Interface Engineering of Current Collector Using Resistive ALD-Grown Nanofilms for Fast Charging of Lithium Metal Batteries
Authors: Sanroman Gutierrez Kenzie Marie , Cui Yi , Bent Stacey F. 
Published: December 2024

Electrification of the transportation sector has been an important development in the global renewable energy transition. However, electric vehicle adoption has been hindered by concerns about the range from a full charge, as well as opposition to hours-long charging times. Thus, more energy-dense batteries that can withstand aggressive fast charging conditions are essential to the widespread adoption of electric vehicles. While lithium-ion batteries have been the staple for rechargeable products, including electric vehicles, they are approaching their theoretical energy density limits. Lithium metal batteries (LMB) present a solution to concerns about vehicle range since Li metal plates directly onto the Cu current collector, drastically improving the energy density.

Commercialization of the LMB has been limited due to a variety of degradation mechanisms, including the formation of high surface area filamentary lithium deposits, known as dendrites, at the anode and capacity loss due to repairing the fractured solid electrolyte interphase (SEI). Under fast charging conditions, the formation of dendrites is exacerbated because 1. high current densities pin the anode to high potentials, supporting the formation of small, high surface area lithium deposits and 2. entering the Sand’s time regime (when Li+ concentrations at the electrode drop to zero) confines Li plating to the tips of Li deposits. Additionally, fast charging conditions exacerbate the breakdown of the SEI by intensifying ion concentrations at low impedance fractures in the SEI.

In our work, we aim to make LMBs viable for fast charging conditions by growing resistive Al2O3 thin films via atomic layer deposition (ALD) on the Cu current collector using TMA and water. The deposited thin films, although resistive, contain defects of low resistance which serve as the sites of Li nucleation. These nucleation sites then act like ultramicroelectrodes and encourage radial diffusion of Li+,which in turn leads to the formation of low surface area, dense, planar Li deposits. Dense and low surface area Li morphology is known to be favorable as it reduces Li corrosion, as well as SEI fracturing due to volume expansion. ALD ensures the thickness is precisely varied to identify the thin film resistance at which favorable Li deposition morphology and SEI quality are best conserved under fast charging conditions. Scanning electron microscopy (SEM) results show that despite high current densities pinning the anode to high potentials, low surface area Li deposition morphology is preserved at current densities up to 20 mA/cm2
. Additionally, the resistive films slow down electron transfer to delay the onset of Sand’s time. X-ray photoelectron spectroscopy (XPS) also shows that the Al2O3 thin films promote higher incorporation of anionic species into the SEI than the bare Cu current collector control under fast charging conditions, a difference that we attribute to the presence of acidic sites on the Al2O3. Anion-derived SEIs are more homogeneous, strong, and robust. Collectively, these improvements in the SEI and Li properties lead to cells made with the Al2O3-coated current collectors having enhanced performance, including Coulombic efficiencies of >80% for three times as many charge/discharge cycles as the control at 5 mA/cm2.