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3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices
Science Bulletin xxx (xxxx) xxx
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Article
3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices Jian Gou a,1, Yuxiao Wang b,1, Hongzhang Zhang a,⇑, Yeqiang Tan b, Ying Yu a,c, Chao Qu a, Jingwang Yan a, Huamin Zhang a, Xianfeng Li a,⇑ a b c
Division of Energy Storage Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China State Key Laboratory of Bio-Fibers and Eco-Textiles, Institute of Marine Biobased Materials, School of Materials Science and Engineering, Qingdao University, Qingdao 266071, China University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e
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Article history: Received 6 November 2019 Received in revised form 21 December 2019 Accepted 8 January 2020 Available online xxxx Keywords: Selective deposition Multi-dimensional deposition Weldability High conductivity Flexible batteries
a b s t r a c t Flexible and Personalizable battery is a promising candidate for energy storage, but suffers from the weldablity and large-scale producibility of the electrode. To address the issues, we design a nickel foam catalyzed electroless deposition (NFED) derived 3D-metal-pattern embroidered electrodes. This is the first attempt to utilize this type of electrode in battery field. It’s found that the current collector can be embroidered on any selected areas of any complex-shape electrodes, with high controllability and economical feasibility. As a result, the electronic conductivity of the flexible electrodes can be improved by nearly one order of magnitude, which can be easily and firmly weldded to the metal tab using the industry generic ultrasonic heating process. The embroidered electrodes could substantially promote the electrochemical performance under bending deformation, with both Li-S and Li-LiFePO4 batteries as the models. This innovation is also suitable to embroider all the VIII group elements on any electrodes with personalized shapes, which is widely attractive for the development of next generation flexible and personalizable energy storage devices. Ó 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
1. Introduction Flexible and personalized electronics such as smart clothes, rollup displays and implantable biosensors are ushering a booming market [1–11]. It has triggered an urgent need for various electronic components, such as bendable screen, personalized shell, and flexible energy storage devices. Over the past several years, most of the related flexible components and techniques have been developed, such as development of plastic substrates for flexible display [12], and 3D printing technique for personalized shell [13]. However, it’s still unrealistic to manufacture flexible energy storage devices in large-scale with high performance and low cost. It’s mainly caused by several technical difficulties, including: (1) to combine the electrode with current collectors owning satisfactory electronic conductivity, flexibility and bonding strength; (2) to weld the electrode with external tabs tightly; (3) to manufacture flexible electrodes with personalized shapes or structures [14,15]. In order to solve this series of technique problems, metal nano ⇑ Corresponding authors. 1
E-mail addresses: [email protected] (H. Zhang), [email protected] (X. Li). These authors contributed equally to this work.
particles and carbon nano particles are usually added onto the surface of the electrodes with methods like sputtering, spray painting, electrodeposition, electroless deposition and etc. [16–20]. Among these methods, the electroless deposition technique is recognized as an advanced and universal one, due to its outstanding low cost and compatibility with electrodes of any shape. And we also developed a quasi-stable electroless technique or flexible Li-S batteries with satisfactory electrochemical performance and flexibility [21]. However, neither the electroless deposition nor other techniques mentioned above can meet requirements of electrodes with personalized or non-standard shapes, such as alphabet, LOGO or other complicated shapes. Herein, a nickel foam catalyzed electroless deposition (NFED) technique is proposed for the first time to solve this issue. As shown in Fig. 1, this technique can embroider multi-dimensional metal patterns on any selected areas of the electrode, attributed to the priority of electroless growth at the spots where nickel foam/electrodes contacts. The nickel foam can initiate and catalyze electroless deposition reaction and it works similarly as a reverse template in the screen-printing field. The embroidered pattern is not only capable of fulfilling effective current collection but also can be easily weld with metal tab in the external circuit to solve
https://doi.org/10.1016/j.scib.2020.01.022 2095-9273/Ó 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 1. (Color online) Schematic illustration of embroidering Ni-P conductive layers on flexible electrodes by nickel foam initiated electroless deposition.
current collection issues for personalizable and flexible energy storage devices. As a result, it could improve the conductivity of the electrodes by one order of magnitude, and it could also improve the tough deformation tolerance and welding strength of the electrodes as well. Take the Sulfur/Carbon electrodes (cathode for Li-S battery) and LiFePO4 electrodes (cathode for Li-ions battery) as the models, their electrochemical performance can also be drastically increased [22–28], pespecially under bending deformation in the large area (5.0 cm 8.0 cm) soft package battery type. Besides that, the embroidered metal atoms, such as nickel, can further bring other advantages such as anchoring the polysulfide and catalyze the polysulfide reaction process in the Li-S batteries [14,15]. As should be noted that, almost all the VIII group elements (Fe, Co, Ni, Rh, Pd and Pt) could be modified on this kind of electrodes [29], which might also arouse the interest of readers in electrochemical catalysis fields and energy storage fields [30]. The whole process of electrode preparation and performance characterization is carried out with Li-S and Li-LiFePO4 battery as the model system. 2. Materials and methods
2.2. Electroless Ni-P deposition on S/C electrode S/C composites and PVDF-HFP with a weight ratio of 2:1 were first mixed with 1-methyl-2-pyrrolidinone (NMP). The obtained slurry was then uniformly coated onto glass plate and immersed into water to obtain original free-standing S/C electrodes (FSC). The FSC@Ni is prepared by means of nickel foam catalyzed electroless deposition (NFED) on the FSC. The detailed process is like this: firstly, arrange the foamed nickel, electrodes, and glass plates in the order mentioned, and fix them with rubber bands, and secondly dipping the FSC and nickel foam into electroless bath. The temperature of electroless bath is maintained at 65 and 85 °C separately. Electroless deposition bath for Ni-P is prepared by dissolving NiSO46H2O (25 g L–1), Na3C6H5O7H2O (15 g L–1), CH3COONa (15 g L–1) and NaH2PO2H2O (15 g L–1) in water with pH controlled at 4.8. Electroless Co-P bath is prepared by dissolving CoSO47H2O (25 g L–1), Na3C6H5O7H2O (15 g L–1), (NH4)2SO4 (20 g L–1) and NaH2PO2H2O (20 g L–1) in water with pH controlled at 9. When the whole process is complete, the nickel foam will be removed from the electrodes. The thickness of the nickel is about 1.4 mm, and the pore size is about 400 lm.
2.1. Preparation of S/C composite
2.3. Electroless Ni-P deposition on LiFePO4 electrode
S/C composites were prepared as follows: Firstly, 10 g pristine KB nanoparticles were transferred into the furnace and heated to 900 °C at 5 °C min 1 under argon atmosphere. Then, the temperature was kept constant for 90 min with a flux of water steam (600 mL min 1). And then the activated KB nanoparticles can be obtained, after cooling down to room temperature. Secondly, the activated KB nanoparticles and sulfur were mixed at weight ratio of 1:3 and ball milled for 6 h, the composites were then put into the furnace and heated at 155 °C for 15 h in argon filled vessel. Finally, the S/C composites containing 75 wt% S were obtained. The content of S was calculated via TGA, shown in Fig. S19 (online).
