Sulfurized polyacrylonitrile (SPAN) is the most promising cathode for next-generation lithium−sulfur (Li−S) batteries due to the much improved stability. However, the molecular structure and reaction mechanism have not yet been fully understood. Herein, we present a new take on the structure and mechanism to interpret the electrochemical behaviors. We find that the thiyl radical is generated after the cleavage of the S−S bond in molecules in the first cycle, and then a conjugative structure can be formed due to electron delocalization of the thiyl radical on the pyridine backbone. The conjugative structure can react with lithium ions through a lithium coupled electron transfer process and form an ion-coordination bond reversibly. This could be the real reason for the superior lithium storage capability, in which the lithium polysulfide may not be formed. This study refreshes current knowledge of SPAN in Li−S batteries. In addition, the structural analysis is applicable to analyze the current organic cathodes in rechargeable batteries and also allows further applications in Al−S batteries to achieve high performance.

Molecular doping has recently been shown to improve the operating characteristics of organic photovoltaics (OPVs). Here, we prepare neutral Diquat (DQ) and use it as n-dopant to improve the performance of state-of-the-art OPVs. Adding DQ in ternary bulk-heterojunction (BHJ) cells based of PM6:Y6:PC 71 BM is found to consistently increase their power conversion efficiency (PCE) from 16.7 to 17.4%. Analyses of materials and devices reveal that DQ acts as n-type dopant and morphology modifier for the BHJ leading to observable changes in its surface topography. The resulting n-doped BHJs exhibit higher optical absorption coefficients, balanced ambipolar transport, longer carrier lifetimes and suppressed bimolecular recombination, which are ultimately responsible for the increased PCE. The use of DQ was successfully extended to OPVs based on PM6:BTP-eC9:PC 71 BM for which a maximum PCE of 18.3% (uncertified) was achieved. Our study highlights DQ as a promising dopant for application in next generation organic solar cells.

Over the past two decades, the solid–electrolyte interphase (SEI) layer that forms on an electrode’s surface has been believed to be pivotal for stabilizing the electrode’s performance in lithium-ion batteries (LIBs). However, more and more researchers currently are realizing that the metal-ion solvation structure (e.g., Li+) in electrolytes and the derived interfacial model (i.e., the desolvation process) can affect the electrode’s performance significantly. Thus, herein we summarize recent research focused on how to discover the importance of an electrolyte’s solvation structure, develop a quantitative model to describe the solvation structure, construct an interfacial model to understand the electrode’s performance, and apply these theories to the design of electrolytes. We provide a timely review on the scientific relationship between the molecular interactions of metal ions, anions, and solvents in the interfacial model and the electrode’s performance, of which the viewpoint differs from the SEI interpretations before. These discoveries may herald a new, post-SEI era due to their significance for guiding the design of LIBs and their performance improvement, as well as developing other metal-ion batteries and beyond.

Graphite anodes are not stable in most noncarbonate solvents (e.g., ether, sulfoxide, sulfone) upon Li ion intercalation, known as an urgent issue in present Li ions and next-generation Li−S and Li−O 2 batteries for storage of Li ions within the anode for safety features. The solid electrolyte interphase (SEI) is commonly believed to be decisive for stabilizing the graphite anode. However, here we find that the solvation structure of the Li ions, determined by the electrolyte composition including lithium salts, solvents, and additives, plays a more dominant role than SEI in graphite anode stability. The Li ion intercalation desired for battery operation competes with the undesired Li + −solvent co-insertion, leading to graphite exfoliation. The increase in organic lithium salt LiN(SO 2 CF 3 ) 2 concentration or, more effectively, the addition of LiNO 3 lowers the interaction strength between Li + and solvents, suppressing the graphite exfoliation caused by Li + −solvent co-insertion. Our findings refresh the knowledge of the well-known SEI for graphite stability in metal ion batteries and also provide new guidelines for electrolyte systems to achieve reliable and safe Li−S full batteries.

Solid electrolyte interphase (SEI)-forming agents such as vinylene carbonate, sulfone, and cyclic sulfate are commonly believed to be film-forming additives in lithium-ion batteries that help to enhance graphite anode stability. However, we find that the film-forming effect and the resultant SEI may not be the only reasons for the enhanced graphite stability. This is because the as-formed SEI cannot inhibit Li + −solvent cointercalation once the additive is removed from the electrolyte. Instead, we show that the Li + solvation structure, which is modified by these additives, plays a critical role in achieving reversible Li + (de)intercalation within graphite. This discovery is confirmed in both carbonate and ether-based electrolytes. We show that the problem of graphite exfoliation caused by Li + −solvent cointercalation can be mitigated by adding ethene sulfate to tune the Li + coordination structure. This work brings new insight into the role of additives in electrolytes, expanding the prevailing thinking over the past 2 decades. In addition, this finding can guide the design of more versatile electrolytes for advanced rechargeable metal-ion batteries.