Verification method of lithium ion battery charging lithium precipitation current boundary

Abstract

The application discloses a verification method for lithium ion battery charging lithium precipitation current boundary, and relates to the field of power batteries. Through the step-by-step charging and combined test method of the button half battery, the SOC of the lithium ion battery when lithium precipitation occurs is measured, the temperature, the SOC and the current rate boundary when the lithium ion battery occurs lithium precipitation can be effectively tested, that is, after the state of the battery in which lithium precipitation is easy to occur is accurately known, the charging current can be adjusted, the probability of lithium precipitation of the battery is reduced, and finally the battery short circuit caused by lithium precipitation of the battery is reduced, so that the generation of the battery combustion phenomenon is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power batteries, in particular to a verification method for lithium ion battery charging lithium precipitation current boundary. BACKGROUND

[0002] With the rapid development of portable devices, electric vehicles, and stationary energy storage, the demand for lithium ion battery fast charging technology is increasing. Battery fast charging strategy is important for improving the convenience of use, but fast charging can have adverse effects on the life and safety of the battery. Specifically, in the case of low temperature, high state of charge and large current charging, the polarization phenomenon inside the battery is enhanced and the current impact may cause lithium precipitation on the electrode surface. Lithium deposition will not only lead to a decrease in the available capacity of the battery, reducing the charge and discharge performance of the battery. Secondly, the deposition of lithium forms metallic lithium, which is prone to exothermic side reactions with electrolyte, etc., which can easily cause internal short circuit and overheating of the battery, thereby increasing the risk of thermal runaway, explosion or fire of the battery. The gas sprayed out of the battery after explosion also has a great harm to the environment. In summary, the problem of lithium precipitation in lithium ion batteries not only affects the performance of the battery, but also directly relates to the safety and reliability of the battery. Therefore, it is necessary to accurately calibrate the lithium precipitation current boundary of the battery fast charging.

[0003] However, the current verification method for lithium ion battery charging lithium precipitation current boundary still faces the challenges of inaccurate boundary value and unstable test results in practical application.

[0004] File [CN202011236159.5] proposes a method for judging the possibility of lithium precipitation according to the battery characteristic charging current and the threshold voltage at which lithium precipitation begins.

[0005] File [CN202310620210.X] proposes a method for determining the lithium precipitation state according to the reference voltage-SOC curve of the battery at the working temperature, the lithium precipitation prone SOC interval and the lithium precipitation threshold.

[0006] However, in general, the above lithium precipitation test method is implemented on the premise of knowing the lithium precipitation state of the battery, but the above patents cannot determine the lithium precipitation boundary of the battery.

[0007] For the determination of the lithium precipitation state of the battery, the inventions disclosed in [CN201910453255.6], [CN202310863514.9], [CN202110438295.0] etc. mainly focus on the use of three-electrode test method. However, the limitation of this method mainly lies in the serious dependence on the reliability of the three-electrode tooling. Due to the lack of universal three-electrode test tooling, it is often difficult to obtain repeatable experimental results when testing the lithium precipitation boundary of the three-electrode battery due to the strong polarization effect inside the battery.

[0008] At the same time, from the perspective of actual engineering application, when the lithium ion battery needs to be fast charged frequently in the actual operation of the electric vehicle, lithium precipitation still occurs from time to time, which is also one of the main reasons for the spontaneous combustion of the battery at the end of charging or after the electric vehicle is parked. This also shows that the existing lithium precipitation detection method lacks an effective verification method. Therefore, it is urgent to propose a more convenient and accurate lithium precipitation verification method for lithium ion batteries to reduce the spontaneous heating of the battery caused by lithium precipitation and thus the occurrence of battery combustion.

[0009] In view of the limitations of the above aspects, it is particularly important to find a more convenient and feasible method to determine when lithium precipitation occurs.

