A method for optimizing a lithium-ion battery charging strategy

Abstract

The present invention discloses a method for optimizing a lithium-ion battery charging strategy, comprising: step S1, for a certain type of battery for which the charging strategy needs to be optimized, obtaining the initial discharge capacity C of the battery of this type; step S2, dividing the battery charging SOC interval within a preset range into n battery charging SOC subintervals; step S3, obtaining the limit charging rate of each battery charging SOC subinterval through a voltage relaxation test method; step S4, obtaining the average charging rate C of the battery charging SOC interval within the preset range. ave Step S5: Obtain the optimal charge rate for the battery type in each of the n battery charging SOC subranges, i.e., obtain the optimal charging strategy for the battery type. This method utilizes voltage relaxation to obtain a limiting charge current, then optimizes the limiting charge current to ultimately achieve an optimal charging strategy. This method can reduce the risk of lithium plating and increase battery life.

Description

Technical Field

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

[0002] New energy vehicles have garnered significant attention in recent years. Lithium-ion batteries, a key component of these vehicles, directly impact vehicle performance, including range, safety, charging time, and service life. Battery life directly impacts vehicle cost, making it crucial for the continued adoption of new energy vehicles.

[0003] The battery charging strategy directly affects the battery life. A good charging strategy can improve the battery cycle life. Therefore, optimizing the charging strategy is very important to improve the battery cycle life. It can increase the battery life without increasing costs and enhance the competitiveness of the product.

[0004] Given that traditional constant current and constant voltage charging methods increase the risk of lithium deposition in batteries at high SOC states, reduce battery life, and pose safety risks, a step-by-step constant current charging strategy is now commonly used. The selection of step-by-step charging SOC intervals and corresponding charging currents is crucial and directly affects the battery's cycle life.

[0005] At present, for the charging strategy of step constant current charging, there are many ways to match the step charging SOC interval segments and charging current. Most battery manufacturers determine the current for step charging through the experimental method of cycle testing. Not only is the test time long and resource utilization low, but the test cost is also high. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for optimizing the charging strategy of a lithium-ion battery in view of the technical defects in the prior art.

[0007] To this end, the present invention provides a method for optimizing a lithium-ion battery charging strategy, comprising the following steps:

[0008] Step S1: For a battery model requiring optimized charging strategy, multiple batteries of the same model and production batch are selected, and after testing the discharge capacity of each battery, the average discharge capacity of all batteries is calculated, and the average discharge capacity of all batteries is used as the initial discharge capacity C of the battery model;

[0009] Step S2, dividing the battery charging SOC interval within the preset range into n battery charging SOC sub-intervals; n is a natural number greater than 1;

[0010] Step S3, obtaining the limit charge rate of each battery charging SOC sub-interval through a voltage relaxation test method;

[0011] Step S4, according to the limit charging rate of n battery charging SOC sub-intervals, by calculating the weighted average, thereby obtaining the average charging rate C of the battery charging SOC interval within the preset range. ave ;

[0012] In step S5, based on the average charging rate C0 required for this type of battery during cyclic use, the limit charging rate of the n battery charging SOC sub-intervals is multiplied by the same discount coefficient K to obtain the optimal charging rate of this type of battery in the n battery charging SOC sub-intervals, that is, to obtain the optimal charging strategy for this type of battery.

[0013] Preferably, in step S2, the preset range of the battery charging SOC interval is the entire battery charging SOC interval, that is, 0 to 100% SOC.

[0014] Preferably, in step S2, the battery charging SOC interval within the preset range is divided into n battery charging SOC sub-intervals, specifically as follows:

[0015] Starting from the starting end SOC to the ending SOC of the battery charging SOC interval within the preset range, the battery charging SOC interval within the preset range is evenly divided into n battery charging SOC sub-intervals.

[0016] Preferably, in step S3, the limit charge rate of each battery charging SOC sub-interval is obtained by a voltage relaxation test method, including the following steps:

[0017] Step S31: For the multiple batteries in step S1, using the initial discharge capacity C as the battery charging current rate reference, constant current charging is performed at different charging current rates to the end SOC of the battery charging SOC sub-interval, and then the batteries are left to rest for the same preset time. During the rest period, the battery voltage V and the rest time t of each battery are recorded in real time, as well as the corresponding relationship between them.

