• Molecular dynamics and experimental results confirm that adjusting the interlayer spacing by changing the C3N4 content effectively improves the reaction kinetics.
• The synergistic effect of K+ and C3N4 co-intercalation lowers the energy barrier, reduces the electrostatic interaction, and enhances the kinetics and structural stability.
• The K+/C3N4 co-intercalated NH4V4O10 cathode exhibits excellent electrochemical performance at room temperature and under extreme environments.
• The KNVO-C3N4 electrode delivers high rate capability (228.4 mAh g−1 at 20 A g−1) and long-term cycling stability (174.2 mAh g−1 after 10,000 cycles) at room temperature, and remarkable storage performance at −20 °C and 60 °C.