Method for judging excessive residual N-methyl pyrrolidone of battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a method for judging excessive residual of N-methyl pyrrolidone of a battery, which comprises the following steps: detecting open-circuit voltage OCV0 of the battery in an inactive state, testing hot-pressing Hi-pot resistance, forming first-step charging end voltage, observing a full-charge negative electrode interface waist line and the like. Whether the residual amount of the N-methyl pyrrolidone is excessive or not is rapidly judged, the judgment process and the test time of the excessive residual amount of the N-methyl pyrrolidone in the battery are simplified, and the method is more efficient and rapid.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a method for determining excessive residual N-methylpyrrolidone in a battery. Background Art

[0002] In the battery production process, N-methylpyrrolidone (NMP) is a commonly used electrolyte solvent and binder dissolution medium. Its good chemical stability and solubility are crucial for battery manufacturing. However, after the battery manufacturing is completed, if there is excessive NMP residue, it will have a series of negative effects on battery performance. Specifically, excessive NMP residue may bring the following effects:

[0003] (1) Reduction in battery capacity: Residual NMP will react with the metallic lithium in the battery, increasing the irreversible capacity of the battery, thereby reducing the battery capacity;

[0004] (2) Reduced cycle life: Residual NMP will damage the SEI layer of the negative electrode, resulting in increased SEI film instability and Li + The conductivity of the battery is reduced, thereby reducing the cycle efficiency of the battery. At the same time, residual NMP will react with other components in the electrolyte to generate substances that are not conducive to battery performance, such as HF, which will further damage the cycle performance of the battery;

[0005] (3) Increased internal pressure and bulging of the battery: Residual NMP reacts with water to generate gas, which increases the internal pressure of the battery and may cause battery bulging, thus posing a safety hazard;

[0006] (4) Thermal runaway risk: Residual NMP may cause thermal runaway reaction inside the battery at high temperature, especially when the battery is overcharged or stimulated by external heat source, this risk is more significant;

[0007] (5) Decreased slurry stability: Residual NMP will directly affect the stability and dispersion effect of the slurry, thereby affecting the coating quality and consistency of the battery;

[0008] (6) Increased production costs: Since excessive NMP residues may lead to decreased battery performance and increased safety risks, manufacturers may need to take additional measures to remove residual NMP, such as increasing drying time and drying temperature. These measures will undoubtedly increase production costs.

[0009] At present, traditional methods for detecting NMP residues mainly rely on chemical analysis and instrumental testing, such as gas chromatography and mass spectrometry. However, these methods often require special environments, are time-consuming, costly, and require complex sample pretreatment. They are also difficult to adapt to the needs of online rapid detection.

[0010] Therefore, it is particularly urgent and important to develop a new method for determining excessive NMP residue in batteries. The industry urgently needs a simple, efficient and accurate method for determining excessive NMP residue to meet the needs of the modern battery manufacturing industry, which will have a positive impact on the quality control and safety supervision of the battery manufacturing industry. Summary of the invention

[0011] The purpose of the present invention is to provide a simple, efficient and accurate method for determining excessive residual NMP in a battery in order to meet the needs of the modern battery manufacturing industry.

[0012] In view of this, the present invention provides a method for determining excessive residual N-methylpyrrolidone in a battery, comprising the steps of:

[0013] S1, measure the hot pressure Hi-pot resistance of multiple batteries to be tested, draw a scatter plot to analyze the distribution of the hot pressure Hi-pot resistance, and establish the qualified range Q of the hot pressure Hi-pot resistance according to the distribution of the hot pressure Hi-pot resistance 1 ;

[0014] S2, setting the screening condition T according to the distribution state of the hot pressing Hi-pot resistance value obtained in step S1 1 ;

[0015] S3, measuring the open circuit voltage OCV0 of multiple batteries to be tested, drawing a scatter plot to analyze the distribution state of OCV0, and establishing the voltage qualified range Q of OCV0 according to the distribution state of OCV0 2 ;

[0016] S4, setting the screening condition T according to the distribution state of OCV0 obtained in step S3 2 ;