[0018] Step S32 , obtaining a limit charging rate of the battery charging SOC sub-interval according to a corresponding relationship between the battery voltage V and the rest time t of the plurality of batteries in the rest stage.

[0019] Preferably, in step S32, according to the corresponding relationship between the battery voltage V and the rest time t of the multiple batteries in the rest stage, the limit charging rate of the battery charging SOC sub-interval is obtained, which specifically includes the following sub-steps:

[0020] Step S321: Differentiate the battery voltage V of each battery during the rest phase with respect to the rest time t of the battery to calculate dV / dt. Then, plot the relationship between the battery voltage differential dV / dt during the rest phase and the rest time t for each battery using the rest time t as the horizontal axis and dV / dt as the vertical axis. This curve is defined as the voltage differential curve of each battery.

[0021] Step S322 : For the voltage differential curves of the multiple batteries, when the voltage differential curve of one of the batteries does not show a voltage drop, it is determined that the charging rate corresponding to the voltage differential curve of the battery is the limit charging rate of the battery charging SOC sub-interval.

[0022] Preferably, the voltage differential curve that has just not experienced a voltage sag is a voltage differential curve having the largest charge rate among all voltage differential curves having a lower charge rate than the voltage differential curve having experienced a voltage sag, among the voltage differential curves of the plurality of batteries;

[0023] The voltage differential curve in which a voltage drop has occurred is a voltage differential curve in which the battery voltage differential first increases, then decreases, and then increases again.

[0024] Preferably, the average charging rate C of the battery charging SOC interval within the preset range is obtained by calculating the weighted average. ave , as follows:

[0025] C ave =(C max1 *S1+C max2 *S2+…+C maxn *Sn) / (S1+S2+…+Sn);

[0026] Among them, the limit charging rate of the n-segment battery charging SOC sub-interval is expressed as C max1 、C max2 …C maxn ;

[0027] The SOC range values ​​of the n battery charging SOC sub-intervals are represented as S1, S2...Sn respectively.

[0028] Preferably, in step S5, the discount coefficient K=C0 / C ave .

[0029] Preferably, in step S5, the optimal charging strategy for the battery of this type specifically includes: n battery charging SOC sub-intervals of the battery of this type and the optimal charging rate corresponding to each battery charging SOC sub-interval.

[0030] It can be seen from the technical solution provided by the present invention above that, compared with the prior art, the present invention provides a method for optimizing the charging strategy of a lithium-ion battery. The method is scientifically designed and obtains the limiting charging current through a voltage relaxation method, and then optimizes the limiting charging current to finally obtain the optimal charging strategy. This method can reduce the risk of lithium plating in the battery and increase the service life of the battery, and has great practical significance.

[0031] The method provided by the present invention has a scientific workflow, is convenient and fast, can save testing time, and has certain guiding significance for the formulation of charging strategies for batteries of different models. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A basic flow chart of a lithium-ion battery charging strategy optimization method provided by the present invention;

[0033] Figure 2 This is a schematic diagram of the dV / dt-t curves of two batteries at rest after charging to 80% SOC at different rates, using 80% SOC as an example, for optimizing the charging strategy of a lithium-ion battery provided by the present invention (i.e., the method of obtaining the limiting charging current through voltage relaxation testing).

[0034] Figure 3 A method for optimizing a lithium-ion battery charging strategy provided by the present invention is provided, which shows a schematic diagram of the capacity retention rate during cyclic charging and discharging under the preferred charging strategy in Example 1 and other charging strategies, and charging and discharging at 1C. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and implementation methods.

[0036] See also Figures 1 to 3 The present invention provides a method for optimizing a lithium-ion battery charging strategy, comprising the following steps:

[0037] Step S1: For a battery model requiring optimized charging strategy, multiple batteries of the same model and production batch are selected. After testing the discharge capacity of each battery, the average discharge capacity of all batteries is calculated. The average discharge capacity of all batteries is used as the initial discharge capacity C of the battery model, and the initial discharge capacity C is used as the rate reference for the battery charging current.

