Fluorinated Rocksalt Cathode with Ultra-high Active Li Content for Lithium-ion Batteries

摘要

The key to increasing the energy density of lithium-ion batteries is to incorporate high contents of extractable Li into the cathode. Unfortunately, this triggers formidable challenges including structural instability and irreversible chemistry under operation. Here, we report a new kind of ultra-high Li compound: Li_(4+) xMoO5Fx (1≤x≤3) for cathode with an unprecedented level of electrochemically active Li (> 3 Li~+ per formula), delivering a reversible capacity up to 438mAhg~(-1). Unlike other reported Li-rich cathodes, Li_(4+)MoO5Fx presents distinguished structure stability to immunize against irreversible behaviors. Through spectroscopic and electrochemical techniques, we find an anionic redox-dominated charge compensation with negligible oxygen release and voltage decay. Our theoretical analysis reveals a "reductive effect" of high-level fluori-nation stabilizes the anionic redox by reducing the oxygen ions in pure-Li conditions, enabling a facile, reversible, and high Li-portion cycling.