A lithium metal battery and a method of repairing a lithium metal battery negative electrode

Abstract

The application discloses a lithium metal battery and a repairing method of a negative electrode of the lithium metal battery. The lithium metal battery comprises a positive electrode sheet, a positive electrode tab, a negative electrode sheet, a negative electrode tab, a lithium metal foil, an auxiliary electrode tab and a diaphragm. The positive electrode sheet, the negative electrode sheet and the lithium metal foil are separated by the diaphragm. The positive electrode tab is electrically connected with the positive electrode sheet. The negative electrode tab is electrically connected with the negative electrode sheet. The auxiliary electrode tab is electrically connected with the lithium metal foil. By introducing the lithium metal foil and the auxiliary electrode, the auxiliary electrode is switched to be electrically connected with the positive electrode when repairing is needed. The negative electrode can be repaired by using a suitable electrochemical method to eliminate dendrites, and damage to the positive electrode capacity is avoided, so that the battery life is greatly increased.

Description

TECHNICAL FIELD

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

[0002] Higher energy density and longer cycle life of rechargeable batteries are essential factors to improve the attractiveness of electric vehicles (EVs). Lithium metal has attracted increasing attention and research due to its extremely high mass specific capacity (3860 mAh g-1) and extremely low redox potential (-3.04 V vs SHE).

[0003] However, lithium metal electrodes have a serious dendrite growth problem during charging and discharging, especially when dendrites continuously grow and cause positive and negative short circuits, which not only causes the end of the service life of the battery, but also causes serious safety accidents. In view of the dendrite growth problem, traditional strategies include electrolyte composition optimization, construction of surface protective coating, negative electrode alloying, etc., in addition, the control of charging and discharging parameters such as charging and discharging current has been gradually proved to be able to realize the in-situ elimination of dendrites. For example, when the charging current density is high enough, the lithium metal electrode can self-repair and inhibit the formation of dendrites (Li L, Science, 2018, DOI: 10.1126 / science.aap8787); for example, under the action of electric field, the so-called "dead lithium" is also believed to respond to electrochemical process, and can be reactivated by electrochemical method (Liu F, nature, 2021, DOI: 10.1038 / s41586-021-04168-w).

[0004] However, this method of repairing the lithium metal electrode has great limitations in the application of the conventional two-electrode system. On the one hand, the charging and discharging process with large current or large rate will increase the damage to the structure of the positive active material and accelerate the capacity decline of the battery; on the other hand, the deposition or stripping treatment of the negative electrode under the full charge state or the empty charge state will cause serious overcharge and overdischarge problems. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a lithium metal battery and a repairing method of a negative electrode of a lithium metal battery, which uses a suitable electrochemical method to repair the lithium metal negative electrode and greatly increases the service life of the battery.

[0006] The technical scheme adopted by the present application to solve the above technical problems is:

[0007] A lithium metal battery comprises a positive electrode sheet, a positive electrode tab, a negative electrode sheet, a negative electrode tab, a lithium metal foil, an auxiliary tab and a separator, the positive electrode sheet, the negative electrode sheet and the lithium metal foil being separated by the separator, the positive electrode tab being electrically connected with the positive electrode sheet, the negative electrode tab being electrically connected with the negative electrode sheet, and the auxiliary tab being electrically connected with the lithium metal foil.

[0008] Preferably, the negative electrode sheet is a lithium-copper composite negative electrode sheet.

[0009] Preferably, the thickness of the lithium metal foil is 10-100 μm.

[0010] A method for repairing a lithium metal battery negative electrode, using the lithium metal battery described above, comprises the following steps:

[0011] S1. Perform a charge-discharge operation, calculate the battery capacity retention rate, if the capacity retention rate is greater than a first preset value, perform step S2, if the capacity retention rate is less than or equal to the first preset value, determine that the lithium metal battery has reached its service life;

[0012] S2. Calculate the battery charge-discharge coulombic efficiency, if the charge-discharge coulombic efficiency is less than or equal to a second preset value, determine that the lithium metal battery needs to be repaired, perform step S3, if the charge-discharge coulombic efficiency is greater than the second preset value, the lithium metal battery does not need to be repaired, and return to step S1;

