Development of non-aqueous aprotic electrolytes for high voltage LiNi0.5Mn1.5O₄||graphite cell chemistry
Zian Hu1, Christian Wölke1, Martin Winter1, Isidora Cekic-Laskovic1*
1: Helmholtz-Institute Münster (IMD-4), Forschungszentrum Jülich GmbH, Corrensstraße 48, 48149 Münster, Germany

High-voltage LiNi₀.5Mn1.5O₄||graphite (LNMO||Gr) cell chemistry provides a cobalt-free and energy-dense alternative to conventional Li ion batteries (LIBs), yet its practical application is hindered by electrolyte instability at elevated voltages (∼5 V) [1]. Conventional lithium hexafluorophosphate (LiPF₆)-based electrolytes formulated with non-fluorinated organic carbonate-based solvents (e.g., ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC)) are highly susceptible to oxidative and hydrolytic decomposition at elevated potentials, producing hydrogen fluoride (HF) and other reactive species that trigger such as transition-metal dissolution and impedance growth [2]. To address these challenges, new electrolyte formulations containing different conducting salts and fluorinated solvents (e.g., fluoroethylene carbonate (FEC)) have been developed to improve both electrochemical and chemical stability under high-voltage operation. The introduction of fluorinated components alters the Li⁺ ion solvation environment, decreases the reactivity of free solvent molecules, and facilitates the formation of lithium fluoride (LiF)-rich, compact, and effective interphases on both LNMO and graphite electrodes [3]. Initial electrochemical results demonstrate improved capacity retention, reduced polarization, and enhanced galvanostatic cycling stability compared to conventional systems with 1 mol/kg LiPF6 in EC:EMC=3:7 wt% electrolyte. Ongoing surface analyses, including SEM, EDX, ICP-OES, XPS, etc., aim to elucidate the compositional and structural evolution of the interphases (CEI and SEI) and their correlation with electrochemical performance. In situ DEMS will provide a direct identification of electrolyte decomposition pathways by correlating gas evolution with electrode potentials, evaluating electrolyte stability and interphase formation of high voltage developed electrolytes for LNMO||Gr cell chemistry [4].

References:
[1] Kim, T., Oh, H., Yang, S., & Lee, H. J, ACS Applied Energy Materials 2025 8(18), 13155–13178.
[2] Yao, W., Li, Y., Olguin, M., Bai, S., Schroeder, M. A., Li, W., … Meng, Y. S., Next Energy 2024 4, 100136–100136.
[3] Leopold, M., Pfeiffer, F., Muschiol, E. C., Wölke, C., Yan, P., Brüning, K., … Isidora Cekic Laskovic., Small 2025, 2505254.
[4] Zenonas Jusys, Binder, M., Schnaidt, J., & Behm, R. J, Electrochimica Acta 2019 314, 188–201.