Electrode and power storage device

Abstract

The purpose of the present invention is to provide an electrode (11) and a power storage device (10) capable of reducing charge transfer resistance. The electrode contains particles (20) of a solid electrolyte. The ratio of the particles is 0.1-30 vol%, and the average of the distance (D) between the particles in a range (18) in which six or more particles appear in a width of 400 μm2 on the cross-section of the electrode is 1 μm or more. The average of the equivalent circle diameters of the particles appearing in the cross section is preferably 10 μm or less, and the average of the equivalent circle diameters of an active material (19) appearing in the cross section is preferably 5 μm or more. The power storage device includes the electrode.

Description

Electrodes and energy storage devices

[0001] The present invention relates to an electrode and an electricity storage device containing particles of a solid electrolyte.

[0002] Reducing the internal resistance of an electricity storage device is advantageous for improving the input / output characteristics of the electricity storage device. Solid electrolyte particles contained in the electrodes of an electricity storage device contribute to reducing the resistance to ion migration (charge transfer), and therefore, Patent Document 1 discloses a prior art technique for setting the material of the particles and the proportion of the particles in the electrode.

[0003] International Publication No. 2018 / 198494

[0004] There is room for improvement in the prior art with regard to reducing charge transfer resistance.

[0005] The present invention has been made to meet this demand, and an object of the present invention is to provide an electrode and an electricity storage device that can reduce charge transfer resistance.

[0006] A first aspect for achieving this object is an electrode containing particles of a solid electrolyte, the proportion of the particles being 0.1 vol % or more and 30 vol % or less, and the particles are within 400 μm on the cross section of the electrode. ２ In the area where six or more particles appear, the average distance between particles is 1 μm or more.

[0007] In the second embodiment, the average equivalent circle diameter of the particles appearing in the cross section of the first embodiment is 10 μm or less.

[0008] In the third embodiment, the average equivalent circle diameter of the particles appearing in the cross section of the first embodiment is 5 μm or less.

[0009] In a fourth aspect, in any one of the first to third aspects, an active material is further contained, and the average equivalent circle diameter of the active material exposed in cross section is 5 μm or more.

[0010] In a fifth aspect, in any one of the first to fourth aspects, the particles are oxides.

[0011] In a sixth aspect, in the fifth aspect, the particles have a garnet-type crystal structure containing Li, La, and Zr.

[0012] A seventh aspect is an electricity storage device, which includes the electrode of any one of the first to sixth aspects.

[0013] The electrode of the present invention contains particles of a solid electrolyte in an amount of 0.1 vol % to 30 vol % and has a cross section of 400 μm ２ The average distance between particles in the area where six or more particles appear is 1 μm or more. The number of reaction sites due to the particles dispersed in the electrode can be increased, thereby reducing the charge transfer resistance.

[0014] It is a cross-sectional view of an electricity storage device according to an embodiment. It is a diagram schematically showing a garnet-type crystal structure. It is a cross-sectional view of an active material and particles appearing in the range of an active material layer. It is a cross-sectional view of particles appearing in the range.

[0015] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view of an electricity storage device 10 according to one embodiment. The electricity storage device 10 includes a positive electrode 11, a negative electrode 15, and a separator 14 that separates the positive electrode 11 from the negative electrode 15. Ions (hereinafter referred to as "charge carriers") that move between the positive electrode 11 and the negative electrode 15 through the separator 14 are Li. ＋ , Na ＋ , K. ＋ , Mg ２＋ , Cu ＋ , Ag ＋ Examples of cations include:

[0016] The separator 14 contains an electrolyte through which charge carriers move. The electrolyte is appropriately selected from solid, gel, and liquid (electrolytic solution). When an electrolytic solution is used, the separator 14 is made of a porous body having electronic insulation properties. Examples of the porous body include nonwoven fabric and porous membrane, through which charge carriers pass. Examples of the material of the porous body include cellulose, polypropylene, polyethylene, polyimide, alumina, etc.

