Bacteria-Assisted Synthesis of Electrode Materials for Li or Na Batteries

Abstract

The production of materials for high-energy Li-ion batteries is generally associated with negative environmental footprints, due to high temperatures required and chemical toxicity of their components [1]. Our goal is to explore new bio-assisted low-temperature routes of synthesis in order to reduce this environmental impact and possibly improve their electrochemical performances. Bacteria are easy to grow; able to mineralize transition metals and other elements [2], with controlled morphology, crystal structure and texture; they also constitute a potential source of conductive carbon. For these reasons, bacteria assisted synthesis caught our attention, especially as exceptional power performances were already shown for biomineralized hollow shells of hematite (α-Fe2O3) [3] when compared to those of non-textured material. Hydrated amorphous ferric phosphate (a-FeIIIPO4·~3H2O) was precipitated from aqueous solution at 30°C under air at the contact of bacteria (Sporosarcina pasteurii). The resulting materials were investigated using various techniques (e.g. thermal analysis, mass spectrometry, infrared spectroscopy, electron microscopy) and consist of dead bacteria (2-3 µm x 0.5 µm) coated by a 70 nm thick layer of interconnected a-FeIIIPO4·~3H2O particles (40-80 nm), as presented by the following microscopy image. Surface chemistry of the bacterial cell wall plays a key role in the nucleation process thereby controlling particle size. After a mild temperature treatment, a 90 mAh/g capacity has been achieved versus Li (at 3.0 Volts mean voltage) with an excellent cyclability, constant coulombic efficiency (~100%) and interesting power performances. This approach allows overcoming the intrinsic poor conductivity of Fe phosphate without any use of harsh mixing treatments with conductive additive, or complex synthetic procedure. Bacteria are capable of many things and we are now applying this strategy for other materials and other metals like manganese. We will also address the positive attributes of these bio-assisted synthesis for application in Na-based batteries. [1] Samaras C., Meisterling K., Environmental Science & Technology. 42, 3170 (2008). [2] Dupraz S. et al., Chemical Geology. 265, 54 (2009). [3] Miot J. et al., Energy & Environmental Science. 7, 451 (2014). Figure 1