A cathode material for lithium-ion batteries and a preparation method thereof

Abstract

The present invention relates to the technical field of electrode materials, and particularly relates to a cathode material for a lithium-ion battery and a preparation method thereof. The cathode material is obtained by high-temperature calcination of a cathode material precursor; the cathode material precursor is formed by carboxylating carbon nanotubes, freeze-drying to form carboxylated carbon nanotube aerogel powder, and then mixing with an impregnating solution and calcining. The lithium-ion battery prepared from the cathode material provided by the present invention has a high Coulomb efficiency, excellent rate performance, excellent cycle stability and long-life characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and particularly to a cathode material for a lithium-ion battery and a preparation method thereof. Background Art

[0002] With the rapid growth of the demand for portable electronic devices, electric vehicles, and energy storage systems in modern society, lithium-ion batteries have become one of the most widely used secondary batteries due to their high energy density, long cycle life, and excellent rate performance. However, in order to meet the application requirements of high energy density, high rate performance, and long life, the performance improvement of lithium-ion battery cathode materials remains the focus and difficulty of research.

[0003] Currently, the research on lithium-ion battery cathode materials mainly focuses on improving their specific capacity, rate performance, and cycle stability. During the preparation of traditional cathode materials, the dispersion of metal ions is poor, and large and unevenly distributed metal oxide particles are easily formed after calcination, resulting in low conductivity and lithium-ion transmission rate of the materials, serious electrode polarization, and thus limiting the rate performance and cycle life of the battery. In addition, the cathode material is prone to volume change and side reactions during the cycling process, further reducing the cycle stability and long-life characteristics of the battery. Therefore, how to optimize the composition and preparation process of the cathode material to improve its microstructure and electrochemical performance has become an important research direction in the current field of lithium-ion batteries. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a cathode material for a lithium-ion battery and a preparation method thereof to solve the problems of low conductivity and lithium-ion transmission rate of the existing cathode material, serious electrode polarization, and insufficient cycle stability and long-life characteristics caused by volume change and side reactions during the cycling process.

[0005] Based on the above purpose, the present invention provides a cathode material for a lithium-ion battery, which is obtained by calcining a cathode material precursor; the preparation method of the cathode material precursor is as follows:

[0006] (1) Treat carbon nanotubes with a mixed solution of sulfuric acid and nitric acid to obtain carboxylated carbon nanotubes;

[0007] (2) Add the carboxylated carbon nanotubes into deionized water, then adjust the pH to 8 - 8.5 with sodium hydroxide, freeze-dry, grind and sieve to obtain carboxylated carbon nanotube aerogel powder;

[0008] (3) Add polyvinyl alcohol, acrylic acid, dipropylene glycol diacrylate into deionized water, stir for 20 - 40 min, then add lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate, ammonium persulfate and tetramethylethylenediamine, and continue to stir for 0.5 - 1.5 h to obtain an impregnation solution;

[0009] (4) Add carboxylated carbon nanotube aerogel powder into the impregnation solution, ultrasonically disperse for 20 - 40 min, heat up to 65 - 75 °C, stir for 2.5 - 3.5 h, wash with water, wash with alcohol, and vacuum dry to obtain a precursor of the positive electrode material.

[0010] Preferably, in the step (1), the concentration of sulfuric acid is 98% and the concentration of nitric acid is 65%.

[0011] Preferably, in the mixed solution of the step (1), the volume ratio of sulfuric acid to nitric acid is 3:1.

[0012] Preferably, in the step (1), the weight ratio of carbon nanotubes to the mixed solution is 1:8 - 12.

[0013] Preferably, in the step (1), the treatment time is 0.5 - 1.5 h.

[0014] Preferably, in the step (2), the weight ratio of carboxylated carbon nanotubes to deionized water is 1:4 - 6.

[0015] Preferably, in the step (2), the temperature of freeze-drying is -75 ± 5 °C and the time is 20 - 28 h.

[0016] Preferably, in the step (3), the weight ratio of polyvinyl alcohol, acrylic acid, dipropylene glycol diacrylate, deionized water, lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate and cobalt acetate tetrahydrate is 0.3 - 0.8:2 - 4:0.1 - 0.5:15 - 25:0.51 - 1.53:1 - 3:0.12 - 0.37:0.12 - 0.37.

