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Achieving Ultrahigh Energy Density and Long Durability in a Flexible Rechargeable Quasi-Solid-State Zn–MnO2 Battery

Yinxiang Zeng, Xiyue Zhang, Yue Meng, Minghao Yu, Jianan Yi, Yiqiang Wu,* Xihong Lu,* and Yexiang Tong

Y. X. Zeng, X. Y. Zhang, Y. Meng, M. H. Yu, Prof. X. H. Lu, Prof. Y. X. TongMOE of the Key Laboratory of Bioinorganic and Synthetic ChemistryKLGHEI of Environment and Energy ChemistrySchool of ChemistrySun Yat-Sen UniversityGuangzhou 510275, P. R. ChinaE-mail: [email protected]. N. Yi, Prof. Y. Q. WuSchool of Materials Science and EngineeringHunan Provincial Collaborative Innovation Center for High-efficiency Utilization of Wood and Bamboo ResourcesCentral South University of Forestry and TechnologyChangsha 410004, Hunan, P. R. ChinaE-mail: [email protected], [email protected]

DOI: 10.1002/adma.201700274

and high capacity, are emerging as one of the most compelling candidates.[13–16] Recently, growing attention has been paid to developing various flexible Zn–MnO2 batteries.[17–20] For example, Gaikwad et al. demonstrated a flexible, printed alkaline Zn–MnO2 battery with a mesh support and Ag current collector.[17] The fiber-shaped Zn–MnO2 battery could deliver a discharge capacity of 158 mA h g−1 at a low current density of 0.07 A g−1.[18] Another flexible alkaline Zn–MnO2 bat-tery using composites of CNTs and MnO2 as cathode materials was assembled by Wang et al., achieving a high capacity of 236 mA h g−1 at 0.3 mA cm−2.[19] How-ever, similar to conventional aqueous Zn–MnO2 batteries, these available flexible Zn–MnO2 batteries are nonrechargeable and suffer from sharp capacity attenuation, resulting in resource waste and environ-mental pollution.[13,14,18,21] Additionally, bulk Zn foil/paste and binders are mostly

used, rendering large resistance, inferior capacity, and rate capa-bility.[17,18,22] These drawbacks prevent these Zn–MnO2 batteries from satisfying the critical demands of next-generation flexible electronics. Very recently, Liu and co-workers drastically boosted the stability of an aqueous Zn–MnO2 battery by ameliorating the electrolyte, which is believed to open new opportunities for the development of aqueous rechargeable Zn–MnO2 batteries.[13] Nevertheless, the breakthrough on flexible quasi/all-solid-state rechargeable Zn–MnO2 batteries with high capacity, high rate capability, and good cycling durability remains an elusive challenge.

Herein, we rationally construct the first paradigm of a flexible quasi-solid-state rechargeable Zn–MnO2 battery using a MnO2@PEDOT (poly(3,4-ethylenedioxythiophene)) cathode, a Zn nanosheet anode, and a modified poly(vinyl alcohol) (PVA) gel electrolyte. The MnO2@PEDOT and Zn electrodes are directly grown on flexible carbon cloth as binder-free elec-trodes. Our fabricated Zn–MnO2 battery with a voltage of 1.8 V can deliver an ultrahigh capacity of 366.6 mA h g−1 at a cur-rent density of 0.74 A g−1 in aqueous electrolyte. Benefiting from the protective layer of PEDOT as well as the mild neu-tral electrolyte containing a moderate concentration of Mn2+ ions, the rechargeable Zn–MnO2 battery exhibits a favorable capacity retention of 83.7% after 300 cycles with high Cou-lombic efficiency. More importantly, when assembled with

