A gradient lithium-rich manganese-based material, a preparation method thereof and application thereof as a battery cathode material

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a gradient lithium-rich manganese-based material, a preparation method thereof and application of the material as a battery positive electrode material. The gradient lithium-rich manganese-based material provided by the application is surface-modified with a transition layer and a perovskite layer. The perovskite layer serves as an excellent ion conductor material, which can improve the ion conductivity of the gradient lithium-rich manganese-based material, and reversibly absorbs oxygen ions as an oxygen buffer, thereby hindering the release of oxygen, widening the electrochemical window of the cathode material, inhibiting the side reaction on the surface of the gradient lithium-rich manganese-based material, impedance growth and electrochemical degradation, and improving the discharge capacity, average discharge voltage and rate performance of the battery. The gradient lithium-rich manganese-based material provided by the application has high discharge capacity, high average discharge voltage, high rate performance and excellent electrochemical performance.

Description

Technical Field

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

[0002] With the rapid development of pure electric vehicles and plug-in hybrid electric vehicles, the improvement of the energy density and cycle performance of lithium-ion batteries has become the focus of attention in the current energy field.

[0003] Due to its advantages of high specific capacity (>250 mAh / g), high working voltage, and high safety, lithium-rich manganese-based cathode materials are considered to be the most promising cathode materials for next-generation power batteries. However, problems such as low initial Coulomb efficiency, serious voltage decay, and low cycle and rate performance of lithium-rich manganese-based cathode materials limit their practical applications. Researchers have modified lithium-rich manganese-based cathode materials and improved their electrochemical performance to a certain extent. However, the overall discharge performance is still insufficient. Summary of the Invention

[0004] The purpose of the present invention is to provide a gradient lithium-rich manganese-based material, a preparation method thereof, and an application as a battery cathode material. The gradient lithium-rich manganese-based material provided by the present invention has a high discharge capacity and a high average discharge voltage.

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

[0006] The present invention provides a gradient lithium-rich manganese-based material, including a phase structure gradient lithium-rich manganese-based material, a transition layer covering the surface of the phase structure gradient lithium-rich manganese-based material, and a perovskite layer covering the surface of the transition layer; the chemical formula of the phase structure gradient lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiTMO2 - yLi2MnO3·(1 - y)LiTMO2, 0 < y < x < 1, and the TM element is Ni, Co, and Mn; the chemical formula of the perovskite layer is A

[0009] B w TMO3, 0 ≤ w < 1, the A element is one or more of La, Sm, Ba, Sr, and Pr, the B element is one or more of Fe, Mo, and Cr, and the TM element is Ni, Co, and Mn; the transition layer is a phase structure gradient lithium-rich manganese-based material doped with A elements and B elements, and the contents of the A element and the B element independently increase from the inside to the outside.

[0007] Preferably, the particle size of the phase structure gradient lithium-rich manganese-based material is 1 - 30 μm.

[0008] Preferably, the thickness of the transition layer is 2 - 10 nm.

[0009] Preferably, the thickness of the perovskite layer is 2–10 nm.

[0010] Preferably, in the perovskite layer, the molar ratio of Ni to Co is 0.05–0.3:0.05–0.2; and the molar ratio of Ni to Mn is 0.05–0.3:0.5–0.9.

[0011] Preferably, the chemical formula of the phase structure gradient lithium-rich manganese-based material is: core center 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 O2, core surface layer 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 )O2.

[0012] Preferably, the chemical composition of the perovskite layer is La. 0.5 Fe 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3, Sm 0.5 Mo 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3, La 0.3 Fe 0.7 Ni 0.294 Co 0.112 Mn 0.594 O3, PrNi 0.294 Co 0.112 Mn 0.594 O3, SmNi 0.294 Co 0.112 Mn 0.594 O3, BaNi 0.294 Co 0.112 Mn 0.594 O3 or SrNi 0.294 Co 0.112 Mn 0.594 O3.

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

[0014] The gradient lithium-rich manganese-based material is obtained by mixing source A, source B, water, and phase structure gradient lithium-rich manganese-based material, followed by adsorption and annealing.

[0015] Preferably, the annealing temperature is 500–900°C, and the holding time for annealing is 4–10 hours; the annealing atmosphere is one or more of air and oxygen.

