Modified lithium-rich manganese-based precursor as well as preparation method and application thereof

Abstract

The invention provides a modified lithium-rich manganese-based precursor as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, enabling a mixed metal salt solution, an indium salt solution and a precipitant solution to flow into a reaction base solution in parallel, and carrying out coprecipitation reaction to obtain a half-step precursor material with a target particle size; mixing the half-step precursor material with a solution containing an organic niobium compound to obtain a precursor material; and finally, carrying out spray pyrolysis treatment on the precursor material and a phosphate solution to obtain the modified lithium-rich manganese-based precursor. According to the invention, the surface and interface stability and the structural stability of the lithium-rich manganese-based precursor material are enhanced through a composite modification technical means of combining multi-metal co-doping and phosphate coating, so that the effective capacity, the cycling stability and the electrochemical performance consistency of the lithium-rich manganese-based positive electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of cathode material precursor technology, specifically relating to a modified lithium-rich manganese-based precursor, its preparation method, and its application. Background Technology

[0002] Lithium-rich manganese-based cathode materials are considered the next generation of high-energy-density lithium-ion battery cathode materials due to their advantages such as high specific capacity (>250 mAh / g), low cost, and environmental friendliness. Unlike traditional layered oxide materials, the high specific capacity of lithium-rich manganese-based materials mainly originates from the redox activity of anionic oxygen. However, while oxygen participation in redox reactions breaks through the redox capacity limits of traditional transition metals, it also causes problems such as lattice oxygen loss, transition metal ion migration, and irreversible structural evolution, leading to a continuous decay of discharge voltage during cycling and a significant decrease in initial coulombic efficiency and capacity retention. Furthermore, changes in crystal structure can cause stress accumulation, further affecting the performance of the cathode material. These factors severely restrict the practical application of lithium-rich manganese-based cathode materials.

[0003] To address the aforementioned issues, researchers have focused on modifying lithium-rich manganese-based precursor materials to further improve the initial coulombic efficiency, rate performance, and cycle stability of cathode materials. While existing modification techniques, such as elemental doping and surface coating, have made some progress in enhancing the performance of lithium-rich manganese-based cathode materials, single modification methods often have limitations and cannot comprehensively solve the material's performance problems, as detailed below:

[0004] (1) During element doping, when the ionic radius of the dopant atom differs significantly from that of the lattice atom, the dopant ion may not be able to integrate smoothly into the original lattice, leading to lattice distortion. This distortion can induce lattice stress, damage the crystal structure of the material, and even trigger phase transitions or structural collapse, ultimately affecting the cycle stability of the cathode material. In addition, uneven distribution of dopant elements in the precursor may form inactive regions, reducing the effective capacity of the cathode material or causing localized differences in electrochemical performance.

[0005] (2) During the surface coating process, the interfacial characteristics between the coating layer and the substrate material are key factors determining the performance and stability of the precursor. For example, mismatch in the coefficients of thermal expansion or improper process conditions may lead to the formation of cracks or voids, thereby weakening the protective effect of the coating layer. At the same time, the island-like distribution of the coating layer causes local areas to be exposed, which exacerbates the side reactions between the cathode material and the electrolyte (such as the dissolution of transition metals), further deteriorating the electrochemical performance of the battery.

[0006] In addition, existing doping and coating methods generally require multiple high-temperature processes (such as solid-state reactions or atomic layer deposition), which increases energy consumption and time costs. Furthermore, the high cost of some coating agents (such as high-purity oxides) or doping elements (such as noble metals) limits their application in large-scale production.

[0007] Therefore, how to provide a simple and efficient modification method for lithium-rich manganese-based precursors to comprehensively improve their structural stability and interfacial properties, thereby enhancing the electrochemical performance of cathode materials, is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium-rich manganese-based precursor, its preparation method, and its application. By employing a composite modification technique combining multi-metal co-doping and phosphate coating, the surface and interfacial stability and structural stability of the lithium-rich manganese-based precursor material are enhanced, thereby improving the effective capacity, cycle stability, and electrochemical performance consistency of the lithium-rich manganese-based cathode material.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a modified lithium-rich manganese-based precursor, the method comprising the following steps:

[0011] S1. A mixed metal salt solution, indium salt solution, and precipitant solution are fed into the reaction substrate in a co-precipitation reaction to obtain a half-step precursor material with the target particle size.