Advanced flexible batteries with high energy density and long cycle life are an important research target. Herein, the first paradigm of a high-performance and stable flexible rechargeable quasi-solid-state Zn–MnO2 battery is con-structed by engineering MnO2 electrodes and gel electrolyte. Benefiting from a poly(3,4-ethylenedioxythiophene) (PEDOT) buffer layer and a Mn2+-based neu-tral electrolyte, the fabricated Zn–MnO2@PEDOT battery presents a remark-able capacity of 366.6 mA h g−1 and good cycling performance (83.7% after 300 cycles) in aqueous electrolyte. More importantly, when using PVA/ZnCl2/MnSO4 gel as electrolyte, the as-fabricated quasi-solid-state Zn–MnO2@PEDOT battery remains highly rechargeable, maintaining more than 77.7% of its initial capacity and nearly 100% Coulombic efficiency after 300 cycles. Moreover, this flexible quasi-solid-state Zn–MnO2 battery achieves an admi-rable energy density of 504.9 W h kg−1 (33.95 mW h cm−3), together with a peak power density of 8.6 kW kg−1, substantially higher than most recently reported flexible energy-storage devices. With the merits of impressive energy density and durability, this highly flexible rechargeable Zn–MnO2 battery opens new opportunities for powering portable and wearable electronics.

Zn–MnO2 Batteries

The new wave of smart wearable technologies such as rollup displays, wearable devices, and implantable medical devices highlights the urgent demand for flexible and wearable energy-storage devices.[1–4] Considerable efforts have been devoted to flexible power devices, yielding highly impressive flexible solid-state supercapacitors,[5–7] Li-ion batteries,[8–10] and recharge-able batteries.[11,12] Among the various options, flexible quasi/all-solid-state Zn–MnO2 batteries, characterized by cost effec-tiveness, good safety, eco-friendliness, high output voltage,

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polymer electrolyte into a quasi-solid-state device, it still affords a prominent capacity of 282.4 mA h g−1 (19 mA h cm−3). After 300 consecutive charge–discharge cycles, a highly reversible capacity of 219.4 mA h g−1 is well preserved, revealing its good electrochemical stability. Besides, this flexible quasi-solid-state Zn–MnO2 battery achieves a remarkable energy density of 504.9 W h kg−1 (33.95 mW h cm−3), together with a peak power density of 8.6 kW kg−1, outperforming most recently reported flexible energy-storage devices.

The structure of the flexible quasi-solid-state Zn–MnO2 bat-tery is schematically illustrated in Figure 1a. Briefly, the device with classical sandwich structure consists of a MnO2@PEDOT cathode, a Zn anode, a separator, and a PVA gel electrolyte. Both the cathode and anode were synthesized on flexible carbon cloth via a facile and scalable electrodeposition method. Scanning electron microscopy (SEM) images showed that freestanding Zn nanosheets with ≈50 nm in thickness were homogeneously grown on the carbon fiber without any binder, ensuring a favorable low-resistance pathway for electron transfer (Figure 1b). The high-resolution transmission electron microscopy (HRTEM) images and selected area electron dif-fraction (SAED) pattern in Figure S1 (Supporting Information) confirm the highly crystalline nature of the Zn nanosheets. The measured lattice fringes of 0.24 nm are in agreement with the (002) plane of hexagonal zinc (JCPDS # 87-0713). The hexagonal structure and high crystallinity of these Zn nanosheets were fur-ther confirmed by X-ray diffraction (XRD) analysis. Excluding the peaks from the carbon substrate, all of the other diffraction peaks can be well indexed to hexagonal zinc (JCPDS # 87-0713) (Figure 1c). To understand the growth process of these Zn nanosheets, SEM images of the samples at different deposi-tion times are collected and discussed in Figure S2 (Supporting Information). Figure S3 (Supporting Information) depicts SEM

