Rapid Ion Migration and High Stability in SiOx Anodes Enabled by Co Doping and Core–Shell Architecture

The huge volume expansion (200%) and poor electrical conductivity of SiOx have seriously hampered its commercial application. To solve the problem of SiOx-based negative electrodes, SiOx@CoC composites were prepared by using a self-assembly strategy in which heat-treated nano-Si (SiOx) acts as the core structure while Co NPs deposited the carbon layer as the shell structure. The experimental results showed that the presence of Co nanoparticles increased the Li⁺ migration rate (10^–11 cm² s^–1) and enhanced the mechanical strength of the outer layer (volume expansion of 20%). As a result of these advantages, SiOx@CoC has a reversible capacity of 500 mA h g^–1 and 97% capacity retention after 400 cycles. Theoretical calculations show that the presence of Co nanoparticles enhances the Li⁺ adsorption by SiOx (ΔE_ads = −3.36 eV) and reduces the Li⁺ migration energy barrier. In addition, the density of electronic states (DOS) indicates that the overall electrical conductivity of the material is significantly improved by Co doping. Finally, SiOx@CoC mixed with graphite can be well matched with LiFePO₄ to form a full battery. There is no temperature runaway, and 130 mA h g^–1 reversible capacity is retained in 5.2 and 1.5 V overcharge/discharge experiments.