A high-nickel ternary positive electrode surface coating modified coating and its preparation method and application

Abstract

The present invention relates to a high-nickel ternary positive electrode surface coating modification, its preparation method, and its application. NiFe2O4 and ZrV2O7 bimetallic oxide coatings are coated on the surface of high-nickel ternary NCM622 or NCM811 positive electrode materials through a co-precipitation method. Compared with the prior art, the modified NCM622 positive electrode material maintains a capacity retention rate of 84.96% even after 200 cycles under high-voltage conditions of 4.5V; the modified NCM811 positive electrode material maintains a capacity retention rate of 93.67% after 100 cycles. This demonstrates that the presence of the NiFe2O4 and ZrV2O7 bimetallic oxide coatings can effectively increase the lithium ion diffusion rate, inhibit irreversible phase changes and a series of harmful side reactions during long-term cycling, and slow the dissolution of transition metals, providing a theoretical basis for surface modification of high-nickel materials.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a high-nickel ternary positive electrode surface coating modification coating, a preparation method and an application thereof. Background Art

[0002] With the continuous development and progress of human society, the massive consumption of traditional energy sources has led to serious environmental pollution problems, making the energy crisis and environmental pollution two major challenges that are difficult to resolve, and have also significantly impacted human production and daily life. Renewable clean energy sources such as solar and wind energy are naturally renewable, but these clean energy sources are limited by geographical and utilization efficiency, hindering their large-scale application. In contrast, further improvement of electrochemical energy storage technology is a key goal in building a low-carbon, environmentally friendly society in the 21st century. While valve-regulated lead-acid batteries and nickel-metal hydride batteries can alleviate these problems, their high environmental pollution, low operating potential, and low energy density limit their application in meeting today's sustainable development requirements. Against the backdrop of the rapid global development of electric vehicles and portable electronic devices, rechargeable lithium-ion batteries are considered the best choice for electrochemical energy storage technology due to their high energy density, low cost, and environmental friendliness.

[0003] Lithium-ion batteries primarily consist of three components: electrode materials, electrolyte, and separator. However, compared to negative electrode materials, the capacity of lithium-ion cathode materials is far from satisfactory, limiting the development of high-energy-density lithium-ion batteries. For one thing, cathode materials require complex synthesis processes; even minor variations in the preparation process can lead to structural variations, impacting performance. Furthermore, traditional cathode materials contain a high proportion of rare metals, contributing to their contribution to approximately 40% of the battery's cost. Therefore, cathode materials are a crucial factor in determining the overall performance of lithium-ion batteries and represent a key breakthrough in improving battery performance.

[0004] Under comprehensive considerations, driven by the high energy density and low cost requirements of electric vehicles and portable electronic devices, low-nickel NCM111 and NCM424 materials are gradually being replaced by high-nickel NCM (Ni ≥ 60%) cathode materials with higher reversible capacity. Among high-nickel cathode materials, NCM622 and NCM811 have been widely selected for research and analysis due to their suitable capacity and cycling performance. However, NCM622 and NCM811 cathode materials still suffer from instability during cycling and under high-temperature conditions, and this issue urgently needs to be addressed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned NCM622 and NCM811 positive electrode materials that are unstable during the cycle process and at high temperatures, and to provide a high-nickel ternary positive electrode surface coating modification coating and its preparation method and application. A mixed solution of bimetallic salts is used as the matrix solution, and NCM622 and NCM811 positive electrode materials are used as research objects. Uniform NiFe2O4 and ZrV2O7 bimetallic oxide coatings are formed on the surfaces of NCM622 and NCM811 positive electrode materials respectively by co-precipitation method.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a high-nickel ternary positive electrode surface coating modified coating, including a NCM622 type positive electrode surface coated with a bimetallic oxide coating or an NCM811 type positive electrode surface coated with a bimetallic oxide coating.

[0008] Furthermore, the bimetallic oxide coating coated on the surface of the NCM622 positive electrode is NiFe2O4; and the bimetallic oxide coating coated on the surface of the NCM811 positive electrode is ZrV2O7.

