Hydrogel-derived foams of nitrogen-doped carbon loaded with Sn nanodots for high-mass-loading Na-ion storage

Metallic Sn exhibits high theoretical capacity and low operating voltage for Na+ storage, but it suffers from huge volume changes during Na+ insertion/extraction and from big experimental difficulties to achieve high areal capacities with mass loadings larger than 10 mg cm(-2). Here we propose a facile and novel synthesis strategy towards hierarchically porous foams of Sn nanodots (3.2 nm) uniformly distributed in a three-dimensional sheet-like nitrogen-doped carbon (SNC) framework derived from a low-cost SnO2/polyacrylamide composite hydrogel. The resulting Sn@SNC foams effectively integrate the intriguing merits of the two building blocks, namely both Sn nanodots and SNC framework as active materials providing capacity and the SNC framework as a flexible buffer for the volume change, as an excellent conductor for electrons and as a spacer for the Sn nanodots suppressing aggregation. Moreover, the hierarchically porous structure of the Sn@SNC foam enables fast Na+ diffusion in thick electrodes, finally offering high-performance Na+ storage at high mass loadings of up to 20 mg cm(-2) with a reversible areal capacity of 1.0 mA h cm(-2) at 3 mA cm(-2) over 700 cycles.