Vanadium-doped nickel-cobalt-manganese ternary positive electrode material, preparation method and application thereof

Abstract

The application provides a vanadium-doped nickel-cobalt-manganese ternary positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: providing a vanadium citrate aqueous solution, evaporating and crystallizing the vanadium citrate aqueous solution and performing primary roasting to obtain anhydrous vanadium citrate; mixing the anhydrous vanadium citrate with a lithium nickel cobalt manganese oxide to obtain a mixture, and performing secondary roasting on the mixture to obtain the vanadium-doped nickel-cobalt-manganese ternary positive electrode material. The molecular formula of the obtained vanadium-doped nickel-cobalt-manganese ternary positive electrode material is LiNi x Co y Mn z V a O2, 0.8≤x≤0.96, 0.02≤y≤0.2, 0.02≤z≤0.2, 0.0013≤a≤0.0043. The preparation method is simple, and the vanadium-doped nickel-cobalt-manganese ternary positive electrode material prepared by the method is beneficial to significantly improving the performance of the positive electrode material, reducing the production cost and saving the energy consumption.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery positive electrode material preparation methods, in particular to a vanadium-doped nickel-cobalt-manganese ternary positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Nickel-cobalt-manganese ternary positive electrode materials (NCM) are widely used in lithium ion positive electrode materials. In order to further improve the capacity and reduce the cost, the current NCM material is developing towards high nickel. However, due to the sudden change of the lattice volume in the charging and discharging process, the high-nickel NCM material particles are easily subjected to internal stress and produce microcracks, which expand along the interface between the active material and the electrolyte, accelerate the particle pulverization and electrolyte decomposition, and cause the cycle capacity attenuation. The means for modifying the high-nickel NCM material to solve the above problems include element doping.

[0003] However, doping elements in the high-nickel NCM material will affect the band gap, interlayer spacing, defect concentration and the binding force between atoms to some extent, but the performance improvement effect of the high-nickel NCM material after doping modification still needs to be improved, and the doping process needs to go through a long calcination time, which consumes a large amount of energy and is not conducive to controlling the production cost. SUMMARY

[0004] Therefore, the application provides a modified high-nickel NCM material to solve at least one of the above technical problems.

[0005] To achieve the above-mentioned purpose, the application provides a preparation method of a vanadium-doped nickel-cobalt-manganese ternary positive electrode material, comprising: providing a vanadous citrate aqueous solution, evaporating and crystallizing the vanadous citrate aqueous solution and performing primary calcination to obtain anhydrous vanadous citrate; mixing the anhydrous vanadous citrate with lithium nickel cobalt manganese oxide to obtain a mixture, and performing secondary calcination on the mixture to obtain the vanadium-doped nickel-cobalt-manganese ternary positive electrode material.

[0006] In some possible implementation manners, the providing of the vanadous citrate aqueous solution comprises mixing vanadium pentoxide and citric acid, heating, and allowing the vanadium pentoxide to react with the citric acid.

[0007] In some possible implementation manners, the temperature of the evaporating and crystallizing is 60-100 DEG C, and the time is 2-4 hours.

[0008] In some possible implementation manners, the primary calcination is performed in an oxygen-containing atmosphere, the temperature of the primary calcination is 180-220 DEG C, and the time is 2-3 hours.

[0009] In some possible implementation manners, the particle size of the anhydrous vanadous citrate is 500-800 nm.

[0010] In some possible implementations, the rotating speed of the mixing is 200 r / min to 300 r / min.

[0011] In some possible implementations, the secondary calcination is performed in an oxygen-containing atmosphere, and the temperature of the secondary calcination is 400 DEG C to 730 DEG C, and the time is 3 h to 6 h.

[0012] The application also provides a vanadium-doped nickel-cobalt-manganese ternary positive electrode material prepared by the preparation method, and the vanadium-doped nickel-cobalt-manganese ternary positive electrode material has a molecular formula of LiNi x Co y Mn z V a O2, 0.8≤x≤0.96, 0.02≤y≤0.2, 0.02≤z≤0.2, 0.0013≤a≤0.0043.

[0013] The application also provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises the vanadium-doped nickel-cobalt-manganese ternary positive electrode material.

[0014] The application also provides a lithium ion battery, which comprises an electrode assembly, and the electrode assembly comprises a separator film, a negative electrode tab and the positive electrode tab, and the separator film is arranged between the positive electrode tab and the negative electrode tab.

