Energy storage devices

Abstract

To provide a power storage device capable of securing an output while reducing diffusion of lithium ions that do not involved in charging and discharging.SOLUTION: A power storage device includes, in order, a positive electrode layer, an electrolyte layer, and a negative electrode layer. The positive electrode layer, the electrolyte layer, and the negative electrode layer each include an electrolyte having lithium ion conductivity. The electrolyte of the positive electrode layer includes a solid electrolyte and the positive electrode layer further includes an active material in contact with the electrolyte. The atomic number concentration of Li in the electrolyte of the positive electrode layer is higher than the atomic number concentration of Li in the electrolyte of the electrolyte layer and higher than the atomic number concentration of Li in the electrolyte of the negative electrode layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electricity storage device that uses lithium ions as a diffusion species. [Background technology]

[0002] As a prior art related to an electricity storage device including a positive electrode layer, an electrolyte layer, and a negative electrode layer, Patent Document 1 discloses a device in which the positive electrode layer, electrolyte layer, and negative electrode layer each include an electrolyte having lithium ion conductivity, and the positive electrode layer further includes an active material. In the positive electrode layer, lithium ions move between the active material and the electrolyte during charge and discharge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 033424 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-216300 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, for example, when the temperature of the positive electrode layer rises, the difference in lithium concentration between the active material and the electrolyte can act as a driving force to cause diffusion of lithium ions unrelated to charging and discharging, which can lead to a decrease in the discharge capacity of the power storage device and the collapse of the crystalline structure of the active material.

[0005] Patent Document 2 discloses a technique for coating the surface of lithium-containing metal particles with metal oxide particles. This technique has the potential to reduce the diffusion of lithium ions that are not involved in charging and discharging. However, the metal oxide particles coating the lithium-containing metal particles act as resistance, reducing the output of the power storage device.

[0006] The present invention has been made to solve this problem, and has an object to provide an electricity storage device that can ensure output while reducing the diffusion of lithium ions that are not involved in charging and discharging. [Means for solving the problem]

[0007] To achieve this object, the power storage device of the present invention includes, in order, a positive electrode layer, an electrolyte layer, and a negative electrode layer, each of which includes an electrolyte having lithium ion conductivity. The electrolyte of the positive electrode layer includes a solid electrolyte, and the positive electrode layer further includes an active material in contact with the electrolyte. The atomic concentration of Li in the electrolyte of the positive electrode layer is higher than the atomic concentration of Li in the electrolyte layer and higher than the atomic concentration of Li in the electrolyte of the negative electrode layer. [Effects of the Invention]

[0008] According to the first aspect, the Li atomic concentration (hereinafter referred to as "Cp") in the electrolyte of the positive electrode layer is higher than the Li atomic concentration (hereinafter referred to as "Ce") in the electrolyte of the electrolyte layer and higher than the Li atomic concentration (hereinafter referred to as "Cn") in the electrolyte of the negative electrode layer. Therefore, the difference between the Li atomic concentration (hereinafter referred to as "Ca") of the active material contained in the positive electrode layer and Cp can be reduced compared to when Cp≦Ce or Cp≦Cn. This reduces the diffusion of lithium ions that is not involved in charge and discharge, driven by the difference in lithium concentration between the active material and the electrolyte of the positive electrode layer. Furthermore, compared to when Cp≦Ce or Cp≦Cn, it is easier to set the electrolyte contained in the electrolyte layer and the negative electrode layer to an optimal ionic conductivity, thereby ensuring the output of the power storage device.

