CN117012907A - Composite positive electrode containing lithium supplementing additive, and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of lithium ion battery lithium supplement, and particularly relates to a composite anode containing a lithium supplement additive, and a preparation method and application thereof. The composite positive electrode comprises a positive electrode material and a lithium supplementing additive, wherein the lithium supplementing additive is silver-lithium alloy. The silver-lithium alloy powder is prepared by an electroplating method. The silver-lithium alloy is used as a lithium supplementing additive to be uniformly filled in a gap of the positive electrode material, lithium in the silver-lithium alloy is used for supplementing lithium ions consumed by forming an SEI film on a negative electrode in a first charging process, so that the coulomb efficiency of the battery is improved, the battery capacity is improved, and meanwhile, silver in the alloy has high electronic conductivity, the charge transfer of a positive electrode/electrolyte interface can be improved, and the multiplying power performance of the battery is improved, so that the silver-lithium alloy has wide market application prospect. Meanwhile, the invention also provides a preparation method of the composite positive electrode containing the lithium supplementing additive, which is simple and convenient to operate and suitable for industrial mass production.

Description

A composite positive electrode containing lithium supplement additive and its preparation method and application

Technical field

The invention belongs to the technical field of lithium supplementation for lithium ion batteries, and is specifically a composite positive electrode containing a lithium supplementation additive and its preparation method and application.

Background technique

Lithium-ion battery is a kind of secondary battery with the advantages of high energy density, long cycle life and high working voltage. Since it was put on the market in 1991, it has been widely used in the fields of electronic communications, energy storage systems and new energy vehicles. Lithium-ion batteries usually consist of positive electrode sheets, separators, negative electrode sheets, electrolytes, and casings. Most of the active materials in the negative electrode are graphite and silicon-carbon negative electrodes. When the battery is first charged and discharged, a solid electrolyte interface film will be formed on the surface of the graphite. (SEI film), consumes a large amount of lithium ions and this process is irreversible, resulting in a first irreversible capacity loss of 6 to 14%, which seriously limits the capacity and energy density of the battery.

In order to solve the problem of low battery capacity due to the loss of lithium ions, pre-lithiation technology is usually used. Pre-lithiation technology is to introduce additional lithium into the battery system. During the first charging process, the active lithium released can make up for the negative electrode. Irreversible lithium loss caused by the formation of SEI film on the surface of active materials. Common prelithiation methods mainly include adding lithium to the negative electrode and adding lithium to the positive electrode. Lithium replenishment for the negative electrode is mainly implemented by methods such as metallic lithium powder, lithium flakes, lithium foil, lithium silicide powder, and chemical lithium insertion. However, in actual operation, this type of technology uses highly active metals, which makes the operation complex and harsh on environmental conditions. It also requires precise control of the degree of lithium supplementation. Otherwise, the remaining lithium metal can easily cause battery failure and cause safety hazards. For example, patents CN202111132592.9 and patent CN202210224673.X basically use lithium foil to replenish lithium for the negative electrode plate.

The cathode lithium replenishment technology usually adds a small amount of highly irreversible lithium-rich compounds as additives to the cathode. The cathode lithium replenishment has the advantages of stability, low price, easy synthesis, etc., and the method is highly compatible with the existing production process, safe, stable and controllable. , during the first charging process, a large amount of lithium ions are released from the additive to supplement the lithium ions consumed by the negative electrode to form the SEI film. However, existing cathode lithium supplement additives still have certain shortcomings. For example, CN115692698A discloses a method for preparing a core-shell positive electrode lithium supplement additive, the core of which is Li _2+c A _c B _1-c ; where, 0≤c≤1, A is at least one of N and P, B is at least one of S and O, and the cladding layer is an isolation conductive encapsulation layer. This manufacturing process is complex and costly, which is not conducive to industrial production. CN115312771A discloses two different crystal phases of lithium nitride: α crystal phase lithium nitride and/or β crystal phase lithium nitride mixed positive electrode lithium additive, but lithium nitride will produce a large amount of gas after delithiation, causing internal damage to the battery. If cracks occur, there will be great safety risks.

