Monocrystal lithium-manganese-rich positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to a single-crystal lithium-manganese-rich positive electrode material as well as a preparation method and application thereof. The single-crystal lithium-manganese-rich positive electrode material comprises a lithium-manganese-rich positive electrode material inner layer and a fast lithium ion conductor coating layer coating the surface of the lithium-manganese-rich positive electrode material, the lithium-rich manganese positive electrode material inner layer sequentially comprises a main body layer, an oxygen vacancy layer and a spinel layer from the center to the outside. The invention provides a single-crystal lithium-manganese-rich positive electrode material and an in-situ multiple synergistic modification method thereof, a precursor is prepared by a sol-gel method, a modifier is added for secondary sintering, controllable preparation of the single-crystal lithium-manganese-rich positive electrode material is realized, the lithium-manganese-rich positive electrode material on the inner layer sequentially comprises a main body layer, an oxygen vacancy layer and a spinel layer from the center to the outside, and the main body layer and the oxygen vacancy layer are uniformly distributed. The lithium ion transmission efficiency is further improved, and the first discharge specific capacity, the first coulombic efficiency and the cycling stability of the single crystal lithium-rich manganese positive electrode material are obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a single-crystal lithium-manganese-rich positive electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of electric vehicles and portable electronic devices, there is an increasing demand for high-performance lithium-ion batteries with high energy density, high safety, and low cost. The cathode material is one of the main determining factors. Lithium-rich manganese-rich cathode materials have become promising candidates for next-generation cathode materials due to their high specific capacity (≥250mAh / g, 0.1C), high operating voltage (≥3.6V), relatively high safety, and low cost. However, the unique initial activation mechanism of lithium-rich manganese-rich cathode materials leads to low initial coulombic efficiency, poor rate capability, continuous structural degradation, and voltage decay during cycling, which limits the promotion and application of this material.

[0003] Numerous studies have found that the performance degradation of lithium-rich manganese cathode materials is caused by surface transition metal migration, structural rearrangement, and side reactions. Therefore, current performance improvements for lithium-rich manganese cathode materials at home and abroad are mainly focused on surface modification. Currently, common lithium-rich manganese cathode materials are secondary spherical particles formed by the accumulation of primary particles. They have low mechanical strength and intergranular cracks will appear inside the particles during the cycle. Surface modification is only effective on the outer surface of the secondary particles, and the surface of most primary particles cannot be effectively modified, resulting in limited performance improvements for the final material. Single crystal materials have high mechanical strength, no internal grain boundaries or phase boundaries, small specific surface area, and the surface is exposed to the outside, making it easy to achieve effective surface modification.

[0004] CN116632218A and CN108557905A respectively disclose Ni 0.13 Co 0.13 Mn 0.54 The methods for preparing single-crystalline lithium-rich manganese positive electrode materials using (OH)2 and carbonate precursors are all based on the traditional co-precipitation route. The prepared single crystal particles have a large particle size (>1μm) and an uneven particle size distribution, which limits the application of lithium-rich manganese positive electrode materials with poor electronic and ionic conductivity.

[0005] CN109244397A discloses lithium vanadium phosphate / lithium manganese phosphate coated lithium-rich manganese-based positive electrode materials, which improves the cyclic stability of the material. This method is based on the coating modification of polycrystalline particle secondary balls, and its effect has certain limitations. In addition, based on the defects of the lithium-rich manganese positive electrode material itself, the simple lithium ion conductor coating has limited improvement on the comprehensive electrochemical performance of the material.

[0006] CN119092675A discloses a multi-layer coated lithium-rich manganese positive electrode material and its preparation method. The first coating layer is O2-type lithium nickel manganese oxide, and the second coating layer is cobalt boride. It can improve the mechanical toughness of the lithium-rich manganese positive electrode material and alleviate irreversible phase transitions. This type of method increases manufacturing difficulty and cost through multiple coating and calcination, and cannot fully overcome the inherent defects of lithium-rich manganese positive electrode materials.

[0007] In summary, due to the inherent defects of lithium-rich manganese positive electrode materials, the single functional surface modification based on polycrystalline particles has limited effect. How to provide a single crystal lithium-rich manganese positive electrode material with uniform and small particle size and a multiple composite modification method with simple process has become a problem that needs to be solved urgently. Summary of the Invention

[0008] In order to solve the above technical problems, the purpose of the present invention is to provide a single crystal lithium-rich manganese positive electrode material and its preparation method and application. The single crystal lithium-rich manganese positive electrode material of the present invention is modified through in-situ multiple synergistic modifications to achieve the effect of improving the first coulombic efficiency and cycle stability of the single crystal lithium-rich manganese positive electrode material while improving its first charge and discharge specific capacity.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a single crystal lithium-rich manganese positive electrode material, which includes an inner layer of a lithium-rich manganese positive electrode material and a fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; the inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside.

