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Crystal structure and electrochemical properties of LiFe1−xZnxPO4 (x ≤ 1.0)

Published online by Cambridge University Press:  05 March 2012

Yanming Zhao ,
Ling Chen ,
Xiren Chen ,
Quan Kuang  and
Youzhong Dong
Yanming Zhao
Affiliation:
School of Physics, South China University of Technology, Guangzhou 510640, China
Ling Chen
Affiliation:
School of Physics, South China University of Technology, Guangzhou 510640, China
Xiren Chen*
Affiliation:
School of Physics, South China University of Technology, Guangzhou 510640, China
Quan Kuang
Affiliation:
School of Physics, South China University of Technology, Guangzhou 510640, China
Youzhong Dong
Affiliation:
School of Physics, South China University of Technology, Guangzhou 510640, China
*
a)Author to whom correspondence should be addressed. Electronic mail: [email protected]
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Abstract

A series of LiFe1−xZnxPO4 (0.0 ≤ x ≤ 1.0) compounds were prepared by solid-state reaction. Effects of the substitution of Zn for Fe on crystal structure and electrochemical properties of LiFe1−xZnxPO4 were investigated. The results show that single-phase regions of LiFe1−xZnxPO4 with orthorhombic (space group Pmna) and monoclinic (Cc) structures were found for the compounds with low Zn (or high Fe) contents of 0.0 ≤ x ≤ 0.30 and high Zn (or low Fe) contents of 0.90 ≤ x ≤ 1.0, respectively. The LiFe1−xZnxPO4 compounds with medium Zn (or Fe) contents of 0.35 ≤ x ≤ 0.80 are two-phase mixtures containing both the orthorhombic and the monoclinic phases. Systematic variations of unit-cell parameters a, b, c, and volume V with the Zn content determined by X-ray diffraction have also been obtained. Our electrochemical study show that the conductivity of LiFe1−xZnxPO4 increases by almost 2 orders of magnitude from 2.13 × 10−9 to 1.27 × 10−7 Scm−1 as the Zn content increasing from x = 0 to 0.3. The initial specific capacity decreases and the cycle performance increase with increasing Zn-doping content in the four orthorhombic LiFe1−xZnxPO4 compounds. Among the four LiFe1−xZnxPO4 compounds, LiFe0.8Zn0.2PO4 has the highest capacity retentions after 6 to 20 cycles and the capacity retention is 93.7% after 20 cycles, even though the initial discharge specific capacity of LiFe0.8Zn0.2PO4 is lower than those of LiFeZnPO4 and LiFe0.9Zn0.1PO4. LiFe0.7Zn0.3PO4 has the highest capacity retention of 97% after 20 cycles.

Keywords

LiFe1−xZnxPO4unit-cell parameterselectrochemical performancelithium batteries
Type
Technical Articles
Information
Powder Diffraction , Volume 26 , Issue 3 , September 2011 , pp. 238 - 243
Copyright
Copyright © Cambridge University Press 2011

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