New Class of Titanium Niobium Oxide for a Li-Ion Host: TiNbO₄ with Purely Single-Phase Lithium Intercalation

Abstract

Entropy-stabilized titanium niobium oxides (TNOs) with crystallographic shear structures (e.g., TiNb2O7 and Ti2Nb10O29) are generally synthesized by high-temperature calcination in an air or an oxygen atmosphere to compensate for their positive enthalpies of formation. In this work, we demonstrate that changing the reaction atmosphere into a slightly reductive environment using in situ carbonization leads to the creation of a new class of TNO with a formula of TiNbO4. Unlike its predecessors, this new lithium reservoir is a rutile phase, and most strikingly, in situ X-ray diffraction analysis revealed that its lithium intercalation occurs via a purely solid-solution process. Since solid-electrolyte-interface-free, high capacity anode materials with long cyclic life are required to meet the stringent requirements of widespread lithium-ion battery utilization, this finding of a new electrode material with purely single-phase lithium intercalation is of great interest for the development of high-performance anode materials. Distinctive electrochemical behavior that is different from that of crystallographic shear structured TNO is revealed by in-depth electrochemical analyses, which is ascribed to the unique structural and electronic properties of TiNbO4. We believe this work opens a new avenue for the development of feasible oxide-based alternatives to graphite, which can be safer and suitable for high-power performance.

Evidence of Intrinsic Pseudocapacitive Lithium Intercalation in Rutile TiNbO4

“…Recently, we reported a new host for Li-ions: rutile TiNbO 4 , which stores Li-ions via intercalation pseudocapacitance (Figure S1). In this work, we show that TiNbO 4 also possesses intrinsic intercalation pseudocapacitance due to its open structure.…”

“…Most mixed oxides of Ti and Nb store Li-ions via a mixture of phase transformation and intercalation pseudocapacitive mechanisms . However, as revealed recently, even in bulk form, TiNbO 4 stores Li-ions via only an intercalation pseudocapacitance mechanism, mostly in the (110) and (200) planes . It only goes through lattice expansion during Li insertion and does not show any phase transformations.…”

“…This limitation can be eased to some extent with Nb doping that increases the a -parameter, hence leading to better rate performance . However, unlike TiO 2 , TiNbO 4 has a 24% larger a -parameter, which allows easier Li insertion in the (110) and (200) planes . When TiNbO 4 was formed into nanostructures, the a -parameter did not show any significant changes (Table S2).…”

Carbon-Doped TiNb2O7 Suppresses Amorphization-Induced Capacity Fading

“…In 2011, the Goodenough group , proposed titanium niobium oxide (TNO, TiNb 2 O 7 ) with a Wadsley–Roth crystallographic sheared structure and a higher specific capacity of 388 mAh g –1 as a more energy-dense alternative to LTO. Since then, many other TNO analogs, such as Ti 2 Nb 10 O 29 , TiNb 6 O 17 , TiNb 24 O 62 , and TiNbO 4 , have been introduced. − Promising results have also been reported for TNO, and its analogs, tungsten- and niobium-based larger block phases (W 5 Nb 16 O 55 and W 8 Nb 18 O 69 ), , are raising more interest in Wadsley–Roth materials as alternatives to graphite.…”

Memory Effect in Lithium Titanate Driven by Interfacial Oxygen Vacancies

“…To investigate the changes at the interface with an increase in t P , we performed electrochemical impedance spectroscopy (EIS) after each holding time. The Nyquist spectra of all samples consisted of three semicircles and a capacitive tail. , The first semicircle was attributed to the charge transfer at the solid-electrolyte interface (SEI) layer with the resistance of R SEI and the capacitance of C SEI . The second circle was assigned to the charge transfer at the particle interface.…”