Triphenyl phosphate as an Efficient Electrolyte Additive for Nirich NCM Cathode Materials

Nickel-rich lithium nickel-cobalt-manganese oxides (NCM) are viewed as promising cathode materials for lithium-ion batteries (LIBs); however, their poor cycling performance at high temperature is a critical hurdle preventing expansion of their applications. We propose the use of a functional electrolyte additive, triphenyl phosphate (TPPa), which can form an effective cathode-electrolyte interphase (CEI) layer on the surface of Ni-rich NCM cathode material by electrochemical reactions. Linear sweep voltammetry confirms that the TPPa additive is electrochemically oxidized at around 4.83 V (vs. Li/Li+) and it participates in the formation of a CEI layer on the surface of NCM811 cathode material. During high temperature cycling, TPPa greatly improves the cycling performance of NCM811 cathode material, as a cell cycled with TPPa-containing electrolyte exhibits a retention (133.7 mA h g(-1)) of 63.5%, while a cell cycled with standard electrolyte shows poor cycling retention (51.3%, 108.3 mA h g(-1)). Further systematic analyses on recovered NCM811 cathodes demonstrate the effectiveness of the TPPa-based CEI layer in the cell, as electrolyte decomposition is suppressed in the cell cycled with TPPa-containing electrolyte. This confirms that TPPa is effective at increasing the surface stability of NCM811 cathode material because the TPPa-initiated POx-based CEI layer prevents electrolyte decomposition in the cell even at high temperatures.

Automated summary

In this study, the use of triphenyl phosphate as an electrolyte additive greatly improved the cycling performance of nickel-rich lithium nickel-cobalt-manganese oxide (NCM811) cathode material at high temperatures, by forming an effective cathode-electrolyte interphase (CEI) layer that suppressed electrolyte decomposition.