With the widespread adoption of lithium-ion batteries (LIBs), safety concerns associated with flammable organic electrolytes have become increasingly critical. Solid-state lithium batteries (SSLBs), with enhanced safety and higher energy density potential, are regarded as a promising next-generation energy storage technology. However, the practical application of solid-state electrolytes (SSEs) remains hindered by several challenges, including low Li⁺ ion conductivity, poor interfacial compatibility with electrodes, unfavorable mechanical properties and difficulties in scalable manufacturing. This review systematically examines recent progress in SSEs, including inorganic types (oxides, sulfides, halides), organic types (polymers, plastic crystals, poly(ionic liquids) (PILs)), and the emerging class of soft solid-state electrolytes (S³Es), especially those based on “rigid-flexible synergy” composites and “Li⁺-desolvation” mechanism using porous frameworks. Critical assessment reveals that single-component SSEs face inherent limitations that are difficult to be fully overcome through compositional and structural modification alone. In contrast, S³Es integrate the strength of complementary components to achieve a balanced and synergic enhancement in electrochemical properties (e.g., ionic conductivity and stability window), mechanical integrity, and processability, showing great promise as next-generation SSEs. Furthermore, the application-oriented challenges and emerging trends in S³E research are outlined, aiming to provide strategic insights into future development of high-performance SSEs.

Developing a high sulfur (S)-loading cathode with high capacity utilization and long term cyclability is a key challenge for commercial implementation of Li-S battery technology. To overcome this challenge, we propose a solid-phase conversion sulfur cathode by using an edible fungus slag-derived porous carbon (C_FS) as sulfur host to fabricate the S/C_FS composite and meanwhile, utilizing the vinyl carbonate (VC) as co-solvent of the ether-based electrolyte to in-situ form a protective layer on the S/C_FS composite surface through its nucleophilic reaction with the freshly generated lithium polysulfides (LiPSs) at the very beginning of initial discharge, thus isolating the interior sulfur from the outer electrolyte and inhibiting the further generation of soluble LiPSs. Benefitting from the ultrahigh specific surface area of > 3,000 m²·g⁻¹, ideal pore size of < 4 nm, and large pore volume of > 2.0 cm³·g⁻¹ of the C_FS host matrix, the S/C_FS cathode even with a high S-loading of 80 wt.% (based on the weight of S/C_FS composite) can still operate in a solid-phase conversion manner in the VC-ether co-solvent electrolyte to exhibit a high reversible capacity of 1,557 mAh·g⁻¹, a high rate capability with 50% remaining capacity at 2 A·g⁻¹ and a high cycling efficiency of 99.9% over 500 cycles. The results presented in this work suggest that a combined action of solid-phase conversion electrochemistry and nanoarchitectured host structure may provide a new path for the design and development of practical lithium-sulfur batteries.