A lithium-rich manganese-based core-shell material, a preparation method and application thereof

Abstract

The present application belongs to the technical field of lithium ion batteries, and particularly relates to a lithium-rich manganese-based core-shell material, a preparation method and application thereof. The present application coats phosphate on a phase structure gradient lithium-rich manganese-based material, so that part of phosphate ions are doped into the surface layer of the phase structure gradient lithium-rich manganese-based material, the surface layer has more rhombic LiTMO2 phases, a stronger binding energy between transition metal cations and phosphate polyanions is formed, and thus the energy density of the lithium-rich manganese-based core-shell material is further improved. The present application coats an outer shell on an inner core, gradient setting is performed, lithium ion transmission is stably and quickly performed, and the conversion from a layered structure to a spinel structure caused by structural degradation is significantly reduced, and thus the cycle stability of the lithium-rich manganese-based core-shell material is improved. Therefore, the lithium-rich manganese-based core-shell material provided by the present application has high energy density, excellent cycle stability, discharge specific capacity and safety performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium-rich manganese-based core-shell material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high power, small size, and good cycle performance. However, with the development of electronic technology and electric vehicles, higher requirements are put forward for the performance of lithium-ion batteries. As an important component of lithium-ion batteries, the cathode material is closely related to the energy density of lithium-ion batteries. Lithium-rich manganese-based cathode materials are regarded as promising cathode materials because of their low cost and specific capacity higher than 300 mAhg -1 , high energy density. However, the interfacial reaction between lithium-rich manganese-based cathode materials and electrolytes, as well as the problem of oxygen release under high voltage, lead to the decline of the cycle stability of this material, thus limiting the commercial application of lithium-rich manganese-based cathode materials.

[0003] Among many modification methods of lithium-rich manganese-based cathode materials, surface coating of lithium-rich manganese-based cathode materials can effectively alleviate the lack of lattice oxygen on the surface of lithium-rich manganese-based cathode materials and the interfacial reaction between electrode materials. The coating layer physically isolates the cathode material and the electrolyte, inhibits the release of lattice oxygen on the surface of lithium-rich manganese-based cathode materials, and prevents side reactions between high-valent metal cations and reactive oxygen species on the material surface and the electrolyte. However, the first cycle performance of the modified lithium-rich manganese-based cathode material is poor, and the overall electrochemical performance is not good. Summary of the Invention

[0004] The purpose of the present invention is to provide a lithium-rich manganese-based core-shell material, a preparation method thereof, and an application thereof. The lithium-rich manganese-based core-shell material provided by the present invention has excellent electrochemical performance.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a lithium-rich manganese-based core-shell material, which includes a phase structure gradient lithium-rich manganese-based material and a shell covering the surface of the phase structure gradient lithium-rich manganese-based material; the general formula of the phase structure gradient lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiTMO2 - yLi2MnO3·(1 - y)LiTMO2, 0 < y < x < 1, where TM is one or more of Ni, Co, and Mn; the surface layer of the phase structure gradient lithium-rich manganese-based material is infiltrated with phosphate; the shell includes Li3P 1+a O4S 4a , 0 ≤ a ≤ 1.

[0007] Preferably, the phase structure gradient lithium-rich manganese-based material includes a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase; the content of the monoclinic Li2MnO3 phase decreases from the inside to the outside; and the content of the rhombic LiTMO2 phase increases from the inside to the outside.

[0008] Preferably, the content of the monoclinic Li2MnO3 phase decreases linearly from the inside to the outside; and the content of the rhombic LiTMO2 phase increases linearly from the inside to the outside.

[0009] Preferably, the phosphate is lithium phosphate; the mass ratio of the phosphate to the lithium-rich manganese-based material with phase structure gradient is 0.1 to 5:100.

[0010] Preferably, the content of S in the outer shell increases sequentially from the inside to the outside.

[0011] Preferably, the mass ratio of the phase structure gradient lithium-rich manganese-based material to the shell is 1000:5 to 20.

[0012] Preferably, the lithium-rich manganese-based core-shell material is spherical in shape with a particle size of 0.5–20 μm.

[0013] The present invention also provides a method for preparing the lithium-rich manganese-based core-shell material described above, comprising the following steps:

[0014] (1) A lithium-rich manganese-based material with phase structure gradient, lithium source, phosphorus source and complexing agent are mixed and subjected to complexation reaction and then sintered to obtain a preliminary lithium-rich manganese-based material.

