Positive electrode active material, preparation method thereof and lithium ion battery
By introducing porous carbon skeleton and potassium doping into the lithium-rich manganese-based positive electrode active material, the problem of poor conductivity and rate performance is solved, and the high energy density and stability of lithium-ion batteries are improved.
Patent Information
- Application Number
- CN202510490494.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-18
- Publication Date
- 2025-07-29
AI Technical Summary
The conductivity and rate performance of lithium-rich manganese-based positive electrode active materials are poor, which makes it difficult to exert the advantages of high energy density in practical applications.
Lithium-rich manganese-based material loaded with potassium doped with porous carbon skeleton is used to dopant potassium into the body phase of the lithium-rich manganese-based material, combined with the porous carbon skeleton formed in situ, broaden the lithium ion channel, improve conductivity and limit particle aggregation, and improve electron transmission rate and cycling performance.
It improves the rate performance and cycle stability of lithium-ion batteries, enhances the electron transfer rate of the positive electrode material and the cycle performance of the battery.
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of battery materials, and particularly relates to a positive electrode active material, a preparation method thereof, and a lithium-ion battery. Background Art
[0002] The deterioration of the environment and the intensification of energy consumption have increased people's demand for green energy. However, most green energies have the characteristics of intermittency and regionality and are difficult to meet actual applications, while secondary batteries can well avoid this shortcoming. Lithium-ion batteries have the advantages of long cycle life, high energy density, etc., and have been widely studied and applied by people, playing an important role in the power market and the energy storage market. With the progress of the times, people have an increasingly high pursuit of the energy density of lithium-ion batteries. The theoretical specific capacity of lithium-rich manganese-based positive electrode active materials is as high as 250-320 mAh / g, and they are considered to be the positive electrodes of the next generation of high-energy density batteries. However, the lithium-rich manganese-based positive electrode active materials have poor conductivity and rate performance, resulting in difficulty in exerting the advantage of high energy density during actual application. In order to improve the electrochemical performance of lithium-rich manganese-based positive electrode active materials, common modification strategies mainly include element doping, surface modification, morphology design, etc., but relevant research shows that the electrochemical performance of lithium-rich manganese-based positive electrode active materials still cannot be effectively improved. Summary of the Invention
[0003] The present application provides a positive electrode active material and a preparation method thereof to solve the problem of poor conductivity and rate performance of the existing lithium-rich manganese-based positive electrode active materials.
[0004] In a first aspect, the present application provides a positive electrode active material, including a porous carbon skeleton and a potassium-doped lithium-rich manganese-based material uniformly loaded on the porous carbon skeleton, and the median particle size Dv50 of the potassium-doped lithium-rich manganese-based material is 30 nm - 180 nm.
[0005] In an optional embodiment, based on the mass of the positive electrode active material, the content of the porous carbon skeleton is 0.5% - 3%.
[0006] In an optional embodiment, the pore size of the porous carbon skeleton is 4 nm - 500 nm.
[0007] In an optional embodiment, based on the mass of the positive electrode active material, the content of potassium is 0.01% - 0.01%.
[0008] In an optional embodiment, the chemical general formula of the lithium-rich manganese-based material is Li 1+x Mn a Ni b M cO2, wherein M is selected from any one of Fe, Co, and Al, and a trace amount of K is doped in the Li position and is not presented in the expression, 0.2≥x≥0.1, x+a+b+c=1, 0.7≥a≥0.5, 0.4≥b≥0.2, 0.1≥c≥0.
[0009] In a second aspect, the present application also provides a method for preparing a positive electrode active material, comprising the following steps:
[0010] S1, dissolving potassium hexacyanomanganese, a manganese source compound, a nickel source compound, and an M source compound in a sodium citrate aqueous solution to form respective aqueous solutions, mixing and stirring the aqueous solutions to react, collecting the precipitate by filtration, and drying to obtain a Prussian blue-like precursor;
[0011] S2, uniformly mixing the Prussian blue-like precursor prepared in S1 with the lithium source compound, heating to a first calcination temperature, maintaining the temperature for the first calcination time, then heating to a second calcination temperature and maintaining the temperature for the second calcination time;
[0012] The first calcination temperature is 200°C-500°C, and the second calcination temperature is 750°C-1200°C.
[0013] In an optional embodiment, the first calcination temperature is 300° C.-400° C., and the first calcination time is 2 h-4 h.
[0014] In an optional embodiment, the second calcination temperature is 850° C.-900° C., and the second calcination time is 6 h-48 h.
[0015] In an optional embodiment, the molar ratio of the Prussian blue-like precursor to the lithium source compound is 1:1.1-1.3.
[0016] In an optional embodiment, the materials are mixed by ball milling in S2, and the ball milling process parameters include: ball mill speed 100r / min-500r / min, ball milling time 1h-6h, and ball-to-material ratio 3-25:1.
