Method for determining charging capability of pole piece, testing method, device, equipment and medium

Abstract

The embodiment of the application discloses a kind of determination methods of the charging capacity of pole piece, test method, device, equipment and medium, wherein, method includes: obtaining the charging data of existing lithium precipitation after battery is charged at first charging rate, wherein charging data includes voltage and SOC;Based on the charging data of voltage and SOC, the first dV / dSOC value corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval are determined respectively;Wherein, the first SOC interval corresponds to the charging platform of LiC m Formed by graphite when embedding lithium, the second SOC interval corresponds to the charging platform of LiC n Formed by graphite when embedding lithium, and the lower limit of second SOC interval is greater than or equal to the upper limit of first SOC interval, m And n All are positive integers;Based on the second dV / dSOC value and the first dV / dSOC value, the charging capacity of negative pole piece is determined. By large charging rate as the acceleration factor of lithium precipitation and simple data processing, the charging capacity of negative pole piece under these extreme conditions can be obtained.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of batteries, and in particular to a method, testing method, apparatus, equipment, and medium for determining the charging capability of an electrode. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles, and the market demand for fast-charging performance of these batteries is increasing daily. Electrode kinetics is a crucial factor influencing the kinetic performance of power batteries. By testing and monitoring the kinetics at the electrode level, the kinetic performance of the battery can be assessed in advance, and substandard electrodes can be eliminated.

[0003] Electrochemical impedance spectroscopy (EIS) testing can effectively obtain impedance information of battery electrodes, providing important parameters for analyzing the quality of electrode kinetics. However, since EIS testing mainly evaluates the electrochemical reaction capability of the electrode, it is difficult to reflect the true charging capability of the electrode using the EIS method. Summary of the Invention

[0004] In view of this, embodiments of this application provide at least one method, testing method, apparatus, device, and medium for determining the charging capability of an electrode.

[0005] The technical solution of this application embodiment is implemented as follows:

[0006] In a first aspect, embodiments of this application provide a method for determining the charging capability of an electrode, the method comprising:

[0007] The battery is charged at a first charging rate, and the charging data shows the presence of lithium plating. The charging data includes voltage and state of charge (SOC). The battery includes a negative electrode made of graphite. The first charging rate is greater than or equal to 2 times the charging rate.

[0008] Based on the charging data of voltage and SOC, the differential value of the first voltage with respect to SOC (dV / dSOC) corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval are determined respectively; wherein, the first SOC interval corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers;

[0009] The charging capability of the negative electrode is determined based on the second dV / dSOC value and the first dV / dSOC value.

[0010] In some embodiments, determining a first dV / dSOC value corresponding to a first SOC range and a second dV / dSOC value corresponding to a second SOC range based on voltage and SOC charging data includes: obtaining charging data located in the first SOC range and charging data located in the second SOC range from the voltage and SOC charging data; determining a first dV / dSOC value based on the charging data located in the first SOC range; and determining a second dV / dSOC value based on the charging data located in the second SOC range.

[0011] In some embodiments, the charging data of voltage and SOC is a charging curve of voltage and SOC; determining the first dV / dSOC value based on the charging data located in the first SOC range includes: determining the first voltage corresponding to the upper limit of the first SOC range and the second voltage corresponding to the lower limit of the first SOC range from the charging curve of the first SOC range; and determining the first dV / dSOC value as the ratio of the voltage difference between the first voltage and the second voltage to the difference between the upper limit and the lower limit of the first SOC range.

[0012] In some embodiments, the first SOC range is between 20% and 45%, and the second SOC range is between 50% and 80%.

[0013] In some embodiments, the battery is a lithium iron phosphate battery, with a first SOC range of 25% to 35% and a second SOC range of 55% to 75%.

[0014] In some embodiments, determining the charging capability of the negative electrode based on the second dV / dSOC value and the first dV / dSOC value includes: determining the ratio of the second dV / dSOC value to the first dV / dSOC value as an evaluation index of the charging capability of the negative electrode; or, determining the difference between the second dV / dSOC value and the first dV / dSOC value as an evaluation index of the charging capability of the negative electrode.

[0015] In some embodiments, the battery is a lithium iron phosphate battery. Determining the charging capability of the negative electrode based on the second dV / dSOC value and the first dV / dSOC value includes: determining a target SOC range from the first SOC range and the second SOC range; determining the target dV / dSOC value corresponding to the target SOC range as an evaluation index of the charging capability of the negative electrode; wherein the target dV / dSOC value is the second dV / dSOC value or the first dV / dSOC value.

[0016] In some embodiments, the determination method further includes: acquiring charging data of the voltage and SOC corresponding to lithium plating in each battery in a group of batteries; the manufacturing process parameters of the corresponding negative electrode sheet and the material parameters of graphite in each battery are different; for a group of batteries, determining the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode sheet; based on the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode sheet, determining the negative electrode sheet that can characterize the charging capability to meet the conditions as the negative electrode sheet that meets the test requirements.

[0017] Secondly, embodiments of this application provide a method for testing the charging capability of an electrode, the method comprising:

[0018] A button cell is obtained by assembling a negative electrode sheet made of graphite into a button cell.

[0019] Measurements were taken during the charging process of the coin cell at a first charging rate to obtain charging data showing lithium plating. The charging data included voltage and SOC, and the first charging rate was greater than or equal to 2 times the charging rate.

[0020] Based on the charging data of voltage and SOC, the first dV / dSOC value corresponding to the first SOC range and the second dV / dSOC value corresponding to the second SOC range are determined respectively; wherein, the first SOC range corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers;

[0021] The charging capability of the negative electrode is determined based on the second dV / dSOC value and the first dV / dSOC value.

[0022] In some embodiments, the test method further includes: charging the coin cell battery at a first charging rate until it reaches a first preset voltage, the first preset voltage being greater than the battery's standard cutoff voltage.

[0023] In some embodiments, the battery is a lithium iron phosphate battery, the first charging rate includes at least one charging rate determined from a charging rate greater than or equal to 2 times and less than or equal to 5 times, and the first preset voltage is greater than 3.65V and less than or equal to 4V.

[0024] In some embodiments, the first charging rate includes at least two charging rates, and the test method further includes: charging the same battery multiple times in ascending order of the first charging rate to obtain multiple voltage and SOC charging data of the same battery at multiple charging rates; and determining the charging capability of the negative electrode at multiple charging rates based on the multiple voltage and SOC charging data of the same battery.

[0025] Thirdly, embodiments of this application provide an apparatus for determining the charging capability of an electrode, the apparatus comprising:

[0026] The first acquisition module is used to acquire charging data showing the presence of lithium plating after the battery is charged at a first charging rate, wherein the charging data includes voltage and SOC; wherein the battery includes a negative electrode sheet made of graphite; and the first charging rate is greater than or equal to 2 times the charging rate.

[0027] The first determining module is used to determine, based on the charging data of voltage and SOC, a first dV / dSOC value corresponding to a first SOC range and a second dV / dSOC value corresponding to a second SOC range; wherein, the first SOC range corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers;

[0028] The second determining module is used to determine the charging capability of the negative electrode based on the second dV / dSOC value and the first dV / dSOC value.

[0029] Fourthly, embodiments of this application provide a computer device, including a memory and a processor. The memory stores a computer program that can run on the processor, and the processor executes the program to implement some or all of the steps in the determination method described above.

[0030] Fifthly, embodiments of this application provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements some or all of the steps in the determination method described above.

[0031] Sixthly, embodiments of this application provide a computer program including computer-readable code. When the computer-readable code is run in a computer device, a processor in the computer device executes some or all of the steps in the determination method described above.

[0032] In a seventh aspect, embodiments of this application provide a computer program product, which includes a non-transitory computer-readable storage medium storing a computer program. When the computer program is read and executed by a computer, it implements some or all of the steps in the determination method described above.

[0033] In this embodiment, firstly, charging data showing lithium plating is obtained by charging the battery at a high charging rate, wherein the battery uses graphite as the negative electrode. This effectively captures the voltage change characteristics caused by lithium plating, i.e., the high charging rate triggers or exacerbates lithium plating; that is, the high charging rate acts as an accelerating factor for lithium plating to obtain the charging data showing lithium plating. Then, based on the charging data from two preset high and low SOC ranges, the dV / dSOC values ​​for each SOC range are determined. This more accurately reflects the lithium intercalation behavior and kinetic characteristics of the negative electrode within different SOC ranges; that is, by simply processing the charging data, two charging platforms formed by graphite during lithium intercalation can be obtained. Finally, based on the dV / dSOC values ​​of the two SOC ranges, the charging capability of the negative electrode can be determined.

