Porous TiO₂ urchins for high performance Li-ion battery electrode : Facile synthesis, characterization and structural evolution

Porous TiO₂ urchins have been synthesized by a hydrothermal route using TiO₂/oleylamine as precursors with subsequent ion-exchange and calcination. The resultant material consists of porous spherical cores and nanochains-constructed shells with straight channels. Electrochemical measurements indicate the TiO₂ urchins deliver superior lithium storage capability in terms of high capacity (206.2 mA h g^-1 at 0.5 C), superior rate performance (94.4 mA h g^-1 at 20 C) and stable cycling stability (94.3% capacity retention over 1000 cycles at 10 C versus the third cycle). Such performance enhancement is mainly due to the increased electrode/electrolyte contact interface, reduced Li⁺ diffusion pathways and improved mass transfer of electrolyte in the unique 3D interconnected hierarchical network. In addition, ex-situ XRD, SEM and TEM analyses further reveal high structure integrity of the porous TiO₂ urchins during the electrochemical lithiation, leading to enhanced lithium storage stability. Moreover, we detected that some anatase nanocrystals evolved into electrochemically inactive Li₁TiO₂ dots (∼10 nm in size) during long-term electrochemical cycling. Our findings provide more insights for better understanding of the structure evolution and capacity decay mechanism in porous TiO₂ nanostructures.