Positive electrode lithium supplement additive, preparation method thereof and positive electrode material

Abstract

The invention discloses a positive electrode lithium supplement additive, a preparation method thereof and a positive electrode material, and belongs to the technical field of lithium ion batteries. The positive electrode lithium supplement additive comprises a positive electrode lithium supplement agent matrix, and an amorphous niobium oxide layer and a conductive carbon layer which are sequentially coated on the outer surface of the matrix, and the conductive carbon layer is a modified carbon nanotube (at) AgNPs (at) PDA. According to the lithium supplement additive for the positive electrode, Li5FeO4 serves as a matrix, the amorphous niobium oxide layer and the conductive carbon layer are sequentially wrapped on the outer layer of Li5FeO4, the phenomenon that the matrix of the lithium supplement additive for the positive electrode reacts with water and carbon dioxide in air is avoided, and the content of residual alkali is reduced; the surface stability and the structural integrity of the positive electrode lithium supplementing material in the circulation process are improved; and the cycle performance and the specific capacity of the battery are improved. The research can provide great help in development of reliable anode lithium supplement materials and any other anode lithium supplement materials for high-energy lithium ion batteries.

Description

Technical Field

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

[0002] With the booming development of the electric vehicle industry, lithium-ion batteries have been widely used in the fields of new energy vehicles, energy storage systems, etc. due to their outstanding advantages such as high energy density, high working voltage, and low self-discharge rate. Currently, how to further improve the energy density of lithium-ion batteries to meet the continuously increasing performance requirements in the industrial field has become the research focus in this field. In a lithium-ion battery system using a graphite-based anode, a solid electrolyte interface (SEI) film will be formed on the anode surface during the first charging process. This process is accompanied by the decomposition of the liquid electrolyte, resulting in the irreversible consumption of some active lithium ions, causing capacity attenuation during the first charge and discharge process of the battery. For a silicon-based anode material with a higher specific capacity, significant volume expansion and contraction will occur during the lithium ion insertion / extraction process, resulting in continuous damage and reconstruction of the SEI film, further exacerbating the loss of active lithium ions, seriously restricting the improvement of the energy density of lithium-ion batteries. To compensate for the above capacity loss, lithium supplement technology has become the key solution. Currently, the lithium supplement methods mainly include cathode lithium supplement, anode lithium supplement, and electrolyte lithium supplement. Among them, cathode lithium supplement has developed into the mainstream direction of current lithium supplement technology due to its significant advantages such as high safety, good process compatibility, and controllable cost, and shows important application prospects in the field of power batteries.

[0003] Li5FeO4 stands out among a group of lithium supplement agents due to its high theoretical specific capacity. However, currently, there are still problems such as too high residual lithium and poor cycle performance in the use of Li5FeO4, restricting the application scenarios of Li5FeO4. Summary of the Invention

[0004] The purpose of the present invention is to provide a cathode lithium supplement additive, a preparation method thereof, and a cathode material to solve the problems of too high residual lithium and poor cycle performance still existing in the use of Li5FeO4 in the background art.

[0005] The purpose of the present invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a cathode lithium supplement additive, including a cathode lithium supplement agent matrix Li5FeO4 and an amorphous niobium oxide layer and a conductive carbon layer sequentially coated on the outer surface of the matrix; The dosage ratio of the amorphous niobium oxide solution in the amorphous niobium oxide layer to Li5FeO4 is 2g:10 - 16mL; The mass of the carbon source in the conductive carbon layer is 1% - 5% of the mass of Li5FeO4; The carbon source is modified carbon nanotubes@AgNPs@PDA.

[0006] In the present invention, by coating amorphous niobium oxide (NbO x C y ) on the matrix of the cathode lithium supplement agent, it is possible to isolate the surface of the cathode lithium supplement agent matrix from water and carbon dioxide in the air, increase the stability in the air, and at the same time avoid the reaction of the cathode lithium supplement agent matrix with water and carbon dioxide in the air; and the oxide can react with the residual lithium on the surface of the inner core, thereby reducing the residual lithium of the lithium supplement agent and reducing the side reactions during the application of the material, and can effectively alleviate the erosion of the electrolyte on the inner core. However, the electrical conductivity of the amorphous niobium oxide layer is limited, which is not conducive to preparing a cathode lithium supplement additive with good electrical conductivity. If the electrical conductivity of the cathode lithium supplement additive is poor, the charge and discharge efficiency of the battery will be affected, and further the performance of the battery will decline. Therefore, the present invention adds a layer of conductive carbon layer on the basis of the amorphous niobium oxide layer, which can further improve the electrochemical performance of the battery.

