Lithium secondary battery

Abstract

The purpose of the present invention is to provide a means that, by using manganese dioxide as a positive electrode active material, is capable of increasing discharge capacity of a lithium secondary battery including a solid electrolyte.　The present invention provides a lithium secondary battery that is provided with a power generation element comprising: a positive electrode that has a positive electrode active material layer containing, as a positive electrode active material, manganese dioxide having a specific surface area of 20 m2 / g or less and containing a first solid electrolyte; a negative electrode that has a negative electrode active material layer containing a negative electrode active material; and a solid electrolyte layer that is interposed between the positive electrode and the negative electrode and that contains a second solid electrolyte.

Description

Lithium secondary battery

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

[0002] In recent years, there has been active research and development into lithium secondary batteries that use oxide- or sulfide-based solid electrolytes. Solid electrolytes are materials primarily composed of ionic conductors that allow ionic conduction in a solid state. Therefore, lithium secondary batteries that use solid electrolytes do not, in principle, encounter the various problems associated with flammable organic electrolytes that occur in conventional liquid-based lithium secondary batteries. In addition, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the battery's power density and energy density.

[0003] Manganese dioxide is widely used as a positive electrode material for batteries that use liquid electrolytes, such as alkaline manganese dry batteries. For example, Japanese Patent Application Laid-Open No. 2004-186127 discloses a positive electrode active material made of electrolytic manganese dioxide whose weight loss upon heating is controlled within a predetermined range. According to Japanese Patent Application Laid-Open No. 2004-186127, the positive electrode active material can improve the high-rate characteristics and high-rate pulse characteristics of the battery.

[0004] However, according to the investigations of the present inventors, it has been found that even if the technology described in JP 2004-186127 A is used, a sufficient discharge capacity cannot be obtained in a lithium secondary battery that uses manganese dioxide as a positive electrode active material and a solid electrolyte.

[0005] Therefore, an object of the present invention is to provide a means for increasing the discharge capacity of a lithium secondary battery that uses manganese dioxide as a positive electrode active material and contains a solid electrolyte.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that in a lithium secondary battery using manganese dioxide as a positive electrode active material and containing a solid electrolyte, the above-mentioned problems can be solved by controlling the specific surface area of ​​the manganese dioxide within a predetermined range, thereby completing the present invention.

[0007] That is, one embodiment of the present invention is a cathode active material having a specific surface area of ​​20 m ２The lithium secondary battery is provided with a power generating element including: a positive electrode having a positive electrode active material layer containing a first solid electrolyte, the positive electrode containing manganese dioxide having a specific surface area of ​​0.1 μm / g or less; a negative electrode having a negative electrode active material layer containing a negative electrode active material; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a second solid electrolyte.

[0008] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention.

[0009] In one embodiment of the present invention, a cathode active material having a specific surface area of ​​20 m ２ The lithium secondary battery includes a power generating element having a positive electrode having a positive electrode active material layer containing manganese dioxide having a specific surface area of ​​1 / g or less and containing a first solid electrolyte, a negative electrode having a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a second solid electrolyte. According to the lithium secondary battery of this embodiment, the positive electrode active material layer contains manganese dioxide as a positive electrode active material, and in a lithium secondary battery containing a solid electrolyte, the discharge capacity of the battery can be improved.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the claims and is not limited to the following embodiments. Note that the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0011] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. The stacked-type structure allows the battery to be compact and have a high capacity. In this specification, the stacked-type lithium secondary battery (hereinafter also simply referred to as a "stacked-type battery") shown in FIG. 1 will be described in detail as an example.

[0012] As shown in FIG. 1 , the stacked battery 10 a of this embodiment has a structure in which a flat, approximately rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11 ″. The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11 ′. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are laminated in this order so that one positive electrode active material layer 15 and the adjacent negative electrode active material layer 13 face each other with the solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one cell layer 19. Therefore, the stacked battery 10a shown in FIG. 1 can be said to have a configuration in which a plurality of cell layers 19 are stacked and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27 that are electrically connected to the respective electrodes (negative and positive electrodes) are attached to the negative electrode current collector 11' and the positive electrode current collector 11" respectively, and are configured to be sandwiched between the ends of the laminate film 29 and extended to the outside of the laminate film 29. A restraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the power generation element 21 by a pressure member (not shown). Therefore, the volume of the power generation element 21 is kept constant.

[0013] The main components of the lithium secondary battery according to this embodiment will be described below.

[0014] [Current Collector] The current collector has a function of mediating the transfer of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0015] The current collector may have a single layer structure made of a single material, or may have a laminate structure made of an appropriate combination of layers made of these materials. From the viewpoint of reducing the weight of the current collector, it is preferable that the current collector include at least a conductive resin layer made of a resin having electrical conductivity. Furthermore, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided on a part of the current collector.

[0016] [Positive Electrode Active Material Layer] (Positive Electrode Active Material) In the lithium secondary battery according to this embodiment, the positive electrode active material layer contains a positive electrode active material. The positive electrode active material contained in the positive electrode active material layer has a specific surface area of ​​20 m ２ / g or less of manganese dioxide (MnO ２ This configuration makes it possible to improve the battery capacity of a lithium secondary battery that uses manganese dioxide as a positive electrode active material and a solid electrolyte.

