Method for improving battery cell matching consistency and battery cell group

Abstract

The invention relates to the technical field of battery cell matching, and discloses a method for improving battery cell matching consistency and a battery cell group. The method comprises the following steps: preliminarily screening battery cells into a plurality of first battery cell groups according to the preliminary formation voltage of the battery cells; screening the first battery cell group into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cells in the formation process and the formation finishing voltage; performing pre-grouping on the second battery cells in the second battery cell group according to the battery cell discharge capacity and the grouping reference voltage to obtain a battery cell pre-grouping group; and finally grouping the battery cell pre-groups according to the voltage, the internal resistance and the K value of the third battery cell after standing to obtain a plurality of final battery cell groups. According to the invention, through a method of simulating battery cell pack assembly in a battery cell capacity grading stage, and through a mode of high-rate constant-current pressurization and temperature rise monitoring, the battery cells with better consistency are selected, the reliability degree of battery cell matching is enhanced, the capacity grading process is saved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery cell grouping, and in particular to a method for improving battery cell grouping consistency and a battery cell group. Background Art

[0002] In the production process of soft-pack battery cells, the battery cell matching method is mainly based on the static parameters and dynamic characteristics of the battery cells for screening and matching, aiming to improve the consistency and life of the battery pack; currently, the conventional matching method is generally based on the basic parameters of the battery cells such as capacity, voltage, internal resistance, etc., and the battery cells with higher consistency are screened by setting thresholds, and then the voltage drop rate (K value) and self-discharge rate are tested at high temperature / normal temperature to further screen the battery cells with good long-term stability; however, relying solely on static parameters such as capacity and voltage cannot reflect the differences in polarization characteristics of the battery cells under dynamic working conditions (such as high-rate charge and discharge). Since the self-discharge rate test requires a long period of standing (such as 1 month), the efficiency is low and the cost is high, which makes it difficult to meet the needs of rapid production; therefore, the existing matching methods are rarely deeply integrated with thermal management strategies, and the matching reliability is general.

[0003] In view of the above-mentioned process status, the present invention aims to solve the problem that current battery cells, after rigorous multi-parameter screening, may still lead to reduced grouping rate, poor grouping efficiency and high cost. Summary of the Invention

[0004] The object of the present invention is to provide a method for improving the consistency of battery cell grouping and a battery cell group, so as to solve or at least partially solve the technical problems mentioned in the above background technology.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for improving the consistency of battery cell grouping, comprising:

[0007] Preliminarily screening the battery cells into a plurality of first battery cell groups according to the preliminary formation voltage of the battery cells; wherein the battery cells in the first battery cell group are recorded as first battery cells;

[0008] The first battery cell group is further divided into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cell during the formation process and the formation end voltage;

[0009] Discharging the second battery cell to a preset lower limit voltage using a preset discharge current, obtaining the battery capacity of the second battery cell at this time and recording it as the battery cell discharge capacity; then charging the second battery cell to a predetermined state of charge using a preset charge current, obtaining the voltage of the second battery cell at this time and recording it as the pairing reference voltage;

[0010] Pre-grouping the second battery cell in the second battery cell group according to the battery cell discharge capacity and the grouping reference voltage to obtain a battery cell pre-group; wherein the battery cell in the battery cell pre-group is recorded as a third battery cell;

[0011] The pre-matched battery cell groups are finally grouped according to the voltage, internal resistance and K value of the third battery cell after standing still, to obtain a plurality of final battery cell groups.

