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

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• High-energy-density lithium-sulfur (Li-S) batteries require high sulfur loading and lean electrolytes for practical application.
• Current Li-S batteries suffer from poor sulfur and polysulfide utilization under these conditions, resulting in low capacity and rapid degradation.
• Efficient management of the liquid-solid sulfur redox reaction is crucial for overcoming these limitations.

Purpose of the Study:

• To design and synthesize a homogeneous catalyst to optimize the liquid-involved sulfur redox reaction in Li-S batteries.
• To investigate the catalytic mechanism of the designed complex on lithium polysulfide binding and conversion.
• To evaluate the performance enhancement of Li-S batteries with the catalyst under practical operating conditions.

Main Methods:

• Self-assembly of a macrocyclic Cu(II) complex (CuL) as a catalyst.
• Characterization of the Cu(II) ion's electronic structure and coordination environment.
• Electrochemical testing of Li-S cells with CuL additive under high sulfur loading and lean electrolyte conditions.

Main Results:

• The CuL catalyst exhibits strong binding affinity towards lithium polysulfides (LiPSs) through its planar Cu(II) center.
• CuL effectively lowers the energy barrier for LiPS conversion and promotes uniform deposition of discharge products.
• Li-S cells with 1 wt% CuL additive achieved a high initial capacity (925 mAh g⁻¹) and areal capacity (9.62 mAh cm⁻²) with low decay (0.3%/cycle) at 10.4 mg cm⁻² sulfur loading and a 6 µL mg⁻¹ electrolyte/sulfur ratio.

Conclusions:

• The designed macrocyclic Cu(II) complex acts as an effective homogeneous catalyst for Li-S batteries.
• CuL significantly improves sulfur utilization, polysulfide management, and overall battery performance.
• This work provides a promising strategy for developing advanced catalysts to accelerate the commercialization of high-energy-density Li-S batteries.