A positive electrode lithium replenishment material and its preparation method, positive electrode sheet and secondary battery

Abstract

This invention belongs to the field of secondary battery technology, and particularly relates to a positive electrode lithium replenishment material, a positive electrode sheet, and a secondary battery. The positive electrode lithium replenishment material includes lithium ferrite, a stabilizing layer coated on the outer surface of the lithium ferrite, and a hydrophobic layer coated on the outer surface of the stabilizing layer. In this invention, a positive electrode lithium replenishment material has a stabilizing layer and a hydrophobic layer sequentially coated on the surface of the lithium ferrite. The stabilizing layer can mitigate the generation of oxygen free radicals during the lithium ferrite delithiation process, preventing structural instability of the lithium ferrite. The hydrophobic layer can prevent lithium loss from the lithium ferrite, prevent lithium ion diffusion, ensure material capacity, and improve processing performance.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a positive electrode lithium replenishment material and its preparation method, a positive electrode sheet and a secondary battery. Background Technology

[0002] Lithium-ion batteries have attracted much attention due to their high energy density, long cycle life, environmental friendliness, and lack of memory effect, and are widely used in 3C digital products, automobiles, and other fields. Silicon materials have a high theoretical capacity (~4200mAh / g) and a low discharge voltage (~0.5V vs Li / Li+), and are currently considered one of the most promising anode materials to replace graphite. However, silicon materials consume some lithium source during the first charge to form SEI, and there are other irreversible losses, resulting in a low initial coulombic efficiency. Among the many lithium replenishment solutions, positive electrode lithium replenishment is favored due to its safety, simplicity, and low cost. LFO has received increasing research and use due to its high theoretical specific capacity (867mAh / g) and low cost. However, LFO releases oxygen during charging, which compromises structural stability; in addition, LFO is usually high in residual alkali and is sensitive to water during processing. These factors have become obstacles to the widespread application of LFO materials in lithium batteries. Summary of the Invention

[0003] One of the objectives of this invention is to provide a positive electrode lithium replenishment material that addresses the shortcomings of existing technologies. The material has a stabilizing layer and a hydrophobic layer sequentially coated on the surface of lithium ferrite. The stabilizing layer can mitigate the generation of oxygen free radicals during the delithiation process of lithium ferrite, thus preventing structural instability of lithium ferrite. The hydrophobic layer can prevent the loss of lithium in lithium ferrite, prevent the diffusion of lithium ions, ensure material capacity, and improve processing performance.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A positive electrode lithium replenishment material includes lithium ferrite, a stabilizing layer coated on the outer surface of the lithium ferrite, and a hydrophobic layer coated on the outer surface of the stabilizing layer.

[0006] Preferably, the stabilizing layer is a selenium layer and the hydrophobic layer is a titanium dioxide layer.

[0007] Preferably, the thickness of the stabilizing layer is 1–5 μm, and the thickness of the hydrophobic layer is 1–20 μm.

[0008] The second objective of this invention is to provide a method for preparing a positive electrode lithium supplement material, addressing the shortcomings of existing technologies. The method involves mixing lithium ferrite with selenium powder and heating to obtain lithium ferrite, adding lithium ferrite to a titanium dioxide precipitate solution, mixing, centrifuging, drying, and calcining to obtain the positive electrode lithium supplement material.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a positive electrode lithium supplement material includes the following steps:

[0011] Step S1: Mix lithium ferrite with selenium powder to obtain a lithium ferrite core coated with selenium powder. Heat the selenium powder to form a stable layer and obtain an intermediate product.

[0012] Step S2: Dissolve tetrabutyl titanate in a solvent, add intermediate product, stir, add alkaline solution dropwise, centrifuge, wash, dry, and calcine to obtain a positive electrode lithium replenishment material with a hydrophobic layer on the outer surface of the intermediate product.

[0013] Preferably, in step S1, the weight ratio of lithium ferrite to selenium powder is 1-5:10-30.

[0014] Preferably, in step S2, the weight ratio of tetrabutyl titanate to the intermediate product is 0.1-0.8:0.5-10.

