Negative plate capable of being rapidly charged at low temperature and battery cell preparation method thereof

Abstract

The invention belongs to the technical field of lithium batteries, and provides a negative plate capable of being rapidly charged at low temperature and a preparation method of a battery cell of the negative plate, and the preparation method comprises the following steps: S100, coating two sides of a negative current collector with conductive slurry through a coating machine to obtain a double-side coating pole piece; s200, acquiring an infrared image of a coating area of the double-sided coating pole piece and marking an abnormal area; s300, determining the defect grade of the current pole piece according to the marked abnormal region; s400, finely adjusting parameters of the coating machine according to the defect grade of the pole piece to obtain a qualified pole piece; s500, rolling the double-sided coated pole piece to obtain a finished pole piece; S600, slitting the finished pole piece to form a negative pole piece; working parameters of the coating machine can be monitored and dynamically adjusted in real time, accurate control over the coating process is achieved, the quality of a pole piece and a battery cell is improved, the analysis phenomenon generated when a secondary battery is charged at low temperature is avoided, and the charging speed of the battery is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a negative electrode sheet capable of rapid charging at low temperatures and a method for preparing a battery cell thereof. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the advantages of being environmentally friendly, having high energy density, and having a long cycle life. They are widely used in mobile phones, computers, wearable devices, consumer drones, power tools, electric motorcycles, electric vehicles, or large energy storage devices. Among them, solid lithium batteries have attracted much attention in the market due to their high safety and high energy density. The charging performance of solid lithium batteries remains fast and stable, which can enhance their competitiveness in the market. However, in the vast northern regions of my country, the temperature can reach -5 to -40°C in winter. Under extreme weather conditions, the charging performance of many solid lithium batteries is adversely affected: the negative electrode material in the solid lithium battery system is mainly graphite. In relatively low temperature application scenarios (≤-20°C), the large charge transfer resistance makes it difficult for lithium-ion batteries to charge at low temperatures. The current solution to this problem is to add low-temperature additives to the electrolyte or use small particles of negative electrode active materials to accelerate the intercalation and deintercalation of lithium ions into the graphite interlayer. However, the lithium intercalation potential of graphite is low (Li / Li+ ~ 0.1V), which is prone to low-temperature lithium precipitation, posing a safety hazard. To solve the above problems, the existing technology adds high lithium insertion potential particles to wrap the outer surface of the negative electrode active particles, thereby achieving high-speed low-temperature lithium insertion, enhancing the conductivity of the negative electrode sheet, preventing excessive lithium deposition during the charging and discharging process of the solid lithium battery at low temperatures, and maintaining a longer cycle life. However, wrapping the high lithium insertion potential particles on the outer surface of the negative electrode active particles is not only cumbersome to operate and cannot be applied to large-scale production, but also increases the volume of the negative electrode active particles. If unevenness occurs during the coating process, a large resistance will be generated in the uneven conductive slurry, which will affect the charging rate. Summary of the Invention

[0003] The purpose of the present invention is to propose a negative electrode sheet and a method for preparing a battery cell that can be quickly charged at low temperatures, so as to solve one or more technical problems existing in the prior art and at least provide a beneficial option or create conditions.

[0004] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a negative electrode sheet capable of rapid charging at low temperatures is provided. The method comprises the following steps:

[0005] S100, applying the conductive slurry to the negative electrode current collector on both sides by a coating machine to obtain a double-sided coated electrode sheet;

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

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

[0008] S400, fine-tune the coating machine parameters according to the electrode defect level to obtain qualified electrodes;

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

[0010] S600: Cut the finished electrode sheets into negative electrode sheets.

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

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

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

[0014] Furthermore, in S600, the finished product is cut into finished electrode pieces using a Wanying Machinery WYSL-1300M microcomputer-controlled dual-center-split-axis aluminum foil slitting machine.

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

[0016] Furthermore, in S100, the speed ratio of the steel roller to the rubber roller of the coating machine is 1.3, the thickness of the coating on one side of the current collector is 45 mm, and the surface density is not greater than 100 g / cm.

