Battery and method for manufacturing the battery

Abstract

To improve the capacity of a battery, a carbon material being used as a negative electrode material of the battery.SOLUTION: Provided is a battery including a positive electrode, a separator, a negative electrode and an electrolyte, the positive electrode and the negative electrode being stacked via the separator. The negative electrode includes: a negative electrode mixture layer containing a negative electrode active material; and a negative electrode current collecting material containing at least one transition metal element selected from among transition metal elements belonging to group 9, group 10 and group 11 of the periodic table of elements. The negative electrode current collecting material is in contact with the opposite side of the positive electrode of the negative electrode mixture layer, and, in a contact area between the negative electrode and the separator, the ratio of area occupied by the transition metal element is 5% or less. The negative electrode active material contains a carbon material. The carbon material has a BET specific surface area of 900 m2 / g or more. The carbon material has an average pore diameter measured by the gas adsorption method of 0.5 nm or more and 5 nm or less. The electrolyte is an alkaline aqueous solution.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a battery and a method for manufacturing a battery.

Background Art

[0002] Currently, the lithium-ion battery has the highest energy storage density among secondary batteries. Lithium-ion batteries are used in portable devices, hybrid vehicles, electric vehicles, etc. In a lithium-ion battery, since the oxidation-reduction of lithium, which is the negative electrode active material, occurs at a very low potential, a high battery voltage can be obtained. On the other hand, lithium is extremely easily oxidized and generates a large amount of heat when oxidized. Also, since lithium is oxidized by contact with water, in a lithium-ion battery, an aqueous electrolyte cannot be used, and an organic solvent-based electrolyte must be used. However, the generally used organic solvent-based electrolyte is flammable.

[0003] Also, the charging of a lithium electrode is a reaction in which a solid precipitates from a solution, and needle-like precipitates called dendrites are likely to occur. These dendrites can cause a short circuit. For this reason, in a lithium-ion battery, the generation of dendrites is suppressed by intercalating the reduced lithium into the carbon layer. However, if the generation rate of this intercalation becomes fast due to charging at a large current, dendrites may precipitate on the carbon surface. Therefore, in a lithium-ion battery, it is necessary to avoid charging at a large current. In particular, at the end of charging, it is necessary to perform charging extremely slowly, so charging takes a relatively long time. Thus, in a lithium-ion battery, the cost of the entire system including auxiliary devices for carefully performing charge control, temperature detection, etc. is high, and the manufacturing cost for environmental control during manufacturing also increases. Also, the cost of battery disposal or recycling is relatively high. Furthermore, lithium has limited production areas where it can be efficiently mined, is not abundant in resources, and is expensive.

[0004] Therefore, it is desired to provide a battery that improves such demerits of lithium-ion batteries and has high performance. In particular, for large batteries for power storage such as natural energy and surplus power, and for in-vehicle use, etc., not only a high storage energy density, but also low cost, high safety, and ease of disposal or recycling are required. However, at present, there is no battery that fully satisfies these conditions.

[0005] As a typical secondary battery other than lithium-ion batteries, there is a nickel-hydrogen battery that uses a hydrogen storage alloy for the negative electrode. In a nickel-hydrogen battery, a non-flammable aqueous electrolyte can be used, and high safety can be ensured. However, since the battery voltage is low, the storage energy density of nickel-hydrogen batteries is considerably lower than that of lithium-ion batteries. In addition, the rare earth elements used in the hydrogen storage alloy of the negative electrode are expensive, the production volume is small, and the producing countries are limited, so there are also concerns about the stable supply of raw materials.

[0006] On the other hand, it is also possible to use iron as another type of negative electrode active material instead of the hydrogen storage alloy negative electrode of nickel-hydrogen batteries. Iron can be charged and discharged by the reactions shown in the following reaction formulas (1) and (2), respectively.

[0007] 〔Charging〕 Fe(OH)2 + 2e - → Fe + 2OH - ···(1) 〔Discharging〕 Fe + 2OH - → Fe(OH)2 + 2e - ···(2) It is also possible to use zinc as another type of negative electrode active material. Zinc can be charged and discharged by the reactions shown in the following reaction formulas (3) and (4), respectively.

[0008] 〔Charging〕 ZnO + H2O + 2e - → Zn + 2OH - ···(3) 〔Discharging〕 Zn + 2OH - → ZnO + H2O + 2e -···(4) Iron and zinc are inexpensive and abundant resources, and there are no problems with raw material supply, making them ideal materials as electrode active substances. In addition, an iron electrode exhibits a redox potential relatively close to that of a hydrogen storage alloy electrode, and since an aqueous electrolyte, which is an alkaline aqueous solution, can be applied in the same way as in a nickel-metal hydride battery, it is safe. On the other hand, since the electrode potential of zinc is more negative than the redox potential of hydrogen, water may be reduced thermodynamically and hydrogen may be generated. However, since the hydrogen overvoltage of zinc is high, an aqueous electrolyte, which is an alkaline aqueous solution, can actually be applied, so it is safe.

[0009] Also, in the case of reactions such as the above reaction formulas (1) and (2) for iron, and in the case of reactions such as the above reaction formulas (3) and (4) for zinc, each has two electrons that can be taken in and out per atom, and potentially has a large theoretical capacity. Therefore, there is also a possibility that the low voltage can be compensated by the large capacity.

[0010] Furthermore, although different from a pure battery, a hybrid capacitor that utilizes the electric double layer capacitance of a carbon material with a large specific surface area and uses it as a negative electrode has also been proposed. Carbon is also inexpensive and is a resource that exists abundantly anywhere on the earth. In addition, a capacitor electrode forms an electric double layer by arranging negative charges and positive charges at the solid-liquid interface between the electrode and the electrolyte, and a redox reaction of a substance does not occur. Therefore, since there is no specific redox potential for the capacitor electrode and there is a capacitance corresponding to an arbitrary potential, the potential can be adjusted and used within a range where hydrogen generation due to water reduction does not occur. Therefore, an aqueous electrolyte can be applied and it is safe. Furthermore, since there is no process of substance diffusion in the solid, the charge and discharge rate is extremely fast.

