Electrodes in batteries undergo a variety of changes during function. These include, but are not limited to intercalation, alloying and conversion reactions, evolution of the oxidation state of elements, crystal structures and the particle size (and distribution). Ideally minimal or controlled structural, morphological and macroscopic changes are desired for long term rechargeable battery function, and indeed many electrodes undergo transitions that are both highly reversible and irreversible. Furthermore, a variety of tools exist to probe these changes both in an in situ/operando and ex situ manner, e.g. Raman and NMR spectroscopy, X-ray, electron and neutron diffraction, to name a few techniques.

This presentation will detail two inter-related but unconventional aspects of research recently performed by our group.

We have been working towards using batteries or electrochemical cells as part of a synthetic strategy, whereby the changes induced by electrochemical reactions are purposefully used to generate new phases. These new phases are likely feature new properties and possibly new functionalities thus new applications. The energy storage aspects of the battery are replaced with the synthetic flexibility provided by applying controlled amounts of charge, for controlled amounts of time and being able to visualise changes using various in situ methods.

We have coined the term electrochemically activated solid state synthesis, whereby an electrode reacted in an electrochemical cell is subsequently extracted and heated resulting in the generation of a range of new or metastable phases, most of which have not been previously reported. This has been demonstrated for materials within the Ta_1-x­Nb_xVO₅ and Sc₂W_3-xMo_xO₁₂ families of electrodes used in Li, Na and K-based cells. A multitude of phase transitions are found with thermal treatments approximately at the onset of the decomposition of the binder used in the electrode. The talk will highlight the electrode preparation parameter space that can result in the generation of new phases, the identification of the phases and preliminary development of the mechanistic model associated with the synthetic strategy.

The second part of this talk will detail our recent investigation into solar batteries, where an electrode is able to both generate photocurrent and store charge carriers with exposure to light. We detail a new in situ electrochemical cell used to verify structural evolution (charge storage) during photo-irradiation of a MoO₃ electrode providing direct experimental evidence for this process.

The culmination of these ideas allows batteries to be more than batteries, or possibly more appropriately it allows electrodes to have multiple functions in electrochemical cells.