[0013] S3. Change the positive electrode wire connected to the positive electrode tab to the auxiliary tab, so that the positive electrode is in a resting state, and perform step S4 after resting for a predetermined time;

[0014] S4. Discharge at a discharge current of 3C for 1s, then charge at a charge current of 0.01C for 1s, and perform step S5 after 5-300 cycles of such operation;

[0015] S5. Change the positive electrode wire connected to the auxiliary tab to the positive electrode tab, so that the auxiliary electrode is in a resting state, and then perform step S6;

[0016] S6. Perform a charge-discharge operation, calculate the battery charge-discharge coulombic efficiency, if the charge-discharge coulombic efficiency is less than the second preset value, determine that the repair of the lithium metal battery is ineffective, determine that the lithium metal battery has reached its service life, and stop repairing the lithium metal battery; if the charge-discharge coulombic efficiency is greater than or equal to the second preset value and less than or equal to a third preset value, return to S3; if the charge-discharge coulombic efficiency is greater than the third preset value, determine that the repair of the lithium metal battery is effective, and return to step S1.

[0017] Preferably, in step S1, the first preset value is 80%.

[0018] Preferably, in step S2, the second preset value is 88%-95%.

[0019] As preferred, in the step S6, the third preset value is 95%.

[0020] As preferred, in the step S3, the predetermined time is 5min-10min.

[0021] Compared with the prior art, the lithium metal battery and the repairing method of the lithium metal battery negative electrode have the advantages that:

[0022] (1) By introducing the lithium metal foil and the auxiliary electrode, the auxiliary electrode is electrically connected with the positive electrode when repair is needed, not only can the negative electrode be repaired by using appropriate electrochemical method to eliminate dendrites, but also the damage to the positive electrode capacity is avoided, thereby greatly increasing the battery life.

[0023] (2) By repairing the battery with the charge-discharge coulomb efficiency lower than 91%, the charge-discharge coulomb efficiency can be restored to more than 99.0%, avoiding the occurrence of battery short circuit, and significantly increasing the cycle life of the battery.

[0024] (3) The layout design of the three electrodes helps to eliminate the lithium dendrites generated by the stress unevenness, the electric field unevenness and the micro-battery complex reaction of the lithium metal negative electrode geometric edge, and improves the cycle life and safety performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a structural schematic diagram of the lithium metal battery in the application;

[0026] Figure 2 is a flowchart of the lithium metal battery repair in the application;

[0027] Figure 3 is a relationship diagram of the coulomb efficiency and the cycle number of the comparative example 1 in the application;

[0028] Figure 4 is a relationship diagram of the coulomb efficiency and the cycle number of the example in the application.

[0029] In the figure: 1, positive electrode sheet; 2, positive electrode tab; 3, negative electrode sheet; 4, negative electrode tab; 5, lithium metal foil; 6, auxiliary tab; 7, separator. DETAILED DESCRIPTION

[0030] The application will be further described in detail below in combination with the embodiments of the drawings.

[0031] Example 1,

[0032] As Figure 1As shown, a lithium metal battery includes a positive sheet, a positive tab, a negative sheet, a negative tab, a lithium metal foil, an auxiliary tab, and a separator, wherein the positive sheet serves as a positive electrode, the negative sheet serves as a negative electrode, the lithium metal foil serves as an auxiliary electrode, the positive sheet, the negative sheet, and the lithium metal foil are separated by the separator, the positive tab is electrically connected to all the positive sheets, the negative tab is electrically connected to all the negative sheets, and the auxiliary tab is electrically connected to the plurality of lithium metal foils.

[0033] As understood by those skilled in the art, the purpose of introducing the lithium metal foil is to achieve dendrite elimination by electrochemical method while avoiding damage to the positive electrode capacity, so the lithium metal foil can be arranged outside the combination of a plurality of positive sheets, negative sheets separated by a separator and assembled, separated from the positive sheet or the negative sheet by a separator, such as Figure 1 As shown, the lithium metal foil can also be arranged between the positive sheet and the negative sheet, and then separated from the positive sheet and the negative sheet by a separator, respectively.

[0034] In this embodiment, the negative sheet is a lithium-copper composite negative sheet.

[0035] In this embodiment, the thickness of the lithium metal foil is 10-100 μm.

