Energy storage devices

Abstract

To provide a power storage device capable of achieving higher energy density at a large current.SOLUTION: A power storage device includes: a positive electrode containing a positive electrode active material and having a comb tooth structure in which multiple positive electrode comb teeth project to be spaced apart from each other from a main surface of a plate-like positive electrode base; a negative electrode containing a negative electrode active material and having a comb tooth structure in which multiple negative electrode comb teeth project to be spaced apart from each other from a main surface of a plate-like negative electrode base, the negative electrode being disposed such that the negative electrode comb teeth are alternated with the positive electrode comb teeth, tips of the negative electrode comb teeth face the main surface of the positive electrode base, and the main surface of the negative electrode base face the tips of the positive electrode comb teeth; and an ion conduction medium interposed between the negative electrode and the positive electrode and conducting carrier ions. In a cross section perpendicular to an extension direction of comb grooves each existing between the comb teeth in the comb tooth structure, when a size in a direction parallel to the main surface is defined as a width, the width of each of the positive electrode comb teeth and the width of each of the negative electrode comb teeth are a same value of 110 μm or more and 250 μm or less, and are constant from a base end to the tip.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to an energy storage device. [Background technology]

[0002] Conventionally, energy storage devices have been proposed that include a positive electrode having a comb-tooth structure, a negative electrode having a comb-tooth structure with the positive and negative electrode comb teeth arranged alternately, and an ion-conducting medium interposed between the positive and negative electrodes to conduct carrier ions (see, for example, Patent Document 1 and Non-Patent Documents 1 and 2). Patent Document 1 and Non-Patent Documents 1 and 2 aim to improve the energy density of the energy storage device by adjusting the shape of the comb teeth of the positive and negative electrodes. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0159476 [Non-patent literature]

[0004] [Non-Patent Document 1] Miyamoto et al., Cell Rep. Phys. Sci., 2, 100504 (2021). [Non-Patent Document 2] Miyamoto et al., J. Power Sources, 536, 231473 (2022). [Overview of the project] [Problems that the invention aims to solve]

[0005] However, while energy storage devices described in Patent Document 1 and Non-Patent Documents 1 and 2 can increase energy density, there was a desire to further increase energy density at high currents.

[0006] This disclosure was made to address these issues, with the primary objective being to further increase energy density at high currents. [Means for solving the problem]

[0007] Through diligent research to achieve the above-mentioned objectives, the inventors discovered that by setting the width of the positive electrode comb teeth and the negative electrode comb teeth to the same value of 110 μm to 250 μm, and keeping them constant from the base to the tip, the energy density at high currents can be further increased, leading to the completion of the invention disclosed herein.

[0008] In other words, the energy storage device of this disclosure is A positive electrode containing a positive electrode active material, having a comb-like structure in which multiple positive electrode comb teeth protrude from the main surface of a plate-shaped positive electrode base at intervals from each other, A negative electrode comprising a negative electrode active material, having a comb-tooth structure in which a plurality of negative electrode comb teeth protrude from the main surface of a plate-shaped negative electrode base at intervals from each other, wherein the negative electrode comb teeth are staggered with the positive electrode comb teeth, and the tips of the negative electrode comb teeth face the main surface of the positive electrode base, and the main surface of the negative electrode base faces the tips of the positive electrode comb teeth, The system comprises an ion-conducting medium interposed between the negative electrode and the positive electrode, which conducts carrier ions, In a cross-section perpendicular to the direction of extension of the comb grooves between the comb teeth of the comb tooth structure, if the dimension in the direction parallel to the main surface is defined as the width, then the width of the positive electrode comb tooth and the width of the negative electrode comb tooth are the same value, between 110 μm and 250 μm, and are constant from the base to the tip. [Effects of the Invention]

[0009] This energy storage device can achieve a higher energy density at high currents. The reason for this effect is presumed to be that, for example, if the width of the positive electrode comb teeth and the negative electrode comb teeth are the same value, between 110 μm and 250 μm, and are constant from the base to the tip, then ion conduction within the electrodes becomes smoother at high currents. [Brief explanation of the drawing]

[0010] [Figure 1] Explanatory drawing showing an example of the power storage device 10. [Figure 2] Explanatory drawing showing an outline of the configuration of the power storage devices of Experimental Examples 1 to 8. [Figure 3] Explanatory drawing showing an outline of the configuration of the power storage devices of Experimental Examples 9 to 10. [Figure 4] Explanatory drawing showing an outline of the configuration of the power storage devices of Experimental Examples 11 to 13. [Figure 5] Lag plots of Experimental Examples 5, 11 to 13.

Mode for Carrying Out the Invention

[0011] The power storage device of the present disclosure described in the embodiments includes a positive electrode, a negative electrode, and an ion conductive medium. This power storage device may include a positive electrode current collector electrically connected to the positive electrode, or may include a negative electrode current collector electrically connected to the negative electrode. This power storage device may be, for example, an electric double layer capacitor, a hybrid capacitor, a pseudo-electric double layer capacitor, an alkali metal secondary battery, an alkali metal ion battery, or the like. The carrier ions of the power storage device include alkali metal ions such as lithium ions, sodium ions, and potassium ions, group 2 ions such as magnesium ions, strontium ions, and calcium ions, and the like. Here, for the sake of convenience of explanation, a lithium ion secondary battery having lithium ions as carrier ions will be mainly described as an example below.