[0009] The second technical solution of the present invention is to provide a method for preparing a high nickel ternary positive electrode surface coated modified coating as described in one of the technical solutions, including a method for preparing a bimetallic oxide coating on the surface of an NCM622 positive electrode or a method for preparing a bimetallic oxide coating on the surface of an NCM811 positive electrode, wherein

[0010] The preparation method of the bimetallic oxide coating on the surface of the S1 and NCM622 positive electrodes comprises the following steps:

[0011] S1-1, mixing a nickel source, an iron source, and anhydrous ethanol, and stirring to obtain a mixed solution A;

[0012] S1-2, adding an NCM622 cathode to the mixed solution A obtained in step S1-1, mixing and stirring to obtain a solution C;

[0013] S1-3, adding ammonia water to the solution C obtained in step S1-2, adjusting the pH and stirring to obtain a solution E, which is then evaporated and dried to obtain a powder;

[0014] S1-4, grinding, calcining and heat-insulating the powder obtained in step S1-3 to obtain a NiFe2O4 coating on the surface of the NCM622 positive electrode, which is marked as x% NFO-NCM622;

[0015] The preparation method of the bimetallic oxide coating on the surface of the S2 and NCM811 positive electrodes comprises the following steps:

[0016] S2-1, mixing a zirconium source, a vanadium source and anhydrous ethanol to obtain a mixed solution B;

[0017] S2-2, adding the NCM811 positive electrode to the mixed solution B obtained in step S2-1, mixing and stirring to obtain solution D;

[0018] S2-3, adding ammonia water to the solution D obtained in step S2-2, adjusting the pH and stirring to obtain a solution F, which is then evaporated and dried to obtain a powder;

[0019] S2-4. Grind, calcine and keep the powder obtained in step S2-3 to obtain a ZrV2O7 coating on the surface of the NCM811 positive electrode, which is marked as x% ZVO-NCM811.

[0020] Furthermore, in step S1-1, the molar ratio of the nickel source to the iron source is 1:(1.5-3.0).

[0021] Furthermore, in step S2-1, the molar ratio of the zirconium source to the vanadium source is 1:(1.0-3.0).

[0022] Furthermore, in step S1-1 and step S2-1, the constant temperature of the mixing and stirring is 20 to 40°C.

[0023] Furthermore, in step S1-3 and step S2-3, the pH is adjusted to 8-11; the evaporation temperature is 50-80°C; and the drying temperature is 60-90°C.

[0024] Furthermore, in step S1-4 and step S2-4, the calcination temperature is 400-800° C., and the holding time is 2-6 hours.

[0025] Furthermore, in step S1-4 and step S2-4, x is the mass percentage of the modified coating portion to the total mass, and x is any integer selected from 1 to 4.

[0026] The third technical solution of the present invention is to provide an application of the high-nickel ternary positive electrode surface coating modified coating as described in one of the technical solutions, wherein the high-nickel ternary positive electrode surface coating modified coating is used to prepare a lithium battery.

[0027] The principle of the present invention is that NiFe2O4 and ZrV2O7 have good lithium ion conductivity and are very promising lithium ion battery anode materials. The MON bonding network between the modified coating and the positive electrode material not only promotes the close bonding of the modified coating and the substrate to form a stable interface, but also prevents structural degradation of the positive electrode material during the electrochemical process and the dissolution of transition metals such as Mn. In addition, the modified coating can also capture lithium residues (LiOH and Li2CO3) on the surface of NCM622 and NCM811 positive electrode materials, further improving the cycle stability of the positive electrode material.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The preparation method of the present invention has a simple process. The prepared bimetallic oxide NiFe2O4 and ZrV2O7 coating has good lithium ion conductivity, can effectively improve the lithium ion diffusion rate, and inhibit the irreversible phase change and the generation of a series of harmful side reactions during long-term circulation, slow down the dissolution of transition metals, so that the modified positive electrode material can exhibit good structural stability during long-term circulation and at high temperatures, providing a theoretical basis for the surface modification of high-nickel materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the X-ray diffraction (XRD) pattern of the NiFe2O4 spinel phase ferrite and ZrV2O7 material phases prepared in Example 1 without adding positive electrode materials.

[0031] Figure 2 These are the X-ray diffraction (XRD) patterns of x% NFO-NCM622 and x% ZVO-NCM811 with different modified coating amounts prepared in Examples 2 to 5.

[0032] Figure 3 These are scanning electron microscope (SEM) images of the positive electrode material in Example 3 before (left) and after being coated with the modified coating.

[0033] Figure 4 The EDS mapping diagrams of the overall and various elements of the modified coatings coated on the positive electrode surfaces prepared in Examples 2 to 5 are shown.

[0034] Figure 5 These are the cycle performance test data of x% NFO-NCM622, x% ZVO-NCM811 coated with different coating amounts prepared in Examples 2 to 5, as well as the original materials NCM622 and NCM811.

