Silicon carbide (SiC) rollers are widely used in lithium battery cathode material production due to their high-temperature stability and mechanical strength.

However, under different process conditions, their corrosion behavior can vary significantly.

This case study analyzes the performance of SiC rollers in LFP (LiFePO₄) and NCM (Nickel Cobalt Manganese) production environments, focusing on corrosion mechanisms, failure modes, and optimization strategies.

Operating Conditions Comparison

LFP Production Environment

• Lithium source: Li₂CO₃
• Furnace atmosphere: Low corrosion, mainly water vapor
• Maximum temperature: ~1000°C

Observed performance:

• Uniform gray surface deposition
• No significant density reduction
• No fracture during operation
• Service life: ~2 years

The rollers maintained stable performance under relatively mild conditions.

NCM Production Environment

• Lithium source: LiOH
• Atmosphere: Oxidizing + corrosive gases
• Temperature-critical zone: 700–800°C

Observed issues:

• Large-scale surface spalling
• Significant density reduction
• Internal structural degradation
• Service life: ~2 months
• Failure: 2 roller fractures recorded

Corrosion and mechanical failure significantly affected production stability.

Corrosion Mechanism Analysis

1. Surface Reaction Behavior

XRD and XRF analysis revealed that:

• Original SiC phase significantly decreased
• New compounds formed:
  • Lithium silicates (Li₂SiO₃, Li₂Si₂O₅)
  • Nickel-containing compounds
  • Lithium-manganese oxides

This indicates intense chemical reactions altering the material structure.

2. Microstructure Degradation

SEM analysis showed:

• Increased porosity
• Enlarged pore size
• Loosened internal structure

Measured change:

• Density decreased from ≥3.05 g/cm³ → ~2.8 g/cm³

 Corrosion penetrated beyond the surface into the bulk material.

3. Key Corrosion Reactions

(1) Thermal Oxidation

SiC reacts with oxygen:

• Forms a temporary protective layer
• Can fail under aggressive conditions

(2) Chemical Reaction with Lithium Compounds

At high temperature:

• LiOH decomposes → reactive lithium species
• Reacts with SiO₂:

At 700–800°C:

• Lithium silicates soften → form molten phase
• Dissolve protective SiO₂ layer

Leads to continuous exposure and accelerated corrosion

(3) Molten Salt Corrosion

SiC reacts with molten lithium compounds:

Results in rapid material consumption

4. Failure Mechanism

• Lithium silicates penetrate along grain boundaries
• Grain boundary phases dissolve
• Intergranular bonding weakens

Leads to:

• Structural disintegration
• Reduced mechanical strength
• Roller fracture

Why NCM Conditions Are More Aggressive

Key differences between LFP and NCM:

LiOH + high-temperature molten phase is the main driver of corrosion

Improvement Strategies

1. Surface Coating Optimization

• Method: Plasma spraying
• Coating: Y₂O₃ / Al₂O₃

Function:

• Prevent molten salt wetting
• Block gas penetration
• Delay corrosion

Advantages:

• Cost-effective (~1000 RMB per roller)
• Fast implementation

Suitable for short-term improvement

2. Material Upgrade (CVD SiC Coating)

• Method: Chemical Vapor Deposition (CVD)
• Result: High-purity SiC surface layer

Benefits:

• Dense structure
• Strong bonding
• Blocks corrosion pathways

Provides long-term stability and longer service life

Engineering Recommendations

1. Prioritize NCM Process Optimization

• Implement coating or CVD upgrades
• Start with small-batch trials

2. Control Critical Temperature Zone

• Optimize heating rate in 700–800°C range
• Reduce molten phase formation

3. Monitoring and Maintenance

• Regular density testing
• Surface inspection
• Replace severely corroded rollers early

Conclusion

This case demonstrates that:

• SiC rollers perform well in mild LFP environments
• But face severe degradation in NCM processes with LiOH

 The combination of:

• High temperature
• Reactive lithium compounds
• Molten phase formation

leads to rapid corrosion and structural failure.

Key Takeaway

For demanding applications such as NCM production:

Material design and surface engineering are critical
Upgraded SiC solutions can significantly improve reliability and service life