Positive electrode for non-aqueous electrolyte battery, and non-aqueous electrolyte battery

Abstract

A positive electrode 5 for a non-aqueous electrolyte battery according to the present disclosure comprises: a positive electrode active material that contains a layered oxide; and industrial lignin. The industrial lignin includes, e.g., lignin sulfonate. The content ratio of the industrial lignin to the total of the positive electrode active material, an electroconductive assistant, a binder, and the industrial lignin is, e.g., within the range of 0.1-6.0 mass%.

Description

Positive electrode for non-aqueous electrolyte batteries and non-aqueous electrolyte batteries

[0001] This disclosure relates to a positive electrode for a non-aqueous electrolyte battery and a non-aqueous electrolyte battery.

[0002] The demand for non-aqueous electrolyte batteries, such as lithium-ion batteries, is increasing year by year. As described in Patent Documents 1 and 2, sodium-ion batteries are another example of non-aqueous electrolyte batteries.

[0003] Sodium-ion batteries have advantages such as a low risk of resource depletion and the potential for excellent input / output characteristics based on high ionic conductivity. Therefore, sodium-ion batteries are attracting attention as a next-generation battery to replace lithium-ion batteries. On the other hand, sodium-ion batteries have disadvantages such as poor cycle characteristics and low energy density.

[0004] International Publication No. 2010 / 109889, International Publication No. 2019 / 078965

[0005] The purpose of this disclosure is to provide a technology for improving the cycle characteristics of non-aqueous electrolyte batteries.

[0006] This disclosure provides a positive electrode for a non-aqueous electrolyte battery comprising a positive electrode active material containing a layered oxide and industrial lignin.

[0007] The technology described herein can improve the cycle characteristics of non-aqueous electrolyte batteries.

[0008] Figure 1 is a cross-sectional view of the positive electrode for a non-aqueous electrolyte battery in Embodiment 1. Figure 2 is a schematic cross-sectional view showing an example of a non-aqueous electrolyte battery in Embodiment 2. Figure 3A is an SEM image of the lignin sulfonate particles used in each embodiment. Figure 3B is an SEM image of the surface of the positive electrode in Embodiment 3.

[0009] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0010] (Embodiment 1) Figure 1 is a cross-sectional view of the positive electrode for a non-aqueous electrolyte battery in Embodiment 1. The positive electrode 5 for the non-aqueous electrolyte battery comprises a positive electrode current collector 5a and a positive electrode active material layer 5b. The positive electrode active material layer 5b is supported by the positive electrode current collector 5a. Hereinafter, the positive electrode 5 for the non-aqueous electrolyte battery may be simply referred to as "positive electrode 5".

[0011] As the positive electrode current collector 5a, a sheet or film made of a metallic material such as aluminum, aluminum alloy, stainless steel, titanium, or titanium alloy may be used. The sheet or film may be porous or non-porous. As the sheet or film, metal foil, metal mesh, etc., may be used. A carbon material may be coated on the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0012] The positive electrode active material layer 5b contains a positive electrode active material and industrial lignin. The positive electrode active material layer 5b may also contain other materials such as conductive additives and binders.

[0013] The inclusion of industrial lignin as an additive in the positive electrode active material layer 5b improves the cycle characteristics of a non-aqueous electrolyte battery using the positive electrode 5. Although the reason for this is not entirely clear, the inventors speculate as follows: Reactive oxygen species generated in the non-aqueous electrolyte during charging and discharging are absorbed by the industrial lignin, thereby suppressing the decomposition of the non-aqueous electrolyte. As a result, the cycle characteristics of the non-aqueous electrolyte battery are improved.

[0014] In this specification, "industrial lignin" means a compound that satisfies the following requirements: Industrial lignin has a lignin skeleton. The lignin skeleton includes a benzene ring, a hydroxyl group (-OH) bonded to the benzene ring, a methoxy group (-OCH3) bonded to the benzene ring, and a carbon chain bonded to the benzene ring. No functional group is present at the ortho position of the benzene ring, as viewed from the bonding position of the carbon chain. The carbon chain has a functional group containing an oxygen atom (O). No hydrogen atom is bonded to the oxygen atom in the functional group. Therefore, examples of industrial lignin include lignin sulfonates, soda lignin, organolignin, and soda anthraquinone lignin. One or more of these industrial lignins can be used.

