Development of Next Generation DRX Cathodes through the Lenses of Electron Microscopes

Lithium-ion (Li-ion) batteries are crucial to technological advancement due to their remarkable energy density and lifespan. However, traditional cathode materials, mainly based on layered and spinel structures, rely on scarce and contentious resources like nickel (Ni) and cobalt (Co). Disordered rocksalt (DRX) materials have surfaced as a novel category of high-capacity, earth-abundant cathodes. Since the discovery of DRX materials, advanced electron microscopy has been essential in unraveling the microstructural complexities of DRX cathodes. This presentation will explore the fundamental insights that electron microscopy has contributed to the study of DRX cathode materials. From short-range ordering to high-entropy DRX materials, electron microscopy has provided significant insights into the DRX platform. After a brief overview of DRX progress, we will examine the development of high Mn-content large particle (1 μm) DRX materials, which seems to be facilitated by the material's transformation to a spinel-like (δ-phase). This phase exhibits partial disorder across multiple length scales, posing challenges for classical characterization techniques. We employ scanning electron nano diffraction (SEND) with a pixelated detector to investigate the phase transformation of DRX cathodes to the δ-phase during chemical delithiation. Our findings indicate that the δ-phase is a partially disordered spinel with transition metals (Mn and Ti) displaying 16c/16d order over short coherence lengths. Additionally, high-resolution HAADF-STEM imaging reveals the presence of antiphase boundaries, which separate nanoscale (3 nm) spinel domains. These atomic-level insights help to elucidate the superior performance of the large particle chemically delithiated DRX cathodes.