CN116914119A - Lithium supplementing anode and preparation method and application thereof - Google Patents

Abstract

The application relates to the technical field of lithium ion battery lithium supplementation, and provides a lithium supplementing anode, a preparation method and application thereof. The lithium supplementing anode provided by the application comprises: a nickel-based positive electrode current collector, a lithium supplementing layer and a positive electrode active layer; the lithium supplementing layer is composed of lithium silver alloy and has the thickness of 0.1-1 mu m; the positive electrode active layer contains: positive electrode active material, conductive agent, and binder. The lithium supplementing layer is made of lithium silver alloy, silver can be used as a conductive agent after lithium removal, internal resistance between a current collector and an anode active substance is reduced, and conductivity is effectively improved. Therefore, the method has wide market application prospect. Meanwhile, the application also provides a preparation method of the lithium-supplementing anode, which has simple steps and convenient operation and is suitable for large-scale industrial production.

Description

Lithium-replenishing cathode and its preparation method and application

Technical field

The present invention relates to the technical field of lithium replenishment for lithium ion batteries, and more specifically, to a lithium replenishment positive electrode and its preparation method and application.

Background technique

Lithium-ion batteries have been widely used in electronic communications, energy storage systems and new energy vehicles due to their high operating voltage, high energy density and long cycle life. However, during the operation of lithium-ion batteries, the formation of the SEI film on the negative electrode consumes a large amount of active lithium. Especially when some high-capacity silicon-based negative electrode materials are added, the Coulombic efficiency of the first cycle of the battery is low, which in turn causes the battery energy density to decrease. One of the effective ways to solve this problem is to supplement active lithium.

There are many ways to supplement active lithium that have been reported, mainly divided into two categories: negative electrode lithium supplementation and positive electrode lithium supplementation.

Negative lithium supplementation involves adding negative electrode lithium supplementation agents, such as metallic lithium powder, lithium foil, and lithium silicide powder, to the end of the negative electrode. This type of technology is complex to operate, harsh on environmental conditions, and costly. It also requires precise control of the degree of lithium supplementation, otherwise Residual lithium metal can easily cause battery failure and cause safety hazards, and is difficult to be compatible with existing assembly processes.

Recently, the cathode prelithiation method has attracted the attention of many researchers. The common solution for cathode lithium replenishment is to blend the lithium replenisher and the cathode active material in the homogenization stage, and use the excess lithium released when the lithium replenisher is first charged. ions to compensate for the consumption of active lithium ions on the negative electrode side to improve the energy density and cycle life of the cell. However, most of the current cathode lithium replenishing agents, such as Li ₂ S, Li ₂ O, Li ₂ O ₂ , LiF, Li ₅ FeO ₄ and Li ₂ NiO ₂ mentioned in the patent CN115939536A, all have the problem of poor conductivity, which must be combined with A higher proportion of conductive agents can effectively extract the lithium ions contained therein. If the positive electrode lithium replenishing agent is simply blended with the positive electrode active material, the lithium ions released by the lithium replenishing agent are often lower than the theoretical predetermined value, and the lithium replenishing effect is poor; in addition, due to the low conductivity of the lithium replenishing agent remaining after removal of lithium Substances increase the resistance of the positive electrode piece, which not only blocks the transmission of lithium ions on the positive electrode side and affects the performance of the gram capacity, but also causes the energy density of the battery core to decrease.

Contents of the invention

The purpose of the present invention is to solve the problems of the existing technology and provide a lithium-replenishing positive electrode that does not affect the gram capacity of the positive active material itself and can improve the energy density and cycle life of the battery core and its preparation method and application.

In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

In a first aspect, the present invention provides a lithium-replenishing cathode, which includes a nickel-based cathode current collector, a lithium-replenishing layer and a cathode active layer, wherein the lithium-replenishing layer is composed of a lithium-silver alloy.

Preferably, the nickel-based cathode current collector has a three-dimensional porous structure, more preferably nickel foam, sponge nickel, etc., and more preferably, the nickel-based cathode current collector has a pore diameter of 0.1-10 mm, a porosity of 60-98%, and has Large surface area, high porosity, good permeability and other advantages; more preferably, the lithium-replenishing cathode uses a nickel-based cathode current collector as a base, and a lithium-replenishing layer and a cathode active layer are sequentially provided on the nickel-based cathode current collector, that is, The lithium replenishing layer and the positive electrode active layer are sequentially coated on the three-dimensional skeleton of the nickel-based positive electrode current collector.

