Method for reducing voltage difference of battery module and battery pack

Abstract

The invention provides a method for reducing the voltage difference of a battery module and a battery pack, and the method comprises the following steps: providing a battery module which comprises a plurality of electrically connected battery cells; carrying out pre-charging treatment on a battery cell in the battery module; and discharging the battery cells in the battery module, and obtaining the voltage difference between the battery cells in the battery module as the voltage difference of the battery module. According to the battery module, the battery cells in the battery module are pre-charged before the battery cells in the battery module are discharged, so that the temperature of the battery cells in the battery module is increased, the influence of the temperature on the voltage difference between the battery cells is reduced, and the voltage difference of the battery module is further reduced.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for reducing a voltage difference of a battery module and a battery pack. Background Art

[0002] Usually, multiple battery cells (also called battery cells) are electrically connected to form a battery module, and multiple battery modules are electrically connected to form a battery pack. However, due to certain differences between battery cells, different degrees of voltage difference (also called voltage difference) appear after forming the battery module, resulting in poor cycle life of the battery module, low energy conversion coefficient, and ultimately affecting the performance of the battery pack. Summary of the invention

[0003] The embodiments of the present application provide a method for reducing the voltage difference of a battery module and a battery pack, which can improve the technical problem of large voltage difference of the battery module.

[0004] In a first aspect, an embodiment of the present application provides a method for reducing a voltage difference of a battery module, comprising:

[0005] Providing a battery module, the battery module comprising a plurality of electrically connected battery cells;

[0006] Pre-charging the battery cells in the battery module;

[0007] The battery cells in the battery module are discharged, and the voltage difference between the battery cells in the battery module is obtained as the voltage difference of the battery module.

[0008] In one embodiment, the pre-charging process enables the capacity increment of the battery cell to reach 5% to 20% of the rated capacity.

[0009] In one embodiment, the pre-charging process includes: charging the battery cell at a constant current of 0.5C to 2C for 5 minutes to 20 minutes.

[0010] In one embodiment, providing a battery module includes:

[0011] Provide multiple battery cells;

[0012] Performing charge and discharge processing on the plurality of battery cells to obtain capacity data of the battery cells;

[0013] Dividing the plurality of battery cells into a plurality of gears according to the capacity data;

[0014] Dividing the plurality of cells in the same gear into a plurality of sub-gears according to the capacity data;

[0015] A plurality of the battery cells of the same sub-level are electrically connected together to obtain a battery module.

[0016] In one embodiment, the charge and discharge process includes:

[0017] The battery cell is charged at a constant current to a first cut-off voltage using a first current, and then the battery cell is charged at a constant voltage to a first cut-off current using the first cut-off voltage;

[0018] The battery cell is discharged at a constant current with a second current to a second cut-off voltage, and data of the voltage value of the battery cell changing with time during the discharge process is recorded.

[0019] In one embodiment, the capacity data includes a first capacity and a second capacity, the first capacity is the discharge capacity of the battery cell within a range of a first voltage to a second voltage, the second capacity is the discharge capacity of the battery cell within a range of a third voltage to a fourth voltage, the second voltage is less than or equal to the first cut-off voltage, the fourth voltage is less than the second voltage but greater than the third voltage, the third voltage is greater than or equal to the first voltage, and the first voltage is greater than or equal to the second cut-off voltage.

[0020] In one embodiment, dividing the plurality of battery cells into a plurality of gears according to the capacity data includes: dividing the plurality of battery cells into a plurality of gears according to the first capacity; dividing the plurality of battery cells of the same gear into a plurality of sub-grades according to the capacity data includes: dividing the plurality of battery cells of the same gear into a plurality of sub-grades according to the second capacity.

[0021] In one embodiment, the capacity difference between the battery cells in the same gear is less than or equal to Δ1, the capacity difference between the battery cells in the same sub-gear is less than or equal to Δ2, and Δ1 is greater than Δ2.

[0022] In one embodiment, the Δ1 is 2Ah to 4Ah, and the Δ2 is 0.5Ah to 1Ah.

[0023] In one embodiment, the first current is 0.3C to 0.5C; and / or,

[0024] The first cut-off voltage is 3.6V to 3.75V; and / or,

[0025] The first cut-off current is 0.02C to 0.05C; and / or,

[0026] The second current is 0.3C to 0.5C; and / or,

[0027] The second cut-off voltage is 2V to 2.5V.

