Germanium-doped high-nickel positive electrode material, preparation method thereof and battery

Abstract

This invention discloses a germanium-doped high-nickel cathode material, its preparation method, and a battery. The preparation method of the germanium-doped high-nickel cathode material includes the following steps: S1, Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder is mixed uniformly with LiOH·H₂O and germanium salt, wherein n(Li):n(Ni+Co+Mn+Ge)=1.05:1; S2, the powder mixed in S1 is sintered in sections and cooled to room temperature; S3, the product obtained in S2 is ground and sieved to obtain Li(Ni)₂ powder. 0.90 Co 0.05 Mn 0.05 ) 0.995 Ge 0.005 O2 material. The cathode material prepared by the method proposed in this invention has uniform particle size, high crystallinity, high specific capacity, and good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to germanium-doped high-nickel cathode materials, their preparation methods, and batteries. Background Technology

[0002] High-nickel LiNi x Co y Mn 1-x-y O2 (x≥0.8) layered oxides are used as cathode materials for high-performance electric vehicles due to their high specific capacity, high energy density, and reasonable material cost. Current high-nickel cathodes are typically polycrystalline structures with high packing density and small specific surface area. Typical polycrystalline particles consist of many densely packed nanoscale primary particles to improve energy density and suppress interfacial side reactions. However, during charge and discharge, the severe lattice c-axis contraction during the H2-H3 phase transition leads to anisotropic mechanical stress, resulting in microcracks. With continued cycling, the presence and further formation of these microcracks cause severe interfacial side reactions, affecting battery performance. Furthermore, cation mixing affects the Li-ion exchange rate during the charge and discharge process of high-nickel cathode materials. + Diffusion can affect the overall electrical performance of the battery. Therefore, it is necessary to reduce Li diffusion through appropriate modifications, such as bulk doping and surface coating of the material. + / Ni 2+ Mixing and cation mixing suppresses lattice distortion during charge and discharge, thereby improving the material's cycle stability and high-rate discharge performance. Ge doping can suppress cation mixing, increase the energy barrier for phase transitions in high-nickel cathodes, inhibit structural degradation from layered phases to spinel / rock-salt phases, and simultaneously lower the diffusion kinetic barrier, promoting Li... + Diffusion under high-rate conditions. Due to the increase in the phase transition energy barrier and Li + The reduction of the diffusion barrier improves the reversible capacity retention, voltage stability, and rate performance of the layered high-nickel cathode under high voltage.

[0003] CN108448081A discloses a high-nickel ternary lithium battery material and its preparation method using a germanium oxide aerogel network. This method involves preparing a uniform network structure of germanium oxide and carbon nanotube gel, pre-stabilizing nickel hydroxide to form plate-shaped nickel hydroxide within the microporous structure of the network, and then further dispersing cobalt salt, lithium salt, and manganese salt within it to grow a precursor. Finally, the precursor is calcined to obtain the cathode material. The material prepared by this method exhibits significantly improved cycle stability. However, this method requires extensive control of synthesis conditions, making precise parameter control difficult. It is suitable for experimental investigation but not for industrial applications.

[0004] CN103872315B discloses a method for preparing germanium-doped high-energy-density lithium cobalt oxide composite cathode material. The method first uses cobalt chloride, ammonium oxalate, sodium hydroxide, and ammonia as raw materials. After reaction precipitation and aging, the mixture is washed, dried, and calcined to prepare cobalt tetroxide. Then, lithium oxide, cobalt tetroxide, aluminum oxide, magnesium oxide, and germanium oxide are melted, cooled, ball-milled into powder, and sintered to obtain a precursor for the germanium-doped lithium cobalt oxide composite cathode material. Finally, the precursor is mixed with acetylene black and phenolic resin, ball-milled, and sintered in a mixed atmosphere of helium and oxygen to obtain the cathode material. This method improves the specific capacity and lifespan of the cathode material, but the synthesis steps are cumbersome and the process is complex, lacking advantages for large-scale production. Furthermore, the actual discharge specific capacity of lithium cobalt oxide is far lower than that of high-nickel ternary cathode materials with the same layered structure, which does not meet future development needs.