[0038] In step S1, for each of the multiple batteries, charge and discharge for multiple cycles (e.g., three cycles, i.e., three charge-discharge cycles, where charging to the charge cutoff voltage and then discharging to the discharge cutoff voltage constitutes one cycle) at 0.33 times the nominal current to obtain the discharge capacities C1, C2, C3, ..., Cn of all the batteries. The average discharge capacity of all the batteries, C, is then calculated.

[0039] It should be noted that the method for testing the discharge capacity of each battery can directly adopt the commonly known method, which will not be described in detail here.

[0040] It should be noted that, in the present invention, step S1 can obtain the standard capacity of the battery (i.e., the initial discharge capacity C) and determine the benchmark for charging at different rates. Using the initial discharge capacity C as a standard, the magnitude of the current at different rates of the test battery can be determined.

[0041] Step S2, dividing the preset range of battery charging SOC interval (e.g., 0-80% SOC) into n battery charging SOC sub-intervals; n is a natural number greater than 1;

[0042] In step S2, in specific implementation, the preset range of battery charging SOC interval can be the entire battery charging SOC interval (ie, 0-100% SOC), or can be other user-preset range of battery charging SOC interval, such as 0-80% SOC.

[0043] In step S2, in a specific implementation, the battery charging SOC interval within the preset range is divided into n battery charging SOC sub-intervals, as follows:

[0044] Starting from the starting SOC (for example, SOC is 0) of the battery charging SOC interval within the preset range to the ending SOC, the battery charging SOC interval within the preset range is divided into (specifically, can be evenly divided into) n battery charging SOC sub-intervals.

[0045] In step S2, it should be noted that the SOC range values ​​of the n battery charging SOC sub-intervals can be respectively expressed as S1, S2, ..., Sn. The SOC range values ​​of the n battery charging SOC sub-intervals can be the same or different.

[0046] Step S3, obtaining the limit charge rate of each battery charging SOC sub-interval through a voltage relaxation test method;

[0047] In step S3, in a specific implementation, the limit charging rate of each battery charging SOC sub-interval is obtained through a voltage relaxation test method, including the following steps:

[0048] Step S31, for the plurality of batteries in step S1, and with the initial discharge capacity C as the rate reference of the battery charging current, respectively with the charging current with different rate size, constant current charging to the end of the battery charging SOC sub-interval, and then static for the same pre-set time, record the battery voltage V and the static time t and their corresponding relationship in real time during the static stage;

[0049] In step S31, the plurality of batteries are respectively charged with the charging current with different rate size, in order to obtain the voltage relaxation data under different current charging, and obtain the maximum charging current supported.

[0050] The rate in step S31 is the charging rate with the initial discharge capacity C as the standard, for example, 1.5C, 1.6C, 1.7C and the like.

[0051] Step S32, according to the corresponding relationship (i.e. the change relationship) of the battery voltage V of the plurality of batteries with the static time t in the static stage, the limit charging rate (i.e. the limit charging current) of the battery charging SOC sub-interval is obtained;

[0052] In detail, in step S32, according to the corresponding relationship (i.e. the change relationship) of the battery voltage V of the plurality of batteries with the static time t in the static stage, the limit charging rate (i.e. the limit charging current) of the battery charging SOC sub-interval is obtained, which specifically includes the following sub-steps:

[0053] Step S321, differentiating the battery voltage V of each battery with the static time t in the static stage, calculating dV / dt, and then taking the static time t as the abscissa and dV / dt as the ordinate, drawing the relationship curve of the battery voltage differential (dV / dt) and the static time (t) in the static stage of each battery, and defining it as the voltage differential curve of each battery;

[0054] Step S322, for the voltage differential curves of the plurality of batteries, when the voltage differential curve of one of the batteries just does not appear voltage drop (i.e. the voltage differential value does not drop), it is judged that the charging rate corresponding to the voltage differential curve of the battery is the limit charging rate (i.e. the limit charging current) of the battery charging SOC sub-interval;

[0055] The voltage differential curve that just does not appear voltage drop is the voltage differential curve with the maximum charging rate among all the voltage differential curves (which may include one or more voltage differential curves) with lower charging rate than the voltage differential curve that has appeared voltage drop in the voltage differential curves of the plurality of batteries;

[0056] The voltage differential curve having experienced a voltage drop is a voltage differential curve showing a trend in which the battery voltage differential first increases, then decreases, and then increases again (ie, a trough appears).