[0011] As described above, iron electrodes, zinc electrodes, and capacitor electrodes are originally ideal electrodes for secondary batteries in terms of price, safety, abundance of resources, large potential capacity, fast charge and discharge rate, etc. (for example, Patent Document 1: Japanese Patent Application Laid-Open No. 2006-080335).

[0012] However, since iron electrodes have low activity for charge-discharge reactions and low active material utilization rates, they are hardly put into practical use at present. Since iron oxides (hydroxides) have low solubility in alkaline aqueous solutions, in order for reactions such as the above reaction formulas (1) and (2) to proceed, large-sized oxygen ions, hydroxide ions, etc. need to move within the solid of the iron oxides (hydroxides). In iron oxides (hydroxides) that do not dissolve in the electrolyte and have a stable and dense structure, the substance movement speed is slow and the electrode activity becomes low. Therefore, it is particularly difficult for the reaction to penetrate deep inside the electrode, which is an aggregate of iron oxide (hydroxide) particles. Despite the large potential capacity, the utilization rate becomes low.

[0013] In addition, zinc electrodes are such that zinc in the oxidized state easily dissolves in the alkaline electrolyte in the form of zincate ions (Zn(OH)4 2- )). That is, the charge-discharge reaction of the zinc electrode occurs as a dissolution-precipitation reaction, and it is difficult to maintain the form of the electrode. There are problems such as zinc detaching from the electrode or dendrites of the generated metallic zinc penetrating the separator to cause a short circuit. Thus, since the form of the zinc electrode is unstable, sufficient durability cannot be obtained as a battery.

[0014] Furthermore, since capacitor electrodes use only the charges accumulated on the carbon surface, their capacity is significantly smaller than that of ordinary battery electrodes. There is a limit to increasing the specific surface area of carbon, and it is difficult to improve the electric double layer capacitance. Also, for the carbon material used for capacitor electrodes, it is necessary to use one with a large specific surface area such as activated carbon. However, carbon materials with a large specific surface area have a low bulk density and a large volume, and the capacity per unit volume (capacity density), which is important for practical use of the battery, becomes extremely small.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0016] The inventors of the present invention have found that by charging a battery using a capacitor electrode having a specific configuration in an alkaline electrolyte, a large amount of hydrogen generated by the reduction of water is adsorbed on carbon, accumulated as capacitance in the electrode, that is, the capacitance increases. Further, it has been found that the capacitance further increases when the capacitor electrode contains iron or zinc.

[0017] The present disclosure aims to improve the capacitance of a battery using a carbon material as a negative electrode material.

Means for Solving the Problems

[0018] 〔1〕 A battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are laminated via the separator, the negative electrode includes a negative electrode composite material layer containing a negative electrode active material and a negative electrode current collector containing at least one transition metal element selected from transition metal elements belonging to Groups 9, 10, and 11 of the periodic table, the negative electrode current collector is in contact with the negative electrode composite material layer on the side opposite to the positive electrode, in the contact region between the negative electrode and the separator, the proportion of the area occupied by the transition metal element is 5% or less, the negative electrode active material includes a carbon material, the carbon material has a BET specific surface area of 900 m 2 / g or more, the carbon material has an average pore diameter measured by a gas adsorption method of 0.5 nm or more and 5 nm or less, and the electrolyte is an alkaline aqueous solution.

[0019] 〔2〕 The battery according to 〔1〕, wherein the capacitance of the carbon material is 100 mAh / g or more. 〔3〕 The battery according to 〔1〕 or 〔2〕, wherein hydrogen atoms are adsorbed on the surface of the carbon material.

[0020] [4] The negative electrode composite material layer has at least one metal of iron and zinc, and a metal compound containing at least one metal of iron and zinc. In the battery according to any one of [1] to [3], at least a part of the metal and the metal compound is present on the inner surface of the pores of the carbon material.

[0021] [5] In the battery according to [4], the molar ratio of the metal atoms in the metal and the metal compound to the carbon atoms in the carbon material is 0.1 or more and 0.7 or less.

[0022] [6] A method for manufacturing a battery according to any one of [1] to [5], including a step of kneading the carbon material, the conductive material, and polytetrafluoroethylene, and molding a kneaded product bound by fibrillation of the polytetrafluoroethylene.

[0023] [7] In the method for manufacturing a battery according to [6], the mass ratio of the polytetrafluoroethylene to the kneaded product is 1% by mass or more and 20% by mass or less.

[0024] [8] A method for manufacturing a battery according to [4] or [5], including a step of immersing the carbon material in a solution containing at least one metal ion of iron ion and zinc ion, and adding an alkali to the solution while the metal ions are present on the inner surface of the pores of the carbon material.

[0025] [9] In the method for manufacturing a battery according to [8], the concentration of the metal ions in the solution is 1 mol / L or more.

[0026]

[10] After 3 hours or more have elapsed in a state where the carbon material is immersed in the solution, an alkali is added to the solution. The method for manufacturing a battery according to [8] or [9].

[0027] The method for manufacturing a battery according to any one of [8] to

[10] , wherein after irradiating ultrasonic waves in a state where the carbon material is immersed in the solution, an alkali is added to the solution.

[0028] By using a carbon material as described above as the negative electrode material of the battery, hydrogen generated by the reduction of water is not released as gas, but is adsorbed in a large amount on carbon and can be accumulated as capacitance in the electrode. This adsorbed hydrogen can also be reversibly discharged, redox capacitance is exhibited in addition to the electric double layer capacitance, and the capacitance of the battery is greatly increased. Since this adsorption of electrolytic hydrogen is realized by taking advantage of the property of strongly suppressing the release of hydrogen gas and the characteristic of carbon with a very large hydrogen overvoltage, it is necessary to eliminate the exposure of metal components with a small hydrogen overvoltage other than carbon in the contact region between the negative electrode and the separator.

[0029] On the other hand, as described above, a carbon material with a large specific surface area has a low bulk density and capacitance density. However, the presence of at least one metal of iron and zinc and a metal compound containing at least one metal of iron and zinc on the inner surface of the pores of the carbon material enables smooth charge and discharge, and the redox capacitance further increases.

