Self-Assembled Protein Nanofilter for Trapping Polysulfides and

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Energy Conversion and Storage; Plasmonics and Optoelectronics

Self-Assembled Protein Nanofilter for Trapping Polysulfides and Promoting Li+-Transport in Lithium-Sulfur Batteries Xuewei Fu, Chunhui Li, Yu Wang, Jin Liu, Louis Scudiero, and Wei-Hong Zhong J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b00836 • Publication Date (Web): 24 Apr 2018 Downloaded from http://pubs.acs.org on April 25, 2018

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The Journal of Physical Chemistry Letters

Self-Assembled Protein Nanofilter for Trapping Polysulfides and Promoting Li+-Transport in Lithium-Sulfur Batteries

Xuewei Fu1, Chunhui Li1, Yu Wang1*, Louis Scudiero2, Jin Liu1*, Wei-Hong Zhong1*

1. School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164, USA. 2. Department of Chemistry, Washington State University, Pullman, WA 99164, USA.

E-mail:

[email protected]

(Dr.

Y.

Wang);

[email protected]

[email protected] (Prof. W. H. Zhong)

1 ACS Paragon Plus Environment

(Prof.

J.

Liu);

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract The diffusion of polysulfides in lithium-sulfur (Li-S) batteries represents a critical issue deteriorating the electrochemical performance. Here borrowing the concepts from air filtration, we design and fabricate a protein-based nanofilter for effectively trapping polysulfides but facilitating Li+-transport. The unique porous structures are formed through a protein-directed self-assembly process, and the surfaces are functionalized by the protein residues. The experiments and molecular simulations results demonstrate that our polysulfide nanofilter can effectively trap the dissolved polysulfides and promote Li+-transport in Li-S batteries. Adding the polysulfide nanofilter in a Li-S battery, the electrochemical performances of the battery have been significantly improved. Moreover, the contribution of the protein nanofilter to the ion-transport is further analyzed by correlating filter properties and battery performance. This study is of universal significance for the understanding, design and fabrication of advanced battery interlayers that can help realize a good management of the ion-transport inside advanced energy storage devices. TOC Graphic


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The rapid development of portable electronics, electric vehicles and stationary storage systems[1–3] raises an urgent demand for advanced energy storage devices such as rechargeable batteries[4,5], fuel cells[6,7], solar cells[8,9], supercapacitors[10,11], etc. Over the past years, substantial efforts have been made to develop various advanced battery systems such as lithiumion (Li-ion) batteries, sodium-ion (Na-ion) batteries, lithium-air and lithium-sulfur (Li-S) batteries.[12–15]Among these systems, Li-S batteries have received considerable attention due to their remarkable advantages including high theoretical energy density (2600 Wh/kg),[16] high specific capacity (1675 mAh/g),[17] low cost and environmental benignity. However, major challenges exist limiting their applications. The practical energy density, rate capability and especially cycling stability of Li-S batteries have been severely limited by several factors, including poor electron-/ion-conductivity of S-related species, diffusion of intermediate polysulfides and large volume changes.[18–20] In particular, the shuttle effect, which results from the dissolution and migration of the polysulfides (Li2Sn, 4 ≤ n ≤ 8) during charge/discharge process, is believed to be one of the main reasons for rapid capacity fading and low columbic efficiency.[21–23] Dissolution of polysulfides gradually consumes the sulfur active material and creates more “dead” S-species. Also, the polysulfides on the Li-metal surface can be reduced to Li2S, which will deposit on the Li-metal surface and affect the uniformity and dynamics of lithium ion deposition on the Li-anode. Therefore, most of the efforts have been focused on how to suppress the diffusion of polysulfides and various strategies to reduce diffusion have been reported. One strategy is to introduce blocking function inside the sulfur cathode. To do so, nanomaterials with blocking function for the diffusion of polysulfides are usually employed to form special composites with sulfur.[24–27] Various core-shell structures have been reported [22,28] to confine sulfur active material. Different conductive materials and methods have been employed to construct such structures, for example, graphene-wrapped sulfur cathode,[29–31] porous 3 ACS Paragon Plus Environment


carbon/sulfur composites,[32,33] hollow-structured sulfur materials[34,35] and sulfur nanoparticles with conducting polymer as the shell,[36,37]etc. Although these conductive shells can greatly improve the initial capacity and utilization of sulfur, they still experience a fast capacity decay in initial cycles, indicating that they are insufficient to prevent the dissolution and diffusion of polysulfides.[38] In addition, fabrication of the core-shell structures is usually difficult to scale up or be cost-effective, which hinders their practical applications. In order to enhance the blocking function, new nanomaterials showing stronger interactions with polysulfides have been reported, which include nitrogen-doped carbon-based nanomaterials (such as graphene,[39,40]carbon nanotubes,[41,42] etc.), WS2 nanosheets,[43] and metal oxides (e.g. Ti4O7),[44,45]etc. Another important strategy is to replace the organic liquid electrolytes with other polysulfidesinsoluble electrolytes such as solid electrolytes or ionic liquid electrolytes. Theoretically, this strategy may fundamentally solve the shuttle effect issues. However, in practice, this strategy has some problems. First, the dissolution of polysulfides can greatly facilitate the electrochemical reactions and significantly improve the cell performance in terms of specific capacity and rate-performance.[46,47] Second, the electrolytes with low or without solubility of polysulfides usually show inferior ion-conductivity, interface stability or processability.[38,48,49] As a result, the solid electrolyte was usually employed as an interlayer, and combined with the use of an organic liquid electrolyte.[50,51] In addition to above approaches, introducing an additional layer traditionally called interlayer, to block the diffusion of polysulfides is also one feasible strategy. Two main methods have been reported to produce this interlayer. The first method is to create a separator coating. Various materials, including carbon-based conductive nanomaterials (such as carbon black,[17,52] carbon nanotubes,[53,54] graphene[55,56]), polymers (such as Nafion)[57] and metal oxides nanoparticles,[58,59] have been employed to coat the surface on either the separator side 4 ACS Paragon Plus Environment

