Cathode material for coated and modified lithium ion battery, preparation method of cathode material, cathode and battery

Abstract

The invention relates to the field of lithium ion batteries, and discloses a coated modified positive electrode material for a lithium ion battery, a preparation method of the coated modified positive electrode material, a positive electrode and a battery, and the preparation method of the positive electrode material comprises the following steps: mixing a lanthanum source, lithium phosphoric acid inorganic salt and a lithium-rich manganese-based positive electrode material to obtain a mixture, and sintering the mixture at low temperature to obtain the lithium-rich manganese-based positive electrode material. The temperature of the low-temperature sintering is 300-600 DEG C, and the time of the low-temperature sintering is 4-10 hours. The positive electrode material has high cycling stability and high rate performance, and has relatively high specific discharge capacity and first-cycle coulombic efficiency.

Description

Technical Field

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

[0002] Due to their high energy density and long cycle life, lithium-ion batteries are widely used in new energy vehicles, energy storage systems, and other fields. Lithium-rich manganese-based cathode materials possess advantages in high specific capacity and low cost, making them one of the core materials for next-generation high-energy-density batteries. However, their electrochemical performance still has significant drawbacks: on the one hand, lithium-rich manganese-based cathode materials are prone to structural phase transitions during charge and discharge, leading to rapid capacity decay; on the other hand, the high residual lithium content on the material surface easily reacts with the electrolyte to generate byproducts, causing increased interfacial impedance and reduced thermal stability, severely limiting their commercial application.

[0003] Surface coating can improve the electrochemical performance of lithium-rich manganese-based cathode materials, but traditional coating materials such as Al2O3 and TiO2 have low ionic conductivity (<10). -9 The S / cm ratio significantly hinders lithium-ion transport, leading to a decrease in the rate performance of the battery.

[0004] Therefore, providing a lithium-rich manganese-based cathode material with high capacity retention, high rate performance, and high safety, and its preparation method, is of great significance for promoting the commercial application of high-energy-density lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor cycle stability and low rate performance of existing lithium-rich manganese-based cathode materials, and to provide a coated and modified cathode material for lithium-ion batteries, its preparation method, cathode, and battery. This cathode material combines high cycle stability and high rate performance, and also has high discharge specific capacity and first-cycle coulombic efficiency.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a cathode material, wherein the method comprises: mixing a lanthanum source, a lithium phosphate inorganic salt, and a lithium-rich manganese-based cathode material to obtain a mixture, and subjecting the mixture to low-temperature sintering to obtain a cathode material, wherein the low-temperature sintering temperature is 300-600°C and the time is 4-10 hours.

[0007] A second aspect of the present invention provides a cathode material, wherein the cathode material is prepared by the preparation method described in the first aspect of the present invention.

[0008] A third aspect of the present invention provides a positive electrode, wherein the positive electrode comprises a positive electrode material prepared by the preparation method described in the first aspect of the present invention or a positive electrode material described in the second aspect of the present invention.

[0009] A fourth aspect of the present invention provides a battery, wherein the battery includes the positive electrode described in the third aspect of the present invention.

[0010] Through the above technical solution, the present invention prepares a cathode material in which lanthanum ions can undergo a solid-phase reaction with phosphate ions and residual lithium on the surface of the lithium-rich manganese-based cathode material to form a stable Li-La-PO interface layer. This effectively suppresses manganese dissolution and phase transition problems during the charge and discharge process of the cathode material, as well as side reactions between the cathode material and the electrolyte, thereby improving the structural stability of the material and extending the cycle life of the battery. Lithium ions in the lithium phosphate inorganic salt can replenish the lithium ion deficiency on the material surface, while phosphate ions can combine with lithium ions on the material surface, reducing lithium ion loss and jointly maintaining the stoichiometry of the cathode material, repairing the surface structure, reducing capacity decay during charge and discharge, and improving cycle stability and safety. Furthermore, the lithium phosphate inorganic salt constructs an ion conduction network in the coating layer, optimizing the ion transport path and reducing the interfacial impedance of the material, thereby improving the charge and discharge rate performance and energy density of the battery.