LiFePO4 nanoparticles, PVDF-HFP and conductive additives Super P with a weight ratio of 4:1:1 were first mixed with 1methyl-2-pyrrolidinone (NMP) to form a slurry. Free-standing LiFePO4 electrodes (LFP) were obtained by phase inversion process (LiFePO4 loading is 4 mg cm 2), similar as FSC. LFP@Ni is fabricated by means of NFED as FSC@Ni did, which is mentioned above. The observation of Ni-P extension growth on flexible S/C electrodes was conducted with optical microscope (VK-8510, KEYENCE) at different immersion time in electroless bath. Looking for the same scratch under the optical microscope to ensure that we observe the same area.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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2.4. Materials characterization The scanning electron microscopy (SEM, JSM-7800F, QUANTA 200 FEG and Hitachi SU-1510) was used to observe the morphology and elemental analysis of the samples. The crystal structure of the synthesized samples was studied by X-ray diffraction (XRD) using a powder X-ray diffractometer (Regaku Ultima IV) with Cu Ka radiation at k = 1.541 Å in the 2h range of 10°–70°. The conductivity of samples was measured by the four-probe method using a digital Four-Probe resistivity tester (SX1934 (SZ82), Suzhou Dianxun Instrument Factory). Contact angles of prepared coatings were obtained by using a sessile drop method with a JC-2000D contact angle analyzer. The sulfur content of FSC@Ni electrodes was determined by using thermogravimetric analysis (TGA, Pyris-Elmer). The temperature rises from 50 to 500 °C at a heating rate of 5 °C min 1 under N2 atmosphere. 2.5. Electrochemical measurements The electrochemical performance test was first tested on Li-S coin cell and Li-S soft package batteries. The sulfur loading of the cathode was about 6.5 mg cm 2 and 12 mg cm 2 for CR2016 coin cells (U10 mm) and 6.5 mg cm 2 for flexible soft package batteries (20 mm 15 mm), which were assembled with the anode (lithium foil) and Celgard 2325 membrane in an Ar-filled glove box. The electrolyte contains 1 mol L–1 bis(trifluoromethylsulfonyl) imide (LiTFSI) in 1,2-dimethoxymethane (DME)/1,3-dioxolane (DOL) (1:1, v/v) with 5 wt% LiNO3 additive. Meanwhile, Li-LiFePO4 coin cell and Li-LiFePO4 soft package batteries were assembled to test electrochemical performance. The LiFePO4 loading of the cathode was about 4 mg cm 2 for CR2016 coin cells (U10 mm) and flexible soft package batteries (20 mm 25 mm), which were assembled with the anode (lithium foil) in an Ar-filled glove box using a Celgard 2325 membrane as a separator and 1 mol L–1 LiPF6 in ethylene carbonate, diethyl carbonate and ethyl methyl carbonate (EC/DMC/ EMC, 1:1:1, vol.) as the electrolyte. The electrochemical impedance spectroscopy (EIS) measurement was conducted at open-circuit condition. The frequency ranges from 3.0 106 to 1.0 10–1 Hz with the amplitude of 10 mV on a Solartron 1287 electrochemical work station. The charge/discharge test was carried out through LAND CT-2001A system. The voltage arranges from 1.85 to 2.8 V for coin cell and flexible soft package Li-S batteries. And 2 to 4.2 V were chosen for coin cell and flexible soft package LiLiFePO4 batteries. All measurements were carried out at a temperature of 25 °C. 2.6. Ultrasonic welding process The Ni-P embroidered electrode was welded with Nickel tab by untrasonic welding instrument (PC750-1ZHENJIANG Tian Hua electromechanical company) conducted at 600 Watts. 2.7. Peeling test The peeling force test was measured according to our previous report [31]. In detail, metal tab and FSC@Ni were clamped to the tension tester AG-2000A (Shimadzu) tightly. Then a pulling force was applied between FSC@Ni and metal tab, until they were totally separated. All the samples were tested using a programmed elongation rate of 50 mm min 1 at room temperature. 2.8. Tensile stress-strain test FSC and FSC@Ni were fabricated and cut into 1 cm 7 cm strip. After that, the electrodes were clamped to the tension tester AG2000A (Shimadzu) tightly. Then, a pulling force was applied into
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both ends of the electrodes until they broke. All the samples were tested using a programmed elongation rate of 1 mm min 1 at room temperature. 2.9. Polysulfide diffusion visual test The polysulfide solution (taking Li2S6 on behalf of lithium polysulfides) was prepared by chemically reacting sublimed sulfur and an appropriate amount of lithium sulfide in 1,2-dimethoxyethane solution to form Li2S6 (0.2 mol L–1) in the solution. The solution was then stirred at 40 °C in an Ar-filled glove box overnight to produce a brownish-red Li2S6 solution. The Li2S6 solution was then diluted to 10 mmol L–1 for the polysulfide diffusion test. Two pieces of FSC@Ni and FSC with the diameter of 16 mm were first placed fitly at the bottom of the syringe, respectively, and then 1 mL diluted Li2S6 solution was added into the injection syringe. The polysulfide (Li2S6) will diffuse across the FSC or FSC@Ni to outside of the injection syringe, where a glass bottle was layed up and filled with 1,2-dimethoxyethane (DME) to collect polysulfide solution. The resulting color change was evaluated by visual examination at variable time. 3. Results and discussion The mechanism of NFED method is first studied to illustrate its capability of depositing metal patterns selectively and multidimensionally. Here, it is verified in Li-S batteries, via embroidering Ni-P pattern on flexible S/C electrodes. As far as we know, it is the first time to employ nickel foam and prove its priority of electroless growth in the area where nickel foam covered, contributing to highly controllable and selective deposition. And there are three key points why nickel foam is employed here (Fig. 1). For one point, nickel foam can provide abundant catalytic sites at the electrode surface for autocatalytic Ni-P electroless deposition when nickel foam contacts tightly with S/C electrodes. The Ni can lead to dehydrogenation of hypophosphite in the electroless bath and produce active hydrogen [H] (Eq. (S1) online), which would further reduce Ni2+ into Ni0 (trace amount of phosphate would be reduced into P0) and deposit on the S/C electrodes [32]. For another point, the porous structure of nickel foam can facilitate the influx of electroless solution to the nickel foam/electrode interface and provide sufficient nickel sources and reductants. As a result, the metal electroless deposition can be very accurate and controllable, compared with the traditional electroless deposit methods which need to implant metal catalysts [18,33]. As shown in Fig. 2a, the Ni-P deposition occurred in priority on the nickel foam covered areas, and then the pattern slowly spread on the blank area of S/C electrodes due to its autocatalytic electroless deposition. The extension growth of Ni-P pattern was captured by optical microscope along with its immersion time increasing in the electroless bath, shown in Fig. 2b. Spreading rates of Ni-P pattern can be controlled by tuning the temperature and the concentration of the electroless bath (Fig. 2a). As a result, NFED technique is as controllable as Chinese embroidering, which can selectively deposit arbitrary-shaped Ni-P pattern on the electrode such as ‘‘NFED” letters shown in Fig. 1, where also shows arbitraryshaped 2D and 3D electrodes covered with Ni-P pattern uniformly. Therefore, this novel method suits for different types of flexible electrodes such as shape-conformable, fiber-shaped or even complex-shaped electrodes in personalization energy storage devices [2,4,11]. In addition, the Ni particles deposit sites could be exactly controlled on the electrode instead of the membrane, due to their great difference in electrical insulation (Fig. 1). During the whole process, the nickel foam only plays a role in initiating and controlling the electroless reaction. When the electroless
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 2. (Color online) (a) selective deposition of Ni-P pattern on S/C electrodes controlled by configuration of nickel foam, and spreading depostion rate controlled by concentration (composition of C0 shown in experimental section) and temperature of electroless bath; (b) spreading growth of Ni-P pattern on S/C electrodes captured by optical microscope (the white bar represents 200 lm).
