Meaning
Electrochemical processes responsible for the irreversible reduction in discharge capacity define the longevity of secondary battery systems. These capacity fade mechanisms involve a loss of mobile lithium or a degradation of the electrode structure that prevents the return to the original state of charge.
Chemical Degradation
Side reactions at the electrode interface often result in the consumption of active material. Various capacity fade mechanisms contribute to the thickening of the solid electrolyte interphase layer which traps ions permanently. This growth increases internal resistance and slows down the movement of charges.
Structural Change
Mechanical stress during cycling leads to micro-cracking of individual particles. These capacity fade mechanisms result in electrical isolation of material fragments that can no longer participate in charge storage (a process known as pulverization). Particle fracturing is particularly prevalent in high nickel cathode chemistries where volume changes are more extreme.
The resulting increase in surface area leads to further side reactions with the electrolyte and a faster rate of decay.
Operational Impact
Thermal management influences the rate of energy loss over the life of the asset. Capacity fade mechanisms accelerate when cells operate outside optimal temperature ranges or undergo high current discharge. Prolonged exposure to heat destabilizes the binder and conductive additives.
