A lithium metal battery formation method

Abstract

The application discloses a lithium metal battery formation method, comprising the following steps: S1, installing lithium metal batteries on a formation equipment provided with an expansion force feedback system respectively, and charging and discharging the lithium metal batteries according to set formation steps; S2, collecting expansion force data of the lithium metal batteries in the charging and discharging process through the expansion force feedback system; S3, fitting a simulation curve for the continuously changing voltage and the expansion force data in the charging and discharging process, and obtaining an expansion force change trend in the charging and discharging process; S4, according to the simulation curve, exerting a certain pre-tightening force on a formation clamp before formation of the lithium metal battery; and S5, according to the simulation curve, exerting different pressures on the formation clamp in the charging and discharging process of subsequent lithium metal batteries according to the formation steps until the formation is completed. The SEI film of the lithium metal battery is optimized through the formation mode of changing the pressure, so that the growth of lithium dendrites and expansion are effectively inhibited, and the cycle performance and safety performance of the lithium metal battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium metal batteries, in particular to a lithium metal battery formation method. BACKGROUND

[0002] With the continuous improvement of people's quality of life, under the background of the environmental protection department advocating green environmental protection, various electric vehicles for various purposes have emerged. With the increasing development of lithium ion battery technology, the actual capacity of traditional lithium ion batteries with graphite as the negative electrode is getting closer to the theoretical capacity, and it is difficult for lithium ion batteries to have a major breakthrough, so it is difficult to meet the increasing demand for specific energy. The lithium metal electrode used in lithium metal batteries has the inherent advantages of high mass energy density and volume energy density, and is therefore considered to be the most ideal secondary battery negative electrode material.

[0003] However, during the cyclic charging and discharging process of the lithium metal electrode, lithium dendrites are generated on the surface of the electrode in a disordered and uneven manner, and the growing lithium dendrites continuously damage the SEI film on the surface of the negative electrode, continuously generate side reactions on the surface of the negative electrode, and eventually lead to the failure of the battery, and the growing lithium dendrites can also pierce the separator and cause internal short circuit of the lithium metal, causing the risk of combustion or explosion. On the other hand, lithium metal batteries have the problem of battery swelling during actual application, which causes bubbles between the positive and negative electrodes, making it difficult for Li+ ions to migrate, causing capacity decay and rapid cycle failure. Therefore, how to solve the problem of lithium dendrites generated on the surface of the lithium metal electrode and how to form a stable SEI film on the surface of the lithium metal to reduce side reactions and inhibit battery swelling are major challenges for the commercialization of lithium metal batteries.

[0004] In the production process of lithium metal batteries, the formation process is an important process for fully activating the positive and negative active materials inside the battery and forming a dense and stable SEI film. At the same time, the quality and density of the SEI film directly affect the electrochemical performance of the lithium metal battery, such as stability, safety, cycle performance, and self-discharge. For example, the patent with the authorization announcement number CN111430822B discloses that the existing formation process of lithium metal batteries usually uses open negative pressure and low-rate current multi-section floating charging, which has limited effect on improving the cycle performance of the battery, inhibiting the swelling of the battery, and inhibiting the growth of lithium dendrites. Therefore, it is necessary to develop a new formation process to effectively inhibit the growth of lithium dendrites and swelling, and improve the cycle performance and safety performance of lithium metal batteries. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a lithium metal battery formation method, which simulates the expansion force of the lithium metal battery during the charging and discharging process, reveals the expansion force change trend, optimizes the SEI film of the lithium metal battery by changing the pressure formation method, effectively inhibits the growth of lithium dendrites and expansion, and improves the cycle performance and safety performance of the lithium metal battery.

