Building Ion-Conduction Highways in Polymeric Electrolytes by

Subscriber access provided by UNIVERSITY OF LEEDS

Article

Building Ion-conduction Highways in Polymeric Electrolytes by Manipulating Protein Configuration Xuewei Fu, Chunhui Li, Yu Wang, Lucas Paul Kovatch, Louis Scudiero, Jin Liu, and Wei-Hong Zhong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17156 • Publication Date (Web): 15 Jan 2018 Downloaded from http://pubs.acs.org on January 16, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 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

ACS Applied Materials & Interfaces

Building Ion-conduction Highways in Polymeric Electrolytes by Manipulating Protein Configuration Xuewei Fu1, Chunhui Li1, Yu Wang1*, Lucas Paul Kovatch2, Louis Scudiero3, Jin Liu1* and Weihong Zhong1* 1. School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99163, USA. 2. Department of Chemical Engineering, Washington State University, Pullman, WA 99163, USA. 3. Department of Chemistry, Washington State University, Pullman, WA 99163, USA. Corresponding Author * [email protected] (Y. Wang), [email protected] (J. Liu) and [email protected] (W. Zhong) Keywords: composite polymer electrolytes, biotechnology, protein denaturation, ion-conduction manipulation, adhesion.

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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

Page 2 of 30

Abstract Solid polymer electrolytes play a critical role in the development of safe, flexible and all-solid-state energy storage devices. However, the low ion-conductivity has been the primary challenge impeding them from practical applications. Here, we propose a new biotechnology to fabricate novel protein-ceramic hybrid nanofillers for simultaneously boosting the ionic conductivity, mechanical properties and even adhesion properties of solid polymer electrolytes. This hybrid nanofiller is fabricated by coating ion-conductive soy-proteins onto TiO2 nanoparticles via a controlled denaturation process in appropriate solvent and conditions. It is found that the chain configuration and protein/TiO2 interactions in the hybrid nanofiller play critical roles in improving not only the mechanical properties, but also the ion-conductivity, electrochemical stability and adhesion properties. Particularly, the ion-conductivity is improved by one magnitude from 5 x 10-6 to 6 x 10-5 S/cm at room temperature. To understand the possible mechanisms, we perform molecular simulation to study the chain configuration and protein/TiO2 interactions. Simulation results indicate that the denaturation environment and procedures can significantly change the protein configuration and the protein/TiO2 interactions, both of which are found critical for the ion-conductivity and mechanical properties of the resultant solid composite electrolytes. This study indicates that biotechnology of manipulating protein configuration can bring novel and promising strategies to build unique ion channels for fast ion-conduction in solid polymer electrolytes.


2

Page 3 of 30 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


1. Introduction Energy storage devices (ESDs) such as lithium ion batteries (LIBs) assembled with liquid electrolytes (LEs) have gained significant success in commercial applications over the past decades.1,2 With the rapid development of electric vehicles, flexible and wearable electronic devices, there is an increasing demand on advanced ESDs which show excellent safety and mechanical flexibility, in addition to high energy/power densities. As is well known that, the widely used LEs are the main reason for safety concerns of LIBs due to their flammability and leakage issues, which represents the most critical issue for current LIBs technology.3-4 Replacing the LEs by solid electrolytes, such as solid polymer electrolytes (SPEs) or inorganic ceramic electrolytes, is believed the most attractive solution to resolve the safety issues5-6. Among the two types of solid electrolytes, SPEs are very attractive owing to their excellent mechanical flexibility and also materials processability, which cannot be realized in inorganic solid electrolytes. As a result, considerable attention has been paid to fabricating SPEs by dissolving lithium salts (e.g., LiClO4, LiPF6, LiTFSI, etc.) in different kinds of polymer hosts, such as poly(ethylene oxide) (PEO)7,8, polyacrylonitrile (PAN)9,10, poly(propylene carbonate)11,12 and so on. However, these simple salt-polymer solid solution systems always give rise to an extremely low ionic conductivity well below 10-5 S/cm at room temperature1,13-14 which blocks them from practical applications. Therefore, improving the ion-conductivity of SPEs to be on the level for practical application (e.g. 10-4 S/cm at room temperature) is the key task for the development of SPEs. To improve the ionic conductivity, different strategies have been reported in previous studies. Addition of plasticizer is the first common strategy. The plasticizer usually include liquid electrolytes with high ionic conductivity or low molecular weight polymers, which can