[0010] Therefore, a new solution to the above problems is needed. SUMMARY

[0011] The purpose of the present application is to provide a verification method for the lithium precipitation current boundary of a lithium ion battery during charging, that is, to quickly determine when lithium precipitation occurs in the battery, a test battery is prepared by a relatively mature button cell preparation method, and the temperature, current rate and state of charge at which lithium precipitation occurs during fast charging of the lithium ion battery are more accurately determined based on a step discharge verification test method, so as to reduce the possibility of lithium precipitation of the lithium ion battery during fast charging, thereby solving the technical problems proposed in the background art.

[0012] To achieve the above purpose, the present application provides the following technical solution: a verification method for the lithium precipitation current boundary of a lithium ion battery during charging, at least comprising the following steps:

[0013] S1: disassemble the full battery to obtain its positive electrode material, negative electrode material, separator material and electrolyte;

[0014] S2: make a button full battery composed of the positive electrode, separator, negative electrode and electrolyte of the full battery, and calibrate the available capacity thereof at different temperatures and rates;

[0015] S3: make a button half battery with the full battery negative electrode as the positive electrode, lithium metal as the negative electrode, the separator and electrolyte consistent with the full battery;

[0016] S4: pretreat the button half battery, and then use a step discharge test method to obtain the positive electrode potential of the button half battery at a certain current rate, that is, to obtain the lithium precipitation boundary potential of the button half battery at different rates by testing, and the lithium precipitation boundary potential is the negative electrode lithium precipitation potential of the full battery;

[0017] S5: Calculate the discharge capacity accumulated by the step ladder, divided by the available capacity of the full battery, that is, the lithium extraction boundary condition of the battery at the temperature and current rate, and the above S1-S4 steps are obtained. The calibration data of the lithium extraction verification method obtained by disassembling the button cell test includes at least the calibration of the SOC corresponding to the lithium extraction potential of the button half cell.

[0018] Further, the negative electrode of the full battery corresponds to the positive electrode in the button half cell.

[0019] Further, the discharge of the button half cell corresponds to the charging of the full battery.

[0020] Further, the lithium extraction boundary potential of the button half cell at different rates obtained by testing at least includes the following steps:

[0021] Because the internal resistance of the assembled button cell is large, it is difficult to judge in real time by potential, so after discharging for a period of time, the current is suddenly removed, and then the potential change of the positive electrode is observed. At this time, the positive electrode potential of the button half cell is the potential of the negative electrode of the full battery;

[0022] When the current is removed, the positive electrode voltage of the button half cell rebounds to about 0V, and the difference between the positive electrode voltage and 0V is less than or equal to 0.02V, then the positive electrode voltage is considered to reach the target value, that is, the negative electrode lithium extraction boundary voltage of the full battery;

[0023] When the current is removed, the difference between the positive electrode potential of the button half cell and 0V is greater than 0.02V, which indicates that the positive electrode of the test button half cell has not occurred lithium extraction, and the above-mentioned current of the rate is used to continue discharging the battery for a certain period of time.

[0024] Through repeated testing, when the positive electrode potential of the button half cell approaches 0V, it is considered that the negative electrode of the full battery has lithium extraction at this moment.

[0025] Further, the calibration of the SOC corresponding to the lithium extraction potential of the button half cell at least includes the following steps:

[0026] Set the temperature of the thermostat to 30 degrees, and charge the full battery with a small current;

[0027] When the cut-off voltage is reached, stop charging;

[0028] At this time, the capacity is the actual capacity of the full battery. As the charging proceeds, the capacity of the full battery gradually increases, and the final actual capacity is obtained.

