Abstract: Integrating a lithium-metal anode and a high-voltage cathode into a solid-state battery remains a formidable challenge, especially when the battery is charged beyond 4V. Most electrolytes genuinely do not possess such a wide electrochemical stability window, but have to rely on the formation of a passivating solid electrolyte interphase, require protective electrode coatings, or have to be combined with a secondary electrolyte to achieve stable dis-/charge cycling, adding complexity.
We recently employed a polymer electrolyte based on a polymerized ionic liquid to demonstrate a 4 V class solid-state battery with a lithium metal anode and a LiNi 0.8Mn 0.1Co0.1 cathode operating at room temperature and delivering an initial capacity of 162 mAh/g and a capacity retention of 72% after 600 cycles to 4.4 V [1]. The polymer matrix consists of poly(diallyldimethylammonium) bis(fluorosulfonyl)imide (PDADMAFSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (PYR 13 FSI) is employed as plasticizer in combination with lithium bis(fluorosulfonyl)imide (LiFSI) as lithium salt. PDADMAFSI and PYR13 FSI were selected because of their outstanding chemical stability and wide electrochemical stability window. Comparing to typical lithium-ion coordinating polymer matrices, the positively charged PDADMA+ chains reduce lithium-ion coordination with the polymer promoting high lithium-ion mobility. LiFSI also exhibits low binding energy between Li + and FSI- and the ability to form stable interphases in contact with lithium metal. To confirm the high oxidative stability of this electrolyte, we also assembled a solid-state lithium-metal cell with a high-voltage spinel LiMn 1.5 Ni0.5 O4 cathode reaching an initial capacity of 132 mAh/g and a capacity retention of 76% after 300 cycles to an upper cut-off voltage of 5 V at room temperature.
References:
[1] C. Fu, G. Homann, R. Grissa, D. Rentsch, W. Zhao, T. Gouveia, A. Falgayrat, R. Lin, S. Fantini, C. Battaglia, Adv. Energy Materials 2022412 (2022)
[2] G. Homann, Q. Wang, A. Devincenti, P. Karanth, M. Weijers, F. Mulders, M. Piesins, T. Gouveia, A. Ladam, S. Fantini, C. Battaglia, submitted