# Effect of Annealing on Direct Recycled NMC Cathodes

## TL;DR

This paper studies how annealing improves the performance of recycled NMC cathodes used in electric vehicle batteries.

## Contribution

The study reveals that high-temperature annealing is crucial for restoring the structural and electrochemical properties of recycled NMC 622 cathodes.

## Key findings

- Annealing at 720 °C is necessary to restore the crystal structure of relithiated NMC 622.
- Annealing restores electrochemical properties without affecting particle porosity or morphology.
- Surface reconstruction is limited, but full structural recovery requires high temperatures.

## Abstract

A substantial number of electric
vehicle batteries are
poised to
reach end-of-life conditions in the next decade. Direct recycling
has advantages over typical recycling processes because it preserves
the chemical structure of the material. One key step of direct recycling
materials like nickel manganese cobalt oxide (NMC) cathodes is relithiation,
which includes replacing the depleted lithium inventory in the cathode
and annealing the material to fix crystallographic degradation. This
work uses multiple characterization techniques (synchrotron X-ray
diffraction, Ni X-ray absorption near edge structure, scanning transmission
electron microscopy) to understand the lithiation mechanism of degraded
and chemically relithiated NMC 622. Despite the necessary reconstruction
after relithiation being limited to the surface of the degraded NMC
622, a high annealing temperature of 720 °C is still necessary
to restore the NMC 622 structure back to pristine condition after
relithiation. This work also finds that treating degraded NMC 622
with an annealing step is sufficient to restore key electrochemical
and structural properties, other essential features of pristine NMC
622 material such as particle porosity and morphology are largely
unaffected. Understanding the effect of this annealing step has important
implications on defining the degree of success of any given direct
recycling strategy.