[0015] In the application, vanadium citrate is used as a doping carrier of vanadium and lithium nickel cobalt manganese oxide, which helps to reduce the degree of lithium nickel mixing and improve the order of cations, has the effect of stabilizing the crystal structure skeleton, can stabilize the lattice oxygen, inhibit the release of oxygen, and improve the cycle life and safety performance of the material. Compared with other vanadium doping carriers, the use of vanadium citrate for doping modification can obtain a positive electrode material with more remarkable performance improvement effect after modification. The preparation method of the application is simple, and the vanadium-doped nickel-cobalt-manganese ternary positive electrode material prepared by the method is beneficial to more significantly improving the performance of the positive electrode material, reducing the production cost and saving energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 (a) in FIG. 1 is a charge-discharge cycle curve of Comparative Example 1 of the application at 3-4.5 V and 0.2 C;

[0017] Figure 1 (b) in FIG. 1 is a charge-discharge cycle curve of Example 1 of the application at 3-4.5 V and 0.2 C;

[0018] Figure 1 (c) in FIG. 1 is a cycle performance test result of Example 1 and Comparative Example 1 of the application at 3-4.5 V and 0.2 C;

[0019] Figure 1 (d) is the rate performance test result of Example 1 and Comparative Example 1 of the present application in the present application;

[0020] Figure 1 (e) is the CV graph of Comparative Example 1 of the present application at 3-4.5V, 0.2mV / s;

[0021] Figure 1 (f) is the CV graph of Example 1 of the present application at 3-4.5V, 0.2mV / s;

[0022] Figure 1 (g) is the EIS graph of Example 1 and Comparative Example 1 of the present application before charge-discharge cycle;

[0023] Figure 1 (h) is the EIS graph of Comparative Example 1 of the present application after 10 cycles of charge-discharge cycle at 3-4.5V, 0.2C.

[0024] Figure 2 (a) is the charge-discharge cycle curve graph of Comparative Example 2 of the present application at 3-4.3V, 0.2C;

[0025] Figure 2 (b) is the charge-discharge cycle curve graph of Example 2 of the present application at 3-4.3V, 0.2C;

[0026] Figure 2 (c) is the cycle performance test result of Example 2 and Comparative Example 2 of the present application at 3-4.3V, 0.2C;

[0027] Figure 2 (d) is the cycle performance test result of Example 2 and Comparative Example 2 of the present application at 3-4.5V, 0.2C;

[0028] Figure 2 (e) is the CV graph of Comparative Example 2 of the present application at 3-4.5V, 0.2mV / s;

[0029] Figure 2 (f) is the CV graph of Example 2 of the present application at 3-4.5V, 0.2mV / s;

[0030] Figure 2 (g) is the rate performance test result of Example 2 and Comparative Example 2 of the present application;

[0031] Figure 2 (h) is the EIS graph of Example 2 and Comparative Example 2 of the present application before charge-discharge cycle;

[0032] Figure 2The (i) in the figure is the EIS figure of the Example 2 and the Comparative Example 2 of the present application after 10 cycles of charge-discharge at 3-4.5V, 0.2C.

[0033] Figure 3 The (a) in the figure is the charge-discharge cycle curve of the Comparative Example 3 of the present application at 3-4.5V, 1C;

[0034] Figure 3 The (b) in the figure is the charge-discharge cycle curve of the Example 3 of the present application at 3-4.5V, 1C;

[0035] Figure 3 The (c) in the figure is the cycle performance test result of the Example 3 and the Comparative Example 3 of the present application at 3-4.5V, 1C;

[0036] Figure 3 The (d) in the figure is the rate performance test result of the Example 3 and the Comparative Example 3 of the present application.

[0037] Figure 4 The (a) in the figure is the charge-discharge cycle curve of the Comparative Example 4 of the present application at 3-4.5V, 1C;

[0038] Figure 4 The (b) in the figure is the charge-discharge cycle curve of the Example 4 of the present application at 3-4.5V, 1C;

[0039] Figure 4 The (c) in the figure is the cycle performance test result of the Example 4 and the Comparative Example 4 of the present application at 3-4.5V, 1C;

[0040] Figure 4 The (d) in the figure is the rate performance test result of the Example 4 and the Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0041] The embodiments of the present application are described in detail below. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation on the present application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by those skilled in the art to which the present application belongs; the embodiments of the present application and the features in the embodiments can be combined with each other without conflict; in the following description, many specific details are set forth in order to fully understand the present application, and the described embodiments are only part of the embodiments of the present application, but not all the embodiments.

