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The widespread applications of lithium-ion batteries (LIBs) generate tons of spent LIBs. Therefore, recycling LIBs is of paramount importance in protecting the environment and saving the resources. Current commercialized LIBs mostly adopt layered oxides such as LiCoO2 (LCO) or LiNixCoyMn1−x−yO2 (NMC) as the cathode materials. Converting the intercalation-type spent oxides into conversion-type cathodes (such as metal fluorides (MFs)) offers a valid recycling strategy and provides substantially improved energy densities for LIBs. Herein, two typical Co-based cathodes, LCO and LiNi0.6Co0.2Mn0.2O2 (NMC622), in spent LIBs were successfully converted to CoF2 and (NixCoyMnz)F2 cathodes by a reduction and fluorination technique. The as converted CoF2 and (NixCoyMnz)F2 delivered cell energy densities of 650 and 700 Wh/kg, respectively. Advanced atomic-level electron microscopy revealed that the used LCO and NMC622 were converted to highly phase pure Co metal and Ni0.6Co0.2Mn0.2 alloys in the used graphite-assisted reduction roasting, simultaneously producing the important product of Li2CO3 using only environment friendly solvent. Our study provided a versatile strategy to convert the intercalation-type Co-based cathode in the spent LIBs into conversion-type MFs cathodes, which offers a new avenue to recycle the spent LIBs and substantially increase the energy densities of next generation LIBs. [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]