JP7500928B2 - Electrode structure, secondary battery, and method for manufacturing electrode structure - Google Patents

Description

This specification discloses an electrode structure, a secondary battery, and a method for manufacturing the electrode structure.

Conventionally, as a secondary battery of this type, a separator having ion conductivity is arranged between a pair of electrodes having an active material layer, and a porous insulating layer having ion conductivity is arranged at least on one side between the separator and the electrode (see, for example, Patent Document 1). In this secondary battery, the separator has a shutdown function when the temperature of the battery rises abnormally, and even if the temperature rises further and the resin melts and becomes fluid, it is possible to prevent a short circuit between the positive electrode and the negative electrode. In addition, as a secondary battery, a positive electrode mixture layer or a negative electrode mixture layer formed of electrode mixture particles formed by granulating an electrode active material and a binder on at least one of the current collectors of the positive electrode plate and the negative electrode plate has been proposed, and a separator particle layer formed of separator particles formed by granulating polyolefin particles has been proposed between the positive electrode plate and the negative electrode plate (see, for example, Patent Document 2). It is said that this secondary battery can reduce the battery resistance while reducing costs. Furthermore, a separatorless battery has been proposed as a secondary battery, which has an electrode body having an insulating layer containing amino acids, ceramic particles and a binder on at least one of the surfaces of the positive electrode facing the negative electrode and the negative electrode facing the positive electrode, and a non-aqueous electrolyte layer, and the non-aqueous electrolyte layer is in direct contact with the positive electrode, the negative electrode or the insulating layer on those surfaces, and does not have a separator between the positive electrode and the negative electrode (see, for example, Patent Document 3). It is said that this secondary battery can provide a battery with high long-term safety that can suppress thermal runaway even in an overcharged state.

JP 2006-351386 A JP 2014-41793 A JP 2018-156844 A

However, in the secondary batteries of Patent Documents 1 to 3, when an attempt is made to thin the separator or insulating layer in order to improve the battery output and energy density, there is a problem that Li dendrites grow in the pores or directly short-circuit through the pores. Meanwhile, in secondary batteries, a separator that exhibits ionic conductivity may be obtained by impregnating a nonporous polymer partition with an electrolyte to form a gel electrolyte. However, when impregnated with an electrolyte, the nonporous polymer partition swells, which can cause the electrode body to deform.

The present disclosure has been made in consideration of these problems, and has as its main objective the provision of an electrode structure, a secondary battery, and a method for manufacturing an electrode structure that can further suppress the expansion of the separation membrane and further improve battery performance.

After extensive research to achieve the above-mentioned objective, the inventors discovered that adding a certain amount of ceramic particles to a non-porous separation membrane can further suppress the expansion of the separation membrane and improve the ionic conductivity and capacity, leading to the completion of the invention disclosed in this specification.

That is, the electrode structure disclosed in the present specification is
A columnar first electrode containing an active material;
A separation membrane that is non-porous and contains a resin having ion conductivity and insulation properties, covers the first electrode, and contains ceramic particles in an amount of 5% by mass to 70% by mass.
It is equipped with the following:

The secondary battery disclosed in this specification is
The electrode structure described above;
a second electrode that is disposed between the first electrodes via the separation membrane and contains an active material;
It is equipped with the following:

The method for producing an electrode structure disclosed in the present specification includes the steps of:
The method includes a forming step of forming a membrane containing a resin having ion conductivity and insulation properties and containing ceramic particles in a range of 5% by mass to 70% by mass on the outer periphery of a columnar first electrode containing an active material, and heating and melting the membrane to form a nonporous separation membrane on the surface of the first electrode.

The present disclosure can further improve battery performance by further suppressing the expansion of the separation membrane and improving ionic conductivity and discharge capacity. The reason for this effect is believed to be as follows. For example, it is believed that when ceramic particles are added within a specified range of addition amount, the skeleton formed by the ceramic particles suppresses the decrease in ionic conductivity while suppressing the swelling of the resin.

FIG. 1 is a schematic diagram showing an example of a secondary battery 10. FIG. 4 is a schematic diagram showing an example of a secondary battery 10B. 3A to 3C are explanatory diagrams showing an example of a manufacturing process for a secondary battery 10 including an electrode structure 20. FIG. 1 is a graph showing the relationship between the amount of alumina particles added and the ionic conductivity and the rate of increase in film thickness.

