Battery sorting method and apparatus

Abstract

The application provides a battery sorting method and device, which comprises the following steps: charging a battery pack by constant current to an upper limit voltage, wherein the battery pack is composed of a plurality of batteries to be sorted in series, and the upper limit voltage is the sum of the upper limit voltages of the plurality of batteries; charging the battery pack by constant voltage until the charging current is reduced to a first threshold value; and sorting the plurality of batteries into a plurality of grades according to the voltages of the plurality of batteries and the upper limit voltages of the plurality of batteries when the constant voltage charging is completed. The battery sorting method and device can realize the subdivision of the capacity grades of the batteries, improve the consistency of the battery pack, reduce the charging and discharging voltage difference between the battery packs, and further improve the service life of the battery pack.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to battery sorting methods and apparatus. Background Technology

[0002] Battery packs consist of hundreds or even thousands of lithium-ion battery cells connected in series and parallel. However, due to inconsistencies in capacity and / or internal resistance among individual cells, the lifespan of the battery pack is shorter than that of the individual cells, directly affecting the performance of electric vehicles or energy storage devices, and in severe cases, causing safety issues. Individual cell sorting and grouping based on lean manufacturing is a common method to improve individual cell consistency. The factors affecting battery consistency in a battery pack are not singular; the interaction of multiple factors often manifests as voltage inconsistency, i.e., voltage difference, which is the most common form of failure in battery packs. Existing lithium-ion battery consistency screening methods are basically based on the premise of "consistent intrinsic product characteristics." However, the intrinsic characteristics of lithium-ion batteries are complex, and it is difficult to find a single method that can effectively solve all the current problems. It has been proven that existing methods cannot adequately meet the module's requirements for individual cell consistency. Therefore, current lithium-ion battery systems generally incorporate battery management systems, using the controllability of power electronics technology to address the inconsistencies and uncertainties of lithium batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a battery sorting method and apparatus that can subdivide battery capacity levels, improve battery pack consistency, reduce the charge and discharge voltage difference between batteries in a pack, and thus improve the battery pack lifespan.

[0004] To achieve the above objectives, embodiments of the present invention provide a battery sorting method, the method comprising: performing constant current charging on a battery pack to an upper limit voltage, wherein the battery pack is composed of multiple batteries to be sorted connected in series, and the upper limit voltage is the sum of the upper limit charging voltages of the multiple batteries; performing constant voltage charging on the battery pack after constant current charging until the charging current drops to a first threshold and charging is stopped; and classifying the multiple batteries into multiple grades according to the voltage of the multiple batteries at the end of constant voltage charging and the upper limit charging voltage of the multiple batteries.

[0005] Preferably, the multiple batteries are divided into multiple levels based on the voltage of the multiple batteries at the end of constant voltage charging and the upper limit voltage of the multiple batteries, including: batteries whose voltage at the end of constant voltage charging is greater than the second threshold of the upper limit voltage are divided into the first level; batteries whose voltage at the end of constant voltage charging is less than or equal to the second threshold of the upper limit voltage are divided into the second level; and batteries whose voltage at the end of constant voltage charging is less than the second threshold of the upper limit voltage are divided into the third level.

[0006] Preferably, the first threshold is 0.1C and the second threshold is 20mV.

[0007] Preferably, the charging current of the constant current charging is 1C.

[0008] This invention also provides a battery sorting device, which includes a constant current charging unit, a constant voltage charging unit, and a sorting unit. The constant current charging unit is used to charge a battery pack at a constant current up to an upper limit voltage. The battery pack is composed of multiple batteries to be sorted connected in series, and the upper limit voltage is the sum of the upper limit charging voltages of the multiple batteries. The constant voltage charging unit is used to charge the battery pack after constant current charging at a constant voltage until the charging current drops to a first threshold and then stops charging. The sorting unit is used to divide the multiple batteries into multiple grades based on the voltage of the multiple batteries at the end of constant voltage charging and the upper limit charging voltage of the multiple batteries.

[0009] Preferably, the sorting unit is used to: classify batteries whose voltage at the end of constant voltage charging is greater than the second threshold of the upper limit charging voltage into a first category; classify batteries whose voltage at the end of constant voltage charging is less than or equal to the second threshold of the upper limit charging voltage into a second category; and classify batteries whose voltage at the end of constant voltage charging is less than the second threshold of the upper limit charging voltage into a third category.

[0010] Preferably, the first threshold is 0.1C and the second threshold is 20mV.

[0011] Preferably, the charging current of the constant current charging is 1C.

[0012] Through the above technical solutions, the embodiments of the present invention provide a battery sorting method and apparatus, which sorts individual batteries by the difference between the constant voltage charging terminal voltage and the set voltage. By utilizing the principle that the current is the same in a series circuit, it can realize the subdivision of battery capacity levels, improve the consistency of battery packs, reduce the charging and discharging voltage difference between batteries in a pack, and thus improve the service life of the battery pack.

