A positive electrode lithium supplement additive and its preparation method and positive electrode material

Abstract

The present invention discloses a positive electrode lithium replenishing additive, a preparation method thereof, and a positive electrode material, belonging to the technical field of lithium ion batteries. A positive electrode lithium replenishing additive comprises a positive electrode lithium replenishing agent matrix and an amorphous niobium oxide layer and a conductive carbon layer sequentially coated on the outer surface of the matrix, wherein the conductive carbon layer is a modified carbon nanotube @AgNPs@PDA. The positive electrode lithium replenishing additive of the present invention uses Li5FeO4 as a matrix, and sequentially wraps an amorphous niobium oxide layer and a conductive carbon layer on its outer layer, which avoids the reaction of the positive electrode lithium replenishing agent matrix with water and carbon dioxide in the air, and is beneficial to reducing the residual alkali content; improving the surface stability and structural integrity of the positive electrode lithium replenishing material during the cycle; and improving the cycle performance and specific capacity of the battery. This research can provide great help in the development of reliable positive electrode lithium replenishing materials, as well as any other positive electrode lithium replenishing materials for high-energy lithium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a positive electrode lithium supplement additive, a preparation method thereof, and a positive electrode material. Background Art

[0002] With the booming electric vehicle industry, lithium-ion batteries (LIBs) have gained widespread application in new energy vehicles and energy storage systems due to their outstanding advantages, including high energy density, high operating voltage, and low self-discharge. Currently, further improving the energy density of LIBs to meet the ever-increasing performance demands of the industrial sector has become a research priority. In LIBs using graphite-based anodes, a solid electrolyte interphase (SEI) film forms on the anode surface during the initial charge. This process, accompanied by the decomposition of the liquid electrolyte, leads to the irreversible consumption of some active lithium ions, resulting in capacity decay during the initial charge and discharge cycle. Silicon-based anode materials, with higher specific capacity, experience significant volume expansion and contraction during lithium ion insertion and deintercalation, causing the SEI film to continuously break down and rebuild, further exacerbating the loss of active lithium ions and severely limiting the improvement of LIB energy density. To compensate for this capacity loss, LIB replenishment technology has become a key solution. Currently, LIB replenishment methods mainly include positive electrode replenishment, negative electrode replenishment, and electrolyte replenishment. Among them, positive electrode lithium replenishment has developed into the mainstream direction of current lithium replenishment technology due to its significant advantages such as high safety, good process compatibility and controllable cost, and has shown important application prospects in the field of power batteries.

[0003] Li5FeO4 stands out among a number of lithium supplements due to its high theoretical specific capacity. However, Li5FeO4 currently still has problems such as excessive residual lithium and poor cycle performance during use, which limits the application scenarios of Li5FeO4. Summary of the Invention

[0004] The purpose of the present invention is to provide a positive electrode lithium supplement additive and a preparation method thereof and a positive electrode material, so as to solve the problem that the background technology Li5FeO4 still has excessive residual lithium and poor cycle performance during use.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a positive electrode lithium replenishing additive, comprising a positive electrode lithium replenishing agent matrix Li5FeO4 and an amorphous niobium oxide layer and a conductive carbon layer sequentially coated on the outer surface of the matrix;

[0007] The ratio of the amorphous niobium oxide solution to Li5FeO4 in the amorphous niobium oxide layer is 2 g: 10-16 mL;

[0008] The mass of the carbon source in the conductive carbon layer is 1%-5% of the mass of Li5FeO4;

[0009] The carbon source is modified carbon nanotubes@AgNPs@PDA.

[0010] The present invention wraps amorphous niobium oxide (NbO x C y ) can isolate the surface of the positive electrode lithium supplement matrix from water and carbon dioxide in the air, increasing its stability in air and preventing it from reacting with water and carbon dioxide in the air. Furthermore, the oxide can react with residual lithium on the surface of the core, thereby reducing the residual lithium content of the lithium supplement, minimizing side reactions during use, and effectively alleviating electrolyte erosion of the core. However, the limited conductivity of the amorphous niobium oxide layer hinders the preparation of a highly conductive positive electrode lithium supplement. Poor conductivity of the positive electrode lithium supplement affects the battery's charge and discharge efficiency, leading to decreased battery performance. Therefore, the present invention adds a conductive carbon layer to the amorphous niobium oxide layer to further improve the battery's electrochemical performance.

