Surface Antisite Defect-Induced Three-Dimensional Li ⁺ Diffusion Enables Stable and Kinetic-Enhanced LiFe _{1– <i>x</i>} Mn _<i>x</i> PO ₄ Cathodes

Interfacial degradation is a major bottleneck for LiFe_1-<i>x</i>Mn_<i>x</i>PO₄ (LMFP) cathodes. Conventional surface modifications, such as inert coatings or doped layers, can mitigate interfacial metal dissolution but often at the cost of Li⁺ transport, leading to a long-standing trade-off between interfacial stability and interfacial electrochemical kinetics. Here, we reconciles this conflict by constructing a surface-confined Li-Fe antisite defect layer via a simple ferrocene-assisted thermal treatment. A moderate antisite concentration (∼3.2%) simultaneously densifies the surface lattice, significantly suppressing Mn and Fe dissolution while enabling a transition of Li⁺ diffusion from one-dimensional (1D) to three-dimensional (3D) at the surface. This dual-function surface significantly improves both cycling stability and kinetics of the LMFP. Beyond practical improvements, these results overturn the conventional view of antisite defects as purely detrimental, establishing controlled antisite engineering as a versatile paradigm for reconciling interfacial stability with fast ion transport in phosphate cathodes.