Sulfurized polyacrylonitrile cathodes with electrochemical and structural tuning for high capacity all-solid-state lithium-sulfur batteries

All-solid-state lithium–sulfur batteries (ASSLSBs) possess higher safety, longer lifespan, and elevated energy density compared to the traditional liquid lithium–sulfur batteries (LLSBs). However, the ion-electron insulating nature along with the large volume changes of sulfur and Li2S significantly hinder the full exploitation of their high theoretical specific capacities, especially in ASSLSBs. In this work, dense composite sulfur carbon (S/C) cathodes featuring sulfurized polyacrylonitrile (SPAN) supported by a macroporous carbon (MaPC) conductive matrix (SPAN@MaPC) are prepared to solve the above issues. ASSLSBs consisting of the SPAN@MaPC-Li6PS5Cl-vapor grown carbon fiber (VGCF) composite cathode are evaluated. With ∼1 mg cm−2 pure sulfur loading in the cathode, the assembled ASSLSBs achieved a high reversible capacity of 1396.2 mA h g−1 under an applied current of 0.1C at room temperature and still retained 715.5 mA h g−1 after 200 cycles. The reason it has achieved such performance is that the sulfur in SPAN, which is uniformly dispersed at the atomic level and covalently bonded to the polyacrylonitrile (PAN) carbon skeleton, has higher electrochemical reactivity. Further, the electrochemical behavior of SPAN@MaPC in the first cycle is revealed. Also, it is evidenced that the irreversible C–Li bonding contributes partially to the super-theoretical capacity.