Molecular Dynamics Simulation Of Average Velocity Of Lithium Iron Across The End Of Modified Carbon Nanotube

Energy, as the foundation of economic development, is very important. The convenient and high efficient energy storage devices have become the key point and the main bottleneck of a product in the process of its innovation and development, and also in the new enrgy development. Amongst various energy and power batteries, rechargeable Li-ion batteries(LIB) are receiving more and more researches and applications. Electrode material, as the core component of the baterry, has a significant impact on the performance of the LIB.CNT(Carbon Nano Tube), with its unique structure, excellent electrical conductivity, strong mechanical strength and chemical stability, is the ideal material used to construct electrode for LIB. In consideration of that the morphology of CNT has a great influence on the performance of LIB, CNTs are often cut using physical and chemical methods, in order to change the geometry and surface structure. The cut ports will be add a large amount of functional groups on the places where the chemical bonds broken, such as hydrogen(-H), hydroxyl(-OH), amino(-NH2) and(-COOH) group. The topological structures and electronic cloud distribution of these functional groups will affect the lithium ion migration velocity. Using the molecular dynamics simulation method, the factors including the diameter of carbon nanotube, functional group type and its number on the port, have been chosen to study their effects on the mean axial velocity of lithium irons across the entrance of carbon nanotube VLi。The simulation were performed by building four types of armchair single-walled carbon nanotubes with each diameter respectively being12.20?[CNT(9, 9)], 14.92 ?[CNT(11, 11)], 17.63 ?[CNT(13, 13)], 20.34 ?[CNT(15, 15)] and the length being 39.35 ? and solvated into lithium chloride aqueous solution of 5.6mol/L(Li Cl). Firstly, the factors of the diameter of CNT, functional group type and its number on the port were investigated. The conclusions can be drawn as follows: VLi will rise gradually with the increase of CNT diameter due to lithium irons migration resistance decreasing; as the port of CNT is successively modified to-H,-OH,-NH2 and-COOH, the corresponding migration resistance is enhanced resulting in the dropping of VLi; When the number of a given non-hydrogen functional group on the port sequentially increases, VLi decreases in turn. The more influential the functional group, the greater the impact of functional group number changes on VLi.Then, choosing the CNTs modified by-H, the effects of temperature(278-378K) and electric field strength(0.2-1.2V/?) were calculated. VLi and lithium ion diffusion coefficient Di were analysised. The effects of temperature on VLi are small and exsit difference with diameter variation; In the smaller diameter of CNT, the velocity fluctuations are relatively large. However, this volatility will gradually become stable with the increase of the diameter; Although the temperature has little effect on VLi, The temperature increase favors the diffusion of lithium ions in the core of CNT; The electric field strength has a great influence on VLi and make VLi increase vastly with its strength increasing. Although the vaviation of Di is not linear but fluctuant, the overall trend is that Di increases rapidly with the increase of electric field intensity.The above-mentioned studies all used the one-factor-at-a-time strategy to study the influences. This strategy involves changing factor levels one at a time, while leaving the others unaltered. The one-factor-at-a-time approach requires fewer tests than the full-factorial approach, but only analyzes some aspects of the system. In this work, we use the Taguchi method to study the effect of control factors on VLi, which include electric strength, functional group type, the diameter of CNT and temperature. Based on the L16(45) orthogonal array table, the simulations are conducted. The order of influence of control factors is electric filed intensity > functional group > diameter > temperature; VLi increases with the diameter of CNT and electric field strength increasing; VLi decreases with successively modifying the functional group-H,-OH,-NH2 and-COOH at the end of carbon nanotube. With the increasing of temperature, VLi firstly increases then decreases. However, the overall volatility skew is little pieces.In a word, the influence of the fields, the diameter of CNT and especially port functional groups on VLi has been investigated through the molecular dynamics simulation method. The results of the study not only have a certain theoretical significance on the development and manufacture of new type high efficient performance LIB, but also can indirectly play a role of cooperativity in the process of new energy developing and environment improvement.