Lithium dual-ion batteries (LDIBs) are an emerging class of energy storage devices that enable the simultaneous intercalation of anions into the cathode and lithium cations into the anode. This dual ion mechanism allows LDIBs to achieve high operating voltages (>4.5 V) while utilizing cost-effective electrode materials, offering strong potential for next-generation high-energy, low cost battery systems.

Despite these advantages, the development of LDIBs is hindered by limitations in electrolyte performance. Since both anions and cations participate in charge storage, the electrolyte must provide fast ion transport, wide electrochemical stability, and stable electrode–electrolyte interfaces. Conventional carbonate-based electrolytes, optimized for lithium-ion batteries, often exhibit poor oxidative stability and limited anion mobility, resulting in rapid capacity fading.

To address these challenges, we designed a high-entropy liquid electrolyte (HELE) that combines multiple solvents and multiple lithium salts to enhance ionic conductivity and molecular-level disorder. Two HELE formulations were designed: HELE 1, containing five salts (LiPF₆, LiBF₄, LiBOB, LiDFOB, LiTFSI), and HELE 2, containing four salts (LiPF₆, LiBF₄, LiFSI, LiTFSI). Their physicochemical and electrochemical properties were systematically compared with a conventional 1 M LiPF₆ in EC/EMC electrolyte to evaluate the impact of compositional complexity on LDIB performance.

Electrochemical impedance spectroscopy revealed that the HELE systems exhibited higher ionic conductivity through glass fiber separators, attributed to weaker solvation structures and enhanced ion mobility. Raman spectroscopy showed a higher proportion of free EC and a lower degree of Li⁺ coordination with the solvent. Cyclic voltammetry showed that the HELEs lowered the onset potential for anion intercalation into graphite by 50–70 mV, suggesting reduced energy barriers and increased anion accessibility.

Long-term galvanostatic cycling at 200 mA g⁻¹ revealed higher retained capacity, higher maximum capacity, and lower degradation rates compared to the baseline electrolyte. Post-cycling impedance measurements confirmed the formation of stable, low-resistance charge-transfer interfaces. These findings highlight entropy-driven electrolyte design as a transformative approach for optimizing ion transport and stability in dual-ion systems, offering a scalable pathway toward high performance, durable, and tunable LDIBs for advanced energy storage applications. The development of high-entropy electrolytes also enables improvements to other battery chemistries, further expanding the capabilities of liquid electrolytes and driving continued advances in electrochemical performance.