Among the examined organic electrodes for aqueous mono and multivalent ions batteries, polyimide is considered a promising candidate because of its high capacity and good cyclability in different electrolyte solutions. While most of the studies so far were focused on the energetic performance of polyimide anodes, much less is known about their charge storage mechanism and particularly how such electrodes are affected by the solvation properties of the inserted cations. Using in situ EQCM-D, a direct assessment of the cationic fluxes and their hydration shells inserted/extracted to/from PI electrodes upon potential application was performed for a large variety of mono and multivalent cations. Our observations demonstrated a pronounced withdrawal of water molecules from the polymeric electrodes during insertion of chaotropic cations and significantly less water withdrawal upon insertion of kosmotropic cations. These findings are well correlated with the capacity and the rate capability of the polyimide electrodes in the examined systems and shed light on their charge storage mechanism.

Identifying and understanding charge storage mechanisms is important for advancing energy storage, especially when new materials and electrolytes are explored. Well-separated peaks in cyclic voltammograms (CVs) are considered key indicators of diffusion-controlled electrochemical processes with distinct Faradic charge transfer. Herein, we report on an electrochemical system with separated CV peaks, accompanied by surface-controlled partial charge transfer, in 2D Ti3C2Tx MXene in water-in-salt electrolytes. The process involves the insertion/desertion of desolvation-free cations, leading to an abrupt change of the interlayer spacing between MXene sheets. This unusual behavior increases charge storage at positive potentials, thereby increasing the amount of energy stored. This also demonstrates new opportunities for the development of high-rate aqueous energy storage devices and electrochemical actuators using safe and inexpensive aqueous electrolytes.

The purpose of this paper is to suggest frontier inter‐disciplinary research directions that can be considered as important horizons of modern electrochemistry in the field of energy storage and conversion. We selected several topics that call for advancements in solid‐state, interfacial, analytical and energy‐related electrochemical science. A dramatic improvement in the performance of energy storage and conversion devices is needed to meet the urgent demands of our society. Significantly more efficient devices are needed to meet two major challenges: electro‐mobility, namely electrochemical propulsion of electric vehicles, and the ability to store and convert large quantities of energy generated from sustainable sources such as sun and wind. We suggest promotion of breakthroughs in several important directions. The examples chosen include: Development of novel in‐situ methodologies for design and testing composite electrodes for advanced energy storage devices; Improving the electrochemical performance of high specific capacity, but hard to control, LiNiO2 cathodes for advanced lithium ion batteries designed for electric vehicles, with a quantitative goal of stable specific capacity >230 mAh/g with a charging potential lower than 4.3 V; Advancing aqueous electrochemical systems for large energy storage based on sodium electrochemistry; Promoting development of batteries based on multivalent active metals with magnesium as the most advanced example. There is a strong incentive to promote fundamental and practical progress in the field of rechargeable Mg batteries using new electrodes’ configurations and advanced electroanalytical methods. All these directions require deep efforts in basic, fundamental studies, in order to reach important practical goals.

Identifying and understanding charge storage mechanisms is important for advancing energy storage, especially when new materials and electrolytes are explored. Well-separated peaks in cyclic voltammograms (CVs) are considered key indicators of diffusion-controlled electrochemical processes with distinct Faradic charge transfer. Herein, we report on an electrochemical system with separated CV peaks, accompanied by surface-controlled partial charge transfer, in 2D Ti3C2Tx MXene in water-in-salt electrolytes. The process involves the insertion/desertion of desolvation-free cations, leading to an abrupt change of the interlayer spacing between MXene sheets. This unusual behavior increases charge storage at positive potentials, thereby increasing the amount of energy stored. This also demonstrates new opportunities for the development of high-rate aqueous energy storage devices and electrochemical actuators using safe and inexpensive aqueous electrolytes.