Battery cell grading method and equipment and storage medium

Abstract

The invention belongs to the technical field of battery processing, and particularly relates to a battery cell grading method and device and a storage medium, and the method comprises the following steps: obtaining a to-be-graded battery cell, performing formation operation on the battery cell to activate the battery cell, and charging the battery cell to an upper limit voltage at a first preset rate; after standing for a first preset duration, discharging for a second preset duration at a second preset rate; standing for a third preset time length, and acquiring a first voltage of the battery cell; and based on a first voltage grading model, grading the plurality of battery cells to obtain a plurality of groups of battery cells with different voltage grades. According to the method provided by the embodiment of the invention, the battery cells are graded by measuring the voltage of the fully-charged battery cells after being discharged to the preset duration, complete charging and discharging do not need to be carried out, the grading duration of the battery cells is greatly shortened, and the electric energy and the labor cost are reduced.

Description

Technical Field

[0001] The present application relates to the field of battery processing technology, and in particular to a battery cell grading method, equipment and storage medium. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long service life, no memory effect, and good safety performance. They have been widely used in energy storage, electric vehicles, digital electronic products and other fields.

[0003] In battery pack applications, such as power battery packs for electric vehicles or battery packs in energy storage systems, the performance of each battery cell during the charging and discharging process is required to be as consistent as possible. The existing battery cell grading method usually measures the capacity of the battery through complete charging and discharging, then charges the battery to a certain capacity, and finally grades it according to the capacity and voltage of the battery. For example, the invention application patent with publication number CN111786035A discloses a method for lithium-ion batteries. This method facilitates the battery information management system to collect single cell information by attaching a QR code on the surface of the battery cell, can screen out unqualified batteries and grade single cells, and reduce manpower. However, this technical solution needs to be left to stand for 2-10 hours, and needs to be aged at a temperature of 40-60 degrees Celsius for 5-12 days, which takes too long, and the capacity after grading is greatly affected by temperature, and the capacity data is inaccurate. Therefore, how to shorten the time of battery cell grading and at the same time accurately obtain capacity data is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The main purpose of the present invention is to provide a battery cell binning method, device and storage medium, aiming to solve the technical problem of how to shorten the battery cell binning time.

[0005] In a first aspect, an embodiment of the present application provides a cell grading method, comprising:

[0006] Obtaining battery cells to be binned, and performing a formation operation on the battery cells to activate the battery cells;

[0007] Charging the battery cell that has undergone the formation operation to an upper limit voltage at a first preset rate;

[0008] After being left to rest for a first preset time, the battery is discharged at a second preset rate for a second preset time;

[0009] Allowing the battery to stand for a third preset time to obtain a first voltage of the battery cell;

[0010] Based on the first voltage classification model, the plurality of battery cells are classified into different levels to obtain a plurality of groups of battery cells with different voltage levels.

[0011] Furthermore, after the step of grading the plurality of battery cells based on the first voltage grading model to obtain a plurality of groups of battery cells with different voltage levels, the method further includes:

[0012] Allowing the plurality of groups of battery cells at different voltage levels to stand for a fourth preset time to obtain a second voltage of the battery cells;

[0013] Calculating a self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage;

[0014] determining whether the self-discharge rate is within a first threshold range,

[0015] If not, the battery cells that are not within the first threshold range are eliminated;

[0016] If yes, obtaining the DC internal resistance of the battery cell within the first threshold range;

[0017] determining whether the DC internal resistance is within a second threshold range,

[0018] If not, the battery cells that are not within the second threshold range are removed;

[0019] If so, the battery cells within the second threshold range are retained to obtain multiple groups of graded battery cells with different voltage levels.

[0020] Furthermore, the first voltage classification model classifies the battery cells whose battery cell voltages fall within a corresponding range into corresponding voltage levels according to a predetermined corresponding relationship between the voltage level range and the battery cell voltage.

[0021] Further, the step of calculating the self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage includes the following calculation formula:

[0022]

[0023] Further, after the step of determining whether the DC internal resistance is within a second threshold range, and if not, eliminating the battery cells that are not within the second threshold range; and if so, retaining the battery cells that are within the second threshold range, and obtaining multiple groups of graded battery cells with different voltage levels, the following steps are also included:

[0024] The graded battery cells are charged at a first preset rate to a fully charged state, and then discharged at a first capacity percentage to a preset state to obtain battery cells at a first capacity percentage state;

[0025] Placing the graded cells in the first capacity percentage state under different preset temperature states to obtain open circuit voltages under different preset temperature states;

[0026] Based on the first capacity percentage and the open circuit voltage under different preset temperature states, a capacity calculation model under a preset temperature difference is obtained.

[0027] Furthermore, the capacity calculation model includes the following formula:

[0028] SOC = A% + K(OCV-OCV A )*B;

[0029] Wherein, SOC is the capacity of the battery cell after being discharged at the second preset rate to the second preset time and standing for the third preset time, A% is the percentage of the current remaining capacity (power) of the battery cell and the rated capacity of the battery cell, K is the slope of OCV / SOC, B is the unit conversion constant, OCV A is the OCV corresponding to A% SOC, where OCV is the open circuit voltage.

