Double-gradient lithium-rich manganese-based positive electrode material and preparation method thereof
By preparing "dual-gradient" lithium-rich manganese-based cathode materials, the material performance problems existing in the prior art have been solved, the requirements of high-energy-density lithium-ion batteries have been met, and the cycle stability and voltage decay performance of the materials have been improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF TECH
- Filing Date
- 2024-11-14
- Publication Date
- 2026-05-15
AI Technical Summary
Existing lithium-rich manganese-based cathode materials suffer from problems such as low first-cycle coulombic efficiency, severe capacity and voltage decay, poor rate performance, and severe gas generation. Furthermore, existing modification schemes have failed to fundamentally solve these problems, and the processes are complex, have poor controllability, and are costly.
A "dual-gradient" lithium-rich manganese-based cathode material design was adopted, including domain structure gradient and doping element gradient. By controlling the structure and doping element content distribution inside and outside the lithium-rich manganese-based cathode material particles, combined with specific preparation methods such as co-precipitation reaction, thermal sintering and surface coating, a cathode material with excellent performance was prepared.
It significantly improves the long-cycle stability and voltage decay performance of the material, enhances the electrochemical performance of the material, and meets the requirements of high-energy-density lithium-ion batteries.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a lithium-rich manganese-based cathode material and its preparation method. Background Technology
[0002] Currently, commercially available lithium-ion battery cathode materials include lithium cobalt oxide, nickel-cobalt-manganese ternary materials, and lithium iron phosphate, with specific capacities mostly ranging from 110 to 200 mAh / g, which is insufficient to meet the demands of high-energy-density lithium-ion batteries. Therefore, improving the electrochemical performance of cathode materials is crucial for realizing high-energy-density next-generation lithium-ion batteries and advancing the development of industries such as electric vehicles and electric aircraft.
[0003] Lithium-rich manganese-based cathode materials (xLi₂MnO₃·(1-x)LiTMO₂, where TM is selected from any one or at least two of Ni, Mn, or Co) possess reversible specific capacity exceeding 250 mAh / g and outstanding high energy density, making them a key cathode material for high-energy lithium-ion batteries and contributing to the green transformation of transportation electrification. However, lithium-rich manganese-based cathode materials still face numerous challenges, including low first-cycle coulombic efficiency, severe capacity and voltage decay, poor rate performance, and significant gas generation. To address these issues, researchers have proposed a series of material modification schemes, such as surface coating, surface doping, nanostructure control, and material compositing. However, these schemes do not fundamentally alter the intrinsic structure of lithium-rich manganese-based cathode materials, making it difficult to effectively solve the aforementioned problems. Furthermore, these schemes often require additional processing steps, resulting in complex processes, poor controllability, and high costs. Therefore, there is an urgent need to develop efficient, low-cost, and compatible new design schemes for lithium-rich manganese-based cathode materials to effectively solve these problems and significantly improve their electrochemical performance. Summary of the Invention
[0004] This invention provides a "dual-gradient" lithium-rich manganese-based cathode material, which includes two gradient types: domain structure gradient and doping element gradient. The purpose is to improve the long-cycle stability, voltage decay, thermal stability and other properties of the lithium-rich manganese-based cathode material.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] A "dual-gradient" lithium-rich manganese-based cathode material, characterized in that the chemical formula of the lithium-rich manganese-based cathode material is xLi₂MnO₃·(1-x)LiTM 1-y D yO2, where 0 < x < 1 and 0 < y < 0.1, TM represents a transition metal element selected from any one or at least two combinations of Ni, Co, or Mn, D represents a doping element selected from any one or at least two combinations of elements such as Al, Mg, Ti, Nb, Ta, W, Sb, Ce, Zr, etc., and the morphology of the lithium-rich manganese-based cathode material particles is secondary spherical aggregates. The "dual-gradient" lithium-rich manganese-based cathode material includes two gradient types: domain structure gradient and doping element gradient. The domain structure gradient means that the content of monoclinic Li2MnO3 domains in the lithium-rich manganese-based cathode material decreases sequentially from the inside to the outside of the particles, and the content of rhombic LiTMO2 domains increases sequentially from the inside to the outside of the particles; the doping element gradient means that the content of the doping element D increases sequentially from the inside to the outside of the particles.
