Adiponitrile as Lithium-Ion Battery Electrolyte Additive: A Positive and Peculiar Effect on High-Voltage Systems

Due to its novel properties and unique utility, nitriles are attractive as an additive to lithium-ion battery electrolytes. However, when it is applied to high-voltage batteries, the effects and mechanisms are not clearly explained. In particular, we need to explore its mechanism. In this work, adiponitrile (ADN) has been employed as the additive in the electrolyte 1 M LiPF6-EC/DMC/EMC (1:1:1 by weight). The cycling tests for LiNi0.5Mn1.5O4 half-cells after 150 cycles at 1 C (1 C = 147 mA/g) from 3.5 to 5.0 V show that adding 1 wt % ADN into the electrolyte can improve the capacity retention of the battery from 69.9% to 84.4%. Moreover, the rate performance can also be significantly improved. Based on the EIS measurement, a little ADN can stabilize the interfacial impedance avoiding a possible increase during cycling. To further clarify its mechanism, XRD, SEM, XPS measurements, and DFT calculations have been conducted, which display that when adding it into the liquid electrolyte, the cathode particles maintain good spinel shape and the molecule groups of ADN-S tend to be oxidized primarily to form a very thin film on the cathode surface. All these results indicate that ADN has potential applications in high performance electrolytes for storage systems.