[0035] Figure 6These are the rate test data of x% NFO-NCM622, x% ZVO-NCM811 coated with different coating amounts prepared in Examples 2 to 5, as well as the original materials NCM622 and NCM811. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] In the following examples and comparative examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0038] Example 1:

[0039] Use an electronic balance to weigh 0.5864g Ni(NO3)2·6H2O and 1.0549g Fe(NO3)3·9H2O particles and add them to a beaker. Use a graduated cylinder to accurately measure 50mL of anhydrous ethanol and slowly add it to the beaker to mix. Place the mixed solution in a 30℃ water bath and stir for 1h. Take 20mL of NH3·H2O was added dropwise to the mixed solution as a precipitant, and the pH value of the mixed solution was monitored in real time using a calibrated pH meter. When the pH value of the mixed solution reached 10, the addition of NH3·H2O was stopped, and the mixed solution containing the precipitate was stirred for 2 hours. Subsequently, the reaction mixture was filtered and separated using a vacuum filter, and washed with anhydrous ethanol and deionized water until the pH value reached 7-8. The obtained precipitate was placed in an 80°C forced air drying oven and dried overnight. The precipitate was then taken out and ground, and the powder was transferred to a corundum crucible. After gently vibrating, it was placed in a tubular furnace for calcination to remove moisture to obtain a powder with good crystallinity. The heating temperature was set to 600°C and kept warm for 4 hours. After the end, it was cooled to room temperature with the furnace to obtain the final powder, which was labeled as NiFe2O4.

[0040] Use an electronic balance to weigh 0.4293g Zr(NO3)4·5H2O and 0.1818g V2O5 powder and add them to a beaker. Use a graduated cylinder to accurately measure 50mL of anhydrous ethanol and slowly add it to the beaker to mix. Place the mixed solution in a 30℃ water bath and stir for 1h. Take 20mL of NH3·H2O was added dropwise to the mixed solution as a precipitant, and the pH value of the mixed solution was monitored in real time using a calibrated pH meter. When the pH value of the mixed solution reached 10, the addition of NH3·H2O was stopped, and the mixed solution containing the precipitate was stirred for 2 hours. Subsequently, the reaction mixture was filtered and separated using a vacuum filter, and washed with anhydrous ethanol and deionized water until the pH value reached 7-8. The obtained precipitate was placed in an 80°C forced air drying oven and dried overnight. The precipitate was then taken out and ground, and the powder was transferred to a corundum crucible. After gently vibrating, it was placed in a tubular furnace for calcination to remove moisture to obtain a powder with good crystallinity. The heating temperature was set to 600°C and kept warm for 4 hours. After the end, it was cooled to room temperature with the furnace to obtain the final powder, which was labeled as ZrV2O7.

[0041] Take appropriate amount of NiFe2O4 and ZrV2O7 powders to conduct XRD test analysis to confirm that the products are pure substances of NiFe2O4 and ZrV2O7. The XRD patterns are as follows: Figure 1 shown.

[0042] Example 2:

[0043] Using an electronic balance, 0.0384g of Ni(NO₃)₂·6H₂O and 0.1044g of Fe(NO₃)₃·9H₂O pellets were weighed and added to a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM622 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with a standard solution. After washing and drying with anhydrous ethanol, each was placed in the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and maintained at this temperature for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled as 1% NFO-NCM622.

[0044] Using an electronic balance, 0.0211g of Zr(NO₃)₄·5H₂O and 0.0089g of V₂O₅ powder were weighed into a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM811 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with the calibration solution. After washing and drying with anhydrous ethanol, each sample was placed into the mixture to monitor its pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and kept warm for 4 hours at a heating rate of 2°C / min. After the furnace was cooled to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 0.5% ZVO-NCM811.

[0045] An appropriate amount of the obtained 1% NFO-NCM622 and 0.5% ZVO-NCM811 powders was subjected to XRD test analysis to determine the phase composition of the obtained product. After the test was completed, the product was sealed and stored for subsequent production of battery electrodes.

[0046] Example 3:

[0047] Using an electronic balance, 0.0769g of Ni(NO₃)₂·6H₂O and 0.2089g of Fe(NO₃)₃·9H₂O pellets were weighed and added to a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM622 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with the calibration solution, washed and dried with anhydrous ethanol, and then placed in the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and maintained at this temperature for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 2% NFO-NCM622.

