A method for detecting lithium plating of a lithium ion battery during charging

Abstract

The application discloses a kind of lithium ion battery charging lithium precipitation detection method, obtains the charging condition data of power battery system;Charging data is filtered, and the charging data of the charging condition that both includes constant-current charging stage and constant-voltage charging stage is selected;The charging data obtained is split into constant-current charging section and constant-voltage charging section according to charging stage;The voltage of the two stages in step three is obtained, and voltage is differentially processed, respectively the voltage change rate of constant-current charging section and constant-voltage charging section;The voltage change rate of constant-current charging section and constant-voltage charging section obtained in step four is carried out outlier detection, and whether the cell is lithium precipitation is judged according to detection result.The application utilizes whole vehicle charging condition data to carry out lithium precipitation detection, and long time standing condition is not needed after charging, save time, more in line with actual working condition of whole vehicle;Lithium precipitation detection is carried out using charging section data, whether lithium precipitation occurs in this charging, more real-time, help to adjust charging strategy in time.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and in particular relates to a method for detecting lithium plating during lithium-ion battery charging. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in electric vehicles due to their high energy density and long cycle life. However, some adverse reactions occurring inside the battery during cycling can seriously affect its cycle life and safety performance. Among these, lithium plating at the negative electrode is one of the most important factors causing battery aging. Lithium plating at the negative electrode occurs during the charging process, referring to the reduction of lithium ions from the positive electrode to lithium metal on the surface of the negative electrode, which then deposits on the surface. Most of this deposited lithium metal cannot be intercalated between the negative electrode layers, nor can it be reinserted into the positive electrode, thus failing to participate in the normal lithium-ion intercalation / deintercalation reaction, leading to battery capacity decay. Furthermore, as cycling progresses, lithium dendrites continue to grow, eventually piercing the separator and causing a short circuit, resulting in battery safety issues. Therefore, understanding the lithium plating mechanism of lithium-ion batteries and evaluating and detecting lithium plating reactions are crucial measures to ensure the safe and reliable operation of lithium-ion batteries.

[0003] Currently, lithium plating detection methods can be mainly divided into online detection, offline detection, selection methods, and qualitative and quantitative detection methods. Quantitative detection methods all require battery disassembly, which is time-consuming, labor-intensive, and costly; these methods are only suitable for experimental research and are completely unsuitable for actual vehicle conditions. Qualitative analysis, such as the relaxation voltage differential curve method, the discharge differential voltage curve method, and the AC impedance method, analyzes data based on battery performance curves to determine the lithium plating status. The relaxation voltage differential curve method requires a long resting period after fast charging. The discharge differential method requires continuous low-current discharge from the entire vehicle, but continuous low-current conditions are rare in actual driving because discharge conditions vary, making this algorithm difficult to apply. The AC impedance method is currently mainly based on experimental data; it is difficult to obtain relevant parameters based on actual vehicle conditions, and this method has no application in the detection of lithium plating in the entire vehicle.

[0004] The above-mentioned lithium plating detection methods all have shortcomings. When lithium plating occurs in a battery, it is characterized by uneven distribution and extremely low concentration. Lithium plating and re-intercalation can be considered as two electrochemical side reactions on the negative electrode surface, as shown in the attached figure. Figure 9As shown, in Stage I, the negative electrode overpotential remains above 0V. At this stage, only the main reaction occurs on the negative electrode surface: lithium ion insertion into graphite, with no lithium ion deposition. In Stage II, when the negative electrode overpotential is below 0V, a lithium deposition reaction begins on the negative electrode surface. At this stage, the voltage change rate of the lithium-deposited cell is slower compared to the non-lithium-deposited cell. In Stage III, during the constant-voltage charging stage, the negative electrode overpotential gradually rises back above 0V. During this stage, some of the deposited lithium is re-inserted into the negative electrode. At this stage, the voltage change rate of the lithium-deposited cell is faster compared to the non-lithium-deposited cell. In Stage IV, all reversible lithium has dissolved, and no further electrochemical reactions occur on the negative electrode surface. The lithium ions inside the battery gradually reach equilibrium under the influence of diffusion. This scheme analyzes the voltage characteristics by splitting the vehicle charging data into two charging curves: constant-current charging and constant-voltage charging. It fully considers the electrochemical principles of lithium deposition and re-insertion, and then uses an outlier algorithm to detect and obtain the lithium-deposited cell number. The calculation results are reliable. Summary of the Invention

[0005] This invention provides a method for detecting lithium plating during the charging of lithium-ion batteries.