Preferably, the lithium silver alloy is Li _x Ag _y , where x:y is 3:1, 8:5, 1:1, 1:3, 4:6, 3:7, 2:8, 1:9 one or more of them. More preferably, the weight ratio content of lithium in the silver-lithium alloy is 5-15%, and the weight ratio content of silver is 85-95%.

Preferably, the thickness of the nickel-based positive electrode current collector is 1-10 mm.

Preferably, the thickness of the lithium replenishing layer is 0.1-1 μm.

Preferably, the thickness of the positive electrode active layer is 100-300 μm.

Preferably, the positive electrode active layer contains: a positive electrode active material, a conductive agent, and a binder.

Preferably, in the positive active layer, the positive active material is at least one of lithium iron phosphate, an oxide positive electrode and a sulfur positive electrode, and the conductive agent is at least one of conductive carbon black, graphite, carbon nanotubes and Ketjen black. One, the binder is at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyvinyl alcohol (PVA) and polytetrafluoroethylene (PTFE).

Preferably, in the positive active layer, the mass proportion of the positive active material is: 80-90%, the mass proportion of the conductive agent is: 5-10%, and the mass proportion of the binder is: 5~10%.

Preferably, the lithium supplement layer is prepared on the nickel-based positive electrode current collector by electroplating, and the positive electrode active layer is prepared on the lithium supplement layer by coating.

More preferably, the lithium supplement layer is prepared by first depositing silver elements on the surface of the nickel-based current collector through a silver mirror reaction, and then diffusing the lithium elements to the silver surface through electrochemical lithium insertion to form a lithium-silver alloy Li _x Ag _y , thereby preparing the supplement layer. Lithium layer.

In a second aspect, the present invention provides a method for preparing the above-mentioned lithium-replenishing cathode. The method is to deposit silver onto the surface of a nickel-based current collector through a silver mirror reaction, and then diffuse lithium to the silver surface through electrochemical lithium insertion to form lithium silver. Alloy Li _x Ag _y to prepare a lithium replenishing layer; mix the positive active material, conductive agent, binder and organic solvent to obtain a positive active slurry, and coat the positive active slurry on the lithium replenishing layer to prepare a positive active layer. Lithium-replenishing positive electrode was obtained.

Preferably, the preparation of the lithium replenishing layer specifically includes the following steps:

S1. Prepare silver ammonia solution;

More preferably, the mass concentration of the silver ammonia solution is 2 to 5%;

More preferably, the preparation method of the silver ammonia solution is: add ammonia water drop by drop to the silver nitrate solution until a brownish yellow precipitates, continue to add ammonia water dropwise until the precipitates disappear, the solution becomes transparent, and the volume is adjusted to a percentage concentration of 2 to 5%. silver ammonia solution;

S2. Place the nickel-based positive electrode current collector in the reaction tank, add the silver ammonia solution obtained in S1 into the reaction tank, then add the glucose solution, and carry out the reaction at a temperature of 30 to 70°C. After the reaction is completed, post-processing is performed to obtain Nickel/silver cathode current collector;

More preferably, a glucose solution with a mass percentage concentration of 2 to 5% is added, and more preferably the volume ratio of the silver ammonia solution to the glucose solution is 1:1 to 3:1;

More preferably, the reaction time is 0.5 to 1 h; preferably, it is a water bath reaction;

More preferably, the post-treatment is to clean the nickel-based positive electrode current collector whose surface is covered with silver metal and dry it in a vacuum;

More preferably, the vacuum drying temperature is 50-80°C and the time is 5-8 hours;

S3. Electrolysis: Under an inert atmosphere, electrolysis is performed with the lithium source as the anode and the nickel/silver positive electrode current collector as the cathode; after electrolysis, post-processing is performed to obtain a nickel-based positive electrode current collector with a lithium supplement layer on the surface;

More preferably, the electrolysis temperature is 30 to 70°C;

More preferably, the reaction voltage of electrolysis is 5-10V, and the current density is 155-800mAcm ^-2 ;

More preferably, the lithium source is one or more of lithium sheets, lithium belts, lithium foils and lithium blocks;