[0012] Optionally, the method for obtaining the preliminary formation voltage is:

[0013] After liquid injection, multiple battery cells of the same batch are placed at a preset high-temperature shelf temperature for a preset first shelf time to obtain a batch of liquid-filled battery cells to be grouped; wherein the high-temperature shelf temperature is 45°C ± 3°C and the first shelf time is 36 ± 3 hours;

[0014] Set initialization parameters, perform preliminary formation on a batch of liquid-filled cells after being stored at high temperature, and obtain the initial formation voltage of each liquid-filled cell;

[0015] The setting is initialized into parameters, specifically including:

[0016] The formation temperature is set to 75-85°C, and the surface pressure of the formed battery cell is set to 1.0-1.2Mpa;

[0017] The current at the beginning of the formation was set to 0.2±0.05C, and the state of charge after the initial formation was set to 30±5%.

[0018] Optionally, the preliminarily screening the battery cells into a plurality of first battery cell groups according to the preliminary formation voltage of the battery cells specifically includes:

[0019] Sorting the batch of liquid-filled battery cells in descending order of initial formation voltage, and screening out liquid-filled battery cells with abnormal initial formation voltage;

[0020] Preliminarily grouping the liquid-filled battery cells according to each level of the first preset voltage to obtain a plurality of first battery cell groups;

[0021] The liquid-filled cells in the first cell group are referred to as first cells. In each first cell group, the difference between the maximum and minimum values of the initial formation voltage of the first cells does not exceed a first preset voltage.

[0022] Optionally, before the first battery cell group is divided into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cells during the formation process and the formation end voltage, the method further includes:

[0023] Increase the formation pressure to 1.6±0.3 MPa and use an infrared temperature rise monitoring system to monitor the surface temperature rise data of the first battery cell;

[0024] Adjust the formation current to the maximum charging current designed for the first cell chemistry system, charge at constant current to the designed full charge upper limit voltage of the cell, and then charge at constant voltage to 0.8±0.3C and cut off;

[0025] After the first battery cell is left for a first preset time to eliminate polarization, a maximum surface temperature rise value T of the first battery cell during the formation process and a formation end voltage V2 of the first battery cell are obtained.

[0026] Optionally, the step of further dividing the first battery cell group into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cells during the formation process and the formation end voltage specifically includes:

[0027] Sort the first battery cells in the first battery cell group in descending order of V2, and remove the first battery cells with abnormal forming end voltage;

[0028] Performing a first grouping of the first battery cell group according to each level of the second preset voltage to obtain a plurality of first battery cell groups;

[0029] Sort the first battery cells in the first battery cell group in order of T from low to high, and group the first battery cell group a second time according to each first preset temperature level to obtain a plurality of second battery cell groups;

[0030] Among them, the first battery cell in the second battery cell group is recorded as the second battery cell. In each second battery cell group, the difference between the maximum and minimum values of the second battery cell's formation end voltage does not exceed the second preset voltage, and the difference between the maximum and minimum values of the surface maximum temperature rise value does not exceed the first preset temperature.

[0031] Optionally, discharging the second battery cell to a preset lower limit voltage using a preset discharge current, obtaining the battery cell capacity of the second battery cell at this time and recording it as the battery cell discharge capacity, specifically includes:

[0032] At room temperature of 25±3℃, the capacity of the second battery cell after formation is divided;

[0033] The second cell is discharged to 3.0 V using a current of 0.2±0.05 C, and the capacity C0 of the second cell at this time is obtained and recorded as the discharge capacity of the cell;

[0034] The step of charging the second battery cell to a predetermined state of charge using a preset charging current, obtaining the voltage of the second battery cell at that state and recording it as the pairing reference voltage specifically includes:

[0035] The second battery cell is charged for 36±2 min using a current of 0.5±0.1 C to obtain a battery cell with a state of charge of 30%±5%. The voltage V3 of the second battery cell at this time is measured and recorded as the pairing reference voltage.

