Tunnel-Structured Phosphate Exhibiting High Proton Conductivity and Thermal Stability over a Wide Intermediate Temperature Range.

For the practical application of fuel cells in vehicles, it is a challenge to develop a proton solid electrolyte that coexhibits thermal stability and high proton conductivity at wide intermediate temperatures. Here, we report on the tunnel structured phosphate KNi1-xH2x(PO3)3·yH2O, which exhibits high proton conductivity at room temperature up to 500 °C, with the conductivity value reaching 1.7 × 10-2 S cm-1 at 275 °C for x = 0.18. This material, composed of the smallest cations that form the tunnel framework with face-shared (KO6) and (NiO6) chains and PO4 tetrahedral chains, retained the rigid framework up to 600 °C. Two oxygen sites of water molecules located adjacent to each other along the PO4 tetrahedral chains in the tunnel provided the proton conduction pathway. The sample maintained a conductivity of 5.0 × 10-3 S cm-1 for 10 h at 150 °C while changing the measurement atmosphere to a N2 gas flow, a 4% H2-96% Ar gas flow, and an O2 gas flow. The conductivity value at x = 0.18 obtained from the DC measurement was in the order of 10-6 S cm-1, close to the instrument's measurement limit. These results demonstrate that tunnel phosphate has potential as a proton solid electrolyte for next-generation fuel cells.

Flexible High Lithium-Ion Conducting PEO-Based Solid Polymer Electrolyte with Liquid Plasticizers for High Performance Solid-State Lithium Batteries.

Lithium-ion secondary batteries (LIB) with high energy density have attracted much attention for electric vehicle (EV) applications. However, LIBs have a safety problem because these batteries contain a flammable organic electrolyte. As such, all-solid secondary batteries that are not flammable have been extensively reported recently. In this study, we have focused on polymer electrolytes, which is flexible and is expected to address the safety problem. However, the conventional polymer electrolytes have low electrial conductivity at room temperature. Various attempts have been made to solve this problem, such as the addition of inorganic fillers and ionic liquids; however, these composite polymer electrolytes have not yet reached a practical level of lithium-ion conductivity. In this study, high electrical conductivity and lithium dendrite formation-free PEO based composite electrolytes are developed with both a filler of Li6,4La3Zr1.4Ta0.6O12 and liquid plasticizers of tetraethylene glycol dimethyl ether and 1,2 dimethoxyethane. The proposed flexible polymer electrolyte shows a high electrical conduciviy of 6.01×10-4 S cm-1 at 25 °C.