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or the S-cathode side. Among these coating materials, the separator coated with a conductive nanomaterial shows better improvement than the non-conductive coating such as an Al2O3 nanoparticle coating[38]. Similarly, the second method is to insert an individual interlayer, usually a free-standing thin layer of conductive materials (such as carbon fiber cloth,[57,60] carbon paper[61,62]), between the S-cathode and the separator. In this method, the interlayer is designed and fabricated independently. In summary, creating advanced nanostructures to block the diffusion of polysulfides remains the most promising strategy to address the shuttle effects without sacrificing the intrinsic advantages of the batteries. In particular, the introduction of a conductive interlayer is one of the most cost-effective methods. Meanwhile, the interlayer in a form of either a surface coating or an individual free-standing film can be easily integrated into the current fabrication technology for lithium ion batteries. Therefore, the design of an advanced multi-functional interlayered structure is critical for developing high-performance metal-sulfur batteries.[39] An ideal interlayer for enhancing metal-sulfur battery performance should have several properties: strong interactions with polysulfides for trapping them, low resistance for lithium-ion transport, high electron-conductivity allowing electrochemical reactions of trapped polysulfides, good mechanical and electrochemical stability as well as compatibility with other components in the Li-S system. As is well known, air filters are designed to remove pollutants in air with low flow resistance. Inspired by the concepts in air filtration, we propose a protein-based nanofilter for filtering polysulfides in Li-S batteries with low Li+ transport resistance, namely polysulfide nanofilter (PSNF), as shown in Figure 1 (a). From a filter point of view, the main function of air filter is to trap the pollutants (e.g. particulate matter (PM) of various sizes, chemical vapors, etc.[63]) and only allow clean air to pass through. An ideal air filter should achieve high efficiency for filtering pollutants but low air-flow resistance, or low pressure drop.[64] Correspondingly, the 5 ACS Paragon Plus Environment


polysulfides generated in Li-S batteries can also be treated as “pollutants”, and the PSNF in our work is designed to capture the polysulfides “pollutants” and meanwhile provide low resistance for Li+ transport. Such PSNF is realized by compositing proteins with conductive particles, followed by a protein-directed self-assembly process. Due to the unique self-assembled porous structures and surface properties, the PSNF efficiently works to selectively trap the polysulfides “pollutants”, and meanwhile promotes the Li+ transport between the two electrodes. As a result, significant improvements in electrochemical performance of Li-S batteries are achieved. The dissolved polysulfides “pollutants” in Li-S batteries not only result in serious shuttle effects, but also deteriorate the electrolyte performance, such as the decreased ionic conductivity.[8] Therefore, developing a high-performance PSNF is an attractive solution for resolving the polysulfides dissolution issues. It is noted that conductive and porous interlayers have been of great interest in Li-S systems as reported in previous studies, such as the ones showing strong affinity with polysulfides (e.g. MoS2 nanomaterial coating).[4] In spite of this fact, treating polysulfides as “pollutants” and using the concepts from air filtration are novel and significant. This sets new requirements for the development of Li-S battery interlayers. As shown in Figure 1 (b) for an effective interlayer, the porous structures should be designed, and the surfaces should be functionalized, such that it cannot only trap and hold polysulfides, but also reduce separator/electrode resistance and facilitate fast Li+ transport. Moreover, some approaches in air filtration may also be adopted in design, fabrication and even characterization of the new interlayers, as will be discussed in detail in this study.


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Figure 1. Design and fabrication of polysulfides nano-filter (PSNF) based on selfassembled protein@CB nanocomposite. (a) Illustration of PSNF interlayer for filtration of polysulfides in Li-S cells; (b) Critical properties for achieving a high-performance PSNF; (c) Schematic of the facile bio-nanotechnology proposed in this study for the fabrication of PSNF with 3D porous structures and functional surface via protein-directed self-assembly. The fabrication strategy for the proposed PSNF is illustrated in Figure 1 (c). As shown, the 3D porous structures of PSNF are generated via a protein-directed self-assembly process, which has been reported to be an attractive method to fabricate self-assembled nanomaterials.[65] Here one of the abundant natural proteins, gelatin, has been adopted for assisting the assembly process. The specific gelatin-particle and gelatin-gelatin interactions will lead to a unique porous structure, and the trapping of polysulfides is realized through the interactions from the functional groups along the protein chain. (Description of the fabrication details can be found in the Supporting Info.).



Figure 2. Processing and morphological studies on PSNF in comparasion of traditional conductive coating. (a) – (c) Schematic illustration of situations for different CB dispersions: (a) PVDF/CB, (b) gelatin/CB by deionized (DI) water and (c) gelatin/CB (PSNF) by mixture solvent of acetice acid (AA) and DI water (AA/DI). (d) – (f) SEM images of different separator coatings: PVDF/CB, gelatin/CB by DI and gelatin/CB (PSNF) by AA/DI mixture solvent, respectively. (g) – (i) Schematic illustration showing morphological features of (g) PVDF/CB, (h) gelatin/CB by DI and (i) gelatin/CB (PSNF) by AA/DI mixture solvent. We first investigate our PSNF by comparison with the traditional conductive coating, which have been widely employed to block the diffusion of polysulfides.[17,52] From processing standpoint, a good affinity of the coating material with the separator in both wet and dry states 8 ACS Paragon Plus Environment

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is a prerequisite to achieve a high-quality coating on the separator surface. Via coating the carbon black (CB) dispersions onto separator surface, we investigated the wetting behavior of the dispersion and microstructure of the nanocomposite coating after drying. As shown in Figure 2 (a), for the control sample, polyvinylidene fluoride/CB (PVDF/CB), there are weak interactions between CB and PVDF, despite that the dispersion shows good affinity to the separator and good wetting properties with a small contact angle of 49°(see Figure S2 (a), Supporting Info.). However, as revealed by SEM images in Figure 2 (d) (see more SEM images in Figure S2 (b) and (c), Supporting Info.), the PVDF/CB nanocomposite coating shows inhomogeneous microstructure with cracks, and inferior porous structure with a porosity of 33.7% (see Table S1, Supporting Info.). As illustrated in Figure 2 (g), the CB particles accumulate randomly to finally result in a compact porous structure, which will be further discussed in the battery studies. In contrast to PVDF/CB system, the proposed PSNF via gelatin/CB nanocomposite shows excellent wetting properties and better porous structures. As shown in Figure 2 (b) and (c), protein shows much stronger interactions with CB particles due to its functional groups[65]. However, interestingly the self-assembled porous microstructures highly depend on specific solvent environment. When we use deionized (DI) water as solvent (usually used for proteinbased dispersion), the gelatin/CB dispersion shows a higher contact angle to the separator (60°) (see Figure S3 (a), Supporting Info.) and wrapping behavior of the separator due to shrinkage during drying (see Figure S3 (b), Supporting Info.). The wrapping behavior is significant in this study. Firstly, it indicates that the gelatin protein can bring about strong adhesion with the substrate, which is critical for the stability of separator coating. Secondly, as shown in Figure 2 (b), there are numerous free protein chains in the gelatin/CB dispersion, which leads to strong hydrogen bonding and less gelatin chains attached onto the CB surface (also see Figure S3 (c), Supporting Info.). More importantly, as shown in Figure 2 (e) and illustrated in Figure 2 (h), 9 ACS Paragon Plus Environment


