Electrolyte for lithium metal battery and lithium metal battery comprising the same
By adding strontium aluminate to the electrolyte of lithium metal batteries, the stability of the SEI film is improved, the problem of lithium dendrite growth is solved, and the cycle performance and safety of lithium metal batteries are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GREE ALTAIRNANO NEW ENERGY INC
- Filing Date
- 2020-12-18
- Publication Date
- 2026-06-26
AI Technical Summary
The safety hazards and poor cycle performance caused by lithium dendrite growth in existing lithium metal batteries cannot be effectively solved by the instability of SEI film.
Adding strontium aluminate as an additive to the electrolyte of lithium metal batteries allows it to participate in the formation of the SEI film through a pre-cycling process, improving the stability of the lithium metal-electrolyte interface and inhibiting lithium dendrite growth.
It improves the battery's coulombic efficiency to 99%, extends cycle life, and after 300 cycles, the discharge capacity only drops to 93.5% of the initial capacity, significantly improving the battery's cycle performance and safety.
Smart Images
Figure CN112635829B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium battery technology, and more specifically, to an electrolyte for lithium metal batteries and a lithium metal battery containing the electrolyte. Background Technology
[0002] Lithium metal batteries have a high theoretical specific capacity of 3860 mAh g. -1 With the lowest reduction potential (-3.045V relative to the standard hydrogen electrode), it has become the most promising next-generation energy storage electrode. The lowest reduction potential allows batteries with lithium metal as the negative electrode to have higher voltage and theoretical density. However, there are still many problems in the research of lithium metal negative electrodes. The main reasons restricting the development of lithium metal secondary batteries are as follows: (1) The lithium metal negative electrode reacts with the electrolyte, and the lithium in the battery is irreversibly consumed, which reduces the coulombic efficiency of the battery. The electrolyte is consumed in large quantities as the number of cycles increases, and the battery capacity decays rapidly; (2) The uneven deposition of lithium metal leads to the generation and growth of lithium dendrites in the negative electrode, which may puncture the separator and cause the battery to short-circuit, resulting in thermal runaway or even explosion; the breakage of dendrites will cause the irreversible generation of "dead lithium", reducing the available active material, increasing the internal resistance of the battery, and reducing the cycle efficiency and life. The SEI (solid electrolyte interphase) film is a solid electrolyte layer formed on the surface of lithium metal by the reaction of lithium metal and electrolyte. The SEI film is a passivation film with lithium-ion conductivity and electronic insulation. Lithium metal is deposited under the film, preventing further reaction between the electrolyte and lithium metal. However, the SEI film is mainly composed of inorganic salts and has a low mechanical modulus. The growth of lithium dendrites can lead to the fragmentation of the SEI film, causing lithium metal and electrolyte to react again. This repeated fragmentation and formation leads to a decrease in the battery's coulombic efficiency, and the thickening of the SEI film also increases the interfacial impedance. Therefore, to ensure stable battery cycling, the main focus is on suppressing lithium dendrite growth and improving the stability of the SEI film.
[0003] As the core component of a battery, the properties of the electrolyte significantly affect its cycle performance. Electrolyte additives are economically feasible because they do not require significant changes to the electrode and battery manufacturing processes, and have been extensively studied by scholars in hopes of finding the optimal electrolyte composition. Electrolyte additives are mainly divided into the following two types: (1) Film-forming additives. Most film-forming additives can react with lithium metal to form a stable SEI film, and this SEI film can stabilize the lithium anode. These additives generally have lower LUMO orbitals (the lowest energy level orbitals without occupied electrons), which preferentially react with lithium to form an SEI film, thereby protecting the stability of other components of the electrolyte; (2) Deposition additives. These additives do not react with the electrolyte and lithium metal, but instead suppress dendrites by regulating the deposition behavior of lithium ions, resulting in more uniform lithium deposition.
