Solid-state self-template synthesis of Ta-doped Li2ZnTi3O8 spheres for efficient and durable lithium storage.

ABSTRACT

Ta-doped Li2ZnTi3O8 (LZTO) spheres (Li2ZnTi3-x Ta x O8; where x is the synthetic chemical input, x = 0, 0.03, 0.05, 0.07) are synthesized via solid-state reaction using mesoporous TiO2 spheres as the self-template. The majority of Ta5+ ions are uniformly doped into crystal lattices of LZTO through the Ti↔Ta substitution, and the rest forms the piezoelectric LiTaO3 secondary phase on the surface, as confirmed by X-ray diffraction refinement, Raman spectroscopy, density functional theory, and electron microscopy. Electrochemical impedance spectroscopy demonstrates that the Ta5+ doping creates rapid electronic transportation channels for high Li+ ion diffusion kinetics; however, the LiTaO3 surface coating is beneficial to improve the electronic conductivity. At the optimal x = 0.05, Li2ZnTi3-x Ta x O8 spheres exhibit a reversible capacity of 90.2 mAh/g after 2000 cycles with a high coulombic efficiency of ≈100% at 5.0 A/g, thus enabling a promising anode material for lithium-ion batteries with high power and energy densities.