The orthorhombic CuNb₂O₆ (O–CNO) is established as a competitive anode for lithium-ion capacitors (LICs) owing to its attractive compositional/structural merits. However, the high-temperature synthesis (>900 ℃) and controversial charge-storage mechanism always limit its applications. Herein, we develop a low-temperature strategy to fabricate a nano-blocks-constructed hierarchical accordional O–CNO framework by employing multilayered Nb₂CT_x as the niobium source. The intrinsic stress-induced formation/transformation mechanism of the monoclinic CuNb₂O₆ to O–CNO is tentatively put forward. Furthermore, the integrated phase conversion and solid solution lithium-storage mechanism is reasonably unveiled with comprehensive in(ex) situ characterizations. Thanks to its unique structural merits and lithium-storage process, the resulted O–CNO anode is endowed with a large capacity of 150.3 mAh g⁻¹ at 2.0 A g⁻¹, along with long-duration cycling behaviors. Furthermore, the constructed O–CNO-based LICs exhibit a high energy (138.9 Wh kg⁻¹) and power (4.0 kW kg⁻¹) densities with a modest cycling stability (15.8% capacity degradation after 3000 consecutive cycles). More meaningfully, the in-depth insights into the formation and charge-storage process here can promote the extensive development of binary metal Nb-based oxides for advanced LICs.