images of MnO2 sample, in which carbon cloth covered with a uniform and smooth MnO2 film is observed. After coating with a PEDOT layer, the surface turned rough and formed a core–shell structure (Figure 1d; Figure S4a, Supporting Infor-mation). Both the HRTEM image and SAED pattern dem-onstrate that the PEDOT shell with a thickness of ≈9 nm is amorphous, while the MnO2 core is polycrystalline (Figure 1e). The observed lattice spacings of 0.32 and 0.24 nm correspond to the (201) and (210) planes of MnO2 (JCPDS # 65-5787), respectively (Figure 1e). Energy-dispersive spectroscopy map-ping of Mn, O, C, and S clearly verifies the homogeneous distribution of these elements and the core–shell structure of the MnO2@PEDOT sample (Figure S4b, Supporting Infor-mation). Furthermore, the MnO2 and MnO2@PEDOT sam-ples were studied by XRD and Raman analysis. As shown in Figure S5 (Supporting Information), in addition to the signal of the carbon substrate, similar peaks are observed for both MnO2 and MnO2@PEDOT samples, matching well with the reference data for MnO2 (JCPDS # 65-5787). The Raman band at 650 cm−1 for the MnO2 sample can be attributed to the three major Mn–O stretching vibrations of the [MnO6] group in MnO2 (Figure S6a, Supporting Information).[23] Upon coating with PEDOT, the MnO2 signals were attenuated dra-matically and typical peaks of PEDOT appeared, confirming the existence of the PEDOT shell on the surface of the MnO2 core (Figure S6b, Supporting Information).[24] The MnO2 and MnO2@PEDOT samples were further characterized by X-ray photoelectron spectroscopy (XPS). In comparison to the pris-tine MnO2 sample, the MnO2@PEDOT samples exhibited distinct S signals (Figure S7a, Supporting Information), again indicating the formation of PEDOT. The energy separation of 4.8 eV in the Mn 3s spectrum reveals that Mn4+ is the domi-nant valence state in the MnO2@PEDOT sample (Figure 1f).[25]

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Figure 1. a) Schematic illustration of flexible quasi-solid-state Zn–MnO2@PEDOT battery. b,c) SEM images (b) and XRD profile (c) of Zn cathode. d) SEM images, e) HRTEM images, and f) core-level Mn 3s spectrum of MnO2@PEDOT sample. The insets in panel (e) are the SAED patterns.



Additionally, the two peaks centered at 165.01 and 163.82 eV in the S 2p spectrum are attributed to S 2p1/2 and S 2p3/2 in PEDOT (Figure S7b, Supporting Information).[26]

To evaluate the electrochemical properties of the Zn–MnO2 battery, two-electrode Zn–MnO2 batteries (denoted Zn–MnO2 and Zn–MnO2@PEDOT) were assembled using MnO2 or MnO2@PEDOT as cathode and Zn as anode in aqueous elec-trolyte containing 2 m ZnCl2 and 0.4 m MnSO4. The presence of MnSO4 in aqueous electrolyte can suppress the dissolution of MnO2, and thus boost the stability of Zn–MnO2 batteries to a certain extent.[13] In our case, the fabricated Zn–MnO2 battery yielded the best durability in the electrolyte con-taining 0.4 m MnSO4 (Figure S8, Supporting Information). Figure 2a compares the discharge curves of the Zn–MnO2 and Zn–MnO2@PEDOT batteries. Both batteries present similar discharge plateau and capacity. In addition, both of them have similar capacities and rate performance at various discharge cur-rent densities (Figure 2b). All of these observations prove that the PEDOT shell has no discernible influence on the capacity of the Zn–MnO2 battery. Evidently, the PEDOT serves only as a protective layer and has no involvement in the electrochemical reaction of the Zn–MnO2 battery, which is consistent with a previous report.[27] The cyclic voltammetry (CV) curves of the Zn–MnO2@PEDOT battery display a typical well-defined redox couple at different scan rates, manifesting the highly revers-ible redox reaction of the battery (inset in Figure 2c). Figure 2c presents the discharging voltage profiles of the Zn–MnO2@PEDOT battery at various current densities. All of these curves have a prolonged discharge voltage platform situated at about 1.19–1.37 V, consistent with the CV curves. More encouragingly, this Zn–MnO2@PEDOT battery yielded an incredibly high discharge capacity of 366.6 mA h g−1 (118.9 mA h g−1 based

