Edge-Protected Ni-Enriched LiNi_<i>x</i>Co_<i>y</i>Mn_<i>z</i>O₂ Cathode Materials by Interface Modification with a Si- and F-Functionalized Surface Modifier

Abstract

Many advances made in recent years have highlighted Ni-enriched nickel, cobalt, manganese (NCM) material as a prospective positive electrode material for lithium-ion batteries. However, prolonged cycling is limited by several critical issues, including surface instability, gas generation, and transitional metal dissolution upon cycling. Here, we propose a simple interfacial modification approach that uses 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POS) as a coating precursor to improve surface stability. A one-step thermal heat treatment creates bifunctional cathode electrolyte interphase (CEI) layers from F- and Si-functionalized POS, especially at the edge sites of the Ni-enriched NCM cathode, where serious undesired reactions occur during cycling. The POS-modified Ni-enriched NCM cathode exhibits improved cycling retention compared to the unmodified Ni-enriched NCM cathode because parasitic reactions are well suppressed upon cycling. Systematic analyses show an apparent inhibition of electrolyte decomposition in the POS-modified Ni-enriched NCM cathode due to the effective protection of the active edge sites by the artificial POS-derived CEI layers. The dissolution of metal components is also greatly decreased because the Si-functional groups that develop on the POS-derived CEI layers selectively scavenge F– species formed by electrolyte decomposition.