[0017] As described in JP 2004-186127 A and the like, manganese dioxide is widely used as a positive electrode active material in batteries that use a liquid electrolyte, such as alkaline manganese batteries. However, it has been found that when manganese dioxide is used as a positive electrode active material in batteries that use a solid electrolyte (such as an all-solid-state lithium secondary battery), the capacity of the battery decreases.

[0018] Manganese dioxide, which is used as a positive electrode active material in alkaline manganese batteries and the like, is often produced by a liquid-phase method such as electrolysis, and has a significantly larger specific surface area than positive electrode active materials such as lithium-transition metal composite compounds, which are mainly produced by solid-state sintering. Furthermore, manganese dioxide particles exist in the positive electrode active material layer containing a solid electrolyte in the form of secondary particles formed by aggregation of primary particles. In this case, in the positive electrode active material layer containing a solid electrolyte, the contact points of the manganese dioxide particles with the solid electrolyte are limited to the outer surface regions of the secondary particles, which is thought to prevent sufficient contact points between the manganese dioxide positive electrode active material and the solid electrolyte, resulting in a decrease in battery capacity.

[0019] In contrast, in the lithium secondary battery according to the present embodiment, the positive electrode active material is a material having a specific surface area of ​​20 m ２Manganese dioxide having a specific surface area of ​​1 / g or less is used. In the positive electrode active material layer, lithium ions migrate from the solid electrolyte to the positive electrode active material and diffuse within the particles of the positive electrode active material. The diffusion of lithium ions within the secondary particles of the positive electrode active material can proceed through intragranular diffusion of primary particles and grain boundary diffusion between primary particles. However, the contact points between the manganese dioxide particles and the solid electrolyte are limited to the outer surface regions of the secondary particles, and the primary particles present inside the secondary particles cannot contact the solid electrolyte. This increases the resistance to grain boundary diffusion compared to when a liquid electrolyte is used. In the lithium secondary battery of this embodiment, controlling the specific surface area of ​​manganese dioxide to a predetermined value reduces the frequency of grain boundaries, thereby reducing the distance and resistance of grain boundary diffusion of lithium ions. As a result, the discharge capacity of the battery can be improved.

[0020] In the case of batteries using a liquid electrolyte, the liquid electrolyte fills the spaces between the primary particles, resulting in low resistance to grain boundary diffusion. Therefore, the specific surface area of ​​the positive electrode active material has little effect on the battery's discharge capacity. In other words, the present invention can be said to solve the problems specific to lithium secondary batteries containing solid electrolytes.

[0021] The specific surface area of ​​the positive electrode active material, manganese dioxide, is 20 m ２ / g or less. ２ If the specific surface area of ​​the manganese dioxide positive electrode active material exceeds 15 m / g, the diffusion resistance of lithium ions increases, and therefore a sufficient discharge capacity cannot be obtained. ２ / g or less, more preferably 10m ２ / g or less, and more preferably 8m ２ / g or less, and even more preferably 6m ２ / g or less, and even more preferably 5m ２ / g or less, and particularly preferably 4m ２ Within the above range, the effects of the present invention can be more significantly achieved. ２When the specific surface area of ​​the manganese dioxide positive electrode active material is less than 1 / g, the manganese dioxide positive electrode active material has a structure closer to a single particle, which reduces the diffusion distance and diffusion resistance of the lithium ions at the grain boundaries, thereby enabling the effects of the present invention to be particularly pronounced. ２ / g or more, preferably 1m ２ / g or more. Within this range, the effects of the present invention can be more significantly achieved. In a preferred embodiment, the specific surface area of ​​manganese dioxide, which is the positive electrode active material, is 0.36 to 20 m ２ In a preferred embodiment, the specific surface area of ​​manganese dioxide, which is the positive electrode active material, is 0.36 to 4 m ２ / g.

[0022] The specific surface area (BET specific surface area) of manganese dioxide, which is the positive electrode active material, is measured by the method described in the Examples below.

[0023] Manganese dioxide as a positive electrode active material can form secondary particles. Secondary particles are aggregates of primary particles. Primary particles refer to the smallest unit of separable solid particles having interparticle boundaries. The average secondary particle diameter of manganese dioxide as a positive electrode active material is, for example, less than 2 μm, preferably less than 1.5 μm. Within this range, contact with the solid electrolyte can be further improved, resulting in a higher discharge capacity. The lower limit of the average secondary particle diameter of manganese dioxide is not particularly limited, but can be, for example, 0.1 μm or more, 0.3 μm or more, or 0.6 μm or more. That is, the average secondary particle diameter of manganese dioxide as a positive electrode active material is, for example, 0.1 μm or more and less than 2 μm, preferably 0.3 μm or more and less than 1.5 μm, and more preferably 0.6 μm or more and less than 1.5 μm.

[0024] In this specification, the average secondary particle diameter of manganese dioxide as a positive electrode active material is measured by a particle size distribution measuring device using a laser diffraction / scattering method, and is the 50% cumulative diameter (D ５０ Specifically, the value measured by the method described in the Examples below is used.

