A low-temperature nickel-hydrogen battery formula and preparation process

Abstract

The application provides a low-temperature nickel-hydrogen battery formula and a preparation process. A positive electrode of the low-temperature nickel-hydrogen battery comprises a base body of foamed nickel, active material of spherical nickel hydroxide, a conductive agent of cobaltous oxide, a binder of sodium carboxymethyl cellulose, an additive of zinc oxide and cerium chloride; a negative electrode comprises a base body of copper mesh, active material of hydrogen storage alloy powder, a binder of polytetrafluoroethylene emulsion, and an additive of yttrium oxide; an electrolyte comprises sodium hydroxide, potassium hydroxide, barium hydroxide and carboxymethyl cellulose. The positive electrode, a polypropylene diaphragm and the negative electrode are wound into an electric core, a layer of polyimide film is wound outside the electric core, and then the electric core is loaded into a battery steel shell, electrolyte is injected, the battery shell is sealed, and the low-temperature nickel-hydrogen battery is obtained through charging and discharging treatment. The low-temperature nickel-hydrogen battery of the application inhibits the release of oxygen in the positive electrode by adding zinc oxide to the positive electrode, and the addition of cerium chloride can prevent the failure of the spherical nickel hydroxide to a certain extent at a low temperature greater than 40 DEG, so that the charging efficiency of the positive electrode is obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of nickel-metal hydride battery technology, specifically, it relates to a low-temperature nickel-metal hydride battery formulation and preparation process. Background Technology

[0002] Nickel-metal hydride (NiMH) batteries typically consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is usually a nickel electrode, formed by electrochemical impregnation of foamed nickel as a substrate. The negative electrode is made by attaching hydrogen storage alloy powder to a negative electrode substrate. The separator isolates the positive and negative electrodes, preventing electrons from passing through, but allowing ions in the separator to transport the charge generated during the reactions at the positive and negative electrodes. Environmental temperature changes during charging and discharging have a significant impact on battery performance. Traditional NiMH batteries experience a marked decrease in charging and discharging efficiency below -20°C, and may fail to charge and discharge effectively below -40°C. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a low-temperature nickel-metal hydride battery formulation and preparation process to overcome the defects in the prior art.

[0004] To achieve the above objectives, the present invention provides a low-temperature nickel-metal hydride battery formulation, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a matrix of nickel foam, an active material of cobalt-coated spherical nickel hydroxide, a conductive agent of graphene, a binder of sodium carboxymethyl cellulose, and additives of ytterbium oxide and lanthanum oxide. The negative electrode comprises a matrix of copper mesh, an active material of hydrogen storage alloy powder, a conductive agent of graphene, a binder of polytetrafluoroethylene emulsion, and an additive of copper oxide. The electrolyte comprises sodium hydroxide, potassium hydroxide, barium hydroxide, and carboxymethyl cellulose.

[0005] Using the above technical solutions, cobalt-coated spherical nickel hydroxide as the active material in the positive electrode can reduce the battery's internal resistance and improve the utilization rate of nickel hydroxide. Adding graphene increases conductivity under low-temperature conditions. Adding ytterbium oxide and lanthanum oxide increases the oxygen evolution overpotential under low-temperature conditions, resulting in higher discharge capacity. Adding copper oxide to the negative electrode improves the specific energy and specific power under low-temperature conditions. Adding carboxymethyl cellulose to the electrolyte improves the electrolyte's low-temperature performance, maintaining a liquid state in low-temperature environments.

[0006] As a further explanation of the low-temperature nickel-metal hydride battery formulation of the present invention, preferably, the weight ratio of spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide, and lanthanum oxide in the positive electrode is 90:9:3:1:1.

[0007] As a further explanation of the low-temperature nickel-metal hydride battery formulation of the present invention, preferably, the weight ratio of hydrogen storage alloy powder, graphene, polytetrafluoroethylene emulsion, and copper oxide in the negative electrode is 90:9:3:12.

[0008] As a further explanation of the low-temperature nickel-hydrogen battery formulation of the present invention, preferably, the hydrogen storage alloy powder comprises: 45 wt.% nickel, 12 wt.% cobalt, 7 wt.% manganese, 2 wt.% copper, 4 wt.% titanium, 12 wt.% cerium, and 18 wt.% lanthanum.

