Verification method for lithium ion battery charging lithium precipitation current boundary

Abstract

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

Description

Technical Field

[0001] The present invention relates to the field of power batteries, and in particular to a method for verifying a lithium ion battery charging lithium deposition current boundary. Background Art

[0002] With the rapid development of portable devices, electric vehicles, and fixed energy storage, the demand for fast charging technology for lithium-ion batteries is increasing. Battery fast charging strategies are of great significance for improving the convenience of use, but fast charging will have an adverse effect on the life and safety of the battery. Specifically, under low temperature, high state of charge, and high current charging conditions, the enhanced polarization phenomenon inside the battery and the current shock may lead to the precipitation of lithium on the electrode surface. On the one hand, the deposition of lithium will lead to a decrease in the available capacity of the battery and reduce the charge and discharge performance of the battery. Secondly, the deposition of lithium forms metallic lithium, which is easy to react with the electrolyte and other exothermic side reactions, which can easily cause short circuits and overheating inside the battery, thereby increasing the risk of thermal runaway, explosion or fire in the battery. The gas ejected after the battery explosion is also a huge hazard to the environment. In summary, the problems after lithium-ion battery lithium precipitation not only affect the battery performance, but are also directly related to the safety and reliability of the battery. Therefore, it is necessary to accurately calibrate the current boundary of fast-charging lithium precipitation of the battery.

[0003] However, the current verification method of the lithium-ion battery charging lithium deposition current boundary still faces the challenges of inaccurate boundary values ​​and unstable test results in practical applications.

[0004] The document [CN202011236159.5] proposes a method for judging the possibility of lithium plating based on the characteristic charging current of the battery and the threshold voltage at which lithium plating begins to occur.

[0005] The document [CN202310620210.X] proposes a method for determining the lithium deposition state based on the reference voltage-SOC curve of the battery at the operating temperature, the lithium deposition-prone SOC interval and the lithium deposition threshold.

[0006] However, in general, the premise for implementing the above-mentioned lithium deposition inspection method is to know the lithium deposition state of the battery, but the above-mentioned patent cannot realize how to determine the lithium deposition boundary of the battery.

[0007] Regarding the determination of the lithium deposition state of the battery, the inventions disclosed in [CN201910453255.6], [CN202310863514.9], [CN202110438295.0], etc. mainly focus on the use of three-electrode testing methods. However, the limitation of this type of method is that it is heavily dependent on the reliability of the three-electrode tooling. Due to the lack of a universal three-electrode test tooling, when conducting a three-electrode battery lithium deposition boundary test, it is often difficult to obtain experimental results with good repeatability due to the strong internal polarization of the battery.

[0008] At the same time, from the perspective of practical engineering applications, when lithium-ion batteries need to be frequently fast-charged during the actual operation of electric vehicles, lithium plating still occurs from time to time, which is one of the main reasons why electric vehicles are prone to spontaneous combustion at the end of charging or when they are stationary after charging. This also shows that the existing lithium plating detection methods lack effective verification methods. Therefore, it is urgent to propose a more convenient and accurate method for verifying lithium plating of lithium-ion batteries to reduce the occurrence of battery combustion caused by self-heating due to lithium plating.

[0009] Considering the above limitations, it is particularly important to find a more convenient and feasible method to determine when lithium is deposited.

[0010] Therefore, a new solution to the above problems needs to be proposed. Summary of the invention

[0011] The purpose of the present invention is to provide a method for verifying the current boundary of lithium deposition during charging of a lithium-ion battery, that is, in order to quickly determine when lithium deposition occurs in the battery, a test battery is prepared by a relatively mature button battery preparation method, and a test method based on a step-by-step discharge verification is used to more accurately determine the temperature, current rate and state of charge at which lithium deposition occurs during fast charging of the lithium-ion battery, thereby reducing the possibility of lithium deposition occurring in the lithium-ion battery during fast charging, so as to solve the technical problems raised in the background technology.

