Ni-rich layered oxide cathode materials such as LiNi0.8Mn0.1Co0.1O2(NMC811) are
widely
tipped as the next-generation cathodes for lithium-ion batteries.
The NMC class offers high capacities but suffers an irreversible first
cycle capacity loss, a result of slow Li+diffusion kinetics
at a low state of charge. Understanding the origin of these kinetic
hindrances to Li+mobility inside the cathode is vital
to negate the first cycle capacity loss in future materials design.
Here, we report on the development ofoperandomuon
spectroscopy (μSR) to probe the Å-length scale Li+ion diffusion in NMC811 during its first cycle and how this can
be compared to electrochemical impedance spectroscopy (EIS) and the
galvanostatic intermittent titration technique (GITT). Volume-averaged
muon implantation enables measurements that are largely unaffected
by interface/surface effects, thus providing a specific characterization
of the fundamental bulk properties to complement surface-dominated
electrochemical methods. First cycle measurements show that the bulk
Li+mobility is less affected than the surface Li+mobility at full depth of discharge, indicating that sluggish surface
diffusion is the likely cause of first cycle irreversible capacity
loss. Additionally, we demonstrate that trends in the nuclear field
distribution width of the implanted muons during cycling correlate
with those observed in differential capacity, suggesting the sensitivity
of this μSR parameter to structural changes during cycling.