Prussian Blue Microcubes-Derived Fef3 Cathodes for High-Energy and Ultra-Stable Lithium and Lithium-Ion Batteries

Iron trifluoride (FeF3) is highlighted as a competitive cathode for next-generation lithium and lithium-ion batteries with higher energy densities and lower cost. However, the FeF3 cathode is typically hindered by rapid capacity fade for their poor electronic/ionic conductivity and unstable electrode/electrolyte interphase. Herein, a microcubic FeF3@C composite, where the nanosized FeF3 particles (<40 nm) are encapsulated by graphitized carbon and linked through surrounding amorphous carbon matrix, is firstly synthesized through the Prussian blue microcubes. When using as the cathode of coin-type lithium batteries, it can achieve stable and ultralong lifespan (over 1000 cycles) at FeF3 mass loading of ∼2 mg cm−2, ascribing to the compact and thick wrapping of carbon shell and stable cathode solid electrolyte interphase (CEI) during cycling. Besides, the FeF3–Li pouch cell, FeF3 full batteries with pre-lithiated Li4Ti5O12 (PLLTO) and pre-lithiated mesocarbon microbeads (PLMCMB) anodes are successfully constructed. To interpret the capacity rising of as-prepared FeF3 cathodes within initial cycles, the detailed electrochemical behaviors and electrode kinetics are investigated. The results show that the decay of the high-potential decomposition process cannot catch up with the activation of the low-potential conversion reaction The repeated electrochemical activation within initial cycles causes multiple interface and increased Li+ diffusion coefficient (resulted from the amorphization of FeF3 particle), which induce the capacity rising.