the resulting gelatin/CB nanocomposite shows poor porous structures and most of the CB nanoparticles are severely covered by gelatin (see more SEM images in Figure S4 (a) – (d), Supporting Info.) to finally result in a very low porosity of 12.0% as indicated in Table S1. However, this situation dramatically changed when we use aqueous acetic acid solution (pH = 2) to prepare the dispersion. As shown in Figure S5 (a), the wetting behavior of the dispersion is notably improved with smaller contact angle (51°) as compared with the one in DI water (60°). In addition, the dried coating layer shows no wrapping behavior as indicated in Figure S5 (b), indicating that acetic acid can assist the protein coating onto the CB particles and prevent gelation of gelatin as illustrated by Figure 2 (c) (also see Figure S5 (c), Supporting Info.). This is important to realize the designed functional surface for the protein@CB nanocomposites as illustrated in Figure 1 (c). Finally, a self-assembled porous nanostructure with homogeneous gelatin coating on CB surface that shows the highest porosity of 45.7% (see Table S1) can be achieved as shown in Figure 2 (f) and (i) (see more SEM images in Figure S6 (a) – (d), Supporting Info.). Based on the above fabrication studies, we find that dispersion of gelatin/CB in acetic acid solution represents a feasible method for fabrication of separator coating with good wettability, structure uniformity and 3D porous structures. Good mechanical properties of the coating materials are demanded to ensure the stable performance for the batteries. In this work, we measured the mechanical properties of the PSNF and PVDF-CB composites via indentation method. The results are shown in Figure S7 in Supporting Information. In this measurement, a tip with flat surface kept compressing the coating materials at a constant speed of 1 µm/s until reaching a maximum compression force of 35 N. The evolution of compression force with time was recorded. As shown, in compression stage, the compression stress sharply increased due to the increasing strain. The growth rate, which was defined as the slope for compression, can reflect the compression modulus. It can be seen that the PVDF-50%CB composite shows only a slightly higher slope of 0.046 than that 10 ACS Paragon Plus Environment

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of the PSNF (0.041). This indicates that the PSNF shows comparable mechanical properties with PVDF-50%CB. The PSNF should be electrically conductive to allow in-situ conversion of the trapped polysulfides and have good capability of inhibiting polysulfides from diffusion through the separator. We first measured the electric conductivity of PSNF via four-point probe method. The electric conductivity of PSNF is determined to be ca. 1.1 x 10-4 S/cm via equation (1): σ = I/(2πSV) (S/cm)

(1)

where V is the voltage between inner probes (V); I is current through outer probes (A); S is probe spacing (cm). The result indicates that PSNF is highly electrical conductive to ensure electrochemical reactions of polysulfides. Furthermore, to demonstrate its polysulfides filtration capability, we performed polysulfides diffusion test for the separators with and without PSNF coating and the results are shown in Figure 3. In the test, a bottle filled with dark yellow polysulfides-polluted liquid electrolyte (concentration of polysulfides: ca. 0.6 mol/L) and another bottle filled with clean liquid electrolyte were connected by the separator sample. The bare Celgard separator causes quick diffusion of polysulfides and the color of the originally clean liquid electrolyte changes notably after 2 h, as shown in Figure 3 (a). After 4 to 6 hours, the color becomes darker due to the increasing polysulfides concentration. In contrast as shown in Figure 3 (b), when the separator is coated with PSNF, the clean electrolyte is mostly clear up to 4 hours and then starts to become yellowish because of the oversaturation of polysulfides beyond the capacity of PSNF.



Figure 3. Polysulfides filtration studies by diffusion testing and molecular simulation studies. (a), Digital photos showing the diffusion process of polysulfides in a system separated by bare Celgard separator; (b), Digital photos showing the diffusion process of polysulfides in a system separated by PSNF coated Celgard separator. (c) – (d), Snapshots of the initial and final states (after 200 ns) of interactions between Li2S4 and gelatin in the liquid electrolyte, respectively; (e) and (f), Interactions between Li2S4 molecules and the oxygen atom from the backbone of gelatin, and the COO- end groups. To further understand the specific interactions between polysulfides and the gelatin coating at molecular level, we performed molecular dynamic simulations to study the adsorption process of polysulfides (e.g. Li2S4) onto the gelatin. The simulation details, including molecular 12 ACS Paragon Plus Environment

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structures, force fields and simulation setup, can be found in the Supporting Info. Figure 3 (c) and (d) are the snapshots of the initial and final states during the adsorption process of Li2S4 onto gelatin. As shown the polysulfide molecules have been mostly adsorbed onto the protein surface in 200 ns. We also noted that the unique spatial structures of protein chains may form some special “molecular cages” for effectively trapping and accommodating the polysulfides, which is quite different from conventional chemical trapping. A closer look at the adsorption sites on protein surface in Figure 3 (e) and (f) shows that polysulfides can be attracted by the oxygen atoms in the backbone (Figure 3 (e)) and COO- end groups in the protein chains (Figure 3 (f)) due to strong electrostatic interactions. Moreover, the side groups on the primary amino acids (e.g. proline, hydroxyproline) are short enough to make the oxygen atoms and COO- end groups accessible to the polysulfides, which provide a great number of “active-sites” having strong affinity with polysulfides. It is noted that the PSNF after 4-hour exposure to polysulfides also showed some diffusion of polysulfides as shown in Figure 3 (b). This phenomenon is related to the filtration capacity of the filter. After about 4-hour absorption, the PSNF may reach its trapping capacity limit. The filtration capacity is a critical factor for the design of separator coating in Li-S batteries. It should match the loading of active materials in the sulfur cathode to prolong the life span of the Li-S cells. Based on the simulation results, the filtration capacity can be roughly estimated from the structure unit of gelatin[66] (Figure S8, Supporting Info.) and molecular weight of gelatin (50,000 ~ 100,000 g/mol). Assuming that one functional group can only interact with one lithium polysulfide molecule, and all the gelatin chains in the separator coating (gelatin loading of 0.23 ± 0.01 mg/cm2 as employed in our work) are involved in the filtration, it is estimated that the PSNF can provide a filtration capability of ca. 18.3 mol/g.

However, it should be

noted that the actual capacity is affected by many other factors (e.g. surface area, temperature, current density, etc.), which will be investigated in future studies.



