Quantitative Detection Method for Lithium Deposition Amount in Automotive Lithium Batteries

Abstract

The present application discloses a method for quantitatively detecting the amount of lithium plating in an automotive lithium battery. The method for quantitatively detecting the amount of lithium plating in the automotive lithium battery includes the following steps: obtaining the powder of the material to be measured on the surface of the negative electrode plate of the automotive lithium battery; mixing the powder of the material to be measured with an electrolyte to obtain a first mixture to be measured; and detecting the first mixture to be measured by a differential scanning calorimeter to determine the amount of lithium plating in the automotive lithium battery. The present application solves the technical problem of the relatively high detection cost of quantitatively detecting the amount of lithium plating in an existing automotive lithium battery.

Description

Technical Field

[0001] This application relates to the technical field of automotive lithium batteries, and particularly to a method for quantitatively detecting the amount of lithium plating in automotive lithium batteries. Background Art

[0002] With the rapid development and popularization of new energy vehicles, the safety of new energy vehicle batteries has gradually become a hot topic of concern. During long-term use, lithium-ion batteries are prone to lithium plating. When the lithium plating is slight, it will affect performance parameters such as the capacity and power of the battery. When the lithium plating is severe, it may lead to thermal runaway of the lithium-ion battery and cause safety accidents. Therefore, in order to confirm the safety risks of lithium-plated battery cores, it is necessary to detect the amount of lithium plating in lithium-ion batteries.

[0003] Currently, common methods for detecting the amount of lithium plating include the observation interface method, solid nuclear magnetic resonance method, neutron diffraction method, electron paramagnetic resonance method, etc. Among them, the observation interface method is simple to operate and has a low detection cost, but it cannot obtain an accurate amount of lithium plating and belongs to a semi-quantitative method. Methods such as the solid nuclear magnetic resonance method, neutron diffraction method, and electron paramagnetic resonance method have high detection costs and are difficult to popularize in the actual detection of commercial battery cores. Summary of the Invention

[0004] The main purpose of this application is to provide a method for quantitatively detecting the amount of lithium plating in automotive lithium batteries, aiming to solve the technical problem of the high detection cost of quantitatively detecting the amount of lithium plating in automotive lithium batteries in the prior art.

[0005] To achieve the above object, this application provides a method for quantitatively detecting the amount of lithium plating in automotive lithium batteries, and the method for quantitatively detecting the amount of lithium plating in automotive lithium batteries includes the following steps:

[0006] Obtain the powder of the material to be tested on the surface of the negative electrode plate of the automotive lithium battery;

[0007] Mix the powder of the material to be tested with the electrolyte to obtain a first mixture to be tested;

[0008] Detect the first mixture to be tested by a differential scanning calorimeter to determine the amount of lithium plating in the automotive lithium battery.

[0009] Optionally, the step of mixing the powder of the material to be tested with the electrolyte to obtain a first mixture to be tested includes:

[0010] Load the powder of the material to be tested into a high-pressure crucible;

[0011] Add the electrolyte to the high-pressure crucible containing the powder of the material to be tested to obtain a first mixture to be tested;

[0012] After sealing the high-pressure crucible containing the first mixture to be tested, place it in a differential scanning calorimeter.

[0013] Optionally, the step of detecting the first mixture to be measured by a differential scanning calorimeter and determining the amount of lithium plating in the automotive lithium battery includes:

[0014] Detect the first mixture to be measured by a differential scanning calorimeter to obtain a sample thermogram;

[0015] Determine the amount of lithium plating in the automotive lithium battery according to the sample thermogram and at least one preset standard thermogram.

[0016] Optionally, the step of determining the amount of lithium plating in the automotive lithium battery according to the sample thermogram and at least one preset standard thermogram includes:

[0017] Integrate the exothermic peak in the range of 100 - 180 °C in the sample thermogram to obtain the area of the first exothermic peak;

[0018] Compare the area of the first exothermic peak with the areas of the second exothermic peaks in each of the preset standard thermograms to determine the amount of lithium plating in the automotive lithium battery.

[0019] Optionally, the step of comparing the area of the first exothermic peak with the areas of the second exothermic peaks in each of the preset standard thermograms to determine the amount of lithium plating in the automotive lithium battery includes:

[0020] Based on the areas of the second exothermic peaks in each of the preset standard thermograms, draw a standard curve;

[0021] Substitute the area of the first exothermic peak into the regression equation corresponding to the standard curve to calculate the amount of lithium plating in the automotive lithium battery.