[0007] In a second aspect, the present invention provides a preparation method of a cathode lithium supplement additive, comprising the following steps: S1. Prepare the matrix of the cathode lithium supplement agent: Take lithium nitrate and lithium hydroxide monohydrate, mix and grind them, then place them in a muffle furnace for melting, take them out and grind after cooling to obtain a mixed lithium salt, and then mix and grind the mixed lithium salt with nano-ferric oxide and press into tablets, and calcine in an inert atmosphere, take it out and grind after cooling to obtain Li5FeO4; S2. Prepare the matrix material wrapped with amorphous niobium oxide: Dissolve niobium ethoxide and sucrose in a mixed solvent, the mixed solvent is composed of water and an organic solvent, stir for 1-2 h to obtain an amorphous niobium oxide solution; add Li5FeO4 to the amorphous niobium oxide solution and stir, and then calcine in an inert atmosphere to obtain the matrix material wrapped with amorphous niobium oxide; S3. Prepare the cathode lithium supplement additive: Disperse the matrix material wrapped with amorphous niobium oxide obtained in S2 and a carbon source into absolute ethanol, grind and stir, and then calcine in an inert atmosphere to obtain the cathode lithium supplement additive.

[0008] Further, in step S1, the molar ratio of lithium nitrate to lithium hydroxide monohydrate is (0.55-0.59):0.41; the molar ratio of the Fe element in nano-ferric oxide to the Li element in the mixed lithium salt is (5.2-5.6):1.

[0009] Further, in step S1, the inert atmosphere is one or more of nitrogen, argon, and helium.

[0010] Further, in step S1, the calcination temperature is 750-800 °C, the heating rate is 5-10 °C / min, and the calcination time is 10-12 h.

[0011] Further, 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, absolute methanol, propanol, isopropanol, and acetone.

[0012] Further, 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 - 6 h.

[0013] Further, 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 - 5 h.

[0014] Further, in step S3, the preparation method of the carbon source is as follows: A1. Preparation of modified carbon nanotubes: Add carbon nanotubes to the mixed acid, ultrasonicate at 50 °C for 3 - 5 h, wash with deionized water 5 - 6 times, and dry at 70 °C for 10 h to obtain acidified carbon nanotubes; Mix the acidified carbon nanotubes with 3 - amino - 4 - fluorobenzenesulfonic acid, dicyclohexylcarbodiimide, and DMF, ultrasonicate for 30 - 40 min to fully dissolve and disperse, deoxygenate by passing nitrogen for 20 min, and then reflux and react under stirring at 120 °C for 24 - 48 h. After the reaction, filter, wash, and dry the product to obtain modified carbon nanotubes; Among them, the dosage ratio of carbon nanotubes to the mixed acid 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 dosage 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.

[0015] In the above steps, by adding carbon nanotubes to the mixed acid, acidified carbon nanotubes containing carboxyl groups are obtained. Then, using dicyclohexylcarbodiimide as a condensing agent and DMF as a solvent, the carboxyl groups of the acidified carbon nanotubes react with the amino groups in 3 - amino - 4 - fluorobenzenesulfonic acid to undergo an amide reaction, 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 effects, thus helping to obtain a uniform coating layer and improving the electrochemical performance of the battery. Moreover, after subsequent sintering, the modified carbon nanotubes can obtain a sulfur - doped carbon layer and a fluorine - doped carbon layer, which can synergistically improve the conductivity of carbon nanotubes, thereby preparing a cathode lithium - supplementing additive with better performance.

[0016] A2. Preparation of modified carbon nanotubes@AgNPs: Ultrasonically disperse the modified carbon nanotubes in DMF, then add AgNO3 and stir for 6 - 8 h; then add NaBH4 and stir for 10 - 15 min for washing and drying to obtain modified carbon nanotubes@AgNPs; Among them, the dosage ratio of the modified carbon nanotubes, DMF, AgNO3, and NaBH4 is 2 g: 30 mL: 0.1 - 0.15 g: 0.1 - 0.2 g.

[0017] In the above steps, silver ions are ionized from silver nitrate in water. As a strong reducing agent, sodium borohydride can reduce silver ions to silver atoms, and then form AgNPs particles. The surface of the modified carbon nanotubes contains sulfonic acid groups, and there is an interaction between the sulfonic acid groups and silver ions, thus stabilizing the AgNPs particles and preventing their aggregation, which helps the AgNPs to be evenly dispersed on the surface of the modified carbon nanotubes. The evenly dispersed AgNPs have strong conductivity and can synergistically improve the electrochemical performance of the battery with carbon nanotubes.