[0011] In a second aspect, the present invention provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0012] S1. Preparation of a positive electrode lithium supplement matrix: lithium nitrate and lithium hydroxide monohydrate are mixed and ground, then melted in a muffle furnace, cooled, taken out and ground to obtain a mixed lithium salt, and then the mixed lithium salt is mixed with nano-ferric oxide, ground, and pressed into tablets, calcined under an inert atmosphere, cooled, taken out and ground to obtain Li5FeO4;

[0013] S2. Preparing an amorphous niobium oxide-coated matrix material: dissolving niobium ethanol and sucrose in a mixed solvent consisting of water and an organic solvent, and stirring for 1-2 hours to obtain an amorphous niobium oxide solution; adding Li₅FeO₄ to the amorphous niobium oxide solution, stirring, and then calcining under an inert atmosphere to obtain an amorphous niobium oxide-coated matrix material;

[0014] S3. Preparation of positive electrode lithium supplement additive: The amorphous niobium oxide-coated matrix material and the carbon source obtained in S2 are dispersed in anhydrous ethanol, ground and stirred, and then calcined under an inert atmosphere to obtain the positive electrode lithium supplement additive.

[0015] Furthermore, in step S1, the molar ratio of lithium nitrate to lithium hydroxide monohydrate is (0.55-0.59):0.41; the molar ratio of Fe element in nano-ferric oxide to Li element in the mixed lithium salt is (5.2-5.6):1.

[0016] Furthermore, in step S1, the inert atmosphere is one or more of nitrogen, argon, and helium.

[0017] Furthermore, in step S1, the calcination temperature is 750-800°C, the heating rate is 5-10°C / min, and the calcination time is 10-12h.

[0018] Furthermore, in step S2, the molar ratio of niobium ethanol to sucrose is 1:(0.2-0.5); the volume ratio of water to organic solvent in the mixed solvent is (2-4):1; and the organic solvent is any one of ethanol, anhydrous methanol, propanol, isopropanol and acetone.

[0019] Furthermore, in step S2, the inert atmosphere is one or more of nitrogen, argon, and helium; the calcination temperature is 600-1200°C, the heating rate is 5-10°C / min, and the sintering time is 4-6h.

[0020] Furthermore, in step S3, the inert atmosphere is one or more of nitrogen, argon, and helium; the calcination temperature is 700-850°C, the heating rate is 5-10°C / min, and the sintering time is 2-5h.

[0021] Furthermore, in step S3, the carbon source is prepared by:

[0022] A1. Preparation of modified carbon nanotubes: adding carbon nanotubes to mixed acid, ultrasonicating at 50°C for 3-5 hours, washing with deionized water 5-6 times, and drying at 70°C for 10 hours to obtain acidified carbon nanotubes; mixing the acidified carbon nanotubes with 3-amino-4-fluorobenzenesulfonic acid, dicyclohexylcarbodiimide, and DMF, ultrasonicating for 30-40 minutes to fully dissolve and disperse them, deoxygenating with nitrogen for 20 minutes, and reflux reacting at 120°C with stirring for 24-48 hours. After the reaction, filtering, washing, and drying the product to obtain modified carbon nanotubes;

[0023] The amount ratio of carbon nanotubes to mixed acid is 2g:40-50mL; the mixed acid is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of (1-3):1; the amount ratio of acidified carbon nanotubes, 3-amino-4-fluorobenzenesulfonic acid, dicyclohexylcarbodiimide, and DMF is 2g:2-5g:0.2-0.3g:80mL.

[0024] In the above steps, carbon nanotubes are added to a mixed acid to obtain acidified carbon nanotubes containing carboxyl groups. Subsequently, dicyclohexylcarbodiimide is used as a condensing agent and DMF is used as a solvent to cause an amide reaction between the carboxyl groups of the acidified carbon nanotubes and the amino groups in 3-amino-4-fluorobenzenesulfonic acid, thereby grafting 3-amino-4-fluorobenzenesulfonic acid onto the surface of the acidified carbon nanotubes to obtain modified carbon nanotubes. 3-Amino-4-fluorobenzenesulfonic acid can improve the dispersibility of carbon nanotubes through steric hindrance, thereby helping to obtain a uniform coating layer and improving the electrochemical performance of the battery. Furthermore, after subsequent sintering, the modified carbon nanotubes can obtain sulfur-doped carbon layers and fluorine-doped carbon layers, which can synergistically improve the conductivity of the carbon nanotubes, thereby preparing a positive electrode lithium supplement additive with better performance.

[0025] A2. Preparation of modified carbon nanotubes@AgNPs: The modified carbon nanotubes were ultrasonically dispersed in DMF, followed by addition of AgNO3 and stirring for 6-8 h; then NaBH4 was added, stirred for 10-15 min, washed, and dried to obtain modified carbon nanotubes@AgNPs;

[0026] The usage ratio of modified carbon nanotubes, DMF, AgNO3 and NaBH4 is 2g:30mL:0.1-0.15g:0.1-0.2g.

[0027] In the above steps, silver nitrate dissociates into silver ions in water. Sodium borohydride, acting as a strong reducing agent, reduces the silver ions to silver atoms, thereby forming AgNPs. The modified carbon nanotubes contain sulfonic acid groups on their surface, which interact with the silver ions to stabilize the AgNPs and prevent their aggregation. This helps to evenly disperse the AgNPs on the surface of the modified carbon nanotubes. These evenly dispersed AgNPs have strong conductivity, which synergizes with the carbon nanotubes to enhance the electrochemical performance of the battery.