[0011] The single-crystal lithium-rich manganese cathode material provided by the present invention has a core-shell structure. First, the submicron single crystal structure shortens the lithium ion diffusion path. Second, a fast lithium ion conductor layer is formed on its outermost surface, and oxygen-consuming ions decompose and oxygen-absorb oxygen-inducing to form a spinel layer and an oxygen vacancy layer in the inner layer, further improving the lithium ion transmission efficiency, so that the comprehensive electrochemical performance of the single-crystal lithium-rich manganese cathode material, such as the first discharge specific capacity, the first coulomb efficiency and the cycle performance, is significantly improved.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] Preferably, the chemical formula of the inner layer of the single crystal lithium-rich manganese positive electrode material is xLi2MnO3·(1-x)LiMO2, wherein M includes Ni a 、Co b or Mn cAny one or a combination of at least two of them, 0.1 ≤ x < 0.5, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1;

[0014] Preferably, the chemical formula of the inner layer of the single-crystal lithium-rich manganese cathode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0015] Preferably, the fast lithium-ion conductor coating layer includes any one or a combination of at least two of lithium vanadium phosphate, lithium niobate or lithium tungstate. Typical but non-limiting combinations include the combination of lithium vanadium phosphate and lithium niobate, the combination of lithium niobate and lithium tungstate, the combination of lithium vanadium phosphate and lithium tungstate, and the combination of lithium vanadium phosphate, lithium niobate and lithium tungstate.

[0016] In a second aspect, the present invention provides a method for preparing the single-crystal lithium-rich manganese cathode material as described in the first aspect. The preparation method includes the following steps:

[0017] (1) Mix the transition metal source solution, lithium salt solution and complexing agent, adjust the pH, heat the reaction, cool and perform a first calcination to obtain a first calcined oxide;

[0018] (2) Mix the first calcined oxide and a modifier, and perform a second calcination to obtain the single-crystal lithium-rich manganese cathode material.

[0019] The present invention first prepares a sol-gel precursor and adopts a process of first calcination → introducing a modifier → second calcination. Compared with the conventional method of preparing a precursor by co-precipitation, it is easier to control the particle size of single-crystal particles;

[0020] On the other hand, after the first calcination, a modifier is introduced and a second calcination is performed to achieve the preparation and surface in-situ multiple synergistic modification of the single-crystal lithium-rich manganese cathode material. The modifier decomposes to form a fast lithium-ion conductor layer on the surface, and the oxygen-consuming ions in the modifier decompose to夺取 oxygen and induce the formation of a spinel layer and an oxygen vacancy layer in the inner layer, stabilizing the material structure and improving the lithium-ion transport efficiency;

[0021] In addition, the preparation method of the present invention realizes in-situ multiple synergistic modification during the preparation process, has a short process flow, and is beneficial to industrial production and commercial application.

[0022] Preferably, the transition metal source solution in step (1) includes nickel salt, cobalt salt, manganese salt, water and ethanol.

[0023] Preferably, the nickel salt, cobalt salt, manganese salt includes any one of nitrate, acetate or oxalate or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrate and acetate, a combination of acetate and oxalate, a combination of nitrate and oxalate, and a combination of nitrate, acetate and oxalate.

[0024] Preferably, the lithium salt solution comprises lithium salt, water and ethanol.

[0025] Preferably, the lithium salt includes any one or a combination of at least two of lithium nitrate, lithium carbonate or lithium hydroxide. Typical but non-limiting combinations include a combination of lithium nitrate and lithium carbonate, a combination of lithium carbonate and lithium hydroxide, a combination of lithium nitrate and lithium hydroxide, and a combination of lithium nitrate, lithium carbonate and lithium hydroxide.

[0026] Preferably, the complexing agent comprises any one of citric acid, ethylenediaminetetraacetic acid or glycolic acid or a combination of at least two thereof. Typical but non-limiting combinations include a combination of citric acid and ethylenediaminetetraacetic acid, a combination of ethylenediaminetetraacetic acid and glycolic acid, a combination of citric acid and glycolic acid, and a combination of citric acid, ethylenediaminetetraacetic acid and glycolic acid.

[0027] Preferably, the pH adjustment process includes adding ammonia water to adjust the pH to 7.0-9.0, for example, 7.0, 7.5, 8.0, 8.5 or 9.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the heating temperature is 60°C-90°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, step (1) further includes drying after cooling and before the first calcination.

