High performance of Co-free LiNixMn1-xO2 cathodes realized by nonmagnetic ion substitution for Li-ion batteries
Ni-rich LiNi x Mn 1- x O 2 cathodes have been extensively probed to resolve the electrochemical performance degradation in the absence of Co 3+ compared to LiNi x Co y Mn 1- x - y O 2 cathodes for lithium-ion batteries. Herein, LiNi 0.6 Mn 0.4 O 2 (NM64) and a series of nonmagnetic Al 3+ 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 Mn 3+ 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 Al 3+ 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 interfacial stabilities are enhanced for NM64 cathode owing to Al 3+ substitution, contributing to fewer byproducts after a long cycle. Consequently, LiNi 0.582 Mn 0.388 Al 0.03 O 2 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 Al 3+ complementary substitution.
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