[0028] A3. Preparation of carbon source: Disperse the modified carbon nanotubes@AgNPs and dopamine hydrochloride in Tris buffer, stir at room temperature for 40-48 hours, wash, and dry to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source.

[0029] The usage ratio of modified carbon nanotubes@AgNPs, dopamine hydrochloride, and Tris buffer is 2-2.5 g: 0.1-0.4 g: 80 mL.

[0030] The modified carbon nanotubes@AgNPs@PDA were prepared through the self-polymerization of dopamine in the aforementioned steps. PDA can further enhance the dispersion of AgNPs and coat their surface, improving their conductivity.

[0031] PDA has strong adhesion, which enhances the compatibility between the carbon layer and the amorphous niobium oxide-coated substrate. This allows the carbon layer to form a uniform and tightly bonded carbon coating on the surface of the amorphous niobium oxide-coated substrate, resulting in excellent cycling performance for the lithium-supplementing cathode material obtained by the present invention. After sintering, PDA forms a nitrogen-doped carbon layer, which has high conductivity and provides a continuous electron transport path for the Li₅FeO₄ particles, reducing the overall electrode resistance and improving the battery's cycling performance.

[0032] In a third aspect, the present invention provides a positive electrode material, comprising a positive electrode active material and a positive electrode lithium replenisher, wherein the positive electrode lithium replenisher is the above-mentioned positive electrode lithium replenisher additive, or a positive electrode lithium replenisher additive prepared by the above-mentioned preparation method of the positive electrode lithium replenisher additive.

[0033] Furthermore, the positive electrode active material is at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and lithium nickel cobalt manganese oxide.

[0034] Furthermore, the mass ratio of the positive electrode active material to the positive electrode lithium replenisher is 9:(0.5-1).

[0035] Beneficial effects of the present invention:

[0036] The present invention's positive-electrode lithium replenisher additive uses Li₅FeO₄ as a matrix, with an amorphous niobium oxide layer and a conductive carbon layer sequentially coated on its outer surface. The conductive carbon layer is made of modified carbon nanotubes@AgNPs@PDA. This prevents the positive-electrode lithium replenisher matrix from reacting with water and carbon dioxide in air, thereby reducing residual alkali content. It also improves the surface stability and structural integrity of the positive-electrode lithium replenisher during cycling, and enhances the battery's cycling performance and specific capacity. This invention is of great significance for the development of reliable positive-electrode lithium replenishers or any other positive-electrode lithium replenisher materials for high-energy lithium-ion batteries, as follows:

[0037] (1) The amorphous niobium oxide layer and the conductive carbon layer are tightly connected to form a tightly bound composite wrapping layer, so that the positive electrode lithium supplement additive obtained by the present invention has excellent electrochemical performance and surface stability, and reduces the residual alkali content on the substrate surface.

[0038] (2) The conductive carbon layer is doped with nitrogen, sulfur, and fluorine. This composite doping can improve the conductivity of the carbon layer, thereby improving the conductivity of the positive electrode lithium supplement additive. The conductive carbon layer also contains uniformly dispersed nanosilver, which can further improve the conductivity of the positive electrode lithium supplement additive. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below with reference to the accompanying drawings.

[0040] Figure 1This is a SEM image of the positive electrode lithium supplement additive obtained in Example 1 of the present invention;

[0041] Figure 2 This is a SEM image of the positive electrode lithium supplement additive obtained in Comparative Example 8 of the present invention. DETAILED DESCRIPTION

[0042] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0043] The carbon nanotubes in the present invention have a diameter of 20 nanometers and an average length of 10 micrometers.

[0044] Preparation Example 1

[0045] The preparation method of the carbon source is:

[0046] A1. Preparation of modified carbon nanotubes: 2g of carbon nanotubes were added to 40mL of mixed acid, which was composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. The mixture was ultrasonicated at 50°C for 3h, washed 5 times with deionized water, and dried at 70°C for 10h to obtain acidified carbon nanotubes; 2g of acidified carbon nanotubes were mixed with 2g of 3-amino-4-fluorobenzenesulfonic acid, 0.2g of dicyclohexylcarbodiimide, and 80mL of DMF. Ultrasonicated for 30min to fully dissolve and disperse the mixture, deoxygenated with nitrogen for 20min, and then refluxed at 120°C for 24h under stirring. After the reaction, the product was filtered, washed, and dried to obtain modified carbon nanotubes.

[0047] A2. Preparation of modified carbon nanotubes@AgNPs: 2 g of modified carbon nanotubes were ultrasonically dispersed in 30 mL of DMF, followed by the addition of 0.1 g of AgNO3 and stirring for 6 h; then 0.1 g of NaBH4 was added, stirred for 10 min, washed, and dried to obtain modified carbon nanotubes@AgNPs;

[0048] A3. Preparation of carbon source: 2 g of modified carbon nanotubes@AgNPs and 0.1 g of dopamine hydrochloride were dispersed in 80 mL of Tris buffer, stirred at room temperature for 40 h, washed, and dried to obtain modified carbon nanotubes@AgNPs@PDA, which was the carbon source.