[0057] It should be noted that when the voltage differential curve shows a monotonically increasing trend, there is no voltage drop, and the charging current does not exceed the battery's limit charging current; when the battery voltage differential in the voltage differential curve shows a trend of first increasing, then decreasing, and then increasing again, it means that a voltage drop has occurred, and at this time the charging current exceeds the limit charging current.

[0058] It should be noted that, for the present invention, whether the battery's limit charging current is reached is determined based on whether the battery's voltage differential curve has a voltage drop (i.e., whether the voltage differential value has dropped). This is divided into three situations: (1) If a voltage drop occurs in a battery's voltage differential curve, it means that the charging rate corresponding to the voltage differential curve exceeds the limit charging rate (i.e., the limit charging current) of the battery's charging SOC sub-interval; (2) If a battery's voltage differential curve does not have a voltage drop, it means that the charging rate corresponding to the voltage differential curve does not reach the limit charging rate (i.e., the limit charging current) of the battery's charging SOC sub-interval. (3) When the charging rate selected by a battery results in the voltage differential curve (i.e., the battery's voltage differential curve) not having a voltage drop, then the charging rate (i.e., the charging rate corresponding to the battery's voltage differential curve) is the battery's limit charging rate.

[0059] It should be noted that the current is tested from large to small, and the voltage differential curves are obtained one by one. When a voltage drop occurs in the differential curve, it means that the limit charging current is exceeded. The charging rate is then reduced by 0.1C, and the test is continued to obtain the voltage differential curve. This is repeated. When the current is reduced to the point where no voltage drop occurs in the obtained voltage differential curve, it means that no voltage drop occurs. At this time, the corresponding current is the limit charging rate.

[0060] Step S4, according to the limit charging rate of n battery charging SOC sub-intervals, by calculating the weighted average, thereby obtaining the average charging rate C of the battery charging SOC interval within the preset range. ave ;

[0061] In step S4 , the weight corresponding to the limit charge rate of each battery charging SOC sub-interval is equal to the SOC range value of the battery charging SOC sub-interval (ie, the difference between the end SOC and the starting SOC of the sub-interval), for example, 20%.

[0062] In specific implementation, the limit charging rate of the n-segment battery charging SOC sub-interval is expressed as C max1 、C max2 …C maxnThe SOC range values ​​of the n-segment battery charging SOC sub-intervals can be expressed as S1, S2...Sn, respectively. S1, S2...Sn are used as the weights of the limit charging rate of the n-segment battery charging SOC sub-intervals. Then, by calculating the weighted average, the average charging rate C of the battery charging SOC interval in the preset range is obtained. ave , as follows:

[0063] C ave =(C max1 *S1+C max2 *S2+…+C maxn *Sn) / (S1+S2+…+Sn).

[0064] Step S5: Based on the average charging rate C0 required (i.e., needed) for this type of battery during cycling, the limit charging rates of the n battery charging SOC sub-intervals are multiplied by the same discount factor K to obtain the optimal charging rate (i.e., optimized charging rate) of this type of battery in the n battery charging SOC sub-intervals, that is, to obtain the optimal charging strategy for this type of battery.

[0065] It should be noted that the required average charge rate refers to the charge rate used during cycle testing of unoptimized batteries, typically 1C. Alternatively, it can be the charge rate pre-set during actual use of batteries in new energy vehicles (electric vehicles).

[0066] In step S5, in specific implementation, the discount coefficient K=C0 / C ave .