It can be seen that lithium supplementation technology still needs to be further improved and developed.

Contents of the invention

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to solve the problems of the prior art and provide a composite positive electrode containing a lithium supplement additive and its preparation method and application. The present invention uses silver-lithium alloy as a lithium supplement additive, and adds silver-lithium alloy powder during the preparation process of the positive electrode slurry, thereby preparing a composite positive electrode. During the first charging process, the lithium in the silver-lithium alloy is used to supplement the consumption of the negative electrode to form the SEI film. The lithium ions improve the Coulombic efficiency of the battery and improve the battery capacity. At the same time, the silver in the alloy has high electronic conductivity, which can improve the charge transfer at the cathode/electrolyte interface, reduce the interface impedance, and improve the rate performance of the battery.

In order to achieve the above objects, the present invention provides the following technical solutions:

According to one aspect of the present invention, a composite positive electrode containing a lithium supplement additive is provided. The composite positive electrode includes a positive electrode material and a lithium supplement additive, and the lithium supplement additive is a silver-lithium alloy. By adopting the technical solution of the present invention, the silver-lithium alloy is uniformly filled in the gap of the positive electrode material as a lithium supplement additive. During the first charging process of the battery, the lithium in the silver-lithium alloy loses electrons and is converted into lithium ions, supplementing the The lithium ions consumed to form the SEI film on the surface of the negative electrode effectively improve the Coulombic efficiency, specific capacity and energy density of the battery; at the same time, the silver in the alloy has high electronic conductivity, acting as a conductive agent between the positive electrode and the electrolyte, improving the positive electrode The charge transfer between the /electrolyte interface reduces the interface resistance, thereby improving the rate performance of the battery.

Further, the cathode material includes cathode active material, conductive agent and binder; further, the cathode material includes 80-90wt% cathode active material, 5-10wt% conductive agent and 5-10wt% in mass fraction. Binder; further, the positive active material is at least one of lithium iron phosphate, lithium nickel cobalt manganate, lithium cobalt oxide, lithium manganate, and lithium nickel cobalt aluminate, and is spherical particles of 15-30 μm. , the conductive agent is at least one of carbon black (such as SP, Ketjen black, acetylene black, etc.), conductive graphene, carbon nanotubes, etc., the binder is polyvinylidene fluoride, and the size is 20 ~30μm.

Further, the silver-lithium alloy is a powder with a particle size of 0.5-3 μm. Furthermore, the silver-lithium alloy has a core-shell structure in which an outer layer of lithium coats an inner layer of silver.

Further, the weight ratio content of lithium in the silver-lithium alloy is 15-25%, and the weight ratio content of silver is 75-85%.

Further, in the composite positive electrode, the weight ratio content of the positive electrode material is 85% to 95%, and the weight ratio content of the silver-lithium alloy is 5% ~ 15%.

Further, the silver-lithium alloy is prepared by electroplating lithium on the silver surface. Furthermore, the preparation method of the silver-lithium alloy includes the following steps:

S1. Install the electroplating cell: In an inert atmosphere glove box that is water-free and oxygen-free (water content and oxygen content are not higher than 0.01ppm), place the electrolyte in the electroplating cell in a pure copper container, add silver powder and lithium The source is fixed on the copper electrode clip;

Furthermore, the lithium source is one or more of lithium sheets, lithium belts, and lithium foils;

Furthermore, the silver powder particle size is 0.4~2.8μm, and the silver powder dosage is 300-500mg;

Furthermore, the electrolyte is an ester electrolyte; more preferably, the solvent is at least one of cyclic carbonate esters such as EC, PC, etc., or linear carbonate esters such as DMC, DEC, EMC, etc.; the lithium salt is LiPF6 , at least one of LiBF4, LiBOB, LiODFB, etc., more preferably 1.0M LiPF6in EC:DEC:EMC=1:1:1Vol%.

