Structural and electrochemical study of lithium iron (II) pyrophosphate

Abstract

Lithium iron(II) pyrophosphate, Li2FeP2O7, attracts attention of researchers for application as a cathode material in rechargeable lithium batteries. Li2FeP2O7 has somewhat higher voltage than commercial LiFePO4 (3.5 and 3.4 V, respectively), thus enables higher energy density, and also provides the possibility of two-electron reaction during intercalation. Within this study, pristine Li2FeP2O7 and its composite with carbon Li2FeP2O7/C were synthesized, with the carbon being formed by the pyrolysis of organic precursor in situ during formation of Li2FeP2O7 at high temperature. The polymer of methylcellulose was used as carbon source because of its ability to reversibly, depending on temperature, dissolve or gel in water. The structural, electrical and electrochemical characteristics of prepared powders were investigated by means of X-ray diffraction analysis, Mossbauer spectroscopy, impedance spectroscopy and galvanostatic charge/discharge testing. The results imply that in situ formation of carbon alters lattice parameters, decreases crystallite size, and facilitates lithium ion intercalation/deintercalation processes. The Ministry of Education, Science and Technological Development of the Republic of Serbia provided financial support for this study under Grant No. III 45004