High-Performance Aqueous Sodium-Ion Batteries with Hydrogel

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High-Performance Aqueous Sodium-Ion Batteries with Hydrogel Electrolyte and Alloxazine/CMK-3 Anode Liqiao Zhong, Yong Lu, Haixia Li, Zhanliang Tao, and Jun Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00663 • Publication Date (Web): 25 Apr 2018 Downloaded from http://pubs.acs.org on April 26, 2018

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ACS Sustainable Chemistry & Engineering

High-Performance Aqueous Sodium-Ion Batteries with Hydrogel Electrolyte and Alloxazine/CMK-3 Anode Liqiao Zhong, Yong Lu, Haixia Li, Zhanliang Tao and Jun Chen* Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071, China

Corresponding Author * E-mail: [email protected]

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ABSTRACT: Aqueous rechargeable sodium-ion batteries (ARSIBs) are promising candidates for large scale energy storage applications due to their high safety, low cost and environmental friendliness. However, appropriate anode materials with high capacity for ARSIBs are limited and their cycling stability is generally unsatisfactory. Here we report high-performance ARSIBs with polyacrylamide hydrogel as electrolyte and alloxazine (ALO) encapsulated in CMK-3 as anode. The hydrogel with solid content of 60% could effectively mitigate the dissolution issue of sodiated ALO because its crosslinked structure is helpful to reserve H2O. The ALO/CMK-3 anode based on a two-electron transfer reaction could deliver a high capacity of 160 mA h g-1. The introduction of CMK-3 could improve the electrical conductivity of ALO and further reduce the dissolution of sodiated ALO due to its high conductivity and nanochannel structure. The full ARSIBs exhibit an energy density of 50 W h kg-1 (based on the total mass of active electrode materials) with good capacity retention of 90% after 100 cycles at 2 C and high rate capability of 146 mA h g-1 at 10 C (1 C = 250 mA g-1). This work paves the way to construct highperformance ARSIBs with high-capacity organic anode and hydrogel electrolyte.

KEYWORDS: aqueous sodium-ion batteries, organic anode, alloxazine, polyacrylamide hydrogel, CMK-3, dissolution issue


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INTRODUCTION Aqueous rechargeable sodium-ion batteries (ARSIBs) show great potentials for the applications of stationary large-scale energy storage devices due to their high safety, low cost, and environmental friendliness.1-4 Developing anode materials with proper working potential and high capacity is important for ARSIBs. Inorganic anode materials with appropriate operating potential for ARSIBs are limited due to the narrow electrochemical stability window of H2O.5-8 Compared with inorganic materials, organic materials are considered as good anode materials for ARSIBs because of their proper working potentials (mostly -1.0-0 V vs SHE), high capacity, and structural diversity.9-10 For example, Yang’s group employed poly-(naphthalene four formyl ethylenediamine) as anode for ARSIBs, which showed a reversible capacity of 130 mA h g-1 and good cycling performance.11 Liang et al. used polymerized quinone as anode and Na3V2(PO4)3 as cathode to fabricated full ARSIBs, which delivered an energy density of 30 Wh kg-1.12 However, the reported ARSIBs using organic materials as anodes generally showed low energy density due to the limited specific capacity or high working potential of the organic anodes. Therefore, developing high-capacity organic anode materials with relatively low operating potential for ARSIBs is necessary. Recently, organic alloxazine (ALO) have attracted lots of attentions due to its high theoretical capacity of 250 mA h g-1. Kang’s group reported ALO as electrode materials for sodium batteries in organic electrolyte.13 The results revealed that ALO showed an average working potential at about 2.0 V (vs Na+/Na). Due to its high theoretical capacity and appropriate working potential, we believe that ALO would be a good candidate anode for ARSIBs. To the best of our knowledge, there is no report about the applications of ALO in aqueous batteries. Similar to



