Double-Enhanced Core-Shell-Shell SbS/Sb@TiO@C Nanorod Composites for Lithium- and Sodium-Ion Batteries.

For most alloying- and conversion-type anode materials, a huge volume expansion and structure degradation of the electrodes always hinder their applications. In this work, a novel core-shell-shell SbS/Sb@TiO@C nanorod composite has been designed layer by layer, which includes an inner SbS/Sb heterostructure core protected by an oxygen-deficient TiO shell and a conductive carbon shell. It is interesting to observe that, during the carbothermic reduction process, the previous SbS nanorod cores are partially reduced into a metallic Sb phase and the reduced TiO also creates many oxygen vacancies, which can greatly enhance the conductivity of the semiconductor SbS. Thanks to the double effects of the TiO middle shell and carbon outer shell, the unique double-shelled structure design creates an enhanced dual protection, which can better accommodate the volume-expansive deformation and preserve the structural integrity of the active SbS/Sb core. Especially, the TiO middle layer is self-assembled by numerous nanoparticles acting as a nanopillar backbone, which supports between the nanorod core and outer carbon shell to better buffer the volume changes. As a result, the core-shell-shell SbS/Sb@TiO@C anode shows lithium and sodium storage performances superior to those of the pristine SbS and core-shell SbS@TiO electrodes. For lithium-ion batteries, the SbS/Sb@TiO@C nanorod composite achieves an initial discharge/recharge capacity of 1244.9/1005.1 mAh g with an initial Coulombic efficiency of about 80.7%, an enhanced rate capability with a capacity of 593.2 mA h g at 5.0 A g, and prolonged cycling life for 500 cycles with a reversible capacity of 495.8 mAh g at 0.5 A g. For sodium-ion batteries, the nanorodalso exhibits an improved performance with an initial discharge/recharge capacity of 781.4/574.0 mAh g (initial Coulombic efficiency of about 73.46%) and cycling for 400 cycles with a reversible capacity of 422.6 mAh g at 0.8 A g. This research sheds light upon double-shell structure designs with an effective middle shell to enhance the energy storage performance of electrode materials.