Technical breakthrough of composite polymer electrolyte (CPE) is one of the key factors that determines the commercial process of the current solid-state lithium battery. However, high interface impedance limits its electrochemical performances. It is crucial to optimize the design of multiphase interfaces among different components in CPE for regulating Li⁺ transport. Herein, a multi-affinity self-assembled 12-crown-4-TFSI (12C4-TFSI) supramolecular nanolayer is introduced into poly(vinylidene difluoride)-Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (PVDF-LLZTO) CPE as interface modifier. As a result, enhanced Li⁺ conductivity of 4.29 × 10⁻⁴ S·cm⁻¹, Li⁺ transfer number of 0.44, and stable electrochemical window voltage of 4.8 V vs. Li/Li⁺ at 30 °C are obtained. The symmetric Li||Li cell exhibits an improved critical current density (CCD) of 1.2 mA·cm⁻² and steady cycling at 0.2 mA·cm⁻² for over 850 h without visible voltage fluctuation. The assembled LiǁLiFePO₄ coin solid-state cell delivers a high initial discharge capacity of 172.9 mAh·g⁻¹ at 0.1 C, rate capability (up to 5.0 C) and outstanding cycling stability with a capacity retention of 87.2% after over 750 cycles at 1.0 C. The associated LiǁLiFePO₄ pouch cell presents an initial specific discharge capacity of 112.3 mAh·g⁻¹ and successfully runs 30 cycles with a final capacity of 101.8 mAh·g⁻¹. This work offers a facile strategy to optimize multiphase interfaces of PVDF-LLZTO CPE for stable solid-state lithium battery.

Poly(ethylene oxide) (PEO) and Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO)-based composite polymer electrolytes (CPEs) are considered one of the most promising solid electrolyte systems. However, agglomeration of LLZTO within PEO and lack of Li⁺ channels result in poor electrochemical properties. Herein, a functional supramolecular combination (CD-TFSI) consisting of active β-cyclodextrin (CD) supramolecular with self-assembled LiTFSI salt is selected as an interface modifier to coat LLZTO fillers. Benefiting from vast H-bonds formed between β-CD and PEO matrix and/or LLZTO, homogeneous dispersion and tight interface contact are obtained. Moreover, ⁶Li NMR spectra confirm a new Li⁺ transmission pathway from PEO matrix to LLZTO ceramic then to PEO matrix in the as-prepared PEO/LLZTO@CD-TFSI CPEs due to the typical cavity structure of β-CD. As a proof, the conductivity is increased from 5.3 × 10⁻⁴ S cm⁻¹ to 8.7 × 10⁻⁴ S cm⁻¹ at 60 °C, the Li⁺ transference number is enhanced from 0.38 to 0.48, and the electrochemical stability window is extended to 5.1 V versus Li/Li⁺. Li‖LiFePO₄ CR2032 coin full cells and pouch cells prove the practical application of the as-prepared PEO/LLZTO@CD-TFSI CPEs. This work offers a new strategy of interface modifying LLZTO fillers with functional supramolecular combination to optimize PEO/LLZTO CPEs for solid lithium batteries.