Preparation process of high-nickel lithium-rich manganese-based multi-doped positive electrode material

Abstract

The invention relates to the technical field of electrode materials, in particular to a preparation process of a high-nickel lithium-rich manganese-based multi-doped positive electrode material. The process comprises the following steps: firstly, realizing bulk phase Nb / F co-doping through complexing and segmented sintering to obtain main body powder with a stable structure; then carrying out surface phosphorus doping treatment by utilizing a lithium dihydrogen phosphate solution to form an interface template; then introducing an initiating group through silane esterification, and sequentially grafting a zwitterionic chain segment and a fluorine-containing chain segment by adopting atom transfer radical polymerization to construct a double-grafting interface layer; and finally, carrying out non-contact mild fluorination treatment with ammonium difluoride to finish surface modification. According to the process, through the synergistic effect of bulk phase multi-element doping and the interface multifunctional grafting layer, the structural stability and interface compatibility of the material are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a preparation process for a high-nickel, lithium-rich manganese-based multi-doped cathode material. Background Technology

[0002] High-nickel, lithium-rich manganese-based cathode materials (Li1+xM1-xO2, M=Ni, Co, Mn, etc.) are considered ideal candidates for next-generation high-energy-density lithium-ion batteries due to their high specific capacity (>250 mAh / g) and low cost. However, their practical application is limited by a series of problems caused by their unique electrochemical behavior at high voltages. When the material is first charged to above 4.5V, a redox reaction of lattice oxygen needs to be activated to obtain high capacity. Although this process contributes additional capacity, it is accompanied by the irreversible precipitation of some lattice oxygen, forming oxygen vacancies, which lead to the migration of transition metal ions (especially Ni ions) to the lithium layer, causing an irreversible transformation of the layered structure to the spinel or rock salt phase. This bulk structure degradation is one of the fundamental reasons for the low coulombic efficiency (usually below 90%) in the first cycle and the continuous decrease in discharge voltage during subsequent cycles.

[0003] Besides bulk structural instability, interfacial side reactions between the material and electrolyte under high voltage are also prominent. Newly formed highly reactive lattice oxygen species readily undergo oxidative decomposition with organic electrolyte components, forming a thick and unstable cathode electrolyte interphase (CEI) film on the particle surface. This interfacial film not only has high impedance, hindering lithium-ion transport and leading to increased polarization and capacity decay, but its continuous breakdown and reconstruction process also continuously consumes active lithium and electrolyte, accelerating performance degradation. Especially under high-temperature conditions (such as above 45°C), the rate of interfacial side reactions accelerates significantly, further amplifying capacity decay and voltage instability.

[0004] To address these issues, existing technologies have employed various strategies. Bulk doping is a common method for stabilizing crystal structures, such as using cations (e.g., Mg). 2+ Al 3+ Ti 4+ (etc.) or anions (such as F) - PO4 3-Doping with bulk materials (such as Al2O3 and ZrO2) aims to suppress transition metal migration and oxygen loss. However, single bulk doping often fails to achieve both high capacity and structural stability, and its improvement on interface problems is limited. Surface coating is another common method, reducing direct contact between the material and the electrolyte by constructing physical barriers (such as inert oxide layers like Al2O3 and ZrO2). However, traditional coatings may hinder lithium-ion conduction, leading to a decrease in rate performance, and the integrity of the coating is difficult to maintain under high-voltage long-term cycling. In addition, some studies have attempted to combine doping and coating, but if the two fail to form an effective synergy—for example, if the bulk dopant elements fail to establish a stable chemical bond with the surface modification layer, or if the modification layer itself fails to adapt to volume changes under high voltage—the improvement effect remains unsatisfactory, especially in suppressing voltage decay and improving high-temperature cycle life. Therefore, developing a synergistic stabilization strategy that can systematically address the inherent defects of high-nickel lithium-rich manganese-based materials from the bulk phase to the interface remains a critical technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a preparation process for high-nickel lithium-rich manganese-based multi-doped cathode materials, in order to solve the problem that during the high-voltage activation process of high-nickel lithium-rich manganese-based cathode materials, the irreversible precipitation of lattice oxygen causes bulk structure distortion and intensified interfacial side reactions, resulting in low first-cycle efficiency, continuous decay of cycle voltage and high-temperature performance degradation, which restricts their long-life application.

