Lithium ion intercalation mechanism for LiCoPO4 electrode

Recently, there exists a discrepancy on the lithium ion de-intercalation mechanism for LiCoPO4 electrode. In the present work, the study was focused upon exploring the origin of this discrepancy by studying the dependence of the impedance spectrum on the state of charge and the carbon content. For the pure LiCoPO4 electrode, the two plateaus in the charge curve are at 4.82 and 4.92 V. We have also studied the variation of electrochemical impedance spectroscopies (EISs) with the state of charge. The EIS measurement has shown that the total interfacial resistance increases as the state of charge increases for the pure LiCoPO4 electrode. If higher content of sucrose was added in the precursor (this implies higher carbon content in the synthesized sample), only one potential plateau can be found in the charge curve. For this electrode, the total interfacial resistance decreases with the state of charge. Especially, the total interfacial resistance has a dramatic decrease when the state of charge increases from 20% to 40%. It is believed that the influence of carbon impurity on the variation tendency of the EIS pattern may reflect the change of the fine structure. For the pure LiCoPO4 electrode, the intermediate phase is Li0.20~0.45CoPO4.