A compaction process to improve cycle life of lithium batteries

Abstract

The application discloses a compaction process for improving cycle times of lithium batteries, and relates to the technical field of lithium battery manufacturing, and comprises the following steps: a traveling wave vibration sequence with different phases is applied to a compression roller, so that a standing wave node is formed at an arc-shaped area position on a pole piece to directionally cancel local rebound stress on the pole piece; a yield stress of a magneto-rheological fluid damper is dynamically adjusted through a pressure change rate of a flexible pressure bag at an inner side wall position of a shell, so that a pressure maintaining pressure and a real-time thickness expansion rate on a battery cell present a negative correlation dynamic matching. Through the application of the traveling wave vibration sequence with different phases to the compression roller, the standing wave node can be formed at the maximum rebound stress position to directionally cancel the local rebound stress, and then the yield stress of the magneto-rheological fluid damper is adjusted through the pressure change rate of the flexible pressure bag, so that the residual rebound stress superposition and local overpressure on the pole piece are reduced, the cycle stability and cycle times of the battery cell are improved, and the service life of the lithium battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium battery production technology, and in particular to a compaction process for improving the cycle life of lithium batteries. Background Technology

[0002] As the primary site of electrochemical reactions in lithium-ion batteries, the structural integrity and interfacial stability of the electrodes directly determine the battery's electrochemical performance and service life. The compaction state of the electrodes serves as a crucial bridge connecting the battery's structural integrity and cycle life. Proper and stable electrode compaction ensures close contact between active material particles, reduces interfacial contact resistance, and suppresses structural loosening during cycling, thereby extending the cycle life of lithium-ion batteries. Therefore, the compaction process employed in the processing of lithium-ion battery electrodes has become a key technological direction for improving the cycle life of lithium-ion batteries.

[0003] However, the compaction process of traditional lithium battery electrodes typically involves compacting the electrodes as a whole using fixed roller pressure before stacking, and then using rigid limiting or constant pressure for shaping and pressure maintenance after the cell is installed in the casing. However, during the coating, drying, and rolling processes of lithium battery electrodes, factors such as coating thickness differences, material shrinkage, and uneven force on the pressure rollers can easily lead to bending and springback stress in localized areas. Current compaction processes cannot target and reduce the maximum springback stress in the curved areas of the electrode, nor can they adjust the pressure maintenance according to the real-time thickness expansion after the cell is installed in the casing. This can easily cause residual localized springback stress from before stacking to accumulate inside the cell, leading to localized overpressure during subsequent expansion and affecting the interlayer bonding of the electrodes and the cycle stability of the cell.

[0004] Therefore, in order to solve the above-mentioned technical problems, a compaction process to improve the cycle life of lithium batteries is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a compaction process to improve the cycle life of lithium batteries, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a compaction process for improving the cycle life of lithium batteries, comprising the following steps: First compaction process: After the electrode coating process, a traveling wave vibration sequence with different phases is applied to the pressure roller to form standing wave nodes in the arc-shaped area of ​​the electrode to directionally counteract the local rebound stress on the electrode. The second compaction process: After the electrode sheets are stacked into a battery cell and enter the housing, the pressure change rate of the flexible pressure bladder on the inner wall of the housing is monitored. The yield stress of the magnetorheological fluid damper is dynamically adjusted by the pressure change rate, so that the holding pressure and the real-time thickness expansion rate on the battery cell show a negative correlation and dynamic matching.

[0007] Preferably, the traveling wave vibration sequence with different phases is calculated from the curvature radius distribution data of the arc region on the electrode, and the position of the standing wave node coincides with the position of the maximum rebound stress in the arc region on the electrode. The position of the maximum rebound stress in the arc region of the electrode is determined by the curvature transition zone where the curvature radius gradient of the arc region is reversed and the recovery peak zone where the thickness recovery peak is located after unloading. When the positional change of the overlapping area formed by the curvature transition zone and the recovery peak zone in adjacent compaction strokes is less than the positional change of any single zone, the overlapping area is determined as the location of the maximum rebound stress, so as to exclude the instantaneous recovery peak caused by local thickness difference of the coating.

[0008] Preferably, the location of the maximum rebound stress is used as the phase convergence location, and multiple pairs of traveling wave excitation sections are set on both sides of it. Based on the propagation delay from each traveling wave excitation segment to the phase convergence position and the curvature radius gradient corresponding to the propagation path, a phase difference is set between paired traveling wave excitation segments so that the vibration displacements of the two traveling waves cancel each other out when they reach the phase convergence position, and dynamic linear pressure peaks acting in opposite directions are formed on both sides of the position.