[0034] Therefore, on the one hand, compared to existing EIS tests which can only characterize electron transfer capabilities under low current, this application embodiment can obtain the charging capability of the negative electrode sheet under these extreme conditions by using a large charging rate as an accelerating factor for lithium plating and simple data processing. In other words, this application embodiment utilizes the differential information in the actual high-rate charging curve, which is closer to actual working conditions, thereby more effectively evaluating the true charging performance of the negative electrode sheet. On the other hand, graphite forms multiple SOC charging platforms during lithium intercalation, and the SOC range changes under different charging rates. With a large charging rate as an accelerating factor for lithium plating, the dV / dSOC values ​​of the negative electrode sheet in the two SOC ranges can better reflect the characteristics of the negative electrode sheet itself, such as the manufacturing process parameters and the material parameters of graphite, thus providing a basis for screening target negative electrode sheets and optimizing negative electrode sheets. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with this application and, together with the specification, serve to explain the technical solutions of this application.

[0036] Figure 1 A schematic diagram of the charging curves of a lithium iron phosphate (LFP) battery provided in the embodiments of this application at three different charging rates;

[0037] Figure 2 for Figure 1 A schematic diagram of the dV / dQ curves corresponding to the three charging curves in the diagram;

[0038] Figure 3 A schematic diagram illustrating the implementation process of a method for determining the charging capability of an electrode sheet, provided in an embodiment of this application;

[0039] Figure 4 A schematic diagram illustrating the implementation process of a method for testing the charging capability of an electrode sheet provided in an embodiment of this application;

[0040] Figure 5 A schematic diagram showing the charging curves and evaluation indicators of a full-button battery prepared with negative electrode sheets of different compaction densities, provided for embodiments of this application;

[0041] Figure 6 A schematic diagram of the composition structure of a device for determining the charging capability of an electrode sheet provided in an embodiment of this application;

[0042] Figure 7 This is a schematic diagram of the hardware entity of a computer device provided in an embodiment of this application. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application are further described in detail below with reference to the accompanying drawings and embodiments. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0045] The terms “first / second / third” are used merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that “first / second / third” may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used herein is for descriptive purposes only and is not intended to limit the scope of this application.

[0047] Before providing a more detailed description of the embodiments of this application, the nouns and terms used in the embodiments of this application will be explained.

[0048] State of Charge (SOC) is a physical quantity that describes the ratio of a battery's current remaining usable charge to its rated capacity, usually expressed as a percentage (%) or a decimal. SOC values ​​range from 0% to 100%.

[0049] The compaction density of an electrode refers to the mass of active material per unit volume of a negative electrode after it has undergone a rolling process.

[0050] Graphitization degree (g or DOG) refers to the proportion of graphite crystals in a carbon material. g=100% corresponds to ideal graphite, and g=0% corresponds to completely amorphous carbon. Generally, the graphitization degree of natural graphite is 90–98%.

[0051] The coating thickness refers to the average physical thickness of the shell layer, such as amorphous carbon, oxides, and polymers, that coats the surface of graphite particles, and is usually measured in nm.

[0052] The integrity of the coating layer refers to the proportion of the area covered by the coating layer on the surface of the graphite particles that is continuous and without defects, and also includes the uniformity of the shell.

[0053] Lithium plating is a phenomenon that occurs during the charging process of lithium batteries. It refers to the phenomenon that lithium ions fail to be properly inserted into the lattice of the negative electrode material (such as graphite) and instead are reduced to metallic lithium and deposited on the surface of the negative electrode.

[0054] Charging curve: The curve showing the relationship between battery voltage (V) and charging capacity (Q) or state of charge (SOC) during the charging process. It is usually plotted with charging capacity (horizontal axis, unit mAh or Ah) as the independent variable and voltage (vertical axis, unit volt V) as the dependent variable; or with state of charge as the horizontal axis and voltage as the vertical axis.

[0055] dQ / dV curve (capacity-voltage differential curve): During charging, this curve shows the relationship between the differential of capacity with respect to voltage (dQ / dV) and voltage (V). The horizontal axis represents voltage (expressed in units of V on a coordinate axis), and the vertical axis represents dQ / dV. The dQ / dV curve reflects the capacity change corresponding to a unit voltage change. Its peak value corresponds to the voltage plateau region in the charging curve, meaning that the voltage change is small but the capacity change is large in the plateau region.

[0056] dV / dQ curve (differential voltage versus capacity curve): During the charging process, the curve shows the relationship between the differential voltage with respect to capacity (dV / dQ) and the capacity (Q). The horizontal axis represents the charging capacity (Q), and the vertical axis represents dV / dQ.

[0057] The dV / dQ-SOC curve is the relationship between the differential of voltage and capacity (dV / dQ) and the state of charge. With SOC on the horizontal axis and dV / dQ on the vertical axis, it reflects the voltage response to capacity changes under different states of charge. The shape of the dV / dQ-SOC curve is determined by the electrochemical characteristics of the electrode material (such as phase transition, ion diffusion, and polarization). The curve characteristics differ significantly for different types of batteries (such as ternary, LFP, and graphite systems).

[0058] To better understand the embodiments of this application, the charging and discharging process of a lithium battery will be introduced first.

[0059] The charging and discharging process of a lithium battery is an electrochemical process in which lithium ions migrate back and forth between the positive and negative electrodes (a "rocking chair" motion) accompanied by electron transfer. Its core is the insertion and extraction of lithium ions. During charging, the lithium battery is connected to an external power source, and electrical energy is converted into chemical energy and stored in the battery. The core process involves lithium extraction at the positive electrode and lithium insertion at the negative electrode. After charging is complete, the negative electrode stores a large number of lithium ions, while the positive electrode is in a lithium-deficient state, and the battery voltage rises to the rated voltage, for example, approximately 4.2V for a ternary lithium battery.

[0060] During discharge, the battery supplies power to the outside world, converting chemical energy into electrical energy. The core process involves lithium delithiation at the negative electrode and lithium insertion at the positive electrode. After discharge, lithium ions return from the negative electrode to the positive electrode, leaving the negative electrode in a lithium-deficient state and the positive electrode in a lithium-rich state. The battery voltage drops to the discharge cutoff voltage (approximately 2.5-3.0V for ternary lithium batteries).

[0061] To better understand the method for determining the electrode charging capability provided in the embodiments of this application, the principle of this solution will be explained below.

[0062] During high-rate charging, graphite anodes exhibit significant electrode polarization, causing the electrode surface potential to easily reach the lithium plating potential, resulting in lithium plating on the electrode surface. When lithium plating occurs, some lithium is intercalated into the graphite, while some is deposited on the electrode surface as metallic lithium. Because the potential polarization of lithium deposition is smaller than that of lithium intercalation, it generally exhibits a flatter charging plateau, reducing the overall polarization of the anode and thus slowing the rise in voltage across the full cell. (See also...) Figure 1 For the same LFP battery, the charging curves at three different charging rates, including 0.33C, 1.2C and 1.5C, show that when the SOC is less than p, for example 0.2, the slope of each charging curve is relatively large; when the SOC is around 0.2 to 0.8, the slope of each charging curve is smaller than the slope of the charging curves before or after this SOC range, which is considered to correspond to the charging platform of graphite.

[0063] Depend on Figure 1The charging curves at different charging rates also show that when charging at a high charging rate, the slope of the voltage rise at high SOC is significantly reduced due to lithium plating on the negative electrode.

[0064] Currently, the main methods for processing charge / discharge data include differential capacitance (dQ / dV) curves and differential voltage (dV / dQ) curves. The differential voltage (dV / dQ) curve is used to determine the phase changes of the positive and negative electrode active materials during charge and discharge. The peak shift and peak capacity changes of dV / dQ are useful indicators for understanding the capacity decay of the electrodes within the battery. Let's first introduce the characteristics of the dV / dQ curve. The dV / dQ curve can generally be divided into three intervals: low SOC interval, medium SOC interval, and high SOC interval.

