High-pressure synthesis and electrochemical behavior of layered (1-a)LiNi1-yAlyO2·aLi[Li1/3Ni2/3]O2(1-a)LiNi1-yAlyO2·aLi[Li1/3Ni2/3]O2 oxides

Layered (1-a)LiNi1-yAlyO2·aLi[Li1/3Ni2/3]O2(1-a)LiNi1-yAlyO2·aLi[Li1/3Ni2/3]O2 oxides, 0⩽a<0.40⩽a<0.4, have been prepared by solid state reaction between NiO, Al2O3Al2O3 and Li2O2Li2O2 under high pressure. The structural characterization of the layered oxides was performed using powder XRD, IR spectroscopy and EPR spectroscopy at 9.23 and 115 GHz. It has been found that the high-pressure favors Al substitution for Ni in the NiO2NiO2-layers of layered LiNiO2LiNiO2. A random Al/Ni distribution in the layer was found. The incorporation of extra Li in the Ni1-yAlyO2Ni1-yAlyO2-layer starts at a precursor composition Li/(Ni+Al)>1.2Li/(Ni+Al)>1.2. While pure NiO2NiO2-layers are able to incorporate under high-pressure up to 1/3Li, the appearance of Al in the NiO2NiO2-layers hinders Li+Li+ dissolution (Li<(1-y)/3)(Li<(1-y)/3). In addition, with increasing Al content there is a strong cationic mixing between the layers. High-frequency EPR of Ni3+Ni3+ indicates that the structural interaction of LiAlyNi1-yO2LiAlyNi1-yO2 with Li[Li1/3Ni2/3]O2Li[Li1/3Ni2/3]O2 proceeds via the formation of domains comprising different amount of Ni3+Ni3+ ions. The use of Li1.08Al0.09Ni0.83O2Li1.08Al0.09Ni0.83O2 as a cathode material in a lithium ion cells displays a first irreversible Li extraction at 4.8 V, after which a reversible lithium insertion/extraction between 3.0 and 4.5 V is observed on further cycling.

High-frequency EPR of Ni3+Ni3+ indicates that structure interaction of LiAlyNi1-yO2LiAlyNi1-yO2 with Li[Li1/3Ni2/3]O2Li[Li1/3Ni2/3]O2 proceeds via the formation of domains characterized with different amount of Ni3+Ni3+ ions.Figure optionsDownload full-size imageDownload as PowerPoint slide