  In layered LiNixMnyCozO2 cathode material for lithium-ion batteries, the
spins of transition metal (TM) ions construct a two-dimensional triangular
networks, which can be considered as a simple case of geometrical frustration.
By performing neutron powder diffraction experiments and magnetization
measurements, we find that long-range magnetic order cannot be established in
LiNixMnyCozO2 even at low temperature of 3 K. Remarkably, the frustration
parameters of these compounds are estimated to be larger than 30, indicating
the existence of strongly frustrated magnetic interactions between spins of TM
ions. As frustration will inevitably give rise to lattice instability, the
formation of Li/Ni exchange in LiNixMnyCozO2 will help to partially relieve the
degeneracy of the frustrated magnetic lattice by forming a stable
antiferromagnetic state in hexagonal sublattice with nonmagnetic ions located
in centers of the hexagons. Moreover, Li/Ni exchange will introduce 180{\deg}
superexchange interaction, which further relieves the magnetic frustration
through bringing in new exchange paths. Thus, the variation of Li/Ni exchange
ratio vs. TM mole fraction in LiNixMnyCozO2 with different compositions can be
well understood and predicted in terms of magnetic frustration and
superexchange interactions. This provides a unique viewpoint to study the Li/Ni
ions exchange in layered Li(NixMnyCoz)O2 cathode materials.
