Preparation method of composite coating modified Li5FeO4

Abstract

The invention discloses a preparation method of composite coating modified Li5FeO4, and belongs to the technical field of lithium ion batteries. Comprising the following steps: (1) uniformly mixing iron oxide powder and lithium source powder to obtain a powdery mixture; (2) sintering the powdery mixture in an inert gas atmosphere, cooling, crushing and sieving to obtain a lithium supplement additive base material; and (3) mixing the lithium supplement additive base material with the coating modifier, and carrying out heat treatment to obtain the lithium supplement additive with the coating layer 1, and (4) treating a coating layer 2 on the lithium supplement additive with the coating layer 1 by adopting an atomic deposition method to obtain the double-layer coated core-shell lithium supplement material. According to the prepared coating modified material, the conductivity of Li5FeO4 is effectively improved, the oxygen release amount of a lithium supplementing material is greatly reduced, the overall performance of a battery system is improved, and the charging specific capacity is improved; meanwhile, the environmental adaptability is improved, and the charging specific capacity change is optimally controlled to be 5% after the battery is placed for 10 h at the humidity of 20%.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for preparing composite coated modified Li5FeO4. Background Technology

[0002] During the initial charge and discharge cycle of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. This process consumes the active lithium in the positive electrode, resulting in the initial capacity loss of the lithium-ion battery. Currently, the irreversible capacity loss of graphite negative electrodes widely used in mass production lines can reach 10%, while for silicon-based and tin-based negative electrodes with high specific capacities, the irreversible capacity loss can exceed 30%, significantly reducing the energy density of lithium-ion batteries. Therefore, lithium replenishment is typically used to compensate for the irreversible capacity loss of lithium-ion batteries, restore the capacity of the positive electrode, and improve the energy density of the lithium-ion battery.

[0003] Currently, common lithium replenishment methods include positive electrode lithium replenishment, negative electrode lithium replenishment, and electrochemical lithium replenishment. Negative electrode lithium replenishment often uses lithium powder and lithium foil, but because metallic lithium reacts violently with water, it has very high environmental requirements, necessitating significant investment in production line modifications and equipment procurement. However, positive electrode lithium replenishment, due to its higher safety and ease of operation, has become the most promising method for industrial production. Commonly used positive electrode lithium replenishment additives include Li5FeO4, Li2NiO2, Li6CoO4, Li6MnO4, and Li5ReO6, among others. Li5FeO4, theoretically, can release five Li ions. + With a theoretical specific capacity exceeding 850 mAh / g, Li₅FeO₄ is considered an ideal lithium-ion additive for cathode materials. Adding a certain amount of Li₅FeO₄ to traditional cathode materials can significantly improve the initial efficiency and energy density of lithium-ion batteries. However, pure Li₅FeO₄ has poor conductivity, making it difficult to guarantee the electrical performance of lithium-ion batteries. Therefore, it is particularly important to prepare a conductive lithium-ion additive that combines excellent lithium-ion replenishment performance with good conductivity.

[0004] Currently, the existing technology patent CN 120398124 A (a method for preparing a composite lithium-rich lithium supplement additive) discloses a technical solution for preparing a composite lithium-rich lithium supplement additive Li5FeO4@C@Li2NiO2 using atomic layer deposition, but the charging specific capacity and environmental adaptability of the composite lithium-rich lithium supplement additive obtained by this solution still need to be improved.

[0005] Patent CN 119297233 A (Composite lithium replenishment material and its preparation method, secondary battery) discloses a technical solution involving the formation of a deposition layer by atomic deposition, but the specific capacity of the composite lithium replenishment material obtained by this solution is generally low and there is still much room for improvement. Summary of the Invention

[0006] Technical issues Current conductive lithium-ion additives suffer from poor charging capacity and limited environmental adaptability.