[0006] To achieve the above objectives, this invention provides a process for preparing a high-nickel, lithium-rich manganese-based multi-doped cathode material, comprising the following steps: (1) Using citric acid as a complexing agent, lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate, niobium pentoxide, and lithium fluoride were dissolved in a mixed solvent of deionized water / anhydrous ethanol, the pH was adjusted to 6.7-7.1, and the mixture was evaporated into a gel in a water bath at about 80°C. Under oxygen-permeable conditions, the mixture was heated in two stages and sintered at 540-560°C and 830-870°C respectively to obtain the main powder. (2) The main powder is dispersed in a 0.8wt%-1.2wt% lithium dihydrogen phosphate ethanol solution, and after ultrasonic and vacuum impregnation, it is rotary evaporated, vacuum dried, and kept at 400-440°C for 2 hours under oxygen conditions to obtain phosphorus-doped main powder; (3) The phosphorus-doped host powder is reacted with 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropionate in an anhydrous toluene / acetic acid aqueous solution to introduce surface initiation groups and obtain initiation group-grafted host powder; (4) 2-methacryloyloxyethyl phosphate choline and fluorine-containing monomer 1H,1H,2H,2H-perfluorodecyl acrylate are sequentially grafted onto the initiator group grafted host powder by atom transfer controlled free radical polymerization, and 2-methacryloyloxyethyl phosphate choline is added between and after the two to construct a double grafted surface layer of amphoteric segment / fluorine-containing segment, thus obtaining a double grafted host powder; (5) The double-grafted main body powder and ammonium difluoride are placed far apart in the same sealed reactor, with a distance of 20-30 mm between them. They are subjected to non-contact mild fluorination treatment at 190-210°C for 2 hours under nitrogen atmosphere and 0.2 MPa. After cooling, a high-nickel lithium-rich manganese-based multi-doped cathode material is obtained.

[0007] Preferably, in step (1), the mass ratio of lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate, niobium pentoxide, lithium fluoride and citric acid is 11.3-12.3:12.5-13.7:5.7-6.3:0.9-1.1:0.2-0.34:0.03-0.08:35.

[0008] Preferably, the oxygen flow rate in step (1) is 80-120 mL / min.

[0009] Preferably, the heating rate in step (1) is 2-4°C / min, and the holding time for the first and second stages is 4-6h and 10-14h, respectively.

[0010] Preferably, based on 10g of main powder, the amount of lithium dihydrogen phosphate ethanol solution used in step (2) is 40-60mL.

[0011] Preferably, in step (2), the ultrasonic time is 20-40 min, the decompression degree is -0.07 to -0.09 MPa, and the decompression immersion time is 15-30 min.

[0012] Preferably, in step (3), the mass ratio of phosphorus-doped host powder to 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropionate is 10:0.8-1.2.

[0013] Preferably, based on 10g of initiator group grafting body powder, the first grafting in step (4) is carried out in a medium with an ethanol / water volume ratio of 1:1, with the addition of 1.5-2.5g of 2-methacryloyloxyethyl phosphocholine, 90-140mg of copper bromide, 40-60mg of sodium ascorbate and 80-120mg of tris[2-(dimethylamino)ethyl]amine, and stirred for 25-35min after bubbling under nitrogen at room temperature; the second grafting is carried out in ethanol, with the addition of 0.3-0.6g of the fluorinated monomer, 90-140mg of copper bromide, 40-60mg of sodium ascorbate and 80-120mg of tris[2-(dimethylamino)ethyl]amine, and stirred for 15min, followed by the addition of 1.5-2.5g of 2-methacryloyloxyethyl phosphocholine and stirring for 8-12min.

[0014] Preferably, in step (5), the mass ratio of the double-grafted main body powder to ammonium difluoride is 10:0.6-1.4.