[0009] Preferably, multiple pairs of traveling wave excitation sections are started sequentially from farthest to closest to the phase convergence position. The next pair of traveling wave excitation sections is started when the previous pair of traveling waves passes the zero-crossing moment of vibration displacement, so that the peak value of the dynamic linear pressure formed by each pair of traveling waves gradually approaches the phase convergence position. If any dynamic linear pressure peak exceeds the phase convergence position, the phase difference of the corresponding traveling wave is corrected in the opposite direction to return it to the same side of the phase convergence position, without increasing the basic compaction load of the pressure roller.

[0010] Preferably, when the vibration phase reversal boundary on both sides of the standing wave node moves continuously in the same direction, and the amplitude on the side closer to the moving direction decreases while the amplitude on the other side increases, it is determined that the standing wave node has experienced a real drift. When only the amplitude changes and the vibration phase reversal boundary remains at the position of maximum rebound stress, it is determined to be a local stiffness change of the electrode, and the phase difference of the traveling wave vibration sequence remains unchanged.

[0011] Preferably, when the standing wave node experiences actual drift, only the arrival time of the traveling wave on one side of the drift direction is adjusted so that the zero-crossing times of the vibration displacements of the traveling waves on both sides of the standing wave node coincide again. Furthermore, the amount of phase adjustment each time is determined based on the curvature radius gradient within the drift interval. The faster the curvature radius changes, the smaller the amount of phase adjustment per time, so as to avoid the standing wave node from crossing the maximum rebound stress position and causing reverse drift.

[0012] Preferably, when the thickness recovery amplitude at the location of the maximum rebound stress decreases after the standing wave node returns to the location of the maximum rebound stress, and the peak curvature recovery at the adjacent location moves away from the standing wave node, it is determined that the rebound stress has shifted. The standing wave nodes are sequentially migrated along the moving direction of the curvature recovery peak, and the holding time of the standing wave node at the later migration position is less than the holding time at the previous migration position, until the thickness recovery amplitude difference between each migration position is within a preset range.

[0013] Preferably, the residual springback distribution of the electrode sheet is formed based on the migration direction and range of the standing wave nodes at the end of the first compaction process and the thickness recovery amplitude at each migration position. During the stacking process, according to the stacking sequence and orientation of each electrode, the residual rebound distribution of each electrode is superimposed onto the inner sidewall of the outer casing after the cell is installed, and the position of the sidewall where the residual rebound is concentrated after stacking is established in correspondence with the different pressure zones of the flexible pressure bladder.

[0014] Preferably, the pressure zone corresponding to the sidewall location where the residual rebound is concentrated is established with a holding pressure before the other pressure zones; If the real-time thickness expansion at the sidewall location of the residual rebound concentration occurs before the pressure change rate inside the flexible pressure bladder increases, the yield stress of the corresponding magnetorheological fluid damper is reduced in advance, so that the limiting module moves in a controlled manner with the expansion of the battery cell. If the pressure change inside the flexible pressure bladder precedes the increase in the real-time thickness expansion rate, the yield stress of the corresponding magnetorheological fluid damper should be maintained or increased to prevent the pressure transmitted from adjacent pressure zones from causing local overpressure.

[0015] Preferably, when the pressure change rate of adjacent pressure zones is in the opposite direction and the real-time thickness expansion peak migrates from the pressure zone with increasing pressure change rate to the pressure zone with decreasing pressure change rate, it is determined that interlayer slip has occurred inside the cell, and the yield stress of the adjacent magnetorheological fluid damper is reduced sequentially along the migration direction of the thickness expansion peak, and then the yield stress is restored in the reverse order. When the pressure change rate of adjacent pressure zones is in the same direction and the position of the real-time thickness expansion peak remains stable, it is determined that the cell has undergone overall elastic expansion, and the negative correlation dynamic matching continues to be performed.

[0016] The technical effects and advantages of this invention are as follows: This invention generates a traveling wave vibration sequence with different phase differences based on the radius of curvature distribution of the arc-shaped region of the electrode before lamination. This causes the pressure roller to form a standing wave node at the position of maximum rebound stress, thereby directionally offsetting the local rebound stress. Simultaneously, after the cell is inserted into the casing, the yield stress of the magnetorheological fluid damper is adjusted by the pressure change rate of the flexible pressure bladder. This makes the holding pressure and the real-time thickness expansion rate negatively correlated and dynamically matched. In this way, the stress reduction before electrode lamination and the expansion compensation after insertion into the casing are linked, reducing the superposition of residual rebound stress on the electrode and local overpressure, thereby improving the cycle stability and cycle number of the cell.

