CN-121578160-B - Lithium battery thermal runaway test method based on critical trigger energy

CN121578160BCN 121578160 BCN121578160 BCN 121578160BCN-121578160-B

Abstract

The invention discloses a thermal runaway test method of a lithium battery based on critical trigger energy, which belongs to the technical field of thermal runaway tests of lithium batteries and comprises the following steps of constructing a thermal runaway model, dividing the thermal runaway process of the lithium battery along with temperature rise into solid electrolyte membrane decomposition, anode-electrolyte reaction, cathode-electrolyte reaction and electrolyte decomposition, superposing and calculating to obtain the total unit volume heat generation rate of the thermal runaway exothermic reaction, determining the convection boundary condition and the thermal conduction boundary condition of the thermal runaway model according to actual heat exchange conditions, determining the power range of a heating plate, carrying out numerical simulation, predicting the critical thermal runaway scene, and verifying and analyzing the result by using a thermal runaway test device of the lithium battery. According to the invention, the energy transfer process of the thermal runaway of the lithium battery is quantified through the combination of numerical simulation and test verification, and the heating and stopping conditions of the thermal runaway test of the lithium battery are determined, so that the thermal safety of different lithium batteries can be conveniently analyzed and compared, and the controllability of the thermal runaway triggering mode of the lithium battery is improved.

Inventors

ZHOU XUANYI
CONG BEIHUA
JI YIFAN

Assignees

同济大学

Dates

Publication Date: 20260508
Application Date: 20260129

Claims (7)