[0009] Through the above technical solutions, cerium and lanthanum can store hydrogen, have good corrosion resistance, and a longer lifespan, but have lower capacity and slower activation. Adding 12% cerium in combination with 45% nickel is beneficial to improving the hydrogen evolution catalytic activity and electrochemical stability of the negative electrode. Adding copper and manganese can improve hydrogen storage performance. Adding manganese can increase the capacity of the negative electrode, thereby increasing the capacity of the nickel-metal hydride battery. Adding copper can increase the specific energy and specific power of the battery, thereby improving the cycle life of the nickel-metal hydride battery.

[0010] As a further explanation of the low-temperature nickel-metal hydride battery formulation of the present invention, preferably, the mass percentage concentrations of sodium hydroxide, potassium hydroxide, barium hydroxide, and carboxymethyl cellulose in the electrolyte are 10-15%, 50-60%, 5-10%, and 5-8%, respectively.

[0011] As a further explanation of the low-temperature nickel-metal hydride battery formulation of the present invention, preferably, the concentration of the electrolyte is controlled between 6.5-10 mol / L.

[0012] To achieve another objective of the present invention, the present invention also provides a process for preparing a low-temperature nickel-metal hydride battery, the process comprising the following steps:

[0013] Step 1): Spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide and lanthanum oxide are mixed evenly to form a first mixture. The first mixture is filled into the positive electrode matrix nickel foam by mechanical mixing. Then, after rolling and cutting, the positive electrode of the nickel-metal hydride battery is obtained.

[0014] Step 2): Mix hydrogen storage alloy powder, graphene, and copper oxide evenly to form a second mixture. Roll the second mixture onto the negative electrode substrate copper mesh. Impregnate the surface of the negative electrode substrate copper mesh with polytetrafluoroethylene emulsion. Then, after drying and cutting, the negative electrode of the nickel-metal hydride battery is obtained.

[0015] Step 3): Dissolve sodium hydroxide, potassium hydroxide, and barium hydroxide in purified water, then add carboxymethyl cellulose and stir until homogeneous to obtain the electrolyte.

[0016] Step 4): The positive electrode, polypropylene separator, and negative electrode are wound into a battery cell, the electrolyte is injected, the battery casing is sealed, and a low-temperature nickel-metal hydride battery is obtained after charge-discharge treatment.

[0017] As a further explanation of the preparation process described in this invention, preferably, the weight ratio of spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide, and lanthanum oxide is 90:9:3:1:1; the weight ratio of hydrogen storage alloy powder, graphene, polytetrafluoroethylene emulsion, and copper oxide is 90:9:3:12; the mass percentage concentrations of sodium hydroxide, potassium hydroxide, barium hydroxide, and carboxymethyl cellulose in the electrolyte are 10-15%, 50-60%, 5-10%, and 5-8%, respectively; and the concentration of the electrolyte is controlled between 6.5-10 mol / L.

[0018] As a further explanation of the preparation process described in this invention, preferably, the hydrogen storage alloy powder comprises: 45 wt.% nickel, 12 wt.% cobalt, 7 wt.% manganese, 2 wt.% copper, 4 wt.% titanium, 12 wt.% cerium, and 18 wt.% lanthanum.

[0019] The beneficial effects of this invention are:

[0020] 1. The low-temperature nickel-metal hydride battery formulation of this invention uses cobalt-coated spherical nickel hydroxide as the active material in the positive electrode, which can reduce the battery's internal resistance and improve the utilization rate of nickel hydroxide. Graphene is added to increase conductivity under low-temperature conditions. Ytterbium oxide and lanthanum oxide are added to increase the oxygen evolution overpotential under low-temperature conditions, resulting in higher discharge capacity. Copper oxide is added to the negative electrode to improve specific energy and specific power under low-temperature conditions. The addition of carboxymethyl cellulose to the electrolyte improves the low-temperature performance of the electrolyte, maintaining a liquid state in low-temperature environments. The high ratio of potassium ions in the electrolyte contributes to the low-temperature characteristics.