3


Page 4 of 30

significantly improve the mobility of polymer chains and so the ionic conductivity.15,16 However, unfortunately, this strategy requires a high loading of plasticizer to achieve an ionic conductivity around the liquid electrolyte level, which, most of the time, destroys the attractive advantages of SPEs, such as good mechanical properties and safety. Efforts to achieve a good balance between ion-conductivity and mechanical properties have been the main focus for the studies on this type of solid polymer electrolytes, also well-known as gel-type polymer electrolytes.17,18 Different from the first strategy, addition of functional fillers represents another attractive method to improve the ion-conductivity without sacrificing mechanical properties. It is generally believed that the introduction of nanofillers into SPEs, e.g. ceramic nanofillers, can effectively improve the ionic conductivity primarily due to two different mechanisms. The first one is the reduction of crystallinity of the polymer host by the effects of nanofillers.19,20 The second one is the possible fast ion-conduction at the filler-polymer interfaces, which is contributed by Lewis acid-base interactions between the ions and the ceramics surface21,22. Some of the ceramic nanofillers, including MgO,19,23,24 Al2O3,25–27 SiO2,21,28,29 TiO2,8,30,31 etc. have been found very effective to increase the ionic conductivity of SPEs. However, for these nanofillers, due to agglomeration caused by weak polymer-ceramic interaction and non-conductive nature of the nanofillers, further improvement remains a big challenge.21,32 Therefore, efforts on solid composite polymer electrolytes (CPEs), have been focused on modifying the traditional nanofillers or developing new nanofillers for improved ion-conductivity. Surface modification of the nanofillers represents a simple but significant approach. It can improve not only the dispersion quality of the nanofillers, but also enables the control of interfaces and interactions among the polymer host and ions. To realize fast ion-conduction, the surface functionalization is usually aimed to achieve appropriate interactions between the


4

Page 5 of 30 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


nanofiller surface and ions, which can facilitate the ion-dissociation and improve the ionic conductivity. For example, it is found that core-shell silica with boron moiety on the shell by Shim and Lee et. al33, and TiO2 grafted-PEGMEM/SMA nanohybrid by Ma and Wei et. al34 can extensively enhance the ionic conductivity of the CPEs. Design of new naofillers with special morphology or ion-conductive properties is another attractive method to build fast pathways for ion-transport, such as the mesoporous silica by Kim and Park et. al35; metal-organic frames (MOFs) by Yuan and Liu et. al22. Among these new nanofillers, ion-conductive nanofillers, such as Li3N19, Li1.3Al0.3Ti1.7(PO4)336, are very effective as they can provide additional conduction pathways and mechanisms for fast ion-conduction. In particular, one-dimensional (1-D) ion-conductive nanofillers have been reported as advanced nanofillers for solid CPEs.37,38 1-D ion-conductive nanofillers can help to build fast ion-conduction pathways through the interface or the ion-conductive filler itself. Therefore, it is believed that design of advanced nanofillers with unique surface structures and properties for fast ion-conduction is a primary and promising method for fabrication of high-performance composite solid polymer electrolytes. In our previous work, we have demonstrated that denatured soy-protein can form unique protein-ion complex and finally result in a solid ion-conductor, that is, a protein ion-conductor, showing ionic conductivity at the level of 10-5 S/cm at room temperature.39 At the same time, proteins have been well studied as effective surfactant for dispersing nanoparticles in polymer matrix to exhibit good interfacial properties.40,41 Based on these previous studies, in this study, we further developed a new hybrid nanofiller via combining the ion-conductive soy-protein and one classic ceramic nanoparticle, TiO2, to form a unique protein-ceramic hybrid nanofiller for improving the ion-conductivity of solid polymer electrolytes. The matrix of the solid polymer electrolyte is an amorphous material based on the complex of ultrahigh molecular weight


5


Page 6 of 30

poly(ethylene oxide) (UHMWPEO) and LiClO4.42,43 Through experiments and molecular simulations, here we demonstrate that possible fast ion-conductive pathways may be constructed by proper adjusting the structure of the soy-protein attached onto the TiO2 nanoparticles.

