Mitigating electro-chemo-mechanical failures enables nearly all-active-material Ni- and Co-free disordered rock-salt cathodes for Li-ion batteries.

Disordered rock-salt oxides and oxyfluorides are promising positive electrode materials for high-performance lithium-ion batteries free of nickel and cobalt. However, conventional synthesis methods rely on post-synthesis pulverization to achieve cycling-appropriate particle sizes, offering limited control over particle microstructure and crystallinity. This accelerates degradation and complicates secondary particle processing. Here we present a synthesis strategy that enhances nucleation while suppressing particle growth and agglomeration across various disordered rock-salt compositions, including lithium–manganese–titanium oxide, lithium–manganese–niobium oxide, and lithium–nickel–titanium oxide systems. Applied to Li_1.2Mn_0.4Ti_0.4O₂, this method yields highly crystalline, well-dispersed sub-200 nm particles that form homogeneous electrode films with stable cycling behavior. Tested in cells with lithium metal as the counter electrode, these electrodes deliver ~200 mAh/g with 85% capacity retention relative to the first cycle after 100 cycles (20 mA/g, 1.5–4.8 V), and an average discharge voltage loss of 4.8 mV per cycle, compared to 38.6% retention and 7.5 mV loss per cycle for electrodes derived from pulverized solid-state particles. This approach suggests a route to enhance the performance and durability of disordered rock-salt electrodes for sustainable lithium-ion batteries.

The pursuit of high‐performance and cost‐effective Li‐ion batteries emphasizes the need for cathode materials composed of abundant elements, such as Fe. Disordered rock‐salt (DRX) cathode materials, known for their high compositional flexibility, offer a unique opportunity in this regard. However, Fe‐rich DRX (Fe‐DRX) cathodes, potentially the most cost‐effective among all DRXs, have seen limited research interest due to their comparatively restrained performance. This limitation stems from the inaccessibility of the Fe³⁺/Fe⁴⁺ redox in the DRX structure, prompting the need for redox engineering to enable Fe‐DRXs with readily utilizable redox mechanisms. In this work, utilizing both experiments and theoretical study, reversible Fe²⁺/Fe³⁺ redox in an Fe²⁺‐based DRX cathode is demonstrated. This design minimizes the reliance on O redox, resulting in a high capacity (≈290 mAh g⁻¹) and energy density (≈700 Wh kg⁻¹), as opposed to an Fe³⁺‐based DRX operating on the limited Fe³⁺/Fe⁴⁺ redox and extensive O redox upon cycling. Overall, the study introduces a novel approach to redox engineering to develop low‐cost, high‐performing Fe‐rich cathode materials.