lithium secondary batteries

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 separator (300) and at least one of the positive electrode (200) and the negative electrode (100), and a non-aqueous electrolyte having lithium ion conductivity. Lithium metal is deposited in the negative electrode (100) during charging and dissolved during discharging. A region of the negative electrode (100) facing the positive electrode (200) comprises a first region (R1) facing the spacer (400) and a second region (R2) not facing the spacer (400). The spacer (400) is non-porous or porous, and a height (t) of the spacer (400) is greater than 20 μm. When the spacer (400) is porous, the porosity Psp of the spacer (400) is less than the porosity Pse of the separator (300).

Description

Technical Field

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

[0002] Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. The higher capacity of lithium-ion batteries can be achieved by using, for example, alloy active materials such as graphite and silicon compounds as the negative electrode active material. However, the higher capacity of lithium-ion batteries is gradually 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. During charging, lithium metal is deposited on the negative electrode, and during discharge, 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 comprises: a substrate composed of a porous film; and a porous surface layer formed on at least one surface of the above-mentioned substrate, containing particles and a resin material, and having a concave-convex shape with an arithmetic mean roughness Sa of the surface being greater than or equal to 1.0 μm and less than or equal to 4.0 μm.

[0005] Patent document 2 proposes an electrode group for a non-aqueous secondary battery, which is a positive electrode plate and a negative electrode plate that are spirally wound or stacked in a bent shape with a porous insulator interposed therebetween. The positive electrode plate is formed by applying a positive electrode mixture coating formed by mixing and dispersing an active material composed of at least a composite oxide containing lithium, a conductive material, and a binding material using a dispersion medium to a positive electrode current collector to form a positive electrode mixture layer. The negative electrode plate is formed by applying a negative electrode mixture coating formed by mixing and dispersing an active material composed of at least a material capable of retaining lithium and a binding material using a dispersion medium to a negative electrode current collector to form a negative electrode mixture layer. The electrode group for a non-aqueous secondary battery is characterized in that a spacer is arranged between at least either the positive electrode plate and the porous insulator or between the negative electrode plate and the porous insulator, the spacer being made of resin and utilizing a non-aqueous electrolyte to soften and thereby alleviate stress caused by expansion and contraction of the electrode plate during charge and discharge.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-137984

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2011-8929 Summary of the Invention

[0010] In lithium secondary batteries, lithium metal is deposited on the negative electrode during charge and dissolves during discharge, causing significant changes in the volume of the negative electrode. This can easily lead to electrode breakage and buckling.

[0011] In contrast, when the lithium secondary battery proposed in Patent Document 1 is used, as the charge and discharge cycles proceed, the deposition of lithium metal on the protrusions increases, damaging the negative electrode or the positive electrode, thereby significantly reducing the capacity.

[0012] Furthermore, if the lithium secondary battery proposed in Patent Document 2 is used, the resin spacer becomes less able to mitigate expansion and contraction during charge and discharge cycles, causing strain to concentrate near the spacer, damaging the negative electrode or positive electrode and significantly reducing capacity.

[0013] A technical solution disclosed herein relates to a lithium secondary battery, comprising: a positive electrode; a negative electrode; a porous separator arranged between the positive electrode and the negative electrode; a spacer arranged between at least one of the positive electrode and the negative electrode and the separator; and a non-aqueous electrolyte having lithium ion conductivity, wherein lithium metal is deposited at the negative electrode during charging and dissolved during discharging, and the relative region of the negative electrode relative to the positive electrode has a first region opposite to the spacer and a second region not opposite to the spacer, the spacer is non-porous or porous, the height of the spacer is greater than 20 μm, and when the spacer is porous, the porosity Psp of the spacer is less than the porosity Pse of the separator.

[0014] According to the present disclosure, in a lithium secondary battery, electrode breakage and electrode buckling are suppressed, thereby improving cycle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a cross-sectional view schematically showing a main part of an electrode group of a lithium secondary battery according to one embodiment of the present disclosure.

[0016] Figure 2 It is a longitudinal sectional view schematically showing a lithium secondary battery according to one embodiment of the present disclosure.

[0017] Figure 3 It is schematically represented Figure 2 An enlarged view of the main parts of a lithium secondary battery.

[0018] Figure 4 It is a plan view schematically showing a spacer arranged on the surface of a separator.

[0019] Figure 5 It is a plan view schematically showing another spacer arranged on the surface of the separator.

[0020] Figure 6 It is a plan view schematically showing another spacer arranged on the surface of the separator.

[0021] Figure 7 It is a plan view schematically showing another spacer arranged on the surface of the separator.

[0022] Figure 8 It is a plan view schematically showing another spacer arranged on the surface of the separator. DETAILED DESCRIPTION

[0023] The lithium secondary battery disclosed herein 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 is deposited at the negative electrode during charging and dissolved during discharging. Specifically, the negative electrode has at least a negative electrode current collector, and lithium metal is deposited on the negative electrode current collector. The lithium secondary battery disclosed herein is also referred to as a lithium metal secondary battery.