[0004] In summary, while many approaches to suppressing lithium dendrite growth have been proposed by focusing on electrolyte additives, none have completely solved the direct problem, and lithium metal anode-based batteries remain only in the laboratory stage. If a substance could be added to the electrolyte to in situ regulate the SEI film composition and improve its stability, it would effectively enhance the ability of lithium metal anodes to suppress lithium dendrite growth during use, which would be of great significance for improving the safety performance of lithium metal batteries. Summary of the Invention
[0005] The present invention aims to provide an electrolyte for lithium metal batteries and a lithium metal battery containing the electrolyte, so as to solve the problem of poor cycle performance of lithium metal batteries in the prior art.
[0006] To achieve the above objectives, according to one aspect of the present invention, an application of strontium aluminate as an electrolyte additive for lithium metal batteries is provided.
[0007] Furthermore, the mass fraction of strontium aluminate in the electrolyte for lithium metal batteries is 0.5% to 2%.
[0008] Furthermore, the electrolyte uses lithium hexafluorophosphate as the solute and a mixed solution of ethylene carbonate and diethyl carbonate as the solvent.
[0009] Furthermore, in the mixed solution of ethylene carbonate and diethyl carbonate, the volume ratio of ethylene carbonate to diethyl carbonate is 1:1.
[0010] Furthermore, 1M lithium hexafluorophosphate is added to the mixed solution of ethylene carbonate and diethyl carbonate; preferably, the lithium metal battery uses a carbon black / lithium iron phosphate composite electrode as the positive electrode, a lithium sheet as the negative electrode, and polypropylene as the separator; preferably, the assembly of the lithium metal battery includes: using a carbon black / lithium iron phosphate composite electrode as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, and polypropylene as the separator, and packing them together with 50 microliters of strontium aluminate-containing lithium metal battery electrolyte in a battery case; preferably, after the lithium metal battery is assembled and left to stand for 20 hours, a multi-channel battery tester is used to perform pre-cycle and charge-discharge cycle tests, with the pre-cycle voltage range selected as 2.0–4.2V, the number of cycles as 5–10, and the pre-cycle rate as 0.2C.
[0011] Furthermore, the lithium metal battery assembly is completed in an argon atmosphere glove box, where the oxygen and moisture levels are both less than 0.01 ppm. Preferably, the preparation method of the carbon black / lithium iron phosphate composite electrode includes the following steps: mixing carbon black and lithium iron phosphate powder at a mass ratio of 1:8, grinding, mixing the resulting mixed powder with a PVDF NMP solution, stirring, coating the positive electrode slurry onto an aluminum foil current collector and fixing it onto a glass plate with a thickness of 100 micrometers, drying in a vacuum drying oven, and stamping with a punching machine to obtain the carbon black / lithium iron phosphate composite electrode. Preferably, the carbon black / lithium iron phosphate composite electrode is a disc with a diameter of 12 mm; in the PVDF NMP solution, PVDF is the solute and NMP is the solvent, with a solute mass fraction of 5%.
[0012] According to another aspect of the present invention, an electrolyte for lithium metal batteries is provided. This electrolyte for lithium metal batteries comprises the additive strontium aluminate.
[0013] Furthermore, the mass fraction of strontium aluminate in the electrolyte for lithium metal batteries is 0.5% to 2%; preferably, the electrolyte for lithium metal batteries uses lithium hexafluorophosphate as the solute and a mixed solution of ethylene carbonate and diethyl carbonate as the solvent; preferably, the volume ratio of ethylene carbonate to diethyl carbonate in the mixed solution of ethylene carbonate and diethyl carbonate is 5:1 to 1:5, more preferably 1:1; preferably, 1M lithium hexafluorophosphate is added to the mixed solution of ethylene carbonate and diethyl carbonate to form the electrolyte for lithium metal batteries.
[0014] According to another aspect of the present invention, a lithium metal battery is provided. The lithium metal battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the aforementioned electrolyte for lithium metal batteries.
