A lignin-based polyelectrolyte with fast 3D Li+ transportation network

Abstract

In this work, we have developed a lignin-derived polymer electrolyte (LSELi), which demonstrates exceptional ionic conductivity of 1.6 × 10⁻³ S cm⁻¹ and a high cation transference number of 0.57 at 25 °C. Time of flight secondary ion mass spectrometry (TOF-SIMS) analysis shows that the large-size 1-ethyl-3-methylimidazolium cations (EMIM⁺) can induce the aggregation of the anionic segments in lignosulfonate to reconstruct the three-dimensional (3D) spatial structure of polyelectrolyte, thereby forming a fluent Li⁺ transport 3D network. Dielectric loss spectroscopy further reveals that within this transport network, Li⁺ transport is decoupled from the relaxation of lignosulfonate chain segments, exhibiting characteristics of rapid Li⁺ transport. Furthermore, in-situ distribution of relaxation times analysis indicates that a stable solid electrolyte interface layer is formed at the Li plating interface with LSELi, optimizing the Li plating interface and exhibiting low charge transfer impedance and stable Li plating and stripping. Thus, a substantially prolonged cycling stability and reversibility are obtained in the Li||LSELi||Li battery at 25 °C (1800 h at 0.1 mA cm⁻², 0.1 mAh cm⁻²). At 25 °C, the Li||LSELi||LiFePO₄ cell shows 132 mAh g⁻¹ of capacity with 92.7% of retention over 120 cycles at 0.1 mA cm⁻².