[0007] A preparation method of a "dual-gradient" lithium-rich manganese-based cathode material includes the following steps:
[0008] Step (1): Independently prepare solution A containing a first nickel source, a first cobalt source, and a first manganese source, and solution B containing a second nickel source, a second cobalt source, and a second manganese source respectively. Among them, the molar ratio of manganese element in the first manganese source in solution A to the total transition metal elements > the molar ratio of manganese element in the second manganese source in solution B to the total transition metal elements;
[0009] Step (2): Add solution A in the satellite kettle to the main reaction kettle through a peristaltic pump for stirring. At the same time, add an alkali solution and a complexing agent solution to the main reaction kettle through a peristaltic pump in a co-current manner, and continuously add solution B to the satellite kettle where solution A is located through a peristaltic pump for stirring. After the main reaction kettle undergoes a coprecipitation reaction, wash and dry the precipitate to obtain a lithium-rich manganese-based cathode material precursor;
[0010] Step (3): Mix the lithium-rich manganese-based cathode material precursor obtained in step (2) with a lithium source, and then perform thermal sintering to obtain a domain structure gradient lithium-rich manganese-based cathode material.
[0011] Step (4): Perform surface coating on the domain structure gradient lithium-rich manganese-based cathode material obtained in step (3), and the coating material is a compound containing the doping element D.
[0012] Step (5): Heat-treat the coated lithium-rich manganese-based cathode material obtained in step (4) to completely consume the coating layer, and make the element D diffuse into the interior of the domain structure gradient lithium-rich manganese-based cathode material particles, thus preparing the "dual-gradient" lithium-rich manganese-based cathode material.
[0013] In this preparation method, the total concentration of TM ions (total transition metal ions) in solution A and solution B in step (1) is 0.2 - 4.0 mol / L; the first nickel source and the second nickel source include, but are not limited to, any one or a combination of at least two of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the first cobalt source and the second cobalt source include, but are not limited to, any one or a combination of at least two of cobalt nitrate, cobalt acetate, cobalt chloride, and cobalt sulfate; the first manganese source and the second manganese source include, but are not limited to, any one or a combination of at least two of manganese nitrate, manganese acetate, manganese chloride, and manganese sulfate.
[0014] In this preparation method, the concentration of the alkali solution in step (2) is 0.1 - 6 mol / L, and the alkali in the alkali solution includes, but is not limited to, any one or a combination of at least two of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide, etc.; the concentration of the complexing agent solution is 0.1 - 6 mol / L, and the complexing agent in the complexing agent solution includes, but is not limited to, any one or a combination of at least two of citric acid, oxalic acid, ammonia water, and ethylenediaminetetraacetic acid.
[0015] In this preparation method, the stirring speed of the main reaction kettle in step (2) is 500 - 1500 rpm; the atmosphere in the main reaction kettle is an inert atmosphere; the pH value of the coprecipitation reaction is 7.0 - 12.0; the temperature inside the main reaction kettle is 40 - 70 °C; the stirring reaction time is 2 - 40 h. From the start to the end of the coprecipitation reaction, the stirring speed of satellite kettle A is 100 - 500 rpm, and the temperature of the satellite kettle solution is room temperature; the stirring reaction time of the satellite kettle is the same as that of the main reaction kettle.
[0016] In this preparation method, in step (3), the molar ratio of the total of metal elements in the lithium-rich layered oxide precursor to the lithium source is 1:n, where 1 < n ≤ 1.5; the lithium source includes, but is not limited to, any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium acetate.
[0017] In this preparation method, in step (3), the material sintering can adopt a one-step sintering method or a two-step sintering method. The sintering atmosphere is any one of oxygen, air, or a mixed gas of oxygen and an inert gas.
[0018] In this preparation method, the coating material in step (4) includes, but is not limited to, compounds formed by elements such as Al, Mg, Ti, Nb, Ta, W, Sb, Ce, Zr, etc., and the compounds include, but are not limited to, oxides, hydroxides, carbonates, phosphates, sulfates, and their mixtures.
[0019] In this preparation method, the coating method in step (4) includes, but is not limited to, atomic layer deposition, liquid phase coating, mechanical fusion, high-speed mixing, and sol-gel methods.
[0020] In this preparation method, the heat treatment temperature in step (5) is 200-800℃, the heating rate is 1-10℃ / min, the holding time is 1-20h, and the sintering atmosphere is any one of air, oxygen, argon, nitrogen, carbon dioxide or a mixture thereof.
[0021] The preferred embodiment of the above preparation method is as follows:
[0022] In step (1), the total concentration of TM ions in solution A and solution B is preferably 1 to 4 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 3 mol / L, or 4 mol / L, but is not limited to the listed values. The listed values are also applicable within the range of values. The manganese, nickel, and cobalt source compounds are preferably one or more of manganese sulfate, nickel sulfate, cobalt sulfate, or their hydrated compounds.
