Testing methods and optimization methods for charging strategies of lithium-ion batteries

Abstract

This disclosure relates to a charging strategy testing method and a charging strategy optimization method for lithium-ion batteries. The testing method includes: acquiring a specified charging requirement of the lithium-ion battery and determining a charging strategy to be tested based on the specified charging requirement; performing a charging test on a target three-electrode cell based on the charging strategy, and obtaining charging test data of the target three-electrode cell by monitoring the negative electrode-reference potential of the target three-electrode cell during the charging test. The target three-electrode cell is a three-electrode cell with the same design as a cell in a lithium-ion battery but with a smaller capacity; determining the test result of the charging strategy based on the charging test data of the target three-electrode cell, and the test result characterizing whether the charging strategy is a qualified charging strategy, so as to determine the qualified charging strategy as the charging strategy used by the lithium-ion battery. This improves the testing efficiency of lithium-ion battery charging strategies and reduces testing costs.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion batteries, and in particular to a method for testing and optimizing charging strategies for lithium-ion batteries. Background Technology

[0002] In recent years, lithium-ion batteries have experienced rapid development. With the application of power batteries in automobiles, people have increasingly higher requirements for battery charging speed and energy density. Therefore, it is necessary to test battery charging strategies during the battery development process to obtain charging strategies that meet the requirements of fast charging.

[0003] Currently, the common practice is to directly fabricate reference electrodes in high-capacity lithium-ion batteries to conduct three-electrode cell testing to obtain lithium-ion battery charging strategies. However, this method is complex to fabricate, costly, and has low testing efficiency. Summary of the Invention

[0004] In view of this, this disclosure proposes a charging strategy testing method and a charging strategy optimization method for lithium-ion batteries, which can improve the testing efficiency of the charging strategy of lithium-ion batteries, improve the determination efficiency of the charging strategy of lithium-ion batteries, and reduce the testing cost without complicated manufacturing processes.

[0005] According to one aspect of this disclosure, a method for testing the charging strategy of a lithium-ion battery is provided, comprising: acquiring a specified charging requirement of the lithium-ion battery, and determining a charging strategy to be tested based on the specified charging requirement, wherein the specified charging requirement characterizes a specified state of charge range and the average charging rate and maximum charging rate under the state of charge range, and the charging strategy characterizes the charging rate used under different states of charge and different battery temperatures; performing a charging test on the target three-electrode cell based on the charging strategy, and obtaining the target three-electrode cell's negative electrode-reference potential by monitoring the negative electrode-reference potential during the charging test. The charging test data of the target three-electrode cell includes the negative electrode-reference potential under different states of charge during the charging test. The target three-electrode cell is a three-electrode cell with the same design as the cell in the lithium-ion battery but with a smaller capacity. The negative electrode-reference potential characterizes the potential of the negative electrode relative to the reference electrode. Based on the charging test data of the target three-electrode cell, the test results of the charging strategy are determined. The test results characterize whether the charging strategy is a qualified charging strategy, so that the qualified charging strategy is determined as the charging strategy used by the lithium-ion battery.

[0006] In one possible implementation, the preparation process of the target three-electrode cell includes: fabricating an initial three-electrode cell with the same design as the cell in the lithium-ion battery but with a smaller capacity than the cell in the lithium-ion battery; cyclically activating the initial three-electrode cell with a preset current; and, after the cyclic activation is completed, plating lithium onto the reference electrode in the initial three-electrode cell to obtain the target three-electrode cell.

[0007] In one possible implementation, the preset current is less than 1C, and the number of cyclic activations is less than or equal to 5.

[0008] In one possible implementation, the step of lithium plating on the reference electrode in the initial three-electrode cell to obtain the target three-electrode cell includes: performing forward lithium plating on the initial three-electrode cell with a preset lithium plating current for a preset lithium plating time, and then statically resting it for a preset resting time to obtain an intermediate three-electrode cell; performing reverse lithium plating on the intermediate three-electrode cell with a preset lithium plating current for a preset lithium plating time, and then statically resting it for a preset resting time to obtain the target three-electrode cell; wherein, the preset lithium plating time includes the time after the positive electrode-reference potential or negative electrode-reference potential has stabilized, and the preset resting time includes the time after the voltage polarization phenomenon in the initial three-electrode cell has disappeared; the positive electrode-reference potential characterizes the potential of the positive electrode relative to the reference electrode.

[0009] In one possible implementation, the preset lithium plating time includes 2 to 12 hours, the preset lithium plating current includes 10 to 500 uA, and the preset resting time includes 2 to 12 hours.

[0010] In one possible implementation, determining the charging strategy to be tested based on the specified charging demand includes: determining multiple states of charge (SOCs) based on the SOC range; determining the charging rate used for each SOC based on the average charging rate and the maximum charging rate; determining the battery temperature corresponding to each SOC based on the maximum charging rate and the charging rate used for each SOC; wherein the multiple SOCs include an initial SOC and a final SOC; the battery temperature includes an initial temperature and a maximum temperature; the maximum temperature is less than or equal to the maximum temperature of the lithium-ion battery when charging at the maximum charging rate; when the SOC at the end of charging at the maximum charging rate is greater than a preset SOC, the initial SOC and... The battery temperature in the charging strategy corresponding to the state of charge at the end of charging at the maximum charging rate increases from the initial temperature to the maximum temperature in stages as the state of charge increases. Furthermore, when the state of charge at the end of charging at the maximum charging rate is greater than the preset state of charge, the battery temperature in the charging strategy corresponding to the state of charge at the end of charging at the maximum charging rate and the final state of charge remains at the maximum temperature; or, when the state of charge at the end of charging at the maximum charging rate is less than or equal to the preset state of charge, the battery temperature in the charging strategy corresponding to the initial state of charge and the final state of charge increases from the initial temperature to the maximum temperature in stages as the state of charge increases; wherein the preset state of charge includes 50% SOC.

[0011] In one possible implementation, determining the test result of the charging strategy based on the charging test data of the target three-electrode battery cell includes: determining the charging strategy as a qualified charging strategy if there is no negative electrode-reference potential lower than a preset safety potential in the charging test data; or, determining the charging strategy as a unqualified charging strategy if there is a negative electrode-reference potential lower than the preset safety potential in the charging test data, and modifying the unqualified charging strategy to re-charge the target three-electrode battery cell using the modified charging strategy until there is no negative electrode-reference potential lower than the preset safety potential in the charging test data of the target three-electrode battery cell, thus obtaining a qualified charging strategy.

