A lithium ion battery dynamic liquid absorption speed evaluation device and method

Abstract

The application relates to the technical field of batteries, and discloses a lithium ion battery dynamic liquid absorption speed evaluation device and method. Through the provision of a clamping plate group, a thin film pressure sensor, a container, a charging and discharging device and a processor, the charging and discharging process of a bare battery can be simulated, and the consistency of the pressure on the bare battery in the charging and discharging process due to the expansion of the bare battery can be monitored, so that the consistency of the dynamic liquid absorption speed of the bare battery in the charging and discharging process can be evaluated, and the risk of liquid deficiency of the battery fast charging and thick electrode can be better evaluated.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a device and method for evaluating the dynamic liquid absorption rate of lithium-ion batteries. Background Technology

[0002] The structure of a lithium-ion battery is quite complex and intricate, with its core components including the positive electrode, negative electrode, separator, electrolyte, and a series of structural parts. In the external structure of a lithium-ion battery, the efficient conduction of electrons from the negative electrode to the positive electrode is achieved through the arrangement of wires and loads. Inside the battery, the positive and negative electrodes are connected via the electrolyte, a crucial medium. During battery discharge, lithium ions (Li+) diffuse from the negative electrode to the positive electrode through the electrolyte and embed themselves within the crystal structure of the positive electrode. Therefore, the electrolyte plays a vital role in lithium-ion batteries, profoundly impacting their overall performance.

[0003] Ideally, a sufficient amount of electrolyte should be maintained between the positive and negative electrodes, ensuring that the lithium-ion concentration in the electrolyte remains at a suitable level throughout the charging and discharging process, thereby minimizing performance degradation caused by electrolyte concentration polarization. However, in actual charging and discharging processes, due to factors such as the diffusion rate of lithium ions, a lithium-ion concentration gradient often occurs between the positive and negative electrodes, causing the lithium-ion concentration to fluctuate during the charging and discharging process. Furthermore, due to limitations in structural design and the complexity of manufacturing processes, the distribution of electrolyte within the battery cell is often uneven. Especially during charging, as the electrodes expand, some "dry areas" form inside the cell. The presence of these "dry areas" reduces the amount of active material that can participate in the charging and discharging reactions, leading to uneven distribution of localized state of charge (SOC) within the battery and accelerating the localized aging process.

[0004] During charging and discharging, both the positive and negative electrode plates undergo a certain degree of volume expansion, causing the battery cell to also experience corresponding volume expansion and contraction, much like "breathing," constantly "inhaling" and "exhaling" electrolyte. Therefore, the wetting state of the electrolyte within the battery cell changes in real time.

[0005] Specifically, during charging, lithium ions are extracted from the positive electrode and inserted into the negative electrode. During this process, the graphite particles enlarge due to lithium ion insertion, increasing the battery's expansion force. Simultaneously, the porosity of the negative electrode decreases, causing the electrolyte filled in the electrode to be expelled under pressure (electrolysis), reducing the amount of electrolyte in the electrode. During discharging, the graphite particles shrink due to lithium de-lithiation, the battery's expansion force decreases, the porosity of the negative electrode increases, and electrolyte is drawn in (electrolysis), increasing the amount of electrolyte in the electrode. Therefore, during charging and discharging, the porosity of the negative electrode and the amount of electrolyte filling are both dynamically changing as lithium ions are intercalated and deintercalated between the positive and negative electrodes.

[0006] However, in fast charging mode, the insertion and extraction rate of lithium ions is relatively fast. If the discharge and electrolyte absorption rate of the negative electrode cannot match this, the electrolyte required for lithium ion transport in the electrode pores may not be able to fill in time during recharging, leading to lithium plating during charging—that is, lithium ions fail to successfully insert into the negative electrode pores. Therefore, the electrolyte absorption rate has a crucial impact on fast charging performance and battery safety.

[0007] Currently, industry-standard methods for assessing the electrolyte absorption rate in separators and electrodes primarily focus on static processes. Specifically, this involves cutting the electrode or separator to a fixed size, suspending it on a balance, immersing its lower end in the electrolyte, and recording changes in the electrode's mass or height in real time. However, this commonly used testing method cannot accurately simulate the dynamic electrolyte absorption process exhibited by the battery during charging and discharging due to changes in expansion forces, thus failing to accurately assess the risk of electrolyte shortage in fast-charging batteries and thick electrodes.

[0008] Therefore, improvements to existing technologies are necessary.

[0009] The above information is provided as background information only to aid in understanding this disclosure and does not constitute an assertion or admission that any of the above content can be used as prior art relative to this disclosure. Summary of the Invention

[0010] This invention provides a device and method for evaluating the dynamic liquid absorption rate of lithium-ion batteries, in order to solve the problems existing in the prior art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] In a first aspect, the present invention provides a device for evaluating the dynamic liquid absorption rate of a lithium-ion battery, the device comprising a clamping plate assembly, a thin-film pressure sensor, a container, a charging / discharging device, and a processor; wherein...

[0013] The clamping plate assembly includes two fastened first clamping plates and a second clamping plate, used to clamp the bare battery cell to be evaluated after the first immersion.

[0014] The thin-film pressure sensor is disposed between the second clamping plate and the bare battery cell and is connected to the processor. It is used to detect the pressure at different positions of the bare battery cell during charging and discharging and transmit the detected pressure data to the processor.

[0015] The container contains an electrolyte solution for the first immersion of the bare battery cell placed flat inside, and for the second immersion of the clamping plate assembly, the bare battery cell, and the thin-film pressure sensor placed vertically inside.

[0016] The charging and discharging device is connected to the bare battery cell and the processor respectively, which are erected in the container, and is used to charge and discharge the bare battery cell under the control of the processor.

[0017] The processor is used to monitor the uniformity of pressure on the bare cell in its height direction based on the detected pressure data, in order to evaluate the liquid absorption rate of the bare cell during charging and discharging.

[0018] Furthermore, in the lithium-ion battery dynamic liquid absorption speed evaluation device, a limiting groove is provided on the side of the first clamping plate that contacts the bare cell;

[0019] The bare battery cell is located within the limiting groove.

[0020] Furthermore, in the lithium-ion battery dynamic liquid absorption rate evaluation device, the first clamp and the second clamp are metal plates, and the surfaces of the first clamp and the second clamp facing the bare battery cell are coated with an insulating coating.

[0021] Furthermore, in the lithium-ion battery dynamic liquid absorption rate evaluation device, the thin-film pressure sensor is attached to the side of the second clamp facing the bare cell.

[0022] Furthermore, in the lithium-ion battery dynamic liquid absorption rate evaluation device, the surface of the thin-film pressure sensor is covered with a protective film.

[0023] Furthermore, in the lithium-ion battery dynamic liquid absorption rate evaluation device, the thin-film pressure sensor includes a plurality of thin-film pressure sensors, which are arranged in an array along the height and width directions of the bare cell.

[0024] Furthermore, in the lithium-ion battery dynamic liquid absorption rate evaluation device, in the direction along the thin-film pressure sensor toward the first clamping plate, the projection of the thin-film pressure sensor covers and is larger than the projection of the bare cell.