[0028] In one embodiment, the method for reducing the voltage difference of the battery module further includes: after the charge and discharge process, recharging the battery cell so that the capacity increment of the battery cell reaches 30% to 50% of the rated capacity.

[0029] In one embodiment, the recharging process includes: charging the battery cell at a constant current of 0.2C to 0.4C for 60 minutes to 90 minutes.

[0030] In a second aspect, an embodiment of the present application further provides a battery pack, comprising a plurality of battery modules obtained according to the method for reducing the voltage difference of battery modules according to the first aspect, wherein the voltage difference of the battery modules is less than or equal to a preset value.

[0031] Beneficial effects of the embodiments of the present application:

[0032] In an embodiment of the present application, before the battery cells in the battery module are discharged, the battery cells in the battery module are first pre-charged. The pre-charging process increases the temperature of the battery cells in the battery module, thereby improving the temperature consistency between different battery cells. At the same time, after the temperature of the battery cells increases, the rate of change of the capacity of the battery cells will slow down, thereby reducing the impact of temperature on the pressure difference between the battery cells, thereby reducing the pressure difference of the battery module. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 is a flow chart of a method for reducing a battery module pressure difference provided in an embodiment of the present application;

[0035] Figure 2 It is a flow chart of the method for preparing a battery module provided by the implementation of this application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0037] In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0038] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0039] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0040] The terms "comprises," "includes," or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0041] In the description of the embodiments of the present application, words such as "example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "example" or "for example" in the embodiments of the present application is not to be interpreted as being more preferred or having more advantages than another embodiment or design. The use of words such as "example" or "for example" is intended to present relative concepts in a clear manner.

[0042] To facilitate understanding of the scheme of the present application, the spline curves and arrows used in the drawings are explained here: the components indicated by the spline curves without arrows are solid components, that is, components with solid structures; the components indicated by the spline curves with arrows are virtual components, that is, components without solid structures.

[0043] First, see Figure 1 , the embodiment of the present application provides a method for reducing the voltage difference of a battery module, comprising:

[0044] S1. Providing a battery module, wherein the battery module includes a plurality of electrically connected battery cells;

[0045] S2, pre-charging the cells in the battery module;

[0046] S3. Discharging the battery cells in the battery module, and obtaining the voltage difference between the battery cells in the battery module as the voltage difference of the battery module.

[0047] A battery module is also called a battery module. It is a unit composed of multiple cells (also called battery monomers). The cells can be electrically connected in series and / or in parallel. The battery module here is used to form a battery pack together with a BMS (Battery Management System), a cooling system, etc.

[0048] A battery pack generally includes multiple electrically connected battery modules. The voltage difference of the battery modules will affect the performance of the battery pack. Therefore, before assembling the battery modules into a battery pack, the battery modules are first screened, and the battery modules with too large voltage difference are removed, and the battery modules with smaller voltage difference are assembled into a battery pack, thereby improving the performance of the battery pack.

[0049] Specifically, sorting the battery modules includes: discharging the battery cells in the battery module, obtaining the pressure difference between the battery cells in the battery module as the pressure difference of the battery module, and screening the battery modules according to the pressure difference of the battery module. Screening the battery modules according to the pressure difference of the battery module includes: retaining the battery modules with a pressure difference less than or equal to a preset value, and eliminating the battery modules with a pressure difference greater than the preset value. The preset value here can be set according to the specific battery module, and the preset value may be different for different battery modules. As an example, obtaining the pressure difference between the battery cells in the battery module as the pressure difference of the battery module includes obtaining the maximum pressure difference or the average pressure difference between the battery cells in the battery module as the pressure difference of the battery module.

[0050] Since the battery module includes multiple cells, the capacity difference between the cells will affect the pressure difference between the cells and then the pressure difference of the battery module. The capacity of the cell is easily affected by temperature. As an example, the cell is a lithium iron phosphate cell. As the temperature of the cell rises, the capacity of the cell first increases and then tends to stabilize; when the temperature of the cell drops, the capacity of the cell decays rapidly, and the lower the temperature, the faster the rate of capacity decay of the cell. In the battery module, multiple cells are stacked and assembled together, and the cells in different positions have different degrees of contact with the environment. Therefore, the degree of influence of the ambient temperature on different cells is different, and the heat dissipation effect of different cells is different, resulting in a temperature difference between different cells, and then the pressure difference of the battery module increases. Especially in low temperature conditions, the pressure difference of the battery module is more obviously affected by the temperature, and the pressure difference is larger.

