Lithium-rich manganese-based positive electrode material having lithium concentration gradient, and preparation method therefor and use thereof

Abstract

The present application provides a lithium-rich manganese-based positive electrode material having a lithium concentration gradient, and a preparation method therefor and a use thereof. The preparation method comprises the following steps: uniformly mixing a lithium-rich manganese-based positive electrode material with a modifier, and calcining the resulting mixture in an inert atmosphere to obtain a coated modified positive electrode material; and carrying out pure water ultrasonic treatment on the obtained coated modified positive electrode material and drying the treated material to obtain the lithium-rich manganese-based positive electrode material having a lithium concentration gradient, wherein the modifier can react with Li to generate a lithium salt readily soluble in water. The preparation method of the present application realizes lithium concentration distribution by means of water immersion and has the advantages of environmental optimization, low costs, and easy scale-up. A lithium concentration gradient layer can inhibit the transition of a layered structure to a spinel structure, and thus, the thermal stability of the structure is significantly improved and high-rate performance, inhibited voltage attenuation, and excellent long-term stability are achieved.

Description

A lithium concentration gradient lithium-rich manganese-based cathode material, its preparation method and application Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, and relates to a lithium-rich manganese-based cathode material, and more particularly to a lithium concentration gradient lithium-rich manganese-based cathode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and grid-scale energy storage, but their energy density is significantly limited by the cathode material. Lithium-rich layered oxides (LLOs) are considered one of the most promising next-generation cathode materials. However, LLOs typically suffer from suboptimal structural / chemical stability, leading to severe cracking during long-term cycling, resulting in severe pulverization and rapid performance degradation. Furthermore, electrolyte penetration along the cracks further intensifies the activation and accumulation of various side reactions, accelerating structural and performance degradation. These effects can lead to severe performance losses and safety issues.

[0003] Studies suggest that doping with a concentration gradient can improve the rate performance of lithium-rich manganese-based cathode materials. It also helps protect the migration of metal ions on the cathode particle surface, mitigating capacity and voltage decay issues.

[0004] CN114050262A discloses a phosphate gradient modified lithium manganese oxide material and its preparation method. The surface coating of this composite modified lithium manganese oxide material is a multi-metal phosphate gradient coating layer. The surface near the main material is mainly lithium-rich manganese-based phosphate, and the outermost layer is mainly low-lithium or lithium-free manganese-based phosphate. The synthesis method specifically includes: firstly, calcining manganese oxide and lithium salt to synthesize lithium manganese oxide material; dispersing the prepared lithium manganese oxide material in an aqueous solution; adding manganese salt, lithium salt, phosphate precipitant and organic complexing agent; after reacting for a period of time, continuing to add a certain proportion of manganese salt and phosphate, and carrying out the precipitation reaction again; after washing the resulting mixture with water and alcohol and drying it, further calcining it to finally obtain the phosphate composite modified lithium manganese oxide material.

[0005] The preparation method is complex and costly, making it difficult to promote industrialization. Therefore, there is a need for a lithium concentration gradient lithium-rich manganese-based cathode material that is simple to prepare, low in cost, highly reproducible, and suitable for large-scale production.

[0006] Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] This application provides a lithium concentration gradient lithium-rich manganese-based cathode material, its preparation method, and its application. The preparation method achieves lithium concentration distribution through water immersion, which has the advantages of environmental optimization, low cost, and easy scalability. Furthermore, the lithium concentration gradient layer can suppress the transformation of the layered structure to the spinel structure, significantly improving the thermal stability of the structure, while achieving high rate performance, suppressing voltage decay, and excellent long-term stability.

[0009] In a first aspect, this application provides a method for preparing a lithium-concentration gradient lithium-rich manganese-based cathode material, the method comprising the following steps:

[0010] A lithium-rich manganese-based cathode material is uniformly mixed with a modifier, and the resulting mixture is calcined in an inert atmosphere to obtain a coated and modified cathode material; the obtained coated and modified material is subjected to ultrasonic treatment with pure water and dried to obtain the lithium concentration gradient lithium-rich manganese-based cathode material.