[0017] S5, measuring the first step charge end voltage of the formation of multiple batteries to be tested, drawing a scatter plot to analyze the distribution state of the first step charge end voltage, and establishing a qualified range Q of the first step charge end voltage according to the obtained distribution state of the first step charge end voltage 3 ;

[0018] S6, setting the screening condition T according to the distribution state of the first step charging end voltage obtained in step S5 3 ;

[0019] S7, judging whether the battery to be predicted satisfies the screening condition T at the same time 1 、T 2 With T 3 If yes, then continue to execute step S8; if no, then it is considered that the N-methylpyrrolidone residual amount of the battery to be predicted is normal;

[0020] S8, for all the items that meet the screening conditions T 1 、T 2 With T 3 The predicted battery is fully charged at constant current and then disassembled to confirm the state of the negative electrode interface and observe whether a black through waistline appears on the negative electrode interface. If a black through waistline appears on the negative electrode interface, it is determined that the predicted battery has excessive N-methylpyrrolidone residue.

[0021] Further, in the step S1, the qualified range Q of the hot pressing Hi-pot resistance is established according to the distribution state of the hot pressing Hi-pot resistance. 1 The process is as follows:

[0022] First, the Anderson-Darling normality calculation is performed on multiple hot pressure Hi-pot resistance values ​​measured by multiple batteries to be tested to obtain their overall average value R 0 With standard deviation δ 1 ;

[0023] Then the standard deviation δ 1 To measure the discreteness of the array, N 1 times δ 1 As the discrete standard level, the qualified range Q of the hot pressing Hi-pot resistance value is obtained 1 For: R 0 ±N 1 ·δ 1 .

[0024] Furthermore, in step S2, the screening condition T 1 Set to:

[0025] The battery to be predicted is subjected to thermal pressure Hi-pot resistance measurement, and the measured value of the thermal pressure Hi-pot resistance of the battery to be predicted is R 实 and Q 1 The lower limit R 0 -N 1 ·δ 1 For comparison, if R 实 Below the qualified range Q 1 The lower limit R 0 -N 1 ·δ 1 , then the battery to be predicted meets the screening condition T 1 .

[0026] Furthermore, in step S3, a voltage qualified range Q of OCV0 is established according to the distribution state of OCV0. 2 The process is as follows:

[0027] First, the Anderson-Darling normality calculation is performed on multiple OCV0s measured by multiple batteries to be tested to obtain their overall average value U 0 With standard deviation δ 2 ;

[0028] Then the standard deviation δ 2 To measure the discreteness of the array, N 2 times δ 2 As the discrete standard level, the voltage qualified range Q of OCV0 is obtained. 2 For: U 0 ±N 2 ·δ 2 .

[0029] Furthermore, in step S4, the screening condition T 2 Set to:

[0030] The open circuit voltage OCV0 of the battery to be predicted is tested to obtain the actual measured value U of the open circuit voltage of the battery to be predicted. 实1 , will U 实1 and Q 2 The lower limit value U 0 -N 2 ·δ 2 For comparison, if U 实1 Lower than U 0 -N 2 ·δ 2 , then the battery to be predicted meets the screening condition T 2 .

[0031] Further, in step S5, the qualified range Q of the first step charging end voltage of the battery formation is established according to the measured first step charging end voltage of the battery formation. 3 The process is as follows:

[0032] First, the Anderson-Darling normality calculation is performed on multiple first-step charge end voltages of multiple batteries to be tested to obtain their overall average value U 1 With standard deviation δ 3 ;

[0033] Then the standard deviation δ 3 To measure the discreteness of the array, N 3 times δ 3 As the discrete standard level, the qualified range Q of the first step charge end voltage of formation is obtained. 3 For: U 1 ±N 3 ·δ 3 .

[0034] Furthermore, in step S6, the screening condition T 3 Set to:

[0035] The battery to be predicted is also subjected to the same formation test as the battery to be tested, and the measured value U of the first step of formation charging end voltage of the battery to be predicted is measured. 实2 ; If ▏(U 实2 -U 1 )▏≤N 3 ·δ 3 , then the battery to be predicted meets the screening condition T 3 .