[0006] The technical solution adopted by the present application to solve the above technical problem is:

[0007] A lithium metal battery formation method, comprising the following steps:

[0008] S1, installing the lithium metal battery after liquid injection and immersion in a formation device provided with an expansion force feedback system, and charging and discharging the lithium metal battery according to the set formation steps;

[0009] S2, collecting the expansion force data of the lithium metal battery during the charging and discharging process through the expansion force feedback system;

[0010] S3, fitting a simulation curve for the constantly changing voltage and expansion force data of the lithium metal battery during the entire charging and discharging process, so as to obtain the expansion force change trend of the lithium metal battery during the charging and discharging process;

[0011] S4, applying a certain pre-tightening force to the formation clamp before the formation of the lithium metal battery according to the simulation curve of the voltage and expansion force of the lithium metal battery;

[0012] S5, applying different pressures to the formation clamp during the charging and discharging of the subsequent lithium metal battery according to the formation steps according to the simulation curve of the voltage and expansion force of the lithium metal battery, until the formation is completed.

[0013] As a preferred, the formation steps in the step S1 and / or step S5 include constant current constant voltage charging, standing and constant current discharging.

[0014] As a preferred, the charging current is 0.05C-1.0C, the limit voltage of the constant current constant voltage charging is 3.7V-4.35V, and the cut-off current of the constant current constant voltage charging is 0.02C-0.05C during the constant current constant voltage charging process in the step S1 and / or step S5.

[0015] As a preferred, the standing time in the step S1 and / or step S5 is 15min-60min.

[0016] As a preferred, the discharging current is 0.1C-2.0C, and the limit voltage of the constant current discharging is 2.5V-3.0V during the constant current discharging process in the step S1 and / or step S5.

[0017] Preferably, the expansion force during the charging and discharging process of the lithium metal battery in step S2 is 50 kg to 3000 kg.

[0018] Preferably, the preload in step S4 is 50 kg to 2000 kg.

[0019] Preferably, during the formation process of step S5, the pressure applied by the clamping plate of the formation fixture to the lithium metal battery at different stages of the charging and discharging process is 110% to 150% of the maximum expansion force.

[0020] Preferably, the pressure in the constant current and constant voltage charging stage of step S5 is 55Kg to 4500Kg, the pressure in the resting stage is 50Kg to 4500Kg, and the pressure in the constant current discharging stage is 110Kg to 4500Kg.

[0021] Preferably, the positive electrode of the lithium metal battery adopts a ternary system.

[0022] Compared with the prior art, the advantages of the lithium metal battery formation method of the present invention are as follows:

[0023] By using the expansion force feedback system to obtain the expansion force data and the constantly changing voltage during charging and discharging, a simulation curve of the metal battery voltage and expansion force during the conventional formation process is obtained. Based on the simulation curve, the pressure applied by the formation fixture to the lithium metal battery at different stages of charging and discharging is adjusted so that lithium is deposited into neat columnar shapes during charging and discharging, without any pores in the middle, and almost no space for the formation of lithium dendrites. A dense and stable SEI film is formed on the lithium metal surface, thereby reducing side reactions, suppressing cell expansion, and improving the cycle performance and safety performance of the lithium metal battery. Attached Figure Description

[0024] Figure 1 The expansion force curve of a lithium metal battery during charging and discharging. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example

[0027] A method for forming a lithium metal battery includes the following steps:

[0028] S1. Install the lithium metal batteries that have been injected with liquid into a formation equipment equipped with an expansion force feedback system, and charge and discharge the lithium metal batteries according to the set formation steps.

[0029] S2. Collect expansion force data of lithium metal batteries during charging and discharging through an expansion force feedback system;

[0030] S3. Fit the simulation curve of the voltage and expansion force data of the lithium metal battery during the entire charging and discharging process to obtain the trend of expansion force change of the lithium metal battery during the charging and discharging process.

[0031] S4. Based on the simulation curve of lithium metal battery voltage and expansion force, apply a certain pre-tightening force to the formation fixture before the formation of lithium metal battery.

[0032] S5. Based on the simulation curve of lithium metal battery voltage and expansion force, apply different pressures to the formation fixture during the subsequent charging and discharging process of the lithium metal battery according to the formation steps, until the formation is completed.