[0007] Technical content To address the aforementioned technical problems, this invention provides a method for preparing composite-coated modified Li5FeO4, comprising the following steps: (1) Mix iron oxide powder and lithium source powder evenly to obtain a powdered mixture; (2) The powder mixture obtained in step (1) is sintered in an inert gas atmosphere, cooled, crushed and sieved to obtain Li5FeO4 lithium supplementation additive substrate. (3) The prepared Li5FeO4 lithium supplementing additive substrate and the coating modifier are mixed and heat-treated to obtain the lithium supplementing additive Li5FeO4 with coating layer 1. (4) The lithium supplementation additive Li5FeO4 with coating layer 1 obtained in step (3) is treated with atomic deposition to form coating layer 2, and finally a double-coated core-shell lithium supplementation material is obtained.

[0008] Furthermore, the particle size range of the iron oxide powder in step (1) is 50 nm to 20 μm.

[0009] Furthermore, in step (1), the lithium source powder is one or more of Li2O, LiOH, LiOH·H2O, and Li2CO3.

[0010] Furthermore, in step (1), the molar ratio of Fe element in the iron oxide powder to Li element in the lithium source powder is 1:8~12.

[0011] Furthermore, the inert gas in step (2) includes one or more of nitrogen and argon.

[0012] Furthermore, in step (2), sintering refers to pre-sintering at 500~600℃ for 5-15 h, followed by high-temperature sintering at 700-1000℃ for 10-24 h. Furthermore, in step (2), the mesh size of the sieve is 250~350 mesh.

[0013] Furthermore, the coating modifier in step (3) includes graphene oxide, modified MOF composite material, and carbon-coated modified metal oxide powder.

[0014] Furthermore, the carbon-coated modified metal oxides in step (3) include nano-active alumina, titanium dioxide, iron oxide, etc.

[0015] Furthermore, the preparation method of the carbon-coated modified metal oxide in step (3) is as follows: the oxide powder is mixed with an organic carbon source, dissolved in water, spray-dried, and then heat-treated to obtain the carbon-coated metal oxide powder.

[0016] Furthermore, the oxide powder includes one or more of aluminum oxide, titanium oxide, and iron oxide.

[0017] Furthermore, organic carbon sources include one or more of glucose and sucrose.

[0018] Furthermore, the amount of organic carbon source added is 10-20% of the molar amount of oxide powder.

[0019] Preferably, the amount of organic carbon source added is 12-18% of the molar amount of oxide powder.

[0020] Furthermore, the amount of water added is 10 to 100 wt% of the oxide powder mass.

[0021] Furthermore, the parameters for spray drying are: inlet air temperature 200-240℃ and outlet air temperature 90-100℃.

[0022] Furthermore, the heat treatment conditions are 400-700℃ for 5-10 hours.

[0023] Furthermore, the amount of coating modifier added in step (3) is 0.5-5 wt% of the mass of the Li5FeO4 lithium supplementation additive substrate.

[0024] Furthermore, the amount of coating modifier added in step (3) is 2-5 wt% of the mass of the Li5FeO4 lithium supplementation additive substrate.

[0025] Preferably, the amount of coating modifier added in step (3) is 3-4 wt% of the mass of the Li5FeO4 lithium supplementation additive substrate.

[0026] Furthermore, the heat treatment conditions in step (3) are 600~800℃ and the time is 5~10h.

[0027] Furthermore, the atomic deposition method in step (4) is as follows: using Li5FeO4 with coating layer 1 as the substrate, under conditions of 150~200℃, aluminum source pulse for 1~5s, oxygen source pulse for 2~8s, purging for 5~15s, and gas source flow rate controlled at 150~200cm³. 3 / min, until an oxide layer of 2~8nm thick is formed on the substrate surface.

[0028] Furthermore, the aluminum source precursors used during aluminum source pulses include trimethylaluminum, triethylaluminum, or triisobutylaluminum.

[0029] Furthermore, the oxygen source used during oxygen pulses includes ozone, water, or oxygen plasma.

