Synergistic effect of an 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 a Li⁺-rich polyacrylic acid binder (Li_50%-PAA) provides uniform, protective coverage around the TNO particles, resulting in better electrolyte stability and Li⁺ transport properties at the TNO/electrolyte interface. The charge storage mechanism in the OD-TNO/Li_50%-PAA anode involves pseudocapacitive-type Li⁺ intercalation redox reactions for charging times of >40 minutes (scan rates < 1 mV s⁻¹), while faster charging shows that the intercalation process occurs entirely through a diffusion mechanism. A full cell of an OD-TNO/Li_50%-PAA anode with a LiNi_0.5Mn_1.5O₄ cathode exhibits a capacity of 153.78 mA h g⁻¹ over 400 cycles with 92.4% capacity retention at 1C, highlighting the practical potential of OD-TNO/Li_50%-PAA for high-energy and high-power density Li⁺ storage.