Unconventional capacity increase kinetics of a chemically engineered SnO2 aerogel anode for long-term stable lithium-ion batteries

Abstract

Conversion-type materials are attractive candidates as anodes for next-generation batteries due to their high theoretical capacity. However, their irreversible conversion and excessive volume expansion during charge and discharge cycles present many limitations in practical applications. Here, we report a chemically engineered 3D SnO₂ aerogel anode with significantly improved reversible capacity and excellent cyclic retention for Li-ion storage. Uniformly distributed SnO₂ nanoparticles with sub-3 nm size are chemically bonded on 3D porous carbon nanotube networks through a facile dip coating method without heat treatment. The ultrafine SnO₂ nanoparticles contribute significantly to capacity improvement by increasing the interdiffusion layer by the size effect. Also, the electrochemical synergistic effect between the SnO₂ and carbon matrix and the open porous structures of the aerogel electrode facilitates significantly enhanced reversibility in the conversion between Li₂O/Sn and SnO₂ through rapid electron transfer and multidimensional Li-ion accessibility, respectively. Furthermore, the robust structure of the binder-free, freestanding aerogel electrode effectively buffers the massive volume expansion during the charge/discharge process through novel spatial confinement. As a result, the chemically engineered SnO₂ anode delivers the highest reversible capacity of about 2031 mA h g⁻¹ with a 200% capacity increase after the 600^th cycle at 1C. Such an increased capacity is mainly driven by a rise of the conversion reaction activity where the capacity ratio of the conversion reaction to the dealloying reaction increases up to 2.6 fold. It also presents gradually increasing capacity up to 224 mA h g⁻¹ at 10C and superior cyclability over 10 000 cycles under high C-rates without an evident capacity fading tendency. This study provides new insights into the practical design of highly reversible conversion-type electrodes and ultralight energy storage devices.