Dual lithium uptake anode materials: crystalline Fe3O4 nanoparticles supported over graphitic matrices for lithium-ion batteries

EMILIANO N. PRIMO; GUILLERMINA L. LUQUE; LISANDRO VENOSTA; DANIEL E. BARRACO; M. VICTORIA BRACAMONTE; PAULA BERCOFF

Buenos Aires

Conferencia; 20th Topical Meeting of the International Society of Electrochemistry Advances in Lithium and Hydrogen Electrochemical Systems for Energy Conversion and Storage; 2017

To fulfil the rapidly growing demand for lithium-ion batteries (LIB) with higher energy density and long cycle life, transition-metal oxides have been investigated as promising high-capacity anodes [1]. Among them, magnetite (Fe3O4) is a low cost, environmentally friendly metal oxide that can undertake a reversible conversion reaction with Li+ ions which results in a theoretical capacity of 924 mA hg−1, almost 3 times higher than the industry-standard graphite [2]. As the complete utilization of the electroactive metal centers can be a challenge for a densely structured material as Fe3O4, whit no well defined layers or tunnels for facile Li+ insertion, the utilization of nano-sized Fe3O4 hybrid structures is almost mandatory. Its utilization, also favors the complete employment of the material for the conversion reaction,.In this work, we report the employment of several graphitic samples (G), with different particle sizes and characteristics, used as support for the precipitation of Fe3O4 nanoparticles (NPs) to obtain Fe3O4-G hybrids. The obtained hybrids were characterized as a function of the carbon support and further utilized as anode materials for the development of LIBs. The cyclability and charge-discharge profiles were compared considering the simultaneous capacity of lithiation of both Fe3O4 NPs and graphite.The graphite samples employed (G1, G2 and G3) were of 2, 17 and 410 m lateral size; respectively. Fe3O4 NPs (12 nm) are mainly located at the edges of the structures; as determined by SEM images and Raman analysis. Hysteresis loops obtained through magnetometric measurements showed that the Fe3O4 wt% of each sample were 9% (Fe3O4-G1), 16% (Fe3O4-G2) and 18% (Fe3O4-G3).Fe3O4-G samples exhibit 2 different regions when cycling them between 3.000 and 0.010 V. The first one (around 0.700 V) corresponds to the lithiation of Fe3O4 NPs and the formation of Li2O and metallic Fe. The second one (around 0.100 V) arises from the intercalation of Li ions in the graphitic planes. As a consequence, both constituents play a synergistic role in the lithium uptake and observed capacity profile. The great advantage of using this material is that the present one is less inexpensive and more efficient alternative for immobilizing Fe3O4 NPs, in comparison to other extensively-used carbon nanostructures such as carbon nanotubes or graphene cannot act as active materials for lithium storage. Fe3O4-G1 and G2 based anode retain its specific capacity after cycling the battery several times while Fe3O4-G2 loses its capacity up to half of the initial one in the first cycles. This shows that the differences in carbon material size play a major role in the performance of the LIB by modulating the connectivity of the active Fe3O4 zones.In conclusion, Fe3O4-G hybrid materials were synthesized, producing Fe3O4 NPs which are uniformly dispersed over the carbon surfaces. The Fe3O4-G hybrids with different sizes were employed for the development of anodes for LIB. A synergistic effect between the magnetite lithiation conversion reaction and the graphite lithium intercalation was observed. We also determined that Fe3O4 loading and carbon material size determines the LIB cyclability.