[0029] Compared with the prior art, the beneficial effects of the present application are:

[0030] The application realizes the determination of SOC when lithium ion battery occurs lithium precipitation by the button half battery and the step charging and joint test method, and can effectively test the temperature, SOC and current rate boundary when lithium ion battery occurs lithium precipitation, that is, after the state of the battery in which lithium precipitation is easy to occur is accurately known, the probability of lithium precipitation of the battery can be reduced by adjusting the charging current, and finally the battery short circuit caused by lithium precipitation of the battery is reduced, so that the battery combustion phenomenon is generated. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed for the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0032] Figure 1 The flowchart of the application;

[0033] Figure 2 The positive electrode potential curve of the button half battery under the condition of ambient temperature 30 degrees and 3C charging rate of the application;

[0034] Figure 3 The positive electrode potential curve of the button half battery under the condition of ambient temperature 30 degrees and 5C charging rate of the application;

[0035] Figure 4 The actual capacity diagram of the button full battery under the condition of ambient temperature 30 degrees of the application;

[0036] Figure 5 The capacity released when the positive electrode of the button half battery occurs lithium precipitation under the condition of ambient temperature 30 degrees and 3C charging rate of the application;

[0037] Figure 6 The capacity released when the positive electrode of the button half battery occurs lithium precipitation under the condition of ambient temperature 30 degrees and 5C charging rate of the application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the application will be described clearly and completely in the following with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some embodiments of the application, not all embodiments.

[0039] This embodiment is aimed at a lithium iron phosphate / graphite system lithium ion battery, and the calibration data of the lithium precipitation verification method is obtained by making button batteries.

[0040] Please refer to Figure 1 - Figure 6 A verification method for lithium ion battery charging lithium precipitation current boundary, at least comprising the following steps:

[0041] The positive electrode material, negative electrode material, separator material and electrolyte of the full battery are obtained by disassembling the full battery.

[0042] First, a button full battery composed of a full battery positive electrode, a separator, a full battery negative electrode and an electrolyte is prepared, and the available capacity of the button full battery is calibrated at different temperatures and rates.

[0043] A button half battery is prepared, wherein the positive electrode of the button half battery is composed of the negative electrode of the full battery, the negative electrode of the button half battery is composed of lithium metal, and the separator and the electrolyte of the button half battery are consistent with those of the full battery. The negative electrode of the full battery corresponds to the positive electrode in the button half battery. That is, according to the battery preparation scheme proposed in the present application, the discharge of the button half battery corresponds to the charging of the full battery.

[0044] Next, the lithium precipitation boundary potential of the button half battery at different rates is obtained by testing, and the lithium precipitation boundary potential is the lithium precipitation potential of the negative electrode of the full battery. In order to reduce the influence of internal resistance on the battery potential, the entire test process is carried out in a stepwise discharge manner.

[0045] The specific test process is as follows: Since the internal resistance of the assembled button battery is large, it is difficult to judge in real time by potential, therefore, after discharging for a period of time, the current is suddenly removed, and then the potential change of the positive electrode is observed. At this time, the positive electrode potential of the button half battery is the potential of the negative electrode of the full battery. When the current is removed, the positive electrode voltage of the button half battery rebounds to about 0V, and the difference between the positive electrode voltage and 0V is less than or equal to 0.02V, then it is considered that the positive electrode voltage reaches the target value, that is, the lithium precipitation boundary voltage of the negative electrode of the full battery. If the difference between the positive electrode potential of the button half battery and 0V is greater than 0.02V after the current is removed, it indicates that the lithium precipitation of the positive electrode of the tested button half battery has not occurred, and the battery is continued to be discharged for a certain period of time using the current of the above-mentioned rate. Through repeated testing, when the positive electrode potential of the button half battery approaches 0V, it is considered that the lithium precipitation of the negative electrode of the full battery occurs at this moment. Figure 2 and Figure 3 are the positive electrode potential-time curves of the button half battery when tested at 3C and 5C charging rates at an ambient temperature of 30°C, respectively.

