Abstract
End-of-life lithium-ion batteries represent an important secondary raw material source for nickel, cobalt, manganese and lithium compounds in order to obtain starting materials for the production of new cathode material. Each process step in recycling must be performed in such a way contamination products on the cathode material are avoided or reduced. This paper is dedicated to the first step of each recycling process, the deep discharge of lithium-ion batteries, as a prerequisite for the safe opening and disassembling. If pouch cells with different states of charge are connected in series and deep-discharged together, copper deposition occurs preferably in the cell with the lower charge capacity. The current forced through the cell with a low charge capacity leads, after lithium depletion in the anode and the collapse of the solid-electrolyte-interphase (SEI) to a polarity reversal in which the copper collector of the anode is dissolved and copper is deposited on the cathode surface. Based on measurements of the temperature, voltage drop and copper concentration in the electrolyte at the cell with the originally lower charge capacity, the point of dissolution and incipient deposition of copper could be identified and a model of the processes during deep discharge could be developed.
Highlights
The deep discharge of individual cells was performed with the help of constant resistors (8 mΩ ... 5.9 Ω); cell voltage and discharge current were recorded via a data log system (Arduino Uno, time interval of the measuring points = 2 s)
A new pair of pouch cells was used for each deep discharge test in a series connection
If the voltage of the working cell in the deep discharge reached a defined value (UCV = -0.8, -1.2, -1.5, -1.77, -1.91, -1.0 V after the minimum), the test was stopped and the electrolyte was taken from the working cell immediately
Summary
Discharge tests.Pouch cells with cathodes mainly consisting of NMC 622 and a remaining capacity of 20Ah were used for the experiments. 5.9 Ω); cell voltage and discharge current were recorded via a data log system (Arduino Uno, time interval of the measuring points = 2 s). Both cells were previously charged to 100% capacity; cell 2 was discharged via a resistor of 41 mΩ to a clamp voltage ( UCV) of 3 V, which corresponds to a capacity of 15%. A new pair of pouch cells was used for each deep discharge test in a series connection. The temperature of the working cell was recorded during deep discharge, as described above
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