In Situ Orthorhombic to Amorphous Phase Transition of Nb 2 O 5 and Its Temperature Effect on Pseudocapacitive Behavior.

Niobium pentoxide (Nb 2 O 5 ) represents an exquisite class of negative electrode materials with unique pseudocapacitive kinetics that engender superior power and energy densities for advanced electrical energy storage devices. Practical energy devices are expected to maintain stable performance under real-world conditions such as temperature fluctuations. However, the intercalation pseudocapacitive behavior of Nb 2 O 5 at elevated temperatures remains unexplored because of the scarcity of suitable electrolytes. Thus, in this study, we investigate the effect of temperature on the pseudocapacitive behavior of submicron-sized Nb 2 O 5 in a wide potential window of 0.01-2.3 V. Furthermore, ex situ X-ray diffraction and X-ray photoelectron spectroscopy reveal the amorphization of Nb 2 O 5 accompanied by the formation of NbO via a conversion reaction during the initial cycle. Subsequent cycles yield enhanced performance attributed to a series of reversible Nb V, IV /Nb III redox reactions in the amorphous Li x Nb 2 O 5 phase. Through cyclic voltammetry and symmetric cell electrochemical impedance spectroscopy, temperature elevation is noted to increase the pseudocapacitive contribution of the Nb 2 O 5 electrode, resulting in a high rate capability of 131 mAh g -1 at 20,000 mA g -1 at 90 °C. The electrode further exhibits long-term cycling over 2000 cycles and high Coulombic efficiency ascribed to the formation of a robust, [FSA] - -originated solid-electrolyte interphase during cycling.