Latent-heat storage material composition and latent-heat storage tank

A latent-heat storage material composition in which a latent-heat storage material capable of storing heat or releasing heat utilizing absorption or release of latent heat in association with phase change is mixed with an additive capable of adjusting a property of the latent-heat storage material, the latent-heat storage material composition comprising the latent-heat storage material, water, and the additive,

• wherein the additive comprises at least a first additive that is a water-soluble substance belonging to a polysaccharide and is a thickener to increase viscosity of a melt of the latent-heat storage material composition in a state of a liquid phase based on interaction of the thickener with water and a cation included in the latent-heat storage material composition,
• wherein the first additive is dissolved in the water included in the latent-heat storage material composition to have a random coil structure when the latent-heat storage material composition is in a temperature range of a state of a liquid phase, while, when the latent-heat storage material composition is in a temperature range before changing from the state of a liquid phase to a state of a complete solid phase, the structure of the first additive changes into a double spiral structure reversible from the random coil structure and also the first additive has a property to cause gelation by assembly of the double spiral structures next to each other based on presence of the cation in the latent-heat storage material composition, and
• wherein a mixing amount of the first additive relative to a whole weight of the latent-heat storage material composition is 1 wt % or less.