Lithium ferrite lithium supplement, its preparation method and application

Abstract

The application belongs to the technical field of batteries, and particularly relates to a lithium-iron oxide lithium supplementing agent, a preparation method and application thereof. Compared with the prior art, a solid-state electrolyte coating layer is formed on the surface of a carbon-doped lithium-iron oxide material through a low-temperature molten salt method, air can be effectively isolated, the air stability of the material can be improved, the delithiation phenomenon can be reduced, the structural integrity and lithium supplementing performance of the material can be maintained, the lithium-iron oxide lithium supplementing agent combines the high theoretical lithium supplementing capacity of Li5FeO4 and the excellent ion conductivity of the solid-state electrolyte, the electrochemical performance of the material can be improved while maintaining high lithium supplementing capacity, and a new technical scheme is provided for the commercial application of high-energy-density lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a lithium iron ferrite lithium replenisher, its preparation method and application. Background Technology

[0002] In modern energy storage technology, lithium-ion batteries have become the dominant force due to their high energy density, long cycle life, and relatively mature technological foundation. To meet the ever-increasing demand for high energy density, researchers have been exploring cathode materials with higher theoretical specific capacities. Li5FeO4, as a cathode material with an olivine structure, has attracted much attention due to its high specific capacity and low-cost iron source.

[0003] However, Li5FeO4 materials face some challenges in practical applications, mainly including:

[0004] Air stability: Li5FeO4 readily reacts with moisture and carbon dioxide in the air, leading to delithiation of the material and the formation of LiFeO2, which affects its performance as a lithium supplement.

[0005] Structural stability: Li5FeO4 may undergo structural changes during charge and discharge, including phase transitions and volume expansion, which may lead to a decrease in the mechanical strength of the material, thereby affecting the cycle stability of the battery;

[0006] Interface reaction issues: Side reactions with the electrolyte may lead to the formation of an unstable SEI layer, increasing irreversible capacity loss in the battery;

[0007] Insufficient electronic and ionic conductivity: The low electronic and ionic conductivity limits the charge and discharge performance of Li5FeO4, especially under high rate conditions.

[0008] To address these issues, surface coating technology has been extensively studied. LATP, as a solid electrolyte material, possesses excellent lithium-ion conductivity and chemical stability, making it an ideal choice for coating modification. However, traditional LATP coating methods often require high-temperature treatment, which may lead to structural damage to the Li5FeO4 material and uneven coating layers. Summary of the Invention

[0009] In view of this, the technical problem to be solved by the present invention is to provide a lithium ferrite lithium supplement, its preparation method and application. The preparation method uses a low-temperature molten salt method and a rapid annealing method to coat LATP on the surface of Li5FeO4, so as to solve the shortcomings of Li5FeO4 as a lithium supplement in terms of air stability and lithium supplementation efficiency in the prior art.

[0010] This invention provides a method for preparing a lithium ferrite lithium supplement, comprising the following steps:

[0011] S1) The organic carbon source is mixed with iron oxide and calcined for the first time in a protective atmosphere to obtain carbon-loaded iron oxide material;

[0012] S2) The carbon-loaded iron oxide material is mixed with a lithium source and calcined a second time in a protective atmosphere to obtain a carbon-doped lithium iron oxide material.

[0013] S3) The mixed lithium salt and the raw material of the surface coating layer (excluding lithium element) are mixed for the first time, and then the lithium iron oxide material doped with carbon is added for the second mixing. After the mixture is calcined for the third time in an oxygen-containing atmosphere and cooled down, lithium iron ferrite lithium supplement is obtained. The mixed lithium salt includes a first lithium salt, a second lithium salt and a third lithium salt. The melting point of the first lithium salt is greater than that of the second lithium salt and the difference is greater than 100°C. The melting point of the third lithium salt is greater than that of the first lithium salt and the difference is greater than 100°C. The surface coating layer is a solid electrolyte.

[0014] Preferably, the mass ratio of the first lithium salt, the second lithium salt and the third lithium salt is (80~95):(3~15):(2~5).

[0015] Preferably, the organic carbon source is selected from one or more of glucose, polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, tannic acid, citric acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, and aniline;

[0016] The lithium source is selected from one or more of lithium oxide, lithium hydroxide, lithium oxalate, and lithium carbonate;

[0017] The first lithium salt is selected from lithium carbonate and / or lithium hydroxide;

[0018] The second lithium salt is selected from one or more of lithium nitrate, lithium squaric acid, lithium acetate, and lithium oxalate;

[0019] The third lithium salt is selected from lithium fluoride and / or lithium chloride.

