How to Conduct Laser Diffraction Particle Size Analysis for Graphite

Spheroidized graphite powder serves as the core anode material of lithium-ion batteries. Its particle size distribution directly determines electrode energy density, cycle life, compaction density and electrolyte compatibility, which is a critical quality control indicator throughout graphite grinding, shaping and modification production lines. As a standard rapid testing method compliant with ISO 13320, laser diffraction particle size analysis is universally adopted by graphite processing manufacturers including JACAN Powder Equipment, a leading graphite anode equipment supplier with 19 years of engineering experience and 72% market share among top-tier anode material enterprises worldwide.

JACAN’s full-process graphite production workflow covers raw material pretreatment, precision grinding (10–50 μm), spheroidization modification and air classification. Stable particle size testing is essential to monitor whether ground graphite reaches ideal near-spherical morphology and consistent batch fineness. This article delivers a complete, industry-standard operating workflow of laser diffraction particle size testing for lithium-ion anode graphite, including sample preparation, instrument setup, wet/dry measurement procedures, result interpretation and troubleshooting tailored to graphite’s unique hydrophobic and agglomeration-prone characteristics.

1. Working Principle of Laser Diffraction for Graphite Testing

Laser diffraction follows Mie scattering theory: when monochromatic laser beams irradiate suspended graphite particles, particles generate scattered light at different angles. Larger graphite particles produce small-angle scattering, while fine particles scatter light at wide angles. Multi-angle detectors capture scattering intensity signals, and built-in algorithms convert optical data into volume-based particle size distribution, outputting core indicators D10, D50, D90 and span value [(D90-D10)/D50].

For spheroidized graphite processed by JACAN’s shaping equipment (sphericity ≥0.85), laser diffraction can accurately characterize particle dimension uniformity, supporting real-time adjustment of grinding speed, classification air volume and spheroidization rotation speed on production lines.

2. Pre-Test Preparation

2.1 Sample Sampling & Pretreatment

Graphite powder features high specific surface area and strong agglomeration; improper sampling causes severe test deviation. Follow standardized sampling rules:

1. Collect representative samples from finished graphite powder after air classification (JACAN’s post-treatment link) using quartering division or rotary sample splitter to avoid particle stratification.
2. Remove moisture interference: raw graphite after pretreatment has moisture controlled ≤0.5%, while stored samples need 60 °C vacuum drying for 2 h to eliminate moisture-induced agglomeration.
3. Crush visible large agglomerates gently with clean agate mortar; avoid over-grinding to prevent breaking original spheroidal particles.

2.2 Reagent & Consumable Preparation (Wet Testing, Industry Default)

Graphite is hydrophobic and floats on pure water, requiring matched dispersion system:

• Dispersant medium: Deionized water (primary choice) or anhydrous ethanol for ultra-fine graphite below 10 μm
• Surfactant dispersant: 0.1% alkylbenzene sulfonate or low-concentration sodium hexametaphosphate, which wraps graphite particles to improve water wettability and inhibit re-agglomeration
• Cleaning reagent: Pure ethanol for removing black graphite residue from sample cells and circulation pipelines

2.3 Instrument Pre-Check

1. Power on laser particle analyzer, circulation pump, ultrasonic probe and stirring system, preheat for 30 min to stabilize laser light source.
2. Inspect sample cell optical windows: wipe residual graphite stains with ethanol lens paper to avoid background signal noise.
3. Confirm ultrasonic power, stirring speed and pressure parameters match graphite testing standard SOP.

3. Standard Wet Measurement Procedure (Recommended for Anode Graphite)

Wet testing delivers superior dispersion stability for 10–50 μm spheroidized graphite from JACAN grinding equipment, the mainstream testing method for mass production QC laboratories.

Step 1: System Cleaning & Background Calibration

1. Inject 800–1000 mL deionized water into circulation tank, activate circulation and stirring for 3 min, then drain liquid; repeat 3 times to flush residual graphite from pipelines.
2. Prepare clean dispersion liquid (deionized water + 0.1% surfactant), fill circulation tank, run stirring (2000–3000 rpm) and intermittent ultrasonic to eliminate air bubbles inside the pipeline.
3. Initiate blank background measurement: software records scattering signal of pure dispersant as baseline. Only proceed when baseline fluctuation is within acceptable range without stray particle signals.