[0017] Furthermore, the ball milling process parameters include: ball mill speed 100r / min-300r / min, ball milling time 3h-6h, and ball-to-material ratio 13-19:1.
[0018] In an optional embodiment, the lithium source compound includes at least one of lithium carbonate, lithium hydroxide, and lithium hydride.
[0019] In an optional embodiment, the reaction temperature in S1 is 0°C-60°C, and the reaction time is 2h-48h.
[0020] In an alternative embodiment, the molar ratio of the sum of the moles of potassium hexacyanomanganate and the manganese source compound to the nickel source compound and the M source compound is 0.5 - 0.7: 0.2 - 0.4: 0 - 0.1.
[0021] In an alternative embodiment, the molar concentration of sodium citrate in the aqueous sodium citrate solution is 1 mol / L - 5 mol / L.
[0022] In an alternative embodiment, the molar concentration of manganese ions in the aqueous solution of the manganese source compound prepared in S1 is 0.5 mol / L - 2 mol / L.
[0023] In an alternative embodiment, the manganese source compound is at least one of manganese sulfate, manganese nitrate, and manganese acetate.
[0024] In an alternative embodiment, the molar concentration of nickel ions in the aqueous solution of the nickel source compound prepared in S1 is 0.2 mol / L - 1 mol / L.
[0025] In an alternative embodiment, the nickel source compound is at least one of nickel sulfate, nickel nitrate, and nickel acetate.
[0026] In an alternative embodiment, the molar concentration of M ions in the aqueous solution of the M source compound prepared in S1 is 0 - 0.1 mol / L, and M is any one of Fe, Co, and Al.
[0027] In an alternative embodiment, the M source compound is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt acetate, aluminum sulfate, aluminum nitrate, aluminum acetate, iron sulfate, iron nitrate, and iron acetate.
[0028] In a third aspect, the present application also provides a lithium-ion battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector; the positive electrode active material layer includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the preparation method described in the second aspect of the present application.
[0029] The technical solution of the present application has the following advantages:
[0030] The positive electrode active material provided by this application includes a porous carbon framework and a potassium-doped lithium-rich manganese-based material uniformly loaded on the porous carbon framework. The median particle size Dv50 of the potassium-doped lithium-rich manganese-based material is 30 nm - 180 nm. By doping potassium elements into the bulk phase of the lithium-rich manganese-based material, it can play a role in broadening the lithium-ion channels and supporting the lithium-ion diffusion channels, which is beneficial to the rapid deintercalation and intercalation of lithium ions and can improve the cycle stability of the positive electrode material. At the same time, the in-situ formed porous carbon framework can, on the one hand, improve the conductivity of the lithium-rich manganese-based material and enhance the electron transport rate of the material. On the other hand, the pore structure of the porous carbon framework can also limit the aggregation and growth of the primary particles of the lithium-rich manganese-based material, reducing the transport distance of lithium ions in the bulk phase of the lithium-rich manganese-based positive electrode. Thus, the rate performance of the lithium-ion battery can be improved. Thirdly, the porous carbon framework can also effectively prevent the direct contact between the electrolyte and the lithium-rich positive electrode, improving the cycle performance of the battery.
[0031] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or will be explained through the implementation of the embodiments of this application. Detailed implementation manners
[0032] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.
[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the description and claims of this application are intended to cover non-exclusive inclusion.
[0034] Related technologies mostly use transition metal precursors, lithium sources, and oxides of doping elements to obtain element-doped lithium-rich manganese-based materials through one firing, and then blend them with modifier materials for a second firing to achieve surface modification. This method requires two sintering processes, which not only affects production efficiency but also lacks a structure to limit the growth of lithium-rich manganese-based materials during sintering, making it unfavorable for synthesizing lithium-rich manganese-based positive electrode materials with small particle sizes.
[0035] To solve the problems existing in the above-mentioned related technologies, according to the first aspect of this application, a positive electrode active material is provided, including a porous carbon framework and a potassium-doped lithium-rich manganese-based material uniformly loaded on the porous carbon framework. The median particle size Dv50 of the potassium-doped lithium-rich manganese-based material is 30 nm - 180 nm.
[0036] By doping potassium element into the bulk phase of the lithium-rich manganese-based material in this application, it can play a role in broadening the lithium-ion channels and supporting the lithium-ion diffusion channels, which is beneficial to the rapid deintercalation and intercalation of lithium ions and improves the cycle stability of the cathode material. At the same time, the in-situ formed porous carbon framework can, on the one hand, improve the conductivity of the lithium-rich manganese-based material and enhance the electron transport rate of the material, and on the other hand, the pore structure of the porous carbon framework can also limit the aggregation and growth of the primary particles of the lithium-rich manganese-based material, reducing the transport distance of lithium ions in the bulk phase of the lithium-rich manganese-based cathode, thereby improving the rate performance of the lithium-ion battery. Thirdly, the porous carbon framework can also effectively hinder the direct contact between the electrolyte and the lithium-rich cathode, improving the cycle performance of the battery.
