Lithium ion battery rapid charging strategy selection method

Abstract

The invention discloses a rapid charging strategy selection method for a lithium ion battery. The rapid charging strategy selection method comprises the following steps: step 1, setting priority options of charging; step 2, a user selects a charging priority and a secondary priority; 3, obtaining a charging scheme according to the charging priority; 4, acquiring different charging condition data of the lithium ion battery; and step 5, selecting a corresponding charging scheme for charging according to the charging priority sequence of the user in combination with the charging scheme and the test data, and realizing autonomous selection of quick charging. The rapid charging strategy selection method of the lithium ion battery can optimize the rapid charging strategy of the lithium ion battery, save the development cost of a battery management system, delay the degradation of battery performance, meet the use requirements of users, realize independent selection of rapid charging, and more accord with practical application.

Description

Technical Field

[0001] The present invention relates to the technical field of rapid charging of lithium-ion batteries, and specifically to a method for selecting a rapid charging strategy for lithium-ion batteries. Background Art

[0002] With the rapid development of multiple industries such as electric vehicles and renewable energy, the demand for power batteries is increasing continuously. Among them, lithium-ion batteries are widely used in electric vehicles due to their high energy density, long cycle life, and low self-discharge rate. Compared with traditional fuel vehicles, electric vehicles have a longer energy replenishment time and need to be charged frequently during long-distance driving. In order to better meet the user's usage requirements, the application of rapid charging technology (fast charging) in the charging process of electric vehicles is increasing continuously. At present, the general standard for rapid charging in the electric vehicle industry is to charge to 80% SOC (State of Charge) within 30 minutes. The fast charging technology can significantly reduce the battery charging time and improve the efficiency. Therefore, the fast charging technology has become an important research direction for lithium-ion batteries.

[0003] There are many fast charging methods for lithium-ion batteries, mainly including constant current constant voltage charging, multi-stage constant current constant voltage charging, constant power constant voltage charging, pulse charging, combined charging, etc.

[0004] Constant current constant voltage is the current mainstream charging method, which is simple and convenient to control, but has problems such as low energy efficiency, serious polarization, lithium deposition, and accelerated life decline.

[0005] Multi-stage constant current constant voltage charging divides the constant current stage into multiple stages, which can dynamically adjust the current in the charging stage, reduce charging temperature rise and decline, but the control is complex and the hardware cost is high.

[0006] Constant power constant voltage charging maintains a constant power during the charging process, with simple control, strong adaptability, and high energy efficiency, but the charging time at the end of charging is long.

[0007] Pulse charging relieves polarization through intermittent charging, improves efficiency and extends life, requires high-precision control hardware, has a high cost, and is difficult to adapt to various batteries.

[0008] Combined charging is composed of multiple charging methods, which can improve charging flexibility, but has high complexity and large cost.

[0009] The above fast charging methods have their own advantages and disadvantages, but in the actual battery management system, some charging methods have complex control and high costs, resulting in a single fast charging condition setting in the battery management system, which is not adjusted according to the actual usage requirements of users, will cause loss of battery performance and affect the user experience. Therefore, it is necessary to improve the charging strategy. Summary of the Invention

[0010] In view of the deficiencies of the prior art, the present invention provides a method for selecting a fast charging strategy for a lithium-ion battery, which solves the problem of xxxx.

[0011] To achieve the above object, the present invention is realized through the following technical solutions: A method for selecting a fast charging strategy for a lithium-ion battery includes the following steps:

[0012] Step 1, set the priority options for charging;

[0013] Step 2, the user selects the primary and secondary priorities for charging;

[0014] Step 3, obtain the charging scheme according to the charging priority;

[0015] Step 4, obtain the data of different charging conditions of the lithium-ion battery;

[0016] Step 5, according to the charging priority order of the user, combine the charging scheme and the test data, select the corresponding charging scheme for charging, and achieve autonomous selection of fast charging.