[0049] Preparation Example 2

[0050] The preparation method of the carbon source is:

[0051] A1. Preparation of modified carbon nanotubes: 2g of carbon nanotubes were added to 40mL of mixed acid, which was composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. The mixture was ultrasonicated at 50°C for 3h, washed with deionized water 5 times, and dried at 70°C for 10h to obtain acidified carbon nanotubes; 2g of acidified carbon nanotubes were mixed with 5g of 3-amino-4-fluorobenzenesulfonic acid, 0.3g of dicyclohexylcarbodiimide, and 80mL of DMF. Ultrasonicated for 30min to fully dissolve and disperse the mixture, deoxygenated with nitrogen for 20min, and then refluxed at 120°C for 24h under stirring. After the reaction, the product was filtered, washed, and dried to obtain modified carbon nanotubes.

[0052] A2. Preparation of modified carbon nanotubes@AgNPs: 2 g of modified carbon nanotubes were ultrasonically dispersed in 30 mL of DMF, followed by the addition of 0.15 g of AgNO3 and stirring for 6 h; then 0.2 g of NaBH4 was added, stirred for 10 min, washed, and dried to obtain modified carbon nanotubes@AgNPs;

[0053] A3. Preparation of carbon source: 2 g of modified carbon nanotubes@AgNPs and 0.4 g of dopamine hydrochloride were dispersed in 80 mL of Tris buffer, stirred at room temperature for 40 h, washed, and dried to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source.

[0054] Preparation Example 3

[0055] Compared with Preparation Example 1, this Preparation Example differs in that dopamine hydrochloride is omitted. The specific steps are as follows:

[0056] A1. Preparation of modified carbon nanotubes: 2g of carbon nanotubes were added to 40mL of mixed acid, which was composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. The mixture was ultrasonicated at 50°C for 3h, washed 5 times with deionized water, and dried at 70°C for 10h to obtain acidified carbon nanotubes; 2g of acidified carbon nanotubes were mixed with 2g of 3-amino-4-fluorobenzenesulfonic acid, 0.2g of dicyclohexylcarbodiimide, and 80mL of DMF. Ultrasonicated for 30min to fully dissolve and disperse the mixture, deoxygenated with nitrogen for 20min, and then refluxed at 120°C for 24h under stirring. After the reaction, the product was filtered, washed, and dried to obtain modified carbon nanotubes.

[0057] A2. Preparation of carbon source: ultrasonically disperse 2 g of modified carbon nanotubes in 30 mL of DMF, then add 0.1 g of AgNO3 and stir for 6 h; then add 0.1 g of NaBH4 and stir for 10 min, then wash and dry to obtain the carbon source.

[0058] Preparation Example 4

[0059] This preparation example is different from preparation example 3 in that 3-amino-4-fluorobenzenesulfonic acid is omitted. The specific steps are as follows:

[0060] A1. Preparation of modified carbon nanotubes: 2 g of carbon nanotubes were added to 40 mL of mixed acid consisting of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. The mixture was sonicated at 50°C for 3 h, washed five times with deionized water, and dried at 70°C for 10 h to obtain modified carbon nanotubes.

[0061] A2. Preparation of carbon source: ultrasonically disperse 2 g of modified carbon nanotubes in 30 mL of DMF, then add 0.1 g of AgNO3 and stir for 6 h; then add 0.1 g of NaBH4 and stir for 10 min, then wash and dry to obtain the carbon source.

[0062] Preparation Example 5

[0063] The difference between this preparation example and preparation example 4 is that the carbon source is acidified carbon nanotubes. The specific steps are as follows:

[0064] 2 g of carbon nanotubes were added to 40 mL of mixed acid consisting of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1, ultrasonicated at 50°C for 3 h, washed with deionized water 5 times, and dried at 70°C for 10 h to obtain acidified carbon nanotubes.

[0065] Preparation Example 6

[0066] The difference between this preparation example and preparation example 1 is that the carbon source is carbon nanotubes.