[0024] In a lithium (metal) secondary battery, more than 70% of the rated capacity, for example, is represented 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 at the negative electrode. Specifically, 70% to 100% (for example, 80% to 100%, 90% to 100%) of the movement of electrons in the negative electrode during charging and discharging (current in other viewpoints) is due to the precipitation and dissolution of lithium metal. That is, the negative electrode of the present embodiment is different from the negative electrode in which the movement of electrons in the negative electrode during charging and discharging is mainly due to the absorption and release of lithium ions by the negative electrode active material (graphite, etc.).

[0025] The opposite region of the negative electrode relative to the positive electrode has a first region opposite to the spacer and a second region not opposite to the spacer. The spacer is non-porous or porous. In the case of a porous spacer, the porosity Psp of the spacer is lower than the porosity Pse of the separator. Therefore, during charging, lithium metal is preferentially precipitated in the second region of the negative electrode not opposite to the spacer. On the other hand, the precipitation of lithium metal is suppressed in the first region of the negative electrode opposite to the spacer. As a result, stress is no longer concentrated in the first region, suppressing electrode fracture and electrode buckling. Therefore, the cycle characteristics are improved.

[0026] In other words, when the spacer is porous, the ratio R of the porosity Psp of the spacer to the porosity Pse of the separator (ie, Psp / Pse) satisfies 0 < R < 1. When the spacer is non-porous, R=0.

[0027] R (Psp / Pse ratio) may also satisfy 0<R<0.75, or 0<R<0.3. Preferably, the spacer is not formed of a material that does not allow lithium ions to pass through, but is formed of a porous material that allows lithium ions to pass through. Thus, it is easy to suppress the depletion of the electrolyte in the positive electrode portion opposite to the separator. In addition, the porous material has flexibility and elasticity, and has the function of contracting to relieve stress when the volume of the negative electrode expands with charging. Thus, damage and buckling of the electrode can be more effectively prevented. However, if the height of the spacer is low, in addition to reducing the room for relieving stress, the ratio of the shrinkage per unit height will become larger, so sometimes it is difficult to restore the height of the spacer.

[0028] The height of the spacer is greater than 20 μm, or greater than 25 μm, or greater than 30 μm. 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 photographing a cross section of the spacer in the direction T using a scanning electron microscope (SEM), measuring the height at any 10 locations, and calculating the average value. The upper limit of the height of the spacer is not particularly limited, but for example, it can be less than 100 μm, less than 80 μm, or less than 60 μm. These upper and lower limits can be arbitrarily combined.

[0029] It is believed that, in the past, increasing the spacer height (e.g., to 20 μm or more) as described above made it difficult to properly control the deposition of lithium metal. This is because the greater the spacer height, the less restriction on the growth direction of lithium ions, making it easier to generate dendritic lithium metal.

[0030] However, in reality, when the height of the spacer is small, the storage space for lithium metal becomes smaller, so a considerable amount of lithium metal will also be precipitated near the spacer. In particular, the precipitation of lithium metal tends to become significant in the boundary portion between the second region that is not opposite to the spacer and the first region that is opposite to the spacer. As a result, the stress caused by the volume change of the negative electrode is concentrated near the spacer, which easily causes the electrode to break, the electrode to buckle, etc. When the Psp / Pse ratio R is less than 1 (further, less than 0.75 (especially less than 0.3)), and the spacer is difficult to allow the electrolyte to pass through, the precipitation of lithium metal at the boundary portion between the first region and the second region can be suppressed by increasing the height of the spacer. It is believed that when the height of the spacer is sufficiently large, sufficient lithium metal storage space is ensured in the second region, so the precipitation of lithium metal at the boundary portion between the first region and the second region can be suppressed.

[0031] In addition, the starting point of lithium metal precipitation is less likely to form in the first region opposite the spacer, and is more likely to form in the second region. Therefore, compared with the case where lithium metal is precipitated throughout the first and second regions, the precipitation site of lithium metal is limited, making it less likely that lithium metal will be locally isolated. In this case, it is preferable to increase the height of the spacer to ensure space for lithium metal precipitation in the direction T. This promotes the precipitation of lithium metal in the direction T, making it more difficult for lithium metal to be isolated.

[0032] However, when the spacer is porous, the greater the height of the spacer, the higher the probability of lithium ions entering the pores within the spacer, and the greater the amount of lithium ions that can be deposited in the first region. When a considerable amount of lithium metal is deposited in the first region, the stress caused by the volume change of the negative electrode is concentrated in the first region, which can easily cause electrode fracture, electrode buckling, etc. Therefore, it is preferred that the greater the height of the spacer, the smaller the Psp / Pse ratio R, thereby increasing the resistance to lithium ion penetration into the spacer.

[0033] As described above, in lithium secondary batteries, in order to suppress electrode breakage and electrode buckling and improve cycle characteristics, it is important to control the Psp / Pse ratio R and the height of the spacer in a well-balanced manner.

[0034] The ratio of the area of the first region to the total area of the first region and the second region is not particularly limited, but when considering the balance between cycle characteristics and internal resistance, it can be, for example, more than 5% and less than 30%, or more than 5% and less than 20%. The larger the ratio of the area of the first region, the more likely it is that the amount of lithium metal precipitated per unit area of the second region will increase. Therefore, the precipitation of lithium metal in the direction T can be promoted, and the amount of isolated lithium metal can be easily reduced. In addition, by controlling the ratio of the area of the first region within the above range, a more uniform squeezing force can be applied from the separator to the entire precipitated lithium metal. Moreover, the resistance to the electrode reaction can be reduced.

