Fig. 4: Electrochemical reaction kinetics.

GITT potential profiles and corresponding Na+ diffusion coefficients of a Na||HESSe, b Na||LESSe and c Na||CuS cells in the first two cycles, d polarization curves of GITT at 1st discharge process. Nyquist plots of e, f Na||HESSe, g, h Na||LESSe and i, j Na||CuS cells in first cycle (solid lines represent fitting results) and k Impedance comparison diagram of three electrodes; detailed fitting data are provided in Supplementary Table 10.