[0025] In a second aspect, the present invention provides a method for evaluating the dynamic liquid absorption rate of a lithium-ion battery, applied to a processor in the lithium-ion battery dynamic liquid absorption rate evaluation device provided in the first aspect above, the method comprising:

[0026] S101. The processor generates a height-pressure distribution map based on the detected pressure data; the horizontal axis of the height-pressure distribution map is the height of the bare cell, and the vertical axis is the pressure exerted on the bare cell in its height direction;

[0027] S102. The processor determines whether there is a data point in the height-pressure distribution map where dFyn / dyn≥±0.1; yn is the height of the bare cell at any position in the container, and Fyn is the pressure on the bare cell at its corresponding height; if yes, then execute S103; if no, then execute S104.

[0028] S103. It is determined that the bare battery cell is subjected to uneven force in its height direction, thereby determining that the liquid absorption rate of the bare battery cell is inconsistent;

[0029] S104. Determine that the bare battery cell is subjected to uniform force in its height direction, thereby determining that the liquid absorption rate of the bare battery cell is consistent.

[0030] Furthermore, after S103, the method further includes:

[0031] S105. The abscissa of the data point corresponding to the first dFyn / dyn≥±0.1 from bottom to top in the height direction of the bare cell is determined as the maximum liquid absorption height of the bare cell;

[0032] S106. The interval from 0 to the maximum liquid absorption height in the height direction of the bare battery cell is defined as the normal interval with uniform force and consistent liquid absorption speed, and the interval from the maximum liquid absorption height to the height of the bare battery cell in the height direction of the bare battery cell is defined as the liquid-deficient interval with uneven force and inconsistent liquid absorption speed.

[0033] Thirdly, the present invention provides a method for evaluating the dynamic liquid absorption rate of a lithium-ion battery, applied to a processor in the lithium-ion battery dynamic liquid absorption rate evaluation device provided in the first aspect above, the method comprising:

[0034] S201, the processor performs the following operations for different fast charging conditions:

[0035] After receiving the pressure data detected at different numbers of cycles under the current fast charging condition, the processor performs a center trend measurement calculation on the pressure experienced by the bare battery cell at the same height under different numbers of cycles.

[0036] The processor generates height-pressure distribution maps corresponding to different numbers of cycles based on the central trend measurement of the pressure corresponding to different heights of the bare cell at different cycle counts; the horizontal axis of the height-pressure distribution map is the height of the bare cell, and the vertical axis is the pressure on the bare cell in its height direction;

[0037] The processor determines whether there is a data point in each height-pressure distribution map where dFyn / dyn ≥ ±0.1; yn is the height of the bare battery cell at any position in the container, and Fyn is the pressure on the bare battery cell at its corresponding height; if yes, it determines that the bare battery cell is subjected to uneven force in its height direction under the corresponding number of cycles, thus determining that the liquid absorption rate of the bare battery cell is inconsistent; if no, it determines that the bare battery cell is subjected to uniform force in its height direction under the corresponding number of cycles, thus determining that the liquid absorption rate of the bare battery cell is consistent.

[0038] The processor determines the number of cycles corresponding to data points in the height-pressure distribution map that do not have dFyn / dyn≥±0.1 as the target number of cycles for the current fast charging condition, in order to provide early warning of low electrolyte or failure.

[0039] S202, The processor compares the target number of cycles under different fast charging conditions and determines the fast charging condition corresponding to the largest target number of cycles as the target fast charging condition to guide its use.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention provides a device and method for evaluating the dynamic liquid absorption rate of lithium-ion batteries. By providing a clamping plate assembly, a thin-film pressure sensor, a container, a charging and discharging device, and a processor, it is possible to simulate the charging and discharging process of bare cells and monitor the consistency of pressure on the height of the bare cells due to their own expansion during the charging and discharging process. This allows for the evaluation of the consistency of the dynamic liquid absorption rate of the bare cells during the charging and discharging process, thereby enabling a better assessment of the risk of liquid shortage in fast charging and thick electrodes.

[0042] The present invention has other features and advantages, which will be apparent from or will be set forth in detail in the accompanying drawings and the following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery dynamic liquid absorption rate evaluation device provided in Embodiment 1 of the present invention;

[0045] Figure 2 This is a schematic diagram of the structure of the thin-film pressure sensor 3 provided in an embodiment of the present invention;

[0046] Figure 3 This is one of the flowcharts of a method for evaluating the dynamic liquid absorption rate of a lithium-ion battery provided in an embodiment of the present invention;

[0047] Figure 4 This is a second schematic flowchart of a method for evaluating the dynamic liquid absorption rate of a lithium-ion battery according to an embodiment of the present invention;

[0048] Figure 5 This is a force distribution diagram in the direction of the core height during the charging process of 500 fast charging cycles at 25°C, provided by an embodiment of the present invention;

[0049] Figure 6 This is a differential distribution diagram of the force in the core height direction provided in an embodiment of the present invention;

[0050] Figure 7 This is a differential distribution diagram of the force in the height direction of the stacked battery cell under different operating conditions provided in the embodiments of the present invention;

[0051] Figure 8 This is a schematic diagram of the liquid shortage distribution of stacked batteries under different operating conditions provided in the embodiments of the present invention.

[0052] Figure label:

[0053] First clamping plate 1, second clamping plate 2, thin film pressure sensor 3, container 4, charging and discharging equipment 5, processor 6, bare battery cell 7, limiting groove 8, screw 9;

[0054] Pressure sensing point 31. Detailed Implementation

[0055] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0056] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0057] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0058] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0059] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0060] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0061] In this application, expressions such as "greater than", "less than", and "exceeding" are understood to exclude the stated number; expressions such as "above", "below", and "within" are understood to include the stated number. Furthermore, in the description of the embodiments of this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times", unless otherwise explicitly specified.

[0062] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0063] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0064] Example 1

[0065] Please refer to Figure 1 This invention provides a device for evaluating the dynamic liquid absorption rate of a lithium-ion battery. The device includes a clamping plate assembly, a thin-film pressure sensor 3, a container 4, a charging / discharging device 5, and a processor 6.

[0066] The clamping assembly consists of two clamping plates, a first clamping plate 1 and a second clamping plate 2, connected by fastening means. Its main function is to securely clamp the bare battery cell 7 to be evaluated after its first immersion treatment. Since the bare battery cell 7 is usually compressed within the casing, this design simulates the "breathing" scenario of a real bare battery cell 7, ensuring that its battery performance during testing is consistent with that of a real bare battery cell. Specifically, the first clamping plate 1 and the second clamping plate 2 clamp the side of the bare battery cell 7, and more specifically, clamp the side with the larger area. Compared to the side with the smaller area, the "breathing" effect of the larger area is more significant, allowing for more accurate assessment of liquid absorption. The bare battery cell 7 can be a wound cell or a stacked cell.

[0067] A thin-film pressure sensor 3 is cleverly placed between the second clamping plate 2 and the bare battery cell 7, and is connected to the processor 6 for signal transmission. This sensor can accurately detect and record the pressure changes at different locations of the bare battery cell 7 during charge-discharge cycles, and then transmit this pressure data to the processor 6 in real time for further analysis.