[0065] 1) Low SOC range (e.g., 0%-20%, or 0%-30%): dV / dQ is higher because the electrode material (e.g., the cathode) is in a lithium-poor state, with low lithium-ion concentration and high diffusion resistance. Simultaneously, the battery's internal resistance is typically higher at low SOC, leading to a faster rate of voltage increase with capacity, meaning a larger voltage rise per unit capacity change. For example, in LFP batteries at SOC 0%-10%, the cathode begins accepting lithium ions from the lithium-poor phase, experiencing high resistance in the initial structural transition, resulting in a significantly higher dV / dQ than in the intermediate range.

[0066] 2) Mid-SOC range (e.g., 20%-80%, 30%-70%): dV / dQ is lower, showing a trough on the dV / dQ curve. This range is the main reaction region of the electrode material, where lithium-ion insertion / extraction is smooth, the material undergoes a stable phase transition, and the voltage changes gradually with capacity. The reaction occurs in the plateau region of the charging curve, hence the smaller dV / dQ value, forming a trough. Generally, the width and depth of the trough reflect the reversibility and kinetic performance of the material. A wider trough indicates a higher capacity proportion in the main reaction region, meaning higher material utilization; a deeper trough indicates a more stable voltage plateau, meaning less polarization.

[0067] 3) High SOC range (e.g., 80%-100% or 70%-100%): dV / dQ increases again. This is because when the battery is close to full charge, the electrode material (e.g., the negative electrode) is close to a lithium-rich state, the lithium-ion insertion sites are saturated, and the diffusion resistance increases sharply; at the same time, side reactions (e.g., electrolyte decomposition) begin to appear, polarization is significantly enhanced, leading to a sharp increase in the rate of voltage increase with capacity (a large voltage increase corresponding to a unit capacity change). If dV / dQ suddenly rises sharply in the high SOC range (e.g., after SOC 95%), it may indicate an overcharge risk (e.g., lithium plating at the negative electrode, oxygen release at the positive electrode).

[0068] Processed using dV / dQ curves Figure 1 The charging curves shown at the three different charging rates yield the following results. Figure 2 ,Right now Figure 2 Yes Figure 1 The dV / dQ curve obtained after differential voltage processing.

[0069] Figure 2 This illustrates the difference between lithium plating and non-lithium plating, from which... Figure 2 It can be seen that: At a charging rate of 0.33C, because there is no lithium plating, the dV / dQ curve increases consistently with the SOC starting at 0.3. However, at charging rates of 1.2C and 1.5C, because lithium plating occurs, the dV / dQ curve shows an inflection point. Comparing the dV / dQ curves at 1.2C and 1.5C, the inflection point (corresponding SOC value) appears earlier for the 1.5C charging rate than for the 1.2C charging rate. In other words, the higher the charging rate, the earlier the inflection point appears; that is, the higher the charging rate, the lower the SOC at which lithium plating begins.

[0070] It should be noted that the inflection point on the dV / dQ curve is the lithium plating point. The lithium plating point is generally understood as the SOC value at which lithium plating occurs in the lithium battery at that charging rate.

[0071] For a given electrode, even if the lithium plating point of the battery is known, in practical applications, it is still necessary to know the degree of lithium plating. That is, it is necessary to find an evaluation index for the degree of lithium plating of an electrode. Of course, this evaluation index can also be used as an indicator to evaluate the charging capacity of the electrode in the embodiments of this application. If a negative electrode is selected whose evaluation index for the degree of lithium plating meets the conditions (e.g., greater than a certain threshold), it can be considered that a target negative electrode has been selected. In other words, the more severe the degree of lithium plating, the more severe the capacity loss or performance degradation of the battery, and the more likely safety problems will occur.

[0072] For different electrodes, such as three negative electrodes at the same charging rate, if the lithium deposition point of a particular negative electrode is further back, it indicates that the safety margin during charging is wider and the performance is superior. However, further, if the lithium deposition points of these three electrodes are the same at the same charging rate, it is necessary to further evaluate the degree of lithium deposition of these three electrodes. That is, by comparing the evaluation indicators of the degree of lithium deposition of these three electrodes, the target negative electrode can be selected.

[0073] See further Figure 2Analysis of the dV / dQ curves at 1.2C and 1.5C also reveals that the lithium plating plateau significantly causes a noticeable decrease in the dV / dQ curve at high SOC. In subsequent embodiments of this application, a higher charging rate is desired to bring the inflection point to an earlier occurrence, for example, by using a fast charging rate of 1.5C or 2C during the charging process.

[0074] In subsequent embodiments of this application, electrodes with different characteristics are charged at the same rate to compare which lithium plating point appears earlier or later on the dV / dQ curve. That is, when the process parameters or material parameters of the electrodes are different, if all batteries (formed by coin cell assembly of each electrode) are charged at the same rate, by comparing the dV / dQ curves of each battery at the same rate, the size of the SOC point at which the dV / dQ curve of each battery begins to decline can be determined, which can effectively compare the charging capabilities of different negative electrode plates. Among them, the worse the charging capability of the negative electrode plate, the more obvious the lithium plating plateau of the battery, and the more significant the decline in the dV / dQ curve of its charging curve at a lower SOC.

[0075] Graphite intercalation is a multi-stage phase transition reaction in which graphite intercalation compounds (GICs) are sequentially formed at the graphite anode electrode, for example... (Fourth-order GIC) (Third-order GIC) (Second-order GIC) (First-order GIC). Specifically, on the charging curve at a 0.3C charging rate, , The corresponding SOC range is even smaller, see [link / reference] Figure 1 Generally, when the SOC is below 20% and the charging curve is relatively steep, there are not many obvious platform characteristics.

[0076] Generally, graphite electrodes typically have two charging platforms, one formed during lithium intercalation and the other formed during the process of lithium intercalation. The charging platform, and the graphite formed during lithium intercalation. The charging platform. When charging LFP batteries using a high charging rate (e.g., 2C), The charging platform may be between 25% and 35%. The charging platform may be located between 55% and 75%. Since lithium plating is more likely to occur in the high SOC range of a battery, meaning that the charging capability of the electrode is better reflected in the high SOC range, the high SOC range can be used as the target charging platform or target SOC range for analysis.

[0077] For the rate of change of voltage in a certain SOC range of the charging curve, its relationship with the dV / dQ curve can be obtained as follows: (1)

[0078] (1);

[0079] Formula (1), where V represents voltage and SOC represents state of charge. Indicates the upper limit of the SOC range. V1 represents the lower limit of the SOC range, V2 represents the voltage value corresponding to the upper limit of the SOC range, V1 represents the voltage value corresponding to the lower limit of the SOC range, and Q0 is the total capacity of the battery.

[0080] From the above relationship (1), it can be seen that the dV / dSOC value in a certain SOC range is directly proportional to the dV / dQ curve of the charging curve, that is, the greater the polarization growth, the greater the dV / dQ. During lithium plating of the battery, the polarization growth slows down due to lithium plating, and its dV / dQ value decreases. Based on this, there are differences between the low SOC no-lithium-plating range and the high SOC lithium-plating range for the charging curve.

[0081] It should be noted that the state of charge (SOC) of a battery determines the open-circuit voltage (OCV). In other words, SOC and OCV are positively correlated; the higher the SOC, the higher the OCV. Conversely, the battery voltage also determines the battery's SOC. Furthermore, SOC is directly proportional to the battery's capacity, and the battery capacity is a fixed product of current and time. Thus, according to formula (1)... Further derivation of formula (2):

[0082] (2)

[0083] in, dSOC=I*t / Q 0 ， =V 2 -V 1, t represents the time period from SOC1 to SOC2, which is the time period corresponding to the voltage from V1 to V2; I represents the charging current; I*t represents the increase in battery capacity during the time period t; Q0 represents the total battery capacity; and R represents the impedance.

[0084] It can be seen from formula (2) that, It is positively correlated with the impedance R. Because... It is positively correlated with impedance R, and since impedance R can, to some extent, measure the charging capability of the electrode, therefore, in some cases, It can be used to measure the charging capability of the electrode.

[0085] In the low SOC range without lithium plating, the worse the charging capability of graphite, the faster its polarization growth, i.e., the larger the dV / dSOC value. In the high SOC range with lithium plating, the worse the charging capability of graphite, the more severe the lithium plating, and the lower its polarization growth, i.e., the smaller the dV / dSOC value. As shown in formula (3), the dV / dSOC in the high SOC range is divided by the dV / dSOC in the low SOC range, and the value R1 obtained by the division is used as the final index for evaluating the charging capability. The index R1 is positively correlated with the impedance R. In order to distinguish it, the index is represented by R1 in this application. As can be seen from the previous rules, the worse the charging capability of graphite, the smaller the evaluation index R1 value.

