Structural degradation of graphite anode induced by dissolved manganese ions in lithium-ion batteries

Abstract

Manganese (Mn) species deposited on anodes have been identified as one of the primary sources of capacity and power fading in Li-ion batteries (LIBs). Previous studies have overwhelmingly focused on the effect of Mn species present on the anode surface on the electrochemical performance of LIBs and their relation to chemical degradation of the solid electrolyte interphase (SEI). This study investigates the role of Mn ions dissolved in electrolytes in the structural degradation of a graphite anode. X-ray diffraction results find evidence for the hypothesis that dissolved Mn ions could co-intercalate into the graphite structure at an early stage of the Li-ion intercalation. Furthermore, Raman spectroscopy results demonstrate severe local surface disordering of graphite in the presence of Mn ions. Calculations based on density functional theory (DFT) support the experimental findings, revealing that Mn co-intercalated into the graphite structure inhibits the expansion of the graphite interlayers upon Li-ion intercalation. Results from this study provide new insights into the current mechanisms of the degradation of manganese-based cathode–graphite battery cells. The proposed mechanism of graphite structural degradation induced by Mn ions can help researchers and engineers design LIBs with longer lifespans.