Revealing the effect of external pressure on solid-electrolyte interphase and lithium plating in lithium-ion batteries

Lithium plating is a detrimental phenomenon in lithium-ion cells that compromises both functionality and safety. This study investigates electro-chemo-mechanical behaviors of lithium plating in lithium iron phosphate pouch cells under different external pressures. Atomic force microscopy nanoindentation is performed on the graphite electrode to analyze the influence of external pressure on solid-electrolyte interphase (SEI), revealing that the mechanical strength of SEI, indicated by Young's modulus, increases with the presence of external pressure. Then, an improved phase field model for lithium plating is developed by incorporating electrochemical parameterization based on nonequilibrium thermodynamics. The results demonstrate that higher pressure promotes lateral lithium deposition, covering a larger area of SEI. Moreover, electrochemical impedance spectroscopy and thickness measurements of the pouch cells are conducted during overcharge, showing that external pressure suppresses gas generation and thus increases the proportion of lithium deposition among galvanostatic overcharge reactions. By integrating experimental results with numerical simulations, it is demonstrated that moderate pressure mitigates SEI damage during lithium plating, while both insufficient and excessive pressure may exacerbate it. This study offers new insights into optimizing the design and operation of lithium iron phosphate pouch cells under external pressures.