In-situ constructing a rigid and stable dual-layer CEI film improving high-voltage 4.6 V LiCoO₂ performances

As the most important cathode used in digital devices, LiCoO₂ can extract more specific capacity by lifting the operational voltage. But the cyclic performance suffers from rapid decay due to the unstable electrode/electrolyte interphase (CEI) at high voltage. In this work, a novel in-situ dual-layer CEI film with high electrochemical stability and mechanical strength is constructed by sequential oxidation potentials of multiply additives. The inner layer of fluorinated-alkyl amide compounds displays a good oxidative stability to ~4.75 V vs. Li⁺/Li, and the outer layer of polymerized diphenylamine (DPA) shows an ultrahigh Young's modulus ~ 25.4 GPa. This dual-layer CEI film not only prevents the decomposition of electrolyte and dissolution of Co element, but also mitigates the particles cracking. With the protection of this dual-layer CEI film, the capacity retention of Li/LiCoO₂ cells has been improved from ~ 59% to 75% at 4.6 V vs. Li⁺/Li in 200 cycles. This work provides a new design of constructing stable CEI film for high-energy-density lithium ion batteries (LIBs).