The European Union has established a policy to achieve climate neutrality by 2050. Therefore, one of the strategies is to increase renewable energy sources drastically and, in turn, develop efficient energy storage devices and batteries of particular interest. For large-scale stationary applications, sustainability and cost-effective batteries are more attractive. In this context, lithium-ion batteries (LIBs) are not the most interesting battery chemistry due to their mass production comes with environmental and social challenges, which will even increase more as the market expands. Indeed, lithium-based technology production involves several critical raw materials, where suppliers concentrate in third countries and conflict zones, and expensive elements (i.e., natural graphite, cobalt, lithium, nickel, etc.) [1,2]. In this scenario, the development of alternative energy storage devices based on sustainable and cost-effective materials is crucial [3].

Sodium-ion batteries (NIBs) are postulated as a complementary technology to lithium-ion batteries (LIBs) for stationary applications and light electromobility due to their lower cost and sustainability, as they are made of non-critical raw materials [3]. Recently, several companies have been presented with potential applications of SIB to bolster their commercialization. For example, CATL, one of the biggest battery manufacturers in the world, recently announced on production of SIBs. Potassium-ion batteries (KIBs) might be another attractive alternative due to they keep the sustainability and cost aspects, with several advantages over NIBs. Potassium, as sodium, is abundant and widely distributed on the Earth’s crust and ocean, while it exhibits lower reduction potential than Na (i.e., -2.71 V and −2.93 V vs. SHE for Na and K, respectively). Moreover, K ions diffuse faster in liquid than Na ions -and Li ions, leading to higher energy density and higher power density than NIBs. The Group 1 start-up has recently released a KIB prototype, and they announced a large-scale production of KIBs by 2027, demonstrating that KIBs could be a reality. Unfortunately, the current performance of KIBs is inferior to that of both LIBs and NIBs. Therefore, further advances are necessary to enhance the viability of KIBs [4]. Thus, this work will be focused on the comparison of Na- and K-based electroactive materials (electrode and/or electrolyte) and identify the key parameters affecting the electrochemical properties to achieve high-performing NIBs and KIBs.