Towards the Realization of Aqueous Electrode Processing for Sustainable High-Energy Lithium-Ion Cathodes

Abstract

The rapidly growing use of lithium-ion batteries in a multitude of applications, ranging from handheld portable devices over electric bikes and scooters to (hybrid) electric cars and stationary energy storage, has awakened an increasing awareness for a more sustainable cell manufacturing. In fact, improving the environmental benignity of lithium-ion batteries is of utmost importance for their large-scale employment.1,2 To achieve this goal, all stages of cell fabrication must be taken into consideration. This includes not only the incorporation of non-toxic and readily available active materials, but also the development of environmentally-friendly and cheap binding agents, which can ideally be processed in water, thus sparing energy-intensive drying procedures and dry-room conditions and, as a result, turning the whole battery fabrication more eco-efficient. For graphite anodes, for instance, the utilization of water-soluble cellulose-based binders did not only render the use of toxic N-methyl-2-pyrrolidone as solvent unnecessary, but moreover led to substantial improvement in terms of cycling stability and first cycle coulombic efficiency.3,4 For the cathode side, however, the pronounced sensitivity of lithium transition metal oxides (e.g., LiNi0.5Mn1.5O4 (LNMO), Li[Ni1/3Mn1/3Co1/3]O2 (NMC), or Li2MnO3*NMC) towards water in combination with the resulting severe pitting corrosion of the aluminum current collector has so far prevented the implementation of aqueous binders and processing techniques.5–7 In this regard, our recent results, following a complementary approach to enable the aqueous processing of high-voltage LNMO by introducing suitable processing additives in order to stabilize the active material/water as well as the electrode/electrolyte/current collector interface, demonstrate the great potential to realize more sustainable lithium-ion cathodes. The synergistic interaction of an in situ surface coating of the active material particles paired with the crosslinking of the cellulose-based binder yields water-processed electrodes without pitting corrosion, enhanced cycling stability, improved rate performance, and overall higher specific capacities.8 Herein, we will address the remaining challenges encountered after establishing the aqueous lab-scale processing of these high-voltage lithium-ion cathodes to eventually achieve commercially viable cathode tapes, readily available for large-scale, high-energy lithium-ion batteries. These addressed challenges include improvements concerning the electrode to current collector adhesion, the binder distribution and electrode components cohesion, as well as the realization of highly stable cycling without a steady initial capacity increase and coulombic efficiencies, exceeding those for LNMO-based electrodes comprising the state-of-the-art poly(vinylidene difluoride) (PVdF) binder. References D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015).C. J. Barnhart and S. M. Benson, Energy Environ. Sci., 6, 1083 (2013).H. Buqa, M. Holzapfel, F. Krumeich, C. Veit, and P. Novák, J. Power Sources, 161, 617–622 (2006).S. F. Lux, F. Schappacher, A. Balducci, S. Passerini, and M. Winter, J. Electrochem. Soc., 157, A320 (2010).X. Zhang et al., J. Power Sources, 196, 5102–5108 (2011).M. M. Thackeray, J. Am. Ceram. Soc., 82, 3347–3354 (1999).N. Loeffler et al., ChemSusChem, 9, 1112–1117 (2016).M. Kuenzel et al., ChemSusChem, 11, 562–573 (2018).