[0017] Preferably, in the above step 1, the priority options for the charging mode at least include charging time, energy efficiency, and battery charging loss. The charging time refers to the time required for the battery to be charged to the target SOC; the energy efficiency refers to the ratio of the energy consumed when discharging at 1C to 0% SOC after being fully charged under the selected charging condition to the energy actually charged under the selected charging condition; the battery charging loss refers to the degree of influence of the charging condition on the battery capacity degradation.

[0018] Preferably, in the above step 2, the primary priority is the first goal to be achieved, and the secondary priority is the second goal to be achieved. When the charging time is the goal to be achieved, it is all processed according to the requirement of fully charging 80% SOC within 30 minutes.

[0019] Preferably, the above step 3 is to obtain the charging scheme according to the charging priority, including the set priority options and the user's priority selection results, enter the processing and analysis, and obtain the optional charging scheme:

[0020] Taking the charging time as the priority and the battery charging loss as the secondary priority, select the charging scheme with the fastest charging time and less battery loss; taking the energy efficiency as the secondary priority, select the charging scheme with the fastest charging time and higher energy efficiency;

[0021] Taking the energy efficiency as the priority and the charging time as the secondary priority, select the charging method with the highest energy efficiency and faster charging time; taking the battery charging loss as the secondary priority, select the charging scheme with the highest energy efficiency and less battery loss;

[0022] Prioritize battery charging loss and secondary prioritize charging time, and select a charging scheme that minimizes battery loss and has a relatively fast charging time; secondary prioritize energy efficiency and select a charging scheme that minimizes battery loss and has a relatively high energy efficiency.

[0023] Preferably, the data of the battery under different charging conditions obtained in step four at least includes: the charging time to 80% SOC at three different rates under two charging methods; the charging capacity, discharge capacity, energy efficiency, and Coulomb efficiency of charging cycles at three different rates under two charging methods.

[0024] The two charging methods are any two of constant current constant voltage, constant power constant voltage, multi-stage constant current constant voltage, pulse charging, and combined charging.

[0025] The three charging rates include: normal charging rate (theoretically fully charged within 60 minutes), fast charging rate (theoretically fully charged within 30 minutes), and extreme fast charging rate (theoretically fully charged within 20 minutes).

[0026] Charging capacity: The capacity stored by the battery during charging.

[0027] Discharge capacity: The capacity released by the battery during discharge.

[0028] Coulomb efficiency: The ratio of the discharge capacity to the charging capacity during charge and discharge.

[0029] Based on the above experimental scheme, the steps to obtain experimental data are as follows:

[0030] S1. Set the SOC range for charging time test to 0% - 80%; set the expected cyclic charge and discharge SOC range to 0% - 100%; the number of cycles is defaulted to 350 times; set the cyclic discharge condition to 1C constant current discharge.

[0031] S2. Select two charging modes.

[0032] S3. Set three charging rates: normal charging rate (theoretically fully charged within 60 minutes), fast charging rate (theoretically fully charged within 30 minutes), and extreme fast charging rate (theoretically fully charged within 20 minutes).

[0033] The combination of the two charging modes and three charging rates results in six charging conditions:

[0034] Charging mode 1: normal charging rate, fast charging rate, extreme fast charging rate

[0035] Charging mode 2: normal charging rate, fast charging rate, extreme fast charging rate

[0036] All of the six charging conditions are to charge until the charging cut-off voltage of the battery and then continue constant voltage charging until the charging cut-off current, and there is a 20-minute rest between charge and discharge;

[0037] S4. Start the cyclic test.

[0038] Preferably, step five is to analyze and select according to the optional solutions and experimental data obtained above to achieve autonomous selection of fast charging. The lithium-ion battery is a nickel-cobalt-manganese ternary lithium-ion battery or a lithium iron phosphate battery.

