Nonconventional Electrochemical Reactions in Rechargeable Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur (Li-S) batteries are promising for high-energy storage. However, conventional redox reactions involving sulfur (S) and lithium (Li) can lead to unstable intermediates. Over the past decade, many strategies have emerged to address this challenge, enabling nonconventional electrochemical reactions in Li-S batteries. In our Perspective, we provide a brief review of these strategies and highlight their potential benefits. Specifically, our group has pioneered a top-down approach, investigating Li-S reactions at molecular and subatomic levels, as demonstrated in our recent work on stable S isotopes. These insights not only enhance understanding of charge transfer and storage properties but also offer exciting opportunities for advancements in battery materials research.

Potential Controllable Redox Couple for Mild and Efficient Lithium Recovery from Spent Batteries.

The prosperity of the lithium-ion battery market is dialectically accompanied by the depletion of corresponding resources and the accumulation of spent batteries. It is an urgent priority to develop green and efficient battery recycling strategies for helping ease resources and environmental pressures at the current stage. Here, we propose a mild and efficient lithium extracting strategy based on potential controllable redox couples. Active lithium in the spent battery without discharging is extracted using a series of tailored aprotic solutions comprised of polycyclic aromatic hydrocarbons and ethers. This ensures a safe yet efficient recycling process with nearly ≈100 % lithium recovery. We further investigate the Li+ -electron concerted redox reactions and the effect of solvation structure on kinetics during the extraction, and broaden the applicability of the Li-PAHs solution. This work can stimulate new inspiration for designing novel solutions to meet efficient and sustainable demands in recycling batteries.

High-Performance Quasi-Solid-State Lithium-Sulfur Battery with a Controllably Solidified Cathode-Electrolyte Interface.

Lithium-sulfur batteries are considered a promising "beyond Li-ion" energy storage technology. Currently, the practical realization of Li-S batteries is plagued by rapid electrochemical failure of S cathodes due to aggravated polysulfide dissolution and shuttle in the conventional liquid ether-based electrolytes. A gel polymer electrolyte obtained by in situ polymerization of liquid electrolyte solvent at the cathode-electrolyte interface has been proven an effective strategy to prevent polysulfide shuttle. However, notably reduced polysulfide solubility in the gel electrolyte leads to enrichment of poorly conductive sulfide species, which hinders charge migration across the interface and therefore accounts for retarded polysulfide conversion and a low capacity/energy output of batteries. Here, we show that thioacetamide, as a cathode additive, inhibits interfacial polymerization of ether molecules while assisting dissolution of polysulfides and Li2S at the cathode/electrolyte interface. In this way, a layer of liquid, sulfide-soluble electrolyte is preserved between the highly gelled electrolyte and the S particle surface, avoiding interfacial sulfide accumulation and improving polysulfide conversion kinetics. A Li-S battery with the controllably solidified interface demonstrates, without adding other performance-boosting agents or catalysts, a high reversible capacity, a long cycle life, and a favorable rate performance, showing promises for the next-generation storage applications.

Noncoordinating Flame-Retardant Functional Electrolyte Solvents for Rechargeable Lithium-Ion Batteries.

In Li-ion batteries, functional cosolvents could significantly improve the specific performance of the electrolyte, for example, the flame retardancy. In case the cosolvent shows strong Li+-coordinating ability, it could adversely influence the electrochemical Li+-intercalation reaction of the electrode. In this work, a noncoordinating functional cosolvent was proposed to enrich the functionality of the electrolyte while avoiding interference with the Li storage process. Hexafluorocyclotriphosphazene, an efficient flame-retardant agent with proper physicochemical properties, was chosen as a cosolvent for preparing functional electrolytes. The nonpolar phosphazene molecules with low electron-donating ability do not coordinate with Li+ and thus are excluded from the primary solvation sheath. In graphite-anode-based Li-ion batteries, the phosphazene molecules do not cointercalate with Li+ into the graphite lattice during the charging process, which helps to maintain integral anode structure and interface and contributes to stable cycling. The noncoordinating cosolvent was also applied to other types of electrode materials and batteries, paving a new way for high-performance electrochemical energy storage systems with customizable functions.