[0067] Example 1

[0068] The preparation method of the positive electrode lithium supplement additive is as follows:

[0069] S1. Preparation of a positive electrode lithium supplement matrix: lithium nitrate and lithium hydroxide monohydrate are mixed and ground, with the molar ratio of lithium nitrate to lithium hydroxide monohydrate being 0.55:0.41, and then placed in a muffle furnace for melting. After cooling, the mixture is taken out and ground to obtain a mixed lithium salt, and then the mixed lithium salt is mixed with nano-ferric oxide and ground and pressed into tablets. The molar ratio of Fe to Li elements in the nano-ferric oxide and the mixed lithium salt is 5.2:1. The tablets are calcined under an argon atmosphere at a calcination temperature of 750°C, a heating rate of 5°C / min, and a calcination time of 10 hours. After cooling, the tablets are taken out and ground to obtain Li5FeO4;

[0070] S2. Preparation of an amorphous niobium oxide-coated matrix material: dissolving niobium ethanolate and sucrose in 10 mL of a mixed solvent consisting of water and isopropanol, wherein the molar ratio of niobium ethanolate to sucrose is 1:0.2 and the volume ratio of water to isopropanol in the mixed solvent is 2:1, and stirring for 1 hour to obtain an amorphous niobium oxide solution; adding 2 g of Li5FeO4 to 10 mL of the amorphous niobium oxide solution and stirring, and then calcining under an argon atmosphere at a calcination temperature of 800° C., a heating rate of 5° C. / min, and a sintering time of 4 hours to obtain an amorphous niobium oxide-coated matrix material;

[0071] S3. Preparation of positive electrode lithium replenishing additive: The amorphous niobium oxide-coated matrix material obtained in S2 and the carbon source prepared in Preparation Example 1 are dispersed in anhydrous ethanol, where the mass of the carbon source is 1% of the mass of Li5FeO4. After grinding and stirring, the mixture is calcined under an argon atmosphere at a calcination temperature of 700°C, a heating rate of 5°C / min, and a sintering time of 5h to obtain a positive electrode lithium replenishing additive.

[0072] The SEM image of the prepared positive electrode lithium supplement additive is as follows: Figure 1 As shown, from Figure 1 It can be seen that the positive electrode lithium supplement additive has uniform size.

[0073] Example 2

[0074] The preparation method of the positive electrode lithium supplement additive is as follows:

[0075] S1. Preparation of a positive electrode lithium supplement matrix: lithium nitrate and lithium hydroxide monohydrate are mixed and ground, with the molar ratio of lithium nitrate to lithium hydroxide monohydrate being 0.55:0.41, and then placed in a muffle furnace for melting. After cooling, the mixture is taken out and ground to obtain a mixed lithium salt, and then the mixed lithium salt is mixed with nano-ferric oxide and ground and pressed into tablets. The molar ratio of Fe to Li elements in the nano-ferric oxide and the mixed lithium salt is 5.2:1. The tablets are calcined under an argon atmosphere at a calcination temperature of 750°C, a heating rate of 5°C / min, and a calcination time of 10 hours. After cooling, the tablets are taken out and ground to obtain Li5FeO4;

[0076] S2. Preparation of an amorphous niobium oxide-coated matrix material: dissolving niobium ethanolate and sucrose in 10 mL of a mixed solvent consisting of water and isopropanol, wherein the molar ratio of niobium ethanolate to sucrose is 1:0.35 and the volume ratio of water to isopropanol in the mixed solvent is 2:1, and stirring for 1 hour to obtain an amorphous niobium oxide solution; adding 2 g of Li5FeO4 to 16 mL of the amorphous niobium oxide solution and stirring, and then calcining under an argon atmosphere at a calcination temperature of 800° C., a heating rate of 5° C. / min, and a sintering time of 4 hours to obtain an amorphous niobium oxide-coated matrix material;

[0077] S3. Preparation of positive electrode lithium replenishing additive: The amorphous niobium oxide-coated matrix material obtained in S2 and the carbon source prepared in Preparation Example 2 are dispersed in anhydrous ethanol, where the mass of the carbon source is 2% of the mass of Li5FeO4. After grinding and stirring, the mixture is calcined under an argon atmosphere at a calcination temperature of 700°C, a heating rate of 5°C / min, and a sintering time of 5h to obtain a positive electrode lithium replenishing additive.

[0078] Example 3

[0079] The difference between this embodiment and embodiment 2 is that the mass of the carbon source is 3% of the mass of Li5FeO4, and the remaining raw materials and steps are the same as those in embodiment 2.

[0080] Example 4

[0081] The difference between this embodiment and embodiment 2 is that the mass of the carbon source is 4% of the mass of Li5FeO4, and the remaining raw materials and steps are the same as those in embodiment 2.

[0082] Example 5

[0083] The difference between this embodiment and embodiment 2 is that the mass of the carbon source is 5% of the mass of Li5FeO4, and the remaining raw materials and steps are the same as those in embodiment 2.

[0084] Example 6

[0085] The difference between this embodiment and embodiment 5 is that the molar ratio of niobium ethoxide to sucrose is 1:0.5, and the remaining raw materials and steps are the same as those in embodiment 5.

[0086] Comparative Example 1

[0087] Compared with Example 1, this comparative example is different in that the mass of the carbon source is 0.5% of the mass of Li5FeO4, and the remaining raw materials and steps are the same as Example 1.

