| Layered LiNi0.5Mn0.5O2 owning quite a lot of advantages, such as environmentally friendly, low cost, good thermal stability, high theoretical capacity and so on, comparing to current commercial cathode material LiCoO2, excluding Co element which is relatively scarce and toxic, is a promising cathode material in lithium ion battery. It attracts widespread attention since T Ohzuku research group reported it in 2001. However, some Li/Ni ration in LiNi0.5Mn0.5O2 lattice structure plays a disaster effect on its electrochemical performance. Meanwhile, LiNi0.5Mn0.5O2 presents the poor electro-conductivity, leading to an unsatisfied rate capacity, which is also a common problem in the cathode material of lithium ion battery. In this paper, some studies are focus on these weak points.Some lattice structure nuances are caused by the different synthesized methods. Even a little nuance in the lattice structure of LiNi0.5Mn0.5O2 can lead to different electrochemical performance.The synthesized conditions and modifying the morphology are two main works in this paper:(1) The synthesized conditions will impose an effect on the forming of lattice structure, which will lead to different electrochemical performance. In this paper, we seek the most appropriate synthesized condition which will lead to the best electrochemical performance of LiNi0.5Mn0.5O2. The calacined temperature and the calcined atmosphere are two factors we investigated. The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscope (TEM), electrochemical impedance spectroscopy (EIS) measurements and charge-discharge tests. The results show that the Li/Ni disorder in the lattice structure plays a vital effect on its electrochemical performance. In the air atmosphere, the material which was synthesized at 800℃presents the best electrochemical performance, the first discharge capacity is 164mAh/g, after 50 charge and discharge cycles, it still can reach to 137 mAh·g-1 and presenting a 83.3% capacity retention rate. The Li/Ni disorder ratio in its lattice structure is 8.5%。Fixing the synthesized temperature and synthesizing LiNi0.5Mn0.5O2 in air and oxygen respectively. The first discharge capacity of the material synthesized under oxygen atmosphere is of 178 mAh·g-1, and after 50 charge and discharge cycles, the discharge capacity can still reach 165 mAh·g-1 presenting a 92.7% capacity retention rate. The Li/Ni disorder ratio in its lattice structure is 7.3%(2) The poor electro conductivity of cathode materials is a vital factor which undermines its rate capacity Two popular methods to improve the performance of LiNi05Mn05O2 as a cathode material for lithium ion batteries are to coat the particles with electronic conductivity agents such as carbon and to modify its micro-morphology. In this paper, LiNi0.5Mn0.5O2 with macroporous structure is obtained by so-gel method. The macroporous structure can provide more pores for increasing the electrode-electrolyte interface area which means better electrolyte penetration. The results show that LiNi0.5Mn0.5O2 with macroporous structure presents better electrochemical performance comparing to the nano-particle LiNi0.5Mn0.5O2 which was synthesized by solid state reaction method. Its first discharge capacity is 174 mAh·g-1,the Li/Ni disorder ratio in the lattice structure is 7.7%, while for the material synthesized under air atmosphere, the first discharge capacity at 0.1C rate is of 165 mAh·g-1 and the Li/Ni disorder ratio in the lattice structure is 9.8%,... |
