Gel Electrolytes Incorporated with Graphene-Oxide Quantum Dots for High Performance in Lithium Ion Batteries

Abstract

This study incorporates graphene oxide quantum dots (GOQDs) in to a gel polymer electrolyte (GPE) designed for lithium ion batteries (LIBs). The GPE comprises poly(acrylonitrile-co-vinyl acetate) copolymer (PVA) blending poly(methyl methacrylate) (PMMA) as a host swelled by a liquid electrolyte (LE) of 1-M LiPF6 in a carbonate solvent. The major concerns for GPE-based LIBs is the capacity retention and cycle life under high-rate operation. Among numerous functional polymer segments used for GPEs,1 poly(acrylonitrile) (PAN) exhibits excellent thermal stability, ion-solvating ability, material processibility, and electrochemical stability,2 whereas poly(vinyl acetate) (PVAc) strongly absorbs solvent molecules to facilitate polymer swelling and ion transport. The segmental motion of PVA can be further promoted by blending PMMA; therefore, the polymer framework developed in this study represents an ideal host for GPEs. Previous studies have used inorganic oxide nanoparticles, such as SiO2, TiO2, Al2O3, ZrO2, as fillers to improve both the mechanical strength and ionic conductivity of GPEs.3 GOQDs,which contain numerous oxygen functional groups on the surface, have strong affinity to polymer chains for uniform dispersion in GPEs. The present study finds that the incorporated GOQDs substantially increase the mobility of lithium ions in the developed GPE by accelerating lithium-ion hopping along the polymer chains. A resulting Li/GPE/LiFePO4 battery delivers a high discharge capacity of 70 mAh g-1 at 17 C-rate, which is much higher than that of a Li/LE/LiFePO4 battery (35 mAh g-1). References P. Hu, Y. Duan, D. Hu, B. Qin, J. Zhang, Q. Wang, Z. Liu, G. Cui, L. Chen, ACS Appl. Mater. Interfaces 2015, 7, 4720-4727.S.H. Wang, P.L Kuo, C.T Hsieh, H. Teng, ACS Appl. Mater. Interfaces 2014, 6, 19360−19370M. Osińska, T. Jesionowski, K. S-S. Tefańska, M. Walkowiak, Cent. Eur. J. Chem. 2010,8(6),1311-1317 Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, 105-3113-E-006-005, and 104-3113-E-006-011-CC2), and by the Ministry of Education, Taiwan, The Aim for the Top University Project to the National Cheng Kung University.