Developing high-voltage Li ion batteries (LIBs) is an important trend to fit high energy and power density requirement of electric vehicles and hybrid electric vehicles. This requires the cathode materials and concomitant electrolyte to accommodate the high voltage working condition. However, continually exposed to high voltage, the cathode materials could gradually deteriorate and eventually cause the failure of battery. To address this issue, electrolyte additives can be an economic solution based on current existing electrolyte system, since it can decompose on the electrodes forming thin protective layer during formation cycles to prevent further deleterious reactions. The nominal electrolyte additives here are the precursors, which can spontaneously react with electrolyte when introduced into the electrolyte to yield the target surface-modifying products that can effectively protect the cathode. These additives were proved exceptional, since they delay both the impedance rise and capacity fade in the LIBs. To extend the library of this type of additives and explore more effective additives, we applied the molecular engineering to tune molecular backbone, functionality and substitution to obtain different surface-modifying products and maximize the battery performance. In addition, the in situ method is particularly beneficial to scale up electrolyte preparation, since it doesn’t need any post separation and purification process. By varying the structure of the additive precursor, we clearly see a trend that is governed by thermodynamics which determine the product configuration. The electrochemistry of these additives and their application in composite cathodes will be also discussed. Our strategy of synthesizing new electrolyte additives by in situ method will open up and facilitate the development of the lithium ion batteries toward high energy and high power density.