[0030] Furthermore, the aluminum source pulse can be replaced with a silicon source pulse; the silicon source used includes trimethylchlorosilane, tetraethoxysilane, or silane.

[0031] Preferably, the oxide layer thickness is 3~5nm.

[0032] The present invention provides a composite coated modified Li5FeO4 prepared according to the above method.

[0033] The application of the composite-coated modified Li5FeO4 provided by this invention in the field of lithium-ion batteries.

[0034] Beneficial effects The modified coating material prepared in this invention contains dual modules of oxygen adsorption and conductive carbon, which effectively improves the conductivity of Li5FeO4 and greatly reduces the oxygen release of the lithium replenishment material, thereby enhancing the overall performance of the battery system and enabling a maximum charge specific capacity of 800 mAh·g. -1 Meanwhile, atomic deposition is used for the final dense coating layer, which effectively improves the environmental adaptability of the material. The change in specific capacity during charging is optimally controlled within 5% after being placed at 20% humidity for 10 hours. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the composite-coated modified Li5FeO4 of the present invention. Detailed Implementation

[0036] Source of raw materials Iron oxide was purchased from Xingxing Electronic New Materials (Wuxi) Co., Ltd., with a particle size of 50 nm to 20 μm; battery-grade lithium carbonate was purchased from Ganfeng Lithium Group Co., Ltd.

[0037] Example 1 A method for preparing composite-coated modified Li5FeO4, comprising: (1) Weigh 1.3 mol of battery-grade lithium carbonate, 1.25 mol of lithium oxide and 0.5 mol of iron oxide, place them in a ball mill jar, and ball mill for 2 hours to obtain a powdered mixture.

[0038] (2) The powdered mixture was placed in a tube furnace under nitrogen atmosphere protection. The heating rate was 2°C / min. The temperature was raised to 580°C and held for 7 h. Then the temperature was raised to 830°C and held for 14 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The Li5FeO4 lithium supplementation additive base material was obtained by crushing and sieving (300 mesh).

[0039] (3) The prepared Li5FeO4 lithium supplement additive substrate was mixed with carbon-coated modified alumina, wherein the amount of carbon-coated modified alumina added was 3.5wt% of the mass of the lithium supplement additive substrate. After ball milling for 2h, it was placed in a tube furnace under nitrogen atmosphere protection, the heating rate was 2°C / min, the temperature was raised to 750°C and held for 6h, and after the reaction was completed, it was naturally cooled to room temperature to obtain the lithium supplement additive Li5FeO4 with coating layer 1. Preparation method of carbon-coated modified alumina: Alumina is mixed with glucose, wherein the amount of glucose added is 15% of the molar amount of alumina. Deionized water is added to dissolve the mixture, and a solution with a mass concentration of 45% is obtained. The solution is then spray-dried, and the powder obtained by spray drying is placed in a tube furnace under nitrogen atmosphere protection. The heating rate is 2°C / min, and the temperature is raised to 600°C and held for 6 hours. After natural cooling to room temperature, carbon-coated alumina powder is obtained.

[0040] (4) The lithium-replenishing additive Li5FeO4 with coating layer 1 was treated with atomic deposition to form coating layer 2. The method is as follows: Trimethylaluminum TMA was used as the aluminum source precursor, ozone was used as the oxygen source, and Li5FeO4 with the first coating layer was used as the substrate. Under the condition of 170℃, the aluminum source TMA pulse was 3s, the oxygen source pulse was 4s, the purging was 10s, and the gas source flow rate was controlled at 180 cm. 3 / min, through repeated cycles, a 4nm thick aluminum oxide layer is formed on the substrate surface, ultimately obtaining a double-layer coated core-shell lithium replenishment material.

[0041] Example 2 A method for preparing composite-coated modified Li5FeO4, comprising: (1) Weigh 2.8 mol of battery-grade lithium hydroxide, 2.3 mol of lithium hydroxide monohydrate, and 0.5 mol of iron oxide, place them in a ball mill jar, and ball mill for 2 hours to obtain a powdered mixture.

