Atomic Layer Deposition of Aluminum Phosphorus Oxynitride and Its Application as a Passivation Layer on Aluminum Metal Anode

Aqueous aluminum (Al) batteries are an attractive energy storage technology due to the high theoretical capacity of Al, low reduction potential, low cost, and environmental friendliness. However, the practical application of aqueous Al batteries has been hindered by aggressive parasitic reactions, such as Al corrosion, at the Al and aqueous electrolyte interface. For the first time, this work developed aluminum phosphorus oxynitride (AlPON) by plasma-enhanced atomic layer deposition (PEALD) and applied it to suppress side reactions at the Al and electrolyte interface. The AlPON is obtained by PEALD in a temperature range of 100-180 °C using trimethylaluminum, water, tris(dimethylamino)phosphine, and plasma oxygen as precursors. It is noteworthy that the doubly and triply valent N environment (P-N = P and P- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>N</mml:mi> <mml:mrow><mml:mo>-</mml:mo> <mml:mi>P</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mi>P</mml:mi></mml:mrow> </mml:msubsup> <mml:annotation>${\mathrm{N}}_{ - {\mathrm{P}}}^{ - {\mathrm{P}}}$</mml:annotation></mml:semantics> </mml:math> ) in AlPON is disclosed by X-ray photoelectron spectroscopy and synchrotron radiation analysis. The growth rate and composition of AlPON exhibits a strong dependence on the deposition temperature, and therefore, a proposed growth mechanism for AlPON is identified. More importantly, electrochemical evaluation through Tafel curves and electrochemical impedance spectroscopy in the Al|Al symmetric cells revealed that the AlPON coating significantly reduced the self-corrosion of the Al metal anode and improve its (electro-)chemical stability in the acidic environment of 1 M Al(OTf)₃ aqueous electrolyte. It is expected that the AlPON-coated Al can be used as an anode for aqueous Al-ion batteries.