With the accelerating consumption of fossil fuel and the rapid grow th of the global population,energy storage and energy transformation have become an urgent topic in the modern society[1].Supercapacitors appear as potential candidates for energy storage system since they exhibit many desirable properties such as rapid charge/discharge rate,high power density and superior cyclic stability[2,3].Besides that,due to the rapid development of portable and wearable electronic industries in recent years,the demands for flexible storage devices have greatly increased[4-6].Therefore,the research needs of flexible supercapacitors devices have also been created[7].

According to the energy storage mechanisms,supercapacitors can be mainly categorized into two types: electric double-layer capacitors(EDLCs)and pseudocapacitors[8].EDLCs store energy through the electrostatic charge adsorbing at the interface between electrode and electrolyte,while pseudocapacitors store energy through fast faradaic redox reaction[9].Due to only electrostatic reaction concerned in the EDLCs,EDLCs usually exhibit excellent power density[10-12].On the other hand,pseudocapacitors usually exhibit higher energy density[6,13,14].

对于一个完善的国际建筑市场，工程索赔是一种正常的现象。但在我国，由于建设工程索赔尚处于起步阶段，合同双方忌讳索赔、索赔意识不强、索赔处理程序不清的现象普遍存在。随着市场经济的不断发展、法律的不断完善以及国际竞争的需要，建设工程施工中的索赔与反索赔问题，已经引起工程管理者的高度重视。

How to further increase energy density is a core issue of developing supercapacitors since the energy density of supercapacitors is generally less than 10 Wh/kg[1,15,16].Based on the equation of energy density(E)for supercapacitors:E=CV2/2[17,18],which indicates that the energy density can be improved by widening the potential window(V).One way to increase the potential window is using organic electrolyte,which can extend the operating voltage to 4 V(compared to 1 V for aqueous electrolyte).How ever,organic electrolyte usually suffers from lower conductivity,unsafety,and toxicity[19].Another choice to increase the potential window is constructing an asymmetric supercapacitors in aqueous system.Via making full use of different operating voltages of each electrode,the purpose of extending the potential window for the cell system can be achieved[20,21].Thus,selecting proper materials for both positive and negative electrodes is the key point of building a high performance asymmetric supercapacitors.For the positive electrode materials,among all the transition metal oxides,Mn O2 has the advantages of high theoretical specific capacitance(～1370 F/g),non-toxicity,low cost,and high performance in neutral aqueous electrolyte[15,22,23].As for the negative electrode materials,carbonaceous materials are commonly used due to their high specific area and moderate cost.Besides,owing to the mature technology and ultrahigh specific area,activated carbon is often used[19,20].

除了颅内出血，其他不良反应发生概率较低，包括全身出血、过敏反应和口舌血管性水肿等，其中口舌血管性水肿发生于患侧大脑对侧，症状轻微且是暂时性的，估计1.3%～5.1%接受阿替普酶溶栓治疗的患者会出现此反应，通常与使用血管紧张素转换酶抑制剂或大脑岛、额叶皮质梗死有关。早期暂时性神经损害与阿替普酶溶栓治疗引起的脑实质水肿及阿替普酶潜在的神经毒性有关［33，53］。

The SEM images of different depositing time using Mn(Ac)2 electrolyte are summarized in Fig.1.Different electrolytes were used in the depositing and the resulting samples are shown in Fig.S3(Supporting information).It is observed that as the electroplating time is increased,the morphology of Mn O2 is changed correspondingly.Initially,Mn O2 nanosheets grow perpendiculary on the carbonized fabrics(Fig.1b).When prolonging deposition time to 30 min,Mn O2 nanosheets self-assembled and formed a 3D honeycomb structure(Fig.1a).This stereoscopic structure allows electrolyte penetrating more efficiently,and thus enables the Mn O2 to react thoroughly.As we further increase the deposition time,the stereoscopic structure gradually vanished and turned into a flattened appearance instead(Fig.1c).The transmission electron microscopy(TEM)image further con firmed that Mn O2 honeycomb structure was originally formed by Mn O2 nanosheets with average 20 nm width growing on the carbonized fabrics(Fig.1d).