[0025] The average primary particle size of manganese dioxide as a positive electrode active material is not particularly limited, but the crystallite size estimated by Scherrer's formula from the 110 peak confirmed by XRD measurement is, for example, 0.01 μm to 1.5 μm. In addition, the ratio of the average primary particle size to the average secondary particle size of manganese dioxide (average secondary particle size / average primary particle size) is not particularly limited, but is, for example, 1 to 10.

[0026] There are no particular limitations on the method for obtaining manganese dioxide having a predetermined specific surface area as a positive electrode active material. Manganese dioxide may be obtained by electrolysis, chemical synthesis, or other methods. However, from the viewpoint of more easily obtaining manganese dioxide having a predetermined specific surface area, manganese dioxide obtained by electrolysis or chemical synthesis is preferred, and chemical synthesis is more preferred. In this specification, "electrolytic manganese dioxide" refers to manganese dioxide obtained by electrolysis. In addition, in this specification, "chemically synthesized manganese dioxide" refers to manganese dioxide obtained by chemical synthesis.

[0027] Electrolytic manganese dioxide can be appropriately produced by conventionally known methods. For example, it can be produced by the method described in JP 2017-179583 A. Specifically, for example, a mixture of an aqueous sulfuric acid solution and an aqueous manganese sulfate solution is used as an electrolyte, an anode and a cathode are appropriately selected to prepare an electrolytic cell, and an electrolytic reaction is carried out, thereby depositing and depositing electrolytic manganese dioxide on the anode. In this case, the specific surface area of ​​the electrolytic manganese dioxide can be changed by changing the electrolysis conditions, such as the temperature, electrolysis current density, and sulfuric acid concentration. For example, increasing the temperature during electrolysis tends to reduce the specific surface area. For example, decreasing the electrolysis current density tends to reduce the specific surface area. Note that electrolytic manganese dioxide may also be produced by electrolytic reactions other than those described above.

[0028] Chemically synthesized manganese dioxide can be appropriately produced by a conventionally known method. Specific examples include a method in which potassium permanganate is dissolved in an aqueous hydrochloric acid solution and hydrothermal synthesis is performed. The heat treatment (calcination) temperature during hydrothermal synthesis is, for example, 140 to 180°C, and preferably 150 to 170°C. The heat treatment (calcination) time is, for example, 2 to 24 hours, and preferably 6 to 18 hours. Alternatively, it can be synthesized by mixing an aqueous potassium permanganate solution, an aqueous manganese sulfate solution, and an aqueous sodium hydroxide solution. Chemically synthesized manganese dioxide may also be produced by chemical reactions other than those described above.

[0029] Alternatively, manganese dioxide obtained by electrolysis, chemical synthesis, or other methods may be appropriately pulverized to obtain a positive electrode active material having a desired particle size. For pulverization, for example, a roller mill, a jet mill, or the like may be used, but is not limited to these. Furthermore, manganese dioxide having a desired average secondary particle size may be produced by classification using an appropriate classification device, for example, a sieve, a classifier, or the like.

[0030] The positive electrode active material may contain a positive electrode active material other than manganese dioxide, or the positive electrode active material may contain only manganese dioxide. In a preferred embodiment, the positive electrode active material layer does not contain a positive electrode active material other than manganese dioxide. That is, in this preferred embodiment, the positive electrode active material consists only of manganese dioxide. When the positive electrode active material consists only of manganese dioxide, the battery capacity of the lithium secondary battery according to the present invention is improved and the battery can be produced inexpensively, resulting in excellent economic efficiency.

[0031] The positive electrode active material may contain two or more types of manganese dioxide having different specific surface areas, but all of them should not exceed 20 m ２ Preferably, the manganese dioxide has a specific surface area of ​​1 / g or less.

[0032] The positive electrode active material other than manganese dioxide contained in the positive electrode active material layer is not particularly limited, but may be LiCoO ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , Li(Ni-Mn-Co)O２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ For example, Li(Ni—Mn—Co)O ２ Also usable are those in which part of these transition metals is replaced by other elements (hereinafter simply referred to as "NMC composite oxides").

[0033] In addition, a sulfur-based positive electrode active material may be used as a positive electrode active material other than manganese dioxide. Examples of the sulfur-based positive electrode active material include particles of an organic sulfur compound or an inorganic sulfur compound, and any material may be used as long as it utilizes the oxidation-reduction reaction of sulfur to release lithium ions during charging and absorb lithium ions during discharging. Examples of the organic sulfur compound include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbon sulfide, etc., as typified by the compounds described in International Publication No. 2010 / 044437, but are not limited thereto. Examples of the inorganic sulfur compound include elemental sulfur (S), Li ２ S, S-carbon composite, TiS ２ , TiS ３ , TiS ４ , NiS, NiS ２ , CuS, FeS ２ , Li ２ S, MoS ２ , MoS ３ , MnS, MnS ２ , CoS, CoS ２ These include, but are not limited to, the following.

[0034] Here, the proportion of the manganese dioxide content relative to the total mass of the positive electrode active material is preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 97% by mass or more, and most preferably 100% by mass.

[0035] The content of the positive electrode active material in the positive electrode active material layer is preferably 30 to 99 mass %, more preferably 40 to 85 mass %, even more preferably 50 to 70 mass %, and even more preferably 50 to 60 mass %, relative to the total mass of the positive electrode active material layer.

