A fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material, its preparation method, and its applications.

Abstract

This invention relates to a fast-ion conductor-stabilizer composite-coated lithium manganese iron phosphate material, its preparation method, and its applications. The lithium manganese iron phosphate material of this invention comprises a lithium manganese iron phosphate core and a coating layer on its surface. The coating layer is obtained by coating the surface of the lithium manganese iron phosphate core with a mixture of sodium aluminosilicate, magnesium aluminate, a carbon source, and a lithium supplement, followed by sintering. This invention utilizes sodium aluminosilicate and magnesium aluminate combined with conductive carbon for co-coating lithium manganese iron phosphate, achieving partial Na+ ionization during high-temperature sintering. + / Al 3+ / Mg 2+ Multiple ions are co-intercalated into the near-surface layer of lithium manganese iron phosphate crystals, thereby forming a more stable structure and Li + A cellular structure that facilitates diffusion. During high-temperature sintering, some magnesium aluminate reacts with the lithium supplement to form an Al-based fast ion conductor, coupled with the wider Li-ion diffusion of sodium aluminosilicate. + The diffusion channels give the material excellent rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and in particular to a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material, its preparation method, and its application. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x Lithium manganese iron phosphate (LMP) is considered a promising next-generation cathode material for lithium-ion batteries due to its high voltage plateau and energy density. Compared to lithium iron phosphate (LFP), its voltage plateau is approximately 0.6V higher, and its mass energy density can be increased by 10-20%. Currently, the common method for preparing LMP involves mixing iron, manganese, phosphorus, lithium, and carbon sources in a specific ratio during the wet grinding stage, based on the LFP preparation process, followed by spray drying, atmosphere sintering, and pulverization to obtain the product. However, LMP itself has several performance issues, such as a high specific surface area and high powder resistivity, resulting in poor processing performance and low production efficiency during battery manufacturing. Furthermore, the lack of a continuous coplanar octahedral network in its structure restricts the movement of lithium ions in one-dimensional channels, leading to poor conductivity. To improve the performance of lithium manganese iron phosphate (LMP), existing technologies often optimize carbon coating methods to enhance the conductivity of LMP materials. This involves using different types of carbon sources or applying carbon in batches multiple times to form a uniform coating layer on the surface of the material particles, thereby reducing the resistivity to some extent. However, carbon coating alone only improves the electronic conductivity of the material and cannot fully address the inherent low ionic conductivity and manganese leaching issues of LMP.

[0003] Lithium manganese iron phosphate (LiMn) x Fe 1-x The question for PO4 is as follows:

[0004] Conductivity and ion transport issues: Although carbon coating can reduce resistivity, lithium manganese iron phosphate lacks a continuous coplanar octahedral network in its structure, which severely restricts the transport of lithium ions in one-dimensional channels. As a result, the lithium ion diffusion rate cannot meet the requirements during high-power charging and discharging, thus limiting the rate performance of the battery.

[0005] Insufficient structural stability: During battery charging and discharging, lithium manganese iron phosphate is corroded by the electrolyte, and Mn is also present. 3+ The Jahn-Teller effect causes manganese to dissolve, which in turn disrupts the material's crystal structure and shortens battery cycle life. Commonly used carbon coating methods have limited effectiveness in inhibiting manganese dissolution and maintaining structural stability.

[0006] Bottlenecks in overall performance improvement: Due to limitations in conductivity and structural stability, the capacity utilization, rate performance, and cycle stability of lithium manganese iron phosphate materials are difficult to further improve, making it impossible to meet the high-performance and long-life requirements of high-demand application scenarios such as electric vehicles and large-scale energy storage. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the prior art by providing a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material, its preparation method, and its application, especially a lithium manganese iron phosphate cathode material with a unique composite coating structure and multi-ion co-intercalation synergistic effect and its preparation process.

[0008] The objective of this invention can be achieved through the following methods:

[0009] This invention provides a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material, the lithium manganese iron phosphate material comprising a lithium manganese iron phosphate core and a coating layer on the surface of the lithium manganese iron phosphate core;

[0010] The coating layer is obtained by coating the surface of the lithium manganese iron phosphate core with a mixture of sodium aluminosilicate, magnesium aluminate, coating carbon source, and lithium supplement, followed by sintering.

