CN110071284B - Protection method of lithium metal electrode - Google Patents

Abstract

The invention discloses a method for protecting a lithium metal electrode, which utilizes a simple alloying method and utilizes antimony trifluoride to form an artificial protective film on the surface of a lithium negative electrode, thereby effectively reducing the polarization of the lithium negative electrode and inhibiting the generation of dendritic crystals. The method mainly comprises the steps of reacting antimony trifluoride with lithium to generate a compact artificial protective film, dissolving antimony trifluoride in propylene carbonate to prepare a uniform solution, pretreating the surface of a lithium sheet to remove oxidized lithium on the surface, cutting the lithium sheet into wafers, immersing the wafers into the antimony trifluoride solution to react to obtain a treated lithium electrode, and finally assembling the lithium electrode into a symmetrical battery. The invention can generate a compact alloy layer on the surface of the lithium metal through low-concentration long-time reaction. The method fully reduces the polarization of the lithium metal negative electrode, has good cycle stability, effectively inhibits the generation of lithium dendrite, obtains the stable lithium metal negative electrode, is applied to the lithium battery, can improve the cycle performance and the safety performance of the lithium battery, and has potential commercial application value.

Description

Protection method of lithium metal electrode

technical field

The invention relates to a preparation method of a lithium ion battery, in particular to a preparation method and a maintenance method of an electrode of the lithium ion battery, and is applied to the technical field of lithium ion batteries.

Background technique

In recent years, the continuous consumption of fossil energy and the resulting environmental pollution have been paid more and more attention by people. In order to alleviate the above problems, the development and effective utilization of renewable and clean energy such as solar energy and wind energy, which can replace traditional energy sources such as coal, oil, and natural gas, has become an important research topic, and the development momentum of the new energy industry is also growing stronger. However, new energy sources such as solar energy and wind energy are intermittent and cannot provide a continuous and stable energy supply to the grid. Due to the advantages of high energy density and stable cycle performance, in addition to being widely used in mobile phones, notebook computers, electric vehicles and other fields, lithium-ion batteries also have potential application prospects in storing intermittent new energy such as solar energy and wind energy.

With the gradual popularization of hybrid vehicles and electric vehicles around the world, rechargeable lithium batteries have gradually penetrated into people's daily life. However, even though the energy density of the lithium-ion battery system has been optimized by each component of the modular battery, such as electrode materials, electrolytes, current collectors, etc., and is close to its theoretical value, it still cannot meet people's expectations for a new generation of high-capacity lithium-ion batteries. demand. One of the main reasons for this embarrassment is that the single-ion intercalation reaction during battery charge-discharge cycles severely limits the capacity of lithium-containing cathodes. The demand for high-energy-density electrical energy storage devices has led researchers to turn their attention to lithium metal anodes.

The current commercial lithium-ion battery anode is graphitized carbon. Compared with the traditional graphite anode, the lithium metal anode has a very high energy density, 3800mAh/g, and a lower potential, -3.045V. However, the lithium metal negative electrode also has a fatal problem - the formation of lithium dendrites. During the precipitation and deposition of lithium ions on the surface of the lithium negative electrode, nanowire-like dendrites are easily formed on the surface of the lithium negative electrode, resulting in short circuit or even explosion of the battery. How to suppress the generation of lithium dendrites and achieve effective protection of lithium metal anodes is one of the key technologies. At present, the main researchers at home and abroad mainly realize the protection of lithium metal anode by means of optimization and improvement of electrolyte and surface modification of metal lithium anode. The optimization of the electrolyte mainly starts from the additives. The use of the additives greatly optimizes the uniformity and stability of the SEI film of the metal lithium anode. The additives mainly include 2-methylfuran, CO ₂ , SO ₂ and N ₂ O gas molecules, VC and fluorine-containing compounds, etc. The surface modification of metal lithium anode mainly involves artificial SEI film and interface nano-modification. The interfacial nano-modification process is complex, limited to the laboratory stage, and has no industrial basis. Linda F. Nazar found that the use of precious metal indium to form a layer of lithium fluoride and alloy substances on the surface of lithium, the phenomenon of effectively inhibiting the formation of lithium dendrites, can significantly improve the stability of lithium batteries, but the cost is high and not economical. Therefore, it is particularly important to seek more effective and simpler protection measures for lithium metal anodes, which has become an urgent technical problem to be solved.

