Method for detecting residual quantity of target volatile substance

Abstract

The invention provides a method for detecting the residual quantity of a target volatile substance. The method comprises the following steps: providing a to-be-detected sample containing the target volatile substance; providing a first closed system, to be more specific, placing the to-be-tested sample in a closed container, enabling the target volatile substance to reach a distribution balance state in the closed container under preset conditions to obtain the first closed system, and enabling the distribution balance state to indicate that the target volatile substance reaches distribution balance in gas phase components of the to-be-tested sample and the closed container; and performing gas chromatography detection on the gas phase component of the first closed system to obtain a target peak area of a characteristic chromatographic peak of a target volatile substance in the gas phase component of the first closed system, so as to determine the residual quantity of the target volatile substance according to the target peak area and a standard curve of the peak area and the residual quantity of the target volatile substance under a preset condition. The residual quantity of the target volatile substances of the sample to be detected is obtained.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for detecting the residual amount of a target volatile substance. Background Art

[0002] Secondary batteries rely on active ions to be reciprocated between the positive and negative electrodes for charging and discharging. Secondary batteries represented by lithium-ion batteries have outstanding features such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy, secondary batteries have gradually spread from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.

[0003] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements on the performance of secondary batteries. In the process of battery preparation, harmful organic solvents, additives and other substances may remain in the raw material powder or battery components used to prepare the battery. When the residual amount of these substances is too high, it will not only deteriorate the cycle performance of the battery, shorten the cycle life of the battery, and reduce the reliability of the battery, but also cause the consistency of the battery to deteriorate, affecting the use of the battery.

[0004] Therefore, during the battery preparation process, it is necessary to monitor the harmful substances remaining in the raw material powders or battery components used to prepare the battery. Summary of the invention

[0005] In order to achieve the above-mentioned purpose, since the organic solvents, additives, etc. remaining in the battery materials have certain volatility, the present application provides a method for detecting the residual amount of target volatile substances, which can efficiently and accurately detect the residual amount of target volatile substances in the sample to improve the performance of the battery.

[0006] The embodiment of the first aspect of the present application provides a method for detecting the residual amount of a target volatile substance, comprising:

[0007] Providing a sample to be tested containing a target volatile substance;

[0008] Providing a first closed system, including placing a sample to be tested in a sealed container, allowing the target volatile substance to reach a distribution equilibrium state in the sealed container under preset conditions, to obtain a first closed system, wherein the distribution equilibrium state indicates that the target volatile substance reaches a distribution equilibrium in the sample to be tested and the gas phase component of the sealed container;

[0009] The gas phase component of the first closed system is subjected to gas chromatography detection to obtain a target peak area of ​​a characteristic chromatographic peak of a target volatile substance in the gas phase component of the first closed system, so as to obtain a target volatile substance residue of a sample to be tested according to the target peak area and a standard curve of peak area and target volatile substance residue under preset conditions.

[0010] Without intending to be limited by any theory or explanation, according to the method of the embodiment of the present application, a sample is taken from the electrode plate to be tested or the raw material powder of the battery to be tested to obtain a sample to be tested containing a target volatile substance, and the sample to be tested is placed in a closed container, so that the target volatile substance reaches a distribution equilibrium state in the closed container under preset conditions to obtain a first closed system. After the target volatile substance reaches a distribution equilibrium state, the distribution ratio of the gas phase component in the closed container and the target volatile substance in the sample to be tested is constant, and the gas phase component of the first closed system is subjected to gas chromatography detection, and the target volatile substance residue of the original sample to be tested can be calculated by the target peak area. According to the method of the embodiment of the present application, the target volatile substance residue of the sample to be tested is detected by utilizing the property that the distribution ratio of the target volatile substance in the solid phase component and the gas phase component is constant after the target volatile substance reaches a distribution equilibrium in a fixed closed container under fixed preset conditions. The embodiment of the present application does not need to extract the target volatile substance in the sample to be tested, nor does it need to fully evaporate the target volatile substance in the sample to be tested. It only takes a short time for the target volatile substance to reach a distribution equilibrium state in the closed container. As a result, not only the detection process of the target volatile substance residue is greatly simplified and the detection time of the target volatile substance residue is shortened, but also the risk of low detection accuracy caused by insufficient extraction of the target volatile substance can be greatly reduced. In some embodiments, the time consumed from placing the sample to be tested in a closed container to obtaining the target peak area is only 8min-30min. In addition, according to the method of the embodiment of the present application, the repeatability and accuracy of the detection are good. In some embodiments, the standard deviation (Cov, used to characterize the discrete degree of the value relative to the average value) of the detection can reach less than 5%, and the test accuracy deviation can fluctuate within the range of ±10%.

[0011] Therefore, the method of the embodiment of the present application is applied to the field of batteries, and can efficiently and accurately detect the residual amount of volatile substances in the raw material powder or battery components used to prepare the battery during the battery preparation process. The method of the embodiment of the present application has a high detection efficiency, which can make the monitoring of the residual amount of volatile substances compatible with the production rhythm of battery preparation, thereby improving the efficiency of battery production; the method of the embodiment of the present application also has a high accuracy, and can accurately monitor the residual amount of volatile substances in the raw material powder or battery components used to prepare the battery, thereby facilitating strict control of the quality of the battery and improving the cycle performance, consistency and reliability of the battery.

[0012] In any embodiment of the present application, before determining the target volatile substance residue of the sample to be tested, the method further comprises:

[0013] Providing a plurality of standard samples, each of which has the same specification parameters as the sample to be tested, the specification parameters including mass and / or size, and the plurality of standard samples having different, predetermined target volatile substance residual amounts;

[0014] Providing a second closed system, including placing a plurality of standard samples in sealed containers respectively, so that the target volatile substance reaches a distribution equilibrium state in the sealed containers under preset conditions, thereby obtaining a second closed system;

[0015] Performing gas chromatography detection on the gas phase component of the second closed system to obtain a calibrated peak area of ​​a characteristic chromatographic peak of the target volatile substance in the gas phase component of the second closed system;

[0016] Based on the calibration peak areas corresponding to the multiple standard samples and their predetermined target volatile substance residues, a standard curve of the peak area and the target volatile substance residue is obtained by fitting.

[0017] The above implementation can accurately and efficiently determine the standard curve of the peak area and the target volatile substance residue, thereby improving the efficiency and accuracy of the volatile substance residue detection.

[0018] In any embodiment of the present application, the sample to be tested is sampled from the electrode plate to be tested or the battery raw material powder to be tested, and multiple standard samples are provided, including:

[0019] Sampling from the electrode sheet to be tested or the battery raw material powder to be tested to obtain a plurality of test specimens having the same specification parameters as the sample to be tested;

[0020] The sample is baked to remove the target volatile substances in the sample to obtain a plurality of blank samples;

[0021] The target volatile substances are added to the plurality of blank samples respectively, so that the plurality of blank samples have different predetermined residual amounts of the target volatile substances, thereby obtaining a plurality of standard samples.

[0022] According to the above embodiment, a plurality of samples having the same specification parameters as the sample to be tested are sampled from the electrode plate to be tested or the battery raw material powder to be tested, and the target volatile substances in the samples are removed by baking to obtain a plurality of blank samples. The blank samples and the sample to be tested have the same material composition and specification parameters except for the target volatile substance residue. The standard sample is prepared using the blank sample, and the standard curve of the peak area and the target volatile substance residue obtained by fitting has a high accuracy, which is conducive to improving the accuracy of the detection.

[0023] In any embodiment of the present application, adding target volatile substances to a plurality of blank samples respectively comprises:

[0024] Provide target volatile substance standard solution;

[0025] According to the preset residual amount gradient, different volumes of target volatile substance standard solution are added to multiple blank samples respectively.

[0026] The above embodiment adds different volumes of target volatile substance standard solution to multiple blank samples according to a preset residual amount gradient, which is conducive to accurately preparing multiple standard samples with different and predetermined target volatile substance residual amounts, thereby helping to improve the accuracy of detection.

[0027] In any embodiment of the present application, the sealed container is a headspace bottle.

[0028] Optionally, the volume of the headspace bottle is 10 mL-20 mL.

[0029] The headspace bottle can be used in conjunction with gas chromatography. The headspace-gas chromatography technique has the advantages of high analytical efficiency, wide coverage, low detection limit, high accuracy, and simple operation, which is conducive to further improving the detection efficiency and accuracy. In addition, the headspace bottle has a suitable size, which is conducive to accommodating an appropriate amount of sample to be tested. As a result, the target volatile substance can reach a distribution equilibrium state in a shorter processing time, thereby taking into account both the efficiency and accuracy of the detection.

[0030] In some embodiments, allowing the target volatile substance to reach a distribution equilibrium state in a closed container under preset conditions comprises:

[0031] The sealed container is heated to a preset temperature and kept warm so that the target volatile substance reaches a distribution equilibrium state at the preset temperature.

[0032] In this way, the operational difficulty of the detection can be reduced, while taking into account both the accuracy and efficiency of the detection.

[0033] In any embodiment of the present application, the preset temperature is 80°C-200°C.

[0034] In any embodiment of the present application, the insulation time is 8 minutes to 20 minutes.

[0035] At the above preset temperature, the distribution coefficient K and the relative ratio β of the target volatile substance in the closed container have appropriate values, which is conducive to reducing the detection error and further improving the detection accuracy. In addition, at the above preset temperature, the target volatile substance can reach a distribution equilibrium state in a shorter time, thereby shortening the detection time and improving the detection efficiency.

[0036] In any embodiment of the present application, a sample to be tested is provided, including:

[0037] The electrode sheet to be tested is cut to obtain N test pieces with preset sizes as samples to be tested, wherein N is a positive integer; optionally, the mass of the sample to be tested is 0.3g-1.0g.

[0038] According to the method of the embodiment of the present application, the sample to be tested can be obtained by cutting the electrode piece to be tested, without the need for complicated pre-processing operations on the electrode piece to be tested, thereby significantly improving the detection efficiency of the residual volatile substance.

[0039] In any embodiment of the present application, the preset size is (2mm-8mm)*(10mm-70mm). When the preset size is within the above appropriate range, on the one hand, the closed container can be allowed to have a smaller size, thereby accelerating the distribution balance of the target volatile substance; on the other hand, the sample to be tested can have a larger surface area, thereby accelerating the migration of the target volatile substance to the gas phase component, so that the target volatile substance quickly reaches a distribution equilibrium state. Therefore, it is beneficial to further improve the detection efficiency of the residual amount of volatile substances.

