Tzu-Yang Huang1,2,Bryan McCloskey1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2
Tzu-Yang Huang1,2,Bryan McCloskey1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2
Voltage hysteresis can significantly drag down the round-trip energy efficiency of a Li-ion battery cathode. For Li-excess cathode materials, coexisting transition-metal and oxygen redox makes it challenging to evaluate how each redox mechanism impacts voltage hysteresis. In this work, we re-designed conventional aqueous redox titration with the aid of mass spectrometry (MS) gas analyzer to quantify two coexisting solid-phase analytes, namely oxidized oxygen and Mn<sup>3+/4+</sup>, in a representative Li-excess cation-disordered rock salt — Li<sub>1.2</sub>Mn<sub>0.4</sub>Ti<sub>0.4</sub>O<sub>2</sub>(LMTO). Two MS-countable gas molecules evolve from two separate titrant-analyte reactions, which allows decoupling Mn and O redox capacities. As incremental redox capacities are quantitatively decoupled, each redox voltage hysteresis can be further evaluated through deconvoluted energy efficiency and overvoltage distribution, which unambiguously inform how different each redox mechanism contributes to the overall voltage hysteresis. Our results show promise of designing new analytical workflow to experimentally measure intermixed redox capacities and their round-trip energy efficiencies, even in a disordered material having complex local coordination environments.