Furthermore, the inert atmosphere is an argon atmosphere;

S2. Preparation of silver-lithium alloy: The electrode clip is connected to a DC regulated power supply, the electrode clip connected to the pure copper container is connected to the negative electrode of the power supply as the cathode, and the electrode clip connected to lithium is connected to the positive electrode of the power supply as the anode. Electroplating starts, and the anode immediately produces lithium. ions and deposit on the surface of silver powder in contact with the copper container, eventually forming a silver-lithium alloy;

Furthermore, the specific parameters of electroplating are: the current of the DC regulated power supply is 30~150mA, the current density is 157~785mA cm ^-2 , the voltage is set at 8V, the termination voltage is 0.2~0.4V, and the entire electroplating time is 60 ~120min;

One step further, during electroplating, place the plating cell in the ultrasonic machine, turn on the ultrasound, and then start electroplating; one step further, the ultrasonic power is 60W;

Furthermore, after electroplating is completed, it is filtered, washed and dried in a glove box to obtain pure silver-lithium alloy powder; more preferably, drying is to dry the powder in a vacuum oven set to 120°C for 12 hours, and then dry the powder after drying. The powder is stored in an inert atmosphere.

According to another aspect of the present invention, a method for preparing a composite positive electrode with the above lithium supplement additive is provided. The preparation method is to add the lithium supplement additive and the positive electrode material into a solvent and homogenize them to obtain a positive electrode slurry. After coating on the substrate and drying, a composite positive electrode is obtained.

Further, the solvent is at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), ethylene glycol dimethyl ether (EGDME), etc. Furthermore, the solid content of the positive electrode slurry is 25-30%.

Further, the substrate is aluminum foil; further, the drying is first placed in a blast oven at 80°C, and after the solvent is dried, it is transferred to a vacuum oven at 120°C for drying for 12 hours.

Further, the preparation method specifically includes the following steps:

S1. Install the electroplating cell: In an argon atmosphere glove box with both water and oxygen content below 0.01ppm, place the electrolyte in the electroplating cell in a pure copper container, add silver powder and fix the lithium source on the copper electrode clip superior;

S2. Preparation of silver-lithium alloy: The electrode clip is connected to the DC regulated power supply, the electrode clip connected to the pure copper container is connected to the negative electrode of the power supply as the cathode, and the electrode clip connected to lithium is connected to the positive electrode of the power supply as the anode. At the same time, the electroplating cell is placed in the ultrasonic In the instrument, turn on the ultrasound and start electroplating. The anode immediately generates lithium ions and deposits them on the surface of the silver powder in contact with the copper container, eventually forming a silver-lithium alloy. After electroplating is completed, it is filtered, washed and dried in a glove box to obtain pure silver-lithium alloy powder;

S3. Use the homogenization method to add the silver-lithium alloy powder and cathode material into the solvent, coat it on the aluminum foil, and dry it to prepare a composite cathode.

According to another aspect of the present invention, there is provided an application of any of the above composite positive electrodes containing a lithium supplement additive in the field of lithium ion batteries.

Further, the application includes a lithium-ion battery, which includes a composite positive electrode, a separator, a negative electrode, and an electrolyte. The composite positive electrode is any one of the above composite positive electrodes containing a lithium supplement additive.

Compared with the prior art, the beneficial effects of the present invention are: the present invention provides a composite positive electrode containing a lithium supplement additive. By applying the composite positive electrode of the technical solution of the present invention, during the first charging process of the battery, the lithium in the silver-lithium alloy The lost electrons are converted into lithium ions, which replenish the lithium ions consumed by forming the SEI film on the surface of the negative electrode, effectively improving the Coulombic efficiency, specific capacity and energy density of the battery; at the same time, the remaining silver acts as a conductive agent between the positive electrode and the electrolyte, improving The charge transfer between interfaces reduces the interface resistance, thereby improving the rate performance of the battery, so it has broad market application prospects. At the same time, the present invention also provides a method for preparing the composite positive electrode. The preparation method provided by the present invention is simple to operate and can be suitable for large-scale industrial production applications.

