Method for detecting lithium precipitation amount of lithium ion battery

Abstract

The application relates to a method for detecting lithium precipitation amount of a lithium ion battery, which comprises the following steps: taking a negative plate of a to-be-detected battery as a to-be-detected negative plate; placing the to-be-detected negative plate in a first closed container and injecting a solvent containing a hydroxyl group into the first closed container, so that the deposited metallic lithium and SEI in the to-be-detected negative plate react with the solvent to generate hydrogen and other interference gases; after the reaction is completed, the pressure in the first closed container and the volume content of the hydrogen and the other interference gases are measured; taking a negative plate of a control BOL battery as a control negative plate; placing the control negative plate in a second closed container and injecting the solvent containing the hydroxyl group into the second closed container, and after the reaction is completed, the pressure in the second closed container is measured as a control pressure; and S5: according to the pressure in the first closed container, the volume content of the hydrogen and the other interference gases, the control pressure, the volume of the first closed container and the volume of the solvent, the amount of generated hydrogen is determined, and according to the amount of hydrogen, the lithium precipitation amount of the battery is determined. Thus, quantitative detection of the lithium precipitation amount of the battery is realized.

Description

Technical Field

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

[0002] In recent years, lithium-ion batteries have been increasingly widely used in computers, communications, consumer electronics, electric vehicles, and energy storage. However, during the production and use of lithium-ion batteries, lithium metal deposition, known as lithium plating, often occurs on the surface of the negative electrode. Lithium plating is related to factors such as electrode structure, electrolyte wettability, conductivity, and temperature. For example, excessively high charging rates, excessively low charging temperatures, capacity loss due to damage to the negative electrode structure during cycling, uneven distribution of separator pores, and inconsistent spacing between the positive and negative electrode layers can all contribute to lithium plating. Lithium plating on the negative electrode can severely affect the safety, cycle life, low-temperature performance, and fast-charging capability of lithium-ion batteries, and may even lead to serious safety accidents.

[0003] Currently, researchers are conducting direct or indirect experimental studies on lithium metal deposition side reactions from the perspectives of aging characteristics, voltage curves, battery physicochemical properties, and electrode physicochemical properties to achieve lithium plating detection. However, these research methods are mostly limited to determining whether lithium metal deposition has occurred, and can only perform qualitative analysis of lithium plating, but cannot achieve quantitative detection. Although semi-quantitative methods such as inductively coupled plasma optical emission spectroscopy (ICP-OES) have been used, they require expensive equipment and lengthy pretreatment, making rapid on-site detection difficult. This, to some extent, restricts in-depth research on the lithium plating mechanism and effective prevention and control. Summary of the Invention

[0004] In view of this, the present application provides a method for detecting the amount of lithium plating in lithium-ion batteries to solve at least one problem existing in the background art.

[0005] In a first aspect, embodiments of this application provide a method for detecting the amount of lithium plating in a lithium-ion battery, the method comprising the following steps: S1: Disassemble the battery under test that is in an empty state to obtain an electrode assembly, and take the negative electrode of the electrode assembly as the negative electrode to be tested. S2: The negative electrode sheet to be tested is placed in a first sealed container and a solvent containing hydroxyl groups is injected to carry out a first reaction. The metallic lithium deposited in the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate hydrogen gas, and the SEI film on the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate other interfering gases. After the reaction is completed, the pressure in the first sealed container and the volume content of hydrogen gas and other interfering gases are measured. S3: Disassemble the control BOL battery with the same specifications as the battery under test and in an empty state, and take its negative electrode sheet as the control negative electrode sheet. No metallic lithium is deposited in the control negative electrode sheet. S4: Place the control negative electrode in a second sealed container with the same volume as the first sealed container, and inject the same amount of the hydroxyl-containing solvent as in step S2 to carry out the second reaction. After the reaction is completed, measure the pressure inside the second sealed container as the control pressure. S5: Based on the pressure inside the first sealed container, the volume content of hydrogen and the other interfering gases, the control pressure, the volume of the first sealed container, and the volume of the solvent containing hydroxyl groups, determine the amount of hydrogen generated by the reaction between the negative electrode sheet to be tested and the solvent containing hydroxyl groups, and then determine the amount of lithium plating in the lithium-ion battery based on the amount of hydrogen.

[0006] In conjunction with the first aspect of this application, in an optional embodiment, the method further includes: a step of calibrating and testing the first sealed container before step S2, and / or a step of calibrating and testing the second sealed container before step S4; using the first sealed container and / or the second sealed container as the sealed container to be tested, and the solvent containing hydroxyl groups as the detection solvent, the step of calibrating and testing includes: After injecting the test solvent of volume V1 into a sealed container of volume V0, the sealed container is sealed, and the pressure P0 inside the sealed container is measured. A lithium sheet of mass m1 is placed in the sealed container to be tested. After injecting the test solvent of volume V1 into the sealed container to be tested, the sealed container to be tested is sealed and the reaction is carried out to generate hydrogen gas. After the reaction is completed, the pressure P1 inside the sealed container to be tested is measured. Based on V0, V1, P0, and P1, the amount of hydrogen generated by the lithium sheet is determined, and then the theoretical mass m2 of the lithium sheet is calculated based on the amount of hydrogen generated. If the relative difference between m2 and m1 is within a preset deviation, the calibration test is qualified and can be used for testing in steps S2 and / or S4. If the relative difference between m2 and m1 is greater than the preset deviation, the calibration test is unqualified and cannot be used for testing in steps S2 and / or S4. The preset deviation is determined at least based on the measurement accuracy of pressure and volume.

[0007] In conjunction with the first aspect of this application, in an alternative embodiment, The formula for calculating the relative difference Δm between m2 and m1 is: ; And / or, the preset deviation is less than or equal to 10%.

[0008] In conjunction with the first aspect of this application, in an optional embodiment, in step S5, the amount of hydrogen in the negative electrode to be tested is determined according to the ideal gas law; the formula for calculating the amount of hydrogen is: ; Where n is the amount of hydrogen produced, p is the pressure inside the first sealed container, p0 is the control pressure, x1 is the volume content of hydrogen in the first sealed container, x2 is the volume content of other interfering gases in the first sealed container, and V 器 V is the volume of the first sealed container. 液 R is the volume of the solvent containing hydroxyl groups, R is the ideal gas constant, and T is the ambient temperature of the test environment.