[0051] Based on this, the present application implements a pre-charging process on the battery cells in the battery module before discharging the battery cells in the battery module. The pre-charging process increases the temperature of the battery cells in the battery module, thereby improving the temperature consistency between different battery cells. At the same time, after the temperature of the battery cells increases, the rate of change of the capacity of the battery cells will slow down, thereby reducing the impact of temperature on the pressure difference between the battery cells, and thereby reducing the pressure difference of the battery module.

[0052] In some embodiments, in step S2, the pre-charging process causes the capacity increment of the battery cell to reach 5% to 20% of the rated capacity. Within this range, the temperature of the battery cell can be effectively increased while taking into account the production efficiency. As an example, the capacity increment is 5%, 10%, 15% or 20% of the rated capacity.

[0053] In some embodiments, in step S2, the pre-charging process includes: charging the battery cell with a constant current of 0.5C to 2C for 5 minutes to 20 minutes. By controlling the charging current and time during the pre-charging process, it is beneficial to improve production efficiency. As an example, in the pre-charging process, the constant current charging current is 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, 1.0C, 1.2C, 1.0C, 1.2C, 1.4C, 1.6C, 1.8C or 2C, and the charging time is 5 minutes, 10 minutes, 15 minutes or 20 minutes.

[0054] In some embodiments, see Figure 2 In step S1, providing a battery module includes a process of preparing a battery module, specifically including:

[0055] S11, providing multiple battery cells;

[0056] S12, performing charge and discharge processing on multiple battery cells to obtain capacity data of the battery cells;

[0057] S13, dividing the plurality of cells into a plurality of gears according to the capacity data;

[0058] S14, dividing multiple cells in the same gear into multiple sub-gears according to the capacity data;

[0059] S15, electrically connecting multiple battery cells of the same sub-level together to obtain a battery module.

[0060] By using the charge and discharge process to obtain the capacity data of the battery cells, and classifying the battery cells at least twice based on the capacity data, the battery cells with closer capacities are grouped to obtain battery modules, effectively reducing the voltage difference of the battery modules. Moreover, this method uses the capacity data of the battery cells obtained from the same charge and discharge process to sort the battery cells multiple times, which can effectively shorten the time consumption of the grouping process and improve the efficiency of battery production.

[0061] As an example, step S11 provides a plurality of battery cells, and in step S12, the plurality of battery cells are charged and discharged. In step S13, the plurality of battery cells are sorted once, and the plurality of battery cells are divided into a plurality of gears, and each gear includes a plurality of battery cells; step S14 sorts the plurality of battery cells in the same gear again, and divides the plurality of battery cells into a plurality of sub-gears, and each sub-gear also includes a plurality of battery cells. It should be noted here that a plurality refers to at least two, but the number represented by the different "pluralities" mentioned above is not necessarily equal. Exemplarily, step S11 provides 50 battery cells, and in step S12, the 50 battery cells are charged and discharged. In step S13, the 50 battery cells are sorted once, and the 50 battery cells are divided into 5 gears, and each gear includes 10 battery cells; step S14 sorts the 10 battery cells in the same gear again, and divides the 10 battery cells into 5 sub-gears, and each sub-gear includes 2 battery cells.

[0062] In some embodiments, the charge and discharge process includes: 11 The battery cell is charged with constant current to the first cut-off voltage V 11 , and then the first cut-off voltage V 11 The battery cell is charged at a constant voltage to the first cut-off current I 21 ; With the second current I 12 Discharge the battery cell with constant current to the second cut-off voltage V 12 , record the data of the voltage value of the battery cell changing with time during the discharge process. Usually the first current I 11 Greater than the first cut-off current I 21 , the first cut-off voltage V 11 Greater than the second cut-off voltage V 12By first charging the battery cell with a constant current, a larger current can be used for charging at this stage to improve the charging efficiency; then charging the battery cell with a constant voltage, during which the charging current can be gradually reduced to prevent the battery cell from being overcharged; after the battery cell is fully charged, the battery cell is discharged with a constant current, and the voltage and time of the battery cell during the discharge process are recorded to facilitate the subsequent calculation of the discharge capacity of the battery cell.

