Unravelling the Interface Layer Formation and Gas Evolution/Suppression on a TiNb2O7 Anode for Lithium-Ion Batteries.

TiNb2O7 (TNO) has been regarded as a promising anode material for high-power lithium-ion batteries because of the high theoretical capacity and rate performance within the operation voltage range of 1.0-3.0 V. Herein, the electrochemical performance and interface evolution of TNO are comprehensively investigated by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The prepared TNO shows a high initial reversible capacity of 256 mA h g-1 and a satisfactory capacity retention of 68.4% after 200 cycles at 0.1 C. It is generally believed that the formation of solid electrolyte interface (SEI) film could be avoided at the high operating voltage beyond 1.0 V. However, we find that the thin SEI layer is formed during the lithium insertion process and partially dissolved during the following lithium extraction process, and subsequently the SEI layer increases gradually during long-term cycles. Most importantly, we find obvious gassing behavior in the TNO/LiFePO4 pouch cell for the first time and demonstrate effective suppression effects of VC additive on the swelling phenomenon of full batteries.