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Lithium-metal fluoride (MF) batteries offer the highest theoretical energy density, exceeding that of the sulfur-lithium cells. However, conversion-type MF cathodes suffer from high resistance, small capacity utilization at room temperature, irreversible structural changes, and rapid capacity fading with cycling. In this study, the successful application of the approach to overcome such limitations and dramatically enhance electrochemical performance of Li-MF cells is reported. By using iron fluoride (FeF2) as an example, Li-MF cells capable of achieving near-theoretical capacity utilization are shown when MF is infiltrated into the carbon mesopores. Most importantly, the ability of electrolytes based on the lithium bis(fluorosulfonyl)imide (LiFSI) salt is presented to successfully prevent the cathode dissolution and leaching via in situ formation of a Li ion permeable protective surface layer. This layer forms as a result of electrolyte reduction/oxidation reactions during the first cycle of the conversion reaction, thus minimizing the capacity losses during cycling. Postmortem analysis shows the absence of Li dendrites, which is important for safer use of Li metal anodes. As a result, Li-FeF2 cells demonstrate over 1000 stable cycles. Quantum chemistry calculations and postmortem analysis provide insights into the mechanisms of the passivation layer formation and the performance boost. [ABSTRACT FROM AUTHOR]

Nanocomposites of selenium (Se) and ordered mesoporous silicon carbide-derived carbon (OM-SiC-CDC) are prepared for the first time and studied as cathodes for lithium-selenium (Li-Se) batteries. The higher concentration of Li salt in the electrolytes greatly improves Se utilization and cell cycle stability. Se-CDC shows significantly better performance characteristics than Se-activated carbon nanocomposites with similar physical properties. Se-CDC also exhibits better rate performance and cycle stability compared to similarly produced sulfur (S)-CDC for Li/S batteries. [ABSTRACT FROM AUTHOR]

Composite cathodes based on spherical iron fluoride (FeF2)‐based nanocomposite particles are shown to form an effective protective surface layer in situ, which allows for 1000 stable cycles in high energy Li–FeF2 cells. On page 1507, G. Yushin and co‐workers explore the mechanism of the protective layer formation and the performance boost, via quantum chemistry calculations. [ABSTRACT FROM AUTHOR]