Molecularly Imprinted Polymer Enables High-Efficiency Recognition

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Molecularly Imprinted Polymer Enables High-Efficiency Recognition and Trapping Lithium Polysulfides for Stable Lithium Sulfur Battery jie liu, Tao Qian, Mengfan Wang, Xuejun Liu, Na Xu, Yizhou You, and Chenglin Yan Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.7b02332 • Publication Date (Web): 10 Jul 2017 Downloaded from http://pubs.acs.org on July 11, 2017

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Molecularly

Imprinted

Polymer

Enables

High-Efficiency

Recognition and Trapping Lithium Polysulfides for Stable Lithium Sulfur Battery Jie Liu, Tao Qian,* Mengfan Wang, Xuejun Liu, Na Xu, Yizhou You, and Chenglin Yan*

Soochow Institute for Energy and Materials InnovationS, College of Physics, Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, China. Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province, Soochow University, Suzhou 215006, China. Correspondence and requests for materials should be addressed to T.Q. (email: [email protected]), or to C.L.Y (email: [email protected]).

ABSTRACT: Using molecularly imprinted polymer to recognize various target molecules emerges as a fascinating research field. Herein, we applied this strategy, for the first time, to efficiently recognize and trap long-chain polysulfides (Li2Sx, x = 6 ~ 8) in lithium sulfur battery to minimize the polysulfide shuttling between anode and cathode, which enables us to achieve remarkable electrochemical performance including a high specific capacity of 1262 mAh g-1 at 0.2 C and superior capacity retention of over 82.5% after 400 cycles at 1 C. The outstanding performance is attributed to the significantly reduced concentration of long-chain polysulfides in electrolyte as evidenced by in-situ UV/Vis spectroscopy and Li2S nucleation tests, which were further confirmed by DFT calculations. The molecular imprinting is demonstrated as a promising approach to effectively prevent the free diffusion of long-chain polysulfides, providing a new avenue to efficiently recognize and trap lithium polysulfides for high performance lithium sulfur battery with greatly suppressed shuttle effect. KEYWORDS: Molecularly imprinted polymer, Lithium sulfur battery, Long-chain polysulfides, Li2S nucleation test, In-situ UV/Vis spectroscopy

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Molecularly imprinted polymers (MIPs), which are made by polymerizing polymerizable reagents in the presence of the template, are synthetic materials that are able to selectively recognize and bind target molecules with tailor-made molecular recognition binding sites.1-3 By noncovalent interactions or forming covalent bonds between template molecules and functional groups, the molecularly imprinted materials can be constructed.4,5 The typical construction scheme consists of (1) formation of the complex between polymerizable functional monomer and template molecule, (2) thermal/photo-initiated polymerization, (3) removal of template molecule from the polymer frame, leaving characteristic binding sites in the matrix or on the surface of the polymers.6,7 The obtained MIPs are crosslinked polymeric materials that demonstrate superior binding ability and selectivity specific to target molecule. MIPs presently attract widespread interests, especially arising from their use in the development of tools for organic synthesis due to high specificity, stability, easy availability and low cost of these materials.8-10 Indeed, most of proposes for MIPs were applied in sensors,11 analytical chemistry,12 catalysis,13 water treatment14 and biochemistry fields,15 and well-established approaches were efficiently used. Such research was adequately conducted for some years, whereas it is still an active area of science with the aim of constructing different binding sites and proposing new applications. The increasing desire for clean energy by modern industries including military power supplies, civil transportation and stationary storage, placed urgent demands on the energy density of the battery. Lithium sulfur (Li-S) batteries have been considered promising for powering portable electronics because they have an overwhelming advantage in energy density, with a theoretical value of about 2600 Wh kg-1.16-20 However, the inherent non-conductivity of sulfur and its finally reduced product (Li2S) as well as the damage of electrode caused by severe volumetric change (80%) of active material upon lithium insertion/extraction become deterrents to commercial application of Li-S batteries.21-24 Another major issue is the dissolution of lithium polysulfides in electrolyte and their migration from cathode to anode, resulting in notorious “shuttle effect”, which lead to the low utilization of active material, rapid degeneration of capacity, and low Coulombic efficiency.23,24 In Li-S battery system, it has been the focus point of our struggle to fight against the polysulfides, especially long-chain polysulfides (Li2Sx, x = 6 ~ 8), and minimizing 2