[0021] 2. The low-temperature nickel-metal hydride battery manufacturing process of the present invention can meet the discharge rate within 0.1C in the temperature range of -10℃ to 50℃, and can discharge more than 70% of the rated capacity. Detailed Implementation

[0022] To further understand the structure, features and other objectives of the present invention, the following detailed description is provided in conjunction with the accompanying preferred embodiments. These embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention.

[0023] Example 1: Preparation of low-temperature nickel-metal hydride batteries.

[0024] Preparation of the positive electrode:

[0025] A first mixture is formed by uniformly mixing spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide, and lanthanum oxide in a weight ratio of 90:9:3:1:1. This first mixture is then filled into nickel foam, the positive electrode matrix, by mechanical mixing. After rolling and cutting, the positive electrode of a nickel-metal hydride battery is obtained. The drying temperature is preferably 40–80°C.

[0026] Preparation of the negative electrode:

[0027] Hydrogen storage alloy powder, graphene, polytetrafluoroethylene emulsion, and copper oxide were prepared in a weight ratio of 90:9:3:12. The hydrogen storage alloy powder consisted of: 45 wt.% nickel, 12 wt.% cobalt, 7 wt.% manganese, 2 wt.% copper, 4 wt.% titanium, 12 wt.% cerium, and 18 wt.% lanthanum.

[0028] Hydrogen storage alloy powder, graphene, copper oxide, and 30% polytetrafluoroethylene emulsion are mixed evenly and rolled onto a copper mesh substrate. The remaining 70% polytetrafluoroethylene emulsion is evenly impregnated onto the surface of the substrate. After the polytetrafluoroethylene emulsion has completely penetrated, it is rolled to the required thickness, dried, and then cut to the required size to obtain the negative electrode of the nickel-metal hydride battery.

[0029] The polytetrafluoroethylene (PTFE) emulsion is an aqueous dispersion made by concentrating the dispersion of polymerized PTFE to a PTFE solid content of 60 wt.% and stabilizing it with a nonionic surfactant. PTFE emulsion possesses excellent chemical stability and corrosion resistance. Adding PTFE emulsion to the negative electrode can improve its chemical stability, thereby enhancing the stability and chemical corrosion resistance of the prepared negative electrode, and ultimately improving the cycle life and performance of the nickel-metal hydride battery.

[0030] Electrolyte preparation:

[0031] Sodium hydroxide, potassium hydroxide, and barium hydroxide are dissolved in purified water, and then carboxymethyl cellulose is added and stirred until homogeneous to obtain the electrolyte. The mass percentages of sodium hydroxide, potassium hydroxide, barium hydroxide, and carboxymethyl cellulose in the electrolyte are 10–15%, 50–60%, 5–10%, and 5–8%, respectively. The electrolyte concentration is preferably controlled at 8 mol / L. Adding carboxymethyl cellulose improves the low-temperature performance of the electrolyte, maintaining its liquid state at low temperatures.

[0032] Battery assembly:

[0033] The positive electrode, polypropylene separator, and negative electrode are wound into a battery cell, injected with the electrolyte, sealed in a battery casing, and subjected to charge-discharge treatment to obtain a low-temperature nickel-metal hydride battery.

[0034] Comparative Example 1:

[0035] Nickel-metal hydride batteries were prepared according to the method described in Example 1, except that ytterbium oxide and lanthanum oxide were not added to the positive electrode.

[0036] Comparative Example 2:

[0037] Nickel-metal hydride batteries were prepared according to the method described in Example 1, except that copper oxide was not added to the negative electrode.

[0038] Comparative Example 3:

[0039] Nickel-metal hydride batteries were prepared according to the method described in Example 1, except that carboxymethyl cellulose was not added to the electrolyte.

[0040] Comparative Example 4:

[0041] The conventional nickel-metal hydride battery in the existing technology.

[0042] Comparative Example 5:

[0043] Nickel-metal hydride batteries were prepared according to the method described in Example 1, except that the amounts of sodium hydroxide (15%) and barium hydroxide (10%) in the electrolyte remained unchanged, while the amount of potassium hydroxide was varied (comparative experiments were conducted at 60%, 50%, 40%, 30%, 20%, and 10%, respectively).

