Potassium ion hybrid capacitors (KIHCs) have drawn growing interest owing to their outstanding energy density, power density and excellent cycling stability. However, the large ionic radius of potassium triggers a huge volume change during continuous K⁺ insertion/extraction processes, restricting the development of KIHCs. Here, we report N-doped carbon nanotubes (NCNTs) for high-performance K⁺ storage. The NCNTs possess a hierarchical structure and N functional groups and not only offer sufficient space to relieve the volume expansion, but also provide highly efficient channels to transport electrons and ions. As a result, the NCNTs anode presents a high specific capacity and an excellent cycling stability with an average decay rate of 0.0238% per cycle (the lowest value among the reported carbon-based anodes for K-ions batteries) during 3600 continuous cycles. A potassium ion hybrid capacitor (KIHC) was also designed with the NCNT anode and a commercial active carbon cathode and achieved both a high energy/power density (117.1 W h kg⁻¹/1713.4 W kg⁻¹) and a long cycle life (2000 cycles at 1 A g⁻¹). Moreover, the in situ Raman and ex situ element mapping characterization demonstrate the outstanding electrochemical reversibility of the NCNTs. This work provides a superior strategy to design low-cost anode materials with excellent K⁺ storage electrochemistry.

中文翻译：

---

氮掺杂碳纳米管作为高强度钾离子混合电容器的阳极

钾离子混合电容器（KIHC）由于其出色的能量密度，功率密度和出色的循环稳定性而引起了越来越多的关注。然而，钾的大离子半径在连续的K ⁺插入/萃取过程中触发了巨大的体积变化，从而限制了KIHC的发展。在这里，我们报告了用于高性能K ^+的N掺杂碳纳米管（NCNT）存储。NCNT具有分层结构和N个官能团，不仅提供了足够的空间来缓解体积膨胀，而且还提供了高效的通道来传输电子和离子。结果，NCNTs阳极表现出高比容量和出色的循环稳定性，在3600个连续循环中，每个循环的平均衰减率为0.0238％（在报道的用于K离子电池的碳基阳极中，最小值）。还设计了带有NCNT阳极和商用活性炭阴极的钾离子混合电容器（KIHC），实现了高能量/功率密度（117.1 W h kg ^-1 /1713.4 W kg ^-1）和长循环寿命（在1 A g ^-1时2000次循环。而且，就地拉曼和易地元素分布特征表现出NCNTs的优秀电化学可逆性。这项工作为设计具有出色K ⁺存储电化学性能的低成本阳极材料提供了一种出色的策略。