In

addition, we found that, for the resultant composite solid polymer electrolytes, the mechanical properties, electrochemical stability, as well as adhesion properties are significantly improved by the unique protein-ceramic hybrid nanofillers. 2. Results and Discussion

Figure 1. Schematic for the preparation of TiO2-soy protein hybrid nanofillers with different protein configuration and ion-conductive properties: (a) Conventional TiO2-soy protein hybrid with insufficient and weak attachment of denatured soy protein chains onto TiO2 surface. This type of hybrid can be prepared simply by dispersing TiO2 nanoparticles into denatured soy protein solution; (b) Ion-conductive TiO2-soy protein hybrid with unique surface coating of soy protein chains forming special ion-channel. This unique hybrid is prepared by


6

Page 7 of 30 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


denaturation of soy protein directly in TiO2 nano-dispersion. The solvent employed for these two procedures is a mixture of acetic acid (AA) and DI-water with a weight ratio of 8:2. For details, see the text. To prepare the protein-ceramic hybrid nanofillers, we proposed two different procedures as shown in Figure 1. The soy proteins (SPs) in aqueous environments at native state are compact with several levels of structures through various inter-chain bonding and interactions, such as H-bonding, salt-bridges, hydrophobic interactions and disulfide bonding.44,45 In order to open the structures of protein and expose the functional groups, denaturation of SP at different conditions was first studied. As shown in Figure 1 (a), in our first procedure, the soy protein was first denatured at high temperature (95 °C) in acidic environment (aq. acetic acid, pH=2) for 1 h.46 Then, the TiO2 nanoparticles were added into the solution and dispersed through ultrasonication. In this case, the denatured soy protein works simply as a surfactant to TiO2 particles. In the second procedure as shown in Figure 1 (b), the TiO2 nanoparticles were first pre-dispersed in acidic environment (aq. acetic acid, pH=2), then the SP was added and denatured together with the TiO2 nanoparticles at 95 °C in the same acidic solvent for 1 h. In this situation, the TiO2 nanoparticles actively participate in the protein denaturation process. The rutile surface of TiO2 is polar47 due to the negative charge on oxygen atoms and positive charge on the Ti atoms. Moreover, on the surface the Ti atoms may even be hydroxylated and the oxygen atoms may be protonated to certain degree depending under certain experimental conditions.48,49 Therefore, the presence of the TiO2 nanoparticle may significantly affect the protein denaturation environment, lead to more open and flexible protein structures as illustrated in Figure 1. We expect that the promoted denaturation of the protein and exposure of the protein functional groups will greatly impact the interactions as well as protein configurations, and eventually lead to CPEs with much


7


Page 8 of 30

improved electrochemical, mechanical and adhesive properties. In the following sections we will investigate such CPEs in details through both experiments and simulations.

Figure 2. Morphology studies of the TiO2 nanoparticles, TiO2-SP hybrids and the resultant composite polymer electrolytes (CPEs). (a) – (c) SEM images of untreated TiO2, TiO2-(SP-close) and TiO2-(SP-open) hybrids, respectively; (d) – (f) SEM images of the CPEs with 5 wt% loading of untreated TiO2, TiO2-(SP-close) and TiO2-(SP-open) hybrids, respectively. The matrix is an amorphous solid polymer electrolyte based on ultra-high molecular weight poly(ethylene oxide).43 2. 1. Morphology study For CPEs, the dispersion of the nanofillers is a critical factor affecting the ion-conduction pathways as well as the mechanical properties.33,50,51 The dispersion of different nanofillers in the suspension was first examined by SEM and the results are shown in Figures 2 (a) – (c) (also see the particle size distribution in Supporting Info Figure S1). From these SEM images, significant differences in dispersion between the hybrid nanofillers and the untreated TiO2 nanoparticles are


8

Page 9 of 30 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


observed. For the untreated TiO2, the nanoparticles tend to severely aggregate (Figure 2a) and form agglomerates; however, as shown in Figures 2 (b) and (c), the two types of TiO2-SP hybrids both exhibit significantly reduced particle size, indicating a much-improved dispersion in the suspension. Similar results have been found for the resultant CPEs as shown in Figures 2 (d) – (e). In specific, one can find a poor dispersion of the untreated TiO2 in the electrolyte matrix (the PEO-based solid polymer electrolyte with LiClO4 loading of 28 wt%). The size of the agglomerates as shown in Figure 2d is about 1 µm (see Figure S1 (a)). In contrast, for the CPEs with the two hybrid nanofillers, the dispersion of the hybrid nanofillers in the matrix is greatly improved with much reduced agglomerate size of 50 ~ 60 nm in average as shown in Figures 2 (e) and (f) (also see the size distribution in Figures S1 (b) and (c)). These results indicate that the protein treatment on the TiO2 surface plays an important role in improving the dispersion quality and enhancing the compatibility between the nanoparticle and polymer host, which will significantly affect the ionic transport as will be discussed later. In addition, to evaluate the thermal stability of the hybrid nanofillers and prove the presence of protein on the TiO2 surface, thermogravimetric analysis (TGA) was performed and the results are shown in Figure S2. As shown, the TiO2-(SP-open) hybrid nanofiller shows dramatic weight loss from ca. 250 °C due to degradation of protein. At the same time, the TGA data indicate that there is about 12 wt% protein coated onto the TiO2 surface. 2. 2. Electrochemical properties and mechanical properties