[0022] Optionally, the step of drawing a standard curve based on the areas of the second exothermic peaks in each of the preset standard thermograms includes:

[0023] Weigh at least five metal lithium standard samples with different masses;

[0024] Mix each of the metal lithium standard samples with the electrolyte to obtain a second mixture to be measured;

[0025] Test each of the second mixtures to be measured by a differential scanning calorimeter to obtain the areas of the second exothermic peaks in the range of 100 - 180 °C corresponding to each of the metal lithium standard samples;

[0026] Perform linear fitting according to the areas of the second exothermic peaks and the masses of the corresponding metal lithium standard samples to obtain a preset standard curve.

[0027] Optionally, the step of obtaining the powder of the material to be measured on the surface of the negative electrode plate of the automotive lithium battery includes:

[0028] Obtain the negative electrode plate of the automotive lithium battery;

[0029] Clean the negative electrode plate, and after drying, scrape the powder of the material to be measured from the surface of the negative electrode plate.

[0030] Optionally, the step of cleaning the negative electrode plate includes:

[0031] Put the negative electrode plate into dimethyl carbonate and soak it for 0.5 - 2 hours.

[0032] Optionally, the mass of the powder of the material to be measured is 0.05 mg - 10 mg.

[0033] Optionally, the step of obtaining the powder of the material to be measured on the surface of the negative electrode plate of the automotive lithium battery is carried out in a glove box under an inert atmosphere;

[0034] And / or, the step of mixing the powder of the material to be measured with the electrolyte to obtain the first mixture to be measured is carried out in a glove box under an inert atmosphere.

[0035] The present application provides a method for quantitatively detecting the amount of lithium plating in an automotive lithium battery. By obtaining the powder of the material to be measured on the surface of the negative electrode plate of the automotive lithium battery and mixing the powder of the material to be measured with the electrolyte to obtain the first mixture to be measured, the pretreatment of the sample to be detected by differential scanning calorimetry is realized, and the first mixture to be measured that can react and generate heat change at a certain temperature is obtained. Then, the first mixture to be measured is detected by a differential scanning calorimeter to determine the amount of lithium plating in the automotive lithium battery, realizing the quantitative detection of the amount of lithium plating in the automotive lithium battery based on the differential scanning calorimetry method. Compared with the observation interface method, the present application can directly measure the content of metallic lithium in the sample to achieve quantitative detection. Compared with methods such as solid nuclear magnetic method, neutron diffraction method, and electron paramagnetic resonance method, the differential scanning calorimetry method adopted in the present application is relatively simple in operation and low in detection cost, overcoming the technical problem of high detection cost for quantitatively detecting the amount of lithium plating in an automotive lithium battery in the prior art. Description of the Drawings

[0036] The drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principle of the present application.

[0037] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 It is a schematic flow chart of an embodiment of the method for quantitatively detecting the amount of lithium plating in the automotive lithium battery of the present application;

[0039] Figure 2 It is a schematic flow chart of another embodiment of the method for quantitatively detecting the amount of lithium plating in the automotive lithium battery of the present application;

[0040] Figure 3 It is a schematic diagram of the standard thermogram of standard samples of metallic lithium with different masses in an implementable manner of the present application;

[0041] Figure 4 It is a schematic diagram of the standard curve in an implementable manner of the present application.

[0042] The realization of the purpose, functional features, and advantages of the present application will be further described with reference to the embodiments and the drawings. Specific Embodiments

[0043] To make the above-mentioned objects, features, and advantages of the present invention more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0044] With the rapid development and popularization of new energy vehicles, the safety of new energy vehicle batteries has gradually become a hot topic of concern. During the long-term use of lithium-ion batteries, lithium plating is likely to occur. When the lithium plating is slight, it will affect the performance parameters such as the capacity and power of the battery. When the lithium plating is severe, it may lead to thermal runaway of the lithium-ion battery and cause safety accidents. Therefore, in order to confirm the safety risks of the lithium-plated battery cells, it is necessary to detect the amount of lithium plating in the lithium-ion battery.

[0045] When lithium plating occurs in a lithium-ion battery, there will be three forms of lithium elements in the negative electrode at the same time: inorganic and organic lithium salts in the SEI film, lithium elements in the lithium-inserted graphite, and metallic lithium precipitated on the surface of the negative electrode. In the process of detecting the amount of lithium plating in a lithium-ion battery, how to accurately identify metallic lithium from the three forms of lithium elements is the key to ensuring the accuracy of the detection result. That is, it is necessary to separate metallic lithium from the other two forms of lithium elements or clearly distinguish metallic lithium from the other two forms of lithium elements.

