Structural Characterization of the Surface-Modified Li[sub x]Ni[sub 0.9]Co[sub 0.1]O[sub 2] Cathode Materials by MPO[sub 4] Coating (M=Al, Ce, SrH, and Fe) for Li-Ion Cells

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Abstract
Structural characterization of surface-modified LixNi0.9Co0.1O2LixNi0.9Co0.1O2 cathodes ( x=0.3x=0.3 and 0.15) using an MPO4MPO4 coating ( M=AlM=Al , Ce, SrH, and Fe) were investigated for their potential applications to Li-ion cells. MPO4MPO4 nanoparticles that were precipitated from metal nitrate and (NH4)2HPO4(NH4)2HPO4 in water at pH=10pH=10 were coated on the cathodes via mixing and heat treatment at 700°C700°C . The CePO4CePO4 and SrHPO4SrHPO4 -coated Li0.3Ni0.9Co0.1O2Li0.3Ni0.9Co0.1O2 cathodes heat treated at 300°C300°C were mainly made up of the rock-salt phase (Fm3m)(Fm3m) , while AlPO4AlPO4 and FePO4FePO4 -coated cathodes showed disordered [Li1−x(Ni,Co)x]3b[(Ni,Co)y]3aO2[Li1−x(Ni,Co)x]3b[(Ni,Co)y]3aO2 -type hexagonal structure (R3¯m)(R3¯m) with a cation mixing. However, when the xx value decreased from 0.3 to 0.15, bare and coated cathodes which had a spinel (Fd3m)(Fd3m) or hexagonal structure (R3¯m)(R3¯m) at x=0.3x=0.3 were transformed into a NiO-type rock-salt structure. AlPO4AlPO4 -coated sample exhibited lowest degree of oxygen generation after 300°C300°C annealing at x=0.15x=0.15 , indicating the highest thermal stability among the bare and coated cathodes.