[0035] The first region opposite to the spacer is preferably configured in the negative electrode in a state as uniform and dispersed as possible. Thus, the rise in internal resistance can be suppressed, and the location where lithium metal may be precipitated in large quantities locally can be reduced, and the isolated lithium metal can be easily limited to the smallest possible amount. Typically, the positive electrode and the negative electrode are strip-shaped with long and short sides. When the length (width) of the short side direction of the strip-shaped negative electrode is set to L and an arbitrary circular area with a diameter of L / 3 is set on the surface of the negative electrode, it is preferred that the first region and the second region always coexist in such a circular area.

[0036] The spacer may also be a composite material comprising a resin material and particles. In this case, a porous spacer can be easily formed. In addition, the porosity of the spacer can be easily controlled. The particles may be inorganic or organic.

[0037] <Measurement of Porosity Psp of Spacer>

[0038] The porosity Psp of the spacer can be determined by photographing a cross section of the spacer in the direction T using a scanning electron microscope (SEM), for example, within a field of view of 2000 μm × 100 μm. The image is then subjected to image processing such as binarization to distinguish between the pore portion A and the remaining portion B. The porosity Psp is then determined as the area ratio of portion A to the total area of portion A and portion B. Preferably, the porosity Psp (volume %) of the spacer is determined by measuring the area ratios of portion A at any 10 locations in the image. The average of the area ratios of portion A determined at the 10 locations is used to determine the porosity Psp (volume %) of the spacer.

[0039] <Measurement of Porosity Pse of Separator>

[0040] The porosity Pse of the separator is, for example, measured by measuring the mass after the separator is cut into a certain area. The volume is calculated as area × thickness. The apparent density (Va) is calculated by dividing the mass by the volume. The porosity is calculated based on the apparent density and the true density of the constituent material of the separator (density in the case of 0% porosity: Vr) (Pse = 100 × (1-Va / Vr)). In the case where the separator has a multi-layer structure, the volume ratio of each layer is calculated by determining the thickness of each layer using a scanning electron microscope (SEM), and the average true density Vre is calculated based on the true density and volume ratio of the constituent material of each layer. The porosity is calculated in the same way based on the apparent density and the average true density Vre.

[0041] The thickness of the separator is measured at arbitrary 10 locations of the sample in a state where no load in the direction T is applied to the separator, and the thickness is determined as the average value.

[0042] From the viewpoint of ensuring sufficient ion permeability and mechanical strength, 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.

[0043] exist Figure 1Schematically shows the main parts 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 arranged between the first electrode 100 and the second electrode 200, and a spacer 400 arranged 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 relative region of the first electrode 100 (second electrode 200) relative to the second electrode (first electrode 100) is divided into a first region R1 opposite to the spacer 400 and a second region R2 not opposite to 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.

[0044] [Spacer]

[0045] The spacer 400 provided between the electrodes 100 and 200 and the separator 300 forms a space S for accommodating the deposited lithium metal, thereby reducing the volume change of the negative electrode caused by the deposition of the lithium metal.

[0046] The separator 300 generally has a strip shape having a long side and a short side. Here, the direction along the short side of the separator is set to D1. In the cross section of the spacer parallel to the direction T and parallel to the direction D1 (hereinafter referred to as the reference cross section), 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, the stress applied to the spacer 400 is easily dispersed evenly to the separator 300 and the electrodes 100, 200. In addition, the first region R1 opposite to the spacer 400 is easily configured relative to the electrodes 100, 200 in a uniform and dispersed state. In addition, the contact length is the average value of the contact lengths in the reference cross sections of 5 different locations.

[0047] The shape of the reference cross section of the spacer 400 is not particularly limited and may be, for example, a rectangle, a rectangle having a curve at at least one corner, a trapezoid, an ellipse, a partial ellipse, or a shape similar to these.

[0048] The material constituting the spacer 400 is not particularly limited. The spacer 400 is made of a non-porous material and / or a porous material. In addition, the spacer 400 is made of an insulating material.

[0049] The spacer 400 can also be formed, for example, by applying a solution or dispersion containing a resin material or the like on the surface of the separator 400 or any of the electrodes 100 and 200 and drying it. The solvent or dispersion medium is not particularly limited, but for example, N-methyl-2-pyrrolidone (NMP) can be used. In addition, the spacer 400 can also be formed by spreading particles in a desired shape on the surface of the separator 300 or any of the electrodes 100 and 200. The spacer 400 can also be formed by applying a curable resin to the surface of the separator 300 or any of the electrodes 100 and 200 in a desired shape and curing it. The cured product of the curable resin has a Young's modulus of, for example, 0.01 GPa or more and 10 GPa or less, so it is easy to alleviate the stress caused by the expansion and contraction of the negative electrode and it is easy to maintain a space for accommodating lithium metal. In addition, the spacer 400 can also be formed by attaching an adhesive tape to the surface of the separator 300 or any of the electrodes 100 and 200. Among the above methods, the method using a solution or dispersion containing a resin material is preferred.