[0012] In one possible implementation, the preset safety potential includes 10 to 50 mV.

[0013] In one possible implementation, the cell in the lithium-ion battery is a pouch cell, a cylindrical cell, or a prismatic cell, and the capacity of the cell in the lithium-ion battery is greater than 15Ah; the capacity of the initial three-electrode cell includes 2Ah, 6Ah, or 15Ah.

[0014] According to another aspect of this disclosure, a method for optimizing a charging strategy for a lithium-ion battery is provided, including any of the testing methods described in the present invention. The optimization method further includes: when the charging strategy is a qualified charging strategy, performing a cyclic charge-discharge test on the lithium-ion battery according to the charging strategy to obtain the charge-discharge test results of the lithium-ion battery, the charge-discharge test results including: a cyclic capacity curve and / or a cyclic coulombic efficiency curve; determining whether the charge-discharge capability of the lithium-ion battery meets the specified capability requirement based on the charge-discharge test results, the charge-discharge capability characterizing the capacity decay degree and / or coulombic efficiency decay degree of the lithium-ion battery; when the charge-discharge capability of the lithium-ion battery does not meet the specified capability requirement, optimizing the charging strategy, and re-determining the test results of the optimized charging strategy using any of the testing methods described in the present invention, until the charge-discharge capability of the lithium-ion battery after performing a cyclic charge-discharge test on the lithium-ion battery using the qualified charging strategy obtained by the testing method meets the specified capability requirement.

[0015] In one possible implementation, the optimization method further includes: after performing a cycle charge-discharge test on the lithium-ion battery, fully charging the cells in the lithium-ion battery and then disassembling them to check whether lithium plating occurs at the negative electrode of the cells; if lithium plating occurs at the negative electrode of the cells in the lithium-ion battery, optimizing the charging strategy, and re-determining the test results of the optimized charging strategy using any of the aforementioned test methods, until the qualified charging strategy obtained by any of the aforementioned test methods results in no lithium plating at the negative electrode of the cells in the lithium-ion battery after performing a cycle charge-discharge test on the lithium-ion battery.

[0016] According to various aspects of this disclosure, the charging strategy of a lithium-ion battery is tested by using a target three-electrode cell with the same design as the cell in a lithium-ion battery but with a smaller capacity. Since the small-capacity target three-electrode cell is simple to manufacture and inexpensive, compared with directly manufacturing a reference electrode in a large-capacity lithium-ion battery to test the charging strategy of the lithium-ion battery, the testing efficiency of the charging strategy can be improved. That is, it is beneficial to improve the determination efficiency of the charging strategy of large-capacity lithium-ion batteries and reduce the testing cost without complicated manufacturing processes.

[0017] Other features and aspects of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0018] The accompanying drawings, which are included in and form part of this specification, illustrate exemplary embodiments, features, and aspects of this disclosure together with the specification and serve to explain the principles of this disclosure.

[0019] Figure 1 A flowchart illustrating a method for testing a charging strategy for a lithium-ion battery according to an embodiment of the present disclosure is shown.

[0020] Figure 2 A flowchart illustrating a method for optimizing the charging strategy of a lithium-ion battery according to an embodiment of the present disclosure is shown.

[0021] Figure 3 A flowchart illustrating another method for optimizing the charging strategy of a lithium-ion battery according to an embodiment of the present disclosure is shown.

[0022] Figure 4 A schematic diagram showing the test results of Example 1 in Table 2 according to an embodiment of the present disclosure is illustrated.

[0023] Figure 5 A schematic diagram showing the test results of Example 2 in Table 2 according to an embodiment of the present disclosure is provided.

[0024] Figure 6 A schematic diagram showing the test results of Example 3 in Table 2 according to an embodiment of the present disclosure is provided.

[0025] Figure 7 A schematic diagram showing the test results of Example 4 in Table 2 according to an embodiment of the present disclosure is provided.

[0026] Figure 8 The diagram shows a cyclic curve of charging strategy 1 using a prismatic cell test table 3 according to an embodiment of the present disclosure.

[0027] Figure 9 The image shows a photograph of the electrode disassembly after cyclic charging and discharging of a battery cell according to an embodiment of the present disclosure. Detailed Implementation

[0028] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0029] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0030] In this document, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0031] It should be understood that the terms “comprising” and “including” used in the specification and claims of this disclosure indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0032] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this disclosure can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of this disclosure.

[0033] Figure 1 A flowchart illustrating a testing method for a charging strategy of a lithium-ion battery according to an embodiment of the present disclosure is shown. Figure 1 As shown, the method includes steps S11 to S13.

[0034] In step S11, the specified charging requirements of the lithium-ion battery are obtained, and the charging strategy to be tested is determined based on the specified charging requirements.

[0035] The specified charging requirements include a specified state of charge (SOC) range, as well as the average and maximum charging rates within that range. The charging strategy includes the charging rates used at different SOCs and battery temperatures. The specified charging requirements can be understood as a rough charging strategy based on customer needs, while the charging strategy to be tested can be understood as a detailed charging strategy developed based on those customer needs. For example, Table 1 shows a dataset of one charging strategy.

[0036] Table 1 Datasets for charging strategies

[0037]

[0038]

[0039] Here, SOC0 can represent the initial state of charge, such as 0% SOC, SOC mThis can represent the final state of charge, such as 100% SOC. SOC can range from SOC0 to SOC. m Divide into m equal parts, for example, by dividing into multiple parts in increments of 5% or 10%. rn The reference battery temperature can be divided from low to high within the operating temperature range of the lithium-ion battery. The operating temperature range includes the minimum and maximum allowable temperature limits for the lithium-ion battery. For example, it can be divided in increments of 5°C or 10°C between -5°C and 50°C. Alternatively, it can be divided in increments of 5°C or 10°C between a specified initial temperature (e.g., 25-35°C) and a maximum temperature (e.g., the maximum temperature when the lithium-ion battery is charged at its maximum charging rate). This disclosure does not limit this approach. nm Represents the battery temperature T rn State of charge (SOC) m The charging rate is calculated below, and other values ​​follow the same logic.