[0020] Preferably, the mass ratio of the organic carbon source to iron oxide is (0.01~0.05):(1~5).

[0021] The molar ratio of iron oxide to lithium source in the carbon-supported iron oxide material is 1:(5~7).

[0022] Preferably, the mixing in step S1) is carried out in an organic solvent, and after drying, a first calcination is performed in a protective atmosphere; the ratio of iron oxide to organic solvent is (1~5) kg: (3~5) L; the mixing speed is 100~500 rpm; and the mixing time is 3~12 h.

[0023] The mixing in step S2) is carried out by grinding;

[0024] In step S3), the rotation speed for the first mixing is 500-1000 rpm; the mixing time for the first mixing is 1-10 min; the rotation speed for the second mixing is 2000-3000 rpm; and the mixing time for the second mixing is 20-60 min.

[0025] Preferably, the temperature of the first calcination is 300℃~500℃; the time of the first calcination is 3~6 h; and the heating rate of the first calcination is 1~10℃ / min.

[0026] The temperature of the second calcination is 650℃~850℃; the time of the second calcination is 12~30 h; and the heating rate of the second calcination is 1~10℃ / min.

[0027] The temperature of the third calcination is 500℃~700℃; the time of the third calcination is 6~15 h; and the heating rate of the third calcination is 1~10℃ / min.

[0028] Preferably, the cooling rate in step S3) is 20~40℃ / min.

[0029] Preferably, the surface coating layer is a lithium titanium aluminum phosphate solid electrolyte or a lithium lanthanum zirconium oxide solid electrolyte;

[0030] The total mass ratio of the mixed lithium salt and the raw material of the surface coating layer (excluding lithium elements) to the mass ratio of the carbon-doped lithium iron oxide material is (1~10):(8~12).

[0031] The present invention also provides a lithium ferrite supplement prepared by the above preparation method.

[0032] The present invention also provides a lithium-ion battery comprising the lithium ferrite supplement prepared by the above preparation method.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1) Improved air stability: This invention forms a solid electrolyte coating layer on the surface of carbon-doped lithium iron oxide materials using a low-temperature molten salt method, which can effectively isolate air, improve the air stability of the material, reduce delithiation, and maintain the structural integrity and lithium replenishment performance of the material.

[0035] 2) Optimizing Lithium Supplementation Efficiency: When Li5FeO4 is used as a lithium supplement agent, its lithium supplementation efficiency is limited by the material's electronic conductivity and ion diffusion properties. The low-temperature molten salt method used in this invention can achieve uniform coating of solid electrolyte at a lower temperature, which helps to improve the electronic conductivity and ion diffusion properties of carbon-doped lithium iron oxide materials, thereby optimizing lithium supplementation efficiency;

[0036] 3) Formation of a composite lithium replenishing agent: This invention proposes to use a low-temperature molten salt method to coat the surface of carbon-doped lithium iron oxide materials with a solid electrolyte to form a novel composite lithium replenishing agent. This composite lithium replenishing agent combines the high theoretical lithium replenishing capacity of Li5FeO4 with the excellent ionic conductivity of solid electrolytes, and can improve the electrochemical performance of materials while maintaining high lithium replenishing capacity;

[0037] 4) Expanding application scenarios: Through solid electrolyte coating modification, the composite lithium replenisher of the present invention not only has potential applications in high energy density lithium-ion batteries, but can also play a role in a wider range of application scenarios, such as in extreme temperature conditions or applications requiring higher safety.

[0038] 5) Lowering the delithiation energy barrier: The introduction of the solid electrolyte coating layer can lower the delithiation energy barrier of Li5FeO4, making it easier to release lithium ions during the electrochemical process, thereby more effectively compensating for the active lithium consumed by the formation of the negative electrode SEI during the first charge.

[0039] 6) Improve overall battery performance: By improving the air stability and lithium replenishment efficiency of the lithium replenishing agent, the composite lithium replenishing agent of the present invention helps to improve the initial coulombic efficiency and cycle stability of the battery, thereby improving the overall performance of the battery.