[0017] The electrolyte is a solution in which a supporting electrolyte is dissolved in an aqueous solvent or a non-aqueous solvent. The supporting electrolyte may also be dissolved in a mixed solvent of an aqueous solvent and a non-aqueous solvent. Non-aqueous solvents are broadly classified into molecular solvents, which are mostly composed of molecules, and ionic liquids, which are composed of cations and anions. One of the reasons for using a non-aqueous solvent in the electrolyte is to widen the potential window compared to aqueous solvents. Ionic liquids are preferred because they can widen the potential window compared to aqueous solvents.

[0018] When a molecular solvent is used as the nonaqueous solvent, an aprotic solvent is preferred to widen the potential window of the electrolyte. Examples of aprotic solvents include cyclic esters, chain esters, aliphatic carboxylic acid esters, phosphate esters, nitriles, amides, sulfur compounds, ketones, ethers, nitro compounds, and fluorous solvents. Mixtures of these solvents are also acceptable.

[0019] Ionic liquids are compounds consisting of cations and anions, and are liquid at room temperature and pressure. If the solvent of an electrolyte is an ionic liquid, the flame retardancy of the electrolyte can be improved. The ionic liquid is preferably one having one or more cation species selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0020] The anion component of the ionic liquid is not particularly limited. ４ － , N(SO ２ F) ２ － inorganic anions such as B(C ６ H ５ ) ４ － , CH ３ SO ３ － , C.F. ３ SO ３ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ４ F ９ ) ２ － Examples of organic anions include:

[0021] The ionic liquid may be a solvated ionic liquid, such as a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme, in which a supporting electrolyte is dissolved.

[0022] The charge carrier is Li ＋ In this case, the supporting electrolyte is a lithium salt. The anion of the supporting electrolyte is OH. － , halide ions (I － , Cl － ,Br － etc.), SCN － , BF ４ － , BF ３ (CF ３ ) － , BF ３ (C ２ F ５ ) － , P.F. ６ － , ClO ４ － , SbF ６ － , N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － , B(C ６ H ５ ) ４ － , B(O ２ C ２ H ４ ) ２ － , C(SO ２ F) ３ － , C(SO ２ CF ３ ) ３ － , C.F. ３ COO － , C.F. ３ SO ２ O － , C ６F ５ SO ２ O － , B(O ２ C ２ O ２ ) ２ － , RCOO － (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group), etc. The supporting electrolyte may be a mixture of these.

[0023] The concentration of the supporting electrolyte in the electrolyte solution is 0.2 mol / dm ３ or more, preferably 0.5 mol / dm ３ More preferably, 1.0 mol / dm ３ As the concentration of the supporting electrolyte increases, the number of solvent molecules coordinated to the charge carrier increases, resulting in less uncoordinated solvent and the predominant coordination with counter anions (so-called ionic association). This suppresses the reductive decomposition of the electrolyte, while increasing the oxidation potential and widening the potential window. The concentration of the supporting electrolyte is 4.0 mol / dm ３ Preferably, it is 2.0 mol / dm or less, more preferably 2.0 mol / dm ３ The concentration of the supporting electrolyte is 4.0 mol / dm or less. ３ This is because, when the temperature exceeds this value, the ionic conductivity tends to decrease significantly due to an increase in the viscosity of the electrolyte.

[0024] The solid or gel electrolyte contains one or more selected from sulfides, oxides, hydrides, halides, and organic electrolytes. Examples of the separator 14 include a sintered body containing such an electrolyte, a compact formed by compressing an aggregate of electrolyte particles, and a mixture of electrolyte particles and an electrolytic solution.

