Another new energy vehicle is "hot"! How should I choose a car?

In recent years, with the popularization of new energy vehicles, news related to spontaneous combustion of new energy vehicles has gradually increased.

Last week, a new energy vehicle spontaneously caught fire on the Nanpu Bridge, which attracted widespread public attention. Thick smoke billowed from the scene, and the vehicle on fire was burned to a shell. Traffic from Pudong to Puxi on the Nanpu Bridge was temporarily interrupted.

Image source: Kankan News

New energy vehicles have attracted many friends who need to buy cars due to their advantages such as energy saving, environmental protection and no travel restrictions, but the safety hazard of "spontaneous combustion" makes many people stay away.

Why do new energy vehicles catch fire spontaneously? How to avoid accidents? How to choose new energy vehicles? Today, let's talk about it.

01

Why do new energy vehicles catch fire spontaneously?

Most of the spontaneous combustion accidents of new energy vehicles are caused by thermal runaway of the power battery. The causes of thermal runaway are very complex. Mechanical damage, improper operating temperature and electrical abuse are three common causes.

1) Mechanical damage

Vehicle collisions are an important cause of thermal runaway[1]. Batteries are prone to short circuits when squeezed or punctured[2], which can cause local overheating and even fire.

2) Improper working temperature

The electrolyte inside the battery tends to release a large amount of gas and heat under high temperature conditions, providing conditions for combustion to occur[3].

3) Electrical abuse

Battery abuse includes overcharging and over-discharging. Both overcharging[4] and over-discharging[5] can cause abnormal heating of the battery and may cause the battery to spontaneously combust.

We all know that the three elements of combustion are combustibles, combustion-supporting materials (usually oxygen) and temperature reaching the ignition point. In the above cases, the temperature of the lithium-ion battery continues to rise. After reaching the ignition point, combustibles such as electrolytes and diaphragms react with oxygen, releasing a large amount of energy and gas in a very short time and limited space, which is very likely to cause an explosion.

On April 16, a new energy car caught fire on Shanghai Jiamin Elevated Road.

Source: Daily Economic News

02

How to prevent power battery combustion?

Combustion requires the simultaneous presence of three elements. It is difficult to isolate oxygen, but we can improve the thermal runaway phenomenon of the battery by starting from the two aspects of combustible materials and temperature.

1) Solid electrolyte

The main components of the electrolyte are organic matter composed of carbon and hydrogen, which easily react with oxygen and play the role of "combustible" in the combustion process.

Solid-state electrolytes are a new research direction for many car and battery companies. Solid-state electrolytes exist in solid form and are not easy to burn[6]. They can also increase the energy density of batteries[7] and solve users' range anxiety. At present, the application of all-solid-state batteries is still difficult, but many companies are actively producing transitional products - semi-solid-state batteries[8].

Schematic diagram of the structure of a solid-state battery

Image source: Reference [9]

2) Battery Management System (BMS)

The battery management system can monitor the battery voltage, current and temperature in real time, and provide protection against overcharge, over-discharge, over-temperature and under-temperature[10], ensuring that the battery works efficiently under safe conditions.

Researchers are working hard to improve the safety of power batteries. As ordinary consumers, what we can do is:

1) Use the battery correctly, charge it in time, and unplug it as soon as possible after charging to avoid overcharging;

2) Drive safely to avoid collisions;

3) If the battery is burning, please flee the scene as quickly as possible and call the fire department at 119. Do not try to extinguish the fire by yourself to avoid causing casualties.

03

How to choose a new energy vehicle?

From the perspective of battery practicality and safety, when choosing a new energy vehicle, you can pay attention to the following points:

1) Battery life

It is recommended to purchase new energy vehicles with appropriate range according to actual needs. The longer the range of a pure electric vehicle and the higher the battery level, the more violent and serious the spontaneous combustion will be if it occurs.

2) Fast charging

Although fast charging and ultra-fast charging can save time, the high charging speed will have a negative impact on the battery life. If the vehicle has both fast charging and normal charging modes, it is recommended not to fast charge if possible, and fast charge only when needed.

3) Battery life

From a material perspective, the cycle life of lithium iron phosphate batteries is longer and safer than that of ternary lithium batteries. However, the energy density of lithium iron phosphate batteries is lower than that of ternary lithium batteries. Under the same weight, the battery life of ternary lithium batteries is longer.

4) Security

Vehicles need to meet national standards (such as "Safety Requirements for Electric Vehicles" and "Safety Requirements for Power Batteries for Electric Vehicles") to ensure safety. In addition, the outer shell of the entire battery pack on the car should be as strong as possible, as a strong outer shell can effectively reduce external force damage to the battery.

Of course, whether it is a new energy vehicle or a gasoline vehicle, safe driving always comes first. Preventing accidents before they happen and handling them calmly can greatly reduce the losses caused by risky accidents. Finally, I wish everyone can buy a suitable car.

References
[1] SHAN T, WANG Z, HONG J, et al. Overview of “Mechanical Abuse-thermal Runaway” of Electric Vehicle Power Battery and Its Safety Prevention and Control Technology [J]. Journal of Mechanical Engineering, 2022, 58(14).

[2] LIU B, YIN S, XU J. Integrated computation model of lithium-ion battery subject to nail penetration [J]. Applied Energy, 2016, 183:278-289.

[3] Yu Zhixiang. Research on thermal runaway fault diagnosis of electric vehicle power battery[J]. Automobile Science and Technology, 2023, (2): 48-55.

[4] REN D, FENG X, LU L, et al. Overcharge behaviors and failure mechanism of lithium-ion batteries under different test conditions [J]. Applied Energy, 2019, 250:323-332.

[5] GUO R, LU L, OUYANG M, et al. Mechanism of the entire overdischarge process and overdischarge-induced internal short circuit in lithium-ion batteries [J]. Scientific Reports, 2016, 6(1).

[6] TAKADA K. Progress and prospective of solid-state lithium batteries [J]. Acta Materialia, 2013, 61(3):759-770.

[7] WANG C, FU K, KAMMAMPATA SP, et al. Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries [J]. Chemical Reviews, 2020, 120(10):4257-4300.

[8] People’s Daily Online. Solid-state battery market continues to be hot [EB/OL]. (2024-2-26) [2024-3-7]. http://paper.people.com.cn/zgnyb/html/2024-02/26/content_26044994.htm

[9] XU L, TANG S, CHENG Y, et al. Interfaces in Solid-State Lithium Batteries [J]. Joule, 2018, 2(10):1991-2015.

[10] PAKDEL R, YAVARINASAB M, ZIBAD MR, et al. Design and Implementation of Lithium Battery Management System for Electric Vehicles [M]. 2022 9th Iranian Conference on Renewable Energy & Distributed Generation (ICREDG). 2022: 1-6.

Author: Zhang Jiayun, a direct doctoral student in the Department of Materials Science at Fudan University, whose research direction is cathode materials for lithium-ion batteries

Planning: Hua Wenyi

Editor: Tinker Bell

Acknowledgements: Professor Ma Ruguang from the School of Materials Science and Engineering at Suzhou University of Science and Technology provided scientific guidance for this article

Title image source: Xinmin Evening News