Minimization of the cation mixing in Li1+x(NMC)1−xO2 as cathode material
Résumé
Li1+x(Ni1/3Mn1/3Co1/3)1−xO2 layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M=Ni +Mn + Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined -NaFeO2 structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li1−yNiy]3b[Lix+yNi(1−x)/3−yMn(1−x)/3Co(1−x)/3]3aO2 (x = 0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni2+-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M= 1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge-discharge cycling. Data obtained with Li1+x(Ni1/3Mn1/3Co1/3)1−xO2 reflected the high degree of sample optimization. An initial discharge capacity of 150mAhg−1 was delivered at 1 C-rate in the cut-off voltage of 3.0-4.3 V. More than 95% of its initial capacity was retained after 30 cycles at 1 C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li1+x(Ni1/3Mn1/3Co1/3)1−xO2.