[0042] An embodiment of the present application provides a preparation method of a vanadium-doped nickel-cobalt-manganese ternary positive electrode material, comprising:

[0043] The first step is to provide a vanadium citrate aqueous solution, evaporate and crystallize the vanadium citrate aqueous solution and perform a first calcination to obtain anhydrous vanadium citrate (C 15 H 14 O9V2).

[0044] Evaporate and crystallize the vanadium citrate aqueous solution to obtain vanadium citrate crystals. The evaporative crystallization method is more conducive to maintaining the stability of the vanadium citrate structure, thereby making it easier to obtain vanadium citrate crystals. In other crystallization methods, such as temperature reduction crystallization, the solution may precipitate citric acid crystals when the temperature drops to about 36°C, affecting the output of vanadium citrate, and the required crystallization time is relatively longer. Therefore, obtaining vanadium citrate crystals by evaporative crystallization can help avoid the risk of precipitating citric acid in the crystallization product and reduce the time cost of the preparation process.

[0045] After calcining the obtained vanadium citrate crystals, the crystal water can be removed to obtain anhydrous vanadium citrate, which can avoid damage to the structure and performance of the ternary positive electrode material in the subsequent mixing process with the ternary positive electrode material.

[0046] In some embodiments, the providing of the vanadium citrate aqueous solution includes mixing vanadium pentoxide with citric acid, heating, and allowing the vanadium pentoxide to react with the citric acid. Preferably, the molar ratio of the vanadium pentoxide to the citric acid can be 3:1, and the heating temperature can be 80°C, wherein an oil bath can be selected to improve the uniformity of heating. The reaction can produce a clear deep blue solution, i.e., a vanadium citrate aqueous solution.

[0047] In some embodiments, the evaporative crystallization temperature is 60°C to 100°C, and the time is 2h to 4h. Controlling the evaporative crystallization temperature within the above range is conducive to reducing the risk of precipitating citric acid crystals in the vanadium citrate aqueous solution, and controlling the crystallization time within the above range is conducive to the full crystallization of vanadium citrate.

[0048] In some embodiments, the first calcination is performed in an oxygen-containing atmosphere, the first calcination temperature is 180°C to 220°C, and the time is 2h to 3h.

[0049] Performing the first calcination in an oxygen-containing atmosphere helps to fully convert the vanadium element in the vanadium citrate to +5 valence vanadium, promoting doping with +5 valence vanadium, V 5+ No change in valence state occurs during charging, so there is no change in volume, which can serve as a skeleton to stabilize the crystal structure. Controlling the first calcination temperature and time within the above range is conducive to fully removing the crystal water in the vanadium citrate crystals.

[0050] The second step is to mix the anhydrous vanadium citrate with lithium nickel cobalt manganese oxide (LiNi x Co yMn z The mixture is obtained by mixing O2, and the mixture is then subjected to a second calcination to obtain the vanadium-doped nickel-cobalt-manganese ternary cathode material.

[0051] Anhydrous vanadium citrate was used as a vanadium dopant carrier and mixed with lithium nickel cobalt manganese oxide. This allowed the high-valence (e.g., +5 valence) vanadium in the anhydrous vanadium citrate to be doped into the lithium nickel cobalt manganese oxide material, thereby increasing the Ni content in the material. 2+ Converted to Ni 3 + This reduces the degree of lithium-nickel mixing and improves the orderliness of cations. In related technologies, during charging, nickel ions undergo Ni... 3+ To Ni 4+ The transformation, accompanied by volume shrinkage, easily leads to an irreversible phase transition and ultimately the loss of electrochemical activity. In this application, anhydrous vanadium citrate is incorporated into V... 5+ Occupy Ni 3+ Position, V 5+ During charging, there is no change in valence state, and therefore no change in volume, which helps stabilize the crystal structure framework. Simultaneously, the vanadium atoms in anhydrous citric acid form strong bonds with oxygen atoms. The VO bond between vanadium and oxygen is stronger than the MO bond between transition metals and oxygen, thus stabilizing lattice oxygen in the cathode material, inhibiting oxygen release from the lattice, reducing the risk of structural collapse due to oxygen vacancies, and helping to maintain the stability of the crystal structure, thereby improving the material's cycle life and safety performance.