on the total mass of the cathode) at a high current density of 0.74 A g−1 (4 mA cm−2), outperforming most recently reported Zn–MnO2 batteries and other aqueous rechargeable batteries (Table S1, Supporting Information), such as Zn–MnO2 battery (210 mA h g−1 at 0.105 A g−1),[28] Ni–Zn battery (203 mA h g−1 at 0.5 mA cm−2),[29] Zn–Co3O4 battery (162 mA h g−1 at 1 A g−1),[30] Zn–ZnMn2O4 battery (150 mA h g−1 at 0.05 A g−1),[14] and Ni–Fe battery (126 mA h g−1 at 1.5 A g−1).[31] Furthermore, when the current density increased to 7.43 A g−1 (40 mA cm−2), the dis-charge capacity still retained 143.3 mA h g−1 (0.77 mA h cm−2) with a short discharge time of only 69 s, indicating its good rate capability and ultrafast charge–discharge ability. Such fast charge/discharge feature is markedly different from the con-ventional Zn–MnO2 battery, which generally needs hours to be charged.[19,32] In addition, the effect of the MnO2 electrodeposi-tion time on the discharge capacity of the Zn–MnO2 battery was also explored, and the MnO2 cathode fabricated with a 15 min deposition time achieved the optimal performance (Figure S9, Supporting Information).

The poor cycling stability of Zn–MnO2 batteries is a major obstacle to their widespread commercialization. The cycling performance of our Zn–MnO2@PEDOT batteries was studied by continually charging–discharging at a current density of 1.11 A g−1. As shown in Figure 2d, the Zn–MnO2@PEDOT battery exhibited acceptable cyclic durability with about 83.7% capacity retention after 300 cycles, while the Zn–MnO2 bat-tery retained only 47.2% of its initial capacity. The increase in capacity at the initial cycling stage is attributed to the activation of the active materials.[33,34] Such remarkably enhanced dura-bility is derived from the protection of the PEDOT shell.[27] As revealed by the SEM images in Figure S10 (Supporting Infor-mation), the pristine MnO2 cathode with a smooth surface

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Figure 2. a,b) Galvanostatic discharge curves at 0.74 A g−1 (a) and specific capacity as a function of current density (b) of the aqueous Zn–MnO2 and Zn–MnO2@PEDOT batteries. c–e) Galvanostatic discharge profiles at different current densities (c), cycling performance at 1.11 A g−1 (d), and rate performance and corresponding Coulombic efficiency (e) of the aqueous Zn–MnO2@PEDOT battery. The inset in panel (b) shows the corresponding CV curves.



underwent obvious changes in morphology after 300 cycles and its surface turned rough. By contrast, the morphology of the MnO2@PEDOT cathode was well preserved with little variation after PEDOT coating. Importantly, our as-fabricated Zn–MnO2@PEDOT battery displayed superb rate performance and reversible stability. At a discharge current of 1.11 A g−1, the Zn–MnO2@PEDOT battery delivered a reversible spe-cific capacity of ≈310 mA h g−1 at 1.11 A g−1, and recovered to ≈280 mA h g−1 when the current was reset to 1.11 A g−1 after 300 cycles (Figure 2e). Moreover, the Coulombic efficiency of our Zn–MnO2@PEDOT battery was more than 95% during the rate cycling process. This cyclability is superior to most of the reported aqueous Zn–MnO2 batteries.[15,16,35,36] We have also studied the influence of the PEDOT thickness on the cycling stability of the Zn–MnO2 battery, and the MnO2 cathode with a PEDOT electrodeposition time of 15 min yielded the best dura-bility (Figure S11, Supporting Information).

As a proof-of-concept demonstration, a flexible quasi-solid-state Zn–MnO2@PEDOT battery with a voltage of 1.8 V was also assembled with PVA electrolyte. From the CV curve, one pair of pronounced redox peaks can be observed (Figure S12a, Supporting Information), which is in agree-ment with the charge–discharge curves in Figure 3a. Obvi-ously, all of the charge–discharge curves exhibit charac-teristic plateaus with relatively small voltage hysteresis. Encouragingly, this quasi-solid-state Zn–MnO2@PEDOT battery achieved a remarkable capacity of 282.4 mA h g−1 (91.6 mA h g−1, based on the total mass of the cathode) at a high current density of 0.37 A g−1 (2 mA cm−2), surpassing most recently reported quasi-solid-state batteries, including a primary Li-ion battery (40 mA h g−1 at 0.2 A g−1),[8] Ni–Fe battery (118 mA h g−1 at 0.3 A g−1),[37] Zn–MnO2 bat-tery (140 mA h g−1 at 0.5 mA cm−2),[22] and Ni–Zn battery