[0015] The following formula (1) represents a partial structure of lignin sulfonate. The partial structure of lignin sulfonate includes a benzene ring, a carbon chain bonded to the benzene ring, a hydroxyl group bonded to the benzene ring, and a methoxy group bonded to the benzene ring. The carbon chain contains a hydroxyl group and a sulfo group (-SO3M). In formula (1), "lignin" represents the molecular chain of lignin. M represents the countercation.

[0016]

[0017] The following formula (2) represents a partial structure of soda lignin. The partial structure of soda lignin includes a benzene ring, a carbon chain bonded to the benzene ring, a hydroxyl group bonded to the benzene ring, and a methoxy group bonded to the benzene ring. The carbon chain contains a hydroxyl group and an ether group (-O-). In formula (2), "lignin" represents the molecular chain of lignin.

[0018]

[0019] The following formula (3) represents a partial structure of organolignin. The partial structure of organolignin includes a benzene ring, a carbon chain bonded to the benzene ring, a hydroxyl group bonded to the benzene ring, and a methoxy group bonded to the benzene ring. The carbon chain is an ester group (-COR 1 ), and alkoxy group (-OR 2 ) includes. In formula (3), "lignin" represents the molecular chain of lignin. 1 and R 2 These elements independently represent alkyl groups.

[0020]

[0021] The following formula (4) represents a partial structure of sodaanthraquinone lignin. The partial structure of sodaanthraquinone lignin includes a benzene ring, a carbon chain bonded to the benzene ring, a hydroxyl group bonded to the benzene ring, and a methoxy group bonded to the benzene ring. The carbon chain includes an ether group (-O-) and a hydroxyl group. n represents a natural number.

[0022]

[0023] Industrial lignin may contain lignin sulfonates. Lignin sulfonates are industrial lignin produced during the pulp manufacturing process and are readily available at low cost. Lignin sulfonates are industrial lignin produced during the pulp manufacturing process using the sulfite method.

[0024] The countercation of the lignin sulfonate includes, for example, at least one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, magnesium ions, and calcium ions. By selecting an appropriate countercation, the initial capacity of a non-aqueous electrolyte battery using the positive electrode 5 is improved. For example, when the positive electrode 5 is used in a sodium-ion battery, a sodium ion is suitable as the countercation of the lignin sulfonate. The sodium ions supplied from the lignin sulfonate compensate for the sodium deficiency in the positive electrode active material, and as a result, the initial capacity of the sodium-ion battery is improved. When the positive electrode 5 is used in a lithium-ion battery, for the same reason, a lithium ion is suitable as the countercation of the lignin sulfonate.

[0025] In the positive electrode active material layer 5b, the content ratio of industrial lignin to the total mass of the positive electrode active material, conductive additive, binder, and industrial lignin is, for example, in the range of 0.1% by mass or more and 6.0% by mass or less, preferably in the range of 2.5% by mass or more and 6.0% by mass or less, and more preferably in the range of 2.5% by mass or more and 5.0% by mass or less. When the industrial lignin content is within this range, it is possible to obtain the effect of improving cycle characteristics by industrial lignin while suppressing the decrease in discharge capacity that occurs with increasing industrial lignin content.

[0026] In this embodiment, the positive electrode active material includes a layered oxide. Layered oxides tend to exhibit high discharge capacity due to the insertion of metal ions into and the desorption of metal ions from the interlayers, making them suitable for the positive electrode 5 in this embodiment.

[0027] The layered oxide includes, for example, a material represented by the following formula (I). In formula (I), A is an alkali metal element. M1, M2 and M3 are mutually different elements, and are Mg, Ca, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn. x, y and z satisfy the relationship 0 < x + y + z ≦ 1.

[0028] AM1 x M2 y M3 z O2 ··· (I)

[0029] The alkali metal element is Li, Na, K, Rb or Cs, and typically Li or Na. When the layered oxide in which the alkali metal element in formula (I) is Na is contained in the positive electrode 5, it is more preferable that the positive electrode 5 contains industrial lignin. A layered oxide containing Na has lower structural stability than, for example, a layered oxide containing Li. When a layered oxide containing Na is used under a high voltage, structural distortion is likely to occur, and oxygen and active oxygen are likely to be generated. Therefore, by adding industrial lignin to the positive electrode 5 containing the layered oxide containing Na, a high effect of suppressing decomposition of the electrolytic solution due to active oxygen can be obtained.

