Negative electrode sheet for fast charging at low temperature and method for manufacturing battery cell using same

Abstract

The application belongs to the technical field of lithium batteries, and provides a negative pole piece for fast charging at low temperature and a preparation method of a battery cell, comprising the following steps: S100, electrically conductive paste is coated on both sides of a negative current collector by a coating machine to obtain a double-sided coating pole piece; S200, an infrared image of the coating area of the double-sided coating pole piece is obtained, and an abnormal area is marked; S300, the defect level of the current pole piece is determined according to the marked abnormal area; S400, the coating machine parameters are fine-tuned according to the defect level of the pole piece to obtain a qualified pole piece; S500, the double-sided coating pole piece is rolled to obtain a finished pole piece; and S600, the finished pole piece is slitted to form a negative pole piece. The application can monitor and dynamically adjust the working parameters of the coating machine in real time, accurately control the coating process, improve the quality of the pole piece and the battery cell, avoid the electrolysis phenomenon of the secondary battery during charging at low temperature, and accelerate the charging speed of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a negative plate for fast charging at low temperature and a preparation method of a battery cell. BACKGROUND

[0002] Secondary batteries such as lithium ion batteries have the advantages of environmental friendliness, high energy density, long cycle life, etc., and are widely used in mobile phones, computers, wearable devices, consumer drones, electric tools, electric motorcycles, electric vehicles or large-scale energy storage devices. Among them, solid lithium batteries are highly concerned in the market due to their high safety and large energy density. The charging performance of solid lithium batteries remains fast and stable, which can improve the competitiveness in the market. However, in the vast northern region of China, the temperature in winter can reach -5 to -40℃, and in extreme weather, the charging performance of many solid lithium batteries is adversely affected. The negative material in the solid lithium battery system is mainly graphite. In the low-temperature application scene (≤-20℃), there is a large charge transfer resistance, which makes it difficult for lithium ion batteries to charge at low temperature. At present, the problems are solved by adding low-temperature additives to the electrolyte or using small-particle negative active materials to accelerate the deintercalation of lithium ions between the layers of graphite. However, the low lithium intercalation potential of graphite (Li / Li+ ~ 0.1V) is prone to lithium precipitation at low temperature, which causes safety hazards. To solve the above problems, the prior art wraps high lithium intercalation potential particles on the outer surface of the negative active particles to achieve high-speed low-temperature lithium intercalation, enhance the conductivity of the negative plate, prevent excessive lithium precipitation during the charging and discharging process of the solid lithium battery at low temperature, and maintain a long cycle life. However, wrapping high lithium intercalation potential particles on the outer surface of the negative active particles not only is complicated to operate and cannot be applied to large-scale production, but also increases the volume of the negative active particles, which may cause unevenness in the coating process, resulting in a large resistance at the uneven conductive paste, thereby affecting the charging rate. SUMMARY

[0003] The purpose of the present application is to provide a negative plate for fast charging at low temperature and a preparation method of a battery cell to solve one or more technical problems in the prior art and at least provide a beneficial choice or create conditions.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of a negative plate for fast charging at low temperature is provided, which comprises the following steps:

[0005] S100, coating conductive paste on both sides of the negative current collector by a coating machine to obtain a double-sided coated plate;

[0006] S200, obtaining an infrared image of the coating area of the double-sided coated plate and marking the abnormal area;

[0007] S300, determining the defect level of the current pole piece according to the marked abnormal area;

[0008] S400, fine-tuning the coating machine parameters according to the pole piece defect level to obtain qualified pole pieces;

[0009] S500, rolling the qualified pole pieces to obtain finished pole pieces;

[0010] S600, slitting the finished pole pieces to form negative pole pieces.

[0011] Further, in S100, the current collector is one of copper foil and carbon-coated copper foil.

[0012] Further, in S100, the coating machine is MSTB-1-600 double-sided coating machine.

[0013] Further, in S100, the conductive paste is any one of the conductive pastes with publication numbers CN114551784B, CN109192923B and CN116525765B.

