Positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a positive electrode material and a preparation method thereof, and the structural safety index epsilon of the positive electrode material is greater than or equal to 2 and less than 201; the structural safety index epsilon is equal to 117 delta * [d003 / d104] * kappa-1, delta is the percentage of the area of the cavity on the cross section of the positive electrode material passing through the sphere center to the total area of the cross section, kappa is the specific surface area of the positive electrode material, the unit is m < 2 > / g, d003 is the interplanar spacing of the crystal face of the positive electrode material (003), and d104 is the interplanar spacing of the crystal face of the positive electrode material (104). The positive electrode material has high specific capacity, long cycle life and high safety performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a cathode material and its preparation method. Background Technology

[0002] As the global energy structure shifts towards cleaner and lower-carbon energy, the rapid development of electric vehicles, smart grids, and large-scale energy storage systems places higher demands on the performance of lithium-ion batteries. Cathode materials, as a core component of lithium-ion batteries, directly affect the overall battery performance through their energy density, cycle life, and safety. High-nickel cathode materials possess high theoretical energy density, effectively enhancing the energy storage capacity of lithium-ion batteries and making them the preferred material for electric vehicles (EVs), energy storage systems, and portable electronic devices. However, while increasing the Ni content in high-nickel cathode materials achieves higher capacity, the material's cycle performance tends to deteriorate, leading to rapid capacity decay and even safety issues. High capacity and long cycle life are key indicators for battery materials, directly impacting battery life and economics. In electric vehicles and energy storage systems, long-cycle-life battery materials are fundamental to ensuring the long-term stable operation of equipment; therefore, special attention needs to be paid to the cycle stability of high-nickel cathode materials.

[0003] Traditional cathode materials have dense particles, allowing lithium ions to diffuse only through limited surface channels, resulting in poor electrical performance and low utilization of active materials. Furthermore, during charge and discharge, anisotropic volumetric strain can easily cause the propagation of microcracks within the particles, accelerating material degradation and leading to a decline in cycle life and safety performance. Therefore, there is an urgent need to improve the cycle performance of high-nickel cathode materials without compromising high-capacity and high-rate performance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of structural degradation and capacity decay caused by volumetric strain in high-nickel cathode materials in the prior art, and to provide a cathode material and its preparation method, which has high specific capacity, long cycle life and high safety performance.

[0005] To achieve the above objectives, the present invention provides a cathode material, wherein the structural safety index ε of the cathode material satisfies: 2 ≤ ε < 201; the structural safety index ε = 117δ·[d 003 / d 104 ]·κ -1 δ is the percentage of the cavity area on the cross-section of the positive electrode material passing through the center of the sphere to the total cross-sectional area, and κ is the specific surface area of ​​the positive electrode material, in m². 2 / g,d 003 d is the interplanar spacing of the (003) crystal plane of the cathode material. 104 The interplanar spacing of the positive electrode material (104) is the interplanar spacing of the crystal plane.

[0006] A second aspect of the present invention provides a method for preparing a cathode material, comprising the following steps: (1) Mix the doped element precursor and the water washing concentrate to obtain a mixture, spray the mixture onto the cathode material precursor, and dry it to obtain an intermediate; The cathode material precursor is prepared by co-precipitation of a sulfate of nickel, optionally cobalt, and optionally metal X; the metal element X is selected from at least one of Mn, Al, Ti, Mg, and Zr. (2) The intermediate is mixed with a lithium source and then sintered; (3) The product obtained in step (2) is washed with water, and after solid-liquid separation, a washing solution and a positive electrode material precursor are obtained; wherein, the washing solution is concentrated and the resulting concentrated washing solution is returned to step (1). (4) The cathode material precursor and the coating element precursor are mixed and then subjected to heat treatment.

[0007] The third aspect of this invention provides a cathode material prepared by the preparation method described in the second aspect.

[0008] The cathode material provided by this invention, which satisfies the structural safety index formula for cathode materials, exhibits high specific capacity, long cycle life, and high safety performance, effectively reducing capacity decay caused by structural degradation of battery cathode materials. The cathode material preparation method provided by this invention utilizes a mixed salt concentrate recovered and purified from high-nickel cathode washing filtrate, and prepares a precursor with specific coating through a wet coating process. Furthermore, the washing filtrate can be continuously recycled. This achieves the recycling of cathode wastewater and precursor washing water, improving material performance while reducing the manufacturing costs of the precursor and cathode material, thus facilitating widespread adoption in industrial production. Attached Figure Description

[0009] Figure 1 This is a cross-sectional SEM image of the positive electrode material through the center of the sphere in Embodiment 1 of the present invention.

[0010] Figure 2 This is a cross-sectional SEM image of the positive electrode material through the center of the sphere in Embodiment 2 of the present invention.

[0011] Figure 3 This is a cross-sectional SEM image of the positive electrode material through the center of the sphere in Embodiment 3 of the present invention.