[0036] The above lithium metal battery is prepared by a conventional method, and the nominal capacity is 1 Ah. The formation method is to charge to 4.25 V at a charge current of 0.1 C, and then to discharge to 3.0 V at a discharge current of 0.1 C after 1 h of standing.

[0037] In this embodiment, the thickness of the lithium metal foil is 10-100 μm.

[0038] As shown in Figure 2 A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Embodiment 1, comprising the following steps:

[0039] S1, performing charge and discharge operation, calculating the capacity retention rate of the battery, if the capacity retention rate is greater than a first preset value, performing step S2, if the capacity retention rate is less than or equal to the first preset value, it is determined that the lithium metal battery has reached the service life;

[0040] S2, calculating the charge and discharge coulombic efficiency of the battery, if the charge and discharge coulombic efficiency is less than or equal to a second preset value, it is determined that the lithium metal battery needs to be repaired, and step S3 is performed, if the charge and discharge coulombic efficiency is greater than the second preset value, the lithium metal battery does not need to be repaired, and returns to step S1;

[0041] S3, changing the positive electrode connection wire connected to the positive tab to the auxiliary tab, so that the positive electrode is in a standby state, and performing step S4 after standing for a predetermined time;

[0042] S4, discharging at 3C for 1s, then charging at 0.01C for 1s, and repeating the above process for 5-300 times, and then performing step S5;

[0043] S5, changing the positive electrode connection to the positive electrode tab to the auxiliary electrode tab, so that the auxiliary electrode is in a resting state, and then performing step S6;

[0044] S6, performing a charge-discharge operation, calculating the charge-discharge coulombic efficiency, if the charge-discharge coulombic efficiency is less than the second preset value, determining that the repair of the lithium metal battery is ineffective, determining that the lithium metal battery has reached the service life, and stopping the repair of the lithium metal battery; if the charge-discharge coulombic efficiency is greater than or equal to the second preset value and less than or equal to the third preset value, returning to S3; if the charge-discharge coulombic efficiency is greater than the third preset value, determining that the repair of the lithium metal battery is effective, and returning to step S1.

[0045] Generally, in step S1, the first preset value is 80%; in step S2, the second preset value is 88%-95%, and when the second preset value is relatively low, no matter how to repair, it cannot achieve a relatively good effect. In step S6, the third preset value is 95%, in step S3, the predetermined time is 5-10 min; in step S5, the time for the auxiliary electrode to be in a resting state is also 5-10 min, and then step S6 is performed.

[0046] Example 3,

[0047] A repair method for a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, wherein the thickness of the lithium metal foil is 100 μm, comprising the following steps:

[0048] S1, performing a charge-discharge operation, calculating the capacity retention rate of the battery, if the capacity retention rate is greater than the first preset value 80%, performing step S2, if the capacity retention rate is less than or equal to the first preset value, determining that the lithium metal battery has reached the service life;

[0049] S2, calculating the charge-discharge coulombic efficiency of the battery, if the charge-discharge coulombic efficiency is less than or equal to the second preset value 91%, determining that the lithium metal battery needs to be repaired, and performing step S3, if the charge-discharge coulombic efficiency is greater than the second preset value 91%, the lithium metal battery does not need to be repaired, and returning to step S1;

[0050] S3, changing the positive electrode connection to the positive electrode tab to the auxiliary electrode tab, so that the auxiliary electrode is in a resting state, and then performing step S4;

[0051] S4, discharging at 3C for 1s, then charging at 0.01C for 1s, and repeating the above process for 5 times, and then performing step S5;

[0052] S5, the positive electrode connecting auxiliary electrode is changed to the positive electrode tab, the auxiliary electrode is in the standby state for 8 min, and then step S6 is performed;

[0053] S6, performing a charge and discharge operation, calculating the charge and discharge coulomb efficiency, if the charge and discharge coulomb efficiency is less than a second preset value 93%, determining that the repair of the lithium metal battery is invalid, determining that the lithium metal battery has reached the service life, and stopping the repair of the lithium metal battery; if the charge and discharge coulomb efficiency is greater than or equal to the second preset value 93% and less than or equal to a third preset value 95%, returning to S3; if the charge and discharge coulomb efficiency is greater than the third preset value 95%, determining that the repair of the lithium metal battery is effective, and returning to step S1.

