Magnetic Frustration Effect on the Rate Performance of LiNi_(0.6)Co_(0.4?x)Mn_xO_2 Cathodes for Lithium-Ion Batteries

摘要

Cobalt-free LiNi_xMn_(1?x)O_2 (NM, x ≥ 0.5) layered oxides are considered tobe promising cathode materials for next-generation lithium-ion batteriesbecause of exceptionally high capacity and low cost, yet the fundamental roleof manganese ions in the NM layered structure and rate performance has notbeen fully addressed to date. Herein, a series of Ni-fixed LiNi_(0.6)Co_(0.4?x)Mn_xO_2(x = 0, 0.1, 0.2, 0.3, and 0.4) systems are employed as cathode materials toinvestigate the functionality of Mn ions on their structures and electrochemicalproperties. It is found that contrary to prior reports, the change in thec-axis lattice parameter is not in close connection with the rate performanceof NM cathodes. In particular, superconducting quantum interference device(SQUID) measurements are performed to verify the fact that Mn~(3+) and Mn~(4+)ions with high spin states cause severe magnetic frustration in the structuresof cathode materials, which profoundly aggravates the Li/Ni ionic disorderand blocks Li~+ migration, contributing to inferior rate performance. In addition,Li~+ migration hindered by Li/Ni disorder, is theoretically demonstratedby ab initio calculation. This work not only provides fresh insight into the roleof Mn in NM layered oxide cathodes but also proposes an effective strategyto resolve their inferior rate performance.