Bulk phase gradient high-aluminum doped lithium-rich manganese precursor, preparation method and application

Abstract

The invention discloses a bulk phase gradient high-aluminum doped lithium-rich manganese precursor, a preparation method and application, the chemical general formula of the precursor is MnxNiyCo (1-x-y) (OH) 2 or MnxNiyCo (1-x-y) CO3, x is 0.6-0.8, y is 0.2-0.4, and the structure comprises an inner core layer, a middle layer and a shell layer; the total doping amount of the aluminum element is 10000-20000 ppm, and the doping concentration of aluminum is continuously increased in a gradient manner from inside to outside. The preparation method comprises the following steps: firstly, simultaneously introducing a manganese-based mixed salt solution, a precipitant solution, a complexing agent solution and a first-concentration aluminum solution into a base solution, carrying out a first coprecipitation reaction, completing nucleation and forming an inner core layer; secondly, introducing a second-concentration aluminum solution into the inner core layer system, and carrying out a second coprecipitation reaction to realize crystal growth of an intermediate layer; and finally, switching to an aluminum solution with a third concentration, carrying out a third coprecipitation reaction, completing crystal growth and aging of a shell layer, and finally obtaining the gradient doped lithium-rich manganese precursor. The material is used for manufacturing a battery positive electrode.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a bulk high-aluminum doped lithium-rich manganese precursor, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage, and other fields, the market has placed higher demands on the energy density, cycle stability, and safety of lithium-ion batteries. Lithium-rich manganese-based cathode materials are considered one of the important candidate materials for next-generation high-energy-density lithium-ion batteries due to their advantages such as ultra-high specific capacity (theoretical specific capacity > 250 mAh / g), low cost, and environmental friendliness.

[0003] However, lithium-rich manganese-based materials still have significant shortcomings in practical applications: First, manganese is easily dissolved during cycling, causing the material structure to gradually collapse and reducing cycling stability; second, they generally suffer from rapid capacity decay, low initial coulombic efficiency, and are prone to volume expansion and microcracks during cycling, which restricts their large-scale application.

[0004] To address these issues, the industry commonly employs aluminum doping for modification, enhancing structural stability by having aluminum atoms occupy lattice sites or form stable phases. Currently, most common aluminum doping methods are surface doping, which, while providing some protection on the material surface, suffer from uneven aluminum distribution and weak bonding with the matrix, leading to eventual failure after long-term cycling. Furthermore, the aluminum doping level in existing lithium-rich manganese cathode materials is typically below 10,000 ppm, making it difficult to fully leverage aluminum's stabilizing effect on the material structure. Therefore, developing a method for preparing lithium-rich manganese precursors that achieves high bulk aluminum doping, controllable compositional gradients, and structural stability is a key approach to overcoming the application bottlenecks of lithium-rich manganese-based materials. Summary of the Invention

[0005] This invention aims to overcome the problems of uneven aluminum doping distribution, poor structural stability, and insufficient cycle performance in existing lithium-rich manganese precursors. It provides a bulk gradient high-aluminum-doped lithium-rich manganese precursor and its preparation method. By designing a gradient structure with a core layer, an intermediate layer, and a shell layer, and controlling the aluminum doping amount to continuously increase from the inside to the outside, the material's structural stability and electrochemical performance are synergistically improved, while meeting the requirements of industrial production.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A bulk gradient high-alumina doped lithium-rich manganese precursor, wherein the general chemical formula of the bulk gradient high-alumina doped lithium-rich manganese precursor is Mn x Ni y Co 1-x-y (OH)2 or Mn x Ni y Co 1-x-yCO3, where x is 0.6-0.8 and y is 0.2-0.4; structurally, it includes a core layer, an intermediate layer and a shell layer from the inside out; the total aluminum doping amount is 10,000 to 20,000 ppm, and the aluminum doping concentration increases continuously from the inside to the outside.

[0007] As an improvement to the above technical solution, the particle size of the core layer, intermediate layer and shell layer of the precursor is gradient distributed, wherein the D50 of the core layer is 2.0-4.0 μm, the intermediate layer grows to a D50 of 8.0-11.0 μm, and the shell layer finally grows to a D50 of 12.0-15.0 μm.