[0011] In the resulting coating layer, sodium aluminosilicate and magnesium aluminate can form a protective film on the material surface, effectively blocking electrolyte erosion, inhibiting manganese dissolution, enhancing the stability of the material structure, and improving cycle performance. Therefore, sodium aluminosilicate and magnesium aluminate can act as stabilizers. In the LiAlPO4, LiAlO2, and sodium aluminosilicate formed by the reaction of the lithium supplement with magnesium aluminate, Li... + They can diffuse more quickly, thus they act as fast ion conductors.

[0012] As one embodiment of the present invention, sodium ions (Na+) are embedded in the near-surface crystal layer of the lithium manganese iron phosphate core. + ), aluminum ions (Al) 3+ ), magnesium ions (Mg 2+ ).

[0013] Sodium ions (Na) + ), aluminum ions (Al) 3+ ), magnesium ions (Mg 2+ The embedding of these ions is achieved by coating sodium aluminosilicate and magnesium aluminate onto the surface of lithium manganese iron phosphate particles, followed by sintering (temperature 650-750℃, time 6h~15h). During sintering, these ions embed into the near-surface crystal layer of the lithium manganese iron phosphate core.

[0014] As one embodiment of the present invention, the particle size of the lithium manganese iron phosphate core is 100~550 nm (primary particle size); the thickness of the coating layer is 2~13 nm.

[0015] As one embodiment of the present invention, the conductive carbon is obtained by coating a carbon source onto the surface of lithium manganese iron phosphate raw material particles and then sintering it (temperature 650-750℃, time 6h~15h).

[0016] As one embodiment of the present invention, the lithium supplement includes one or more of lithium carbonate, lithium oxalate, lithium acetate, lithium phosphate, lithium sulfate, lithium dihydrogen phosphate, and lithium difluorooxalate borate.

[0017] As one embodiment of the present invention, the coated carbon source includes one or more of monosaccharides, disaccharides, polysaccharides, organic acids, polymers, and conductive agents.

[0018] Monosaccharides include one or more of glucose and fructose;

[0019] Disaccharides include one or more of sucrose and lactose;

[0020] Polysaccharides include starch;

[0021] Organic acids include one or more of citric acid, tannic acid, oleic acid, stearic acid, and malic acid;

[0022] The polymers include one or more of polyvinylpyrrolidone, polyethylene glycol (PEG), polyvinyl alcohol, polyacrylic acid, and phenolic resin;

[0023] Conductive agents include one or more of acetylene black, conductive carbon black, Super P, carbon nanotubes, graphene, and graphite.

[0024] Preferably, the carbon source for coating includes one or more of glucose, PEG, and tannic acid. The preferred carbon source for coating is glucose and PEG6000; the mass ratio of glucose to PEG6000 is 1:0.25~1.50.

[0025] This invention provides a method for preparing a fast-ion conductor-stabilizer composite-coated lithium manganese iron phosphate material, comprising the following steps:

[0026] S1. Lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source, and lithium supplementer are added to a solvent to obtain a mixed slurry. The mixed slurry is then sand-milled and spray-dried to obtain a post-processed spherical precursor.

[0027] S2. The post-processed spherical precursor is sintered to obtain a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material.

[0028] As one embodiment of the present invention, in step S1,

[0029] The amount of sodium aluminosilicate used is 0.1% to 3% of the mass of lithium manganese iron phosphate raw material, preferably 0.5% to 2%;

[0030] The amount of magnesium aluminate used is 0.1% to 3% of the mass of lithium manganese iron phosphate raw material, preferably 0.5% to 2%;

[0031] The amount of carbon source used for coating is 2% to 15% of the mass of lithium manganese iron phosphate raw material, preferably 7.5% to 15%, and more preferably 10% to 15%.

