Lithium ion battery pack and discharge curve fitting matching method and system thereof

Abstract

The invention provides a lithium ion battery pack and a discharge curve fitting matching method and system thereof, and relates to the technical field of lithium ion battery packs, and the method comprises the following steps: S1, obtaining discharge voltage data of each single battery; s2, based on the discharge voltage data of each single battery, obtaining a discharge voltage curve of integration of a plurality of batteries; s3, in the discharge voltage curve integrated by the plurality of batteries, based on the cut-off voltage V0 of constant-current discharge, selecting the battery with the minimum capacity C0 as a base point; s4, recording corresponding voltages when the capacities of other batteries are C0 based on a discharge voltage curve integrated by the plurality of batteries; s5, according to the set dynamic voltage difference delta V, calculating the highest voltage V1 in the selected multiple batteries used for matching; and S6, on the basis of the calculated maximum voltage V1, obtaining a characteristic voltage range of V0-V1, and grouping the batteries of which the corresponding voltage is within the characteristic voltage range when the capacity is C0.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery packs, and in particular to a lithium-ion battery pack, a method and a system for fitting and matching the discharge curve thereof. Background Art

[0002] Due to its high energy density and long cycle life characteristics, lithium-ion batteries are widely used in various fields such as electric vehicles and energy storage systems. However, the consistency problem of lithium-ion batteries directly affects the performance and service life of the batteries. Battery manufacturers combine batteries with similar electrochemical characteristics through a matching method to ensure the stable performance and safety reliability of the battery pack.

[0003] The existing battery matching methods mainly measure the capacity, internal resistance, and voltage of the batteries, and then group the batteries according to these parameters. However, there are some problems and limitations in the existing battery matching methods. First, the traditional capacity and internal resistance grading methods often cannot accurately reflect the electrochemical characteristics of the batteries, ignoring the dynamic behavior of the batteries under different working conditions. Moreover, the capacity data measured by the traditional capacity and internal resistance grading methods has great instability, resulting in inconsistent measurement results each time, which affects the accuracy of the grouping results. Second, although the matching method based on the discharge voltage curve can consider the dynamic behavior of the batteries, it requires a large amount of data processing and complex calculations, which is unrealistic in actual production.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium-ion battery pack, a method and a system for fitting and matching the discharge curve thereof. The matching method of the present invention based on the discharge voltage curve converts curve fitting into characteristic voltage for matching, which can not only reflect the electrochemical characteristics of the batteries, does not depend on static parameters such as capacity and internal resistance, but also can efficiently match the batteries based on the discharge voltage curve, avoiding a large amount of data processing and complex calculations.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for fitting and matching the discharge curve of a lithium-ion battery, including the following steps:

[0008] S1: First, charge multiple lithium-ion batteries of the same model with constant current and constant voltage, and then perform a constant current discharge test. Discharge at a constant current until the cut-off voltage V 0 , and collect the voltage during the discharge process at fixed time intervals to obtain the discharge voltage data of each single battery.

[0009] S2: Based on the discharge voltage data of each single battery obtained in step S1, with the discharge capacity as the abscissa and the voltage as the ordinate, plot the discharge voltage curve of each single battery, and integrate the discharge voltage curves of each single battery in the same coordinate system to obtain the integrated discharge voltage curve of multiple batteries;

[0010] S3: Among the integrated discharge voltage curves of multiple batteries obtained in step S2, based on the cut-off voltage V of constant current discharge 0 , select the battery with the smallest capacity as the base point, and denote the capacity of the battery with the smallest capacity as C 0 ;

[0011] S4: Based on the integrated discharge voltage curve of multiple batteries obtained in step S2, record the voltage corresponding to the capacity C of other batteries 0 ;

[0012] S5: According to the set dynamic pressure difference ΔV, calculate the highest voltage V of the selected multiple batteries for grouping 1 = V 0 + ΔV;

[0013] S6: Based on the calculated highest voltage V 1 , obtain the characteristic voltage range of V 0 ~ V 1 , and group the batteries whose voltage corresponding to the capacity C 0 is within the characteristic voltage range.