[0048] Using an electronic balance, 0.0422g of Zr(NO₃)₄·5H₂O and 0.0178g of V₂O₅ powder were weighed into a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM811 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with a standard solution, washed with anhydrous ethanol, dried, and placed into the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and kept warm for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 1% ZVO-NCM811.

[0049] An appropriate amount of the obtained 2% NFO-NCM622 and 1% ZVO-NCM811 powders was subjected to XRD test analysis to determine the phase composition of the obtained product. After the test was completed, the product was sealed and stored for subsequent production of battery electrodes.

[0050] Example 4:

[0051] Using an electronic balance, 0.11532g of Ni(NO₃)₂·6H₂O and 0.31335g of Fe(NO₃)₃·9H₂O pellets were weighed and added to a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM622 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with a standard solution, washed and dried with anhydrous ethanol, and then placed in the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and maintained at this temperature for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 3% NFO-NCM622.

[0052] Using an electronic balance, 0.0844g of Zr(NO₃)₄·5H₂O and 0.0357g of V₂O₅ powder were weighed into a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM811 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with a standard solution, washed with anhydrous ethanol, dried, and placed into the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and kept warm for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 2% ZVO-NCM811.

[0053] An appropriate amount of the obtained 3% NFO-NCM622 and 2% ZVO-NCM811 powders was subjected to XRD test analysis to determine the phase composition of the obtained product. After the test was completed, the product was sealed and stored for subsequent production of battery electrodes.

[0054] Example 5:

[0055] Using an electronic balance, 0.15736g of Ni(NO₃)₂·6H₂O and 0.41780g of Fe(NO₃)₃·9H₂O pellets were weighed and added to a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM622 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with the calibration solution, washed with anhydrous ethanol, dried, and placed in the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and maintained at this temperature for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 4% NFO-NCM622.

[0056] Using an electronic balance, 0.1266g of Zr(NO₃)₄·5H₂O and 0.0536g of V₂O₅ powder were weighed into a beaker. Using a graduated cylinder, 50mL of anhydrous ethanol was accurately measured and slowly added to the beaker. The mixture was stirred in a 30°C waterbath for 1 hour until completely dissolved. 3g of commercial NCM811 cathode material powder was weighed and slowly added to the mixture, stirring for 2 hours. A pH meter was then calibrated with a standard solution, washed with anhydrous ethanol, dried, and placed into the mixture to monitor the pH in real time. Using a dropper, an appropriate amount of NH₃·H₂O was added dropwise to the mixture as a precipitant. When the pH reached 10, the addition of NH₃·H₂O was stopped, and the mixture containing the precipitate was stirred for 1 hour. Subsequently, the water bath temperature was raised to 70°C, and the solvent was slowly evaporated under constant stirring. The resulting evaporated material was placed in an 80°C vacuum drying oven and dried overnight to prevent the formation of impurities on the material surface. The powder was then removed and ground, transferred to a corundum crucible, gently vibrated, and placed in a tube furnace for calcination to remove moisture and other impurities. The tube furnace was set to a heating temperature of 600°C and kept warm for 4 hours at a heating rate of 2°C / min. After cooling to room temperature, a well-crystalline positive electrode surface-coated modified coating material powder was obtained, labeled 3% ZVO-NCM811.

[0057] An appropriate amount of the obtained 4% NFO-NCM622 and 3% ZVO-NCM811 powders was subjected to XRD test analysis to determine the phase composition of the obtained product. After the test was completed, the product was sealed and stored for subsequent production of battery electrodes.

[0058] Example 6:

[0059] Compared with Example 2, most of them are the same, except that the ratio of the amount of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O particles is replaced with 1:1.5, and the ratio of the amount of Zr(NO3)4·5H2O and V2O5 is replaced with 1:3.0, and the rest remain unchanged. X-ray diffraction analysis found that NFO-NCM622 and ZVO-NCM811 both have a good layered structure, Ni, Co and Fe elements are evenly distributed on the surface of NFO-NCM622, and Ni, Zr and V elements are evenly distributed on the surface of ZVO-NCM811. And the cycle performance test and rate test analysis show that NFO-NCM622 and ZVO-NCM811 both have higher capacity retention and high discharge capacity.

[0060] Example 7:

[0061] Compared with Example 2, most of them are the same, except that the ratio of the amount of substance of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O particles is changed to 1:3.0, and the rest remain unchanged. X-ray diffraction analysis found that NFO-NCM622 and ZVO-NCM811 both have a good layered structure, Ni, Co and Fe elements are evenly distributed on the surface of NFO-NCM622, and Ni, Zr and V elements are evenly distributed on the surface of ZVO-NCM811. And the cycle performance test and rate test analysis show that NFO-NCM622 and ZVO-NCM811 both have higher capacity retention and high discharge capacity.