[0009] In conjunction with the first aspect of this application, in an optional embodiment, the other interfering gases include CO2, CO, CH4, C2H4, C2H2, C2H6, and C3H8; in step S2, measuring the volume content of the other interfering gases includes: The volume contents of CO2, CO, CH4, C2H4, C2H2, C2H6, C3H8, and O2 in the first sealed container are measured. The volume contents of CO2 in the other interfering gases are determined by the measured volume contents of CO2 and O2, and the calculation formula is as follows: ; in, The volume content of CO2 in the other interfering gases. To determine the volumetric content of CO2, The measured volume content of O2; The volume content of the other interfering gases is the sum of the measured volume contents of CO, CH4, C2H4, C2H2, C2H6, and C3H8, plus... .

[0010] In conjunction with the first aspect of this application, in an optional embodiment, the method further includes: For the electrode assembly of the battery under test, negative electrode sheets located at the head, middle and tail of the electrode assembly are taken along its winding direction and used as the first negative electrode sheet to be tested, the second negative electrode sheet to be tested and the third negative electrode sheet to be tested, respectively. For the electrode assembly of the control BOL battery, negative electrode sheets at the same positions are taken as the first control negative electrode sheet, the second control negative electrode sheet and the third control negative electrode sheet. Steps S2-S5 are performed on the first negative electrode sheet to be tested, the second negative electrode sheet to be tested, the third negative electrode sheet to be tested, the first control negative electrode sheet, the second control negative electrode sheet, and the third control negative electrode sheet respectively, to obtain the amount of lithium plating on each negative electrode sheet to be tested, wherein each negative electrode sheet to be tested and each control negative electrode sheet have the same number of folds, and the number of folds is greater than or equal to 3. The average amount of lithium plating is obtained based on the amount of lithium plating in each negative electrode and the fold number. The amount of lithium plating in the lithium-ion battery is determined based on the average amount of lithium plating and the total number of folds in the lithium-ion battery.

[0011] In conjunction with the first aspect of this application, in an optional embodiment, in step S1, the battery under test is first discharged to obtain the battery under test in an empty state, and in step S3, the control BOL battery is second discharged to obtain the control BOL battery in an empty state, wherein the discharge rate of the first discharge and the second discharge are the same.

[0012] In conjunction with the first aspect of this application, in an optional embodiment, the discharge rate of the first discharge is 0.05C to 0.3C.

[0013] In conjunction with the first aspect of this application, in an alternative embodiment, the first reaction and / or the second reaction are carried out under stirring conditions.

[0014] In conjunction with the first aspect of this application, in an alternative embodiment, the hydroxyl-containing solvent includes at least one of water, ethanol, and isopropanol.

[0015] Compared with the prior art, the embodiments of this application have the following beneficial effects: The lithium-ion battery lithium plating detection method provided in this application first detects the amount of hydrogen gas generated by the reaction of metallic lithium deposited in the negative electrode with a solvent containing hydroxyl groups. Then, the amount of lithium plating in the lithium-ion battery can be determined based on the amount of hydrogen gas, thus quantifying the amount of lithium plating in the lithium-ion battery. Furthermore, considering that the reaction between the SEI (Solid Electrolyte Interface) film on the negative electrode under test and the solvent containing hydroxyl groups will generate other interfering gases, in this embodiment, not only the volume content of hydrogen in the first sealed container is measured, but also the volume content of other interfering gases is measured. This removes the influence of the gases generated by the reaction between the SEI film and the solvent containing hydroxyl groups on the pressure change in the first sealed container (i.e., the difference between the pressure in the first sealed container and the control pressure). Thus, the accurate value of the pressure change in the first sealed container caused by the hydrogen generated by the reaction between the lithium metal deposited in the negative electrode under test and the solvent containing hydroxyl groups can be obtained. Combined with the volume of the first sealed container and the volume of the solvent containing hydroxyl groups, the accurate amount of hydrogen generated by the reaction between the lithium metal deposited in the negative electrode under test and the solvent containing hydroxyl groups can be obtained. Based on the obtained amount of hydrogen, the accurate amount of lithium plating in the lithium-ion battery can be determined. As can be seen from the above, in the embodiments of this application, not only can the amount of lithium plating in lithium-ion batteries be quantitatively detected by detecting the amount of hydrogen generated by the reaction of metallic lithium deposited in the negative electrode sheet with a solvent containing hydroxyl groups, but the accuracy of the detection is also well guaranteed. This has important reference value for in-depth research on the lithium plating mechanism and effective prevention and control.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic flowchart illustrating a method for detecting the amount of lithium plating in a lithium-ion battery, provided in an embodiment of this application; Figure 2 This is a schematic diagram of the electrode assembly obtained by disassembling the control BOL battery in Example 1. Detailed Implementation

[0018] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0019] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0020] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0021] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0022] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0023] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0024] In related technologies, a fully charged battery is disassembled and photographed, and then software is used to analyze the lithium deposition area of ​​the negative electrode to determine the amount of lithium deposition in the battery. However, this method only analyzes the amount of lithium deposition on the surface. Since the metallic lithium deposited in the negative electrode has a thick accumulation, it is difficult to obtain the accurate amount of lithium deposition in the battery.

[0025] Based on this, this application provides a method for detecting the amount of lithium plating in a lithium-ion battery. Please refer to [link / reference]. Figure 1 The method for detecting the amount of lithium plating in a lithium-ion battery provided in this application includes the following steps: S1: Disassemble the battery under test in an empty state to obtain the electrode assembly, and take the negative electrode of the electrode assembly as the negative electrode to be tested. S2: Place the negative electrode sheet to be tested in the first sealed container and inject a solvent containing hydroxyl groups to carry out the first reaction. The lithium metal deposited in the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate hydrogen gas. The SEI film on the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate other interfering gases. After the reaction is completed, measure the pressure in the first sealed container and the volume content of hydrogen gas and other interfering gases. S3: Disassemble the control BOL battery with the same specifications as the battery under test and in an empty state, and take its negative electrode sheet as the control negative electrode sheet. No metallic lithium is deposited in the control negative electrode sheet. S4: Place the control negative electrode in a second sealed container with the same volume as the first sealed container, and inject an equal amount of solvent containing hydroxyl groups as in step S2 to carry out the second reaction. After the reaction is completed, measure the pressure inside the second sealed container as the control pressure. S5: Based on the pressure inside the first sealed container, the volume content of hydrogen and other interfering gases, the control pressure, the volume of the first sealed container, and the volume of the solvent containing hydroxyl groups, determine the amount of hydrogen generated by the reaction between the negative electrode sheet to be tested and the solvent containing hydroxyl groups. Then, based on the amount of hydrogen, determine the amount of lithium plating in the lithium-ion battery.