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other organic materials,9,14-16 the main challenges for the application of ALO in ARSIBs are the serious dissolution issue of sodiated ALO in H2O and the poor electrical conductivity of ALO. Combination with conductive carbon materials such as CMK-3 is a common way to improve the conductivity of organic materials.17-18 Many approaches such as polymerization of small organic molecules and surface coating have been applied to solve the dissolution problem.19-24 For instance, the ARSIBs with polyimide as anode showed ultralong cycling life.19 However, less attention has been paid to modifying electrolyte to solve the dissolution problem. Developing quasi-solid-state electrolyte (namely hydrogel) for ARSIBs would be a good way to mitigate the dissolution issue. Among various hydrogels,25-28 polyacrylamide hydrogel has been widely used in many devices such as high-performance ionic cable due to its good stretchability and high ionic conductivity.29 However, there is no report about the applications of polyacrylamide hydrogel in ARSIBs. We here report full ARSIBs with polyacrylamide hydrogel as electrolyte, ALO/CMK-3 as anode, and carbon coated Na3V2(PO4)3 (NVP@C) as cathode. The ALO/CMK-3 anode could deliver a high capacity of 160 mA h g-1. The redox mechanism of the anode during charge/discharge processes is revealed by ex situ infrared spectra (IR). Compared with common aqueous solution electrolyte, the polyacrylamide hydrogel could inhibit the dissolution of sodiated ALO. The batteries using the hydrogel with solid content of 60% as electrolyte exhibit a capacity retention of 90% after 100 cycles at 2 C and high rate capability of 146 mA h g-1 at 10 C (1 C = 250 mA g-1). Moreover, the full batteries show a high average discharge voltage of 1.03 V and an energy density of 50 W h kg-1 (based on the total mass of active electrode materials). EXPERIMENTAL SECTION


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Preparation of ALO/CMK-3. The ALO/CMK-3 nanocomposites were prepared by a simple impregnation method. ALO (Santa Cruz, 50 mg) was first dissolved in 1 mL dimethyl sulfoxide (Aladdin) and 50 mg CMK-3 (JiCang, Nanjing) was then added to the above solution. After ultrasonic treatment for 30 min, the solution was dried under vacuum at 110 °C to remove the solvent. When the solvent disappeared completely, the ALO/CMK-3 nanocomposites were obtained. Synthesis of NVP@C. The carbon coated NVP samples were obtained by a hydrothermal assisted sol-gel approach.30 Typically, 4 mmol V2O5 (Guangfu, Tianjin), 12 mmol NH4H2PO4 (Guangfu, Tianjin) and 6 mmol Na2CO3 (Aladdin) were added to 70 mL distilled water and magnetically stirred at room temperature. Then, 6 mmol ascorbic acid (Guangfu, Tianjin) and 6 mL polyethylene glycol 400 (Guangfu, Tianjin) were added to form a blue suspension, which was stirred for 30 mins before transferred to a 100 mL Teflon-lined autoclave. The sealed autoclave was kept at 180 °C for 40 h, and then naturally cooled to room temperature. The resulting brown mixture was ultrasonically treated for 90 mins to obtain a uniform dispersion and then heated on a hot plate at 95 °C with stirring to evaporate water. The obtained brown sol was dried at 120 °C overnight. This precursor was thoroughly ground and preheated at 350 °C for 4 h. The preheated sample was ground to powders and finally sintered at 750 °C for 6 h in flowing Ar atmosphere. Synthesis of polyacrylamide hydrogel containing CF3SO3Na. Acrylamide (J&K) powders and CF3SO3Na (Aldrich) grains were dissolved in deionized water, in which the amount of acrylamide was adjusted according to the required solid content of the hydrogel and the concentration of CF3SO3Na electrolyte was fixed at 1 mol L-1 (1 M). The crosslinking agent (N, N-methylenebisacrylamide, Merck Millipore), thermo-initiator (ammonium persulphate, Alfa 5 ACS Paragon Plus Environment


