Electrochemical performance enhancement by the salt-type electrolyte additive, lithium difluoro(oxalato)borate, in high-voltage lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) are the energy devices that the chemical energy is converted to electrical energy by electrochemical reduction-oxidation reaction and are mainly composed of four materials including cathode, anode, separator and electrolyte. Lithium is well known as light metal in natural condition and have the lowest reduction potential. LIBs are considered to be one of the promising energy storage system due to high energy density and high power density compared to different batteries. LIBs have rapidly grown with the development of portable electronic devices. The interest in LIBs has considerably increased and LIBs have improved the performance of batteries for years. For the application of electrical vehicles (EV), the demand on LIBs with a high capacity and energy density has increased. A key way to increase the capacity of LIBs is the development of electrode with high capacity and power density. Currently, LiCoO2 cathode is the most commercially available electrode but is not suitable for EV due to low energy density. To increase the energy1 density for lithium-ion batteries, one of candidates, Li-rich cathodes have a large capacity (> 200 mAh g-1) and high operating voltage (~4.6 V). Despite of its high capacity, several challenges such as long cyclability of batteries hinder for Li-rich cathode to be commercialized for Li-ion batteries. To resolve related challenges, there are various solution including elemental doping, coating, blending materials and electrolyte additives. In this study, we demonstrate that LiDFOB, used as a salt-type additive, effectively preserves the electrochemical properties of Li-rich cathodes in half-cells and full cells coupled with graphite anodes and allows fast charge transport at the interface between the electrode and electrolyte. In addition, the surface chemistries and morphologies of Li-rich cathodes and graphite anodes cycled in electrolytes with and without 1% LiDFOB were examined by means of ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).