More preferably, the electrolyte in the electrolyte is one or more of lithium perchlorate, lithium hexafluorophosphate, and lithium tetrafluoroborate, and the organic solvent is ethylene carbonate (EC), diethyl carbonate (DEC), or dimethyl carbonate. (DMC), one or more of ethyl methyl carbonate (EMC);

More preferably, the electrolysis cell is prepared as follows: in an argon atmosphere glove box, the electrolyte is added to the electrolytic cell, the lithium source is placed in the electrolytic cell as the anode, and the cathode is a nickel/silver positive electrode current collector and sealed;

More preferably, the post-processing after the electrolysis reaction includes cleaning and vacuum drying. More preferably, the pressure of vacuum drying is -0.1Mpa, the drying temperature is 50-80°C, and the time is 8-12 hours.

Preferably, the organic solvent of the positive electrode active slurry is toluene, benzene, dimethylformamide (DMF), anhydrous acetonitrile, anhydrous ethanol, N-methylpyrrolidone (NMP), ethylene carbonate (EC) and dicarbonate. One or more ethyl esters (DEC).

Preferably, the solid content of the positive electrode active slurry is 30-35%.

Preferably, the coating is to evenly apply the positive electrode active slurry on the lithium _replenishing layer Ni/ _Li ~80℃, the time is 8~12h, and the pressure during tableting is 1~20MPa.

Preferably, a slurry blade coating method is used to apply the positive electrode active slurry.

In a third aspect, the present invention also provides an application of a lithium-replenishing cathode in the field of lithium-ion batteries.

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

(1) The lithium-replenishing positive electrode provided by the present invention releases active lithium ions during formation or the first charge and discharge process, which is used to compensate for the loss of active lithium caused by the irreversible reaction of forming an SEI film on the surface of the negative electrode, effectively improving the first efficiency and effectiveness of the battery. Cycle performance.

(2) In the present invention, the lithium-replenishing layer is a lithium-silver alloy. After lithium removal, the silver can be used as a conductive agent, which reduces the internal resistance between the current collector and the cathode active material and effectively improves the conductive performance. At the same time, the lithium-replenishing cathode provided by the present invention does not It will affect the performance of the gram capacity of the positive active material itself, improve the energy density and cycle life of the battery core, and maximize the effect of lithium supplementation. Therefore, it has broad market application prospects.

(3) The preparation method of the lithium-replenishing positive electrode provided by the present invention has simple steps, convenient operation, and is suitable for large-scale industrial production.

Description of the drawings

Figure 1 is a schematic cross-sectional structural diagram of the lithium-replenishing cathode in Example 1;

Figure 2 is a schematic diagram of the three-dimensional skeleton structure of the lithium-supplemented cathode in Example 1;

Figure 3 is the first charge and discharge curve of the full battery using a lithium-supplemented cathode in Example 1;

Figure 4 is the first charge and discharge curve of the full battery using a lithium-supplemented cathode in Example 3;

Figure 5 is the first charge and discharge curve of the full battery using a lithium-supplemented positive electrode in Example 5;

Among them, 1 is the positive electrode active layer, 2 is the lithium replenishing layer, 3 is the nickel-based positive electrode current collector, and 4 is the three-dimensional skeleton lithium replenishing cathode. Figure 1 is the crown cross section of the branch indicated by 4 in Figure 2.

Detailed ways

For the convenience of understanding, the technical solutions and implementation modes of the present invention are further described clearly, completely and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in the present invention are based on the present invention. The invention is implemented based on the technical solution of the invention, and detailed implementation modes and specific operating processes are given. However, these are only some of the embodiments of the present invention, not all of them. The described specific implementation modes are limited to illustrating and explaining the present invention. invention and does not limit the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the examples can be obtained from commercial sources unless otherwise specified.

Example 1:

Embodiment 1 provides a method for preparing a lithium-supplemented positive electrode. The specific steps are as follows:

S1. Add ammonia solution drop by drop to the silver nitrate solution until a brownish yellow precipitates. Continue to add ammonia solution dropwise until the precipitate disappears and the solution becomes transparent. Adjust to volume and prepare a silver ammonia solution with a percentage concentration of 2%;

S2. Place 1g of nickel foam with a thickness of 5mm, a pore diameter of 0.2mm, and a porosity of 75% in the reaction tank. Add 50ml of the silver ammonia solution obtained in S1 into the beaker, and then add glucose with a percentage concentration of 2%. Solution, the volume ratio of silver ammonia solution and glucose solution is 2:1, react in a 50°C water bath for 30 minutes, after the reaction is completed, clean the nickel foam covered with silver metal on the surface, and vacuum dry it at 80°C to obtain 1.6g Nickel/silver cathode current collector;