[0018] A3. Preparation of carbon source: Disperse the modified carbon nanotubes@AgNPs and hydrochloric acid dopamine in Tris buffer solution and stir at room temperature for 40 - 48 h, wash and dry to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source.

[0019] Among them, the dosage ratio of the modified carbon nanotubes@AgNPs, hydrochloric acid dopamine, and Tris buffer solution is 2 - 2.5 g: 0.1 - 0.4 g: 80 mL.

[0020] In the above steps, modified carbon nanotubes@AgNPs@PDA is prepared through the self - polymerization of dopamine. PDA can further enhance the dispersion of AgNPs, wrap on the surface of AgNPs, and improve the conductivity of AgNPs.

[0021] PDA has strong adhesion, and its adhesion enhances the compatibility between the carbon layer and the amorphous niobium oxide - coated matrix material, enabling the carbon layer to form a uniform and tightly - bound carbon - coated layer on the surface of the amorphous niobium oxide - coated matrix material, making the positive electrode lithium - supplementing material obtained by the present invention have excellent cycle performance. After sintering, PDA can generate a nitrogen - doped carbon layer, and the nitrogen - doped carbon layer has high conductivity, providing a continuous electron transport path for Li5FeO4 particles, reducing the overall resistance of the electrode, and improving the cycle performance of the battery.

[0022] In the third aspect, the present invention provides a positive electrode material, including a positive electrode active material and a positive electrode lithium - supplementing agent. The positive electrode lithium - supplementing agent is the above - mentioned positive electrode lithium - supplementing additive or the positive electrode lithium - supplementing additive prepared by using the preparation method of the above - mentioned positive electrode lithium - supplementing additive.

[0023] Further, the positive electrode active material is at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, and lithium nickel cobalt manganate.

[0024] Further, the mass ratio of the positive electrode active material to the positive electrode lithium supplement agent is 9:(0.5 - 1).

[0025] Beneficial effects of the present invention: The positive electrode lithium supplement additive of the present invention uses Li5FeO4 as the matrix, and is sequentially coated with an amorphous niobium oxide layer and a conductive carbon layer on its outer layer. The material of the conductive carbon layer is modified carbon nanotubes@AgNPs@PDA, which avoids the reaction of the positive electrode lithium supplement agent matrix with water and carbon dioxide in the air, is beneficial to reducing the residual alkali content; improves the surface stability and structural integrity of the positive electrode lithium supplement material during the cycling process; improves the cycling performance and specific capacity of the battery. It is of great help to develop reliable positive electrode lithium supplement materials or any other positive electrode lithium supplement materials for high-energy lithium-ion batteries, specifically as follows: (1) The amorphous niobium oxide layer and the conductive carbon layer are tightly connected, and a tightly combined composite coating layer can be formed, 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 matrix surface.

[0026] (2) There is nitrogen, sulfur, and fluorine doping between the conductive carbon layers. This composite doping can improve the conductivity of the carbon layer, thereby enhancing the conductivity of the positive electrode lithium supplement additive. The conductive carbon layer also contains uniformly dispersed nano-silver, which can further enhance the conductivity of the positive electrode lithium supplement additive. Description of the drawings

[0027] The present invention will be further described below with reference to the drawings.

[0028] Figure 1 is the SEM image of the positive electrode lithium supplement additive obtained in Example 1 of the present invention; Figure 2 is the SEM image of the positive electrode lithium supplement additive obtained in Comparative Example 8 of the present invention. Specific embodiments

[0029] The specific embodiments of the present invention will be described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0030] The carbon nanotubes in the present invention have a diameter of 20 nanometers and an average length of 10 micrometers.

[0031] Preparation Example 1

[0032] The preparation method of the carbon source is as follows: A1. Preparation of modified carbon nanotubes: Add 2 g of carbon nanotubes to 40 mL of a mixed acid, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. Ultrasonicate for 3 h at 50 °C, wash 5 times with deionized water, and dry at 70 °C for 10 h to obtain acidified carbon nanotubes; Mix 2 g of acidified carbon nanotubes with 2 g of 3-amino-4-fluorobenzenesulfonic acid, 0.2 g of dicyclohexylcarbodiimide, and 80 mL of DMF. Ultrasonicate for 30 min to fully dissolve and disperse, deoxygenate by passing nitrogen for 20 min, and then reflux and react under stirring at 120 °C for 24 h. After the reaction, filter, wash, and dry the product to obtain modified carbon nanotubes; A2. Preparation of modified carbon nanotubes@AgNPs: 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, stir and react for 10 min, wash, and dry to obtain modified carbon nanotubes@AgNPs; A3. Preparation of carbon source: Disperse 2 g of modified carbon nanotubes@AgNPs and 0.1 g of hydrochloric acid dopamine in 80 mL of Tris buffer solution, stir at room temperature for 40 h, wash, and dry to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source.