[0062] The test results of the above embodiment are evaluated and analyzed as follows:

[0063] like Figure 1 As shown, the NiFe2O4 spinel phase ferrite and ZrV2O7 materials prepared in Example 1 of the present invention were subjected to X-ray diffraction analysis according to standard cards PDF#10-0325 and PDF#16-0422, respectively. By comparison, it can be seen that NiFe2O4 and ZrV2O7 powders without impurity peaks and with good crystallinity can be prepared by the co-precipitation method, which proves that pure phase NiFe2O4 and ZrV2O7 substances can be formed on the surface of the positive electrode material by the co-precipitation method.

[0064] like Figure 2 As shown, NCM622, x% NFO-NCM622, NCM811 and x% ZVO-NCM811 in Examples 2 to 5 of the present invention were subjected to X-ray diffraction analysis. The results showed that NCM622, x% NFO-NCM622, NCM811 and x% ZVO-NCM811 all had α-NaFeO2 layered structures, and I(003) / I(104)>1.2, and the degree of cation mixing was very low; the two pairs of peaks (006) / (102) and (108) / (110) had obvious splitting, indicating that the materials had good layered structures before and after modification.

[0065] like Figure 3 As shown, the NCM622, 2% NFO-NCM622 and NCM811, 1% ZVO-NCM811 in Example 3 of the present invention were subjected to scanning electron microscope SEM test analysis. It can be seen that NCM622, 2% NFO-NCM622 and NCM811, 1% ZVO-NCM811 all appear as spherical secondary particles with a diameter of about 10 μm, and NCM622 and NCM811 have relatively smooth surfaces, while the surfaces of the two modified materials have obviously become rough and are covered with a layer of substance, which can prove the presence of the coating.

[0066] like Figure 4As shown, the x% NFO-NCM622 and x% ZVO-NCM811 in Examples 2 to 5 of the present invention were subjected to EDS mapping test analysis of the whole and each element, as shown in FIG. Figure 4 (a) It can be seen that Ni, Co and Fe elements are evenly distributed on the surface of x% NFO-NCM622, as shown in Figure 4 (b) It can be seen that Ni, Zr and V elements are evenly distributed on the surface of x% ZVO-NCM811, further indicating that NFO and ZVO are uniformly coated on the surface of NCM particles.

[0067] like Figure 5 As shown, the NCM622, x% NFO-NCM622, NCM811, and x% ZVO-NCM811 in Examples 2 to 5 of the present invention were subjected to 0.5C (1C = 200 mAh / g) cycling performance tests at 2.75-4.5V and 28°C. The results showed that after 200 cycles, the discharge capacity of the original NCM622 rapidly decayed from 181.2 mAh / g to 95.4 mAh / g, with a capacity retention rate of only 61.24%. 1% NFO-NCM622, 2% NFO-NCM622, 3% NFO-NCM622, and 4% NFO-NCM622 had higher capacity retention rates of 79.28%, 81.64%, 84.96%, and 78.58%, respectively. In addition, the capacity retention rate of 4% NFO-NCM is lower than that of other samples. This may be because the coating is too thick, which increases the diffusion path of lithium ions, thereby increasing the degree of polarization, resulting in the inability of lithium ions to be fully deintercalated in the NCM622 lattice during the cycle. After 100 cycles, the discharge capacity of NCM811 rapidly decayed from 183.5mAh / g to 152.6mAh / g, with a capacity retention rate of 81.56%. The capacity retention rates of 0.5% ZVO-NCM811, 1% ZVO-NCM811, 2% ZVO-NCM811, and 3% ZVO-NCM811 were 86.44%, 93.67%, 82.19%, and 68.13%, respectively. In addition, the capacity retention rate of 3% ZVO-NCM is lower than that of other samples. This may be because the coating is too thick, which increases the diffusion path of lithium ions, thereby increasing the degree of polarization, resulting in the inability of lithium ions to be fully deintercalated in the NCM811 lattice during the cycle.