S3. Preparation of the electrolytic cell: In an argon atmosphere glove box, add 50 ml of electrolyte with lithium hexafluorophosphate as the solute and ethylene carbonate (EC) as the solvent. Place the lithium sheet as the anode in the electrolytic cell, and the cathode is nickel/silver. Positive current collector, sealed;

S4. Connect the 5V power supply, the current density is 175mAcm ^-2 for electrolysis, and the reaction is carried out at 50°C. After the end, clean it, the pressure is -0.1MPa, the drying temperature is 50~80°C, and the time is 8 After vacuum drying for ~12 hours, a nickel foam with a 1 μm lithium replenishing layer on the surface is obtained, which is a Ni/lithium silver alloy material. The silver content in the lithium silver alloy is 95wt% and the lithium content is 5wt%;

S5. Homogenize the positive electrode active material NCM811, conductive agent SP, binder PVDF (NCM811:PVDF:SP=90:5:5) and organic solvent NMP (solid content: 30%) to obtain positive electrode active slurry. , the positive electrode active slurry is evenly coated on the Ni _{/ Li}

Embodiment 1 provides an application for replenishing lithium cathodes. The specific steps are as follows:

S1. Battery assembly: Combine the positive electrode sheet (NCM811:PVDF:SP=90:5:5), separator (PP), and graphite negative electrode sheet (graphite:CMC:SBR:SP=92) covered with a lithium-silver alloy lithium replenishing layer. :2:4:2) Assemble the full battery in an argon atmosphere glove box;

S2. Battery test: Use Xinwei tester to test the electrochemical performance of the battery, and calculate the first Coulombic efficiency, cycle performance, capacity retention rate and other parameters.

The schematic diagram of the three-dimensional skeleton structure of the positive electrode sheet coated with a lithium-silver alloy lithium replenishing layer in Example 1 is shown in Figure 2. The branch crown cross-sectional structure of the part indicated by 4 in Figure 2 is shown in Figure 1. The positive electrode lithium replenishment method provided in Embodiment 1 of the present invention can increase the first efficiency of the battery from 83.0% before lithium replenishment (the difference from the lithium replenishment battery prepared in this embodiment is that it does not contain a lithium replenishment layer) to 91.3%. See Figure 3 for the discharge curve. In addition, the first cycle discharge capacity of the soft-pack battery prepared according to the embodiment of the present invention is 234.3 mAh, and the capacity retention rate after 40 cycles is 95.6%. This shows that lithium batteries using lithium-supplemented cathode sheets have significantly improved Coulombic efficiency, capacity retention rate and cycle performance.

Example 2:

Embodiment 2 provides a method for preparing a lithium-supplemented positive electrode. The specific steps are as follows:

S1. Add ammonia solution drop by drop to the silver nitrate solution until a brownish yellow precipitates. Continue to add ammonia solution dropwise until the precipitate disappears and the solution becomes transparent. Adjust to volume and prepare a silver ammonia solution with a percentage concentration of 2%;

S2. Place 1g of nickel foam with a thickness of 5mm, a pore diameter of 0.2mm, and a porosity of 75% in the reaction tank. Add 50ml of the silver ammonia solution obtained in S1 into the beaker, and then add glucose with a percentage concentration of 2%. The solution was reacted in a 50°C water bath for 30 minutes. After the reaction, the nickel foam covered with silver metal was washed and vacuum dried at 80°C to obtain 1.6g of nickel/silver positive electrode current collector;

S3. Preparation of the electrolytic cell: In an argon atmosphere glove box, add 50 ml of electrolyte with lithium hexafluorophosphate as the solute and ethylene carbonate (EC) as the solvent. Place the lithium sheet as the anode in the electrolytic cell, and the cathode is nickel/silver. Positive current collector, sealed;

S4. Connect the 5V power supply, the current density is 350mAcm ^-2 for electrolysis, and the reaction is carried out at 50°C. After the end, clean it, the pressure is -0.1MPa, the drying temperature is 50~80°C, and the time is 8 After vacuum drying for ~12 hours, a nickel foam with a 1 μm lithium replenishing layer on the surface was obtained. The silver content in the lithium-silver alloy was 90.71wt% and the lithium content was 9.29wt%;

S5. Homogenize the positive electrode active material NCM811, conductive agent SP, binder PVDF (NCM811:PVDF:SP=80:10:10) and organic solvent NMP (solid content: 30%) to obtain positive electrode active slurry , the positive electrode active slurry is evenly coated on the Ni/Li _x Ag _y material, and then dried at 80°C for 8 hours, and pressed under a pressure of 5MPa to finally obtain a lithium-supplemented positive electrode.

