The working principle of lithium battery separator

    Separator is a separator material with a porous structure and electrical insulation between the positive and negative electrodes of lithium batteries. It has two main functions in lithium batteries: 1. It provides channels for ion migration and provides conditions for battery chemical reactions. When lithium batteries are discharged, Lithium ions are separated from the negative electrode and reach the positive electrode after passing through the electrolyte solution and the diaphragm. When charging, the movement direction of the ions is opposite to that. Second, it has the function of insulating and blocking electrons to prevent short circuit inside the battery. Therefore, the separator needs a high porosity and a large specific surface area to facilitate more lithium ions to pass faster, thereby accelerating the charge and discharge rate. Good thermal closure, solvent resistance, and mechanical stability are the guarantee for the safe use of batteries.

    Due to the high energy density of lithium batteries, the flammability of organic electrolytes, and the easy precipitation of metallic lithium, the safety of lithium batteries has become the primary concern. The United States Battery Safety Association (USABC) has the following requirements for separators; thickness ≤25um, porosity up to 40%, puncture strength ≥300g/ml, elongation at break ≤2%, closing temperature at about 130℃, membrane breaking temperature ≥ 150℃, in addition, it needs to meet the requirements of good wettability and chemical stability.