Development of catholytes with long-cycle lifespan, high interfacial stability, and fast electrochemical kinetics is crucial for the comprehensive deployment of high-energy density lithium metal batteries (LMBs) with cost-efficiency. In this study, a lithiated 2-mercaptopyridine (2-MP-Li) organosulfide was synthesized and used as the soluble catholyte for the first time. Under the routine working mode, the LMB using this 2-MP-Li catholyte possessed high capacity retention of 55.4% with a Coulombic efficiency (CE) of near 100% after 2,000 cycles. When a cell system was fully filled with 2-MP-Li catholyte, it yielded a double capacity with 15% improvement in the capacity retention, corresponding to 0.0182% capacity decay per cycle, as well as excellent rate performance even at 6 mA·cm⁻². These superior achievements resulted from the enhanced interfacial stability of Li anode induced by the salt-type 2-MP-Li molecule and the avoiding of using neutral catholyte as the initial active material, thereby mitigating the side reactions originating from the polysulfide shuttle effect. Furthermore, density functional theory (DFT) calculation and kinetics investigations proved the pseudocapacitive characteristic and faster ion diffusion coefficient with this design. Besides, the fabricated energy storage device showed excellent performance but with low economic cost and easy processing. Such a LMB with an alterable amount of capacity has a high potential to be applied in flow-cell type batteries for large-scale grid energy storage in the future.