Lithium battery recycling technology follows this order: first, production waste and defective products are recycled. Then, retired lithium batteries come next. Therefore, electrode line technology came first, followed by battery line technology.
Dual-shaft slow-speed shredder
Dual-shaft slow-speed shredders are a typical feature of electrode line technology. The process usually sends waste cathode material on a conveyor belt. It goes to a dual-shaft shredder for primary crushing. This results in a particle size of about 100 mm. The material then enters the impact crusher at the lower end for secondary crushing. The particle size ranges from 10 mm to 30 mm. This depends on what the downstream equipment needs. Using a shredder for primary crushing stops the impact crusher from clogging. This happens because there’s less tangled material. The shredder and crusher are stacked one above the other.
Why is it not recommended to use a double-shaft slow shredder?
Many companies and institutions grow their battery lines using electrode technology. They often overlook new innovations designed for retired lithium batteries.
Retired lithium batteries don’t resemble long strips of waste electrodes. They lack a strong outer shell. Lithium batteries usually come in three shapes: cylindrical, soft-pack, and square. The shell material is strong. The internal material is tightly wrapped in a wound or disc shape. This is very different from the loose, long strips of waste electrodes.
Secondly, retired lithium batteries are charged. Any breakage will first damage the diaphragm. This includes penetration, extrusion, lithium dendrite puncture, shrinkage, melting, and collapse. As a result, an internal short circuit will occur. If the breaking method and working conditions are wrong, it can lead to a quick temperature rise and heat buildup. If the temperature rises for a bit, the SEI film in the battery will break down. This will let the electrolyte touch the lithium metal in the negative electrode graphite. The positive and negative electrodes will crosstalk. The positive electrode material will change phase, releasing oxygen. This oxygen will react with the reduced lithium carbide from the negative electrode. Thermal runaway will happen, leading to accidents like smoke, fire, and explosions.
Safety issues during the use of double-shaft slow shredder
Nitrogen flow helps control oxygen levels. This prevents carbonate solvents from the electrolyte from releasing during shredding. These solvents can ignite at flash point temperatures. If the temporary temperature rise causes the cathode material to change phase and release oxygen, the protective effect of nitrogen control will drop a lot. Using a dual-axis slow-speed shredding process will likely cause fires in charged decommissioned ternary batteries. Decommissioned lithium-ion batteries that are charged are more stable and rarely catch fire. However, they can still release harmful fumes and smoke.
The shredding process needs to control the battery’s short-circuit temperature rise effectively. The dual-axis slow-speed shredder runs at 5-70 rpm. This speed allows too much time for short-circuit temperature rise. As a result, it can cause thermal runaway. Time is the only key controllable variable.
Causes of security issues
To prevent smoke, fire, and explosions, companies that make this type of equipment often require battery cells to be discharged. This is especially true for charged ternary batteries. But whether it’s physical load discharge, chemical brine discharge, or other methods, there are major side effects. You can check out the article on the side effects of single-cell discharge on the official WeChat account. Why is it important to discharge battery cells in the national standard project for “Safety Technical Specifications for Disassembly and Crushing of Automotive Power Batteries”? This doesn’t match the current technology for directly crushing charged batteries that industry owners need.
Next, the pyrolysis process comes after the crushing stage. This stage needs the biggest heating surface area for the crushed material. The dual-shaft slow-speed shredder doesn’t tumble the battery material well. This leads to a lack of expansion in the heated surface area. If a hammer crusher is used right after, the copper and aluminum foil wraps around the black powder. This weakens the tumbling effect and reduces the pyrolysis heating surface area even more.
There are several minor engineering innovations:
- Control the oxygen level to convert more fluorine into hydrogen fluoride gas. This helps prevent lithium fluoride from forming in the black powder, aiding wet extraction.
- Address micro-short-circuit temperature rise and prevent electric shocks in crushed materials.
- Maximize the heated surface area of crushed materials to improve the pyrolysis process.
- Keep copper and aluminum foils intact. This stops aluminum powder from forming when crushing. So, it makes it easier to sort and remove copper and aluminum later.
The best choice after technological iteration – high-speed shearing equipment
In the end, we dropped the electrode line technology. Instead, we focused on retired battery raw materials. We changed the dual-axis slow shredding technology based on our engineering team’s research and hands-on work. Now, we use high-speed shearing and crushing technology. We applied it in the Zhejiang Tianneng Huzhou Project and the Ningbo Wei Fu Lishui Project, among others. The results were positive and iterative.
Recommended high-speed shearing equipment
Cyclone Mill Technology: A Revolutionary Breakthrough in Dry Stripping
Cyclone mills utilize high-speed airflow pulverization. High-speed airflow in the special grinding chamber causes materials to collide and rub together. This process efficiently strips electrode materials. This technology solves the problems of traditional mechanical pulverization. It also avoids the pollution from wet processes. Plus, it opens a new way for recycling lithium batteries.
The cyclone mill has a modular design. It mainly includes:
- a feed system,
- a pulverization system,
- a grading system,
- a collection system.
Its core parts are made from tough ceramic. This helps the equipment last longer. The special flow field design spreads materials evenly in the grinding chamber. This boosts stripping efficiency.
Compared to traditional wet processes, cyclone mill technology offers significant advantages. Energy use drops by over 40%. Processing efficiency rises by 50%. Plus, wastewater discharge is fully eliminated. These benefits make it a leading technology in lithium battery recycling.