Method and system for calculating capacity loss of lithium battery under variable temperature condition and storage medium

Abstract

The application discloses a lithium battery capacity loss method and system under a variable temperature condition, and a storage medium, wherein the method comprises the following steps: S1: recording a temperature change curve in a lithium battery charging process; S2: calculating equivalent charging time of each unit charging time under a standard working temperature according to an Arrhenius formula; S3: accumulating the equivalent charging time corresponding to each unit charging time in the lithium battery charging process to obtain equivalent total charging time of the lithium battery under the standard working temperature under the variable temperature condition; and S4: bringing the equivalent total charging time into a battery capacity loss classical equation under the standard working temperature to calculate the capacity loss of the lithium battery under the variable temperature condition. The method converts each unit charging time into equivalent charging time under the standard working temperature, so that the capacity loss calculation equation obtained through experiments under the standard working temperature can be used to calculate the capacity loss of the lithium battery under the variable temperature condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery management, and particularly relates to a lithium battery capacity loss calculation method and system under variable temperature conditions and a storage medium. BACKGROUND

[0002] Accurate battery aging trajectory prediction is crucial for reliable operation and optimized management of energy storage systems. Battery aging is highly sensitive to temperature, which has a strong impact on the calculation results when calculating the capacity loss of the battery. However, current battery loss calculations are limited to fixed temperature conditions, which cannot meet the actual energy storage application scenarios with temperature changes day and night, making it difficult to predict and apply battery capacity loss. SUMMARY

[0003] The purpose of the present application is to provide a lithium battery capacity loss calculation method under variable temperature conditions. According to the actual working temperature of each unit charging time period, the equivalent charging time of each unit charging time under standard working temperature is converted, so that the capacity loss calculation equation obtained under standard working temperature can be used to calculate the lithium battery capacity loss under variable temperature conditions.

[0004] Another purpose of the present application is to provide a lithium battery capacity loss calculation system under variable temperature conditions that can implement the above calculation method, and a storage medium that stores a computer program instantiated by the calculation method.

[0005] Technical solution: The lithium battery capacity loss calculation method under variable temperature conditions disclosed by the present application comprises the following steps:

[0006] S1: Record the temperature change curve during the charging process of the lithium battery;

[0007] S2: Calculate the equivalent charging time of each unit charging time under standard working temperature according to the Arrhenius formula;

[0008] S3: Accumulate the equivalent charging time corresponding to each unit charging time during the charging process of the lithium battery to obtain the equivalent total charging time of the lithium battery under standard working temperature under variable temperature conditions;

[0009] S4: Introduce the equivalent total charging time into the classical equation of battery capacity loss under standard working temperature to calculate the capacity loss of the lithium battery under variable temperature conditions.

[0010] Further, in the step S4, the lithium battery capacity loss calculation equation under variable temperature conditions obtained by introducing the equivalent total charging time into the classical equation of battery capacity loss under standard working temperature is:

[0011]

[0012] In the formula, C loss,k is the capacity loss of lithium battery accumulated to the kth unit charging time, is the equivalent total charging time accumulated to the kth unit charging time, E a,SEI is the activation energy of solvent diffusion in the SEI film, R is the gas constant, T std is the standard working temperature, T k is the actual working temperature of the kth unit charging time, Δt chg,k is the length of the unit charging time, k SEI is the generation reaction coefficient of the SEI film, C loss,0 is the battery capacity loss caused by the formation process before the lithium battery leaves the factory.

[0013] Further, the standard working temperature T std = 303K.

[0014] The lithium battery capacity loss calculation system under the variable temperature working condition provided by the present application comprises: a temperature monitoring module for monitoring and recording the temperature change in the working process of the lithium battery; an equivalent charging time conversion module for calculating the actual working temperature of the unit charging time period according to the Arrhenius formula, and converting each unit charging time into the equivalent charging time under the standard working temperature; a lithium battery capacity loss calculation module for accumulating the equivalent charging time corresponding to each unit charging time to obtain the equivalent total charging time, and bringing the equivalent total charging time into the battery capacity loss classical equation under the standard working temperature to calculate the capacity loss of the lithium battery under the variable temperature working condition.

[0015] The storage medium provided by the present application stores a computer program, which is set to realize the above-mentioned lithium battery capacity loss calculation method under the variable temperature working condition when running.

