Magnesium-ion batteries
(MIBs) suffer from a low energy density
of cathode materials in a conventional nonaqueous electrolyte, contrary
to the expectation due to the divalent Mg ion. Here, we report H2V3O8, or V3O7·H2O, as a high-energy cathode material for MIBs. It exhibits
reversible magnesiation–demagnesiation behavior with an initial
discharge capacity of 231 mAh g–1 at 60 °C,
and an average discharge voltage of ∼1.9 V vs Mg/Mg2+ in an electrolyte of 0.5 M Mg(ClO4)2 in acetonitrile,
resulting in a high energy density of 440 Wh kg–1. The structural water remains stable during cycling. The crystal
structure for Mg0.97H2V3O8 is determined for the first time. Bond valence sum difference mapping
shows facile conduction pathways for Mg ions in the structure. The
high performance of this material with its distinct crystal structure
employing water–metal bonding and hydrogen bonding provides
insights to search for new oxide-based stable and high-energy materials
for MIBs.
In this study, new nanocomposite membranes from sulfonated poly (ether ether ketone) (SPEEK) and proton-conducting Fe2TiO5 nanoparticles are prepared by the solution casting method. Sulfonated core–shell Fe2TiO5 nanoparticles are synthesized by redox polymerization. Therefore, 4-Vinyl benzene sulfonate (VBS) and 2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS) are grafted on the surface of nanoparticles through radical polymerization. The different amounts of hybrid nanoparticles (PAMPS@Fe2TiO5 and PVBS@Fe2TiO5) are incorporated into the SPEEK matrix. The results show higher proton conductivity for all prepared nanocomposites than that of the SPEEK membrane. Embedding the sulfonated Fe2TiO5 nanoparticles into the SPEEK membrane improves proton conductivity by creating the new proton conducting sites. Besides, the nanocomposite membranes showed improved mechanical and dimensional stability in comparison with that of the SPEEK membrane. Also, the membranes including 2 wt% of PAMPS@Fe2TiO5 and PVBS@Fe2TiO5 nanoparticles indicate the maximum power density of 247 mW cm−2 and 226 mW cm−2 at 80 °C, respectively, which is higher than that of for the pristine membrane. Our prepared membranes have the potential for application in polymer electrolyte fuel cells.
Potassium‐ion batteries (KIBs) are one of the potential candidates for large‐scale energy storage devices with low cost due to the abundance of potassium resources. However, the development of cathode materials with high capacity and structural stability has been a challenge due to the difficulties of intercalation of the large size of K‐ions into host materials. In this work, H2V3O8 (or V3O7⋅H2O) is reported as a new cathode material for KIBs. It shows reversible potassium‐intercalation behavior with the first discharge capacity of 168 mAh g−1 at 5 mA g−1 and an average discharge voltage of ∼2.5 V (vs. K/K+) in 0.5 M KPF6 in EC/DEC (1:1 v/v). The specific capacity increases up to 181 mAh g−1 for the third cycle and gradually decreases with 75% of the capacity retention after 100 cycles. The chemical formula of the potassiated phase is K1.77H2V3O8. However, scan‐rate dependent cyclic voltammetry and elemental analyses suggest that ∼28% of the capacity comes from the surface K ions on the H2V3O8 particles; thus, the bulk‐intercalated phase can be formulated as K1.27H2V3O8. The crystal structure is stable during the electrochemical cycling, keeping the structural water, confirming that H2V3O8 can be considered as one of the high‐capacity cathode materials for KIBs.
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