Preparation method of positive electrode material and application thereof

Abstract

The application relates to a preparation method of a positive electrode material, which comprises the following steps: a step of adding thiourea and a nickel hydroxide material into deionized water to form a first mixed slurry; a step of adding a soluble salt and a carbon material into the first mixed slurry to form a second mixed slurry; and a step of carrying out a hydrothermal reaction on the second mixed slurry, and then carrying out filtration, washing and drying in sequence to obtain the positive electrode material. The positive electrode material prepared by the preparation method does not contain cobalt elements, the positive electrode material has high conductivity and high electrochemical activity, and the positive electrode material has excellent stability in the charging and discharging cycle process. The positive electrode material can be applied to a nickel-based alkaline secondary battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and in particular to a method for preparing a cathode material and its application. Background Technology

[0002] This section provides background information relevant to this application, which does not necessarily constitute prior art.

[0003] Nickel hydroxide (Ni(OH)2) is widely used as the cathode material in nickel-based alkaline secondary batteries due to its excellent electrochemical properties, such as Ni-MH, Ni-Fe, Ni-Cd, Ni-Cr, and Ni-Zn alkaline batteries. Technical challenges associated with Ni(OH)2 in nickel-based alkaline secondary batteries include its instability in strongly alkaline media, leading to rapid capacity decay after a few cycles, despite its high specific capacity. Existing solutions address this issue include doping and / or surface-coating Ni(OH)2 with cobalt. Cobalt improves Ni(OH)2 performance by enhancing conductivity, mitigating volume expansion during charge-discharge cycles, suppressing oxygen evolution reactions during charging, and increasing specific capacity to some extent. However, cobalt is expensive and its resources are unevenly distributed. Therefore, developing a cobalt-free Ni(OH)2 cathode material that combines high electrochemical performance with excellent cycle stability is essential.

[0004] Chinese patent CN110943221A discloses a method for preparing a cobalt-free Ni(OH)2 cathode material, specifically involving the preparation of cobalt-free spherical Ni... 1-x-y Zn x M y (OH)₂ cathode material is mixed with a sulfur-soluble salt solution and subjected to sulfidation treatment to obtain NiS. x Cobalt-free spherical Ni 1-x-y Zn x M y (OH)₂ cathode material. NiS is formed on the surface of cobalt-free Ni(OH)₂. x The coating layer can effectively improve the conductivity of Ni(OH)2, making it suitable as a positive electrode material for batteries. However, existing technologies still have the following technical problems: the formed NiS... x The unstable crystal structure of the coating layer leads to problems with NiS during battery charging and discharging. x S in the electrolyte will precipitate into the electrolyte, and the coating structure is easily damaged, which will trigger side reactions and accelerate the degradation of battery performance, making it difficult to meet the application requirements of high stability and long life nickel-based batteries. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a positive electrode material applicable to nickel-based alkaline secondary batteries. The positive electrode material does not contain cobalt and has high conductivity, high electrochemical activity, and excellent stability during charge-discharge cycles.

[0006] In a first aspect, the present invention provides a cathode material that does not contain cobalt. The cathode material has a core-shell structure and includes a core layer and a coating layer from the inside out. The core layer includes nickel hydroxide, and the coating layer includes a composite material formed of a nickel-sulfur compound. The nickel-sulfur compound contains elements Ni, S, C, and M, wherein M contains at least one of F, Se, and Cl.

[0007] In one or more embodiments, the thickness of the coating layer is from 10 nm to 1 μm. Within this range, complete coverage of the core layer by the coating layer can be ensured.

[0008] In one or more embodiments, the core layer comprises β-phase nickel hydroxide (β-Ni(OH)2), wherein the β-phase nickel hydroxide is pure β-phase with a purity ≥99% and a loose packing density of 1.0-1.2 g / cm³. 3 Tap density 1.4-1.6 g / cm³ 3 The D90 particles have a diameter of 20-30 μm and are spherical in shape.

[0009] In one or more embodiments, the core layer comprises N-doped β-phase nickel hydroxide (N-doped β-Ni(OH)2) with a spherical morphology, wherein the doping element N is selected from one or more combinations of Fe, Yb, Ba, Mn, Ca, Pb, Na, Ti, Zr, Mo, V, Nb, Sc, Cr, Cu, Zn, Be, La, Mg, and Al.

