Fast Li+ transport kinetics enabled by TiN nanofibers in hybrid polymer-based electrolytes for long-life Li metal batteries

Abstract

Polymer-based solid-state electrolytes exhibit superior advantages in flexibility, light weight, and large-scale processability, rendering them promising for high-performance solid-state lithium metal batteries (SSLMBs) with enhanced safety. However, challenges like poor structural uniformity, sluggish Li⁺ transport kinetics, and inferior interface compatibility hinder their practical applications. Herein, a hybrid quasi-solid-state electrolyte (PHLT) composed of a titanium nitride (TiN) fibrous nanofiller and a poly(vinylidene fluoride-co-hexafluoropropylene)/lithium bis(trifluoromethanesulfonyl)imide (PVDF–HFP/LiTFSI) matrix was developed. The inorganic filler could decrease the crystallinity of PVDF–HFP, propel the polar transformation of the polymer, as well as adsorb and immobile the TFSI⁻ anions, significantly enhancing Li-ion transport kinetics. Furthermore, the in situ generated fast Li-ion conductor, i.e., Li_xTiN, derived from lithiated TiN, along with a smooth but dense LiF interphase, effectively bridges the electrolyte|electrode interface and suppresses Li dendrite growth. Consequently, the as-fabricated Li|PHLT|LiFePO₄ cells achieve exceptional cycling stability over 3000 cycles at 2 C with a superior average Coulombic efficiency of 99.8%. Notably, this strategy also enables great compatibility with matching high-loading cathodes (9.5 mg cm⁻²), moreover, it delivers impressive performance in large areal pouch cells as well as bilayer stacking cells. This work provides an innovative approach to constructing solid-state electrolytes with enhanced diffusion kinetics and interface compatibility, paving the way for practical SSLMB applications.