[0040] The state of charge (SOC) range includes an initial SOC (e.g., 0–25% SOC) and a final SOC (e.g., 100% SOC). That is, the specified charging requirement can indicate the average and maximum charging rates required to charge from the initial SOC to the final SOC. The initial SOC can be understood as the SOC at the start of charging, and the final SOC as the SOC at the end of charging. It should be understood that customers can set specified charging requirements according to their actual needs, and this disclosure does not limit the specific values ​​of the aforementioned SOC range, average charging rate, and maximum charging rate.

[0041] In practical applications, those skilled in the art can employ known charging strategy formulation methods to determine the charging strategy to be tested based on specified charging requirements, and this disclosure does not impose any limitations on this. Optionally, this disclosure provides a charging strategy formulation method, specifically, determining the charging strategy to be tested based on specified charging requirements includes:

[0042] Based on the range of states of charge, multiple states of charge are determined; and based on the average charging rate and the maximum charging rate, the charging rate used for each state of charge is determined.

[0043] Determine the battery temperature corresponding to each state of charge based on the maximum charging rate and the charging rate used for each state of charge.

[0044] The multiple states of charge include an initial state of charge (SOC) and a final state of charge (SOC). The battery temperature includes an initial temperature and a maximum temperature. The maximum temperature is less than or equal to the maximum temperature of the lithium-ion battery when charged at the maximum charging rate. When the SOC at the end of charging at the maximum charging rate is greater than a preset SOC (i.e., >50% SOC), the battery temperature in the charging strategy corresponding to the initial SOC and the SOC at the end of charging at the maximum charging rate increases from the initial temperature to the maximum temperature in stages as the SOC increases. Alternatively, when the SOC at the end of charging at the maximum charging rate is greater than the preset SOC (i.e., >50% SOC), the battery temperature in the charging strategy corresponding to the SOC at the end of charging at the maximum charging rate and the final state of charge remains at the maximum temperature. It should be understood that the above-mentioned preset state of charge of 50% SOC is one possible implementation provided by the embodiments of this disclosure. In fact, those skilled in the art can customize the specific value of the preset state of charge according to actual needs based on the teachings of the embodiments of this disclosure, and the embodiments of this disclosure do not limit this.

[0045] In this context, determining multiple states of charge (SOCs) based on the range of SOCs can be understood as dividing the initial SOC into multiple SOC stages between the initial SOC and the final SOC. For example, multiple SOC stages can be divided at equal intervals of 5% or 10% SOC. For instance, if the initial SOC is 20% and the final SOC is 100%, then the division can be done at 10% SOCs, resulting in multiple SOCs including 20%, 30%, 40%, 50%, ..., 100%.

[0046] In practical applications, the state of charge corresponding to the maximum charging rate can be preset (for example, the maximum charging rate can be set to correspond to 70% SOC, that is, when charging to 70% SOC, the charging rate can be switched to the maximum charging rate). Then, based on the average charging rate, the maximum charging rate, and the number of divided states of charge, the charging rate can be assigned to each state of charge from the initial state of charge to the state of charge corresponding to the maximum charging rate in an increasing manner, and the charging rate can be assigned to each state of charge from the state of charge corresponding to the maximum charging rate to the final state of charge in a decreasing manner, thereby obtaining the charging rate used for each state of charge.

[0047] It should be understood that the above-described method for determining the charging rate for each state of charge is one possible implementation provided by the embodiments of this disclosure. In fact, those skilled in the art can customize the charging rate allocation method according to actual needs, so as to determine the charging rate used for each state of charge based on the average charging rate and the maximum charging rate according to the customized charging rate allocation method. The embodiments of this disclosure do not limit this.

[0048] In practical applications, those skilled in the art can set the initial temperature and maximum temperature according to actual needs. The initial temperature can be understood as the battery temperature at the start of charging (or the test temperature). The initial temperature can be set to the minimum temperature limit allowed by the lithium-ion battery mentioned above, or it can be any custom temperature. Optionally, the initial temperature can include 25 to 35°C. The maximum temperature can be the maximum temperature limit allowed by the lithium-ion battery mentioned above, or it can be any custom temperature. Optionally, the maximum temperature Tmax can be less than or equal to the maximum temperature of the lithium-ion battery when charging at the maximum charging rate. This maximum temperature can be set based on historical experience, and this disclosure does not limit it.

[0049] The selection of battery temperatures corresponding to each state of charge can follow general rules. Specifically, considering that the temperature rise of lithium-ion battery cells is relatively small during the initial charging process, the initial temperature of a small-capacity target three-electrode cell can be 25–35°C. As the charging rate and SOC increase, the temperature rise of the lithium-ion battery cells will gradually increase, so the battery temperature of the small-capacity target three-electrode cell should also gradually increase. If the state of charge at the end of charging at the maximum charging rate is 'a', then 'a' > 50%. State of Charge (SOC) (e.g., if the maximum charging rate corresponds to 70% SOC, then the state of charge 'a' at the end of charging at the maximum charging rate can be 80% SOC, with a preset state of charge of 50% SOC). Therefore, between the initial state of charge and 'a', the battery temperature of the target three-electrode cell can rise to Tmax in stages. The number of stages can be determined by the initial temperatures T1 and Tmax corresponding to the initial state of charge, and the number of stages x can conform to x = (Tmax - T1) / n (rounded if not an integer, n = 5 or 10). The battery temperature between the initial state of charge (SOC) and state 'a' can be evenly distributed. The battery temperature in each stage increases by n°C relative to the previous stage. The battery temperature from 'a' to 100% SOC can maintain a constant Tmax. This allows the battery temperature in the charging strategy to rise in stages from the initial temperature to the maximum temperature as the SOC increases between the initial SOC and the SOC at the end of charging at the maximum charging rate. Furthermore, the battery temperature remains at the maximum temperature between the SOC at the end of charging at the maximum charging rate and the final SOC. If 'a' ≤ 50% SOC, the battery temperature of the target three-electrode cell can rise in stages to Tmax between the initial SOC and the final SOC. The method for determining the number of stages and the temperature is the same as when 'a' > 50% SOC. This allows the battery temperature in the charging strategy to rise in stages from the initial temperature to the maximum temperature as the SOC increases between the initial and final SOC.

