Visualizing Interfacial Collective Reaction Behaviour of Li-S Batteries

Developing high-energy-density and efficient secondary battery systems has become a critical research priority. Lithium-sulfur (Li-S) batteries are among the most promising candidates, offering energy densities exceeding 500 Wh kg –1 , compared to approximately 200 Wh kg –1 for commercial lithium-ion batteries. However, Li-S batteries face significant scientific challenges, including the dissolution and shuttle effect of lithium polysulfide (LiPSs) intermediates, unclear reaction pathways, and transient solid-phase intermediates during discharge. The current limitations of in situ characterization tools in tracing interfacial reaction dynamics at high temporal-spatial resolution impede the development of next-generation Li-S batteries. Addressing these challenges requires a fundamental understanding of the chemical reactions at the electrode-electrolyte interface at the atomic/molecular level—a key focus of this research. This work has been devoted to advancing high temporal-spatial resolution electrochemical in situ liquid-cell transmission electron microscopy (EC-TEM) for studying interfacial reactions in Li-S batteries, a field critical to both battery science and electron microscopy. Characterizing interfacial electrochemical reactions in Li-S batteries is particularly challenging due to the continuous phase transformation of metastable LiPSs, complex solid-liquid interfaces, and coupled electrochemical processes. This work achieved unprecedented insights into atomic-level dynamics, crystal structures, and elemental distributions through the integration of advanced TEM detectors. This work systematically investigated electron beam effects and optimized spatiotemporal resolution by constructing a Li-S nanobattery within a liquid cell and fine-tuning imaging parameters for high-resolution observation. This work resulted in the first real-time visualization of electrochemical transformations across different interfaces in liquid Li-S batteries at the nano- and atomic scale ( Fig. 1 ). Combining with density functional theory calculations and density of state analysis, the study further found that the concentration-driven aggregation of LiPSs dramatically alters their geometric structure, electronic properties, and hybridization orbitals, leading to the collective charge transfer behaviors. Building on these insights, this work successfully linked reaction mechanisms with LiPSs concentration, crucial parameters affecting Li-S battery performance, thereby advancing design considerations for high-energy, long-life, and efficient Li-S batteries ( Fig. 2 ).