[0011] The cathode material prepared by this invention exhibits a first-cycle discharge specific capacity of over 290 mAh / g and a first-cycle coulombic efficiency of over 87%. It demonstrates excellent cycle stability, with a discharge specific capacity of over 270 mAh / g after 400 cycles at 1C and a capacity retention rate of over 90%. It also exhibits good rate performance, with an average discharge specific capacity of over 280 mAh / g at 0.1C, over 240 mAh / g at 0.3C, over 220 mAh / g at 0.5C, over 210 mAh / g at 1C, over 155 mAh / g at 3C, over 120 mAh / g at 5C, and over 65 mAh / g at 10C. Furthermore, after high-rate charge-discharge testing, the average discharge specific capacity after re-charging and discharging at 0.1C is over 265 mAh / g. Attached Figure Description

[0012] Figure 1 SEM images and EDS elemental distribution diagrams of the cathode material prepared in Example 2; Figure 2 The first-cycle charge-discharge curves of the cathode materials prepared in Comparative Example 1 and Examples 1, 2, and 3 are shown in the comparison graph. Figure 3 The rate curves of the cathode materials prepared in Comparative Example 1 are compared with those prepared in Examples 1, 2, and 3. Figure 4 The graphs show the cycling curves of the cathode materials prepared in Comparative Example 1 and Example 2 at a 1C rate. Detailed Implementation

[0013] 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.

[0014] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0015] In this invention, room temperature refers to 20-30°C. The average discharge specific capacity of the cathode material is the average value of the discharge specific capacity obtained by performing 5 or 7 charge-discharge tests on a battery assembled from the cathode material under the same rate conditions.

[0016] The first aspect of the present invention provides a method for preparing a cathode material, characterized in that the preparation method includes: mixing a lanthanum source, a lithium phosphate inorganic salt and a lithium-rich manganese-based cathode material to obtain a mixture, and sintering the mixture at a low temperature to obtain the cathode material, wherein the low temperature sintering temperature is 300-600℃ and the time is 4-10h.

[0017] Lanthanum ions can undergo solid-state reactions with phosphate ions and residual lithium on the surface of lithium-rich manganese-based cathode materials to form a stable Li-La-PO interface layer. This effectively suppresses manganese dissolution and phase transitions during charge and discharge, as well as side reactions between the cathode material and the electrolyte, improving material structural stability and extending battery cycle life. Lithium ions in lithium phosphate inorganic salts can replenish lithium ion deficiencies on the material surface, while phosphate ions can combine with lithium ions on the surface, reducing lithium ion loss. Together, they maintain the stoichiometry of the cathode material, repair the surface structure, reduce capacity decay during charge and discharge, and improve cycle stability and safety. Furthermore, lithium phosphate inorganic salts construct an ion conduction network in the coating layer, optimizing ion transport paths and reducing interfacial impedance, thereby improving the battery's charge / discharge rate performance and energy density.

[0018] In some embodiments, preferably, the molar ratio of lanthanum in the lithium-rich manganese-based cathode material and phosphate ions in the lithium phosphate inorganic salt is 1:0.002-0.02:0.02-0.02.

[0019] In some embodiments, preferably, the molar ratio of lanthanum in the lithium-rich manganese-based cathode material and phosphate ions in the lithium phosphate inorganic salt is 1:0.005-0.015:0.005-0.015. In lithium-rich manganese-based cathode materials, the molar ratio of lanthanum in the lanthanum source to phosphate ions in the lithium phosphate inorganic salt can be 1:0.002:0.002, 1:0.005:0.002, 1:0.01:0.002, 1:0.015:0.002, 1:0.002:0.005, 1:0.002:0.01, 1:0.002:0.015, 1:0.005:0.005, 1:0.01:0.01, 1:0.015:0.015, 1:0.02:0.02, etc. This range of ratios allows for the formation of a dense, uniform, and moderately thick coating layer on the surface of the lithium-rich manganese-based cathode material, avoiding an excessively thick coating layer that hinders Li-ion exchange. + Diffusion and electronic conduction reduce rate performance.

[0020] In some embodiments, preferably, the lanthanum source includes at least one of lanthanum nitrate, lanthanum carbonate, lanthanum chloride, and lanthanum acetate.

[0021] In some embodiments, preferably, the lithium phosphate inorganic salt includes at least one of Li3PO4, Li2HPO4, and LiH2PO4.

[0022] In some embodiments, preferably, the low-temperature sintering temperature is 400-500°C and the time is 5-7 hours.

[0023] In some embodiments, preferably, the heating rate of the low-temperature sintering is 5-10°C / min.