[0036] Optionally, pre-grouping the second battery cells in the second battery cell group according to the battery cell discharge capacity and the grouping reference voltage to obtain a battery cell pre-group specifically includes:

[0037] Sort the second battery cells in the second battery cell group in order of C0 from low to high;

[0038] The second battery cells in the second battery cell group are grouped according to each level of the A%C0 interval to obtain a plurality of second battery cell subgroups; wherein A is a preset value;

[0039] Sort the second battery cells in the second battery cell group in descending order of V3;

[0040] Assigning the second battery cells in the second battery cell group according to each level of the third preset voltage to obtain a plurality of pre-assigned battery cell groups;

[0041] Among them, the battery cell in the battery cell pre-matching group is recorded as the third battery cell.

[0042] Optionally, before finally grouping the pre-matched battery cells according to the voltage, internal resistance, and K value of the third battery cell after standing to obtain a plurality of final matched battery cell groups, the method further includes:

[0043] Vacuuming and sealing the third battery cell to remove gas generated during the battery cell film formation process;

[0044] The third battery cell is left at rest for a preset rest time t at room temperature, and the voltage, internal resistance, and K value of the third battery cell after the rest time are obtained;

[0045] The step of placing the third battery cell at room temperature for a preset rest time t and obtaining the voltage, internal resistance, and K value of the third battery cell after the rest period specifically includes:

[0046] Under the condition of 25±3° C., the third battery cell is allowed to stand at room temperature for a second preset time, and the voltage V4 and internal resistance R4 of the third battery cell after the standing time are obtained;

[0047] The K value of the battery cell is calculated by V3 and V4; where K value = (V3-V4) / t, unit: mV / h.

[0048] Optionally, the final grouping of the pre-matched battery cells according to the voltage, internal resistance and K value of the third battery cell after standing to obtain a plurality of final battery cell groups specifically includes:

[0049] Sorting the third battery cells in the battery cell pre-assignment group in order of K value from low to high;

[0050] Grouping the third battery cells in the pre-grouped battery cells according to the preset K value in each group to obtain a plurality of first groups;

[0051] Sort the third cells in the first group according to V4 from high to low;

[0052] Grouping the third battery cells in the first grouping according to each level of the fourth preset voltage to obtain a plurality of second groupings;

[0053] Sort the third cells in the second group in order of R4 from low to high;

[0054] The third battery cells in the second grouping are finally grouped according to the preset resistance values in each level to obtain a plurality of final battery cell groups.

[0055] Optionally, the first preset voltage, the second preset voltage, the third preset voltage and the fourth preset voltage are all 15mv, the first preset time is 10min, the first preset temperature is 3°C, A is 1, the second preset time is 2 days, the preset tier K value is 0.02, and the preset tier resistance is 6mΩ.

[0056] In a second aspect, the present invention provides a battery cell group, which is assembled using the above-mentioned method for improving the consistency of battery cell grouping.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The present invention simulates the method of cell pack assembly in the cell capacity division stage, selects cells with better consistency through high-rate constant current pressurization and temperature rise monitoring, and enhances the reliability of cell grouping; and adopts a cell grading and grouping process, which helps to improve the consistency between the series-connected units of the battery pack. The grading and grouping process is significantly better than the original capacity grading and grouping process, which is beneficial to the improvement of module performance, and the cell discharge capacity can be read in the formation stage, which saves the capacity division process and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0060] Figure 1 A flow chart of a method for improving the consistency of battery cell grouping provided by an embodiment of the present invention.

[0061] Figure 2 A curve diagram showing the relationship between energy retention rate and cycle number provided in an embodiment of the present invention.

[0062] Figure 3Another relationship curve diagram between energy retention rate and cycle number provided in an embodiment of the present invention.

[0063] Figure 4 A curve diagram showing the relationship between discharge voltage difference and cycle number provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0065] Example 1:

[0066] Please refer to Figure 1 , Figure 1 A flow chart of a method for improving the consistency of battery cell grouping provided by an embodiment of the present invention, the method specifically includes:

[0067] Presetting step 100: After liquid injection, multiple battery cells of the same batch are placed at a preset high-temperature storage temperature for a preset first storage time to obtain a batch of liquid-filled battery cells to be assembled.

