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Title: 4d Transition Metal Doped LiNi0.5Mn1.5O4 Cathodes for High Power Lithium Batteries
Keywords: Lithium batteries, Cathodes, transition metal, doping, conductivity,high rate performances
Issue Date: 30-Jun-2011
Source: WANG HAILONG (2011-06-30). 4d Transition Metal Doped LiNi0.5Mn1.5O4 Cathodes for High Power Lithium Batteries. ScholarBank@NUS Repository.
Abstract: <HTML>Cathode materials for lithium batteries with high power density are in great demand to power electric vehicles and hybrid electric vehicles. Hence, spinel-structured LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> cathode has received great attentions due to its high operation voltage of around 4.7 V. However, its poor high rate performances cannot satisfy with high power applications. Many strategies have been employed to improve its high rate performances. The aim of this research was to firstly design and synthesis LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> cathodes modified by 4d transition metals; and then thoroughly investigate their crystal structures, particle morphologies, charge transportation properties as well as electrochemical performances. Ru, Rh and Nb doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> spinels have been synthesized by solid state reactions. Ru doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> exhibited the best electrochemical performances and can deliver a capacity of 117 mAh g<sup>-1</sup> even at an extremely high discharge rate of 1470 mA g<sup>-1</sup> (10 C rate), and excellent cyclic performances at the 10 C charge/discharge rate for 500 cycles are achieved. The electronic conductivties of Ru doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> can be as high as 3.2 times of that of the LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub>. Delocalized 4d orbitals and large 4d orbitals? radius overlapping with O 2p orbitals have been proposed to be main mechanisms for enhanced electronic conductivity. Lithium diffusivity has also been improved through Ru doping. Ru doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> synthesized by solid state reactions exhibited much better electrochemical performances at high rates compared to pristine LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub>, which can be attributed to greatly enhanced charge transportation properties. Although electrochemical results show that Rh doping can improve the high rate performances of LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub>, it cannot compete with the effects of Ru doping. Synthesis of phase pure Nb doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> spinels are not successful. LiNbO<sub>3</sub> impurity with poor electronic conductivity presents in Nb doped samples. Suffering from LiNbO<sub>3</sub>, Nb doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> exhibit poor electrochemical performances even at low rates. Several methods attempting to obtain Ru doped LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> spinels with reduced particle size were investigated. Phase pure spinel-structured LiNi<sub>0.5-2z</sub>Ru<sub>z</sub>Mn<sub>1.5</sub>O<sub>4</sub> particles have been successfully synthesized by polymer assisted method (PA). With reduced particle size, the high rate electrochemical performances have been further improved compared to micron sized LiNi<sub>0.5-2z</sub>Ru<sub>z</sub>Mn<sub>1.5</sub>O<sub>4</sub>. The results presented here have demonstrated the ability of 4d transition metals doping to improve high-rate electrochemical performances of spinel-structured LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> cathode materials. We believe that this strategy may pave the way for the practical application of spinel-structured transition metal oxides as cathode materials for next generation of high power lithium-ion batteries.</HTML>
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