[0009] According to the second aspect, in the first aspect, the electrolyte of the positive electrode layer includes an organic compound having lithium ion conductivity. Because the organic compound is in contact with the active material, lithium ions migrate between the organic compound and the active material. The Li atomic concentration (Cpo) in the organic compound is higher than the Li atomic concentration (Ce) in the electrolyte of the electrolyte layer and higher than the Li atomic concentration (Cn) in the electrolyte of the negative electrode layer. Therefore, the difference between Ca and Cp can be reduced compared to when Cpo≦Ce or Cpo≦Cn. This reduces the diffusion of lithium ions, which is not related to charge and discharge and is driven by the lithium concentration difference between the active material and the organic compound in the positive electrode layer. Furthermore, compared to when Cpo≦Ce or Cpo≦Cn, it is easier to optimize the ionic conductivity of the electrolyte contained in the electrolyte layer or the negative electrode layer, ensuring the output of the power storage device.

[0010] According to the third aspect, the organic compound in the second aspect contains an electrolyte solution, which can reduce the interfacial resistance between the organic compound and the active material compared to when the organic compound does not contain an electrolyte solution. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view of a power generating element included in the electricity storage device according to the embodiment. [Figure 2] 2 is a partial cross-sectional view of the positive electrode layer, enlarging a portion indicated by II in FIG. 1. FIG. [Figure 3] 2 is a partial cross-sectional view of the electrolyte layer, enlarging a portion indicated by III in FIG. 1. FIG. [Figure 4] 4 is a partial cross-sectional view of the negative electrode layer, enlarging a portion indicated by IV in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view of a power generating element 10 included in an electricity storage device 1 according to one embodiment. The electricity storage device 1 according to this embodiment is a lithium ion solid state battery in which the power generating element 10 is housed in a case (not shown), and the power generating element 10 is made of a solid. "The power generating element 10 being made of a solid" means that the skeleton of the power generating element 10 is made of a solid, and does not exclude, for example, a form in which the skeleton is impregnated with a liquid.

[0013] 1, the power generating element 10 includes, in order, a positive electrode layer 11, an electrolyte layer 14, and a negative electrode layer 15. The positive electrode layer 11, the electrolyte layer 14, and the negative electrode layer 15 include a solid electrolyte 18.

[0014] The positive electrode layer 11 is formed by stacking a current collecting layer 12 and an active material layer 13. The current collecting layer 12 is a conductive member. Examples of materials for the current collecting layer 12 include a metal selected from Ni, Ti, Fe, and Al, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0015] The active material layer 13 includes a solid electrolyte 18 and an active material 19. The active material layer 13 may contain a conductive additive to reduce the resistance of the active material layer 13. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0016] The active material 19 is exemplified by a metal oxide containing a transition metal. The metal oxide containing a transition metal is exemplified by an oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. The metal oxide containing a transition metal is exemplified by LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4,LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Examples include O4 and LiFePO4.

[0017] The negative electrode layer 15 has a current collector layer 16 and an active material layer 17 superimposed thereon. The current collector layer 16 is a conductive member. Examples of the material of the current collector layer 16 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0018] The active material layer 17 contains a solid electrolyte 18 and an active material 20. In order to lower the resistance of the active material layer 17, a conductive assistant may be included in the active material layer 17. Examples of the conductive assistant include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0019] The active material 20 includes Li, Li-Al alloy, Li4Ti5O 12 , graphite, In, Si, Sn, Si-Li alloy, Sn-Li alloy, and oxides containing Si. The oxide containing Si is preferably SiO X (X>0). Particularly, SiO X (0<X<2) is suitable because it has a large discharge capacity and good charge-discharge cycle performance.

[0020] FIG. 2 is a partial cross-sectional view of the active material layer 13 (positive electrode layer 11) obtained by enlarging the portion shown by II in FIG. 1. The active material layer 13 contains an active material 19 and an electrolyte 22 having lithium ion conductivity. In this embodiment, the electrolyte 22 contains a solid electrolyte 18 and an organic compound 21. The solid electrolyte 18 contains one or more inorganic compounds selected from, for example, oxide-based, sulfide-based, and hydride-based.