Embodiment 2 provides an application for replenishing lithium cathodes. The specific steps are as follows:

S1. Battery assembly: Combine the positive electrode sheet (NCM811:PVDF:SP=80:10:10), the separator (PP), and the silicon-carbon negative electrode sheet (Si/C:SP:PAA= 6:2:2) Assemble the full battery in an argon atmosphere glove box;

S2. Battery test: Use Xinwei tester to test the electrochemical performance of the battery, and calculate the first Coulombic efficiency, cycle performance, capacity retention rate and other parameters.

The positive electrode lithium supplement method provided in Embodiment 2 of the present invention can increase the first efficiency of the battery from 86.4% before lithium supplement to 93.1%.

Example 3:

Embodiment 3 provides a method for preparing a lithium-supplemented positive electrode. The specific steps are as follows:

S1. Add ammonia solution drop by drop to the silver nitrate solution until a brownish yellow precipitates. Continue to add ammonia solution dropwise until the precipitate disappears and the solution becomes transparent. Adjust to volume and prepare a silver ammonia solution with a percentage concentration of 2%;

S2. Place 1g of nickel foam with a thickness of 5mm, a pore diameter of 0.2mm, and a porosity of 75% in the reaction tank. Add 50ml of the silver ammonia solution obtained in S1 into the beaker, and then add glucose with a percentage concentration of 2%. The solution was reacted in a 50°C water bath for 30 minutes. After the reaction, the nickel foam covered with silver metal on the surface was washed and vacuum dried at 80°C to obtain 1.6g of nickel/silver positive electrode current collector;

S3. Preparation of the electrolytic cell: In an argon atmosphere glove box, 50 ml of electrolyte with lithium hexafluorophosphate as the solute and ethylene carbonate (EC) as the solvent is added to the electrolytic cell. The lithium sheet is placed in the electrolytic cell as the anode, and the cathode is the nickel/silver positive electrode. Current collector, seal;

S4. Connect the 5V power supply, the current density is 175mA cm ^-2 for electrolysis, and react at 50℃ at the same time. After the end, clean it, the pressure is -0.1MPa, the drying temperature is 50~80℃, and the time is After vacuum drying for 8 to 12 hours, a nickel foam with a 1 μm lithium replenishing layer on the surface is obtained. The silver content in the lithium-silver alloy is 95wt% and the lithium content is 5wt%;

S5. Homogenize the positive electrode active material LFP, conductive agent SP, binder PVDF and organic solvent NMP (solid content: 30%) to obtain positive electrode active slurry, and evenly apply the positive electrode active slurry on Ni/ Li _x Ag _y material, then dried at 80°C for 8 hours, and pressed under a pressure of 5 MPa to finally obtain a lithium-supplemented positive electrode.

Embodiment 3 provides an application for replenishing lithium cathodes. The specific steps are as follows:

S1. Battery assembly: Combine the positive electrode sheet (LFP:PVDF:SP=85:7.5:7.5), separator (PP), and graphite negative electrode sheet (graphite:CMC:SBR:SP=92) covered with an aluminum-lithium alloy lithium replenishing layer. :2:4:2) Assemble the full battery in an argon atmosphere glove box;

S2. Battery test: Use Xinwei tester to test the electrochemical performance of the battery, and calculate the first Coulombic efficiency, cycle performance, capacity retention rate and other parameters.

The positive electrode lithium supplement method provided in Embodiment 3 of the present invention can increase the first efficiency of the battery from 89.4% before lithium supplement to 93.0%. See Figure 4 for the first charge and discharge curve.

