Electrodes and energy storage devices

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

[Technical Field]

[0001] This invention relates to electrodes and energy storage devices containing solid electrolyte particles. [Background technology]

[0002] Reducing the internal resistance of an energy storage device is advantageous for improving the input / output characteristics of the device. Since the solid electrolyte particles contained in the electrodes of an energy storage device contribute to reducing the resistance of ion movement (charge transfer), prior art for setting the material of the particles and the proportion of particles in the electrodes is disclosed in Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 198494 [Overview of the project] [Problems that the invention aims to solve]

[0004] Regarding the reduction of charge transfer resistance, there is room for improvement in the prior art.

[0005] This invention was made to meet this requirement and aims to provide electrodes and energy storage devices that can reduce charge transfer resistance. [Means for solving the problem]

[0006] A first embodiment for achieving this objective is an electrode containing solid electrolyte particles, wherein the proportion of particles is 0.1 vol% or more and 30 vol% or less, and the cross-section of the electrode is 400 μm 2 In the area where six or more particles appear, the average distance between particles is 1 μm or greater.

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

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

[0009] The fourth embodiment is one in which any of the first to third embodiments further includes an active material, and the average equivalent circular diameter of the active material appearing in the cross-section is 5 μm or more.

[0010] The fifth aspect is that, in any of the first to fourth aspects, the particles are oxides.

[0011] The sixth aspect is the fifth aspect, wherein the particles have a garnet-type crystalline structure containing Li, La, and Zr.

[0012] The seventh embodiment is an energy storage device comprising an electrode according to any of the first to sixth embodiments. [Effects of the Invention]

[0013] The electrode of the present invention contains 0.1 vol% to 30 vol% of solid electrolyte particles, and the cross-section of the electrode has a 400 μm 2 In the area where six or more particles appear, the average distance between particles is 1 μm or more. Since the number of reaction sites due to the dispersed particles within the electrode can be increased, the charge transfer resistance can be reduced. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view of an energy storage device in one embodiment. [Figure 2] This is a schematic diagram showing the crystal structure of a garnet-type crystal. [Figure 3] This is a cross-sectional view of the active material and particles appearing within the active material layer. [Figure 4] This is a cross-sectional view of the particles appearing within the specified range. [Modes for carrying out the invention]

[0015] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a schematic cross-sectional view of an energy storage device 10 in one embodiment. The energy storage device 10 includes a positive electrode 11 and a negative electrode 15, and a separator 14 that separates the positive electrode 11 and 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 the following.

[0016] The separator 14 contains an electrolyte through which the charge carrier moves. The electrolyte can be appropriately selected from solid, gel, or liquid (electrolyte solution). When an electrolyte solution is used, the separator 14 is made of a porous material having electronic insulating properties. Examples of porous materials include nonwoven fabrics or porous membranes through which the charge carrier passes. Examples of porous material materials include cellulose, polypropylene, polyethylene, polyimide, alumina, etc.

[0017] The electrolyte is a solution in which a supporting electrolyte is dissolved in an aqueous or non-aqueous solvent. The supporting electrolyte may also be dissolved in a mixed solvent of an aqueous and aqueous solvent. Non-aqueous solvents are broadly classified into molecular solvents, which consist mostly of molecules, and ionic liquids, which consist of cations and anions. One reason for using a non-aqueous solvent as an 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 using a molecular solvent as a non-aqueous solvent, an aprotic solvent is preferred to broaden the potential window of the electrolyte. Examples of aprotic solvents include cyclic esters, linear esters, aliphatic carboxylic acid esters, phosphate esters, nitriles, amides, sulfur compounds, ketones, ethers, nitro compounds, and fluorescein solvents. Mixtures of these are also acceptable.

[0019] An ionic liquid is a compound composed of cations and anions, and is liquid at normal temperature and normal pressure. If the solvent of the electrolytic solution is an ionic liquid, the flame retardancy of the electrolytic solution can be improved. Preferable ionic liquids are those having, as the cation species, one or more types selected from the group consisting of ammonium, imidazolium, pyrrolidinium and piperidinium.

[0020] The anion component of the ionic liquid is not particularly limited. The anion component is BF4 - , N(SO2F)2 - and other inorganic anions; B(C6H5)4 - , CH3SO3 - , CF3SO3 - , N(SO2CF3)2 - , N(SO2C4F9)2 - and other organic anions are exemplified.

[0021] The ionic liquid may be a solvated ionic liquid. Examples of the solvated ionic liquid include those obtained by dissolving a supporting electrolyte in a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme.

