Two-dimensional (2D) transition metal carbide/nitrides, also called MXenes, have emerged an important family of 2D materials. Characterization of the properties of MXenes in the past few years has revealed their high potential for various applications. MXenes have a general formula of M_n+1X_nT_x, where M stands for an early transition metal, X denotes carbon or nitrogen, and T_x symbolizes surface terminations. Various MXene compositions are demonstrated to have high electrical conductivities and are shown to be dispersible in water and a range of organic solvents. Ti₃C₂T_x, the first discovered MXene, has shown exceptional properties as an electrode material for energy storage applications. This is because of the high electrical conductivity of this 2D material and fast redox reactions that can take place at its surface. Although both of these properties are expected to be highly dependent on the dimensions of 2D Ti₃C₂T_X sheets, the limited control over the size of Ti₃C₂T_x during its common synthesis method has prevented clear understanding of the size-dependent properties of this material. In this talk, we will first introduce a general method to accurately control the lateral dimension of Ti₃C₂T_x sheets and then, present our recent results on the effect of the lateral dimensions on the electrochemical performance of Ti₃C₂T_x electrodes. Our results indicate that the electrical and electrochemical properties of MXene electrodes can be controlled by changing the dimension of flakes. Applying our findings to the design of freestanding MXene electrodes makes it possible to achieve exceptional high electrochemical performances. For example, Ti₃C₂ electrode designed using sheets of various lateral dimensions can reach specific capacitances as high as 450 F/g, when tested as an electrode in electrochemical capacitors.