Polymeric Backbone Eutectogel Electrolytes for High-Energy Lithium-Ion Batteries

This work introduces a polymeric backbone eutectogel (P-ETG) hybrid solid-state electrolyte with an N-isopropylacrylamide (NIPAM) backbone for high-energy lithium-ion batteries (LIBs). The NIPAM-based P-ETG is (electro)chemically compatible with commercially relevant positive electrode materials such as the nickel-rich layered oxide LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622). The chemical compatibility was demonstrated through (physico)chemical characterization methods. The nonexistence (within detection limits) of interfacial reactions between the electrolyte and the positive electrode, the unchanged bulk crystallographic composition, and the absence of transition metal ions leaching from the positive electrode in contact with the electrolyte were demonstrated by Fourier transform infrared spectroscopy, powder X-ray diffraction, and elemental analysis, respectively. Moreover, the NIPAM-based P-ETG demonstrates a wide electrochemical stability window (1.5-5.0 V vs Li⁺/Li) and a reasonably high ionic conductivity at room temperature (0.82 mS cm^-1). The electrochemical compatibility of a high-potential NMC622-containing positive electrode and the P-ETG is further demonstrated in Li|P-ETG|NMC622 cells, which deliver a discharge capacity of 134, 110, and 97 mAh g^-1 at C/5, C/2, and 1C, respectively, after 90 cycles. The Coulombic efficiency is >95% at C/5, C/2, and 1C. Hence, gaining scientific insights into the compatibility of the electrolytes with positive electrode materials that are relevant to the commercial market, like NMC622, is important because this requires going beyond the electrolyte design itself, which is essential to their practical applications.