[0040] In any embodiment of the present application, a sample to be tested is provided, including:

[0041] A preset mass of the sample to be tested is weighed from the battery raw material powder to be tested; optionally, the preset mass is 0.3g-0.5g.

[0042] According to the method of the embodiment of the present application, the raw material powder of the battery to be tested is directly weighed to obtain the sample to be tested, without the need for complicated pre-treatment operations on the raw material powder of the battery to be tested, thereby significantly improving the detection efficiency of the residual volatile substances.

[0043] In any embodiment of the present application, the target volatile substance includes one or more of a volatile organic solvent or a volatile plasticizer.

[0044] Optionally, the target volatile substance includes at least one of N-methylpyrrolidone, ethylene carbonate, ethanol, propylene glycol, or dimethyl sulfoxide.

[0045] When the residual amount of the above target volatile substances is high, the negative impact on the battery performance is greater. Selecting the above appropriate target volatile substances for monitoring is conducive to strictly controlling the quality of the battery and improving the performance of the battery.

[0046] In any embodiment of the present application, the target volatile substance residue in the sample to be tested is 50ppm-1500ppm. The method according to the embodiment of the present application has a suitable detection range and is suitable for detecting the target volatile substance residue in the sample to be tested, and thus can be applied to the detection of the residual amount of volatile substances commonly used in the battery preparation process, and has a high application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is the standard curve of the peak area and the residual amount of the target volatile substance in Example 1 of the present application.

[0048] Figure 2 This is the gas chromatogram of sample-1 in Example 1 of the present application.

[0049] Figure 3 It is the standard curve of the peak area and the residual amount of the target volatile substance of Comparative Example 1 of the present application.

[0050] Figure 4 It is the gas chromatogram of sample-1 in comparative example 1 of the present application. DETAILED DESCRIPTION

[0051] Hereinafter, the embodiment of the method for detecting the residual amount of a target volatile substance of the present application is specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0052] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0056] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0057] Herein, volatile substances may include volatile organic compounds (VOCs). Volatile organic compounds may refer to various organic compounds having a boiling point of 50° C. to 260° C. at normal pressure.

[0058] In this article, a closed system refers to a system that only exchanges energy but not matter with the external environment.

[0059] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements on the performance of secondary batteries.

[0060] The raw material powder used to prepare the battery may contain volatile organic solvents left over from the production process; in addition, in order to reduce the difficulty of battery processing, organic solvents or additives and other substances are also used in the battery preparation process, and these substances are usually volatile substances. The volatile organic solvents and other volatile substances must be removed by baking, but inevitably a small amount of volatile substances will remain in the battery components. When there are too many volatile substances remaining in the battery, the performance of the battery will inevitably be negatively affected.

[0061] As an example, there may be residual ethanol in the electrode active material powder during the preparation process. When the residual amount of ethanol is too high, it may be oxidized into acetic acid during the charge and discharge process of the battery, thereby corroding the electrode plate and deteriorating the cycle life of the battery. As another example, there may be residual N-methylpyrrolidone (NMP) in the electrode plate. NMP is a good solvent for the binder polyvinylidene fluoride (PVDF) and is one of the commonly used solvents for preparing positive electrode slurry. After the positive electrode slurry is applied to the surface of the positive electrode collector, solvents such as NMP can be removed by baking. However, it is inevitable that a small amount of NMP will remain in the positive electrode plate. The residual NMP will also migrate from the positive electrode plate to the negative electrode plate during the processing, storage or use of the battery. When the residual amount of NMP in the electrode plate is too high, it will not only deteriorate the internal resistance and interface performance of the battery, resulting in a shortened cycle life of the battery, but also cause the consistency of the battery to deteriorate, affecting the use of the battery. As another example, there may be residual volatile organic additives in the negative electrode plate. During the preparation of negative electrode slurry, volatile organic additives are sometimes added to improve processing performance. Similar to NMP, after baking, volatile organic additives will inevitably remain in the negative electrode sheet. When the residual amount of volatile organic additives in the negative electrode sheet is too high, the impedance of the negative electrode sheet will increase, the electrolyte will be difficult to infiltrate, and the high-temperature cycle performance of the battery will be reduced, causing the risk of interfacial lithium precipitation and reducing the reliability of the battery.

[0062] Therefore, during the battery preparation process, it is necessary to monitor the volatile substances remaining in the raw material powders or battery components used to prepare the battery.

[0063] In view of this, an embodiment of the present application provides a method for detecting the residual amount of a target volatile substance, which can efficiently and accurately detect the residual amount of a target volatile substance in a sample to improve the performance of a battery.

[0064] The embodiment of the present application provides a method for detecting the residual amount of a target volatile substance, comprising the following steps S110 to S130.

[0065] S110, providing a sample to be tested containing a target volatile substance.

[0066] In step S110, the target volatile substance may include a volatile substance whose residual amount has a certain influence on the performance of the battery, for example, including but not limited to a volatile organic solvent or an additive. The target volatile substance may include one volatile substance or may include multiple volatile substances.

[0067] In step S110, the sample to be tested can be sampled from the electrode plate to be tested or the raw material powder of the battery to be tested. The electrode plate to be tested may include the positive electrode plate to be tested and / or the negative electrode plate to be tested. The electrode plate to be tested may be an electrode plate obtained in any process before the battery injection process, for example, it may be an electrode plate after cold pressing, or it may be an electrode plate disassembled from an electrode assembly, and so on. The raw material powder of the battery to be tested may include but is not limited to powders for forming a positive electrode film layer and / or a negative electrode film layer, for example, it may include but is not limited to positive electrode active materials, negative electrode active materials, conductive agents, isolation membranes, and electrode current collectors (including but not limited to copper foil and aluminum foil).

[0068] S120, providing a first closed system, including placing the sample to be tested in a sealed container, allowing the target volatile substance to reach a distribution equilibrium state in the sealed container under preset conditions, to obtain a first closed system, wherein the distribution equilibrium state indicates that the target volatile substance reaches a distribution equilibrium in the sample to be tested and the gas phase component of the sealed container.

[0069] The distribution equilibrium may indicate that under constant temperature and pressure conditions, the solute reaches a distribution equilibrium in two mutually immiscible phases. In a closed container and under fixed preset conditions, when the target volatile substance reaches a distribution equilibrium in the sample to be tested (solid phase component) and the gas phase component of the closed container, the ratio of its concentration in the solid phase component to that in the gas phase component is constant; and in the embodiment of the present application, the volume of the solid phase component and the volume of the gas phase component are both constant, therefore, when the target volatile substance reaches a distribution equilibrium in the sample to be tested and the gas phase component of the closed container, its concentration in the solid phase component and the gas phase component is constant. In other words, in step S120, the distribution equilibrium state may also indicate that the concentration of the target volatile substance in the closed container and under preset conditions in the gas phase component of the sample to be tested and / or the closed container is constant. The above-mentioned preset conditions may include preset temperature conditions and / or preset pressure conditions. In some embodiments, the target volatile substance reaches a distribution equilibrium state in a closed container, which can mean that in a closed container of a fixed volume at a certain temperature, the target volatile substance reaches a distribution equilibrium in the gas phase components of the sample to be tested and the first closed system. The target volatile substance reaching a distribution equilibrium state in a closed container can be determined in a variety of ways. In some embodiments, the time for the target volatile substance in the sample system to be tested to reach a distribution equilibrium state under preset conditions can be determined by preliminary experiments, which is recorded as the equilibrium time; in the subsequent detection process, the closed container can be treated under preset conditions, and when the treatment time reaches the equilibrium time determined in advance by the experiment, it can be considered that the target volatile substance has reached a distribution equilibrium state. The sample system to be tested can represent a closed system formed by placing the same matrix as the sample to be tested in the closed container under the same preset conditions. "The same matrix as the sample to be tested" can refer to a sample with the same size, mass and basic composition as the sample to be tested. As an example, the sample to be tested is sampled from a positive electrode sheet with lithium iron phosphate as the positive electrode active material. The same matrix as the sample to be tested can be a sample with the same size and mass as the sample to be tested, which is sampled from a positive electrode sheet with lithium iron phosphate as the positive electrode active material. The preliminary experiment can set up multiple groups of parallel experiments, and the target volatile substance concentration of the gas phase component in the closed system of each group of parallel experiments is detected by gas chromatography at different times. When the target volatile substance concentration no longer changes, it is considered that the target volatile substance has reached a distribution equilibrium state in the closed system, and the time at this time is recorded as the equilibrium time. In some embodiments, after the processing time of the sample to be tested under preset conditions reaches the equilibrium time, it can continue to be processed under preset conditions for a certain time, for example, continue to process for 1min, 2min, 3min, etc. This can reduce the error of the detection and further improve the accuracy of the detection. In some embodiments, the volume of the closed container can be 10mL-20mL. In this way, the equilibrium time of the target volatile substance can be made within an appropriate range, thereby taking into account both the detection efficiency and the detection accuracy.

[0070] S130, performing gas chromatography detection on the gas phase component of the first closed system to obtain a target peak area of ​​a characteristic chromatographic peak of the target volatile substance in the gas phase component of the first closed system, so as to obtain a target volatile substance residue of the sample to be tested according to the target peak area and a standard curve of peak area and target volatile substance residue under preset conditions.

[0071] The distribution coefficient K and the relative ratio β of the target volatile substance in the solid phase component sample to be tested and the gas phase component can be defined by the following formula 1 and formula 2 respectively.

[0072] K=C s / C g Formula 1

[0073] β=V g / V s Formula 2

[0074] In formula 1, C s Indicates the residual amount of the target volatile substance in the sample to be tested, in ppm; C g represents the concentration of the target volatile substance in the gas phase component, and the unit can be ppm. In Formula 2, V g Indicates the volume of the gas phase component, the unit can be mL; V s Indicates the volume of the sample to be tested, the unit can be cm 3 .

[0075] The system in the sealed container hardly exchanges substances with the outside world, so the mass of the target volatile substance contained in the sample to be tested provided in step S110 is equal to the mass of the target volatile substance in the first closed system. Therefore, the sample to be tested provided in step S110 and the first closed system satisfy the following formula 3.