[0033] Preparation Example 2

[0034] The preparation method of the carbon source is as follows: A1. Preparation of modified carbon nanotubes: Add 2 g of carbon nanotubes to 40 mL of a mixed acid, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. Ultrasonicate for 3 h at 50 °C, wash 5 times with deionized water, and dry at 70 °C for 10 h to obtain acidified carbon nanotubes; Mix 2 g of acidified carbon nanotubes with 5 g of 3-amino-4-fluorobenzenesulfonic acid, 0.3 g of dicyclohexylcarbodiimide, and 80 mL of DMF. Ultrasonicate for 30 min to fully dissolve and disperse, deoxygenate by passing nitrogen for 20 min, and then reflux and react under stirring at 120 °C for 24 h. After the reaction, filter, wash, and dry the product to obtain modified carbon nanotubes; A2. Preparation of modified carbon nanotubes@AgNPs: Ultrasonically disperse 2 g of modified carbon nanotubes in 30 mL of DMF, then add 0.15 g of AgNO3 and stir for 6 h; then add 0.2 g of NaBH4, stir and react for 10 min, wash, and dry to obtain modified carbon nanotubes@AgNPs; A3. Preparation of carbon source: Disperse 2 g of modified carbon nanotubes@AgNPs and 0.4 g of hydrochloric acid dopamine in 80 mL of Tris buffer solution, stir at room temperature for 40 h, wash, and dry to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source.

[0035] Preparation Example 3

[0036] This preparation example is different from Preparation Example 1 in that dopamine hydrochloride is omitted. The specific steps are as follows: A1. Preparation of modified carbon nanotubes: Add 2 g of carbon nanotubes to 40 mL of mixed acid, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. Ultrasonic for 3 h at 50 °C, wash 5 times with deionized water, and dry at 70 °C for 10 h to obtain acidified carbon nanotubes; Mix 2 g of acidified carbon nanotubes with 2 g of 3-amino-4-fluorobenzenesulfonic acid, 0.2 g of dicyclohexylcarbodiimide, and 80 mL of DMF. Ultrasonic for 30 min to fully dissolve and disperse, deoxygenate by passing nitrogen for 20 min, and then reflux and react for 24 h under stirring at 120 °C. After the reaction, filter, wash, and dry the product to obtain modified carbon nanotubes; 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 and react for 10 min, wash, and dry to obtain the carbon source.

[0037] Preparation Example 4

[0038] This preparation example is different from Preparation Example 3 in that 3-amino-4-fluorobenzenesulfonic acid is omitted. The specific steps are as follows: A1. Preparation of modified carbon nanotubes: Add 2 g of carbon nanotubes to 40 mL of mixed acid, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. Ultrasonic for 3 h at 50 °C, wash 5 times with deionized water, and dry at 70 °C for 10 h to obtain modified carbon nanotubes; 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 and react for 10 min, wash, and dry to obtain the carbon source.

[0039] Preparation Example 5

[0040] This preparation example is different from Preparation Example 4 in that the carbon source is acidified carbon nanotubes. The specific steps are as follows: Add 2 g of carbon nanotubes to 40 mL of mixed acid, which is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2:1. Ultrasonic for 3 h at 50 °C, wash 5 times with deionized water, and dry at 70 °C for 10 h to obtain acidified carbon nanotubes.

[0041] Preparation Example 6

[0042] This preparation example is different from Preparation Example 1 in that the carbon source is carbon nanotubes.

