Unraveling manganese dissolution/deposition mechanisms on the negative electrode in lithium ion batteries

Abstract

The structure, chemistry, and spatial distribution of Mn-bearing nanoparticles dissolved from the Li_1.05Mn₂O₄ cathode during accelerated electrochemical cycling tests at 55 °C and deposited within the solid electrolyte interphase (SEI) are directly characterized through HRTEM imaging and XPS. Here we use air protection and vacuum transfer systems to transport cycled electrodes for imaging and analytical characterization. From HRTEM imaging, we find that a band of individual metallic Mn nanoparticles forms locally at the SEI/graphite interface while the internal and outermost layer of the SEI contains a mixture of LiF and MnF₂ nanoparticles, which is confirmed with XPS. Based on our experimental findings we propose a new interpretation of how Mn is reduced from the cathode and how metallic Mn and Mn-bearing nanoparticles form within the SEI during electrochemical cycling.