[0068] The container 4 contains an appropriate amount of electrolyte. It is designed to first provide an immersion environment for the bare battery cell 7, which is placed flat inside, for the first immersion. Then, when the clamping plate assembly, the bare battery cell 7 and the thin-film pressure sensor 3 are placed upright in the container 4, a second immersion process is carried out to fully simulate the liquid absorption process of the battery in actual use.

[0069] The charging and discharging device 5 is electrically connected to the bare battery cell 7 and the processor 6, which are erected in the container 4. Under the precise control of the processor 6, it performs charging and discharging operations on the bare battery cell 7 to simulate the actual working state of the battery.

[0070] The processor 6, as the core of the entire evaluation device, is responsible for receiving pressure data from the thin-film pressure sensor 3 and, based on this data, closely monitoring the uniformity of pressure on the bare cell 7 in the height direction. Through this monitoring process, the processor 6 can assess the consistency of the dynamic liquid absorption rate of the bare cell 7 during charge-discharge cycles, thereby providing a scientific basis for evaluating the battery's fast-charging performance and the potential liquid shortage risk of thick electrodes.

[0071] In summary, this invention successfully constructed a comprehensive evaluation device capable of simulating the charging and discharging process of a bare battery cell 7 and monitoring its pressure consistency along its height direction by organically combining a clamping plate assembly, a thin-film pressure sensor 2, a container 3, a container 4, a charging and discharging device 5, and a processor 6. This device not only improves the ability to evaluate the dynamic liquid absorption rate of lithium-ion batteries but also provides strong technical support for the optimization of battery fast charging technology and thick electrode design, effectively reducing the risks caused by insufficient liquid in practical applications.

[0072] It should be noted that during battery charging, if a higher charging rate is used, the electrolyte absorption rate inside the battery is more likely to be uneven. Within the same time period, differences in absorption rate lead to inconsistent electrolyte height distribution within the bare cell, i.e., uneven electrolyte distribution. This uneven electrolyte distribution directly affects the lithium intercalation process at the negative electrode, resulting in uneven lithium intercalation and consequently, uneven expansion forces within the cell.

[0073] For the bare battery cell 7 standing upright inside container 4, the liquid absorption process proceeds gradually from the bottom upwards. The inventors discovered that the uniformity of the force experienced by the bare battery cell 7 in the height direction actually reflects the consistency of the liquid absorption speed during fast charging. Uneven force distribution means that the liquid absorption speed varies in different parts of the battery cell.

[0074] During the first soaking, when immersing the bare battery cell 7, which is placed flat in container 4, it is necessary to ensure that the amount of electrolyte added is sufficient to submerge the bare battery cell 7. Specifically, the electrolyte level should be controlled at: the thickness of the bare battery cell 7 ≤ the electrolyte level ≤ the thickness of the bare battery cell 7 + 10 mm, to ensure that the battery cell is fully wetted. At the same time, the soaking time should be no less than 24 hours to ensure that the battery cell fully absorbs the electrolyte and that the electrolyte is evenly distributed.

[0075] In addition, during the soaking process, the positive and negative tabs of the bare battery cell 7 need to be bent upwards to avoid direct contact with the electrolyte. For safety, it is best to use insulating adhesive to protect the positive and negative tabs.

[0076] During the second immersion, when the clamping plate assembly, bare battery cell 7, and thin-film pressure sensor 3, which are all erected in container 4, are immersed as a whole, it is essential to ensure that the positive and negative tabs of the bare battery cell 7 are facing upwards. At this time, the amount of electrolyte in container 4 should be controlled to less than half the height of the battery cell to simulate the electrolyte height in the battery's BOL state, avoiding excessive electrolyte that could affect the accuracy of the test results. The bare battery cell 7, erected in container 4, simulates the state of a bare battery cell during actual operation, thereby improving the accuracy of the detection and evaluation.

[0077] When using the charging and discharging equipment 5 to perform charging and discharging operations on the bare battery cells 7, the insulating adhesive on the tabs must be removed first to ensure that the current can pass through normally. The above operations must be performed in a low-humidity environment, with humidity controlled to be less than or equal to -30°C.

[0078] Furthermore, regarding the fastening method between the first clamping plate 1 and the second clamping plate 2, this embodiment uses screws 9 for connection. The use of screws 9 not only ensures a tight connection between the clamping plates but also enables the clamping plate assembly to stably clamp the bare battery cell 7, providing a reliable guarantee for subsequent testing. The screw connection method also facilitates adjustment of the distance between the first clamping plate 1 and the second clamping plate 2, thereby accommodating different bare battery cells. Simultaneously, for the same bare battery cell, it is also convenient to adjust the clamping force according to design requirements.

[0079] Please refer to this again. Figure 1 In one embodiment of this invention, a limiting groove 8 is specifically formed on the side of the first clamping plate 1 that contacts the bare battery cell 7. The shape, size, and position of the limiting groove 8 are precisely designed according to the size and shape of the bare battery cell 7 to ensure that the bare battery cell 7 can be stably and accurately placed within the limiting groove 8. Screws 9 are evenly arranged around the bottom circumference of the limiting groove 8 to improve the clamping stability and uniformity of the first clamping plate 1 and the second clamping plate 2, and to ensure the accuracy of pressure detection.

[0080] When the bare cell 7 is placed in the limiting groove 8, its sides and bottom are surrounded or supported by the groove walls of the first clamping plate 1. This design not only provides a stable support surface for the bare cell 7, preventing it from shifting during subsequent evaluation processes, but also ensures the accurate positioning of the bare cell 7 during assembly through physical constraints.

[0081] Furthermore, the design of the limiting groove 8 can also protect the bare cell 7 to a certain extent, preventing it from being directly impacted or contaminated by the external environment. This is very important for improving the overall performance and safety of the battery pack. At the same time, the design of the limiting groove 8 also ensures that the bare cell 7 contains sufficient electrolyte, improving detection sensitivity.

[0082] In summary, using a limiting groove 8 on the first clamping plate 1 to accommodate the bare battery cell 7 is a simple and effective assembly method. It not only ensures the stability and accuracy of the bare battery cell 7 during the assembly process, but also improves the safety, reliability and sensitivity of its detection.

[0083] In one embodiment of this invention, the first clamping plate 1 and the second clamping plate 2 are metal plates, and the surfaces of the first clamping plate 1 and the second clamping plate 2 facing the bare battery cell 7 are coated with an insulating coating. This coating is not only based on careful consideration of safety, but also enhances the overall stability of the device performance.

[0084] The first clamping plate 1 and the second clamping plate 2 are made of metal, primarily because metal possesses excellent mechanical strength and rigidity, providing stable clamping and support for the bare battery cell 7 and ensuring its stability during testing. Furthermore, it simulates a real battery casing, more closely resembling the actual expansion of a battery. Simultaneously, the good thermal conductivity of metal helps to quickly conduct and dissipate heat generated during charging and discharging, maintaining the temperature stability of the bare battery cell 7, thereby ensuring the accuracy of the test and the normal operation of the equipment.

[0085] However, metals are inherently conductive, and without proper treatment, this can lead to safety hazards such as current leakage or short circuits. Therefore, applying an insulating coating to the surface of the metal plate facing the bare battery cell has become a crucial protective measure.