[0033] Specifically, the formation steps in steps S1 and S5 are constant current and constant voltage charging, resting, and constant current discharging, respectively. During constant current and constant voltage charging, the charging current is 0.05C to 1.0C, the limiting voltage of constant current and constant voltage charging is 3.7V to 4.35V, and the cutoff current of constant current and constant voltage charging is 0.02C to 0.05C; the resting time is 15min to 60min; during constant current discharging, the discharging current is 0.1C to 2.0C, and the limiting voltage of constant current discharging is 2.5V to 3.0V.

[0034] The expansion force during the charging and discharging process of the lithium metal battery in step S2 is 50Kg to 3000Kg.

[0035] The preload in step S4 is 50 kg to 2000 kg.

[0036] During the formation and discharge process in step S5, the pressure applied by the clamping plates of the formation fixture to the lithium metal battery at different stages of the charging and discharging process is 110% to 150% of the maximum expansion force. Specifically, the pressure in the constant current and constant voltage charging stage of step S5 is 55 kg to 4500 kg, the pressure in the resting stage is 50 kg to 4500 kg, and the pressure in the constant current discharge stage is 110 kg to 4500 kg.

[0037] The lithium metal battery formation method in this embodiment is applicable to lithium metal batteries that use a ternary system for the positive electrode and lithium metal for the negative electrode.

[0038] Example 1

[0039] A lithium metal battery formation method is disclosed, which uses NCM523 as the positive electrode material, lithium metal as the negative electrode material, has a thickness of 60 μm, and a battery capacity of 10 Ah.

[0040] The formation method includes the following steps:

[0041] 1) After the lithium metal battery has been fully immersed in the electrolyte and left to stand for 24 hours, it is placed in a formation equipment with an expansion force feedback system. It is charged at a constant current of 0.1C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. After standing for 15 minutes, it is discharged at a constant current of 0.2C to 3.0V. The expansion force data of the lithium metal battery during the charging and discharging process is collected and recorded through the expansion force feedback system.

[0042] 2) By fitting the simulation curves of the constantly changing voltage and expansion force data during the entire charging and discharging process of the lithium metal battery, the curve of the expansion force of the lithium metal battery changing with the voltage of the lithium metal battery during the charging and discharging process can be obtained.

[0043] 3) The fitting results show that the maximum expansion forces of the 10Ah lithium metal battery at different stages are 1800Kg (4.35V), 800Kg (3.5V), and 1200Kg (3.85V), respectively.

[0044] 4) Select lithium metal batteries that have been fully immersed after being injected with liquid and left to stand for 24 hours, place them in the formation equipment and apply a pre-tightening force of 50 kg for 15 minutes.

[0045] 5) After the lithium metal battery has been placed in the resting period, charge it to 3.5V at a current of 0.1C. During the charging process, the clamping plate of the forming fixture applies a pressure of 950Kg to the lithium metal battery.

[0046] 6) After charging to 3.5V, the lithium metal battery is charged in the second stage: charged to 3.85V at a current of 0.1C. During the charging process, the clamp of the formation fixture applies a pressure of 1450Kg to the lithium metal battery.

[0047] 7) After charging to 3.85V, the lithium metal battery is charged in the third stage: charged to 4.35V at a current of 0.1C, and then switched to constant voltage charging until the current drops to 0.05C. During the charging process, the clamp applies a pressure of 2150Kg.

[0048] 8) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 2150 kg to the lithium metal battery.

[0049] 9) After the resting period, perform the first constant current discharge: discharge to 3.85V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 2150Kg to the lithium metal battery.

[0050] 10) After discharging to 3.85V, perform a second constant current discharge: discharge to 3.3V with a current of 0.2C. During the discharge process, the clamping plate of the formation fixture applies a pressure of 1450Kg to the lithium metal battery.

[0051] 11) After discharging to 3.3V, perform a third constant current discharge: discharge to 3.0V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 950Kg to the lithium metal battery.

[0052] 12) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 50 kg to the lithium metal battery.

