Lithium (Li) metal anodes could increase the energy density of next generation batteries due to the high specific capacity of Li. However, they are currently not applied in rechargeable lithium-ion batteries (LIB) with liquid electrolytes due to safety concerns ascribed to the inherent reactivity of lithium metal and the growth of dendrites upon cycling that leads to electrical short circuits. Solid-state batteries (SSB) with solid electrolytes could enable safe and dendrite-free operation. One of the main challenges in these systems is the fabrication of thin layers of solid electrolytes with high lithium-ion conductivities and their compatibility with Li metal anodes.The focus of this thesis is the synthesis of lithium thiophosphate (LPS) solid electrolyte thin-films as separators for SSB by chemical solution deposition.LPS glasses with different stoichiometries were initially dissolved in N-methylformamide (NMF) and used as precursors to formulate suitable coating solutions. Interestingly, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-Ray spectroscopy (EDX) revealed high oxygen contents in the final thin-films. The chemistry of the coating solution was analysed by time-dependant NMR measurements, which confirmed an S-O exchange between the solvent NMF and the LPS precursors. This reaction also leads to ageing of the coating solution.Coatings derived from balled milled 70Li2S-30P2S5 precursors lead to amorphous LPS thin-films with high oxygen contents, well adjustable thicknesses up to 3 µm, lithium-ion conductivities of 3.2 10-5 S/cm, and activation energies of 0.38 eV after optimisation of the deposition parameters. Finally, the electrochemical performance of the LPS thin-films as solid electrolytes and their compatibility with Li metal was investigated in Si/LPS/Li and LTO/LPS/Li half-cells. The formation of a thin solid electrolyte interphase (SEI) between lithium metal and LPS layers was revealed by In situ XPS. Stable conductivities and cycling performance up to 500 cycles of cells composed of Li anode and LPS electrolyte indicate the protecting function of the SEI and demonstrate the excellent electrochemical properties of LPS thin-films as solid electrolyte in microbatteries. Deposition of LPS thin-films on composite cathodes and bulk solid electrolytes show potential application of LPS thin-films in SSB as separator or protective coating, to prevent the reduction of conventional solid electrolytes by Li metal anodes. Solution-prepared LPS thin-films show great potential to be applied as cost-effective separators in SSB.
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