[0063] In some embodiments, during the charge and discharge process, the first current I 11 As an example, the first current I 11 It is 0.3C, 0.35C, 0.4C, 0.45C or 0.5C.

[0064] In some embodiments, during the charge and discharge process, the first cut-off voltage V 11 As an example, the first cut-off voltage V 11 3.6V, 3.65V, 3.7V or 3.75V.

[0065] In some embodiments, during the charge and discharge process, the first cut-off current I 21 is 0.02C to 0.05C. As an example, the first cut-off current I 21 It is 0.02C, 0.03C, 0.04C or 0.05C.

[0066] In some embodiments, during the charge and discharge process, the second current I 12 is 0.3C to 0.5C. As an example, the second current I 12 It is 0.3C, 0.35C, 0.4C, 0.45C or 0.5C.

[0067] In some embodiments, during the charge and discharge process, the second cut-off voltage V 12 As an example, the second cut-off voltage V 12 It is 2.0V, 2.1V, 2.2V, 2.3V, 2.4V or 2.5V.

[0068] In some embodiments, the charge and discharge process can be performed at room temperature, low temperature or high temperature. Here, low temperature and high temperature are relative to room temperature, a temperature higher than room temperature is high temperature, and a temperature lower than room temperature is low temperature.

[0069] In some embodiments, the charge and discharge process further includes placing the battery cell on hold. Specifically, placing the battery cell on hold after charging and before discharging. The time for placing the battery cell on hold, i.e., the placing time, is 2 min to 10 min. As an example, the placing time is 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min.

[0070] As an example, the charge and discharge process of the battery cell specifically includes: charging the battery cell at a constant current of 0.5C to 3.65V at 25°C, and then charging the battery cell at a constant voltage of 3.65V to 0.03C; leaving the battery cell at 25°C for 5 minutes; discharging the battery cell at a constant current of 0.5C to 2V at 25°C.

[0071] In some embodiments, a capacity division device, such as a capacity division cabinet, is used to charge and discharge the battery cells. The capacity division device can be used to monitor the parameters of the battery cells in the capacity division process in real time, including but not limited to temperature, current, voltage, etc.

[0072] In some embodiments, the capacity data includes a first capacity C 1 and the second capacity C 2 , the first capacity is C 1 The cell is at a first voltage V 21 To the second voltage V 22 Discharge capacity within the range, the second capacity C 2 The cell is at the third voltage V 23 To the fourth voltage V 24 The discharge capacity within the range, the second voltage V 22 Less than or equal to the first cut-off voltage V 11 , the fourth voltage V 24 is less than the second voltage V 22 But greater than the third voltage V 23 , the third voltage V 23 Greater than or equal to the first voltage V 21 , the first voltage V 21 Greater than or equal to the second cut-off voltage V 12 . Since the data of the voltage value of the battery cell changing with time is recorded during the discharge process, the corresponding time point can be determined by the voltage of the battery cell, and the corresponding discharge time can be obtained for the determined voltage interval. When the battery cell is discharged in a constant current manner, the discharge capacity of the battery cell is equal to the product of the discharge current and the discharge time. During the constant current discharge process of the battery cell, the SOC (State of Charge) of the battery cell decreases, the voltage value of the battery cell will gradually decrease, and the polarization will increase. The first cut-off voltage V 11 Also commonly called the upper limit voltage, the second cut-off voltage V 12 Also called the lower limit voltage, where V11 ≥V 22 >V 24 >V 23 ≥V 21 ≥V 12 . First capacity C 1 The cell is provided with a first voltage V 21 Discharge to the second voltage V 22 The discharge capacity at the time, the second capacity C 2 The cell is provided with a third voltage V 23 Discharge to the fourth voltage V 24 The discharge capacity at this time can be understood that the first capacity C 1 and the second capacity C 2 The discharge capacity corresponding to different discharge intervals. Since the polarization degree of the battery cell is different under different discharge voltages, the embodiment of the present application uses the first voltage V 21 To the second voltage V 22 The discharge capacity and the third voltage V 23 To the fourth voltage V 24 The discharge capacity during the discharge period is divided into multiple grades for the battery cell, which can effectively reduce the voltage difference problem caused by polarization.