[0040] In summary, the low-temperature molten salt method of coating Li5FeO4 with a solid electrolyte to form a composite lithium replenisher provides a new technical solution for the commercial application of high-energy-density lithium-ion batteries by improving air stability and lithium replenishment efficiency. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] This invention provides a method for preparing a lithium ferrite supplement, comprising the following steps: S1) mixing an organic carbon source with iron oxide and performing a first calcination in a protective atmosphere to obtain a carbon-loaded iron oxide material; S2) mixing the carbon-loaded iron oxide material with a lithium source and performing a second calcination in a protective atmosphere to obtain a carbon-doped lithium iron oxide material; S3) performing a first mixing of a mixed lithium salt with a raw material for a surface coating layer to remove lithium elements, then adding the carbon-doped lithium iron oxide material for a second mixing, and performing a third calcination in an oxygen-containing atmosphere followed by cooling to obtain a lithium ferrite supplement; wherein the mixed lithium salt comprises a first lithium salt, a second lithium salt, and a third lithium salt; the melting point of the first lithium salt is greater than that of the second lithium salt and the difference is greater than 100°C; the melting point of the third lithium salt is greater than that of the first lithium salt and the difference is greater than 100°C; and the surface coating layer is a solid electrolyte.

[0043] The carbon coating on the surface of lithium-rich lithium iron ferrite increases the surface temperature of the lithium iron ferrite material. At the same time, a composite lithium salt is used to form a molten salt, which increases the internal reaction temperature and the fluidity of the lithium salt. A solid electrolyte coating layer is synthesized at low temperature. Finally, rapid annealing is used to cool down and construct internal defects, so that the solid electrolyte coating on the surface forms lithium ion channels, expands the lithium ion transport rate, and increases ionic conductivity.

[0044] After conventional lithium-rich lithium ferrite is replenished, inert lithium ferrite is formed. However, this invention uses a solid electrolyte to coat lithium-rich lithium ferrite. After lithium replenishment, the solid electrolyte can provide fast ion channels, mitigate the effects of inert matter, and reduce internal resistance.

[0045] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0046] An organic carbon source is mixed with iron oxide. The organic carbon source can be any organic carbon source known to those skilled in the art, and there are no special limitations. In this invention, it is preferably one or more of glucose, polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, tannic acid, citric acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, and aniline. The mass ratio of the organic carbon source to iron oxide is preferably (0.01~0.05):(1~5), more preferably (0.01~0.03):(1~3), even more preferably 0.01:(1~2), and most preferably 0.01:1. The mixing method can be any method known to those skilled in the art, and there are no special limitations. In this invention, liquid-phase mixing is preferred, specifically in an organic solvent, followed by drying. The organic solvent can be any organic solvent known to those skilled in the art, and there are no special limitations. In this invention, an alcohol solvent is preferred, more preferably ethanol. The ratio of iron oxide to organic solvent is preferably (1~5) kg:(3~5) L. In some embodiments provided by this invention, the ratio of iron oxide to organic solvent is specifically 1 kg:3 L or 1 kg: 1 L; the mixing speed is preferably 100~500 rpm, more preferably 200~500 rpm; the mixing time is preferably 3~12 h; the drying temperature is preferably 50℃~100℃; the drying time is preferably 12~24 h.

[0047] After drying, the material is preferably ground and then calcined for the first time in a protective atmosphere to obtain carbon-loaded iron oxide material. The protective atmosphere can be any atmosphere known to those skilled in the art and is not particularly limited. In this invention, nitrogen is preferred. The temperature of the first calcination is preferably 300℃~500℃. The time of the first calcination (i.e., the holding time) is preferably 3~6 h. The heating rate of the first calcination is preferably 1~10℃ / min, more preferably 2~8℃ / min, even more preferably 4~6℃ / min, and most preferably 5℃ / min.

