Method for determining proper charging rate and segmented charging strategy of lithium ion battery

Abstract

The invention relates to the technical field of batteries, and discloses a method for determining an appropriate charging rate and a segmented charging strategy of a lithium ion battery. The method for determining the appropriate charging multiplying power of the lithium ion battery comprises the steps that a breathing tool is provided, specifically, the breathing tool comprises a battery body and a transparent tube, the transparent tube is inserted into the battery body from the exterior of the battery body, and the specific liquid level height of electrolyte can be observed in the transparent tube; charging test: within the defined SOC charging range, charging the battery body at any rate value, after charging is finished, observing the liquid level height h1 at the end of charging and the liquid level height h2 after standing for 10-30 min after charging, if the difference between the liquid level height h1 and the liquid level height h2 is within the range of 0-10 mm, determining that the rate value is the appropriate charging rate value within the defined SOC charging range, and if the difference between the liquid level height h2 and the liquid level height h1 is within the range of 0-10 mm, determining that the charging rate value is the appropriate charging rate value within the defined SOC charging range. Otherwise, the charging rate value is an improper charging rate value. According to the method, the proper charging rate of the lithium ion battery can be determined.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a method for determining a suitable charging rate and a segmented charging strategy for a lithium-ion battery. Background Art

[0002] The charge rate is the current value required to charge a battery to its rated capacity within a specified time. In practical applications, the higher the charge rate, the faster the battery charges and discharges. For lithium-ion batteries, excessive charge rates can cause problems such as poor electrolyte wetting of the battery electrodes and lithium precipitation, thus affecting the battery's cycle life.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The object of the present invention is to provide a method for determining a suitable charging rate and a segmented charging strategy for a lithium-ion battery.

[0005] The present invention is achieved in that: In a first aspect, the present invention provides a method for determining a suitable charging rate of a lithium-ion battery, comprising: Provide breathing tooling: The breathing tooling includes a battery body and a transparent tube. The transparent tube is inserted from the outside of the battery body into the battery body, and the electrolyte is injected so that the specific liquid level of the electrolyte can be observed in the transparent tube; Charging test: Within the specified SOC charging range, charge the battery at any rate value. After charging, observe the liquid level height h1 just after charging and the liquid level height h2 after standing for 10 to 30 minutes after charging. If the difference between h1 and h2 is within the range of 0 to 10 mm, the rate value is a suitable charging rate value within the specified SOC charging range, otherwise it is an inappropriate charging rate value.

[0006] In an optional embodiment, the inner diameter of the transparent tube is 0.5-5 mm.

[0007] In an optional embodiment, the outer wall of the transparent tube is provided with scales.

[0008] In an optional embodiment, multiple charging tests are repeated, each charging test is performed at a different charging rate value, and appropriate charging rate values ​​within multiple defined SOC charging ranges are obtained, and the maximum rate value is taken as the optimal charging rate value.

[0009] In an optional implementation, multiple rate values ​​are selected within the range of 0.1-1.5C for charging testing.

[0010] In a second aspect, the present invention provides a method for determining a segmented charging strategy for a lithium-ion battery, comprising: dividing 0-100% SOC into at least 3 segments, selecting a plurality of charging rate values ​​for each segment and determining the optimal charging rate value therein according to the method of the aforementioned embodiment; Then the battery is charged in each of at least three segments according to the optimal charging rate value corresponding to each segment, which is a better segmented charging strategy.

[0011] In an optional implementation, 0~100% SOC is divided into three sections, namely 0~27% SOC, 27~75% SOC and 75~100% SOC.

[0012] In an optional implementation, within the SOC charging range of 0~27%, multiple charging rate values ​​from 0.1~0.8C are selected for charging to determine the optimal charging rate value; within the SOC charging range of 27~75%, multiple charging rate values ​​from 0.8~1.6C are selected for charging to determine the optimal charging rate value; within the SOC range of 75~100%, multiple charging rate values ​​from 1~0.7C are selected for charging to determine the optimal charging rate value.

[0013] The present invention has the following beneficial effects: The method for determining a suitable charging rate of a lithium-ion battery provided by the present invention observes the electrolyte level after the battery is charged. If the liquid level remains basically unchanged just after the charging is completed and after being left standing for a period of time, it proves that the electrolyte charged at this rate can be absorbed into the negative electrode sheet in time, and it proves that black spots or lithium deposition on the negative electrode sheet will not be caused at this charging rate; if the liquid level changes, it proves that there is a problem that the negative electrode has no time to absorb the electrolyte back during the charging process, and charging at this rate will cause black spots or lithium deposition on the negative electrode sheet.