Advantages of the Invention

[0030] According to the present disclosure, the capacitance of a battery using a carbon material as a negative electrode material can be improved.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

MODE FOR CARRYING OUT THE INVENTION

[0032] Hereinafter, embodiments in the present disclosure will be described. However, the following description does not limit the scope of the claims.

[0033] <Battery> The battery of the present disclosure can be used, for example, in batteries for portable devices, in-vehicle batteries, power storage batteries, etc. The battery may be a primary battery or a secondary battery.

[0034] FIG. 2 is a schematic diagram showing an example of the configuration of the battery of the present disclosure. The battery 60 includes an exterior body 50. The exterior body 50 is a cylindrical case. The exterior body 50 is made of metal. However, the exterior body 50 can have any form. The exterior body 50 may be, for example, a rectangular case. The exterior body 50 may be, for example, a pouch made of an aluminum laminate film or the like. The exterior body 50 may be, for example, made of resin.

[0035] The exterior body 50 houses the power storage element 40 and the electrolyte. The power storage element 40 includes a positive electrode 20, a negative electrode 10, and a separator 30. The illustrated power storage element 40 is of a wound type.

[0036] FIG. 1 is a schematic cross-sectional view showing an example of the power storage element of the present disclosure. The power storage element 40 may be, for example, of a laminated type. In the illustrated power storage element 40, the positive electrode 20 and the negative electrode 10 are laminated via the separator 30.

[0037] Negative Electrode The negative electrode 10 is in a sheet shape. The negative electrode 10 may have a thickness of, for example, 10 μm to 1 mm. The negative electrode 10 has a lower potential than the positive electrode 20. The negative electrode 10 includes a negative electrode composite material layer 12 containing a negative electrode active material and a negative electrode current collector containing at least one transition metal element selected from transition metal elements belonging to Group 9, Group 10, and Group 11 of the periodic table. The negative electrode current collector 11 is in contact with the side of the negative electrode composite material layer 12 opposite to the positive electrode 20. In the contact region between the negative electrode and the separator, the proportion of the area occupied by the transition metal element is 5% or less. The negative electrode active material includes a carbon material. The carbon material has a BET specific surface area of 900 m 2 / g or more and has an average pore diameter measured by the gas adsorption method of 0.5 nm or more and 5 nm or less.

[0038] The negative electrode composite material layer 12 contains the negative electrode active material as a main component, and the negative electrode active material includes a carbon material. Here, "containing as a main component" means, for example, that the content of the negative electrode active material is more than 50% by mass with respect to the total amount of the negative electrode composite material layer 12. The content rate of the negative electrode active material in the negative electrode composite material layer 12 is preferably 70% by mass or more, more preferably 80% by mass or more. The negative electrode active material may consist essentially of only a carbon material.

[0039] The carbon material is not particularly limited, but from the viewpoints of conductivity and hydrogen adsorption property, it is preferably a graphite-based material. Specifically, carbon black generally called activated carbon, graphene, carbon nanotubes, fullerenes, or a mixture thereof, etc., whose specific surface area is increased by activation treatment, can be mentioned, and activated carbon is mainly used. The carbon material may be in a state where a part of it is oxidized and may contain impurities. The content rate of the carbon material in the negative electrode composite material layer 12 is, for example, 70% by mass or more and 90% by mass or less, and preferably 75% by mass or more and 85% by mass or less.

[0040] The carbon material has a BET specific surface area of 900 m 2 / g or more. When the BET specific surface area of the carbon material is 900 m 2In the case of / g or more, a sufficient amount of capacity can be charged and discharged. The BET specific surface area of the carbon material is preferably 1000 m 2 / g or more, and more preferably 3000 m 2 / g or more.

[0041] The "BET specific surface area" in this specification refers to the specific surface area calculated by the BET multipoint method in the adsorption isotherm measured by the gas adsorption method. The adsorbate gas is nitrogen gas. For one measurement object, the BET specific surface area is measured 3 times or more. The arithmetic mean of the results of 3 times or more is regarded as the BET specific surface area of the measurement object.

[0042] The carbon material has an average pore diameter measured by the gas adsorption method of 0.5 nm or more and 5 nm or less. When the average pore diameter of the carbon material is less than 0.5 nm, the electrolyte is difficult to penetrate, and the function of the battery may deteriorate. When the average pore diameter of the carbon material exceeds 5 nm, the BET specific surface area becomes small and the charge-discharge capacity decreases. The average pore diameter of the carbon material is preferably 0.8 nm or more and 4 nm or less, and more preferably 1 nm or more and 3 nm or less.

[0043] The "average pore diameter" in this specification is obtained using the following formula (5). D = 4V / A ··· Formula (5) In the above formula (1), "D" represents the average pore diameter, "V" represents the total pore volume obtained by the gas adsorption method, and "A" represents the BET specific surface area. Also, the total pore volume V is obtained from the adsorption amount when the relative vapor pressure of the nitrogen adsorption isotherm is 0.990.

[0044] Hydrogen atoms are adsorbed on the surface of the carbon material. Atomic hydrogen generated by the reduction of water on the negative electrode surface either adsorbs on the negative electrode surface or forms hydrogen molecules and desorbs as hydrogen gas. On the surface of a material with a low hydrogen overvoltage, it is easy to desorb as hydrogen gas, and the desorbed gaseous hydrogen cannot contribute to an increase in the battery capacity. On the other hand, since carbon has a very high hydrogen overvoltage, the hydrogen adsorbed on carbon is difficult to desorb as gas and can contribute to an increase in the battery capacity. Also, when the pore diameter of carbon is small, it contributes to suppressing the desorption as hydrogen gas.

[0045] Since the negative electrode 10 smoothly transfers electrons to and from the carbon material and stably supports the structure of the electrode, the negative electrode 10 includes a metal negative electrode current collector 11. The negative electrode current collector 11 contains at least one transition metal element selected from transition metal elements belonging to Groups 9, 10, and 11 of the Periodic Table of the Elements, and it is preferable to use nickel from the viewpoint of alkali resistance.