[0015] Preferably, the alkaline solution in step S2 is 0.05 to 2 ml of ammonia water.

[0016] Preferably, the method for preparing lithium ferrite is as follows: mixing an iron source and a lithium source at a temperature of 500–700°C, heating for 10–15 h, raising the temperature to 780–850°C, heating for 30–48 h, cooling, and grinding to obtain lithium ferrite.

[0017] Preferably, the molar ratio of the iron source to the lithium source is 1-3:5-7.

[0018] The third objective of this invention is to provide a positive electrode sheet, including the aforementioned positive electrode lithium supplementation material, which has good electrochemical performance and structural stability, in order to address the shortcomings of the prior art.

[0019] To achieve the above objectives, the present invention adopts the following technical solution:

[0020] A positive electrode sheet comprising the aforementioned positive electrode lithium replenishment material.

[0021] The fourth objective of this invention is to provide a secondary battery with good quality and good cycle performance, addressing the shortcomings of existing technologies.

[0022] To achieve the above objectives, the present invention adopts the following technical solution:

[0023] A secondary battery comprising the aforementioned positive electrode plate.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: The positive electrode lithium replenishment material of the present invention has a stabilizing layer and a hydrophobic layer sequentially coated on the surface of lithium ferrite. The stabilizing layer can alleviate the generation of oxygen free radicals during the delithiation process of lithium ferrite and avoid the instability of the lithium ferrite structure. The hydrophobic layer can prevent the loss of lithium in lithium ferrite and prevent the diffusion of lithium ions, thus ensuring the material capacity and improving the processing performance. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0026] A positive electrode lithium replenishment material includes lithium ferrite, a stabilizing layer coated on the outer surface of the lithium ferrite, and a hydrophobic layer coated on the outer surface of the stabilizing layer.

[0027] Lithium ferrite releases oxygen during charging, compromising its structural stability. Furthermore, lithium ferrite typically has high residual alkali content and is sensitive to water during processing, making its application difficult. This invention provides a positive electrode lithium replenishment material, in which a stabilizing layer and a hydrophobic layer are sequentially coated on the surface of lithium ferrite. The stabilizing layer mitigates the generation of oxygen free radicals during lithium ferrite delithiation, preventing structural instability. The hydrophobic layer prevents lithium loss and lithium-ion diffusion, ensuring material capacity and thus improving processing performance.

[0028] In some embodiments, the stabilizing layer is a selenium layer, and the hydrophobic layer is a titanium dioxide layer. Selenium is a group VIA element, which can form a stable bonding layer with lithium ferrite, preventing oxygen release during charging and thus avoiding structural instability, material cracking, and significantly reduced material lifespan. Similarly, a sulfur layer can also be used, but preferably, a selenium layer provides better structural stability. Titanium dioxide contains titanium-oxygen bonds, which are highly polar. Water adsorbed on the surface dissociates due to polarization, easily forming hydroxyl groups. These surface hydroxyl groups can improve the performance of titanium dioxide as an adsorbent and various monomers, facilitating surface modification.

[0029] In some embodiments, the thickness of the stabilizing layer is 1–5 μm, and the thickness of the hydrophobic layer is 1–20 μm. Preferably, the thickness of the stabilizing layer is 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, and the thickness of the hydrophobic layer is 1 μm, 3 μm, 5 μm, 9 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm, or 20 μm.

[0030] A method for preparing a positive electrode lithium supplement material includes the following steps:

[0031] Step S1: Mix lithium ferrite with selenium powder to obtain a lithium ferrite core coated with selenium powder. Heat the selenium powder to form a stable layer and obtain an intermediate product.

[0032] Step S2: Dissolve tetrabutyl titanate in a solvent, add intermediate product, stir, add alkaline solution dropwise, centrifuge, wash, dry, and calcine to obtain a positive electrode lithium replenishment material with a hydrophobic layer on the outer surface of the intermediate product.