[0021] The oxide-based solid electrolyte 18 is preferable because no toxic gas is generated when exposed to air. The solid electrolyte 18 may be, for example, a composite in which a hydride is bonded to the surface of an oxide. Examples of the oxide-based solid electrolyte 18 include oxides having a NASICON-type structure, oxides having a perovskite structure, and oxides having a garnet-type structure.

[0022] Oxides having a NASICON structure include oxides containing at least Li, M (M is one or more elements selected from Ti, Zr, and Ge) and P, such as Li(Al,Ti)2(PO4)3 and Li(Al,Ge)2(PO4)3. Oxides having a perovskite structure include oxides containing at least Li, Ti, and La, such as La 2 / 3-X Li 3X Examples include TiO3.

[0023] The basic composition of garnet-type oxides is Li5La3M2O 12 (M=Nb, Ta). The solid electrolyte 18 made of an oxide with a garnet structure preferably contains Li, La, Zr, and O. The solid electrolyte 18 is Li7La3Zr2O, in which the pentavalent M cation in the basic composition is replaced with a tetravalent cation. 12 is exemplified.

[0024] In addition to Li, La, and Zr, the solid electrolyte 18 may contain at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La). For example, Li6La3Zr 1.5 W 0.5 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 ,Li 6.25 La3Zr2Ga 0.25 O 12 ,Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li 6.5 La3Zr 1.75 Te 0.25 O 12 ,Li 6.75 La3Zr 1.75 Nb 0.25 O 12,Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 ,Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 ,Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 ,Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 ,Li 6.20 Ba 0.30 La 2.95 Rb 0.05 ZrO 12 Examples include:

[0025] Solid electrolyte 18 preferably contains at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr, and Ba), with the molar ratio of each element satisfying all of the following (1) to (3), or contains both Mg and element A, with the molar ratio of each element satisfying all of the following (4) to (6). Element A is preferably Sr, as this increases the ionic conductivity of solid electrolyte 18. (1) 1.33≦Li / (La+A)≦3 (2) 0≦Mg / (La+A)≦0.5 (3) 0≦A / (La+A)≦0.67 (4) 2.0≦Li / (La+A)≦2.5 (5) 0.01≦Mg / (La+A)≦0.14 (6) 0.04≦A / (La+A)≦0.17.

[0026] The sulfide-based solid electrolyte 18 is a crystalline thiolithium-type, Li 10 GeP2S 12 type, argyrodite type, Li7P3S 11Examples of the hydride-based solid electrolyte 18 include a solid solution of LiBH4 with a lithium halide compound (LiI, LiBr, LiCl) and lithium amide (LiNH2).

[0027] The organic compound 21 has lithium ion conductivity. The organic compound 21 includes one or more compounds selected from a liquid, a gel, and a solid. The organic compound 21 may be a mixture of two or more compounds selected from a liquid, a gel, and a solid. The organic compound 21 is in contact with the active material 19.

[0028] An example of the liquid organic compound 21 is an electrolyte solution. The electrolyte solution is a solution in which a lithium salt is dissolved in a solvent. There are no particular limitations on the solvent as long as the solvent is capable of dissolving the lithium salt. The lithium salt provides lithium ions that transfer electrons between the positive electrode layer 11 and the negative electrode layer 15. The anions of the lithium salt are halide ions (I - , Cl - , Br - etc.), SCN - , BF4 - , BF3(CF3) ― , BF3(C2F5) - , PF6 - , ClO4 - , SbF6 - , N(SO2F)2 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , B(C6H5)4 - , B(O2C2H4)2 - , C(SO2F)3 - , C(SO2CF3)3 - , CF3COO - , CF3SO2O - , C6F5SO2O - , B(O2C2O2)2 - is exemplified.

[0029] N(SO2F)2 - is abbreviated as [FSI] - : It is called bis(fluorosulfonyl)imide anion, N(SO2CF3)2- abbreviated as [TFSI] - : It is called bis(trifluoromethanesulfonyl)imide anion, B(O2C2O2)2 - is abbreviated as [BOB] - : It is called bis(oxalate)borate anion, C(SO2F)3 - abbreviated as [F3C] - :It is sometimes called tris(fluorosulfonyl)carbanion.