[0086] Specifically, the presence of the insulating coating first provides necessary electrical isolation for the clamping assembly, effectively preventing safety accidents that may be caused by accidental current leakage or short circuits. During battery testing and evaluation, especially during charge-discharge cycles, direct or indirect contact with current can threaten the accuracy of test results and the safety of equipment or personnel. Therefore, the application of the insulating coating becomes an indispensable protective barrier.

[0087] In addition, the insulating coating also protects the clamping plate assembly from environmental corrosion. It effectively resists the damage from electrolytes, moisture, and other potentially corrosive substances, thereby extending the service life of the clamping plate assembly and ensuring its stability and reliability during long-term testing.

[0088] In summary, the method of coating the surfaces of the first clamping plate 1 and the second clamping plate 2 with an insulating coating in this embodiment not only improves the safety of the device, but also enhances its durability and the accuracy of the test results.

[0089] In one embodiment of this invention, the thin-film pressure sensor 3 is precisely attached to the side of the second clamping plate 2 facing the bare battery cell 7.

[0090] It should be noted that the thin-film pressure sensor 3 is attached to the direct contact surface between the second clamping plate 2 and the bare battery cell 7. This ensures that the sensor can directly and accurately capture the pressure changes generated by the bare battery cell 7 during charging and discharging. This direct measurement method greatly improves the accuracy and real-time performance of the data, enabling a more precise assessment of the dynamic liquid absorption rate of the bare battery cell 7 and the uniformity of its pressure in the height direction.

[0091] Furthermore, attaching the thin-film pressure sensor 3 to the second clamping plate 2 facilitates its fixation and protection during testing. This design effectively prevents the sensor from moving or being damaged during testing, thus ensuring the continuity and stability of the test.

[0092] In summary, the adhesive design of the thin-film pressure sensor 3 on the second clamping plate 2 in this embodiment not only improves the accuracy and reliability of the test, but also enhances the continuity and stability of the test.

[0093] In one embodiment of this invention, the surface of the thin-film pressure sensor 3 is covered with a protective film.

[0094] This design not only reflects the meticulous consideration given to sensor protection measures in this embodiment.

[0095] Specifically, the protective film coating first provides a physical barrier for the thin-film pressure sensor 3, effectively resisting the damage from various contaminants and corrosive substances that may exist in the testing environment. This includes factors such as electrolytes, moisture, and dust that may damage the sensor. Through the isolation of this protective film, the stability and reliability of the sensor are ensured during long-term testing, thereby extending its service life.

[0096] Furthermore, the protective film helps reduce scratches and wear on the sensor surface. During testing, the sensor may experience slight friction with the bare battery cell 7 or other components. The protective film significantly reduces this frictional damage to the sensor surface, thus ensuring the accuracy and consistency of the test data.

[0097] More importantly, this protective film does not affect the sensor's sensitivity to pressure or its response speed. It merely acts as a protective barrier, ensuring that the sensor maintains its original performance even in harsh testing environments.

[0098] In summary, the design of covering the surface of the thin-film pressure sensor 3 with a protective film in this embodiment not only improves the protection effect of the sensor and extends its service life, but also ensures the accuracy and consistency of the test data.

[0099] Please refer to Figure 2 In one embodiment of this invention, the thin-film pressure sensor 3 includes a plurality of pressure sensing points 31, which are located along the height direction of the bare battery cell 7. Figure 2 (in the H direction) and width direction ( Figure 2 The W direction in the middle is arranged in an array.

[0100] For example, such as Figure 2 As shown, 16 sensing points 31 can be arranged along the height direction of the bare battery cell 7, and 14 sensing points 31 can be arranged along the width direction of the bare battery cell 7, forming a 16×14 array, for a total of 224 sensing points 31. The spacing between each sensing point 31 can be adjusted according to the size of the bare battery cell 7 and the testing requirements to ensure coverage of the entire cell surface. Each pressure sensing point 31 is connected to the processor 6 via a wire. The processor 6 can read the pressure value of each sensing point 31 in real time and process and analyze it.

[0101] This design not only significantly improves the sensor's accuracy in sensing pressure, but also enhances its adaptability and reliability in complex testing environments.

[0102] Each pressure sensing point 31 has independent and accurate pressure sensing capabilities, enabling it to capture and respond to pressure changes at its location in real time. When the bare cell 7 expands or contracts during charging and discharging, these pressure sensing points 31 can quickly capture pressure fluctuations at different heights on the cell surface and at different locations at the same height, thus providing comprehensive and detailed pressure distribution data.

[0103] The array of pressure sensing points 31 enables the sensor to achieve full coverage and precise monitoring of the surface of the bare cell 7. This layout not only improves the density and accuracy of data acquisition, but also allows for a more intuitive observation of subtle changes in the pressure distribution of the cell during charging and discharging, thereby enabling a more in-depth assessment of the cell's dynamic liquid absorption rate and internal stress state.

[0104] By increasing the number of sensing points 31 and decreasing the spacing between them, the resolution of pressure monitoring can be improved. This allows for more precise observation of subtle changes in the pressure distribution of the bare cell 7 during charging and discharging, thereby enabling a more in-depth evaluation of the dynamic liquid absorption rate and internal stress state of the bare cell 7.

[0105] Furthermore, the array-shaped arrangement of pressure sensing points 31 enhances the sensor's adaptability to complex testing environments. Regardless of the testing environment, the sensor maintains its original performance and provides accurate and stable pressure data.

[0106] In summary, the thin-film pressure sensor 3 in this embodiment adopts an array-like arrangement of pressure sensing points 31, which not only improves the sensor's sensing accuracy and adaptability, but also provides more comprehensive and accurate pressure distribution data, providing strong technical support for evaluating the dynamic liquid absorption rate and internal stress state of lithium-ion batteries.

[0107] In one embodiment of this invention, the layout design of the thin-film pressure sensor 3 is further optimized to ensure comprehensive and accurate monitoring of the bare battery cell 7. Specifically, the coverage area of ​​the sensor projection is intentionally set along the direction of the thin-film pressure sensor 3 toward the first clamping plate 1, so that it not only completely covers the projection of the bare battery cell 7, but also extends beyond the boundary of the bare battery cell 7.

[0108] The importance of this design detail lies in the fact that it ensures the sensor can capture all pressure changes that may occur in the bare cell 7 during charging and discharging, whether these changes occur in the central area or the edge of the cell. This allows for a more comprehensive understanding of the pressure distribution and changes in the cell during dynamic processes, and thus a more accurate assessment of the cell's liquid absorption rate, internal stress state, and potential safety hazards.

[0109] Furthermore, this design enhances the stability and reliability of the sensor during testing. Because the sensor projection covers the battery cell and its surrounding area, even if the battery cell undergoes slight displacement or deformation during testing, the sensor can maintain the continuity and accuracy of its monitoring, thereby avoiding data distortion caused by changes in the battery cell's position.

[0110] In summary, the design of the thin-film pressure sensor 3 in this embodiment, which covers a larger area than the bare battery cell 7, not only enhances the sensor's comprehensive monitoring capability of the battery cell but also strengthens its stability and reliability during the testing process.