SUMMARY OF THE INVENTION

In order to solve the problems of the prior art, the object of the present invention is to overcome the deficiencies existing in the prior art, and provide a protection method for a lithium metal electrode, which can realize the protection of the lithium metal negative electrode simply and effectively, through lithium metal and antimony trifluoride ( SbF ₃ ) reaction method, an alloy and lithium fluoride are formed on the surface of the lithium metal negative electrode, and the low-cost metal fluoride antimony trifluoride is used to prevent the generation of dendrites of the lithium negative electrode, which can reduce the negative electrode caused by the lithium negative electrode. The process of the invention is simple, the effect is obvious, the cost is low, the industrialization is easy to be realized, and the practical application of the lithium negative electrode is expected to be realized.

To achieve the above object, the present invention adopts the following technical solutions:

A method for protecting lithium metal electrodes. A low-concentration antimony trifluoride solution is used to react with metal lithium on the surface of the lithium metal electrode to generate lithium antimony alloy and lithium fluoride, thereby forming a dense layer of lithium antimony on the surface of the lithium metal electrode. The composite protective layer of alloy and lithium fluoride, wherein the concentration of antimony trifluoride in the antimony trifluoride solution is 0.05-0.2 mole per liter.

As the preferred technical solution of the present invention, the protection method of the lithium metal electrode comprises the following steps:

a. Weigh 53.6-107.2 mg of antimony trifluoride, pour it into a 20 ml glass bottle with a lid, add 3-6 ml of propylene carbonate as a solvent with a pipette, stir to make antimony trifluoride in propylene carbonate is fully dissolved in the solution to obtain an antimony trifluoride solution, which is for subsequent use;

b. Prepare a disc-shaped lithium sheet, control the diameter of the lithium sheet to be no greater than 12 mm, and the thickness of the lithium sheet to be no greater than 0.2 mm, for use;

c. Press the lithium sheet in the b on the stainless steel gasket, so that the lithium sheet and the stainless steel gasket are fully adhered and bonded;

d. Put the lithium sheet processed in the c. together with the stainless steel gasket into the glass bottle used in the step a, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle. After 3 to 6 minutes of surface modification reaction of the lithium negative electrode, the lithium sheet is taken out from the antimony trifluoride solution, and then the residual solution on the surface of the lithium sheet is cleaned with absorbent paper, thereby obtaining a lithium antimony alloy and lithium fluoride. The composite protective layer of the lithium metal electrode.

As a preferred technical solution of the present invention, an antimony trifluoride solution with an antimony trifluoride concentration of 0.1 mol per liter is used as the reaction solution, and the surface modification reaction of the metal lithium negative electrode is carried out with the metal lithium on the surface of the lithium metal electrode.

As a preferred technical solution of the present invention, at least one lithium salt is selected to be dissolved in an organic solvent, a lithium ion electrolyte is prepared, and a lithium metal electrode having a composite protective layer of lithium antimony alloy and lithium fluoride is used as the negative electrode to assemble into metal lithium Symmetrical battery, the battery assembly process is carried out in an argon atmosphere, and the water in the argon atmosphere is controlled to <0.01ppm and oxygen <0.01ppm.

As a preferred technical solution of the present invention, in the preparation process of the lithium ion electrolyte, the selected lithium salt is lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or lithium hexafluorophosphate (LiPF ₆ ). Not less than 1.0 moles per liter.

As a preferred technical solution of the present invention, during the preparation process of the lithium ion electrolyte, lithium nitrate is continuously added on the basis of the lithium salt in the lithium ion electrolyte, so that the lithium nitrate concentration of the lithium ion electrolyte is not less than 0.01 mol per liter.

As a preferred technical solution of the present invention, during the preparation process of the lithium ion electrolyte, the organic mixed solvent is a mixture of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1 solution, or a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1.

As a preferred technical solution of the present invention, in the process of assembling the metal-lithium symmetrical battery, a polypropylene hollow membrane is used as the separator.

As a preferred technical solution of the present invention, the entire process of implementing the lithium metal electrode protection method is carried out in an argon-filled glove box.

