Battery and method of manufacturing a battery

Abstract

The present application relates to a battery and a manufacturing method of a battery. A negative electrode of the battery includes a negative electrode mixture layer containing a negative electrode active material, and a negative electrode current collector 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, the negative electrode current collector being in contact with the opposite side of the negative electrode mixture layer with respect to a positive electrode, in a contact region of the negative electrode with a separator, the proportion of the area occupied by the transition metal element being 5% or less, the negative electrode active material containing a carbon material, the carbon material having a BET specific surface area of 900 m 2 / g or more, the carbon material having an average pore diameter of 0.5 nm or more and 5 nm or less as measured by a gas adsorption method, and an electrolyte of the battery being an alkaline aqueous solution.

Description

Technical Field

[0001] The present disclosure relates to batteries and methods of manufacturing batteries. Background Art

[0002] Currently, lithium-ion batteries have the highest energy storage density among secondary batteries. They are used in portable devices, hybrid vehicles, electric vehicles, and the like. In lithium-ion batteries, the redox reaction of lithium, the negative electrode active material, occurs at a very low potential, resulting in a high battery voltage. On the other hand, lithium is easily oxidized, and the heat released during oxidation is large. Furthermore, lithium is also oxidized by contact with water, so aqueous electrolytes cannot be used in lithium-ion batteries. Organic solvent electrolytes are required, but commonly used organic solvent electrolytes are flammable.

[0003] Furthermore, charging a lithium electrode involves the precipitation of solids from solution, which can easily produce needle-shaped precipitates called dendrites, which can cause short circuits. Therefore, in lithium-ion batteries, the formation of dendrites is suppressed by intercalating the lithium generated by reduction between carbon layers. However, when charging at high currents accelerates the rate of intercalation, dendrites may form on the carbon surface. Therefore, charging at high currents should be avoided in lithium-ion batteries. In particular, extremely slow charging is required at the end of charging, requiring a relatively long time. As a result, the overall system cost of lithium-ion batteries, including auxiliary equipment for precise charge control and temperature detection, is high, and manufacturing costs for environmental control during manufacturing also increase. Furthermore, the cost of discarding or reusing the batteries is relatively high. Furthermore, the efficient production of lithium is limited, the resource is scarce, and the price is high.

[0004] Therefore, there is a desire to provide high-performance lithium-ion batteries that mitigate the shortcomings of these batteries. In particular, large-scale batteries for storing electricity from natural energy, surplus electricity, and other sources, as well as for use in vehicles, require not only high energy density but also low cost, high safety, and ease of disposal and recycling. However, currently, there are no batteries that fully meet these requirements.

[0005] A representative secondary battery other than lithium-ion batteries is the nickel-metal hydride battery, which uses a hydrogen storage alloy in its negative electrode. Nickel-metal hydride batteries can use a non-flammable aqueous electrolyte, ensuring high safety. However, due to the low battery voltage, the stored energy density of nickel-metal hydride batteries is significantly lower than that of lithium-ion batteries. Furthermore, the rare earth elements used in the hydrogen storage alloy for the negative electrode are expensive, their production is low, and their production countries are limited, so there are concerns about the stable supply of raw materials.

[0006] On the other hand, iron can be used as another type of negative electrode active material to replace the hydrogen storage alloy negative electrode of nickel-hydrogen batteries. It should be noted that 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)

[0008] [Discharge]Fe+2OH - →Fe(OH)2+2e - ···(2)

[0009] Alternatively, zinc may be used 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.

[0010] [Charging] ZnO+H2O+2e - →Zn+2OH - ···(3)

[0011] [Discharge] Zn+2OH - →ZnO+H2O+2e - ···(4)

[0012] Iron and zinc are inexpensive and abundant resources, making them ideal as electrode active materials in terms of no raw material supply issues. Furthermore, iron electrodes exhibit a redox potential close to that of hydrogen storage alloy electrodes, making them safe for use in aqueous electrolytes such as alkaline aqueous solutions, similar to nickel-hydrogen batteries. On the other hand, zinc's electrode potential is lower than hydrogen's redox potential, so thermodynamically, there's a possibility that water will be reduced to produce hydrogen. However, zinc has a high hydrogen overvoltage, so it can actually be used in aqueous electrolytes such as alkaline aqueous solutions, making it safe.

[0013] In addition, in the case of reactions such as those in the above reaction formulas (1) and (2), and in the case of reactions such as those in the above reaction formulas (3) and (4), each atom of iron has two electrons that can enter and exit, and since they have potentially large theoretical capacities, it is also possible to use large capacities to compensate for low voltages.

[0014] Furthermore, unlike pure batteries, hybrid capacitors have been proposed that utilize the double-layer capacity of carbon materials with large specific surface areas and use them as negative electrodes. Carbon is also cheap and is a resource that is abundant everywhere on Earth. In addition, the capacitor electrodes form a double layer by arranging negative and positive charges at the solid-liquid interface between the electrode and the electrolyte, and do not cause redox reactions of substances. Therefore, capacitor electrodes do not have a specific redox potential. Since there is a corresponding capacitance at any potential, the potential can be adjusted to a range where hydrogen is not generated due to the reduction of water. Therefore, aqueous electrolytes can be used safely. Furthermore, since there is no diffusion process of substances in the solid, the charging and discharging speeds are extremely fast.

[0015] As described above, iron electrodes, zinc electrodes, and capacitor electrodes are ideal electrodes for secondary batteries from the perspectives of price, safety, resource abundance, potential capacity, and charge and discharge speed (e.g., Japanese Patent Application Laid-Open No. 2006-080335).

