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September 10, 2025

Joule Heating Driven Graphitization Regulation and Ni Single‐Atom Modification in Hard Carbon for Low‐Voltage and High‐Rate Potassium‐Ion Storage

LYLei YangOcean University of China HPHuaipeng PangOcean University of China WRWei RenNational Laboratory for Superconductivity

Key Points

Optimized nickel single-atom modified hard carbon achieves a remarkable low-voltage charging capacity of 290 mAh g −1 at 0.1 A g −1.
Joule heating coupled with metal salt catalysis enhances the graphitization process, controlling the degree of graphitization effectively.
The NiNHC−J anode demonstrates excellent rate capability of 144 mAh g −1 at 10 A g −1, alongside impressive cycling stability over 2000 cycles.
Potassium-ion hybrid capacitors using this anode exhibit high energy/power densities of 122 Wh kg −1 and 16,167 W kg −1, respectively.

Abstract

Abstract Hard carbon (HC), a promising anode for potassium‐ion hybrid capacitors (PIHCs), must deal with the tradeoff between low‐voltage (≤1 V) charging capacity and rate capability, which are two important but mutually restrictive properties. Herein, a Joule heating coupled with a metal salt catalysis strategy is reported to rapidly construct Ni single‐atom modified N‐doped HC (NiNHC−J) with controllable graphitization. The metal salt acts both as a single‐atom dopant and a graphitization catalyst, with Joule heating temperature optimization enabling precise control over graphitization degree. Furthermore, the Joule heating drives Ni single‐atom content up to 2.29 wt.%, which can induce a local electric field to accelerate electron/ion transportation and meanwhile promote electrolyte decomposition to form an ultrathin and KF‐enriched solid‐electrolyte interphase. Consequently, the optimized NiNHC−J delivers extraordinary low‐voltage charging capacity (290 mAh g −1 at 0.1 A g −1 ), excellent rate capability (144 mAh g −1 at 10 A g −1 ), and outstanding cycling stability for 2000 cycles (capacity decay < 0.0145% per cycle). Impressively, the as‐assembled PIHC based on NiNHC−J anode achieves impressive energy/power densities (122 Wh kg −1 /16 167 W kg −1 ). This work establishes an innovative strategy combined with graphitization regulation and metal single‐atom modification, offering fundamental insights in the HC anode with low‐voltage and high‐rate potassium‐ion storage.

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