Lithium ion battery internal temperature estimation method based on surface temperature

Abstract

The invention relates to the field of lithium ion battery detection, in particular to a lithium ion battery internal temperature estimation method based on surface temperature. Firstly, a control equation and boundary conditions are constructed based on a one-dimensional heat conduction model; then, performing time discretization on the control equation by adopting a display Euler method, and performing spatial discretization on the control equation by adopting a central difference method; and finally, initializing the heat production rate, and substituting the initialized heat production rate into the control equation to obtain a battery surface temperature calculated value. If the difference between the calculated value and the measured value of the surface temperature of the battery is less than 0.001, increasing the heat production rate, otherwise, reducing the heat production rate; and continuously iterating the heat production rate until the absolute value of the difference between the calculated value and the measured value of the surface temperature of the battery is less than 0.001, and stopping iteration to obtain the heat production rate and the internal temperature of the battery in the current time step length. The heat production rate and the internal temperature of the battery are reversely deduced through numerical solution, the limitation of the prior art on the temperature equalization hypothesis is overcome, and the calculation precision under the large temperature difference working condition is improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery detection, in particular to a method for estimating the internal temperature of a lithium ion battery based on surface temperature. Background Art

[0002] Lithium-ion batteries have the characteristics of high energy density, long cycle life, and low self-discharge rate. They are widely used in energy systems such as electric vehicles and energy storage power stations as energy support devices. As an electrochemical element, the conversion of electrochemical energy to electrical energy is usually accompanied by heat generation, which increases the battery temperature. If the generated heat cannot be dissipated in time, the lithium-ion battery will be in a high temperature environment for a long time, which will lead to a decrease in capacity and even thermal runaway. Therefore, accurately estimating the internal temperature of the battery is crucial to the design of a thermal management system.

[0003] Existing studies usually use theoretical or experimental methods to obtain the internal temperature of the target battery. In terms of theoretical calculation, the most famous method is the Bernardi method. This method assumes that the heat generation rate is composed of reversible heat and irreversible heat. By monitoring the current, voltage and temperature during the experiment, as well as the target battery entropy increase coefficient obtained in advance, the heat generation rate of the battery can be obtained by the Bernardi method. In addition, some researchers have established a multi-scale multi-domain (MSMD) model to describe the electrochemical behavior of the battery. However, the premise of calculating the heat generation using these theoretical methods is that the complex electrochemical parameters are known. These electrochemical parameters are extremely complex during the measurement process, and some parameters are even obtained through experimental fitting. Therefore, the theoretical method has great limitations in practical application. The experimental method is divided into direct experimental method and indirect experimental method. The direct experimental method is to place the target battery in a calorimetric instrument or an isothermal calorimeter, and directly test the heat generation of the battery through the calorimetric instrument, such as the heat generation behavior of the battery under overheating conditions. However, the required calorimetric instrument is relatively expensive and the test environment is quite different from the real environment. Therefore, the direct experimental method cannot be widely promoted under real working conditions. The indirect experimental method is based on the measurement of battery surface temperature. The most commonly used method is the lumped heat capacity calculation (LHCP) based on the battery surface temperature. This method assumes that the internal temperature of the battery is uniform and ignores thermal resistance. When the internal temperature differs significantly (such as thermal runaway), the error is large. The LHCP method essentially assumes that the battery is a uniform temperature object and cannot accurately reflect the temperature gradient. Summary of the invention

[0004] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a method for estimating the internal temperature of a lithium-ion battery based on the surface temperature.

[0005] The present invention solves the technical problem by adopting the following technical solution: A method for estimating the internal temperature of a lithium-ion battery based on the surface temperature comprises the following steps: Step 1: Construct the control equation based on the one-dimensional heat conduction model. The expression is as follows: (1) The boundary conditions are: (2) In the formula, represents density, represents the specific heat capacity, Indicates temperature, represents the thermal conductivity, express The heat generation rate at the time, express The battery surface temperature at the moment, Represents the distance from the battery surface to the center, Indicates the thickness of the battery; Step 2: Discretize the control equations in time and space; Divide into N nodes along the thickness direction of the battery, and the node spacing ; Use the explicit Euler method to time discretize the control equation, then: (3) In the formula, , Respectively , Time Node The temperature at express and the time interval between moments; The central difference method is used to discretize the control equation in space, and we have: (4) In the formula, , Respectively Time Node , The temperature at Substituting equations (3) and (4) into the control equation, we have: (5) After rearrangement, formula (5) can be obtained: (6) To deal with boundary conditions: The surface temperature is known ( ): (7) Central symmetry condition ( ): (8) The stability conditions are: (9) Step 3: Iteratively solve the internal temperature of the battery; Heat generation rate Initialize and bring the initialized heat generation rate into the control equation to get the calculated value of the battery surface temperature ;like , then the heat generation rate increases Otherwise, the heat generation rate will be reduced. ;in, Represents the measured value of the battery surface temperature; the heat generation rate is continuously iterated until , the iteration is stopped, and the heat generation rate in the current time step is obtained, and the internal temperature of the battery in the current time step is obtained.

