Small coin cell batteries are predominantly used for testing lithium-ion batteries(LIBs)in academia because they require small amounts of material and are easy to assemble.However,insufficient attention is given to di...Small coin cell batteries are predominantly used for testing lithium-ion batteries(LIBs)in academia because they require small amounts of material and are easy to assemble.However,insufficient attention is given to difference in cell performance that arises from the differences in format between coin cells used by academic researchers and pouch or cylindrical cells which are used in industry.In this article,we compare coin cells and pouch cells of different size with exactly the same electrode materials,electrolyte,and electrochemical conditions.We show the battery impedance changes substantially depending on the cell format using techniques including Electrochemical Impedance Spectroscopy(EIS)and Galvanostatic Intermittent Titration Technique(GITT).Using full cell NCA-graphite LIBs,we demonstrate that this difference in impedance has important knock-on effects on the battery rate performance due to ohmic polarization and the battery life time due to Li metal plating on the anode.We hope this work will help researchers getting a better idea of how small coin cell formats impact the cell performance and help predicting improvements that can be achieved by implementing larger cell formats.展开更多
Over the past few decades,polydimethylsiloxane(PDMS)has become the material of choice for a variety of microsystem applications,including microfluidics,imprint lithography,and soft microrobotics.For most of these appl...Over the past few decades,polydimethylsiloxane(PDMS)has become the material of choice for a variety of microsystem applications,including microfluidics,imprint lithography,and soft microrobotics.For most of these applications,PDMS is processed by replication molding;however,new applications would greatly benefit from the ability to pattern PDMS films using lithography and etching.Metal hardmasks,in conjunction with reactive ion etching(RIE),have been reported as a method for patterning PDMS;however,this approach suffers from a high surface roughness because of metal redeposition and limited etch thickness due to poor etch selectivity.We found that a combination of LOR and SU8 photoresists enables the patterning of thick PDMS layers by RIE without redeposition problems.We demonstrate the ability to etch 1.5-μm pillars in PDMS with a selectivity of 3.4.Furthermore,we use this process to lithographically process flexible fluidic microactuators without any manual transfer or cutting step.The actuator achieves a bidirectional rotation of 50°at a pressure of 200 kPa.This process provides a unique opportunity to scale down these actuators as well as other PDMS-based devices.展开更多
Despite the ever-increasing demand of nanofillers for thermal enhancement of polymer composites with higher thermal conductivity and irregular geometry,nanomaterials like carbon nanotubes(CNTs)have been constrained by...Despite the ever-increasing demand of nanofillers for thermal enhancement of polymer composites with higher thermal conductivity and irregular geometry,nanomaterials like carbon nanotubes(CNTs)have been constrained by the nonuniform dispersion and difficulty in constructing effective three-dimensional(3D)conduction network with low loading and desired isotropic or anisotropic(specific preferred heat conduction)performances.Herein,we illustrated the in-situ construction of CNT based 3D heat conduction networks with different directional performances.First,to in-situ construct an isotropic percolated conduction network,with spherical cores as support materials,we developed a confined-growth technique for CNT-core sea urchin(CNTSU)materials.With 21.0 wt.%CNTSU loading,the thermal conductivity of composites reached 1.43±0.13 W/(m·K).Secondly,with aligned hexagonal boron nitride(hBN)as an anisotropic support,we constructed CNT-hBN aligned networks by in-situ CNT growth,which improved the utilization efficiency of high density hBN and reduced the thermal interface resistance between matrix and fillers.With~8.5 wt.%loading,the composites possess thermal conductivity up to 0.86±0.14 W/(m·K),374%of that for neat matrix.Due to the uniformity of CNTs in hBN network,the synergistic thermal enhancement from one-dimensional(1D)+two-dimensional(2D)hybrid materials becomes more distinct.Based on the detailed experimental evidence,the importance of purposeful production of a uniformly interconnected heat conduction 3D network with desired directional performance can be observed,particularly compared with the traditional direct-mixing method.This study opens new possibilities for the preparation of high-power-density electronics packaging and interfacial materials when both directional thermal performance and complex composite geometry are simultaneously required.展开更多
基金funding from the ERC(Consolidator Grant MIGHTY,866005)the Innovate UK(UKRI:104174)Faraday Institution-Future CAT(FIRG017)and Degradation(FIRG001)
文摘Small coin cell batteries are predominantly used for testing lithium-ion batteries(LIBs)in academia because they require small amounts of material and are easy to assemble.However,insufficient attention is given to difference in cell performance that arises from the differences in format between coin cells used by academic researchers and pouch or cylindrical cells which are used in industry.In this article,we compare coin cells and pouch cells of different size with exactly the same electrode materials,electrolyte,and electrochemical conditions.We show the battery impedance changes substantially depending on the cell format using techniques including Electrochemical Impedance Spectroscopy(EIS)and Galvanostatic Intermittent Titration Technique(GITT).Using full cell NCA-graphite LIBs,we demonstrate that this difference in impedance has important knock-on effects on the battery rate performance due to ohmic polarization and the battery life time due to Li metal plating on the anode.We hope this work will help researchers getting a better idea of how small coin cell formats impact the cell performance and help predicting improvements that can be achieved by implementing larger cell formats.
