Fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material as well as preparation method and application thereof

Abstract

The invention relates to a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material as well as a preparation method and application thereof. The lithium manganese iron phosphate material comprises a lithium manganese iron phosphate inner core and a coating layer on the surface of the lithium manganese iron phosphate inner core, the coating layer is obtained by mixing sodium aluminosilicate, magnesium metaaluminate, a coating carbon source and a lithium supplement agent, coating the surface of the lithium manganese iron phosphate inner core with the mixture, and performing sintering treatment. According to the invention, sodium aluminosilicate and magnesium metaaluminate are combined with conductive carbon to carry out co-coating treatment on lithium manganese iron phosphate, and in a high-temperature sintering process, part of Na < + > / Al < 3 + > / Mg < 2 + > multi-ions are co-embedded into a near surface layer of a lithium manganese iron phosphate crystal, so that a unit cell structure which is more stable in structure and easier in Li < + > diffusion is formed. In the high-temperature sintering process, part of magnesium metaaluminate reacts with the lithium supplement agent to form an Al-based fast ion conductor, and sodium aluminosilicate has a wider Li < + > diffusion channel, so that the material has excellent rate capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery cathode material, and particularly relates to a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material and a preparation method and application thereof. BACKGROUND

[0002] Lithium manganese iron phosphate (LiMn x Fe 1-x PO4) as a lithium ion battery cathode material, has a high voltage platform and energy density, and is considered as a potential next-generation cathode material. Compared with lithium iron phosphate, the voltage platform is about 0.6V higher, and the mass energy density can be increased by 10-20%. At present, the common method for preparing lithium manganese iron phosphate is to mix iron source, manganese source, phosphorus source, lithium source and carbon source in proportion on the basis of the lithium iron phosphate preparation process in the wet grinding stage, and to obtain the product through the steps of spray drying, atmosphere sintering and crushing. However, the lithium manganese iron phosphate material itself has many performance problems, such as high specific surface area and high powder resistivity of the material, which leads to poor processing performance and low production efficiency in the battery preparation process. At the same time, due to the absence of continuous coplanar octahedral network in the structure, the movement of lithium ions in the one-dimensional channel is limited, resulting in poor conductivity of the material. In order to improve the performance of lithium manganese iron phosphate, the existing technology optimizes the carbon coating means to improve the conductivity of lithium manganese iron phosphate material. By using different types of carbon sources or batch coating, the carbon forms a uniform coating layer on the surface of the material particles, thereby reducing the material resistivity to a certain extent. However, single carbon coating can only improve the electronic conductivity of the material, and cannot fully solve the problems of low ionic conductivity and manganese dissolution of lithium manganese iron phosphate.

[0003] Lithium manganese iron phosphate (LiMn x Fe 1-x PO4) has the following problems: Conductivity and ion transport problem: although carbon coating can reduce the resistivity, the lithium manganese iron phosphate itself lacks continuous coplanar octahedral network in the structure, and the transmission of lithium ions in the one-dimensional channel is severely limited, which leads to the fact that the lithium ion diffusion rate cannot meet the demand when the material is charged and discharged at high power, thereby limiting the rate performance of the battery.

[0004] Insufficient structural stability: during the charging and discharging of the battery, the lithium manganese iron phosphate is eroded by the electrolyte, and there is a Jahn-Teller effect of Mn 3+ , which leads to the dissolution of manganese elements, and further destroys the crystal structure of the material, thereby shortening the cycle life of the battery. The commonly used carbon coating method has limited effect on inhibiting manganese dissolution and maintaining structural stability.

[0005] Comprehensive performance bottleneck: due to the limitation of conductivity and structural stability, the capacity development, rate performance and cycle stability of lithium manganese iron phosphate material are difficult to further improve, which cannot meet the demand of high performance and long service life of battery in high requirement application scenarios such as electric vehicles and large-scale energy storage. SUMMARY

[0006] The purpose of the present application is to solve the problems existing in the prior art, and to provide a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material, a preparation method and application thereof, especially a lithium manganese iron phosphate positive electrode material with unique composite coating structure and multi-ion co-embedding synergistic effect and a preparation process thereof.

[0007] The purpose of the present application can be achieved by the following scheme: The present application provides a fast ion conductor-stabilizer composite coated lithium manganese iron phosphate material, which comprises 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 mixing sodium silicoaluminate, magnesium metahydroxide, a carbon source for coating and a lithium supplementing agent, and then coating on the surface of the lithium manganese iron phosphate core, and then sintering.