[0043] Example 1

[0044] The preparation method of the cathode lithium supplement additive is as follows: S1. Preparation of the cathode lithium supplement matrix: Mix lithium nitrate and lithium hydroxide monohydrate and grind them. The molar ratio of lithium nitrate to lithium hydroxide monohydrate is 0.55:0.41. Then place it in a muffle furnace for melting. After cooling, take it out and grind it to obtain a mixed lithium salt. Then mix the mixed lithium salt with nano-ferric oxide and grind them and press into tablets. The molar ratio of Fe to Li elements in nano-ferric oxide to the mixed lithium salt is 5.2:1. Calcinate it under an argon atmosphere. The calcination temperature is 750 °C, the heating rate is 5 °C / min, and the calcination time is 10 h. After cooling, take it out and grind it to obtain Li5FeO4; S2. Preparation of the amorphous niobium oxide-coated matrix material: Dissolve niobium ethoxide and sucrose in a mixed solvent composed of 10 mL of water and isopropanol. The molar ratio of niobium ethoxide to sucrose is 1:0.2, and the volume ratio of water to isopropanol in the mixed solvent is 2:1. Stir for 1 h to obtain an amorphous niobium oxide solution; Add 2 g of Li5FeO4 to 10 mL of the amorphous niobium oxide solution and stir. Then calcinate it under an argon atmosphere. The calcination temperature is 800 °C, the heating rate is 5 °C / min, and the sintering time is 4 h to obtain the amorphous niobium oxide-coated matrix material; S3. Preparation of the cathode lithium supplement additive: Disperse the amorphous niobium oxide-coated matrix material obtained in S2 and the carbon source prepared in Preparation Example 1 into absolute ethanol. The mass of the carbon source is 1% of the mass of Li5FeO4. After grinding and stirring, calcinate it under an argon atmosphere. The calcination temperature is 700 °C, the heating rate is 5 °C / min, and the sintering time is 5 h to obtain the cathode lithium supplement additive.

[0045] The SEM image of the prepared cathode lithium supplement additive is as Figure 1 shown. It can be seen from Figure 1 this that the size of the cathode lithium supplement additive is uniform.

[0046] Example 2

[0047] The preparation method of the cathode lithium supplement additive is as follows: S1. Preparation of the cathode lithium supplement matrix: Mix lithium nitrate and lithium hydroxide monohydrate and grind them. The molar ratio of lithium nitrate to lithium hydroxide monohydrate is 0.55:0.41. Then place it in a muffle furnace for melting. After cooling, take it out and grind it to obtain a mixed lithium salt. Then mix the mixed lithium salt with nano-ferric oxide and grind them and press into tablets. The molar ratio of Fe to Li elements in nano-ferric oxide to the mixed lithium salt is 5.2:1. Calcinate it under an argon atmosphere. The calcination temperature is 750 °C, the heating rate is 5 °C / min, and the calcination time is 10 h. After cooling, take it out and grind it to obtain Li5FeO4; S2. Preparation of amorphous niobium oxide-coated matrix material: Dissolve niobium ethoxide and sucrose in a mixed solvent composed of 10 mL of water and isopropanol. The molar ratio of niobium ethoxide to sucrose is 1:0.35, and the volume ratio of water to isopropanol in the mixed solvent is 2:1. Stir for 1 h to obtain an amorphous niobium oxide solution; Add 2 g of Li5FeO4 to 16 mL of the amorphous niobium oxide solution and stir. Then, calcine it under an argon atmosphere. The calcination temperature is 800 °C, the heating rate is 5 °C / min, and the sintering time is 4 h to obtain the amorphous niobium oxide-coated matrix material; S3. Preparation of cathode lithium supplement additive: Disperse the amorphous niobium oxide-coated matrix material obtained in S2 and the carbon source prepared in Preparation Example 2 into absolute ethanol. The mass of the carbon source is 2% of the mass of Li5FeO4. After grinding and stirring, calcine it under an argon atmosphere. The calcination temperature is 700 °C, the heating rate is 5 °C / min, and the sintering time is 5 h to obtain the cathode lithium supplement additive.

[0048] Example 3

[0049] Compared with Example 2, the difference in this example is that the mass of the carbon source is 3% of the mass of Li5FeO4, and the other raw materials and steps are the same as those in Example 2.

[0050] Example 4

[0051] Compared with Example 2, the difference in this example is that the mass of the carbon source is 4% of the mass of Li5FeO4, and the other raw materials and steps are the same as those in Example 2.

[0052] Example 5

[0053] Compared with Example 2, the difference in this example is that the mass of the carbon source is 5% of the mass of Li5FeO4, and the other raw materials and steps are the same as those in Example 2.

[0054] Example 6

[0055] Compared with Example 5, the difference in this example is that the molar ratio of niobium ethoxide to sucrose is 1:0.5, and the other raw materials and steps are the same as those in Example 5.

[0056] Comparative Example 1

[0057] Compared with Example 1, the difference in this comparative example is that the mass of the carbon source is 0.5% of the mass of Li5FeO4, and the other raw materials and steps are the same as those in Example 1.

[0058] Comparative Example 2

[0059] Compared with Example 5, the difference in this comparative example is that the mass of the carbon source is 5.5% of the mass of Li5FeO4, and the other raw materials and steps are the same as those in Example 5.