[0017] Preferably, in the step (4), the weight ratio of carboxylated carbon nanotube aerogel powder to the impregnation solution is 0.5:15 - 25.

[0018] Further, the present invention also provides a preparation method of a positive electrode material for a lithium-ion battery, comprising the following steps: Put the precursor of the positive electrode material into a muffle furnace, heat from room temperature to 450 - 550 °C at a rate of 3 - 8 °C / min, keep warm for 10 - 14 h, then heat from 450 - 550 °C to 650 - 750 °C, keep warm for 0.5 - 1.5 h, cool down to room temperature, grind and sieve to obtain the positive electrode material for a lithium-ion battery.

[0019] The beneficial effects of the present invention:

[0020] The lithium-ion battery prepared from the cathode material provided by the present invention has a relatively high initial discharge specific capacity, and its Coulomb efficiency can reach more than 95%. In terms of rate performance, the discharge specific capacity at 10C can reach more than 90% of the discharge specific capacity at 0.1C, showing excellent rate performance. At the same time, after 500 cycles, the discharge specific capacity can still remain above 95%, demonstrating excellent cycle stability and long-life characteristics.

[0021] Through the carboxylation treatment on the surface of carbon nanotubes, the present invention significantly improves the dispersion of metal ions in the cathode material precursor. After calcination, metal oxide particles with smaller particle sizes and uniform distribution are formed, thereby improving the conductivity, rate performance, and cycle stability of the material. Further, the carboxylated carbon nanotube aerogel powder prepared by freeze-drying treatment constructs a three-dimensional porous network structure, enhancing the dispersion of the material and the stability of the microstructure, and significantly improving the electrochemical performance of the battery.

[0022] Through the cross-linked structure formed by dipropylene glycol diacrylate and acrylic acid, and the addition of polyvinyl alcohol, the present invention effectively improves the dispersion of the carboxylated carbon nanotube aerogel powder and the structural integrity of the cathode material, further enhancing the cycle stability. Reasonably controlling the calcination temperature to avoid the decomposition of carbon nanotubes ensures the integrity of the framework structure of the cathode material and the stability of the conductive network. The cathode material prepared by the present invention is suitable for the field of lithium-ion batteries with high requirements for energy density, rate performance, and cycle life, and has broad application prospects. Specific Embodiments

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further details the present invention in combination with specific embodiments.

[0024] In the specific embodiments of the present invention, the carbon nanotubes are purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with the model C121257, an inner diameter of 2-5 nm, an outer diameter of <8 nm, and a length of 10-30 μm; the concentration of sulfuric acid is 98%; the concentration of nitric acid is 65%.

[0025] Example 1:

[0026] (1) Add 1 g of carbon nanotubes to a mixed solution of 8 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonicate for 0.5 h, then wash with deionized water three times, and vacuum dry at 80°C for 24 h to obtain carboxylated carbon nanotubes;

[0027] (2) Add 1 g of carboxylated carbon nanotubes to 4 g of deionized water, then adjust the pH to 8.0 with sodium hydroxide, and then freeze-dry at -70°C for 20 h and grind through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0028] (3) Add 0.3 g of polyvinyl alcohol (PVA1788), 2 g of acrylic acid, and 0.1 g of dipropylene glycol diacrylate to 15 g of deionized water, stir for 20 min, then add 0.51 g of lithium acetate dihydrate, 1 g of nickel acetate tetrahydrate, 0.12 g of manganese acetate tetrahydrate, 0.12 g of cobalt acetate tetrahydrate, 35 mg of ammonium persulfate, and 25 mg of tetramethylethylenediamine, and continue stirring for 0.5 h to obtain an impregnating solution;

[0029] (4) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 15 g of the impregnating solution, ultrasonically disperse for 20 min, then raise the temperature to 65 °C, stir for 2.5 h, wash with water, wash with alcohol, and finally vacuum dry at 80 °C for 24 h to obtain a precursor of the positive electrode material;

[0030] (5) Put the precursor of the positive electrode material into a muffle furnace, heat it from room temperature to 450 °C at a rate of 3 °C / min, hold for 10 h, then heat it from 450 °C to 650 °C, hold for 0.5 h, cool down, grind it through a 100-mesh sieve to obtain the positive electrode material for lithium-ion batteries.