[0088] Comparative Example 2

[0089] Compared with Example 5, this comparative example is different in that the mass of the carbon source is 5.5% of the mass of Li5FeO4, and the remaining raw materials and steps are the same as Example 5.

[0090] Comparative Example 3

[0091] Compared with Example 1, this comparative example is different in that the carbon source prepared in Preparation Example 1 is replaced by the carbon source prepared in Preparation Example 3, and the remaining raw materials and steps are the same as in Example 1.

[0092] Comparative Example 4

[0093] Compared with Example 1, this comparative example is different in that the carbon source prepared in Preparation Example 1 is replaced by the carbon source prepared in Preparation Example 4, and the remaining raw materials and steps are the same as in Example 1.

[0094] Comparative Example 5

[0095] Compared with Example 1, this comparative example is different in that the carbon source prepared in Preparation Example 1 is replaced by the carbon source prepared in Preparation Example 5, and the remaining raw materials and steps are the same as in Example 1.

[0096] Comparative Example 6

[0097] The difference between this comparative example and Example 1 is that the carbon source prepared in Preparation Example 1 is replaced by the carbon source prepared in Preparation Example 6, and the remaining raw materials and steps are the same as in Example 1.

[0098] Comparative Example 7

[0099] Compared with Example 1, this comparative example is different in that the coating layer contains only amorphous niobium oxide. The specific steps are as follows:

[0100] S1. Preparation of a positive electrode lithium supplement matrix: lithium nitrate and lithium hydroxide monohydrate are mixed and ground, with the molar ratio of lithium nitrate to lithium hydroxide monohydrate being 0.55:0.41, and then placed in a muffle furnace for melting. After cooling, the mixture is taken out and ground to obtain a mixed lithium salt, and then the mixed lithium salt is mixed with nano-ferric oxide and ground and pressed into tablets. The molar ratio of Fe to Li elements in the nano-ferric oxide and the mixed lithium salt is 5.2:1. The tablets are calcined under an argon atmosphere at a calcination temperature of 750°C, a heating rate of 5°C / min, and a calcination time of 10 hours. After cooling, the tablets are taken out and ground to obtain Li5FeO4;

[0101] S2. Preparation of a positive electrode lithium replenishing additive: dissolving ethanolic niobium and sucrose in a mixed solvent consisting of 10 mL of water and isopropanol, wherein the molar ratio of ethanolic niobium and sucrose is 1:0.2 and the volume ratio of water to isopropanol in the mixed solvent is 2:1, and stirring for 1 hour to obtain an amorphous niobium oxide solution; adding 2 g of Li5FeO4 to 10 mL of the amorphous niobium oxide solution and stirring, and then calcining under an argon atmosphere at a calcination temperature of 800°C, a heating rate of 5°C / min, and a sintering time of 4 hours to obtain a positive electrode lithium replenishing additive.

[0102] Comparative Example 8

[0103] Compared with Example 1, this comparative example is different in that the wrapping layer only contains a carbon layer. The specific steps are as follows:

[0104] S1. Preparation of a positive electrode lithium supplement matrix: lithium nitrate and lithium hydroxide monohydrate are mixed and ground, with the molar ratio of lithium nitrate to lithium hydroxide monohydrate being 0.55:0.41, and then placed in a muffle furnace for melting. After cooling, the mixture is taken out and ground to obtain a mixed lithium salt, and then the mixed lithium salt is mixed with nano-ferric oxide and ground and pressed into tablets. The molar ratio of Fe to Li elements in the nano-ferric oxide and the mixed lithium salt is 5.2:1. The tablets are calcined under an argon atmosphere at a calcination temperature of 750°C, a heating rate of 5°C / min, and a calcination time of 10 hours. After cooling, the tablets are taken out and ground to obtain Li5FeO4;

[0105] S2. Preparation of positive electrode lithium replenishing additive: dissolve sucrose in 10 mL of a mixed solvent consisting of water and isopropanol, wherein the volume ratio of water to isopropanol in the mixed solvent is 2:1, and stir for 1 hour to obtain a sucrose solution; add 2 g of Li5FeO4 to 10 mL of the sucrose solution and stir, and then calcine under an argon atmosphere at a calcination temperature of 800°C, a heating rate of 5°C / min, and a sintering time of 4 hours to obtain a positive electrode lithium replenishing additive.

[0106] The positive electrode lithium supplement additives prepared in Examples 1 to 5 and Comparative Examples 1 to 7 were assembled into button-type batteries, specifically as follows: the positive electrode was composed of LiNi 0.8 Co 0.1 Mn 0.1 O2 (90wt%) and the lithium supplement agent (10wt%) prepared by the present invention are composed, and the negative electrode is composed of artificial graphite (95wt%) and SiO x The battery was composed of a mixture of 5wt% and 100% MgCl2 (5wt%). CR2032 button cells were used, with a 1:1 N / P ratio between the positive and negative electrodes. The battery testing method included measuring the initial charge specific capacity at a current density of 0.1C over a voltage range of 2.5V-4.3V. This was followed by 200 charge-discharge cycles at a constant current density of 0.5C, and calculating the capacity retention after each cycle.

