The development of high-voltage electrolyte system is a key factor in the commercialization of high-voltage spinel lithium nickel manganese oxide (LNMO) battery materials. This article carries out the optimization and exploration of LiBOB electrolyte additives in high voltage LNMO cathode materials. The test results show that the performance is best when the electrolyte is added at 30–50 μL. In order to study the mechanism of LiBOB on the LNMO anode, combining the characterization results of XRD, XPS, IR, Raman, and electron microscopy, it can be seen that LiBOB is preferentially oxidized and a layer of boron-rich CEI film with a thickness of about 8 nm is formed on the surface of the LNMO anode. This passivation film physically blocks the contact between the electrolyte and the surface of the highly active electrode, maintains the stability of the LNMO structure under high voltage, and improves the electrochemical performance.