[0013] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0015] Figure 1 This is a flowchart of a battery sorting method provided in an embodiment of the present invention;

[0016] Figure 2This is a schematic diagram of battery connection provided in an embodiment of the present invention;

[0017] Figure 3 This is a schematic diagram of battery consistency provided in an embodiment of the present invention;

[0018] Figure 4A This is a schematic diagram of battery voltage change provided in an embodiment of the present invention;

[0019] Figure 4B This is a schematic diagram of battery voltage changes provided in another embodiment of the present invention;

[0020] Figure 5A This is a schematic diagram of battery voltage changes provided in another embodiment of the present invention;

[0021] Figure 5B This is a schematic diagram of battery voltage change provided in another embodiment of the present invention;

[0022] Figure 6 This is a schematic diagram of battery voltage changes provided in another embodiment of the present invention;

[0023] Figure 7 This is a comparison of the room temperature cycle performance of a battery pack sorted by the technology of this invention and a battery pack not sorted by the technology of this invention, provided in an embodiment of the present invention.

[0024] Figure 8 A schematic diagram illustrating the change in discharge terminal voltage difference between a battery pack sorted by the technology of the present invention and a battery pack not sorted by the technology of the present invention during a room temperature cycling process, according to an embodiment of the present invention.

[0025] Figure 9 This is a schematic diagram of the structure of a battery sorting device provided in an embodiment of the present invention.

[0026] Explanation of reference numerals in the attached figures

[0027] 1-Constant current charging unit, 2-Constant voltage charging unit, 3-Sorting unit Detailed Implementation

[0028] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0029] Figure 1 This is a flowchart of a battery sorting method provided in an embodiment of the present invention. Figure 1 As shown, the method includes:

[0030] Step S101: The battery pack is charged at a constant current to the upper limit voltage. The battery pack is composed of multiple batteries to be sorted connected in series. The upper limit voltage is the sum of the upper limit charging voltages of the multiple batteries.

[0031] In one embodiment of the present invention, the constant current charging current is 1C. Here, C represents the battery charge / discharge rate, and 1C represents the current intensity when the battery is fully discharged in one hour. For example, if a 2200mAh 18650 battery is discharged completely at 1C intensity in one hour, the discharge current is 2200mA. Charge / discharge rate = charge / discharge current / rated capacity; for example, a battery with a rated capacity of 100Ah is discharged at 20A, its discharge rate is 0.2C; if the used capacity is discharged completely in one hour, it is called 1C discharge; if it is discharged completely in 5 hours, it is called 0.2C discharge.

[0032] Step S102: Perform constant voltage charging on the battery pack after constant current charging until the charging current drops to the first threshold and then stop charging.

[0033] In one embodiment of the present invention, the first threshold is lower than 0.35C, preferably 0.1C.

[0034] Step S103: Based on the voltage of the multiple batteries at the end of constant voltage charging and the upper limit voltage of the multiple batteries, the multiple batteries are divided into multiple levels.

[0035] In this embodiment of the invention, batteries whose voltage at the end of constant voltage charging is greater than the second threshold of the upper limit charging voltage are classified into a first category; batteries whose voltage at the end of constant voltage charging is less than or equal to the second threshold of the upper limit charging voltage are classified into a second category; and batteries whose voltage at the end of constant voltage charging is less than the second threshold of the upper limit charging voltage are classified into a third category.

[0036] Preferably, the second threshold is 20mV. A single-cell voltage at the end of constant-voltage charging is defined as equal to the set upper limit voltage of the single-cell if the difference is within ±20mV, and the single-cell capacity of this grade II cell is equal to the rated capacity; a single-cell voltage at the end of constant-voltage charging is defined as higher than the set upper limit voltage of the single-cell if it is 20mV higher, and the single-cell capacity of this grade III cell is lower than the rated capacity; a single-cell voltage at the end of constant-voltage charging is defined as lower than the set upper limit voltage of the single-cell if it is 20mV lower, and the single-cell capacity of this grade I cell is higher than the rated capacity.

[0037] This invention provides a grading method, but it is not limited to this. Those skilled in the art can modify the provided grading method according to application needs, such as modifying the second threshold or setting more thresholds to divide individual batteries into more grades, which will not be elaborated here.

