The rapid growth of renewable energy technologies and the need for sustainable energy storage systems have brought electrochemistry to the forefront of modern science. Electrochemical methods provide the fundamental basis for storing electrical energy in chemical form and releasing it when required. This thesis explores the principles of electrochemistry, the types of electrochemical cells, and their applications in modern energy storage technologies such as batteries, fuel cells, and supercapacitors. The paper also examines recent advances in electrode materials, electrolyte systems, and nanotechnology-based innovations that have significantly improved energy density, cycle life, and environmental sustainability of electrochemical systems. Keywords: Electrochemistry, energy storage, batteries, fuel cells, supercapacitors, nanomaterials, renewable energy, sustainability