The recent proliferation of sustainable and eco-friendly renewable energy engineering is a hot topic of worldwide significance with regard to combatting the global environmental crisis. To curb renewable energy intermittency and integrate renewables into the grid with stable electricity generation, secondary battery-based electrical energy storage (EES) technologies are regarded as the most promising solution, due to their prominent capability to store and harvest green energy in a safe and cost-effective way. Due to the wide availability and low cost of sodium resources, sodium-ion batteries (SIBs) are regarded as a promising alternative for next-generation large-scale EES systems. This review discusses in detail the key differences between lithium-ion batteries (LIBs) and SIBs for different application requirements and describes the current understanding of SIBs. By comparing technological evolutions among LIBs, lead-acid batteries (LABs), and SIBs, the advantages of SIBs are unraveled. This review also offers highlights on commercial achievements that have been realized based on current SIB technology, focusing on an introduction of five major SIB companies, each with SIB chemistry and technology, as well as commercialized SIB products. Last but not least, it discusses outlooks and key challenges for the commercialization of next-generation SIBs.