[0014] Further, in S600, the finished products are slit by using WYSL-1300M microcomputer controlled double middle slitting aluminum foil slitting machine of WanYing Machinery to obtain finished pole pieces.

[0015] Further, in S600, the slitting speed is 200-300 m / min.

[0016] Further, in S100, the speed ratio of the steel roller and the rubber roller in the coating machine is 1.3, the thickness of the single-sided coating of the current collector is 45 mm, and the area density is not greater than 100 g / cm.

[0017] Secondary batteries such as lithium ion batteries have the advantages of environmental friendliness, high energy density, long cycle life, etc., and are widely used in mobile phones, computers, wearable devices, consumer drones, electric tools, electric motorcycles, electric vehicles or large-scale energy storage devices. However, the performance and life of lithium ion batteries are greatly affected by temperature conditions. Currently, the problem of low-temperature charging difficulty is solved by adding low-temperature additives to the electrolyte or using small-particle negative active materials to accelerate the intercalation of lithium ions into the graphite interlayer. However, the low lithium intercalation potential of graphite (Li / Li+ ~ 0.1V) is prone to lithium precipitation at low temperature, which poses a safety hazard. To solve the above problems, a Chinese invention patent named "Negative plate for fast charging at low temperature, preparation method thereof and battery cell" with publication number CN114551784B was applied for on October 21, 2021. By adding high lithium intercalation potential particles wrapped on the outer surface of the negative active particles, high-speed low-temperature lithium intercalation is achieved, the conductivity of the negative plate is enhanced, the problem of excessive lithium precipitation during the charging and discharging process of solid lithium batteries at low temperature is prevented, and a long cycle life is maintained. However, wrapping high lithium intercalation potential particles on the outer surface of the negative active particles not only is cumbersome to operate and cannot be applied to large-scale production, but also increases the volume of the negative active particles, resulting in a large resistance at the uneven part of the conductive paste during the coating process, which in turn affects the charging rate. The present invention proposes the following method: by acquiring the infrared image of the plate in real time, marking the abnormal area in the infrared image, and determining the defect level of the current plate according to the abnormal area, the working parameters of the coating machine are dynamically adjusted according to the defect level of the plate to achieve precise control of the plate quality:

[0018] Further, in S200, the specific method of acquiring the infrared image of the double-sided coating plate coating area and marking the abnormal area is: heating the double-sided coating plate at 140-180℃ for 30-50S, then naturally cooling for 30S, acquiring the infrared image through the collection angle of the infrared thermal imager which is directly opposite the coating area of the double-sided coating plate, dividing the infrared image into multiple sub-regions TS using the sobel edge algorithm, wherein the pixel value contained in the sub-region represents the temperature value of the plate at that pixel position, taking i as the serial number of the sub-region, TS i represents the i-th sub-region;

[0019] In the acquired infrared image, mark the sub-region with the largest average pixel value as the thick coating area, and mark the sub-region with the smallest average pixel value as the thin coating area. Take the geometric center point of the thick coating area as the anchor point and the geometric center point of the thin coating area as the target point. Take the direction from the anchor point to the target point as the fluid direction. Draw a straight line Line1 from the anchor point along the fluid direction. Mark the sub-regions passed by Line1 as unstable sub-regions UTS. Take j as the serial number of the unstable sub-region, UTS jThe jth unstable sub-region is represented, all unstable sub-regions are added to the list List1, and the collapse coefficient of all unstable sub-regions is calculated in turn. The specific method is: according to the formula Wherein UTS(r) represents the pixel value contained in the unstable sub-region other than the jth unstable sub-region in the list List1, Max{UTS(j)-UTS(r)} represents the maximum absolute difference value between all pixel values in the jth unstable sub-region in the list and all pixel values in the other unstable sub-regions in the list1, P(r) represents the distance between the two pixel points corresponding to the maximum absolute difference value between all pixel values in the jth unstable sub-region in the list and all pixel values in the other unstable sub-regions in the list1, N represents the number of unstable sub-regions in the list List1, SC j The collapse coefficient of the jth unstable sub-region in the list List1 is represented, the average collapse coefficient of all unstable sub-regions in the list List1 is calculated, and the unstable sub-region with a collapse coefficient greater than the average collapse coefficient is marked as an abnormal region.