[0030] Furthermore, before the step of charging the battery cell to an upper limit voltage at a first preset rate, the following steps are also included:

[0031] Acquire the activated battery cell, and perform an aging operation on the battery cell to enable the battery cell to reach a pre-stable state;

[0032] The battery cell after the aging operation is obtained, and a degassing operation is performed on the battery cell to obtain a battery cell in a stable state.

[0033] In a second aspect, an embodiment of the present application provides a cell grading method, comprising:

[0034] Obtaining battery cells to be binned, and performing a formation operation on the battery cells to activate the battery cells;

[0035] Charging the battery cell to an upper limit voltage at a first preset rate;

[0036] After being left to rest for a first preset time, the battery is discharged at a second preset rate for a second preset time;

[0037] Allowing the battery to stand for a third preset time to obtain a first voltage of the battery cell;

[0038] Inputting the first voltage into a capacity calculation model to obtain a capacity value of the battery cell;

[0039] Based on the first capacity grading model, the battery cells are graded to obtain a plurality of groups of battery cells with different capacity grades.

[0040] Furthermore, after the step of grading the battery cells based on the first capacity grading model to obtain a plurality of groups of battery cells with different capacity grades, the step further includes the following steps:

[0041] Allowing the plurality of groups of battery cells with different capacity levels to stand for a fourth preset time to obtain a second voltage of the battery cells;

[0042] Calculating a self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage;

[0043] determining whether the self-discharge rate is within a first threshold range,

[0044] If not, the battery cells that are not within the first threshold range are eliminated;

[0045] If yes, obtaining the DC internal resistance of the battery cell within the first threshold range;

[0046] determining whether the DC internal resistance is within a second threshold range,

[0047] If not, the battery cells that are not within the second threshold range are removed;

[0048] If so, the battery cells within the second threshold range are retained to obtain multiple groups of graded battery cells with different capacity levels.

[0049] Furthermore, the capacity calculation model includes the following formula:

[0050] SOC = A% + K(OCV-OCV A )*B;

[0051] Wherein, SOC is the capacity of the battery cell after being discharged at the second preset rate to the second preset time and standing for the third preset time, A% is the percentage of the current remaining capacity (power) of the battery cell and the rated capacity of the battery cell, K is the slope of OCV / SOC, B is the unit conversion constant, OCV A is the OCV corresponding to A% SOC, where OCV is the open circuit voltage.

[0052] Further, the step of calculating the self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage includes the following calculation formula:

[0053]

[0054] Furthermore, before the step of charging the battery cell to an upper limit voltage at a first preset rate, the following steps are also included:

[0055] Acquire the activated battery cell, and perform an aging operation on the battery cell to enable the battery cell to reach a pre-stable state;

[0056] The battery cell after the aging operation is obtained, and a degassing operation is performed on the battery cell to obtain a battery cell in a stable state.

[0057] In a third aspect, the present application also provides another computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the battery cell grading method as described in any one of the above items are implemented.

[0058] Beneficial effects:

[0059] Compared with the prior art, the battery cell grading method provided in the embodiment of the present invention includes: obtaining the battery cell to be graded, performing a formation operation on the battery cell to activate the battery cell; charging the battery cell to an upper limit voltage at a first preset rate; after standing for a first preset time, discharging at a second preset rate to a second preset time; standing for a third preset time, obtaining the first voltage of the battery cell; and grading a plurality of the battery cells based on the first voltage grading model to obtain a plurality of groups of the battery cells with different voltage levels. In the method of the embodiment of the present invention, the battery cells are graded by measuring the voltage of the fully charged battery cells after being discharged for a preset time, and there is no need to perform complete charging and discharging, which shortens the time and reduces the electricity and labor costs.

[0060] Compared with the prior art, another embodiment of the present invention provides a method for grading battery cells, including: obtaining battery cells to be graded within a preset temperature range, performing a formation operation on the battery cells to activate the battery cells; charging the battery cells that have undergone the formation operation to an upper limit voltage at a first preset rate; discharging the battery cells at a second preset rate to a second preset time after standing for a first preset time; standing for a third preset time to obtain a first voltage of the battery cells; inputting the first voltage into a capacity calculation model to obtain a capacity value of the battery cells; grading the battery cells based on the first capacity grading model to obtain multiple groups of battery cells with different capacity gears. In the method of the embodiment of the present invention, the capacity is calculated by measuring the voltage of a fully charged battery cell after it is discharged to a preset time, and the battery cells are graded according to their capacity. There is no need to perform complete charging and discharging and capacity testing, which shortens the time and reduces electricity and labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the implementation manner will be briefly introduced below. Obviously, the drawings described below are only some implementation manners of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0062] Figure 1 It is a flow chart of a method for classifying battery cells provided in one embodiment of the present application;

[0063] Figure 2 is a flow chart of a cell grading method provided in another embodiment of the present application;

[0064] Figure 3 It is a schematic block diagram of the structure of a computer device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0066] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "a", "an", "above", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of features, integers, steps, operations, elements, modules, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, modules, components, and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be an intermediate element. In addition, the "connection" or "coupling" used herein may include wireless connection or wireless coupling. The term "and / or" used herein includes all or any module and all combinations of one or more associated listed items.