depostion finished, the nickel foam will be moved away from electrodes. In order to fabricate highly flexible and personalizable electrodes, free-standing flexible S/C substrates (FSC) were prepared by phase inversion method first, which can construct ‘‘tricontinuous porous structure” with fast ion transportation and high flexibility, according to our previously work [31] (Fig. 3a and 3c). And then the desired Ni-P pattern was deposited on the flexible S/C electrode by NFED, which is named as FSC@Ni as shown in Fig. 3b and 3d. Due to the high quality deposition control of Ni particles, the thickness of the Ni layers on the S/C electrodes is only about 1 lm, with areal density of only 0.7 mg cm 2, much lighter than the traditional Al foil with thickness of 12–16 lm (areal density of 3.2–4.2 mg cm 2). In addition, the Ni-P pattern can not only deposit on the surface of the electrode, but also permeate deep inside (Fig. S1 online). This finally forms a 3D framework with high electric conductivity, which can efficiently accelerate the current collection of the whole electrode. As a result, the conductivity of S/C electrodes is increased by one order of magnitude (Table S1 online), while its flexibility is still kept excellent (Fig. S2 online). The NFED can also change the polarity of electrode, which could enhance the wettability between electrode and water (Fig. S3 online), and enhance the polysulfide confine ability (Fig. S5 online), attributed to the formation of polar metal sulfides (Ni-S compounds) during the electroless deposition process (Fig. S4 online) [19,34].
Due to the increase of electric conductivity, the electrochemical performances of FSC@Ni were enhanced as well. The electrochemical impedance spectroscopy (EIS) is tested to reveal the charge transfer kinetics of electrodes. Both plots are consisted of a semicircle and a sloping line as usual, in which the intercept of real impedance (Z’) corresponds to the resistance of cell components (Rs) while the diameter of the semicircle is associated with the charge transfer resistance (Rct) at electrode/electrolyte interface, and the inclined line is related to the Warburg inpedence (Wo). The charge transfer resistance (Rct) of FSC@Ni (sulfur loading of 6.5 mg cm 2) was one order of magnitude less (44.3 X cm 2) than that of FSC (320.0 X cm 2), according to the electrochemical impedance spectroscopy (EIS) characterization (shown in Fig. 3e and Table S2 online). Furthermore, compared with FSC, FSC@Ni show more complete CV cathodic peaks at about 2.3 V and 2.0 V, corresponding to the transition between S and soluble lithium polysulfides (Li2Sx, 4 x 8), as well as the transition between lithium polysulfides (Li2Sx, 4 x 8) and Li2S/Li2S2, respectively. In addition, FSC@Ni also show more complete anodic peaks at approximately 2.4 V, corresponding to the oxidation of Li2S/Li2S2 to Li2S8 (shown in Fig. 3f) [30]. As expected, performance of Li-S battery assembled with FSC@Ni is far better than that assembled with FSC (Fig. 3g). The FSC@Ni reached initial discharge capacity of 1341 mAh g 1 and retained 1000 mAh g 1 after 100 cycles, however, the batteries assembled with FSC cannot be fully charged and discharged (both with sulfur loading of 6.5 mg cm 2).
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 3. (Color online) (a) Surface and (c) cross-sectional morphology of FSC; (b) surface and (d) cross-sectional morphology of FSC@Ni; (e) EIS plots of the coin cells assembled with FSC and FSC@Ni before cycling. Inset is equivalent circuits; (f) the CV curves of FSC, FSC@Ni plotted within the potential ranging from 1.7 to 2.9 V at a scanning rate of 0.05 mV s 1; (g) cycling performance of the coin cells assembled with FSC and FSC@Ni (Sulfur loading of 6.5 mg cm 2) over 100 cycles at 0.1C; (h) cycling performance of the soft package batteries assembled by FSC@Ni (Sulfur loading of 6.5 mg cm 2) at 0.05C.