[0016] Advantages: Compared with the prior art, the present application has the following advantages: the calculation of the lithium battery capacity loss under the actual energy storage application scenario of the temperature day and night change can be realized, it is suitable for different environmental temperatures and different aging degree batteries, the calculation amount is small and easy to implement. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the flowchart of the lithium battery capacity loss calculation method under the variable temperature working condition of the embodiment of the present application;

[0018] Figure 2 is the prediction effect curve diagram of the calculation method of the embodiment of the present application. DETAILED DESCRIPTION

[0019] The technical solutions of the present application will be further described below with reference to the drawings.

[0020] Referring toFigure 1 The lithium battery capacity loss calculation system under the variable temperature condition according to the embodiment of the application comprises the following steps:

[0021] S1: record the temperature change curve in the charging process of the lithium battery;

[0022] S2: calculate the equivalent charging time of each unit charging time at the standard working temperature according to the Arrhenius formula;

[0023] S3: accumulate the equivalent charging time corresponding to each unit charging time in the charging process of the lithium battery to obtain the equivalent total charging time of the lithium battery at the standard working temperature under the variable temperature condition;

[0024] S4: bring the equivalent total charging time into the classical equation of battery capacity loss at the standard working temperature to calculate the capacity loss of the lithium battery under the variable temperature condition.

[0025] In the conventional use stage of the battery, the capacity loss is mainly caused by the consumption of the internal recyclable lithium of the battery in the generation and thickening process of the solid electrolyte interface (SEI film) of the negative electrode. The classical equation of the battery capacity loss constructed based on the active lithium loss is as follows:

[0026]

[0027] In the formula, C loss is the capacity loss (Ah) of the battery, LLI a is the active lithium capacity loss (Ah) of the battery in the aging process, LLI0 is the initial active lithium capacity loss (Ah) of the battery after the factory formation, t chg is the charging time, E a,SEI is the activation energy (J / mol) of the solvent diffusion in the SEI film, R is the gas constant, R = 8.314 J / (mol·K), k SEI is the SEI film generation reaction related coefficient. Through the fitting of the above model by using the charging experimental data at the standard working temperature for multiple times, the values of k SEI , E a,SEI and LLI0 can be obtained, the fitted battery capacity loss equation is obtained, and the prediction and calculation of the battery capacity loss at the standard working temperature are realized. However, in some application scenarios, the temperature in the actual working of the battery is variable, and the battery aging is sensitive to the temperature, so the above equation cannot be applied to the capacity loss calculation of the battery in the whole life cycle under the variable temperature condition.

[0028] At standard operating temperature, the battery charging time can be used as an equivalent characteristic parameter of the core physical quantity of the loss process—SEI film thickness. Furthermore, the relationship between the electrochemical reaction rate and reaction temperature during the battery charging process conforms to the Arrhenius empirical formula. Therefore, the battery capacity estimation method of the embodiment of the present invention, by differentiating the charging process into several unit charging times, is relatively short, so the temperature change within the unit charging time can be ignored and can be regarded as an endpoint temperature value or median. Based on the actual operating temperature of each unit charging time, the standard operating temperature, and the Arrhenius empirical formula, each unit charging time can be converted into an equivalent charging time at a standard operating temperature. By summing the equivalent charging times corresponding to each unit charging time at different temperatures, the equivalent total charging time of the battery under variable temperature conditions at a constant standard operating temperature can be obtained. Substituting the equivalent total charging time into formula (1) can realize the calculation of battery capacity loss under variable temperature conditions. This method uses the equivalent charging time of batteries at different temperatures under standard conditions as the transfer variable, expanding the application scope of the battery capacity loss equation derived under standard conditions. This allows for the prediction and calculation of lithium battery capacity loss under variable temperature conditions. Furthermore, this method, based on the classic battery capacity loss equation, eliminates the need for complex mathematical models, minimizes computational effort, and is easy to implement.

[0029] According to the above method, the final calculation equation for the lithium battery capacity loss under variable temperature conditions is as follows:

[0030]

[0031] in, The total equivalent charging time is obtained by adding up the equivalent charging times corresponding to each unit charging time up to the kth unit charging time.

[0032]

[0033] Where, T std is the standard operating temperature, T k is the actual operating temperature of the kth unit charging time, Δt chg,k The length of the unit charging time. Standard operating temperature T std Usually take T std =303K.