[0042] (2) The powdered mixture was placed in a tube furnace under nitrogen atmosphere protection. The heating rate was 2°C / min. The temperature was raised to 580°C and held for 7 h. Then the temperature was raised to 830°C and held for 14 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The Li5FeO4 lithium supplementation additive base material was obtained by crushing and sieving (300 mesh).

[0043] (3) The prepared Li5FeO4 lithium supplement additive substrate was mixed with carbon-coated modified alumina, wherein the amount of carbon-coated modified alumina added was 3.5wt% of the mass of the lithium supplement additive substrate. After ball milling for 2h, it was placed in a tube furnace under nitrogen atmosphere protection, the heating rate was 2°C / min, the temperature was raised to 750°C and held for 6h, and after the reaction was completed, it was naturally cooled to room temperature to obtain the lithium supplement additive Li5FeO4 with coating layer 1. Preparation method of carbon-coated modified alumina: Alumina is mixed with glucose, wherein the amount of glucose added is 15% of the molar amount of alumina. Deionized water is added to dissolve the mixture, and a solution with a mass concentration of 45% is obtained. The solution is then spray-dried, and the powder obtained by spray drying is placed in a tube furnace under nitrogen atmosphere protection. The heating rate is 2°C / min, and the temperature is raised to 600°C and held for 6 hours. After natural cooling to room temperature, carbon-coated alumina powder is obtained.

[0044] (4) The lithium-replenishing additive Li5FeO4 with coating layer 1 was treated with atomic deposition to form coating layer 2. The method is as follows: Trimethylaluminum TMA was used as the aluminum source precursor, ozone was used as the oxygen source, and Li5FeO4 with the first coating layer was used as the substrate. Under the condition of 170℃, the aluminum source TMA pulse was 3s, the oxygen source pulse was 4s, the purging was 10s, and the gas source flow rate was controlled at 180 cm. 3 / min, through repeated cycles, a 4nm thick aluminum oxide layer is formed on the substrate surface, ultimately obtaining a double-layer coated core-shell lithium replenishment material.

[0045] Example 3 A method for preparing composite-coated modified Li5FeO4, comprising: (1) Weigh 1.55 mol of battery-grade lithium carbonate, 2 mol of lithium hydroxide and 0.5 mol of iron oxide, place them in a ball mill jar and ball mill for 2 hours to obtain a powdered mixture.

[0046] (2) The powdered mixture was placed in a tube furnace under nitrogen atmosphere protection. The heating rate was 2°C / min. The temperature was raised to 580°C and held for 7 h. Then the temperature was raised to 830°C and held for 14 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The Li5FeO4 lithium supplementation additive base material was obtained by crushing and sieving (300 mesh).

[0047] (3) The prepared Li5FeO4 lithium supplement additive substrate was mixed with carbon-coated modified alumina, wherein the amount of carbon-coated modified alumina added was 3.5wt% of the mass of the lithium supplement additive substrate. After ball milling for 2h, it was placed in a tube furnace under nitrogen atmosphere protection, the heating rate was 2°C / min, the temperature was raised to 750°C and held for 6h, and after the reaction was completed, it was naturally cooled to room temperature to obtain the lithium supplement additive Li5FeO4 with coating layer 1. Preparation method of carbon-coated modified alumina: Alumina is mixed with glucose, wherein the amount of glucose added is 15% of the molar amount of alumina. Deionized water is added to dissolve the mixture, and a solution with a mass concentration of 45% is obtained. The solution is then spray-dried, and the powder obtained by spray drying is placed in a tube furnace under nitrogen atmosphere protection. The heating rate is 2°C / min, and the temperature is raised to 600°C and held for 6 hours. After natural cooling to room temperature, carbon-coated alumina powder is obtained.

