Spatially-resolved lithiation dynamics from operando X-ray diffraction and electrochemical modeling of lithium-ion cells

Energy dispersive X-ray diffraction is used to profile the time evolution of ordered LixC6 phases in solid electrodes of lithium-ion cells charged at rates between 0.2 and 4.7C (where 1C corresponds to full discharge in 1 h). The methods for quantifying lithium concentration in these phases from the acquired diffraction patterns are described. Compact expressions for time-dependent concentration gradients in the solid electrodes using orthogonal polynomial expansions are presented. Experimentally, these gradients persisted in lithiated graphite electrodes even after the cells rested at open-circuit for over 9 h. A multiphase electrochemical model of graphite intercalation captured many of the observed behaviors, including the progression of phase transitions and the persistent gradients at zero current. However, the magnitude of concentration gradients in both the oxide cathode and graphite anode is underestimated by the model, even at moderate currents.

Automated summary

This study uses energy dispersive X-ray diffraction to analyze the evolution of ordered LixC6 phases in solid electrodes of lithium-ion cells, presenting methods for determining lithium concentration and concentration gradients. Experimental results show that concentration gradients persist in lithiated graphite electrodes even after long periods of open-circuit conditions. A multiphase electrochemical model can explain many observed behaviors, but underestimates concentration gradients in both the oxide cathode and graphite anode.