Nowadays, Li-ion batteries (LIBs) have been gained a lot of attention in the energy storage field since its widely used for many applications. However, the misuse or misoperation of the batteries can generate electrolyte decomposition causing a short life span and safety hazards. Herein, two types of Ni-rich NMC811 i.e., single-crystal and polycrystal were used to study the electrolyte evolution under conventional and abused battery testing protocols. The in-house in situ cells shed light on electrolyte decomposition analyzed by NMR, GC-MS, and ICP, DEMS, and computational calculation. We found that the amount of gas was produced under the system using the polycrystalline NMC811cathode was significantly more than that using the single crystalline NMC811.