[0031] Example 2:

[0032] (1) Add 1 g of carbon nanotubes to a mixed solution of 10 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonically treat for 1 h, then wash with deionized water 3 times, and vacuum dry at 80 °C for 24 h to obtain carboxylated carbon nanotubes;

[0033] (2) Add 1 g of carboxylated carbon nanotubes to 5 g of deionized water, then adjust the pH to 8.2 with sodium hydroxide, and then freeze-dry at -75 °C for 24 h, grind it through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0034] (3) Add 0.5 g of polyvinyl alcohol (PVA1788), 3 g of acrylic acid, and 0.3 g of dipropylene glycol diacrylate to 20 g of deionized water, stir for 30 min, then add 1.02 g of lithium acetate dihydrate, 1.99 g of nickel acetate tetrahydrate, 0.25 g of manganese acetate tetrahydrate, 0.25 g of cobalt acetate tetrahydrate, 40 mg of ammonium persulfate, and 30 mg of tetramethylethylenediamine, and continue stirring for 1 h to obtain an impregnating solution;

[0035] (4) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 20 g of the impregnating solution, ultrasonically disperse for 30 min, then raise the temperature to 70 °C, stir for 3 h, wash with water, wash with alcohol, and finally vacuum dry at 80 °C for 24 h to obtain a precursor of the positive electrode material;

[0036] (5) Put the cathode material precursor into a muffle furnace, heat it from room temperature to 500 °C at a rate of 5 °C / min, hold for 12 h, then heat it from 500 °C to 700 °C, hold for 1 h, cool down, grind and pass through a 100-mesh sieve to obtain the cathode material for lithium-ion batteries.

[0037] Example 3:

[0038] (1) Add 1 g of carbon nanotubes to a mixed solution of 12 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonicate for 1.5 h, then wash with deionized water 3 times and vacuum dry at 80 °C for 24 h to obtain carboxylated carbon nanotubes;

[0039] (2) Add 1 g of carboxylated carbon nanotubes to 6 g of deionized water, then adjust the pH to 8.5 with sodium hydroxide, and then freeze-dry at -80 °C for 28 h, grind and pass through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0040] (3) Add 0.8 g of polyvinyl alcohol (PVA1788), 4 g of acrylic acid, 0.5 g of dipropylene glycol diacrylate to 25 g of deionized water, stir for 40 min, then add 1.53 g of lithium acetate dihydrate, 3 g of nickel acetate tetrahydrate, 0.37 g of manganese acetate tetrahydrate, 0.37 g of cobalt acetate tetrahydrate, 45 mg of ammonium persulfate and 35 mg of tetramethylethylenediamine, and continue to stir for 1.5 h to obtain an impregnating solution;

[0041] (4) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 25 g of the impregnating solution, ultrasonically disperse for 40 min, then heat up to 75 °C and stir for 3.5 h, wash with water and alcohol, and finally vacuum dry at 80 °C for 24 h to obtain the cathode material precursor;

[0042] (5) Put the cathode material precursor into a muffle furnace, heat it from room temperature to 550 °C at a rate of 8 °C / min, hold for 14 h, then heat it from 550 °C to 750 °C, hold for 1.5 h, cool down, grind and pass through a 100-mesh sieve to obtain the cathode material for lithium-ion batteries.

[0043] Comparative Example 1:

[0044] The difference between Comparative Example 1 and Example 2 is that the carboxylated carbon nanotubes in step (2) are replaced with carbon nanotubes;

[0045] The specific steps are as follows:

[0046] (1) Add 1 g of carbon nanotubes to 5 g of deionized water, then adjust the pH to 8.2 with sodium hydroxide, and then freeze-dry at -75 °C for 24 h, grind and pass through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0047] (2) Add 0.5 g of polyvinyl alcohol (PVA1788), 3 g of acrylic acid, and 0.3 g of dipropylene glycol diacrylate to 20 g of deionized water, stir for 30 min, then add 1.02 g of lithium acetate dihydrate, 1.99 g of nickel acetate tetrahydrate, 0.25 g of manganese acetate tetrahydrate, 0.25 g of cobalt acetate tetrahydrate, 40 mg of ammonium persulfate, and 30 mg of tetramethylethylenediamine, and continue stirring for 1 h to obtain an impregnation solution;

