Interface Engineering of Thin-Film Lithium Phosphorus Oxynitride Electrolyte by Appropriate Oxygen Plasma Treatment...

The interfacial incompatibility between lithium phosphorus oxynitride (LiPON) and anode greatly deteriorates the performance of thin-film all-solid-state supercapacitors (ASSSCs). This article investigates oxygen plasma treatment to improve the interface. Through appropriate plasma treatment, a Li₂O/Li₃PO₄ composite layer is formed by replacing nitrogen with oxygen at the LiPON surface owing to strong reactivity of oxygen plasma. This composite layer inherits the merits of both Li₂O (including good mechanical strength and ultralow electrical conductivity) and Li₃PO₄ (including good chemical stability and relatively high ionic conductivity), and thus is quite desirable for service as a LiPON/anode buffer layer with excellent chemical and mechanical stability, high ionic conductivity and low electrical conductivity. Consequently, the corresponding plasma-treated ASSSC displays much better electrochemical performance than the no-treated one in terms of its higher specific capacitance (≈15.4 mF cm^-2 at 0.5 µA cm^-2), better cycling stability (≈95.1% of the retained capacity after 15 000 cycles) and lower self-discharge rate (66.4% of the retained voltage after 20 h). The plasma-treated one also shows both excellent flexible and electrochromic characteristics and demonstrates the ability of self-adaptive temperature adjustment for smart window applications.