[0046] However, when the negative electrode 10 includes the negative electrode current collector 11, preferential desorption of hydrogen gas occurs from the transition metal portion during charging, and sufficient adsorption of hydrogen in the carbon material does not occur. Also, once desorbed, the hydrogen does not adsorb back to the negative electrode 10. Thus, it is necessary to suppress the exposure of the transition metal portion in the negative electrode 10, and particularly in the contact region between the negative electrode 10 and the separator 30, the proportion of the area occupied by the transition metal element needs to be 5% or less. This can be suppressed by providing the negative electrode current collector 11 on the side opposite to the positive electrode 20 of the negative electrode mixture layer 12.

[0047] The capacity of the carbon material of the present disclosure is 100 mAh / g or more, and may be 200 mAh / g or more. Here, "capacity" means the chargeable capacity of the electrode of the carbon material alone. The capacity can be obtained by charging the electrode of the carbon material alone in an alkaline electrolyte, determining the capacity other than the capacity accumulated in the electrode, i.e., the capacity used for hydrogen gas generation, by gas collection, and subtracting the capacity used for hydrogen gas generation from the total supplied electricity amount. Alternatively, simply, the charged capacitor electrode can be discharged once and determined as the capacity at an appropriate discharge cut-off potential (voltage).

[0048] The negative electrode composite layer 12 preferably has at least one metal of iron and zinc, and a metal compound containing at least one metal of iron and zinc, and at least a part of the metal and the metal compound is present on the inner surface of the pores of the carbon material. The presence of the metal and the metal compound in the pores of the carbon material in the negative electrode composite layer 12 increases the charge-discharge capacity. Further, it is preferable that all of the metal and the metal compound contained in the negative electrode composite layer 12 are present on the inner surface of the pores of the carbon material. Note that the negative electrode composite layer 12 may contain only one of the above metal or metal compound.

[0049] For the charge-discharge reactions of the above formulas (1) and (2) to proceed with respect to iron, large-sized oxygen ions, hydroxide ions, etc. need to move within the iron oxide (hydroxide). However, the substance movement speed is slow within the iron oxide (hydroxide) having a stable and dense structure, and it is difficult for the reaction to penetrate deep inside the iron oxide (hydroxide) particles of normal size. Therefore, if the carbon material has a pore diameter of 0.5 nm or more and 5 nm or less as in the present disclosure, the iron oxide (hydroxide) present on the inner surface of the pores of the carbon material has size constraints, and oxygen ions, hydroxide ions, etc. do not need to move over a long distance, so the charge-discharge reaction activity increases, and as a result, the charge-discharge capacity increases.

[0050] Also, as described above, the charge-discharge reaction of zinc occurs as a dissolution-precipitation reaction, and it is difficult to maintain the form of the electrode, and there are problems such as the detachment of zinc from the electrode and the generation of dendrites. However, as in the present disclosure, zinc present on the inner surface of the pores of the carbon material is less likely to dissolve and detach from the electrode even when oxidized by discharge. Further, even if it elutes, when it is reduced and precipitated by charging, it is again taken into the inner surface of the pores of the carbon material, and the possibility of precipitating outside the negative electrode or forming dendrites is reduced. Therefore, the charge-discharge capacity can be stably maintained, and as a result, the charge-discharge capacity increases.

[0051] The molar ratio of the metal atoms in the metal and metal compounds to the carbon atoms in the carbon material is preferably 0.1 or more and 0.7 or less. When the molar ratio of the metal atoms in the metal and metal compounds to the carbon atoms in the carbon material is less than 0.1, the charge-discharge capacity may not increase. Further, when the molar ratio of the metal atoms in the metal and metal compounds to the carbon atoms in the carbon material exceeds 0.7, the amount of metal that cannot enter the inner surface of the pores of the carbon material increases. As a result, in the case of iron, the charge-discharge capacity may decrease due to an increase in those with low charge-discharge activity, and in the case of zinc, problems such as detachment from the electrode and generation of dendrites may be caused.

[0052] Examples of the iron compound which is a metal compound include iron oxide and iron hydroxide, but are not limited thereto. For example, salts of iron and anions such as carbonate ions, and those containing water of hydration may also be used. Further, it may contain a metal element other than iron.

[0053] Examples of the zinc compound which is a metal compound include zinc oxide and zinc hydroxide, but are not limited thereto. For example, those containing water of hydration may also be used. Further, it may contain a metal element other than zinc.

[0054] The negative electrode composite material layer 12 of the present disclosure may contain a conductive material, a binder, etc. in addition to the carbon material. Since charge and discharge reactions require the transfer of electrons, the reaction activity can be improved by including a conductive material in the negative electrode composite layer 12. Examples of the conductive material include nickel, copper, graphite, etc. For nickel, copper, etc., it is necessary to be in a metallic state in order to function as a conductive material. Conductive agents of metals such as nickel and copper are conductive agents of transition metals belonging to Group 10 and Group 11 in the periodic table, and it is necessary to make the proportion of the area occupied in the contact region with the separator 5% or less based on the present disclosure. Graphite is not particularly limited as long as it has conductivity, and for example, carbon black, carbon nanotubes, graphene, etc. are also applicable. The content rate of the conductive material in the negative electrode composite layer 12 is, for example, 1% by mass or more and 20% by mass or less, and preferably 5% by mass or more and 15% by mass or less.

[0055] The binder binds the negative electrode active material and the negative electrode current collector. The binder can contain any component. Examples of the binder include styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), etc., and from the viewpoint of hydrogen adsorption property, it is preferably PTFE. The content rate of the conductive material in the negative electrode composite layer 12 is, for example, 1% by mass or more and 20% by mass or less, and preferably 5% by mass or more and 15% by mass or less.

[0056] The present disclosure is characterized by the negative electrode active material, and there are no particular restrictions on the positive electrode, separator, etc. combined with the negative electrode.