[0016] The present invention also provides the application of the gradient lithium-rich manganese-based material described in the above scheme or the gradient lithium-rich manganese-based material obtained by the preparation method described in the above scheme as a battery cathode material.

[0017] This invention provides a gradient lithium-rich manganese-based material. The gradient lithium-rich manganese-based material provided by this invention has a transition layer and a perovskite layer modified on its surface. The perovskite layer, as an excellent ion conductor, can improve the ionic conductivity of the gradient lithium-rich manganese-based material. Simultaneously, it acts as an oxygen buffer, reversibly absorbing oxygen ions, thereby hindering oxygen release, widening the electrochemical window of the cathode material, suppressing side reactions, impedance growth, and electrochemical degradation on the surface of the gradient lithium-rich manganese-based material, and improving the battery's discharge capacity, average discharge voltage, and rate performance. The gradient lithium-rich manganese-based material provided by this invention has high discharge capacity, high average discharge voltage, high rate performance, and excellent electrochemical performance. Example results show that the gradient lithium-rich manganese-based material provided by this invention has a discharge specific capacity of 265 mAh g⁻¹ at 0.2C. -1 Above, the discharge specific capacity at 5C is 165mAhg. -1 The average discharge voltage is above 3.65V.

[0018] This invention also provides a method for preparing the gradient lithium-rich manganese-based material described above. By modifying the surface of the phase-structure gradient lithium-rich manganese-based material, this invention obtains a transition layer with varying doping elements and an ultrathin perovskite layer. The preparation method provided by this invention has simple steps and is suitable for large-scale production.

[0019] This invention also provides the application of the gradient lithium-rich manganese-based material described in the above-described scheme or the gradient lithium-rich manganese-based material prepared by the above-described scheme as a battery cathode material. The gradient lithium-rich manganese-based material provided by this invention has high discharge capacity, high average discharge voltage, and high rate performance, which can meet the requirements of batteries, especially lithium-ion batteries, for cathode materials, and has broad application prospects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the gradient lithium-rich manganese-based material prepared in Example 1 of the present invention;

[0022] Figure labels: 1 represents lithium-rich manganese-based material with phase structure gradient, 2 represents transition layer, and 3 represents perovskite layer. Detailed implementation manners

[0023] The present invention provides a gradient lithium-rich manganese-based material, including a phase structure gradient lithium-rich manganese-based material, a transition layer covering the surface of the phase structure gradient lithium-rich manganese-based material, and a perovskite layer covering the surface of the transition layer; the chemical formula of the phase structure gradient lithium-rich manganese-based material is xLi2MnO3·(1-x)LiTMO2-yLi2MnO3·(1-y)LiTMO2, 0 < y < x < 1, and the TM element is Ni, Co, and Mn; the chemical formula of the perovskite layer is A 1-w B w TMO3, 0 ≤ w < 1, the A element is one or more of La, Sm, Ba, Sr, and Pr, the B element is one or more of Fe, Mo, and Cr, and the TM element is Ni, Co, and Mn; the transition layer is a phase structure gradient lithium-rich manganese-based material doped with A element and B element, and the contents of the A element and the B element independently increase from inside to outside.

[0024] The gradient lithium-rich manganese-based material provided by the present invention includes a phase structure gradient lithium-rich manganese-based material (inner core); the chemical 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), 0 < y < x < 1, and the TM element is Ni, Co, and Mn.

[0025] In the present invention, 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 preferably decreases sequentially from inside to outside, more preferably linearly decreases from inside to outside, and the content of the rhombic LiTMO2 phase preferably increases sequentially from inside to outside, more preferably linearly increases from inside to outside.

[0026] In a specific embodiment of the present invention, the chemical formula of the phase structure gradient lithium-rich manganese-based material may specifically be: 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 )O2 at the core center and 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 )O2 at the core surface layer.

[0027] The gradient lithium-rich manganese-based material provided by this invention includes a transition layer; the transition layer is a phase structure gradient lithium-rich manganese-based material doped with elements A and B, wherein the contents of elements A and B preferably increase linearly and independently from the inside to the outside. The doping of elements A and B in the transition layer of this invention can expand the lithium insertion / extraction diffusion channels of the gradient lithium-rich manganese-based material, improve the lattice constant, and give the doped gradient lithium-rich manganese-based material a better layered structure, thereby further improving the overall electrochemical performance of the gradient lithium-rich manganese-based material.