The protection method of the lithium metal negative electrode of the present invention forms a protective layer on the surface of the lithium metal negative electrode. Weigh a certain amount of antimony trifluoride, pour it into a glass bottle with a lid, add a certain amount of propylene carbonate, and stir to fully dissolve the antimony trifluoride. Take a lithium sheet with a diameter of 15.6 mm, press it into a sheet with a thickness of about 0.2 mm, and cut it into a circular sheet with a diameter of 12 mm. Lightly press the treated lithium sheet on the stainless steel gasket to fully adhere the lithium sheet to the stainless steel gasket. Put the treated lithium sheet together with the stainless steel gasket into the glass bottle gently, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle, take it out after a period of reaction, and treat its surface solution with absorbent paper clean.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

1. The method of the present invention utilizes antimony trifluoride and lithium metal to react to generate a layer of dense lithium antimony alloy and lithium fluoride layer and place it on the surface of the lithium negative electrode, which is helpful for the uniform extraction and deposition of lithium ions and prevents the formation of lithium dendrites. produced, thereby improving the stability and safety performance of lithium batteries;

2. The method of the present invention utilizes an inexpensive metal fluoride antimony trifluoride (SbF ₃ ) to prevent the generation of dendrites of the lithium negative electrode, the experimental process is simple, the effect is obvious, and the polarization brought by the lithium negative electrode can be reduced, It is expected to realize the practical application of lithium anode;

3. The method of the present invention improves the overall life and quality of the battery while improving the life of the battery electrode;

4. The key of the method of the present invention is that a dense layer of lithium antimony alloy and lithium fluoride can be formed on the surface of lithium metal through a low concentration and long time reaction. It can be seen from electrochemical tests that the method of the present invention can fully reduce the polarization of the lithium metal negative electrode, and the polarization is reduced to 50 mV after charging and discharging per square centimeter at 1 mA for 1 hour, and the cycle stability is good, indicating that the lithium dendrites The generation is effectively suppressed, and a stable lithium metal negative electrode is obtained, which can be used in lithium batteries to improve the cycle performance and safety performance of lithium batteries, and has potential commercial application value.

Description of drawings

Fig. 1 is the lithium sheet adopted in the present invention, the treated lithium sheet and the final assembled symmetrical button battery comparison diagram, wherein the figure a is the lithium sheet, and the figure b is the lithium obtained after the surface modification reaction treatment of the metal lithium negative electrode Figure c shows the final assembled symmetrical coin cell battery.

FIG. 2 is a powder X-ray diffraction pattern of a composite protective layer of lithium antimony alloy and lithium fluoride prepared by reacting the lithium sheet with antimony trifluoride in Example 1 of the present invention.

FIG. 3 is the electrochemical performance curve of the metal lithium symmetrical battery assembled in Example 1 of the present invention.

FIG. 4 is the electrochemical performance curve of the metal lithium symmetrical battery assembled in Example 2 of the present invention.

FIG. 5 is the electrochemical performance curve of the metal lithium symmetrical battery assembled in Example 3 of the present invention.

FIG. 6 is the electrochemical performance curve of the metal lithium symmetrical battery assembled in Example 4 of the present invention.

FIG. 7 is the electrochemical performance curve of the metal lithium symmetric battery assembled in Example 5 of the present invention.

Detailed ways

The above scheme will be further described below in conjunction with specific embodiments, and preferred embodiments of the present invention are described in detail as follows:

Example 1:

In this embodiment, referring to FIGS. 1 to 3 , a method for protecting lithium metal electrodes includes the following steps:

a. Weigh 53.6 mg of antimony trifluoride, pour it into a 20 ml glass bottle with a lid, add 3 ml of propylene carbonate as a solvent with a pipette, stir to fully dissolve antimony trifluoride in propylene carbonate, Obtain antimony trifluoride solution, standby;

b. Take a lithium sheet with a diameter of 15.6 mm, press it into a sheet with a thickness of 0.2 mm with a smooth cylinder, and then cut it into a circular sheet with a diameter of 12 mm with a die for use;

c. Press the lithium sheet in the b on the stainless steel gasket, so that the lithium sheet and the stainless steel gasket are fully adhered and bonded;

d. Put the lithium sheet processed in the c. together with the stainless steel gasket into the glass bottle used in the step a, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle. After the surface modification reaction of the lithium negative electrode for 5 minutes, the lithium sheet was taken out from the antimony trifluoride solution, and then the residual solution on the surface of the lithium sheet was cleaned with absorbent paper to obtain a composite with lithium antimony alloy and lithium fluoride. Lithium metal electrode with protective layer;

e. Put the lithium metal electrode prepared in the d into the CR2032 battery shell, select the polypropylene hollow membrane as the diaphragm, and select 1 mole per liter of lithium bis(trifluoromethylsulfonyl)imide for the electrolyte. (LiTFSI) was dissolved in a 1:1 volume ratio of 1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME) mixed solution, and lithium nitrate was added at the same time to make the prepared lithium ion electrolyte The lithium nitrate concentration is 0.01 moles per liter. In this example, a lithium salt is selected to be dissolved in an organic solvent to prepare a lithium ion electrolyte, and a lithium metal electrode with a composite protective layer of lithium antimony alloy and lithium fluoride is used as the negative electrode to assemble a metal lithium symmetrical battery. The battery assembly process is as follows: It is carried out in an argon atmosphere, and the water in the argon atmosphere is controlled to be <0.01ppm and oxygen <0.01ppm.

