The green (clean) energy transition must be achieved in order to realize carbon neutrality in the world. Instead of relying on existing fossil fuels as energy sources, it is required to introduce renewable energy such as solar photovoltaic, wind power, geothermal, and so on. According to the IEA report, the new energy devices including electric vehicles (EVs) require more critical raw minerals (materials) to build than their fossil fuel-based ones. Consequently, mankind confronts a crucial challenge to secure additional sources of those critical minerals. Taking an example of lithium-ion battery (LiB), which is indispensable for EVs, lithium, nickel, and cobalt are crucial minerals to produce cathode of LiB. There exist vast amounts of these three minerals on land; however, it seems to be difficult to increase their production rapidly without burdening the surrounding environment so as to meet the world demand of EVs. Then, apart from lithium, vast amounts of manganese nodules on the deep seabed could be another solution for a source for sustainable supply of nickel and cobalt. In this chapter, the author discusses comparisons between land-based mining and deep-sea mining regarding resource quality and quantity, commercial viability, and environment, social, and governance (ESG) risks, especially focusing on nickel and cobalt. While deep-sea mining may have certain disadvantages due to unconventional resource base, land-based mining has certain difficulties from ESG perspective and is a monopoly-driven market. Decoupling of the global economy may highlight deep-sea mining as a part of the solution toward achieving sustainable critical minerals supply chains.