[0025] Sulfide-based electrolytes include crystalline thiolithium type, Li １０ GeP ２ S １２ type, argyrodite type, Li ７ P ３ S １１ Type, Li ２ S-P ２ S ５Examples of oxide electrolytes include glass and glass ceramics, such as those listed below. Examples of oxide electrolytes include NASICON-based materials, LISICON-based materials, oxides having a perovskite structure, and oxides having a garnet structure.

[0026] The hydride electrolyte is LiBH ４ and lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH ２ ) is an example of a solid solution. ３ YCl ６ Examples of organic solid electrolytes include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

[0027] NASICON-based materials are represented by the general formula A ｘ M ２ (TO ４ ) ３ Examples of A include Na and Li, examples of M include Zr, Ti, V, Mn, Cr, Fe, Ni, Al, and Ge, and examples of T include P, Si, and As. For example, Na ３ V ２ (P.O. ４ ) ３ , Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ , Li １＋ｘ Ge ｘ Ti ２－ｘ (P.O. ４ ) ３ LISICON-based materials include Li ４－２ｘ Zn ｘ GeO ４ (0≦x≦1). Oxides having a perovskite structure include Li ｘ La （１－ｘ）／３ NbO ３ , La ２／３－Ｘ Li ３Ｘ TiO ３ (0≦x≦1).

[0028] The positive electrode 11 is formed by stacking a current collector 12 and an active material layer 13. The current collector 12 is a conductive member. Examples of materials for the current collector 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.

[0029] The active material layer 13 includes an active material and particles of a solid electrolyte. Examples of the active material include a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. ＋ In this case, the metal oxide containing a transition metal is exemplified by a metal 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 LiCoO ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiMn ２ O ４ , LiNiVO ４ , LiNi ０．５ Mn １．５ O ２ , LiNi １／３ Mn １／３ Co １／３ O ２ and LiFePO ４ is exemplified.

[0030] The sulfur-based active material is S, TiS ２ , NiS, FeS ２ , Li ２ S, MoS ３ Examples of organic active materials include radical compounds such as 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, and phenazine oxide.

[0031] The solid electrolyte contained in the active material layer 13 is exemplified by one or more materials selected from sulfide-based, oxide-based, hydride-based, halide-based, and organic-based materials. Since the solid electrolyte is similar to that contained in the separator 14, a description of the material will be omitted.

[0032] The solid electrolyte contained in the active material layer 13 is preferably an oxide-based electrolyte, and in particular, a composite oxide having a garnet-type crystal structure containing Li, La, and Zr is preferred. －３ This is because they have an ionic conductivity of the order of 50 S / cm and high chemical stability. ３ A ２ B ３ O １２ It is expressed as:

[0033] FIG. 2 is a diagram schematically showing a garnet-type crystal structure. In the garnet-type crystal structure, the C site Sc is dodecahedrally coordinated with an oxygen atom Oa, the A site Sa is octahedrally coordinated with an oxygen atom Oa, and the B site Sb is tetrahedrally coordinated with an oxygen atom Oa. In a solid electrolyte, Li can exist in a position that is octahedrally coordinated with an oxygen atom Oa in a normal garnet-type crystal structure, but becomes a void V. The void V is, for example, a position sandwiched between the B site Sb1 and the B site Sb2. The Li present in the void V is octahedrally coordinated with an oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 that forms the B site Sb1 and the tetrahedral face Fb2 that forms the B site Sb2. For example, Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ In the formula, La can occupy the C site Sc, Zr can occupy the A site Sa, and Li can occupy the B site Sb and the void V.

[0034] The garnet-type crystal structure can be identified by X-ray diffraction. The garnet-type crystal structure is identified by X-ray diffraction file No. 422259 (Li) in the Cambridge Structural Database (CSD). ７ La ３ Zr ２ O １２ ) has an XRD pattern similar to that of No. 422259. Compared to No. 422259, the solid electrolyte may differ in the type of constituent elements, Li concentration, etc., and therefore the diffraction angle and intensity ratio may differ. A typical crystal structure of this type is a cubic system (space group Ia-3d (- indicates an overline indicating a reversal operation), JCPDS: 84-1753).

