Lithium metal battery charging control method capable of prolonging cycle life

Abstract

This invention discloses a charging control method for lithium metal batteries that can improve cycle life, belonging to the field of battery charging technology. Firstly, it uses a charging rate C... c Charging for a certain period of time t c Then, at a discharge rate C d Discharge for a certain time t d This cycle continues until the charging cutoff voltage reaches 4.35V, where the charging rate C... c With discharge rate C d Satisfies: 0.1 ≤ discharge rate C d / Charging rate C c ≤0.5, charging time t c Satisfy: 0 < charging time t c ≤2s, charging time t c With discharge time t d Satisfy: 0 < discharge time t d / charging time t c ≤0.5. This invention discloses a lithium metal battery charging control method that can improve cycle life, eliminate lithium dendrite growth, shorten current charging time, and extend battery cycle life.

Description

Technical Field

[0001] This invention relates to the field of battery charging technology, and in particular to a charging control method for lithium metal batteries that can improve cycle life. Background Technology

[0002] Lithium metal is considered one of the most promising anodes for next-generation high-energy lithium batteries because it has an extremely high theoretical specific capacity (3860 mAh g⁻¹). -1 It also has a lower redox potential (-3.04V vs RHE). Unfortunately, many challenges need to be overcome before lithium metal batteries become a widely adopted technology, the most serious of which is the cycle stability and safety issue caused by uncontrolled lithium dendrite growth.

[0003] During the charging process of lithium metal batteries, Li + Electrons are gained on the negative electrode surface, reducing it to lithium metal. Due to the complex physicochemical properties and non-uniform morphology of the negative electrode surface, the electrodeposition process is difficult to control, and the resulting lithium metal is unevenly distributed. More seriously, this uneven deposition of lithium metal becomes more pronounced with subsequent charge-discharge cycles, gradually forming so-called lithium dendrites. Sharp lithium dendrites on the negative electrode surface can pierce the separator, causing short circuits and safety issues. In addition, the large volume change of the lithium metal negative electrode leads to fluctuations in internal stress and various contact interfaces, resulting in decreased battery stability.

[0004] In addition, researchers have established predictive models for dendrite nucleation and growth through extensive practical and theoretical analysis. They generally agree that higher current density leads to more severe "space charge" phenomena, resulting in more intense lithium dendrite growth. Therefore, achieving rapid and uniform lithium metal deposition is a significant challenge for realizing lithium metal battery applications.

[0005] The inventors discovered by chance that pulse charging can improve the cycle life of lithium metal batteries during the conventional charging process, and the improvement in cycle life is very significant. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a charging control method for lithium metal batteries that can improve cycle life, eliminate the growth of lithium dendrites, shorten the current charging time, and extend the battery cycle life.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A charging control method for lithium metal batteries that can improve cycle life firstly uses a charging rate C c Charging for a certain period of time t c Then, at a discharge rate C d Discharge for a certain time td This cycle continues until the charging cutoff voltage reaches 4.35V, where the charging rate C... c With discharge rate C d Satisfies: 0.1 ≤ discharge rate C d / Charging rate C c ≤0.5.

[0009] Preferably, the charging time t c Satisfy: 0 < charging time t c ≤2s.

[0010] Preferably, the charging time t c With discharge time t d Satisfy: 0 < discharge time t d / charging time t c ≤0.5.

[0011] Preferably, the charging rate C c Determination: By charging and discharging a Li-Li symmetric battery, the relationship curve between the charging rate and cycle life is obtained. Then, the charging rate C of the lithium metal battery is determined based on this curve. c .

[0012] As a preferred option, the optimal value C is obtained by using the relationship curve between the charging rate and cycle life of a Li-Li symmetric battery. Li The charging rate C c Satisfy: C Li -0.2C≤charging rate C c ≤C Li +0.4C.

[0013] Preferably, the charging rate C is [value missing] throughout the entire charging process. c Let C be the charging rate for each charge. c Under the premise of satisfying the above relationship, the order can be increasing, decreasing, or randomly selected.

[0014] Compared with the prior art, the advantages of the lithium metal battery charging control method of the present invention, which can improve cycle life, are as follows:

[0015] 1) By selecting appropriate charging rate, charging time, discharging rate and discharging time, repeated charging and discharging are carried out. During the charging process, appropriate reverse current is used to eliminate the "space charge" phenomenon in time, while gently curing lithium dendrites and avoiding the cumulative growth of lithium dendrites during long-term cycling.

[0016] 2) Compared with conventional constant current and constant voltage charging, the charging time can be shortened and the cycle life can be extended to a certain extent by means of the charging method of the present invention; compared with conventional constant current charging, although the charging time cannot be shortened, the cycle life can be greatly extended.

