Oxygen vacancies enable excellent electrochemical kinetics of carbon coated mesoporous SnO2 nanoparticles in lithium ion batteries

Abstract

Herein, we report the synthesis, characterization and electrochemical performance of carbon coated mesoporous SnO₂ nanoparticles (NPs) prepared by adopting a simple hydrothermal process. BET analysis shows that the formed SnO₂ nanoparticles are porous with a high surface area which accommodates volume expansion. Morphological and Raman studies reveal that the carbon coating on SnO₂ by a non-conventional carbon coating (NCC) process resulted in the formation of a homogenous carbon layer with a thickness of around 4–10 nm with predominant graphitic nature. The influence of the thermal treatment of SnO₂ in air and carbon coating, which decide the oxygen vacancies, particle size, electrical conductivity and electrochemical performance, has been systematically studied. Electrochemical studies reveal that carbon coated (by the NCC process) H-SnO₂ (calcined at 400 °C) with an average particle size and carbon coating thickness of 3 nm and 66 nm, respectively, delivered a discharge capacity of 440 mA h g⁻¹ at a 1C rate with excellent electrochemical stability. Furthermore, it delivers capacities of 396 mA h g⁻¹, 272 mA h g⁻¹ and 129 mA h g⁻¹ at 5C, 8C and 10C, respectively. The excellent electrochemical performance of carbon coated H-SnO₂ by the NCC process can be attributed to the oxygen vacancies which can inhibit Sn coarsening and enhance electrical conductivity together with the carbon coating, high surface area, short Li⁺-ion diffusion length, and porous structure of SnO₂ which buffers the volume expansion.