[0035] Solid electrolytes with a garnet-type crystal structure are typically Li ７ La ３ Zr ２ O １２ The solid electrolyte is Li ７ La ３ Zr ２ O １２ A part of the constituent elements may be substituted with another element, or a small amount of another element may be added without substituting the constituent elements. Examples of the other element include 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).

[0036] The solid electrolyte is, for example, Li ６ La ３ Zr １．５ W ０．５ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Al ０．２ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Ga ０．２ O １２ , Li ６．２５ La ３ Zr ２ Ga ０．２５ O １２ , Li ６．４ La ３ Zr １．４ Ta ０．６ O １２ , Li ６．５ La ３ Zr １．７５ Te ０．２５ O １２ , Li ６．７５ La ３ Zr １．７５ Nb ０．２５ O １２ , Li ６．９ La ３ Zr １．６７５ Ta ０．２８９ Bi ０．０３６ O １２ , Li６．４６ Ga ０．２３ La ３ Zr 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 Zr ２ O １２ Examples include:

[0037] The solid electrolyte 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, in order to increase the ionic conductivity of the solid electrolyte. (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

[0038] Returning to Fig. 1, the negative electrode 15 is formed by stacking a current collector 16 and an active material layer 17. The current collector 16 is a conductive member. Examples of materials for the current collector 16 include a metal selected from Ni, Ti, Fe, Cu, and Si, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0039] The active material layer 17 contains an active material. In order to reduce the electron transfer resistance of the active material layer 17, the active material layer 17 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0040] The active material contained in the active material layer 17 is not limited to any material as long as it can absorb and release charge carriers. The active material is appropriately selected depending on the type of charge carrier. The active material may be a carbon-based material such as porous carbon, natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, or carbon fiber; Li ４ Ti ５ O １２ Examples of the oxides include Si, Si-Li alloys, compounds containing Si and O as constituent elements (hereinafter referred to as "SiOx" where 0.5≦x≦1.5), metallic lithium, lithium alloys such as Li-Al alloys, Li-Sn alloys, Li-Si alloys, Li-Mg alloys, and Li-Si alloys, In-Sb alloys, and Si-Li alloys. SiOx includes oxides of Si, amorphous SiO ２ Examples include those having a structure in which microcrystalline or amorphous Si is dispersed in a matrix.

[0041] The electricity storage device 10 is manufactured, for example, as follows: The active material, solid electrolyte particles, and conductive additive are mixed, and then a solution in which a binder is dissolved in a solvent is mixed to form a slurry. The slurry is then applied onto the current collector 12 and dried to obtain a positive electrode sheet.

[0042] The active material and the conductive additive are mixed, and then mixed with a solution in which a binder is dissolved in a solvent to form a slurry. The slurry is applied onto the current collector 16 and then dried to obtain a negative electrode sheet.

[0043] A separator 14 separating the positive electrode sheet from the negative electrode sheet, the positive electrode sheet, and the negative electrode sheet are stacked and wound up using a winding machine to produce a cylindrical or rectangular cell. Terminals (not shown) are connected to the current collectors 12 and 16, respectively, and a container (not shown) containing the cell is filled with an electrolyte solution. The container is then sealed to obtain an electricity storage device 10 including a positive electrode 11, a separator 14, and a negative electrode 15.

[0044] 3 is a cross-sectional view of the active material 19 and solid electrolyte particles 20 appearing in the region 18 of the active material layer 13 of the positive electrode 11. The cross-section of the active material layer 13 is a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling. The ion milling conditions are an acceleration voltage of 4.0 kV, an environmental temperature of −80° C., a processing time of 8 hours, and a vacuum degree of 10. －３Pa or less is an example.

