is a negative electrode. The region of the first electrode 100 (second electrode 200) facing the second electrode (first electrode 100) is divided into a first region R1 facing the spacer 400 and a second region R2 not facing the spacer 400. The height t of the spacer 400 is the dimension of the spacer 400 in the thickness direction T of the separator 300.

[0032] [Spacer] Spacer 400 provided between electrodes 100, 200 and separator 300 forms space S for accommodating deposited lithium metal, and reduces the volume change of the negative electrode that accompanies the deposition of lithium metal.

[0033] The separator 300 typically has a strip-like shape with long and short sides. Here, the direction along the short side of the separator is designated as D1. In a cross section (hereinafter referred to as the reference cross section) parallel to the direction T and the direction D1 of the spacer, the contact length (width of the first region R1) between the separator 300 and the electrodes 100, 200 and the spacer 400 is not particularly limited, but is, for example, 500 μm or more and 2000 μm or less. When the contact length is within this range, stress applied to the spacer 400 is likely to be uniformly distributed to the separator 300 and the electrodes 100, 200. Furthermore, the first region R1 facing the spacer 400 is likely to be disposed facing the electrodes 100, 200 in a uniform and distributed state. The contact length is the average of the contact lengths at five different reference cross sections.

[0034] There are no particular limitations on the shape of the reference cross section of the spacer 400. The shape of the reference cross section of the spacer may be, for example, a rectangle, a rectangle with at least one curved corner, a trapezoid, an ellipse, a part of an ellipse, or a shape similar to these.

[0035] There are no particular limitations on the material that constitutes the spacer 400. The spacer 400 may be made of a non-porous material and / or a porous material. The spacer 400 may also be made of an insulating material.

[0036] The spacer 400 may be formed, for example, by applying a solution or dispersion containing a resin material or the like to the surface of the separator 400 or one of the electrodes 100, 200 and drying the applied solution. The solvent or dispersion medium is not particularly limited, but N-methyl-2-pyrrolidone (NMP) can be used, for example. Alternatively, the spacer 400 may be formed by scattering particles in a desired shape on the surface of the separator 300 or one of the electrodes 100, 200. Alternatively, the spacer 400 may be formed by applying a curable resin in a desired shape to the surface of the separator 300 or one of the electrodes 100, 200 and curing the resin. The cured curable resin has a Young's modulus of, for example, 0.01 GPa or more and 10 GPa or less, which facilitates the relaxation of stress due to the expansion and contraction of the negative electrode and facilitates the maintenance of the space for accommodating lithium metal. Alternatively, the spacer 400 may be formed by adhering adhesive tape to the surface of the separator 300 or one of the electrodes 100, 200. Among the above methods, the method using a solution or dispersion containing a resin material is preferred.

[0037] Examples of resin materials include fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydrogenated product, acrylonitrile-butadiene copolymer or its hydrogenated product, acrylonitrile-butadiene-styrene copolymer or its hydrogenated product, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, and polyacetic acid Examples of the resin include rubbers such as vinyl, cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose, acrylic resins such as acrylic acid-methacrylic acid copolymers, polyamides such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, and wholly aromatic polyamide (aramid), polyimide, polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0038] The spacer may be a composite containing a resin material and particles. In this case, the resin material serves at least to bind the particles together. Such a spacer may be formed using a dispersion containing the resin material and the particles.

[0039] Examples of the particles include inorganic particles such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Examples of metal oxides include aluminum oxide (alumina and boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silica). Examples of metal hydroxides include aluminum hydroxide. Examples of metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of metal carbides include silicon carbide and boron carbide. Examples of metal sulfides include barium sulfate. Minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate may also be used. Among these, alumina, silica, titania, and the like are preferably used.

[0040] The average particle size of the particles is not particularly limited, but is preferably 10 μm or less, and more preferably 0.1 μm or more and 2.0 μm or less. The average particle size can be determined by photographing the cross section of the spacer in direction T inside the secondary battery with an electron microscope, identifying particle portion C by performing image processing such as binarization of the photographed image, and calculating the average diameter of an equivalent circle having the same area as each particle. It is desirable to calculate the average from, for example, 100 or more particles.

