Self-Standing and Binder Free Cathode: Facile and Scalable Fabrication with MWCNT for Recyclable and Sustainable Application of Li-O2 Battery
Authors: Su Zeliang , De Andrade Vincent , Shevchenko Elena , Franco Alejandro A. , Demortiere Arnaud 
Published: May 2020

It’s well known that the Li-O2 battery can achieve theoretically1 ten times as much energy density (5200Wh/kg) as Li-ion battery but often limited in reality on the capacity and the cycling. In this system, the carbon cathode provides merely a framework for the lithium peroxide deposition but is not an active material. The dissolved oxygen in the electrolyte is indeed the active material. In other words, the capacity depends on the porosity and the framework architecture. Our previous X-ray tomographic study2 pointed out that a sparse structure is needed to increase the capacity by impeding the pore clogging and oxygen depletion. The conventional fabrication by evaporating the solvent of a slurry can only provide ~20% porosity which is insignificant. Other templating fabrications3,4 are often reported in the literature, but procedures are tedious. To fabricate sparse and self-standing cathode with the multi-wall carbon nanotubes (MWCNTs), we propose a facile and scalable two steps Buchner approach.

The MWCNTs are firstly dispersed in a solvent by sonification. A direct filtration with the separator of a battery can omit a stacking step in the battery assembling (Figure 1). Preceded by a drying process, the cathode is then investigated in the overall cell for electrochemical performance and cyclability. The data of X-ray nano-Computed Tomography acquired in APS synchrotron (ID32) shows that the material is highly porous and the pores are fully filled with the discharge product Li2O2 which conducts to a capacity improvement. Impedance is utilized alongside with tomography data for a complementary understanding of the dominance between lithium ion and oxygen depletion during the discharge.

The self-standing and flexible properties of such cathode even without polymer binder are beneficial for industrial application. We demonstrate the possibility of loading other particles with our approach. A gain of specific surface area for the deposition of lithium peroxide can be obtained with the loading at a price of the mechanical property detriment. Thereby, several percentages of loading are studied to obtain the best trade-off. Besides, bared carbon-nanotube framework with loaded particle trends to loss the structural stability. A sandwich-like structure is hence investigated for the efficiency of the particle confinement.

Finally, our approach is highly eco-friendly. The solvent for nanotube dispersion can be reused after the filtration. And the aged cathode is entirely recyclable by proceeding a low-cost acid retreatment then ultrasonic re-dispersion. The impact of the recycling in terms of electrochemistry and pressure evolution have also been studied.

Figure 1. (a) image of the homogeneous laid out cathode in a Buchner (b) SEM image of the intersection separator and cathode and (c) sandwich structure (d) electrochemical curve with pressure evolution Reference:

(1) Abraham, K. M. A Polymer Electrolyte-Based Rechargeable Lithium/Oxygen Battery. Journal of The Electrochemical Society
1996, 143 (1), 1. https://doi.org/10.1149/1.1836378.

(2) Su, Z.; De Andrade, V.; Cretu, S.; Yin, Y.; Wojcik, Michael. J.; Franco, Alejandro. A.; Demortière, A. X-Ray Nano-Computed Tomography in Zernike Phase Contrast for Study 3D Morphology of Li-O2 Battery Electrode. ACS Applied Energy Materials (submitted)

(3) Cho, S. A.; Jang, Y. J.; Lim, H.-D.; Lee, J.-E.; Jang, Y. H.; Nguyen, T.-T. H.; Mota, F. M.; Fenning, D. P.; Kang, K.; Shao-Horn, Y.; et al. Hierarchical Porous Carbonized Co 3 O 4 Inverse Opals via Combined Block Copolymer and Colloid Templating as Bifunctional Electrocatalysts in Li-O 2 Battery. Advanced Energy Materials
2017, 7 (21), 1700391. https://doi.org/10.1002/aenm.201700391.

(4) Gaya, C.; Yin, Y.; Torayev, A.; Mammeri, Y.; Franco, A. A. Investigation of Bi-Porous Electrodes for Lithium Oxygen Batteries. Electrochimica Acta
2018, 279, 118–127. https://doi.org/10.1016/j.electacta.2018.05.056.

Figure 1