Method for modifying surface of lithium-rich manganese-based positive electrode material

Abstract

The invention provides a surface modification method for a lithium-rich manganese-based positive electrode material, which comprises the following steps of: washing by using a peroxide-containing aqueous solution, properly increasing the washing temperature (preferably 40-80 DEG C), regulating the reaction pH value to 1-7, accurately controlling the ratio of acidity to free radical oxidation reaction, and optimizing the interface stability, oxygen vacancy density and Li < + > diffusion rate, thereby obtaining the lithium-rich manganese-based positive electrode material. Meanwhile, the dosage of peroxide (preferably persulfate) is reduced, the reaction time is shortened, the modification efficiency is improved, the raw material consumption is reduced, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium-rich manganese-based cathode materials, and more specifically to a method for surface modification of lithium-rich manganese-based cathode materials. Background Technology

[0002] Lithium-rich manganese-based layered oxide cathode materials benefit from their high specific capacity (>250 mAh·g). -1 With its excellent energy density, it is considered an important candidate for next-generation high-energy lithium-ion battery cathode materials. However, this type of material suffers from problems such as low initial coulombic efficiency, poor rate performance, significant voltage decay during cycling, and severe interfacial side reactions under high voltage, which seriously limit its engineering application.

[0003] To address the aforementioned shortcomings, surface water washing modification technology has been widely used in the preparation of lithium-rich manganese-based cathode materials due to its ease of operation, low cost, environmental friendliness, and ability to effectively remove surface alkaline residues (Li₂CO₃, LiOH). Water washing modification can not only reduce the probability of HF side reactions during high-voltage charge and discharge processes, but also partially improve the material's initial efficiency and cycle stability.

[0004] Among numerous water-washing modification systems, the persulfate solution washing method possesses a dual mechanism of strong oxidation and acidity, simultaneously removing surface alkaline residues, regulating surface structure, inducing the generation of appropriate oxygen vacancies, and improving electrochemical performance. Its modification principle mainly includes: ① Acidic effect: Persulfate ions decompose to release acidic species, which, under heated or catalytic conditions, form S2O8... 2- First, it decomposes into sulfate free radicals: S2O8 2- →2SO4· - Then, the sulfate radical reacts with water to release H+. + SO4·- + H2O → SO4 2- +·OH+H + It enhances acidity, reacts with Li2CO3 and LiOH on the material surface to form water-soluble salts, removes alkaline residues, and the acidic conditions can induce H2O reaction on the material surface. + –Li + Exchange reactions affect the layered structure of the material, forming a spinel phase coating layer in situ after calcination, reducing interfacial side reactions; ② Strong oxidizing free radical action: persulfate decomposes in aqueous solution to release SO4· - Free radicals such as ·OH oxidize surface active sites and lattice oxygen, inducing the generation of oxygen vacancies, which is beneficial for O2. - Migration lowers the oxygen extraction energy barrier, avoids violent oxygen evolution, slows down the oxygen release process, optimizes the lithium insertion / extraction diffusion channel, slows down oxygen release, adjusts the TM valence state, and reduces interface impedance, thereby effectively improving the first-cycle coulombic efficiency.

[0005] However, existing persulfate washing processes generally have limitations: relying solely on room temperature conditions, single acidic action, or prolonged reactions makes it difficult to achieve synergistic regulation of both acidic dissolution and free radical oxidation mechanisms, resulting in inaccurate oxygen vacancy generation and poor interface modification. To improve the modification effect, existing methods often rely on excessive ammonium persulfate and extended soaking time, which not only exacerbates the rapid dissipation of free radicals, leading to low activity utilization, but also wastes raw materials and results in low reaction efficiency. Moreover, persulfate itself has significant limitations in performance; its anion (S₂O₈) 2- It exhibits high stability in aqueous solutions at room temperature, with extremely low free radical generation efficiency, and can persist for extended periods (months). However, when the temperature rises to 40–80℃, the decomposition rate significantly accelerates, and the half-life can be shortened to several hours. Furthermore, the H₂ produced by the decomposition of persulfate ions... + The concentration is limited, making it difficult to effectively remove residual alkali from the material surface, and H + –Li+ ion exchange kinetics are slow and the acid effect is insufficient. Existing water washing techniques often face problems such as the inability to effectively coordinate free radical activity and acid effects, resulting in problems such as the separation and control of the two, uncontrollable reactions, and low modification efficiency.

