3D current collector for stable lithium metal anode

Abstract

The lithium metal battery is one of the lightest battery systems with an extremely high theoretical specific capacity (3860 mAh g^-1), a low density (0.59 g cm^-3), and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode). However, for the past 40 years, lithium metal batteries have been investigated but remain unsuccessful in commercialization due to the low coulombic efficiency and the safety concerns accompanied by dendrite growth of lithium metal anode. Addressing the problems of the lithium metal anode is essential to realize the application of high energy battery systems including lithium sulfur and lithium air batteries. To optimize the electrochemical performance of lithium metal anode, two types of 3-dimensional (3D) current collector were designed. The first one is copper (Cu) based 3D current collector that was synthesized by first employing the chemical reaction between copper and ammonium ion, hydroxide ion to produce blanket of copper hydroxide nanowires on copper foam skeleton, then further dehydration and reduction. The 3D Cu current collector exhibited a high Coulombic efficiency (CE) above 97% for lithium stripping and plating after 400 cycles and a much lower dendrite formation. The improvement may be attributed to the increased surface area and the decreased areal current density during charge/discharge process suppressing the dendrite growth rate. The second one is carbon nanofiber (CNF) based current collector with two sides having different compositions. It was synthesized by electrospinning and magnetron sputtering. The freestanding CNF membrane was first obtained by simple electrospinning of polyacrylonitrile (PAN) and carbonization at 1000 ˚C. Then its two sides were sputtered with two components for certain time and depth. The upper side (facing the separator) was coated with non-conducive zinc oxide (ZnO) which can effectively prevent the lithium dendrite from further growth and the bottom side with highly conductive Cu layer, aiming to induce the lithium ion deposition. The CE performance was much enhanced by using this CNF based current collector and the cell assembled with lithium titanate (LTO) electrode revealed a reversible capacity of around 160 mAh g^-1 under 1C current density for 100 cycles. The dendrite forming phenomenon in the lithium anode surface was also alleviated.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology