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Metal fluorides (MFs) are regarded as high‐capacity conversion cathode materials for next‐generation lithium‐ion batteries with high energy density. However, these cathodes suffer from poor electronic conductivity, sluggish reaction kinetics, and deleterious cathode solid electrolyte interface (CEI) formation, which may cause rapid cell degradation upon cycling. Herein, a low temperature chemical vapor deposition (CVD) carbon coating technology is successfully achieved to coat MFs‐FeF2 with a thin amorphous carbon layer, which promotes the formation of a stable CEI with improved electronic and ionic transport property. Consequently, a discharge capacity higher than 450 mAh g−1 of the CVD coated FeF2 is achieved with a capacity retention at about 75% after 2500 cycles in a saturated electrolyte. Moreover, an unprecedented cycling performance with the discharge capacity of 350 mAh g−1 after 500 cycles in a super diluted electrolyte is also achieved. Advanced cryo‐electron microscopy reveals that the carbon coating significantly suppresses the undesirable CEI formation and promotes the formation of a thin CEI with excellent chemo‐mechanical property. This work provides a feasible technology to stabilize the important interface on MFs and offers a new strategy to accelerate the commercial adoption of such cathodes. [ABSTRACT FROM AUTHOR]

High interfacial impedance is a major obstacle in the application of solid‐state Li metal batteries (SSLMBs). Understanding the atomic‐scale structure of the interfaces in SSLMBs is thus critical to their practical implementations. However, due to the beam sensitivity of battery materials, such information is not accessible by conventional electron microscopy (EM). Herein, by using cryogenic‐EM (cryo‐EM), the atomic‐scale structures of interfaces in garnet electrolyte based SSLMBs are revealed. A LiF‐rich interlayer exhibiting intimate contacts with both Li and LLZTO is shown, thus rendering uniform Li+ transport across the interface in turn inhibiting Li dendrite growth. Consequently, the Li symmetric cell based on the LiF‐rich interlayer exhibits a high critical current density of 3.2 mA cm−2 and a long lifespan over 1800 cycles at 1 mA cm−2. Moreover, a full cell with a LiNi0.88Co0.1Al0.02O2 cathode at a high mass loading ≈12 mg cm−2 reached over 400 cycles at 1.2 mA cm−2, which represents a major progress in the performance of the garnet‐type SSLMBs. This study provides atomic‐scale understanding of interfaces in SSLMBs and an effective strategy to design dendrite‐free SSLMBs for practical applications. [ABSTRACT FROM AUTHOR]

Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF2 and polymer‐derived carbon (FeF2@PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod‐shaped FeF2 embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF2@PDC enables a reversible capacity of 500 mAh g–1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF2@PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g–1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe3O4 layers on the surface of FeF2 prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF2 electrochemistry, and a strategy to radically improve the electrochemical performance of FeF2 cathode for lithium‐ion battery applications. [ABSTRACT FROM AUTHOR]