Figure 4. Charge/discharge profiles of Li-S batteries with PSNF-coated Celgard separator (PSNF@CS) as compared with control systems. (a) Initial charge/discharge profiles at a low current density of 0.1 A/g. (b) Charge/discharge profiles at a medium current density of 0.5 A/g. (c) Charge/discharge profiles of the Li-S battery with PSNF-coating at different current densities; (d) Comparison of the charge/discharge voltage drop at a current density of 0.1 A/g. The effects of PSNF on battery performance by PSNF were further demonstrated in Li-S batteries. We first compared the initial charge/discharge capacity in Figure 4 (a). It is well known that the initial discharge capacity is a key parameter reflecting the utilization percentage of the sulfur active material. As shown, the Li-S battery with the PSNF-coated separator (PSNF@CS) gives rise to the highest initial discharge capacity of 1318 mAh/g at a current density of 0.1 A/g. This is almost 80% utilization rate of active materials since the theoretical 14 ACS Paragon Plus Environment

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capacity of sulfur is 1672 mAh/g. In contrast, the cell with the bare Celgard separator (CS) shows a much lower capacity around 770 mAh/g. Meanwhile, to eliminate the effect of the LiNO3 additive for suppressing the shuttle effects, we also compared the initial cycle in an electrolyte solution free of LiNO3 and the result is shown in Figure S9. It clearly indicates that our PSNF indeed plays a critical role in suppressing the shuttle effects with a higher initial efficiency of 98% than that of the cell with bare separator (95%). These results indicate that the PSNF coating significantly improves the utilization percentage of the active material and effectively traps the dissolved polysulfides. In addition, we also evaluated the specific capacity and compared with the case with traditional coating of PVDF/CB composites. Two different ratios between PVDF and CB have been considered. The first control sample is PVDF-CB50%@CS with 50 wt% loading of CB; the second control sample is PVDF-CB80%@CS with 80 wt% loading of CB. Higher loading ratio of CB will generate more porous structure and thus assist the Li+ transport. As shown in Figure 4 (a) for the Li-S cell with PVDF-CB50%@CS, the initial discharge capacity is about 1279 mAh/g, which is close to that for the PSNF@CS. While, for PVDF-CB80%@CS, the initial discharge capacity is only about 934 mAh/g, which is much lower than that of PVDFCB50%@CS. This result implies that the main mechanism for the PVDF-CB coating to suppress the diffusion of polysulfides is physical blocking. The PVDF-CB coating with a higher loading of PVDF (PVDF-CB50%@CS) can block more polysulfides and results in higher capacity, since a higher loading of PVDF in the PVDF/CB nanocomposites can generate less porous structures (see Figure S10 (a) – (d), Supporting Info.). This physical blocking mechanism usually will lead to a trade-off between blocking efficiency and ion-transport capability, which will be discussed later. In addition to the higher initial capacity, the PSNF coating also significantly reduces the cell resistance and improve the capacity at different current densities. Figure 4 (b) shows the 15 ACS Paragon Plus Environment


charge/discharge profiles of the Li-S cells under a medium current density of 0.5 A/g. As shown the capacity decreases and the voltage drop between the charge and discharge plateaus increases remarkably when the current density increases from 0.1 A/g to 0.5 A/g. The Li-S cell with PSNF@CS shows the highest capacity of ca. 950 mAh/g and all the cells with conductive separator coating yield higher capacity than the cell with bare separator. Moreover, the capacity of the Li-S cell with PVDF-CB80%@CS overtakes that of the cell with PVDF-CB50%@CS. Meanwhile, the voltage profiles become more sensitive to the separator coating at higher current density. At 0.5 A/g, the second discharge plateau for the PSNF-coated cell is around 2.0 V, which is higher than that of the cell with bare separator. In contrast, the discharge plateaus drop down to around 1.7 V for the cell with PVDF-CB50%@CS, and 1.9 V for the cells with PVDFCB80%@CS. These results indicate that a higher loading of PVDF results in a higher resistance for the ion transport due to the blocking effect from PVDF as shown in Figure S10. This is consistent with the initial discharge capacity and voltage drop as discussed above. Figure 4 (c) shows the charge/discharge profiles for only the Li-S cell with the PSNF@CS at different current densities. The profiles are similar for all the current densities from 0.1 to 0.8 A/g. The voltage drop between the charge/discharge profiles increases notably only at a high current density, such as 0.8 A/g. In addition, the voltage drop between charge and discharge plateaus as defined in Figure 4 (d) is the lowest for the PSNF@CS cell (~ 0.17 V), compared with that of the cells with bare separator (~ 0.22 V) and PVDF-CB80%@CS (~ 0.30 V). The results suggest that the PSNF coating shows lowest cell resistance as compared with traditional separator. The coating of PSNF also significantly impacts other electrochemical performances, including rate capability and cycle stability. There are basically two factors controlling rate capability, the transport efficiency of ions/electrons and the kinetics of the electrochemical reactions between the active materials and lithium ions. Here, the rate capability is primarily controlled 16 ACS Paragon Plus Environment

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by the first factor since we have employed exactly the same sulfur cathode and liquid electrolyte. Therefore, the rate capability shown in Figure 5 (a) can well reflect the effects of different separator coatings on the ion and polysulfides transport. The PSNF@CS shows the best rate capability when compared with the two control samples. More specifically, the PSNF@CS results in much less capacity decay from 1100 mAh/g @0.2 A/g to 900 mAh/g@ 0.8 A/g. In addition, the rate capacity is quite stable at different current densities. In contrast for the cell with PVDF-CB80%@CS, the rate capacity at a current density of 0.5 A/g is unstable and keeps decaying. When increasing the current density to 0.8 A/g, the rate capacity dramatically drops to around 240 mAh/g, which is even lower than that of the cell with bare separator. This indicates that the conventional conductive coating PVDF/CB can improve the capacity, but not the rate performance. However, the PSNF coating can simultaneously improve the capacity and rate capability, due to the unique surface property and microstructures of PSNF. In specific, the presence of gelatin on CB surface provides strong capture capability for polysulfides, which effectively increases the utilization of active materials to improve the capacity. Meanwhile, the good porous structure of PNSF offers more pathways for transporting Li+, which significantly prompts the Li+-transport process at varying current rates.



Figure 5. Rate capability, cycle stability and impedance studies of the PSNF-coating as compared with other separator coatings: (a) rate capability comparison at varying current densities; (b) Nyquist plots of fresh Li-S cells containing different separator coatings in a frequency range of 0.01-1M Hz; (c) cycle performance comparison at a current density of 0.3 A/g; (d) and (e) SEM images of PSNF before and after 200 cycles of charging/discharging, respectively.