[0053] To make the simulation curve and the pressure applied to the lithium metal battery by the clamping plate of the formation fixture during the subsequent charging and discharging process more accurate, at least three sets of lithium metal batteries of the same specifications were selected for steps 1), 2), and 3). Abnormal data were repeatedly measured, and the average value was taken after eliminating abnormal data to obtain the best voltage and expansion force data for simulation.

[0054] Example 2

[0055] A method for forming a lithium metal battery differs from Example 1 in that...

[0056] The formation method includes the following steps:

[0057] 1) After the lithium metal battery has been fully immersed in the electrolyte and left to stand for 24 hours, it is placed in a formation equipment with an expansion force feedback system. It is charged at a constant current of 0.05C to 4.35V, then switched to constant voltage charging until the current drops to 0.02C. After standing for 15 minutes, it is discharged at a constant current of 0.1C to 3.0V. The expansion force data of the lithium metal battery during the charging and discharging process is collected and recorded through the expansion force feedback system.

[0058] 2) By fitting the simulation curves of the constantly changing voltage and expansion force data during the entire charging and discharging process of the lithium metal battery, the curve of the expansion force of the lithium metal battery changing with the voltage of the lithium metal battery during the charging and discharging process can be obtained.

[0059] 3) The fitting results show that the maximum expansion forces of the 10Ah lithium metal battery at different stages are 1800Kg (4.35V), 1000Kg (3.7V), and 800Kg (3.5V), respectively.

[0060] 4) Select lithium metal batteries that have been fully immersed after being injected with liquid and left to stand for 24 hours, place them in the formation equipment and apply a pre-tightening force of 50 kg for 15 minutes.

[0061] 5) Perform the first stage of charging on the lithium metal battery after the resting period: charge it to 3.5V with a current of 0.05C. During the charging process, the clamping plate of the forming fixture applies a pressure of 950Kg to the lithium metal battery.

[0062] 6) After charging to 3.5V, the lithium metal battery is charged in the second stage: charged to 3.7V at a current of 0.05C. During the charging process, the clamp of the formation fixture applies a pressure of 1200Kg to the lithium metal battery.

[0063] 7) After charging to 3.7V, the lithium metal battery is charged in the third stage: charged to 4.35V at a current of 0.05C, and then switched to constant voltage charging until the current drops to 0.02C. During the charging process, the clamp applies a pressure of 2150Kg.

[0064] 8) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 2150 kg to the lithium metal battery.

[0065] 9) After the resting period, perform the first constant current discharge: discharge to 3.7V with a current of 0.1C. During the discharge process, the clamp of the formation fixture applies a pressure of 2150Kg to the lithium metal battery.

[0066] 10) After discharging to 3.7V, perform a second constant current discharge: discharge to 3.5V with a current of 0.1C. During the discharge process, the clamp of the formation fixture applies a pressure of 1200Kg to the lithium metal battery.

[0067] 11) After discharging to 3.0V, perform a third constant current discharge: discharge to 3.0V with a current of 0.1C. During the discharge process, the clamp of the formation fixture applies a pressure of 950Kg to the lithium metal battery.

[0068] 12) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 50 kg to the lithium metal battery.

[0069] Example 3

[0070] A method for forming a lithium metal battery differs from Example 1 in that...

[0071] The formation method includes the following steps:

[0072] 1) After the lithium metal battery has been fully immersed in the electrolyte and left to stand for 24 hours, it is placed in a formation equipment with an expansion force feedback system. It is charged at a constant current of 0.5C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. After standing for 15 minutes, it is discharged at a constant current of 0.2C to 3.0V. The expansion force data of the lithium metal battery during the charging and discharging process is collected and recorded through the expansion force feedback system.

[0073] 2) By fitting the simulation curves of the constantly changing voltage and expansion force data during the entire charging and discharging process of the lithium metal battery, the curve of the expansion force of the lithium metal battery changing with the voltage of the lithium metal battery during the charging and discharging process can be obtained.