[0028] In this invention, the thickness of the transition layer is preferably 2 to 10 nm, specifically 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm.

[0029] In this invention, the particle size of the phase structure gradient lithium-rich manganese-based material is preferably 1 to 30 μm, specifically 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0030] The gradient lithium-rich manganese-based material provided by this invention includes a perovskite layer; the chemical formula of the perovskite layer is A. 1- w B w TMO3, w is preferably 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, A is preferably a mixture of La and Sm, a mixture of Sm and Ba, a mixture of Ba and Sr, or a mixture of Sr and Pr, and B is preferably a mixture of Fe and Mo, a mixture of Mo and Cr, or a mixture of Fe and Cr.

[0031] In this invention, TM elements are Ni, Co, and Mn; the preferred molar ratio of Ni to Co is 0.05–0.3:0.05–0.2, specifically 0.05:0.05, 0.05:0.1, 0.05:0.15, 0.05:0.2, 0.1:0.05, 0.1:0.1, 0.1:0.15, 0.1:0.2, 0.2:0.05, 0.2:0.1, 0.2:0.15, 0.2:0.2, 0.3:0.05, 0.3:0.1 The molar ratio of Ni to Mn is preferably 0.05–0.3:0.5–0.9, specifically 0.05:0.5, 0.1:0.5, 0.15:0.5, 0.2:0.5, 0.3:0.5, 0.05:0.7, 0.1:0.7, 0.15:0.7, 0.2:0.7, 0.3:0.7, 0.05:0.9, 0.1:0.9, 0.15:0.9, 0.2:0.9, or 0.3:0.9.

[0032] In this invention, the thickness of the perovskite layer is preferably 2 to 10 nm, specifically 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm.

[0033] In a specific embodiment of the present invention, the chemical composition of the perovskite layer is preferably La. 0.5 Fe 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3, Sm 0.5 Mo 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3, La 0.3 Fe 0.7 Ni 0.294 Co 0.112 Mn 0.594 O3, PrNi 0.294 Co 0.112 Mn 0.594 O3, SmNi 0.294 Co 0.112 Mn 0.594 O3, BaNi 0.294 Co 0.112 Mn 0.594 O3 or SrNi 0.294 Co 0.112 Mn 0.594 O3.

[0034] The structure of the gradient lithium-rich manganese-based material provided by this invention is as follows: Figure 1 As shown, from the inside out, the structure sequentially includes a lithium-rich manganese-based material with a phase structure gradient, a transition layer covering the surface of the lithium-rich manganese-based material with a phase structure gradient, and a perovskite layer covering the surface of the transition layer. The lithium-rich manganese-based material with a gradient provided by this invention has a dense structure and is suitable as a cathode material for batteries.

[0035] The present invention also provides a method for preparing the gradient lithium-rich manganese-based material described above, characterized by comprising the following steps:

[0036] The gradient lithium-rich manganese-based material is obtained by mixing source A, source B, water, and phase structure gradient lithium-rich manganese-based material, followed by adsorption and annealing.

[0037] This invention involves mixing source A, source B, water, and a lithium-rich manganese-based material with a phase structure gradient (referred to as the first mixture, resulting in a mixed solution) for adsorption. In this invention, source A preferably includes one or more of the following: chloride salts, sulfate salts, and nitrate salts of element A; more preferably, it is a mixture of chloride salts and sulfate salts of element A, a mixture of sulfate salts and nitrate salts of element A, or a mixture of chloride salts and nitrate salts of element A.

[0038] In this invention, the chloride salt of element A preferably includes one or more of lanthanum chloride, samarium chloride, barium chloride, strontium chloride, and praseodymium chloride; the sulfate salt of element A preferably includes one or more of lanthanum sulfate, samarium sulfate, barium sulfate, strontium sulfate, and praseodymium sulfate; and the nitrate salt of element A preferably includes one or more of lanthanum nitrate, samarium nitrate, barium nitrate, strontium nitrate, and praseodymium nitrate.

[0039] In this invention, the B source preferably includes one or more of the following: B chloride, B sulfate, and B nitrate; more preferably, it is a mixture of B chloride and B sulfate, a mixture of B sulfate and B nitrate, or a mixture of B chloride and B nitrate.

