CN116706028B - A method for preparing cathode material, cathode material, application and lithium battery - Google Patents

Abstract

The invention discloses a method for preparing a cathode material, comprising the following steps: S1: dissolving a carbon-coated LiFePO ₄ composite material in anhydrous ethanol, and then adding an oxidizing acid to form active points on the surface of LiFePO ₄ ; S2: adding a 0.1-0.5 mol/L CuCl ₂ solution dropwise into the system obtained in step S1, stirring during the dropping process, filtering, washing, and drying after the reaction, and heating in a reducing gas to obtain a cathode material. The method has a simple preparation process and is suitable for industrial production. The cathode material obtained by the above method comprises LiFePO ₄ , a carbon layer wrapped on the outside of LiFePO ₄ , and CuO for repairing an incomplete carbon network in the carbon layer. The cathode material is applied in a lithium battery, and the introduced CuO can repair an incomplete carbon network, and is used to increase the number of active site connections of the lithium iron phosphate material, so as to improve the rate performance and the cycle life of the LFP battery.

Description

A method for preparing cathode material, cathode material, application and lithium battery

Technical Field

The present invention belongs to the technical field of battery materials, and in particular relates to a preparation method of a cathode material, the cathode material, an application and a lithium battery.

Background Art

Rechargeable lithium batteries are key components of portable electronic devices (computers and mobile phones, etc.). For example, the cathode material of a lithium-ion battery is a polyanionic compound with the general formula LixMy(XO)z (M=transition metal; X=P, S, As, Mo or W). Among them, lithium iron phosphate has attracted special interest. The theoretical capacity of lithium iron phosphate is 170mAh/g, and it has the advantages of low price, non-toxicity and environmental protection. However, the very low conductivity of lithium iron phosphate is the main obstacle to its application. Therefore, scientists have a strong interest in how to improve the rate and power of its practical application. The existing carbon coating method still has many disadvantages, such as the carbon coating usually cannot form a complete coating network on the lithium iron phosphate particles, so that during the intercalation process, electrons cannot reach all the positions where Li+ intercalation occurs, thereby causing polarization of the electrode, affecting the rate capacity and cycle performance. The existing methods for improving the surface properties of LFP cathode materials still have many disadvantages, such as: requiring complex manufacturing processes or high costs, and difficult to commercialize.

Summary of the invention

In view of the above technical problems, the present invention provides a method for preparing a cathode material, a cathode material and an application thereof.

In order to achieve the above-mentioned object of the invention, the technical solution of the present invention includes:

A method for manufacturing a cathode material comprises the following steps:

S1: taking a set amount of carbon-coated LiFePO ₄ composite material and dissolving it in anhydrous ethanol, performing ultrasonic dispersion treatment, and continuously stirring at room temperature to obtain a suspension, and then dropping an oxidizing acid into the suspension until no bubbles are generated in the suspension, thereby forming active points on the surface of LiFePO ₄ ;

S2: adding 0.1-0.5 mol/L _CuCl2 solution dropwise to the system obtained in step S1, stirring during the dropping process, stirring the mixed solution continuously for 5-9 hours, filtering the mixture, washing and drying it, and then heating it at 300-450°C for 1-3 hours in a reducing gas to obtain a cathode material,

The weight ratio of the carbon-coated _LiFePO4 composite material to _CuCl2 is (6-12):1.

According to the cathode material manufactured by the method of the present invention, CuO and carbon coatings are more tightly coated on the surface of LiFePO ₄ , the preparation process is simple, and it is suitable for industrial production.

The manufacturing method of the present invention enhances the electrochemical properties of the _LiFePO4 cathode material through CuO and carbon coating, improves electronic conductivity, and significantly improves rate capacity and cycle performance. Specifically, since the carbon coating cannot form a complete coating network on the surface of lithium iron phosphate particles, the CuO introduced by the present invention can repair the incomplete carbon network, which is used to increase the number of active site connections of the lithium iron phosphate material, so as to improve the rate performance and LFP battery cycle life; it solves the technical problem that during the intercalation process, the incomplete carbon network prevents electrons from reaching all the locations where Li+ intercalation occurs, thereby causing electrode polarization.