[0036] (Solid Electrolyte) In the lithium secondary battery according to this embodiment, the positive electrode active material layer contains a solid electrolyte. In this specification, the solid electrolyte contained in the positive electrode active material layer is referred to as a "first solid electrolyte," and the solid electrolyte contained in the solid electrolyte layer described below is referred to as a "second solid electrolyte." Therefore, the order of "first" and "second" is meaningless, and these terms are merely used to distinguish the locations where the solid electrolyte is present. The solid electrolyte (first solid electrolyte) contained in the positive electrode active material layer is not particularly limited as long as it has Li ion conductivity. Examples include halide solid electrolytes, sulfide solid electrolytes, hydride solid electrolytes, and oxide solid electrolytes. Among these, it is preferable to contain at least one of a halide solid electrolyte and a sulfide solid electrolyte because these are materials softer than manganese dioxide and can further improve contact with manganese dioxide. It is particularly preferable to contain a halide solid electrolyte from the viewpoint of chemical stability when in contact with manganese dioxide. That is, in a preferred embodiment of the present invention, the solid electrolyte (first solid electrolyte) contained in the positive electrode active material layer is a halide solid electrolyte. In this specification, the term "sulfide solid electrolyte" refers to a solid electrolyte containing elemental sulfur, and the term "halide solid electrolyte" refers to a solid electrolyte containing a halogen element but not containing elemental sulfur.

[0037] The halide solid electrolyte includes Li ｐ Mｑ X ｒ (wherein M is a metal element, X is a halogen element, p=1, 2, or 3, q=0 or 1, and r=an integer of 1 to 6. In this case, p, q, and r are appropriately selected so that the charge of the entire compound represented by the above composition formula is 0.)

[0038] Examples of the metal element M include, but are not limited to, Al, Mg, Fe, Ga, Y, Zr, and In. The halogen element X is F, Cl, Br, or I. X in the above composition formula may be composed of a single halogen element or multiple halogen elements.

[0039] The composition formula of the halide solid electrolyte is specifically LiX, LiMX ４ , Li ２ MX ４ , Li ２ MX ６ , and Li ３ MX ６ Among them, the halide solid electrolyte includes, but is not limited to, Li ３ MX ６ Preferably, the halide solid electrolyte is represented by the following composition formula: ｐ M ｑ X ｒ The definitions of M and X are the same as those in the above. By adopting this configuration, the effects of the present invention can be more significantly obtained.

[0040] Li ３ MX ６ As the halide solid electrolyte represented by the composition formula, for example, Li ３ AlF ６ , Li ３ AlCl ６ , Li ３ AlBr ６ , Li ３ All I ６ , Li ３ GaF ６ , Li ３ GaCl ６ , Li ３ GaBr ６, Li ３ GaI ６ , Li ３ YF ６ , Li ３ YCl ６ , Li ３ YBr ６ , Li ３ YI ６ , Li ３ InF ６ , Li ３ InCl ６ , Li ３ InBr ６ , and Li ３ InI ６ These can be produced by conventionally known methods, for example, by referring to Interdisciplinary Materials 2023;2:365-389. In one embodiment, the first solid electrolyte is Li ３ YCl ６ , Li ３ YBr ６ , and Li ３ YI ６ Preferably, the compound is at least one of Li ３ YCl ６ and / or Li ３ YBr ６ More preferably, Li ３ YBr ６ It is more preferable that:

[0041] Examples of sulfide solid electrolytes include LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ , LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S.４ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -Li ２ O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Z ｍ S ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions.

[0042] The sulfide solid electrolyte is, for example, Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of sulfide solid electrolytes having a skeleton include LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ In addition, Li ４ P ２ S ７ Examples of the sulfide solid electrolyte having a skeleton include a Li-P-S solid electrolyte called LPS (for example, Li ７ P ３ S １１ ) can be mentioned. In addition, examples of sulfide solid electrolytes include Li （４－ｘ） Ge （１－ｘ） P ｘ S ４ (x satisfies 0<x<1), or the like. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing Li ２ S-P ２ S ５ It is more preferable that the sulfide solid electrolyte contains a halogen (F, Cl, Br, I). As the sulfide solid electrolyte containing a halogen, an argyrodite-type solid electrolyte (Li ６ P.S. ５ CX (wherein X is a halogen atom) is also a preferred material. The argyrodite-type solid electrolyte can be produced by a conventionally known method, for example, by referring to Solid State Ionics 318 (2018) 102-112.

[0043] The sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method.

[0044] The shape of the first solid electrolyte may be, for example, a particulate shape, such as a spherical shape or an oval spherical shape. ５０ ) is not particularly limited, but is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less. The lower limit is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. That is, the average secondary particle diameter of the first solid electrolyte is, for example, 0.01 μm or more and 500 μm or less, preferably 0.1 μm or more and 100 μm or less, more preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. When the average secondary particle diameter of the first solid electrolyte is within the above range, it is advantageous in that the contact area between the first solid electrolyte and the positive electrode active material is more ensured.

[0045] In this specification, the average secondary particle diameter of the solid electrolyte is the 50% cumulative diameter (D) based on the number of particles observed in several to several tens of fields of view when observed with a scanning electron microscope (SEM) (the maximum distance between any two points on the outline of the observed particles). ５０ ) will be adopted.

