Differentiating Molecular and Solid‐State Vanadium Oxides as Active Materials in Battery Electrodes

Abstract

Molecular vanadium oxides – polyoxovanadates (POVs) – have recently received widespread interest as new, high performance active materials in lithium ion and sodium ion battery electrodes. This is due to their low molecular weight and their high redox activity. However, little attention has been paid to the structural and chemical stability of the POVs under typical electrode fabrication processes. Here, we report how molecular polyoxovanadates can be differentiated from solid‐state vanadium oxides as active materials in battery electrodes using combined spectroscopic, X‐ray diffraction and element‐analytical data. Our study highlights that novel electrode fabrication processes are required as prototype POVs are not stable under classical fabrication conditions. We explore POV degradation pathways and show how thermal POV conversion leads to the formation of layered solid‐state lithium vanadium oxide phases. A facile protocol is presented to detect and prevent POV degradation. In future, this will enable energy materials science to unambiguously identify and use molecular or solid‐state vanadium oxides as next‐generation active materials in lithium or post‐lithium battery electrodes.

Atomically precise vanadium-oxide clusters

“…This is mainly due to the small ionic radius of vanadium which presents challenges in isolating stable Keggin-and Dawson-type POVs, as well as their corresponding Lacunary derivatives. 51 Seminal contributions into the generation of heteroion-installed polyoxovanadates have been led by Streb [164][165][166][167][168][169][170][171][172][173][174] and others 34,[175][176][177] Fig. 16).…”

Highly Crystalline Mesoporous Phosphotungstic Acid: A High‐Performance Electrode Material for Energy‐Storage Applications

“…Considering that structural rearrangement of polyoxometalates to metal oxides typically occurs at temperatures above 200 °C, no phase transition of the mPTA is attributed to their low synthetic temperature of 100 °C. [14] The primary crystallite size of the materials calculated from Scherrer equation to the main peak of (222) is found to be 20.32, 17.78 and 22.46 nm for 2.5-mPTA, 5.0-mPTA and 10-mPTA. The highly crystalline PTA consists in the wall structure of the porous materials.…”

Highly Crystalline Mesoporous Phosphotungstic Acid: A High‐Performance Electrode Material for Energy‐Storage Applications

“…The wide‐angle XRD patterns of these samples exactly coincide with that of K 3 PW 12 O 40 (Figure b), confirming that no phase transition of PTA to tungsten oxides occurred during the synthetic reactions. Considering that structural rearrangement of polyoxometalates to metal oxides typically occurs at temperatures above 200 °C, the failure of mPTA to undergo a phase transition is attributed to the low synthesis temperature of 100 °C . The primary crystallite size of the materials as calculated from the Scherrer equation for the main peak of (222) was 20.32, 17.78, and 22.46 nm for 2.5‐mPTA, 5.0‐mPTA, and 10‐mPTA.…”