[0046] At present, the commonly used methods for detecting the amount of lithium deposition include interface observation method, solid nuclear magnetic resonance method, neutron diffraction method, electron paramagnetic resonance method, etc. Among them, the interface observation method is to disassemble the battery cell after it is fully charged. Normal lithium-embedded graphite will appear golden yellow, while the precipitated metallic lithium will appear silver / gray. The area ratio of lithium deposition is obtained by calculating the color difference between the two. The interface observation method is simple to operate and has a low detection cost. However, the difference between the area ratio and the mass ratio is large, so the interface observation method cannot obtain a more accurate lithium deposition amount, which is a semi-quantitative method; NMR (Nuclear magnetic The nuclear magnetic resonance (NMR) method is based on the NMR testing principle. The integral area of ​​the NMR characteristic peak shows a good linear relationship with the molar amount of lithium. Based on this linear relationship, the NMR test of the negative electrode of the lithium-deposited battery cell can obtain the corresponding molar amount of lithium, so the quantitative detection of the amount of lithium deposition can be achieved. However, the purchase cost of the solid nuclear magnetic equipment used in the NMR method is relatively high, and the corresponding testing cost is also high. The neutron diffraction method indirectly confirms whether the battery cell is lithium-deposited by calculating the content of different lithium-embedded graphite and comparing it with the reference group. For example, if the experimental group is compared with the reference group LiC 6 The peak area decreased while LiC1 2 Increase, that is, the overall graphite lithium intercalation ratio decreases, which means that the amount of lithium precipitation in the experimental group increases. It can be seen that the neutron diffraction method cannot directly detect the amount of lithium precipitation, and the neutron diffraction resources are limited and the cost is high; the EPR (electron paramagnetic resonance) method is based on the obvious difference between the EPR signals of metallic lithium and lithium intercalated graphite. The peak width of the metallic lithium EPR signal is only about 1 / 5 of that of the lithium intercalated graphite, and the amplitude of the EPR signal is linearly related to the content of the two, realizing the quantitative detection method of the amount of lithium precipitation. However, the EPR method requires the use of special batteries for testing, for example, adding inert reference materials (such as manganese oxide, etc.) to correct the phase and amplitude of the EPR signal, and using quartz glass tube packaging to avoid the interference of stainless steel shells on the EPR signal, etc. It can be seen that the detection process of the EPR method is relatively complicated and the cost is relatively high. In summary, the existing technology for quantitatively detecting the amount of lithium precipitation in automotive lithium batteries has a high detection cost, which is difficult to popularize in the actual detection of commercial batteries.

[0047] The present application provides a method for quantitatively detecting the amount of lithium plating in automotive lithium batteries. Based on the difference in the temperature ranges at which the heat is released when lithium elements in different forms in the automotive lithium battery react with the electrolyte, the reaction heat of the metallic lithium deposited on the surface of the negative electrode plate reacting with the electrolyte can be distinguished from the reaction heat of other forms of lithium elements reacting with the electrolyte. Furthermore, the reaction heat of the metallic lithium deposited on the surface of the negative electrode plate reacting with the electrolyte is detected by differential scanning calorimetry. The metallic lithium and other forms of lithium elements can be distinguished based on the temperature range where the reaction heat is located. Moreover, based on the positive correlation between the reaction heat of the lithium element reacting with the electrolyte and the number of lithium atomic nuclei, the quantitative detection of the amount of lithium plating in the automotive lithium battery can be achieved. Compared with methods such as solid nuclear magnetic resonance method, neutron diffraction method, and electron paramagnetic resonance method, the detection cost of differential scanning calorimetry is lower, overcoming the technical problem of the high detection cost of quantitatively detecting the amount of lithium plating in existing automotive lithium batteries.

[0048] An embodiment of the present application provides a method for quantitatively detecting the amount of lithium plating in an automotive lithium battery. In one embodiment of the method for quantitatively detecting the amount of lithium plating in the automotive lithium battery of the present application, with reference to Figure 1 , the method for quantitatively detecting the amount of lithium plating in the automotive lithium battery includes:

[0049] Step S10, obtaining the powder of the material to be tested on the surface of the negative electrode plate of the automotive lithium battery;

[0050] In this embodiment, it should be noted that throughout the entire process of the method for quantitatively detecting the amount of lithium plating in the automotive lithium battery, contact between lithium elements and water and oxygen should be avoided. The ways to avoid contact between lithium elements and water and oxygen can be to operate in an environment isolated from water and oxygen, or to seal the lithium elements in a container that does not contain water and oxygen, etc.