[0041] In a composite containing a resin material and particles, the particles are preferably contained in a proportion of 70 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the resin material, which makes it easier to ensure sufficient strength of the spacer, and also makes it easier to form appropriate pores in the spacer, making it easier to control the porosity Psp of the spacer.

[0042] The arrangement of the spacers is not particularly limited. For example, when viewed from direction T (the normal direction of the main surface of the separator), the spacers are preferably arranged so that a straight line SL can be drawn along direction D1 so as to pass through three or more (preferably four or more, and even five or more) spacers. In this case, lithium metal is less likely to deposit unevenly or in a dendritic form on the negative electrode. Furthermore, local expansion of the negative electrode is suppressed, making it less likely that the electrode will be damaged. In addition, the spacers increase the number of fulcrums that support the separator and electrode, so that the separator and electrode receive stress from the spacers relatively evenly. Therefore, electrode damage is further suppressed. Furthermore, the separator can apply a more uniform pressing force to the entire deposited lithium metal. Therefore, the deposition direction of lithium metal is more easily controlled toward the surface of the negative electrode.

[0043] When viewed from the direction T, the ratio d / h of the minimum distance d (μm) between adjacent spacers to the spacer height h (μm) on the line SL may be, for example, 10 or more and 800 or less, or may be 40 or more and 400 or less. By controlling the d / h ratio within the above range, it becomes easier to ensure sufficient space for accommodating lithium metal. Furthermore, a more uniform pressing force can be applied from the separator to the entire deposited lithium metal. The minimum distance d between adjacent spacers can be determined by measuring one point on each of any 10 lines SL and averaging the measurements.

[0044] The spacer may be, for example, a plurality of linear protrusions arranged in a stripe pattern on the surface of the electrode or separator, intersecting direction D1. For example, one protrusion may be provided on each end of the separator surface in direction D1, extending along the long side of the separator (hereinafter referred to as direction D2), and one or more protrusions may be provided between the two ends along direction D2. In this case, a straight line SL can be drawn so as to pass through the spacer at three or more points in total, including two points at both ends and one or more points between the two ends. Such spacers consisting of a plurality of linear protrusions can be formed relatively easily on the surface of the separator or electrode. Furthermore, parameters such as the height h and the d / h ratio can be easily controlled.

[0045] [Lithium secondary battery] The configuration of a lithium secondary battery according to the present disclosure will be described below with reference to the drawings, taking as an example a cylindrical battery including a wound-type electrode group, although the present disclosure is not limited to the following configuration.

[0046] FIG. 2 is a longitudinal cross-sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery including a cylindrical battery case and a wound electrode group 14 and a nonaqueous electrolyte housed in the battery case. The battery case is composed of a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15. The case body 15 has an annular step 21 formed by pressing a portion of the side wall from the outside near the opening. The sealing body 16 is supported by the surface of the step 21 on the opening side. A gasket 27 is disposed between the case body 15 and the sealing body 16, thereby ensuring the hermeticity of the battery case. Within the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction.

[0047] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The cap 26 is disposed outside the case body 15, and the filter 22 is disposed inside the case body 15. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with an insulating member 24 interposed between their respective peripheral edges. The filter 22 and the lower valve body 23 are connected to each other at their respective peripheral edges. The upper valve body 25 and the cap 26 are connected to each other at their respective peripheral edges. The lower valve body 23 has an air vent. If the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This breaks the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged through an opening formed in the cap 26.

[0048] Here, the electrode group 14 is composed of a positive electrode 110, a negative electrode (negative electrode current collector) 120, and a separator 300. The positive electrode 110, the negative electrode 120, and the separator 300 interposed therebetween are all strip-shaped, and are spirally wound so that their width directions are parallel to the winding axis.