[0011] The modifier can react with Li to form a water-soluble lithium salt.

[0012] The preparation method provided in this application achieves lithium concentration distribution through water immersion, i.e., a lithium concentration gradient distribution with low lithium concentration in the outer layer and high lithium concentration in the inner layer. The preparation method provided in this application has the advantages of environmental optimization, low cost and easy scalability, and the lithium concentration gradient layer can suppress the transformation of the layered structure to the spinel structure, significantly improving the thermal stability of the structure, while achieving high rate performance, suppressing voltage decay and excellent long-term stability.

[0013] In one embodiment, the modifier comprises any one or a combination of at least two of oxalic acid, molybdenum oxide, silicon oxide, or tungsten oxide. Typical but non-limiting combinations include combinations of oxalic acid and molybdenum oxide, combinations of silicon oxide and tungsten oxide, combinations of molybdenum oxide and tungsten oxide, combinations of oxalic acid and tungsten oxide, or combinations of oxalic acid, molybdenum oxide, silicon oxide, and tungsten oxide, optionally oxalic acid and / or molybdenum oxide.

[0014] In this application, the molybdenum oxide includes MoO3, the silicon oxide includes SiO2, and the tungsten oxide includes WO3.

[0015] In one embodiment, the amount of the modifier is 2-8 wt% of the lithium-rich manganese-based cathode material, for example, it can be 2 wt%, 4 wt%, 5 wt%, 6 wt% or 8 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 4 wt%.

[0016] In one embodiment, the calcination temperature is 300-500°C, for example, 300°C, 350°C, 400°C, 450°C or 500°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 400°C.

[0017] In one embodiment, the calcination time is 2-6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 4 hours.

[0018] In one embodiment, the gas used in the inert atmosphere includes any one or a combination of at least two of nitrogen, helium, or argon. Typical but non-limiting combinations include combinations of nitrogen and helium, helium and argon, nitrogen and argon, or nitrogen, helium, and argon.

[0019] In one embodiment, the solid-liquid mass ratio of the pure water ultrasonic treatment is 1:(1-4), for example, it can be 1:1, 1:2, 1:3 or 1:4, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, and 1:2 can be selected.

[0020] In one embodiment, the ultrasonic treatment time for pure water is 0.5-2 hours, for example, it can be 0.5 hours, 1 hour, 1.5 hours or 2 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 1 hour.

[0021] In one embodiment, the power of the pure water ultrasonic treatment is 55-65W, for example, it can be 55W, 58W, 60W, 62W or 65W, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 60W.

[0022] In one embodiment, the frequency of the tidal ultrasonic treatment is 35-45kHz, for example, it can be 35kHz, 38kHz, 40kHz, 42kHz or 45kHz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 40kHz.

[0023] In one embodiment, the preparation method of the lithium-rich manganese-based cathode material includes the following steps: mixing a lithium source with a lithium-rich manganese-based hydroxide precursor, heat-treating the resulting mixture, and obtaining the lithium-rich manganese-based cathode material.

[0024] In one embodiment, the molar ratio of lithium in the lithium source to the lithium-rich manganese-based hydroxide precursor is (1.3-1.6):1, for example, it can be 1.3:1, 1.4:1, 1.5:1 or 1.6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 1.4:1.

[0025] In one embodiment, the lithium source includes lithium carbonate and / or lithium hydroxide.

[0026] In one embodiment, the heat treatment includes a pre-firing and a roasting process performed sequentially.

[0027] In one embodiment, the preheating temperature is 450-550°C, for example, 450°C, 480°C, 500°C, 520°C or 550°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 500°C.

[0028] The preheating time is 4.5-5.5 hours, for example, it can be 4.5 hours, 4.8 hours, 5 hours, 5.2 hours or 5.5 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, and 5 hours can be selected.

[0029] In one embodiment, the roasting temperature is 800-1000℃, for example, it can be 800℃, 850℃, 900℃, 950℃ or 1000℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 900℃.

[0030] In one embodiment, the roasting time is 10-14 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours or 14 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, such as 12 hours.