[0006] To address this, the present invention proposes a surface modification method for lithium-rich manganese-based cathode materials. By adjusting the pH value and reaction temperature of the persulfate washing system, a highly efficient synergistic effect of acidic action and free radical oxidation is achieved, thereby breaking through the bottleneck of traditional technology and improving the modification effect and raw material utilization. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for surface modification of lithium-rich manganese-based cathode materials. The method uses an aqueous solution containing peroxide for water washing treatment. By appropriately increasing the water washing temperature (preferably 40-80°C) and adjusting the reaction pH value to 1-7, the proportion of acidic reaction and free radical oxidation reaction is precisely controlled, optimizing interface stability, oxygen vacancy density and Li+ diffusion rate. At the same time, the amount of peroxide (preferably persulfate) is reduced, the reaction time is shortened, the modification efficiency is improved, the raw material consumption is reduced, and the production cost is reduced.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] The purpose of this invention is to provide a method for surface modification of lithium-rich manganese-based cathode materials, the method comprising the following steps:

[0010] Prepare lithium-rich manganese-based cathode material and mix it evenly with an aqueous solution containing peroxide. Adjust the pH of the solution system to 1-7, perform water washing, and calcine the solid obtained from solid-liquid separation to complete the surface modification of the lithium-rich manganese-based cathode material.

[0011] In this invention, the pH value of the solution system is adjusted to 1 to 7, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5 or 7.

[0012] Currently, there is no specific method to control the rate and intensity ratio of acidic and free radical oxidation reactions by adjusting parameters such as solution pH and temperature, thereby achieving precise regulation of oxygen vacancy generation, surface phase stability, and interfacial reactivity. This limits the applicability and performance ceiling of the modification process. Furthermore, to further stabilize the surface structure of the material after water washing and improve interfacial reactivity, this invention incorporates a calcination step after water washing modification. This causes in-situ structural rearrangement of the lithium-rich manganese-based cathode material surface under high-temperature conditions, partially transforming it into a dense and uniform spinel phase coating layer. This coating layer effectively suppresses interfacial side reactions under high voltage, increases the lithium-ion diffusion rate, and alleviates the oxygen release rate, achieving dual optimization of structural stability and electrochemical performance, further improving the first-cycle coulombic efficiency and rate performance of the cathode material.

[0013] This invention aims to address the problems of low first-cycle coulombic efficiency, poor rate performance, and severe interfacial side reactions under high voltage in existing lithium-rich manganese-based cathode materials. Specifically, it addresses the shortcomings of low free radical activity utilization, uncontrollable acidity and oxidation effects, imprecise oxygen vacancy control, and low modification efficiency during peroxide washing modification. By adjusting the pH of the washing system (1–7) and the reaction temperature, a dual mechanism of acidity and free radical oxidation is synergistically regulated, precisely controlling the surface oxygen vacancy density and interfacial chemical reactivity. This improves the lithium-ion diffusion rate, the slow-release oxygen rate, reduces the intensity of interfacial side reactions, and enhances both first-cycle coulombic efficiency and rate performance.

[0014] As a preferred technical solution of the present invention, in the lithium-rich manganese-based cathode material, the molar ratio of lithium to precursor metal n(Li):n(TM) = 1.3 to 1.7, for example 1.3, 1.4, 1.5, 1.6 or 1.7.

[0015] Preferably, the precursor metals in the lithium-rich manganese-based cathode material include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is x:y:(1-xy), where 0 < x < 0.3 and 0 < y < 0.3.

