Bacteria-inspired Fabrication of Fe₃O₄-Carbon/Graphene Foam for Lithium-Ion Battery Anodes

Abstract

Although lithium-ion batteries are commonly used to our daily life, achieving superior properties in low-cost is still our current challenge. Here we report the fabrication of a bacteria-inspired, micro-/nanostructured Fe₃O₄-carbon/graphene foam hybrid material for lithium-ion battery anodes. The process employing biological adsorption is featured with low-cost and can have mass-production. Attributed to the graphene foam substrate, the fabricated micro-/nanostructure can be directly employed as a binder-free LIB anode without the need of complex treatments. The product used as an anode delivers a high reversible capacity of 1112 mAh g⁻¹ at the current density of 100 mA g⁻¹ even after 200 cycles, and exhibits good rate performance. These results demonstrate fabrication and electrochemical properties of a bacteria-inspired Fe₃O₄-carbon/graphene foam, suggesting a facile method for making anodes to be used in high-performance lithium-ion batteries.

Introduction

Rechargeable lithium-ion batteries (LIBs) are considered as a promising power source for the portable electronic devices in our daily life [1], [2], [3], [4], [5]. Energy stored in LIBs is basically by the shuttle of lithium ions (Li⁺) between cathode and anode. Some practical applications have been achieved, but critical issues such as cost, stability, energy capacity and rate performances for electrode materials are still needed to be addressed [6], [7], [8]. Many interests are drawn to the development of anode materials based on transition metal oxides: MO_x, where M can be Fe, Co, Ni, etc [5], [6], [7], [8], [9], [10]. Their discharge/charge in LIBs is actually a reversible conversion reaction with Li⁺, including formation and decomposition of lithium oxide, accompany with the reduction and oxidation of MO_x [6], [7], [8]. This mechanism endows them with high theoretical capacity reaching to 500–1000 mAh g⁻¹, much higher than ∼372 mAh g⁻¹ of conventional graphite anode material [9], [10], [11], [12].

Magnetite (Fe₃O₄), an MO_x, possessing relatively high theoretical capacity (∼926 mAh g⁻¹), low-cytotoxicity nature and low-cost for large-scale production, is extensively studied as an anode for LIBs [12], [13], [14], [15]. However, the large volume variation, particle agglomeration, and intrinsic kinetic limitations exist of Fe₃O₄ during discharge/charge processes, have been reported resulting in its irreversible capacity loss and poor stability [17], [18], [19], [20], [21], [22]. Hybridization with carbon-based materials e.g., activated carbon, carbon nanotube, and graphene at nanoscale offers one promising strategy to overcome these challenges of Fe₃O₄ [22], [23], [24], [25], [26]. Due to small dimensions and relatively high specific surface area, nanoscale Fe₃O₄ can shorten effective diffusion length of ions and electrons, thus provides abundant active sites for Li⁺ storage, and accommodates volume variation caused by Li⁺ insertion/extraction [23], [24], [25], [26], [27], [28], [29], [30]. Meanwhile, the carbon-based component can act as a buffer to reduce or even remove the aggregation and volume effects, as well as a conductive media to improve electron transport of Fe₃O₄ [31], [32], [33], [34], [35]. Of various carbon-based materials, three-dimensional (3-D) graphene foam (GF) constituting sheets of graphene is of excellent electron transport and many other superior properties e.g., light weight and chemical resistance, representing one of powerful substrate candidates for LIBs [36], [37], [38], [39], [40]. So far, several works have reported hybrid Fe₃O₄/carbon-based LIB anodes, Li et al., had successfully fabricated a bio-inspired hierarchical nanofibrous Fe₃O₄-TiO₂-carbon composite by employing the natural cellulose. Such composite showed a significant improvement in stability and rate capability while using as the anode for LIBs [33]; Luo et al., used atomic layer deposition (ALD) to synthesize hierarchical porous Fe₃O₄/VO_x/graphene nanowires. The product exhibited high Coulombic efficiency and outstanding reversible specific capacity [34]; Hu et al., had developed a supercritical carbon dioxide (scCO₂) method to anchor Fe₃O₄ nanoparticles onto the graphene foam, and the composite could be able to deliver excellent capacity [35].

Bacteria, micro-organism widely distributed in nature, exhibit unique structures and functionalities [41], [42], [43], [44], [45], [46], [47], [48], [49]. To our interest, they provide abundant biomass for the batch fabrication of micro-/nanostructures with controlled size, structure, and functionality in a low-cost manner. In this study, we developed a route utilizing biological adsorption to synthesize bacteria-inspired Fe₃O₄-carbon/GF for LIB anodes. The Escherichia coli (E. coli)-based fabrication is demonstrated as an example. The fabricated Fe₃O₄-carbon/GF being of hierarchical structures can be directly employed as a binder-free LIB anode without any complex treatments. Results from electrochemical measurements reveal that this kind of anode with a high reversible capacity, long cycle stability and good rate performance. The fabrication of this bacteria-inspired LIB anode takes advantage of biological adsorption, suggesting a versatile and facile method for the low-cost production of high-performance LIBs.