[0050] In step S12, a charging test is performed on the target three-electrode cell based on the charging strategy, and the charging test data of the target three-electrode cell is obtained by monitoring the negative electrode-reference potential of the target three-electrode cell during the charging test. The charging test data includes the negative electrode-reference potential under different states of charge during the charging test. The target three-electrode cell is a three-electrode cell with the same design as the cell in a lithium-ion battery but with a smaller capacity than the cell in a lithium-ion battery.

[0051] In one possible implementation, the fabrication process of the target three-electrode battery cell may include:

[0052] To manufacture an initial three-electrode cell with the same design as a cell in a lithium-ion battery but with a smaller capacity.

[0053] The initial three-electrode cell is cyclically activated with a preset current, and after the cyclic activation is completed, the reference electrode in the initial three-electrode cell is lithium plated to obtain the target three-electrode cell.

[0054] Among them, a three-electrode cell with the same design as a lithium-ion battery cell but a smaller capacity can be understood as having the same structure and materials as a lithium-ion battery cell but a smaller capacity. Furthermore, the initial three-electrode cell also includes a reference electrode compared to a lithium-ion battery cell. It is known that a lithium-ion battery cell includes two electrodes, positive and negative, while a three-electrode cell introduces a reference electrode outside the positive and negative electrodes. The reference electrode can be copper-plated lithium or directly composed of lithium, and is used to monitor the potential changes of the positive or negative electrode during charging and discharging.

[0055] In practical applications, those skilled in the art can use known three-electrode cell manufacturing techniques to produce an initial three-electrode cell with the same design as a lithium-ion battery cell but a smaller capacity. This disclosure does not limit this process. A typical manufacturing method involves: selecting electrode sheets of the same design to produce a small-capacity bare cell for later use; using copper wire as a reference electrode carrier, soaking the copper wire in dilute sulfuric acid, deionized water, and anhydrous ethanol to remove the oxide layer; folding the separator three times to form a separator sleeve 2–5 cm long and 0.5–1 cm wide; welding tabs to one end of the copper wire; placing the un-tapered side of the copper wire in the middle of the separator sleeve and fixing it, with two separator layers on one side and one separator layer on the other; then placing it in the middle layer of the bare cell, with the two separator layers contacting the electrode sheets and the single separator layer contacting the cell separator, ensuring that there are two separator layers between the copper wire and the electrode sheets on both sides; fixing the copper wire with the tabs to the punched aluminum-plastic film; and then performing normal encapsulation and subsequent processes on the cell.

[0056] Optionally, the cells in a lithium-ion battery can be pouch cells, cylindrical cells, or prismatic cells. Considering that the manufacturing processes of cylindrical and prismatic cells are relatively complex, the initial three-electrode cell can be, for example, a small-capacity three-electrode pouch cell. The capacity of the cells in a lithium-ion battery can be greater than 15 ampere-hours (Ah). The capacity of the initial three-electrode cell can be less than or equal to 15 Ah. Optionally, the capacity of the initial three-electrode cell can include 2 Ah, 6 Ah, or 15 Ah.

[0057] It should be understood that those skilled in the art can use known cyclic activation methods to achieve cyclic activation of the initial three-electrode cell with a preset current, and this disclosure does not limit this. The preset current is less than 1C, and the number of cyclic activations is less than or equal to 5. Optionally, the preset current includes 0.2C, 0.33C, or 0.5C; the number of cyclic activations includes 2 or 3 times. By cyclically activating the initial three-electrode cell before lithium plating of the reference electrode, the stability of the initial three-electrode cell can be improved, the internal chemical reaction of the battery can be more complete, and the electrode materials can be better wetted and activated, thereby improving the stability of subsequent lithium plating of the reference electrode.

[0058] In one possible implementation, lithium plating is performed on the reference electrode in the initial three-electrode cell to obtain the target three-electrode cell. This may include: performing forward lithium plating on the initial three-electrode cell with a preset lithium plating current for a preset lithium plating time, and then statically resting it for a preset resting time to obtain an intermediate three-electrode cell; performing reverse lithium plating on the intermediate three-electrode cell with a preset lithium plating current for a preset lithium plating time, and then statically resting it for a preset resting time to obtain the target three-electrode cell.

[0059] The preset lithium plating time includes the time after the positive electrode-reference potential or negative electrode-reference potential has stabilized, and the preset resting time includes the time after the voltage polarization phenomenon in the initial three-electrode cell has disappeared; the positive electrode-reference potential represents the potential of the positive electrode relative to the reference electrode, and the negative electrode-reference potential represents the potential of the negative electrode relative to the reference electrode. Optionally, the preset lithium plating time may include 2 to 12 hours (h), the preset resting time may include 2 to 12 hours, and the preset lithium plating current may include 10 to 500 microamps (uA). Preferably, the preset lithium plating current may specifically include 10 to 50 uA.

[0060] Forward lithium plating can be understood as using the positive electrode as the positive electrode for lithium plating and the reference electrode as the negative electrode for lithium plating, and charging the positive electrode and the reference electrode with a preset lithium plating current for a preset lithium plating time; reverse lithium plating can be understood as using the negative electrode as the positive electrode for lithium plating and the reference electrode as the negative electrode for lithium plating, and charging the negative electrode and the reference electrode with a preset lithium plating current for a preset lithium plating time.

[0061] As we know, in the forward lithium plating process, lithium ion transfer between the positive electrode and the reference electrode involves lithium ions moving from the positive electrode to the reference electrode. During this process, the potential of the positive electrode relative to the reference electrode continuously changes. When the positive electrode-reference potential stabilizes (i.e., no longer changes), it means that the forward lithium plating process is over. Therefore, the preset lithium plating time in the forward lithium plating process can be set to the time after the positive electrode-reference potential stabilizes. Similarly, in the reverse lithium plating process, lithium ion transfer between the negative electrode and the reference electrode involves lithium ions moving from the negative electrode to the reference electrode. During this process, the potential of the negative electrode relative to the reference electrode continuously changes. When the negative electrode-reference potential stabilizes (i.e., no longer changes), it means that the reverse lithium plating process is over. Therefore, the preset lithium plating time in the reverse lithium plating process can be set to the time after the negative electrode-reference potential stabilizes.