[0006] Compared with the prior art, the present invention has the following beneficial effects: This method uses numerical solution to reversely infer the heat generation rate and the internal temperature of the battery, overcomes the limitation of the existing technology on the uniform temperature assumption, and improves the calculation accuracy under large temperature difference conditions. The measurement process is simple, requiring only surface temperature data, without complex electrochemical parameters or calorimeters. A one-dimensional heat conduction model is used to ignore the radial and axial heat transfer of the battery, reducing the calculation complexity. It is suitable for large temperature difference conditions such as high-rate charging and discharging and thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is the overall flow chart of the present invention. DETAILED DESCRIPTION

[0008] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and are not intended to limit the protection scope of the present application.

[0009] The present invention provides a method for estimating the internal temperature of a lithium-ion battery based on the surface temperature, comprising the following steps: Step 1: Construct the control equation based on the one-dimensional heat conduction model. The expression is as follows: (1) The boundary conditions are: (2) In the formula, Indicates density (kg / m 3 ), represents specific heat capacity (J / (kg·k)), represents temperature (K), Indicates thermal conductivity (W / (m·k)), express Heat generation rate at the time (W / m 3 ), express The battery surface temperature at the moment, Represents the distance from the battery surface to the center, Indicates the thickness of the battery; Step 2: Discretize the control equations in time and space; Divide into N nodes along the thickness direction of the battery, and the node spacing ; Use the explicit Euler method to time discretize the control equation, then: (3) In the formula, , Respectively , Time Node The temperature at express and the time interval between moments; The central difference method is used to discretize the control equation in space, and we have: (4) In the formula, , Respectively Time Node , The temperature at Substituting equations (3) and (4) into the control equation, we have: (5) After rearrangement, formula (5) can be obtained: (6) To deal with boundary conditions: The surface temperature is known ( ): (7) Central symmetry condition ( ): (8) The stability conditions are: (9) Step 3: Iteratively solve the internal temperature of the battery; Heat generation rate Initialize and bring the initialized heat generation rate into the control equation to get the calculated value of the battery surface temperature ;like , then the heat generation rate increases Otherwise, the heat generation rate will be reduced. ;in, Represents the measured value of the battery surface temperature; the heat generation rate is continuously iterated until , the iteration is stopped, and the heat generation rate in the current time step is obtained, and the internal temperature of the battery in the current time step is obtained.

[0010] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for estimating the internal temperature of a lithium-ion battery based on surface temperature, characterized in that: The method comprises the following steps: Step 1: Construct the control equation based on the one-dimensional heat conduction model. The expression is as follows: （1） The boundary conditions are: （2） In the formula, represents density, represents the specific heat capacity, Indicates temperature, represents the thermal conductivity, express The heat generation rate at the time, express The battery surface temperature at the moment, Represents the distance from the battery surface to the center, Indicates the thickness of the battery; Step 2: Discretize the control equations in time and space; Divide into N nodes along the thickness direction of the battery, and the node spacing ; Use the explicit Euler method to time discretize the control equation, then: （3） In the formula, , Respectively , Time Node The temperature at express and the time interval between moments; The central difference method is used to discretize the control equation in space, and then: （4） In the formula, , Respectively Time Node , The temperature at Substituting equations (3) and (4) into the control equation, we have: （5） After rearrangement, formula (5) can be obtained: （6） To deal with boundary conditions: The surface temperature is known ( ): （7） Central symmetry condition ( ): （8） The stability conditions are: （9） Step 3: Iteratively solve the internal temperature of the battery; Heat generation rate Initialize and bring the initialized heat generation rate into the control equation to get the calculated value of the battery surface temperature ;like , the heat generation rate increases, otherwise it decreases. Represents the measured value of the battery surface temperature; the heat generation rate is continuously iterated until , the iteration is stopped, and the heat generation rate in the current time step is obtained, and the internal temperature of the battery in the current time step is obtained.

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