[0014] Further, on the basis of the above technical solution, in step S1, the lithium-ion battery is one of a lithium iron phosphate lithium battery, a ternary lithium-ion battery, a lithium cobalt oxide lithium-ion battery, and a lithium manganese oxide lithium-ion battery.

[0015] Further, on the basis of the above technical solution, in step S1, the constant current and constant voltage charging means charging multiple lithium-ion batteries of the same model at a constant current of 0.5C to 3.65 - 4.2V, and then charging at a constant voltage of 3.65 - 4.2V until the cut-off current of 0.02C.

[0016] Further, on the basis of the above technical solution, in step S1, the discharge current of the constant current discharge test is 0.2 - 1C.

[0017] Further, on the basis of the above technical solution, in step S1, the discharge cut-off voltage of the constant current discharge test is 2.5 - 3V.

[0018] Further, on the basis of the above technical solution, the fixed time interval is 1 - 5s.

[0019] Further, on the basis of the above technical solution, the ΔV is 50 - 300mV.

[0020] The present invention also provides a lithium-ion battery discharge curve fitting and matching system, which is used to execute the lithium-ion battery discharge curve fitting and matching method as described above.

[0021] Further, on the basis of the above technical solution, the system includes a grading control module, a data processing module and a matching module;

[0022] The grading control module is used to control each lithium-ion battery cell to be fully charged in a constant current and constant voltage manner, and then discharge each lithium-ion battery cell to the cut-off voltage in a constant current manner;

[0023] The data processing module is used to collect the discharge voltage data of each single battery at different time points and form a discharge voltage curve of multiple integrated batteries, and then determine the minimum capacity C corresponding to the cut-off voltage V 0 when based on the discharge voltage curve of multiple integrated batteries, and then obtain the voltage value corresponding to each battery when the capacity is C 0 ; based on the set dynamic voltage difference ΔV, calculate the highest voltage value V corresponding to the batteries that can be used for matching when the capacity is C 0 ; 0 when 1 ;

[0024] The matching module is used to determine the batteries whose voltage values corresponding to the capacity C 0 are within the characteristic voltage range V 0 ~V 1 and use them as the batteries for matching.

[0025] The present invention also provides a lithium-ion battery pack, which is matched by using the lithium-ion battery discharge curve fitting and matching method or the lithium-ion battery discharge curve fitting and matching system as described above.

[0026] A lithium-ion battery pack, its discharge curve fitting and matching method and system provided by the present invention have the following beneficial effects:

[0027] 1. More accurate battery matching: By selecting the discharge voltage curves of multiple lithium batteries and grouping them in a specific manner, the present invention can more accurately reflect the electrochemical characteristics of the batteries, thereby improving the accuracy of battery matching and ensuring the stable performance, safety and reliability of the battery pack.

[0028] 2. Simplified grouping process: Compared with the existing battery grouping methods, the present invention does not require measuring the capacity and internal resistance of the batteries. Instead, it only groups the batteries according to the discharge voltage curves, greatly simplifying the grouping process and improving the production efficiency. Generally speaking, compared with the prior art, the present invention can not only more accurately reflect the electrochemical characteristics of the batteries, improve the accuracy of battery grouping, but also simplify the grouping process, cancel the internal resistance and capacity grading grouping, and improve the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It is the discharge voltage curve diagram integrated by 20 batteries provided in Embodiment 1 of the present invention;

[0031] Figure 2 It is the discharge voltage curve diagram of 20 batteries in the battery pack in Verification Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0033] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0034] According to the first aspect of the present invention, a method for fitting and grouping the discharge curves of lithium-ion batteries is provided, including the following steps:

[0035] S1: First, charge multiple lithium-ion batteries of the same model with constant current and constant voltage, and then conduct a constant current discharge test, and discharge at a constant current until the cut-off voltage V0 During a fixed time interval, the voltage of the discharging process is collected to obtain the discharging voltage data of each single battery.

[0036] S2: Based on the discharging voltage data of each single battery obtained in step S1, with the discharging capacity as the abscissa and the voltage as the ordinate, plot the discharging voltage curve of each single battery, and integrate the discharging voltage curves of each single battery in the same coordinate system to obtain the integrated discharging voltage curve of multiple batteries.