[0033] A method for preparing a positive electrode lithium supplement material involves mixing lithium ferrite with selenium powder and heating to obtain lithium ferrite, adding lithium ferrite to a titanium dioxide precipitate solution, mixing, centrifuging, drying, and calcining to obtain the positive electrode lithium supplement material.

[0034] This invention involves mixing lithium ferrite with selenium powder and heating to obtain an intermediate product, Se@LFO, i.e., lithium ferrite with a selenium layer. The Se@LFO lithium ferrite material is then added to a titanium dioxide precipitation solution, causing the surface of the Se@LFO lithium ferrite material to be coated with titanium dioxide precipitate. After centrifugation, washing, drying, and calcination, a positive electrode lithium replenishment material is obtained. The titanium dioxide precipitate solution is prepared by dissolving tetrabutyl titanate in a solvent, then adding an alkaline solution to allow for complete hydrolysis, resulting in an amorphous titanium dioxide precipitate. The alkaline solution is a 0.2–1.2 mol / L ammonia solution, added in an amount of 0.05–10 ml, preferably 0.05–6 ml, 1–5 ml, or 2–4 ml.

[0035] In some embodiments, the weight ratio of lithium ferrite to selenium powder in step S1 is 1–5:10–30. Preferably, the weight ratio of lithium ferrite to selenium powder is 1–5:10–30, 2–5:10–28, 2–5:13–26, 2–4:10–26, 2–4:12–26, or 2–4:14–22. Specifically, the weight ratio of lithium ferrite to selenium powder is 1:10, 2:12, 3:15, 2:16, 4:20, 1:23, 4:25, 3:28, 5:27, or 5:30.

[0036] In some embodiments, the weight ratio of tetrabutyl titanate to the intermediate product in step S2 is 0.1–0.8:0.5–10. The specific weight ratios of tetrabutyl titanate to the intermediate product are 0.1–0.8:0.5–10, 0.1–0.8:0.5–10, 0.1–0.8:0.5–10, 0.1–0.8:0.5–10, and 0.1–0.8:0.5–10.

[0037] In some embodiments, the alkaline solution in step S2 is 0.05–2 ml of ammonia water. The alkaline solution can be ammonia water, sodium hydroxide solution, or calcium hydroxide solution; specifically, 0.05–2 ml of ammonia water with a concentration of 0.02–0.5 mol / L is used.

[0038] In some embodiments, the preparation method of lithium ferrite in step S1 involves mixing an iron source and a lithium source at 500–700°C and heating for 10–15 hours, then raising the temperature to 780–850°C and heating for 30–48 hours, followed by cooling and grinding to obtain lithium ferrite. The lithium ferrite preparation method of this invention involves mixing the iron source and lithium source, pre-sintering at a lower temperature, and then heating to a higher temperature for calcination. This secondary calcination allows for a more complete reaction, resulting in a more stable lithium ferrite structure that is less prone to structural instability due to deoxidation during charging.

[0039] In some embodiments, the molar ratio of iron source to lithium source in step S1 is 1–3:5–7. Preferably, the molar ratio of iron source to lithium source is 1–3:5–7, 1.2–3:5–7, 1.5–3:5–7, 1.6–3:5–7, or 1.7–3:5–7. Specifically, the molar ratio of iron source to lithium source is 1:5, 1:6, 1:7, 2:5.5, or 3:6.

[0040] A positive electrode sheet, comprising the aforementioned positive electrode lithium supplementation material, exhibits good electrochemical performance and structural stability.

[0041] A positive electrode sheet includes the aforementioned positive electrode lithium replenishment material. Specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode active coating disposed on at least one surface of the positive electrode current collector, the positive electrode active coating including the aforementioned positive electrode lithium replenishment material. The aforementioned positive electrode lithium replenishment material contains lithium ions and can provide a lithium source for the positive electrode sheet, thereby replenishing the losses during the initial charge-discharge cycle and the losses during cycling.

[0042] A type of secondary battery with good quality and good cycle performance.

[0043] A secondary battery includes the aforementioned positive electrode. Specifically, the secondary battery includes a negative electrode, a separator, an electrolyte, a casing, and the aforementioned positive electrode.