[0016] However, the iron electrode has low activity in charge and discharge reactions, and the utilization rate of active materials is also low, so the current situation is that it is almost not practical. Since the solubility of iron oxide (hydroxide) in alkaline aqueous solution is low, in order to carry out the reactions such as the above-mentioned reaction formulas (1) and (2), large-sized oxygen ions, hydroxide ions, etc. need to move in the solid of iron oxide (hydroxide). In the iron oxide (hydroxide) that does not dissolve in the electrolyte, is stable and has a dense structure, the movement speed of the material is slow, and the electrode activity becomes low. Therefore, it is particularly difficult for the reaction to penetrate deep into the interior of the electrode, which is an aggregate of iron oxide (hydroxide) particles. Although the potential capacity is large, the utilization rate becomes low.

[0017] In addition, in the case of zinc electrodes, oxidized zinc is easily converted to zincate ions (Zn(OH)4 2- ) dissolves in an alkaline electrolyte in a form such as . Specifically, the charge and discharge reactions of the zinc electrode occur as dissolution / precipitation reactions, making it difficult to maintain the electrode morphology. This can lead to problems such as zinc detaching from the electrode or the generated metallic zinc dendrites penetrating the separator and causing a short circuit. As a result, the unstable morphology of the zinc electrode prevents sufficient battery durability.

[0018] Furthermore, the capacitor electrode uses only the charge accumulated on the carbon surface, so the capacity is significantly smaller than that of a conventional battery electrode. There is a limit to increasing the specific surface area of ​​carbon, and it is difficult to improve the double-layer capacity. In addition, the carbon material used in the capacitor electrode needs to use a material with a large specific surface area such as activated carbon, but the volume density of the carbon material with a large specific surface area is low, the volume becomes larger, and the capacity per unit volume (capacity density) of the battery, which is important in practical applications, becomes significantly smaller. Summary of the Invention

[0019] The present inventors have discovered that by charging a battery using capacitor electrodes having a specific structure in an alkaline electrolyte, a large amount of hydrogen generated by water reduction is adsorbed on carbon and stored as capacitance within the electrode, thereby increasing the capacity. Furthermore, they have discovered that the capacity is further increased by including iron or zinc in the capacitor electrodes.

[0020] The present disclosure improves the capacity of a battery using a carbon material as a negative electrode material.

[0021] [1] A battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are stacked with the separator interposed therebetween.

[0022] The negative electrode comprises: a negative electrode composite 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.

[0023] The negative electrode current collector is in contact with the negative electrode composite layer on the opposite side to the positive electrode.

[0024] In the contact region between the negative electrode and the separator, the area ratio occupied by the transition metal element is 5% or less,

[0025] The negative electrode active material comprises a carbon material,

[0026] The carbon material has 900m 2 / g or more BET specific surface area,

[0027] The carbon material has an average pore diameter of 0.5 nm or more and 5 nm or less measured by a gas adsorption method,

[0028] The electrolyte is an alkaline aqueous solution.

[0029] [2] The capacity of the carbon material may be greater than 100 mAh / g.

[0030] [3] Hydrogen atoms can be adsorbed on the surface of the carbon material.

[0031] [4] The negative electrode composite layer may contain at least one metal selected from the group consisting of iron and zinc, and a metal compound containing at least one metal selected from the group consisting of iron and zinc, and at least a portion of the metal and the metal compound may be present on the inner surface of the pores of the carbon material.

[0032] [5] The molar ratio of the metal atoms in the metal and the metal compound to the carbon atoms in the carbon material may be 0.1 or more and 0.7 or less.

[0033] [6] The content of the carbon material in the negative electrode composite layer may be 70% by mass or more and 90% by mass or less.

[0034] [7] The content of the carbon material in the negative electrode composite layer may be 75% by mass or more and 85% by mass or less.

[0035] [8] The method for manufacturing a battery according to any one of [1] to [7] may include the following steps: kneading the carbon material, the conductive material, and polytetrafluoroethylene, and molding the kneaded product bonded by fibrillation of the polytetrafluoroethylene.

[0036] [9] The mass ratio of the polytetrafluoroethylene to the kneaded product may be 1 mass % or more and 20 mass % or less.

[0037]

[10] The method for manufacturing a battery according to [4] or [5] may include the following steps: 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 while the metal ions are present on the inner surfaces of the pores of the carbon material.

[0038]

[11] The concentration of the metal ions in the solution may be greater than 1 mol / L.

[0039]

[12] Alternatively, after the carbon material has been immersed in the solution for 3 hours or more, an alkali may be added to the solution.

[0040]

[13] Alternatively, the carbon material may be immersed in the solution and then irradiated with ultrasonic waves, and then a base may be added to the solution.

[0041] By using the aforementioned carbon material as the negative electrode material for the battery, hydrogen generated by water reduction does not escape as a gas, but is instead adsorbed in large quantities by the carbon, allowing it to be stored as capacity within the electrode. This adsorbed hydrogen can also be reversibly discharged, contributing to redox capacity in addition to double-layer capacity, significantly increasing the battery's capacity. This adsorption of electrolytic hydrogen is achieved by effectively utilizing the properties of carbon, which has a strong property of inhibiting hydrogen gas release and a very high hydrogen overvoltage. Therefore, it is necessary to prevent the exposure of metal components other than carbon, which have a low hydrogen overvoltage, in the contact area between the negative electrode and the separator.

[0042] On the other hand, as mentioned above, carbon materials with large specific surface areas have low volume density and capacity density. However, by having at least one metal of iron and zinc, or a metal compound containing at least one metal of iron and zinc, present on the inner surface of the pores of the carbon material, charge and discharge are facilitated, further increasing the redox capacity.