[0032] The amount of lithium supplement is 0.5%-3% of the mass of lithium manganese iron phosphate raw material, preferably 0.5%-1.1%, and more preferably 0.9%-1.1%.

[0033] When sodium aluminosilicate and magnesium aluminate are used as coating agents, excessive amounts can lead to two problems. First, excess coating agent particles may adhere to the surface of lithium manganese iron phosphate nanoparticles or fill the gaps between the nanoparticles, resulting in ineffective coating. Second, an excessively thick coating layer can hinder the insertion and extraction of lithium ions, leading to a slower charge transfer rate at the interface during charging and discharging, resulting in poorer rate capability, cycle performance, and reduced efficiency of the material.

[0034] Preferably, the total mass percentage of sodium aluminosilicate and magnesium aluminate does not exceed 3% of the lithium manganese iron phosphate raw material, and more preferably 2%-3%.

[0035] As one embodiment of the present invention, in step S1, the lithium supplement includes one or more of lithium carbonate, lithium oxalate, lithium acetate, lithium phosphate, lithium sulfate, lithium dihydrogen phosphate, and lithium difluorooxalate borate.

[0036] In one embodiment of the present invention, in step S1, the solvent includes one or more of water, ethanol, and methanol.

[0037] As one embodiment of the present invention, in step S1, the solid content of the mixed slurry is 20 wt%-50 wt%.

[0038] In one embodiment of the present invention, in step S1, the particle size of the mixed slurry after sand milling is 250-500 nm.

[0039] In one embodiment of the present invention, the parameters for spray drying in step S1 are: inlet air temperature 180-260℃, outlet air temperature 85-95℃, induced draft fan frequency 30-50HZ, and atomizer air pressure 0.10-0.45MPa. Preferably, the inlet air temperature is 225℃, the outlet air temperature is 91℃, the induced draft fan frequency is 45HZ, and the atomizer air pressure is 0.2MPa.

[0040] In one embodiment of the present invention, in step S2, the sintering temperature is 650-750℃, and the time is 6h-15h. The heating rate is 2℃ / min.

[0041] At the sintering temperature of this invention, some Na can be sintered. + / Al 3+ / Mg 2+ Multi-ion co-intercalation into the near-surface layer of lithium manganese iron phosphate crystals results in lithium manganese iron phosphate materials with higher capacity, better rate capability, and better cycling performance. If the sintering temperature is too low, on the one hand, the fusion effect between the coating agent and the lithium manganese iron phosphate raw material is poor, and the coating layer is prone to detachment; on the other hand, the lower temperature cannot achieve near-surface ion intercalation. If the sintering temperature is too high, the nanoparticles of the lithium manganese iron phosphate raw material suffer from severe adhesion or even secondary fusion, which is not conducive to lithium-ion diffusion, leading to a decline in the material's rate capability and cycling performance.

[0042] As one embodiment of the present invention, in step S1, the preparation method of lithium manganese iron phosphate raw material includes the following steps:

[0043] Lithium, manganese, iron, and phosphorus sources are added to a solvent and stirred until homogeneous. Then, a carbon source is added. The resulting slurry is milled and spray-dried to obtain a spherical lithium manganese iron phosphate precursor. The spherical lithium manganese iron phosphate precursor is then sintered to obtain a spherical lithium manganese iron phosphate raw material.

[0044] Preferably, the stoichiometric ratio of each element in the raw material is Li:(Mn + Fe):P = 1-1.06:1:1-1.05; wherein, Mn:Fe = 0.1-0.9:0.1-0.9.

[0045] Preferably, the lithium source includes one or more of lithium carbonate, lithium acetate, lithium phosphate, lithium citrate, and lithium dihydrogen phosphate.

[0046] Preferably, the manganese source includes one or more of manganese tetroxide, manganese carbonate, manganese oxalate, and ferromanganese precursors.

[0047] Preferably, the iron source includes one or more of the following: ferric phosphate, ferric oxide, ferric sulfate, ferrous oxalate, and ferromanganese precursors (such as ferromanganese phosphate).

[0048] Preferably, the phosphorus source includes one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, lithium phosphate, and phosphoric acid.