[0008] This invention also provides a method for preparing the above-mentioned bulk gradient high-aluminum doped lithium-rich manganese precursor, the preparation method comprising the following steps: S1. Simultaneously introduce manganese-based mixed salt solution, precipitant solution, complexing agent solution, and aluminum solution of the first concentration into the bottom liquid to carry out the first co-precipitation reaction, complete the nucleation and form the core layer (equivalent to the seed crystal preparation stage), at a temperature of 50-55℃, a pH value of 8.0-8.1, and an aluminum solution concentration of 0.3-0.4 g / L; S2. Introduce a second concentration of aluminum solution (higher than the first concentration) into the core layer system to carry out a second co-precipitation reaction, thereby achieving crystal growth in the intermediate layer; temperature 56-58℃, pH 8.2-8.3, aluminum solution concentration 0.4-0.5g / L; S3. Switch to the third concentration aluminum solution (concentration higher than the second concentration) to carry out the third co-precipitation reaction, complete the crystal growth and aging of the shell layer, and finally obtain the gradient-doped lithium-rich manganese precursor; temperature 59-62℃, pH value 8.4-8.6, aluminum solution concentration 0.5-0.6g / L. The concentration of the third aluminum solution is greater than that of the second aluminum solution, which in turn is greater than that of the first aluminum solution, ensuring a continuous gradient increase in aluminum doping concentration across the core, intermediate, and shell layers. The first, second, and third coprecipitation reactions are all conducted under a nitrogen atmosphere.

[0009] As an improvement to the above technical solution, the complexing agent solution is any one of ammonia, citric acid, sodium oxalate, and EDTA, or a mixture of at least two or more; the precipitant solution is sodium oxide solution or sodium carbonate solution; the concentration of sodium hydroxide solution or sodium carbonate solution is 2 mol / L; and the concentration of complexing agent solution (calculated as ammonia) is 10 g / L.

[0010] As an improvement to the above technical solution, the manganese-based mixed salt solution is a soluble aqueous solution of nickel salt, cobalt salt and manganese salt, and the total metal ion concentration of the manganese-based mixed salt solution is 2.0-2.2 mol / L; As an improvement to the above technical solution, the nickel salt, cobalt salt and manganese salt are nickel sulfate, cobalt sulfate and manganese sulfate, respectively.

[0011] As an improvement to the above technical solution, the bulk gradient high-alumina doped lithium-rich manganese precursor of the present invention is applied to the production of cathode materials. The bulk gradient high-alumina doped lithium-rich manganese precursor is mixed with a lithium source and sintered to obtain a lithium-rich manganese-based cathode material. The sintering process is as follows: first, the temperature is raised to the pre-sintering temperature at a heating rate of 2-5℃ / min, and then held at 300-500℃ for 1-2 hours to fully remove volatiles and achieve preliminary oxidation. Then, the temperature is raised to 700-850℃ at a heating rate of 5℃ / min and held for 8-12 hours.

[0012] Compared with the prior art, the advantages and positive effects of this invention are: 1. Achieving high-content and uniform bulk gradient doping: By adopting a process that combines multi-step co-precipitation with precise control of concentration gradient, and by drawing on and optimizing the control ideas for high-uniformity doping (such as ensuring orderly ion release through appropriate complexing agents and reaction stage control), the aluminum doping content was successfully increased to 10,000-20,000 ppm, and a continuous gradient distribution of aluminum elements from the inside to the outside was achieved, fundamentally solving the problems of easy segregation and uneven distribution of high aluminum doping.

[0013] 2. Synergistic Improvement of Structural Stability and Electrochemical Performance: The bulk gradient aluminum doping structure effectively suppresses manganese dissolution and crystal structure collapse during cycling, alleviating stress concentration caused by volume changes. High and uniform aluminum doping further stabilizes the crystal framework, and combined with the gradient distribution of transition metal elements, it significantly improves the cycle life, rate performance, and structural integrity of the material while maintaining its high specific capacity.

[0014] 3. The preparation process is controllable, highly reproducible, and suitable for mass production: The method has clear process steps, and by controlling the reaction conditions in stages (such as aluminum salt concentration, pH, temperature, etc.), precise control over the precursor particle size, morphology, and composition gradient is achieved. The entire process requires no complex post-processing, is highly operable, easy to scale up, and meets the requirements of industrial production.