[0005] Therefore, in order to ensure the doping effect, it is imperative to develop a simple doping method for ternary cathode materials. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a germanium-doped high-nickel cathode material, its preparation method, and a battery, addressing the shortcomings of existing technologies. Through germanium doping modification, the process is simple, offering advantages for large-scale production, while simultaneously reducing Li... + / Ni 2+ Mixing increases the energy barrier for phase transition in high-nickel cathodes, promoting Li + Diffusion under high-rate conditions stabilizes the material structure and improves the overall electrochemical performance of the material.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing germanium-doped high-nickel cathode material, comprising the following steps:

[0008] S1, Ni 0.90 Co 0.05 Mn 0.05 (OH)2 powder is mixed evenly with LiOH·H2O and germanium salt, wherein n(Li):n(Ni+Co+Mn+Ge)=1.05:1;

[0009] S2. The powder mixed in S1 is sintered in sections and cooled to room temperature;

[0010] S3. After grinding and sieving the product obtained in S2, Li(Ni) is obtained. 0.90 Co 0.05 Mn 0.05 ) 0.995 Ge 0.005 O2 materials.

[0011] The germanium doping of this invention can effectively improve the cycle stability of the cathode material. Compared with the method of mixing germanium salt and precursor in ethanol and then adding lithium salt for sintering, the cathode material obtained by sintering a solid mixed germanium salt is superior.

[0012] In a preferred embodiment of the present invention, the germanium salt in S1 is GeO2 or germanium carbonate.

[0013] In this invention, the germanium salt is preferably germanium oxide with a purity of 99%. This invention does not impose any special restrictions on the source of the germanium oxide; commercially available products or homemade products well-known to those skilled in the art can be used.

[0014] In a preferred embodiment of the present invention, Ni 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)₂ powder to GeO₂ is 1.8341-1.8990:0.0107-0.0642, preferably, Ni 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)2 powder to GeO2 is 1.8557-1.8882:0.0107-0.0428, and more preferably, Ni... 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)₂ powder to GeO₂ is 1.8665-1.8882:0.0107-0.0321. More preferably, Ni... 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)2 powder to GeO2 is 1.867-1.88:0.011-0.031.

[0015] Appropriate germanium doping can effectively improve the cycle stability of cathode materials. The discharge specific capacity in this range is superior; appropriate Ge doping can effectively reduce the lithium-ion diffusion barrier and promote Li-ion diffusion. + Diffusion under high-rate conditions improves the rate performance of the cathode material.

[0016] In a preferred embodiment of the present invention, Ni 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)₂ powder to LiOH·H₂O is 1.8341-1.8990:0.9094-0.9133; preferably, Ni 0.90 Co 0.05 Mn 0.05The mass ratio of (OH)₂ powder to LiOH·H₂O is 1.8557-1.8882:0.9107-0.9126; more preferably, Ni 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)2 powder to LiOH·H2O is 1.867-1.88:0.9114-0.9125.

[0017] In this invention, the ratio of hydroxide precursor to LiOH·H2O is 1:1.05 (molar ratio). The difference in mass is due to the different doping amount of Ge. An excess of 0.05 mol of LiOH·H2O is introduced during the synthesis process to compensate for the loss of Li2O through sublimation and to suppress Li / Ni mixing.

[0018] In a preferred embodiment of the present invention, the method of uniform mixing in S1 is grinding for 8-20 minutes, preferably, the method of uniform mixing in S1 is grinding for 10-15 minutes.

[0019] This invention employs direct grinding and mixing. Direct solid-phase mixing ensures the integrity of the material particles and does not damage the material's morphology and crystal structure. Ball milling, on the other hand, leads to particle breakage, affecting the material's crystallinity and consequently its electrochemical properties.

[0020] In a preferred embodiment of the present invention, the segmented sintering in S2 is calcined in an oxygen atmosphere. The segmented sintering temperature in S2 is 400-600℃ for 4-6 hours, and then 650℃-850℃ for 12-16 hours. Preferably, the segmented sintering temperature in S2 is 500-600℃ for 4-6 hours, and then 700-800℃ for 12-16 hours.

