Overview Of Phase Change Energy Storage Materials

Energy storage phase change materials：

• Energy storage phase change materials refer to substances that use the latent heat of phase change for energy storage.
• It is also known as phase change energy storage or heat storage, energy storage, heat storage materials, latent heat energy storage materials, referred to as phase change materials.

Characteristics of energy storage phase change materials：

• Energy storage phase change materials have the advantages of high energy storage density, small temperature change in heat absorption and release process, and easy process control, and have a variety of materials and are widely used. Energy storage PCMs have the ability to change their physical state and absorb or release latent heat within a certain temperature range.

• Taking solid-liquid phase change as an example, when heated to the melting point, the phase change material absorbs and stores a large amount of latent heat during the melting process. When cooled to the freezing point, the PCM releases latent heat during the solidification process.
• Energy storage phase change materials should have the following characteristics: non-toxicity, suitable phase change temperature, large latent heat of phase change, stable performance, good reversibility of phase change, small expansion and contraction rate during phase change, excellent thermal conductivity, and low price and easy availability of raw materials.

Classification of phase change materials for energy storag：

• Energy storage phase change materials can be divided into four categories according to the form of phase change.
• Solid-liquid phase change materials, solid-gas phase change materials, liquid-gas phase change materials and solid-solid phase change materials. The latent heat of phase change between solid-gas phase change materials and liquid-gas phase change materials is large, but the large volume change, high pressure and poor thermal conductivity limit their application range. The latent heat of phase change of solid-solid phase change materials is low, the phase change process is slow, and the application range is small.
• Solid-liquid phase change materials have the advantages of large latent heat of phase change, wide range of phase change temperature and low cost, and are energy storage phase change materials with great practical value and mature technology, so energy storage phase change materials usually refer to solid-liquid phase change materials.

• Energy storage phase change materials can be divided into inorganic, organic (including polymers) and composite phase change materials according to their composition. Inorganic phase change materials mainly include metals and alloys, crystalline hydrate salts, molten salts, etc., which have the advantages of large latent heat of phase change, high volumetric energy storage density and large thermal conductivity, but have the disadvantages of easy subcooling and phase separation, corrosion container and liquid phase leakage.
• Organic phase change materials mainly include aliphatic hydrocarbons (paraffin, etc.), fatty acids, alcohols, polyenols, etc., which have the advantages of large latent heat of phase change, stable performance and low cost, but have the disadvantages of small thermal conductivity, low density, volatile and easy aging.
• Composite phase change materials mainly refer to organic and inorganic eutectic phase change materials to overcome the shortcomings of single inorganic or organic phase change materials, and the most studied ones are shaped phase change materials (SSPCMs) and microencapsulated phase change materials (MEPCMs).
• Energy storage PCMs are divided into high temperature (above 250°C), medium temperature (250~100°C) and low temperature (below 100°C) phase change materials according to the phase change temperature range.
• High-temperature phase change energy storage materials are mainly used in concentrated solar thermal power generation, industrial waste heat recovery, high-temperature heat engine and other fields.
• Medium-temperature phase change energy storage materials are mainly used in solar thermal utilization, drying and dehumidification and other fields; Low-temperature phase change energy storage materials have broad application prospects in the fields of building energy conservation, thermal management of electronic devices, and low-temperature cold storage.

Research and development of phase change energy storage materials：

• The design, preparation and intensification of energy storage phase change materials are the key to materials research and development. In order to obtain the appropriate phase change temperature and latent heat of phase change, it is necessary to synthesize a variety of phase change materials into multi-component mixed phase change materials according to a certain ratio.

• The preparation of energy storage phase change materials mainly includes mechanical methods (loading phase change materials into containers), physical methods (blending method, impregnation method, etc.), chemical methods (polymer polymerization method, sol-gel method, etc.) and microencapsulation method.
• For low thermal conductivity phase change materials, it is necessary to add excellent thermal conductivity materials (metal fillers, graphite, carbon fiber, etc.), add ribs or capsule encapsulation for strengthening. In addition, the durability and economy of energy storage PCMs are the key to their application development.