Meaning
Metallic lithium accumulation occurs on the surface of graphite anodes when battery charging takes place at temperatures below freezing. Slow solid-state diffusion within carbon particles and high charge transfer resistance at the solid electrolyte interphase force lithium ions to deposit as metallic lithium rather than intercalate into the host structure. This subzero lithium plating reduces active cyclable lithium inventory while forming sharp dendritic structures that risk penetrating separator membranes.
Battery longevity and safety rely on avoiding operational conditions that trigger metallic deposition.
Dendrite Growth
Uncontrolled metallic deposition forms microscopic filamentary structures that extend across the porous separator layer. Dendrites bridging positive and negative electrodes create internal micro-shorts that elevate self-discharge rates. Continuous subzero lithium plating accelerates capacity fade while escalating risks of catastrophic thermal failure.
Capacity Loss
Deposited metallic lithium reacts irreversibly with liquid electrolyte, forming secondary interphase layers that consume active species. Locked metallic lithium cannot participate in subsequent discharge cycles, reducing available pack energy. Quantifying subzero lithium plating rates helps refine safe charging current limits at low ambient temperatures.
Anode Overpotential
High current rates at low temperatures push anode potential below zero volts against the lithium reference potential. Negative anode potentials create the thermodynamic driving force required for metallic metal deposition over intercalation. Controlling charging current based on localized anode overpotential prevents subzero lithium plating during cold weather operation.
