Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.

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Rational optimization of OER activity of catalysts based on LaNiO3 oxide is achieved by maximizing the presence of trivalent Ni in the surface structure. DFT investigations of the LaNiO3 catalyst and surface structures related to it predict the improvement of OER activity for these materials to levels comparable with the top of the OER volcano if the La content is minimized while maintaining the oxidation state of Ni. These theoretically predicted structures of high intrinsic OER activity can be prepared by a templated spray-freeze freeze-drying synthesis followed by simple post-synthesis exfoliation-like treatment in acidic media. These nanocrystalline LaNiO3 related materials confirm the theoretical predictions showing a dramatic improvement in OER activity. The exfoliated surfaces remain stable in OER catalysis as shown by an in-operando ICP-OES study. The unprecedented OER activation of the synthesized LaNiO3-based materials is related to close juxtaposition of the theoretical conception of ideal structural motifs and the ability to engender such using a unique synthetic procedure, both principally related to stabilization and pinning of Ni oxidation state within the local coordination environment of the perovskite structure.

Batteries are utilized in a multitude of devices encountered in our daily lives. Here we describe a comparative study of Magnesium‐air and Zinc‐air primary batteries using silk fibroin‐ionic liquid polymer electrolytes (composed of Bombyx mori silk fibroin and choline nitrate). The ionic conductivity of the films was of the order of mS cm−1 which is sufficient to satisfy the conductivity requirements for many battery applications, the open circuit voltages (V) for the Mg 1:1 SF:IL and 1:3 SF:IL batteries just after fabrication were ca. 1.8 and 1.7 V, respectively; the 1:1 SF:IL battery had a capacity of 0.84 mAh cm−2, whereas the 1:3 SF:IL battery had a capacity of 0.68 mAh cm−2. The open circuit voltages (V) for the Zn 1:1 SF:IL and 1:3 SF:IL batteries were in the range of 1.3 and 1.2 V just after fabrication; the 1:3 SF:IL battery displayed a capacity of 0.96 mAh cm−2 and the 1:3 SF:IL battery displayed a capacity of 0.72 mAh cm−2. Integration of the PE and substitution of the carbon cloth electrodes with degradable materials would offer routes to production of transient primary batteries helping to address the global issue of electronic waste (e‐waste).

Lithium-sulfur battery chemistry has garnered global attention as a promising next-generation energy storage technology due to its significantly higher theoretical capacity (450 Wh/kg) compared to lithium-ion (265 Wh/kg), and the fact that its elemental components are green, safe and abundant[1]. As opposed to lithium-ion, the cathode solution chemistry is rich, as elemental sulfur forms polysulfide chains during discharge which can transport and deposit on the metallic lithium anode during a dissolution-migration-deposition “shuttle” mechanism which in effect a) cause a constant internal shorting current proportional to the transport of polysulfides and b) cause a build-up of lithium- and sulfur-rich solid-electrolyte interphase (SEI) on the anode which irreversibly passivates the lithium metal anode. This effect must be supressed at all costs in conventional lithium-sulfur batteries, and is achieved by encouraging rapid precipitation of Li2S salts by the use of low-donor number solvents for the electrolyte such as diglyme (DME) and dioxolane (DOL). However, polysulfide chains (Li2Sx, 3 ≤ x ≤ 8) have great potential as redox couples due to their stable, successive multistep redox behaviour and have been successfully demonstrated in hybrid redox-flow battery configurations[2], in particular enabled by lithium nitrate as an additive to the catholyte that forms a stable SEI on the lithium metal surface that greatly reduces the polysulfide deposition. The lithium-polysulfide redox flow battery in theory far outstrips current state of the art vanadium redox flow batteries due to the higher capacity density in the catholyte (50-150 Wh/L vs 30 Wh/L), and the energy dense lithium metal[2]. However, the solubility of polysulfides decrease with chain length and depth of discharge, and high polarity, high donor number solvents that can enable high polysulfide concentrations[3] are typically far more reactive towards lithium metal[4]. Moreover lithium nitrate have little effect as anode protectant in this class of solvents compared to low donor number, low polarity solvents such as DME and DOL, and the polysulfide reduction pathway is dependent on the stabilising property of the solvent[5]. In collaboration with our commercial partner StorTera under the Faraday Institute, we have developed novel techniques for catholyte analysis. We show the role of nitrate consumption rate on protection of the anode, and the relative corrosive rate of lithium in a high polarity, high donor number class solvent (DMSO) versus conventional low polarity, low donor number class solvent (DOL/DME). Further we explore avenues to protect metallic lithium in highly concentrated polysulfide catholyte that enables large-scale energy storage that surpasses lithium-ion and vanadium redox flow batteries for cost, safety, serviceability and environmental impact. Such factors will be key for commercial deployment, in particular suitable for developing countries where microgrids for remote communities rely on intermittent renewable power supply. Zhang, G., Zhang, Z. W., Peng, H. J., Huang, J. Q. & Zhang, Q. A Toolbox for Lithium–Sulfur Battery Research: Methods and Protocols. Small Methods 1, 1–32 (2017). Yang, Y., Zheng, G. & Cui, Y. A membrane-free lithium/polysulfide semi-liquid battery for large-scale energy storage. Energy Environ. Sci. 6, 1552–1558 (2013). Pan, H. et al. On the Way Toward Understanding Solution Chemistry of Lithium Polysulfides for High Energy Li-S Redox Flow Batteries. Adv. Energy Mater. 5, (2015). Gupta, A., Bhargav, A. & Manthiram, A. Highly Solvating Electrolytes for Lithium–Sulfur Batteries. Adv. Energy Mater. 9, 1–9 (2019). Lu, Y. C., He, Q. & Gasteiger, H. A. Probing the lithium-sulfur redox reactions: A rotating-ring disk electrode study. J. Phys. Chem. C 118, 5733–5741 (2014).

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