[0023] In step (2), the molar concentration of the alkaline solution is preferably 2 to 4 mol / L, for example, it can be 2 mol / L, 3 mol / L or 4 mol / L, but is not limited to the listed values, and the listed values within the range are also applicable; the alkali in the alkaline solution is preferably any one or a combination of at least two of sodium carbonate, sodium bicarbonate and ammonium bicarbonate; the complexing agent is preferably ammonia water, and the molar concentration of ammonia water is preferably 0.1 to 3 mol / L, for example, it can be 0.2 mol / L, 1.2 mol / L, 2 mol / L or 3 mol / L, but is not limited to the listed values, and the listed values within the range are also applicable.
[0024] In step (2), the stirring speed of the reaction is preferably 800-1100 rpm, for example, 800 rpm, 900 rpm, 1000 rpm or 1100 rpm, but not limited to the listed values, and the listed values within the range are also applicable; the pH of the coprecipitation reaction is preferably 7.5-9, for example, 7.5, 8.0, 8.5 or 9.0, but not limited to the listed values, and the listed values within the range are also applicable; the temperature of the reaction is preferably 50-60℃, for example, 50℃, 55℃ or 60℃, but not limited to the listed values, and the listed values within the range are also applicable; the stirring reaction time is preferably 15-30h, for example, 15h, 20h, 25h or 30h, but not limited to the listed values, and the listed values within the range are also applicable; under these preferred reaction conditions, the preparation of lithium-rich layered oxide precursors can further improve the tap density and sphericity of the material.
[0025] In step (3), the molar ratio of the total metal elements in the lithium-rich layered oxide precursor to the lithium source is preferably 1:1-1.1, for example, it can be 1:1, 1:1.01, 1:1.03 or 1:1.05, but is not limited to the listed values. The listed values are also applicable within the range of values. The lithium source is preferably any one or a combination of two of lithium hydroxide and lithium carbonate.
[0026] In step (3), the material sintering is preferably a two-step sintering method, and the sintering atmosphere is preferably air. In the two-step sintering method, the heating rate of the first step is preferably 2-5℃ / min, for example, it can be 2℃ / min or 5℃ / min, but is not limited to the listed values; the listed values within the range are also applicable. The sintering temperature is preferably 500-550℃, for example, it can be 500℃ or 550℃, but is not limited to the listed values; the listed values within the range are also applicable. The sintering time is preferably 4-6h, for example, it can be 4h or 5h, but is not limited to the listed values; the listed values within the range are also applicable. The values listed within the specified range also apply; the preferred heating rate in the second step is 2-5℃ / min, for example, 2℃ / min or 5℃ / min, but not limited to the listed values, and the values listed within the specified range also apply; the preferred sintering temperature is 850-900℃, for example, 850℃ / min or 900℃ / min, but not limited to the listed values, and the values listed within the specified range also apply; the preferred sintering time is 8-12h, for example, 8h, 10h or 12h, but not limited to the listed values, and the values listed within the specified range also apply. The lithium-rich layered oxide with a domain structure gradient prepared under these preferred reaction conditions exhibits high crystallinity and high sphericity, and no residual alkali exists on the surface of the aggregates.
[0027] In step (4), the coating material is preferably an oxide, carbonate, sulfate or mixture thereof formed by Al, Mg, Ti, Ce or Zr elements, and more preferably an oxide.
[0028] In step (4), the coating method is preferably atomic layer deposition or mechanical fusion. In step (5), the heat treatment temperature of the coated lithium-rich layered oxide with domain structure gradient is preferably 400-600℃, for example, 500℃ / min or 600℃ / min, but not limited to the listed values; the listed values within the range are also applicable; the heating rate is 2-5℃ / min, for example, 2℃ / min or 5℃ / min, but not limited to the listed values; the listed values within the range are also applicable; the holding time is 3-8h, for example, 3h or 6h, but not limited to the listed values; the listed values within the range are also applicable; the sintering atmosphere is preferably air. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the lithium-rich manganese-based cathode material of the present invention;
[0030] Figure 2 This is a comparison of the long-cycle performance of Embodiment 1 and Comparative Example 1 of the present invention;
[0031] Figure 3 This is a comparison of the average voltage drop between Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation
[0032] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0033] Example 1:
[0034] This embodiment provides a method for preparing a "dual-gradient" lithium-rich manganese-based cathode material for lithium-ion batteries, the method comprising the following steps:
[0035] (1) MnSO4·H2O, NiSO4·6H2O and CoSO4·7H2O were dissolved in deionized water in a certain molar ratio to prepare mixed salt solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Mn:Ni:Co in solution A was 0.71:0.21:0.08, and the molar ratio of Mn:Ni:Co in solution B was 0.53:0.34:0.13. A 2 mol / L Na2CO3 solution was prepared as a precipitant, and a 0.2 mol / L ammonia solution was prepared as a complexing agent.