(0.39 mA h cm−2 at 0.5 mA cm−2).[29] A discharge capacity of 76 mA h g−1 (0.41 mA h cm−2) was maintained when the current density increased to 5.58 A g−1 (30 mA cm−2) (Figure 3b). In comparison with the aqueous electrolyte, the quasi-solid-state Zn–MnO2@PEDOT battery possessed rela-tively poor rate capability, which can be ascribed to the higher charge transfer resistance of the polymer electrolyte, as cer-tified by the electrochemical impedance spectroscopy result (Figure S12b, Supporting Information). Furthermore, this quasi-solid-state Zn–MnO2@PEDOT battery owned prom-ising long-term cycling stability, which could retain more than 77.7% of its initial capacity with an ultraslow capacity decay rate (only 0.075% per cycle) and high Coulombic effi-ciency (always near 100%) after 300 cycles at a high current density of 1.86 A g−1 (Figure 3c). Also, more than 61.5% of its initial capacity was still remained even the cyclic number extended to 1000 cycles (Figure S13, Supporting Informa-tion). The capacity decay can be ascribed to the slow dissolu-tion and destruction of the MnO2@PEDOT cathode and/or the irreversible reaction of the Zn anode. To our best knowl-edge, this is the first demonstration of a rechargeable quasi-solid-state Zn–MnO2 battery with a long lifespan.[17–19,22] Additionally, our device can be arbitrarily bent or twisted without deteriorating the discharge profile and capacity (Figure 3d) and can function normally in a wide temperature window of 5–40 °C (Figure 3e). Such exceptional flexibility and high environmental suitability endow our flexible quasi-solid-state Zn–MnO2@PEDOT battery with great feasibility in the application in smart/portable electronics.

The energy and power densities of our flexible Zn–MnO2@PEDOT battery are compared with other reported energy-storage devices in Figure 4a. Encouragingly, our flex-ible Zn–MnO2@PEDOT battery could output a maximum

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Figure 3. a,b) Galvanostatic charge–discharge curves (a) and specific capacities (b) of the quasi-solid-state Zn–MnO2@PEDOT battery at various current densities. Capacity-A presents the gravimetric capacity based on the mass of active materials of the cathode and Capacity-T presents the gravi-metric capacity based on the total mass of the cathode. c) Cycling performance and Coulombic efficiency of the quasi-solid-state Zn–MnO2@PEDOT battery collected at 1.86 A g−1 for 300 cycles. d,e) Galvanostatic discharge curves under different deformation conditions (d) and different environmental temperatures (e) for the quasi-solid-state Zn–MnO2@PEDOT battery collected at 1.86 A g−1.



gravimetric energy density of 599.8 W h kg−1 at a power den-sity of 1.34 kW kg−1 in aqueous electrolyte. When assembled into a quasi-solid-state device, an extraordinary energy density of 504.9 W h kg−1 and peak power density of 8.6 kW kg−1 were achieved with a short discharge time ranging from 49 s to 45 min. The overall performance is superior to some represent-ative aqueous batteries and asymmetric supercapacitors (ASCs) reported previously. Taking the total mass of the cell into con-sideration, the use of a lightweight carbon cloth as the current collector in our quasi-solid-state Zn–MnO2@PEDOT battery results in a gravimetric energy density of 34 W h kg−1, which is more than threefold that of typical commercial SCs and comparable to the existing commercial lead-acid batteries.[21,38] More importantly, the highest volumetric energy density of our quasi-solid-state Zn–MnO2@PEDOT battery reached 33.95 mW h cm−3 (with a thickness of 0.08 cm, Figure S14, Supporting Information), considerably overmatching the reported alkali-ion batteries (1.3 mW h cm−3),[39] supercapaci-tors (6.8 mW h cm−3),[40] Ni–Zn batteries (7.76 mW h cm−3),[29] and Ni–Fe batteries (16.6 mW h cm−3)[37] and more than three times higher than that of commercial 4 V-500 uAh thin-film lithium batteries (0.3–10 mW h cm−3) (Figure 4b).

