Three-Dimensional Hierarchical Porous Hard Carbon for Excellent Sodium/Potassium Storage and Mechanism Investigation

2021 
Abstract Hard carbons (HCs) are one of the most promising anode materials for sodium/potassium-ion batteries (SIBs/PIBs), which demonstrate favorable long charge/discharge plateaus, but suffer from low rate performance. Herein, we report a new design of N-P co-doped hard carbon (NPHC) with three-dimensional (3D) hierarchical porous frameworks. Such unique structure provides bi-continuous ion/electron transportation paths, regulated electronic structure, enlarged interlayer spacing, and moderate surface area. The as prepared NPHC demonstrates a high reversible specific capacity (336 mAh g-1 for SIBs, 339 mAh g-1 for PIBs), along with a good rate performance of ∼5.3 C. Particularly, an in-depth study on the charge storage mechanism for both SIBs and PIBs is conducted by combining in-situ Raman spectra and quasi in-situ synchrotron XRD analysis, whereby the coexistence of physical adsorption/graphitic layer intercalation, or intercalation/pore filling within certain potential ranges is detected, and the ion storage behavior at different charge/discharge stages is precisely identified.
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