[0037] Exemplarily, the median particle size Dv50 of the potassium-doped lithium-rich manganese-based material can be 30nm, 60nm, 90nm, 120nm, 150nm, 180nm, etc. or within the range composed of any of the above values. It is found in the research of this application that if the median particle size Dv50 of the potassium-doped lithium-rich manganese-based material is too large or too small, it is not conducive to the rate and cycle performance of the battery.
[0038] It can be understood that introducing a porous carbon material into the cathode active material can improve the conductivity of the cathode material. In an optional embodiment, based on the mass of the cathode active material, the content of the porous carbon framework is 0.5%-3%. As an example, the content of the porous carbon framework is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. or within the range composed of any of the above values.
[0039] In some embodiments, the pore size of the porous carbon framework is 4nm - 500nm, which can limit the aggregation and growth of the cathode active material particles. As an example, the pore size of the porous carbon framework can be 4nm, 20nm, 50nm, 100nm, 150nm, 200nm, 400nm, 600nm, 500nm, etc. or within the range composed of any of the above values.
[0040] It should be noted that the chemical general formula of the lithium-rich manganese-based material is Li 1+x Mn a Ni b M cO2, wherein M is selected from any one of Fe, Co, and Al elements, 0.2 ≥ x ≥ 0.1, x + a + b + c = 1, 0.7 ≥ a ≥ 0.5, 0.4 ≥ b ≥ 0.2, 0.1 ≥ c ≥ 0. Compared with ordinary ternary materials, in the lithium-rich manganese-based material, Mn and O will participate in the redox reaction during the charge and discharge process, and the reaction kinetics of the above two is slower than that of Ni and M, resulting in poor kinetic performance of the lithium-rich manganese-based material. In this application, a trace amount of potassium element is doped at the Li site of the lithium-rich manganese-based material, and at the same time, the porous carbon framework is used to limit the particle size of the lithium-rich manganese-based material, thereby improving the reaction kinetics of the lithium-rich manganese-based material, and thus increasing the specific capacity and cycle stability.
[0041] In some embodiments, based on the mass of the positive electrode active material, the content of potassium is 0.25% - 0.45%. As an example, the doping amount of potassium is 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, etc. or within the range composed of any of the above values.
[0042] According to the second aspect of the present application, a method for preparing a positive electrode active material is provided, including the following steps:
[0043] S1. Dissolve potassium hexacyanomanganate, manganese source compound, nickel source compound, and M source compound in sodium citrate aqueous solution to form their respective aqueous solutions, mix and stir the aqueous solutions to react, filter and collect the precipitate, and obtain a Prussian blue-like precursor after drying;
[0044] S2. Mix the Prussian blue-like precursor obtained in S1 with the lithium source compound evenly, heat to the first calcination temperature, keep the temperature for the first calcination time, then raise the temperature to the second calcination temperature and keep the temperature for the second calcination time;
[0045] The first calcination temperature is 200°C - 500°C, and the second calcination temperature is 750°C - 1200°C.
[0046] In this application, potassium hexacyanomanganate is used to convert transition metal salts into a Prussian blue-like precursor, and then the precursor is mixed with a lithium source and calcined. Only one-step calcination can in-situ form a porous carbon framework and simultaneously achieve the doping of potassium element in the bulk phase of the lithium-rich manganese-based material. Compared with the existing two-step calcination method, it not only simplifies the process operation and improves the production efficiency, but also the pore structure of the porous carbon framework can limit the aggregation and growth of the lithium-rich manganese-based material during the sintering process, thus facilitating the synthesis of potassium-doped lithium-rich manganese-based materials with small particle sizes. When used in lithium-ion batteries, it can improve the rate and cycle performance of the battery.
[0047] The present application study found that controlling the first calcination temperature in the range of 200°C-500°C is conducive to the slow carbonization of the Prussian blue precursor, thereby forming a porous carbon skeleton structure. If the first calcination temperature is too high, the porous carbon structure will collapse. On the contrary, if the first calcination temperature is too low, the effect of stable carbonization cannot be achieved. In some embodiments, the first calcination temperature can be, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, etc. or within the range of any of the above values. Controlling the second calcination temperature in the range of 750°C-1200°C is conducive to the synthesis of small-particle potassium-doped lithium-rich manganese-based materials. If the second calcination temperature is too high, the positive electrode active material particles will grow excessively. On the contrary, if the second calcination temperature is too low, the crystallinity of the positive electrode active material will be affected. In some embodiments, the second calcination temperature may be, for example, 750° C., 850° C., 900° C., 1000° C., 1100° C., 1200° C., or any of the above values.
