Figure 5. In situ Raman measurements of NCM||Cu cells with E1 (a-b) and E2 (c-d) electrolytes. Microscopic images on the surface of copper current collector at different cycling states with E1 (a) and E2 (c) electrolytes; In situ Raman spectra for the copper current collector with E1 (b) and E2 (d) electrolytes during the first cycle. The potential curves (left) and pseudocolor plots (right) are shown together.