[0068] In step 100, the high temperature shelf temperature is set to 45°C ± 3°C, and the first shelf time is 36±3h.

[0069] For example, in this embodiment, soft-pack cells with a capacity of 655463-4676 mAh are selected, and 50 pcs of the cells after injection are placed at 45° C. for 36 hours.

[0070] Preset step 101: setting initialization parameters, performing preliminary formation on a batch of liquid-filled cells after being stored at high temperature, and obtaining preliminary formation voltages of the liquid-filled cells.

[0071] In step 101, the initialization parameters specifically include:

[0072] The formation temperature is set to 75-85°C, and the surface pressure of the formed battery cell is set to 1.0-1.2Mpa;

[0073] The initial current of formation is set to 0.2±0.05C, and the state of charge after initial formation is set to 30±5%, where 0.2C means discharging at a current of 0.2 times the battery capacity, and C is the design capacity of the battery cell.

[0074] For example, after the battery cells (50 of which are taken as an example) are placed on hold, they are charged at 80° C. and 1.1 MPa with a constant current of 935 mA for 90 minutes to obtain V1 data, as shown in Table 1 below.

[0075] Table 1

[0076]

[0077]

[0078]

[0079] Step 110 : Preliminarily screening the battery cells into a plurality of first battery cell groups according to the initial formation voltage of the battery cells.

[0080] Step 110 specifically includes:

[0081] Step 1101 : sorting a batch of liquid-filled battery cells in descending order of initial formation voltage, and screening out liquid-filled battery cells with abnormal initial formation voltage.

[0082] Step 1102: preliminarily group the liquid-filled cells according to each level of 15 mV to obtain a plurality of first cell groups.

[0083] The liquid-filled cells in the first cell group are referred to as first cells. In each first cell group, the difference between the maximum and minimum values of the initial formation voltage of the first cells does not exceed 15 mV.

[0084] For example, as shown in Table 1, the voltage of the 13# battery cell is abnormal and needs to be removed; the 34# battery cell is in other gears, so it is not considered for grouping here.

[0085] Step 111: Increase the formation pressure to 1.6±0.3 MPa, and use an infrared temperature rise monitoring system to monitor the surface temperature rise data of the first battery cell.

[0086] Step 112: Adjust the formation current to the maximum charging current designed for the first cell chemistry system, perform constant current charging to the designed upper limit voltage of the cell, and then perform constant voltage charging to 0.8±0.3C and then cut off.

[0087] For example, the initially formed battery cell is charged with a constant current of 9352 mA at 1.6 MPa, with a cutoff of 4.51 V; then the charge is switched to constant voltage charging with a cutoff of 3741 mA; the surface temperature rise data of the battery cell in each process is recorded in real time to obtain the maximum surface temperature rise value T.

[0088] Step 113 : After the first battery cell is left for 10 minutes to eliminate polarization, the maximum surface temperature rise T of the first battery cell during the formation process and the formation end voltage V2 of the first battery cell are obtained.

[0089] After the first cell was left standing for 10 minutes to eliminate polarization, V2 was obtained.

[0090] Step 120 : Screening the first battery cell group into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cells during the formation process and the formation end voltage.

[0091] Sort the first cells in the first cell group in descending order of V2, and remove the first cells with abnormal formation end voltage;

[0092] The first battery cell group is first grouped according to each level of 15mv to obtain a number of first battery cell groups;

[0093] Sort the first cells in the first cell group in order of T from low to high, and group the first cell group a second time according to each 3°C level to obtain a number of second cell groups;

[0094] Among them, the first battery cell in the second battery cell group is recorded as the second battery cell. In each second battery cell group, the difference between the maximum and minimum values of the second battery cell's formation end voltage does not exceed 15mv, and the difference between the maximum and minimum values of the surface maximum temperature rise does not exceed 3°C.