(Secondary battery)
The secondary battery of the present disclosure described in the embodiment includes an electrode structure including a first electrode and a separation membrane, and a second electrode. The electrode structure includes a columnar first electrode including an active material, and a separation membrane that is non-porous, includes a resin having ion conductivity and insulation properties, covers the first electrode, and includes ceramic particles in a range of 5% by mass to 70% by mass. The second electrode is present between a plurality of first electrodes via the separation membrane and includes an active material. Here, it is preferable that the first electrode is a negative electrode and the second electrode is a positive electrode, but the first electrode may be a positive electrode and the second electrode may be a negative electrode. In addition, the term "columnar" includes not only those with a thickness that does not bend, but also those with a fibrous thickness that can be bent. The first electrode may be columnar, and the cross section may be circular or polygonal. The second electrode may be present around the first electrode, or may be filled in the space between the first electrodes. In addition, the secondary battery may have a structure in which a plurality of negative electrodes are bound together in a state adjacent to the positive electrode via a separation membrane. This secondary battery may contain an electrolyte in one or more of the first electrode, the second electrode, and the separator. In addition, the positive electrode and the negative electrode may have a current collecting member such as a current collecting wire embedded therein, or may not have such a current collecting member. For ease of explanation, the following description will be given mainly as an example of a lithium secondary battery in which the first electrode is the negative electrode, the second electrode is the positive electrode, and lithium ions are used as the carrier.

Next, the secondary battery disclosed in this embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a secondary battery 10. FIG. 2 is a schematic diagram showing an example of a secondary battery 10B. As shown in FIG. 1, the secondary battery 10 includes a negative electrode 11 as a first electrode, a negative electrode current collector 12, a separation membrane 15, a positive electrode 16 as a second electrode, and a positive electrode current collector 17. The electrode structure 20 is composed of the negative electrode 11 and the separation membrane 15. This secondary battery 10 includes a negative electrode 11 made of a columnar negative electrode active material, and a positive electrode 16 made of a positive electrode active material layer formed around the negative electrode 11 through the separation membrane 15. This secondary battery 10 has a structure in which a plurality of negative electrodes 11 are bound together with the separation membrane 15 and the positive electrode 16 interposed therebetween. In addition, this secondary battery 10 may have a structure in which 50 or more negative electrodes 11 are bound together. The secondary battery 10B has an electrode structure 20 having a columnar negative electrode 11 and a separation membrane 15 formed on the surface of the negative electrode 11, and a positive electrode 16 is filled between the multiple electrode structures 20.

The negative electrode 11 is a columnar material containing an active material. In this secondary battery 10, multiple columnar negative electrodes are arranged in a predetermined direction. The outer periphery of the negative electrode 11, except for the end faces, faces the positive electrode 16 via a separation membrane 15. For example, the negative electrode 11 may have a capacity of 1/n of the negative electrode capacity of the entire cell, and n pieces may be connected in parallel to the negative electrode current collector 12. The negative electrode 11 preferably has a diameter D of 10 μm or more in a cross section perpendicular to the longitudinal direction, more preferably 15 μm or more, and may be 30 μm or more. The diameter D of the negative electrode 11 is preferably 800 μm or less, more preferably 500 μm or less, and may be 400 μm or less. When the diameter D is 10 μm or more, the strength of the electrode structure can be ensured, and stable charging and discharging can be performed. When the diameter D is 800 μm or less, the movement distance of the carrier ions is not too long, and high output performance can be obtained. In addition, when the diameter D is in the range of 10 to 500 μm, the energy density per unit volume can be increased. Alternatively, in this range, the moving distance of the carrier ions can be shortened, and charging and discharging can be performed with a larger current. The length of the columnar body in the longitudinal direction can be appropriately determined depending on the application of the secondary battery, and may be, for example, in the range of 20 mm to 200 mm. When the length of the columnar body is 20 mm or more, the battery capacity can be increased, and when it is 200 mm or less, the electrical resistance of the negative electrode can be reduced, which is preferable. The negative electrode may contain a carbon material as a negative electrode active material. Examples of the carbon material include one or more of graphites, cokes, glassy carbons, non-graphitizable carbons, and pyrolytic carbons. Among these, graphites such as artificial graphite and natural graphite are preferable. In addition, carbon fibers having a graphite structure may be used. For example, such carbon fibers are preferably those in which the crystals are oriented in the longitudinal direction, which is the fiber direction. In addition, it is preferable that the crystals are oriented radially from the center to the outer peripheral surface when viewed in cross section in a direction perpendicular to the longitudinal direction (fiber direction). Alternatively, the columnar negative electrode may be a columnar body made of a complex oxide capable of absorbing and releasing carrier ions. Examples of the complex oxide include lithium titanium complex oxide and lithium vanadium complex oxide. This negative electrode may have a conductive component formed on at least a part of its surface. The conductive component can further increase the conductivity. The conductive component is not particularly limited as long as it is a highly conductive material, but it may be, for example, a metal.