[0048] The carbon-loaded iron oxide material is mixed with a lithium source and calcined a second time in a protective atmosphere to obtain a carbon-doped lithium iron oxide material. The lithium source can be any lithium source known to those skilled in the art and is not particularly limited; in this invention, it is preferably one or more of lithium oxide, lithium hydroxide, lithium oxalate, and lithium carbonate. The molar ratio of iron oxide to lithium source in the carbon-loaded iron oxide material is preferably 1:5 to 1:7, more preferably 1:5 to 1:6. The mixing is performed by grinding. The protective atmosphere can be any protective atmosphere known to those skilled in the art and is not particularly limited; in this invention, nitrogen is preferred. The temperature of the second calcination is preferably 650℃ to 850℃. The time of the second calcination (i.e., the holding time) is preferably 12 to 30 h, more preferably 12 to 24 h. The heating rate of the second calcination is 1 to 10℃ / min, more preferably 2 to 8℃ / min, even more preferably 4 to 6℃ / min, and most preferably 5℃ / min.

[0049] The mixed lithium salt is first mixed with the raw material for the surface coating layer to remove lithium elements; the mixed lithium salt includes a first lithium salt, a second lithium salt, and a third lithium salt; the melting point of the first lithium salt is greater than that of the second lithium salt by a difference greater than 100°C, preferably greater than 120°C; the melting point of the third lithium salt is greater than that of the first lithium salt by a difference greater than 100°C, preferably greater than 120°C; more specifically, the first lithium salt is preferably lithium carbonate and / or lithium hydroxide; the second lithium salt is preferably one or more of lithium nitrate, lithium squaric acid, lithium acetate, and lithium oxalate; the third lithium salt is preferably lithium fluoride and / or... Lithium chloride; the preferred mass ratio of the first lithium salt, the second lithium salt, and the third lithium salt is (80~95):(3~15):(2~5); in some embodiments provided by the present invention, the specific mass ratio of the first lithium salt, the second lithium salt, and the third lithium salt is 80:15:5 or 95:3:2; the surface coating layer is a solid electrolyte, preferably lithium titanium aluminum phosphate solid electrolyte or lithium lanthanum zirconium oxide solid electrolyte; when the surface coating layer is lithium titanium aluminum phosphate solid electrolyte, the raw materials other than the lithium salt preferably include an aluminum source, a titanium source, and a phosphorus source; the aluminum source can be any aluminum source well known to those skilled in the art, and there is no need for... With particular limitations, alumina is preferred in this invention; the titanium source can be any titanium source well known to those skilled in the art, and there are no particular limitations, but titanium oxide is preferred in this invention; the phosphorus source can be any phosphorus source well known to those skilled in the art, and there are no particular limitations, but ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate are preferred in this invention; the molar ratio of the mixed lithium salt, aluminum source, titanium source and ammonium dihydrogen phosphate is preferably x:y:z:3; x+z=3, y=x-1, y is 0.1~0.5, more preferably 0.2~0.4, and even more preferably 0.3~0.4; when the surface coating layer is lithium lanthanum zirconium oxide The solid electrolyte, excluding lithium salt, preferably includes a zirconium source and a lanthanum source; the zirconium source can be any zirconium source known to those skilled in the art, without any special limitations, and zirconium oxide is preferred in this invention; the lanthanum source can be any lanthanum source known to those skilled in the art, without any special limitations, and lanthanum oxide is preferred in this invention; the molar ratio of the mixed lithium salt, zirconium source and lanthanum source is preferably x1:y1:z1; x1+z1=10, y1=z1-1, y is preferably 1~2.5, more preferably 1.5~2.5, and even more preferably 2~2.5; the rotation speed of the first mixing is preferably 500~1000 rpm, more preferably 600~900 rpm, even more preferably 700~900 rpm, and even more preferably 800 rpm; the time of the first mixing is preferably 1~10 min, more preferably 3~8 min, even more preferably 4~6 min, and most preferably 5 min.

[0050] Then, the carbon-doped lithium iron oxide material is added for a second mixing; the preferred mass ratio of the total mass of the mixed lithium salt and the raw material for the surface coating layer (excluding lithium elements) to the carbon-doped lithium iron oxide material is (1~10):(8~12); in some embodiments provided by the present invention, the specific mass ratio of the total mass of the mixed lithium salt and the raw material for the surface coating layer (excluding lithium elements) to the carbon-doped lithium iron oxide material is 5:8, 7.5:12, 6.19:10, or 1:10; the preferred rotation speed for the second mixing is 2000~3000 rpm; in some embodiments provided by the present invention, the specific rotation speed for the second mixing is 2000 rpm, 2500 rpm, or 3000 rpm; the preferred time for the second mixing is 20~60 min, more preferably 30~60 min.

