| Recently, because of the rapid development of electric vehicle and electrocommunications, the innovation of battery material with high performance and low cost has been brought to widespread attention. The Li-Ni-Co-Mn-O cathode materials, such as LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Co0.2Mn0.3O2, are considered to be one of the candidates to substitude the conventional LiCoO3 cathode, owing to their excellent electrochemical performance. The Li-Ni-Co-Mn-O cathode with high security and lower cost are widely used in various portable electronic devices, such as mobile phones, notebook computers, and digital cameras. In addition, this kind of material has the potential to develop in the field of electric vehicles(EV) and hybrid electric vehicles(HEV). In this paper, we chose the LiNi1/3Co1/3Mn1/3O2 cathode material as the focus of our research. Since LiNi1/3Co1/3Mn1/3O2 has the problems of a low-rate capacity, a low-electronic conductivity, and cation mixing, a variety of methods were used to overcome these shortbacks, such as the synthesis modification, ionic substitution and surface coating. Through these methods, the Li Ni1/3Co1/3Mn1/3O2 cathode materials with high capacity and excellent rate performance are prepared.The LiNi1/3Co1/3Mn1/3O2 cathode materials are synthesized by solid state reaction method, using the Nil/3Co1/3Mnl/3(OH)2 precursor and Li2CO3 as the raw material. The influence of the calcination temperatures, sinter time and Li/(Ni+Co+Mn) mole ratio on the structure and electrochemical performances of Li Ni1/3Co1/3Mn1/3O2 are studied and the optimal conditions are characterized. The results of XRD show that, on the condition of 980 oC, 12 h, 1.1:1 Li/(Ni+Co+Mn), the prepared materials is well-crystallized. When the calcination temperature or the sinter time is too low, the crystallinity of materials will decrease; when the calcination temperature or the sinter time is too high, the degree of cation mixing will increase. The proper Li/(Ni+Co+Mn) mole ratio can make up the lost of Li in the process of calcination. The electrochemical performances of materials prepared on the optimal conditions are studied by using cell testing. The results show that, the initial discharge capacity at 0.2C of the material is 143.5mAh/g, the capacity retention of 30 cycles is 92%, and a good rate performance is achieved.A series of Eu-doped LiNi1/3Co1/3-xMn1/3EuxO2 cathode materials are synthesized by a solid state reaction route, and the effects of Eu substitution on the electrochemical properties of the cathode are investigated in detail. The results of XRD show that, the Eu substitution can improve the crystallinity of materials and cation mixing of the layered structure. When x=0.5%, the degree of cation mixing is the lowest of the prepared sample. With the increase of substitution ratio, the impurity Eu2O3 will exist. The analyzed results of electrochemical properties tests demonstate that the optimal substitution ratio is 0.5%, the initial discharge capacity is 156.3mAh/g at 0.2C, the capacity retention of 50 cycles is 91%, and a better rate performance is achieved.The LiNi1/3Co1/3Mn1/3O2 cathode materials are modified by coating with Ag and Carbon nanotubes respectively and the effects of Ag and CNTs coating on the electrochemical properties of the cathode are studied. The dispersed Ag particles can promote the efficiency of electron transfer across the LiNi1/3Co1/3Mn1/3O2. The optimal Ag coating amount is 0.5%, the initial discharge capacity is 137.87mAh/g at 1C, the capacity retention of 30 cycles is 94%. The interconnected CNTs could serve as long range pathways around LiNi1/3Co1/3Mn1/3O2 particles. The optimal CNTs coating amount is 1%, the initial discharge capacity is 136.99mAh/g at 1C, the capacity retention of 30 cycles is 95%.In order to make full use of the synergistic effect of Ag and CNTs, a hybrid CNTs/Ag conductive network is introduced into the LiNi1/3Co1/3Mn1/3O2 cathode and the actual role of CNTs/Ag hybrids are studied. The as-obtained LiNi1/3Co1/3Mn1/3O2-CNT/Ag electrode exhibits excellent rate capability(120.6mAh/g at 5C) and cycle performance(134.2mAh/g at 1C with a capacity retention of 94.4% over 100 cycles). |
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