[0030] Preferably, the drying temperature is 100°C-120°C, for example, 100°C, 105°C, 110°C, 115°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the temperature of the primary calcination is 350°C-550°C, for example, 350°C, 380°C, 400°C, 420°C, 450°C, 480°C, 500°C, 520°C or 550°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the primary calcination time is 4 h-6 h, for example, 4 h, 4.5 h, 5 h, 5.5 h or 6 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, step (1) is accompanied by stirring during the mixing, pH adjustment and heating stages.

[0034] Preferably, the structural formula of the modifier in step (2) includes an oxygen-consuming group and a group that combines with lithium to form a fast lithium ion conductor.

[0035] Preferably, the modifier includes any one or a combination of at least two of ammonium tungstate, niobium ethoxide, or a mixture of ammonium metavanadate and ammonium dihydrogen phosphate. Typical but non-limiting combinations include a combination of ammonium tungstate and niobium ethoxide, a combination of niobium ethoxide and a mixture of ammonium metavanadate and ammonium dihydrogen phosphate, a combination of ammonium tungstate and a mixture of ammonium metavanadate and ammonium dihydrogen phosphate, and a combination of ammonium tungstate, niobium ethoxide, ammonium metavanadate, and a mixture of ammonium dihydrogen phosphate.

[0036] In the present invention, the modifier is preferably selected from a mixture of ammonium tungstate, niobium ethoxide or ammonium metavanadate and ammonium dihydrogen phosphate, wherein the ammonium ion and the ethoxy group are oxygen-consuming parts, ammonium tungstate reacts with the primary calcined oxide to produce lithium tungstate, niobium ethoxide reacts with the primary calcined oxide to produce lithium niobate, and ammonium metavanadate and ammonium dihydrogen phosphate react with the primary calcined oxide to produce lithium vanadium phosphate.

[0037] Preferably, the amount of the modifier added is 1.0wt.%-5.0wt.% of the mass of the lithium-rich manganese positive electrode material. For example, it can be 1.0wt.%, 1.5wt.%, 2wt.%, 2.5wt.%, 3wt.%, 3.5wt.%, 4wt.%, 4.5wt.% or 5.0wt.%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0038] The present invention further controls the amount of the modifier added to be 1.0wt.%-5.0wt.% of the mass of the lithium-rich manganese positive electrode material. The amount of the modifier added affects the thickness of the multiple modified layers. If the amount of the modifier added is too much, the structure of the main lithium-rich manganese positive electrode material is destroyed, reducing the material capacity. If the amount of the modifier added is too little, the modification effect is insufficient and the performance improvement is limited.

[0039] Preferably, the mixing in step (2) comprises ball milling mixing.

[0040] Preferably, the ball milling speed is 500 rpm-700 rpm, for example, 500 rpm, 550 rpm, 600 rpm, 650 rpm or 700 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] In the present invention, by further controlling the rotation speed and time of ball milling, the controllable preparation of single-crystalline lithium-rich manganese cathode materials with uniform particle size can be achieved, especially the preparation of single-crystalline lithium-rich manganese cathode materials with small particle size (submicron level) can be achieved; if the rotation speed of the ball milling is too low or the ball milling time is too short, single-crystalline particles with good dispersion cannot be prepared; if the rotation speed of the ball milling is too high or the ball milling time is too long, the structure of the single-crystalline particles is further destroyed, and free chips appear.

[0042] Preferably, the ball milling time is 2 h-10 h, for example, 2 h, 5 h, 6 h, 8 h or 10 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, the temperature of the secondary calcination is 750°C-950°C, for example, 750°C, 800°C, 850°C, 900°C or 950°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] The present invention further controls the temperature of the secondary calcination to 750°C-950°C, and through secondary sintering, realizes the preparation of a single-crystal lithium-rich manganese positive electrode material and performs in-situ multiple synergistic modifications on its surface. The modifier decomposes to form a fast lithium ion conductor layer on the surface, and the oxygen-consuming ions decompose to extract oxygen and induce the formation of a spinel layer and an oxygen vacancy layer in the inner layer. If the temperature of the secondary sintering is too low, the material is insufficiently lithiated and the capacity decreases. If the temperature of the secondary sintering is too high, the single crystal particles continue to grow, increasing the lithium ion diffusion distance.