[0017] Secondary batteries, such as lithium-ion batteries, have the advantages of being environmentally friendly, having high energy density, and having a long cycle life. They are widely used in mobile phones, computers, wearable devices, consumer drones, power tools, electric motorcycles, electric vehicles, or large energy storage devices. However, the performance and life of lithium-ion batteries are largely affected by temperature conditions. The current solution to the problem of low-temperature charging difficulties is to add low-temperature additives to the electrolyte or use small particles of negative electrode active materials to accelerate the intercalation and deintercalation of lithium ions into the graphite interlayer. However, the lithium intercalation potential of graphite is relatively low (Li / Li+ ~ 0.1V), and low-temperature lithium precipitation is prone to occur, posing a safety hazard. In order to solve the above problems, a Chinese invention patent entitled "A negative electrode sheet for fast charging at low temperature, its preparation method, and battery cell" was applied for on October 21, 2021, with announcement number CN114551784B. By adding high lithium insertion potential particles to wrap the outer surface of the negative electrode active particles, high-speed low-temperature lithium insertion is achieved, the conductivity of the negative electrode sheet is enhanced, and the problem of excessive lithium precipitation during the charging and discharging process of solid lithium batteries at low temperatures is prevented, and a longer cycle life is maintained. However, wrapping the high lithium insertion potential particles on the outer surface of the negative electrode active particles is not only cumbersome to operate and cannot be applied to large-scale production, but also because the volume of the negative electrode active particles is increased, if unevenness occurs during the coating process, a larger resistance will be generated in the uneven conductive slurry, which will affect the charging rate. The present invention proposes the following method, by acquiring an infrared image of the electrode in real time, marking the abnormal area in the infrared image, and determining the defect level of the current electrode based on the abnormal area, and dynamically adjusting the working parameters of the coating machine according to the defect level of the electrode to achieve precise control of the electrode quality:

[0018] Furthermore, in S200, the specific method for obtaining an infrared image of the coating area of ​​the double-sided coated electrode and marking the abnormal area is as follows: the double-sided coated electrode is heated at 140-180°C for 30-50S, and then naturally cooled for 30S, and then an infrared image is obtained by facing the coating area of ​​the double-sided coated electrode through the acquisition angle of the infrared thermal imager, and the infrared image is divided into multiple sub-areas TS using the Sobel edge algorithm, where the pixel value contained in the sub-area is represented as the temperature value of the electrode at the pixel position, and i is used as the sequence number of the sub-area, TS i represents the i-th sub-region;

[0019] In the acquired infrared image, the sub-region with the largest pixel average value is marked as the thick coating region, and the sub-region with the smallest pixel average value is marked as the thin coating region. The geometric center point of the thick coating region is used as the anchor point, and the geometric center point of the thin coating 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-region through which Line1 passes is marked as the unstable sub-region UTS. j is used as the serial number of the unstable sub-region, UTS jIndicates the jth unstable sub-region, add all unstable sub-regions to the list List1, and calculate the collapse coefficients of all unstable sub-regions in turn. The specific method is: according to the formula Where UTS(r) represents the pixel values ​​contained in the unstable subregions except the j-th unstable subregion in List1, Max{UTS(j)-UTS(r)} represents the maximum absolute difference between all pixel values ​​in the j-th unstable subregion and all pixel values ​​in other unstable subregions in List1, P(r) represents the distance between the two pixel points corresponding to the maximum absolute difference between all pixel values ​​in the j-th unstable subregion and all pixel values ​​in other unstable subregions in List1, N represents the number of unstable subregions in List1, SC j The collapse coefficient of the jth unstable sub-region in List1 is represented, the average collapse coefficient of all unstable sub-regions in List1 is calculated, and the unstable sub-regions with collapse coefficients greater than the average collapse coefficient are marked as abnormal regions.