Example 4:

Embodiment 4 provides a method for preparing a lithium-supplemented positive electrode. The specific steps are as follows:

S1. Add ammonia solution drop by drop to the silver nitrate solution until a brownish yellow precipitates. Continue to add ammonia solution dropwise until the precipitate disappears and the solution becomes transparent. Adjust to volume and prepare a silver ammonia solution with a percentage concentration of 2%;

S2. Place 1g of nickel foam with a thickness of 5mm, a pore diameter of 0.2mm, and a porosity of 75% in the reaction tank. Add 50ml of the silver ammonia solution obtained in S1 into the beaker, and then add glucose with a percentage concentration of 2%. The solution was reacted in a 50°C water bath for 30 minutes. After the reaction, the nickel foam covered with silver metal on the surface was washed and vacuum dried at 80°C to obtain 1.6g of nickel/silver positive electrode current collector;

S3. Preparation of the electrolytic cell: In an argon atmosphere glove box, 50 ml of electrolyte with lithium hexafluorophosphate as the solute and ethylene carbonate (EC) as the solvent is added to the electrolytic cell. The lithium sheet is placed in the electrolytic cell as the anode, and the cathode is the nickel/silver positive electrode. Current collector, seal;

S4. Connect the 5V power supply, the current density is 350mAcm ^-2 for electrolysis, and the reaction is carried out at 50°C. After the end, clean it, the pressure is -0.1MPa, the drying temperature is 50~80°C, and the time is 8 After vacuum drying for ~12 hours, a nickel foam with a 1 μm lithium replenishing layer on the surface was obtained. The silver content in the lithium-silver alloy was 90.71wt% and the lithium content was 9.29wt%;

S5. Homogenize the positive electrode active material LFP, conductive agent SP, binder PVDF and organic solvent NMP (solid content: 30%) to obtain positive electrode active slurry, and evenly apply the positive electrode active slurry on Ni/ Li _x Ag _y material, then dried at 80°C for 8 hours, and pressed under a pressure of 5 MPa to finally obtain a lithium-supplemented positive electrode.

Embodiment 4 provides an application for replenishing lithium cathodes. The specific steps are as follows:

S1. Battery assembly: The surface is covered with a lithium-silver alloy lithium replenishing layer, the active material is LFP, the positive electrode piece, the silicon carbon negative electrode piece (gram capacity is 450mAh g ^-1 , the first Coulombic efficiency is 88.1%) and the separator (PP ) Assemble the full battery in the glove box;

S2. Battery test: Use Xinwei tester to test the electrochemical performance of the battery, and calculate the first Coulombic efficiency, cycle performance, capacity retention rate and other parameters. The positive electrode lithium replenishment method provided in Embodiment 4 of the present invention can increase the first efficiency of the battery to 94.8%.

Example 5:

Embodiment 5 provides a method for preparing a lithium-supplemented positive electrode. The specific steps are as follows:

S1. Add ammonia solution drop by drop to the silver nitrate solution until a brownish yellow precipitates. Continue to add ammonia solution dropwise until the precipitate disappears and the solution becomes transparent. Adjust to volume and prepare a silver ammonia solution with a percentage concentration of 2%;

S2. Place 1g of nickel foam with a thickness of 5mm, a pore diameter of 0.2mm, and a porosity of 75% in the reaction tank. Add 50ml of the silver ammonia solution obtained in S1 into the beaker, and then add glucose with a percentage concentration of 2%. The solution was reacted in a 50°C water bath for 30 minutes. After the reaction, the nickel foam covered with silver metal was washed and vacuum dried at 80°C to obtain 1.6g of nickel/silver positive electrode current collector;

S3. Preparation of the electrolytic cell: In an argon atmosphere glove box, 50 ml of electrolyte with lithium hexafluorophosphate as the solute and ethylene carbonate (EC) as the solvent is added to the electrolytic cell. The lithium sheet is placed in the electrolytic cell as the anode, and the cathode is the nickel/silver positive electrode. Current collector, seal;

S4. Connect the 5V power supply, the current density is 175mAcm ^-2 for electrolysis, and the reaction is carried out at 50°C. After the end, clean it, the pressure is -0.1MPa, the drying temperature is 50~80°C, and the time is 8 After vacuum drying for ~12 hours, a nickel foam with a 1 μm lithium replenishing layer on the surface was obtained. The silver content in the lithium-silver alloy was 95wt% and the lithium content was 5wt%;

S5. Homogenize the positive active material sulfur carbon 64, conductive agent SP, binder PVDF and organic solvent NMP (solid content: 30%) to obtain positive active slurry, and apply the positive active slurry evenly on Ni _{/ Li}

Embodiment 5 provides an application for replenishing lithium cathodes. The specific steps are as follows:

S1. Battery assembly: Combine the positive electrode sheet (sulfur carbon 64:PVDF:SP=80:10:10), separator (PP), and graphite negative electrode sheet (graphite:CMC:SBR:SP) covered with an aluminum-lithium alloy lithium replenishing layer. =92:2:4:2) Assemble the full battery in an argon atmosphere glove box;

S2. Battery test: Use Xinwei tester to test the electrochemical performance of the battery, and calculate the first Coulombic efficiency, cycle performance, capacity retention rate and other parameters.