The negative electrode collector 12 is a conductive member, and the end faces of the negative electrodes 11 are electrically connected to the negative electrode collector 12. 50 or more negative electrodes 11 are connected in parallel to the negative electrode collector 12. The negative electrode collector 12 can be made of, for example, carbon paper, aluminum, copper, titanium, stainless steel, nickel, iron, platinum, baked carbon, conductive polymer, conductive glass, or aluminum or copper whose surface is treated with carbon, nickel, titanium, silver, platinum, gold, or the like for the purpose of improving adhesion, conductivity, and oxidation (reduction) resistance. The shape of the negative electrode collector 12 is not particularly limited as long as it can connect multiple negative electrodes 11, and examples of the shape include plate, foil, film, sheet, net, punched or expanded, lath, porous, foam, and fiber group formation.

The separation membrane 15 has ion conductivity for the carrier ions (e.g., lithium ions) and insulates the negative electrode 11 from the positive electrode 16. The separation membrane 15 is formed on the entire outer peripheral surface of the negative electrode 11 facing the positive electrode 16, and prevents short-circuiting between the negative electrode 11 and the positive electrode 16. The separation membrane 15 includes a resin 21 having ion conductivity and insulating properties, and ceramic particles 22 that are not conductive (insulating). The separation membrane 15 may be formed, for example, by preparing a free-standing membrane from a raw material solution containing the resin 21 and the ceramic particles 22 and coating the surface of the negative electrode 11 with the free-standing membrane, or by immersing the negative electrode 11 in the raw material solution and coating the surface. Examples of the resin 21 of the separation membrane 15 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 case of a copolymer of PVdF and HFP, a part of the electrolyte swells and gels the membrane, forming an ion-conductive membrane. The thickness L of the separation membrane 15 is, for example, preferably 2 μm or more, more preferably 5 μm or more, and may be 8 μm or more. A thickness L of 2 μm or more is preferable in terms of ensuring insulation. In particular, a thickness of 2 μm or more of the separation membrane 15 is easy to manufacture. The thickness L of the separation membrane 15 is preferably 15 μm or less, more preferably 10 μm or less. A thickness L of 15 μm or less is preferable in terms of suppressing a decrease in ion conductivity and further reducing the volume occupied by the cell. A thickness L in the range of 2 to 15 μm is preferable in terms of ion conductivity and insulation.

The ceramic particles 22 form a skeleton inside the separation membrane 15. The ceramic particles 22 may be, for example, one or more of aluminum oxide (alumina), silicon oxide (silica), titanium oxide (titania), aluminum hydroxide oxide (boehmite), zirconium oxide (zirconia), silicon carbide, silicon nitride, etc. Among these, alumina, silica, titania, and boehmite are preferred, and alumina is more preferred. The average particle size of the ceramic particles 22 is preferably in the range of 0.4 μm to 4 μm, and more preferably in the range of 0.44 μm to 3.5 μm. The smaller the average particle size, the more improved the ion conductivity can be, and 1 μm or less is even more preferred. The average particle size can be determined by averaging the longest length of each particle using an image captured by a scanning electron microscope. The ceramic particles 22 are contained in the range of 5% by mass to 70% by mass of the entire resin. When the amount of ceramic particles 22 is 5% by mass or more, the increase in film thickness can be suppressed while suppressing the decrease in ion conductivity. Furthermore, when the amount of ceramic particles 22 is 70% by mass or less, the increase in film thickness can be further reduced and the decrease in ion conductivity can be suppressed. The amount of ceramic particles 22 added is more preferably 9% by mass or more, and even more preferably 20% by mass or more. Furthermore, the amount of ceramic particles 22 added is more preferably 67% by mass or less, and even more preferably 60% by mass or less.

