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Designing compatible electrode–electrolyte interfaces is critical to achieve high and consistent performance and life span in next-generation rechargeable lithium batteries. In the study of nanoscopic interfaces, ab initio molecular dynamics (AIMD) simulations allow for a highly accurate description of interface dynamics and reactions. However, due to the high computational cost, simulations are limited in the size and time domains and therefore merit the need for a new interpretational approach that can deduce the long-term reactivity from such short yet highly accurate simulations. In this study, this is established by means of bond length distribution analysis through which the reactivity of key solid polymer electrolyte (SPE) polymer functional groups in contact with key electrode materials (graphite, silicon, lithium) and the influence of the electric field and temperature was successfully determined. Bond length distributions were found to respond to environmental changes and relate to the long-term reactivity in which the strength of electrode surface interactions and the accessibility of functional groups were found to be critical factors. Furthermore, the balancing of the SPE polymer mobility and functional group–electrode surface attraction, respectively, kinetic and thermodynamic properties, further suggests a selective spatial orientation of functional groups when exposed to an electric field, which could have great implications for low-temperature and high-current-density environments. The obtained knowledge on how reactive key SPE polymer functional groups are and also how their reactivity changes in terms of the electric field orientation effect could provide new insights for designing new stable SPE polymers.

Lithium–ion solvation governs the performance of lithium metal anode (LMA) by tuning its interfacial stability. Solvation degree is modulated by adopting fluorinated non-solvating cosolvents (FNSC) to induce anion-rich solvation structure which is beneficial in constructing mechanically stable interface to suppress lithium dendrite. However, FNSC exhibits low cathodic stability owing to their low lowest unoccupied molecular orbital (LUMO) level, aggravating long-term cycling of LMA. We establish that spectroscopically measured Lewis basicity and polarity are critical parameters for designing optimal non-solvating cosolvents. Non-fluorinated non-solvating cosolvents (NFNSC) proposed by our design rule (i.e. anisole, ethoxybenzene and furan) delivered 99.0 % coulombic efficiency over 1400 cycles. In these molecules, the aromatic ring delocalizes oxygen electron pairs and lowers solvation capability, confirmed by electrochemical cycling, Raman spectroscopy, and DFT binding energy calculation. Finally, the quantification of remaining NFNSC in the electrolytes using nuclear magnetic resonance spectroscopy proves their reductive stability for extended cycles.

Localized high-concentration electrolyte (LHCE) has been adopted to derive resilient inorganic-rich solid-electrolyte interphase (SEI) layer for lithium-metal anodes (LMA) and increase the ionic conductivity of high-concentration electrolyte (HCE). While the ideal diluent molecules used in LHCE should be miscible in electrolyte system, it should not solvate lithium-ion effectively. To date, systematic investigation to reveal the design rule of diluent molecules remain poorly investigated. In addition, the choice of diluents is largely limited to fluorinated organic molecules which are expensive and environmentally hazardous and unstable at the reductive potential. Because of poor cathodic stability, fluorinated diluents (FDs) have failed to achieve cycle lives longer than 500 cycles in lithium metal half-cell. Herein, we establish the design rule of diluents for the ideal LHCE, which allows to derive three non-fluorinated diluents (NFDs) systematically. We present that two solvatochromic parameters, HBA basicity (β) and normalized electronic transition energy (ET N), unravel the generalization rule for the lithium-ion solvation capability and miscibility of diluents. Our design rule discovers three NFDs: anisole, ethoxybenzene, and furan. These NFDs have the unique resonance structures which effectively delocalize the oxygen lone pair electrons and thus enhance non-solvating characteristics, confirmed by the β value and the density functional theory (DFT) calculation. In addition, nuclear magnetic resonance (NMR) spectroscopy studies confirm that our NFDs remains stable and unreacted after long-term cycling. Finally, NFD-containing electrolytes achieve superior cyclability up to 1400 cycles, the record for LHCE to date. The results obtained in this study may pave the way for designing advanced electrolyte for next generation LMA.