High performance of Co-free LiNixMn1-xO2 cathodes realized by nonmagnetic ion substitution for Li-ion batteries

Ni-rich LiNixMn1-xO2 cathodes have been extensively probed to resolve the electrochemical performance degradation in the absence of Co3+ compared to LiNixCoyMn1-x-yO2 cathodes for lithium-ion batteries. Herein, LiNi0.6Mn0.4O2 (NM64) and a series of nonmagnetic Al3+ ions substituted NM64 cathode materials are designed and prepared via a sol-gel route. It is found that the inferior electrochemical performance of NM64 derives from the magnetic frustration arising from Mn ions and the unstable Mn3+ ions, which will lead to severe Li/Ni mixing, and weak structural and interfacial stabilities of the cathode. The superconducting quantum interference device (SQUID) analysis proves that the nonmagnetic Al3+ ion can lower the Li/Ni disorder in NM64 cathode by relieving magnetic frustration. Moreover, the dQ/dV and XPS analyses confirm that both structural and inter-facial stabilities are enhanced for NM64 cathode owing to Al3+ substitution, contributing to fewer byproducts after a long cycle. Consequently, LiNi0.582Mn0.388Al0.03O2 cathode delivers a high discharging capacity of 179 mAh g-1 at 1.0C with a capacity retention of 87.6% after 100 cycles. This study not only gives an in-depth understanding of the mechanism of electrochemical performance degradation for NM64 cathode, but also demonstrates an efficient solving approach through Al3+ complementary substitution.