[0046] The solid electrolyte may be synthesized using a known method, or a commercially available product may be used. Furthermore, these materials may be appropriately pulverized to obtain a solid electrolyte having a desired average secondary particle size. For pulverization, for example, a roller mill, a jet mill, or the like may be used, but this is not limited thereto. Furthermore, a solid electrolyte having a desired average secondary particle size may be produced by classifying the solid electrolyte using an appropriate classification device, for example, a sieve, a classifier, or the like.

[0047] In one embodiment, the proportion of the content of the halide solid electrolyte relative to the total mass of the first solid electrolyte is preferably more than 50 mass%, more preferably 80 mass% or more, even more preferably 90 mass% or more, particularly preferably 95 mass% or more, and most preferably 100 mass%.

[0048] The content of the first solid electrolyte is, for example, preferably in the range of 1 to 60 mass %, more preferably in the range of 10 to 55 mass %, and even more preferably in the range of 25 to 50 mass %, relative to the total mass of the positive electrode active material layer.

[0049] In one embodiment, the ratio of the average secondary particle size of manganese dioxide to the average secondary particle size of the first solid electrolyte (average secondary particle size of manganese dioxide / average secondary particle size of first solid electrolyte) is not particularly limited, but is, for example, less than 0.9, preferably less than 0.3, and more preferably 0.2 or less. Within this range, the contact area between manganese dioxide and the first solid electrolyte becomes larger, thereby further improving the battery capacity. The lower limit of the ratio of the average secondary particle size of manganese dioxide to the average secondary particle size of the first solid electrolyte (average secondary particle size of manganese dioxide / average secondary particle size of first solid electrolyte) is also not particularly limited, but is, for example, 0.01 or more, preferably 0.03 or more, and more preferably 0.05 or more. Within this range, the contact area between manganese dioxide and the first solid electrolyte becomes larger, thereby further improving the battery capacity. That is, the ratio of the average secondary particle size of manganese dioxide to the average secondary particle size of the first solid electrolyte is, for example, 0.01 or more and less than 0.9, preferably 0.03 or more and less than 0.3, and more preferably 0.05 or more and 0.2 or less.

[0050] In one embodiment, the ratio of the mass of the positive electrode active material to the total mass of the positive electrode active material and the first solid electrolyte contained in the positive electrode active material layer is, for example, 30 to 90 mass%, preferably 40 to 80 mass%, more preferably 50 to 70 mass%, and even more preferably 50 to 60 mass%. Within this range, the effects of the present invention can be obtained even more significantly.

[0051] The positive electrode active material layer may further contain at least one of a conductive additive and a binder in addition to the above-mentioned positive electrode active material and solid electrolyte.

[0052] Examples of conductive additives include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNT), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). Also, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives. Among these conductive additives, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, more preferably at least one selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon, and even more preferably at least one carbon. These conductive additives may be used alone or in combination of two or more.

[0053] The conductive additive is preferably in the form of particles or fibers. When the conductive additive is in the form of particles, the shape of the particles is not particularly limited and may be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, scale, or spindle shape.

[0054] When the conductive additive is in a particulate form, the average particle size (primary particle size) is not particularly limited, but is preferably 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery.

[0055] When the positive electrode active material layer contains a conductive additive, the content of the conductive additive in the positive electrode active material layer is not particularly limited, but is preferably 0 to 10 mass %, more preferably 1 to 5 mass %, relative to the total mass of the positive electrode active material layer. Within such a range, a stronger electron conduction path can be formed in the positive electrode active material layer, which can effectively contribute to improving battery characteristics.

[0056] On the other hand, the binder is not particularly limited, but examples thereof include the following materials:

[0057] Thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), carboxymethyl cellulose, polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene (PTFE), polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and hydrogenated products thereof, styrene-isoprene-styrene block copolymer and hydrogenated products thereof, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene Fluorine resins such as polytetrafluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc., vinylidene fluoride-hexafluoropropylene fluoroelastomers (VDF-HFP fluoroelastomers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluoroelastomers (VDF-HFP-TFE fluoroelastomers), vinylidene fluoride-pentafluoropropylene fluoroelastomers (VDF-PFP fluoroelastomers), etc. Examples of the binder include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferred. The binder content is not particularly limited.

[0058] The proportion of the total mass of the positive electrode active material, the first solid electrolyte, the conductive additive, and the binder relative to the total mass of the positive electrode active material layer is preferably 90 mass% or more, more preferably 95 mass% or more, even more preferably 98 mass% or more, particularly preferably 99 mass% or more, and most preferably 100 mass%.

[0059] The proportion of the total mass of the positive electrode active material, the first solid electrolyte, and the conductive additive relative to the total mass of the positive electrode active material layer is preferably 90 mass% or more, more preferably 95 mass% or more, even more preferably 98 mass% or more, particularly preferably 99 mass% or more, and most preferably 100 mass%.

[0060] The thickness of the positive electrode active material layer varies depending on the configuration of the intended lithium secondary battery, but is preferably within the range of 1 to 1000 μm, more preferably within the range of 10 to 100 μm, and even more preferably within the range of 10 to 50 μm.

