Spinel-type crystals based on LiFeSiO4 with high electrical conductivity for lithium ion battery formed by melt-quenching method

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Spinel-type lithium-iron-silicate crystals were synthesized by using the melt-quenching method and the subsequent heat treatment for the sample with the composition of 25Li2O–25Fe2O3–50SiO2 (mol %), i.e., LiFeSiO4. It was found from X-ray diffraction analyses and transmission electron microscope observations that crystals formed in the heat treatment at 560°C for 3 h in Ar have the structure of Fd3m (A-227) with a lattice constant of a = 0.8317 nm and contain both Fe and Si elements. The heat-treated sample showed an electrical conductivity of 2.5 × 10−4 S cm−1 at room temperature and the activation energy is 0.21 eV, suggesting the presence of both Li+ ion conduction and hopping conduction between Fe2+ and Fe3+ ions. The charge–discharge performance of the heat-treated sample showed the total capacity (at 0.1C rate) of 95 mAh/g for 1.0–4.5 V cutoff ranges, demonstrating that a new spinel-type oxide synthesized works as cathode materials in LiB.