[0026] In this embodiment, the amount of hydrogen gas generated by the reaction of the deposited metallic lithium in the negative electrode sheet with a solvent containing hydroxyl groups is first detected. Then, the amount of lithium plating in the lithium-ion battery can be determined based on the amount of hydrogen gas, thus quantifying the amount of lithium plating in the lithium-ion battery. Furthermore, considering that the reaction between the SEI (Solid Electrolyte Interface) film on the negative electrode under test and the solvent containing hydroxyl groups will generate other interfering gases, in this embodiment, not only the volume content of hydrogen in the first sealed container is measured, but also the volume content of other interfering gases is measured. This removes the influence of the gases generated by the reaction between the SEI film and the solvent containing hydroxyl groups on the pressure change in the first sealed container (i.e., the difference between the pressure in the first sealed container and the control pressure). Thus, the accurate value of the pressure change in the first sealed container caused by the hydrogen generated by the reaction between the lithium metal deposited in the negative electrode under test and the solvent containing hydroxyl groups can be obtained. Combined with the volume of the first sealed container and the volume of the solvent containing hydroxyl groups, the accurate amount of hydrogen generated by the reaction between the lithium metal deposited in the negative electrode under test and the solvent containing hydroxyl groups can be obtained. Based on the obtained amount of hydrogen, the accurate amount of lithium plating in the lithium-ion battery can be determined. As can be seen from the above, in this embodiment, not only can the amount of lithium plating in lithium-ion batteries be quantitatively detected by detecting the amount of hydrogen gas generated from the reaction of deposited metallic lithium in the negative electrode with a solvent containing hydroxyl groups, but the accuracy of the detection is also well guaranteed. This has important reference value for in-depth research on the lithium plating mechanism and effective prevention and control. At the same time, it eliminates the need for high-cost large-scale analytical instruments, significantly reducing the entry barrier for testing in laboratories and production lines.

[0027] In step S1, the battery under test, which is in an empty state, is disassembled to obtain the electrode assembly. The negative electrode of the electrode assembly is taken as the negative electrode to be tested.

[0028] In some embodiments, the battery under test can be subjected to a first discharge to obtain a battery in a depleted state. In this way, the reversible lithium on the negative electrode of the battery under test can be converted into lithium ions through the first discharge, avoiding the impact of reversible lithium on the accuracy of lithium deposition detection.

[0029] Furthermore, the discharge rate of the first discharge can be between 0.05C and 0.3C, for example, it can be 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, or any value between any two of the above ranges. Controlling the discharge rate of the first discharge within this range ensures that the reversible lithium on the negative electrode of the battery under test is fully converted into lithium ions, thereby better guaranteeing the accuracy of the lithium deposition detection results. In a specific example, the discharge rate of the first discharge is 0.05C.

[0030] In step S2, the negative electrode sheet to be tested is placed in a first sealed container and a solvent containing hydroxyl groups is injected to carry out the first reaction. The metallic lithium deposited in the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate hydrogen gas, and the SEI film on the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate other interfering gases. After the reaction is completed, the pressure in the first sealed container and the volume content of hydrogen gas and other interfering gases are measured.

[0031] In this embodiment, the lithium metal deposited in the negative electrode under test reacts with a solvent containing hydroxyl groups to generate hydrogen gas. The amount of hydrogen gas corresponds to the amount of lithium metal. Therefore, by detecting the amount of hydrogen gas, the amount of lithium metal deposited in the negative electrode under test can be determined. The SEI film on the negative electrode under test refers to the newly formed SEI film on the negative electrode after the battery under test has undergone charge-discharge cycles. Exemplarily, the solvent containing hydroxyl groups includes at least one of water, ethanol, and isopropanol. Specifically, the solvent containing hydroxyl groups is at least one of water, ethanol, and isopropanol. In a specific example, the solvent containing hydroxyl groups is water.

[0032] In some specific embodiments, the first reaction can be carried out under stirring conditions. This allows for a faster, more thorough, and complete reaction between the negative electrode sheet under test and the hydroxyl-containing solvent. Furthermore, hydrogen, being relatively light, can rotate within the first sealed container by stirring the hydroxyl-containing solvent above it. This ensures a more uniform mixing of the hydrogen generated from the deposited lithium metal on the negative electrode sheet, the SEI film, and other interfering gases produced by the reaction with the hydroxyl-containing solvent, along with the existing air in the first sealed container. Consequently, when testing the volume content of hydrogen and other interfering gases in the first sealed container after the reaction, the accuracy of the detection can be improved.

[0033] In practical testing, for example, the magnetic stirrer and the negative electrode to be tested can be placed simultaneously in a first sealed container. After injecting a solvent containing hydroxyl groups into the first sealed container, the container is immediately sealed. Then, the first sealed container is placed on a magnetic stirrer to stir the solvent containing hydroxyl groups. After the reaction is complete (e.g., by judging from the reading of a pressure sensor installed in the first sealed container), stirring is stopped, and the gas in the first sealed container is taken. The composition of the gas is measured using gas chromatography (GC) to obtain the volume content of hydrogen and other interfering gases in the first sealed container.

[0034] In some embodiments, other interfering gases include CO2, CO, CH4, C2H4, C2H2, C2H6, and C3H8; in step S2, measuring the volume content of other interfering gases includes: measuring the volume content of CO2, CO, CH4, C2H4, C2H2, C2H6, C3H8, and O2 in the first sealed container. The volume content of CO2 among the other interfering gases is determined by the measured volume contents of CO2 and O2, and the calculation formula is as follows: ;in, This represents the volumetric content of CO2 in other interfering gases. To determine the volumetric content of CO2, The volume content of O2 is the measured value; the volume content of other interfering gases is the sum of the measured volume contents of CO, CH4, C2H4, C2H2, C2H6, and C3H8, plus... .

[0035] It can be understood that the measured volume contents of CO, CH4, C2H4, C2H2, C2H6, and C3H8 in the first sealed container are equivalent to the volume contents of CO, CH4, C2H4, C2H2, C2H6, and C3H8 in other interfering gases. The measured volume content of CO2 in the first sealed container includes both the volume content of CO2 in other interfering gases and the volume content of CO2 in the original air within the first sealed container. Therefore, in this embodiment, by measuring the volume content of O2 in the first sealed container (which can be considered as the volume content of O2 in the original air within the first sealed container), the volume content of CO2 in the original air within the first sealed container is calculated as follows: The volume content of CO2 in other interfering gases In this way, the influence of the volume content of CO2 in the first sealed container on the measurement results can be eliminated, and the accurate volume content of CO2 in other interfering gases can be obtained, thereby improving the accuracy of the final lithium-ion battery lithium plating detection.

