Fundamentals, Status, and Prospects of Liquid Organic Electrolytes for High-Energy Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have emerged as one of the most promising candidates among post-Li-ion batteries (LIBs) due to abundance and low cost of sodium resources. However, the commercialization of SIBs is hindered by their limited cell performance. Although great efforts have been made, it is still challenging to balance the trade-off between energy density and cycle life while simultaneously meeting the requirements for practical applications, which are largely governed by the stability of the electrode/electrolyte interfaces. Therefore, it is crucial to design new electrolyte components or formulations to stabilize the interphases and thus the cycling stability for high-energy and high-capacity cathodes/anodes. In this review, based on a comprehensive comparison of the fundamental mechanisms between SIBs and LIBs, the challenges and governing principles for electrolyte design in SIBs are first introduced. The progress in electrolyte designs for various high-energy cathodes is summarized according to their ion-transport characteristics and the interphase formation. Electrolyte design strategies, particularly for the high-capacity anodes, are also surveyed, together with effective electrolyte design strategies to fulfill the requirements under practical operating conditions. Finally, future perspectives on electrolyte development from the viewpoints of full cell-level performance, cost, and feasibility are highlighted. This review aims to provide a roadmap for advancing electrolyte design toward practical SIBs competitive with LIBs.