[0045] Preferably, the secondary calcination time is 10 h-18 h, for example, 10 h, 12 h, 14 h, 16 h or 18 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0047] (1) nickel salt, cobalt salt, manganese salt, water and ethanol are mixed in a stoichiometric ratio to obtain solution A; lithium salt and complexing agent are dissolved in water and ethanol to obtain solution B;

[0048] (2) slowly adding solution A to solution B to obtain a mixed solution C, adding aqueous ammonia to adjust the pH of the mixed solution C to 7.0-9.0, heating the mixed solution at 60°C-90°C under stirring to form a sol, cooling the sol to room temperature to form a gel, and drying the gel at 100°C-120°C to obtain a sol-gel precursor;

[0049] (3) Under an oxygen atmosphere, the sol-gel precursor is calcined at 350°C-550°C for 4h-6h to obtain a calcined oxide;

[0050] (4) ball milling the primary calcined oxide and the modifier at a rotation speed of 500 rpm-700 rpm, and after ball milling for 2 h-10 h to mix evenly, the mixture is secondary calcined at 750 ° C-950 ° C in an oxygen atmosphere for 10 h-18 h to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of the modifier added is 1.0 wt.%-5.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

[0051] In a third aspect, the present invention provides a positive electrode plate, which includes the single crystal lithium-rich manganese positive electrode material described in the first aspect.

[0052] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0053] The lithium ion battery provided by the present invention has higher initial discharge specific capacity, initial coulombic efficiency and more excellent cycle performance.

[0054] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) The single-crystal lithium-rich manganese cathode material provided by the present invention has a core-shell structure. First, the single-crystal structure shortens the lithium ion diffusion path. Second, a fast lithium ion conductor layer is formed on its outermost surface, and oxygen-consuming ions decompose and oxygen-deprive to induce the formation of a spinel layer and an oxygen vacancy layer in the inner layer, further improving the lithium ion transmission efficiency, so that the comprehensive electrochemical performance of the single-crystal lithium-rich manganese cathode material, such as the first discharge specific capacity, the first coulomb efficiency and the cycle performance, is significantly improved.

[0057] (2) The present invention first prepares a sol-gel precursor, and adopts a process of one calcination → introduction of a modifier → secondary calcination, which has the advantages of a short process flow and easy control of the single crystal particle size; after the one calcination, the modifier is introduced, and after the secondary calcination, the preparation of the single crystal lithium-rich manganese positive electrode material and the in-situ multiple synergistic modification of the surface are achieved. The modifier decomposes to form a fast lithium ion conductor layer on the surface, and at the same time, the modifier decomposes oxygen-consuming ions to induce oxygen to form a spinel layer and an oxygen vacancy layer in the inner layer. The spinel phase stabilizes the material structure, and the oxygen vacancies improve the lithium ion transmission capacity. The preparation method of the present invention realizes in-situ multiple synergistic modifications during the preparation process, with a short process flow, which is conducive to industrial production and commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1This is a process flow chart of the method for preparing a single crystal lithium-rich manganese positive electrode material provided in Example 1 of the present invention;

[0059] Figure 2 This is a scanning electron microscope image of the lithium-rich manganese positive electrode material prepared in Example 1 of the present invention;

[0060] Figure 3 This is a transmission electron microscope image of the lithium-rich manganese positive electrode material prepared in Example 1 of the present invention;

[0061] Figure 4 1 is a graph showing the first charge and discharge curves of the lithium-rich manganese cathode materials prepared in Example 1 and Comparative Example 1 of the present invention;

[0062] Figure 5 1 is a cycle curve diagram of the lithium-rich manganese positive electrode material prepared in Example 1 of the present invention and Comparative Example 1.

[0063] Figure 6 This is a scanning electron microscope image of the lithium-rich manganese positive electrode material prepared using a commercial co-precipitation precursor in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0064] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0065] In the following examples and comparative examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0066] Example 1

[0067] This embodiment provides a single crystal lithium-rich manganese positive electrode material, wherein the single crystal lithium-rich manganese positive electrode material comprises Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 An O2 inner layer and a lithium vanadium phosphate fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; the inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside;

[0068] The method for preparing the single crystal lithium-rich manganese positive electrode material provided in this embodiment includes the following steps:

[0069] (1) Dissolve 12.42 g of manganese acetate tetrahydrate, 3.03 g of nickel acetate tetrahydrate, and 3.04 g of cobalt acetate tetrahydrate in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) in a molar ratio of Mn:Co:Ni=54:13:13 to obtain solution A; dissolve 4.16 g of lithium carbonate and 21.28 g of citric acid in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL), and add nitric acid until no bubbles are generated to obtain solution B;

[0070] (2) Under stirring conditions, solution A was slowly added to solution B to obtain a mixed solution C, ammonia was added to adjust the pH of the mixed solution C to 8.5, and the solution was heated at 80°C to form a sol. The sol was cooled to room temperature to form a gel, and the gel was dried at 120°C for 12 hours to obtain a sol-gel precursor.

