Synthesis and Characterization of Lithium Phosphate (Li3PO4) as a Solid Electrolyte

Due to its high thermal stability, environmental friendliness, and safety, lithium phosphate (Li3PO4) is used as a solid electrolyte in battery applications, but it is usually used with dopants due to its lower ionic conductivity, which is required for ion transport. However, due to its stability and environmentally friendly aspect, lithium phosphate is still a hot topic among suitable energy materials that need further research to improve its electrochemical properties. In the current work, a novel synthesis of lithium phosphate was proposed from the raw materials lithium carbonate (Li2CO3) and trisodium phosphate dodecahydrate (Na3PO4*12H2O) under suitable stoichiometric conditions using the co-precipitation method. In the set of synthesized samples, a single-phase β-Li3PO4 (named LPO-4) with 99.7% purity and 93.49% yield was successfully prepared under appropriate stoichiometric conditions and pH 13 at 90 °C. The average particle size was 10 nm with a large surface area of 9.02 m2g−1. Electrochemical impedance spectroscopy (EIS) of LPO-4 revealed a conductivity of 7.1 × 10−6 S.cm−1 at room temperature and 2.7 × 10−5 S.cm−1 at 80 °C with a low activation energy of 0.38 eV. This performance is attributed to the morphology of the nanotubes and the smaller particle size, which enlarge the reaction interfaces and shorten the diffusion distance of lithium ions. The kinetic and thermodynamic key parameters showed that the β-Li3PO4 exhibits thermal stability in the room temperature range up to 208.8 °C. All these property values indicate a promising application of lithium phosphate as a solid electrolyte in solid-state batteries and a new route for further investigation.