[0043] According to the present disclosure, the capacity of a battery using a carbon material as a negative electrode material can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0045] Figure 1 This is a schematic cross-sectional view showing an example of an electric storage element of the battery of the present disclosure.

[0046] Figure 2 This is a schematic diagram showing an example of the configuration of the battery of the present disclosure.

[0047] Figure 3 (a) is a graph showing discharge voltage curves of the batteries of Example 1 and Comparative Example 1.

[0048] Figure 3 (b) is a graph showing discharge voltage curves of the batteries of Example 2 and Comparative Example 2.

[0049] Figure 4 This is a graph showing a discharge voltage curve to 0V for the battery of Example 2.

[0050] Figure 5 This is a graph showing the results of measuring the capacity of the carbon material alone in the negative electrode of the battery of Example 3.

[0051] Figure 6 Graph showing discharge voltage curves of batteries of Examples 2, 4 to 6, and Comparative Example 3.

[0052] Figure 7 Graph showing discharge voltage curves of Examples 2 and 7 and Comparative Example 4. DETAILED DESCRIPTION

[0053] Hereinafter, embodiments of the present disclosure will be described. However, the following description does not limit the claims.

[0054] <Battery>

[0055] The battery disclosed herein can be used, for example, as a battery for portable devices, a battery for vehicle use, a battery for power storage, etc. The battery may be a primary battery or a secondary battery.

[0056] Figure 2 This is a schematic diagram showing an example of the configuration of the battery of the present disclosure.

[0057] The battery 60 includes an outer package 50. The outer package 50 is a cylindrical casing. The outer package 50 is made of metal. However, the outer package 50 can have any shape. For example, the outer package 50 can be a square casing. The outer package 50 can also be a bag made of aluminum laminate film, for example. The outer package 50 can also be made of resin, for example.

[0058] The outer package 50 houses the electricity storage element 40 and the electrolyte. The electricity storage element 40 includes a positive electrode 20, a negative electrode 10, and a separator 30. The illustrated electricity storage element 40 is a wound type.

[0059] Figure 1 This is a schematic cross-sectional view showing an example of the energy storage element of the present disclosure. The energy storage element 40 may be, for example, a laminated type. In the illustrated energy storage element 40 , a positive electrode 20 and a negative electrode 10 are laminated with a separator 30 interposed therebetween.

[0060] "negative electrode"

[0061] The negative electrode 10 is in sheet form. The negative electrode 10 can 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 comprises: a negative electrode composite 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 opposite side of the negative electrode composite layer 12 relative to the positive electrode 20. In the contact area 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 comprises a carbon material. The carbon material has 900 m 2 / g or more, and an average pore diameter measured by a gas adsorption method of 0.5 nm to 5 nm.

[0062] The negative electrode composite layer 12 contains a negative electrode active material as its main component, and the negative electrode active material comprises a carbon material. Here, "containing as its main component" means, for example, that the negative electrode active material content exceeds 50% by mass relative to the total amount of the negative electrode composite layer 12. The content of the negative electrode active material in the negative electrode composite layer 12 is preferably 70% by mass or greater, and more preferably 80% by mass or greater. The negative electrode active material may be composed essentially solely of a carbon material.

[0063] There are no particular restrictions on the carbon material, but graphite-based materials are preferred from the perspective of electrical conductivity and hydrogen adsorption. Specifically, carbon black, graphene, carbon nanotubes, fullerenes, or mixtures thereof, which are generally called activated carbons and have an increased specific surface area through activation treatment, can be cited, with activated carbon being primarily used. The carbon material may be partially oxidized or may contain impurities. The content of the carbon material in the negative electrode composite layer 12 is, for example, 70% by mass or more and 90% by mass or less, preferably 75% by mass or more and 85% by mass or less.

[0064] Carbon material has 900m 2 / g or more BET specific surface area. The BET specific surface area of ​​carbon materials is 900m 2 When the BET specific surface area of ​​the carbon material is preferably 1000 m 2 / g or more, more preferably 3000m 2 / g or above.

[0065] The term "BET specific surface area" as used herein refers to the specific surface area calculated using the BET multipoint method from an adsorption isotherm measured using a gas adsorption method. The adsorbate gas is nitrogen. The BET specific surface area is measured three or more times for each measurement object. The arithmetic average of these three or more measurements is considered the BET specific surface area of ​​the measurement object.

[0066] 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. When the average pore diameter of the carbon material is less than 0.5 nm, the electrolyte is difficult to penetrate, and the battery function may be reduced. When the average pore diameter of the carbon material exceeds 5 nm, the BET specific surface area decreases, 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.

[0067] The "average pore diameter" in this specification is determined using the following formula (5).

[0068] D=4V / A···Formula (5)

[0069] In the above formula (1), "D" represents the average pore diameter, "V" represents the total pore volume determined by gas adsorption, and "A" represents the BET specific surface area. The total pore volume V is determined from the adsorption amount of nitrogen at a relative vapor pressure of 0.990 based on the adsorption isotherm.

[0070] Hydrogen atoms are adsorbed on the surface of carbon materials. Atomic hydrogen generated by water reduction on the negative electrode surface is adsorbed on the negative electrode surface, or forms hydrogen molecules and desorbs as hydrogen gas. Hydrogen desorbs easily from the surface of materials with low hydrogen overvoltage, and hydrogen that desorbs and becomes gaseous does not contribute to increasing the battery's capacity. On the other hand, carbon has a very high hydrogen overvoltage, so hydrogen adsorbed on carbon is unlikely to desorb as gas, which can contribute to increasing the battery's capacity. Furthermore, when the pore diameter of carbon is small, this also helps to suppress desorption as hydrogen gas.

