Unraveling Nano-Engineered Microstructure in Large Particle DRX Cathode Particles

Lithium-ion (Li-ion) batteries are pivotal to technological progress, thanks to their impressive energy density and longevity. However, conventional cathode materials, which predominantly rely on layered and spinel structures, depend on limited and controversial resources such as nickel (Ni) and cobalt (Co). Disordered rocksalt (DRX) materials have emerged as a new class of high-capacity earth-abundant cathodes. The remarkable performance of high Mn-content large particle (~1 μm) DRX materials appears to be enabled by a transformation of the material to a spinel-like (δ-phase). This phase shows partial disorder at multiple length scales making classical characterization techniques challenging. In this work, we use scanning electron nano diffraction (SEND) with the help of a pixelated detector to understand the phase transformation of the DRX cathodes to the δ-phase upon chemical delithiation. We find the δ-phase to be a partially disordered spinel with the transition metals (Mn and Ti) showing 16c/16d order over a short coherence length. Furthermore, using high-resolution HAADF-STEM imaging, we observe the existence of the antiphase boundaries that separate nanoscale (~3 nm) spinel domains. The atomic insights help to explain the superior performance of the large particle chemically delithiated DRX cathodes. Through this study, we will showcase how correlative microscopy can solve exciting material problems across different length scales.