[0074] 3) The fitting results show that the maximum expansion forces of the 10Ah lithium metal battery at different stages are 1800Kg (4.35V), 800Kg (3.5V), and 1200Kg (3.85V), respectively.

[0075] 4) Select lithium metal batteries that have been fully immersed after being injected with liquid and left to stand for 24 hours, place them in the formation equipment and apply a pre-tightening force of 50 kg for 15 minutes.

[0076] 5) After the lithium metal battery has been placed in the resting period, charge it to 3.5V at a current of 0.1C. During the charging process, the clamping plate of the forming fixture applies a pressure of 950Kg to the lithium metal battery.

[0077] 6) After charging to 3.5V, the lithium metal battery is charged in the second stage: charged to 3.85V at a current of 0.1C. During the charging process, the clamp of the formation fixture applies a pressure of 1450Kg to the lithium metal battery.

[0078] 7) After charging to 3.85V, the lithium metal battery is charged in the third stage: charged to 4.35V at a current of 0.1C, and then switched to constant voltage charging until the current drops to 0.05C. During the charging process, the clamp applies a pressure of 2150Kg.

[0079] 8) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 2150 kg to the lithium metal battery.

[0080] 9) After the resting period, perform the first constant current discharge: discharge to 3.85V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 2150Kg to the lithium metal battery.

[0081] 10) After discharging to 3.85V, perform a second constant current discharge: discharge to 3.3V with a current of 0.2C. During the discharge process, the clamping plate of the formation fixture applies a pressure of 1450Kg to the lithium metal battery.

[0082] 11) After discharging to 3.3V, perform a third constant current discharge: discharge to 3.0V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 950Kg to the lithium metal battery.

[0083] 12) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 50 kg to the lithium metal battery.

[0084] Example 4

[0085] A lithium metal battery formation method differs from Example 1 in that, in step 1), the lithium metal battery, after being injected with electrolyte and left to stand for 24 hours, is placed in a formation device equipped with an expansion force feedback system. It is charged at a constant current of 1.0C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. After standing for 15 minutes, it is discharged at a constant current of 2.0C to 3.0V. The expansion force data of the lithium metal battery during the charging and discharging process is collected and recorded through the expansion force feedback system.

[0086] Example 5

[0087] A lithium metal battery formation method differs from Example 1 in that the resting time in steps 1), 4), 8), and 12) is 60 min.

[0088] Example 6

[0089] A method for forming a lithium metal battery differs from Example 1 in that...

[0090] The formation method includes the following steps:

[0091] 1) After the lithium metal battery has been fully immersed in the electrolyte and left to stand for 24 hours, it is placed in a formation equipment with an expansion force feedback system. It is charged at a constant current of 0.1C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. After standing for 15 minutes, it is discharged at a constant current of 0.2C to 3.0V. The expansion force data of the lithium metal battery during the charging and discharging process is collected and recorded through the expansion force feedback system.

[0092] 2) By fitting the simulation curves of the constantly changing voltage and expansion force data during the entire charging and discharging process of the lithium metal battery, the curve of the expansion force of the lithium metal battery changing with the voltage of the lithium metal battery during the charging and discharging process can be obtained.

[0093] 3) The fitting results show that the maximum expansion forces of the 10Ah lithium metal battery at different stages are 1800Kg (4.35V), 800Kg (3.5V), and 1200Kg (3.85V), respectively.

[0094] 4) Select lithium metal batteries that have been fully immersed after being injected with liquid and left to stand for 24 hours, place them in the formation equipment and apply a pre-tightening force of 50 kg for 15 minutes.

[0095] 5) After the lithium metal battery has been placed in the resting period, charge it to 3.5V at a current of 0.1C. During the charging process, the clamping plate of the forming fixture applies a pressure of 880Kg to the lithium metal battery.

[0096] 6) After charging to 3.5V, the lithium metal battery is charged in the second stage: charged to 3.85V at a current of 0.1C. During the charging process, the clamp of the formation fixture applies a pressure of 1320Kg to the lithium metal battery.