[0049] Preferably, the solvent is water.

[0050] Preferably, the carbon source of the raw material includes one or more of monosaccharides, disaccharides, polysaccharides, organic acids, polymers, and conductive agents. Monosaccharides include one or more of glucose and fructose; disaccharides include one or more of sucrose and lactose; polysaccharides include starch; organic acids include one or more of citric acid, tannic acid, oleic acid, stearic acid, and malic acid; polymers include one or more of polyvinylpyrrolidone, polyethylene glycol (PEG), polyvinyl alcohol, polyacrylic acid, and phenolic resin; and conductive agents include one or more of acetylene black, conductive carbon black, Super P, carbon nanotubes, graphene, and graphite.

[0051] Preferably, the carbon source includes one or more of glucose, PEG6000, and tannic acid. The total mass of the raw material carbon source is 3% to 15% of the mass of the raw material dry powder (lithium source, manganese source, iron source, and phosphorus source), preferably 3% to 5%, and more preferably 3.5% to 4.5%. Glucose and PEG6000 are preferred; the mass ratio of glucose to PEG6000 is 1:0.5 to 1.5.

[0052] Preferably, the particles are milled to a particle size of 150-500 nm.

[0053] Preferably, the spray drying parameters are: inlet air temperature 180-260℃, outlet air temperature 85-95℃, induced draft fan frequency 30-50HZ, and atomizer air pressure 0.10-0.45MPa. More preferably, the inlet air temperature is 225℃, the outlet air temperature is 91℃, the induced draft fan frequency is 45HZ, and the atomizer air pressure is 0.2MPa.

[0054] Preferably, the sintering temperature is 450-750℃, and the sintering time is 6-15 hours.

[0055] Preferably, the obtained spherical lithium manganese iron phosphate raw material is subjected to air jet milling treatment to control the particle size D50 = 1~1.3μm to obtain nano lithium manganese iron phosphate raw material.

[0056] The present invention also provides a positive electrode sheet, which includes the aforementioned fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material.

[0057] The present invention also provides a battery comprising the aforementioned positive electrode plate.

[0058] The present invention also provides an application of the fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material in the preparation of lithium-ion batteries.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The core of this invention lies in the innovative use of sodium aluminosilicate and magnesium aluminate combined with conductive carbon to co-coat lithium manganese iron phosphate, and in the high-temperature coating sintering process, partial Na+ / Al 3+ / Mg 2+ The near-surface structure of lithium manganese iron phosphate crystals exhibits multi-ion co-intercalation. Sodium aluminosilicate and magnesium aluminate possess excellent chemical stability and mechanical properties, forming a robust protective film on the material surface. This effectively blocks electrolyte erosion, inhibits manganese dissolution, and significantly enhances the material's structural stability. During high-temperature sintering, some magnesium aluminate reacts with the lithium supplement to form Al-based fast ion conductors. Combined with the wider Li+ diffusion channels of sodium aluminosilicate, this results in excellent rate performance.

[0061] (2) During high-temperature sintering, some Na + / Al 3+ / Mg 2+ Multi-ion co-intercalation in the near-surface layer of lithium manganese iron phosphate crystals, with stronger metal bond energies, not only stabilizes the crystal structure but also suppresses Mn. 3+ The Jahn-Teller effect further broadens the lithium-ion transport path, significantly improving the lithium-ion diffusion rate. Combined with the excellent chemical stability and ionic conductivity of the coating material, as well as the synergistic co-doping of multiple ions near the surface, the capacity, rate capability, and cycle performance of lithium manganese iron phosphate materials are comprehensively enhanced. Attached Figure Description

[0062] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0063] Figure 1 The TEM image of the finished product in Comparative Example 1;

[0064] Figure 2 TEM image of the finished product from Example 1;

[0065] Figure 3 The constant current injection ratio test is shown in the embodiments and comparative examples of this invention;

[0066] Figure 4 For the rate performance tests of the embodiments and comparative examples of the present invention;

[0067] Figure 5 This is a cycle performance test for embodiments and comparative examples of the present invention. Detailed Implementation

[0068] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0069] Example 1

[0070] I. Preparation of Lithium Manganese Iron Phosphate Raw Material (Single Sintering)

[0071] (1) Weigh the raw materials: lithium dihydrogen phosphate (LiH2PO4) 4.718Kg, lithium carbonate (Li2CO3) 1.057Kg, manganese tetroxide (Mn3O4) 3.336Kg, iron phosphate (FePO4) 4.459Kg, glucose (C6H 12 O6) 0.271Kg, polyethylene glycol (PEG6000) 0.271Kg.