[0014] The method for determining the segmented charging strategy provided by the present invention is based on the different suitable charging rate values ​​of the battery at different SOC stages. Combined with the method for determining the appropriate charging rate of the lithium-ion battery provided by the present invention, a better segmented charging strategy can be obtained that can avoid black spots or lithium precipitation on the negative electrode sheet and significantly reduce the charging time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 It is a structural schematic diagram of the breathing tooling involved in the present invention; Figure 2 This is the appearance of the negative electrode sheet of the experimental group of Example 1; Figures 3 to 5 The appearance of the negative electrode sheets of control groups 1 to 3 of Example 1 are respectively; Figure 6 This is the appearance of the negative electrode sheet of the experimental group of Example 2; Figures 7 to 9 They are the appearance of the negative electrode sheets of control groups 1 to 3 of Example 2 respectively. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0018] The present invention provides a method for determining a suitable charging rate of a lithium-ion battery, comprising: Provide breathing equipment: Figure 1 As shown, the breathing tooling includes a battery body and a transparent tube. The transparent tube is inserted from the outside of the battery body into the battery body, and a proper amount of electrolyte is injected so that the specific liquid level of the electrolyte can be observed in the transparent tube; Charging test: Within the specified SOC charging range, charge the battery at any rate value. After charging, observe the liquid level height h1 just after charging and the liquid level height h2 after standing for 10 to 30 minutes after charging. If the difference between h1 and h2 is within the range of 0 to 10 mm, the rate value is a suitable charging rate value within the specified SOC charging range, otherwise it is an inappropriate charging rate value.

[0019] If the charging rate value of a lithium-ion battery is inappropriate during the charging process, the negative electrode will expand too fast during charging and will not be able to absorb the electrolyte in time, causing local liquid shortage at the negative electrode, resulting in black spots or lithium precipitation. Based on this, the present invention provides a breathing tool to observe the electrolyte level after the battery is charged. If the liquid level remains basically unchanged after the charging is completed and after standing for a period of time, it proves that the charging electrolyte at this rate can be absorbed into the negative electrode sheet in time, which proves that the charging rate will not cause black spots or lithium precipitation on the negative electrode sheet; if the liquid level changes, it proves that there is a problem that the negative electrode has no time to absorb the electrolyte during the charging process, and charging at this rate will cause black spots or lithium precipitation on the negative electrode sheet. Therefore, the method provided by the present invention can determine whether the charging rate of a lithium-ion battery is appropriate.

[0020] Optionally, in order to avoid the setting of the transparent tube affecting the charging test results, the transparent tube should not be too thick, and an inner diameter of 0.5 to 5 mm (eg, 0.5 mm, 1 mm, 3 mm, or 5 mm) is optimal.

[0021] It should be noted that, for transparent tubes with larger inner diameters, higher requirements can be placed on the difference between h1 and h2 when judging whether it is an appropriate rate value after charging, that is, the difference between h1 and h2 needs to be closer to 0; and for transparent tubes with smaller inner diameters, lower requirements can be placed on the difference between h1 and h2 when judging whether it is an appropriate rate value after charging, that is, the difference between h1 and h2 can be slightly larger, which can be determined according to the specific type of battery and the usage requirements of the battery.

[0022] Optionally, the outer wall of the transparent tube is provided with scales, and the setting of the scales can facilitate the experimenter to judge whether there is an obvious liquid level difference just after charging and after charging for a period of time.

[0023] Furthermore, in order to obtain a better charging rate value, multiple charging tests are repeated, each charging test is charged at a different rate value, and appropriate charging rate values ​​within multiple defined SOC charging ranges are obtained, and the maximum rate value is taken as the optimal charging rate value.

[0024] Generally, a charging rate that is too high can easily cause black spots or lithium deposition on the negative electrode, but a charging rate that is too low can result in a too long charging time. Therefore, selecting the largest charging rate value from the appropriate charging rate values ​​can avoid black spots or lithium deposition on the negative electrode, ensuring that it will not affect the battery's cycle performance and avoid too long charging time.

[0025] Optionally, the charging rate value that can be accepted by the lithium-ion battery in the entire charging process is usually in the range of 0.1~1.5C, so a rate value in the range of 0.1~1.5C can be selected within the defined SOC charging range for charging test.

[0026] An embodiment of the present invention provides a method for determining a segmented charging strategy, comprising: Divide 0-100% SOC into at least 3 segments, select multiple charging rate values ​​in each segment and determine the best charging rate value according to the above method; Then the battery is charged in each of at least three segments according to the optimal charging rate value corresponding to each segment, which is a better segmented charging strategy.