[0012] Figure 4 This is a cross-sectional SEM image of the positive electrode material of Comparative Example 1 of this invention through the center of the sphere.

[0013] Figure 5 This is a cross-sectional SEM image of the positive electrode material of Comparative Example 2 of this invention through the center of the sphere.

[0014] Figure 6 This is a cross-sectional SEM image of the positive electrode material of Comparative Example 3 of this invention through the center of the sphere.

[0015] Figure 7 These are cycle test diagrams of 18650 batteries prepared with the cathode materials of Examples 1-3 and Comparative Examples 1-3 of the present invention after activation. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] In one aspect, this invention provides a cathode material, wherein the structural safety index ε of the cathode material satisfies: 2 ≤ ε < 201; the structural safety index ε = 117δ·[d 003 / d 104 ]·κ -1 δ is the percentage of the cavity area on the cross-section of the positive electrode material passing through the center of the sphere to the total cross-sectional area, and κ is the specific surface area of ​​the positive electrode material, in m². 2 / g,d 003 d is the interplanar spacing of the (003) crystal plane of the cathode material. 104 The interplanar spacing of the positive electrode material (104) is the interplanar spacing of the crystal plane.

[0018] In this invention, the method for testing the ratio of the cavity area to the total area of ​​the cross-section of the positive electrode material through the center of the sphere is as follows: the positive electrode material is first polished with argon ions to obtain a nanoscale flat cross-section, then a SEM image of the material cross-section is taken, and finally the image is processed using ImageJ to obtain the total area ratio of the cavity on the cross-section of the material particles.

[0019] In this invention, d 003 and d 104 The XRD method yielded the following results: The cathode material powder was uniformly spread on an XRD sample holder. The scanning range 2θ was set to 10°-80°, the scanning speed to 4° / min, and the step size to 0.02°. The instrument was then started to complete the scan, obtaining the corresponding XRD diffraction pattern for the cathode material. The required interplanar spacing was obtained using the XRD data analysis software Jade.

[0020] In this invention, the specific surface area of ​​the cathode material is tested using a laser particle size analyzer. The specific method is as follows: Cathode material powder is weighed, 2 wt% sodium hexametaphosphate is added, and the powder is ultrasonically dispersed in an ultrasonic cleaner for 5 minutes. The instrument is then started for testing. The system automatically performs light and background measurements. After the background measurement is complete, the dispersed sample suspension is slowly injected into the instrument's sample cell, controlling the occlusion level between 9% and 11% for testing. After the test is completed, complete particle size distribution data is obtained, and the specific surface area is calculated using software.

[0021] In this invention, when the structural safety index ε of the cathode material satisfies 2≤ε<201, the material has excellent structural safety performance, which can effectively reduce the capacity decay caused by structural degradation of the battery cathode material, and exhibit high specific capacity, long cycle life and high safety performance during use.

[0022] According to the present invention, preferably, the chemical composition of the positive electrode material includes: Li a Ni b Co c X 1-b-c O2, 0.9≤a≤1.3, 0.7≤b≤1, 0≤c≤0.3; X is selected from at least one of Mn, Al, Ti, Mg, and Zr.

[0023] Preferably, the cathode material further includes doping elements and coating elements.

[0024] Preferably, the doping element is selected from at least one of Zr, Y, Sr, Al, Mg, W, Ti, Mo, Cd, Ce, V, In, and Ga. More preferably, it is at least one of Zr, Y, Sr, Al, and Mg, and even more preferably, it is Zr and Y.

[0025] Preferably, the content of the doping element is 0.015-1% based on the total mass of the cathode material, more preferably 0.03-0.7%.

[0026] In this invention, the content of the doped element can be obtained by ICP-MS testing. The specific testing method is as follows: Weigh 0.2g of cathode material powder, add 10mL of aqua regia, and place it in a digester. Digest at 240℃, boil for 20min, cool, and then dilute to 100mL with ultrapure water. Filter to remove any possible insoluble matter. Prepare a series of standard solutions covering the doped element content range, add internal standard elements, and plot a calibration curve. Correct for isotope interference using instrument software to reduce the influence of matrix effects. Inject the prepared sample solution into the ICP-MS, detect the ion signal intensity of the target doped element, and calculate the element content by comparing with the calibration curve.

[0027] According to the present invention, the use of the above-mentioned preferred doping elements and their contents is beneficial to improving the electronic / ionic conductivity of the cathode material, stabilizing the crystal structure, suppressing phase transitions and reducing cation mixing, improving the thermal stability of the material, and increasing the specific capacity and voltage stability of the cathode material.

[0028] Preferably, the coating element is selected from at least one of Nb, Al, W, Ti, Mo, Co, and B. More preferably, it is at least one of Al, Co, and B, and even more preferably, it is B and Al.

