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Open AccessArticle

The Li2SO4–Na2SO4 System for Thermal Energy Storage

CIC energiGUNE, 01510 Vitoria-Gasteiz, Spain
Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
Author to whom correspondence should be addressed.
Materials 2019, 12(22), 3658;
Received: 9 September 2019 / Revised: 25 October 2019 / Accepted: 4 November 2019 / Published: 7 November 2019
(This article belongs to the Special Issue Phase Change Materials for Thermal Energy Storage)
In this paper, the system Li2SO4–Na2SO4 is proposed as a candidate material for thermal energy storage applications at high temperatures (450–550 °C). Depending on the composition, the thermal energy can be stored by using a eutectoid reaction and solid–solid phase transition. In these types of systems, all the components (reagent and products) are in the solid state. This work includes the theoretical analysis (based on the Calphad method) of the system selected obtaining all the theoretical parameters (for example, enthalpies of reaction, transition temperatures, volume expansion, and the heat capacities) necessary to determine the theoretical performance in terms of thermal energy storage. The theoretical analysis allowed to identify two compositions (Li2SO4/Na2SO4 79/21 and 50/50) in the phase diagram with the most promising theoretical enthalpy of transformation (270 J/g and 318 J/g, respectively) corresponding to a eutectoid reaction and a solid–solid phase transition (stoichiometric compound LiNaSO4). The experimental analysis carried out allowed to confirm the great potential of this system for TES application even if some discrepancies with the theoretical calculation have been observed experimentally (energy densities lower than expected). For the two compositions studied, 79/21 and 50/50, the enthalpies of reaction are 185 J/g and 160 J/g, respectively. The reactivity of the system was tested under different experimental conditions preparing materials with a different degree of nanocrystallization to favor the diffusion in the solid state, testing the reactivity of the materials under controlled atmosphere and under air, and performing preliminary durability analysis (cycling behavior up to 20 cycles) to test the stability and reversibility. View Full-Text
Keywords: solid state reactions; solid-state phase transitions; thermal energy storage; energy density; ball milling solid state reactions; solid-state phase transitions; thermal energy storage; energy density; ball milling
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MDPI and ACS Style

Doppiu, S.; Dauvergne, J.-L.; Serrano, A.; Palomo del Barrio, E. The Li2SO4–Na2SO4 System for Thermal Energy Storage. Materials 2019, 12, 3658.

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