[0027] The appropriate charging rate value for different SOC stages of the battery is different. Therefore, the battery 0~100% SOC can be divided into multiple segments. Multiple charging rate values ​​are selected for each segment for charging test to determine the optimal charging rate value, thereby obtaining a better segmented charging strategy that can avoid black spots or lithium plating on the negative electrode and significantly reduce the charging time.

[0028] Preferably, 0-100% SOC can be divided into three sections, namely 0-27% SOC, 27-75% SOC and 75-100% SOC. The inventors have found that by dividing the charging process into the above three sections and measuring the optimal charging rate values ​​of the above three sections, a better segmented charging strategy can be obtained.

[0029] More preferably, in the SOC charging range of 0~27%, multiple charging rate values ​​in the range of 0.1~0.8C are selected for charging to determine the optimal charging rate value; in the SOC charging range of 27~75%, multiple charging rate values ​​in the range of 0.8~1.6C are selected for charging to determine the optimal charging rate value; in the SOC range of 75~100%, multiple charging rate values ​​in the range of 0.1~0.8C are selected for charging to determine the optimal charging rate value.

[0030] By selecting multiple charging rate values ​​within the above rate range for testing at each stage, a better segmented charging strategy can be obtained.

[0031] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0032] Example 1 Determine the best segmented charging strategy: A 38.5Ah soft-pack laminated battery is provided as a battery body. The positive electrode sheet of the battery is prepared by slurrying according to a formula of lithium iron phosphate: conductive agent (SP): binder (PVDF): dispersant (HFF-2918) = 96.4%: 1.4%: 1.9%: 0.3%, and an aluminum foil with a surface density of 31.2 mg / cm^2 and 12μm is used; the negative electrode sheet is prepared by slurrying according to a formula of graphite: conductive agent (SP): dispersant (CMC): binder (SBR) = 95.0%: 2.0%: 1.0%: 2.0%, and a copper foil with a surface density of 16.15 mg / cm^2 and 6μm is used; the diaphragm is a 7+3μm single-sided ceramic; the solvent of the electrolyte is composed of EC, EMC, DEC and PC in a volume ratio of 32:60:5:3, and the lithium salt in the electrolyte is LiPF6 with a concentration of 1mol / L.

[0033] Discharge the battery and assemble it with a transparent tube with scale and inner diameter of 3mm to form a breathing tool. A total of sufficient breathing tools are assembled for use; Take four breathing fixtures, and charge the battery bodies of the four breathing fixtures at 0.1C, 0.3C, 0.5C and 0.7C respectively in the 0~27% SOC stage. When all are charged to 27% SOC, stop charging and record the h1 of the transparent tube of each breathing fixture. After 30 minutes, record the h2 of the transparent tube. Compare h1 and h2. The liquid level difference of the transparent tube in the breathing fixtures charged at 0.1C, 0.3C and 0.5C is almost 0. Therefore, these three values ​​are appropriate charging rate values. The maximum charging rate value of 0.5C is selected as the best charging rate value. Take another three breathing tools, all of which are charged to 27% SOC at 0.5C, and then test them again together with the previous group of breathing tools charged to 27% SOC at 0.5C. Select 0.8C, 1C, 1.3C and 1.6C to continue charging the battery body of the breathing tools to 75%, stop charging and record the h1 of the transparent tube of each breathing tool, and record the h2 of the transparent tube after 30 minutes. Compare h1 and h2. The liquid level difference of the transparent tube in the breathing tools charged at 0.8C, 1C, and 1.3C is almost 0. Therefore, these three values ​​are appropriate charging rate values, and the largest charging rate value of 1.3C is selected as the best charging rate value; Take another 3 breathing tools, all of which are first charged to 27% SOC at 0.5C, and then charged to 75% at 1.3C. After that, they are tested again together with the previous group of breathing tools charged to 75% at 1.3C. Select 0.1C, 0.2C, 0.3C and 0.5C respectively to continue charging the battery body of the breathing tooling to 100% SOC. Stop charging and record the h1 of the transparent tube of each breathing tooling. Record the h2 of the transparent tube after 30 minutes. Compare h1 and h2. The difference in liquid level of the transparent tube in the breathing tools charged with 0.1C, 0.2C and 0.3C is almost 0. Therefore, these three values ​​are appropriate charging rate values, and the largest charging rate value of 0.3C is selected as the best charging rate value.

[0034] Therefore, based on the above tests, the optimal segmented charging strategy for 38.5Ah soft-pack laminated batteries is 0.5C at 0-27% SOC, 1.3C at 27-75% SOC, and 0.3C at 75-100% SOC.