[0036] (2) Solution A was added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and complexing agent solution were added to the main reactor in parallel by a peristaltic pump. Simultaneously, solution B was added to the satellite reactor containing solution A by a peristaltic pump and stirred. The reaction temperature was controlled at 55℃, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was protected by N2 as an inert gas and carried out a co-precipitation reaction. After 30 hours of co-precipitation reaction, a carbonate precursor material of lithium-rich layered oxides with a full concentration gradient of nickel, manganese and cobalt was obtained.
[0037] (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.05 and then placed in a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, the temperature was held at 600℃ for 5 h, then the temperature was raised to 900℃ and held for 12 h at a heating rate of 5℃ / min. Finally, the temperature was naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a domain structure gradient.
[0038] (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is coated using atomic layer deposition. 1.5g of cathode material is weighed and placed in a specially made round-bottom flask. The reaction flask is then placed in the ALD reaction chamber. The ALD equipment is turned on and a vacuum is drawn. The temperature of the reaction chamber is heated to 150°C and the temperature of the pipeline is 85°C. (CH3)3Al(TMA) is used as the Al source with a pulse time of 0.3s and a reaction time of 60s. Mg(C5H5)2 is used as the Mg source with a pulse time of 0.2s and a reaction time of 120s. Deionized water is used with a pulse time of 0.6s and a reaction time of 60s. In the deposition process of ALD, the deposition sequence is as follows: (CH3)3Al-purge(60s)-H2O-purge(60s)-Mg(C5H5)2-purge(60s)-H2O(0.5s pulse)-purge(60s); N2 (99.999%) is used as the carrier gas; the above steps are repeated twice to obtain a lithium-rich manganese-based cathode material with a domain structure gradient coated with Al / Mg elements.
[0039] (5) The lithium-rich manganese-based cathode material described in step (4) is heated to 400°C at a rate of 5°C / min and held for 5 hours to completely consume the coating layer. After natural cooling, a "dual gradient" is obtained.
[0040] Lithium-rich manganese-based cathode material.
[0041] The electrochemical performance of the obtained "dual-gradient" lithium-rich manganese-based cathode material was tested. Cyclic performance was tested using CR2032 coin cells. The ratio of "dual-gradient" lithium-rich manganese-based cathode material: conductive carbon (SP): binder (PVDF) in the coin cell cathode was 8:1:1. A Celgard 2400 separator was used, and a lithium metal sheet was used for the anode. The electrolyte was a high-voltage electrolyte purchased from Guotai Huarong Company. The assembled battery was charged and discharged once at a rate of 0.1C within a voltage range of 2.0-4.8V at 25℃, and then charged and discharged 500 times at a rate of 1C within a voltage range of 2.0-4.6V. Figure 2 Electrochemical tests showed that the lithium-rich manganese-based cathode material with a "dual gradient" design exhibited excellent cycle stability, retaining 86% of its capacity after 500 cycles. This is significantly better than the lithium-rich manganese-based cathode material in Comparative Example 1, which only exhibited a domain structure gradient and retained only 80% of its capacity. Furthermore, Figure 3 The average discharge voltage shows that the lithium-rich manganese-based cathode material with the "dual gradient" design also has the characteristic of low voltage decay. The average discharge voltage decay after 500 cycles is 0.3mV / cycle, which is significantly better than the 0.42mV / cycle of Comparative Example 1.
[0042] Example 2:
[0043] This embodiment provides a method for preparing a "dual-gradient" lithium-rich manganese-based cathode material for lithium-ion batteries, the method comprising the following steps:
[0044] (1) MnSO4·H2O, NiSO4·6H2O and CoSO4·7H2O were dissolved in deionized water in a certain molar ratio to prepare mixed salt solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Mn:Ni:Co in solution A was 0.7:0.2:0.1, and the molar ratio of Mn:Ni:Co in solution B was 0.5:0.35:0.15. A 2 mol / L Na2CO3 solution was prepared as a precipitant. A 0.4 mol / L ammonia solution was prepared as a complexing agent.
[0045] (2) Solution A was added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and complexing agent solution were added to the main reactor in parallel by a peristaltic pump. Solution B was added to the satellite reactor containing solution A by a peristaltic pump and stirred. The reaction temperature was controlled at 55℃, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was protected by N2 as an inert gas. After co-precipitation reaction for 30 h, a lithium-rich layered oxide carbonate precursor material with a full concentration gradient of nickel, manganese and cobalt was obtained. (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.03 and then loaded into a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, it was kept at 600℃ for 5 h, then heated to 900℃ for 12 h at a heating rate of 5℃ / min, and finally cooled naturally to room temperature to obtain a domain structure gradient lithium-rich manganese-based cathode material.
