Abstract:

Owing to their advantages such as safe operation, high power density, long cycle life, and low self-discharge rate, lithium-ion batteries (LIBs) have attracted attention for applications ranging from portable electronics to electric vehicles (EVs)/hybrid EVs (HEVs). However, the striking exothermic reaction and growth of lithium dendrites during lithiation-delithiation cycles for commercial graphite anodes are hidden safety risks associated with LIBs. Titanium dioxide (TiO₂) is considered as an important material for LIBs because of its high safety and excellent cycling stability. In addition, TiO₂ anode used in lithium-ion storage system has a relatively high voltage (~1.5 V vs. Li/Li⁺), and thus, it meets the strict safety standards of commercial LIBs. However, the unsatisfactory conductivity and ion diffusion rate prevent the further application of TiO₂ in LIBs. To date, the combination of graphene, carbon nanotubes (CNTs), carbon quantum dots (QDs) and porous carbon with TiO₂ has attracted significant research attention. Nevertheless, it is still challenging to introduce a unique nanostructure design by organically compounding TiO₂ with N-doped porous carbon matrix. Herein, N-doped porous carbon incorporating fine TiO₂ nanoparticles (NPs) with a flower-like structure (denoted as FL-TiO₂/NPC) is successfully prepared using flower-like NH₂-MIL-125(Ti) as the hard template. The as-prepared Ti-based framework shows a flower-like structure, which is assembled with two-dimensional (2D) corrugated porous nanosheets. On the one hand, the corrugated carbon nanosheets incorporating fine TiO₂ particles can offer a magnifying contact area between electrode matrix and electrolyte. On the other hand, the N-doped porous carbon plays a crucial role in improving the conductivity and structural integrity of the whole matrix. Therefore, the as-prepared FL-TiO₂/NPC can deliver an excellent reversible lithium storage capacity of 384.2 mAh·g^-1 at the current density of 0.5 A·g^-1 after 300 cycles and 279.1 mAh·g^-1 at 1 A·g^-1 after 500 cycles. Furthermore, even when tested at 2 A·g^-1, FL-TiO₂/NPC can deliver a reversible capacity of 256.5 mAh·g^-1 with a coulombic efficiency of 100% after 2000 cycles. The superior electrochemical performance and the structural toughness of LIBs originate from the unique flower-like structure. We believe that the proposed synthesis strategy will provide a new idea for the preparation of metal oxides/N-doped porous carbon composites with high lithium storage performance.

Key words: TiO₂ nanoparticles, N-doped porous carbon nanosheet, Flower-like structure, NH₂-MIL-125 (Ti), Anode, Lithium-ion battery