Heat capacity (Cp) and entropy of olivine-type LiFePO4 in the temperature range (2 to 773) K

Abstract

The heat capacity of olivine-type lithium iron phosphate (LiFePO4 – LFP) has been measured covering a temperature range from (2 to 773)K. Three different calorimeters were used. The Physical Property Measurement System (PPMS) from Quantum Design was applied in the range between T=(2 and 300)K, a Micro-DSC II from Setaram within the range between T=(283 and 353)K and data between T=(278 and 773)K were measured by means of a Sensys DSC (Setaram) using the Cp-by-step method. Experimental data are given with an error of (1 to 2)% above T=20K and up to 8% below 20K. The data were subdivided into appropriate temperature intervals and fitted using common heat capacity functions. The low temperature results permit the calculation of standard entropies and temperature coefficients of electronic, lattice, as well as magnetic (antiferromagnetic transition at T=49.2K) contributions to the heat capacity. The obtained experimental values were compared to results of a recently published first principles phonon study (DFT) and to few available experimental data from the literature.