[0071] (3) Under an oxygen atmosphere, the sol-gel precursor is calcined at 450 °C for 5 h to obtain a calcined oxide;

[0072] (4) The primary calcined oxide, 0.03 g of ammonium metavanadate and 0.03 g of ammonium dihydrogen phosphate were mixed by ball milling at a rotation speed of 500 rpm. After ball milling for 8 h to mix evenly, the mixture was secondary calcined at 900 ° C for 12 h in an oxygen atmosphere to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of ammonium metavanadate and ammonium dihydrogen phosphate added was 2.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

[0073] The scanning electron microscope images and transmission electron microscope images of the prepared single crystal lithium-rich manganese cathode material are shown in Figure 2. Figure 2 and Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that the outermost layer of the material is a fast lithium ion conductor lithium vanadium phosphate coating layer, the second outermost layer of the material is a spinel layer, the third layer is an oxygen vacancy layer, and the innermost layer is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 main structure.

[0074] The first charge and discharge curve of the prepared single crystal lithium-rich manganese cathode material is shown in the figure below: Figure 4 As shown, from Figure 4 It can be seen that the discharge specific capacity of the obtained material is 292.2 mAh / g.

[0075] The cycle diagram of the prepared single crystal lithium-rich manganese cathode material is shown in Figure 5 As shown, from Figure 5 It can be seen that the first coulombic efficiency is 81.0%, and the capacity retention rate after 100 cycles at 1.0C is 89.8%.

[0076] Example 2

[0077] This embodiment provides a single crystal lithium-rich manganese positive electrode material, wherein the single crystal lithium-rich manganese positive electrode material comprises Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 An O2 inner layer and a lithium vanadium phosphate fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; the inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside;

[0078] The method for preparing the single crystal lithium-rich manganese positive electrode material provided in this embodiment includes the following steps:

[0079] (1) Dissolve 12.72 g of manganese nitrate hexahydrate, 3.54 g of nickel nitrate hexahydrate, and 3.55 g of cobalt nitrate hexahydrate in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) in a molar ratio of Mn:Co:Ni=54:13:13 to obtain solution A; dissolve 7.76 g of lithium carbonate and 20.62 g of glycolic acid in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) to obtain solution B;

[0080] (2) Under stirring conditions, solution A was slowly added to solution B to obtain a mixed solution C, ammonia was added to adjust the pH of the mixed solution C to 7.0, and the solution was heated at 60°C to form a sol. The sol was cooled to room temperature to form a gel. The gel was dried at 120°C for 12 hours to obtain a sol-gel precursor.

[0081] (3) Under an oxygen atmosphere, the sol-gel precursor was calcined at 350 °C for 4 h to obtain a calcined oxide;

[0082] (4) The primary calcined oxide, 0.03 g of ammonium metavanadate and 0.03 g of ammonium dihydrogen phosphate were mixed by ball milling at a rotation speed of 500 rpm, and after ball milling for 2 h to mix evenly, the mixture was secondary calcined at 750 ° C for 10 h in an oxygen atmosphere to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of the modifier added was 1.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

[0083] Example 3

[0084] This embodiment provides a single crystal lithium-rich manganese positive electrode material, wherein the single crystal lithium-rich manganese positive electrode material comprises Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 An O2 inner layer and a lithium vanadium phosphate fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; the inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside;

[0085] The method for preparing the single crystal lithium-rich manganese positive electrode material provided in this embodiment includes the following steps:

[0086] (1) 9.07 g of manganese oxalate dihydrate, 2.23 g of nickel nitrate hexahydrate, and 2.23 g of cobalt nitrate hexahydrate were dissolved in water and ethanol (the volume ratio of water to ethanol was 20 mL:20 mL) in a molar ratio of Mn:Co:Ni=54:13:13 to obtain solution A; 4.72 g of lithium carbonate and 15.30 g of glycolic acid were dissolved in water and ethanol (the volume ratio of water to ethanol was 20 mL:20 mL) to obtain solution B;

[0087] (2) Under stirring conditions, solution A was slowly added to solution B to obtain a mixed solution C, ammonia was added to adjust the pH of the mixed solution C to 7.5, and the solution was heated at 70°C to form a sol. The sol was cooled to room temperature to form a gel. The gel was dried at 120°C for 12 hours to obtain a sol-gel precursor.

[0088] (3) Under an oxygen atmosphere, the sol-gel precursor is calcined at 400 °C for 6 h to obtain a calcined oxide;

[0089] (4) The primary calcined oxide, 0.03 g of ammonium metavanadate and 0.03 g of ammonium dihydrogen phosphate were mixed by ball milling at a rotation speed of 500 rpm, and after ball milling for 4 hours to mix evenly, the mixture was secondary calcined at 800 ° C for 14 hours in an oxygen atmosphere to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of the modifier added was 3.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

[0090] Example 4

[0091] This embodiment provides a single crystal lithium-rich manganese positive electrode material, wherein the single crystal lithium-rich manganese positive electrode material comprises Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 An O2 inner layer and a lithium tungstate fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; the inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside;