[0072] (2) Preparation of lithium manganese iron phosphate raw material:

[0073] ① Add all materials except glucose and PEG6000 to a mixing tank containing 24.5 kg of water. After stirring evenly, add glucose powder and a 50 wt.% PEG aqueous solution sequentially to prepare a primary slurry. During the mixing process, control the Li:(Mn+Fe):P ratio to be 1.03:1:1.03, and the Mn:Fe ratio to be 0.6:0.4. Simultaneously, the total mass of glucose and PEG6000 should be 4% of the total mass of the dry powder (lithium, manganese, iron, and phosphorus sources), and the mass ratio of glucose to PEG6000 should be 1:1. Next, pump the primary slurry into a sand mill for single-tank circulating fine grinding (zirconium bead diameter 0.3-0.4 mm) until the particle size D50 = 300 nm. Next, the milled slurry is pumped into a two-fluid spray dryer for drying, with the inlet air temperature controlled at 225℃, the outlet air temperature at 91℃, the induced draft fan frequency at 45HZ, and the atomizer pressure at 0.2MPa, thereby obtaining a spherical lithium manganese iron phosphate precursor.

[0074] ② The precursor obtained in the previous step was sintered at high temperature under an inert atmosphere. The specific sintering steps were as follows: the temperature was increased from room temperature to 600℃ at a rate of 2℃ / min, and held at 600℃ for 8 hours to obtain spherical materials. Finally, the spherical materials were crushed, and the particle size D50 was controlled to be 1~1.3μm to obtain nano-lithium manganese iron phosphate raw material.

[0075] II. Post-treatment of fast ion conductor composite coating (secondary sintering)

[0076] (1) Weigh 10Kg of lithium manganese iron phosphate raw material, 0.104Kg of lithium carbonate, 0.600Kg of glucose, 0.600Kg of PEG6000, 0.1Kg of sodium aluminosilicate and 0.1Kg of magnesium aluminate.

[0077] (2) Preparation of lithium manganese iron phosphate materials:

[0078] ① Add 16.7 kg of water to the sand mill jar, and then add the above materials sequentially to obtain a secondary slurry. The mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source (glucose and PEG6000), and lithium supplement (lithium carbonate) is 1:1%:1%:12%:1.04%, of which the mass ratio of glucose and PEG6000 is 1:1.

[0079] The secondary slurry is then pumped into a sand mill for single-tank circulating fine grinding (zirconium bead diameter 0.3-0.4 mm) until the particle size D50 = 400 nm. Finally, the sand-ground slurry is subjected to two-fluid spray drying, with the inlet air temperature controlled at 225℃, the outlet air temperature at 91℃, the induced draft fan frequency at 45 Hz, and the atomizer air pressure at 0.15 MPa, to obtain the post-processed spherical precursor.

[0080] ② The post-treatment precursor was sintered under an inert atmosphere. The sintering process was as follows: the temperature was increased from room temperature to 730℃ at a rate of 2℃ / min, and held at 730℃ for 10 hours, finally obtaining a fast ion conductor composite-coated lithium manganese iron phosphate material, in which the core particle size was 150-350nm and the coating thickness was about 7nm. TEM images are shown below. Figure 2 As shown.

