Hard carbon (HC) displays great potential for high-performance sodium-ion batteries (SIBs) due to its cost-effective, simple fabrication and most likely to be commercialized. However, the complicated microstructures of HC lead to difficulties in deeply understanding the structure-performance correlation. Particularly, evaluation of influence of pore structure on Na storage performances is still causing disputes and rational strategies of designing pore architecture of HC are still necessary. In this work, the skillful and controllable phase-inversion method is applied to construct porous HC with abundantly interconnected and permeable tunnel-like pores, which can promote ionic diffusion and improve electrode-electrolyte interfacial affinity. Structure-performance investigation reveals that porous HC with cross-coupled macropore architecture can boost Na storage performances comprehensively. Compared to pristine HC with negligible pores, well-regulated porous HC anodes show an obvious enhancement on initial Coulombic efficiency (ICE) of 68.3% (only 51.5% for pristine HC), reversible capacity of 332.7 mAh g-1 at 0.05 A g-1, rate performance with 67.4% capacity retention at 2 A g-1 (46.5% for pristine HC), and cycling stability with 95% capacity maintained for 90 cycles (86.4% for pristine HC). Additionally, the ICE can be optimized up to 76% by using sodium carboxymethyl cellulose as a binder. This work provides an important view of optimizing Na storage performances of HC anodes by pore engineering, which can be broadened into other electrode materials.
Keywords: hard carbon; initial Coulombic efficiency; pore engineering; rate performance; sodium-ion batteries.