[0012] To achieve the above object, the present invention provides the following technical solution: a method for verifying the current boundary of lithium deposition during charging of a lithium-ion battery, comprising at least the following steps:

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

[0014] S2: Make a button full battery consisting of a full battery positive electrode, a separator, a negative electrode and an electrolyte, and calibrate its available capacity at different temperatures and rates;

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

[0016] S4: pre-treating the button half-cell, and then using a step discharge test method to obtain the positive electrode potential of the button half-cell at a certain current rate, that is, obtaining the lithium deposition boundary potential of the button half-cell at different rates through testing, and this lithium deposition boundary potential is the negative electrode lithium deposition potential of the full battery;

[0017] S5: Calculate the cumulative discharge capacity of the step discharge and divide it by the available capacity of the whole battery, which is the lithium deposition boundary condition of the battery at the temperature and current rate. Arrange the above steps S1-S4 to obtain the calibration data of the lithium deposition verification method obtained by disassembling and testing the button battery, and the calibration data at least includes the calibration of the SOC corresponding to the lithium deposition potential of the button half-battery.

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

[0019] Furthermore, the discharge of the button half-cell corresponds to the charging of the full cell.

[0020] Furthermore, the step of obtaining the lithium deposition boundary potential of the button half-cell at different rates by testing at least comprises the following steps:

[0021] Since the internal resistance of the assembled button battery is large, it is difficult to make real-time judgments through 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-cell is the potential of the negative electrode of the full battery.

[0022] When the current is withdrawn, 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 considered that the positive electrode voltage has reached the target value, which is the negative electrode lithium deposition boundary voltage of the whole battery.

[0023] When the current is removed, if the difference between the positive electrode potential of the button half-cell and 0V is greater than 0.02V, it means that lithium deposition has not occurred at the positive electrode of the tested button half-cell, and the battery is discharged for a certain period of time using the current of the above rate;

[0024] The above test is repeated until the positive electrode potential of the button half-cell approaches 0V, and it is considered that lithium deposition occurs at the negative electrode of the full battery at this moment.

[0025] Furthermore, the calibration of the SOC corresponding to the lithium deposition potential of the button half-cell comprises at least the following steps:

[0026] Set the temperature of the thermostat to 30 degrees and charge the full battery at a low rate current;

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

[0028] The capacity at this time is the actual capacity of the whole battery. As charging progresses, the capacity of the whole battery gradually increases to obtain the final actual capacity.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention realizes the determination of the SOC when lithium deposition occurs in a lithium-ion battery through a button half-cell, a step-type charging and a combined testing method. The present invention can effectively test the temperature, SOC and current rate boundary of the lithium-ion battery when lithium deposition occurs, that is, after accurately knowing the state in which the battery is prone to lithium deposition, the probability of lithium deposition occurring in the battery can be reduced by adjusting the charging current, and finally reducing the occurrence of battery combustion caused by battery short circuit due to lithium deposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0032] Figure 1 It is a schematic diagram of the process of the present invention;

[0033] Figure 2 This is the positive electrode potential curve of the button half-cell at an ambient temperature of 30 degrees and a 3C charging rate of the present invention;

[0034] Figure 3 This is the positive electrode potential curve of the button half-cell at an ambient temperature of 30 degrees and a charging rate of 5C of the present invention;

[0035] Figure 4 This is a diagram of the actual capacity of the button full battery of the present invention at an ambient temperature of 30 degrees;

[0036] Figure 5 It is the capacity released when lithium deposition occurs at the positive electrode of the button half-cell of the present invention at an ambient temperature of 30 degrees and a charging rate of 3C;

[0037] Figure 6 It is the capacity released when lithium deposition occurs at the positive electrode of the button half-cell of the present invention at an ambient temperature of 30 degrees and a charging rate of 5C. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

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

[0040] See also Figure 1 - Figure 6 A method for verifying the current boundary of lithium deposition during charging of a lithium-ion battery comprises at least the following steps:

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

[0042] Firstly, a button full battery consisting of a full battery positive electrode, a separator, a full battery negative electrode and an electrolyte is made, and its available capacity is calibrated at different temperatures and rates.

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

[0044] Next, the lithium deposition boundary potential of the button half-cell at different rates was obtained through testing. This lithium deposition boundary potential is the negative electrode lithium deposition potential of the full battery. In order to reduce the influence of internal resistance on the battery potential, the entire test process was carried out in a step-by-step discharge.

[0045] The specific test process is as follows: Since the internal resistance of the assembled button battery is large, it is difficult to make real-time judgments through the 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 withdrawn, the positive electrode voltage of the button half-battery rebounds to near 0V, and the difference between the positive electrode voltage and 0V is less than or equal to 0.02V. It is considered that the positive electrode side voltage has reached the target value at this time, which is the negative electrode lithium precipitation boundary voltage corresponding to 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 withdrawn, it means that lithium precipitation has not occurred at the positive electrode of the tested button half-battery, and the above-mentioned rate current is used to continue to discharge the battery for a certain period of time. By repeatedly performing the above test until the positive electrode potential of the button half-battery is close to 0V, it is considered that lithium precipitation occurs at the negative electrode of the full battery at this moment. Figure 2 and Figure 3 The curves showing the change of positive electrode potential with time when the button half-cell was tested at 3C and 5C charging rates at an ambient temperature of 30°C.