[0021] The low-temperature sintering in the first stage of this invention is to keep LiOH·H2O (melting point 462℃) in a molten state and react with Ni. 0.90 Co 0.05 Mn 0.05 To achieve better uniform bonding of the (OH)2 powder, the subsequent high-temperature sintering is used to control the crystallization of the powder at an appropriate temperature, thereby forming a better layered crystal structure. Too short a sintering time will affect crystal nucleus growth, too low a temperature will be detrimental to its crystallinity, and too high a sintering temperature and too long a sintering time will cause Li to volatilize (LiOH·H2O boiling point 920℃).

[0022] In a preferred embodiment of the present invention, the Ni 0.90 Co 0.05 Mn 0.05(OH)2 powder needs to be vacuum dried first, at a temperature of 60-100℃. Vacuum drying is to remove moisture from the precursor powder, thereby reducing errors in the weighing process and ensuring that the precursor is not oxidized.

[0023] In a preferred embodiment of the present invention, the mesh size of the sieve in S3 is 250-350 mesh. This avoids large-area agglomeration of particles, which would affect the subsequent electrode preparation and battery electrical performance.

[0024] The present invention also discloses a germanium-doped high-nickel cathode material prepared by the aforementioned preparation method.

[0025] The present invention also discloses a ternary lithium-ion battery made using the germanium-doped high-nickel cathode material.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The preparation method proposed in this invention effectively suppresses phase transitions and cation mixing through germanium doping modification, thereby improving the overall electrochemical performance of the material. Furthermore, the nickel-cobalt-manganese cathode material prepared by this method has advantages such as uniform chemical composition, high purity, uniform particle size, low heat treatment temperature, precise control of stoichiometry, simple operation, easy control of conditions, good reproducibility, and stable electrochemical performance. Attached Figure Description

[0028] Figure 1 The XRD patterns are of Examples 1-6 and Comparative Examples 1-13 of the present invention;

[0029] Figure 2 The cycling performance curves are for Examples 1-4 and Comparative Example 1;

[0030] Figure 3 Rate performance curves of Examples 1-4 and Comparative Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of 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. Unless otherwise specified, the equipment and reagents used in the present invention are commercially available products conventional in this technical field. The room temperature mentioned in the present invention refers to 25°C.

[0032] Example 1

[0033] Weigh out 1.8882g of Ni 0.90 Co 0.05 Mn 0.05(OH)₂ powder was uniformly mixed with 0.9126 g LiOH·H₂O and 0.0107 g GeO₂ by grinding for 10 min, wherein Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.995 Ge 0.005 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0034] Example 2

[0035] Weigh out 1.8773g Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was uniformly mixed with 0.9120 g LiOH·H₂O and 0.0214 g GeO₂ by grinding for 10 min, wherein Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.990 Ge 0.01 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0036] Example 3

[0037] Weigh out 1.8665g of Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was uniformly mixed with 0.9113g LiOH·H₂O and 0.0321g GeO₂ by grinding for 10 min, wherein Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ powder was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.985 Ge 0.015 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0038] Example 4

[0039] Weigh out 1.8557g Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was uniformly mixed with 0.9107 g LiOH·H₂O and 0.0428 g GeO₂ by grinding for 10 min, wherein Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ powder was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.98 Ge 0.02 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0040] Example 5

[0041] Weigh out 1.8449g Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was uniformly mixed with 0.9100g LiOH·H₂O and 0.0535g GeO₂ by grinding for 10 min, wherein Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ powder was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.975 Ge 0.025 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0042] Example 6

[0043] Weigh out 1.8341g Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was uniformly mixed with 0.9094 g LiOH·H₂O and 0.0642 g GeO₂ by grinding for 10 min, wherein Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ powder was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.97 Ge 0.03 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0044] Comparative Example 1

[0045] Weigh 1.8990g Ni 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was uniformly mixed with 0.9133 g of LiOH·H₂O, wherein Li:(Ni+Co+Mn)=1.05:1 (molar ratio). The mixture was then sintered in a tube furnace with oxygen supply in sections. The furnace was first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, LiNi was obtained. 0.90 Co 0.05 Mn 0.05 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0046] Comparative Example 2

