1,2-Propyleneglycol sulfite as a surface stabilizing agent for Ni-rich layered oxide cathodes of lithium-ion batteries

Ni-rich LiNi_xCo_yMn_zO₂ (NCM) cathode material has received a lot of attention as an advanced cathode material for lithium-ion batteries (LIBs). However, increasing internal resistance triggered by continuous electrolyte decomposition has become an important issue, as it seriously decreases the cycling retention of cells. Herein, this study will describe the means of a functional additive to improve the interfacial stability of Ni-rich NCM cathode materials, 1,2-propyleneglycol sulfite (PGS), which has a –SO₃– functional group. The PGS can create layers of artificial cathode-electrolyte interphase (CEI) through electrochemical oxidation reactions, which inhibit electrolyte decomposition in the cell. The cells without the PGS additive suffered seriously from low-cycling retention (57.1%) after 100 cycles, but their cycling performance increased to 76.9% for the cell with 2.0 wt% PGS. Electrolyte decomposition is subsequently suppressed considerably in cells, indicating that artificial CEI layers incorporated by the electrochemical reaction of PGS improve the interfacial stability. First-principle calculations reveal that PGS exhibited a higher oxidation preference and stronger Ni²⁺ affinity compared with solvents, and inhibited the formation of detrimental F⁻-like species.