Uniform Li-metal growth on renewable lignin with lithiophilic functional groups derived from wood for high-performance Li-metal batteries

Lithium metal batteries (LMBs) are promising energy storage devices with high energy density owing to their high theoretical capacity (3860 mAh g⁻¹) and low reduction potential of lithium (Li)-metal anodes. However, their practical application is limited by poor Coulombic efficiency (CE) and safety issues due to Li dendrite growth during Li plating/stripping. Herein, a three-dimensional (3D) structure of lignin with a lithiophilic functional group derived from waste wood is suggested as an additional functional layer of LMBs, i.e., a lignosulfonic acid sodium salt (LASS) with a negatively charged sulfonate group (SO₃⁻) in its chemical structure. The SO₃⁻ group enhances the Li-ion (Li⁺) affinity and enables Li⁺-flux control, supplying homogeneous Li growth sites. It induces stable electrochemical dendrite-free Li growth. Consequently, in the LASS-Cu||Li half-cell, a high CE of 96.7 % at 210 cycles and stable operation is achieved without a short circuit and, symmetric-cell with LASS layers shows stable cycling over 2000 h. Moreover, full-cells with LiFePO₄ (LFP) and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM 811) cathodes exhibit enhanced electrochemical performance. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) reveal that the LASS layer suppressed dendritic Li growth and stimulated densely packed Li growth. This work suggests an effective strategy for improving the performance of LMBs using renewable lignin materials.