[0008] In the obtained coating layer, sodium silicoaluminate and magnesium metahydroxide can form a protective film on the surface of the material, effectively block the corrosion of electrolyte, inhibit the dissolution of manganese, enhance the stability of the material structure, improve the cycle performance, so sodium silicoaluminate and magnesium metahydroxide can be used as stabilizers; among LiAlPO4, LiAlO2 and sodium silicoaluminate formed by the reaction of the lithium supplementing agent and magnesium metahydroxide, Li + can diffuse faster, so they act as fast ion conductors.

[0009] As an embodiment of the present application, sodium ions (Na + ), aluminum ions (Al 3+ ) and magnesium ions (Mg 2+ ) are embedded in the crystals in the near-surface layer of the lithium manganese iron phosphate core.

[0010] The embedding of sodium ions (Na + ), aluminum ions (Al 3+ ) and magnesium ions (Mg 2+ ) is achieved by coating sodium silicoaluminate and magnesium metahydroxide on the surface of lithium manganese iron phosphate particles, and then sintering (temperature 650-750℃, time 6h~15h). During the sintering process, the above-mentioned ions are embedded in the crystals in the near-surface layer of the lithium manganese iron phosphate core.

[0011] As an embodiment of the present application, 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.

[0012] As an embodiment of the present application, the conductive carbon is coated carbon source coated on the surface of lithium iron manganese phosphate raw material particles, and obtained by sintering treatment (temperature 650-750℃, time 6h~15h).

[0013] As an embodiment of the present application, the lithium supplement agent includes one or more of lithium carbonate, lithium oxalate, lithium acetate, lithium phosphate, lithium sulfate, lithium dihydrogen phosphate, lithium difluoro oxalate borate.

[0014] As an embodiment of the present application, the coated carbon source includes one or more of monosaccharide, disaccharide, polysaccharide, organic acid, polymer, conductive agent.

[0015] The monosaccharide includes one or more of glucose, fructose; The disaccharide includes one or more of sucrose, lactose; The polysaccharide includes starch; The organic acid includes one or more of citric acid, tannic acid, oleic acid, stearic acid, malic acid; The polymer includes one or more of polyvinylpyrrolidone, polyethylene glycol (PEG), polyvinyl alcohol, polyacrylic acid, phenolic resin; The conductive agent includes one or more of acetylene black, conductive carbon black, Super P, carbon nanotube, graphene, graphite.

[0016] Preferably, the coated carbon source includes one or more of glucose, PEG, tannic acid. The coated carbon source is preferably glucose and PEG6000; the mass ratio of glucose and PEG6000 is 1:0.25~1.50.

[0017] The present application provides a preparation method of a lithium iron manganese phosphate material coated with a fast ion conductor-stabilizer composite, comprising the following steps: S1, adding lithium iron manganese phosphate raw material, sodium aluminosilicate, magnesium metaaluminate, coated carbon source, lithium supplement agent into a solvent to obtain a mixed slurry, and then sand milling and spray drying the mixed slurry to obtain a post-processing spherical precursor; S2, sintering the post-processing spherical precursor to obtain the lithium iron manganese phosphate material coated with the fast ion conductor-stabilizer composite.

[0018] As an embodiment of the present application, in step S1, The amount of sodium aluminosilicate is 0.1%-3% of the mass of the lithium iron manganese phosphate raw material, preferably 0.5%-2%; The amount of magnesium metaaluminate is 0.1%-3% of the mass of the lithium iron manganese phosphate raw material, preferably 0.5%-2%; The amount of coated carbon source is 2%-15% of the mass of the lithium iron manganese phosphate raw material, preferably 7.5%-15%, more preferably 10%-15%.

[0019] The amount of the lithium supplement agent is 0.5% to 3% of the mass of the lithium manganese iron phosphate raw material, preferably 0.5% to 1.1%, and more preferably 0.9% to 1.1%.

[0020] When the amount of the sodium aluminosilicate and magnesium metasilicate as the coating agent is too large, on the one hand, the excess coating agent particles adhere to the surface of the lithium manganese iron phosphate nanoparticles or fill the gaps between the nanoparticles, which is invalid coating. On the other hand, the too thick coating layer hinders the embedding and extraction of lithium ions, resulting in a slow charge transfer speed at the interface during the charging and discharging process, poor rate and cycle performance of the material, and reduced efficiency.