[0040] In this invention, the chloride salt of element B preferably includes one or more of ferric chloride, molybdenum chloride, and chromium chloride; the sulfate salt of element B preferably includes one or more of ferric sulfate, molybdenum sulfate, and chromium sulfate; and the nitrate salt of element B preferably includes one or more of ferric nitrate, molybdenum nitrate, and chromium nitrate.

[0041] This invention utilizes a B source to provide transition metal ions. By doping these ions into lithium-rich manganese-based materials with a phase structure gradient, stronger MO chemical bonds than active transition metals such as Ni, Co, and Mn can be provided. This improves the structural stability of the material by suppressing the precipitation of lattice oxygen under high voltage. Furthermore, the coating of transition metal ions further improves the cycling stability and corrosion resistance of the material, thereby enhancing the interfacial compatibility of the lithium-rich manganese-based materials with a phase structure gradient.

[0042] In this invention, the solid content of the phase structure gradient lithium-rich manganese-based material in the mixed solution is preferably 0.1–10 g / mL, specifically 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, 0.5 g / mL, 0.7 g / mL, 0.9 g / mL, 1 g / mL, 2 g / mL, 3 g / mL, 4 g / mL, 5 g / mL, 6 g / mL, 7 g / mL, 8 g / mL, 9 g / mL, or 10 g / mL. This invention uses the above-mentioned solid content to improve the coating effect, avoid uneven element distribution caused by excessively high solid content, and also avoid insufficient surface adsorption of elements and the generation of a large amount of waste liquid caused by excessively low solid content.

[0043] In this invention, the first mixing is preferably: mixing source A and a portion of water to obtain source A solution, mixing source B and the remaining portion of water to obtain source B solution, and mixing source A solution, source B solution and lithium-rich manganese-based material with phase structure gradient.

[0044] In this invention, the concentration of the source A solution is preferably 0.2 to 1 mol / L, specifically 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L.

[0045] In this invention, the concentration of the B source solution is preferably 0.2–1 mol / L, specifically 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L. This invention controls the content of elements A and B in the gradient lithium-rich manganese-based material by using different concentrations.

[0046] In this invention, the temperature of the first mixing is preferably 15-60°C, specifically 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C, and the mixing time is preferably 2-48 hours, specifically 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours; the first mixing preferably includes ultrasonic dispersion.

[0047] In this invention, the first mixing process preferably further includes washing and drying the resulting product sequentially.

[0048] In this invention, the washing is preferably done with water; and the water used for washing is preferably deionized water.

[0049] In this invention, the drying temperature is preferably 50-120°C, specifically 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, and the heat preservation drying time is preferably 10-20h, specifically 10h, 12h, 14h, 16h, 18h or 20h.

[0050] After adsorption, the resulting mixed solution is annealed to obtain the gradient lithium-rich manganese-based material. In this invention, the annealing temperature is preferably 500–900℃, specifically 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃; the annealing time is preferably 4–10 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours; the annealing atmosphere is preferably one or more of air and oxygen. During annealing, the A and B source substances decompose on the surface of the gradient lithium-rich manganese-based material, forming perovskite minerals. Simultaneously, some A and B elements gradually diffuse into the interior of the gradient lithium-rich manganese-based material under thermodynamic effects, thus forming a gradient distribution.

[0051] This invention involves ion exchange on the surface of a lithium-rich manganese-based material with a phase structure gradient using a solution containing elements A and B. After annealing, a lithium-free perovskite layer and a transition layer with gradient doping of elements A and B are formed on the surface of the lithium-rich manganese-based material with a phase structure gradient.

[0052] The present invention also provides the application of the gradient lithium-rich manganese-based material described in the above scheme or the gradient lithium-rich manganese-based material obtained by the preparation method described in the above scheme as a battery cathode material.

[0053] The gradient lithium-rich manganese-based material provided by this invention exhibits high discharge capacity, high average discharge voltage, and high rate performance. Example results show that the gradient lithium-rich manganese-based material provided by this invention achieves a discharge specific capacity of 265 mAh g⁻¹ at 0.2C. -1 Above, the discharge specific capacity at 5C is 165mAhg. -1 The average discharge voltage is above 3.65V, which meets the requirements of batteries, especially lithium-ion batteries, for cathode materials, 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 gradient lithium-rich manganese-based material, with the structure as follows: Figure 1 As shown, the surface of the phase-structure gradient lithium-rich manganese-based material 1 is provided with a 4 nm transition layer 2 and a 4 nm perovskite layer 3; the chemical composition of the phase-structure gradient lithium-rich manganese-based material is: the core center is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 O2, with a core surface layer of 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42Co 0.16 O2; Transition layer 2 is a lithium-rich manganese-based material with a phase structure gradient doped with La and Fe elements, wherein the content of La and Fe elements increases independently from the inside to the outside; the chemical formula of perovskite layer 3 is La 0.5 Fe 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3 (each mole of phase structure gradient lithium-rich manganese-based material has 0.5 mol of La and 0.5 mol of Fe dissolved on its surface).

