The Effect of Functional Groups and Co-Additives on the Performance of an Electrolyte Additive for Li-Ion Cells

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It is very common to add additives in lithium-ion cells in order to improve their performance. However, it is not well-known what makes a good additive. The goal of this research was to study how different functional groups in the para position affect the performance of the relatively new additive PDO (3-phenyl-1,4,2-dioxazol-5-one). The PDO additive was developed following previous work by the Winter group on MDO (3-methyl-1,4,2-dioxazol-5-one)1. Each PDO-type additive was synthesized in our lab from the corresponding acyl chloride and was tested in NMC622/graphite cells. Differential capacity analysis (dQ/dV), electrochemical impedance spectroscopy (EIS), high-temperature storage, and long-term cycling tests have been used to characterize the corresponding cells. The well-known additives DTD (Ethylene Sulfate), MMDS (Methylene Methyl Disulfonate), LFO (Lithium difluorophosphate) and VC (Vinylene Carbonate) have been added as co-additives in the hope of forming binary blends with improved performance. It was found that unsubstituted and nitro-substituted PDO blends have the best long-term cycling performance, while unsubstituted and methoxy-substituted PDO blends have the best storage performance at 60°C. S. Röser, A. Lerchen, L. Ibing, X. Cao, J. Kasnatscheew, F. Glorius, M. Winter, and R. Wagner, Chem. Mater., 29, 7733–7739 (2017). Figure 1