[0036] In some embodiments, prior to step S2, the method for detecting the amount of lithium plating in a lithium-ion battery may further include a step of calibrating and detecting a first sealed container; specifically, the step of calibrating and detecting a first sealed container as the sealed container to be tested and a solvent containing hydroxyl groups as the detection solvent includes: Step 1: After injecting a volume of V1 of test solvent into a sealed container of volume V0, seal the sealed container and measure the pressure P0 inside the sealed container.

[0037] In actual testing, the sealed container to be tested is immediately sealed after the test solvent is injected. The pressure P0 inside the sealed container can be measured by a pressure sensor installed inside the container. The volume V0 of the sealed container can be obtained, for example, by the water filling method. Specifically, the sealed container can be filled with water, and the volume of water in the sealed container can be measured using a graduated measuring instrument (such as a graduated cylinder or measuring cup), which can then be recorded as the volume V0 of the sealed container. Alternatively, the water in the sealed container can be weighed, and the volume of the water can be calculated based on its weight and density, thus obtaining the volume V0 of the sealed container.

[0038] In addition, the sealing performance of the sealed container under test can also be tested in step 1. Specifically, after sealing the sealed container under test and keeping it closed for a certain period of time (e.g., 30 minutes), the pressure P' inside the sealed container under test can be measured. If the difference between P0 and P' is less than or equal to a preset value (e.g., 0.02 kPa), the sealing performance of the sealed container under test can be judged to be qualified, and the subsequent calibration test steps can be carried out; otherwise, the sealing performance of the sealed container under test is judged to be unqualified, and the subsequent calibration test steps will not be carried out.

[0039] Step 2: Place a lithium sheet of mass m1 into the sealed container to be tested. After injecting a test solvent of volume V1 into the sealed container, seal the sealed container and allow it to react to generate hydrogen gas. After the reaction is complete, measure the pressure P1 inside the sealed container.

[0040] It is understandable that the sealed container to be tested should be cleaned and dried before placing the lithium sheet in it. In actual testing, the lithium sheet and the magnetic stirrer can be placed in the sealed container simultaneously. After injecting the test solvent into the sealed container, it should be immediately sealed. Then, the sealed container should be placed on a magnetic stirrer to stir the test solvent. After the reaction is complete, the pressure P1 inside the sealed container is measured using a pressure sensor installed inside the container. Whether the reaction is complete can be determined by the reading of the pressure sensor inside the container. For example, the reaction is considered complete when the pressure sensor reading remains basically unchanged.

[0041] In this embodiment, stirring the detection solvent allows the lithium sheet to react more quickly, fully, and completely. However, this application does not exclude the possibility of not stirring the detection solvent in the sealed container, i.e., reacting the lithium sheet with the detection solvent while it is stationary. In this case, the reaction time can be appropriately extended to ensure a full and complete reaction of the lithium sheet.

[0042] Step 3: Determine the amount of hydrogen generated by the lithium sheet based on V0, V1, P0, and P1. Then, calculate the theoretical mass m2 of the lithium sheet based on the amount of hydrogen generated. If the relative difference between m2 and m1 is within the preset deviation, the calibration test is qualified and can be used for the test in step S2. If the relative difference between m2 and m1 is greater than the preset deviation, the calibration test is unqualified and cannot be used for the test in step S2. The preset deviation is determined at least based on the measurement accuracy of pressure and volume.

[0043] In practical testing, the amount of hydrogen produced by lithium-ion batteries can be determined using the ideal gas law (also known as the Clapeyron equation). The ideal gas law, PV = nRT, describes the relationship between pressure (P), volume (V), amount of substance (n), and temperature (T) of an ideal gas under different states; where P represents the gas pressure in Pascals (Pa); V represents the gas volume in cubic meters (dm³); n represents the amount of substance in moles (mol); R is the ideal gas constant, with a value of 8.314 J / (mol·K); and T represents the gas temperature in Kelvin (K). It can be understood that, in the context of a gas, pressure and pressure intensity can be considered the same concept. Specifically, the formula for calculating the amount of hydrogen produced by lithium-ion batteries can be: Where N is the amount of hydrogen gas produced by the lithium sheet (in mol), and T is the ambient temperature (in K). At room temperature, T can be taken as 298.15 K. Alternatively, the temperature measured by a temperature sensor placed inside the sealed container under test can also be recorded as T.

[0044] According to the reaction equation of lithium metal and the detection solvent (water): 2Li + 2H₂O = H₂ + 2LiOH, the amount of lithium in the sheet is twice the amount of hydrogen gas produced, which is 2N; therefore, the theoretical mass of the lithium sheet is m² = 2N * M. Li , of which M Li M is the molar mass of lithium metal. Li =6.96 g / mol.

[0045] In some embodiments, the formula for calculating the relative difference Δm between m2 and m1 is: .

[0046] In this embodiment, the preset deviation is determined at least based on the measurement accuracy of pressure and volume. Specifically, it is determined based on the measurement accuracy of pressure, temperature, and volume. For example, if the measurement accuracy of pressure is 0.01 kPa, the measurement accuracy of volume is 0.001 L, and the measurement accuracy of temperature is 0.1 °C (0.1 K), the measurement accuracy deviation = If ≈0.1, then the preset deviation can be set to less than or equal to 10%.

[0047] In this embodiment, the first sealed container is calibrated using a lithium metal sheet. This not only tests the sealing performance of the first sealed container but also assesses the error of the detection system, which measures the mass of lithium metal by the amount of hydrogen generated. In other words, the container's sealing performance and measurement error can be comprehensively evaluated. If the calibration test fails, the detection system can be adjusted, such as by replacing it with a sealed container with better sealing performance or using higher precision detection equipment, thereby improving the accuracy and reliability of subsequent tests.

[0048] In step S3, the control BOL battery, which has the same specifications as the battery under test and is in an empty state, is disassembled, and its negative electrode is taken as the control negative electrode. No metallic lithium is deposited in the control negative electrode.

