Oxygen Defect and Cl - -Doped Modulated TiNb 2 O 7 Compound with High Rate Performance in Lithium-Ion Batteries.

TiNb 2 O 7 has attracted extensive attention from lithium-ion battery researchers due to its superior specific capacity and safety. However, its poor ion conductivity and electron conductivity hinder its further development. To improve the ion/electron transport of TiNb 2 O 7 , we report that chlorine doping and oxygen vacancy engineering regulate the energy band and crystal structure simultaneously through a simple solid-phase method. NH 4 Cl was used to realize Cl - doping and oxygen vacancy production. A Rietveld refinement demonstrates an effective substitution of Cl in the O sites of Nb-O octahedra, with an enlarged crystal plane spacing. The oxygen vacancies provide more active sites for lithium intercalation. The diffusion coefficient of Li + is inceased from 2.39 × 10 -14 to 1.50 × 10 -13 cm 2 s -1 , which reveals the positive influence of Cl - doping and oxygen vacancies on the promoted Li + transport behavior. Charge compensation is introduced by the doping of Cl - and the generation of oxygen vacancies, leading to the formation of Ti 3+ and Nb 4+ and the adjustment of the electronic structure. DFT calculations reveal that TiNb 2 O 7 with Cl - doping and an O vacancy shows a metallic property with a finite value at the Fermi level, which is conducive to electron transfer in the electrode material. Benefiting from these advantages, the modified TiNb 2 O 7 presents superior rate performance with a commendable capacity of 172.82 mAh g -1 at 50 C. This work provides guidance to design high-performance anode materials for high-rate lithium-ion batteries.