[0030] When the layered oxide contains an alkali metal, the counter cation of the lignin sulfonate is preferably a cation of the same type of alkali metal as the alkali metal contained in the layered oxide. According to such a configuration, the initial capacity of the non-aqueous electrolyte battery using the positive electrode 5 is improved. This effect is presumed to result from the fact that defects in the positive electrode active material are compensated for by the counter cation of the lignin sulfonate.

[0031] The conductive auxiliary agent is used to reduce the resistance of the positive electrode 5. Examples of the conductive auxiliary agent include carbon materials, conductive polymer compounds, and the like. Examples of the carbon material include carbon black, graphite, carbon nanotubes, carbon nanofibers, graphene, fullerene, graphite oxide, and the like. Examples of the conductive polymer compound include polyaniline, polypyrrole, polythiophene, and the like. One type or a combination of two or more types selected from these may be used.

[0032] The binder is used to improve the binding property of the materials contained in the positive electrode 5. As the binder, polymeric materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, polypropylene, polyethylene, and polyimide can be used. One type selected from these or a combination of two or more types can be used.

[0033] The positive electrode 5 is manufactured by applying a positive electrode mixture to the positive electrode current collector 5a and drying the applied film. The positive electrode mixture is a slurry containing a positive electrode material and a solvent. Examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone (NMP). The O3-type layered oxide used in sodium-ion batteries decomposes upon contact with water. Therefore, an organic solvent is used for the positive electrode mixture. The positive electrode material is a mixture of a positive electrode active material, industrial lignin, a conductive auxiliary agent, and a binder.

[0034] The industrial lignin contained in the positive electrode material is in particulate form. When an organic solvent such as NMP is used in the positive electrode mixture, industrial lignin is hardly dissolved in the organic solvent. Therefore, particles of industrial lignin are distributed in the positive electrode 5. In addition, industrial lignin is also hardly dissolved in non-aqueous electrolytes. By the industrial lignin remaining in the positive electrode 5, the effect of improving cycle characteristics can be continuously obtained.

[0035] Industrial lignin has water-soluble properties. Here, "water-soluble" means the property of dissolving 3 g or more in 100 ml of water at 25°C.

[0036] The presence of industrial lignin particles in the positive electrode 5 can be confirmed by observing the surface or cross section of the positive electrode 5 using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). For example, lignin sulfonate contains sulfo groups. Therefore, it can be confirmed that the industrial lignin particles are contained in the positive electrode 5 by examining the distribution of sulfur atoms.

[0037] (Embodiment 2) Figure 2 is a cross-sectional view of a non-aqueous electrolyte battery according to one embodiment of the present disclosure. The non-aqueous electrolyte battery 100 comprises a container 1 and an electrode group 4. The electrode group 4 has a wound structure. The electrode group 4 is housed in the container 1. The electrode group 4 has a positive electrode 5, a negative electrode 6, and a pair of separators 7. The electrode group 4 is impregnated with a non-aqueous electrolyte. The opening of the container 1 is sealed with a sealing plate 2. The positive electrode 5 has a positive electrode current collector 5a and a positive electrode active material layer 5b. One end of a positive electrode lead 5c is connected to the positive electrode 5. The other end of the positive electrode lead 5c is connected to the back surface of the sealing plate 2. An insulating packing 3 is arranged around the sealing plate 2. The negative electrode 6 has a negative electrode current collector 6a and a negative electrode active material layer 6b. One end of a negative electrode lead 6c is connected to the negative electrode 6. The other end of the negative electrode lead 6c is connected to the bottom surface of the container 1. Insulating rings 8 are positioned on the upper and lower surfaces of the electrode group 4, respectively.

[0038] In this embodiment, the container 1 has negative polarity and the sealing plate 2 has positive polarity. However, the container 1 may have positive polarity and the sealing plate 2 may have negative polarity.

