Preparation process of magnesium powder metallurgical porous materials and their application in energy storage field

Magnesium powder metallurgical porous materials exhibit unique advantages in the field of energy storage, such as battery electrodes, hydrogen storage carriers, and thermal management media, due to their high specific surface area, adjustable pore structure, and intrinsic chemical activity. The preparation process and performance control are the core directions for expanding applications.

1、 Preparation process and pore control of porous materials

The pore characteristics (pore size, porosity, connectivity) of magnesium powder metallurgy porous materials are directly determined by the preparation process, and the main methods include:

powder metallurgy method

Add pore forming agent: Mix volatile or soluble particles (such as NaCl, NH ₄ HCO ∝, polymer microspheres) into magnesium powder, and remove them through dissolution/volatilization after sintering to form pores. The pore size is controlled by the size of the pore forming agent (10-500 μ m), and the porosity can reach 30% -70%. For example, adding 150 μ m NaCl particles can prepare a connected pore structure with a pore size of 100-180 μ m.

Foaming method: Using decomposed foaming agents such as MgH ₂ to release gas (H ₂) at high temperatures, or introducing bubbles through mechanical stirring to form closed or open cell structures. It is necessary to accurately control the matching between the decomposition temperature of the foaming agent and the sintering rate.

Additive Manufacturing (3D Printing)

Selective Laser Melting (SLM): Magnesium powder is melted layer by layer by laser, and the pore structure is supported by unmelted powder to prepare complex three-dimensional connected pores (pore size 50-500 μ m) with a porosity of 10% -50%. Scanning strategies such as cross scanning can regulate pore morphology.

Gel casting sintering: magnesium powder and gel precursor (such as sodium alginate) are mixed to form, and gel is cured and sintered to remove organic matter, forming nano micron multi-level pores.

templating

Biological template method: Using natural porous materials such as wood and sponge as templates, the template is removed by impregnating magnesium slurry and sintering to replicate the natural pore structure. It is suitable for preparing biomimetic porous magnesium (pore size 100-1000 μ m).

2、 Typical applications in the field of energy storage

Battery electrode materials

Lithium ion battery negative electrode: The porous magnesium structure alleviates the volume expansion during charge and discharge (~300%), and the connected pores promote electrolyte penetration and ion transport. For example, the capacity retention rate of a porous magnesium negative electrode with a porosity of 45% increased by 25% after 100 cycles compared to dense magnesium.

Solid state battery composite positive electrode: Magnesium porous skeleton loaded with sulfur/selenium active material (such as Mg/S composite electrode), through physical confinement to suppress polysulfide shuttle effect, the battery energy density can reach 350 Wh/kg.

Hydrogen storage material

Chemical hydrogen storage: Porous magnesium framework (specific surface area 5-10 m ²/g) loaded with catalysts (such as Ni, LaNi ₅) to enhance the hydrogen absorption and desorption kinetics of MgH ₂. The hydrogen absorption capacity of porous magnesium hydrogen storage material with a pore size of 200 μ m can reach 5.6 wt% at 300 ℃, and the hydrogen absorption rate is four times higher than that of bulk magnesium.

Physical hydrogen storage: Nanoscale pores (<20 nm) enhance hydrogen molecule adsorption through quantum confinement effect, with a theoretical hydrogen storage density of up to 8 kg/m ³ (higher than high-pressure gaseous hydrogen storage).

Thermal management medium

Phase change energy storage (PCM) carrier: Porous magnesium skeleton adsorbs molten salts (such as LiNO3 ∝ - KNO3) or organic phase change materials (such as paraffin), utilizing high thermal conductivity (~150 W/m · K) to quickly conduct heat, with a thermal response rate 30% higher than pure PCM. For example, when used for thermal runaway protection of electric vehicle batteries, local temperature rise can be reduced by more than 20 ℃.

3、 Key challenges and optimization strategies

Insufficient corrosion resistance: Magnesium substrates are prone to corrosion in electrolytes or humid environments, and chemical stability can be improved by surface coating with a carbon layer (CVD method) or composite coating (Ni-P/Al ₂ O3).

Mechanical strength limitation: High porosity leads to a decrease in compressive strength (such as strength<50 MPa when porosity is 60%). Ceramic particle reinforcement phases (such as MgO SiC) can be introduced or gradient pore design (dense outer layer, porous inner layer) can be used to balance strength and functional performance.

The challenges of large-scale preparation include uneven dispersion of pore forming agents and high additive manufacturing costs, which restrict their application. Therefore, it is necessary to develop low-cost templates (such as plant fibers) and continuous sintering processes (such as tunnel kilns).