[0036] Furthermore, in step S5, after the first step of charging the multiple batteries to be tested is completed, the batteries to be tested should continue to be fully formed.

[0037] Furthermore, in the step S8, the battery is fully charged with a constant current of 0.3C to 0.8C and then disassembled.

[0038] Further, the complete test steps include:

[0039] The first step is charging: charging rate: 0.05~0.1C, charging time: 30~60min;

[0040] The second step is charging: charging rate: 0.1~0.15C, charging time: 40~60min;

[0041] The third step is charging: charging rate: 0.18~0.2C, charging time: 30~176min;

[0042] The fourth step is discharge: discharge rate: 0.2~0.25C, discharge time: 1~2min.

[0043] The beneficial effects of the present invention are as follows: the method for determining excessive residual N-methylpyrrolidone in a battery according to the present invention has the following advantages:

[0044] 1. The present invention studies the characteristics of N-methylpyrrolidone and its influence on battery performance, and adopts the steps of detecting the open circuit voltage (OCV0) of the battery in an unactivated state, hot pressing Hi-pot resistance test, the first step of formation charging end voltage and observing the waistline of the fully charged negative electrode interface, so as to quickly determine whether N-methylpyrrolidone remains excessive, simplifying the determination process and test time of excessive residual N-methylpyrrolidone in the battery, and making it more efficient and quick;

[0045] 2. The present invention reduces the risk of battery cycle failure by determining whether excessive N-methylpyrrolidone remains, and provides a new technical means for battery quality control and safety testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a physical example of the black through waistline appearing at the negative electrode interface described in the present invention. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0048] In the description of the present application, it should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. For ease of description, the techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0049] It should be noted that, in the present application, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises one..." does not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be noted that the scope of the method and device in the embodiment of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0050] The applicant found through research that:

[0051] First, although N-methylpyrrolidone itself is a non-conductive solvent, if there is an excess of N-methylpyrrolidone residue during the battery manufacturing process, these residues may interact with other impurities or battery materials to form conductive substances. These conductive substances will become more fluid and easy to diffuse due to the high temperature and pressure during the hot pressing process. They may penetrate along the pores and cracks of the electrode or diaphragm and aggregate and crystallize therein. As the residues continue to accumulate, they may form continuous conductive channels that can transmit current, thereby reducing the insulation properties of the material and thus reducing the Hi-pot resistance.

[0052] Second, pores are an important component of the electrode structure and are very important for the performance of the battery. They provide channels for the infiltration of electrolytes and the transmission of ions. The ability of the electrolyte to fully infiltrate the electrode is a prerequisite for the normal operation of the battery. If the pores are blocked, the electrolyte cannot fully infiltrate the electrode, which will affect the electrochemical performance of the battery. During the battery manufacturing process, if there are too many N-methylpyrrolidone residues, they will occupy the pore space inside the electrode, which will have an adverse effect on the pores. Excessive N-methylpyrrolidone residues will fill the pores of the electrode, making the pore space smaller or even blocked. This will make it difficult for the electrolyte to fully infiltrate the electrode, and the transmission of ions inside the electrode will be limited. Because the pores are occupied by N-methylpyrrolidone residues, the infiltration and transmission of the electrolyte are affected, resulting in a decrease in the electrochemical performance of the battery, which is manifested as a decrease in battery capacity, a decrease in cycle life, and a low OCV0 voltage. Among them, the OCV0 voltage is the open circuit voltage measured after the battery is first filled with liquid and aged at high temperature, which reflects the electrochemical state inside the battery.

