Isovolumetric design of layered oxide cathodes for high-rate sodium ion batteries: A multi-scale predictive approach

The widespread adoption of sodium-ion batteries (SIBs) is hindered by the absence of cathode materials that simultaneously deliver high energy density, rapid charge-discharge kinetics, and long-term structural stability. Layered oxide cathodes for sodium-ion batteries often suffer from sodiation-induced lattice strain and declining electronic conductivity during deep desodiation. Conventional Single Particle Models (SPM) typically overestimate rate capabilities by neglecting the coupling between mechanical stress and electronic transport. Here, we develop a first-principles-informed Modified Single Particle Model (MSPM) that integrates DFT calculations to unify chemo-mechanical stress feedback and stoichiometry-dependent electronic barriers within a Nernst–Planck transport framework. Our results reveal a critical trade-off between theoretical energy density and structural stability. While high Mn concentrations NaNb 0.375 Mn 0.625 O 2 maximize capacity, they trigger severe anisotropic strain and surface stresses exceeding ~664 MPa, creating a mechanochemical barrier that limits high-rate kinetics. Conversely, the NaNb 0.5 Mn 0.5 O 2 composition is identified as optimal, exhibiting a unique synergy of thermodynamic stability and a near-isovolumetric response ( Δ V / V 0 ≈ − 2 % ), which suppresses stress-induced polarization and maintains high-capacity retention at 5C. This study demonstrates that the interplay between electronic bandgap tuning and isovolumetric lattice design provides a key screening criterion for optimizing the transport kinetics and cyclic stability of layered oxide hosts.