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Aesar) and accelerator (N, N, N′, N′-tetramethylethylenediamine, Aldrich) of molar ratio 0.028, 0.031 and 0.152 mol%, respectively, relative to acrylamide monomer, were subsequently added into the solution. The mixture became a homogeneous and transparent solution at room temperature. The solution was transferred into a glass mold, which was separated by a silicon spacer. The mold was then put in an oven at 50 °C for 3 h to obtain the polyacrylamide hydrogel containing CF3SO3Na. The solid content means all the solid substance in the hydrogel except water. Materials characterizations. Powder X-ray diffraction (XRD) patterns were collected in the wide 2θ range of 10-60° or 10-80° (Rigaku MiniFlex600, CuKα radiation). The morphologies of particles were characterized by scanning electron microscopy (SEM, JEOL JSM78500F) and transmission electron microscopy (TEM, Philips Tecnai-F20). The ionic conductivities of different electrolyte were performed by an impedance analyzer (PARSTAT 2273 electrochemical workstation) with an amplitude of 5 mV over the frequency range from 100 kHz to 100 mHz. Fourier transform infrared spectroscopy (FTIR) were tested at 25 °C in the range of 1800-1100 cm-1 (Bruker Tensor II Sample Compartment RT-DLaTGS). The content of carbon in the NVP@C was measured by thermogravimetric analyzer (NETZSCH, STA 449F3). Electrochemical measurements. The cathode electrodes were prepared by mixing 80 wt% NVP@C with 10 wt% Super P and 10 wt% binder (polytetrafluoroethylene, PTFE) using ethanol as solvent. The ALO anode electrodes were fabricated by mixing 40 wt% ALO with 20 wt% of Super P and 20 wt% PTFE. The ALO/CMK-3 anode electrodes were prepared by mixing 80 wt% ALO/CMK-3 and 20 wt% PTFE. The as-prepared electrodes were cut into squares (12 mm in length) or circles (10 mm in diameter) and pressed on stainless steel mesh at a pressure of 10 MPa using a manual hydraulic press, then dried inside a vacuum oven at 60 °C overnight. The 6 ACS Paragon Plus Environment

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mass loading of the active materials in each cathode and anode is ca. 2.2-3.3 and 1-1.5 mg cm-2, respectively. The capacity ratio of anode and cathode is about 0.8: 1. The three-electrode devices for cyclic voltammetry (CV) consist of NVP@C or ALO electrodes on stainless steel mesh as working electrode, a large piece of pure platinum as the counter electrode, and saturated calomel electrode (SCE) as the reference electrode. The electrolyte was 1 M CF3SO3Na aqueous solution purged with Ar flow for 1 h before use. The full batteries with CR2032-type were assembled in Ar filled glovebox using NVP@C cathode, ALO/CMK-3 anode, and 1 M CF3SO3Na aqueous solution or hydrogel with different solid content as electrolyte. The charge/discharge capacities are based on the mass of the active materials (ALO) in the anode. CV tests of full batteries were performed using a CHI 660E electrochemical workstation (ChenHua, Shanghai, China). Land CT2001A cell testing system was used to test galvanostatic charge/discharge within the voltage range of 0.5-1.6 V at different current rates. Electrochemical impedance spectra (EIS) were conducted by an impedance analyzer (PARSTAT 2273 electrochemical workstation) with an amplitude of 5 mV over the frequency range from 100 kHz to 100 mHz at 25 °C. RESULTS AND DISCUSSIOIN The schematic diagram and redox mechanism of the full batteries are shown in Figure 1. The anode of the full batteries is the composite of commercial ALO and CMK-3. The IR of ALO in Figure 2a shows the absorption peaks of C=O, C=N, and C=C, indicating high purity of the raw materials. From Figure S1 (Supporting Information), we can know that the commercial ALO is composed of bars with about 300 nm in length. In order to confirm the working potential of ALO, we conduct the cyclic voltammetry (CV) tests by using ALO, pure platinum, and saturated calomel electrode (SCE) as working, counter, and reference electrode, respectively. As shown in 7 ACS Paragon Plus Environment


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Figure S2, ALO exhibits a cathodic peak at -0.88 V (vs SCE), and the corresponding anodic peak appears at -0.74 V (vs SCE). Moreover, there is no hydrogen evolution during the reduction process of ALO. The relatively low redox potential of ALO would contribute to realize high output voltage of the full batteries with ALO as anode active materials.

