Self-Assembled Macrocyclic Copper Complex Enables Homogeneous Catalysis for High-Loading Lithium-Sulfur Batteries.

The practical viability of high energy density lithium-sulfur (Li-S) batteries stipulates the use of a high-loading cathode and lean electrolyte. However, under such harsh conditions, the liquid-solid sulfur redox reaction is much-retarded due to the poor sulfur and polysulfides utilization, leading to low capacity and fast fading. Herein, a self-assembled macrocyclic Cu(II) complex (CuL) is designed as an effective catalyst to homogenize and maximize the liquid-involved reaction. The four-N atoms coordinated Cu(II) ion features a planar d sp 2 hybridization, showing a strong bonding affinity towards lithium polysulfides (LiPSs) along the d z 2 orbital via steric effect. Such a structure not only lowers the energy barrier of the liquid-solid conversion (Li 2 S 4 to Li 2 S 2 ) but also guides a 3D deposition of Li 2 S 2 /Li 2 S. As such, with a 1 wt% electrolyte additive of CuL, a high initial capacity of 925 mAh g -1 and areal capacity of 9.62 mAh cm -2 with a low decay of 0.3%/cycle can be achieved under a high sulfur loading of 10.4 mg cm -2 and low electrolyte/sulfur ratio of 6 μL mg s -1 . This work is expected to inspire the design of homogenous catalysts and accelerate the uptake of high-energy-density Li-S batteries. This article is protected by copyright. All rights reserved.