[0029] Preferably, the content of the coating element is 0.05-5% based on the total mass of the cathode material, more preferably 0.07-3%.

[0030] In this invention, the content of the coated elements can be obtained by ICP-MS testing. The specific testing method is as follows: Weigh 0.2g of cathode material powder, add 10mL of aqua regia, and place it in a digester. Digest at 240℃, boil for 20min, cool, and then dilute to 100mL with ultrapure water. Filter to remove any possible insoluble matter. Prepare a series of standard solutions covering the dopant element content range, add internal standard elements, and plot a calibration curve. Correct for isotope interference using instrument software to reduce matrix effects. Inject the prepared sample solution into the ICP-MS, detect the ion signal intensity of the target dopant element, and calculate the element content by referring to the calibration curve.

[0031] In this invention, the use of the above-mentioned preferred coating elements and mass ratios is beneficial for consuming residual alkali on the surface, repairing the surface structure of the cathode material, and suppressing interfacial side reactions; the synergistic doping elements can significantly improve structural stability, improve the electrochemical stability, interfacial compatibility and mechanical strength of the material.

[0032] According to the present invention, preferably, 1.5% ≤ δ ≤ 10%; more preferably, 3.2% ≤ δ ≤ 8%.

[0033] In this invention, δ represents the percentage of the total area of ​​the cavity on the cross-section of the cathode material particle passing through the center of the sphere. Appropriately increasing the percentage of the total cavity area can improve the structural safety factor of the material. It also increases the contact area between the material and the electrolyte, improves Li+ transport efficiency, absorbs lattice strain, and inhibits crack propagation, thereby mitigating volume expansion and reducing particle breakage during charging and discharging. However, excessively high δ can lead to a decrease in the energy density and weakened mechanical strength of the cathode material, while excessively low δ can result in increased ion transport resistance, stress concentration due to volume changes, and potential degradation.

[0034] Preferably, 0.14≤κ≤1.7; more preferably, 0.2≤κ≤1.2.

[0035] In this invention, κ represents the specific surface area of ​​the material as measured by a laser particle size analyzer. When the specific surface area of ​​the cathode material is within the aforementioned preferred range, it is beneficial to improve the compaction density of the cathode material, reduce side reactions, and enhance the reactivity and electrolyte wettability of the cathode material. An excessively high specific surface area of ​​the cathode material leads to increased side reactions, decreased compaction density, and poorer thermal stability; conversely, an excessively low specific surface area leads to poorer rate performance, poorer electrolyte wettability, and poorer low-temperature performance.

[0036] Preferably, 2≤d 003 / d 104 ≤2.4; more preferably, 2.10≤d 003 / d 104 ≤2.35.

[0037] In this invention, d 003 d represents the spacing of the (003) crystal planes obtained from XRD testing of the cathode material. 104 The spacing of the (104) crystal planes obtained from XRD testing of the cathode material is d. 003 / d 104 This directly reflects the balance between c-axis stability and TM-O bond strength in the layered structure. The d of the cathode material... 003 / d 104 An excessively large ratio indicates an abnormal increase in the Li interlayer spacing or a shrinkage of the TM layer, leading to increased distortion and polarization of the lithium diffusion channels and a worsening of cycling performance. An excessively small ratio indicates intensified cation mixing or an increased H2→H3 phase transition, resulting in increased microcracks within the particles, increased impedance, a decreased oxygen release temperature, and a deterioration in structural safety.

[0038] According to the present invention, preferably, the structural safety index ε of the positive electrode material satisfies: 6.6 ≤ ε < 110.

[0039] In this invention, a structural safety index ε of the cathode material within the aforementioned preferred range is beneficial for maximizing the structural safety performance of the cathode material within a certain range of technical difficulty and production cost, thereby comprehensively improving the battery's safety performance and key performance characteristics such as cycle life and specific capacity. If the structural safety index ε is too large, the improvement in specific capacity, cycle life, and safety performance of the cathode material is limited; however, the adjustable range for reducing the specific surface area, increasing the cavity area ratio, and increasing d003 / d104 is relatively small, significantly increasing technical difficulty and production cost. If the structural safety index ε is too small, the structural safety performance of the cathode material deteriorates, leading to accelerated material structure degradation and resulting in low specific capacity, short cycle life, and low safety performance during material use.

[0040] A second aspect of the present invention provides a method for preparing a cathode material, comprising the following steps: (1) Mix the doped element precursor and the water washing concentrate to obtain a mixture, spray the mixture onto the cathode material precursor, and dry it to obtain an intermediate; The cathode material precursor is prepared by co-precipitation of a sulfate of nickel, optionally cobalt, and optionally metal X; the metal element X is selected from at least one of Mn, Al, Ti, Mg, and Zr. (2) The intermediate is mixed with a lithium source and then sintered; (3) The product obtained in step (2) is washed with water, and after solid-liquid separation, a washing solution and a positive electrode material precursor are obtained; wherein, the washing solution is concentrated and the resulting concentrated washing solution is returned to step (1). (4) The cathode material precursor and the coating element precursor are mixed and then subjected to heat treatment.