The separation membrane 15 may contain an electrolyte that conducts ions, which are carriers. Examples of the electrolyte include non-aqueous solvents. Examples of the solvent for the electrolyte include solvents for non-aqueous electrolytes. Examples of the solvent include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which may be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; sulfolanes such as sulfolane and tetramethylsulfolane; and dioxolanes such as 1,3-dioxolane and methyldioxolane. The electrolyte may have dissolved therein a supporting salt containing ions that are carriers for the secondary battery 10. Examples of supporting salts include _LiPF6 , _LiBF4 , _{LiAsF6 , LiCF3SO3 ,} LiN( _CF3SO2 ) ₂ , LiC( _CF3SO2 ) ₃ , _LiSbF6 , _LiSiF6 , LiAlF4, _LiSCN , _LiClO4 , LiCl, LiF, LiBr, LiI _, and _LiAlCl4 . Among these, it is preferable from the _viewpoint of electrical properties to use a combination of _{one or} more salts selected from the group consisting of inorganic salts such as _LiPF6 , _LiBF4 , _LiClO4 , and organic salts such as _LiCF3SO3 , LiN( _CF3SO2 ) ₂ , LiC( _CF3SO2 ) ₃ . The concentration of this supporting salt in the 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.

The positive electrode 16 has a positive electrode active material and is formed on the outer periphery of the negative electrode 11 via a separation film 15. The positive electrode 16 may be formed to have a hexagonal cross-sectional shape that includes the columnar negative electrode 11 when the secondary battery 10 is produced (see FIG. 1). This shape is preferable because when the negative electrodes 11 with the positive electrode active material formed on the outer periphery are bound, the positive electrode 16 is easily filled between the negative electrodes 11. The positive electrode 16 may be formed between a plurality of negative electrodes 11, and is not limited to having a hexagonal outer shape as shown in FIG. 1. The positive electrode 16 may be conductive in itself, and a current collecting member may be omitted. The positive electrode 16 may be formed such that its end face is directly connected to the positive electrode current collector 17, or the positive electrode current collector is connected to the entire side surface. The positive electrode 16 may be formed, for example, by forming a separation film 15 on the outer periphery of the negative electrode 11, and then applying the raw material of the positive electrode 16 to the outer periphery.

The positive electrode 16 includes a positive electrode active material, but when the positive electrode active material does not have electrical conductivity, it may be formed by mixing, for example, a conductive material having electrical conductivity. The positive electrode 16 may be formed by mixing, for example, a positive electrode active material, and, if necessary, a conductive material and a binder. The positive electrode active material may be, for example, a material capable of absorbing and releasing lithium, which is a carrier. The positive electrode active material may be, for example, a compound having lithium and a transition metal, such as an oxide containing lithium and a transition metal element, or a phosphate compound containing lithium and a transition metal element. Specifically, lithium manganese composite oxides having a basic composition formula of Li _{(1-x) MnO2} (0≦x≦1, etc., the same applies below) or Li _{(1-x) Mn2O4 , etc.} , lithium cobalt composite oxides having a basic composition formula of Li _{(1-x) CoO2} , etc., lithium nickel composite oxides having a basic composition formula of Li _{(1-x) NiO2} , etc., lithium _cobalt nickel manganese composite oxides having a basic composition formula of Li _{(1-x) CoaNibMncO2} (a>0, _b >0, c>0, a+b+c=1), Li _{(1-x) CoaNibMncO4} ( ₀ <a<1, 0<b _{< 1 ,} 1≦c<2, a+b+c= ₂ ), etc., lithium vanadium composite oxides having a basic composition formula of _LiV2O3 , _etc. , ₅ , etc. can be used. In addition, a lithium iron phosphate compound having a basic composition formula of LiFePO ₄ , etc. can be used as the positive electrode active material. Among these, lithium cobalt nickel manganese composite oxides, such as LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.4 Co _0.3 Mn _0.3 O ₂ , are preferred. The term "basic composition formula" means that other elements, such as Al and Mg, may be included.

The conductive material contained in the positive electrode is not particularly limited as long as it is an electronically conductive material that does not adversely affect the battery performance, and can be, for example, a mixture of one or more of graphite such as natural graphite (scale graphite, flake graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.). The binder plays a role in connecting the active material particles and the conductive material particles to maintain a predetermined shape, and can be, for example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine rubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), etc., used alone or as a mixture of two or more. In addition, a cellulose-based aqueous binder or an aqueous dispersion of styrene butadiene rubber (SBR) can also be used.

