Probing microstructure of solid-state synthesized LiCoO2 with MAS NMR spectroscopy

LiCoO 2 is an important category of active cathode materials in lithium-ion batteries due to its high compacted electrode density, good thermal stability , and stable voltage platform. Recent works on LiCoO 2 have focused on the realization of higher charging voltages to fully utilize its high theoretical capacity. However, an unambiguous atomic-level local probe is essential for the understanding of structure-function correlation. Here we employ high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy to study the local atomic environments in LiCoO 2 synthesized with three common sintering methods. While one-dimensional 7 Li NMR shows distinct linewidth and subtle dependence on lithium over-stoichiometry, both 7 Li and 59 Co relaxation times are highly dependent on the sintering method. We prove that the two-step sintering method favors the elimination of unreacted Co 3 O 4 , thereby enabling the best discharge capacity in all-solid-state lithium batteries assembled with LiCoO 2 /LGPS/LiIn, which is in accordance with its narrowest 7 Li linewidth and the longest 7 Li/ 59 Co T 1 .