[0076] C s 0 V s =C s V s + C g V g Formula 3

[0077] In formula 3, C s 0 represents the target volatile substance residue of the sample to be tested provided in step S110, in units of ppm; C s 、V s , C g 、V g As respectively defined above.

[0078] Combining equations 1 to 3, we can get equation 4.

[0079] Cs 0 =C g / (K+β) Formula 4

[0080] Under fixed preset conditions, when the target volatile substance reaches a distribution equilibrium state in the closed container, the distribution coefficient K and the relative ratio β of the target volatile substance in the solid phase component to be tested and the gas phase component are constant. In step S130, the target peak area of ​​the characteristic chromatographic peak of the target volatile substance in the gas phase component of the first closed system is determined. The target peak area is proportional to the C g According to the target peak area and the standard curve of peak area and target volatile substance residue under preset conditions, C 0 S In some embodiments, the standard curve of peak area and target volatile substance residue can be a functional relationship between peak area and target volatile substance residue, for example, a linear relationship between peak area and target volatile substance residue.

[0081] During the battery preparation process, it is necessary to monitor the volatile substances remaining in the raw material powder or battery components for preparing the battery. In order to solve this technical problem, the relevant technology involves using ethyl acetate or other organic solvents to ultrasonically extract NMP in the positive electrode sheet, or using organic solvents such as ethanol to extract volatile additives in the negative electrode sheet, and after filtering, quantitatively detecting the NMP or volatile additives in the extract. However, both the positive electrode binder PVDF and the negative electrode binder styrene butadiene rubber (SBR) are difficult to dissolve in organic solvents in a short time, which makes it difficult for organic solvents to extract NMP or volatile additives from the electrode sheet. The detection method involved in the related technology, on the one hand, requires a long time for extraction, resulting in a long detection process and low detection efficiency, affecting the production efficiency of the battery; on the other hand, the organic solvent does not extract NMP or volatile additives sufficiently, which also leads to low detection accuracy. In addition, in the filtration process after ultrasonic extraction, the positive active material powder is extremely difficult to filter, and the operability is poor, which further reduces the efficiency of the detection.

[0082] Without intending to be limited by any theory or explanation, according to the method of the embodiment of the present application, a sample is taken from the electrode plate to be tested or the raw material powder of the battery to be tested to obtain a sample to be tested containing a target volatile substance, and the sample to be tested is placed in a closed container, so that the target volatile substance reaches a distribution equilibrium state in the closed container under preset conditions to obtain a first closed system. After the target volatile substance reaches a distribution equilibrium state, the distribution ratio of the gas phase component in the closed container and the target volatile substance in the sample to be tested is constant, and the gas phase component of the first closed system is subjected to gas chromatography detection, and the target volatile substance residue of the original sample to be tested can be calculated by the target peak area. According to the method of the embodiment of the present application, the target volatile substance residue of the sample to be tested is detected by utilizing the property that the distribution ratio of the target volatile substance in the solid phase component and the gas phase component is constant after the target volatile substance reaches a distribution equilibrium in a fixed closed container under fixed preset conditions. The embodiment of the present application does not need to extract the target volatile substance in the sample to be tested, nor does it need to fully evaporate the target volatile substance in the sample to be tested. It only takes a short time for the target volatile substance to reach a distribution equilibrium state in the closed container. As a result, not only the detection process of the target volatile substance residue is greatly simplified and the detection time of the target volatile substance residue is shortened, but also the risk of low detection accuracy caused by insufficient extraction of the target volatile substance can be greatly reduced. In some embodiments, the time consumed from placing the sample to be tested in a closed container to obtaining the target peak area is only 8min-30min. In addition, according to the method of the embodiment of the present application, the repeatability and accuracy of the detection are good. In some embodiments, the standard deviation (Cov, used to characterize the discrete degree of the value relative to the average value) of the detection can reach less than 5%, and the test accuracy deviation can fluctuate within the range of ±10%.

[0083] Therefore, the method of the embodiment of the present application is applied to the field of batteries, and can efficiently and accurately detect the residual amount of volatile substances in the raw material powder or battery components used to prepare the battery during the battery preparation process. The method of the embodiment of the present application has a high detection efficiency, which can make the monitoring of the residual amount of volatile substances compatible with the production rhythm of battery preparation, thereby improving the efficiency of battery production; the method of the embodiment of the present application also has a high accuracy, and can accurately monitor the residual amount of volatile substances in the raw material powder or battery components used to prepare the battery, thereby facilitating strict control of the quality of the battery and improving the cycle performance, consistency and reliability of the battery.

[0084] In some embodiments, before determining the target volatile substance residual amount of the electrode plate to be tested or the battery raw material powder to be tested, the method may further include:

[0085] A plurality of standard samples are provided, each of which has the same specification parameters as the sample to be tested, the specification parameters including mass and / or size, and the plurality of standard samples have different, predetermined target volatile substance residual amounts.

[0086] A second closed system is provided, including placing a plurality of standard samples in sealed containers respectively, so that the target volatile substance reaches a distribution equilibrium state in the sealed containers under preset conditions to obtain the second closed system.

[0087] The gas phase component of the second closed system is subjected to gas chromatography detection to obtain the calibrated peak area of ​​the characteristic chromatographic peak of the target volatile substance in the gas phase component of the second closed system.

[0088] Based on the calibration peak areas corresponding to the multiple standard samples and their predetermined target volatile substance residues, a standard curve of the peak area and the target volatile substance residue is obtained by fitting.

[0089] In the above embodiment, each standard sample has the same specification parameters as the sample to be tested, which can be expressed as follows: when the sample to be tested is sampled from the electrode plate to be tested, each standard sample has the same size and mass as the sample to be tested; when the sample to be tested is sampled from the battery raw material powder to be tested, the mass of each standard sample is equal to the mass of the sample to be tested.

[0090] In the above embodiment, a plurality of standard samples with known target volatile substance residues are placed in a sealed container, so that the target volatile substance reaches a distribution equilibrium state in the sealed container under preset conditions to obtain a second closed system. When the samples are placed in the same sealed container and under the same preset conditions, after the target volatile substance contained therein reaches a distribution equilibrium state, the distribution coefficient K and the relative ratio β are constant. In other words, the distribution coefficient K of the target volatile substance in the second closed system is equal to the distribution coefficient K of the target volatile substance in the first closed system; the relative ratio β of the target volatile substance in the second closed system is equal to the relative ratio β of the target volatile substance in the first closed system. Therefore, C can be determined by the target volatile substance residues corresponding to the plurality of standard samples and the concentration of the target volatile substance in the gas phase component of the second closed system. g With C 0 S In gas chromatography, C g It can be determined by the calibration peak area, so based on the calibration peak areas corresponding to the multiple standard samples and their predetermined target volatile substance residues, a standard curve of the peak area and the target volatile substance residue can be directly fitted. In some embodiments, the correlation coefficient R between the peak area and the target volatile substance residue can reach 0.995 or above.

[0091] The above implementation can accurately and efficiently determine the standard curve of the peak area and the target volatile substance residue, thereby improving the efficiency and accuracy of the volatile substance residue detection.

[0092] In some embodiments, the sample to be tested is sampled from the electrode plate to be tested or the battery raw material powder to be tested, and multiple standard samples are provided, which may specifically include:

[0093] Sampling is performed from the electrode plate to be tested or the battery raw material powder to be tested to obtain a plurality of test specimens having the same specification parameters as the sample to be tested.

[0094] The samples were baked to remove target volatile substances in the samples and obtain multiple blank samples.

[0095] The target volatile substances are added to the plurality of blank samples respectively, so that the plurality of blank samples have different predetermined residual amounts of the target volatile substances, thereby obtaining a plurality of standard samples.

[0096] In the above embodiment, in the process of baking the sample to remove the target volatile substance in the sample and obtaining multiple blank samples, the target volatile substance in the sample can be monitored to determine whether the target volatile substance in the sample is completely removed. As an example, the target volatile substance content in the sample can be monitored by a gas chromatograph to determine whether the target volatile substance in the sample is completely removed. When the mass and size of the sample are the same, the time required for the target volatile substance to be completely removed is basically the same. For example, a sample with a mass of 0.3-0.5g and a size of (2mm-8mm)*(10mm-70mm) is baked at 80°C, and the time for the ethanol contained therein to be completely removed is about 12h. Therefore, the baking time required for the target volatile substance to be completely removed at the baking temperature can also be pre-calibrated. When the sample is baked at the baking temperature to the pre-calibrated baking time, it can be considered that the target volatile substance in the sample is completely removed.

[0097] According to the above embodiment, a plurality of samples having the same specification parameters as the sample to be tested are sampled from the electrode plate to be tested or the battery raw material powder to be tested, and the target volatile substances in the samples are removed by baking to obtain a plurality of blank samples. The blank samples and the sample to be tested have the same material composition and specification parameters except for the target volatile substance residue. The standard sample is prepared using the blank sample, and the standard curve of the peak area and the target volatile substance residue obtained by fitting has a high accuracy, which is conducive to improving the accuracy of the detection.

[0098] In some embodiments, adding the target volatile substance to the plurality of blank samples respectively may specifically include: providing a target volatile substance standard solution. According to a preset residual amount gradient, adding different volumes of the target volatile substance standard solution to the plurality of blank samples respectively.

[0099] In the above-mentioned embodiment, the target volatile substance standard solution can be a liquid target volatile substance, or a target volatile substance solution. For example, when the target volatile substance is NMP, the target volatile substance can be a pure liquid NMP; when the target volatile substance is propylene glycol, the target volatile substance can be an aqueous solution of propylene glycol. When the target volatile substance includes multiple substances, the target volatile substance standard solution can be provided separately and added to the blank sample, or a mixed standard solution containing multiple target volatile substances can be provided and added to the blank sample. When the target volatile substance includes multiple substances, the mass proportion of each target volatile substance can be adjusted according to the actual detection range, which is not limited here. The preset residual amount gradient can be selected according to the detection range. As an example, the target volatile substance standard solution can be added to multiple blank samples in a residual amount range of 50ppm-1500ppm with a gradient of 100ppm, 200ppm or 300ppm. In some embodiments, multiple blank samples can be placed in headspace vials respectively, and a 1 μL syringe can be used to measure 0.2 μL, 0.4 μL, 0.6 μL, 0.8 μL, and 1 μL of the target volatile substance standard solution, respectively, and soak them into the blank samples in the headspace vials, which are then sealed immediately to reduce the volatilization of the target volatile substance into the air outside the sealed container, thereby improving the accuracy of the detection.