[0071] To facilitate electron transfer to and from the carbon material and to stably support the electrode structure, the negative electrode 10 includes a metal negative electrode current collector 11. The negative electrode current collector 11 includes at least one transition metal element selected from transition metal elements belonging to Groups 9, 10, and 11 of the periodic table. Nickel is preferably used from the perspective of alkali resistance.

[0072] However, when the negative electrode 10 includes a negative electrode current collector 11, hydrogen gas preferentially escapes from the transition metal portion during charging, preventing sufficient hydrogen from being absorbed by the carbon material. Furthermore, the temporarily released hydrogen is not reabsorbed into the negative electrode 10. Therefore, it is necessary to suppress the exposure of the transition metal portion in the negative electrode 10. In particular, in the contact area between the negative electrode 10 and the separator 30, the area occupied by the transition metal element must be kept below 5%. This can be suppressed by placing the negative electrode current collector 11 on the opposite side of the negative electrode composite layer 12 from the positive electrode 20.

[0073] The capacity of the carbon material disclosed herein is 100 mAh / g or more, and can be 200 mAh / g or more. Here, "capacity" refers to the capacity of the electrode that can charge the carbon material alone. The capacity can be obtained by charging the carbon material alone in an alkaline electrolyte, collecting gas to obtain the capacity other than the capacity stored in the electrode, that is, the capacity used for hydrogen generation, and subtracting the capacity used for hydrogen generation from the total power supply. Alternatively, the temporarily charged capacitor electrode can be simply discharged to obtain the capacitance at an appropriate discharge termination potential (voltage).

[0074] The negative electrode composite layer 12 preferably contains at least one metal selected from iron and zinc and a metal compound containing at least one metal selected from iron and zinc, with at least a portion of the metal and metal compound present on the inner surface of the pores of the carbon material. The presence of the metal and metal compound in the negative electrode composite layer 12 on the inner surface of the pores of the carbon material increases the charge and discharge capacity. Furthermore, it is preferred that all of the metal and metal compound contained in the negative electrode composite layer 12 be present on the inner surface of the pores of the carbon material. It should be noted that the negative electrode composite layer 12 may also contain only one of the above-mentioned metals or metal compounds.

[0075] For iron, in order to carry out the charge and discharge reactions of the above-mentioned formulas (1) and (2), large-sized oxygen ions, hydroxide ions, etc. need to move in the iron oxide (hydroxide). However, in the iron oxide (hydroxide) having a stable and dense structure, the movement speed of the substance is slow, and the reaction is difficult to penetrate deep into the interior of the iron oxide (hydroxide) particles of normal size. Therefore, as disclosed in the present invention, if the pore diameter is 0.5 nm or more and 5 nm or less, the size of the iron oxide (hydroxide) present on the inner surface of the pores of the carbon material is restricted, and oxygen ions, hydroxide ions, etc. do not need to move over long distances, so the charge and discharge reaction activity increases, and as a result, the charge and discharge capacity increases.

[0076] In addition, as mentioned above, the charge and discharge reaction of zinc occurs as a dissolution and precipitation reaction, and the morphology of the electrode is difficult to maintain, and there are problems such as zinc detaching from the electrode and dendrite formation. However, as disclosed in the present invention, zinc present on the inner surface of the pores of the carbon material is difficult to dissolve and detach from the electrode even when oxidized by discharge. In addition, even if it is dissolved, when it is reduced and precipitated by charging, it will enter the inner surface of the pores of the carbon material again, precipitating outside the negative electrode, or the possibility of forming dendrites is reduced. Therefore, the charge and discharge capacity can be stably maintained, and as a result, the charge and discharge capacity is increased.

[0077] The molar ratio of the metal atoms in the metal and the metal compound relative to the carbon atoms in the carbon material is preferably greater than 0.1 and less than 0.7. When the molar ratio of the metal atoms in the metal and the metal compound relative to the carbon atoms in the carbon material is less than 0.1, the charge-discharge capacity may not increase. In addition, when the molar ratio of the metal atoms in the metal and the metal compound relative to the carbon atoms in the carbon material exceeds 0.7, the metal on the inner surface that cannot enter the pores of the carbon material increases. As a result, in the case of iron, the iron with low charge-discharge activity increases, and the charge-discharge capacity may decrease. In the case of zinc, it may cause problems such as detachment from the electrode and the generation of dendrites.

[0078] Examples of the iron compound as the metal compound include iron oxide and iron hydroxide, but are not limited thereto. For example, the iron compound may be a salt of iron with an anion such as carbonate ion, or an iron compound containing water of hydration. Furthermore, the iron compound may contain metal elements other than iron.

[0079] Examples of the zinc compound as the metal compound include zinc oxide and zinc hydroxide, but are not limited thereto. For example, the zinc compound may include water of hydration. Furthermore, the zinc compound may include a metal element other than zinc.

[0080] The negative electrode composite layer 12 of the present disclosure may contain a conductive material, a binder, and the like in addition to the carbon material.

[0081] Since the charge and discharge reaction requires the exchange of electrons, the reaction activity can be improved by including a conductive material in the negative electrode composite layer 12. Examples of conductive materials include nickel, copper, and graphite. In order for nickel, copper, and the like to function as conductive materials, they need to be in a metallic state. Metallic conductive agents such as nickel and copper are conductive agents of transition metals belonging to Groups 10 and 11 in the periodic table. Based on the present disclosure, it is necessary to make the proportion of the area occupied in the contact area with the separator 5% or less. Graphite is not particularly limited as long as it has conductivity, and for example, carbon black, carbon nanotubes, graphene, and the like can also be applied. The content of the conductive material in the negative electrode composite layer 12 is, for example, not less than 1% by mass and not more than 20% by mass, and preferably not less than 5% by mass and not more than 15% by mass.

