低维石墨炔体系的储能与热导性能研究
发布时间：2018-08-28 20:39
【摘要】：低维材料，特别是低维碳纳米材料，一直是材料学的研究热点。自从2004年实验上成功制备以来，石墨烯（Graphene）这种由碳原子以sp2杂化轨道组成的六角型蜂巢状二维结构，凭借其独特的性能在碳材料领域备受关注。继石墨烯之后，实验上分别制备出石墨炔（Graphdiyne）等新的碳同素异形体。与石墨烯不同，石墨炔是以sp和sp2杂化形成的二维结构，拥有更丰富的碳化学键，具有与很多石墨烯截然不同的性质，甚至在某些性能上有望超越石墨烯，比如其有天然的孔结构、热导率较低等特性。在传统能源短缺、新能源亟待开发的大背景下，石墨炔体系具有良好的应用前景。因此本文主要针对其孔结构和低热导特性，研究了石墨炔体系在锂电池材料和热电材料等能源领域的性能。取得的成果如下： （1）石墨炔是以sp2和sp两种杂化态形成的二维碳同素异形体。通过改变碳六元环之间炔键的数目，可以改变碳链的长度，进而得到不同代数的石墨炔。通过基于密度泛函理论的第一性原理计算方法，我们研究了石墨炔体系的储锂性能，结果表明石墨炔体系是一种理想的储锂材料，锂原子通过向衬底转移电荷而带正电，彼此之间的库仑排斥作用避免了锂原子的团簇化。通过比较石墨一炔到石墨五炔的储锂性能，发现对于石墨炔体系，并不是炔键数目越多，原子密度越低，结构对应的储锂性能就会越好，还需考虑炔键的增多对结构稳定性的影响。在保证石墨炔类结构稳定的前提下，石墨二炔和石墨五炔可以达到LiC3的最大储锂量，对应Li的平均吸附能分别为-2.00和-2.05eV。 （2）通过将石墨炔纳米带沿固定轴卷曲可以得到石墨炔纳米管（GNT）这种一维材料，，并且改变碳六元环之间炔键的数目，可得到不同代数的石墨炔纳米管，记作GNT-n。利用非平衡分子动力学模拟，我们对GNT体系的热导性能进行了研究，讨论了代数n、直径d和长度L等变量对体系热导率的影响。计算结果表明随代数n增加，热导率降低并遵循~n0.57关系。直径变化对体系热导率的影响较弱，当d5nm时遵循~d0.03关系。随GNT体系长度的增加，结构热导率也增加并符合~L关系，且关系曲线存在拐点，拐点两边对应不同的指数。通过推算我们得到长度为2.6μm的GNT-n（n=1～5）的热导率分别为92.4，43.6，30.4，27.4和23.0W/(m.K)，与相同长度的CNT（λ=2820.6W/(m.K)）相比热导率小两个数量级，在二者拥有相同或相近的电导率情况下，更低的热导率使得GNT相对于CNT拥有更高的热电品质因子，有望在将来成为优异的热电材料。
[Abstract]:Low-dimensional materials, especially low-dimensional carbon nanomaterials, have been the focus of materials research. Since its successful preparation in 2004, graphene (Graphene), a hexagonal honeycomb structure composed of carbon atoms and sp2 hybrid orbitals, has attracted much attention in the field of carbon materials due to its unique properties. After graphene, new carbon isomorphs such as graphite acetylene (Graphdiyne) were prepared. Unlike graphene, graphite acetylene is a two-dimensional structure formed by sp and sp2 hybrids. It has a richer carbon chemical bond and has distinct properties from many graphene, and is expected to surpass graphene in some properties. For example, it has natural pore structure, low thermal conductivity and other characteristics. Under the background of the shortage of traditional energy and the urgent development of new energy, graphite acetylene system has a good application prospect. Therefore, based on the pore structure and low thermal conductivity, the performance of graphite system in lithium battery materials and thermoelectric materials is studied in this paper. The results obtained are as follows: (1) Graphite acetylene is a two-dimensional carbon isomorphism formed in two hybrid states of sp2 and sp. The length of carbon chain can be changed by changing the number of acetylene bonds between six carbon rings, and then different algebraic graphite acetylene can be obtained. Based on the density functional theory (DFT), we have studied the lithium storage properties of graphite acetylene system. The results show that graphite acetylene system is an ideal lithium storage material. Lithium atoms are positively charged by transfer of charge to the substrate. The Coulomb repulsion between each other avoids the cluster of lithium atoms. By comparing the lithium-storage properties of graphite-acetylene to graphite-pentylene, it is found that the higher the number of acetylene bonds, the lower the atomic density, and the better the lithium-storage performance of the corresponding structure. It is also necessary to consider the influence of the increase of acetylene bond on the stability of the structure. On the premise of ensuring the stability of graphite acetylene structure, graphite diacetylene and graphite pentylene can reach the maximum lithium storage capacity of LiC3. The average adsorption energies corresponding to Li are -2.00 and -2.05 EV respectively. (2) by curling graphene nanobelts along a fixed axis, one-dimensional materials such as (GNT) can be obtained, and the number of acetylene bonds between carbon six-member rings can be changed. Graphite nanotubes of different algebras can be obtained, denoted as GNT-n. The thermal conductivity of GNT system is studied by using nonequilibrium molecular dynamics simulation. The effects of algebraic variables n, diameter d and length L on the thermal conductivity of the system are discussed. The results show that with the increase of algebra n, the thermal conductivity decreases and follows the n0.57 relation. The influence of diameter change on the thermal conductivity of the system is weak, and the relationship between the thermal conductivity and the thermal conductivity is observed when d5nm is observed. With the increase of the length of GNT system, the thermal conductivity of the structure also increases and accords with the L relation, and the curve has inflection point, and the inflection point corresponds to different exponents on both sides of the inflection point. The thermal conductivities of 2.6 渭 m long GNT-n (ng1 / 5) are 92. 4 渭 m, 43. 6 and 30. 440. 4 and 23.0W/ (m. K), respectively, which are two orders of magnitude smaller than that of CNT of the same length (位 2 820. 6 W / (m 路K). Under the condition of the same or similar electrical conductivity, the thermal conductivity of CNT (位 2 820. 6 W / (m. K) is lower than that of CNT (位 2 820. 6 W / (m 路K). Lower thermal conductivity makes GNT have a higher thermoelectric quality factor than CNT and is expected to be an excellent thermoelectric material in the future.