[0048] (3) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 20 g of the impregnation solution, ultrasonically disperse for 30 min, then raise the temperature to 70 °C, stir for 3 h, wash with water, wash with alcohol, and finally vacuum dry at 80 °C for 24 h to obtain a precursor of the positive electrode material;

[0049] (4) Place the precursor of the positive electrode material in a muffle furnace, heat from room temperature to 500 °C at a rate of 5 °C / min, hold for 12 h, then heat from 500 °C to 700 °C, hold for 1 h, cool down, grind through a 100-mesh sieve to obtain the positive electrode material.

[0050] Comparative Example 2:

[0051] The difference between Comparative Example 2 and Example 2 is that the carboxylated carbon nanotube aerogel powder in step (4) is replaced with carboxylated carbon nanotubes;

[0052] The specific steps are as follows:

[0053] (1) Add 1 g of carbon nanotubes to a mixed solution of 10 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonically treat for 1 h, then wash with deionized water 3 times, and vacuum dry at 80 °C for 24 h to obtain carboxylated carbon nanotubes;

[0054] (2) Add 0.5 g of polyvinyl alcohol (PVA1788), 3 g of acrylic acid, and 0.3 g of dipropylene glycol diacrylate to 20 g of deionized water, stir for 30 min, then add 1.02 g of lithium acetate dihydrate, 1.99 g of nickel acetate tetrahydrate, 0.25 g of manganese acetate tetrahydrate, 0.25 g of cobalt acetate tetrahydrate, 40 mg of ammonium persulfate, and 30 mg of tetramethylethylenediamine, and continue stirring for 1 h to obtain an impregnation solution;

[0055] (3) Add 0.5 g of carboxylated carbon nanotubes to 20 g of the impregnation solution, ultrasonically disperse for 30 min, then raise the temperature to 70 °C, stir for 3 h, wash with water, wash with alcohol, and finally vacuum dry at 80 °C for 24 h to obtain a precursor of the positive electrode material;

[0056] (4) Place the precursor of the positive electrode material in a muffle furnace, heat from room temperature to 500 °C at a rate of 5 °C / min, hold for 12 h, then heat from 500 °C to 700 °C, hold for 1 h, cool down, grind through a 100-mesh sieve to obtain the positive electrode material.

[0057] Comparative Example 3:

[0058] The difference between Comparative Example 3 and Example 2 is that: in step (3), dipropylene glycol diacrylate is not added;

[0059] The specific steps are as follows:

[0060] (1) Add 1 g of carbon nanotubes to a mixed solution of 10 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonicate for 1 h, then wash with deionized water 3 times, and vacuum dry at 80 °C for 24 h to obtain carboxylated carbon nanotubes;

[0061] (2) Add 1 g of carboxylated carbon nanotubes to 5 g of deionized water, then adjust the pH to 8.2 with sodium hydroxide, and then freeze-dry at -75 °C for 24 h, grind through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0062] (3) Add 0.5 g of polyvinyl alcohol (PVA1788), 3 g of acrylic acid to 20 g of deionized water, stir for 30 min, then add 1.02 g of lithium acetate dihydrate, 1.99 g of nickel acetate tetrahydrate, 0.25 g of manganese acetate tetrahydrate, 0.25 g of cobalt acetate tetrahydrate, 40 mg of ammonium persulfate and 30 mg of tetramethylethylenediamine, and continue to stir for 1 h to obtain an impregnating solution;

[0063] (4) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 20 g of the impregnating solution, ultrasonically disperse for 30 min, then raise the temperature to 70 °C, stir for 3 h, wash with water and alcohol, and finally vacuum dry at 80 °C for 24 h to obtain a precursor of the positive electrode material;

[0064] (5) Put the precursor of the positive electrode material into a muffle furnace, heat from room temperature to 500 °C at a rate of 5 °C / min, hold for 12 h, then heat from 500 °C to 700 °C, hold for 1 h, cool down, grind through a 100-mesh sieve to obtain the positive electrode material.

