Using Solid, Quasi-Solid, Liquid, and Hybrid Electrolytes in Sodium-Ion Battery (SIBs): A Competition of SIBs vs. LIBs for Vehicles

The global push for sustainable energy has intensified the need for efficient, reliable energy storage, exposing the limitations of lithium-ion batteries (LIBs) due to lithium scarcity and cost. Sodium-ion batteries (SIBs) have emerged as a promising, cost-effective alternative for large-scale stationary storage, especially to support intermittent renewable sources. SIBs rely on reversible sodium-ion intercalation between anodes and cathodes, with electrolytes critically influencing ion transport, electrochemical stability, and overall performance. Electrolytes can be liquid, quasi-solid, solid, or hybrid, each balancing ionic conductivity, mechanical strength, and safety. Key factors include ionic conductivity, cation transference number, electrochemical stability, interfacial resistance, and formation of stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers, which govern charge/discharge kinetics, cycle life, and power density. Liquid electrolytes, often carbonate- or ether-based, remain dominant due to high ionic mobility and compatibility, while emerging hybrid systems aim to combine liquid-like conductivity with solid-state stability, suppressing dendrites and enhancing safety. Optimizing electrolyte properties is central to advancing scalable, high-performance SIBs.