[0044] The positive current collector is typically a structure or component that collects current. The positive current collector can be any material suitable for use as a positive current collector in lithium-ion batteries. For example, the positive current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0045] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which may be one or more of the following: graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector in lithium-ion batteries, for example, it may be, but is not limited to, metal foil, and more specifically, copper foil.

[0046] The lithium-ion battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0047] Preferably, the shell is made of stainless steel or aluminum-plastic film. More preferably, the shell is made of aluminum-plastic film.

[0048] Example 1

[0049] (1) LFO was prepared by a high-temperature solid-state method. Nano-Fe2O3 and LiOH·H2O were mixed and ground at a molar ratio of 1:5.5 and placed in a tube furnace (Ar). The mixture was then heated to 600℃ at a heating rate of 2℃ / min and held for 12 h for pre-sintering. The mixture was then heated to 800℃ at a heating rate of 2℃ / min and held for 36 h. After cooling to room temperature, the LFO material was ground and passed through a 400-mesh standard sieve to obtain particles with relatively uniform particle size.

[0050] (2) Mix the LFO obtained in the previous step with Se powder at a mass ratio of 1:25. Transfer the mixture to a tube furnace (Ar) and heat it to 250°C at a heating rate of 2°C / min and continue heating for 50 min to obtain Se@LFO.

[0051] (3) Tetrabutyl titanate (TBOT, 0.1918 g) was added to 40 mL of ethanol and stirred for 1 h. Then, 6 g of the above Se@LFO was added to the mixed solution and stirred for 2 h. Next, 0.5 mL of NH3·H2O was slowly added to the above solution. Then, the powder obtained by centrifugation was repeatedly washed several times with anhydrous ethanol and deionized water, and vacuum dried at 120 °C for 10 h to obtain powder. Finally, it was heated in a muffle furnace at 500 °C for 5 h to obtain nano-TiO2@Se@LFO.

[0052] Example 2

[0053] (1) LFO was prepared by a high-temperature solid-state method. Nano-Fe2O3 and LiOH·H2O were mixed and ground at a molar ratio of 1:4 and placed in a tube furnace (Ar). The mixture was then heated to 600℃ at a heating rate of 2℃ / min and held for 12 h for pre-sintering. The mixture was then heated to 800℃ at a heating rate of 2℃ / min and held for 32 h. After cooling to room temperature, the LFO material was ground and passed through a 400-mesh standard sieve to obtain particles with relatively uniform particle size.

[0054] (2) Mix the LFO obtained in the previous step with Se powder at a mass ratio of 1:25. Transfer the mixture to a tube furnace (Ar) and heat it to 200-300℃ at a heating rate of 2℃ / min and continue heating for 10-60min to obtain Se@LFO.

[0055] (3) Tetrabutyl titanate (TBOT, 0.1918 g) was added to 40 mL of ethanol and stirred for 1 h. Then, a certain amount of 7 g of the above Se@LFO was added to the mixed solution and stirred for 2 h. Next, 0.2 mL of NH3·H2O was slowly added to the above solution. Then, the powder obtained by centrifugation was repeatedly washed several times with anhydrous ethanol and deionized water, and vacuum dried at 120 °C for 10 h to obtain powder. Finally, it was heated in a muffle furnace at 500 °C for 5 h to obtain nano-TiO2@Se@LFO.

[0056] Example 3

[0057] (1) LFO was prepared by a high-temperature solid-state method. Nano-Fe2O3 and LiOH·H2O were mixed and ground at a certain molar ratio of 1:5 and placed in a tube furnace (Ar). The mixture was then heated to 600℃ at a heating rate of 2℃ / min and held for 12h for pre-sintering. The mixture was then heated to 800℃ at a heating rate of 2℃ / min and held for 32h. After cooling to room temperature, the LFO material was ground and passed through a 400-mesh standard sieve to obtain particles with relatively uniform particle size.

[0058] (2) Mix the LFO obtained in the previous step with Se powder at a mass ratio of 1:15. Transfer the mixture to a tube furnace (Ar) and heat it to 240°C at a heating rate of 2°C / min and continue heating for 10-60 min to obtain Se@LFO.