[0067] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0068] Embodiment 1:

[0069] like Figure 1 As shown, an embodiment of the present invention provides a battery cell grading method, comprising steps S1-S5:

[0070] S1, obtaining battery cells to be classified, and performing a formation operation on the battery cells to activate the battery cells;

[0071] S2, charging the battery cell to an upper limit voltage at a first preset rate;

[0072] S3, after standing for a first preset time, discharging at a second preset rate for a second preset time;

[0073] S4, leaving the battery cell to stand for a third preset time, and obtaining a first voltage of the battery cell;

[0074] S5. Based on the first voltage classification model, classify the plurality of battery cells into different voltage levels to obtain a plurality of groups of battery cells.

[0075] In the method of the embodiment of the present invention, by performing a formation operation on the battery cell, the chemical substances inside the battery cell can be activated so that it reaches a relatively stable initial state, laying the foundation for subsequent performance tests and grading such as charging and discharging; charging the battery cell that has undergone the formation operation to the upper limit voltage at the first preset rate can allow the battery cell to fully absorb electricity and reach a relatively saturated charging state. The present application can be that the battery cell is charged to the upper limit voltage at 0.33C constant current and 0.05C constant voltage. The present application does not impose specific restrictions on the specific value of the first preset rate, which can be set according to the actual design and production conditions of the battery cell. After standing for a first preset time, in the step of discharging at a second preset rate to a second preset time, the standing operation is to allow the electrochemical state inside the battery cell to have a short stabilization process after the charging is completed, so as to avoid the subsequent discharge test results being affected by the unstable state at the end of charging. The discharge process simulates the discharge of the battery cell in actual use. By discharging for a specific period of time at a specific rate, such as discharging for a specified period of time at a constant current of 0.33C, the change in the battery cell voltage is further observed to obtain more accurate first voltage data for grading. The first voltage of the battery cell is obtained after standing for a third preset period of time. After standing again, the electrochemical state inside the battery cell is more stable. At this time, the first voltage obtained can more accurately reflect the true voltage characteristics of the battery cell. Based on this voltage value, it can be graded according to the first voltage grading model. Among them, the first voltage grading model works according to the correspondence between the pre-set voltage gear range and the battery cell voltage. After obtaining the first voltage of the battery cell, it is compared with the various voltage gear ranges set in the model. If the battery cell voltage falls into a certain range, the battery cell is divided into the corresponding voltage gear, thereby realizing the classification of the battery cell. The method of the embodiment of the present invention only obtains the voltage of the fully charged battery cell after it is discharged to a preset time, and divides the battery cell into grades. It does not need to perform a complete charge and discharge test, and can divide the battery cells with similar voltage characteristics into multiple different gears in a relatively short time. The voltages of the battery cells in the same gear are more consistent, which facilitates the combination of the battery cells in the same gear to form a battery pack. During the charge and discharge process of the battery pack, the voltage change trends of each battery cell are relatively consistent, avoiding problems such as overcharging and over-discharging of some batteries due to excessive differences in battery cell voltages, thereby improving the overall charge and discharge performance and work efficiency of the battery pack. In addition, since the battery cells are divided into grades by measuring the voltage of the fully charged battery cell after discharging the specified capacity, it is not necessary to perform a complete charge and discharge, which greatly shortens the time for the battery cell division, and can effectively solve the problem of taking a long time to divide the battery cells in the prior art.

[0076] In one embodiment, before the step of charging the battery cell to an upper limit voltage at a first preset rate, the following steps are also included:

[0077] Acquire the activated battery cell, and perform an aging operation on the battery cell to enable the battery cell to reach a pre-stable state;

[0078] The battery cell after the aging operation is obtained, and a degassing operation is performed on the battery cell to obtain a battery cell in a stable state.

[0079] In the embodiment of the present invention, after the formation operation, although the battery cell is activated, the reaction between the electrode material and the electrolyte is not sufficient and stable. The aging operation can make the chemical substances inside the battery cell further react and balance, so that the performance of the battery is more stable in the subsequent grading process.

[0080] It should be noted that during the formation process, when the battery cell is charged for the first time, some substances on the surface of the electrode will react with the electrolyte to produce a small amount of gas, causing the surface of the battery cell to swell. During the aging process, this reaction will continue, and due to environmental factors such as temperature, the amount of gas produced will increase. Therefore, this embodiment performs a degassing operation on the aged battery cell to obtain a battery cell in a stable state.

[0081] In one embodiment, after the step of grading the plurality of battery cells based on the first voltage grading model to obtain a plurality of groups of battery cells with different voltage levels, the step further includes:

[0082] Allowing the plurality of groups of battery cells at different voltage levels to stand for a fourth preset time to obtain a second voltage of the battery cells;

[0083] Calculating a self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage;

[0084] determining whether the self-discharge rate is within a first threshold range,

[0085] If not, the battery cells that are not within the first threshold range are eliminated;

[0086] If yes, obtaining the DC internal resistance of the battery cell within the first threshold range;

[0087] determining whether the DC internal resistance is within a second threshold range,

[0088] If not, the battery cells that are not within the second threshold range are removed;

[0089] If so, the battery cells within the second threshold range are retained to obtain multiple groups of graded battery cells with different voltage levels.