[0010] In one or more embodiments, the core layer comprises β-phase nickel hydroxide powder and elemental N-doped β-phase nickel hydroxide.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned cathode material, the method comprising the following steps: The process of adding thiourea and nickel hydroxide materials to deionized water to form a first mixed slurry; The process of adding carbon materials and soluble salts to a first mixed slurry to form a second mixed slurry; The process involves subjecting the second mixed slurry to a hydrothermal reaction followed by filtration, washing, and drying to obtain the cathode material.

[0012] The nickel hydroxide material includes Ni(OH)2, and the solid-liquid ratio of the nickel hydroxide material to deionized water ranges from 1:15 (meaning 1 g of nickel hydroxide material corresponds to 15 mL of deionized water) to 1:30. The molar ratio of thiourea to Ni(OH)2 is (2-8):5, more preferably (4-6):5.

[0013] In one or more embodiments, the nickel hydroxide material comprises β-phase nickel hydroxide powder and element N-doped β-phase nickel hydroxide.

[0014] The carbon material is selected from at least one of organic carbon, artificial or natural graphite, graphene, carbon nanotubes, Super P, acetylene black, carbon black, and Ketjen black. In one or more embodiments, the carbon material is at least one of acetylene black, carbon black, and Ketjen black.

[0015] Preferably, the soluble salt is selected from at least one of potassium salts, sodium salts, ammonium salts, and nickel salts, and the soluble salt contains at least one of F, Se, and Cl. In one or more embodiments, the soluble salt is at least one of NiCl2, NaF2, and NaSeO3.

[0016] Based on the amount of Ni(OH)2 added, preferably, the amount of the soluble salt added is 1.5wt%-6wt% of Ni(OH)2, and the amount of the carbon material added is 0.5wt%-5wt% of Ni(OH)2.

[0017] Specifically, the hydrothermal reaction involves placing the second mixed slurry in a closed reactor, then heating it to 120-200°C for a hydrothermal reaction, which takes 1-4 hours. After the hydrothermal reaction is complete, the mixture is cooled to room temperature, and finally discharged and filtered to obtain the reaction product.

[0018] In one or more embodiments, the specific process of washing and drying is as follows: the reaction product obtained by hydrothermal reaction is washed with deionized water at least three times, and then placed in a forced-air drying oven for drying at a temperature of 30-70°C for no less than 6 hours to obtain the positive electrode material.

[0019] The cathode material prepared by the above method has the advantages of being cobalt-free, having high conductivity, high electrochemical activity, and high cycle stability. The reasons for this are speculated to be as follows: (1) A uniform and complete coating layer is formed on the surface of the core layer through a hydrothermal reaction. The coating layer consists of a composite material formed by nickel-sulfur compounds and carbon, which can play a "supporting" and "stabilizing" role, suppressing the excessive expansion and contraction of the core layer during the conversion process. During the charging and discharging process, even if volume strain occurs, the coating layer can help maintain the integrity of the structure, reduce the distortion and deformation of the crystal lattice of the core layer, thereby effectively suppressing crystal distortion and improving the cycle stability of the cathode material; (2) During charge-discharge cycles, the nickel-sulfur compounds in the coating layer can effectively suppress the β-Ni(OH)2 phase transition to α-Ni(OH)2 in the core layer. The carbon in the coating layer can construct a continuous conductive pathway between cathode material particles, increasing the electronic conductivity of the cathode material by 2-3 orders of magnitude, significantly improving conductivity and electrochemical activity. The synergistic effect of nickel-sulfur compounds and carbon optimizes the band structure of the material and may introduce defect energy levels, promoting electron jumping, thereby optimizing Ni 2+ / Ni 3+ The electron transfer path allows electrons to move more quickly and smoothly in Ni. 2+ and Ni 3+ This facilitates charge transfer between components, reduces charge transfer resistance, and significantly improves the conductivity of the cathode material. (3) The nickel-sulfur compound doped with element M formed by hydrothermal reaction has a stable crystal structure. By combining with carbon, the precipitation of S in the nickel-sulfur compound is significantly suppressed during the charging and discharging process.