[0086] (3)

[0087] It should be noted that dividing the dV / dSOC in the high SOC range by the low SOC range is merely a data processing method. The division is used to make the differences in the final evaluation of charging capability more apparent. In some cases, the voltage differences between multiple electrodes may be very small in the low SOC range (e.g., almost completely overlapping), while the voltage differences are larger in the high SOC range. Therefore, the dV / dSOC value in the high SOC range can also be used to evaluate the charging capability of that electrode. In other words, the final evaluation index of the electrode's charging capability can be characterized by differentiated dV / dSOC values.

[0088] To facilitate standardized data processing, the magnitude of evaluation indicators can be used to compare the differences in electrode charging capabilities.

[0089] This application provides a method for determining the charging capability of an electrode, such as... Figure 3 As shown, the method includes the following steps S102 to S106:

[0090] Step S102: Obtain charging data showing lithium plating after charging the battery at a first charging rate, wherein the charging data includes voltage and SOC; wherein the battery includes a negative electrode sheet made of graphite; the first charging rate is greater than or equal to 2 times the charging rate.

[0091] Lithium plating occurs during the charging process of lithium batteries, and external conditions (such as high charging rates and overcharging) can trigger or worsen this process. Generally, high charging rates are not used for coin cell batteries. For example, for batteries that undergo multiple charge-discharge cycles, both the charging rate and the charging cutoff voltage need to be within safe ranges. However, the coin cell battery in this embodiment can be understood to some extent as disposable. Therefore, to accelerate lithium plating, a higher charging rate and a higher cutoff voltage can be used. In fact, using a high charging rate and a high cutoff voltage once or multiple times may damage the battery. However, since the coin cell battery in this embodiment does not require multiple charge-discharge cycles, a high charging rate and a high cutoff voltage can be used as factors to accelerate lithium plating.

[0092] In this embodiment, the battery is obtained by assembling the electrodes into coin cells. Coin cell assembly (i.e., button cell assembly) is a method used in the laboratory to evaluate the electrochemical performance of electrode materials. In this embodiment, the coin cell assembly method is used, and the preparation process is relatively simple.

[0093] Step S104: Based on the charging data of voltage and SOC, determine the first dV / dSOC value corresponding to the first SOC range and the second dV / dSOC value corresponding to the second SOC range, respectively.

[0094] The first SOC range corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers;

[0095] The first SOC range corresponds to the low SOC range on the charging curve, and the second SOC range corresponds to the high SOC range on the charging curve. Figure 1 As can be seen, given the charging curve of the battery, the dV / dSOC curve of the battery can be obtained. On the dV / dSOC curve, the first dV / dSOC value corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval can be obtained.

[0096] In some embodiments, the first SOC range is between 20% and 45%, and the second SOC range is between 50% and 80%. When the battery is an LFP battery, the first SOC range is between 25% and 35%, and the second SOC range is between 55% and 75%.

[0097] Step S106: Determine the charging capability of the negative electrode plate based on the second dV / dSOC value and the first dV / dSOC value.

[0098] In some embodiments, step S106 includes: determining the ratio of the second dV / dSOC value to the first dV / dSOC value as an evaluation index of the charging capability of the negative electrode; or, determining the difference between the second dV / dSOC value and the first dV / dSOC value as an evaluation index of the charging capability of the negative electrode.

[0099] In this embodiment of the application, the difference in charging capability of the negative electrode under high current conditions can be quantitatively evaluated by the ratio between two dV / dSOC values ​​corresponding to two SOC intervals (high and low).

[0100] For example, when charging coin cells with multiple graphite negative electrode sheets at a high charging rate, the ratio between the two dV / dSOC values ​​may be between 1.1 and 2.5. A higher ratio indicates better charging capability of the negative electrode sheet. There are several screening methods when selecting target negative electrode sheets:

[0101] Method 1: A threshold, such as 2, can be set to identify negative electrode plates with a ratio greater than 2 as target negative electrode plates.

[0102] Method 2 involves arranging the ratios of multiple negative electrode plates in descending or ascending order, and then selecting the top J plates with the largest ratios as target negative electrode plates, where J is a natural number greater than 1. For example, if there are 8 negative electrode plates to be tested, the ratios of the 8 negative electrode plates are arranged in descending order, and the top 2 negative electrode plates with the largest ratios are identified as target negative electrode plates.

[0103] For another example, when charging coin cells with multiple graphite negative electrode sheets at a high charging rate, the difference between two dV / dSOC values ​​may be greater than 0 and less than 1. A larger difference indicates a better charging capability of the electrode sheet. There are also multiple screening methods when selecting target negative electrode sheets:

[0104] Method 1: A threshold, such as 0.1, can be set to identify negative electrode plates with a difference greater than 0.1 as target negative electrode plates.

[0105] Method 2 involves arranging the differences between multiple negative electrode plates in descending or ascending order, and then selecting the J plates with the largest differences as the target negative electrode plates, where J is a natural number greater than 1. For example, if there are 6 negative electrode plates to be tested, the differences between the 6 negative electrode plates are arranged in descending order, and the top 3 negative electrode plates with the largest differences are identified as the target negative electrode plates.

[0106] In some other embodiments, the battery is an LFP battery, and step S106 includes: determining a target SOC range from the first SOC range and the second SOC range; determining the target dV / dSOC value corresponding to the target SOC range as an evaluation index of the charging capability of the negative electrode; wherein the target dV / dSOC value is the second dV / dSOC value or the first dV / dSOC value.

[0107] In the low SOC range, a smaller dV / dSOC value indicates a better charging capability of the negative electrode; in the high SOC range, a larger dV / dSOC value indicates a better charging capability of the negative electrode.

[0108] In some embodiments, the target SOC range is determined based on actual needs. In one case, as mentioned above, considering factors such as the degree of lithium plating in the battery, a high SOC range can be used as the target SOC range.

[0109] In another scenario, if multiple negative electrode plates exhibit similar charging curves in the high SOC range, or other situations requiring analysis of the low SOC range, the low SOC range can be used as the target SOC range.

[0110] For example, when charging a coin cell with multiple graphite negative electrode sheets using 2C, assume the dV / dSOC value in the high SOC range is between 0.3 and 0.8. In one example, a threshold, such as 0.4, can be set to identify negative electrode sheets with a dV / dSOC value greater than 0.4 in the high SOC range as target negative electrode sheets.

[0111] For example, when charging multiple graphite negative electrode sheets corresponding to coin cells at 4C, assuming that the dV / dSOC value in the high SOC range is between 0.25 and 0.5, a threshold such as 0.3 can be set to identify negative electrode sheets with a dV / dSOC value greater than 0.3 in the high SOC range as target negative electrode sheets.

[0112] For example, when charging multiple graphite negative electrode sheets corresponding to coin cells at 4.5C, assuming that the dV / dSOC value in the high SOC range is between 0.2 and 0.4, a threshold such as 0.25 can be set to identify negative electrode sheets with a dV / dSOC value greater than 0.25 in the high SOC range as target negative electrode sheets.

[0113] For another example, when charging multiple graphite negative electrode sheets corresponding to coin cells using 2C, the dV / dSOC value in the low SOC range is between 0.1 and 0.3. A threshold, such as 0.2, can be set to identify negative electrode sheets with a dV / dSOC value less than 0.2 in the low SOC range as target negative electrode sheets.

[0114] This is because for LFP batteries, the voltage difference of the electrode is relatively large in the high SOC range. Therefore, the dV / dSOC value in the high SOC range can also be used to evaluate the charging capability of the electrode.

