Titanium Monoxide with in Situ Grown Rutile TiO₂ Nanothorns as a Heterostructured Job-Sharing Anode Material for Lithium-Ion Storage

Developing high-performance anodes is highly desired to meet the recent ever-increasing demands for high-energy lithium-ion batteries (LIBs). Titanium dioxide (TiO₂) shows extremely stable performance as an anode material in LIBs, but its intrinsic structural limit critically inhibits the full utilization of the TiO₂ material. Herein, we report a uniquely integrated heterostructure of rutile TiO₂ (r-TiO₂) nanothorns grown in situ over a new porous and conductive cubic crystalline titanium monoxide (TiO) core. The new cubic crystalline TiO is prepared from phase transformation of anatase TiO₂ by pyrolysis with Mg metal at 650 °C, and subsequent oxidative HCl treatment enables in situ growth of r-TiO₂ nanothorns on the surface of the porous TiO. Interestingly, the mixed-phased novel hybrid as an anode exhibits a new Li-ion charging mechanism consisting of two independent reactions of intercalation and pseudocapacitive interaction corresponding to the two different phases of r-TiO₂ and TiO, respectively, in the composite for Li-ion storage. Thus, it illustrates high reversible capacity and almost no capacity decay during 1000 cycles at a high current density of 20 C (4000 mA g⁻¹), overcoming the issues of conventional TiO₂. In particular, the excellent rate capability along with a long cycle life enables the new hybrid to have ultrafast charging of the system. Furthermore, unlike a conventional TiO₂ anode working in the potential range (1.0−3.0 V), the hybrid with the job-sharing property exhibits stable charge−discharge performance over a wider potential window range of 0.01−3.0 V, particularly even in the low potential range of 0.01−1.0 V. All the properties including the wider potential window allow the hybrid to realize the highest electrochemical performance that titanium oxides have ever achieved so far.