1、Aqueous Rechargeable Batteries 1. A New FreeStanding Aqueous ZincIon Capacitor Based on MnO2-CNTs Cathode and MXene Anode 2. UltraHigh MassLoading Cathode for Aqueous ZincIon Battery Based on GrapheneWrapped Aluminum Vanadate Nanobelts 3. Novel Insights into Energy Storage Mechanism of Aqueous Recha
2、rgeable Zn/MnO2 Batteries with Participation of Mn2+ 4. NASICONStructured NaTi2(PO4)3 for Sustainable Energy Storage 5. V2O5 Nanospheres with Mixed Vanadium Valences as High Electrochemically Active Aqueous ZincIon Battery Cathode Vol.:(0123456789)1 3A New FreeStanding Aqueous ZincIon Capacitor Base
3、d on MnO2CNTs Cathode andMXene AnodeSiliangWang1,2, QiangWang1,2, WeiZeng1,2*, MinWang1,2, LiminRuan1,2, YananMa3* * Wei Zeng, ; Yanan Ma, 1 Key Laboratory ofIntelligent Computing andSignal Processing, Ministry ofEducation, Anhui University, No. 3 Feixi Road, Hefei230039, AnhuiProvince, PeoplesRepub
4、licofChina2 National Engineering Research Center forAgroEcological Big Data Analysis andApplication, School ofElectronics andInformation Engineering, Anhui University, No. 111 Jiulong Road, Hefei230601, AnhuiProvince, PeoplesRepublicofChina3 School ofSciences, Hubei University ofAutomotive Technolog
5、y, No. 167 Checheng West Road, Shiyan442002, HubeiProvince, PeoplesRepublicofChinaHIGHLIGHTS A new zincion capacitor (ZIC) was realized by assembling the freestanding manganese dioxidecarbon nanotubes (MnO2CNTs) batterytype cathode and MXene (Ti3C2Tx) capacitortype anode in an aqueous electrolyte. T
6、he large specific capacitance of the MXene anode avoids the mismatch in capacitance between the cathode and anode of the ZIC. The superior performance of the proposed ZIC makes it a promising candidate for the nextgeneration energy storage devices.ABSTRACT Restricted by their energy storage mechanis
7、m, current energy storage devices have certain drawbacks, such as low power density for batteries and low energy density for supercapacitors. Fortunately, the nearest ion capacitors, such as lithiumion and sodiumion capacitors containing batterytype and capacitortype electrodes, may allow achieving
8、both high energy and power densities. For the inspiration, a new zincion capacitor (ZIC) has been designed and realized by assembling the freestanding manganese dioxidecarbon nanotubes (MnO2CNTs) batterytype cathode and MXene (Ti3C2Tx) capacitortype anode in an aqueous electrolyte. The ZIC can avoid
9、 the insecurity issues that frequently occurred in lithiumion and sodiumion capacitors in organic electrolytes. As expected, the ZIC in an aqueous liquid electrolyte exhibits excellent electrochemical performance (based on the total weight of cathode and anode), such as a high specific capacitance o
10、f 115.1Fg1 (1mVs1), high energy density of 98.6Whkg1 (77.5Wkg1), high power density of 2480.6Wkg1 (29.7Whkg1), and high capacitance retention of 83.6% of its initial capacitance (15,000 cycles). Even in an aqueous gel electrolyte, the ZIC also exhibits excellent performance. This work provides an es
11、sential strategy for designing nextgeneration highperformance energy storage devices.KEYWORDS Energy storage; Zincion capacitor; Batterytype and capacitortype electrodes; MXene; Electrochemical performanceeDischargeAnodeCathodeChargeeeH2OSO4e2Zn2+ ISSN 23116706eISSN 21505551 CN 312103/TBARTICLECite
12、asNanoMicro Lett. (2019) 11:70 Received: 13 June 2019 Accepted: 13 August 2019 The Author(s) 2019https:/doi.org/10.1007/s4082001903011 NanoMicro Lett. (2019) 11:70 70 Page 2 of 12https:/doi.org/10.1007/s4082001903011 The authors1 IntroductionThe issues of energy depletion and greenhouse effect owing
13、 to the overconsumption of nonrenewable resources urgently require alternative green energy and efficient energy storage devices 13. Currently, batteries (e.g., lithiumion batteries, alkaline zincmanganese batteries, and leadacid batteries) and supercapacitors are the main energy storage devices 47.