[0047] After weighing 0.0107g of GeO2 and ball milling it for 30 minutes, add 0.9126g of LiOH·H2O and 1.8882g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was ball-milled for 30 min, with Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). It was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.995 Ge 0.005 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0048] Comparative Example 3

[0049] After weighing 0.0214g of GeO2 and ball milling it for 30 minutes, add 0.9120g of LiOH·H2O and 1.8773g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was ball-milled for 30 min, with Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). It was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.990 Ge 0.01 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0050] Comparative Example 4

[0051] After weighing 0.0321g of GeO2 and ball milling it for 30 minutes, add 0.9113g of LiOH·H2O and 1.8665g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was ball-milled for 30 min, with Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). It was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.985 Ge 0.015 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0052] Comparative Example 5

[0053] After weighing 0.0428g of GeO2 and ball milling it for 30 minutes, add 0.9107g of LiOH·H2O and 1.8557g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was ball-milled for 30 min, with Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). It was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.98 Ge 0.02 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0054] Comparative Example 6

[0055] After weighing 0.0535g of GeO2 and ball milling it for 30 minutes, add 0.9100g of LiOH·H2O and 1.8449g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was ball-milled for 30 min, with Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). It was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn0.05 ) 0.975 Ge 0.025 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0056] Comparative Example 7

[0057] After weighing 0.0642g of GeO2 and ball milling it for 30 minutes, add 0.9094g of LiOH·H2O and 1.8341g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was ball-milled for 30 min, with Li:(Ni+Co+Mn+Ge)=1.05:1 (molar ratio). It was then sintered in a tube furnace with oxygen supply in sections, first held at 500℃ for 5 h, then at 700℃ for 14 h, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.97 Ge 0.03 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0058] Comparative Example 8

[0059] Weigh 0.0107 g GeO2 and add it to 10 mL of anhydrous ethanol. Stir for 30 min, then add 1.8882 g Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was stirred for 2 hours, dried at 80℃, ground and sieved. 0.9126 g of LiOH·H₂O was added and mixed uniformly, with a molar ratio of Li:(Ni+Co+Mn+Ge)=1.05:1. The mixture was then placed in an oxygen-filled tube furnace for segmented sintering, first held at 500℃ for 5 hours, then at 700℃ for 14 hours, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.995 Ge 0.005 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0060] Comparative Example 9

[0061] Weigh 0.0214 g of GeO2 and add it to 10 mL of anhydrous ethanol. Stir for 30 min, then add 1.8773 g of Ni. 0.90 Co 0.05 Mn 0.05(OH)₂ powder was stirred for 2 hours, dried at 80℃, ground and sieved. 0.9120 g of LiOH·H₂O was added and mixed uniformly, with a molar ratio of Li:(Ni+Co+Mn+Ge)=1.05:1. The mixture was then placed in an oxygen-filled tube furnace for segmented sintering, first held at 500℃ for 5 hours, then at 700℃ for 14 hours, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.990 Ge 0.01 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0062] Comparative Example 10 (NCMG15)

[0063] Weigh 0.0321g GeO2 and add it to 10mL of anhydrous ethanol. Stir for 30 minutes, then add 1.8665g Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was stirred for 2 hours, dried at 80℃, ground and sieved. 0.9113 g of LiOH·H₂O was added and mixed uniformly, with a molar ratio of Li:(Ni+Co+Mn+Ge)=1.05:1. The mixture was then placed in an oxygen-filled tube furnace for segmented sintering, first held at 500℃ for 5 hours, then at 700℃ for 14 hours, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.985 Ge 0.015 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0064] Comparative Example 11 (NCMG20)

[0065] Weigh 0.0428 g of GeO2 and add it to 10 mL of anhydrous ethanol. Stir for 30 min, then add 1.8557 g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was stirred for 2 hours, dried at 80℃, ground and sieved. 0.9107 g of LiOH·H₂O was added and mixed uniformly, with a molar ratio of Li:(Ni+Co+Mn+Ge)=1.05:1. The mixture was then placed in an oxygen-filled tube furnace for segmented sintering, first held at 500℃ for 5 hours, then at 700℃ for 14 hours, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.98 Ge 0.02O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0066] Comparative Example 12 (NCMG25)