[0039] The non-aqueous electrolyte battery 100 is, for example, a lithium-ion battery or a sodium-ion battery. In particular, sodium-ion batteries are attracting attention as next-generation batteries, so there is high value in applying the technology of this disclosure.

[0040] The positive electrode 5 is the positive electrode for the non-aqueous electrolyte battery described in Embodiment 1.

[0041] As the negative electrode current collector 6a, a sheet or film made of a metallic material such as aluminum, aluminum alloy, stainless steel, nickel, nickel alloy, copper, or copper alloy may be used. The sheet or film may be porous or non-porous. As the sheet or film, metal foil, metal mesh, etc., may be used. A carbon material may be coated on the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0042] The negative electrode active material layer 6b contains a negative electrode active material capable of intercepting and releasing metal ions.

[0043] Examples of the negative electrode active material include carbon materials, elemental metals, alloys, metal oxides, sulfides, and the like. Examples of the carbon materials include artificial graphite, natural graphite, reduced graphene, graphene sheets, hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), activated carbon, and the like. Examples of the elemental metals include Sn, Bi, Sb, and the like. Examples of the alloys include Sn alloys, Pb alloys, Ni alloys, and the like. Examples of the metal oxides include titanium oxide, tin oxide, and the like. Examples of the titanium oxide include Na₂Ti₃O₇, Na₂Ti₆O 13 , Li₄Ti₅O 12 , TiO₂, and the like. Examples of the sulfides include WS₂, and the like. One or a combination of two or more selected from these may be used.

[0044] Among these, at least one selected from the group consisting of hard carbon, soft carbon, reduced graphene, Sn alloys, Pb alloys and Ni alloys is desirable from the viewpoint of metal ion storage capacity. These negative electrode materials can also occlude and release alkali metal ions other than lithium ions. The reduced graphene is a material obtained by reducing graphene oxide.

[0045] The negative electrode active material layer 6b may contain a conductive aid, a binder, and the like. As the conductive aid and the binder, the same materials as those usable for the positive electrode active material layer 5b can be used for the negative electrode active material layer 6b.

[0046] The nonaqueous electrolytic solution is impregnated into the positive electrode 5, the negative electrode 6 and the separator 7. The nonaqueous electrolytic solution may fill the internal space of the container 1. By the function of the nonaqueous electrolytic solution, metal ions can move back and forth between the positive electrode 5 and the negative electrode 6.

[0047] The nonaqueous electrolytic solution contains an electrolyte salt and a nonaqueous solvent. The electrolyte salt is dissolved in the nonaqueous solvent. The concentration of the electrolyte salt in the nonaqueous electrolytic solution is, for example, 0.5 mol / liter or more and 2.5 mol / liter or less.

[0048] Examples of cations in the electrolyte salt include alkali metal cations and alkaline earth metal cations. There may be one type of cation or two or more types. If the non-aqueous electrolyte battery 100 is a lithium-ion battery, the cation in the electrolyte salt may be a lithium ion. If the non-aqueous electrolyte battery 100 is a sodium-ion battery, the cation in the electrolyte salt may be a sodium ion.

[0049] As an anion in electrolyte salts, PF6 - TFSI - FSI - BF4 - , OTf - These are some examples. One or more combinations of these can be used.

[0050] The non-aqueous solvent includes, for example, at least one selected from the group consisting of esters, carbonates, ethers, and sulfolanes. One of these solvents may be used, or two or more may be used in combination.

[0051] The separator 7 is ion-permeable and is positioned between the positive electrode 5 and the negative electrode 6. The material of the separator 7 may be at least one selected from the group consisting of gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 7 is made of one of these materials, the safety of the non-aqueous electrolyte battery 100 can be sufficiently ensured. Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVDF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resin and porous membranes containing glass paper obtained by weaving glass fibers into a nonwoven fabric.

[0052] Container 1 is, for example, a metal container such as aluminum or stainless steel. Container 1 may have a cylindrical shape or a rectangular tube shape.

[0053] The electrode group 4 may be wound in a cylindrical shape or in an elliptical shape.

[0054] The shape of the non-aqueous electrolyte battery 100 is not limited to a cylindrical shape. Various shapes such as coin-shaped, prismatic, sheet-shaped, button-shaped, flat, and stacked can be used for the non-aqueous electrolyte battery 100.