[0049] Here, BOL batteries refer to batteries in the early stages of their lifespan. The negative electrode of this type of battery does not have deposited metallic lithium. Therefore, using the negative electrode of a control BOL battery of the same specifications as the battery under test, which is in a depleted state, as a control negative electrode helps ensure the accuracy of the lithium deposition test of the battery under test.

[0050] In some embodiments, a second discharge can be performed on the control BOL battery to obtain a control BOL battery in a depleted state, with the first and second discharge rates being the same. In this way, the reversible lithium on the negative electrode of the control BOL battery can be converted into lithium ions through the second discharge, avoiding the influence of reversible lithium on the accuracy of lithium deposition detection. Furthermore, the fact that the first and second discharge rates are the same can effectively reduce detection errors, thereby improving the accuracy of lithium deposition detection in the battery under test.

[0051] In step S4, the control negative electrode is placed in a second sealed container with the same volume as the first sealed container, and an equal amount of solvent containing hydroxyl groups is injected as in step S2 to carry out the second reaction. After the reaction is completed, the pressure inside the second sealed container is measured as the control pressure.

[0052] The original SEI film formed during the formation of the control BOL battery in the negative electrode can react with a solvent containing hydroxyl groups. The SEI film in the negative electrode under test is a newly formed SEI film on the negative electrode after charge-discharge cycles, and can be considered as an additional SEI film added on top of the original SEI film formed during formation. Therefore, in this embodiment, the second sealed container has the same volume as the first sealed container, and an equal amount of solvent containing hydroxyl groups is injected into it in step S2. This eliminates the influence of the original SEI film formed during battery formation on the pressure changes within the first sealed container, thereby improving the accuracy of lithium plating detection in the battery under test.

[0053] In some embodiments, the second reaction can be carried out under stirring conditions. This allows for a faster, more complete, and thorough reaction between the control negative electrode and the hydroxyl-containing solvent. In practical testing, for example, the magnetic stirrer and the control negative electrode can be placed simultaneously in a second sealed container. After the hydroxyl-containing solvent is injected into the second sealed container, it is immediately sealed. The second sealed container is then placed on a magnetic stirrer to stir the hydroxyl-containing solvent. After the reaction is complete (e.g., determined by the reading of a pressure sensor installed inside the second sealed container), the gas in the second sealed container can be taken, and the composition of the gas can be measured using gas chromatography to obtain the volume content of each gas.

[0054] In some embodiments, before step S4, the method for detecting the amount of lithium plating in a lithium-ion battery may further include a step of calibrating and testing a second sealed container. Specifically, the second sealed container is used as the sealed container to be tested, and a solvent containing hydroxyl groups is used as the detection solvent. The step of calibrating and testing the second sealed container can be understood with reference to the step of calibrating and testing the first sealed container before step S2 in the above embodiments, and will not be repeated here. By calibrating and testing the second sealed container, both the sealing performance of the second sealed container and the error of the detection system for detecting the mass of metallic lithium by the amount of hydrogen generated can be detected. That is, the sealing performance and measurement error of the container can be comprehensively evaluated. When the calibration and testing fails, the detection system can be adjusted, such as replacing the sealed container with one with better sealing performance or using a higher precision detection device, thereby improving the accuracy and reliability of subsequent tests.

[0055] In step S5, based on the pressure inside the first sealed container, the volume content of hydrogen and other interfering gases, the control pressure, the volume of the first sealed container, and the volume of the solvent containing hydroxyl groups, the amount of hydrogen generated by the reaction between the negative electrode sheet to be tested and the solvent containing hydroxyl groups is determined. Then, based on the amount of hydrogen, the amount of lithium plating in the lithium-ion battery is determined.

[0056] In some embodiments, in step S5, the amount of hydrogen in the negative electrode to be tested is determined according to the ideal gas law; the formula for calculating the amount of hydrogen is: Where n is the amount of hydrogen produced, p is the pressure inside the first sealed container measured in step S2, p0 is the control pressure measured in step S4, x1 is the volume content of hydrogen in the first sealed container measured in step S2, x2 is the volume content of other interfering gases in the first sealed container measured in step S2, and V 器 V is the volume of the first closed container. 液 Let T be the volume of the solvent containing hydroxyl groups, R be the ideal gas constant, and T be the ambient temperature. At room temperature, T can be taken as 298.15 K. Alternatively, the temperature measured by the temperature sensor located inside the first sealed container can also be denoted as T.

[0057] According to the reaction equation of lithium metal and the detection solvent (water): 2Li + 2H₂O = H₂ + 2LiOH, the amount of lithium metal deposited in the negative electrode is twice the amount of hydrogen gas produced, which is 2n. Therefore, the mass of lithium metal deposited in the negative electrode is 2n*M. Li , of which M Li M is the molar mass of lithium metal. Li =6.96 g / mol. Therefore, by detecting the amount of hydrogen gas generated from the reaction of deposited metallic lithium in the negative electrode with a solvent containing hydroxyl groups, the amount of lithium plating in the lithium-ion battery can be determined based on the amount of hydrogen gas, thus quantifying the amount of lithium plating in the lithium-ion battery.

[0058] It should be noted that in the above method for detecting the amount of lithium plating in lithium-ion batteries, the step S1 of taking the negative electrode sheet of the electrode assembly as the negative electrode sheet to be tested can be either taking all the negative electrode sheets in the electrode assembly as the negative electrode sheet to be tested, or taking a representative portion of the negative electrode sheets in the electrode assembly as the negative electrode sheet to be tested.

[0059] In some specific embodiments, the negative electrode sheet of the electrode assembly is selected as the negative electrode sheet to be tested, including: taking negative electrode sheets located at the head, middle, and tail of the electrode assembly along its winding direction, which are respectively used as the first negative electrode sheet to be tested, the second negative electrode sheet to be tested, and the third negative electrode sheet to be tested. Each negative electrode sheet to be tested has the same number of folds, and the number of folds is greater than or equal to 3. Correspondingly, in step S3, a control BOL battery with the same specifications as the battery to be tested and in an empty state is disassembled, and its negative electrode sheet is selected as the control negative electrode sheet, including: for the electrode assembly of the control BOL battery, taking negative electrode sheets at the same positions as the first, second, and third negative electrode sheets to be tested along its winding direction, which are respectively used as the first, second, and third control negative electrode sheets. Each control negative electrode sheet has the same number of folds as each negative electrode sheet to be tested.