[0115] In this embodiment, firstly, charging data showing lithium plating is obtained by charging the battery at a high charging rate, wherein the battery uses graphite as the negative electrode. This effectively captures the voltage change characteristics caused by lithium plating, i.e., the high charging rate triggers or exacerbates lithium plating; that is, the high charging rate acts as an accelerating factor for lithium plating to obtain charging data showing lithium plating. Then, based on the charging data from two preset high and low SOC ranges, the dV / dSOC values ​​for each SOC range are determined. This more accurately reflects the lithium intercalation behavior and kinetic characteristics of the negative electrode in different SOC ranges; that is, by simply processing the charging data, the two charging platforms formed by graphite during lithium intercalation can be obtained. Finally, based on the dV / dSOC values ​​of the two SOC ranges, the charging capability of the negative electrode can be determined. In summary, compared to existing EIS testing which can only characterize electron transfer capability under low current, this embodiment, by using a high charging rate as an accelerating factor for lithium plating and simple data processing, can obtain the charging capability of the negative electrode under these extreme conditions. In other words, the embodiments of this application utilize the differential information in the actual high-rate charging curve, which is closer to the actual working conditions, thereby more effectively evaluating the true charging performance of the negative electrode sheet.

[0116] In some embodiments, step S104, based on the charging data of voltage and SOC, determines the first dV / dSOC value corresponding to the first SOC range and the second dV / dSOC value corresponding to the second SOC range, including:

[0117] Step S141: Obtain charging data located in the first SOC range and charging data located in the second SOC range from the charging data of voltage and SOC respectively.

[0118] Step S142: Determine the first dV / dSOC value based on the charging data located in the first SOC range;

[0119] Step S143: Determine the second dV / dSOC value based on the charging data located in the second SOC range.

[0120] In this embodiment, by clearly defining different SOC intervals (high SOC interval and low SOC interval) and extracting corresponding charging data for analysis, the calculated dV / dSOC value becomes more targeted and accurate. By distinguishing between the high and low SOC intervals, this embodiment can more meticulously reflect the stage differences in the lithium intercalation process, thereby improving the reliability of the evaluation results.

[0121] In some embodiments, the charging data for voltage and SOC is a charging curve for voltage and SOC; step S142, based on the charging data located in the first SOC range, determines a first dV / dSOC value, including:

[0122] Step S1421: Determine the first voltage corresponding to the upper limit of the first SOC range and the second voltage corresponding to the lower limit of the first SOC range from the charging curve of the first SOC range; Step S1422: Determine the first dV / dSOC value as the ratio of the voltage difference between the first voltage and the second voltage to the difference between the upper limit and the lower limit of the first SOC range.

[0123] Step S143, based on the charging data located in the second SOC range, determines the second dV / dSOC value, including:

[0124] Step S1431: Determine the third voltage corresponding to the upper limit and the fourth voltage corresponding to the lower limit of the second SOC range from the charging curve of the second SOC range; Step S1432: Determine the second dV / dSOC value as the ratio of the voltage difference between the third voltage and the fourth voltage to the difference between the upper limit and the lower limit of the second SOC range.

[0125] In this embodiment, the ratio of voltage difference to SOC difference is used to calculate the dV / dSOC value, which makes the dV / dSOC calculation objective and repeatable.

[0126] In some embodiments, the method further includes steps S110 to S130, wherein:

[0127] Step S110: Obtain the charging data of voltage and SOC corresponding to each battery in a group of batteries; the manufacturing process parameters and / or graphite material parameters of the corresponding negative electrode sheet in each battery are different;

[0128] Step S120: For a group of batteries, determine the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode.

[0129] Step S130: Based on the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode, the negative electrode that can characterize the charging capability to meet the conditions is determined as the negative electrode that meets the test requirements.

[0130] Here, in step S130, for each negative electrode, the ratio between the second dV / dSOC value and the first dV / dSOC value can be used as the final evaluation index that can characterize the charging capability. Then, the negative electrode that meets the conditions based on the final evaluation index is used as the negative electrode that meets the test requirements.

[0131] In this embodiment of the application, the charging capability of the coin cell at a high charging rate is tested to measure the charging capability of the negative electrode at a high charging rate. Furthermore, by comparing the differences in the charging capabilities of different negative electrode sheets, the purpose of screening and monitoring the quality of the negative electrode sheets is achieved.

[0132] Based on the above, embodiments of this application provide a method for testing the charging capability of an electrode, such as... Figure 4 As shown, the method includes steps 401 to 404, wherein:

[0133] Step S401: The negative electrode sheet made of graphite is assembled into a full coin cell to obtain a coin cell.

[0134] Step S402: During the charging process of the coin cell battery at a first charging rate, the voltage and SOC charging data are measured to obtain the charging data; wherein, the first charging rate is greater than or equal to 2 times the charging rate.

[0135] Step S403: Based on the charging data of voltage and SOC, determine the first dV / dSOC value corresponding to the first SOC range and the second dV / dSOC value corresponding to the second SOC range, respectively.

[0136] The first SOC range corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers;

[0137] Step S404: Determine the charging capability of the negative electrode plate based on the second dV / dSOC value and the first dV / dSOC value.

[0138] Here, steps S403 and S404 can be understood with reference to steps S104 and S106 above.

[0139] In some embodiments, the method further includes: charging the coin cell battery at a first charging rate until it reaches a first preset voltage, the first preset voltage being greater than the battery's standard cutoff voltage.

[0140] In some embodiments, the battery is an LFP battery, the first charging rate includes at least one charging rate determined from a charging rate greater than or equal to 2 times and less than or equal to 5 times, and the first preset voltage is greater than 3.65V and less than or equal to 4V. For example, the standard cutoff voltage of an LFP battery is generally considered to be 3.65V.

[0141] The coin cell battery in this application embodiment can be understood as disposable. While using a higher charging rate and / or a higher cutoff voltage may accelerate battery damage, it also allows for measurement of the charging capability of the negative electrode under these extreme conditions. Therefore, in some embodiments, the first charging rate includes at least two charging rates, and the method further includes steps S410 and S420, wherein:

[0142] Step S410: For the same battery, charge it multiple times in order of increasing first charging rate to obtain multiple voltage and SOC charging data of the same battery at multiple charging rates.

[0143] Step S420: Based on multiple voltage and SOC charging data of the same battery, determine the charging capability of the negative electrode at multiple charging rates.

[0144] For a single negative electrode, multiple charging rates can be used in ascending order until a first preset voltage is reached (here, the first preset voltage serves as the cutoff voltage of the battery under test during charging in this embodiment). The first preset voltage can also include multiple voltages. In one embodiment, the battery's cutoff voltage and charging rate can be combined in the following order: a smaller charging rate and a smaller cutoff voltage have the highest priority (testing begins first), a slightly larger charging rate and a slightly larger cutoff voltage have the next highest priority, and the highest charging rate and the highest cutoff voltage have the lowest priority. This priority order takes into account that for the same electrode, testing can begin under milder conditions and end under more stringent conditions; a larger charging rate and a higher cutoff voltage imply more stringent testing conditions.

[0145] For example, at a charging rate of 2C, the LFP battery is charged to 3.70V; at a charging rate of 2.5C, the LFP battery is charged to 3.70V; at a charging rate of 3C, the LFP battery is charged to 3.70V; at a charging rate of 3.5C, the LFP battery is charged to 3.80V; at a charging rate of 4C, the LFP battery is charged to 3.90V; at a charging rate of 4.5C, the LFP battery is charged to 3.85V; and at a charging rate of 5C, the LFP battery is charged to 3.85V. This demonstrates the charging capability of an electrode at different charging rates and cutoff voltages.

[0146] The testing process is described below:

[0147] First, a set of graphite electrodes is prepared. This set of electrodes comprises 12 different negative electrode sheets to be tested. These negative electrode sheets have different material parameters and / or different preparation process parameters. Preparation process parameters include compaction density and coating thickness; material parameters include graphitization degree, coating thickness, and coating integrity. The particle size of the graphite material is mainly affected by the compaction density.

[0148] In one embodiment, a group of negative electrode sheets can be prepared according to the principle of a single variable. For example, a group of 12 negative electrode sheets can have different compaction densities while keeping other conditions the same; or they can have different coating thicknesses while keeping other conditions the same; or they can have different degrees of graphitization while keeping other conditions the same; and so on. If multiple variables are involved, the experiment can be conducted in multiple groups.

[0149] In another embodiment, multiple different material parameters or preparation process parameters can be set. For example, among the 12 negative electrode sheets, there are different compaction densities, different coating thicknesses, and different coating layer thicknesses. In this way, the negative electrode sheet with better evaluation indicators can be selected.

[0150] This set of negative electrode sheets can be processed according to the following procedure to obtain 12 evaluation indicators corresponding to each negative electrode sheet. The negative electrode sheet that is the largest among the 12 evaluation indicators, or is considered to be greater than a certain threshold, is considered to meet the conditions.

