The utilization of hybrid ion batteries (HIBs) effectively reduces the consumption of scarce Li resources and harnesses the synergistic effect of mixed ions to achieve performance comparable to that of lithium-ion batteries. However, there is currently a lack of anode materials that possess both high safety and excellent performance for HIBs. Herein, we present a novel structure of enclosed hard carbon nanotubes (HCNTs) doped with high levels of nitrogen and oxygen as anodes for HIBs. When utilized in Li—Na—K HIBs, they exhibit superior reversible capacity (440.1 mA·h·g⁻¹ at 100 mA/g) and enhanced rate performance (327.7 mA·h·g⁻¹ at 1 A/g) compared to single alkali metal ion batteries. These improvements can be attributed to the design of a one-dimensional structure that features highly doped hard carbon, which significantly enhances carrier transport. Furthermore, first-principles calculations reveal the synergistic effect of hybrid ions in nitrogen-doped hard carbon nanotubes, enhancing the ion adsorption stability in the carbon layer. This study introduces a substantial anode material for HIBs and expands the scope from binary to ternary HIB systems.

Potassium-ion batteries (PIBs) are promising next-generation energy storage candidates due to abundant resources and low cost. Sb-based materials with high theoretical capacity (660 mAh·g^–1) and low working potential are considered as promising anode for PIBs. The remaining challenge is poor stability and slow kinetics. In this work, FeSb@N-doped carbon quantum dots anchored in three-dimensional (3D) porous N-doped carbon (FeSb@C/N⊂3DC/N), a Sb-based material with a particular structure, is designed and constructed by a green salt-template method. As an anode for PIBs, it exhibits extraordinarily high-rate and long-cycle stability (a capacity of 245 mAh·g^–1 at 3, 080 mA·g^–1 after 1, 000 cycles). The pseudocapacitance contribution (83%) is demonstrated as the origin of high-rate performance of the FeSb@C/N⊂3DC/N electrode. Furthermore, the potassium storage mechanism in the electrode is systematically investigated through ex-situ characterization techniques including ex-situ transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Overall, this study could provide a useful guidance for future design of high-performance electrode materials for PIBs.