基金BG is a Doctoral Fellow of the Research Foundation—Flanders(F.W.O.),Belgium.MDV acknowledges support from the ERC starting grant HIENA(no.337739).
文摘Over the past few decades,polydimethylsiloxane(PDMS)has become the material of choice for a variety of microsystem applications,including microfluidics,imprint lithography,and soft microrobotics.For most of these applications,PDMS is processed by replication molding;however,new applications would greatly benefit from the ability to pattern PDMS films using lithography and etching.Metal hardmasks,in conjunction with reactive ion etching(RIE),have been reported as a method for patterning PDMS;however,this approach suffers from a high surface roughness because of metal redeposition and limited etch thickness due to poor etch selectivity.We found that a combination of LOR and SU8 photoresists enables the patterning of thick PDMS layers by RIE without redeposition problems.We demonstrate the ability to etch 1.5-μm pillars in PDMS with a selectivity of 3.4.Furthermore,we use this process to lithographically process flexible fluidic microactuators without any manual transfer or cutting step.The actuator achieves a bidirectional rotation of 50°at a pressure of 200 kPa.This process provides a unique opportunity to scale down these actuators as well as other PDMS-based devices.
基金supported by the National Key R&D Program of China(Nos.2018YFA0208402 and 2020YFA0714700)the National Natural Science Foundation of China(Nos.52172060,51820105002,11634014,and 51372269),Magna International,and EPSRC project“Advanced Nanotube Application and Manufacturing(ANAM)Initiative”(No.EP/M015211/1).
文摘Despite the ever-increasing demand of nanofillers for thermal enhancement of polymer composites with higher thermal conductivity and irregular geometry,nanomaterials like carbon nanotubes(CNTs)have been constrained by the nonuniform dispersion and difficulty in constructing effective three-dimensional(3D)conduction network with low loading and desired isotropic or anisotropic(specific preferred heat conduction)performances.Herein,we illustrated the in-situ construction of CNT based 3D heat conduction networks with different directional performances.First,to in-situ construct an isotropic percolated conduction network,with spherical cores as support materials,we developed a confined-growth technique for CNT-core sea urchin(CNTSU)materials.With 21.0 wt.%CNTSU loading,the thermal conductivity of composites reached 1.43±0.13 W/(m·K).Secondly,with aligned hexagonal boron nitride(hBN)as an anisotropic support,we constructed CNT-hBN aligned networks by in-situ CNT growth,which improved the utilization efficiency of high density hBN and reduced the thermal interface resistance between matrix and fillers.With~8.5 wt.%loading,the composites possess thermal conductivity up to 0.86±0.14 W/(m·K),374%of that for neat matrix.Due to the uniformity of CNTs in hBN network,the synergistic thermal enhancement from one-dimensional(1D)+two-dimensional(2D)hybrid materials becomes more distinct.Based on the detailed experimental evidence,the importance of purposeful production of a uniformly interconnected heat conduction 3D network with desired directional performance can be observed,particularly compared with the traditional direct-mixing method.This study opens new possibilities for the preparation of high-power-density electronics packaging and interfacial materials when both directional thermal performance and complex composite geometry are simultaneously required.