[0015] Furthermore, the lithium metal battery uses a carbon black / lithium iron phosphate composite electrode as the positive electrode, a lithium sheet as the negative electrode, and polypropylene as the separator. Preferably, the assembly of the lithium metal battery includes: using a carbon black / lithium iron phosphate composite electrode as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, and polypropylene as the separator, and packing them together with 50 microliters of strontium aluminate-containing lithium metal battery electrolyte in a battery case. Preferably, after the lithium metal battery is assembled and left to stand for 20 hours, pre-cycle and charge-discharge cycle tests are performed using a multi-channel battery tester. The pre-cycle voltage range is selected as 2.0–4.2V, the number of cycles is 5–10, and the pre-cycle rate is 0.2C. Preferably, the lithium metal battery is assembled in an argon atmosphere glove box. The composition, with oxygen and moisture values in the chamber both less than 0.01 ppm; preferably, the preparation method of the carbon black / lithium iron phosphate composite electrode includes the following steps: mixing carbon black and lithium iron phosphate powder at a mass ratio of 1:8, grinding, mixing the obtained mixed powder with a PVDF NMP solution, stirring, coating the positive electrode slurry onto an aluminum foil current collector and fixing it onto a glass plate with a thickness of 100 micrometers, drying in a vacuum drying oven, and stamping with a punching machine to obtain the carbon black / lithium iron phosphate composite electrode; more preferably, the carbon black / lithium iron phosphate composite electrode is a disc with a diameter of 12 mm; in the PVDF NMP solution, PVDF is the solute and NMP is the solvent, with a solute mass fraction of 5%.
[0016] By applying the technical solution of this invention, a small amount of strontium aluminate is added to the electrolyte. Strontium aluminate can be oxidized at a lower voltage and participates in the formation of the SEI film through a simple pre-cycle process. The introduction of a small amount of strontium aluminate will not affect the normal charging and discharging of the battery. A simple pre-cycle can improve the SEI film composition in situ, achieve the formation of a stable lithium metal and electrolyte interface, thereby improving the battery energy utilization rate and cycle life. This not only inhibits the growth of lithium dendrites, but also reduces the occurrence of side reactions, improves the coulombic efficiency of the battery to 99%, and extends the cycle life. After 300 cycles, the discharge capacity only decreases to 93.5% of the initial capacity. Attached Figure Description
[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:
[0018] Figure 1 The diagram shows a comparison of the cycle performance of the battery (a) containing strontium aluminate additive and the battery (b) with blank electrolyte in Example 1.
[0019] Figure 2 A comparison diagram of the lithium deposition morphology on the positive electrode surface of the battery containing strontium aluminate additive electrolyte (a) and blank electrolyte (b) in Example 1 is shown. Detailed Implementation
[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0021] In view of the problem of poor cycle performance of existing lithium metal batteries, the present invention improves the SEI film composition by using an additive in situ, thereby improving the problems of easy growth of lithium dendrites, low safety and poor cycle performance in current lithium metal batteries.
[0022] According to a typical embodiment of the present invention, an application of strontium aluminate as an electrolyte additive for lithium metal batteries is provided.
[0023] By applying the technical solution of this invention, a small amount of strontium aluminate is added to the electrolyte. Strontium aluminate can be oxidized at a lower voltage and participates in the formation of the SEI film through a simple pre-cycle process. The introduction of a small amount of strontium aluminate will not affect the normal charging and discharging of the battery. A simple pre-cycle can improve the SEI film composition in situ, achieve the formation of a stable lithium metal and electrolyte interface, thereby improving the battery energy utilization rate and cycle life. This not only inhibits the growth of lithium dendrites, but also reduces the occurrence of side reactions, improves the coulombic efficiency of the battery to 99%, and extends the cycle life. After 300 cycles, the discharge capacity only decreases to 93.5% of the initial capacity.
[0024] Preferably, the mass fraction of strontium aluminate in the electrolyte for lithium metal batteries is 0.5% to 2%. Controlling the proportion within this range can reduce dendrite formation in the lithium metal anode, improve coulombic efficiency, and increase cycle life.