Meanwhile, FSC@Ni with higher sulfur loading (12 mg cm 2) was also tested, which can still reach to 1150 mAh g 1 for the initial discharge capacity and remain 650 mAh g 1 after 100 cycles at
0.1C (Fig. S6 online). Especially for the flexible soft package Li-S batteries, which demand the electronic conductivity for the most, it’s initial discharge capacity reached to about 1600 mAh g 1
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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(Fig. 3h). A comparison on the areal capacity vs. sulfur loading with previously reported flexible Li-S coin and soft package batteries is listed in Fig. S7 (online) [21,35–45], which show satisfactory battery performance for those assembled with flexible S/C electrodes by means of NFED. In addition, the 3D-metal-pattern embroidered electrodes kept stable after 100 cycles (Fig. S8 online), which demonstrates excellent bonding strength with the electrode substrates although the huge volume change exists in S/C cathode during charge and discharge [39,46]. Another most important thing, for the manufacture and practical application of flexible (or personalizable) electrodes, is their weldability with the external circuit. As for the FSC@Ni, it can be easily welded to the metal tab of the external circuit via sample ultrasonic welding process. And the electric resistance between the welded FSC@Ni and metal tab was decreased by over one magnitude compared with that connected by conductive tapes (from 82.7 to 7.7 X as shown in Fig. 4a). In addition, the binding strength between the welded FSC@Ni and metal tab was also enhanced obviously, which still kept intact with the dragging force between them increasing (Fig. S9 online). Furthermore, peeling strength of the welding point along vertical direction was also excellent, which still keeps integrity and with none active materials peeled off as shown in Fig. 4a (inset). The NFED method is also quite adoptable for the personalizable energy storage devices. Taking the tubeshaped electrodes for example, it can be easily manufactured with NFED method, and can easily light up the commercial lightemitting diode (Fig. 4b inset) with a normal output voltage of 2.6 V (Fig. S10 online). Furthermore, the FSC@Ni electrodes also exhibit excellent flexibility and toughness, as evaluated by tensile stress-strain test (shown in Fig. 4c). The electronic conductivity can be significantly retained simultaneously, ascribed to the strong conductive metal framework in the electrode, which can ensure the excellent battery performance during bending, straining or other deformation process. As for the assembled planar-shaped flexible soft package bat-
teries, it can maintain the same brightness of LEDs under roughly bending deformation (Fig. 4d and video S1 online). Even after bending the pouch battery from 0° to 90° for 100 times, the ohm resistance and charge transfer resistance did not change (Fig. 4e). In order to further evaluate the versatility of NFED method, flexible LiFePO4 electrodes were chosen to assemble flexible lithium ion batteries. Similarly, free-standing flexible LiFePO4 substrates (LFP) were prepared by phase inversion method first, and then deposit with ultrathin yet uniform Ni-P pattern on the electrodes (LFP@Ni), both of which were analyzed by XRD and SEM, shown in Fig.s S11–S14 (online). Compared with LFP, electronic conductivity of LFP@Ni was also one order of magnitude higher than that of LFP, which can be seen in Table S3 (online). And the results of the EIS profile in Fig. 5a revealed that the charge transfer resistance of LFP was significantly reduced after NFED embroidering. Additionally, From Fig. 5b, it can be seen that LFP@Ni show sharper and higher current peak than LFP. The potential gap between redox peaks for LFP@Ni was much narrower than that of LFP, reflecting that NFED embroidering can significantly improve the kinetics of the electrode electrochemical reactions. Meanwhile, the LFP@Ni presented higher discharge capacity at different current densities than FSC especially at 10C, where LFP@Ni can deliver about 100 mAh g 1 but almost none of LFP, shown in Fig. 5c. Furthermore, the pouch batteries assembled with LFP and LFP@Ni (LiFePO4 loading is 4 mg cm 2) were further tested at 0.5C (Fig. 5d). A much higher discharge capacity (154 mAh g 1) was remained for LFP@Ni after 100 cycles, attributed to the effective current collection and integrity of the deposition pattern after cycles, shown in Fig. S15 (online). In addition, cycling performance of pouch battery assembled with LFP@Ni was further tested when bending deformation from 0° to 90° was carried out. As shown in Fig. S16 (online), the cycling performance kept stable before and after bending deformation, demonstrating the toughness and flexibility of LFP@Ni assembled pouch battery.
Fig. 4. (Color online) (a) Measurement of resistance between FSC@Ni and metal tab via ultrasonic welding (left) and conductive tape (right). The inset of (a) is the optical image of welding point of FSC@Ni after peeling test; (b) wearable tube-shaped electrodes before (top) and after (bottom) NFED embroidering (the inserted photograph displays a blue LED lit up by the batteries assembled with tube-shaped FSC@Ni electrodes); (c) Typical tensile stress strain curves of FSC@Ni and FSC (the inset is the photograph of the tensile stress–strain testing instrument); (d) photographs of LED lit by the flexible Li-S soft package batteries with size of 50 mm 80 mm under bending deformation; (e) EIS plots of Li-S soft package battery assembled with FSC@Ni before and after bending from 0° to 90° for 100 times.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 5. (Color online) (a) EIS plots of the coin cells assembled with LFP and LFP@Ni before cycling. Inset is equivalent circuits; (b) the CV curves of LFP, LFP@Ni plotted within the potential ranging from 2 to 4.2 V at a scanning rate of 0.1 mV s 1; (c) c-rate performance of the coin cells assembled with LFP and LFP@Ni at different current densities from 0.5C to 10C; (d) cycling performance of the soft package batteries assembled by LFP and LFP@Ni at 0.5C.
Last but not least, the NFED is capable of embroidering pattern with other metals, such as most of the VIII group elements (Fe, Co, Ni and etc.). Herein, Co-P electroless system was simply adopted and carried out. It is found that the Co-P electroless reaction could be initiated by nickel foam as it did in Ni-P system. And the [H] could reduce Co2+ into Co0 and uniform Co-P pattern was thus deposited on the S/C electrodes by spreading growth attributed to autocatalysis of Co0, shown in Figs. S17 and S18 (online). On this basis, it is worthwhile to conduct more extensive research, rendering NFED extremely attractive for energy storage and electrochemical catalysis fields.
4. Conclusions It is the first attempt to use NFED method to solve the welding and electron collecting issues of flexible electrodes especially with personalized shapes, by embroidering 3D conductive pattern on any targeted areas of any electrodes with high performance and high personalizability. Taking flexible Li-S and Li-LiFePO4 plenary and tube type soft package batteries as example, it simultaneously achieves many benefits, such as one order of magnitude higher conductivity, better and stable electrochemical properties even under bending deformation, strong welding strength and low contact resistance with external circuit, as well as tough deformation tolerance. Additional anchoring effect of polysulfides in Li-S batteries was also found with Ni-P pattern via NFED. As a result, satisfac-
tory battery performance was obtained compared with previously reported flexible Li-S battery related results. What’s more interesting, the NFED of Co-P pattern was also confirmed applicable on the S/C electrodes, and it is also possible to deposit other metals such as VIII group elements in the periodic table (Fe, Co, Ni, Rh, Pd and Pt), rendering it attractive for other energy storage or electrochemical catalysis fields. Declaration of Competing Interest The authors declare that they have no conflict of interest. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51673199, 51677176), Youth Innovation Promotion Association of CAS (2015148), Innovation Foundation of DICP (ZZBS201615, ZZBS201708) and Dalian Science and Technology Star Program (2016RQ026). Author contributions Jian Gou and Hongzhang Zhang designed the experiments. Jian Gou and Yuxiao Wang performed the experiments, analysed the data and prepared the manuscript. Hongzhang Zhang and Yu Ying substantively revised it. Xianfeng Li and Jingwang Yan edited the
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Jian Gou is currently a doctor in Intellectual Property and Technology Transfer Department, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. He received his B.S. degree from Dalian University of Technology in 2010. He received his Ph.D. degree from University of Dundee. His research interests focus on the development of flexible energy storage devices.
Yuxiao Wang is currently a master student in the Materials School of Materials Science and Engineering, Qingdao University. She obtained her B.E. degree in Qingdao University in 2016. Her research is focused on Long-cycle Lithium-Sulfur batteries and the structureactivity relationship between electrode structure and cycle performance.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
J. Gou et al. / Science Bulletin xxx (xxxx) xxx Hongzhang Zhang is currently a professor at the Division of Energy Storage, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. He received his B. S. degree from Shandong University in 2008 and then his Ph.D. degree from University of Chinese Academy of Sciences. His research interests focus on the development of novel batteries with high energy density.