[0012] Here, the power storage device disclosed in the present embodiment will be described with reference to the drawings. FIG. 1 is an explanatory drawing showing an example of the power storage device 10. The power storage device 10 includes a positive electrode 20, a negative electrode 30, an ion conductive medium 40, a positive electrode current collector 42, and a negative electrode current collector 44. In this power storage device 10, in any cross section cut along a plane parallel to the plane of FIG. 1, the positive electrode 20, the negative electrode 30, the ion conductive medium 40, the positive electrode current collector 42, and the negative electrode current collector 44 may appear in the same shape as the cross section that appears in front of the plane of FIG. 1.

[0013] In the power storage device 10, the positive electrode 20 and the negative electrode 30 have a comb-tooth structure. The comb-tooth structure is a structure in which comb teeth and comb grooves alternately exist, and comb grooves exist between the comb teeth. Specifically, the positive electrode 20 has a comb-tooth structure in which a plurality of positive electrode comb teeth 24 protrude from the main surface 23 of the plate-shaped positive electrode base 22 at intervals from each other. The negative electrode 30 has a comb-tooth structure in which a plurality of negative electrode comb teeth 34 protrude from the main surface 33 of the plate-shaped negative electrode base 32 at intervals from each other. The negative electrode 30 is arranged such that the tips of the negative electrode comb teeth 34 face the main surface 23 of the positive electrode base 22, and the main surface 33 of the negative electrode base 32 faces the tips of the positive electrode comb teeth 24. That is, the negative electrode 30 is arranged to face the positive electrode 20 such that the plurality of negative electrode comb teeth 34 engage with the plurality of positive electrode comb teeth 24. The comb-tooth structure of the positive electrode 20 has a comb groove 25 formed by the opposing side surfaces of adjacent positive electrode comb teeth 24 and the main surface 23 of the positive electrode base 22 connecting the two, and the negative electrode comb teeth 34 are arranged in this comb groove 25. The comb-tooth structure of the negative electrode 30 has a comb groove 35 formed by the opposing side surfaces of adjacent negative electrode comb teeth 34 and the main surface 33 of the negative electrode base 32 connecting the two, and the positive electrode comb teeth 24 are arranged in this comb groove 35. In this specification, in a cross section perpendicular to the extending direction of the comb grooves 25 and 35 of the above-described comb-tooth structure, the dimension in the direction parallel to the main surfaces 23 and 33, that is, the dimension in the up-down direction of the paper surface of FIG. 1, is referred to as the width, and the dimension in the direction perpendicular to the main surfaces 23 and 33, that is, the dimension in the left-right direction of the paper surface of FIG. 1, is referred to as the thickness. Also, the dimension in the extending direction of the above-described comb grooves 25 and 35 is referred to as the depth. Note that the dimension in the thickness direction may also be referred to as the height.

[0014] In the energy storage device 10, the width wp of the positive electrode comb teeth 24 and the width wn of the negative electrode comb teeth 34 are the same value, between 110 μm and 250 μm, and are constant from the base to the tip. From the viewpoint of further increasing the energy density at high currents, the width wp of the positive electrode comb teeth 24 and the width wn of the negative electrode comb teeth 34 are preferably between 130 μm and 230 μm, more preferably between 150 μm and 210 μm, and even more preferably between 170 μm and 190 μm. The width wp of the positive electrode comb teeth 24 and the width wn of the negative electrode comb teeth 34 may be smaller than the depth of the positive electrode comb teeth 24 and the depth of the negative electrode comb teeth 34 (here, the same as the depth D described later), and may be 1 / 2 or less of the depth, 1 / 5 or less, or 1 / 10 or less.

[0015] The positive electrode 20 contains a positive electrode active material and, as described above, has a comb-tooth structure in which a plurality of positive electrode comb teeth 24 protrude from the main surface 23 of a plate-shaped positive electrode base 22 at intervals from each other. Of the plurality of positive electrode comb teeth 24, one positive electrode end comb tooth 26 is positioned next to one of the end teeth (on the lower side in Figure 1), spaced apart from that positive electrode comb tooth 24. The number of positive electrode comb teeth 24 may be, for example, 3 to 100, or 5 to 20. The positive electrode end comb tooth 26 is a comb tooth with a different width from the positive electrode comb teeth 24. The width wxp of the positive electrode end comb tooth 26 may be, for example, smaller than the width wp of the positive electrode comb tooth 24, or half or less of the width wp of the positive electrode comb tooth 24. The width wxp of the positive electrode end comb tooth 26 may be constant from its base to its tip. The height hp of the positive electrode comb teeth 24 and the positive electrode end comb teeth 26 may be, for example, 100 μm to 30,000 μm, 200 μm to 800 μm, or 400 μm to 600 μm. The thickness tp of the positive electrode base 22 may be, for example, 10 μm to 100 μm, 30 μm to 70 μm, 40 μm to 60 μm, 45 μm to 55 μm, or 50 μm. From the viewpoint of increasing energy density, a thinner thickness tp of the positive electrode base 22 is preferable, and may be, for example, 50 μm or less.