[0053] Third, in the battery, a layer of solid electrolyte interface (SEI) film will be formed on the surface of the negative electrode. This film is crucial for protecting the negative electrode and stabilizing the battery performance. However, when excessive N-methylpyrrolidone residues are adsorbed on the graphite surface, the formation of the SEI film is affected, so that the SEI film can only be superimposed on the N-methylpyrrolidone layer, resulting in a weak bond between the SEI film and the graphite. During the battery charging and discharging process, ions need to be embedded and deintercalated back and forth between the positive and negative electrodes, but because the SEI film is superimposed on the N-methylpyrrolidone layer and the bond is not strong, the ions will be hindered during the transmission process, resulting in a decrease in battery performance. Due to the instability of the SEI film and the obstruction of ion transmission, abnormal deposition or reaction may occur on the negative electrode surface, forming the so-called "black waistline". In terms of the initial performance of the battery, such as capacity, internal resistance, rate, charge and discharge voltage, etc., the effect of excess N-methylpyrrolidone residue is relatively small. As the number of battery cycles increases, the effect of excess N-methylpyrrolidone residue on battery performance gradually becomes apparent. The instability of the SEI film and the obstruction of ion transmission lead to accelerated battery decay in the late cycle, which is manifested as a cycle diving phenomenon. This means that after a certain number of charge and discharge cycles, the performance of the battery will decline rapidly and cannot meet normal use requirements.

[0054] Therefore, excessive N-methylpyrrolidone residue will significantly affect the performance of the battery. The usage and residue of N-methylpyrrolidone should be strictly controlled during the battery manufacturing process, and effective prevention and solution measures should be taken to ensure the performance and life of the battery.

[0055] Based on this, in order to solve the technical problems that the N-methylpyrrolidone (N-methylpyrrolidone) solvent used in the production process of existing batteries is difficult to remove and the detection is cumbersome, so as to avoid the adverse effects of excessive residual N-methylpyrrolidone solvent on battery performance and safety, the present application provides a method for comprehensive analysis of the open circuit voltage (OCV0) of the battery, the hot pressing Hi-pot resistance value and the battery interface state, which can effectively determine whether the N-methylpyrrolidone residue is excessive, and provides a new technical means for battery quality control and safety testing.

[0056] Specifically, Figure 1 As shown, the method for determining excessive residual N-methylpyrrolidone in a battery according to the present invention comprises the following steps:

[0057] S1, measure the hot pressure Hi-pot resistance of multiple batteries to be tested, draw a scatter plot to analyze the distribution of the hot pressure Hi-pot resistance, and establish the qualified range Q of the hot pressure Hi-pot resistance according to the distribution of the hot pressure Hi-pot resistance 1 ;

[0058] S2, setting the screening condition T according to the distribution state of the hot pressing Hi-pot resistance value obtained in step S1 1 ;

[0059] S3, measuring the open circuit voltage OCV0 of multiple batteries to be tested, drawing a scatter plot to analyze the distribution state of OCV0, and establishing the voltage qualified range Q of OCV0 according to the distribution state of OCV0 2 ;

[0060] S4, setting the screening condition T according to the distribution state of OCV0 obtained in step S3 2 ;

[0061] S5, measuring the first step charge end voltage of the plurality of batteries to be tested, drawing a scatter plot to analyze the distribution state of the first step charge end voltage, and establishing a qualified range Q of the first step charge end voltage according to the obtained distribution state of the first step charge end voltage 3 ;

[0062] S6, setting the screening condition T according to the distribution state of the first step charging end voltage obtained in step S5 3 ;

[0063] S7, judging whether the battery to be predicted satisfies the screening condition T at the same time 1 、T 2 With T 3 If yes, then continue to execute step S8; if no, then it is considered that the N-methylpyrrolidone residual amount of the battery to be predicted is normal;

[0064] S8, for all the items that meet the screening conditions T 1 、T 2 With T 3 The predicted battery is fully charged at constant current and then disassembled to confirm the state of the negative electrode interface and observe whether a black through waistline appears on the negative electrode interface. If a black through waistline appears on the negative electrode interface, it is determined that the predicted battery has excessive N-methylpyrrolidone residue.

[0065] Preferably, in step S1, the qualified range Q of the hot pressing Hi-pot resistance is established according to the distribution state of the hot pressing Hi-pot resistance. 1 The process is as follows:

[0066] First, the Anderson-Darling normality calculation is performed on multiple hot pressure Hi-pot resistance values ​​measured by multiple batteries to be tested to obtain their overall average value R 0 With standard deviation δ 1 ;

[0067] Then the standard deviation δ 1 To measure the discreteness of the array, specifically N1 times δ 1 (i.e. N 1 ·δ 1 ) as the discrete standard level, and obtain the qualified range Q of the hot pressing Hi-pot resistance value 1 For: R 0 ±N 1 ·δ 1 .