[0060] In subsequent testing steps, steps S2-S5 as described in the above embodiment are performed on the first negative electrode sheet to be tested, the second negative electrode sheet to be tested, the third negative electrode sheet to be tested, and the first control negative electrode sheet, the second control negative electrode sheet, and the third control negative electrode sheet to obtain the amount of lithium plating on each negative electrode sheet to be tested. Based on the amount of lithium plating and the number of folds of each negative electrode sheet to be tested, the average amount of lithium plating on a single-fold negative electrode sheet is obtained. Based on the average amount of lithium plating and the total number of folds of the lithium-ion battery, the amount of lithium plating on the lithium-ion battery can be determined.

[0061] Specifically, taking a fold count of 3 for each negative electrode to be tested as an example, according to steps S2-S5, the lithium deposition amounts of the first, second, and third negative electrode to be tested are measured to be m respectively. a1 m a2m a3 Then the average lithium deposition in each folded negative electrode (i.e., a single-folded negative electrode) is m' = (m a1 +m a2 +m a3 ) / 9, therefore, the total amount of lithium deposited in the lithium-ion battery is M=m'*x, where x is the total number of folds in the negative electrode of the lithium-ion battery.

[0062] It is understandable that the deposited lithium metal in the negative electrode sheets at the head, middle, and tail of the electrode assembly may differ, and the thickness of the SEI film on the negative electrode sheet may also differ. Therefore, by taking three negative electrode sheets to be tested and three control negative electrode sheets from the head, middle, and tail of the electrode assembly, respectively, compared to taking a single local negative electrode sheet as the negative electrode sheet to be tested and the control negative electrode sheet, the distribution of lithium plating at different locations in the cell can be evaluated, providing data support for analyzing the non-uniformity of lithium plating and ensuring the accuracy of the final lithium plating amount detection results of the lithium-ion battery. At the same time, compared to taking the entire negative electrode sheet in the electrode assembly as the negative electrode sheet to be tested and the control negative electrode sheet, the detection efficiency can be significantly improved.

[0063] In this embodiment, the detection can be completed through only three practical steps: disassembly and sampling, sealing reaction, and gas detection. The cycle from sampling to obtaining lithium plating data for a single sample can be controlled within 4 to 6 hours. Compared to the 24 to 48-hour processing cycle of ICP-OES, the overall detection efficiency is significantly improved, meeting the high-efficiency detection needs of batch battery sampling, production line quality control, and dynamic monitoring of cycle experiments, thus significantly improving overall efficiency. Furthermore, compared to qualitative detection methods that can only determine whether lithium plating has occurred, this embodiment achieves precise quantification of lithium plating, providing data support for studying the correlation between different influencing factors (such as charging rate, cycle number, and ambient temperature) and lithium plating, which helps in the in-depth analysis of the lithium plating mechanism.

[0064] The following two specific embodiments further illustrate the method for detecting the amount of lithium plating in lithium-ion batteries in this application.

[0065] Example 1

[0066] In this embodiment, the method for detecting the amount of lithium plating in a lithium-ion battery includes the following steps (steps S101-S104 are all performed in a constant temperature environment of 25±0.5℃, and the measurement accuracy of the pressure sensor in the sealed container is 0.01kPa): Step S101: 200 ml of water (a solvent containing hydroxyl groups) is injected into a sealed container equipped with a pressure sensor. After the water injection is complete, the sealed container is immediately sealed. The volume V0 of the sealed container is 860 ml. After injecting 200 ml of water, the internal pressure P0 is 30.51 kPa. Here, internal pressure refers to the pressure exceeding standard atmospheric pressure, which is 101.3 kPa. Therefore, the absolute pressure at this point is 131.8 kPa.

[0067] Step S102: After cleaning and drying the sealed container to be tested, place a lithium sheet with a mass m1 of 0.0447 g in the sealed container (containing air), insert a magnetic stir bar, and pour in water with a volume V1 of 200 ml. Place the sealed container on a magnetic stirrer to stir the water in the container. After the reaction is complete, the gas pressure P1 inside the sealed container is 42.87 kPa. The amount of hydrogen gas generated by the lithium sheet... =0.00329 mol, the theoretical mass of lithium sheet m2=2N*M Li =0.0458g, the relative difference between m2 and m1 =2.4%. Less than 10% indicates the calibration test is successful. Thus, calibration testing allows for a comprehensive assessment of the sealing performance of the closed container and the measurement error of the system before testing, helping to improve testing accuracy and data reliability. Furthermore, using water as a solvent is inexpensive and has stable reactivity with metallic lithium. Compared to the corrosive reagents used in some existing testing methods, this not only reduces reagent costs and operational risks but also avoids the environmental pressure of waste liquid disposal.

[0068] Step S103: Discharge the control BOL battery (fresh battery) of the LFP battery (lithium iron phosphate battery) with a capacity of 104Ah at 0.05C, disassemble to obtain the electrode assembly, and take three folds (i.e., three single folds) of the electrode assembly roll head, roll middle, and roll tail as the first control negative electrode, the second control negative electrode, and the third control negative electrode, respectively. The first, second, and third control negative electrode sheets were placed in three calibrated and tested sealed containers, each with a magnetic stirrer. 200 ml of water was added to each container. The containers were then placed on a magnetic stirrer to stir the water. After the reaction was complete, the pressure inside the container containing the first control negative electrode sheet was 32.22 kPa, the pressure inside the container containing the second control negative electrode sheet was 32.08 kPa, and the pressure inside the container containing the third control negative electrode sheet was 32.32 kPa. The average pressure of each three folds of the control BOL battery's negative electrode sheet was 32.21 kPa. Specifically, in this embodiment, the control BOL battery contains two identical cores, each core containing a total of 62 folds in the negative electrode sheet. Disassembling any core yields... Figure 2 The electrode assembly shown has three single-fold negative electrode sheets taken from the first control negative electrode sheet sampling area (i.e., three folds randomly selected from the ten folds of negative electrode sheets in that area), three single-fold negative electrode sheets taken from the second control negative electrode sheet sampling area (i.e., three folds randomly selected from the ten folds of negative electrode sheets in that area), and three single-fold negative electrode sheets taken from the third control negative electrode sheet sampling area (i.e., three folds randomly selected from the ten folds of negative electrode sheets in that area). Of course, the fact that the number of folds in each sampling area is 10 and the number of folds in each control negative electrode sheet is 3 is just an example. The specific number can be adjusted according to actual conditions (such as the total number of folds in the negative electrode sheet in the core, the volume of the sealed container used for testing, etc.) to better ensure the representativeness and balance of the sampling, thereby ensuring the accuracy of the battery lithium plating detection.