[0015] The beneficial effects of this invention are: This invention achieves simultaneous optimization of the bulk structure and interfacial properties of high-nickel lithium-rich manganese-based cathode materials through a step-by-step, zone-based synergistic preparation strategy, thereby comprehensively improving their electrochemical performance.

[0016] Regarding bulk stability, the co-doping of specific elements effectively stabilized the crystal framework of the material during high-temperature crystallization. After the dopant elements enter the lattice, they suppress the migration of transition metal ions to the lithium layer and the irreversible loss of lattice oxygen during cycling, slowing the transition rate from layered structure to defect phase. This allows the material to maintain higher structural integrity during high-voltage charge-discharge processes, laying the foundation for achieving high reversible capacity and stable lithium-ion insertion / extraction channels.

[0017] In terms of interface regulation, a uniform phosphate template layer was first constructed, providing an ideal reaction platform for subsequent grafting of organic molecules. This template layer not only possesses certain ionic conductivity and chemical stability, but more importantly, it guides the formation of a unique dual-graft interface structure. The hydrophilic zwitterionic segments endow the interface with excellent lithium-ion solubilization and transport capabilities, effectively reducing interfacial impedance; while the hydrophobic fluorinated segments form a dense molecular barrier, significantly inhibiting the corrosion of the material surface by electrolyte components, especially strong oxidizing species, under high voltage. This dual-functional graft layer works together to form a stable interfacial film with both high ionic conductivity and strong antioxidant capacity.

[0018] In particular, this invention achieves a gentle modification of the surface chemical environment by precisely controlling the sequence of fluorination treatment steps. Fluorination based on an existing double-grafted structure avoids damage to the material surface caused by violent reactions, while the introduction of highly electronegative fluorine further enhances the chemical inertness and stability of the interfacial film, exhibiting excellent resistance to decomposition, especially under high-temperature conditions.

[0019] Ultimately, the stable bulk structure and the multifunctional protective layer at the interface create a positive synergistic effect. The stable bulk reduces internal stress caused by structural distortion at the interface, ensuring the long-term maintenance of the protective layer; while the excellent interface stability effectively blocks the impact of electrolyte side reactions on the bulk structure. This inside-out synergistic protection mechanism significantly improves the material's structural reversibility and interface compatibility at high voltages, resulting in higher capacity retention and a more stable discharge voltage plateau during long-cycle cycling, effectively overcoming the voltage decay problem common in this type of material. Simultaneously, the material's storage performance and cycle life at high temperatures are significantly enhanced, exhibiting a wider application temperature range and longer service life. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Figure 1 The infrared spectrum of the high-nickel, lithium-rich manganese-based multi-doped cathode material in Example 2 of this invention is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0022] Example 1: (1) Take 200mL of deionized water, 200mL of anhydrous ethanol and 35g of citric acid and put them into a 1000mL beaker. Add 11.3g of lithium acetate dihydrate, 12.5g of nickel acetate tetrahydrate, 5.7g of manganese acetate tetrahydrate, 0.9g of cobalt acetate tetrahydrate, 0.20g of niobium pentoxide and 0.03g of lithium fluoride. Stir for 60min. Adjust the pH to 6.7 dropwise with ammonia water (concentration 28w%). Evaporate in an 80°C water bath until a viscous gel is formed. Take all the gel and place it in an alumina boat. First, heat it to 540°C at 2°C / min with an oxygen flow rate of 80mL / min and keep it at that temperature for 4h. Then heat it to 830°C at 2°C / min and keep it at that temperature for 10h. Let it cool naturally to room temperature and grind it to obtain the main powder. (2) Take 10g of the main powder and disperse it in 200mL of anhydrous ethanol. Add 40mL of 0.8% lithium dihydrogen phosphate ethanol solution, sonicate for 20min, impregnate under reduced pressure (-0.07MPa) for 15min, evaporate to wet powder at 78°C, vacuum dry at 110°C for 2h, transfer to oxygen-filled box furnace and heat to 400°C at 2°C / min and hold for 2h, cool to room temperature to obtain phosphorus-doped main powder; (3) Take 10g of phosphorus-doped host powder, add 200mL of anhydrous toluene and 1mL of 10wt% acetic acid aqueous solution, add 0.8g of 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropionate, react at 75°C under nitrogen protection for 2h, filter and wash 3 times each with toluene and ethanol, and dry under vacuum at 80°C for 2h to obtain the host powder with initiator group grafted. (4) Take 10g of the initiator group grafted host powder and add it to 200mL of ethanol / water solution with a volume ratio of 1:1. Add 1.5g of 2-methacryloyloxyethyl phosphocholine, 90mg of copper bromide, 40mg of sodium ascorbate, and 80mg of tris[2-(dimethylamino)ethyl]amine. Bubble the mixture with nitrogen at room temperature for 4min and stir for 25min. Filter the mixture and wash it 3 times each with ethanol and water. Then redisperse the mixture in 200mL of ethanol. Add 0.3g of 1H,1H,2H,2H-perfluorodecyl acrylate, 90mg of copper bromide, 40mg of sodium ascorbate, and 80mg of tris[2-(dimethylamino)ethyl]amine. Stir the mixture at room temperature for 15min and then add 1.5g of 2-methacryloyloxyethyl phosphocholine. Stir for another 8min, filter the mixture and wash it with ethanol. Dry the mixture under vacuum at 115°C for 1h to obtain the double-grafted host powder. (5) Take 10g of double-grafted main body powder and put it into the reactor. Place 0.6g of ammonium difluoride at the bottom of the reactor away from the powder position. The closest straight distance between the two is 20mm. Under nitrogen atmosphere, 0.2MPa, constant temperature at 190°C for 2h. After cooling to room temperature, take it out and cool to room temperature to obtain high nickel-rich lithium manganese-based multi-doped cathode material.

