Lithium-manganese-rich positive electrode material with annual ring structure as well as preparation method and application of lithium-manganese-rich positive electrode material

Abstract

The invention relates to the technical field of lithium battery positive electrode materials, in particular to a lithium-manganese-rich positive electrode material with an annual ring structure as well as a preparation method and application of the lithium-manganese-rich positive electrode material. The lithium-manganese-rich positive electrode material with the annual ring structure is obtained by adopting three precipitants in a carbonic acid series lithium-manganese-rich system to regulate and control the precipitation process in the growth process of a carbonate precursor structure and control the solid content of the system; the composite ball is a secondary ball formed by alternating multiple layers of dense structures and loose structures, modification elements Al and B are further introduced into each layer to realize coating and doping of interfaces between the structures, and internal multiple-layer gaps and pores in the layers can improve the infiltration effect of an electrolyte and cannot increase the contact area with the electrolyte, so that the service life of the composite ball is prolonged, and the service life of the composite ball is prolonged. Therefore, the surface porosity is reduced, excessive interface side reactions are reduced, gas production is improved, meanwhile, the capacity can be exerted, the high-voltage cycle life is prolonged, and the problem that in the prior art, when the gas production behavior of the carbonic acid series lithium-rich manganese positive electrode material is improved, the capacity or / and the cycle life are / is obviously degraded is solved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode material technology, and in particular to a lithium-rich manganese cathode material with an annual ring structure, its preparation method, and its application. Background Technology

[0002] The most widely used synthesis method for lithium-rich manganese cathode materials is the co-precipitation method, which involves high-temperature sintering of a lithium-rich manganese precursor with a lithium salt. Based on the synthesis system, lithium-rich manganese precursors are divided into two main categories: hydroxyl-based and carbonate-based. It is generally believed in the industry that hydroxyl-based lithium-rich manganese cathode materials will be the first to enter the market, while carbonate-based materials face greater resistance in market application due to high gas production and low compaction density. These defects in carbonate-based lithium-rich manganese cathode materials are closely related to their structure: carbonate precursors consist of nanoscale primary particles stacked to form secondary spheres. The low interparticle bonding force and high interparticle porosity make them unable to withstand high pressures, leading to particle breakage. This is also one of the factors contributing to the higher initial capacity of carbonate-based materials compared to hydroxyl-based materials; the larger specific surface area results in more electrolyte wetting interfaces, which in turn leads to more interfacial side reactions and gas production. In addition to the above reasons, the high cutoff voltage of carbonate-based materials is also a significant cause of gas production. Currently used electrolytes are mostly liquid ester systems, which have poor high voltage resistance and are prone to decomposition to generate carbon dioxide above 4.5V. The mismatch between the battery system and the current carbonic acid system is also an important reason why it is difficult to commercialize.

[0003] To address the gas generation problem in carbonate-based lithium-rich manganese precursors, the following three modification methods are commonly used in material synthesis to reduce interfacial side reactions and thus lower gas generation: 1. Monocrystalline formation: For example, Chinese patent CN118099409B introduces elements that refine grains and aid sintering. By adjusting the ratio of these elements, a synergistic effect is achieved, ultimately synthesizing a monodisperse monocrystalline ion with high compaction density and low specific surface area. This effectively suppresses interfacial side reactions and improves the energy density and cycle life of lithium-rich manganese cathode materials. 2. Bulk doping: For example, Chinese patent CN120364763A introduces a boron source during primary sintering. Then, the boron-doped primary product is etched with ammonia to construct oxygen vacancies on the surface, inducing the formation of a spinel coating layer, thereby improving initial efficiency, cycle life, and gas generation. 3. Surface coating.

[0004] However, the single-crystallization modification route mainly addresses interface issues. It reduces the contact area between the active material and the electrolyte by monocrystallizing particles, while increasing particle structure uniformity to improve compaction density. However, single-crystallization typically lengthens the lithium-ion diffusion path, and the uniform reduction in specific surface area leads to a decrease in capacity, limiting the high-capacity performance of carbonate-based materials and diminishing their advantage over hydroxide-based materials. Surface coating modification typically introduces coating agents or structural modifiers into the surface and subsurface regions of the cathode material, or induces the formation of new surface structures with stable structures and low gas production characteristics. This reduces direct contact between the lithium-rich manganese phase and the electrolyte under high voltage. However, gas production in carbonate-based materials is not limited to the surface area in contact with the electrolyte; more importantly, gas production occurs during the anionic redox reaction of the internal Li₂MnO₃ phase under high voltage. This is the main cause of gas production in the material. Therefore, surface modification alone cannot fundamentally reduce gas production and improve cycle life. As for bulk doping, it can better anchor the irreversible oxidation reaction of oxygen compared to the two modification methods mentioned above. However, it has the problem of insufficient capacity compensation in the first cycle due to the reduction of oxygen activity, resulting in a decrease in the first efficiency and discharge specific capacity. Therefore, it is necessary to make up for the loss of the first efficiency caused by anchoring oxygen by treating some surface oxygen vacancies. However, surface oxygen vacancy treatment will lead to poor interface stability, making the electrolyte more likely to attack the positive electrode and accelerating the capacity decay in the later stage of the cycle, thus deteriorating the cycle life.