[0050] Examples of the resin material include polyvinylidene fluoride (PVdF), polytetrafluoroethylene and other fluorine-containing resins, vinylidene fluoride-tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers and other fluorine-containing rubbers, styrene-butadiene copolymers or their hydrogenates, acrylonitrile-butadiene copolymers or their hydrogenates, acrylonitrile-butadiene-styrene copolymers or their hydrogenates, methacrylate-acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene-propylene rubber, polyvinyl alcohol, polyvinyl acetate and other rubbers, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and other cellulose derivatives, acrylic resins such as acrylic acid-methacrylic acid copolymers, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid), polyimide, polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, polyurethane resin, melamine resin, urea resin, and epoxy resin.

[0051] The spacer may also be a composite material comprising a resin material and particles. In this case, the resin material at least serves to bind the particles together. Such a spacer may also be formed using a dispersion comprising a resin material and particles.

[0052] As particles, inorganic particles such as insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides can be listed. As metal oxides, aluminum oxide (Alumina, boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, silicon oxide (silicon dioxide), etc. can be listed. As metal hydroxides, aluminum hydroxide, etc. can be listed. As metal nitrides, silicon nitride, aluminum nitride, boron nitride, titanium nitride, etc. can be listed. As metal carbides, silicon carbide, boron carbide, etc. can be listed. As metal sulfides, barium sulfate, etc. can be listed. In addition, minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate can also be used. Among them, aluminum oxide, silicon dioxide, titanium dioxide, etc. are preferably used.

[0053] The average particle size of the particles is not particularly limited, but is preferably 10 μm or less, more preferably 0.1 μm or more and 2.0 μm or less. The average particle size can be determined by imaging a cross section of the spacer in a direction T within the secondary battery using an electron microscope, performing image processing such as binarization of the captured image to identify the particle portion C, and then calculating the average diameter of an equivalent circle having the same area as each particle. The average is preferably determined based on, for example, 100 or more particles.

[0054] In the composite comprising the resin material and the particles, the particles are preferably contained in a ratio of 70 parts by mass to 100 parts by mass per 100 parts by mass of the resin material. This makes it easier to ensure sufficient strength of the spacer, and to form appropriate pores in the spacer, thereby facilitating control of the porosity Psp of the spacer.

[0055] The configuration of the spacer is not particularly limited. For example, when observed from the direction T (the normal direction of the main surface of the separator), the spacer is preferably configured in a manner to draw a straight line SL along the direction D1, and the straight line SL passes through more than 3 parts of the spacer (preferably more than 4 parts, more preferably more than 5 parts). In this case, lithium metal is not easy to precipitate unevenly or dendritically at the negative electrode. Moreover, the local expansion of the negative electrode is suppressed, and therefore it is not easy to cause damage to the electrode. In addition, the fulcrums at which the spacer supports the separator and the electrode become more, and the separator and the electrode are subjected to stress more evenly from the spacer. Therefore, the damage to the electrode is further suppressed. In addition, a more uniform extrusion force can be given from the separator to the entirety of the precipitated lithium metal. Therefore, the precipitation direction of the lithium metal is more easily controlled in the surface direction of the negative electrode.

[0056] When viewed from the direction T, on the straight line SL, the ratio of the minimum distance d (μm) between adjacent spacers to the height h (μm) of the spacer: d / h, for example, can be greater than 10 and less than 800, or can be greater than 40 and less than 400. By controlling the d / h ratio within the above range, it is easy to ensure sufficient space for accommodating lithium metal. In addition, a more uniform squeezing force can be applied from the separator to the entire precipitated lithium metal. The minimum distance d between adjacent spacers can be obtained by measuring one location on each of 10 arbitrary straight lines SL and taking the average value thereof.

[0057] The spacer may also be, for example, a plurality of linear protrusions arranged as stripes on the surface of the electrode or separator in a manner intersecting the direction D1. For example, a protrusion along the long side direction of the separator (hereinafter referred to as the second direction D2) may be provided at each of the two ends in the direction D1 of the surface of the separator, and one or more protrusions along the direction D2 may be provided between the two ends. In this case, a straight line SL can be drawn in a manner passing through a total of three or more locations of the spacer at two locations at both ends and one or more locations between the two ends. A spacer composed of a plurality of linear protrusions like this can be formed relatively easily on the surface of the separator or electrode. In addition, it is also easy to control parameters such as the height h and the d / h ratio.

[0058] [Lithium secondary battery]

[0059] Hereinafter, the structure of the lithium secondary battery of the present disclosure will be described with reference to the accompanying drawings, taking a cylindrical battery having a wound electrode group as an example. However, the present disclosure is not limited to the following structure.

[0060] Figure 2 This is a longitudinal cross-sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery having a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte. The battery case is composed of a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16, which seals the opening of the case body 15. The case body 15 has an annular step portion 21 formed by partially pressing the side wall from the outside near the opening. The sealing body 16 is supported by the surface of the step portion 21 on the opening side. A gasket 27 is arranged between the case body 15 and the sealing body 16, thereby ensuring the sealing of the battery case. In the case body 15, insulating plates 17 and 18 are respectively arranged at both ends in the winding axis direction of the electrode group 14.