[0023] Example 2: (1) Take 200 mL of deionized water, 200 mL of anhydrous ethanol, and 35 g of citric acid and place them in a 1000 mL beaker. Add 11.8 g of lithium acetate dihydrate, 13.1 g of nickel acetate tetrahydrate, 6 g of manganese acetate tetrahydrate, 1 g of cobalt acetate tetrahydrate, 0.27 g of niobium pentoxide, and 0.05 g of lithium fluoride. Stir for 60 min and adjust the pH to 6.9 dropwise with ammonia water (concentration 28 w%). Evaporate in an 80°C water bath until a viscous gel is formed. Take all the gel and place it in an alumina boat. First, heat it to 550°C at 3°C / min with an oxygen flow rate of 100 mL / min and keep it at that temperature for 5 h. Then, heat it to 850°C at 3°C / min and keep it at that temperature for 12 h. Let it cool naturally to room temperature and grind it to obtain the main powder. (2) Take 10g of the main powder and disperse it in 200mL of anhydrous ethanol. Add 50mL of 1% lithium dihydrogen phosphate ethanol solution, sonicate for 30min, impregnate under reduced pressure (-0.08MPa) for 20min, evaporate to wet powder at 80°C, vacuum dry at 120°C for 2h, transfer to oxygen-filled box furnace and heat to 420°C at 2°C / min and keep warm for 2h, cool to room temperature to obtain phosphorus-doped main powder; (3) Take 10g of phosphorus-doped host powder, add 200mL of anhydrous toluene and 1mL of 10wt% acetic acid aqueous solution, add 1g of 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropionate, react at 80°C under nitrogen protection for 2h, filter and wash 3 times each with toluene and ethanol, and dry under vacuum at 80°C for 2h to obtain the host powder grafted with initiating groups; (4) Take 10g of the initiator group grafted host powder and add it to 200mL of ethanol / water solution with a volume ratio of 1:1. Add 2g of 2-methacryloyloxyethyl phosphocholine, 113mg of copper bromide, 50mg of sodium ascorbate, and 100mg of tris[2-(dimethylamino)ethyl]amine. Bubble the mixture under nitrogen at room temperature for 5min and stir for 30min. Filter the mixture and wash it 3 times each with ethanol and water. Then redisperse the mixture in 200mL of ethanol. Add 0.4g of 1H,1H,2H,2H-perfluorodecyl acrylate, 113mg of copper bromide, 50mg of sodium ascorbate, and 100mg of tris[2-(dimethylamino)ethyl]amine. Stir the mixture at room temperature for 15min and then add 2g of 2-methacryloyloxyethyl phosphocholine. Stir for another 10min, filter the mixture and wash it with ethanol. Dry the mixture under vacuum at 120°C for 1h to obtain the double-grafted host powder. (5) Take 10g of double-grafted main body powder and put it into the reactor. Place 1g of ammonium difluoride at the bottom of the reactor away from the powder position. The closest straight distance between the two is 25mm. Under nitrogen atmosphere, 0.2MPa, constant temperature at 200°C for 2h. After cooling to room temperature, take it out and cool to room temperature to obtain high nickel-rich lithium manganese-based multi-doped cathode material.

