a,b, Cyclic voltammograms of anode-free Na–S batteries using NaDCA and NaCl electrolytes, respectively. The insets in the bottom-left corners illustrate the cell configuration, in which a S cathode served as the working electrode (WE). An initial positive scan was applied at a scan rate of 1 mV s−1, corresponding to Na metal deposition on the Al foil, which serves as both the counter electrode (CE) and the reference electrode (RE). The insets in the upper-left corners show the charge passed during charge and discharge in the cyclic voltammogram, with Q 0 denoting the initial charge. The CE was calculated as the ratio of the total charge transferred during the cathodic scan to that during the anodic scan. The mass loading of S is 1.04 mg cm−2 unless otherwise specified. c,d, Temperature-dependent Nyquist plots of anode-free Na–S batteries using NaDCA and NaCl electrolytes, respectively. The insets show the corresponding equivalent circuits for impedance fitting. R 1 , R 2 , CPE 1 and W 1 are the bulk resistance, charge-transfer resistance, constant phase element and Warburg impedance, respectively. e, Arrhenius plots and reaction activation energies derived from the charge-transfer resistance of anode-free Na–S batteries using NaDCA and NaCl electrolytes at increasing temperatures from 293 to 333 K. f, Nyquist plots of anode-free Na–S battery at the 100th, 500th, 1,000th and 1,400th cycles. The charge capacity and current density are 200 mAh g−1 (0.21 mAh cm−2) and 1 A g−1 (1.04 mA cm−2), respectively. g, Cycling performance of the anode-free Na–S battery using the NaDCA electrolyte at 800 mAh g−1 (0.83 mAh cm−2). The battery was initially charged and discharged for ten cycles at 800 mAh g−1 (0.83 mAh cm−2) and 500 mA g−1 (0.52 mA cm−2), with a discharge cut-off voltage of 2.0 V for activation. h, Galvanostatic charge–discharge curves of the activation step for the anode-free Na–S battery.