This study examines the thermal runaway of a lithium ion battery caused by poor heat dissipation performances. The heat transfer process is analyzed on the basis of standard theoretical concepts. Water mist additives are considered as a tool to suppress the thermal runaway process. The ensuing behaviour of the battery in terms of surface temperature and heat generation is analyzed for different charge and discharge rates. It is found that when the remaining charge is 100%, the heat generation rate of the battery is the lowest, and the surface temperature with a 2C charge rate is higher than that obtained for a 0.5C charge rate. The experimental results show that when the additive concentration is 20% NaCl, its ability to inhibit the thermal runaway is the strongest.
In recent years, people’s demand for industrial production and energy has grown ever larger with the rapid development of the global economy and science and technology. People’s unrestrained exploitation and use of non-renewable resources make the energy situation tenser and tenser. In order to alleviate energy tension, the development of renewable resources has become a global research hotspot, and the battery has gradually become a necessity of production and life. The main problem in battery development is its service life, and the thermal runaway phenomenon o is the biggest factor affecting this service life. Hence, it is of great importance for future sustainable battery development to restrain the thermal runaway phenomenon.
The lithium ion battery is currently recognized as a form of recyclable clean energy which has great development potential for the future. In order to understand the status of research into the lithium ion battery, this paper reviews recent relevant research.
Researchers | Time | Research contents |
---|---|---|
Ning et al. [ |
2020 | A simulation method for thermal runaway behavior of lithium ion batteries was provided, through which the surface temperature change and the thermal reaction of electrode material could be obtained. The thermal runaway temperature and thermal runaway mechanism of the battery were analyzed through the model and fitting parameters were obtained. |
Maheswari et al. [ |
2020 | A unique thermal control strategy to improve aging of the battery was proposed, mainly to control the internal temperature of the battery used in electric vehicles (EV) within the range of 20°C–40°C, and reduce the frequent voltage fluctuation in the DC bus, so as to increase the life of the storage battery. The unique thermal control strategy of the hybrid EV system can effectively control the frequent charge and discharge of the lithium ion battery, and eliminate thermal runaway problems such as leakage, smoke, exhaust, rapid disassembly and flames. |
Bugryniec et al. [ |
2020 | A computational method was proposed to investigate potential thermal runaway propagation (TRP) in LFP cathode batteries. It was mainly based on the 2D model of the battery pack. If one of the batteries experiences an internal short circuit, thermal runaway propagation will not occur even under various extreme environmental conditions, which indicates that controlling the battery with LFP as cathode can realize the potential of battery safety and large-scale use. |
Zhang et al. [ |
2020 | A composite barrier technology was proposed, and the soft clad nickel cobalt manganese (NCM811) battery was taken as the main experimental research object to determine the relationship between the surface temperature of the battery and thermal runaway, as well as the relationship between microstructure and thermal barrier properties. The study shows that the thermal barrier effect is greatest in the thermal barrier test of microstructure-size materials with a millimeter thickness. |
The results from
According to the arrangement of internal materials, lithium ion batteries can be divided into cylindrical and square structures. The most commonly used is the square battery, which is stacked by the chemical reaction mechanism of the battery [
In the discharging process of the lithium ion battery, the anions on the cathode material come out and embed into the surface of the cathode material. The LEP battery is taken as an example. During the charging process of the battery, Li+ migrates from the [FePO4]− layer of the cathode material, passes through the electrolyte layer of the battery and enters the negative electrode material of the battery. Fe2+ on the negative electrode material is oxidized to Fe3+, and the electrons reach the negative electrode of the battery from the external circuit through the contact conductive solvent and battery current collector [
Positive reaction:
Negative reaction:
Total battery reaction:
The analysis of the reaction mechanism of the lithium ion battery shows that the heat generation mechanism of lithium ion power battery broadly comprises the following: (1) the heat generated by the electrochemical reaction inside the battery; (2) the ohmic resistance heat generated by the physical resistance of lithium ion when it is transferred in the positive material and electrolyte solution [
In
The total calorific value of the lithium ion battery can be obtained from the above equations, as follows:
In (8),
When thermal runaway occurs in lithium ion batteries, the main processes of heat transfer to the outside world are thermal radiation, thermal convection and thermal conduction [
Thermal conduction is a hypothetical analysis of energy transfer during thermal runaway in a lithium ion battery. If the second battery of a lithium ion battery pack belongs to a single equilibrium object, when there is no thermal runaway taking place, the temperature of the first battery increases due to the thermal conduction effect. The specific calculation equation is as follows [
Thermal convection is the heat transfer reaction generated by fluid flowing between the surface of the lithium ion battery and the environment around the battery when the thermal runaway occurs. The calculation equation is as follows [
In
Water mist additives can be divided into two categories according to their physical and chemical properties; namely, water-soluble salt additives and surfactants [
The experimental equipment used in this experiment is the HAIGINT sea view humidifying water mist system equipment, as shown in
Additives | Function | Category | Concentration (%) |
---|---|---|---|
NaCl | Enhance the fire extinguishing effect of water mist | Inorganic salts | 10 |
SDBS | Improve the physical properties of water mist | Surfactants | 0.2 |
CO(NH2)2 | Decomposing to absorb heat and accelerate cooling | Decomposable class | 7 |
In order to study the energy transfer of a lithium ion battery after thermal runaway, the corresponding state of charge (SOC) at different discharge rates is selected; that is, the heat generating rate of the battery with residual power (usually expressed as SOC percentage) from 10% to 100%.
