Electrochemical discharge of nanocrystalline magnetite: structure analysis using X-ray diffraction and X-ray absorption spectroscopy

Abstract

Magnetite (Fe3O4) is an abundant, low cost, environmentally benign material with potential application in batteries. Recently, low temperature coprecipitation methods have enabled preparation of a series of nanocrystalline magnetite samples with a range of crystallite sizes. Electrochemical cells based on Li/Fe3O4 show a linear increase in capacity with decreasing crystallite size at voltages ≥1.2 V where a 2× capacity improvement relative to commercial (26.2 nm) magnetite is observed. In this report, a combination of X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) is used to measure magnetite structural changes occurring upon electrochemical reduction, with parent Fe3O4 crystallite size as a variable. Notably, XAS provides evidence of metallic iron formation at high levels of electrochemical reduction.

Correlating Preparative Approaches with Electrochemical Performance of Fe3O4-MWNT Composites Used as Anodes in Li-Ion Batteries

“…22 as supported by recent X-ray absorption spectroscopy results. 24 From points A to B, less than one Li + ion can get into Fe 3 O 4 . At this level of lithiation, a rock salt type phase Li x Fe 3 O 4 (0 < 'x' < 2) is formed and at this discharge level, the lithiation process occurs via the insertion mechanism.…”

Modeling the Mesoscale Transport of Lithium-Magnetite Electrodes Using Insight from Discharge and Voltage Recovery Experiments

“…To address this issue, several authors have synthesized Fe 3 O 4 nano-crystallites in attempts to minimize the path length for ion transport. [9][10][11][12][13][14] The smaller path length increases the utilization of the active material by making it possible for ions to penetrate to the center of the crystals, especially at high rates of discharge. Electrodes fabricated with nano-crystalline magnetite have shown significant improvement in capacity; however, the theoretical capacity has still proven difficult to obtain.…”

“…[2][3][4] In particular, considerable work has focused on the advancement of magnetite (Fe 3 O 4 ) as an electrode in lithium-ion batteries due to its high theoretical capacity (926 mAh g −1 ), low cost and safety (non-toxic). [5][6][7][8][9][10][11][12][13][14] Despite these advantages, one of the major challenges limiting the advancement of magnetite electrodes is a considerable difference between the maximum, theoretical capacity and the observed, experimental capacity of the active material. This difference increases the anticipated cost of magnetite batteries because it requires the electrodes to be overdesigned with excess amounts of active material.…”

Electrochemistry of Cu0.5VOPO4·2H2O: A Promising Mixed Metal Phosphorous Oxide for Secondary Lithium based Batteries

“…However, there are examples of materials where a metallic phase resulting from electrochemical reduction is not detectable by XRD. 32 Thus, it is possible that copper metal is formed as an electrochemical reduction product.…”