2D MXenes are attractive for energy storage applications because of their high electronic conductivity. However, it is still highly challenging for improving the sluggish sodium (Na)-ion transport kinetics within the MXenes interlayers. Herein, a novel nitrogen-doped Ti₃C₂T_x MXene was synthesized by introducing the in situ polymeric sodium dicyanamide (Na-dca) to tune the complex terminations and then utilized as intercalation-type pseudocapacitive anode of Na-ion capacitors (NICs). The Na-dca can intercalate into the interlayers of Ti₃C₂T_x nanosheets and simultaneously form sodium tricyanomelaminate (Na₃TCM) by the catalyst-free trimerization. The as-prepared Ti₃C₂T_x/Na₃TCM exhibits a high N-doping of 5.6 at.% in the form of strong Ti–N bonding and stabilized triazine ring structure. Consequently, coupling Ti₃C₂T_x/Na₃TCM anode with different mass of activated carbon cathodes, the asymmetric MXene//carbon NICs are assembled. It is able to deliver high energy density (97.6 Wh kg⁻¹), high power output (16.5 kW kg⁻¹), and excellent cycling stability (≈ 82.6% capacitance retention after 8000 cycles).