[0065] Comparative Example 4:

[0066] The difference between Comparative Example 4 and Example 2 is that: in step (3), polyvinyl alcohol is not added;

[0067] The specific steps are as follows:

[0068] (1) Add 1 g of carbon nanotubes to a mixed solution of 10 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonicate for 1 h, then wash with deionized water 3 times, and vacuum dry at 80 °C for 24 h to obtain carboxylated carbon nanotubes;

[0069] (2) Add 1 g of carboxylated carbon nanotubes to 5 g of deionized water, then adjust the pH to 8.2 with sodium hydroxide, and then freeze-dry at -75 °C for 24 h, grind through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0070] (3) Add 3 g of acrylic acid and 0.3 g of dipropylene glycol diacrylate to 20 g of deionized water, stir for 30 min, then add 1.02 g of lithium acetate dihydrate, 1.99 g of nickel acetate tetrahydrate, 0.25 g of manganese acetate tetrahydrate, 0.25 g of cobalt acetate tetrahydrate, 40 mg of ammonium persulfate and 30 mg of tetramethylethylenediamine, and continue to stir for 1 h to obtain an impregnation solution;

[0071] (4) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 20 g of the impregnation solution, ultrasonically disperse for 30 min, then raise the temperature to 70 °C, stir for 3 h, wash with water and then with alcohol, and finally vacuum-dry at 80 °C for 24 h to obtain the precursor of the positive electrode material;

[0072] (5) Put the precursor of the positive electrode material into a muffle furnace, heat from room temperature to 500 °C at a rate of 5 °C / min, hold for 12 h, then heat from 500 °C to 700 °C, hold for 1 h, cool down, grind through a 100-mesh sieve to obtain the positive electrode material.

[0073] Comparative Example 5:

[0074] The difference between Comparative Example 5 and Example 2 is that in step (5), directly heat from room temperature to 700 °C and hold for 13 h;

[0075] The specific steps are as follows:

[0076] (1) Add 1 g of carbon nanotubes to a mixed solution of 10 g of sulfuric acid and nitric acid (volume ratio 3:1), ultrasonically treat for 1 h, then wash with deionized water 3 times, and vacuum-dry at 80 °C for 24 h to obtain carboxylated carbon nanotubes;

[0077] (2) Add 1 g of carboxylated carbon nanotubes to 5 g of deionized water, then adjust the pH to 8.2 with sodium hydroxide, and then freeze-dry at -75 °C for 24 h, grind through a 200-mesh sieve to obtain carboxylated carbon nanotube aerogel powder;

[0078] (3) Add 0.5 g of polyvinyl alcohol (PVA1788), 3 g of acrylic acid and 0.3 g of dipropylene glycol diacrylate to 20 g of deionized water, stir for 30 min, then add 1.02 g of lithium acetate dihydrate, 1.99 g of nickel acetate tetrahydrate, 0.25 g of manganese acetate tetrahydrate, 0.25 g of cobalt acetate tetrahydrate, 40 mg of ammonium persulfate and 30 mg of tetramethylethylenediamine, and continue to stir for 1 h to obtain an impregnation solution;

[0079] (4) Add 0.5 g of carboxylated carbon nanotube aerogel powder to 20 g of the impregnating solution, disperse it by ultrasonic wave for 30 min, then heat it up to 70 °C, stir for 3 h, wash it with water, wash it with alcohol, and finally dry it in vacuum at 80 °C for 24 h to obtain the precursor of the positive electrode material;

[0080] (5) Put the precursor of the positive electrode material into a muffle furnace, heat it from room temperature to 700 °C at a rate of 5 °C / min, keep it warm for 13 h, cool it down, grind it and sieve it through a 100-mesh sieve to obtain the positive electrode material for lithium-ion batteries.

[0081] Battery preparation:

[0082] Positive electrode sheet: Use the positive electrode materials prepared in the examples and comparative examples as the active materials, acetylene black as the conductive agent, and a 1-methyl-2-pyrrolidone solution of polyvinylidene fluoride with a mass fraction of 4% as the binder. Weigh the positive electrode active material, 4% PVDF, and acetylene black according to the mass ratio of 75:15:10, mix them evenly, stir at room temperature for 6 hours, evenly coat the obtained slurry on a clean aluminum foil, and vacuum dry it overnight at 60 °C to remove the organic solvent. Then, punch the sheet with a punching machine with a punch diameter of 12 mm to obtain the positive electrode sheet;

