Mn2O3 Incorporated Carbonized Bacterial Cellulose As Sulfur Host for Lithium-Sulfur Batteries

Abstract

Early development and commercialization of lithium-ion batteries (LIBs) have enabled the portable electronic devices and powered the world. However, the ever-increasing demand for higher energy batteries have led to the quest for further improvement. Lithium-sulfur batteries (LSBs), with lithium anode and sulfur-based composite as cathode, have high theoretical specific energy of 2600 W h kg-1 (around 10 folds higher than LIBs system). Moreover, sulfur is produced as a by-product from petroleum refineries making research in LSBs more lucrative. However, there are a few critical challenges which restrict the commercialization of LSBs. First, insulating nature of sulfur (5 × 10-30 S cm-1) and lithium sulfide (Li2S, 10-13 S cm-1) impedes the electronic conductivity which results in low utilization of active sulfur. Secondly, the dissolution and diffusion of long-chain lithium polysulfides in electrolyte to lithium anode under concentration gradient causes series of severe issues such as loss of active sulfur, pulverization of lithium anode. Thirdly, the volume change during lithiation (up to 80%) results in degradation of cathode.To tackle aforementioned issues, we have utilized Mn2O3 incorporated carbonized bacterial cellulose (Mn2O3@CBC) as sulfur host for LSB. A facile melt-diffusion approach was adopted to encapsulate sulfur into Mn2O3@CBC matrix. The material was characterized using various physicochemical techniques - X-ray diffraction spectroscopy, Raman spectroscopy, Thermal gravimetric analysis, and Surface area analyzer. The Mn2O3@CBC system developed in this work offers the following benefits: (a) interconnected carbon nanofiber assembly which helps in fast diffusion of Li-ion and electrons; (b) porous morphology to accommodate volume change and to act as a reservoir for long-chain lithium polysulfides accumulation; (c) Mn2O3 as long-chain lithium polysulfide binding site and catalyst for conversion of long-chain lithium polysulfides to short-chain lithium polysulfides.To investigate the electrochemical property of the material, the performance is compared to bare sulfur and sulfur incorporated carbonized bacterial cellulose (S-CBC). Various electrochemical characterization such as cyclic voltammograms, galvanostatic charge-discharge, rate capability, long-term cycling was performed to investigate the performance of the materials. The material (S-Mn2O3@CBC) exhibited initial reversible capacity of 1150 mA h g-1 at 0.1C and retained 254.4 mA h g-1 at the extremely high current rate of 15C which is far ahead than the bare sulfur and S-CBC. Furthermore, the cycle life of LSB with low and high-sulfur loading was performed to further establish the advantage of using Mn2O3 as electro catalyst. Moreover, first-principles calculation was carried out to understand the functional mechanism for interaction of Mn2O3@CBC and intermediate lithium polysulfides. The excellent electrochemical performance substantiates that the S-Mn2O3@CBC is a good choice for cathode for LSBs. Figure 1