[0020] The unevenness of the conductive paste in the thick coating area and the thin coating area in the above method is that the temperature value is higher in the thick coating area, and the temperature value is generally lower in the thin coating area. In a Chinese patent with the patent number CN117969533B, entitled Insulating coating detection method, device, system, equipment and storage medium, the infrared image is collected by the infrared camera, and the region with abnormal temperature value is marked as an abnormal region, which can accurately identify the heat difference caused by uneven distribution of insulating coating. However, the above method does not consider the flowability of the paste and the heat transfer, and cannot guarantee that the temperature distribution in the infrared image collected by the infrared device is stable. The above steps mark the region with the largest temperature difference first, and then screen out the unstable sub-regions that may be affected according to the heat transfer. At the same time, the collapse coefficient is calculated to accurately calculate the sub-regions that will be affected in all unstable regions, so as to accurately mark all abnormal regions in the infrared image. The abnormal region can reflect the current paste distribution of the pole piece. Through real-time monitoring of the current paste distribution of the pole piece, the working parameters of the coating machine are dynamically adjusted to realize precise control of the coating process, and the quality and service life of the pole piece are guaranteed.

[0021] Further, in S300, the specific method for determining the defect level of the current pole piece according to the marked abnormal region is: marking all abnormal regions on the obtained infrared image, marking the point corresponding to the maximum value of the pixels in all abnormal regions as P k , k is the serial number of the abnormal region, and P kA plurality of line segments line2 are formed with the geometric centers of all sub-regions, and the edge of the sub-region corresponding to the shortest line segment Line2 is marked as RL k All pixel values on Rl are sequentially traversed k The point corresponding to the minimum value among all traversed pixel values is marked as Plk_min, and the point corresponding to the maximum value among all traversed pixel values is marked as Plk_max. A curve formed between the point Plk_min and the point Plk_max on the edge RLk is added to the point P k and P K+1 in a proportionally scaled manner, and all points P k are connected to form a closed region. The area ratio of the closed region to the entire infrared image is calculated. If the area ratio is less than or equal to 0.33, the defect level of the current pole piece is level 1; if the area ratio is greater than 0.33 and less than or equal to 0.66, the defect level of the current pole piece is level 2; and if the area ratio is greater than 0.66, the defect level of the current pole piece is level 3.

[0022] Further, in S400, the specific method for fine-tuning the coating machine parameters to obtain qualified pole pieces according to the defect level of the pole piece is as follows: if the defect level of the current pole piece is level 1, the current coating machine working parameters are kept unchanged; if the defect level of the current pole piece is level 2, the coating machine doctor blade is adjusted to be perpendicular to the surface of the steel roller, the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.0, the thickness of single-side coating of the copper foil is 43 mm, and the areal density is not greater than 110 g / cm2; and if the defect level of the current pole piece is level 3, the coating machine doctor blade is adjusted to be perpendicular to the surface of the steel roller, the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.5, the thickness of single-side coating of the copper foil is 47 mm, and the areal density is not greater than 110 g / cm2. The pole piece coated by the coating machine after the adjustment of the working parameters is recorded as a qualified pole piece.

[0023] Further, in S500, the specific method for rolling the qualified pole piece to obtain a finished pole piece is as follows: the qualified pole piece is rolled by a rolling machine at a speed of 20 m / min to obtain a finished pole piece, wherein the pressure of the rolling machine is 10 t-60 t, t being a unit of pressure.

[0024] Further, the rolling includes secondary rolling, which is a combination of patterned rolling and smooth rolling, or a combination of hot rolling and flat rolling.

[0025] Preferably, the patterned rolling is rolling in which a wear-resistant pattern is arranged on the pressure roller, the smooth rolling is rolling in which the surface of the pressure roller is smooth, the hot rolling is rolling in which a temperature of 160°C is applied when the pressure roller is rolling, and the flat rolling is rolling in which a series of rotatable roller surfaces are installed on an arc-shaped mandrel through bearings to achieve a flattening effect.

