A unique dual-shell encapsulated structure design achieves stable and high-rate lithium storage of Si@a-TiO2@a-C anode

Abstract

Due to high theoretical capacity and low lithium-storage potential, silicon (Si)-based anode materials are considered as one kind of the most promising options for lithium-ion batteries. However, their practical applications are still limited because of significant volume expansion and poor conductivity during cycling. In this study, we prepared a double core–shell nanostructure through coating commercial Si nanoparticles with both amorphous titanium dioxide (a-TiO₂) and amorphous carbon (a-C) via a facile sol–gel method combined with chemical vapor deposition. Elastic behaviors of a-TiO₂ shells allowed for the release of strain, maintaining the integrity of Si cores during charge–discharge processes. Additionally, outer layers of a-C provided numerous pore channels facilitating the transport of both Li⁺ ions and electrons. Using the distribution of relaxation time analysis, we provided a precise kinetic explanation for the observed electrochemical behaviors. Furthermore, the structural evolution of the anode was explored during cycling processes. The Si@a-TiO₂@a-C-6 anode was revealed to exhibit excellent electrochemical properties, achieving a capacity retention rate of 86.7% (877.1 mA·h·g⁻¹ after 500 cycles at a 1 A·g⁻¹). This result offers valuable insights for the design of high-performance and cyclically stable Si-based anode materials.