Controlled SnO2 Crystallinity Effectively Dominating Sodium Storage Performance

The exploration of sodium ion batteries (SIBs) is a profound challenge due to the rich sodium abundance and limited supply of lithium on earth. Here, amorphous SnO2/graphene aerogel (a-SnO2/GA) nanocomposites have been successfully synthesized via a hydrothermal method for use as anode materials in SIBs. The designed annealing process produces crystalline SnO2/graphene aerogel (c-SnO2/GA) nanocomposites. For the first time, the significant effects of SnO2 crystallinity on sodium storage performance are studied in detail. Notably, a-SnO2/GA is more effective than c-SnO2/GA in overcoming electrode degradation from large volume changes associated with charge-discharge processes. Surprisingly, the amorphous SnO2 delivers a high specific capacity of 380.2 mAh g(-1) after 100 cycles at a current density of 50 mA g(-1), which is almost three times as much as for crystalline SnO2 (138.6 mAh g(-1)). The impressive electrochemical performance of amorphous SnO2 can be attributed to the intrinsic isotropic nature, the enhanced Na+ diffusion coefficient, and the strong interaction between amorphous SnO2 and GA. In addition, amorphous SnO2 particles with the smaller size better function to relieve the volume expansion/shrinkage. This study provides a significant research direction aiming to increase the electrochemical performance of the anode materials used in SIBs.