[0021] Preferably, the total mass of the sodium aluminosilicate and magnesium metasilicate accounts for no more than 3% of the lithium manganese iron phosphate raw material, preferably 2% to 3%.

[0022] As an embodiment of the present application, in step S1, the lithium supplement agent includes one or more of lithium carbonate, lithium oxalate, lithium acetate, lithium phosphate, lithium sulfate, lithium dihydrogen phosphate, and lithium difluoro oxalate borate.

[0023] As an embodiment of the present application, in step S1, the solvent includes one or more of water, ethanol, and methanol.

[0024] As an embodiment of the present application, in step S1, the solid content of the mixed slurry is 20 wt% to 50 wt%.

[0025] As an embodiment of the present application, in step S1, the particle size of the mixed slurry after sanding is 250 nm to 500 nm.

[0026] As an embodiment of the present application, in step S1, the parameters of the spray drying are as follows: the inlet air temperature is 180 to 260℃, the outlet air temperature is 85 to 95℃, the frequency of the air blower is 30 to 50 HZ, and the pressure of the atomizer is 0.10 to 0.45 MPa. Preferably, the inlet air temperature is 225℃, the outlet air temperature is 91℃, the frequency of the air blower is 45 HZ, and the pressure of the atomizer is 0.2 MPa.

[0027] As an embodiment of the present application, in step S2, the sintering temperature is 650 to 750℃, and the time is 6 h to 15 h. The heating rate is 2℃ / min.

[0028] At the sintering temperature of the present application, part of the Na + / Al 3+ / Mg 2+The multi-ion co-embedded manganese iron lithium phosphate crystal near the surface layer, the capacity of the obtained manganese iron lithium phosphate material is higher, the rate is better, and the cycle is better. If the sintering temperature is too low, on the one hand, the fusion effect of the coating agent and the manganese iron lithium phosphate raw material is poor, and the coating layer is easy to fall off; on the other hand, the lower temperature cannot realize the near-surface embedding of ions. If the sintering temperature is too high, the nanoparticles of the manganese iron lithium phosphate raw material are seriously adhered or even secondarily fused, which is not conducive to the diffusion of lithium ions, resulting in poor material rate and cycle.

[0029] As an embodiment of the present application, in step S1, the preparation method of the manganese iron lithium phosphate raw material comprises the following steps: The lithium source, the manganese source, the iron source and the phosphorus source are added into the solvent and stirred uniformly, and then the carbon source is added. The obtained slurry is sand-milled and then spray-dried to obtain a spherical manganese iron lithium phosphate precursor. The spherical manganese iron lithium phosphate precursor is sintered to obtain a spherical manganese iron lithium phosphate raw material.

[0030] 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.

[0031] Preferably, the lithium source includes one or more of lithium carbonate, lithium acetate, lithium phosphate, lithium citrate, and lithium dihydrogen phosphate.

[0032] Preferably, the manganese source includes one or more of trimanganese tetraoxide, manganese carbonate, manganese oxalate, and manganese iron precursor.

[0033] Preferably, the iron source includes one or more of iron phosphate, diiron trioxide, iron sulfate, ferrous oxalate, and manganese iron precursor (manganese iron phosphate, etc.).

[0034] Preferably, the phosphorus source includes one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, lithium phosphate, and phosphoric acid.

[0035] Preferably, the solvent is water.

[0036] Preferably, the carbon source of the raw material includes one or more of monosaccharide, disaccharide, polysaccharide, organic acid, polymer, and conductive agent. The monosaccharide includes one or more of glucose and fructose; the disaccharide includes one or more of sucrose and lactose; the polysaccharide includes starch; the organic acid includes one or more of citric acid, tannic acid, oleic acid, stearic acid, and malic acid; the polymer includes one or more of polyvinylpyrrolidone, polyethylene glycol (PEG), polyvinyl alcohol, polyacrylic acid, and phenolic resin; and the conductive agent includes one or more of acetylene black, conductive carbon black, Super P, carbon nanotube, graphene, and graphite.

[0037] Preferably, the carbon source comprises one or more of glucose, PEG6000, 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%-5%, more preferably 3.5%-4.5%. Preferably, glucose and PEG6000; the mass ratio of glucose and PEG6000 is 1:0.5-1.5.