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or even eradicating the shuttle effect has become the task of top priority. Tremendous efforts have been made, including impregnating sulfur into different carbon matrixes or conducting polymers,23,25-27 trapping soluble polysulfides in the sandwich structure or interlayer fabrication,28,29 restricting the dissolution and diffusion by new binder or electrolyte,30,31 but the effect on maintaining the stability or capacity enhancement was proved to be limited. It was recently demonstrated that amino groups have strong affinity to lithium sulfides and verified that ethylenediamine can be an ideal linker to join polar lithium polysulfides and nonpolar carbon surface together via interaction.32,33 However, their strategy proved to be more conducive to capturing short-chain polysulfides (Li2Sx, x = 1 ~ 4) and just restrict them on the surface of cathode materials. In fact, long-chain polysulfides play a destructive role in ruining the performance of Li-S batteries during electrochemical cycle.34,35 In this case, the characteristic of selective recognition to polysulfides makes MIPs a promising tool for suppressing the shuttle effect in Li-S battery. Molecular imprinting method, therefore, provides potential opportunities for specifically trapping long-chain polysulfides inside the frame of MIPs when appropriate template molecules are employed. In this work, we demonstrate for the first time that well-designed MIPs were synthesized and employed as recognition sites for polysulfides in Li-S battery system to trap long-chain polysulfides pertinently. Specifically, acrylamide with strong chemical adsorption for polysulfides was chosen as the polymerizable functional monomer, and polyacrylamide is an ideal polymer to anchor polar lithium polysulfides. MIPs were ultimately obtained by simultaneous polymerization under argon atmosphere with Li2S8 as the target molecule, then the removal of template molecule. It should be noted that the removal of these templates leaves their sites with shape and functionality in the polymer matrix, which can selectively rebind the template.36 Permeation experiment and Li2S nucleation test combined with density functional theory (DFT) calculations reveal the pointed restriction and absorption to Li2S8. The obtained MIPs were employed as interlayer of Li-S battery (denoted as S/MIPs) between cathode and separator, which are capable to efficiently trap assigned polysulfides in the matrix of polymer. As a result, this promising approach effectively prevents the free diffusion of long-chain polysulfides in S/MIPs electrode during cycling, which can be testified by high cycle stability of Li-S batteries and 3


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the significantly reduced concentration of long-chain polysulfides in electrolyte as derived from in-situ UV/Vis spectroscopy in comparison to conventional Li-S battery. The S/MIPs cell showed a high initial specific capacity of 1262 mAh g-1 at a current of 0.2 C and exhibited excellent capacity retention of over 82.5% after 400 cycles at 1 C. MIPs with Li2S8 recognition characteristics were prepared by polymerization of acrylamide monomer molecular with Li2S8 as the target template. Figure 1 provides a schematic description of the synthetic procedures, which can be summarized in the following steps: (1) preparation of Li2S8 solution and the ultrasonic dispersed multiwall carbon nanotubes (CNTs) with anhydrous dimethyl formamide (DMF) as solvent, followed by the addition of monomer acrylamide, (2) polymerization by initiation when the system was heated to 70 °C with azodiisobutyronitrile (AIBN) as the initiator, (3) the removal of template molecule by DMF washing repeatedly and cyclic voltammetry (CV) scans, leaving featured binding sites in the polymer matrix. To tell the difference and effect on Li-S battery performance between MIPs material and non-molecule imprinting polymers (NIPs), the controlled experiment was carried on simply as the same procedures with the exception of template molecule. Detailed procedures are provided in the experimental section. Evidence of imprinting sites buried in the matrix can be found through careful characterization of

the

imprinted material.