[0051] Specifically, in an environment isolated from water and oxygen, disassemble the battery cell of the automotive lithium battery, collect the negative electrode plate of the battery cell, scrape the powder from the surface of the negative electrode plate, weigh all the scraped powder, and weigh part or all of the powder from the scraped powder as the powder of the material to be tested. Among them, the environment isolated from water and oxygen can be a vacuum environment, under an inert gas atmosphere, etc., to avoid the influence of water and oxygen in the environment on lithium elements; the mass of the powder of the material to be tested can be determined according to the detection requirements of the differential scanning calorimeter, big data, actual test results, etc., and this embodiment does not limit this; in the sampling process of scraping the powder from the surface of the negative electrode plate, all the powder on the surface of the negative electrode plate can be scraped, or sampling can be carried out at at least one representative position, and then through area conversion, the amount of lithium plating in the entire automotive lithium battery can be determined. For example, if the surface area of the automotive lithium battery is a 1 cm 2, find n representative regions from the surface of the automotive lithium battery, and the total surface area of ​​the n regions is a 2 cm 2 After the powders scraped from n areas are mixed evenly, it is measured that there are b mg of metallic lithium in the powders scraped from n areas. Then the amount of lithium precipitated from the automotive lithium battery is b*a 1 / a 2 .

[0052] Optionally, the step of obtaining the powder of the material to be tested on the surface of the negative electrode plate of the automotive lithium battery is carried out in a glove box with an inert atmosphere.

[0053] In this embodiment, specifically, the undisassembled battery cell is placed in a glove box, and the battery cell is disassembled in the glove box filled with inert gas protection to obtain the material powder to be tested on the surface of the negative electrode plate of the automotive lithium battery, so that after the battery cell is disassembled, the lithium element in the battery cell can be subsequently operated in an environment isolated from water and oxygen to avoid water and oxygen from reacting with the lithium element, wherein the inert atmosphere is a gas environment filled with one or more inert gases such as argon and nitrogen. The glove box can be well isolated from the external environment, and operators or automated equipment can complete related operations in the glove box outside the glove box, which is low in cost.

[0054] Optionally, the mass of the powder of the material to be tested is 0.05 mg-10 mg.

[0055] In this embodiment, the mass of the powder of the material to be tested is too large. The thicker the powder is spread in the high-pressure crucible, the more likely it is to affect the heat transfer, and thus the quality of the thermal spectrum. In addition, the mass of the powder of the material to be tested is too large, the wider the peak width of the peak in the measured sample thermal spectrum, and the more impurity peaks may be wrapped, which in turn affects the accuracy of the result. Therefore, it is determined that the mass of the powder of the material to be tested is 0.05mg-10mg, for example, 0.05mg, 1mg, 2.52mg, 6.5mg, 10mg, etc.

[0056] Optionally, the step of obtaining the material powder to be tested on the surface of the negative electrode plate of the automotive lithium battery includes:

[0057] Step S11, obtaining the negative electrode plate of the automotive lithium battery;

[0058] In this embodiment, specifically, in an environment isolated from water and oxygen, the battery cells of the automotive lithium battery are disassembled and the negative electrode plates of the battery cells are collected.

[0059] Step S12, cleaning the negative electrode plate, and after drying, scraping the powder of the material to be tested from the surface of the negative electrode plate.

[0060] In this embodiment, specifically, an ester solvent is used to clean the impurities and lithium salts on the surface of the negative electrode sheet to avoid interference of the impurities and lithium salts with the test results of the subsequent differential scanning calorimeter. After drying the cleaned negative electrode sheet, powder is scraped from the surface of the dried negative electrode sheet, and all the scraped powder is weighed. From the scraped powder, part or all of the powder is weighed as the powder of the material to be tested.

[0061] Optionally, the step of cleaning the negative electrode sheet includes:

[0062] Put the negative electrode sheet into dimethyl carbonate and soak it for 0.5 - 2 hours.

[0063] In this embodiment, specifically, the negative electrode sheet is put into dimethyl carbonate and soaked for 0.5 - 2 hours to clean and remove the impurities and lithium salts on the surface of the negative electrode sheet. In an implementable manner, the process of putting the negative electrode sheet into dimethyl carbonate and soaking it for 0.5 - 2 hours can be carried out once or multiple times. For example, the negative electrode sheet can be put into dimethyl carbonate, soaked for 0.5 - 2 hours, taken out and dried for standby, or the negative electrode sheet can be put into dimethyl carbonate, soaked for 0.5 - 2 hours, taken out, and then put into another portion of unused dimethyl carbonate, soaked for 0.5 - 2 hours, and then taken out and dried for standby.