Furthermore, in step S1, the oxidizing acid is dilute sulfuric acid or dilute nitric acid, and the concentration of the oxidizing acid is 0.1-1 mol/L.

Furthermore, in step S1, the ultrasonic dispersion treatment process is to disperse the carbon-coated LiFePO ₄ composite material in anhydrous ethanol through ultrasonic treatment for 0.2 to 1 hour.

Furthermore, in step S2, the reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 2-8%.

Furthermore, in step S2, the washing and drying process is to wash the filtered mixture with distilled water for 2 to 5 times, and then dry it at 45 to 65° C. for 2 to 5 hours.

Furthermore, in step S2, the particle size of the CuCl ₂ is 20 to 50 nm. The present invention uses nano-scale CuCl _2. On the one hand, an integrated nano-layer is formed on the surface of LiFePO ₄ to improve the electrochemical performance of lithium iron phosphate to improve the cycle life and rate performance of LFP batteries; on the other hand, nano-scale CuO has a more ideal filling effect in the vacancies of the incomplete carbon network.

Furthermore, the carbon-coated _LiFePO4 composite material in step S1 is prepared by the following steps:

S1-1: Take a set amount of ferric citrate and dissolve it in water at 55-70°C. During the dissolution process, take oxalic acid and add it to the ferric citrate solution. The mass ratio of oxalic acid to ferric citrate is (1.5-4):1. Add oxalic acid to the ferric citrate solution to chelate with iron. On the one hand, the added oxalic acid serves as a carbon source; on the other hand, oxalic acid has reducing properties and can prevent Fe2+ from being converted into Fe3+.

S1-2: Dissolve H ₃ PO ₄ and LiPO ₄ in a solvent according to a set ratio respectively, and then mix the obtained solution with the solution obtained in step S1-1, and continue stirring at 55-70°C until a sol is formed, wherein the molar ratio of ferric citrate, H ₃ PO ₄ and LiPO ₄ is (4-2): (4-2): 1;

S1-3: Grind the product obtained in step S1-1, the sol and the isoprene gel, and then sinter them at 450-650°C in a reducing gas for 5-9 hours, and filter the obtained powder with a 200-300 mesh sieve to obtain a carbon-coated _LiFePO4 composite material, wherein the ratio of the apparent volume of the isoprene gel to the apparent volume of the _sum of ferric citrate, _H3PO4 and Li3PO4 is greater than 1:1.

The present invention adopts a sol-gel method to prepare a carbon-coated _LiFePO4 composite material, and the added organic additive forms a conductive carbon coating on the surface of lithium iron phosphate particles, which can improve electronic conductivity and significantly improve rate capacity and cycle performance.

Furthermore, in step S1-3, the reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 2-8%; in step S1-2, the solvent is N-methylpyrrolidone.

Another aspect of the present invention provides a cathode material, which is prepared by the above method, and the cathode material includes LiFePO ₄ , a carbon layer wrapped on the outside of LiFePO ₄ , and CuO for repairing an incomplete carbon network in the carbon layer, and the mass percentage of the carbon layer and CuO is 8-12wt.%. The present invention forms a CuO layer on the surface of the carbon-coated LiFePO ₄ composite material to improve the electrochemical properties of lithium iron phosphate to improve the cycle life and rate performance of the LFP battery. Specifically, the introduced CuO can repair the incomplete carbon network, which is used to increase the number of active site connections of the lithium iron phosphate material, so as to improve the rate performance; it solves the problem that during the intercalation process, the incomplete carbon network hinders electrons from reaching all positions where Li+ intercalation occurs, thereby causing electrode polarization.

Another aspect of the present invention provides a use of the above-mentioned cathode material in a lithium battery.

Another aspect of the present invention provides a lithium battery, which uses the above-mentioned cathode material.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) According to the cathode material manufactured by the method of the present invention, CuO and carbon coatings are more tightly coated on the surface of _LiFePO4 , the preparation process is simple, and it is suitable for industrial production.

