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-involving reaction. The Cu(II) ion coordinated with four N atoms features a planar d(sp2) hybridization, showing a strong bonding affinity toward lithium polysulfides (LiPSs) along the d(z2) orbital via steric effects. Such a structure not only lowers the energy barrier of the liquid-solid conversion (Li2S4 to Li2S2) but also guides a 3D deposition of Li2S2/Li2S. 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 mu L 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.

Automated summary

In this study, a self-assembled macrocyclic Cu(II) complex was designed as an effective catalyst for high-energy-density Li-S batteries. By improving the efficiency of the liquid-solid sulfur redox reaction, the capacity, cycling stability, and energy decay rate of the batteries were enhanced. This research provides important insights for the design of homogenous catalysts and the promotion of high-energy-density Li-S batteries.