Unravelling the anion-dominated interfacial structure of hybrid solid electrolytes via ssNMR

Abstract

Hybrid solid electrolytes (HSEs) offer a promising route to high-performance solid-state lithium batteries, but the chemically and structurally heterogeneous phase boundaries between polymers and fillers impede ion transport. The origin of these phase boundaries and how their components and structure govern Li⁺ transport kinetics remain elusive. Here, we tackle this issue by comprehensively investigating a series of polyethylene oxide-based HSEs with different preparation conditions where various interfacial reactions occur. We reveal that the strong coordination of anions (such as TFSI⁻, ClO₄⁻ and DFOB⁻) in the polymer phase accelerates the degradation of the polyphosphate framework. This degradation fosters the formation of resistive phase boundaries, which are primarily responsible for sluggish Li⁺ kinetics, as revealed by nondestructive cross polarization and exchange-NMR measurements. To address this, we propose a novel lithium tricyanomethanide (LiTCM) as a weakly coordinating additive to regulate interfacial chemistry and reconstruct phase boundaries. As a result, the ionic conductivity of HSEs is enhanced up to 5.48 × 10⁻⁴ S cm⁻¹ (60 °C). The developed all-solid-state lithium–sulfur batteries deliver a high specific capacity of 973.6 mAh g⁻¹, with 0.03% capacity fade per cycle over 300 cycles. It also enables LiFePO₄||Li batteries to cycle 300 times with a high capacity retention of 89.5%. This work elucidates the close relationship between the interfacial configuration and Li⁺ diffusion kinetics and offers fundamental insights for HSE design.