The passivation of the Li-ion battery (LIB) cell is a crucial feature to influence battery performance. When the LIB cell is charged, the passivation layers are formed at the interface of the anode/electrolyte by chemical reactions of the electrolytes and the anode. The passivation layers are typically thin and highly resistive, which prevents quick self-discharge and material degradation.
The formation and existence of the passivation layers can be observed as a voltage delay. When an external load is applied to the LIB cell, a voltage delay can be seen at the beginning of the loading. Due to the passivation layer formation, the internal resistance is increased, and in turn, the rapid voltage drop occurs. During the discharge of the cell, the layers are slowly removed and the initial voltage is recovered, which reduces the increased internal resistance. If the loading is increased, the further removal of the passivation layers takes place until they are fully removed.
After the load (or charging), the passivation layers reform, and the voltage drop (or delay) may occur in the subsequent discharge at a later use.
The characteristics of passivation layers are influenced by many factors, namely rate capability, type of chemical reactions, storage time and temperature, discharge conditions. At higher discharge rates (high loads), the voltage delay may longer, and at lower rates, it is not observable. The longer the cell in storage is, the thicker passivation is formed. It is known that more passivation is formed at a higher temperature.
Passivation is also called SEI (solid-electrolyte-interphase).
