Saturday, February 10, 2018

Spatial atomic layer deposition for coating flexible porous Li-ion battery electrodes

Here is important step forward in fast roll to roll processing of Li-battery electrodes using fast spatial ALD from CU Boulder, Colorado. Spatial ALD (SALD) is based on separating the precursors and inert gas purges in space rather than in time and therefore the deposition rates up to a hundred times faster are achievable. SALD can be performed at ambient atmosphere and therefore is a cheaper technology due to less need of expensive vacuum technology compared to conventional low pressure ALD.

High speed and low cost of ownership opens the door to high volume manufacturing of bulk quantities of energy materials for applications including solar energy, energy storage, or smart windows. Previously ALD Nanosolutions has announced a Spatial ALD technology for conformal encapsulation of ALD on powder material like for instance Li-battery cathode powder (LINK). A good overview of Spatial ALD for energy applications is this review paper by David Muñoz-Rojas et al: "Spatial Atomic Layer Deposition (SALD), an emerging tool for energy materials. Application to new-generation photovoltaic devices and transparent conductive materials" https://doi.org/10.1016/j.crhy.2017.09.004 [OPEN ACCESS]

Please find the JVSTA abstract below for the recent article form Boulder:

Spatial atomic layer deposition for coating flexible porous Li-ion battery electrodes

Alexander S. Yersak, Kashish Sharma, Jasmine M. Wallas, Arrelaine A. Dameron, Xuemin Li, Yongan Yang Katherine E. Hurst, Chunmei Ban, Robert C. Tenent, and Steven M. George

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 36, 01A123 (2018); https://doi.org/10.1116/1.5006670

Abstract: Ultrathin atomic layer deposition (ALD) coatings on the electrodes of Li-ion batteries can enhance the capacity stability of the Li-ion batteries. To commercialize ALD for Li-ion battery production, spatial ALD is needed to decrease coating times and provide a coating process compatible with continuous roll-to-roll (R2R) processing. The porous electrodes of Li-ion batteries provide a special challenge because higher reactant exposures are needed for spatial ALD in porous substrates. This work utilized a modular rotating cylinder spatial ALD reactor operating at rotation speeds up to 200 revolutions/min (RPM) and substrate speeds up to 200 m/min. The conditions for spatial ALD were adjusted to coat flexible porous substrates. The reactor was initially used to characterize spatial Al2O3 and ZnO ALD on flat, flexible metalized polyethylene terephthalate foils. These studies showed that slower rotation speeds and spacers between the precursor module and the two adjacent pumping modules could significantly increase the reactant exposure. The modular rotating cylinder reactor was then used to coat flexible, model porous anodic aluminum oxide (AAO) membranes. The uniformity of the ZnO ALD coatings on the porous AAO membranes was dependent on the aspect ratio of the pores and the reactant exposures. Larger reactant exposures led to better uniformity in the pores with higher aspect ratios. The reactant exposures were increased by adding spacers between the precursor module and the two adjacent pumping modules. The modular rotating cylinder reactor was also employed for Al2O3 ALD on porous LiCoO2 (LCO) battery electrodes. Uniform Al coverages were obtained using spacers between the precursor module and the two adjacent pumping modules at rotation speeds of 25 and 50 RPM. The LCO electrodes had a thickness of ∼49 μm and pores with aspect ratios of ∼12–25. Coin cells were then constructed using the ALD-coated LCO electrodes and were tested to determine their battery performance. The capacity of the Al2O3 ALD-coated LCO battery electrodes was measured versus the number of charge-discharge cycles. Both temporal and spatial ALD processing methods led to higher capacity stability compared with uncoated LCO battery electrodes. The results for improved battery performance were comparable for temporal and spatial ALD-coated electrodes. The next steps are also presented for scale-up to R2R spatial ALD using the modular rotating cylinder reactor.