[0083] Battery assembly: Use the positive electrode sheet obtained above as the positive electrode, the lithium sheet as the negative electrode, the electrolyte as an organic solution of 1 M LiPF6, the solvent component is dimethyl carbonate / diethyl carbonate / ethylene carbonate (volume ratio 1:1:1), the separator is a polypropylene film, and assemble a 2032-type button battery. The battery assembly sequence is the positive electrode case, the positive electrode sheet, the separator, the negative electrode sheet, and the negative electrode case. A total of 6 drops of the electrolyte are added, and then the battery is encapsulated with a battery encapsulation machine. The encapsulated battery is allowed to stand for 12 hours for performance testing.

[0084] Performance testing:

[0085] Constant current charge and discharge test: Use a Neware battery test system to test the charge and discharge specific capacity, cycle performance, and rate performance of the batteries prepared from the positive electrode materials in the examples and comparative examples. Use a current of 0.1C to measure the charge and discharge specific capacity at room temperature, use a current of 1C to measure the cycle performance at room temperature, the rate performance test range is 0.1C, 0.2C, 0.5C, 1C, and 2C for 5 cycles each, and the voltage test range is 2.0 - 4.75V. The results are shown in Table 1.

[0086] Table 1 Performance test results

[0087]

[0088] Data analysis:

[0089] From the data of Examples 1-3 in Table 1, it can be seen that the lithium-ion battery prepared with the cathode material provided by the present invention has a high initial discharge specific capacity, and its Coulomb efficiency can reach more than 95%. Moreover, in the rate test, the discharge specific capacity at 10C can reach more than 90% of the discharge specific capacity at 0.1C, indicating its excellent rate performance. Most importantly, after 500 cycles, its discharge specific capacity can still remain above 95, indicating its excellent cycle stability and long-life characteristics. This shows that the cathode material of the present invention can still maintain excellent electrochemical performance under high-rate charge and discharge conditions, and is suitable for lithium-ion battery application scenarios with high requirements for energy density, rate performance, and cycle life.

[0090] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that the carboxylation of the carbon nanotube surface can effectively improve the Coulomb efficiency, rate performance, and cycle stability of the battery. This is mainly because the carboxylation of the carbon nanotube surface helps to assist acrylic acid in improving the dispersion of metal ions in the cathode material precursor, thereby forming smaller and uniformly dispersed metal oxides during the subsequent calcination process, thus significantly improving the microstructure and electrochemical performance of the cathode material. The smaller and uniformly distributed metal oxide particles can effectively improve the conductivity and lithium-ion transport rate of the material, reduce electrode polarization, and enhance the rate performance. At the same time, the uniform particle distribution and stable structure can reduce the volume change and side reactions during the cycle, thus significantly improving the cycle stability and long-life characteristics of the battery.

[0091] From the data of Example 2 and Comparative Example 2, it can be seen that compared with directly using carboxylated carbon nanotubes, the carboxylated carbon nanotube aerogel powder formed by freeze-drying treatment can effectively improve the Coulomb efficiency, rate performance, and cycle stability of the battery. This is mainly attributed to the fact that the freeze-drying treatment constructs a three-dimensional porous network structure between the carboxylated carbon nanotubes. This structure effectively enhances the dispersion of metal ions in the cathode material precursor and promotes the formation of more uniform and stable metal oxide particles during the subsequent calcination process. In addition, the three-dimensional porous network structure significantly improves the conductivity and lithium-ion transport rate of the cathode material, reduces electrode polarization, and thus significantly improves the rate performance. At the same time, this network structure can buffer the volume change of the material during the battery cycle and inhibit the occurrence of side reactions, further enhancing the cycle stability and long-life characteristics of the battery. This structural optimization provides an important guarantee for the electrochemical performance of the cathode material.

[0092] From the data of Example 2 and Comparative Example 3, it can be seen that the addition of dipropylene glycol diacrylate can improve the cycle stability of the battery, which is mainly attributed to the cross-linked structure formed by dipropylene glycol diacrylate and acrylic acid, which helps to enhance the dispersion of carboxylated carbon nanotube aerogel powder in the precursor of the positive electrode material, so as to form a more uniform and stable microstructure of the positive electrode material after calcination. This cross-linked structure not only improves the mechanical strength and structural integrity of the positive electrode material, but also effectively alleviates the volume change of the material during the cycle, reducing the occurrence of side reactions. In addition, the uniform and stable microstructure can improve the lithium ion transport efficiency and the conductivity of the electrode, thus further improving the cycle stability and long-life characteristics of the battery.

