Composite solid electrolyte, preparation method thereof and solid lithium-sulfur battery

The invention relates to a composite solid electrolyte. The composite solid electrolyte comprises a polymer electrolyte skeleton with a porous structure and a liquid electrolyte filled in the polymer electrolyte skeleton, the liquid electrolyte comprises a lithium salt, an organic solvent and an additive, and the additive comprises one or more of a lipophilic additive, a nitrile additive and a lithium-containing additive. The composite solid electrolyte comprises the polymer electrolyte framework with the porous structure, on one hand, a diaphragm is replaced, and the effect of separating a positive electrode from a negative electrode is achieved; on one hand, electrolyte is replaced, the shuttle effect of lithium polysulfide is effectively avoided, and the loss of irreversible capacity is reduced; and on the other hand, the porous polymer electrolyte skeleton is filled with the liquid electrolyte, so that the electrochemical compatibility problem, the interface problem and the like of the polymer electrolyte