[0090] In an embodiment of the present invention, after the preliminary test based on the first voltage grading model, the electrochemical state inside the battery cell may be in an unstable state due to previous operations (such as charging, discharging, transportation, etc.). The static process can allow the chemical substances inside the battery cell to fully react and reach a relatively stable equilibrium state. For example, after the battery cell is charged and discharged, the ion concentration on the electrode surface, the distribution of the electrolyte, etc. may take a certain amount of time to reach uniformity and stability. By standing still for a fourth preset time, a stable battery cell state basis is provided for subsequent accurate measurement of the second voltage. The magnitude of the second voltage and its difference with the first voltage can help evaluate the performance stability of the battery cell. If the second voltage drops more than the first voltage, it means that the self-discharge phenomenon of the battery cell is more serious, which may be caused by factors such as the quality of the internal material of the battery cell, the sealing performance or the stability of the electrolyte, that is, the performance stability of the battery cell is poor, which may affect the performance of the battery pack during long-term use or storage. Therefore, the second voltage is obtained to screen out high-quality batteries with stable performance and low self-discharge rate. The self-discharge rate refers to the rate at which the chemical substances inside the battery react in the absence of an external load (i.e., in an open circuit state), resulting in natural power loss. The self-discharge rate is one of the key indicators for measuring the stability of battery performance. A battery with a low self-discharge rate indicates that its internal chemical system is relatively stable and can better maintain power during storage and intermittent use. On the contrary, a battery with a high self-discharge rate will lose more power in a shorter period of time, which will not only affect the standby time and overall capacity of the battery pack, but may also cause the battery pack to have an unbalanced power during use. By detecting the self-discharge rate, an important battery performance indicator, cells that do not meet the requirements are eliminated, so that cells with better comprehensive performance are selected for battery pack assembly. The first threshold range is set to clarify the qualified standard for the self-discharge performance of the battery. This range is usually determined based on the application scenario of the battery, industry standards, and expectations for battery performance. For example, for high-performance electronic product batteries, the self-discharge rate is required to be less than 1%-2% per month; while for some energy storage applications with slightly lower self-discharge requirements, the threshold will be appropriately relaxed.

[0091] When the self-discharge rate of a battery cell exceeds the first threshold range, it means that the self-discharge performance of the battery cell does not meet the requirements, and the battery cell will experience excessive power loss during storage or use, which will cause the overall performance of the battery pack to decline. By eliminating the battery cells whose self-discharge rate does not meet the requirements, it can be ensured that the battery cells used in the battery pack have good consistency in self-discharge performance. This helps to improve the battery pack's ability to retain power during long-term use and reduce the problem of uneven battery pack performance caused by excessive self-discharge of individual batteries.

[0092] Furthermore, for cells with a self-discharge rate within the first threshold range, it is necessary to further detect their DC internal resistance. DC internal resistance is the resistance inside the cell that prevents current from passing through, which reflects the energy loss of the cell during the charging and discharging process. Through professional testing equipment, such as an electrochemical workstation or an internal resistance tester, a small DC current is applied to the cell, the voltage change at both ends of the cell is measured, and the DC internal resistance is calculated according to Ohm's law (R=U / I). The second threshold range is also set according to the type, application scenario and performance requirements of the cell. For example, for cells used in high-power applications, the DC internal resistance is required to be as small as possible to reduce energy loss and heat during high-rate charging and discharging. If the DC internal resistance of the cell exceeds the second threshold range, it means that the cell will generate too much energy loss and heat during the charging and discharging process, which will reduce the efficiency of the battery pack and may cause safety problems due to overheating. By detecting the DC internal resistance and judging the threshold, cells whose energy loss and heat generation during the charging and discharging process meet the requirements can be screened out.

[0093] In one embodiment, the first voltage classification model classifies the battery cells whose battery cell voltages fall within a corresponding range into corresponding voltage levels according to a predetermined correspondence between the voltage level range and the battery cell voltage.

[0094] In an embodiment of the present invention, the first voltage classification model is a correspondence between a preset voltage gear range and a cell voltage. The correspondence is determined based on a large amount of experimental data, the electrochemical characteristics of the cell, and actual application requirements. For example, for lithium-ion cells, the entire voltage interval is divided into multiple sub-intervals as different voltage gears according to their nominal voltage (such as 3.7V or 3.2V, etc.) and the voltage variation range under different charge and discharge states. After obtaining the first voltage of the cell, the cell whose cell voltage falls into a specific range is divided into the corresponding voltage gear by comparing it with the preset voltage gear range. It is convenient for subsequent unified management and processing of cells with similar voltage characteristics. For example, if the voltage gear range is set to 5.0-6.0V as one gear and 6.0-7.0V as another gear, when the first voltage of a cell is 5.6V, it will be divided into the voltage gear of 5.0-6.0V. By dividing the battery cells into different voltage levels through the first voltage classification model, when assembling the battery pack, the battery cells of the same voltage level or appropriately matched different voltage levels can be selected. This ensures that the voltage change trend of each battery cell is relatively consistent during the charging and discharging process of the battery pack, avoiding problems such as overcharging and over-discharging of some batteries due to excessive differences in battery cell voltages, thereby improving the overall charging and discharging performance and working efficiency of the battery pack.