1. The lithium battery thermal runaway testing method based on the critical trigger energy is characterized by comprising the following steps of: firstly, constructing a thermal runaway model, and determining reaction kinetic parameters; The thermal runaway process of the lithium battery sequentially comprises decomposition of a solid electrolyte membrane, anode-electrolyte reaction, cathode-electrolyte reaction and electrolyte decomposition along with the temperature rise, and the total unit volume heat generation rate of the thermal runaway exothermic reaction is obtained through superposition calculation; secondly, determining a convection boundary condition and a heat conduction boundary condition of the thermal runaway model according to the actual heat exchange condition; the convection boundary condition and the heat conduction boundary condition are respectively determined by the following formulas: ; ; Wherein k s represents the thermal conductivity of the heating plate or the lithium battery, ∂ T/∂ n represents the temperature gradient, h is the equivalent convective heat transfer coefficient, T s is the surface temperature of the heating plate or the lithium battery, and ambient temperature T amb =293.15K; k 1 represents the heat conductivity of the heating plate or the heat conductivity of the lithium battery, k layer and delta layer are the heat conductivity and the thickness of an equivalent thermal resistance layer respectively, wherein the equivalent thermal resistance layer refers to the contact thermal resistance at the junction of the lithium battery and the heating plate, and T 1 and T 2 are the temperature of the heating plate or the lithium battery at the interface; thirdly, determining the power range of the heating plate, performing numerical simulation, and predicting a critical thermal runaway scene; under the heating of the heating plate, when the energy input by the heating plate reaches critical triggering energy, the lithium battery can generate irreversible thermal runaway chain exothermic reaction, wherein the critical triggering energy is a minimum energy threshold value required for triggering the thermal runaway of the lithium battery, namely a critical threshold value; three scenarios of the lithium battery under external heating conditions are as follows: Scene 1, heating the lithium battery by a heating plate is stopped in advance, the input energy does not reach a critical threshold, and the self-acceleration thermal runaway reaction cannot be maintained; Scene 2, stopping heating when the input energy just reaches a critical threshold for triggering thermal runaway, and introducing no excessive energy at the moment; Scene 3, when the temperature rise rate is detected to exceed 1 ℃ per second, the thermal runaway occurs, and the heating is immediately stopped; Scene 2 is a critical condition for triggering thermal runaway, and the total input energy value from the heating plate heating starting time to the heating plate heating stopping time is accumulated input energy, namely the critical triggering energy, which is an ideal condition for triggering and judging the thermal runaway; The thermal runaway scene 2 is a critical thermal runaway scene, and the corresponding minimum heating time for causing the thermal runaway of the battery is defined as t cr , namely the critical heating time; According to different heating powers set by the heating plate, calculating and predicting critical heating time and critical triggering energy of the scene 2 by using a thermal runaway model, wherein the determination principle is as follows: 1) The temperature rise rate of the battery is not reduced after the heating plate stops heating; 2) The exothermic reaction is self-sustaining after the heating plate stops heating and completely exothermic after an incubation period has been experienced; Under the working condition of determining the critical thermal runaway scene, the critical trigger energy calculation formula is as follows: ; wherein t 0 represents the heating time of the heating plate, t cr is the heating time required for reaching scenario 2, q (t) represents the instantaneous heat flow change between the heating plate and the battery, A is the heat transfer area; And fourthly, manufacturing a lithium battery thermal runaway test device, performing test verification and analyzing the result.
2. The method for testing thermal runaway of a lithium battery based on critical trigger energy according to claim 1, wherein in the step (A), a thermal runaway model is constructed: the energy conservation equation of the heating plate and the lithium battery is as follows, ; Where ρ is density, C p is specific heat capacity, T is temperature, k is thermal conductivity, and Q rec is the heat source term.
3. The method for thermal runaway testing of lithium batteries based on critical trigger energy according to claim 2, wherein in the content (one), the reaction kinetic parameters are determined as follows: The solid electrolyte membrane decomposition reaction expression is: ; Wherein, the Dimensionless amounts for SEI reactant concentrations; Is a frequency factor; r is molar gas constant, T is temperature; the anode-electrolyte reaction has the expression: ; Wherein, the A dimensionless quantity that is the anode reactant concentration; Is a dimensionless measure of SEI film thickness reflecting lithium content; is an initial value of the SEI film thickness; And Is the frequency factor and activation energy; the expression of the cathode-electrolyte reaction is: ; Wherein, the Is the degree of reaction of the cathode material; And Is a kinetic parameter of the reaction; the reaction equation expression of the electrolyte decomposition is as follows: ; Wherein, the Is the dimensionless concentration of the electrolyte, And Is a kinetic parameter of the reaction; The total heat generation rate per unit volume of the thermal runaway exothermic reaction is obtained by superposition calculation of four exothermic reactions, namely solid electrolyte membrane decomposition, anode-electrolyte reaction, cathode-electrolyte reaction and electrolyte decomposition The calculation formula is as follows: ; Wherein, the Represents the specific enthalpy of the decomposition reaction of the solid electrolyte membrane, the anode-electrolyte reaction and the electrolyte decomposition reaction, To represent the rates of solid electrolyte membrane decomposition reactions, anode-electrolyte reactions, and electrolyte decomposition reactions, Is the specific enthalpy of the cathode-electrolyte reaction, Is the rate of the cathode-electrolyte reaction.
4. The lithium battery thermal runaway testing method based on the critical trigger energy according to any one of claims 1 to 3 is characterized in that in the fourth step, the lithium battery thermal runaway testing device comprises a heating plate, a lithium battery and a data acquisition instrument, wherein the heating plate is arranged on one side of the positive electrode of the lithium battery, a probe of the data acquisition instrument is arranged on one side of the negative electrode of the lithium battery and is used for acquiring temperature and voltage data of the surface of the lithium battery, and the data acquisition instrument is connected with a controller, and the controller is connected with a computer.
5. The lithium battery thermal runaway testing method based on critical trigger energy of claim 4, wherein K-type thermocouples are arranged in the middle of the back side surface and the corner of the lithium battery, in the middle of the two side surfaces and in the positions of the top surface close to the exhaust valve, and the 4K-type thermocouples are connected with a data acquisition instrument.
6. The method for testing the thermal runaway of the lithium battery based on the critical trigger energy of claim 5, wherein the front side of the heating plate and the back side of the lithium battery are respectively provided with a steel plate, and heat insulation pads are respectively arranged between the front side steel plate and the heating plate and between the back side steel plate and the lithium battery; The lithium battery comprises a lithium battery body, wherein the back side of the lithium battery body is provided with two steel plates, a pressure sensor is arranged between the two steel plates, the pressure sensor is connected with a controller, and four corners of the front steel plate and the rear steel plate are fixedly connected through pre-tightening bolts.
7. The method for testing thermal runaway of a lithium battery based on critical trigger energy of claim 6, wherein the heating plate is made of a cast aluminum plate, the data acquisition instrument captures temperature and voltage changes on the surface of the lithium battery at a sampling frequency of 1Hz, and the pressure sensor value is adjusted to 1000N through a pre-tightening bolt.