[0045] The polished surface is, for example, a surface that is polished after freezing the active material layer 13 or embedding and solidifying the active material layer 13 in a tetrafunctional epoxy resin or the like. The active material 19 and particles 20 that appear in the cross section are analyzed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) to identify the element distribution or by image analysis of the contrast of the backscattered electron image.

[0046] The proportion of the active material 19 in the active material layer 13 is preferably 70 vol % or more and 99.9 vol % or less. This is to ensure the capacity of the electricity storage device 10. ２ When the thickness of the active material layer 13 is less than 50 μm, the ratio of the cross-sectional area of ​​the active material 19 to the total area of ​​the active material layer 13 is regarded as the ratio (vol %) of the active material 19. ２ Since it is not possible to set a square range of 2500 μm, a rectangular range (area 2500 μm) consisting of two short sides extending in the thickness direction (the length of the short sides corresponds to the thickness of the active material layer 13) and two long sides perpendicular to the short sides is set. ２ ) is set, and the proportion of the active material 19 therein is determined.

[0047] The average equivalent circle diameter of the active material 19 appearing on the cross section of the active material layer 13 is preferably 5 μm or more. This is to prevent the interface of the active material 19 from expanding, which is one of the causes of an increase in charge transfer resistance. The equivalent circle diameter of the active material 19 is the diameter of a circle having an area equal to the area of ​​the cross section of the active material 19 determined by image analysis. ２ The circle-equivalent diameter of each of the active material particles 19 appearing in this range is determined, and the average is obtained by dividing the sum of the determined circle-equivalent diameters by the total number of active material particles 19. The average circle-equivalent diameter of the active material particles 19 appearing in the cross section of the active material layer 13 is preferably 15 μm or less. This is to ensure the packing density of the active material particles 19.

[0048] The proportion of the particles 20 in the active material layer 13 is preferably 0.1 vol % or more and 30 vol % or less. This is to ensure the capacity of the electricity storage device 10 and to ensure reaction sites between the active material 19 and the particles 20.２ The ratio of the cross-sectional area of ​​the particle 20 to the range is regarded as the ratio (vol %) of the particle 20.

[0049] The average equivalent circle diameter of the particles 20 appearing on the cross section of the active material layer 13 is preferably 10 μm or less, and more preferably 5 μm or less. This is to ensure the number of reaction sites between the active material 19 and the particles 20. The equivalent circle diameter of the particles 20 is the diameter of a circle having an area equal to the cross section area of ​​the particles 20 determined by image analysis. ２ The circle-equivalent diameter of each of the particles 20 appearing in this range is determined, and the average is obtained by dividing the sum of the determined circle-equivalent diameters by the total number of particles 20. The average circle-equivalent diameter of the particles 20 appearing in the cross section of the active material layer 13 is preferably 0.5 μm or more. This is to make the particles 20 easier to handle.

[0050] The active material layer 13 may contain a binder that binds the active material 19 and a conductive additive that reduces the electron transfer 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.

[0051] There are no particular limitations on the binder as long as it binds the active material 19. Examples of binders include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and rubber-like polymers such as styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0052] The area 18 is a 400 μm area on the cross section of the active material layer 13. ２The area is a square section with a side length of 20 μm, in which six or more particles 20 appear. After an SEM image of the square section with a side length of 20 μm on the cross section of the active material layer 13 is acquired, particles 20 are detected by image analysis. The image consists of 160,000 pixels, with one side of the square section divided into 400. In order to reduce false detection due to image noise, particles 20 are defined as those with a size of four pixels or more.

[0053] 4 is a cross-sectional view of particles 20 appearing in a region 18 of the active material layer 13. The following description will be given taking as an example a region 18 in which seven particles 20 appear. The region 18 is an area for calculating the average distance D between particles 20. The reason for setting the region in which six or more particles 20 appear as the region 18 is to ensure the accuracy of the calculated average distance D.

