Constructing low N/P ratio sodium-based batteries by reversible Na metal electrodeposition on sodiophilic zinc-metal-decorated hard carbons

Nowadays, the main deficiency in boosting the commercialization of sodium ion battery is the relatively low energy density. Herein, we propose a new way to significantly improve the energy density by constructing low negative/positive (N/P) ratio sodium-based batteries enabled by reversible Na metal electrodeposition on sodiophilic zinc-metal-decorated hard carbons (HC–Zn) anode. HC-Zn is used as a typical insertion anode, and simultaneously as a substrate for Na metal plating, leading to the formation of a composite NaxC-Na metal anode with a hybrid energy storage process. We also provide a general and low-cost method of Zn metal coating on various hard carbons. The compatibility between Zn and Na metal is firstly revealed by molecular dynamics simulations. As a result, HC-Zn electrode exhibits a highly reversibility even at a high-capacity of 1100 mA h g−1 and 5C rate, which can stably cycle 1400 cycles with a high Coulombic efficiency around 100%. Finally, the full cells of HC-Zn anode coupling with sodium vanadyl phosphate cathode with low NP ratio (NP = 0.8 and 0.6) are constructed which display good cycling stability and remarkably improved energy density from 220 Wh/kg of regular NP 1.1 to 286 Wh/kg.