High-resolution

transmission

electron

microscopy (HRTEM) image of MIPs shows the amorphous surface structure of CNTs, demonstrating that CNTs has been connected with the polymer matrix, as shown in Figure 2a. Figure 2b displays scanning transmission electron microscopy (STEM) and elemental mapping results of MIPs which were repeatedly washed by DMF. It has a clear exhibition on the presence of elements carbon, nitrogen and oxygen on the surface of CNTs, which reveals that polyacrylamide was uniformly attached onto carbon nanotubes. Moreover, it is noteworthy to mention that sulfur signal was found, indicating that the template molecule was embedded in MIPs matrix, as well as its homogenous distribution. An uniform molecular-level distribution of recognition sites is of critical importance for the application of MIPs as cathode interlayer for Li-S batteries so that the long-chain polysulfides derived from the reduction of elemental sulfur during discharge can be rebound efficiently. X-ray photoelectron spectroscopy (XPS) was performed to discern the surface 4


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chemical species of materials. As shown in Figure 2c, the peaks of N 1s and enhanced O 1s in MIPs and NIPs are obviously emerged compared with the pristine CNTs, which further confirmed that acrylamide with acyl and amino-containing groups was successfully decorated onto the CNTs. Two new peaks were located at 165.1 eV and 229.1 eV for MIPs corresponding to S 2p and S 2s, respectively, indicating the efficient absorption of amide groups to Li2S8. More sufficient information of the surface composition was supported by high-resolution XPS spectra of C 1s and S 2p regions. The C 1s peak at 284.8 eV for pristine CNT (Figure S1) is attributed to C−C/C=C, and the impurity of CNTs results in another weak peak at 285.7 eV corresponding to C-O.37 However, the new peak at 288.7 eV (Figure S2) was observed for MIPs, which could be ascribed to C-N after the introduction of acrylamide to CNTs, and the peak at 285.7 eV increases significantly after polymerization. Furthermore, S 2p spectra of MIPs can be deconvoluted into four different signals (Figure S3), which respectively correspond to S 2p3/2 at 163.8 eV, S 2p1/2 at 164.9 eV and sulfate species at 168.0 and 168.9 eV, formed by the oxidation of sulfide in air.38 This finding reconfirms the presence of Li2S8 template molecule in MIPs. Although enormous quantities of template molecules can be removed by repeatedly washing with DMF, it is necessary to eliminate the effect of Li2S8 survivals on cycling. CV scan is an effective approach to completely clean Li2S8 absorbed by -NH2 and embedded in MIPs matrix. Figure 2d shows the cyclic voltammograms of MIPs material washed by DMF. The decreased oxidation and reduction peaks indicate that the remaining Li2S8 was gradually reduced. Li2S8 is believed to be completely removed till these redox peaks are not detectable after several CV scans. After that, MIPs were used as adsorbent material and the interlayer of Li-S cathode for further permeation experiment and electrochemical tests, respectively. To give a conspicuous visual comparison of absorptivity to polysulfides of different materials, we performed permeation experiments, comparing the MIPs, NIPs composites, and pristine CNTs by well-designed devices as shown in Figure 3a. The sample vial was filled with 2.5 mL of blank electrolyte, and 1 mL of Li2S8 solution was injected into a plastic tube inside the vial. The MIPs material was sealed in the small tube, which was pre-punched at the bottom so that the electrolyte and scarlet Li2S8 solution can be actually 5