[0024] Example 3: (1) Take 200mL of deionized water, 200mL of anhydrous ethanol and 35g of citric acid and put them into a 1000mL beaker. Add 12.3g of lithium acetate dihydrate, 13.7g of nickel acetate tetrahydrate, 6.3g of manganese acetate tetrahydrate, 1.1g of cobalt acetate tetrahydrate, 0.34g of niobium pentoxide and 0.08g of lithium fluoride. Stir for 60min. Adjust the pH to 7.1 dropwise with ammonia water (concentration 28w%). Evaporate in an 80°C water bath until a viscous gel is formed. Take all the gel and place it in an alumina boat. First, heat it to 560°C at 4°C / min with an oxygen flow rate of 120mL / min and keep it at that temperature for 6h. Then heat it to 870°C at 4°C / min and keep it at that temperature for 14h. Let it cool naturally to room temperature and grind it to obtain the main powder. (2) Take 10g of the main powder and disperse it in 200mL of anhydrous ethanol. Add 60mL of 1.2% lithium dihydrogen phosphate ethanol solution, sonicate for 40min, impregnate under reduced pressure (-0.09MPa) for 30min, evaporate to wet powder at 82°C, vacuum dry at 125°C for 2h, transfer to oxygen-filled box furnace and heat to 440°C at 2°C / min and hold for 2h, cool to room temperature to obtain phosphorus-doped main powder; (3) Take 10g of phosphorus-doped host powder, add 200mL of anhydrous toluene and 1mL of 10wt% acetic acid aqueous solution, add 1.2g of 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropionate, react at 85°C under nitrogen protection for 2h, filter and wash 3 times each with toluene and ethanol, and dry under vacuum at 80°C for 2h to obtain the host powder with initiator group grafted. (4) Take 10g of the initiator group grafted host powder and add it to 200mL of ethanol / water solution with a volume ratio of 1:1. Add 2.5g of 2-methacryloyloxyethyl phosphocholine, 140mg of copper bromide, 60mg of sodium ascorbate, and 120mg of tris[2-(dimethylamino)ethyl]amine. Bubble the mixture under nitrogen at room temperature for 6min and stir for 35min. Filter the mixture and wash it 3 times each with ethanol and water. Then redisperse the mixture in 200mL of ethanol. Add 0.6g of 1H,1H,2H,2H-perfluorodecyl acrylate, 140mg of copper bromide, 60mg of sodium ascorbate, and 120mg of tris[2-(dimethylamino)ethyl]amine. Stir the mixture at room temperature for 15min and then add 2.5g of 2-methacryloyloxyethyl phosphocholine. Stir for another 12min, filter the mixture and wash it with ethanol. Dry the mixture under vacuum at 125°C for 1h to obtain the double-grafted host powder. (5) Take 10g of double-grafted main body powder and put it into the reactor. Place 1.4g of ammonium difluoride at the bottom of the reactor away from the powder position. The closest straight distance between the two is 30mm. Under nitrogen atmosphere, 0.2MPa, constant temperature at 210°C for 2h. After cooling to room temperature, take it out and cool to room temperature to obtain high nickel-rich lithium manganese-based multi-doped cathode material.