[0151] Secondly, for a set of prepared graphite electrodes, the testing procedure provided in this application includes the following steps:

[0152] Step 1: Cut the 12 negative electrode sheets and the corresponding LFP positive electrode sheets into small round pieces of the required size, and dry the electrode sheets for use in coin cell assembly.

[0153] Step 2: Assemble the negative electrode sheet into a full coin cell in the order of negative electrode-separator-positive electrode to obtain 12 coin cells for subsequent testing.

[0154] Step 3: For each coin cell, perform formation and capacity setting on the assembled LFP coin cells; wherein, the charging rate for formation is 0.02C and the charging rate for capacity setting is 0.33C.

[0155] Step 4: Based on the fixed capacity, charge each coin cell at a high charging rate to obtain the charging curve of the coin cell at the high charging rate where lithium plating exists, resulting in a set of 12 charging curves showing lithium plating.

[0156] Depending on the actual charging capacity of the electrode, the charging rate can be between 2C and 5C, and a higher cutoff voltage can be used, exceeding the standard charging cutoff voltage. For example, the standard charging cutoff voltage for a typical LFP battery is 3.65V. In the embodiments of this application, the charging cutoff voltage for LFP batteries can reach as high as 3.85V or even 4V, taking into account that coin cells have a larger ohmic impedance.

[0157] Step 5: For each charging curve exhibiting lithium plating, determine the first dV / dSOC value corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval. Based on the second dV / dSOC value and the first dV / dSOC value, determine the final evaluation index for evaluating the charging capability of the negative electrode. This results in a set of 12 evaluation indexes corresponding to 12 negative electrode sheets. Negative electrode sheets that meet the evaluation index conditions are determined to be negative electrode sheets that meet the testing requirements.

[0158] The lithium plating phenomenon that occurs during the charging process of lithium batteries is the result of the combined effects of excessively low thermodynamic potential and impeded kinetic intercalation. External conditions (such as low temperature, high charging rate, and overcharging) trigger or worsen lithium plating by exacerbating these two problems. The metallic lithium dendrites formed by lithium plating not only consume active lithium (reducing capacity) but may also puncture the separator and cause a short circuit, posing a key threat to the safety and lifespan of lithium batteries.

[0159] In this embodiment, a higher charging rate and a higher cutoff voltage are used to accelerate lithium plating. Generally, high charging rates are not used for coin cell batteries. For example, for batteries undergoing multiple charge-discharge cycles, both the charging rate and the charging cutoff voltage need to be within safe ranges. However, the coin cell batteries in this embodiment can be understood as disposable. While using a higher charging rate and / or a higher cutoff voltage may accelerate battery damage, it also allows for the measurement of the charging capacity of the negative electrode under these extreme conditions.

[0160] For a single negative electrode, multiple charging rates can be used to charge it until a preset charging cutoff voltage is reached. For example, at a charging rate of 2C, the LFP battery is charged to 3.85V; at 2.5C, it's 3.85V; at 3C, it's 3.90V; at 4C, it's 3.9V; at 4.5C, it's 4.0V; and at 5C, it's 4.0V. This demonstrates the charging capability of a single electrode at different charging rates.

[0161] The following section uses compaction density as an example to illustrate the data verification part of the above method:

[0162] In the preparation of lithium-ion battery anode sheets, the compaction density of the anode sheet is a comprehensive reflection of materials, formulation, and process. Compaction density is a core process parameter for measuring the quality of electrode forming, affecting key indicators such as battery energy density, cycle life, and rate performance. Both excessively high and low compaction densities can lead to deterioration of battery performance. This is because compaction density affects three aspects:

[0163] 1) Compacted density affects the volumetric energy density of a battery: Higher compacted density means that more negative electrode active material (such as graphite) can be accommodated per unit volume, and the amount of active material determines the theoretical capacity of the battery. With a fixed battery casing volume, the higher the negative electrode compacted density (within a reasonable range), the higher the battery's volumetric energy density generally is.

[0164] 2) Compaction density affects lithium-ion diffusion and cycle performance: Too low a compaction density results in excessively high porosity in the electrode coating. While this allows for sufficient electrolyte wetting, it reduces the effective contact area of ​​the active material, potentially increasing electron conduction resistance. Furthermore, during charging and discharging, the active material particles are prone to displacement due to loosening, leading to electrode structure collapse and shortened cycle life. Too high a compaction density causes excessive compression of the active material particles during rolling, potentially damaging their crystal structure and blocking lithium-ion insertion / extraction channels. Additionally, excessively high compaction density reduces coating porosity, making it difficult for the electrolyte to penetrate the coating and decreasing the utilization rate of the active material.

[0165] 3) Compaction density is related to the mechanical properties and production stability of the electrode: If the compaction density is too high, the electrode coating will become more brittle, and powder shedding and cracking will easily occur during subsequent slitting, stacking or winding, and may even lead to internal short circuits in the battery; if the compaction density is too low, the bonding force between the coating and the current collector will be insufficient, and powder shedding and delamination will also occur, affecting the production yield.

[0166] Example 1:

[0167] The following example uses a set of negative electrode sheets with different compaction densities (the compaction density of electrode sheet B is greater than that of electrode sheet A), with all other conditions being the same: The charging capability of the negative electrode sheets is compared using the method provided in the embodiments of this application. This process includes:

[0168] Step 11: Assemble the negative electrode sample A into a coin cell according to the above method (steps 1 and 2 above), and then perform formation and capacity setting (step 3) to obtain the battery A corresponding to the negative electrode sample A;

[0169] Furthermore, the negative electrode sample B is assembled into a coin cell according to the above method (steps 1 and 2 above), and then formed and capacitated (step 3) to obtain the battery B corresponding to the negative electrode B;

[0170] Step 12: Obtain the charging curves of the 3C charging rate for battery A and battery B respectively (Step 4).

[0171] Step 13, refer to Figure 5 In the left figure, the 0.25-0.35 SOC range is obtained from the charging curve of battery A at the 3C charging rate, which is taken as the low SOC range; similarly, the 0.55-0.7 SOC range is obtained from the 3C charging rate curve of battery A, which is taken as the high SOC range.

[0172] Step 14: For the low SOC range of battery A, calculate the corresponding low SOC difference (= low ΔSOC1, i.e., low dSOC1) and low voltage difference ΔV1 (i.e., low dV1). The low SOC difference is the difference between SOC of 0.35 and SOC of 0.25, i.e., low dSOC1 = 0.35 - 0.25 = 0.1. The low voltage difference dV1 is the difference between the voltage value corresponding to SOC of 0.35 and the voltage value corresponding to SOC of 0.25, i.e., low dV1 = V SOC=0.35 - V SOC=0.25 Finally, the index r11 corresponding to battery A in the low SOC range is low dV1 / low dSOC1.

[0173] For the high SOC range of battery A, calculate the high SOC difference corresponding to the high SOC range: high ΔSOC1 (i.e., dSOC1) and high voltage difference ΔV1 (i.e., dV1). Here, the high SOC difference is the difference between SOC of 0.7 and SOC of 0.55, i.e., high dSOC1 = 0.7 - 0.55 = 0.15. Then, the high voltage difference is the difference between the voltage corresponding to SOC of 0.7 and the voltage corresponding to SOC of 0.55, i.e., high dV1 = V. SOC=0.7 - V SOC=0.55Finally, the index r12 corresponding to battery A in the high SOC range is high dV1 / high dSOC1.

[0174] Based on the above, the final evaluation index R1 for battery A is equal to r12 divided by r11, i.e., r12 / r11.

[0175] Step 15, refer to Figure 5 In the left figure, the 0.25-0.35 SOC range is obtained from the 3C charging rate curve of battery B as the low SOC range; at the same time, the 0.55-0.7 SOC range is obtained from the 3C charging rate curve of battery B as the high SOC range.

[0176] Step 16, similarly, calculate the low SOC difference of battery B in the low SOC range according to step 14, i.e., low dSOC2 = 0.35 - 0.25 = 0.1; and the low voltage difference, low dV2 = V SOC=0.35 - V SOC=0.25 Finally, the index r21 corresponding to battery B in the low SOC range is low dV2 / low dSOC2.

