• Energy Research

AbstractThe development of room‐temperature sodium‐metal batteries (SMBs) presents a cost‐effective solution for both large‐scale energy storage and high‐energy applications. However, challenges in finding suitable electrolytes that ensure stable cycling of the Na metal anode and the lack of cathodes capable of achieving high‐performance under practical conditions have impeded their commercialization. In this study, a high‐performance SMB combining a concentrated liquid ammonia‐based electrolyte (NaI·3.3NH3) and an organic cathode featuring an anthraquinone‐based conjugated microporous polymer hybrid (IEP‐11‐SR) are introduced. This ammoniate electrolyte effectively stabilizes the sodium anode, allowing reversible plating/stripping and preventing dendrite formation, even at extreme current densities (400 mA cm−2). The hybrid polymer cathode, with its intrinsic extended conjugated and microporous structure, exhibits outstanding electrochemical performance in rate‐capability and long‐term cyclability in the ammoniate electrolyte. The resulting SMB achieves a high capacity (100 mAh g−1 at 1C), excellent rate capability (51 mAh g−1 at 250C), and stable cycling performance (≈70% capacity retention after 4000 cycles at 15C). Notably, the utilization of remarkably thick cathodes (60 mg cm−2) with low carbon content (≈20 wt%) achieves an unprecedented areal capacity, close to 7 mAh cm−2, marking a significant advancement in practical SMB technology.

In this study, we develop a membrane-free Zn hybrid redox flow battery (RFB) using an unconventional water-in-salt aqueous biphasic system (WIS-ABS). This membrane-free Zn hybrid battery employs soluble ferrocene (Fc) derivative and Zn salt as the active species in the immiscible catholyte and anolyte, respectively. Initially, we demonstrate the potential of using WIS-ABS for a totally aqueous membrane-free Zn battery under static conditions. This static battery operates at a cell voltage of 1.01 V and effectively eradicates the detrimental self-discharge observed in membrane-free batteries, achieving excellent coulombic efficiency (CE) consistently around 100 % over 2000 cycles. However, due to transport limitations in the static configuration, the battery exhibits a low capacity utilization of 17.4 % for the catholyte, ultimately restricting the energy density of the battery. Further improvements in the battery performance are achieved by employing a specially designed RFB cell reactor to operate under real flowing conditions. Impressively, the developed membrane-free Zn hybrid RFB cell significantly shows an improved catholyte utilization, reaching up to 95 %. Furthermore, the membrane-free RFB consistently maintains CE higher than 95 % throughout the cycling process, ultimately achieving a capacity retention as high as 96.5 % after 30 cycles at 100 % depth of discharge. This work highlights the potential of utilizing a water-in-salt aqueous biphasic system to develop a membrane-free Zn hybrid RFB with excellent electrochemical performance, effectively avoiding the undesired self-discharge phenomena.

New redox-active polymer nanoparticles present that the redox potential of the catechol group is affected by the presence of the pyridine. This positive potential gain is associated to the proton trap effect, which benefits the performance of lithium-ion–polymer batteries.

Faradaic deionization (FDI) is an emerging and promising electrochemical technology for stable and efficient water desalination. Battery-type energy storage materials applied in FDI have demonstrated to achieve higher salt removal capacities than carbon-based conventional capacitive deionization (CDI) systems. However, most of the reported FDI systems are based on inorganic intercalation compounds that lack cost, safety and sustainability benefits, thereby curtailing the development of a feasible FDI cell. In this work, we introduce an all-polymer rocking chair practical FDI cell, with a symmetric system composed by a redox-active naphthalene-polyimide (named as PNDIE) buckypaper organic electrodes. First, electrochemical performance of PNDIE in 0.05 M NaCl under open-air conditions is evaluated in both three-electrode half- and symmetric FDI full-cell using typical lab-scale electrode dimensions (1.6 mgPNDIE; 0.78 cm2), revealing promising specific capacity (115 mAh g-1) and excellent cycle stability for full-cell experiments (77 % capacity retention over 1000 cycles). Then, all-polymer rocking chair FDI flow cell was constructed with practical PNDIE electrodes (92.2 mgPNDIE; 9.6 cm2) that delivered large desalination capacity (155.4 mg g-1 at 0.01 A g-1) and high salt removal rate and productivity (3.42 mg g-1 min-1 at 0.04 A g-1 and 62 L h-1 m-2, respectively). In addition, long-term stability (23 days) experiments revealed salt adsorption capacity (SAC) retention values over 95% after 100 cycles. The overall electrochemical and deionization performances of the reported technology is far superior than the state-of-the-art CDI and FDI techniques, making it a competitive choice for robust and sustainable “water-energy” electrochemical applications. NP appreciates fellowship IJC2020-043076-I-I funded by MCIN/AEI/0.13039/501100011033 and by the European Union NextGenerationEU/PRTR. NP and RM acknowledge PID2021-124974OB-C21 financed by MCIN/AEI/10.13039/501100011033/FEDER "A way of making Europe". NG acknowledges the funding from the European Union’s Horizon 2020 framework programme under the Marie Skłodowska-Curie agreement No. 101028682. AFP and JJL appreciates the Talento’s program of the Community of Madrid which involves the project SELECTVALUE (2020-T1/AMB-19799). The authors also would like to thank Gonzalo Castro and Ignacio Almonacid for collaborating in the laboratory experiments and the sample analysis.