[0025] According to a typical embodiment of the present invention, the electrolyte for a lithium metal battery uses lithium hexafluorophosphate as the solute and a mixed solution of ethylene carbonate and diethyl carbonate as the solvent. Preferably, the volume ratio of ethylene carbonate to diethyl carbonate in the mixed solution is 1:1. Preferably, 1M lithium hexafluorophosphate is added to the mixed solution of ethylene carbonate and diethyl carbonate. In a typical embodiment of the present invention, the lithium metal battery uses a carbon black / lithium iron phosphate composite electrode as the positive electrode, a lithium sheet as the negative electrode, and a polypropylene separator. Preferably, the assembly of the lithium metal battery includes: a carbon black / lithium iron phosphate composite electrode as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, a polypropylene separator, and 50 microliters of strontium aluminate-containing electrolyte, all housed together in a battery case. Preferably, after the lithium metal battery is assembled and left to stand for 20 hours, pre-cycle and charge-discharge cycle tests are performed using a multi-channel battery tester. The pre-cycle voltage range is selected as 2.0–4.2V, the number of cycles is 5–10, and the pre-cycle rate is 0.2C. More preferably, the lithium metal battery is assembled in an argon atmosphere glove box, where the oxygen and moisture levels are both less than 0.01 ppm.
[0026] In a typical embodiment of the present invention, the preparation method of the carbon black / lithium iron phosphate composite electrode includes the following steps: mixing carbon black and lithium iron phosphate powder at a mass ratio of 1:8, grinding, mixing the resulting mixed powder with a PVDF NMP solution, stirring, coating the positive electrode slurry onto an aluminum foil current collector and fixing it onto a glass plate with a thickness of 100 micrometers, drying in a vacuum drying oven, and stamping with a punching machine to obtain the carbon black / lithium iron phosphate composite electrode. Preferably, the carbon black / lithium iron phosphate composite electrode is a disc with a diameter of 12 mm; in the PVDF NMP solution, PVDF is the solute and NMP is the solvent, with a solute mass fraction of 5%.
[0027] According to a typical embodiment of the present invention, an electrolyte for lithium metal batteries is provided, the electrolyte for lithium metal batteries comprising the additive strontium aluminate. Preferably, the mass fraction of strontium aluminate in the electrolyte for lithium metal batteries is 0.5% to 2%.
[0028] According to a typical embodiment of the present invention, the electrolyte uses lithium hexafluorophosphate as the solute and a mixed solution of ethylene carbonate and diethyl carbonate as the solvent; preferably, the volume ratio of ethylene carbonate to diethyl carbonate in the mixed solution of ethylene carbonate and diethyl carbonate is 1:1; preferably, 1M lithium hexafluorophosphate is added to the mixed solution of ethylene carbonate and diethyl carbonate to form an electrolyte for lithium metal batteries.
[0029] According to a typical embodiment of the present invention, a lithium metal battery is provided. The lithium metal battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the aforementioned electrolyte for lithium metal batteries.
[0030] In a typical embodiment of the present invention, the lithium metal battery uses a carbon black / lithium iron phosphate composite electrode as the positive electrode, a lithium sheet as the negative electrode, and a polypropylene separator. Preferably, the assembly of the lithium metal battery includes: using a carbon black / lithium iron phosphate composite electrode as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, and a polypropylene separator, along with 50 microliters of strontium aluminate-containing lithium metal battery electrolyte, all packaged together in a battery case. Preferably, after the lithium metal battery assembly is completed and allowed to stand for 20 hours, pre-cycle and charge-discharge cycle tests are performed using a multi-channel battery tester. The pre-cycle voltage range is selected as 2.0–4.2V, the number of cycles is 5–10, and the pre-cycle rate is 0.2C. Preferably, the lithium metal battery is assembled in an argon atmosphere. The composition of the glove box is such that the oxygen and moisture values inside the box are both less than 0.01 ppm; preferably, the preparation method of the carbon black / lithium iron phosphate composite electrode includes the following steps: mixing carbon black and lithium iron phosphate powder at a mass ratio of 1:8, grinding, mixing the obtained mixed powder with a PVDF NMP solution, stirring, coating the positive electrode slurry onto an aluminum foil current collector and fixing it on a glass plate with a thickness of 100 micrometers, drying in a vacuum drying oven, and stamping with a punching machine to obtain the carbon black / lithium iron phosphate composite electrode; more preferably, the carbon black / lithium iron phosphate composite electrode is a disc with a diameter of 12 mm; in the PVDF NMP solution, PVDF is the solute and NMP is the solvent, and the mass fraction of the solute is 5%.
