Comparative Study on the Electrochemical Behaviors of Positive Electrode Materials of Lithium-ion Batteries during Overdischarge

As lithium-ion battery (LIB) use rises, recycling becomes imperative. Efficiently overdischarging LIBs for residual energy extraction is crucial for safe recycling. Our study analyzes the electrochemical behavior during overdischarge for positive electrode materials, including LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiFePO 4 (LFP), LiCoO 2 (LCO), and LiMn 2 O 4 (LMO). Electrochemical evaluations involve half cells and full cells subjected to constant current overdischarge beyond normal operating ranges. In positive electrode half-cells, a material-dependent conversion reaction was observed, while full cells exhibited similar behaviors during overdischarge to 0 V due to increasing voltage at the negative electrode. Distinct electrochemical variations emerged under forced discharge below 0 V, particularly in the NCM series, showing a gradual voltage decrease to −2 V followed by an internal short circuit. In contrast, LFP, LCO, and LMO swiftly stabilized near 0 V, attributed to the lower initial Coulombic efficiency of NCM materials leading to an early rise in negative electrode potential. To recycle used lithium-ion batteries (LIBs), it’s crucial to optimize conditions that ensure both efficient and safe overdischarge, considering the characteristics of positive electrode materials.