[0092] The method for preparing the single crystal lithium-rich manganese positive electrode material provided in this embodiment includes the following steps:

[0093] (1) Dissolve 12.42 g of manganese acetate tetrahydrate, 3.03 g of nickel acetate tetrahydrate, and 3.04 g of cobalt acetate tetrahydrate in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) in a molar ratio of Mn:Co:Ni=54:13:13 to obtain solution A; dissolve 4.16 g of lithium carbonate and 21.28 g of citric acid in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) to obtain solution B;

[0094] (2) Under stirring conditions, solution A was slowly added to solution B to obtain a mixed solution C, ammonia was added to adjust the pH of the mixed solution C to 8.0, and the solution was heated at 90°C to form a sol. The sol was cooled to room temperature to form a gel. The gel was dried at 120°C for 12 hours to obtain a sol-gel precursor.

[0095] (3) Under an oxygen atmosphere, the sol-gel precursor is calcined at 500 °C for 5 h to obtain a calcined oxide;

[0096] (4) The primary calcined oxide and 0.09 g of ammonium tungstate were mixed by ball milling at a rotation speed of 600 rpm, and after being evenly mixed by ball milling for 6 hours, the mixture was secondary calcined at 850 ° C for 16 hours in an oxygen atmosphere to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of the modifier added was 2.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

[0097] Example 5

[0098] This embodiment provides a single crystal lithium-rich manganese positive electrode material, wherein the single crystal lithium-rich manganese positive electrode material comprises Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 An O2 inner layer and a lithium niobate fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; the inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside;

[0099] The method for preparing the single crystal lithium-rich manganese positive electrode material provided in this embodiment includes the following steps:

[0100] (1) Dissolve 12.42 g of manganese acetate tetrahydrate, 3.03 g of nickel acetate tetrahydrate, and 3.04 g of cobalt acetate tetrahydrate in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) in a molar ratio of Mn:Co:Ni=54:13:13 to obtain solution A; dissolve 4.16 g of lithium carbonate and 21.28 g of citric acid in water and ethanol (the volume ratio of water to ethanol is 20 mL:20 mL) to obtain solution B;

[0101] (2) Under stirring conditions, solution A was slowly added to solution B to obtain a mixed solution C, ammonia was added to adjust the pH of the mixed solution C to 8.0, and the solution was heated at 80°C to form a sol. The sol was cooled to room temperature to form a gel. The gel was dried at 120°C for 12 hours to obtain a sol-gel precursor.

[0102] (3) Under an oxygen atmosphere, the sol-gel precursor was calcined at 580 °C for 5 h to obtain a calcined oxide;

[0103] (4) The primary calcined oxide and 0.10 g of niobium ethanol were mixed by ball milling at a rotation speed of 700 rpm, and after being evenly mixed by ball milling for 6 h, the mixture was secondary calcined at 850 ° C for 16 h in an oxygen atmosphere to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of the modifier added was 2.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

[0104] Example 6

[0105] This embodiment provides a single crystal lithium-rich manganese positive electrode material, which differs from Example 1 only in that, when preparing the single crystal lithium-rich manganese positive electrode material, the amount of the modifiers ammonium metavanadate and ammonium dihydrogen phosphate added in step (4) is 0.5 wt.% of the mass of the lithium-rich manganese positive electrode material, and the other steps remain unchanged.

[0106] Example 7

[0107] This embodiment provides a single crystal lithium-rich manganese positive electrode material, which differs from Example 1 only in that, when preparing the single crystal lithium-rich manganese positive electrode material, the amount of the modifiers ammonium metavanadate and ammonium dihydrogen phosphate added in step (4) is 8 wt.% of the mass of the lithium-rich manganese positive electrode material, and the other steps remain unchanged.

[0108] Example 8

[0109] This embodiment provides a single crystal lithium-rich manganese positive electrode material, which differs from Example 1 only in that, when preparing the single crystal lithium-rich manganese positive electrode material, the ball milling speed in step (4) is changed from 500 rpm to 200 rpm, and the other steps remain unchanged.

[0110] Example 9

[0111] This embodiment provides a single crystal lithium-rich manganese positive electrode material, which differs from Example 1 only in that, when preparing the single crystal lithium-rich manganese positive electrode material, the calcination temperature in step (4) is changed from 900° C. to 650° C., and the other steps remain unchanged.

[0112] Comparative Example 1

[0113] This comparative example provides a single crystal lithium-rich manganese positive electrode material, which differs from Example 1 only in that no modifier is added in step (2) when preparing the single crystal lithium-rich manganese positive electrode material.

[0114] Comparative Example 2

[0115] This comparative example provides a single crystal lithium-rich manganese positive electrode material, which differs from Example 1 only in that when preparing the single crystal lithium-rich manganese positive electrode material, steps (1) and (2) are not performed, and the sol-gel precursor in step (3) is replaced by a coprecipitation precursor.