[0059] (3) Tetrabutyl titanate (TBOT, 0.1918 g) was added to 40 mL of ethanol and stirred for 1 h. Then, 3 g of the above Se@LFO was added to the mixed solution and stirred for 2 h. Next, 0.2 mL of NH3·H2O was slowly added to the above solution. Then, the powder obtained by centrifugation was repeatedly washed several times with anhydrous ethanol and deionized water, and vacuum dried at 120 °C for 10 h to obtain the powder. Finally, it was heated in a muffle furnace at 500 °C for 5 h to obtain nano-TiO2@Se@LFO.

[0060] Example 4

[0061] The difference from Example 1 is that the weight ratio of lithium ferrite to selenium powder in step S1 is 2:15.

[0062] The rest is the same as in Example 1.

[0063] Example 5

[0064] The difference from Example 1 is that the weight ratio of lithium ferrite to selenium powder in step S1 is 3:16.

[0065] The rest is the same as in Example 1.

[0066] Example 6

[0067] The difference from Example 1 is that the weight ratio of lithium ferrite to selenium powder in step S1 is 4:25.

[0068] The rest is the same as in Example 1.

[0069] Example 7

[0070] The difference from Example 1 is as follows: The preparation method of lithium ferrite is as follows: the iron source and the lithium source are mixed at 500°C and heated for 10 hours, the temperature is increased to 780°C and heated for 30 hours, then cooled and ground to obtain lithium ferrite.

[0071] The rest is the same as in Example 1.

[0072] Example 8

[0073] The difference from Example 1 is as follows: The preparation method of lithium ferrite is as follows: the iron source and the lithium source are mixed at 600°C and heated for 12 hours, the temperature is increased to 800°C and heated for 35 hours, then cooled and ground to obtain lithium ferrite.

[0074] The rest is the same as in Example 1.

[0075] Example 9

[0076] The difference from Example 1 is as follows: The preparation method of lithium ferrite is as follows: the iron source and the lithium source are mixed at 680°C and heated for 15 hours, the temperature is increased to 830°C and heated for 40 hours, then cooled and ground to obtain lithium ferrite.

[0077] The rest is the same as in Example 1.

[0078] Example 10

[0079] The difference from Example 1 is as follows: The preparation method of lithium ferrite is as follows: the iron source and the lithium source are mixed at 600°C and heated for 14 hours, the temperature is increased to 830°C and heated for 45 hours, then cooled and ground to obtain lithium ferrite.

[0080] The rest is the same as in Example 1.

[0081] Comparative Example 1

[0082] Li4FeO4 was used as a lithium supplement material.

[0083] The materials prepared in Examples 1-10 and Comparative Example 1 were subjected to initial coulombic efficiency and specific capacity tests, and the test results are recorded in Table 1.

[0084] Table 1

[0085] project ICE Capacity (mAh / g) Example 1 90.0 184 Example 2 89.6 183.8 Example 3 89.0 182.8 Example 4 87 183.6 Example 5 89 183 Example 6 86 182 Example 7 85 185 Example 8 87 184 Example 9 86 186 Example 10 85 182 Comparative Example 1 53 164

[0086] 1. Electrical performance: The electrochemical performance of the lithium-ion batteries of Examples 1-10 and Comparative Example 1 under 3C buck charging / 0.7C discharging cycles and rate charging (2C discharge to 3V) was tested and recorded in Table 2.

[0087] Table 2

[0088]

[0089]

[0090] As shown in Tables 1 and 2 above, the positive electrode lithium replenishment material prepared by this invention exhibits better performance than the lithium replenishment material of Comparative Example 1, demonstrating significant improvement. Comparison of Examples 1 and 4-6 shows that when the weight ratio of lithium ferrite to selenium powder in step S1 is set to 1:25, the prepared positive electrode lithium replenishment material performs better. This is because a certain amount of selenium powder coats the outer surface of lithium ferrite, forming a stable layer with a certain coating rate, making the lithium ferrite structure more stable. During charging, the selenium powder can combine with the oxygen free radicals released during delithiation to form a stable structure, preventing structural instability and cracking caused by delithiation. Setting a certain weight ratio of lithium ferrite to selenium powder results in a higher coating rate of the stable layer and better stability. The prepared secondary battery exhibits better initial coulombic efficiency, higher specific capacity, higher cycle capacity, and higher rate charge capacity.