Description of the drawings

Figure 1 is a schematic structural diagram of lithium silver alloy particles in Example 1;

Figure 2 is a schematic structural diagram of a composite positive electrode containing a lithium replenishing agent used in Example 2;

Figure 3 is the first charge and discharge curve of the full battery using a lithium nickel cobalt manganate composite positive electrode containing a lithium supplement additive in Example 1;

Figure 4 is the first charge and discharge curve of the full battery using a lithium iron phosphate composite positive electrode containing a lithium supplement additive in Example 1;

Figure 5 shows the rate performance of the full battery using the nickel-cobalt lithium manganate composite cathode containing lithium-replenishing additives in Example 1.

Among them, 1 is Li layer, 2 is Ag core, 3 is aluminum foil, 4 is lithium supplement additive, and 5 is positive electrode active material particles.

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:

A composite positive electrode containing lithium supplement additive and its preparation method and lithium-ion battery. The specific steps are as follows:

S1. Install the electroplating cell: In an argon atmosphere glove box with water content and oxygen content both below 0.01ppm, add lithium ion electrolyte (specifically 1.0M LiPF6 in EC:DEC:EMC=1:1:1Vol%) Pour it into a copper container, add 500mg of silver powder, then fix a lithium piece with a diameter of 15.6mm on the electrode clip, and seal the installed electroplating cell to ensure that the silver powder is not oxidized.

S2. Preparation of silver-lithium alloy: The electrode clip is connected to a DC regulated power supply, the electrode clip connected to the pure copper container is connected to the negative electrode of the power supply as the cathode, and the electrode clip connected to the lithium sheet is connected to the positive electrode of the power supply as the anode. The current size is 30mA, and the current density is is 157mA cm ^-2 , the voltage is 8V, and the termination voltage is 0.4V. At the same time, place the sealed copper container in the ultrasonic cleaner, turn on the ultrasound, and electroplat for 60 minutes. During the process, the anode generates lithium ions, and lithium is deposited on the surface of the silver powder in contact with the copper container, eventually forming a silver-lithium alloy. After the electroplating is completed, filter and wash it four times in the glove box, and then dry the obtained silver-lithium alloy in a vacuum oven to obtain a clean silver-lithium alloy, in which the silver content is 85wt% and the lithium content is 15wt%. The alloy The size is 2.2~3.0μm.

S3. When making the lithium nickel cobalt manganate (NCM83) composite positive electrode piece, the silver-lithium alloy is filled into the voids of the lithium nickel cobalt manganate cathode using a homogenization method. When preparing the positive electrode slurry, add 1.7g of NCM83, 0.1g of the above-mentioned lithium silver alloy, 0.1g of conductive carbon black, and 0.1g of polyvinylidene fluoride. The solid content is 35%, and the solvent is N-methylpyrrolidone. The preparation method is to apply the homogenized positive electrode slurry on aluminum foil, first place it in a blast oven at 80°C, wait until the solvent is dried, and then transfer it to a vacuum oven at 120°C to dry for 12 hours to obtain a composite positive electrode.

S4. Battery assembly and testing. Assemble the composite positive electrode sheet containing lithium-silver alloy prepared in the above steps into a full battery in the glove box. The electrolyte is 1.0M LiPF6 in EC:DEC:EMC=1:1:1Vol%, and the separator is The polypropylene separator is used with a thickness of 25 μm and a porosity of 41%. The negative electrode sheet is a graphite electrode sheet and the N/P ratio is 1.05. Use the Xinwei tester to test the electrochemical performance of the battery. Use a current density of 0.1C (1C=200mAh g ^-1 ) to charge and discharge. Charge first and then discharge. The test voltage range is 2.7~4.3V, and the first Coulombic efficiency is calculated. Referring to Figure 3, the positive electrode lithium supplement method provided by the present invention can reduce the first efficiency of the graphite negative electrode from 83.1% (the same as the S4 battery assembly, the difference is that the positive electrode sheet uses the lithium nickel cobalt manganate positive electrode sheet prepared in Comparative Example 1) Improved to 89.6%. Its capacity at current densities of 0.1, 0.2C, 0.5C, 1C and 2C (1C=200mAh g ^-1 ) is 215mAh g ^-1 , 210mAh g ^-1 , 190mAh g ^-1 , 180mAh g ^-1 , 165mAh g respectively. ^-1 .