[0051] A third calcination is performed in an oxygen-containing atmosphere, followed by cooling to obtain a lithium ferrite supplement. The oxygen-containing atmosphere can be any atmosphere well-known to those skilled in the art and is not particularly limited; compressed air is preferred in this invention. The temperature of the third calcination is preferably 500℃~700℃. In some embodiments provided by this invention, the temperature of the third calcination is specifically 500℃, 600℃, or 700℃. The time of the third calcination is preferably 6~15 h, more preferably 6~12 h. In some embodiments provided by this invention, the time of the third calcination (i.e., the holding time) is specifically 6 h, 8 h, or 12 h. The heating rate of the third calcination is preferably 1~10℃ / min, more preferably 2~8℃ / min, even more preferably 4~6℃ / min, and most preferably 5℃ / min. The cooling rate is preferably 20~40℃ / min.

[0052] The present invention also provides a lithium ferrite supplement prepared by the above preparation method.

[0053] The present invention also provides a lithium-ion battery comprising the above-mentioned lithium iron phosphate supplement.

[0054] More specifically, the lithium-ion battery includes a positive electrode; the positive electrode includes a positive electrode active layer; the positive electrode active layer includes a positive electrode active material, a lithium iron phosphate supplement, a conductive agent, and a binder; the positive electrode active material can be any positive electrode active material well known to those skilled in the art, and there are no special limitations. In this invention, it is preferably one or more of lithium cobalt oxide, lithium manganese oxide, ternary nickel-cobalt-manganese lithium, nickel-manganese lithium oxide, lithium iron phosphate, and lithium manganese iron phosphate; the mass of the lithium iron phosphate supplement is preferably 1% to 5% of the mass of the positive electrode active layer, more preferably 3% to 5%; the mass of the conductive agent is preferably 1% to 5% of the mass of the positive electrode active layer, more preferably 3% to 5%; the mass of the binder is preferably 1% to 5% of the mass of the positive electrode active layer, more preferably 3% to 5%.

[0055] More specifically, the lithium-ion battery further includes a negative electrode; the negative electrode includes a negative electrode active material; the negative electrode active material is preferably one or more of artificial graphite, natural graphite, lithium titanate, lithium metal, silicon-carbon composite material and silicon suboxide.

[0056] More specifically, the lithium-ion battery also includes a separator; the separator is preferably a polypropylene separator, a polyethylene separator, or a polyethylene separator with alumina single-sided coating.

[0057] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, describes a lithium ferrite supplement agent provided by the present invention, its preparation method, and its application.

[0058] All reagents used in the following examples are commercially available.

[0059] Example 1

[0060] Preparation of Li5FeO4 / C: 10 g of glucose and 1 kg of iron oxide were uniformly mixed in 3 L of anhydrous ethanol and stirred at 500 rpm for 3 hours. The mixture was then dried in an 80°C oven for 12 hours. After drying, the mixture was ground into a fine powder and placed in an atmosphere furnace. Under nitrogen protection, it was heated to 300°C at a rate of 5°C / min and held at this temperature for 6 hours to synthesize carbon-supported iron oxide (Fe2O3 / C) material. The synthesized Fe2O3 / C material was then mixed with lithium oxide at a molar ratio of 1:5. The mixed powder was placed in a crucible and heated again in a nitrogen atmosphere furnace at a rate of 5°C / min to 650°C and held at this temperature for 24 hours to finally prepare carbon-doped lithium iron oxide (Li5FeO4 / C) material.

[0061] LATP coating: 40 g of mixed lithium salt (mass ratio: lithium carbonate: lithium nitrate: lithium fluoride = 95:3:2), 20 g of alumina, 120 g of titanium dioxide, and 320 g of ammonium dihydrogen phosphate were mixed in a high-speed mixer at 800 rpm for 5 min. Then, 800 g of Li5FeO4 / C was added and mixed at high speed at 3000 rpm for 30 min. The mixture was then placed in a box furnace, compressed air was introduced, and the temperature was raised to 500°C at a rate of 5°C / min and held for 12 hours. Finally, the temperature was lowered to room temperature at a rate of 20°C / min to obtain lithium ferrite supplement.