[0015] 4. Broad application prospects: The lithium-rich manganese-based cathode material prepared based on this precursor has the characteristics of high capacity, long cycle life and good stability. It can be widely used in fields with extremely high requirements for energy density and reliability, such as electric vehicles, large-scale energy storage systems and high-end consumer electronics products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a SEM image of the bulk gradient high-alumina doped lithium-rich manganese precursor obtained by the preparation method described in Example 1 of this invention.

[0018] Figure 2 This is a SEM image of the bulk gradient high-alumina doped lithium-rich manganese cathode material obtained by the preparation method described in Example 1 of this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art to all other embodiments obtained without creative effort should be included within the protection scope of the present invention.

[0020] Example 1: This example provides a method for preparing a bulk high-alumina doped lithium-rich manganese precursor, the preparation method comprising the following steps: (1) Preparation of manganese-based mixed salt solution: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in deionized water according to the target stoichiometric ratio (e.g., Ni:Co:Mn molar ratio of 0.2:0.1:0.7) to prepare a homogeneous solution with a total metal ion concentration of 2.0 mol / L. Use sodium carbonate to prepare a precipitant solution with a sodium carbonate concentration of 2 mol / L; use ammonia water to prepare a complexing agent with a concentration of 10 g / L ammonia water solution.

[0021] (2) Prepare three aluminum sulfate solutions of different concentrations respectively: First concentration aluminum solution: concentration is 0.35 g / L (core layer).

[0022] Second concentration aluminum solution: concentration is 0.45 g / L (transition layer).

[0023] Third concentration aluminum solution: concentration is 0.55 g / L (outer shell layer).

[0024] (3) A co-precipitation reaction was carried out under a nitrogen atmosphere. Appropriate amounts of deionized water and ammonia were added to the reactor as a base solution, maintaining the system temperature at 55°C and the stirring speed at 350 rpm. A manganese-based mixed salt solution, sodium carbonate precipitant solution, ammonia complexing agent solution, and a first-concentration aluminum solution (0.35 g / L) were added in parallel using a metering pump. The feed rate was controlled to stabilize the pH of the reaction system at 8.0 and maintain the ammonia concentration at 5 g / L. The reaction proceeded until the precursor seed crystals reached a particle size D50 of approximately 3 μm, resulting in a core layer characterized by low aluminum doping. In the formed seed slurry, while keeping the other solutions constant, the aluminum solution was switched to a second-concentration aluminum solution (0.45 g / L). The reaction conditions could be finely adjusted, for example, by raising the temperature to 58°C and maintaining the pH at 8.2, to continue the reaction and allow crystal growth. During this stage, the aluminum doping concentration increased, forming an intermediate transition layer, achieving the first gradient increase in aluminum content from the inside out. When the precursor particles grow to a D50 of approximately 10 μm, the aluminum solution is switched to a third concentration aluminum solution (0.55 g / L). The reaction temperature is maintained at 60°C and the pH is stabilized at 8.5 for the deposition of the outer shell layer and crystal aging. The aluminum doping concentration is highest at this stage, forming the outer shell layer. When the final particle size D50 reaches approximately 12 μm, feeding is stopped, and aging continues for another 2 hours.

[0025] (4) After the reaction is completed, the slurry is filtered, washed and dried to obtain a lithium-rich manganese precursor with a core-intermediate-shell structure and a continuous gradient increase in aluminum doping from the inside to the outside (total aluminum doping is about 15000ppm). Its chemical composition can be expressed as Mn0.7Ni0.2Co0.1CO3 (gradient doped aluminum).

[0026] (5) The above-obtained bulk gradient high-alumina doped lithium-rich manganese precursor is uniformly mixed with lithium carbonate (Li2CO3) at a certain molar ratio. The mixture is calcined in an air atmosphere: first, the temperature is raised to 830°C at 5°C / min, held for 12 hours, cooled with the furnace, crushed and sieved to obtain the lithium-rich manganese-based cathode material.

[0027] (6) The obtained positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 80:10:10 to form a slurry, which is then coated onto aluminum foil, dried, rolled, and cut into sheets to form a positive electrode sheet. A coin cell is assembled using a lithium metal sheet as the negative electrode for testing.