Considering the merits and the trend mentioned above,we carbonized silk fabrics and decorated with carbon nanotube on their surface,which were used as a flexible substrate(denoted as SC950),then further loaded with Mn O2 and activated carbon powders as the positive and the negative electrode,respectively.The honeycomb structured Mn O2 was grow n on the SC950 by a typical anodizing method.The SC950 was immersed into a mixed solution of 100 mmol/L of Mn(Ac)2 and 100 mmol/L of Na2SO4.Different electrolytes were comparatively used while Mn(Ac)2 was selected because its derived material exhibited better electrochemical behavior and performance as shown in Fig.S2(Supporting information).In Fig.S2a,high frequency ranges for all materials have small semicircle which suggests a low interfacial charge resistance.How ever,only the materials from Mn(Ac)2 and Mn SO4 have nearly vertical line in the low frequency range which represents ideal capacitive behavior.Fig.S2b-d show cyclic voltammetry(CV)curves of different materials at various scan rates.Both materials from Mn(Ac)2 and Mn SO4 remained rectangular shape at a scan rate of 100 m V/s while the material from Mn Cl2 did not,which consists with the previous electrochemical impedance spectroscopy(EIS)result shown in Fig.S2a.The specific capacitances of samples from Mn(Ac)2,Mn SO4,and Mn Cl2 calculating based on CV curves were 716.5,513.1 and 152.9 F/g at a scan rate of 2 m V/s.Though the sample from Mn Cl2 has the largest current response,the deviation of ideal capacitive behavior resulted in a non-rectangular shape(Fig.S2d).Both samples from Mn(Ac)2 and Mn SO4 show ideal capacitive behaviors in EIS and CV results,while the material from Mn(Ac)2 has a better specific capacitance owing to the material’s unique structure which allowing more Na2SO4 electrolyte penetrating through.For Mn(Ac)2 electrolyte,Mn O2 nanosheets were electroplated on the SC950 at a constant current of 0.42 m A for 20,30,and 60 min(samples denoted as SC950-EP20,SC950-EP30,and SC950-EP60),with platinum wire and Ag/AgCl electrode as the counter electrode and the reference electrode,respectively.The optimal electroplating time was 30 min in the present work,which presents a honeycomb structure under the scanning electron microscopy(SEM)image(Fig.1a).

In summary,w e fabricated an ideal positive electrode by simply adjusting the electroplating time of Mn O2 to achieve a unique honeycomb structure,which exhibits a high specific capacitance(1110.85 F/g at a current density of 1 A/g)and superior rate capability(77.44%capacity retention from 1 A/g to 10 A/g)in 1 mol/L Na2SO4 electrolyte.Thus,the optimal device assembled by this material as positive electrode and activated carbon as the negative electrode with an operation voltage of 1.8 V can deliver a maximum energy density of 43.84 Wh/kg and a maximum power density of 6.62 k W/kg.

X-ray photoelectron spectroscopy(XPS)measurement was conducted to investigate the surface chemical composition and element boding con figurations of the SC950-EP30.The XPS survey spectrum of Mn O2/carbonized fabrics is shown in Fig.2a.The XPS spectrum reveals the presence of C,O and Mn elements in the electrode.Fig.2b show s the Mn 2p core-level XPS spectrum.The Mn 2p 3/2 and Mn 2p 1/2 peak values are located at 642.0 eV and 653.8 eV,respectively,with a separated spin-energy of 11.8 eV which agrees well with those reported values[15,23],demonstrating 4+oxidation state for Mn that con firmed the existence of Mn O2 on the fabrics.The X-ray diffraction(XRD)measurement was conducted to identify the phase of electroplating Mn O2.Pattern of XRD in Fig.S4(Supporting information)show s the existence of α-Mn O2 with tetragonal phase(JCPDS No.44-0141).The weak and broad peaks suggest the poor crystallinity of the electrodepositing Mn O2.

Fig.2.(a)The survey XPS spectrum and(b)high-resolution Mn 2p of SC950-EP30.

Fig.1.SEM images of positive electrode with different electroplating time for(a)30 min,(b)20 min,(c)60 min and(d)TEM image of positive electrode with electroplating time for 30 min.

Fig.3.(a)Nyquist plots of positive electrodes.(b)CV curves of positive electrodes at 100 m V/s.(c)GCD curves of positive electrodes at 1 A/g.(d)Specific capacitances of positive electrodes at different current densities.