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connected. Representative results are given in Figure 3b. The Li2S8 solution in the plastic tube exhibits a conspicuous decolorization after silencing some hours and the vial keeps clear all the time, indicating that Li2S8 was sieved and unable to traverse the MIPs. After 10 h, the electrolytes both in vial and tube were completely colorless. For comparison, the permeation devices with NIPs and CNTs as adsorbents, respectively, were performed under similar conditions. The color fading of Li2S8 solution and dyeing to blank electrolyte within several hours imply that Li2S8 undergoes permeation through the NIPs and CNTs interlayers easily. Although the vial containing NIPs presents a delayed coloration to blank electrolyte in contrast to CNTs, the limited impact results in inevitably diffusion of Li2S8 and two systems eventually change the color of different electrolyte to bright yellow. The significant comparison result convinced that MIPs matrix has an incomparable superiority in stereospecific restriction and trapping Li2S8 to CNTs and NIPs. After manufacturing these materials into electrodes, the same conclusion can be drawn by the Li2S nucleation test at a constant potential. As we know, it occurs to different cells where Li2S was electrodeposited from polysulfides solutions onto electrode materials while keeping the cells at the potential below equilibrium potential. Thus, the deposition of polysulfides can be monitored by current flow.39,40 The affinity of cathode to polysulfides is directly linked to the deposition efficiency, which can be used to investigate the absorbability of different materials to polysulfides. Here, we further studied the kinetics of Li2S nucleation by potentiostatically discharging at 2.08 V using MIPs, NIPs, and CNTs as electrodes, respectively. Noted that 20 mM Li2S8 was dissolved in 1,3-dioxolane and 1,2-dimethoxyethane (DOL/DME = 1/1, v/v), and conventional Li-S electrolyte was used as the catholyte and anolyte, respectively. As shown in Figure 3c, the MIPs electrode exhibits an obvious current peak, revealing a significant deposition of Li2S. In contrast, such great peak intensity can’t be observed in NIPs and CNTs experiments. The comparison of Li2S8 entrapment with the same weight of different adsorbents reveals that MIPs have a strong absorption to Li2S8, which can be subsequently confirmed by density functional theory (DFT) calculations as shown in Figure 3d. The strong interaction between Li2S8 and acrylamide monomer was attributed to the electrostatic adsorption of animo group and carbonyl group in acrylamide to lithium ion in Li2S8. DFT calculations revealed that the binding energies of 6


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animo group and carbonyl group in acrylamide monomer to Li2S8 were 0.69 eV and 0.98 eV, respectively, guaranteeing the formation of binding sites and rebinding of target molecules. S/MIPs cathodes were fabricated by coating the treated MIPs material on conventional sulfur cathodes. The sulfur cathodes with pristine CNTs and NIPs as interlayers (denoted as S/CNTs and S/NIPs) were used as controls, respectively. After assembling coin cells with Li-metal as anode, 1.0 M LiTFSI in DOL/DME (1:1 in volume) with 1.0 wt% LiNO3 as electrolyte and Celgard 2300 as separator, discharge/charge electrochemical performance of the cell was examined. Figure 4a shows the cycle behaviors of all cells, which were cycled at a current of 0.5 C. The S/MIPs cell displays an initial specific capacity of 1,059 mAh g-1, and the discharge capacity was retained at 826 mAh g-1 after 150 cycles, showing its conspicuous advantage to S/NIPs and S/CNTs. In addition, it can be speculated that NIPs materials work well on the restriction to polysulfides due to surface adsorption in initial cycles by contrasting to S/CNTs cathode, but the interaction is not efficient any more after several cycles, and the cell has a similar degradation on capacity with S/CNTs cathode. The S/MIPs cathode exhibits remarkable behaviors, demonstrating that MIPs material plays a constructive role on trapping polysulfides, which can be effectively evidenced by the differences in morphology of lithium plates for S/MIPs//Li, S/NIPs//Li and S/CNTs//Li cells after 50 cycles. In the S/MIPs//Li cell, the cycled lithium surface still has uniform morphology as shown in Figure S4a. However, in the S/NIPs and S/CNTs cathodes, lithium polysulfides formed in the cathode and reacted with lithium metal easily when transferring to anode, which finally results in the intricate morphologies in high density with the coexistence of lithium dendrites and Li2S/Li2S2 (Figure S4b, S4c).41 Typical CV profiles for the S/MIPs electrode were obtained between 1.7 V and 2.8 V at a scan rate of 0.1 mV s-1 (Figure 4b). The two representative reduction peaks were contributed to the transformation from sulfur to long-chain lithium polysulfides (Li2Sx, 4≤x≤8) at ~ 2.28 V and the further reduction to Li2S2/Li2S at ~ 2.02 V.25 Two anodic peaks corresponded to the oxidation of Li2S/Li2S2 to Li2S3/Li2S4 and then transition to elemental sulfur.42 The positive shifts in reduction peaks and negative shifts in oxidation peaks reveal the improved kinetics of polysulfide redox. The overlapped CV profiles after initial sweep demonstrate high reversibility of the redox reactions and excellent stability. In addition, the 7