14、 Owing to their clear advantages (e.g., higher power density, longer cycle life, better cycle stability, and higher safety), supercapacitors are more promising energy storage devices compared with batteries 810. However, restricted by their energy storage mechanisms, supercapacitors possess low ener
15、gy density 11, 12. To improve energy density without sacrificing the power density of supercapacitors, constructing ion capacitors, such as lithiumion or sodiumion capacitors, is possible. In the ion capacitors, batterytype electrodes and capacitortype electrodes are paired in electrolytes 1318. For
16、 example, in the lithiumion capacitor, the lithiumion batterytype anode (cathode) contributes a high capacity using the lithiumion insertion/extraction reaction, while the capacitortype cathode (anode) provides high power by rapid ion adsorption/desorption. Therefore, lithiumion capacitors possess h
17、igher energy density than supercapacitors and higher power density than batteries 16, 17. Although considerable progress has been made in the area of lithiumion and sodiumion capacitors, the following drawbacks severely restrict their practical application 14, 15. First, most lithiumion and sodiumio
18、n capacitors contain organic electrolytes that are flammable, volatile, and toxic. Second, the kinetics and capacitance mismatch owing to the sluggish kinetics of lithiumion and sodiumion batterytype electrodes and low specific capacitance of capacitortype electrodes in organic electrolytes bring hu
19、ge difficulties in implementing highperformance devices. Finally, determined by the intrinsic properties of lithiumion and sodiumion batterytype electrodes, the cycle life of these ion capacitors remains low. Therefore, employing new ion capacitor containing aqueous electrolytes that are safe and ha
20、ve long cycle life is essential.Currently, rechargeable aqueous zincion batteries have attracted considerable attention for their high capacity, fast kinetics, and high safety 1922. These unique properties of zincion batteries give us an inspiration for designing novel zincion capacitors (ZIC) that
21、is composed of zincion insertion/extraction batterytype cathodes and suitable capacitortype anodes. Many materials (e.g., such as manganesebased oxides, vanadiumbased oxides, Prussian blue analogs, Chevrel phase compounds, and polyanion compounds) have been used as the cathodes in zincion batteries
22、23, 24. Among these materials, manganesebased oxides, such as manganese dioxide (MnO2), have unique advantages of natural abundance, low toxicity, low cost, and multiple valence states of Mn 20, 21, which makes them potential batterytype cathode materials for ZIC.Activated carbon (AC) is commonly us
23、ed for a capacitortype electrode in lithiumion and sodiumion capacitors 16, 25, 26. However, using AC for capacitortype electrode has following two defects: (1) ACbased electrodes exhibit limited capacity owing to the energy storage mechanism of electrochemical doublelayer capacitors. (2) ACbased el
24、ectrodes require the binder and conductiveadditive, which increases the weight of the electrodes and decreases the final specific capacitance of the devices. Therefore, AC is unsuitable for the highperformance ZIC. MXene, a new type of twodimensional (2D) layered materials with the formula of Mn+1Xn
25、Tx (M represents the early transition metal, X represents carbon or nitrogen, and Tx represents F, O, and OH surface termination, n = 1, 2, 3), is extensively used in the field of energy storage owing to its superior properties of high conductivity, hydrophilic surface, and energy storage mechanism