To exemplify the viability for practical applications in wearable and portable electronic devices, our flexible

quasi-solid-state Zn–MnO2@PEDOT battery was tested in various situations mimicking real usage. As shown in Figure 5a, the dis-charge capacity and energy density doubled when two devices were connected in parallel. Moreover, two quasi-solid-state Zn–MnO2@PEDOT batteries could be readily integrated in serial to provide doubled voltage, thus con-tributing to higher energy and power output (Figure 5b). In addition, three flexible quasi-solid-state Zn–MnO2@PEDOT batteries were connected in series to power a neon sign consisting of 45 light-emitting diodes (LEDs). After being charged at 1.86 A g−1 for 5 min, the tandem device illuminated the neon sign with a dazzling brightness under bending condition and the LEDs continued to shine after 30 min (Figure 5c). More inter-estingly, the flexible batteries connected in serial could be pasted onto clothes as a wear-able power source to illuminate the LED lights of a wristwatch (Figure 5d). All of these results conclusively demonstrate the prom-ising application of our fabricated flexible quasi-solid-state Zn–MnO2@PEDOT battery in smart/wearable electronics.

In summary, a highly flexible rechargeable Zn–MnO2@PEDOT battery with ultrahigh energy density was demonstrated for the first time. When tested in a mild neutral aqueous electrolyte, our Zn–MnO2@PEDOT bat-tery not only possesses a remarkable capacity of 366.6 mA h g−1 (1.97 mA h cm−2) at high current density but also presents admirable electrochemical durability (83.7% retention

after 300 cycles). Significantly, when using PVA/ZnCl2/MnSO4 gel as electrolyte, the as-fabricated quasi-solid-state Zn–MnO2@PEDOT battery was still highly rechargeable, which can main-tain more than 77.7% of its initial capacity and nearly 100% Coulombic efficiency after 300 cycles. Such enhanced cycling stability is attributed to the PEDOT buffer layer and Mn2+-based neutral electrolyte, which can effectively suppress the structural pulverization and dissolution of MnO2. Furthermore, the energy density of this quasi-solid-state battery achieved 504.9 W h kg−1 (33.95 mW h cm−3), considerably outstripping most recently reported batteries and SCs. Additionally, this quasi-solid-state Zn–MnO2@PEDOT battery exhibited outstanding mechanical flexibility and functioned across the ambient-temperature range. The successful construction of flexible and rechargeable Zn–MnO2 batteries by surface engineering of electrodes and modification of the electrolyte sheds light on the exploration of next-generation energy-storage devices for portable and wearable electronics.

Experimental SectionPreparation of MnO2: MnO2 was synthesized by electrodeposition

at room temperature using a CHI 760E electrochemical workstation. The electrodeposition was conducted in a solution of 0.1 m manganese

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Figure 4. a,b) Ragone plots (a) and volumetric energy density (b) of the quasi-solid-state Zn–MnO2@PEDOT battery. The values reported for other quasi/all-solid-state batteries and supercapacitors are shown for comparison. Data taken from refs. [24,29,31,32,34,37,39–51].



acetate (Mn(CH3COO)2·4H2O) and 0.1 m sodium sulfate (Na2SO4) at 1.0 V for 15 min. After electrodeposition, the MnO2 was further thermally annealed at a temperature of 300 °C in air for 1 h to improve the crystallinity of MnO2. The mass of MnO2 electrode (3.6 mg cm−2) was obtained by electronic scales (BT25S, 0.01 mg).