[0057] The negative electrode active material of the present disclosure can be applied to nickel-carbon batteries, nickel-iron (carbon) batteries, and nickel-zinc (carbon) batteries using nickel hydroxide as the positive electrode active material, manganese-carbon batteries, manganese-iron (carbon) batteries, and manganese-zinc (carbon) batteries using manganese oxide as the positive electrode active material, air-carbon batteries, air-iron (carbon) batteries, and air-zinc (carbon) batteries using oxygen in the air as the positive electrode active material, etc.

[0058] 《Electrolyte》 The electrolyte is an alkaline aqueous solution. The alkaline aqueous solution includes, for example, water and an alkali metal hydroxide dissolved in water. The alkali metal hydroxide may have a concentration of, for example, 1 to 20 mol / L. Examples of the alkali metal hydroxide include potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), etc.

[0059] 《Positive Electrode》 The positive electrode 20 is sheet-shaped. The positive electrode 20 may have a thickness of, for example, 10 μm to 1 mm. The positive electrode 20 has a higher potential than the negative electrode 10. The positive electrode 20 contains a positive electrode active material. The positive electrode active material may contain any components. Examples of the positive electrode active material include nickel hydroxide, manganese dioxide, silver oxide, etc.

[0060] The positive electrode 20 may consist essentially of only the positive electrode active material. In addition to the positive electrode active material, the positive electrode 20 may further contain a positive electrode current collector, a conductive material, a binder, etc. The positive electrode current collector may include, for example, a porous metal sheet, etc. The current collector is, for example, made of nickel.

[0061] The conductive material has electronic conductivity. The conductive material may contain any components. The conductive material may include, for example, carbon black, cobalt, cobalt oxide, etc. The blending amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. The binder binds the positive electrode current collector and the positive electrode active material. The binder may contain any components. The binder may include, for example, polyvinylidene fluoride (PVdF), etc. The blending amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.

[0062] 《Separator》 The separator 30 is in the form of a sheet. The separator 30 is disposed between the positive electrode 20 and the negative electrode 10. The separator 30 physically separates the positive electrode 20 and the negative electrode 10. The separator 30 may have a thickness of, for example, 20 to 500 μm. The separator 30 is porous. The separator 30 may include, for example, a stretched porous membrane, a nonwoven fabric, etc. The separator 30 is electrically insulating. The separator 30 may be made of, for example, polyolefin, polyphenylene sulfide (PPS), polyvinyl alcohol (PVA), etc.

[0063] <Method for manufacturing a battery> 《Manufacture of the negative electrode》 The negative electrode containing the carbon material of the present disclosure can be manufactured by the following general methods. For example, a paste containing a powder of a carbon material, a conductive material, and a binder (such as SBR latex, polyvinylidene fluoride, etc.) can be applied to a metal substrate such as a punching metal sheet or a metal mesh to produce a negative electrode.

[0064] Alternatively, a powder of a carbon material, a conductive material, and PTFE can be kneaded, and a kneaded product bound by fibrillation of PTFE can be formed into a sheet and combined with a metal substrate to produce a negative electrode. Since PTFE has high hydrophobicity and high affinity for hydrogen gas, it contributes to stabilizing the adsorbed hydrogen.

[0065] The mass ratio of PTFE to the kneaded product is, for example, 1% by mass or more and 20% by mass or less. When the mass ratio of PTFE to the kneaded product is less than 1% by mass, the binding property becomes insufficient. When the mass ratio of PTFE to the kneaded product exceeds 20% by mass, it causes a decrease in the conductivity of the electrode, reduces the active material filling amount, and thus reduces the capacity. The mass ratio of PTFE to the kneaded product is preferably 5% by mass or more and 15% by mass or less.

[0066] The negative electrode comprising the carbon material of the present disclosure, at least one metal of iron and zinc, and a metal compound containing at least one metal of iron and zinc can be manufactured by the following method. Immerse the carbon material in a solution containing at least one metal ion of iron ion and zinc ion, and add an alkali to the solution while metal ions are present on the surface inside the pores of the carbon material. At this time, as the solution containing iron ions, for example, a solution obtained by dissolving a salt of iron such as iron sulfate, iron chloride, or iron acetate in a solvent can be used. As the solution containing zinc ions, for example, a solution obtained by dissolving a salt of zinc such as zinc sulfate, zinc chloride, or zinc acetate in a solvent can be used. These salts are not particularly limited as long as they can be dissolved in a solvent. Further, the solvent needs to be one that can dissolve iron ions or zinc ions and can infiltrate into the pores of the carbon material. For example, water, alcohol, etc. can be used. When the solvent is alcohol or contains alcohol, infiltration into the pores becomes easy.

[0067] As the alkali, potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), ammonia (NH3), etc. can be used. When these alkalis are added to a salt of a metal, iron oxide, iron hydroxide, zinc oxide, zinc hydroxide, etc. are deposited inside the pores of the carbon material and immobilized on the surface inside the pores. Further, when sodium carbonate, potassium carbonate, etc. are added to the solution while iron ions are present inside the pores of the carbon material, iron carbonate is deposited and immobilized on the surface inside the pores. The alkali to be used is not particularly limited as long as a desired compound of iron or zinc is generated, and it may be added in a solid state or as a solution. Further, for example, a solution containing iron ions or zinc ions may be impregnated into carbon and then immersed in an alkali solution.

[0068] The concentration of the metal ions in the solution is preferably 1 mol / L or more. By doing so, the amount of metal present on the surface inside the pores of the carbon material can be increased.

[0069] Since the average pore diameter of the carbon material is small and it takes time for metal ions to sufficiently infiltrate into the pores, it is preferable to add an alkali to the solution after 3 hours or more have elapsed with the carbon material immersed in the solution. If the immersion time is less than 3 hours, the metal compound may precipitate outside the pores. In the case of an iron compound, it may not contribute to the capacity, and in the case of a zinc compound, there may be problems such as detachment from the negative electrode and dendrite formation.

[0070] Also, it is preferable to irradiate ultrasonic waves with the carbon immersed in the solution. By irradiating ultrasonic waves, the infiltration of metal ions into the pores can be promoted. The irradiation time of the ultrasonic waves is not particularly limited, but for example, it may be irradiated for 3 minutes or more.

