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

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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.