[0028] Tested within a voltage window of 2.3–4.52 V and a charge / discharge rate of 1 C (approximately 200 mA / g), the initial discharge specific capacity of this cathode material can reach over 205 mAh / g. After 200 cycles, the average voltage decay per cycle is less than 0.2 mV, demonstrating excellent capacity retention and structural stability.

[0029] Beneficial Effects: This embodiment successfully constructed a microstructure with a continuous gradient increase in aluminum element concentration from the core to the shell through a three-step co-precipitation method and precise control of the switching timing of three aluminum salt solutions with increasing concentrations. This process draws on the concept of staged reaction control, ensuring the uniformity of co-precipitation of aluminum ions with nickel, cobalt, and manganese ions by adjusting the pH, temperature, and complexing agent concentration at each stage, effectively avoiding segregation. The final material achieved a bulk aluminum doping concentration of up to 15,000 ppm with an ideal gradient distribution, resulting in high specific capacity and significantly improved cycle stability in electrochemical tests, verifying the effectiveness and superiority of the technical solution described in the claims of this invention.

[0030] Example 2: This example provides a method for preparing a bulk gradient high-aluminum doped lithium-rich manganese precursor. Except for the concentration of sodium oxalate in the complexing agent group in step (1) being 0.8 mol / L, the concentration of the aluminum salt solution in the core layer being 0.30 g / L, the concentration of the transition layer being 0.45 g / L, and the concentration of the outer shell being 0.60 g / L, the preparation method is the same as in Example 1.

[0031] Comparative Example 1: This comparative example provides a method for preparing a non-gradient high-aluminum doped lithium-rich manganese precursor, the method comprising the following steps: (1) Preparation of manganese-based mixed salt solution: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in deionized water according to the target stoichiometric ratio (e.g., Ni:Co:Mn molar ratio of 0.2:0.1:0.7) to prepare a homogeneous solution with a total metal ion concentration of 2.0 mol / L. Use sodium carbonate to prepare a precipitant solution with a sodium carbonate concentration of 2 mol / L; use ammonia water to prepare a complexing agent with a concentration of 10 g / L ammonia water solution.

[0032] (2) Prepare an aluminum sulfate solution with a concentration of 0.45 g / L (transition layer).

[0033] (3) The co-precipitation reaction was carried out under a nitrogen atmosphere. Appropriate amounts of deionized water and ammonia were added to the reactor as a base solution, maintaining the system temperature at 55°C and the stirring speed at 350 rpm. A manganese-based mixed salt solution, sodium carbonate precipitant solution, ammonia complexing agent solution, and aluminum solution (0.45 g / L) were added in parallel using a metering pump. The feeding rate was controlled to stabilize the pH of the reaction system at 8.0 and maintain the ammonia concentration at 5 g / L. When the final particle size D50 reached approximately 12 μm, the feeding was stopped, and aging continued for 2 hours.

[0034] (4) After the reaction is completed, the slurry is filtered, washed and dried to obtain a lithium-rich manganese precursor with aluminum doping (total aluminum doping is about 15,000 ppm). Its chemical composition can be expressed as Mn0.7Ni0.2Co0.1CO3 (non-gradient doped aluminum).

[0035] (5) The high-alumina doped lithium-rich manganese precursor obtained above is uniformly mixed with lithium carbonate (Li2CO3) at a certain molar ratio. The mixture is calcined in an air atmosphere: first, the temperature is raised to 830°C at 5°C / min, held for 12 hours, cooled with the furnace, crushed and sieved to obtain the lithium-rich manganese-based cathode material.

[0036] (6) The obtained positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 80:10:10 to form a slurry, which was then coated onto aluminum foil. The slurry was dried, rolled, and cut into sheets to form a positive electrode. A coin cell was assembled using a lithium metal sheet as the negative electrode and tested. The test was conducted at a voltage window of 2.3-4.52V and a charge / discharge rate of 1C (approximately 200mA / g).

[0037] Comparative Example 2: This comparative example provides a method for preparing a non-gradient high-aluminum doped lithium-rich manganese precursor. The preparation method is the same as that of Comparative Example 1, except that the concentration of sodium oxalate complexing agent in the reaction system in step (1) is 0.8 mol / L.