[0038] Preferably, sand grinding to a particle size of 150-500nm.

[0039] Preferably, the parameters of spray drying are: inlet air temperature 180-260℃, outlet air temperature 85-95℃, air blower frequency 30-50HZ, atomizer gas pressure 0.10-0.45MPa. Preferably, the inlet air temperature is 225℃, the outlet air temperature is 91℃, the air blower frequency is 45HZ, and the atomizer gas pressure is 0.2MPa.

[0040] Preferably, the sintering temperature is 450-750℃, the sintering time is 6-15h, Preferably, the obtained spherical manganese iron lithium phosphate raw material is subjected to airflow crushing treatment, and the crushing particle size D50 is controlled to be 1-1.3μm, to obtain a nanometer manganese iron lithium phosphate raw material.

[0041] The application also provides a positive electrode sheet, which comprises the fast ion conductor-stabilizer composite coated manganese iron lithium phosphate material.

[0042] The application also provides a battery comprising the positive electrode sheet.

[0043] The application also provides application of the fast ion conductor-stabilizer composite coated manganese iron lithium phosphate material in preparation of a lithium ion battery.

[0044] Compared with the prior art, the application has the following beneficial effects: (1) The core of the application is to innovatively use sodium silicoaluminate and magnesium metahydroxide combined with conductive carbon to co-coat the manganese iron lithium phosphate, and in the high-temperature coating and sintering process, part of the Na + / Al 3+ / Mg 2+ multi-ion co-embedded manganese iron lithium phosphate crystal near-surface structure. Sodium silicoaluminate and magnesium metahydroxide have good chemical stability and mechanical properties, can form a firm protective film on the surface of the material, effectively block the corrosion of the electrolyte, inhibit the dissolution of manganese elements, and significantly enhance the structural stability of the material. In the high-temperature sintering process, part of the magnesium metahydroxide reacts with the lithium supplementing agent to form an Al-based fast ion conductor, plus the wider Li+ diffusion channel of sodium silicoaluminate, so that the material has excellent rate performance.

[0045] (2) In the high-temperature sintering process, part of the Na + / Al3+ / Mg 2+ Multi-ion co-embedded manganese iron phosphate crystal near the surface layer, stronger metal bond energy substitution, not only stabilizes the crystal structure, inhibits the Jahn-Teller effect of Mn 3+ , but also widens the lithium ion transmission path, greatly improves the lithium ion diffusion rate. The comprehensive coating material has good chemical stability and ion conductivity, and the multi-ion near-surface synergistic co-doping comprehensively improves the capacity, rate and cycle performance of the manganese iron phosphate material. BRIEF DESCRIPTION OF DRAWINGS

[0046] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the following drawings: Figure 1 TEM image of the finished product of Comparative Example 1; Figure 2 TEM image of the finished product of Example 1; Figure 3 Constant current injection ratio test of the inventive examples and comparative examples; Figure 4 Rate performance test of the inventive examples and comparative examples; Figure 5 Cycle performance test of the inventive examples and comparative examples. DETAILED DESCRIPTION

[0047] The present application will be described in detail below with reference to the drawings and specific examples. The following examples are implemented on the premise of the technical solution of the present application, and provide detailed implementation methods and specific operation processes, which will help those skilled in the art to further understand the present application. It should be pointed out that the protection scope of the present application is not limited to the following examples, and several adjustments and improvements made on the premise of the concept of the present application all belong to the protection scope of the present application.

[0048] Example 1 I. Preparation of manganese iron phosphate raw materials (primary sintering) (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.

[0049] (2) Preparation of manganese iron phosphate raw materials:

[0050] ②The precursor obtained in the previous step is sintered at high temperature under an inert atmosphere. The sintering process is as follows: the temperature is raised from room temperature to 600°C at a rate of 2°C / min, and the temperature is maintained at 600°C for 8h, to obtain spherical materials. Finally, the spherical materials are crushed, and the crushed particle size D50 is controlled to be 1-1.3μm, to obtain nanometer lithium manganese iron phosphate raw materials.

[0051] II. Fast ion conductor composite coating post-treatment (secondary sintering) (1) 10Kg of lithium manganese iron phosphate raw materials, 0.104Kg of lithium carbonate, 0.600Kg of glucose, 0.600Kg of PEG6000, 0.1Kg of sodium silicoaluminate, and 0.1Kg of magnesium metaaluminate are weighed.