[0022] When the charge carrier is Li + , the supporting electrolyte is a lithium salt. The anions of the supporting electrolyte include OH - , halide ions (I - , Cl - , Br - and the like), 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 - RCOO - Examples include (where R is an alkyl group having 1-4 carbon atoms, a phenyl group, or a naphthyl group). The supporting electrolyte may be a mixture of these.

[0023] The concentration of the supporting electrolyte in the electrolyte solution is 0.2 mol / dm³ 3 The above is preferable, and preferably 0.5 mol / dm 3 The above is a comfortable 1.0 mol / dm³ 3 That concludes the explanation. As the concentration of the supporting electrolyte increases, the number of solvent molecules coordinating to the charge carrier increases, reducing the amount of uncoordinated solvent, and counter-anion coordination (so-called ion association) becomes dominant. 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 / dm³. 3 The following are preferred, and more preferably, 2.0 mol / dm³ 3 The following applies: The concentration of the supporting electrolyte is 4.0 mol / dm³. 3 This is because beyond a certain point, the ionic conductivity tends to decrease significantly due to the increased viscosity of the electrolyte.

[0024] Solid or gel-like electrolytes include one or more selected from sulfide-based, oxide-based, hydride-based, halide-based, and organic-based electrolytes. Examples of separators 14 include sintered bodies containing these electrolytes, molded bodies formed by compressing aggregates of electrolyte particles, and mixtures of electrolyte particles and electrolyte solution.

[0025] Sulfide-based electrolytes include crystalline thiolysicone-type, Li 10 GeP2S 12 Type, argyrodite type, Li7P3S 11 Examples of oxide-based electrolytes include glass and glass-ceramic systems, such as Li2S-P2S5. Examples of oxide-based electrolytes include NASICON-based materials, LISICON-based materials, oxides with a perovskite structure, and oxides with a garnet-type structure.

[0026] Examples of hydride-based electrolytes include solid solutions of LiBH4 with lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH2). An example of a halide-based solid electrolyte is Li3YCl6. Examples of organic-based solid electrolytes include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

[0027] NASICON-based materials are based on general formula A x This material is represented as M2(TO4)3. A is exemplified by Na and Li, M is exemplified by Zr, Ti, V, Mn, Cr, Fe, Ni, Al, and Ge, and T is exemplified by P, Si, and As. For example, Na3V2(PO4)3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Ge x Ti 2-x (PO4)3 is one example. LiSICON-based materials include Li 4-2x Zn x An example is GeO4 (0 ≤ x ≤ 1). Oxides having a perovskite structure include Li x La (1-x) / 3 NbO3, La 2 / 3-X Li 3X One example is TiO3 (0 ≤ x ≤ 1).

[0028] The positive electrode 11 consists of a current collector 12 and an active material layer 13 superimposed on each other. The current collector 12 is a conductive material. Examples of materials for the current collector 12 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0029] The active material layer 13 includes an active material and particles of a solid electrolyte. Examples of active materials include metal oxides having transition metals, sulfur-based active materials, and organic active materials. The charge carrier is Li + In this case, examples of metal oxides containing transition metals include metal oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V, and Li. Examples of metal oxides containing transition metals include LiCoO2 and LiNi 0.8 Co 0.15 Al 0.05O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O2, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and LiFePO4 are examples.

[0030] Examples of sulfur-based active materials include S,TiS2,NiS,FeS2,Li2S,MoS3, and sulfur-carbon composites. 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 it is the same as the solid electrolyte contained in the separator 14, a description of the material is omitted.

[0032] The solid electrolyte contained in the active material layer 13 is preferably an oxide system, and among these, a composite oxide having a garnet-type crystal structure containing Li, La, and Zr is preferred. -3 This is because it has an ionic conductivity in the S / cm range and high chemical stability. The garnet-type crystal structure is general formula C3A2B3O 12 It is represented as follows.

[0033] Figure 2 schematically shows a garnet-type crystal structure. In a garnet-type crystal structure, the C site Sc coordinates dodecahedrally with the oxygen atom Oa, the A site Sa coordinates octahedrally with the oxygen atom Oa, and the B site Sb coordinates tetrahedrally with the oxygen atom Oa. In a typical garnet-type crystal structure, Li can be present in the void V, which is the site where Li would normally coordinate octahedrally with the oxygen atom Oa. The void V is, for example, the area between B site Sb1 and B site Sb2. The Li present in void V is octahedrally coordinated with the oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 forming B site Sb1 and the tetrahedral face Fb2 forming B site Sb2. For example, Li7La3Zr2O has a garnet-type crystal structure. 12 In this case, La may occupy site C (Sc), Zr may occupy site A (Sa), and Li may occupy site B (Sb) and the void V.