26、of intercalation/deintercalation pseudocapacitance 2729. Based on the properties and applications of MXene, we believe that MXene is a suitable capacitortype electrode material for the ZIC.Herein, we designed and realized an aqueous ZIC based on freestanding manganese dioxidecarbon nanotubes (MnO2CN
27、Ts) batterytype cathode and Ti3C2Tx (as a representative of the MXene family) capacitortype anode. In summary, the aqueous ZIC has the following advantages compared with the stateoftheart lithiumion and sodiumion capacitors based on organic electrolytes: (1) The use of aqueous liquid or gel electrol
28、ytes does not pose any serious safety issues. (2) The use of MXene capacitortype anode (intercalation/deintercalation energy storage mechanism) eliminates the abovementioned mismatch in kinetics and capacitance. (3) Compared with organic electrolytes, aqueous electrolytes are more stable during the
29、chargedischarge cycles, which contribute to the long cycle life of the ZIC. As a proof of concept, the ZIC in an aqueous liquid electrolyte exhibits a high specific capacitance of 115.1Fg1 (scan NanoMicro Lett. (2019) 11:70 Page 3 of 12 70 1 3rate of 1mVs1), a high energy density of 98.6Whkg1 (power
30、 density of 77.5Wkg1), a high power density of 2480.6Wkg1 (energy density of 29.7Whkg1), a high capacitance retention of 83.6% of its initial capacitance after 15,000 cycles, and a high Coulombic efficiency of above 93.3% during the cycles. Even in an aqueous gel electrolyte, the ZIC also exhibits a
31、n excellent performance. This study provides an effective way to design nextgeneration energy storage devices exhibiting high energy and power densities, excellent cycle stability, long life, and high safety.2 Experimental Section2.1 Reagents andMaterialsCarbon nanotubes (CNTs, multiwalled, diameter
32、 8nm, length = 0.52m) were purchased from Beijing Boyu Gaoke New Material Technology Co., Ltd. Manganese acetate tetrahydrate Mn(CH3COO)24H2O, ammonium persulfate (NH4)2S2O8, 1octanol, manganese sulfate monohydrate (MnSO4H2O), hydrochloric acid (HCl), sodium dodecylbenzenesulfonate (SDBS), gelatin,
33、and borax were purchased from Sinopharm Chemical Reagent Co., Ltd. Lithium fluoride (LiF) and zinc sulfate heptahydrate (ZnSO47H2O) were purchased from Aladdin Industrial Corporation and Sahn Chemical Technology (Shanghai) Co., Ltd., respectively.2.2 Fabrication ofFreeStanding MnO2CNTs ElectrodesMnO
34、2 nanowires (NWs) were prepared by a method similar to our previous work 30. CNTs, MnO2 NWs, and SDBS with appropriate weight ratios were mixed and put into deionized water (30mL). The mixture was probe ultrasonicated for 30min to form a homogeneous suspended solution. The prepared suspended solutio
35、n was filtered through a membrane (pore size of 450nm). After the filtered cake was dried and peeled off, a freestanding MnO2CNTs electrode was obtained.2.3 Fabrication ofFreeStanding MXene ElectrodesThe MXene (Ti3C2Tx) nanosheets were prepared according to our previous work 31, 32. Briefly, LiF (1g
36、) was added to HCl (9M, 20mL), followed by magnetic stirring until LiF completely dissolved. Ti3AlC2 (1g) was gently added to the above solution and magnetically stirred for 24h (35C). After etching, the mixture was centrifuged several times. After centrifugation, the precipitate was redispersed in
37、deionized water and sonicated for 1h (Ar atmosphere below 35C) followed by centrifugation. Finally, the dark green supernatant of MXene nanosheets was achieved. The freestanding MXene electrodes were fabricated by directly filtering the MXene solution through a membrane (pore size of 450nm) followed
38、 by drying and peeling off the filtered cake of MXene.2.4 Fabrication ofAqueous Liquid andAqueous Gel ElectrolytesTo prepare the aqueous liquid electrolyte, ZnSO47H2O (23g) and MnSO4H2O (0.676g) were dissolved in deionized water (29.8mL) and stirred until the solution was clarified. To prepare the a