[0030] Examples of the lithium salt include at least one selected from the group consisting of LiPF6, LiBF4, Li[FSI], Li[TFSI], Li[F3C], Li[BOB], LiClO4, LiBF3(CF3), LiBF3(C2F5), LiBF3(C3F7), LiBF3(C4F9), LiC(SO2CF3)3, LiCF3S02O, LiCF3COO, and LiRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

[0031] Examples of the solvent for the electrolyte include carbonate esters, aliphatic carboxylic acid esters, phosphate esters, γ-lactones, ethers, nitriles, sulfolane, dimethyl sulfoxide, fluorous solvents, and ionic liquids, and mixtures thereof may also be used.

[0032] Examples of carbonate esters include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, and chain carbonate esters such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

[0033] Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of γ-lactones include γ-butyrolactone. Examples of ethers include chain ethers such as 1,3-dioxolane and 1,2-dialkoxyethane, and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. Examples of nitriles include acetonitrile and propionitrile. Fluorous solvents are compounds in which the hydrogen atoms of hydrocarbons are substituted with fluorine atoms, and derivatives thereof.

[0034] Ionic liquids are compounds consisting of cations and anions, and are liquid at room temperature and normal pressure. If the solvent of an electrolyte is an ionic liquid, the flame retardancy of the electrolyte can be improved. Examples of ionic liquids include those containing one or more cation components selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0035] The anion component of the ionic liquid is not particularly limited. The anion component is BF4 - ,N(SO2F)2 - Inorganic anions such as B(C6H5)4 - ,CH3SO3 - ,CF3SO3 - ,N(SO2CF3)2 - ,N(SO2C4F9)2 - It is preferable that the anion component of the electrolyte solution is the same as the anion component of the lithium salt, since this makes it easier to control the coordination (interaction) between the lithium ions and the anions contained in the electrolyte solution.

[0036] Examples of ionic liquids include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME-FSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), N-butyl-N-methylpiperidinium bis(fluorosulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13-FSI), and N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13-TFSI).

[0037] The various physical properties and functions of the electrolyte are determined by the type of lithium salt and solvent, as well as the salt concentration. The salt concentration of the electrolyte is, for example, 0.5-5 mol / dm 3 In particular, when the salt concentration is 3 mol / dm 3 The above values ​​are preferable because they have the effect of reducing volatility and flammability and widening the potential window.

[0038] Examples of the gel or solid organic compound 21 include polyethylene oxide, polypropylene oxide, and polyacrylonitrile. The active material layer 13 may contain a binder that binds particles of the solid electrolyte 18 and the like. A semi-solidified binder dissolved in a solvent for the electrolyte solution is one type of gel organic compound 21. Examples of binders include polyimides, acrylics, polysiloxanes, polyalkylene glycols, polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, ethylene-vinyl alcohol copolymers, and polyvinylidene fluoride-hexafluoropropylene copolymers. The gel and solid organic compounds 21 are elastic.

[0039] 3 is a partial cross-sectional view of the electrolyte layer 14, enlarging a portion indicated by III in FIG. 1. The electrolyte layer 14 includes an electrolyte 23 having lithium ion conductivity. In this embodiment, the electrolyte 23 includes a solid electrolyte 18 and an organic compound 21. The electrolyte layer 14 may include a binder that binds particles of the solid electrolyte 18 and the like together. The solid electrolyte 18 and the organic compound 21 included in the electrolyte layer 14 may be of the same type as the solid electrolyte 18 and the organic compound 21 included in the positive electrode layer 11, or may be of different types. When the organic compound 21 included in the electrolyte layer 14 includes an electrolyte solution, the salt concentration of the electrolyte solution is, for example, 1 mol / dm 3 That's about it.