[0049] The positive electrode 110 is electrically connected to a cap 26, which also serves as a positive electrode terminal, via a positive electrode lead 19. One end of the positive electrode lead 19 is connected, for example, near the center of the positive electrode 110 in the longitudinal direction. The other end of the positive electrode lead 19 extending from the positive electrode 110 is welded to the inner surface of the filter 22 through a through-hole formed in the insulating plate 17.

[0050] The negative electrode 120 is electrically connected to the case body 15, which also serves as a negative electrode terminal, via the negative electrode lead 20. One end of the negative electrode lead 20 is connected to, for example, an end of the negative electrode 120 in the longitudinal direction, and the other end is welded to the inner bottom surface of the case body 15.

[0051] FIG. 3 is an enlarged view schematically illustrating the discharge state of region X surrounded by a dashed line in FIG. 2. In the illustrated example, the cross-sectional shape of the spacer 400 is trapezoidal. However, embodiments of the present disclosure are not limited thereto, and the cross-sectional shape may be, for example, a rectangle, a rectangle with at least one curved corner, an ellipse, or a partial ellipse. In the illustrated example, the spacer 400 is disposed between the positive electrode 110 and the separator 300. However, embodiments of the present disclosure are not limited thereto, and the spacer 400 may be disposed between the negative electrode 120 and the separator 300, or between the positive electrode 110 and the separator 300, or between the negative electrode 120 and the separator 300.

[0052] The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode composite layer 112. A spacer 400 is provided between the positive electrode composite layer 112 and the separator 300. The spacer 400 includes linear protrusions 401 provided along direction D2 (longer side direction) of the separator 300. In a discharged state, lithium metal is not deposited on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300. On the other hand, in a charged state, lithium metal is deposited on the surface of the negative electrode current collector 121 and is accommodated in the space between the positive electrode 110 and the separator 300 while being subjected to the pressing force of the separator 300. That is, the negative electrode 120 includes the negative electrode current collector 121 in a discharged state, and includes the negative electrode current collector 121 and lithium metal deposited on its surface in a charged state.

[0053] Because the lithium metal is accommodated in the space between the positive electrode 110 and the separator 300, the apparent volume change of the electrode assembly due to the deposition of lithium metal during charge-discharge cycles is reduced. This also reduces the stress applied to the negative electrode current collector 121. Furthermore, because pressure is applied from the separator 300 to the lithium metal accommodated between the positive electrode 110 and the separator 300, the deposition state of the lithium metal is controlled, making it less likely for the lithium metal to become isolated, and reducing a decrease in charge-discharge efficiency.

[0054] In the illustrated example, a cylindrical lithium secondary battery having a wound-type electrode group has been described, but the shape of the lithium secondary battery is not limited to this and can be appropriately selected from various shapes such as cylindrical, coin, prismatic, sheet, and flat depending on the application. The shape of the electrode group is also not particularly limited and may be a laminated type. In addition, known components other than the electrode group and non-aqueous electrolyte of the lithium secondary battery can be used without any particular limitation.

[0055] Next, the arrangement of the spacers will be described with reference to the drawings. In the illustrated example, the spacers are provided on the surface of the separator. However, the embodiment of the present disclosure is not limited to this, and the spacers may be provided on the surface of the electrode.

[0056] 4 is a plan view schematically illustrating a spacer disposed on the surface of a separator. The spacer 400 includes linear protrusions 401 provided at both ends of the surface of the separator 300 in direction D1, extending along direction D2, and a linear protrusion 401 provided in the center between the ends, also extending along direction D2. That is, the spacer 400 includes a total of three linear protrusions 401 that are substantially parallel to each other. Therefore, a straight line SL drawn along direction D1 passes through the spacer 400 at three points. Note that "substantially parallel" means roughly parallel, and the linear protrusions 401 may intersect at an angle of, for example, 0° to 20° or 0° to 10°.

