Application prospects of magnesium hydroxide in fire prevention of new energy batteries

——Scientific breakthroughs from thermal runaway blocking to system safety protection

With the explosive growth of new energy vehicles and energy storage industries, fires caused by thermal runaway of batteries have become a fatal threat to the development of the industry. Magnesium hydroxide (Mg(OH)₂) is becoming a core material for improving battery safety with its high decomposition temperature of 340–490°C, halogen-free environmental protection characteristics and triple fire prevention mechanism. This article systematically analyzes its technological breakthroughs and industrialization paths from thermochemical mechanisms, material design to engineering applications.

1. Thermal runaway prevention and control mechanism: triple defense lines of heat absorption, oxygen isolation and ceramicization

1. Accurately match the critical point of thermal runaway

When the internal temperature of the battery exceeds 240°C (lithium iron phosphate battery) or 180°C (ternary battery), the electrolyte decomposes violently to release flammable gases. Magnesium hydroxide starts a step-by-step decomposition reaction at 340°C:

\ceMg(OH)2−>MgO+H2OΔH=−44.8 kJ/mol

· Endothermic cooling: 1.3 kJ of heat is absorbed per gram, causing the local temperature of the battery pack to drop by more than 150°C, delaying the triggering of thermal runaway;

· Gas phase dilution: 18.6% mass fraction of water vapor is released, the volume expands 200 times, and the oxygen concentration is diluted to <15% (below the critical value of combustion).

2. In-situ construction of ceramic barriers

The generated nano-magnesium oxide (specific surface area>20 m²/g) reacts with the electrolyte decomposition residue to form a porous MgO-carbon composite layer:

· Thermal conductivity <0.5 W/m·K, blocking heat transfer to adjacent cells;

· The oxygen diffusion path is extended by 300%, inhibiting chain combustion reactions.

3. Toxic gas neutralization and efficiency enhancement

Magnesium oxide reacts with acidic gases such as HF and SOₓ released by thermal runaway:

\ce2HF+MgO−>MgF2+H2O

It can reduce the release of hydrogen fluoride by 85% and avoid corrosion and perforation of the battery pack shell.

2. Material design breakthrough: from nano-sizing to intelligent compounding

1. Precise control of morphology and particle size

· Hexagonal flake nanoparticles (D₅₀=0.8–1.5μm): layered stacking enhances the density of thermal insulation air gaps, and the flame retardant efficiency is increased by 3 times compared with the micron level;

· Zirconium-doped flower ball structure: Improve the thermal shock resistance of the magnesium oxide layer, and the fire resistance limit exceeds 180 minutes.

2. Surface modification overcomes compatibility bottleneck

· KH-570 silane grafting: surface energy is reduced by 40%, and the bonding strength with the polyolefin matrix is increased by 300%, solving the electrolyte wetting degradation caused by high filling;

· Microencapsulation: The polyurethane shell isolates moisture and avoids the risk of electrode pre-lithiation failure.

3. Design of compound synergistic system

Component

Functional principle

Performance improvement

Zinc borate (2%)

Catalyzes carbonization reaction, and the density of the residual carbon layer reaches 0.92 g/cm³

The peak heat release rate is reduced by 62%

Expanded graphite

Expands 100 times when heated and fills the cracks in the ceramic layer

Smoke density peak <150 (reduced by 85.3%)

Nano clay

Loading Mg(OH)₂ increases melt viscosity and inhibits molten droplets

Needle puncture test pass rate increased to 99%

III. Engineering evidence: Safety upgrade from battery pack to energy storage system

1. Fire protection solution for power battery pack

· Battery module separator: Ceramic silicone rubber with 35% nano magnesium hydroxide added, which remains intact under 1500℃ flame impact and passes GB 38031-2020 thermal diffusion test;

· Shell coating: Modified epoxy resin-based composite coating (thickness 0.5mm), which extends the thermal runaway propagation time from 3 minutes to >30 minutes.

2. Innovation in fire prevention of energy storage system

· Liquid cooling pipe flame retardant seal: magnesium hydroxide/cyanate compound system, fire resistance limit>120 minutes, VOC emission<5 ppm;

· Fireproof gel between battery cells: temperature-sensitive hydrogel loaded with Mg(OH)₂, automatically expands at 60℃ to fill gaps and inhibit module cascade out of control.

3. Key performance benchmarking

Parameters

Traditional polymer separator

Magnesium hydroxide modified system

Thermal runaway trigger temperature

180℃

>240℃

Smoke density peak (NBS)

>800

<150

HF release

>50 ppm

<5 ppm

IV. Future breakthroughs: intelligent response and bio-based evolution

1. Self-healing microcapsule technology

· Polyurethane shell wrapped with phase change paraffin, release repair agent at temperature>300℃, crack healing rate>85%;

2. Bionic mineralization hybrid layer

· Sodium alginate guides Mg(OH)₂ directional crystallization, the addition amount is reduced to 18%, and the modulus retention rate is>90%;

3. Ionic liquid synergistic system

· Phosphorus-based ionic liquid catalyzes the densification of the ceramic layer, shortening the thermal runaway warning response time to milliseconds.

The value of magnesium hydroxide in fire prevention of new energy batteries is essentially the molecular-level defense art of converting thermal energy into chemical bond energy and phase change energy. With the integration of technologies such as atomic layer deposition coating and AI thermal management algorithms, the future fire prevention system will realize the intelligent closed loop of "thermal runaway prediction-directional activation of flame retardants-damage self-repair". Driven by the demand for battery safety in the TWh era, magnesium hydroxide is expected to become an "invisible firewall" to protect industrial development.