[0040] FIG. 4 is a partial cross-sectional view of the active material layer 17 (negative electrode layer 15) enlarging a portion indicated by IV in FIG. 1. The active material layer 17 includes an active material 20 and an electrolyte 24 having lithium ion conductivity. In this embodiment, the electrolyte 24 includes a solid electrolyte 18 and an organic compound 21. The active material layer 17 may include a binder that binds particles of the solid electrolyte 18 and the like together. The solid electrolyte 18 and the organic compound 21 included in the active material layer 17 may be of the same type as or different from the solid electrolyte 18 and the organic compound 21 included in the positive electrode layer 11 and the electrolyte layer 14. When the organic compound 21 included in the active material layer 17 includes an electrolyte solution, the salt concentration of the electrolyte solution is set to, for example, 1 mol / dm 3 That's about it.

[0041] The electricity storage device 1 is manufactured, for example, as follows: A solution in which a binder is dissolved is mixed with a mixture of an electrolytic solution and a solid electrolyte 18 to form a slurry. After tape casting, the mixture is dried to obtain a green sheet (electrolyte sheet) for the electrolyte layer 14.

[0042] A mixture of the electrolytic solution and solid electrolyte 18 is mixed with the active material 19, and then a solution in which a binder is dissolved is mixed to form a slurry. After tape casting on the current collecting layer 12, it is dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 11.

[0043] A mixture of the electrolytic solution and solid electrolyte 18 is mixed with the active material 20, and then a solution in which a binder is dissolved is mixed to form a slurry. After tape casting on the current collecting layer 16, it is dried to obtain a green sheet (negative electrode sheet) for the negative electrode layer 15.

[0044] The electrolyte sheet, positive electrode sheet, and negative electrode sheet are each cut to a predetermined shape, and then the positive electrode sheet, electrolyte sheet, and negative electrode sheet are stacked in this order and pressed together to form the power generating element 10. Terminals (not shown) are connected to the current collecting layers 12 and 16, respectively, and the assembly is sealed in a case (not shown), thereby obtaining the electricity storage device 1 which includes the positive electrode layer 11, the electrolyte layer 14, and the negative electrode layer 15 in this order.

[0045] For example, when the electricity storage device 1 is used at high temperatures, the temperature of the positive electrode layer 11 rises due to the influence of the temperature around the electricity storage device 1. This increases the likelihood of lithium ion diffusion, driven by the difference in lithium concentration between the active material 19 and the electrolyte 22. This lithium ion diffusion occurs regardless of the charge and discharge of the electricity storage device 1, and therefore, if diffusion occurs, the discharge capacity of the electricity storage device 1 may decrease and the crystalline structure of the active material 19 may collapse.

[0046] In order to reduce diffusion of lithium ions not involved in charging and discharging, the energy storage device 1 is set so that the atomic concentration of Li (Cp) in the electrolyte 22 of the positive electrode layer 11 is higher than the atomic concentration of Li (Ce) in the electrolyte 23 of the electrolyte layer 14 (Cp>Ce), and is also higher than the atomic concentration of Li (Cn) in the electrolyte 24 of the negative electrode layer 15 (Cp>Cn).

[0047] In this embodiment, the electrolytes 22, 23, and 24 contain the organic compound 21, which generally has a lower activation barrier for ion conduction than the solid electrolyte 18, and therefore the Li atom number concentration of the organic compound 21 is defined as the Li atom number concentration of the electrolytes 22, 23, and 24. Specifically, the Li atom number concentration of the organic compound 21 in the electrolyte 22 is defined as the Li atom number concentration of the electrolyte 22 (Cp), the Li atom number concentration of the organic compound 21 in the electrolyte 23 is defined as the Li atom number concentration of the electrolyte 23 (Ce), and the Li atom number concentration of the organic compound 21 in the electrolyte 24 is defined as the Li atom number concentration of the electrolyte 24 (Cn).

