greatly limits the further large-scale application of LIBs. [5][6][7][8] Therefore, it is quite important to explore alternative energy storage technologies with low cost and high electrochemical performance beyond LIBs for a sustainable development. Toward this end, potassium-ion batteries (PIBs) are recognized as one of the most promising candidates for the next-generation energy storage devices, owing to their advantages of abundant resources, low cost, and high interface diffusion. [9][10][11] More importantly, PIBs have a potential to achieve high work voltage and energy density because the redox potential of K/ K + (−2.93 V vs Standard Hydrogen Electrode (SHE)) is much closer to that of Li/ Li + (−3.04 V vs SHE). [3,12,13] Attracted by these merits, much effort has been made to design and fabricate high-performance PIBs.In spite of the similarity of PIBs to LIBs, however, numerous well-established electrode materials in LIBs cannot be directly applied in PIBs owing to the larger ionic size of K + (1.38 Å) in comparison with Li + (0.76 Å). [14,15] Particularly, commercial graphite anode can only exhibit a theoretical specific capacity of 279 mAh g −1 for PIBs, much lower than 372 mAh g −1 for LIBs. [12,16] Besides, the confined interlayer spacing (3.5 Å) in graphitic carbon is unfavorable for fast K + intercalation/ deintercalation, and severe volume change will occur when accommodating more K + , leading to poor rate, low capacity, and inferior cycling stability. [17] Different from graphite, hard carbon Pore-structure design with increased ion-diffusion ability is usually regarded as an effective strategy to improve K-storage performance in hard carbon (HC). However, the relationship between porous structure and K + migration behavior remains unclear and requires further exploration. Herein, a series of chemically activated hard carbon spheres (denoted as AHCSs) with controllable micro/ mesopores structure are successfully synthesized to explore intercorrelation between micro/mesopores and K migration behavior. The experimental results indicate AHCSs have two different K + storage ways, that is, adsorption behavior at high potential region and intercalation process at low potential region. These behaviors are closely related to the pores structure evolution: the micropores afford extra active sites for efficient K-ions adsorption, and therefore positive correlation between micropores and adsorption-contributed capacity is confirmed; the mesopores permit more K-ions intercalation/deintercalation by offering adequate pathways, and as a result positive correlations between mesopores and intercalation-contributed capacity as well as initial Coulombic efficiency are revealed. All these together contribute to achieving excellent reversible capacity, and exceptional rate capability with an ultra-long cycle lifespan in PIBs, and simultaneously exhibit a high energy density as well as considerable cycling stability for potassium-ion full cells. These results promote a fundamental understanding of K + migration beha...
