Quantifying spectral thermal transport properties in framework of molecular dynamics simulations:a comprehensive review

Over the past few decades,significant progress has been made in micro-and nanoscale heat transfer.Numerous computational methods have been developed to quantitatively characterize the thermal transport in bulk materials and across the interfaces,which benefit the thermal management design in microelectronics and energy conversion in thermoelectrics largely.In this paper,the methods and studies on quantifying thermal transport properties using molecular dynamics simulations are comprehensively reviewed.Two classical methods based on molecular dynamics simulations are first introduced,i.e.,equilibrium molecular dynamics and nonequilibrium molecular dynamics,to calculate the thermal transport properties in bulk materials and across the interfaces.The spectroscopy methods are then reviewed,which are developed in the framework of equilibrium molecular dynamics(i.e.,time domain normal mode analysis,spectral energy density,Green-Kubo modal analysis) and methods proposed based on the nonequilibrium molecular dynamics(i.e.,time domain direct decompose method,frequency domain direct decompose method and spectral heat flux method).In the subsequent section,the calculations of spectral thermal conductivities using these computational methods in various systems are presented,including simple crystals,low-dimensional materials,complex materials and nanostructures.Following that,spectral thermal transport across the interfacial systems is discussed,which includes solid/solid interfaces,solid/solid interfaces with interfacial engineering and solid/liquid interfaces.Some fundamental challenges in molecular dynamics simulations,such as including quantum effects and quantifying the anharmonic contributions,are discussed as well.Finally,some open problems on spectroscopy thermal transport properties in the framework of molecular dynamics simulations are given in the summary.

Thermal transport in lithium-ion battery: A micro perspective for thermal management

In recent years, lithium ion (Li-ion) batteries have served as significant power sources in portable electronic devices and electric vehicles because of their high energy density and rate capability. There are growing concerns towards the safety of Li-ion batteries, in which thermal conductivities of anodes, cathodes, electrolytes and separator play key roles for determining the thermal energy transport in Li-ion battery. In this review, we summarize the state-of-the-art studies on the thermal conductivities of commonly used anodes, cathodes, electrolytes and separator in Li-ion batteries, including both theoretical and experimental reports. First, the thermal conductivities of anodes and cathodes are discussed, and the effects of delithiation degree and temperature of materials are also discussed. Then, we review the thermal conductivities of commonly used electrolytes, especially on solid electrolytes. Finally, the basic concept of interfacial thermal conductance and simulation methods are presented, as well as the interfacial thermal conductance between separator and cathodes. This perspective review would provide atomic perspective knowledge to understand thermal transport in Li-ion battery, which will be beneficial to the thermal management and temperature control in electrochemical energy storage devices.

Liquid metal welding enabling high loading binder/carbon-free layered oxide cathode toward high-performance liquid and solid-state battery

High loading cathode with high active material proportion is a practical demand but far below the desirable value to achieve high energy density lithium-ion batteries(LIBs).Normally,the Li^(+)/electron transport between active materials and electrolyte/c arbon,however,it is poor and areal resistance is extremely high for a high loading/thick cathode.In this manuscript,taking high-voltage lithium cobalt oxide LiCoO_(2)(LCO)as an example,we design a facile liquid metal welding method enabled by a low melting-point indium-tin oxide In_(2)O_(3)/SnO_(2)(ITO)during a thermal treatment process,the strongly adhesion active particles show robust mechanical property for the free-standing LCO cathode with a pellet architecture.We also demonstrate that the O_(2)atmosphere plays a critical role on the interfacial property,that is preventing the layered structure to rock-salt Co_(3)O_(4)as well as further enhancing the interfacial mechanical integration.As expected,the LCO-ITO free-standing cathode not only shows robust mechanical property with densely packed configuration but also provides a fast Li^(+)/electron pathway at the interface.Consequently,the LCO-ITO composite cathode exhibits excellent electrochemical cycling performance in both liquid and solid-state cells.For example,even at a high active material mass of 56 mg·cm^(-2),the LCO cathode still delivers a specific capacity of 151 mAh·g^(-1)and maintains132.5 mAh·g^(-1)(corresponding to 7.4 mAh·cm^(-2))after 80cycles.The LCO-ITO-O_(2)cathode is also applicable to a solidstate cell,which exhibits a high capacity of 100.4 mAh·g^(-1)after 200 cycles of long-term cycling.The excellent electrochemical of the LCO-ITO-O_(2)reveals the successful engineering mechanical architecture and interfacial carriers transport,which may be expected as an alternative approach to achieve high energy density LIBs.