[0061] The sealing body 16 includes a filter 22, a lower valve core 23, an insulating member 24, an upper valve core 25, and a cover 26. The cover 26 is arranged on the outside of the shell body 15, and the filter 22 is arranged on the inside of the shell body 15. The lower valve core 23 and the upper valve core 25 are connected to each other at their respective central portions, and the insulating member 24 is interposed between the peripheral portions of the lower valve core 23 and the upper valve core 25. The filter 22 and the lower valve core 23 are connected to each other at their respective peripheral portions. The upper valve core 25 and the cover 26 are connected to each other at their respective peripheral portions. A vent is formed in the lower valve core 23. When the internal pressure of the battery case rises due to abnormal heating, etc., the upper valve core 25 expands toward the cover 26 and moves away from the lower valve core 23. As a result, the electrical connection between the lower valve core 23 and the upper valve core 25 is cut off. When the internal pressure rises further, the upper valve core 25 breaks, and gas is discharged from the opening formed in the cover 26.

[0062] Here, the electrode group 14 comprises 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 in a strip shape and are spirally wound with their width directions parallel to the winding axis.

[0063] The positive electrode 110 is electrically connected to the cover 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, to a portion near the center in the longitudinal direction of the positive electrode 110. The other end of the positive electrode lead 19 extending from the positive electrode 110 is welded to the inner side surface of the filter 22 via a through-hole formed in the insulating plate 17.

[0064] Negative electrode 120 is electrically connected to case body 15 , which also serves as a negative electrode terminal, via negative electrode lead 20 . Negative electrode lead 20 has one end connected to, for example, a longitudinal end of negative electrode 120 and the other end welded to the inner bottom surface of case body 15 .

[0065] Figure 3 It is a schematic representation of Figure 2 : An enlarged view of the discharge state of the area X surrounded by the dotted line in FIG. In the example shown in the figure, the cross-sectional shape of the spacer 400 is a trapezoid. However, the embodiments of the present disclosure are not limited thereto, and may be, for example, a rectangle, a rectangle having a curve at at least one corner, an ellipse, a portion of an ellipse, etc. In the example shown in the figure, the spacer 400 is provided between the positive electrode 110 and the separator 300. However, the embodiments of the present disclosure are not limited thereto, and the spacer 400 may be provided between the negative electrode 120 and the separator 300, or provided between the positive electrode 110 and the separator 300 and between the negative electrode 120 and the separator 300, respectively.

[0066] The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode composite material layer 112. A spacer 400 is provided between the positive electrode composite material layer 112 and the separator 300. The spacer 400 is composed of linear protrusions 401 arranged along the direction D2 (longitudinal direction) of the separator 300. In the 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 the 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 pressed by the separator 300. That is, the negative electrode 120 includes the negative electrode current collector 121 in the discharged state and includes the negative electrode current collector 121 and lithium metal deposited on its surface in the charged state.

[0067] The lithium metal is contained in the space between the positive electrode 110 and the separator 300, thus minimizing the apparent volume change of the electrode assembly caused by the precipitation of lithium metal during the charge-discharge cycle. Consequently, stress applied to the negative electrode current collector 121 is also suppressed. Furthermore, pressure is applied from the separator 300 to the lithium metal contained between the positive electrode 110 and the separator 300, thereby controlling the precipitation of the lithium metal, making it less likely to become isolated and suppressing a decrease in charge-discharge efficiency.

[0068] In the example, a cylindrical lithium secondary battery with a wound electrode group is described, but the shape of the lithium secondary battery is not limited thereto. Depending on its use, it can be appropriately selected from various shapes such as cylindrical, coin-shaped, square, sheet-shaped, flat, etc. The form of the electrode group is not particularly limited and can also be a stacked type. In addition, for structures other than the electrode group and the non-aqueous electrolyte of the lithium secondary battery, known structures can be used without particular restriction.

[0069] Next, the arrangement of the spacers will be described with reference to the accompanying drawings. In the illustrated example, the spacers are provided on the surface of the separator. However, the embodiments of the present disclosure are not limited thereto, and the spacers may also be provided on the surface of the electrodes.

[0070] Figure 4 This is a top view schematically showing a spacer disposed on the surface of a separator. Spacer 400 includes linear protrusions 401 located at both ends of the surface of separator 300 in direction D1 and extending along direction D2, and a linear protrusion 401 located in the center between the two ends and extending along direction D2. In other words, spacer 400 is composed of a total of three substantially parallel linear protrusions 401. Therefore, a straight line SL drawn along direction D1 passes through spacer 400 at three locations. Furthermore, "substantially parallel" means approximately parallel, and the linear protrusions 401 may intersect at angles of, for example, 0° to 20° or 0° to 10°.

[0071] Figure 5 This is a top view schematically showing another spacer disposed on the surface of the separator. Spacer 400 is composed of a plurality of linear protrusions 401 arranged in a stripe pattern along direction D2 on the surface of separator 300. 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 in the illustrated example).

[0072] Figure 6 This is a top view schematically showing another spacer disposed on the surface of a separator. Spacer 400 is composed of a plurality of dot-shaped protrusions 401 evenly distributed across the surface of separator 300. In the illustrated example, when a straight line SL is drawn along direction D1, the number of dot-shaped protrusions 401 that it passes through varies depending on the position of the straight line SL. Straight line SL1 passes through four protrusions 401, and straight line SL2 passes through five protrusions 401. In such cases, at least one of the multiple straight lines SL drawn in different patterns can pass through three or more protrusions.