Figure 1. The schematic diagram and redox mechanism of the full ARSIBs with polyacrylamide hydrogel electrolyte, ALO/CMK-3 anode, and NVP@C cathode. To enhance the conductivity of ALO, we use the highly conductive CMK-3 to combine with ALO by a simple impregnation method. CMK-3 has been widely used as both conductive and suitable matrix due to its well-ordered porous network, large specific surface area, and large pore volume.31-32 The mass ratio of ALO and CMK-3 in the composite is 1:1. Figure 2b displays the powder X-ray diffraction (XRD) patterns of pure ALO, CMK-3 and the as-prepared composite (ALO/CMK-3). We can know that ALO shows multiple peaks of varying intensity, indicating that ALO has obvious crystal state. The XRD pattern of CMK-3 shows a broad peak at 22.71°, 8 ACS Paragon Plus Environment

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which is assigned to the (002) crystal face.31 For the ALO/CMK-3 composite, no sharp diffraction peaks of ALO can be observed, which implies that ALO is well-dispersed in the nanochannels of CMK-3.32

Figure 2. Characterization of pristine ALO and the ALO/CMK-3 composite, respectively. (a) IR spectrum of commercial ALO. (b) XRD patterns of ALO, CMK-3 and ALO/CMK-3 composite. The successful encapsulation of ALO in CMK-3 can be further confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM image of pristine CMK-3 in Figure 3a exhibits well-ordered nanoscaffolds of CMK-3. After impregnation with ALO, the surface of CMK-3 becomes smooth, which suggests that the pores are filled with ALO (Figure 3b). The TEM image of CMK-3 in Figure 3c clearly shows its nanochannel structure. The restriction of ALO in CMK-3 nanochannels can be seen in the TEM image of ALO/CMK-3 (Figure 3d). The above results demonstrate that ALO has been successfully encapsulated in the nanochannels of CMK-3.



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Figure 3. SEM images of (a) pristine CMK-3, and (b) ALO/CMK-3 composites. TEM images of (c) pristine CMK-3, and (d) ALO/CMK-3 composites. The cathode of the full ARSIBs is NVP@C, which was obtained by a hydrothermal assisted sol-gel approach according to the previous report.33 NVP exhibits the NASICON structure with an R3c space-group (Figure 4a). XRD pattern of the obtained NVP@C sample is shown in Figure 4b. The results reveal that the diffraction peaks of synthesized NVP@C are well in agreement with the standard JCPDF card (No. 53-0018, a = 8.72 Å and c = 21.76 Å). From the SEM image of NVP@C (Figure 4c), we can know that NVP@C exists in the form of homogeneous nanoparticles with an average size of 40 nm. Moreover, the nanoparticles seem to arrange themselves to form inter-particle voids, resulting in large specific surface area. The large specific surface area is favorable to enhance the contact between electrode materials and electrolyte, and thus effectively promote ions diffusion during charge and discharge processes. The thermogravimetric curve of the NVP@C sample under air atmosphere in Figure 4d indicates that the carbon content in the composite is about 13 wt%. The CV curve of NVP@C in Figure S2 reveal that there is a pair of distinct redox peaks (0.34, 0.52 V), without oxygen evolution.