[0025] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that niobium pentoxide is not added in step (1), and the amount of lithium fluoride is still 0.05g; the other conditions are the same as in Example 2.

[0026] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that lithium fluoride is not added in step (1), and the amount of niobium pentoxide is still 0.27g; the other conditions are the same as in Example 2.

[0027] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the lithium dihydrogen phosphate vacuum impregnation and 420°C heat treatment in step (2) are not performed; the other conditions are the same as in Example 2.

[0028] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that in step (4), only 2-methacryloyloxyethyl phosphocholine is added, and 1H,1H,2H,2H-perfluorodecyl acrylate is not added; the other conditions are the same as in Example 2.

[0029] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that in step (4), only 1H,1H,2H,2H-perfluorodecyl acrylate is added, and 2-methacryloyloxyethyl phosphocholine is not added; the other conditions are the same as in Example 2.

[0030] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the order of steps (5) and (4) is reversed, that is, ammonium difluoride treatment at 200°C for 2 hours is performed first, followed by the grafting operation in step (4); the other conditions are the same as in Example 2.

[0031] Performance testing: Sample preparation and battery assembly: All samples, conductive carbon black, and polyvinylidene fluoride were mixed at a mass ratio of 92:4:4. N-methylpyrrolidone was added to adjust the slurry to a solid content of 42 wt%. The mixture was then planetarily stirred (800 r / min, 30 min), followed by vacuum degassing (-0.09 MPa, 10 min). The mixture was then coated onto a 12 µm aluminum foil, achieving a wet film thickness of 120 µm. The film was dried with hot air at 80°C for 10 min, followed by vacuum drying at 120°C for 12 h. The film was then pressed into sheets at room temperature (roller pressing, linear pressing 8 t / cm), resulting in sheets with a diameter of 14 mm and an active material areal density of 10.0 ± 0.3 mg / cm³. 2 CR2032 lithium foil half-cells were assembled in an argon glove box. The separator was a polypropylene microporous membrane, and the electrolyte was 1.0 mol / L LiPF6 (EC:EMC:DMC volume ratio 1:1:1). 2 wt% vinylene carbonate and 1 wt% lithium difluorophosphate were added. The electrolyte was charged at 250 mA·g at 1C. -1 This standardized assembly condition is defined and applied to all subsequent electrochemical testing items.

[0032] Infrared spectroscopy: KBr pellet (sample:KBr=1:150, mass ratio), resolution 4cm. -1 4000-400cm -1 .

[0033] Particle size distribution, specific surface area and tap density: Laser diffraction particle size was determined according to GB / T19077-2024; specific surface area according to GB / T19587-2017; tap density according to GB / T5162-2021. The results are shown in Table 1.

[0034] First discharge specific capacity and first charge-discharge efficiency (0.1C, 2.0-4.6V): According to GB / T37201-2018, the first capacity and efficiency were determined according to the general procedure for testing the electrochemical performance of lithium nickel cobalt manganese oxide. Combined with the high voltage characteristics of lithium-rich materials, the upper limit voltage was set to 4.6V and constant voltage was maintained until 0.02C cutoff. The results are shown in Table 1.

[0035] Discharge plateau capacity ratio and cycle life: (0.5C, 25°C, 200 cycles): According to GB / T37201-2018, after 200 charge-discharge cycles at 25°C and 0.5C, the plateau capacity ratio and capacity retention rate were statistically analyzed, and the voltage decay was measured by the average discharge voltage decay ΔV (V / 100 cycles). The results are shown in Table 1.

[0036] High-temperature electrochemical performance: According to GB / T43092-2023, the half-cell was stored at 60°C and 50% state of charge for 7 days and then recovered at 25°C for three cycles at 0.2C. The capacity retention rate was calculated. At the same time, the high-temperature cycling retention rate was evaluated by cycling at 45°C and 0.5C for 100 cycles. The results are shown in Table 1.