[0024] Existing processes involve high-temperature surface coating, which can easily damage the layered structure of lithium-rich manganese-based cathode materials. This invention, through low-temperature sintering, effectively avoids lattice distortion caused by high temperatures, maintaining the interlayer ion transport channels required for reversible lithium storage and preserving the lithium storage performance of the layered structure. Low-temperature sintering promotes a mild interfacial reaction between the coating material and the surface of the lithium-rich manganese-based cathode material, forming a stable Li-La-PO solid solution interface layer. The low-temperature sintering temperature can be any value between any two of 300℃, 400℃, 450℃, 500℃, 600℃, and 700℃; the time can be any value between any two of 4h, 5h, 6h, 7h, 8h, 9h, and 10h; and the heating rate can be any value between any two of 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min.

[0025] In some embodiments, preferably, the mixing is carried out in a solvent.

[0026] In some embodiments, preferably, the mixing step includes: dissolving the lanthanum source and the lithium phosphate inorganic salt in the solvent to form a suspension, then adding the lithium-rich manganese-based cathode material to the suspension, and then removing the solvent.

[0027] In some embodiments, preferably, the step of removing the solvent includes: evaporating the suspension to dryness at a temperature of 45-70°C.

[0028] In some embodiments, preferably, the solvent comprises deionized water, and the pH of the solvent is 4.5-6.

[0029] Compared to using ethanol as a solvent, deionized water is non-flammable, requiring no special safety facilities for the preparation of cathode materials. Furthermore, its slower evaporation rate during the drying process is beneficial for forming a dense and uniform coating layer. Lanthanum ions readily hydrolyze in alkaline environments, forming hydroxide agglomerates, which is detrimental to the formation of a uniform coating layer. Adjusting the pH of deionized water to 4.5-6 effectively inhibits the hydrolysis of lanthanum ions and promotes the dissolution of lithium phosphate inorganic salts, ensuring uniform ion dispersion and preventing premature precipitation of lanthanum phosphate. This facilitates the formation of a uniform and dense coating layer during the low-temperature sintering stage. The pH of deionized water can be adjusted using acetic acid solution; the pH can be any value between 4.5, 5, 5.5, and 6.

[0030] The evaporation temperature can be any value between any two of 45℃, 60℃, 65℃, and 70℃, and the heating time is unlimited, until the deionized water is completely evaporated. Stirring should be performed during evaporation to ensure uniform coating.

[0031] In some embodiments, preferably, the mixture obtained by evaporation is further dried at a temperature of 50-80°C, which can be any value between any two of 50°C, 60°C, 70°C, and 80°C. The temperature should not be too high to prevent reactions from occurring within or between the materials. The drying time is 10-12 hours.

[0032] In some embodiments, preferably, the lithium-rich manganese-based cathode material has the chemical formula Li. x Ni a Mn b Co c O2, 1.5 <x<1.7,0.05<a<0.35,0.5<b<0.9,0.05<c<0.25。

[0033] This invention does not have any special requirements for the source of lithium-rich manganese-based cathode materials; they can be purchased commercially or prepared in-house.

[0034] In some embodiments, preferably, the preparation method of the lithium-rich manganese-based cathode material includes: (1) Prepare a metal salt solution, wherein the metal salt solution includes salts of transition metal elements, wherein the transition metal elements include nickel, manganese and cobalt; mix the metal salt solution, chelating agent and precipitant, and carry out a co-precipitation reaction, and age to obtain a precursor containing the transition metal elements; wherein the molar ratio of nickel, manganese and cobalt in the metal salt solution is 0.05-0.35:0.5-0.9:0.05-0.25; (2) The lithium source and the precursor are mixed and subjected to a first calcination and a second calcination to obtain the lithium-rich manganese-based cathode material, wherein the molar ratio of the transition metal element in the precursor to the lithium element in the lithium source is 1:1.1-1.3.

[0035] The electrochemical performance of the cathode material can be optimized by adjusting the molar ratio of nickel, manganese, and cobalt in the metal salt solution. Nickel ions provide a higher redox potential, increasing the energy density of the material. The presence of manganese helps maintain the structural integrity of the cathode material during multiple charge-discharge cycles, thereby extending the battery's lifespan. Cobalt stabilizes the layered structure of the cathode material, contributing to improved cycle stability and thermal stability, and enhancing the battery's power performance. When the molar ratio of nickel, manganese, and cobalt in the metal salt solution is 0.05-0.35:0.5-0.9:0.05-0.25, the cathode material exhibits good capacity and cycle stability. The concentration of the metal salt solution is 1-3 mol / L, and the anions in the metal salt solution are selected from sulfate and / or nitrate.

