Место издания:Lobachevsky State University of Nizhni Novgorod Nizhni Novgorod
Первая страница:313
Последняя страница:313
Аннотация:This work is a part of systematic investigations of the thermodynamic properties of new
materials synthesized on the basic of compounds of transition elements. It is carried out at
Luginin’s Laboratory of Thermochemistry and Inorganic Synthesis Laboratory of Inorganic
Chemistry division. It is devoted to the study of thermochemical properties of substitution solid
solutions: NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O. The choice of reasearch object is
caused by its application as precursors for synthesis of cathode material in Li-ion batteries. The
reproducible synthesis of such compounds and application of materials based on them require
knowledge of thermodynamic properties of double lithium and transition elements phosphates
and its precursors.
There is no literature data on thermochemical properties of NH4Fe1−xMnxPO4⋅H2O and
NH4Co1−xMnxPO4⋅H2O solid solutions. Only one work [1] was concerned with the determination
of the NH4FePO4⋅H2O enthalpy of formation. According to the IUPAC classification, the data
obtained in single work can be considered only as preliminary.
The samples of NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O (х = 0, 0.25, 0.5, 0.75, 1)
were prepared by coprecipitation method. The ammonium and phosphates groups are introduced
in the M(OH)2 matrices. The precipitates were washed out by the distilled water and dried up.
The synthesized samples were checked by X-ray, ICP-MS and TG analysis. The X-ray
examination supported the single-phase nature of samples. It state by using X-ray and TG
analysis that investigated solid solutions are monohydrates.
To determinate the enthalpies of formation of studied solid solutions, the enthalpies of reactions
of NH4Fe1−xMnxPO4⋅H2O and NH4Co1−xMnxPO4⋅H2O with 1 M hydrochloric acid were
measured at 298.15 K in a hermetically sealed swinging calorimeter with an isothermal coat.
Temperature rise in each run was measured by platinum resistance thermometer. Thermometric
sesitivity of circuit was 3⋅10−5 K. The energy equivalent of calorimeter was determined by
electric technique. The enthalpies of formation of specified solid solution were calculated on
basis of experimental data and the reliable literature data on thermochemical properties of
ammonium, iron, cobalt, manganese chlorides and phosphoric acid solutions.
The enthalpies of formation of studied systems depend on type of transition element. These
values decrease by an increase of x (the degree of Mn substitution for Fe and Co). The enthalpies
of mixing are negative for Fe−Mn system and the dependence of these values on x has the
minimum at x = 0.5. The solid solution of NH4Fe1−xMnxPO4⋅H2O can be considered as regular
solution. The enthalpies of mixing are not near from 0 within measurement errors for Co−Mn
systems. The entropy factor can play the role in thermodynamic stability of
NH4Co1−xMnxPO4⋅H2O solution.
The NH4FePO4⋅H2O enthalpy of formation found by us coincides with data [1] within
measurement errors. All of other thermochemical parameters were obtained for the first time in
this work.