Meaning
Rate of lithium-ion insertion and extraction within the layered carbon structure of a negative electrode during charge and discharge. The efficiency of graphite anode kinetics determines the maximum charging speed of a lithium-ion cell before metallic lithium begins to plate on the surface. Sourcing decisions for high-power applications focus heavily on these reaction rates to ensure rapid refueling times.
Phase Transition
Structural changes occur as lithium ions intercalate between the carbon sheets in distinct steps. The mobility of ions through the matrix during these transitions limits the overall current density.
Temperature Dependency
Diffusion of ions slow down dramatically when the battery cools. At low temperatures, graphite anode kinetics decrease to the point where the insertion rate cannot match the incoming current, causing ions to accumulate on the surface as metal. This metal layer can react with the electrolyte, reducing the active lithium inventory.
Rate Capability
Electrode design choices like particle size and coating thickness are tailored to balance energy density and reaction speed. Smaller graphite particles shorten the path that ions must travel, which enhances the reaction rates but increases the surface area exposed to parasitic reactions. Thicker coatings provide higher energy density but increase the total travel distance, which reduces the fast-charging performance of the cell.
