高能量密度锂电池及其原位表征技术 | 本周物理学讲座

来源：中国物理学会期刊网

1高能量密度锂电池及其原位表征技术

报告人：张跃钢，清华大学物理系

时间：1月15日（周三）10:00

单位：中科院物理所

地点：M255

新型的高效能源转换／高密度能源存储是实现可再生能源的高效利用必不可少的关键技术。本报告以锂离子电池、锂硫电池、镁硫电池为例，展示了功能化纳米材料在提高电池能量密度及其循环稳定性中的关键作用。为了研究这些材料在电池充放电过程中的结构与化学变化，我们自主研发了原位液体电化学芯片， 实现了对电极材料及其界面在真实电化学反应过程中的实时电子显微镜观测和同步辐射X射线能谱测量。这有利于我们从微观角度理解物质和能量传输机制及其与电解液等环境因素的关联，为设计具有更高能量密度的二次电池提供了依据。

2Remarks on fission dynamics in medium and heavy nuclei

报告人：Artur Dobrowolski，波兰玛丽居里大学理论物理研究所

时间：1月15日（周三）14:00

单位：清华大学

地点：物理系理科楼B315

The first part of the talk will pertain to the time-dependent generator coordinate method with the Gaussian overlap approximation (TDGCM+GOA) formalism applied to describe the fission of 252Cf nucleus. An analysis of fission from the initial states laying in the energetic range from the ground state to the state located 4 MeV above the fission barrier is performed. The fission fragment mass distributions obtained for different parity, energy of levels, and types of mixed states are calculated and compared with experimental data. The impact of the total time of wave packet propagation on the final results is studied as well. The weak dependence of obtained mass yields on the initial conditions is shown.

Another part of the talk is devoted to the kinetic properties of the fissioning system. In particular, the fission fragment mass yields are obtained by using an approximate solution of the collective Hamiltonian defined on the space of the most relevant degrees of freedom on the way to fission, as nuclear elongation, mass asymmetry of left and right fragments and shape of the neck. The latter is given within the effective Fourier shape parametrization which describes well nuclear shapes in the 3D collective model. The predicted mass fragmentations for isotopic chains of Pt to Rn even-even nuclei are compared with available experimental data. Their main characteristics are well reproduced when the neck rapture probability depends on the neck shape. The potential energy surface entering the Hamiltonian is evaluated in the macroscopic-microscopic approach based on the LSD macroscopic energy and Yukawa-folded mean-field potential. A phenomenological inertia parameters are used to simulate the dynamics of the fission process in a simplistic way.

Finally, one will propose an approximate analytical expression allowing for a fast and quite accurate evaluation of transmission coefficients (TC) for emission of neutrons, protons and alpha particles from deformed nuclei that carry both a thermal and rotational excitation. This expression is based on the famous Weisskopf formula. For a proton or alpha particle the TC is given within the Hill-Wheeler WKB approach.

3Evolution of large-scale flow from turbulence in a two-dimensional superfluid

报告人：Kristian Peter Helmerson，Monash University

时间：1月16日（周四）10:00

单位：清华大学

地点：物理系理科楼C109

In two-dimensional turbulent flow the seemingly random swirling motion of a fluid can evolve towards persistent large-scale vortices. To explain such behavior, Lars Onsager proposed a statistical hydrodynamic model based on quantized vortices, in which the persistent large-scale vortices correspond to negative temperature states. We have confirmed Onsager’s model in an experiment on a superfluid gas of atoms. By dragging grid barriers, formed by an array of laser beams, through an oblate atomic gas Bose-Einstein condensate we generate non-equilibrium distributions of vortices. We subsequently use velocity-selective Bragg scattering and absorption imaging to identify the sign of the circulation and location of the vortices in order to determine the vortex distributions and resultant flow fields. We observe, in the subsequent evolution of the superfluid, signatures of an inverse energy cascade driven by the evaporative heating of vortices, leading to steady-state configurations of clustered vortices characterized by negative absolute temperatures. Our results open a pathway for quantitative studies of emergent structures in interacting quantum systems driven out of equilibrium.

