Metal fluorides (MF) are one of the most attractive cathode candidates for Li ion batteries (LIBs) due to their high conversion potentials with large capacities. However, only a limited number of synthetic methods, generally involving highly toxic or inaccessible reagents, currently exist, which has made it difficult to produce well-designed nanostructures suitable for cathodes; consequently, harnessing their potential cathodic properties has been a challenge. Herein, we report a new bottom-up synthetic method utilizing ammonium fluoride (NHF) for the preparation of anhydrous MF (CuF, FeF, and CoF)/mesoporous carbon (MSU-F-C) nanocomposites, whereby a series of metal precursor nanoparticles preconfined in mesoporous carbon were readily converted to anhydrous MF through simple heat treatment with NHF under solventless conditions. We demonstrate the versatility, lower toxicity, and efficiency of this synthetic method and, using XRD analysis, propose a mechanism for the reaction. All MF/MSU-F-C prepared in this study exhibited superior electrochemical performances, through conversion reactions, as the cathode for LIBs. In particular, FeF/MSU-F-C maintained a capacity of 650 mAh g across 50 cycles, which is ∼90% of its initial capacity. We expect that this facile synthesis method will trigger further research into the development of various nanostructured MF for use in energy storage and other applications.

a b s t r a c tThis study investigates the electrochemical sodium insertion/extraction of Na x VS 2 , and Na x TiS 2 in the voltage range where either intercalation (0.2 ≤ x ≤ 1) or displacement-conversion reaction (x > 1) occurs. Both Na x VS 2 and Na x TiS 2 showed good reversible capacities, as high as ∼160 mAh/g at an average voltage of ∼1.9 V vs. Na in the region for the intercalation reaction (0.2 ≤ x ≤ 1). When sodium (Na) insertion was forced further to the x > 1 composition, Na x VS 2 exhibited the direct displacement-conversion reaction at 0.3 V vs. Na without further Na intercalation, which contrasted with the wider lithium intercalation range of 0 < x ≤ 2 for Li x VS 2 . The displacement-conversion reaction for Na x VS 2 (x > 1) was reversible with a specific capacity of above 200 mAh/g up to 15 cycles, but the displacement reaction for Na x TiS 2 (x > 1) was not observed.