Surface Functionalization for a High-Performance Lithium Metal Anode

Abstract

Lithium-ion batteries (LIB) have been the backbone of the success of numerous electronics in our everyday lives. Nonetheless, the development of large-scale Energy Storage Systems (ESS) and Electric Vehicles (EV) now require battery systems with capacities that far surpass the current lithium-ion batteries. Lithium metal batteries (LMB) have been actively researched thanks to the lithium metal that is used as their anode. The lithium metal anode is considered as the ‘holy grail’ of anode materials due to its low density (0.54 g/cm3), low redox potential (-3.04 V vs SHE), and its high specific capacity(3860 mAh/g). However, the severe performance degradation due to the intrinsic characteristics of lithium metal prevents it from being utilized as a battery material despite its excellent properties. A great deal of the research aiming for a practical lithium metal anode targets the electrolyte yet does not consider how this would affect the cathode. Herein, an electrode of which its surface is modified using thermal treatment with silica (SiO2) and silicon nitride (Si3N4) as to negate performance damaging phenomenon and having no change to the electrolyte is proposed. The lithium metal anode modification is confined to the surface of the electrode thus having minimum influence on the cathode. Electrode surface characterization is carried out by SEM observation and XPS analysis revealing the SEI layer structure. Electrochemical performance evaluated using symmetrical cells reveal that modified electrodes show a significantly lower overpotential for over 1000 cycles at a current density of 1 mA/cm2. Kinetic properties were also evaluated through Tafel plots and the activation energies of each electrode. Full cell (NCM622 cathode) electrochemical evaluation reveals a capacity retention of over 75% at 700cycles, and an extremely high coulombic efficiency over 99.9% for the modified electrodes. Operando optical microscope observation of lithium plating on the surface of each electrode is also conducted to further confirm the modification’s effect on the property of the electrode. Overall, the modified electrodes show significantly enhanced performance and surface properties. This work proposes a simple method to produce surface modified lithium metal anodes based on thermal treatment for practical lithium metal batteries.