[0060] Comparative Example 3

[0061] In this comparative example, compared with Example 1, the difference lies in that the carbon source prepared in Preparation Example 1 is replaced with the carbon source prepared in Preparation Example 3, and the other raw materials and steps are the same as those in Example 1.

[0062] Comparative Example 4

[0063] In this comparative example, compared with Example 1, the difference lies in that the carbon source prepared in Preparation Example 1 is replaced with the carbon source prepared in Preparation Example 4, and the other raw materials and steps are the same as those in Example 1.

[0064] Comparative Example 5

[0065] In this comparative example, compared with Example 1, the difference lies in that the carbon source prepared in Preparation Example 1 is replaced with the carbon source prepared in Preparation Example 5, and the other raw materials and steps are the same as those in Example 1.

[0066] Comparative Example 6

[0067] In this comparative example, compared with Example 1, the difference lies in that the carbon source prepared in Preparation Example 1 is replaced with the carbon source prepared in Preparation Example 6, and the other raw materials and steps are the same as those in Example 1

[0068] Comparative Example 7

[0069] In this comparative example, compared with Example 1, the difference lies in that the coating layer only contains amorphous niobium oxide, and the specific steps are as follows: S1. Prepare the matrix of the cathode lithium supplement agent: Take lithium nitrate and lithium hydroxide monohydrate and mix and grind them. The molar ratio of lithium nitrate to lithium hydroxide monohydrate is 0.55:0.41. Then place it in a muffle furnace for melting, take it out and grind it after cooling to obtain a mixed lithium salt. Then mix and grind the mixed lithium salt with nano-ferric oxide and press it into tablets. The molar ratio of Fe to Li elements in nano-ferric oxide to the mixed lithium salt is 5.2:1. Calcinate it in an argon atmosphere. The calcination temperature is 750 °C, the heating rate is 5 °C / min, and the calcination time is 10 h. Take it out and grind it after cooling to obtain Li5FeO4; S2. Prepare the cathode lithium supplement additive: Dissolve niobium ethoxide and sucrose in a mixed solvent composed of 10 mL of water and isopropanol. The molar ratio of niobium ethoxide to sucrose is 1:0.2, and the volume ratio of water to isopropanol in the mixed solvent is 2:1. Stir for 1 h to obtain an amorphous niobium oxide solution; Add 2 g of Li5FeO4 to 10 mL of the amorphous niobium oxide solution and stir. Then calcinate it in an argon atmosphere. The calcination temperature is 800 °C, the heating rate is 5 °C / min, and the sintering time is 4 h to obtain the cathode lithium supplement additive.

[0070] Comparative Example 8

[0071] In this comparative example, compared with Example 1, the difference lies in that the coating layer only contains a carbon layer, and the specific steps are as follows: S1. Preparation of the matrix of the cathode lithium supplement: Mix lithium nitrate and lithium hydroxide monohydrate and grind them. The molar ratio of lithium nitrate to lithium hydroxide monohydrate is 0.55:0.41. Then place it in a muffle furnace for melting, take it out and grind it after cooling to obtain a mixed lithium salt. Then mix the mixed lithium salt with nano-ferric oxide and grind them and then press them into tablets. The molar ratio of nano-ferric oxide to Fe and Li elements in the mixed lithium salt is 5.2:1. Calcinate it in an argon atmosphere. The calcination temperature is 750 °C, the heating rate is 5 °C / min, and the calcination time is 10 h. Take it out and grind it after cooling to obtain Li5FeO4; S2. Preparation of the cathode lithium supplement additive: Dissolve sucrose in a mixed solvent composed of 10 mL of water and isopropanol. The volume ratio of water to isopropanol in the mixed solvent is 2:1. Stir for 1 h to obtain a sucrose solution; Add 2 g of Li5FeO4 to 10 mL of the sucrose solution and stir. Then calcinate it in an argon atmosphere. The calcination temperature is 800 °C, the heating rate is 5 °C / min, and the sintering time is 4 h to obtain the cathode lithium supplement additive.

[0072] Assemble the cathode lithium supplement additives prepared in Examples 1 to 5 and Comparative Examples 1 to 7 into button cells as follows: The cathode is composed of LiNi 0.8 Co 0.1 Mn 0.1 O2 (90 wt%) and the lithium supplement prepared in the present invention (10 wt%). The anode is composed of a mixture of artificial graphite (95 wt%) and SiO x (5 wt%). Use a CR2032 type button cell, and the N / P ratio of the cathode to the anode is 1:1. The battery test methods include: Measuring the first charge specific capacity at a current density of 0.1 C and a voltage range of 2.5 V - 4.3 V; Subsequently, perform 200 charge-discharge cycle tests at a constant current density of 0.5 C and calculate the capacity retention rate after cycling.