[0054] Example 4,

[0055] A repair method of a lithium metal battery negative electrode, using the lithium metal battery disclosed in Example 1, comprising the following steps: the difference from Example 3 is that step S5 is performed after 10 cycles in step S4.

[0056] Example 5,

[0057] A repair method of a lithium metal battery negative electrode, using the lithium metal battery disclosed in Example 1, comprising the following steps: the difference from Example 3 is that step S5 is performed after 30 cycles in step S4.

[0058] Example 6,

[0059] A repair method of a lithium metal battery negative electrode, using the lithium metal battery disclosed in Example 1, comprising the following steps: the difference from Example 3 is that step S5 is performed after 50 cycles in step S4.

[0060] Example 7,

[0061] A repair method of a lithium metal battery negative electrode, using the lithium metal battery disclosed in Example 1, comprising the following steps: the difference from Example 3 is that step S5 is performed after 100 cycles in step S4.

[0062] Example 8,

[0063] A repair method of a lithium metal battery negative electrode, using the lithium metal battery disclosed in Example 1, comprising the following steps: the difference from Example 3 is that step S5 is performed after 200 cycles in step S4.

[0064] Example 9,

[0065] A repair method of a lithium metal battery negative electrode, using the lithium metal battery disclosed in Example 1, comprising the following steps: the difference from Example 3 is that step S5 is performed after 300 cycles in step S4.

[0066] Example 10,

[0067] A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, comprising the following steps: in step S2, the second preset value is 88%.

[0068] Example 11,

[0069] A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, comprising the following steps: in step S2, the second preset value is 95%.

[0070] Example 12,

[0071] A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, comprising the following steps: in step S3, the shelf time is 5 min.

[0072] Example 13,

[0073] A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, comprising the following steps: in step S3, the shelf time is 10 min.

[0074] Example 14,

[0075] A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, comprising the following steps: in step S5, the auxiliary electrode is also in a shelf state for 5 min, and then step S6 is performed.

[0076] Example 15,

[0077] A method for repairing a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 8, wherein the thickness of the lithium metal foil is 10 μm.

[0078] Comparative Example 1,

[0079] A lithium metal battery, comprising a positive electrode sheet, a positive electrode tab, a negative electrode sheet, a negative electrode tab, and a separator, the positive electrode sheet and the negative electrode sheet being separated by the separator, the positive electrode tab being electrically connected to the positive electrode sheet, and the negative electrode tab being electrically connected to the negative electrode sheet.

[0080] Specifically, the negative electrode of the lithium metal battery is a lithium-copper composite negative electrode sheet, which is prepared by a conventional method, and has a nominal capacity of 1 Ah. The formation method is to charge to 4.25 V at a charging current of 0.1 C, and then discharge to 3.0 V at a discharging current of 0.1 C after a shelf time of 1 h. Then, the lithium metal battery is subjected to charge and discharge tests according to the following Table 1:

[0081]

[0082] Table 1

[0083] When the capacity retention rate is reduced to 80% or the charge-discharge coulombic efficiency is reduced to 90%, the lithium metal battery is considered to reach the service life. According to the test results, a graph of cycle number versus charge-discharge coulombic efficiency is plotted, as shown in Figure 3 The results show that the charge-discharge coulombic efficiency gradually decreases to about 90% after 30 cycles, and then rapidly decreases to 50%, indicating that a micro-short circuit occurs inside the battery.

[0084] Comparative Example 2,

[0085] The same lithium metal battery as in Comparative Example 1 is used, and after formation, the lithium metal battery is subjected to charge-discharge tests according to the steps shown in Table 1. During the charge-discharge process, when the charge-discharge coulombic efficiency reaches 91%, the lithium metal battery is immediately repaired. The repair method is as follows: discharging at a discharge current of 5C for 1s, and then charging at a charge current of 0.01C for 1s, and repeating this cycle 100 times.

[0086] After the repair is completed, the lithium metal battery is subjected to charge-discharge tests according to the steps shown in Table 1. The results show that the first cycle charge-discharge coulombic efficiency of the repaired lithium metal battery is restored to 99.0%, but the capacity retention rate is less than 80%.

[0087] Comparative Example 3,

[0088] The difference from Example 7 is that in step S2, the second preset value is 70%.