[0057] 5 is a plan view schematically showing another spacer arranged on the surface of a separator. Spacer 400 is composed of a plurality of linear protrusions 401 arranged in stripes on the surface of separator 300 along direction D2. In this case, a straight line SL can be drawn along direction D1 so as to pass through the same number of locations as the linear protrusions 401 (seven locations in the illustrated example).

[0058] 6 is a plan view schematically illustrating yet another spacer disposed on the surface of a separator. The spacer 400 is composed of a plurality of spot-like protrusions 401 evenly distributed on the surface of the separator 300. In the illustrated example, when a straight line SL is drawn along the direction D1, the number of spot-like protrusions 401 that the line SL passes through varies depending on its position. The straight line SL1 passes through four protrusions 401, and the straight line SL2 passes through five protrusions 401. In such a case, it is sufficient that at least one of the multiple straight lines SL that can be drawn in different ways passes through three or more protrusions.

[0059] 7 is a plan view schematically showing yet another spacer arranged on the surface of a separator. Spacer 400 is a continuous body of honeycomb-shaped ribs evenly distributed on the surface of separator 300. In this case, too, when a straight line SL is drawn along direction D1, the number of ribs that the line SL passes through varies depending on its position. Line SL1 passes through ribs at five points, and line SL2 passes through ribs at four points.

[0060] 8 is a plan view schematically illustrating yet another spacer disposed on the surface of a separator. Spacer 400 is composed of multiple linear protrusions 401 evenly distributed on the surface of separator 300. Linear protrusions 401 are arranged so as to intersect alternately along direction D1. In this case, too, when a straight line is drawn along direction D1, the number of linear protrusions 401 passing through varies depending on the position of line SL. For example, line SL1 passes through three or four protrusions 401, line SL2 passes through three protrusions 401, and line SL3 passes through two protrusions 401.

[0061] Each component of the lithium secondary battery will be described in more detail below.

[0062] [Negative electrode] The negative electrode includes a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode upon charging, becoming lithium metal, which is then deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte upon discharging. The lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte, may be supplied from the positive electrode active material upon charging, or may be both.

[0063] The negative electrode may include a lithium ion absorption layer (a layer that develops capacity by absorption and desorption of lithium ions by a negative electrode active material (such as graphite)) supported on a negative electrode current collector. In this case, the open circuit potential of the negative electrode when fully charged may be 70 mV or less relative to lithium metal (dissolution and deposition potential of lithium). If the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion absorption layer when fully charged. In other words, the negative electrode develops capacity by deposition and dissolution of lithium metal.

[0064] Here, "fully charged" refers to a state in which the battery is charged to a state of charge of, for example, 0.98 × C or more, where C is the rated capacity of the battery. The open circuit potential of the negative electrode at full charge can be measured by disassembling a fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The nonaqueous electrolyte in the cell may have the same composition as the nonaqueous electrolyte in the disassembled battery.

[0065] The lithium ion occlusion layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0066] Examples of the negative electrode active material include a carbonaceous material, a Si-containing material, and a Sn-containing material. The negative electrode may contain one type of negative electrode active material or a combination of two or more types. Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0067] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0068] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0069] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0070] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloy. The conductive material may be a metallic material such as a metal or alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form an alloy or an intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, as well as graphite with a preferentially exposed basal plane. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys, which have high conductivity, are preferred.

[0071] 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.

[0072] [Positive electrode] The positive electrode includes, for example, a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode composite layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode composite slurry including the positive electrode active material, the conductive material, and the binder to both sides of the positive electrode current collector, drying the coating, and then rolling.

[0073] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred because of their low production cost and high average discharge voltage.

[0074] The lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions during charging and precipitates as lithium metal on the negative electrode or negative electrode current collector. During discharging, the lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed into the composite oxide of the positive electrode. In other words, the lithium ions involved in charging and discharging are generally derived from the solute in the nonaqueous electrolyte and the positive electrode active material.

[0075] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Co, Ni, and / or Mn. The lithium-containing transition metal oxide may contain one or more typical elements as needed. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al, etc.