[0016] As a preferred embodiment of the present invention, the lithium-rich manganese-based cathode material is prepared by the following method, comprising:

[0017] A precursor metal salt solution is prepared, and the precursor is obtained by co-precipitation. The precursor is mixed with a lithium source and the molar ratio of lithium in the lithium source to precursor metal in the precursor is controlled to be n(Li):n(TM) = 1.3 to 1.7. The lithium-rich manganese-based cathode material is obtained by high-temperature solid-state treatment.

[0018] As a preferred technical solution of the present invention, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide or lithium acetate, preferably lithium carbonate; the mixing process is carried out in a mixer and stirred at room temperature for 0.25-1h, preferably 0.5h, to ensure uniform mixing.

[0019] As a preferred technical solution of the present invention, in the coprecipitation method, the pH value of the reaction system is controlled to be 10 to 12, such as 10, 10.3, 10.5, 10.7, 11, 11.2, 11.5, 11.8 or 12.

[0020] As a preferred embodiment of the present invention, the high-temperature solid-state treatment includes pre-calcination and main calcination. The calcination atmosphere is a mixture of air or oxygen and a protective gas (e.g., nitrogen or argon), with a gas flow rate of 3–6 m³ / s. 3 / h, for example 3m 3 / h, 3.5m 3 / h、4m 3 / h, 4.5m 3 / h、5m 3 / h, 5.5m 3 / h or 6m 3 / h etc.

[0021] Preferably, the target temperature for pre-calcination is 300–700℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or 700℃, etc., the holding time is 3–8h, such as 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, or 8h, etc., and the heating rate is 2–5℃ / min, such as 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, or 5℃ / min, etc.

[0022] Preferably, the target temperature for the main calcination is 800–1000℃, such as 800℃, 820℃, 850℃, 880℃, 900℃, 930℃, 950℃, 970℃, or 1000℃, etc., the holding time is 8–20h, such as 8h, 10h, 12h, 14h, 16h, 18h, or 20h, etc., and the heating rate is 2–5℃ / min, such as 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, or 5℃ / min, etc.

[0023] As a preferred technical solution of the present invention, the peroxide in the aqueous solution containing peroxide includes any one or a combination of at least two of persulfate, hydrogen peroxide, peracetic acid, perbenzoic acid or benzoyl peroxide, preferably persulfate.

[0024] It should be noted that this invention preferably utilizes a surface modification method based on a peroxide washing system. By adjusting the solution pH to 1–7 and the reaction temperature, the acidity and free radical oxidation are synergistically controlled, achieving precise regulation of the oxygen vacancy density and interfacial chemical activity on the surface of the lithium-rich manganese-based cathode material. This enhances the lithium-ion diffusion rate, reduces oxygen release, and thus improves the first-cycle coulombic efficiency. Simultaneously, because the half-life of free radicals released by peroxides is significantly shortened at high temperatures, more free radicals can be released for reaction in a shorter time, reducing reaction time and raw material usage, thus saving costs. Therefore, this invention significantly reduces the amount of peroxide used and reaction time, improves modification efficiency, reduces production costs, and is simple in process, suitable for industrial applications. This invention's method, by regulating reaction kinetics and interfacial chemical reactivity, fully leverages the synergistic advantages of acidity and oxidation, effectively improving the first-cycle coulombic efficiency and rate performance of lithium-rich manganese-based cathode materials, and is simple in process, suitable for industrial production.

[0025] Preferably, the persulfate includes any one or a combination of at least two of ammonium persulfate, sodium persulfate, or potassium persulfate.

[0026] As a preferred embodiment of the present invention, the mass ratio of the peroxide in the aqueous solution containing peroxide to the lithium-rich manganese-based cathode material is (0.01-0.1):1, for example, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1 or 0.1:1, etc.

[0027] Preferably, the mass ratio of deionized water in the aqueous solution containing peroxide to the lithium-rich manganese-based cathode material is (1-50):1, for example, 1:1, 2:1, 5:1, 8:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1.