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S/MIPs cathode shows excellent rate performance as the current density changes from 0.2 C to 4 C (Figure S5). The average discharge capacities for S/MIPs electrode at 0.2 C, 0.5 C, 1 C, 2 C and 4 C are, respectively, 1262 mAh g-1, 1038 mAh g-1, 846 mAh g-1, 691 mAh g-1 and 535 mAh g-1, exhibiting the high discharge capability. When the current rate was restored to 0.2 C, the specific capacity can be recovered to 1102 mAh g-1 for the S/MIPs electrode, demonstrating that the electrode keeps anchored after the high-rate test and has excellent stability. Figure 4c shows the charge/discharge curves of the S/MIPs electrodes at different C-rates. In conformity with the two reduction peaks in the CV profiles, two plateaus were observed at ~ 2.30 V and 2.05 V in the discharge process at 1 C. The long-term cycling tests show that the S/MIPs electrode can exhibit high capacity retention of over 82.5% for 400 cycles at a high rate of 1 C (as shown in Figure 4d). Such prominent performance is superior to that of all control cells, which lose almost all of the capacity upon cycling. Moreover, the S/MIPs cell exhibits a high specific capacity of 949.1 Ah g-1 when the sulfur loading was increased to 2.5 mg cm-2, and it still keeps excellent stability even the loading was as high as 4.5 mg cm-2, which indicates that our unique strategy works well with high mass loadings of sulfur (Figure S6). Apparently, the MIPs with Li2S8 as target molecule play a critical role in enhancing the cycle life and rate capability of Li-S battery. A great retention in capacity is because the polysulfides were effectively trapped due to the uniform contribution of recognition sites in MIPs materials, thereby avoiding the shuttle effect. In-situ UV/Vis spectroscopy is an effective tool to investigate the intermediate polysulfides during battery cycling.43,44 In order to collect the information of discharge products in real time, a well-designed cell based on a pouched lithium plate as well as a pouch cathode shell configuration with a thin optical glass covered was assembled. Figure 5a-c show the measured UV/Vis spectra of Li-S batteries assembled with S/MIPs, S/NIPs and S/CNTs electrode, respectively. The continuous shifts of reflection are attributed to the formation of soluble polysulfides upon cycling.43 In the conventional Li-S cell, the reflection first shifts to higher wavelength before the cell discharged to 2.08 V, which is directly traceable to the development of long-chain polysulfides. Then the persistence of discharge from 2.08 V to 1.7 V renders the absorption shift to shorter wavelength owing to the 8


