Battery fast charging method

Abstract

The invention relates to the technical field of batteries, and particularly discloses a battery fast charging method which comprises the following steps: assembling a total battery and a plurality of reference electrodes into a three-electrode battery, and enabling the plurality of reference electrodes to be positioned at different positions; plating lithium on the plurality of reference electrodes in sequence to prepare a stable reference electrode; the three-electrode battery is subjected to direct current charging with different current densities to the same cut-off condition, the SOC of charging when the different current densities reach the cut-off condition is recorded, and the potential difference between each reference electrode and the negative electrode is recorded; and S3, making a stepped fast charging scheme based on the direct current charging data recorded at different positions in the step S3, disassembling the battery cell after multi-circle fast charging circulation, and further optimizing the stepped fast charging scheme according to the state of the negative plate. According to the method, potentials of different positions of the negative pole piece are monitored in the charging process, potential differences on the pole piece are compared, the lowest potential position is determined, a fast charging scheme is optimized and explored, and the fast charging process most matched with the design is determined.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for fast charging batteries. Background Technology

[0002] Electric vehicles (EVs), with their low carbon emissions, high environmental friendliness, and more comfortable driving experience, are impacting the traditional gasoline-powered vehicle market. Although EVs have made significant progress in recent years, charging them takes longer than refueling traditional gasoline vehicles. Therefore, the current main development direction of power batteries focuses on higher energy density and faster charging capabilities, which also brings considerations regarding safety and cost. Higher charging speeds place higher demands on battery design; the conventional approach is to sacrifice energy density, otherwise, high-rate charging can lead to lithium plating or even more serious thermal runaway. Therefore, how to balance energy density and fast charging speed requires continuous research.

[0003] Lithium-ion batteries consist of a positive electrode, a negative electrode, an electrolyte, a separator, and foil materials. Improving fast-charging performance primarily involves controlling the N / P ratio and employing fast-charging graphite and highly kinetic electrolytes. However, evaluating the actual fast-charging capability of a well-designed cell system is crucial. A conservative fast-charging approach contradicts the original design; a more aggressive approach may not show significant performance degradation in the early stages of cycling, but a sharp decline in performance later on often results in wasted development time. The conventional process for evaluating cell fast-charging capability involves assembling the same design system into a small (pouch) cell with three electrodes, monitoring the negative electrode potential to investigate the fast-charging capability, and then conducting a long-term evaluation in a larger cell. However, for prismatic cells, differences exist in electrode size and electrolyte injection coefficient compared to small cells, thus limiting the applicability of this process for evaluating the actual fast-charging capability of prismatic cells. Therefore, designing a reasonable evaluation method or structure to monitor the negative electrode potential inside the battery cell at different charging rates and SOCs is particularly important for evaluating the fast charging capability of a particular design. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a battery fast charging method. By using multi-position reference electrodes to monitor the potential at different positions of the negative electrode during the charging process, the potential differences on the negative electrode are compared to determine the position with the lowest potential, which is also the position most prone to lithium deposition in long-term testing, and to explore and optimize the fast charging scheme.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a battery fast charging method, which includes the following steps: S1. Assemble a full cell and several reference electrodes into a three-electrode cell, with the several reference electrodes located in different positions; S2. Sequentially plate lithium onto several of the reference electrodes to prepare stable reference electrodes; S3. Charge the three-electrode battery with DC current at different current densities until the same cutoff condition, record the SOC when the cutoff condition is reached at different current densities, and record the potential difference between each reference electrode and the negative electrode; S4. Based on the DC charging data recorded at different locations in step S3, formulate a stepped fast charging scheme. After multiple fast charging cycles, disassemble the battery cells and further optimize the stepped fast charging scheme according to the state of the negative electrode.

[0006] As a further improvement to the above-mentioned solution of the present invention, in step S1, the full battery includes a casing and a cell encapsulated inside the casing. The cell includes a positive electrode, a negative electrode and a first separator. A plurality of reference electrodes are disposed at different positions between adjacent first separators and negative electrodes in the cell. The reference electrodes are connected to wires and the wires extend out of the casing.

[0007] As a further improvement of the above-mentioned solution of the present invention, there are multiple positive electrode sheets, multiple negative electrode sheets and multiple first separators, and the positive electrode sheets, the first separators and the negative electrode sheets are stacked in sequence to form the battery cell; a plurality of reference electrodes are disposed between the third layer of the first separator and the third layer of the negative electrode sheets, and the reference electrodes are wrapped with a second separator.

[0008] As a further improvement of the above-mentioned solution of the present invention, the battery cell has a two-end tab structure, at least one of the reference electrodes is disposed near the negative tab position of the battery cell, at least one of the reference electrodes is disposed near the positive tab position of the battery cell, and at least one of the reference electrodes is disposed on the large surface position of the battery cell.

