Fast-Charging Lithium Iron Phosphate Cathodes by Flash Carbon Coating

Carbon coating has been used to address the poor rate performance of lithium iron phosphate (LiFePO4, LFP) due to its low intrinsic electronic and ionic conductivities. Various processes have been developed to synthesize carbon coated LFP. However, most in situ strategies introduce carbon sources during synthesis, which can interact with the LFP growth process. In this work, we developed an ex situ carbon coating method by rapidly decomposing the precursors through flash Joule heating (FJH). A uniform, amorphous carbon layer was achieved on LFP by depositing carbon-heteroatom species in a confined space within 10 seconds. Simultaneously, different heteroatoms can be introduced into the surface carbon layer to facilitate a uniform cathode-electrolyte interphase (CEI). LFP cathodes with fluorinated carbon coatings exhibited the highest capacity of 151 mAh g-1 at 0.2 C and 96 mAh g-1 at 10 C, indicating its excellent rate capability over commercial LFP (58 mAh g-1 at 10 C). A dense CEI layer with a thickness of 10 nm was observed during cycling, which effectively promotes electron and ion transport and restricts side reactions. This solvent-free, versatile cathode surface modification is shown for other cathode types, providing an efficient platform for electrode-electrolyte interphase engineering through a surface post-treatment.