Synergistic Effect of Oxygen-Defective TiNb2O7 Anode and Lithiated Polyacrylic Acid for High-Power Lithium-Ion Storage

Abstract

TiNb2O7 (TNO) is a promising anode material for lithium-ion batteries due to its higher power capability and theoretical capacity compared to traditional graphite anodes. This study addresses three issues with TNO: low electronic conductivity, time- and energy-consuming synthesis methods, and the absence of a stable interface with the electrolyte when discharged to below 1 V. The ultrafast (≈ 60 s) Joule heating method yields an oxygen-defective TNO (OD-TNO) with enlarged d-spacings and oxygen vacancies at the edge-shared octahedral sites, enhancing Li+ diffusion and increasing electronic conductivity by 60,000 times. The use of Li+-rich polyacrylic acid binder (Li50%-PAA) provides uniform, protective coverage around the TNO particles, resulting in better electrolyte stability and Li+ transport property at the TNO/electrolyte interface. The charge storage mechanism in the OD-TNO/Li50%-PAA anode involves pseudocapacitive-type Li+ intercalation redox reactions for charging times of > 40 minutes (scan rates > 1 mV/s), while faster charging shows that the intercalation process behaves entirely through diffusion mechanism. A full cell of OD-TNO/Li50%-PAA anode with a LiNi0.5Mn1.5O4 cathode shows a capacity of 153.78 mAh g⁻¹ over 400 cycles with 92.4% capacity retention at 1 C, highlighting the practical potential of OD-TNO/Li50%-PAA for high-energy and high-power density Li+ storage.