Lithium-ion battery safety issues

Lithium-ion battery safety issues

Under the dual pressure of energy crisis and environmental problems, new energy vehicles have become a major trend in the development of the global automobile industry. Electric vehicle (EV) is one of the solutions to the current transportation problems. It can reduce our dependence on oil and reduce emissions of greenhouse gases and standard pollutants. The performance, cost and life of new energy vehicles are determined by the technical level of the vehicle power battery system. Lithium-ion batteries can meet the needs of electric vehicles because of their excellent energy density, safety, and cyclability. While lithium-ion batteries are rapidly taking over NiMH and NiCd in portable and handheld devices, they are not yet widely used in automotive products. The reasons relate to the safety, cycle and service life of lithium batteries, cost, and high temperature performance of the batteries. These are all related to the thermal effect of the battery. In recent years, the development of hybrid electric vehicles has promoted the research and development of high-power batteries. High-power battery design puts forward higher requirements for reducing cost and improving safety performance.

The many safety accidents in the actual operation of lithium-ion batteries have greatly damaged people’s confidence in new energy vehicles. Therefore, the safety of lithium-ion batteries has always been the focus of the industry and scientific research. Most of the research focuses on improving the specific energy, power and cycle life of electrode materials, and less on the thermal management system of the battery. The lack of timely communication between battery manufacturers and developers hinders the design and manufacture of safe and reliable electric vehicles.

A high-performance battery thermal management system can increase the cruising range of electric vehicles in high temperature operation, so thermal management of battery packs is of great significance for the safe operation of electric vehicles. Conducting thermal analysis and research on lithium batteries for electric vehicles can predict the temperature and thermal field distribution of the lithium battery during discharge, understand the safety of the battery, and ensure that the battery works within its optimal temperature range. For lithium-ion power batteries, the optimal operating temperature range is generally 298.15~313.15K. Within this range, the battery can maintain good performance and service life, and reduce the possibility of combustion and explosion of the battery due to excessive temperature. At the same time, reducing and ensuring that the temperature difference between the single cells in the battery pack is not higher than 5K, which can avoid the performance degradation due to the excessive temperature difference between the batteries, thereby prolonging the life of the lithium battery and improving the safety of the battery. The thermal runaway behavior of lithium-ion batteries at high temperature, and how to optimize the influencing factors, reduce the maximum temperature of the battery pack, and improve the temperature uniformity of the battery have become an important frontier of research.

Lithium-ion battery safety issues

Lithium-ion batteries are one of the most popular types of batteries for portable electronic products, such as mobile phones and notebook computers (more than 90% of the batteries are lithium-ion batteries), they have good weight ratio, no memory effect, high energy density, low self-discharge and other characteristics. Lithium batteries have developed from 3C to power batteries and medium and large batteries, and the demand for lithium batteries has also increased relatively. Among different lithium-ion batteries, chemical composition, performance, cost and safety characteristics vary. In recent years, a number of battery safety accidents have occurred around the world, which has drawn attention to the safety of lithium-ion batteries. Due to high temperature, puncture, improper use or poor external environment, the positive and negative electrodes inside the battery are connected, forming an internal short circuit, and triggering a series of reactions to generate high temperature. These problems are often the cause of lithium-ion battery explosions and fires.

In September 1995, SONY recalled the battery. The lithium-ion battery manufactured by the company exploded due to heat, causing all lithium-ion batteries of this type to be recycled. Since then, other lithium batteries have also experienced overheating problems, which has raised questions about the safety of lithium batteries. The heat accumulation generated by the lithium battery at high temperature causes the battery to heat up, and a series of side reactions occur inside the battery. If the heat accumulation of the battery is far greater than the heat loss, it will cause a fire or even an explosion.