[0016] The positive electrode 20 may include a positive electrode active material, a conductive material, and a binder. The positive electrode active material may be capable of occluding and releasing lithium ions, and examples thereof include compounds having lithium and transition metals, such as oxides containing lithium and transition metal elements, and phosphate compounds containing lithium and transition metal elements. Specifically, the basic composition formula is Li (1-x) MnO2 (0 ≦ x ≦ 1, etc., the same applies hereinafter), Li (1-x) Mn2O4, etc., lithium manganese composite oxides having a basic composition formula of Li (1-x) CoO2, etc., lithium cobalt composite oxides having a basic composition formula of Li (1-x) NiO2, etc., lithium nickel composite oxides having a basic composition formula of Li (1-x) Co a Ni b Mn c O2 (a > 0, b > 0, c > 0, a + b + c = 1), Li (1-x) Co a Ni b Mn cLithium cobalt nickel manganese composite oxides such as O4 (0 < a < 1, 0 < b < 1, 1 ≤ c < 2, a + b + c = 2), lithium vanadium composite oxides with a basic composition formula such as LiV2O3, transition metal oxides with a basic composition formula such as V2O5, etc. can be used. Further, a lithium iron phosphate compound with a basic composition formula of LiFePO4, etc. can be used as a positive electrode active material. Among these, composite oxides containing lithium and manganese, for example, spinel-type LiMn2O4, etc. are preferable. Note that the "basic composition formula" means that it may contain components of other elements, for example, Al, Mg, etc. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect battery performance. For example, graphite such as natural graphite (scaly graphite, flaky graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fibers, metals (copper, nickel, aluminum, silver, gold, etc.), etc., a mixture of one or more of these can be used. The binder serves to connect and hold the active material particles and the conductive material particles to maintain a predetermined shape. For example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, or thermoplastic resins such as polypropylene, polyethylene, etc., ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), etc. can be used alone or as a mixture of two or more. Also, an aqueous binder such as an aqueous dispersion of a cellulose-based or styrene butadiene rubber (SBR) can be used. In the positive electrode 20, the content of the positive electrode active material is preferably higher, preferably 60% by mass or more, more preferably 70% by mass or more, based on the total mass of the positive electrode 20. In the positive electrode 20, the content of the positive electrode active material may be 99% by mass or less. The positive electrode 20 may be a porous body, and its porosity may be 50% by volume or more and 70% by volume or less, or 55% by volume or more and 65% by volume or less. The voids of the positive electrode 20 may be filled with a non-aqueous electrolyte etc. resulting from the ion conduction medium 40.

[0017] The negative electrode 30 contains a negative electrode active material and, as described above, has a comb-tooth structure in which a plurality of negative electrode comb teeth 34 protrude from the main surface 33 of a plate-shaped negative electrode base 32 at intervals from each other. Of the plurality of negative electrode comb teeth 34, one negative electrode end comb tooth 36 is positioned next to one of the end teeth (upper in Figure 1), spaced apart from that negative electrode comb tooth 34. The number of negative electrode comb teeth 34 may be, for example, 3 to 100, or 5 to 20. The negative electrode end comb teeth 36 are comb teeth with a different width from the negative electrode comb teeth 34. The width wxn of the negative electrode end comb teeth 36 may be, for example, smaller than the width wn of the negative electrode comb teeth 34, or half or less of the width wn of the negative electrode comb teeth 34. The width wxn of the negative electrode end comb teeth 36 may be constant from its base to its tip. The height hn of the negative electrode comb teeth 34 and the negative electrode end comb teeth 36 may be, for example, 100 μm to 30,000 μm, 200 μm to 800 μm, or 400 μm to 600 μm. The thickness tn of the negative electrode base 32 may be, for example, 10 μm to 100 μm, 30 μm to 70 μm, 40 μm to 60 μm, 45 μm to 55 μm, or 50 μm. The thickness tn of the negative electrode base 32 may be the same as the thickness tp of the positive electrode base 22.

[0018] The negative electrode 30 may have the same volume as the positive electrode 20. Furthermore, the negative electrode 30 may have the same shape and dimensions as the positive electrode 20.

[0019] The negative electrode 30 may include a negative electrode active material and a binder, and may also include a conductive material as needed. The negative electrode active material may be capable of intercalating and deintercalating lithium ions, and examples include inorganic compounds such as tin compounds, carbonaceous materials capable of intercalating and deintercalating lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of carbonaceous materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among these, graphites such as artificial graphite and natural graphite are preferred because they have an operating potential close to metallic lithium, allow for charging and discharging at high operating voltages, suppress self-discharge when a lithium salt is used as a supporting salt, and reduce irreversible capacity during charging. Examples of composite oxides include lithium titanium composite oxide and lithium vanadium composite oxide. Among these, carbonaceous materials are preferred as the negative electrode active material from a safety standpoint. The conductive material and binder used in the negative electrode 30 can be those exemplified in the positive electrode 20. In the negative electrode 30, the content of the negative electrode active material is preferably higher, preferably 60% by mass or more, and more preferably 70% by mass or more, relative to the total mass of the negative electrode 30. In the negative electrode 30, the content of the negative electrode active material may be 99% by mass or less. The negative electrode 30 may be a porous body, and its porosity may be 45% by volume or more and 65% by volume or less, or 50% by volume or more and 60% by volume or less. The voids in the negative electrode 30 may be filled with a non-aqueous electrolyte solution resulting from the ion conducting medium 40.