[0061] [Negative Electrode (Negative Electrode Active Material Layer)] In the lithium secondary battery according to the above embodiment, the negative electrode active material layer 13 contains a negative electrode active material. When the positive electrode active material further contains a lithium-containing positive electrode active material in addition to manganese dioxide, the negative electrode active material is not particularly limited, and may include, but is not limited to, a carbon material, a metal oxide, and a metal active material. On the other hand, when the positive electrode active material does not contain a lithium-containing positive electrode active material, the negative electrode active material is a lithium-containing negative electrode active material. A lithium-containing metal may be used as the lithium-containing negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples thereof include metallic lithium and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, and Sn. In some cases, two or more negative electrode active materials may be used in combination. Of course, negative electrode active materials other than those specifically listed above may also be used. From the viewpoint of improving the battery capacity, the negative electrode active material preferably contains metallic lithium. Alternatively, the negative electrode active material may consist solely of metallic lithium.

[0062] The negative electrode active material may be in the form of particles (spherical, fibrous), thin film, etc. When the negative electrode active material is in the form of particles, the average particle diameter is preferably in the range of, for example, 1 nm to 100 μm.

[0063] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 100 mass %. The negative electrode active material layer may further contain a solid electrolyte, a conductive additive, and / or a binder, and specific and preferred forms thereof may be the same as those described in the section on the positive electrode active material layer above.

[0064] The thickness of the negative electrode active material layer varies depending on the intended configuration of the lithium secondary battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0065] [Solid Electrolyte Layer] In the lithium secondary battery according to the above embodiment, the solid electrolyte layer is a layer interposed between the above-described positive electrode active material layer and negative electrode active material layer, and essentially contains a solid electrolyte. The specific form of the solid electrolyte (second solid electrolyte) contained in the solid electrolyte layer is not particularly limited, and the exemplary and preferred forms described in the section on the positive electrode active material layer may be similarly adopted. However, from the viewpoint of excellent ionic conductivity and further improvement of battery performance, the second solid electrolyte preferably contains a sulfide solid electrolyte, and more preferably contains an argyrodite-type solid electrolyte.

[0066] The solid electrolyte layer may further contain a binder in addition to the second solid electrolyte described above. The examples and preferred embodiments described in the section on the positive electrode active material layer may also be used for the binder that can be contained in the solid electrolyte layer.

[0067] The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 700 μm or less. On the other hand, there is no particular restriction on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more.

[0068] [Positive electrode current collector plate and negative electrode current collector plate] The material constituting the current collector plate (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material or different materials.

[0069] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collectors (11", 11') and the current collector plates (27, 25) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium secondary batteries can be similarly adopted. Note that the portion removed from the exterior is preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like so as to prevent contact with peripheral devices or wiring, etc., causing electrical leakage and affecting products (e.g., automobile parts, particularly electronic devices, etc.).

[0070] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element as shown in FIG. 1 can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable as the exterior material because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0071] The stacked battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a power source for driving EVs and HEVs.

[0072] Although one embodiment of a lithium secondary battery has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0073] For example, the type of battery to which the lithium secondary battery according to the present invention is applied includes a bipolar battery including a bipolar electrode having a positive electrode active material layer electrically coupled to one surface of a current collector and a negative electrode active material layer electrically coupled to the opposite surface of the current collector.

[0074] Furthermore, the lithium secondary battery according to the present embodiment may or may not be an all-solid-state type. That is, the solid electrolyte layer may or may not contain a conventionally known liquid electrolyte (electrolytic solution). When the solid electrolyte layer contains a liquid electrolyte (electrolytic solution), there is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount be such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolytic solution) does not occur.

[0075] The following items are also included in the scope of the present invention: Item 1: A cathode active material having a specific surface area of ​​20 m ２ Item 2: A lithium secondary battery comprising a power generating element including: a positive electrode having a positive electrode active material layer containing manganese dioxide having a specific surface area of ​​4 m / g or less and containing a first solid electrolyte; a negative electrode having a negative electrode active material layer containing a negative electrode active material; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a second solid electrolyte; ２ Item 3: The lithium secondary battery according to Item 1, wherein the specific surface area of ​​the manganese dioxide is 0.36 m / g or less; ２ / g or more; Item 4: The lithium secondary battery according to any one of Items 1 to 3, wherein the first solid electrolyte is a halide solid electrolyte; Item 5: The first solid electrolyte is a halide solid electrolyte, and the halide solid electrolyte is Li ３ MX ６(wherein M is a metal element and X is a halogen element); Item 6: The lithium secondary battery according to any one of Items 1 to 5, wherein the manganese dioxide has an average secondary particle diameter of less than 2 μm (preferably less than 1.5 μm); Item 7: The lithium secondary battery according to any one of Items 1 to 6, wherein the manganese dioxide has an average secondary particle diameter of 0.1 μm or more (preferably 0.3 μm or more, more preferably 0.6 μm or more); Item 8: The lithium secondary battery according to any one of Items 1 to 7, wherein the manganese dioxide is electrolytic manganese dioxide or chemically synthesized manganese dioxide; Item 9: The lithium secondary battery according to any one of Items 1 to 8, wherein the positive electrode active material consists solely of manganese dioxide; Item 10: The lithium secondary battery according to any one of Items 1 to 9, wherein the average secondary particle diameter of the first solid electrolyte is 0.01 μm or more and 500 μm or less (preferably 0.1 μm or more and 100 μm or less, more preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less); Item 11: The lithium secondary battery according to any one of Items 1 to 10, wherein the average secondary particle diameter of the manganese dioxide is less than 0.9 (preferably less than 0.3) the average secondary particle diameter of the first solid electrolyte; Item 12: The lithium secondary battery according to any one of Items 1 to 11, wherein the negative electrode active material contains metallic lithium.

