The need for sustainable mobility leads to a growth of the market of electric cars. In all roadmaps for battery development, solid-state batteries are the next step after advanced lithium-ion batteries (LIBs). They offer the potential to significantly increase the energy density, combined with a higher safety due to the absence of a flammable liquid electrolyte. During the last years, research on solid-state batteries has significantly increased, but still, they face many challenges, such as the development of a high performant solid electrolyte, the integration of the positive electrode material with the solid electrolyte, and the integration of the lithium metal anode with is needed to obtain the predefined energy densities.
This work introduces a polymeric eutectogel (P-ETG) hybrid solid-state electrolyte with an N-isopropyl acrylamide (NIPAM) backbone for high-energy LIBs. The polymeric backbone eutectogel (P-ETG) is a hybrid solid-state electrolyte in which a Li-ion conducting deep eutectic solvent is confined within the polymeric backbone. Such an electrolyte allows the combination of the processability advantage of polymers with the high Li-ion conductivity of liquid electrolytes, thus overcoming the primary disadvantages of solid polymer electrolytes. The NIPAM-based P-ETG is electrochemically compatible with commercially relevant positive electrode materials, such as the nickel-rich layered oxide LiNi0.6Mn0.2Co0.2O2 (NMC622). The chemical compatibility was demonstrated through (physico)chemical characterization methods. The non-existence (within detection limits) of interfacial reactions between the electrolyte and the positive electrode, and the unchanged bulk crystallographic composition were shown by Fourier Transform Infrared Spectroscopy (FT-IR), and powder X-ray diffraction (PXRD), 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 compatibility of high-potential NMC622-containing positive electrode materials and the P-ETG has further demonstrated in Li|P-ETG|NMC622 cells which deliver a discharge capacity of 134, 110, and 97 mAh/g at C/5, C/2, and 1C, respectively, after 90 cycles. The coulombic efficiency is >95% at C/5, C/2, and 1C. Therefore, the NIPAM-based P-ETG shows potential as a safe, inexpensive, and flexible electrolyte for next-generation solid-state LIBs with high-potential positive electrode materials.
This project receives financial support from VLAIO (Baekeland project) and Umicore.
C. Sun, et al., Nano Energy, vol. 33, pp. 363–386, 2017
J. Janek, W. G. Zeier, Nature Energy, vol. 1, no. 9. pp. 1–4, 2016
A. Manthiram, et al., Nat. Publ. Gr., vol. 2, 2017
B. Joos et al., Chem. Mater., vol. 32, no. 9, pp. 3783–3793, 2020