A Stable Fe₃O₄-Based Hybrid Anodes for High Performance Li-Ion Batteries

Abstract

There is an increasing demand for high-performance Li-ion batteries especially due to environmental concerns. To meet the high-performance requirements of the Li-ion batteries, conversion-type anodes stand out with their capacities. The crystal structure of magnetite (Fe 3 O 4 ) benefits from its empty interstitial sites which hinders volume changes during the insertion and extraction of lithium ions. Combined with its high theoretical lithium storage capacity and abundance, Fe 3 O 4 has great potential as an alternative anode. Yet in its practical use, the material suffers from severe capacity degradation, mainly due to the formation of a passive metallic iron layer on the electrode [1]. Another suggested mechanism responsible for the deterioration of the performance is the formation of electrochemically inactive FeO-based side products upon delithiation process [2]. In this study, we utilize reduced graphene oxide (rGO) as a substrate for the ultrafine Fe 3 O 4 nanoparticles to form a two-dimensional hybrid material with improved characteristics. Under a mild hydrothermal condition, nanoparticles were deposited by a simple redox process in an interconnected porous network of graphene. Graphene aids in improving the Fe 3 O 4 performance not only by reducing the charge transfer resistance, buffering the volume change induced stresses and facilitating the ion transport but also by forming an effective interface with the delocalized electrons of Fe 3 O 4 to further result in the increase of battery capacitance by the interfacial conjugation mechanism, as confirmed by in-situ EIS measurements. The Fe 3 O 4 particles have been effectively stabilized on the rGO surface, becoming less prone to agglomeration during cycling. Consequently, the deliverable specific capacity of the hybrid material was gradually improved upon extended cycling, reaching from 1500 mAh/g up to 2200 mAh/g at 0.5 A/g at the end of 100 cycles of operation. The increase of the specific capacity during the extended cycling was attributed to the chemical and structural changes of the electrode material evaluated by TEM and ex-situ EELS measurements. It was confirmed that the particle size is greatly reduced to 1-2 nm scale, improving the lithium-ion diffusion kinetics by the increased surface area and reversibility of the redox reaction upon graphene contribution. Moreover, the aged cells were observed to still deliver around 1100 mAh/g capacity upon more than 250 times cycling at 1 A/g, indicating the great potential of the ultrafine Fe 3 O 4 decorated reduced graphene hybrids as superior performance Li-ion battery anode materials. References: Li, J., Hwang, S., Guo, F., Li, S., Chen, Z., Kou, R., Sun, K., Sun, C.-J., Gan, H., Yu, A., Stach, E.A., Zhou, H., Su, D. (2019) Phase evolution of conversion-type electrode for lithium ion batteries, Nature Communications , 10(1), 2224. Xu, Z.-L., Zhang, B., Gang, Y., Cao, K., Garakani, M.A., Abouali, S., Huang, J., Huang, J.-Q., Heidari, E.K., Wang, H., Kim, J.-K. (2015) In-situ TEM examination and exceptional long-term cyclic stability of ultrafine Fe 3 O 4 nanocrystal/carbon nanofiber composite electrodes, Energy Storage Materials , 1, 25-34.