[0034] Garnet-type crystal structures can be identified by X-ray diffraction. The garnet-type crystal structure is found in the CSD (Cambridge Structural Database) X-ray diffraction file No. 422259 (Li7La3Zr2O 12 It has an XRD pattern similar to ). The solid electrolyte may differ from No. 422259 in terms of the types of constituent elements and Li concentration, so the diffraction angle and intensity ratio may differ. A typical crystal structure of this type is cubic (space group Ia-3d (- indicates an overline meaning reversal operation), JCPDS:84-1753).

[0035] Solid electrolytes with a garnet-type crystal structure are typically Li7La3Zr2O 12 Examples include: The solid electrolyte is Li7La3Zr2O 12 Some of the constituent elements may be substituted with other elements, or trace amounts of other elements may be added without substituting any constituent elements. Examples of other elements 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, 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 Zr2O 12 can be mentioned.

[0037] The solid electrolyte is preferably one that contains Mg and at least one of element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba), and the molar ratio of each element satisfies all of (1) to (3) below, or one that contains both Mg and element A, and the molar ratio of each element satisfies all of (4) to (6) below. 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] Let's return to Figure 1 for explanation. The negative electrode 15 consists of a current collector 16 and an active material layer 17 superimposed on each other. The current collector 16 is a conductive material. Examples of materials for the current collector 16 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0039] The active material layer 17 contains an active material. To lower the electron transfer resistance of the active material layer 17, a conductive additive may be included in the active material layer 17. Examples of conductive additives 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 is a carbon-based material such as porous carbon, natural graphite, artificial graphite, easily graphitizable carbon, difficult-to-graphitize carbon, carbon fiber, or Li4Ti5O 12Examples 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. Examples of SiOx include those having a structure in which microcrystalline or amorphous Si is dispersed in an amorphous SiO2 matrix, such as Si oxides.

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

[0042] A slurry is made by mixing the active material and conductive additive, and then mixing in a solution of the binder dissolved in a solvent. After applying the slurry onto the current collector 16, it is dried to obtain the negative electrode sheet.

[0043] A separator 14 separates the positive electrode sheet from the negative electrode sheet. The positive electrode sheet and the negative electrode sheet are then wound together on a winding machine to create a cylindrical or rectangular cell. Terminals (not shown) are connected to the current collectors 12 and 16, respectively. An electrolyte solution is then filled into a container (not shown) containing the cell. The container is then sealed to obtain an energy storage device 10 including a positive electrode 11, a separator 14, and a negative electrode 15.

[0044] Figure 3 is a cross-sectional view of the active material 19 and solid electrolyte particles 20 appearing in the area 18 of the active material layer 13 of the positive electrode 11. The cross-sections of the active material layer 13 are the polished surface, the surface obtained by irradiation with a focused ion beam (FIB), and the surface obtained by ion milling. The ion milling conditions were: acceleration voltage: 4.0kV, ambient temperature: -80℃, processing time: 8 hours, vacuum level: 10 -3 Examples below Pa are given.

[0045] The polished surface is, for example, a surface polished after the active material layer 13 has been frozen or after the active material layer 13 has been embedded and solidified 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 elemental distribution or to perform image analysis of the contrast of the backscattered electron image.

[0046] The proportion of active material 19 in the active material layer 13 is preferably 70 vol% to 99.9 vol%. This is to ensure the capacity of the energy storage device 10. On the cross-section of the active material layer 13, a square area with sides of 50 μm (area 2500 μm) is used. 2 The ratio of the cross-sectional area of ​​the active material 19 to the total area is considered to be the proportion of the active material 19 (vol%). If the thickness of the active material layer 13 is less than 50 μm, the area is 2500 μm. 2 Since it is not possible to define the square area, a rectangular area (area 2500 μm²) is defined, 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. 2 Set the parameters and determine the proportion of active material 19 within them.

[0047] The average equivalent circle diameter of the active material 19 appearing in the cross-section of the active material layer 13 is preferably 5 μm or more. This is to prevent the expansion of the interface of the active material 19, which is one of the causes of increased 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, as determined by image analysis. On the cross-section of the active material layer 13, the area is 2500 μm. 2 The equivalent circular diameter of each active material 19 appearing within the specified range is determined, and the average is obtained by dividing the sum of the determined equivalent circular diameters by the total number of active material 19. The average equivalent circular diameter of the active material 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 19.

