Lithium-rich manganese-based precursor and preparation method thereof, lithium-rich manganese-based positive electrode material and lithium ion battery

Abstract

The invention provides a lithium-rich manganese-based precursor and a preparation method thereof, a lithium-rich manganese-based positive electrode material and a lithium ion battery. The preparation method comprises the following steps: mixing a manganese-based metal salt solution and a complexing agent solution in a carbon dioxide atmosphere, and then sequentially carrying out a nucleation reaction and a coprecipitation reaction to obtain a lithium-rich manganese-based precursor; in the coprecipitation reaction process, the pH value of the reaction system is gradually reduced. The preparation method is simple in process and low in cost, carbon dioxide is both a precipitator and a protective gas, raw materials can be saved, and a precursor material is prevented from being oxidized; the precursor material is synthesized by adopting a mode of gradually reducing the pH value of a reaction system, so that the precipitation performance and the structural performance of the precursor material can be improved, reaction equipment can be better protected, and the requirement on the reaction equipment is reduced. Based on the preparation method, the lithium-rich manganese-based precursor with high compaction density and regular morphology can be prepared, and the lithium-rich manganese-based precursor is more convenient and efficient in the washing process, and the impurity content is reduced.

Description

Technical Field

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

[0002] The lithium-rich manganese-based cathode material is a new type of lithium-ion battery cathode material with high specific capacity and high energy density. It can achieve rapid insertion and extraction of lithium ions, and the specific capacity can be as high as more than 250 mAh / g, far higher than that of traditional cathode materials, which can significantly improve the battery endurance. At the same time, it is rich in resources, low in cost, and environmentally friendly. However, at present, there are still many problems with the lithium-rich manganese-based cathode material. For example, when preparing a precursor with a relatively high manganese content, the hydroxide coprecipitation method has certain drawbacks. First, during the preparation process, Mn 2+ is easily oxidized to Mn 3+ , forming MnOOH, which affects the stoichiometric ratio between elements. Secondly, using sodium hydroxide as a precipitating agent will result in a high content of impurities such as sodium ions in the prepared precursor material, and the water washing process is complex. Finally, the generated manganese-rich hydroxide precursor usually has an irregular morphology and a low bulk density, which affects the energy density and electrochemical performance.

[0003] Therefore, finding a synthesis method for a lithium-rich manganese-based precursor with simple process and low cost, so as to prepare a lithium-rich manganese-based precursor with high tap density and regular morphology, is an important problem that needs to be studied urgently. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a lithium-rich manganese-based precursor, a preparation method thereof, a lithium-rich manganese-based cathode material, and a lithium-ion battery. The preparation method provided by the present invention has a simple process and low cost. Among them, carbon dioxide is both a precipitating agent and a protective gas, which can save raw materials and prevent the precursor material from being oxidized. During the coprecipitation reaction process, the precursor material is synthesized by gradually reducing the pH value of the reaction system, which can not only improve the precipitation performance and structural performance of the precursor material, but also better protect the reaction equipment and reduce the requirements for the reaction equipment. Based on this preparation method, a lithium-rich manganese-based precursor with high tap density and regular morphology can be prepared, and it is more convenient and efficient in the water washing process, reducing the impurity content, so that the lithium-rich manganese-based cathode material prepared therefrom exhibits excellent electrochemical performance.

[0005] To achieve the purpose of this invention, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a preparation method for a lithium-rich manganese-based precursor, and the preparation method includes the following steps:

[0007] In a carbon dioxide atmosphere, a manganese-based metal salt solution and a complexing agent solution are mixed, and then a nucleation reaction and a coprecipitation reaction are carried out in sequence to obtain the lithium-rich manganese-based precursor.

[0008] Among them, during the coprecipitation reaction, the pH value of the reaction system gradually decreases.

[0009] The preparation method provided by the present invention has a simple process and low cost. Carbon dioxide is both a precipitating agent and a protective gas, which can save raw materials and prevent the precursor material from being oxidized. During the coprecipitation reaction, synthesizing the precursor material by gradually decreasing the pH value of the reaction system can not only improve the precipitation performance and structural performance of the precursor material, but also better protect the reaction equipment and reduce the requirements for the reaction equipment. Based on this preparation method, a lithium-rich manganese-based precursor with a high tap density and regular morphology can be prepared, and it is more convenient and efficient during the water washing process, reducing the impurity content, so that the energy density of the lithium-rich manganese-based cathode material prepared therefrom is improved.

[0010] In the present invention, by gradually decreasing the pH value of the reaction system, since the change of the pH value will affect the surface properties of the precipitate particles, gradually decreasing the pH value of the reaction system during the coprecipitation reaction may change the surface properties of the precipitate particles, improve the agglomeration state between the particles, make the precipitate particles easier to achieve solid-liquid separation, and reduce the difficulty and cost of subsequent treatment. Secondly, it helps to control the nucleation and growth process of the precipitate, so as to form precipitate particles with uniform particle size and regular morphology, and improve the purity and performance of the lithium-rich manganese-based precursor.

[0011] It should be noted that the above coprecipitation reaction refers to the growth stage after particle nucleation.

