Introduction

Graphite saggers are the core containers for the graphitization process of lithium battery anode materials, and also serve as important vessels for sintering lithium iron phosphate (LFP) cathode materials. With the rapid growth in global demand for anode materials, the design optimization and lifespan extension of graphite saggers have become focal points of industry attention. A high-quality graphite sagger must not only maintain structural integrity at ultra-high temperatures up to 3000°C, but also balance furnace loading efficiency and operating costs.

Core Performance Requirements

Graphite saggers are manufactured from high-purity graphite (C% ≥ 99.9%), with key performance indicators including:

- Ultra-high temperature resistance:** No deformation or softening at graphitization temperatures of 2800–3200°C
- Oxidation resistance:** Nitrogen atmosphere protection is required during sintering to reduce graphite oxidation loss
- Thermal conductivity efficiency:** Electrical resistivity ≤ 12 μΩ·m to ensure uniform temperature field distribution
- Dimensional accuracy:** Allowable tolerance of ±0.5 mm to guarantee furnace loading compatibility

For LFP sintering, some graphite saggers are treated with a vacuum impregnation process using an aluminum sol and boric acid composite solution to form a protective layer, effectively resisting the penetration and corrosion of lithium oxides.

Design Innovations

The innovative design of square graphite saggers has been a significant trend in recent years. The adoption of an arc-shaped design at both inner and outer four-edge corners effectively reduces mechanical stress concentration and improves impact strength. The 510 × 570 mm size configuration maximizes furnace loading utilization across different kiln specifications, improving graphitization furnace space utilization by more than 20%.

In addition, the wedge-shaped or conical design on the inner side of the sagger lid effectively enhances the overall compressive strength of the cover, preventing lid collapse and cracking. Jilin Longchang New Energy's proprietary patented products—the 9-hole graphite crucible and anti-cracking protective structure—allow customers to replace only a portion of the main body rather than the entire crucible, significantly reducing operating costs.

Industrial Applications

Graphite saggers are widely used in Acheson graphitization furnaces and internal series resistance furnaces. Carbonaceous materials or natural graphite anode powders are loaded into saggers, sealed with lids, and surrounded by resistance filler and insulation materials before power is applied to raise the temperature to approximately 3000°C. This process vaporizes and volatilizes non-carbon ash components, achieving both graphitization and purification. At present, Longchang New Energy has an annual production capacity of 300,000 sets of graphite crucibles, with a market share of approximately 20%, and has established long-term cooperative relationships with leading anode material manufacturers such as Shanghai Shanshan and BTR.

Conclusion

The design of graphite saggers is continuously evolving toward larger sizes, greater precision, and extended service life. From material purity control to structural mechanical optimization, every detail improvement contributes to reducing the production cost of anode materials.