[0081] Example 2

[0082] The difference between this embodiment and Embodiment 1 is that, during the first sintering, tannic acid and glucose are used as raw material carbon sources in the batching process, with the total mass of the carbon sources being 3% of the total dry powder weight, and the mass ratio of tannic acid to glucose being 1:4; during the second sintering, tannic acid and glucose are used as coating carbon sources, with the mass ratio of tannic acid to glucose being 1:4, and the total mass of the coating carbon sources being 7.5% of the lithium manganese iron phosphate raw material.

[0083] Example 3

[0084] The difference between this embodiment and Embodiment 1 is that, during the secondary sintering, the mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source, and lithium supplement is 1:2%:1%:12%:1.04%.

[0085] Example 4

[0086] The difference between this embodiment and Embodiment 1 is that, during the secondary sintering, the mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source, and lithium supplement is 1:0.5%:1.5%:12%:1.04%.

[0087] Example 5

[0088] The difference between this embodiment and Embodiment 1 is that the temperature during the second sintering is 650°C.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that no coating agent was used during the secondary sintering. The mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coating carbon source, and lithium supplementer was 1:0%:0%:12%:1.04%. The TEM image of the obtained lithium manganese iron phosphate material is shown below. Figure 1 As shown.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that during the secondary sintering, only sodium aluminosilicate is used as the coating agent. The mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coating carbon source, and lithium supplement is 1:2:0%:12%:1.04%.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that during the secondary sintering, only a single coating agent, magnesium aluminate, is used. The mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coating carbon source, and lithium supplement is 1:0:2%:12%:1.04%.

[0095] Comparative Example 4

[0096] The difference between this comparative example and Example 1 is that, during the secondary sintering, the mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source, and lithium supplement is 1:2%:2%:12%:1.04%.

[0097] Comparative Example 5

[0098] The difference between this comparative example and Example 1 is that the sintering temperature during the second sintering is 600°C (a lower second sintering temperature cannot promote the formation of Na contained in the coating agent). + / Al 3+ / Mg 2+ Embedded into the near-surface structure of the substrate.

[0099] Performance testing:

[0100] (1) Test method:

[0101] The cathode materials obtained from the examples and comparative examples were assembled into CR2016 coin cells and electrochemical tests were performed. The assembly sequence was as follows.

[0102] ① Slurry preparation: The positive electrode material, PVDF5130, and SP are mixed at a mass ratio of 90:7:3, and a certain amount of NMP is added according to a solid content of 35%. After the slurry is mixed evenly, it is coated evenly onto aluminum foil using a coating machine, with a coating thickness of 200μm. Then, the electrode is placed in a forced-air drying oven at 120℃ for 12 hours to allow the NMP to completely evaporate. The dried electrode is then rolled to maintain the compaction of the positive electrode within the range of 1.9±0.1g / cm³. Finally, the positive electrode is cut into 12mm round pieces, and the mass of each round piece is recorded. The round pieces are then placed in gloves for later use.

[0103] ② Button Cell Assembly: CR2016 button half-cells were assembled in a glove box under an Ar protective atmosphere. The electrolyte was prepared by dissolving 1M LiPF6 in a solvent mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. The separator used was a Cellgard 2325 PP-PE-PP composite separator, and the negative electrode was a 15mm diameter lithium sheet.

[0104] ③ Electrochemical Performance Testing: The assembled batteries were tested using a Xinwei battery system (MIHW-200-160CH-B). Constant current / constant voltage charge-discharge rate testing was conducted at 25℃ within a voltage range of 2.5-4.5V, with a theoretical specific capacity of 170mAh / g and test rates of 0.1C / 1C / 3C / 5C. 200 cycles of 1C constant current / constant voltage charge-discharge were performed at 45℃ to complete the high-temperature cycling performance test of the material.

[0105] Test results are as follows Figure 3-5 As shown.

