Biomimetic Bipolar Microcapsules Derived from Staphylococcus aureus for Enhanced Properties of Lithium-Sulfur Battery Cathodes

Lithium-sulfur (Li-S) batteries suffer from some serious issues, such as volume expansion, polysulfide migration, and so on, which lead to inferior rate properties, low Coulombic efficiency, and poor cycling stability. To a great extent, the significantly changing polarities, conductivities, and solubilities of sulfur species complicate these issues and make them hard to deal with. In this study, a biomimetic bipolar microcapsule is developed via bacteria fermentation and chemical modification. The biomimetic hierarchical microcapsule has a nonpolar core to load active materials and a polar shell to "selectively" control mass transport in and out. Each capsule acts as a microreactor, which adsorbs sulfur with the porous carbon core, retards polysulfide migration with the polar TiO2 shell, and only facilitates lithium ion diffusion through the shell. The advantages of bipolar microcapsules are able to concurrently address S hosting, electron conducting, and polysulfide migration issues in particle scales instead of electrode scales. Because the resulting sulfur cathodes effectively interact with all sulfur species and confine them inside microcapsules, those intractable issues that lead to poor cycling properties are significantly managed. Thus, a high specific capacity and excellent cycling stability are achieved by using this novel structure design.