All-solid-state lithium batteries (ASSLBs) are considered promising alternatives to current lithium-ion batteries as their use poses less of a safety risk. However, the fabrication of composite cathodes by the conventional slurry (wet) process presents technical challenges, such as limited stability of sulfide electrolytes against organic solvents and the increase of ionic resistance due to the use of insulating polymer binder. Herein, we develop a composite cathode fabricated using a solvent-free (dry) process. The composite cathode is prepared with a Li+-conducting ionomer binder, poly(tetrafluoroethylene-co-perfluoro(3-oxa-4-pentenesulfonic acid)) lithium salt. The ionomer facilitates Li+ transport and ensures good interfacial contact between the active material (LiNi0.7Co0.1Mn0.2O2), conducting carbon, and solid electrolyte (Li6PS5Cl) during cycling. Consequently, an ASSLB featuring a composite cathode with an ionomer delivers a high discharge capacity of 180.7 mAh g–1 (3.05 mAh cm–2) at 0.1 C and demonstrates stable cycling performance, retaining 90% of its initial capacity after 300 cycles at 0.5 C.