[0052] This application discovers that using vanadium citrate as a vanadium doping support, compared with other vanadium doping supports (such as vanadium pentoxide V2O5 and ammonium metavanadate NH4VO3), can yield cathode materials with more significant performance improvements after doping modification, while using vanadium doping supports of the same size and obtaining the same amount of vanadium doping.

[0053] In some embodiments, the anhydrous vanadium citrate (C 15 H 14 Anhydrous vanadium citrate (O9V2) is at the nanoscale; in some embodiments, the particle size of the anhydrous vanadium citrate is 500 nm to 800 nm. 15 H 14 When vanadium (O9V2) is at the nanoscale, its smaller particle size and larger specific surface area help to increase the vanadium doping amount and improve the uniformity of doping, thus making the doping modification effect of lithium nickel cobalt manganese oxide more significant. In some embodiments, the vanadium doping amount is 0.13% to 0.43% of the molar amount of lithium nickel cobalt manganese oxide, or 0.3% to 1% of the mass of lithium nickel cobalt manganese oxide, achieving a high doping amount.

[0054] In some embodiments, the mixing is performed at a low speed, for example, the rotating speed can be 200 r / min to 300 r / min. The application uses vanadium citrate as a doping carrier of vanadium element and lithium nickel cobalt manganese oxide, and can achieve sufficient and uniform mixing at a low speed, thereby achieving a good doping effect. The low speed reduces the energy consumption of the preparation process.

[0055] In some embodiments, the secondary calcination is performed in an oxygen-containing atmosphere, the temperature of the secondary calcination is 400°C to 730°C, and the time is 3h to 6h. In the O2-containing gas atmosphere, the temperature and time are controlled within the above ranges, the high temperature promotes the nucleation of the crystal grains of the mixture of vanadium citrate and lithium nickel cobalt manganese oxide, and then promotes the growth of the nucleated crystal grains of the mixture, to form a vanadium-doped nickel cobalt manganese ternary positive electrode material. In this process, if O2 is lacking, it is difficult to oxidize Ni 2+ to Ni 3+ , resulting in too high a degree of lithium-nickel mixing, which affects the lithium ion transmission. If the temperature is too high or the time is too long, an oxygen-deficient compound is easily generated, and secondary recrystallization is also promoted, and at the same time, the crystal grains of the material become large and the specific surface area becomes small, which is not conducive to the extraction and embedding of lithium ions in the material. If the temperature is too low or the time is too short, the reaction is incomplete, and amorphous material is easily generated, the material has poor crystallization performance, and is easy to contain impurities, which greatly affects the electrochemical performance of the material.

[0056] In some embodiments, the lithium nickel cobalt manganese oxide LiNi x Co y Mn z O2, 0.8≤x≤0.96, 0.02≤y≤0.2, 0.02≤z≤0.2.

[0057] An embodiment of the application provides a vanadium-doped nickel cobalt manganese ternary positive electrode material, which is prepared by the preparation method, and has a molecular formula of LiNi x Co y Mn z V a O2, 0.8≤x≤0.96, 0.02≤y≤0.2, 0.02≤z≤0.2, 0.0013≤a≤0.0043.

[0058] Another embodiment of the application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises the vanadium-doped nickel cobalt manganese ternary positive electrode material.

[0059] Another embodiment of the application further provides a lithium ion battery, which comprises an electrode assembly, the electrode assembly comprises a separator, a negative electrode sheet and the positive electrode sheet, and the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0060] The vanadium doped lithium nickel cobalt manganese oxide prepared by the method has the advantages that the vanadium doped lithium nickel cobalt manganese oxide is prepared by using vanadium citrate as a vanadium element and a doping carrier of lithium nickel cobalt manganese oxide, which helps to reduce the degree of lithium nickel mixing and improve the order of cations, has the effect of stabilizing the crystal structure skeleton, can stabilize the lattice oxygen, inhibit oxygen release, and improve the cycle life and safety performance of the lithium ion battery. Compared with other vanadium doping carriers, the positive electrode material after modification has more significant performance improvement by using vanadium citrate for doping modification. The preparation method is simple, and the vanadium doped nickel cobalt manganese ternary positive electrode material prepared by the method is beneficial to reduce the production cost and save energy consumption.

[0061] The scheme of the present application will be explained below in combination with examples. Those skilled in the art will understand that the following examples are only used to explain the present application and cannot be understood as a limitation of the present application. Unless otherwise stated, the reagents, software and instruments involved in the following examples are conventional commercially available products or open source.

