The heavy reliance of lithium-ion batteries has caused rising concerns on the sustainability of lithium and transition metal and the ethic issue around mining practice. Developing alternative energy storage technologies beyond lithium has become a prominent slice of global energy research portfolio. The alternative technologies play a vital role in shaping the future landscape of energy storage, from electrified mobility to the efficient utilisation of renewable energies and further to large-scale stationary energy storage. Potassium-ion batteries (PIBs) are a promising alternative given its chemical and economic benefits, making a strong competitor to lithium-ion and sodium-ion batteries for different applications. However, many are unknown regarding potassium storage processes in materials and how it differs from lithium and sodium and understanding of solid-liquid interfacial chemistry is massively insufficient in PIBs. Therefore, there remain outstanding issues to advance the commercial prospects of the PIB technology. This Roadmap highlights the up-to-date scientific and technological advances and the insights into solving challenging issues to accelerate the development of PIBs. We hope this Roadmap aids the wider PIB research community and provides a cross-referencing to other beyond lithium energy storage technologies in the fast-pacing research landscape.

The key to develop earth-abundant energy storage technologies sodium-and potassium-ion batteries (SIBs and PIBs) is to identify low-cost electrode materials that allow fast and reversible Na + /K + intercalation. Here, we report an intercalation-type material TiNb 24 O 62 as a versatile anode for SIBs and PIBs, via a synergistic strategy of oxygen vacancy and carbon incorporation to enhance ion and electron diffusion. The TiNb 24 O 62−x /reduced graphene oxide (rGO) composite anode delivers high reversible capacities (130 mA h g −1 for SIBs and 178 mA h g −1 for PIBs), great rate performance (54 mA h g −1 for SIBs and 37 mA h g −1 for PIBs at 1 A g −1 ), and superior cycle stability (73.7% after 500 cycles for SIBs and 84% after 300 cycles for PIBs). The performance is among the best results of intercalation-type metal oxide anodes for SIBs and PIBs. The better performance of TiNb 24 O 62−x /rGO in SIBs than PIBs is due to the better reaction kinetics of the former. Moreover, mechanistic study confirms that the redox activity of Nb 4+ / 5+ is responsible for the reversible intercalation of Na + /K + . Our results suggest that TiNb 24 O 62−x /rGO is a promising anode for SIBs and PIBs and may stimulate further research on intercalation-type compounds as candidate anodes for large ion batteries.

Rechargeable potassium-ion batteries (PIBs) are of great interest as a sustainable, environmentally friendly, and cost-effective energy storage technology. The electrochemical performance of a PIB is closely related to the reaction kinetics of active materials, ionic/electronic transport, and the structural/electrochemical stability of cell components. Alongside the great effort devoted in discovering and optimising electrode materials, recent research unambiguously demonstrates the decisive role of the interphases that interconnect adjacent components in a PIB. Knowledge of interphases is currently less comprehensive and satisfactory compared to that of electrode materials, and therefore, understanding the interphases is crucial to facilitate electrode materials design and advance battery performance. The present review aims to summarise the critical interphases that dominate the overall battery performance of PIBs, which includes solid-electrolyte interphase (SEI), cathode-electrolyte interphase (CEI), and solid-solid interphases in composite electrodes, via exploring their formation principles, chemical compositions, and determination of reaction kinetics. State-of-the-art design strategies of robust interphases are discussed and analysed. Finally, perspectives are given to stimulate new ideas and open questions to further the understanding of interphases and the development of PIBs.

The field of printed electronics strives for lower processing temperatures to move toward flexible substrates that have vast potential: from wearable medical devices to animal tagging. Typically, ink formulations are optimized using mass screening and elimination of failures; as such, there are no comprehensive studies on the fundamental chemistry at play. Herein, findings which describe the steric link to decomposition profile: combining density functional theory, crystallography, thermal decomposition, mass spectrometry, and inkjet printing, are reported. Through the reaction of copper(II) formate with excess alkanolamines of varying steric bulk, tris-co-ordinated copper precursor ions: "[CuL 3 ]," each with a formate counter-ion (1-3) are isolated and their thermal decomposition mass spectrometry profiles are collected to assess their suitability for use in inks (I 1-3 ). Spin coating and inkjet printing of I 1,2 provides an easily up-scalable method toward the deposition of highly conductive copper device interconnects (𝝆 = 4.7-5.3 × 10 −7 𝛀 m; ≈30% bulk) onto paper and polyimide substrates and forms functioning circuits that can power light-emitting diodes. The connection among ligand bulk, coordination number, and improved decomposition profile supports fundamental understanding which will direct future design.

There is currently an enormous drive to move away from the use of Pt group metals in catalysis, particularly for fuel cells, because of their increasing rarity and cost. Simultaneously, there have been advances in the application of graphene supported nanoparticular catalysts. However, these Pt-free, graphene supported catalysts can be complex to produce, show poor catalytic activity and degrade quickly due to particle agglomeration or isolation. Herein, we report a one-pot synthesis of silver nanoparticles (NPs) tethered to a reduced graphene oxide (rGO) template via organic linkages. This is one of the few silver precursor formations that have been combined with graphene oxide (GO) to simultaneously establish linkage binding sites, reduce GO and yield tethered nanoparticles. These materials are shown to efficiently catalyze the oxygen reduction reaction in alkaline environments, with aminoethanol linkages to 21.55 ± 2.88 nm Ag particles exhibiting the highest catalytic activity via the four-electron pathway. This method, therefore, offers a straightforward route to produce effective catalysts from inexpensive precursors, which could be developed further for significant industrial application. Graphical abstract