Deploying Proteins as Electrolyte Additives in Li-S Batteries: The Multifunctional Role of Fibroin in Improving Cell Performance

It is widely acceptedthat the commercial application of lithium-sulfurbatteries is inhibited by their short cycle life, which is primarilycaused by a combination of Li dendrite formation and active materialloss due to polysulfide shuttling. Unfortunately, while numerous approachesto overcome these problems have been reported, most are unscalableand hence further hinder Li-S battery commercialization. Mostapproaches suggested also only tackle one of the primary mechanismsof cell degradation and failure. Here, we demonstrate that the useof a simple protein, fibroin, as an electrolyte additive can bothprevent Li dendrite formation and minimize active material loss toenable high capacity and long cycle life (up to 500 cycles) in Li-Sbatteries, without inhibiting the rate performance of the cell. Througha combination of experiments and molecular dynamics (MD) simulations,it is demonstrated that the fibroin plays a dual role, both bindingto polysulfides to hinder their transport from the cathode and passivatingthe Li anode to minimize dendrite nucleation and growth. Most importantly,as fibroin is inexpensive and can be simply introduced to the cellvia the electrolyte, this work offers a route toward practical industrialapplications of a viable Li-S battery system.