[0073] Figure 7 This is a schematic top view of another spacer disposed on the surface of a separator. Spacer 400 is a continuous body of honeycomb-shaped ribs evenly distributed across the surface of separator 300. In this case, when a straight line SL is drawn along direction D1, the number of ribs it passes through varies depending on the position of the straight line SL. Straight line SL1 passes through the ribs at five locations, while straight line SL2 passes through the ribs at four locations.

[0074] Figure 8 This is a schematic top view of another spacer disposed on the surface of the separator. Spacer 400 is composed of a plurality of line-segment-shaped protrusions 401 evenly distributed on the surface of separator 300. Line-segment-shaped protrusions 401 are arranged so as to alternately intersect along direction D1. In this case, when a straight line is drawn along direction D1, the number of line-segment-shaped protrusions 401 that it passes 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.

[0075] Hereinafter, each component of the lithium secondary battery will be described in more detail.

[0076] [negative electrode]

[0077] The negative electrode has a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode during charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons at the negative electrode during charging, becoming lithium metal and 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 during discharge. In addition, the lithium ions contained in the non-aqueous electrolyte can come from a lithium salt added to the non-aqueous electrolyte, can be supplied by the positive electrode active material during charging, or can be a combination of both.

[0078] The negative electrode may also include a lithium ion storage layer (a layer that exhibits capacity by absorbing and releasing 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 may 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 storage layer when fully charged. In other words, the negative electrode exhibits capacity based on the precipitation and dissolution of lithium metal.

[0079] Here, "fully charged" refers to a state where the battery is charged to a rated capacity of C, for example, 0.98 × C or higher. 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 single cell using lithium metal as the counter electrode. The non-aqueous electrolyte in the single cell may have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0080] The lithium ion storage layer is formed by forming a negative electrode composite material containing a negative electrode active material into a layer. The negative electrode composite material may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0081] 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).

[0082] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0083] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber polymers. Examples of the fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0084] The negative electrode current collector may be a conductive sheet, and foil, film, or the like may be used as the conductive sheet.

[0085] The material of the negative electrode current collector (conductive sheet) is any conductive material other than lithium metal and lithium alloy. The conductive material may also be a metal material such as a metal or alloy. The conductive material is preferably a material that does not react with lithium. More specifically, it is preferably a material 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 a base surface preferentially exposed. As alloys, copper alloys, stainless steel (SUS), etc. are listed. Among them, copper and / or copper alloys with higher conductivity are preferred.

[0086] 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.

[0087] [positive electrode]

[0088] The positive electrode, for example, comprises a positive electrode current collector and a positive electrode composite material layer supported by the positive electrode current collector. The positive electrode composite material layer, for example, comprises a positive electrode active material, a conductive material, and a binder. The positive electrode composite material layer may be formed on only one side of the positive electrode current collector or on both sides. The positive electrode is obtained, for example, by coating a positive electrode composite material slurry comprising 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.

[0089] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of positive electrode active materials 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.

[0090] During charging, lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions and deposited as lithium metal at the negative electrode or negative electrode current collector. During discharge, lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed by the composite oxide at the positive electrode. In other words, the lithium ions involved in charging and discharging primarily come from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0091] As the transition metal elements contained in the transition metal oxide containing lithium, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. are listed. The transition metal oxide containing lithium can contain one transition metal element, or it can contain two or more. The transition metal element can also be Co, Ni and / or Mn. The transition metal oxide containing lithium can contain one or more typical elements as needed. As typical elements, Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc. are listed. Typical elements can also be Al, etc.

[0092] Among lithium-containing transition metal oxides, composite oxides containing Co, Ni, and / or Mn as transition metal elements and Al as an optional component, preferably have a layered rock salt-type crystal structure in order to achieve high capacity. In this case, in a lithium secondary battery, the molar ratio of the total amount of lithium in the positive and negative electrodes, mLi, to the amount of metal M other than lithium in the positive electrode, mM, is set to, for example, 1.1 or less.

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

[0094] Examples of materials for the positive electrode current collector (conductive sheet) include metal materials such as Al, Ti, and Fe. The metal material may also be Al, Al alloys, Ti, Ti alloys, or Fe alloys. The Fe alloy may also be stainless steel (SUS).

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

[0096] [Separator]

[0097] The separator uses a porous sheet with ion permeability and insulation. Examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. The material of the separator is not particularly limited and may be a polymer material. Examples of polymer materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may also contain additives as needed. Examples of additives include inorganic fillers and the like.

[0098] The thickness of the separator is not particularly limited, but is, for example, 5 μm or more and 20 μm or less, more preferably 10 μm or more and 20 μm or less.

[0099] [Non-aqueous electrolyte]

[0100] The non-aqueous electrolyte having lithium ion conductivity includes, 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 or gel form.

[0101] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. When the lithium salt dissolves in the non-aqueous solvent, lithium ions and anions are generated.

[0102] The gel-like non-aqueous 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, and polyether resins.

[0103] As lithium salts or anions, known lithium salts or anions used in non-aqueous electrolytes of lithium secondary batteries can be used. Specifically, BF4-, ClO4-, PF6-, CF3SO3-, CF3CO2-, anions of imides, anions of oxalate complexes, etc. are listed. As anions of imides, 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 greater, x and y are each independently 0, 1 or 2, and satisfy x+y=2), etc. The anion of the oxalate complex may also contain boron and / or phosphorus. As the anion of the oxalate complex, bisoxalate borate anion, BF2(C2O4)-, PF4(C2O4)-, PF2(C2O4)2-, etc. are listed. The non-aqueous electrolyte may contain these anions alone, or may contain two or more types.