[0071] Furthermore, by heating the solution with the carbon material immersed in it, the infiltration of metal ions into the pores can be promoted. The temperature of the solution may be heated to, for example, 30°C or higher and 100°C or lower.

[0072] 《Manufacture of the positive electrode》 The positive electrode can be manufactured by a general method. For example, a positive electrode can be formed by coating a positive electrode current collector with a positive electrode active material, a conductive material, and a binder.

[0073] 《Manufacture of the power storage element》 The power storage element can have any form. The power storage element may be, for example, a laminated type or a wound type. For example, a separator is prepared. One separator may be used, or two separators may be used. For example, a laminate can be formed by laminating a separator, a negative electrode, a separator, and a positive electrode in this order. In the case of a wound type, a power storage element can be formed by winding the laminate in a spiral shape.

[0074] 《Manufacture of the battery》 The manufacturing method of the battery includes manufacturing a battery including a power storage element and an electrolytic solution. For example, an exterior body is prepared, the power storage element is incorporated into the exterior body, and the electrolytic solution is injected to manufacture the battery.

Examples

[0075] Examples in the present disclosure will be described below. However, the following description does not limit the scope of the claims.

[0076] (Example 1) This example is an example of a battery using the above carbon material as a negative electrode active material.

[0077] As the carbon material, activated carbon (AP11 - 0010, electrode material for electric double - layer capacitor, manufactured by AT Electrodes Co., Ltd.) was used. The BET specific surface area of this activated carbon was 1100 ± 200 m 2 / g, and the average pore diameter was 1.8 nm. For the measurement of the BET specific surface area and the average pore diameter, a gas adsorption amount measuring device (BELSORP - MAX, manufactured by MicrotracBEL Corp.) was used (the same applies to the following examples and comparative examples).

[0078] Next, an electrode (negative electrode) was fabricated using this activated carbon as the negative electrode active material. Specifically, 84% by mass of activated carbon powder, 10% by mass of carbon black powder (Kishida Chemical), and 6% by mass of PTFE (Sigma - Aldrich) were kneaded, and the kneaded product bound by fibrillation of PTFE was formed into a circular sheet with a diameter of 20 mm. A nickel mesh (diameter 20 mm) as a negative electrode current collector was attached to one side of the circular sheet, and pressed at a pressure of 34 MPa to obtain a negative electrode. The mass of activated carbon contained in the negative electrode was 0.1 g.

[0079] The negative electrode thus produced was combined with a sulfonated polypropylene nonwoven fabric (circular, 23 mm in diameter) used in a normal nickel-hydrogen battery and a nickel hydroxide electrode (a nickel porous body filled with nickel hydroxide, disc-shaped, 20 mm in diameter) used in a normal nickel-hydrogen battery, and set in a commercially available battery container (Takumi Giken, flat cell). At this time, the negative electrode was set so that the surface with the nickel mesh was in contact with the opposite side (back side) of the positive electrode of the negative electrode composite layer, and there was no exposure of the nickel mesh in the contact area between the negative electrode and the separator. That is, in the contact area between the negative electrode and the separator, the proportion of the area occupied by nickel is 0%.

[0080] 0.3 mL of an alkaline electrolyte (KOH 27 wt%, NaOH 3 wt%, LiOH 1 wt%) was injected into the battery. The positive electrode capacity was about 35 mAh, and the positive electrode capacity was made excessive compared to the negative electrode capacity. In a practical battery, the positive electrode capacity is made less than the negative electrode capacity and the positive electrode capacity is dominant, but in this example, the positive electrode capacity was made excessive with respect to the negative electrode capacity so that the performance of the negative electrode could be directly manifested, and the negative electrode capacity was dominant. The battery was subjected to constant current charge and discharge at a current of 60 mA per 1 g of activated carbon mass in a thermostat at 25°C. The discharge cut-off voltage was set to 0.8 V.

[0081] (Example 2) As the carbon material, activated carbon was produced by alkali activation of petroleum coke. Specifically, it was produced by adding potassium hydroxide hydrate (about 15% water) 5 times the weight ratio of petroleum coke, mixing well, dehydrating at 400°C for 30 minutes, and then activating at 800°C for 100 minutes. The BET specific surface area of this activated carbon was 3000 m 2 / g, and the average pore diameter was 2.1 nm. Otherwise, the negative electrode and the battery were produced in the same manner as in Example 1, and a battery test was conducted.

[0082] (Example 3) As the carbon material, the same activated carbon as in Example 2 was used, and the negative electrode was fabricated in the same manner as in Example 1. However, the nickel mesh was placed at the center of the circular sheet to eliminate exposure in the contact area between the negative electrode and the separator, and to be on the side opposite to the positive electrode from both sides. Further, a copper lead wire coated with resin was attached to the nickel mesh, and the attachment part was also covered with resin to eliminate exposure in the contact area between the negative electrode containing the transition metal component and the separator. The negative electrode thus fabricated was immersed in a 30 mass% potassium hydroxide aqueous solution, and constant current charging was performed at a current of 60 mA per 1 g of the activated carbon mass in a constant temperature bath at 25°C with a nickel plate as the positive electrode. The hydrogen gas generated during charging was collected with a gas burette, and the capacity charged to the electrode was determined by subtracting the amount of electricity consumed for hydrogen gas generation from the total amount of electricity charged. Since almost no capacity is charged other than the activated carbon, the capacity charged to this electrode can be regarded as almost entirely the capacity charged to the activated carbon alone.

[0083] (Example 4) In this example, a battery was fabricated in which the negative electrode active material contains a carbon material and an iron compound, and at least a part of the iron compound is present in the pores of the carbon material. The same activated carbon as in Example 2 was immersed in an aqueous solution of iron(II) sulfate heptahydrate (Kishida Chemical) with a concentration of 1 mol / L. After immersion for 3 hours, a 3 mol / L aqueous sodium hydroxide solution was dropped into the above aqueous solution until the pH exceeded 10 to precipitate iron ions as iron oxide or iron hydroxide, and the solid content was filtered off, washed with warm water, and dried to fabricate the negative electrode active material. At this time, the molar ratio of iron atoms per 1 mol of the activated carbon was 0.2. Using the negative electrode active material thus fabricated, a negative electrode and a battery were fabricated in the same manner as in Example 1, and a battery test was conducted.

