Improved Sufur/Lithium Suflide Nano-composite Electrodes for Next-Generation Lithium Cells

Abstract

A new generation of batteries with a capability of at least 400 Wh/kg is urgently needed since current lithium ion cells are reaching their maximum energy storage capability (~200 Wh/kg). The lithium/sulfur cell, with a theoretical specific energy of 2680 Wh/kg, is an attractive candidate. However, its rapid capacity decay owing to polysulfide dissolution requires good protection of the cathode materials before it can be commercialized. In our research, we are working on improving the performance of the Li/S cell by modifying the active material structure, electrolyte and binder. For the sulfur electrode, graphene oxide and other carbon materials with various surface functional groups are used as a component of nanostructured composite electrode materials. With the help of these functional groups as well as a new binder, nanostructured sulfur can be retained during cell cycling. The latest results show that the new C-S materials are exhibiting a capacity higher than 800 mAh/g(sulfur) even after cycling for 1000 times. For Li2S as the starting material, structured nanoparticles that contain carbon or other conductive materials are under evaluation. Recent results show that the capacity fading of Li2S electrodes can be alleviated using carbon. In addition to these experiments, simulations of the Li/S cell are being performed. The computational model includes a description of electrochemical kinetics, mass and charge transport in the electrolyte as well as the formation of solid phases. Different reaction mechanisms can be chosen to represent the operation of Li/S cells. Simulated results include charge and discharge curves, concentrations of dissolved ions and polysulfides, volumes of solid and liquid phases in different regions of the cell as well as electrochemical impedance spectra. These results facilitate the interpretation of experimental results. The refinement and validation of the model based on our most recent data is the subject of ongoing studies.