[0106] After composite coating of sodium aluminosilicate and magnesium aluminate with lithium manganese iron phosphate feedstock, the rate performance and cycling performance of the material were significantly improved. Results showed that the electrochemical performance was optimal when the coating amount of sodium aluminosilicate and magnesium aluminate was 1%:1% (Example 1). Compared with Comparative Example 1, the 5C discharge specific capacity of the composite-coated Examples 1, 3, and 4 was 27.5, 19.8, and 23.0 mAh / g higher, respectively; the retention rate after 200 high-temperature cycles was more than 20% higher; and the highest 0.1C constant current charge-in ratio reached 93.3%. The excellent rate performance of the composite-coated material is attributed to the wider lithium-ion diffusion channels of sodium aluminosilicate and the aluminum-based fast ion conductor formed by the reaction of magnesium aluminate and the lithium replenishment agent. Furthermore, during the high-temperature sintering process, Na… + / Al 3+ / Mg 2+Multi-ion co-intercalation into the near-surface layer of lithium manganese iron phosphate primary particles reduces Li-Fe antisite defects and broadens the lithium-ion transport path, accelerating charge separation and transfer at the interface. Simultaneously, sodium aluminosilicate and magnesium aluminate form a protective film on the material surface, effectively preventing electrolyte corrosion. Multi-ion intercalation also allows for fine-tuning of lattice parameters, stabilizing the crystal structure, and suppressing the Jahn-Teller effect, thereby giving the material excellent high-temperature cycling performance.

[0107] Compared to using a single coating agent, the combined use of sodium aluminosilicate and magnesium aluminate maximizes the advantages of both. In Example 1, compared to Comparative Examples 2 and 3, the former exhibited approximately 9 mAh / g higher 5C capacity and 8%-14% higher capacity retention after 200 cycles. When the total coating agent content reached 3%, an excessively thick coating layer began to hinder Li... + As the coating diffuses, the advantage of the coating agent in terms of rate capability is gradually offset, so the rate capability of Example 3 is slightly higher than that of Comparative Example 2. When the amount of coating agent reaches 4% (Comparative Example 4), the damage to the carbon layer caused by the coating agent and the excessively thick coating layer have seriously reduced the electronic conductivity and ionic conductivity of the material, resulting in a 5C capacity of only 107 mAh / g.

[0108] Sintering temperature affects the contact tightness between the coating agent and the substrate, and also weakens the ion intercalation reaction near the substrate surface. Results show that a sintering temperature of at least 650℃ is required for the coating agent to function. When the sintering temperature is 600℃ (Comparative Example 5), most of the coating agent is merely adsorbed on the substrate surface, failing to form a dense coating layer adhered to the substrate, and no ion intercalation reaction occurs. Therefore, the 5C capacity of the material sintered at 600℃ is only about 80% of that at 730℃, the retention rate after 200 cycles is only 78%, and the constant current infiltration ratio is comparable to that of the uncoated material.

[0109] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A fast-ion conductor-stabilizer composite-coated lithium manganese iron phosphate material, characterized in that, The lithium manganese iron phosphate material includes a lithium manganese iron phosphate core and a coating layer on the surface of the lithium manganese iron phosphate core. The coating layer is obtained by coating the surface of the lithium manganese iron phosphate core with a mixture of sodium aluminosilicate, magnesium aluminate, coating carbon source, and lithium supplement, followed by sintering. The preparation method of the fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material includes the following steps: S1. Lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source, and lithium supplementer are added to a solvent to obtain a mixed slurry. The mixed slurry is then sand-milled and spray-dried to obtain a post-processed spherical precursor. S2. The post-processed spherical precursor is sintered to obtain lithium manganese iron phosphate material with fast ion conductor-stabilizer composite coating. In step S1, the preparation method of lithium manganese iron phosphate raw material includes the following steps: adding lithium source, manganese source, iron source and phosphorus source into solvent and stirring, then adding carbon source and stirring, grinding the obtained slurry and spray drying it to obtain spherical lithium manganese iron phosphate precursor; then sintering the spherical lithium manganese iron phosphate precursor to obtain spherical lithium manganese iron phosphate raw material. In step S1, the amount of sodium aluminosilicate is 0.1% to 2% of the mass of lithium manganese iron phosphate raw material; the amount of magnesium aluminate is 0.1% to 2% of the mass of lithium manganese iron phosphate raw material; the total mass ratio of sodium aluminosilicate and magnesium aluminate does not exceed 3% of the mass of lithium manganese iron phosphate raw material. In step S2, the sintering temperature is 650-750℃ and the time is 6h~15h.