[0048] This reduces the difference between Cp and the Li atomic concentration (Ca) of the active material 19 contained in the positive electrode layer 11, compared to when Cp≦Ce or Cp≦Cn. This reduces the diffusion of lithium ions that is not involved in charging and discharging, driven by the difference in lithium concentration between the active material 19 and the organic compound 21 of the electrolyte 22. Furthermore, compared to when Cp≦Ce or Cp≦Cn, there are fewer restrictions on the electrolytes 23 and 24 contained in the electrolyte layer 14 and the negative electrode layer 15, making it easier to set the electrolytes 23 and 24 to have optimal ionic conductivity, thereby ensuring the output of the electricity storage device 1.

[0049] The Li atomic concentration in the electrolytes 22, 23, and 24 can be determined by analyzing a cross section of the electricity storage device 1 using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The cross section of the electricity storage device 1 can be obtained by freezing the electricity storage device 1 or by embedding and solidifying the electricity storage device 1 in a tetrafunctional epoxy resin or the like, and then cutting and polishing the device or irradiating it with a focused ion beam (FIB).

[0050] In the SEM-EDS analysis, three rectangular fields of view, each 45 μm long and 60 μm wide, are randomly selected on the cross sections of the active material layers 13 and 17 and the electrolyte layer 14, and the positions of the electrolytes 22, 23, and 24 (solid electrolyte 18 and organic compound 21) appearing in the fields of view are identified by identifying the distribution of elements and performing image analysis of the contrast of the backscattered electron images. Note that, since it is sufficient to identify the positions of the electrolytes 22, 23, and 24 (solid electrolyte 18 and organic compound 21), the rectangular fields of view may be, for example, 30 μm long and 40 μm wide.

[0051] Next, five locations of the electrolytes 22, 23, and 24 (organic compound 21 in this embodiment) are randomly selected within the field of view, and the Li atom concentration (%) at each measurement location is determined by point analysis or area analysis. The area of ​​the area analysis is appropriately set according to the size of the electrolytes 22, 23, and 24 so that it fits within the electrolytes 22, 23, and 24 appearing in the field of view. The sum of all the determined values ​​(Li atom concentration) is divided by the number of values ​​to calculate the average value for each electrolyte 22, 23, and 24, and the average values ​​for the electrolytes 22, 23, and 24 are compared.

[0052] When the Li atomic concentration is lower than the detection limit of SEM-EDS, the electrolytes 22, 23, and 24 can be removed from the electricity storage device 1 and the Li atomic concentration in the electrolytes 22, 23, and 24 can be determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0053] It is preferable that the organic compound 21 contains an electrolyte (including a semi-solid electrolyte in which the binder has been dissolved) because the interfacial resistance between the organic compound 21 and the active material 19 can be reduced compared to when the organic compound 21 does not contain an electrolyte. The electrolyte (liquid or gel-like) can be identified by image analysis using SEM-EDS.

[0054] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0055] In the embodiment, the electricity storage device 1 has been described as having a power generating element 10 including a positive electrode layer 11 in which an active material layer 13 is provided on one side of a current collecting layer 12, and a negative electrode layer 15 in which an active material layer 17 is provided on one side of a current collecting layer 16, but this is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to an electricity storage device including electrode layers in which an active material layer 13 and an active material layer 17 are provided on both sides of a current collecting layer 12 (so-called bipolar electrodes). If a power generating element in which bipolar electrodes and electrolyte layers 14 are alternately stacked is housed in a case (not shown), an electricity storage device with a so-called bipolar structure can be obtained.

[0056] In the embodiment, the case where all of the electrolytes 22, 23, and 24 contain the organic compound 21 has been described, but this is not necessarily limited to this. Of course, it is possible to omit the organic compound 21 from one or more of the electrolytes 22, 23, and 24.