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Figure 4. (a) Crystal structure of NASICON Na3V2(PO4)3. (b) XRD pattern, (c) SEM images, and (d) TG curve (in air) of prepared Na3V2(PO4)3@C. The electrolyte of the full ARSIBs is polyacrylamide hydrogel. The detailed preparation of the hydrogel can be seen in the Experimental Section. Polyacrylamide hydrogel is composed of crosslinked polymer chains, CF3SO3Na and H2O. The crosslinked structure is beneficial for water retention and enhancing mechanical properties.33-34 The chemical structure of the polyacrylamide hydrogel can be seen in Figure 1. The IR spectrum of the hydrogel is shown in Figure S3. The absorption peaks of C=O (1669 cm-1), N-H (3200, 1608 cm-1) and O-H (3350 cm1

) all appear, indicating the successful synthesis of the polyacrylamide hydrogel.35-38 As shown in Figure 5a, the obtained hydrogel membrane is self-standing and transparent. The

thickness of the hydrogel is about 300 µm (Figure 5b). The elemental mappings of the hydrogel in Figure 5c display that the elements of F, S, O, Na, and N distribute homogeneously in the 11 ACS Paragon Plus Environment


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hydrogel. The homogeneous distribution of the F, S, Na elements from CF3SO3Na salt and the N element from polyacrylamide indicates that the salt is well dissolved in the polyacrylamide hydrogel. Prior to further investigation, we study the properties of hydrogels with different solid contents. Figure S4 shows the electrochemical impedance spectra (EIS) of the hydrogels with different solid contents. Note that the electrolyte with solid contents of 0% means the liquid electrolyte of 1 M CF3SO3Na aqueous solution. According to the EIS results, we can obtain the ionic conductivity of different hydrogels.39-43 As shown in Figure 5d, the ionic conductivity of the hydrogels decreases with the increase of solid content due to the less and less H2O in the hydrogel. The ionic conductivities (25 °C) of the hydrogels with solid contents of 60% and 63% are 1.18 and 0.35 mS cm-1, respectively. We then study the electrochemical stability window of the hydrogels with different solid contents by using three-electrode devices consisting of Ti foil as working electrode and counter electrode, saturated calomel electrode (SCE) as reference electrode. The linear sweep voltammograms (LSV) of different hydrogels at a scan rate of 5 mV s-1 are shown in Figure 5e. Potential has been converted to Na/Na+ reference for convenience. The electrochemical stability window of 1 M CF3SO3Na aqueous solution is about 4.2 V. Polyacrylamide hydrogel is a kind of water swelling type functional polymer material with three-dimensional network structure which exhibits a superior water-retention ability. With the increase of solid content, the overall stability window expands, which may be attributed to the decreased free water molecules in the solvation sphere of Na+ and the reduced electrochemical activity of water.44-47 In particular, the stability window of the hydrogels with solid contents over 55% could extend to 5 V. Cross-link initiator


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and accelerator cannot cause the side reactions and compromise the window (Figure S5). The extended stability window is helpful to avoid side reactions during discharge/charge processes.

Figure 5. Physicochemical properties of different hydrogel electrolyte. (a) Optical photograph, (b) cross-sectional SEM image, and (c) elemental mappings of the elementals F, S, O, Na, N of a typical polyacrylamide hydrogel film. (d) Ionic conductivity of the hydrogels with different solid contents (25 °C). (e) LSV curves of batteries with different solid contents at a scan rate of 5 mV s-1. In order to optimize the hydrogels with different solid contents, we fabricated the full ARSIBs with different hydrogels as electrolyte, ALO as anode, and NVP@C as cathode. In the full batteries, the mass ratio of anode and cathode electrode is about 1:2.2, implying the batteries are



