Speciation of Transition Metal Dissolution in Electrolyte from Common Cathode Materials

Abstract

Significant capacity loss has been observed across extended cycling of lithium-ion batteries to high temperatures and high voltages. This occurs due to transition metal dissolution from the high voltage spinel or layered oxide cathode material, ion migration through the electrolyte, and deposition on the solid-electrolyte interphase (SEI) on the anode. While much research has been done to track the oxidation state of the transition metal in the cathode material or deposited on the anode, there have been mixed reports on the chemical state of the transition metal ions dissolved in the electrolyte depending on the type of cathode used. X-ray absorption near edge spectroscopy (XANES) was performed on electrolytes extracted from full cells built with four different cathode materials that were cycled at either high or standard voltages to determine the chemical state of Mn and Ni in solution. Inductively coupled plasma-mass spectrometry (ICP-MS) was performed on the anodes from these cells to determine the concentration of deposited metal ions.