[0035] Verify the feasibility of the optimal charging strategy: Take 4 38.5Ah soft-pack laminated batteries that are the same as those used to make the breathing tooling above, one as the experimental group and the other three as the control group: Experimental group: After being discharged, the battery was charged according to the best segmented charging strategy. Control group 1: charging at 0.7C from 0 to 27% SOC, 1.3C from 27 to 75% SOC, and 0.3C from 75 to 100% SOC; Control group 2: charging at 0.5C from 0 to 27% SOC, 1.6C from 27 to 75% SOC, and 0.3C from 75 to 100% SOC; Control group 3: Charging was carried out at 0.5C at 0-27% SOC, 1.3C at 27-75% SOC, and 0.5C at 75-100% SOC.

[0036] Each experimental group and control group were subjected to charge and discharge cycle tests according to the above charging strategy. After 1000 cycles, the batteries were disassembled to observe whether there were black spots or lithium precipitation on the negative electrode sheet. Figure 2 The appearance of the negative electrode sheet in the experimental group is shown in Figure 2. Figure 3-Figure 5 The appearance of the negative electrode sheets of control groups 1 to 3 are shown in turn. It can be seen from the figure that Figure 3 The negative electrode shows no black spots and no lithium precipitation. Figures 3 to 5 The negative electrode sheets all showed different degrees of black spots and lithium precipitation, indicating that the segmented charging strategy obtained in this embodiment is effective.

[0037] Example 2 Determine the best segmented charging strategy: A 100Ah soft-pack laminated battery is provided as a battery body. The positive electrode sheet of the battery is prepared by slurrying according to a formula of lithium iron phosphate: conductive agent (SP): binder (PVDF): dispersant (BYK6420) = 96.0%: 1.7%: 2.0%: 0.3%, and an aluminum foil with a surface density of 32.05 mg / cm^2 and 12μm is used; the negative electrode sheet is prepared by slurrying according to a formula of graphite: conductive agent (SP): dispersant (CMC): binder (SBR) = 95.0%: 1.7%: 1.4%: 1.9%, and a copper foil with a surface density of 16.43 mg / cm^2 and 6μm is used; the diaphragm is a 16+2μm single-sided ceramic; the solvent of the electrolyte is composed of EC, EMC, DEC and PC in a volume ratio of 32:60:5:3, and the lithium salt in the electrolyte is LiPF6 with a concentration of 1mol / LL.

[0038] Discharge the battery and assemble it with a transparent tube with scale and inner diameter of 3mm to form a breathing tool. A total of sufficient breathing tools are assembled for use; Take four breathing fixtures, and charge the battery bodies of the four breathing fixtures at 0.2C, 0.4C, 0.6C and 0.8C respectively in the 0~27% SOC stage. When all are charged to 27% SOC, stop charging and record the h1 of the transparent tube of each breathing fixture. After 30 minutes, record the h2 of the transparent tube. Compare h1 and h2. The liquid level difference of the transparent tube in the breathing fixtures charged at 0.2C, 0.4C and 0.6C is almost 0. Therefore, these three values ​​are appropriate charging rate values. The maximum charging rate value of 0.6C is selected as the best charging rate value. Take another three breathing tools, all of which are charged to 27% SOC at 0.6C, and then test them again together with the previous group of breathing tools charged to 27% SOC at 0.6C. Select 1.0C, 1.3C, 1.6C and 1.9C to continue charging the battery body of the breathing tools to 75%, stop charging and record the h1 of the transparent tube of each breathing tool, and record the h2 of the transparent tube after 30 minutes. Compare h1 and h2. The liquid level difference of the transparent tube in the breathing tools charged at 1.0C, 1.3C and 1.6C is almost 0. Therefore, these three values ​​are appropriate charging rate values, and the largest charging rate value 1.6C is selected as the best charging rate value; Take another 3 breathing tools, all of which are first charged to 27% SOC at 0.6C, and then charged to 75% at 1.6C. After that, they are tested again together with the previous group of breathing tools charged to 75% at 1.6C. Select 0.2C, 0.4C, 0.6C and 0.8C respectively to continue charging the battery body of the breathing tooling to 100% SOC. Stop charging and record the h1 of the transparent tube of each breathing tooling. Record the h2 of the transparent tube after 30 minutes. Compare h1 and h2. The difference in liquid level of the transparent tube in the breathing tools charged at 0.2C and 0.4C is almost 0. Therefore, these three values ​​are appropriate charging rate values, and the largest charging rate value of 0.4C is selected as the best charging rate value. Therefore, based on the above tests, the optimal segmented charging strategy for 100Ah soft-pack laminated batteries is 0.6C at 0-27% SOC, 1.6C at 27-75% SOC, and 0.4C at 75-100% SOC.

