Investigation of New Electrolyte Additives for Improvement of Nickel-Rich Cathode Materials at High-Voltage in Lithium Ion Batteries

Abstract

The continuous optimization of lithium ion batteries regarding the energy density, cycle life and safety has enabled their widespread application various fields, such as for electric vehicles. To satisfy the ever-increasing demands on both high gravimetric and volumetric energy density, high voltage and high capacity materials are being intensively studied. Promising candidates are the Ni-rich layered LiNixCoYMn1-x-yO2 materials. High Ni content LiNixCoyMn1-x-yO2 materials are attracting more attention in the last years due to their high specific capacity. Compared to the other commercial cathode materials, e.g. LiFePO4, LiCoO2 and Li-rich materials, the high Ni content LiNixCoyMn1-x-yO2 materials such as LiNi0.5Co0.2Mn0.3O2 (NMC-532) possess high specific capacity ca. 200 mAh g-1 at a cut-off potential of 4.6 V vs. Li/Li+.(1) However, the oxidative decomposition of conventional carbonate-based electrolytes at high voltages ( > 4.5 V vs. Li/Li+) and the deterioration of the active material particles result in rapid capacity fading. Different strategies are known to improve the cycle life of the high voltage cathode material NMC-532. One opportunity is to protect the cathode surface by inorganic coatings. Su et al. demonstrated the use of an Al203 coating which resulted in a significant improvement of the cycle life of NMC-532 by minimizing the structural transformation (2). A further option to improve the cycle life of NMC-532 is to use electrolyte additives (3). On the basis that the added additive decomposed prior to the electrolyte components, a cathode electrolyte interface (CEI) layer is formed on the cathode particles. This CEI layer on the cathode can prevent the electrochemical and chemical oxidation of the electrolyte. In this work, we present the combination of both an inorganic coating and the use of electrolyte additives to significantly improve the cycle life of NMC-532/graphite LIB full cells at 4.6 V vs. Li/Li+.