Introduction
In the natural graphite anode material industry, you’ve likely heard customers make requests like:
- “We need spherical graphite with fixed carbon content ≥99.5%”
- “Can you provide stable supply of 99.9% high-purity graphite?”
- “Can your purification equipment increase carbon content from 94% to what level?”
These seemingly simple numbers actually determine whether your product can enter high-end markets, meet stringent power battery customer standards, and how much pricing power you have.
A harsh reality is: In the lithium battery anode material field, every 1% increase in fixed carbon content can boost product value by 20%-50%. From 94% flotation concentrate (approximately $1,500/ton) to 99.9% high-purity graphite (up to $8,000/ton), this represents not just numerical differences but worlds apart in market positioning.
As a manufacturer specializing in anode material graphite production equipment and EPC solutions, we understand deeply that mastering core knowledge of fixed carbon content is your first step toward optimizing production line configuration and enhancing product competitiveness.
This article will guide you comprehensively through the “past and present” of fixed carbon content in the most accessible way possible.
Executive Summary
Fixed carbon content is the core metric for measuring natural graphite purity, directly impacting its application value in lithium battery anode materials, refractory materials, and other fields. This guide provides graphite producers with a systematic overview covering the definition of fixed carbon content, international grading standards (50%-99.9%+), professional testing methods (LOI vs TGA), and its decisive influence on product market positioning. Whether you’re new to the anode material industry or a producer seeking to enhance product competitiveness, this guide will help you understand why fixed carbon content ≥99.5% is the entry threshold for lithium battery-grade graphite.
What Is Fixed Carbon Content?
Fixed Carbon Content refers to the percentage of pure carbon remaining in graphite material after excluding moisture, ash, and volatile matter. This metric directly reflects the purity level of the graphite material.
To use a simple analogy: if you compare graphite material to gold, then fixed carbon content is equivalent to gold’s purity marking (like 99.9% pure gold). The higher the content, the greater the material’s “gold content” and application value.
From a chemical analysis perspective, the calculation formula for fixed carbon content is:
Fixed Carbon Content (%) = 100% – Moisture (%) – Ash (%) – Volatile Matter (%)
Where:
- Moisture: Water adsorbed or crystallized in the material
- Ash: Inorganic oxides remaining after combustion (such as SiO₂, Al₂O₃, Fe₂O₃, etc.)
- Volatile Matter: Gaseous components released during heating
According to data from the United States Geological Survey (USGS) and academic research literature, natural graphite’s carbon content varies significantly depending on processing stage:
- Raw ore stage: Graphite carbon content in ore typically ranges from 5-85%
- Flotation concentrate: Physical beneficiation can achieve 85-98%
- After chemical purification: Can reach 99.5-99.9% or higher
International Grading Standards for Fixed Carbon Content
According to Chinese national standard GB/T 3518-2008 and international graphite industry classification standards, natural flake graphite is divided into four main grades based on fixed carbon content:
Table 1: Natural Graphite Fixed Carbon Content Grading Standards and Application Fields
Grade | Fixed Carbon Content | Primary Applications | Typical Price Range (Reference) |
High-Purity Graphite | ≥99.9% | Flexible graphite sealing materials, premium lithium battery anodes, nuclear reactor materials | $3,000-8,000/ton |
High-Carbon Graphite | 94.0%-99.9% | Lithium battery anode materials, refractory materials, brush raw materials, carbon products | $1,500-3,000/ton |
Medium-Carbon Graphite | 80%-94% | Foundry crucibles, refractory bricks, foundry coatings, pencil raw materials | $800-1,500/ton |
Low-Carbon Graphite | 50%-80% | Foundry release agents, low-end coating fillers | $300-800/ton |
Pricing data sources: East Carbon market analysis, Northern Graphite industry reports, 2024 market reference prices
Key Notes:
- According to Northern Graphite’s market data, flotation graphite concentrate typically has fixed carbon content ≥94%
- For lithium-ion battery anode materials, fixed carbon content typically needs to reach 99.5% or above to meet performance requirements for commercial applications
- Prices fluctuate significantly based on market supply and demand, particle size, purity grade; table prices are for reference only
How to Measure Fixed Carbon Content?