[0039] Beneficial effects

[0040] The present invention provides a method for selecting a fast charging strategy for a lithium-ion battery. Compared with the prior art, it has the following beneficial effects:

[0041] This method for selecting a fast charging strategy for a lithium-ion battery can optimize the fast charging strategy of the lithium-ion battery, save the development cost of the battery management system, delay the decline of battery performance, meet the user's usage requirements, and achieve autonomous selection of fast charging. The present invention proposes priority options for charging, which can simplify the complexity of autonomous selection of fast charging by users. Based on a single charging method, the present invention adds another charging method, and also designs multiple charging conditions based on different charging rates for users to choose from to improve charging efficiency and flexibility. Therefore, it improves the problem of single charging conditions in the existing battery management system, can achieve efficient and fast charging of lithium-ion batteries, delay the decline of battery performance, and can meet the user's selection requirements for battery charging, which is more in line with practical applications. Description of the drawings

[0042] Figure 1 It is a flowchart of the method for selecting a fast charging strategy for a lithium-ion battery;

[0043] Figure 2 It is the time and energy efficiency curve of the first cycle for a lithium-ion battery to charge from 0% SOC to 80% SOC under different charging conditions;

[0044] Figure 3 It is the discharge capacity curve of a lithium-ion battery during cycling under different charging conditions;

[0045] Figure 4 It is the energy efficiency curve of a lithium-ion battery during cycling under different charging conditions. Detailed implementation manners

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] Please refer to Figures 1-4 , a method for selecting a fast charging condition of a lithium-ion battery according to the present invention, wherein the lithium-ion battery is a ternary lithium-ion battery or a lithium iron phosphate battery.

[0048] The following further elaborates on the specific embodiments of the present invention:

[0049] Embodiment 1

[0050] In this embodiment, a ternary lithium-ion battery with a model of 18650 and a rated capacity of 2 Ah is used as the research object. As Figure 1 shown, a method for selecting a fast charging condition of a lithium-ion battery is established as follows:

[0051] The battery characteristic data required in this paper is obtained by performing charge and discharge cycles on a 18650 ternary lithium-ion battery under different charging conditions using a Wuhan Blue Electric CT3002K battery test system.

[0052] The SOC range for charging time testing is set to 0% - 80%; the expected cyclic charge and discharge SOC range is set to 0% - 100%; the number of cycles is defaulted to 350 times; the cyclic discharge condition is set to 1C constant current discharge; two charging methods, constant current constant voltage and constant power constant voltage, are set; three charging rates are set, including a normal charging rate (fully charged within 60 minutes theoretically), a fast charging rate (fully charged within 30 minutes theoretically), and an extreme fast charging rate (fully charged within 20 minutes theoretically). According to this setting, six charging conditions are obtained, including: 1C (2A) - constant current constant voltage charging, 2C (4A) - constant current constant voltage charging, 3C (6A) - constant current constant voltage charging, 1P (8W) - constant power constant voltage charging, 2P (15W) - constant power constant voltage charging, and 3P (23W) - constant power constant voltage charging.

[0053] Calculation method of charging current:

[0054] I CC = C rate ×Cnom#(1)

[0055] In formula (1): I CC is the charging current in the constant current stage, with the unit of ampere (A), C rate represents the charging rate, C nomIndicates the rated capacity of the battery, with the unit of ampere-hour (Ah). The calculation method of the charging power is as follows:

[0056] P CP = C rate × Cnom × Vnom #(2)

[0057] In formula (2): P CP is the charging power in the constant power stage, with the unit of watt (W), V nom represents the rated voltage of the battery, with the unit of volt (V), C rate and C nom are the same as above.

[0058] In the constant power and constant voltage charging protocol, nP (n = 1, 2, 3) represents the constant power value equivalent to the nC rate. Its theoretical charging time is the same as that of the nC constant current and constant voltage mode (both are 1 / n hours). However, the actual charging time is extended due to the voltage rise. Therefore, the charging power P CP is all rounded up to an integer for research.

[0059] The charging cut-off voltage for all six charging conditions is 4.2V, the charging cut-off current is 0.05C, the cyclic discharge is all carried out in the 1C-constant current discharge mode, the discharge cut-off voltage is 2.8V, the charge-discharge interval is 20 min, and the battery state parameters are monitored in real time during the charge-discharge process.

[0060] The selection process of the charging priority of lithium-ion batteries is as Figure 1 shown.