[0073] In some embodiments, the first capacity C can be directly obtained from the capacity division device. 1 and the second capacity C 2 .

[0074] In some embodiments, the fourth voltage V 24 As an example, the fourth voltage V 24 It is 2.0V, 2.01V, 2.1V, 2.2V, 2.3V, 2.4V, 2.5V, 2.6V or 2.7V.

[0075] In some embodiments, the second voltage V 22 Equal to the first cut-off voltage V 11 , the first voltage V 21 Equal to the second cut-off voltage V 12 , then the first capacity C 1 is the discharge capacity of the cell from the upper limit voltage to the lower limit voltage, the second capacity C 2 It corresponds to the discharge capacity of the battery cell at low SOC.

[0076] In some embodiments, the plurality of cells are divided into a plurality of gears according to the capacity data, including: according to the first capacity C 1 Divide multiple cells into multiple gears; divide multiple cells in the same gear into multiple sub-gears according to capacity data, including: according to the second capacity C 2Divide multiple cells in the same gear into multiple sub-gears. 22 >V 24 >V 23 ≥V 21 , the first voltage V 21 To the second voltage V 22 The discharge time of the discharge interval is greater than the third voltage V 23 To the fourth voltage V 24 The discharge time of the discharge interval, the first capacity C 1 Greater than the second capacity C 2 , but the polarization has a great influence on the second capacity C 2 The impact is greater than that on the first capacity C 1 The effect of this is therefore achieved by utilizing the first capacity C 1 First, the battery cells are divided into different classes, and then the second capacity C is used. 2 Secondary grading of battery cells can effectively reduce the phenomenon of large module voltage difference due to large polarization when the battery cells are discharged at low SOC after forming a battery module.

[0077] In the embodiments of the present application, a plurality of gears refers to at least two. A plurality of gears refers to at least two gears, for example, two gears, three gears, four gears, five gears, six gears, ten gears or twenty gears. A plurality of sub-gears refers to at least two sub-gears, for example, two sub-gears, three sub-gears, four sub-gears, five sub-gears, six sub-gears, ten sub-gears or twenty sub-gears. Here, dividing the sub-gears refers to further dividing the same gear into smaller levels.

[0078] In some embodiments, the capacity difference between the cells in the same gear is less than or equal to Δ1, the capacity difference between the cells in the same sub-gear is less than or equal to Δ2, and Δ1 is greater than Δ2. By sorting the cells step by step, the capacity difference between the cells in the same group is continuously reduced, thereby reducing the voltage difference of the battery module. As an example, according to the first capacity C 1 The multiple cells are divided into three levels, namely, level A, level B, and level C. The capacity difference between the cells in level A is less than or equal to Δ1. Similarly, the cells in levels B and C also follow this principle. 2 Divide the multiple cells in the A gear into two sub-gears, namely: a 1 Sub-gear and a 2 Sub-gear, divide the multiple cells in gear B into three sub-gears, namely: b 1 Sub-gear, b 2 Sub-gear and b 3 Sub-gear, divide the multiple cells in C gear into two sub-gears, namely: C 1 Sub-gear and c2 Sub-gear, where a 1 The capacity difference between the cells in the sub-level is less than or equal to Δ2. Similarly, a 2 Sub-gear, b 1 Sub-gear, b 2 Sub-gear, b 3 Sub-gear, c 1 Sub-gear and c 2 The sub-level battery cells also follow this principle.

[0079] In some embodiments, Δ1 is 2Ah to 4Ah, and Δ2 is 0.5Ah to 1Ah. As an example, Δ1 is 2Ah, 2.1A, 2.2A, 2.3A, 2.4A, 2.5A, 2.6A, 2.7A, 2.8A, 2.9A, 3Ah, 3.1A, 3.2A, 3.3A, 3.4A, 3.5A, 3.6A, 3.7A, 3.8A, 3.9A or 4Ah, and Δ2 is 0.5Ah, 0.6Ah, 0.7Ah, 0.8Ah, 0.9A or 1Ah.

