Tailoring the microstructure and solid electrolyte interface of hard carbon to realize high-initial-coulombic-efficiency and high-rate sodium storage

As the most promising anode material for sodium-ion batteries (SIBs), hard carbon still suffers the drawbacks of low initial Coulombic efficiency (ICE) and poor rate performance, which restrict its practical application. How to tailor-design its microstructure and solid electrolyte interface (SEI) is crucial to address these challenges. Herein, a novel hard carbon material was fabricated by pyrolyzing the intermediate carbon precursor with crosslinked network structure generated through the interaction between phenolic resin and lignin. Its microstructure, consisting of the defect sites and interlayer distance, has been tailored and optimized through adjusting the carbonizing conditions. By employing ether electrolytes, the generated thinner SEI film endows the hard carbon electrode with lower interface impedance and faster Na+ transport kinetics. Benefiting from the tailored microstructure and SEI film, the obtained hard carbon material shows a higher ICE of 87%, a remarkable reversible capacity of 338 mA h g−1 after 500 cycles and superior rate performance of 268 mA h g−1 at 1C over 200 cycles (205 mA h g−1 at 6 C), much higher than the recently reported work. This work provides an effective strategy to develop the hard carbon anode with high ICE and high-rate sodium storage for practical SIBs.