Active Material Layer Separation From Positive Electrodes in Lithium–Ion Batteries by Joule Heating During Pulsed Discharge in Air and Water

Separation of the positive electrode active material (PEAM) layer including the critical metal is necessary for recycling of lithium-ion batteries (LiBs). Herein, we applied the pulsed discharge to one side coated positive electrode sample in air and water as environments with different heat transfer conditions for the separation. Performing the pulsed discharge at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ED=1.20$ </tex-math></inline-formula> J/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in water was beneficial for separating in this study. Notably, 99.6% of the PEAM layer was separated at energy density (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ED</i>) = 1.20 J/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in water, whereas the sample was pulverized at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ED=1.10$ </tex-math></inline-formula> J/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in air. The simulations indicated that the polyvinylidene difluoride (PVDF) binder melted because the temperature exceeded the melting point. The maximum thermal stress acting on the Al foil and the volume expansion of the surrounding medium were 41% and 20% larger in air than in water, respectively, resulting in a greater expansion force and pulverization of the sample in air. The separation mechanism by pulsed discharge is the decrease in adhesion at the interface due to PVDF melting and the thermal stress acting at the timing that prevents Al from tearing. Thus, the separation by pulsed discharge is based on the control of Joule heating and its heat conduction.