[0062] Example 1:

[0063] A vanadium doped nickel cobalt manganese lithium ion battery positive electrode material, the preparation method comprises:

[0064] Step 1, citric acid monohydrate (C6H8O7·H2O) and vanadium pentoxide (V2O5) are weighed respectively, wherein the molar ratio of C6H8O7·H2O to V2O5 is 3:1, the weighed C6H8O7·H2O and V2O5 are dissolved in deionized water, and stirred uniformly at 80°C oil bath for 1h, to obtain a vanadium citrate aqueous solution, and the solution is evaporated in a 60°C air oven for 4h to obtain a vanadium citrate crystal.

[0065] Step 2, the crystal of step 1 is calcined in a tube furnace for 3h, oxygen is passed, and the calcination temperature is 200°C, to obtain anhydrous vanadium citrate (C 15 H 14 O9V2).

[0066] Step 3, 400mg of lithium nickel cobalt manganese oxide of single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2, 1.2mg of anhydrous vanadium citrate (C 15 H 14 O9V2) of step 2 are weighed, that is, the doping amount of anhydrous vanadium citrate is 1.2% of the single crystal LiNi 0.8 Co 0.1 Mn 0.10.3% of O2 mass, and the two are mixed to obtain a mixture, wherein the mixing is performed using a micro-shaking instrument at a speed of 280 r / min for 9 min; the mixture is calcined in a tube furnace with oxygen at 400℃ for 3 h and at 710℃ for 3 h to obtain the vanadium-doped nickel-cobalt-manganese lithium-ion battery positive electrode material.

[0067] Example 2:

[0068] The difference from Example 1 is that in Step 1, the evaporation is adjusted to be uniform-speed stirring evaporation in an oil bath at 100℃ for 2 h; in Step 2, the obtained anhydrous vanadium citrate (C 15 H 14 O9V2) is ground to obtain nanoscale anhydrous vanadium citrate with a particle size of 500-800 nm; in Step 3, the lithium nickel cobalt manganese oxide is adjusted to be polycrystalline LiNi 0.96 Co 0.02 Mn 0.02 O2; in Step 3, calcination is performed at 400℃ for 3 h and at 730℃ for 3 h.

[0069] Example 3:

[0070] The difference from Example 1 is that in Step 3, the lithium nickel cobalt manganese oxide is adjusted to be single-crystal LiNi 0.8 Mn 0.2 O2; in Step 2, the obtained anhydrous vanadium citrate (C 15 H 14 O9V2) is ground to obtain nanoscale anhydrous vanadium citrate with a particle size of 500-800 nm; in Step 3, 400 mg of single-crystal LiNi 0.8 Mn 0.2 O2 and 4 mg of anhydrous vanadium citrate (C 15 H 14 O9V2) are weighed.

[0071] Example 4:

[0072] The difference from Example 1 is that in Step 3, the lithium nickel cobalt manganese oxide is adjusted to be single-crystal LiNi 0.8 Co 0.2 O2; in Step 2, the obtained anhydrous vanadium citrate (C 15 H 14 O9V2) is ground to obtain nanoscale anhydrous vanadium citrate with a particle size of 500-800 nm; in Step 3, 400 mg of single-crystal LiNi 0.8 Mn 0.2 O2 and 2 mg of anhydrous vanadium citrate (C 15 H 14 O9V2) are weighed.

[0073] Comparative Example 1:

[0074] The difference from Example 1 is that no doping modification is made, i.e. polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 is used as the battery cathode material.

[0075] Comparative Example 2:

[0076] The difference from Example 2 is that no doping modification is made, i.e. polycrystalline LiNi 0.96 Co 0.02 Mn 0.02 O2 is used as the battery cathode material.

[0077] Comparative Example 3:

[0078] The difference from Example 3 is that no doping modification is made, i.e. single-crystal LiNi 0.8 Mn 0.2 O2 is used as the battery cathode material.

[0079] Comparative Example 4:

[0080] The difference from Example 4 is that no doping modification is made, i.e. single-crystal LiNi 0.8 Co 0.2 O2 is used as the battery cathode material.

[0081] Comparative Example 5:

[0082] The difference from Example 1 is that steps 1 and 2 are not performed, and in step 3, vanadium pentoxide (V2O5) is used instead of anhydrous vanadium citrate, and the particle size of the vanadium pentoxide (V2O5) used is 5-10 μm.

