|Left. High-magnification SEM images of L- BIOX. Right. Discharge−charge curves at 33.3 mA/g (0.05 C) between 0.5 and 3.0 V. Insets show the cycle-life performance. Credit: ACS, Hashimoto et al. Click to enlarge.|
Researchers in Japan report in a paper in the journal ACS Applied Materials & Interfaces that amorphous Fe3+-based oxide nanoparticles produced by Leptothrix ochracea, an aquatic bacteria living worldwide, show a potential as an Fe3+/Fe0 conversion anode material for lithium-ion batteries. The presence of minor components of silicon (Si) and phosphorous (P), in the original nanoparticles leads to a specific electrode architecture with Fe-based electrochemical centers embedded in a Si, P-based amorphous matrix.
They reported relatively high capacity and good cyclability were found for L-BIOX (L. ochracea’s biogeneous iron oxide), which was used as produced, by simple washing and drying steps. After an “unreasonably high capacity” for the first discharge of ~1500 mAh/g (which they attributed to an extrinsic phenomenon resulting from the formation of the solid−electrolyte interface), the material settled down to reduced yet still high reversible capacity of ~ 900 mAh/g for the second and subsequent cycles.
At the 1 C rate, a capacity of ∼550 mAh/g was maintained over 50 cycles. Even when the voltage range was limited to 0.5−3.0 V, a capacity of ∼600 mAh/g was maintained over at least 50 cycles.
The new material to be proposed in the present work is nanometric amorphous oxide particles produced by Leptothrix ochracea, a species of aquatic bacteria living worldwide, in which iron, silicon, and phosphorus are mixed atomically. In the initial discharge process, a specific composite is formed where the Fe-based active species are embedded in an amorphous Si, P-oxide matrix.
… In this study, we have focused on Leptothrix ochracea’s product (L-BIOX), which can be identified as ocher deposits in natural streams, irrigation canals, ditches, and even near ocean hydrothermal vents. The L-BIOX obtained from a water purifying tank in Joyo, Japan have already been shown to have a number of potential applications, including catalyst supports, carriers for cell culture, battery electrodes, and precursors for pigments.—Hashimoto et al.
The L-BIOX tubules have a fixed bore diameter of ∼1 μm and a variable length of up to several centimeters. The structure results because the nanometric oxide particles precipitate on an extracellular microtubular template made of bacterial organic excrement, the researchers explained. The outer surface of each tubule is covered with ∼20 nm wide and 50−100 nm long fibrils, whereas the inner surface is composed of 20−120 nm-sized globules. The L-BIOX tubules are hierarchical (nano−meso−micro) with respect to both their framework and clearance, and the surface area of the tubules is 280 m2/g.
Optimization of electrode architecture is an important target of electrode materials research. Intimate hybridization with carbon materials like conductive carbon nanofibers has been the most common measure to improve the performance of Fe2O3. In the present architecture the nanometric Fe-based electrochemical centers seem to be intimately linked to the amorphous and therefore flexible Li-transporting network. A similar composite structure was reported by Idota et al. for a Sn-based electrode material. They succeeded in drastically improving the cyclability by dispersing the tin oxide particles in a glassy B3+-, P5+-, and Al3+-oxide matrix. It is interesting that L-BIOX naturally provides this kind of advantageous composite architecture.—Hashimoto et al.
L-BIOX, noted the researchers, can be ceaselessly produced at a high rate and at an extremely low cost.
Hideki Hashimoto, Genki Kobayashi, Ryo Sakuma, Tatsuo Fujii, Naoaki Hayashi, Tomoko Suzuki, Ryoji Kanno, Mikio Takano, and Jun Takada (2014) “Bacterial Nanometric Amorphous Fe-Based Oxide: A Potential Lithium-Ion Battery Anode Material,” ACS Applied Materials & Interfaces 6 (8), 5374-5378 doi: 10.1021/am500905y