[0020] In the above method, the thick coating area and the thin coating area correspond to the unevenness of the conductive paste. The thick coating area is manifested as a higher temperature value, while the thin coating area is generally manifested as a lower temperature value. In a Chinese patent entitled "Insulating Coating Detection Method, Device, System, Equipment and Storage Medium" with publication number CN117969533B, an infrared camera is used to capture infrared images, and areas with abnormal temperature values ​​are marked as abnormal areas, which can accurately identify the heat difference caused by the uneven distribution of the insulating coating. However, the above method does not take into account the fluidity and heat transfer properties of the slurry, and cannot guarantee that the temperature distribution in the infrared image when the infrared device is collecting is stable. The above steps first mark the area with the largest temperature difference, and then screen out the unstable sub-areas that may be affected according to the heat transfer properties. At the same time, by calculating the collapse coefficient, the affected sub-areas in all unstable areas are accurately calculated, and all abnormal areas in the infrared image can be accurately marked. The abnormal area can reflect the slurry distribution of the current electrode. By real-time monitoring of the slurry distribution of the current electrode and dynamically adjusting the working parameters of the coating machine, the coating process can be accurately controlled, ensuring the quality and service life of the electrode.

[0021] Furthermore, in S300, the specific method for determining the defect level of the current electrode according to the marked abnormal area is as follows: mark all abnormal areas on the acquired infrared image, and mark the points corresponding to the maximum values ​​of pixels in all abnormal areas as P k , k is the serial number of the abnormal area, connected in sequence to P kConstruct multiple line segments line2 with the geometric centers of all sub-regions, and mark the edge of the sub-region corresponding to the shortest line segment Line2 as RL k , traverse Rl in turn k All pixel values ​​on the edge RLk are added to the point Plk_min by scaling the curve between the points Plk_min and Plk_max. k With P K+1 In the same way, all points P k Connect to form a closed area, and calculate the area ratio of the closed area to 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 the area ratio is 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.

[0022] Furthermore, in S400, the specific method of fine-tuning the coating machine parameters according to the electrode defect level to obtain a qualified electrode is as follows: if the defect level of the current electrode is level 1, the current coating machine working parameters are kept unchanged; if the defect level of the current electrode is level 2, the coating machine scraper is adjusted to be perpendicular to the surface of the steel roller, and the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.0, the thickness of the copper foil single-sided coating is 43 mm, and the surface density is not greater than 110 g / cm; if the defect level of the current electrode is level 3, the coating machine scraper is adjusted to be perpendicular to the surface of the steel roller, and the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.5, the thickness of the copper foil single-sided coating is 47 mm, and the surface density is not greater than 110 g / cm, and the electrode coated by the coating machine after adjusting the working parameters is recorded as a qualified electrode;

[0023] Furthermore, in S500, the specific method of rolling the qualified electrode sheet to obtain the finished electrode sheet is: rolling the qualified electrode sheet through a roller press at a speed of 20m / min to obtain the finished electrode sheet, wherein the roller press pressure is 10t-60t, and t is the unit of pressure.

[0024] Furthermore, the rolling includes secondary rolling, which is a combination of pattern rolling and smooth rolling, or a combination of hot pressing and flat rolling.

[0025] Preferably, patterned roller pressing is a roller with a wear-resistant pattern, smooth roller pressing is a roller with a smooth surface, hot pressing roller pressing is a roller with a temperature of 160°C during rolling, and flat roller is a series of rotatable roller surfaces installed on an arc-shaped core shaft through bearings to achieve the flattening effect.

[0026] The beneficial effects are: the present invention can use temperature values ​​to accurately identify abnormal areas in infrared images caused by uneven distribution of conductive slurry, and significantly improve the accuracy and practicality of defect detection. By analyzing the local temperature differences caused by the unevenness of the conductive slurry, the initial form of the abnormal area and its subsequent diffusion path are captured, effectively avoiding the problem of missed detection of minor 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, the present invention adopts a dynamic correction strategy, combined with the thermal physical properties of the conductive slurry, to clearly distinguish between real defects and thermal interference signals, significantly reducing the risk of misjudgment, and by correlating the temperature characteristics and diffusion behavior of the abnormal area with the coating process parameters of the electrode, a direct optimization basis is provided for the production process, assisting in the rapid diagnosis of uneven slurry mixing or coating process abnormalities, solving the uneven phenomenon caused by the coating process, improving the quality of the electrode and battery cell, avoiding the analysis phenomenon that occurs when the secondary battery is charged at low temperature, and accelerating the charging speed of the battery.