[0005] This application is made to address the problem that existing technologies, when improving the gas generation issue of carbonate-based lithium-rich manganese cathode materials, can have a significant negative impact on capacity and cycle life. Summary of the Invention

[0006] Based on the background technology, this invention provides a ring-structured lithium-rich manganese cathode material, its preparation method, and its application, aiming to solve the gas generation problem of carbonate-based lithium-rich manganese cathode materials without significantly adversely affecting capacity and cycle life.

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention are as follows.

[0008] Firstly, this invention proposes a method for preparing a lithium-rich manganese cathode material with a growth ring structure, comprising the following steps: S1. Add the aluminum-containing solution to the mixed salt solution of Ni, Co, and Mn and stir until homogeneous. Then add precipitant I and complexing agent, stir, and maintain the pH of the system at 7-9 for 2-8 hours. The molar ratio of Ni, Co, and Mn in the mixed salt solution is (25-35):(0-9):(56-75), the molar amount of Al in the aluminum-containing solution is 3%-9% of the total molar amount of Ni, Co, and Mn, and the solid content of the slurry in the system is 8%-10%. S2. Stop stirring and remove the supernatant to make the solid content of the slurry in the system 15%-30%. Add precipitant II to adjust the pH of the system to 11-13 and age for 1-3 hours. Then add boron-containing solution, precipitant II and complexing agent to maintain the pH of the system at 11-13 and react for 2-4 hours. After the reaction is completed, add precipitant III dropwise to adjust the pH of the system to 7-9. Then introduce a mixed salt solution of Ni, Co and Mn, precipitant I and complexing agent again to maintain the pH of the system at 7-9 and react for 5-8 hours. The molar amount of B in the boron-containing solution is 0.5%-2% of the total molar amount of Ni, Co and Mn. In this step, under the premise of controlling the solid content, dynamic precipitation and static aging are carried out alternately to construct a multilayer carbonate-based lithium-rich manganese precursor matrix structure (NiCoMnCO3) and generate loose B and Al hydroxides (B(OH)3+Al(OH)3) between the matrix structures of each layer. S3. Repeat step S2 until the reaction is complete. Collect the product, wash and dry it to obtain the carbonate precursor. The structural diagram of the carbonate precursor is shown in the figure below. Figure 3 As shown in Figure A; S4. The obtained carbonate precursor is mixed with a lithium source to obtain a first mixed powder. The first mixed powder is then subjected to multi-stage sintering. During this process, B reacts with the lithium source at high temperature to generate lithium tetraborate L, which has flexibility and high ionic conductivity. i2 B4O7 and Al enter the transition metal layer and play a stabilizing role in the structure, ultimately resulting in Li. m (Ni a Co b Mn c Al x B y O2-rich lithium manganese cathode material B, wherein: 1≤m≤1.2, a+b+c=1, a≥0.2 or c≤0.6, 0≤b≤0.08, 0.03≤x≤0.09, 0.005≤y≤0.02; S5. The lithium-rich manganese cathode material B is mixed with the coating material A to obtain a second mixed powder. The content of the coating material in the second mixed powder is 200-5000 ppm. The second mixed powder is then subjected to a one-stage sintering process to obtain the final product A@B. A schematic diagram of its cross-sectional structure is shown below. Figure 3 As shown in Figure B; As described above, precipitant I is an aqueous solution of an alkali metal carbonate, precipitant II is an aqueous solution of an alkali metal hydroxide, and precipitant III is an aqueous solution of at least one of sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate. The addition of precipitant I, precipitant II, and precipitant III is not continuous. The specific amount and rhythm of addition depend on the pH requirements of the system and should be determined to meet the required pH value of the system. The system temperature in steps S1 and S2 is 50-80℃.