[0020] The ion-conducting medium 40 is interposed between the positive electrode 20 and the negative electrode 30. More specifically, the ion-conducting medium 40 is interposed between the positive electrode surface, which consists of the main surface 23 of the positive electrode base 22, the side and tip surfaces of the positive electrode comb teeth 24, and the side and tip surfaces of the positive electrode end comb teeth 26, and the negative electrode surface, which consists of the main surface 33 of the negative electrode base 32, the side and tip surfaces of the negative electrode comb teeth 34, and the side and tip surfaces of the negative electrode end comb teeth 36. The ion-conducting medium 40 is arranged to fill the gap between the positive electrode surface and the negative electrode surface, and the thickness ts of the ion-conducting medium 40 corresponding to this gap may be, for example, 1 μm or more and 30 μm or less, 5 μm or more and 25 μm or less, or 10 μm or more and 20 μm or less.

[0021] The ion-conducting medium 40 conducts lithium ions, which are carrier ions. The ion-conducting medium may be, for example, a non-aqueous electrolyte containing a supporting salt (supporting electrolyte) and an organic solvent. As the supporting salt, for example, when lithium ions are used as carriers in the positive electrode, it may contain known lithium salts. Examples of these lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, Li(CF3SO2)2N, and LiN(C2F5SO2)2, of which LiPF6 and LiBF4 are preferred. The concentration of this supporting salt in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration of the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when it is 5 mol / L or less, the electrolyte can be made more stable. In addition, flame retardants such as phosphorus-based and halogen-based agents may be added to this non-aqueous electrolyte. As the organic solvent, for example, an aprotic organic solvent can be used. Examples of such organic solvents include cyclic carbonates, linear carbonates, cyclic esters, cyclic ethers, and linear ethers. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of linear carbonates include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of cyclic ester carbonates include gamma-butyrolactone and gamma-valerolactone. Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of linear ethers include dimethoxyethane and ethylene glycol dimethyl ether. These may be used individually or in combination. In addition, nitrile solvents such as acetonitrile and propylnitrile, or ionic liquids may be used as non-aqueous electrolytes. Alternatively, aqueous electrolytes may be used instead of non-aqueous electrolytes.

[0022] The ion-conducting medium 40 may be an ion-conducting membrane containing a resin and the electrolyte described above. Examples of resins include polyvinylidene fluoride (PVdF), a copolymer of PVdF and hexafluoropropylene (PVdF-HFP), polymethyl methacrylate (PMMA), and a copolymer of PMMA and an acrylic polymer. For example, in the copolymer of PVdF and HFP, a portion of the non-aqueous electrolyte swells and gels the membrane, forming an ion-conducting membrane.

[0023] The positive electrode current collector 42 is electrically connected to the positive electrode 20. Here, the positive electrode current collector 42 is formed on the entire surface 27 of the positive electrode base 22 opposite to the positive electrode comb teeth 24. The arrangement of the positive electrode current collector 42 is not limited to this; for example, it may be formed on a part of the surface 27, or on the end face of the positive electrode 20 perpendicular to the direction of extension of the comb groove 25, i.e., on the entire surface or part of the front or back surface in Figure 1. The positive electrode current collector 42 is not particularly limited as long as it is chemically and electrically stable with respect to the positive electrode active material, etc., and can be made of aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., or aluminum or copper whose surface has been treated with carbon, nickel, titanium, or silver for the purpose of improving adhesion, conductivity, and oxidation resistance. Of these, aluminum is preferred. The positive electrode current collector is particularly suitable for the positive electrode of a lithium secondary battery because it is less susceptible to lithium ion doping in the potential range in which it is used as a positive electrode current collector, and it has high corrosion resistance. The shape of the positive electrode current collector 42 can be a sheet, a net, a punched or expanded material, a lath, etc. The sheet shape includes foil and film shapes. The thickness of the positive electrode current collector 42 is preferably 10 μm or more and 20 μm or less, and more preferably 12 μm or more and 17 μm or less. If the thickness of the positive electrode current collector 42 is 10 μm or more, the mechanical strength of the positive electrode current collector 42 can be further increased. Also, if the thickness of the positive electrode current collector 42 is 20 μm or less, the volume fraction of the positive electrode current collector 42 in the energy storage device 10 can be reduced and the volume fraction of the positive electrode 20 etc. can be increased, thereby increasing the energy density of the energy storage device 10.