[0012] S2. Mix the semi-step precursor material with a solution containing an organoniobium compound to obtain the precursor material;

[0013] S3. The precursor material and phosphate solution are subjected to spray pyrolysis to obtain the modified lithium-rich manganese-based precursor.

[0014] This invention, by controlling the precursor preparation process, ultimately yields a phosphate-coated / multi-metal co-doped lithium-rich manganese-based precursor. The phosphate coating layer is uniform and continuous, and the doped metal elements are evenly distributed both inside and on the surface of the material. Through the aforementioned combined modification techniques, the capacity, long-term cycle stability, and rate performance of the lithium-rich manganese-based cathode material can be effectively improved, as specifically as follows:

[0015] (1) The present invention selects indium as the doping metal element because indium ions are electrochemically inert and do not change their valence state during charge-discharge cycles, and therefore do not change their volume. In this way, indium can play the role of a framework, stabilize the crystal structure, and thus achieve the technical effect of improving the cycle performance and safety of the cathode material.

[0016] (2) This invention achieves uniform niobium doping on the surface of the semi-step precursor material by mixing the semi-step precursor material with a solution containing organic niobium compounds, thereby forming a double-shell surface reconstruction layer of "Nb-doped / phosphate coated" on the material surface, which can effectively alleviate the degradation of the material's crystal structure, thereby achieving the technical effect of improving the cycle performance and structural stability of the cathode material.

[0017] (3) The phosphate coating layer formed by the present invention has a low lattice mismatch with the precursor and is firmly attached and not easy to peel off; the coating layer isolates the erosion of the cathode material by air and electrolyte, slows down the phase transition rate of the cathode material during cycling, and improves the interface stability; moreover, the synergistic effect of the co-doping of the two metal elements and the lithium phosphate conductor coating layer can significantly improve the capacity, cycle performance and rate performance of the cathode material in battery applications.

[0018] Preferably, in step S1, the mixed metal salt solution includes nickel and manganese.

[0019] Preferably, in step S1, the molar ratio of nickel to manganese in the mixed metal salt solution is (22-25):(75-78), for example, it can be 22:78, 23:77, 24:76 or 25:75, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, in step S1, the total concentration of all metal ions in the mixed metal salt solution is 1 mol / L to 4 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, in step S1, the flow rate of the mixed metal salt solution is 2L / h-4L / h, for example, it can be 2L / h, 2.5L / h, 3L / h, 3.5L / h or 4L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, in step S1, the concentration of the indium salt solution is 100ppm-2000ppm, for example, it can be 100ppm, 200ppm, 500ppm, 800ppm, 1000ppm, 1200ppm, 1500ppm, 1800ppm or 2000ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] In this invention, by adjusting the concentration of the indium salt solution to the aforementioned suitable range, the structural stability and rate performance of the prepared cathode material are both improved. If a lower concentration of indium salt solution is used, the structure of the cathode material cannot be stabilized better; if a higher concentration of indium salt solution is used, more inert components will be introduced into the precursor, thereby reducing the capacity of the cathode material.

[0024] Preferably, in step S1, the flow rate of the indium salt solution is 0.08 L / h to 0.12 L / h, for example, it can be 0.08 L / h, 0.09 L / h, 0.10 L / h, 0.11 L / h or 0.12 L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, in step S1, the precipitant solution comprises a mixed solution of ammonia and sodium carbonate.