[0028] As a preferred technical solution of the present invention, the pH value of the solution system is adjusted to 1 to 7, and the acid used includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, oxalic acid, ammonium chloride or boric acid, and the base used includes any one or a combination of at least two of ammonia water, NaOH or KOH.

[0029] It should be noted that the acid and base used to adjust the pH of the solution system must not have reducing properties to avoid preferential reaction with peroxides. Therefore, ammonium chloride is preferred as the acid used, and ammonia is preferred as the base used.

[0030] As a preferred technical solution of the present invention, the temperature of the water washing treatment is 25-90℃, such as 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃, etc., and the water washing time is 0.1-48h, such as 0.1h, 1h, 5h, 10h, 15h, 18h, 20h, 26h, 30h, 34h, 38h, 42h or 48h, etc.

[0031] As a preferred embodiment of the present invention, the target temperature for the calcination treatment is 200–700℃, such as 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or 700℃, etc., the holding time is 1–10h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, etc., the heating rate is 2–10℃ / min, such as 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, etc., and the calcination atmosphere is air.

[0032] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0033] (1) This invention modifies lithium-rich manganese-based cathode materials by calcining and then washing them with an aqueous solution containing peroxides (preferably persulfate). By rationally controlling the pH of the washing system to 1-7 and the reaction temperature, the synergistic regulation of acidic effects and free radical oxidation on the material surface can be achieved. This effectively removes alkaline residues (such as Li2CO3 and LiOH), improves the cleanliness of the material interface, reduces the risk of side reactions under high pressure, and induces H+ oxidation on the material surface. + –Li + The exchange reaction forms a spinel phase coating layer in situ; at the same time, the strong oxidizing free radicals generated during the water washing process can induce the generation of a suitable amount of oxygen vacancies on the cathode surface, improve the lithium ion diffusion channels and transition metal valence state distribution in the surface region, optimize the delithiation kinetics, and slow down the oxygen release process.

[0034] (2) By performing calcination treatment after water washing, the present invention can promote in-situ structural rearrangement in the surface area, generating a dense and uniform spinel phase coating layer. This coating structure is beneficial to improving the structural stability of the material during high-pressure cycling, slowing down the phase transformation-induced volume expansion effect, inhibiting the accumulation of interfacial side reaction products, and further reducing interfacial impedance.

[0035] (3) This invention can improve the first-cycle coulombic efficiency, capacity and rate performance of lithium-rich manganese-based cathode materials through a simple water washing and calcination process without adding additional coating precursors or complicated coating steps. It has the advantages of easy reaction process control, high modification efficiency, low cost and suitability for mass industrial application. Attached Figure Description

[0036] Figure 1 Here is a SEM image of the lithium-rich manganese-based cathode material obtained from the preparation example;

[0037] Figure 2 This is a SEM image of the lithium-rich manganese-based cathode material obtained in Comparative Example 1;

[0038] Figure 3 The image shows the SEM image of the lithium-rich manganese-based cathode material obtained in Comparative Example 2.

[0039] Figure 4 This is a SEM image of the lithium-rich manganese-based cathode material obtained in Example 1;

[0040] Figure 5 This is a comparison chart of the first-cycle curves of the lithium-rich manganese-based cathode materials obtained in the preparation examples, Comparative Example 1, Comparative Example 2, and Example 1.

[0041] Figure 6 This is a comparison chart of the rate curves of the lithium-rich manganese-based cathode materials obtained in the preparation example, comparative example 1, comparative example 2, and example 1;

[0042] Figure 7 These are XRD comparison images of the lithium-rich manganese-based cathode materials obtained from the preparation examples, Comparative Example 1, Comparative Example 2, and Example 1. Detailed Implementation

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0045] Preparation example (blank example)

[0046] This preparation example uses a co-precipitation method to prepare lithium-rich manganese-based cathode materials. The preparation method includes the following steps:

[0047] Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in deionized water in stoichiometric ratios to prepare a precursor metal salt solution. The molar ratio of Ni, Co, and Mn in the precursor metal salt solution was 0.17:0.17:0.66. The precursor metal salt solution was placed in a constant-temperature reaction vessel, and under continuous stirring, a precipitant (sodium carbonate solution) and a complexing agent (ammonia) were added dropwise at a constant rate using a peristaltic pump. The pH of the system was controlled to be stable at 11. The dropping rate was adjusted according to the volume of the reaction vessel, the concentration of the solution, and the equilibrium state of the system to ensure that the reaction proceeded stably.