[0068] Preferably, in step S2, the screening condition T 1 Set to:

[0069] The battery to be predicted is subjected to thermal pressure Hi-pot resistance measurement, and the measured value of the thermal pressure Hi-pot resistance of the battery to be predicted is R 实 and Q 1 The lower limit R 0 -N 1 ·δ 1 For comparison, if R 实 Below the qualified range Q 1 The lower limit R 0 -N 1 ·δ 1 , then the battery to be predicted meets the screening condition T 1 .

[0070] That is, when the measured value of the thermal pressure Hi-pot resistance of the battery to be predicted is R 实 Falling into the qualified range Q 1 If the value is below the lower limit, it satisfies the screening condition T 1 , further testing is required to determine whether the N-methylpyrrolidone residue therein is excessive; otherwise, it is considered that the N-methylpyrrolidone residue of the battery to be predicted is not excessive.

[0071] Preferably, in step S3, the voltage qualified range Q of OCV0 is established according to the distribution state of OCV0. 2 The process is as follows:

[0072] First, the Anderson-Darling normality calculation is performed on multiple OCV0s measured by multiple batteries to be tested to obtain their overall average value U 0 With standard deviation δ 2 ;

[0073] Then the standard deviation δ 2 To measure the discreteness of the array, N 2 times δ 2 As the discrete standard level, the voltage qualified range Q of OCV0 is obtained. 2 For: U 0 ±N 2 ·δ2 .

[0074] Preferably, in step S4, the screening condition T 1 Set to:

[0075] The open circuit voltage OCV0 of the battery to be predicted is tested to obtain the actual measured value U of the open circuit voltage of the battery to be predicted. 实1 , will U 实1 and Q 2 The lower limit value U 0 -N 2 ·δ 2 For comparison, if U 实1 Lower than U 0 -N 2 ·δ 2 , then the battery to be predicted meets the screening condition T 2 .

[0076] That is, when the OCV0 measured value U of the battery to be predicted 实1 Falling within the voltage qualified range Q 2 If the value is below the lower limit, it satisfies the screening condition T 2 , further testing is required to determine whether the N-methylpyrrolidone residue therein is excessive; otherwise, it is considered that the N-methylpyrrolidone residue of the battery to be predicted is not excessive.

[0077] The OCV0 voltage described in the present invention is the open circuit voltage measured after the battery is first filled with liquid and aged, which reflects the electrochemical state inside the battery.

[0078] As some examples of the present invention, the aging process of the battery is as follows: temperature 40-60°C, dew point -60°C ≤ DP ≤ -35°C; aging time 30 to 60 hours.

[0079] Preferably, in step S5, the qualified range Q of the first step charging end voltage of the battery formation is established according to the measured first step charging end voltage of the battery formation. 3 The process is as follows:

[0080] First, the Anderson-Darling normality calculation is performed on multiple first-step charge end voltages of multiple batteries to be tested to obtain their overall average value U 1 With standard deviation δ 3 ;

[0081] Then the standard deviation δ 3 To measure the discreteness of the array, specifically N 3 times δ 3 (i.e. N 3 ·δ 3) as the discrete standard level, and obtain the qualified range Q of the first step charge end voltage of the formation 3 For: U 1 ±N 3 ·δ 3 , then U 1 ±N 3 ·δ 3 That is the qualified range of the charging end voltage of the first step of formation Q 3 The upper and lower limits of U 1 ±N 3 ·δ 3 The range covered is the qualified range Q of the first step charging end voltage established in step S5. 3 .

[0082] Preferably, in step S6, the screening condition T 3 Set to:

[0083] The battery to be predicted is also subjected to the same formation test as the battery to be tested, and the measured value U of the first step of formation charging end voltage of the battery to be predicted is measured. 实2 ; If ▏(U 实2 -U 1 )▏≤N 3 ·δ 3 , then the battery to be predicted meets the screening condition T 3 .