[0068] like Figure 6The figures show the rate analysis of NCM622 and x% NFO-NCM622 in Examples 2 to 5 of the present invention during cycling at 2.75-4.5V, 28°C, 0.2-10C, and different current densities; as well as the rate analysis of NCM811 and x% ZVO-NCM811 during cycling at 2.75-4.4V, 25°C, 0.2-10C, and different current densities. As the discharge rate increases, the discharge capacity of each sample decreases. At a low current density of 0.2C, the discharge capacity difference between NCM622 and x% NFO-NCM622 is not significant. However, at a high current density of 10C, the discharge capacity of x% NFO-NCM622 is significantly higher than that of NCM622. Even at a high rate of 10C, the discharge capacity of 3% NFO-NCM is still 103.5mAh / g, higher than the 48.6mAh / g of the original sample. For NCM811 materials, the discharge capacity of the ZVO-modified sample is significantly higher than that of the original NCM811 sample in the voltage range of 2.75-4.4 V. At a high rate of 10C, the discharge capacity of the 1% ZVO-NCM811 is still 140.8 mAh / g, higher than the 110.4 mAh / g of the original sample.

[0069] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A high nickel ternary positive electrode surface coated with a modified coating, characterized in that: Including NCM622 type positive electrode surface coated with a bimetallic oxide coating or NCM811 type positive electrode surface coated with a bimetallic oxide coating; The bimetallic oxide coating coated on the surface of the NCM622 positive electrode is NiFe2O4; the bimetallic oxide coating coated on the surface of the NCM811 positive electrode is ZrV2O7.

2. A method for preparing a high-nickel ternary positive electrode surface coating modified coating according to any one of claim 1, characterized in that: The invention comprises a method for preparing a bimetallic oxide coating on the surface of an NCM622 positive electrode or a method for preparing a bimetallic oxide coating on the surface of an NCM811 positive electrode, wherein The preparation method of the bimetallic oxide coating on the surface of the S1 and NCM622 positive electrodes comprises the following steps: S1-1, mixing a nickel source, an iron source, and anhydrous ethanol, and stirring to obtain a mixed solution A; S1-2, adding an NCM622 cathode to the mixed solution A obtained in step S1-1, mixing and stirring to obtain a solution C; S1-3, adding ammonia water to the solution C obtained in step S1-2, adjusting the pH and stirring to obtain a solution E, which is then evaporated and dried to obtain a powder; S1-4, grinding, calcining and heat-insulating the powder obtained in step S1-3 to obtain a NiFe2O4 coating on the surface of the NCM622 positive electrode, marked as x % NFO-NCM622; The preparation method of the bimetallic oxide coating on the surface of the S2 and NCM811 positive electrodes comprises the following steps: S2-1, mixing a zirconium source, a vanadium source and anhydrous ethanol to obtain a mixed solution B; S2-2, adding the NCM811 positive electrode to the mixed solution B obtained in step S2-1, mixing and stirring to obtain solution D; S2-3, adding ammonia water to the solution D obtained in step S2-2, adjusting the pH and stirring to obtain a solution F, which is then evaporated and dried to obtain a powder; S2-4, grinding, calcining and heat-insulating the powder obtained in step S2-3, and finally obtaining a ZrV2O7 coating on the surface of the NCM811 positive electrode, marked as x % ZVO-NCM811.

3. The method for preparing a high-nickel ternary positive electrode surface coating modification coating according to claim 2, characterized in that: In step S1-1, the molar ratio of the nickel source to the iron source is 1:(1.5~3.0).

4. The method for preparing a high-nickel ternary positive electrode surface coating modification coating according to claim 2, characterized in that: In step S2-1, the molar ratio of the zirconium source to the vanadium source is 1:(1~3.0).

5. The method for preparing a high-nickel ternary positive electrode surface coating modification coating according to claim 2, characterized in that: In step S1-1 and step S2-1, the constant temperature for mixing and stirring is 20-40°C.

6. The method for preparing a high-nickel ternary positive electrode surface coating modification coating according to claim 2, characterized in that: In steps S1-3 and S2-3, the pH is adjusted to 8-11; the evaporation temperature is 50-80°C; and the drying temperature is 60-90°C.

7. The method for preparing a high-nickel ternary positive electrode surface coating modification coating according to claim 2, characterized in that: In steps S1-4 and S2-4, the calcination temperature is 400-800°C, and the holding time is 2-6 h.

8. The method for preparing a high-nickel ternary positive electrode surface coating modification coating according to claim 2, characterized in that: In steps S1-4 and S2-4, x is the mass percentage of the modified coating part in the total mass, x Any integer selected from 1 to 4.

9. An application of the high nickel ternary positive electrode surface coating modified coating as claimed in claim 1, characterized in that: The high-nickel ternary positive electrode surface-coated modified coating is used to prepare a lithium battery.

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