[0104] From the perspective of suppressing the dendritic precipitation of lithium metal, the non-aqueous electrolyte preferably contains at least an oxalate complex anion, and is particularly preferably an oxalate complex anion containing fluorine. Through the interaction between the oxalate complex anion containing fluorine and lithium, lithium metal is easily and uniformly precipitated in a fine particle form. Therefore, it is easy to suppress the local precipitation of lithium metal. The oxalate complex anion containing fluorine can also be combined with other anions. Other anions can also be PF6- and / or imide anions.

[0105] Examples of non-aqueous solvents 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 halogen-substituted products include fluorides and the like.

[0106] 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.

[0107] 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.

[0108] 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 also be set to 0.5 mol / L or more and 3.5 mol / L or less. Alternatively, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may also be set to 0.05 mol / L or more and 1 mol / L or less.

[0109] The non-aqueous electrolyte may also contain additives. The additives may also form a coating on the negative electrode. By forming a coating from the additive on the negative electrode, the formation of dendrites is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and vinyl ethylene carbonate (VEC).

[0110] [Example]

[0111] Hereinafter, the lithium secondary battery of 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.

[0112] Example 1

[0113] (1) Preparation of positive electrode

[0114] A rock salt-type lithium-containing transition metal oxide (NCA: positive electrode active material) containing Li, Ni, Co and Al (the molar ratio of Li to the total of Ni, Co and Al is 1.0) and having a layered structure, acetylene black (AB: conductive material) and polyvinylidene fluoride (PVdF: binding material) are mixed in a mass ratio of NCA:AB:PVdF=95:2.5:2.5, and then an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added and stirred to prepare a positive electrode composite material slurry. The obtained positive electrode composite material slurry is applied to both sides of a strip of Al foil (positive electrode collector), dried and rolled with a roller. Finally, the obtained stack of the positive electrode collector and the positive electrode composite material is cut into a predetermined electrode size to obtain a positive electrode having a positive electrode composite material layer on both sides of the positive electrode collector.

[0115] (2) Formation of spacers

[0116] A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF) as a resin material, 90 parts by mass of alumina (containing alumina with an average particle size of 1 μm and alumina with an average particle size of 0.1 μm at a mass ratio of 10 / 1) as inorganic particles, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium. Separately, a polyethylene separator (microporous membrane) with a thickness of 20 μm and a porosity Pse of 40% was prepared.

[0117] Spacer ink was applied along direction D2 to both ends of the separator's surface in direction D1 and in the center between the ends. This was then dried with hot air to create a total of three parallel linear protrusions, or spacers. The spacer ink was applied using a dispenser. The 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.

[0118] In the direction D1 , the minimum distance d between adjacent convex portions is 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 is approximately 14%.

[0119] (3) Preparation of negative electrode

[0120] A strip-shaped electrolytic copper foil (15 μm thick) was prepared as a negative electrode current collector.

[0121] (4) Preparation of non-aqueous electrolyte

[0122] Ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed in a volume ratio of EC:DMC=30:70, and LiPF6 and LiBF2(C2O4) are dissolved in the resulting mixed solvent at a concentration of 1 mol / L and 0.1 mol / L, respectively, to prepare a liquid non-aqueous electrolyte.

[0123] (5) Battery assembly

[0124] In an inert gas atmosphere, the positive and negative electrode current collectors were spirally wound with the separator interposed therebetween to produce an electrode assembly. All the lithium contained in the electrode assembly originated from the positive electrode, so the molar ratio of the total amount of lithium in the positive and negative electrodes (mLi) to the amount of metal M (here, Ni, Co, and Al) in the positive electrode (mM) was 1.0: mLi / mM.

[0125] The electrode group was housed in a bag-shaped outer casing formed of a laminate sheet having an Al layer, the non-aqueous electrolyte was injected, and the outer casing was sealed to complete the lithium secondary battery A1.

[0126] In a reference cross section obtained by cutting the electrode group, the cross-sectional shape of the projection is close to a trapezoidal shape.

[0127] Example 2

[0128] A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF), 90 parts by mass of aluminum oxide (average particle size of 1 μm), and a dispersion medium of N-methyl-2-pyrrolidone (NMP). The porosity Psp of the spacer was changed to 11%, and the Psp / Pse ratio R was changed to 0.28. Except for this, a lithium secondary battery A2 was produced in the same manner as in Example 1.

[0129] Example 3

[0130] A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF), 90 parts by mass of aluminum oxide (average particle size of 5 μm), and a dispersion medium of N-methyl-2-pyrrolidone (NMP). The porosity Psp of the spacer was changed to 29.5%, and the Psp / Pse ratio R was changed to 0.74. Except for this, a lithium secondary battery A3 was produced in the same manner as in Example 1.