[0095] The voltage is sorted from high to low, and the temperature is sorted from low to high. The voltage level is 15mV and the temperature rise is 3℃ for secondary grouping.

[0096] For example, in Table 1, 7 / 10 / 25 / 27 / 30 / 38 / 45 / 48 / 50 are other gears and are not considered for grouping here.

[0097] Step 130: Discharge the second battery cell to a preset lower voltage limit using a preset discharge current, obtain the battery cell capacity of the second battery cell at this time and record it as the battery cell discharge capacity.

[0098] At room temperature of 25±3℃, the capacity of the second battery cell after formation is divided;

[0099] Use a current of 0.2±0.05C to discharge the second battery cell to 3.0V, and obtain the capacity C0 of the second battery cell at this time and record it as the battery cell discharge capacity;

[0100] For example, at room temperature of 25±3° C., the capacity of the formed battery cell is divided, and the battery cell is discharged to 3.0 V with a current of 935 mA to obtain a capacity C0.

[0101] Step 140: Use a preset charging current to charge the second battery cell to a predetermined state of charge, obtain the voltage of the second battery cell at this time and record it as the pairing reference voltage.

[0102] The second battery cell is charged to a predetermined state of charge using a preset charging current, and the voltage of the second battery cell at this time is obtained and recorded as the pairing reference voltage, specifically including:

[0103] The second cell is charged for 36±2 min using a current of 0.5±0.1 C to obtain a cell with a state of charge of 30%±5%. The voltage V3 of the second cell at this time is measured and recorded as the pairing reference voltage.

[0104] For example, for the battery cell in Table 1, a current of 2338 mAh is used to charge for 36 minutes, and the voltage V3 is measured.

[0105] Step 150 : pre-grouping the second battery cells in the second battery cell group according to the battery cell discharge capacity and the grouping reference voltage to obtain a battery cell pre-group.

[0106] Sort the second cells in the second cell group in order of C0 from low to high;

[0107] The second battery cells in the second battery cell group are grouped according to each level of the 1% C0 interval to obtain a plurality of second battery cell groups;

[0108] Sort the second cells in the second cell group in descending order of V3;

[0109] The second battery cells in the second battery cell group are grouped according to each level of 15mv to obtain a plurality of pre-grouped battery cells;

[0110] Among them, the battery cell in the battery cell pre-matching group is recorded as the third battery cell.

[0111] The initial grouping is based on the capacity of 46mAh and the voltage of 15mV;

[0112] For example, the capacities are sorted from low to high, and the voltages are sorted from high to low. Finally, cells 2 / 4 / 6 / 9 / 11 / 15 / 16 / 17 / 20 / 21 / 25 / 26 / 28 / 29 / 32 / 33 / 37 / 39 / 40 / 41 / 42 / 43 in Table 1 are selected for pre-grouping. Other cells are not considered for grouping here.

[0113] After step 150, the method further includes:

[0114] Step 151: evacuate and seal the third battery cell to remove the gas generated during the battery cell film forming process.

[0115] Step 152: Leave the third battery cell at room temperature for a preset rest time t, and obtain the voltage, internal resistance, and K value of the third battery cell after the rest time.

[0116] Under the condition of 25±3°C, the third battery cell is left at room temperature for 2 days, and the voltage V4 and internal resistance R4 of the third battery cell after the rest are obtained;

[0117] The K value of the battery cell is calculated by V3 and V4; where K value = (V3-V4) / t, unit: mV / h.

[0118] For example, after the capacity is measured, the gas is pumped out and sealed, and the container is placed at room temperature for two days to obtain the voltage internal resistance and self-discharge K. The K group gear is controlled at 0.02;

[0119] The V4 position is controlled at 15mV, and the resistance R4 is controlled at 6mΩ. The K values are sorted from low to high, the voltages are sorted from high to low, and the internal resistances are sorted from low to high.

[0120] Step 160 : finally grouping the pre-matched battery cell groups according to the voltage, internal resistance, and K value of the third battery cell after standing still to obtain a plurality of final battery cell groups.