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

[0058] A 0.4 mol / L LaCl3 aqueous solution, a 0.4 mol / L FeCl3 aqueous solution, and 2 g of phase-gradient lithium-rich manganese-based material were ultrasonically dispersed at 25 °C for 24 h (the solid content of the solution obtained by ultrasonic dispersion was 0.4 g / mL). The solution was washed with deionized water, dried at 80 °C for 15 h, and annealed at 700 °C for 7 h in air to obtain the phase-gradient lithium-rich manganese-based material.

[0059] The preparation method of the phase structure gradient lithium-rich manganese-based material includes the following steps:

[0060] (1) Dissolve nickel sulfate (NiSO4·6H2O), cobalt sulfate (NiSO4·7H2O), and manganese sulfate (MnSO4·H2O) in deionized water to prepare solutions A and B with a total metal salt concentration of 2 mol / L, respectively. The molar ratio of Ni, Co, and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co, and Mn in solution B is 0.343:0.1305:0.5265. Prepare a 2 mol / L Na2CO3 solution and a 0.2 mol / L ammonia solution.

[0061] (2) Add 600 mL of solution B prepared in step (1) to 600 mL of solution A under stirring by a constant flow pump. At the same time, add the mixed salt solution of solution A and solution B to the reaction vessel by a constant flow pump. Add Na2CO3 solution and ammonia water to the reaction vessel in parallel by a constant flow pump. Control the stirring speed to 1000 rpm, the pH value to 8.1, and co-precipitate at 55℃ for 10 h to obtain a lithium-rich manganese-based material precursor with phase structure gradient.

[0062] (3) The phase structure gradient lithium-rich manganese-based material precursor prepared in step (2) is filtered, washed and dried, 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℃ in air for 5h, and then heated to 900℃ and held for 10h to obtain the phase structure gradient lithium-rich manganese-based material.

[0063] Example 2

[0064] This embodiment prepares a gradient lithium-rich manganese-based material. The surface of the phase-structure gradient lithium-rich manganese-based material is provided with a 2nm transition layer and a 2nm perovskite layer. The chemical formula of the phase-structure gradient lithium-rich manganese-based material is: core center 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 O2, core surface layer 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 O2; the transition layer is a lithium-rich manganese-based material with a phase structure gradient doped with Sm and Mo elements, wherein the content of Sm and Mo elements decreases independently from the outside to the inside; the chemical formula of the perovskite layer is Sm 0.5 Mo 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3 (each mole of phase structure gradient lithium-rich manganese-based material has 0.5 mol of Sm and 0.5 mol of Mo dissolved on its surface).

[0065] The preparation method of the gradient lithium-rich manganese-based material in this embodiment includes the following steps:

[0066] Sm3SO4 with a concentration of 0.2 mol / L, Mo3SO4 with a concentration of 0.2 mol / L, and lithium-rich manganese-based cathode material with phase gradient were ultrasonically dispersed at 15 °C for 48 h (the solid content of the ultrasonically dispersed solution was 10 g / mL), washed with deionized water, dried at 50 °C for 20 h, and annealed at 500 °C for 10 h in air atmosphere to obtain the gradient lithium-rich manganese-based material.

[0067] Example 3

[0068] This embodiment prepares a gradient lithium-rich manganese-based material. The surface of the phase-structure gradient lithium-rich manganese-based material is provided with a 10 nm transition layer and a 10 nm perovskite layer. The chemical formula of the phase-structure gradient lithium-rich manganese-based material is: core center 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 O2, core surface layer 0.3Li2MnO3·0.7Li(Ni)0.42 Mn 0.42 Co 0.16 O2; the transition layer is a lithium-rich manganese-based material with a phase structure gradient doped with Sr, wherein the Sr content decreases from the outside to the inside; the chemical formula of the perovskite layer is SrNi. 0.294 Co 0.112 Mn 0.594 O3.

