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Synthesis And Research Of LiMn0.8Fe0.2PO4 As Cathode Materials

Posted on:2015-02-03Degree:MasterType:Thesis
Country:ChinaCandidate:F L MengFull Text:PDF
GTID:2321330518471181Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
LiMPO4(M=Fe,Mn) has attracted a great deal of attention because of its high energy density, good electrochemical performance, high operation voltage, nontoxic, high thermal stability, and low cost.LiMn0.8Fe0.2PO4/C is the best with synthesized conditions: citric acid as carbon source,the ratio of metal ions and citric acid is 2:1, calcinations temperature and time is 700?/8h via a sol-gel route in this paper. It delivers a high capacity of 97.2 mAh·g-1 at 0.05C.Meanwhile, A series of Na, Mg, Si co-doped LiMn0.8Fe0.2PO4 and Li doped LiMn0.8Fe0.2PO4 materials,i-e. Li1-3xNa2xMgxMn0.8Fe0.2P1-xSixO4 (x=0, 0 01,0.02, 0.03, 0.04, 0.08, 0.16) and Li1+x[Mn0.8Fe0.2]1-xPO4/C(x=0,0.01,0.02,0.03,0.04,0.08,0.16),were prepared via a sol-gel route. The effects of Na, Mg, Si co-doping and Li doped on the physical and electrochemical characteristics of LiMn0.8Fe0.2PO4 were systematically investigated. Single phase material with the orthorhombic structure is obtained in both doped methods when x is not higher than 0.08, and the impurity begins to form as a secondary phase as x increase to 0.16. XPS analyses of Na, Mg Si doped samples indicate that the oxidation state of Mn, Fe,are not changed. Moreover,Li0.97Na0.02Mg0.01Mn0.8Fe0.2P0.99Si0.01O4 (x=0.01) is the best among the series materials. The first charge/discharge capacities is 163.4mAh·g-1 at 0.05C.It delivers a high capacity of 116.94 mAh·g-1 at 10C and 80.32 mAh·g-1 at 20C and excellent capacity retention of 98.2% after 100 cycles at 20C. Li1.03[Mn0.8Fe0.2]0.97PO4/C (x=0.03), Li doped sample,is the best among the series materials. The first charge/discharge capacities is 158.5 mAh·g-1 at 0.05C. It delivers a high capacity of 148.32 mAh·g-1 at 1 C and 128.34 mAh·g-1 at 5C and excellent capacity retention of 97.4% after 100 cycles at 1C. The improved electrochemical performance can be attributed to the larger lattice parameters,smaller particle size and better lithium ion transfer capability induced by Na, Fe, Si codoping and Li doping.
Keywords/Search Tags:Lithium ion battery, LiMn0.8Fe0.2PO4 cathode material, Sol-gel method, Electrochemical properties
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