[0020] It should be noted that the N-doped β-phase nickel hydroxide described in this invention can be prepared using existing methods. The raw materials for the N dopant are selected from one or more combinations of sulfates, phosphates, nitrates, chlorides, oxalates, acetates, and carbonates of any one of Fe, Yb, Ba, Mn, Ca, Pb, Na, Ti, Zr, Mo, V, Nb, Sc, Cr, Cu, Zn, Be, La, Mg, and Al. Examples of the preparation methods include: (1) Liquid phase method / gel method: Soluble nickel source and soluble dopant element raw material are fully dissolved in aqueous solution, filtered, and alkaline substances are added to adjust the pH value for co-precipitation crystallization; the slurry is filtered to obtain filter cake and thoroughly washed with pure water; the filter cake is dried and sintered to obtain element N doped β phase nickel hydroxide; (2) Hydrothermal method or critical hydrothermal method: Soluble nickel source and soluble dopant raw material are placed in an aqueous solution according to the stoichiometric ratio, transferred to a hydrothermal reactor, and subjected to hydrothermal reaction under certain pressure and temperature. The material is discharged and filtered to obtain a filter cake. After drying and sieving the filter cake, element N doped β phase nickel hydroxide is obtained.

[0021] Thirdly, the present invention also discloses the application of the above-mentioned positive electrode material in nickel-based alkaline secondary batteries, wherein the positive electrode active material of the nickel-based alkaline secondary battery includes the aforementioned positive electrode material. The nickel-based alkaline secondary batteries include, but are not limited to, nickel-metal hydride batteries, nickel-iron batteries, and nickel-zinc batteries.

[0022] The cathode material provided by this invention does not contain cobalt. By controlling the formation and composition of the coating layer, the integrity of the cobalt-free nickel hydroxide structure during charge-discharge cycles can be significantly improved, effectively suppressing crystal distortion and reducing charge transfer resistance during charge-discharge cycles, while also improving the material's conductivity, capacity, and cycle stability.

[0023] It was specifically discovered that existing core-shell structured nickel hydroxide cathode materials prepared by high-temperature sintering processes (such as nickel hydroxide cathode materials with a thin coating) may exhibit degradation compared to the core-shell structured cathode materials prepared by hydrothermal reaction in this invention. The reason for this is speculated to be that when the hydrothermal reaction is carried out below 200°C (120-200°C), the hydrothermal reaction between carbon materials and nickel hydroxide is mainly a mild recombination, and the carbon materials are moderately oxidized to generate more oxygen-containing functional groups (such as -COOH, -C=O), which enhances the coordination ability with Ni(OH)2. However, under high-temperature sintering conditions, a phase transformation or grain coarsening of nickel hydroxide is triggered, leading to a decrease in the structural stability of the material and a deterioration in electrochemical performance.

[0024] The following description is based on specific embodiments. Attached Figure Description

[0025] The accompanying drawings further illustrate the invention, but the embodiments in the drawings do not constitute any limitation on the invention.

[0026] Figure 1 The images show the SEM morphology of spherical pure β-phase nickel hydroxide used in the embodiments and comparative examples of this invention.

[0027] Figure 2 The XRD patterns of spherical pure β-phase nickel hydroxide used in the embodiments and comparative examples of this invention are shown.

[0028] Figure 3 This is a SEM morphology image of the cathode material provided in Example 4.

[0029] Figure 4 This is the EDS composition diagram of the cathode material provided in Example 4.

[0030] Figure 5 This is a SEM morphology image of the cathode material provided in Example 5.

[0031] Figure 6 This is the EDS composition diagram of the cathode material provided in Example 5.

[0032] Figure 7 The image shows the SEM morphology of the cathode material provided in Comparative Example 1.

[0033] Figure 8 These are the XRD patterns of the cathode materials provided in Examples 1-3. Detailed Implementation

[0034] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0037] It should be noted that the raw materials used in the embodiments and comparative examples of this invention are all commercially available products. The nickel hydroxide described in the embodiments and comparative examples of this invention is spherical pure β-phase nickel hydroxide, which meets the requirements for spherical nickel hydroxide products in the standard "Spherical Nickel Hydroxide" (GB / T20507-2018). The D50 (average particle size) of this spherical β-phase nickel hydroxide is approximately 9.5 μm, and the four-probe conductivity test result of this spherical β-phase nickel hydroxide is approximately 6.87 × 10⁻⁶. -8 The discharge specific capacity of this spherical β-phase nickel hydroxide is approximately 280 mAh / g at 0.2C discharge.