[0062] Example 2

[0063] Preparation of Li5FeO4 / C: 50 g of polyvinylpyrrolidone and 5 kg of iron oxide were uniformly mixed in 5 L of anhydrous ethanol and stirred at 200 rpm for 12 hours. The mixture was then dried in a forced-air oven at 50 °C for 24 h. After drying, the mixture was ground into a fine powder and placed in an atmosphere furnace. Under nitrogen protection, it was heated to 500 °C at a rate of 5 °C / min and held at this temperature for 3 hours, thus synthesizing carbon-supported iron oxide (Fe2O3 / C) material. Subsequently, the synthesized Fe2O3 / C material was mixed with lithium oxide at a molar ratio of 1:6 and ground. The mixed powder was placed in a ceramic boat and heated again in a nitrogen atmosphere furnace at a rate of 5 °C / min to 850 °C and held at this temperature for 12 hours, finally preparing carbon-doped lithium iron oxide (Li5FeO4 / C) material.

[0064] LATP coating: 60 g of mixed lithium salt (lithium hydroxide: lithium nitrate: lithium chloride = 80:15:5), 30 g of alumina, 180 g of titanium dioxide, and 480 g of ammonium dihydrogen phosphate were mixed in a high-speed mixer at 500 rpm for 10 min. Then, 1200 g of Li5FeO4 / C was added and mixed at high speed at 2000 rpm for 60 min. The mixture was then placed in a box furnace, compressed air was introduced, and the temperature was raised to 700°C at a rate of 5°C / min and held for 6 hours. Finally, the temperature was lowered to room temperature at a rate of 40°C / min to obtain lithium ferrite supplement.

[0065] Example 3

[0066] Preparation of Li5FeO4 / C: Same as in Example 1

[0067] LATP coating: 45 g of mixed lithium salt (lithium carbonate: lithium squarnet: lithium fluoride = 90:12:8), 24 g of alumina, 150 g of titanium dioxide, and 400 g of ammonium dihydrogen phosphate were mixed in a high-speed mixer at 1000 rpm for 5 min. Then, 1000 g of Li5FeO4 / C was added and mixed at high speed at 3000 rpm for 30 min. The mixture was then placed in a box furnace, compressed air was introduced, and the temperature was raised to 600°C at a rate of 5°C / min and held for 8 hours. Finally, the temperature was lowered to room temperature at a rate of 30°C / min to obtain lithium ferrite supplement.

[0068] Comparative Example 1

[0069] The difference from Example 1 is as follows:

[0070] Replace the Li5FeO4 / C with conventional Li5FeO4.

[0071] Preparation of Li5FeO4: Fe2O3 material and lithium oxide were mixed at a molar ratio of 1:5. The mixed powder was placed in a crucible and heated again in a nitrogen atmosphere furnace at a rate of 5℃ / min to 650℃, and held at this temperature for 24 hours to finally prepare lithium iron oxide Li5FeO4 material.

[0072] LATP coating: 40 g of mixed lithium salt (mass ratio: lithium carbonate: lithium nitrate: lithium fluoride = 95:3:2), 20 g of alumina, 120 g of titanium dioxide, and 320 g of ammonium dihydrogen phosphate were mixed in a high-speed mixer at 800 rpm for 5 min. Then, 800 g of Li5FeO4 was added and mixed at high speed at 3000 rpm for 30 min. The mixture was then placed in a box furnace, compressed air was introduced, and the temperature was raised to 500°C at a rate of 5°C / min and held for 12 hours. Finally, the temperature was lowered to room temperature at a rate of 20°C / min to obtain lithium ferrite supplement.

[0073] Comparative Example 2

[0074] The difference from Example 1 is as follows:

[0075] The mixed lithium salt in the LATP coating process is replaced with a single lithium salt.

[0076] Preparation of Li5FeO4 / C: 10 g of glucose and 1 kg of iron oxide were uniformly mixed in 3 L of anhydrous ethanol and stirred at 500 rpm for 3 hours. The mixture was then dried in an 80°C oven for 12 hours. After drying, the mixture was ground into a fine powder and placed in an atmosphere furnace. Under nitrogen protection, it was heated to 300°C at a rate of 5°C / min and held at this temperature for 6 hours to synthesize carbon-supported iron oxide (Fe2O3 / C) material. The synthesized Fe2O3 / C material was then mixed with lithium oxide at a molar ratio of 1:5. The mixed powder was placed in a crucible and heated again in a nitrogen atmosphere furnace at a rate of 5°C / min to 650°C and held at this temperature for 24 hours to finally prepare carbon-doped lithium iron oxide (Li5FeO4 / C) material.

