A comparative study of electrodes comprising nanometric and submicron particles of LiNi_0.50Mn_0.50O₂, LiNi_0.33Mn_0.33Co_0.33O₂, and LiNi_0.40Mn_0.40Co_0.20O₂ layered compounds

In this paper we compare the behavior of LiNi_0.5Mn_0.5O₂, LiNi_0.33Mn_0.33Co_0.33O₂ (NMC) and LiNi_0.4Mn_0.4Co_0.2O₂ as cathode materials for advanced rechargeable Li-ion batteries. These materials were prepared by a self-combustion reaction (SCR) from the metal nitrates and sucrose, followed by calcination at elevated temperatures. The temperature and duration of calcination enabled the adjustment of the average particle size and size distribution. It was established that the annealing temperature (700-900 °C) of the as-prepared oxides influences strongly the crystallite and particle size, the morphology of the material, and the electrochemical performance of electrodes in Li-cells. Capacities up to 190, 180 and 170 mAh g^-1 could be obtained with Li[NiMn]O₂, LiNi_0.4Mn_0.4Co_0.2O₂ and LiNi_0.33Mn_0.33Co_0.33O₂, respectively. In terms of rate capability, the order of these electrodes is NMC < LiNi_0.4Mn_0.4Co_0.2O₂ ≪ Li[NiMn]O₂. Many hundreds of cycles at full DOD could be obtained with Li[NiMn]O₂ and NMC electrodes in Li-cells, at room temperature. All of these materials develop a unique surface chemistry that leads to their passivation and stabilization in standard electrolyte solutions (alkyl carbonates/LiPF₆). The surface chemistry was studied by FTIR, XPS and Raman spectroscopy and is discussed herein.