[0082] The binder combines the negative electrode active material with the negative electrode current collector. The binder may contain any component. Examples of the binder include styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and the like. From the perspective of hydrogen adsorption, PTFE is preferred. The content 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, preferably 5% by mass or more and 15% by mass or less.

[0083] The present disclosure is characterized by the negative electrode active material, and there are no particular limitations on the positive electrode, separator, and the like combined with the negative electrode.

[0084] The negative electrode active material disclosed in the present invention 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.

[0085] Electrolyte

[0086] The electrolyte is an alkaline aqueous solution. The alkaline aqueous solution includes, for example, water and an alkali metal hydroxide dissolved in the 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), and lithium hydroxide (LiOH).

[0087] "positive electrode"

[0088] The positive electrode 20 is sheet-shaped. For example, the thickness of the positive electrode 20 can be 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 can contain any optional components. Examples of the positive electrode active material include nickel hydroxide, manganese dioxide, and silver oxide.

[0089] The positive electrode 20 can be composed essentially of only the positive electrode active material. In addition to the positive electrode active material, the positive electrode 20 can further include a positive electrode current collector, a conductive material, and a binder. For example, the positive electrode current collector can include a porous metal sheet. For example, the current collector is made of nickel.

[0090] The conductive material has electron conductivity. The conductive material may contain optional components. The conductive material may contain, for example, carbon black, cobalt, cobalt oxide, etc. As for the amount of the conductive material, it may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material. The binder combines the positive electrode collector with the positive electrode active material. The binder may contain optional components. The binder may contain, for example, polyvinylidene fluoride (PVdF), etc. As for the amount of the binder, it may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material.

[0091] Separator

[0092] The separator 30 is sheet-shaped. It is positioned between the positive electrode 20 and the negative electrode 10 . The separator 30 physically separates the positive electrode 20 from the negative electrode 10 . The separator 30 can have a thickness of, for example, 20 to 500 μm. The separator 30 is porous. For example, the separator 30 can include a stretched porous film, a nonwoven fabric, or the like. The separator 30 is electrically insulating. For example, the separator 30 can be made of polyolefin, polyphenylene sulfide (PPS), or polyvinyl alcohol (PVA).

[0093] <Battery Manufacturing Method>

[0094] Manufacturing of the Negative Electrode

[0095] The negative electrode comprising a carbon material of the present disclosure can be manufactured using the following conventional methods. For example, a negative electrode can be made by applying a paste comprising a powder of a carbon material, a conductive material, and a binder (SBR latex, polyvinylidene fluoride, etc.) to a metal substrate such as a punched metal sheet or a metal mesh.

[0096] Alternatively, a carbon material powder, a conductive material, and PTFE can be mixed, the resulting mixture bonded by fibrillation of the PTFE formed into a sheet, and then combined with a metal substrate to produce a negative electrode. PTFE has high hydrophobicity and a high affinity for hydrogen, thus helping to stabilize the adsorbed hydrogen.

[0097] PTFE is for example more than 1 mass % and below 20 mass % with respect to the mass ratio of kneading.When PTFE is less than 1 mass % with respect to the mass ratio of kneading, cohesiveness becomes insufficient.When PTFE surpasses 20 mass % with respect to the mass ratio of kneading, causes the electrical conductivity of electrode to reduce, and makes active material filling amount reduce, and then capacity is reduced.PTFE is preferably more than 5 mass % and below 15 mass % with respect to the mass ratio of kneading.

[0098] The negative electrode disclosed herein, comprising a carbon material, at least one metal selected from iron and zinc, and a metal compound comprising at least one metal selected from iron and zinc, can be manufactured by the following method. The carbon material is immersed in a solution comprising at least one metal ion selected from iron ions and zinc ions, and an alkali is added to the solution in a state where metal ions are present on the surface of the pores of the carbon material. At this time, as a solution comprising iron ions, for example, a solution obtained by dissolving an iron salt such as iron sulfate, iron chloride, or iron acetate in a solvent can be used. As a solution comprising zinc ions, for example, a solution obtained by dissolving a zinc salt 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 are soluble in the solvent. In addition, the solvent needs to be a solvent that can dissolve iron ions and zinc ions and can infiltrate into the pores of the carbon material, for example, water, alcohol, etc. can be used. When the solvent is an alcohol or contains an alcohol, infiltration into the pores becomes easy.

[0099] As alkali, potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), ammonia (NH 3 ) etc. can be used.When these alkalis are added to the salt of metal, iron oxide, iron hydroxide, zinc oxide, zinc hydroxide etc. are separated out in the pores of carbon material and are fixed on the surface in the pores. In addition, under the state that there is iron ion in the pores of carbon material, if sodium carbonate, potassium carbonate etc. are added in solution, then iron carbonate is separated out and is fixed on the surface in the pores. As long as the alkali used is not particularly limited to generate the compound of desired iron and zinc, it can be added in the state of solid or as a solution. In addition, for example, the solution comprising iron ion or zinc ion can also be infiltrated into carbon in advance and impregnated in alkaline solution.

[0100] The concentration of the metal ions in the solution is preferably 1 mol / L or higher. This increases the amount of metal that can exist on the surface of the pores of the carbon material.

[0101] The average pore diameter of the carbon material is small, and sufficient infiltration of the metal ions into the pores takes time. Therefore, it is preferable to add the base to the solution after the carbon material has been immersed in the solution for at least three hours. If the immersion time is less than three hours, the metal compound will precipitate outside the pores, which may not contribute to the capacity in the case of iron compounds, or may cause detachment from the negative electrode and dendrite formation in the case of zinc compounds.

