Reaction Uniformity Visualized by Raman Imaging in Composite Electrode Layers of All-Solid-State Lithium Batteries
The reaction uniformity of LiCoO2 composite positive electrodes in all-solid-state cells was compared quantitatively by investigating the Raman band shifts corresponding to the state-of-charge (SOC) of LiCoO2. Raman imaging was conducted for the composite electrodes using different particle sizes of solid electrolytes. Raman spectra of each LiCoO2 particle were obtained and SOC distributions in composite electrodes were compared. The electrodes exhibited different reaction uniformity although the cells showed the similar initial charge capacities. When the larger solid electrolytes were used in composite electrodes, insufficient contacts between LiCoO2 and solid electrolytes brought about inhomogeneous SOC distributions. The quantitative analysis of SOC in LiCoO2 demonstrated that a variable SOC outside the average SOC resulted in larger irreversible capacity and lower rate performance.