[0067] Weigh 0.0535g GeO2 and add it to 10mL of anhydrous ethanol. Stir for 30 minutes, then add 1.8449g Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was stirred for 2 hours, dried at 80℃, ground and sieved. 0.9100 g of LiOH·H₂O was added and mixed uniformly, with a molar ratio of Li:(Ni+Co+Mn+Ge)=1.05:1. The mixture was then placed in an oxygen-filled tube furnace for segmented sintering, first held at 500℃ for 5 hours, then at 700℃ for 14 hours, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 0. 975 Ge 0.025 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0068] Comparative Example 13 (NCMG30)

[0069] Weigh 0.0642 g of GeO2 and add it to 10 mL of anhydrous ethanol. Stir for 30 min, then add 1.8341 g of Ni. 0.90 Co 0.05 Mn 0.05 (OH)₂ powder was stirred for 2 hours, dried at 80℃, ground and sieved. 0.9094 g of LiOH·H₂O was added and mixed uniformly, with a molar ratio of Li:(Ni+Co+Mn+Ge)=1.05:1. The mixture was then placed in an oxygen-filled tube furnace for segmented sintering, first held at 500℃ for 5 hours, then at 700℃ for 14 hours, and finally cooled to room temperature with the furnace. After grinding and sieving, Li(Ni)₂ was obtained. 0.90 Co 0.05 Mn 0.05 ) 0.97 Ge 0.03 O2 material. The test results of button cell fabrication using the material are shown in Table 1.

[0070] The positive electrode materials prepared in Examples 1-4 and Comparative Examples 1-4 were used to fabricate 2032 coin cell simulated batteries to test their electrochemical performance. The specific steps are as follows: (1) Weigh the above positive electrode material, conductive acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10. First, dissolve PVDF in an appropriate amount of N-methylpyrrolidone (NMP). Then, add the uniformly mixed positive electrode material and acetylene black powder to NMP and stir evenly to form a slurry; (2) Coat the slurry evenly on an aluminum foil substrate. Place the wet electrode in a vacuum drying oven and dry it at 110°C for 12 hours. Cut it into positive electrode sheets; (3) Assemble the simulated battery in a dry vacuum glove box. The above self-made electrode sheet is used as the positive electrode, lithium metal sheet is used as the negative electrode, Celgard 2500 membrane is used as the separator, and 1 mol / L LiPF6 is used. A solution dissolved in ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) (volume ratio 1:1:1) was used as the electrolyte, and its electrochemical performance was tested, as shown in Table 1.

[0071] from Figure 1 It can be seen that the cathode materials before and after germanium doping both exhibit the typical structural characteristics of LiNiO2 cathode materials. Their diffraction peaks are characteristic peaks of the α-NaFeO2 layered structure, belonging to the hexagonal crystal system, R-3m space group. The diffraction peaks of the materials before and after doping did not change significantly, and there were no impurity peaks. However, the (006) / (012) and (018) / (110) pairs of diffraction peaks of the cathode materials of Comparative Examples 8-13 did not split significantly, and the characteristic peak values ​​were low, indicating poor crystallinity. In contrast, Examples 1-6 and Comparative Examples 2-7 showed better crystallinity, indicating that the cathode materials obtained by solid-state mixing and sintering are superior compared with the method of adding germanium salt and precursor to ethanol and then adding lithium salt and sintering. Therefore, only the cathode materials prepared by solid-state mixing and sintering were selected for coin cell testing. Comparing Examples 1-6 with Comparative Examples 2-7, it can be found that the characteristic peaks of the cathode materials of Comparative Examples 2-7, especially the main peak (003), are significantly weaker than those of Examples 1-6. This may be because ball milling causes the material to break into spherical shapes, affecting the crystallinity of the material.