[0038] The present invention also provides the following embodiments:

[0039] A schematic diagram of the battery connection for battery sorting using series constant voltage charging in an embodiment of the present invention is shown below. Figure 2 As shown, the selected batteries consist of 200 square lithium iron phosphate / graphite batteries with a nominal capacity of 21Ah, all of grade A. Their factory-specified capacity, internal resistance, and voltage standard deviation are 53.7mAh, 0.1mΩ, and 0.89mV, respectively. Figure 3 As shown, this demonstrates relatively high consistency among individual cells. All experiments in this embodiment were conducted at room temperature using a Beijing Soying 60V 100A charge-discharge tester with a 32-channel auxiliary temperature and voltage recorder.

[0040] Example 1. To ensure accurate results, two possible upper charging voltage limits were selected for testing.

[0041] Five cells were randomly selected from 200 individual cells and connected in series. They were then charged at 1C to 17.25V (equivalent to 3.45V for a single cell), followed by constant-voltage charging until the current dropped to 0.1C. The voltage changes of each cell during the constant-voltage charging phase were observed. Figure 4A As shown, the voltage difference between the five individual cells is small when charged at a constant voltage of 3.45V. The difference only appears after the current drops to 0.35C. Even so, the voltage difference at the end of the 3.45V constant voltage charging is only 4.5mV.

[0042] Then, charge at a 1C current to 18.25V (equivalent to 3.65V for a single cell), and then maintain a constant voltage until the current drops to 0.1C, ending the charging process. Observe the voltage changes of each single cell during the constant voltage charging phase. Figure 4B As shown, the five individual batteries exhibit a very significant voltage difference when entering the series constant voltage charging stage at 3.65V. Batteries 1-4 have voltages higher than 3.65V, while only battery 5 has a voltage lower than 3.65V. By the end of the 3.65V constant voltage charging phase, the voltage difference reaches 229.4mV. This demonstrates that the series constant voltage charging mode can differentiate the batteries, thereby achieving grade selection.

[0043] Example 2. To ensure accurate results, two possible upper charging voltage limits were selected for testing.

[0044] The No. 5 battery with a decreased constant-voltage charging voltage in Example 1 was removed, and the remaining four batteries were subjected to constant-voltage charging. First, the four batteries were discharged at a constant current of 1C to 12V, then charged at a constant current of 1C to 14.1V (equivalent to 3.525V for a single cell). Constant-voltage charging was stopped when the current dropped to 0.1C. The constant-voltage charging curve is shown in [Figure number missing]. Figure 5AThe results for batteries 1 and 4, and batteries 2 and 3, were relatively consistent, but the voltage difference was not obvious. The difference only became more obvious after the current reached 0.35C. The voltage difference at the end of constant voltage charging was 10.1mV.

[0045] Then, charge at a 1C current to 14.6V (equivalent to 3.65V for a single cell), followed by constant-voltage charging until the current drops to 0.1C, at which point charging ends. Observe the voltage changes of each single cell during the constant-voltage charging phase. Figure 5B As shown, the four individual cells after removing the No. 5 battery exhibit good voltage consistency when entering the series constant voltage charging stage at 3.65V. Only after the current drops to 0.35C does a significant voltage difference appear. The voltage difference at the end of the 3.65V constant voltage charging is only 37mV, but the voltage difference between any cell and 3.65V is less than 20mV.

[0046] Comparing the results of Example 1 and Example 2, constant voltage charging under high charge state is beneficial to discover inconsistencies between batteries. At the same time, it is effective to sort batteries by the deviation of individual battery voltage from the set voltage under series constant voltage charging mode. After removing No. 5 individual battery, the remaining 4 batteries have good consistency.

[0047] Example 3.

[0048] Ten cells were randomly selected from the 195 individual cells and connected in series. They were charged at 1C to 36.5V (equivalent to 3.65V for a single cell), and then charged at a constant voltage until the current dropped to 0.1C. The constant voltage charging curves of the ten cells showed a significant deviation from 3.65V. Figure 6 As shown, we connected three batteries with the highest voltage (constant voltage charging terminal voltage above 3.65V) in series, denoted as the HG battery pack, and connected three batteries with the lowest voltage (constant voltage charging terminal voltage below 3.65V) in series, denoted as the HD battery pack. At the same time, we randomly selected 6 batteries from the remaining 185 batteries to form two three-series battery packs as control groups, denoted as the 111 battery pack and the 123 battery pack, respectively.

