storage. [3] Recently, as a result of the abundance of K, potassium-ion batteries (PIBs) provide a cheaper alternative to LIBs and thus attract more attention. [4] The standard electrode potential of K/K + (−2.93 V vs E 0 ) is close to Li/Li + (−3.04 V vs E 0 ) in aqueous system, even lower than Li/Li + in nonaqueous electrolytes, [5] indicating that PIBs would potentially perform at a higher voltage/power operation. Additionally, recent studies have shown that high-energy metal-O 2 batteries based on K metal have higher round-trip efficiency than their Li and Na counterparts because potassium superoxide, the species generated in the O 2 cathode, is both thermodynamically and kinetically stable. [6] Using K metal anodes poses a particular challenge because K is highly reactive and reacts spontaneously with solvents and salt anions, forming a solid-electrolyte interphase (SEI) layer on the K surface. [7] However, the SEI layer is not optimized to accommodate large volume change during K plating/stripping, resulting in the unrecoverable cracking of the SEI layer. These phenomena will become serious especially at high deposition capacity. Furthermore, the resultant inhomogeneities in resistance and ion flux on SEI layer drive the morphologically nonuniform K growth (dendrite, granule, etc.) that could induce internal short-circuit and other serious safety hazards. [8] This highlights a compelling issue regarding safe cyclability of metal anode, that is, how to regulate the surface reactivity of metal toward organic electrolytes. However, the Secondary batteries based on earth-abundant potassium metal anodes are attractive for stationary energy storage. However, suppressing the formation of potassium metal dendrites during cycling is pivotal in the development of future potassium metal-based battery technology. Herein, a promising artificial solid-electrolyte interphase (ASEI) design, simply covering a carbon nanotube (CNT) film on the surface of a potassium metal anode, is demonstrated. The results show that the spontaneously potassiated CNT framework with a stable self-formed solid-electrolyte interphase layer integrates a quasi-hosting feature with fast interfacial ion transport, which enables dendrite-free deposition of potassium at an ultrahigh capacity (20 mAh cm −2 ). Remarkably, the potassium metal anode exhibits an unprecedented cycle life (over 1000 cycles, over 2000 h) at a high current density of 5 mA cm −2 and a desirable areal capacity of 4 mAh cm −2 . Dendrite-free morphology in carbon-fiber and carbon-black-based ASEI for potassium metal anodes, which indicates a broader promise of this approach, is also observed.