Physical/Chemical Mismatch Elimination Enabling Ultra‐Uniform Composite Solid Electrolyte for High Performance Solid‐State Lithium Metal Batteries

ABSTRACT Filler agglomeration in composite solid electrolytes (CSEs), primarily caused by the physical and chemical mismatch with the polymer matrixes, severely degrades the mechanical integrity, ionic conductivity, and lithium (Li) ion transportation of CSEs. Here, a distinctive dual mismatch‐elimination strategy is proposed to construct ultra‐uniform PEO‐based CSEs by utilizing polymer‐like hydroxyapatite sub‐nanowires (HAP SNWs) coupled with matching PEG grafting. The polymer‐like morphology eliminates physical mismatch and the identical PEG‐PEO composition ensures chemical compatibility, synergistically enabling high filler dispersion without agglomeration. Phase‐field simulations further verify that this uniform filler distribution enables homogeneous Li + flux, which, together with a HAP‐induced Li 3 N/Li‐Ca‐alloy solid electrolyte interphase, effectively suppresses Li dendrite growth. Moreover, combined with molecular dynamics simulations confirming the higher Li + mobility in flexible PEG than in rigid PEO and the HAP‐induced charge delocalization in PEG to weaken Li + coupling, the ionic conductivity of CSEs is elevated to 0.5 mS cm −1 at 60°C. Consequently, the corresponding symmetric cells deliver stably over 3000 h at 0.1 mA cm −2 , with full cells retaining ≈83% capacity after 800 cycles.