Over-discharge of lithium-ion batteries does not directly trigger lithium plating, but it initiates a series of side reactions that indirectly raise the risk of lithium plating during subsequent charging.
Direct Consequences of Over-Discharge
Copper Foil Dissolution and Copper Dendrite Formation
When over-discharged to an abnormally high negative electrode potential (typically above 1.5 V vs. Li/Li⁺), the copper current collector on the anode undergoes oxidative dissolution to generate Cu²⁺ ions. After migrating to the cathode, Cu²⁺ ions are reduced to metallic copper and deposited to form copper dendrites. These dendrites may pierce the separator and induce internal short circuits.
SEI Film Decomposition and Gas Generation
Over-discharge leads to excessive lithium deintercalation from the anode. The SEI film decomposes, releasing heat and gases (such as CO and H₂), which aggravate battery swelling.
Indirect Link Between Over-Discharge and Lithium Plating
Elevated Lithium Plating Risk in Subsequent Charging
Over-discharge damages the internal battery structure (e.g., broken SEI film, copper dendrite generation) and increases internal resistance. If charging is performed under such conditions, the following issues will occur:
Deteriorated kinetic conditions: Damaged anode interfaces and consumed electrolyte hinder lithium-ion intercalation, easily pulling the anode potential below 0 V and triggering lithium plating.
Increased local current density: Copper dendrites or separator blockages may cause localized polarization and accelerate lithium plating.
Experimental Evidence
When over-discharged batteries are charged, off-white lithium plating zones alongside black spots (lithium-free regions) may appear on the anode surface, proving that lithium plating is correlated with interface damage induced by over-discharge.
Trigger Conditions for Lithium Plating
Lithium plating inherently occurs during charging and requires two prerequisites:
Thermodynamic condition: Anode potential ≤ 0 V (vs. Li/Li⁺).
Kinetic condition: The lithium-ion intercalation rate is lower than the lithium deposition rate (e.g., low temperature, high-rate charging).
While over-discharge cannot independently satisfy the thermodynamic requirement for lithium plating, it compromises the battery structure and creates hidden risks that enable lithium plating conditions during later charging.
Conclusion
Over-discharge drastically boosts the risk of lithium plating in subsequent charging indirectly via three mechanisms: internal short circuits from copper dendrites, SEI film decomposition, and severe interface damage. For practical applications, over-discharge must be strictly prevented (e.g., by configuring a discharge cut-off voltage). After over-discharge occurs, conservative charging protocols (e.g., low-current recovery charging) should be adopted to mitigate safety hazards.