[0083] Comparative Example 6:

[0084] The difference from Example 1 is that steps 1 and 2 are not performed, and in step 3, ammonium metavanadate (NH4VO3) is used instead of anhydrous vanadium citrate, and the particle size of the ammonium metavanadate (NH4VO3) used is 5-10 μm.

[0085] Comparative Example 7:

[0086] The difference from Example 1 is that steps 1 and 2 are not performed, and in step 3, vanadium pentoxide (V2O5) is used instead of anhydrous vanadium citrate, and the temperature and time of calcination are adjusted so that the amount of vanadium doping in the vanadium-doped nickel-cobalt-manganese lithium-ion battery cathode material obtained is similar to that of Example 1.

[0087] Comparative Example 8:

[0088] The difference from Example 1 is that there are no Step 1 and Step 2, and in Step 3, ammonium metavanadate (NH4VO3) is used to replace anhydrous vanadium citrate, and the temperature and time of calcination are adjusted so that the amount of vanadium doping in the vanadium-doped nickel-cobalt-manganese lithium ion battery positive electrode material obtained is similar to that of Example 1.

[0089] The vanadium-doped nickel-cobalt-manganese lithium ion battery positive electrode materials obtained in Examples 1-4 and the materials of Comparative Examples 1-6 were prepared into lithium ion batteries, and these lithium ion batteries were subjected to charge-discharge cycles under the conditions of a set voltage and a rate, and the first discharge specific capacity, coulombic efficiency, capacity retention rate, and impedance were detected. The detection results are shown in Table 1.

[0090] The vanadium-doped nickel-cobalt-manganese lithium ion battery positive electrode materials obtained in Example 1 and Comparative Examples 7-8 were also subjected to ICP detection to detect the amount of vanadium doping therein, and the detection results and the calcination conditions required to achieve the amount of vanadium doping are shown in Table 2.

[0091] Table 1. First discharge specific capacity and cycle capacity retention rate test results of Example 1 and Comparative Examples 5-6 of the present application

[0092] Initial discharge specific capacity (mAh / g) Capacity retention after 100 cycles Example 1 203 85％ Comparative Example 5 200 81％ Comparative Example 6 199 79％

[0093] Referring to Table 1, compared with Comparative Example 5 and Comparative Example 6, Example 1 has a relatively higher first discharge specific capacity and cycle capacity retention rate under the condition of using the same particle size level of vanadium source and the same preparation conditions, indicating that compared with vanadium pentoxide or ammonium metavanadate, using anhydrous vanadium citrate as a vanadium doping carrier and using the preparation method of the present application can obtain a positive electrode material with better doping modification effect.

[0094] Table 2. Vanadium doping amount and calcination conditions of Example 1 and Comparative Examples 7-8 of the present application

[0095] Doping amount of vanadium Step 3 calcination temperature (°C) Step 3 calcination time (h) Example 1 0.13％ 400+710 3+3 Comparative Example 7 0.13％ 400+760 5+10 Comparative Example 8 0.13％ 400+770 5+10

[0096] Referring to Table 2, compared with Comparative Example 7 and Comparative Example 8, Example 1 has milder calcination conditions to achieve a similar amount of vanadium doping, such as calcination at 400°C to promote the nucleation stage of crystal grains, and the calcination time required by Example 1 is significantly less than that of Comparative Example 7 or Comparative Example 8. In the stage of promoting the growth of nucleated crystal grains by increasing the temperature, the calcination temperature and time required by Example 1 are also significantly less than those of Comparative Example 7 or Comparative Example 8. This indicates that compared with vanadium pentoxide or ammonium metavanadate, using anhydrous vanadium citrate as a vanadium doping carrier and using the preparation method of the present application can reduce the energy consumption and time required for doping, effectively reducing the preparation cost.

[0097] Example 1 compared with Comparative Example 1:

[0098] Referring to Figure 1The discharge specific capacity of the first cycle of Comparative Example 1 was 198 mAh / g, the coulombic efficiency was 82.2%, the capacity retention rate after 100 cycles was 75%, and the capacity retention rate after 300 cycles was 40% under the condition of 3-4.5V, 0.2C, please refer to Figure 1 The discharge specific capacity of the first cycle of Example 1 was 203 mAh / g, the coulombic efficiency was 82.5%, the capacity retention rate after 100 cycles was 85%, and the capacity retention rate after 300 cycles was 49% under the condition of 3-4.5V, 0.2C, please refer to Figure 1 When reaching 10C, the capacity of Example 1 was 119.0 mAh / g, while that of Comparative Example 1 was only 84.4 mAh / g. It is shown that after vanadium doping modification with vanadium citrate as a doping carrier, the first coulombic efficiency, capacity retention rate and rate performance of the positive electrode material of Example 1 are all improved significantly.

