本文選題：鋰離子電池 + Si��； 參考：《哈爾濱工業(yè)大學(xué)》2014年博士論文

【摘要】：由于Si對Li有著很強的存儲能力，近些年來人們?yōu)榱嗽O(shè)計出對Li離子儲存能力更強、使用壽命更長的新一代Li離子電池，將Si以及Si的各種納米結(jié)構(gòu)視為新一代鋰離子電池中最熱門的電極材料。但Li在進入Si后，會導(dǎo)致Si產(chǎn)生將近400%的大變形，如此強烈的大變形將使Si極鋰離子電池的壽命大大降低。伴隨著變形的產(chǎn)生，Si中必然會產(chǎn)生各種缺陷用來釋放變形所造成的應(yīng)力，位錯是其中最重要的一類缺陷。因此研究Si中位錯與Li的相互作用就顯得非常必要，這方面的研究能幫助我們深入理解Li在含位錯Si體系中的動力學(xué)特性，并能幫助人們解決大變形帶來的問題，早日設(shè)計出性能優(yōu)異的Si極Li離子電池。本文使用耦合了第一性原理（DFT）以及分子動力學(xué)(MD)的QM/MM多尺度計算方法模擬Li在含位錯Si中的穩(wěn)定構(gòu)型以及動力學(xué)特性，這將對日后解決Si電極大變形問題有著重要的理論參考價值。 首先本文使用多尺度方法模擬了Li原子在Bulk Si中的穩(wěn)定構(gòu)型以及擴散運動過程。Li原子在Bulk Si中的最穩(wěn)定位置處于四面體晶格的中心(Td)。它的擴散路徑是周期性鋸齒形（zig-zag）路徑，過渡態(tài)位置位于四面體晶格的底面六邊形原子環(huán)中心處。這一結(jié)果與已存在的第一性原理研究結(jié)果相吻合。并且在這部分內(nèi)容中還計算了Li原子在Bulk Si中的結(jié)合能以及擴散勢壘，并將這一結(jié)果和完全第一性原理(DFT)計算結(jié)果對比，證明了本文中所使用的這種多尺度方法無論是在能量數(shù)值計算精度上還是能量計算收斂性上都比較讓人滿意。 接著模擬了Si中Li原子與glide型60°位錯的相互作用。通過模擬發(fā)現(xiàn)，，Li原子在glide型60°位錯內(nèi)部的穩(wěn)定位置處于每兩個位錯芯重構(gòu)時形成的Si-Si原子對所夾的開闊區(qū)域的中心處。通過這種每兩個Si-Si原子對之間的開口，Li原子可以以較小的勢壘由位錯芯周邊擴散進入位錯芯內(nèi)部。Li原子在位錯芯內(nèi)部擴散時，過渡態(tài)在沿著位錯線上的兩種七邊形原子環(huán)與一個Si-Si原子對構(gòu)成的區(qū)域內(nèi)，另外存在兩種局部過渡態(tài)位置位于兩種七邊形原子環(huán)的中心。通過計算發(fā)現(xiàn)Si中g(shù)lide型60°位錯對于Li原子的擴散具有加速的作用，這與已存在的研究中提到的位錯對于粒子擴散的加速現(xiàn)象（pipe diffusion）相一致。 其后模擬了shuffle型60°位錯對于Si中Li原子動力學(xué)特性的影響。包括：Li原子在位錯芯內(nèi)部以及周邊的穩(wěn)定構(gòu)型和在位錯芯內(nèi)部的擴散過程。通過模擬發(fā)現(xiàn)，Li原子在位錯芯中存在兩種穩(wěn)定位置，這兩種位置分別處于兩種由兩個七邊形原子環(huán)所圍成的區(qū)域中。當(dāng)Li原子在位錯芯內(nèi)部發(fā)生擴散時，過渡態(tài)位于七邊形原子環(huán)的中心。通過計算發(fā)現(xiàn)，Li原子在shuffle型60°位錯中構(gòu)型更加穩(wěn)定，并且擴散的加速效果也更加明顯。 最后還研究了30°部分位錯和堆垛層錯對于Li原子在Si中的動力學(xué)性質(zhì)的影響。模擬了Li原子在位錯芯內(nèi)部以及周圍的穩(wěn)定構(gòu)型、從周邊位置擴散進入位錯芯內(nèi)部以及在位錯芯里發(fā)生擴散的過程。在30°位錯中Li原子也存在兩種穩(wěn)定位置Oct-A和Oct-B，分別位于位錯芯在（111）面上投影的八邊形中心處，處在不同的（111）面中。Li原子在這兩種穩(wěn)定位置的結(jié)合能也都比在Bulk Si中要低。Li原子在30°部分位錯中的擴散路徑有兩條，分別是以兩種不同的穩(wěn)定位置為起點，且擴散路徑互不干擾。通過計算發(fā)現(xiàn)，與兩種60°位錯不同，30°部分位錯對于Li的擴散有明顯的阻礙作用。通過對堆垛層錯與Li原子相互作用的模擬，同樣發(fā)現(xiàn)了堆垛層錯也對Li原子的擴散有阻礙作用。在這一部分的末尾還討論和總結(jié)了Li原子在兩種60°位錯、30°位錯以及堆垛層錯中的穩(wěn)定位置和過渡態(tài)位置的規(guī)律。
[Abstract]:Since Si has a strong storage capacity for Li, in recent years, in order to design a new generation of Li ion batteries with more Li ion storage capacity and longer service life, Si and the various nanostructures of Si are considered as the most popular electrode materials in the new generation of lithium ion batteries. But Li will lead to the production of nearly 400% of Si after entering Si. Shape, such strong large deformation will greatly reduce the life of Si polar lithium ion battery. With the formation of deformation, various defects will be produced in Si to release the stress caused by deformation. Dislocation is one of the most important defects. Therefore, it is necessary to study the interaction between dislocation and Li in Si, and this research can help. It is helpful to understand the dynamic characteristics of Li in the dislocated Si system, and help people to solve the problems caused by the large deformation, and to design a Si polar Li ion battery with excellent performance at an early date. This paper uses the QM/MM multiscale calculation method coupled with the first principle (DFT) and molecular dynamics (MD) to simulate the stable configuration of Li in the dislocation containing Si. And dynamic characteristics, which will have important theoretical reference value for solving the problem of large deformation of Si electrode in the future.