[0100] The above embodiment adds different volumes of target volatile substance standard solution to multiple blank samples according to a preset residual amount gradient, which is conducive to accurately preparing multiple standard samples with different and predetermined target volatile substance residual amounts, thereby helping to improve the accuracy of detection.

[0101] In some embodiments, the closed container can be a headspace vial.

[0102] Optionally, the volume of the headspace bottle can be 10 mL-20 mL.

[0103] The headspace bottle can be used in conjunction with gas chromatography. The headspace-gas chromatography technique has the advantages of high analytical efficiency, wide coverage, low detection limit, high accuracy, and simple operation, which is conducive to further improving the detection efficiency and accuracy. In addition, the headspace bottle has a suitable size, which is conducive to accommodating an appropriate amount of sample to be tested. As a result, the target volatile substance can reach a distribution equilibrium state in a shorter processing time, thereby taking into account both the efficiency and accuracy of the detection.

[0104] In some embodiments, the gas phase components in the sealed container can be extracted by a syringe and injected into a gas chromatograph to perform gas chromatography detection on the gas phase components in the first closed system.

[0105] In some embodiments, the sealed container is a headspace bottle, and the gas in the bottle can be automatically extracted by a headspace device and injected into a gas chromatograph.

[0106] In some embodiments, allowing the target volatile substance to reach a distribution equilibrium state in a closed container under preset conditions may specifically include:

[0107] The sealed container is heated to a preset temperature and kept warm so that the target volatile substance reaches a distribution equilibrium state at the preset temperature.

[0108] As mentioned above, when the sample is placed in the same closed container and under the same preset conditions, after the target volatile substance contained therein reaches a distribution equilibrium state, the distribution coefficient K and the ratio β are constant. Since the volume of the closed container is fixed, without applying additional pressure, after the closed container is heated to a preset temperature, the pressure inside the closed container is theoretically also a constant. In other words, when detecting the residual amount of the target volatile substance, there is no need to monitor the pressure of the closed system. It is only necessary to adjust the temperature of the closed system to a preset temperature and keep it warm for a sufficient period of time so that the target volatile substance can reach a predetermined distribution equilibrium state. In this way, the operational difficulty of the detection can be reduced, while taking into account both the accuracy and efficiency of the detection.

[0109] In some embodiments, the preset temperature may be 80°C-200°C, for example, 80°C, 90°C, 100°C, 120°C, 150°C, 180°C, 200°C, or a fixed point value in the range of any two of the above values.

[0110] In some embodiments, the insulation time can be 8 min-20 min, for example, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, or a range consisting of any two of the above values.

[0111] As an example, providing a first closed system may specifically include: placing the sample to be tested in a closed container, keeping it at a preset temperature for 8 minutes to 20 minutes, so that the target volatile substance reaches a distribution equilibrium state in the closed container, and obtaining the first closed system.

[0112] As an example, providing a second closed system may specifically include: placing a plurality of standard samples in closed containers, heating them to a preset temperature, and keeping them warm at the preset temperature, so that the target volatile substance reaches a distribution equilibrium state in the closed container to obtain a second closed system.

[0113] At the above preset temperature, the distribution coefficient K and the relative ratio β of the target volatile substance in the closed container have appropriate values, which is conducive to reducing the detection error and further improving the detection accuracy. In addition, at the above preset temperature, the target volatile substance can reach a distribution equilibrium state in a shorter time, thereby shortening the detection time and improving the detection efficiency.

[0114] In some embodiments, the sample to be tested is sampled from the electrode plate to be tested, and the sample to be tested includes a current collector and an electrode film layer located on at least one side of the current collector.

[0115] Providing the sample to be tested may specifically include: cutting the electrode plate to be tested to obtain N test pieces with preset sizes as the sample to be tested, wherein N is a positive integer.

[0116] Cutting the electrode sheet to be tested may include cutting the electrode sheet to be tested along the thickness direction. The cutting position may be any position of the electrode sheet to be tested. In one embodiment, the electrode sheet to be tested may be an electrode sheet that has been dried and cold pressed. After drying and cold pressing, the electrode sheet is usually rolled up for standby use. Compared with other parts of the electrode sheet, the residual amount of the target volatile substance in the inner roll of the electrode sheet may be higher, and the middle and lower part of the inner roll of the electrode sheet may be selected for cutting to obtain a sample to be tested. This is conducive to more strictly controlling the residual amount of volatile substances in the electrode sheet and improving the cycle performance, consistency and reliability of the battery.

[0117] According to the method of the embodiment of the present application, the sample to be tested can be obtained by cutting the electrode piece to be tested, without the need for complicated pre-processing operations on the electrode piece to be tested, thereby significantly improving the detection efficiency of the residual volatile substance.

[0118] In some embodiments, the mass of the sample to be tested can be 0.3g-0.5g, for example, it can be 0.3g, 0.32g, 0.35g, 0.38g, 0.4g, 0.42g, 0.45g, 0.48g, 0.5g, or a range consisting of any two of the above values.

[0119] The mass of the sample to be tested can be adjusted according to the actual situation. As an example, the types of target volatile substances are different, and their usage in the battery preparation process is different, so the residual amount in the sample to be tested may be different; according to the pre-estimated residual amount interval, the sample to be tested of suitable mass can be selected. For example, NMP is often used in positive electrode slurry, and the usage is usually large, and the residual amount in the positive electrode sheet is high, and the mass of the sample to be tested can be 0.3±0.02g; the usage of volatile additives in electrode sheets is usually small, and the residual amount in the electrode sheet is low, and the mass of the sample to be tested can be 0.5±0.02g. As another example, the types of target volatile substances are different, and their volatility is different. The difficulty of being baked and removed during the battery preparation process is also different, so the residual amount in the sample to be tested may be different; according to the pre-estimated residual amount interval, the sample to be tested of suitable mass can be selected. For example, ethanol has a higher volatility, a lower residual rate in the sample to be tested, a smaller residual amount, and the mass of the sample to be tested can be 0.5±0.02g; propylene glycol has a weaker volatility than ethanol, a higher residual rate in the sample to be tested, a smaller residual amount, and the mass of the sample to be tested can be 0.3±0.02g.

[0120] Without intending to be bound by any theory or explanation, when the mass of the sample to be tested is within the above-mentioned appropriate range, the sample to be tested may contain an appropriate amount of the target volatile substance. Therefore, when the target volatile substance reaches a distribution equilibrium state, the gas phase component of the first closed system may have an appropriate target volatile substance content. Thus, the content of the target volatile substance in the gas phase component of the first closed system can be matched with the detection range of the gas chromatography, thereby improving the accuracy of the detection of the residual amount of the volatile substance.

[0121] In some embodiments, the preset size can be (2mm-8mm)*(10mm-70mm). For example, the width of the specimen can be 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, or a range consisting of any two of the above values; the length of the specimen can be 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, or a range consisting of any two of the above values. As an example, the preset size can be 2mm*10mm, 2mm*30mm, 2mm*50mm, 2mm*70mm, 3mm*20mm, 3mm*40mm, 3mm*60mm, 5mm*10mm, 5mm*30mm, 5mm*50mm, 5mm*70mm, 8mm*20mm, 8mm*40mm, 8mm*60mm, and the like.

[0122] Without intending to be limited by any theory or explanation, when the preset size is within the above-mentioned suitable range, on the one hand, the closed container can be allowed to have a smaller size, thereby accelerating the distribution equilibrium of the target volatile substance; on the other hand, the sample to be tested can have a larger surface area, thereby accelerating the migration of the target volatile substance to the gas phase component, so that the target volatile substance quickly reaches a distribution equilibrium state. Therefore, it is beneficial to further improve the detection efficiency of the residual amount of volatile substances.

[0123] In some embodiments, the sample to be tested is sampled from the raw material powder of the battery to be tested. Providing the sample to be tested may specifically include: weighing a preset mass of the sample to be tested from the raw material powder of the battery to be tested.

[0124] In some embodiments, the raw material powder of the battery to be tested may be stirred evenly first, and then a preset mass of the sample to be tested may be weighed.

[0125] According to the method of the embodiment of the present application, the raw material powder of the battery to be tested is directly weighed to obtain the sample to be tested, without the need for complicated pre-treatment operations on the raw material powder of the battery to be tested, thereby significantly improving the detection efficiency of the residual volatile substances.

[0126] In some embodiments, the preset mass can be 0.3g-1.0g, for example, 0.3g, 0.32g, 0.35g, 0.38g, 0.4g, 0.42g, 0.45g, 0.48g, 0.5g, 1.0g, or a range consisting of any two of the above values.

[0127] In the above implementation, the preset mass can be adjusted according to the actual situation. For details, please refer to the method for adjusting the mass of the sample to be tested when sampling from the electrode plate to be tested, which will not be described in detail here.

[0128] Without intending to be limited by any theory or explanation, when the sample to be tested of the preset mass is weighed from the battery raw material powder to be tested, the sample to be tested may contain an appropriate amount of the target volatile substance. Therefore, when the target volatile substance reaches a distribution equilibrium state, the gas phase component of the first closed system may have an appropriate target volatile substance content. Thus, the content of the target volatile substance in the gas phase component of the first closed system can be matched with the detection range of the gas chromatograph, thereby improving the accuracy of the detection of the residual amount of volatile substances.

[0129] In some embodiments, the target volatile material may include one or more of a volatile organic solvent or a volatile plasticizer.

[0130] Alternatively, in some embodiments, the target volatile substance may include at least one of N-methylpyrrolidone, ethylene carbonate, ethanol, propylene glycol, or dimethyl sulfoxide.

[0131] When the residual amount of the above target volatile substances is high, the negative impact on the battery performance is greater. Selecting the above appropriate target volatile substances for monitoring is conducive to strictly controlling the quality of the battery and improving the performance of the battery.

[0132] In some embodiments, the target volatile substance residue in the sample to be tested may be 50 ppm-1500 ppm.

[0133] The method according to the embodiment of the present application has a suitable detection range and is suitable for detecting the residual amount of target volatile substances in the above-mentioned sample to be tested. Therefore, it can be applied to the residual amount detection of volatile substances commonly used in the battery preparation process, and has a high application value.