[0046] (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is coated on the surface using a mechanical fusion method; 300g of domain structure gradient lithium-rich manganese-based cathode material and 3g of nano-Al2O3 are weighed and put into the mechanical fusion coating machine cavity, and mechanically mixed for 4min at a low linear speed of 1000rpm / min to achieve a preliminary mixing effect between Al2O3 and domain structure gradient lithium-rich manganese-based cathode material; the mechanical fusion machine speed is adjusted to 3000rpm / min and 5000rpm / min respectively, and mechanical fusion coating is performed for 4min respectively to uniformly coat nano-Al2O3 on the domain structure gradient lithium-rich manganese-based cathode material;
[0047] (5) The lithium-rich manganese-based cathode material described in step (4) is heated to 600°C at a rate of 5°C / min and held for 5 hours to completely consume the coating layer. After natural cooling, a "dual gradient" is obtained.
[0048] Lithium-rich manganese-based cathode material.
[0049] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 84%, and the average voltage decay is 0.34 mV / cycle.
[0050] Example 3:
[0051] (1) Dissolve MnSO4·H2O, NiSO4·6H2O and CoSO4·7H2O in deionized water at a certain molar ratio to prepare mixed salt solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Mn:Ni:Co in solution A is 0.7:0.2:0.1, and the molar ratio of Mn:Ni:Co in solution B is 0.5:0.35:0.15. Prepare a 2 mol / L Na2CO3 solution as a precipitant and a 0.2 mol / L ammonia solution as a complexing agent.
[0052] (2) Solution A was added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and complexing agent solution were added to the main reactor in parallel by a peristaltic pump. Solution B was added to the satellite reactor containing solution A by a peristaltic pump and stirred. The reaction temperature was controlled at 55℃, the pH was maintained at 7.8, and the stirring speed was 1000 rpm / min. The entire reaction process was protected by N2 as an inert gas. After co-precipitation reaction for 30 h, a lithium-rich layered oxide carbonate precursor material with nickel, manganese and cobalt full concentration gradient was obtained. (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.03 and then loaded into a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, it was kept at 600℃ for 5 h, then raised to 900℃ and kept for 12 h at a heating rate of 5℃ / min. Finally, it was naturally cooled to room temperature to obtain a domain structure gradient lithium-rich manganese-based cathode material.
[0053] (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is coated on the surface using a mechanical fusion method; 300g of domain structure gradient lithium-rich manganese-based cathode material and 3g of nano-Al2O3 are weighed and put into the mechanical fusion coating machine cavity, and mechanically mixed for 4min at a low linear speed of 1000rpm / min to achieve a preliminary mixing effect between Al2O3 and domain structure gradient lithium-rich manganese-based cathode material; the mechanical fusion machine speed is adjusted to 3000rpm / min and 5000rpm / min respectively, and mechanical fusion coating is performed for 4min respectively to uniformly coat nano-Al2O3 on the domain structure gradient lithium-rich manganese-based cathode material;
[0054] (5) The lithium-rich manganese-based cathode material described in step (4) is heated to 600°C at a rate of 5°C / min and held for 5 hours to completely consume the coating layer. After natural cooling, a "dual gradient" is obtained.
[0055] Lithium-rich manganese-based cathode material.
[0056] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 85%, and the average voltage decay is 0.32 mV / cycle.
[0057] Example 4:
[0058] (1) Dissolve MnSO4·H2O and NiSO4·6H2O in deionized water at a certain molar ratio to prepare mixed salt solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Mn:Ni in solution A is 0.75:0.25, and the molar ratio of Mn:Ni in solution B is 0.59:0.41. Prepare a 2 mol / L Na2CO3 solution as a precipitant and a 0.2 mol / L ammonia solution as a complexing agent.
[0059] (2) Solution A was added to the main reactor via a peristaltic pump and stirred. Simultaneously, the alkaline solution and complexing agent solution were added to the main reactor in parallel via a peristaltic pump, and solution B was added to the satellite reactor containing solution A via a peristaltic pump and stirred. The reaction temperature was controlled at 55℃, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was carried out under N2 as an inert gas protection. After a co-precipitation reaction for 30 hours, a lithium-rich layered oxide carbonate precursor material containing nickel and manganese with a full concentration gradient was obtained.
[0060] (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.03 and then placed in a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, the temperature was held at 600℃ for 5 h, then the temperature was raised to 900℃ and held for 12 h at a heating rate of 5℃ / min. Finally, the temperature was naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a domain structure gradient.