9 Xianfeng Li is a full professor at Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences. He currently serves as Head of Energy Storage Division at DICP. He received his Ph.D. degree in Polymer Chemistry in 2006 form Jilin University. After three years’ postdoctor at KULeuven University, he joined in DICP in 2009. His research interests mainly focus on electrochemical energy storage.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Article
3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices Jian Gou a,1, Yuxiao Wang b,1, Hongzhang Zhang a,⇑, Yeqiang Tan b, Ying Yu a,c, Chao Qu a, Jingwang Yan a, Huamin Zhang a, Xianfeng Li a,⇑ a b c
Division of Energy Storage Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China State Key Laboratory of Bio-Fibers and Eco-Textiles, Institute of Marine Biobased Materials, School of Materials Science and Engineering, Qingdao University, Qingdao 266071, China University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e
i n f o
Article history: Received 6 November 2019 Received in revised form 21 December 2019 Accepted 8 January 2020 Available online xxxx Keywords: Selective deposition Multi-dimensional deposition Weldability High conductivity Flexible batteries
a b s t r a c t Flexible and Personalizable battery is a promising candidate for energy storage, but suffers from the weldablity and large-scale producibility of the electrode. To address the issues, we design a nickel foam catalyzed electroless deposition (NFED) derived 3D-metal-pattern embroidered electrodes. This is the first attempt to utilize this type of electrode in battery field. It’s found that the current collector can be embroidered on any selected areas of any complex-shape electrodes, with high controllability and economical feasibility. As a result, the electronic conductivity of the flexible electrodes can be improved by nearly one order of magnitude, which can be easily and firmly weldded to the metal tab using the industry generic ultrasonic heating process. The embroidered electrodes could substantially promote the electrochemical performance under bending deformation, with both Li-S and Li-LiFePO4 batteries as the models. This innovation is also suitable to embroider all the VIII group elements on any electrodes with personalized shapes, which is widely attractive for the development of next generation flexible and personalizable energy storage devices. Ó 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
1. Introduction Flexible and personalized electronics such as smart clothes, rollup displays and implantable biosensors are ushering a booming market [1–11]. It has triggered an urgent need for various electronic components, such as bendable screen, personalized shell, and flexible energy storage devices. Over the past several years, most of the related flexible components and techniques have been developed, such as development of plastic substrates for flexible display [12], and 3D printing technique for personalized shell [13]. However, it’s still unrealistic to manufacture flexible energy storage devices in large-scale with high performance and low cost. It’s mainly caused by several technical difficulties, including: (1) to combine the electrode with current collectors owning satisfactory electronic conductivity, flexibility and bonding strength; (2) to weld the electrode with external tabs tightly; (3) to manufacture flexible electrodes with personalized shapes or structures [14,15]. In order to solve this series of technique problems, metal nano ⇑ Corresponding authors. 1
E-mail addresses: [email protected] (H. Zhang), [email protected] (X. Li). These authors contributed equally to this work.
particles and carbon nano particles are usually added onto the surface of the electrodes with methods like sputtering, spray painting, electrodeposition, electroless deposition and etc. [16–20]. Among these methods, the electroless deposition technique is recognized as an advanced and universal one, due to its outstanding low cost and compatibility with electrodes of any shape. And we also developed a quasi-stable electroless technique or flexible Li-S batteries with satisfactory electrochemical performance and flexibility [21]. However, neither the electroless deposition nor other techniques mentioned above can meet requirements of electrodes with personalized or non-standard shapes, such as alphabet, LOGO or other complicated shapes. Herein, a nickel foam catalyzed electroless deposition (NFED) technique is proposed for the first time to solve this issue. As shown in Fig. 1, this technique can embroider multi-dimensional metal patterns on any selected areas of the electrode, attributed to the priority of electroless growth at the spots where nickel foam/electrodes contacts. The nickel foam can initiate and catalyze electroless deposition reaction and it works similarly as a reverse template in the screen-printing field. The embroidered pattern is not only capable of fulfilling effective current collection but also can be easily weld with metal tab in the external circuit to solve
https://doi.org/10.1016/j.scib.2020.01.022 2095-9273/Ó 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 1. (Color online) Schematic illustration of embroidering Ni-P conductive layers on flexible electrodes by nickel foam initiated electroless deposition.
current collection issues for personalizable and flexible energy storage devices. As a result, it could improve the conductivity of the electrodes by one order of magnitude, and it could also improve the tough deformation tolerance and welding strength of the electrodes as well. Take the Sulfur/Carbon electrodes (cathode for Li-S battery) and LiFePO4 electrodes (cathode for Li-ions battery) as the models, their electrochemical performance can also be drastically increased [22–28], pespecially under bending deformation in the large area (5.0 cm 8.0 cm) soft package battery type. Besides that, the embroidered metal atoms, such as nickel, can further bring other advantages such as anchoring the polysulfide and catalyze the polysulfide reaction process in the Li-S batteries [14,15]. As should be noted that, almost all the VIII group elements (Fe, Co, Ni, Rh, Pd and Pt) could be modified on this kind of electrodes [29], which might also arouse the interest of readers in electrochemical catalysis fields and energy storage fields [30]. The whole process of electrode preparation and performance characterization is carried out with Li-S and Li-LiFePO4 battery as the model system. 2. Materials and methods
2.2. Electroless Ni-P deposition on S/C electrode S/C composites and PVDF-HFP with a weight ratio of 2:1 were first mixed with 1-methyl-2-pyrrolidinone (NMP). The obtained slurry was then uniformly coated onto glass plate and immersed into water to obtain original free-standing S/C electrodes (FSC). The FSC@Ni is prepared by means of nickel foam catalyzed electroless deposition (NFED) on the FSC. The detailed process is like this: firstly, arrange the foamed nickel, electrodes, and glass plates in the order mentioned, and fix them with rubber bands, and secondly dipping the FSC and nickel foam into electroless bath. The temperature of electroless bath is maintained at 65 and 85 °C separately. Electroless deposition bath for Ni-P is prepared by dissolving NiSO46H2O (25 g L–1), Na3C6H5O7H2O (15 g L–1), CH3COONa (15 g L–1) and NaH2PO2H2O (15 g L–1) in water with pH controlled at 4.8. Electroless Co-P bath is prepared by dissolving CoSO47H2O (25 g L–1), Na3C6H5O7H2O (15 g L–1), (NH4)2SO4 (20 g L–1) and NaH2PO2H2O (20 g L–1) in water with pH controlled at 9. When the whole process is complete, the nickel foam will be removed from the electrodes. The thickness of the nickel is about 1.4 mm, and the pore size is about 400 lm.
2.1. Preparation of S/C composite
2.3. Electroless Ni-P deposition on LiFePO4 electrode
S/C composites were prepared as follows: Firstly, 10 g pristine KB nanoparticles were transferred into the furnace and heated to 900 °C at 5 °C min 1 under argon atmosphere. Then, the temperature was kept constant for 90 min with a flux of water steam (600 mL min 1). And then the activated KB nanoparticles can be obtained, after cooling down to room temperature. Secondly, the activated KB nanoparticles and sulfur were mixed at weight ratio of 1:3 and ball milled for 6 h, the composites were then put into the furnace and heated at 155 °C for 15 h in argon filled vessel. Finally, the S/C composites containing 75 wt% S were obtained. The content of S was calculated via TGA, shown in Fig. S19 (online).
