Alkali metal‐ion capacitors integrate two electrodes from both batteries and supercapacitors (SCs), combining the advantages of large capacity, high‐rate performance, and long cycle life. Potassium (K) has similar properties to sodium (Na) and lithium (Li), however, the abundance of K in the crust is the same with Na, and much higher than Li. Due to the fast kinetics and low self‐discharge of
... [Show full abstract] Potassium‐ion capacitors (PICs), PICs attract more interest from researchers in the field of electrochemical energy storage. The current dilemma is that the research on PICs is more inherited from sodium‐ion capacitors (SICs) and lithium‐ion capacitors (LICs). Despite advancements in electrode materials, there is still a lack of profound understanding of the intrinsic issues and key challenges of PICs. In order to provide a detailed and systematic analysis of the development of PICs, in this review, special attention is given on the following Accordingly, full eight key sections: i) development history, ii) defining equations, iii) energy storage mechanism, iv) device configuration, v) electrode materials, vi) electrolyte design, vii) key technologies, and viii) future perspectives. This review provides an intensive theoretical foundation for the development of PICs and is able to pave the path for the practical application of PICs.
![a) Schematic illustration of the preparation for EGOC. Reproduced with permission from Ref. [33]. Copyright (2022) Royal Society of Chemistry. b) Schematic diagram of PIHCs assembly and the preparation process for LAP‐rGO‐CDs. Reproduced with permission from Ref. [35]. Copyright (2021) Elsevier. c) CV curves of P‐CVO N@GO and AC in half cells (top) and full of PIHCs (bottom). Reproduced with permission from Ref. [38]. Copyright (2019) Wiley‐VCH. d) Cycling stability of PIHCs using CBC@G as an anode. Reproduced with permission from Ref. [41]. Copyright (2020) Wiley‐VCH. e) Schematic illustration of pristine KTO and ALD KTO regarding electron/charge diffusion and transport. Reproduced with permission from Ref. [42]. Copyright (2021) Elsevier.](https://www.researchgate.net/publication/372383518/figure/fig3/AS:11431281245755801@1716218080489/a-Schematic-illustration-of-the-preparation-for-EGOC-Reproduced-with-permission-from_Q320.jpg)
![a) Schematic illustration of the preparation of SCNs. b) Cycling properties of SCNs at 0.1 A g⁻¹. Reproduced with permission from Ref. [43]. Copyright (2022) Elsevier. c and d) FESEM images of PCNF. e) Rate performance of the PIHCs (PCNF//aPCNF). Reproduced with permission from Ref. [44]. Copyright (2022) Wiley‐VCH. f) SEM images and g) schematic illustration of potassium‐ion storage mechanism of N‐GQD@ASC‐500. Reproduced with permission from Ref. [45]. Copyright (2021) Wiley‐VCH.](https://www.researchgate.net/publication/372383518/figure/fig4/AS:11431281245802380@1716218080938/a-Schematic-illustration-of-the-preparation-of-SCNs-b-Cycling-properties-of-SCNs-at_Q320.jpg)
![a) Schematic illustration of the preparation process for the HC−X (X=A, B, C) samples. b) Schematic illustration of potassium‐ions storage mechanism in HCs. c) BJH (Barrett‐Joyner‐Halenda) pore size distribution plots of the HC−X. Reproduced with permission from Ref. [46]. Copyright (2021) Wiley‐VCH. d) TEM image of the carbon foam. Reproduced with permission from Ref. [47]. Copyright (2020) Elsevier. e) SEM image of PNTCDA. f) Rate property of PIHCs (PNTCDA@900//AC) from 0.1 to 1 A g⁻¹. Reproduced with permission from Ref. [48]. Copyright (2020) Elsevier.](https://www.researchgate.net/publication/372383518/figure/fig5/AS:11431281245773970@1716218081340/a-Schematic-illustration-of-the-preparation-process-for-the-HC-X-XA-B-C-samples-b_Q320.jpg)