[0044] Performance comparison:

[0045] Methods for testing the charge-discharge efficiency of nickel-metal hydride batteries at different temperatures:

[0046] The nickel-metal hydride (NiMH) batteries were left to stand for 8 hours at -10℃, -20℃, -30℃, -40℃, and -50℃ respectively to bring their temperature to the same as the ambient temperature. Then, they were charged with a charging current of 0.1C for 6 hours and discharged with a discharging current of 0.2C until the cutoff voltage reached 1.0V. The battery discharge capacity was calculated and compared with the discharge capacity of the NiMH batteries at room temperature to obtain the charging efficiency of the NiMH batteries under low-temperature conditions.

[0047] (1) The nickel-metal hydride batteries obtained in Example 1 and Comparative Examples 1-4 were tested respectively, and the average value of the test results was taken. The charging efficiency (i.e., the ratio of the discharge capacity to the charge capacity of the nickel-metal hydride battery, expressed as a percentage) of the nickel-metal hydride batteries obtained in each example and comparative example at low temperature is shown in Table 1:

[0048] Table 1

[0049]

[0050]

[0051] As shown in Table 1, after the nickel-metal hydride batteries obtained in Example 1 and Comparative Example 3 were placed at -50°C and then dissected, the electrolyte inside the nickel-metal hydride battery obtained in Comparative Example 3 had frozen. After the nickel-metal hydride batteries obtained in Example 1 and Comparative Example 3 were placed at -40°C and then dissected, most of the electrolyte inside the nickel-metal hydride battery obtained in Comparative Example 3 had frozen, while the electrolyte inside the nickel-metal hydride battery obtained in Example 1 remained in a liquid state.

[0052] In environments ranging from -10°C to 50°C, Examples 1 and Comparative Examples 1-3 showed a significant improvement in low-temperature performance compared to the ordinary nickel-metal hydride battery in Comparative Example 4. At -50°C, the ordinary nickel-metal hydride battery in Comparative Example 4 could no longer be used normally, and the nickel-metal hydride battery in Comparative Example 3 also failed to function properly due to electrolyte freezing, while the batteries in Comparative Examples 1-3 remained functional.

[0053] Comparative Examples 1 and 2 show that adding ytterbium oxide and lanthanum oxide to the positive electrode or adding copper oxide to the negative electrode has a certain impact on the low-temperature performance of nickel-metal hydride batteries. In Comparative Example 2, the effect of not adding copper oxide to the negative electrode on the low-temperature performance of the nickel-metal hydride battery is significantly less than the effect of not adding ytterbium oxide and lanthanum oxide to the positive electrode on the low-temperature performance of the nickel-metal hydride battery in Comparative Example 1.

[0054] (2) The nickel-metal hydride batteries obtained in Comparative Example 5 were tested respectively. The charging efficiency of the nickel-metal hydride batteries at high temperature (i.e., the ratio of the discharge capacity to the charge capacity of the nickel-metal hydride battery, expressed as a percentage) is shown in Table 2:

[0055] Table 2

[0056]

[0057] As shown in Table 2, increasing the ratio of potassium ions in the electrolyte contributes to the low-temperature characteristics of nickel-metal hydride batteries.

[0058] In summary, the low-temperature nickel-metal hydride battery provided by this invention can meet the discharge rate within 0.1C in the temperature range of -10℃ to 50℃, and can discharge more than 70% of the rated capacity.

[0059] It should be stated that the above-described invention content and specific embodiments are intended to demonstrate the practical application of the technical solution provided by this invention and should not be construed as limiting the scope of protection of this invention. Those skilled in the art can make various modifications, equivalent substitutions, or improvements within the spirit and principles of this invention. The scope of protection of this invention is defined by the appended claims.