[0017] This invention determines the location of maximum springback stress by the overlap relationship between the curvature transition zone and the recovery peak zone, and distinguishes between the actual node drift and the local stiffness change of the electrode sheet based on the phase reversal boundary and amplitude change on both sides of the standing wave node. This avoids mistaking coating thickness difference or stiffness fluctuation as a change in springback position. Furthermore, it compensates for this by adjusting the arrival time of the traveling wave and gradually migrating the standing wave node, thereby improving the compaction uniformity of the arc-shaped area without increasing the basic compaction load of the pressure roller, thus improving the processing quality of electrode sheet compaction.

[0018] This invention stacks the residual springback distribution of the electrode sheets formed on the electrode sheets in the first compaction process onto the inner wall of the battery cell shell according to the stacking sequence and the orientation of the front and back sides of the electrode sheets. The flexible pressure bladder implements directional pressure holding by corresponding pressure zones. Then, the interlayer slippage and overall elastic expansion phenomena are distinguished according to the pressure change direction and thickness expansion peak migration state of adjacent pressure zones. In this way, the interlayer misalignment and local pressure concentration inside the battery cell are reduced by sequentially adjusting the yield stress of the magnetorheological fluid damper, thereby improving the bonding state of each electrode sheet and the consistency of the battery cell thickness. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the overall compaction process of the present invention.

[0020] Figure 2 This is a flowchart illustrating the determination of the dynamic pressure peak value and phase convergence position in this invention.

[0021] Figure 3 This is a flowchart illustrating the process of determining the actual drift of the standing wave node in this invention.

[0022] Figure 4 This is a flowchart illustrating the process of determining interlayer slippage within the battery cell of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides, for example Figures 1-4 The compaction process shown to improve the cycle life of lithium batteries includes the following steps: First compaction process: After the electrode coating process, a traveling wave vibration sequence with different phases is applied to the pressure roller to form standing wave nodes in the arc-shaped area of ​​the electrode to directionally counteract the local rebound stress on the electrode. The second compaction process: After the electrode sheets are stacked into a battery cell and enter the housing, the pressure change rate of the flexible pressure bladder on the inner wall of the housing is monitored. The yield stress of the magnetorheological fluid damper is dynamically adjusted by the pressure change rate, so that the holding pressure and the real-time thickness expansion rate on the battery cell show a negative correlation and dynamic matching.

[0025] In practice, the coated and dried electrode sheet is placed between a pair of rollers of a roller press. The rollers are equipped with multiple traveling wave vibrators, each arranged along the roller axis and its vibration phase is independently controlled. While rolling the lithium battery electrode sheet, a traveling wave vibration sequence is applied to the rollers. This vibration sequence generates alternating contact stress on the electrode sheet surface, causing standing wave nodes to form in the arc-shaped area on the electrode sheet that was originally formed due to the difference in elastic modulus between the coating and the current collector. Since the vibration displacement at the standing wave node is equivalent to zero, but the dynamic linear pressure reaches its peak value, an additional compaction effect is formed locally. Thus, in addition to the basic compaction load, it can offset the local rebound stress generated by elastic failure in this area after the rollers are unloaded, significantly reducing the thickness recovery range at this location on the electrode sheet.

[0026] Simultaneously, after the first compaction process is completed, the electrode sheets are stacked according to a predetermined layer sequence to form a bare cell. The bare cell is then installed into the lithium battery casing. A flexible pressure bladder, filled with silicone oil and connected to an external pressure sensor, is pre-installed on the inner wall of the casing. This allows for real-time monitoring of the pressure change rate on each side of the cell. A magnetorheological fluid damper is then installed on the outer side of the casing and connected to a limiting module. This allows the damper, in conjunction with the limiting module, to constrain the cell's expansion in the thickness direction. Based on the pressure change rate measured by the flexible pressure bladder, the excitation current of the magnetorheological fluid damper can be dynamically adjusted, thereby changing its yield stress. This creates a negative correlation between the holding pressure on the cell and its real-time thickness expansion rate, allowing for a controlled release when the cell's expansion trend intensifies, and an increase in the holding pressure when the expansion trend weakens to maintain tight contact within the cell. By combining the first and second compaction processes, the stress reduction before lithium battery electrode stacking is linked to the expansion compensation after casing, reducing the superposition of residual rebound stress and local overpressure on the electrode. This effectively suppresses the interface separation and active material shedding caused by electrode rebound and cell cyclic expansion, thereby improving the cell's cycle stability and cycle life.