[0041] In the method for preparing cathode materials provided by this invention, the water washing filtrate of high-nickel cathode materials is used. The treatment water generated during the concentration of the filtrate is reused for washing cathode materials or washing precursors, realizing the recycling of cathode wastewater and precursor washing water. While improving material performance, it reduces the manufacturing cost of precursors and cathode materials, which is conducive to its widespread promotion in industrial production.

[0042] According to the present invention, preferably, in step (3), the temperature of the concentration treatment is 60-250℃; the gauge pressure is -100 to -10kPa; and the time is 2-10h.

[0043] In this invention, under the above-mentioned preferred conditions, the desired concentrate can be obtained faster and more energy-efficiently.

[0044] Preferably, the water washing concentrate contains lithium sulfate, and the concentration of lithium sulfate is 20-350 g / L, more preferably 50-250 g / L.

[0045] In this invention, the lithium sulfate in the water washing concentrate helps to increase the total area ratio δ of cavities on the cross-section of the cathode material particles, optimize lithium-ion diffusion channels, and improve the electrochemical performance and structural safety factor of the material at a lower manufacturing cost. Preferably, the doping element precursor is a soluble compound selected from at least one element selected from Zr, Y, Sr, Al, Mg, W, Ti, Mo, Cd, Ce, V, In, and Ga.

[0046] In this invention, the use of the aforementioned doped element precursor is beneficial for improving electronic / ionic conductivity, stabilizing the crystal structure, suppressing phase transitions and reducing cation mixing, improving material thermal stability, and increasing specific capacity and voltage stability. In this invention, the use of the aforementioned doped element precursor in conjunction with a concentrated water washing solution allows for a more uniform distribution of the doped elements, creating more and more uniform cavities, and synergistically enhancing crystal structure stability and material safety performance.

[0047] Preferably, the coating element precursor contains at least one coating element selected from Nb, Al, W, Ti, Mo, Co, and B.

[0048] According to the present invention, preferably, the dopant precursor is selected from a soluble compound of at least one element selected from Zr, Y, Sr, Al, Mg, W, Ti, Mo, Cd, and Ce. More preferably, it is a soluble compound of at least one element selected from Zr, Y, Sr, Al, and Mg. More preferably, it is a soluble compound of Zr and a soluble compound of Y.

[0049] In this invention, using the above-mentioned preferred doped element precursors is more conducive to improving electronic / ionic conductivity, stabilizing crystal structure, suppressing phase transitions and reducing cation mixing, improving material thermal stability, and increasing specific capacity and voltage stability.

[0050] Preferably, in the mixture, based on the metal element content in the dopant precursor, the mixing ratio of the dopant precursor and the water washing concentrate is 5-100g of metal element per liter of water washing concentrate, more preferably 10-80g of metal element.

[0051] In this invention, an excessively high metal element content in the mixture leads to an increased doping amount in the cathode material, which not only increases costs but also easily damages the integrity of the material's layered structure, resulting in deteriorated electrochemical performance and, conversely, reduced thermal safety. Conversely, an excessively low doping amount results in a reduced cathode material doping amount, failing to achieve the expected effect and leaving the material's original defects unaddressed.

[0052] According to the present invention, preferably, in step (1), the mass ratio of the positive electrode material precursor to the mixture is 1:(0.003-0.1), more preferably 1:(0.006-0.08), and even more preferably 1:(0.01-0.06).

[0053] In this invention, using the above-mentioned preferred mass ratio is beneficial for forming a coating layer of suitable thickness on the surface of the precursor, which is beneficial for preparing cathode materials with better structural stability and material safety performance.

[0054] According to the present invention, preferably, in step (1), the drying conditions include a temperature of 50-350°C, more preferably 110-250°C; a gauge pressure of -100 to -10 kPa, more preferably -100 to -50 kPa; and a time of 1-6 h, more preferably 2-5 h.

[0055] In this invention, the above-mentioned preferred drying conditions are beneficial to obtain the intermediate more quickly and energy-efficiently while ensuring the stability and firm adhesion of the coating layer structure.

[0056] According to the present invention, preferably, in step (2), the total content of metal elements in the intermediate and the molar ratio of lithium elements in the lithium source are 1:(0.9-1.1), more preferably 1:(1.0-1.05).

[0057] In this invention, the above-mentioned preferred ratio is beneficial for achieving better structural stability, capacity, and cycle life of the cathode material. Considering the Li content in the mixed salt concentrate itself, the amount of lithium salt is appropriately reduced, allowing the mixed salt to deeply participate in the material microstructure reconstruction during sintering, thereby creating more and more uniform cavities; this also appropriately reduces raw material costs.