[0024] The negative electrode current collector 44 is electrically connected to the negative electrode 30. Here, the negative electrode current collector 44 is formed on the entire surface 37 of the negative electrode base 32 opposite to the negative electrode comb teeth 34. The arrangement of the negative electrode current collector 44 is not limited to this; for example, it may be formed on a part of the surface 37, or on the end face of the negative electrode 30 perpendicular to the direction of extension of the comb groove 35, i.e., on the entire surface or part of the front or back surface in Figure 1. The negative electrode current collector 44 is not particularly limited as long as it is chemically and electrically stable with respect to the negative electrode active material, and can be made of copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., or, for the purpose of improving adhesion, conductivity, and reduction resistance, a surface treated with carbon, nickel, titanium, or silver, for example, can also be used. Of these, copper is preferred. This is because the negative electrode current collector 44 is particularly suitable for the negative electrode of a lithium secondary battery due to its low susceptibility to lithium ion doping in the potential range in which it is used, and its high corrosion resistance. The shape of the negative electrode current collector 44 can be a sheet, a net, a punched or expanded material, a lath, etc. The sheet shape includes foil and film shapes. The thickness of the negative electrode current collector 44 is preferably 5 μm to 15 μm, and more preferably 8 μm to 12 μm. If the thickness of the negative electrode current collector 44 is 5 μm or more, the mechanical strength of the negative electrode current collector 42 can be further increased. Also, if the thickness of the negative electrode current collector 44 is 15 μm or less, the volume fraction of the negative electrode current collector 44 in the energy storage device 10 can be reduced and the volume fraction of the negative electrode 30 etc. can be increased, thereby increasing the energy density of the energy storage device 10.

[0025] The thickness T of this energy storage device 10 may be, for example, 100 μm or more and 30,000 μm or less, 300 μm or more and 1,000 μm or less, 500 μm or more and 700 μm or less, or 600 μm. However, the thickness T excludes the positive electrode current collector 42 and the negative electrode current collector 44. The width W of this energy storage device 10 may be, for example, 500 μm or more and 30,000 μm or less, 1,000 μm or more and 7,000 μm or less, 2,000 μm or more and 5,000 μm or less, or 3,000 μm. The depth D of this energy storage device 10 may be, for example, 100 μm or more and 30,000 μm or less, 1,000 μm or more and 7,000 μm or less, 2,000 μm or more and 5,000 μm or less, or 3,000 μm. A power storage device 10 of these dimensions can be suitably used as a microbattery for powering IoT (Internet of Things) devices, etc.

[0026] The energy storage device 10 may be formed, for example, using 3D printing technology. When manufacturing the energy storage device 10 using 3D printing technology, for example, as described in Sun et al., Adv. Mater., 25, 4539 (2013), a 3D structure may be fabricated by first applying a high-viscosity electrode ink, then the 3D structure may be heated to remove liquids and polymers, and then an electrolyte may be injected for packaging. The electrode inks used for the positive and negative electrodes may, for example, have an active material content of 45% to 65% by mass, or 50% to 60% by mass. Alternatively, the energy storage device 10 may be formed using lithography technology, for example, as described in Ning et al., 112, 6573 (2015).

[0027] In the energy storage device 10 of the embodiment described above, the energy density can be further increased at high currents. The reason for this effect is presumed to be that, for example, if the width of the positive electrode comb teeth 24 and the width of the negative electrode comb teeth 34 are the same value, between 110 μm and 250 μm, and constant from the base to the tip, then ion conduction within the electrodes proceeds more smoothly at high currents. In general, in flat-plate opposed lithium-ion batteries, the electrode thickness is 50 μm to 100 μm, and if the thickness is increased beyond this, the energy density decreases, especially when high currents are flowed, due to the increase in resistance caused by lithium ion diffusion. In contrast, in a three-dimensional (3D) battery composed of comb-shaped electrodes, lithium ions can access the inside of the electrodes from both sides of the comb-shaped electrodes, so it is presumed that the diffusion distance of lithium ions can be halved. In this disclosure, it is further presumed that by optimizing the width of the positive electrode comb teeth 24 and the width of the negative electrode comb teeth 34, the energy density at high currents (for example, 9.45 mA or more, or 15.75 mA or more) can be improved.

[0028] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0029] For example, in the embodiment described above, the number of positive electrode comb teeth 24 and negative electrode comb teeth 34 are the same, but the number of positive electrode comb teeth 24 may be increased, or the number of negative electrode comb teeth 34 may be increased. Also, although there is one positive end comb tooth 26 and one negative end comb tooth 36, one or both may be omitted. Alternatively, the positive electrode 20 may have two positive end comb teeth 26 with multiple positive electrode comb teeth 24 arranged between them. In that case, the negative electrode 30 may not have a negative end comb tooth 36, but may have one more negative electrode comb tooth 34 than positive electrode comb teeth 24. Or, the negative electrode 30 may have two negative end comb teeth 36 with multiple negative electrode comb teeth 34 arranged between them. In that case, the positive electrode 20 may not have a positive end comb tooth 26, but may have one more positive electrode comb tooth 24 than negative electrode comb teeth 34.