[0015] (2) The preliminary lithium-rich manganese-based material and P4S 16 After mixing with an ether solvent and drying, the lithium-rich manganese-based core-shell material is obtained.

[0016] Preferably, the sintering temperature is 200–600°C, and the sintering time is 2–7 hours.

[0017] The present invention also provides the application of the lithium-rich manganese-based core-shell material described in the above-described scheme or the lithium-rich manganese-based core-shell material obtained by the preparation method described in the above-described scheme in the field of lithium-ion batteries.

[0018] This invention provides a lithium-rich manganese-based core-shell material. Using a phase-gradient lithium-rich manganese-based material as the core, and by controlling the phase-gradient gradient and coating the surface of the phase-gradient lithium-rich manganese-based material with phosphate, a high-energy-density lithium-rich manganese-based core-shell material is obtained in conjunction with the outer shell, exhibiting excellent cycle stability, discharge specific capacity, and safety performance.

[0019] In the present invention, by coating a phosphate on the phase structure gradient lithium-rich manganese-based material, some phosphate ions are doped into the surface layer of the phase structure gradient lithium-rich manganese-based material, combining with more rhombic LiTMO2 phases in the surface layer, forming a stronger binding bond energy between the transition metal cations (Ni, Co, Mn) and the polyanionic phosphate, thereby further improving the energy density of the lithium-rich manganese-based core-shell material and having a high capacity retention rate. In the present invention, by coating the inner core with an outer shell and setting a gradient, the lithium ions are transported stably and rapidly, and the transformation from layered to spinel-like caused by structural degradation is significantly reduced, thereby improving the cycle stability of the lithium-rich manganese-based core-shell material.

[0020] The present invention also provides a preparation method for the lithium-rich manganese-based core-shell material described in the above solution. The preparation method provided by the present invention has simple steps, convenient operation, low cost, and is suitable for industrial production.

[0021] The present invention also provides an application of the lithium-rich manganese-based core-shell material described in the above solution or the lithium-rich manganese-based core-shell material obtained by the preparation method described in the above solution in the field of lithium-ion batteries. The lithium-rich manganese-based core-shell material provided by the present invention has a high energy density, a high capacity retention rate, and good cycle performance, can meet the electrochemical performance requirements of lithium-ion batteries, is suitable as a battery cathode material, and has a broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 It is a schematic diagram of the lithium-rich manganese-based core-shell material prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The present invention provides a lithium-rich manganese-based core-shell material, including a phase structure gradient lithium-rich manganese-based material and an outer shell coated on the surface of the phase structure gradient lithium-rich manganese-based material; the general formula of the phase structure gradient lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiTMO2 - yLi2MnO3·(1 - y)LiTMO2, 0 < y < x < 1, where TM is one or more of Ni, Co, and Mn; the surface layer of the phase structure gradient lithium-rich manganese-based material is infiltrated with phosphate; the outer shell includes Li3P 1+a O4S 4a , 0 ≤ a ≤ 1.

[0025] The lithium-rich manganese-based core-shell material provided by the present invention includes a phase-structure gradient lithium-rich manganese-based material; the general formula of the phase-structure gradient lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiTMO2 (core center) - yLi2MnO3·(1 - y)LiTMO2 (core surface layer), where 0 < y < x < 1, and TM in the formula is one or more of Ni, Co, and Mn; the phase-structure gradient lithium-rich manganese-based material includes a monoclinic Li2MnO3 phase and a rhombohedral LiTMO2 phase; the content of the monoclinic Li2MnO3 phase preferably decreases sequentially from the inside to the outside, and more preferably decreases linearly from the inside to the outside; the content of the rhombohedral LiTMO2 phase preferably increases sequentially from the inside to the outside, and more preferably increases linearly from the inside to the outside. By adjusting the ratio of monoclinic Li2MnO3 and rhombohedral LiTMO2 from the inside to the outside as described above, the present invention improves the electrochemical properties such as the cycle stability, discharge specific capacity, and safety performance of the lithium-rich manganese-based core-shell material in a lithium-ion battery.

