Is there a common reaction pathway for chromium sulfides as anodes in sodium-ion batteries? A case study about sodium storage properties of MCr2S4 (M = Cr, Ti, Fe)

Abstract We present new insights into the electrochemical properties of three metal sulfides MCr 2 S 4 ( M = Cr, Ti, Fe) probed as anode materials in sodium-ion batteries for first time. The electrodes deliver decent reversible capacities and good long-term cycle stability, e.g., 470, 375, 524 mAh g −1 are obtained after 200 cycles applying 0.5 A Fe, respectively. reaction mechanisms investigated via synchrotron-based X-ray powder diffraction pair distribution function analyses. highly crystalline educts decomposed Na nanoparticles ultra-small particles during initial discharge without formation intermediate NaCrS domains previously reported CuCrS NiCr . After a full cycle, structural integrity is not recovered. Thus, storage attributed to redox reactions between nanoscopic amorphous conversion products with only local atomic correlations M···S/S···S charged M···M/Na···S discharged state. Graphical