Edge-Protected Ni-Enriched LiNi<sub><i>x</i></sub>Co<sub><i>y</i></sub>Mn<sub><i>z</i></sub>O<sub>2</sub> Cathode Materials by Interface Modification with a Si- and F-Functionalized Surface Modifier
Jungyoung Ahn, Yongho Lee, Hyojeong J. Kim, Seokjae Lim, Seul Ki Han, Byong‐June Lee, Jeonghan Kim, Taeeun Yim
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 1 H,1 H,2 H,2 H -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.