[0076] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0077] <Preparation of Positive Electrode Active Material> (Manganese Dioxide 1) Electrolytic manganese dioxide powder (manganese dioxide 1) was obtained by referring to the method described in JP 2017-179583 A with appropriate modifications.

[0078] The specific surface area of ​​the obtained manganese dioxide 1 was measured by the following method, and it was found to be 19.6 m ２ / g.

[0079] [Measurement of Specific Surface Area of ​​Manganese Dioxide] The specific surface area (BET specific surface area) of manganese dioxide as a positive electrode active material was measured by nitrogen adsorption / desorption measurement. This nitrogen adsorption / desorption measurement was performed at a temperature of −196° C. using a multipoint method. The BET specific surface area was determined from the adsorption isotherm.

[0080] The average secondary particle diameter of the obtained manganese dioxide 1 was measured by the following method and was found to be 0.9 μm.

[0081] [Measurement of Average Secondary Particle Diameter of Manganese Dioxide] The average secondary particle diameter of manganese dioxide particles was measured using a particle size distribution measuring device that uses a laser diffraction / scattering method, and the 50% cumulative diameter (D ５０ ) was taken as the average secondary particle diameter: Measuring device: SALD-2000A manufactured by Shimadzu Corporation: Measurement solvent: water.

[0082] (Manganese dioxide 2) Potassium permanganate was dissolved in an aqueous hydrochloric acid solution (0.7 M) and calcined in a hydrothermal synthesis pot at 160°C for 12 hours to obtain manganese dioxide 2.

[0083] The specific surface area and average secondary particle diameter of the obtained manganese dioxide 2 were measured by the same method as above. The specific surface area was 3.7 m ２ / g and the average secondary particle diameter was 1.31 μm.

[0084] (Manganese Dioxide 3) Manganese Dioxide 3 was obtained by referring to the methods described in JP 2017-179583 A and JP 2004-186127 A and making appropriate modifications.

[0085] The specific surface area and average secondary particle diameter of the obtained manganese dioxide 3 were measured by the same method as above. The specific surface area was 25.5 m ２ / g and the average secondary particle diameter was 0.9 μm.

[0086] <Preparation of solid electrolyte> Li, a halide solid electrolyte ３ YBr ６Interdisciplinary Materials 2023;2:365-389 as appropriate, and then pulverized and sieved to obtain a solid electrolyte having an average secondary particle diameter of 10 μm. The average secondary particle diameter of the particles of the solid electrolyte is a 50% cumulative diameter (D) based on the number of particles observed in a field of view of several to several tens of particles (the maximum distance between any two points on the outline of the observed particles) observed under a scanning electron microscope (SEM). ５０ ) was used (measuring device: JEOL JSM-6610LV).

[0087] [Example 1] (Preparation of Positive Electrode Material) In a glove box in an argon atmosphere with a dew point of -68°C or lower, 54 parts by mass of the manganese dioxide 1 prepared above, 44 parts by mass of the halide solid electrolyte produced above, and 2 parts by mass of acetylene black (manufactured by Denka Co., Ltd.) as a conductive additive were kneaded in an agate mortar for 30 minutes to obtain a positive electrode material. The ratio of the average secondary particle diameter of manganese dioxide 1 to the average secondary particle diameter of the sulfide solid electrolyte (average secondary particle diameter of manganese dioxide 1 / average secondary particle diameter of sulfide solid electrolyte) was 0.09.

[0088] (Preparation of Test Cell) The preparation of the test cell was carried out in a glove box in an argon atmosphere with a dew point of −68° C. or lower.

[0089] A cylindrical convex punch (10 mm diameter) made of stainless steel was inserted into one side of a cylindrical tube jig (tube inner diameter 10 mm, outer diameter 23 mm, height 20 mm) made by Macol, and an argyrodite-type solid electrolyte (Li ６ P.S. ５Cl) was inserted. Then, another SUS cylindrical convex punch was inserted to sandwich the solid electrolyte, and a hydraulic press was used to press the solid electrolyte at a pressure of 400 MPa (Φ10 equivalent) for 1 minute, thereby forming a solid electrolyte layer with a diameter of 10 mm and a thickness of 650 μm in the cylindrical tube jig. Next, the cylindrical convex punch inserted from above was temporarily removed, and the positive electrode material prepared above was placed on one side of the solid electrolyte layer in the cylindrical tube. A cylindrical convex punch (also serving as a positive electrode current collector) was inserted again from above, and pressed at a pressure of 400 MPa (Φ10 equivalent) for 1 minute, thereby forming a positive electrode active material layer with a diameter of 10 mm and a thickness of 20 μm on one side of the solid electrolyte layer. Next, the lower cylindrical convex punch (which also served as the negative electrode current collector) was removed, and a 0.1 mm thick In foil (manufactured by Honjo Metals Co., Ltd., diameter 9 mm) and a 0.1 mm thick Li foil (manufactured by Nilaco Corporation, diameter 5 mm) were inserted as negative electrodes from the bottom of the cylindrical tube jig so that the In foil was positioned on the solid electrolyte layer side, and the cylindrical convex punch was inserted again, followed by pressing at a pressure of 100 MPa for 1 second.