Example 2:

A composite positive electrode containing lithium supplement additive and its preparation method and lithium-ion battery. The specific steps are as follows:

S1. Install the electroplating cell: In an argon atmosphere glove box with both water and oxygen content below 0.01ppm, pour the lithium ion electrolyte specifically 1.0M LiPF6 in EC:DMC:EMC=1:1:1Vol% In a copper container, add 500 mg of silver powder, then fix a lithium sheet with a diameter of 15.6 mm on the electrode clip, and seal the installed electroplating cell to ensure that the silver powder is not oxidized.

S2. Preparation of silver-lithium alloy: The electrode clip is connected to a DC regulated power supply, the electrode clip connected to the pure copper container is connected to the negative electrode of the power supply as the cathode, and the electrode clip connected to the lithium sheet is connected to the positive electrode of the power supply as the anode. The current size is 100mA and the current density is 100mA. is 523mAcm ^-2 , the voltage is 8V, and the termination voltage is 0.3V. At the same time, place the sealed copper container in the ultrasonic cleaner, turn on the ultrasonic, and electroplat for 90 minutes. During the process, the anode generates lithium ions, and lithium is deposited on the surface of the silver powder in contact with the copper container, ultimately forming a silver-lithium alloy. After the electroplating is completed, filter and wash it four times in the glove box, and then dry the obtained silver-lithium alloy in a vacuum oven to obtain a clean silver-lithium alloy, in which the silver content is 80.21wt% and the lithium content is 19.79wt%. The alloy size is 1.7~1.2μm.

S3. When making the lithium nickel cobalt manganate (NCM83) composite positive electrode piece, the silver-lithium alloy is filled into the voids of the lithium nickel cobalt manganate cathode using a homogenization method. When preparing the positive electrode slurry, add 1.6g NCM83, 0.2g lithium silver alloy, 0.1g conductive carbon black, 0.1g polyvinylidene fluoride, the solid content is 35%, and the solvent is N-methylpyrrolidone. The preparation method is to apply the homogenized positive electrode slurry on aluminum foil, first place it in a blast oven at 80°C, wait until the solvent is dried, and then transfer it to a vacuum oven at 120°C to dry for 12 hours to obtain a composite positive electrode.

S4. Battery assembly and testing. Assemble the full battery in the glove box with the positive electrode sheet containing lithium silver alloy prepared in the above steps. The electrolyte is 1.0M LiPF6 in EC:DEC:EMC=1:1:1Vol%, and the separator is The thickness of the polypropylene separator is 25 μm, the porosity is 41%, the negative electrode sheet is a graphite electrode sheet, and the N/P ratio is 1.05. Use Xinwei tester to test the electrochemical performance of the battery. Use a current density of 0.1C (1C=200mAh g ^-1 ) to charge and discharge. Charge first and then discharge. The test voltage range is 2.7~4.3V, and the first Coulombic efficiency is calculated. The positive electrode lithium supplement method provided by the present invention can increase the first efficiency of the graphite negative electrode from 83.1% (the same as the S4 battery assembly, except that the positive electrode sheet uses the NCM83 positive electrode sheet prepared in Comparative Example 1) to 91.2%.

Example 3:

A composite positive electrode containing lithium supplement additive and its preparation method and lithium-ion battery. The specific steps are as follows:

S1. Install the electroplating cell: In an argon atmosphere glove box with both water and oxygen content below 0.01ppm, pour the lithium ion electrolyte specifically 1.0M LiPF6 in EC:DMC=1:1Vol% into a copper container , add 500mg silver powder, then fix the lithium sheet with a diameter of 15.6mm on the electrode clip, and seal the installed electroplating cell to ensure that the silver powder is not oxidized.