[0012] Preferably, the manganese-based metal salt solution is a nickel-manganese mixed salt solution. Exemplarily, the nickel-manganese mixed salt solution includes a manganese sulfate solution and a nickel sulfate solution.

[0013] Preferably, the complexing agent solution includes any one or a combination of at least two of ammonia water, ethylenediaminetetraacetic acid solution or citric acid solution.

[0014] Exemplarily, the chemical equation of the coprecipitation reaction is as follows:

[0015]

[0016] Among them, the value range of x is 0-1, for example, it can be 0.2, 0.4, 0.6 or 0.8, etc., and it is not 0.

[0017] Preferably, the concentration of the ammonia water is 10-50 g / L, for example, it can be 10 g / L, 20 g / L, 30 g / L, 40 g / L or 50 g / L, etc.

[0018] Preferably, the specific method of mixing includes:

[0019] Flow the manganese metal salt solution and the complexing agent solution into the bottom liquid of the reaction kettle in parallel.

[0020] Preferably, the bottom liquid of the reaction kettle includes water and an alkaline solution. Exemplarily, the alkaline solution can be ammonia water, etc.

[0021] Preferably, the pH value of the bottom liquid of the reaction kettle is 8 - 9, such as 8, 8.2, 8.4, 8.6, 8.8 or 9, etc.

[0022] Preferably, during the nucleation reaction, the flow rate of the manganese metal salt solution introduced satisfies the following condition: the volume of the manganese metal salt solution entering the reaction kettle per hour is 6 - 10% of the volume of the reaction kettle, such as 6%, 7%, 8%, 9% or 10%, etc.

[0023] Preferably, during the nucleation reaction, the flow rate ratio of the manganese metal salt solution to the complexing agent solution is 1:(0.2 - 0.5), such as 1:0.2, 1:0.3, 1:0.4 or 1:0.5, etc.

[0024] Preferably, the temperature of the nucleation reaction is 45 - 65 °C, such as 45 °C, 50 °C, 55 °C, 60 °C or 65 °C, etc.

[0025] Preferably, the time of the nucleation reaction is 30 - 300 min, such as 30 min, 50 min, 100 min, 150 min, 200 min, 250 min or 300 min, etc.

[0026] Preferably, during the nucleation reaction, the pH value of the reaction system is 10.5 - 11.5, such as 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4 or 11.5, etc.

[0027] Preferably, within 1 - 10 h (such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc.) after the nucleation reaction ends, the flow rate of the manganese metal salt solution introduced is reduced to 45 - 60% of the flow rate of the manganese metal salt solution introduced during the nucleation reaction and remains unchanged, such as 45%, 50%, 55% or 60%, etc.

[0028] In the present invention, within 1 - 10 h after the nucleation reaction ends, the feeding flow rate of the manganese metal salt solution is reduced to 45 - 60% of the feeding flow rate of the manganese metal salt solution during the nucleation reaction process. That is to say, within 1 - 10 h at the beginning of the coprecipitation reaction, the feeding flow rate of the manganese metal salt solution is adjusted, and then the flow rate remains unchanged. The purposes are as follows: 1) Control particle growth. Reducing the feeding speed can slow down the concentration of the precursor in the solution, avoid excessive particle growth, and thus better control the particle size and morphology; 2) Avoid secondary nucleation. A high feeding speed may lead to too high local concentration, triggering secondary nucleation. Reducing the speed helps to maintain a uniform particle growth environment and reduce polydispersity; 3) A slower feeding speed is beneficial to the full diffusion and reaction of the reactants, improving the crystallinity and purity of the product; 4) Optimize the reaction conditions. Reducing the feeding speed helps to maintain stable reaction conditions, reduce side reactions, and improve the controllability and repeatability of the reaction.

[0029] Preferably, during the coprecipitation reaction process, the pH value of the reaction system gradually decreases to 7.5 - 8.5. For example, it can be 7.5, 7.6, 7.7, 7.8, 7.9, 8, 8.1, 8.2, 8.3, 8.4 or 8.5, etc.

[0030] In the present invention, during the coprecipitation reaction process, the pH value of the reaction system is gradually decreased to 7.5 - 8.5. Under weak alkaline conditions, certain side reactions (such as hydrolysis or oxidation of metal ions) can be inhibited, thereby reducing the generation of by-products and improving the selectivity of the reaction. In addition, this pH range helps to stabilize the surface charge of the particles, prevent particle agglomeration, improve the dispersibility of the product, and facilitate subsequent processing and application.

[0031] Preferably, during the coprecipitation reaction process, the decrease in the pH value of the reaction system satisfies the following conditions: the pH value of the reaction system decreases by 0.1 - 0.2 every 4 h. For example, it can be 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc.

[0032] In the present invention, the specific decrease in the pH value of the reaction system helps the metal ions in the reaction system to precipitate gradually, avoiding composition inhomogeneity caused by rapid precipitation, which is particularly important for preparing multi-component coprecipitation materials and can ensure uniform distribution of each component.

[0033] Preferably, during the nucleation reaction process, the stirring rate of the reaction system is less than the stirring rate of the reaction system during the coprecipitation reaction process.

