Highly oxygen/nitrogen doped enclosed carbon nanotubes as anode materials for advanced Li⁺/Na⁺/K⁺ hybrid ion batteries

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.