[0031] In one embodiment, the lithium-rich manganese-based hydroxide precursor has the chemical formula Ni x Co y Mn 1-x-y (OH)2, where 0.3≤x≤0.4, 0≤y≤0.1, and 0.3≤x+y≤0.5.

[0032] The preparation method provided in this application is particularly suitable for preparing cobalt-free or low-cobalt lithium-rich manganese-based cathode materials.

[0033] In one embodiment, the lithium-rich manganese-based hydroxide precursor has the chemical formula Ni 0.4 Mn 0.6 (OH)2.

[0034] Specifically, the lithium-rich manganese-based hydroxide precursor is a lithium-rich manganese-based hydroxide precursor prepared by co-precipitation method.

[0035] As an optional embodiment of the preparation method described in the first aspect of this application, the preparation method includes the following steps:

[0036] (1) A mixture of lithium source and lithium-rich manganese-based hydroxide precursor is heat-treated to obtain a lithium-rich manganese-based cathode material.

[0037] The chemical formula of the lithium-rich manganese-based hydroxide precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.3≤x≤0.4, 0≤y≤0.1, and 0.3≤x+y≤0.5;

[0038] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium source is (1.3-1.6):1;

[0039] The heat treatment includes pre-firing and calcination performed sequentially; the pre-firing temperature is 450-550℃ and the time is 4.5-5.5h; the calcination temperature is 800-1000℃ and the time is 10-14h.

[0040] (2) The lithium-rich manganese-based cathode material is uniformly mixed with the modifier, and the resulting mixture is calcined at 300-500℃ for 2-6 hours in an inert atmosphere to obtain the coated modified cathode material.

[0041] The modifier can react with Li to form a water-soluble lithium salt, and the amount of the modifier is 2-8 wt% of the lithium-rich manganese-based cathode material.

[0042] (3) The obtained coated modified material was subjected to ultrasonic treatment with pure water for 0.5-2 hours and then dried to obtain the lithium concentration gradient lithium-rich manganese-based cathode material.

[0043] The solid-liquid mass ratio of the pure water ultrasonic treatment is 1:(1-4), and the unit of the solid content is mg / L.

[0044] Secondly, this application provides a lithium concentration gradient lithium-rich manganese-based cathode material, which is prepared by the preparation method described in the first aspect.

[0045] Thirdly, this application provides a lithium-ion battery, the lithium-ion battery comprising the lithium concentration gradient lithium-rich manganese-based cathode material described in the second aspect.

[0046] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0047] Compared with related technologies, the beneficial effects of this application are as follows:

[0048] The preparation method provided in this application achieves lithium concentration distribution through water immersion, which has the advantages of environmental optimization, low cost and easy scalability. Moreover, the lithium concentration gradient layer can suppress the transformation of the layered structure to the spinel structure, significantly improve the thermal stability of the structure, and achieve high rate performance, suppression of voltage decay and excellent long-term stability.

[0049] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0050] The technical solution of this application will be further described below through specific implementation methods.

[0051] To clearly illustrate the technical solution of this application, in the following examples and comparative examples, the lithium-rich manganese-based hydroxide precursor is Ni prepared by a co-precipitation method. 0.4 Mn 0.6 (OH)2.

[0052] Example 1-1

[0053] This embodiment provides a method for preparing a lithium-concentration gradient lithium-rich manganese-based cathode material, the method comprising the following steps:

[0054] (1) A mixture of lithium carbonate and lithium-rich manganese-based hydroxide precursor was heat-treated to obtain a lithium-rich manganese-based cathode material.

[0055] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium carbonate is 1.4:1;

[0056] The heat treatment includes pre-firing and calcination performed sequentially; the pre-firing temperature is 500℃ and the time is 5h; the calcination temperature is 900℃ and the time is 12h.

[0057] (2) The lithium-rich manganese-based cathode material was uniformly mixed with the modifier MoO3, and the resulting mixture was calcined at 400°C for 4 hours in an argon atmosphere to obtain the coated modified cathode material.

