Electrode interface modification of advanced lithium secondary batteries for improving cycle performance

Abstract

As the demand for mobile electronic devices has been increased, the energy storage system has also been gradually increased which based on lithium ion batteries (LIBs). In the past, energy storage devices were based on primary cells, but LIBs have been used due to the growing demand and availability of secondary batteries that can be continuously charge and discharge. Therefore, the LIBs have been commercialized from small size such as earphone and cellular phone to large size of battery mounted on automobile or energy storage system (ESS). Especially, the batteries used for mobile devices, are required to have light weight and small volume for convenience. Furthermore, the plug-in electric vehicles are required long runs on a single charge, so the batteries used need to be small and light. However, the commercialized LIBs have less than gravimetric energy density of 150Wh/kg and volumetric energy density of 250Wh/L that this energy density is can only drive a car 400km on a single charge. The limitation of increasing energy density of LIBs is due to the graphite anode material energy density and the metal oxide cathode material which are LCO, LMO, NCM. The capacity of graphite which is 372mAh/g is not enough for satisfying the developing high energy density of battery. For overcoming the limitation of graphite anode capacity, the Li-metal anode has been got a great attention due to its high capacity of 3860mAh/g and low redox potential (3.04V vs. standard hydrogen electrode). However, the Li-metal has some obstacles for using anode instead of graphite, such as Li dendritic growth, low coulombic efficiency that originated from the high reactivity of Li-metal toward liquid electrolyte. These unavoidable irreversible reaction between Li-metal and electrolyte is came from the lowest redox potential of Li-metal that a solid electrolyte interphase (SEI) layer is naturally created at the interphase. For design a high coulombic efficiency of Li-metal battery, formation of stable SEI layer is significant due to the severe volumetric change of Li-metal. A stable SEI interface design is important for battery designs with higher coulombic efficiency by inducing a uniform lithium ion flux and suppressing side reactions with the electrolyte. In this thesis, for interfacial stabilization of lithium metal anode, fluoroethylene carbonate electrolyte is considered for high performance Li/LCO batteries in Chapter 1. And silicon dioxide additive is studied for inducing uniform Li deposit and inducing stable SEI layer for Li-metal in Chapter 2. Furthermore, a single ion conductive organic and inorganic composite protective layer is used for sustaining stable SEI layer on Li-metal in Chapter 3.