[0027] In a preferred embodiment, the traveling wave vibration sequence with different phases is calculated from the curvature radius distribution data of the arc-shaped region on the electrode, and the position of the standing wave node coincides with the position of the maximum rebound stress in the arc-shaped region on the electrode. The position of the maximum rebound stress in the arc-shaped region of the electrode is determined by the curvature transition zone where the curvature radius gradient of the arc-shaped region reverses and the recovery peak zone where the thickness recovery peak is located after unloading. When the position change of the overlapping area formed by the curvature transition zone and the recovery peak zone in adjacent compaction strokes is less than the position change of any single zone, the overlapping area is determined as the position of the maximum rebound stress to exclude the instantaneous recovery peak caused by the local thickness difference of the coating.

[0028] In practice, after the coating process and before the compaction process, a three-dimensional morphological scan of the electrode surface is performed using a laser profilometer or white light interferometer to obtain the coating thickness distribution and surface curvature data at various locations on the electrode surface. The radius of curvature at each location and its gradient change along the electrode's travel direction are then calculated. By inputting the obtained radius of curvature distribution data into the traveling wave generation algorithm, the initial phase difference value that should be set between different exciters is determined based on the radius of curvature gradient curve of the arc-shaped region along the electrode's length, thereby generating a traveling wave vibration sequence with a spatially distributed phase difference.

[0029] Simultaneously, when the curvature radius gradient changes from positive to negative, its corresponding position on the electrode is defined as the curvature transition zone, corresponding to the stress concentration point between the coating and the current collector. Furthermore, by conducting small-sample pre-compaction tests on the coated electrode, the thickness recovery at different locations after unloading is measured, and the region with the largest thickness recovery is defined as the recovery peak zone. Then, the position coordinates of the curvature transition zone and the recovery peak zone are superimposed to obtain their overlap interval along the electrode length. During multiple consecutive compaction strokes of the electrode, the positional changes of the curvature transition zone and the recovery peak zone are recorded, along with the positional change of their overlap interval. When the positional change of the overlap interval is less than both the individual positional changes of the curvature transition zone and the recovery peak zone, it indicates that the overlap region has high positional stability across different samples or sections, rather than being an instantaneous recovery peak caused by random fluctuations in the local coating thickness. Therefore, this overlap region is determined as the location of maximum rebound stress. Thus, the combined constraints of the curvature transition zone and the recovery peak zone can be used to accurately locate the rebound stress concentration point on the electrode, thereby improving the accuracy of standing wave node placement.

[0030] In a preferred embodiment, the position of maximum rebound stress is taken as the phase convergence position, and multiple pairs of traveling wave excitation sections are set on both sides of it. According to the propagation time delay from each traveling wave excitation section to the phase convergence position and the curvature radius gradient corresponding to the propagation path, the phase difference between the pairs of traveling wave excitation sections is set so that the vibration displacements of the traveling waves on both sides cancel each other when they reach the phase convergence position, and dynamic linear pressure peaks acting in opposite directions are formed on both sides of the position.

[0031] In practice, the location of the maximum rebound stress is determined as the phase convergence position. Along the axial direction of the pressure roller or the traveling direction of the electrode sheet, multiple traveling wave excitation sections are set on both sides of the phase convergence position. Each excitation section on each side is spatially symmetrical or asymmetrically distributed, and the number of excitation sections on both sides is the same, forming a pair.

[0032] Simultaneously, for each pair of excitation sections, the time required for the traveling wave to propagate from that excitation section to the phase convergence position is first calculated. At the same time, the curvature radius gradient data of the electrode region traversed by the traveling wave propagation path is obtained. Based on the propagation time delay and curvature radius gradient, the expected phase of the traveling waves emitted from the two excitation sections when they reach the phase convergence position is determined. Then, an initial phase difference is set between the paired excitation sections, ensuring that the left and right traveling waves have opposite phases when they reach the phase convergence position, thus canceling out the vibration displacements and forming a standing wave node with zero vibration displacement at that position. Furthermore, because the phase distribution of the two traveling waves on both sides of the node is opposite, additional pressure pointing towards the node is generated on both sides of the standing wave node, concentrating the compaction energy on the location of maximum rebound stress and its adjacent area, thereby enhancing the directional cancellation of rebound stress at that location.

[0033] In a preferred embodiment, multiple pairs of traveling wave excitation sections are started sequentially from farthest to closest to the phase convergence position. The next pair of traveling wave excitation sections is started when the previous pair of traveling waves passes the zero-crossing moment of vibration displacement, so that the peak values ​​of dynamic linear pressure formed by each pair of traveling waves gradually approach the phase convergence position. If any peak value of dynamic linear pressure crosses the phase convergence position, the phase difference of the corresponding traveling wave is corrected in the reverse direction to return it to the same side of the phase convergence position without increasing the basic compaction load of the pressure roller.