[0048] The proportion of particles 20 in the active material layer 13 is preferably between 0.1 vol% and 30 vol%. This is to ensure the capacity of the energy storage device 10 and to ensure reaction sites between the active material 19 and the particles 20. The area of ​​the cross-section of the active material layer 13 is 2500 μm².2 The proportion of the cross-sectional area of ​​particle 20 within the given range is considered to be the proportion of particle 20 (vol%).

[0049] The average equivalent circle diameter of the particles 20 appearing in 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 a sufficient 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 area of ​​the cross-section of the particles 20, as determined by image analysis. The area on the cross-section of the active material layer 13 is 2500 μm. 2 The equivalent circular diameter of each particle 20 appearing within the specified range is determined, and the average is obtained by dividing the sum of the determined equivalent circular diameters by the total number of particles 20. The average equivalent circular diameter of the particles 20 appearing in the cross-section of the active material layer 13 is preferably 0.5 μm or larger. This is to facilitate the handling of the particles 20.

[0050] The active material layer 13 may contain a binder for binding the active material 19, and a conductive additive for reducing the electron transfer resistance of the active material layer 13. Examples of conductive additives include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

[0051] The binder is not particularly limited as long as it binds the active material 19. Examples of binders include rubbery polymers such as fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and 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] Range 18 is 400 μm on the cross-section of the active material layer 13. 2This is a square section with sides of 20 μm in size, where six or more particles 20 appear. After acquiring an SEM image of the 20 μm square section on the cross-section of the active material layer 13, the particles 20 are detected by image analysis. The image consists of 160,000 pixels, obtained by dividing one side of the square section into 400 parts. To reduce false detections due to image noise, particles 4 pixels or larger are defined as particles 20.

[0053] Figure 4 is a cross-sectional view of particles 20 appearing in area 18 of the active material layer 13. Below, we will explain using an example of area 18 where seven particles 20 appear. Area 18 is the area for calculating the average distance D between particles 20. The reason for defining area 18 as the area where six or more particles 20 appear is to ensure the accuracy of the calculated average distance D.

[0054] The distance D between particles 20 is the length of the line segment connecting the centroids 21 of the cross-sections of the particles 20. The centroid 21 is the geometric center when the cross-section of the particle 20 is represented as a planar figure. The distance D between two selected particles 20 from all particles 20 appearing in range 18 is determined, and the sum of the determined distances D is divided by the number of combinations of particles 20 (in this embodiment, 7C2 = 21) to obtain the average. The average distance D is 1.0 μm or more. This allows the particles 20 to be dispersed within the active material layer 13. Since the particles 20 contribute to the movement of charge carriers, the number of reaction sites can be increased by the particles 20 dispersed within the active material layer 13. Therefore, the charge transfer resistance within the positive electrode 11 can be reduced.

[0055] Regarding the dispersibility of the particles 20, it is preferable that the average distance D is moderately large. This is because the particles 20 are dispersed over a wide area within the active material layer 13. The average 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 still more preferably 10.0 μm or more.

[0056] It is even more preferable that the average distance D between particles 20 in any 10 locations 18 on the cross-section of the active material layer 13 is 1.0 μm or more. This is because the dispersibility of particles 20 within the active material layer 13 can be further improved. [Examples]

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

[0058] (Cell creation) Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed accordingly. Li2CO3 was kept in excess by approximately 15 mol% elementally, considering the volatilization of Li during calcination. The weighed raw materials and ethanol were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. After drying the slurry removed from the pot, it was calcined at 1100°C for 15 hours on an MgO plate. The resulting powder was ground, placed in an MgO sieve, and further calcined at 1100°C for 4 hours. The resulting powder was ground in a glove box under an argon atmosphere to obtain various oxide solid electrolytes with different particle sizes (hereinafter referred to as "LLZ"). The garnet-type crystal structure of LLZ was confirmed by powder X-ray diffraction.

[0059] The active material is LiNi 0.6 Mn 0.2 Co 0.2 O2, acetylene black (a conductive additive), LLZ (a solid electrolyte particle), and polyvinylidene fluoride (a binder) dissolved in N-methylpyrrolidone were weighed in a ratio of active material:conductive additive:particles:binder = 93.5:3.0:0.5:3.0 (volume ratio) and then mixed. Four types of slurries were prepared by varying the mixing time. Each slurry was applied to aluminum foil, which serves as the current collector, and dried at 80°C to obtain four types of positive electrode sheets. The positive electrode sheets were cut into 20 mm squares to obtain four types of positive electrodes. For comparison, a comparative positive electrode was also prepared in the same manner except that the solid electrolyte particles were not mixed.