【学位授予单位】：华东交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;TQ127.11
本文编号：2210553
[Abstract]:Low-dimensional materials, especially low-dimensional carbon nanomaterials, have been the focus of materials research. Since its successful preparation in 2004, graphene (Graphene), a hexagonal honeycomb structure composed of carbon atoms and sp2 hybrid orbitals, has attracted much attention in the field of carbon materials due to its unique properties. After graphene, new carbon isomorphs such as graphite acetylene (Graphdiyne) were prepared. Unlike graphene, graphite acetylene is a two-dimensional structure formed by sp and sp2 hybrids. It has a richer carbon chemical bond and has distinct properties from many graphene, and is expected to surpass graphene in some properties. For example, it has natural pore structure, low thermal conductivity and other characteristics. Under the background of the shortage of traditional energy and the urgent development of new energy, graphite acetylene system has a good application prospect. Therefore, based on the pore structure and low thermal conductivity, the performance of graphite system in lithium battery materials and thermoelectric materials is studied in this paper. The results obtained are as follows: (1) Graphite acetylene is a two-dimensional carbon isomorphism formed in two hybrid states of sp2 and sp. The length of carbon chain can be changed by changing the number of acetylene bonds between six carbon rings, and then different algebraic graphite acetylene can be obtained. Based on the density functional theory (DFT), we have studied the lithium storage properties of graphite acetylene system. The results show that graphite acetylene system is an ideal lithium storage material. Lithium atoms are positively charged by transfer of charge to the substrate. The Coulomb repulsion between each other avoids the cluster of lithium atoms. By comparing the lithium-storage properties of graphite-acetylene to graphite-pentylene, it is found that the higher the number of acetylene bonds, the lower the atomic density, and the better the lithium-storage performance of the corresponding structure. It is also necessary to consider the influence of the increase of acetylene bond on the stability of the structure. On the premise of ensuring the stability of graphite acetylene structure, graphite diacetylene and graphite pentylene can reach the maximum lithium storage capacity of LiC3. The average adsorption energies corresponding to Li are -2.00 and -2.05 EV respectively. (2) by curling graphene nanobelts along a fixed axis, one-dimensional materials such as (GNT) can be obtained, and the number of acetylene bonds between carbon six-member rings can be changed. Graphite nanotubes of different algebras can be obtained, denoted as GNT-n. The thermal conductivity of GNT system is studied by using nonequilibrium molecular dynamics simulation. The effects of algebraic variables n, diameter d and length L on the thermal conductivity of the system are discussed. The results show that with the increase of algebra n, the thermal conductivity decreases and follows the n0.57 relation. The influence of diameter change on the thermal conductivity of the system is weak, and the relationship between the thermal conductivity and the thermal conductivity is observed when d5nm is observed. With the increase of the length of GNT system, the thermal conductivity of the structure also increases and accords with the L relation, and the curve has inflection point, and the inflection point corresponds to different exponents on both sides of the inflection point. The thermal conductivities of 2.6 渭 m long GNT-n (ng1 / 5) are 92. 4 渭 m, 43. 6 and 30. 440. 4 and 23.0W/ (m. K), respectively, which are two orders of magnitude smaller than that of CNT of the same length (位 2 820. 6 W / (m 路K). Under the condition of the same or similar electrical conductivity, the thermal conductivity of CNT (位 2 820. 6 W / (m. K) is lower than that of CNT (位 2 820. 6 W / (m 路K). Lower thermal conductivity makes GNT have a higher thermoelectric quality factor than CNT and is expected to be an excellent thermoelectric material in the future.
【学位授予单位】：华东交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;TQ127.11
【参考文献】
相关期刊论文 前1条
1 赵晗;周丽娜;魏东山;周新建;史浩飞;;石墨炔类结构储锂性能的第一性原理研究[J];高等学校化学学报;2014年08期
本文编号：2210553
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