[0026] The beneficial effects are as follows: This invention can accurately identify abnormal areas in infrared images caused by uneven distribution of conductive paste using temperature values, and significantly improves the accuracy and practicality of defect detection. By analyzing the local temperature differences caused by the non-uniformity of conductive paste, it captures the initial morphology of the abnormal area and its subsequent diffusion path, effectively avoiding the problem of missing small defects that may be caused by traditional fixed thresholds. At the same time, for the temperature gradient area at the edge of the abnormal area caused by heat conduction, this invention adopts a dynamic correction strategy, combined with the thermophysical characteristics of conductive paste, to clearly distinguish between real defects and thermal interference signals, significantly reducing the risk of misjudgment. By correlating the temperature characteristics and diffusion behavior of the abnormal area with the coating process parameters of the electrode, it provides a direct basis for optimizing the production process, assists in the rapid diagnosis of uneven paste mixing or coating process abnormalities, solves the problem of unevenness during the coating process, improves the quality of the electrode and cell, avoids the cleavage phenomenon that occurs when charging secondary batteries at low temperatures, and accelerates the charging speed of the battery.

[0027] The present invention also provides a battery cell, comprising a negative electrode sheet prepared by the above-described method for preparing a negative electrode sheet, wherein the negative electrode sheet and a positive electrode sheet are assembled together under an inert gas atmosphere at a pressure of 6 to 10 MPa, and the battery cell is formed into a final finished battery cell through cell formation.

[0028] Furthermore, the battery cell also includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode material, wherein the positive electrode material can be lithium iron phosphate (LFP) material, ternary (NCM) material, nickel manganese aluminum (NCA) material, lithium manganese iron phosphate (LMFP) material, lithium manganese oxide (LMP) material, layered sodium battery material, or Prussian-type sodium battery positive electrode material.

[0029] The beneficial effects of this invention are as follows: This invention can accurately identify abnormal areas in infrared images caused by uneven distribution of conductive paste using temperature values, and significantly improves the accuracy and practicality of defect detection. By analyzing the local temperature differences caused by the non-uniformity of conductive paste, it captures the initial morphology of the abnormal area and its subsequent diffusion path, effectively avoiding the problem of missing small defects that may be caused by traditional fixed thresholds. At the same time, for the temperature gradient area caused by heat conduction at the edge of the abnormal area, this invention adopts a dynamic correction strategy, combined with the thermophysical characteristics of conductive paste, to clearly distinguish between real defects and thermal interference signals, significantly reducing the risk of misjudgment. By correlating the temperature characteristics and diffusion behavior of the abnormal area with the coating process parameters of the electrode, it provides a direct basis for optimizing the production process, assists in quickly diagnosing uneven paste mixing or coating process abnormalities, and solves the problem that the large resistance generated at the non-uniform conductive paste during the coating process affects the charging rate. Attached Figure Description

[0030] Figure 1A flow chart of a preparation method of a negative electrode sheet for fast charging at low temperature is shown. DETAILED DESCRIPTION

[0031] Embodiments of the present application are described in detail below with reference to examples shown in the accompanying drawings, in which the same or similar components or components having the same or similar functions are denoted by the same or similar reference numerals throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0032] Embodiment 1

[0033] Figure 1 A flow chart of a preparation method of a negative electrode sheet for fast charging at low temperature is shown.

[0034] Referring to Figure 1 The present application proposes a preparation method of a negative electrode sheet for fast charging at low temperature, which comprises the following steps:

[0035] S100, coating conductive paste on both sides of the negative current collector by a coating machine to obtain a double-sided coated electrode sheet;

[0036] S200, obtaining an infrared image of the coating area of the double-sided coated electrode sheet and marking the abnormal area;

[0037] S300, determining the defect level of the current electrode sheet according to the marked abnormal area;

[0038] S400, fine-tuning the coating machine parameters according to the defect level of the electrode sheet to obtain a qualified electrode sheet;

[0039] S500, rolling the qualified electrode sheet to obtain a finished electrode sheet;

[0040] S600, slitting the finished electrode sheet to form a negative electrode sheet.

