Separator-free Li–S thin-film battery with spin-coated S/CNT/SP cathode and PEO/PVDF/LTFSI/LLZO composite electrolyte

Abstract

The advancement of miniaturized energy storage systems is essential for the next generation of electronics. Lithium–sulfur (Li–S) microbatteries are able to offer exceptional theoretical capacity and energy density for microdevices. However, their practical implementation is hindered by challenges in material stability and electrode design. In this study, we introduced a spin-coated sulfur–carbon nanotube–Super P (S/CNT/SP) cathode integrated with a spin-coated polyethylene oxide (PEO)/polyvinylidene fluoride (PVDF)/lithium lanthanum zirconium oxide (LLZO) composite electrolyte. The spin-coating technique ensured the formation of uniform electrode and electrolyte thin films, which could work without a separator. The polymer-ceramic composite electrolyte with nanopores effectively suppressed polysulfide dissolution, improved ionic conductivity, and stabilized the electrode–electrolyte interface. Electrochemical evaluation revealed that the quasi-solid-state Li–S battery achieved near-theoretical capacity with enhanced cycling stability, retaining approximately 1000 mA h g⁻¹ (60% of its initial capacity) after 150 cycles across various C-rates. In a pouch-cell configuration, the cell retained 64% of its initial capacity over 60 cycles. These findings underscore the potential of spin-coating and composite quasi-solid electrolytes in enabling high-performance, safe, and compact Li–S battery technologies for next-generation energy storage applications.