In the positive electrode 16, the content of the positive electrode active material is preferably higher, and is preferably 70% by mass or more, and more preferably 80% by mass or more, relative to the total mass of the positive electrode 16. The content of the conductive material is preferably in the range of 0% by mass or more and 20% by mass or less, and more preferably in the range of 0% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode 16. In such a range, the decrease in battery capacity can be suppressed and sufficient conductivity can be imparted. In addition, the content of the binder is preferably in the range of 0.1% by mass or more and 5% by mass or less, and more preferably in the range of 0.2% by mass or more and 3% by mass or less, relative to the total mass of the positive electrode 16.

The positive electrode collector 17 is a conductive member and is electrically connected to the positive electrode 16. The end faces of 50 or more positive electrodes 16 are connected in parallel to the positive electrode collector 17. This positive electrode collector 17 may be made of the same material as the negative electrode collector 12.

In this secondary battery 10, the ion conductivity is preferably higher, but is preferably 0.1 mS/cm or more, more preferably 0.18 mS/cm or more, and even more preferably 0.2 mS/cm or more. If the ion conductivity is higher, the discharge capacity can be increased. In this secondary battery 10, the film thickness increase rate is preferably smaller, but is preferably 1.6 or less, more preferably 1.5 or less, and even more preferably 1.4 or less. If the film thickness increase rate is smaller, it is easier to maintain the structure of the positive electrode formed on its periphery. This film thickness increase rate is obtained by measuring the film thickness tb before the addition of the electrolyte and the film thickness ta after the addition of the electrolyte from an SEM observation image, and calculating ta/tb. In addition, in this secondary battery 10, the discharge capacity is preferably higher, but is preferably 0.16 mAh or more, more preferably 0.17 mAh or more, and even more preferably 0.18 mAh or more. In this case, the volumetric energy density of the secondary battery 10 is preferably higher, for example, 650 Wh/L or more, more preferably 830 Wh/L or more, and even more preferably 900 Wh/L or more.

In this secondary battery 10, the positive/negative electrode capacity ratio (negative electrode capacity/positive electrode capacity), which is the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material, is preferably in the range of 1.0 to 1.5, more preferably in the range of 1.2 or less. The thickness of the positive electrode is set appropriately according to the diameter of the negative electrode and the positive/negative electrode capacity ratio, but may be, for example, in the range of 5 μm to 50 μm. The thickness of the positive electrode refers to, for example, the maximum thickness of the portion formed on the negative electrode.

(Method of manufacturing secondary battery (electrode structure))
Next, a method for manufacturing a secondary battery (electrode structure) will be described. This manufacturing method may include a forming step and a second electrode fabricating step. In the forming step, a membrane containing a resin having ion conductivity and insulation properties and containing ceramic particles in the range of 5% by mass to 70% by mass is formed on the outer periphery of a columnar first electrode containing an active material, and is heated and melted to form a non-porous separation membrane on the surface of the first electrode. In the second electrode fabricating step, a second electrode is formed on the outer surface of the electrode structure. FIG. 3 is an explanatory diagram showing an example of a manufacturing process of a secondary battery 10 including an electrode structure 20, in which FIG. 3A is a separation membrane forming process, FIG. 3B is a heating process, FIG. 3C is a cutting process of the excess part, FIG. 3D is a shaping process of the excess part, FIG. 3E is an explanatory diagram of the electrode structure 20, and FIG. 3F is a second electrode fabricating step. The membrane as a raw material may be obtained by putting resin and ceramic particles into a solvent to form a slurry, applying it to a substrate, and drying it to obtain a self-supporting membrane of a predetermined thickness. The resin, ceramic particles, etc. may be appropriately used as described above. The solvent is preferably one capable of dissolving the resin, and examples thereof include N-methylpyrrolidone (NMP). The thickness of the film is preferably 2 μm or more, more preferably 5 μm or more, and may be 8 μm or more. The thickness of the film is preferably 15 μm or less, and more preferably 10 μm or less. The ceramic particles preferably have an average particle size in the range of 0.4 μm to 4 μm, and more preferably 0.44 μm to 3.5 μm. The first electrode may have a diameter in the range of 10 μm to 800 μm, for example. The amount of the ceramic particles 22 added is more preferably 9% by mass or more, and even more preferably 20% by mass or more. The amount of the ceramic particles 22 added is more preferably 67% by mass or less, and even more preferably 60% by mass or less.