[0037] Table 1 Performance Test Results

[0038] Data Analysis: As can be seen from the data in Examples 1-3 in Table 1, this invention achieves synergistic stability of the main structure and interface by combining bulk Nb / light F stabilization with surface LiH2PO4 template treatment, followed by alternating grafting of zwitterionic segments and fluorinated hydrophobic segments, and a timing sequence of grafting followed by mild fluorination. This results in a significant improvement in first-cycle reversibility, a markedly slower discharge plateau decay rate, and more stable capacity under high-temperature storage and cycling conditions. Simultaneously, the particle size distribution and tap density remain within a range conducive to electrode formation without excessively sacrificing ion flux. This synergistic effect of bulk stabilization, surface composite film, and directional fluorination makes the activation-stabilization process more controllable, reduces irreversible structural evolution caused by oxygen-involved red oxidation, and effectively constrains interfacial side reactions, thus achieving a comprehensive performance that balances high capacity and low voltage decay.

[0039] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, the absence of Nb results in insufficient charge compensation and lattice stability, significantly lower reversibility and plateau stability in the first week, and increased voltage decay. The main reason is that the irreplaceable crystal-stabilizing effect of the Nb site is weakened, making transition metal migration and interlayer slip more likely, and making it difficult to passivate irreversible processes involving oxygen in a timely manner. Although a slight amount of F can suppress interfacial reactions to some extent, it is insufficient to compensate for the cumulative effect of bulk defects.

[0040] As can be seen from the data in Example 2 and Comparative Example 2 in Table 1, when Nb is used for stabilization without the participation of F, it is difficult for a stable LiF-rich phase to form rapidly at the interface, leading to an increase in side reactions and a decrease in reversibility in the first week. Capacity recovery and maintenance are also limited at high temperatures. The main reason is that the bulk stability is not aligned with the interfacial chemical stability, and the active intermediates generated during the redox process are difficult to be adsorbed by the interface in a timely manner.

[0041] As can be seen from the data in Table 1 for Example 2 and Comparative Example 3, the absence of the phosphate layer as an interfacial template led to decreased uniformity of subsequent organic grafting, disordered fluorine source infiltration, and more pronounced plateau shrinkage during cycling. The main reason for this is the difficulty in forming an ion-conducting and chemically stable composite network on the surface, resulting in mutually reinforcing interfacial side reactions and structural reconstruction, thus impairing voltage maintenance.

[0042] As can be seen from the data in Example 2 and Comparative Example 4 in Table 1, when only zwitterionic segments are grafted, the interfacial ion transport is relatively smooth, but the hydrophobic shielding is insufficient, the suppression of side reactions under high-temperature storage is limited, and the improvement in voltage stability is limited. The main reason is that although the zwitterionic layer can construct solvation channels, it is difficult to provide effective antioxidant and anti-swelling barriers, and the interfacial tolerance is not as good as that of the bisegment system.

[0043] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, when only fluorine segments are present, the interfacial chemical stability is better, and high-temperature maintenance has certain advantages. However, the limited ion transport leads to insufficient utilization and plateau maintenance. The main reason is that the hydrophobic layer inhibits the electrolyte reaction, but lacks the synergy of amphoteric channels, making it easy for interfacial impedance to accumulate, and difficult to balance capacity release and voltage maintenance.

[0044] As can be seen from the data in Example 2 and Comparative Example 6 in Table 1, reversing the process causes non-uniform etching and roughening of the surface, resulting in an abnormally large specific surface area, a decrease in tap density, and a significant amplification of voltage decay during cycling. The main reason is that the fluorination process first causes surface embrittlement, making it difficult for subsequent grafting to form a continuous and dense composite film. Interface defects are solidified, exhibiting an anti-synergistic phenomenon of 1+1<2.

[0045] from Figure 1 It can be seen that the sample is between 124-1056 cm. -1 A strong absorption appears in the interval, corresponding to the P=O / PO2 of the surface phosphate.- The POM ( / POC) stretching and overlapping with the CF and COC vibrations of the fluorine-grafted layer indicate that the surface templated phosphate and fluorine-containing / ampholy segments were successfully constructed; 1730cm -1 The ester group C=O at 2956 / 2924 / 2853cm -1 The stretching of the hydrocarbon chains further confirms the existence of the grafted layer; 520 and 610 cm -1 The clear MO vibration of the skeleton indicates that the main layered structure is intact.