[0073] Perform tests on the residual alkali content and gas production expansion rate of the cathode lithium supplement additives prepared in Examples 1 - 5 and Comparative Examples 1 - 7. The test methods are as follows: (1) Residual alkali content: Weigh the lithium supplement sample (denoted as m 样 ), dissolve it in 50 mL of deionized water that has been boiled and cooled (removing CO2), ultrasonically assist in dissolving for 10 min, filter it through a 0.22 μm filter membrane, transfer it to a volumetric flask, and dilute it 10 times with deionized water. Record the fixed volume V. Then use an ion chromatography instrument to measure the concentration c; The formula is as follows, where D represents the dilution factor: Residual alkali content (%) = ρ × V × D / m 样 × 10 6 × 100% (2)Gas production expansion rate: Weigh a certain mass of the lithium supplement agent sample, grind it and sieve it to ensure uniform particle size, and then perform drying treatment. Use a pressure-resistant reactor with a pressure sensor to record the pressure change in the reactor (volume V0) in real time, and calculate the gas volume (under standard atmospheric pressure) according to the ideal gas law PV = nRT.

[0074] ΔV = ΔP × V0 / P0 (P0 is the standard atmospheric pressure)

[0075] Gas production expansion rate (%) = ΔV / V0 × 100%

[0076] The test results are shown in Table 1.

[0077] Table 1

[0078] It can be seen from Table 1 that the performance of the additive prepared in the example is better than that of the additive prepared in the comparative example. Compared with Example 1, Examples 2-6 only differ in the adjustment of raw materials within a reasonable range. From the test results, cathode materials with good electrochemical performance can be obtained. Compared with Example 5, Example 6 has better performance, indicating that （乙醇铌） : n （蔗糖） when n:n = 1:0.5, the effect of the lithium supplement agent is the best.

[0079] Compared with Example 1, in Comparative Example 1, less carbon source is added, and its performance is lower than that of Example 1; compared with Example 5, in Comparative Example 2, more carbon source is added, and its performance is lower than that of Example 5. The above results show that the addition amount of the carbon source in the present invention is the optimal amount, and too much or too little addition of the carbon source will affect the overall performance of the additive.

[0080] Compared with Example 1, the performance of Comparative Example 3 has decreased, indicating that PDA has strong adhesion. Its adhesion enhances the compatibility between the carbon layer and the amorphous niobium oxide-coated matrix material, and can form a uniform and tightly bonded carbon coating layer on the surface of the amorphous niobium oxide-coated matrix material, making the cathode lithium supplement material obtained in the present invention have excellent cycle performance. And PDA can generate a nitrogen-doped carbon layer after sintering. The nitrogen-doped carbon layer has high conductivity, provides a continuous electron transport path for Li5FeO4 particles, reduces the overall resistance of the electrode, and improves the cycle performance of the battery. And PDA can further improve the dispersion of nano-silver and improve its conductivity.

[0081] Compared with Example 1, the performance of Comparative Example 4 decreased, indicating that there is an interaction between the sulfonic acid group and silver ions, which stabilizes the AgNPs particles and prevents their aggregation, contributing to the uniform dispersion of AgNPs on the surface of modified carbon nanotubes. 3-Amino-4-fluorobenzenesulfonic acid can improve the dispersibility of carbon nanotubes through steric hindrance effect, thus helping to obtain a uniform coating layer and improve the electrochemical performance of the battery. After subsequent sintering, the modified carbon nanotubes can obtain a sulfur-doped carbon layer and a fluorine-doped carbon layer, which can synergistically improve the conductivity of the carbon nanotubes, thus contributing to the preparation of a cathode lithium supplement additive with better performance.

[0082] Compared with Example 1, Comparative Example 5 and Comparative Example 6 have poor performance, both proving 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 because the dispersibility of the acidified carbon nanotubes in Comparative Example 5 is higher than that in Comparative Example 6.

[0083] The performance of Comparative Example 7 and Comparative Example 8 is lower than that of Example 1, and the performance of Comparative Example 8 is lower than that of Comparative Example 7, indicating that the effect of carbon-doped amorphous niobium oxide is higher than that of a single carbon layer.