[0034] In practice, when initiating the traveling wave vibration sequence, the pair of excitation sections furthest from the phase convergence position is activated first. When the traveling waves generated by this pair reach a point of zero vibration displacement during propagation, the pair of excitation sections closest to the previous pair is activated, and so on, until the closest pair is activated. This sequential activation from far to near ensures that the dynamic pressure peaks generated by each pair of traveling waves gradually converge towards the phase convergence position. During compaction, the position of each dynamic pressure peak is monitored in real time. If the dynamic pressure peak generated by a pair of traveling waves crosses the phase convergence position, it indicates that the phase setting of that pair has shifted. By adjusting the phase difference between the two excitation sections in that pair, the dynamic linear pressure peak returns to the same side of the phase convergence position. This reverse correction method avoids affecting the compaction uniformity of the entire electrode due to adjustments in the base load, thereby improving the quality of directional compaction at localized rebound stress locations.

[0035] In a preferred embodiment, when the vibration phase reversal boundary on both sides of the standing wave node moves continuously in the same direction, and the amplitude on the side closer to the moving direction decreases while the amplitude on the other side increases, it is determined that the standing wave node has experienced a real drift; when only the amplitude changes while the vibration phase reversal boundary remains at the position of maximum rebound stress, it is determined that there is a change in the local stiffness of the electrode, and the phase difference of the traveling wave vibration sequence remains unchanged.

[0036] In practice, the vibration displacement distribution of the standing wave node and its two sides is monitored in real time during compaction. Since the vibration phases on both sides of the standing wave node are opposite, there is a dividing point where the vibration phase reverses. If this dividing point moves continuously along the length of the electrode, and the vibration amplitude on one side gradually decreases while the amplitude on the other side gradually increases, it indicates that the standing wave node has experienced a true drift. However, if the amplitudes on both sides of the standing wave node increase or decrease simultaneously, but the dividing point where the vibration phase reverses remains unchanged at the position of maximum rebound stress, it indicates that the local stiffness of the electrode at that position has changed, and it is not a positional drift of a non-standing wave node. In this case, since the standing wave node is still at the target position, the phase difference of the traveling wave vibration sequence remains constant, and the amplitude change is addressed only by adjusting the power of the exciter. This allows for the differentiation between two different types of responses during compaction: standing wave node positional drift and changes in local electrode stiffness, preventing phase adjustments due to misjudgment and ensuring the stability of the electrode compaction process.

[0037] In a preferred embodiment, when a standing wave node experiences actual drift, the arrival time of the traveling wave on one side of the drift direction is adjusted so that the vibration displacements of the traveling waves on both sides of the standing wave node re-overlap at their zero-crossing times. Furthermore, the amount of phase adjustment each time is determined based on the curvature radius gradient within the drift interval. The faster the curvature radius changes, the smaller the amount of phase adjustment per time, in order to avoid the standing wave node from drifting in the opposite direction due to exceeding the maximum rebound stress position.

[0038] In practice, if a real drift of the standing wave node is detected during compaction, the arrival time of the traveling wave on one side of the drift direction of the standing wave node needs to be adjusted so that the zero-crossing time of the vibration displacement of the traveling wave on that side when it reaches the position of maximum rebound stress coincides with the zero-crossing time of the traveling wave on the downstream side, thereby returning the standing wave node to its target position. During each adjustment, the rate of change of the radius of curvature along the length of the electrode section through which the standing wave node drifts is calculated based on the radius of curvature gradient data. If the radius of curvature changes rapidly, it indicates high phase sensitivity of the traveling wave propagation; in this case, a smaller single phase adjustment amount is used to prevent over-adjustment from causing the standing wave node to cross the position of maximum rebound stress and drift in the opposite direction. If the radius of curvature changes relatively gently, a larger adjustment amount can be used. This adjustment method after a real drift of the standing wave node can prevent overshoot during the adjustment process, thus ensuring the stability of directional rebound stress compensation.

[0039] In a preferred embodiment, after the standing wave node returns to the position of maximum rebound stress, the thickness recovery amplitude at that position decreases, and when the curvature recovery peak at the adjacent position moves away from the standing wave node, it is determined that the rebound stress has been transferred; the standing wave nodes are moved sequentially along the moving direction of the curvature recovery peak, and the holding time of the standing wave node at the later moving position is less than the holding time at the previous moving position, until the thickness recovery amplitude difference between each moving position is within a preset range.