[0177] Similarly, following step 14, calculate the high SOC difference of battery B in the high SOC range, i.e., high dSOC2 = 0.7 - 0.55 = 0.15; and the high voltage difference, high dV2 = V. SOC=0.7 - V SOC=0.255 Finally, the index r22 corresponding to battery B in the high SOC range is high dV2 / high dSOC2.

[0178] Based on the above, the final evaluation index R1 for battery B is equal to r22 divided by r21, i.e., r22 / r21.

[0179] Step 17: The final evaluation index R1 obtained for battery A is used to characterize the charging capability of electrode A; the final evaluation index R1 obtained for battery B is used to characterize the charging capability of electrode B, referring to... Figure 5 As shown in the right figure, the R1 value of electrode A is greater than that of electrode B, indicating that the charging capacity of electrode A is greater than that of electrode B.

[0180] Before the test, it was known that the compaction density of electrode B was greater than that of electrode A. In other words, for the negative electrode B with a larger compaction density, its charging capacity should theoretically be worse than that of group A because its porosity and pore size (these are the results after the electrode is formed). However, the test results showed that the R1 value of group B electrode was smaller, which was consistent with the expected results.

[0181] Example 2:

[0182] Below, taking a set of negative electrode sheets with different compaction densities (the compaction density of electrode sheet B is greater than that of electrode sheet A), with all other conditions being the same, as an example: the charging capability of the negative electrode sheets is compared using the method provided in the embodiments of this application. This process includes:

[0183] Steps 21 and 22 are respectively steps 11 and 12 in Example 1.

[0184] Step 23, refer to Figure 5 The left figure shows that only the 0.55-0.7 SOC range is obtained on the charging curve of battery A at the 3C charging rate, which is taken as the high SOC range.

[0185] For the high SOC range, the following calculation is performed according to step 14 in Example 1: the index r12 corresponding to battery A in the high SOC range is high dV1 / high dSOC1.

[0186] Step 24, refer to Figure 5 The left figure shows that only the 0.55-0.7 SOC range is obtained from the charging curve of battery B at the 3C charging rate, which is taken as the high SOC range.

[0187] For the high SOC range, the following calculation is performed according to step 16 in Example 1: the index r22 corresponding to battery B in the high SOC range is high dV2 / high dSOC2.

[0188] Step 25: Use the index r12 corresponding to the high SOC range of battery A as the final evaluation index R1 to characterize the charging capability of electrode A; use the index r22 corresponding to the high SOC range of battery B as the final evaluation index R1 to characterize the charging capability of electrode B.

[0189] Depend on Figure 5 As can be seen in the left figure, the index r12 value of electrode A is greater than the index r22 value of electrode B, indicating that the charging capacity of electrode A is greater than that of electrode B.

[0190] Before the test, it was known that the compaction density of electrode B was greater than that of electrode A. In other words, for the negative electrode B with a larger compaction density, its charging capacity should theoretically be worse than that of group A because its porosity and pore size (these are the results after the electrode is formed). However, the test results showed that the R1 value of group B electrode was smaller, which was consistent with the expected results.

[0191] For the charging curves of batteries A and B, since they overlap in the low SOC range (meaning the voltages are almost the same in the low SOC range), but differ in the high SOC range, it is possible to set only one high SOC region to calculate the evaluation index.

[0192] In summary, this embodiment provides a test method for evaluating the charging capability of graphite negative electrode sheets. By analyzing and comparing the impact of triggering lithium plating with a large charging rate on the charging curve, the charging capability of negative electrode sheets can be effectively compared, thereby enabling the screening and monitoring of negative electrode sheet performance.

[0193] Based on the foregoing embodiments, this application provides a device for determining the charging capability of an electrode. The device includes various modules and units included in each module, which can be implemented by a processor in a computer device; of course, it can also be implemented by specific logic circuits. In the implementation process, the processor can be a central processing unit (CPU), a microprocessor unit (MPU), a digital signal processor (DSP), or a field programmable gate array (FPGA), etc.

[0194] Figure 6 This is a schematic diagram of the composition of a device for determining the charging capability of an electrode sheet, provided in an embodiment of this application. Figure 6 As shown, the electrode charging capability determining device 600 includes:

[0195] The first acquisition module 610 is used to acquire charging data showing the presence of lithium plating after the battery is charged at a first charging rate, wherein the charging data includes voltage and SOC; wherein the battery includes a negative electrode sheet made of graphite; and the first charging rate is greater than or equal to 2 times the charging rate.

[0196] The first determining module 620 is used to determine, based on the charging data of voltage and SOC, a first dV / dSOC value corresponding to a first SOC range and a second dV / dSOC value corresponding to a second SOC range; wherein, the first SOC range corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers;

[0197] The second determining module 630 is used to determine the charging capability of the negative electrode plate based on the second dV / dSOC value and the first dV / dSOC value.

[0198] In some embodiments, the first determining module includes:

[0199] The first acquisition unit is used to acquire charging data located in the first SOC range and charging data located in the second SOC range from the charging data of voltage and SOC, respectively.

[0200] The first determining unit is used to determine a first dV / dSOC value based on charging data located in the first SOC range;

[0201] The second determining unit is used to determine the second dV / dSOC value based on charging data located in the second SOC range.

[0202] In some embodiments, the charging data for voltage and SOC are charging curves for voltage and SOC.

[0203] The first determining unit is further configured to determine a first voltage corresponding to the upper limit of the first SOC range and a second voltage corresponding to the lower limit of the first SOC range from the charging curve of the first SOC range; and to determine the ratio of the voltage difference between the first voltage and the second voltage to the difference between the upper limit and the lower limit of the first SOC range as the first dV / dSOC value.

[0204] The second determining unit is further configured to determine the third voltage corresponding to the upper limit of the second SOC range and the fourth voltage corresponding to the lower limit of the second SOC range from the charging curve of the second SOC range; and to determine the ratio of the voltage difference between the third voltage and the fourth voltage to the difference between the upper limit and the lower limit of the second SOC range as the second dV / dSOC value.

[0205] In some embodiments, the first SOC range is between 20% and 45%, and the second SOC range is between 50% and 80%.

[0206] In some embodiments, the battery is an LFP battery, with a first SOC range of 25% to 35% and a second SOC range of 55% to 75%.

[0207] In some embodiments, the second determining module is used to determine the ratio of the second dV / dSOC value to the first dV / dSOC value as an evaluation index of the charging capability of the negative electrode sheet; or, to determine the difference between the second dV / dSOC value and the first dV / dSOC value as an evaluation index of the charging capability of the negative electrode sheet.

[0208] In some embodiments, the battery is an LFP battery, and the second determining module is further configured to determine the target SOC range formed by graphite during lithium intercalation from the first SOC range and the second SOC range; and to determine the target dV / dSOC value corresponding to the target SOC range as an evaluation index of the charging capability of the negative electrode sheet; wherein the target dV / dSOC value corresponding to the target SOC range is the second dV / dSOC value or the first dV / dSOC value.

[0209] In some embodiments, the device further includes:

[0210] The second acquisition module is used to acquire the charging data of voltage and SOC of each battery in a group of batteries; the manufacturing process parameters and / or graphite material parameters of the corresponding negative electrode sheet in each battery are different;

[0211] The third determining module is used to determine the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode for a group of batteries.

[0212] The fourth determination module is used to determine the negative electrode that can characterize the charging capability as meeting the test requirements based on the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode.

[0213] The descriptions of the apparatus embodiments above are similar to those of the method embodiments above, and have similar beneficial effects. In some embodiments, the functions or modules included in the apparatus provided in this application can be used to perform the methods described in the method embodiments above. For technical details not disclosed in the apparatus embodiments of this application, please refer to the descriptions of the method embodiments of this application for understanding.

[0214] It should be noted that, in the embodiments of this application, if the above-described method for determining the electrode charging capability is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the embodiments of this application, or the part that contributes to the related technology, can be embodied in the form of a software product. This software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, mobile hard drives, read-only memory (ROM), magnetic disks, or optical disks. Thus, the embodiments of this application are not limited to any specific hardware, software, or firmware, or any combination of hardware, software, and firmware.

[0215] This application provides a computer device including a memory and a processor. The memory stores a computer program that can run on the processor. When the processor executes the program, it implements some or all of the steps in the above-described method.

[0216] This application provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements some or all of the steps in the above-described method. The computer-readable storage medium can be transient or non-transient.