[0006] The technical solution adopted in this invention is:

[0007] A method for detecting lithium plating during lithium-ion battery charging, comprising the following steps:

[0008] Step 1: Obtain charging status data of the power battery system;

[0009] Step 2: Filter the charging data and select charging data that includes both constant current charging and constant voltage charging stages.

[0010] Step 3: Divide the obtained charging data into constant current charging segment and constant voltage charging segment according to the charging stage;

[0011] Step 4: Obtain the cell voltage in the two stages of Step 3, perform differential processing on the voltage, and obtain the voltage change rate of the constant current charging stage and the constant voltage charging stage respectively.

[0012] Step 5: Perform outlier detection on the voltage change rate of the constant current charging section and constant voltage charging section obtained in Step 4, and determine whether the cell has lithium plating based on the detection results.

[0013] The battery is a lithium-ion battery, which includes lithium iron phosphate batteries, ternary lithium batteries, lithium manganese oxide batteries, and lithium cobalt oxide batteries.

[0014] In step one, the charging status data of the power battery system is obtained from the cloud or the local BMS.

[0015] In step four, before the differential processing of the voltage data in the constant current section and the constant voltage section, the data is preprocessed; the preprocessing includes one or more of the following: sorting, mean interpolation, mean interpolation of the same type, modeling prediction, and mean filtering.

[0016] In step four, before the differential processing of voltage data in the constant current and constant voltage sections, the data is resampled according to the data acquisition cycle.

[0017] In step five, the outlier detection method is one or more of the following: Nair test, Laida test, 4D test, quartile test, and 3sigma.

[0018] The advantages of this invention are as follows:

[0019] 1. Lithium plating detection is performed using vehicle charging condition data, eliminating the need for prolonged static conditions after charging, saving time and better reflecting actual vehicle conditions; lithium plating detection is performed using charging segment data, providing real-time monitoring of whether lithium plating occurs during the current charge, which helps to adjust charging strategies in a timely manner and protect the battery cells.

[0020] 2. The vehicle charging data is split into constant current charging data and constant voltage charging data. The voltage change rate of the two segments is calculated using the differential method. The lithium plating and lithium re-intercalation mechanism of the battery cells are fully considered and conform to the electrochemical law. The outlier algorithm is used to perform outlier analysis on the voltage change rate to find abnormal battery cells, which are lithium plating cells. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for detecting lithium plating during charging of a lithium-ion battery, as described in this invention.

[0022] Figure 2 This is a schematic diagram of the constant current charging section and the constant voltage charging section in an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0023] Figure 3 This is a schematic diagram of constant current charging stage data in an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0024] Figure 4 This is a schematic diagram of data during the constant voltage charging stage in an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0025] Figure 5 This is a schematic diagram of the voltage change rate of the constant current charging section in an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0026] Figure 6 This is a schematic diagram of the voltage change rate in the constant voltage charging section of an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0027] Figure 7 This is a schematic diagram of outlier detection results in the constant current charging stage of an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0028] Figure 8 This is a schematic diagram of outlier detection results in the constant voltage charging stage in an embodiment of a lithium-ion battery charging lithium plating detection method of the present invention.