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To further confirm the polysulfides trapping function of PSNF in Li-S cell, we prepared another control S-cathode with 47 wt% sulfur loading. Considering the carbon black in the PSNF layer, C/S ratio is 1 : 1 at cathode. The result shown in Figure S11 indicates that the capacity of 47 wt%-sulfur cathode cell at 0.3 A/g is improved to be around 720 mAh/g simply by increasing the C/S ratio, but it is still far lower than 980 mAh/g for the cell with PSNF. Another factor that may also contribute to the trapping of polysulfides is the 2 wt% PEO in PNSF layer. To confirm the effect of PEO, we prepared another control sample by adding 2 wt% PEO into PVDF/CB nanocomposite coating. The microstructures of the coating and battery performance are summarized in Figure S12. As shown, addition of 2 wt% PEO indeed improves the specific capacity to 1140 mAh/g @ 0.1A/g. However, this is still much lower than 1318 mAh/g @ 0.1 A/g for the cell with PSNF. The results confirm that the significant improvements of performance for the Li-S cell with PSNF are mainly contributed from the gelatin coating. In addition to effectively trapping the dissolved polysulfides, the PSNF coating can also reduce the Li+ transport resistance. Figure 5 (b) shows the electrochemical impedance of the fresh cells. The Nyquist plots confirm that the PSNF coating can notably reduce the charge transfer resistance while the PVDF/CB coating increases it when compared with the bare separator and PSNF coated separator. Moreover, the cycle stability is also improved with PSNF. Compared with the PVDF-CB80%@CS cell, the PSNF@CS cell shows not only much higher capacity, but also better stability as shown in Figure 5 (c). After 200 cycles, 75% of the initial capacity is retained for the PSNF@CS cell, while it is only 63% for the PVDF-CB80%@CS cell. Moreover, the SEM images in Figure 5 (d) and (e) (see more SEM images in Figure S13, Supporting Info.) further prove that the polysulfides are effectively trapped by PSNF interlayer as all the pores are filled with solid active materials. Meanwhile, the capacity becomes more stable at ca. 670 mAh/g after about 250 cycles for the PSNF@CS cell. The capacity retention after ~200 cycles is important for understanding the diffusion of polysulfides inside the cells. 19 ACS Paragon Plus Environment


The decaying of the discharge capacities with cycling indicates that both the PSNF and PVDF coating are not able to completely suppress or block the diffusion of polysulfides into the liquid electrolyte. However, the decaying rate is much faster for PVDF-CB80%@CS cell, suggesting that the PSNF coating is more effective in trapping and holding the polysulfides than PVDF coating.

For the bare separator, the discharge capacity is low and quite stable with cycling.

This is due to the fact that, without coating a large amount of polysulfides dissolve into the liquid electrolyte during the first couple of cycles and the system quickly reaches the final equilibrium or saturation state.

Figure 6. Air and ions flow resistance studies of separator coatings. (a) Schematic of the home-made set-up for air-flow resistance testing of the separators w/ or w/o coating layer; (b) Pressure drop of the separators versus different flow rates; (c) Voltage drop versus different current densities for the Li-S cells with the separators; (d) – (e) Schematics showing the effects of separator coating on the ions transportation for bare Celgard separator, separator with PVDF/CB nanocomposite coating, and separator with PSNF coating, respectively.


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In air filtration, pressure drop tests are usually performed to characterize and evaluate the porous structures in air filters. Due to the similarities between pressure-driven flow in air filters and voltage-driven ionic transport across the porous separators, we carried out pressure drop tests for the separators with different coating materials to evaluate the effects of the interlayer porous structures on the Li+ transport. Figure 6 (a) shows our testing system, small and steady flows were produced in our tests to prevent the separators from breaking or damaging. The pressure drops for three battery separators were tested with flow rates from 15 to 30 mL/min and the results are summarized in Figure 6 (b). As shown, the bare separator (CS) shows the lowest pressure drop among all separator samples throughout the tested flow rates, indicating that separator coating will inevitably increase the flow resistance. Comparing the two separators with nanocomposite coatings, PSNF coating yields much lower pressure drop at all the tested flow rates compared with PVDF/CB coating. Meanwhile, the pressure drop of PVDF/CB coated separator is more sensitive to the flow rates. Adding an extra layer of porous material will inevitably increases the flow resistance, but the resistance is much lower for PSNF coating compared with PVDF/CB coating. The results are consistent with the observations from SEM images (see Figure 2 (d) – (f)), in which more pathways with larger pore sizes were observed in PSNF coating favoring the flow transport. Furthermore, we also performed the voltage drop tests for Li-S cells with different separators. As shown in Figure 6 (c), for the Li-S cells with PVDF/CB coated separators the voltage drop at different current densities is highest. This is consistent with the pressure drop testing, the extra coating layer will also reduce the ionic transport. Surprisingly, if we look at the Li-S cells with PSNF coated separator, the voltage drops are even smaller than that for cells with the bare separator. However, the pressure drops for separators with PSNF coating are much higher than that for bare separators (Figure 6 (b)). The seemly “inconsistent” results between pressure drop and voltage drop tests suggest that new mechanisms exist affecting the ionic transport. Clearly as shown in Figure 6 (d) – (f), the 21 ACS Paragon Plus Environment


voltage drop tests were performed using Li-S cells, where the separators with or without coating are in direct contact with the two electrodes by compression force during cell assembly. While the pressure drop tests was performed in an open condition. As shown in Figure 6 (d), with bare separator and under the compression force, the soft sulfur particles and CB agglomerates can be squeezed and thus block the separator pores increasing the Li+ transport resistance. In case when PVDF/CB nanocomposite coating is employed, as shown in Figure 6 (e), the poor porous structures in PVDF/CB coating block more the pathways for Li+ transport leading to much higher resistance. This is consistent with the impedance results in Figure 5 (b). On the other hand, when the separator is coated with PSNF as shown in Figure 6 (f), the PSNF coating is in direct contact with S-cathode. The large number of pores with bigger pore sizes in in PSNF open up more pathways promoting Li+ transport. Therefore, adding a PSNF coating on the separator not only effectively traps the dissolved polysulfides, but also improves the separatorcathode contact and facilitates Li+ transport. In summary, we have reported a novel polysulfide nanofilter (PSNF) that is fabricated and functionalized by a natural protein (e.g. gelatin) to address the polysulfide diffusion issues in Li-S batteries. The PSNF is fabricated through a protein-directed self-assembly process under appropriate conditions and the porous structures show more pathways with larger pore size. The PSNF surfaces are functionalized by gelatin proteins, and our simulations and experiments show that PSNF can effectively suppress the shuttle effects from migration of polysulfides. In addition, coating PSNF on a separator significantly improves the separator-cathode contact due to the unique porous structures and generates more pathways for Li+ transport. Therefore, our PSNF is able to trap polysulfides and promote Li+-transport simultaneously. As a result, the PSNF remarkably improves Li-S battery performances in capacity, rate-capability and cycle stability compared with previous studies. Moreover, a simple and facile pressure drop test


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which is usually used for air filters, can be employed to evaluate the coating quality and predict its contribution to electrochemical performances. Acknowledgements This work was supported by USDA NIFA 2015-67021-22911 and NSF CMMI 1463616. The work was also supported by NSF under grant number CBET 1604211. Computational resources were provided in part by the Extreme Science and Engineering Discovery Environment (XSEDE) under Grant No. MCB170012. The authors also gratefully acknowledge the support on characterizations from the Franceschi Microscopy & Imaging Center, and the Composite Materials and Engineering Center at Washington State University. Supporting Information Available: Experimental and simulation sections; SEM images and porosity

of

nanocomposite

coatings;

Mechanical

properties

of

nanocomposites;

Electrochemical performances of controlled samples.