Experimental test analysis:

Refer to Figure 1 for the lithium sheet used in the method of this embodiment, the treated lithium sheet and the final assembled symmetrical button battery, where Figure a is the lithium sheet, and Figure b is the lithium obtained after the surface modification reaction treatment of the metal lithium negative electrode Figure c shows the final assembled symmetrical coin cell battery. The powder of the composite protective layer of lithium antimony alloy and lithium fluoride prepared by reacting the lithium sheet with antimony trifluoride in the method of this embodiment is analyzed by X-ray diffraction experiment. Referring to FIG. 2, it can be seen from FIG. 2 that the artificial protective film contains LiF and Li ₃ Sb. The electrochemical performance of the lithium metal symmetric battery assembled by the method of this embodiment is tested, and the electrochemical performance curve of the metal lithium ^symmetric battery is obtained. It can be seen that the polarization is still less than 100 mV after cycling for 600 hours, and it can be seen from the inset that the voltage has been in a stable state during the galvanostatic charge-discharge process, indicating that the generation of lithium dendrites during the charge-discharge process has been effectively suppressed. In this example, a low-concentration antimony trifluoride solution is used to react with metallic lithium on the surface of the lithium metal electrode to generate lithium antimony alloy and lithium fluoride, thereby forming a dense layer of lithium antimony alloy and lithium fluoride on the surface of the lithium metal electrode. Composite protective layer. In this embodiment, a simple alloying method is used to form an alloy and a lithium fluoride substance on the surface of the lithium negative electrode by using antimony trifluoride (SbF ₃ ), which can effectively reduce the polarization of the lithium negative electrode and suppress the generation of dendrites. The method of this embodiment mainly utilizes the reaction of antimony trifluoride and lithium to form a dense alloy and a lithium fluoride protective layer. The surface of the lithium sheet was pretreated to remove the oxidized lithium on the surface, cut into a 12 mm diameter disc, and the obtained disc was immersed in an antimony trifluoride solution to react to obtain a treated lithium electrode, and finally assembled into a symmetrical battery. The key to this method is that a dense layer of alloy and lithium fluoride can be formed on the surface of lithium metal through a low concentration and long time reaction. Electrochemical tests show that this method can fully reduce the polarization of the lithium metal negative electrode. The polarization is reduced to 50 mV after charging and discharging per square centimeter at 1 mA for 1 hour, and the cycle stability is good, indicating the formation of lithium dendrites. It is effectively inhibited to obtain a stable lithium metal negative electrode, which can be used in lithium batteries to improve the cycle performance and safety performance of lithium batteries, and has potential commercial application value.

Embodiment 2:

This embodiment is basically the same as the first embodiment, and the special features are:

In this embodiment, referring to FIG. 4 , a method for protecting lithium metal electrodes includes the following steps:

a. Weigh 107.2 mg of antimony trifluoride, pour it into a 20 ml glass bottle with a lid, add 6 ml of propylene carbonate as a solvent with a pipette, stir to fully dissolve antimony trifluoride in propylene carbonate, Obtain antimony trifluoride solution, standby;

b. Take a lithium sheet with a diameter of 15.6 mm, press it into a sheet with a thickness of 0.2 mm with a smooth cylinder, and then cut it into a circular sheet with a diameter of 12 mm with a die for use;

c. Press the lithium sheet in the b on the stainless steel gasket, so that the lithium sheet and the stainless steel gasket are fully adhered and bonded;

d. Put the lithium sheet processed in the c. together with the stainless steel gasket into the glass bottle used in the step a, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle. After the surface modification reaction of the lithium negative electrode for 5 minutes, the lithium sheet was taken out from the antimony trifluoride solution, and then the residual solution on the surface of the lithium sheet was cleaned with absorbent paper to obtain a composite with lithium antimony alloy and lithium fluoride. Lithium metal electrode with protective layer;

e. Put the lithium metal electrode prepared in the described d into the CR2032 battery shell, select the polypropylene hollow membrane as the diaphragm, and select the bis(trifluoromethylsulfonyl)sulfoxide with a concentration of 1 mole per liter for the electrolyte. Lithium amide (LiTFSI) was dissolved in a 1:1 volume ratio of 1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME) mixed solution. In this example, a lithium salt is selected to be dissolved in an organic solvent to prepare a lithium ion electrolyte, and a lithium metal electrode with a composite protective layer of lithium antimony alloy and lithium fluoride is used as the negative electrode to assemble a metal lithium symmetrical battery. The battery assembly process is as follows: It is carried out in an argon atmosphere, and the water in the argon atmosphere is controlled to be <0.01ppm and oxygen <0.01ppm.