[0030] This disclosure may be any of the following [1] to [7]. [1] A positive electrode having a comb-like structure in which a plurality of positive electrode comb teeth protrude from the main surface of a plate-shaped positive electrode base at intervals from each other, and A negative electrode comprising a negative electrode active material, having a comb-tooth structure in which a plurality of negative electrode comb teeth protrude from the main surface of a plate-shaped negative electrode base at intervals from each other, wherein the negative electrode comb teeth are staggered with the positive electrode comb teeth, and the tips of the negative electrode comb teeth face the main surface of the positive electrode base, and the main surface of the negative electrode base faces the tips of the positive electrode comb teeth, The system comprises an ion-conducting medium interposed between the positive electrode and the negative electrode, which conducts carrier ions, In a cross-section perpendicular to the direction of extension of the comb grooves between the comb teeth of the comb structure, if the dimension in the direction parallel to the main surface is defined as the width, then the width of the positive electrode comb tooth and the width of the negative electrode comb tooth are the same value, between 110 μm and 250 μm, and are constant from the base to the tip. Energy storage device. [2] The energy storage device according to [1], wherein the width of the positive electrode comb teeth and the width of the negative electrode comb teeth are 150 μm or more and 210 μm or less. [3] The energy storage device according to [1] or [2], wherein the width of the positive electrode comb teeth and the width of the negative electrode comb teeth are 170 μm or more and 190 μm or less. [4] In the cross-section, if the dimension perpendicular to the main surface is defined as thickness, the thickness of the positive electrode base is 40 μm or more and 60 μm or less, and the thickness of the negative electrode base is 40 μm or more and 60 μm or less, the energy storage device according to any one of [1] to [3]. [5] The energy storage device according to any one of [1] to [4], wherein the negative electrode has the same volume as the positive electrode. [6] A power storage device described in any one of [1] to [5], A positive electrode current collector electrically connected to the positive electrode, A negative electrode current collector electrically connected to the negative electrode, A power storage device equipped with [a specific feature / ability]. [7] The energy storage device according to any one of [1] to [6], wherein the carrier ion is a lithium ion. [Examples]

[0031] The following describes specific examples of the energy storage device described herein. Experimental Examples 2-8 are considered examples, Experimental Examples 1, 9, and 10 are considered comparative examples, and Experimental Examples 11-13 are considered reference examples.

[0032] [Energy storage devices] In Experimental Examples 1-13, the energy storage devices shown in Figures 2A-2H, 3A-3B, and 4A-4C were examined. Figures 2A-2H, 3A-3B, and 4A-4C correspond to the front views in Figure 1. For Experimental Examples 1-10, the energy storage devices had a thickness T (thickness excluding the current collector) of 600 μm and a depth D of 3000 μm. For Experimental Examples 11-13, the energy storage devices had thicknesses T (thickness excluding the current collector) of 720 μm, 840 μm, and 960 μm, respectively, and a depth D of 3000 μm in all cases. The separator thickness was 20 μm. In Experimental Examples 1-13, the positive electrode active material was spinel-type lithium manganese composite oxide (LMO). The negative electrode active material was graphite (Osaka Gas Co., Ltd., MCMB25-10). The ion-conducting medium (ion-conducting membrane) was a gel electrolyte composed of an electrolyte solution made by adding 1.0 M LiPF6 to a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of EC:DMC = 1:2, and a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP). The content of the positive electrode active material was 90% by mass of the total mass of positive electrode 20, and the content of the negative electrode active material was 95% by mass of the total mass of negative electrode 30. Positive electrode 20 was a porous material with a porosity of 63% by volume. Negative electrode 30 was a porous material with a porosity of 50% by volume. The specific dimensions of experimental examples 1 to 13 are described below.

[0033] (Experimental Example 1) The energy storage device shown in Figure 2A was examined. The thickness tp of the positive electrode base was 50 μm, the width wp of the positive electrode comb teeth was 100 μm and there were 8 teeth, and the width wxp of the positive electrode end comb teeth was 50 μm and there was 1 tooth. The thickness tn of the negative electrode base was 50 μm, the width wn of the negative electrode comb teeth was 100 μm and there were 8 teeth, and the width wxn of the negative electrode end comb teeth was 50 μm and there was 1 tooth. The width W of this energy storage device is 2040 μm. (Experimental Example 2) The energy storage device shown in Figure 2B was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode (wp) and the width of the comb teeth for the negative electrode (wn) were set to 120 μm. The width W of this energy storage device is 2360 μm. (Experimental Example 3) The energy storage device shown in Figure 2C was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode (wp) and the width of the comb teeth for the negative electrode (wn) were set to 140 μm. The width W of this energy storage device is 2680 μm. (Experimental Example 4) The energy storage device shown in Figure 2D was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode wp and the width of the comb teeth for the negative electrode wn were set to 160 μm. The width W of this energy storage device is 3000 μm. (Experimental Example 5) The energy storage device shown in Figure 2E was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode (wp) and the width of the comb teeth for the negative electrode (wn) were set to 180 μm. The width W of this energy storage device is 3320 μm. (Experimental Example 6) The energy storage device shown in Figure 2F was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode (wp) and the width of the comb teeth for the negative electrode (wn) were set to 200 μm. The width W of this energy storage device is 3640 μm. (Experimental Example 7) The energy storage device shown in Figure 2G was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode (wp) and the width of the comb teeth for the negative electrode (wn) were set to 220 μm. The width W of this energy storage device is 3960 μm. (Experimental Example 8) The energy storage device shown in Figure 2H was examined. It was the same as in Experimental Example 1, except that the width of the comb teeth for the positive electrode (wp) and the width of the comb teeth for the negative electrode (wn) were set to 240 μm. The width W of this energy storage device is 4280 μm.