[0017] 3) The method provided by this invention, which can significantly improve cycle life, can be easily implemented at the cell, module, or battery pack level without affecting the preparation method or process. It is applicable to solid-state or liquid batteries, does not increase costs, and is easy to promote on a large scale. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the charging rate value, charging time value, discharging rate value, and discharging time value in this embodiment.

[0019] Figure 2 This is the curve showing the relationship between the charging rate and cycle life of the Li-Li symmetric battery in this embodiment;

[0020] Figure 3 The curve showing the relationship between capacity retention and cycle life in Comparative Example 2;

[0021] Figure 4 This is the curve showing the relationship between capacity retention and cycle life in Example 2. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Implementation examples

[0024] A charging control method for lithium metal batteries that can improve cycle life, such as... Figure 1 As shown, set the charging rate value (C). c ), charging time value (t) c ), discharge rate value (C) d ), discharge time value (t) d ).

[0025] First, let's consider the charging rate C. c Charging for a certain period of time t c Then, at a discharge rate C d Discharge for a certain time t d This process is repeated until the charging cutoff voltage reaches 4.35V.

[0026] Among them, the charging rate value (C) cThe determination of the charge rate (C) is achieved by charging and discharging Li-Li symmetric batteries and systematically studying the electrochemical performance of a wide range of charging rates and Li dissolution / deposition using multiple sets of data. This yields a curve showing the relationship between charging rate and cycle life. The charging rate value (C) of the lithium metal battery is then determined based on this curve. c ),like Figure 2 As shown, based on the relationship curve between charging rate and cycle life, the optimal value C can be obtained. Li The aforementioned Li-Li symmetric battery is assembled by replacing the positive electrode of the lithium metal battery to be charged in this embodiment with lithium metal foil.

[0027] Charging rate C c Preferred condition: C Li -0.2C≤charging rate C c ≤C Li +0.4C. If the charging rate is too high, lithium dendrite growth in the lithium metal battery will be severe, and the battery life will decrease rapidly; if the charging rate is too low, the charging time will be too long.

[0028] Discharge rate C d Preferably, the discharge rate C is 0.1 ≤ discharge rate C. d / Charging rate C c ≤0.5.

[0029] Charging time t c Ideally, the following condition should be met: 0 < charging time t c ≤2s. The lithium deposition process mainly includes nucleation, 2D growth, and 3D growth. As the charging time increases, 3D growth gradually becomes dominant, and dendrite growth becomes more intense. Therefore, each charging time should not be too long.

[0030] Discharge time t d Ideally, the following condition should be met: 0 < discharge time t d / charging time t c ≤0.5.

[0031] Those skilled in the art should understand that if the charging rate C for each charge... c The discharge rate C for each discharge can be inconsistent, and can be increased, decreased, or randomly selected within a certain range. d Inconsistency is acceptable. That is, the charging rate C... c Let C be the charging rate for each charge. c Under the premise of satisfying the above relationship, the discharge rate C increases, decreases, or is randomly selected within this range, while the discharge rate C... d It still satisfies: 0.1 < discharge rate C d / Charging rate C c ≤0.5 is acceptable.

[0032] Since the lithium deposition process involves nucleation, 2D growth, and 3D growth, 3D growth gradually becomes dominant as charging time increases, and lithium dendrite growth becomes more intense. By selecting appropriate charging rates, charging times, discharging rates, and discharging times and repeatedly charging and discharging, and by using appropriate reverse current during the charging process to promptly cure mild lithium dendrites, the cumulative growth of lithium dendrites during long-term cycling is avoided, thereby extending the cycle life of lithium metal batteries.

[0033] In this invention, Examples 1-11 and Comparative Examples 1-2 use the same battery system, and the capacity of all batteries is in the range of 5.0 Ah to 5.3 Ah. The negative electrode is lithium metal foil, and the positive electrode is NCM523 and a solid electrolyte. The system also includes a separator and a solid electrolyte membrane. Soft-pack batteries are prepared through battery assembly, formation, and other processes. All batteries were tested at 25°C, with voltage tests ranging from 3.0V to 4.35V and discharge rates of 1C. A battery is considered to have reached its service life when its discharge capacity retention rate is below 80.0%.

[0034] In Examples 1-11 of this invention, a Li-Li symmetric battery was first charged and discharged, and the relationship curve between the charging rate and cycle life was obtained, ultimately yielding C. Li =0.6C.

[0035] Example 1

[0036] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.06C for 0.01 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 1.8 hours.

[0037] Example 2

[0038] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.06C for 0.1 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 1.95 hours.

[0039] Example 3

[0040] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.06C for 0.2 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 2.12 hours.

[0041] Example 4

[0042] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.06C for 0.3 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 2.32 hours.