[0026] In the present invention, the phosphate is preferably lithium phosphate; the mass ratio of the phosphate to the phase-structure gradient lithium-rich manganese-based material is preferably 0.1 - 5:100, and specifically can be 0.1:100, 0.2:100, 0.3:100, 0.5:100, 0.8:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, or 5:100. By controlling the content of the phosphate, the thickness of the outer shell is adjusted during the preparation process. Through the setting of the phosphate, a small amount of phosphate ions are doped into the interior of the phase-structure gradient lithium-rich manganese-based material. Due to the strong binding bond energy between the phosphate polyanion and the transition metal cation (especially Ni), the energy density of the phase-structure gradient lithium-rich manganese-based material is increased; the doping of the phosphate polyanion enhances the binding bond energy between the cations of Ni and Co and the anions, and has almost no effect on the oxidation state of the Mn cation. Since the content of Co and Ni on the surface of the phase-structure gradient lithium-rich manganese-based material of the present invention is high and the content of Mn is reduced, the bonding energy between the phosphate polyanion and the transition metal will be greatly increased.

[0027] The lithium-rich manganese-based core-shell material provided by the present invention includes an outer shell; the Li3P 1+a O4S 4a represents the reaction product of P4S 16 and the phosphate, where the content of S changes in a gradient, that is, the content of the thiophosphate changes in a gradient.

[0028] In this invention, the S content in the shell preferably increases sequentially from the inside to the outside, and more preferably increases linearly from the inside to the outside. The shell of this invention has a gradient structure, which enables stable and rapid lithium-ion transport and significantly reduces the layered to spinel-like transformation caused by structural degradation, thereby improving the cycling stability of the material.

[0029] In this invention, the value of 'a' is preferably 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0030] In this invention, the mass ratio of the phase structure gradient lithium-rich manganese-based material to the shell is preferably 1000:5 to 20, specifically 1000:5, 1000:8, 1000:10, 1000:12, 1000:15, 1000:17 or 1000:20.

[0031] In this invention, the lithium-rich manganese-based core-shell material is preferably spherical in shape, and the particle size is preferably 0.5 to 20 μm, specifically 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm or 20 μm.

[0032] The present invention also provides a method for preparing the lithium-rich manganese-based core-shell material described above, comprising the following steps:

[0033] (1) A lithium-rich manganese-based material with phase structure gradient, lithium source, phosphorus source and complexing agent are mixed and subjected to complexation reaction and then sintered to obtain a preliminary lithium-rich manganese-based material.

[0034] (2) The preliminary lithium-rich manganese-based material and P4S 16 After mixing with an ether solvent and drying, the lithium-rich manganese-based core-shell material is obtained.

[0035] This invention involves mixing a phase-gradient lithium-rich manganese-based material, a lithium source, a phosphorus source, and a complexing agent (denoted as Mixture A) and then sintering the mixture to obtain a preliminary lithium-rich manganese-based material. This invention utilizes a wet coating process with phosphate to incorporate a small amount of phosphate ions into the surface layer of the phase-gradient lithium-rich manganese-based material. Due to the strong bonding energy between the phosphate polyanions and transition metal cations, the energy density of the material is increased, enhancing lithium-ion transport performance. Uniform phosphate coating also mitigates side reactions between the material and the electrolyte to some extent.

[0036] In this invention, the lithium source preferably includes one or more of lithium hydroxide and lithium salt; the lithium hydroxide is preferably lithium hydroxide; the lithium salt preferably includes one or more of lithium chloride, lithium acetate and lithium nitrate; and the lithium source is more preferably lithium hydroxide and lithium nitrate.

[0037] In this invention, the phosphorus source is preferably phosphoric acid.

[0038] In this invention, the molar ratio of the lithium source to the phosphorus source is preferably 2 to 4:1, specifically 2:1, 2.2:1, 2.5:1, 2.7:1, 3:1, 3.2:1, 3.5:1, 3.7:1, or 4:1. This invention adjusts the final phosphate content by controlling the above-mentioned content.

[0039] In this invention, the complexing agent is preferably an inorganic acid; the inorganic acid is preferably citric acid. Under the action of the complexing agent, lithium ions and phosphate ions complex on the surface of a lithium-rich manganese-based material with a phase structure gradient, and then form phosphates after sintering.

[0040] In this invention, the molar ratio of the complexing agent to the phosphorus source is preferably 2 to 4:1, specifically 2:1, 2.2:1, 2.5:1, 2.7:1, 3:1, 3.2:1, 3.5:1, 3.7:1, or 4:1. This invention adjusts the final phosphate content by controlling the above-mentioned content.