[0034] (Experimental Example 9) The energy storage device shown in Figure 3A was examined. In this energy storage device, the tips of the comb teeth on the positive and negative electrodes were narrower than the base teeth. The thickness tp of the positive electrode base was 50 μm, the width of the base teeth of the positive electrode comb teeth was 160 μm, the width of the tip teeth was 100 μm, there were 10 teeth, and there were no comb teeth for the positive electrode end. The thickness tn of the negative electrode base was 50 μm, the width of the base teeth of the negative electrode comb teeth was 160 μm, the width of the tip teeth was 100 μm, there were 10 teeth, and the width wxn of the comb tooth for the negative electrode end was 50 μm, there was 1 tooth. The width W of this energy storage device is 3000 μm. Note that the structure of Experimental Example 9 is the structure optimized by Monte Carlo Tree Search (MCTS) in Non-Patent Document 2, and corresponds to Figure 3C(a) in Non-Patent Document 2. (Experimental Example 10) The energy storage device shown in Figure 3B was examined. In this energy storage device, the negative electrode comb teeth were thinner than the positive electrode comb teeth. The thickness tp of the positive electrode base was 50 μm, the width wp of the positive electrode comb teeth was 160 μm, there were 10 teeth, and there were no comb teeth for the positive electrode end. The thickness tn of the negative electrode base was 50 μm, the width wn of the negative electrode comb teeth was 100 μm, there were 9 teeth, and the width wxn of the comb teeth for the negative electrode end was 50 μm, there were 2 teeth. The width W of this energy storage device is 3000 μm. Note that the structure of Experimental Example 10 is the structure optimized using random search and Monte Carlo Tree Search (MCTS) in Non-Patent Documents 1 and 2, and corresponds to 5E(a) in Non-Patent Document 1 and Figure 4C(a) in Non-Patent Document 2.

[0035] (Experimental Example 11) The energy storage device shown in Figure 4A was examined. This energy storage device was the same as in Experimental Example 5, except that the thickness tp of the positive electrode base and the thickness tn of the negative electrode base were 110 μm, and the thickness T of the energy storage device (thickness excluding the current collector) was 720 μm. The width W of this energy storage device is 3320 μm. (Experimental Example 12) The energy storage device shown in Figure 4B was examined. This energy storage device was the same as in Experimental Example 5, except that the thickness tp of the positive electrode base and the thickness tn of the negative electrode base were 170 μm, and the thickness T of the energy storage device (thickness excluding the current collector) was 840 μm. The width W of this energy storage device is 3320 μm. (Experimental Example 13) The energy storage device shown in Figure 4C was examined. This energy storage device was the same as in Experimental Example 5, except that the thickness tp of the positive electrode base and the thickness tn of the negative electrode base were 230 μm, and the thickness T of the energy storage device (thickness excluding the current collector) was 960 μm. The width W of this energy storage device is 3320 μm.

[0036] [evaluation] Energy density was evaluated by continuum simulation using the COSMOL Multiphysics Software package. For the continuum simulation, the battery model described in Doyle, et al., J. Electrochem. Soc., 143, 1890 (1996) (a model combining porous electrode theory and concentrated solution theory) was used. Current density was defined as the surface formed by the width W and depth D of the energy storage device (e.g., 2040 μm × 3000 μm in Experimental Example 1). Current density was given by XC = X × 3.16 mA / cm². 2 It is expressed as follows: 1C = 3.16mA / cm². 2 Therefore, 6C = 18.96mA / cm² 2 It was assumed that the following conditions were met. Furthermore, the energy density was defined by the surface formed by the width W and thickness T of the energy storage device (for example, 2040 μm × 600 μm in Experimental Example 1). Except for the points mentioned above, the method described in Non-Patent Document 1 (Miyamoto et al., Cell Rep. Phys. Sci., 2, 100504 (2021)) was followed.

[0037] [Results and Discussion] Table 1 summarizes the thickness of the positive electrode base, the thickness of the negative electrode base, the width of the positive electrode comb teeth, the width of the negative electrode comb teeth, and the thickness of the energy storage device for Experimental Examples 1-13. Table 2 shows the energy density of the energy storage devices for Experimental Examples 1-10.