[0061] The charging time of lithium-ion batteries from 0% SOC to 80% SOC under different charging conditions and the energy efficiency of the first cycle under different charging conditions are as Figure 2 shown. In the normal charging rate range, both constant current and constant voltage charging and constant power and constant voltage charging can charge to 80% SOC within 51 min; in the fast charging rate range, both constant current and constant voltage charging and constant power and constant voltage charging can charge to 80% SOC within 26 min, meeting the current fast charging regulations; in the ultra-fast charging rate range, both constant current and constant voltage charging and constant power and constant voltage charging can charge to 80% SOC within 18 min, meeting the current fast charging regulations. Under the fast charging condition, the constant power and constant voltage charging is about 1 min slower than the constant current and constant voltage charging, but the cyclic energy efficiency is higher than that of the constant current and constant voltage charging. From the perspective of charging time, it meets the fast charging requirements under the ultra-fast charging and fast charging rates.

[0062] The discharge capacity of lithium-ion batteries during cycling under different charging conditions is as Figure 3As shown, in the extreme fast charging mode, the capacity of the constant current and constant voltage mode drops rapidly after 250 cycles, and the capacity at the end of the cycle is 1.515 Ah. While the capacity of the constant power and constant voltage mode starts to drop rapidly after 300 cycles, and the capacity at the end of the cycle is 1.777 Ah. In the fast charging mode, the cycle discharge capacity of the two schemes drops slowly. The capacity of the constant current and constant voltage mode at the end of the cycle is 1.923 Ah, and the capacity of the constant power and constant voltage mode at the end of the cycle is 1.921 Ah. In the normal charging mode, the two charging modes have little impact on the capacity. The capacity of the constant current and constant voltage mode at the end of the cycle is 2 Ah, and the capacity of the constant power and constant voltage mode at the end of the cycle is 2.005 Ah. From the perspective of charging loss, the higher the charging rate, the higher the loss to the battery. In the extreme fast charging mode, it is better to choose the constant power and constant voltage charging mode. In the fast charging mode and normal charging mode, both charging modes can be selected.

[0063] The energy efficiency of the lithium-ion battery during cycling under different charging conditions is as Figure 4 shown. In the extreme fast charging mode, the energy efficiency at the end of the cycle of the constant power and constant voltage charging mode is 86.24%, and that of the constant current and constant voltage charging mode is 83.45%. In the fast charging mode, the energy efficiency at the end of the cycle of the constant power and constant voltage charging mode is 91.38%, and that of the constant current and constant voltage charging mode is 87.35%. In the normal charging mode, the energy efficiency at the end of the cycle of the constant power and constant voltage charging mode is 93.32%, and that of the constant current and constant voltage charging mode is 93.37%. From the perspective of energy efficiency, it is more appropriate to choose the constant power and constant voltage charging mode during fast charging.

[0064] Taking charging time as the priority and battery charging loss as the secondary priority, select the 3P-constant power and constant voltage scheme with the fastest charging time and less loss to the battery. Taking energy efficiency as the secondary priority, select the 3P-constant power and constant voltage scheme with the fastest charging time and higher energy efficiency.

[0065] Taking energy efficiency as the priority and charging time as the secondary priority, select the 2P-constant power and constant voltage scheme with higher energy efficiency and faster charging time. Taking battery charging loss as the secondary priority, select the 1C-constant current and constant voltage scheme or 1P-constant power and constant voltage scheme with higher energy efficiency and less loss to the battery.

[0066] Taking battery charging loss as the priority and charging time as the secondary priority, select the 2C-constant current and constant voltage charging scheme with the least loss to the battery and faster charging time. Taking energy efficiency as the secondary priority, select the 1C-constant current and constant voltage scheme or 1P-constant power and constant voltage scheme with the least loss to the battery and higher energy efficiency. The optional schemes are shown in Table 1.

[0067] Table 1 Fast charging strategy schemes

[0068]

[0069]

[0070] It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus.