(2) The present invention enhances the electrochemical properties of _LiFePO4 cathode materials through CuO and carbon coatings, improves electronic conductivity, and significantly improves rate capacity and cycle performance. Specifically, since the carbon coating cannot form a complete coating network on the surface of lithium iron phosphate particles. On the one hand, the CuO introduced in the present invention can repair the incomplete carbon network, which is used to increase the number of active site connections of the lithium iron phosphate material, so as to improve the rate performance and cycle life of the LFP battery. On the other hand, CuO repairs the incomplete carbon network, so that the _LiFePO4 particles are completely covered with the conductive layer, so that they can obtain electrons from all directions, thereby alleviating the polarization phenomenon; it solves the technical problem that during the intercalation process, the incomplete carbon network prevents electrons from reaching all positions where Li+ intercalation occurs, thereby causing electrode polarization.

(3) The present invention forms an integrated nanolayer on the surface of LiFePO ₄ to improve the electrochemical performance of lithium iron phosphate to improve the cycle life and rate performance of LFP batteries. In addition, nanoscale CuO has a more ideal filling effect in the vacancies of the incomplete carbon network, so that the surface of LiFePO ₄ particles is completely covered with a conductive nanolayer, allowing it to obtain electrons from all directions, thereby alleviating this polarization phenomenon.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a molecular structure diagram of carbon-coated LiFePO ₄ composite material.

FIG. 2 is a molecular structure diagram of copper oxide-doped LiFePO ₄ composite material.

Figure 3 is the EIS graph of carbon-coated LiFePO ₄ composite material.

FIG. 4 is an EIS graph of the copper oxide-doped LiFePO ₄ composite material.

DETAILED DESCRIPTION

The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

Example 1

The present embodiment provides a method for manufacturing a cathode material, comprising the following steps:

S1: a set amount of carbon-coated LiFePO ₄ composite material is dissolved in anhydrous ethanol, subjected to ultrasonic dispersion treatment for 0.5 hours, and then continuously stirred at room temperature to obtain a suspension, and then two drops of dilute sulfuric acid are added to the suspension, the concentration of which is 0.5 mol/L, to form active points on the surface of LiFePO ₄ ;

Wherein, the carbon-coated _LiFePO4 composite material is prepared by the following steps:

S1-1: taking a set amount of ferric citrate and dissolving it in water at 62° C., during the dissolution process, taking oxalic acid and adding it to the ferric citrate solution to chelate the iron, wherein the mass ratio of the oxalic acid to the ferric citrate is 2:1;

S1-2: Dissolve H ₃ PO ₄ and LiPO ₄ in N-methylpyrrolidone according to a set ratio, then mix the obtained solution with the solution obtained in step S1-1, and continue stirring at 62° C. until a sol is formed, wherein the molar ratio of ferric citrate, H ₃ PO ₄ and Li3PO4 is 3:2:1;

S1-3: Grind the product obtained in step S1-1, the sol and the isoprene gel, and then sinter them at 600°C in a reducing gas for 8 hours. Filter the obtained powder with a 280-mesh sieve to obtain a carbon-coated _LiFePO4 composite material (as shown in Figure 1), wherein the ratio of the apparent volume of the isoprene gel to the apparent volume of the sum of ferric citrate _{, H3PO4} and Li3PO4 is greater than 1:1; the reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 5%.

S2: adding 0.1 mol/L _CuCl2 solution dropwise to the system obtained in step S1, stirring during the dropping process, stirring for 2 hours, stirring the mixed solution continuously for 8 hours, washing with distilled water 3 times, filtering the obtained mixture, drying at 60°C for 4 hours, and then heating at 400°C in a reducing gas for 2 hours to obtain a cathode material, as shown in FIG2;

The reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 5%; the weight ratio of the carbon-coated _LiFePO4 composite material and _CuCl2 is 9:1, and the particle size of _CuCl2 is 30nm.