[0049] The four three-cell battery packs were subjected to the following charge-discharge cycle at room temperature: 1) 1C constant current charging to 10.95V, then constant voltage charging to 0.1C, followed by a 30-minute rest; 2) constant current discharging to 7.5V, followed by a 30-minute rest; this cycle was repeated 700 times. During the cycle, a protection condition was set so that the cycle would stop if the voltage of a single cell exceeded 4V or fell below 2V. The results are as follows... Figure 7As shown, the average capacity of the HD battery pack is higher than that of the 111 and 123 battery packs, while the capacity of the HG battery pack is slightly lower than that of the 111 and 123 battery packs. This indicates that individual cells with a series constant voltage charging voltage higher than the set voltage have an actual capacity higher than their rated capacity, while individual cells with a series constant voltage charging voltage lower than the set voltage have an actual capacity lower than their rated capacity. The 111 and 123 battery packs, which were not sorted by constant voltage charging, have the same cycle curve, with a capacity retention rate of 91.8% after 700 cycles, lower than the capacity retention rate (92.4%) of the HG and HD battery packs after constant voltage charging sorting. This further proves that the technology of this invention can achieve better battery sorting. Figure 8 The changes in the voltage difference at the end of constant current discharge of the battery pack during the cycle are shown. The voltage difference of the HD group is the smallest, while that of the 111 battery pack is the largest. The reason why the voltage difference of the HD group is better than that of the HG group is that the voltage difference of the three highest voltage batteries in the constant voltage charging in this embodiment is 186.5mV, which is higher than the voltage difference of the three lowest voltage batteries in the HD battery pack (33.6mV). This further illustrates that in addition to further classifying the batteries by capacity level through the difference between the voltage at the end of constant voltage charging and the set voltage, further refined classification can also be carried out by the consistency between the constant voltage charging curves.

[0050] Figure 9 This is a schematic diagram of the structure of a battery sorting device provided in an embodiment of the present invention. Figure 9 As shown, the device includes: a constant current charging unit 1, a constant voltage charging unit 2, and a sorting unit 3. The constant current charging unit is used to charge the battery pack at a constant current to an upper limit voltage. The battery pack is composed of multiple batteries to be sorted connected in series. The upper limit voltage is the sum of the upper limit charging voltages of the multiple batteries. The constant voltage charging unit is used to charge the battery pack after constant current charging at a constant voltage until the charging current drops to a first threshold and then stops charging. The sorting unit is used to divide the multiple batteries into multiple grades according to the voltage of the multiple batteries at the end of constant voltage charging and the upper limit charging voltage of the multiple batteries.

[0051] Preferably, the sorting unit is used to: classify batteries whose voltage at the end of constant voltage charging is greater than the second threshold of the upper limit charging voltage into a first category; classify batteries whose voltage at the end of constant voltage charging is less than or equal to the second threshold of the upper limit charging voltage into a second category; and classify batteries whose voltage at the end of constant voltage charging is less than the second threshold of the upper limit charging voltage into a third category.

[0052] Preferably, the first threshold is 0.1C and the second threshold is 20mV.

[0053] Preferably, the charging current of the constant current charging is 1C.

[0054] The embodiments of the battery sorting device described above are similar to the embodiments of the battery sorting method described above, and will not be repeated here.

[0055] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0056] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0057] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0058] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0059] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0060] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0061] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0062] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0063] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A battery sorting method, characterized in that, The method includes: The battery pack is charged at a constant current to the upper limit voltage. The battery pack is composed of multiple batteries to be sorted connected in series. The upper limit voltage is the sum of the upper limit voltages of the multiple batteries. The charging current of the constant current charging is 1C. The battery pack after constant current charging is charged with constant voltage until the charging current drops to a first threshold, which is 0.1C. Based on the voltage of the multiple batteries at the end of constant voltage charging and the upper limit voltage of the multiple batteries, the multiple batteries are divided into multiple levels, including: batteries whose voltage at the end of constant voltage charging is greater than the second threshold of the upper limit voltage are divided into the first level; batteries whose voltage at the end of constant voltage charging is less than or equal to the second threshold of the upper limit voltage are divided into the second level; and batteries whose voltage at the end of constant voltage charging is less than the second threshold of the upper limit voltage are divided into the third level, where the second threshold is 20mV.

2. A battery sorting device, characterized in that, The device includes: The system comprises a constant current charging unit, a constant voltage charging unit, and a sorting unit. The constant current charging unit is used to charge the battery pack to the upper limit voltage using a constant current. The battery pack is composed of multiple batteries to be sorted connected in series. The upper limit voltage is the sum of the upper limit voltages of the multiple batteries. The charging current of the constant current charging is 1C. The constant voltage charging unit is used to charge the battery pack after constant current charging at a constant voltage until the charging current drops to a first threshold, where the charging stops when the charging current drops to a first threshold of 0.1C. The sorting unit is used to divide the multiple batteries into multiple grades based on the voltage of the multiple batteries at the end of constant voltage charging and the upper limit voltage of the multiple batteries, including: classifying batteries whose voltage at the end of constant voltage charging is greater than the second threshold of the upper limit voltage into the first grade; classifying batteries whose voltage at the end of constant voltage charging is less than or equal to the second threshold into the second grade; and classifying batteries whose voltage at the end of constant voltage charging is less than the second threshold of the upper limit voltage into the third grade, where the second threshold is 20mV.

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