Decoupling surface from bulk degradation in Ni-rich Li-ion battery cathodes using operando muon spin relaxation spectroscopy

Ni-rich cathodes offer high energy densities yet are plagued by degradation processes which limit cycle life. Despite enormous promise, an outstanding challenge remains in deconvoluting the contributions of phase transitions, oxygen loss, and aging to ion diffusivity. Through an ISIS Facility Development PhD, we designed and made available a battery cell for operando muon spectroscopy measurement. In recent beamtime (RB2220654), we evaluated the operando study of LiNiO2 where we tracked changes in field fluctuation rate and static field distribution width (Δ) to uncover how Li hopping rate and local nuclear magnetic field change as a function of state of charge in the 1st cycle. To date, muon operando studies have been limited to early cycles with no reports on the critical influence of long-term cycling on Li-diffusion. Our current proposal applies Li2NiO3 as a model for LiNiO2 surface degradation to discover:
-Influence of structural transformations occurring >4.4 V on Li-diffusion
-Li-diffusivity changes and evolution of Δ during oxygen loss
-Properties of decomposition products formed in Li2NiO3 (and hence LiNiO2 surfaces)
-Influence of long-term cycling on Li+ diffusivity behaviour and delineating surface from bulk contributions to capacity degradation
These questions which remain unanswered despite being widely studied via traditional approaches. We anticipate the publication of a high impact paper from the unique insights gleaned from operando muon spectroscopy.