Free-standing nanostructured vanadium pentoxide films for metal-ion batteries

Abstract

Owing to their unique layer structure, high aspect ratio and intercalation capability, vanadium pentoxide (V2O5) nanofibers are close-to-ideal building blocks for high performance electrodes for metal-ion batteries. However, thus far investigated electrodes composed of V2O5 nanofibers mostly contain binders and conductive agents, which reduce the electrodes' gravimetric capacity. Here we demonstrate self-supporting V2O5 nanofiber-based films that combine high mechanical flexibility and stability with good electrical conductivity. This has been achieved by suitable adjustment of the nanofiber length, in combination with a suitable humidity controlled post-treatment, to ensure an effective nanofiber interconnection and aging of the films. The optimization of these two parameters allows for an impressive 81%, 184%, and 281% enhancement in Young's modulus, tensile strength and toughness respectively, along with an increase of electrical conductivity by up to 165%. Such films can reach storage capacities of up to 150 mA h g-1 without the support of conductive agents and binders. Our findings provide fundamental design guidelines for advanced binder-free electrode materials, which unite high specific storage capacity, excellent mechanical stability and good intrinsic electrical conductivity - the key to technologically advanced battery performance and lifetime.

Binder-Free V2O5 Cathode for High Energy Density Rechargeable Aluminum-Ion Batteries

“…Our conclusion was corroborated by the determination of the electrical conductivity, which is significantly enhanced by the Cu doping [26]. The electrical conductivity of our V2O5 cathodes is comprised of an electronic and ionic contribution, specifically electron hopping along the vanadium centers (V 5+ and V 4+ ) and proton diffusion alongside the nanofiber's surface, respectively [21,25]. The in-plane electrical conductivity in the range of 2 S cm -1 [25,31], which is parallel to the V2O5 sheets, is approximately five orders higher than the out-of-plane electrical conductivity [31].…”

“…Such distance is large enough to accommodate ions or even small molecules [2,21]. The length of the nanofibers is in the range of several micrometers and can be adjusted by the storage temperature and the age of the nanofibers solution [25,30]. In this study, the used V2O5 nanofibers have a length of approximately 2 μm.…”

“…The electrical conductivity of our V2O5 cathodes is comprised of an electronic and ionic contribution, specifically electron hopping along the vanadium centers (V 5+ and V 4+ ) and proton diffusion alongside the nanofiber's surface, respectively [21,25]. The in-plane electrical conductivity in the range of 2 S cm -1 [25,31], which is parallel to the V2O5 sheets, is approximately five orders higher than the out-of-plane electrical conductivity [31]. In the present work, we investigated the out-of-plane conductivity of our V2O5 cathodes, as it is the limiting factor for electrochemical testing.…”

“…The films are characterized by a high mechanical stability (tensile strength up to 116 MPa and Youngs modulus of 42 GPa), which can be tailored by the nanofiber length and water content. The mechanical stability and moderate in-plane electrical conductivity of ~2 S cm −1 render them as a suitable binderfree cathode for metal-ion batteries, such as LIBs [25]. However, in order to take full advantage of the three-electron transfer during Al 3+ intercalation a higher electrical conductivity in-plane and out-ofplane would be beneficial.…”

“…Here, we report the use of a binder-free and self-supporting cathode, for Al 3+ intercalation, comprised of V2O5 nanofibers in the form of micrometer-thick self-supporting thin films. The cathode is fabricated via a self-assembly approach resulting in an aligned and layered structure of high mechanical stability [25]. The optimized cell setup and testing parameters included a suitable current collector and a potential window that avoids undesired side reactions with the electrolyte.…”