[0061] (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is surface coated using a mechanical fusion method; 300g of domain structure gradient lithium-rich manganese-based cathode material, 1.5g of nano-Al2O3, and 1.5g of nano-MgO are weighed and put into the mechanical fusion coating machine cavity. First, mechanical mixing is performed at a low linear speed of 1000rpm / min for 4min to achieve a preliminary mixing effect between Al2O3 and MgO and the domain structure gradient lithium-rich manganese-based cathode material; the mechanical fusion machine speed is adjusted to 3000rpm / min and 5000rpm / min respectively, and mechanical fusion coating is performed for 4min respectively to uniformly coat nano-Al2O3 and MgO on the domain structure gradient lithium-rich manganese-based cathode material.
[0062] (5) The lithium-rich manganese-based cathode material described in step (4) is heated to 600°C at a rate of 5°C / min and held for 5 hours to completely consume the coating layer. After natural cooling, a "dual gradient" is obtained.
[0063] Lithium-rich manganese-based cathode material.
[0064] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 85%, and the average voltage decay is 0.33 mV / cycle.
[0065] Example 5:
[0066] (1) Dissolve MnSO4·H2O and NiSO4·6H2O in deionized water at a certain molar ratio to prepare mixed salt solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Mn:Ni in solution A is 0.75:0.25, and the molar ratio of Mn:Ni in solution B is 0.59:0.41. Prepare a 2 mol / L Na2CO3 solution as a precipitant and a 0.2 mol / L ammonia solution as a complexing agent.
[0067] (2) Solution A was added to the main reactor via a peristaltic pump and stirred. Simultaneously, the alkaline solution and complexing agent solution were added to the main reactor in parallel via a peristaltic pump, and solution B was added to the satellite reactor containing solution A via a peristaltic pump and stirred. The reaction temperature was controlled at 55℃, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was carried out under N2 as an inert gas protection. After a co-precipitation reaction for 30 hours, a lithium-rich layered oxide carbonate precursor material containing nickel and manganese with a full concentration gradient was obtained.
[0068] (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.03 and then placed in a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, the temperature was held at 600℃ for 5 h, then the temperature was raised to 900℃ and held for 12 h at a heating rate of 5℃ / min. Finally, the temperature was naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a domain structure gradient.
[0069] (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is coated on the surface using the liquid phase coating method; 0.05g of nano Al2O3 and 0.05g of nano MgO are placed in a round bottom flask and mixed thoroughly at 80°C for 1h. Then, 10g of domain structure gradient lithium-rich manganese-based cathode material is added and mixed for another 8h. After the reaction is completed, the material is filtered and dried in a vacuum oven at 80°C for 12h to obtain a domain structure gradient lithium-rich manganese-based cathode material uniformly coated with nano Al2O3 and MgO.
[0070] (5) The lithium-rich manganese-based cathode material described in step (4) is heated to 600°C at a rate of 5°C / min and held for 5 hours to completely consume the coating layer. After natural cooling, a "dual gradient" is obtained.
[0071] Lithium-rich manganese-based cathode material.
[0072] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 85%, and the average voltage decay is 0.35 mV / cycle.
[0073] Example 6:
[0074] (1) Dissolve MnSO4·H2O, NiSO4·6H2O, and CoSO4·7H2O in deionized water at a certain molar ratio to prepare 2 mol / L mixed salt solutions A and B, respectively. The molar ratio of Mn:Ni:Co in solution A is 0.8:0.1:0.1, and the molar ratio of Mn:Ni:Co in solution B is 0.3:0.5:0.2. Prepare a 2 mol / L Na2CO3 solution as a precipitant. Prepare a 0.6 mol / L ammonia solution as a precipitant. (2) Solution A was added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and the complexing agent solution were added to the main reactor in parallel by a peristaltic pump. Simultaneously, solution B was added to the satellite reactor containing solution A by a peristaltic pump and stirred. The reaction temperature was controlled at 55°C, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was protected by N2 as an inert gas. After co-precipitation reaction for 30 h, a carbonate precursor material containing lithium-rich layered oxides with a full concentration gradient of nickel, manganese, and cobalt was obtained.
[0075] (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.03 and then placed in a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, the temperature was held at 600℃ for 5 h, then the temperature was raised to 900℃ and held for 12 h at a heating rate of 5℃ / min. Finally, the temperature was naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a domain structure gradient.
