Lithium-sulfur (Li-S) batteries that undergo a multi-electron chemical reaction has shown great potential to boost the endurance mileage of next-generation electric vehicles (EV). The reduction of sulfur, in the form of lithium polysulfides and lithium sulfide via a multistep process of complex equilibrium states between long- and short-chain polysulfides, can theoretically boost the energy density to 2600 W h kg^-1. However, the intermediate product, liquid polysulfides, is highly soluble in ether-based liquid electrolyte (LE), which corrodes the lithium metal anode. Suppression of lithium polysulfides dissolution in LE and addressing lithium metal safety concerns are critical to the commercialization of Li-S batteries.

To address these issues, we replace LE with a gel polyme...[ Read more ]

Lithium-sulfur (Li-S) batteries that undergo a multi-electron chemical reaction has shown great potential to boost the endurance mileage of next-generation electric vehicles (EV). The reduction of sulfur, in the form of lithium polysulfides and lithium sulfide via a multistep process of complex equilibrium states between long- and short-chain polysulfides, can theoretically boost the energy density to 2600 W h kg^-1. However, the intermediate product, liquid polysulfides, is highly soluble in ether-based liquid electrolyte (LE), which corrodes the lithium metal anode. Suppression of lithium polysulfides dissolution in LE and addressing lithium metal safety concerns are critical to the commercialization of Li-S batteries.

To address these issues, we replace LE with a gel polymer electrolyte (GPE). While traditional GPE typically exhibits low ionic conductivity and poor electrode/GPE interface, we report a facile in-situ synthesis of pentaerythritol tetraacrylate (PETEA)-based GPE with an extremely high ionic conductivity (1.13×10⁻² S cm⁻¹). Installation of a bare sulfur cathode with low electrode/GPE interfacial resistance did not sacrifice rate capacity or retention, resulting in rates of 601.2 mA h g⁻¹ at 1 C and 81.9% after 400 cycles at 0.5 C, respectively. In order to eliminate the commercial separator, we synthesize a freestanding acrylate-based hierarchical electrolyte (AHE). The structural similarity and synergetic compatibility between the matrix and the inner framework allow for the AHE to exhibit a desirable ester-rich robust structure.

To enhance the safety index of the battery, we further replace the lithium metal with a stable SnO₂ anode to be assembled as a lithium-ion sulfur polymer battery (LISPB). We demonstrate that graphene and carboxymethyl cellulose (CMC) are able to form a robust anode structure and simultaneously maintain a stable SEI in ether-based electrolyte, while the acrylate-based GPE immobilizes the polysulfides and protects the anodic SEI from side deposition reactions. Moreover, the proposed LISPB exhibits strong recovery against over-charge, over-discharge and short-circuiting, showing great potential for practical operation and suitable for energy conversion.

Keywords: Li-S battery; Li-ion sulfur battery; Li-polysulfide battery; gel polymer electrolyte; hierarchical electrolyte; electrolyte additive; ester functional group; non-lithium anode; anode protection; energy density; power density.