[0084] The above only discloses several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A cathode lithium supplement additive, characterized in that, It includes a cathode lithium supplement matrix Li5FeO4, an amorphous niobium oxide layer and a conductive carbon layer that are successively coated on the outer surface of the matrix; The dosage ratio of the amorphous niobium oxide solution in the amorphous niobium oxide layer to Li5FeO4 is 2 g: 10 - 16 mL; The mass of the carbon source in the conductive carbon layer is 1% - 5% of the mass of Li5FeO4; The carbon source is modified carbon nanotubes@AgNPs@PDA.

2. A preparation method of a cathode lithium supplement additive for preparing the cathode lithium supplement additive according to claim 1, characterized in that, It includes the following steps: S1. Prepare the cathode lithium supplement matrix: Take lithium nitrate and lithium hydroxide monohydrate, mix and grind them, then melt them. After cooling, take them out and grind them to obtain a mixed lithium salt. Then mix and grind the mixed lithium salt with nano-ferric oxide and press them into tablets. Calcinate them in an inert atmosphere, and after cooling, take them out and grind them to obtain Li5FeO4; S2. Prepare the amorphous niobium oxide-coated matrix material: Dissolve niobium ethoxide and sucrose in a mixed solvent. The mixed solvent is composed of water and an organic solvent. Stir for 1 - 2 h to obtain an amorphous niobium oxide solution; Add Li5FeO4 to the amorphous niobium oxide solution and stir. Then calcinate it in an inert atmosphere to obtain the amorphous niobium oxide-coated matrix material; S3. Prepare the cathode lithium supplement additive: Disperse the amorphous niobium oxide-coated matrix material obtained in S2 and the carbon source into absolute ethanol. After grinding and stirring, calcinate them in an inert atmosphere to obtain the cathode lithium supplement additive.

3. The preparation method of the cathode lithium supplement additive according to claim 2, wherein, 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; the inert atmosphere is one or more of nitrogen, argon, and helium; the temperature of the calcination is 750 - 800 °C, the heating rate is 5 - 10 °C / min, and the calcination time is 10 - 12 h.

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

5. The preparation method of the cathode lithium supplement additive according to claim 2, wherein In step S3, the inert atmosphere is one or more of nitrogen, argon, and helium; the temperature of the calcination is 700 - 850 °C, the heating rate is 5 - 10 °C / min, and the sintering time is 2 - 5 h.

6. The preparation method of the cathode lithium supplement additive according to claim 2, characterized in that In step S3, the preparation method of the carbon source is: A1. Prepare modified carbon nanotubes: Add carbon nanotubes to a mixed acid, ultrasonically treat them at 50 °C for 3 - 5 h, wash them 5 - 6 times, and dry them to obtain acidified carbon nanotubes; Mix the acidified carbon nanotubes with 3 - amino - 4 - fluorobenzenesulfonic acid, dicyclohexylcarbodiimide, and DMF, ultrasonically treat them for 30 - 40 min, deoxygenate them by passing nitrogen for 20 min, and then reflux and react at 120 °C with stirring for 24 - 48 h. After the reaction ends, filter the product, wash it, and dry it to obtain modified carbon nanotubes; A2. Preparation of modified carbon nanotubes@AgNPs: Ultrasonically disperse the modified carbon nanotubes in DMF, then add AgNO3 and stir for 6 - 8 h; then add NaBH4, stir and react for 10 - 15 min, wash and dry to obtain modified carbon nanotubes@AgNPs; A3. Preparation of carbon source: Disperse the modified carbon nanotubes@AgNPs and hydrochloric acid dopamine in Tris buffer solution and stir at room temperature for 40 - 48 h, wash and dry to obtain modified carbon nanotubes@AgNPs@PDA, which is the carbon source.

7. The preparation method of the cathode lithium supplement additive according to claim 6, characterized in that, The dosage ratio of the carbon nanotubes to the 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 dosage ratio of the 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 dosage ratio of the 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 dosage ratio of the modified carbon nanotubes@AgNPs, hydrochloric acid dopamine, and Tris buffer solution in step A3 is 2 - 2.5 g : 0.1 - 0.4 g : 80 mL.

8. A cathode material, characterized in that, It includes a positive electrode active material and a positive electrode lithium supplementing agent, and the positive electrode lithium supplementing agent is the positive electrode lithium supplementing additive described in claim 1, or a positive electrode lithium supplementing additive prepared by the preparation method of the positive electrode lithium supplementing additive described in any one of claims 2 - 7.

9. The cathode material according to claim 8, wherein The positive electrode active material is at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, and lithium nickel cobalt manganate; the mass ratio of the positive electrode active material to the positive electrode lithium supplementing agent is 9 : (0.5 - 1).

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