A phenazine-based conjugated microporous polymer cathode provides high cycle stability (75% retention after 127 days), low capacity fade (0.19 mA h g−1 per day) and excellent rate capability (62 mA h g−1; 54% retention at 50C).

The development of room-temperature sodium-metal batteries (SMBs) presents a cost-effective solution for both large-scale energy storage and high-energy applications. However, challenges in finding suitable electrolytes that ensure stable cycling of the Na metal anode and the lack of cathodes capable of achieving high-performance under practical conditions have impeded their commercialization. In this study, we introduce a high-performance SMB combining a concentrated liquid ammonia-based electrolyte (NaI·3.3NH3) and an organic cathode featuring an anthraquinone-based conjugated microporous polymer hybrid (IEP-11-SR). This ammoniate electrolyte effectively stabilizes the sodium anode, allowing reversible plating/stripping and preventing dendrite formation, even at extreme current densities (400 mA cm-2). The hybrid polymer cathode, with its intrinsic extended conjugated and microporous structure, exhibits outstanding electrochemical performance in rate-capability and long-term cyclability in the ammoniate electrolyte. The resulting SMB achieves a high capacity (100 mAh g-1 at 1C), excellent rate capability (51 mAh g-1 at 250C), and stable cycling performance (~70% capacity retention after 4000 cycles at 15C). Notably, the utilization of remarkably thick cathodes (60 mg cm-2) with low carbon content (~20 wt%) achieves an unprecedented areal capacity, close to 7 mAh cm-2, marking a significant advancement in practical SMB technology. Acknowledgements Authors thank the European Union's Horizon 2020 research and innovation programme under the Мarie Skłodowska-Curie Grant agreement (Grant No 860403) and Spanish Government; MCIN/AEI/10.13039/501100011033/FEDER "A way of making Europe" (PID2021-124974OB-C21 and PID2019-106315RB-I00) for the funding. NP appreciates fellowship IJC2020-043076-I-I funded by MCIN/AEI/0.13039/501100011033 and by the European Union NextGenerationEU/PRTR. The project LIGHT-CAP has received funding from the European Union’s Horizon 2020 Research and Innovation program under grant agreement no.[101017821].

Abstract Battery technologies based in multivalent charge carriers with ideally two or three electrons transferred per ion exchanged between the electrodes have large promises in raw performance numbers, most often expressed as high energy density, and are also ideally based on raw materials that are widely abundant and less expensive. Yet, these are still globally in their infancy, with some concepts (e.g. Mg metal) being more technologically mature. The challenges to address are derived on one side from the highly polarizing nature of multivalent ions when compared to single valent concepts such as Li+ or Na+ present in Li-ion or Na-ion batteries, and on the other, from the difficulties in achieving efficient metal plating/stripping (which remains the holy grail for lithium). Nonetheless, research performed to date has given some fruits and a clearer view of the challenges ahead. These include technological topics (production of thin and ductile metal foil anodes) but also chemical aspects (electrolytes with high conductivity enabling efficient plating/stripping) or high-capacity cathodes with suitable kinetics (better inorganic hosts for intercalation of such highly polarizable multivalent ions). This roadmap provides an extensive review by experts in the different technologies, which exhibit similarities but also striking differences, of the current state of the art in 2023 and the research directions and strategies currently underway to develop multivalent batteries. The aim is to provide an opinion with respect to the current challenges, potential bottlenecks, and also emerging opportunities for their practical deployment.