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Heterojunctions in electrode materials offer diverse improvements during the cycling process of energy storage devices, such as volume change buffering, accelerated ion/electron transfer, and better electrode structure integrity, however, obtaining optimal heterostructures with nanoscale domains remains challenging within constrained materials. A novel in situ electrochemical method is introduced to develop a reversible CuSe/PSe p‐n heterojunction (CPS‐h) from Cu3PSe4 as starting material, targeting maximum stability in potassium ion storage. The CPS‐h formation is thermodynamically favorable, characterized by its superior reversibility, minimized diffusion barriers, and enhanced conversion post K+ interaction. Within CPS‐h, the synergy of the intrinsic electric field and P‐Se bonds enhance electrode stability, effectively countering the Se shuttling phenomenon. The specific orientation between CuSe and PSe leads to a 35° lattice mismatch generates large space at the interface, promoting efficient K ion migration. The Mott‐Schottky analysis validates the consistent reversibility of CPS‐h, underlining its electrochemical reliability. Notably, CPS‐h demonstrates a negligible 0.005% capacity reduction over 10,000 half‐cell cycles and remains stable through 2,000 and 4,000 cycles in full cells and hybrid capacitors, respectively. This study emphasizes the pivotal role of electrochemical dynamics in formulating highly stable p‐n heterojunctions, representing a significant advancement in potassium‐ion battery (PIB) electrode engineering. [ABSTRACT FROM AUTHOR]

[Display omitted] • The utilization of 3D nitrogen-doped carbon confined Co 0.85 Se nanocrystals (Co 0.85 Se@NC) as an anode for potassium ion batteries leads to the achievement of a long cycle life exceeding 4000 cycles. • Co 0.85 Se@NC anode provide a capacity of 155.6 mA h g−1 at 10 A g−1. • Co 0.85 Se@NC anode shows the areal capacity up to 1.03 mA h cm−2 at 500 mA g−1. • Finite element analysis shows the 3D confinement strategy has the lowest interfacial stress. • Hundreds of LED bulbs were lighted by a pouch-type potassium-ion full battery composed of Co 0.85 Se@NC anodes. Conversion-type transition metal chalcogenide anodes could bring relatively high specific capacity in potassium ion storage due to multiple electron transport reactions, but often accompanying huge volume changes and resulting in low cycle life and rapid capacity fading. While electrode materials are closely packed, the contact at the interface during potassiation/depotassiation is similar to point-to-point contact, generating strong stress to make self-aggregation occur. In this work, we constructed a 3D carbon framework to confine Co 0.85 Se nanocrystals in three-dimensional space, both fulfilling the requirements of the material's size in the nano-scale and providing the largest contact area for releasing stress. With this optimization, nitrogen-doped carbon confined Co 0.85 Se nanocrystals (Co 0.85 Se@NC) reach an ultra-stable cycle life over 4000 times with a specific capacity of 190.9 mA h g−1 at 500 mA g−1 and provide 155.6 mA h g−1 at 10 A g−1 in the rate capability test. It also renders the areal capacity up to 1.03 mA h cm−2 at 500 mA g−1 in the high-mass loading test. Furthermore, based on the finite element analysis, the 3D confinement strategy has the lowest interfacial stress, ensuring Co 0.85 Se nanocrystals with high structural integrity. This strategy can relieve the stress issue in the conversion-type anode and demonstrate superior electrochemical performance even at high-loading mass electrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-entropy transition metal disulfide (HES 2) spheres were used for K+ storage. • The substantial configurational entropy of HES 2 minimizes the shuttle effect. • HES 2 anode exhibit a capacity of 348 mA h g−1 after 1800 cycles at 500 mA g−1. • HES 2 anode in potassium-ion full battery exhibits a capacity of 258.6 mA h g−1. • HES 2 potassium-ion hybrid capacitor delivers 63.7 Wh kg−1 after 6000 cycles. High-entropy metal disulfide (HES 2) colloid clusters were synthesized through a two-step templated solvothermal method for used as anode materials for potassium-ion storage devices. HES 2 's large configuration entropy stabilizes its crystal structure and promotes chemical diversity by introducing multiple cations, thus reducing the impact of the shuttle effect, retaining active materials and extending cycling life up to 1800 cycles. During cycling, crystalline-amorphous grain boundaries formed in situ enhance electrochemical reaction activities and ensure the exposure of active sites. Elements with lower electronegativity allow S to bring more negative charges, improving the electrostatic force between S and K+ and enabling better anchoring of potassium polysulfide. Meanwhile, the retained close-packed cluster structure of HES 2 provides a large contact area to accelerate the reduction reaction of the electrolyte in the sphere during the repeating K+ insertion/extraction. We further demonstrate the excellent performance of HES 2 anodes on practical potassium-ion full battery and hybrid capacitor applications. The pioneering concept in atomic compositional engineering and structural design of transition metal sulfide electrodes presented in this work marks a significant step forward in the development of chalcogenide electrode systems for energy storage devices. [ABSTRACT FROM AUTHOR]