“…Additionally, it should be noted that the in situ generated Na 2 S species served as a buffer matrix is another key factor for realizing reversible and stable Na-metal batteries. 37 Indeed, it is noteworthy to mention that Sb alone is not sufficient enough to withstand the huge volume expansion (up to 390%), as evidenced by previous studies. 38,39 Moreover, even at high current densities and capacities (Figure 4b and c), the Na/Sb 2 S 3 electrodes still show low overpotentials of 27.2 and 28.5 mV with superior cycling stability over 700 cycles (namely, 1400 h, 3 mA cm −2 /3 mA h cm −2 ) and 500 cycles (namely, 1000 h, 5 mA cm −2 /5 mA h cm −2 ), respectively, whereas Na/Cu electrodes exhibit unstable voltage profiles with high overpotential (Figure 4b), even resulting in short circuit (Figure 4c).…”