[0058] According to the present invention, preferably, in step (2), the sintering temperature is 600-900℃ and the time is 5-15h.

[0059] More preferably, in step (2), the sintering temperature is 660-850℃ and the time is 6-11h.

[0060] In this invention, the above-mentioned preferred sintering conditions are beneficial to promoting the uniform diffusion of dopant elements and mixed salts into the grains, and are more conducive to the structural reconstruction and grain growth of the cathode material, resulting in a cathode material with moderate grain size, stable structure, and excellent performance.

[0061] According to the present invention, preferably, in step (4), the coating element precursor contains at least one coating element selected from Nb, Al, W, Ti, Mo, Co, and B; more preferably, the coating element precursor contains at least one coating element selected from Al, W, Ti, Co, and B. According to some preferred embodiments of the present invention, the coating element precursor contains at least one coating element selected from Al, Co, and B, and more preferably Al and B.

[0062] In this invention, preferably, the mass ratio of the coating element in the cathode material precursor to the coating element precursor is 1:(0.0005-0.05), more preferably 1:(0.0007-0.03).

[0063] According to the present invention, preferably, the use of the above-mentioned preferred coating elements and mass ratios is beneficial for consuming residual alkali on the surface, repairing the surface structure of the cathode material, and suppressing interfacial side reactions; in combination with the aforementioned doping element precursor and water washing concentrate, it is beneficial for significantly improving structural stability, improving the electrochemical stability, interfacial compatibility and mechanical strength of the material.

[0064] According to the present invention, preferably, in step (4), the temperature of the heat treatment is 150-600℃ and the time is 3-10h.

[0065] More preferably, in step (4), the heat treatment temperature is 240-540℃ and the time is 4-8h.

[0066] In this invention, the above-mentioned preferred heat treatment conditions are beneficial to promote more uniform coating of the coating element precursor on the surface and near the surface of the material, and to repair the surface structure of the cathode material; the synergistic effect of the aforementioned doping element precursor and water washing concentrate is beneficial to improve structural stability, electrochemical stability, interfacial compatibility and mechanical strength of the material.

[0067] The third aspect of this invention provides a cathode material prepared by the preparation method described in the second aspect.

[0068] The present invention will be described in detail below through embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0069] Example 1 This embodiment provides a method for preparing a high-performance cathode material, the steps of which are as follows: (1) Add 40g of Zr(SO4)2 and 60g of Y2(SO4)3 to each 1L of water washing concentrate to obtain a mixture. The obtained mixture is then sprayed at high speed onto Ni. 0.90 Co 0.06 Mn 0.04 The mixture was prepared using an (OH)₂ precursor material, wherein the mass ratio of the precursor to the mixture was 1:0.04. Then, it was heated at -80 kPa pressure and 180 °C for 3 h to obtain an intermediate uniformly coated with lithium sulfate.

[0070] (2) The obtained intermediate and lithium salt LiOH·H2O were added to a high-speed mixer for solid-phase mixing, wherein the molar ratio of lithium in the lithium salt to the total metal in the intermediate was 1.02; the uniformly mixed material was spread in a corundum sagger and sintered at 700℃ for 8 hours in an oxygen atmosphere at a heating rate of 2℃ / min, and then cooled.

[0071] (3) The product obtained in step (2) is crushed and then washed with water. The washing conditions are: using a 5L reactor, at 25°C, with a material-to-water ratio of 1:1, stirring at 100rpm for 8min; after solid-liquid separation, the solid product is dried to obtain a washing solution and a positive electrode material precursor; wherein, the washing solution is concentrated and the resulting concentrated washing solution is returned to step (1). The concentration conditions are: heating the washing solution at -50Kpa pressure and 120°C for 4h to obtain a concentrated washing solution with a lithium sulfate content of 180g / L.

[0072] (4) The effective element B in the cathode material precursor, the coating element precursor (H3BO3), and the effective element Al in the coating element precursor (Al2O3) are mixed uniformly at a mass ratio of 1:0.001:0.0015. The mixture is sintered at 350℃ for 5 hours under an oxygen atmosphere at a heating rate of 3℃ / min. After cooling, the high-performance cathode material is obtained. Based on the total mass of the obtained cathode material, the content of Zr is 0.16%, the content of Y is 0.24%, the content of B is 0.10%, and the content of Al is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0073] Figure 1 This is a cross-sectional SEM image of the cathode material prepared in this embodiment, from... Figure 1 It can be seen that the cathode material has many uniformly distributed cavities and good radial distribution of primary particles, which can improve the structural safety factor of the material. The presence of cavities can realize bulk transport instead of surface transport, increase the contact area between the material and the electrolyte, and improve Li+ transport efficiency; at the same time, it can absorb lattice strain, inhibit crack propagation, alleviate the volume expansion generated during charging and discharging, reduce particle breakage, and effectively improve the occurrence of material degradation.