[0038] First, the width of the positive and negative electrode comb teeth was examined using Experimental Examples 1 to 10. When comparing energy densities, Experimental Examples 2 to 8 showed higher values ​​for 5C and 6C carbon rates than Experimental Example 10, which is the optimized structure described in Non-Patent Documents 1 and 2. In Experimental Example 10, similar to Experimental Examples 2 to 8, the width of the positive and negative electrode comb teeth is constant from the base to the tip, but the width of the positive electrode comb teeth is greater than the width of the negative electrode comb teeth, and the volume ratio of the positive electrode to the negative electrode is 6:4. Furthermore, in Experimental Examples 2 to 8, all carbon rates from 1C to 6C showed values ​​equal to or higher than those of Experimental Example 9, which is the optimized structure described in Non-Patent Document 2, and the carbon rates of 5C and 6C showed higher values ​​than those of Experimental Example 9. In Experimental Example 9, similar to Experimental Examples 2-8, the widths of the positive and negative electrode comb teeth are the same, between 110 μm and 250 μm, and the volume ratio of the positive electrode to the negative electrode is 5:5. However, the width of the positive and negative electrode comb teeth is not constant from the base to the tip, but is narrower towards the tip. Therefore, it was found that in Experimental Examples 2-8, where the width of the positive and negative electrode comb teeth is the same, between 110 μm and 250 μm, and constant from the base to the tip, the energy density is good, and in particular the energy density at high rates of 5C or higher is good, which is preferable. Of the experimental examples 2-8, experimental examples 3-7, where the width of the positive and negative electrode comb teeth was between 130 μm and 230 μm, showed better energy density at high rates of 5C or higher. Experimental examples 4-6, where the width of the positive and negative electrode comb teeth was between 150 μm and 210 μm, showed even better energy density at high rates of 5C or higher. Experimental example 5, where the width of the positive and negative electrode comb teeth was between 170 μm and 190 μm, showed even better energy density at high rates of 5C or higher, making it preferable. Thus, it was found that the energy density at high rates can be further increased by bringing the width of the positive and negative electrode comb teeth closer to 180 μm.

[0039] Next, the thickness of the positive and negative electrode bases was investigated using experimental examples 5, 11-13. Figure 5 shows the Ragon plots for experimental examples 5, 11-13. Note that the power density on the horizontal axis of Figure 5 is proportional to the applied current, so in Figure 5, the plots on the right show performance at higher current values ​​(high rates). As shown in Figure 5, it was found that the thinner the thickness of the positive and negative electrode bases, for example, the closer it is to 50 μm, the higher the energy density at high rates can be, which is preferable. Although the energy density at high rates in experimental examples 11-13 is lower than in experimental example 5, it was inferred that a higher energy density can be obtained compared to examples where the thickness of the positive and negative electrode bases is the same as in experimental examples 11-13, but the width of the positive and negative electrode comb teeth is less than 110 μm or more than 250 μm, or where the width of the positive and negative electrode comb teeth is different.

[0040] [Table 1]

[0041] [Table 2] [Industrial applicability]

[0042] This disclosure is applicable to the field of energy storage devices. [Explanation of Symbols]

[0043] 10 Energy storage device, 20 Positive electrode, 22 Positive electrode base, 23 Main surface, 24 Positive electrode comb teeth, 25 Comb grooves, 26 Positive electrode end comb teeth, 27 Surface, 30 Negative electrode, 32 Negative electrode base, 33 Main surface, 34 Negative electrode comb teeth, 35 Comb grooves, 36 Negative electrode end comb teeth, 37 Surface, 40 Separation membrane, 42 Positive electrode current collector, 44 Negative electrode current collector, W, wp, wxp, wn, wxn width, T, tp, tn, ts thickness, hp, hn height, D depth.

Claims

1. A positive electrode containing a positive electrode active material, having a comb-like structure in which multiple positive electrode comb teeth protrude from the main surface of a plate-shaped positive electrode base at intervals from each other, A negative electrode comprising a negative electrode active material, having a comb-tooth structure in which a plurality of negative electrode comb teeth protrude from the main surface of a plate-shaped negative electrode base at intervals from each other, wherein the negative electrode comb teeth are staggered with the positive electrode comb teeth, and the tips of the negative electrode comb teeth face the main surface of the positive electrode base, and the main surface of the negative electrode base faces the tips of the positive electrode comb teeth, The system comprises an ion-conducting medium interposed between the positive electrode and the negative electrode, which conducts carrier ions, In a cross-section perpendicular to the direction of extension of the comb grooves between the comb teeth of the aforementioned comb structure, if the dimension in the direction parallel to the main surface is defined as the width, then the width of the positive electrode comb tooth and the width of the negative electrode comb tooth are the same value, between 170 μm and 190 μm, and are constant from the base to the tip. Energy storage device.

2. The energy storage device according to claim 1, wherein, in the cross-section, if the dimension perpendicular to the main surface is defined as the thickness, the thickness of the positive electrode base is 40 μm or more and 60 μm or less, and the thickness of the negative electrode base is 40 μm or more and 60 μm or less.

3. The energy storage device according to claim 1 or 2, wherein the negative electrode has the same volume as the positive electrode.

4. A power storage device according to claim 1 or 2, A positive electrode current collector electrically connected to the positive electrode, A negative electrode current collector electrically connected to the negative electrode, A power storage device equipped with [a specific feature / ability].

5. The energy storage device according to claim 1 or 2, wherein the carrier ion is a lithium ion.

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