Transition-metal diselenides (TMDs) are promising materials for capacitive deionization (CDI) technol. due to their high theor. storage capacity and reversible intercalation/deintercalation behavior.However, drawbacks of TMDs like low conductivity, interlayer self-stacking and volume expansion severely impede ion migration, undermine the structural stability, and limit the accessibility of active sites, ultimately leading to unsatisfactory CDI performance.Herein, we elaborately designed a three-dimensional hydrangea-like MoSe2@N-doped carbon nanoflowers (MoSe2@N-CF) composite to enhance the efficiency and selectivity of cation capture.In this configuration, N-CF can not only serve as the growth substrate to prevent the aggregation of MoSe2 nanosheets and enhance the conductivity, but also effectively increases the interlayer spacing of MoSe2 in the mols. level.Meanwhile, the unique pseudocapacitive intercalation behavior of MoSe2 provides abundant active sites for cation storage and fast ion diffusion kinetics for ion transfer.Benefited from the synergistic functional regulation of MoSe2 and N-CF, the MoSe2@N-CF electrode demonstrates a remarkable specific capacitance (217.3 F g-1), reduced ion diffusion resistance, and superior electrochem. stability.The asym. CDI cell (AC//MoSe2@N-CF) presents excellent desalination capacity (40.83 mg g-1), rapid desalination rate (6.93 mg g-1 min-1), and demonstrates a 90 % retention rate (from 16.42 mg g-1 to 14.78 mg g-1) over 35 cycles.Addnl., the MoSe2@N-CF electrode exhibits unique ion selectivity in multi-ion solutions, which reflects the combined influence of intercalation effect and elec. double-layer effect arising from the distinct functional structures within the composite material, where their relative contributions vary with solution concentrationD. functional theory calculations further validate the ion selectivity mechanism based on ion diffusion energy.This work offers valuable insights into leveraging unique structural characteristics of pseudo-capacitive intercalation material and carbon-based material, advancing the development of CDI.