[0040] In practice, after the standing wave node returns to the position of maximum rebound stress through phase adjustment, the thickness recovery amplitude and curvature distribution of the electrode surface at that position and in adjacent areas are continuously monitored. If the thickness recovery amplitude at the position of maximum rebound stress is significantly reduced, and the curvature recovery peak at adjacent positions moves away from that position, this indicates a shift in the rebound stress originally concentrated at the position of maximum rebound stress. In this case, the phase convergence position of the standing wave node needs to be moved sequentially from the current position of maximum rebound stress along the direction of curvature recovery peak movement to the new position of curvature recovery peak.

[0041] Simultaneously, upon migrating to a new location, the current phase parameters are maintained at that location for a period of time, with the maintenance time gradually decreasing according to the migration sequence until the maximum difference in thickness recovery amplitude between adjacent migration locations does not exceed a preset range. This implementation, by employing a standing wave node migration method, enables the standing wave node to quickly track the stress transfer path, thereby avoiding the formation of new local rebound concentration points due to stress transfer. This results in a more consistent thickness of the electrode along its length and more uniform compaction, thereby improving the flatness and cycle stability of the subsequent cell stacking interface.

[0042] In a preferred embodiment, the residual rebound distribution of the electrode is formed according to the migration direction and range of the standing wave nodes at the end of the first compaction process and the thickness recovery amplitude at each migration position; during the stacking process, the residual rebound distribution of each electrode is superimposed onto the inner sidewall of the outer shell after the cell is inserted into the casing according to the stacking sequence and the orientation of the front and back sides of each electrode, and the position of the sidewall where the residual rebound is concentrated after superposition is established in correspondence with the different pressure zones of the flexible pressure bladder.

[0043] In practice, at the end of the first compaction process, the migration direction and range of the standing wave nodes and the thickness recovery amplitude data corresponding to each migration position of the standing wave nodes are recorded throughout the compaction process. The residual springback distribution map of the electrode is established with the position coordinates on the electrode as the horizontal axis and the thickness recovery amplitude at each position as the vertical axis to reflect the magnitude of the residual springback stress that has not been completely offset at different positions of the electrode.

[0044] Simultaneously, during the electrode stacking process, based on the stacking sequence and orientation of each electrode, the rebound distribution of different electrode layers is mapped to the corresponding height and orientation of the inner wall of the outer casing after the cell is inserted, forming a residual rebound distribution map of the entire cell. Multiple independent pressure zones are pre-divided on the flexible pressure bladder, each equipped with an independent pressure sensor to monitor pressure changes in the corresponding outer casing sidewall area. This establishes a correspondence between the location of the sidewall where residual rebound is concentrated after stacking and the different pressure zones of the flexible pressure bladder. This allows the residual rebound distribution of each electrode to be converted into a predicted distribution of the internal expansion potential experienced by the sidewall after the cell is inserted, enabling the control of the magnetorheological fluid damper in the second compaction process to be adjusted according to the degree of rebound accumulation in each zone.

[0045] In a preferred embodiment, the pressure zone corresponding to the sidewall position of the residual rebound concentration is established with a holding pressure before the other pressure zones; if the real-time thickness expansion at the sidewall position of the residual rebound concentration increases before the pressure change rate inside the flexible pressure bladder increases, the yield stress of the corresponding magnetorheological fluid damper is reduced in advance, so that the limiting module moves in a controlled manner with the expansion of the battery cell; if the pressure change inside the flexible pressure bladder increases before the real-time thickness expansion rate increases, the yield stress of the corresponding magnetorheological fluid damper is maintained or increased to prevent the pressure transmitted from adjacent pressure zones from causing local overpressure.

[0046] In practice, after the battery cell is inserted into the casing and encapsulated, based on the established correspondence between the sidewall positions of the superimposed residual rebound concentration and the different pressure zones of the flexible pressure bladder, a holding pressure is preferentially established in the pressure zone corresponding to the sidewall position of the residual rebound concentration, thereby ensuring that the compaction energy is preferentially applied to the area with the highest rebound risk. During the cyclic charging and discharging process of the battery cell, the pressure change rate of each pressure zone and the thickness expansion rate at the corresponding location are monitored in real time.

