With the transformation of the energy structure and the rapid development of renewable energy, the research of energy storage materials has become a crucial topic. In recent years, hexagonal magnesium hydroxide nanosheets have shown great potential in the field of energy storage (such as batteries, capacitors, and phase change energy storage systems) due to their unique two-dimensional layered structure, high thermal stability, abundant surface hydroxyl groups, and tunability.
1. Advantages and Characteristics of Magnesium Hydroxide in Energy Storage
The hexagonal platelet morphology endows magnesium hydroxide with a series of advantages in energy storage applications:
- High specific surface area: Provides more charge storage sites.
- Layered structure: Facilitates ion transport and intercalation reactions.
- Strong thermal stability: Can be used as high-temperature energy storage materials or battery thermal insulation layers.
- Abundant surface hydroxyl groups: Easy to perform surface functionalization, improving interface stability.
- Low cost, non-toxic, and environmentally friendly: Meets the green development needs of sustainable energy storage.
2. Application Potential in Lithium-ion Batteries (LIBs)
Although magnesium hydroxide is not a traditional electrode material, its modification or compositing has application possibilities:
(1) As a Modification Coating:
- Coating the surface of positive electrode materials (such as LiCoO₂, LiNiMnCoO₂) can prevent direct contact between the electrolyte and active materials, improving cycle stability.
- Enhances the safety performance of batteries at high temperatures, acting as a thermal buffer and providing corrosion resistance.
(2) Precursor Material:
- Magnesium hydroxide can be converted into oxide materials such as MgO, MgCO₃, and Mg₂SiO₄ after heat treatment. These materials possess good electrochemical stability and can be used as negative electrode materials or additives.
(3) Doping and Structure Regulation:
- Doping Mg²⁺ into LIB electrode materials can improve the structural stability and electronic conductivity of the materials.
- Constructing composite materials with graphene, CNTs, etc., enhances conductivity and cycle life.
3. Exploration of Applications in Magnesium-ion Batteries (MIBs)
Due to the advantages of magnesium element itself, such as high volumetric capacity and the non-dendritic formation of metallic magnesium, MIBs are a promising next-generation battery technology.
Hexagonal magnesium hydroxide nanosheets can be used as:
- Additives in the electrolyte: To improve ion migration rate.
- Electrode interface modifiers: To optimize the deposition and stripping behavior of Mg²⁺.
- Modification phase of conductive framework materials: To enhance ion diffusion channels and structural stability.
4. Application in Supercapacitors (SCs)
As Electrode Materials or Additives:
- The electrical conductivity of magnesium hydroxide alone is low, but its charge storage capacity can be improved after compositing with conductive carbon materials (such as graphene, carbon black, carbon nanotubes).
- The layered structure of magnesium hydroxide is conducive to the formation of an electrochemical double layer. Simultaneously, doping with metals or oxides can generate pseudocapacitive reactions.
Performance Optimization Research:
- Constructing heterostructure materials by compositing hexagonal magnesium hydroxide with Ni(OH)₂ and Co(OH)₂ can improve rate performance and cycle stability.
- Surface functionalization treatment can enhance its compatibility and electrochemical window width in aqueous supercapacitors.
5. Role in Phase Change Energy Storage Materials (PCMs)
Phase change materials utilize the heat absorption and release characteristics of material phase transitions to achieve thermal energy storage and release, suitable for building energy saving, solar energy utilization, and thermal management systems.
The Roles of Magnesium Hydroxide:
- Added to organic PCMs (such as paraffin): To improve thermal conductivity and inhibit liquid leakage.
- Decomposes endothermically at high temperatures (Mg(OH)₂ → MgO + H₂O): Can be applied to medium- and high-temperature phase change energy storage systems.
- Combined with composite support materials (such as carbon materials and graphite): To construct composite energy storage materials with high thermal conductivity, high latent heat of phase change, and strong thermal stability.