Design of Highly Stable Lithium Metal Batteries for Next Generation Energy Storage System

Abstract

Since Paris agreement in 2015, environmental regulation on fossil fuel energy has been reinforced, resulting more attention to renewable energy and storage devices for such energy. Especially, the electric vehicle (EV) market would be estimated to grow more than 100 times bigger than present. However, batteries, key components of EV, is still far away for commercial popularization. Therefore, the demands for high energy density batteries to realize long distance driving have been increased for long-distance driving EV. There are several candidates for high energy density such as Si, Ge, Sn and Li for anodes materials. Especially, lithium metal batteries (LMBs) which utilized metallic Li for anode instead of intercalation graphite is taken much attention due to the high theoretical capacity (3860 mAh g-1) and lowest electrochemical potential (-3.04 V vs SHE). However, Li dendrite growths caused by uneven Li plating due to the heterogenous solid electrolyte interphase (SEI) result in low Coulombic efficiency, increase of concentration polarization and eventually short-circuit, and finally impeding practical application of LMBs. Here in, we introduce two strategies for effective Li dendrite control. Firstly, we prepared covalently bonded inorganic filler combined gel-polymer electrolyte for enhanced mechanical properties. We synthesized vinyl group modified silica nanoparticles and direct covalent bond between vinyl modified silica and acrylate monomer (ETPTA) constructs mechanically enhanced polymer network. Because we adopted gel-polymer electrolyte system, relatively sufficient basic electrochemical properties such as ionic conductivity and Li-ion transference numbers. Not only this, in-situ crosslinking also improved compatibility between electrodes and gel-polymer electrolyte. Furthermore, we observed effective suppression by SEM analysis and it finally resulted in improved cyclability of Li/Li symmetric and Li/NCM811 full-cells Secondly, ferroelectric ceramic/polymer combined artificial layer was established on Cu substrate. The goals of this artificial layer were developing Li-ion migration favorable conditions by ferroelectric BaTiO3 and adopting volume change during consecutive cycling. This artificial layer was prepared by spin coating and physical rubbing, and fairly uniform BaTiO3 monolayer was observed by SEM analysis. Considering voltage profiles and asymmetric cycle results of series of samples demonstrated the effect of BaTiO3 but the higher overpotential still accelerate degradation of the cell performance The morphology of this artificial layer after cycling was most superior compared with pristine and SIS only coated Cu. Thus, it is considered that the BaTiO3 is helpful to improving performances but additional analysis and further studies are required to maximize effect of BaTiO3.