Here an Li ion conductive oxysulfide of LiSnOS with a layered structure, grown from a layered SnOS phase by reacting with different amounts of LiNO3 to form the Li-ion intercalation compound, is developed in order to find the best LiSnOS with the highest Li ion conductivity for assembling a totally solid LiCoO2/(LiSnOS + gel polymer)/Li lithium ion battery (LIB). With this approach, there is no need for utilizing the moisture-sensitive Li2S precursor. The variations of crystal parameter, morphology, and Li ion conductivity of LiSnOS with the Li/Sn precursor ratio are investigated in terms of its composition and lattice defect. The LiSnOS with the Li/Sn molar ratio of 2 or LiSnOS-2 is expected to have the Li vacancy-free Li[Li1/3Sn2/3(O,S)2] or Li2Sn(O,S)3 layered structure and show the highest Li ion conductivity of 1.92 × 10−4 S cm−1. The hybrid electrolytes with different amounts of LiSnOS-2 in poly(vinylidene fluoride-hexafluoropropylene) or PVDF-HFP gel are studied. The battery with the 30 wt% LiSnOS-2/70% gel electrolyte performs the enhanced discharge capacity of 134.6 mA h g−1 and behaves well for the 30 charge-discharge cycles. A schematic mechanism in terms of the LiSnOS content in gel electrolyte is proposed to explain the performance enhancement of LIB.