[0009] As a further improvement to the above-mentioned solution of the present invention, the reference electrode is made of copper or gold, the material of the wire is the same as that of the reference electrode, and the section of the wire located inside the housing is wrapped with an insulating layer.

[0010] As a further improvement to the above-mentioned solution of the present invention, the housing is provided with a through hole for the wire to pass through, and the through hole is sealed with sealant.

[0011] As a further improvement to the above-mentioned solution of the present invention, step S2, before lithium plating, further includes a step of calibrating the charge and discharge capacity of the three-electrode battery and then charging it to a predetermined state of charge. Specifically, this includes: calibrating the three-electrode battery with a 0.33C1 charge and discharge capacity for several cycles, taking the average discharge capacity of the several cycles as the calibration capacity C0, and then charging the three-electrode battery with a 0.33C0 charge to adjust its SOC to 40% or 80%; wherein, C1 is the design capacity of the full battery.

[0012] As a further improvement to the above-mentioned solution of the present invention, in step S2, the lithium plating is performed by sequentially connecting each of the reference electrodes to the negative electrode of the three-electrode battery and applying a current of 1-2 μA to the reference electrodes for continuous lithium plating for 5-6 hours.

[0013] As a further improvement to the above-mentioned solution of the present invention, in step S2, the stability of the reference electrode is determined by the following method: several lithium-plated reference electrodes are sequentially connected to the negative electrode of the three-electrode battery, and the potential difference between the reference electrode and the negative electrode is monitored within 24-30 hours. If the potential difference between the reference electrode and the negative electrode remains stable, the reference electrode is determined to be stable.

[0014] As a further improvement to the above-mentioned solution of the present invention, in step S3, the cutoff condition is that the potential difference between several reference electrodes and the negative electrode in the three-electrode battery is 0V, or the cutoff voltage of the full battery is reached.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention monitors the potential at different positions of the negative electrode during the charging process using multi-position reference electrodes, compares the potential differences on the negative electrode, determines the position with the lowest potential which is also the position most prone to lithium deposition in long-term testing, explores and optimizes the fast charging scheme, and determines the best-matched fast charging process. At the same time, this design also has some guiding significance for the differences in the electrode manufacturing process.

[0016] This invention incorporates a built-in reference electrode in the full battery design to quickly identify potential differences at different locations in the negative electrode during full battery charging. Compared to small pouch systems, this design is closer to real-world conditions, facilitating the rapid selection of suitable fast charging solutions and shortening evaluation time. It also helps identify differences in the negative electrode of the stacked structure, providing strong guidance for cell design. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the three-electrode battery in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the reference electrode in an embodiment of the present invention; Figure 3This is a graph showing the monitoring results of the negative electrode potential at a 2C charging rate in an embodiment of the present invention.

[0018] Reference numerals: 1. Housing; 2. Battery cell; 3. Positive terminal; 4. Negative terminal; 5. Explosion-proof valve; 6. Reference electrode; 7. Wire; 8. Insulation layer; 9. Through hole. Detailed Implementation

[0019] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0021] This embodiment proposes a battery fast charging method, which includes the following steps: S1. Assemble a full cell and several reference electrodes into a three-electrode cell, with the reference electrodes located in different positions.

[0022] like Figure 1 As shown, the full battery includes a casing 1 and a cell 2 encapsulated inside the casing 1. The cell 2 includes a positive electrode, a negative electrode, and a first separator. There are multiple positive electrode, negative electrode, and first separator. The positive electrode, the first separator, and the negative electrode are stacked sequentially to form the cell 2.

[0023] During lamination, several reference electrodes 6 are placed between the third layer of the first separator and the third layer of the negative electrode, and the reference electrodes 6 are wrapped with a second separator (not shown in the figure; the second separator can be a base film without a coating). Figure 2 As shown, the reference electrode 6 is connected to a wire 7, and the wire 7 extends out of the housing 1.

[0024] The number of reference electrodes 6 is determined by the actual size of the prismatic battery. For example, if the battery electrode size is larger, there will be more potential gradient differences, requiring more reference electrodes to be placed in different locations. The purpose of multiple reference electrodes is to find the weakest point of lithium plating on the negative electrode. The fast charging process needs to consider the differences in lithium plating ability at different locations. This embodiment uses three reference electrodes as an example: one reference electrode is placed near the negative electrode tab, one reference electrode is placed near the positive electrode tab, and one reference electrode is placed on the large surface of the cell. Before the cell 2 is inserted into the casing, a through hole 9 is pre-drilled on the cover plate of the casing 1 for the wires to pass through, and the through hole 9 is sealed with sealant. In this embodiment, the reference electrode 6 is a copper sheet with a size of 2mm*2mm*20μm. The material of the wire 7 is the same as that of the reference electrode 6, and the section of the wire 7 inside the casing 1 is wrapped with an insulating layer 8. Of course, in other embodiments, the reference electrode 6 can also be made of gold, and the size of the reference electrode 6 can be reasonably set according to the actual size of the electrode.

