ZnO-Coated Silicon Oxide Nano-Anode: Synergistic Enhancement of Cycling and Thermal Stability of Lithium-Ion Batteries

Abstract

Silicon oxide (SiO) has great potential as a high-capacity anode for lithium-ion batteries, but its practical use is limited by excessive volume expansion (>200%) and rapid capacity fade, especially at high temperatures. Traditional strategies, like carbon coating and nanostructuring, only partially address these issues. This study introduces a novel approach by synthesizing porous SiO microspheres encapsulated within a conformal ZnO shell (MS-ZnO). The internal porosity absorbs volumetric strain, while the ZnO shell provides mechanical stability, preventing electrode disintegration. MS-ZnO (M-Z: Zinc oxide coating on SiO) shows significantly reduced swelling (32.4% vs 94.8% for ZnO unmodified SiO (P-M)) and a high reversible capacity of 978.65 mAh g⁻¹ after 500 cycles, double that of unmodified SiO. At 90 °C, MS-ZnO maintains a stable Coulombic efficiency of ~75%, compared with ~32% for unmodified SiO, indicating excellent thermal stability. In full-cell tests with LiFePO₄, MS-ZnO delivers 151 mAh g⁻¹ at 0.2C with 83.5% capacity retention after 100 cycles. GITT and DFT analysis reveal that the ZnO shell enhances Li⁺ diffusion and mechanical strength. This work presents ZnO encapsulation as a transformative strategy to overcome volume change and thermal instability, unlocking the potential of SiO anodes for high-performance, high-safety lithium-ion batteries.