Preparation of MnO2@PEDOT: The PEDOT layer was then coated on the surface of MnO2 by electrodeposition in a solution of 0.03 m 3,4-ethylenedioxythiophene, 0.2 m lithium perchlorate (LiClO4), and 0.07 m sodium dodecyl sulfate at 1.0 V for 15 min at room temperature. The mass of PEDOT (1.78 mg cm−2) was obtained by electronic scales (BT25S, 0.01 mg).

Preparation of Zn Cathode: Zn was deposited on carbon cloth by an electrodeposition method, employing a CHI 760E workstation. In brief, a piece of carbon cloth was used as work electrode (1 cm × 2 cm) and precleaned by ultrasounding in ethyl alcohol for 15 min. 12.5 g zinc sulfate (ZnSO4·7H2O), 12.5 g sodium sulfate (Na2SO4), and 2 g boric acid (H3BO3) was dissolved in 100 mL distilled water and used as electrolyte. The electrodeposition was conducted with a constant current density of −40 mA cm−2 for 10 min at room temperature. The mass loading of the Zn cathode is 6.14 mg cm−2, which was obtained by electronic scales (BT25S, 0.01 mg).

Fabrication of Quasi-Solid-State Zn–MnO2 Battery: The quasi-solid-state Zn–MnO2 battery was assembled by separating the MnO2@PEDOT and Zn electrodes with a separator (NKK separator, Nippon Kodoshi Corporation) and PVA/LiCl–ZnCl2–MnSO4 gel as electrolyte. PVA/LiCl–ZnCl2–MnSO4 gel was prepared by mixing 3 m LiCl (2.54 g), 2 m ZnCl2 (5.45 g), 0.4 m MnSO4 (5.45 g), lignocellulose (0.05 g), and PVA (2 g) in deionized water (20 mL), and heated at 85 °C for 1 h under vigorous stirring. Prior to the assembling, electrodes and the separator were soaked with the gel electrolyte and then left under ambient condition to remove the unnecessary water. Finally, they were assembled together and after the electrolyte was solidified, a mechanically robust quasi-solid-state Zn–MnO2 battery can be packed and tested. The area

and thickness of the fabricated quasi-solid-state Zn–MnO2 battery devices are about 0.5 cm2 and 0.08 cm.

Material Characterization: The microstructures and compositions of the electrode materials were analyzed using field-emission SEM (JSM-6330F), transmission electron microscopy (FEI Tecnai G2 F30), Raman spectroscopy (Renishaw inVia), XPS (ESCALab250, Thermo VG), and X-ray diffractometry (D8 ADVANCE).

Electrochemical Measurement: Cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy were conducted employing an electrochemical workstation (CHI 760E). The electrochemical characterizations of the aqueous Zn–MnO2 battery were performed in a two-electrode cell in a solution of 2 m ZnCl2 and 0.4 m MnSO4.

Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.

AcknowledgementsThe authors acknowledge the financial support of this work received by the National Natural Science Foundation of China (Grant Nos. 21403306, 2016YFA0202604, and 31530009), Guangdong Natural Science Funds for Distinguished Young Scholar (Grant No. 2014A030306048), Tip-top Scientific and Technical Innovative Youth Talents of Guangdong Special Support Program (Grant No. 2015TQ01C205), Technology Planning Project of Guangdong Province (Grant No. 2015B090927007), and the Pearl River Nova Program of Guangzhou (Grant No. 201610010080).

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Figure 5. a,b) Galvanostatic charge–discharge curves of single quasi-solid-state Zn–MnO2@PEDOT battery device and two devices in series (a) and parallel collected at 1.11 A g−1 (b). c) Photographs of a neon sign consisting of 45 light-emitting diodes powered by three quasi-solid-state Zn–MnO2@PEDOT battery devices in series. d) Photograph of a watch with LED lights powered by three devices in series.



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Note: The article was corrected after an editorial error on initial publication online to make it clear that the article refers to Zn–MnO2 batteries.

Conflict of InterestThe authors declare no conflict of interest.

Keywordsdurability, flexible, rechargeable, ultrahigh energy density, Zn–MnO2 batteries

Received: January 13, 2017Revised: March 10, 2017

Published online: April 27, 2017

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