Example 2

The present embodiment provides a method for manufacturing a cathode material, comprising the following steps:

First, a carbon-coated _LiFePO4 composite material is prepared, comprising the following steps:

S1-1: taking a set amount of ferric citrate and dissolving it in water at 60° C., during the dissolution process, taking oxalic acid and adding it to the ferric citrate solution to chelate the iron, wherein the mass ratio of the oxalic acid to the ferric citrate is 3:1;

S1-2: Dissolve H ₃ PO ₄ and LiPO ₄ in a set ratio respectively, and then mix the obtained solution with the solution obtained in step S1-1, and continue stirring at 62°C until a sol is formed, wherein the molar ratio of ferric citrate, H ₃ PO ₄ and Li3PO4 is 3.5:3:1;

S1-3: Grind the product obtained in step S1-1, the sol and the isoprene gel, and then sinter them at 650°C in a reducing gas for 7 hours. Filter the obtained powder with a 250-mesh sieve to obtain a carbon-coated _LiFePO4 composite material (as shown in Figure 1), wherein the ratio of the apparent volume of the isoprene gel to the apparent volume of the sum of ferric citrate _{, H3PO4} and Li3PO4 is greater than 1:1; the reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 5%.

S1: a set amount of carbon-coated LiFePO ₄ composite material is dissolved in anhydrous ethanol, subjected to ultrasonic dispersion treatment for 1 hour, and then continuously stirred at room temperature to obtain a suspension, and then two drops of dilute nitric acid are added to the suspension, the concentration of which is 0.2 mol/L, to form active points on the surface of LiFePO ₄ ;

S2: 0.5 mol/L CuCl ₂ solution was added dropwise to the system obtained in step S1, and the mixture was stirred during the dropping process for 2.5 hours. The mixed solution was stirred continuously for 7 hours, washed with distilled water twice, filtered, dried at 65°C for 3 hours, and then heated at 450°C for 1 hour in a reducing gas to obtain a cathode material, as shown in Figure 2. The reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 5%; the weight ratio of the carbon-coated LiFePO ₄ composite material to CuCl ₂ is 6:1, and the particle size of CuCl ₂ is 50nm.

Example 3

The present embodiment provides a method for manufacturing a cathode material, comprising the following steps:

First, a carbon-coated _LiFePO4 composite material is prepared, comprising the following steps:

S1-1: taking a set amount of ferric citrate and dissolving it in water at 70° C., during the dissolution process, taking oxalic acid and adding it to the ferric citrate solution to chelate the iron, wherein the mass ratio of the oxalic acid to the ferric citrate is 1.5:1;

S1-2: Dissolve H ₃ PO ₄ and LiPO ₄ in a solvent according to a set ratio respectively, then mix the obtained solution with the solution obtained in step S1-1, and continue stirring at 70°C until a sol is formed, wherein the molar ratio of ferric citrate, H ₃ PO ₄ and Li3PO4 is 4:2:1;

S1-3: Grind the product obtained in step S1-1, the sol and the isoprene gel, and then sinter them at 500°C in a reducing gas for 6 hours, and filter the obtained powder with a 260-mesh sieve to obtain a carbon-coated LiFePO ₄ composite material (as shown in FIG. 1 ), wherein the ratio of the apparent volume of the isoprene gel to the apparent volume of the sum of ferric citrate, H ₃ PO ₄ and Li3PO4 is greater than 1:1. The reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 5%.

S1: a set amount of carbon-coated LiFePO ₄ composite material is dissolved in anhydrous ethanol, subjected to ultrasonic dispersion treatment for 1 hour, and then continuously stirred at room temperature to obtain a suspension, and then two drops of dilute sulfuric acid are added to the suspension, the concentration of which is 0.1 mol/L, to form active points on the surface of LiFePO ₄ ;

S2: 0.5 mol/L CuCl ₂ solution is added dropwise to the system obtained in step S1, and the mixture is stirred during the dropping process for 3 hours. The mixed solution is continuously stirred for 9 hours, washed with distilled water 4 times, filtered, dried at 65°C for 5 hours, and then heated at 450°C for 2 hours in a reducing gas to obtain a cathode material, as shown in Figure 2. The reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 5%; the weight ratio of the carbon-coated LiFePO ₄ composite material to CuCl ₂ is 9:1, and the particle size of CuCl ₂ is 20nm.