[0027] The present invention also provides a battery cell, comprising a negative electrode sheet prepared by the above-mentioned negative electrode sheet preparation method, wherein the negative electrode sheet and the positive electrode sheet are assembled together under inert gas at 6 to 10 MPa, and the battery cell is formed into a final finished battery cell.

[0028] Furthermore, the battery cell also includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, and 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, and Prussian sodium battery positive electrode material.

[0029] The beneficial effects of the present invention are: the present invention can use temperature values ​​to accurately identify abnormal areas in infrared images caused by uneven distribution of conductive paste, and significantly improve the accuracy and practicality of defect detection. By analyzing the local temperature differences caused by the unevenness of the conductive paste, the initial form of the abnormal area and its subsequent diffusion path are captured, effectively avoiding the problem of missed detection of minor 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, the present invention adopts a dynamic correction strategy, combined with the thermal physical properties of the conductive paste, to clearly distinguish between real defects and thermal interference signals, significantly reducing the risk of misjudgment, and by correlating the temperature characteristics and diffusion behavior of the abnormal area with the coating process parameters of the electrode, a direct optimization basis is provided for the production process, assisting in the rapid diagnosis of uneven slurry mixing or coating process abnormalities, and solving the problem of unevenness in the coating process causing large resistance in the uneven conductive paste to affect the charging rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1Shown is a flow chart of a method for preparing a negative electrode sheet for rapid charging at low temperature; DETAILED DESCRIPTION

[0031] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0032] Example 1

[0033] Figure 1 Shown is a flow chart of a method for preparing a negative electrode sheet for rapid charging at low temperature.

[0034] Reference Figure 1 The present invention provides a method for preparing a negative electrode sheet capable of rapid charging at low temperature, the method comprising the following steps:

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

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

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

[0038] S400, fine-tune the coating machine parameters according to the electrode defect level to obtain qualified electrodes;

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

[0040] S600: Cut the finished electrode sheets into negative electrode sheets.

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

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

[0043] Furthermore, the conductive paste in S100 is the conductive paste in publication number CN114551784B.

[0044] Furthermore, in S600, the finished product is cut into finished electrode pieces using a Wanying Machinery WYSL-1300M microcomputer-controlled dual-center-split-axis aluminum foil slitting machine.

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

[0046] Furthermore, in S100, the speed ratio of the steel roller to the rubber roller of the coating machine is 1.3, the thickness of the coating on one side of the current collector is 45 mm, and the surface density is not greater than 100 g / cm.

[0047] Furthermore, in S200, the specific method for obtaining an infrared image of the coating area of ​​the double-sided coated electrode and marking the abnormal area is as follows: the double-sided coated electrode is heated at 160°C for 30 seconds, and then naturally cooled for 30 seconds, and then an infrared image is obtained by facing the coating area of ​​the double-sided coated electrode through the acquisition angle of the infrared thermal imager, and the infrared image is divided into multiple sub-areas TS using the Sobel edge algorithm, where the pixel value contained in the sub-area is represented as the temperature value of the electrode at the pixel position, and i is used as the sequence number of the sub-area, TS i represents the i-th sub-region;

[0048] In the acquired infrared image, the sub-region with the largest pixel average value is marked as the thick coating region, and the sub-region with the smallest pixel average value is marked as the thin coating region. The geometric center point of the thick coating region is used as the anchor point, and the geometric center point of the thin coating 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-region through which Line1 passes is marked as the unstable sub-region UTS. j is used as the serial number of the unstable sub-region, UTS j Indicates the jth unstable sub-region, add all unstable sub-regions to the list List1, and calculate the collapse coefficients of all unstable sub-regions in turn. The specific method is: according to the formula Where UTS(r) represents the pixel values ​​contained in the unstable subregions except the j-th unstable subregion in List1, Max{UTS(j)-UTS(r)} represents the maximum absolute difference between all pixel values ​​in the j-th unstable subregion and all pixel values ​​in other unstable subregions in List1, P(r) represents the distance between the two pixel points corresponding to the maximum absolute difference between all pixel values ​​in the j-th unstable subregion and all pixel values ​​in other unstable subregions in List1, N represents the number of unstable subregions in List1, SC j The collapse coefficient of the jth unstable sub-region in List1 is represented, the average collapse coefficient of all unstable sub-regions in List1 is calculated, and the unstable sub-regions with collapse coefficients greater than the average collapse coefficient are marked as abnormal regions.