[0041] In this invention, the mixture A is preferably: a lithium source, a complexing agent, and a phosphorus source are first mixed to obtain a phosphorus-containing solution, and the phosphorus-containing solution is secondly mixed with a lithium-rich manganese-based material with a phase structure gradient; the first mixing time is preferably 0.5 to 5 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours; the second mixing time is preferably 0.5 to 2 hours, specifically 0.5 hours, 1 hour, 1.5 hours, or 2 hours.

[0042] In this invention, the temperature of the complexation reaction is preferably room temperature, and the reaction time is the total time of the mixture A.

[0043] In this invention, the complexation reaction preferably further includes solid-liquid separation of the resulting product; the solid-liquid separation is preferably filtration; the solid-liquid separation preferably further includes drying the resulting solid; the drying is preferably oven drying.

[0044] In this invention, the sintering temperature is preferably 200–600℃, specifically 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, or 600℃, and the holding time for sintering is preferably 2–7 hours, specifically 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or 7 hours. This invention promotes the combination of lithium ions and phosphate ions through sintering to form phosphate, resulting in a preliminary lithium-rich manganese-based material that is a phosphate-coated phase-gradient lithium-rich manganese-based material.

[0045] After obtaining the preliminary lithium-rich manganese-based material, the present invention combines the preliminary lithium-rich manganese-based material with P4S. 16The mixture was mixed with an ether solvent (denoted as Mixture B) and then dried to obtain the lithium-rich manganese-based core-shell material. This invention employs an in-situ solution method to prepare the outer shell, due to the P4S... 16 Power supply and P4S in sulfur-rich solution environments 16 SS bridging bonds in the molecular structure, P4S 16 There is a -40 meVatom between it and lithium phosphate. -1 The negative reaction energy of P4S 16 This will cause lithium phosphate to sulfide, forming Li3P. 1+a O4S 4a .

[0046] In this invention, the preliminary lithium-rich manganese-based material and P4S 16 The preferred mass ratio is 1000:5 to 20, specifically 1000:5, 1000:7, 1000:9, 1000:10, 1000:12, 1000:15, 1000:17, or 1000:20. This invention controls the above dosage to adjust the sulfur content in the shell, thereby regulating the electrochemical performance of lithium-rich manganese-based core-shell materials.

[0047] In this invention, the ether solvent is preferably diethylene glycol dimethyl ether.

[0048] In this invention, the mixture B is preferably: the initial lithium-rich manganese-based material and P4S. 16 The solution is mixed for the third time.

[0049] In this invention, the P4S 16 The preferred concentration of the solution is 5–20 mg / mL, specifically 5 mg / mL, 8 mg / mL, 10 mg / mL, 12 mg / mL, 14 mg / mL, 16 mg / mL, 18 mg / mL, or 20 mg / mL. This invention controls P4S... 16 The concentration of the solution affects the sulfur content in the shell, P4S 16 The higher the concentration of the solution, the higher the sulfur content in the shell.

[0050] In this invention, the temperature of the third mixing is preferably room temperature; the time of the third mixing is preferably 1 to 3 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0051] In this invention, the drying temperature is preferably 60-100℃, specifically 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃, and the heat preservation drying time is preferably 1-3h, specifically 1h, 1.5h, 2h, 2.5h or 3h.

[0052] The present invention also provides the application of the lithium-rich manganese-based core-shell material described in the above-described scheme or the lithium-rich manganese-based core-shell material obtained by the preparation method described in the above-described scheme in the field of lithium-ion batteries.

[0053] The lithium-rich manganese-based core-shell material provided by this invention has high energy density and good cycle performance, which can meet the electrochemical performance requirements of lithium-ion batteries and has broad application prospects.

[0054] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0055] Example 1

[0056] This embodiment prepares a lithium-rich manganese-based core-shell material with the structure as follows: Figure 1 As shown; the core of the lithium-rich manganese-based core-shell material is a phase-gradient lithium-rich manganese-based material, and the chemical composition of the particle center of the phase-gradient lithium-rich manganese-based material is 0.5Li2MnO3·0.5Li(Ni) 0.42 Mn 0.42 Co 0.16 The chemical composition of the surface layer of the particles is 0.3Li2MnO3·0.7Li(Ni)O2. 0.42 Mn 0.42 Co 0.16 O2; the outer shell of the lithium-rich manganese-based core-shell material includes Li3P 1+a O4S 4a , 0≤a≤1, the value of a gradually increases from the inside to the outside of the shell.