Description

Lithium battery thermal runaway test method based on critical trigger energy Technical Field The invention belongs to the technical field of lithium battery thermal runaway tests, and particularly relates to a lithium battery thermal runaway test method based on critical trigger energy. Background With the rapid development of energy storage systems, new energy automobiles and portable electronic devices, safety accidents related to lithium batteries frequently occur, and the safety performance of the lithium batteries is widely focused in the industry. The thermal runaway is the most serious safe failure mode of the lithium battery, shows the phenomenon of uncontrollable self-heating mode temperature rise, has the characteristics of high reaction speed, severe energy release, complex propagation chain and the like, and can cause system fire or explosion accidents when serious. Therefore, the lithium battery thermal runaway research has great significance for evaluating the safety of the battery and preventing and reducing the disaster of the energy storage system. Currently, the commonly used thermal runaway assessment methods mainly include an external heating test, a needling test, an extrusion test, an overcharge test, and the like. These test methods are typically performed in accordance with relevant standards, such as UL9540A, IEC62619 and GB/T36276, etc. Due to a complex chemical reaction system of the lithium battery, different thermal runaway triggering methods have great influence on the thermal runaway performance of the battery, and lack of consistency and comparability among different test results is caused, so that the accuracy of the battery safety evaluation is influenced. In view of the advantages of external heating tests in terms of convenience of test operation and repeatability of test results, many researchers and battery safety standards have adopted testing methods for thermal runaway caused by external heating conditions to study macroscopic features and mechanisms of thermal runaway of batteries to evaluate safety thereof. However, the above-described tests are different in terms of triggering manner, triggering condition control, thermal runaway determination index, and the like, and it is difficult to perform systematic, quantitative, and repeatable evaluation of battery thermal stability. Therefore, establishment of a standardized decision criterion for triggering a lithium battery thermal runaway test method by an external heating method is highly needed. With the development of the research on the thermal runaway mechanism of lithium batteries, many scholars have studied the influence of the heating power and the heating time of an external heat source on the thermal runaway characteristics of batteries. Based on this, the prior studies have generally used a battery temperature rise rate of up to 1 ℃. However, the conventional manner of triggering the thermal runaway of the battery using an external heat source introduces additional energy, thereby significantly affecting the progress of the thermal runaway of the lithium iron phosphate battery. The test mode and the thermal runaway judgment condition have difficulty in accurately reflecting the thermal risk of the batteries under the actual working conditions. In the existing thermal runaway test process, an effective quantitative characterization method is lack of energy introduced into a lithium battery. Meanwhile, the judging condition of the thermal runaway mainly depends on a single or empirical temperature index, and the judging condition is lagged and ambiguous, so that the test result is difficult to accurately reflect the evolution characteristic of the thermal runaway, and the objectivity and consistency of the test conclusion are further affected. Therefore, the invention provides a lithium battery thermal runaway test method based on critical trigger energy, which provides references for testing heating conditions and thermal runaway judgment conditions. Disclosure of Invention In order to solve the problems, the invention provides a lithium battery thermal runaway test method based on critical trigger energy. In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a lithium battery thermal runaway test method based on critical trigger energy comprises the following steps: Firstly, constructing a thermal runaway model to determine reaction kinetic parameters, wherein the thermal runaway process of the lithium battery sequentially comprises decomposition of a solid electrolyte membrane, anode-electrolyte reaction, cathode-electrolyte reaction and electrolyte decomposition along with temperature rise and exothermic side reaction; secondly, determining a convection boundary condition and a heat conduction boundary condition of the thermal runaway model according to the actual heat exchange condition; thirdly, determining the power range of the heating plate, performing num