References (1)

Scrosati, B.; Hassoun, J.; Sun, Y.-K. Lithium-Ion Batteries. A Look into the Future. Energy Environ. Sci. 2011, 4 (9), 3287–3295.

(2)

Chen, L.; Shaw, L. L. Recent Advances in Lithium-Sulfur Batteries. J. Power Sources 2014, 267, 770–783.

(3)

Deng, Y.; Li, J.; Li, T.; Gao, X.; Yuan, C. Life Cycle Assessment of Lithium Sulfur Battery for Electric Vehicles. J. Power Sources 2017, 343, 284–295.

(4)

Ghazi, Z. A.; He, X.; Khattak, A. M.; Khan, N. A.; Liang, B.; Iqbal, A.; Wang, J.; Sin, H.; Li, L.; Tang, Z. MoS2/Celgard Separator as Efficient Polysulfide Barrier for LongLife Lithium–Sulfur Batteries. Adv. Mater. 2017, 29 (21), 1–6.

(5)

Xiao, Z.; Xia, Y.; Ren, Z.; Liu, Z.; Xu, G.; Chao, C.; Li, X.; Shen, G.; Han, G. Facile Synthesis of Single-Crystalline Mesoporous α-Fe2O3 and Fe3O4 Nanorods as Anode Materials for Lithium-Ion Batteries. J. Mater. Chem. 2012, 22, 20566.

(6)

Wang, C.; Mo, B.; He, Z.; Shao, Q.; Pan, D.; Wujick, E.; Guo, J.; Xie, X.; Xie, X.; Guo, Z. Crosslinked Norbornene Copolymer Anion Exchange Membrane for Fuel Cells. J. Memb. Sci. 2018, 556, 118–125.

(7)

Du, H.; Zhao, C. X.; Lin, J.; Guo, J.; Wang, B.; Hu, Z.; Shao, Q.; Pan, D.; Wujcik, E. K.; Guo, Z. Carbon Nanomaterials in Direct Liquid Fuel Cells. Chem. Rec. 2018, 18, 1–9. 23 ACS Paragon Plus Environment


(8)

Luo, Q.; Chen, H.; Lin, Y.; Du, H.; Hou, Q.; Hao, F.; Wang, N.; Guo, Z.; Huang, J. Discrete Iron(III) Oxide Nanoislands for Efﬁcient and Photostable Perovskite Solar Cells. Adv. Funct. Mater. 2017, 27, 1702090.

(9)

Liu, T.; Yu, K.; Gao, L.; Chen, H.; Wang, N.; Hao, L.; Li, T.; He, H.; Guo, Z. A Graphene Quantum Dot Decorated SrRuO3 Mesoporous Film as an Efficient Counter Electrode for High-Performance Dye-Sensitized Solar Cells. J. Mater. Chem. A 2017, 5 (34), 17848– 17855.

(10)

Wang, X.; Xiaofei, Z.; Cao, D. Biomass-Derived Nitrogen-Doped Porous Carbons (NPC) and NPC/Polyaniline Composites as High Performance Supercapacitor Materials. Eng. Sci. 2018, 1, 1–23.

(11)

Du, P.; Liu, H. C.; Yi, C.; Wang, K.; Gong, X. Polyaniline-Modified Oriented Graphene Hydrogel Film as the Free-Standing Electrode for Flexible Solid-State Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7 (43), 23932–23940.

(12)

Lin, C.; Hu, L.; Cheng, C.; Sun, K.; Guo, X.; Shao, Q.; Li, J.; Wang, N.; Guo, Z. NanoTiNb2O7/Carbon Nanotubes Composite Anode for Enhanced Lithium-Ion Storage. Electrochim. Acta 2018, 260, 65–72.

(13)

Guo, Z.; Li, C.; Liu, J.; Wang, Y.; Xia, Y. A Long-Life Lithium – Air Battery in Ambient Air with a Polymer Electrolyte Containing a Redox Mediator. Angew. Chemie Int. Ed. 2017, 56 (26), 7505–7509.

(14)

Lou, X.; Lin, C.; Luo, Q.; Zhao, J.; Wang, B.; Li, J.; Shao, Q.; Guo, X.; Wang, N.; Guo, Z. Crystal Structure Modification Enhanced FeNb11O29 Anodes for Lithium-Ion Batteries. ChemElectroChem 2017, 3171–3180.

(15)

Bai, S.; Zhu, K.; Wu, S.; Wang, Y.; Yi, J.; Ishida, M.; Zhou, H. A Long-Life Lithium– sulphur Battery by Integrating Zinc–organic Framework Based Separator. J. Mater. Chem. A 2016, 4 (43), 16812–16817.

(16)

Zhang, S. S.; Tran, D. T.; Zhang, Z. Poly(Acrylic Acid) Gel as a Polysulphide Blocking Layer for High-Performance Lithium/Sulphur Battery. J. Mater. Chem. A 2014, 2 (43), 18288–18292.

(17)

Chung, S. H.; Manthiram, A. Bifunctional Separator with a Light-Weight CarbonCoating for Dynamically and Statically Stable Lithium-Sulfur Batteries. Adv. Funct. Mater. 2014, 24 (33), 5299–5306.

(18)

Xu, R.; Lu, J.; Amine, K. Progress in Mechanistic Understanding and Characterization Techniques of Li-S Batteries. Adv. Energy Mater. 2015, 5 (16), 1500408.

(19)

Barghamadi, M.; Best, A. S.; Bhatt, A. I.; Hollenkamp, A. F.; Musameh, M.; Rees, R. J.; Rüther, T. Lithium–sulfur Batteries—the Solution Is in the Electrolyte, but Is the Electrolyte a Solution? Energy Environ. Sci. 2014, 7 (12), 3902–3920.

(20)

Kang, W.; Deng, N.; Ju, J.; Li, Q.; Wu, D.; Ma, X.; Li, L.; Naebe, M.; Cheng, B. A Review of Recent Developments in Rechargeable Lithium-Sulfur Batteries. Nanoscale 2016, 1, 16541–16588.

(21)

Yin, Y. X.; Xin, S.; Guo, Y. G.; Wan, L. J. Lithium-Sulfur Batteries: Electrochemistry, Materials, and Prospects. Angew. Chemie - Int. Ed. 2013, 52 (50), 13186–13200.