[0009] In lithium-rich manganese cathode material systems, boron tends to bind with oxygen atoms in the lithium-rich phase, forming short-length, higher-energy BO bonds. This effectively reduces excessive oxidation of oxygen atoms, improving gas production and structural stability. However, simply introducing boron is detrimental to Li... + The transport kinetics of boron (BO) are such that excessive boron can reduce anion redox activity, potentially affecting capacity utilization. To achieve the positive effects of boron on gas production and structural stability while avoiding the aforementioned negative impacts, this invention introduces boron and aluminum in the form of precipitates after the stage reaction by controlling the solid content of the slurry during the co-precipitation process. Loose hydroxides containing these two elements are generated between the stage reactions. These hydroxides are then mixed with a lithium source for a high-temperature solid-state reaction. Based on the different shrinkage rates of the carbonate-based lithium-rich manganese precursor matrix and the loose hydroxides generated between the matrix layers, a ring-like profile structure is formed. Simultaneously, based on the diffusion of the high-temperature solid phase, an interface coating layer composed of Li-B-Al-O is formed at the interface junctions between the rings. The synergistic effect of the ring-like profile structure and the Li-B-Al-O interface coating layer not only reduces gas production and stabilizes the structure but also compensates for the insufficient ionic conductivity between the two phases at the interface, thereby improving cycle life without sacrificing capacity and rate capability.

[0010] The method for preparing lithium-rich manganese cathode material with a ring-like structure proposed in this invention, compared with traditional surface coating, introduces more boron (B) elements into the bulk phase to stabilize oxygen atoms, improve the redox reversibility of anions, increase structural strength and cycle stability, and further reduce gas production. Compared with traditional bulk doping, the construction of a three-layer ring-like structure increases the porosity of the material, increases the contact area between the electrolyte and the active material, and can effectively maintain the electrochemical performance of the material. At the same time, the coating structure at the solid-liquid interface can also suppress excessive interfacial side reactions and improve cycle life. Compared with traditional single-crystal modification, maintaining the secondary spherical structure can ensure lithium-ion transport kinetics, which has a greater advantage in electrical performance than single-crystal particles. Therefore, the obtained product not only has low gas production, but also exhibits excellent performance in terms of capacity and cycle life.

[0011] Furthermore, in steps S1 and S2, the complexing agent is selected from at least one of ammonia, citric acid, stearic acid, tartaric acid, and glycine; the molar amount of the complexing agent is generally 0.1%-20% of the mixed salt solution of Ni, Co, and Mn.

[0012] Furthermore, considering the doping effects of the modifying elements Al and B, in step S1, the aluminum-containing solution is an aqueous solution of sodium aluminate and / or aluminum sulfate with a concentration of 0.5-3 mol / L. Specifically, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc. In step S2, the boron-containing solution is boric acid and / or metaboric acid with a concentration of 0.1-1 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc.

[0013] Furthermore, in step S4, the multi-stage sintering is a three-stage sintering, with the first stage sintering temperature at 250-650℃ and the time at 3-8h, the second stage sintering temperature at 500-700℃ and the time at 0-10h, and the third stage sintering temperature at 700-950℃ and the time at 2-15h. Preferably, the sintering temperature of the first stage is 300-500℃, the sintering temperature of the second stage is 500-650℃, and the sintering temperature of the third stage is 750-900℃. Preferably, the lithium source is lithium carbonate and / or lithium hydroxide.

[0014] Furthermore, in step S5, the coating material A is selected from at least one of lithium aluminum phosphate, lithium phosphate, aluminum phosphate, lithium titanium magnesium aluminum phosphate, aluminum fluoride, and lithium fluoride. The temperature of the one-stage sintering is 200-650℃, the time is 3-8h, and the atmosphere is dry air. Preferably, the temperature of the one-stage sintering is 250-550℃.

[0015] Secondly, this invention proposes a lithium-rich manganese cathode material with a ring-like structure in cross-section. Compared to the secondary spherical structure of conventional lithium carbonate-based lithium-rich manganese cathode materials, this invention divides the secondary spherical structure into three layers and introduces modified elements Al and B at the interlayer interfaces of each layer. After high-temperature lithium sintering, a Li-B-Al-O synergistic composite structure is formed at the interface. In terms of the ring structure dimension, this invention achieves Li-B-Al-O coating at the interlayer interfaces; in terms of the overall secondary spherical particles, it achieves Al-B composite doping. This synergistic composite structure possesses both the soft oxide properties and ionic conductivity of Li₂B₄O₇ and the role of Al atoms in maintaining the material's capacity and rate performance. Working synergistically with the ring structure, it solves the gas generation problem of carbonate-based lithium-rich manganese cathode materials without significantly adversely affecting capacity and cycle life.

