Ultrafast 1h and 7li Solid-State MAS NMR Studies of Materials for Next-Generation Li-Based Batteries

Li-based batteries are considered as one of the most promising advanced energy storage systems for electrical vehicles (EV) and stationary energy storage. However, their successful implementation in these emerging technologies is a significant challenge because energy requirements, system safety, and manufacturing costs are subject to more stringent demands than in current commercial batteries. Therefore, optimization of battery components such as electrode materials and electrolytes is a key step for the rational development of advanced battery systems. 

Solid-state magic-angle-spinning (MAS) NMR has emerged in the last decades as a unique technique for obtaining very accurate information on the atomic-level structure and dynamics of complex materials (1). This technique is sensitive to short-range order and therefore is not limited to crystalline materials. In particular, ultrafast MAS NMR (>60 kHz) generates spectral resolution enhancements that facilitate the identification of different species in complex systems (2).

In this work, we present solid state NMR structural and dynamic characterizations of two highly Li-ion-conductive ceramic materials and a novel hybrid organic-inorganic composite. The results obtained by NMR were successfully applied to improve the performance of such materials.

In the first part of this work, ⁷Li and ¹³C ultrafast MAS NMR were used to characterize a hybrid anode material composed of inorganic SnLi particles coated with a polymer phase based on the polymerization of vinyl-ethylene carbonate (VEC).  The presence of 6 different SnLi alloy phases in the material was clearly differentiated together with some residual metallic lithium due to the different ⁷Li Knight shifts(3) of the individual compositions. ¹³C MAS NMR was used to characterize the organic phase in this compound. Results obtained provide a deeper understanding of the chemical composition and the possible synergistic interactions within this composite. 

In the second part of this work, ultrafast ¹H and ⁷Li solid-state MAS NMR were applied in the study of two highly Li-ion-conductive ceramic materials. In particular, the effects of protonation by exposure to moisture on the conductivity of lithium in the perovskite Li_3xLa_2/3-x□_1/3-2xTiO₃ and the garnet Li_7-3xGa_x□_2xLa₃Zr₂O₁₂were followed by NMR (where □=defect). The large grain boundary contributions to the overall Li-ion conductivity were monitored and the effects of moisture on the sintering of these electrolyte materials determined. Based on these results, an effective strategy to improve the total Li-ion conductivity of these materials was designed.

(1)      a) NMR of Quadrupolar Nuclei in Solid Materials, Roderick E. Wasylishen, Sharon E. Ashbrook, and Stephen Wimperis (Eds.) John Wiley & Sons Ltd, Chichester, UK (2012). b) Solid-State NMR in Materials Science: Principles and Applications, Vladimir I. Bakhmutov, CRC Press(2011). c) NMR Crystallography, Robin K. Harris, Roderick E. Wasylishen, and Melinda J. Duer (Eds.), Wiley, Chichester (2009).

(2)      I. Bertini, L. Emsley, M. Lelli, C. Luchinat, J. Mao, G. Pintacuda. J. Am. Chem. Soc. 2010, 132, 5558-9.

(3)      E. Bekaert, F. Robert, P. E. Lippens, and M. Menetrier. J. Phys Chem. C 2010, 114, 6749-6754.