Novel Use of a Pyridinium Salt to Form a Solid Electrolyte Interphase (SEI) on High Voltage Lithium-Excess Layered Positive Active Material

Lithium-excess layered positive electrodes containing Fe and Ni are promising materials for the next generation of high voltage lithium ion batteries (LIB) because they are more chemically stable than those using Co and use more widely available metals. However, a positive electrode driven with a high voltage generates an electrochemical decomposition reaction of the electrolyte at the electrode interface and a significant deterioration in performance occurs. In order to suppress electrolysis of the electrolyte solution, a promising solution is to form a solid electrolyte interphase (SEI) on the electrode to mediate contact between the electrolyte solution and the electrode. In this study, we discovered that a pyridinium series salt, an ionic liquid, used as an additive, forms a good SEI on the positive electrode surface to improve the overall performance of the LIBs, such as improved cycle capacity and inhibited gas generation. Furthermore, from XPS, TOF-SIMS, 1H NMR and SEM measurements, we discuss the chemical makeup of the SEI and its formation mechanism, and propose a powerful method to achieve the next generation of high energy-density lithium ion batteries.