Confronted with the fast-growing marked demand for high energy and power Li-ion batteries in electrical vehicles and hybrid electrical vehicles. Numerous efforts have been applied to develop battery systems with higher charge voltage to achieve higher cell energy. However, a more severe capacity fading is usually observed for the high voltage cell, accompanied with sever battery swelling, which could be attributed to more side reactions. Online electrochemical Mass Spectrometry (OEMS) is an analytical technique that combines electrochemical half-cell experimentation with mass spectrometry. It allows in-situ mass resolved determination of gaseous or volatile electrochemical reactants, reaction intermediates and products in real time. In this work, we will discuss the setup of a laboratory grade OEMS and reported the initial test towards several popular NMC cathode//Graphite lithium ion batteries with different electrolyte choices, and comparison of our results with reported literature will be presented.