[0039] Verify the feasibility of the optimal charging strategy: Take 4 100Ah soft-pack laminated batteries that are the same as those used to make the breathing tooling above, one as the experimental group and the other three as the control group: Experimental group: After being discharged, the battery was charged according to the best segmented charging strategy. Control group 1: charging at 0.9C from 0 to 27% SOC, 1.6C from 27 to 75% SOC, and 0.4C from 75 to 100% SOC; Control group 2: charging at 0.6C from 0 to 27% SOC, 1.9C from 27 to 75% SOC, and 0.4C from 75 to 100% SOC; Control group 3: Charging was carried out at 0.6C at 0-27% SOC, 1.6C at 27-75% SOC, and 0.6C at 75-100% SOC.

[0040] Each experimental group and control group were charged and discharged according to the above charging strategy. After 1000 cycles, the battery was disassembled to observe whether there were black spots or lithium precipitation on the negative electrode sheet. Figure 6The appearance of the negative electrode sheet in the experimental group is shown in Figure 2. Figure 7-Figure 9 The appearance of the negative electrode sheets of control groups 1 to 3 are shown in turn. It can be seen from the figure that Figure 6 The negative electrode shows no black spots and no lithium precipitation. Figures 7 to 9 The negative electrode sheets all showed different degrees of black spots and lithium precipitation, indicating that the segmented charging strategy obtained in this embodiment is effective.

[0041] In summary, the method for determining the appropriate charging rate of a lithium-ion battery provided by the present invention is to observe the electrolyte level after the battery is charged. If the liquid level remains basically unchanged just after the charging is completed and after standing for a period of time, it proves that the charging electrolyte at this rate can be absorbed into the negative electrode sheet in time, and it proves that black spots or lithium deposition on the negative electrode sheet will not be caused at this charging rate; if the liquid level changes, it proves that there is a problem that the negative electrode has no time to absorb the electrolyte back during the charging process, and charging at this rate will cause black spots or lithium deposition on the negative electrode sheet.

[0042] The method for determining the segmented charging strategy provided by the present invention is based on the different suitable charging rate values ​​of the battery at different SOC stages. Combined with the method for determining the appropriate charging rate of the lithium-ion battery provided by the present invention, a better segmented charging strategy can be obtained that can avoid black spots or lithium precipitation on the negative electrode sheet and significantly reduce the charging time.

[0043] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining a suitable charging rate of a lithium-ion battery, characterized in that: include: Providing a breathing tool: the breathing tool comprises a battery body and a transparent tube, wherein the transparent tube is inserted into the battery body from the outside of the battery body, and an electrolyte is injected so that the specific liquid level of the electrolyte can be observed in the transparent tube; Charging test: within the specified SOC charging range, the battery body is charged at any rate value. After charging, the liquid level height h1 just after the end of charging and the liquid level height h2 after standing for 10 to 30 minutes after charging are observed. If the difference between h1 and h2 is within the range of 0 to 10 mm, the rate value is a suitable charging rate value within the specified SOC charging range, otherwise it is an inappropriate charging rate value.

2. The method according to claim 1, characterized in that The inner diameter of the transparent tube is 0.5-5 mm.

3. The method according to claim 1, characterized in that: The outer wall of the transparent tube is provided with scales.

4. The method according to claim 1, characterized in that: The charging test is repeated multiple times, each charging test is performed at a different charging rate value, and multiple appropriate charging rate values ​​within the defined SOC charging range are obtained, and the maximum rate value is taken as the optimal charging rate value.

5. The method according to claim 1, characterized in that A plurality of rate values ​​were selected within the range of 0.1 to 1.5 C to perform the charging test.

6. A method for determining a segmented charging strategy for a lithium-ion battery, characterized in that: include: Divide 0-100% SOC into at least 3 segments, select multiple charging rate values ​​in each segment and determine the best charging rate value according to the method as claimed in claim 3; Then the battery is charged in each of the at least three sections according to the optimal charging rate value corresponding to each section, which is a better segmented charging strategy.

7. The determination method according to claim 6, characterized in that: 0~100% SOC is divided into three sections, namely 0~27% SOC, 27~75% SOC and 75~100% SOC.

8. The determination method according to claim 6, characterized in that: In the 0~27% SOC charging range, select multiple charging rate values ​​from 0.1~0.8C for charging and determine the optimal charging rate value; in the 27~75% SOC charging range, select multiple charging rate values ​​from 0.8~1.6C for charging and determine the optimal charging rate value; in the 75~100% SOC range, select multiple charging rate values ​​from 0.1~0.8C for charging and determine the optimal charging rate value.

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