[0029] Figure 9 This is a schematic diagram showing the changes in negative electrode overpotential and lithium plating products during the charging process. Detailed Implementation

[0030] The present invention will be further illustrated by specific embodiments below. These embodiments are preferred implementations of the present invention, but the implementation of the present invention is not limited to these embodiments. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0031] In an embodiment, such as Figure 1 As shown:

[0032] Step 1: Obtain power battery charging condition data, and then filter the charging condition data including the constant current charging stage and the constant voltage charging stage, such as... Figure 2 As shown;

[0033] Step 2: In this embodiment, the voltage threshold for entering the constant voltage charging stage is determined to be 4.142V. The constant current charging stage data is then obtained as follows: Figure 3 And constant voltage charging section data such as Figure 4 ;

[0034] Step 3: Missing values ​​in the data are supplemented using the average of the previous and next time steps; the data sampling period is 30 seconds, and the interval meets the calculation requirements, that is, there are almost no cases where adjacent voltages have equal values, so the voltage sampling interval is not processed.

[0035] Step 4: Perform differential processing on the constant current charging section voltage and the constant voltage charging section voltage to obtain the voltage change rate of each cell within the same time period, such as... Figure 5 and Figure 6 As shown;

[0036] Step 5: Perform outlier detection on all cells in the battery pack using quartiles for the voltage change rate during constant current charging, and perform upper outlier detection on the voltage change rate during constant voltage charging. Substitute the values ​​into the following formula to calculate the differential detection results for each step, such as... Figure 7 and Figure 8 As shown;

[0037] Q1 = (n+1) / 4

[0038] Q2 = 2*(n+1) / 4

[0039] Q3 = 3*(n+1) / 4

[0040] IQR = Q3 – Q1

[0041] Th1 = Q1 – 1.5 * IQR

[0042] Th2 = Q3 + 1.5 * IQR

[0043] Perform a bitwise AND operation on the two calculation results from step five. If the result is not 0, the cell is determined to be a lithium-plated battery cell, and the test is complete.

[0044] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for detecting lithium plating during charging of a lithium-ion battery, the method comprising: The method comprises the following steps: ​ Step 1: obtaining charging condition data of the power battery system; Step 2: screening the charging data to select charging data including both constant current charging phase and constant voltage charging phase in the charging condition; Step 3: splitting the obtained charging data into constant current charging section and constant voltage charging section according to the charging phase; Step 4: obtaining the cell voltage of the two phases in step 3, and performing differential processing on the voltage to obtain the voltage change rate of the constant current charging section and the constant voltage charging section respectively; Step 5: performing outlier detection on the voltage change rate of the constant current charging section and the constant voltage charging section obtained in step 4, and judging whether the cell is lithiumized according to the detection result; The outlier detection method in step 5 is quartile method, which specifically comprises: calculating the quartiles and interquartile range of the voltage change rate of the constant current charging section and the constant voltage charging section, and setting an outlier threshold, the calculation formula of which is: Q1=(n+1) / 4 Q2=2*(n+1) / 4 Q3=3*(n+1) / 4 IQR=Q3–Q1 Th1=Q1–1.5*IQR Th2=Q3+1.5*IQR Wherein, n represents the total number of data points in the data set, Q1 represents the first quartile, Q2 represents the second quartile, Q3 represents the third quartile, IQR represents the interquartile range, Th1 represents the lower outlier threshold, and Th2 represents the upper outlier threshold; performing lower outlier detection on the voltage change rate of the constant current charging section, and performing upper outlier detection on the voltage change rate of the constant voltage charging section; If the detection results of the cell in the constant current charging section and the constant voltage charging section are both outliers, it is determined that the cell is lithiumized.

2. The method of claim 1, wherein the method comprises: The battery is a lithium ion battery, which includes lithium iron phosphate battery, ternary battery, lithium manganate battery and lithium cobaltate battery.

3. The method of claim 1, wherein the method comprises: The charging condition data of the power battery system in step 1 is obtained from the cloud or local BMS. ​ 4. The method of claim 1, wherein the method comprises: Before the differential processing of the constant current section and the constant voltage section voltage data in step 4, the data is preprocessed; the preprocessing is one or more of sorting, mean interpolation, similar mean interpolation, modeling prediction and mean filtering. ​ 5. The method of claim 1, wherein the method comprises: Before the differential processing of the constant current section and the constant voltage section voltage data in step 4, the data is resampled according to the data acquisition period. ​

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