[0026] Preferably, in step S1, the pH value of the reaction substrate is 9.0-12.0, for example, it can be 9.0, 9.5, 10.0, 10.5, 11.0, 11.5 or 12.0, etc.; the ammonia concentration of the reaction substrate is 3g / L-7g / L, for example, it can be 3g / L, 4g / L, 5g / L, 6g / L or 7g / L, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] Preferably, in step S1, the pH value of the coprecipitation reaction is 10.3-10.7, for example, it can be 10.3, 10.35, 10.4, 10.45, 10.5, 10.55, 10.6, 10.65 or 10.7, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, in step S1, the temperature of the coprecipitation reaction is 40℃-60℃, for example, it can be 40℃, 45℃, 50℃, 55℃ or 60℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, in step S1, the average particle size of the target particle size is 9μm-11μm, for example, it can be 9μm, 9.5μm, 10μm, 10.5μm or 11μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, in step S2, the concentration of the solution containing the organoniobium compound is 0.4 mol / L-0.6 mol / L, for example, it can be 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L or 0.6 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] In this invention, by adjusting the concentration of the solution containing organoniobium compounds to the aforementioned suitable range, the irreversible dissolution of transition metal elements in the cathode material during charging and discharging can be mitigated, thereby enhancing cycle stability and structural stability. This overcomes the problems of poor rate performance, poor cycle stability, and crack formation found in existing cathode materials. The aforementioned effects cannot be achieved by using solutions containing organoniobium compounds at either lower or higher concentrations.

[0032] Preferably, the organoniobium compound includes niobium ethanol.

[0033] Preferably, in step S2, the solvent in the solution containing the organoniobium compound includes ethanol.

[0034] Preferably, in step S2, the mixing temperature is 50℃-70℃, for example, it can be 50℃, 55℃, 60℃, 65℃ or 70℃, etc.; the mixing time is 1h-3h, for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] Preferably, in step S3, the phosphate solution includes a lithium phosphate solution.

[0036] Preferably, in step S3, the mass concentration of the phosphate solution is 20%-30%, for example, it can be 20%, 22%, 25%, 28% or 30%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] In this invention, the rate performance of the cathode material is enhanced by adjusting the mass concentration of the phosphate solution to the above-mentioned suitable range.

[0038] Preferably, in step S3, the temperature of the spray pyrolysis is 600℃-800℃, for example, it can be 600℃, 650℃, 700℃, 750℃ or 800℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, in step S3, the spray pyrolysis time is 50s-70s, for example, it can be 50s, 55s, 60s, 65s or 70s, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] In this invention, by adjusting the range of conditions and parameters of spray pyrolysis, it is beneficial to form a phosphate coating layer with uniform distribution and appropriate thickness, and to enhance the mechanical strength of the coating layer and the bonding strength between the coating layer and the matrix material, thereby alleviating the side reactions at the electrolyte contact interface and inhibiting the peeling of the coating layer during cycling.

[0041] In a second aspect, the present invention provides a modified lithium-rich manganese-based precursor, which is prepared by the method for preparing a modified lithium-rich manganese-based precursor as described in the first aspect. The modified lithium-rich manganese-based precursor comprises, from the inside out, an indium-doped precursor core, a niobium-doped intermediate layer, and a phosphate coating layer covering the surface of the niobium-doped intermediate layer.

[0042] In this invention, based on the total mass of the modified lithium-rich manganese-based precursor as 100%, the mass percentage content of indium is 100ppm-2000ppm, for example, it can be 100ppm, 200ppm, 500ppm, 800ppm, 1000ppm, 1200ppm, 1500ppm, 1800ppm or 2000ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] In this invention, taking the total mass of the modified lithium-rich manganese-based precursor as 100%, the mass percentage content of niobium in the niobium-doped intermediate layer is 500ppm-5000ppm, for example, it can be 500ppm, 800ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm or 5000ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the niobium content on the surface of the niobium-doped interlayer is 1 wt.%-2 wt.%, for example, it can be 1 wt.%, 1.2 wt.%, 1.5 wt.%, 1.8 wt.%, or 2 wt.%, etc., and is not limited to the listed values; other unlisted values ​​within this range are also applicable. This invention further improves the electrochemical performance of lithium-rich manganese-based cathode materials by controlling the niobium content on the surface of the niobium-doped interlayer.