[0031] The beneficial effects of the present invention will be further illustrated below with reference to embodiments.
[0032] Example 1
[0033] (1) Preparation of electrolyte. Take a certain amount of blank electrolyte (1.0M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 1:1), add 1% strontium aluminate by mass, and stir thoroughly to obtain an electrolyte with 1% strontium aluminate.
[0034] (2) Preparation of positive electrode material. Commercial carbon black and lithium iron phosphate powder were mixed at a mass ratio of 1:8 and ground for 1 hour. The resulting mixed powder was then mixed with PVDF solution and NMP solvent and stirred for 12 hours. The positive electrode slurry was coated onto an aluminum foil current collector and fixed onto a flat glass plate with a thickness of 100 micrometers. After complete drying in a vacuum drying oven, the carbon black / lithium iron phosphate composite positive electrode sheet was obtained by stamping with a stamping machine. The electrode sheet was a circular sheet with a diameter of 12 mm. In the PVDF solution, PVDF was the solute and NMP was the solvent, with a mass fraction of 5%.
[0035] (3) Battery Assembly. Additive Experimental Group: The carbon black / lithium iron phosphate composite electrode obtained in step two was used as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, and commercially available polypropylene as the separator. These were then packed together with 50 microliters of 1% (w / w) strontium aluminate electrolyte in a CR2025 button battery casing. Control Group: A blank electrolyte without strontium aluminate (1.0M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 1:1) was used, with other conditions identical to the experimental group.
[0036] (4) Performance Testing: After a 20-hour resting period, pre-cycle and charge-discharge cycle tests were performed using a multi-channel battery tester. The pre-cycle voltage range was 2.0–4.2V, with 5 cycles. The pre-cycle rate was 0.2C, and the long-cycle rate was 1C. The battery cycle performance was as follows: Figure 1 As shown, where Figure 1 (a) shows the long-cycle performance of the battery in the additive experimental group. Figure 1 (b) shows the long-cycle performance of the blank control group battery. After the addition of strontium aluminate, the battery exhibited more stable cycle efficiency, and the lower capacity decay indicated a longer cycle life. The coulombic efficiency reached 99%, and the discharge capacity only decreased to 93.5% of the initial capacity after 300 cycles.
[0037] (5) Observation of lithium deposition morphology at the electrode / electrolyte interface. Additive experimental group: A lithium sheet was used as the negative electrode, a copper sheet as the positive electrode, and a commercially available polypropylene separator. The electrolyte, containing 50 μL of strontium aluminate (1% by mass), was placed in a CR2025 button battery case. After 12 hours, pre-cycle and charge-discharge cycle tests were performed using a multi-channel battery tester. The lithium deposition amount was 1.0 mAh cm⁻¹. -2 The pre-cycle current density is selected as 0.2 mA cm⁻¹. -2 The number of revolutions is 3, and the long-cycle current density is selected as 1.0 mA / cm². -2 After 20 cycles, the discharged battery was examined using a scanning electron microscope to observe the lithium deposition morphology on the positive electrode surface. Control group: A blank electrolyte without strontium aluminate (1.0 M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 1:1) was used, with all other conditions identical to the experimental group. The lithium deposition morphology at the electrode / electrolyte interface after 20 cycles is shown below. Figure 2 As shown, where Figure 2 (a) corresponds to the additive experimental group. Figure 2 (b) corresponds to the blank control group. Unlike the dendritic deposition and porous morphology of the control group, after the addition of strontium aluminate, a smooth and uniform interface layer can be observed on the cathode surface, which effectively inhibits dendrite growth.