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conversion reaction from long-chain polysulfides to short-chains. This result is quite similar to the spectra of S/NIPs cell, which indicates that NIPs have no significant influence on absorption polysulfides. However, there is an obvious difference in the UV/Vis spectra of S/MIPs cell, where the reflection changes take place in a small range in contrast to S/CNTs and S/NIPs electrodes. Although the performed UV/Vis spectra exhibit obvious differences in reflections between S/MIPs cathodes and other two control electrodes, quantitative determination of polysulfides in the electrolyte needs to be focused on. The wavelengths of different peaks for Li2Sx (2 ≤ x ≤ 8) have been studied in our previous reports (λ = 450 nm for Li2S2, λ = 505 nm for Li2S4, λ = 530 nm for Li2S6 and λ = 560 nm for Li2S8).44 The concentrations of different polysulfides were obtained according to the following procedures: (1) corresponding to these preselected wavelengths, we collect the intensities of reflection for each UV/Vis spectrum, respectively. (2) the intensity of first curve is normalized to one, and then all intensities are normalized according to the rate to the first spectrum. (3) the normalized intensities at shorter wavelengths are subtracted by longer wavelengths and then the actual intensities (Ia) are obtained. (Ia560 nm=1− I560nm, Ia530 nm= I560nm − I530nm, Ia505 nm= I530nm

− I505nm, Ia450 nm= I505nm – I450nm,). The concentration values of different polysulfides

can be derived by the relationship between actual intensity and the concentration as our previous paper.30 Figure 5e shows the comparison of concentrations of Li2S8 in three cells as the discharging goes on (Figure 5d). It is obvious that the concentrations of Li2S8 in different cells are at the same level at the beginning of discharge, but soon exhibit a significant increase in the S/NIPs and S/CNTs cell. In contrast, it keeps a very small value and has little change in the concentration of Li2S8 during the whole discharge process in S/MIPs cell. More importantly, the MIPs matrix can also absorb Li2S6 to reduce the shuttle effect, which can be evidenced by the comparison of the concentration of Li2S6 in different cells as shown in Figure 5f. A high concentration both of Li2S8 and Li2S6 projected on S/NIPs cell comparing to S/MIPs indicates that NIPs polymer has a rather limited cohesive force, which can be attributed to the -NH2 group on the surface of NIPs. Both the small-scale shift of UV/Vis reflections and the persistent low concentrations of Li2S8 and Li2S6 during cycling testified that MIPs material anchor Li2S8 effectively in the electrode and prevent it from diffusion in the electrolyte. 9


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In summary, we proposed a new strategy of using molecularly imprinted polymer as recognition sites for polysulfides in Li-S battery system to trap long-chain polysulfides. Acrylamide and Li2S8 molecule were employed as functional monomer and template, respectively, for the construction of MIPs material, which can constraint Li2S8 in the MIPs matrix by rebinding the target molecules. This approach allows us to achieve high capacity retention of over 82.5 % after 400 cycles at 1 C. In-situ UV/Vis spectroscopy revealed low concentration of Li2S8 in the electrolyte, indicating MIPs matrix has excellent ionic-sieving ability to Li2S8 during the electrochemical cycle. Moreover, visual characterizations give direct evidence on the affinity and absorbability of MIPs to Li2S8, which was theoretically confirmed by DFT calculations. Undoubtedly, the original design demonstrated here opens a new direction of the electrochemical application of MIPs materials in Li-S batteries.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: nl-2017-02332w. Experimental Section, computational method, XPS spectra, SEM results, rate performance and cycling performance of high sulfur loadings. This material is available free of charge via the Internet at http://pubs.acs.org

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

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We acknowledge the support from the National Natural Science Foundation of China (no. 51622208 and no. 51402202), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