[0054] The distance D between the particles 20 is the length of a line segment connecting the centers of gravity 21 of the cross sections of the particles 20. The centers of gravity 21 are the geometric centers when the cross sections of the particles 20 are viewed as a plane figure. The distance D between two particles 20 selected from all the particles 20 appearing in the range 18 is calculated, and the sum of the calculated distances D is multiplied by the number of combinations of the particles 20 (in this embodiment, ７ C ２ = 21) to obtain the average. The average of the distances D is 1.0 μm or more. This allows the particles 20 to be dispersed in the active material layer 13. Since the particles 20 contribute to the movement of charge carriers, the particles 20 dispersed in the active material layer 13 can increase the number of reaction sites. Therefore, the charge transfer resistance in the positive electrode 11 can be reduced.

[0055] With regard to the dispersibility of particles 20, it is preferable that the average of distance D is appropriately large, because particles 20 are dispersed over a wide range within active material layer 13. The average of distance D is preferably 2.0 μm or more, more preferably 3.0 μm or more, even more preferably 5.0 μm or more, and even more preferably 10.0 μm or more.

[0056] It is more preferable that the average distance D between particles 20 in any 10 areas 18 on the cross section of active material layer 13 is 1.0 μm or more, because this can further improve the dispersibility of particles 20 in active material layer 13.

[0057] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0058] (Cell Preparation) Li ６．９５ Mg ０．１５ La ２．７５ Sr ０．２５ Zr ２．０ O １２ So that Li ２ CO ３ , MgO, La(OH) ３ , SrCO ３ , ZrO ２ was weighed. ２ CO ３ Considering the volatilization of Li during firing, the amount of Li was approximately 15 mol% in excess in elemental terms. The weighed raw materials and ethanol were placed in a nylon pot along with zirconia balls and milled and mixed for 15 hours in a ball mill. The slurry removed from the pot was dried and then fired on an MgO plate at 1100°C for 15 hours. The fired powder was crushed, placed in an MgO sagger, and further fired at 1100°C for 4 hours. The fired powder was crushed in a glove box under an argon atmosphere to obtain various oxide solid electrolytes (hereinafter referred to as "LLZ") with different particle sizes. The crystalline structure of LLZ was confirmed to be garnet-type by powder X-ray diffraction.

[0059] The active material is LiNi ０．６ Mn ０．２ Co ０．２ O ２ Acetylene black as a conductive additive, LLZ as solid electrolyte particles, and polyvinylidene fluoride (binder) dissolved in N-methylpyrrolidone were weighed and mixed to a ratio of active material:conductive additive:particles:binder = 93.5:3.0:0.5:3.0 (volume ratio). Four types of slurries were prepared by varying the mixing time. Each slurry was applied to an aluminum foil current collector and dried at 80 ° C to obtain four types of positive electrode sheets. The positive electrode sheets were cut into squares with sides of 20 mm to obtain four types of positive electrodes. For comparison, a positive electrode in a comparative example was also prepared in the same manner except that the solid electrolyte particles were not mixed.

[0060] Graphite as an active material, acetylene black as a conductive additive, carboxymethyl cellulose as a thickener, and styrene butadiene rubber (binder) dispersed in pure water were weighed and mixed to a ratio of active material: conductive additive: thickener: binder = 97.7: 0.3: 1.0: 1.0 (volume ratio). A slurry was prepared. The slurry was applied to a copper foil current collector and dried at 120 ° C. to obtain a negative electrode sheet. The negative electrode sheet was cut into a square with a side length of 25 mm to obtain a negative electrode.

[0061] The supporting electrolyte LiPF was added to a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1. ６ The electrolyte solution was prepared by dissolving the above in a solution of 1 mol / L of the supporting electrolyte. Five types of positive and negative electrodes were sandwiched between polypropylene separators and housed in containers made of coated film. The containers were filled with the electrolyte solution and then sealed to obtain five types of cells, including a comparative example.