[0048] It is understandable that in addition to the calcination temperature, the calcination time will also have a certain impact on the structure and performance of the calcined product. Therefore, the present application controls the first calcination time to be 2h-4h, thereby forming a porous carbon structure with complete carbonization and complete skeleton, and controls the second calcination time to be 6h-48h, so that a positive electrode active material with suitable crystallinity and particle size can be prepared. As an example, the first calcination time can be, for example, 2h, 2.5h, 3h, 4h, etc. or within the range of any of the above values, and the second calcination time can be, for example, 6h, 12h, 18h, 24h, 30h, 36h, 42h, 48h, etc. or within the range of any of the above values.
[0049] In some embodiments, the molar ratio of the Prussian blue-like precursor to the lithium source compound is 1:1.1-1.3, thereby ensuring that the obtained material is rich in lithium, thereby successfully preparing a lithium-rich positive electrode active material. As an example, the molar ratio of the Prussian blue-like precursor to the lithium source compound can be, for example, 1:1.1, 1:1.15, 1:1.2, 1:1.25, 1.3, etc., or within a range consisting of any of the above values. Exemplarily, the lithium source compound includes at least one of lithium carbonate, lithium hydroxide, and lithium hydride.
[0050] In some embodiments, the materials are mixed by ball milling in S2, and the ball milling process parameters mainly include: ball milling speed of 100r / min-500r / min, ball milling time of 1h-6h and ball-to-material ratio of 3-25:1. The present application found that too fast ball milling speed will transfer higher energy, which may damage the main structure of the Prussian blue-like substance and is not conducive to the subsequent formation of the carbon skeleton; too short ball milling time and too low ball-to-material ratio are not conducive to the uniform mixing of the raw materials, while too long ball milling time and too high ball-to-material ratio are not conducive to production efficiency. Therefore, by controlling the above-mentioned ball milling conditions, the present application can ensure the uniform mixing of the precursor and the lithium source, and the Prussian blue-like precursor will not decompose prematurely. As an example, the ball mill speed can be 100r / min, 200r / min, 300r / min, 400r / min, 500r / min, etc. or within the range of any of the above values, the ball milling time can be 1h, 2h, 3h, 4h, 5h, 6h, etc. or within the range of any of the above values, and the ball-to-material ratio can be 3:1, 5:1, 10:1, 13:1, 15:1, 19:1, 22:1, 25:1, etc. or within the range of any of the above values.
[0051] It is understood that the reaction temperature in S1 is 0°C-60°C, and the reaction time is 2h-48h. By controlling the above reaction conditions, a Prussian blue-like precursor of suitable size can be obtained. As an example, the reaction temperature in S1 can be, for example, 0°C, 20°C, 30°C, 40°C, 50°C, 60°C, or the like, or within a range thereof, and the reaction time can be, for example, 2h, 12h, 24h, 36h, 48h, or the like, or within a range thereof.
[0052] In an optional embodiment, the molar ratio of the sum of the moles of the potassium hexacyanomanganese and the manganese source compound to the nickel source compound and the M source compound is 0.5-0.7:0.2-0.4:0-0.1, thereby preparing a lithium-rich positive electrode active material with a corresponding element ratio.
[0053] It is understandable that the concentration of the reactants also has a certain impact on the reaction results. In some embodiments, the molar concentration of manganese ions in the aqueous solution of the manganese source compound prepared by S1 is 0.5mol / L-2mol / L; the molar concentration of nickel ions in the aqueous solution of the nickel source compound prepared by S1 is 0.2mol / L-1mol / L; the molar concentration of M ions in the aqueous solution of the M source compound prepared by S1 is 0-0.1mol / L, where M is selected from any one of Fe, Co, and Al; thereby, a Prussian blue-like precursor of suitable size can be obtained.
[0054] Exemplarily, the manganese source compound includes at least one of manganese sulfate, manganese nitrate, and manganese acetate, the nickel source compound is at least one of nickel sulfate, nickel nitrate, and nickel acetate, and the M source compound is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt acetate, aluminum sulfate, aluminum nitrate, aluminum acetate, ferric sulfate, ferric nitrate, and ferric acetate.
[0055] It should be noted that, in some embodiments, S1 uses a 1M-5M sodium citrate aqueous solution to prepare various metal ion solutions, which can ensure high crystallinity of the Prussian blue-like precursor. If the sodium citrate concentration is too low, it will be difficult to improve the crystallinity of the Prussian blue-like precursor, and the carbon framework formation during the subsequent sintering process will be incomplete. When the sodium citrate concentration is further increased, the effect of improving the crystallinity of the precursor is not significant, resulting in unnecessary waste.