[0076] (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is coated on the surface using a mechanical fusion method; 300g of domain structure gradient lithium-rich manganese-based cathode material and 3g of nano-Al2O3 are weighed and put into the mechanical fusion coating machine cavity, and mechanically mixed for 4min at a low linear speed of 1000rpm / min to achieve a preliminary mixing effect between Al2O3 and domain structure gradient lithium-rich manganese-based cathode material; the mechanical fusion machine speed is adjusted to 3000rpm / min and 5000rpm / min respectively, and mechanical fusion coating is performed for 4min respectively to uniformly coat nano-Al2O3 on the domain structure gradient lithium-rich manganese-based cathode material;
[0077] (5) The lithium-rich manganese-based cathode material described in step (4) is heated to 600°C at a rate of 5°C / min and held for 5 hours to completely consume the coating layer. After natural cooling, a "dual gradient" is obtained.
[0078] Lithium-rich manganese-based cathode material.
[0079] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 86%, and the average voltage decay is 0.35 mV / cycle.
[0080] Comparative Example 1:
[0081] (1) MnSO4·H2O, NiSO4·6H2O and CoSO4·7H2O were dissolved in deionized water in a certain molar ratio to prepare mixed salt solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Mn:Ni:Co in solution A was 0.71:0.21:0.08, and the molar ratio of Mn:Ni:Co in solution B was 0.53:0.34:0.13. A 2 mol / L Na2CO3 solution was prepared as a precipitant, and a 0.2 mol / L ammonia solution was prepared as a complexing agent.
[0082] (2) Solution A was added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and complexing agent solution were added to the main reactor in parallel by a peristaltic pump. Simultaneously, solution B was added to the satellite reactor containing solution A by a peristaltic pump and stirred. The reaction temperature was controlled at 55℃, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was protected by N2 as an inert gas. After co-precipitation reaction for 30 h, a carbonate precursor material of lithium-rich layered oxides with nickel, manganese and cobalt in full concentration gradient was obtained.
[0083] (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.05 and then placed in a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, the temperature was held at 600℃ for 5 h, then the temperature was raised to 900℃ and held for 12 h at a heating rate of 5℃ / min. Finally, the temperature was naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a domain structure gradient.
[0084] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 80%, and the average voltage decay is 0.42 mV / cycle.
[0085] Comparative Example 2:
[0086] (1) Dissolve MnSO4·H2O, NiSO4·6H2O and CoSO4·7H2O in deionized water at a certain molar ratio to prepare a mixed salt solution A with a concentration of 2 mol / L, wherein the molar ratio of Mn:Ni:Co in solution A is 0.71:0.21:0.08; prepare a 2 mol / L Na2CO3 solution as a precipitant; and prepare a 0.2 mol / L ammonia solution as a complexing agent.
[0087] (2) Solution A was added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and complexing agent solution were added to the main reactor in parallel by a peristaltic pump. The reaction temperature was controlled at 55℃, the pH was maintained at 7.7, and the stirring speed was 1000 rpm / min. The entire reaction process was protected by N2 as an inert gas and carried out a co-precipitation reaction. After 30 hours of co-precipitation reaction, a carbonate precursor material of lithium-rich layered oxide with uniform composition was obtained.
[0088] (3) The precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:1.05 and then placed in a crucible. Sintering was carried out in an air atmosphere using a two-step sintering method. First, the temperature was held at 600℃ for 5 h, then the temperature was raised to 900℃ and held for 12 h at a heating rate of 5℃ / min. Finally, the temperature was naturally cooled to room temperature to obtain a gradeless lithium-rich manganese-based cathode material.
[0089] The electrochemical performance testing conditions and methods for the above materials are the same as those in Example 1. The capacity retention rate after 500 cycles is 70%, and the average voltage decay is 0.78 mV / cycle.
Claims
1. A "dual-gradient" lithium-rich manganese-based cathode material, characterized in that, The chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiTM 1-y D y O2, where 0 < x < 1, 0 < y < 0.1, TM represents a transition metal element selected from any one or a combination of at least two of Ni, Co, or Mn, D represents a doping element selected from any one or a combination of at least two of elements such as Al, Mg, Ti, Nb, Ta, W, Sb, Ce, Zr, etc., and its particle morphology is secondary spherical aggregates; the "dual-gradient" lithium-rich manganese-based cathode material includes two gradient types: domain structure gradient and doping element gradient; the domain structure gradient means that the content of monoclinic Li2MnO3 domains in the lithium-rich manganese-based cathode material decreases sequentially from the inside to the outside of the particle, and the content of rhombic LiTMO2 domains increases sequentially from the inside to the outside of the particle; the doping element gradient means that the content of the doping element D increases sequentially from the inside to the outside of the particle.