[0134] It should be noted that in the method of the embodiment of the present application, gas chromatography detection can be achieved by equipment and methods known in the art. As an example, a gas chromatography device, such as Agilent 7890B, can be used to measure the chromatogram of the gas phase components using nitrogen or helium as the carrier gas, and the test parameters are as follows: the carrier gas flow rate is 1.0mL / min-1.5mL / min, the injection port temperature is 250°C, the split ratio is 20:1, the temperature program is to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and a hydrogen flame ionization detector (FID) is used, and the detector temperature is 300°C.

[0135] The method of the embodiment of the present application can detect the residual amount of the target volatile substance in the range of 50ppm-1500ppm, the repeatability and reproducibility (GRR%) of the measurement system can reach less than 10%, the resolution of the ndc (Number of Distinct Categories) measurement system can reach more than 5, Cov can reach less than 5%, and the detection efficiency can reach 8min / ea-30min / ea.

[0136] Example

[0137] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0138] Example 1

[0139] (1) Set up a standard curve of peak area and target volatile substance residue

[0140] Cut the dried and cold-pressed positive electrode sheets to obtain 5 samples, each sample weighing 0.3±0.02g, including the positive electrode current collector and the positive electrode film layer. Cut each sample into a specimen with a size of 5mm*30mm, and obtain 5 groups of samples containing multiple specimens.

[0141] Each group of samples was baked at 120°C under vacuum for 24 h to obtain 5 groups of blank samples.

[0142] Take out the blank samples, and transfer each group of blank samples to a headspace bottle with a volume of 20 mL within 1 min; use a 1 μL syringe to measure 0.06 μL, 0.12 μL, 0.24 μL, 0.40 μL, and 0.50 μL of the target volatile substance NMP, respectively, and infiltrate them into each group of blank samples, respectively, to obtain standard samples, which are immediately sealed and recorded as standard samples-1 to standard samples-5.

[0143] The liquid volume and the theoretical residual amount of the target volatile substances in the standard sample are shown in the following table.

[0144] serial number Liquid volume / μL Theoretical residual amount / ppm Standard sample-1 0.06 206 Standard sample-2 0.12 411 Standard sample-3 0.24 822 Standard sample-4 0.40 1371 Standard-5 0.50 1713

[0145] The headspace bottle was placed in the headspace device, heated and kept at 180°C for 8 min to allow NMP to reach a distribution equilibrium state in the headspace bottle.

[0146] The gas phase components in the headspace bottles of each group of standard samples were extracted respectively, injected into the gas chromatograph, and detected by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 20:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used, and the detector temperature was 300°C. The calibrated peak area of ​​the NMP characteristic chromatographic peak in the gas chromatogram corresponding to each group of standard samples was determined respectively.

[0147] Based on the calibration peak areas and theoretical NMP residues corresponding to the five groups of standard samples, the following was obtained: Figure 1 Shown is a standard curve of peak area versus residual amount of target volatile substances.

[0148] (2) Detection of target volatile substance residues in the sample to be tested

[0149] The positive electrode sheets after drying and cold pressing were cut to obtain 10 samples, each sample weighing 0.3±0.02g, and the sample included a positive electrode current collector and a positive electrode film layer. Each sample was cut into a specimen with a size of 5mm*30mm, and 10 groups of samples containing multiple specimens were obtained.

[0150] Each group of samples was baked at 120°C under vacuum for 24 hours to obtain 10 groups of blank samples. The blank samples were taken out and each group of blank samples was transferred to a headspace bottle with a volume of 20 mL and sealed within 1 minute; 0.10 μL, 0.18 μL (6 parallel samples), 0.26 μL, 0.34 μL, and 0.42 μL of the target volatile substance NMP were measured with a 1 μL syringe, respectively, and infiltrated into each group of blank samples, respectively, to obtain samples-1 to sample-5 to be tested, and immediately sealed. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0151] serial number Liquid volume / μL Theoretical residual amount / ppm Sample-1 0.10 343 Sample-2-1 0.18 617 Sample-2-2 0.18 617 Sample-2-3 0.18 617 Sample-2-4 0.18 617 Sample-2-5 0.18 617 Sample-2-6 0.18 617 Sample-3 0.26 891 Sample-4 0.34 1165 Sample-5 0.42 1439

[0152] The headspace bottle was placed in the headspace device, heated and kept at 180°C for 8 min to allow NMP to reach a distribution equilibrium state in the headspace bottle.

[0153] The gas components in the headspace bottles of each group of samples were extracted respectively, injected into the gas chromatograph, and detected by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 20:1, and the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min. The FID detector was used, and the detector temperature was 300°C. The peak area of ​​the NMP characteristic chromatographic peak in the gas chromatogram corresponding to each group of samples was determined as the target peak area. As an example, the gas chromatogram of sample-1 is as follows Figure 2 As shown, Figure 2 Through analysis, it can be determined that the chromatographic peak at retention time t=4.1 min is the characteristic chromatographic peak of NMP. Through further analysis, the peak area of ​​the characteristic chromatographic peak of NMP corresponding to sample-1 can be determined.

[0154] The NMP residual test results of each group of samples were calculated based on the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residual amount. Among them, the NMP residual test result of sample 2 is the average value of the NMP residual test results of samples-2-1 to sample-2-6. The test results are shown in Table 1 below.

[0155] Table 1 - Example 1 test results

[0156] Table 1-1

[0157]

[0158] Table 1-2

[0159]

[0160] The detection method was evaluated based on the NMP residue test results of each group of samples and the NMP theoretical residue of each group of samples. The repeatability Cov was evaluated by the NMP residue test results of samples-2-1 to sample-2-6.

[0161] Evaluation results: accuracy deviation within ±6%, repeatability Cov<1%, test time about 13min / ea.

[0162] Comparative Example 1

[0163] (1) Set up a standard curve of peak area and target volatile substance residue

[0164] Weigh 0.05g of NMP and add it to 0.95g of N,N-dimethylformamide (DMF) to obtain a DMF standard mother solution with an NMP content of 0.5%; weigh 5 portions of DMF, each weighing 5g, and add 0.05g, 0.1g, 0.2g, 0.3g, and 0.4g of the standard mother solution to 5 portions of DMF, respectively. Seal the solution immediately and shake it evenly to obtain 5 groups of gradient standard solution sample-1 to standard solution sample-5. The theoretical residual amounts of NMP in the solutions are 50ppm, 98ppm, 192ppm, 283ppm, and 370ppm, respectively.

[0165] Take about 1mL of standard solution samples respectively, put them into 1.5mL gas chromatography liquid injection vials, and inject the liquid directly into the gas chromatograph by automatic injection, and perform hydrogen flame ionization detector (FID) detection. The test parameters are as follows: the carrier gas is nitrogen, the carrier gas flow rate is 1.5mL / min, the injection port temperature is 250℃, the split ratio is 5:1, the temperature program increases the column oven temperature from 40℃ to 220℃ at a heating rate of 20℃ / min, and the FID detector is used, and the detector temperature is 300℃. Determine the calibrated peak area of ​​the NMP characteristic chromatographic peak in the gas chromatogram corresponding to each group of standard solution samples.

[0166] Based on the calibration peak areas and theoretical NMP residues corresponding to the five groups of standard solution samples, the following was obtained: Figure 3 Shown is a standard curve of peak area versus residual amount of target volatile substances.

[0167] (2) Detection of target volatile substance residues in the sample to be tested

[0168] The positive electrode sheets after drying and cold pressing were cut to obtain 10 samples, each with a mass of 1.0±0.02 g. The samples included a positive electrode current collector and a positive electrode film layer.

[0169] Each group of samples was baked at 120°C under vacuum for 24 h to obtain 10 groups of blank samples.

[0170] The blank sample was taken out, cut into pieces of about 5mm*5mm, and placed in a 15mL vial. A 1μl syringe was used to measure 0.30μl, 0.60μl (6 parallel samples), 0.90μl, 1.1μl, and 1.4μl of the target volatile substance NMP, respectively, and infiltrated into each group of blank sample electrodes, respectively, to obtain samples-1 to sample-5 to be tested, and immediately sealed after adding 5g of DMF solution. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0171] serial number Liquid volume / μL Theoretical residual amount / ppm Sample-1 0.30 308 Sample-2-1 0.60 617 Sample-2-2 0.60 617 Sample-2-3 0.60 617 Sample-2-4 0.60 617 Sample-2-5 0.60 617 Sample-2-6 0.60 617 Sample-3 0.90 925 Sample-4 1.10 1131 Sample-5 1.40 1439

[0172] Place the vial in an ultrasonic machine and continue ultrasonicating at a frequency of >6 h until all the active materials on the electrode are observed to fall off the current collector.

[0173] Use a disposable syringe to take 1 mL of liquid from each vial, filter out the clear liquid with a 0.45 μm filter, and put it into a gas chromatography liquid injection bottle.

[0174] The liquid was directly injected into the gas chromatograph automatically for detection by flame ionization detector (FID). The test parameters were as follows: nitrogen as carrier gas, 1.5 ml / min carrier gas flow rate, 250°C injection port temperature, split ratio 5:1, and the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min. The FID detector was used, and the detector temperature was 300°C. The peak area of ​​the NMP characteristic chromatographic peak in the gas chromatogram corresponding to each group of samples was determined as the target peak area. As an example, the gas chromatogram of sample-1 is as follows Figure 4 As shown, Figure 4 Through analysis, it can be determined that the chromatographic peak at retention time t=5.3 min is the characteristic chromatographic peak of NMP. Through further analysis, the peak area of ​​the characteristic chromatographic peak of NMP corresponding to sample-1 can be determined.

[0175] The NMP residual test results of each group of samples were calculated based on the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residual amount. Among them, the NMP residual test result of sample 2 is the average value of the NMP residual test results of samples-2-1 to sample-2-6. The test results are shown in Table 2 below.

[0176] Table 2 - Comparative Example 1 Test Results

[0177] Table 2-1

[0178]

[0179] Table 2-2

[0180]

[0181] The detection method was evaluated based on the NMP residue test results of each group of samples and the NMP theoretical residue of each group of samples. The repeatability Cov was evaluated by the NMP residue test results of samples-2-1 to sample-2-6.

[0182] Evaluation results: accuracy deviation is within ±6%, repeatability Cov>1%, a standard curve of peak area and target volatile substance residue must be established for each test, and the test time is >7h / ea.