[0034] In the present invention, it is defined that the stirring rate of the reaction system during the nucleation reaction is less than that during the coprecipitation reaction. The effect is to reduce the turbulence and shear force in the reaction system, avoid too large local concentration gradient, and thus be conducive to uniform nucleation. If the stirring rate is too high during the nucleation reaction, it may lead to uneven distribution of nucleation sites and form particles with large size differences.

[0035] Preferably, the preparation method includes the following steps:

[0036] (1) Under a carbon dioxide atmosphere, a nickel-manganese mixed salt solution and ammonia water with a concentration of 10 - 50 g / L are introduced into the bottom liquid of the reaction kettle in parallel flow, and a nucleation reaction is carried out at a temperature of 45 - 65 °C for 30 - 300 min; wherein, the flow rate of the nickel-manganese mixed salt solution introduced satisfies the following conditions: the volume of the nickel-manganese mixed salt solution entering the reaction kettle per hour is 6 - 10% of the volume of the reaction kettle; the flow rate ratio of the nickel-manganese mixed salt solution to the ammonia water is 1:(0.2 - 0.5); during the nucleation reaction, the pH value of the reaction system is 10.5 - 11.5, and the stirring rate of the reaction system is 300 - 600 rpm (for example, it can be 300 rpm, 400 rpm, 500 rpm or 600 rpm, etc.); the bottom liquid of the reaction kettle includes water and an alkaline solution.

[0037] (2) After the nucleation reaction in step (1) is completed, a coprecipitation reaction is carried out at 45 - 65 °C (for example, it can be 45 °C, 50 °C, 55 °C, 60 °C or 65 °C, etc.) and 300 - 600 rpm (for example, it can be 300 rpm, 400 rpm, 500 rpm or 600 rpm, etc.). During the coprecipitation reaction, the pH value of the reaction system is gradually decreased to 7.5 - 8.5 at a decreasing rate of 0.1 - 0.2 per 4 h, and at the same time, the supernatant in the reaction kettle is discharged (exemplarily, the discharge methods include a thickener or a physical sedimentation tank, etc.) until the precursor reaches the target particle size value, and a lithium-rich manganese-based precursor is obtained; wherein, within 1 - 10 h after the nucleation reaction is completed, the flow rate of the nickel-manganese mixed salt solution introduced is reduced to 45 - 60% of the flow rate of the nickel-manganese mixed salt solution introduced during the nucleation reaction, and the stirring rate of the reaction system during the nucleation reaction is less than that during the coprecipitation reaction.

[0038] In the second aspect, the present invention provides a lithium-rich manganese-based precursor, which is prepared by using the preparation method as described in the first aspect.

[0039] The particle size D50 of the lithium-rich manganese-based precursor is 4 - 10 μm, for example, it can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.

[0040] Preferably, the chemical formula of the lithium-rich manganese-based precursor is Ni x Mn 1-x CO3, where the value range of x is 0-1, and for example, it can be 0.2, 0.4, 0.6 or 0.8, etc.

[0041] In a third aspect, the present invention provides a lithium-rich manganese-based cathode material, which is prepared by mixing and sintering the lithium-rich manganese-based precursor described in the second aspect with a lithium salt.

[0042] The tap density of the lithium-rich manganese-based cathode material is greater than 3 g / cm 3 , and for example, it can be 3.2 g / cm 3 , 3.4 g / cm 3 , 3.5 g / cm 3 , 3.7 g / cm 3 , 4 g / cm 3 or 4.2 g / cm 3 , etc.

[0043] Preferably, the lithium salt includes lithium hydroxide and / or lithium carbonate.

[0044] Preferably, the molar ratio between the metal elements in the lithium-rich manganese-based precursor and the lithium element in the lithium salt is 1:(1.1-1.4), and for example, it can be 1:1.1, 1:1.2, 1:1.3 or 1:1.4, etc.

[0045] Preferably, the sintering is gradient sintering, and the gradient sintering includes first-order sintering, second-order sintering and third-order sintering, and the temperature of the first-order sintering < the temperature of the second-order sintering < the temperature of the third-order sintering.

[0046] In the present invention, adopting the method of gradient sintering helps the lithium-rich manganese-based cathode material to gradually form a stable crystal structure, thereby improving the electrochemical performance of the material; it is beneficial to make the crystal phase development inside the material more perfect, reduce lattice defects and stress, and improve the electronic conductivity and ion diffusion rate of the material; it is beneficial to the insertion and extraction of lithium ions in the material, and further improves the electrochemical performance of the battery; it is beneficial to reduce the occurrence of side reactions, form particles with uniform particle size distribution and regular morphology, and thus increase the energy density of the battery.

[0047] Preferably, the atmosphere of the sintering is an air atmosphere.

[0048] Preferably, the temperature of the first-order sintering is 120-400 °C, and for example, it can be 120 °C, 150 °C, 200 °C, 250 °C, 300 °C, 350 °C or 400 °C, etc.

[0049] Preferably, the temperature of the second-stage sintering is 500-700 °C, for example, it can be 500 °C, 550 °C, 600 °C, 650 °C or 700 °C, etc.