[0041] Further, in S100, the current collector is a carbon-coated copper foil.

[0042] Further, in S100, the coating machine is an MSTB-1-600 double-sided coating machine.

[0043] Further, in S100, the conductive paste is the conductive paste in CN114551784B.

[0044] Further, in S600, the finished product is slit by a WYSL-1300M microcomputer-controlled double-slitting shaft aluminum foil slitting machine of Wanling Machinery to obtain a finished electrode sheet.

[0045] Further, in S600, the slitting speed is 200 m / min.

[0046] Further, in S100, the speed ratio of the steel roller and the rubber roller in the coating machine is 1.3, the thickness of the single-sided coating of the current collector is 45 mm, and the area density is not greater than 100 g / cm.

[0047] Further, in S200, the specific method for obtaining the infrared image of the double-sided coated pole piece coating area and marking the abnormal area is as follows: the double-sided coated pole piece is heated at 160 DEG C for 30 S, and then naturally cooled for 30 S, then the infrared image is obtained through the collection angle of the infrared thermal imager which is directly opposite the coating area of the double-sided coated pole piece, the infrared image is divided into a plurality of sub-regions TS using the sobel edge algorithm, wherein the pixel value contained in the sub-region represents the temperature value of the pole piece at the pixel point position, i is used as the serial number of the sub-region, TS i represents the i-th sub-region;

[0048] In the obtained infrared image, the sub-region with the maximum average pixel value is marked as the thick coating area, the sub-region with the minimum average pixel value is marked as the thin coating area, the geometric center point of the thick coating area is used as the anchor point, the geometric center point of the thin coating area is used as the target point, the direction from the anchor point to the target point is used as the fluid direction, a straight line Line1 is drawn from the anchor point along the fluid direction, the sub-regions passed by Line1 are marked as unstable sub-regions UTS, j is used as the serial number of the unstable sub-region, UTS j represents the j-th unstable sub-region, all unstable sub-regions are added to the list List1, and the collapse coefficient of all unstable sub-regions is calculated in turn, the specific method is as follows: according to the formula wherein UTS(r) represents the pixel value contained in the unstable sub-region other than the j-th unstable sub-region in the list List1, Max{UTS(j)-UTS(r)} represents the maximum absolute difference value between all pixel values in the j-th unstable sub-region in the list and all pixel values in the other unstable sub-regions in the list1, P(r) represents the distance between the two pixel points corresponding to the maximum absolute difference value between all pixel values in the j-th unstable sub-region and all pixel values in the other unstable sub-regions in the list1, N represents the number of unstable sub-regions in the list List1, SC j represents the collapse coefficient of the j-th unstable sub-region in the list List1, the average collapse coefficient of all unstable sub-regions in the list List1 is calculated, and the unstable sub-region with a collapse coefficient greater than the average collapse coefficient is marked as an abnormal area.

[0049] The unevenness of the conductive paste corresponding to the thick coating area and the thin coating area in the above method is that the temperature value is higher in the thick coating area and generally lower in the thin coating area. In a Chinese patent with the title of insulation coating detection method, device, system, equipment and storage medium and the publication number CN117969533B, the infrared image is collected by the infrared camera, and the area with abnormal temperature value is marked as an abnormal area, so that the heat difference caused by uneven distribution of the insulation coating can be accurately identified. However, the above method does not consider the flowability of the paste and the heat transfer, and cannot guarantee that the temperature distribution in the infrared image collected by the infrared device is stable. The above steps mark the area with the largest temperature difference first, and then screen the unstable sub-area that may be affected according to the heat transfer. At the same time, the sub-area that will be affected in all unstable areas is accurately calculated by calculating the dissipation coefficient, so that all abnormal areas in the infrared image can be accurately marked. The abnormal area can reflect the current paste distribution of the pole piece. Through real-time monitoring of the current paste distribution of the pole piece, the working parameters of the coating machine are dynamically adjusted to realize precise control of the coating process, and the quality and service life of the pole piece are guaranteed.