[0095] In one embodiment, the step of calculating the self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage comprises the following calculation formula:

[0096]

[0097] In this embodiment, the above formula can express the self-discharge phenomenon with a specific value (self-discharge rate), making the evaluation of the self-discharge performance of the battery cell more intuitive and accurate. By calculating the self-discharge rate to select the battery cell, it can be ensured that the battery cells in the battery pack are more matched in terms of self-discharge performance, avoiding the situation where the overall performance of the battery pack is reduced due to the excessive self-discharge of individual batteries, thereby improving the performance stability of the battery pack during use.

[0098] In one embodiment, after the step of determining whether the DC internal resistance is within a second threshold range, and if not, eliminating the battery cells that are not within the second threshold range; and if so, retaining the battery cells that are within the second threshold range, and obtaining multiple groups of graded battery cells with different voltage levels, the following steps are also included:

[0099] The graded battery cells are charged at a first preset rate to a fully charged state, and then discharged at a first capacity percentage to a preset state to obtain battery cells at a first capacity percentage state;

[0100] Placing the graded cells in the first capacity percentage state under different preset temperature states to obtain open circuit voltages under different preset temperature states;

[0101] Based on the first capacity percentage and the open circuit voltage under different preset temperature states, a capacity calculation model under a preset temperature difference is obtained.

[0102] In an embodiment of the present invention, a capacity calculation model is established to evaluate the performance of the battery cell under different temperature conditions. Specifically, the performance of the battery cell includes voltage and capacity. The model can provide a basis for the subsequent accurate estimation of the capacity of the battery cell at different temperatures. The battery cell is charged to a full charge state at a first preset rate in order to put the battery cell in a known initial state to ensure the consistency of subsequent experiments. Then, the battery cell is discharged to a preset state at a first capacity percentage in order to adjust the battery cell to a specific capacity level, so as to facilitate the study of the influence of temperature on the performance of the battery cell under this capacity state. For example, the first capacity percentage can be 50%, that is, the battery cell is discharged to a remaining capacity of 50% of the initial capacity. When the battery cell is in the first capacity percentage state, it is placed at different preset temperature states. Since the temperature affects factors such as the chemical reaction rate and ion migration speed inside the battery cell, the open circuit voltage of the battery cell will change. From an electrochemical point of view, when the temperature increases, the activity of the ions increases, and the open circuit voltage of the battery cell may increase; conversely, when the temperature decreases, the open circuit voltage may decrease. By accurately measuring the open circuit voltage at different temperatures, the relationship between temperature and open circuit voltage can be obtained.

[0103] Exemplarily, the three cells are first charged to full power, then discharged to a specified capacity to 50% SOC or 60% SOC (discharging 50% rated capacity or 40% rated capacity), and then adjusted to different temperatures to test OCV, to obtain the data shown in Table 1 below.

[0104] Table 1 Test data on the impact of temperature on SOC

[0105]

[0106] As shown in Table 1, the OCV fluctuation is ≤3mV at 20-35℃, and ≤5mV at 15-40℃. In the range of 50%SOC to 60%SOC, the OCV / SOC curve is basically a straight line, and the capacity calculation model can be fitted: SOC = A% + K (OCV-OCV A )*B;

[0107] Wherein, SOC is the capacity of the battery cell after being discharged at the second preset rate to the second preset time and standing for the third preset time, A% is the percentage of the current remaining capacity (power) of the battery cell and the rated capacity of the battery cell, K is the slope of OCV / SOC, B is the unit conversion constant, OCV A is the OCV corresponding to A% SOC, where OCV is the open circuit voltage.

[0108] At 20-35°C, the functional relationship between SOC and OCV is: SOC = 50% + 0.084% * (OCV-3.726) * 1000. At 20-35°C, OCV fluctuation is ≤ 3mV, and input into the above relationship, SOC = 0.252%.

[0109] because Among them, C is the rated capacity, C1 is the specified discharge capacity, then the impact of 0.252% SOC on capacity At SOC = 50%, C' = 2.01C1, C = 2C 1， It can be obtained that C'=100.5% C. C'=100.5% C indicates that by adopting the grading method provided by the present invention, within the temperature range of 20-35°C, the maximum effect of temperature difference on capacity is 0.5%; that is, when the temperature rises from 20°C to 35°C, the capacity ratio rises by 0.5 percentage points.

[0110] However, in the prior art, the capacity test method is to directly test the capacity through complete charge and discharge (first charge the battery to a full state, and then discharge it to the termination voltage). The capacity of two groups of batteries is directly tested through complete charge and discharge at different temperatures, and the data shown in Table 2 can be obtained:

[0111]

[0112] As shown in Table 2, within the temperature range of 20-35°C, when the temperature rises from 20°C to 35°C, the capacity ratio increases by 6.5 percentage points (calculated as: the difference between the maximum capacity ratio and the minimum capacity ratio within the temperature range of 20-35°C, i.e. 6.5% = 104.6% - 98.1%). This indicates that the maximum impact of temperature difference on capacity is 6.5% within the temperature range of 20-35°C by using the method of directly testing capacity with complete charge and discharge.