[0069] The preparation method of the gradient lithium-rich manganese-based material in this embodiment includes the following steps:

[0070] A source solution with a concentration of 1 mol / L, a source solution with a concentration of 1 mol / L, and a phase structure gradient lithium-rich manganese-based material were ultrasonically dispersed at 60 °C for 2 h (the solid content of the ultrasonically dispersed solution was 0.5 g / mL). The solution was washed with deionized water, dried at 120 °C for 10 h, and annealed at 900 °C for 4 h in air to obtain the gradient lithium-rich manganese-based material.

[0071] Example 4

[0072] The preparation method in this embodiment is the same as that in Example 1, except that the annealing temperature is replaced with 300°C.

[0073] Example 5

[0074] The preparation method in this embodiment is the same as that in Example 1, except that the annealing temperature is replaced with 1000℃.

[0075] Comparative Example 1

[0076] The preparation method of this comparative example is the same as that of Example 1, except that LaCl3 solution is not used.

[0077] Comparative Example 2

[0078] 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 without surface modification.

[0079] Comparative Example 3

[0080] The preparation method of this comparative example is the same as that of Example 1, except that the lithium-rich manganese-based material with phase structure gradient is replaced with nickel-cobalt-manganese cathode material with CAS number 346417-97-8.

[0081] Test Example 1

[0082] The materials prepared in Examples 1-5 and Comparative Examples 1-3 were mixed with acetylene black and PVDF binder at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil current collector, dried, and then stamped and rolled to obtain a positive electrode sheet. The negative electrode sheet of the battery was a lithium sheet, and the electrolyte was LiPF6 / EC+DEC (Klude). The positive electrode sheet, lithium sheet, separator, and electrolyte were assembled in the battery case to form a 2032 coin cell. After the battery was prepared, it was left to stand for 8-12 hours.

[0083] Batteries prepared from the materials of Examples 1-5 and Comparative Examples 1-3 were tested for discharge specific capacity and average discharge voltage at different rates (0.2C and 5C). The test results are shown in Table 1. The average discharge voltage was calculated by averaging the voltage values ​​of the battery at different time points.

[0084] Table 1. Performance data of batteries prepared from the materials of Examples 1-5 and Comparative Examples 1-3.

[0085] Discharge specific capacity at 0.2C Average discharge voltage 5C discharge specific capacity Example 1 <![CDATA[282mAhg -1 ]]> 3.98V <![CDATA[193mAhg -1 ]]> Example 2 <![CDATA[279mAhg -1 ]]> 3.92V <![CDATA[194mAhg -1 ]]> Example 3 <![CDATA[280mAhg -1 ]]> 3.85V <![CDATA[192mAhg -1 ]]> Example 4 <![CDATA[267mAhg -1 ]]> 3.65V <![CDATA[170mAhg -1 ]]> Example 5 <![CDATA[266mAhg -1 ]]> 3.68V <![CDATA[168mAhg -1 ]]> Comparative Example 1 <![CDATA[263mAhg -1 ]]> 3.54V <![CDATA[164mAhg -1 ]]> Comparative Example 2 <![CDATA[271mAhg -1 ]]> 3.60V <![CDATA[180mAhg -1 ]]> Comparative Example 3 <![CDATA[265mAhg -1 ]]> 3.70V <![CDATA[160mAhg -1 ]]>

[0086] As shown in Table 1, and based on the analysis of Examples 1-3, this invention, on the basis of lithium-rich manganese-based materials with phase structure gradients, forms a transition layer and a perovskite layer on the surface of the lithium-rich manganese-based materials through ion exchange followed by annealing. The perovskite layer, as an oxygen buffer, can reversibly absorb oxygen ions, thereby hindering the release of oxygen. Through the setting of the transition layer and the perovskite layer, the anodic stability window of the cathode is expanded, and the side reactions, impedance growth, and electrochemical degradation on the surface are suppressed, thereby improving the discharge capacity, average discharge voltage, and rate performance of the battery.

[0087] Analysis of Examples 4 and 5 shows that when the annealing temperature is too high or too low, if the annealing temperature is too high, the perovskite layer cannot be formed; if the annealing temperature is too low, the diffusion of the metal used for modification in the lithium-rich manganese-based material lattice cannot be activated, resulting in the inability to form a transition layer. In both cases, the material performance deteriorates.