2. The method for preparing a "dual-gradient" lithium-rich manganese-based cathode material according to claim 1, characterized in that, The preparation method includes: (1) Prepare solutions A containing a first nickel source, a first cobalt source and a first manganese source, and solutions B containing a second nickel source, a second cobalt source and a second manganese source independently, wherein the molar ratio of manganese element in solution A to total transition metal elements in solution A is greater than the molar ratio of manganese element in solution B to total transition metal elements in solution B. (2) Solution A in the satellite reactor is added to the main reactor by a peristaltic pump and stirred. At the same time, the alkaline solution and complexing agent solution are added to the main reactor in parallel by a peristaltic pump. Simultaneously, solution B is added to the satellite reactor containing solution A by a peristaltic pump and stirred. After co-precipitation reaction, the precipitate is washed with water and dried to obtain lithium-rich manganese-based cathode material precursor. (3) After mixing the lithium-rich manganese-based cathode material precursor described in step (2) with a lithium source, the mixture is sintered to obtain a domain-structure gradient lithium-rich manganese-based cathode material. (4) The domain structure gradient lithium-rich manganese-based cathode material described in step (3) is coated with a compound containing dopant element D. (5) The coated lithium-rich manganese-based cathode material described in step (4) is heated to completely consume the coating layer and allow element D to diffuse into the particles of the domain structure gradient lithium-rich manganese-based cathode material, thus preparing a "dual gradient" lithium-rich manganese-based cathode material.
3. The preparation method according to claim 2, characterized in that, The total concentration of TM ions in solutions A and B in step (1) is 0.2–4.0 mol / L; Step (1) The first nickel source and the second nickel source include, but are not limited to, any one or at least two of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the first cobalt source and the second cobalt source include, but are not limited to, any one or at least two of cobalt nitrate, cobalt acetate, cobalt chloride, or cobalt sulfate; the first manganese source and the second manganese source include, but are not limited to, any one or at least two of manganese nitrate, manganese acetate, manganese chloride, or manganese sulfate.
4. The preparation method according to claim 2, characterized in that, The concentration of the alkaline solution in step (2) is 0.1 to 6 mol / L, and the alkaline solution includes, but is not limited to, any one or at least two combinations of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide, etc.; the concentration of the complexing agent solution is 0.1 to 6 mol / L, and the complexing agent solution includes, but is not limited to, any one or at least two combinations of citric acid, oxalic acid, ammonia, or ethylenediaminetetraacetic acid.
5. The preparation method according to claim 2, characterized in that, In step (2), the stirring speed of the main reactor is 500-1500 rpm; the atmosphere of the main reactor is inert; the pH value of the coprecipitation reaction is 7.0-12.0; the temperature inside the main reactor is 40-70℃; the stirring reaction time is 2-40 h; from the start to the end of the coprecipitation reaction, the stirring speed of the satellite reactor A is 100-500 rpm, and the temperature of the solution in the satellite reactor is room temperature; the stirring reaction time of the satellite reactor is the same as that of the main reactor.
6. The preparation method according to claim 2, characterized in that, The molar ratio of the total metal elements in the lithium-rich layered oxide precursor described in step (3) to the lithium source is 1:n, where 1 < n ≤ 1.5; the lithium source includes, but is not limited to, any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium oxalate, or lithium acetate.
7. The preparation method according to claim 2, characterized in that, In step (3), the material is sintered using a one-step sintering or two-step sintering method; in the one-step sintering method, first heat it from room temperature to 850 - 950 °C at a rate of 1 - 10 °C / min, hold for 4 - 12 h, and then cool it naturally to room temperature; in the two-step sintering method, first heat it to 450 - 600 °C at a rate of 2 - 10 °C / min, sinter for 4 - 8 h, then heat it to 850 - 950 °C at a rate of 1 - 10 °C / min, hold for 4 - 12 h, and then cool it naturally to room temperature; the sintering atmosphere is any one of oxygen, air, or a mixed gas of oxygen and an inert gas.
8. The preparation method according to claim 2, characterized in that, The coating material in step (4) includes, but is not limited to, compounds formed by elements such as Al, Mg, Ti, Nb, Ta, W, Sb, Ce, Zr, etc., and the compounds include, but are not limited to, oxides, hydroxides, carbonates, phosphates, sulfates, and mixtures thereof.
9. The preparation method according to claim 2, characterized in that, The coating method in step (4) includes, but is not limited to, atomic layer deposition, liquid-phase coating, mechanical fusion, high-speed mixing, sol-gel method.
10. The preparation method according to claim 2, characterized in that, In step (5), the temperature of the heat treatment is 200 - 800 °C, the heating rate is 1 - 10 °C / min, and the holding time is 1 - 20 h. The sintering atmosphere is any one of air, oxygen, argon, nitrogen, carbon dioxide, or a mixed gas thereof, preferably air.