[0102] It is also preferable to irradiate the carbon with ultrasound while it is immersed in the solution. Ultrasonic irradiation can promote the infiltration of metal ions into the pores. The duration of ultrasonic irradiation is not particularly limited, and for example, irradiation can be performed for 3 minutes or longer.

[0103] Furthermore, by heating the carbon material while immersed in the solution, the infiltration of metal ions into the pores can be promoted. The temperature of the solution can be heated to, for example, 30° C. or higher and 100° C. or lower.

[0104] Manufacturing of Positive Electrodes

[0105] The positive electrode can be manufactured by a common method. For example, the positive electrode can be formed by coating a positive electrode active material, a conductive material, and a binder on a positive electrode current collector.

[0106] Manufacturing of Energy Storage Devices

[0107] The energy storage element can have any form. For example, the energy storage element can be a stacked type or a wound type. For example, a separator is prepared. A single separator or two separators can be used. For example, a stack can be formed by sequentially stacking a separator, a negative electrode, a separator, and a positive electrode. In the case of a wound type, the energy storage element can be formed by winding the stack into a spiral shape.

[0108] Battery Manufacturing

[0109] The battery manufacturing method includes manufacturing a battery including an energy storage element and an electrolyte solution. For example, an outer package is prepared, the energy storage element is assembled into the outer package, and the electrolyte solution is injected to manufacture the battery.

[0110] The following describes embodiments of the present disclosure, but the following description does not limit the scope of the patent claims.

[0111] (Example 1)

[0112] This embodiment is an example of a battery using the above-mentioned carbon material as a negative electrode active material.

[0113] As the carbon material, activated carbon (manufactured by AT Electron Co., Ltd., electrode material for electric double layer capacitors AP11-0010) was used. The BET specific surface area of ​​the activated carbon was 1100±200 m 2 / g, and the average pore diameter was 1.8 nm. The BET specific surface area and the average pore diameter were measured using a gas adsorption measurement device (BELSORP-MAX, manufactured by Microtrac BEL Co., Ltd.) (the same applies to the following Examples and Comparative Examples).

[0114] Then, using this activated carbon as negative electrode active material, make electrode (negative pole). Specifically, 84 mass % of activated carbon powder, 10 mass % of carbon black powder (Kishida Chemicals), and 6 mass % of PTFE (Sigma Aldrich) are mixed, and the mixed product bonded by the fibrillation of PTFE is formed into a circular sheet with a diameter of 20 mm. The circular sheet is matched with a nickel mesh (20 mm in diameter) as a negative electrode current collector on one side, and is pressed with a pressure of 34 MPa to make a negative pole. The activated carbon mass contained in the negative pole is 0.1 g.

[0115] The negative electrode prepared in this way was combined with a sulfonated polypropylene nonwoven fabric (circular, 23 mm diameter) used in conventional nickel-metal hydride batteries and a nickel hydroxide electrode (a disc-shaped electrode filled with nickel hydroxide in a porous nickel body, 20 mm in diameter) used in conventional nickel-metal hydride batteries. The electrode was then placed in a commercially available battery container (Takumi Giken, FLAT CELL). The negative electrode was placed so that the surface with the nickel mesh was in contact with the negative electrode composite layer on the opposite side (back side) from the positive electrode. The nickel mesh was not exposed in the contact area between the negative electrode and the separator. In other words, the area occupied by nickel in the contact area between the negative electrode and the separator was 0%.

[0116] 0.3 mL of alkaline electrolyte (KOH 27 wt%, NaOH 3 wt%, LiOH 1 wt%) was injected into the battery. The positive electrode capacity was about 35 mAh, which made the positive electrode capacity excessive relative to the negative electrode capacity. In practical batteries, the positive electrode capacity is made less than the negative electrode capacity, and the positive electrode capacity dominates. However, in this embodiment, the positive electrode capacity is excessive relative to the negative electrode capacity in a manner that directly manifests the performance of the negative electrode, and the negative electrode capacity dominates. The battery was charged and discharged at a constant current of 60 mA per 1 g of activated carbon in a thermostatic chamber at 25°C. The discharge termination voltage was 0.8 V.

[0117] (Example 2)

[0118] As a carbon material, activated carbon was produced by alkali activation of petroleum coke. Specifically, 5 times the weight ratio of potassium hydroxide (about 15% water) was added to petroleum coke and mixed thoroughly, dehydrated at 400°C for 30 minutes, and then activated at 800°C for 100 minutes. The BET specific surface area of ​​the activated carbon was 3000 m 2 / g, and the average pore diameter was 2.1 nm. Except for this, a negative electrode and a battery were prepared in the same manner as in Example 1, and a battery test was carried out.

[0119] (Example 3)

[0120] As a carbon material, the same activated carbon as in Example 2 was used, and the negative electrode was prepared in the same manner as in Example 1. However, a nickel mesh was placed in the center of the circular piece to eliminate exposure in the contact area between the negative electrode and the separator, and to make it the opposite side of the positive electrode from any side. In addition, a copper wire coated with resin was installed on the nickel mesh, and the installation portion was covered with resin to eliminate exposure of the contact area between the negative electrode of the transition metal component and the separator. The negative electrode prepared in this way was immersed in a 30% by mass potassium hydroxide aqueous solution, and a nickel plate was used as the positive electrode. Constant current charging was performed in a constant temperature bath at 25°C with a current of 60 mA per 1g of activated carbon mass. The hydrogen generated during charging was collected with a gas burette, and the amount of electricity consumed due to the generation of hydrogen was subtracted from the total amount of electricity charged to determine the capacity charged to the electrode. Since there is almost no capacity charged except for the activated carbon, the capacity charged to the electrode can be regarded as almost entirely charged to the capacity of the activated carbon alone.