[0038] [Example 1] This embodiment provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 4.567g of thiourea and 4.635g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:6. Step two: Add acetylene black and Na2SeO3 to the first mixed slurry and continue stirring for 10 minutes to form the second mixed slurry. The amount of acetylene black added is 3 wt% of the amount of nickel hydroxide added, and the amount of Na2SeO3 added is 3 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 150°C for 4 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0039] [Example 2] This embodiment provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 4.567g of thiourea and 4.635g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:4. Step 2: Add carbon black and NiCl2 to the first mixed slurry and continue stirring for 10 minutes to form the second mixed slurry. The amount of carbon black added is 5 wt% of the amount of nickel hydroxide added, and the amount of NiCl2 added is 6 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 200℃ for 1 hour), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0040] [Example 3] This embodiment provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 3.04g of thiourea and 4.64g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:4. Step two: Add Ketjen black carbon and NaF2 to the first mixed slurry, and continue stirring for 10 minutes to form the second mixed slurry. The amount of Ketjen black carbon added is 2 wt% of the amount of nickel hydroxide added, and the amount of NaF2 added is 4 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 140℃ for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0041] [Example 4] This embodiment provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 3.04g of thiourea and 4.64g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:4. Step two: Add acetylene black and Na2SeO3 to the first mixed slurry and continue stirring for 10 minutes to form the second mixed slurry. The amount of acetylene black added is 9 wt% of the amount of nickel hydroxide added, and the amount of Na2SeO3 added is 3 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 140℃ for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0042] [Example 5] This embodiment provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 4.567g of thiourea and 4.635g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:6. Step two: Add acetylene black and Na2SeO3 to the first mixed slurry and continue stirring for 10 minutes to form the second mixed slurry. The amount of acetylene black added is 4 wt% of the amount of nickel hydroxide added, and the amount of Na2SeO3 added is 4 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 140℃ for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0043] In step three, the hydrothermal reaction temperature is 140℃. At this temperature, Na2SeO3 provides Se(IV), which is reduced to generate Se²⁻ / Se, and reacts with S produced by the decomposition of thiourea. 2- Ni(OH)2 provides Ni 2+ Combined, it forms a nickel-sulfur compound (NiS). x Se y Carbon materials (acetylene black) load selenide / sulfide particles onto their surface through physical adsorption (van der Waals forces) and chemical bonding (CO-Ni, CS-Ni, C-Se-Ni), forming a composite structure. The final product is a coating layer composed of nickel-sulfur compounds / carbon composite materials formed on the surface of nickel hydroxide.

[0044] [Comparative Example 1] This comparative example provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 4.567g of thiourea and 4.635g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:6. Step two: The first mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 180°C for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0045] [Comparative Example 2] This comparative example provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 4.567g of thiourea and 4.635g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:6. Step two: Add Na2SeO3 to the first mixed slurry and continue stirring for 10 minutes to form the second mixed slurry. The amount of Na2SeO3 added is 10 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 140℃ for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0046] [Comparative Example 3] This comparative example provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 3.04g of thiourea and 4.64g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:4. Step two: The first mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 100°C for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0047] [Comparative Example 4] This comparative example provides a cathode material, the preparation method of which includes the following steps: Step 1: Add 0.76g of thiourea and 4.64g of nickel hydroxide to 100mL of deionized water simultaneously. Stir magnetically for 20 minutes to form the first mixed slurry. The molar ratio of thiourea to nickel hydroxide is 5:1. Step two: Add NaF to the first slurry and continue stirring for 10 minutes to form the second slurry. The amount of NaF added is 0.5 wt% of the amount of nickel hydroxide added. Step 3: The second mixed slurry is transferred to a hydrothermal reactor for hydrothermal reaction (hydrothermal reaction at 150°C for 2 hours), and then filtered, washed and dried in sequence to obtain the positive electrode material.

[0048] Figure 1 This is a SEM image of spherical pure β-phase nickel hydroxide. Figure 3 This is a SEM image of the cathode material provided in Example 4. Figure 5 The image shows the SEM morphology of the cathode material provided in Example 5. Figure 7 SEM morphology image of the cathode material provided for Comparative Example 1. Figure 1 , Figure 3 and Figure 5 It can be seen that the cathode material prepared by the preparation method provided by this invention has a good spherical structure, and the coating layer on the surface is complete, uniform, and dense. (Comparison) Figure 7 , Figure 3 and Figure 5It can be seen that the coating layer of the cathode material prepared by the preparation method provided in Comparative Example 1 is incomplete.

[0049] Figure 4 The surface EDS composition analysis results of the cathode material provided in Example 4 are as follows. Figure 6 The surface EDS composition analysis results of the cathode material provided in Example 5 are as follows. Figure 4 and Figure 6 This indicates that the coating layer of the cathode material formed by the preparation method provided by the present invention comprises a composite material formed from nickel-sulfur compounds and carbon. Figure 8 The XRD patterns of the cathode materials provided in Examples 1, 2, and 3 are shown. Figure 2 The XRD pattern of spherical pure β-phase nickel hydroxide is shown in the comparison. Figure 2 and Figure 8 The XRD peaks of NiS and carbon materials are clearly visible.