[0057] The preparation method of the lithium-rich manganese-based core-shell material in this embodiment includes the following steps:

[0058] (1) After mixing lithium hydroxide, citric acid and phosphoric acid in a molar ratio of 3:3:1 for 3 hours, lithium-rich manganese-based material with phase structure gradient was added and mixed, filtered and dried in sequence, and then sintered at 400℃ for 4.5 hours to obtain preliminary lithium-rich manganese-based material.

[0059] (2) The preliminary lithium-rich manganese-based material and P4S at a concentration of 12 mg / mL were mixed. 16 Solution (solvent is diethylene glycol dimethyl ether, solute is P4S) 16 After mixing the powders for 2 hours, the mixture was dried at 80°C for 2 hours to obtain the lithium-rich manganese-based core-shell material; wherein, the initial lithium-rich manganese-based material and P4S 16 The mass ratio of the powders is 1:0.01.

[0060] The preparation method of the phase structure gradient lithium-rich manganese-based material includes the following steps:

[0061] (a) Nickel sulfate (NiSO4·6H2O), cobalt sulfate (NiSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in deionized water to prepare solutions A and B with a total sulfate concentration of 2 mol / L, respectively. The molar ratio of Ni, Co, and Mn in solution A was 0.21:0.08:0.71, and the molar ratio of Ni, Co, and Mn in solution B was 0.343:0.1305:0.5265. At the same time, a 2 mol / L Na2CO3 solution and a 0.2 mol / L ammonia solution were prepared.

[0062] (b) 600 mL of solution B prepared in step (a) was added to 600 mL of solution A under stirring by a constant flow pump. At the same time, the mixed salt solution obtained by mixing solution A and solution B was added to the reaction vessel by a constant flow pump. Na2CO3 solution and ammonia water were added to the reaction vessel in parallel by constant flow pumps. The stirring speed was controlled at 1000 rpm, the pH value was adjusted to 8.1, and the co-precipitation reaction was carried out at 55℃ for 10 h to obtain a lithium-rich manganese-based material precursor with phase structure gradient.

[0063] (c) The phase structure gradient lithium-rich manganese-based material precursor prepared in step (b) is filtered, washed and dried in sequence, and then uniformly mixed with Li2CO3 at a ratio of 1.6:1 of the molar number of Li to the total molar number of Ni, Co and Mn. The mixture is pre-calcined at 500°C in air for 5 hours, and then heated to 900°C and held for 10 hours to obtain the phase structure gradient lithium-rich manganese-based material.

[0064] Example 2

[0065] This embodiment prepares a lithium-rich manganese-based core-shell material. The core of the lithium-rich manganese-based core-shell material is a phase-gradient lithium-rich manganese-based material, and the chemical composition of the particle center of the phase-gradient lithium-rich manganese-based material is 0.5Li2MnO3·0.5Li(Ni) 0.42 Mn 0.42 Co 0.16 The chemical composition of the surface layer of the particles is 0.3Li2MnO3·0.7Li(Ni)O2. 0.42 Mn 0.42 Co 0.16 O2; the outer shell includes Li3P 1+a O4S 4a , 0≤a≤1, the value of a gradually increases from the inside to the outside of the shell.

[0066] The preparation method of the lithium-rich manganese-based core-shell material in this embodiment includes the following steps:

[0067] (1) Lithium acetate, citric acid and phosphoric acid in a molar ratio of 2:2:1 were mixed for 0.5 h, and then lithium-rich manganese-based material with phase structure gradient was added and mixed, filtered and dried in sequence. Then it was sintered at 200 °C for 7 h to obtain preliminary lithium-rich manganese-based material. The preparation method of the phase structure gradient lithium-rich manganese-based material is the same as that in Example 1.

[0068] (2) The preliminary lithium-rich manganese-based material described in step (1) and P4S with a concentration of 5 mg / mL 16 Solution (solvent is diethylene glycol dimethyl ether, solute is P4S) 16 After mixing the powders for 1 hour, the mixture was dried at 60°C for 3 hours to obtain the lithium-rich manganese-based core-shell material; wherein, the initial lithium-rich manganese-based material and P4S 16 The mass ratio of the powders is 1:0.005.

