Li iontronics in single-crystalline T-Nb2O5 thin films with vertical ionic transport channels

Abstract

The niobium oxide polymorph T-Nb2O5 has been extensively investigated in its bulk form especially for applications in fast-charging batteries and electrochemical (pseudo)capacitors. Its crystal structure, which has two-dimensional (2D) layers with very low steric hindrance, allows for fast Li-ion migration. However, since its discovery in 1941, the growth of single-crystalline thin films and its electronic applications have not yet been realized, probably due to its large orthorhombic unit cell along with the existence of many polymorphs. Here we demonstrate the epitaxial growth of single-crystalline T-Nb2O5 thin films, critically with the ionic transport channels oriented perpendicular to the film’s surface. These vertical 2D channels enable fast Li-ion migration, which we show gives rise to a colossal insulator–metal transition, where the resistivity drops by 11 orders of magnitude due to the population of the initially empty Nb 4d0 states by electrons. Moreover, we reveal multiple unexplored phase transitions with distinct crystal and electronic structures over a wide range of Li-ion concentrations by comprehensive in situ experiments and theoretical calculations, which allow for the reversible and repeatable manipulation of these phases and their distinct electronic properties. This work paves the way for the exploration of novel thin films with ionic channels and their potential applications.

Emerging on-chip microcells in electrocatalysis: functions of window and circuit

“…18 Parkin et al realized the epitaxial growth of single-crystalline T-Nb 2 O 5 thin films with vertical 2D channels, showing a larger and faster resistance change and a wider voltage operation range during Li interaction. 104 Besides, Cui et al first reported the in situ study of the electrochemical generation of sulfur on 2D layered materials, and correlated the varied sulfur states with the corresponding electrochemical behaviors, which shed light on the electrode design for high-performance Li–S batteries. 105…”

Highly Reversible Lithiation of Additive Free T‐Nb2O5 for a Quarter of a Million Cycles

“…Then, anhydrous ethanol was added incrementally following a previously published method. [ 41 ] After micellization, the DCM was removed via rotary evaporation and the resulting kinetically trapped micelle stock had a concentration of 8.53 g mL −1 .…”

“…[ 40 ] Similarly, single crystal T‐Nb 2 O 5 thin films were reported to transform reversibly into a monoclinic version and then irreversibly into an amorphous version with progressively higher extents of lithiation. [ 41 ] Such electrochemically induced crystallographic changes are important to understand for the realization of long‐term cycling stability in T‐Nb 2 O 5 electrodes. Herein, the effects of the electrochemical cycling conditions on T‐Nb 2 O 5 capacity retention are examined using CV.…”

Electric Field Induced Ion Migration and Property Tuning in Functional Oxides

“…7 An alternative approach involves introducing alkali metal ions, such as Li + , into the ILs to enhance response rates. 17 Ionic gels, created via polymer network gelation in an IL, offer a blend of solid-like stability and IL-like performance, making them suitable for various applications, such as gate electrolytes in thin-film transistors. In this perspective, our primary focus is on ionic-liquid-or ion-gelbased electrolytes, which have demonstrated their effectiveness in numerous recent studies.…”