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(19) Fang, R. P.; Zhao, S. Y.; Hou, P. X.; Cheng, M.; Wang, S. G.; Cheng, H. -M.; Liu, C.; Li, F. Adv. Mater. 2016, 28, 3374–3382. (20) Pang, Q.; Liang, X.; Kwok, C. Y.; Nazar, L. F. Nat. Energy 2016, 1, 16132–16142. (21) Manthiram, A.; Fu, Y.; Chung, S. H.; Zu, C.; Su, Y. S. Chem. Rev. 2014, 114, 11751–11787. (22) Yuan, Z.; Peng, H. -J.; Hou, T. -Z.; Huang, J. -Q.; Chen, C. -M.; Wang, D. -W.; Cheng, X. -B.; Wei, F.; Zhang, Q. Nano Lett. 2016, 16, 519–527. (23) Zhou, G. M.; Sun, J.; Jin, Y.; Chen, W.; Zu, C. X.; Zhang, R. F.; Qiu, Y. C.; Zhao, J.; Zhuo, D.; Liu, Y. Y.; Tao, X. Y.; Liu, W.; Yan, K.; Lee, H. R.; Cui, Y. Adv. Mater. 2017, 29, 1603366. (24) Yin, Y. -X.; Xin, S.; Guo, Y. -G.; Wan, L. -J. Angew. Chem. Int. Ed. 2013, 52, 13186–13200. (25) Hu, G.; Sun, Z.; Shi, C.; Fang, R.; Chen, J.; Hou, P.; Liu, C.; Cheng, H. –M.; Li, F. Adv. Mater. 2017, 29, 1603835. (26) Zhou, G. M.; Paek, E.; Hwang, G. S.; Manthiram, A. Adv. Energy Mater. 2016, 6, 1501355. (27) Xiao, L. F.; Cao, Y. L.; Xiao, J.; Schwenzer, B.; Engelhard, M. H.; Saraf, L. V.; Nie, Z. M.; Exarhos, G. J.; Liu, J. Adv. Mater. 2012, 24, 1176−1181. (28) Zhou, G. M; Pei, S.; Li, L.; Wang, D. –W.; Wang, S.; Huang, K.; Yin, L. –C.; Li, F.; Cheng, H. –M. Adv. Mater. 2014, 26, 625–631. (29) Shaibani, M.; Akbari, A.; Sheath, P.; Easton, C. D.; Banerjee, P. C.; Konstas, K.; Fakhfouri, A.; Barghamadi, M.; Musameh, M. M.; Best, A. S.; Rüther, T.; Mahon, P. J.; Hill, M. R.; Hollenkamp, A. F.; Majumder, M. ACS Nano 2016, 10, 7768−7779. (30) Chen, W.; Qian, T;. Xiong, J.; Xu, N.; Liu, X. J.; Liu, J.; Zhou, J. Q.; Shen, X. W.; Yang, T. Z.; Chen, Y.; Yan, C. Adv. Mater. 2017, 29, 1605160. (31) Zheng, J.; Engelhard, M. H.; Mei, D.; Jiao, S.; Polzin, B. J.; Zhang, J. –G.; Xu, W. Nat. Energy 2017, 2, 17012-17019. (32) Wang, Z. Y.; Dong, Y. F.; Li, H. J.; Zhao, Z. B.; Wu, H. B.; Hao, C.; Liu, S. H.; Qiu, J. S.; Lou, X. W. Nat. Commun. 2014, 5, 5002–5009. (33) Ma, L.; Zhuang, H. L.; Wei, S. Y.; Hendrickson, K. E.; Kim, M. S.; Cohn, G.; Hennig, R. 12


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G.; Archer, L. A. ACS Nano 2016, 10, 1050–1059. (34) Harks, P. P. R. M. L.; Robledo, C. B.; Verhallen, T. W.; Notten, P. H. L.; Mulder, F. M. Adv. Energy Mater. 2017, 7, 1601635. (35) Wild, M.; O’Neill, L.; Zhang, T.; Purkayastha, R.; Minton, G.; Marinescu, M.; Offer, G. J. Energy Environ. Sci. 2015, 8, 3477–3494. (36) Wang, D. S.; Zhang, X. X.; Nie, S. Q.; Zhao, W. F.; Lu, Y.; Sun, S. D.; Zhao, C. S. Langmuir 2012, 28, 13284–13293. (37) Cao, J.; Chen, C.; Zhao, Q.; Zhang, N.; Lu, Q. Q.; Wang, X. Y.; Niu, Z. Q.; Chen, J. Adv. Mater. 2016, 28, 9629–9636. (38) Zhou, G. M.; Paek, E.; Hwang, G. S.; Manthiram, A. Nat. Commun. 2015, 6, 7760–7770. (39) Fan, F. Y.; Carter, W. C.; Chiang, Y. -M. Adv. Mater. 2015, 27, 5203–5209. (40) Chen, C. -Y.; Peng, H. -J.; Hou, T. -Z.; Zhai, P. -Y.; Li, B. -Q.; Tang, C.; Zhu, W. C.; Huang, J. -Q.; Zhang, Q. Adv. Mater. 2017, 29, 1606802. (41) Cheng, X. –B.; Peng, H. –J.; Huang, J. –Q. Zhang, R.; Zhao, C. –Z.; Zhang, Q. ACS Nano 2015, 9, 6373–6382. (42) Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F. Nat. Commun. 2015, 6, 5682–5689. (43) Patel, M. U. M.; Dominko, R. ChemSusChem 2014, 7, 2167–2175. (44) Xu, N.; Qian, T.; Liu, X. J.; Liu, J. Chen, Y.; Yan, C. Nano Lett. 2017, 17, 538−543.