[0067] In step S5, in specific implementation, the optimal charging strategy for the battery model includes: n battery charging SOC sub-intervals of the battery model and the optimized charging rate (i.e., the optimal charging rate) corresponding to each battery charging SOC sub-interval.

[0068] In step S5, the optimal charging rate (i.e., optimized charging rate) of the n battery charging SOC sub-intervals is specifically implemented as follows: the product of the limit charging rate of each battery charging SOC sub-interval and the discount coefficient K, which can be expressed as: KC max1 , KC max2 …KC maxn .

[0069] In order to more clearly understand the technical solution of the present invention, the technical solution of the present invention is described below through specific embodiments.

[0070] Example 1.

[0071] In the first step, multiple soft-pack batteries of the same model and the same batch were selected, and the initial discharge capacity of the battery was measured to be 3Ah.

[0072] The second step is to pre-divide the preset range of battery charging SOC into n intervals (i.e., n battery charging SOC sub-intervals). For example, the preset range of charging SOC is set to 0-80% SOC, which is evenly divided into four intervals: 0-20%, 20%-40%, 40%-60%, and 60%-80%. The SOC range value of each battery charging SOC sub-interval (i.e., S1, S2, S3, and S4 are equal) is equal to 20%.

[0073] In a specific implementation, the value range of each battery charging SOC sub-interval is between 5% and 30%. The specific value can be set according to actual conditions and is not specifically limited here.

[0074] The third step is to charge any battery to 20%, 40%, 60% and 80% SOC (i.e. the end SOC of the multi-segment battery charging SOC sub-interval) using different current rates, and then let it rest for 10 minutes. The battery voltage and rest time are recorded. Then, a dV / dt-t curve is drawn and the judgment is made based on the curve. Taking the 60%-80% interval as an example, Figure 2 After charging the two batteries to 80% SOC at 1.8C and 1.9C respectively, the dV / dt-t curves obtained after the static stage are shown. Figure 2 It can be seen that when the current is 1.9C, the dV / dt-t curve shows a voltage drop between 50 and 100 seconds. By reducing the charge rate by 0.1C and testing a 1.8C charge, the voltage differential curve shows no voltage drop, so 1.8C is determined to be the limit charge rate for the 60%-80% range. Similarly, using the same method, the limit charge rates for 0-20% SOC, 20%-40% SOC, 40%-60% SOC, and 60%-80% SOC are 3.4C, 3.0C, 2.5C, and 1.8C, respectively.

[0075] Table 1 shows the limit charging current obtained according to the voltage relaxation method

[0076]

[0077]

[0078] According to the data in Table 1 above, the average charging rate C of the charging range 0-80% SOC is calculated when the four SOC intervals (i.e., the four battery charging SOC sub-intervals) are all at the limit charging rate. ave=(3.4*0.2+3.0*0.2+2.5*0.2+1.8*0.2)* / 0.8, calculate the limit average charging rate C of the battery charging SOC interval in the preset range (0-80%) ave is 2.675C.

[0079] Since the battery requires a charging rate C0 of 2C, the discount factor K = C0 / C ave =0.748.

[0080] Then, the limit charging rates of 0-20% SOC, 20%-40% SOC, 40%-60% SOC, and 60%-80% SOC (i.e., the four battery charging SOC sub-intervals) are multiplied by the discount coefficient K to obtain the optimal charging strategy: the charging rates of the four intervals of 0-20%, 20%-40%, 40%-60%, and 60%-80% (i.e., the four battery charging SOC sub-intervals) are 2.54C, 2.24C, 1.87C, and 1.35C, respectively.

[0081] Among them, since batteries are prone to lithium deposition when charged at high rates, lithium deposition can lead to a rapid decline in the battery's cycle life. Therefore, in the present invention, the limit charge rate of the battery at different SOC segments is found based on the voltage relaxation test method, and then uniformly multiplied by a discount factor. This can uniformly reduce the risk of lithium deposition at each SOC and improve the battery's cycle life. Preferably, the discount factor K used in the present invention is usually less than 0.9.