[0049] In the above method, the thick coating area and the thin coating area correspond to the unevenness of the conductive paste. The thick coating area is manifested as a higher temperature value, while the thin coating area is generally manifested as a lower temperature value. In a Chinese patent entitled "Insulating Coating Detection Method, Device, System, Equipment and Storage Medium" with publication number CN117969533B, an infrared camera is used to capture infrared images, and areas with abnormal temperature values ​​are marked as abnormal areas, which can accurately identify the heat difference caused by the uneven distribution of the insulating coating. However, the above method does not take into account the fluidity and heat transfer properties of the slurry, and cannot guarantee that the temperature distribution in the infrared image when the infrared device is collecting is stable. The above steps first mark the area with the largest temperature difference, and then screen out the unstable sub-areas that may be affected according to the heat transfer properties. At the same time, by calculating the collapse coefficient, the affected sub-areas in all unstable areas are accurately calculated, and all abnormal areas in the infrared image can be accurately marked. The abnormal area can reflect the slurry distribution of the current electrode. By real-time monitoring of the slurry distribution of the current electrode and dynamically adjusting the working parameters of the coating machine, the coating process can be accurately controlled, ensuring the quality and service life of the electrode.

[0050] Furthermore, in S300, the specific method for determining the defect level of the current electrode according to the marked abnormal area is as follows: mark all abnormal areas on the acquired infrared image, and mark the points corresponding to the maximum values ​​of pixels in all abnormal areas as P k , k is the serial number of the abnormal area, and Pk is connected with the geometric center of all sub-areas in sequence to form multiple line segments line2. The edge of the sub-area corresponding to the shortest line segment Line2 is marked as RL k , traverse Rl in turn k All pixel values ​​on the edge RLk are added to the point Plk_min by scaling the curve between the points Plk_min and Plk_max. k With P K+1 In the same way, all points P k Connect to form a closed area, and calculate the area ratio of the closed area to 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 the area ratio is 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.

[0051] Furthermore, in S400, the specific method for fine-tuning the coating machine parameters according to the electrode defect level to obtain a qualified electrode is as follows: if the defect level of the current electrode is level 1, the current coating machine working parameters are kept unchanged; if the defect level of the current electrode is level 2, the coating machine scraper is adjusted to be perpendicular to the surface of the steel roller, and the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.0, the thickness of the single-sided copper foil coating is 43 mm, and the surface density is 105 g / cm; if the defect level of the current electrode is level 3, the coating machine scraper is adjusted to be perpendicular to the surface of the steel roller, and the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.5, the thickness of the single-sided copper foil coating is 47 mm, and the surface density is 105 g / cm. The electrode coated by the coating machine after adjusting the working parameters is recorded as a qualified electrode;

[0052] Furthermore, in S500, the specific method of rolling the qualified electrode sheet to obtain the finished electrode sheet is: rolling the qualified electrode sheet through 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 the unit of pressure.

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

[0054] Preferably, the patterned roller pressing is a roller provided with a wear-resistant pattern, and the smooth roller pressing is a roller with a smooth surface.