[0064] Step S20: Mix the powder of the material to be tested with the electrolyte to obtain a first mixture to be tested;

[0065] In this embodiment, specifically, in an environment isolated from water and oxygen, the electrolyte is added to the weighed powder of the material to be tested and mixed to obtain a first mixture to be tested. Among them, the powder of the material to be tested and the electrolyte in the first mixture to be tested can react at a certain temperature and generate a heat change. The composition and addition amount of the electrolyte should enable the metallic lithium in the powder of the material to be tested to fully react and generate a heat change, which can be specifically determined according to big data or actual test results, etc. This embodiment does not limit this. In an implementable manner, the electrolyte can be the same as the electrolyte used in the automotive lithium battery.

[0066] Optionally, the step of mixing the powder of the material to be tested with the electrolyte to obtain a first mixture to be tested is carried out in a glove box under an inert atmosphere.

[0067] In this embodiment, specifically, in a glove box filled with inert gas protection, the powder of the material to be tested is mixed with the electrolyte to obtain a first mixture to be tested, so that all operations of lithium elements can be completed in an environment isolated from water and oxygen, avoiding the reaction between water and oxygen and lithium elements. Among them, the inert atmosphere is a gas environment filled with one or more of inert gases such as argon and nitrogen. The glove box can better isolate the external environment, and operators or automated equipment can complete relevant operations inside the glove box outside the glove box, with relatively low costs.

[0068] Optionally, the step of mixing the powder of the material to be tested with the electrolyte to obtain a first mixture to be tested includes:

[0069] Step S21, loading the powder of the material to be tested into a high-pressure crucible;

[0070] In this embodiment, specifically, in an environment isolated from water and oxygen, the weighed powder of the material to be tested is completely transferred to a high-pressure crucible supporting a differential scanning calorimeter, and the powder of the material to be tested is laid flat on the bottom of the high-pressure crucible.

[0071] Step S22, adding the electrolyte to the high-pressure crucible containing the powder of the material to be tested to obtain a first mixture to be tested;

[0072] Step S23, after sealing the high-pressure crucible containing the first mixture to be tested, placing it in a differential scanning calorimeter.

[0073] In this embodiment, specifically, add the electrolyte to the high-pressure crucible containing the powder of the material to be tested, mix to obtain a first mixture to be tested, seal the high-pressure crucible containing the first mixture to be tested, and place the sealed high-pressure crucible in the designated position of the differential scanning calorimeter.

[0074] Step S30, detecting the first mixture to be tested by a differential scanning calorimeter to determine the lithium precipitation amount of the automotive lithium battery.

[0075] In this embodiment, specifically, the first mixture to be measured is detected by a differential scanning calorimeter to obtain a sample thermogram corresponding to the first mixture to be measured. By analyzing the sample thermogram, based on the exothermic temperature corresponding to the reaction between metallic lithium and the electrolyte, the peak corresponding to metallic lithium can be determined in the sample thermogram. Furthermore, based on the peak height or peak area of the peak corresponding to metallic lithium, the content of metallic lithium in the first mixture to be measured can be calculated. Based on the content of metallic lithium in the first mixture to be measured, the amount of lithium plating in the automotive lithium battery can be determined. Herein, the amount of lithium plating is the content of metallic lithium deposited on the surface of the negative electrode plate of the automotive lithium battery, and the amount of lithium plating can be in terms of mass, molar mass, etc.; the content of metallic lithium in the first mixture to be measured can be the mass percentage of metallic lithium in the first mixture to be measured. For example, the ratio of the height or peak area of the peak corresponding to metallic lithium in the sample thermogram to the sum of the heights or peak areas of all the peaks in the sample thermogram can be determined as the mass percentage of metallic lithium in the first mixture to be measured. The content of metallic lithium in the first mixture to be measured can also be the mass or molar mass of metallic lithium in the first mixture to be measured, etc. For example, the sample thermogram can be compared with the standard thermograms of at least one metallic lithium standard sample, and the mass or molar mass of metallic lithium in the first mixture to be measured can be determined based on the peak height or peak area.

