A team of researchers from institutions in China and the US report the design of a negatively charged graphene composite separator for the effective suppression of the polysulfide shuttling effect in Li-sulfur batteries. The negatively charged 3D porous structure effectively inhibits the translocation of negatively charged polysulfide ions to enable highly robust Li-S batteries.

In their paper on the work published in the journal Joule, the researchers reported that by using a reduced graphene oxide (rGO)/sodium lignosulfonate (SL) composite on the standard polypropylene (PP) separator (rGO@SL/PP), they demonstrated a highly robust Li-S battery with a capacity retention of 74% over 1,000 cycles.

… the commercialization of lithium-sulfur (Li-S) batteries has been severely hindered by the polysulfide (PS) shuttling effect whereby PSs dissolve into the electrolyte and shuttle across the separator to react with anode materials, leading to a rapidly fading capacity with repeated charge/discharge cycles. Tremendous efforts have been devoted to developing advanced cathodes to address the PS shuttling issue … However, these cathode designs usually introduce additional passive weight into the electrodes and decrease the overall energy density, and the addition of 3D porous carbon structures reduces the electrode tapping density, severely reducing the volumetric energy capacity. Therefore, despite extensive efforts, the improvement to date remains rather unsatisfactory, especially in energy density.

… Alternatively, “adsorption coatings” (e.g., separators with mesoporous coatings, including carbon/graphene coating, metal-organic frameworks, and functionalized interlayers) have been reported for mitigating the PS shuttling effect and alleviating capacity-fading problem. Although “adsorption coating” design approach has proved helpful, it is often highly complex, making it difficult to fully encapsulate and retain all the sulfur species to completely inhibit the PS shuttling. A recent study demonstrated “charge environment” as an effective way to mitigate the PS shuttling effect. Such an approach does not involve the electrode design, and may potentially offer a much simpler and more effective approach to address the PS shuttling effect. However, compared with extensive efforts in electrode design or adsorption coating approaches to combat PS dissolution, the charge environment approach is far less explored. Therefore, a proper design of charged separator to effectively inhibit PS shuttling without compromising Li-ion transport is of considerable interest.

Herein we report the design of a charge-repulsion approach using a negatively charged multi-function graphene composite separator to effectively suppress the shuttling of the negatively charged PS ions.

—Lei et al.

Lignosulfonate (SL)—a low-cost byproduct of the chemical industry—features abundant negatively charged sulfonic and dendritic groups. By combining SL with reduced graphene oxide (rGO) through covalent bonds, the researchers created a composite with rich negative charges to enable a robust separator that can effectively retard PS shuttling while simultaneously ensuring excellent Li-ion transport characteristics.

Such a separator could simply replace traditional separators without modifying the electrode structure of batteries, allowing rapid deployment in the field to exert a rapid impact on practical technologies, the researchers said.

Resources

• Tianyu Lei, Wei Chen, Weiqiang Lv, Jianwen Huang, Jian Zhu, Junwei Chu, Chaoyi Yan, Chunyang Wu, Yichao Yan, Weidong He, Jie Xiong, Yanrong Li, Chenglin Yan, John B. Goodenough, and Xiangfeng Duan (2018) “Inhibiting Polysulfide Shuttling with aGraphene Composite Separator for HighlyRobust Lithium-Sulfur Batteries” Joule doi: 10.1016/j.joule.2018.07.022