[0116] The scanning electron microscope image of the prepared lithium-rich manganese cathode material is as follows Figure 6As shown in the figure, it can be seen that the particle size distribution of single crystal particles is extremely uneven and the dispersion is poor.

[0117] Test method: The single crystal lithium-rich manganese positive electrode material prepared in the embodiment and the comparative example was assembled into a button battery, and the negative electrode was a lithium sheet; the electrolyte was a 1.15M LiPF6 ethyl carbonate + dimethyl carbonate (volume ratio 1:1) solution; its first discharge specific capacity (0.1C, 2.0~4.8V), first coulombic efficiency (0.1C, 2.0~4.8V) and cycle stability (1.0C, 2.0~4.8V) were tested. The test results are shown in Table 1 below.

[0118] Table 1

[0119]

[0120] The test results show that:

[0121] (1) It can be seen from Examples 1 to 5 that the present invention provides a single crystal lithium-rich manganese cathode material and an in-situ multiple synergistic modification method thereof, wherein a precursor is prepared by a sol-gel method, a modifier is added to the precursor after a single calcination and ball milling dispersion is performed to achieve a single crystal Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is controllably prepared and in-situ multiple synergistic modifications are performed on its surface to obtain a single crystal lithium-rich manganese positive electrode material with a lithium-rich manganese positive electrode material as the inner layer and a fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material. Among them, the inner layer of the lithium-rich manganese positive electrode material is composed of a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside, which further improves the lithium ion transmission efficiency and achieves a significant improvement in the first discharge specific capacity, first coulomb efficiency and cycle stability of the single crystal lithium-rich manganese positive electrode material.

[0122] (2) By comparing Example 1 with Example 6-Example 7, it can be seen that the present invention further controls the amount of the added modifier to be 1.0wt.%-5.0wt.% of the mass of the lithium-rich manganese positive electrode material. The amount of the added modifier affects the thickness of the multiple modified layers; if the amount of the modifier added is too much, the structure of the main lithium-rich manganese positive electrode material is destroyed, and the material capacity is reduced; if the amount of the modifier added is too little, the modification effect is insufficient and the performance improvement is limited.

[0123] (3) By comparing Example 1 with Example 8, it can be seen that the present invention can achieve single crystal Li with uniform particle size by further controlling the rotation speed and time of ball milling. 1.2 Ni 0.13 Co 0.13 Mn 0.54 Controllable preparation of O2, especially the realization of small particle size (submicron level) single crystal Li 1.2 Ni0.13 Co 0.13 Mn 0.54 Preparation of O2; if the ball milling speed is too low or the ball milling time is too short, single crystal particles with good dispersion cannot be prepared; if the ball milling speed is too high or the ball milling time is too long, the single crystal particle structure will be further destroyed and free chips will appear.

[0124] (4) By comparing Example 1 with Example 9, it can be seen that the present invention further controls the temperature of the secondary calcination to 750°C-950°C, and realizes the preparation of single-crystalline lithium-rich manganese positive electrode material through secondary sintering and performs in-situ multiple synergistic modification on its surface. The modifier decomposes to form a fast lithium ion conductor layer on the surface, and the oxygen-consuming ions decompose and deprive oxygen to induce the formation of a spinel layer and an oxygen vacancy layer in the inner layer; if the temperature of the secondary sintering is too low, the material is insufficiently lithiated and the capacity decreases; if the temperature of the secondary sintering is too high, the single crystal particles continue to grow, increasing the lithium ion diffusion distance.

[0125] (5) It can be seen from Example 1 and Comparative Example 1 that the present invention introduces a modifier and performs secondary sintering to achieve the preparation of a single-crystal lithium-rich manganese positive electrode material and performs in-situ multiple synergistic modifications on its surface. The modifier decomposes to form a fast lithium ion conductor layer on the surface, and the oxygen-consuming ions decompose and oxygen-induce to form a spinel layer and an oxygen vacancy layer in the inner layer, thereby improving the comprehensive electrochemical properties of the material, such as the first discharge specific capacity, the first coulomb efficiency and the cycle performance.

[0126] (6) Through Example 1 and Comparative Example 2 and Figure 2 and Figure 6 It can be seen that the present invention prepares the precursor by the sol-gel method. Compared with the conventional co-precipitation method for preparing the precursor, the present invention is easier to control the size of the single crystal particles, thereby obtaining a higher first discharge specific capacity and better cycle stability.