[0183] Example 2

[0184] (1) Set up a standard curve of peak area and target volatile substance residue

[0185] Cut the dried and cold-pressed negative electrode sheets to obtain 5 samples, each sample weighing 0.5±0.02g, including the negative electrode current collector and the negative electrode film layer. Cut each sample into a specimen with a size of 5mm*30mm, and obtain 5 groups of samples containing multiple specimens.

[0186] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 5 groups of blank samples.

[0187] Take out the blank samples and transfer each group of blank samples to a headspace bottle with a volume of 20 mL within 1 min; use a 1 μL syringe to measure 0.06 μL, 0.12 μL, 0.24 μL, 0.48 μL, and 0.70 μL of the target volatile substance solution (50% propylene glycol aqueous solution), respectively, and soak them into each group of blank samples, respectively, to obtain standard samples, which are immediately sealed and recorded as standard sample-1 to standard sample-5.

[0188] serial number Liquid volume / μL Theoretical residual amount / ppm Standard sample-1 0.06 62 Standard sample-2 0.12 123 Standard sample-3 0.24 247 Standard sample-4 0.48 493 Standard-5 0.70 720

[0189] The headspace bottle was placed in a headspace device, heated and kept at 180°C for 8 minutes to allow propylene glycol to reach a distribution equilibrium state in the headspace bottle.

[0190] The gas phase components in the headspace bottles of each group of standard samples were extracted respectively, injected into the gas chromatograph, and detected by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 20:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used with a detector temperature of 300°C. The calibrated peak area of ​​the propylene glycol characteristic chromatographic peak in the gas chromatogram corresponding to each group of standard samples was determined respectively.

[0191] Based on the calibrated peak areas corresponding to the five groups of standard samples and their theoretical residual amounts of propylene glycol, a standard curve of peak area and residual amount of target volatile substances was obtained by fitting.

[0192] (2) Detection of target volatile substance residues in the sample to be tested

[0193] The negative electrode sheets after drying and cold pressing were cut to obtain 10 samples, each sample weighing 0.5±0.02g, and the sample included the negative electrode current collector and the negative electrode film layer. Each sample was cut into a specimen with a size of 5mm*30mm, and 10 groups of samples containing multiple specimens were obtained.

[0194] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 10 groups of blank samples.

[0195] Take out the blank samples, and transfer each group of blank samples to a 20mL headspace bottle within 1 minute and seal it; use a 1μl syringe to measure 0.08μl, 0.16μl (take 6 parallel samples), 0.30μl, 0.40μl, and 0.50μl of the target volatile substance solution (50% propylene glycol aqueous solution), respectively, and infiltrate it into each group of blank samples to obtain samples-1 to sample-5 to be tested, and immediately seal it. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0196] serial number Liquid volume / μL Theoretical residual amount / ppm Sample-1 0.08 82 Sample-2-1 0.16 164 Sample-2-2 0.16 164 Sample-2-3 0.16 164 Sample-2-4 0.16 164 Sample-2-5 0.16 164 Sample-2-6 0.16 164 Sample-3 0.30 308 Sample-4 0.40 411 Sample-5 0.50 514

[0197] The headspace bottle was placed in a headspace device, heated and kept at 180°C for 8 minutes to allow propylene glycol to reach a distribution equilibrium state in the headspace bottle.

[0198] The gas phase components in the headspace bottles of each group of samples were extracted and injected into the gas chromatograph for detection by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 20:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used with a detector temperature of 300°C. The peak area of ​​the propylene glycol characteristic chromatographic peak in the gas chromatogram corresponding to each group of samples was determined as the target peak area.

[0199] The propylene glycol residue test results of each group of samples were calculated based on the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residue. Among them, the propylene glycol residue test result of sample 2 is the average value of the propylene glycol residue test results of samples-2-1 to sample-2-6. The test results are shown in Table 3 below.

[0200] Table 3 - Test results of Example 2

[0201] Table 3-1

[0202]

[0203] Table 3-2

[0204]

[0205] The detection method was evaluated based on the test results of propylene glycol residue in each group of samples and the theoretical propylene glycol residue in each group of samples. The repeatability Cov was evaluated by the test results of propylene glycol residue in samples-2-1 to sample-2-6.

[0206] Evaluation results: accuracy deviation within ±10%, repeatability Cov <3%, test time about 13min / ea.

[0207] Comparative Example 2

[0208] (1) Set up a standard curve of peak area and target volatile substance residue

[0209] Weigh 0.05 g of the target volatile substance propylene glycol, add it to 0.95 g of ethanol to obtain an ethanol standard mother solution with a propylene glycol content of 0.5%; weigh 5 parts of ethanol, each with a mass of 5 g, and add 0.01 g, 0.05 g, 0.1 g, 0.15 g, and 0.2 g of the standard mother solution to the 5 parts of ethanol, respectively. Seal immediately, and shake evenly to obtain 5 groups of gradient standard solution sample-1 to standard solution sample-5, and the residual amounts of propylene glycol in the solutions are 10 ppm, 50 ppm, 98 ppm, 146 ppm, and 192 ppm, respectively.

[0210] Take about 1mL of standard solution sample respectively, put it into 1.5mL gas chromatography liquid injection vial, inject the liquid directly into gas chromatograph by automatic injection, and detect it with hydrogen flame ionization detector (FID). Test parameters: carrier gas is nitrogen, carrier gas flow rate is 1.5mL / min, injection port temperature is 250℃, split ratio is 5:1, temperature program increases the column oven temperature from 40℃ to 220℃ at a heating rate of 20℃ / min, and FID detector is used, and the detector temperature is 300℃. Determine the calibrated peak area of ​​the propylene glycol characteristic chromatographic peak in the gas chromatogram corresponding to each group of standard samples.

[0211] Based on the calibrated peak areas corresponding to the five groups of standard samples and their theoretical residual amounts of propylene glycol, a standard curve of peak area and residual amount of target volatile substances was obtained by fitting.

[0212] (2) Detection of the residual amount of target volatile substances in the sample to be tested

[0213] The negative electrode sheet after drying and cold pressing was cut to obtain 10 samples, each sample had a mass of 1.0±0.02g, and the sample included a negative electrode current collector and a negative electrode film layer.

[0214] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 10 groups of blank samples.

[0215] The blank sample was taken out, cut into pieces of about 5mm*5mm, and placed in a 15mL vial. 0.16μl, 0.32μl (6 parallel samples), 0.60μl, 0.80μl, and 1.00μl of the target volatile substance solution (50% propylene glycol aqueous solution) were measured with a 1μl syringe, respectively, and infiltrated into each group of blank samples, respectively, to obtain samples-1 to sample-5 to be tested, and immediately sealed after adding 5g of ethanol solution. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0216] serial number Liquid volume / μL Theoretical residual amount / ppm Sample-1 0.16 82 Sample-2-1 0.32 164 Sample-2-2 0.32 164 Sample-2-3 0.32 164 Sample-2-4 0.32 164 Sample-2-5 0.32 164 Sample-2-6 0.32 164 Sample-3 0.60 308 Sample-4 0.80 411 Sample-5 1.00 514

[0217] Place the vial in an ultrasonic machine and continue ultrasonicating at a frequency of >6 h until all the active materials on the electrode are observed to fall off the current collector.

[0218] Use a disposable syringe to take 1 mL of liquid from each vial, filter out the clear liquid with a 0.45 μm filter, and put it into a gas chromatography liquid injection bottle.

[0219] The liquid was directly injected into the gas chromatograph automatically for detection by a hydrogen flame ionization detector (FID). The test parameters were as follows: nitrogen as carrier gas, a carrier gas flow rate of 1.5 ml / min, an injection port temperature of 250°C, a split ratio of 5:1, a temperature program to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and an FID detector at a detector temperature of 300°C. The peak area of ​​the propylene glycol characteristic chromatographic peak in the gas chromatogram corresponding to each group of samples was determined as the target peak area.

[0220] The propylene glycol residue test results of each group of samples were calculated based on the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residue. Among them, the propylene glycol residue test result of sample 2 is the average value of the propylene glycol residue test results of samples-2-1 to sample-2-6. The test results are shown in Table 4 below.

[0221] Table 4 - Comparative Example 2 Test Results

[0222] Table 4-1

[0223]

[0224] Table 4-2

[0225]

[0226] The detection method was evaluated based on the test results of propylene glycol residue in each group of samples and the theoretical propylene glycol residue in each group of samples. The repeatability Cov was evaluated by the test results of propylene glycol residue in samples-2-1 to sample-2-6.

[0227] Evaluation results: accuracy deviation is within ±10%, repeatability Cov>3%, a standard curve of peak area and target volatile substance residue must be established for each test, and the test time is >7h / ea.

[0228] Example 3

[0229] (1) Set up a standard curve of peak area and target volatile substance residue

[0230] Cut the dried and cold-pressed negative electrode sheets to obtain 5 samples, each sample weighing 0.5±0.02g, including the negative electrode current collector and the negative electrode film layer. Cut each sample into a specimen with a size of 5mm*30mm, and obtain 5 groups of samples containing multiple specimens.

[0231] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 5 groups of blank samples.

[0232] Take out the blank sample, and transfer each group of blank samples to a headspace bottle with a volume of 20mL within 1min; use a 1μl syringe to measure 0.06μl, 0.12μl, 0.24μl, 0.40μl, 0.50μl of the target volatile substance NMP, and 0.06μl, 0.12μl, 0.24μl, 0.48μl, 0.70μl of the target volatile substance solution (50% propylene glycol aqueous solution), respectively, and soak them into each group of blank samples to obtain standard samples, which are immediately sealed and recorded as standard samples-1 to standard samples-5. The liquid volume and the theoretical residual amount of the target volatile substance in the standard sample are shown in the following table.

[0233]

[0234] The headspace bottle was placed in the headspace device, heated and kept at 180°C for 8 min to allow NMP to reach a distribution equilibrium state in the headspace bottle.

[0235] The gas phase components in the headspace bottles of each group of standard samples were extracted respectively, injected into the gas chromatograph, and detected by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 20:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used with a detector temperature of 300°C. The calibrated peak areas of the characteristic chromatographic peaks of NMP and propylene glycol in the gas chromatograms corresponding to each group of standard samples were determined respectively.