[0060] A slurry was prepared by weighing and mixing graphite (active material), acetylene black (conductive additive), carboxymethylcellulose (thickener), and styrene-butadiene rubber (binder) dispersed in pure water in a ratio of active material:conductive additive:thickener:binder = 97.7:0.3:1.0:1.0 (volume ratio). The slurry was applied to copper foil, which served as the current collector, and dried at 120°C to obtain a negative electrode sheet. The negative electrode sheet was cut into a square with sides of 25 mm to obtain the negative electrode.

[0061] An electrolyte was prepared by dissolving the supporting electrolyte LiPF6 in a solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio). The concentration of the supporting electrolyte in the electrolyte was 1 mol / L. Five types of cells, including a comparative example, were obtained by placing a polypropylene separator between the positive and negative electrodes of each cell into a coated film container, filling them with the electrolyte, and then sealing the containers.

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

[0063] After measurements using the AC impedance method, the cell was disassembled, and a cross-section of the positive electrode was prepared by ion milling. Images of the cross-section of the active material layer were obtained by SEM, and the average distance D between particles was measured in the region where 6 or more particles (LLZ) were present in a square section with sides of 20 μm.

[0064] The charge transfer resistance of the cells in the comparative example, which had a positive electrode without solid electrolyte particles, was used as a baseline, and the ratio of charge transfer resistance to that of the comparative example was determined. The average distance D of each cell and the ratio (%) of charge transfer resistance are shown in Table 1.

[0065] [Table 1]

[0066] The charge transfer resistance of a cell with an average inter-particle distance D of 0.60 μm increased by 6% compared to the charge transfer resistance of a cell in a comparative example without particles. This cell exhibited abnormalities such as two-stage discharge during discharge.

[0067] In contrast, the charge transfer resistance of cells with an average interparticle distance D of 1.00 μm or more decreased compared to the charge transfer resistance of cells in the comparative example without particles. Specifically, cells with an average distance D of 1.00 μm showed a 5% decrease, cells with an average distance D of 1.10 μm showed a 15% decrease, and cells with an average distance D of 1.86 μm showed a 22% decrease. It was found that the charge transfer resistance decreased as the average distance D increased.

[0068] According to the examples, if the average distance D between particles in the positive electrode is 1 μm or more, the overvoltage caused by the resistance component of the positive electrode is reduced, which is expected to improve the input / output characteristics of the energy storage device. Furthermore, since the non-uniformity of the reaction sites of the charge carrier is reduced, an increase in the discharge capacity of the energy storage device is expected due to an improvement in the utilization rate of the active material.

[0069] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0070] In the embodiment, the energy storage device 10 was described as comprising a positive electrode 11 with an active material layer 13 provided on one side of a current collector 12, and a negative electrode 15 with an active material layer 17 provided on one side of a current collector 16, but it is not necessarily limited to this. For example, it is certainly possible to apply each element of the embodiment to an energy storage device that comprises electrode layers (so-called bipolar electrodes) with an active material layer 13 and an active material layer 17 provided on both sides of a current collector 12. By alternately stacking bipolar electrodes and separators 14 and housing them in a case (not shown), a so-called bipolar structure energy storage device can be obtained. [Explanation of symbols]

[0071] 10 Energy Storage Devices 11 Positive electrode 18 range 19 Active material 20 particles D is the distance between particles.

Claims

1. An electrode comprising solid electrolyte particles and an active material, The solid electrolyte is a composite oxide having a garnet-type crystalline structure containing Li, La, and Zr. The proportion of the aforementioned particles is 0.1 vol% or more and 30 vol% or less. The proportion of the active material is 70 vol% or more and 99.9 vol% or less. 400 μm on the cross-section of the electrode ２ In the area where six or more of the aforementioned particles appear, the average distance between the particles is 1 μm or more. An electrode in which the average equivalent circle diameter of the particles appearing in the cross-section is smaller than the average equivalent circle diameter of the active material appearing in the cross-section.

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

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

4. Furthermore, it contains active material, The electrode according to any one of claims 1 to 3, wherein the average equivalent diameter of the active material appearing in the cross-section is 5 μm or more.

5. An energy storage device comprising an electrode according to any one of claims 1 to 3.

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