Enhancing the high voltage interface compatibility of LiNi0.5Co0.2Mn0.3O2 in the succinonitrile-based electrolyte

Abstract

A stable electrolyte system with wide electrochemical window and excellent interface compatibility is the key to successfully obtaining higher power and energy density of lithium ion batteries. Here we report that cycle life and rate performance of LiNi0.5Co0.2Mn0.3O2 (NCM) at a high charge cutoff voltage of 4.7 V can be greatly extended by manipulating the electrode/electrolyte interphases with succinonitrile (SN) and fluoroethylene carbonate (FEC) simultaneously as solvents. Remarkably, NCM//Li cells can retain extraordinary capacity retention up to 73.6% after 100 stable cycles, which far surpasses the commercial electrolyte counterpart (35.5%). It also delivers a high discharge capacity of >80 mA h g−1 at 5 C, significantly higher than that of commercial electrolytes (20 mA h g−1). Meanwhile, the characteristics of interface layer on NCM are investigated in detail using scanning electron microscopy, transmission electron microscopy, electron diffraction images, X-ray diffraction, X-ray photoelectron spectroscopy with and without Ar ion etching technology, and electrochemical impedance spectroscopy. This is mainly attributed to a stable, uniform, N-containing and high ionic conductive electrolyte interphase layer on the surface of NCM positive material using this optimized electrolyte. So it reveals the importance of controlling electrode/electrolyte interphases through manipulation of electrolyte compositions, and opens a new avenue for developing NCM as high-capacity electrode materials for lithium ion batteries.