[0048] (4) The lithium-replenishing additive Li5FeO4 with coating layer 1 was treated with atomic deposition to form coating layer 2. The method is as follows: Trimethylaluminum TMA was used as the aluminum source precursor, ozone was used as the oxygen source, and Li5FeO4 with the first coating layer was used as the substrate. Under the condition of 170℃, the aluminum source TMA pulse was 3s, the oxygen source pulse was 4s, the purging was 10s, and the gas source flow rate was controlled at 180 cm. 3 / min, through repeated cycles, a 4nm thick aluminum oxide layer is formed on the substrate surface, ultimately obtaining a double-layer coated core-shell lithium replenishment material.

[0049] Example 4 A method for preparing composite-coated modified Li5FeO4, comprising: (1) Weigh 1.3 mol of battery-grade lithium carbonate, 1.25 mol of lithium oxide and 0.5 mol of iron oxide, place them in a ball mill jar, and ball mill for 2 hours to obtain a powdered mixture.

[0050] (2) The powdered mixture was placed in a tube furnace under nitrogen atmosphere protection. The heating rate was 2°C / min. The temperature was raised to 580°C and held for 7 h. Then the temperature was raised to 830°C and held for 14 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The Li5FeO4 lithium supplementation additive base material was obtained by crushing and sieving (300 mesh).

[0051] (3) The prepared Li5FeO4 lithium supplement additive substrate was mixed with carbon-coated modified iron oxide, wherein the amount of carbon-coated modified iron oxide added was 3.5wt% of the mass of the lithium supplement additive substrate. After ball milling for 2h, it was placed in a tube furnace under nitrogen atmosphere protection, the heating rate was 2°C / min, the temperature was raised to 750°C and held for 6h, and after the reaction was completed, it was naturally cooled to room temperature to obtain the lithium supplement additive Li5FeO4 with coating layer 1. Preparation method of carbon-coated modified iron oxide: Iron oxide is mixed with glucose, wherein the amount of glucose added is 15% of the molar amount of iron oxide, and deionized water is added to dissolve it to obtain a solution with a mass concentration of 45%. The solution is then spray-dried, and the powder obtained by spray drying is placed in a tube furnace under nitrogen atmosphere protection. The heating rate is 2°C / min, and the temperature is raised to 600°C and held for 6 hours. After naturally cooling to room temperature, carbon-coated alumina powder is obtained.

[0052] (4) The lithium-replenishing additive Li5FeO4 with coating layer 1 was treated with atomic deposition to form coating layer 2. The method is as follows: Trimethylaluminum TMA was used as the aluminum source precursor, ozone was used as the oxygen source, and Li5FeO4 with the first coating layer was used as the substrate. Under the condition of 170℃, the aluminum source TMA pulse was 3s, the oxygen source pulse was 4s, the purging was 10s, and the gas source flow rate was controlled at 180 cm. 3 / min, through repeated cycles, a 4nm thick aluminum oxide layer is formed on the substrate surface, ultimately obtaining a double-layer coated core-shell lithium replenishment material.

[0053] Example 5 A method for preparing composite-coated modified Li5FeO4, comprising: (1) Weigh 1.3 mol of battery-grade lithium carbonate, 1.25 mol of lithium oxide and 0.5 mol of iron oxide, place them in a ball mill jar, and ball mill for 2 hours to obtain a powdered mixture.

[0054] (2) The powdered mixture was placed in a tube furnace under nitrogen atmosphere protection. The heating rate was 2°C / min. The temperature was raised to 580°C and held for 7 h. Then the temperature was raised to 830°C and held for 14 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The Li5FeO4 lithium supplementation additive base material was obtained by crushing and sieving (300 mesh).

