Research On Transtion Metal Oxides/carbon Nanotube Double Nano-composite Anode Materials For Lithium-ion Battery

Lithium batteries have attracted much attention since 1990 s for its high operation voltage, high energy densities and environmental friendly. And it has been widely used in cellular phones, portable computers, digital camera, and so on. Graphite is the commonly used lithium ion anode material. It has the advantages such as abundant raw material and low cost. But the low capacity(theoretical capacity is 372 mAh/g), short cycle life and poor safety performance hinders its application in present electrical equipments, which put forward more advanced requests on energy density, safety and cycle life. Therefore, researchers have focused on developing novel anode materials with high capacity, low cost, good rate capacity, long cycle life and high safety.In recent years, transition metal oxides have attracted much attention because of the high specific capacity(500-1200 mAh/g). But the excessive volume change leads to electrode pulverization, collapse of the electrode and reversible capacity drops rapidly. In addition, its poor conductivity leads to the poor rate performance. Nowadays, some methods are put forward to overcome these problems: preparation nano-sized materials, coating or doping carbon materials to form composite materials. These methods are relatively complex, difficult to control, or the raw materials are expensive, so it is hard to scale up.In this paper, transition metal oxide/carbon nanotube composite materials have been synthesized by vacuum solution infiltration method. The synthesis process was optimized, and their electrochemical performances were studied. Results show that carbon nanotubes(CNTs), with high electrical conductivity and a tubular structure, can not only buffer the large volume change during the lithium insertion/extraction process, but also can reduce size of the particles, enhance the conductivity of the active materials. The main contents were summarized as follows:1. MnO/MWCNT composites are synthesized by a vacuum solution infiltration method. The s optimized calcination temperature and ratio is: 300 °C and 1:2. Results show that diameter of the MnO in the composites is 18 nm. Meanwhile, the MnO/MWCNT electrode shows an initial discharge specific capacity of 1455 mAh/g. The reversible capacity increases gradually until the fifth cycles, and reaches 1202 mAh/g after 100 cycles.2. MnO2/MWCNT composites are synthesized by a vacuum solution infiltration method. When calcined at 200 °C, the ratio of MWCNTs and MnO2 is 1:2, the electrochemical properties is the best. Results show that diameter of the MnO2 in the composites is 14.88 nm and disperses on the MWCNTs uniformly. The MnO2/MWCNT electrode delivers an initial discharge capacity of higher than 1700 mAh/g and it remains 922 mAh/g after 100 cycles at 0.1 C.3. CeO2/MWCNT composites were synthesized by vacuum solution infiltration method. The best electrochemical performance is obtained by calcined at 200 °C with the ratio of 1:1. Results show that the particle size of CeO2 in CeO2/MWCNT composites is 11 nm. The initial discharge capacity is 756 mAh/g and the reversible capacity remains 564mAh/g after 50 cycles at 0.1 C.4. NiFe2O4/MWCNT composites were synthesized by vacuum solution infiltration method. The best electrochemical performance is obtained by calcined at XX °C with the ratio of XX. Results show that the particle size of NiFe2O4 in NiFe2O4/MWCNT composites is XX nm. And the oxide particles disperse on the carbon nanotubes uniformly. The electrode shows an initial capacity of 1294 mAh/g at 0.1 C and maintains 1093 mAh/g after 50 cycles. At 2 C rate, the electrode still remains 900 mAh/g.