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anode-limited types. The discharge/charge capacities are based on the mass of ALO in the anode. The full batteries first charge and then discharge. Figure 6a shows the typical charge/discharge curves of the batteries with different kinds of electrolyte in the voltage range of 0.5-1.6 V at 1 C. The initial charge capacities of all the batteries are close to 153 mA h g-1, indicating the insoluble properties of ALO in H2O. However, the initial discharge capacity of the batteries with 1 M CF3SO3Na aqueous solution is only 77 mA h g-1, corresponding to low Coulombic efficiency of 50 %. This is due to the serious dissolution issue of the sodiated ALO, which is demonstrated by the fact that the electrolyte turns yellow after initial charging process (Figure S6). Figure S7 shows the UV-Vis spectra of 1 M CF3SO3Na aqueous electrolyte (pristine and after initial charging process). Compared with pristine electrolyte, two absorption peaks which can be attributed to the sodiated ALO with conjugated structure appear in the UV-Vis spectra of the electrolyte after charging process.48 The results demonstrate the dissolution of sodiated ALO in H2O. With the increase of solid content in the hydrogel (35 to 60%), the initial discharge capacity of the batteries becomes higher and higher. In particular, the batteries deliver the highest initial discharge capacity of 149 mA h g-1 when the solid content of the hydrogel is 60%. Figure S3 shows the IR spectrum of hydrogel electrolyte with solid contents of 60% before and after initial charging process. Compared with pristine electrolyte, no new absorption peak comes up in the infrared absorption spectra of the electrolyte after charging process. Furthermore, the color of hydrogel electrolyte does not change after the initial charging process (Figure S8). The results show that hydrogel electrolyte with solid contents of 60% inhibits the dissolution of sodiated ALO in H2O. Therefore, sodiated ALO is difficult to dissolve into the electrolyte, exhibiting a more excellent electrochemical


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performance. However, when the solid content increases to 63%, the initial discharge capacity decreases, which may be due to the low ionic conductivity of the hydrogel (0.35 mS cm-1). The cycling performance of different batteries becomes better and better with the increase of solid content (Figure 6b). When the solid content of hydrogel is 60%, the batteries still remain a reversible capacity of 146 mA h g-1 after 10 cycles with a high capacity retention of 99%. The results reveal that the polyacrylamide hydrogel with high solid content is very helpful to suppress the dissolution of sodiated ALO in H2O. Figure 6c displays the Coulombic efficiency of different batteries. In aqueous solution or hydrogel with low solid contents such as 35%, the Coulombic efficiency is relatively low, indicating the dissolution of the sodiated ALO is serious. By contrast, the Coulombic efficiency could reach nearly 97% after 30 cycles when the solid content is higher than 60%. Considering the specific capacity, cycling stability, and Coulombic efficiency of different batteries, we select the hydrogel with solid content of 60% as the optimized one for further study. Subsequently, we investigate the electrochemical performance of the full ARSIBs with the optimized hydrogel as electrolyte, ALO/CMK-3 as anode, and NVP@C as cathode. Figure 6d shows the CV curves of the full batteries at a scan rate of 0.1 mV s-1. Two well-defined peaks can be observed at 1.19 V (oxidation) and 1.03 V (reduction) and there are no other peaks of side reactions in the whole voltage window of 0.5-1.6 V. In addition, the oxidation/reduction peaks remain unchanged upon cycling, indicating the redox reactions in the batteries are reversible and stable.



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Figure 6. Optimization of different hydrogels and electrochemical performance of the full batteries. (a) Initial charge/discharge curves, (b) cycling performance, and (c) corresponding Coulombic efficiency of the batteries consisting of ALO anode, and hydrogel electrolyte with different solid contents at 1 C. (d) CV curves of the batteries with ALO/CMK-3 anode and hydrogel electrolyte (solid content of 60%) at a scan rate of 0.1 mV s-1. (e) Rate performance, and (f) cycling stability at 2 C rate of the batteries with ALO or ALO/CMK-3 anode and hydrogel electrolyte (solid content of 60%). Figure 6e shows the rate performance of the full batteries with ALO and ALO/CMK-3 anode. At every same current rate, the capacities of the batteries with ALO/CMK-3 anode are higher that of the batteries with ALO anode. In particular, the batteries with ALO/CMK-3 anode deliver reversible discharge capacity of 161, 156, 153, 150, 146 mA h g-1 at 1, 2, 3, 5, 10 C, respectively. The reversible discharge capacity of the batteries can return to 154 mA h g-1 when the current rate recovers to 1 C after 30 cycles. However, the discharge capacity of the batteries with ALO anode is only 135 mA h g-1 at 10 C, and it just turns back to 147 mA h g-1 when the rate recovers 16 ACS Paragon Plus Environment