[0099] Please refer to Figure 1 The peaks near 3.8V, 4.1V and 4.3V in (e) and (f) of Comparative Example 1 represent H1-M, M-H2 and H2-H3 phase changes respectively under the condition of 3-4.5V, 0.2C. With the charging, the structure transition of hexagonal-monoclinic-hexagonal occurs, accompanied by a large anisotropic lattice mutation, which is an important reason for micro-cracks. However, the H2-H3 phase change degree of Example 1 is lower, and the curve coincidence degree of different cycle numbers is higher, which shows that vanadium doping with vanadium citrate as a doping carrier inhibits the adverse phase change in the charging and discharging process, and improves the phase change reversibility and structural stability.

[0100] Please refer to Figure 1 The ohmic resistance (R0) of Comparative Example 1 was 1.871Ω, the charge transfer resistance (R ct ) was 181.1Ω, the R0 of Example 1 was 12.03Ω, and the R ct was 151.1Ω, that is, Example 1 has a relatively smaller charge transfer resistance. And please refer to Figure 1 (h) of Comparative Example 1, the internal resistance of the battery increases significantly with the cycle, which is one of the reasons for the capacity decline.

[0101] Example 2 compared with Comparative Example 2:

[0102] Please refer to Figure 2 The discharge specific capacity of the first cycle of Comparative Example 2 was 173.2 mAh / g, the coulombic efficiency was 76.1%, and the capacity retention rate after 100 cycles was 97.1% under the condition of 3-4.3V, 0.2C, please refer to Figure 2In examples (b) and (c), Example 2 showed a discharge specific capacity of 188.6 mAh / g in the first cycle, a coulombic efficiency of 78.3%, and a capacity retention of 98.2% after 100 cycles. Please refer to [link to relevant documentation]. Figure 2 In Example 2 (d), under conditions of 3-4.5V and 0.2C, the discharge specific capacity of the first cycle was 204.7 mAh / g, the coulombic efficiency was 81.9%, and the capacity retention rate after 200 cycles was 35.7%. In Example 2, the discharge specific capacity of the first cycle was 206.4 mAh / g, the coulombic efficiency was 82.7%, and the capacity retention rate after 200 cycles was 42.6%. This demonstrates that after vanadium doping modification using anhydrous vanadium citrate as the doping support, the initial coulombic efficiency and capacity retention rate of the cathode material obtained in Example 2 were significantly improved.

[0103] Please see Figure 2 In (e) and (f), the degree of H2-H3 phase transition in Example 2 is lower than that in Comparative Example 2, and the curves of different cycle numbers have a high degree of overlap, indicating that vanadium doping with anhydrous vanadium citrate as the doping support suppresses the unfavorable phase transition during the charge and discharge process and improves the structural stability.

[0104] Please see Figure 2 In Example 2, the capacity at 10C was 116.1 mAh / g, while in Comparative Example 2 it was only 106.1 mAh / g. This indicates that after vanadium doping modification using anhydrous vanadium citrate as the doping support, the rate performance of the resulting cathode material in Example 2 was significantly improved.

[0105] Please see Figure 2 In the example (h), the ohmic impedance (R0) of Comparative Example 2 is 1.237Ω, and the charge transfer impedance (R) is... ct The R0 in Example 2 is 208.2Ω, and the R0 in Example 2 is 1.361Ω. ct The resistance is 200.1 Ω, meaning Example 2 has a relatively smaller charge transfer impedance. After ten cycles, SEI forms; please refer to [link to documentation]. Figure 2 In example (i), (R0) of comparative example 2 is 1.062Ω, R SEI It is 21.61Ω, R ct The R0 in Example 1 is 75.6Ω, while the R0 in Example 2 is 3.683Ω. SEI It is 35.06Ω, R ct The impedance is 29.5Ω, indicating that the internal resistance of the battery increases with cycling. However, under the same conditions, the impedance of Example 2 is smaller than that of Comparative Example 2, suggesting that after vanadium doping modification using anhydrous vanadium citrate as the doping support in Example 2, R... ct The reduction in charge transfer resistance and the acceleration of lithium ion diffusion result in better rate performance.