[0038] Example 2
[0039] The basic process is the same as the example, except that the electrolyte is prepared by taking a certain amount of blank electrolyte (1.0M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 1:1), adding 0.5% strontium aluminate by mass, and stirring thoroughly to obtain an electrolyte with 0.5% strontium aluminate.
[0040] The performance indicators were similar to those in Example 1, and the lithium deposition morphology at the electrode / electrolyte interface was also similar to that in Example 1.
[0041] Example 3
[0042] The basic process is the same as the example, except that the electrolyte is prepared by taking a certain amount of blank electrolyte (1.0M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 1:1), adding 2% strontium aluminate by mass, and stirring thoroughly to obtain an electrolyte with 2% strontium aluminate.
[0043] The performance indicators were similar to those in Example 1, and the lithium deposition morphology at the electrode / electrolyte interface was also similar to that in Example 1.
[0044] Example 4
[0045] The basic process is the same as the previous example, except for the preparation of the electrolyte. A certain amount of electrolyte (1.0M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 5:1) was taken, and 1% strontium aluminate was added. After stirring thoroughly, an electrolyte containing 1% strontium aluminate was obtained.
[0046] The performance indicators were similar to those in Example 1, and the lithium deposition morphology at the electrode / electrolyte interface was also similar to that in Example 1.
[0047] Example 5
[0048] The basic process is the same as the previous example, except for the preparation of the electrolyte. A certain amount of electrolyte (1.0M lithium hexafluorophosphate, ethylene carbonate EC: diethyl carbonate DEC = 1:5) was taken, and 1% strontium aluminate was added. After stirring thoroughly, an electrolyte containing 1% strontium aluminate was obtained.
[0049] The performance indicators were similar to those in Example 1, and the lithium deposition morphology at the electrode / electrolyte interface was also similar to that in Example 1. From the above description, it can be seen that the embodiments of the present invention achieve the following technical effects: adding a small amount of strontium aluminate to the electrolyte can form an SEI film at the lithium metal-electrolyte interface during pre-cycling, inhibiting lithium dendrite growth, reducing side reactions, and improving the electrochemical performance of the battery.
[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. An application of strontium aluminate as an electrolyte additive for lithium metal batteries, wherein the strontium aluminate has a mass fraction of 0.5% to 2% in the electrolyte for lithium metal batteries.
2. The application according to claim 1, characterized in that, The electrolyte for the lithium metal battery uses lithium hexafluorophosphate as the solute and a mixed solution of ethylene carbonate and diethyl carbonate as the solvent.
3. The application according to claim 2, characterized in that, In the mixed solution of ethylene carbonate and diethyl carbonate, the volume ratio of ethylene carbonate to diethyl carbonate is 1:5 to 5:
1.
4. The application according to claim 2, characterized in that, 1M lithium hexafluorophosphate was added to the mixed solution of ethylene carbonate and diethyl carbonate.
5. The application according to claim 4, characterized in that, The lithium metal battery uses a carbon black / lithium iron phosphate composite electrode as the positive electrode, a lithium sheet as the negative electrode, and polypropylene as the separator.
6. The application according to claim 5, characterized in that, The assembly of the lithium metal battery includes: using the carbon black / lithium iron phosphate composite electrode as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, and polypropylene as the separator, and packing them together with 50 microliters of the lithium metal battery electrolyte containing strontium aluminate in a battery case.
7. The application according to claim 6, characterized in that, After the lithium metal battery was assembled and left to stand for 20 hours, pre-cycle and charge-discharge cycle tests were performed using a multi-channel battery tester. The pre-cycle voltage range was selected as 2.0~4.2V, the number of cycles was 5~10, and the pre-cycle rate was 0.2C.
8. The application according to any one of claims 4 to 7, characterized in that, The lithium metal battery was assembled in an argon atmosphere glove box, where the oxygen and moisture levels were both less than 0.01 ppm.
