Core-Shell Structured SiOx-TiO2@C Nanocomposites As High-Rate and Long-Cycle Anode for Lithium Ion Batteries

Abstract

Silicon suboxide (SiOx, 0˂x˂2) is one of the promising anode materials for lithium-ion batteries (LIBs) due to its high specific capacity, low operating voltage (˂0.4 V) and rich abundance [1]. SiOx produces inert components (lithium oxide and lithium silicate) and nano-Si particles during initial lithiation/delithiation process. The former can act as buffer matrix to significantly reduce the volume change of nano-sized Si. Therefore, compared to pure Si, SiOx electrode shows relatively good cycling stability and thus appears promising for high energy density Li-ion batteries. Nevertheless, the poor intrinsic electronic and ionic conductivity of SiOx often leads to a low specific capacity and inferior rate capability [2]. In addition, the SiOx electrode cannot withstand long-period cycling due to the inevitable volume variation of SiOx. In this work, we prepared core-shell SiOx-TiO2/C nanoparticles with unique watermelon-like structured by a simple sol-gel combined with a following carbon coating process. Ultrafine TiO2 nanocrystals are homogeneously distributed inside SiOx particles, forming SiOx-TiO2 dual-phase cores, which are coated with outer carbon shells. The incorporation of TiO2 component can effectively enhance the electronic and lithium ionic conductivities, release the structure stress caused by alloying/dealloying of Si component and maximize the capacity utilization by decreasing the O/Si ratio (x value). The synergetic combination of these advantages enables the synthesized SiOx-TiO2@C nanocomposite to have outstanding electrochemical performances, including high specific capacity, excellent rate capability and stable long term cycleability. A stable specific capacity of ~910 mAh g-1 is achieved after 200 cycles at the current density of 0.1 A g-1 . These results suggest the synthesized SiOx-TiO2/C composite is a promising high performance anode material for lithium ion batteries.