Study of Various (“Super Iron”) MFeO[sub 4] Compounds in Li Salt Solutions as Potential Cathode Materials for Li Batteries

Abstract

In this work we studied the possibility of using Fe+6 “super iron” compounds, including BaFenormalO4,normalK2FenormalO4,CuFenormalO4 , and SrFenormalO4 as potential cathode materials for rechargeable Li batteries, and their behavior in several nonaqueous Li salt solutions. Classic electrochemical techniques, such as cyclic voltammetry and chronopotentiometry combined with X-ray photoelectron spectroscopy, X-ray diffraction, Mössbauer spectroscopy, atomic adsorption, atomic emission, in situ and ex situ atomic force microscopy imaging, and diffuse reflectance Fourier Transform infrared spectroscopy were used in order to obtain a full picture of the electrochemical behavior of these compounds. Fe6+ compounds such as normalK2FenormalO4 and BaFenormalO4 are reduced in the presence of Li ions to Fe3+ compounds. Fe2normalO3,Li2O , and normalK2O or BaO are formed in amorphous or nanocrystalline structures. The reaction is partially reversible, i.e., Fe6+ compounds can be reformed by oxidation. The mechanisms of the lithiation–delithiation of these systems and what limited their reversibility are discussed.

Advances in Fe(VI) charge storage

“…While rechargeable lithium and metal hydride anodes have increased the energy The most recent development in super-iron cathode chemistry is that it is reversible, which has led to the demonstration of rechargeable super-iron batteries. In accord with recent studies [22,24,30,32], the principal limitation to Fe(VI) reversibility has been the passivation of Fe(VI)/Fe(III) redox couple due to resistive buildup of low-conductivity ferric salts. Recently, it has been shown that ultra-thin Fe(VI) layers are reversible cathodes.…”

“…However, the more recent evidence suggests that the iron centers undergo a partially reversible Faradaic reduction in the compounds from 6 + to 3 + states, central to this interpretation is direct Mössbauer measurement of the iron valence state of the cathode during charge storage [32]. Fig.…”

“…Recently, it has been shown that ultra-thin Fe(VI) layers are reversible cathodes. Consequently they are rechargeable in electrolytes, respectively, conducive to both lithium-ion [32] and metal hydride [24,30] anode batteries. This review paper first focuses on the reversible alkaline super-iron cathodes, then provides a summary of the primary and rechargeable nonaqueous super-iron batteries.…”

A High Capacity Li-Ion Cathode: The Fe(III/VI) Super-Iron Cathode

“…Development Reference 1999 introduction of super-iron charge storage & super-iron alkaline battery [5] 2000** introduction of super-iron lithium primary (single discharge) battery [7] 2001 demonstration of the solid state stability of the hexavalent iron [8] 1999-5 chemical syntheses of an array of super-iron salts [5,7,[9][10][11][12][13][14][15][16] 2000-4 inexpensive, electrochemical syntheses of super-iron salts [17][18][19][20][21][22][23][24][25][26] 2003-5** electrolyte optimization for super-iron lithium batteries [27,28] 2003 reversibility of alkaline, nanothick (3 nm) Fe(VI) cathodes [29] 2006 rechargeable alkaline super-iron battery [30] 2006** reversibility of non-aqueous, nanothick (3 nm) Fe(VI) cathodes [31] 2007-8 zirconia encapsulation-stabilization of alkali super-irons [32][33][34][35] 2009** rechargeable super-iron lithium battery, 4 V cathode [6] **=lithium super-iron battery development.…”

“…FTIR provides not only a specific "fingerprint" distinguishing the various Fe(VI) oxides, as shown in Figure 5, but importantly we have also developed it as a quantitative technique to determine the Fe(VI) salt purity through the addition of a standardized BaSO 4 salt [8]. Discharge of cathode replaced, commercial alkaline button cells provides rapid screening of the redox activity of alternative salts [6,10,11,14,15,19,[27][28][29][30][31][32][33][34][35].…”