[0050] Preferably, the temperature of the third-stage sintering is 800-950 °C, for example, it can be 800 °C, 850 °C, 900 °C or 950 °C, etc.

[0051] Preferably, the heat preservation time of the first-stage sintering is 2-4 h, for example, it can be 2 h, 3 h or 4 h, etc.

[0052] Preferably, the heat preservation time of the second-stage sintering is 4-6 h, for example, it can be 4 h, 5 h or 6 h, etc.

[0053] Preferably, the heat preservation time of the third-stage sintering is 10-15 h, for example, it can be 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc.

[0054] In a third aspect, the present invention provides a lithium-ion battery, and the positive electrode of the lithium-ion battery includes the lithium-rich manganese-based positive electrode material as described in the second aspect.

[0055] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) The preparation method provided by the present invention has a simple process and low cost. Among them, carbon dioxide is both a precipitant and a protective gas, which can save raw materials and prevent the precursor material from being oxidized; in the process of the coprecipitation reaction, the pH value of the reaction system is gradually decreased to synthesize the precursor material, which can not only improve the precipitation performance and structural performance of the precursor material, but also better protect the reaction equipment and reduce the requirements for the reaction equipment. Based on this preparation method, a lithium-rich manganese-based precursor with high tap density and regular morphology can be prepared, and it is more convenient and efficient in the water washing process, reducing the impurity content.

[0058] (2) The lithium-rich manganese-based positive electrode material prepared based on the lithium-rich manganese-based precursor provided by the present invention has excellent electrochemical performance. Description of the Drawings

[0059] Figure 1 It is a SEM diagram of the lithium-rich manganese-based positive electrode material provided in Example 1 of the present invention. Detailed Embodiments

[0060] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0061] Example 1

[0062] This embodiment provides a preparation method of a lithium-rich manganese-based precursor. The preparation method includes the following steps:

[0063] (1) Under a carbon dioxide atmosphere, a nickel-manganese mixed salt solution (including a manganese sulfate solution and a nickel sulfate solution) and ammonia water with a concentration of 30 g / L are simultaneously introduced into the bottom liquid of the reaction kettle, and a nucleation reaction is carried out at a temperature of 55 °C for 150 min; wherein, the flow rate of the nickel-manganese mixed salt solution introduced satisfies the following conditions: the volume of the nickel-manganese mixed salt solution entering the reaction kettle per hour is 8% of the volume of the reaction kettle; the flow rate ratio of the nickel-manganese mixed salt solution to the ammonia water is 1:0.35; during the nucleation reaction, the pH value of the reaction system is 11, and the stirring rate of the reaction system is 450 rpm; the bottom liquid of the reaction kettle includes water and ammonia water, and the pH value is 8.5.

[0064] (2) After the nucleation reaction in step (1) ends, a coprecipitation reaction is carried out at 55 °C and 550 rpm. During the coprecipitation reaction, the pH value of the reaction system is gradually reduced to 8 at a decreasing rate of 0.15 per 4 h, and at the same time, the supernatant in the reaction kettle is discharged through a physical sedimentation tank until the precursor reaches the target particle size value, and a lithium-rich manganese-based precursor is obtained; wherein, within 5 h after the nucleation reaction ends, the flow rate of the nickel-manganese mixed salt solution introduced is reduced to 50% of the flow rate of the nickel-manganese mixed salt solution during the nucleation reaction and remains unchanged.

[0065] This embodiment also provides a lithium-rich manganese-based precursor, which is prepared by the above preparation method.

[0066] The chemical formula of the lithium-rich manganese-based precursor is Ni x Mn 1-x CO3, where x is 0.45.

[0067] The particle size D50 of the lithium-rich manganese-based precursor is 7.5 μm.

[0068] This embodiment also provides a lithium-rich manganese-based cathode material, which is prepared by mixing and sintering the above lithium-rich manganese-based precursor with lithium hydroxide. The specific steps include:

[0069] Mix the lithium-rich manganese-based precursor with lithium hydroxide, then carry out gradient sintering under an air atmosphere, and after completion, mechanically crush, screen, and store in a sealed manner.

[0070] Among them, the molar ratio between the metal elements (Ni + Mn) in the lithium-rich manganese-based precursor and the lithium element in lithium hydroxide is 1:1.3; the gradient sintering includes first-order sintering, second-order sintering and third-order sintering, and the temperature of the first-order sintering is 260 °C, the heat preservation time is 3 h, the temperature of the second-order sintering is 600 °C, the heat preservation time is 5 h, the temperature of the third-order sintering is 900 °C, and the heat preservation time is 12 h.

[0071] Figure 1 The SEM image of the lithium-rich manganese-based cathode material provided in this embodiment is shown. It can be seen from the figure that the lithium-rich manganese-based cathode material has a high tap density, good crystallinity, and regular morphology.