[0072] As shown in Table 1, the material in Example 2 still retains a discharge specific capacity of 166.8 mAh·g after 200 cycles at a 1C rate. -1The capacity retention rate reached 91.8%, and the cycle stability was superior to Comparative Example 1 and other examples. Compared with Comparative Example 1, the 0.1C initial discharge specific capacity of the cathode materials in Examples 1-4 and Comparative Examples 2-4 was lower or close, while the 0.1C initial charge-discharge efficiency of the cathode materials in Examples 2-4 was improved. The discharge specific capacity and capacity retention rate of the cathode materials in Examples 1-4 and Comparative Examples 2-4 after 200 cycles were superior to Comparative Example 1, indicating that appropriate germanium doping can effectively improve the cycle stability of the cathode material. Meanwhile, the initial charge-discharge efficiency and cycle performance of the cathode materials in Comparative Examples 2-4 were lower than those in Examples 1-4, possibly due to particle breakage caused by ball milling, which affected the crystallinity of the material and thus its electrochemical performance. The above indicates that direct solid-phase mixing can ensure the integrity of the material particles without damaging the material morphology and crystal structure, and that appropriate germanium doping can effectively improve the cycle stability of the cathode material. Figure 3 It can be seen that different germanium doping contents have a certain impact on the rate performance of the material. Under 5C conditions, the discharge specific capacity of Examples 1-3 is better than that of Comparative Example 1. Under 10C high-rate conditions, Examples 1-4 are all better than Comparative Example 1, and Example 2 has the highest discharge specific capacity of 150.2 mAh·g. -1 This indicates that appropriate Ge doping can effectively reduce the lithium-ion diffusion barrier and promote Li-ion diffusion. + Diffusion under high-rate conditions improves the rate performance of the cathode material.

[0073] Table 1. Electrochemical performance of cathode materials in Examples 1-4 and Comparative Examples 1-4 at 2.7-4.3V.

[0074]

[0075] Table 2 Comparison of process parameters between Examples 1-18 and Comparative Example 1

[0076]

[0077]

[0078] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a germanium-doped high-nickel cathode material, characterized in that... It consists of the following steps: S1, Ni 0.90 Co 0.05 Mn 0.05 (OH)2 powder was mixed evenly with LiOH·H2O and germanium salt, wherein n(Li):n(Ni +Co + Mn+Ge) = 1.05:1; S2. The powder mixed in S1 is sintered in sections and cooled to room temperature; S3. After grinding and sieving the product obtained in S2, Li(Ni) is obtained. 0.90 Co 0.05 Mn 0.05 ) 0.995 Ge 0.005 O2 materials; The germanium salt mentioned in S1 is GeO2; Ni 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)2 powder to GeO2 is 1.867-1.88:0.011-0.031; Ni 0.90 Co 0.05 Mn 0.05 The mass ratio of (OH)2 powder to LiOH·H2O is 1.867-1.88:0.9114-0.9125; The method for achieving uniform mixing in S1 is grinding.

2. The method for preparing germanium-doped high-nickel cathode material according to claim 1, characterized in that, The method for achieving uniform mixing in S1 is grinding for 8-20 minutes.

3. The method for preparing germanium-doped high-nickel cathode material according to claim 1, characterized in that, The method for achieving uniform mixing in S1 is to grind for 10-15 minutes.

4. The method for preparing germanium-doped high-nickel cathode material according to any one of claims 1-3, characterized in that, The S2 section sintering is carried out in an oxygen atmosphere. The temperature of the S2 section sintering is 400-600℃ and held for 4-6 hours, and then held at 650℃-850℃ for 12-16 hours.

5. The method for preparing germanium-doped high-nickel cathode material according to claim 4, characterized in that, The sintering temperature for S2 is 500-600℃ for 4-6 hours, followed by 700-800℃ for 12-16 hours.

6. The method for preparing germanium-doped high-nickel cathode material according to any one of claims 1-3, characterized in that, The Ni 0.90 Co 0.05 Mn 0.05 (OH)2 powder needs to be vacuum dried first, and the vacuum drying temperature is 60-100℃.

7. The method for preparing germanium-doped high-nickel cathode material according to any one of claims 1-3, characterized in that, The mesh size of the sieve in S3 is 250-350 mesh.

8. A germanium-doped high-nickel cathode material prepared by the preparation method according to any one of claims 1-3.

9. A ternary lithium-ion battery made using the germanium-doped high-nickel cathode material as described in claim 8.

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