[0055] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0056] (Technology 1) A positive electrode for a non-aqueous electrolyte battery comprising a positive electrode active material containing a layered oxide, industrial lignin, and

[0057] The technology described herein can improve the cycle characteristics of non-aqueous electrolyte batteries.

[0058] (Technology 2) The industrial lignin is a positive electrode for a non-aqueous electrolyte battery as described in Technology 1, comprising a lignin sulfonate. The lignin sulfonate is lignin produced during the pulp manufacturing process and is readily available at low cost.

[0059] (Technology 3) The positive electrode for a non-aqueous electrolyte battery according to Technology 2, wherein the countercation of the lignin sulfonate comprises at least one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, magnesium ions, and calcium ions. By selecting an appropriate countercation, the initial capacity of a non-aqueous electrolyte battery using the positive electrode is improved.

[0060] (Technical 4) A positive electrode for a non-aqueous electrolyte battery according to any one of Technical 1 to 3, further comprising a conductive additive and a binder, wherein the content ratio of industrial lignin to the total of the positive electrode active material, the conductive additive, the binder and the industrial lignin is in the range of 0.1% by mass or more and 6.0% by mass or less. When the content ratio of industrial lignin is in this range, it is possible to obtain the effect of improving cycle characteristics by industrial lignin while suppressing the decrease in discharge capacity that occurs with increasing industrial lignin content.

[0061] (Technical 5) The layered oxide comprises a material represented by the following formula (I), where A is an alkali metal element, M1, M2 and M3 are different elements, and are Mg, Ca, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn, and x, y and z satisfy the relationship 0 < x + y + z ≤ 1, the positive electrode for a non-aqueous electrolyte battery according to any one of Technical 1 to 4. Since layered oxides tend to exhibit high discharge capacity, they are suitable for the positive electrode of this disclosure. AM1 x M2 y M3 z O2...(I)

[0062] (Technical 6) A positive electrode for a non-aqueous electrolyte battery according to Technical 2, wherein the layered oxide contains an alkali metal, and the countercation of the lignin sulfonate is a cation of the same alkali metal as the alkali metal contained in the layered oxide. With such a configuration, the initial capacity of a non-aqueous electrolyte battery using the positive electrode is improved.

[0063] (Technical 7) A non-aqueous electrolyte battery comprising: a positive electrode according to any one of Technical 1 to 6; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0064] The technology described herein can improve the cycle characteristics of non-aqueous electrolyte batteries.

[0065] (Technology 8) The non-aqueous electrolyte battery described in Technology 7, wherein the non-aqueous electrolyte battery is a sodium-ion battery. Since sodium-ion batteries are attracting attention as next-generation batteries, there is high value in applying the technology of this disclosure.

[0066] (Technical 9) The non-aqueous electrolyte battery according to Technical 8, wherein the negative electrode comprises at least one selected from the group consisting of hard carbon, soft carbon, reduced graphene, Sn alloy, Pb alloy, and Ni alloy. These negative electrode materials can also intercalate and release alkali metal ions other than lithium ions.

[0067] (Technical 10) The non-aqueous electrolyte further comprises a non-aqueous solvent and an electrolyte salt, wherein the electrolyte salt contains sodium ions as cations and PF6 as an anion. - TFSI- FSI - BF4 - and OTf - A non-aqueous electrolyte battery according to any one of the Art 7 to 9, comprising at least one selected from the group consisting of, wherein the non-aqueous solvent comprises at least one selected from the group consisting of esters, carbonates, ethers and sulfolanes.

[0068] (Example 1) NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 A positive electrode slurry was prepared by mixing and stirring a positive electrode active material having an O2 composition, acetylene black (AB), polyvinylidene fluoride (PVDF), sodium ligninsulfonate (LSS, manufactured by Tokyo Chemical Industry Co., Ltd.), and N-methylpyrrolidone (NMP). The mass ratio of the positive electrode active material, AB, PVDF, and LSS was positive electrode active material:AB:PVDF:LSS = 91.9:4:4:0.1. The positive electrode slurry was applied to the surface of aluminum foil to form a coating film. The coating film was then dried and rolled. This obtained the positive electrode of Example 1.