[0084] That is, when the first step of the battery formation to be predicted, the measured value of the charging end voltage U 实2 Falling into the qualified range Q 3 If it is within, then it meets the screening condition T 3 , further testing is required to determine whether the N-methylpyrrolidone residue therein is excessive; otherwise, it is considered that the N-methylpyrrolidone residue of the battery to be predicted is not excessive.

[0085] Preferably, it is determined whether the battery to be predicted satisfies the screening conditions T 1 、T 2 With T 3 If yes, then continue to execute step S8; if no, it is considered that the N-methylpyrrolidone residual amount of the battery to be predicted is normal.

[0086] Preferably, for the two groups that simultaneously meet the screening conditions T 1 、T 2 With T 3 The predicted battery is fully charged at constant current and then disassembled to confirm the state of the negative electrode interface and observe whether a black through waistline appears on the negative electrode interface. If a black through waistline appears on the negative electrode interface, it is determined that the predicted battery has excessive N-methylpyrrolidone residue.

[0087] It should be noted that, in actual operation, steps S1 and S2 constitute a determination process based on the hot pressing Hi-pot resistance value, steps S3 and S4 constitute a determination process based on OCV0, and steps S5 and S6 constitute a determination process based on the first step of formation charging end voltage. These three determination processes are executed sequentially as the production process proceeds, and the order of their respective processes can be adjusted according to the actual production process.

[0088] As some examples of the present invention, during the detection process, the order of detecting and determining the open circuit voltage (OCV0), hot pressure Hi-pot resistance test, and the first step charging end voltage of the battery can also be adjusted. For example, the determination process based on OCV0 can be performed first, and then the determination process based on the hot pressure Hi-pot resistance and the determination process based on the first step charging end voltage of the formation can be performed in sequence.

[0089] Preferably, in step S8, the battery is fully charged with a constant current of 0.3C to 0.8C and then disassembled.

[0090] It should be noted that in step S5, after the first step of charging of the multiple batteries to be tested is completed, the batteries to be tested should continue to be fully formed (i.e., the second step of charging, the third step of charging and the fourth step of discharging in the complete formation process are continued).

[0091] As some examples of the present invention, the complete formation process of the battery is as follows:

[0092] The first step is charging: charging rate: 0.05~0.1C, charging time: 30~60min;

[0093] The second step is charging: charging rate: 0.1~0.15C, charging time: 40~60min;

[0094] The third step is charging: charging rate: 0.18~0.2C, charging time: 30~176min;

[0095] The fourth step is discharge: discharge rate: 0.2-0.25C, discharge time: 1-2min. In the fourth step, the purpose of short-time discharge is to achieve the passivation of the battery cell.

[0096] It should be noted that the battery formation may include two formations, namely the first formation and the second formation. Usually, the battery that fails the first formation will be retested by the second formation; if the first formation is OK, there is no need for the second formation.

[0097] Preferably, the first step of forming is as follows:

[0098] The first step is charging: charging rate: 0.05~0.1C, charging time: 30~60min;

[0099] The second step is charging: charging rate: 0.1~0.15C, charging time: 40~60min;

[0100] The third step is charging: charging rate: 0.18~0.2C, charging time: 30~176min;

[0101] The fourth step is discharge: discharge rate: 0.2~0.25C, discharge time: 1~2min.

[0102] Preferably, the steps of the second formation are as follows:

[0103] The first step is charging: charging rate: 0.05~0.1C, charging time: 30~60min;

[0104] The second step is charging: charging rate: 0.1~0.15C, charging time: 40~60min;

[0105] The third step is charging: charging rate: 0.18~0.2C, charging time: 30~176min;

[0106] The fourth step is discharge: discharge rate: 0.2~0.25C, discharge time: 1~2min.