39、queous gel electrolyte, gelatin (4.0g) and borax (0.4g) were added to deionized water (29.8mL) and continuously magnetically stirred at 80C. After gelatin completely dissolved, ZnSO47H2O (23g) and MnSO4H2O (0.676g) were added to the solution, and the stirring continued until a homogeneous solution w
40、as formed.2.5 Assembling theZICThe freestanding MnO2CNTs and MXene films were cut to suitable sizes. The aqueous liquid ZIC was prepared by assembling the freestanding MnO2CNTs cathode (preactivated at a current density of 0.256Ag1 for three chargedischarge cycles) and MXene anode with a liquid elec
41、trolytesoaked (2M ZnSO4 and 0.1M MnSO4) separator in between. After changing the liquid electrolyte to gel electrolyte, the quasisolid ZIC was prepared by the fabrication process similar to that for the aqueous liquid ZIC.2.6 CharacterizationThe morphology, structure, and composition of the samples
42、were investigated using scanning electron microscopy (SEM, S4800), transmission electron microscopy (TEM, JEM2100), and Xray diffraction (XRD, SmartLab, 9 KW). The electrochemical performances of the MnO2CNTs NanoMicro Lett. (2019) 11:70 70 Page 4 of 12https:/doi.org/10.1007/s4082001903011 The autho
43、rscathode and MXene anode, such as cyclic voltammograms (CV), galvanostatic chargedischarge (GCD), and electrochemical impedance spectrum (EIS), were conducted on an electrochemical workstation (CHI660E) using metallic zinc foils as a counterelectrode and 2M ZnSO4 and 0.1M MnSO4 as an electrolyte in
44、 an electrolytic cell. The electrochemical performances of the ZIC in aqueous liquid and gel electrolyte were tested using a twoelectrode system. The mass ratio of the MnO2CNTs cathode to MXene anode was 1:2.14 according to the charge balance between the cathode and anode.3 Results andDiscussionThe
45、schematic diagram of the ZIC is shown in Fig.1a. The ZIC consists of a MnO2CNTs batterytype cathode (preactivated by chargedischarge cycles), MXene capacitortype anode, and 2M ZnSO4 and 0.1M MnSO4 electrolyte. In the steady state, the energy storage mechanism of the ZIC can be described briefly as f
46、ollows. During charging, the zinc ions are extracted from the tunnels of MnO2 into electrolyte and subsequently intercalate into the interlayer of MXene. During discharging, the zinc ions deintercalate from MXene into electrolyte and subsequently insert into the tunnels of MnO2. Both batterytype and
47、 capacitortype energy storage mechanisms such as zincion insertion/extraction (MnO2) and intercalation/deintercalation (MXene) result in high energy and power densities of the ZIC. MnSO4 with an appropriate concentration was added to effectively inhibit the dissolution of MnO2, which significantly i
48、mproved the cycle life of the ZIC. Figure1b shows the fabrication procedure of the freestanding MnO2CNTs cathode and MXene anode. To prepare the MnO2CNTs electrode, MnO2 nanowires (NWs) and CNTs were probe sonicated for 30min. Then, the wellmixed solution was vacuumfiltered through a membrane follow
49、ed by vacuum drying. Finally, freestanding MnO2CNTs film was peeled off from the membrane. A similar method was adopted to prepare a freestanding MXene electrode. Because the MXene solution with high dispersion can be obtained by liquid exfoliation, the solution was directly vacuumfiltered and did n
50、ot require the step of probe sonication.To prepare the freestanding MnO2CNTs electrodes, MnO2 NWs need to be synthesized. Figure2a shows the SEM image of MnO2, which shows the entangled MnO2 NWs. The TEM image of MnO2 NWs is shown in Fig.2b. In the TEM image, the lattice fringes can be clearly obser
