Researchers at India's Cochin University of Science and Technology have developed a bifunctional polyaniline/reduced graphene oxide (PRGO) interlayer integrated into a lithium-sulfur (Li-S) battery separator, demonstrating a practical route to mitigating polysulfide shuttling while improving electrochemical performance.
Li-S systems offer a theoretical specific capacity of 1675 mAh g−1 and energy density approaching 2600 Wh kg−1, but their commercialization has been hindered by sulfur’s extremely low conductivity (~5×10−30 S cm−1) and the dissolution and migration of lithium polysulfides (LiPSs). These soluble intermediates form during discharge - initially at 2.1–2.4V (long-chain polysulfides, ~25% of capacity, 418 mAh g−1) and then at 1.6–2.1V (short-chain species, ~75%, 1257 mAh g−1) - and readily diffuse toward the lithium anode, causing active material loss and rapid capacity fading.
The proposed PRGO interlayer is fabricated via a simple physical mixing process and coated onto one side of a conventional polypropylene separator (using PVDF binder), enabling a dual function design: one side acts as a functional interlayer while the other maintains separator integrity. Structural characterization (XRD, Raman, SEM) confirms successful formation of the composite and its interconnected morphology.
Mechanistically, the performance gains arise from complementary roles of the two components. Reduced graphene oxide (RGO) provides a conductive, two-dimensional network with abundant surface sites that physically anchor polysulfides and facilitate electron transport. Polyaniline (PANI), a conductive polymer with conjugated structure and porous morphology, contributes strong chemical adsorption of LiPSs while enabling efficient ion transport through its high void fraction. This combination creates a conductive and chemically active barrier that both traps polysulfides near the cathode and promotes their redox conversion, effectively suppressing the shuttle effect.
In parallel, the sulfur cathode is modified with the same PANI/RGO components (SPR cathode), further enhancing conductivity and utilization of active material. As a result, the assembled cells deliver an initial discharge capacity of 994 mAh g−1 at 0.5C, and 893.06mAh g−1at 1C. Cycling stability shows retention of approximately 42% capacity after 100 cycles at 0.5C, indicating partial mitigation of degradation mechanisms, though still leaving room for improvement compared to state-of-the-art long-cycle systems.
Compared to thicker free-standing interlayers, the separator-integrated PRGO design avoids significant penalties in gravimetric energy density while improving interfacial compatibility. The work highlights how combining conductive polymers with graphene-derived materials can create multifunctional interlayers that simultaneously address conductivity limitations and polysulfide migration - two of the most persistent barriers in Li–S batteries.