[0034] Formula (2) can also be written as follows:

[0035]

[0036] In this embodiment, by std =303K experiment, obtain k SEI 、E a,SEIand the value of LLI0, a calculation equation of the capacity loss of the lithium battery under the variable temperature condition is constructed as shown in formula (4), for 1C current charge-discharge rate cycles, the temperature is switched every 100 cycles, the switching mode is the capacity loss calculation of the battery under the variable temperature condition of 298K and 318K alternately, the battery capacity loss prediction curve as shown in formula (4) can be obtained. Figure 2 It can be seen that the predicted value is basically fitted with the measured value, and the above method can accurately realize the prediction of the capacity loss of the lithium battery under the variable temperature condition. Figure 2

[0037] The variable temperature condition lithium battery capacity loss calculation system according to the embodiment of the present application can implement the above calculation method, including a temperature monitoring module, an equivalent charging time conversion module and a lithium battery capacity loss calculation module. The temperature monitoring module is used for monitoring and recording the temperature change in the working process of the lithium battery; the equivalent charging time conversion module is used for converting each unit charging time into the equivalent charging time under the standard working temperature according to the Arrhenius formula calculation and the actual working temperature of the unit charging time period; and the lithium battery capacity loss calculation module is used for accumulating the equivalent charging time corresponding to each unit charging time to obtain the equivalent total charging time, and bringing the equivalent total charging time into the classical equation of the battery capacity loss under the standard working temperature to calculate the capacity loss of the lithium battery under the variable temperature condition. The storage medium according to the embodiment of the present application stores the computer program instantiated by the above variable temperature condition lithium battery capacity loss calculation method.​

Claims

1. A method for estimating lithium battery capacity loss under variable temperature conditions, characterized in that: The steps include: S1: Record the temperature change curve of the lithium battery during charging; S2: Calculate the equivalent charging time of each unit charging time at standard operating temperature according to the Arrhenius formula; S3: Accumulate the equivalent charging time corresponding to each unit charging time during the lithium battery charging process to obtain the equivalent total charging time of the lithium battery at the standard operating temperature under variable temperature conditions; S4: Substitute the equivalent total charging time into the classic equation for battery capacity loss at standard operating temperature to calculate the capacity loss of lithium batteries under variable temperature conditions; In step S4, the equivalent total charging time is substituted into the battery capacity loss classic equation at standard operating temperature to obtain the lithium battery capacity loss under variable temperature conditions: Where C loss,k is the lithium battery capacity loss accumulated to the kth unit charging time, is the equivalent total charging time accumulated to the kth unit charging time, E a,SEI is the activation energy of solvent diffusion in SEI film, R is the gas constant, T std is the standard operating temperature, T k is the actual operating temperature of the kth unit charging time, Δt chg,k is the length of unit charging time, k SEI is the SEI film formation reaction coefficient, C loss,0 It is the battery capacity loss caused by the formation process of lithium batteries before leaving the factory.

2. The method for estimating lithium battery capacity loss under variable temperature conditions according to claim 1, characterized in that: The standard operating temperature T std =303K.

3. A system for estimating lithium battery capacity loss under variable temperature conditions, characterized in that: include: Temperature monitoring module, used to monitor and record temperature changes during the operation of the lithium battery; An equivalent charging time conversion module is used to convert each unit charging time into an equivalent charging time at a standard operating temperature based on the Arrhenius formula and the actual operating temperature of the unit charging time period; The lithium battery capacity loss estimation module is used to accumulate the equivalent charging time corresponding to each unit charging time to obtain the equivalent total charging time, and then substitute the equivalent total charging time into the classic battery capacity loss equation at standard operating temperature to calculate the capacity loss of lithium batteries under variable temperature conditions; In the lithium battery capacity loss calculation module, the lithium battery capacity loss calculation equation under variable temperature conditions is obtained by substituting the equivalent total charging time into the battery capacity loss classic equation at standard operating temperature: Where C loss,k is the lithium battery capacity loss accumulated to the kth unit charging time, is the equivalent total charging time accumulated to the kth unit charging time, E a,SEI is the activation energy of solvent diffusion in SEI film, R is the gas constant, T std is the standard operating temperature, T k is the actual operating temperature of the kth unit charging time, Δt chg,k is the length of unit charging time, k SEI is the SEI film formation reaction coefficient, C loss,0 It is the battery capacity loss caused by the formation process of lithium batteries before leaving the factory.

4. A storage medium storing a computer program, characterized in that: The computer program is configured to implement the method for estimating lithium battery capacity loss under variable temperature conditions according to any one of claims 1 to 2 when running.

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