In the present work, we compare the electrochemical behavior of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_0.5O₂ electrodes prepared from micro- or nano-particles of the active material, in Li-ion cells. The electrochemical performance in terms of capacity, rate capability, electrode impedance, stability at elevated temperature, and ageing of the nano-materials in solutions, was compared to that of micro-particles. Nano-particles of the layered LiNi_0.5Mn_0.5O₂ and spinel LiNi_0.5Mn_1.5O₄ materials were synthesized by a modified self-combustion reaction, and micron sized particles were prepared via a solid-state reaction method.

It was established that stable electrochemical behavior could be obtained during prolonged cycling of these electrodes even at elevated temperatures (60⁰C) in LiPF6/alkyl-carbonates solutions. We have found that nano-LiNi_0.5Mn_0.5O ₂ and nano-LiNi _0.5Mn_1.5O₄ electrodes demonstrate a faster kinetics, more reversible electrochemical behavior, and superior capacity retention at high rates compared to their micro-sized counterparts.

We proposed that a stable electrochemical behavior of nano-LiNi_0.5Mn_0.5O₂ electrodes under conditions of high temperature cycling/ageing and high oxidation potentials (> 4.5 V), may be related, in part, to stabilization of the electrode/solution interphase by developing surface films. The latter contain polycarbonates, LiF, Ni and Mn oxides and fluorides. An important finding is nearly constant impedance of nano- and micro-LiNi_0.5Mn_0.5O₂ electrodes during ageing and cycling after these electrodes being stabilized at elevated temperatures. It was demonstrated that ageing of nano-particles proceeded with a partial Ni and Mn dissolution from LiNi_0.5Mn_1.5O₄, as a result of which the complex domain structure of nano-particles is changed in terms of a more homogeneous Ni²⁺-to-Mn⁴⁺ distribution. For micro-particles, the partial dissolution of Ni and Mn was found to be limited.

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