Researchers in Europe, with colleagues from Samsung R&D Institute in Japan, have developed a highly stable Fe₃O₄/C composite for use as a conversion electrode in all-solid-state Li-ion batteries. The material shows shows high specific capacity values of 506 mAhg⁻¹ after 350 cycles at a specific current of 250 mAg⁻¹, with very high stability and coulombic efficiency. An open-access paper on their work is published in the Journal of the Electrochemical Society.

… increasing demand for battery systems with higher energy density requests a breakthrough in finding new materials. In the last decade, the industry standard has been represented by insertion materials for both anode and cathode, while recently alloy-forming materials with Li_xZ (Z = Si, Sn, Sb, Bi) formula have emerged as viable, alternative anodes materials. In addition, recently a new chemistry has surfaced, allowing to store more Li⁺ by the so-called conversion mechanism. In this process the active material is reversibly reduced into metallic nanoclusters embedded in a Li₂O matrix …

Among the others, several transition metal oxides, sulfides, nitrides, phosphides and fluorides have been explored and tested as conversion anodes. Considering 3d-transition metal oxides, among iron oxides α-Fe₂O₃ and Fe₃O₄ have received great attention. Fe₃O₄, also known as magnetite, is a low cost, environmentally benign metal oxide that can undertake a reversible conversion reaction with Li⁺ ions … which results in a theoretical capacity of 924 mAhg⁻¹, almost 3 times higher than the commercially available graphite anode.

… Despite these premises, transition metal oxides associated with the conversion mechanism usually suffer from a series of issues intimately connected with the conversion reaction itself. In fact, remarkable structural changes and volume expansion are associated with this mechanism, eventually leading to pulverization and loss of contact between active material particles and the current collector, which result in poor electron and ion transport limiting the overall cycle-life.

… Here, we report the synthesis, characterization and evaluation of the electrochemical properties of pristine Fe₃O₄ nanoparticles synthesized from a base catalyzed method mechanically mixed with electrospun Polyacrylonitrile (PAN) derived carbon fibers as simple composite material. The Fe₃O₄/C electrodes are characterized by galvanostatic cycling experiments using currents as high as 2000 mA g⁻¹, revealing high capacity values and capacity retention, together with a very good capacity recovery during the rate capability experiment.

—Maroni et al.

Rate capability experiments showed very good performance with a remarkable capacity recovery during the long cycling at the end of the experiment.

Prolonged cycling experiments at high current rate, 500 and 1000 mA g⁻¹ showed strong performance for more than 1000 cycles.

… the use of all-solid-state cell configuration combined with the synthesis of inexpensive oxide like Fe₃O₄, easily synthesizable electrolyte and electrospun carbon fibers is very promising for the building of future LiBs with improved cycle-life and safety.

—Maroni et al.

Resources

• F. Maroni et al. (2020) “Highly Stable Fe₃O₄/C Composite: A Candidate Material for All Solid- State Lithium-Ion Batteries” J. Electrochem. Soc. 167 070556 doi: 10.1149/1945-7111/ab80ce