[0045] Preferably, the thickness of the phosphate coating layer is 0.5μm-2μm, for example, it can be 0.5μm, 0.52μm, 0.55μm, 0.58μm, 0.6μm, 0.62μm, 0.65μm, 0.68μm, 0.7μm, 0.72μm, 0.75μm, 0.78μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm or 2μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Thirdly, the present invention provides a lithium-rich manganese-based cathode material, which is obtained from a modified lithium-rich manganese-based precursor as described in the second aspect.

[0047] Specifically, the preparation method of the lithium-rich manganese-based cathode material includes the following steps: mixing the modified lithium-rich manganese-based precursor as described in the second aspect with a lithium source, and sintering the mixture under an oxygen atmosphere to obtain the lithium-rich manganese-based cathode material.

[0048] In this invention, the lithium source exemplarily includes LiOH·H2O.

[0049] In this invention, the molar ratio of lithium in the lithium source to transition metal in the modified lithium-rich manganese-based precursor is 1.25:1.

[0050] In this invention, the sintering temperature is 800℃-900℃, for example, it can be 800℃, 820℃, 850℃, 880℃ or 900℃; the sintering time is 11h-12h, for example, it can be 11h, 11.5h or 12h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] The lithium-rich manganese-based cathode material prepared by this invention has high initial charge-discharge coulombic efficiency as well as good cycle performance and rate performance.

[0052] Fourthly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode comprises the lithium-rich manganese-based positive electrode material as described in the third aspect.

[0053] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] This invention provides a method for preparing a modified lithium-rich manganese-based precursor, wherein the phosphate coating layer is uniform and continuous, and the doped metal elements are uniformly distributed inside and on the surface of the material. Through the above-mentioned composite modification, the capacity, long-term cycle stability, and rate performance of the lithium-rich manganese-based cathode material can be effectively improved, as shown in the following details:

[0056] (1) By selecting indium as the first doping metal element, the present invention can play the role of skeleton and stabilize the crystal structure, thereby achieving the technical effect of improving the cycle performance and safety of the cathode material.

[0057] (2) The present invention forms a double-shell surface reconstruction layer of “Nb-doped / phosphate coated” on the surface of lithium-rich manganese-based precursor material, which can effectively alleviate the degradation of the material’s crystal structure, thereby achieving the technical effect of improving the cycle performance and structural stability of the cathode material.

[0058] (3) The phosphate coating layer formed by the present invention has a low lattice mismatch with the precursor and is firmly attached and not easy to peel off; the coating layer isolates the erosion of the cathode material by air and electrolyte, slows down the phase transition rate of the cathode material during cycling, and improves the interface stability; moreover, the synergistic effect of the co-doping of the two metal elements and the lithium phosphate conductor coating layer can significantly improve the capacity, cycle performance and rate performance of the cathode material in battery applications. Detailed Implementation

[0059] 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.

[0060] Example 1

[0061] This embodiment provides a modified lithium-rich manganese-based precursor and its preparation method, the preparation method comprising the following steps:

[0062] S1. Mix nickel nitrate, manganese nitrate and pure water to obtain a nickel-manganese mixed salt solution with a total concentration of 3 mol / L of all metal ions, wherein the molar ratio of nickel to manganese is 25:75;

[0063] 300L of pure water, 1kg of ammonia solution, and 0.5kg of sodium carbonate were added to a 500L reactor as the reaction base solution. The initial pH of the reaction base solution was controlled at 10.5, the ammonia concentration at 5g / L, and the temperature at 50℃. The above nickel-manganese mixed salt solution, a 1000ppm indium trichloride solution, and an ammonia-sodium carbonate mixed solution were fed concurrently into the reactor containing the above reaction base solution for co-precipitation reaction. The feed flow rate of the nickel-manganese mixed salt solution was controlled at 3L / h, the feed flow rate of the indium trichloride solution was controlled at 0.1L / h, the stirring speed of the reactor was set at 800rpm, and the reaction temperature was set at 50℃. By controlling the feed flow rate of the ammonia-sodium carbonate mixed solution, the pH value was kept at 10.5 to obtain a semi-step precursor material.

