The Electrochemistry of Fe₃O₄/Polypyrrole Composite Electrodes in Lithium-Ion Cells: The Role of Polypyrrole in Capacity Retention

Abstract

Two series of magnetite (Fe 3 O 4 ) composite electrodes, one group with and one group without added carbon, containing varying quantities of polypyrrole (PPy), and a non-conductive polyvinylidene difluoride (PVDF) binder were constructed and then analyzed using electrochemical and spectroscopic techniques. Galvanostatic cycling and alternating current (AC) impedance measurements were used in tandem to measure delivered capacity, capacity retention, and the related impedance at various stages of discharge and charge. Further, the reversibility of Fe 3 O 4 to iron metal (Fe 0 ) conversion observed during discharge was quantitatively assessed exsitu using X-ray Absorption Spectroscopy (XAS). The Fe 3 O 4 composite containing the largest weight fraction of PPy (20 wt%) with added carbon demonstrated reduced irreversible capacity on initial cycles and improved cycling stability over 50 cycles, attributed to decreased reaction with the electrolyte in the presence of PPy. This study illustrated the beneficial role of PPy addition to Fe 3 O 4 based electrodes was not strongly related to improved electrical conductivity, but rather to improved ion transport related to the formation of a more favorable surface electrolyte interphase (SEI). Li-ion battery (LIB) technology has played a critical role in the widespread adoption of a variety of portable electronic devices. However, due to the applications-driven nature of batteries, especially ambitious capacity and power requirements by potentially new devices, there is an increasing need for the basic understanding of the complicated Li-ion related electrochemistries associated with new electroactive materials. For example, one strategy to increase the capacity of electroactive materials is to use materials capable of multi-electron transfer (such as conversion reactions) resulting in high energy density materials.1 Towards this end, magnetite, Fe 3 O 4 , is a promising nanoscale electroactive material with a high theoretical capacity (926 mAh/g) upon full conversion to Fe metal.2 Thus, over the past several years, the number of published studies of Fe 3 O 4 has been increasing due in part to its high energy density, as well as environmental friendliness and low cost.

Charge injection based electrical stimulation on polypyrrole planar electrodes to regulate cellular osteogenic differentiation

“…1C, the obtained electrode exhibits typical Raman peaks at 1580 and 980 cm À1 , which are assigned to the symmetric C]C backbone stretching mode and C-H plane deformation. [26][27][28][29] The FTIR spectrum (Fig. 1D) shows the broad band around 3000-3500 cm À1 , which could be ascribed to N-H and aromatic C-H stretching vibrations.…”

Temporally and Spatially Resolved Visualization of Electrochemical Conversion: Monitoring Phase Distribution During Lithiation of Magnetite (Fe3O4) Electrodes

“…Continued lithiation proceeds via a conversion reaction forming metallic Fe 0 and Li 2 O . Several approaches have been utilized to improve the electrochemical reversibility and rate capability of Fe 3 O 4 , including (a) reduction of Li + diffusion path length via synthesis of nanomaterials with controlled crystallite size, − (b) control of morphology to minimize structural stresses caused by volume changes during the conversion reaction, , and (c) incorporation of Fe 3 O 4 into composite electrode heterostructures that facilitate ion and electron conductivity. − Previous studies have had success in increasing the reversibility of the conversion reaction at high rates when these strategies were employed …”

Size dependent behavior of Fe3O4crystals during electrochemical (de)lithiation: an in situ X-ray diffraction, ex situ X-ray absorption spectroscopy, transmission electron microscopy and theoretical investigation

“…8,[11][12][13][14][15][16][17][18][19][20] Furthermore, the use of conductive polymers has been found to enhance conductivity between active material particles, resulting in improved performance. [21][22][23][24] Despite these advances, however, ion transport limitations still exist during the initial insertion process, especially in larger nanocrystallites (ca. 30 This journal is © The Royal Society of Chemistry 20xx…”