[0036] A molar ratio of transition metal elements in the precursor to lithium elements in the lithium source within the range of 1:1.1-1.3 helps maintain the structural stability of the cathode material and improves its cycle life; it also facilitates the rapid diffusion of lithium ions, thereby improving the rate performance of the battery. The lithium source is selected from lithium carbonate and / or lithium hydroxide.

[0037] In some embodiments, preferably, the chelating agent is selected from one or more of sodium hydroxide solution, ammonia water, urea solution, and ammonium bicarbonate solution, with a concentration of 3-5 mol / L.

[0038] In some embodiments, preferably, the precipitant is selected from one or more of sodium carbonate solution, sodium hydroxide solution, and sodium bicarbonate solution, and has a concentration of 1-3 mol / L.

[0039] In some embodiments, preferably, the coprecipitation reaction is carried out at a temperature of 45-60°C and a pH of 10-11.5.

[0040] Co-precipitation within the above temperature range is beneficial for the uniform reaction of metal salt solution with precipitant and salt solution, avoiding slow reaction rate or uneven precipitate particles due to excessively low temperature, or side reactions such as metal ion hydrolysis or precipitant decomposition due to excessively high temperature, ensuring the generation of precursor material with uniform composition, laying the foundation for the formation of crystal structure of subsequent lithium-rich manganese-based cathode material.

[0041] By controlling the feed rate of the precipitant, the pH value of the reaction system can be controlled. The above pH range can ensure that the metal ions and the precipitant react uniformly in a suitable alkaline environment, avoiding incomplete precipitation or the formation of soluble complexes due to excessively low pH, or the generation of hydroxide impurities due to excessively high pH.

[0042] In some embodiments, preferably, the coprecipitation reaction is carried out under stirring at a stirring rate of 300-500 r / min.

[0043] In some embodiments, the aging time is preferably 10-12 hours. Aging allows the generated precursor to grow further, promoting the dissolution of small particles and the growth of large particles, thereby reducing particle agglomeration and optimizing particle size distribution.

[0044] In some embodiments, preferably, the co-precipitation reaction and aging are carried out in an inert gas atmosphere. The introduction of an inert gas isolates the air, effectively preventing the formation of transition metal ions (such as Mn). 2+ Ni 2+ Co 2+ During the reaction, the precursor is oxidized to a higher oxidation state by oxygen, preventing the composition from deviating from the stoichiometric ratio due to changes in the oxidation state of metal ions. Simultaneously, it suppresses the interference of dissolved oxygen in the solution on the precipitation process, ensuring that the generated precursor has a uniform composition and high purity. The inert gas can be argon or nitrogen.

[0045] In some embodiments, preferably, the first calcination temperature is 400-500℃, the time is 4-6h, and the heating rate is 5-10℃ / min.

[0046] In some embodiments, preferably, the second calcination temperature is 800-900℃, the time is 12-14h, and the heating rate is 5-10℃ / min.

[0047] Precise control of the heating rate can adjust the primary particle gap of lithium-rich manganese-based cathode materials, avoiding microcracks caused by thermal stress concentration.

[0048] A second aspect of the present invention provides a cathode material, wherein the cathode material is prepared by the preparation method described in the first aspect of the present invention.

[0049] A third aspect of the present invention provides a positive electrode, wherein the positive electrode comprises a positive electrode material prepared by the preparation method described in the first aspect of the present invention or a positive electrode material described in the second aspect of the present invention.

[0050] A fourth aspect of the present invention provides a battery, wherein the battery includes the positive electrode described in the third aspect of the present invention.

[0051] The present invention will be described in detail below through embodiments. In the following embodiments, the characterization or performance testing methods and instruments used for the cathode material are as follows: (1) Scanning electron microscopy (SEM) test: Scanning electron microscope, instrument model: QUANTA, FEI Corporation, USA; (2) Energy dispersive spectroscopy (EDS) test: Energy dispersive X-ray spectrometer, instrument model: QUANTA, FEI Corporation, USA; (3) Battery charge and discharge test: Land battery test system, instrument model: CT 2001A, Wuhan Landian Electronics Co., Ltd.