[0062] By statically setting a preset resting time after both forward and reverse lithium plating are completed, the internal electrochemical state of the target three-electrode cell obtained after lithium plating is made more stable. In particular, it can ensure that the polarization phenomenon in the target three-electrode cell has disappeared, which is beneficial to the stability of subsequent charge and discharge tests based on the charging rate using the target three-electrode cell.

[0063] In practical applications, monitoring instruments known in the art can be used to monitor the positive electrode-reference potential and the negative electrode-reference potential, in order to complete the aforementioned forward and reverse lithium plating processes. By performing forward and reverse lithium plating on the initial three-electrode cell, more uniform lithium plating on the reference electrode can be achieved, which is beneficial for effectively monitoring the negative electrode-reference potential using the reference electrode during the charging test of the target three-electrode cell.

[0064] As described above, the charging strategy includes the charging rate used at different states of charge (SOCs) and different battery temperatures. In practical applications, conventional testing equipment in the art can be used to perform charging tests on the target three-electrode cell according to the charging strategy determined based on the specified charging requirements. During the charging test, the negative electrode-reference potential of the target three-electrode cell can be monitored using monitoring instruments known in the art, thereby obtaining the negative electrode-reference potential at different SOCs throughout the entire charging test process.

[0065] Optionally, a curve showing the relationship between the negative electrode-reference potential and the state of charge can be plotted based on the negative electrode-reference potential at different SOCs throughout the entire charging test. This curve characterizes the change in the negative electrode-reference potential with the state of charge. In other words, the charging test data can be represented as a curve showing the relationship between the negative electrode-reference potential and the state of charge.

[0066] Considering that the actual temperature of the target three-electrode cell may not reach the battery temperature set in the charging strategy during the charging test, the ambient temperature of the target three-electrode cell can be controlled during the charging test to compensate for the actual temperature of the target three-electrode cell to reach the battery temperature in the charging strategy, thereby meeting the battery temperature requirements during the charging test. The embodiments of this disclosure do not limit the charging test process of the target three-electrode cell, as long as it can meet the charging process of using the corresponding charging rate at different SOC and different battery temperatures in the test charging strategy.

[0067] In practical applications, during the charging test of the target three-electrode cell based on the charging strategy, the above-mentioned monitoring equipment can be used to simultaneously monitor the positive electrode-reference potential and the total potential to obtain the positive electrode-reference potential and the total potential under different states of charge. In turn, the relationship curve between the positive electrode-reference potential and the SOC, as well as the relationship curve between the total potential and the SOC, can be plotted. This disclosure does not limit the scope of the embodiments.

[0068] In step S13, the test results of the charging strategy are determined based on the charging test data of the target three-electrode cell. The test results characterize whether the charging strategy is a qualified charging strategy, so that the qualified charging strategy is determined as the charging strategy used by the lithium-ion battery.

[0069] Considering that the actual charging capacity of a lithium-ion battery cell may not meet the charging strategy, the charging capability of the cell can be determined by monitoring the negative electrode-reference potential of the target three-electrode cell to see if lithium plating occurs at the negative electrode. If not, the charging strategy needs to be modified. Therefore, the risk of lithium plating can be determined by checking if there is a negative electrode-reference potential lower than the preset safety potential in the charging test data of the target three-electrode cell. If there is no risk of lithium plating (i.e., no negative electrode-reference potential lower than the preset safety potential in the charging test data), the charging strategy is considered acceptable. If there is a risk of lithium plating (i.e., no negative electrode-reference potential lower than the preset safety potential in the charging test data), the charging strategy is considered unacceptable. In this case, the unacceptable charging strategy can be modified, and the charging test of the target three-electrode cell can be repeated to obtain new charging test data until the charging strategy is acceptable.

[0070] Therefore, the test results for determining the charging strategy based on the charging test data of the target three-electrode battery cell include: determining the charging strategy as a qualified charging strategy if there is no negative electrode-reference potential lower than the preset safety potential in the charging test data; or, determining the charging strategy as a unqualified charging strategy if there is a negative electrode-reference potential lower than the preset safety potential in the charging test data, and modifying the unqualified charging strategy to retest the target three-electrode battery cell using the modified charging strategy, until there is no negative electrode-reference potential lower than the preset safety potential in the charging test data of the target three-electrode battery cell, thus obtaining a qualified charging strategy. Optionally, the preset safety potential includes 10 to 50 millivolts (mV).

[0071] Modifying unqualified charging strategies can be achieved, for example, by modifying the charging rate at different SOCs and battery temperatures, or by modifying the battery temperature or SOC. This disclosure does not limit the scope of such modifications. It should be understood that those skilled in the art can define custom charging strategy modification strategies to modify unqualified charging strategies. For example, the modification strategy can be determined based on the magnitude and number of negative electrode-reference potentials below a preset safety potential in the charging test data. For instance, if the difference between the negative electrode-reference potentials below the preset safety potential and the preset safety potential is large, and the number of such potentials is significant, the charging rate of the entire charging strategy can be modified. Conversely, if the difference is small and the number of such potentials is limited, only a portion of the charging rate in the charging strategy can be modified. This disclosure does not limit the scope of such modifications.

[0072] According to the testing method of this disclosure, the charging strategy of a lithium-ion battery is tested by using a target three-electrode cell with the same design as the cell in the lithium-ion battery but with a smaller capacity. Since the small-capacity target three-electrode cell is simple to manufacture and inexpensive, compared with directly manufacturing a reference electrode in a large-capacity lithium-ion battery to test the charging strategy of the lithium-ion battery, the testing efficiency of the charging strategy can be improved. That is, it is beneficial to improve the determination efficiency of the charging strategy of large-capacity lithium-ion batteries and reduce the testing cost, without the need for complex manufacturing processes.

[0073] According to the testing method of this disclosure, a simple and cost-effective lithium-ion charging strategy testing method is realized. This method simulates the charging strategies of large-capacity pouch cells, cylindrical cells, and prismatic cells in lithium-ion batteries by using a pouch three-electrode cell with the same formulation design but smaller capacity, and can provide charging strategies for large-capacity pouch cells, cylindrical cells, and prismatic cells.