4水在界面的结构、动力学和浸润性

报告人：朱重钦，宾夕法尼亚大学化学系&地球与环境科学系

时间：1月16日（周四）14:00

单位：中国科学院物理研究所

地点：M楼236会议室

水无处不在，而水与固体的界面在很多领域多起到重要的作用。当前，水与界面的相互作用通常停留在如界面水滴接触角的宏观描述上，分子尺度上的理解并不多见。我们一直关注界面水分子特性并开展了一系列研究。这个报告中，我将重点关注在分子尺度上水如何参与调控界面物理功能：（1）研究了晶格参数对水在界面浸润性的影响，提出了分子尺度浸润的概念。基于蛋白质结构，用宏观的接触角表征了所有分子氨基酸的亲疏水性。（2）理论预测了非受限条件下，二维冰在固体表面的形成，其中一个预测的相近期被北大江颖教授研究组在实验上独立观察到；进一步与实验合作，我们给出了表面上二维冰生长的分子机制以及二维冰存在对于宏观冰的生长模式影响。

5Fermionic quantum criticality in fermion-bag inspired Hamiltonianlattice field theories

报告人：Emilie Huffman，Perimeter Institute

时间：1月17日（周五）10:30

单位：中科院物理所

地点：M830

Motivated by the fermion bag approach--a quantum Monte Carlo approach that takes advantage of grouped local degrees of freedom--we construct a new class of Hamiltonian lattice field theories that can help us study fermionic quantum critical points. We construct the partition function of a lattice Hamiltonian in $2+1$ dimensions in discrete time, with a temporal lattice spacing $\varepsilon$. When $\varepsilon \rightarrow 0$, we obtain the partition function of the original lattice Hamiltonian. But when $\varepsilon = 1$, we obtain a new type of space-time lattice field theory which treats space and time differently, but still lacks fermion doubling in the time dimension, in contrast to Lagrangian lattice field theories. Here we show that both continuous-time and discrete-time lattice field theories derived from the $t$-$V$ model have a fermionic quantum critical point with critical exponents that match within errors. The fermion bag algorithms run relatively faster on the discrete-time model and allow us to compute quantities even on $100^3$ lattices near the quantum critical point. We then discuss how this class of fermion-bag amenable Hamiltonian lattice field theories also include simple $Z_2$ gauge theories coupled to fermions, and explore one such theory in $1+1$ dimensions with a coupling $h$. We demonstrate how even in such a simple theory nontrivial behavior arises, from the emergence of the Gauss law at low temperature to a nontrivial mass scaling.

6Mg3Sb2 Based Thermoelectric Materials

报告人：G. Jeffrey Snyder，Materials Science and Engineering, Northwestern University

时间：1月17日（周五）9:30

单位：中国科学院物理研究所

地点：M楼236会议室

Bi2Te3 alloys are the most widely used thermoelectric, because they have had the highest efficiency in the 250-500K temperature range relevant for cooling and low-grade waste-heat recovery. The new Mg3Sb2 based Zintl thermoelectric materials have achieved remarkable zT > 1 performance at high temperatures that has lead to many new discoveries in several laboratories worldwide. Recently, through the use of alloying, band structure engineering and grain boundary engineering we have shown that n-type Mg3Sb0.6Bi1.4, with a thermoelectric figure-of-merit zT of 1.0-1.2 at 400-500K, finally surpasses n-type Bi2Te3.

In this talk I will review the lengthy, step-wise achievements in materials processing and physical understanding that lead to this breakthrough. From the realization that chemical phase equilibria is a dominant factor determining dopability we explain the unexpected discovery of n-type  Mg3Sb2 based Zintl thermoelectric materials and show that the principles of Phase Boundary Mapping can be applied to most other thermoelectric systems to optimize and control doping, explaining and predicting how processing affects thermoelectric properties. Despite the simple crystal structure, the peculiar bonding of Mg leads to the high valley degeneracy in the conduction band as well as soft phonon modes that both lead to its exceptional thermoelectric performance. With this careful understanding of the electronic structure, the band structure can be engineered to maximize performance in the low temperature region.

更多报告信息：中国物理学会期刊网学术讲座列表

▼

往期精彩回顾

▼

1.2019年，十大科学发现

2.数学符号与数学公式的规范表达

3.光子真是简单的无质量粒子吗？——光子概念再剖析

4.中子散射在磁性材料研究中的应用

5.牛顿的苹果 真的？假的？

6.基于第二代高温超导带材的磁体研究进展与挑战（上）

7.我国天文学家利用LAMOST发现迄今最大的恒星级黑洞

8.钱学森、郭永怀、钱伟长…...哥廷根力学学派在中国的继承与发展

9.量子关联呈现出一种新的形态

10.宇宙中元素的起源