[0052] All raw materials used in this invention are commercially available products.

[0053] Preparation Example 1 (1) Dissolve MnSO4•H2O, NiSO4•6H2O and CoSO4•7H2O in deionized water to prepare 1000 mL of a 2 mol / L metal salt solution, wherein the molar ratio of nickel, manganese and cobalt is 0.19:0.69:0.12; prepare 1000 mL of a 4 mol / L ammonia solution and 1000 mL of a 2 mol / L sodium carbonate solution.

[0054] 1000 mL of deionized water was poured into the reactor as the base solution. Then, 1000 mL of metal salt solution was pumped into the reactor at a feed rate of 1500 mL / h. Simultaneously, sodium carbonate solution and ammonia solution were pumped into the reactor, with the feed rates of sodium carbonate solution and ammonia solution adjusted to approximately 1500 mL / h to ensure the pH of the reaction system was maintained within the range of 11 ± 0.2. The coprecipitation reaction was carried out under an argon atmosphere at a reaction temperature of 55℃, with stirring at a speed of 350 r / min.

[0055] After the metal salt solution is fed in, the aging process continues for 12 hours. The precipitate is then filtered and washed until the pH of the filtrate is close to neutral and it is transparent and colorless. The filtrate is then vacuum dried for 24 hours to obtain the precursor.

[0056] (2) The precursor and lithium carbonate are dry-mixed for 5 minutes, wherein the molar ratio of the transition metal element in the precursor to the lithium element in the lithium source is 1:1.2. Then, alcohol is added to the mixture for wet mixing, and the mixture is ground on a 55°C heating table until the alcohol is completely evaporated.

[0057] The mixture was placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min, and calcined for 5 hours. After cooling to room temperature, it was ground for 5 minutes. The material was then placed in a muffle furnace again and heated to 900°C at a heating rate of 5°C / min, and calcined for 12 hours. After cooling to room temperature, lithium-rich manganese-based cathode material was obtained.

[0058] Example 1 Add 2-5 drops of acetic acid solution (mass fraction ≥99.8%) to 20 mL of deionized water to adjust the pH to 5 ± 0.5. Dissolve lanthanum nitrate and lithium phosphate in the deionized water and stir for 10 min. Then add the lithium-rich manganese-based cathode material from Preparation Example 1 and stir thoroughly at room temperature until completely dispersed. Next, stir and evaporate the deionized water under a heating table at 60 °C to obtain a dry mixture. The molar ratio of lithium-rich manganese-based cathode material, lanthanum ions in lanthanum nitrate, and phosphate ions in lithium phosphate is 1:0.005:0.005.

[0059] The mixture was dried in a vacuum oven at 80°C for 12 hours, then placed in a muffle furnace and heated to 450°C at a heating rate of 5°C / min. The mixture was then sintered at 450°C for 6 hours to obtain the cathode material.

[0060] Example 2 The procedure was carried out according to Example 1, with the only difference being that the molar ratio of lanthanum ions in lanthanum nitrate and phosphate ions in lithium phosphate was 1:0.01:0.01.

[0061] Example 3 The method of Example 1 was followed, except that the molar ratio of lanthanum ions in lanthanum nitrate and phosphate ions in lithium phosphate was 1:0.015:0.015.

[0062] Example 4 The method was carried out according to Example 2, except that the low-temperature sintering temperature was 400°C, the time was 7 hours, and the heating rate was 8°C / min.

[0063] Example 5 The method was carried out according to Example 2, except that the low-temperature sintering temperature was 500°C, the time was 5 hours, and the heating rate was 10°C / min.

[0064] Example 6 The procedure was carried out according to Example 2, except that lanthanum nitrate and lithium phosphate were dissolved in anhydrous ethanol.

[0065] The cathode materials prepared in Examples 1-6 have similar SEM images and EDS elemental distribution maps. Taking Example 2 as an example, for instance... Figure 1 As shown, the first row, from left to right, displays the SEM image and the EDS elemental distribution maps of P and Mn. The second row, from left to right, displays the EDS elemental distribution maps of Co, Ni, and La. The small squares below the images indicate a scale bar of 2 μm. It can be seen that the material consists of secondary particles composed of primary particles, and uniform coating of La and P elements has been achieved.