[0046] Next, the SOC corresponding to the lithium deposition potential of the above button half-cell is calibrated. First, the capacity of the 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 rate current of 0.1mA (0.03C). When the cut-off voltage is reached, the charging is stopped. The capacity at this time is the actual capacity of the full battery. As the charging progresses, the capacity of the full battery gradually increases, and the final actual capacity is 3.1mAh. Figure 4This is the actual capacity diagram of the whole battery. The battery lithium deposition boundary voltage has been obtained through experiments in the early stage. This voltage is obtained under discharge, so the discharged capacity will be obtained. At this time, the ratio of the discharged capacity to the total capacity of the whole battery is the SOC when lithium deposition occurs. Figure 5 and Figure 6 When the battery is tested at 3C and 5C charging rates at an ambient temperature of 30°C, the capacity released when lithium deposition occurs is 1.447mAh and 0.28mAh respectively. Therefore, in the experiment, when the ambient temperature is 30°C and the full battery is tested at a 3C charging rate, the SOC when lithium deposition occurs is (0.253+0.838+0.356) / 3.1=0.47, i.e. 47%; when lithium deposition occurs at a 30°C 5C charging rate, the SOC of the full battery is 0.28 / 3.1=0.09, i.e. 9%.

[0047] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for verifying the current boundary of lithium deposition during charging of a lithium-ion battery, characterized in that: At least the following steps are included: S1: Disassemble the whole battery to obtain its positive electrode material, negative electrode material, separator material and electrolyte; S2: Make a button full battery consisting of a full battery positive electrode, a separator, a negative electrode and an electrolyte, and calibrate its available capacity at different temperatures and rates; S3: making a button half-cell with the above full battery negative electrode as the positive electrode, lithium metal as the negative electrode, and the separator and electrolyte consistent with the above full battery; S4: pre-treating the button half-cell, and then using a step discharge test method to obtain the positive electrode potential of the button half-cell at a certain current rate, that is, obtaining the lithium deposition boundary potential of the button half-cell at different rates through testing, and this lithium deposition boundary potential is the negative electrode lithium deposition potential of the full battery; S5: Calculate the cumulative discharge capacity of the step discharge and divide it by the available capacity of the whole battery, which is the lithium deposition boundary condition of the battery at the temperature and current rate. Arrange the above steps S1-S4 to obtain the calibration data of the lithium deposition verification method obtained by disassembling and testing the button battery, and the calibration data at least includes the calibration of the SOC corresponding to the lithium deposition potential of the button half-battery.

2. A method for verifying the current boundary of lithium deposition during charging of a lithium ion battery according to claim 1, characterized in that: The negative electrode of the full cell corresponds to the positive electrode in the button half cell.

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

4. A method for verifying the current boundary of lithium deposition during charging of a lithium ion battery according to claim 1, characterized in that: The step of obtaining the lithium plating boundary potential of the button half-cell at different rates by testing at least comprises the following steps: Since the internal resistance of the assembled button battery is large, it is difficult to make real-time judgments through 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-cell is the potential of the negative electrode of the full battery. When the current is withdrawn, 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 considered that the positive electrode voltage has reached the target value, which is the negative electrode lithium deposition boundary voltage of the whole battery. When the current is removed, if the difference between the positive electrode potential of the button half-cell and 0V is greater than 0.02V, it means that lithium deposition has not occurred at the positive electrode of the tested button half-cell, and the battery is discharged for a certain period of time using the current of the above rate; The above test is repeated until the positive electrode potential of the button half-cell approaches 0V, and it is considered that lithium deposition occurs at the negative electrode of the full battery at this moment.

5. A method for verifying the current boundary of lithium deposition during charging of a lithium ion battery according to claim 1, characterized in that: The calibration of the SOC corresponding to the lithium deposition potential of the button half-cell comprises at least the following steps: Set the temperature of the thermostat to 30 degrees and charge the full battery at a low rate current; When the cut-off voltage is reached, charging stops; The capacity at this time is the actual capacity of the whole battery. As charging progresses, the capacity of the whole battery gradually increases to obtain the final actual capacity.

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