[0074] Example 2 The method described in Example 1 differs in that, in step (1), the mass ratio of the precursor to the mixture is 1:0.01; based on the total mass of the obtained cathode material, the Zr content is 0.04%; the Y content is 0.06%; the B content is 0.10%; and the Al content is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0075] Figure 2 This is a cross-sectional SEM image of the cathode material prepared in this embodiment, from... Figure 2 It can be seen that the cathode material also has many uniformly distributed cavities and good radial distribution of primary particles, which can improve the structural safety factor of the material.

[0076] Example 3 The method described in Example 1 differs in that, in step (1), 50g of Zr(SO4)2 and 25g of Y2(SO4)3 are added to each 1L of concentrated water washing solution; based on the total mass of the obtained cathode material, the Zr content is 0.20%; the Y content is 0.10%; the B content is 0.10%; and the Al content is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0077] Figure 3 This is a cross-sectional SEM image of the cathode material prepared in this embodiment, from... Figure 3It can be seen that the cathode material also has many uniformly distributed cavities, and the radial distribution of primary particles is good, which can improve the structural safety factor of the material.

[0078] Example 4 The method described in Example 1 differs in that the concentration treatment in step (3) is performed under the following conditions: heating at -50 kPa pressure and 120°C for 2 hours to obtain a 40 g / L concentrate. The obtained cathode material, by its total mass, contains 0.16% Zr, 0.24% Y, 0.10% B, and 0.15% Al. The physical properties of the obtained cathode material are shown in Table 1.

[0079] Example 5 The method described in Example 1 differs in that the concentration treatment in step (3) is performed under the following conditions: heating at -50 kPa pressure and 120°C for 6 hours to obtain a 300 g / L concentrate. The obtained cathode material, by its total mass, contains 0.16% Zr, 0.24% Y, 0.10% B, and 0.15% Al. The physical properties of the obtained cathode material are shown in Table 1.

[0080] Example 6 The method described in Example 1 differs from that in step (1), Y2(SO4)3 is not added. Based on the total mass of the obtained cathode material, the Zr content is 0.16%, the B content is 0.10%, and the Al content is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0081] Example 7 The method described in Example 1 differs in that, in step (1), the mass ratio of the precursor to the mixture is 1:0.006; and the obtained cathode material, based on its total mass, contains 0.024% Zr, 0.036% Y, 0.10% B, and 0.15% Al. The physical properties of the obtained cathode material are shown in Table 1.

[0082] Example 8 The method described in Example 1 differs in that, in step (1), the mass ratio of the precursor to the mixture is 1:0.07; based on the total mass of the obtained cathode material, the Zr content is 0.28%; the Y content is 0.42%; the B content is 0.10%; and the Al content is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0083] Example 9 The method described in Example 1 is different in that, in step (2), the molar ratio of lithium to total intermediate metal in the lithium salt is replaced by 1.055 instead of 1.02; based on the total mass of the obtained cathode material, the content of Zr is 0.16%; the content of Y is 0.24%; the content of B is 0.10%; and the content of Al is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0084] Example 10 The method described in Example 1 is different in that, in step (4), no coating element precursor (Al2O3) is added; based on the total mass of the obtained cathode material, the Zr content is 0.16%; the Y content is 0.24%; and the B content is 0.10%. The physical properties of the obtained cathode material are shown in Table 1.

[0085] Example 11 The method described in Example 1 is different in that, in step (2), the temperature is increased to 855°C and sintered for 5 hours in an oxygen atmosphere at a heating rate of 2°C / min, followed by cooling. Based on the total mass of the obtained cathode material, the Zr content is 0.16%; the Y content is 0.24%; the B content is 0.10%; and the Al content is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0086] Comparative Example 1 The method described in Example 1 differs in that, in step (1), the concentrated solution of the filtrate from the high-nickel cathode material washing process is not added; in order to obtain an intermediate in which the precursor does not encapsulate lithium sulfate, the cathode material finally obtained has the following content by weight: Zr content is 0.16%; Y content is 0.24%; B content is 0.10%; and Al content is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0087] Figure 4 This is a cross-sectional SEM image of the cathode material prepared in this comparative example, by... Figure 4 It can be seen that the cathode material has a small number of cavities and a relatively disordered distribution of primary particles, resulting in a low structural safety factor. The limited number of cavities leads to insufficient electrolyte wetting, affecting Li... + The restricted transport path increases the resistance to ion transport, and the volumetric strain generated during charging and discharging cannot be buffered by the cavity, leading to microcracks and thus accelerating material deterioration.

[0088] Comparative Example 2 The method described in Example 1 differs in that, in step (1), no dopant precursor is added, and the concentrated water washing solution is directly sprayed onto the precursor material. Based on the total mass of the obtained cathode material, the content of B is 0.10% and the content of Al is 0.15%. The physical properties of the obtained cathode material are shown in Table 1.

