Black rutile (Sn, Ti)O₂ initializing electrochemically reversible Sn nanodots embedded in amorphous lithiated titania matrix for efficient lithium storage

Binary oxides MO₂ (M = Ti, Sn) are promising anode materials for Li-ion batteries, but they suffer from rather low capacities (TiO₂: ∼340 mA h g^-1) and poor cycling stability (SnO₂: <50 cycles). Here, the black (Sn, Ti)O₂ solid solution of a core-shell structure Sn_xTi_1-xO₂@Sn_xTi_1-xO_2-yH_y is first designed to simultaneously harvest a large reversible capacity, high rate performance and superior cycling stability. The conductive amorphous shell of the new material obtained from hydrogen plasma reduction leads to a significant improvement of conductivity from 0.1 to 35.7 μS cm^-1. The rutile solid solution with a homogenous mixing of Sn and Ti helps to form a uniform distribution of Sn nanodots in an amorphous lithiated titania matrix after lithiation, and subsequently maintains a sub 10 nm scale nanostructure even after long-term cycling. The lithiated titania matrix prevents the aggregation of tin nanodots, accommodates the volume change, and provides a stable conductive network for ion kinetics, which consequently results in excellent lithium-ion battery performance. The black (Sn, Ti)O₂ achieves a remarkable reversible capacity of 583.4 mA h g^-1 after 100 cycles at 0.2 A g^-1, retaining stable specific capacities of 419.2 mA h g^-1 at 2 A g^-1 after 500 cycles and 335.3 mA h g^-1 at 5 A g^-1. The overall performances of this material, including capacity, high-rate performance and cycling stability, are among the best for transition metal oxide anode materials. The ability to fundamentally improve the electrical conductivity and structure stability of the black material should open up new opportunities for high-performance Li-ion batteries.