[0111] Although this application frequently uses terms such as first clamp, second clamp, and thin-film pressure sensor, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention.

[0112] This invention provides a device and method for evaluating the dynamic liquid absorption rate of lithium-ion batteries. By providing a clamping plate assembly, a thin-film pressure sensor, a container, a charging and discharging device, and a processor, it can simulate the charging and discharging process of bare cells and monitor the consistency of pressure on the height of the bare cells due to their expansion during the charging and discharging process. This allows for the evaluation of the consistency of the dynamic liquid absorption rate of the bare cells during the charging and discharging process, thereby enabling a better assessment of the risk of liquid shortage in fast charging and thick electrodes.

[0113] Example 2

[0114] Please refer to Figure 3 This is a flowchart illustrating a method for evaluating the dynamic liquid absorption rate of a lithium-ion battery according to Embodiment 2 of the present invention. The method is applied to the processor in the dynamic liquid absorption rate evaluation device for lithium-ion batteries described in Embodiment 1 above. The method specifically includes the following steps:

[0115] S101. The processor generates a height-pressure distribution map based on the detected pressure data; the horizontal axis of the height-pressure distribution map is the height of the bare cell, and the vertical axis is the pressure exerted on the bare cell in its height direction.

[0116] It should be noted that the processor receives and processes pressure data from a thin-film pressure sensor, which reflects the pressure experienced by the bare battery cell at different heights and at different locations within the same height. The variation in pressure experienced by the bare battery cell along the height direction is displayed in a visually intuitive graphical format.

[0117] S102, The processor determines whether there is a data point in the height-pressure distribution map where dFyn / dyn≥±0.1; yn is the height of the bare cell at any position in the container, and Fyn is the pressure on the bare cell at its corresponding height; if yes, then execute S103; if no, then execute S104.

[0118] It should be noted that the processor sets a threshold (±0.1 in this example) to determine whether the rate of pressure change is significant. If, during the process of traversing all data points in the altitude-pressure distribution map, the absolute value of the rate of pressure change at a certain data point is found to be greater than or equal to this threshold, then it is considered that there is a significant pressure change at that altitude.

[0119] Specifically, in this step, d represents the derivative. Specifically, dFyn refers to the minute change in the pressure Fyn exerted on the bare cell in the height direction, while dyn refers to the minute change in the height yn at any position on the bare cell. Therefore, dFyn / dyn represents the rate at which the pressure Fyn exerted on the bare cell in the height direction changes with the height yn of the bare cell, i.e., the rate of change of force relative to height. When this rate of change is greater than or equal to a threshold, it means that there is uneven force distribution in the height direction of the cell.

[0120] The threshold was chosen to be an absolute value of 0.1 because pressure sensors have a certain level of accuracy, which is subject to fluctuations within that accuracy range. Within the range dFyn / dyn ≤ ±0.1, the data exhibits fluctuations, which is an effect of the testing process and must be taken into account.

[0121] S103. It is determined that the bare battery cell is subjected to uneven force in its height direction, thereby determining that the liquid absorption rate of the bare battery cell is inconsistent.

[0122] It should be noted that when there are data points in the height-pressure distribution map where the pressure change rate is greater than or equal to the threshold, it indicates that the pressure distribution in the bare cell is uneven along the height direction. This uneven force leads to differences in the electrolyte absorption rate at different locations within the bare cell during the electrolyte absorption process. This is because pressure differences affect the flow rate and direction of the electrolyte within the cell. Therefore, the processor uses this information to determine the inconsistency in the electrolyte absorption rate of the bare cell, which can be used for further analysis and adjustments to improve battery performance and consistency.

[0123] S104. Determine that the bare battery cell is subjected to uniform force in its height direction, thereby determining that the liquid absorption rate of the bare battery cell is consistent.

[0124] It's important to note that if the rate of pressure change at all data points in the height-pressure distribution map is less than the threshold, it indicates that the pressure distribution on the bare cell is uniform along the height direction. Uniform force helps the bare cell maintain a consistent electrolyte absorption rate during the electrolyte absorption process. This is because when the pressure distribution is uniform, the flow velocity and direction of the electrolyte within the cell are also more consistent. Therefore, the processor determines that the electrolyte absorption rate of the bare cell is consistent based on this information, indicating good battery performance and consistency. This helps ensure that the battery exhibits stable performance in subsequent use and testing.

[0125] In one embodiment of this example, the process of the method for evaluating the dynamic liquid absorption rate of lithium-ion batteries is further enriched. After step S103, i.e., after determining that the bare cell is subjected to uneven force in its height direction, thus determining that its liquid absorption rate is inconsistent, the method continues to include the following two important steps:

[0126] S105. The abscissa of the first data point corresponding to dFyn / dyn≥±0.1 from bottom to top in the height direction of the bare cell is determined as the maximum liquid absorption height of the bare cell.

[0127] It should be noted that this data point represents the initial height position where the pressure change becomes significant along the height direction of the bare cell. The significance of this step lies in its identification of the highest position to which the electrolyte can uniformly penetrate the bare cell during charging and discharging.

[0128] S106. The interval from 0 to the maximum liquid absorption height in the height direction of the bare battery cell is defined as the normal interval with uniform force and consistent liquid absorption speed, and the interval from the maximum liquid absorption height to the height of the bare battery cell in the height direction of the bare battery cell is defined as the liquid-deficient interval with uneven force and inconsistent liquid absorption speed.

[0129] It should be noted that this step is based on the previous step, and it involves dividing the bare cell into the normal range and the low electrolyte range.

[0130] Specifically, based on the maximum liquid absorption height determined in step S105, the processor divides the height direction of the bare cell into two intervals:

[0131] Normal Range: This range is defined as the area from the bottom of the bare cell (height 0) to the maximum electrolyte absorption height. Within this range, due to the uniform pressure distribution, the electrolyte can smoothly penetrate the cell, so the electrolyte absorption rate of the cell can be considered consistent. This range represents the part of the cell where performance is stable and efficient, which is crucial for ensuring the overall performance and safety of the battery.

[0132] The electrolyte-deficient region: This region refers to the area remaining from the maximum electrolyte absorption height to the top of the bare cell. Within this region, due to uneven pressure distribution, the electrolyte cannot fully penetrate the cell, resulting in inconsistent electrolyte absorption rates. This uneven absorption phenomenon may lead to electrolyte-deficient areas within the cell, thereby affecting battery performance and safety.

[0133] For example, if the height of a bare cell is 100mm, and under a certain operating condition or a certain number of cycles, the absolute value of dFyn / dyn is >0.1 at a height of 60mm, then the maximum electrolyte creepage height of the bare cell under this operating condition or a certain number of cycles is 60mm. The electrolyte distribution is uniform in the 0-60mm range, which is the normal range. The electrolyte distribution is uneven in the 60-100mm range, which is the electrolyte-deficient range, meaning that the electrolyte cannot fully wet the cell.

[0134] By dividing the bare cell into sections through steps S105 and S106, we can not only more accurately assess the dynamic liquid absorption rate of lithium-ion batteries during charging and discharging, but also promptly identify areas within the cell that may be deficient in liquid, thus providing strong data support for subsequent battery optimization and improvement.

