Operando Identification of Chemical and Structural Origin of Li-Ion Battery Aging at Near-Ambient Temperature.

Integrated with heat generating devices, a Li-ion battery (LIB) often operates at 20-40oC higher than the ordinary working temperature. Although macroscopic investigation of thermal contribution has shown significant reduction on LIB performance, the molecular-level structural and chemical origin of battery aging in mild thermal environment has not been elucidated. Based on the combined experiments of electrochemical measurements, Cs-corrected electron microscopy, and in situ analyses, we herein provide operando structural and chemical insights on how mild thermal environment affects the overall battery performance, using anatase TiO2 as a model intercalation compound. Interestingly, mild thermal condition induces excess lithium intercalation even at near-ambient temperature (45 oC), which does not occur in the ordinary working temperature. The anomalous intercalation enables excess lithium storage in the first few cycles but exert severe intra-crystal stress, consequently cracking the crystal that leads to battery aging. Importantly, this mild thermal effect is accumulated upon cycling, resulting in irreversible capacity loss even after the thermal condition is removed. Battery aging at high working temperature is universal in nearly all intercalation compounds, and therefore it is significant to understand how thermal condition contributes to battery aging for designing intercalation compounds for advanced battery electrode materials.