9. The application according to claim 5, characterized in that, The preparation method of the carbon black / lithium iron phosphate composite electrode includes the following steps: mixing carbon black and lithium iron phosphate powder at a mass ratio of 1:8, grinding, mixing the obtained mixed powder with PVDF NMP solution, stirring, coating the positive electrode slurry onto an aluminum foil current collector and fixing it on a glass plate with a thickness of 100 micrometers, drying in a vacuum drying oven, and stamping with a punching machine to obtain the carbon black / lithium iron phosphate composite electrode.
10. The application according to claim 9, characterized in that, The carbon black / lithium iron phosphate composite electrode is a disc with a diameter of 12 mm; in the PVDF NMP solution, PVDF is the solute and NMP is the solvent, and the mass fraction of the solute is 5%.
11. An electrolyte for lithium metal batteries, characterized in that, The electrolyte for lithium metal batteries contains strontium aluminate as an additive, and the mass fraction of strontium aluminate in the electrolyte for lithium metal batteries is 0.5% to 2%.
12. The electrolyte for lithium metal batteries according to claim 11, characterized in that, The electrolyte for the lithium metal battery uses lithium hexafluorophosphate as the solute and a mixed solution of ethylene carbonate and diethyl carbonate as the solvent.
13. The electrolyte for lithium metal batteries according to claim 12, characterized in that, In the mixed solution of ethylene carbonate and diethyl carbonate, the volume ratio of ethylene carbonate to diethyl carbonate is 5:1 to 1:
5.
14. The electrolyte for lithium metal batteries according to claim 13, characterized in that, In the mixed solution of ethylene carbonate and diethyl carbonate, the volume ratio of ethylene carbonate to diethyl carbonate is 1:
1.
15. The electrolyte for lithium metal batteries according to claim 12, characterized in that, 1M lithium hexafluorophosphate is added to the mixed solution of ethylene carbonate and diethyl carbonate to form the electrolyte for the lithium metal battery.
16. A lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the electrolyte for lithium metal batteries as described in any one of claims 11 to 15.
17. The lithium metal battery according to claim 16, characterized in that, The lithium metal battery uses a carbon black / lithium iron phosphate composite electrode as the positive electrode, a lithium sheet as the negative electrode, and polypropylene as the separator.
18. The electrolyte for lithium metal batteries according to claim 17, characterized in that, The assembly of the lithium metal battery includes: using the carbon black / lithium iron phosphate composite electrode as the positive electrode, a 450-micrometer-thick lithium sheet as the negative electrode, and polypropylene as the separator, and packing them together with 50 microliters of the lithium metal battery electrolyte containing strontium aluminate in a battery case.
19. The electrolyte for lithium metal batteries according to claim 18, characterized in that, After the lithium metal battery was assembled and left to stand for 20 hours, pre-cycle and charge-discharge cycle tests were performed using a multi-channel battery tester. The pre-cycle voltage range was selected as 2.0~4.2V, the number of cycles was 5~10, and the pre-cycle rate was 0.2C.
20. The electrolyte for lithium metal batteries according to claim 17, characterized in that, The lithium metal battery is assembled in an argon atmosphere glove box, where the oxygen and moisture levels are both less than 0.01 ppm.
21. The electrolyte for lithium metal batteries according to claim 17, characterized in that, The preparation method of the carbon black / lithium iron phosphate composite electrode includes the following steps: mixing carbon black and lithium iron phosphate powder at a mass ratio of 1:8, grinding, mixing the obtained mixed powder with PVDF NMP solution, stirring, coating the positive electrode slurry onto an aluminum foil current collector and fixing it on a glass plate with a thickness of 100 micrometers, drying in a vacuum drying oven, and stamping with a punching machine to obtain the carbon black / lithium iron phosphate composite electrode.
22. The electrolyte for lithium metal batteries according to claim 21, characterized in that, The carbon black / lithium iron phosphate composite electrode is a disc with a diameter of 12 mm; in the PVDF NMP solution, PVDF is the solute and NMP is the solvent, and the mass fraction of the solute is 5%.