In the separation membrane forming process, a coating jig 30 having a semicircular recess for accommodating the first electrode may be used (FIG. 3A). For example, the membrane as a raw material and the first electrode may be placed on the coating jig 30, and the first electrode may be covered with the membrane and then pressed with the coating jig 30. Then, the coating jig 30 may be heated by the heating unit 31 (FIG. 3B). The heating temperature is appropriately determined according to the characteristics of the resin contained in the membrane, and may be, for example, in the range of 100°C to 200°C or in the range of 120°C to 180°C. At this time, if a part of the membrane exists as an excess part, the excess part is cut off (FIG. 3C), and the excess part is aligned with the recess of the coating jig 30 and is heated again by the heating unit 31 together with the coating jig 30 (FIG. 3D). This reheating adjusts the outer peripheral surface of the separation membrane 15 (FIG. 3E). Then, a slurry containing the active material of the second electrode is coated on the surface of the separation membrane 15 to obtain a single cell (FIG. 3F). The second electrode may be appropriately configured as the positive electrode described above. In this manner, the electrode structure 20 and the secondary battery 10 can be produced.

The electrode structure 20 and secondary battery 10 described above can further improve battery performance by further suppressing the expansion of the separation membrane 15 and making the ionic conductivity and discharge capacity more favorable. The reason for such effects is presumed to be as follows. For example, it is presumed that when ceramic particles 22 are added within a specified addition amount range, the skeleton formed by the ceramic particles 22 suppresses the decrease in ionic conductivity while suppressing the swelling of the resin.

It goes without saying that the present disclosure is in no way limited to the above-described embodiments, and may be implemented in various forms as long as they fall within the technical scope of the present disclosure.

For example, in the above embodiment, the negative and positive electrodes of the secondary battery 10 are described as not including a current collecting member, but this is not particularly limited, and each electrode may have a current collecting member such as a current collecting wire embedded therein.

In the above-described embodiment, the carrier of the secondary battery is lithium ion, but is not limited thereto, and may be alkali metal ions such as sodium ions and potassium ions, or Group 2 element ions such as calcium ions and magnesium ions. The positive electrode active material may contain carrier ions. Although the electrolyte is a non-aqueous electrolyte, it may be an aqueous electrolyte.

In the above embodiment, the columnar negative electrode is described as being cylindrical, but is not limited thereto and may be in the shape of a square prism, a hexagonal prism, or the like.

In the above-described embodiment, a method for manufacturing a secondary battery 10 is used, but the second electrode fabrication process may be omitted and a method for manufacturing an electrode structure 20 may be used.

Below, specific examples of fabricating the above-mentioned secondary batteries are described as experimental examples. Experimental examples 3 to 6, 8 to 13, and 17 to 19 correspond to examples of the present disclosure, and experimental examples 1, 2, 7, and 14 to 16 correspond to comparative examples.

(Separation membrane of Experimental Example 1)
A self-supporting resin membrane (membrane to be a separation membrane) containing ceramic particles and having ion conductivity and insulation properties was prepared. First, polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) was mixed with N-methylpyrrolidone (NMP) and stirred overnight or more to dissolve the PVdF-HFP. The separation membrane of Experimental Example 1 was prepared using this.

(Separation membranes of Experimental Examples 2 to 7)
Alumina powder (Al ₂ O ₃ , manufactured by Sumitomo Chemical Co., Ltd.) having an average particle size of 0.44 μm as ceramic particles was mixed into N-methylpyrrolidone (NMP), and ultrasonic treatment was performed for 30 minutes to obtain a dispersion. Polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) was mixed into this dispersion, and the mixture was stirred overnight or more to dissolve PVdF-HFP in the dispersion. The amount of alumina was adjusted to 2 mass%, 9 mass%, 33 mass%, 50 mass%, 67 mass%, and 75 mass% relative to the total mass of alumina and PVdF-HFP, and these were used as separation membranes of Experimental Examples 2 to 7, respectively.

