Anode-free sodium-ion batteries represent an intriguing alternative to current battery technologies due to their intrinsic high energy and power densities.¹ During the operation of Na-ion batteries, plating and stripping of sodium metal occurs in-situ on a substrate. The cathode material is the exclusive source of ions while an ad-hoc designed current collector functions as an anode. The current bottleneck of the technology is the unstable electrodeposition of Na metal on the current collector, which leads to dendrite formation, low coulombic efficiency, and therefore short lifetime during battery charge-discharge cycling.² In this study, we use molecular vapor deposition (MVD) as a scalable synthesis method to coat Cu foil with an amorphous Al₂O₃ layer. We then evaluate the impact of the thickness of the Al₂O₃ layer on plating and stripping in terms of coulombic efficiency, voltage hysteresis, cycle life, and morphology of the deposit. Furthermore, we examine factors to mitigate the thermodynamic barrier of nucleation and growth during the first few cycles. We demonstrate how we can maintain >99.98% coulombic efficiency over more than 1000 cycles at 0.5 mAh cm^-2 using 15 nm Al₂O₃ coated Cu in a half cell set up and in a full cell set up where Prussian blue is used as a cathode.

References:

1. Mazzali, F.; Orzech, M. W.; Adomkevicius, A.; Pisanu, A.; Malavasi, L.; Deganello, D.; Margadonna, S., Designing a High-Power Sodium-Ion Battery by in Situ Metal Plating. ACS Applied Energy Materials 2019, 2, (1), 344-353.
2. Ma, B.; Lee, Y.; Bai, P., Dynamic Interfacial Stability Confirmed by Microscopic Optical Operando Experiments Enables High-Retention-Rate Anode-Free Na Metal Full Cells. Advanced Science 2021, 8, (12), 2005006.