[0091] Comparing Examples 1 and 7-10, it is found that when the following method parameters are used in the preparation of lithium ferrite, the prepared lithium ferrite performs better when applied to cathode lithium replenishment materials and batteries. The iron source and lithium source are mixed and heated at 600°C for 12 hours, then the temperature is increased to 800°C and heated for 35 hours. After cooling, the mixture is ground to obtain lithium ferrite. The resulting secondary battery exhibits good initial coulombic efficiency (up to 90%), high specific capacity (up to 184 mAh / g), higher cycle capacity retention (up to 82.5%), and good rate-charge capacity retention (up to 94.1%).

[0092] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A positive electrode lithium supplementing material, characterized by, The lithium iron oxide, a stable layer coated on the outer surface of the lithium iron oxide, and a hydrophobic layer coated on the outer surface of the stable layer, the stable layer is a selenium layer, the hydrophobic layer is a titanium dioxide layer, the weight ratio of lithium iron oxide to selenium powder is 1-5:10-30. 2.The positive-electrode lithium supplementing material of claim 1, characterized in that, The thickness of the stable layer is 1-5 μm, and the thickness of the hydrophobic layer is 1-20 μm.

3. The method of producing a positive electrode lithium supplementing material according to any one of claims 1 to 2, characterized by, The method comprises the following steps: Step S1, mixing lithium iron oxide and selenium powder to obtain an intermediate product with lithium iron oxide as the inner core, the outer surface of which is coated with selenium powder, and the selenium powder is heated to form a stable layer; Step S2, dissolving tetrabutyl titanate in a solvent, adding the intermediate product, stirring, adding an alkaline solution dropwise, centrifuging, washing, drying, and calcining to obtain a positive electrode lithium supplement material with a hydrophobic layer coated on the outer surface of the intermediate product. 4.The method of claim 3, wherein the lithium supplementing material is prepared by the steps of: preparing a lithium source; and mixing the lithium source with a lithium metal oxide. The weight ratio of lithium iron oxide to selenium powder in step S1 is 1-5:10-30. 5.The method of claim 3, wherein the lithium supplementing material is prepared by a method comprising: preparing a lithium source; and mixing the lithium source with the lithium metal oxide. The weight ratio of tetrabutyl titanate to the intermediate product in step S2 is 0.1-0.8:0.5-10. 6.The method of claim 3, wherein the lithium supplementing material is prepared by a method comprising: preparing a mixture of a lithium source and a carbon source; and sintering the mixture at a temperature of 600-1000 ℃ in an inert gas atmosphere. The alkaline solution in step S2 is 0.05-2 ml of ammonia. 7.The method of claim 3, wherein the lithium supplementing material is prepared by a method comprising: preparing a lithium source; and mixing the lithium source with the lithium metal oxide. The preparation method of the lithium iron oxide comprises the following steps: mixing an iron source and a lithium source, heating at a temperature of 500-700 ℃ for 10-15 h, increasing the temperature to 780-850 ℃, heating for 30-48 h, cooling, and grinding to obtain lithium iron oxide. 8.The method of claim 7, wherein the lithium supplementing material is prepared by a method comprising: preparing a mixture of a lithium source and a carbon source; and sintering the mixture at a temperature of 600-1000 ℃ in an inert gas atmosphere. The molar ratio of the iron source to the lithium source is 1-3:5-7.

9. A positive electrode sheet characterized by comprising: The method comprises the positive electrode lithium supplement material according to any one of claims 1-2.

10. A secondary battery characterized by comprising: The positive electrode sheet comprises the positive electrode lithium supplement material according to claim 9.

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