Meaning
Metallic lithium formation on the negative electrode surface occurs when the local potential drops below the reference potential of lithium metal. This graphite anode deposition takes place primarily during rapid charging or under low temperature conditions where ion insertion is kinetically limited. The metal deposits can grow into dendritic structures that threaten the integrity of the cell.
Voltage Hazard
High current density creates a polarization effect that drives the anode potential below zero volts versus lithium. When this threshold is crossed, graphite anode deposition becomes thermodynamically favorable compared to the intercalation of lithium ions. This side reaction competes directly with the normal insertion process, reducing the coulombic efficiency of the cycle.
Cell Degradation
Continuous accumulation of metallic lithium leads to capacity fade and elevated impedance as active lithium is permanently consumed. These lithium deposits can penetrate the separator and cause an internal short circuit, which creates a thermal runaway risk. If the dendritic paths are thick enough, the resulting short circuit can cause rapid heating and potential fire hazards.
Sourcing Consideration
Purchase contracts for high power batteries often specify fast charge limits to prevent the onset of this degradation mechanism. Buyers require manufacturers to demonstrate anode designs with optimized porosity and appropriate negative-to-positive capacity ratios to mitigate graphite anode deposition. Testing involves analyzing the voltage relaxation curve after charging to detect the characteristic plateau associated with the stripping of deposited lithium.