[0084] (Example 5) The negative electrode active material was fabricated in the same manner as in Example 4 except that the activated carbon was immersed for 30 minutes. Using the negative electrode active material thus fabricated, a negative electrode and a battery were fabricated in the same manner as in Example 1, and a battery test was conducted.

[0085] (Example 6) A negative electrode active material was prepared in the same manner as in Example 4, except that the activated carbon was immersed for 30 minutes and ultrasonic waves were irradiated for 3 minutes using an ultrasonic cleaner (AS ONE MCS-2, oscillation frequency 40 kHz) with the activated carbon immersed. Using the negative electrode active material thus prepared, a negative electrode and a battery were prepared in the same manner as in Example 1, and a battery test was conducted.

[0086] (Example 7) In this example, a battery was fabricated in which the negative electrode active material contains a carbon material and a zinc compound, and at least a part of the zinc compound is present in the pores of the carbon material. Activated carbon similar to that in Example 2 was immersed in an aqueous solution of zinc sulfate heptahydrate (Kishida Chemical) with a concentration of 1 mol / L. After immersion for 3 hours, a 3 mol / L aqueous sodium hydroxide solution was added dropwise to the above aqueous solution until the pH exceeded 10, and zinc ions were precipitated as zinc oxide or zinc hydroxide. The solid content was filtered off, washed with warm water, and dried to prepare the negative electrode active material. At this time, the molar ratio of zinc atoms per mole of activated carbon was 0.2.

[0087] A negative electrode was prepared in the same manner as in Example 1, except that the negative electrode active material thus prepared was used and a copper mesh (diameter 20 mm) plated with tin was used instead of a nickel mesh. A battery was prepared in the same manner as in Example 1, except that the inside of the negative electrode side of the battery container was plated with tin, and a battery test was conducted.

[0088] (Comparative Example 1) As Comparative Example 1, an example of a battery in which the negative electrode current collector is not in contact with the positive electrode of the negative electrode composite material layer is shown. As the carbon material, the same activated carbon as in Example 1 was used.

[0089] 90% by mass of activated carbon powder and 10% by mass of carbon black powder (Kishida Chemical) were mixed, and 1.5% by mass of carboxymethyl cellulose sodium salt (CMCNa salt) (Kishida Chemical) was added to this powder mixture to prepare a paste. At this time, the mixing ratio of the powder mixture and the CMCNa salt aqueous solution was 4:6 by mass. The paste was filled into a nickel porous body (Sumitomo Electric Industries, Celmex (R)) punched into a disk shape with a diameter of 20 mm, dried, and pressed at a pressure of 34 MPa to produce a negative electrode. The mass of activated carbon contained in the negative electrode was 0.06 g. Using the negative electrode thus produced, a battery was produced in the same manner as in Example 1, and a battery test was conducted. In addition, in the contact region between the negative electrode and the separator, the proportion of the area occupied by the nickel porous body was more than 5%.

[0090] (Comparative Example 2) As Comparative Example 2, a negative electrode and a battery were produced in the same manner as in Comparative Example 1 except that the same activated carbon as in Example 2 was used as the carbon material, and a battery test was conducted.

[0091] (Comparative Example 3) As Comparative Example 3, an example of a battery in which the negative electrode active material contains an iron compound but does not contain a carbon material is shown. The negative electrode active material was prepared by dropping a 3 mol / L aqueous sodium hydroxide solution into an aqueous solution of iron(II) sulfate heptahydrate (Kishida Chemical) with a concentration of 1 mol / L until the pH exceeded 10, precipitating iron ions as iron oxide or iron hydroxide, filtering off the solid content, washing with warm water, and drying.

[0092] Except for using the negative electrode active material thus produced, a negative electrode and a battery were produced in the same manner as in Example 1, and a battery test was conducted.

[0093] (Comparative Example 4) As Comparative Example 4, an example of a battery in which the negative electrode active material contains a zinc compound but does not contain a carbon material is shown. The negative electrode active material was prepared by dropping a 3 mol / L aqueous sodium hydroxide solution into an aqueous solution of zinc sulfate heptahydrate (Kishida Chemical) with a concentration of 1 mol / L until the pH exceeded 10, precipitating zinc ions as zinc oxide or zinc hydroxide, filtering off the solid content, washing with warm water, and drying.

[0094] Except for using the negative electrode active material produced in this way and using a copper mesh (diameter 20 mm) plated with tin instead of a nickel mesh, a negative electrode was produced in the same manner as in Example 1. Also, except for tin-plating the inside of the negative electrode side of the battery container, a battery was produced in the same manner as in Example 1, and a battery test was conducted.

[0095] In FIGS. 3(a) and (b), the results of the discharge voltage curves in the battery tests of Example 1 and 2 and Comparative Example 1 and 2 are shown. The capacity shown on the horizontal axis of FIG. 3 is a value obtained by converting the battery capacity per 1 g of the activated carbon as the negative electrode active material (the same applies to FIGS. 4 and 5).

[0096] From the results shown in FIG. 3, it can be seen that the batteries of Example 1 and 2 show a large capacity, and in Example 2, even when the discharge ends at 0.8 V, a large capacity of 100 mAh / g or more is shown.

[0097] In FIG. 4, the results of the discharge voltage curve discharged to 0 V in the battery test of Example 2 are shown. From the results shown in FIG. 4, it can be seen that in the battery of Example 2, the negative electrode, and thus the carbon material as the active material therein, shows a capacity of 200 mAh / g or more.

[0098] In FIG. 5, the measurement results of the capacity of the carbon material alone in the battery of Example 3 are shown. From the results shown in FIG. 5, it can be seen that the capacity charged into the carbon material alone is 200 mAh / g or more.