[0047] For pressure zones with concentrated residual rebound, if the real-time thickness expansion rate at that location is detected to rise before the pressure change rate within the pressure bladder, the yield stress of the corresponding magnetorheological fluid damper is pre-reduced. This allows the limiting module to move in a controlled manner as the cell expands, releasing some expansion space and preventing a sharp increase in internal stress due to rigid constraints. Conversely, if the pressure change within the flexible pressure bladder is detected to rise before the thickness expansion rate, the yield stress of the corresponding magnetorheological fluid damper is maintained or increased, allowing the limiting module to maintain or strengthen its constraint force. This prevents pressure transmission from adjacent pressure zones from causing localized overpressure in that area, thus avoiding cell deformation or diaphragm puncture due to pressure concentration. By determining the order of the increase in thickness expansion rate and pressure change rate within the pressure bladder, a dynamic balance can be achieved between external constraints and internal expansion, thereby improving the safety of lithium-ion battery cells.

[0048] In a preferred embodiment, when the pressure change rates of adjacent pressure zones are opposite in direction and the real-time thickness expansion peak migrates from the pressure zone with increasing pressure change rate to the pressure zone with decreasing pressure change rate, it is determined that interlayer slip has occurred inside the cell, and the yield stress of the adjacent magnetorheological fluid dampers is reduced sequentially along the migration direction of the thickness expansion peak, and then the yield stress is restored in the reverse order; when the pressure change rates of adjacent pressure zones are consistent in direction and the position of the real-time thickness expansion peak remains stable, it is determined that the cell has undergone overall elastic expansion, and negative correlation dynamic matching continues to be performed.

[0049] In practice, the direction of pressure change rate in each adjacent pressure zone and the position change of the real-time thickness expansion peak are continuously monitored. When it is detected that the pressure in one zone is rising while the pressure in another adjacent zone is falling, and the position of the real-time thickness expansion peak migrates from the zone with the increasing pressure change rate to the zone with the decreasing pressure change rate, it indicates that the relative displacement between the electrode layers inside the cell has occurred under the action of shear force, resulting in a redistribution of pressure distribution and a corresponding shift in the thickness expansion peak. Therefore, it is necessary to reduce the yield stress of the magnetorheological fluid damper corresponding to the current position of the expansion peak along the migration direction of the thickness expansion peak, and then reduce the yield stress of subsequent magnetorheological fluid dampers one by one along the migration direction, so that the limiting module releases the constraint step by step. This allows the interlayer slippage to be released in a preset direction, thereby avoiding problems such as electrode tearing or diaphragm damage due to excessive constraint. At the same time, after the interlayer slippage process tends to stabilize, the yield stress of each magnetorheological fluid damper is restored step by step in the reverse order of reduction, re-establishing the constraint force on the cell, thereby maintaining the integrity of the overall cell structure.

[0050] In addition, when the pressure change rate of adjacent pressure zones is detected to be in the same direction, and the position of the real-time thickness expansion peak remains stable without migration, it indicates that the cell has not experienced interlayer relative slippage, but rather has generated uniform elastic expansion as a whole. This can be dynamically adjusted by dynamically adjusting the negative correlation dynamic matching method of the holding pressure according to the change of the overall expansion rate. This can solve the interlayer slippage fault that may occur in the cell cycle, thereby improving the safety and reliability of the cell.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A compaction process for improving the cycle life of lithium batteries, characterized in that, Includes the following steps: First compaction process: After the electrode coating process, a traveling wave vibration sequence with different phases is applied to the pressure roller to form standing wave nodes in the arc-shaped area of ​​the electrode to directionally counteract the local rebound stress on the electrode. The second compaction process: After the electrode sheets are stacked into a battery cell and enter the housing, the pressure change rate of the flexible pressure bladder on the inner wall of the housing is monitored. The yield stress of the magnetorheological fluid damper is dynamically adjusted by the pressure change rate, so that the holding pressure and the real-time thickness expansion rate on the battery cell show a negative correlation and dynamic matching.

2. The compaction process for improving the cycle life of lithium batteries according to claim 1, characterized in that, The traveling wave vibration sequence with different phases is calculated from the curvature radius distribution data of the arc region on the electrode. The position of the standing wave node coincides with the position of the maximum rebound stress in the arc region on the electrode. The position of the maximum rebound stress in the arc region of the electrode is determined by the curvature transition zone where the curvature radius gradient of the arc region is reversed and the recovery peak zone where the thickness recovery peak is located after unloading. When the positional change of the overlapping area formed by the curvature transition zone and the recovery peak zone in adjacent compaction strokes is less than the positional change of any single zone, the overlapping area is determined as the location of the maximum rebound stress, so as to exclude the instantaneous recovery peak caused by local thickness difference of the coating.