[0066] Comparative Example 1 The lithium-rich manganese-based cathode material prepared in Preparation Example 1 is used as Comparative Example 1.

[0067] Comparative Example 2 The procedure was carried out according to Example 2, except that lanthanum nitrate was not added, and the molar ratio of phosphate ions in the lithium-rich manganese-based cathode material and lithium phosphate was 1:0.01.

[0068] Comparative Example 3 The procedure was carried out according to Example 2, except that lithium phosphate was not added, and the molar ratio of lanthanum ions in the lithium-rich manganese-based cathode material and lanthanum nitrate was 1:0.01.

[0069] Comparative Example 4 The method of Example 2 was followed, except that the temperature for low-temperature sintering was 750°C.

[0070] Test case Using the positive electrode materials prepared in Examples 1-6 and Comparative Examples 1-4 as active materials, the active material, conductive agent (Super P / acetylene black), and binder (PVDF-polyvinylidene fluoride) were weighed at a mass ratio of 8:1:1 and mixed evenly in a mortar. An appropriate amount of N-methylpyrrolidone (NMP) was added as a dispersant and ground into a uniform slurry. The slurry was coated onto aluminum foil using a coater, dried in a drying oven at 60°C for 12 hours, and then dried in a vacuum drying oven at 120°C for 2 hours. The resulting sheet was then cut to prepare a positive electrode sheet with a diameter of 11 mm required for a button cell. A button cell half-cell was assembled in an argon atmosphere glove box with a water and oxygen content of less than 0.01 ppm. The positive electrode was the aforementioned positive electrode sheet, the negative electrode was a lithium metal sheet, the separator was Celgard 2500, and the electrolyte was a solution prepared with 1 mol / L LiPF6 as the solute and a mixture of dimethyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:1:1 as the solvent.

[0071] Figure 2The figures show the first-week charge-discharge comparison curves of batteries assembled with the cathode materials of Comparative Example 1 and Examples 1, 2, and 3 at 30°C, 2.0-4.8V, and a 0.1C rate (1C=250mAh / g). (Pristine represents Comparative Example 1, 0.5LP represents Example 1, 1LP represents Example 2, and 2LP represents Example 3.) It can be seen that the cathode material of Example 2 has the highest first-week discharge specific capacity of 302.2mAh / g, which is significantly higher than the 290.5mAh / g of the traditional lithium-rich manganese-based cathode material (Comparative Example 1). Meanwhile, the cathode materials of Examples 1-3 exhibit higher first-week coulombic efficiency, indicating that coating modification of the lithium-rich manganese-based cathode material significantly improves the reversibility of the redox reaction, reduces side reactions, and enhances the safety of the cathode material.

[0072] Figure 3 The figures show the rate performance curves of batteries assembled with the cathode materials of Comparative Example 1 and Examples 1, 2, and 3 at 30°C and 2.0-4.8V. From left to right, the rate performance curves are 0.1C, 0.3C, 0.5C, 1C, 3C, 5C, 10C, and 0.1C (1C = 250mAh / g; Pristine represents Comparative Example 1, 0.5LP represents Example 1, 1LP represents Example 2, and 2LP represents Example 3). As can be seen from the figures, the coating modification improved the rate performance of the cathode material, especially at high rates. The cathode material of Example 2 still has an average discharge specific capacity of 111.6mAh / g at 10C, while the cathode material of Comparative Example 1 only has an average discharge specific capacity of 55.5mAh / g. The average discharge specific capacity of the cathode material in Example 2 during the initial charge-discharge cycle at 0.1C was 299.2 mAh / g. After high-rate charge-discharge cycles, the discharge specific capacity during the subsequent charge-discharge cycle at 0.1C was 283 mAh / g, which is close to the initial state. This indicates that the coated and modified cathode material of the present invention can effectively suppress structural phase transitions and side reactions at high rates and maintain capacity stability.

[0073] Figure 4 This is a comparison of the cycling curves of batteries assembled with the cathode materials of Comparative Example 1 and Example 2 at 30°C, 2.0-4.8V, and a 1C rate (1C=250mAh / g) (Pristine represents Comparative Example 1, and 1LP represents Example 2). As shown in the figure, the cathode material of Example 2 exhibits excellent cycling stability, with a capacity retention of 96.14% after 400 cycles, while the cathode material of Comparative Example 1 only retains 23.08% of its capacity after 200 cycles, significantly lower than the cathode material of the Example 2.

