Montmorillonite as a sodium-ion-conductor interface for stable sodium metal anodes

The sodium anode is an ideal anode material in next-generation high-energy batteries due to its high theoretical capacity (1165 mA h g-1), low potential (-2.71 V) and natural abundance of Na resources. However, its practical application is restricted by irregular growth of sodium dendrites, which arises from unstable solid electrolyte interface (SEI) and high activity of sodium. To prevent dendrite growth, herein, a highly sodiophilic Na+-intercalated montmorillonite (Na-MMT) is directly embedded into sodium metal through a simple mechanical-rolling method. In the Na@Na-MMT composite anode, Na-MMT is highly dispersed into the whole sodium electrode, which affords a stable sodium-ion-conductor interface to provide faster diffusion channels and effectively lower the nucleation potential of Na, thus guiding the uniform deposition of sodium. By optimizing the mass ratio between sodium and montmorillonite, the as-prepared Na@Na-MMT anode exhibits superior plating/stripping reversibility (over 600 h at 1 mAh cm- 2) and fast electrochemical kinetics (200 h at 4 mA cm-2 with a capacity of 4 mAh cm-2) in a carbonate-based electrolyte, which outperforms the performance of Na@Ca-MMT and bare Na anodes. Moreover, the Na full cell (Na@Na-MMT||Na3V2(PO4)3) exhibits a long cycling stability over 1000 cycles and good rate capability (30 C).

Automated summary

In this study, a highly sodiophilic Na+-intercalated montmorillonite (Na-MMT) is directly embedded into sodium metal to form a Na@Na-MMT composite anode. The Na@Na-MMT anode exhibits superior plating/stripping reversibility and fast electrochemical kinetics, while the Na full cell shows long cycling stability and good rate capability.