[0055] The beneficial effects of the present invention are as follows: the present invention can use temperature values ​​to accurately identify abnormal areas in infrared images caused by uneven distribution of conductive paste, and significantly improve the accuracy and practicality of defect detection. By analyzing the local temperature differences caused by the unevenness of the conductive paste, the initial form of the abnormal area and its subsequent diffusion path are captured, effectively avoiding the problem of missed detection of minor 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, the present invention adopts a dynamic correction strategy, combined with the thermal physical properties of the conductive paste, to clearly distinguish between real defects and thermal interference signals, significantly reducing the risk of misjudgment, and by correlating the temperature characteristics and diffusion behavior of the abnormal area with the coating process parameters of the electrode, a direct optimization basis is provided for the production process, assisting in the rapid diagnosis of uneven slurry mixing or coating process abnormalities, solving the uneven phenomenon caused by the coating process, improving the quality of the electrode and battery cell, avoiding the analysis phenomenon that occurs when the secondary battery is charged at low temperature, and accelerating the charging speed of the battery.

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

[0057] Comparative Example 1

[0058] The Chinese invention patent application, with publication number CN114551784B, filed on October 22, 2021, is titled "A negative electrode sheet for rapid charging at low temperature, a preparation method thereof, and a battery cell production method in Example 1 of the battery cell."

[0059] Furthermore, the present invention is further verified by testing the performance of the battery cells produced in the examples and comparative examples:

[0060] The DC impedance of the finished battery cells produced in the examples and comparative examples under low-temperature charging was measured. The specific method was as follows: the finished battery cells produced in the examples and comparative examples were placed at -20°C and -30°C, and each battery cell was charged at 200A for 10 seconds under different power conditions. The voltage difference before and after 10 seconds was recorded, and the DC impedance was obtained by dividing the voltage difference by 200. The power of the battery cell was expressed as a percentage of the SOC. The smaller the DC impedance, the less obstruction there is during low-temperature charging. The measurement results are shown in Tables 1 and 2 for details.

[0061] Table 1. DC impedance data of the battery cells obtained in Examples and Comparative Examples at -20°C

[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 battery cells obtained in the examples and comparative examples at -30°C

[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 battery cells measured in Table 2 is generally higher than that in Table 1 under a -20°C environment, indicating that the lower the temperature, the stronger the DC impedance of the battery cells and the more difficult it is to charge. By observing Table 1 and Table 2, it is found that the DC impedance of Example 1 is smaller than that in Comparative Example 1, indicating that the method provided by the present invention can monitor the coating quality of the electrode in real time during the electrode coating process, and dynamically adjust the working parameters of the coating machine according to the electrode coating quality, so as to avoid the partial high resistance of the electrode due to uneven coating, thereby affecting the charging rate and overall DC impedance of the finished battery cells.

[0066] Although the present invention has been described in considerable detail and with particularity with respect to several embodiments, it is not intended to limit the present invention to any of these details or embodiments or any particular embodiment, so as to effectively encompass the intended scope of the present invention. In addition, the present invention has been described above with respect to embodiments foreseen by the inventors for the purpose of providing a useful description, and those insubstantial modifications of the present invention that are not currently foreseen may still represent equivalent modifications of the present invention.

Claims

1. A method for preparing a negative electrode sheet for rapid charging at low temperature, characterized in that: The method comprises the following steps: S100, applying the conductive slurry to the negative electrode current collector on both sides by a coating machine to obtain a double-sided coated electrode sheet; S200, acquiring an infrared image of the double-sided coated electrode coating area and marking abnormal areas; S300, determining the defect level of the current electrode according to the marked abnormal area; S400, fine-tune the coating machine parameters according to the electrode defect level to obtain qualified electrodes; S500, rolling the qualified electrode pieces to obtain finished electrode pieces; S600: Cut the finished electrode sheets into negative electrode sheets.