[0107] The positive electrode lithium supplement additives prepared in Examples 1 to 5 and Comparative Examples 1 to 7 were tested for residual alkali content and gas expansion rate. The test method is as follows:

[0108] (1) Residual alkali content: Weigh the lithium supplement sample (denoted as m 样 ), dissolved in 50 mL of boiled and cooled deionized water (to remove CO2), ultrasonically dissolved for 10 minutes, filtered through a 0.22 μm filter membrane, transferred to a volumetric flask, and diluted 10-fold with deionized water, recording the constant volume V. The concentration c was then measured using an ion chromatograph; the formula is as follows, where D represents the dilution factor:

[0109] Residual alkali content (%) = ρ × V × D / m 样 ×10 6 ×100%

[0110] (2) Gas expansion rate: Weigh a certain mass of lithium supplement sample, grind and sieve to ensure uniform particle size, and then dry it. Use a pressure-resistant reactor equipped with a pressure sensor to record the pressure change in the reactor (volume V0) in real time. Calculate the gas volume (at standard atmospheric pressure) according to the ideal gas law PV = nRT.

[0111] ΔV=ΔP×V0 / P0 (P0 is standard atmospheric pressure)

[0112] Gas expansion rate (%) = ΔV / V0×100%

[0113] The test results are shown in Table 1.

[0114] Table 1

[0115]

[0116] It can be seen from Table 1 that the performance of the additives prepared in the examples is better than that of the additives prepared in the comparative examples. The only difference between Examples 2-6 and Example 1 is that the raw materials are adjusted within a reasonable range. From the test results, it can be seen that positive electrode materials with good electrochemical performance can be obtained. Compared with Example 5, Example 6 has better performance, which shows that n （乙醇铌） :n （蔗糖） =1:0.5 when the lithium supplement is most effective.

[0117] Compared with Example 1, Comparative Example 1 has a lower carbon source addition amount and its performance is lower than Example 1; compared with Example 5, Comparative Example 2 has a higher carbon source addition amount and its performance is lower than Example 5. The above results show that the addition amount of the carbon source of the present invention is the optimal amount, and adding too much or too little carbon source will affect the overall performance of the additive.

[0118] Compared to Example 1, the performance of Comparative Example 3 declined, indicating that PDA has strong adhesion. This adhesion enhances the compatibility between the carbon layer and the amorphous niobium oxide-coated substrate, allowing the carbon layer to form a uniform and tightly bonded carbon coating on the surface of the amorphous niobium oxide-coated substrate, resulting in excellent cycling performance for the positive lithium-supplementing material obtained in the present invention. Furthermore, after sintering, PDA can generate a nitrogen-doped carbon layer. This nitrogen-doped carbon layer has high conductivity, providing a continuous electron transport path for the Li5FeO4 particles, reducing the overall electrode resistance and improving the battery's cycling performance. PDA can also further enhance the dispersibility of nanosilver and improve its conductivity.

[0119] Compared to Example 1, the performance of Comparative Example 4 declined, indicating that the sulfonic acid groups interact with silver ions, stabilizing the AgNPs and preventing their aggregation, contributing to their uniform dispersion and surface modification. 3-Amino-4-fluorobenzenesulfonic acid, through its steric hindrance effect, improves the dispersion of the carbon nanotubes, thereby contributing to a uniform coating and enhancing the battery's electrochemical performance. Furthermore, subsequent sintering of the modified carbon nanotubes yields sulfur- and fluorine-doped carbon layers, which synergistically enhance the carbon nanotubes' electrical conductivity, thus contributing to the preparation of a higher-performing positive electrode lithium supplement.

[0120] Compared with Example 1, the performance of Comparative Examples 5 and 6 is poor, both of which prove that the modified carbon nanotubes@AgNPs@PDA of the present invention can improve the comprehensive performance of the additive. The effect of Comparative Example 6 is slightly worse than that of Comparative Example 5. The reason is that the dispersion of the acidified carbon nanotubes in Comparative Example 5 is higher than that in Comparative Example 6.

[0121] The performance of Comparative Examples 7 and 8 is lower than that of Example 1, and Comparative Example 8 is lower than Comparative Example 7, indicating that the effect of carbon-doped amorphous niobium oxide is higher than that of a single carbon layer.