(Separation membranes of Experimental Examples 8 to 16)
The separation membranes of Experimental Examples 8 to 10 were prepared in the same manner as in Experimental Example 4, except that the alumina powders had an average particle size of 0.88 μm (manufactured by Sumitomo Chemical), 1.6 μm (manufactured by Sumitomo Chemical), and 3.5 μm (manufactured by Sumitomo Chemical) were used. The separation membranes of Experimental Examples 11 to 13 were prepared in the same manner as in Experimental Example 6, except that the alumina powders had an average particle size of 0.88 μm, 1.6 μm, and 3.5 μm were used. The separation membranes of Experimental Examples 14 to 16 were prepared in the same manner as in Experimental Example 7, except that the alumina powders had an average particle size of 0.88 μm, 1.6 μm, and 3.5 μm were used.

(Separation membranes of Experimental Examples 17 to 19)
The separation membrane of Experimental Example 17 was prepared in the same manner as in Experimental Example 4, except that titania powder (rutile type _TiO2 , manufactured by Nippon Aerosil) having an average particle size of 0.5 μm was used as the ceramic particles. The separation membrane of Experimental Example 18 was prepared in the same manner as in Experimental Example 4, except that silica powder ( _SiO2 , manufactured by Nippon Aerosil) having an average particle size of 0.8 μm was used as the ceramic particles. The separation membrane of Experimental Example 19 was prepared in the same manner as in Experimental Example 4, except that aluminum oxide hydroxide powder (AiOOH) having an average particle size of 0.8 μm was used as the ceramic particles.

(Preparation of electrode structure and evaluation cell)
The electrode structure was produced by the process shown in FIG. 3. First, the above-mentioned PVdF-HFP solution or ceramic particle-PVdF-HFP slurry was applied to a glass plate, and the NMP was dried to obtain a self-supporting resin film (separation film) having a thickness of 5 μm. A columnar carbon electrode having a diameter of 400 μm was wrapped in either of these resin films, and a columnar electrode/alumina-PVdF-HFP film integral was obtained by heat fusion at 150 ° C. (FIGS. 3A, B). Unnecessary resin films were cut off (FIG. 3C), and the surplus part was heat fused again at 150 ° C. to adjust the shape (FIG. 3D), and the outer periphery was dip-coated with a positive electrode paste, followed by drying to form a positive electrode composite layer having a thickness of 50 μm, thereby obtaining a columnar electrode structure. The positive electrode paste was prepared by weighing out LiNi1 _/ 3Co1 _{/3Mn1 / 3O2} as a positive electrode active material, carbon black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and PVdF binder as a binder in a mass ratio of 95:3:2 and dispersing them in water. The columnar electrode structure was immersed in a non-aqueous electrolyte solution overnight or more, and the separator impregnated with the non-aqueous electrolyte solution was sealed to prepare a columnar secondary battery as an evaluation cell. The non-aqueous electrolyte solution was a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30/40/30, in which _LiPF6 was dissolved at a concentration of 1M.

(Evaluation of separation membrane)
The ionic conductivity and the membrane thickness increase rate of the separation membrane were evaluated as follows. A predetermined amount of the above-mentioned PVdF-HFP or ceramic particle-PVdF-HFP slurry was weighed into a polytetrafluoroethylene petri dish, and NMP was evaporated to obtain a separation membrane having a thickness of 100 μm. This membrane was immersed in the above-mentioned electrolytic solution for 2 days or more. The membrane thickness before and after immersion was compared to calculate the membrane thickness increase rate (-). In addition, a measurement cell was prepared in which the separation membrane after immersion was sandwiched between two Ni electrodes, and the conductivity of the separation membrane was evaluated by an AC impedance method. The measurement cell prepared above was measured using an AC impedance analyzer (Agilent 4294A) at an open circuit voltage with an amplitude of ±500 mV, a frequency range of 1 Hz to 100 kHz, and a measurement temperature of 25 ° C., and the ionic conductivity (mS / cm) was calculated from the resistance between the current collectors.

(Evaluation of Evaluation Cells)
A charge/discharge test of the prepared columnar evaluation cell was carried out in a thermostatic chamber at 20° C. at a voltage range of 2 V to 4.2 V and a charge/discharge rate of 0.2 C. Charging was carried out in CCCV mode, and discharging was carried out in CC mode.