[0052] (2) Preparation of lithium manganese iron phosphate material: ① 16.7Kg of water is added to the sand mill tank, and then the above materials are added in sequence to obtain a secondary slurry. The mass ratio of lithium manganese iron phosphate raw materials, sodium silicoaluminate, magnesium metaaluminate, coating carbon source (glucose and PEG6000), and lithium supplement (lithium carbonate) is 1:1%:1%:12%:1.04%, and the mass ratio of glucose and PEG6000 is 1:1.

[0053] Then the secondary slurry is pumped into the sand mill for single-tank circulation fine grinding (zirconium beads with a diameter of 0.3-0.4mm), and the particle size D50 is ground to 400nm. Finally, the ground slurry is subjected to two-fluid spray drying, the inlet air temperature is controlled at 225°C, the outlet air temperature is controlled at 91°C, the frequency of the air blower is controlled at 45HZ, and the pressure of the atomizer is controlled at 0.15MPa, to obtain a post-treated spherical precursor.

[0054] ​②Sintering the post-treated precursor under inert atmosphere. The sintering process is: heating from room temperature to 730℃ at a rate of 2℃ / min, and keeping at 730℃ for 10h. Finally, the fast ionic conductor composite coated lithium manganese iron phosphate material is obtained, in which the particle size of the inner core is 150-350nm, and the thickness of the coating layer is about 7nm, and the TEM image is shown in Figure 2 .

[0055] Example 2 The difference between this example and Example 1 is that, in the first sintering, tannic acid and glucose are used as the carbon source in the batching process, the total mass of the carbon source is 3% of the total weight of the dry powder, and the mass ratio of tannic acid to glucose is 1:4; in the second sintering, tannic acid and glucose are used as the coating carbon source, the mass ratio of tannic acid to glucose is 1:4, and the total mass of the coating carbon source is 7.5% of the lithium manganese iron phosphate raw material.

[0056] Example 3 The difference between this example and Example 1 is that, in the second sintering, the mass ratio of lithium manganese iron phosphate raw material, sodium silicoaluminate, magnesium metasilicate, coating carbon source, and lithium supplementing agent is 1:2%:1%:12%:1.04%.

[0057] Example 4 The difference between this example and Example 1 is that, in the second sintering, the mass ratio of lithium manganese iron phosphate raw material, sodium silicoaluminate, magnesium metasilicate, coating carbon source, and lithium supplementing agent is 1:0.5%:1.5%:12%:1.04%.

[0058] Example 5 The difference between this example and Example 1 is that, in the second sintering, the temperature is 650℃.

[0059] Comparative Example 1 The difference between this comparative example and Example 1 is that, in the second sintering, there is no coating agent, and the mass ratio of lithium manganese iron phosphate raw material, sodium silicoaluminate, magnesium metasilicate, coating carbon source, and lithium supplementing agent is 1:0%:0%:12%:1.04%. The TEM image of the obtained lithium manganese iron phosphate material is shown in Figure 1 .

[0060] Comparative Example 2 The difference between this comparative example and Example 1 is that, in the second sintering, there is only a single coating agent, sodium silicoaluminate, and the mass ratio of lithium manganese iron phosphate raw material, sodium silicoaluminate, magnesium metasilicate, coating carbon source, and lithium supplementing agent is 1:2:0%:12%:1.04%.

[0061] Comparative Example 3 The difference between the present comparative example and Example 1 is that only single coating agent magnesium meta-aluminate is used in the secondary sintering, and the mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium meta-aluminate, coated carbon source, and lithium supplementing agent is 1:0:2%:12%:1.04%.

[0062] Comparative Example 4 The difference between the present comparative example and Example 1 is that in the secondary sintering, the mass ratio of lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium meta-aluminate, coated carbon source, and lithium supplementing agent is 1:2%:2%:12%:1.04%.

[0063] Comparative Example 5 The difference between the present comparative example and Example 1 is that in the secondary sintering, the sintering temperature is 600℃ (a lower secondary sintering temperature cannot promote the Na + / Al 3+ / Mg 2+ in the coating agent to be embedded into the near-surface structure of the substrate).

[0064] Performance test: (1) Test method: The positive electrode materials obtained in the examples and comparative examples are assembled into CR2016 button-type half-batteries and subjected to electrochemical tests, and the installation sequence is as follows.