[0025] S2. After calibrating the charge and discharge capacity of the three-electrode battery, charge it to the predetermined state of charge, and then plate several reference electrodes with lithium to prepare a stable reference electrode.

[0026] The method for calibrating the charge-discharge capacity of a three-electrode battery and then charging it to a predetermined state of charge is as follows: Perform several cycles of 0.33C1 charge-discharge calibration on the three-electrode battery, take the average discharge capacity of these cycles as the calibrated capacity C0, and then charge the three-electrode battery again using 0.33C0 to adjust its SOC to 40% or 80%; where C1 is the designed full-cell capacity. For graphite anode system batteries, at 40% and 80% SOC, which are plateau regions, using the lithium source in the anode to plate lithium on the reference electrode 6 results in essentially no change in voltage.

[0027] In this embodiment, lithium plating is performed by sequentially connecting each reference electrode to the negative electrode of a three-electrode battery and applying a current of 1-2 μA (preferably 1 μA) to the reference electrode 6 for a continuous period of 5-6 hours (preferably 5 hours).

[0028] In this embodiment, the stability of the reference electrode is determined as follows: several lithium-plated reference electrodes are sequentially connected to the negative electrode of the three-electrode battery, and the potential difference between the reference electrode and the negative electrode is monitored for 24-30 hours. If the potential difference between the reference electrode and the negative electrode remains stable, the reference electrode is considered stable. In this embodiment, multiple three-electrode batteries can be assembled in step S1, and subsequent evaluation can be performed on groups where the negative electrode potential of all reference electrodes remains stable after lithium plating and 24 hours of rest.

[0029] S3. Charge the three-electrode battery with DC current at different current densities until the same cutoff condition is reached. Record the state of charge (SOC) when the cutoff condition is reached at different current densities and record the potential difference between each reference electrode and the negative electrode.

[0030] In this embodiment, the current density ranges from 1C to 10C; the cutoff condition is that the potential difference between all reference electrodes and the negative electrode in the three-electrode battery is 0V, or the cutoff voltage of the entire battery is reached. The potential of the built-in reference electrodes at different locations relative to the negative electrode is monitored simultaneously to obtain the actual potential of the negative electrode during charging. It is generally believed that there is a risk of lithium plating if the potential is lower than the lithium plating potential. Due to polarization, multiple measurements are required for different charging schemes.

[0031] S4. Based on the DC charging data recorded at different locations in step S3, formulate a tiered fast charging scheme. After multiple fast charging cycles, disassemble the battery cells and further optimize the tiered fast charging scheme according to the state of the negative electrode.

[0032] Based on the DC charging data obtained in step S3, a curve is plotted with SOC as the abscissa and the negative electrode potential monitored by different reference electrodes as the ordinate. The location with the lowest potential or the most likely lithium plating during the charging process is identified. Based on the comparison results, a stepped charging rate and the corresponding SOC are selected to formulate a stepped fast charging scheme.

[0033] The fast charging scheme was tested with multiple cycles (e.g., 50 cycles) and the three-electrode battery was disassembled after the cycle test to verify the reliability of the negative electrode state and potential monitoring results, and to further revise the fast charging scheme.

[0034] Next, taking a graphite-based prismatic battery as an example, the fast charging scheme for the graphite-based prismatic battery will be optimized according to the method described above in this embodiment.

[0035] First, assemble a three-electrode battery by placing three reference electrodes inside the square battery according to the method of step S1 above. One reference electrode is located near the negative electrode tab and is denoted as position 1; one reference electrode is located near the positive electrode tab and is denoted as position 2; and the other reference electrode is located on the large surface of the square battery and is denoted as position 3.

[0036] The three-electrode battery was calibrated by charging and discharging at 0.33C1 (C1=86.9Ah) for several cycles. The average discharge capacity of the several cycles was taken as the calibration capacity C0 (C0=87.15Ah). The three-electrode battery was then charged at 0.33C0 to adjust its SOC to 40%.

