Development of Electrolytes for Improving Electrochemical Performances of High-voltage LiNi0.5Mn1.5O4.

Abstract

Currently there is an urgent need to maximize the energy density of lithium ion batteries (LIBs). LiNi0.5Mn1.5O4 (LNMO) is a promising candidate for the high-energy LIBs due to its high operating voltage, low price, and reasonable capacity. However, LNMO suffers from anodic decomposition of the electrolyte under high-voltage operation, leading to severe capacity fading. Here, we examine the effects of linear carbonates (LC: DMC, DEC, and EMC) in 1 M LiPF6 EC/LC (3/7, v/v) on LNMO/graphite, LNMO/Li, and graphite/Li cells. We also investigate LNMO symmetric cell test in cycle at 60 oC because the use of symmetric cells complementarily suggests that transition metal dissolution is mainly responsible for the LNMO/electrolyte interface degradation. The LNMO cells with EC/DMC show better cyclability and coulombic efficiency at 25 oC, 55 oC and 60 oC than those with EC/EMC and EC/DEC. Also, the cells with EC/DMC exhibit superior self-discharge suppression at 60 oC to other compositions. The improved performances in the cells with EC/DMC are attributed to diminished HF formation compared to the others, which is evidenced by both HF titration and surface analysis of LNMO using X-ray photoelectron spectroscopy (XPS). Also, through LSV analysis, Oxidation stability of EC/DMC is higher than EC/EMC and EC/DEC. ⓒ 2017 DGIST