Carbonized Bacterial Cellulose-Derived Binder-Free, Flexible, and Free-Standing Cathode Host for High-Performance Stable Potassium–Sulfur Batteries

Abstract

In search of improved advanced energy storage systems to meet our fast-growing energy demands for large-scale applications, potassium–sulfur batteries (KSBs) provide an essential alternative due to their high specific capacity apart from the low cost and abundance of potassium and sulfur. However, the insulating nature of sulfur, volume changes, and shuttle effect impede the development of these batteries. Further, the binder, carbon additives, and current collector used in the assembly of cells in a conventional approach decrease the energy density of cells. To overcome these challenges, we propose a binder-free and free-standing carbonized bacterial cellulose (CBC) as a cathode host that not only provides a conducting pathway but also has a porous network that is resilient to volume change. To ensure the uniform loading of sulfur, CBC was dipped into the sulfur/carbon disulfide solution, followed by melt diffusion at 160 °C to prepare a sulfur-infused CBC (S-CBC) cathode. This S-CBC cathode with an interconnected fiber network delivers a significantly high reversible capacity of 1311 mA h g–1 at a current density of 50 mA g–1. While connected for long-term cycling, the potassium sulfur cell delivers an initial reversible capacity of 475 mA h g–1 at 100 mA g–1. Once the cell is stabilized after 80 cycles, it maintains a capacity of 123 mA h g–1 with a capacity retention of 86% after 500 cycles. This enhanced electrochemical performance of flexible and free-standing S-CBC cathode is further analyzed using first-principles calculations. Moreover, the efficacy of the S-CBC cathode is also tested under high sulfur loading (1.6 and 2.4 mg cm–2, respectively) for the practical development of KSBs.