[0121] (Example 4)

[0122] In this embodiment, a battery is prepared in which the negative electrode active material comprises a carbon material and an iron compound, and at least a portion of the iron compound is present in the pores of the carbon material. The same activated carbon as in Example 2 is immersed in an aqueous solution of iron (II) sulfate 7 hydrate (Kishida Chemical) at a concentration of 1 mol / L. After immersion for 3 hours, a 3 mol / L aqueous sodium hydroxide solution is added dropwise to the above aqueous solution until the pH exceeds 10, so that the iron ions are precipitated in the form of iron oxide or iron hydroxide, the solid component is filtered out, washed with warm water, and dried to prepare the negative electrode active material. At this time, the molar ratio of iron atoms per 1 mol of activated carbon is 0.2. Using the negative electrode active material prepared in this way, a negative electrode and a battery are prepared in the same manner as in Example 1, and a battery test is carried out.

[0123] (Example 5)

[0124] 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. 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 performed.

[0125] (Example 6)

[0126] A negative electrode active material was prepared in the same manner as in Example 4, except that the activated carbon was impregnated for 30 minutes and ultrasonic waves were irradiated for 3 minutes using an ultrasonic cleaner (ASONE MCS-2, oscillation frequency 40 kHz) while the activated carbon was impregnated. 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 performed.

[0127] (Example 7)

[0128] In this example, a battery was prepared in which the negative electrode active material contained a carbon material and a zinc compound, and at least a portion of the zinc compound was present in the pores of the carbon material. The activated carbon used in Example 2 was immersed in an aqueous solution of zinc sulfate 7 hydrate (Kishida Chemical) at a concentration of 1 mol / L. After immersion for 3 hours, a 3 mol / L aqueous sodium hydroxide solution was added dropwise to the aqueous solution until the pH exceeded 10, causing the zinc ions to precipitate in the form of zinc oxide or zinc hydroxide. The solid component was filtered out, washed with warm water, and dried to produce the negative electrode active material. At this time, the molar ratio of zinc atoms per 1 mol of activated carbon was 0.2.

[0129] A negative electrode was prepared in the same manner as in Example 1, except that the negative electrode active material prepared in this manner was used and a tin-plated copper mesh (20 mm in diameter) was used instead of the nickel mesh. Furthermore, a battery was prepared in the same manner as in Example 1, except that the interior of the negative electrode side of the battery container was tin-plated, and a battery test was performed.

[0130] (Comparative Example 1)

[0131] As Comparative Example 1, a battery example in which the negative electrode current collector and the negative electrode composite layer on the side opposite to the positive electrode are not in contact is shown. As the carbon material, the same activated carbon as in Example 1 was used.

[0132] 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 the 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, Celmet (R)) punched into a disc with a diameter of 20 mm, and after drying, it was pressed at a pressure of 34 MPa to prepare a negative electrode. The mass of activated carbon contained in the negative electrode was 0.06 g. Using the negative electrode prepared in this way, a battery was prepared in the same manner as in Example 1, and a battery test was carried out. It should be noted that in the contact area between the negative electrode and the separator, the proportion of the area occupied by the nickel porous body is greater than 5%.

[0133] (Comparative Example 2)

[0134] As Comparative Example 2, a negative electrode and a battery were prepared 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 performed.

[0135] (Comparative Example 3)

[0136] Comparative Example 3 shows an example of a battery in which the negative electrode active material contains an iron compound but no carbon material. The negative electrode active material was prepared by dropwise adding a 3 mol / L aqueous sodium hydroxide solution to a 1 mol / L aqueous solution of iron(II) sulfate heptahydrate (Kishida Chemical) until the pH exceeded 10, thereby precipitating iron ions as iron oxide or iron hydroxide. The solid component was then filtered, washed with warm water, and dried.

[0137] A negative electrode and a battery were produced in the same manner as in Example 1 except that the negative electrode active material produced in this manner was used, and a battery test was performed.

[0138] (Comparative Example 4)

[0139] Comparative Example 4 shows an example of a battery in which the negative electrode active material contains a zinc compound but no carbon material. The negative electrode active material was prepared by dropwise adding a 3 mol / L aqueous sodium hydroxide solution to a 1 mol / L aqueous solution of zinc sulfate heptahydrate (Kishida Chemical) until the pH exceeded 10, thereby precipitating zinc ions as zinc oxide or zinc hydroxide. The solid content was then filtered, washed with warm water, and dried.

[0140] A negative electrode was prepared in the same manner as in Example 1, except that the negative electrode active material prepared in this manner was used and a tin-plated copper mesh (20 mm in diameter) was used instead of the nickel mesh. Furthermore, a battery was prepared in the same manner as in Example 1, except that the interior of the negative electrode side of the battery container was tin-plated, and a battery test was performed.

[0141] exist Figure 3 (a) and (b) show the results of the discharge voltage curves in the battery tests of Examples 1 and 2 and Comparative Examples 1 and 2. Figure 3 The capacity shown on the horizontal axis is the value of converting the battery capacity into the capacity of activated carbon per 1g as the negative electrode active material (in Figure 4 and Figure 5 (The same applies to Chinese).

[0142] Depend on Figure 3 The results shown show that the batteries of Examples 1 and 2 exhibited large capacities, and that of Example 2 exhibited a large capacity of 100 mAh / g or more even after discharge was terminated at 0.8 V.

[0143] exist Figure 4 The results of the discharge voltage curve when the battery is discharged to 0V in the battery test of Example 2 are shown in FIG. Figure 4 The results shown show that the negative electrode of the battery of Example 2, and furthermore, the carbon material as the active material therein, exhibits a capacity of 200 mAh / g or more.