[0056] In a third aspect, the present application also provides a lithium-ion battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode collector; the positive electrode active material layer comprises the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the preparation method described in the second aspect of the present application.
[0057] The lithium-ion battery of the present application adopts the aforementioned positive electrode active material, and thus has the advantages of good rate and cycle performance.
[0058] The present invention is further described in detail below with reference to specific examples, which should not be construed as limiting the scope of protection claimed in the present invention. In all examples and comparative examples of the present invention, the unit % represents mass percentage, and the unit M represents mol / L.
[0059] Example 1
[0060] The method for preparing the positive electrode active material provided in this embodiment includes the following steps:
[0061] S1. Synthesis of low potassium content Prussian blue precursor
[0062] 1 mol of potassium hexacyanomanganese, 0.3 mol of MnSO4·1H2O and 0.35 mol of Ni2(SO4)3·6H2O were placed in a 1M aqueous sodium citrate solution and stirred for half an hour to prepare the corresponding solution with a transition metal concentration of 1M. The above three solutions were then added to a beaker and stirred for 6 hours. The resulting solution was filtered through a circulating water vacuum pump, washed three times with deionized water and anhydrous ethanol each, and the filtered product was placed in a vacuum oven at 90°C and dried for 24 hours to obtain a low-potassium content Prussian blue precursor.
[0063] S2. Preparation of positive electrode active materials
[0064] The precursor obtained in S1 and lithium carbonate were ball-milled and mixed evenly at a molar ratio of 1:1.2. The ball-milling process parameters included: the rotational speed of the ball mill was 200 r / min, the ball-milling time was 4 h, and the ball-to-material ratio was 15:1. Then, it was placed in a tube furnace and heated to 400 °C for 4 h to allow the precursor to slowly carbonize to form a porous carbon structure. Then, the temperature was raised to 900 °C for 16 h and cooled to room temperature to obtain the cathode active material.
[0065] Example 2
[0066] The preparation method was the same as that in Example 1, except that the reactants in S1 also included 0.2 mol of CoSO4·7H2O, and it was prepared into a solution with a cobalt ion concentration of 0.2 M using 1 M aqueous sodium citrate solution.
[0067] Example 3
[0068] The preparation method was the same as that in Example 1, except that the second calcination temperature was adjusted to 1000 °C.
[0069] Example 4
[0070] The preparation method of the cathode active material provided in this example included the following steps:
[0071] S1. Synthesis of low-potassium-content Prussian blue precursor
[0072] 1 mol of potassium hexacyanomanganate, 0.4 mol of MnSO4·1H2O, and 0.7 mol of Ni(NO3)3 were respectively placed in 1 M aqueous sodium citrate solution and stirred for half an hour to prepare the corresponding solutions with a transition metal concentration of 1 M. 0.1 mol of CoSO4·7H2O was placed in 3 M aqueous sodium citrate solution and stirred for half an hour to prepare a solution with a cobalt ion concentration of 0.1 M. Then, the above four solutions were simultaneously added to a beaker and stirred for 2 h. The obtained solution was filtered by a circulating water vacuum pump, washed three times with deionized water and anhydrous ethanol respectively, and the filtered product was placed in a vacuum oven at 90 °C and dried for 24 h to obtain the low-potassium-content Prussian blue precursor.
[0073] S2. Preparation of cathode active material
[0074] The precursor obtained in S1 and lithium carbonate were ball-milled and mixed evenly at a molar ratio of 1:1.3. The ball-milling process parameters included: the rotational speed of the ball mill was 100 r / min, the ball-milling time was 6 h, and the ball-to-material ratio was 19:1. Then, it was placed in a tube furnace and heated to 500 °C for 2 h to allow the precursor to slowly carbonize to form a porous carbon structure. Then, the temperature was raised to 1050 °C for 20 h and cooled to room temperature to obtain the cathode active material.
[0075] Example 5
[0076] The preparation method of the cathode active material provided by this embodiment includes the following steps:
[0077] S1. Synthesis of the low-potassium-content Prussian blue precursor
[0078] Put 1 mol of potassium hexacyanomanganate and 0.6 mol of Ni(NO3)3 into 1 M aqueous sodium citrate solution respectively and stir for half an hour to prepare the corresponding solutions with a transition metal concentration of 1 M. Then add the above three solutions into a beaker and stir for 6 hours. The obtained solution is filtered by a circulating water vacuum pump, washed three times with deionized water and anhydrous ethanol respectively, and the product obtained by suction filtration is placed in a vacuum oven at 100 °C for drying for 24 h to obtain the low-potassium-content Prussian blue precursor.
