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

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.