[0043] Example 5

[0044] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.06C for 0.5 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 2.7 hours.

[0045] Example 6

[0046] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.3C for 0.2 seconds, and so on, until the charging cutoff voltage is 4.35V, and the charging time is 2.3 hours.

[0047] Example 7

[0048] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 1 second, then discharges at a discharging rate of 0.18C for 0.2 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 2.2 hours.

[0049] Example 8

[0050] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.6C for 2 seconds, then discharges at a discharging rate of 0.06C for 0.1 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 1.83 hours.

[0051] Example 9

[0052] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 1.0C for 1 second, then discharges at a discharging rate of 0.06C for 0.1 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 1.2 hours.

[0053] Example 10

[0054] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.4C for 1 second, then discharges at a discharging rate of 0.06C for 0.1 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 2.8 hours.

[0055] Example 11

[0056] A lithium metal battery charging control method that can improve cycle life first charges at a charging rate of 0.8C for 1 second, then discharges at a discharging rate of 0.06C for 0.1 seconds, and repeats this cycle until the charging cutoff voltage is 4.35V, with a charging time of 1.4 hours.

[0057] After charging is completed in Examples 1-11 above, the battery reaches its cycle life when the discharge capacity retention rate is below 80%. Specific parameters are shown in the table below. The actual charging rate C in the table is calculated as: (Charging rate * Charging time - Discharge rate * Discharge time) / (Charging time + Discharge time).

[0058] Comparative Example 1

[0059] A charging method for a lithium metal battery involves constant current and constant voltage charging at a charging rate of 0.5C, a charging cutoff rate of 0.01C, a discharging rate of 1.0C, and a charging time of 2.4 hours. The battery reaches its cycle life when the discharge capacity retention rate falls below 80%. Results are as follows... Figure 3 As shown, the capacity retention rate after 75 laps is less than 80%.

[0060] Comparative Example 2

[0061] A charging method for a lithium metal battery involves constant current and constant voltage charging at a charging rate of 0.5C and a discharging rate of 1.0C, with a charging time of 2.4 hours. The battery reaches its cycle life when the discharge capacity retention rate is below 80%.

[0062]

[0063]

[0064] Example 2 test results are as follows Figure 4 As shown, the capacity retention rate after 407 cycles is less than 80%. Its charging time is slightly shorter than that of 0.5C constant current charging (Comparative Example 2), but the cycle life is significantly improved by about 65%. Compared with conventional constant current and constant voltage charging (Comparative Example 1), the charging time is reduced by 16.6% and the cycle life is extended by 35%.

[0065] Comparing Examples 1-5, it can be seen that, under the same charging rate, charging time, and discharging rate, a longer discharging time is more beneficial to improving the cycle life of the battery, but it will increase the charging time to a certain extent.

[0066] Comparing Examples 3, 6, and 7, it can be seen that, under the same charging rate, charging time, and discharging time, a higher discharging rate is more beneficial to improving the cycle life of the battery.

[0067] Comparing Examples 2 and 8, it can be seen that, under the same charging rate, discharging rate, and discharging time, a shorter charging time is more beneficial to improving the cycle life of the battery.

[0068] Comparative Examples 1 and 10-11 show that, under the same charging time, discharging rate, and discharging time, a smaller charging rate is more beneficial to improving the cycle life of the battery.

[0069] 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 charging control method for lithium metal batteries that can improve cycle life, characterized in that: The negative electrode of the lithium metal battery is lithium metal; First, let's consider the charging rate C. c Charging for a certain period of time t c Then, at a discharge rate C d Discharge for a certain time t d This cycle continues until the charging cutoff voltage reaches 4.35V, where the charging rate C... c With discharge rate C d Satisfies: 0.1 ≤ discharge rate C d / Charging rate C c ≤0.5; Charging time t c Satisfy: 0 < charging time t c ≤2s; Charging time t c With discharge time t d Satisfy: 0 < discharge time t d / charging time t c ≤0.5; The charging rate C c Determination: By charging and discharging a Li-Li symmetric battery, the relationship curve between the charging rate and cycle life is obtained. Then, the charging rate C of the lithium metal battery is determined based on this curve. c ; The optimal value C was obtained by using the relationship curve between the charging rate and cycle life of a Li-Li symmetric battery. Li The charging rate C c Satisfy: C Li -0.2C≤charging rate C c ≤C Li +0.4C.

2. The lithium metal battery charging control method for improving cycle life according to claim 1, characterized in that: Throughout the charging process, the charging rate C c Let C be the charging rate for each charge. c In satisfying C Li -0.2C≤charging rate C c ≤C Li Under the premise of +0.4C, it can increase, decrease, or be randomly selected.

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