Meaning
Porous, high-surface-area metallic deposition that forms on the anode surface during poor charging conditions presents a severe risk to the safety and lifespan of a lithium-ion battery. This mossy lithium is a form of non-uniform plating that occurs when the rate of lithium insertion is slower than the supply of ions from the electrolyte. Sourcing agents monitor this phenomenon to avoid purchasing cells that are prone to early degradation or thermal runaway.
It applies during high-rate charging or low-temperature operation, representing a dangerous boundary of the cell’s operating window.
Deposition Process
Deposition occurs when lithium ions are reduced to metallic form on the electrode surface rather than inserting into the graphite lattice. This metallic deposit is highly reactive and consumes active lithium and electrolyte to form a thick, resistive layer. Sourcing specialists evaluate the design of the electrode and electrolyte to ensure they have been engineered to minimize the risk of this deposit forming.
The growth of this porous metal layer reduces the capacity of the cell and increases its internal resistance, leading to rapid performance decline.
Safety Hazards
Safety is compromised because these porous metallic deposits can grow across the separator and cause an internal short circuit. When a short circuit occurs, the high current flow can trigger thermal runaway, presenting a severe hazard to the user. Sourcing contracts specify that cells must be designed with sufficient negative-to-positive capacity ratio to prevent the formation of these deposits.
Sourcing teams use this requirement to ensure that the cells can be operated safely under all expected conditions.
Detection Methods
Identification of this form of plating involves post-mortem analysis of the cycled cells or advanced electrochemical techniques such as relaxation voltage measurements. These diagnostic methods help engineers detect the presence of metallic deposits before they cause a catastrophic failure. Sourcing agreements depend on these results to verify that the manufacturer has designed the cell to prevent plating during fast charging.
This verification is essential for ensuring the long-term safety and reliability of the battery pack in the field.