[0046] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A preparation process of a high-nickel lithium-rich manganese-based multi-doped positive electrode material, characterized in that, The method comprises the following steps: (1) dissolving lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate, and niobium pentoxide and lithium fluoride in a mixed solvent of deionized water and anhydrous ethanol, adjusting the pH to 6.7-7.1, evaporating into a gel at about 80°C water bath, sintering at 540-560°C and 830-870°C respectively under oxygen condition, and obtaining the main body powder; (2) dispersing the main body powder in a 0.8wt%-1.2wt% lithium dihydrogen phosphate ethanol solution, ultrasonic and vacuum impregnating, rotary evaporation, vacuum drying, and heat preservation at 400-440°C for 2h under oxygen condition, and obtaining the phosphorus-doped main body powder; (3) reacting the phosphorus-doped main body powder with 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropionate in anhydrous toluene to introduce surface initiation groups, and obtaining the initiation group grafted main body powder; (4) grafting 2-methacryloyloxyethyl phosphorylcholine and fluorine-containing monomer 1H,1H,2H,2H-perfluorodecyl acrylate on the initiation group grafted main body powder in turn by atom transfer radical polymerization, and supplementing 2-methacryloyloxyethyl phosphorylcholine between them and after them to construct a double-grafted surface layer of amphoteric segment / fluorine-containing segment, and obtaining the double-grafted main body powder; (5) placing the double-grafted main body powder and ammonium bifluoride in the same sealed reaction kettle, and performing non-contact mild fluorination treatment at 190-210°C for 2h, and obtaining the high-nickel lithium-rich manganese-based multi-doped positive electrode material after cooling; In the step (4), the first grafting is performed in a medium of ethanol / water with a volume ratio of 1:1, 1.5-2.5g of 2-methacryloyloxyethyl phosphorylcholine, 90-140mg of copper bromide, 40-60mg of sodium ascorbate, and 80-120mg of tris[2-(dimethylamino)ethyl]amine are added, nitrogen bubbling is performed at room temperature for 4-6min, and stirring is performed for 25-35min; the second grafting is performed in ethanol, 0.3-0.6g of the fluorine-containing monomer, 90-140mg of copper bromide, 40-60mg of sodium ascorbate, and 80-120mg of tris[2-(dimethylamino)ethyl]amine are added, stirring is performed for 15min, and then 1.5-2.5g of 2-methacryloyloxyethyl phosphorylcholine is added and stirring is performed for 8-12min.

2. The preparation process of high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, In the step (1), the mass ratio of lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate, niobium pentoxide, lithium fluoride, and citric acid is 11.3-12.3:12.5-13.7:5.7-6.3:0.9-1.1:0.2-0.34:0.03-0.08:

35.

3. The preparation process of high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, In the step (1), the oxygen flow rate of oxygen during oxygenation is 80-120mL / min.

4. The preparation process of high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, In the step (1), the heating rate is 2-4°C / min, and the heat preservation time of the first and second stages is 4-6h and 10-14h respectively.

5. The process for preparing a high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, The amount of the lithium dihydrogen phosphate ethanol solution in step (2) is 40-60 mL, based on 10 g of the main powder.

6. The process for preparing a high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, The ultrasonic time in step (2) is 20-40 min, the reduced pressure is -0.07 to -0.09 MPa, and the reduced pressure immersion time is 15-30 min.

7. The process for preparing a high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, The mass ratio of the phosphorus-doped main powder to 3-(trimethoxysilyl)propyl-2-bromo-2-methylpropylate in step (3) is 10:0.8-1.

2.

8. The process for preparing a high nickel lithium-rich manganese-based multi-doped cathode material according to claim 1, characterized in that, The mass ratio of the double-grafted main powder to ammonium bifluoride in step (5) is 10:0.6-1.4.

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