Sodium is low cost and abundant resource and its distribution geographically makes it attractive over the lithium counterpart. Like graphite for lithium ion batteries, finding standard negative electrode materials for sodium ion batteries with good stability and long cycling life is still a challenge. Therefore, focus on new material and optimization of the known electrode material is important. In the present work, dynamic electrochemical impedance spectroscopy (DEIS) is used as a tool to probe the electrochemical processes occurring in these cells. In normal electrochemical impedance there is no control over the state of charge while measurement is performed. DEIS facilitates static state of charge, which will not disturb state of the cell. Therefore, we have the opportunity to perform impedance measurement during charging as well as discharging of the cell at different potential steps that will help in optimization of potential window of the cell. Hard carbon is well known insertion anode material compatible with sodium and lithium ion batteries. Therefore sodium ion and lithium ion half-cells are assembled by using hard carbon as anode material. Using DEIS and cyclic voltammetry, potential window for galvanostatic cycling is optimized which minimizes capacity fading. The optimized potential window is verified by performing galvanostatic cycling at various potential steps and correlating with DEIS. By optimizing the potential window capacity fading got reduced from 30% to 3%.