[0131] Example 4

[0132] A spacer ink was prepared by mixing 10 parts by mass of polyvinylidene fluoride (PVdF), 90 parts by mass of aluminum oxide (average particle size of 10 μm), and a dispersion medium of N-methyl-2-pyrrolidone (NMP). The porosity Psp of the spacer was changed to 39%, and the Psp / Pse ratio R was changed to 0.97. Except for this, a lithium secondary battery A4 was produced in the same manner as in Example 1.

[0133] Comparative Example 1

[0134] A spacer ink was prepared by mixing 30 parts by mass of polyvinylidene fluoride (PVdF), 70 parts by mass of aluminum oxide (average particle size of 1 μm), and a dispersion medium of N-methyl-2-pyrrolidone (NMP). The porosity Psp of the spacer was changed to 60%, and the Psp / Pse ratio R was changed to 1.5. Except for this, a lithium secondary battery B1 was produced in the same manner as in Example 1.

[0135] Comparative Example 2

[0136] A lithium secondary battery B2 was produced in the same manner as in Example 2, except that the height of the protrusions of the spacer was changed to 15 μm. The porosity Psp of the spacer was 9.6%, and the Psp / Pse ratio R was 0.24.

[0137] [Evaluation 1]

[0138] The obtained battery was subjected to a charge and discharge test and evaluated. The results are shown in Table 1.

[0139] In the charge-discharge test, three batteries were charged in a thermostatic chamber at 25°C under the following conditions, then left to stand for 20 minutes, 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 1st cycle (MR50) was calculated as the capacity retention rate (%).

[0140] (Charge)

[0141] Constant current charging was performed at a current of 10 mA per unit area (cm2) 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.

[0142] (Discharge)

[0143] Constant current discharge was performed at a current of 10 mA per unit area of the electrode until the battery voltage reached 3.0 V.

[0144] The number of cycles at which cycling stopped, presumably due to cracks in the negative electrode current collector (copper foil), occurred in the three batteries was determined. Furthermore, when cycling stopped in some batteries, the average MR50 value was determined for the remaining batteries.

[0145] [Table 1]

[0146] Height t(μm) R(Psp / Pse) MR50 Cracks in copper foil A1 30 0.05 82 none A2 30 0.28 64 none A3 30 0.74 60 none A4 30 0.97 55 none B1 30 1.5 46 have B2 15 0.24 Less than 50 cycles have

[0147] In batteries A5 and B1, cycling stopped due to cracks in the negative electrode current collector. Furthermore, in battery B1, the capacity retention rate at the 50th cycle was significantly lower. Batteries A1, A2, A3, and A4, whose R ratios satisfied 0 < R < 0.75, achieved particularly good MR50.

[0148] Example 5

[0149] Lithium secondary battery A5 was fabricated in the same manner as in Example 2, except that the number of protrusions on the spacer was set to six. Specifically, four (six in total) parallel linear protrusions, or spacers, were provided at both ends of the separator in direction D1 and between the ends. The ratio SR of the area of the first region to the total area of the first and second regions was approximately 28%.

[0150] Example 6

[0151] A lithium secondary battery A6 was produced 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 region and the second region was approximately 28%.

[0152] Example 7

[0153] A lithium secondary battery A7 was produced in the same manner as in Example 2, except that the spacer projections were arranged in a total of six and the width of the spacer projections 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 56%.

[0154] [Evaluation 2]

[0155] The obtained battery was evaluated in the same manner as above. The results are shown in Table 2.

[0156] [Table 2]

[0157] SR (%) R(Psp / Pse) MR50 Cracks in copper foil A2 14 0.05 64 none A5 28 0.05 62 none A6 28 0.05 60 none A7 56 0.05 56 none

[0158] Table 2 shows 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. Furthermore, in order to form a spacer with sufficient strength, the width of the convex portion is required, and SR needs to be set to 5% or more.

[0159] Industrial applicability

[0160] 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 vehicles, and household batteries combined with solar cells.

[0161] Description of Reference Numerals

[0162] 10. Lithium secondary battery; 14. Electrode group; 15. Shell body; 16. Sealing body; 17, 18. Insulating plate; 19. Positive electrode lead; 20. Negative electrode lead; 21. Step portion; 22. Filter; 23. Lower valve core; 24. Insulating member; 25. Upper valve core; 26. Cover; 27. Gasket; 100. First electrode; 110. Positive electrode; 111. Positive electrode collector; 112. Positive electrode composite material layer; 120. Negative electrode; 121. Negative electrode collector; 200. Second electrode; 300. Separator; 400. Spacer; 401. Protrusion.

Claims

1. A lithium secondary battery, wherein: The lithium secondary battery has: positive electrode; negative electrode; a porous separator disposed between the positive electrode and the negative electrode; a spacer disposed between at least one of the positive electrode and the negative electrode and the separator; and a non-aqueous electrolyte having lithium ion conductivity, At the negative electrode, lithium metal is deposited during charging and dissolved during discharging. The 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 of the spacer is greater than 20 μm. When the spacer is porous, the porosity Psp of the spacer is less than the porosity Pse of the separator. The height of the spacer is a dimension of the spacer in the thickness direction of the separator.

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

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

75.

4. The lithium secondary battery according to any one of claims 1 to 3, wherein The ratio of the area of the first region to the total area of the first region and the second region is 5% to 30%.

5. The lithium secondary battery according to any one of claims 1 to 3, wherein The spacer is a composite material including a resin material and particles.

Images