[0064] S2. After the average particle size of the above semi-step precursor material reaches 10 μm, stop the machine. After stopping the machine, wash it three times with dilute sodium hydroxide solution and hot water respectively, and dehydrate it for later use. Then replace the solution in the reactor with an ethanol solution of niobium ethanol with a concentration of 0.5 mol / L. Return the dehydrated semi-step precursor material to the reactor and immerse it completely in the niobium ethanol solution. Stir at 60°C for 2 hours to form a niobium-doped intermediate layer (the niobium content on the surface is 1.5 wt.%). After the process is completed, wash it with pure water to dehydrate it for later use to obtain the precursor material.

[0065] S3. The above-mentioned precursor material and a 25% lithium phosphate solution are placed together in a spray pyrolysis feed tank and ultrasonically mixed at 60 Hz. Then, spray pyrolysis is performed at a temperature of 700 ℃ and a residence time of 60 s to obtain the modified lithium-rich manganese-based precursor with a lithium phosphate coating thickness of 1 μm.

[0066] Example 2

[0067] This embodiment provides a modified lithium-rich manganese-based precursor and its preparation method, the preparation method comprising the following steps:

[0068] S1. Mix nickel nitrate, manganese nitrate and pure water to obtain a nickel-manganese mixed salt solution with a total concentration of 1 mol / L of all metal ions, wherein the molar ratio of nickel to manganese is 25:75;

[0069] 300L of pure water, 1kg of ammonia solution, and 0.5kg of sodium carbonate were added to a 500L reactor as the reaction base solution. The initial pH of the reaction base solution was controlled at 10.3, the ammonia concentration at 3g / L, and the temperature at 40℃. The above nickel-manganese mixed salt solution, a 100ppm indium trichloride solution, and an ammonia-sodium carbonate mixed solution were fed concurrently into the reactor containing the above reaction base solution for co-precipitation reaction. The feed flow rate of the nickel-manganese mixed salt solution was controlled at 2L / h, the feed flow rate of the indium trichloride solution was controlled at 0.08L / h, the stirring speed of the reactor was set at 800rpm, and the reaction temperature was set at 40℃. By controlling the feed flow rate of the ammonia-sodium carbonate mixed solution to maintain the pH at 10.3, a semi-step precursor material was obtained.

[0070] S2. After the average particle size of the above semi-step precursor material reaches 9 μm, stop the machine. After stopping the machine, wash it three times with dilute sodium hydroxide solution and hot water respectively, and dehydrate it for later use. Then replace the solution in the reactor with an ethanol solution of niobium ethanol with a concentration of 0.4 mol / L. Put the dehydrated semi-step precursor material back into the reactor and immerse it completely in the niobium ethanol solution. Stir at 50°C for 3 hours to form a niobium-doped intermediate layer (the niobium content on the surface is 1 wt.%). After the process is completed, wash it with pure water to dehydrate it for later use to obtain the precursor material.

[0071] S3. The above-mentioned precursor material and a lithium phosphate solution with a mass concentration of 20% are placed together in a spray pyrolysis feed tank and ultrasonically mixed at 60 Hz. Then, spray pyrolysis is performed at a temperature of 600 ℃ and a residence time of 70 s to obtain the modified lithium-rich manganese-based precursor with a lithium phosphate coating thickness of 0.5 μm.

[0072] Example 3

[0073] This embodiment provides a modified lithium-rich manganese-based precursor and its preparation method, the preparation method comprising the following steps:

[0074] S1. Nickel nitrate, manganese nitrate and pure water are mixed to obtain a nickel-manganese mixed salt solution with a total concentration of 4 mol / L of all metal ions, wherein the molar ratio of nickel to manganese is 22:78.