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to 1 C. The results indicate that the introduction of CMK-3 could enhance rate capability of the batteries due to the high conductivity of CMK-3. We further investigate the cycling performance of the full batteries with ALO and ALO/CMK3 anode (Figure 6f). The discharge capacity of the batteries with ALO/CMK-3 could retain 144 mA h g-1 after 100 cycles at 2 C, corresponding to a capacity retention of 90%. However, the discharge capacity of the batteries with ALO anode only maintains at 118 mA h g-1 after 100 cycles. The better cycling performance of the batteries with ALO/CMK-3 anode could be attributed to the mesoporous CMK-3, where ALO is embedded in the nanochannel structure. The well encapsulated structure of the ALO/CMK-3 anode is beneficial for mitigating the dissolution of sodiated ALO. Compared with other reported ARSIBs (Table S1), the batteries with ALO/CMK-3 as anode, polyacrylamide hydrogel as electrolyte, and NVP@C as cathode exhibit a high energy density of 50 W h kg-1 (based on the total mass of the active electrode materials). Finally, we investigate the structural evolution of ALO during the charge/discharge processes in the full batteries. The IR spectra of ALO in different charge/discharge state are shown in Figure S9. We mainly focus on the stretching vibration of C=N bond in ALO. In the charge process, the peak assigned to the stretching vibration of C=N bond became weak and almost indiscernible when the battery charged to 1.6 V, implying the formation of Na2ALO. In the subsequent discharging process, the peak assigned to the stretching vibration of C=N bond recovered gradually and became obvious at the full discharge state (Figure S9). The change of the stretching vibration of C=N bond indicates that the C=N groups are active sites, and the redox reaction of ALO molecules can be regarded as reversible bonding of Na with ALO. The reversible structural evolution of ALO during charge/discharge processes is well consistent with



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the results in the half sodium batteries with organic electrolyte.13 The detailed reaction equations during charge/discharge processes can be seen in Figure 1. CONCLUSION In summary, we have successfully fabricated aqueous full batteries using polyacrylamide hydrogel with solid content of 60% as electrolyte, ALO/CMK-3 as anode, and NVP@C as cathode. Benefiting from the crosslinked structure of hydrogel and nanochannels of CMK-3, the dissolution problem of sodiated ALO could be inhibited effectively. The aqueous batteries exhibit a capacity retention of 90% after 100 cycles at 2 C, which is much higher than that with aqueous solution electrolyte. Moreover, the aqueous batteries show high rate capability of 146 mA h g-1 at 10 C due to the introduction of highly conductive CMK-3. Meanwhile, the aqueous batteries could deliver a high average discharge voltage of 1.03 V and an energy density of 50 W h kg-1 based on the total mass of the active electrode materials. Our work illustrates the applications of high-capacity organic anode and hydrogel electrolyte for high-performance aqueous rechargeable sodium-ion batteries.

ASSOCIATED CONTENT Supporting Information SEM images, CV curve, infrared spectra, UV-Vis spectra, electrochemical impedance spectra, LSV curves, ex situ IR spectra. Figures S1 to S9 and Tables S1. (PDF) AUTHOR INFORMATION Corresponding Author 18 ACS Paragon Plus Environment

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*E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Projects of MOST (2017YFA0206700 and 2016YFB0901502), NSFC (21673243), MOE 111 (B12015), Tianjin Key (16PTSYJC00030).

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Synopsis: Aqueous sodium-ion batteries with polyacrylamide hydrogel electrolyte and ALO/CMK-3 anode show good electrochemical performance.


High-Performance Aqueous Sodium-Ion Batteries with Hydrogel

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