[0082] Figure 3 Figure 3 is a schematic diagram of battery cycle performance under different charging strategies at 25°C, where battery P1 is charged using the optimal charging strategy and discharged at 1C; battery P2 is charged at a 2C constant current and discharged at 1C; battery P3 is charged using other charging strategies equivalent to 2C, specifically, the charging rates in the four intervals of 0-20%, 20%-40%, 40%-60%, and 60%-80% are 2.7C, 2.3C, 2.0C, 1.0C, and the discharge is 1C. Figure 3 The results show that the battery cycle life is significantly improved by the charging strategy optimized by the method of the present invention.

[0083] Example 2:

[0084] In the first step, multiple soft-pack batteries of the same model and the same batch were selected, and the initial discharge capacity of the battery was measured to be 3Ah.

[0085] The second step is to pre-divide the preset battery charging SOC range into n intervals. For example, the preset charging range is set to 0-80% SOC, divided into four intervals: 0-20%, 20%-40%, 40%-60%, and 60%-80%. The SOC range value of each battery charging SOC sub-range (i.e., S1, S2, S3, and S4 are equal) is equal to 20%.

[0086] The third step is to charge any battery to 20%, 40%, 60%, and 80% SOC (i.e., the end SOC of multiple battery charging SOC sub-intervals) using currents of different rates, let it rest for 10 minutes, and record the battery voltage and rest time. A dV / dt-t curve is drawn, and the limit charging current of each battery charging SOC sub-interval is determined based on whether the curve has a voltage drop. The ultimate limit charging rates for 0-20% SOC, 20%-40% SOC, 40%-60% SOC, and 60%-80% SOC are 3.4C, 3.0C, 2.5C, and 1.8C, respectively.

[0087] According to the obtained data, the average charging rate C of the charging range 0-80% SOC is calculated when the four SOC intervals (i.e., the four battery charging SOC sub-intervals) are all at the limit charging rate. ave =(3.4*0.2+3.0*0.2+2.5*0.2+1.8*0.2)* / 0.8, calculate the limit average charging rate C of the battery charging SOC interval in the preset range (0-80%) ave is 2.675C.

[0088] In this embodiment 2, the required charging rate C0 of the battery is 1C, so the discount coefficient K=C0 / C ave =0.374.

[0089] Then, the limit charging rates of 0-20% SOC, 20%-40% SOC, 40%-60% SOC, and 60%-80% SOC (i.e., the four battery charging SOC sub-intervals) are multiplied by the discount coefficient K to obtain the optimal charging strategy: the charging rates of the four intervals of 0-20%, 20%-40%, 40%-60%, and 60%-80% (i.e., the four battery charging SOC sub-intervals) are 1.27C, 1.12C, 0.94C, and 0.67C, respectively.

[0090] Therefore, when the battery cycle requires a charging rate of 1C, the same method obtains the optimal charging strategy.

[0091] In summary, compared with the existing technology, the optimization method of the lithium-ion battery charging strategy provided by the present invention is scientifically designed. It is a method that obtains the limiting charging current through the voltage relaxation method, and then optimizes the limiting charging current to finally obtain the optimal charging strategy. It can reduce the risk of battery lithium plating and increase the service life of the battery, and has great practical significance.

[0092] The method provided by the present invention has a scientific workflow, is convenient and fast, can save testing time, and has certain guiding significance for the formulation of charging strategies for batteries of different models.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for optimizing a lithium-ion battery charging strategy, characterized in that: The following steps are involved: Step S1: For a battery model requiring optimized charging strategy, multiple batteries of the same model and production batch are selected, and after testing the discharge capacity of each battery, the average discharge capacity of all batteries is calculated, and the average discharge capacity of all batteries is used as the initial discharge capacity C of the battery model; Step S2, dividing the battery charging SOC interval within the preset range into n battery charging SOC sub-intervals; n is a natural number greater than 1; Step S3: Obtaining the limit charge rate for each battery charging SOC sub-interval through a voltage relaxation test method; when the battery voltage differential curve just does not show a voltage drop, determining that the charge rate corresponding to the battery voltage differential curve is the limit charge rate for the battery charging SOC sub-interval; Step S4, according to the limit charging rate of n battery charging SOC sub-intervals, by calculating the weighted average, thereby obtaining the average charging rate C of the battery charging SOC interval within the preset range. ave ; Step S5: Based on the average charging rate C0 required by the battery model during the cycle, the limit charging rate of the n battery charging SOC sub-intervals is multiplied by the same discount coefficient K to obtain the optimal charging rate of the battery model in the n battery charging SOC sub-intervals, that is, to obtain the optimal charging strategy for the battery model; the discount coefficient K = C0 / C ave .

