3.1 Discharging & Deactivating

Discharging and deactivation are critical steps of the battery recycling process to ensure safety and efficiency. These processes neutralize stored energy, minimizing the risk of thermal runaway and other hazards. There are three primary methods used for discharging and deactivation: electrical discharge, chemical deactivation, and thermal deactivation. 

Electrical discharge involves safely draining the battery's stored energy using controlled systems. There are two main approaches to this method: regenerative discharge and resistive discharge. 

• In regenerative discharge, the positive and negative poles of the battery are connected to a discharging system programmed to perform the routine automatically according to predefined limits. During the discharging process, the direct current (DC) power is converted into alternating current (AC) power compatible with the electrical grid. This enables the energy to be either fed back into the grid or stored in a stationary storage system, though this requires another AC/DC conversion. For effective programming, it is essential to understand the battery's chemistry, voltage/state of charge (SOC) curve, and architecture, including the number of cells connected in series or parallel. 
• In resistive discharge, the battery's positive and negative poles are connected to a discharging load. The system may be programmable or have a set resistance or cascading resistance, which can be adjusted according to the discharge phase and voltage windows. In this method, the discharged DC power is converted into heat, which, aside from potential use for heating the facility, cannot be reused. 

Thermal Monitoring: For all electrical discharge processes, thermal monitoring is recommended to detect temperature hotspots and enable timely interventions to prevent overheating. 

Depth of Discharge (DoD): Determining how much to discharge the battery is crucial. Whether the target is 0% SOC, 1V per cell, or 0V per pack, the deeper the discharge, the longer the process takes. It is essential to test various DoD levels in the subsequent material separation system to identify the minimum required discharge level for effective processing. 

Chemical Deactivation involves immersing the battery in a brine solution. This method depletes the chemical energy either through an electrolysis process, where the battery's electrodes act as an anode and cathode generating hydrogen, or by allowing the brine solution to penetrate the cell and deactivate it. 

This approach is particularly suitable for compromised batteries or single cells where connecting each unit to a discharging system would be impractical due to the sheer number of channels required. However, after processing multiple batches, the used brine solution contains traces of electrolyte and requires specialized wastewater treatment before disposal. 

Thermal deactivation involves placing charged batteries in a furnace and heating them until they are safely neutralized. Several furnace types can be used for this purpose, including rotary kilns, batch furnaces, vacuum furnaces, and retard furnaces. During the process, the batteries contribute to the heating through self-heating. This process removes the electrolyte, destroys the separator, and degrades the binders. 

Each method has its own advantages depending on the battery type and condition. Proper selection and execution of these processes are essential for safe, efficient, and environmentally responsible battery recycling.