Anchored Mediator Enabling Shuttle‐Free Redox Mediation in Lithium‐Oxygen Batteries

• Published in: Angewandte Chemie International Edition Vol. 59; no. 13; pp. 5376 - 5380
• Main Authors: Ko, Youngmin, Park, Hyunji, Lee, Kyunam, Kim, Sung Joo, Park, Hyeokjun, Bae, Youngjoon, Kim, Jihyeon, Park, Soo Young, Kwon, Ji Eon, Kang, Kisuk
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 23-03-2020
• Edition: International ed. in English
• Subjects: Anchoring; Batteries; Charge transfer; Charge transport; Current carriers; energy conversion; Lithium; lithium-oxygen batteries; Oxygen; Polymers; Rechargeable batteries; redox chemistry; redox mediator; shuttle phenomena; lithium-oxygen batteries; energy conversion; redox mediator; shuttle phenomena; redox chemistry
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201916682

Redox mediators (RMs) are considered an effective countermeasure to reduce the large polarization in lithium‐oxygen batteries. Nevertheless, achieving sufficient enhancement of the cyclability is limited by the trade‐offs of freely mobile RMs, which are beneficial for charge transport but also trigger the shuttling phenomenon. Here, we successfully decoupled the charge‐carrying redox property of RMs and shuttling phenomenon by anchoring the RMs in polymer form, where physical RM migration was replaced by charge transfer along polymer chains. Using PTMA (poly(2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐4‐yl methacrylate)) as a polymer model system based on the well‐known RM tetramethylpiperidinyloxyl (TEMPO), it is demonstrated that PTMA can function as stationary RM, preserving the redox activity of TEMPO. The efficiency of RM‐mediated Li2O2 decomposition remains remarkably stable without the consumption of oxidized RMs or degradation of the lithium anode, resulting in an improved performance of the lithium‐oxygen cell.
The shuttling phenomenon is the most severe drawback of redox mediators (RMs) in lithium‐oxygen batteries, caused by the freely mobile nature of RMs. The shuttle effect was eliminated by anchoring RMs on the air electrode in form of a polymer. Successful prevention of the shuttle effect results in a remarkable improvement of the lithium‐oxygen cell‐performance.