[0127] In summary, the present invention provides a single crystal lithium-rich manganese cathode material and an in-situ multiple synergistic modification method thereof, wherein a precursor is prepared by a sol-gel method, a modifier is added to the precursor after a single calcination and ball milling dispersion is performed to achieve a single crystal Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is controllably prepared and in-situ multiple synergistic modifications are performed on its surface to obtain a single crystal lithium-rich manganese positive electrode material with a lithium-rich manganese positive electrode material as the inner layer and a fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material. Among them, the inner layer of the lithium-rich manganese positive electrode material is composed of a main layer, an oxygen vacancy layer and a spinel layer from the center to the outside, which further improves the lithium ion transmission efficiency and achieves a significant improvement in the first discharge specific capacity, first coulomb efficiency and cycle stability of the single crystal lithium-rich manganese positive electrode material.

[0128] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A single crystal lithium-rich manganese positive electrode material, characterized in that: The single crystal lithium-rich manganese positive electrode material comprises a lithium-rich manganese positive electrode material inner layer and a fast lithium ion conductor coating layer coated on the surface of the lithium-rich manganese positive electrode material; The inner layer of the lithium-rich manganese positive electrode material includes a main layer, an oxygen vacancy layer and a spinel layer in sequence from the center to the outside.

2. The single crystal lithium-rich manganese positive electrode material according to claim 1, characterized in that The chemical general formula of the inner layer of the single-crystal lithium-rich manganese cathode material is xLi2MnO3·(1-x)LiMO2, where M includes Ni a , Co b or Mn c or a combination of any one or at least two of them, 0.1≤x<0.5, 0<a<1, 0<b<1, 0<c<1, and a + b + c = 1. The fast lithium-ion conductor coating layer includes any one or a combination of at least two of lithium vanadium phosphate, lithium niobate or lithium tungstate.

3. A method for preparing a single crystal lithium-rich manganese positive electrode material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) mixing a transition metal source solution, a lithium salt solution and a complexing agent, adjusting the pH, heating for reaction, cooling and primary calcination to obtain a primary calcined oxide; (2) Mixing the primary calcined oxide and the modifier, and performing secondary calcination to obtain a single crystal lithium-rich manganese positive electrode material.

4. The preparation method according to claim 3, characterized in that The transition metal source solution in step (1) comprises a nickel salt, a cobalt salt, a manganese salt, water and ethanol, the lithium salt solution comprises a lithium salt, water and ethanol, the complexing agent comprises any one of citric acid, ethylenediaminetetraacetic acid or glycolic acid or a combination of at least two thereof, and the pH adjustment process comprises adding ammonia water to adjust the pH to 7.0-9.

0.

5. The preparation method according to claim 3 or 4, characterized in that The heating temperature is 60° C.-90° C., the primary calcination temperature is 350° C.-550° C., and the primary calcination time is 4 h-6 h.

6. The preparation method according to claim 3, characterized in that The structural formula of the modifier in step (2) includes an oxygen-consuming group and a group that combines with lithium to form a fast lithium ion conductor, and the modifier includes any one or a combination of at least two of ammonium tungstate, niobium ethanol or a mixture of ammonium metavanadate and ammonium dihydrogen phosphate, and the amount of the modifier added is 1.0wt.%-5.0wt.% of the mass of the lithium-rich manganese positive electrode material.

7. The preparation method according to claim 3, characterized in that The mixing in step (2) includes ball milling mixing, the temperature of the secondary calcination is 750° C.-950° C., and the time of the secondary calcination is 10 h-18 h.

8. The preparation method according to claim 3, characterized in that The preparation method comprises the following steps: (1) nickel salt, cobalt salt, manganese salt, water and ethanol are mixed in a stoichiometric ratio to obtain solution A; lithium salt and complexing agent are dissolved in water and ethanol to obtain solution B; (2) slowly adding solution A to solution B to obtain a mixed solution C, adding aqueous ammonia to adjust the pH of the mixed solution C to 7.0-9.0, heating the mixed solution at 60°C-90°C under stirring to form a sol, cooling the sol to room temperature to form a gel, and drying the gel at 100°C-120°C to obtain a sol-gel precursor; (3) Under an oxygen atmosphere, the sol-gel precursor is calcined at 350°C-550°C for 4h-6h to obtain a calcined oxide; (4) ball milling the primary calcined oxide and the modifier at a rotation speed of 500 rpm-700 rpm, and after ball milling for 2 h-10 h to mix evenly, the mixture is secondary calcined at 750 ° C-950 ° C in an oxygen atmosphere for 10 h-18 h to obtain a multi-modified single crystal lithium-rich manganese positive electrode material; the amount of the modifier added is 1.0 wt.%-5.0 wt.% of the mass of the lithium-rich manganese positive electrode material.

9. A positive electrode plate, characterized in that: The positive electrode plate comprises the single crystal lithium-rich manganese positive electrode material according to claim 1 or 2.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 9.

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