How to improve the safety of lithium battery cells

Researchers and battery manufacturers need to improve the safety of lithium battery cells by continuously improving processes and technologies. BMS system manufacturers should fully understand the performance of batteries, and design safe and reliable battery systems based on the safety design principles of power batteries. Use is the ultimate barrier to battery safety.

Studying the failure mode of a power battery system is of great significance for improving battery life, safety and reliability of electric vehicles, and reducing the cost of using electric vehicles. This paper analyzes the external failure mode of power battery system and analyzes the consequences and proposes corresponding measures. Various failure modes are considered in the design of the power battery system to improve the safety of the power battery.

The power battery system usually consists of a battery cell, a battery management system, a Pack system containing functional components, a wire harness, and a structural component. The power battery system failure mode can be divided into three different levels of failure modes, namely, cell failure mode, battery management system failure mode, and Pack system integration failure mode.

Pack system integration failure mode

1. Failure of the bus bar:

If it is a bolted connection, during the later use, if the bolt is oxidized off or vibrated, causing the bolt to loosen, a large amount of heat will be generated at the joint of the conductor, and in extreme cases, the power battery will catch fire. Therefore, most manufacturers of power battery systems use laser welding when the battery is connected with the battery core or the module and the module are connected at the time of the package design, or the temperature sensor is added at the connection to avoid the failure of the bus bar by means of detection.

2. The main circuit connector of the power battery system fails:

The high voltage line of the power battery system is connected to the external high voltage system through a connector. The connector performance is unreliable and a virtual connection occurs under vibration, resulting in a high temperature ablation connector. In general, connection failure occurs when the connector temperature exceeds 90 degrees. Therefore, the connector needs to increase the high-voltage interlock function when the system is designed, or the temperature sensor is attached to the connector to monitor the temperature of the connector at all times to prevent the connector from failing.

3, high pressure contactor sticky:

The contactor has a certain number of load breaks, and most of the contactors ablate when the high current load is closed. In the system design, a dual relay scheme is generally adopted, and the control is closed in order to avoid sticking of the high voltage contactor.

4, fuse overcurrent protection failure:

The selection of the fuses in the high-voltage system components is matched, and the gradient is broken first and which one needs to be considered comprehensively. Vibration or external impact crushing causes the power battery to deform, the seal fails, and the IP rating is lowered. Therefore, the collision protection of the battery box structure is required in the system design.

According to the various failure modes of the above power battery system, researchers and battery manufacturers need to improve the safety of lithium battery cells by continuously improving the process and technology. BMS system manufacturers should fully understand the performance of the battery, based on the safety design principles of the power battery. Designing a safe and reliable battery system, while proper use is the ultimate barrier to battery safety. Users should use the power battery system correctly to prevent mechanical abuse, heat abuse and electric abuse, and effectively improve the safety and reliability of electric vehicles.