2D layered MXene (Ti₃C₂T_x) with high conductivity and pseudo-capacitance properties presents great application potential with regard to electrode materials for supercapacitors. However, the self-restacking and agglomeration phenomenon between Ti₃C₂T_x layers retards ion transfer and limits electrochemical performance improvement. In this study, a 3D porous structure of Ti₃C₂T_x was obtained by adding alkali to a Ti₃C₂T_x colloid, which was followed by flocculation. Alkaline-induced flocculation is simple and effective, can be completed within minutes, and provides 3D porous networks. As 3D porous network structures present larger surface areas and more active sites, ions transfer accelerates, which is crucial with regard to the improvement of the superior capacitance and rate performance of electrodes. The sample processed with KOH (K-a-Ti₃C₂T_x) exhibited a high capacity of approximately 300.2 F g⁻¹ at the current density of 1 A g⁻¹. The capacitance of the samples treated with NaOH and LiOH is low. In addition, annealing is essential to further improve the capacitive performance of Ti₃C₂T_x. After annealing at 400 °C for 2 h in a vacuum tube furnace, the sample treated with KOH (K-A-Ti₃C₂T_x) exhibited an excellent specific capacitance of approximately 400.7 F g⁻¹ at a current density of 1 A g⁻¹, which is considerably higher than that of pristine Ti₃C₂T_x (228.2 F g⁻¹). Furthermore, after 5000 charge–discharge cycles, the capacitance retention rate reached 89%. This result can be attributed to annealing, which can further remove unfavourable surface groups, such as –F or –Cl, and then improve conductivity capacitance and rate performance. This study can provide an effective approach to the preparation of high-performance supercapacitor electrode materials.