[0046] Next, the SOC corresponding to the lithium precipitation potential of the above-mentioned button half battery is calibrated. First, the capacity of the prepared button full battery is calibrated. Specifically, the temperature of the thermostat is set to 30 degrees, and the full battery is charged at a small current of 0.1mA (0.03C). When the cut-off voltage is reached, the charging is stopped, and the capacity at this time is the actual capacity of the full battery. As the charging proceeds, the capacity of the full battery gradually increases, and the final actual capacity is 3.1mAh. Figure 4The actual capacity map of the full battery. The lithium precipitation boundary voltage of the battery is obtained through the experiment in the early stage, and the voltage is obtained in the discharge condition, so the discharge capacity is obtained, and the ratio of the discharged capacity to the total capacity of the full battery is the SOC when the lithium precipitation occurs. Figure 5 and Figure 6 The discharged capacity of the battery when the lithium precipitation occurs is 1.447 mAh and 0.28 mAh respectively when the battery is tested at 3C and 5C charging rate at the ambient temperature of 30 DEG C. Therefore, in the experiment, when the full battery is tested at 3C charging rate at the ambient temperature of 30 DEG C, the SOC of the full battery when the lithium precipitation occurs is (0.253+0.838+0.356) / 3.1=0.47, that is, 47%; the SOC of the full battery when the lithium precipitation occurs at 5C charging rate at 30 DEG C is 0.28 / 3.1=0.09, that is, 9%.

[0047] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, but can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and range of equivalency of the claims are embraced therein. Any reference signs in the claims should not be construed as limiting the claims concerned.

Claims

1. A method for verifying the lithium plating current boundary during lithium-ion battery charging, characterized in that: At least the following steps are included: S1: Disassemble the full battery to obtain its positive electrode material, negative electrode material, separator material and electrolyte; S2: Construct a button cell consisting of a positive electrode, separator, negative electrode and electrolyte, and calibrate its usable capacity at different temperatures and rates; The negative electrode of the full cell corresponds to the positive electrode of the button half cell; S3: To manufacture a button half-cell with the negative electrode of a full cell as the positive electrode, lithium metal as the negative electrode, and the same separator and electrolyte as the full cell; S4: Pre-treat the button half-cell, and then use the stepped discharge test method to obtain the positive electrode potential of the button half-cell at a certain current rate. This is to obtain the lithium plating boundary potential of the button half-cell at different rates through testing. This lithium plating boundary potential is the negative electrode lithium plating potential of the full cell. The process of obtaining the lithium plating boundary potential of a button half-cell at different rates through testing includes at least the following steps: After charging for a period of time, the current is removed, and the potential change of the positive electrode is observed. At this time, the potential of the positive electrode of the button half-cell is the potential of the negative electrode of the full cell. When the current is removed, the positive electrode voltage of the button half-cell rebounds to near 0V, and the difference between the positive electrode voltage and 0V is less than or equal to 0.02V. It is then considered that the positive electrode voltage has reached the target value, which corresponds to the negative electrode lithium plating boundary voltage of the full cell. If the difference between the positive electrode potential of the button cell and 0V is greater than 0.02V after the current is removed, it indicates that lithium plating has not yet occurred at the positive electrode of the button cell. In this case, the battery will continue to be discharged for a certain period of time using the current of the above-mentioned rate. By repeatedly performing the above tests until the positive electrode potential of the button cell approaches 0V, it is considered that lithium plating occurs at the negative electrode of the full cell at this point. S5: Calculate the cumulative discharge capacity of the stepped discharge and divide it by the usable capacity of the full cell. This gives the lithium plating boundary conditions of the battery at that temperature and current rate. Organize the steps of S1-S4 above to obtain the calibration data of the lithium plating verification method obtained by disassembling and manufacturing a button cell for testing. The calibration data includes at least the calibration of the SOC corresponding to the lithium plating potential of the button half-cell.

2. The method for verifying the lithium plating current boundary of a lithium-ion battery charging system according to claim 1, characterized in that: The discharge of the button half-cell corresponds to the charging of the full cell.

3. The method for verifying the lithium plating current boundary of a lithium-ion battery charging system according to claim 1, characterized in that: The calibration of the SOC corresponding to the lithium plating potential of a button half-cell includes at least the following steps: Set the temperature of the constant temperature chamber to 30 degrees Celsius and charge the full battery with a low current rate. Charging stops when the cutoff voltage is reached; The capacity at this point is the actual capacity of the full battery. As charging progresses, the capacity of the full battery gradually increases, eventually reaching the final actual capacity.

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