SOC (%) | Discharge rates | |
---|---|---|
5C | 10C | |
10 | 42964.48 | 155679.48 |
20 | 35489.63 | 127614.97 |
30 | 31016.52 | 112124.11 |
40 | 28994.62 | 103452.71 |
50 | 27178.34 | 99173.26 |
60 | 26895.74 | 98774.32 |
70 | 25748.41 | 98573.63 |
80 | 24657.63 | 98138.34 |
90 | 23987.49 | 97146.28 |
100 | 141.34 | 520.15 |
Based on the data in
In order to explore the change of battery surface temperature at normal temperature (25°C) in the thermal runaway of lithium ion battery, three different charging rates are selected and the temperature acquisition instrument is used to measure the battery surface temperature, as shown in
0.5C, 1C and 1.5C charging rates are selected in turn.
Moreover, the surface temperature of the battery varies with the charge rate. At 0.5C charging rate, the surface temperature of the battery rises slowly. As the charging time goes on, the surface temperature of the battery hardly increases. At 1C and 1.5C charging rates, the temperature curve increases with the charging time.
From the above analysis, it can be concluded that, in the process of constant current charging, the larger the battery charging rate, the higher the surface temperature of the battery, and the greater the corresponding power generation of the battery. However, a higher charging rate will lead to a high battery temperature, which may result in an explosion or failure of the battery. Therefore, it is necessary to control the charging current and the rate of rising temperature of the battery during the charging process.
After the thermal runaway reaction of the battery occurs, it is necessary to turn on the water mist, and add the chosen additives into the water in turn. The surface temperature change and effect of each additive on the thermal runaway reaction of the battery are analyzed, as shown in
When NaCl, SDBS and CO(NH2)2 are added to the water mist to act on the battery, under the same conditions, the effect of NaCl is greater than that of SDBS and CO(NH2)2 to inhibit the thermal runaway reaction. Moreover, the temperature of the battery when NaCl is added shows the strongest downward trend and the fastest downward speed, which can effectively prevent the heat transmission process in the thermal runaway of the battery.
Finally, the optimum additive concentration of each common additive is obtained through comparative experiments with different concentrations of additives, as shown in
Additives | Optimum concentration % |
---|---|
SDBS | 1.78 |
CO(NH2)2 | 4.8 |
NaCl | 20 |
The change in the heat generating rate of the battery in a saturated and unsaturated state in discharging is explored. The experimental results show that the heat generating rate of the battery in 100% saturation state is much lower than in 10% saturation. The internal resistance of the battery is the main factor affecting the heat generating capacity of the battery when the battery power is too low. The surface temperature changes of the battery under different charge-discharge rates are explored. The results suggest that the higher the SOC, the worse the safety performance and the shorter the battery life. The inhibition effect of different water mist additives on the thermal runaway of battery is explored. The experimental results show that the temperature of the battery with 20% NaCl in the water mist additive leads to the greatest and fastest reduction in speed, which can effectively prevent the heat transmission process in the thermal runaway in the battery. The results of this experiment will be applied to lithium ion battery installations after technical improvement, which will effectively improve the service life of lithium ion batteries and inhibit the occurrence of the thermal runaway phenomenon.
The LEP form of the lithium ion battery is taken as the research object. The structure and reaction equation of the battery are briefly introduced. First, discharge rates of 5C and 10C are used to study the change in the heat generating rate of lithium ion batteries. Image analysis shows that the heat generating rate of the battery is lowest when the remaining power is 100%, and the highest when the remaining power is 10%. The surface temperature changes of the battery under different charge-discharge rates are explored. The results show that a higher charge and discharge rate leads to a higher surface temperature. Hence, the conclusion is that a lower discharge rate and charge/discharge current should be set to prolong the service life of the battery. Finally, water mist additives are used to inhibit the thermal runaway phenomenon of lithium ion batteries, and the inhibition effects of different water mist additives at different concentrations on thermal runaway are explored. It is found that water mist containing NaCl additive has the best inhibition effect on the thermal runaway of the lithium ion battery, and the inhibition effect is greatest when the concentration of the NaCl additive is 20%. This exploration mainly aims to solve the problem of the thermal runaway reaction in lithium ion batteries caused by poor heat dissipation performance. The results prove that using a water mist with 20% NaCl additive can inhibit the thermal runaway reaction in lithium ion batteries.
It is hoped that the performance of lithium ion batteries can be further improved through other research directions in future research, such as identifying factors that influence poor heat dissipation performance, so as to improve the service life of lithium ion batteries and reduce wastage of energy.