Phase transitions and energy storage properties of some compositions in the (1−x)Li₂SO₄–xNa₂SO₄ system

Abstract

In the binary system (1−x)Li₂SO₄–xNa₂SO₄, the solid–solid phase transitions and energy storage properties of Li₂SO₄, Na₂SO₄, the binary compound LiNaSO₄ and two eutectoids (E₁: 0.726Li₂SO₄–0.274Na₂SO₄; E₂: 0.03Li₂SO₄–0.97Na₂SO₄) were investigated by X-ray diffraction and differential scanning calorimetry. Li₂SO₄ has a solid–solid phase transition at 578 °C with the transition enthalpy 252 J g⁻¹. The binary compound LiNaSO₄ gives a slightly lower enthalpy value, 214 J g⁻¹ and its transition temperature is clearly reduced to 514 °C. The transition enthalpy of the eutectoid E₁ is maintained to 177 J g⁻¹ and its transition temperature is further reduced to 474 °C. Li₂SO₄, LiNaSO₄ and the eutectoid E₁ are applicable phase transition materials because of their large transition enthalpies. The enthalpies of Na₂SO₄ and the eutectoid E₂ are not very high (∼45 J g⁻¹), but their transition temperatures are quite low (∼250 °C); thus their transition properties may be applied at such low temperatures.

Keywords:

• phase transition
• energy storage
• (1−x)Li₂SO₄–xNa₂SO₄ system
• eutectoid

Funding

We are thankful for financial support from the National Basic Research Program of China [grant number 2009CB939901].