Porous Carbon/Borocarbonitride hybrid with enhanced tap density as a polar host for ultralong life Lithium-Sulfur batteries

Abstract The severe shuttle effect and sluggish redox kinetics are the current bottlenecks of lithium-sulfur (Li-S) batteries, resulting in capacity fading and inferior rate performance, especially under the condition of high sulfur loading and low electrolyte/sulfur ratio (E/S). Herein, conductive carbon nanoparticles (Ketjen Black, KB) covered by borocarbonitride (BCN) are assembled into micro-sized particles to form a polar KB@BCN hybrid, which is employed as a sulfur host with enhanced tap density via a facile intergrowth method. At a molecular level, BCN, endowed with abundant adsorption sites as the adsorbent and catalyst, can adsorb polysulfides and catalyze the conversion of polysulfides. On the nanometer scale, the BCN is loaded on the highly conductive KB nanoparticles, which can improve the conductivity of the hybrid (1786 S m−1), thereby improving the conversion of polysulfides. On the micrometer scale, the BCN and the KB nanoparticles together form micro-sized particles to improve the tap density, which is beneficial to build thick electrodes and reduce the amount of electrolyte. When applied as a sulfur cathode, KB@BCN-2 shows good cycling capability (a low-capacity decay of 0.05% after 800 cycles at 0.5C) and high rate performance (765 mA h g−1 at 3.0C). Even under a lean electrolyte condition (E/S = 5 μL mg−1), the KB@BCN-2-S has a high initial capacity of 1266 mA h g−1 at 0.1C. Significantly, incorporating polar electrocatalysts with carbon matrix to form a high-density sulfur host through secondary granulation can provide a new insight for achieving high-performance Li-S batteries.