[0048] After coprecipitation, solid-liquid separation was performed. The resulting precipitate was washed with deionized water and dried to obtain Ni. 0.17 Co 0.17 Mn 0.66 The lithium-rich manganese-based carbonate precursor of CO3 was prepared with a D50 particle size controlled at 10 μm and a spherical particle morphology.

[0049] The lithium-rich manganese-based carbonate precursor was uniformly mixed with a lithium source (lithium carbonate), controlling the molar ratio of lithium in the lithium source to the precursor metal in the precursor, n(Li):n(TM) = 1.4. The mixing process was carried out in an Ericsson mixer at room temperature for 0.5 hours. The uniformly mixed material was then placed in an atmosphere furnace for high-temperature solid-state treatment, which included pre-calcination and main calcination. The calcination atmosphere was a mixture of compressed air and nitrogen, with a gas flow rate of 4 m³ / s. 3 The target temperature for the pre-calcination is 500℃, the holding time is 5h, and the heating rate is 3℃ / min. The target temperature for the main calcination is 900℃, the holding time is 10h, and the heating rate is 3℃ / min, ultimately yielding a lithium-rich manganese-based cathode material.

[0050] Example 1

[0051] This embodiment provides a method for surface modification of lithium-rich manganese-based cathode materials, the method comprising the following steps:

[0052] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into deionized water at 5 times its own weight, add ammonium persulfate, the mass ratio of ammonium persulfate to lithium-rich manganese-based cathode material is 0.05:1, then add ammonium chloride to adjust the pH of the solution system to 5, stir for 1 h in an 80℃ water bath, and perform water washing treatment. After stirring, filter, wash and dry, and place the obtained sample in a muffle furnace, calcine at 400℃ for 5 h at a heating rate of 5℃ / min, with air as the calcination atmosphere, to complete the surface modification of the lithium-rich manganese-based cathode material, and obtain the lithium-rich manganese-based cathode material obtained by high-temperature acid washing and calcination with ammonium persulfate.

[0053] Example 2

[0054] This embodiment provides a method for surface modification of lithium-rich manganese-based cathode materials, the method comprising the following steps:

[0055] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into deionized water at 5 times its own weight, add peracetic acid, the mass ratio of peracetic acid to lithium-rich manganese-based cathode material is 0.05:1, then add ammonia water to adjust the pH of the solution system to 5, stir for 1 h in an 80℃ water bath, and perform water washing treatment. After stirring, filter, wash and dry, and place the obtained sample in a muffle furnace, calcine at 400℃ for 5 h at a heating rate of 5℃ / min, with air as the calcination atmosphere to complete the surface modification of the lithium-rich manganese-based cathode material, and obtain the peracetic acid high-temperature acid-washed and calcined lithium-rich manganese-based cathode material.

[0056] Example 3

[0057] This embodiment provides a method for surface modification of lithium-rich manganese-based cathode materials, the method comprising the following steps:

[0058] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into deionized water at 5 times its own weight, add ammonium persulfate, the mass ratio of ammonium persulfate to lithium-rich manganese-based cathode material is 0.05:1, then add ammonium chloride to adjust the pH of the solution system to 5, stir at room temperature (25℃) for 1 h, and perform water washing treatment. After stirring, filter, wash and dry, and place the obtained sample in a muffle furnace, calcine at 400℃ for 5 h, with a heating rate of 5℃ / min, and the calcination atmosphere is air to complete the surface modification of the lithium-rich manganese-based cathode material, and obtain the lithium-rich manganese-based cathode material that is acid-washed and calcined at room temperature with ammonium persulfate.