[0113] Comparing the test data in Table 1 and Table 2 above, it can be seen that the battery cell grading method provided in the embodiment of the present application has a maximum impact of 0.5% on the capacity due to the temperature difference within the temperature range of 20-35°C, while the existing method of directly testing the capacity by complete charge and discharge has a maximum impact of 6.5% on the capacity due to the long time spent in directly testing the battery capacity by complete charge and discharge. It is understandable that when the battery is charging, lithium ions are removed from the positive electrode and embedded in the negative electrode, and a reaction will occur on the surface of the negative electrode, consuming energy and generating heat; when discharging, lithium ions are removed from the negative electrode and returned to the positive electrode. The electrochemical reaction inside the battery is not completely reversible, and part of the energy will be dissipated in the form of heat energy. This heat generation will increase the temperature of the battery, and as the charge and discharge time increases, the heat continues to accumulate. In addition, the battery has internal resistance. When the charge and discharge current passes through, according to Joule's law, Q=I 2 Rt (where Q is heat, I is current, R is internal resistance, and t is time), the current will generate heat on the internal resistance. The charging and discharging process lasts for a long time, and the heat generated will continue to accumulate. In the grading method provided in the embodiment of the present invention, since there is no need to perform complete charging and discharging, the time is shortened and the heat generated is relatively low. Therefore, the grading method provided by the technical solution of the present application, through voltage grading, the voltage of the same model of battery cells is determined by SOC, the voltage is less affected by temperature, the charging and discharging time is shortened, the heat generation is reduced, and the temperature difference is reduced, which can improve the accuracy of grading.

[0114] Embodiment 2:

[0115] like Figure 2 As shown, the embodiment of the present application also provides another method for grading battery cells, the method comprising:

[0116] Within a preset temperature range, obtaining the battery cells to be graded, and performing a formation operation on the battery cells to activate the battery cells;

[0117] Charging the battery cell to an upper limit voltage at a first preset rate;

[0118] After being left to rest for a first preset time, the battery is discharged at a second preset rate for a second preset time;

[0119] Allowing the battery to stand for a third preset time to obtain a first voltage of the battery cell;

[0120] Inputting the first voltage into a capacity calculation model to obtain a capacity value of the battery cell;

[0121] Based on the first capacity grading model, the battery cells are graded to obtain a plurality of groups of battery cells with different capacity grades.

[0122] In the embodiment of the present invention, the difference from the embodiment 1 is that the grading method of the present embodiment calculates the capacity based on the capacity calculation model derived in the embodiment 1 and groups the capacity.

[0123] In the method of the embodiment of the present invention, the formation operation is performed on the battery cell within a preset temperature range based on the formation operation principle in the voltage grading method in Example 1, the purpose is to activate the chemical substances inside the battery cell so that it reaches a relatively stable initial state. Through the formation process, a series of chemical reactions occur in the electrode materials inside the battery cell to form a stable electrochemical interface, which will affect the subsequent performance parameters such as the capacity of the battery cell. The battery cell that has undergone the formation operation is charged to the upper limit voltage at the first preset rate, so that the battery cell can fully absorb the electricity to reach a relatively saturated charging state. Different batteries have different capacity values ​​under the same charging conditions due to differences in materials, manufacturing processes and other factors. This step lays the foundation for the subsequent acquisition of accurate capacity data. After standing for a first preset time, discharge at a second preset rate to a second preset time. Standing is to make the internal electrochemical state of the battery cell have a short stable process after the charging is completed, so as to avoid the unstable state at the end of charging affecting the subsequent discharge test results. The discharge process simulates the discharge situation of the battery cell in actual use, and further observes the performance related to the battery cell capacity through the discharge of a specific rate and duration, so as to accurately obtain the first voltage data used to calculate the capacity later. After the battery is left to stand for a third preset time, the first voltage of the battery cell is obtained. After standing again, the electrochemical state inside the battery cell is more stable, and the first voltage obtained at this time can more accurately reflect the characteristics of the battery cell related to capacity, and can be used as input data for the capacity calculation model to calculate the capacity of the battery cell.

[0124] In an embodiment of the present invention, the first capacity grading model works according to the correspondence between the preset capacity gear range and the cell capacity. After obtaining the capacity value of the cell, it is compared with the capacity gear ranges set in the model. If the cell capacity falls into a certain range, the cell is divided into the corresponding capacity gear, thereby realizing the classification of the cell. Through the capacity-based grading method, cells with similar capacity characteristics can be combined to form a battery pack. During the charging and discharging process of the battery pack, the capacity change trend of each cell is relatively consistent, which avoids the situation that some cells are discharged too early or other cells have remaining power due to the large difference in cell capacity, thereby improving the overall capacity utilization and charging and discharging performance of the battery pack. Due to the fine capacity grading of the cells, the cells in the battery pack are more matched in terms of capacity, which helps to reduce the problems of overcharging and over-discharging that may be caused by the mismatch of cell capacity, reduce the decay rate of the cells, and thus extend the overall service life of the battery pack, while also improving the performance of the battery pack in actual use.

[0125] In one embodiment, before the step of charging the battery cell to an upper limit voltage at a first preset rate, the following steps are also included:

[0126] Acquire the activated battery cell, and perform an aging operation on the battery cell to enable the battery cell to reach a pre-stable state;

[0127] The battery cell after the aging operation is obtained, and a degassing operation is performed on the battery cell to obtain a battery cell in a stable state.

[0128] In this embodiment, the aging and degassing operations are consistent with those in Embodiment 1 and are both for obtaining a stabilized battery cell, which will not be described in detail here.

