Operando detection for lithium plating in lithium-ion batteries via expansion force signal decoupling

Lithium plating is widely recognized as the key factor causing the capacity degradation and safety hazard of lithium-ions batteries. Dynamic evolution of lithium plating boundary, subtle change in impedance and voltage in large capacity lithium-ions batteries pose great challenges to accurate and reliable detection of lithium plating. To address these issues, this study proposes an expansion force-based lithium plating detection framework, which is comprised of expansion force components decoupling, features extraction and threshold determination of the selected feature. Battery thermal expansion coefficient and reference expansion force curve are introduced to decouple the expansion components of lithium intercalation or de-intercalation, thermal expansion, lithium deposition and stripping and other secondary reactions. The ratio of expansion force of lithium stripping (RLSF) representing the proportion of expansion force originating from lithium deposition is developed as an indicator for lithium plating. Subsequently, the threshold of the feature RLSF is determined through clustering method. Experimental results reveal that when lithium plating occurs, the value of RLSF is much enlarged and that the higher the amount of lithium plating, the closer the value is to 100 %. By comparing the real-time RLSF of battery with threshold, the plating of lithium can be detected with high precision. An extra feature that is named the irreversible expansion force (IEF) is defined to propose non-destructive quantitative assessment index of lithium deposition, which can also identify the reversible and irreversible lithium plating. Post-mortem analysis further corroborates the presence of lithium dendrites, and abnormal thickening of the graphite anode resulting from lithium plating. The works provide new insights into real-time regulating of charging and discharging protocols and battery safety early-warning systems.