[0077] LATP coating: 40 g lithium carbonate, 20 g alumina, 120 g titanium dioxide, and 320 g ammonium dihydrogen phosphate were mixed in a high-speed mixer at 800 rpm for 5 min. Then, 800 g Li5FeO4 / C was added and mixed at high speed at 3000 rpm for 30 min. The mixture was then placed in a box furnace, compressed air was introduced, and the mixture was heated to 500°C at a rate of 5°C / min and held at that temperature for 12 hours. Finally, the mixture was cooled to room temperature at a rate of 20°C / min to obtain the lithium ferrite supplement.

[0078] Comparative Example 3

[0079] The difference from Example 1 is as follows:

[0080] The cooling rate during the LATP coating process was adjusted to normal natural cooling.

[0081] Preparation of Li5FeO4 / C: 10 g of glucose and 1 kg of iron oxide were uniformly mixed in 3 L of anhydrous ethanol and stirred at 500 rpm for 3 hours. The mixture was then dried in an 80°C oven for 12 hours. After drying, the mixture was ground into a fine powder and placed in an atmosphere furnace. Under nitrogen protection, it was heated to 300°C at a rate of 5°C / min and held at this temperature for 6 hours to synthesize carbon-supported iron oxide (Fe2O3 / C) material. The synthesized Fe2O3 / C material was then mixed with lithium oxide at a molar ratio of 1:5. The mixed powder was placed in a crucible and heated again in a nitrogen atmosphere furnace at a rate of 5°C / min to 650°C and held at this temperature for 24 hours to finally prepare carbon-doped lithium iron oxide (Li5FeO4 / C) material.

[0082] LATP coating: 40 g of mixed lithium salt (mass ratio: lithium carbonate: lithium nitrate: lithium fluoride = 95:3:2), 20 g of alumina, 120 g of titanium dioxide, and 320 g of ammonium dihydrogen phosphate were mixed in a high-speed mixer at 800 rpm for 5 min. Then, 800 g of Li5FeO4 / C was added and mixed at high speed at 3000 rpm for 30 min. The mixture was then placed in a box furnace, compressed air was introduced, and the temperature was raised to 500°C at a rate of 5°C / min and held for 12 hours. The mixture was then allowed to cool naturally to room temperature to obtain the lithium ferrite supplement.

[0083] Example 4

[0084] Preparation of Li5FeO4 / C: Same as in Example 1.

[0085] LLZO coating: 24 g of mixed lithium salt (mass ratio: lithium carbonate: lithium nitrate: lithium fluoride = 95:3:2), 26 g of zirconium oxide, and 50 g of lanthanum oxide were mixed in a high-speed mixer at 800 rpm for 5 min. Then, 1000 g of Li5FeO4 / C was added and mixed at 2500 rpm for 30 min. The mixture was then placed in a box furnace, compressed air was introduced, and the mixture was heated to 700°C at a rate of 5°C / min and held at that temperature for 12 hours. Finally, the mixture was cooled to room temperature at a rate of 20°C / min.

[0086] Button cell preparation: 0.85g of lithium iron phosphate as the positive electrode active material, 0.05g of lithium iron phosphate supplementer prepared in Examples 1-4 or Comparative Examples 1-3, 0.05g of conductive agent-Sp-Li, and 0.05g of binder-PVDF were uniformly mixed, and 3g of N-methylpyrrolidone was added simultaneously to obtain a mixed slurry. 4g of the mixed slurry was poured onto aluminum foil, and the slurry was uniformly coated onto the aluminum foil using a 250μm scraper. Then, it was placed in a 120℃ forced-air oven with a dew point of -60°C and dried for 12 h. After rolling, the compaction density was 2.8g / cm³, and after stamping, a positive electrode sheet was formed. A lithium metal sheet was used as the negative electrode, a Celgard 2400 polypropylene porous membrane was used as the separator, and a mixed solution of 1 mol / L LiPF6 ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1) was used as the electrolyte. The test cell was assembled in an argon-filled glove box.

[0087] The test battery underwent electrochemical performance testing, including initial charge / discharge specific capacity, initial charge / discharge efficiency, and capacity retention. The battery tests were conducted under a constant temperature of 25°C. The initial charge / discharge mode was 0.1C constant current charging followed by 0.1C constant current discharging. Subsequent long-cycle mode was 0.33C constant current charging followed by 0.33C constant current discharging. The battery was cycled 100 times.