S2. Preparation of silver-lithium alloy: The electrode clip is connected to a DC regulated power supply, the electrode clip connected to the pure copper container is connected to the negative electrode of the power supply as the cathode, and the electrode clip connected to the lithium sheet is connected to the positive electrode of the power supply as the anode. The current size is 150mA and the current density is 150mA. is 785mA cm ^-2 , the voltage is 8V, and the termination voltage is 0.2V. At the same time, place the sealed copper container in the ultrasonic cleaner and turn on ultrasonic plating for 120 minutes. During the process, the anode generates lithium ions, and lithium is deposited on the surface of the silver powder in contact with the copper container, eventually forming a silver-lithium alloy. After the electroplating is completed, filter and wash it four times in the glove box, and then dry the obtained silver-lithium alloy in a vacuum oven to obtain a clean silver-lithium alloy, in which the silver content is 76wt% and the lithium content is 24wt%. The alloy The size is 0.6~1.3μm.

S3. When making the lithium iron phosphate positive electrode piece, use the homogenization method to fill the silver lithium alloy into the voids of the lithium iron phosphate positive electrode. When preparing the positive electrode slurry, add 1.6g of lithium iron phosphate, 0.2g of lithium silver alloy, 0.1g of conductive carbon black, and 0.1g of polyvinylidene fluoride. The solid content is 35%, and the solvent is N-methylpyrrolidone. The preparation method is to apply the homogenized positive electrode slurry on aluminum foil, first place it in a blast oven at 80°C, wait until the solvent is dried, and then transfer it to a vacuum oven at 120°C to dry for 12 hours to obtain a composite positive electrode.

S4. Battery assembly and testing. Assemble the full battery in the glove box with the positive electrode sheet containing lithium silver alloy prepared in the above steps. The electrolyte is 1.0M LiPF6 in EC:DEC:EMC=1:1:1Vol%, and the separator is The thickness of the polypropylene separator is 25 μm, the porosity is 41%, the negative electrode sheet is a silicon carbon negative electrode sheet (silicon accounts for 82.1wt.%), and the N/P ratio is 1.05. Use a current density of 0.1C (1C=150mAh g ^-1 ) to charge and discharge. Charge first and then discharge. The test voltage range is 2.5~3.7V. Use the Xinwei tester to test the electrochemical performance of the battery and calculate the first Coulombic efficiency. The positive electrode lithium supplement method provided by the present invention can increase the first efficiency of the silicon carbon negative electrode from 89.32% (the same as the S4 battery assembly, the difference is that the positive electrode sheet uses the lithium iron phosphate positive electrode sheet prepared in Comparative Example 2) to 93.01%.

Comparative example 1:

Lithium-ion batteries are prepared using lithium nickel cobalt manganate (NCM83) as the positive electrode. The specific steps are as follows:

S1. Use the homogenization method to prepare lithium nickel cobalt manganate (NCM83) positive electrode sheets. When preparing the positive electrode slurry, add 1.8g of NCM83, 0.1g of conductive carbon black, and 0.1g of polyvinylidene fluoride. The solid content is 35%, apply the homogenized positive electrode slurry on the aluminum foil, first place it in a blast oven at 80°C, after the solvent is dried, transfer it to a vacuum oven at 120°C and dry for 12 hours to obtain the positive electrode.

S2. Battery assembly and testing. Assemble the positive electrode sheet prepared in the above steps into a full battery in the glove box. The electrolyte is 1.0M LiPF6 in EC:DEC:EMC=1:1:1Vol%. The separator is made of polypropylene separator. The thickness is 25 μm, the porosity is 41%, the negative electrode sheet is a graphite electrode sheet, and the N/P ratio is 1.05. The Xinwei tester was used to test the electrochemical performance of the battery, and the first Coulombic efficiency was calculated to be 83.1%. Its capacity at current densities of 0.1, 0.2C, 0.5C, 1C and 2C (1C=200mAh g ^-1 ) is 190mAh g ^-1 , 180mAh g ^-1 , 170mAh g ^-1 , 150mAh g ^-1 , 130mAh g respectively. ^-1 .

Comparative example 2:

To prepare lithium-ion batteries using lithium iron phosphate as the positive electrode, the specific steps are as follows:

S1. Use the homogenization method to make lithium iron phosphate positive electrode sheets. When preparing the positive electrode slurry, add 1.8g of lithium iron phosphate, 0.1g of conductive carbon black, and 0.1g of polyvinylidene fluoride. The solid content is 35%. The homogenized positive electrode slurry is coated on the aluminum foil, first placed in a blast oven at 80°C, and after the solvent is dried, it is transferred to a vacuum oven at 120°C and dried for 12 hours to obtain the positive electrode.