[0076] In this embodiment, by obtaining the powder of the material to be measured on the surface of the negative electrode plate of the automotive lithium battery and mixing the powder of the material to be measured with the electrolyte to obtain a first mixture to be measured, the pretreatment of the sample to be detected by differential scanning calorimetry is realized, and a first mixture to be measured that can react and generate heat change at a certain temperature is obtained. Then, the first mixture to be measured is detected by a differential scanning calorimeter to determine the amount of lithium precipitation in the automotive lithium battery, realizing the quantitative detection of the amount of lithium precipitation in the automotive lithium battery based on the differential scanning calorimetry method. Since there are differences in the temperature ranges at which different forms of lithium elements in the automotive lithium battery react with the electrolyte, the reaction heat of the metallic lithium precipitated on the surface of the negative electrode plate reacting with the electrolyte can be distinguished from the reaction heat of other forms of lithium elements reacting with the electrolyte. Furthermore, by using the differential scanning calorimetry method, the reaction heat of the metallic lithium precipitated on the surface of the negative electrode plate reacting with the electrolyte can be detected, and the metallic lithium and other forms of lithium elements can be distinguished according to the temperature range where the reaction heat is located. Moreover, since the reaction heat of lithium elements reacting with the electrolyte is positively correlated with the number of lithium atomic nuclei, the quantitative detection of the amount of lithium precipitation in the automotive lithium battery can be realized. Compared with the observation interface method, the present application can directly measure the content of metallic lithium in the sample to achieve quantitative detection. Compared with methods such as solid nuclear magnetic resonance method, neutron diffraction method, and electron paramagnetic resonance method, the differential scanning calorimetry method adopted in the present application is relatively simple in operation and low in detection cost, overcoming the technical problem of the relatively high detection cost of quantitatively detecting the amount of lithium precipitation in the automotive lithium battery in the prior art.

[0077] Further, referring to Figure 2 , based on the above embodiments of the present application, in another embodiment of the present application, for the same or similar content as the above embodiments, reference can be made to the above introduction and will not be repeated hereinafter. On this basis, the step of detecting the first mixture to be measured by a differential scanning calorimeter to determine the amount of lithium precipitation in the automotive lithium battery includes:

[0078] Step S31, detecting the first mixture to be measured by a differential scanning calorimeter to obtain a sample thermogram;

[0079] In this embodiment, specifically, the first mixture to be measured is heated with variable temperature by a differential scanning calorimeter, and the heat flow rate corresponding to the first mixture to be measured at different temperatures within the test range of the differential scanning calorimeter is detected to obtain a sample thermogram of the heat flow rate varying with temperature. Among them, the test range of the differential scanning calorimeter can be 0 - 500 °C, or can be adjusted according to actual needs, for example, it can be 0 - 300 °C, 100 - 200 °C, 100 - 180 °C, etc.

[0080] Step S32: Determine the amount of lithium deposition in the automotive lithium battery according to the sample thermogram and at least one preset standard thermogram.

[0081] In this embodiment, it should be noted that each of the preset standard thermograms can be obtained by synchronously detecting a metallic lithium standard sample each time the first mixture to be measured is detected, or the metallic lithium standard sample can be detected in advance, and the thermogram corresponding to the measured metallic lithium standard sample can be stored as a preset standard thermogram for subsequent comparison with the sample thermogram. The standard thermogram is valid under certain conditions. When the conditions change, re-measurement should be carried out to update the preset standard thermogram. The conditions include time, environment, replacement of reagents, etc., which can be specifically determined according to the actual situation, and this embodiment does not limit this.

[0082] In an implementable manner, when the concentration or composition of the electrolyte changes, or when a new electrolyte is reconfigured, the metallic lithium standard sample is re-detected to obtain a new standard thermogram. Since the relationship between the peak area and mass in the thermogram is greatly affected by the electrolyte composition, when the electrolyte changes, a new electrolyte should be used to re-determine the new standard thermogram.

[0083] Specifically, analyze the sample thermogram. Based on the exothermic temperature corresponding to the reaction between metallic lithium and the electrolyte, the peak corresponding to metallic lithium can be determined in the sample thermogram, and then the metallic lithium in the first mixture to be measured can be determined. The peak height or peak area of the peak corresponding to metallic lithium in the sample thermogram is compared with the peak height or peak area of the peak corresponding to metallic lithium in at least one preset standard thermogram. By methods such as the direct comparison method, differential method, or standard curve method, the mass or molar mass of metallic lithium in the first mixture to be measured can be determined. Furthermore, based on the mass or molar mass of metallic lithium in the first mixture to be measured, the amount of lithium deposition in the automotive lithium battery can be determined.

[0084] In an implementable manner, refer to Figure 3 , Figure 3 The five curves in are the thermograms obtained by detecting metallic lithium standard samples with different masses using a differential scanning calorimeter. It should be noted that the heat flow rates corresponding to the baselines of each thermogram are basically the same. For the convenience of viewing, after translating each thermogram up and down and separating them, the obtained Figure 3 , Figure 3 Each thermogram in. From top to bottom, the masses of the corresponding metallic lithium standard samples decrease in sequence. As can be seen from the figure, the peak areas also decrease in sequence.