[0106] Example 3 compared to Comparative Example 3:

[0107] Please see Figure 3 In (a) and (c) of the comparison example, under conditions of 3-4.5V and 1C, the discharge specific capacity of the first cycle of the comparative example 3 is 181mAh / g, the coulombic efficiency is 81.9%, and the capacity retention rate after 200 cycles is 27%. Please refer to [link to relevant documentation]. Figure 3 In (b) and (c) of Example 3, under conditions of 3-4.5V and 1C, the discharge specific capacity in the first cycle was 175mAh / g, the coulombic efficiency was 83.1%, and the capacity retention after 200 cycles was 45%. Please refer to [link to relevant documentation]. Figure 3 In Example 3 (d), at 10C, the capacity was 120 mAh / g, while that of Comparative Example 3 was only 108 mAh / g. This indicates that after vanadium doping modification with anhydrous vanadium citrate as the doping support, the initial coulombic efficiency, capacity retention, and rate performance of the cathode material obtained in Example 3 were significantly improved.

[0108] Example 4 compared to Comparative Example 4:

[0109] Please see Figure 4 In (a) and (c) of the comparison example, under conditions of 3-4.5V and 1C, the discharge specific capacity of the first cycle of the comparative example 4 is 198mAh / g, and the capacity retention rate after 100 cycles is 50%. Please refer to [link to relevant documentation]. Figure 4 In examples (b) and (c), under conditions of 3-4.5V and 1C, the discharge specific capacity of Example 4 in the first cycle was 205mAh / g, and the capacity retention rate after 100 cycles was 77%. Please refer to [link to documentation]. Figure 4 In Example 4 (d), at 10C, the capacity was 125 mAh / g, while that of Comparative Example 4 was only 110 mAh / g. This indicates that after vanadium doping modification using anhydrous vanadium citrate as the doping support, the capacity retention and rate performance of the resulting cathode material in Example 4 were significantly improved.

[0110] The above results demonstrate that using anhydrous vanadium citrate as a doping support to modify ternary cathode materials (such as lithium nickel cobalt manganese oxide) with vanadium doping results in a significant performance improvement. The preparation process of this application for doping modification of ternary cathode materials using anhydrous vanadium citrate as a doping support is simple and energy-efficient, which is beneficial for reducing production costs and facilitating large-scale production.

[0111] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A method for preparing a vanadium-doped nickel-cobalt-manganese ternary cathode material, characterized in that, include: An aqueous solution of vanadium citrate is provided, and the aqueous solution of vanadium citrate is evaporated and crystallized and then calcined once to obtain anhydrous vanadium citrate. The anhydrous vanadium citrate is mixed with lithium nickel cobalt manganese oxide to obtain a mixture, and the mixture is calcined a second time to obtain the vanadium-doped nickel cobalt manganese ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The provision of the vanadium citrate aqueous solution comprises mixing vanadium pentoxide with citric acid and heating to cause the vanadium pentoxide to react with the citric acid.

3. The preparation method according to claim 1, characterized in that, The evaporation and crystallization process takes place at a temperature of 60°C to 100°C for 2 to 4 hours.

4. The preparation method according to claim 1, characterized in that, The first roasting is carried out in an oxygen-containing atmosphere, and the temperature of the first roasting is 180°C to 220°C, and the time is 2 hours to 3 hours.

5. The preparation method according to claim 1, characterized in that, The anhydrous vanadium citrate has a particle size of 500 nm to 800 nm.

6. The preparation method according to claim 1, characterized in that, The mixing speed is 200 r / min to 300 r / min.

7. The preparation method according to claim 1, characterized in that, The secondary calcination is carried out in an oxygen-containing atmosphere at a temperature of 400°C to 730°C for 3 to 6 hours.

8. A vanadium-doped nickel-cobalt-manganese ternary cathode material, characterized in that, The vanadium-doped nickel-cobalt-manganese ternary cathode material, prepared by the preparation method according to any one of claims 1-7, has the molecular formula LiNi. x Co y Mn z V a O2, 0.8≤x≤0.96, 0.02≤y≤0.2, 0.02≤z≤0.2, 0.0013≤a≤0.0043.

9. A positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, characterized in that, The positive electrode active material layer includes the vanadium-doped nickel-cobalt-manganese ternary positive electrode material as described in claim 8.

10. A lithium-ion battery, comprising an electrode assembly, the electrode assembly including a separator and a negative electrode sheet, characterized in that, It also includes the positive electrode sheet as described in claim 9, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet.

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