[0050] Further, in S300, the specific method for determining the defect level of the current pole piece according to the marked abnormal area is as follows: marking all abnormal areas on the obtained infrared image, marking the point corresponding to the maximum value of the pixels in all abnormal areas as P k , k is the serial number of the abnormal area, and a plurality of line segments line2 are formed by connecting Pk and the geometric centers of all sub-areas in turn. The edge of the sub-area corresponding to the shortest line segment Line2 is marked as RL k , all pixel values on Rl k are traversed in turn, the point corresponding to the minimum value of all traversed pixel values is marked as Plk_min, and the point corresponding to the maximum value of all traversed pixel values is marked as Plk_max. The curve formed between the point Plk_min and the point Plk_max on the edge RLk is added between the point P k and the point P K+1 by equal ratio scaling, and all points P k are connected to form a closed area according to the same method. If the area ratio is less than or equal to 0.33, the defect level of the current pole piece is 1; if the area ratio is greater than 0.33 and less than or equal to 0.66, the defect level of the current pole piece is 2; and if the area ratio is greater than 0.66, the defect level of the current pole piece is 3.

[0051] Furthermore, in S400, the specific method for fine-tuning the coating machine parameters to obtain qualified electrodes based on the electrode defect level is as follows: If the current electrode defect level is level 1, the current coating machine operating parameters remain unchanged; if the current electrode defect level is level 2, the coating machine doctor blade is adjusted to be perpendicular to the steel roller surface, and the speed ratio between the steel roller and the rubber roller is adjusted to 1.0, the thickness of the copper foil coating on one side is 43mm, and the surface density is 105g / cm³; if the current electrode defect level is level 3, the coating machine doctor blade is adjusted to be perpendicular to the steel roller surface, and the speed ratio between the steel roller and the rubber roller is adjusted to 1.5, the thickness of the copper foil coating on one side is 47mm, and the surface density is 105g / cm³. The electrode coated by the coating machine after adjusting the operating parameters is recorded as a qualified electrode.

[0052] Furthermore, in S500, the specific method for rolling the qualified electrode sheet to obtain the finished electrode sheet is as follows: the qualified electrode sheet is rolled by a roller press at a speed of 20m / min to obtain the finished electrode sheet, wherein the roller press pressure is 30t, and t is a pressure unit.

[0053] Furthermore, roll forming includes secondary roll forming, which is a combination of pattern roll forming and smooth roll forming.

[0054] Preferably, the patterned roller has wear-resistant patterns on its roller, while the smooth roller has a smooth surface.

[0055] The beneficial effects of this invention are as follows: This invention can accurately identify abnormal areas in infrared images caused by uneven distribution of conductive paste using temperature values, and significantly improves the accuracy and practicality of defect detection. By analyzing the local temperature differences caused by the non-uniformity of conductive paste, it captures the initial morphology of the abnormal area and its subsequent diffusion path, effectively avoiding the problem of missing small defects that may be caused by traditional fixed thresholds. At the same time, for the temperature gradient area at the edge of the abnormal area caused by heat conduction, this invention adopts a dynamic correction strategy, combined with the thermophysical characteristics of conductive paste, to clearly distinguish between real defects and thermal interference signals, significantly reducing the risk of misjudgment. By correlating the temperature characteristics and diffusion behavior of the abnormal area with the coating process parameters of the electrode, it provides a direct basis for optimizing the production process, assists in the rapid diagnosis of uneven paste mixing or coating process abnormalities, solves the problem of unevenness during the coating process, improves the quality of the electrode and cell, avoids the cleavage phenomenon that occurs when charging secondary batteries at low temperatures, and accelerates the charging speed of the battery.

[0056] Under an argon atmosphere and at 80 standard atmospheres, the negative electrode and positive electrode are assembled together and then formed into the final battery cell through cell formation. The positive electrode is a ternary NCM positive electrode.