2. The lithium manganese iron phosphate material according to claim 1, characterized in that, Sodium, aluminum, and magnesium ions are embedded in the near-surface crystal of the lithium manganese iron phosphate core. And / or, the lithium supplement includes one or more of lithium carbonate, lithium oxalate, lithium acetate, lithium phosphate, lithium sulfate, lithium dihydrogen phosphate, and lithium difluorooxalate borate; And / or, the coated carbon source includes one or more of monosaccharides, disaccharides, polysaccharides, and organic acids; And / or, the particle size of the lithium manganese iron phosphate core is 100~550nm; And / or, the thickness of the coating layer is 2 ~ 13 nm.

3. The lithium manganese iron phosphate material according to claim 1, characterized in that, The coated carbon source includes one or more of polymers and conductive agents.

4. A method for preparing a fast-ion conductor-stabilizer composite-coated lithium manganese iron phosphate material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium aluminate, coated carbon source, and lithium supplementer are added to a solvent to obtain a mixed slurry. The mixed slurry is then sand-milled and spray-dried to obtain a post-processed spherical precursor. S2. The post-processed spherical precursor is sintered to obtain lithium manganese iron phosphate material with fast ion conductor-stabilizer composite coating. In step S1, the preparation method of lithium manganese iron phosphate raw material includes the following steps: adding lithium source, manganese source, iron source and phosphorus source into solvent and stirring, then adding carbon source and stirring, grinding the obtained slurry and spray drying it to obtain spherical lithium manganese iron phosphate precursor; then sintering the spherical lithium manganese iron phosphate precursor to obtain spherical lithium manganese iron phosphate raw material. In step S1, the amount of sodium aluminosilicate is 0.1% to 2% of the mass of lithium manganese iron phosphate raw material; the amount of magnesium aluminate is 0.1% to 2% of the mass of lithium manganese iron phosphate raw material; the total mass ratio of sodium aluminosilicate and magnesium aluminate does not exceed 3% of the mass of lithium manganese iron phosphate raw material. In step S2, the sintering temperature is 650-750℃ and the time is 6h~15h.

5. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that, In step S1, the amount of carbon source used for coating is 2% to 15% of the mass of lithium manganese iron phosphate raw material; And / or, the amount of lithium supplementer used is 0.5%-3% of the mass of lithium manganese iron phosphate raw material; And / or, the solids content of the mixed slurry is 20wt%-50wt%; And / or, the particle size of the ground mixture is 250-500 nm; And / or, spray drying parameters: inlet air temperature 180-260℃, outlet air temperature 85-95℃, induced draft fan frequency 30-50HZ, atomizer air pressure 0.10-0.45MPa.

6. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that, In the preparation of lithium manganese iron phosphate raw material in step S1, the stoichiometric ratio of each element in the raw material is Li:(Mn + Fe):P =1-1.06:1:1-1.05; where Mn:Fe = 0.1-0.9:0.1-0.9; And / or, the carbon source includes one or more of monosaccharides, disaccharides, polysaccharides, and organic acids; And / or, the total mass of carbon source is 3% to 15% of the mass of dry powder; the dry powder includes lithium source, manganese source, iron source and phosphorus source; And / or, mill to a particle size of 150-500 nm; And / or, sintering temperature 450-750℃, sintering time 6-15h; And / or, the obtained spherical lithium manganese iron phosphate raw material is subjected to air jet milling to obtain nano-lithium manganese iron phosphate raw material.

7. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that, The coated carbon source includes one or more of polymers and conductive agents.

8. A positive electrode sheet, characterized in that, Including lithium manganese iron phosphate materials with fast ion conductor-stabilizer composite coating as described in any one of claims 1-3.

9. A battery, characterized in that, Including the positive electrode sheet as described in claim 8.

10. The application of a fast-ion conductor-stabilizer composite coated lithium manganese iron phosphate material as described in any one of claims 1-3 in the preparation of lithium-ion batteries.

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