The positive electrode lithium supplement method provided in Embodiment 5 of the present invention can increase the first efficiency of the battery from 89.2% before lithium supplement to 94.4%. See Figure 5 for the first charge and discharge curve.

The first-cycle Coulombic efficiency before and after lithium supplementation in Examples 1 to 5 was tested, which further shows that the lithium-supplemented cathode sheet of the present application can effectively improve the first-cycle Coulombic efficiency. For details, see the table below:

The above-described embodiments are only preferred solutions of the present invention and do not limit the present invention in any form. There are other variations and modifications without departing from the technical solutions described in the claims.

Claims (10)

1. A lithium-replenishing cathode, characterized in that the lithium-replenishing cathode includes a nickel-based cathode current collector, a lithium-replenishing layer and a positive electrode active layer, wherein the lithium-replenishing layer is composed of a lithium-silver alloy, and the thickness of the lithium-replenishing layer is 0.1~1μm. 2. A lithium-replenishing cathode according to claim 1, characterized in that the nickel-based cathode current collector has a three-dimensional porous structure. 3. A lithium-replenishing cathode according to claim 1, characterized in that the weight ratio content of lithium in the lithium silver alloy is 5-15%, and the weight ratio content of silver is 85-95%. 4. A lithium-replenishing positive electrode according to claim 1, characterized in that the positive electrode active layer contains: a positive electrode active material, a conductive agent, and a binder. 5. A lithium-replenishing cathode according to claim 4, characterized in that the cathode active material is at least one of lithium iron phosphate, oxide cathode and sulfur cathode, and the conductive agent is conductive carbon black, graphite, carbon nanoparticles At least one of pipe and Ketjen black, and the binder is at least one of polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol and polytetrafluoroethylene. 6. A lithium-replenishing positive electrode according to claim 4, characterized in that, the mass proportion of the positive active material is: 80 to 90%, the mass proportion of the conductive agent is: 5 to 10%, and the mass proportion of the conductive agent is 5 to 10%. The mass proportion of binder: 5~10%. 7. A lithium-replenishing cathode according to claim 1, characterized in that the thickness of the nickel-based cathode current collector is 1-10 mm, and the thickness of the cathode active layer is 100-300 μm. 8. A method for preparing a lithium-replenishing positive electrode according to any one of claims 1 to 7, characterized in that the method is to deposit silver onto the surface of a nickel-based current collector through a silver mirror reaction, and then electrochemically insert lithium into the nickel-based current collector. Lithium diffuses to the silver surface to form a lithium-silver alloy, and a lithium supplement layer is prepared; the positive electrode active material, conductive agent, binder and organic solvent are mixed to obtain a positive electrode active slurry, and the positive electrode active slurry is coated on the lithium supplement layer to prepare The positive electrode active layer is used to obtain a lithium-replenishing positive electrode. 9. A method for preparing a lithium-replenishing positive electrode according to claim 8, characterized in that the preparation of the lithium-replenishing layer specifically includes the following steps: S1. Prepare silver ammonia solution; S2. Place the nickel-based positive electrode current collector in the reaction tank, add the silver ammonia solution obtained in S1 into the reaction tank, then add the glucose solution, and carry out the reaction at a temperature of 30 to 70°C. After the reaction is completed, post-processing is performed to obtain Nickel/silver cathode current collector; S3. Electrolysis: Under an inert atmosphere, electrolysis is performed with a lithium source as the anode and a nickel/silver positive electrode current collector as the cathode. After electrolysis, post-processing is performed to obtain a nickel-based positive electrode current collector with a lithium supplement layer on the surface. 10. An application of the lithium-replenishing cathode according to any one of claims 1 to 7 in the field of lithium-ion batteries.