[0065] ① Slurry preparation: the positive electrode material, PVDF5130, and SP are mixed in 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, it is uniformly coated on an aluminum foil by a coating machine, and the coating knife thickness is 200μm. Then the electrode sheet is placed in a forced air drying oven at 120℃ for 12h to completely volatilize the NMP. The dried electrode sheet is rolled to keep the positive electrode sheet in the range of 1.9±0.1g / cm³. Finally, the positive electrode sheet is cut into 12mm round pieces and the mass of each round piece is recorded, and the round pieces are placed in a glove for standby.

[0066] ② Button cell assembly: CR2016 button-type half-batteries are assembled in an Ar-protected glove box. The electrolyte is 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 is a PP-PE-PP composite separator Cellgard 2325, and the negative electrode is a lithium sheet with a diameter of 15mm.

[0067] ③ Electrochemical performance test: The assembled battery was tested using a new battery system (MIHW-200-160CH-B). The rate test was carried out at 25°C in the voltage range of 2.5-4.5V by constant current-constant voltage charging-constant current discharging, with the theoretical specific capacity of 170mAh / g and the test rate of 0.1C / 1C / 3C / 5C. The high-temperature cycle performance test of the material was completed by 1C constant current-constant voltage charging-constant current discharging for 200 cycles at 45°C.

[0068] The test results are shown in Table 1. Figures 3-5

[0069] After the raw material of lithium manganese iron phosphate is coated with sodium silicoaluminate and magnesium meta-aluminate, the rate and cycle performance of the material are significantly improved. The results show that when the coating amount of sodium silicoaluminate and magnesium meta-aluminate is 1%:1% (Example 1), the electrochemical performance is optimal. Compared with Comparative Example 1, the 5C discharge specific capacity of the composite coated Example 1, 3 and 4 is 27.5, 19.8 and 23.0 mAh / g respectively, the high-temperature cycle retention rate of 200 cycles is all above 20%, and the 0.1C constant current charge-in ratio is up to 93.3%. The excellent rate performance of the composite coated material is due to the wider lithium ion diffusion channel of sodium silicoaluminate and the aluminum-based fast ion conductor generated by the reaction of magnesium meta-aluminate and the lithium supplementing agent. On the other hand, during the high-temperature sintering process, Na + / Al 3+ / Mg 2+ Multi-ion co-embedded in the near-surface layer of lithium manganese iron phosphate primary particles reduces the Li-Fe anti-site defects in the near-surface layer and widens the lithium ion transmission path, accelerating the charge separation and transfer process at the interface. At the same time, sodium silicoaluminate and magnesium meta-aluminate can form a protective film on the surface of the material, effectively blocking the corrosion of the electrolyte, and the multi-ion embedding can fine-tune the lattice parameters, stabilize the crystal structure and suppress the Jahn-Teller effect, so that the material has excellent high-temperature cycle performance.

[0070] Compared with the use of a single coating agent, the combined use of sodium silicoaluminate and magnesium meta-aluminate can maximize the advantages of both. Compared with Comparative Examples 2 and 3, the 5C capacity of Example 1 is about 9mAh / g higher than that of the former, and the cycle capacity retention rate of 200 cycles is 8%-14% higher. When the total amount of coating agent reaches 3%, the diffusion of Li + is hindered by the too thick coating layer, and the advantage of the coating agent in terms of rate is gradually offset, so the rate of Example 3 is slightly improved compared with Comparative Example 2. When the amount of coating agent reaches 4% (Comparative Example 4), the destruction of the coating agent to the carbon layer and the too thick coating layer have seriously reduced the electronic conductivity and ionic conductivity of the material, resulting in a 5C capacity of only 107mAh / g.

[0071] ​The sintering temperature affects the contact tightness of the coating agent and the substrate, and also weakens the ion intercalation reaction near the surface of the substrate. The results show that the sintering temperature should be at least 650°C to make the coating agent work. When the sintering temperature is 600°C (Comparative Example 5), most of the coating agent is only adsorbed on the surface of the substrate, and does not form a dense coating layer that fits the substrate, and the ion intercalation reaction does not occur. Therefore, the material 5C sintered at 600°C has a capacity of only about 80% of 730°C, and a retention rate of 200 cycles of only 78%, and a constant current injection ratio comparable to that of the uncoated material.

[0072] The above describes specific embodiments of the present application. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essential content of the present application.

