A sulfur-linked carbonyl-based poly(2,5-dihydroxyl-1,4-benzoquinonyl sulfide) (PDHBQS) compound is synthesized and used as cathode material for lithium-ion batteries (LIBs). Flexible binder-free composite cathode with single-wall carbon nanotubes (PDHBQS-SWCNTs) is then fabricated through vacuum filtration method with SWCNTs. Electrochemical measurements show that PDHBQS-SWCNTs cathode can deliver a discharge capacity of 182 mA h g (0.9 mA h cm ) at a current rate of 50 mA g and a potential window of 1.5 V-3.5 V. The cathode delivers a capacity of 75 mA h g (0.47 mA h cm ) at 5000 mA g , which confirms its good rate performance at high current density. PDHBQS-SWCNTs flexible cathode retains 89% of its initial capacity at 250 mA g after 500 charge-discharge cycles. Furthermore, large-area (28 cm ) flexible batteries based on PDHBQS-SWCNTs cathode and lithium foils anode are also assembled. The flexible battery shows good electrochemical activities with continuous bending, which retains 88% of its initial discharge capacity after 2000 bending cycles. The significant capacity, high rate performance, superior cyclic performance, and good flexibility make this material a promising candidate for a future application of flexible LIBs.