(Results and discussion)
Table 1 shows the type of ceramic particles, particle size (μm), addition ratio (mass%), conductivity of the separation membrane (mS/cm), membrane thickness increase rate (-), and discharge capacity (mAh) at the first cycle for Experimental Examples 1 to 19. FIG. 4 is a relationship diagram of the ionic conductivity (mS/cm) and membrane thickness increase rate (-) with respect to the addition amount of the separation membrane for Experimental Examples 1 to 8. As shown in Table 1 and FIG. 4, it was found that the membrane thickness increase rate decreases as the addition amount of the alumina particles increases, and the ionic conductivity increases as the addition amount of the alumina particles decreases. It was found that the addition amount of the alumina particles to this ion conductive polymer can achieve both high ionic conductivity and low membrane thickness increase rate in the range of 5 mass% to 70 mass%. It was also found that the addition amount is more preferably 9 mass% or more, and even more preferably 20 mass% or more. It was also found that the addition amount is more preferably 67 mass% or less, and even more preferably 60 mass% or less. It was also found that Experimental Examples 3 to 6 showed a higher discharge capacity than Experimental Example 1. In Experimental Example 1, it is presumed that the volume expansion of the separator is large, causing cracks in the positive electrode active material layer, and therefore, it is presumed that the discharge capacity is small in Experimental Example 1. In addition, in Experimental Example 7, which contains a large amount of alumina particles, it is presumed that the discharge capacity is reduced due to a decrease in ion conductivity.

In Experimental Examples 4, 8 to 10, the amount of alumina added as ceramic particles was 33 mass%, in Experimental Examples 6, 11 to 13, the amount of alumina added was 67 mass%, and in Experimental Examples 7, 14 to 16, the amount of alumina added was 75 mass%. In all of these cases, the conductivity tended to improve as the alumina particle size became smaller. In addition, when the amount added was between 33 mass% and 67 mass%, the discharge capacity showed a nearly constant value. On the other hand, it was found that the capacity decreased when the amount added was 75 mass%. In addition, even when titania, silica, or boehmite (AlOOH) was used as the ceramic particles, it was found that it was possible to achieve both high ion conductivity and a reduction in the film thickness increase rate by adding particles, regardless of the type of ceramic particles added. It was also found that the discharge capacity of the columnar (fibrous) electrode battery showed a higher value due to the effect of reducing the film thickness increase rate.

It goes without saying that the present disclosure is in no way limited to the above-mentioned embodiments, and may be implemented in various forms as long as they fall within the technical scope of the present disclosure.

10, 10B secondary battery, 11 negative electrode, 12 negative electrode current collector, 15 separation membrane, 16 positive electrode, 17 positive electrode current collector, 20 electrode structure, 21 resin, 22 ceramic particles, 30 coating jig, 31 heating unit.

Claims (10)

A columnar first electrode containing an active material;
A separation membrane that is non-porous and contains a resin having ion conductivity and insulation properties, covers the first electrode, and contains ceramic particles in a range of 5% by mass to 70% by mass ,
The electrode structure , wherein the separation membrane contains one or more of aluminum oxide, silicon oxide, titanium oxide, and aluminum oxide hydroxide as the ceramic particles . The electrode structure according to claim 1, wherein the separation membrane contains the ceramic particles in a range of 9% by mass to 67% by mass. The electrode structure according to claim 1 or 2, wherein the separation membrane contains the ceramic particles in a range of 20% by mass to 60% by mass. 4. The electrode structure according to claim 1, wherein the separator contains the ceramic particles having an average particle size in the range of 0.4 μm to 4 μm. 5. The electrode structure according to claim 1, wherein the separator contains the ceramic particles having an average particle size of 1 μm or less . 6. The electrode structure according to claim 1, wherein the separator contains the resin selected from the group consisting of polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer. The electrode structure according to any one of claims 1 to 6 , wherein the first electrode has a diameter D in the range of 10 µm to 800 µm. The electrode structure according to any one of claims 1 to 7 ,
a second electrode that is disposed between the first electrodes via the separation membrane and contains an active material;
A secondary battery comprising: The first electrode is a negative electrode,
The secondary battery according to claim 8 , wherein the second electrode is a positive electrode. a forming step of forming a membrane containing a resin having ion conductivity and insulation properties and containing ceramic particles in a range of 5% by mass to 70% by mass on the outer periphery of a columnar first electrode containing an active material, and then heating and melting the membrane to form a non-porous separator on the surface of the first electrode ;
The ceramic particles include one or more of aluminum oxide, silicon oxide, titanium oxide, and aluminum oxide hydroxide .