[0074] In practical applications, after obtaining a qualified charging strategy (i.e., a charging strategy without lithium plating risk), the qualified charging strategy can be used for charging and discharging lithium-ion batteries. However, considering that although the lithium-ion battery cell and the target three-electrode cell have the same design but different capacities, a charging strategy qualified by the target three-electrode cell may still be incompatible with the charging and discharging capabilities of the lithium-ion battery. Therefore, if... Figure 2 As shown in the embodiments of this disclosure, a method for optimizing the charging strategy of a lithium-ion battery is also provided, including... Figure 1 The aforementioned testing method, and the optimization method further include:

[0075] Step S14: If the charging strategy is a qualified charging strategy, perform a cycle charge-discharge test on the lithium-ion battery according to the charging strategy to obtain the charge-discharge test results of the lithium-ion battery. The charge-discharge test results include: cycle capacity curve and / or cycle coulombic efficiency curve.

[0076] Step S15: Based on the charge and discharge test results, determine whether the charge and discharge capacity of the lithium-ion battery meets the specified capacity requirements. The charge and discharge capacity characterizes the capacity decay and / or coulombic efficiency decay of the lithium-ion battery.

[0077] Step S16: When the charging and discharging capacity of the lithium-ion battery does not meet the specified capacity requirements, the charging strategy is optimized, and the following is utilized: Figure 1 The test method was redefined to determine the test results of the optimized charging strategy until the charging and discharging capacity of the lithium-ion battery after cyclic charging and discharging tests according to the qualified charging strategy met the specified capacity requirements.

[0078] In practical applications, conventional charge and discharge testing equipment known in the art can be used to perform cyclic charge and discharge tests on lithium-ion batteries according to the charging strategy. The number of charge and discharge test cycles can be customized, for example, it can be set to the number of cycles to reach the end of the lithium-ion battery's lifespan. This disclosure does not limit this.

[0079] During the cyclic charge-discharge test of a lithium-ion battery, monitoring instruments known in the art can be used to monitor the capacity and coulombic efficiency changes throughout the entire test, thereby obtaining a cycle capacity curve and / or a cycle coulombic efficiency curve. That is, the cycle capacity curve characterizes the capacity change of the lithium-ion battery throughout the entire cyclic charge-discharge test, and the cycle coulombic efficiency curve characterizes the coulombic efficiency change. It can be understood that, based on the cycle capacity curve and the cycle coulombic efficiency curve, the degree of capacity decay and coulombic efficiency decay of the lithium-ion battery after the cyclic charge-discharge test can be obtained, respectively.

[0080] It is known that as the number of charge-discharge tests increases, the capacity and coulombic efficiency of lithium-ion batteries will decrease (i.e., their lifespan will decrease accordingly). An effective lithium-ion battery should meet specified capacity and coulombic efficiency requirements after cyclic charge-discharge tests. These requirements may include a capacity decay threshold and / or a coulombic efficiency decay threshold. Therefore, judging whether the charge-discharge capability of a lithium-ion battery meets the specified capability requirements based on the charge-discharge test results can include: determining whether the capacity decay is less than the capacity decay threshold based on the cyclic capacity curve; and determining whether the coulombic efficiency decay is less than the coulombic efficiency decay threshold based on the cyclic coulombic efficiency curve. If the capacity decay is less than the capacity decay threshold and / or the coulombic efficiency decay is less than the coulombic efficiency decay threshold, then the charge-discharge capability of the lithium-ion battery is considered not to meet the specified capability requirements. If the capacity decay is greater than or equal to the capacity decay threshold and the coulombic efficiency decay is greater than or equal to the coulombic efficiency decay threshold, then the charge-discharge capability of the lithium-ion battery is considered to meet the specified capability requirements.

[0081] Specifically, a lithium-ion battery can be considered to have failed when its capacity decay is less than the capacity decay threshold and / or its coulombic efficiency decay is less than the coulombic efficiency decay threshold. In this case, the charging strategy obtained according to the above test method can be considered unsuitable for the charge-discharge performance of the lithium-ion battery. Therefore, when the charge-discharge capacity of the lithium-ion battery does not meet the specified capacity requirements, the charging strategy can be optimized, and [the following can be done]: Figure 1 The test method shown is used to test the optimized charging strategy and obtain the test results. Specifically, refer to... Figure 1 In steps S12 to S13, the test results of the optimized charging strategy are obtained; and if the test results of the optimized charging strategy indicate that the optimized charging strategy is a qualified charging strategy, the lithium-ion battery is subjected to cycle charge-discharge tests according to steps S14 to S16, until the test results are obtained according to the specified steps. Figure 1 The qualified charging strategy obtained by the test method shown indicates that the charging and discharging capacity of the lithium-ion battery after cyclic charge-discharge testing meets the specified capacity requirements. The charging strategy obtained at this time can be used as the charging strategy for lithium-ion batteries.

[0082] In practical applications, those skilled in the art can set up optimization strategies for charging strategies based on the gap between the charging and discharging capabilities of lithium-ion batteries and the specified capability requirements. The optimization strategy can be used to optimize the charging strategy. For example, the optimization strategy can be set such that the greater the gap, the greater the reduction in the charging rate at different SOCs and battery temperatures in the charging strategy. This disclosure does not limit this aspect.

[0083] Considering that although the qualified charging strategy obtained from the above-mentioned target three-electrode cell test is considered a lithium-free charging strategy, the lithium-ion battery cells and the target three-electrode cell have the same design but different capacities. Therefore, after the lithium-ion battery has undergone cycle charging and discharging, it can be fully charged and disassembled to observe whether lithium has been deposited on the negative electrode of the lithium-ion battery cell, in order to verify the feasibility of the charging strategy. Thus, in one possible implementation, such as Figure 3 As shown, the optimization method may further include:

[0084] Step S17: After performing a cycle charge-discharge test on the lithium-ion battery, the cells in the lithium-ion battery are fully charged and then disassembled to check whether lithium is deposited on the negative electrode of the cells.

[0085] Step S18: In the case of lithium plating at the negative electrode of the lithium-ion battery cell, the charging strategy is optimized, and Figure 1 The testing method was used to redetermine the test results of the optimized charging strategy until the results were obtained using [the new method]. Figure 1 The qualified charging strategy obtained by the aforementioned test method ensures that no lithium is deposited on the negative electrode of the lithium-ion battery cell after cyclic charge-discharge testing.

