What are the key focuses of the index requirements for graphitized petroleum coke in different application fields (such as lithium battery anodes and cathodes for aluminum)?

Divergent Index Requirements for Graphitized Petroleum Coke in Two Key Application Fields: Lithium-ion Battery Anodes and Aluminum Cathodes

The index requirements for graphitized petroleum coke exhibit significant differences in chemical composition, physical structure, and electrochemical performance across lithium-ion battery anodes and aluminum cathodes. The key priorities are summarized as follows:

I. Lithium-ion Battery Anodes: Electrochemical Performance as the Core, with Structural Stability Considered

1. Low Sulfur Content (<0.5%)
   Sulfur residues can induce crystal contraction and expansion during graphitization, causing electrode fracture. Additionally, sulfur may release gases at high temperatures, damaging the solid electrolyte interphase (SEI) film and leading to irreversible capacity loss. For instance, GB/T 24533-2019 mandates stringent sulfur content control for graphite used in lithium-ion battery anodes.
2. Low Ash Content (≤0.15%)
   Metallic impurities in ash (e.g., sodium, iron) catalyze electrolyte decomposition, accelerating battery degradation. Sodium impurities can also trigger anode honeycomb oxidation, reducing cycle life. High-purity graphite requires a “three-high” process (high temperature, high pressure, high-purity raw materials) to reduce ash content below 0.15%.
3. High Crystallinity and Oriented Arrangement
   • High True Density: Reflects graphite crystallinity; higher true density ensures ordered channels for lithium-ion insertion/extraction, enhancing rate performance.
   • Low Thermal Expansion Coefficient: Needle coke, with its fibrous structure, exhibits a 30% lower thermal expansion coefficient than sponge coke, minimizing volume expansion during charge/discharge cycles (e.g., anisotropic graphite expands along the C-axis, causing battery swelling).
4. Balanced Particle Size and Specific Surface Area
   • Wide Particle Size Distribution: Optimized D10, D50, and D90 parameters enable smaller particles to fill voids between larger ones, improving tap density (higher tap density increases active material loading per unit volume, though excessive levels reduce electrolyte wettability).
   • Moderate Specific Surface Area: High specific surface area (>10 m²/g) shortens lithium-ion migration paths, boosting rate performance, but enlarges SEI film area, lowering initial coulombic efficiency (ICE).
5. High Initial Coulombic Efficiency (≥92.6%)
   Minimizing lithium consumption during SEI formation during the first charge/discharge cycle is critical for maintaining high energy density. Standards require an initial discharge capacity ≥350.0 mAh/g and ICE ≥92.6%.

II. Aluminum Cathodes: Conductivity and Thermal Shock Resistance as Key Priorities

1. Graded Sulfur Content Control
   • Low-sulfur Coke (S < 0.8%): Used in premium graphite electrodes to prevent sulfur-induced gas bloat and cracking during steelmaking, reducing steel consumption per ton (e.g., one enterprise reduced anode consumption by 12% using low-sulfur coke).
   • Medium-sulfur Coke (S 2%–4%): Suitable for aluminum electrolysis anodes, balancing cost and performance.
2. High Ash Tolerance (with Specific Impurity Controls)
   Vanadium content in ash must be ≤0.03% to avoid periodic declines in aluminum electrolysis current efficiency. Sodium impurities require strict control to prevent anode honeycomb oxidation.
3. High Crystallinity and Thermal Shock Resistance
   Needle coke is preferred for its fibrous structure, which offers high density, strength, low ablation, and excellent thermal shock resistance, enabling it to withstand frequent thermal fluctuations during aluminum electrolysis. A low thermal expansion coefficient minimizes structural damage, extending cathode lifespan.
4. Particle Size and Mechanical Strength
   • Lump Particles Preferred: Reduces powder coke content to prevent breakage during transportation and calcination, ensuring mechanical robustness.
   • High Proportion of Calcined Coke: 70% calcined coke is used in aluminum electrolysis anodes to enhance conductivity and corrosion resistance.
5. High Electrical Conductivity
   Needle coke electrodes can carry 100,000 A currents, achieving steelmaking efficiency of 25 minutes per furnace and conductivity three times higher than conventional coke, significantly reducing energy consumption.

III. Core Differences Summary

IV. Industry Trends

• Lithium-ion Battery Anodes: Novel nuclear-structured coke (radial texture) and pitch-modified calcined coke (enhancing hard carbon anode cycle life) are emerging research hotspots to further optimize energy density and cycle performance.
• Aluminum Cathodes: Growing demand for 750 mm large-scale needle coke electrodes and medium-sulfur coke for silicon carbide grinding is driving material development toward higher conductivity and wear resistance.