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Solid-state sulfur cathodes based on inorganic sulfide solid electrolytes can enable energy-dense lithium batteries. However, volume changes and chemical decomposition can drive delamination and degradation during cycling. To overcome these challenges, this paper reports an in situ approach to encapsulate the solid-state sulfur cathode with a gel polymer electrolyte (GPE). The GPE is covalently bonded with the sulfide solid electrolyte and acts as a barrier that suppresses chemical decomposition between the sulfide solid electrolyte and cathode active material. The elastic GPE maintains interfacial contact within the sulfur cathode allowing for greater sulfur utilization. The solid-state sulfur cathode with GPE demonstrates capacities nearing 700 mAh g −1 and capacity retention over 100 cycles. 

Hybrid solid electrolytes are composed of organic (polymer) and inorganic (ceramic) ion conducting materials, and are promising options for large-scale production of solid state lithium–metal batteries. Hybrid solid electrolytes containing 15 vol% Al-LLZO demonstrate optimal ionic conductivity properties. Ionic conductivity is shown to decrease at high inorganic loadings. This optimum is most obvious above the melting temperature of polyethylene oxide where the polymer is amorphous. Structural analysis using synchrotron nanotomography reveals that the inorganic particles are highly aggregated. The aggregation size grows with inorganic content and the largest percolating clusters measured for 5 vol%, 15 vol% and 50 vol% were ∼12 μm 3 , 206 μm 3 , and 324 μm 3 , respectively. Enhanced transport in hybrid electrolytes is shown to be due to polymer|particle (Al-LLZO) interactions and ionic conductivity is directly related to the accessible surface area of the inorganic particles within the electrolyte. Ordered and well-dispersed structures are ideal for next generation hybrid solid electrolytes.