[0037] S3: In the integrated discharging voltage curve of multiple batteries obtained in step S2, based on the cut-off voltage V of the constant current discharge 0 , select the battery with the smallest capacity as the base point, and denote the capacity of the battery with the smallest capacity as C 0 .

[0038] S4: Based on the integrated discharging voltage curve of multiple batteries obtained in step S2, record the voltages corresponding to the capacities of other batteries being C 0 .

[0039] S5: According to the set dynamic voltage difference ΔV, calculate the highest voltage V of the multiple batteries selected for grouping 1 = V 0 + ΔV.

[0040] S6: Based on the calculated highest voltage V 1 , obtain the characteristic voltage range of V 0 to V 1 , and group the batteries whose voltages corresponding to the capacity of C 0 are within the said characteristic voltage range.

[0041] Specifically, the present invention uses the curve fitting method to simulate the change of the dynamic voltage difference during the discharging process of the battery pack. The dynamic voltage difference ΔV can be an important indicator to measure the performance difference of each single battery in the battery pack. The smaller the dynamic voltage difference ΔV, the better the consistency of the voltage change of each single battery in the battery pack during the charge and discharge process, thus ensuring the overall high efficiency and long life of the battery pack. The present invention can select or set an appropriate dynamic voltage difference ΔV according to the actual grouping requirements, convert the simulated voltage curve into a characteristic voltage range of V 0 to V 1 for grouping, and usually the dynamic voltage difference ΔV ≤ 300 mV.

[0042] Furthermore, through the obtained characteristic voltage range of V 0 to V 1 , the present invention can group multiple batteries, and the batteries whose voltages corresponding to the capacity of C 0 are within the characteristic voltage range of V 0 to V 1Multiple batteries within a certain range are sorted into a group. The multiple batteries within this group have similar electrochemical characteristics. When connecting the multiple batteries in series to form a battery pack, the stability, safety, and reliability of the battery pack can be ensured.

[0043] As an optional implementation manner of the present invention, in step S1, the lithium-ion battery is one of a lithium iron phosphate lithium battery, a ternary lithium-ion battery, a lithium cobalt oxide lithium-ion battery, and a lithium manganese oxide lithium-ion battery.

[0044] As an optional implementation manner of the present invention, in step S1, the constant current and constant voltage charging means charging multiple lithium-ion batteries of the same model at a constant current of 0.5C to 3.65 - 4.2V (such as 3.7V, 3.8V, 3.9V, 4.0V, 4.1V, etc.), and then charging at a constant voltage of 3.65 - 4.2V until the cut-off current is 0.02C.

[0045] Specifically, when selecting a lithium iron phosphate lithium battery for grouping, it is generally controlled to be charged at a constant current of 0.5C to 3.65V. When selecting a ternary lithium-ion battery, a lithium cobalt oxide lithium-ion battery, or a lithium manganese oxide lithium-ion battery for grouping, it is generally controlled to be charged at a constant current of 0.5C to 4.2V.

[0046] As an optional implementation manner of the present invention, in step S1, the temperature of the constant current and constant voltage charging and the constant current discharge test is room temperature.

[0047] As an optional implementation manner of the present invention, in step S1, the discharge current of the constant current discharge test is 0.2 - 1C (such as 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, etc.).

[0048] The discharge cut-off voltage V in the present invention 0 The specific selection can be determined according to the lithium battery material, battery design, and usage environment. As an optional implementation manner of the present invention, in step S1, the discharge cut-off voltage of the constant current discharge test is 2.5 - 3V (such as 2.6V, 2.7V, 2.8V, 2.9V, etc.). Specifically, when selecting a lithium iron phosphate lithium battery for grouping, its discharge cut-off voltage is generally controlled to be 2.5V. When selecting a ternary lithium-ion battery, a lithium cobalt oxide lithium-ion battery, or a lithium manganese oxide lithium-ion battery for grouping, its discharge cut-off voltage is generally controlled to be 3V.

[0049] As an optional implementation manner of the present invention, in step S1, the fixed time interval is 1 - 5s (such as 2s, 3s, 4s, etc.).