[0129] In one embodiment, the step of grading the battery cells based on the first capacity grading model to obtain a plurality of groups of battery cells with different capacity grades further includes the following steps:

[0130] Allowing the plurality of groups of battery cells with different capacity levels to stand for a fourth preset time to obtain a second voltage of the battery cells;

[0131] Calculating a self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage;

[0132] determining whether the self-discharge rate is within a first threshold range,

[0133] If not, the battery cells that are not within the first threshold range are eliminated;

[0134] If yes, obtaining the DC internal resistance of the battery cell within the first threshold range;

[0135] determining whether the DC internal resistance is within a second threshold range,

[0136] If not, the battery cells that are not within the second threshold range are removed;

[0137] If so, the battery cells within the second threshold range are retained to obtain multiple groups of graded battery cells with different capacity levels.

[0138] In an embodiment of the present invention, the capacity calculation model includes the following formula:

[0139] SOC = A% + K(OCV-OCV A )*B;

[0140] Wherein, SOC is the capacity of the battery cell after being discharged at the second preset rate to the second preset time and standing for the third preset time, A% is the percentage of the current remaining capacity (power) of the battery cell and the rated capacity of the battery cell, K is the slope of OCV / SOC, B is the unit conversion constant, OCV A is the OCV corresponding to A% SOC, and OCV is the open circuit voltage.

[0141] In one embodiment, the step of calculating the self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage comprises the following calculation formula:

[0142]

[0143] In the embodiment of the present invention, similar to the voltage grading method in embodiment 1, multiple groups of cells with different capacity gears are left to stand for a fourth preset time in order to allow the cells to be in a relatively static state for a period of time so that the chemical substances inside the cells can fully react and reach a relatively stable electrochemical state. During this period, the cells will self-discharge due to their internal chemical reactions, resulting in voltage changes. By obtaining the first voltage and the second voltage before and after standing, the self-discharge rate of the cells can be calculated according to a specific formula (such as self-discharge rate = (first voltage - second voltage) / fourth preset time × 100%). The first threshold range is set as a standard for measuring whether the self-discharge performance of the cells is qualified. Different types of cells have different application scenarios, and the reasonable range of their self-discharge rates is also different. If the self-discharge rate of the cell exceeds the set first threshold range, it means that the self-discharge performance of the cell is poor. In actual storage or use, it will cause excessive power loss and affect the overall performance of the battery pack, so such cells need to be eliminated. For cells whose self-discharge rates meet the requirements, it is necessary to further obtain their DC internal resistance. The DC internal resistance is the resistance inside the battery cell that blocks the passage of current. It reflects the energy loss and heat generation of the battery cell during the charging and discharging process. A small DC current is applied to the battery cell through professional testing equipment (such as an AC / DC impedance tester), the voltage change at both ends of the battery cell is measured, and the DC internal resistance is calculated according to Ohm's law (R=U / I). Then set the second threshold range to determine whether the DC internal resistance is qualified. If the DC internal resistance is too large, the battery cell will generate too much heat during the charging and discharging process, which will not only reduce the battery efficiency, but also may cause safety problems. Therefore, the battery cells that do not meet the second threshold range need to be eliminated. For the battery cells that meet the requirements for both the self-discharge rate and the DC internal resistance, the first capacity classification model and the second threshold range are used again. At this time, on the basis of ensuring that the battery cell capacity gear is appropriate, the DC internal resistance factor is further considered, and the battery cells that meet the requirements for the DC internal resistance are recombined according to the capacity gear, so that the battery cells in the same capacity gear have better consistency in multiple performance indicators such as capacity, self-discharge rate and DC internal resistance.

[0144] The embodiment of the present application also provides a battery cell grading device, including: a battery cell grading device used for grading battery cells according to the battery cell grading method of the above embodiment.

[0145] Reference Figure 3 The present application also provides a computer device, the internal structure of which can be as follows: Figure 3As shown. The computer device includes a processor, a memory, a network interface and a database connected via a system bus. Among them, the processor designed for the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating device, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store data such as a battery cell grading method. The network interface of the computer device is used to communicate with an external terminal via a network connection. Furthermore, the above-mentioned computer device may also be provided with an input device and a display screen, etc. When the above-mentioned computer program is executed by the processor, the battery cell grading method described in any of the above-mentioned embodiments is implemented. Those skilled in the art can understand that Figure 3 The structure shown in is merely a block diagram of a portion of the structure related to the present application solution and does not constitute a limitation on the computer device to which the present application solution is applied.

[0146] An embodiment of the present application further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the battery cell grading method described in any of the above embodiments is implemented.

[0147] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media provided in this application and used in the embodiments may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (SSRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0148] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, device, article or method including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, device, article or method. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the presence of other identical elements in the process, device, article or method including the element.

[0149] The above description is only a preferred embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for grading battery cells, characterized in that: The method comprises: Obtaining battery cells to be binned, and performing a formation operation on the battery cells to activate the battery cells; Charging the battery cell to an upper limit voltage at a first preset rate; After being left to rest for a first preset time, the battery is discharged at a second preset rate for a second preset time; Allowing the battery to stand for a third preset time to obtain a first voltage of the battery cell; Based on the first voltage classification model, the plurality of battery cells are classified into different levels to obtain a plurality of groups of battery cells with different voltage levels.

