Ion exchange and electrochemical evaluation of the microporous phosphate Li{sub 9}Fe{sub 7}(PO{sub 4}){sub 10}

Journal Article · Mon Dec 01 04:00:00 EST 2008 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2008.02.005· OSTI ID:21195029

Becht, Gregory A ^[1]; Vaughey, John T ^[2]; Britt, Robin L; Eagle, Cassandra T ^[3]; Hwu, Shiou-Jyh ^[1]

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1. Department of Chemistry, Clemson University, Clemson, SC 29634-0973 (United States)
2. Chemical Sciences and Engineering, Argonne National Laboratory, Argonne, IL 60439-4837 (United States)
3. Department of Chemistry, Appalachian State University, Boone, NC 28608-2036 (United States)

A new lithium iron(III) phosphate, Li{sub 9}Fe{sub 7}(PO{sub 4}){sub 10}, has been synthesized and is currently under electrochemical evaluation as an anode material for rechargeable lithium-ion battery applications. The sample was prepared via the ion exchange reaction of Cs{sub 5}K{sub 4}Fe{sub 7}(PO{sub 4}){sub 10}1 in the 1 M LiNO{sub 3} solution under hydrothermal conditions at 200 deg. C. The fully Li{sup +}-exchanged sample Li{sub 9}Fe{sub 7}(PO{sub 4}){sub 10}2 cannot yet be synthesized by conventional high-temperature, solid-state methods. The parent compound 1 is a member of the Cs{sub 9-x}K{sub x}Fe{sub 7}(PO{sub 4}){sub 10} series that was previously isolated from a high-temperature (750 deg. C) reaction employing the eutectic CsCl/KCl molten salt. The polycrystalline solid 1 was first prepared in a stoichiometric reaction via conventional solid-state method then followed by ion exchange giving rise to 2. Both compounds adopt three-dimensional structures that consist of orthogonally interconnected channels where electropositive ions reside. It has been demonstrated that the Cs{sub 9-x}K{sub x}Fe{sub 7}(PO{sub 4}){sub 10} series possesses versatile ion exchange capabilities with all the monovalent alkali metal and silver cations due to its facile pathways for ion transport. 1 and 2 were subject to electrochemical analysis and preliminary results suggest that the latter can be considered as an anode material. Electrochemical results indicate that Li{sub 9}Fe{sub 7}(PO{sub 4}){sub 10} is reduced below 1 V (vs. Li) to most likely form a Fe(0)/Li{sub 3}PO{sub 4} composite material, which can subsequently be cycled reversibly at relatively low potential. An initial capacity of 250 mAh/g was measured, which is equivalent to the insertion of thirteen Li atoms per Li{sub 9+x}Fe{sub 7}(PO{sub 4}){sub 10} (x = 13) during the charge/discharge process (Fe{sup 2+} + 2e {yields} Fe{sup 0}). Furthermore, 2 shows a lower reduction potential (0.9 V), by approximately 200 mV, and much better electrochemical reversibility than iron(III) phosphate, FePO{sub 4}, highlighting the value of improving the ionic conductivity of the sample.

• OSTI ID: 21195029
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 12 Vol. 43; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
ELECTRIC BATTERIES
ELECTROCHEMISTRY
ION EXCHANGE
IONIC CONDUCTIVITY
IRON IONS
IRON PHOSPHATES
LITHIUM IONS
LITHIUM NITRATES
LITHIUM PHOSPHATES
TEMPERATURE RANGE 0400-1000 K