[0107] Preferably:

[0108] When the first formation of the battery is OK, the second formation is not performed, so the "measuring the first charge end voltage of the formation of multiple batteries to be tested" in step S5 means measuring the first charge end voltage of the first formation of multiple batteries to be tested, and the U in step S6 实2 That is, the actual measured value of the first step charging end voltage of the first formation of the battery to be predicted;

[0109] When the battery is formed NG for the first time, and the first step of charging of the first formation is completed, then the "measuring the first step of charging end voltage of the formation of multiple batteries to be tested" in step S5 also means measuring the first step of charging end voltage of the first formation of multiple batteries to be tested, and the U in step S6 实2 That is, the actual measured value of the first step charging end voltage of the first formation of the battery to be predicted;

[0110] When the battery to be predicted is NG in the first formation and the first step of charging in the first formation is interrupted, steps S5 and S6 are not performed (i.e., the screening T is not performed). 3 ), directly execute S8;

[0111] When the battery is NG for the first formation and the first step of charging of the first formation fails to be performed, then the "measuring the first step of charging end voltage of the formation of multiple batteries to be tested" in step S5 means measuring the first step of charging end voltage of the second formation of multiple batteries to be tested, and the U in step S6 实2 That is the actual measured value of the first step of charging end voltage of the second formation of the battery to be predicted.

[0112] Preferably, before executing step S8, the multiple batteries to be tested and the batteries to be predicted have undergone a complete formation process respectively (i.e., if the first formation is NG, a second formation is required before S8), and the formation processes of the multiple batteries to be tested and the batteries to be predicted are exactly the same.

[0113] As some examples of the present invention, the N 1 、N 2 、N 3 It can be set by testing as required, as described in N 1 、N 2 、N 3 The value of can be 0.8~3.

[0114] It should be noted that the "black through waistline" described in the present invention means that for the disassembled continuous electrode, there are multiple fold lines arranged at intervals along the length direction and extending along the width direction, such as Figure 1 The red lines in the middle show the position and direction of some fold lines, which divide the continuous pole piece into several pole surfaces. If black spots visible to the naked eye are observed on each pole surface, it is considered that a "black waistline" appears on the negative electrode interface.

[0115] It should be noted that the battery to be tested and the battery to be predicted in the present invention are batteries of the same model that are manufactured using exactly the same production materials and production processes.

[0116] As some examples of the present invention, during the detection process, when it is found that the battery meets the screening condition T 1 、T 2 or T 3 When the battery meets T 1 、T 2 With T 3 The condition of the battery is marked.

[0117] In summary, the method for determining excessive residual N-methylpyrrolidone in a battery according to the present invention has the following advantages:

[0118] 1. The present invention studies the characteristics of N-methylpyrrolidone and its influence on battery performance, and adopts the steps of detecting the open circuit voltage (OCV0) of the battery in an unactivated state, hot pressing Hi-pot resistance test, the first step of formation charging end voltage and observing the waistline of the fully charged negative electrode interface, so as to quickly determine whether N-methylpyrrolidone remains excessive, simplifying the determination process and test time of excessive residual N-methylpyrrolidone in the battery, and making it more efficient and quick;

[0119] 2. The present invention reduces the risk of battery cycle failure by determining whether excessive N-methylpyrrolidone remains, and provides a new technical means for battery quality control and safety testing.

[0120] The embodiments of the present application are described above in conjunction with the accompanying drawings. In the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. A method for determining excessive residual N-methylpyrrolidone in a battery, characterized in that: Includes steps: S1, measuring the hot pressure Hi-pot resistance values ​​of multiple batteries to be tested, drawing a scatter plot to obtain the distribution of the hot pressure Hi-pot resistance values, and establishing a qualified range Q1 of the hot pressure Hi-pot resistance values ​​according to the distribution of the hot pressure Hi-pot resistance values; S2, setting screening condition T1 according to the distribution state of the hot pressing Hi-pot resistance value obtained in step S1; S3, measuring the open circuit voltage OCV0 of multiple batteries to be tested, drawing a scatter diagram to analyze the distribution state of OCV0, and establishing a voltage qualified range Q2 of OCV0 according to the distribution state of OCV0; S4, setting the screening condition T2 according to the distribution state of OCV0 obtained in step S3; S5, measuring the first step charge end voltage of the formation of multiple batteries to be tested, drawing a scatter plot to analyze the distribution state of the first step charge end voltage, and establishing a qualified range Q3 of the first step charge end voltage of the formation according to the obtained distribution state of the first step charge end voltage; S6, setting a screening condition T3 according to the distribution state of the charging end voltage of the first step of formation obtained in step S5; S7, determining whether the battery to be predicted satisfies the screening conditions T1, T2 and T3 at the same time, if yes, proceeding to step S8; if no, it is considered that the residual amount of N-methylpyrrolidone in the battery to be predicted is normal; S8, after full charging at a constant current, the predicted battery that meets the screening conditions T1, T2 and T3 is disassembled to confirm the state of the negative electrode interface and observe whether a black through waistline appears on the negative electrode interface. If a black through waistline appears on the negative electrode interface, it is determined that the predicted battery has excessive residual N-methylpyrrolidone.

2. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 1, characterized in that: In step S1, the process of establishing the qualified range Q1 of the hot pressing Hi-pot resistance value according to the distribution state of the hot pressing Hi-pot resistance value is as follows: First, Anderson-Darling normality calculation is performed on multiple hot pressure Hi-pot resistance values ​​measured by multiple batteries to obtain their overall mean value R0 and standard deviation δ1; Then, the discrete degree of the array is measured by the standard deviation δ1, and N1 times δ1 is taken as the discrete standard level, and the qualified range Q1 of the hot pressing Hi-pot resistance value is obtained as: R0±N1·δ1.

3. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 2, characterized in that: In step S2, the screening condition T1 is set as: The battery to be predicted is subjected to thermal pressure Hi-pot resistance measurement, and the measured value of the thermal pressure Hi-pot resistance of the battery to be predicted is R 实 Compared with the lower limit R0-N1·δ1 in Q1, if R 实 If it is lower than the lower limit value R0-N1·δ1 in the qualified range Q1, the battery to be predicted meets the screening condition T1.

4. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 1, characterized in that: In step S3, the process of establishing the voltage qualified range Q2 of OCV0 according to the distribution state of OCV0 is as follows: First, the Anderson-Darling normality calculation is performed on multiple OCV0s measured by multiple batteries to obtain their overall mean value U0 and standard deviation δ2; Then, the discrete degree of the array is measured by the standard deviation δ2, and N2 times δ2 is used as the discrete standard level, and the voltage qualified range Q2 of OCV0 is obtained as: U0±N2·δ2.

5. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 4, characterized in that: In step S4, the screening condition T2 is set as: The open circuit voltage OCV0 of the battery to be predicted is tested to obtain the actual measured value U of the open circuit voltage of the battery to be predicted. 实1 , will U 实1 Compared with the lower limit value U0-N2·δ2 in Q2, if U 实1 If it is lower than U0-N2·δ2, the battery to be predicted meets the screening condition T2.

6. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 1, characterized in that: In step S5, the process of establishing the qualified range Q3 of the first step charging end voltage of the battery formation according to the measured first step charging end voltage of the battery formation is as follows: First, Anderson-Darling normality calculation is performed on multiple first-step charge end voltages of formation measured by multiple batteries to obtain their overall average value U1 and standard deviation δ3; Then, the discrete degree of the array is measured by the standard deviation δ3, and N3 times δ3 is taken as the discrete standard level, and the qualified range Q3 of the charging end voltage of the first step of formation is obtained as: U1±N3·δ3.

7. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 6, characterized in that: In step S6, the screening condition T3 is set as: The battery to be predicted is also subjected to the same formation test as the battery to be tested, and the measured value U of the first step of formation charging end voltage of the battery to be predicted is measured. 实2 ; If ▏(U 实2 -U1)▏≤N3·δ3, the battery to be predicted meets the screening condition T3.

8. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 7, characterized in that: In step S5, after the first step of charging of the multiple batteries to be tested is completed, the batteries to be tested should continue to be fully formed.

9. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 1, characterized in that: In step S8, the battery is fully charged with a constant current of 0.3C to 0.8C and then disassembled.

10. The method for determining excessive residual N-methylpyrrolidone in a battery according to claim 8, characterized in that: The complete test steps include: The first step is charging: charging rate: 0.05~0.1C, charging time: 30~60min; The second step is charging: charging rate: 0.1-0.15C, charging time: 40-60min; The third step is charging: charging rate: 0.18~0.2C, charging time: 30~176min; The fourth step is discharge: discharge rate: 0.2~0.25C, discharge time: 1~2min.

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