In industrial production, fixed carbon content measurement primarily employs two standard methods:
Method 1: Loss on Ignition (LOI)
- Principle: Complete combustion of samples in high-temperature (typically 900-1000°C) oxidizing atmosphere
- Steps: Precise weighing → high-temperature ignition → cooling and weighing → calculate fixed carbon
- Advantages: Simple equipment, low cost, rapid operation
- Disadvantages: Relatively lower precision (±0.5%)
- Applications: Routine quality control and high-volume testing
Method 2: Thermogravimetric Analysis (TGA)
- Principle: Continuous recording of sample mass changes during programmed temperature increase
- Features: Can simultaneously measure moisture, volatile matter, fixed carbon, and ash
- Advantages: High precision (±0.1%), detailed data, provides complete thermal decomposition curves
- Applications: Research and premium product quality control, graphite material characterization
According to research published by MDPI, the TGA method can effectively distinguish different carbon materials such as graphite, graphene, and graphite oxide, with maximum mass change temperature (T_max) varying with material purity and crystallinity: graphite oxide at 558-616°C, graphene at 659-713°C, and graphite at 841-949°C.
Research from ScienceDirect confirms that using optimized chemical purification processes, fixed carbon content of microcrystalline graphite can be increased from 83.08% to 98.37%, with TGA test results showing that purified graphite exhibits more stable thermal performance and higher electrical conductivity (21.9 S/cm).
Why Is Fixed Carbon Content the “ID Card” of Graphite Quality?
Fixed carbon content is considered the core quality indicator for natural graphite for four key reasons:
- Directly Reflects Material Purity Higher fixed carbon content means fewer impurities (such as silicates, metal oxides, sulfides). These impurities not only don’t participate in electrochemical reactions but also cause various side effects.
- Determines Material Market Positioning As shown in the previous table, graphite with different fixed carbon contents is suited for completely different application fields, with price differences reaching several times or even more than tenfold.
- Affects All Key Performance Indicators In lithium-ion battery anode applications, fixed carbon content directly affects:
- Specific capacity (mAh/g): Theoretical value 372 mAh/g, actual value affected by impurities
- Initial Coulombic efficiency (%): High-purity graphite can achieve 88-92%
- Cycle life (cycles): Capacity retention after 500 cycles can reach 85-90%
- Rate performance (C-rate): Affects fast-charging capability
- Safety performance: Impurities may cause SEI film instability
- Important Basis for Quality Certification While international battery safety standards (such as UN 38.3, IEC 62133) primarily focus on battery transportation safety and usage safety testing, high-purity graphite material is fundamental to ensuring batteries pass these stringent safety tests. According to technical documents from the European Carbon and Graphite Association (ECGA), graphite anodes for power batteries have strict material purity requirements, which directly relate to overall battery safety performance.
Objective Recommendation: For producers new to the lithium battery anode material field, we recommend prioritizing raw material supply chains with fixed carbon content ≥99.5%. While initial procurement costs are higher, this is the fundamental threshold for ensuring product competitiveness. Long-term, using high-purity raw materials can:
- Reduce quality fluctuations in the production process
- Decrease customer complaints and return rates
- Enhance brand reputation and market positioning
- Meet increasingly stringent downstream customer quality requirements
Conclusion
By now, you should clearly recognize that fixed carbon content is not just a technical parameter, but a key factor determining your product’s market position and profitability.
Three Core Takeaways
- Fixed carbon content is the “universal language” of graphite purity—from raw ore’s 5-85% to post-chemical purification’s 99.9%+, every stage of improvement means higher application value and broader market opportunities.
- 99.5% is the “entry threshold” for lithium battery anode materials—this isn’t industry convention, but a hard standard determined by stringent battery performance requirements (specific capacity, cycle life, safety).
- Purification processes determine final carbon content—from flotation to chemical purification, from LOI detection to TGA precision analysis, process optimization at every stage directly impacts product market competitiveness.
What Should You Do Next?
If you’re facing these challenges:
- ✓ Hitting bottlenecks in improving fixed carbon content on existing production lines
- ✓ Looking to upgrade from 94% concentrate to 99.5%+ battery-grade products
- ✓ Need to design brand new high-purity graphite purification lines
- ✓ Seeking reliable EPC contractors to reduce project risks
Professional Support We Can Provide:
As an integrated equipment and solution supplier focused on natural graphite production for anode materials, we provide not just individual equipment, but excel at:
- Complete production line solution design: Full process routes from flotation concentrate to 99.9% high-purity graphite
- EPC turnkey services: Design, procurement, construction one-stop delivery, reducing your coordination costs
- Technical consulting services: Help optimize existing production lines and break through fixed carbon content improvement bottlenecks
- Quality testing solutions: Supporting LOI and TGA testing equipment to ensure product stability