Heat capacity measurement of LiSi in a temperature range 2 - 730 KTuesday (27.09.2016) 17:45 - 18:00 Part of:
One of the most promising anode materials for lithium ion batteries (LIB) is Silicon. Lithium silicides provide a high theoretical specific energy density (Li17Si4:
4054 mAh/ g) and low discharge potentials. However, the large volume change of silicon during charging and discharging causes electrode pulverization and capacity fading. It is indisputable that fundamental knowledge of the physicochemical properties of the various phases, especially accurate thermodynamic data is essential for future applications of lithium silicides in LIB.
Seven lithium silicide compounds are widely accepted in recent literature. The five stable phases Li17Si4, Li16.42Si4, Li13Si4, Li7Si3 and Li12Si7, the metastable phase Li15Si4 and the so-called high pressure phase LiSi. Li15Si4 is not included in the phase diagram so far, due to its metastable character . In order to achieve a reliable thermodynamic description of the phase diagram, we recently reported experimental heat capacities and entropies of the five stable lithium silicides [2,3]. Until now, experimental thermodynamic data is only missing for LiSi.
This contribution is focused on the accurate experimental determination of the heat capacity and entropy of the high pressure phase LiSi in a temperature range from
2 - 730 K. According to the optimal operational conditions two different calorimeters were used: a PPMS (Physical Property Measurement System) from Quantum Design for 2 – 300 K and a Sensys DSC from SETARAM for 278 – 730 K. The synthesis of a phase pure sample was performed via mechanical alloying. The qualitative and quantitative characterization was carried out using XRD, DSC and chemical analysis. Experimental heat capacity data are given with an error of 1 to 2 % above T = 20 K and up to 7% below T = 20 K. The performance of the measurements at low temperatures permit the calculation of additional thermodynamic parameters such as the standard entropy as well as the temperature coefficients of electronic and lattice contributions to the heat capacity. The results represent a significant contribution to the data basis for thermodynamic calculations and to the understanding of phase transitions and electrochemical equilibria.
 M. H. Braga, J. Alloys Compd. 2014, 616, 581–593.
 D. Thomas, M. Abdel-Hafiez, T. Gruber, R. Hüttl, J. Seidel, A. U. B. Wolter, B. Büchner, J. Kortus, F. Mertens, The Journal of Chemical Thermodynamics 2013, 64, 205–225.
 D. Thomas, M. Zeilinger, D. Gruner, R. Hüttl, J. Seidel, A. U. Wolter, T. F. Fässler, F. Mertens, The Journal of Chemical Thermodynamics 2015, 178–190.