[0079] S2. Preparation of the cathode active material
[0080] Mix the precursor obtained in S1 and lithium carbonate evenly by ball milling at a molar ratio of 1:1.18. The ball milling process parameters include: the rotation speed of the ball mill is 300 r / min, the ball milling time is 3 h, and the ball-to-material ratio is 13:1; then place it in a tube furnace and heat it to 300 °C for insulation for 4 h so that the precursor slowly carbonizes to form a porous carbon structure, and then increase the temperature to 750 °C for insulation for 48 h, and cool it to room temperature to obtain the cathode active material.
[0081] Example 6
[0082] The preparation method of the cathode active material provided by this embodiment includes the following steps:
[0083] S1. Synthesis of the low-potassium-content Prussian blue precursor
[0084] Put 1 mol of potassium hexacyanomanganate, 0.3 mol of MnSO4·1H2O and 0.39 mol of Ni(NO3)3 into 1 M aqueous sodium citrate solution respectively and stir for half an hour to prepare the corresponding solutions with a transition metal concentration of 1 M. Then add the above three solutions into a beaker and stir for 6 hours. Filter the obtained solution, collect the precipitate and wash it three times with deionized water and anhydrous ethanol respectively, and then place it in a vacuum oven at 100 °C for drying for 24 h to obtain the low-potassium-content Prussian blue precursor.
[0085] S2. Preparation of the cathode active material
[0086] Mix the precursor obtained in S1 and lithium carbonate evenly by ball milling at a molar ratio of 1:1.2. The ball milling process parameters include: the rotation speed of the ball mill is 400 r / min, the ball milling time is 3 h, and the ball-to-material ratio is 3:1; then place it in a tube furnace and heat it to 400 °C for insulation for 3 h so that the precursor slowly carbonizes to form a porous carbon structure, and then increase the temperature to 800 °C for insulation for 48 h, and cool it to room temperature to obtain the cathode active material.
[0087] Example 7
[0088] The preparation method of the positive electrode active material provided in this example includes the following steps:
[0089] S1. Synthesis of low-potassium-content Prussian blue precursor
[0090] Put 1 mol of potassium hexacyanomanganate, 0.3 mol of MnSO4·1H2O, and 0.6 mol of Ni(NO3)3 into 5 M aqueous sodium citrate solution and stir for half an hour respectively to prepare corresponding solutions with a transition metal concentration of 0.5 M. Put 0.05 mol of FeSO4 into 5 M aqueous sodium citrate solution and stir for half an hour to prepare a solution with an iron ion concentration of 0.05 M. Then add the above four solutions into a beaker and stir for 24 hours. Filter the obtained solution, collect the precipitate, wash it three times with deionized water and anhydrous ethanol respectively, and then place it in a vacuum oven at 100 °C for 24 h to obtain a low-potassium-content Prussian blue precursor.
[0091] S2. Preparation of positive electrode active material
[0092] Mix the precursor obtained in S1 and lithium carbonate evenly by ball milling at a molar ratio of 1:1.2. The ball milling process parameters include: the rotation speed of the ball mill is 500 r / min, the ball milling time is 1 h, and the ball-to-material ratio is 15:1. Then place it in a tube furnace and heat it to 200 °C for 3 h to slowly carbonize the precursor to form a porous carbon structure, and then raise the temperature to 900 °C for 15 h and cool it to room temperature to obtain the positive electrode active material.
[0093] Example 8
[0094] The preparation method of the positive electrode active material provided in this example includes the following steps:
[0095] S1. Synthesis of low-potassium-content Prussian blue precursor
[0096] Put 1 mol of potassium hexacyanomanganate and 0.3 mol of MnSO4·1H2O into 5 M aqueous sodium citrate solution and stir for half an hour respectively to prepare solutions with a manganese ion concentration of 2 M each. Put 0.6 mol of Ni(NO3)3 into 5 M aqueous sodium citrate solution and stir for half an hour to prepare a solution with a nickel ion concentration of 0.2 M. Put 0.05 mol of Al2(SO4)3 into 5 M aqueous sodium citrate solution and stir for half an hour to prepare a solution with an aluminum ion concentration of 0.05 M. Then add the above four solutions into a beaker and stir for 12 hours. Filter the obtained solution, collect the precipitate, wash it three times with deionized water and anhydrous ethanol respectively, and then place it in a vacuum oven at 100 °C for 24 h to obtain a low-potassium-content Prussian blue precursor.
[0097] S2. Preparation of positive electrode active material
[0098] Mix the precursor obtained in S1 and lithium carbonate evenly by ball milling at a molar ratio of 1:1.3. The ball milling process parameters include: the rotation speed of the ball mill is 200 r / min, the ball milling time is 5 h, and the ball-to-material ratio is 15:1; then place it in a tube furnace and heat it to 350 °C for insulation for 4 h so that the precursor slowly carbonizes to form a porous carbon structure, and then raise the temperature to 900 °C for insulation for 24 h, and cool it to room temperature to obtain the cathode active material.