Experimental test analysis:

The electrochemical performance of the lithium metal symmetric battery assembled by the method of this embodiment is tested, and the electrochemical performance curve of the metal lithium ^symmetric battery is obtained. It can be seen that the polarization is still less than 100mV after 140 hours of cycling, and the inset shows that the voltage has been in a stable state during the galvanostatic charge-discharge process, indicating that the generation of lithium dendrites during the charge-discharge process has been effectively suppressed. In this example, a low-concentration antimony trifluoride solution is used to react with metallic lithium on the surface of the lithium metal electrode to generate a lithium antimony alloy and lithium fluoride, thereby forming a dense protective layer of lithium antimony and lithium fluoride on the surface of the lithium metal electrode . In this embodiment, a simple solvent reaction method is used, and antimony trifluoride (SbF ₃ ) is used to form an alloy and lithium fluoride on the surface of the lithium negative electrode, which can effectively reduce the polarization of the lithium negative electrode and suppress the generation of dendrites. The method of this embodiment mainly utilizes the reaction of antimony trifluoride and lithium to form a dense alloy protective layer. The main method is as follows: firstly, dissolving antimony trifluoride in propylene carbonate to obtain a uniform solution. The surface of the lithium sheet was pretreated to remove the oxidized lithium on the surface, cut into a 12 mm diameter disc, and the obtained disc was immersed in an antimony trifluoride solution to react to obtain a treated lithium electrode, and finally assembled into a symmetrical battery. The key to this method is that a dense alloy layer can be formed on the surface of lithium metal through a long-term reaction at a low concentration. Electrochemical tests show that this method can fully reduce the polarization of the lithium metal negative electrode. The polarization is reduced to 50 mV after charging and discharging per square centimeter at 1 mA for 1 hour, and the cycle stability is good, indicating the formation of lithium dendrites. It is effectively inhibited to obtain a stable lithium metal negative electrode, which can be used in lithium batteries to improve the cycle performance and safety performance of lithium batteries, and has potential commercial application value.

Embodiment three:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, referring to FIG. 5 , a method for protecting lithium metal electrodes includes the following steps:

a. Weigh 53.6 mg of antimony trifluoride, pour it into a 20 ml glass bottle with a lid, add 3 ml of propylene carbonate as a solvent with a pipette, stir to fully dissolve antimony trifluoride in propylene carbonate, Obtain antimony trifluoride solution, standby;

b. Take a lithium sheet with a diameter of 15.6 mm, press it into a sheet with a thickness of 0.2 mm with a smooth cylinder, and then cut it into a circular sheet with a diameter of 12 mm with a die for use;

c. Press the lithium sheet in the b on the stainless steel gasket, so that the lithium sheet and the stainless steel gasket are fully adhered and bonded;

d. Put the lithium sheet processed in the c. together with the stainless steel gasket into the glass bottle used in the step a, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle. After the surface modification reaction of the lithium negative electrode for 5 minutes, the lithium sheet was taken out from the antimony trifluoride solution, and then the residual solution on the surface of the lithium sheet was cleaned with absorbent paper to obtain a composite with lithium antimony alloy and lithium fluoride. Lithium metal electrode with protective layer;

e. Put the lithium metal electrode prepared in the described d into the CR2032 battery shell, select the polypropylene hollow membrane as the diaphragm, and select the bis(trifluoromethylsulfonyl)sulfoxide with a concentration of 1 mole per liter for the electrolyte. Lithium amine (LiTFSI) was dissolved in a 1:1 volume ratio of 1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME) mixed solution, while adding lithium nitrate to make the prepared lithium ion The lithium nitrate concentration of the electrolyte solution was 0.01 moles per liter. In this example, a lithium salt is used to dissolve in an organic solvent to prepare a lithium ion electrolyte, and a lithium metal electrode with a composite protective layer of lithium antimony alloy and lithium fluoride is used as the negative electrode to assemble a metal lithium symmetrical battery. The battery assembly process is as follows: It is carried out in an argon atmosphere, and the water in the argon atmosphere is controlled to be <0.01ppm and oxygen <0.01ppm.