[0072] Example 2

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

[0074] (1) Under a carbon dioxide atmosphere, a nickel-manganese mixed salt solution (including a manganese sulfate solution and a nickel sulfate solution) and ammonia water with a concentration of 10 g / L are introduced into the bottom liquid of the reaction kettle and circulated, and a nucleation reaction is carried out at a temperature of 45 °C for 300 min; among them, the flow rate of the nickel-manganese mixed salt solution introduced satisfies the following conditions: the volume of the nickel-manganese mixed salt solution entering the reaction kettle per hour is 6% of the volume of the reaction kettle; the flow rate ratio of the nickel-manganese mixed salt solution to the ammonia water is 1:0.5; during the nucleation reaction, the pH value of the reaction system is 10.5, and the stirring rate of the reaction system is 300 rpm; the bottom liquid of the reaction kettle includes water and ammonia water, and the pH value is 8.5.

[0075] (2) After the nucleation reaction in step (1) ends, a coprecipitation reaction is carried out at 45 °C and 400 rpm. During the coprecipitation reaction, the pH value of the reaction system is gradually reduced to 7.5 at a decreasing rate of 0.1 per 4 h, and at the same time, the supernatant in the reaction kettle is discharged through a physical sedimentation tank until the precursor reaches the target particle size value, and a lithium-rich manganese-based precursor is obtained; among them, within 1 h after the nucleation reaction ends, the flow rate of the nickel-manganese mixed salt solution introduced is reduced to 60% of the flow rate of the nickel-manganese mixed salt solution introduced during the nucleation reaction and remains unchanged.

[0076] This embodiment also provides a lithium-rich manganese-based precursor, and the lithium-rich manganese-based precursor is prepared by using the above preparation method.

[0077] The chemical formula of the lithium-rich manganese-based precursor is Ni x Mn 1-x CO3, where x is 0.5.

[0078] The particle size D50 of the lithium-rich manganese-based precursor is 6 μm.

[0079] This embodiment also provides a lithium-rich manganese-based cathode material, which is prepared by mixing and sintering the above-mentioned lithium-rich manganese-based precursor with lithium hydroxide. The specific steps include:

[0080] Mix the lithium-rich manganese-based precursor with lithium hydroxide, then perform gradient sintering in an air atmosphere, and after completion, mechanically pulverize, screen, and store it in a sealed manner.

[0081] Among them, the molar ratio of the metal elements (Ni + Mn) in the lithium-rich manganese-based precursor to the lithium element in lithium hydroxide is 1:(1.1 - 1.4); the gradient sintering includes first-order sintering, second-order sintering, and third-order sintering. The temperature of the first-order sintering is 120 °C, the heat preservation time is 4 h, the temperature of the second-order sintering is 500 °C, the heat preservation time is 6 h, the temperature of the third-order sintering is 800 °C, and the heat preservation time is 15 h.

[0082] Example 3

[0083] This embodiment provides a preparation method of a lithium-rich manganese-based precursor, and the preparation method includes the following steps:

[0084] (1) Under a carbon dioxide atmosphere, a nickel-manganese mixed salt solution (including manganese sulfate solution and nickel sulfate solution) and ammonia water with a concentration of 50 g / L are introduced into the bottom liquid of the reaction kettle and circulated, and a nucleation reaction is carried out at a temperature of 65 °C for 30 min; among them, the flow rate of the nickel-manganese mixed salt solution introduced satisfies the following conditions: the volume of the nickel-manganese mixed salt solution entering the reaction kettle per hour is 10% of the volume of the reaction kettle; the flow rate ratio of the nickel-manganese mixed salt solution to ammonia water is 1:0.2; during the nucleation reaction process, the pH value of the reaction system is 11.5, and the stirring rate of the reaction system is 500 rpm; the bottom liquid of the reaction kettle includes water and ammonia water, and the pH value is 8.5.

[0085] (2) After the nucleation reaction in step (1) ends, a coprecipitation reaction is carried out under the conditions of 65 °C and 600 rpm. During the coprecipitation reaction process, the pH value of the reaction system is gradually reduced to 8.5 at a decreasing rate of 0.2 per 4 h, and at the same time, the supernatant in the reaction kettle is discharged through a physical sedimentation tank until the precursor reaches the target particle size value, and a lithium-rich manganese-based precursor is obtained; within 10 h after the nucleation reaction ends, the flow rate of the nickel-manganese mixed salt solution introduced is reduced to 45% of the flow rate of the nickel-manganese mixed salt solution introduced during the nucleation reaction process and remains unchanged.

[0086] This embodiment also provides a lithium-rich manganese-based precursor, which is prepared by using the above preparation method.

[0087] The chemical formula of the lithium-rich manganese-based precursor is Nix Mn 1-x CO3, where x is 0.55.

[0088] The D50 of the lithium-rich manganese-based precursor is 5 μm.

[0089] This embodiment also provides a lithium-rich manganese-based cathode material, which is prepared by mixing and sintering the above-mentioned lithium-rich manganese-based precursor with lithium hydroxide. The specific steps include:

[0090] Mix the lithium-rich manganese-based precursor with lithium hydroxide, then perform gradient sintering in an air atmosphere, and after completion, mechanically crush, screen, and store it in a sealed manner.