[0080] In some embodiments, according to the first capacity C 1 When multiple cells are divided into multiple gears, cells that do not meet the capacity requirements are also removed, such as giving up the first capacity C 1 Oversized or undersized battery cells.

[0081] In some embodiments, the method for reducing the voltage difference of the battery module further includes: after the charge and discharge process, recharging the battery cell so that the capacity increment of the battery cell reaches 30% to 50% of the rated capacity. As an example, the capacity increment is 30%, 35%, 40%, 45% or 50% of the rated capacity. By recharging the battery cell, the capacity of the battery cell is increased to ensure that the battery cell has electricity to discharge when the battery module is discharged.

[0082] In some embodiments, the recharging process includes: charging the battery cell with a constant current of 0.2C to 0.4C for 60 minutes to 90 minutes. As an example, in the recharging process, the constant current charging current is 0.2C, 0.25C, 0.3C, 0.35C or 0.4C, and the charging time is 60 minutes, 70 minutes, 80 minutes or 90 minutes.

[0083] In a second aspect, an embodiment of the present application further provides a battery pack, comprising a plurality of battery modules obtained by adopting the above-mentioned method of reducing the voltage difference of the battery modules, wherein the voltage difference of the battery modules is less than or equal to a preset value.

[0084] Since the voltage difference of the battery module is small, it is beneficial to improve the performance of the battery pack.

[0085] In a third aspect, an embodiment of the present application further provides a method for preparing a battery pack, comprising:

[0086] A battery module is obtained by adopting the above method for reducing the voltage difference of a battery module, and the voltage difference of the battery module is less than or equal to a preset value; and a plurality of battery modules are electrically connected to obtain a battery pack.

[0087] Since the voltage difference of the battery module is small, it is beneficial to improve the performance of the battery pack.

[0088] The following is a description with reference to specific embodiments.

[0089] Example 1

[0090] S01. Use the capacity distribution cabinet to charge and discharge 256 lithium iron phosphate cells: charge the cells to 3.65V at a constant current of 0.5C, and then charge the cells to 0.03C at a constant voltage of 3.65V; leave for 5 minutes, and then discharge the cells to 2.0V at a constant current of 0.5C;

[0091] S02, obtaining the discharge capacity C1 of the battery cell in the range of 2.0V to 3.65V and the discharge capacity C2 in the range of 2.0V to 2.7V;

[0092] S03, dividing the battery cells into 4 levels according to the discharge capacity C1, and the capacity difference between the battery cells in the same level is less than or equal to 4Ah;

[0093] S04, dividing the lithium iron phosphate battery cells of the same level into 4 sub-levels according to the size of the discharge capacity C2, and the capacity difference between the battery cells of the same sub-level is less than or equal to 0.5Ah;

[0094] S05. Electrically connect multiple battery cells of the same sub-level to obtain a battery module, wherein the battery module includes 16 battery cells.

[0095] S06, a process of pre-charging the battery module: charging the cells in the battery module at a constant current of 2C for 5 minutes;

[0096] S07. The process of first discharge and screening of the battery module: discharge the cells in the battery module at a constant current of 0.5C to 2.5V, collect the voltage difference between the cells in the battery module (the voltage difference can be directly read from the test instrument), take the average value of the obtained voltage difference as the voltage difference of the battery module, and record the results in Table 1. The voltage difference ≤ 200mV is qualified.

[0097] S08. Prepare qualified battery modules into battery packs.

[0098] Example 2

[0099] The difference from Example 1 is that there is no S04, and S05 is to electrically connect the 16 battery cells of the same gear together to obtain a battery module.

[0100] Comparative Example 1

[0101] The difference from Example 1 is that there is no S06.

[0102] Comparative Example 2

[0103] The difference from Example 1 is that there is no S04 and S06, and S05 is to electrically connect the 16 battery cells of the same level together to obtain a battery module.

[0104] Table 1

[0105] Group Voltage difference of battery module Example 1 185mV Example 2 195mV Comparative Example 1 221mV Comparative Example 2 233mV

[0106] It can be seen from Table 1 that the voltage difference of the battery modules provided by Example 1 and Example 2 is less than 200mV, and the voltage difference of the battery modules provided by Comparative Example 1 and Comparative Example 2 is greater than 200mV. It can be seen that the battery cells in the battery module can effectively reduce the voltage difference of the battery module after pre-charging treatment; in addition, it can be seen from the comparison between Example 1 and Example 2 that, compared with the battery cells being sorted only once, the voltage difference of the battery module obtained by sorting the battery cells after secondary grading is lower.

