Unraveling the Coupling Effect between Cathode and Anode toward Practical Lithium-Sulfur Batteries

The localized reaction heterogeneity of the sulfur cathode and the uneven Li deposition on the Li anode are intractable issues for lithium-sulfur (Li-S) batteries under practical operation. Despite impressive progress in separately optimizing the sulfur cathode or Li anode, a comprehensive understanding of the highly coupled relationship between the cathode and anode is still lacking. In this work, inspired by the Butler-Volmer equation, a binary descriptor (IBD) assisting the rational structural design of sulfur cathode by simultaneously considering the mass-transport index (Imass) and the charge-transfer index (Icharge) is identified, and subsequently the relationship between IBD and the morphological evolution of Li anode is established. Guided by the IBD, a scalable electrode providing interpenetrated flow channels for efficient mass/charge transfer, full utilization of active sulfur, and mechanically elastic support for aggressive electrochemical reactions under practical conditions is reported. These characteristics induce a homogenous distribution of local current densities and reduced reaction heterogeneity on both sides of the cathode and anode. Impressive energy density of 318 Wh kg-1 and 473 Wh L-1 in an Ah-level pouch cell can be achieved by the design concept. This work offers a promising paradigm for unlocking the interaction between cathode and anode and designing high-energy practical Li-S batteries. The Butler-Volmer equation fundamentally describes the relationship between electrode overpotential and local current densities. Inspired by the equation, a binary descriptor (IBD) is proposed to guide the design of sulfur cathodes. This descriptor can evaluate the influence of mass transport and charge transfer on reaction kinetics, and unravel the coupling effect between sulfur cathode and Li anode.image

Automated summary

This work proposes a binary descriptor (IBD) to guide the design of sulfur cathodes and establishes the relationship between IBD and the morphological evolution of Li anode. The design concept based on IBD achieves high energy density and homogeneous reaction distribution in lithium-sulfur batteries.