[0071] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for selecting a fast charging strategy for a lithium-ion battery, characterized in that: The following steps are involved: Step 1: Set the charging priority options; Step 2: The user selects the priority and sub-priority of charging; Step 3, deriving a charging plan based on charging priority; Step 4, obtaining data of different charging conditions of lithium-ion batteries; Step 5: According to the user's charging priority order, combined with the charging plan and test data, select the corresponding charging plan for charging, and realize independent selection of fast charging.

2. A method for selecting a fast charging strategy for a lithium-ion battery according to claim 1, characterized in that: In the step 1, the priority options of the charging mode include at least charging time, energy efficiency and battery charging loss, wherein the charging time refers to the time required for the battery to be charged to the target SOC; the energy efficiency refers to the ratio of the energy consumed by discharging at 1C to 0% SOC after being fully charged under the selected charging condition to the energy actually charged under the selected charging condition; the battery charging loss refers to the degree of influence of the charging condition on the battery capacity degradation.

3. The method for selecting a fast charging strategy for a lithium-ion battery according to claim 1, characterized in that: In the step 2, the priority is the first target to be achieved, and the second priority is the second target to be achieved. When there is a charging time to achieve the target, it is processed according to the requirement of fully charging 80% SOC within 30 minutes.

4. A method for selecting a fast charging strategy for a lithium-ion battery according to claim 1, characterized in that: The third step is to obtain a charging plan based on the charging priority, including the set priority options and the user's priority selection results, and enter into processing and analysis to obtain an optional charging plan: With charging time as the priority and battery charging loss as the second priority, choose the charging solution with the fastest charging time and the least battery loss; with energy efficiency as the second priority, choose the charging solution with the fastest charging time and the highest energy efficiency; Prioritize energy efficiency and charging time, and choose the charging method with the highest energy efficiency and the fastest charging time; Taking battery charging loss as the second priority, choose the charging scheme with the highest energy efficiency and the least battery loss; Prioritize battery charging loss and charging time, and choose a charging solution with minimal battery loss and faster charging time; prioritize energy efficiency and choose a charging solution with minimal battery loss and higher energy efficiency.

5. A method for selecting a fast charging strategy for a lithium-ion battery according to claim 1, characterized in that: The fourth step is to obtain data of the battery under different charging conditions, including at least: charging time to 80% SOC at three different rates under two charging methods; charging capacity, discharge capacity, energy efficiency and coulomb efficiency of charging cycles at three different rates under two charging methods, The two charging methods are any two of constant current and constant voltage, constant power and constant voltage, multi-stage constant current and constant voltage, pulse charging, and combined charging; The three charging rates include: normal charging rate (theoretically fully charged within 60 minutes), fast charging rate (theoretically fully charged within 30 minutes) and ultra-fast charging rate (theoretically fully charged within 20 minutes); Charge capacity: The capacity stored in the battery during the charging process; Discharge capacity: the capacity released by the battery during the discharge process; Coulomb efficiency: the ratio of discharge capacity to charge capacity during the charge and discharge process; Based on the above experimental scheme, the steps to obtain experimental data are as follows: S1. Set the SOC range of the charging time test to 0% to 80%; set the expected cycle charge and discharge SOC range to 0% to 100%; the default number of cycles is 350 times; set the cycle discharge condition to 1C constant current discharge, S2, choose two charging modes; S3, set three charging rates: normal charging rate (theoretically fully charged within 60 minutes), fast charging rate (theoretically fully charged within 30 minutes) and ultra-fast charging rate (theoretically fully charged within 20 minutes); The two charging modes and three charging rates are combined to form six charging conditions: Charging mode 1: normal charging rate, fast charging rate, extreme charging rate Charging mode 2: normal charging rate, fast charging rate, extreme charging rate The six charging conditions are all to charge to the battery's charging cut-off voltage and then continue to charge at a constant voltage to the charging cut-off current, with a 20-minute rest period between charging and discharging; S4. Start the cycle test.

6. A method for selecting a fast charging strategy for a lithium-ion battery according to claim 1, characterized in that: The step five is to analyze and select based on the optional schemes and experimental data obtained above to achieve autonomous selection of fast charging, and the lithium-ion battery is a nickel-cobalt-manganese ternary lithium-ion battery or a lithium iron phosphate battery.

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