[0016] Furthermore, its specific surface area is <3.0 m². 2 / g, compacted density ≥2.7g / cm³ 3 .

[0017] Testing revealed that the specific surface area of ​​the ring-structured lithium-rich manganese cathode material obtained by the above preparation method is <3.0 m². 2 / g, compacted density ≥2.7g / cm³ 3 It is evident that the above preparation method also helps to improve the adhesion between primary particles and increase the strength of secondary spheres, thereby increasing the compaction density of the carbonate-based lithium-rich manganese cathode. Therefore, the resulting pouch cell does not exhibit significant capacity decay in an ester electrolyte system.

[0018] Thirdly, this invention proposes a cathode sheet containing the above-mentioned annual ring structure of lithium-rich manganese cathode material.

[0019] Fourth, the present invention proposes a lithium-ion battery containing the above-mentioned positive electrode sheet.

[0020] Furthermore, the aforementioned lithium-ion battery also includes a negative electrode, a separator, and an electrolyte. When a carbonate-based electrolyte is used, the resulting lithium-ion battery produces ≤10mL of gas after 500 cycles at 1C under a high voltage of 4.65V, and its cycle life at room temperature of 4.65V is nearly doubled. It can be seen that the ring-structured lithium-rich manganese cathode material prepared by this invention is a high-performance, low-gas-production, high-voltage, long-cycle carbonate-based lithium-rich manganese cathode material. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a cross-sectional SEM image of the product obtained in Example 1.

[0023] Figure 2 The figures show the cycle life curves of the full cells assembled from the products obtained in Examples 2, 4, and 4 of this invention, where Examples 2-1 and 2-2 represent two cells assembled from the products obtained in Example 2, and so on.

[0024] Figure 3 The diagram shows the structure of the carbonate precursor (A) and the cross-sectional view shows the final product (B) of this invention. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] All chemical raw materials used in the following examples and comparative examples are commercially available, and all apparatus and operations involved are conventional in the art.

[0027] Example 1

[0028] S1. Prepare a mixed salt solution of Ni, Co, and Mn by mixing 0.25 mol NiSO4•6H2O, 0.09 mol CoSO4•7H2O, and 0.66 mol MnSO4•H2O. Add 50 mL of 1 mol / L NaAlO2 aqueous solution and stir until homogeneous. Then, add Na2CO3 solution (concentration of 2.5 mol / L) and ammonia water dropwise while stirring continuously. The solid content of the system is 9.2%, the reaction time is 4 h, and the pH of the system is maintained at 7.5 by adding Na2CO3 solution dropwise during the reaction. The temperature of the system is 75 °C throughout the process. S2. Stop stirring, remove the supernatant, add NaOH solution (4 mol / L) to adjust the pH of the system to 11.5, and after aging for 2 hours, add 20 mL of 0.3 mol / L boron oxide aqueous solution, NaOH solution (4 mol / L) and ammonia. After reacting for 3 hours, add NH4HCO3 solution (2.5 mol / L) dropwise to adjust the pH of the system from 11.5 to 7.5. Then introduce a mixed salt solution of Ni, Co, and Mn, Na2CO3 solution (2.5 mol / L) and ammonia, and continue to react at pH 7.5 for 6 hours. The temperature of the system is controlled at 75℃ throughout the process. S3. Repeat S2 until the reaction is complete, then centrifuge, wash, and dry to prepare the carbonate precursor. S4. Mix 100g of carbonate precursor with 44.2g of lithium carbonate and sinter. The sintering process is as follows: first sinter at 300℃ for 3h, then sinter at 600℃ for 6h, and finally sinter at 850℃ for 6h to obtain lithium-rich manganese cathode material B. S5. Mix 50g of lithium-rich manganese cathode material B with 0.1g of lithium aluminum phosphate and sinter at 300℃ for 5h to obtain the lithium-rich manganese cathode material, whose microstructure is as follows. Figure 1 As shown: The product cross-section exhibits an annual ring structure.

[0029] Example 2

[0030] Compared with Example 1, the volume of the boric acid aqueous solution in step S2 was adjusted from 20 ml to 40 ml, while the rest remained the same as in Example 1.

[0031] Example 3

[0032] Compared with Example 1, the volume of the NaAlO2 aqueous solution in step S1 was adjusted from 50 mL to 30 mL, while the rest remained the same as in Example 1.