[0076] Among lithium-containing transition metal oxides, composite oxides containing Co, Ni, and / or Mn as transition metal elements, and optionally containing Al, and having a layered rock-salt crystal structure are preferred in terms of obtaining high capacity. In this case, in the lithium secondary battery, the molar ratio mLi / mM of the total amount of lithium 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.

[0077] As the binder, conductive agent, etc., for example, those exemplified for the negative electrode can be used. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0078] 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, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0079] 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.

[0080] [Separator] The separator is made of a porous sheet having ion permeability and insulating properties. Examples of porous sheets include thin films, woven fabrics, and nonwoven fabrics having micropores. The material of the separator is not particularly limited, but may be a polymeric material. Examples of polymeric materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may contain additives as needed. Examples of additives include inorganic fillers.

[0081] 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.

[0082] [Non-aqueous electrolyte] The non-aqueous electrolyte having lithium ion conductivity contains, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid state or a gel state.

[0083] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0084] The gel-like non-aqueous electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin.

[0085] The lithium salt or anion may be any known material used in non-aqueous electrolytes for lithium secondary batteries. - , ClO4 - , PF6 - , CF3SO3 - , CF3CO2 -, anions of imides, anions of oxalate complexes, etc. Examples of imide anions include N(SO2CF3)2 - , N(C m F 2m+1 SO2) x (C n F 2n+1 SO2)y - (m and n are each independently an integer of 0 or 1 or greater, and x and y are each independently 0, 1, or 2, satisfying x+y=2.) The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion, BF2(C2O4) - , PF4(C2O4) - , PF2(C2O4)2 - The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0086] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains at least an anion of an oxalate complex, and more preferably contains an oxalate complex anion having fluorine. The interaction between the oxalate complex anion having fluorine and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This makes it easier to suppress localized deposition of lithium metal. The oxalate complex anion having fluorine may be combined with another anion. The other anion may be PF6 - and / or an anion of an imide.

[0087] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted derivatives include fluorides.

[0088] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0089] 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 diethylene glycol dimethyl ether.

[0090] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Furthermore, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0091] The non-aqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode makes it easier to suppress the formation of dendrites. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0092] [Example] The lithium secondary battery according to the present disclosure will be described in more detail below based on examples and comparative examples, although the present disclosure is not limited to the following examples.

[0093] Example 1 (1) Preparation of the positive electrode A layered rock-salt lithium-containing transition metal oxide (NCA: cathode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al was 1.0) was mixed with acetylene black (AB: conductive material) and polyvinylidene fluoride (PVdF: binder) in a mass ratio of NCA:AB:PVdF = 95:2.5:2.5. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a cathode composite slurry. The resulting cathode composite slurry was applied to both sides of a strip of Al foil (cathode current collector), dried, and the coating of the cathode composite was rolled using a roller. Finally, the resulting laminate of the cathode current collector and cathode composite was cut to the desired electrode size, yielding a cathode with a cathode composite layer on both sides of the cathode current collector.

[0094] (2) Formation of spacers The spacer ink was prepared by mixing 10 parts by weight of polyvinylidene fluoride (PVdF), 90 parts by weight of inorganic alumina particles (alumina particles with an average particle size of 1 μm and alumina particles with an average particle size of 0.1 μm in a 10 / 1 mass ratio), and N-methyl-2-pyrrolidone (NMP), a dispersion medium. A polyethylene separator (microporous membrane) with a thickness of 20 μm and a porosity Pse of 40% was also prepared.

[0095] Spacer ink was applied along direction D2 to both ends of the separator surface in direction D1 and the center between the ends. The resulting material was then dried with hot air, creating three parallel linear spacers. The spacer ink was applied using a dispenser. The spacer protrusions had a width of 1 mm, a height t of 30 μm, and a porosity Psp of 2%. Therefore, the Psp / Pse ratio R was 0.05.

[0096] In the direction D1, the minimum distance d between adjacent convex portions was 9 mm, and the ratio (SR) of the area of ​​the first region to the total area of ​​the first region and the second region was approximately 14%.