[0050] As an optional implementation manner of the present invention, in step S4, ΔV is 50 - 300mV (such as 100mV, 150mV, 200mV, 250mV, etc.).

[0051] Specifically, according to actual requirements, when the consistency requirement for the battery pack is relatively high, ΔV can be 50 mV, and the obtained characteristic voltage range of the battery pack can be 2.5 V - 2.55 V; or when ΔV = 100 mV, the obtained characteristic voltage range of the battery pack can be 2.5 V - 2.6 V; and so on. When ΔV = 150 mV, the obtained characteristic voltage range of the battery pack can be 2.5 V - 2.65 V; when ΔV = 200 mV, the obtained characteristic voltage range of the battery pack can be 2.5 V - 2.7 V; when ΔV = 250 mV, the obtained characteristic voltage range of the battery pack can be 2.5 V - 2.75 V.

[0052] According to the second aspect of the present invention, there is provided a lithium-ion battery discharge curve fitting and matching system, and the system is implemented by using the lithium-ion battery discharge curve fitting and matching method as described above.

[0053] As an optional implementation manner of the present invention, the system includes a formation control module, a data processing module, and a matching module;

[0054] The formation control module is configured to control each lithium-ion battery cell to be fully charged in a constant current and constant voltage manner, and then discharge each lithium-ion battery cell to the cut-off voltage in a constant current manner;

[0055] The data processing module is configured to collect the discharge voltage data of each single battery at different time points and form a discharge voltage curve integrated by multiple batteries, and then determine the minimum capacity C corresponding to the cut-off voltage V 0 when 0 based on the discharge voltage curve integrated by multiple batteries, and then obtain the voltage value corresponding to each battery when the capacity is C 0 ; based on the set dynamic voltage difference ΔV, calculate the highest voltage value V 0 corresponding to the battery that can be used for matching when the capacity is C 1 ;

[0056] The matching module is configured to determine the batteries whose voltage values corresponding to the capacity C 0 are within the characteristic voltage range V 0 ~V 1 and use them as the batteries for matching.

[0057] According to the third aspect of the present invention, there is provided a lithium-ion battery pack, and the battery pack is matched by using the lithium-ion battery discharge curve fitting and matching method or the lithium-ion battery discharge curve fitting and matching system as described above.

[0058] The present invention will be further described in detail below with specific embodiments and comparative examples.

[0059] Example 1

[0060] This example provides a method for matching 100,000 mAh lithium iron phosphate square aluminum shell batteries:

[0061] S1: First, 20 lithium-ion batteries of the same model and with a capacity of 100,000 mAh are charged at a constant current and constant voltage at room temperature. They are charged at a constant current of 0.5C to 3.65V, and then charged at a constant voltage of 3.65V until the cut-off current of 0.02C; then a constant current discharge test is carried out, the discharge current is 1C, and the constant current discharge is carried out until the cut-off voltage V 0 = 2.5V, and the voltage of the battery is recorded every 1 second to obtain the discharge voltage data of each single battery;

[0062] S2: Based on the discharge voltage data of each single battery obtained in step S1, with the discharge capacity as the abscissa and the voltage as the ordinate, draw the discharge voltage curve of each single battery, and integrate the discharge voltage curves of each single battery in the same coordinate system to obtain as Figure 1 shown in the integrated discharge voltage curve of 20 batteries;

[0063] S3: In the integrated discharge voltage curve of 20 batteries shown in Figure 1 , based on the cut-off voltage V 0 = 2.5V of the constant current discharge, select the battery with the smallest capacity as the base point, and record the capacity of the battery with the smallest capacity as C 0 ;

[0064] Figure 1 In, C 0 is approximately 105,000 mAh, and V 0 is 2.500V, that is, the 19th battery;

[0065] S4: Based on the integrated discharge voltage curve of multiple batteries obtained in step S2, record the corresponding voltage when the capacity of other batteries is C 0 ;

[0066] According to Figure 1 , the voltage data corresponding to each single battery with a capacity of 105,000 mAh is shown in Table 1:

[0067] Table 1

[0068]

[0069]