[0091] Among them, the molar ratio of the metal elements (Ni + Mn) in the lithium-rich manganese-based precursor to the lithium element in lithium hydroxide is 1:(1.1 - 1.4); the gradient sintering includes first-order sintering, second-order sintering, and third-order sintering. The temperature of the first-order sintering is 400 °C, the holding time is 2 h, the temperature of the second-order sintering is 700 °C, the holding time is 4 h, and the temperature of the third-order sintering is 950 °C, the holding time is 10 h.

[0092] Example 4

[0093] The difference between this embodiment and Example 1 is that in step (2), during the coprecipitation reaction, the decrease in pH value is 0.05.

[0094] The remaining preparation methods and parameters are the same as those in Example 1.

[0095] Example 5

[0096] The difference between this embodiment and Example 1 is that in step (2), during the coprecipitation reaction, the decrease in pH value is 0.5.

[0097] The remaining preparation methods and parameters are the same as those in Example 1.

[0098] Example 6

[0099] The difference between this embodiment and Example 1 is that in step (2), during the coprecipitation reaction, the pH value of the reaction system is reduced to 7.

[0100] The remaining preparation methods and parameters are the same as those in Example 1.

[0101] Example 7

[0102] The difference between this embodiment and Example 1 is that in step (2), during the coprecipitation reaction, the pH value of the reaction system is reduced to 9.

[0103] The remaining preparation methods and parameters are the same as those in Example 1.

[0104] Example 8

[0105] The difference between this example and Example 1 is that during the coprecipitation reaction in step (2), the feeding flow rate of the nickel-manganese mixed salt solution is the same as that during the nucleation reaction.

[0106] The remaining preparation methods and parameters are the same as those in Example 1.

[0107] Example 9

[0108] The difference between this example and Example 1 is that during the coprecipitation reaction in step (2), the feeding flow rate of the nickel-manganese mixed salt solution is reduced to 30% of the feeding flow rate of the nickel-manganese mixed salt solution during the nucleation reaction within 5 h after the end of the nucleation reaction.

[0109] The remaining preparation methods and parameters are the same as those in Example 1.

[0110] Example 10

[0111] The difference between this example and Example 1 is that during the coprecipitation reaction in step (2), the feeding flow rate of the nickel-manganese mixed salt solution is reduced to 80% of the feeding flow rate of the nickel-manganese mixed salt solution during the nucleation reaction within 5 h after the end of the nucleation reaction.

[0112] The remaining preparation methods and parameters are the same as those in Example 1.

[0113] Example 11

[0114] The difference between this example and Example 1 is that during the nucleation reaction, the stirring rate of the reaction system is equal to the stirring rate of the reaction system during the coprecipitation reaction, both being 450 rpm.

[0115] The remaining preparation methods and parameters are the same as those in Example 1.

[0116] Example 12

[0117] The difference between this example and Example 1 is that during the nucleation reaction, the stirring rate of the reaction system is greater than the stirring rate of the reaction system during the coprecipitation reaction, that is, the stirring rate of the reaction system during the nucleation reaction is adjusted to 600 rpm.

[0118] The remaining preparation methods and parameters are the same as those in Example 1.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 1 is that the carbon dioxide atmosphere is replaced by a nitrogen atmosphere.

[0121] The rest of the preparation methods and parameters were the same as those in Example 1.

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 1 is that during the coprecipitation reaction, the pH of the reaction system remains unchanged and is 8.

[0124] The rest of the preparation methods and parameters were the same as those in Example 1.

[0125] Performance Testing

[0126] 1. The compaction density of the lithium-rich manganese-based positive electrode materials provided in the above embodiments and comparative examples is tested, and the testing method includes:

[0127] 1. Use the Sansi powder compaction density meter, preheat, connect online, and calibrate.

[0128] 2. Remove the mold and fill it with 0.8g sample.

[0129] 3. Put the mold back into the equipment and start measuring.

[0130] 4. After the measurement is completed, read the compaction density value on the equipment.

[0131] 2. The lithium-rich manganese-based positive electrode material provided in the above embodiments and comparative examples is mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1, N-methylpyrrolidone is added as a solvent to make a slurry, and then coated on an aluminum foil to prepare a positive electrode sheet; a metal lithium sheet is used as a negative electrode sheet, the material of the diaphragm is polypropylene, and the electrolyte is a carbonate solution containing 1 mol / L lithium hexafluorophosphate (the solvent is composed of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1); the above-mentioned positive electrode sheet, negative electrode sheet, diaphragm and electrolyte are assembled to obtain a 2025-type button lithium-ion battery.

[0132] The above 2025 button lithium-ion battery was subjected to charge and discharge tests under the following test conditions: after the battery was left to rest for 3 hours, the charge / discharge test was performed on the LAND battery test system with a voltage range of 2.0-4.8 V. The discharge specific capacity of the battery at a current of 0.1C was recorded, and the first coulombic efficiency of the battery at a current of 0.1C was calculated and recorded, and the calculation method was: 0.1C first discharge capacity / 0.1C first charge capacity×100%.

[0133] The above test results are shown in Table 1.

