Si/C anode materials

Silicon-carbon anode materials are composed of ​nano-scale silicon particles (Si, 20-200nm) compounded with ​carbon matrices (graphite/CNTs/graphene). Based on production processes, they are categorized into two technical routes:

Ball-Milling Method

• Process:

Si+C forms Si/C composite via high−energy ball milling​

-Particle size: D50 <500nm

-Silicon content: 5-15wt%

-Conductivity: 10-100 S/cm

• Advantages

-Low cost (~¥80,000/ton)

-Simple process (compatible with existing graphite production lines)

• Challenges:

-High volume expansion (~300%)

-Limited cycle life (500-600 cycles @80% capacity retention

Nanosizing

• During grinding, the rotor and zirconia beads generate intense impact forces (F=ma) and shear forces (τ=μdydv​) through high-speed rotation effectively pulverizing and dispersing the Si/C anode material. The collisions and friction between zirconia beads (0.03-0.1 mm diameter) and Si/C particles progressively reduce particle size to D50 <100 nm while ensuring uniform dispersion in the liquid medium.As grinding proceeds, internal temperature rises (ΔT ≈15-25°C above ambient), necessitating real-time cooling via a dynamic cooling system to maintain temperature below 40°C. This is critical to:

1.Preserve material properties (e.g., prevent pitch degradation)

2.Ensure stable operation (avoid thermal expansion-induced equipment stress).

• The system monitors temperature through embedded sensors (accuracy ±0.5°C) and adjusts coolant flow (e.g., 10-20 L/min) automatically. After achieving target particle size (verified by laser diffraction), the homogenized slurry is discharged through the outlet valve for subsequent carbonization

Spray Drying( (ball milled Si/C)

• During grinding, the rotor and zirconia beads generate intense impact forces (F=ma) and shear forces (τ=μdydv​) through high-speed rotation effectively pulverizing and dispersing the Si/C anode material. The collisions and friction between zirconia beads (0.03-0.1 mm diameter) and Si/C particles progressively reduce particle size to D50 <100 nm while ensuring uniform dispersion in the liquid medium.As grinding proceeds, internal temperature rises (ΔT ≈15-25°C above ambient), necessitating real-time cooling via a dynamic cooling system to maintain temperature below 40°C. This is critical to:

1.Preserve material properties (e.g., prevent pitch degradation)

2.Ensure stable operation (avoid thermal expansion-induced equipment stress).

• The system monitors temperature through embedded sensors (accuracy ±0.5°C) and adjusts coolant flow (e.g., 10-20 L/min) automatically. After achieving target particle size (verified by laser diffraction), the homogenized slurry is discharged through the outlet valve for subsequent carbonization

Carbonization

Carbonization: graphitized artificial graphite or natural graphite is uniformly mixed with pitch (pre-crushed to a specific particle size using specialized equipment) at a defined ratio in a high-speed mixer. The mixture is then transferred to a nitrogen-protected kiln for high-temperature carbonization at 1,200°C, where the pitch undergoes pyrolysis to form a carbon coating on the graphite surface.

Chemical Vapor Deposition (CVD) Method

• Process:

SiH4​(g) deposits on porous carbon to form ​Si@C core

−shell structure

-Silicon layer thickness: 5

-20nm -Porosity: 30-50% -ICE: 85-89%

• Advantages:

-Superior performance:Capacity: 1,500-2,000 mAh/g

-Expansion rate: <100%

-Cycle life: 1,000+ cycles

• Challenges:

-High equipment cost (CVD reactors ~¥2M/unit)

-Silicon precursor cost (SiH₄: ¥50,000-100,000/ton in 2025)

Fluidized Bed

A fluidized bed reactor suspends silicon/carbon particles in a high-velocity gas stream (e.g., N2​ or Ar), enabling uniform ​chemical vapor deposition (CVD) of silicon from precursors like silane (SiH4​) and carbon coating from acetylene (C2​H2​)

1. ​Fluidization: Porous carbon powder (D50: 10–50μm) is fluidized via gas distribution plates (velocity: 0.1–1 m/s).

2. Silicon Deposition: SiH4​ decomposes at 500–800°C, forming nano-silicon (5–20nm) within carbon pores

3. Carbon Coating: Secondary C2​H2​ cracking at 700–1000°C creates 2–5nm conductive carbon layers.