%0 Journal Article %A Tzu‐Yang Huang %A Zijian Cai %A Matthew J Crafton %A Lori A Kaufman %A Zachary M Konz %A Helen K Bergstrom %A Elyse A Kedzie %A Han‐Ming Hao %A Gerbrand Ceder %A Bryan D McCloskey %B Advanced Energy Materials %D 2023 %G eng %N 21 %R 10.1002/aenm.202300241 %T Quantitative Decoupling of Oxygen‐Redox and Manganese‐Redox Voltage Hysteresis in a Cation‐Disordered Rock Salt Cathode %U https://onlinelibrary.wiley.com/toc/16146840/13/21 %V 13 %8 06/2023 %! Advanced Energy Materials %X

Pronounced voltage hysteresis in Li-excess cathode materials is commonly thought to be associated with oxygen redox. However, these materials often possess overlapping oxygen and transition-metal redox, whose contributions to hysteresis between charge and discharge are challenging to distinguish. In this work, a two-step aqueous redox titration is developed with the aid of mass spectrometry (MS) to quantify oxidized lattice oxygen and Mn³⁺ /⁴⁺ redox in a representative Li-excess cation-disordered rock salt—Li_1.2Mn_0.4Ti_0.4O₂ (LMTO). Two MS-countable gas molecules evolve from two separate titrant-analyte reactions, thereby allowing Mn and O redox capacities to be decoupled. The decoupled O and Mn redox coulombic efficiencies are close to 100% for the LMTO cathode, indicating high charge-compensation reversibility. As incremental Mn and O redox capacities are quantitatively decoupled, each redox voltage hysteresis is further evaluated. Overall, LMTO voltage hysteresis arises not only from an intrinsic charge-discharge voltage mismatch related to O redox, but also from asymmetric Mn-redox overvoltages. The results reveal that O and Mn redox both contribute substantially to voltage hysteresis. This work further shows the potential of designing new analytical workflows to experimentally quantify key properties, even in a disordered material having complex local coordination environments.