Interfacial engineering to achieve an energy density of over 200 Wh kg−1 in sodium batteries

Sodium-based batteries have attracted wide interests in the academic and industrial fields. However, their energy density is still lower than that of Li-based batteries. Here we report an initial anode-free Na battery with an energy density of over 200 Wh kg−1, which is even higher than that of the commercial LiFePO4||graphite battery. Through introducing graphitic carbon coating on the Al current collector and boron-containing electrolytes in the battery, we show that uniform nucleation and robust interphases enable reversible and crack-free Na deposition. Benefitting from the synergetic effects derived from the built cooperative interfaces, the cycling lifetime of the Na battery without applying additional pressure reaches 260 cycles, which is the longest life for large-size cells with zero excess Na. The insights gained from the Na plating/stripping behaviour and interfacial chemistry in this work pave the way for further development of Na batteries with even higher performance. Sodium-ion batteries have long been tipped as a promising post-Li-ion storage technology but their performance is still inferior to Li-ion batteries. Here the authors design an ampere-hour-scale battery with an initial Na-free anode configuration to achieve an energy density that rivals Li-ion batteries.