Negative Electrode Sheet Graphite Microwave Repair and Regeneration Technology

Against the backdrop of the “Dual Carbon” goals, Henan Jufeng Technology has addressed the industry’s longstanding pain points—namely, the “high‑temperature carbonization, structural damage, and difficulty in direct reuse” of spent lithium‑ion battery anode graphite powder—by abandoning low‑end pulverization processes. Under the leadership of Zhang Haitao, a member of Academician Zhang Suojiang’s team and doctoral supervisor at the Institute of Process Engineering, Chinese Academy of Sciences, Jufeng has joined forces with this team to develop advanced graphite regeneration technology. Due to roller pressing and internal stress, spent graphite particles often suffer damage; by manually repairing the interfacial layer of spent graphite anode materials and stripping away the surface coating on the graphite after acid leaching, the company is able to improve and reconstruct the electron/ion transport channels on the graphite surface. After five rounds of technological iteration and upgrades, the company has successfully developed a complete set of “Spent Anode Graphite Repair and Regeneration Technology” along with a full production line process. This technology employs four key steps—thermal cracking, acid leaching to remove impurities, carbon coating, and microwave repair—to achieve high‑performance repair and regeneration of spent graphite, and it has now been put into industrial application, with iterative upgrades culminating in fifth‑generation, fully automated production line equipment.

This technology has already been implemented in numerous lithium‑ion new energy enterprises, including Nandu Power, CN Innovation, Xintaihe Nanomaterials, Ganfeng Lithium, Betray, and BYD. Not only does this technology enable the efficient recovery of graphite from negative electrode sheets, but it also allows the performance of recycled graphite to approach or even surpass that of virgin graphite, thereby reducing battery costs and environmental impact. The technology boasts strong potential for resource utilization and industrial application. Our company is fully equipped with industrial production lines capable of processing more than 10,000 tons per year for each individual line dedicated to negative electrode sheet graphite recycling.

A Brief Overview of the Four-Step Principle

The waste negative electrode sheets undergo a four‑step process—“oxygen‑free pyrolysis → acid leaching for impurity removal → carbon coating → microwave repair”—to complete the graphite regeneration pathway.

(1) Oxygen‑Free Pyrolysis for Powder Production: Typically, at temperatures ranging from 450–800°C and under a nitrogen (N₂) atmosphere, the binder (PVDF) and conductive agent undergo oxygen‑free pyrolysis to prevent graphite oxidation, enabling flexible separation of the graphite from the copper foil while preserving the original structural morphology of the graphite—a process that facilitates subsequent acid washing and repair.

(2) Acid Pickling for Impurity Removal: By jointly using chemical raw materials such as HCl, H₂SO₄, and HF, residual SEI film and metallic impurities (such as Cu, Fe, Al, etc.) can be effectively removed, increasing carbon purity to over 99.95% without affecting the crystal structure.

(3) High‑Temperature Carbon Coating: By adding organic carbon sources such as pitch, glucose, and phenolic resin in appropriate proportions, high‑temperature carbon coating is carried out under anaerobic conditions at around 1200°C to repair surface defects and enhance conductivity and cycling stability.

(4) Microwave repair can rapidly heat graphite; microwaves help promote the reconstruction of the carbon coating on the graphite surface, thereby repairing lattice defects once again, enhancing the adhesion of the coating layer, and increasing the degree of graphitization, ultimately improving the overall performance of recycled graphite.

Brief Overview of Pickling Wastewater Treatment Processes

1. Introduce the settled wastewater into an equalization basin for mixing, thereby achieving wastewater homogenization and maintaining stable concentrations of pollutants such as pH, SS, ammonia nitrogen, and COD in the wastewater, thus preventing uneven pollutant concentrations from compromising treatment efficiency.

2. The hydrated lime storage tank dosing system consists of a lime tank, a dissolution tank, a water supply pump, a slurry dosing pump, and other components. Hydrated lime is fed into the storage tank and, during operation, is quantitatively conveyed to the dissolution tank while water is pumped in to dissolve the hydrated lime. Since hydrated lime releases heat when it comes into contact with water, calcium hydroxide is formed; in the dissolution tank, the calcium hydroxide solution exists in the form of a slurry. After the wastewater has been homogenized in the equalization basin, a pump delivers the wastewater to the neutralization tank.

3. Acid–Base Neutralization: Wastewater flows from the equalization tank into the neutralization system. The neutralization system employs a continuous, composite multi-stage acid–base neutralization process; under acidic conditions, the Fe in the wastewater… ₃ +、Ca²⁺, Mg²⁺ and other metal ions exist in a free state; as acidity decreases, the solubility of metal ions in water gradually declines, and some begin to precipitate in the form of chlorides. The remaining metal ions also progressively combine with OH⁻ to form corresponding precipitates. As pH increases, the metal ions dissolved in water are completely removed. Most of the precipitates formed during the reaction remain suspended in the neutralization tank.

Some of the reaction equations are as follows:

• CuCl₂ + Ca(OH)₂ = CaCl₂ + Cu(OH)₂↓
• 2FeCl₃ + 3Ca(OH)₂ = 3CaCl₂ + 2Fe(OH)₃↓
• FeCl₂ + Ca(OH)₂ = CaCl₂ + Fe(OH)₃↓
• MgCl₂ + Ca(OH)₂ = CaCl₂ + Mg(OH)₂↓
• 2HCl + Ca(OH)₂ = CaCl₂ + 2H₂O

4. Sedimentation and Clarification: After neutralization, the wastewater must be further treated with coagulant PAC and flocculant PAM before being pumped into the existing high‑efficiency sedimentation tank. PAC and PAM are each delivered to the tank via pumps controlled by the operation platform from their respective preparation systems. The PAM preparation system consists of a three‑compartment mixing tank, with the tank body constructed from stainless steel. 5. Sludge Treatment: The clarified wastewater from sedimentation is pumped into an intermediate tank equipped with a water pump; the settled sludge is conveyed via a screw conveyor located at the bottom of the tank to the sludge storage pond. The sludge primarily consists of flocculated precipitates formed after acid–base neutralization. Due to its high moisture content, it is first subjected to pressure filtration. After pressure filtration, the sludge contains less than 40% water. The filtrate is then pumped into the intermediate water tank. The filtered sludge cake is transported offsite for proper disposal. 6. Quartz Sand Filtration: Although the wastewater has been partially clarified through sedimentation, it still contains trace amounts of suspended solids. The wastewater is pumped from the intermediate water tank into the quartz sand filter, where it is filtered before being discharged into the clear water tank—by this point, the wastewater has already met discharge standards.

Images of the flexible powder removal equipment for pyrolytic recycling of waste negative electrode sheets

Negative Electrode Thermal Decomposition and Powdering Equipment

Negative Electrode Thermal Decomposition and Powdering Equipment

Negative Electrode Thermal Decomposition and Powdering Equipment