Experimental test analysis:

The electrochemical performance test of the lithium metal symmetrical battery assembled by the method of the present embodiment is carried out, and the electrochemical performance ^curve of the metal lithium ^symmetrical battery is obtained ^{. 2} , 1mA/cm ^-2 , 1.5mA/cm ^-2 current densities for each charge and discharge for 1 hour, test the electrochemical performance, see Figure 5, it can be seen from Figure 5 that the lithium sheets treated at different current densities show stability . In this example, a low-concentration antimony trifluoride solution is used to react with metallic lithium on the surface of the lithium metal electrode to generate lithium antimony alloy and lithium fluoride, thereby forming a dense layer of lithium antimony alloy and lithium fluoride on the surface of the lithium metal electrode. Composite protective layer. In this embodiment, a simple solvent reaction method is used, and antimony trifluoride (SbF ₃ ) is used to form lithium antimony alloy and lithium fluoride on the surface of the lithium negative electrode, which can effectively reduce the polarization of the lithium negative electrode and suppress the generation of dendrites. The method of this embodiment mainly utilizes the reaction of antimony trifluoride and lithium to form a dense alloy and a lithium fluoride protective layer. The surface of the lithium sheet was pretreated to remove the oxidized lithium on the surface, cut into a 12 mm diameter disc, and the obtained disc was immersed in an antimony trifluoride solution to react to obtain a treated lithium electrode, and finally assembled into a symmetrical battery. The key to this method is that a dense alloy and lithium fluoride layer can be formed on the surface of lithium metal through a low-concentration and long-term reaction. Electrochemical tests show that this method can fully reduce the polarization of the lithium metal negative electrode. The polarization is reduced to 50 mV after charging and discharging per square centimeter at 1 mA for 1 hour, and the cycle stability is good, indicating the formation of lithium dendrites. It is effectively inhibited to obtain a stable lithium metal negative electrode, which can be used in lithium batteries to improve the cycle performance and safety performance of lithium batteries, and has potential commercial application value.

Embodiment 4:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, referring to FIG. 6 , a method for protecting lithium metal electrodes includes the following steps:

a. Weigh 53.6 mg of antimony trifluoride, pour it into a 20 ml glass bottle with a lid, add 3 ml of propylene carbonate as a solvent with a pipette, stir to fully dissolve antimony trifluoride in propylene carbonate, Obtain antimony trifluoride solution, standby;

b. Take a lithium sheet with a diameter of 15.6 mm, press it into a sheet with a thickness of 0.2 mm with a smooth cylinder, and then cut it into a circular sheet with a diameter of 12 mm with a die for use;

c. Press the lithium sheet in the b on the stainless steel gasket, so that the lithium sheet and the stainless steel gasket are fully adhered and bonded;

d. Put the lithium sheet processed in the c. together with the stainless steel gasket into the glass bottle used in the step a, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle. After the surface modification reaction of the lithium negative electrode for 5 minutes, the lithium sheet was taken out from the antimony trifluoride solution, and then the residual solution on the surface of the lithium sheet was cleaned with absorbent paper to obtain a composite with lithium antimony alloy and lithium fluoride. Lithium metal electrode with protective layer;

e. put the lithium metal electrode prepared in the described d into the CR2032 battery shell, select the polypropylene hollow membrane as the diaphragm, and select the lithium hexafluorophosphate (LiPF ₆ ) with a concentration of 1 mole per liter to dissolve the electrolyte in the volume ratio of 1:1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC). In this example, a lithium salt is used to dissolve in an organic solvent to prepare a lithium ion electrolyte, and a lithium metal electrode with a composite protective layer of lithium antimony alloy and lithium fluoride is used as the negative electrode to assemble a metal lithium symmetrical battery. The battery assembly process is as follows: It is carried out in an argon atmosphere, and the water in the argon atmosphere is controlled to be <0.01ppm and oxygen <0.01ppm.