[0069] Step S104: Discharge a 104Ah LFP EOL battery (End of Life, 4C cycle for 10 times) at 0.05C, i.e., the test battery, and disassemble it to obtain the electrode assembly. Take three folds of the electrode assembly (head), middle (middle), and tail (tail) as the first, second, and third negative electrode sheets to be tested, respectively. The positions of the first, second, and third negative electrode sheets in their respective electrode assemblies correspond to the positions of the first, second, and third control negative electrode sheets in their respective electrode assemblies. Place the first, second, and third negative electrode sheets to be tested, along with a magnetic stir bar, into three calibrated and tested sealed containers. Pour 200ml of water into each sealed container and place the containers on a magnetic stirrer to stir the water and initiate the reaction. After the reaction was completed, the pressure inside each sealed container was measured, and the gas composition inside each sealed container was analyzed using gas chromatography. The specific test results are as follows: The pressure inside the sealed container containing the first negative electrode sheet under test was 35.76 kPa. Gas from this container was subjected to GC testing. The measured volume contents of the gas were: O2 92.46%, H2 6.5%, CO2 0.32%, CO 0%, CH4 0.16%, C2H4 0.03%, C2H2 0.4%, C2H6 0.09%, and C3H8 0.01%. The amount of hydrogen gas produced in the sealed container reaction is calculated; where n is the amount of hydrogen gas produced, p is the pressure inside the sealed container where the first negative electrode sheet to be tested is located, measured in step S104, p0 is the average pressure of each three folds of the negative electrode sheet of the control BOL battery (i.e., 32.21 kPa), x1 is the volume content of hydrogen gas inside the sealed container where the first negative electrode sheet to be tested is located, measured in step S104, x2 is the volume content of other interfering gases inside the sealed container where the first negative electrode sheet to be tested is located, measured in step S104, and V 器 V is the volume of the sealed container. 液 Let be the volume of water, R be the ideal gas constant, and T be the ambient temperature, taken as 298.15 K. The mass of lithium metal deposited on the first negative electrode sheet to be tested is 2n*M. Li , of which M Li =6.96g / mol, the calculated lithium deposition in the first negative electrode is 0.0116g.

[0070] The pressure inside the sealed container containing the second negative electrode sheet was 36.34 kPa. A gas sample from this container was subjected to GC testing. The measured volume contents of the gas were: O2 90.87%, H2 7.71%, CO2 0.48%, CO 0%, CH4 0.19%, C2H4 0.04%, C2H2 0.55%, C2H6 0.11%, and C3H8 0.02%. Referring to the method used to calculate the amount of lithium deposited in the first negative electrode sheet, the amount of lithium deposited in the second negative electrode sheet was calculated to be 0.0132 g.

[0071] The pressure inside the sealed container containing the third negative electrode sheet was 36.24 kPa. A gas sample from this container was subjected to GC testing. The measured volume contents of the gas were: O2 92.13%, H2 6.89%, CO2 0.33%, CO 0%, CH4 0.13%, C2H4 0.03%, C2H2 0.38%, C2H6 0.09%, and C3H8 0.01%. Referring to the method used to calculate the amount of lithium deposited in the first negative electrode sheet, the amount of lithium deposited in the third negative electrode sheet was calculated to be 0.0133 g.

[0072] From the above, we know that the amount of lithium deposited in a single negative electrode is (0.0116 + 0.0132 + 0.0133) / 9 = 0.0042 g. The total number of folds in the negative electrode of the battery under test (a 104Ah LFP battery) is 62 in a single core. Therefore, the amount of lithium deposited in a single core is 0.0042 * 62 = 0.26 g, and the total amount of lithium deposited in the entire battery is 0.26 * 2 = 0.52 g.

[0073] Example 2

[0074] In this embodiment, the method for detecting the amount of lithium plating in the lithium-ion battery is basically the same as in Example 1, except that the battery to be tested is replaced with an EOL battery of LFP with a capacity of 104Ah (the cell is tested after 800 cycles at 1.5C).

[0075] Accordingly, in step S104, after the reaction is complete, the pressure inside each sealed container is tested, and the gas composition inside each sealed container is analyzed using gas chromatography. The specific test results are as follows: The pressure inside the sealed container where the first negative electrode sheet to be tested is located is 38.37 kPa. GC testing was performed on the gas in the sealed container where the first negative electrode sheet to be tested is located. The volume contents of the gas were measured to be 77.81% O2, 17.38% H2, 0.94% CO2, 0% CO, 0.46% CH4, 0.24% C2H4, 2.88% C2H2, 0.22% C2H6, and 0.04% C3H8. Referring to the calculation method for the amount of lithium plating in the first negative electrode sheet to be tested in Example 1 above, the amount of lithium plating in the first negative electrode sheet to be tested was calculated to be 0.0180 g.

[0076] The pressure inside the sealed container where the second negative electrode sheet to be tested is 38.85 kPa. GC testing was performed on the gas in the sealed container where the second negative electrode sheet to be tested was performed. The volume contents of the gas were measured to be 77.84% O2, 17.17% H2, 0.8% CO2, 0% CO, 0.43% CH4, 0.16% C2H4, 3.36% C2H2, 0.19% C2H6, and 0.02% C3H8. Referring to the calculation method for the amount of lithium plating in the first negative electrode sheet to be tested in Example 1 above, the amount of lithium plating in the second negative electrode sheet to be tested was calculated to be 0.0192 g.

[0077] The pressure inside the sealed container where the third negative electrode sheet to be tested is located is 39.62 kPa. The gas in the sealed container where the third negative electrode sheet to be tested is taken for GC testing. The volume content of O2 in the gas is measured to be 79.56%, H2 volume content is 16.34%, CO2 volume content is 0.44%, CO volume content is 0%, CH4 volume content is 0.35%, C2H4 volume content is 0.13%, C2H2 volume content is 2.97%, C2H6 volume content is 0.17%, and C3H8 volume content is 0.01%. Referring to the calculation method for the amount of lithium plating in the first negative electrode sheet to be tested in Example 1 above, the amount of lithium plating in the third negative electrode sheet to be tested is calculated to be 0.0221 g.

[0078] As shown above, the amount of lithium deposited in a single negative electrode is (0.0180 + 0.0192 + 0.0221) / 9 = 0.0066 g. The total number of folds in the negative electrode of the battery under test (a 104 Ah LFP battery) is 62 in a single winding. Therefore, the amount of lithium deposited in a single winding is 0.0066 * 62 = 0.41 g, and the total amount of lithium deposited in the entire battery is 0.41 * 2 = 0.82 g.

