Li‐ion batteries are omnipresent in consumer electronics and are seen as the most promising technology for electric vehicles. Na‐ion batteries have emerged as viable and cheaper alternatives for stationary applications where Li‐ion batteries are too expensive. However, the larger size of sodium ion compared to lithium makes traditional positive materials for Li‐ion batteries not always suitable for the reversible insertion of sodium ions. Herein, a microwave‐assisted solution synthesis of NaFeF3 perovskite nanoparticles from presynthesized rutile FeF2 colloidal particles, sodium ethoxide, and ammonium fluoride is presented. This NaFeF3 material shows a reversible electrochemical activity of 1Na or 1Li per iron with low polarization and excellent capacity retention after 100 cycles. The unexpected reversible insertion of both sodium and lithium ions, herein studied through ex situ and operando X‐ray diffraction measurements, is attributed to a kinetic stabilization of corner‐shared cubic AxFeF3 (A = Li, Na) frameworks along the cycles involving low volume change without high thermodynamic cost as supported by a polymorphism theoretical analysis.

Anhydrous nanoscopic CuF is synthesized from alkoxides Cu(OR) (R=Me, tBu) by their reaction either in pure liquid HF at -70 °C, or under solvothermal conditions at 150 °C using excess HF and THF as solvent. Depending on the synthesis method, nanoparticles of sizes between 10 and 100 nm are obtained. The compound is highly hygroscopic and forms different hydrolysis products under moist air, namely CuF ⋅2 H O, Cu (OH)F , and Cu(OH)F, of which only the latter is stable at room temperature. CuF exhibits an electrochemical plateau at a potential of ≈2.7 V when cycled versus Li in half cell Li-ion batteries, which is attributed to a non-reversible conversion mechanism. The cell capacity in the first cycle depends on the particle size, being 468 mAh g for ≈8 nm crystallite diameter, and 353 mAh g for ≈12 nm crystallite diameter, referred to CuF . However, such a high capacity cannot be sustained for several cycles and the capacity rapidly fades out. The cell voltage decreases to ≈2.0 V for CuF ⋅2 H O, Cu (OH)F , and Cu(OH)F. As all the compounds studied in this work show irreversible conversion reactions, it can be concluded that copper-based fluorides are unsuitable for Li-ion battery applications.

Lithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solidstate batteries. These compounds, however, exhibit only limited stability in practice as they react with the electrodes. The decomposition products partially remain redox active hence leading to excess capacity. The redox activity of thiophosphates is explicitly used to act as electrode for sodium-ion batteries. Copper thiophosphate (Cu 3 PS 4 ) is used as a model system. The storage behavior between 0.01 and 2.5 V versus Na + /Na is studied in half cells using different electrolytes with 1 m NaPF 6 in diglyme showing the best result. Cu 3 PS 4 shows highly reversible charge storage with capacities of about 580 mAh g −1 for more than 200 cycles @120 mA g −1 and about 450 mAh g −1 for 1400 cycles @1 A g −1 . The redox behavior is studied by operando X-ray diffraction and X-ray photoelectron spectroscopy. During initial sodiation, Cu 3 PS 4 undergoes a conversion reaction including the formation of Cu and Na 2 S. During cycling, the redox activity seems dominated by sulfur. Interestingly, the capacity of Cu 3 PS 4 for lithium storage is smaller, leading to about 170 mAh g −1 after 200 cycles. The results demonstrate that thiophosphates can lead to reversible charge storage over several hundred cycles without any notable capacity decay.

The search for new cathode materials is primordial for alkali-ion battery systems, which are facing a constantly growing demand for high energy density storage devices. In quest of more performing active compounds on the positive side, anhydrous iron(III) fluoride demonstrated to be a good compromise in terms of high capacity, operating voltage, and low cost. However, its reaction toward lithium leads to complicated insertion/conversion reactions, which hinder its performances in Li-ion cells. Cycling this material against larger ions such as sodium and potassium is hard or simply impossible due to the size of the channels of the FeF 3 framework impeding ions diffusion. Herein, we propose a strategy based on the use of cubic perovskite AFeF 3 (A = K + , NH 4 + ) as starting materials, allowing the straightforward insertion (after a first disinsertion of the alkali and/or NH 4 + ion) of lithium within the structure and enabling the cycling toward larger alkali ions such as sodium and potassium. For example, a cubic KFeF 3 perovskite, produced by a facile synthesis method, shows superior rate capability toward lithium retaining a capacity of up to 132 mA•h•g −1 at 5 C or of 120 mA•h•g −1 at 5 C toward sodium and enabling cycling toward potassium. Moreover, cubic NH 4 FeF 3 perovskite is discussed for the first time as the suitable cathode material for alkali-ion batteries.

We present a one-pot deprotection/polymerisation protocol for the synthesis of crystalline graphdiynes on top of a copper surface starting with stable trimethylsilylated alkyne monomers.