Experimental test analysis:

The electrochemical performance of the lithium metal symmetric battery assembled by the method of this example is tested to obtain the electrochemical performance curve of the metal ^lithium symmetric battery. Fig. 6. It can be seen from Fig. 6 that in the industrialized ester electrolyte, the polarization is still low after 250 hours of cycling. It can be seen from the inset that the voltage remains stable during the galvanostatic charge-discharge process, indicating that lithium dendrites production is effectively suppressed. In this example, a low-concentration antimony trifluoride solution is used to react with metallic lithium on the surface of the lithium metal electrode to generate lithium antimony alloy and lithium fluoride, thereby forming a dense layer of lithium antimony alloy and lithium fluoride on the surface of the lithium metal electrode. Composite protective layer. In this example, a simple solvent reaction method is used, and antimony trifluoride (SbF ₃ ) is used to form a composite of lithium antimony alloy and lithium fluoride on the surface of the lithium negative electrode, which can effectively reduce the polarization of the lithium negative electrode and suppress the dendrite. produce. The method of this embodiment mainly utilizes antimony trifluoride and lithium to react to form a dense lithium-antimony alloy and lithium fluoride composite protective layer. The surface of the lithium sheet was pretreated to remove the oxidized lithium on the surface, cut into a 12 mm diameter disc, and the obtained disc was immersed in an antimony trifluoride solution to react to obtain a treated lithium electrode, and finally assembled into a symmetrical battery. The key to this method is that a dense layer of lithium antimony alloy and lithium fluoride can be formed on the surface of lithium metal through a low concentration and long time reaction. Electrochemical tests show that this method can fully reduce the polarization of the lithium metal negative electrode. The polarization is reduced to 50 mV after charging and discharging per square centimeter at 1 mA for 1 hour, and the cycle stability is good, indicating the formation of lithium dendrites. It is effectively inhibited to obtain a stable lithium metal negative electrode, which can be used in lithium batteries to improve the cycle performance and safety performance of lithium batteries, and has potential commercial application value.

Embodiment 5:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, referring to FIG. 7 , a method for protecting lithium metal electrodes includes the following steps:

a. Weigh 53.6 mg of antimony trifluoride, pour it into a 20 ml glass bottle with a lid, add 3 ml of propylene carbonate as a solvent with a pipette, stir to fully dissolve antimony trifluoride in propylene carbonate, Obtain antimony trifluoride solution, standby;

b. Take a lithium sheet with a diameter of 15.6 mm, press it into a sheet with a thickness of 0.2 mm with a smooth cylinder, and then cut it into a circular sheet with a diameter of 12 mm with a die for use;

c. Press the lithium sheet in the b on the stainless steel gasket, so that the lithium sheet and the stainless steel gasket are fully adhered and bonded;

d. Put the lithium sheet processed in the c. together with the stainless steel gasket into the glass bottle used in the step a, so that the lithium sheet is immersed in the antimony trifluoride solution in the glass bottle. After the surface modification reaction of the lithium negative electrode for 5 minutes, the lithium sheet was taken out from the antimony trifluoride solution, and then the residual solution on the surface of the lithium sheet was cleaned with absorbent paper to obtain a composite with lithium antimony alloy and lithium fluoride. Lithium metal electrode with protective layer;

e. put the lithium metal electrode prepared in the described d into the CR2032 battery shell, select the polypropylene hollow membrane as the diaphragm, and select the lithium hexafluorophosphate (LiPF ₆ ) with a concentration of 1 mole per liter to dissolve the electrolyte in the volume ratio of 1:1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC). In this example, a lithium salt is used to dissolve in an organic solvent to prepare a lithium ion electrolyte, and a lithium metal electrode with a composite protective layer of lithium antimony alloy and lithium fluoride is used as the negative electrode to assemble a metal lithium symmetrical battery. The battery assembly process is as follows: It is carried out in an argon atmosphere, and the water in the argon atmosphere is controlled to be <0.01ppm and oxygen <0.01ppm.

Experimental test analysis:

The electrochemical performance of the lithium metal symmetric battery assembled by the method of this embodiment is tested to obtain the electrochemical performance curve of the metal ^lithium symmetric battery. Figure 7. It can be seen from Figure 7 that the polarization remains stable during the charge-discharge cycle of about 230 hours. It can be seen from the illustration that the voltage remains stable during the constant current charge-discharge process, indicating that the generation of lithium dendrites has been effectively suppressed. . In this example, a low-concentration antimony trifluoride solution is used to react with metallic lithium on the surface of the lithium metal electrode to generate lithium antimony alloy and lithium fluoride, thereby forming a dense layer of lithium antimony alloy and lithium fluoride on the surface of the lithium metal electrode. Composite protective layer. In this embodiment, a simple solvent reaction method is used, and antimony trifluoride (SbF ₃ ) is used to form a lithium antimony alloy and a lithium fluoride layer on the surface of the lithium negative electrode, which can effectively reduce the polarization of the lithium negative electrode and suppress the generation of dendrites. The method of this embodiment mainly utilizes the reaction of antimony trifluoride and lithium to form a dense lithium antimony alloy and a lithium fluoride protective layer. The surface of the lithium sheet was pretreated to remove the oxidized lithium on the surface, cut into a 12 mm diameter disc, and the obtained disc was immersed in an antimony trifluoride solution to react to obtain a treated lithium electrode, and finally assembled into a symmetrical battery. The key to this method is that a dense layer of lithium antimony alloy and lithium fluoride can be formed on the surface of lithium metal through a low concentration and long time reaction. Electrochemical tests show that this method can fully reduce the polarization of the lithium metal negative electrode. The polarization is reduced to 50 mV after charging and discharging per square centimeter at 1 mA for 1 hour, and the cycle stability is good, indicating the formation of lithium dendrites. It is effectively inhibited to obtain a stable lithium metal negative electrode, which can be used in lithium batteries to improve the cycle performance and safety performance of lithium batteries, and has potential commercial application value.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and various changes can also be made according to the purpose of the invention and creation of the present invention. Changes, modifications, substitutions, combinations or simplifications should be equivalent replacement methods, as long as they meet the purpose of the present invention, as long as they do not deviate from the technical principles and inventive concepts of the protection method for lithium metal electrodes of the present invention, all belong to the present invention. scope of protection.

Claims (7)

1. A method for protecting a lithium metal electrode, comprising the steps of:

a. weighing 53.6-107.2 mg of antimony trifluoride, pouring the antimony trifluoride into a 20 ml glass bottle with a cover, adding 3-6 ml of propylene carbonate serving as a solvent into a liquid transfer gun, and stirring to fully dissolve the antimony trifluoride in the propylene carbonate to obtain an antimony trifluoride solution for later use;

b. preparing a disk-shaped lithium sheet, and controlling the diameter of the lithium sheet to be not more than 12 mm and the thickness of the lithium sheet to be not more than 0.2 mm for later use;

c. pressing the lithium sheet in the step b on a stainless steel gasket to ensure that the lithium sheet is fully adhered and attached to the stainless steel gasket;

d. putting the lithium sheet treated in the step c and the stainless steel gasket into the glass bottle used in the step a, immersing the lithium sheet in an antimony trifluoride solution in the glass bottle, taking out the lithium sheet from the antimony trifluoride solution after carrying out surface modification reaction on the lithium metal cathode for 3-6 minutes, and cleaning the solution remained on the surface of the lithium sheet by using absorbent paper to obtain the lithium metal electrode with a lithium antimony alloy and lithium fluoride composite protective layer;

the whole process of carrying out the method for protecting a lithium metal electrode was carried out in an argon-filled glove box.

2. The method for protecting a lithium metal electrode according to claim 1, wherein: antimony trifluoride solution with the concentration of 0.1 mol per liter is adopted as reaction solution to carry out surface modification reaction.

3. The method for protecting a lithium metal electrode according to claim 1, wherein: at least one lithium salt is dissolved in an organic solvent to prepare a lithium ion electrolyte, a lithium metal electrode with a lithium-antimony alloy and lithium fluoride composite protective layer is used as a negative electrode to assemble a lithium metal symmetrical battery, the assembly process of the battery is carried out in an argon environment, and the water content and the oxygen content in the argon environment are controlled to be less than 0.01ppm and less than 0.01 ppm.

4. The method for protecting a lithium metal electrode according to claim 3, wherein: in the preparation process of the lithium ion electrolyte, the selected lithium salt is bis (trifluoromethyl sulfonyl) imide Lithium (LiTFSI) or lithium hexafluorophosphate (LiPF)₆) The lithium ion concentration of the electrolyte is not lower than 1.0 mol/L.

5. The method for protecting a lithium metal electrode according to claim 4, wherein: in the preparation process of the lithium ion electrolyte, lithium nitrate is continuously added on the basis of lithium salt in the lithium ion electrolyte, so that the concentration of the lithium nitrate in the lithium ion electrolyte is not lower than 0.01 mol per liter.

6. The method for protecting a lithium metal electrode according to claim 3, wherein: in the preparation process of the lithium ion electrolyte, the organic mixed solvent is a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1, or a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1.

7. The method for protecting a lithium metal electrode according to claim 3, wherein: in the process of assembling the lithium metal symmetrical battery, a polypropylene porous membrane is used as a diaphragm.

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