The Working Mechanism of Additive in High Voltage Electrolyte for Lithium Cobaltate/Graphite Pouch Cell

1,2,3-Tris (2-cyanoethoxy) propane (TPPN) as a new electrolyte additive has been investigated in 4.55 V high voltage lithium cobaltate (LiCoO₂) /graphite pouch cells. By comparing the cycle performance of cells without and with TPPN, it is found that the addition of TPPN can improve the performance, and the optimal weight proportion is 2%. At 3.00-4.55 V and 1C/1C, the cells with 2%TPPN has a capacity retention rate of 86.4% at 25℃ for 900 cycles compared with the capacity retention rate of 8.7% that without 2%TPPN. According to the theoretical calculation and linear sweep voltammetry, the decomposition of TPPN is preferred to that of the electrolyte solvent. It can be seen from N 1s spectra from X-ray photoelectron spectroscopy on LiCoO₂ surface that TPPN forms an interfacial film on the LiCoO₂ surface. It can be seen from the impedance data that the interface film formed by TPPN has low impedance and high stability. From theoretical calculation, scanning, transmission electron microscopy, X-ray diffraction on LiCoO₂ surface and Co 2p spectra from X-ray photoelectron spectroscopy on graphite surface, it is revealed that the interface film formed by TPPN can effectively suppress the decomposition of electrolyte and the dissolution of cobalt ions, confirming the high stability of the interface film formed by TPPN.