• Energy Research

AbstractEarth-abundant cathode materials are urgently needed to enable scaling of the Li-ion industry to multiply terawatt hours of annual production, necessitating reconsideration of how good cathode materials can be obtained. Irreversible transition metal migration and phase transformations in Li-ion cathodes are typically believed to be detrimental because they may trigger voltage hysteresis, poor kinetics and capacity degradation. Here we challenge this conventional consensus by reporting an unusual phase transformation from disordered Li- and Mn-rich rock salts to a new phase (named δ), which displays partial spinel-like ordering with short coherence length and exhibits high energy density and rate capability. Unlike other Mn-based cathodes, the δ phase exhibits almost no voltage fade upon cycling. We identify the driving force and kinetics of this in situ cathode formation and establish design guidelines for Li- and Mn-rich compositions that combine high energy density, high rate capability and good cyclability, thereby enabling Mn-based energy storage.

Cation-disordered rocksalt oxides and oxyfluorides are promising high energy density lithium-ion cathodes, yet require a detailed understanding of the impact of disorder and short-range order on the structural and electrochemical properties.

Sodium-ion batteries (SIBs) offer a sustainable alternative to lithium-ion batteries but face cathode instability. This work emphasizes the low state of charge phase transition and shows improved cycling performance via calcium substitution.

Using an operando optical scattering technique, we identify markedly asymmetric Li-ion flux in aged single crystalline NMC cathodes, primarily caused by an uneven growth of rocksalt phase across the particle surface.

Design rules for high capacity disordered rocksalt Li-ion cathodes applied to the Li–Mn–V–O–F system.