[0070] In Table 1, the 19th battery is the battery with the smallest capacity. Taking it as the base point, the voltage of the 19th battery is the lowest voltage, that is, the cut-off voltage V 0= 2.500V = 2500mV, the voltage of the 20th battery is the highest voltage V 1 = 2.825V = 2825mV;

[0071] S5: In this embodiment, the selected known dynamic pressure difference ΔV = 300mV is used to calculate the highest voltage V among the selected multiple batteries 1 = V 0 + ΔV = 2.8V;

[0072] S6: Based on the calculated highest voltage V 1 = V 0 + ΔV = 2.8V, a characteristic voltage range of 2.5V - 2.8V is obtained. Batteries with voltages corresponding to a capacity of 105000mAh within the characteristic voltage range are grouped:

[0073] The voltages of the 1st - 19th batteries are all within the characteristic voltage range of 2.5V - 2.8V, indicating that these 1st - 19th batteries can be divided into a group. Within the group, the voltage of the 19th battery is the lowest voltage of 2.500V, and the voltage of the 13th battery is the highest voltage of 2.762V; the 20th battery is not within the characteristic voltage range of 2.5V - 2.8V and cannot be grouped with the 1st - 19th batteries.

[0074] Figure 1 Among them, the voltages of the 1st - 19th batteries are all within the characteristic voltage range of 2.5V - 2.8V, indicating that these 1st - 19th batteries can be divided into a group.

[0075] Verification Example 1

[0076] First of all, it should be noted that: The battery pack is equipped with a BMS (Battery Management System), that is, a battery management system. During the charging and discharging process of the battery, the terminal voltage, temperature, charging and discharging current, and the total voltage of the battery pack of each battery in the battery pack are collected in real time to prevent the battery from overcharging or over-discharging. At the same time, it can timely give the battery status, select the problematic batteries, and maintain the reliability and efficiency of the operation of the entire battery pack, making it possible to realize the remaining power estimation model. In addition, a usage history file of each battery needs to be established to provide data for further optimizing and developing new batteries, chargers, motors, etc., and to provide a basis for offline analysis of system failures.

[0077] The 1st - 19th batteries selected in Example 1 are made into a 1 - in - 19 - series battery pack. The battery pack is first charged at a constant current of 0.2C to 69.35V (3.65V × 19), and then a constant current discharge test is carried out at room temperature. The discharge current is 1C, and the cut-off voltage is 47.5V (2.5V × 19). The voltage of each single battery in the battery pack is recorded every 1 second, and the real-time monitoring obtains the voltage of each single battery in the battery pack as shown in Table 2:

[0078] Table 2

[0079] Serial number 1 2 3 4 5 6 7 8 9 10 Voltage (V) 2.628 2.660 2.596 2.737 2.590 2.695 2.615 2.656 2.648 2.697 Serial number 11 12 13 14 15 16 17 18 19 - Voltage (V) 2.676 2.724 2.778 2.653 2.771 2.722 2.638 2.666 2.500 -

[0080] The BMS system detected that the voltage of the 19th battery reached 2.5V, stopped discharging, and the discharging ended. At this time, the discharging capacity of the battery pack was 104,200 mAh.

[0081] As shown in Table 2, the voltage of the 19th battery was the lowest voltage V 0 = 2.500V = 2500 mV, and the voltage of the 13th battery was the highest voltage V 1 = 2.778V = 2779 mV, which was consistent with the results that the lowest voltage corresponded to the 19th and the highest voltage corresponded to the 13th in the grouping of Example 1; moreover, the difference between the maximum voltage in Table 2 and the maximum voltage in Table 1 was only 0.017V, indicating that the matching method provided in Example 1 of the present invention had high consistency.

[0082] The voltage of each single battery in the battery pack shown in Table 2 was plotted as a Figure 2 discharge voltage curve of the 1st - 19th batteries in the battery pack as shown, which was basically consistent with the Figure 1 integrated discharge voltage curve of the 1st - 19th batteries in, further indicating that the matching method provided in Example 1 of the present invention had high consistency and high accuracy.

