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 SiO x have seriously hampered its commercial application. To solve the problem of SiO x -based negative electrodes, SiO x @CoC composites were prepared by using a self-assembly strategy in which heat-treated nano-Si (SiO x ) 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 cm 2 s –1 ) and enhanced the mechanical strength of the outer layer (volume expansion of 20%). As a result of these advantages, SiO x @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 SiO x (Δ E 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, SiO x @CoC mixed with graphite can be well matched with LiFePO 4 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.