[0122] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A positive electrode lithium supplement additive, characterized in that: It includes a positive electrode lithium supplement matrix Li5FeO4 and an amorphous niobium oxide layer and a conductive carbon layer sequentially coated on the outer surface of the matrix; The preparation method of the positive electrode lithium supplement additive comprises the following steps: S1. preparing a positive electrode lithium supplement matrix; S2. Preparing an amorphous niobium oxide-coated matrix material: dissolving niobium ethanol and sucrose in a mixed solvent consisting of water and an organic solvent, and stirring for 1-2 hours to obtain an amorphous niobium oxide solution; adding Li₅FeO₄ to the amorphous niobium oxide solution, stirring, and then calcining under an inert atmosphere to obtain an amorphous niobium oxide-coated matrix material; S3. Preparation of a positive electrode lithium supplement additive: dispersing the amorphous niobium oxide-coated matrix material obtained in S2 and a carbon source in anhydrous ethanol, grinding and stirring, and then calcining under an inert atmosphere to obtain a positive electrode lithium supplement additive; The preparation method of the carbon source is: A1. Preparation of modified carbon nanotubes: adding carbon nanotubes to mixed acid, sonicating at 50°C for 3-5 hours, washing 5-6 times, and drying to obtain acidified carbon nanotubes; mixing the acidified carbon nanotubes with 3-amino-4-fluorobenzenesulfonic acid, dicyclohexylcarbodiimide, and DMF, sonicating for 30-40 minutes, deoxygenating with nitrogen for 20 minutes, and reflux reacting at 120°C with stirring for 24-48 hours. After completion of the reaction, filtering, washing, and drying the product to obtain modified carbon nanotubes; A2. Preparation of modified carbon nanotubes@AgNPs: The modified carbon nanotubes were ultrasonically dispersed in DMF, followed by addition of AgNO3 and stirring for 6-8 h; then NaBH4 was added, stirred for 10-15 min, washed, and dried to obtain modified carbon nanotubes@AgNPs; A3. Preparation of carbon source: Disperse modified carbon nanotubes@AgNPs and dopamine hydrochloride in Tris buffer, stir at room temperature for 40-48 hours, wash, and dry to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source; The ratio of the amorphous niobium oxide solution to Li5FeO4 is 2g:10-16mL; The mass of the carbon source is 1%-5% of the mass of Li5FeO4.

2. A positive electrode lithium supplement additive according to claim 1, characterized in that: In step S1, the specific steps of preparing the positive electrode lithium supplement agent matrix are: Lithium nitrate and lithium hydroxide monohydrate are mixed and ground, melted, cooled, taken out and ground to obtain a mixed lithium salt, and then the mixed lithium salt is mixed with nano-ferric oxide, ground and pressed into tablets, calcined under an inert atmosphere, cooled, taken out and ground to obtain Li5FeO4; Wherein, the molar ratio of lithium nitrate to lithium hydroxide monohydrate is (0.55-0.59):0.41; The molar ratio of Fe element in nano-ferric oxide to Li element in mixed lithium salt is (5.2-5.6):1; The inert atmosphere is one or more of nitrogen, argon, and helium; The calcination temperature is 750-800°C, the heating rate is 5-10°C / min, and the calcination time is 10-12h.

3. A positive electrode lithium supplement additive according to claim 1, characterized in that: In step S2, the molar ratio of niobium ethoxide to sucrose is 1:(0.2-0.5); The volume ratio of water to organic solvent in the mixed solvent is (2-4):1; The organic solvent is any one of ethanol, anhydrous methanol, propanol, isopropanol and acetone; The inert atmosphere is one or more of nitrogen, argon, and helium; The calcination temperature is 600-1200°C, the heating rate is 5-10°C / min, and the sintering time is 4-6h.

4. A positive electrode lithium supplement additive according to claim 1, characterized in that: In step S3, the inert atmosphere is one or more of nitrogen, argon, and helium; The calcination temperature is 700-850°C, the heating rate is 5-10°C / min, and the sintering time is 2-5h.

5. The positive electrode lithium supplement additive according to claim 1, characterized in that: The ratio of carbon nanotubes to mixed acid in step A1 is 2 g: 40-50 mL; The mixed acid is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of (1-3):1; The ratio of acidified carbon nanotubes, 3-amino-4-fluorobenzenesulfonic acid, dicyclohexylcarbodiimide, and DMF is 2 g: 2-5 g: 0.2-0.3 g: 80 mL; The ratio of modified carbon nanotubes, DMF, AgNO3, and NaBH4 in step A2 is 2 g: 30 mL: 0.1-0.15 g: 0.1-0.2 g; The usage ratio of the modified carbon nanotubes@AgNPs, dopamine hydrochloride, and Tris buffer in step A3 is 2-2.5 g: 0.1-0.4 g: 80 mL.

6. A positive electrode material, characterized in that The invention comprises a positive electrode active material and a positive electrode lithium replenishing agent, wherein the positive electrode lithium replenishing agent is the positive electrode lithium replenishing additive according to any one of claims 1 to 5.

7. A positive electrode material according to claim 6, characterized in that: The positive electrode active material is at least one of lithium cobalt oxide, lithium manganate, lithium iron phosphate and lithium nickel cobalt manganate; the mass ratio of the positive electrode active material to the positive electrode lithium supplement is 9: (0.5-1).

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