3. The compaction process for improving the cycle life of lithium batteries according to claim 2, characterized in that, Using the location of maximum rebound stress as the phase convergence location, multiple pairs of traveling wave excitation sections are set on both sides of it. Based on the propagation delay from each traveling wave excitation segment to the phase convergence position and the curvature radius gradient corresponding to the propagation path, a phase difference is set between paired traveling wave excitation segments so that the vibration displacements of the two traveling waves cancel each other out when they reach the phase convergence position, and dynamic linear pressure peaks acting in opposite directions are formed on both sides of the position.

4. The compaction process for improving the cycle life of lithium batteries according to claim 3, characterized in that, Multiple pairs of traveling wave excitation sections are started sequentially from farthest to closest to the phase convergence position. The next pair of traveling wave excitation sections is started when the previous pair of traveling waves passes the zero-crossing moment of vibration displacement, so that the peak value of the dynamic linear pressure formed by each pair of traveling waves gradually approaches the phase convergence position. If any dynamic linear pressure peak exceeds the phase convergence position, the phase difference of the corresponding traveling wave is corrected in the opposite direction to return it to the same side of the phase convergence position, without increasing the basic compaction load of the pressure roller.

5. The compaction process for improving the cycle life of lithium batteries according to claim 4, characterized in that, When the vibration phase reversal boundary on both sides of the standing wave node moves continuously in the same direction, and the amplitude on the side closer to the direction of movement decreases while the amplitude on the other side increases, it is determined that the standing wave node has experienced a real drift. When only the amplitude changes and the vibration phase reversal boundary remains at the position of maximum rebound stress, it is determined to be a local stiffness change of the electrode, and the phase difference of the traveling wave vibration sequence remains unchanged.

6. The compaction process for improving the cycle life of lithium batteries according to claim 5, characterized in that, When the standing wave node experiences actual drift, the arrival time of the traveling wave on one side of the drift direction is adjusted so that the vibration displacements of the traveling waves on both sides of the standing wave node re-overlap at the zero-crossing time. Furthermore, the amount of phase adjustment each time is determined based on the curvature radius gradient within the drift interval. The faster the curvature radius changes, the smaller the amount of phase adjustment per time, so as to avoid the standing wave node from crossing the maximum rebound stress position and causing reverse drift.

7. The compaction process for improving the cycle life of lithium batteries according to claim 6, characterized in that, When the thickness recovery amplitude at the location of the maximum rebound stress decreases after the standing wave node returns to the location of the maximum rebound stress, and the peak curvature recovery at the adjacent location moves away from the standing wave node, it is determined that the rebound stress has been transferred. The standing wave nodes are sequentially migrated along the moving direction of the curvature recovery peak, and the holding time of the standing wave node at the later migration position is less than the holding time at the previous migration position, until the thickness recovery amplitude difference between each migration position is within a preset range.

8. The compaction process for improving the cycle life of lithium batteries according to claim 7, characterized in that, The residual springback distribution of the electrode sheet is formed based on the migration direction and range of the standing wave nodes at the end of the first compaction process, as well as the thickness recovery amplitude at each migration location. During the stacking process, according to the stacking sequence and orientation of each electrode, the residual rebound distribution of each electrode is superimposed onto the inner sidewall of the outer casing after the cell is installed, and the position of the sidewall where the residual rebound is concentrated after stacking is established in correspondence with the different pressure zones of the flexible pressure bladder.

9. The compaction process for improving the cycle life of lithium batteries according to claim 8, characterized in that, The pressure zone corresponding to the sidewall location of the residual rebound concentration will establish the holding pressure before the other pressure zones; If the real-time thickness expansion at the sidewall location of the residual rebound concentration occurs before the pressure change rate inside the flexible pressure bladder increases, the yield stress of the corresponding magnetorheological fluid damper is reduced in advance, so that the limiting module moves in a controlled manner with the expansion of the battery cell. If the pressure change inside the flexible pressure bladder precedes the increase in the real-time thickness expansion rate, the yield stress of the corresponding magnetorheological fluid damper should be maintained or increased to prevent the pressure transmitted from adjacent pressure zones from causing local overpressure.

10. The compaction process for improving the cycle life of lithium batteries according to claim 9, characterized in that, When the pressure change rate of adjacent pressure zones is opposite and the real-time thickness expansion peak migrates from the pressure zone with increasing pressure change rate to the pressure zone with decreasing pressure change rate, it is determined that interlayer slip has occurred inside the cell. The yield stress of the adjacent magnetorheological fluid dampers is reduced sequentially along the migration direction of the thickness expansion peak, and then the yield stress is restored in the reverse order. When the pressure change rate of adjacent pressure zones is in the same direction and the position of the real-time thickness expansion peak remains stable, it is determined that the cell has undergone overall elastic expansion, and the negative correlation dynamic matching continues to be performed.

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