[0059] Example 4

[0060] This embodiment provides a method for surface modification of lithium-rich manganese-based cathode materials, the method comprising the following steps:

[0061] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into deionized water at 5 times its own weight, add ammonium persulfate, the mass ratio of ammonium persulfate to lithium-rich manganese-based cathode material is 0.05:1, then add ammonium chloride to adjust the pH of the solution system to 5, stir for 1 h in a 90℃ water bath, and perform water washing treatment. After stirring, filter, wash and dry, and place the obtained sample in a muffle furnace, calcine at 400℃ for 5 h at a heating rate of 5℃ / min, with air as the calcination atmosphere, to complete the surface modification of the lithium-rich manganese-based cathode material, and obtain the lithium-rich manganese-based cathode material obtained by high-temperature acid washing and calcination with ammonium persulfate.

[0062] Example 5

[0063] This embodiment provides a method for surface modification of lithium-rich manganese-based cathode materials, the method comprising the following steps:

[0064] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into deionized water at 5 times its own weight, add ammonium persulfate, the mass ratio of ammonium persulfate to lithium-rich manganese-based cathode material is 0.05:1, then add ammonium chloride to adjust the pH of the solution system to 1, stir for 1 h in an 80℃ water bath, and perform water washing treatment. After stirring, filter, wash and dry, and place the obtained sample in a muffle furnace and calcine at 400℃ for 5 h at a heating rate of 5℃ / min in an air atmosphere to complete the surface modification of the lithium-rich manganese-based cathode material, and obtain the lithium-rich manganese-based cathode material obtained by high-temperature acid washing and calcination with ammonium persulfate.

[0065] Comparative Example 1

[0066] This comparative example provides a method for surface modification of a lithium-rich manganese-based cathode material, the method comprising the following steps:

[0067] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into 5 times its own weight of deionized water, stir for 3 hours at room temperature (25℃), and wash it with water. After stirring, filter, wash and dry the sample. Place the obtained sample in a muffle furnace and calcine at 400℃ for 5 hours with a heating rate of 5℃ / min and an air calcination atmosphere to complete the surface modification of the lithium-rich manganese-based cathode material and obtain pure water-washed and calcined lithium-rich manganese-based cathode material.

[0068] Comparative Example 2

[0069] This comparative example provides a method for surface modification of a lithium-rich manganese-based cathode material, the method comprising the following steps:

[0070] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into 5 times its own weight of deionized water, add ammonium chloride to adjust the pH of the solution system to 5, stir at room temperature (25℃) for 1 h, wash with water, filter, wash and dry after stirring, place the obtained sample in a muffle furnace, calcine at 400℃ for 5 h, heating rate 5℃ / min, calcination atmosphere is air, complete the surface modification of lithium-rich manganese-based cathode material, and obtain ammonium chloride acid-washed and calcined lithium-rich manganese-based cathode material.

[0071] Comparative Example 3

[0072] This comparative example provides a method for surface modification of a lithium-rich manganese-based cathode material, the method comprising the following steps:

[0073] Prepare the lithium-rich manganese-based cathode material obtained in the above preparation example, pour it into deionized water at 5 times its own weight, add ammonium persulfate, the mass ratio of ammonium persulfate to lithium-rich manganese-based cathode material is 0.05:1, then add ammonia water to adjust the pH of the solution system to 8, stir for 1 h in an 80℃ water bath, and perform water washing treatment. After stirring, filter, wash and dry, and place the obtained sample in a muffle furnace, calcine at 400℃ for 5 h at a heating rate of 5℃ / min, with air as the calcination atmosphere, to complete the surface modification of the lithium-rich manganese-based cathode material, and obtain the ammonium persulfate high-temperature water-washed and calcined lithium-rich manganese-based cathode material.