[0038] The test results are shown in the table below:

[0039] As can be seen from Examples 1 and 2, as well as Comparative Examples 1 and 2, the present invention can first complex a large number of metal ions with sodium oxalate complexing agent and then slowly release them, thereby improving the uniformity of ion precipitation and improving the performance of lithium-rich manganese cathode. As can be seen from Examples 1 and Comparative Example 1, the gradient doping of the present invention can greatly improve the performance and stability of lithium-rich manganese cathode material.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A bulk gradient high-alumina doped lithium-rich manganese precursor, characterized in that: The general chemical formula of the bulk gradient high-alumina doped lithium-rich manganese precursor is Mn. x Ni y Co 1-x-y (OH)2 or Mn x Ni y Co 1-x-y CO3, where x is 0.6-0.8 and y is 0.2-0.4; structurally, it includes a core layer, an intermediate layer and a shell layer from the inside out; the total aluminum doping amount is 10,000 to 20,000 ppm, and the aluminum doping concentration increases continuously from the inside to the outside.

2. The bulk gradient high-alumina doped lithium-rich manganese precursor as described in claim 1, characterized in that: The particle size distribution of the core layer, intermediate layer and shell layer of the precursor is gradient, wherein the core layer has a D50 of 2.0-4.0 μm, the intermediate layer grows to a D50 of 8.0-11.0 μm, and the shell layer finally grows to a D50 of 12.0-15.0 μm.

3. A method for preparing a bulk gradient high-alumina doped lithium-rich manganese precursor as described in claim 1, characterized in that: S1. Simultaneously introduce manganese-based mixed salt solution, precipitant solution, complexing agent solution, and aluminum solution of the first concentration into the base liquid to carry out the first coprecipitation reaction, complete the nucleation and form the inner core layer; the temperature of the first coprecipitation reaction is 50-55℃, and the pH value is 8.0-8.1; S2. A second concentration of aluminum solution is introduced into the core layer system to carry out a second co-precipitation reaction, thereby achieving crystal growth in the intermediate layer; the temperature of the second co-precipitation reaction is 56-58℃, and the pH value is 8.2-8.

3. S3. Switch to the third concentration of aluminum solution and carry out the third co-precipitation reaction to complete the crystal growth and aging of the shell layer, and finally obtain the gradient-doped lithium-rich manganese precursor; the temperature of the third co-precipitation reaction is 59-62℃ and the pH value is 8.4-8.

6. The first coprecipitation reaction, the third coprecipitation reaction, and the third coprecipitation reaction were all carried out under a nitrogen atmosphere; The concentration of the third aluminum solution is greater than that of the second aluminum solution, which is greater than that of the first aluminum solution, so that the doping concentration of aluminum in the core layer, intermediate layer, and shell layer increases in a continuous gradient.

4. The preparation method according to claim 3, characterized in that: The complexing agent solution is any one of ammonia, citric acid, sodium oxalate, and EDTA, or a mixture of at least two in any proportion; the precipitant solution is sodium oxide or sodium carbonate; the concentration of the sodium hydroxide or sodium carbonate solution is 2 mol / L; and the concentration of the complexing agent solution is 10 g / L.

5. The preparation method according to claim 3, characterized in that: The manganese-based mixed salt solution is a soluble aqueous solution of nickel, cobalt and manganese salts, and the total metal ion concentration of the manganese-based mixed salt solution is 2.0-2.2 mol / L.

6. The preparation method according to claim 5, characterized in that: The nickel salt, cobalt salt, and manganese salt are nickel sulfate, cobalt sulfate, and manganese sulfate, respectively.

7. An application of the bulk phase gradient high-alumina doped lithium-rich manganese precursor as described in claim 1 or 2, characterized in that: The bulk gradient high-alumina doped lithium-rich manganese precursor is mixed with a lithium source and sintered to obtain a lithium-rich manganese-based cathode material. The sintering process is as follows: first, the temperature is raised to the pre-sintering temperature at a heating rate of 2-5℃ / min, and then held at 300-500℃ for 1-2 hours to fully remove volatiles and achieve preliminary oxidation. Then, the temperature is raised to 700-850℃ at a heating rate of 5℃ / min and held for 8-12 hours.

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