2. The method for optimizing the lithium-ion battery charging strategy according to claim 1, wherein: In step S2 , the preset range of the battery charging SOC interval is the entire battery charging SOC interval, that is, 0-100% SOC.

3. The method for optimizing the lithium-ion battery charging strategy according to claim 1, wherein: In step S2, the battery charging SOC interval within the preset range is divided into n battery charging SOC sub-intervals, as follows: Starting from the starting end SOC to the ending SOC of the battery charging SOC interval within the preset range, the battery charging SOC interval within the preset range is evenly divided into n battery charging SOC sub-intervals.

4. The method for optimizing the lithium-ion battery charging strategy according to claim 1, wherein: In step S3, the limit charge rate of each battery charging SOC sub-interval is obtained by a voltage relaxation test method, including the following steps: Step S31: For the multiple batteries in step S1, using the initial discharge capacity C as the battery charging current rate reference, constant current charging is performed at different charging current rates to the end SOC of the battery charging SOC sub-interval, and then the batteries are left to rest for the same preset time. During the rest period, the battery voltage V and the rest time t of each battery are recorded in real time, as well as the corresponding relationship between them. Step S32 , obtaining a limit charging rate of the battery charging SOC sub-interval according to a corresponding relationship between the battery voltage V and the rest time t of the plurality of batteries in the rest stage.

5. The method for optimizing the lithium-ion battery charging strategy according to claim 1, wherein: In step S32, based on the corresponding relationship between the battery voltage V and the rest time t of the multiple batteries in the rest stage, the limit charging rate of the battery charging SOC sub-interval is obtained, which specifically includes the following sub-steps: Step S321: Differentiate the battery voltage V of each battery during the rest phase with respect to the rest time t of the battery to calculate dV / dt. Then, plot the relationship between the battery voltage differential dV / dt during the rest phase and the rest time t for each battery using the rest time t as the horizontal axis and dV / dt as the vertical axis. This curve is defined as the voltage differential curve of each battery. Step S322 : For the voltage differential curves of the multiple batteries, when the voltage differential curve of one of the batteries does not show a voltage drop, it is determined that the charging rate corresponding to the voltage differential curve of the battery is the limit charging rate of the battery charging SOC sub-interval.

6. The method for optimizing the lithium-ion battery charging strategy according to claim 5, wherein: The voltage differential curve for not experiencing a voltage sag is a voltage differential curve having the largest charge rate among all voltage differential curves having a lower charge rate than the voltage differential curve for experiencing a voltage sag, among the voltage differential curves of the plurality of batteries; The voltage differential curve in which a voltage drop has occurred is a voltage differential curve in which the battery voltage differential first increases, then decreases, and then increases again.

7. The method for optimizing the lithium-ion battery charging strategy according to claim 1, wherein: By calculating the weighted average, the average charging rate C of the battery charging SOC interval within the preset range is obtained. ave , as follows: C ave =(C max1 *S1+ C max2 *S2+…+C maxn *Sn) / (S1+S2+…+Sn); Among them, the limit charging rate of the n-segment battery charging SOC sub-interval is expressed as C max1 、C max2 …C maxn ; The difference between the maximum and minimum SOC values ​​within the SOC range of the n battery charging SOC sub-intervals is represented as S1, S2...Sn respectively.

8. The method for optimizing a lithium-ion battery charging strategy according to any one of claims 1 to 7, wherein: In step S5, the optimal charging strategy for the battery type specifically includes: n battery charging SOC sub-intervals of the battery type and the optimal charging rate corresponding to each battery charging SOC sub-interval.

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