[0089] Figure 5 This is a SEM image of the cathode material prepared in this comparative example, created by... Figure 5 It can be seen that the positive electrode material has a small number of cavities, a relatively disordered distribution of primary particles, and a low structural safety factor.

[0090] Comparative Example 3 The method described in Example 1 is different except that step (1) is skipped, and Ni is directly applied. 0.90 Co 0.06 Mn 0.04 The (OH)2 precursor was heated at -80 kPa and 180 °C for 3 h. Subsequent steps were then performed to obtain the cathode material, resulting in an intermediate that did not encapsulate lithium sulfate and doping elements in the precursor. The final cathode material, by its total mass, contained 0.10% B and 0.15% Al. (Physical properties are shown in Table 1).

[0091] Figure 6 This is a SEM image of the cathode material prepared in this comparative example, created by... Figure 6 It can be seen that the positive electrode material has a relatively small number of cavities, a relatively disordered distribution of primary particles, and a low structural safety factor.

[0092] Table 1

[0093] Test case The positive electrode materials prepared according to the embodiments and comparative examples of the present invention are assembled into an 18650 battery. The preparation process includes: mixing the positive electrode material, conductive agent carbon black SP, and binder PVDF in a weight ratio of 96.5:2:1.5 to obtain a positive electrode slurry; uniformly coating the positive electrode slurry onto a specific foil and drying it; then rolling and slitting it to obtain the desired positive electrode sheet. For the negative electrode, graphite, conductive agent carbon black SP, suspending agent CMC, and binder SBR are mixed in a weight ratio of 96:0.5:1.5:1.5 to obtain a negative electrode slurry; uniformly coating the negative electrode slurry onto a specific foil and drying it; then rolling and slitting it to obtain the desired negative electrode sheet. After welding tabs onto the electrode sheets, a separator is added, followed by winding, assembly, bottom welding, baking, electrolyte injection, sealing, and cleaning steps to obtain the 18650 battery. The battery was subjected to a 0.2C charge-discharge test at 25℃ and a voltage range of 2.5-4.2V. The test results are shown in Table 2. After activation at 25℃ and a voltage range of 2.5-4.2V, a cycle test was conducted at 0.5C+ / 1.0C- for 500 cycles. The test results are shown in Table 2. Figure 7 The curves showing the cycle retention rates of Examples 1-3 and Comparative Examples 1-3 are shown.

[0094] Material thermal safety performance testing The positive electrode materials prepared in the embodiments and comparative examples of the present invention were assembled into 18650 batteries according to the above method. The batteries were first activated at 25°C and within a voltage range of 3.0-4.3V, then charged to 4.2V at 0.2C, and then charged at a constant voltage of 4.2V until the current was less than 0.02C. The positive electrode sheet was then removed and subjected to differential scanning calorimetry (DSC) testing. The test results are shown in Table 2.

[0095] Table 2

[0096] From Table 2 and Figure 7 As can be seen, compared with the comparative example, the discharge capacity and first-time efficiency of the cathode material provided in the embodiments of the present invention are significantly better. This indicates that the more uniformly distributed cavities in the cathode material realize bulk transport instead of surface transport, increase the contact area between the material and the electrolyte, increase the proportion of active substances actually participating in the reaction, and improve the Li+ transport efficiency, thereby having a higher specific capacity.

[0097] The cathode material retains no less than 83% of its capacity after 500 cycles at room temperature. The high capacity retention even after multiple cycles indicates that the numerous uniformly distributed cavities in the cathode material improve Li+ transport efficiency. At the same time, it can absorb lattice strain, suppress crack propagation, alleviate volume expansion during charging and discharging, reduce particle breakage, effectively improve material degradation, and enhance cycle stability.

[0098] As can be seen from the above, the safety factor of the cathode structure in the embodiments provided by this invention is within the range defined by this invention, and the material exhibits superior structural safety performance. The numerous uniformly distributed cavities in the cathode material enable bulk transport instead of surface transport, increasing the contact area between the material and the electrolyte, thus increasing the proportion of active material actually participating in the reaction and improving Li+ transport efficiency, resulting in a higher specific capacity. Simultaneously, it can absorb lattice strain, inhibit crack propagation, alleviate volume expansion during charging and discharging, reduce particle breakage, effectively improve material degradation, and enhance cycle stability. Furthermore, the thermal safety performance test results of the cathode material provided by this invention show that the material has good thermal stability, with a DSC peak temperature not lower than 215℃, and the cathode material remains stable even at higher temperatures. Compared with the embodiments, the cathode materials in Comparative Examples 1-3 have fewer cavities and a more disordered primary particle distribution; test results show that they have lower specific capacity, cycle life, and poorer safety performance. In addition, the treated water generated during filtrate concentration during material preparation can be reused for washing the cathode material or the precursor. This technology enables the recycling of cathode wastewater and precursor washing water, which improves material performance while reducing the manufacturing costs of precursors and cathode materials, thus facilitating its widespread adoption in industrial production.