[0062] (Test) The cell was subjected to constant current-constant voltage charge and discharge at 25°C. Charging was performed by constant current charging at 0.2 C until the terminal voltage reached 4.2 V, followed by constant voltage charging until the current value reached 0.01 C. Discharging was performed by constant voltage discharging at 0.2 C until the terminal voltage reached 2.5 V, followed by constant voltage discharging until the current value reached 0.01 C. The charge transfer resistance of the cell at 20°C after charging and discharging was measured by an AC impedance method (frequency 1 MHz-100 mHz).

[0063] After the measurement by the AC impedance method, the cell was disassembled, and a cross section of the positive electrode was prepared by ion milling. An image of the cross section of the active material layer was obtained by SEM, and the average interparticle distance D was measured in a region where six or more particles (LLZ) were present in a square section with a side length of 20 μm.

[0064] The charge transfer resistance of the comparative example cell, which had a positive electrode that did not contain solid electrolyte particles, was used as the standard, and the percentage of the charge transfer resistance relative to the comparative example was calculated. The average distance D and the percentage of the charge transfer resistance (%) of each cell are shown in Table 1.

[0065]

[0066] The charge transfer resistance of the cell with an average particle distance D of 0.60 μm was 6% higher than that of the comparative cell containing no particles. This cell exhibited abnormalities such as two-stage discharge during discharge.

[0067] In contrast, the charge transfer resistance of cells in which the average interparticle distance D was 1.00 μm or more was reduced compared to the charge transfer resistance of cells in the comparative example that did not contain particles. Specifically, the charge transfer resistance of cells in which the average interparticle distance D was 1.00 μm was reduced by 5%, the charge transfer resistance of cells in which the average interparticle distance D was 1.10 μm was reduced by 15%, and the charge transfer resistance of cells in which the average interparticle distance D was 1.86 μm was reduced by 22%. It was found that the charge transfer resistance decreased as the average interparticle distance D increased.

[0068] According to the examples, when the average interparticle distance D in the positive electrode is 1 μm or more, the overvoltage caused by the resistance component of the positive electrode is reduced, and therefore, the input / output characteristics of the electricity storage device can be expected to be improved. Furthermore, since the non-uniformity of the reaction sites of the charge carriers is reduced, the utilization rate of the active material is improved, and therefore, the discharge capacity of the electricity storage device is expected to be expanded.

[0069] 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.

[0070] In the embodiment, the electricity storage device 10 has been described as including a positive electrode 11 in which an active material layer 13 is provided on one side of a current collector 12, and a negative electrode 15 in which an active material layer 17 is provided on one side of a current collector 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 (so-called bipolar electrodes) in which an active material layer 13 and an active material layer 17 are provided on both sides of a current collector 12. If bipolar electrodes and separators 14 are alternately stacked and housed in a case (not shown), an electricity storage device with a so-called bipolar structure can be obtained.

[0071] 10 Electricity storage device 11 Positive electrode (electrode) 18 Area 19 Active material 20 Particle D Distance between particles

Claims

1. An electrode containing solid electrolyte particles, the ratio of the particles being 0.1 vol% or more and 30 vol% or less, and ２ The average distance between the particles in an area in which six or more of the particles appear is 1 μm or more.

2. The electrode according to claim 1, wherein the average equivalent circle diameter of said particles appearing in said cross section is 10 μm or less.

3. The electrode according to claim 1, wherein the average equivalent circle diameter of said particles appearing in said cross section is 5 μm or less.

4. An electrode according to any one of claims 1 to 3, further comprising an active material, the average equivalent circle diameter of the active material appearing in the cross section being 5 µm or more.

5. An electrode according to any one of claims 1 to 3, wherein said particles are oxides.

6. The electrode according to claim 5, wherein said particles have a garnet-type crystal structure containing Li, La and Zr.

7. An electricity storage device comprising the electrode according to any one of claims 1 to 3.

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