Claims

1. A fast ion conductor-stabilizer composite-coated lithium manganese iron phosphate material, characterized in that: The lithium iron manganese phosphate material comprises a lithium iron manganese phosphate core and a coating layer on the surface of the lithium iron manganese phosphate core; The coating layer is obtained by mixing sodium aluminosilicate, magnesium metaaluminate, a coating carbon source and a lithium supplement agent, coating the mixture on the surface of the lithium manganese iron phosphate core, and then sintering the mixture.

2. The lithium manganese iron phosphate material according to claim 1, characterized in that Sodium ions, aluminum ions, and magnesium ions are embedded in the near-surface crystals 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 difluorooxalatoborate; and / or, the coated carbon source comprises one or more of monosaccharides, disaccharides, polysaccharides, organic acids, polymers, and conductive agents; and / or, the particle size of the lithium manganese iron phosphate core is 100 to 550 nm; And / or, the thickness of the coating layer is 2 ~13nm.

3. The lithium iron manganese phosphate material according to claim 2, characterized in that The embedding of sodium ions, aluminum ions, and magnesium ions is achieved by coating sodium aluminosilicate and magnesium aluminate on the surface of lithium manganese iron phosphate particles and then sintering them.

4. A method for preparing a fast ion conductor-stabilizer composite-coated lithium manganese iron phosphate material according to any one of claims 1 to 3, characterized in that: The steps include: S1. Adding lithium manganese iron phosphate raw material, sodium aluminosilicate, magnesium metaaluminate, coated carbon source, and lithium supplement agent into a solvent to obtain a mixed slurry, and then sand-milling and spray-drying the mixed slurry to obtain a post-processed spherical precursor; S2. Sintering the post-processed spherical precursor to obtain a fast ion conductor-stabilizer composite-coated lithium manganese iron phosphate material.

5. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that: In step S1, the amount of sodium aluminosilicate is 0.1% to 3% of the mass of the lithium manganese iron phosphate raw material; And / or, the amount of magnesium metaaluminate is 0.1% to 3% of the mass of the lithium manganese iron phosphate raw material; And / or, the amount of the coating carbon source is 2% to 15% of the mass of the lithium manganese iron phosphate raw material; And / or, the amount of lithium supplement is 0.5%-3% of the mass of lithium iron manganese phosphate raw material; and / or, the solid content of the mixed slurry is 20wt%-50wt%; and / or, the particle size of the mixed slurry after grinding is 250-500 nm; And / or, spray drying parameters: inlet air temperature 180-260°C, outlet air temperature 85-95°C, induced draft fan frequency 30-50 Hz, atomizer air pressure 0.10-0.45 MPa; And / or, in step S2, the sintering temperature is 650-750°C and the sintering time is 6 hours to 15 hours.

6. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that: In step S1, the preparation method of lithium manganese iron phosphate raw material includes the following steps: A lithium source, a manganese source, an iron source and a phosphorus source are added to a solvent and stirred, and then a carbon source is added and stirred. The obtained slurry is sand-milled and spray-dried to obtain a spherical lithium iron manganese phosphate precursor; and the spherical lithium iron manganese phosphate precursor is sintered to obtain a spherical lithium iron manganese phosphate raw material.

7. The method for preparing lithium manganese iron phosphate material according to claim 6, characterized in that: The stoichiometric ratio of each element in the raw material is Li: (Mn + Fe): P = 1-1.06: 1: 1-1.05; among which, Mn: Fe = 0.1-0.9: 0.1-0.9; and / or, the carbon source comprises one or more of monosaccharides, disaccharides, polysaccharides, organic acids, polymers, and conductive agents; and / or, the total mass of the carbon source is 3% to 15% of the mass of the dry powder; the dry powder includes a lithium source, a manganese source, an iron source, and a phosphorus source; and / or, sand-milling to a particle size of 150-500 nm; and / or, sintering temperature 450-750° C., sintering time 6-15 h; And / or, the obtained spherical lithium manganese iron phosphate raw material is subjected to air flow crushing treatment to obtain nano lithium manganese iron phosphate raw material.

8. A positive electrode plate, characterized in that: The invention comprises the lithium manganese iron phosphate material coated with a fast ion conductor-stabilizer composite as described in any one of claims 1 to 3.

9. A battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 8.

10. Use of the fast ion conductor-stabilizer composite-coated lithium manganese iron phosphate material according to any one of claims 1 to 3 in the preparation of lithium ion batteries.

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