Acknowledgements

Based on above results, flexible asymmetric supercapacitors(ASCs)were constructed by assembling SC950-EP30 as positive electrode and dip-coating activated carbon powders as negative electrode,respectively(Fig.4a).The detailed fabrication process is disclosed in the Supporting information.With the advantage of the different potential ranges of Mn O2 and activated carbon(Fig.S6 in Supporting information),the flexible ASCs can display a maximum operating voltage of 1.8 V,a high specific capacitance of 96.7 F/g,an outstanding energy density of 43.84 Wh/kg at a current density of 1 A/g,and a maximum pow er density of 6.62 k W/kg at a current density of 10 A/g in 1 mol/L Na2SO4 aqueous electrolyte.The EIS of the flexible ASCs was measured and compared with the positive electrode mentioned above(Fig.4b).It can be observed that flexible ASCs have a more vertical line in low frequency range and a smaller semicircle in high frequency range than the single positive electrode,which show s better ideal capacitive behavior of the flexible ASCs.This result could be likely contributed to the EDLC essence of the activated carbon,which complements the pseudocapacitive essence of the Mn O2.In addition,CV curves of the flexible ASCs measured at various scan rates present rectangular shapes(Fig.4c),disclosing the ideal capacitive behavior consistent with the EIS result.The excellent electrochemical performances of the flexible ASCs were further verified by GCD measurement.As shown in Fig.4d.GCD curves of the flexible ASCs performed at different current densities from 1 A/g to 10 A/g exhibit almost symmetric triangular shapes,which confirmed the good capacitive properties for this flexible ASCs device.Besides the large energy density,cycling stability is also an important requirement for supercapacitors.The overall specific capacitance loss is only about 5.95%after 3000 cycles and 7.1%after 5000 cycles of charging and discharging at a current density of 2 A/g(Fig.4e),indicating well cyclic performance for this flexible ASCs.Also,there are some latest reported Mn O2-based asymmetric supercapacitors plotted on the Ragone diagram to be compared with our work(Fig.4f)[20,27-31].

老头儿讲了十分钟后开始在黑板上画圆。他教的是初等几何研究，他画图的时候是我们溜走的最好时机，特别是在他画圆的时候，他总是全神贯注地想把圆画得尽善尽美。就是在那个时刻，我像一只老鼠一样，一弓腰，从教室后门悄无声息地溜走了。

Fig.4.(a)Digital image of flexible ASCs device.(b)Nyquist plots of ASCs and positive electrodes.(c)CV curves of ASCs at various scan rate.(d)GCD curves of ASCs at different applied current densities.(e)Cyclic stability of ASCs and(f)Ragone plots of ASCs.

Electrochemical properties of all electrodes were first characterized by EIS,and were further analyzed using Nyquist plots.The nearly vertical line in the low frequency range of all the electrodes in Fig.3a represents the ideal capacitive behavior,and the small semicircle in high frequency range show s the low interfacial charge resistance.The SC950-EP30 exhibits the best performance among all the electrodes in Nyquist plot,which consists with the further cyclic voltammetry(CV)and galvanostatic charge-discharge(GCD)tests.It can be seen that the CV curves of all the electrodes present the quasi-rectangular shape with no distinct redox peaks at a scan rate of 100 m V/s,which consists with the faradic pseudocapacitive behavior of Mn O2(Fig.3b).The nearly triangular shape of GCD cycles exhibits good symmetry and almost linear slope in all electrodes when discharge as shown in Fig.3c,demonstrating the ideal capacitive behavior which is in good agreement with the EIS and CV results.CV curves at various scan rates and GCD curves at different current densities of each electrode were disclosed in the Supporting information(Fig.S5).The specific capacitance(C S)can be calculated by the equation based on CV[6,17,24]and the equation based on GCD[25,26].The specific capacitances of SC950-EP20,SC950-EP30,and SC950-EP60 based on CV were 362.2,716.5,and 258.9 F/g at a scan rate of 2 m V/s,and were 492.6,1110.9,and 395.1 F/g based on GCD at a current density of 1 A/g,respectively.The specific capacitances for the different electrodes at different applied current densities are summarized in Fig.3d.Notice that although area of the SC950-EP60 under CV test is much larger than the SC950-EP20(Fig.3b),but the specific capacitance results were in the opposite way.The detailed electrochemical performances for all samples were disclosed in Fig.S5.This is caused by the over-deposition of the SC950-EP60 electrode,which not only lets the electrode react with more absolute amounts of active materials,but also makes a large portion of the inaccessible region.This is the reason why the SC950-EP60 shows larger area under CV test,but presents lower value when calculating specific capacitance.

3.报道过程上注重互动性。尊重受众主体地位，在报道中努力营造参与情境和氛围。在电视新闻传播中，最有效的方式是开掘人际传播的优势，强调节目主持人或记者与屏前观众的“面对面”交流。在新闻报道中把主持人和记者推到镜头前，在事件现场直接面对观众，现场播报、即兴采访以及评论、反馈等构成新闻的主体信息。“人际交流”具有很强的亲和力，主持人或记者的言谈举止，加上事件现场的动态过程，以最形象化、电视化的方式呈现在观众面前，既保持了新闻的原生态过程，也容易吸引观众的注意力，更重要的是让观众感受到最为平等的传播与接收状态。[1]

This work was financially supported by the National Natural Science Foundation of China(No.51672151)and 973 Program of China(No.2014CB932401).

Appendix A.Supplementary data

Supplementary data associated with this article can be found,in the online version,at https://doi.org/10.1016/j.cclet.2017.12.028.

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