[0135] Example 3

[0136] Please refer to Figure 4 This is a flowchart illustrating a method for evaluating the dynamic liquid absorption rate of a lithium-ion battery according to Embodiment 3 of the present invention. This method is applied to the processor in the dynamic liquid absorption rate evaluation device for lithium-ion batteries described in Embodiment 1 above. Compared to Embodiment 2, which only evaluates the liquid absorption of a bare cell at a certain number of cycles under a certain fast-charging condition, the method provided in Embodiment 3 can be used to further evaluate the maximum number of cycles a bare cell can perform under a certain fast-charging condition, i.e., at which number of cycles will uneven stress occur, and to further evaluate which fast-charging condition is most reasonable, i.e., which fast-charging condition will least likely or latest result in uneven stress. The method specifically includes the following steps:

[0137] S201, the processor performs the following operations for different fast charging conditions:

[0138] After receiving the pressure data detected at different numbers of cycles under the current fast charging condition, the processor performs a center trend measurement calculation on the pressure experienced by the bare battery cell at the same height under different numbers of cycles.

[0139] The processor generates height-pressure distribution maps corresponding to different numbers of cycles based on the central trend measurement of the pressure corresponding to different heights of the bare cell at different cycle counts; the horizontal axis of the height-pressure distribution map is the height of the bare cell, and the vertical axis is the pressure on the bare cell in its height direction;

[0140] The processor determines whether there is a data point in each height-pressure distribution map where dFyn / dyn ≥ ±0.1; yn is the height of the bare battery cell at any position in the container, and Fyn is the pressure on the bare battery cell at its corresponding height; if yes, it determines that the bare battery cell is subjected to uneven force in its height direction under the corresponding number of cycles, thus determining that the liquid absorption rate of the bare battery cell is inconsistent; if no, it determines that the bare battery cell is subjected to uniform force in its height direction under the corresponding number of cycles, thus determining that the liquid absorption rate of the bare battery cell is consistent.

[0141] The processor determines the number of cycles corresponding to data points in the height-pressure distribution map where dFyn / dyn≥±0.1 does not exist as the target number of cycles for the current fast charging condition, in order to provide early warning of low electrolyte levels or failure.

[0142] It should be noted that the processor can receive pressure data detected at each cycle number under the current fast charging condition, or it can receive pressure data detected at several cycles under the current fast charging condition. Specific details are as follows:

[0143] Pressure data detected per cycle: The processor can receive and record pressure data detected per cycle under the current fast charging condition in real time. This method provides continuous and detailed pressure change information, which helps to accurately analyze the pressure change trend of the battery cell during charging and discharging. For example, when the battery cell is undergoing fast charging testing, the processor can record the pressure data for the 1st, 2nd, 3rd, ... up to the nth cycle, thus obtaining the pressure change curve of the battery cell at different cycle numbers. This helps to evaluate the performance stability and lifespan degradation of the battery cell under fast charging conditions, and to promptly identify potential problems, such as damage to the internal structure of the battery cell or abnormal consumption of electrolyte.

[0144] Pressure data detected over several charging cycles: The processor can also receive pressure data detected over several charging cycles under the current fast charging condition, for example, recording pressure data every certain number of cycles (e.g., every 5 cycles, every 10 cycles, etc.). This method reduces data processing and storage space usage while still capturing key pressure change nodes in the battery cell during fast charging. For example, during fast charging testing of the battery cell, the processor can record pressure data at key cycles such as the 5th, 10th, and 15th cycles, thereby analyzing the pressure changes of the battery cell at these critical nodes. This helps to evaluate the performance change trend of the battery cell under fast charging conditions, determine whether the battery cell experiences sudden performance changes or anomalies at a certain stage, and provide a reference for the optimized design and use of the battery cell.

[0145] Understandably, the processor can flexibly choose the method of receiving pressure data based on specific testing needs and data processing requirements. Whether receiving pressure data for each cycle or for several cycles, it can provide strong data support for evaluating the dynamic liquid absorption rate and internal stress state of lithium-ion batteries.

[0146] During battery charging and discharging, the pressure on a bare cell at a certain height may fluctuate slightly due to various external factors (such as temperature fluctuations and vibration) and internal factors (such as material inhomogeneity and electrolyte flow). By calculating the central tendency of multiple data points at different locations at the same height, the impact of these random errors on the final result can be significantly reduced, making the evaluation results more reliable.

[0147] Central tendency measures include the mean, median, and weighted average; among them,

[0148] The average value is suitable for symmetrical cases without extreme values;

[0149] The median is suitable for cases containing extreme values;

[0150] The weighted average is suitable for situations where different values ​​have different levels of importance.

[0151] In this way, the pressure magnitudes of different pressure sensing points 31 in the width direction at the same height can be utilized to reduce the impact of uncertainties on the pressure data of pressure sensing points 31 in the height direction and improve the overall accuracy of the assessment.

[0152] For example, it can be Figure 3 The pressure value in each W direction is averaged F y1 =[F(x1,y1)+F(x2,y1)+F(x3,y1)+……F(x m ,y1)] / m,F y2 =[F(x1,y2)+F(x2,y2)+F(x3,y2)+……F(x m ,y2)] / m,……F y n =[F(x1,y n ) + F(x2, y m ) + F(x3, y m )+……F(x) m y n )] / m, where m is the number of pressure sensing points in the W direction and n is the number of pressure sensing points in the H direction, with y n Let Fy be the x-axis. n Using the vertical axis as the ordinate, the height-pressure distribution map can be determined.

[0153] It should be noted that since the center of the large surface of the bare cell 7 is subjected to the greatest pressure, this embodiment prefers to use a weighted average value to increase the weight of the center area. Specifically, the weight can be increased in both the height center area and the width center area of ​​the bare cell 7.

[0154] At this time, F yj = ,in The weight of each pressure sensing point 31 in the W direction is defined. The weighted average assigns different weights to each data point based on its importance or reliability, thus more accurately reflecting the overall pressure trend of the bare cell 7 at a given height. For example, data points near the center or critical parts of the bare cell 7 can be assigned higher weights, as pressure changes at these locations have a greater impact on the performance and safety of the bare cell 7. Weighted averaging highlights the pressure characteristics at these critical locations, making the evaluation results more refined and reliable.

[0155] Furthermore, during actual testing, various factors (such as sensor errors and environmental interference) may generate outlier data points. If these outlier data points are directly included in the calculation of the average, they may cause significant deviations in the results. Weighted averaging, however, can mitigate the impact of outlier data points by appropriately allocating weights. For example, data points that significantly deviate from the normal range can be assigned lower weights, thereby ensuring the stability and consistency of the evaluation results and avoiding misjudgments caused by individual outlier data points.

[0156] Furthermore, when generating altitude-pressure distribution maps, using a weighted average simplifies multiple data points at different locations at the same altitude into a single value. This not only reduces the amount of data but also simplifies the calculation process and improves computational efficiency. Especially when dealing with large-scale datasets, the calculation of the weighted average can significantly reduce the consumption of computing resources, speed up data processing, and thus obtain evaluation results more quickly.