2. The method for preparing a negative electrode sheet for rapid charging at low temperature according to claim 1, characterized in that: In S200, the method for obtaining an infrared image of the coating area of ​​the double-sided coated electrode and marking the abnormal area is as follows: the double-sided coated electrode is heated at 140-180°C for 30-50 seconds, and then naturally cooled for 30 seconds, and then an infrared image is obtained by facing the coating area of ​​the double-sided coated electrode through the acquisition angle of the infrared thermal imager. The infrared image is divided into multiple sub-areas TS using the Sobel edge algorithm, where the pixel value contained in the sub-area is represented as the temperature value of the electrode at the pixel position, and i is used as the sequence number of the sub-area. TS i represents the i-th sub-region; In the acquired infrared image, the sub-region with the largest pixel average value is marked as the thick coating region, and the sub-region with the smallest pixel average value is marked as the thin coating region. The geometric center point of the thick coating region is used as the anchor point, and the geometric center point of the thin coating 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-region through which Line1 passes is marked as the unstable sub-region UTS. j is used as the serial number of the unstable sub-region, UTS j Indicates the jth unstable sub-region, add all unstable sub-regions to the list List1, and calculate the collapse coefficients of all unstable sub-regions in turn. The specific method is: according to the formula Where UTS(r) represents the pixel values ​​contained in the unstable subregions except the j-th unstable subregion in List1, Max{UTS(j)-UTS(r)} represents the maximum absolute difference between all pixel values ​​in the j-th unstable subregion and all pixel values ​​in other unstable subregions in List1, P(r) represents the distance between the two pixel points corresponding to the maximum absolute difference between all pixel values ​​in the j-th unstable subregion and all pixel values ​​in other unstable subregions in List1, N represents the number of unstable subregions in List1, SC j The collapse coefficient of the jth unstable sub-region in List1 is represented, the average collapse coefficient of all unstable sub-regions in List1 is calculated, and the unstable sub-regions with collapse coefficients greater than the average collapse coefficient are marked as abnormal regions.

3. The method for preparing a negative electrode sheet for rapid charging at low temperature according to claim 2, characterized in that: In S300, the method for determining the defect level of the current electrode according to the marked abnormal area is as follows: mark all abnormal areas on the acquired infrared image, and mark the points corresponding to the maximum pixel values ​​in all abnormal areas as P k , k is the serial number of the abnormal area, and Pk is connected with the geometric center of all sub-areas in sequence to form multiple line segments line2. The edge of the sub-area corresponding to the shortest line segment Line2 is marked as RL k , traverse Rl in turn k All pixel values ​​on the edge RL are marked with the point corresponding to the minimum value of all traversed pixel values ​​as Plk_min, and the point corresponding to the maximum value of all traversed pixel values ​​as Plk_max. k The curve formed between point Plk_min and point Plk_max is added to point P by geometric scaling. k With P K+1 In between, all points Pk are connected in the same way to form a closed area, and the area ratio of the closed area to the area of ​​the entire infrared image is calculated. 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 the area ratio is 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.

4. The method for preparing a negative electrode sheet for rapid charging at low temperature according to claim 3, characterized in that: In S400, the method for fine-tuning the coating machine parameters according to the electrode defect level to obtain a qualified electrode is as follows: if the defect level of the current electrode is level 1, the current coating machine working parameters are kept unchanged; if the defect level of the current electrode is level 2, the coating machine scraper is adjusted to be perpendicular to the surface of the steel roller, and the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.0, the thickness of the single-sided coating of the copper foil is 43 mm, and the surface density is not greater than 110 g / cm; if the defect level of the current electrode is level 3, the coating machine scraper is adjusted to be perpendicular to the surface of the steel roller, and the speed ratio of the coating machine steel roller to the rubber roller is adjusted to 1.5, the thickness of the single-sided coating of the copper foil is 47 mm, and the surface density is not greater than 110 g / cm. The electrode coated by the coating machine after adjusting the working parameters is recorded as a qualified electrode.

5. The method for preparing a negative electrode sheet for rapid charging at low temperature according to claim 4, characterized in that: In S500, the method of rolling the qualified electrode sheets to obtain finished electrode sheets is as follows: the qualified electrode sheets are rolled at a speed of 20 m / min through a roller press to obtain finished electrode sheets, wherein the roller press pressure is 10t-60t, and t is the unit of pressure.

6. A battery cell, characterized in that: The invention relates to a negative electrode sheet prepared by the negative electrode sheet preparation method as described in any one of claims 1 to 5, wherein the negative electrode sheet and the positive electrode sheet are assembled together under inert gas at 6 to 10 MPa, and the final finished battery cell is formed through battery cell formation, wherein the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode material.

Images