S2. Battery assembly and testing. Prepare the positive electrode plate through the above steps and assemble the full battery in the glove box. The electrolyte is 1.0M LiPF6 in EC:DEC:EMC=1:1:1Vol%. The separator is a polypropylene separator with a thickness of 25 μm, the porosity is 41%, the negative electrode sheet is a silicon carbon negative electrode sheet (silicon accounts for 82.1wt.%), and the N/P ratio is 1.05. The Xinwei tester was used to test the electrochemical performance of the battery, and the first Coulombic efficiency was calculated to be 89.32%.

The electrochemical performance test was performed on the batteries of each of the above embodiments, that is, the comparative examples. The test results are shown in the table below:

Table 1 Electrochemical performance of batteries of Examples 1-3 and Comparative Examples 1-2

It can be seen from the battery electrochemical performance test results of each embodiment and comparative example that the present invention can effectively improve the Coulombic efficiency, specific capacity and energy density of the battery, and at the same time improve the rate performance of the battery.

The above-described embodiments are only preferred embodiments 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. The composite positive electrode containing the lithium supplementing additive is characterized by comprising a positive electrode material and the lithium supplementing additive, wherein the lithium supplementing additive is silver-lithium alloy, the weight ratio of lithium in the silver-lithium alloy is 15-25%, and the weight ratio of silver is 75-85%.

2. The composite positive electrode containing a lithium supplementing additive according to claim 1, wherein the particle size of the silver-lithium alloy is 0.5 to 3 μm.

3. The composite positive electrode containing the lithium supplementing additive according to claim 1, wherein the silver-lithium alloy has a core-shell structure with an outer layer of lithium coating an inner layer of silver.

4. The composite positive electrode containing the lithium supplementing additive according to claim 1, wherein the silver-lithium alloy is prepared by electroplating lithium on the surface of silver by an electroplating method.

5. The composite positive electrode containing the lithium supplementing additive according to claim 1, wherein the mass fraction of the positive electrode material in the composite positive electrode is 85-95%, and the mass fraction of the lithium supplementing additive is 5-15%.

6. The composite positive electrode containing a lithium supplementing additive according to claim 1, wherein the positive electrode material comprises 80 to 90wt% of the positive electrode active material, 5 to 10wt% of the conductive agent and 5 to 10wt% of the binder in mass fraction.

7. The composite positive electrode containing the lithium supplementing additive according to claim 6, wherein the positive electrode active material is at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide and lithium nickel cobalt aluminate, the conductive agent is at least one of carbon black, conductive graphene and carbon nanotubes, and the binder is polyvinylidene fluoride.

8. A method for preparing a composite positive electrode containing a lithium supplementing additive according to any one of claims 1 to 7, wherein the preparation method comprises the steps of adding the lithium supplementing additive and a positive electrode material into a solvent for homogenization treatment to obtain positive electrode slurry, and coating the positive electrode slurry on a substrate and drying to obtain the composite positive electrode.

9. The method for preparing a composite positive electrode containing a lithium supplementing additive according to claim 8, wherein the method for preparing a silver-lithium alloy comprises the steps of:

s1, installing an electroplating pool: placing the electrolyte in an electroplating pool of a pure copper container in an anhydrous anaerobic inert atmosphere glove box, adding silver powder and fixing a lithium source on a red copper electrode clamp;

s2, preparing silver-lithium alloy: the electrode clamp is connected to a direct current stabilized voltage power supply, the electrode clamp connected with the pure copper container is connected to a negative electrode of the power supply as a cathode, the electrode clamp connected with lithium is connected to a positive electrode of the power supply as an anode, electroplating is started, lithium ions are generated immediately by the anode, and the lithium ions are deposited on the surface of silver powder contacted with the copper container, so that silver-lithium alloy is finally formed.

10. Use of a composite positive electrode containing a lithium-compensating additive according to any of claims 1 to 7 in the field of lithium ion batteries.