[0093] From the data of Example 2 and Comparative Example 4, it can be seen that the addition of polyvinyl alcohol can improve the cycle stability of the battery, which is mainly because polyvinyl alcohol helps to promote the dispersion of carboxylated carbon nanotube aerogel powder in the precursor of the positive electrode material.

[0094] From the data of Example 2 and Comparative Example 5, it can be seen that during the later calcination process, directly raising the temperature to 700 °C will cause the Coulomb efficiency, rate performance and cycle stability of the battery to decline. This is mainly because long-term calcination at high temperature may cause the decomposition or loss of some carbon nanotubes, thus destroying the integrity and stability of the framework structure of the positive electrode material. The loss of carbon nanotubes will damage the conductive network of the positive electrode material, hinder the lithium ion transport path, and then increase the electrode polarization and reduce the rate performance. In addition, the decrease in the stability of the framework structure will also lead to an increase in the volume change of the material during the cycle and an increase in side reactions, thus significantly reducing the cycle stability and long-life characteristics of the battery.

[0095] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A positive electrode material for a lithium ion battery, characterized in that: The positive electrode material precursor is obtained by calcining; the preparation method of the positive electrode material precursor is as follows: (1) treating carbon nanotubes with a mixed solution of sulfuric acid and nitric acid to obtain carboxylated carbon nanotubes; (2) adding carboxylated carbon nanotubes into deionized water, adjusting the pH to 8-8.5 with sodium hydroxide, freeze-drying, grinding and sieving to obtain carboxylated carbon nanotube aerogel powder; (3) Add polyvinyl alcohol, acrylic acid, and tripropylene glycol diacrylate to deionized water, stir for 20-40 minutes, then add lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate, ammonium persulfate, and tetramethylethylenediamine, and continue stirring for 0.5-1.5 hours to obtain an impregnation solution; (4) Adding the carboxylated carbon nanotube aerogel powder to the impregnation solution, ultrasonically dispersing for 20-40 min, heating to 65-75 ° C, stirring for 2.5-3.5 h, washing with water, washing with alcohol, and vacuum drying to obtain a cathode material precursor; In step (1), the concentration of sulfuric acid is 98%, and the concentration of nitric acid is 65%; In the step (3), the weight ratio of polyvinyl alcohol, acrylic acid, tripropylene glycol diacrylate, deionized water, lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate and cobalt acetate tetrahydrate is 0.3-0.8:2-4:0.1-0.5:15-25:0.51-1.53:1-3:0.12-0.37:0.12-0.37; In the step (4), the weight ratio of the carboxylated carbon nanotube aerogel powder to the impregnation solution is 0.5:15-25; The preparation method of the positive electrode material for lithium ion batteries comprises the following steps: placing a positive electrode material precursor in a muffle furnace, first heating the temperature from room temperature to 450-550°C at a rate of 3-8°C / min, keeping the temperature for 10-14h, then heating the temperature from 450-550°C to 650-750°C, keeping the temperature for 0.5-1.5h, cooling the temperature to room temperature, grinding and sieving, and obtaining the positive electrode material for lithium ion batteries.

2. The positive electrode material for lithium ion battery according to claim 1, characterized in that The volume ratio of sulfuric acid to nitric acid in the mixed solution of step (1) is 3:

1.

3. The positive electrode material for lithium ion battery according to claim 1, characterized in that In the step (1), the weight ratio of the carbon nanotubes to the mixed solution is 1:8-12.

4. The positive electrode material for lithium ion battery according to claim 1, characterized in that The treatment time in step (1) is 0.5-1.5h.

5. The positive electrode material for lithium ion battery according to claim 1, characterized in that In the step (2), the weight ratio of the carboxylated carbon nanotubes to deionized water is 1:4-6.

6. The positive electrode material for lithium ion battery according to claim 1, characterized in that The freeze-drying temperature in step (2) is -75±5°C and the time is 20-28h.

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