Enabling High‐Performance Sodium Battery Anodes by Complete Reduction of Graphene Oxide and Cooperative In‐Situ Crystallization of Ultrafine SnO 2 Nanocrystals

The main bottleneck against industrial utilization of sodium ion batteries (SIBs) is the lack of high‐capacity electrodes to rival those of the benchmark lithium ion batteries (LIBs). Here in this work, we have developed an economical method for in situ fabrication of nanocomposites made of crystalline few‐layer graphene sheets loaded with ultrafine SnO 2 nanocrystals, using short exposure of microwave to xerogel of graphene oxide (GO) and tin tetrachloride containing minute catalyzing dispersoids of chemically reduced GO (RGO). The resultant nanocomposites (SnO 2 @MWG) enabled significantly quickened redox processes as SIB anode, which led to remarkable full anode‐specific capacity reaching 538 mAh g −1 at 0.05 A g −1 (about 1.45 times of the theoretical capacity of graphite for the LIB), in addition to outstanding rate performance over prolonged charge–discharge cycling. Anodes based on the optimized SnO 2 @MWG delivered stable performance over 2000 cycles even at a high current density of 5 A g −1 , and capacity retention of over 70.4% was maintained at a high areal loading of 3.4 mg cm −2 , highly desirable for high energy density SIBs to rival the current benchmark LIBs.