[0121] Optionally, step 160 is implemented as follows:

[0122] Step 161: sort the third battery cells in the battery cell pre-assignment group in descending order of K value;

[0123] Step 162: group the third battery cells in the pre-grouped battery cells according to the 0.02 level to obtain a plurality of first groupings.

[0124] Step 163: Sort the third cells in the first group in descending order of V4;

[0125] Step 164: group the third cells in the first grouping according to each level of 15 mV to obtain a plurality of second groups;

[0126] Step 165: Sort the third cells in the second group in descending order of R4;

[0127] Step 166 : finally group the third battery cells in the second grouping according to each level of 6 mΩ to obtain a plurality of final battery cell groups.

[0128] It is understandable that the order of steps 161 to 166 can be reversed. For example, the sorting and grouping can be performed first according to V4, and then according to R4 and K values, or the sorting and grouping can be performed first according to R4, and then according to V4 and K values, etc. This will not be repeated here.

[0129] For example, according to the above grouping method, the following are finally selected:

[0130] 4 / 6 / 16 / 17 / 29 / 33 / 37 / 41 are grouped together, and 2 / 9 / 11 / 15 / 20 / 21 / 26 / 28 / 32 / 39 / 40 / 42 / 43 are grouped together. The configuration of other batteries is not considered here.

[0131] For example, it is shown in Table 2 below:

[0132] Table 2

[0133]

[0134]

[0135] Please refer to Figure 2 , Figure 2 A graph showing the relationship between energy retention and cycle number provided by an embodiment of the present invention; the cycle curves of the three groups of batteries A1, B1, and C1 are as follows: Figure 2 shown.

[0136] In order to illustrate the superiority of the combination method of this embodiment, a comparative example is provided below. The relevant experimental data are shown in Table 3:

[0137] Table 3

[0138]

[0139] The comparative example is a grouping of cells selected in accordance with conventional grouping (generally selecting capacity, voltage, internal resistance and self-discharge);

[0140] Please refer to Table 3. Figure 3 and Figure 4 Table 3 shows the experimental parameters related to the examples of this embodiment and the comparative examples. Figure 3 Another graph showing the relationship between energy retention rate and cycle number provided in an embodiment of the present invention;

[0141] Figure 4 A curve diagram showing the relationship between discharge voltage difference and cycle number provided in an embodiment of the present invention.

[0142] Table 4

[0143]

[0144]

[0145] It can be seen that the comparative cycle has abnormalities. For the cell voltage difference during the cycle, the A1, B1, and C1 modules are significantly better than the D1, E1, and F1 modules.

[0146] In summary, the grouping method of this embodiment selects cells with better consistency by simulating the cell pack assembly method in the cell capacity division stage through high-rate constant current pressurization and temperature rise monitoring, thereby enhancing the reliability of cell grouping; and, the use of a cell grading and grouping process helps to improve the consistency between the series-connected units of the battery pack. The grading and grouping process is significantly better than the original capacity grading and grouping process, which is beneficial to the improvement of module performance, and the cell discharge capacity can be read in the formation stage, which saves the capacity division process and reduces production costs.

[0147] Example 2:

[0148] This embodiment provides a battery cell group, which is assembled using the method for improving battery cell grouping consistency as described in the first embodiment.

[0149] Since the method for improving the consistency of battery cell grouping has been fully described in the first embodiment, it will not be repeated in this embodiment.

[0150] The battery cell group assembled using this method improves the consistency between the series-connected units in the battery pack, which is beneficial to the improvement of module performance. The battery cell discharge capacity can be read during the formation stage, which saves the capacity separation process and reduces production costs.

