Elucidating the Mechanism Involved in the Performance Improvement of Lithium‐Ion Transition Metal Oxide Battery by Conducting Polymer

Abstract Surface treatments with conducting polymers are effective in ameliorating charge capacities and cycling performances for a wide range of lithium‐ion batteries such as Li‐layered transition metal oxide, Li‐sulfur, and Li‐air batteries. So far, however, very little is known about the key process directly involved with the improvement of cell performance and stability. The present study examines how a conducting polymer can contribute to charge capacity enhancement, employing poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) coating on the lithium‐layered transition metal oxide cathode. The property of the electrode interface layer is studied on the basis of the local atomic environments. The conducting polymer not only hinders the formation of LiF, carbonates, and semicarbonates compounds but also renders the nature of the solid‐electrolyte interphase layer formed during electrochemical cycles. Furthermore, it inhibits the dissolution of the active material into the electrolyte and preserves the initial atomic states including the active material bulk. The coating enables good consistency in the local atomic environment with depth at the electrode interface, which in turn impedes the phase mismatch resulting from the surface reconstruction on the layered oxide electrode. This further mitigates the phase transformation of the active material, resulting in a lower voltage decay on charge–discharge.