| AVS 61st International Symposium & Exhibition | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM+EN+TF-WeA |
| Session: | Thin Films and Materials for Energy Storage |
| Presenter: | Chuan-Fu Lin, University of Maryland, College Park |
| Authors: | C.F. Lin, University of Maryland, College Park A.C. Kozen, University of Maryland, College Park A.J. Pearse, University of Maryland, College Park M. Noked, University of Maryland, College Park M.A. Schroeder, University of Maryland, College Park S.B. Lee, University of Maryland, College Park G.W. Rubloff, University of Maryland, College Park |
| Correspondent: | Click to Email |
Rechargeable Li-metal anode batteries could be considered the holy grail of energy storage systems because Li offers extremely high theoretical specific capacity (3860 mAh/g), low density (0.59 g/cm3), and the lowest negative electrochemical potential (−3.040 V vs. standard hydrogen electrode). However, Li is thermodynamically unstable with organic solvents, inviting serious capacity degradation as well as safety concerns such as Li dendrite growth. The prognosis for Li anodes would be profoundly enhanced for next generation batteries if suitable passivation schemes could be developed to protect Li anodes without significantly reducing ion transport between Li and electrolyte.
In our laboratory, we use atomic layer deposition (ALD) to precisely deposit very thin layer of aluminum oxide (Al2O3) on Li foils, using glove box and UHV environments to avoid air exposure while depositing passivation layers on the Li metal surface. We then characterize the surface morphology of the passivated Li by AFM at varying stages of electrochemical reaction and as a function of time and film thickness. We observed the growth of defects on ALD-passivated Li metal surface, decorated by AFM structures indicative of localized electrochemical reactions. The resulting defect density decreased as the film thickness increased.
For thinner ALD protection layers, EC-AFM showed bubble-like structures decorating the steps and boundaries of ALD/Li metal surface in electrochemical system, suggesting mechanisms associated with volatile products. While thin ALD layers suppress charge transfer processes which lead to electrolyte decomposition and formation of solid electrolyte interphase (SEI) [1-2], defects in the ALD passivation layer may cause localized SEI formation, which in turn involves volatile products (e.g., C2H4, CO). Alternatively, trace H2O in the propylene carbonate electrolyte may react with Li metal through pinholes in the ALD layer, leading to LiOH and volatile H2 products. We are working to differentiate between these by applying in-situ mass spectroscopy to monitor the gas formation in the cell as a function of controlled water content and ALD film thickness. The identification of passivation layer degradation mechanisms and the development of robust approaches to metal anode protection have profound benefit to a variety of beyond-Li-ion batteries.
References:
1. Kevin Leung, J. Phys. Chem. C, 2012, 117, 1539-1547.
2. Kevin Leung et al., JACS, 2011, 133, 14741-14754.