Claims

1. A low-temperature nickel-metal hydride battery formulation, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode, a polypropylene separator, and the negative electrode are wound into a battery cell, the electrolyte is injected, the battery casing is sealed, and a low-temperature nickel-metal hydride battery is obtained through charge-discharge treatment, characterized in that, The positive electrode comprises a nickel foam matrix, cobalt-coated spherical nickel hydroxide as the active material, graphene as the conductive agent, sodium carboxymethyl cellulose as the binder, and ytterbium oxide and lanthanum oxide as additives. The spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide, and lanthanum oxide are uniformly mixed to form a first mixture. This first mixture is then mechanically mixed and filled into the nickel foam matrix, followed by rolling and cutting to obtain the positive electrode of the nickel-metal hydride battery. The negative electrode comprises a copper mesh substrate, hydrogen storage alloy powder as the active material, graphene as the conductive agent, polytetrafluoroethylene emulsion as the binder, and copper oxide as the additive. The hydrogen storage alloy powder comprises 45 wt.% nickel, 12 wt.% cobalt, 7 wt.% manganese, 2 wt.% copper, 4 wt.% titanium, 12 wt.% cerium, and 18 wt.% lanthanum. The hydrogen storage alloy powder, graphene, and copper oxide are mixed evenly with 30% of the polytetrafluoroethylene emulsion to form a second mixture. The second mixture is rolled onto the copper mesh substrate of the negative electrode. The remaining 70% of the polytetrafluoroethylene emulsion is evenly impregnated onto the surface of the copper mesh substrate of the negative electrode, and then dried and cut to obtain the negative electrode of the nickel-metal hydride battery. The electrolyte comprises sodium hydroxide, potassium hydroxide, barium hydroxide, and carboxymethyl cellulose; the concentration of the electrolyte is controlled at 8 mol / L; wherein, sodium hydroxide, potassium hydroxide, and barium hydroxide are dissolved in pure water, and then carboxymethyl cellulose is added and stirred evenly to obtain the electrolyte.

2. The low-temperature nickel-metal hydride battery formulation as described in claim 1, characterized in that, The weight ratio of spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide, and lanthanum oxide in the positive electrode is 90:9:3:1:

1.

3. The low-temperature nickel-metal hydride battery formulation as described in claim 1, characterized in that, The weight ratio of hydrogen storage alloy powder, graphene, polytetrafluoroethylene emulsion, and copper oxide in the negative electrode is 90:9:3:

12.

4. A process for preparing a low-temperature nickel-metal hydride battery, wherein the low-temperature nickel-metal hydride battery adopts the formulation as described in any one of claims 1-3, characterized in that, The preparation process includes the following steps: Step 1): Spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide and lanthanum oxide are mixed evenly to form a first mixture. The first mixture is filled into the positive electrode matrix nickel foam by mechanical mixing. Then, after rolling and cutting, the positive electrode of the nickel-metal hydride battery is obtained. Step 2): The hydrogen storage alloy powder, graphene, copper oxide, and 30% polytetrafluoroethylene emulsion are mixed evenly to form a second mixture. The second mixture is rolled onto the negative electrode substrate copper mesh. The remaining 70% polytetrafluoroethylene emulsion is evenly impregnated onto the surface of the negative electrode substrate copper mesh with the second mixture. After drying and cutting, the negative electrode of the nickel-metal hydride battery is obtained. The hydrogen storage alloy powder includes: 45 wt.% nickel, 12 wt.% cobalt, 7 wt.% manganese, 2 wt.% copper, 4 wt.% titanium, 12 wt.% cerium, and 18 wt.% lanthanum. Step 3): Dissolve sodium hydroxide, potassium hydroxide, and barium hydroxide in purified water, then add carboxymethyl cellulose and stir until homogeneous to obtain an electrolyte; the concentration of the electrolyte is controlled at 8 mol / L; Step 4): The positive electrode, polypropylene separator, and negative electrode are wound into a battery cell, the electrolyte is injected, the battery casing is sealed, and a low-temperature nickel-metal hydride battery is obtained after charge-discharge treatment.

5. The preparation process according to claim 4, characterized in that, The weight ratio of spherical nickel hydroxide, graphene, sodium carboxymethyl cellulose, ytterbium oxide, and lanthanum oxide is 90:9:3:1:1; the weight ratio of hydrogen storage alloy powder, graphene, polytetrafluoroethylene emulsion, and copper oxide is 90:9:3:12.

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