[0097] 7) After charging to 3.85V, the lithium metal battery is charged in the third stage: charged at a current of 0.1C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. During the charging process, the clamp applies a pressure of 1980Kg.

[0098] 8) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 1980 kg to the lithium metal battery.

[0099] 9) After the resting period, perform the first constant current discharge: discharge to 3.85V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 1980Kg to the lithium metal battery.

[0100] 10) After discharging to 3.85V, perform a second constant current discharge: discharge to 3.3V with a current of 0.2C. During the discharge process, the clamping plate of the formation fixture applies a pressure of 1320Kg to the lithium metal battery.

[0101] 11) After discharging to 3.3V, perform a third constant current discharge: discharge to 3.0V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 880Kg to the lithium metal battery.

[0102] 12) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 50 kg to the lithium metal battery.

[0103] Example 7

[0104] A method for forming a lithium metal battery differs from Example 1 in that...

[0105] The formation method includes the following steps:

[0106] 1) After the lithium metal battery has been fully immersed in the electrolyte and left to stand for 24 hours, it is placed in a formation equipment with an expansion force feedback system. It is charged at a constant current of 0.1C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. After standing for 15 minutes, it is discharged at a constant current of 0.2C to 3.0V. The expansion force data of the lithium metal battery during the charging and discharging process is collected and recorded through the expansion force feedback system.

[0107] 2) By fitting the simulation curves of the constantly changing voltage and expansion force data during the entire charging and discharging process of the lithium metal battery, the curve of the expansion force of the lithium metal battery changing with the voltage of the lithium metal battery during the charging and discharging process can be obtained.

[0108] 3) The fitting results show that the maximum expansion forces of the 10Ah lithium metal battery at different stages are 1800Kg (4.35V), 800Kg (3.5V), and 1200Kg (3.85V), respectively.

[0109] 4) Select lithium metal batteries that have been fully immersed after being injected with liquid and left to stand for 24 hours, place them in the formation equipment and apply a pre-tightening force of 50 kg for 15 minutes.

[0110] 5) Perform the first stage of charging on the lithium metal battery after the resting period: charge it to 3.5V with a current of 0.1C. During the charging process, the clamping plate of the forming fixture applies a pressure of 1200Kg to the lithium metal battery.

[0111] 6) After charging to 3.5V, the lithium metal battery is charged in the second stage: charged to 3.85V at a current of 0.1C. During the charging process, the clamping plate of the formation fixture applies a pressure of 1800Kg to the lithium metal battery.

[0112] 7) After charging to 3.85V, the lithium metal battery is charged in the third stage: charged at a current of 0.1C to 4.35V, then switched to constant voltage charging until the current drops to 0.05C. During the charging process, the clamp applies a pressure of 2700Kg.

[0113] 8) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 2700 kg to the lithium metal battery.

[0114] 9) After the resting period, perform the first constant current discharge: discharge to 3.85V with a current of 0.2C. During the discharge process, the clamp of the formation fixture applies a pressure of 2700Kg to the lithium metal battery.

[0115] 10) After discharging to 3.85V, perform a second constant current discharge: discharge to 3.3V with a current of 0.2C. During the discharge process, the clamping plate of the formation fixture applies a pressure of 1800Kg to the lithium metal battery.

[0116] 11) After discharging to 3.3V, perform a third constant current discharge: discharge to 3.0V with a current of 0.2C. During the discharge process, the clamping plate of the formation fixture applies a pressure of 1200Kg to the lithium metal battery.

[0117] 12) Let it rest for 15 minutes. During the resting process, the clamping plate of the forming fixture applies a pressure of 50 kg to the lithium metal battery.

[0118] Comparative Example 1

[0119] A lithium metal battery with a positive electrode material of NCM523 and a negative electrode material of lithium metal, a thickness of 60μm, and a capacity of 10Ah was used. Then, using existing lithium metal battery formation methods, without variable pressure formation, the conventional formation method was employed. After being fully immersed in the electrolyte and left to rest for 24 hours, the lithium metal battery was placed in the formation equipment and charged at a constant current of 0.1C to 4.35V. Then, constant voltage charging was applied until the current dropped to 0.05C, and the battery was left to rest for 15 minutes. Finally, it was discharged at a constant current of 0.2C to 3.0V, and then left to rest for another 15 minutes.