[0097] (3) Preparation of the negative electrode A strip of electrolytic copper foil (thickness: 15 μm) was prepared as a negative electrode current collector.

[0098] (4) Preparation of non-aqueous electrolyte Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC = 30:70, and LiPF6 and LiBF2(C2O4) were dissolved in the resulting mixed solvent at concentrations of 1 mol / L and 0.1 mol / L, respectively, to prepare a liquid non-aqueous electrolyte.

[0099] (5) Battery assembly The positive electrode and the negative electrode current collector were spirally wound with the separator in between in an inert gas atmosphere to prepare an electrode assembly. Since all of the lithium contained in the electrode assembly originated from the positive electrode, the molar ratio of the total amount of lithium mLi in the positive and negative electrodes to the amount of metal M (here, Ni, Co, and Al) in the positive electrode, mLi / mM, was 1.0.

[0100] The electrode group was housed in a bag-shaped exterior body made of a laminate sheet having an Al layer, and after the non-aqueous electrolyte was poured into it, the exterior body was sealed to complete the lithium secondary battery A1.

[0101] In a reference cross section obtained by cutting the electrode group, the cross-sectional shape of the convex portion was close to a trapezoid.

[0102] Example 2 A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF), 90 parts by mass of alumina (average particle size 1 μm), and a dispersion medium N-methyl-2-pyrrolidone (NMP). A lithium secondary battery A2 was fabricated in the same manner as in Example 1, except that the porosity Psp of the spacer was changed to 11% and the Psp / Pse ratio R was changed to 0.28.

[0103] Example 3 A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF), 90 parts by mass of alumina (average particle size 5 μm), and a dispersion medium N-methyl-2-pyrrolidone (NMP). A lithium secondary battery A3 was fabricated in the same manner as in Example 1, except that the porosity Psp of the spacer was changed to 29.5% and the Psp / Pse ratio R was changed to 0.74.

[0104] Example 4 A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF), 90 parts by mass of alumina (average particle size 10 μm), and a dispersion medium N-methyl-2-pyrrolidone (NMP). A lithium secondary battery A4 was fabricated in the same manner as in Example 1, except that the porosity Psp of the spacer was changed to 39% and the Psp / Pse ratio R was changed to 0.97.

[0105] Comparative Example 1 A spacer ink was prepared by mixing 30 parts by mass of polyvinylidene fluoride (PVdF), 70 parts by mass of alumina (average particle size 1 μm), and a dispersion medium N-methyl-2-pyrrolidone (NMP). A lithium secondary battery B1 was fabricated in the same manner as in Example 1, except that the porosity Psp of the spacer was changed to 60% and the Psp / Pse ratio R was changed to 1.5.

[0106] Comparative Example 2 Except for changing the height of the convex portions of the spacer to 15 μm, a lithium secondary battery B2 was produced in the same manner as in Example 2. The porosity Psp of the spacer was 9.6%, and the Psp / Pse ratio R was 0.24.

[0107] [Rating 1] The resulting battery was evaluated by a charge-discharge test, and the results are shown in Table 1.

[0108] In the charge-discharge test, three batteries were charged in a thermostatic chamber at 25°C under the following conditions, followed by a 20-minute break and then discharged under the following conditions. This cycle was repeated 100 times. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle (MR50) was calculated as the capacity retention rate (%).

[0109] (Charging) Constant current charging was performed at a current of 10 mA per unit area (square centimeter) of the electrode until the battery voltage reached 4.3 V, and then constant voltage charging was performed at a voltage of 4.3 V until the current value per unit area of the electrode reached 1 mA.

[0110] (Discharging) Constant current discharging was performed at a current of 10 mA per unit area of the electrode until the battery voltage reached 3.0 V.

[0111] Among the three batteries, the number of cycles at which cycle stop was presumed to be caused by cracks in the negative electrode current collector (copper foil) was determined. When the cycles of some batteries stopped, the average value of MR50 was determined for the remaining batteries.