[0050] [Preparation of Alkaline Nickel-Metal Hydride Batteries] Alkaline nickel-metal hydride batteries were prepared using the cathode materials provided in Examples 1-5 and Comparative Examples 1-5, respectively. The specific steps are as follows: Step 1: Mix 100 parts by weight of the positive electrode material and 1 part by weight of yttrium oxide (Y2O3) to prepare a positive electrode slurry. Then, uniformly coat the positive electrode slurry onto a substrate with an area density of 280 g / m². 2 The foamed nickel substrate is rolled, dried, and then cut into positive electrode sheets; Step two, add 100 parts by weight of hydrogen storage alloy powder (A2B7 type La-Mg-Ni hydrogen storage alloy, La...) 0.7 Mg 0.3 Ni 2.8 C0 0.5 A negative electrode slurry was prepared by mixing 0.2 parts by weight of sodium polyacrylate, 0.04 parts by weight of carboxymethyl cellulose, 1.5 parts by weight of styrene-butadiene rubber latex (50 wt% SBR latex), 0.3 parts by weight of acetylene black, and 22.4 parts by weight of water. The negative electrode slurry was uniformly coated on a copper mesh with a thickness of 60 μm and a nickel-plated surface. After rolling, drying, and cutting, it was cut into negative electrode sheets. Step 3: The diaphragm is formed from a nonwoven fabric made of polypropylene fibers that have undergone sulfonation treatment, with a thickness of 0.16 mm (weight per unit area of ​​55 g / m²). 2 ); Step 4: Dissolve 500 parts by weight of water and 150 parts by weight of KOH to obtain an alkaline electrolyte. Step 5: The positive electrode, negative electrode, and separator are wound and placed in a nickel-plated steel shell. Then, alkaline electrolyte is injected and the shell is sealed to assemble an AA-type alkaline nickel-metal hydride battery with a nominal capacity of 1700mAh.

[0051] [Performance Testing of Alkaline Nickel-Metal Hydride Batteries] The alkaline nickel-metal hydride (NiMH) battery undergoes initial activation treatment. The specific steps are as follows: The alkaline NiMH battery is left to stand at 45°C for 12 hours. Then, the nominal capacity (1700mAh) is set to 1C, and it is charged at 0.02C for 5 hours, followed by charging at 0.1C for 15 hours. Finally, it is discharged at 0.2C until the alkaline NiMH battery voltage reaches 1.0V. This charge and discharge cycle is repeated once. This initial activation treatment brings the alkaline NiMH battery to a testable state.

[0052] The following tests were performed on the activated alkaline nickel-metal hydride batteries: (1) Cyclic performance test The cycle test method for alkaline nickel-metal hydride batteries after activation treatment is as follows: charge at 0.1C for 10 hours at 25℃, let stand for 30 minutes, then discharge at 1C to 1.0V, and let stand for 30 minutes; repeat the above charge-discharge cycle for 200 cycles, record the discharge capacity of the first cycle and the discharge capacity of the 200th cycle, and calculate the capacity retention rate before and after the cycle using the following formula: Capacity retention rate = (Discharge capacity of the 200th cycle / Discharge capacity of the first cycle) × 100%.

[0053] (2) Rate discharge performance test The method for testing the rate discharge performance of alkaline nickel-metal hydride batteries after activation treatment is as follows: At 25℃, charge at 0.1C for 10 hours, let stand for 30 minutes, then discharge at 1C to 1.0V, let stand for 30 minutes, and record the first discharge capacity of the alkaline nickel-metal hydride battery; then charge at 0.1C for 10 hours, let stand for 30 minutes, discharge at 5C to 1.0V, let stand for 30 minutes, and repeat this charge-discharge cycle 50 times to obtain the discharge capacity of the alkaline nickel-metal hydride battery after the 50th cycle. The capacity retention rate before and after the cycle is calculated by the following formula: Capacity retention rate = (50th cycle discharge capacity / first discharge capacity) × 100%.

[0054] (3) Self-discharge test at room temperature The self-discharge test method for activated alkaline nickel-metal hydride batteries is as follows: Charge at 0.1C for 10 hours at 25℃, allow to stand for 30 minutes, then discharge at 1C to 1.0V, allow to stand for 30 minutes, and record the initial discharge capacity of the alkaline nickel-metal hydride battery. Then charge at 0.1C for 10 hours at 25℃, and then place the fully charged alkaline nickel-metal hydride battery at an ambient temperature of 25℃ for 28 days. Discharge at 1C to 1.0V, and record the discharge capacity of the alkaline nickel-metal hydride battery after 28 days of standing at room temperature. Calculate the capacity retention rate before and after standing using the following formula: Capacity retention rate = (Discharge capacity after 28 days of standing / Initial discharge capacity) × 100%.