[0236] Based on the NMP calibration peak area, propylene glycol calibration peak area and NMP theoretical residual amount and propylene glycol theoretical residual amount corresponding to each of the five groups of standard samples, standard curves of peak area and target volatile substance residual amount were fitted, wherein the standard curves of peak area and target volatile substance residual amount included the standard curve of characteristic chromatographic peak area of ​​NMP and NMP residual amount, and the standard curve of characteristic chromatographic peak area of ​​propylene glycol and propylene glycol residual amount.

[0237] (2) Detection of target volatile substance residues in the sample to be tested

[0238] The negative electrode sheets after drying and cold pressing were cut to obtain 10 samples, each sample weighing 0.5±0.02g, and the sample included the negative electrode current collector and the negative electrode film layer. Each sample was cut into a specimen with a size of 5mm*30mm, and 10 groups of samples containing multiple specimens were obtained.

[0239] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 10 groups of blank samples.

[0240] Take out the blank sample, and transfer each group of blank samples to a headspace bottle with a volume of 20mL within 1min and seal it; use a 1 microliter syringe to measure the target volatile substance NMP 0.10 microliters, 0.18 microliters (take 6 parallel samples), 0.26 microliters, 0.34 microliters, 0.42 microliters, and the target volatile substance solution (50% propylene glycol aqueous solution) 0.08 microliters, 0.16 microliters (take 6 parallel samples), 0.30 microliters, 0.40 microliters, 0.50 microliters, respectively, and infiltrate each group of blank samples to obtain samples-1 to sample-5 to be tested, and immediately seal it. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0241]

[0242]

[0243] The headspace bottle was placed in a headspace device, heated and kept at 180°C for 8 min to allow NMP and propylene glycol to reach a distribution equilibrium state in the headspace bottle.

[0244] The gas phase components in the headspace bottles of each group of samples were extracted respectively, injected into the gas chromatograph, and detected by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 20:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used with a detector temperature of 300°C. The peak areas of the characteristic chromatographic peaks of NMP and propylene glycol in the gas chromatograms corresponding to each group of samples were determined respectively as the target peak areas.

[0245] According to the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residue, the NMP and propylene glycol residue test results of each group of samples were calculated. Among them, the NMP and propylene glycol residue test results of sample 2 are the average values ​​of the NMP and propylene glycol residue test results of samples-2-1 to sample-2-6. The test results are shown in Table 5 below.

[0246] Table 5 - Example 3 test results

[0247] Table 5-1

[0248]

[0249] Table 5-2

[0250]

[0251] The detection method was evaluated based on the residual NMP and propylene glycol test results of each group of samples and the theoretical residual NMP and theoretical residual propylene glycol of each group of samples. Among them, the repeatability Cov was evaluated by the residual NMP and propylene glycol test results of samples-2-1 to sample-2-6.

[0252] Evaluation results: accuracy deviation within ±6%, repeatability Cov <3%, test time about 13min / ea.

[0253] Comparative Example 3

[0254] (1) Set up a standard curve of peak area and target volatile substance residue

[0255] Weigh 0.025g of the target volatile substance propylene glycol and 0.05g of the target volatile substance NMP, add them to 0.925g of DMF to obtain a standard mother solution with a propylene glycol content of 0.25% and an NMP content of 0.5%; weigh 5 portions of DMF, each weighing 5g, add 0.05g, 0.1g, 0.2g, 0.3g and 0.4g of the standard mother solution to 5 portions of DMF, respectively, seal immediately, shake evenly, and obtain 5 groups of gradient standard solution sample-1 to standard solution sample-5, in which the residual amounts of propylene glycol in the solutions were 25ppm, 49ppm, 96ppm, 142ppm and 185ppm, respectively, and the residual amounts of NMP were 50ppm, 98ppm, 192ppm, 283ppm and 370ppm, respectively.

[0256] Take about 1mL of standard solution respectively, put it into 1.5mL gas chromatography liquid injection vial, inject the liquid directly into the gas chromatograph by automatic injection, and detect it with hydrogen flame ionization detector (FID). The test parameters are as follows: the carrier gas is nitrogen, the carrier gas flow rate is 1.5mL / min, the injection port temperature is 250℃, the split ratio is 5:1, the temperature program is to increase the column oven temperature from 40℃ to 220℃ at a heating rate of 20℃ / min, and the FID detector is used, and the detector temperature is 300℃. The calibrated peak areas of the characteristic chromatographic peaks of propylene glycol and NMP in the gas chromatogram corresponding to each group of standard samples are determined respectively.

[0257] Based on the NMP calibration peak area, propylene glycol calibration peak area and NMP theoretical residual amount and propylene glycol theoretical residual amount corresponding to each of the five groups of standard samples, standard curves of peak area and target volatile substance residual amount were fitted, wherein the standard curves of peak area and target volatile substance residual amount included the standard curve of characteristic chromatographic peak area of ​​NMP and NMP residual amount, and the standard curve of characteristic chromatographic peak area of ​​propylene glycol and propylene glycol residual amount.

[0258] (2) Detection of target volatile substance residues in the sample to be tested

[0259] The negative electrode sheet after drying and cold pressing was cut to obtain 10 samples, each with a mass of 1.0±0.02g.

[0260] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 10 groups of blank samples.

[0261] The blank sample was taken out, cut into pieces of about 5mm*5mm, and placed in a 15mL vial. A 1μl syringe was used to measure 0.10μl, 0.18μl (6 parallel samples), 0.26μl, 0.34μl, and 0.42μl of the target volatile substance NMP, and 0.08μl, 0.16μl (6 parallel samples), 0.30μl, 0.40μl, and 0.50μl of the target volatile substance solution (50% propylene glycol), respectively, and infiltrated into each group of blank samples, respectively, to obtain samples-1 to sample-5 to be tested, and immediately sealed. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6

[0262]

[0263] Place the vial in an ultrasonic machine and continue ultrasonicating at a frequency of >6 h until all the active materials on the electrode are observed to fall off the current collector.

[0264] Use a disposable syringe to take 1 mL of liquid from each vial, filter out the clear liquid with a 0.45 μm filter, and put it into a gas chromatography liquid injection bottle.

[0265] The liquid was directly injected into the gas chromatograph automatically for detection by a hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 5:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used with a detector temperature of 300°C. The peak areas of the characteristic chromatographic peaks of NMP and propylene glycol in the gas chromatogram corresponding to each group of samples were determined as the target peak areas.

[0266] According to the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residue, the NMP and propylene glycol residue test results of each group of samples were calculated. Among them, the NMP and propylene glycol residue test results of sample 2 are the average values ​​of the NMP and propylene glycol residue test results of samples-2-1 to sample-2-6. The test results are shown in Table 6 below.

[0267] Table 6 - Comparative Example 3 Test Results

[0268] Table 6-1

[0269]

[0270] Table 6-2

[0271]

[0272] The detection method was evaluated based on the residual NMP and propylene glycol test results of each group of samples and the theoretical residual NMP and theoretical residual propylene glycol of each group of samples. Among them, the repeatability Cov was evaluated by the residual NMP and propylene glycol test results of samples-2-1 to sample-2-6.

[0273] Evaluation results: accuracy deviation is within ±6%, repeatability Cov>3%, a standard curve of peak area and target volatile substance residue must be established for each test, and the test time is >7h / ea.

[0274] Example 4

[0275] (1) Set up a standard curve of peak area and target volatile substance residue

[0276] Weigh an appropriate amount of positive electrode material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2(NCM811) powder was prepared to obtain 5 samples, each with a weight of 1.0±0.01g.

[0277] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 5 groups of blank samples.

[0278] Take out the blank samples and transfer each group of blank samples to a headspace bottle with a volume of 20 mL; use a 1 μL syringe to measure 0.04 μL, 0.08 μL, 0.12 μL, 0.20 μL, and 0.30 μL of the target volatile substance ethanol, respectively, and infiltrate them into each group of blank samples to obtain standard samples, which are immediately sealed and recorded as standard sample-1 to standard sample-5.

[0279] serial number Liquid volume / μL Theoretical residual amount / ppm Standard sample-1 0.04 32 Standard sample-2 0.08 63 Standard sample-3 0.12 95 Standard sample-4 0.20 158 Standard-5 0.30 237

[0280] The headspace bottle was placed in a headspace device, heated and kept at 80°C for 20 min to allow the ethanol to reach a distribution equilibrium state in the headspace bottle.

[0281] The gas phase components in the headspace bottles of each group of standard samples were extracted respectively, injected into the gas chromatograph, and detected by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 5:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used, and the detector temperature was 300°C. The calibrated peak area of ​​the ethanol characteristic chromatographic peak in the gas chromatogram corresponding to each group of standard samples was determined respectively.

[0282] Based on the calibrated peak areas and theoretical ethanol residual amounts of the five groups of standard samples, a standard curve of peak area and target volatile substance residual amount was obtained by fitting.

[0283] (2) Detection of target volatile substance residues in the sample to be tested

[0284] An appropriate amount of positive electrode material NCM811 powder was weighed to obtain 10 samples, and the amount of each sample was 1.0±0.01 g.

[0285] Each group of samples was baked at 120°C under vacuum for 12 h to obtain 10 groups of blank samples.

[0286] Take out the blank samples, and transfer each group of blank samples to a headspace bottle with a volume of 20 mL and seal it; use a 1 μL syringe to measure 0.06 μL, 0.10 μL (take 6 parallel samples), 0.14 μL, 0.18 μL, and 0.24 μL of the target volatile substance ethanol, respectively, and infiltrate them into each group of blank samples, respectively, to obtain samples-1 to -5 to be tested, and seal them immediately.

[0287] Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0288] serial number Liquid volume / μL Theoretical residual amount / ppm Sample-1 0.06 47 Sample-2-1 0.10 79 Sample-2-2 0.10 79 Sample-2-3 0.10 79 Sample-2-4 0.10 79 Sample-2-5 0.10 79 Sample-2-6 0.10 79 Sample-3 0.14 111 Sample-4 0.18 142 Sample-5 0.24 189

[0289] The headspace bottle was placed in a headspace device, heated and kept at 80°C for 20 min to allow the ethanol to reach a distribution equilibrium state in the headspace bottle.

[0290] The gas phase components in the headspace bottles of each group of samples were extracted and injected into the gas chromatograph for detection by hydrogen flame ionization detector (FID). The test parameters were as follows: the carrier gas was nitrogen, the carrier gas flow rate was 1.5 ml / min, the injection port temperature was 250°C, the split ratio was 5:1, the temperature program was to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and the FID detector was used with a detector temperature of 300°C. The peak area of ​​the ethanol characteristic chromatographic peak in the gas chromatogram corresponding to each group of samples was determined as the target peak area.