[0058] The amount of the modifier used is 4 wt% of the lithium-rich manganese-based cathode material;

[0059] (3) The obtained coated modified material was subjected to pure water ultrasonic treatment for 1 hour and then dried to obtain the lithium concentration gradient lithium-rich manganese-based cathode material.

[0060] The solid-liquid mass ratio of the pure water ultrasonic treatment is 1:1, the ultrasonic power is 60W, and the frequency is 40kHz.

[0061] Examples 1-2

[0062] This embodiment provides a method for preparing lithium concentration gradient lithium-rich manganese-based cathode material. Except for the solid-liquid mass ratio of 1:2 after ultrasonic treatment with pure water, the rest is the same as in Example 1-1.

[0063] Examples 1-3

[0064] This embodiment provides a method for preparing lithium concentration gradient lithium-rich manganese-based cathode material. Except for the solid-liquid mass ratio of 1:3 after ultrasonic treatment with pure water, the rest is the same as in Example 1-1.

[0065] Examples 1-4

[0066] This embodiment provides a method for preparing lithium concentration gradient lithium-rich manganese-based cathode material. Except for the solid-liquid mass ratio of 1:4 after ultrasonic treatment with pure water, the rest is the same as in Example 1-1.

[0067] Example 2

[0068] This embodiment provides a method for preparing a lithium-concentration gradient lithium-rich manganese-based cathode material, the method comprising the following steps:

[0069] (1) A mixture of lithium carbonate and lithium-rich manganese-based hydroxide precursor was heat-treated to obtain a lithium-rich manganese-based cathode material.

[0070] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium carbonate is 1.3:1;

[0071] The heat treatment includes pre-firing and calcination performed sequentially; the pre-firing temperature is 450℃ and the time is 5.5h; the calcination temperature is 800℃ and the time is 14h.

[0072] (2) The lithium-rich manganese-based cathode material was uniformly mixed with the modifier MoO3, and the resulting mixture was calcined at 300°C for 6 hours in an argon atmosphere to obtain the coated modified cathode material.

[0073] The amount of the modifier used is 2 wt% of the lithium-rich manganese-based cathode material;

[0074] (3) The obtained coated modified material was subjected to ultrasonic treatment with pure water for 0.5 h, and then dried to obtain the lithium concentration gradient lithium-rich manganese-based cathode material.

[0075] The solid-liquid mass ratio of the pure water ultrasonic treatment is 1:2, the ultrasonic power is 60W, and the frequency is 40kHz.

[0076] Example 3

[0077] This embodiment provides a method for preparing a lithium-concentration gradient lithium-rich manganese-based cathode material, the method comprising the following steps:

[0078] (1) A mixture of lithium carbonate and lithium-rich manganese-based hydroxide precursor was heat-treated to obtain a lithium-rich manganese-based cathode material.

[0079] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium carbonate is 1.6:1;

[0080] The heat treatment includes pre-firing and calcination performed sequentially; the pre-firing temperature is 550℃ and the time is 4.5h; the calcination temperature is 1000℃ and the time is 10h.

[0081] (2) The lithium-rich manganese-based cathode material was uniformly mixed with the modifier MoO3, and the resulting mixture was calcined at 300°C for 6 hours in an argon atmosphere to obtain the coated modified cathode material.

[0082] The amount of the modifier used is 8 wt% of the lithium-rich manganese-based cathode material;

[0083] (3) The obtained coated modified material was subjected to ultrasonic treatment with pure water for 2 hours and then dried to obtain the lithium concentration gradient lithium-rich manganese-based cathode material.

[0084] The solid-liquid mass ratio of the pure water ultrasonic treatment is 1:2, the ultrasonic power is 60W, and the frequency is 40kHz.

[0085] Example 4

[0086] This embodiment provides a method for preparing lithium-rich manganese-based cathode materials with lithium concentration gradient. Except for replacing MoO3 with WO3 by mass, the rest is the same as in Examples 1-2.

[0087] Example 5

[0088] This embodiment provides a method for preparing lithium concentration gradient lithium-rich manganese-based cathode materials. Except for replacing MoO3 with SiO2 by mass, the rest is the same as in Examples 1-2.