[0099] Comparative Example 1
[0100] Dissolve 1.3 mol of MnSO4·1H2O and 0.35 mol of Ni2(SO4)3·6H2O in deionized water, adjust the pH to about 8 with 0.1 M Na2CO3 solution. The generated precipitate is washed and then dried in an oven at 80 °C to obtain a carbonate precursor. Then mix it evenly with lithium carbonate by ball milling at a molar ratio of 1:1.2, and then raise the temperature to 850 °C for insulation for 12 h, and cool it to room temperature to obtain a lithium-rich manganese-based material.
[0101] Comparative Example 2
[0102] Dissolve 1.3 mol of MnSO4·1H2O and 0.35 mol of Ni2(SO4)3·6H2O in deionized water, adjust the pH to about 8 with 0.1 M Na2CO3 solution. The generated precipitate is washed and then dried in an oven at 80 °C to obtain a carbonate precursor. Then mix it evenly with lithium carbonate and glucose by ball milling at a molar ratio of 1:1.2:0.3, and then place it in a tube furnace and heat it to 400 °C for insulation for 4 h so that glucose slowly carbonizes, and then raise the temperature to 850 °C for insulation for 12 h, and cool it to room temperature to obtain a carbon composite lithium-rich manganese-based material.
[0103] Comparative Example 3
[0104] Dissolve 1.3 mol of MnSO4·1H2O and 0.35 mol of Ni2(SO4)3·6H2O in deionized water, adjust the pH to about 8 with 0.1 M Na2CO3 solution. The generated precipitate is washed and then dried in an oven at 80 °C to obtain a carbonate precursor. Then mix it evenly with lithium carbonate and potassium carbonate by ball milling at a molar ratio of 1:1.2:0.2, and then raise the temperature to 850 °C for insulation for 12 h, and cool it to room temperature to obtain a potassium-doped lithium-rich manganese-based material.
[0105] Comparative Example 4
[0106] The preparation method is basically the same as that of Example 1, except that deionized water is used instead of sodium citrate aqueous solution in preparing the metal ion solution in S1.
[0107] Comparative Example 5
[0108] The preparation method is basically the same as that of Example 1, except that the sintering conditions are 700° C. and 20 h.
[0109] Comparative Example 6
[0110] The preparation method is basically the same as that of Example 1, except that after the mixing in S2 is completed, the temperature is directly raised to 1100° C. and kept for 30 hours, and then cooled to room temperature to obtain the positive electrode active material.
[0111] Test Example 1: Structural Test
[0112] The structures of the positive electrode active materials prepared in the examples and comparative examples were analyzed, and the results are shown in Table 1.
[0113] The specific test methods are as follows:
[0114] The ICP method was used to test the chemical composition of lithium-rich manganese-based materials.
[0115] The potassium content in the positive electrode active material was tested using the ICP method.
[0116] Thermogravimetric testing was used to test the mass ratio of the porous carbon skeleton.
[0117] The pore size of the porous carbon framework was measured using the BET method.
[0118] The particle size of potassium-doped lithium-rich manganese-based materials was tested using the SEM method.
[0119] Table 1 Structural parameters
[0120]
[0121] Test Example 2: Assembly and Performance Testing of Button Cell Batteries
[0122] The electrochemical performance of the positive electrode active materials prepared in each embodiment and comparative example was tested and analyzed, and the results are shown in Table 2. The specific steps are as follows:
[0123] S1. Preparation of positive electrode sheets: The positive electrode active material, Ketjen black and PVDF were mixed and dispersed in the organic solvent NMP in a weight ratio of 8:1:1 to form a uniform slurry. The slurry was then cast on a carbon-coated aluminum foil by a doctor blade method and vacuum-dried at 120°C for 12 hours. The slurry was then cut into positive electrode sheets with a diameter of 12 mm.
[0124] S2. Assembly of button cells: 2032-type button cells were assembled in a glove box filled with inert gas, where the contents of H2O and O2 were both less than 0.1 ppm; metallic lithium was used as the counter electrode, 1M LiPF6 (EC:EMC=3:7 vol%) + 5% FEC was used as the electrolyte, and a commercial PP diaphragm was used as the separator.
[0125] S3. Electrochemical performance test: The constant current charge / discharge test was carried out at room temperature using the LAND CT2001A battery test system. The test procedure was as follows: The charge / discharge cycle tests were carried out at 0.1C and 1C respectively, and the test voltage range was 2 - 4.65V.