[0217] This application provides a computer program including computer-readable code. When the computer-readable code is run in a computer device, the processor in the computer device performs some or all of the steps in the above-described method.

[0218] This application provides a computer program product, which includes a non-transitory computer-readable storage medium storing a computer program. When the computer program is read and executed by a computer, it implements some or all of the steps in the above-described method. This computer program product can be implemented specifically through hardware, software, or a combination thereof. In some embodiments, the computer program product is specifically embodied as a computer storage medium; in other embodiments, the computer program product is specifically embodied as a software product, such as a software development kit (SDK), etc.

[0219] It should be noted that the descriptions of the various embodiments above tend to emphasize the differences between them, while their similarities or commonalities can be referred to interchangeably. The descriptions of the above embodiments of the device, storage medium, computer program, and computer program product are similar to the descriptions of the above method embodiments and have similar beneficial effects. For technical details not disclosed in the embodiments of the device, storage medium, computer program, and computer program product of this application, please refer to the descriptions of the method embodiments of this application for understanding.

[0220] It should be noted that, Figure 7 This is a schematic diagram of a hardware entity of a computer device in an embodiment of this application, such as... Figure 7 As shown, the hardware entity of the computer device 700 includes: a processor 701, a communication interface 702, and a memory 703, wherein:

[0221] Processor 701 typically controls the overall operation of computer device 700.

[0222] Communication interface 702 enables computer devices to communicate with other terminals or servers over a network.

[0223] The memory 703 is configured to store instructions and applications executable by the processor 701, and can also cache data to be processed or already processed (e.g., image data, audio data, voice communication data, and video communication data) in the processor 701 and various modules in the computer device 700. It can be implemented using flash memory or random access memory (RAM). Data transfer between the processor 701, the communication interface 702, and the memory 703 can be performed via bus 704.

[0224] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above steps / processes do not imply a sequential order of execution; the execution order of each step / process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The sequence numbers of the above embodiments of this application are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0225] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0226] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of modules described above is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0227] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units. They may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0228] In addition, each functional unit in the various embodiments of this application can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0229] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various media that can store program code, such as mobile storage devices, read-only memory (ROM), magnetic disks, or optical disks.

[0230] Alternatively, if the integrated units described above in this application are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to related technologies, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, etc.) to execute all or part of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, ROMs, magnetic disks, or optical disks.

[0231] The above description is merely an embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for determining the charging capability of an electrode, characterized in that, The determination method includes: The battery is charged at a first charging rate to obtain charging data showing lithium plating, wherein the charging data includes voltage and state of charge (SOC); wherein the battery includes a negative electrode made of graphite; and the first charging rate is greater than or equal to 2 times the charging rate. Based on the charging data of voltage and SOC, the differential value of the first voltage with respect to SOC (dV / dSOC) corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval are determined respectively; wherein, the first SOC interval corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, wherein the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers; The charging capability of the negative electrode is determined based on the second dV / dSOC value and the first dV / dSOC value.

2. The determination method according to claim 1, characterized in that, Based on the charging data of voltage and SOC, the first dV / dSOC value corresponding to the first SOC range and the second dV / dSOC value corresponding to the second SOC range are determined, including: The charging data located in the first SOC range and the charging data located in the second SOC range are obtained from the charging data of the voltage and SOC, respectively. The first dV / dSOC value is determined based on the charging data located in the first SOC range; The second dV / dSOC value is determined based on the charging data located in the second SOC range.

3. The determination method according to claim 2, characterized in that, The charging data for voltage and SOC is the charging curve for voltage and SOC. Determining the first dV / dSOC value based on charging data located in the first SOC range includes: Determine the first voltage corresponding to the upper limit and the second voltage corresponding to the lower limit of the first SOC range from the charging curve of the first SOC range; The ratio of the voltage difference between the first voltage and the second voltage to the difference between the upper and lower limits of the first SOC range is determined as the first dV / dSOC value.

4. The determination method according to claim 1, characterized in that, The first SOC range is between 20% and 45%, and the second SOC range is between 50% and 80%.

5. The determination method according to claim 4, characterized in that, The battery is a lithium iron phosphate battery, with the first SOC range being 25% to 35% and the second SOC range being 55% to 75%.

6. The determining method according to any one of claims 1 to 5, characterized in that, Based on the second dV / dSOC value and the first dV / dSOC value, the charging capability of the negative electrode is determined, including: The ratio of the second dV / dSOC value to the first dV / dSOC value is determined as an evaluation index of the charging capability of the negative electrode sheet; or, The difference between the second dV / dSOC value and the first dV / dSOC value is determined as the evaluation index of the charging capability of the negative electrode.

7. The determining method according to any one of claims 1 to 5, characterized in that, The battery is a lithium iron phosphate battery. Based on the second dV / dSOC value and the first dV / dSOC value, the charging capability of the negative electrode is determined, including: Determine the target SOC interval from the first SOC interval and the second SOC interval; The target dV / dSOC value corresponding to the target SOC range is determined as the evaluation index of the charging capability of the negative electrode; wherein the target dV / dSOC value is the second dV / dSOC value or the first dV / dSOC value.

8. The determining method according to any one of claims 1 to 5, characterized in that, The determination method further includes: Obtain the voltage and SOC charging data of each battery in a group of batteries, corresponding to the presence of lithium plating; the manufacturing process parameters of the negative electrode sheet and the material parameters of the graphite in each battery are different; For the aforementioned group of batteries, determine the second dV / dSOC value and the first dV / dSOC value corresponding to each of the aforementioned negative electrode plates; Based on the second dV / dSOC value and the first dV / dSOC value corresponding to each negative electrode sheet, the negative electrode sheet that can characterize the charging capability to meet the conditions is determined as the negative electrode sheet that meets the test requirements.

9. A method for testing the charging capability of an electrode, characterized in that, The testing method includes: A button cell is obtained by assembling a negative electrode sheet made of graphite into a button cell. During the charging process of the coin cell at a first charging rate, measurements are taken to obtain charging data showing lithium plating. The charging data includes voltage and state of charge (SOC). The first charging rate is greater than or equal to 2 times the charging rate. Based on the charging data of voltage and SOC, the differential value of the first voltage with respect to SOC (dV / dSOC) corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval are determined respectively; wherein, the first SOC interval corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, wherein the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers; The charging capability of the negative electrode is determined based on the second dV / dSOC value and the first dV / dSOC value.

10. The test method according to claim 9, characterized in that, The testing method also includes: The button battery is charged at the first charging rate until it reaches a first preset voltage, which is greater than the standard cutoff voltage of the battery.

11. The test method according to claim 10, characterized in that, The battery is a lithium iron phosphate battery, the first charging rate includes at least one charging rate determined from a charging rate greater than or equal to 2 times and less than or equal to 5 times, and the first preset voltage is greater than 3.65V and less than or equal to 4V.

12. The test method according to claim 11, characterized in that, The first charging rate includes at least two charging rates, and the test method further includes: For the same battery, it is charged multiple times in ascending order of the first charging rate to obtain multiple voltage and SOC charging data of the same battery at multiple charging rates. Based on multiple voltage and SOC charging data of the same battery, the charging capability of the negative electrode sheet at multiple charging rates is determined.

13. A device for determining the charging capability of an electrode, characterized in that, include: The acquisition module is used to acquire charging data showing the presence of lithium plating after the battery is charged at a first charging rate; wherein the charging data includes voltage and state of charge (SOC), and the battery includes a negative electrode sheet made of graphite; the first charging rate is greater than or equal to 2 times the charging rate. The first determining module is used to determine, based on the charging data of voltage and SOC, the differential value dV / dSOC of the first voltage with respect to SOC corresponding to the first SOC interval and the second dV / dSOC value corresponding to the second SOC interval; wherein, the first SOC interval corresponds to the graphite formed during lithium intercalation. LiC m The charging platform, wherein the second SOC range corresponds to the graphite formed during lithium intercalation. LiC n The charging platform, and the lower limit of the second SOC range is greater than or equal to the upper limit of the first SOC range. m and n All are positive integers; The second determining module is used to determine the charging capability of the negative electrode plate based on the second dV / dSOC value and the first dV / dSOC value.

14. A computer device comprising a memory and a processor, the memory storing a computer program executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for determining the electrode charging capability according to any one of claims 1 to 8.

15. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps in the method for determining the electrode charging capability according to any one of claims 1 to 8.

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