[0055] (3) The prepared Li5FeO4 lithium supplement additive substrate was mixed with carbon-coated modified alumina, wherein the amount of carbon-coated modified iron oxide added was 3.5wt% of the mass of the lithium supplement additive substrate. After ball milling for 2h, it was placed in a tube furnace under nitrogen atmosphere protection, the heating rate was 2°C / min, the temperature was raised to 750°C and held for 6h, and after the reaction was completed, it was naturally cooled to room temperature to obtain the lithium supplement additive Li5FeO4 with coating layer 1. Preparation method of carbon-coated modified alumina: Alumina is mixed with sucrose, wherein the amount of sucrose added is 15% of the molar amount of alumina. Deionized water is added to dissolve the mixture, and a solution with a mass concentration of 45% is obtained. The solution is then spray-dried, and the powder obtained by spray drying is placed in a tube furnace under nitrogen atmosphere protection. The heating rate is 2°C / min, and the temperature is raised to 600°C and held for 6 hours. After natural cooling to room temperature, carbon-coated alumina powder is obtained.

[0056] (4) The lithium-replenishing additive Li5FeO4 with coating layer 1 was treated with atomic deposition to form coating layer 2. The method is as follows: Trimethylaluminum TMA was used as the aluminum source precursor, ozone was used as the oxygen source, and Li5FeO4 with the first coating layer was used as the substrate. Under the condition of 170℃, the aluminum source TMA pulse was 3s, the oxygen source pulse was 4s, the purging was 10s, and the gas source flow rate was controlled at 180 cm. 3 / min, through repeated cycles, a 4nm thick aluminum oxide layer is formed on the substrate surface, ultimately obtaining a double-layer coated core-shell lithium replenishment material.

[0057] Example 6 A method for preparing composite-coated modified Li5FeO4, comprising: (1) Weigh 1.3 mol of battery-grade lithium carbonate, 1.25 mol of lithium oxide and 0.5 mol of iron oxide, place them in a ball mill jar, and ball mill for 2 hours to obtain a powdered mixture.

[0058] (2) The powdered mixture was placed in a tube furnace under nitrogen atmosphere protection, and the temperature was raised to 830°C at a rate of 2°C / min. The temperature was held for 14 h, and the mixture was allowed to cool naturally to room temperature after the reaction was completed. The Li5FeO4 lithium supplementation additive base material was obtained by crushing and sieving (300 mesh).

[0059] (3) The prepared Li5FeO4 lithium supplement additive substrate was mixed with carbon-coated modified alumina, wherein the amount of carbon-coated modified iron oxide added was 3.5wt% of the mass of the lithium supplement additive substrate. After ball milling for 2h, it was placed in a tube furnace under nitrogen atmosphere protection, the heating rate was 2°C / min, the temperature was raised to 750°C and held for 6h, and after the reaction was completed, it was naturally cooled to room temperature to obtain the lithium supplement additive Li5FeO4 with coating layer 1. Preparation method of carbon-coated modified alumina: Alumina is mixed with glucose, wherein the amount of glucose added is 15% of the molar amount of alumina. Deionized water is added to dissolve the mixture, and a solution with a mass concentration of 45% is obtained. The solution is then spray-dried, and the powder obtained by spray drying is placed in a tube furnace under nitrogen atmosphere protection. The heating rate is 2°C / min, and the temperature is raised to 600°C and held for 6 hours. After natural cooling to room temperature, carbon-coated alumina powder is obtained.

[0060] (4) The lithium-replenishing additive Li5FeO4 with coating layer 1 was treated with atomic deposition to form coating layer 2. The method is as follows: Trimethylaluminum TMA was used as the aluminum source precursor, ozone was used as the oxygen source, and Li5FeO4 with the first coating layer was used as the substrate. Under the condition of 170℃, the aluminum source TMA pulse was 3s, the oxygen source pulse was 4s, the purging was 10s, and the gas source flow rate was controlled at 180 cm. 3 / min, through repeated cycles, a 4nm thick aluminum oxide layer is formed on the substrate surface, ultimately obtaining a double-layer coated core-shell lithium replenishment material.

[0061] Comparative Example 1 The steps in Example 1 are followed, except that step (3) is omitted, to obtain a single-layer coated core-shell lithium supplement material.

[0062] Comparative Example 2 The steps in Example 1 are followed, except that step (4) is omitted, to obtain a single-layer coated core-shell lithium supplement material.