[0126] Table 2 Electrochemical performance
[0127]
[0128] As can be seen from Table 2, compared with Comparative Examples 1 - 6, the positive electrode active materials prepared by constructing the Prussian blue-like precursors in Examples 1 - 8, due to the porous carbon framework formed by the decomposition of the Prussian blue-like precursors, restricted the aggregation and growth of the lithium-rich positive electrode active material particles. Therefore, the capacity utilization ability and rate performance of the positive electrode were improved. On the other hand, the porous carbon framework could also effectively inhibit the direct contact between the electrolyte and the lithium-rich positive electrode active material, improving the cycle performance of the battery. At the same time, the doping of trace K elements could support the structure of the positive electrode active material and also improve the cycle stability of the battery to a certain extent.
[0129] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of this application.
Claims
1. A positive electrode active material, characterized in that, It includes a porous carbon framework and a potassium-doped lithium-rich manganese-based material uniformly loaded on the porous carbon framework, and the median particle size Dv50 of the potassium-doped lithium-rich manganese-based material is 30 nm - 180 nm.
2. The positive electrode active material according to claim 1, wherein Based on the mass of the positive electrode active material, the content of the porous carbon framework is 0.5% - 3%. And / or, the pore size of the porous carbon framework is 4 nm - 500 nm.
3. The positive electrode active material according to claim 1, characterized in that, Based on the mass of the positive electrode active material, the content of potassium is 0.25% - 0.45%.
4. The cathode active material according to any one of claims 1 to 3, characterized in that, The chemical general formula of the lithium-rich manganese-based material is Li 1+x Mn a Ni b M c O2, where M is selected from any one of Fe, Co, and Al, 0.2 ≥ x ≥ 0.1, x + a + b + c = 1, 0.7 ≥ a ≥ 0.5, 0.4 ≥ b ≥ 0.2, 0.1 ≥ c ≥ 0.
5. A method for preparing a positive electrode active material, characterized in that, It includes the following steps: S1. Dissolve potassium hexacyanomanganate, manganese source compound, nickel source compound and M source compound in sodium citrate aqueous solution respectively to form their respective aqueous solutions. Mix and stir the aqueous solutions to react, filter and collect the precipitate, and obtain a Prussian blue-like precursor after drying. S2. Mix the Prussian blue-like precursor prepared in S1 with the lithium source compound evenly, heat to the first calcination temperature, keep the temperature for the first calcination time, then raise the temperature to the second calcination temperature and keep the temperature for the second calcination time. The first calcination temperature is 200°C - 500°C, and the second calcination temperature is 750°C - 1200°C.
6. The method for preparing the positive electrode active material according to claim 5, characterized in that, The first calcination temperature is 300°C - 400°C, and the first calcination time is 2 h - 4 h. And / or, the second calcination temperature is 850°C - 900°C, and the second calcination time is 6 h - 48 h.
7. The method for preparing the positive electrode active material according to claim 5 or 6, characterized in that, The molar ratio of the Prussian blue-like precursor to the lithium source compound is 1:1.1 - 1.
3. And / or, in S2, the materials are mixed by ball milling, and the ball milling process parameters include: the rotation speed of the ball mill is 100 r / min - 500 r / min, the ball milling time is 1 h - 6 h, and the ball-to-material ratio is 3 - 25:
1. And / or, the lithium source compound includes at least one of lithium carbonate, lithium hydroxide, and lithium hydride.
8. The method for preparing the positive electrode active material according to claim 5 or 6, characterized in that, In S1, the reaction temperature is 0°C - 60°C, and the reaction time is 2 h - 48 h. And / or, the molar ratio of the sum of the molar amounts of potassium hexacyanomanganate and the manganese source compound to the nickel source compound and the M source compound is 0.5 - 0.7:0.2 - 0.4:0 - 0.
1.
9. The method for preparing the positive electrode active material according to claim 5 or 6, characterized in that, The molar concentration of sodium citrate in the sodium citrate aqueous solution is 1 mol / L - 5 mol / L. And / or, the molar concentration of manganese ions in the aqueous solution of the manganese source compound prepared in S1 is 0.5 mol / L - 2 mol / L. And / or, the manganese source compound is at least one of manganese sulfate, manganese nitrate, and manganese acetate. And / or, the molar concentration of nickel ions in the aqueous solution of the nickel source compound prepared in S1 is 0.2 mol / L - 1 mol / L. And / or, the nickel source compound is at least one of nickel sulfate, nickel nitrate, and nickel acetate. And / or, the molar concentration of M ions in the aqueous solution of the M source compound prepared in S1 is 0 - 0.1 mol / L, and M is selected from any one of Fe, Co, and Al. And / or, the M source compound is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt acetate, aluminum sulfate, aluminum nitrate, aluminum acetate, iron sulfate, iron nitrate, and iron acetate.
10. A lithium-ion battery, comprising a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; characterized in that, The positive electrode active material layer includes the positive electrode active material according to any one of claims 1 to 4 or the positive electrode active material prepared by the preparation method according to any one of claims 5 to 9.