[0069] A negative electrode slurry was prepared by mixing and stirring hard carbon, acetylene black (AB), carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), and water. The mass ratio of hard carbon, AB, CMC, and SBR was hard carbon:AB:CMC:SBR = 95:1:1.5:2.5. The negative electrode slurry was applied to the surface of aluminum foil to form a coating film. The coating film was then dried and rolled. This obtained the negative electrode.

[0070] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:EMC = 3:7 to obtain a mixed solvent. NaPF6 was dissolved in the mixed solvent at a concentration of 1 mol / liter to prepare a non-aqueous electrolyte.

[0071] The positive and negative electrodes were cut to predetermined sizes. An aluminum tab was welded to the positive electrode. A nickel tab was welded to the negative electrode. The positive electrode, a polypropylene separator, and the negative electrode were stacked to create an electrode assembly. The electrode assembly was placed in a container made of laminate film. A non-aqueous electrolyte was then poured into the container. The container was left to stand under a vacuum of 0.06 MPa for 15 minutes, and then the container was heat-sealed. This yielded the sheet-type sodium-ion battery of Example 1 (hereinafter sometimes simply referred to as "battery").

[0072] (Example 2) The battery of Example 2 was manufactured in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, AB, PVDF, and LSS was changed to positive electrode active material:AB:PVDF:LSS = 91:4:4:1.0.

[0073] (Example 3) The battery of Example 3 was manufactured in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, AB, PVDF, and LSS was changed to positive electrode active material:AB:PVDF:LSS = 89:4:4:3.0.

[0074] (Example 4) The battery of Example 4 was manufactured in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, AB, PVDF, and LSS was changed to positive electrode active material:AB:PVDF:LSS = 87:4:4:5.0.

[0075] (Examples 5 to 10) The batteries of Examples 5 to 10 were prepared in the same manner as in Example 3, except that the type of countercation in the lignin sulfonate was changed to Li, K, Rb, Cs, Mg, or Ca.

[0076] The lignin sulfonates used in Examples 5 to 10 were prepared by the following method: Ligninsulfonic acid (manufactured by Tomoe Industrial Co., Ltd.) was neutralized with an alkali metal salt or an alkaline earth metal salt. This yielded the lignin sulfonates used in Examples 5 to 10.

[0077] (Comparative Example 1) A battery of Comparative Example 1 was prepared in the same manner as in Example 1, except that lignin sulfonate was not used. The mass ratio of the positive electrode active material, AB, and PVDF was positive electrode active material:AB:PVDF = 92:4:4.

[0078] (Comparative Example 2) A pseudo-natural lignin having a structure similar to natural lignin was synthesized by subjecting lignin sulfonate to desulfonation, oxidation, hydrolysis, and demethylation treatment. The "pseudo-natural lignin" in Comparative Example 2 does not fall under the category of "industrial lignin" as described above.

[0079] The battery of Comparative Example 2 was prepared in the same manner as in Example 2, except that pseudo-natural lignin was used instead of lignin sulfonate.

[0080] [Charge and Discharge Test] The batteries of the examples and comparative examples were charged and discharged according to the following procedure, and their discharge capacity was measured. Charging and discharging were performed in an ambient atmosphere of 25°C. When a battery charged to a fully charged state of 4.0V was discharged at a constant current to a completely discharged state of 1.5V, the current value at which the discharge time was 1 hour was defined as "1C".

[0081] Constant current charging was performed at a current of 0.1C until the voltage reached 4.0V, and then constant voltage charging was performed at a voltage of 4.0V until the current reached 0.02C. After a 20-minute rest period, constant current discharge was performed at a current of 0.1C until the voltage reached 1.5V. The discharge capacity measured during the first charge and discharge was considered the "initial capacity".

[0082] After a 20-minute rest period, charging and discharging were repeated. The capacity retention rate after 48 cycles was calculated using the following formula (II). The results are shown in Table 1.

[0083] (Capacity maintenance rate) = 100 x C 48 / C1...(II) C1: Initial capacity C 48 : Discharge capacity at the 48th cycle

[0084]

[0085] As shown in Table 1, the capacity retention rates of the batteries in Examples 1 to 10 all exceeded those of the battery in Comparative Example 1.