[0099] From the results of FIGS. 3 to 5, it can be seen that the battery of the present disclosure shows a large capacity and can reach a capacity of 100 mAh / g or 200 mAh / g or more. These capacities are much larger than the capacity due to the formation of the electric double layer, and since the capacity is greatly affected by the surface exposure of a metal with a smaller hydrogen overvoltage than the carbon material, the increase in the capacity of the battery in the present disclosure is considered to occur due to the hydrogen generated by the reduction of water being adsorbed on the carbon material.

[0100] Figure 6 shows the results of the discharge voltage curves in the battery tests of Examples 2, 4 to 6 and Comparative Example 3. The capacity shown on the horizontal axis of Figure 6 is the value obtained by converting the battery capacity into the capacity density per 1 cc of the battery volume (the same applies to Figure 7).

[0101] From the results in Figure 6, the battery containing the iron compound of Example 4 has a significantly improved capacity density compared to the battery without the iron compound of Example 2. It is considered that this has solved the problem that the capacity density is low due to the low bulk density of the activated carbon. Also, the battery containing only the iron compound of Comparative Example 3 has a significantly reduced capacity compared to the battery containing the activated carbon and iron compound of Example 4. From these results, it can be seen that a large capacity cannot be obtained with only the iron compound, and a large capacity can be obtained by the coexistence of the activated carbon and the iron compound.

[0102] In the batteries of Examples 4 and 5, the time for immersing the activated carbon in the solution containing iron ions is different, 3 hours and 30 minutes respectively. From the results in Figure 6, the battery of Example 5 has a significantly reduced capacity compared to the battery of Example 4. From this result, it can be seen that by increasing the immersion time, the iron ions are sufficiently infiltrated into the pores of the activated carbon, and the capacity increases.

[0103] In the batteries of Examples 5 and 6, whether or not ultrasonic waves are irradiated to the solution containing iron ions for 3 minutes while the activated carbon is immersed is different. From the results in Figure 6, the battery with ultrasonic irradiation of Example 6 has a significantly improved capacity compared to the battery without ultrasonic irradiation of Example 5. From this result, it can be seen that by performing ultrasonic irradiation, the infiltration of iron ions into the pores of the activated carbon is promoted, and the capacity increases.

[0104] Figure 7 shows the results of the discharge voltage curves in the battery tests of Examples 2, 7 and Comparative Example 4. From the results in Figure 7, the battery containing the zinc compound of Example 7 has a significantly improved capacity compared to the battery without the zinc compound of Example 2. From this result, it can be seen that a large capacity can be obtained by the coexistence of the activated carbon and the zinc compound.

[0105] In addition, the battery containing only the zinc compound of Comparative Example 4 shows almost the same capacity as the battery containing the activated carbon and zinc compound of Example 7. However, although the battery of Example 7 did not short-circuit due to repeated charge and discharge, the battery of Comparative Example 4 always short-circuited at the initial stage (the 2nd to 3rd charge and discharge cycles) when charge and discharge were repeated. In Comparative Example 4, it is considered that dendrites were generated and penetrated the separator. From this result, it can be seen that by infiltrating zinc ions into the pores of the activated carbon, a large capacity can be obtained without causing a short circuit.

[0106] The embodiments and examples disclosed this time are illustrative in all respects and not restrictive. The technical scope determined by the description of the claims includes all modifications within the meaning equivalent to the claims. The technical scope determined by the description of the claims includes all modifications within the scope equivalent to the description of the claims.

Description of Reference Numerals

[0107] 10 Negative electrode, 11 Negative electrode current collector, 12 Negative electrode composite material layer, 20 Positive electrode, 21 Positive electrode current collector, 22 Positive electrode composite material layer, 30 Separator, 40 Power storage element, 50 Exterior body, 60 Battery.

Claims

1. A battery comprising a positive electrode, a separator, a negative electrode, and an electrolytic solution, wherein the positive electrode and the negative electrode are laminated with each other via the separator, and the negative electrode includes a negative electrode composite material layer containing a negative electrode active material, and a negative electrode current collector containing at least one transition metal element selected from transition metal elements belonging to Groups 9, 10, and 11 of the periodic table, the negative electrode current collector is in contact with the positive electrode side of the negative electrode composite material layer, in a contact region between the negative electrode and the separator, a ratio of an area occupied by the transition metal element is 5% or less, the negative electrode active material includes a carbon material, The carbon material has a BET specific surface area of 900 m ２ / g or more, the carbon material has an average pore diameter measured by a gas adsorption method of 0.5 nm or more and 5 nm or less, a capacity of the carbon material is 100 mAh / g or more, and the electrolytic solution is an alkaline aqueous solution.

2. The battery according to claim 1, wherein a hydrogen atom is adsorbed on a surface of the carbon material.

3. The negative electrode composite material layer has at least one metal of iron and zinc, and a metal compound containing at least one metal of iron and zinc, and at least a part of the metal and the metal compound is present on an inner surface of pores of the carbon material.

4. The battery according to claim 3, wherein a molar ratio of metal atoms in the metal and the metal compound to carbon atoms in the carbon material is 0.1 or more and 0.7 or less.

5. A method for manufacturing a battery according to any one of claims 1 to 4, the method including a step of kneading the carbon material, a conductive material, and polytetrafluoroethylene, and molding a kneaded product bound by fibrillation of the polytetrafluoroethylene.

6. The method for manufacturing a battery according to claim 5, wherein a mass ratio of the polytetrafluoroethylene to the kneaded product is 1% by mass or more and 20% by mass or less.

7. A method for manufacturing a battery according to claim 3 or claim 4, the method including a step of immersing the carbon material in a solution containing at least one metal ion of iron ions and zinc ions, and adding an alkali to the solution in a state where the metal ions are present on an inner surface of pores of the carbon material.

8. The method for manufacturing a battery according to claim 7, wherein a concentration of the metal ions in the solution is 1 mol / L or more.

9. The method for manufacturing a battery according to claim 7 or claim 8, wherein after a lapse of 3 hours or more in a state where the carbon material is immersed in the solution, an alkali is added to the solution.

10. The method for manufacturing a battery according to any one of claims 7 to 9, wherein after irradiating ultrasonic waves in a state where the carbon material is immersed in the solution, an alkali is added to the solution.

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