Influence of Iron on the Structural Evolution of LiNi0.4Fe0.2Mn1.4O4LiNi_{0.4}Fe_{0.2}Mn_{1.4}O_{4} during Electrochemical Cycling Investigated by in situ Powder Diffraction and Spectroscopic Methods

The cathode materials LiNi0.5Mn1.5O4 and LiNi0.4Fe0.2Mn1.4O4 were synthesized using a citric acid-assisted solgel method with a final calcination temperature of 1000 °C. An impurity phase exists in LiNi0.5Mn1.5O4 powders, which can be eliminated by substituting some of the Ni2+ and Mn4+ ions with Fe3+. The substitution of Fe into the spinel structure was confirmed by NMR and Mössbauer spectroscopy. The initial capacity of LiNi0.4Fe0.2Mn1.4O4 powder synthesized at 1000 °C (LNFMO) is slightly higher than that of LiNi0.5Mn1.5O4 powder synthesized at 1000 °C (LNMO). Additionally, its capacity retention of 92% at room temperature after 300 cycles at C/2 charging-discharging rate between 3.5–5.0 V is higher than that of the Fe-free sample (79.5%) under same conditions which could arise from the difference in their cycling mechanisms. In order to understand the structural evolution of these materials during electrochemical cycling, in situ studies under real operating conditions were performed. Measurements of initial powders in capillaries and in situ experiments during the first galvanostatic cycle were carried out by high resolution powder diffraction using synchrotron radiation

Improving the rate capability of high voltage Lithium-ion battery cathode material LiNi0.5Mn1.5O4LiNi_{0.5}Mn_{1.5}O_{4} by ruthenium doping

The citric acid-assisted sol–gel method was used to produce the high-voltage cathodes LiNi0.5Mn1.5O4 and LiNi0.4Ru0.05Mn1.5O4 at 800 °C and 1000 °C final calcination temperatures. High resolution powder diffraction using synchrotron radiation, inductively coupled plasma – optical emission spectroscopy and scanning electron microscopy analyses were carried out to characterize the structure, chemical composition and morphology. X-ray absorption spectroscopy studies were conducted to confirm Ru doping inside the spinel as well as to compare the oxidation states of transition metals. The formation of an impurity LixNi1−xO in LiNi0.5Mn1.5O4 powders annealed at high temperatures (T ≥ 800 °C) can be suppressed by partial substitution of Ni2+ by Ru4+ ion. The LiNi0.4Ru0.05Mn1.5O4 powder synthesized at 1000 °C shows the highest performance regarding the rate capability and cycling stability. It has an initial capacity of ∼139 mAh g−1 and capacity retention of 84% after 300 cycles at C/2 charging–discharging rate between 3.5 and 5.0 V. The achievable discharge capacity at 20 C for a charging rate of C/2 is ∼136 mAh g−1 (∼98% of the capacity delivered at C/2). Since the electrode preparation plays a crucial role on parameters like the rate capability, the influence of the mass loading of active materials in the cathode mixture is discussed