[0079] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations of this application. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A method for detecting the amount of lithium plating in a lithium-ion battery, characterized in that, The method includes the following steps: S1: Disassemble the battery under test that is in an empty state to obtain an electrode assembly, and take the negative electrode of the electrode assembly as the negative electrode to be tested. S2: The negative electrode sheet to be tested is placed in a first sealed container, and a solvent containing hydroxyl groups is injected to carry out a first reaction. The lithium metal deposited in the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate hydrogen gas, and the SEI film on the negative electrode sheet reacts with the solvent containing hydroxyl groups to generate other interfering gases. After the reaction is completed, the pressure in the first sealed container and the volume content of hydrogen gas and other interfering gases are measured. The other interfering gases include CO2, CO, CH4, C2H4, C2H2, C2H6, and C3H8. The volume content of the other interfering gases is measured, including: The volume contents of CO2, CO, CH4, C2H4, C2H2, C2H6, C3H8, and O2 in the first sealed container are measured. The volume contents of CO2 in the other interfering gases are determined by the measured volume contents of CO2 and O2, and the calculation formula is as follows: ； in, The volume content of CO2 in the other interfering gases. To determine the volumetric content of CO2, The measured volume content of O2; The volume content of the other interfering gases is the sum of the measured volume contents of CO, CH4, C2H4, C2H2, C2H6, and C3H8, plus... ; S3: Disassemble the control BOL battery with the same specifications as the battery under test and in an empty state, and take its negative electrode sheet as the control negative electrode sheet. No metallic lithium is deposited in the control negative electrode sheet. S4: Place the control negative electrode in a second sealed container with the same volume as the first sealed container, and inject the same amount of the hydroxyl-containing solvent as in step S2 to carry out the second reaction. After the reaction is completed, measure the pressure inside the second sealed container as the control pressure. S5: Based on the pressure inside the first sealed container, the volume content of hydrogen and other interfering gases, the control pressure, the volume of the first sealed container, and the volume of the solvent containing hydroxyl groups, and in conjunction with the ideal gas law, determine the amount of hydrogen generated by the reaction between the negative electrode sheet under test and the solvent containing hydroxyl groups. Then, based on the amount of hydrogen, determine the amount of lithium plating in the lithium-ion battery; wherein, The formula for calculating the amount of hydrogen is: ； Where n is the amount of hydrogen produced, p is the pressure inside the first sealed container, p0 is the control pressure, x1 is the volume content of hydrogen in the first sealed container, x2 is the volume content of other interfering gases in the first sealed container, and V 器 V is the volume of the first sealed container. 液 R is the volume of the solvent containing hydroxyl groups, R is the ideal gas constant, and T is the ambient temperature of the test environment.

2. The method for detecting the amount of lithium plating in a lithium-ion battery according to claim 1, characterized in that, The method further includes: a step of calibrating and testing the first sealed container before step S2, and / or a step of calibrating and testing the second sealed container before step S4; using the first sealed container and / or the second sealed container as the sealed container to be tested, and the solvent containing hydroxyl groups as the detection solvent, the step of calibrating and testing includes: After injecting the test solvent of volume V1 into a sealed container of volume V0, the sealed container is sealed, and the pressure P0 inside the sealed container is measured. A lithium sheet of mass m1 is placed in the sealed container to be tested. After injecting the test solvent of volume V1 into the sealed container to be tested, the sealed container to be tested is sealed and the reaction is carried out to generate hydrogen gas. After the reaction is completed, the pressure P1 inside the sealed container to be tested is measured. Based on V0, V1, P0, and P1, the amount of hydrogen generated by the lithium sheet is determined, and then the theoretical mass m2 of the lithium sheet is calculated based on the amount of hydrogen generated. If the relative difference between m2 and m1 is within a preset deviation, the calibration test is qualified and can be used for testing in steps S2 and / or S4. If the relative difference between m2 and m1 is greater than the preset deviation, the calibration test is unqualified and cannot be used for testing in steps S2 and / or S4. The preset deviation is determined at least based on the measurement accuracy of pressure and volume.

3. The method for detecting the amount of lithium plating in a lithium-ion battery according to claim 2, characterized in that, The formula for calculating the relative difference Δm between m2 and m1 is: ; And / or, the preset deviation is less than or equal to 10%.

4. The method for detecting the amount of lithium plating in a lithium-ion battery according to claim 1, characterized in that, The method further includes: For the electrode assembly of the battery under test, negative electrode sheets located at the head, middle and tail of the electrode assembly are taken along its winding direction and used as the first negative electrode sheet to be tested, the second negative electrode sheet to be tested and the third negative electrode sheet to be tested, respectively. For the electrode assembly of the control BOL battery, negative electrode sheets at the same positions are taken as the first control negative electrode sheet, the second control negative electrode sheet and the third control negative electrode sheet. Steps S2-S5 are performed on the first negative electrode sheet to be tested, the second negative electrode sheet to be tested, the third negative electrode sheet to be tested, the first control negative electrode sheet, the second control negative electrode sheet, and the third control negative electrode sheet respectively, to obtain the amount of lithium plating on each negative electrode sheet to be tested, wherein each negative electrode sheet to be tested and each control negative electrode sheet have the same number of folds, and the number of folds is greater than or equal to 3. The average amount of lithium plating is obtained based on the amount of lithium plating in each negative electrode and the fold number. The amount of lithium plating in the lithium-ion battery is determined based on the average amount of lithium plating and the total number of folds in the lithium-ion battery.

5. The method for detecting the amount of lithium plating in a lithium-ion battery according to any one of claims 1 to 4, characterized in that, In step S1, the battery under test is first discharged to obtain the battery under test in an empty state. In step S3, the control BOL battery is second discharged to obtain the control BOL battery in an empty state. The discharge rate of the first discharge and the second discharge are the same.

6. The method for detecting the amount of lithium plating in a lithium-ion battery according to claim 5, characterized in that, The discharge rate of the first discharge is 0.05C~0.3C.

7. The method for detecting the amount of lithium plating in a lithium-ion battery according to any one of claims 1 to 4, characterized in that, The first reaction and / or the second reaction are carried out under stirring conditions.

8. The method for detecting the amount of lithium plating in a lithium-ion battery according to any one of claims 1 to 4, characterized in that, The solvent containing hydroxyl groups includes at least one of water, ethanol, and isopropanol.

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