[0086] As shown in the results of Examples 2 to 4, the initial volume increased with increasing lignin sulfonate content. In particular, the initial volumes of Examples 3 and 4 exceeded those of Comparative Example 1. Considering the initial volume, a lignin sulfonate content of 2.0% to 6.0% by mass is desirable, and 3.0% to 6.0% by mass is more desirable. However, increasing the lignin sulfonate content means decreasing other materials. Therefore, a lignin sulfonate content of 1.0% to 5.0% by mass is most desirable.

[0087] As shown in the results of Examples 3 and 5 to 10, the capacity retention rate could be further improved by selecting the counter-cation of the lignin sulfonate from lithium ions, sodium ions, potassium ions, rubidium ions, and cesium ions. Furthermore, the initial capacity of the battery was highest when the metal species of the counter-cation was Na. In other words, it is desirable to select the metal species of the counter-ion in the lignin sulfonate according to the type of battery, such as sodium-ion batteries, lithium-ion batteries, and magnesium-ion batteries.

[0088] The initial capacity and capacity retention rate of the battery in Comparative Example 2, which used pseudo-natural lignin as an additive, were lower than those of the battery in Comparative Example 1, which did not contain any additives. The reason why the effect was obtained with lignin sulfonate while the effect was not obtained with pseudo-natural lignin is thought to be due to the presence or absence of sulfo groups.

[0089] [Observation by Scanning Electron Microscope (SEM)] Figure 3A shows SEM images of the lignin sulfonate particles used in each example. The lignin sulfonate particles had a shape of micrometer size.

[0090] Figure 3B is a cross-sectional SEM image of the positive electrode of Example 3. The cross-section of the positive electrode of Example 3 contained particles 12 of the positive electrode active material and particles 14 of lignin sulfonate. The fact that particles 14 were lignin sulfonate particles was confirmed by energy-dispersive X-ray spectroscopy (EDX).

[0091] The technology disclosed herein is useful for non-aqueous electrolyte batteries.

Claims

1. A positive electrode for a non-aqueous electrolyte battery comprising a positive electrode active material containing a layered oxide, industrial lignin, and 2. The positive electrode for a non-aqueous electrolyte battery according to claim 1, wherein the industrial lignin comprises a lignin sulfonate.

3. The positive electrode for a non-aqueous electrolyte battery according to claim 2, wherein the countercation of the lignin sulfonate comprises at least one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, magnesium ions, and calcium ions.

4. A positive electrode for a non-aqueous electrolyte battery according to claim 1, further comprising a conductive additive and a binder, wherein the content ratio of the industrial lignin to the total of the positive electrode active material, the conductive additive, the binder and the industrial lignin is in the range of 0.1% by mass or more and 6.0% by mass or less.

5. The layered oxide comprises a material represented by the following formula (I): AM1 x M2 y M3 z O2...(I) where A is an alkali metal element, M1, M2 and M3 are different elements, and are Mg, Ca, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn, and x, y and z satisfy the relationship 0 < x + y + z ≤ 1, the positive electrode for a non-aqueous electrolyte battery according to claim 1.

6. The positive electrode for a non-aqueous electrolyte battery according to claim 2, wherein the layered oxide contains an alkali metal, and the countercation of the lignin sulfonate is a cation of the same alkali metal as the alkali metal contained in the layered oxide.

7. A non-aqueous electrolyte battery comprising: a positive electrode according to claim 1; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

8. The non-aqueous electrolyte battery according to claim 7, wherein the non-aqueous electrolyte battery is a sodium-ion battery.

9. The non-aqueous electrolyte battery according to claim 8, wherein the negative electrode comprises at least one selected from the group consisting of hard carbon, soft carbon, reduced graphene, Sn alloy, Pb alloy, and Ni alloy.

10. Further comprising a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt, wherein the electrolyte salt contains a sodium ion as a cation and PF6 as an anion. - TFSI - FSI - BF4 - and OTf - The non-aqueous electrolyte battery according to claim 7, comprising at least one selected from the group consisting of esters, carbonates, ethers, and sulfolanes, wherein the non-aqueous solvent comprises at least one selected from the group consisting of esters, carbonates, ethers, and sulfolanes.

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