Calcium metal batteries are receiving growing research attention due to significant breakthroughs in recent years that have indicated reversible Ca plating/stripping with attractive Coulombic efficiencies (90-95%), once thought to be out of reach. While the Ca anode is often described as being surface film-controlled, the ability to access reversible Ca electrochemistry is highly electrolyte-dependent in general, which affects both interfacial chemistry on plated Ca along with more fundamental Ca/Ca redox properties. This mini-review describes recent progress towards a reversible Ca anode from the point of view of the most successful electrolyte chemistries identified to date. This includes, centrally, what is currently known about the Ca solvation environment in these systems. Experimental (physico-chemical and spectroscopy) and computational results are summarized for the two major solvent classes - carbonates and ethers - that have yielded promising results so far. Current knowledge gaps and opportunities to improve fundamental understanding of Ca/Ca redox are also identified.

Electrophoretic deposition (EPD) has received increasing attention as an alternative manufacturing approach to slurry casting for the production of battery and supercapacitor electrodes. This process is of relevance for industrial scalability as evidently seen in the current electrophoretic paints industry. Nevertheless, the reported work so far have only concentrated on thin films of electrophoretically deposited electrodes for energy storage. Here, the electrochemical performance of thick films (up to tens of μm) as lithium-ion battery electrodes produced by EPD is reported. A commercially sourced LiNMCO (5 to 25 μm particle size) was used in this exemplary investigation. This work shows the production of binder-free high density active material (>90 %) electrodes. Coin cells were assembled and the battery performance was measured. Tests included: cyclic voltammetry, C-rate vs capacity, battery cycling and electrochemical impedance spectroscopy. Other investigations also studied: colloidal electrolyte formulation, electrode manufacture, microstructure characterisation and elemental mapping analysis. In short, EPD electrode manufacture can be applied as a platform technology for any battery and supercapacitor material, and the reported manufacturing processes and methodologies represent direct relevance to produce energy storage electrodes useful to practical applications.

Polyoxometalates (POM) have been deposited onto carbon nanotube (CNT) electrodes using benchtop ion soft landing (SL) enabled by a vortex-confined electrohydrodynamic desolvation process. The device is based on the dry ion localization and locomotion (DRILL) mass spectrometry interface of Fedorov and co-workers. By adding electrospray emitters, heating the desolvation gas, and operating at high gas flow rates, it is possible to obtain stable ion currents up to -15 nA that are ideal for deposition. Coupled with ambient ion optics, this interface enables desolvated ions to be delivered to surfaces while excluding solvent and counterions. Electron microscopy of surfaces prepared using the device reveal discrete POM and no aggregation that degrades electrode performance. Characterization of POM-coated CNT electrodes in a supercapacitor showed an energy storage capacity similar to that achieved with SL in vacuum. For solutions that produce primarily a single ion by electrospray ionization, benchtop SL offers a simpler and less costly approach for surface modification with applications in catalysis, energy storage, and beyond.