[0120] The test data of lithium metal battery cycle performance and battery expansion rate obtained in Examples 1-7 and Comparative Example 1 are shown in the table below.

[0121] The test method for the number of cycles is as follows: The lithium metal battery is charged and discharged at a charging rate of 0.33C / 0.33C. When the capacity retention rate reaches 80%, the number of cycles is recorded.

[0122]

[0123] By adjusting the pressure applied to the lithium metal battery at different stages of charging and discharging by the formation fixture during the lithium metal battery formation process, lithium is deposited into neat columnar shapes without any pores in the middle, leaving almost no space for the formation of lithium dendrites. A dense and stable SEI film is formed on the lithium metal surface, thereby reducing side reactions, suppressing cell expansion, and improving the cycle performance and safety performance of lithium metal batteries.

[0124] Although preferred embodiments of the present invention have been described in detail above, it should be clearly understood that 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. A lithium metal battery formation method, characterized by: The method comprises the following steps: S1, installing the lithium metal battery after liquid injection and immersion into a formation equipment provided with an expansion force feedback system, and charging and discharging the lithium metal battery according to a set formation step; S2, collecting expansion force data of the lithium metal battery in the charging and discharging process through the expansion force feedback system; S3, fitting and simulating curves of the changing voltage and expansion force data of the lithium metal battery in the whole charging and discharging process, so as to obtain the expansion force change trend of the lithium metal battery in the charging and discharging process; S4, applying a certain pre-tightening force to the formation clamp before formation of the lithium metal battery according to the simulation curve of the voltage and expansion force of the lithium metal battery; S5, applying different pressures to the formation clamp in the charging and discharging process of the subsequent lithium metal battery according to the formation step according to the simulation curve of the voltage and expansion force of the lithium metal battery until the formation is completed; so that the lithium is deposited into a neat columnar shape and a dense and stable SEI film is formed on the surface of the lithium metal in the charging and discharging process.

2. The lithium metal battery formation method of claim 1, wherein: The formation step in the step S1 and / or step S5 comprises constant current constant voltage charging, standing and constant current discharging.

3. The lithium metal battery formation method of claim 2, wherein: In the constant current constant voltage charging process in the step S1 and / or step S5, the charging current is 0.05C-1.0C, the limit voltage of the constant current constant voltage charging is 3.7V-4.35V, and the cutoff current of the constant current constant voltage charging is 0.02C-0.05C.

4. The lithium metal battery formation method of claim 2, wherein: The standing time in the step S1 and / or step S5 is 15min-60min.

5. The lithium metal battery formation method of claim 2, wherein: In the constant current discharging process in the step S1 and / or step S5, the discharging current is 0.1C-2.0C, and the limit voltage of the constant current discharging is 2.5V-3.0V.

6. The lithium metal battery formation method of claim 1, wherein: The expansion force value of the lithium metal battery in the charging and discharging process in the step S2 is 50Kg-3000Kg.

7. The lithium metal battery formation method of claim 1, wherein: The pre-tightening force in the step S4 is 50Kg-2000Kg.

8. The lithium metal battery formation method of claim 2, wherein: In the charging and discharging process of the formation step in the step S5, the pressure applied by the clamping plate of the formation clamp to the lithium metal battery at different stages in the charging and discharging process is 110%-150% of the maximum expansion force.

9. The lithium metal battery formation method of claim 8, wherein: The pressure in the constant current constant voltage charging stage in the step S5 is 55Kg-4500Kg, the pressure in the standing stage is 50Kg-4500Kg, and the pressure in the constant current discharging stage is 110Kg-4500Kg.

10. The lithium metal battery formation method of claim 1, wherein: The positive electrode of the lithium metal battery adopts a ternary system.

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