Interfacial failure analysis and LiTaO3-mediated dual-filler stabilization of LiTa2PO8-based composite solid electrolytes for solid-state lithium metal batteries

Abstract

LiTa₂PO₈ (LTPO) is a promising fast-ion-conducting filler for poly(vinylidene fluoride) (PVDF)-based composite solid electrolytes (CSEs). However, although previous studies have revealed potential instability factors of LTPO-based electrolytes at Li metal interfaces, the evolution process from interfacial heterogeneity to lithium dendrite penetration-induced failure remains insufficiently understood. Herein, we reveal that the instability of LTPO-based electrolytes originates from the coupling between rapid Li⁺ transport and interfacial heterogeneity, induced by uneven surface potential, complex electronic environments, and weak Li affinity. To address these issues, we propose a LiTaO₃ (LTO)-regulated dual-filler composite electrolyte (TP-CSE), where LTO enables interfacial electric-field homogenization and uniform Li nucleation while maintaining the fast Li⁺ transport of LTPO. The optimized TP-CSE achieves a high ionic conductivity of 5.15 × 10⁻⁴ S cm⁻¹, an activation energy of 0.17 eV, and enables Li/TP-CSE/Li symmetric cells to cycle stably for over 1200 h at 0.2 mA cm⁻²/0.2 mAh cm⁻². Moreover, Li/TP-CSE/NCM523 full cells retain 97.8% capacity after 400 cycles at 1 C and deliver a reversible capacity of 108.6 mAh g⁻¹ after 500 cycles at 5 C. This dual-filler strategy offers a viable pathway for stabilizing fast-ion-conducting fillers in high-performance solid-state lithium metal batteries.