[0057] Comparative Example 1

[0058] The Chinese invention patent with the title of a negative plate for fast charging at low temperature, a production method of the negative plate and a cell production method of embodiment 1 of the cell, applied on October 22, 2021, and with the publication number of CN114551784B.

[0059] Further, the performance of the cells produced by the examples and the comparative examples is further verified by the performance test of the cells produced by the examples and the comparative examples:

[0060] The DC impedance of the finished cells produced by the examples and the comparative examples is measured at low temperature, and the specific method is as follows: the finished cells produced by the examples and the comparative examples are placed at-20℃ and-30℃, the voltage difference before and after 10s of 200A charging under the condition of different electric quantity of each cell is recorded, the DC impedance is obtained by dividing the voltage difference by 200, the electric quantity of the cell is expressed by SOC percentage, the smaller the DC impedance, the smaller the resistance at low temperature charging, and the measurement results are shown in Table 1 and Table 2.

[0061] Table 1. DC impedance data of the cells produced by the examples and the comparative examples at-20℃

[0062] -20℃ 20% SOC 50% SOC 70% SOC 80% SOC 90% SOC Comparative Example 1 13.8 13.6 13.3 13.5 13.4 Example 1 10.7 10.5 10.6 10.5 10.4

[0063] Table 2. DC impedance data of the cells produced by the examples and the comparative examples at-30℃

[0064] -30℃ 20% SOC 50% SOC 70% SOC 80% SOC 90% SOC Comparative Example 1 25.3 25.4 25.1 24.8 24.6 Example 1 18.6 18.9 18.8 18.7 18.5

[0065] Analysis: by observing the data in Table 1 and Table 2, it is found that the DC impedance of the cells measured in Table 2 is generally higher than that in Table 1 at-20℃, which indicates that the lower the temperature, the stronger the DC impedance of the cell, and the more difficult the charging. By observing Table 1 and Table 2, it is found that the DC impedance of Example 1 is smaller than that of Comparative Example 1, which shows that the method provided by the present application can monitor the coating quality of the pole piece in real time in the pole piece coating process, dynamically adjust the working parameters of the coating machine according to the coating quality of the pole piece, and avoid the occurrence of partial high resistance due to uneven coating of the pole piece, thereby affecting the charging rate and overall DC impedance of the finished cell.

[0066] Although the description of the present application has been quite detailed and particularly described for several embodiments, it is not intended to be limited to any of these details or embodiments or any special embodiment, so as to effectively cover the intended scope of the present application. In addition, the present application is described above in the embodiments that the inventors can foresee, and the purpose is to provide a useful description, and non-essential modifications of the present application that have not yet been foreseen can still represent equivalent modifications of the present application.

