Due to increasing environmental pollution, depletion of fossile fuels, energy has become a primary focus of the major world power and scientific community. There has been a great interest to reach for renewable and clean energy sources such as sun, wind, hydro, geothermal, biomass etc which are available free of cost.But these are limited to use due to unperpetual supply, therefore, require a high-performance, low cost and environmentally friendly energy conversion and storage systems. Supercapacitor and Lithium ion batteries (LIBs) are promising electrochemical energy conversion and storage, due to their own properties such as long cycle life, high power and energy densities etc. At present, both are successfully used in portable electronic devices, electric and hybrid electric vehicles. But at the higher end application (industrial application), they have some shortcomings like poor cycle life, low safety features, insufficient power and energy densities, high cost etc. Fundamentally, the performance of energy conversion and storage system is directly related to the material properties. Therefore, material technology plays a very important role in the development of electrochemical energy conversion and storage systems.A huge number of compounds have been studied as electrode material for supercapacitor and lithium ion batteries based different charge storage mechanism. However, transition metal carbonates (typically Mn-based carbonates) shows a better performance than other compounds in both application. Mn-based carbonates also have some advantage over other transition metal such low cost, high abundant, easy synthesis and most important Mn can shows multiple oxidation state which is one of the required condition of supercapacitor and lithium ion batteries. Due to the above mention advantages of Mn and Mn-based carbonates for both energy storage devices, we are working in this field.