A double core–shell modification of bulk TiO2 microspheres into porous N-doped-graphene carbon nanoflakes/N-doped TiO2 microspheres for lithium-ion battery anodes

Abstract

In this study, we modified bulk TiO₂ microspheres—using a template-aided, double core–shell modification with N-doped carbon (NC) and N-doped graphene (NG)—for the purpose of forming porous N-doped graphene carbon nanoflakes/N-doped TiO₂ (NG–NC/NTiO₂) microspheres. The effects of surface modification on the properties of the TiO₂ microspheres and the resultant electrochemical performance in a lithium-ion-battery (LIB) anode were thoroughly investigated. The double core–shell modified nanocomposite exhibited a specific capacity of 74 mA h g⁻¹ at a 10 C rate, which was much higher than the capacities of TiO₂, carbon/TiO₂, and core–shell NC/NTiO₂ nanocomposites at rates of 0.2, 1, and 5 C, respectively. The RGO of the double core–shell NC/NTiO₂ nanocomposite provided an effective buffering effect for the TiO₂ microsphere, resulting in a much lower initial specific-capacity loss of 19.6%, on the 200^th cycle, in comparison with the 41.8% loss of the core–shell NC/NTiO₂ nanocomposite at the same cyclic stage. Such excellent performances from the TiO₂ microspheres with the double core–shell assembly in the LIB anode were attributed to a significant reduction of charge transfer resistance (R_ct) and maintenance of electrode stability.