[0088] The results are shown in Table 1.

[0089] Table 1 Electrochemical performance test results

[0090]

[0091] Under the same battery system, the batteries prepared in Examples 1-4 showed better initial charge-discharge specific capacity, initial charge-discharge efficiency, and capacity retention after 100 cycles compared to those prepared in Comparative Examples 1-3. This indicates that the lithium-rich lithium iron phosphate composite solid electrolyte can effectively improve the lithium-ion diffusion coefficient, reduce the internal delithiation energy barrier, reduce lithium-ion consumption, and significantly improve the battery capacity retention.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a lithium ferrite lithium supplement, characterized in that, Includes the following steps: S1) The organic carbon source is mixed with iron oxide and calcined for the first time in a protective atmosphere to obtain carbon-loaded iron oxide material; the mass ratio of the organic carbon source to iron oxide is (0.01~0.05):(1~5). S2) The carbon-supported iron oxide material is mixed with a lithium source and calcined a second time in a protective atmosphere to obtain a carbon-doped lithium iron oxide material; the molar ratio of iron oxide to lithium source in the carbon-supported iron oxide material is 1:(5~7). S3) The mixed lithium salt and the raw material for the surface coating layer (excluding lithium elements) are mixed for the first time, and then the carbon-doped lithium iron oxide material is added for the second mixing. The mixture is then calcined for the third time in an oxygen-containing atmosphere and cooled to obtain a lithium iron ferrite supplement. The mixed lithium salt includes a first lithium salt, a second lithium salt, and a third lithium salt. The melting point of the first lithium salt is greater than that of the second lithium salt, and the difference is greater than 100°C. The melting point of the third lithium salt is greater than that of the first lithium salt, and the difference is greater than 100°C. The surface coating layer is a solid electrolyte. The mass ratio of the first lithium salt, the second lithium salt, and the third lithium salt is (80~95):(3~15):(2~5); The first lithium salt is selected from lithium carbonate and / or lithium hydroxide; The second lithium salt is selected from one or more of lithium nitrate, lithium squaric acid, lithium acetate, and lithium oxalate; The third lithium salt is selected from lithium fluoride and / or lithium chloride; The temperature of the third calcination is 500℃~700℃; the time of the third calcination is 6~15 h; and the heating rate of the third calcination is 1~10℃ / min. The cooling rate in step S3) is 20~40℃ / min; The surface coating layer is either lithium titanium aluminum phosphate solid electrolyte or lithium lanthanum zirconium oxide solid electrolyte. The total mass ratio of the mixed lithium salt and the raw material of the surface coating layer (excluding lithium elements) to the mass ratio of the carbon-doped lithium iron oxide material is (1~10):(8~12).

2. The preparation method according to claim 1, characterized in that, The organic carbon source is selected from one or more of glucose, polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, tannic acid, citric acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, and aniline; The lithium source is selected from one or more of lithium oxide, lithium hydroxide, lithium oxalate, and lithium carbonate.

3. The preparation method according to claim 1, characterized in that, The mixing in step S1) is carried out in an organic solvent, and after drying, a first calcination is performed under a protective atmosphere; the ratio of iron oxide to organic solvent is (1~5) kg: (3~5) L; the mixing speed is 100~500 rpm; the mixing time is 3~12 h; The mixing in step S2) is carried out by grinding; In step S3), the rotation speed for the first mixing is 500-1000 rpm; the mixing time for the first mixing is 1-10 min; the rotation speed for the second mixing is 2000-3000 rpm; and the mixing time for the second mixing is 20-60 min.

4. The preparation method according to claim 1, characterized in that, The temperature of the first calcination is 300℃~500℃; the time of the first calcination is 3~6 h; and the heating rate of the first calcination is 1~10℃ / min. The second calcination temperature is 650℃~850℃; the second calcination time is 12~30 h; and the heating rate of the second calcination is 1~10℃ / min.

5. The lithium ferrite supplement prepared by any one of the preparation methods of claims 1 to 4.

6. A lithium-ion battery, characterized in that, This includes lithium ferrite supplements prepared by any one of the preparation methods of claims 1 to 4.

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