Sustainable 2nd Battery Recycling with Regenerative DC Load: Why Does Negative Voltage Matter for Complete Discharge?

E-mobility has seen its promising growth since Tesla’s initiative of electric replacement of combustion and now following the former the dominant share taken by BYD in the EV industry. Another of ActionPower’s application note contains worldwide market data of EV sales. This is just a part of the story about battery. EV battery inevitably suffers from ageing and deterioration in capacity that eventually they retire from use. End-of-line batteries are alleged to 7.8 million tonnes per year by 2040, as per IDTech EX. [1]

Retired EV batteries would not necessarily all get immediately disposed of, however, some of them are intended for a second-life in typically renewable energy industry as storage battery. The residual capacities and capabilities of battery should be verified through charging and discharging test, alternatively referred to as cycling test, to define the battery is remaining performance metrics like SOH, or in case for recycling, to completely discharge the remained energy.

Battery Life Cycle Overview: From On-Board EV Use to Second Life and Recycling

Batteries like Lithium-Ion ones start their operation typically for electric vehicle until its retirement when their SOH (State-of-Health) is below 80% which is a common recognized threshold in the industry. [2] Before being relaunched for second life applications, batteries go through a series of testing and calibration processes: SOH testing for confirming the remaining life capacity, AC/DC IR testing for checking their chemistry characteristics, sorting and grading, then BMS re-calibration.

When batteries see the drought of their capability and thus incapable of any applications, recycling calls the end of their life, and they disposed of for extracting the rare earth containments and reducing environmental impacts.

Battery Life Cycle: From EV Operation to 2nd Life and Recycling

Reprocessing of Retired EV Battery for Second Life Uses

Retired EV batteries repurposed and re-intended for second life operations should go through a set of data-driven and rigorous reprocessing workflow for validating its safety, status, and as well as for purpose of re-calibration. The testing processes align with the patterns of a standard cycling test with core focuses around the below factors:

• State of Health (SOH) Evaluation & Grading: Not all retired batteries age equally. Precise charge-discharge cycling and internal resistance (DCIR/ACIR) testing are required to evaluate the true residual capacity of each module. Such a screening process segregates viable units from those that must be sent directly to end-of-life recycling.
• Module Balancing & Reassembly: Retired cells suffer from severe voltage and capacity inconsistencies. To prevent the SOC discrepancy where one degraded cell limits an entire pack, modules must be precisely sorted, matched, and electrically balanced before being reassembled into new battery arrays.
• BMS Recalibration & Dynamic Simulation: A battery transitioning from an EV to a solar grid storage system faces entirely different load profiles. The Battery Management System (BMS) must be recalibrated, and the newly assembled packs must undergo dynamic simulation testing to verify their thermal stability and power response under their new operational profiles.

Complete Battery Discharge for Safe Recycling and Why Negative Voltage Operation Matter

Draining the battery’s energy is essential for recycling for avoiding fire hazards, explosions, and damage to processing equipment while processing them through their very end of life-cycle.

Discharging completely a battery pack during recycling confronts a potential worst-case failure due to the cell-imbalance caused by the discrepancy of capability between cell in series-connection. Complete discharge firstly enforces the weak ones to drought status while the rest stronger cells continue to discharge, push current through the circuit, which eventually force current through the depleted cell and charge the latter in reverse.

End-of-line de-energization thus requires a discharging system capable of functioning and continuously drawing current, even when the battery’s output terminal drops to 0V or slightly below.

Electronic load and discharging system used for battery recycling differs from a general one due to the essentialness of capability that enforces the voltage slightly below zero. Battery cycling during recycling is not intended for calibration, validation or test, however, purposed for irreversibly destroy of the cell’s internal structures and achieving absolute chemical passivation.

Discover ActionPower’s Regenerative DC Load for Battery Recycling

ActionPower’s CORTEX series functions as regenerative DC load to completely draw the remaining energy within the battery pack before its disassembly into individual parts. With 30kW in a compact 3U chassis, further scalable to reach up to 3 MW in rack systems, Cortex DC (CD series) supports users to extract the remaining energy from retired batteries before recycling and recovers with regenerative load technology the sunk energy back to utility with a 91% efficiency to both save the energy cost and mitigate thermal address compared to a conventional resistive load.

Bibliography

• [1] End-Of-Life Electric Vehicle Batteries: Recycling or Second-Life? June 11, 2020Dr Alex Holland, Dr Na Jiao, IDTech EX, Link
• [2] Generative learning assisted state-of-health estimation for sustainable battery recycling with random retirement conditions, Shengyu Tao, Ruifei Ma, Zixi Zhao, Nature Communications volume 15, Article number: 10154 (2024), Link