Application Examples

The cathode materials prepared in Examples 1 to 3 and the comparative example were applied to the electrodes of lithium batteries. During the use of the batteries, EIS experimental measurements were performed, as shown in Figures 3 and 4 .

As shown in Figure 3 and Figure 4, the impedance of the LFP electrode material using the CuO-C composite coating in Examples 1 to 3 of the present invention is significantly reduced, which means that when the material is used as an electrode material for a lithium-ion battery, it will have better rate performance and lower polarization.

The above is only a preferred embodiment of the embodiment of the present invention, and does not impose any form of limitation on the embodiment of the present invention. Any simple modification, equivalent change and modification made according to the technical essence of the embodiment of the present invention still falls within the scope of the technical solution of the embodiment of the present invention.

Claims (8)

1. A method for manufacturing a cathode material, characterized in that it comprises the following steps: S1: taking a set amount of carbon-coated LiFePO ₄ composite material and dissolving it in anhydrous ethanol, performing ultrasonic dispersion treatment, and continuously stirring at room temperature to obtain a suspension, and dropping an oxidizing acid into the suspension until no bubbles are generated in the suspension, thereby forming active points on the surface of LiFePO ₄ ; S2: Add 0.1-0.5 mol/L _CuCl2 solution dropwise to the system obtained in step S1 and stir, stir the mixed solution continuously for 5-9 hours, filter, wash and dry, and heat at 300-450°C for 1-3 hours in a reducing gas to obtain a cathode material. The weight ratio of the carbon-coated LiFePO ₄ composite material to CuCl ₂ is (6-12):1; The carbon-coated _LiFePO4 composite material in step S1 is prepared by the following steps: S1-1: taking a set amount of ferric citrate and dissolving it in water at 55-70° C., during the dissolution process, taking oxalic acid and adding it to the ferric citrate solution, wherein the mass ratio of the oxalic acid to the ferric citrate is (1.5-4):1; S1-2: Dissolve H ₃ PO ₄ and LiPO ₄ in a solvent according to a set ratio, respectively, and then mix the obtained solution with the solution obtained in step S1-1, and continue stirring at 55-70°C until a sol is formed, wherein the molar ratio of ferric citrate, H ₃ PO ₄ and LiPO ₄ is (4-2): (4-2): 1; S1-3: grinding the sol and isoprene gel obtained in step S1-2, calcining them at 450-650° C. in a reducing gas for 5-9 hours, and filtering the obtained powder with a 200-300 mesh sieve to obtain a carbon-coated LiFePO ₄ composite material; In step S1, the oxidizing acid is dilute sulfuric acid or dilute nitric acid, and the concentration of the oxidizing acid is 0.1-1 mol/L. 2. The method for manufacturing a cathode material according to claim 1, characterized in that in step S1, the ultrasonic dispersion treatment process is to disperse the carbon-coated _LiFePO4 composite material in anhydrous ethanol through ultrasonic treatment for 0.2 to 1 hour. 3. The method for manufacturing a cathode material according to claim 1, characterized in that in step S2, the reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 2 to 8%. 4. The method for manufacturing a cathode material according to claim 1, characterized in that in step S2, the post-washing drying process is to wash the mixture with distilled water for 2 to 5 times, filter the mixture, and then dry it at 45 to 65°C for 2 to 5 hours. 5. The method for manufacturing a cathode material as described in claim 1 is characterized in that in step S1-3, the reducing gas is nitrogen containing hydrogen, and the volume fraction of the hydrogen is 2-8%; in step S1-2, the solvent is N-methylpyrrolidone. 6. A cathode material, characterized in that it is prepared by any one of the methods of claims 1 to 5, the cathode material comprises _LiFePO4 , a carbon layer wrapped around the outside of _LiFePO4 and CuO for repairing an incomplete carbon network in the carbon layer, the mass percentage of the carbon layer and CuO is 8 to 12 wt.%. 7. Application of a cathode material in a lithium battery, characterized in that the cathode material according to claim 6 is applied to a lithium battery. 8. A lithium battery, characterized by using the cathode material according to claim 6.