[0083] Comparative Example 1

[0084] This comparative example provides a conventional matching method for a 100,000 mAh lithium iron phosphate square aluminum shell battery:

[0085] S1: Twenty lithium - ion batteries of the same model and with a capacity of 100,000 mAh each (the 20 lithium - ion batteries in Comparative Example 1 were obtained by disassembling the battery pack in Verification Example 1) were first charged at a constant current and constant voltage at room temperature. They were charged at a constant current of 0.5C to 3.65V, and then charged at a constant voltage of 3.65V until the cut - off current of 0.02C; then a constant - current discharge test was carried out, the discharge current was 1C, and the constant - current discharge was carried out until the cut - off voltage V 0 = 2.5V, and the voltage of the battery was recorded every 1 second to obtain the discharge capacity data of each single battery;

[0086] S2: Based on the discharge capacity data of each single battery obtained in step S1, with the discharge capacity as the abscissa and the voltage as the ordinate, the discharge capacity curve of each single battery was plotted, and the discharge voltage curves of each single battery were integrated in the same coordinate system to obtain the integrated discharge capacity curve of 20 batteries (the Figure 1 same as the shown discharge voltage curve);

[0087] S3: In Figure 1Among the discharge capacity curves of the integrated 20 batteries shown, based on the cut-off voltage V of constant current discharge 0 = 2.5V, record the capacity data corresponding to other batteries at the cut-off voltage V 0 = 2.5V;

[0088] Figure 1 Among them, the capacity of the battery with the smallest capacity is 105093.9 mAh, that is, the 19th battery;

[0089] Table 3

[0090]

[0091] S5: In this comparative example, the capacity matching is carried out according to the dynamic capacity difference ≤ 1500 mAh, that is, the capacity range of 105000 - 106500 mAh is divided into a group. As shown in Table 3, the maximum capacity of the 13th battery is 106259.1 mAh, and the minimum capacity of the 19th battery is 105093.9 mAh;

[0092] Since the internal resistance of the battery has a great influence on the voltage, if the internal resistances of the individual batteries in the battery pack are inconsistent, it will lead to inconsistent voltages of the individual batteries in the battery pack, thus affecting the consistency of the battery pack; therefore, when using the capacity data for matching in this comparative example, it is also necessary to test the internal resistance data of 20 individual batteries for matching, and determine the final matching result through the matching results of the two data of capacity and internal resistance:

[0093] S6: In this comparative example, the internal resistance matching is carried out according to the internal resistance difference ≤ 0.1 mΩ, that is, the internal resistance range of 0.2 - 0.3 mΩ is divided into a group. As shown in Table 4, the maximum internal resistance of the 20th battery is 0.3568 mQ, and the minimum internal resistance of the 6th battery is 0.2493 mΩ;

[0094] Table 4

[0095]

[0096] As shown in Table 3, the capacities of these 20 batteries are all within the capacity range of 105000 - 106500 mAh, indicating that these batteries numbered 1 - 20 can be divided into a group;

[0097] However, according to Table 4, the internal resistances of batteries numbered 1 - 19 are all within the internal resistance range of 0.2 - 0.3 mΩ, while the internal resistance of the 20th battery is not within the internal resistance range of 0.2 - 0.3 mΩ, indicating that these batteries numbered 1 - 19 can be divided into a group;

[0098] Therefore, combining Table 3 and Table 4, the matching result of dividing batteries numbered 1 - 19 into a group is accurate.

[0099] Verification:

[0100] The single cells numbered 1 to 19 are assembled into a 1-parallel and 19-series battery pack. The battery pack is first charged at a constant current of 0.2C to 69.35V (3.65V × 19), and then a constant current discharge test is carried out at room temperature. The discharge current is 1C, and the cut-off voltage is 47.5V (2.5V × 19). The voltage of the battery is recorded every 1 second to monitor the capacity of the battery pack in real time. The test is carried out 2 times, and the capacities of the battery pack are 104441.3mAh and 104580.5mAh respectively.

[0101] The grouping results measured by the two methods of Example 1 and Comparative Example 1 are consistent. Within the allowable error range, the capacity results of the battery packs measured by the two methods are consistent. Compared with the existing battery matching method, the present invention does not need to measure the capacity and internal resistance of the battery, and only needs to group according to the discharge voltage curve of the battery, which greatly simplifies the matching process and improves the production efficiency; while in Comparative Example 1, the matching is carried out by combining the capacity and internal resistance data, and the data processing is relatively troublesome and the production efficiency is low.