[0291] The ethanol residue test results of each group of samples were calculated based on the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residue. Among them, the ethanol residue test result of sample 2 is the average value of the ethanol residue test results of sample-2-1 to sample-2-6. The test results are shown in Table 7 below.

[0292] Table 7 - Example 4 Test Results

[0293] Table 7-1

[0294]

[0295] Table 7-2

[0296]

[0297] The detection method was evaluated based on the test results of ethanol residue in each group of samples and the theoretical ethanol residue in each group of samples. The repeatability Cov was evaluated by the test results of ethanol residue in samples-2-1 to sample-2-6.

[0298] Evaluation results: accuracy deviation within ±10%, repeatability Cov<5%, test time about 30min / ea.

[0299] Comparative Example 4

[0300] (1) Set up a standard curve of peak area and target volatile substance residue

[0301] Weigh 0.02g of the target volatile substance ethanol, add it to 0.98g of DMF to obtain a DMF standard mother solution with an ethanol content of 0.2%; weigh 5 portions of DMF, each weighing 5g, add 0.01g, 0.05g, 0.1g, 0.15g, and 0.2g of the standard mother solution to 5 portions of DMF respectively, add it to 5g of DMF solution, seal it immediately, and shake it evenly to obtain 5 groups of gradient standard solution sample-1 to standard solution sample-5, and the residual ethanol in the solution is 4ppm, 20ppm, 39ppm, 58ppm, and 77ppm, respectively.

[0302] Take about 1mL of standard solution sample respectively, put it into 1.5mL gas chromatography liquid injection vial, inject the liquid directly into gas chromatograph by automatic injection, and detect it with hydrogen flame ionization detector (FID). Test parameters: carrier gas is nitrogen, carrier gas flow rate is 1.5mL / min, injection port temperature is 250℃, split ratio is 3:1, temperature program increases the column oven temperature from 40℃ to 220℃ at a heating rate of 20℃ / min, and FID detector is used, and the detector temperature is 300℃. Determine the calibrated peak area of ​​the ethanol characteristic chromatographic peak in the gas chromatogram corresponding to each group of standard samples.

[0303] Based on the calibrated peak areas and theoretical ethanol residual amounts of the five groups of standard samples, a standard curve of peak area and target volatile substance residual amount was obtained by fitting.

[0304] (2) Detection of target volatile substance residues in the sample to be tested

[0305] Directly take 6 g of the positive electrode material NCM811 powder and bake it at 120° C. under vacuum for 24 h. After cooling to room temperature, weigh 1.0±0.01 g of the powder into 10 vials respectively.

[0306] Add 5g DMF to each vial, seal it, and use a 1μl syringe to measure 0.06μl, 0.1μl (take 6 parallel samples), 0.14μl, 0.18μl, and 0.24μl of the target volatile substance anhydrous ethanol, respectively, and infiltrate it into each group of blank samples, and immediately seal it to obtain samples-1 to sample-5 to be tested. Among them, sample-2 includes 6 groups of parallel samples, namely sample-2-1 to sample-2-6.

[0307] serial number Liquid volume / μL Theoretical residual amount / ppm Sample-1 0.06 47 Sample-2-1 0.10 79 Sample-2-2 0.10 79 Sample-2-3 0.10 79 Sample-2-4 0.10 79 Sample-2-5 0.10 79 Sample-2-6 0.10 79 Sample-3 0.14 111 Sample-4 0.18 142 Sample-5 0.24 189

[0308] Place the vial in an ultrasound machine and maintain ultrasound at a constant frequency for >6 hours.

[0309] Use a disposable syringe to take 1 mL of liquid from each vial, filter the clear liquid with a 0.45 μm filter and put it into a gas chromatography liquid injection bottle.

[0310] The liquid was directly injected into the gas chromatograph automatically for detection by a hydrogen flame ionization detector (FID). The test parameters were as follows: nitrogen as carrier gas, a carrier gas flow rate of 1.5 ml / min, an injection port temperature of 250°C, a split ratio of 3:1, a temperature program to increase the column oven temperature from 40°C to 220°C at a heating rate of 20°C / min, and an FID detector at a detector temperature of 300°C. The peak area of ​​the ethanol characteristic chromatographic peak in the gas chromatogram corresponding to each group of samples was determined as the target peak area.

[0311] The ethanol residue test results of each group of samples were calculated based on the target peak area corresponding to each group of samples and the pre-set standard curve of peak area and target volatile substance residue. Among them, the ethanol residue test result of sample 2 is the average value of the ethanol residue test results of sample-2-1 to sample-2-6. The test results are shown in Table 8 below.

[0312] Table 8 - Comparative Example 4 Test Results

[0313] Table 8-1

[0314]

[0315] Table 8-2

[0316]

[0317] The detection method was evaluated based on the test results of ethanol residue in each group of samples and the theoretical ethanol residue in each group of samples. The repeatability Cov was evaluated by the test results of ethanol residue in samples-2-1 to sample-2-6.

[0318] Evaluation results: accuracy deviation is within ±10%, repeatability Cov>5%, a standard curve of peak area and target volatile substance residue must be established for each test, and the test time is>7h / ea.

[0319] Based on the test results of Examples 1-4, it can be seen that the method according to the embodiments of the present application can efficiently and accurately detect the target volatile substance residue in raw material powder or battery components.

[0320] In contrast, in Comparative Examples 1-4, the target volatile substances in the raw material powder or battery components are extracted by ultrasonic, and after filtering, the target volatile substances in the extract are quantitatively detected. According to the method of Comparative Examples 1-4, not only a large amount of time is consumed for extraction, but also a standard curve of peak area and target volatile substance residue needs to be established for each test. Therefore, the test time of Comparative Examples 1-4 is much longer than that of Example 1-4, and the detection efficiency is much lower than that of Example 1-4. In addition, according to the method of Comparative Examples 1-4, there is also the risk of insufficient extraction of the target volatile substances, resulting in the detection accuracy and repeatability Cov of Comparative Examples 1-4 being inferior to those of the corresponding embodiments.

[0321] For some compounds given but not listed in the embodiments, since their chemical properties and reaction properties when participating in electrochemical reactions are similar to those of the compounds listed in the embodiments, they are all suitable for the technical scheme of the present invention and are therefore not listed one by one here.

[0322] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for detecting the residual amount of a target volatile substance, comprising: Providing a sample to be tested containing a target volatile substance; Providing a first closed system, including placing the sample to be tested in a sealed container, allowing the target volatile substance to reach a distribution equilibrium state in the sealed container under preset conditions, to obtain a first closed system, wherein the distribution equilibrium state indicates that the target volatile substance reaches a distribution equilibrium in the sample to be tested and the gas phase component of the sealed container; The gas phase component of the first closed system is subjected to gas chromatography detection to obtain a target peak area of ​​a characteristic chromatographic peak of the target volatile substance in the gas phase component of the first closed system, so as to obtain the target volatile substance residue of the sample to be tested according to the target peak area and a standard curve of the peak area and the target volatile substance residue under the preset conditions.

2. The method according to claim 1, wherein: Before determining the target volatile substance residue of the sample to be tested, the method further comprises: Providing a plurality of standard samples, each of which has the same specification parameters as the sample to be tested, wherein the specification parameters include mass and / or size, and the plurality of standard samples have different, predetermined target volatile substance residual amounts; Providing a second closed system, comprising placing the plurality of standard samples in the closed container respectively, allowing the target volatile substance to reach a distribution equilibrium state in the closed container under preset conditions, thereby obtaining a second closed system; Performing gas chromatography detection on the gas phase component of the second closed system to obtain a calibrated peak area of ​​a characteristic chromatographic peak of the target volatile substance in the gas phase component of the second closed system; Based on the calibration peak areas corresponding to the plurality of standard samples and their predetermined target volatile substance residues, a standard curve of the peak areas and the target volatile substance residues is obtained by fitting.

3. The method according to claim 2, wherein: The sample to be tested is obtained by sampling from the electrode plate to be tested or the raw material powder of the battery to be tested, and the multiple standard samples are provided, including: Sampling from the electrode sheet to be tested or the battery raw material powder to be tested to obtain a plurality of test specimens having the same specification parameters as the sample to be tested; Baking the sample to remove target volatile substances in the sample to obtain a plurality of blank samples; The target volatile substances are added to the plurality of blank samples respectively, so that the plurality of blank samples have different predetermined residual amounts of the target volatile substances, thereby obtaining the plurality of standard samples.

4. The method according to claim 3, wherein: The adding the target volatile substance to the plurality of blank samples respectively comprises: Provide target volatile substance standard solution; According to a preset residual amount gradient, different volumes of the target volatile substance standard solution are added to the plurality of blank samples respectively.

5. The method according to any one of claims 1 to 4, wherein: The closed container is a headspace bottle; Optionally, the volume of the headspace bottle is 10mL-20mL.

6. The method according to any one of claims 1 to 5, wherein: The step of causing the target volatile substance to reach a distribution equilibrium state in the closed container under preset conditions includes: The sealed container is heated to a preset temperature and kept warm, so that the target volatile substance reaches a distribution equilibrium state at the preset temperature.

7. The method according to claim 6, wherein: The preset temperature is 80°C-200°C; and / or The insulation time is 8 min to 20 min.

8. The method according to any one of claims 1 to 7, wherein: The providing of the sample to be tested comprises: Cutting the electrode sheet to be tested to obtain N test pieces with preset sizes as the test samples, wherein N is a positive integer; optionally, the mass of the test samples is 0.3 g-1.0 g; or The providing of the sample to be tested comprises: A preset mass of the sample to be tested is weighed from the battery raw material powder to be tested; optionally, the preset mass is 0.3g-0.5g.

9. The method according to claim 8, wherein: The preset size is (2mm-8mm)*(10mm-70mm).

10. The method according to any one of claims 1 to 9, wherein: The target volatile substance includes one or more of a volatile organic solvent or a volatile plasticizer; Optionally, the target volatile substance includes at least one of N-methylpyrrolidone, ethylene carbonate, ethanol, propylene glycol, or dimethyl sulfoxide.

11. The method according to any one of claims 1 to 10, wherein: The target volatile substance residue in the sample to be tested is 50ppm-1500ppm.

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