[0055] (4) High-temperature self-discharge test The self-discharge test method for activated alkaline nickel-metal hydride batteries is as follows: Charge at 0.1C for 10 hours at 25℃, allow to stand for 30 minutes, then discharge at 1C to 1.0V, allow to stand for 30 minutes, and record the initial discharge capacity of the alkaline nickel-metal hydride battery. Then charge at 0.1C for 10 hours at 25℃, and place the fully charged alkaline nickel-metal hydride battery at an ambient temperature of 60℃ for 28 days. Then discharge at 1C to 1.0V, and record the discharge capacity of the alkaline nickel-metal hydride battery after 28 days of standing at high temperature. Calculate the capacity retention rate before and after standing using the following formula: Capacity retention rate = (Discharge capacity after 28 days of standing / Initial discharge capacity) × 100%.

[0056] The results of the above tests are shown in Table 1.

[0057] Table 1 shows that the cathode material prepared by the method provided in this invention can simultaneously possess good cycle performance, rate performance, and self-discharge suppression performance. Comparing the test results of Example 5 and Comparative Examples 1-4, it is evident that when the coating layer includes a composite material formed from nickel-sulfur compounds and carbon, the nickel-sulfur compounds and carbon can synergistically improve the stability of the cathode material during charge-discharge cycles and significantly suppress self-discharge.

[0058] Table 1

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a positive electrode material, characterized in that, The process includes the following steps: The process of adding thiourea and nickel hydroxide materials to deionized water to form a first mixed slurry; The process of adding soluble salts and carbon materials to a first mixed slurry to form a second mixed slurry; The process of subjecting the second mixed slurry to a hydrothermal reaction followed by filtration, washing, and drying to obtain the cathode material; The soluble salt is selected from at least one of potassium salt, sodium salt, ammonium salt, and nickel salt, and the added soluble salt contains at least one of F, Se, and Cl. The hydrothermal reaction specifically involves placing the second mixed slurry in a closed reaction vessel, then heating it to 120-200℃ for a hydrothermal reaction, which takes 1-4 hours. After the hydrothermal reaction is completed, the mixture is cooled to room temperature.

2. The preparation method according to claim 1, characterized in that, The solid-liquid ratio of the nickel hydroxide material and deionized water ranges from 1:15 to 1:

30.

3. The preparation method according to claim 2, characterized in that, The nickel hydroxide material includes Ni(OH)2, and the molar ratio of the thiourea and Ni(OH)2 is (2-8):5; based on the amount of Ni(OH)2 added, the amount of the soluble salt added is 2wt%-6wt% of Ni(OH)2, and the amount of the carbon material added is 0.5wt%-5wt% of Ni(OH)2.

4. The preparation method according to claim 3, characterized in that, The material is selected from at least one of organic carbon, artificial or natural graphite, graphene, carbon nanotubes, Super P, acetylene black, carbon black, and Ketjen black.

5. The preparation method according to claim 2, characterized in that, The soluble salt is at least one of NiCl2, NaF2, and NaSeO3.

6. A positive electrode material, characterized in that, The cathode material is prepared by the preparation method according to any one of claims 1-5, and the cathode material does not contain cobalt.

7. The cathode material according to claim 6, characterized in that, The cathode material has a core-shell structure, comprising a core layer and a coating layer from the inside out. The core layer comprises nickel hydroxide, and the coating layer comprises a composite material formed of nickel-sulfur compounds. The nickel-sulfur compounds contain elements Ni, S, C, and element M, wherein element M contains at least one of F, Se, and Cl.

8. The cathode material according to claim 7, characterized in that, The core layer comprises α-phase nickel hydroxide with a spherical morphology.

9. The cathode material according to claim 8, characterized in that, The core layer comprises element N-doped β-phase nickel hydroxide with a spherical morphology. The doping element N is selected from one or more combinations of Fe, Yb, Ba, Mn, Ca, Pb, Na, Ti, Zr, Mo, V, Nb, Sc, Cr, Cu, Zn, Be, La, Mg, and Al.

10. The application of the cathode material prepared by the preparation method according to any one of claims 1-5 in nickel-based alkaline secondary batteries.

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