Effects of alkali carbonate additives and solvent composition on the electrochemical performances of LiNi0.5Mn1.5O4 cathode for lithium-ion batteries

Abstract

LiNi0.5Mn1.5O4 (LNMO) is a promising and attractive cathode material due to its high operating voltage, low cost and reasonable capacity. However, the stability issue of electrolytes decomposition under the high operating voltage remains a major hurdle to its wide use. In this study, two approaches are tried to address this problem. In the first place, alkali carbonates including CaCO3, MgCO3, and Li2CO3 were employed as an electrolyte and electrode additives. It is revealed that CaCO3 as an electrode and electrolyte additive greatly improves the cycle performances at 25 oC and 55 oC and self-discharge behavior at 60 oC, which is ascribed to the HF scavenging effect of CaCO3. The surface of the LNMO electrode after electrochemical cycling is analyzed by X-ray photoelectron spectroscopy (XPS), and the HF scavenging effect of alkali carbonates was verified by cyclic voltammetry (CV) analysis. Second, the effects of the type of the linear carbonates (LC: DMC, DEC, EMC) in 1 M LiPF6 EC/LC (3/7, v/v) are investigated. It is found that the LNMO cells with EC/DMC exhibits superior cyclability and coulombic efficiency at 25 oC and 55 oC than those with EC/EMC and EC/DEC. The cells with EC/DMC also show better self-discharge performance than other compositions. The improved electrochemical performances in EC/DMC are attributed to the diminished HF formation compared to the others. ⓒ 2015 DGIST