Bi-layer lithium phosphorous oxynitride/aluminium substituted lithium lanthanum titanate as a promising solid electrolyte for long-life rechargeable lithium–oxygen batteries

Abstract

Lithium ion conducting membranes are indispensable for building lithium–air (oxygen) batteries employing aqueous and non-aqueous electrolytes for long-term operation. In this report, we present the high performance of non-aqueous lithium–air batteries, in which a bilayer lithium phosphorous oxynitride/aluminium substituted lithium lanthanum titanate solid electrolyte is employed as a protective layer for a lithium metal electrode and free carbon–manganese dioxide as the cathodic catalyst. Aluminium-doped lithium lanthanum titanate (A-LLTO) pellets were prepared using citrate-gel synthesis followed by pelletization and a sintering process. A thin lithium phosphorous oxynitride (LiPON) layer was then deposited on the A-LLTO using the sputtering method, which was used as a protective interlayer for separating A-LLTO ceramics from the Li metal electrode. With a high ionic conductivity of 2.25 × 10⁻⁴ S cm⁻¹ and a large electrochemical stability window of 0–5 V, the LiPON/A-LLTO ceramics showed promising feasibility as a stable solid electrolyte for application in Li–O₂ batteries. The aprotic Li–O₂ cell containing the Li metal electrode protected by LiPON/A-LLTO exhibited excellent charge–discharge cycling stability with a long life span of 128 cycles under the limited capacity mode of 1000 mA h g⁻¹. After the cycling test, the LiPON/A-LLTO ceramics retained a high ion conductivity of 1.65 × 10⁻⁴ S cm⁻¹. In addition, with the introduction of LiPON/A-LLTO, the Li dendrite growth and electrolyte decomposition are effectively suppressed.