A Step-by-Step Design Strategy to Realize High-Performance Lithium-Sulfur Batteries

In order to increase the energy density and improve the cyclability of lithium-sulfur (Li-S) batteries, a combined strategy is devised and evaluated for high-performance Li-S batteries. It consists of the following steps to reduce the loss of active sulfur and sulfides migrating in the liquid electrolyte to the anode and add electrocatalyst groups in the cathode or catholyte: (i) A hollow porous nanoparticle coating cathode host with a pseudocapacitive PEDOT:PSS binder that also contributes to trapping polysulfides. (ii) A thin interlayer of B-N-graphene (BNG) nanoplatelets on the above cathode trapping polysulfides while participating in the electron transfer and acting as an electrocatalyst, thus ensuring that the trapped sulfides remain active in the cathode. (iii) Added semiconductor phthalocyanine VOPc or CoPc to form an electrocatalyst network in the catholyte, trapping polysulfides and promoting their redox reactions with Li⁺ ions. (iv) Added silk fibroin in the liquid electrolyte, which also suppresses dendritic growth on the lithium anode. This strategy is evaluated step-by-step in Li-S battery cells characterized experimentally and in simulations based on a multipore continuum physicochemical model with adsorption energy data supplied from molecular dynamics simulations. The thin BNG interlayer sprayed on the cathode proved a decisive factor in improving cell performance in all cases. A Li-S cell combining features from (i), (ii), and (iv) and with 45 wt % S in the cathode yields 1372 mAh g_S ^-1 at first discharge and 920 mAh g_S ^-1 at the 100th discharge after a cycling schedule at different C-rates. A Li-S cell combining features from (i), (ii), and (iii) and with 55 wt % S in the cathode yields 805 and 586 mAh g_S ^-1 at the first and the 100th discharge, respectively.