Lignin‐Based Separators for Lithium‐Ion Batteries via a Dry Fibrillation Method

Abstract Separators are critical components in lithium‐ion batteries (LIBs), preventing internal short circuits, mitigating thermal runaway, and influencing rate capability and cycling performance. However, current polyolefin separators suffer from limitations, such as high thermal shrinkage, relatively poor wettability, and inadequate long‐term stability, impacting safety and cycle life in critical applications like electric vehicles. Here, a single‐layer lignin‐based ultrathin separator (as thin as 15 µm) with exceptional intrinsic thermal stability and cycling performance is demonstrated. The separator is fabricated using lignosulfonate, a natural polymer derived as a byproduct of chemical pulping and biorefinery processes. By employing a dry fibrillation method, the process achieves low energy consumption and a 100% raw material conversion rate, highlighting its scalability and sustainability. Interfacial studies reveal the improved cycling performance in both graphite||NMC811 and Si‐Gr||NMC811 cells is attributed to the abundant sulfonate functional groups in lignosulfonates, which promote the formation of a sulfur‐rich cathode/solid electrolyte interphases (CEI/SEI) with low resistance in both the cathode and anode. The high thermal stability, manufacturing feasibility, battery performance, and low cost of such lignin‐based separators offer new inspiration for developing next‐generation, single‐layer functional separators tailored for high‐performance LIBs.