[0057] For example, when the electrolyte 22 of the positive electrode layer 11 does not contain the organic compound 21, the Li atomic concentration of the solid electrolyte 18 of the positive electrode layer 11 is measured and used as the Li atomic concentration (Cp) of the electrolyte 22 of the positive electrode layer 11. When the electrolyte 23 of the electrolyte layer 14 does not contain the organic compound 21, the Li atomic concentration of the solid electrolyte 18 of the electrolyte layer 14 is measured and used as the Li atomic concentration (Ce) of the electrolyte 23 of the electrolyte layer 14. When the electrolyte 24 of the negative electrode layer 15 does not contain the organic compound 21, the Li atomic concentration of the solid electrolyte 18 of the negative electrode layer 15 is measured and used as the Li atomic concentration (Co) of the electrolyte 24 of the negative electrode layer 15.

[0058] In these cases, as in the embodiment, if the Li atomic concentration (Cp) in the electrolyte 22 of the positive electrode layer 11 is higher than the Li atomic concentration (Ce) in the electrolyte 23 of the electrolyte layer 14 and higher than the Li atomic concentration (Cn) in the electrolyte 24 of the negative electrode layer 15, the difference between the Li atomic concentration (Ca) and Cp in the active material 19 contained in the positive electrode layer 11 can be made smaller than when Cp≦Ce or Cp≦Cn. This reduces the diffusion of lithium ions not involved in charge and discharge, which is driven by the difference in lithium concentration between the active material 19 of the positive electrode layer 11 and the electrolyte 22. Furthermore, compared to when Cp≦Ce or Cp≦Cn, it is easier to set the electrolytes 23 and 24 contained in the electrolyte layer 14 and the negative electrode layer 15 to have optimal ionic conductivities, thereby ensuring the output of the electricity storage device 1.

[0059] In the embodiment, the power storage device 1 has been described using a lithium ion battery as an example, but is not necessarily limited to this. Other power storage devices include other secondary batteries such as a lithium-sulfur battery, a lithium-oxygen battery, and a lithium-air battery, and an electrolytic capacitor. [Explanation of symbols]

[0060] 1. Energy storage devices 11 Positive electrode layer 14 Electrolyte layer 15 negative electrode layer 18 Solid electrolyte 19 Active material 21 Organic compounds 22,23,24 Electrolytes

Claims

1. The cathode layer, the electrolyte layer, and the anode layer are included in this order. the positive electrode layer, the electrolyte layer, and the negative electrode layer each contain an electrolyte having lithium ion conductivity, the electrolyte of the positive electrode layer includes a solid electrolyte, the positive electrode layer further includes an active material in contact with the electrolyte, an electric storage device in which, when an amount of electricity equivalent to 50% of the capacity of the electric storage device is stored, the atomic concentration of Li in the solid electrolyte of the positive electrode layer is higher than the atomic concentration of Li in the electrolyte of the electrolyte layer and is also higher than the atomic concentration of Li in the electrolyte of the negative electrode layer.

2. A battery comprising, in order, a positive electrode layer, an electrolyte layer, and a negative electrode layer, the positive electrode layer, the electrolyte layer, and the negative electrode layer each contain an electrolyte having lithium ion conductivity, the electrolyte of the positive electrode layer includes a solid electrolyte, the positive electrode layer further includes an active material in contact with the electrolyte, the electrolyte of the positive electrode layer contains an organic compound having lithium ion conductivity, the organic compound is in contact with the active material, an electric storage device in which, when an amount of electricity equivalent to 50% of the capacity of the electric storage device is stored, the atomic concentration of Li in the organic compound is higher than the atomic concentration of Li in the electrolyte of the electrolyte layer, and is also higher than the atomic concentration of Li in the electrolyte of the negative electrode layer.

3. The electricity storage device according to claim 2 , wherein the organic compound includes an electrolyte solution.

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