[0075] 300L of pure water, 1kg of ammonia solution, and 0.5kg of sodium carbonate were added to a 500L reactor as the reaction base solution. The initial pH of the reaction base solution was controlled at 10.7, the ammonia concentration at 7g / L, and the temperature at 60℃. The above nickel-manganese mixed salt solution, a 2000ppm indium trichloride solution, and an ammonia-sodium carbonate mixed solution were fed concurrently into the reactor containing the above reaction base solution for co-precipitation reaction. The feed flow rate of the nickel-manganese mixed salt solution was controlled at 4L / h, the feed flow rate of the indium trichloride solution was controlled at 0.12L / h, the stirring speed of the reactor was set at 800rpm, and the reaction temperature was set at 60℃. By controlling the feed flow rate of the ammonia-sodium carbonate mixed solution to maintain the pH at 10.7, a semi-step precursor material was obtained.

[0076] S2. After the average particle size of the above semi-step precursor material reaches 11 μm, stop the machine. After stopping the machine, wash it three times with dilute sodium hydroxide solution and hot water respectively, and dehydrate it for later use. Then replace the solution in the reactor with an ethanol solution of niobium ethanol with a concentration of 0.6 mol / L. Put the dehydrated semi-step precursor material back into the reactor and immerse it completely in the niobium ethanol solution. Stir at 70°C for 1 h to form a niobium-doped intermediate layer (the niobium content on the surface is 2 wt.%). After the process is completed, wash it with pure water to dehydrate it for later use to obtain the precursor material.

[0077] S3. The above-mentioned precursor material and a 30% lithium phosphate solution are placed together in a spray pyrolysis tank and ultrasonically mixed at 60 Hz. Then, spray pyrolysis is performed at a temperature of 800 ℃ and a residence time of 50 s to obtain the modified lithium-rich manganese-based precursor with a lithium phosphate coating thickness of 2 μm.

[0078] Example 4

[0079] The difference between this embodiment and Embodiment 1 is that in step S1, the concentration of the indium trichloride solution is 50 ppm, while all other aspects are the same as in Embodiment 1.

[0080] Example 5

[0081] The difference between this embodiment and Embodiment 1 is that in step S1, the concentration of the indium trichloride solution is 2500 ppm, while all other aspects are the same as in Embodiment 1.

[0082] Example 6

[0083] The difference between this embodiment and Embodiment 1 is that, in step S1, the feed flow rate of the indium trichloride solution is 0.05 L / h, while all other aspects are the same as in Embodiment 1.

[0084] Example 7

[0085] The difference between this embodiment and Embodiment 1 is that, in step S1, the feed flow rate of the indium trichloride solution is 0.5 L / h, while all other aspects are the same as in Embodiment 1.

[0086] Example 8

[0087] The difference between this embodiment and Embodiment 1 is that in step S1, the pH value is made to 10.0 by controlling the feed flow rate of the ammonia-sodium carbonate mixed solution; all other aspects are the same as in Embodiment 1.

[0088] Example 9

[0089] The difference between this embodiment and Embodiment 1 is that in step S1, the pH value is made to 12.0 by controlling the feed flow rate of the ammonia-sodium carbonate mixed solution; all other aspects are the same as in Embodiment 1.

[0090] Example 10

[0091] The difference between this embodiment and Embodiment 1 is that in step S2, the concentration of the ethanol solution of niobium ethoxide is 0.01 mol / L, while all other aspects are the same as in Embodiment 1.

[0092] Example 11

[0093] The difference between this embodiment and Embodiment 1 is that in step S3, the mass concentration of the lithium phosphate solution is 15%, while all other aspects are the same as in Embodiment 1.

[0094] Example 12

[0095] The difference between this embodiment and Embodiment 1 is that in step S3, the mass concentration of the lithium phosphate solution is 35%, while all other aspects are the same as in Embodiment 1.

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 1 is that the indium doping treatment in step S1 is not performed, and the remaining steps are adjusted as follows:

[0098] S1. Mix nickel nitrate, manganese nitrate and pure water to obtain a nickel-manganese mixed salt solution with a total concentration of 3 mol / L of all metal ions, wherein the molar ratio of nickel to manganese is 25:75;

[0099] 300L of pure water, 1kg of ammonia solution, and 0.5kg of sodium carbonate were added to a 500L reactor as the reaction base solution. The initial pH of the reaction base solution was controlled at 10.5, the ammonia concentration at 5g / L, and the temperature at 50℃. The above nickel-manganese mixed salt solution and the ammonia-sodium carbonate mixed solution were fed concurrently into the reactor containing the above reaction base solution for co-precipitation reaction. The feed flow rate of the nickel-manganese mixed salt solution was controlled at 3L / h, the stirring speed of the reactor was set at 800rpm, and the reaction temperature was 50℃. By controlling the feed flow rate of the ammonia-sodium carbonate mixed solution to maintain a pH of 10.5, a semi-step precursor material was obtained.

