Non-equilibrium heat flow over patterned interfaces (Ref. 4659)

当电池充电时，离子进入电极的过程会产生热量。这一区域在系统中形成了一个导热系数变化很大的边界。边界上的热流动是一个非常复杂的问题，既涉及宏观尺度的现象，也涉及微观尺度的现象，以及大量的非平衡物理。在实验上产生完美或无缺陷的界面的困难进一步激怒了这一点。在过去的十年里，第一原理Peierls-Boltzmann输运方法的发展使声子输运发生了革命性的变化，这种方法能够预测材料的热性质，而不需要可调整的参数[1]。然而，这些方法受到其规模和对高性能计算资源(超级计算机)的需求的高度限制。最近，赫普斯通博士展示了2D结构的界面可以被操纵来产生电流流动和掺杂[2]。早期的界面散射理论[3，4]和从头计算的结合表明，离子插入界面有望提供操纵热传输的独特方法。原则上，这种嵌入引入了所谓的响尾声，它强烈地散射声子，从而降低了导热系数。这反过来又提供了创造热开关以及通过防止热级联来提高电池性能的机会。在宏观和微观两个尺度上理解这一挑战的物理学是一个巨大而令人兴奋的理论问题。该项目可分为四个阶段：第一阶段，该项目最初的重点将是已知界面的导热系数。利用第一性原理理论和经验模型，对电导率进行了估算。通过直接比较插层界面和非界面的性质，旨在量化插层在改变导热系数中的作用，从而量化这些影响的程度。需要进行三个阶段的评估，第一个阶段是使用冻结声子技术计算声子能带结构，以及非谐力常数。在评估了这些术语之后，有必要考虑不同散射机制的作用，同时量化界面杂质的作用。最后，由此可以估算出导电性。第二阶段在第二阶段，需要一个大型有限差分热流模拟器，以考虑和模拟基于傅立叶-卡特内奥热定律的非均匀温度分布的影响。这将允许考虑非常复杂的几何图形，而不需要微观模拟。在这种有效的介质方法中，我们将能够精确地探索不同几何形状和界面上的热流是如何不均匀的，并研究在什么条件下通过界面的平衡传输原理成立。这种方法将允许我们对多个尺度(100 nm+)进行建模，并推动模型来检查其击穿以及如何增强这样的系统。阶段3在阶段1中讨论的方法依赖于单模弛豫时间方法的假设。有效地，该方法假定系统中的其他载流子仍然服从玻色爱因斯坦分布函数，并且只有散射声子模导致扰动或改变的分布函数。基于探索第二阶段所获得的信息，它旨在探索非平衡函数在界面上的作用，开发一种新的理论来模拟这一制度，建立在批量使用的第一原理工作的基础上，为这种非平衡系统开发一种新的方法。

When a battery charges, the process of ions moving into the electrode results in heat generation. This region creates a boundary in the system where the thermal conductivity varies dramatically. Heat flow over boundaries is a very complicated problem, with both macroscale and microscale phenomena being involved as well as substantial non-equilibrium physics. This is further exasperated by the difficulty experimentally in producing perfect or defect free interfaces. In the past decade, phonon transport has been revolutionised by the development of first principles Peierls-Boltzmann transport approaches, capable of predicting the thermal properties of materials without the need for adjustable parameters [1]. However, these approaches are highly limited by their scale and the need for high powered computing resources (supercomputers). Recently, Dr. Hepplestone has shown that interfaces for 2D structures can be manipulated to create current flow and doping [2]. The combination of early interface scattering theory [3,4] and ab initio calculations has shown that the intercalation of ions into interfaces promise to provide unique ways to manipulate thermal transport. The intercalation introduces, in principle, what are known as rattlers, which scatter phonons strongly, thus reducing the thermal conductivity. This in turn presents the opportunity to create thermal switches as well as enhance battery performance by preventing thermal cascades. Understanding the physics of this challenge at both the macroscale and the microscale is a vast and exciting theoretical problem. This project can be broken down in four phases:Phase 1 The initial focus of the project would be on thermal conductivity of known interfaces. Using first principles theory and empirical models, the conductivity will be evaluated. By directly comparing the properties of a intercalated and non-interfaces, it is intended to quantify the role of intercalation in changing the thermal conductivity, and thus quantify how much these effect it. Three stages of evaluation are necessary, the first is to calculate the phonon band structures, using the frozen phonon technique, as well as the anharmonic force constants. Having evaluated these terms, it is then necessary to consider the role of differing scattering mechanisms, whilst quantifying the role of interface impurities. Finally, from this, one can then evaluate the conductivity. Phase 2 In phase two a large scale finite difference heat flow simulator will be needed, to consider and model the effects of non uniform temperature distributions based upon Fourier-Cattaneo heat law. This will allow very complicated geometries to be considered, without the need for microscopic simulation. In this effective medium approach, we will be able to explore precisely how non-uniform the heat flow is across various geometries and interfaces and examine under what conditions the principle of an equilibrium transport across an interface holds. This approach will allow us to model multiple scales (100 nm+) and push the model to examine its breakdown and how such a system can be enhanced.Phase 3The approach discussed in Phase 1 relies on the assumption of the single mode relaxation time method. Effectively, this approach assumes that other carriers in the system still obey the Bose Einstein Distribution function, and only the scattering phonon mode results in a disturbed or changed distribution function. Based upon the information gained by exploring phase 2, it is intended to explore the role of non-equilibrium functions across the interface, developing a new theory to model this regime, building upon the first principles works used in bulk to develop a new approach for such non-equilibrium systems.