The　development　of　aluminum-ion　batteries　(AIBs)　is　significantly　confined　by　the　limited　high-performance　cathode　materials.　Herein,　organopolysulfides　are　investigated　as　active　cathode　materials　to　fabricate　AIBs.　A　liquid-phase　phenyl　tetrasulfide　(PTS)　can　deliver　a　capacity　above　600　mAh　g−1　after　activation,　with　the　maintenance　of　253　mAh　g−1　after　100　cycles.　Owing　to　the　different　S　locations,　PTS　shows　several　voltage　plateaus　and　an　average　voltage　of　∼0.7　V　vs.　Al3+/Al　with　no　decay　upon　cycling.　More　importantly,　the　liquid　PTS　can　serve　as　a　high-Coulombic-efficiency　cathode　(∼99.88%　±　0.57%　after　stabilization),　enlighting　the　design　of　high-efficiency　and　low-resistance　conversion-type　cathode　materials　for　AIBs.　By　experimental　characterizations　accompanied　by　theoretical　calculations,　it　is　found　that　PTS　undergoes　stepwise　reaction　procedures　during　discharge　with　final　products　of　Al2S3　and　AlCl2-coordinated　phenyl　sulfide,　and　partially　reforms　with　elemental　S　and　other　organopolysulfides　during　charge.　This　study　demonstrates　new　opportunities　for　the　design　of　high-efficiency　conversion-type　cathode　materials　for　advanced　AIBs.　©　2023