Electrochemistry and Cycling Dependent Structural Analysis of High and Low Mn Based Disordered Rocksalt Cathodes for Lithium-Ion Batteries

Cobalt-free cation-disordered rocksalt (DRX) materials have recently emerged as a class of next-generation high-capacity cathodes for lithium-ion batteries which can incorporate earth abundant, low-cost elements such as Mn and Ti. One of the reasons for their enhanced performance is due to the presence of percolating lithium rich clusters which enable facile lithium transport. Structural phenomena such as cation short-range ordering and phase transformations in DRX materials at small length scales are known to dramatically impact local Li clusters and hence the Li diffusion channels, Li transport, and hence electrochemical properties of DRX cathodes. Recently, Mn-rich DRX materials (Mn/Ti ratio >1) have shown to phase transform upon extended cycling, resulting in improved capacity and rate performance in these materials. Therefore, it is crucial to understand the nature of the DRX structure as a function of cycling to maximize the performance in DRX materials. Interestingly, these phase changes are not observed in DRX with a low Mn content (Mn/Ti ratio <1). Keeping this in mind, the goal of this research is to understand the structural changes during electrochemical cycling and investigate the differences in electrochemical properties (Li ion transport, rate capability, cycling) in high and low Mn DRX cathodes. In addition to the electrochemical characterization, a suite of material characterization techniques such as X-ray diffraction, X-ray absorption Spectroscopy, and pair distribution function analysis, are used to perform in depth cycling dependent structural analysis and compared between the high Mn and low Mn DRX compositions. Overall, this study and poster presentation will discuss key scientific insights related to the cycling induced phase transformation and electrochemical performance of Mn-Ti based DRX cathodes. Based on these results, further investigations into synthetic manipulation of the DRX structure can be performed to utilize the full potential of the newly formed phase upon cycling.