In Situ Controlled Syntheses of Electrolyte Additives for High Voltage Lithium Ion Batteries

Abstract

The development of cathode materials needs concomitant electrolyte developments to accommodate the high voltage to reach high energy and power densities required for electric vehicle and personal electronics. Previously we reported that aging TMSPi (trimethylsilylphosphite) additive in a standard 1.2 M LiPF6 carbonate electrolyte can generate a beneficial transient product, PF2(OSi(CH3)3), which was later proven to mitigate impedance rise during long term cycling in composite cathode-graphite cells. However, the generation of PF2(OSi(CH3)3) is spontaneous and cannot be controlled, and as aging process proceeds to a greater extent, PF2(OSi(CH3)3) disappears gradually and other transient detrimental products form along the way and eventually deteriorate the impedance.1,2 By using molecular engineering to tune functionality, ratio, and stability, we can control the in situ electrolyte additive to selectively synthesize the beneficial component in high yield (> 98%) and maximize the battery performance. The in situ method is particularly of interest to scale up electrolyte preparation since it would alleviate any requirements of extra separation and purification of the desired additives. By varying the structure of the additive precursor, we clearly see a trend that is governed by thermodynamics which determine the product ratio and composition. The electrochemistry of these additives and their application in composite cathodes will be discussed. By introducing the novel in situ synthetic method for electrolyte additive syntheses, avenues for new additives that were previously inaccessible will open up and facilitate the development of the lithium ion batteries toward high energy and high power density. References The Journal of Physical Chemistry C 2018, 122 (18), 9811-9824.RSC Advances 2016, 6 (44), 38342-38349.