[0090] In this manner, a test cell (all-solid-state lithium secondary battery) was produced in which the negative electrode current collector (punch), lithium-indium negative electrode, solid electrolyte layer, positive electrode active material layer, and positive electrode current collector (punch) were stacked in this order.

[0091] Example 2 An evaluation cell for this example was produced in the same manner as in Example 1, except that the positive electrode active material was changed from manganese dioxide 1 to manganese dioxide 2. The ratio of the average secondary particle size of manganese dioxide 2 to the average secondary particle size of the sulfide solid electrolyte (average secondary particle size of manganese dioxide 2 / average secondary particle size of sulfide solid electrolyte) was 0.13.

[0092] Comparative Example 1 An evaluation cell for this comparative example was produced in the same manner as in Example 1, except that the positive electrode active material was changed from manganese dioxide 1 to manganese dioxide 3. The ratio of the average secondary particle diameter of manganese dioxide 3 to the average secondary particle diameter of the sulfide solid electrolyte (average secondary particle diameter of manganese dioxide 3 / average secondary particle diameter of sulfide solid electrolyte) was 0.09.

[0093] <Measurement of discharge capacity of all-solid-state lithium secondary battery> A confining pressure of 80 MPa was applied to the evaluation cell prepared above in the stacking direction using a pressure member, and the voltage was measured at a constant current of 0.01 C at a temperature of 25°C. ＋ The discharge capacity was measured at this time. The results are shown in Table 1 below.

[0094]

[0095] As shown in Table 1, the positive electrode active material has a specific surface area of ​​20 m ２ In the batteries of Examples 1 and 2 using manganese dioxide of 0.1g or less, the specific surface area was 20m ２ In comparison with the battery of Comparative Example 1, which used manganese dioxide with a specific surface area of ​​more than 4 m / g, a high discharge capacity was obtained. ２ In Example 2, which used manganese dioxide with a valence of 0.1g or less, a higher discharge capacity was obtained.

[0096] [Reference Examples 1 and 2, Comparative Reference Example 1] Using the manganese dioxides 1 to 3 prepared above as the positive electrode active material, liquid lithium secondary batteries (lithium secondary batteries of Reference Examples 1 and 2 and Comparative Reference Example 1) were fabricated, and their discharge capacities were evaluated. Specifically, the positive electrode active material, acetylene black (average particle diameter: 35 nm) as a conductive additive, and PTFE as a binder were weighed out in a mass ratio of 80:16:4, respectively, and then mixed in an agate mortar to obtain a sheet-like positive electrode material. The positive electrode material was then punched out with a 5 mm diameter belt punch and pressed against a 10 mm diameter aluminum mesh as a positive electrode current collector at room temperature under a pressure of 200 MPa to form a positive electrode active material layer. Positive electrodes were fabricated in this manner.

[0097] Using the above positive electrode, a 2032-type coin cell was fabricated as an evaluation cell. The electrolyte was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 3:7, with LiPF ６ The electrolyte used was a solution containing the compound dissolved at a concentration of 1 M. A Li foil having a thickness of 0.6 mm was used as the negative electrode.

[0098] A pressure of 80 MPa was applied to the evaluation cell prepared above in the stacking direction using a pressure member, and the voltage was set to 2 V (vs. Li / Li) at a constant current of 0.05 C at a temperature of 25 ° C. ＋ ) and then discharged to a current value equivalent to 0.01C at 2V (vs. Li / Li ＋ ) and the discharge capacity was measured.

[0099]

[0100] From the results in Table 2, it was confirmed that in liquid lithium secondary batteries, the discharge capacity hardly changes depending on the specific surface area of ​​manganese dioxide.

[0101] 10a: laminated battery, 11': negative electrode current collector, 11'': positive electrode current collector, 13: negative electrode active material layer, 15: positive electrode active material layer, 17: solid electrolyte layer, 19: single cell layer, 21: power generating element, 25: negative electrode current collector, 27: positive electrode current collector, 29: laminate film.

Claims

1. The specific surface area of ​​the positive electrode active material is 20 m ２ 1. A lithium secondary battery comprising a power generating element including: a positive electrode having a positive electrode active material layer containing manganese dioxide having a specific surface area of ​​1 / 2 μm or less and containing a first solid electrolyte; a negative electrode having a negative electrode active material layer containing a negative electrode active material; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a second solid electrolyte.

2. The specific surface area of ​​the manganese dioxide is 4 m ２ 2. The lithium secondary battery according to claim 1, wherein the SiO2 content is 0.1 / g or less.

3. The specific surface area of ​​the manganese dioxide is 0.36 m ２ 3. The lithium secondary battery according to claim 1, wherein the SiO2 content is 1 / g or more.

4. The lithium secondary battery according to claim 1 or 2, wherein the first solid electrolyte is a halide solid electrolyte.

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