[0074] Figure 1 SEM images of the lithium-rich manganese-based cathode material obtained in the preparation example are shown. Figure 2 The SEM image of the lithium-rich manganese-based cathode material obtained in Comparative Example 1 is shown. Figure 3 The SEM image of the lithium-rich manganese-based cathode material obtained in Comparative Example 2 is shown. Figure 4 The SEM image of the lithium-rich manganese-based cathode material obtained in Example 1 is shown. Figures 1-4 The scanning electron microscope (SEM) images shown indicate that the lithium-rich manganese-based cathode material maintained a good overall morphology after water washing under different conditions. The particles were uniform and intact, and no obvious breakage was observed. This shows that all water washing modification methods have good morphology preservation and do not cause significant mechanical damage to the intrinsic structure of the material.

[0075] Figure 5 and Figure 6 The electrochemical test results demonstrate the specific effects of different washing conditions on material performance. Comparative Example 1, washed with deionized water, showed a decline in performance, with both the first-cycle coulombic efficiency and rate capacity decreasing. The reason for this is that pure water easily induces the dissolution of transition metals from the material surface during washing, and water molecules may react with metal ions (especially Mn) on the material surface. 4+ This process involves the formation of M-OH groups or a hydrated layer, leading to local structural disorder and increased interfacial defects. This increases subsequent side reactions with the electrolyte, thereby weakening the overall electrochemical performance. In Comparative Example 2, the lithium-rich manganese-based cathode material was washed with an ammonium chloride aqueous solution. The acidic conditions induced H2O formation on the material surface. + –Li + An exchange reaction occurs, resulting in the in-situ formation of a small amount of spinel phase coating without disrupting the main layered structure. This coating helps suppress side reactions between the material surface and the electrolyte, improving interfacial stability and lithium-ion transport rate. Therefore, compared to the untreated sample, Comparative Example 2 shows improvements in both first-cycle coulombic efficiency and rate performance. In Example 1, ammonium persulfate (APS) aqueous solution was used to modify the material under acidic conditions at 80°C. This not only effectively removed residual alkaline impurities from the surface but also, through H... + –Li+ Exchange interactions induce the in-situ formation of a spinel phase coating layer on the material surface. More importantly, under heated conditions, the thermal decomposition of APS generates highly oxidizing free radicals (SO4·) - The presence of ·OH can induce a controllable deoxidation reaction on the material surface, promoting the formation of oxygen vacancies and further triggering the reconstruction and stable passivation of the surface structure. This synergistic effect significantly improves the initial discharge capacity, initial coulombic efficiency, and rate performance of the material without damaging the main structure. The sample modified by this water washing method showed an initial coulombic efficiency of 95% and a significantly enhanced rate performance, indicating that the method of this invention can effectively solve the problems of low initial efficiency and poor rate performance in lithium-rich manganese-based cathode materials.

[0076] Figure 7 Further verification using X-ray diffraction (XRD) patterns showed that both samples maintained a typical lithium-rich layered structure before and after water washing, and characteristic peaks of the Li2MnO3 superstructure appeared in the 20°-25° range, indicating that the water washing treatment did not damage the main crystal structure. Although the spinel phase in Comparative Example 2 and Example 1 materials had some in-situ formation on the surface, it was not clearly presented in the XRD patterns due to its low proportion.

[0077] The above samples were subjected to electrochemical performance tests, and the specific test results are shown in Table 1.

