The transition towards renewable energy sources, determined by the problems related to the exploitation of fossil fuels, requires the use of energy storage systems, which allow to overcome the intermittence and the unpredictability of renewable sources. Among the electrochemical systems, the most studied and used one is the lithium-ion technology; due to several interesting features, these batteries are employed for many applications, such as portable electronic devices and electric vehicles. Due to the low availability and uneven distribution of lithium, which considerably increase its cost, it is necessary to find alternative elements: the most promising candidate is potassium. This alkali metal is much more abundant and evenly distributed on the Earth crust; moreover, it allows to obtain performances close to those of lithium, thanks to its standard reduction potential of -2.93 V vs.