[0063] Comparative Example 3 The steps are carried out in Example 1, except that the carbon-coated modified alumina in step (3) is replaced with an equal amount of alumina.

[0064] Comparative Example 4 The steps in Example 1 are followed, except that the carbon-coated modified alumina preparation process in step (3) is replaced by: mixing alumina with glucose, wherein the amount of glucose added is 10% of the molar amount of alumina, dissolving in deionized water to obtain a solution with a mass concentration of 45%, spray drying, and then placing the powder obtained by spray drying in a tube furnace under nitrogen atmosphere protection, heating at a rate of 2°C / min, heating to 600°C and holding for 6 hours, and then naturally cooling to room temperature to obtain carbon-coated alumina powder.

[0065] Comparative Example 5 The steps in Example 1 are followed, except that the amount of carbon-coated modified alumina in step (3) is adjusted to 2 wt% of the mass of the Li5FeO4 lithium supplementation additive substrate.

[0066] Comparative Example 6 The steps in Example 1 are followed, except that the amount of carbon-coated modified alumina in step (3) is adjusted to 5 wt% of the mass of the Li5FeO4 lithium supplementation additive substrate.

[0067] Comparative Example 7 The steps in Example 1 are followed, wherein the thickness of the alumina layer obtained by the atomic deposition method in step (4) is adjusted to 6 nm, and finally a double-layer coated core-shell lithium supplement material is obtained.

[0068] Comparative Example 8 The steps in Example 1 are followed, wherein the thickness of the alumina layer obtained by the atomic deposition method in step (4) is adjusted to 2 nm, and finally a double-layer coated core-shell lithium supplement material is obtained.

[0069] Comparative Example 9 The steps are performed as described in Example 1, except that steps (3) and (4) are omitted.

[0070] The core-shell lithium supplementation materials prepared in the above embodiments and comparative examples were tested. The testing process is as follows: 1. Button cell capacity test: Lithium replenishing agent, SP (conductive carbon black), and PVDF (polyvinylidene fluoride) are weighed in a ratio of 92:4:4, homogenized using a degassing machine, coated and dried on a semi-automatic coating machine, and then assembled into button cells in a glove box after rolling and cutting. The charging capacity is tested on Xinwei charging and discharging equipment at 3.0-4.5V and 0.1C to obtain the lithium replenishing capacity of the material.

[0071] 2. Environmental stability test: Take 4g of the product and place it under 20% humidity for 10 hours. Test the charging capacity of the product before and after the placement.

[0072] 3. Oxygen release of lithium-replenishing materials: Archimedes buoyancy method. Test procedure: The product to be tested is made into a soft-pack battery and suspended on a fixed bracket. The suspended soft-pack battery is completely immersed in a 1000ml beaker containing constant temperature water. The entire beaker is then placed on a three-digit balance and the weight difference of the soft-pack battery before and after the first charge is calculated.

[0073] Soft-pack battery preparation: Lithium iron phosphate, Li5FeO4, PVDF (polyvinylidene fluoride), SP (conductive carbon black), and CNT were weighed in a ratio of 94.8:1.9:2:1:0.3. NMP was used as the solvent, and a double planetary mixer was used to homogenize the slurry. The slurry was coated and dried on an automatic coating machine. After rolling, cutting, stacking, and electrolyte injection, a 2.5Ah soft-pack battery was completed. Formation was carried out on a horizontal hot-pressing formation cabinet. Formation was carried out at 60% SOC, with formation rates of 0.05, 0.1, and 0.2C. The voltage was set to be timed for the first formation and charged to 4.2V and discharged to 2.0V for the second formation. Table 1

[0074] The test results are shown in Table 1, from which it can be seen that: The products prepared from the combination of lithium carbonate and lithium oxide in Examples 1, 2, and 3 exhibited the best performance and the most stable structure. Example 1.

