After 30 years of industrial development, lithium battery products have made great progress in safety technology, effectively controlling the occurrence of side reactions in the battery and ensuring the safety of the battery. However, with the increasing use of lithium batteries and the increasing energy density, incidents such as explosions and injuries or product recalls due to safety hazards have occurred frequently in recent years. We summarize the main reasons for the safety problems of lithium battery products as follows:
The materials used in the cell include: positive active material, negative active material, separator, electrolyte and shell, etc. The selection of materials and the matching of the composed system determine the safety performance of the cell.
When selecting positive and negative active materials and diaphragm materials, the manufacturer did not conduct a certain assessment of the characteristics and matching of raw materials, resulting in the inherent lack of cell safety.
The raw materials of the battery cells are not tested strictly and the production environment is poor, which leads to the mixing of impurities in the production, which not only has a great adverse effect on the capacity of the battery, but also has a great impact on the safety of the battery; in addition, if too much water is mixed into the electrolyte, side reactions may occur and increase the internal pressure of the battery, which will affect the safety.
Due to the limitation of the production technology level of lithium batteries, in the production process of the battery cells, the products cannot achieve good consistency, such as poor flatness of the electrode substrate, falling off of the electrode active material, mixing of other impurities in the active material, the weak welding of the pole lug, the unstable welding temperature, the burr on the edge of the pole piece, the absence of insulating tape in key parts and so on, which may adversely affect the safety of the cell.
In terms of structural design, many key points affecting safety have not been paid attention to by the manufacturer, such as no insulating tape at key parts, no margin or insufficient margin in diaphragm design, unreasonable design of positive and negative capacity ratio, unreasonable design of area ratio of positive and negative active substances, unreasonable design of pole lug length, etc., which may bury hidden dangers for the safety of the battery.
In addition, in the production process of battery cells, some battery cell manufacturers try to save and compress raw materials in order to save costs and improve performance, such as reducing the area of diaphragms, thinning copper foil, aluminum foil, and not using pressure relief valves and insulating tapes, etc., which will reduce the safety of the battery.
At present, the market is pursuing higher-capacity battery products. In order to increase the competitiveness of products, manufacturers continue to increase the volume specific energy of lithium batteries, which increases the danger of batteries to a large extent.