[0074] Table 1. First-cycle discharge performance and cycle performance of cathode materials

[0075] Table 2 Average discharge specific capacity of cathode materials at different discharge rates

[0076] Note: The average discharge specific capacity is the average value of the discharge specific capacity obtained from 5 or 7 charge-discharge tests under the same rate conditions.

[0077] The results in Tables 1 and 2 show that the cathode material prepared by this invention exhibits good cycle stability and rate performance, as well as high first-cycle discharge specific capacity and first-cycle coulombic efficiency. In Example 6, when mixing lithium-rich manganese-based cathode material, lanthanum nitrate, and lithium phosphate using anhydrous ethanol as a solvent, the electrochemical performance decreased compared to Example 2, which used deionized water as a solvent. This is because deionized water evaporates more slowly during the drying process, which is beneficial for forming a dense and uniform coating layer, thereby improving the electrochemical performance of the cathode material. Comparative Example 1 has no coating layer, Comparative Example 2 uses only lithium phosphate as a coating material to form a lithium phosphate coating layer, and Comparative Example 3 uses only lanthanum nitrate as a coating material, which may form a lanthanum oxide coating layer. The electrochemical performance of the cathode material of this invention is superior to that of the cathode materials of Comparative Examples 1-3, indicating that the synergistic effect of lanthanum ions, lithium ions, and phosphate ions in the coating layer improves the structural stability of the cathode material, reduces capacity decay, and enhances cycle stability and rate performance. The low-temperature sintering temperature of Comparative Example 4 is higher than that of the embodiments of the present invention, and the electrochemical performance of the cathode material of Comparative Example 4 is also worse. This is because the higher sintering temperature leads to lattice distortion, causing the collapse of ion diffusion channels, which reduces the structural stability and electrochemical performance of the cathode material.

[0078] 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 method for producing a positive electrode material, characterized by, The preparation method comprises: mixing a lanthanum source, a lithium phosphate inorganic salt and a lithium-rich manganese-based positive electrode material to obtain a mixture, and subjecting the mixture to low-temperature sintering to obtain the positive electrode material, wherein the low-temperature sintering is performed at a temperature of 300-600 DEG C for 4-10 h.

2. The production method according to claim 1, wherein The molar ratio of lanthanum ions in the lanthanum source to phosphate ions in the lithium phosphate inorganic salt is 1:0.002-0.02:0.002-0.

02.

3. The production method according to claim 2, wherein, The molar ratio of lanthanum ions in the lanthanum source to phosphate ions in the lithium phosphate inorganic salt is 1:0.005-0.015:0.005-0.

015.

4. The production method according to any one of claims 1 to 3, wherein The lanthanum source comprises at least one of lanthanum nitrate, lanthanum carbonate, lanthanum chloride and lanthanum acetate. The lithium phosphate inorganic salt comprises at least one of Li3PO4, Li2HPO4 and LiH2PO4.

5. The production method according to any one of claims 1 to 4, wherein The low-temperature sintering is performed at a temperature of 400-500 DEG C for 5-7 h. Preferably, the low-temperature sintering is performed at a temperature increasing rate of 5-10 DEG C / min.

6. The production method according to any one of claims 1 to 5, wherein The mixing is performed in a solvent. Preferably, the mixing step comprises: dissolving the lanthanum source and the lithium phosphate inorganic salt in the solvent to form a suspension, then adding the lithium-rich manganese-based positive electrode material into the suspension, and removing the solvent. More preferably, the step of removing the solvent comprises: evaporating the suspension to dryness at a temperature of 45-70 DEG C. More preferably, the solvent comprises deionized water, and the pH of the solvent is 4.5-6.

7. The production process according to any one of claims 1 to 6, wherein The lithium-rich manganese-based positive electrode material has a chemical formula of Li x Ni a Mn b Co c O2, 1.5 < x < 1.7, 0.05 < a < 0.35, 0.5 < b < 0.9, 0.05 < c < 0.

25.

8. A positive electrode material, characterized by, The positive electrode material is prepared by the preparation method according to any one of claims 1-7.

9. A positive electrode, characterized by comprising: The positive electrode material comprises the positive electrode material prepared by the preparation method according to any one of claims 1-7 or the positive electrode material according to claim 8.

10. A battery, characterized by The positive electrode comprises the positive electrode according to claim 9.

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