[0085] Optionally, the step of determining the amount of lithium plating of the automotive lithium battery according to the sample thermogram and at least one preset standard thermogram includes:

[0086] Step S321: Integrate the exothermic peak in the range of 100 - 180 °C in the sample thermogram to obtain the first exothermic peak area;

[0087] In this embodiment, specifically, based on the exothermic temperature corresponding to the reaction of metallic lithium with the electrolyte, it can be determined that the peak corresponding to metallic lithium is within the temperature range of 100 - 180 °C in the sample thermogram. Then, integrate the exothermic peak in the range of 100 - 180 °C in the sample thermogram to obtain the first exothermic peak area corresponding to metallic lithium in the first mixture to be measured.

[0088] It should be noted that if there is more than one exothermic peak in the range of 100 - 180 °C in the sample thermogram, determine whether the resolution of each exothermic peak is greater than the preset resolution threshold. If the resolution of each exothermic peak is greater than the preset resolution threshold, based on the specific temperature of the exothermic peak in the range of 100 - 180 °C in the preset standard thermogram, determine the target exothermic peak from the multiple exothermic peaks in the sample thermogram and integrate the target exothermic peak. If the resolution of each exothermic peak is less than or equal to the preset resolution threshold, the resolution between multiple exothermic peaks in the range of 100 - 180 °C can be increased by adjusting the composition and concentration of the electrolyte, or by adjusting the cleaning time, cleaning solvent, cleaning temperature, etc. of the negative electrode plate. Specifically, it can be determined according to the actual test results.

[0089] Step S322: Compare the first exothermic peak area with the second exothermic peak areas in each of the preset standard thermograms to determine the amount of lithium plating of the automotive lithium battery.

[0090] In this embodiment, specifically, integrate the exothermic peaks in the range of 100 - 180 °C in each of the preset standard thermograms to obtain at least one second exothermic peak area. Compare the first exothermic peak area with each of the second exothermic peak areas. By methods such as the direct comparison method, differential method, or standard curve method, the mass or molar mass of metallic lithium in the first mixture to be measured can be determined. Then, based on the mass or molar mass of metallic lithium in the first mixture to be measured, the amount of lithium plating of the automotive lithium battery can be determined.

[0091] Optionally, the step of comparing the first exothermic peak area with the second exothermic peak areas in each of the preset standard thermograms to determine the amount of lithium plating of the automotive lithium battery includes:

[0092] Step S3221: Draw a standard curve based on the second exothermic peak areas in each of the preset standard thermograms;

[0093] In this embodiment, specifically, the exothermic peaks in the range of 100-180°C in each of the preset standard thermograms are integrated to obtain at least one second exothermic peak area. Based on the second exothermic peak areas in each of the preset standard thermograms and the masses of the metallic lithium standard samples corresponding to the second exothermic peak areas, a standard curve showing the relationship between the exothermic peak area and the mass is plotted.

[0094] It should be noted that the standard curve can be plotted by synchronously detecting the metallic lithium standard sample each time the first mixture to be measured is detected, or the metallic lithium standard sample can be detected in advance, and the obtained standard thermogram can be saved, or the standard curve plotted based on the standard thermogram can be saved for subsequent comparison with the sample thermogram.

[0095] Optionally, the step of plotting the standard curve based on the second exothermic peak areas in each of the preset standard thermograms includes:

[0096] Step S32211: Weigh at least five metallic lithium standard samples with different masses;

[0097] Step S32212: Mix each of the metallic lithium standard samples with the electrolyte to obtain a second mixture to be measured;

[0098] Step S32213: Test each of the second mixtures to be measured with a differential scanning calorimeter to obtain the second exothermic peak areas in the range of 100-180°C corresponding to the respective metallic lithium standard samples;

[0099] Step S32214: Perform linear fitting according to the second exothermic peak areas and the masses of the respective corresponding metallic lithium standard samples to obtain a preset standard curve.

[0100] In this embodiment, specifically, at least five metal lithium standard samples with different masses are weighed, and each of the metal lithium standard samples is mixed with an electrolyte to obtain a second test mixture corresponding to each of the metal lithium standard samples. The differential scanning calorimeter is used to heat each of the second test mixtures at a varying temperature, and the heat flow rate corresponding to each of the second test mixtures is detected at different temperatures within the test range of the differential scanning calorimeter to obtain a standard heat spectrum of the heat flow rate varying with temperature. The exothermic peaks within the range of 100 - 180 °C in each of the preset standard heat spectra are integrated to obtain a second exothermic peak area corresponding to each of the metal lithium standard samples. Based on the second exothermic peak areas and the masses of the metal lithium standard samples corresponding to the respective second exothermic peak areas, linear fitting is performed to obtain a preset standard curve. Among them, the metal lithium standard sample is a standard substance with a known metal lithium content. The more the number of metal lithium standard samples with different masses, the higher the accuracy of the fitted standard curve, but the greater the workload. During the actual testing process, five or more metal lithium standard samples with different masses can be detected according to the actual situation to draw the standard curve.

