Could the manufacturing process of lithium-ion batteries also have an impact on safety?

Lithium-ion batteries are generally safe, but there have been reports of safety incidents before the public. More famous in recent years, Boeing 737 and B787 aircraft battery fire, BYD electric car fire, Tesla MODELS fire... The earliest time these lithium-ion battery safety accidents entered the public eye can be traced back to four or five years ago. Until now, safety is still a key factor restricting the application of lithium-ion batteries in the field of high energy/high power. Thermal runaway is not only the essential cause of safety problems, but also one of the shortboards restricting the performance of lithium-ion batteries.

Starting from the electrode ingredients, it is necessary to go through a series of steps such as mixing, pulping, cutting, scraping powder, brushing powder, rolling, pole ear riveting, welding, gluing paper, testing, formation and so on.

In this series of processes, even if all steps have been completed, there is still a possibility that the internal resistance of the battery may rise or short circuit because the work is not in place, resulting in safety problems. Such as:

During the welding process, there are virtual welds (between the positive/negative plate and the terminal ear, between the positive plate and the cap, between the negative plate and the case, large rivet and contact internal resistance, etc.), dust, diaphragm paper that is too small or not well padded, diaphragm with holes, burrs that are not cleaned, and so on.

The wrong capacity ratio of positive and negative electrodes may also cause a large number of lithium metal to be deposited on the negative surface, and the insufficient uniformity of the slurry will also cause the uneven distribution of active particles, resulting in a large change in the volume of the charge and discharge negative electrode and lithium, thus affecting its safety performance.

In addition, the quality of SEI film formation in the formation step also directly determines the cycling and safety performance of the battery, and affects its lithium insertion stability and thermal stability.

The factors that affect the SEI film include the type of negative carbon material, electrolyte and solvent, the setting of the current density, temperature and pressure and other parameters during the formation process; through the appropriate selection of materials and adjustment of the parameters of the formation process, the quality of the SEI film can be improved, thereby improving the safety performance of the cell.