[0102] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery discharge curve fitting method, characterized in that: The steps include: S1: Multiple lithium-ion batteries of the same model are first charged at a constant current and constant voltage, and then subjected to a constant current discharge test, and discharged at a constant current to a cut-off voltage V0, and the voltage of the discharge process is collected at a fixed time interval to obtain the discharge voltage data of each single battery; S2: based on the discharge voltage data of each single battery obtained in step S1, a discharge voltage curve of each single battery is plotted with discharge capacity as the horizontal coordinate and voltage as the vertical coordinate, and the discharge voltage curves of each single battery are integrated in the same coordinate system to obtain a discharge voltage curve integrated by multiple batteries; S3: In the discharge voltage curves integrated with the multiple batteries obtained in step S2, based on the cut-off voltage V0 of the constant current discharge, the battery with the smallest capacity is selected as the base point, and the capacity of the battery with the smallest capacity is recorded as C0; S4: Based on the discharge voltage curves of the multiple batteries integrated obtained in step S2, recording the voltages corresponding to the other batteries when the capacity is C0; S5: Calculate the highest voltage V1=V0+ΔV among the multiple batteries selected for grouping according to the set dynamic pressure difference ΔV; S6: Based on the calculated highest voltage V1, a characteristic voltage range of V0 to V1 is obtained, and batteries whose corresponding voltages when the capacity is C0 are within the characteristic voltage range are grouped.

2. The lithium-ion battery discharge curve fitting matching method according to claim 1, characterized in that: In step S1, the lithium-ion battery is one of a lithium iron phosphate battery, a ternary lithium-ion battery, a lithium cobalt oxide battery, and a lithium manganese oxide battery.

3. The lithium-ion battery discharge curve fitting matching method according to claim 1, characterized in that: In step S1, the constant current and constant voltage charging refers to charging multiple lithium-ion batteries of the same model at a constant current of 0.5C to 3.65-4.2V, and then charging at a constant voltage of 3.65-4.2V to a cut-off current of 0.02C.

4. The lithium-ion battery discharge curve fitting matching method according to claim 1, characterized in that: In step S1, the discharge current of the constant current discharge test is 0.2-1C.

5. The lithium-ion battery discharge curve fitting matching method according to claim 1, characterized in that: In step S1, the discharge cut-off voltage of the constant current discharge test is 2.5-3V.

6. The lithium-ion battery discharge curve fitting matching method according to claim 1, characterized in that: The fixed time interval is 1-5s.

7. The lithium-ion battery discharge curve fitting matching method according to claim 1, characterized in that: The ΔV is 50-300 mV.

8. A lithium-ion battery discharge curve fitting system, characterized in that: The system is used to execute the lithium-ion battery discharge curve fitting matching method as described in any one of claims 1 to 7.

9. The lithium-ion battery discharge curve fitting matching system according to claim 8, characterized in that: The system includes a capacity control module, a data processing module and a group matching module; The capacity control module is used to control the full charging of each lithium-ion battery cell in a constant current and constant voltage manner, and then discharge each lithium-ion battery cell to a cut-off voltage in a constant current manner; A data processing module, used to collect the discharge voltage data of each single battery at different time points and form a discharge voltage curve integrated by multiple batteries, and then determine the minimum capacity C0 corresponding to the cut-off voltage V0 based on the discharge voltage curve integrated by multiple batteries, and then obtain the voltage value corresponding to each battery at the capacity C0 based on the discharge voltage curve integrated by multiple batteries; Based on the set dynamic pressure difference ΔV, the maximum voltage value V1 corresponding to the battery capacity C0 that can be used for grouping is calculated; The matching module is used to determine the battery whose voltage value corresponding to the capacity C0 is within the characteristic voltage range V0-V1 and use it as the matching battery.

10. A lithium-ion battery pack, characterized in that: The battery pack is assembled by using the lithium-ion battery discharge curve fitting assembly method as described in any one of claims 1 to 7 or the lithium-ion battery discharge curve fitting assembly system as described in any one of claims 8 to 9.

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