LiFePO4 nanoparticles, PVDF-HFP and conductive additives Super P with a weight ratio of 4:1:1 were first mixed with 1methyl-2-pyrrolidinone (NMP) to form a slurry. Free-standing LiFePO4 electrodes (LFP) were obtained by phase inversion process (LiFePO4 loading is 4 mg cm 2), similar as FSC. LFP@Ni is fabricated by means of NFED as FSC@Ni did, which is mentioned above. The observation of Ni-P extension growth on flexible S/C electrodes was conducted with optical microscope (VK-8510, KEYENCE) at different immersion time in electroless bath. Looking for the same scratch under the optical microscope to ensure that we observe the same area.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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2.4. Materials characterization The scanning electron microscopy (SEM, JSM-7800F, QUANTA 200 FEG and Hitachi SU-1510) was used to observe the morphology and elemental analysis of the samples. The crystal structure of the synthesized samples was studied by X-ray diffraction (XRD) using a powder X-ray diffractometer (Regaku Ultima IV) with Cu Ka radiation at k = 1.541 Å in the 2h range of 10°–70°. The conductivity of samples was measured by the four-probe method using a digital Four-Probe resistivity tester (SX1934 (SZ82), Suzhou Dianxun Instrument Factory). Contact angles of prepared coatings were obtained by using a sessile drop method with a JC-2000D contact angle analyzer. The sulfur content of FSC@Ni electrodes was determined by using thermogravimetric analysis (TGA, Pyris-Elmer). The temperature rises from 50 to 500 °C at a heating rate of 5 °C min 1 under N2 atmosphere. 2.5. Electrochemical measurements The electrochemical performance test was first tested on Li-S coin cell and Li-S soft package batteries. The sulfur loading of the cathode was about 6.5 mg cm 2 and 12 mg cm 2 for CR2016 coin cells (U10 mm) and 6.5 mg cm 2 for flexible soft package batteries (20 mm 15 mm), which were assembled with the anode (lithium foil) and Celgard 2325 membrane in an Ar-filled glove box. The electrolyte contains 1 mol L–1 bis(trifluoromethylsulfonyl) imide (LiTFSI) in 1,2-dimethoxymethane (DME)/1,3-dioxolane (DOL) (1:1, v/v) with 5 wt% LiNO3 additive. Meanwhile, Li-LiFePO4 coin cell and Li-LiFePO4 soft package batteries were assembled to test electrochemical performance. The LiFePO4 loading of the cathode was about 4 mg cm 2 for CR2016 coin cells (U10 mm) and flexible soft package batteries (20 mm 25 mm), which were assembled with the anode (lithium foil) in an Ar-filled glove box using a Celgard 2325 membrane as a separator and 1 mol L–1 LiPF6 in ethylene carbonate, diethyl carbonate and ethyl methyl carbonate (EC/DMC/ EMC, 1:1:1, vol.) as the electrolyte. The electrochemical impedance spectroscopy (EIS) measurement was conducted at open-circuit condition. The frequency ranges from 3.0 106 to 1.0 10–1 Hz with the amplitude of 10 mV on a Solartron 1287 electrochemical work station. The charge/discharge test was carried out through LAND CT-2001A system. The voltage arranges from 1.85 to 2.8 V for coin cell and flexible soft package Li-S batteries. And 2 to 4.2 V were chosen for coin cell and flexible soft package LiLiFePO4 batteries. All measurements were carried out at a temperature of 25 °C. 2.6. Ultrasonic welding process The Ni-P embroidered electrode was welded with Nickel tab by untrasonic welding instrument (PC750-1ZHENJIANG Tian Hua electromechanical company) conducted at 600 Watts. 2.7. Peeling test The peeling force test was measured according to our previous report [31]. In detail, metal tab and FSC@Ni were clamped to the tension tester AG-2000A (Shimadzu) tightly. Then a pulling force was applied between FSC@Ni and metal tab, until they were totally separated. All the samples were tested using a programmed elongation rate of 50 mm min 1 at room temperature. 2.8. Tensile stress-strain test FSC and FSC@Ni were fabricated and cut into 1 cm 7 cm strip. After that, the electrodes were clamped to the tension tester AG2000A (Shimadzu) tightly. Then, a pulling force was applied into
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both ends of the electrodes until they broke. All the samples were tested using a programmed elongation rate of 1 mm min 1 at room temperature. 2.9. Polysulfide diffusion visual test The polysulfide solution (taking Li2S6 on behalf of lithium polysulfides) was prepared by chemically reacting sublimed sulfur and an appropriate amount of lithium sulfide in 1,2-dimethoxyethane solution to form Li2S6 (0.2 mol L–1) in the solution. The solution was then stirred at 40 °C in an Ar-filled glove box overnight to produce a brownish-red Li2S6 solution. The Li2S6 solution was then diluted to 10 mmol L–1 for the polysulfide diffusion test. Two pieces of FSC@Ni and FSC with the diameter of 16 mm were first placed fitly at the bottom of the syringe, respectively, and then 1 mL diluted Li2S6 solution was added into the injection syringe. The polysulfide (Li2S6) will diffuse across the FSC or FSC@Ni to outside of the injection syringe, where a glass bottle was layed up and filled with 1,2-dimethoxyethane (DME) to collect polysulfide solution. The resulting color change was evaluated by visual examination at variable time. 3. Results and discussion The mechanism of NFED method is first studied to illustrate its capability of depositing metal patterns selectively and multidimensionally. Here, it is verified in Li-S batteries, via embroidering Ni-P pattern on flexible S/C electrodes. As far as we know, it is the first time to employ nickel foam and prove its priority of electroless growth in the area where nickel foam covered, contributing to highly controllable and selective deposition. And there are three key points why nickel foam is employed here (Fig. 1). For one point, nickel foam can provide abundant catalytic sites at the electrode surface for autocatalytic Ni-P electroless deposition when nickel foam contacts tightly with S/C electrodes. The Ni can lead to dehydrogenation of hypophosphite in the electroless bath and produce active hydrogen [H] (Eq. (S1) online), which would further reduce Ni2+ into Ni0 (trace amount of phosphate would be reduced into P0) and deposit on the S/C electrodes [32]. For another point, the porous structure of nickel foam can facilitate the influx of electroless solution to the nickel foam/electrode interface and provide sufficient nickel sources and reductants. As a result, the metal electroless deposition can be very accurate and controllable, compared with the traditional electroless deposit methods which need to implant metal catalysts [18,33]. As shown in Fig. 2a, the Ni-P deposition occurred in priority on the nickel foam covered areas, and then the pattern slowly spread on the blank area of S/C electrodes due to its autocatalytic electroless deposition. The extension growth of Ni-P pattern was captured by optical microscope along with its immersion time increasing in the electroless bath, shown in Fig. 2b. Spreading rates of Ni-P pattern can be controlled by tuning the temperature and the concentration of the electroless bath (Fig. 2a). As a result, NFED technique is as controllable as Chinese embroidering, which can selectively deposit arbitrary-shaped Ni-P pattern on the electrode such as ‘‘NFED” letters shown in Fig. 1, where also shows arbitraryshaped 2D and 3D electrodes covered with Ni-P pattern uniformly. Therefore, this novel method suits for different types of flexible electrodes such as shape-conformable, fiber-shaped or even complex-shaped electrodes in personalization energy storage devices [2,4,11]. In addition, the Ni particles deposit sites could be exactly controlled on the electrode instead of the membrane, due to their great difference in electrical insulation (Fig. 1). During the whole process, the nickel foam only plays a role in initiating and controlling the electroless reaction. When the electroless
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 2. (Color online) (a) selective deposition of Ni-P pattern on S/C electrodes controlled by configuration of nickel foam, and spreading depostion rate controlled by concentration (composition of C0 shown in experimental section) and temperature of electroless bath; (b) spreading growth of Ni-P pattern on S/C electrodes captured by optical microscope (the white bar represents 200 lm).