[0086] The process of fully charging a lithium-ion battery cell and then disassembling it can be understood as fully charging the lithium-ion battery and then disassembling the cell to remove the negative electrode. This allows the system to check whether lithium plating occurs at the negative electrode. If no lithium plating occurs at the negative electrode, it is considered that the charging strategy obtained from the above-mentioned target three-electrode cell test does not result in lithium plating. In this case, the qualified charging strategy can be identified as the charging strategy used by the lithium-ion battery.

[0087] If lithium plating occurs at the negative electrode of a lithium-ion battery cell, then the charging strategy obtained from the above-mentioned target three-electrode cell test is considered unqualified. In this case, the charging strategy can be optimized, and... Figure 1 The test method shown is used to test the optimized charging strategy and obtain the test results. Specifically, refer to... Figure 1 In steps S12 to S13, the test results of the optimized charging strategy are obtained; and if the test results of the optimized charging strategy indicate that the optimized charging strategy is a qualified charging strategy, the lithium-ion battery is subjected to cycle charge-discharge tests according to steps S14 to S16, until it is utilized. Figure 1The qualified charging strategy obtained by the aforementioned test method ensures that lithium does not deposit on the negative electrode of the lithium-ion battery cell after cyclic charge-discharge testing. The charging strategy obtained at this time can be used as the charging strategy for lithium-ion batteries.

[0088] In practical applications, those skilled in the art can set up optimization strategies for charging based on the degree of lithium plating on the negative electrode of the lithium-ion battery cell, and optimize the charging strategy based on the optimization strategy. For example, the optimization strategy can be set to be such that the greater the degree of lithium plating, the greater the reduction in the charging rate at different SOCs and different battery temperatures in the charging strategy. This disclosure does not limit this aspect.

[0089] According to the optimization method of this disclosure, a lithium-ion battery is subjected to cyclic charge-discharge tests according to the charging strategy obtained by the above-described test method. Based on the cycle capacity curve and / or cycle coulombic efficiency curve, the method analyzes whether the lithium-ion battery meets the specified capacity requirements (i.e., whether it has failed). After fully charging the cell, the method disassembles it and observes whether large-area lithium plating occurs on the negative electrode to verify whether the charging strategy obtained by the above-described test method can be applied to the lithium-ion battery. If the lithium-ion battery cannot be applied, the charging strategy obtained by the above-described test method is optimized to obtain a charging strategy that can adapt to the actual charge-discharge capacity of the lithium-ion battery and does not plating lithium. This can improve the determination efficiency of the lithium-ion battery charging strategy, reduce costs, and obtain an effective charging strategy adapted to the lithium-ion battery.

[0090] For example, Table 2 shows four embodiments (i.e., Embodiment 1, Embodiment 2, Embodiment 3, and Embodiment 4) of testing two charging strategies using a three-electrode cell, and Tables 3 and 4 show two charging strategies (i.e., Charging Strategy 1 and Charging Strategy 2). Based on Table 2, performing the three-electrode cell test of the four embodiments can yield... Figures 4 to 7 The test results Figure 4 The test results of Example 1 are shown. Figure 5 The test results of Example 2 are shown. Figure 6 The test results of Example 3 are shown. Figure 7 The test results of Example 4 are shown, where the green line represents the change of negative electrode-reference potential (corresponding to the right axis) with SOC, the orange line represents the change of positive electrode-reference potential (corresponding to the left axis) with SOC, and the blue line represents the change of total potential (corresponding to the left axis) with SOC; by comparison Figure 4 and Figure 5It can be concluded that for the three-electrode cell that has been activated before lithium plating, under charging strategy 1 as shown in Table 3, the lowest potential of the negative electrode relative to the reference electrode (i.e., the lowest potential of the negative electrode relative to the reference electrode) can be increased from -25.5mV@70% SOC to 42.5mV@70% SOC. This demonstrates that low-current activation improves the stability of lithium plating. Furthermore, by comparison... Figure 6 and Figure 7 It can be concluded that for a three-electrode cell that compensates for temperature rise, when tested with charging strategy 2 as shown in Table 4, the lowest negative electrode-reference potential can be increased from -6mV@65% SOC to 31.5mV@65% SOC. This shows that temperature compensation can better simulate the temperature rise of a large-capacity cell during charging.

[0091] Table 2. Three-electrode cell test examples

[0092]

[0093]

[0094] Table 3 Charging Strategy 1

[0095]

[0096] Table 4 Charging Strategy 2

[0097]

[0098] Figure 8 The diagram shows the cycle curves of charging strategy 1 as shown in Table 3, tested using a prismatic battery cell. "Cycle" represents the number of test cycles. The orange line represents the change in coulombic efficiency with the number of test cycles, and the blue line represents the change in capacity retention with the number of test cycles. Capacity retention refers to the ratio of the battery's actual capacity to its initial capacity after a certain number of charge-discharge cycles. Figure 8 As shown, after 500 cycles of testing, the capacity retention rate of the prismatic cells is still greater than 75%, and the coulombic efficiency can still reach 99.85%. Figure 9 The image shows a disassembled photograph of the electrode plate of a prismatic battery cell after cyclic charging and discharging. The electrode plate design of this prismatic battery cell is the same as that of the three-electrode battery cell in Example 2. Figure 9 As shown, no obvious lithium plating occurred on the negative electrode when the negative electrode was fully charged. This indicates that when the lowest potential of the negative electrode-reference electrode of the three-electrode cell in Example 2 is 42.5mV greater than the safe potential of 10mV during the test of charging strategy 1, the square-shell cell with the same electrode design can meet the charging capability of not plating lithium on the negative electrode when using charging strategy 1 for cyclic charging and discharging.

