Carambola-shaped SnO2 wrapped in carbon nanotube network for high volumetric capacity and improved rate and cycle stability of lithium ion battery

Constructing nanostructures of high capacity materials and hybridizing the same with conductive carbon networks are important for high performing lithium ion batteries. Here, we demonstrate new carambola-shaped crystalline SnO2 (c-SnO2), which is wrapped in a three-dimensional multiwalled carbon nanotube network (c-SnO2@3D-CNT). The carambola structure of c-SnO2 is constructed by changing the surface energy of a specific crystalline plane using a potassium fluoride capping agent. The as-designed c-SnO2@3D-CNT achieves a high capacity of 1140.2 mA.h.g(-1) at 50 mA.g(-1), a capacity retention of 50.7% retained at 1000 mA.g(-1) relative to 50 mA.g(-1), and a cycling stability of 72.0% over 500 cycles at a high rate of 1000 mA.g(-1). In particular, the c-SnO2@3D-CNT shows a high volumetric capacity of 1674.8 mA.h.cm(-3) at 50 mA.g(-1) and 849.2 mA.h.cm(-3) at 1000 mA.g(-1), which is greater than those of previous SnO2-based materials. This finding is associated with the compact packing of hierarchical carambola structure having multiple concave surfaces into dense and porous electrode. Therefore, the hierarchical carambola structure and 3D hybrid architecture provide a buffer space for volume expansion and fast ion/electronic conducting pathways, which impart a high volumetric capacity, improved cyclic and rate performances, and higher reversibility than other SnO2 materials.