Studies on electrolyte additives for anode performance enhancement of lithium secondary batteries

Abstract

Lithium secondary batteries are now the key technologies for the portable electronic devices, and moreover, for the breakthrough in the energy crisis. Even though the energy density of lithium secondary batteries are impressively increased since the first commercialization of lithium ion batteries (LiBs) in 1991, people stall eager to use batteries with higher performances (i.e., higher capacity, higher voltage, higher power and higher safety). To achieve higher energy density of lithium secondary batteries, new chemistries of electrode for cells with higher capacities and higher operation voltages than current chemistries with graphite anode and LiCoO2 (lithium cobalt oxide) cathode are required. Especially, for anode, non-intercalating materials with higher capacities and low redox potentials such as lithium (Li, 3960 mAh/g, 0 V vs Li/Li+) and silicon (Si, 4200 mAh/g, 0.2 ~ 0.4 V vs Li/Li+) are highlighted as promising candidates for future lithium secondary battery applications. However, these high capacity materials have problems caused by large volume changes, side reactions with electrolyte during charge/discharge processes and so on which hinder the commercialization of lithium or silicon based electrodes. Some of these problems are caused by the improper electrode/electrolyte interfacial property. During the battery operation, electrolytes are decomposed chemically or electrochemically and form a kind of passivation layer on the electrode surface. This layer is called the solid-electrolyte interphase (SEI) layer and the property of SEI layer such as solvent penetration, mechanical stability, thermal stability, and lithium ion diffusivity critically governs the performance of electrode. Lithium and silicon electrodes are not exceptions: i) Side reactions of electrolytes with thermodynamically unstable lithium metal result in resistive and thick layer as cycle prolongs leading to increase in resistance of cells. ii) Volume changes of Si results in surfac...