The solution to solve large-scale energy storage challenges resides in the commercialization of lithium metal batteries which are unsafe given the incompatibility of the lithium metal anode with current state-of-the-art liquid electrolytes. These safety challenges can be mitigated by solid state electrolytes, however they present unique challenges in that they lack the mechanical robustness to support long-term battery cycling. In this dissertation, we develop and study two different classes of solid state electrolytes: hybrid sulfide-polymer electrolytes and molten salt electrolytes. Chapter 2 specifically aims at understanding sulfide, inorganic electrolytes, the various synthetic parameters that impact electrochemical performance, and discovers the most sensitive spectroscopic tool for characterizing these systems. We then develop a robust, reproducible method for synthesizing these sulfide electrolytes with minimal systematic error. In Chapter 3, we expand upon our discussion of sulfide electrolytes by moving into the realm of hybrid sulfide-polymer electrolytes. We discover the classes of polymers that are the most chemically compatible with the sulfide electrolyte. We show that ether based polymers, popular in the sulfide-polymer hybrid literature, are not compatible with state-of-the-art sulfide electrolytes, leading to reductions in conductivity. Chapter 4 takes the discoveries in Chapter 3 a step further by understanding the role of processing and the inorganic-polymer microstructure on the performance of this hybrid sulfide-polymer systems. We show that the method of synthesizing these electrolytes can produce a homogeneous or inhomogeneous distribution of inorganic within the polymer, and that these differences in the microstructure can cause large reductions in electrochemical performance. In Chapter 5, we build off the knowledge of chapters 2-4 by moving beyond physical mixtures of the sulfide and polymer. Here, we develop a novel class of covalently linked sulfide-polymer hybrid electrolytes where the sulfide and polymer are formed in situ through a novel, one pot synthetic paradigm. We use multimodal spectroscopic characterization to demonstrate the covalent linkage between the inorganic and organic components, and finally showcase the improvement of the in situ hybrids over a physically mixed system through nanoindentation and battery cycling. Finally, in Chapter 6, we discuss molten salt electrolytes, a novel system that does not present the same challenges as inorganic-polymer hybrids. In this chapter, we investigate the role of inorganic vs organic degradation products in the solid-electrolyte interphase, and resolve some of the debate in the literature regarding which types of inorganic products lead to long-term electrochemical stability in Li-Cu cells. A conclusion chapter for this dissertation summarizes the key findings and articulates the impact of this work on the overall scientific literature.