[0089] Example 6

[0090] This embodiment provides a method for preparing lithium concentration gradient lithium-rich manganese-based cathode materials. Except for replacing MoO3 with oxalic acid by mass, the rest is the same as in Examples 1-2.

[0091] Comparative Example 1

[0092] This comparative example provides a method for preparing a lithium-rich manganese-based cathode material, the method comprising the following steps:

[0093] (1) A mixture of lithium carbonate and lithium-rich manganese-based hydroxide precursor was heat-treated to obtain a lithium-rich manganese-based cathode material.

[0094] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium carbonate is 1.4:1;

[0095] The heat treatment includes pre-firing and roasting performed sequentially; the pre-firing temperature is 500℃ and the time is 5h; the roasting temperature is 900℃ and the time is 12h.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing a coated and modified cathode material, the method comprising the following steps:

[0098] (1) A mixture of lithium carbonate and lithium-rich manganese-based hydroxide precursor was heat-treated to obtain a lithium-rich manganese-based cathode material.

[0099] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium carbonate is 1.4:1;

[0100] The heat treatment includes pre-firing and calcination performed sequentially; the pre-firing temperature is 500℃ and the time is 5h; the calcination temperature is 900℃ and the time is 12h.

[0101] (2) The lithium-rich manganese-based cathode material was uniformly mixed with the modifier MoO3, and the resulting mixture was calcined at 400°C for 4 hours in an argon atmosphere to obtain the coated modified cathode material.

[0102] The amount of the modifier used is 4 wt% of the lithium-rich manganese-based cathode material.

[0103] Comparative Example 3

[0104] This comparative example provides a method for preparing a coated and modified cathode material, the method comprising the following steps:

[0105] (1) A mixture of lithium carbonate and lithium-rich manganese-based hydroxide precursor was heat-treated to obtain a lithium-rich manganese-based cathode material.

[0106] The molar ratio of lithium to lithium-rich manganese-based hydroxide precursor in the lithium carbonate is 1.4:1;

[0107] The heat treatment includes pre-firing and calcination performed sequentially; the pre-firing temperature is 500℃ and the time is 5h; the calcination temperature is 900℃ and the time is 12h.

[0108] (2) The obtained lithium-rich manganese-based cathode material was calcined at 400°C for 4 hours in an argon atmosphere;

[0109] (3) The material obtained in step (2) is subjected to pure water ultrasonic treatment for 1 hour and then dried to obtain the lithium concentration gradient lithium-rich manganese-based cathode material.

[0110] The solid-liquid mass ratio of the pure water ultrasonic treatment is 1:2, the ultrasonic power is 60W, and the frequency is 40kHz.

[0111] Performance testing

[0112] The performance of the cathode materials obtained in the above embodiments and comparative examples was tested: the cathode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were weighed at a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) and mixed thoroughly; then, the slurry was coated onto aluminum foil using a coater and dried in a vacuum drying oven at 80°C for 8 hours; finally, the aluminum foil was stamped into 1.13 cm thick sheets. 2 A circular positive electrode sheet was obtained. Using this positive electrode sheet as the positive electrode and a lithium metal sheet as the counter electrode, a porous polypropylene membrane (Celgard 2400) was used as a separator to separate the positive and counter electrodes. The CR 2032 button cell was assembled in an argon-filled glove box. Cyclic performance tests were conducted using a battery testing system (Blue Electric CT2001A) at rates of 0.1C and 0.33C under conditions of 2.5–4.55V. The test results are shown in Table 1.

[0113] Table 1

[0114] In summary, the preparation method provided in this application achieves lithium concentration distribution through water immersion, which has the advantages of environmental optimization, low cost and easy scalability. Furthermore, the lithium concentration gradient layer can suppress the transformation of the layered structure to the spinel structure, significantly improving the thermal stability of the structure. At the same time, it achieves high rate performance, suppresses voltage decay and has excellent long-term stability.