Claims

1. A method for preparing a negative electrode sheet for rapid charging at low temperature, characterized in that, The method includes the following steps: S100, a double-sided coated electrode sheet is obtained by coating a conductive paste onto the negative electrode current collector using a coating machine; S200: Acquire infrared images of the double-sided coated electrode coating area and mark abnormal areas; S300, determine the defect level of the current electrode based on the marked abnormal areas; S400: Fine-tuning the coating machine parameters according to the electrode defect level to obtain qualified electrodes; S500: Qualified electrode sheets are rolled to obtain finished electrode sheets; S600 cuts the finished electrode sheets into negative electrode sheets; In step S200, the method for acquiring infrared images of the double-sided coated electrode coating area and marking abnormal areas is as follows: The double-sided coated electrode is heated at 140-180℃ for 30-50 seconds and then naturally cooled for 30 seconds. Infrared images are then acquired by directing the infrared thermal imager at the coating area of ​​the double-sided coated electrode. The Sobel edge algorithm is used to divide the infrared image into multiple sub-regions TS, where the pixel value contained in the sub-region represents the temperature value of the electrode at that pixel location. i is used as the sub-region number, and TSi represents the i-th sub-region. In the acquired infrared image, the sub-region with the largest average pixel value is marked as the thick-coated region, and the sub-region with the smallest average pixel value is marked as the thin-coated region. The geometric center point of the thick-coated region is used as the anchor point, and the geometric center point of the thin-coated region is used as the target point. The direction from the anchor point to the target point is used as the fluid direction. A straight line Line1 is drawn from the anchor point along the fluid direction. The sub-regions traversed by Line1 are marked as unstable sub-regions UTS, with j as the index of the unstable sub-region, and UTSj representing the j-th unstable sub-region. All unstable sub-regions are added to a list List1. The collapse coefficient of all unstable sub-regions is calculated sequentially, using the formula... , where UTS(r) represents the pixel values ​​contained in the unstable sub-regions in List1 other than the j-th unstable sub-region, Max{UTS(j)-UTS(r)} represents the maximum absolute difference between all pixel values ​​in the j-th unstable sub-region of List1 and all pixel values ​​in other unstable sub-regions of List1, P(r) represents the distance between the two pixels corresponding to the maximum absolute difference between all pixel values ​​in the j-th unstable sub-region and all pixel values ​​in other unstable sub-regions of List1, N represents the number of unstable sub-regions in List1, SCj represents the collapse coefficient of the j-th unstable sub-region of List1, calculate the average collapse coefficient of all unstable sub-regions in List1, and mark unstable sub-regions with collapse coefficients greater than the average collapse coefficient as abnormal regions; In step S300, the method for determining the defect level of the current electrode based on the marked abnormal areas is as follows: Mark all abnormal regions on the acquired infrared image. Label the point corresponding to the maximum pixel value in each abnormal region as Pk, where k is the sequence number of the abnormal region. Connect Pk to the geometric center of each sub-region to form multiple line segments line2. Label the edge of the sub-region corresponding to the shortest line segment line2 as RLk. Iterate through all pixel values ​​on RLk, labeling the point corresponding to the minimum value as Plk_min and the point corresponding to the maximum value as Plk_max. Then label the edge RLk... The curve formed between points Plk_min and Plk_max on point k is added proportionally between points Pk and PK+1. All points Pk are connected in the same way to form a closed region. The area of ​​the closed region is calculated as the ratio of the area of ​​the closed region to the area of ​​the entire infrared image. If the area ratio is less than or equal to 0.33, the defect level of the current electrode is level 1; if the area ratio is greater than 0.33 and less than or equal to 0.66, the defect level of the current electrode is level 2; if the area ratio is greater than 0.66, the defect level of the current electrode is level 3.

2. The method for preparing a negative electrode sheet for rapid charging at low temperature according to claim 1, characterized in that, In the S400, the method for fine-tuning the coating machine parameters to obtain qualified electrodes based on the electrode defect level is as follows: If the current electrode defect level is level 1, keep the current coating machine operating parameters unchanged; if the current electrode defect level is level 2, adjust the coating machine doctor blade to be perpendicular to the steel roller surface, and simultaneously adjust the speed ratio of the coating machine steel roller to the rubber roller to 1.0, the thickness of the copper foil coating on one side to 43mm, and the surface density not greater than 110g / cm; if the current electrode defect level is level 3, adjust the coating machine doctor blade to be perpendicular to the steel roller surface, and simultaneously adjust the speed ratio of the coating machine steel roller to the rubber roller to 1.5, the thickness of the copper foil coating on one side to 47mm, and the surface density not greater than 110g / cm. The electrode coated by the coating machine after adjusting the operating parameters is recorded as a qualified electrode.

3. The method for preparing a negative electrode sheet for rapid charging at low temperature according to claim 2, characterized in that, In S500, the method for rolling qualified electrode sheets to obtain finished electrode sheets is as follows: qualified electrode sheets are rolled by a roller press at a speed of 20m / min to obtain finished electrode sheets, wherein the roller press pressure is 10t-60t, where t is the pressure unit.

4. A battery cell, characterized in that, The negative electrode sheet prepared by any of the negative electrode sheet preparation methods described in claims 1-3 is assembled with a positive electrode sheet under an inert gas atmosphere at a pressure of 6-10 MPa, and then formed into a final battery cell through cell formation. The positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode material.

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