[0101] In an implementable manner, with reference to Figure 4 , Figure 4 is a schematic diagram of the standard curve in an implementable manner of this application. Based on five second exothermic peak areas and the masses of the corresponding metal lithium standard samples, linear fitting is performed. The dashed line in the figure is the fitted standard curve, and R 2 is greater than 0.99, indicating good linearity.

[0102] Step S3222: Substitute the first exothermic peak area into the regression equation corresponding to the standard curve to calculate the amount of lithium precipitation in the automotive lithium battery.

[0103] In this embodiment, specifically, the first exothermic peak area is substituted into the regression equation corresponding to the standard curve to calculate the mass or molar mass of metal lithium in the first test mixture. Furthermore, based on the mass or molar mass of metal lithium in the first test mixture, the amount of lithium precipitation in the automotive lithium battery can be determined.

[0104] In this embodiment, by comparing the sample heat spectrum with the standard heat spectrum, the accuracy of quantitative detection of the amount of lithium precipitation in the automotive lithium battery can be effectively improved. Moreover, the method is simple and the detection cost is relatively low. It can simplify the operation and reduce the cost while ensuring the accuracy of quantitative detection.

[0105] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be similarly included within the patent scope of the present application.

Claims

1. A quantitative detection method for the amount of lithium plating in an automotive lithium battery, characterized in that, the quantitative detection method for the amount of lithium plating in the automotive lithium battery comprises the following steps; obtain the powder of the material to be tested on the surface of the negative electrode plate of the automotive lithium battery; load the powder of the material to be tested into a high-pressure crucible; add electrolyte to the high-pressure crucible containing the powder of the material to be tested to obtain a first test mixture; after sealing the high-pressure crucible containing the first test mixture, place it in a differential scanning calorimeter; perform variable-temperature heating on the first test mixture by the differential scanning calorimeter, and detect the heat flow rate of the first test mixture at different temperatures to obtain a sample thermogram characterizing the change of the heat flow rate with temperature; integrate the exothermic peak in the range of 100 - 180 °C in the sample thermogram to obtain the area of the first exothermic peak; draw a standard curve based on the areas of the second exothermic peaks in each preset standard thermogram; substitute the area of the first exothermic peak into the regression equation corresponding to the standard curve to calculate the amount of lithium plating in the automotive lithium battery.

2. The quantitative detection method for the amount of lithium plating in an automotive lithium battery according to claim 1, characterized in that, the step of drawing a standard curve based on the areas of the second exothermic peaks in each preset standard thermogram comprises: weigh at least five metal lithium standard samples with different masses; mix each of the metal lithium standard samples with electrolyte respectively to obtain a second test mixture; test each of the second test mixtures by a differential scanning calorimeter to obtain the area of the second exothermic peak in the range of 100 - 180 °C corresponding to each metal lithium standard sample; perform linear fitting according to the areas of the second exothermic peaks and the masses of the corresponding metal lithium standard samples to obtain a preset standard curve.

3. The quantitative detection method for the amount of lithium plating in an automotive lithium battery according to claim 1, characterized in that, the step of obtaining the powder of the material to be tested on the surface of the negative electrode plate of the automotive lithium battery comprises: obtain the negative electrode plate of the automotive lithium battery; clean the negative electrode plate, and after drying, scrape the powder of the material to be tested from the surface of the negative electrode plate.

4. The quantitative detection method for the amount of lithium plating in an automotive lithium battery according to claim 3, characterized in that, the step of cleaning the negative electrode plate comprises: put the negative electrode plate into dimethyl carbonate and soak it for 0.5 - 2 hours.

5. The quantitative detection method for the amount of lithium plating in an automotive lithium battery according to claim 1, characterized in that, the mass of the powder of the material to be tested is 0.05 mg - 10 mg.

6. The quantitative detection method for the amount of lithium plating in an automotive lithium battery according to any one of claims 1 to 5, characterized in that, the step of obtaining the powder of the material to be tested on the surface of the negative electrode plate of the automotive lithium battery is carried out in a glove box under an inert atmosphere; and / or, the step of mixing the powder of the material to be tested with electrolyte to obtain a first test mixture is carried out in a glove box under an inert atmosphere.

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