[0134] Table 1

[0135]

[0136]

[0137] Analysis:

[0138] As can be seen from Table 1, the lithium-rich manganese-based cathode material with high tap density and regular morphology can be prepared based on the lithium-rich manganese-based precursor provided by the present invention, and the lithium-ion battery prepared based on this shows excellent electrochemical performance.

[0139] As can be seen from the comparison between Example 1 and Examples 4-5, if the decrease in pH value is too small during the coprecipitation reaction, it will lead to insufficient nucleation and growth, uneven particles, and ultimately result in a decrease in the tap density and electrochemical performance of the lithium-rich manganese-based cathode material; if the decrease in pH value is too large during the coprecipitation reaction, it will lead to too fast reaction rate, irregular particle morphology or agglomeration, resulting in a decrease in the tap density and electrochemical performance of the lithium-rich manganese-based cathode material.

[0140] As can be seen from the comparison between Example 1 and Examples 6-7, if the pH value of the reaction system is too small after the decrease during the coprecipitation reaction, it will lead to irregular particle morphology or agglomeration, affecting the packing performance of the particles; if the pH value of the reaction system is too large after the decrease during the coprecipitation reaction, it will lead to an increase in surface defects of the particles, affecting the electrochemical performance, manifested as a decrease in the first discharge specific capacity and Coulomb efficiency. And too large pH value may also trigger side reactions, further affecting the uniformity and performance of the product.

[0141] As can be seen from the comparison between Example 1 and Example 8, if the feeding flow rate of the nickel-manganese mixed salt solution during the coprecipitation reaction is the same as that during the nucleation reaction process, it is not conducive to nucleation. A higher feeding flow rate is required during the nucleation stage to ensure rapid nucleation, while a lower feeding flow rate is required during the growth stage to control the particle growth rate. If the feeding flow rate during the growth stage is the same as that during the nucleation stage, it may cause the particles to grow too fast, forming particles with uneven sizes, thereby reducing the tap density of the lithium-rich manganese-based cathode material.

[0142] As can be seen from the comparison between Example 1 and Examples 9-10, if the decrease in the feeding flow rate of the nickel-manganese mixed salt solution is too large within 5 h after the end of the nucleation reaction during the coprecipitation reaction, it will lead to insufficient supply of reactants and too slow particle growth rate, possibly forming small but uneven particles, thereby reducing the tap density; if the decrease in the feeding flow rate of the nickel-manganese mixed salt solution is too small within 5 h after the end of the nucleation reaction during the coprecipitation reaction, it will lead to agglomeration phenomenon, affecting the packing performance of the particles, further reducing the tap density of the lithium-rich manganese-based cathode material, and the agglomeration will affect the discharge performance of the lithium-rich manganese-based cathode material.

[0143] It can be seen from the comparison between Example 1 and Examples 11-12 that if the stirring rate of the reaction system during the nucleation reaction is equal to the stirring rate of the reaction system during the coprecipitation reaction, it will lead to uneven nucleation and the formation of particles with large size differences; if the stirring rate of the reaction system during the nucleation reaction is greater than the stirring rate of the reaction system during the coprecipitation reaction, a large number of small but uneven particles will be formed, thus reducing the tap density.

[0144] It can be seen from the comparison between Example 1 and Comparative Example 1 that if the carbon dioxide atmosphere is replaced with a nitrogen atmosphere, there are the following adverse effects: 1) It is not conducive to the control of particle morphology. The carbon dioxide atmosphere may form carbonates or bicarbonates during the reaction, which helps to regulate the particle morphology and size distribution. However, the nitrogen atmosphere lacks this regulatory effect, resulting in irregular particle morphology or agglomeration, thus reducing the tap density of the lithium-rich manganese-based cathode material; 2) It affects the reaction kinetics. Carbon dioxide participates in the reaction, adjusts the pH value or the reaction rate, and promotes uniform nucleation and growth; 3) The nitrogen atmosphere cannot provide a similar regulatory effect, resulting in uneven reaction rates and affecting the uniformity and performance of the particles; 4) It reduces the crystallinity of the product. The carbon dioxide atmosphere helps to form a product with high crystallinity, while the nitrogen atmosphere results in a lower crystallinity of the product, affecting the electrochemical performance. The product with lower crystallinity usually shows a decrease in the initial discharge specific capacity and Coulomb efficiency; 5) It reduces surface defects. The carbon dioxide atmosphere helps to reduce the surface defects of the particles, while the nitrogen atmosphere leads to an increase in surface defects, affecting the performance of the electrode material.

[0145] It can be seen from the comparison between Example 1 and Comparative Example 2 that if the pH of the reaction system remains unchanged during the coprecipitation reaction, it will be unfavorable for the regulation of the material morphology and performance during the nucleation and growth stages.

[0146] It should be noted that the present invention uses the above examples to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the raw materials selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of a lithium-rich manganese-based precursor, characterized in that, The preparation method comprises the following steps: Under a carbon dioxide atmosphere, a manganese-based metal salt solution and a complexing agent solution are mixed, and then a nucleation reaction and a coprecipitation reaction are carried out in sequence to obtain the lithium-rich manganese-based precursor; Wherein, during the coprecipitation reaction, the pH value of the reaction system gradually decreases.

