An energy-dense, flowable suspension of hollow carbon nanoshell-hosted sulfur as an electroactive material for flow batteries

We demonstrate an energy-dense, flowable electroactive material by suspending solid sulfur hosted in hollow carbon nanoshells (HCSs) in a liquid electrolyte without extra conductive additives for the pursuit of high-energy-density semi-solid flow batteries. Compared to conventionally used Ketjen Black (KB) additives, the conductive HCSs can confine the insulating active materials within their void space, while maintaining the electroactivity of the outer surface. More importantly, the liquid suspension of well-dispersed HCS/S nanoparticles shows much lower viscosity than that formed by aggregated KB particles with a hyperbranched structure. The cell with the liquid suspension paired with Li metal achieves an average volumetric capacity of ~80 Ah L⁻¹ over 50 stable cycles in the static test and an energy density of 230 Wh L⁻¹ in the intermittent flow test. Our energy-dense HCS/S suspension with high flowability shows great potential for high-energy-density energy storage systems.