Pore‐Stitching Engineering of Biomass‐Derived Hard Carbon for Enhanced Sodium‐Ion Storage

Abstract

Biomass‐derived hard carbon (HC) is a promising and cost‐effective anode for sodium‐ion batteries (SIBs). Prior to carbonization, biomass precursors are commonly subjected to acid/alkali purification to remove metallic and non‐metallic impurities. However, the accompanying ionic etching process often generates abundant through‐pores and disrupts the carbon framework, leading to increased irreversible capacity loss. Herein, we propose a “pore stitching” strategy using hydroxyethyl cellulose (HEC) as a functional reconstruction precursor. The hydroxyl‐rich HEC is proposed to interact with oxygen‐containing sites in the demineralized precursor and to be retained within accessible pore regions during mixing and drying. During subsequent carbonization, HEC‐derived carbon contributes to the reconstruction of the disrupted carbon framework, resulting in reduced open surface exposure and a redistributed micro/ultramicroporous architecture while preserving favorable Na + storage domains. Consequently, the optimized HC delivers a high reversible capacity of 375.3 mAh g − 1 at 20 mA g − 1 . A 700 mAh pouch cell pairing this HC with sodium iron phosphate pyrophosphate (Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 , NFPP) delivers 150 Wh kg − 1 based on the combined active‐material mass of both electrodes and retains 97.8% capacity after 200 cycles at 1 C. This work provides a viable route for converting impurity‐rich agricultural waste into high‐performance HC anodes for practical sodium‐ion energy storage.