Functionalized Thiophosphate and Oxidic Filler Particles for Hybrid Solid Electrolytes

Abstract To achieve the commercialization of solid‐state‐batteries (SSBs), solid electrolyte properties need to be further improved. The hybrid solid electrolyte (HSE) approach is expected to combine the favorable properties of different solid electrolyte classes and is therefore systematically investigated. Mixing low amounts of thiophosphate or oxide filler particles (FP) into a polyethylene oxide (PEO) polyethylene glycol (PEG) and lithium salt bis(trifluoromethane)sulfonimide (LiTFSI) matrix cannot improve the electrochemical properties. Silanization of the thiophosphate FPs significantly increases the ionic conductivity to 0.1 mS cm−1 at room temperature compared to 0.017 mS cm−1 for a pure PEO solid electrolyte. Moreover, a correlation between the intrinsic conductivity of the FPs and the resulting conductivity of the HSE is observed. Also, the functionalization is successfully transferred to oxide FPs. In addition to an equally significant increase in ionic conductivity, a strong influence of the crystallite size of the FPs on the resulting ionic conductivity of the HSE was found. The discovered effect of FP surface structure on overall HSE conductivity indicates a participation of the FP surface in ion transport and emphasizes the need for tailored filler design in HSE applications.