The Use of Solid State NMR in Revealing the Subtle Changes to Material Structure & Chemistry Induced by Al Doping of High-Energy Lithium Battery Cathode Materials

Nicole Leifer, Exact Sciences, Chemistry, Bar Ilan University, Ramat Gan, Israel
Onit Srur-Lavi, Exact Sciences, Chemistry, Bar Ilan University, Ramat Gan, Israel
Chandan Ghanty, Exact Sciences, Chemistry, Bar Ilan University, Ramat Gan, Israel
Boris Markovsky, Exact Sciences, Chemistry, Bar Ilan University, Ramat Gan, Israel
Doron Aurbach, Exact Sciences, Chemistry, Bar Ilan University, Ramat Gan, Israel
Gil Goobes, Exact Sciences, Chemistry, Bar Ilan University, Ramat Gan, Israel

The application of solid state (MAS) NMR in the field of lithium battery research has proven highly relevant and fruitful, especially in recent years.

The current study involves the high-energy density lithium cathode material, LiNi_0.5Co_0.2Mn_0.3O₂ and the effect of low-level Al-doping on its long-term cycling behavior.

Explanations for certain electrochemical improvements seen in these materials, which were not explicable via diffraction methods, were able to be elucidated via solid-state NMR due to its usefulness in characterizing local structure in such disordered materials. In addition, substantial proof as to the location of the dopant ions was realized.

The following results will be presented:

19F NMR studies indicated quantitative and qualitative differences in breakdown mechanisms of electrode additives occuring during material cycling and evidently affected by the presence of the aluminum dopant.

Exploiting the sensitivity of solid-state NMR to local electronic structure, it was possible, via 7Li relaxation studies, to realize the influence of the Al-dopant on particle segregation, a phenomenon closely linked to reductions in cathodic irreversible capacity.

In addition, as NMR allows for the subtle distinction of populations of atoms in different crystallographic lattice sites, 27Al NMR was used to conclusively determine the location of the dopant aluminum ions upon material synthesis, and the subsequent ionic re-arrangements which takes place upon repeated cycling. Such information has not, up to this point, been directly confirmed.