[0107] The embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for reducing the voltage difference of a battery module, characterized in that: include: Providing a battery module, the battery module comprising a plurality of electrically connected battery cells; Pre-charging the battery cells in the battery module; The battery cells in the battery module are discharged, and the voltage difference between the battery cells in the battery module is obtained as the voltage difference of the battery module.

2. The method for reducing the voltage difference of a battery module according to claim 1, characterized in that: The pre-charging process enables the capacity increment of the battery cell to reach 5% to 20% of the rated capacity.

3. The method for reducing the voltage difference of a battery module according to claim 1, characterized in that: The pre-charging process includes: charging the battery cell with a constant current of 0.5C to 2C for 5 minutes to 20 minutes.

4. The method for reducing the voltage difference of a battery module according to any one of claims 1 to 3, characterized in that: The battery module provided comprises: Provide multiple battery cells; Performing charge and discharge processing on the plurality of battery cells to obtain capacity data of the battery cells; Dividing the plurality of battery cells into a plurality of gears according to the capacity data; Dividing the plurality of cells in the same gear into a plurality of sub-gears according to the capacity data; A plurality of the battery cells of the same sub-level are electrically connected together to obtain a battery module.

5. The method for reducing the voltage difference of a battery module according to claim 4, characterized in that: The charge and discharge process comprises: The battery cell is charged at a constant current to a first cut-off voltage using a first current, and then the battery cell is charged at a constant voltage to a first cut-off current using the first cut-off voltage; The battery cell is discharged at a constant current with a second current to a second cut-off voltage, and data of the voltage value of the battery cell changing with time during the discharge process is recorded.

6. The method for reducing the voltage difference of a battery module according to claim 5, characterized in that: The capacity data includes a first capacity and a second capacity, the first capacity is the discharge capacity of the battery cell within a range of a first voltage to a second voltage, the second capacity is the discharge capacity of the battery cell within a range of a third voltage to a fourth voltage, the second voltage is less than or equal to the first cut-off voltage, the fourth voltage is less than the second voltage but greater than the third voltage, the third voltage is greater than or equal to the first voltage, and the first voltage is greater than or equal to the second cut-off voltage.

7. The method for reducing the voltage difference of a battery module according to claim 6, characterized in that: The dividing the plurality of battery cells into a plurality of gears according to the capacity data comprises: dividing the plurality of battery cells into a plurality of gears according to the first capacity; The dividing the plurality of battery cells of the same gear into a plurality of sub-grades according to the capacity data includes: dividing the plurality of battery cells of the same gear into a plurality of sub-grades according to the second capacity.

8. The method for reducing the voltage difference of a battery module according to claim 7, characterized in that: The capacity difference between the battery cells in the same gear is less than or equal to Δ1, the capacity difference between the battery cells in the same sub-gear is less than or equal to Δ2, and Δ1 is greater than Δ2.

9. The method for reducing the voltage difference of a battery module according to claim 8, characterized in that: The Δ1 is 2Ah to 4Ah, and the Δ2 is 0.5Ah to 1Ah.

10. The method for reducing the voltage difference of a battery module according to claim 5, characterized in that: The first current is 0.3C to 0.5C; and / or, The first cut-off voltage is 3.6V to 3.75V; and / or, The first cut-off current is 0.02C to 0.05C; and / or, The second current is 0.3C to 0.5C; and / or, The second cut-off voltage is 2V to 2.5V.

11. The method for reducing the voltage difference of a battery module according to claim 5, characterized in that: The method further comprises: after the charge and discharge process, performing a recharging process on the battery cell so that the capacity increment of the battery cell reaches 30% to 50% of the rated capacity.

12. The method for reducing the voltage difference of a battery module according to claim 11, characterized in that: The recharging process includes: charging the battery cell at a constant current of 0.2C to 0.4C for 60 minutes to 90 minutes.

13. A battery pack, characterized in that: Comprising a plurality of battery modules obtained according to the method for reducing the pressure difference of a battery module according to any one of claims 1 to 12, wherein the pressure difference of the battery modules is less than or equal to a preset value.

Images