NMR study on the motion of Li+ defects and the magnetic behavior in LixNiO2

The motion of Li+ defects and the magnetic behavior have been investigated by 7Li-NMR technique. The spin–lattice relaxation time T1, the spin–spin relaxation time T2 and the Knight shift K were measured in delithiated LixNiO2 from 4.2 to 650 K. The motional narrowing observed in delithiated samples above 200 K indicates that a remarkable motion of Li+ defects exists. A contribution from a development of the magnetic correlation between Ni3+ spins appeared in T1−1 and K below 100 K in LiNiO2. The increase for T1−1 and K at low temperatures was strongly suppressed with decreasing x. This implies that nonmagnetic Ni4+ ion produced by vacancies would cut off the magnetic correlation between inter/intra-Ni layer. The increase of vacancies promotes the motion of Li+ defects and substantially varies the magnetic behavior. The magnetic relaxation process arising from Ni3+ spins which is dominant at low temperatures changes into a relaxation process based on the motion of Li+ defects with increasing temperature.