(22)

Chung, S.-H.; Chang, C.-H.; Manthiram, A. A Core-Shell Electrode for Dynamically and Statically Stable Li-S Battery Chemistry. Energy Environ. Sci. 2016, 9, 3188–3200. 24 ACS Paragon Plus Environment

Page 24 of 27

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23)

Bauer, I.; Thieme, S.; Brückner, J.; Althues, H.; Kaskel, S. Reduced Polysulfide Shuttle in Lithium-Sulfur Batteries Using Nafion-Based Separators. J. Power Sources 2014, 251, 417–422.

(24)

Li, G. C.; Li, G. R.; Ye, S. H.; Gao, X. P. A Polyaniline-Coated Sulfur/Carbon Composite with an Enhanced High-Rate Capability as a Cathode Material for Lithium/Sulfur Batteries. Adv. Energy Mater. 2012, 2 (10), 1238–1245.

(25)

Dörfler, S.; Hagen, M.; Althues, H.; Tübke, J.; Kaskel, S.; Hoffmann, M. J. High Capacity Vertical Aligned Carbon Nanotube/Sulfur Composite Cathodes for Lithium– sulfur Batteries. Chem. Commun. 2012, 48 (34), 4097.

(26)

Ji, L.; Rao, M.; Aloni, S.; Wang, L.; Cairns, E. J.; Zhang, Y. Porous Carbon Nanofiber– sulfur Composite Electrodes for Lithium/Sulfur Cells. Energy Environ. Sci. 2011, 4 (12), 5053.

(27)

Wang, H.; Yang, Y.; Liang, Y.; Robinson, J. T.; Li, Y.; Jackson, A.; Cui, Y.; Dai, H. Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium-Sulfur Battery Cathode Material with High Capacity and Cycling Stability. Nano Lett. 2011, 11 (7), 2644–2647.

(28)

Fu, Y.; Manthiram, A. Core-Shell Structured Sulfur-Polypyrrole Composite Cathodes for Lithium-Sulfur Batteries. RSC Adv. 2012, 2 (14), 5927.

(29)

Deng, W.; Zhou, X.; Fang, Q.; Liu, Z. Graphene/Sulfur Composites with a Foam-Like Porous Architecture and Controllable Pore Size for High Performance Lithium-Sulfur Batteries. ChemNanoMat 2016, 2 (10), 952–958.

(30)

Evers, S.; Nazar, L. F. Graphene-Enveloped Sulfur in a One Pot Reaction: A Cathode with Good Coulombic Efficiency and High Practical Sulfur Content. Chem. Commun. 2012, 48 (9), 1233–1235.

(31)

Gao, X. F.; Li, J. Y.; Guan, D. S.; Yuan, C. A Scalable Graphene Sulfur Composite Synthesis for Rechargeable Lithium Batteries with Good Capacity and Excellent Columbic Efficiency. ACS Appl. Mater. Interfaces 2014, 6 (6), 4154–4159.

(32)

Wei, S.; Zhang, H.; Huang, Y.; Wang, W.; Xia, Y.; Yu, Z. Pig Bone Derived Hierarchical Porous Carbon and Its Enhanced Cycling Performance of Lithium–sulfur Batteries. Energy Environ. Sci. 2011, 4 (3), 736.

(33)

Rao, M.; Li, W.; Cairns, E. J. Porous Carbon-Sulfur Composite Cathode for Lithium/Sulfur Cells. Electrochem. commun. 2012, 17 (1), 1–5.

(34)

Jayaprakash, N.; Shen, J.; Moganty, S. S.; Corona, A.; Archer, L. A. Porous Hollow Carbon@sulfur Composites for High-Power Lithium-Sulfur Batteries. Angew. Chemie Int. Ed. 2011, 50 (26), 5904–5908.

(35)

Li, W. Y.; Zheng, G. Y.; Yang, Y.; Seh, Z. W.; Liu, N.; Cui, Y. High-Performance Hollow Sulfur Nanostructured Battery Cathode through a Scalable, Room Temperature, One-Step, Bottom-up Approach. Proc. Natl. Acad. Sci. U. S. A. 2013, 110 (18), 7148– 7153.

(36)

Yang, Y.; Yu, G.; Cha, J. J.; Wu, H.; Vosgueritchian, M.; Yao, Y.; Bao, Z.; Cui, Y. Improving the Performance of Lithium-Sulfur Batteries by Conductive Polymer Coating. ACS Nano 2011, 5 (11), 9187–9193.

(37)

Li, W.; Zhang, Q.; Zheng, G.; Seh, Z. W.; Yao, H.; Cui, Y. Understanding the Role of Different Conductive Polymers in Improving the Nanostructured Sulfur Cathode 25 ACS Paragon Plus Environment


Performance Understanding the Role of Different Conductive Polymers in Improving the Nanostructured Sulfur Cathode Performance. Nano Lett. 2013, 13, 5534–5540. (38)

Yao, H. Bin; Yan, K.; Li, W.; Zheng, G.; Kong, D.; Seh, Z. W.; Narasimhan, V. K.; Liang, Z.; Cui, Y. Improved Lithium-Sulfur Batteries with a Conductive Coating on the Separator to Prevent the Accumulation of Inactive S-Related Species at the CathodeSeparator Interface. Energy Environ. Sci. 2014, 7, 3381–3390.

(39)

Qiu, Y. C.; Li, W. F.; Zhao, W.; Li, G. Z.; Hou, Y.; Liu, M. N.; Zhou, L. S.; Ye, F. M.; Li, H. F.; Wei, Z. H.; Yang, S. H.; Duan, W. H.; Ye, Y. F.; Guo, J. H.; Zhang, Y. G. High-Rate, Ultra Long Cycle-Life Lithium/Sulfur Batteries Enabled by Nitrogen-Doped Graphene. Nano Lett. 2014, 14 (8), 4821–4827.

(40)

Wang, C.; Su, K.; Wan, W.; Guo, H.; Zhou, H.; Chen, J.; Zhang, X.; Huang, Y. High Sulfur Loading Composite Wrapped by 3D Nitrogen-Doped Graphene as a Cathode Material for Lithium-Sulfur Batteries. J. Mater. Chem. A 2014, 2 (14), 5018–5023.

(41)

Song, J.; Gordin, M. L.; Xu, T.; Chen, S.; Yu, Z.; Sohn, H.; Lu, J.; Ren, Y.; Duan, Y.; Wang, D. Strong Lithium Polysulfide Chemisorption on Electroactive Sites of NitrogenDoped Carbon Composites for High-Performance Lithium-Sulfur Battery Cathodes. Angew. Chemie - Int. Ed. 2015, 54 (14), 4325–4329.