depostion finished, the nickel foam will be moved away from electrodes. In order to fabricate highly flexible and personalizable electrodes, free-standing flexible S/C substrates (FSC) were prepared by phase inversion method first, which can construct ‘‘tricontinuous porous structure” with fast ion transportation and high flexibility, according to our previously work [31] (Fig. 3a and 3c). And then the desired Ni-P pattern was deposited on the flexible S/C electrode by NFED, which is named as FSC@Ni as shown in Fig. 3b and 3d. Due to the high quality deposition control of Ni particles, the thickness of the Ni layers on the S/C electrodes is only about 1 lm, with areal density of only 0.7 mg cm 2, much lighter than the traditional Al foil with thickness of 12–16 lm (areal density of 3.2–4.2 mg cm 2). In addition, the Ni-P pattern can not only deposit on the surface of the electrode, but also permeate deep inside (Fig. S1 online). This finally forms a 3D framework with high electric conductivity, which can efficiently accelerate the current collection of the whole electrode. As a result, the conductivity of S/C electrodes is increased by one order of magnitude (Table S1 online), while its flexibility is still kept excellent (Fig. S2 online). The NFED can also change the polarity of electrode, which could enhance the wettability between electrode and water (Fig. S3 online), and enhance the polysulfide confine ability (Fig. S5 online), attributed to the formation of polar metal sulfides (Ni-S compounds) during the electroless deposition process (Fig. S4 online) [19,34].
Due to the increase of electric conductivity, the electrochemical performances of FSC@Ni were enhanced as well. The electrochemical impedance spectroscopy (EIS) is tested to reveal the charge transfer kinetics of electrodes. Both plots are consisted of a semicircle and a sloping line as usual, in which the intercept of real impedance (Z’) corresponds to the resistance of cell components (Rs) while the diameter of the semicircle is associated with the charge transfer resistance (Rct) at electrode/electrolyte interface, and the inclined line is related to the Warburg inpedence (Wo). The charge transfer resistance (Rct) of FSC@Ni (sulfur loading of 6.5 mg cm 2) was one order of magnitude less (44.3 X cm 2) than that of FSC (320.0 X cm 2), according to the electrochemical impedance spectroscopy (EIS) characterization (shown in Fig. 3e and Table S2 online). Furthermore, compared with FSC, FSC@Ni show more complete CV cathodic peaks at about 2.3 V and 2.0 V, corresponding to the transition between S and soluble lithium polysulfides (Li2Sx, 4 x 8), as well as the transition between lithium polysulfides (Li2Sx, 4 x 8) and Li2S/Li2S2, respectively. In addition, FSC@Ni also show more complete anodic peaks at approximately 2.4 V, corresponding to the oxidation of Li2S/Li2S2 to Li2S8 (shown in Fig. 3f) [30]. As expected, performance of Li-S battery assembled with FSC@Ni is far better than that assembled with FSC (Fig. 3g). The FSC@Ni reached initial discharge capacity of 1341 mAh g 1 and retained 1000 mAh g 1 after 100 cycles, however, the batteries assembled with FSC cannot be fully charged and discharged (both with sulfur loading of 6.5 mg cm 2).
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 3. (Color online) (a) Surface and (c) cross-sectional morphology of FSC; (b) surface and (d) cross-sectional morphology of FSC@Ni; (e) EIS plots of the coin cells assembled with FSC and FSC@Ni before cycling. Inset is equivalent circuits; (f) the CV curves of FSC, FSC@Ni plotted within the potential ranging from 1.7 to 2.9 V at a scanning rate of 0.05 mV s 1; (g) cycling performance of the coin cells assembled with FSC and FSC@Ni (Sulfur loading of 6.5 mg cm 2) over 100 cycles at 0.1C; (h) cycling performance of the soft package batteries assembled by FSC@Ni (Sulfur loading of 6.5 mg cm 2) at 0.05C.
Meanwhile, FSC@Ni with higher sulfur loading (12 mg cm 2) was also tested, which can still reach to 1150 mAh g 1 for the initial discharge capacity and remain 650 mAh g 1 after 100 cycles at
0.1C (Fig. S6 online). Especially for the flexible soft package Li-S batteries, which demand the electronic conductivity for the most, it’s initial discharge capacity reached to about 1600 mAh g 1
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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(Fig. 3h). A comparison on the areal capacity vs. sulfur loading with previously reported flexible Li-S coin and soft package batteries is listed in Fig. S7 (online) [21,35–45], which show satisfactory battery performance for those assembled with flexible S/C electrodes by means of NFED. In addition, the 3D-metal-pattern embroidered electrodes kept stable after 100 cycles (Fig. S8 online), which demonstrates excellent bonding strength with the electrode substrates although the huge volume change exists in S/C cathode during charge and discharge [39,46]. Another most important thing, for the manufacture and practical application of flexible (or personalizable) electrodes, is their weldability with the external circuit. As for the FSC@Ni, it can be easily welded to the metal tab of the external circuit via sample ultrasonic welding process. And the electric resistance between the welded FSC@Ni and metal tab was decreased by over one magnitude compared with that connected by conductive tapes (from 82.7 to 7.7 X as shown in Fig. 4a). In addition, the binding strength between the welded FSC@Ni and metal tab was also enhanced obviously, which still kept intact with the dragging force between them increasing (Fig. S9 online). Furthermore, peeling strength of the welding point along vertical direction was also excellent, which still keeps integrity and with none active materials peeled off as shown in Fig. 4a (inset). The NFED method is also quite adoptable for the personalizable energy storage devices. Taking the tubeshaped electrodes for example, it can be easily manufactured with NFED method, and can easily light up the commercial lightemitting diode (Fig. 4b inset) with a normal output voltage of 2.6 V (Fig. S10 online). Furthermore, the FSC@Ni electrodes also exhibit excellent flexibility and toughness, as evaluated by tensile stress-strain test (shown in Fig. 4c). The electronic conductivity can be significantly retained simultaneously, ascribed to the strong conductive metal framework in the electrode, which can ensure the excellent battery performance during bending, straining or other deformation process. As for the assembled planar-shaped flexible soft package bat-
