Ultrathin Al₂O₃-Coated Biomass Carbon for Sodium-Ion Batteries via a Synergistic Storage Mechanism

Abstract

Hard carbon (HC) is a promising anode candidate for sodium-ion batteries (SIBs), yet its application is plagued by unstable interfaces and poor long-term cyclability. Herein, we develop a facile solvent evaporation strategy to synthesize ultrathin Al₂O₃-coated biomass-derived HC (GSC-Al₂O₃-3%). The conformal Al₂O₃ layer passivates defects and micropores, suppresses side reactions, and promotes the formation of a robust organic–inorganic hybrid solid electrolyte interphase. Comprehensive characterizations, including in situ X-ray diffraction, ex situ Raman spectra, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry, solid-state ²⁷Al nuclear magnetic resonance, and atomic force microscope modulus mapping, demonstrate that Al₂O₃ actively participates in SEI reconstruction, enhancing the chemical and mechanical stability. Electrochemical tests reveal that the optimized GSC-Al₂O₃-3% anode delivers 91% capacity retention after 1000 cycles at 1.0 A g⁻¹, and possesses excellent wide-temperature tolerance (149.3 mAh g⁻¹ at −30°C and 286.8 mAh g⁻¹ at 60°C). Mechanistic studies confirm a synergistic Na⁺ storage process involving “adsorption–intercalation–pore filling,” while density functional theory calculations and electrostatic potential mapping reveal that Al₂O₃ coating regulates interfacial charge distribution and reduces Na⁺ migration barriers. A full cell paired with a NaNi_0.5Fe_0.5MnO₄ cathode exhibits a high initial capacity of 395.7 mAh g⁻¹ and outstanding cycling stability (200 cycles). This work provides fundamental mechanistic insights into interfacial engineering of HC and establishes a cost-effective, scalable route for the next generation high-performance SIBs.

Keywords

biomass-derived carbon / interfacial engineering / sodium-ion batteries / theoretical calculations / wide-temperature application

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2025 The Author(s). Carbon Energy published by Wenzhou University and John Wiley & Sons Australia, Ltd.