Electrolyte design: new advances beyond the Debye-Hückel theory

Traditional electrochemical theories, grounded in the Debye-Hückel model, are inherently limited to ultralow-concentration electrolytes, typically below 0.01 M. These models rely on core assumptions such as the point-charge approximation and dilute-limit hypothesis, which break down in practical high-concentration systems where strong ion correlation effects induce nonlinear phenomena. For instance, in LiFSI/PC electrolytes, the potential of the lithium metal electrode (ELi/Li+) shifts by over 0.6 V with increasing concentration, significantly deviating from Nernst equation predictions. Molecular dynamics (MD) simulations reveal that such deviations stem from the formation of contact ion pairs (CIPs) and aggregates (AGGs) between Li+ and anions. As the LiFSI concentration increases to 4 mol/L, the proportion of FSI− in the first solvation shell of Li+ escalates from 20% to 80%, leading to local electric field reconstruction and significant changes in chemical potential. To address these theoretical limitations, the “liquid Madelung potential” (ELM) framework has been proposed. This framework quantifies the electrostatic contributions of all surrounding atoms, including solvents, anions, and other Li+, to the Li+ ion, thereby enabling accurate prediction of potential shifts in concentrated systems with errors below 5%.This review systematically examines three innovative strategies in electrolyte engineering: Firstly, ion-pair network construction, exemplified by the “water-in-salt” (WiSE) approach using 21 m LiTFSI/H2O, which broadens the electrochemical stability window to 3.0 V and facilitates the formation of a LiF-rich interphase to suppress hydrogen evolution. Secondly, solvent molecular engineering, including the use of fluorinated ether solvents to reduce desolvation energy barriers through weak solvation. Specifically, -CF2-functionalized ethers have demonstrated compatibility with high-voltage cathodes exceeding 5.3 V, while “soft solvent” designs, such as MDFA, stabilize full-cell operation across a broad temperature range from –60°C to +60°C. Thirdly, novel lithium salt development, featuring cyanide-modified LiCTFSI, which enhances aluminum current collector passivation with corrosion currents below 0.1 μA/cm2, and LiDFTFSI, which combines high ionic conductivity (3.7 mS/cm) with excellent thermal stability, retaining 99% capacity at 60°C. Additionally, pseudo-crown ether LiFEA achieves fast-charging power densities of 410 W/kg.Data-driven machine learning is accelerating electrolyte screening through the use of descriptors such as coordination energy and solvation radius, achieving prediction errors as low as 0.05 V. Advanced in situ techniques, including cryo-electron microscopy (cryo-EM) and secondary ion mass spectrometry (SIMS), are unraveling the dynamic evolution of the solid electrolyte interphase (SEI) and lithium dendrite growth patterns. Despite the significant progress achieved, challenges such as high cost, viscosity, and limited compatibility with aggressive battery chemistries persist. Future efforts must focus on integrating multiscale modeling and high-throughput experimentation to advance the development of practical high-energy-density batteries.In conclusion, the shift toward concentrated electrolyte systems demands a rethinking of traditional electrochemical models and the adoption of new frameworks like the liquid Madelung potential. Continued innovation in ion-pair design, solvent chemistry, and salt formulation—supported by machine learning and advanced characterization tools—is critical for unlocking next-generation battery performance. As the field moves forward, integrating theoretical insights with practical engineering and high-throughput experimentation will be essential for overcoming current limitations and achieving safe, scalable, and energy-dense storage technologies. Moreover, a holistic approach that considers sustainability, raw material availability, and recyclability must be embedded into future electrolyte development. Interdisciplinary collaboration across chemistry, materials science, and data science will be the cornerstone of realizing robust electrochemical platforms that meet the growing global demand for renewable energy integration, electric mobility, and grid-scale energy storage.