teries, it can maintain the same brightness of LEDs under roughly bending deformation (Fig. 4d and video S1 online). Even after bending the pouch battery from 0° to 90° for 100 times, the ohm resistance and charge transfer resistance did not change (Fig. 4e). In order to further evaluate the versatility of NFED method, flexible LiFePO4 electrodes were chosen to assemble flexible lithium ion batteries. Similarly, free-standing flexible LiFePO4 substrates (LFP) were prepared by phase inversion method first, and then deposit with ultrathin yet uniform Ni-P pattern on the electrodes (LFP@Ni), both of which were analyzed by XRD and SEM, shown in Fig.s S11–S14 (online). Compared with LFP, electronic conductivity of LFP@Ni was also one order of magnitude higher than that of LFP, which can be seen in Table S3 (online). And the results of the EIS profile in Fig. 5a revealed that the charge transfer resistance of LFP was significantly reduced after NFED embroidering. Additionally, From Fig. 5b, it can be seen that LFP@Ni show sharper and higher current peak than LFP. The potential gap between redox peaks for LFP@Ni was much narrower than that of LFP, reflecting that NFED embroidering can significantly improve the kinetics of the electrode electrochemical reactions. Meanwhile, the LFP@Ni presented higher discharge capacity at different current densities than FSC especially at 10C, where LFP@Ni can deliver about 100 mAh g 1 but almost none of LFP, shown in Fig. 5c. Furthermore, the pouch batteries assembled with LFP and LFP@Ni (LiFePO4 loading is 4 mg cm 2) were further tested at 0.5C (Fig. 5d). A much higher discharge capacity (154 mAh g 1) was remained for LFP@Ni after 100 cycles, attributed to the effective current collection and integrity of the deposition pattern after cycles, shown in Fig. S15 (online). In addition, cycling performance of pouch battery assembled with LFP@Ni was further tested when bending deformation from 0° to 90° was carried out. As shown in Fig. S16 (online), the cycling performance kept stable before and after bending deformation, demonstrating the toughness and flexibility of LFP@Ni assembled pouch battery.
Fig. 4. (Color online) (a) Measurement of resistance between FSC@Ni and metal tab via ultrasonic welding (left) and conductive tape (right). The inset of (a) is the optical image of welding point of FSC@Ni after peeling test; (b) wearable tube-shaped electrodes before (top) and after (bottom) NFED embroidering (the inserted photograph displays a blue LED lit up by the batteries assembled with tube-shaped FSC@Ni electrodes); (c) Typical tensile stress strain curves of FSC@Ni and FSC (the inset is the photograph of the tensile stress–strain testing instrument); (d) photographs of LED lit by the flexible Li-S soft package batteries with size of 50 mm 80 mm under bending deformation; (e) EIS plots of Li-S soft package battery assembled with FSC@Ni before and after bending from 0° to 90° for 100 times.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Fig. 5. (Color online) (a) EIS plots of the coin cells assembled with LFP and LFP@Ni before cycling. Inset is equivalent circuits; (b) the CV curves of LFP, LFP@Ni plotted within the potential ranging from 2 to 4.2 V at a scanning rate of 0.1 mV s 1; (c) c-rate performance of the coin cells assembled with LFP and LFP@Ni at different current densities from 0.5C to 10C; (d) cycling performance of the soft package batteries assembled by LFP and LFP@Ni at 0.5C.
Last but not least, the NFED is capable of embroidering pattern with other metals, such as most of the VIII group elements (Fe, Co, Ni and etc.). Herein, Co-P electroless system was simply adopted and carried out. It is found that the Co-P electroless reaction could be initiated by nickel foam as it did in Ni-P system. And the [H] could reduce Co2+ into Co0 and uniform Co-P pattern was thus deposited on the S/C electrodes by spreading growth attributed to autocatalysis of Co0, shown in Figs. S17 and S18 (online). On this basis, it is worthwhile to conduct more extensive research, rendering NFED extremely attractive for energy storage and electrochemical catalysis fields.
4. Conclusions It is the first attempt to use NFED method to solve the welding and electron collecting issues of flexible electrodes especially with personalized shapes, by embroidering 3D conductive pattern on any targeted areas of any electrodes with high performance and high personalizability. Taking flexible Li-S and Li-LiFePO4 plenary and tube type soft package batteries as example, it simultaneously achieves many benefits, such as one order of magnitude higher conductivity, better and stable electrochemical properties even under bending deformation, strong welding strength and low contact resistance with external circuit, as well as tough deformation tolerance. Additional anchoring effect of polysulfides in Li-S batteries was also found with Ni-P pattern via NFED. As a result, satisfac-
tory battery performance was obtained compared with previously reported flexible Li-S battery related results. What’s more interesting, the NFED of Co-P pattern was also confirmed applicable on the S/C electrodes, and it is also possible to deposit other metals such as VIII group elements in the periodic table (Fe, Co, Ni, Rh, Pd and Pt), rendering it attractive for other energy storage or electrochemical catalysis fields. Declaration of Competing Interest The authors declare that they have no conflict of interest. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (51673199, 51677176), Youth Innovation Promotion Association of CAS (2015148), Innovation Foundation of DICP (ZZBS201615, ZZBS201708) and Dalian Science and Technology Star Program (2016RQ026). Author contributions Jian Gou and Hongzhang Zhang designed the experiments. Jian Gou and Yuxiao Wang performed the experiments, analysed the data and prepared the manuscript. Hongzhang Zhang and Yu Ying substantively revised it. Xianfeng Li and Jingwang Yan edited the
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
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Jian Gou is currently a doctor in Intellectual Property and Technology Transfer Department, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. He received his B.S. degree from Dalian University of Technology in 2010. He received his Ph.D. degree from University of Dundee. His research interests focus on the development of flexible energy storage devices.
Yuxiao Wang is currently a master student in the Materials School of Materials Science and Engineering, Qingdao University. She obtained her B.E. degree in Qingdao University in 2016. Her research is focused on Long-cycle Lithium-Sulfur batteries and the structureactivity relationship between electrode structure and cycle performance.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022
J. Gou et al. / Science Bulletin xxx (xxxx) xxx Hongzhang Zhang is currently a professor at the Division of Energy Storage, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. He received his B. S. degree from Shandong University in 2008 and then his Ph.D. degree from University of Chinese Academy of Sciences. His research interests focus on the development of novel batteries with high energy density.
9 Xianfeng Li is a full professor at Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences. He currently serves as Head of Energy Storage Division at DICP. He received his Ph.D. degree in Polymer Chemistry in 2006 form Jilin University. After three years’ postdoctor at KULeuven University, he joined in DICP in 2009. His research interests mainly focus on electrochemical energy storage.
Please cite this article as: J. Gou, Y. Wang, H. Zhang et al., 3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices, Science Bulletin, https://doi.org/10.1016/j.scib.2020.01.022