[0100] S2. After the average particle size of the above semi-step precursor material reaches 10 μm, stop the machine. After stopping the machine, wash it three times with dilute sodium hydroxide solution and hot water respectively, and dehydrate it for later use. Then replace the solution in the reactor with an ethanol solution of niobium ethanol with a concentration of 0.5 mol / L. Return the dehydrated semi-step precursor material to the reactor and immerse it completely in the niobium ethanol solution. Stir at 60°C for 2 hours to form a niobium-doped intermediate layer (the niobium content on the surface is 1.5 wt.%). After the process is completed, wash it with pure water to dehydrate it for later use to obtain the precursor material.

[0101] S3. The above-mentioned precursor material and a 25% lithium phosphate solution are placed together in a spray pyrolysis feed tank and ultrasonically mixed at 60 Hz. Then, spray pyrolysis is performed at a temperature of 700 ℃ and a residence time of 60 s to obtain the modified lithium-rich manganese-based precursor with a lithium phosphate coating thickness of 1 μm.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that step S2 is not performed, and the semi-precursor material obtained in step S1 is directly coated with lithium phosphate. Everything else is the same as in Example 1.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 1 is that step S3 is not performed, and the precursor material obtained in step S2 is used as the final modified lithium-rich manganese-based precursor. Everything else is the same as in Example 1.

[0106] Test conditions

[0107] The modified lithium-rich manganese-based precursors provided in Examples 1 to 12 and Comparative Examples 1 to 3 were used to prepare lithium-rich manganese-based cathode materials, which were then assembled into lithium-ion batteries for performance testing. The preparation method is as follows:

[0108] LiOH·H2O was mixed with a modified lithium-rich manganese-based precursor and sintered at 900℃ for 12 h in an oxygen atmosphere to obtain a lithium-rich manganese-based cathode material. The molar ratio of lithium in LiOH·H2O to transition metal in the modified lithium-rich manganese-based precursor was 1.25:1.

[0109] The lithium-rich manganese-based cathode material, polyvinylidene fluoride binder, and conductive agent Super P were added to N-methylpyrrolidone in a mass ratio of 98:1:1 and stirred to obtain a cathode slurry. The cathode slurry was then uniformly coated onto aluminum foil, dried, and rolled to obtain a cathode sheet.

[0110] Graphite, conductive agent acetylene black, sodium carboxymethyl cellulose thickener, and styrene-butadiene latex binder are mixed in a mass ratio of 95:2:1.5:1.5, and deionized water is added as solvent and stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0111] Ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a volume ratio of 1:1:1, and then fully dried lithium hexafluorophosphate was dissolved in the mixed solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0112] The positive electrode, separator, and negative electrode are stacked sequentially, and an electrolyte is injected. After processes such as encapsulation, settling, and formation, a lithium-ion battery is obtained.

[0113] After the battery assembly was completed and aged for 12 hours, its initial specific capacity, cycle performance, and rate performance were tested within a voltage range of 2.8-4.3V. The initial specific capacity was measured as the first discharge specific capacity at a 0.1C rate after a full charge. The cycle performance was measured as the capacity retention rate after 200 cycles at a 1C / 1C rate. The rate performance was measured as the discharge capacity retention rate at a 5C rate.

[0114] The test results are shown in Table 1:

[0115] Table 1

[0116]

[0117] As can be seen from Table 1, compared with Comparative Examples 1-3, the lithium-rich manganese-based cathode materials provided in Examples 1-3 of this invention produce lithium-ion batteries with high specific capacity, good cycle performance and rate performance. The comprehensive performance of Example 1 is the best. This is because the composite modification technology combining multi-metal co-doping and phosphate coating enhances the surface and structural stability of the lithium-rich manganese-based precursor material, thereby improving the effective capacity, cycle stability and electrochemical performance consistency of the lithium-rich manganese-based cathode material.