[0075] Compared with Examples 4 and 5, Example 1 shows that using glucose and alumina as coating modifiers results in the best environmental stability and oxygen release. Compared with Example 6, the stability of the product is slightly reduced after removing the low-temperature insulation section.

[0076] As can be seen from Example 1 and the comparative example, the conductivity, environmental stability and oxygen release of the product are greatly improved after adding coating layers 1 and 2 to the Li5FeO4 lithium supplementation additive substrate. Furthermore, the overall performance of the product is best when the coating amount of coating layer 1 is 3.55wt% and the coating layer 2 is 4nm.

[0077] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing composite-coated modified Li5FeO4, characterized in that, Includes the following steps: (1) Mix iron oxide powder and lithium source powder evenly to obtain a powdered mixture; (2) The powder mixture obtained in step (1) is sintered in an inert gas atmosphere, cooled, crushed and sieved to obtain Li5FeO4 lithium supplementation additive substrate. (3) The prepared Li5FeO4 lithium supplement additive substrate and the coating modifier are mixed and heat-treated at 600~800℃ for 5~10h to obtain the lithium supplement additive Li5FeO4 with coating layer 1; the amount of the coating modifier added is 2-5wt% of the mass of the Li5FeO4 lithium supplement additive substrate. The preparation method of the coating modifier is as follows: oxide powder is mixed with an organic carbon source, dissolved in water, spray-dried, and then heat-treated to obtain carbon-coated metal oxide powder; the oxide powder includes one or more of aluminum oxide, titanium oxide, and iron oxide; the organic carbon source includes one or more of glucose and sucrose; the amount of organic carbon source added is 12-18% of the molar amount of the oxide powder; (4) The lithium supplementation additive Li5FeO4 with coating layer 1 obtained in step (3) is treated with coating layer 2 by atomic deposition method to finally obtain a double-coated core-shell lithium supplementation material. The atomic deposition method is as follows: using Li5FeO4 with a coating layer 1 as the substrate, under conditions of 150~200℃, aluminum source pulse for 1~5s, oxygen source pulse for 2~8s, purging for 5~15s, and gas source flow rate controlled at 150~200 cm³ / s. 3 / min until an oxide layer of 2-8 nm thickness is formed on the substrate surface; the aluminum source precursor used in the aluminum source pulse includes trimethylaluminum, triethylaluminum or triisobutylaluminum; the oxygen source used in the oxygen source pulse includes ozone, water or oxygen plasma.

2. The preparation method according to claim 1, characterized in that, In step (1), the particle size range of the iron oxide powder is 50 nm to 20 μm; the lithium source powder is one or more of Li2O, LiOH, LiOH·H2O, and Li2CO3.

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of Fe element in iron oxide powder to Li element in lithium source powder is 1:8~12.

4. The preparation method according to claim 1, characterized in that, In step (2), sintering refers to pre-sintering at 500~600℃ for 5-15 h, followed by high-temperature sintering at 700-1000℃ for 10-24 h.

5. The preparation method according to claim 1, characterized in that, In the preparation method of the coating modifier, the spray drying parameters are: inlet air temperature 200-240℃, outlet air temperature 90-100℃, and heat treatment conditions of 400-700℃ for 5-10 hours.

6. The preparation method according to claim 1, characterized in that, The amount of coating modifier added in step (3) is 3-4 wt% of the mass of the Li5FeO4 lithium supplementation additive substrate.

7. The preparation method according to claim 1, characterized in that, In the atomic deposition method, the aluminum source pulse is replaced with a silicon source pulse; the silicon source precursor used in the silicon source pulse includes trimethylchlorosilane, tetraethoxysilane, or silane.

8. The preparation method according to claim 1, characterized in that, The oxide layer thickness in the atomic deposition method is 3~5 nm.

9. A composite-coated modified Li5FeO4, characterized in that, The composite-coated modified Li5FeO4 was prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the composite-coated modified Li5FeO4 as described in claim 9 in the field of lithium-ion batteries.

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