[0089] Comparative Example 4,

[0090] A repair method for a lithium metal battery negative electrode, using a lithium metal battery as disclosed in Example 1, comprising the following steps: the difference from Example 1 is that step S5 is performed after one cycle in step S4.

[0091] Tests were performed on Examples 3-15:

[0092] The assembly method of the lithium battery cell of the plurality of parallel samples is consistent with Comparative Example 1, and then the lithium metal foil is assembled with the battery cell, as shown in Figure 1 Each example uses 3 sets of parallel samples for testing.

[0093] The formed battery is subjected to charge-discharge tests according to Table 1, and when the charge-discharge coulombic efficiency is lower than the second preset value, it is determined that the battery needs to be repaired. After the repair charge-discharge cycle reaches the specified number of cycles in the example, the performance test is continued according to the steps shown in Table 1.

[0094] According to the above repair method, the charge-discharge coulombic efficiency and the increased life of the lithium metal battery are shown in Table 2 as follows:

[0095]

[0096]

[0097] Table 2

[0098] A graph showing the relationship between cycle number and charge / discharge coulombic efficiency was plotted for sample data with 5-150 charge / discharge cycles, as shown below. Figure 4 As shown, after 30 charge-discharge cycles, the coulombic efficiency of a lithium metal battery gradually decreases to around 91%. After repair, the coulombic efficiency can recover to around 99%. After a certain number of further charge-discharge cycles, when the coulombic efficiency decreases again, further repair can restore it to around 99%. By repairing batteries with a coulombic efficiency below 91%, the efficiency can be restored to over 99.0%, preventing short circuits and significantly increasing cycle life.

[0099] 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 method for repairing the negative electrode of a lithium metal battery, characterized in that: The lithium metal battery includes a positive electrode, a positive electrode tab, a negative electrode, a negative electrode tab, a lithium metal foil, an auxiliary electrode tab, and a separator. The positive electrode, the negative electrode, and the lithium metal foil are separated by the separator. The positive electrode tab is electrically connected to the positive electrode, the negative electrode tab is electrically connected to the negative electrode, and the auxiliary electrode tab is electrically connected to the lithium metal foil. The repair method includes the following steps: S1. Perform charging and discharging operations, calculate battery capacity retention rate. If the capacity retention rate is greater than the first preset value, proceed to step S2. If the capacity retention rate is less than or equal to the first preset value, determine that the lithium metal battery has reached its service life. S2. Calculate the battery charge-discharge coulombic efficiency. If the charge-discharge coulombic efficiency is less than or equal to the second preset value, it is determined that the lithium metal battery needs to be repaired. Proceed to step S3. If the charge-discharge coulombic efficiency is greater than the second preset value, the lithium metal battery does not need to be repaired, and return to step S1. S3. Change the positive terminal connection to the auxiliary terminal to the positive terminal tab, so that the positive terminal is in a resting state. After resting for a predetermined time, proceed to step S4. S4. Discharge with a 3C discharge current for 1 second, then charge with a 0.01C charging current for 1 second. Repeat this cycle 5 to 300 times before proceeding to step S5. S5. Change the positive terminal connection of the auxiliary electrode to the positive electrode to put the auxiliary electrode in a resting state, and then proceed to step S6. S6. Perform charge and discharge operations, calculate the battery charge and discharge coulombic efficiency. If the charge and discharge coulombic efficiency is less than the second preset value, the lithium metal battery repair is deemed invalid, the lithium metal battery is deemed to have reached its service life, and the repair of the lithium metal battery is stopped. If the charge and discharge coulombic efficiency is greater than or equal to the second preset value and less than or equal to the third preset value, return to S3. If the charge and discharge coulombic efficiency is greater than the third preset value, the lithium metal battery repair is deemed valid, and return to step S1. In step S1, the first preset value is 80%; In step S2, the second preset value is 88% to 95%; In step S6, the third preset value is 95%.

2. The method for repairing the negative electrode of a lithium metal battery according to claim 1, characterized in that: In step S3, the predetermined time is 5 min to 10 min.

3. The method for repairing the negative electrode of a lithium metal battery according to claim 1, characterized in that: The negative electrode is a lithium-copper composite negative electrode.

4. The method for repairing the negative electrode of a lithium metal battery according to claim 1, characterized in that: The thickness of the lithium metal foil is 10–100 μm.

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