[0069] Example 3

[0070] This embodiment prepares a lithium-rich manganese-based core-shell material. The core of the lithium-rich manganese-based core-shell material is a phase-gradient lithium-rich manganese-based material, and the chemical composition of the particle center of the phase-gradient lithium-rich manganese-based material is 0.5Li2MnO3·0.5Li(Ni) 0.42 Mn 0.42 Co 0.16 The chemical composition of the surface layer of the particles is 0.3Li2MnO3·0.7Li(Ni)O2. 0.42 Mn 0.42 Co 0.16 O2; the outer shell includes Li3P 1+a O4S 4a , 0≤a≤1, the value of a gradually increases from the inside to the outside of the shell.

[0071] The preparation method of the lithium-rich manganese-based core-shell material in this embodiment includes the following steps:

[0072] (1) After mixing lithium nitrate, citric acid and phosphoric acid in a molar ratio of 4:4:1 for 5 hours, lithium manganese-based material with phase structure gradient was added and mixed, filtered and dried in sequence, and then sintered at 600℃ for 2 hours to obtain preliminary lithium manganese-based material; the preparation method of the phase structure gradient lithium manganese-based material is the same as that in Example 1.

[0073] (2) The preliminary lithium-rich manganese-based material described in step (1) and P4S with a concentration of 20 mg / mL 16 Solution (solvent is diethylene glycol dimethyl ether, solute is P4S) 16 After mixing the powders for 3 hours, the mixture was dried at 100°C for 3 hours to obtain the lithium-rich manganese-based core-shell material; wherein, the initial lithium-rich manganese-based material and P4S 16 The mass ratio of the powders is 1:0.02.

[0074] Example 4

[0075] The preparation method in this embodiment is the same as that in Example 1, except that: the lithium-rich manganese-based material in step (2) and P4S are used. 16 The powder mass ratio has been changed from 1:0.01 to 1:0.05.

[0076] Example 5

[0077] The preparation method in this embodiment is the same as that in Example 1, except that: the lithium-rich manganese-based material in step (2) and P4S are used. 16 The powder mass ratio has been changed from 1:0.01 to 1:0.001.

[0078] Comparative Example 1

[0079] The preparation method of this comparative example is the same as that of Example 1, except that step (2) P4S 16 The solution was replaced with P2S5 solution.

[0080] Comparative Example 2

[0081] The preparation method of this comparative example is the same as that of Example 1, except that step (2) is not performed in this comparative example, but only a layer of lithium phosphate is coated on the surface of the lithium-rich manganese-based material with phase structure gradient.

[0082] Comparative Example 3

[0083] The preparation method of this comparative example is the same as that of Example 1, except that the phase structure gradient lithium-rich manganese-based material is replaced with a layered lithium-rich manganese-based material without phase structure gradient, while the molar ratio of nickel, cobalt and manganese in the lithium-rich manganese-based material remains unchanged.

[0084] Comparative Example 4

[0085] The preparation method of this comparative example is the same as that of Example 1, except that this comparative example directly uses lithium-rich manganese-based materials with phase structure gradient as the target product, that is, without modifying them.

[0086] Test Example 1

[0087] The electrochemical performance of the lithium-rich manganese-based core-shell materials in Examples 1-5 and Comparative Examples 1-4 was tested. The electrochemical performance tests included cycle performance and average voltage decay tests. The cycle performance test method was as follows: at room temperature (25°C), the battery was activated for 3 cycles under the conditions of voltage range 2.0-4.8V and current density of 0.1C, and then charge-discharge cycle tests were performed under the conditions of voltage range 2.0-4.8V and current density of 0.1C. The capacity retention rate within 100 cycles was tested. The average voltage decay test conditions were 3.61V to 3.45V. The results are shown in Table 1.