[0115] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a lithium concentration gradient lithium-rich manganese-based positive electrode material, comprising the following steps: mixing the lithium-rich manganese-based positive electrode material and a modifier, and calcining the mixture in an inert atmosphere to obtain a coated modified positive electrode material; and performing pure water ultrasonic treatment on the coated modified positive electrode material, and drying to obtain the lithium concentration gradient lithium-rich manganese-based positive electrode material; the modifier can react with Li to form a lithium salt that is easily soluble in water.

2. The production method according to claim 1, wherein, the modifier comprises any one or a combination of oxalic acid, molybdenum oxide, silicon oxide or tungsten oxide.

3. The production method according to claim 1 or 2, wherein the amount of the modifier is 2-8 wt% of the lithium-rich manganese-based positive electrode material.

4. The production process according to any one of claims 1 to 3, wherein the calcination temperature is 300-500℃. Optionally, the calcination time is 2-6 h.

5. The production process according to any one of claims 1 to 4, wherein the solid-liquid mass ratio of the pure water ultrasonic treatment is 1:(1-4). Optionally, the pure water ultrasonic treatment time is 0.5-2 h.

6. The method of making according to any one of claims 1-5, wherein, the method for preparing the lithium-rich manganese-based positive electrode material comprises the following steps: mixing a lithium source and a lithium-rich manganese-based hydroxide precursor, and heat treating the mixture to obtain the lithium-rich manganese-based positive electrode material.

7. The production method according to claim 6, wherein the molar ratio of lithium in the lithium source to the lithium-rich manganese-based hydroxide precursor is (1.3-1.6):

1. Optionally, the lithium source comprises lithium carbonate and / or lithium hydroxide.

8. The production method according to claim 6 or 7, wherein the heat treatment comprises pre-burning and calcining in sequence. Optionally, the pre-burning temperature is 450-550℃, and the time is 4.5-5.5 h. Optionally, the calcining temperature is 800-1000℃, and the time is 10-14 h.

9. The method of making according to any one of claims 6-8, wherein, The lithium-rich manganese-based hydroxide precursor has a chemical formula of Ni x Co y Mn 1-x-y (OH)2, wherein 0.3≤x≤0.4, 0≤y≤0.1, and 0.3≤x+y≤0.

5. Optionally, the lithium-rich manganese-based hydroxide precursor has a chemical formula of Ni 0.4 Mn 0.6 (OH)2.

10. The production method according to claim 1, wherein, the method comprises the following steps: (1) mixing a lithium source and a lithium-rich manganese-based hydroxide precursor, and heat treating the mixture to obtain the lithium-rich manganese-based positive electrode material; The lithium-rich manganese-based hydroxide precursor has a chemical formula of Ni x Co y Mn 1-x-y (OH)2, wherein 0.3≤x≤0.4, 0≤y≤0.1, and 0.3≤x+y≤0.

5. the molar ratio of lithium in the lithium source to the lithium-rich manganese-based hydroxide precursor is (1.3-1.6):

1. the heat treatment comprises pre-burning and calcining in sequence; the pre-burning temperature is 450-550℃, and the time is 4.5-5.5 h; and the calcining temperature is 800-1000℃, and the time is 10-14 h; (2) mixing the lithium-rich manganese-based positive electrode material and a modifier, and calcining the mixture in an inert atmosphere at 300-500℃ for 2-6 h to obtain a coated modified positive electrode material; the modifier can react with Li to form a lithium salt that is easily soluble in water, and the amount of the modifier is 2-8 wt% of the lithium-rich manganese-based positive electrode material; (3) performing pure water ultrasonic treatment on the coated modified positive electrode material for 0.5-2 h, and drying to obtain the lithium concentration gradient lithium-rich manganese-based positive electrode material; the solid-liquid mass ratio of the pure water ultrasonic treatment is 1:(1-4). 11.A lithium concentration gradient lithium-rich manganese-based positive electrode material prepared by the method of any one of claims 1-10. 12.A lithium ion battery comprising the lithium concentration gradient lithium-rich manganese-based positive electrode material of claim 11.

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