[0144] exist Figure 5 The results of measuring the capacity of the carbon material alone in the battery of Example 3 are shown in FIG. Figure 5 The results shown show that the charge capacity of the carbon material alone is 200 mAh / g or more.

[0145] Depend on Figures 3-5 The results show that the battery of the present disclosure exhibits a large capacity, even reaching 100 mAh / g or 200 mAh / g or more. These capacities are far greater than those resulting from the formation of an electrical double layer. The capacity is significantly affected by the exposure of the metal surface layer, which has a lower hydrogen overvoltage than the carbon material. This fact suggests that the increased capacity of the battery of the present disclosure is due to the adsorption of hydrogen generated by water reduction into the carbon material.

[0146] exist Figure 6 The results of the discharge voltage curves in the battery tests of Examples 2, 4 to 6 and Comparative Example 3 are shown in FIG. Figure 6 The capacity shown on the horizontal axis is the value obtained by converting the battery capacity into the capacity density per 1cc of battery volume (in Figure 7 (The same applies to Chinese).

[0147] Depend on Figure 6 The results show that the battery containing an iron compound in Example 4 has a significantly higher capacity density than the battery without an iron compound in Example 2. This is believed to have resolved the problem of reduced capacity density due to the low volume density of activated carbon. Furthermore, the battery containing only an iron compound in Comparative Example 3 has a significantly lower capacity than the battery containing activated carbon and an iron compound in Example 4. These results show that a high capacity cannot be achieved using only an iron compound, but that a high capacity can be achieved by coexisting activated carbon with an iron compound.

[0148] In the batteries of Examples 4 and 5, the activated carbon was immersed in the solution containing iron ions for 3 hours and 30 minutes, respectively. Figure 6 As a result, the capacity of the battery of Example 5 was significantly reduced compared to the battery of Example 4. This result shows that by extending the impregnation time, the iron ions fully penetrate the pores of the activated carbon, and the capacity increases.

[0149] The batteries of Examples 5 and 6 differ in whether or not the solution containing iron ions was irradiated with ultrasonic waves for 3 minutes while being impregnated with activated carbon. Figure 6 As a result, the capacity of the battery subjected to ultrasonic irradiation in Example 6 was significantly improved compared to the battery not subjected to ultrasonic irradiation in Example 5. This result shows that ultrasonic irradiation promotes the infiltration of iron ions into the pores of activated carbon, thereby increasing the capacity.

[0150] exist Figure 7 The results of the discharge voltage curves in the battery tests of Examples 2, 7 and Comparative Example 4 are shown in FIG. Figure 7The results show that 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. This result shows that a large capacity can be obtained by coexisting activated carbon and a zinc compound.

[0151] The battery of Comparative Example 4, containing only a zinc compound, exhibited a capacity nearly identical to that of the battery of Example 7, containing activated carbon and a zinc compound. However, while the battery of Example 7 did not short-circuit during repeated charge and discharge, the battery of Comparative Example 4 frequently short-circuited during repeated charge and discharge (after the second and third charge and discharge cycles). In Comparative Example 4, dendrites were believed to have formed and penetrated the separator. This result suggests that zinc ions infiltrate the pores of the activated carbon, preventing short-circuiting and achieving high capacity.

[0152] The embodiments and examples disclosed herein are illustrative in all respects and are not restrictive. The technical scope defined by the claims encompasses all modifications that are equivalent to the claims. The technical scope defined by the claims encompasses all modifications that are equivalent to the claims.

Claims

1. A battery comprising a positive electrode, a separator, a negative electrode and an electrolyte, wherein: The positive electrode and the negative electrode are stacked with the separator interposed therebetween, characterized in that The negative electrode comprises a negative electrode composite 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 Group 9, Group 10, and Group 11 of the periodic table. The negative electrode current collector is in contact with the negative electrode composite layer on the opposite side to the positive electrode. In the contact region between the negative electrode and the separator, the area ratio occupied by the transition metal element is 5% or less, The negative electrode active material comprises a carbon material, The carbon material has 900m 2 / g or more BET specific surface area, The carbon material has an average pore diameter of 0.5 nm or more and 4 nm or less measured by a gas adsorption method, The negative electrode composite layer contains at least one metal selected from the group consisting of iron and zinc, and a metal compound containing at least one metal selected from the group consisting of iron and zinc. At least a portion of the metal and the metal compound is present on the inner surface of the pores of the carbon material, 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, The content of the carbon material in the negative electrode composite layer is 70% by mass or more and 90% by mass or less. The electrolyte is an alkaline aqueous solution.

2. The battery according to claim 1, characterized in that The carbon material has a capacity of 100 mAh / g or more.

3. The battery according to claim 1 or 2, characterized in that Hydrogen atoms are adsorbed on the surface of the carbon material.

4. The battery according to claim 1 or 2, characterized in that The content of the carbon material in the negative electrode mixed material layer is 75% by mass or more and 85% by mass or less.

5. A method for manufacturing a battery according to any one of claims 1 to 4, characterized in that: The method comprises the steps 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 while the metal ions are present on the inner surfaces of the pores of the carbon material.

6. The method for manufacturing a battery according to claim 5, wherein: The concentration of the metal ions in the solution is 1 mol / L or higher.

7. The method for manufacturing a battery according to claim 5 or 6, characterized in that: After 3 hours or more have passed while the carbon material is immersed in the solution, an alkali is added to the solution.

8. The method for manufacturing a battery according to claim 5 or 6, characterized in that: After irradiating the carbon material with ultrasonic waves while it is immersed in the solution, an alkali is added to the solution.

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