[0033] Example 4

[0034] Compared with Example 1, the volume of the NaAlO2 aqueous solution in step S1 was adjusted from 50 mL to 90 mL, while the rest remained the same as in Example 1.

[0035] Example 5

[0036] Compared with Example 1, the reaction time in step S1 was adjusted from 4 hours to 8 hours, while the rest remained the same as in Example 1.

[0037] Example 6

[0038] Compared with Example 1, the NH4HCO3 in step S2 was adjusted to an equal amount of NaHCO3, while the rest remained the same as in Example 1.

[0039] Example 7

[0040] Compared with Example 1, the NH4HCO3 in step S2 was adjusted to an equal amount of (NH4)2CO3, while the rest remained the same as in Example 1.

[0041] Example 8

[0042] Compared with Example 1, the concentration and volume of the NaAlO2 aqueous solution in step S1 were adjusted from "1 mol / L, 50 ml" to "3 mol / L, 17 ml", while the rest remained the same as in Example 1.

[0043] Example 9

[0044] Compared with Example 1, the pH value in step S1 was adjusted from 7.5 to 9, while the rest remained the same as in Example 1.

[0045] Example 10

[0046] Compared with Example 1, the technical parameters of aging in step S2 have been adjusted. The aging time of pH 11.5 for 2 hours has been changed to aging time of pH 13 for 1 hour. All other parameters remain the same as in Example 1.

[0047] Example 11

[0048] Compared with Example 1, in step S1, CoSO4•7H2O was removed and the molar amount of MnSO4•H2O was adjusted from 0.66 mol to 0.75 mol, while the rest remained the same as in Example 1.

[0049] Example 12

[0050] Compared with Example 1, in step S1, CoSO4•7H2O was removed and the molar amount of MnSO4•H2O was adjusted from 0.25 mol to 0.35 mol and the molar amount of MnSO4•H2O was adjusted from 0.66 mol to 0.65 mol. All other steps remained the same as in Example 1.

[0051] Example 13

[0052] Compared with Example 1, the temperature of the one-stage sintering in step S5 was adjusted from 300℃ to 550℃, while the rest remained the same as in Example 1.

[0053] Example 14

[0054] Compared with Example 1, the three-stage sintering in step S4 is adjusted as follows: first sintering at 500°C for 3 hours, then sintering at 600°C for 6 hours, and finally sintering at 850°C for 6 hours, while the rest remains the same as in Example 1.

[0055] Example 15

[0056] Compared with Example 1, the three-stage sintering in step S4 is adjusted as follows: first sintering at 300°C for 3 hours, then sintering at 600°C for 6 hours, and finally sintering at 850°C for 15 hours, while the rest remains the same as in Example 1.

[0057] Example 16

[0058] Compared with Example 1, the three-stage sintering in step S4 is adjusted to: first sintering at 500°C for 8 hours, and then sintering at 850°C for 6 hours, while the rest remains the same as in Example 1.

[0059] Example 17

[0060] Compared with Example 1, the lithium aluminum phosphate in step S5 is adjusted to an equal mass of lithium phosphate, while the rest remains the same as in Example 1.

[0061] Example 18

[0062] Compared with Example 1, the lithium aluminum phosphate in step S5 is adjusted to an equal mass of aluminum phosphate, while the rest remains the same as in Example 1.

[0063] Example 19

[0064] Compared with Example 1, the lithium aluminum phosphate in step S5 is adjusted to an equal mass of lithium titanium magnesium aluminum phosphate, while the rest remains the same as in Example 1.

[0065] Example 20

[0066] Compared with Example 1, the lithium aluminum phosphate in step S5 was adjusted to an equal mass of aluminum fluoride, while the rest remained the same as in Example 1.

[0067] Example 21

[0068] Compared with Example 1, the lithium aluminum phosphate in step S5 was adjusted to an equal mass of lithium fluoride, while the rest remained the same as in Example 1.

[0069] Example 22

[0070] Compared with Example 1, the mass of lithium aluminum phosphate in step S5 was adjusted from 0.1g to 0.25g, while the rest remained the same as in Example 1.

[0071] Example 23

[0072] Compared with Example 1, the temperature of the one-stage sintering in step S5 was adjusted from 300℃ to 250℃, while the rest remained the same as in Example 1.

[0073] Example 24

[0074] Compared with Example 1, the pH value in step S1 was adjusted from 7.5 to 7, and the reaction time was adjusted from 4h to 2h, while the rest remained the same as in Example 1.