[0099] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that, The structural safety index ε of the cathode material satisfies: 2≤ε<201; The structural safety index ε = 117δ·[d 003 / d 104 ]·κ -1 δ is the percentage of the cavity area on the cross-section of the positive electrode material passing through the center of the sphere to the total cross-sectional area, and κ is the specific surface area of ​​the positive electrode material, in m². 2 / g,d 003 d is the interplanar spacing of the (003) crystal plane of the cathode material. 104 The interplanar spacing of the positive electrode material (104) is the interplanar spacing of the crystal plane.

2. The cathode material according to claim 1, wherein, The chemical composition of the cathode material includes: Li a Ni b Co c X 1-b-c O2, 0.9≤a≤1.3, 0.7≤b≤1, 0≤c≤0.3; X is selected from at least one of Mn, Al, Ti, Mg, and Zr; Preferably, the cathode material further includes doping elements and coating elements; Preferably, the doping element is selected from at least one of Zr, Y, Sr, Al, Mg, W, Ti, Mo, Cd, Ce, V, In, and Ga; Preferably, the content of the doping element is 0.015-1% based on the total mass of the cathode material; Preferably, the coating element is selected from at least one of Nb, Al, W, Ti, Mo, Co, and B; Preferably, the content of the coating element is 0.05-5% based on the total mass of the cathode material.

3. The cathode material according to claim 1 or 2, wherein, 1.5%≤δ≤10%; Preferably, 0.14 ≤ κ ≤ 1.7; Preferably, 2≤d 003 / d 104 ≤2.4; Preferably, the structural safety index ε of the cathode material satisfies: 6.6 ≤ ε < 110.

4. A method for preparing a positive electrode material, characterized in that, Includes the following steps: (1) Mix the doped element precursor and the water washing concentrate to obtain a mixture, spray the mixture onto the cathode material precursor, and dry it to obtain an intermediate; The cathode material precursor is prepared by co-precipitation of a sulfate of nickel, optionally cobalt, and optionally metal X; the metal element X is selected from at least one of Mn, Al, Ti, Mg, and Zr. (2) The intermediate is mixed with a lithium source and then sintered; (3) The product obtained in step (2) is washed with water, and after solid-liquid separation, a washing solution and a positive electrode material precursor are obtained; wherein, the washing solution is concentrated and the resulting concentrated washing solution is returned to step (1). (4) The cathode material precursor and the coating element precursor are mixed and then subjected to heat treatment.

5. The preparation method according to claim 4, wherein, In step (3), the concentration treatment is carried out at a temperature of 60-250℃; the gauge pressure is -100 to -10 kPa; and the time is 2-10 h. Preferably, the water washing concentrate contains lithium sulfate, and the concentration of lithium sulfate is 20-350 g / L; Preferably, the doping element precursor is selected from a soluble compound of at least one element selected from Zr, Y, Sr, Al, Mg, W, Ti, Mo, Cd, Ce, V, In, and Ga; Preferably, the coating element precursor contains at least one coating element selected from Nb, Al, W, Ti, Mo, Co, and B.

6. The preparation method according to claim 4 or 5, wherein, The doping element precursor is selected from soluble compounds of at least one element selected from Zr, Y, Sr, Al, Mg, W, Ti, Mo, Cd, and Ce. Preferably, in the mixture, based on the metal element content in the dopant precursor, the mixing ratio of the dopant precursor and the water washing concentrate is 5-100g of metal element per liter of water washing concentrate.

7. The preparation method according to any one of claims 4-6, wherein, In step (1), the mass ratio of the positive electrode material precursor to the mixture is 1:(0.003-0.1), more preferably 1:(0.006-0.08). Preferably, in step (1), the drying conditions include a temperature of 50-350℃, a gauge pressure of -100 to -10 kPa, and a time of 1-6 h.

8. The preparation method according to any one of claims 4-7, wherein, In step (2), the total content of metal elements in the intermediate and the molar ratio of lithium elements in the lithium source are 1:(0.9-1.1).

9. The preparation method according to any one of claims 4-8, wherein, In step (2), the sintering temperature is 600-900℃ and the time is 5-15h; Preferably, in step (2), the sintering temperature is 660-850℃ and the time is 6-11h.

10. The preparation method according to any one of claims 4-9, wherein, In step (4), the coating element precursor contains at least one coating element selected from Al, W, Ti, Co, and B; Preferably, the mass ratio of the coating element in the cathode material precursor to the coating element precursor is 1:(0.0005-0.05).

11. The preparation method according to any one of claims 4-10, wherein, In step (4), the heat treatment temperature is 150-600℃ and the time is 3-10h; Preferably, the heat treatment temperature is 240-540℃ and the time is 4-8h.

12. The cathode material prepared by the preparation method according to any one of claims 4-11.

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