[0078] Table 1

[0079] sample First effect 0.1C 0.2C 0.5C 1C Preparation Example 82％ 281 246 221 203 Comparative Example 1 71％ 244 220 196 174 Comparative Example 2 88％ 291 263 242 220 Comparative Example 3 68％ 246 213 187 153 Example 1 95％ 295 268 248 229 Example 2 91％ 289 260 239 212 Example 3 86％ 292 264 243 221 Example 4 88％ 286 254 233 210 Example 5 75％ 221 203 172 151

[0080] This invention focuses on providing a surface modification method using peroxide washing. The core innovation lies in achieving synergistic regulation of acidic and free radical oxidation effects through adjusting the reaction pH and temperature, resulting in higher capacity, first-cycle efficiency, and rate performance. Conventional acid washing processes often use acidic substances such as sulfuric acid, boric acid, citric acid, and benzoic acid, typically only improving the first-cycle coulombic efficiency to approximately 88%. The method of this invention further overcomes this limitation, exhibiting superior electrochemical performance. Furthermore, this method also shows good results for cobalt-free materials, representing a universal modification method for lithium-rich manganese-based cathode materials. Simultaneously, this invention requires less raw material compared to conventional acid washing, achieving better results, reducing reagent usage and wastewater treatment complexity, and facilitating industrial production.

[0081] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0082] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0083] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0084] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for surface modification of lithium-rich manganese-based cathode materials, characterized in that, The method includes the following steps: Prepare lithium-rich manganese-based cathode material and mix it evenly with an aqueous solution containing peroxide. Adjust the pH of the solution system to 1-7, perform water washing, and calcine the solid obtained from solid-liquid separation to complete the surface modification of the lithium-rich manganese-based cathode material.

2. The method according to claim 1, characterized in that, In the lithium-rich manganese-based cathode material, the molar ratio of lithium to precursor metal n(Li):n(TM) = 1.3 to 1.7; Preferably, the precursor metals in the lithium-rich manganese-based cathode material include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is x:y:(1-xy), where 0 < x < 0.3 and 0 < y < 0.

3.

3. The method according to claim 2, characterized in that, The lithium-rich manganese-based cathode material is prepared using the following method: A precursor metal salt solution is prepared, and the precursor is obtained by co-precipitation. The precursor is mixed with a lithium source and the molar ratio of lithium in the lithium source to precursor metal in the precursor is controlled to be n(Li):n(TM) = 1.3 to 1.

7. The lithium-rich manganese-based cathode material is obtained by high-temperature solid-state treatment.

4. The method according to claim 3, characterized in that, In the coprecipitation method, the pH value of the reaction system is controlled to be 10-12.

5. The method according to claim 3, characterized in that, The high-temperature solid-state treatment includes pre-calcination and main calcination. The calcination atmosphere is a mixture of air or oxygen and a protective gas, with a gas flow rate of 3-6 m³ / h. 3 / h; Preferably, the target temperature for pre-calcination is 300–700°C, the holding time is 3–8 h, and the heating rate is 2–5°C / min; Preferably, the target temperature for the main calcination is 800–1000℃, the holding time is 8–20 h, and the heating rate is 2–5℃ / min.

6. The method according to any one of claims 1 to 5, characterized in that, The peroxide in the aqueous solution containing peroxide includes any one or a combination of at least two of persulfate, hydrogen peroxide, peracetic acid, perbenzoic acid or benzoyl peroxide, preferably persulfate; Preferably, the persulfate includes any one or a combination of at least two of ammonium persulfate, sodium persulfate, or potassium persulfate.

7. The method according to any one of claims 1 to 6, characterized in that, The mass ratio of the peroxide in the aqueous solution containing peroxide to the lithium-rich manganese-based cathode material is (0.01-0.1):

1. Preferably, the mass ratio of deionized water in the aqueous solution containing peroxide to the lithium-rich manganese-based cathode material is (1-50):

1.

8. The method according to any one of claims 1 to 7, characterized in that, The pH value of the adjusted solution system is 1 to 7, and the acid used includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, oxalic acid, ammonium chloride or boric acid, and the base used includes any one or a combination of at least two of ammonia, NaOH or KOH.

9. The method according to any one of claims 1 to 8, characterized in that, The washing temperature is 25–90°C, and the washing time is 0.1–48 h.

10. The method according to any one of claims 1 to 9, characterized in that, The target temperature for the calcination treatment is 200–700℃, the holding time is 1–10 h, the heating rate is 2–10℃ / min, and the calcination atmosphere is air.

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