(42)

Chen, X. Y.; Chen, C.; Zhang, Z. J.; Xie, D. H.; Deng, X. Nitrogen-Doped Porous Carbon Prepared from Urea Formaldehyde Resins by Template Carbonization Method for Supercapacitors. Ind. Eng. Chem. Res. 2013, 52 (30), 10181–10188.

(43)

Lei, T.; Chen, W.; Huang, J.; Yan, C.; Sun, H.; Wang, C.; Zhang, W.; Li, Y.; Xiong, J. Multi-Functional Layered WS 2 Nanosheets for Enhancing the Performance of LithiumSulfur Batteries. Adv. Energy Mater. 2016, 1601843.

(44)

Tao, X.; Wang, J.; Ying, Z.; Cai, Q.; Zheng, G.; Gan, Y.; Huang, H.; Xia, Y.; Liang, C.; Zhang, W.; Cui, Y. Strong Sulfur Binding with Conducting Magne ́li-Phase Ti. Nano Lett. 2014, 14, 5288–5294.

(45)

Pang, Q.; Kundu, D.; Cuisinier, M.; Nazar, L. F. Surface-Enhanced Redox Chemistry of Polysulphides on a Metallic and Polar Host for Lithium-Sulphur Batteries. Nat Commun 2014, 5, 4759.

(46)

Zhang, S. S. Liquid Electrolyte Lithium/Sulfur Battery: Fundamental Chemistry, Problems, and Solutions. J. Power Sources 2013, 231, 153–162.

(47)

Lu, H.; Yuan, Y.; Yang, Q.; Hou, Z.; Lai, Y. Concentrated Lithium Salt-Monoglyme Complex for Restraining Polysulfide Dissolution and Improving Electrochemical Performance of Lithium-Sulfur Batteries. Ionics (Kiel). 2016, 1–6.

(48)

Hassoun, J.; Scrosati, B. A High-Performance Polymer Tin Sulfur Lithium Ion Battery. Angew. Chemie Int. Ed. 2010, 49 (13), 2371–2374.

(49)

Wang, Y.; Zhong, W.-H. Development of Electrolytes towards Achieving Safe and High-Performance Energy-Storage Devices: A Review. ChemElectroChem 2015, 2 (1), 22–36.

(50)

Yu, X.; Bi, Z.; Zhao, F.; Manthiram, A. Hybrid Lithium-Sulfur Batteries with a Solid Electrolyte Membrane and Lithium Polysulfide Catholyte. ACS Appl. Mater. Interfaces 2015, 7 (30), 16625–16631.

(51)

Lin, Z.; Liang, C. Lithium–sulfur Batteries: From Liquid to Solid Cells. J. Mater. Chem. 26 ACS Paragon Plus Environment

Page 26 of 27

Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A 2015, 3 (3), 936–958. (52)

Wei, H.; Li, B.; Zuo, Y.; Xia, D. Enhanced Cycle Performance of Lithium − Sulfur Batteries Using a Separator Modified with a PVDF ‑ C Layer. 2014, 6, 20276–20281.

(53)

Chung, S.; Manthiram, A. High-Performance Li − S Batteries with an Ultra-Lightweight MWCNT- Coated Separator. J. Phys. Chem. Lett. 2014, 5, 1978–1983.

(54)

Wang, G.; Lai, Y.; Zhang, Z.; Li, J.; Zhang, Z. Enhanced Rate Capability and Cycle Stability of Lithium–sulfur Batteries with a Bifunctional MCNT@PEG-Modified Separator. J. Mater. Chem. A 2015, 3 (13), 7139–7144.

(55)

Wu, F.; Qian, J.; Chen, R.; Ye, Y.; Sun, Z.; Xing, Y.; Li, L. Light-Weight Functional Layer on a Separator as a Polysulfide Immobilizer to Enhance Cycling Stability for Lithium–sulfur Batteries. J. Mater. Chem. A 2016, 17033–17041.

(56)

Zhou, G.; Li, L.; Wang, D. W.; Shan, X. Y.; Pei, S.; Li, F.; Cheng, H. M. A Flexible Sulfur-Graphene-Polypropylene Separator Integrated Electrode for Advanced Li-S Batteries. Adv. Mater. 2015, 27 (4), 641–647.

(57)

Huang, J. Q.; Zhang, Q.; Wei, F. Multi-Functional Separator/Interlayer System for HighStable Lithium-Sulfur Batteries: Progress and Prospects. Energy Storage Mater. 2015, 1, 127–145.

(58)

Li, W.; Hicks-garner, J.; Wang, J.; Liu, J.; Gross, A. F.; Sherman, E.; Graetz, J.; Vajo, J. J.; Liu, P. V2O5 Polysulfide Anion Barrier for Long-Lived Li − S Batteries. 2014, No. 26, 3403–3410.

(59)

Zhang, Z.; Lai, Y.; Zhang, Z.; Zhang, K.; Li, J. Al2O3-Coated Porous Separator for Enhanced Electrochemical Performance of Lithium Sulfur Batteries. Electrochim. Acta 2014, 129, 55–61.

(60)

Singhal, R.; Chung, S.-H.; Manthiram, A.; Kalra, V. A Free-Standing Carbon Nanofiber Interlayer for High-Performance Lithium-Sulfur Batteries. J. Mater. Chem. A 2015, 3 (8), 4530–4538.

(61)

Su, Y. S.; Manthiram, A. Lithium-Sulphur Batteries with a Microporous Carbon Paper as a Bifunctional Interlayer. Nat Commun 2012, 3, 1166.

(62)

Zu, C.; Su, Y.-S.; Fu, Y.; Manthiram, A. Improved Lithium-Sulfur Cells with a Treated Carbon Paper Interlayer. Phys. Chem. Chem. Phys. 2013, 15 (7), 2291–2297.

(63)

Souzandeh, H.; Johnson, K. S.; Wang, Y.; Bhamidipaty, K.; Zhong, W. H. Soy-ProteinBased Nanofabrics for Highly Efficient and Multifunctional Air Filtration. ACS Appl. Mater. Interfaces 2016, 8 (31), 20023–20031.

(64)

Souzandeh, H.; Wang, Y.; Zhong, W.-H. “Green” Nano-Filters: Fine Nanofibers of Natural Protein for High Efficiency Filtration of Particulate Pollutants and Toxic Gases. RSC Adv. 2016, 6 (107), 105948–105956.

(65)

Fu, X.; Wang, Y.; Zhong, W.-H.; Cao, G. A Multifunctional Protein Coating for SelfAssembled Porous Nanostructured Electrodes. ACS Omega 2017, 2 (4), 1679–1686.

(66)

Shoulders, M. D.; Raines, R. T. Collagen Structure and Stability. Annu. Rev. Biochem. 2009, 78 (1), 929–958.


Self-Assembled Protein Nanofilter for Trapping Polysulfides and

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