[0157] When determining whether there are data points with significant pressure change rates in the height-pressure distribution map, using a weighted average is more intuitive and convenient. Since the weighted average has already smoothed the original data and considered the importance of each data point, the weighted averages at adjacent heights can be directly compared to determine whether the pressure change rate is significant. This method avoids the tedious process of analyzing each data point individually, making the judgment of pressure change trends more efficient and accurate. It helps to promptly detect potential anomalies in the bare battery cell 7 during charging and discharging, such as localized overvoltage or pressure unevenness, thereby allowing for appropriate measures to be taken to ensure the safety and accuracy of the test.

[0158] In summary, calculating the weighted average of the pressure experienced by bare cells at the same height under different cycle counts not only improves the accuracy of the evaluation but also brings computational convenience, making the entire evaluation process more efficient and reliable. This step has significant application value in the evaluation method of dynamic liquid absorption rate of lithium-ion batteries. By assigning appropriate weights to data points at different locations or of different importance, the weighted average can more accurately reflect the true pressure distribution, effectively suppress the interference of outlier data, simplify the data processing flow, and make the judgment of pressure change trends more intuitive and accurate.

[0159] S202, The processor compares the target number of cycles under different fast charging conditions and determines the fast charging condition corresponding to the largest target number of cycles as the target fast charging condition to guide its use.

[0160] It should be noted that the processor evaluates the dynamic liquid absorption rate of lithium-ion batteries under different fast-charging conditions. First, by calculating the weighted average pressure, generating a height-pressure distribution map, and assessing the uniformity of force application, the consistency of liquid absorption rate among the bare cells is determined. Then, the target number of cycles is determined based on the result of the force uniformity. Finally, by comparing the target number of cycles under different fast-charging conditions, the optimal fast-charging condition is determined to guide usage. This method can effectively evaluate the liquid absorption performance of lithium-ion batteries, providing an important basis for the safe use of batteries.

[0161] Specifically, when comparing different fast charging conditions, select the fast charging condition that has no low electrolyte range in any number of cycles, or the fast charging condition with a large number of cycles that have a low electrolyte range, or the fast charging condition with the same number of cycles but a small low electrolyte range.

[0162] It is understood that, in another implementation, this embodiment may further include the content provided in Embodiment 2.

[0163] To more clearly demonstrate the implementation process of any embodiment of the present invention, a specific example is provided below for detailed description.

[0164] Specific example 1:

[0165] The LFP core has a height of 150mm, a width of 120mm, and a thickness of 15mm. In a low-humidity environment (-30℃), place the core flat in a PE-insulated container (500mm x 500mm x 500mm). Fold the tabs of the core upwards and apply insulating tape. Pour electrolyte into the container, ensuring the electrolyte level is greater than or equal to the core's thickness. To avoid submerging the tabs, the electrolyte level should be ≤15 + 10 = 25mm. Immerse the core in the container for 24 hours. Secure the immersed core between two plates (e.g., insulating steel plates). Attach a thin-film pressure sensor (160mm x 180mm) to one of the insulating steel plates. Secure the core between the two insulating steel plates with screws. Encapsulate the thin-film pressure sensor with a 1mm PE film, adhesively attaching one side to the insulating steel plate. Place the core vertically in the container with the tabs facing upwards. The electrolyte level in the container must be less than the core height / 2 = 75mm, and the electrolyte level must cover the bottom of the core. Remove the insulating adhesive from the tabs, connect the charging / discharging equipment, and connect the thin-film pressure sensor. Perform 500 fast charging cycles at 25℃. The force distribution along the core height direction during different cycle numbers is shown in the diagram. Figure 5As shown. Fast charging conditions are: 1.5C constant current charging to 50% capacity, 1.0C constant current charging to 30% capacity, 0.5C constant current charging to 10% capacity, 0.33C constant current charging to 10% capacity, 1C discharge, 500 cycles. A differential charging graph for each of the 500 cycles can be generated; for simplicity, the results of cycles 1, 100, 300, and 500 are selected. The graph shows that the core expansion force increases with the number of cycles. At the end of the first charging cycle, the expansion force distribution along the core height is uniform, indicating a relatively uniform electrolyte distribution and a relatively uniform electrolyte absorption rate during fast charging. After 100 charging cycles, the expansion force distribution is relatively uniform between 10-100mm in the core height direction; beyond 100mm, the expansion force begins to decrease. At this location, the electrolyte absorption rate cannot keep up, resulting in insufficient electrolyte wetting at the top of the core, leading to less lithium intercalation in the graphite and a decrease in expansion force. Figure 6 As shown, after one cycle, dFyn / dyn in the core height direction is ±0.1, indicating that the electrolyte absorption rate is basically consistent in the core height direction under this charging regime. After 300 cycles, when yn = 100 mm in the height direction, dFyn / dyn > ±0.1, meaning the electrolyte absorption height is 100 mm with each cycle. After 300 cycles, when yn = 80 mm in the height direction, dFyn / dyn > ±0.1, meaning the electrolyte absorption height is 80 mm with each cycle. After 500 cycles, when yn = 60 mm in the height direction, dFyn / dyn > ±0.1, meaning the electrolyte absorption height is 60 mm with each cycle. With increasing cycle count, the expansion force decreases due to differences in electrolyte distribution, and the earlier the point of expansion force decreases with more cycles, the more advanced the cycle count. During charging, under conditions of good electrolyte wetting, lithium intercalation at the negative electrode increases the expansion force. If the electrolyte absorption rate is insufficient during fast charging, a certain location on the winding core may lack free electrolyte, preventing lithium ions from embedding into the negative electrode and reducing expansion force. Therefore, this invention uses a special evaluation device to detect changes in expansion force along the winding core's height to determine the electrolyte absorption height during charging. This method is simple to operate and can simulate the electrolyte absorption rate during fast charging.

[0166] Specific example two:

[0167] The LFP laminated battery cell has a height of 180mm, a width of 300mm, and a thickness of 20mm. In a low-humidity environment (-30℃), place the laminated battery cell flat in a PE insulating container (500mm x 500mm x 500mm). Fold the battery cell tabs upwards and apply insulating tape. Pour electrolyte into the container, ensuring the electrolyte level is at least 20mm above the battery cell thickness. To avoid submerging the tabs, the electrolyte level should be ≤20 + 10 = 30mm. Immerse the battery cell in the container for 24 hours. Secure the immersed battery cell between two insulating steel plates. Attach a thin-film pressure sensor (200mm x 320mm) to one of the insulating steel plates. Secure the battery cell between the two insulating steel plates with screws. Encapsulate the thin-film pressure sensor with a 1mm PE film, applying adhesive to one side and attaching it to the insulating steel plate. Place the battery cell vertically in the container with the tabs facing upwards. The electrolyte level in the container must be less than 90mm (cell height / 2), and the electrolyte level must cover the bottom of the cell. Remove the insulating adhesive from the tabs, connect the charging / discharging equipment, and connect the thin-film pressure sensor. Perform 10 charge / discharge cycles on the battery using the three operating conditions shown in Table 1 below. Take the differential force curve in the cell height direction during the 10th charging cycle. Figure 7 As shown.