[0088] Analysis of Comparative Example 1 shows that without the use of LaCl3 solution, the formed perovskite layer and transition layer contain only transition metal elements and no lanthanide metal elements, resulting in a decrease in electrochemical performance. This indicates that the addition of lanthanide metals is very important for improving performance.

[0089] Analysis of Comparative Example 2 shows that directly using lithium-rich manganese-based materials with phase structure gradients without surface modification leads to a decrease in the electrochemical performance of the battery.

[0090] Analysis of Comparative Example 3 shows that the electrochemical performance of the battery decreased after replacing the phase structure gradient lithium-rich manganese-based material with commercially available nickel-cobalt-manganese cathode material. This indicates that the electrochemical performance can only be improved by combining surface modification and phase structure gradient.

[0091] As can be seen from the above embodiments, the gradient lithium-rich manganese-based material provided by the present invention has high discharge capacity, high average discharge voltage, high rate performance, and excellent electrochemical performance.

[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 gradient lithium-rich manganese-based material, characterized in that, It includes a phase structure gradient lithium-rich manganese-based material, a transition layer covering the surface of the phase structure gradient lithium-rich manganese-based material, and a perovskite layer covering the surface of the transition layer; The chemical formula of the phase structure gradient lithium-rich manganese-based material is xLi2MnO3·(1-x)LiTMO2-yLi2MnO3·(1-y)LiTMO2, where 0 < y < x < 1, and the TM element is Ni, Co, and Mn; The chemical formula of the perovskite layer is A. 1-w B w TMO3, 0≤w<1, element A is one or more of La, Sm, Ba, Sr and Pr, element B is one or more of Fe, Mo and Cr, and element TM is Ni, Co and Mn; The transition layer is a phase structure gradient lithium-rich manganese-based material doped with element A and element B, and the contents of element A and element B independently increase from inside to outside.

2. The gradient lithium-rich manganese-based material according to claim 1, characterized in that, The particle size of the phase structure gradient lithium-rich manganese-based material is 1 to 30 μm.

3. The gradient lithium-rich manganese-based material according to claim 1 or 2, characterized in that, The thickness of the transition layer is 2 to 10 nm.

4. The gradient lithium-rich manganese-based material according to claim 1 or 2, characterized in that, The thickness of the perovskite layer is 2 to 10 nm.

5. The gradient lithium-rich manganese-based material according to claim 1 or 2, characterized in that, In the perovskite layer, the molar ratio of Ni and Co is 0.05 to 0.3:0.05 to 0.2, and the molar ratio of Ni and Mn is 0.05 to 0.3:0.5 to 0.

9.

6. The gradient lithium-rich manganese-based material according to claim 1, characterized in that, The chemical formula of the phase-structure gradient lithium-rich manganese-based material is: core center 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 O2, core surface layer 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 )O2.

7. The gradient lithium-rich manganese-based material according to claim 1, characterized in that, The chemical composition of the perovskite layer is La. 0.5 Fe 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3, Sm 0.5 Mo 0.5 Ni 0.294 Co 0.112 Mn 0.594 O3, La 0.3 Fe 0.7 Ni 0.294 Co 0.112 Mn 0.59 4O3, PrNi 0.294 Co 0.112 Mn 0.594 O3, SmNi 0.294 Co 0.112 Mn 0.594 O3, BaNi 0.294 Co 0.112 Mn 0.594 O3 or SrNi 0.294 Co 0.112 Mn 0.594 O3.

8. The method for preparing the gradient lithium-rich manganese-based material according to any one of claims 1 to 7, characterized in that, It includes the following steps: Mix an A source, a B source, water, and the phase structure gradient lithium-rich manganese-based material, and perform adsorption and annealing to obtain the gradient lithium-rich manganese-based material.

9. The preparation method according to claim 8, characterized in that, The temperature of the annealing is 500 to 900 °C, and the holding annealing time is 4 to 10 h; The atmosphere of the annealing is one or more of air and oxygen.

10. Application of the gradient lithium-rich manganese-based material according to any one of claims 1 to 7 or the gradient lithium-rich manganese-based material obtained by the preparation method according to any one of claims 8 to 9 as a cathode material of a battery.

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