[0075] Example 25

[0076] Compared with Example 1, the technical parameters of aging in step S2 have been adjusted. The aging time of pH 11.5 for 2 hours has been changed to aging time of pH 11 for 3 hours. All other parameters remain the same as in Example 1.

[0077] Comparative Example 1 Compared with Example 1, in step S1, no NaAlO2 aqueous solution was added and the reaction time was adjusted from 4h to 6h, while the rest remained the same as in Example 1.

[0078] Comparative Example 2 Compared with Example 1, the volume of the boric acid aqueous solution in step S2 was adjusted from 20 ml to 60 ml, while the rest remained the same as in Example 1.

[0079] Comparative Example 3 In step S1, the volume of the NaAlO2 aqueous solution was adjusted from 50 mL to 100 mL, while the rest remained the same as in Example 1.

[0080] Comparative Example 4 S1. Prepare a mixed salt solution by mixing 0.25 mol NiSO4•6H2O, 0.09 mol CoSO4•7H2O and 0.66 mol MnSO4•H2O, and add 50 mL of 1 mol / L NaAlO2 aqueous solution and 20 mL of 0.3 mol / L boron oxide aqueous solution. After mixing evenly, add Na2CO3 and ammonia water dropwise to maintain the reaction pH at 7.5 for 30 h. S2. Add NaOH to adjust the pH to 11.5 and let it age for 4 hours; S3. After centrifugation, washing and drying, carbonate precursor A is obtained; S4. Mix 100g of carbonate precursor A with 44.2g of lithium carbonate and then perform three-stage sintering: first sinter at 300℃ for 3h, then sinter at 600℃ for 6h, and finally sinter at 850℃ for 6h to obtain lithium-rich manganese cathode material B. S5. Mix 50g of lithium-rich manganese cathode material B with 0.1g of lithium aluminum phosphate and sinter at 300℃ for 5h.

[0081] Comparative Example 5 Compared with Example 1, the three-stage sintering in step S4 is adjusted as follows: first sintering at 300°C for 3 hours, then sintering at 450°C for 6 hours, and finally sintering at 980°C for 6 hours, while the rest remains the same as in Example 1.

[0082] Comparative Example 6 Compared with Example 1, the temperature of the one-stage sintering in step S5 was adjusted from 300℃ to 750℃, while the rest remained the same as in Example 1.

[0083] The products obtained from Examples 1-25 and Comparative Examples 1-6 were respectively fabricated into positive electrode sheets and assembled into liquid lithium-ion coin cells as working electrodes for charge-discharge testing. The voltage range was 2.0-4.8V, and the initial discharge specific capacity and initial coulombic efficiency were tested at 0.1C / 0.1C. The products obtained from Examples 1-25 and Comparative Examples 1-6 were respectively fabricated into positive electrode sheets and assembled into liquid lithium-ion full cells with graphite negative electrodes for cycle performance and gas production testing, with a voltage range of 2.0-4.65V. The final test results are shown in Table 1.

[0084] It should be noted that, for ease of listing, "Example 1" will be abbreviated as "S1" in Table 1, "Comparative Example 1" will be abbreviated as "D1", and so on.

[0085]

[0086] As shown in Table 1, Figures 1-3 As shown in the following: A comparison of the test results of Example 1 and Comparative Example 4 shows that, under the premise of the same chemical composition of lithium-rich manganese cathode materials, the 0.1C first-cycle efficiency of the ring-structured lithium-rich manganese cathode material of the present invention is 84.1%, the 80% cycle retention rate is 675 cycles, and the gas production after 500 cycles is 4.8 ml. In contrast, the 0.1C first-cycle efficiency of the non-multilayer structure material with co-precipitation of various metal elements with B and Al is 88.1%, the 80% cycle retention rate is 75 cycles, and the gas production after 500 cycles is 21.6 ml. The gas production of the product obtained in Example 1 is significantly reduced, and the cycle life is significantly extended. A comparison of specific surface area and compaction density shows that the specific surface area of ​​the product obtained in Example 1 is significantly reduced, and the compaction density is somewhat increased. The significant reduction in specific surface area effectively reduces interfacial side reactions, thus significantly reducing the gas production. The structural indicators correspond to the electrochemical performance indicators. Compared with Comparative Example 4, the compaction density of the product obtained in Example 1 was improved. Combined with the 0.1C discharge specific capacity, it can be seen that the product obtained in Example 1 did not sacrifice capacity while optimizing cycle performance and gas generation behavior.