[0099] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method of testing a charging strategy of a lithium-ion battery, characterized in that, include: Obtain the specified charging requirements of the lithium-ion battery, and determine the charging strategy to be tested based on the specified charging requirements. The specified charging requirements represent the specified state of charge range and the average charging rate and maximum charging rate under the state of charge range. The charging strategy represents the charging rate used under different states of charge and different battery temperatures. The target three-electrode cell is charged based on the charging strategy, and the charging test data of the target three-electrode cell is obtained by monitoring the negative electrode-reference potential of the target three-electrode cell during the charging test. The charging test data includes the negative electrode-reference potential under different states of charge during the charging test. The target three-electrode cell is a three-electrode cell with the same design as the cell in the lithium-ion battery but with a smaller capacity. The negative electrode-reference potential characterizes the potential of the negative electrode relative to the reference electrode. Based on the charging test data of the target three-electrode cell, the test results of the charging strategy are determined. The test results characterize whether the charging strategy is a qualified charging strategy, so as to determine the qualified charging strategy as the charging strategy used by the lithium-ion battery.

2. The method of claim 1, wherein, The fabrication process of the target three-electrode battery cell includes: An initial three-electrode cell is manufactured with the same design as the cell in the lithium-ion battery but with a smaller capacity. The initial three-electrode cell is cyclically activated with a preset current, and after the cyclic activation is completed, the reference electrode in the initial three-electrode cell is lithium plated to obtain the target three-electrode cell.

3. The method of claim 2, wherein, The preset current is less than 1C, and the number of cyclic activations is less than or equal to 5.

4. The method of claim 2, wherein, The step of lithium plating on the reference electrode in the initial three-electrode cell to obtain the target three-electrode cell includes: According to the preset lithium plating time, the initial three-electrode cell is forward-plated with lithium using a preset lithium plating current, and then statically left to stand for a preset standing time to obtain the intermediate three-electrode cell. According to the preset lithium plating time, the intermediate three-electrode cell is reverse-plated with lithium using a preset lithium plating current, and then statically left to stand for a preset standing time to obtain the target three-electrode cell. The preset lithium plating time includes the time after the positive electrode-reference potential or negative electrode-reference potential has stabilized, and the preset resting time includes the time after the voltage polarization phenomenon in the initial three-electrode cell has disappeared; the positive electrode-reference potential represents the potential of the positive electrode relative to the reference electrode.

5. The method of claim 4, wherein, The preset lithium plating time includes 2 to 12 hours, the preset lithium plating current includes 10 to 500 uA, and the preset resting time includes 2 to 12 hours.

6. The method of claim 1, wherein, The step of determining the charging strategy to be tested based on the specified charging demand includes: Based on the stated state of charge range, multiple states of charge are determined; and based on the average charging rate and the maximum charging rate, the charging rate used for each state of charge is determined. Based on the maximum charging rate and the charging rate used for each state of charge, determine the battery temperature corresponding to each state of charge. The plurality of states of charge include an initial state of charge and a final state of charge; the battery temperature includes an initial temperature and a maximum temperature; the maximum temperature is less than or equal to the maximum temperature of the lithium-ion battery when charged using the maximum charging rate; when the state of charge at the end of charging using the maximum charging rate is greater than a preset state of charge, the battery temperature in the charging strategy corresponding to the initial state of charge and the state of charge at the end of charging using the maximum charging rate increases from the initial temperature to the maximum temperature in stages as the state of charge increases; and when the state of charge at the end of charging using the maximum charging rate is greater than the preset state of charge, the battery temperature in the charging strategy corresponding to the state of charge at the end of charging using the maximum charging rate and the final state of charge remains at the maximum temperature; or, when the state of charge at the end of charging using the maximum charging rate is less than or equal to the preset state of charge, the battery temperature in the charging strategy corresponding to the initial state of charge and the final state of charge increases from the initial temperature to the maximum temperature in stages as the state of charge increases; wherein the preset state of charge includes 50% SOC.

7. The method of claim 1, wherein, The step of determining the test results of the charging strategy based on the charging test data of the target three-electrode battery cell includes: If no negative electrode-reference potential lower than a preset safety potential is found in the charging test data, the charging strategy is determined to be a qualified charging strategy; or, If the charging test data contains a negative electrode-reference potential lower than the preset safety potential, the charging strategy is determined to be an unqualified charging strategy. The unqualified charging strategy is then modified, and the target three-electrode cell is recharged using the modified charging strategy until the charging test data of the target three-electrode cell no longer contains a negative electrode-reference potential lower than the preset safety potential, thus obtaining a qualified charging strategy.

8. The method of claim 7, wherein, The preset safety potential includes 10 to 50 mV.

9. The method according to any one of claims 1 to 8, characterized in that, The lithium-ion battery cell is a pouch cell, a cylindrical cell, or a prismatic cell, and the capacity of the cell in the lithium-ion battery is greater than 15Ah. The initial three-electrode cell has a capacity of 2Ah, 6Ah, or 15Ah.

10. A method for optimizing a charging strategy of a lithium-ion battery, comprising the test method according to any one of claims 1 to 9, characterized in that, The optimization method further includes: When the charging strategy is a qualified charging strategy, the lithium-ion battery is subjected to a cycle charge-discharge test according to the charging strategy to obtain the charge-discharge test results of the lithium-ion battery. The charge-discharge test results include: cycle capacity curve and / or cycle coulombic efficiency curve. Based on the charge and discharge test results, it is determined whether the charge and discharge capacity of the lithium-ion battery meets the specified capacity requirements. The charge and discharge capacity characterizes the capacity decay and / or coulombic efficiency decay of the lithium-ion battery. If the charging and discharging capacity of the lithium-ion battery does not meet the specified capacity requirements, the charging strategy is optimized, and the test results of the optimized charging strategy are re-determined using the test method described in any one of claims 1 to 9, until the charging and discharging capacity of the lithium-ion battery meets the specified capacity requirements after cyclic charging and discharging tests are conducted using the qualified charging strategy obtained by the test method described in any one of claims 1 to 9.

11. The optimization method of claim 10, wherein, The optimization method further includes: After performing a cycle charge-discharge test on the lithium-ion battery, the cells in the lithium-ion battery were fully charged and then disassembled to check whether lithium was deposited on the negative electrode of the cells. In the event of lithium plating at the negative electrode of the lithium-ion battery cell, the charging strategy is optimized, and the test results of the optimized charging strategy are re-determined using the test method described in any one of claims 1 to 9, until lithium plating does not occur at the negative electrode of the lithium-ion battery cell after the lithium-ion battery is cycle-charged and discharged using the qualified charging strategy obtained by the test method described in any one of claims 1 to 9.

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