[0151] Those skilled in the art will appreciate that all or part of the steps of the above-described embodiments can be implemented by hardware or by programs instructing the relevant hardware to perform the steps. The programs can be stored in a computer-readable storage medium, which can be a read-only memory, a magnetic disk, or an optical disk. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0152] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the consistency of battery cell grouping, characterized in that: include: Preliminarily screening the battery cells into a plurality of first battery cell groups according to the preliminary formation voltage of the battery cells; wherein the battery cells in the first battery cell group are recorded as first battery cells; The first battery cell group is further divided into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cell during the formation process and the formation end voltage; Discharging the second battery cell to a preset lower limit voltage using a preset discharge current, obtaining the battery capacity of the second battery cell at this time and recording it as the battery cell discharge capacity; then charging the second battery cell to a predetermined state of charge using a preset charge current, obtaining the voltage of the second battery cell at this time and recording it as the pairing reference voltage; Pre-grouping the second battery cell in the second battery cell group according to the battery cell discharge capacity and the grouping reference voltage to obtain a battery cell pre-group; wherein the battery cell in the battery cell pre-group is recorded as a third battery cell; The pre-matched battery cell groups are finally grouped according to the voltage, internal resistance and K value of the third battery cell after standing still, to obtain a plurality of final battery cell groups.

2. A method for improving the consistency of battery cell grouping according to claim 1, characterized in that: The method for obtaining the preliminary formation voltage is: After liquid injection, multiple battery cells of the same batch are placed at a preset high-temperature shelf temperature for a preset first shelf time to obtain a batch of liquid-filled battery cells to be grouped; wherein the high-temperature shelf temperature is 45°C ± 3°C and the first shelf time is 36 ± 3 hours; Set initialization parameters, perform preliminary formation on a batch of liquid-filled cells after being stored at high temperature, and obtain the initial formation voltage of each liquid-filled cell; The setting is initialized into parameters, specifically including: The formation temperature is set to 75-85°C, and the surface pressure of the formed battery cell is set to 1.0-1.2Mpa; The current at the beginning of the formation was set to 0.2±0.05C, and the state of charge after the initial formation was set to 30±5%.

3. A method for improving the consistency of battery cell grouping according to claim 2, characterized in that: The preliminary screening of the battery cells into a plurality of first battery cell groups according to the preliminary formation voltage of the battery cells specifically includes: Sorting the batch of liquid-filled battery cells in descending order of initial formation voltage, and screening out liquid-filled battery cells with abnormal initial formation voltage; Preliminarily grouping the liquid-filled battery cells according to each level of the first preset voltage to obtain a plurality of first battery cell groups; The liquid-filled cells in the first cell group are referred to as first cells. In each first cell group, the difference between the maximum and minimum values of the initial formation voltage of the first cells does not exceed a first preset voltage.

4. A method for improving the consistency of battery cell grouping according to claim 3, characterized in that: Before the first battery cell group is divided into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cells during the formation process and the formation end voltage, the method further includes: Increase the formation pressure to 1.6±0.3 MPa and use an infrared temperature rise monitoring system to monitor the surface temperature rise data of the first battery cell; Adjust the formation current to the maximum charging current designed for the first cell chemistry system, charge at constant current to the designed full charge upper limit voltage of the cell, and then charge at constant voltage to 0.8±0.3C and cut off; After the first battery cell is left for a first preset time to eliminate polarization, a maximum surface temperature rise value T of the first battery cell during the formation process and a formation end voltage V2 of the first battery cell are obtained.

5. A method for improving the consistency of battery cell grouping according to claim 4, characterized in that: The method further dividing the first battery cell group into a plurality of second battery cell groups according to the maximum surface temperature rise value of the battery cells during the formation process and the formation end voltage specifically includes: Sort the first battery cells in the first battery cell group in descending order of V2, and remove the first battery cells with abnormal forming end voltage; Performing a first grouping of the first battery cell group according to each level of the second preset voltage to obtain a plurality of first battery cell groups; Sort the first battery cells in the first battery cell group in order of T from low to high, and group the first battery cell group a second time according to each first preset temperature level to obtain a plurality of second battery cell groups; Among them, the first battery cell in the second battery cell group is recorded as the second battery cell. In each second battery cell group, the difference between the maximum and minimum values of the second battery cell's formation end voltage does not exceed the second preset voltage, and the difference between the maximum and minimum values of the surface maximum temperature rise value does not exceed the first preset temperature.