[0087] Furthermore, the test results from Examples 1-25 show that, under the preparation conditions specified in this invention, the obtained ring-structured lithium-rich manganese cathode materials all exhibit extremely low gas production, with a gas production of ≤10mL after 500 cycles at 4.65V and 1C. Moreover, the cycle life is significantly extended, with over 500 cycles maintaining 80% capacity at 4.65V and 1C, and some examples even reaching 700 cycles or more. For example, the cycle life curves of the full cells assembled from the products of Examples 2 and 4 are compared with those of the full cells assembled from the products of Comparative Example 4, as shown in the following figures. Figure 2 As shown: Compared with Comparative Example 4, Examples 2 and 4 both have better capacity retention and coulombic efficiency; Example 4 is particularly good, with a capacity retention of up to 95% after 500 cycles, which shows that it still performs well in terms of capacity and cycle life while controlling side reactions and reducing gas production.

[0088] A comparison of the test results of Examples 1, 2, and Comparative Example 2 shows that doping with the specified molar amount of B in this invention can significantly reduce gas production and extend cycle life. The specific surface area of ​​the resulting product is significantly reduced, and the compressibility density is improved. A comparison of the test results of Examples 1, 3, 4, and 8 with Comparative Examples 1 and 3 shows that doping with the modified element Al can effectively stabilize the structure. Its synergistic effect with the specified molar amount of B can further optimize performance. However, the amount of Al doping should not be too high, as excessive doping will hinder lithium-ion transport and cause local structural collapse, which is detrimental to improving cycle performance.

[0089] It should be noted that in controlling the precipitation process, the selection of precipitant III is limited to aqueous solutions of at least one of sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate as defined in this invention (as shown in Examples 1, 6, and 7). Precipitant III itself is a precipitant with pH adjustment function, which, after its addition, reduces the pH value from 11-13 to 7-9 without changing the carbonate system.

[0090] Furthermore, a comparison of the test results from Examples 1, 13, 23, and Comparative Example 6 shows that the preferred sintering temperature for the coating reaction between the lithium-rich manganese cathode material B and the coating material A in step S5 is 250-550°C. Excessively high temperatures (such as 750°C as shown in Comparative Example 6) may cause the coating material to decompose at high temperatures or react with the cathode material to form a harmful interface layer, leading to increased gas production and severely degraded cycle performance. A comparison of the test results from Examples 1, 14, 15, 16, and Comparative Example 5 shows that under the multi-stage sintering conditions defined in this invention, it is beneficial for the dopant element B to generate L... i2 B4O7 allows the dopant element Al to enter the transition metal layer. If this exceeds a certain limit, it may lead to L... i2 The amorphous morphology of B4O7, making its synthesis impossible, and the difficulty of Al entering the transition metal layer, hinder the maximization of their synergistic effect. Therefore, although the gas generation behavior is improved, the cycle performance is unsatisfactory. It is evident that, based on specific doping ranges of the modifying elements B and Al, the sintering conditions of the carbonate precursor also have a significant impact on obtaining lithium-rich manganese-based cathode materials with a ring-like structure that exhibits low gas generation and long cycle performance.

[0091] In summary, this invention utilizes three precipitants in a carbonate-based lithium-rich manganese system to regulate the precipitation process of the carbonate precursor structure growth while controlling the solid content of the system, forming a multilayered, alternating dense and porous secondary sphere structure. Furthermore, modifying elements Al and B are introduced into each layer for interfacial coating and doping. Subsequent lithium-ion sintering results in a ring-structured lithium-rich manganese cathode material due to the varying contraction directions of the internal alternating structures. The interlayer gaps and in-layer pores of this ring-structured lithium-rich manganese cathode material improve electrolyte wetting without increasing the overall contact area between the active material and the electrolyte. Therefore, while reducing surface porosity, minimizing excessive interfacial side reactions, and improving gas production, it also ensures capacity utilization and enhances high-voltage cycle life.

