Preparation Of NiO/CNT And MnO₂/O/TiO₂ Multilayered Sandwich Nanotubes And Their Lithium Batteries Performance

The anode electrode material is one of the important factors that affect the performance of lithium-ion battery,and is also the hot spot of current research.Among many anode materials,transition metal oxides such as NiO,Mn O₂,TiO₂ and so on have attracted a great deal of attention due to their high specific capacity,abundant reserves,low cost and environmental friendliness.However,NiO,MnO₂ and so on have low conductivity and large volume effect that have a bad influence for cycle stability and the rate capability.Although TiO₂ has excellent cycling performance,its theoretical specific capacity is low,which makes the material has a low discharge capacity.In order to improve the specific capacity and cycle life of NiO,MnO₂,TiO₂ and other oxides,NiO composite with the CNT was studed in the paper which was prepared NiO/CNT hierarchical nanosheet composites with high-temperature calcination by chemical bath deposition;The MnO₂/C/TiO₂ multilayer sandwich nanotubes were designed to investigate the effect of TiO₂coating on the properties of MnO₂ nanotubes and to explored the influence of MnO₂ nanotubes wall thickness on the properties of composites.The main contents of this thesis are as follows:?1?The chemical bath deposition and high temperature calcination were used to synthesize the NiO nanosheet composite material grown on CNT.XRD and SEM results showed that the NiO nanosheets grew on the surface of the CNT uniformly and formed ordered and cross-linked hierarchical nanostructures.The cyclic voltammetry and constant current charge-discharge test samples found that NiO/CNT exhibits high specific capacity,good rate capability and cycle performance more stable compared to the pure material NiO.NiO/CNT compared to pure NiO redox have a stronger peaks and larger peak area in cyclic voltammetry curve indicating that the CNT composite enhanced NiO electrochemical activity.At the current density of 100 mA/g,the initial charge/discharge capacity of NiO/CNT was 1335/1990 mAh/g which was 46.7/44.5%higher than pure NiO.After 50 cycles,the NiO/CNT specific capacity was maintained at 1204/1204mAh/g whereas pure NiO was decayed to 107/107 mAh/g.In the rate performance test,the specific capacity of NiO/CNT was 3.7 times of pure NiO at 2.0 C rate.When the rate of recovery from 2.0C to 0.1 C,the average specific capacity of NiO/CNT 84%of the initial capacity,compared to pure NiO 62%the rate performance has greatly improved.?2?A hydrothermal method was used MnO₂ nanotube,then the use of dopamine polymerization carbonized carbon coated Mn O₂ nanotubes obtained MnO₂/C nanotubes,at last TIP reuse hydrolysis reaction TiO₂ coated on MnO₂/C nanotube to obtain MnO₂/C/TiO₂ multilayer sandwich nanotubes.XRD and SEM revealed that TiO₂ and C were sequentially coated on MnO₂nanotubes,and the composite was in the form of multilayer sandwich nanotubes MnO₂/C/TiO₂multilayered sandwich nanotubes with MnO₂ wall thickness of 30,15,and 8 nm and C/TiO₂material completely dissolved with MnO₂ were obtained by dissolving the inner diameter of MnO₂,exploring the impact of MnO₂ wall thickness of the composite structure.After dissolving a part of MnO₂ nanotubes,the structure did not rupture and collapse,the nanotube diameter increased.After all dissolved MnO₂,the nanotube structure loses its strong support and obvious deformation and breakage occurs and only a part of the nanotube structure remains.?3?The MnO₂/C/TiO₂ multilayer sandwich nanotubes and MnO₂/C were used as the anode materials of lithium ion batteries to study the effect of TiO₂ coating on the performance of MnO₂/C nanotubes.MnO₂/C/TiO₂ with 30,15 and 8 nm MnO₂ wall thickness and C/TiO₂ with MnO₂completely dissolved were assembled into a battery to explore the effect of MnO₂ wall thickness on the properties of the composites.Cyclic voltammetry tests showed that after the coating of TiO₂,the oxidation/reduction peak MnO₂/C peak becomes smaller and the peak area is larger,indicating that TiO₂ coating enhances the electrochemical activity of MnO₂/C nanotubes material.The results of constant current charge-discharge test showed that the initial discharge capacity of MnO₂/C/TiO₂was 1777 mAh/g and the MnO₂/C is 1380 mAh/g at 100 mA/g current density and the coating of TiO₂ increases the specific capacity of the material.After 50 cycles,the specific capacity of MnO₂/C/TiO₂ was maintained at 444 mAh/g which was 72%of the 10th cycle and the MnO₂/C was at 263 mAh/g which was 58%of the 10th cycle and the coating of TiO₂ improves the stability of the material cycle.At high current 2.0 C and 5.0 C,the average discharge capacity of MnO₂/C/TiO₂ was 1.8 and 4.0 times higher than that of MnO₂/C respectively.The average discharge capacity of MnO₂/C/TiO₂ was 63.2%of the initial 0.1C and MnO₂/C was only 50%.TiO₂coating on the material improve the rate performance.The tests of Mn O₂/C/TiO₂ with 30,15 and8 nm MnO₂ wall thickness and C/TiO₂ with completely dissolved MnO₂ showed that with the decrease of MnO₂ wall thickness the redox peak area of MnO₂ in CV curve decreased continuously and corresponding the peak area increased TiO₂ gradually showed the dominant.The second discharge capacities of 30,15 and 8 nm MnO₂ wall thickness were 1032,1181 and 961 mAh/g respectively at the current density of 100 mA/g,but the discharge capacity of C/TiO₂ was only 483mAh/g,indicating MnO₂ increased the specific capacity of the material and of which the specific capacity of 15 nm MnO₂ wall thickness is the highest..After 50 cycles,the specific discharge capacities of various materials were 405,465,301 and 215 mAh/g respectively which were 39.2%,39.3%,42.9%and 45%of the second cycle respectively.Corresponding the MnO₂ wall thickness deseased,the stability become stronger.In summary,MnO₂ can improve the specific capacity of the composites but is not conducive to the stability of its cycling performance,of which the specific capacity of 15 nm MnO₂ wall thickness is the highest.