[0112] [Table 1]

[0113] In batteries A5 and B1, cycle stop due to cracks in the negative electrode current collector occurred. Also, in battery B1, the capacity retention rate at the 50th cycle was significantly low. In batteries A1, A2, A3, and A4 where 0 < R < 0.75 was satisfied, particularly good MR50 was achieved.

[0114] [Example 5] A lithium secondary battery A5 was fabricated in the same manner as in Example 2, except that the total number of convex portions of the spacer was six. Specifically, spacers in the form of six mutually parallel linear convex portions were provided at both ends in the direction D1 on both surfaces of the separator and between these two ends. The ratio SR of the area of the first region to the total area of the first and second regions was approximately 28%.

[0115] [Example 6] A lithium secondary battery A6 was fabricated in the same manner as in Example 2, except that the width of the convex portion of the spacer was changed to 2 mm. The ratio SR of the area of the first region to the total area of the first and second regions was approximately 28%.

[0116] Example 7 A lithium secondary battery A7 was produced in the same manner as in Example 2, except that the spacer protrusions were arranged in the same manner as in Example 1, for a total of six, and the width of the spacer protrusions was changed to 2 mm. The ratio SR of the area of ​​the first region to the total area of ​​the first region and the second region was approximately 56%.

[0117] [Rating 2] The obtained battery was evaluated in the same manner as above, and the results are shown in Table 2.

[0118] [Table 2]

[0119] From Table 2, it can be seen that the ratio SR of the area of ​​the first region to the total area of ​​the first and second regions is preferably 30% or less, and more preferably 20% or less. In addition, to form a spacer with sufficient strength, a suitable convex width is required, and it was considered necessary to set SR to 5% or more. [Industrial Applicability]

[0120] The lithium secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrids and plug-in hybrids, and home storage batteries combined with solar cells. [Explanation of symbols]

[0121] 10. Lithium secondary battery 14 electrode group 15 Case body 16 Sealing body 17,18 Insulating plate 19 Positive lead 20 Negative lead 21 Stepped section 22 filters 23 Lower valve body 24 Insulating material 25 Upper valve 26 Cap 27 Gasket 100 1st electrode 110 Positive electrode 111 Positive electrode current collector 112 Positive electrode composite layer 120 negative electrode 121 Negative electrode current collector 200 2nd electrode 300 Separator 400 spacer 401 Convex part

Claims

1. A positive electrode and a negative electrode; a porous separator disposed between the positive electrode and the negative electrode; a spacer disposed between the separator and at least one of the positive electrode and the negative electrode; a non-aqueous electrolyte having lithium ion conductivity; Equipped with In the negative electrode, lithium metal is precipitated during charging, and the lithium metal is dissolved during discharging, a region of the negative electrode facing the positive electrode includes a first region facing the spacer and a second region not facing the spacer, the spacer is non-porous or porous; The height h of the spacer is 20 μm or more, When the spacer is porous, the porosity Psp of the spacer is equal to or less than the porosity Pse of the separator, the separator has a strip shape having long and short sides, When viewed from a normal direction of the main surface of the separator, a straight line SL can be drawn in a direction D1 along the short side of the separator so as to pass through the spacer at three or more locations, and on the straight line SL, a ratio d / h of a minimum distance d (μm) between adjacent spacers to a height h (μm) of the spacer is 10 or more and 800 or less, the spacer is a composite containing a resin material and particles, A lithium secondary battery, wherein a ratio R:Psp / Pse of a porosity Psp of the spacer to a porosity Pse of the separator satisfies 0<R<0.

3.

2. 2. The lithium secondary battery according to claim 1, wherein a ratio R:Psp / Pse of a porosity Psp of the spacer to a porosity Pse of the separator satisfies 0<R≦0.

05.

3. 3. The lithium secondary battery according to claim 1, wherein a ratio of an area of ​​the first region to a total area of ​​the first region and the second region is 5 to 30%.

Images