First, we use the multiscale method to simulate the stable configuration of Li atoms in the Bulk Si and the diffusion motion process. The most stable position of.Li atoms in Bulk Si is in the center of the tetrahedral lattice (Td). Its diffusion path is a periodic serrated (zig-zag) path, and the transition state is located in the hexagonal hexagonal atomic ring of the tetrahedral lattice. The results coincide with the results of the existing first principles. And in this part, the binding energy and the diffusion barrier of Li atoms in the Bulk Si are calculated, and the results are compared with the results of the complete first principle (DFT) calculation, which proves that the multiscale method used in this article is in the energy. The accuracy of numerical calculation is more satisfactory than the convergence of energy calculation.
The interaction between Li atom and glide type 60 degree dislocation in Si is then simulated. Through simulation, it is found that the stable position of the Li atom in the glide type 60 degree dislocation is at the center of the open region of the Si-Si atom formed by each of the two dislocation cores. By this opening, the Li atom can be smaller by each of the two Si-Si original pairs. When the potential barrier diffuses from the periphery of the dislocation core into the internal diffusion of the.Li atom in the dislocation core, the transition state is in the region composed of two kinds of seven - sided atomic rings along the dislocation line and a Si-Si atom, and the other two local transition states are located at the center of the two kinds of seven - sided atomic rings. By calculation, the glide in Si is found. The type 60 degree dislocation has an accelerated effect on the diffusion of Li atoms, which is in accordance with the accelerated phenomenon of particle diffusion (pipe diffusion) of the dislocations mentioned in the present study.
Subsequently, the effect of shuffle type 60 degree dislocation on the dynamic characteristics of Li atom in Si is simulated, including: the stable configuration of Li atoms in the dislocation core and the diffusion process in the dislocation core. Through simulation, there are two stable positions in the Li atom in the dislocation core, and the two positions are in the two form of two seven of the seven sides, respectively. In the region enclosed by the subring, the transition state is located at the center of the seven sided atomic ring when the Li atom is diffused in the dislocation core. It is found that the Li atom is more stable in the shuffle type 60 degree dislocation, and the acceleration effect of the diffusion is more obvious.
Finally, the effect of 30 degree partial dislocations and stacking faults on the dynamic properties of Li atoms in Si is also studied. The process of simulating the stable configuration of the Li atoms in the dislocation core and around the dislocation core and the process of diffusion in the dislocation core in the dislocation core and in the dislocation core are simulated. There are also two stable positions of O in the 30 degree dislocation. Ct-A and Oct-B are located at the eight side center of the dislocation core on (111) surface respectively. In different (111) surfaces, the binding energy of the.Li atom in these two stable positions is also more than two in the 30 degree partial dislocation of the.Li atom in the Bulk Si, respectively, with two different stable positions as the starting point and the diffusion path mutual. No interference. It is found that the partial dislocation of 30 degrees has obvious hindrance to the diffusion of Li through the calculation of two 60 degrees dislocations. Through the simulation of the interaction between stacking faults and Li atoms, the stacking fault also hinders the diffusion of Li atoms. At the end of this part, the Li atom is also discussed and summed up in two 60 degrees. The position of dislocation, 30 degree dislocation and stacking fault in the stable position and transition state.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TM912

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相關(guān)期刊論文 前1條

1 戴曦;唐紅輝;楊平;張傳福;;LiFePO_4正極材料的研究進展[J];材料導(dǎo)報;2005年08期

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