2. The preparation method of the lithium-rich manganese-based precursor according to claim 1, wherein The manganese-based metal salt solution is a nickel-manganese mixed salt solution; Preferably, the complexing agent solution comprises any one or a combination of at least two of ammonia water, ethylenediaminetetraacetic acid solution or citric acid solution; Preferably, the concentration of the ammonia water is 10-50 g / L; Preferably, the specific method of the mixing comprises: The manganese-based metal salt solution and the complexing agent solution are simultaneously introduced into the bottom liquid of the reaction kettle; Preferably, during the nucleation reaction, the feeding flow rate of the manganese-based metal salt solution satisfies the following condition: the volume of the manganese-based metal salt solution entering the reaction kettle per hour is 6-10% of the volume of the reaction kettle; Preferably, during the nucleation reaction, the flow rate ratio of the manganese-based metal salt solution to the complexing agent solution is 1:(0.2-0.5).

3. The preparation method of the lithium-rich manganese-based precursor according to claim 1 or 2, characterized in that, The temperature of the nucleation reaction is 45-65 °C; Preferably, the time of the nucleation reaction is 30-300 min; Preferably, during the nucleation reaction, the pH value of the reaction system is 10.5-11.

5.

4. The preparation method of the lithium-rich manganese-based precursor according to claim 2, characterized in that Within 1-10 h after the nucleation reaction ends, the feeding flow rate of the manganese-based metal salt solution is reduced to 45-60% of the feeding flow rate of the manganese-based metal salt solution during the nucleation reaction and remains unchanged.

5. The preparation method of the lithium-rich manganese-based precursor according to any one of claims 1-4, characterized in that, During the coprecipitation reaction, the pH value of the reaction system gradually decreases to 7.5-8.5; Preferably, during the coprecipitation reaction, the decrease in the pH value of the reaction system satisfies the following condition: the pH value of the reaction system decreases by 0.1-0.2 every 4 h; Preferably, the stirring rate of the reaction system during the nucleation reaction is less than the stirring rate of the reaction system during the coprecipitation reaction.

6. The preparation method of the lithium-rich manganese-based precursor according to any one of claims 1-5, characterized in that, The preparation method comprises the following steps: (1) Under a carbon dioxide atmosphere, a nickel-manganese mixed salt solution and ammonia water with a concentration of 10-50 g / L are simultaneously introduced into the bottom liquid of the reaction kettle, and a nucleation reaction is carried out at a temperature of 45-65 °C for 30-300 min; wherein, the feeding flow rate of the nickel-manganese mixed salt solution satisfies the following condition: the volume of the nickel-manganese mixed salt solution entering the reaction kettle per hour is 6-10% of the volume of the reaction kettle; the flow rate ratio of the nickel-manganese mixed salt solution to the ammonia water is 1:(0.2-0.5); during the nucleation reaction, the pH value of the reaction system is 10.5-11.5, and the stirring rate of the reaction system is 300-600 rpm; the bottom liquid of the reaction kettle comprises water and an alkali solution; (2) After the nucleation reaction described in step (1) is completed, a coprecipitation reaction is carried out at 45-65 °C and 300-600 rpm. During the coprecipitation reaction, the pH value of the reaction system is gradually decreased to 7.5-8.5 at a rate of 0.1-0.2 decrease per 4 h, while the supernatant in the reaction kettle is discharged until the precursor reaches the target particle size value, obtaining a lithium-rich manganese-based precursor; wherein, within 1-10 h after the nucleation reaction is completed, the feeding flow rate of the nickel-manganese mixed salt solution is decreased to 45-60% of the feeding flow rate of the nickel-manganese mixed salt solution during the nucleation reaction, and the stirring rate of the reaction system during the nucleation reaction is less than the stirring rate of the reaction system during the coprecipitation reaction.

7. A lithium-rich manganese-based precursor, characterized in that, The lithium-rich manganese-based precursor is prepared by the preparation method described in any one of claims 1-6; The D50 of the lithium-rich manganese-based precursor is 4-10 μm.

8. A lithium-rich manganese-based cathode material, characterized in that, The lithium-rich manganese-based cathode material is prepared by mixing and sintering the lithium-rich manganese-based precursor described in claim 7 with a lithium salt; The tap density of the lithium-rich manganese-based cathode material is greater than 3 g / cm 3 .

9. The lithium-rich manganese-based cathode material according to claim 8, wherein The molar ratio between the metal elements in the lithium-rich manganese-based precursor and the lithium element in the lithium salt is 1:(1.1-1.4); Preferably, the sintering is gradient sintering, and the gradient sintering includes first-order sintering, second-order sintering and third-order sintering, and the temperature of the first-order sintering < the temperature of the second-order sintering < the temperature of the third-order sintering; Preferably, the temperature of the first-order sintering is 120-400 °C; Preferably, the temperature of the second-order sintering is 500-700 °C; Preferably, the temperature of the third-order sintering is 800-950 °C.

10. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes the lithium-rich manganese-based cathode material described in claim 8 or 9.

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