[0088] Table 1. Electrochemical performance of lithium-rich manganese-based core-shell materials in Examples 1-5 and Comparative Examples 1-4

[0089] Average voltage decay Capacity retention Example 1 0.55mV / cycle 98.8％ Example 2 0.57mV / cycle 98.4％ Example 3 0.56mV / cycle 98.6％ Example 4 0.68mV / cycle 96.2％ Example 5 0.72mV / cycle 95.4％ Comparative Example 1 0.78mV / cycle 93.1％ Comparative Example 2 0.79mV / cycle 94.5％ Comparative Example 3 1.50mV / cycle 85.1％ Comparative Example 4 0.81mV / cycle 92.2％

[0090] As shown in Table 1, the lithium-rich manganese-based core-shell material prepared in this invention exhibits low voltage drop and high cycle stability; Examples 4-5 demonstrate that the preliminary lithium-rich manganese-based material and P4S… 16 When the mass ratio of the powder is too high or too low, the cycle stability of lithium-rich manganese-based core-shell materials decreases; as shown in Comparative Example 1, when P4S... 16 When the solution is replaced with P2S5 solution, the sulfur loading process cannot occur, therefore, no thiophosphate is generated, and the cycle stability of the battery decreases. As shown in Comparative Example 2, coating lithium phosphate only on the surface of the lithium-rich manganese-based material does not significantly improve the cycle performance of the battery. As shown in Comparative Example 3, without using a lithium-rich manganese-based material with a phase structure gradient as the core, and instead using a lithium-rich manganese-based material without a phase structure gradient, the cycle stability of the battery decreases. As shown in Comparative Example 4, directly using a lithium-rich manganese-based material with a phase structure gradient as the target product results in a significantly lower electrochemical cycle stability than the lithium-rich manganese-based core-shell materials in Examples 1-3 of this invention.

[0091] As can be seen from the above embodiments, the lithium-rich manganese-based core-shell material provided by the present invention has high capacity retention and excellent cycle stability.

[0092] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A lithium-rich manganese-based core-shell material, characterized in that, It includes a phase structure gradient rich lithium manganese-based material and a shell covering the surface of the phase structure gradient rich lithium manganese-based material; the general formula of the phase structure gradient rich lithium manganese-based material is xLi2MnO3·(1 - x)LiTMO2 - yLi2MnO3·(1 - y)LiTMO2, where 0 < y < x < 1, and in the formula, TM is one or more of Ni, Co, and Mn; The surface layer of the phase structure gradient rich lithium manganese-based material is infiltrated with phosphate; The outer casing includes Li3P. 1+a O4S 4a , 0≤a≤1; The phase structure gradient rich lithium manganese-based material includes a monoclinic Li2MnO3 phase and a rhombohedral LiTMO2 phase; The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside; The content of the rhombohedral LiTMO2 phase increases sequentially from the inside to the outside; The content of S in the shell increases sequentially from the inside to the outside.

2. The lithium-rich manganese-based core-shell material according to claim 1, characterized in that, The content of the monoclinic Li2MnO3 phase decreases linearly from the inside to the outside; The content of the rhombohedral LiTMO2 phase increases linearly from the inside to the outside.

3. The lithium-rich manganese-based core-shell material according to claim 1, characterized in that, The phosphate is lithium phosphate; the mass ratio of the phosphate to the phase structure gradient rich lithium manganese-based material is 0.1~5:

100.

4. The lithium-rich manganese-based core-shell material according to claim 1, characterized in that, The mass ratio of the phase structure gradient rich lithium manganese-based material to the shell is 1000:5~20.

5. The lithium-rich manganese-based core-shell material according to claim 1 or 4, characterized in that, The shape of the lithium-rich manganese-based core-shell material is spherical, and the particle size is 0.5~20 μm.

6. The method for preparing the lithium-rich manganese-based core-shell material according to any one of claims 1 to 5, characterized in that, It includes the following steps: (1) Mix the phase structure gradient rich lithium manganese-based material, a lithium source, a phosphorus source, and a complexing agent, carry out a complexing reaction, and then sinter to obtain a preliminary lithium-rich manganese-based material; (2) The aforementioned preliminary lithium-rich manganese-based material and P4S 16 After mixing with an ether solvent and drying, the lithium-rich manganese-based core-shell material is obtained.

7. The preparation method according to claim 6, characterized in that, The temperature of the sintering is 200~600 °C, and the heat preservation sintering time is 2~7 h.

8. Application of the lithium-rich manganese-based core-shell material according to any one of claims 1~5 or the lithium-rich manganese-based core-shell material obtained by the preparation method according to any one of claims 6~7 in the field of lithium-ion batteries.

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