[0168] Table 1:

[0169]

[0170] As shown in the diagram, in operating condition 2, dFyn / dyn < ±0.1 in the height direction, indicating a relatively uniform force distribution in the height direction, which in turn indicates a relatively uniform electrolyte distribution inside the battery. In operating condition 1, at the 80-100mm height direction, dFyn / dyn > ±0.1, indicating a electrolyte shortage at this location. Outside this area, dFyn / dyn ≤ 0.1, indicating a relatively uniform electrolyte distribution in other areas. In operating condition 3, at the 70-110mm height direction, dFyn / dyn > ±0.1, indicating a electrolyte shortage at this location. Outside this area, dFyn / dyn ≤ 0.1, indicating a relatively uniform electrolyte distribution in other areas. A schematic diagram of electrolyte shortage under the three operating conditions is shown below. Figure 8 As shown, the electrolyte shortage area is largest in condition 3, while the electrolyte distribution is most uniform in condition 2. The reason for the central electrolyte shortage is that the wetting path of the stacked battery is along the four sides, making the central area most prone to electrolyte deficiency. This method can compare different fast-charging conditions to identify the electrolyte shortage area during cell charging and discharging, and can select the most suitable fast-charging condition.

[0171] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A device for evaluating the dynamic liquid absorption rate of a lithium-ion battery, characterized in that, The device includes a clamping plate assembly, a thin-film pressure sensor (3), a container (4), a charging and discharging device (5), and a processor (6); wherein, The clamping plate assembly includes two fastened first clamping plates (1) and second clamping plates (2) for clamping the bare battery cells to be evaluated after the first immersion in the clamping plate assembly. The thin-film pressure sensor (3) is disposed between the second clamping plate (2) and the bare cell and is connected to the processor (6). It is used to detect the pressure at different positions of the bare cell during charging and discharging and transmit the detected pressure data to the processor (6). The container (4) contains an electrolyte for first immersion of the bare battery cell placed flat inside, and for second immersion of the clamping plate assembly, the bare battery cell and the thin-film pressure sensor (3) placed vertically inside. The charging and discharging device (5) is connected to the bare battery cell and the processor (6) respectively, which are erected in the container (4), and is used to charge and discharge the bare battery cell under the control of the processor (6); The processor (6) is used to monitor the uniformity of pressure on the bare cell in its height direction based on the detected pressure data, so as to evaluate the liquid absorption rate of the bare cell during charging and discharging.

2. The lithium-ion battery dynamic liquid absorption rate evaluation device according to claim 1, characterized in that, A limiting groove (8) is provided on the side of the first clamping plate (1) that contacts the bare battery cell; The bare battery cell is located in the limiting groove (8).

3. The lithium-ion battery dynamic liquid absorption rate evaluation device according to claim 1, characterized in that, The first clamp (1) and the second clamp (2) are metal plates, and the surfaces of the first clamp (1) and the second clamp (2) facing the bare battery cell are coated with an insulating coating.

4. The lithium-ion battery dynamic liquid absorption rate evaluation device according to claim 1, characterized in that, The thin-film pressure sensor (3) is attached to the side of the second clamp (2) facing the bare battery cell.

5. The lithium-ion battery dynamic liquid absorption rate evaluation device according to claim 1, characterized in that, The surface of the thin-film pressure sensor (3) is covered with a protective film.

6. The lithium-ion battery dynamic liquid absorption rate evaluation device according to claim 1, characterized in that, The thin-film pressure sensor (3) includes a plurality of pressure sensing points (31), which are arranged in an array along the height and width directions of the bare cell.

7. The lithium-ion battery dynamic liquid absorption rate evaluation device according to claim 1, characterized in that, In the direction along which the thin-film pressure sensor (3) faces the first clamping plate (1), the projection of the thin-film pressure sensor (3) covers and is larger than the projection of the bare cell.

8. A method for evaluating the dynamic liquid absorption rate of a lithium-ion battery, characterized in that, The processor used in the lithium-ion battery dynamic liquid absorption rate evaluation device as described in any one of claims 1-7, the method comprising: S101. The processor generates a height-pressure distribution map based on the detected pressure data; the horizontal axis of the height-pressure distribution map is the height of the bare cell, and the vertical axis is the pressure exerted on the bare cell in its height direction; S102. The processor determines whether there is a data point in the height-pressure distribution map where dFyn / dyn≥±0.1; yn is the height of the bare cell at any position in the container, and Fyn is the pressure on the bare cell at its corresponding height; if yes, then execute S103; if no, then execute S104. S103. It is determined that the bare battery cell is subjected to uneven force in its height direction, thereby determining that the liquid absorption rate of the bare battery cell is inconsistent; S104. Determine that the bare battery cell is subjected to uniform force in its height direction, thereby determining that the liquid absorption rate of the bare battery cell is consistent.

9. The method for evaluating the dynamic liquid absorption rate of a lithium-ion battery according to claim 8, further comprising, after S103: S105. The abscissa of the data point corresponding to the first dFyn / dyn≥±0.1 from bottom to top in the height direction of the bare cell is determined as the maximum liquid absorption height of the bare cell; S106. The interval from 0 to the maximum liquid absorption height in the height direction of the bare battery cell is defined as the normal interval with uniform force and consistent liquid absorption speed, and the interval from the maximum liquid absorption height to the height of the bare battery cell in the height direction of the bare battery cell is defined as the liquid-deficient interval with uneven force and inconsistent liquid absorption speed.

10. A method for evaluating the dynamic liquid absorption rate of a lithium-ion battery, characterized in that, The processor used in the lithium-ion battery dynamic liquid absorption rate evaluation device as described in any one of claims 1-7, the method comprising: S201, the processor performs the following operations for different fast charging conditions: After receiving the pressure data detected at different numbers of cycles under the current fast charging condition, the processor performs a center trend measurement calculation on the pressure experienced by the bare battery cell at the same height under different numbers of cycles. The processor generates height-pressure distribution maps corresponding to different numbers of cycles based on the central trend measurement of the pressure corresponding to different heights of the bare cell at different cycle counts; the horizontal axis of the height-pressure distribution map is the height of the bare cell, and the vertical axis is the pressure on the bare cell in its height direction; The processor determines whether there is a data point in each height-pressure distribution map where dFyn / dyn ≥ ±0.1; yn is the height of the bare battery cell at any position in the container, and Fyn is the pressure on the bare battery cell at its corresponding height; if yes, it determines that the bare battery cell is subjected to uneven force in its height direction under the corresponding number of cycles, thus determining that the liquid absorption rate of the bare battery cell is inconsistent; if no, it determines that the bare battery cell is subjected to uniform force in its height direction under the corresponding number of cycles, thus determining that the liquid absorption rate of the bare battery cell is consistent. The processor determines the number of cycles corresponding to data points in the height-pressure distribution map that do not have dFyn / dyn≥±0.1 as the target number of cycles for the current fast charging condition, in order to provide early warning of low electrolyte or failure. S202, The processor compares the target number of cycles under different fast charging conditions and determines the fast charging condition corresponding to the largest target number of cycles as the target fast charging condition to guide its use.

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