6. A method for improving the consistency of battery cell grouping according to claim 5, characterized in that: The step of discharging the second battery cell to a preset lower voltage limit by using a preset discharge current, obtaining the battery capacity of the second battery cell at this time and recording it as the battery cell discharge capacity, specifically includes: At room temperature of 25±3℃, the capacity of the second battery cell after formation is divided; The second cell is discharged to 3.0 V using a current of 0.2±0.05 C, and the capacity C0 of the second cell at this time is obtained and recorded as the discharge capacity of the cell; The step of charging the second battery cell to a predetermined state of charge using a preset charging current, obtaining the voltage of the second battery cell at that state and recording it as the pairing reference voltage specifically includes: The second battery cell is charged for 36±2 min using a current of 0.5±0.1 C to obtain a battery cell with a state of charge of 30%±5%. The voltage V3 of the second battery cell at this time is measured and recorded as the pairing reference voltage.

7. A method for improving the consistency of battery cell grouping according to claim 6, characterized in that: The pre-grouping of the second battery cells in the second battery cell group according to the battery cell discharge capacity and the grouping reference voltage to obtain a battery cell pre-group specifically includes: Sort the second battery cells in the second battery cell group in order of C0 from low to high; The second battery cells in the second battery cell group are grouped according to each level of the A%C0 interval to obtain a plurality of second battery cell subgroups; wherein A is a preset value; Sort the second battery cells in the second battery cell group in descending order of V3; Assigning the second battery cells in the second battery cell group according to each level of the third preset voltage to obtain a plurality of pre-assigned battery cell groups; Among them, the battery cell in the battery cell pre-matching group is recorded as the third battery cell.

8. The method for improving the consistency of battery cell grouping according to claim 7, characterized in that: Before the battery cell pre-matching group is finally grouped according to the voltage, internal resistance and K value of the third battery cell after standing to obtain a plurality of final battery cell groups, the method further includes: Vacuuming and sealing the third battery cell to remove gas generated during the battery cell film formation process; The third battery cell is left at rest for a preset rest time t at room temperature, and the voltage, internal resistance, and K value of the third battery cell after the rest time are obtained; The step of placing the third battery cell at room temperature for a preset rest time t and obtaining the voltage, internal resistance, and K value of the third battery cell after the rest period specifically includes: Under the condition of 25±3° C., the third battery cell is allowed to stand at room temperature for a second preset time, and the voltage V4 and internal resistance R4 of the third battery cell after the standing time are obtained; The K value of the battery cell is calculated by V3 and V4; where K value = (V3-V4) / t, unit: mV / h.

9. A method for improving the consistency of battery cell grouping according to claim 8, characterized in that: The final grouping of the pre-matched battery cells according to the voltage, internal resistance and K value of the third battery cell after standing still to obtain a plurality of final battery cell groups specifically includes: Sorting the third battery cells in the battery cell pre-assignment group in order of K value from low to high; Grouping the third battery cells in the pre-grouped battery cells according to the preset K value in each group to obtain a plurality of first groups; Sort the third cells in the first group according to V4 from high to low; Grouping the third battery cells in the first grouping according to each level of the fourth preset voltage to obtain a plurality of second groupings; Sort the third cells in the second group in order of R4 from low to high; The third battery cells in the second grouping are finally grouped according to the preset resistance values in each level to obtain a plurality of final battery cell groups.

10. A battery cell pack, characterized in that: The battery cells are assembled using a method for improving the consistency of battery cell assembly as described in any one of claims 1 to 9.

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