[0118] Comparing Examples 1 and 4-12, it can be seen that the present invention significantly improves the specific capacity, cycle performance and rate performance of lithium-rich manganese-based cathode materials in lithium-ion batteries by further controlling the concentration of doped metal salt, the feed rate of doped metal salt solution, the concentration of phosphate solution and co-precipitation reaction conditions to a suitable range.

[0119] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a modified lithium-rich manganese-based precursor, characterized in that, The preparation method includes the following steps: S1. A mixed metal salt solution, indium salt solution, and precipitant solution are fed into the reaction substrate in a co-precipitation reaction to obtain a half-step precursor material with the target particle size. S2. Mix the semi-step precursor material with a solution containing an organoniobium compound to obtain the precursor material; S3. The precursor material and phosphate solution are subjected to spray pyrolysis to obtain the modified lithium-rich manganese-based precursor.

2. The preparation method according to claim 1, characterized in that, In step S1, the mixed metal salt solution includes nickel and manganese. Preferably, in step S1, the molar ratio of nickel to manganese in the mixed metal salt solution is (22-25):(75-78); Preferably, in step S1, the total concentration of all metal ions in the mixed metal salt solution is 1 mol / L-4 mol / L; Preferably, in step S1, the flow rate of the mixed metal salt solution is 2L / h-4L / h.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, the concentration of the indium salt solution is 100ppm-2000ppm; Preferably, in step S1, the flow rate of the indium salt solution is 0.08 L / h - 0.12 L / h; Preferably, in step S1, the precipitant solution comprises a mixed solution of ammonia and sodium carbonate; Preferably, in step S1, the pH value of the reaction substrate is 9.0-12.0, and the ammonia concentration of the reaction substrate is 3g / L-7g / L; Preferably, in step S1, the pH value of the coprecipitation reaction is 10.3-10.7; Preferably, in step S1, the temperature of the coprecipitation reaction is 40℃-60℃; Preferably, in step S1, the average particle size of the target particle size is 9μm-11μm.

4. The preparation method according to any one of claims 1-3, characterized in that, In step S2, the concentration of the solution containing the organoniobium compound is 0.4 mol / L to 0.6 mol / L; Preferably, the organoniobium compound includes niobium ethanol; Preferably, in step S2, the solvent in the solution containing the organoniobium compound includes ethanol; Preferably, in step S2, the mixing temperature is 50℃-70℃, and the mixing time is 1h-3h.

5. The preparation method according to any one of claims 1-4, characterized in that, In step S3, the phosphate solution includes a lithium phosphate solution; Preferably, in step S3, the mass concentration of the phosphate solution is 20%-30%.

6. The preparation method according to any one of claims 1-5, characterized in that, In step S3, the temperature of the spray pyrolysis is 600℃-800℃; Preferably, in step S3, the spray pyrolysis time is 50s-70s.

7. A modified lithium-rich manganese-based precursor, characterized in that, The modified lithium-rich manganese-based precursor is prepared by the method of any one of the modified lithium-rich manganese-based precursors as described in any one of claims 1-6. The modified lithium-rich manganese-based precursor comprises, from the inside out, an indium-doped precursor core, a niobium-doped intermediate layer, and a phosphate coating layer covering the surface of the niobium-doped intermediate layer.

8. The modified lithium-rich manganese-based precursor according to claim 7, characterized in that, The niobium content on the surface of the niobium-doped intermediate layer is 1 wt.%-2 wt.%. Preferably, the thickness of the phosphate coating layer is 0.5 μm-2 μm.

9. A lithium-rich manganese-based cathode material, characterized in that, The lithium-rich manganese-based cathode material is obtained from the modified lithium-rich manganese-based precursor as described in claim 7 or 8.

10. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode includes the lithium-rich manganese-based positive electrode material as described in claim 9.

Images