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Figure 1. Schematic of fabracation process of MIPs. A schematic description of the synthetic procedure. MIPs were obtained by polymerization of acrylamide monomer with Li2S8 as the template molecule, then the removal of template molecule. It should be noted that the removal of Li2S8 leaves their functional sites in the polymer matrix, which can selectively rebind the template.

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Figure 2. Characterizations of MIPs composite. (a) High-resolution TEM image of MIPs, illustrating a successful polymerization of acrylamide on CNTs. (b) STEM image of MIPs and the homogeneous distribution of elemental maps of carbon, nitrogen, oxygen and sulfur. (c) XPS analysis of CNT, NIPs and MIPs. The N and S peaks in MIPs indicate the template molecule was embedded in MIPs matrix. (d) CV scans of MIPs washed by DMF solvents. The decreased oxidation and reduction peaks indicate that the remaining Li2S8 was gradually reduced.

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Figure 3. Characterization on the absorption and affinity to lithium polysulfide (Li2S8). (a) Schematic of permeation experiments with a well-designed device. (b) Visual comparison of absorptivity of CNT, NIPs and MIPs to Li2S8. Permeation experiment using MIPs as adsorbent show completely colorless after 10 h, indicating MIPs composite has the strongest absorbability. (c) Potentiostatic discharge curves at 2.08 V for Li2S deposition with the same weight of different scaffolds. (d) Atomic conformations and binding energy for Li2S8 adsorption on acrylamide monomer. The binding energies of 0.69 eV and 0.98 eV correspond to the absorption strength of animo group and carbonyl group to Li2S8, respectively.

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Figure 4. Electrochemical measurements. (a) Cycling performance of S/CNT, S/NIPs and S/MIPs cathodes tested at a current rate of 0.5 C. (b) CV profiles of the S/MIPs cathode at a scan rate of 0.1 mV s-1 in a potential window from 1.7 to 2.8 V. (c) Discharge/charge voltage profiles of S/MIPs cathode at different current rates. (d) Long-term discharge capacity and Coulombic efficiency of S/MIPs cathode at a current rate of 1 C. The cell can still retain ultrahigh stability after 400 cycles.

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Figure 5. In-situ investigation of UV/Vis spectroscopy for different electrodes. The in-situ UV/Vis spectra of discharging batteries assembled with (a) S/CNT electrode, (b) S/NIPs electrode and (c) S/MIPs electrode between λ = 300 to 700 nm. Derived from the UV/Vis spectra, the polysulfide concentrations of (e) Li2S8 and (f) Li2S6 at different potentials in different cells demonstrate individual difference corresponding to (d) the voltage change.

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The application of molecularly imprinted polymer for recognizing and trapping long-chain polysulfides (Li2Sx, x = 6 ~ 8) in lithium sulfur battery to minimize the polysulfide shuttling 33x17mm (300 x 300 DPI)


Molecularly Imprinted Polymer Enables High-Efficiency Recognition

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