[0092] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

Claims

1. A method for preparing a lithium-rich manganese cathode material with a growth ring structure, characterized in that: The following steps are included: S1. Add the aluminum-containing solution to the mixed salt solution of Ni, Co, and Mn and stir until homogeneous. Then add precipitant I and complexing agent, stir, and maintain the pH of the system at 7-9 for 2-8 hours. The molar ratio of Ni, Co, and Mn in the mixed salt solution is (25-35):(0-9):(56-75), the molar amount of Al in the aluminum-containing solution is 3%-9% of the total molar amount of Ni, Co, and Mn, and the solid content of the slurry in the system is 8%-10%. S2. Stop stirring and remove the supernatant to make the solid content of the slurry in the system 15%-30%. Add precipitant II to adjust the pH of the system to 11-13 and age for 1-3 hours. Then add boron-containing solution, precipitant II and complexing agent to maintain the pH of the system at 11-13 and react for 2-4 hours. After the reaction is completed, add precipitant III dropwise to adjust the pH of the system to 7-9. Then introduce a mixed salt solution of Ni, Co and Mn, precipitant I and complexing agent again to maintain the pH of the system at 7-9 and react for 5-8 hours. The molar amount of B in the boron-containing solution is 0.5%-2% of the total molar amount of Ni, Co and Mn. S3. Repeat step S2 until the reaction is complete. Collect the product, wash and dry it to obtain the carbonate precursor. S4. The obtained carbonate precursor is mixed with a lithium source to obtain a first mixed powder. The first mixed powder is then subjected to multi-stage sintering to obtain a product with the chemical formula Li. m (Ni a Co b Mn c Al x B y O2-rich lithium manganese cathode material B, wherein: 1≤m≤1.2, a+b+c=1, a≥0.2 or c≤0.6, 0≤b≤0.08, 0.03≤x≤0.09, 0.005≤y≤0.02; S5. Mix lithium-rich manganese cathode material B with coating material A to obtain a second mixed powder. The content of coating material in the second mixed powder is 200-5000ppm. Perform one-stage sintering on the second mixed powder to obtain the final product A@B. The above describes the following: Precipitator I is an aqueous solution of an alkali metal carbonate, Precipitator II is an aqueous solution of an alkali metal hydroxide, Precipitator III is an aqueous solution of at least one of sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate, and the system temperature in steps S1 and S2 is 50-80℃.

2. The method for preparing the lithium-rich manganese cathode material with an annual ring structure according to claim 1, characterized in that: In both steps S1 and S2, the complexing agent is selected from at least one of ammonia, citric acid, stearic acid, tartaric acid, and glycine.

3. The method for preparing the lithium-rich manganese cathode material with an annual ring structure according to claim 1, characterized in that: In step S1, the aluminum-containing solution is an aqueous solution of sodium aluminate and / or aluminum sulfate with a concentration of 0.5-3 mol / L; in step S2, the boron-containing solution is boric acid and / or metaboric acid with a concentration of 0.1-1 mol / L.

4. The method for preparing the lithium-rich manganese cathode material with an annual ring structure according to claim 1, characterized in that: In step S4, the multi-stage sintering is a three-stage sintering, with the first stage sintering temperature at 250-650℃ and time at 3-8h, the second stage sintering temperature at 500-700℃ and time at 0-10h, and the third stage sintering temperature at 700-950℃ and time at 2-15h. Preferably, the sintering temperature of the first stage is 300-500℃, the sintering temperature of the second stage is 500-650℃, and the sintering temperature of the third stage is 750-900℃. Preferably, the lithium source is lithium carbonate and / or lithium hydroxide.

5. The method for preparing the lithium-rich manganese cathode material with an annual ring structure according to claim 1, characterized in that: In step S5, the coating material A is selected from at least one of lithium aluminum phosphate, lithium phosphate, aluminum phosphate, lithium titanium magnesium aluminum phosphate, aluminum fluoride, and lithium fluoride. The temperature of the one-stage sintering is 200-650℃, the time is 3-8h, and the atmosphere is dry air. Preferably, the temperature of the one-stage sintering is 250-550℃.

6. A lithium-rich manganese cathode material with an annual ring structure prepared according to any one of claims 1-5.

7. The lithium-rich manganese cathode material with an annual ring structure according to claim 6, characterized in that: Its specific surface area is <3.0 m². 2 / g, compacted density ≥2.7g / cm³ 3 .

8. A positive electrode plate, characterized in that: The lithium-rich manganese cathode material containing the annual ring structure as described in claim 6 or 7, or the lithium-rich manganese cathode material with an annual ring structure prepared according to the preparation method described in any one of claims 1-5.

9. A lithium-ion battery, characterized in that: It contains the positive electrode as described in claim 8.

10. The lithium-ion battery according to claim 9, characterized in that: It also includes a negative electrode, a separator, and an electrolyte, wherein the electrolyte is a carbonate system electrolyte; Preferably, the lithium-ion battery produces ≤10mL of gas after 500 cycles at 4.65V and 1C.

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