[0037] The reference electrode and negative electrode of the three-electrode battery were sequentially connected to form a two-electrode system. The reference electrode was subjected to a 5-hour lithium plating process using 1 μA. Then, the reference electrode was sequentially connected to the negative electrode at 40% SOC. The potential difference between the reference electrode and the negative electrode was monitored for 24 hours. If the potential difference remained stable, the reference electrode was considered effective. In this embodiment, a total of six three-electrode batteries were assembled. Subsequent evaluation was conducted on groups where the negative electrode potential remained stable after lithium plating and 24-hour resting.

[0038] The three-electrode battery was charged with DC current at different current densities until the cutoff condition was met—the potential of the reference electrode relative to the negative electrode was 0V. The potential differences between the three reference electrodes and the negative electrode were recorded. Figure 3 The results of monitoring the negative electrode potential of the graphite-based prismatic battery at a 2C charging rate show that the reference electrode test results at positions 1 and 2 are highly consistent, while there is a certain deviation at position 3 (the negative electrode potential at this position is higher at the same SOC).

[0039] If a fast charging solution is developed based on the test results at position 3 and a 50-cycle fast charging test is conducted, slight edge lithium plating is found on the negative electrode after disassembling the battery.

[0040] Taking into account the results of different test locations (including location 1, location 2, and location 3), a fast charging scheme was developed and 50 fast charging cycles were conducted. The fast charging rate was reduced, and after disassembling the battery, it was found that the lithium plating on the negative electrode had disappeared.

[0041] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0042] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for fast charging a battery, characterized in that, It includes the following steps: S1. Assemble a full cell and several reference electrodes into a three-electrode cell, with the several reference electrodes located in different positions; S2. Sequentially plate lithium onto several of the reference electrodes to prepare stable reference electrodes; S3. Charge the three-electrode battery with DC current at different current densities until the same cutoff condition, record the SOC when the cutoff condition is reached at different current densities, and record the potential difference between each reference electrode and the negative electrode; S4. Based on the DC charging data recorded at different locations in step S3, formulate a stepped fast charging scheme. After multiple fast charging cycles, disassemble the battery cells and further optimize the stepped fast charging scheme according to the state of the negative electrode.

2. The battery fast charging method according to claim 1, characterized in that, In step S1, the full battery includes a casing and a cell encapsulated inside the casing. The cell includes a positive electrode, a negative electrode, and a first separator. Several reference electrodes are disposed at different positions between adjacent first separators and negative electrodes in the cell. The reference electrodes are connected to wires that extend outside the casing.

3. The battery fast charging method according to claim 2, characterized in that, There are multiple positive electrode plates, multiple negative electrode plates, and multiple first separators. The positive electrode plates, the first separators, and the negative electrode plates are stacked in sequence to form the battery cell. Several reference electrodes are disposed between the third layer of the first separator and the third layer of the negative electrode plates, and the reference electrodes are wrapped with a second separator.

4. The battery fast charging method according to claim 2, characterized in that, The battery cell has a two-end tab structure, at least one of the reference electrodes is located near the negative tab of the battery cell, at least one of the reference electrodes is located near the positive tab of the battery cell, and at least one of the reference electrodes is located on the large surface of the battery cell.

5. The battery fast charging method according to claim 2, characterized in that, The reference electrode is made of copper or gold, and the wire is made of the same material as the reference electrode, with an insulating layer covering a section of the wire located inside the housing.

6. The battery fast charging method according to claim 2, characterized in that, The housing has a through hole for the wire to pass through, and the through hole is sealed with sealant.

7. The battery fast charging method according to claim 1, characterized in that, In step S2, before lithium plating, the three-electrode battery is further calibrated for charge and discharge capacity and then recharged to a predetermined state of charge. Specifically, this includes: calibrating the three-electrode battery for 0.33C1 charge and discharge capacity for several cycles, taking the average discharge capacity of several cycles as the calibration capacity C0, and then charging the three-electrode battery for 0.33C0 to adjust its SOC to 40% or 80%; wherein, C1 is the design capacity of the full battery.

8. The battery fast charging method according to claim 1, characterized in that, In step S2, the lithium plating method is as follows: each of the reference electrodes is connected sequentially to the negative electrode of the three-electrode battery, and a current of 1-2 μA is applied to the reference electrodes for continuous lithium plating for 5-6 hours.

9. The battery fast charging method according to claim 1, characterized in that, In step S2, the stability of the reference electrode is determined by the following method: several lithium-plated reference electrodes are connected sequentially to the negative electrode of the three-electrode battery, and the potential difference between the reference electrode and the negative electrode is monitored within 24-30 hours. If the potential difference between the reference electrode and the negative electrode remains stable, the reference electrode is determined to be stable.

10. The battery fast charging method according to claim 1, characterized in that, In step S3, the cutoff condition is that the potential difference between several reference electrodes and the negative electrode in the three-electrode battery is 0V, or the cutoff voltage of the full battery is reached.

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