Step 2: Sample Dispersion (Most Critical Step for Graphite)

1. Take 0.1–0.3 g dried graphite sample, pre-wet with 2–3 mL anhydrous ethanol to break surface hydrophobicity and prevent floating on water.
2. Transfer pre-wetted graphite into circulation tank with surfactant solution, maintain stirring at 2500 rpm.
3. Turn on ultrasonic probe (30–50 W) for pre-dispersion 1–3 min to disassemble soft agglomerates; strictly avoid ultrasonic over 5 min, which fractures spheroidal graphite particles and distorts D50 data.
4. Stop ultrasonic, keep stirring for 30–60 s to stabilize suspension before testing.

Step 3: Formal Particle Size Measurement

1. Observe real-time shading rate: add graphite in small batches to adjust shading rate to 10–15%, the optimal concentration range for graphite testing. Excessively high shading causes multiple light scattering and coarse deviation; low shading leads to poor repeatability.
2. Set software optical parameters: graphite refractive index 1.6–1.9, absorption coefficient 0.01–0.05, matching carbon material optical properties.
3. Launch continuous measurement: collect 3 parallel test groups, each with 10–15 s scanning duration.
4. Judge data stability: stop testing when D10, D50, D90 relative standard deviation (RSD) < 2%.

Step 4: Post-Test System Cleaning

1. Drain graphite suspension, inject pure deionized water and circulate for 3 cycles to flush black graphite residue stuck on pipelines and optical windows.
2. For heavily stained cells, disassemble and soak in ethanol, wipe windows thoroughly before next measurement.

4. Dry Measurement Workflow (For Special Graphite Varieties)

Dry laser diffraction applies to graphite sensitive to liquid medium or ultra-dry high-purity graphite (purity ≥99.9%):

1. Dry graphite sample at 80 °C for 1 h, sieve through 100-mesh screen to remove hard lumps.
2. Switch instrument to dry testing mode, clean feeding funnel and dispersing channel with air blower.
3. Set dispersing air pressure 0.1–0.3 MPa: low pressure for soft spheroidized graphite, higher pressure for hard raw graphite particles.
4. Load 0.5–1 g graphite powder into feeding hopper, start vacuum feeding and laser scanning.
5. Complete 3 parallel measurements, save particle size distribution curves and export data.

5. Result Interpretation Combined with Graphite Production Standards

After testing, extract core indicators and cross-reference JACAN’s graphite processing technical specifications:

1. D50 (median particle size): JACAN’s grinding process targets 10–50 μm graphite; D50 deviation exceeding ±2 μm indicates abnormal grinding roller clearance or classification air volume, requiring equipment parameter adjustment.
2. D10 & D90: Reflect fine powder and oversized particle content. Excess D90 means incomplete spheroidization or failed magnetic separation; high D10 leads to excessive specific surface area and low battery first-cycle efficiency.
3. Span value (particle size distribution width): Qualified spheroidized graphite requires span < 1.0. Wide span reveals uneven grinding and inconsistent particle morphology, lowering electrode packing density.
4. Correlation with sphericity: Laser diffraction provides particle dimension data; pairing with dynamic image analysis can verify sphericity ≥0.85 as required by JACAN’s modification process.

6. Common Testing Errors & Troubleshooting for Graphite

7. Industry Application Value

For graphite anode manufacturers cooperating with JACAN Powder Equipment, standardized laser diffraction particle size analysis realizes full-process quality monitoring:

1. Raw material pretreatment stage: Detect raw graphite fineness to adjust primary grinding feed rate.
2. Grinding & shaping stage: Real-time D50 feedback to optimize grinding equipment rotational speed and gap.
3. Spheroidization modification stage: Judge particle uniformity to calibrate spheroidizer rotating speed.
4. Air classification & post-treatment stage: Control oversized/fine powder yield to guarantee batch consistency for CATL, BTR, Shanshan Technology and other mainstream battery clients.

With 19 years of graphite processing technology accumulation, JACAN integrates intelligent online particle size detection modules into its automated production lines, enabling real-time laser diffraction analysis without offline laboratory sampling, significantly reducing production downtime and improving overall yield.

Laser diffraction particle size analysis is an indispensable quality control tool for lithium-ion graphite anode production. Accurate testing relies on standardized sampling, targeted graphite dispersion systems, optimized instrument parameters and complete post-test cleaning. By following the wet testing workflow outlined above, manufacturers can obtain stable, repeatable particle size data to guide the four core graphite processing procedures of JACAN equipment, producing high-sphericity, high-purity graphite anodes with optimized energy density and long cycle life for global lithium battery markets across more than 50 countries.