2. The battery cell grading method according to claim 1, characterized in that: After the step of grading the plurality of battery cells based on the first voltage grading model to obtain a plurality of groups of battery cells with different voltage levels, the method further includes: Allowing the plurality of groups of battery cells at different voltage levels to stand for a fourth preset time to obtain a second voltage of the battery cells; Calculating a self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage; determining whether the self-discharge rate is within a first threshold range, If not, the battery cells that are not within the first threshold range are eliminated; If yes, obtaining the DC internal resistance of the battery cell within the first threshold range; determining whether the DC internal resistance is within a second threshold range, If not, the battery cells that are not within the second threshold range are removed; If so, the battery cells within the second threshold range are retained to obtain multiple groups of graded battery cells with different voltage levels.

3. The battery cell grading method according to claim 1, characterized in that: The first voltage classification model classifies the battery cells whose battery cell voltages fall within the corresponding range into corresponding voltage levels according to the corresponding relationship between the preset voltage level range and the battery cell voltage.

4. The battery cell grading method according to claim 2, characterized in that: The step of calculating the self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage includes the following calculation formula:

5. The battery cell grading method according to claim 2, characterized in that: After the step of determining whether the DC internal resistance is within the second threshold range, and if not, eliminating the battery cells that are not within the second threshold range; and if so, retaining the battery cells within the second threshold range, and obtaining multiple groups of graded battery cells with different voltage levels, the following steps are also included: The graded battery cells are charged at a first preset rate to a fully charged state, and then discharged at a first capacity percentage to a preset state, to obtain graded battery cells at a first capacity percentage state; Placing the graded battery cells in the first capacity percentage state under different preset temperature states to obtain open circuit voltages under different preset temperature states; Based on the first capacity percentage and the open circuit voltage under different preset temperature states, a capacity calculation model under a preset temperature difference is obtained.

6. The battery cell grading method according to claim 5, characterized in that: The capacity calculation model includes the following formula: SOC=A%+K(OCV-OCV) A )*B; Wherein, SOC is the capacity of the battery cell after being discharged at the second preset rate to the second preset time and standing for the third preset time, A% is the percentage of the current remaining capacity (power) of the battery cell and the rated capacity of the battery cell, K is the OCV / SOC slope, B is the unit conversion constant, OCV A is the OCV corresponding to A% SOC, where OCV is the open circuit voltage.

7. The battery cell grading method according to claim 1, characterized in that: Before the step of charging the battery cell to an upper voltage limit at a first preset rate, the following step is also included: Acquire the activated battery cell, and perform an aging operation on the battery cell to enable the battery cell to reach a pre-stable state; The battery cell after the aging operation is obtained, and a degassing operation is performed on the battery cell to obtain a battery cell in a stable state.

8. A method for grading battery cells, characterized in that: The method comprises: Obtaining battery cells to be binned, and performing a formation operation on the battery cells to activate the battery cells; Charging the battery cell to an upper limit voltage at a first preset rate; After being left to rest for a first preset time, the battery is discharged at a second preset rate for a second preset time; Allowing the battery to stand for a third preset time to obtain a first voltage of the battery cell; Inputting the first voltage into a capacity calculation model to obtain a capacity value of the battery cell; Based on the first capacity grading model, the battery cells are graded to obtain a plurality of groups of battery cells with different capacity grades.

9. The battery cell grading method according to claim 8, characterized in that: After the step of grading the battery cells based on the first capacity grading model to obtain a plurality of groups of battery cells with different capacity grades, the following steps are also included: Allowing the plurality of groups of battery cells with different capacity levels to stand for a fourth preset time to obtain a second voltage of the battery cells; Calculating a self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage; determining whether the self-discharge rate is within a first threshold range, If not, the battery cells that are not within the first threshold range are eliminated; If yes, obtaining the DC internal resistance of the battery cell within the first threshold range; determining whether the DC internal resistance is within a second threshold range, If not, the battery cells that are not within the second threshold range are removed; If so, the battery cells within the second threshold range are retained to obtain multiple groups of graded battery cells with different capacity levels.

10. The battery cell grading method according to claim 8, characterized in that: The capacity calculation model includes the following formula: SOC=A%+K(OCV-OCV) A )*B; Wherein, SOC is the capacity of the battery cell after being discharged at the second preset rate to the second preset time and standing for the third preset time, A% is the percentage of the current remaining capacity (power) of the battery cell and the rated capacity of the battery cell, K is the slope of OCV / SOC, B is the unit conversion constant, OCV A is the OCV corresponding to A% SOC, where OCV is the open circuit voltage.

11. The battery cell grading method according to claim 8, characterized in that: The step of calculating the self-discharge rate of the battery cell based on the values ​​of the first voltage and the second voltage includes the following calculation formula:

12. The battery cell grading method according to claim 8, characterized in that: Before the step of charging the battery cell to an upper voltage limit at a first preset rate, the following step is also included: Acquire the activated battery cell, and perform an aging operation on the battery cell to enable the battery cell to reach a pre-stable state; The battery cell after the aging operation is obtained, and a degassing operation is performed on the battery cell to obtain a battery cell in a stable state.

13. A computer device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the computer program, the steps of the battery cell grading method according to any one of claims 1 to 12 are implemented.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the battery cell grading method according to any one of claims 1 to 12 are implemented.

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