In Situ Imaging of Lithium-Ion Batteries Via the Secondary Ion Mass Spectrometry

To develop lithium-ion batteries with a high rate-capability and low cost, the prevention of capacity loss is one of major challenges, which needs to be tackled in the lithium-ion battery industry. During electrochemical processes, lithium ions diffuse from and insert into battery electrodes accompanied with the phase transformation, whereas ionic diffusivity and concentration are keys to the resultant battery capacity. In the current study, we compare voltage versus capacity of lithium-ion batteries at different current-rates (C-rates) discharging. Larger hysteresis and voltage fluctuations are observed in higher C-rate samples. We investigate origins of voltage fluctuations by quantifying lithium-ion intensity and distribution via a time-of-flight secondary ion mass spectrometry (ToF-SIMS). The result shows that for fully discharged samples, lithium-ion intensity and distribution are not C-rate dependent, suggesting different lithium-ion insertion mechanisms at a higher C-rate discharging might be solely responsible for the observed low frequency voltage fluctuation.