9


Page 10 of 30

Figure 3. Ionic conductivity and mechanical properties of CPEs with the TiO2-SP hybrids. (a) Comparison of room temperature ionic conductivity for pure PEO-LiClO4 electrolyte, CPEs with 5 wt% loading of untreated TiO2, TiO2-(SP-close) hybrid and TiO2-(SP-open) hybrid nanofillers with weight ratio TiO2/SP of 4:1; (b) Ionic conductivity comparison of CPEs with the two types of hybrid nanofillers at varying loadings (weight ratio of TiO2 : SP = 4:1); (c) The effect of protein percentage in the TiO2-(SP-open) hybrid on ionic conductivity (the loading of the hybrid nanofiller is kept as 5 wt% in the final CPEs); (d) Storage modulus of pure PEO-LiClO4 electrolyte and CPEs with 5 wt% loading of untreated TiO2, TiO2-(SP-close) hybrid and TiO2-(SP-open) hybrid; (e) Summary of ionic conductivity and mechanical properties of the CPEs as compared with the pure SPEs. (f) Ion-conductivity distribution for advanced SPEs and CPEs based on PEO-Li+ system. 12,20–22,38,52–58 The electrochemical and mechanical properties of the CPEs with two types of TiO2-SP hybrids were further studied and compared with the pure SPE (i.e., the matrix of the CPEs without


10

Page 11 of 30 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


nanofillers) and CPE with untreated TiO2. We measured the ionic conductivity and modulus of the CPEs and the results are shown in Figure 3. As shown in Figure 3 (a), the ionic conductivities for all three types of CPEs are much higher than that of the pure PEO-LiClO4 electrolyte which is around 5 x 10-6 S/cm at room temperature. More importantly, the two hybrid nanofillers exhibit significant improvement in the ionic conductivity as compared with the CPE with untreated TiO2 nanoparticles. In specific, the CPE loaded with 5 wt% TiO2-(SP-open) hybrid nanofiller yields the highest ionic conductivity of 6 x 10-5 S/cm at room temperature, which is about one magnitude higher than that of the pure PEO-LiClO4 electrolyte, and 5 times of the CPEs with TiO2-(SP-close) hybrid or untreated TiO2 nanofillers. To identify the optimum loading, the loading of the two hybrid nanofillers was varied from 1 to 10 wt% and the ion-conductivity results of these CPEs are shown in Figure 3 (b). As shown, the ionic conductivity of the CPEs with TiO2-(SP-open) hybrid is evidently higher than that of CPEs with TiO2-(SP-close) hybrid throughout all the loading range, and the maximum ionic conductivity is reached at 5 wt% loading. The ionic conductivity for both cases decreases slightly when the loading exceeds 6 wt% possibly due to formation of agglomerates (See SEM images in Figure S3 Supporting Info.). We further investigate the effect of the weight ratio between the SP and TiO2 on the ionic conductivity. As shown in Figure 3 (c), the ionic conductivity is optimized at 6.5 x 10-5 S/cm by the TiO2-(SP-open) hybrid with TiO2/SP ratio of 4:1. It indicates that the TiO2/SP ratio for the hybrids plays an important role in affecting both dispersion and ionic conductivity (See SEM images in Figure S4 Supporting Info.). The above results reveal that the TiO2-(SP-open) hybrid is more effective for improving the ionic conductivity as compared with conventional TiO2-(SP-close) hybrid, even though they have exactly the same composition as demonstrated in Figure 1.

Based on the above findings, we can conclude that the unique


11


Page 12 of 30

TiO2-SP hybrid (TiO2-(SP-open) hybrid), when prepared by the modified procedure as shown in Figure 1 (b) at appropriate TiO2/SP ratio, can assist in building special ion-conduction pathways for fast ion-conduction in the resultant CPEs. The possible mechanisms will be further discussed in our simulation studies later. In addition to ionic conductivity, mechanical property is another critical property for solid electrolytes. A high modulus and good mechanical flexibility is highly desired for SPEs and CPEs to be used as separator and suppress the growth of lithium dendrites.59,60 Figure 3 (d) shows the mechanical properties of all the CPEs with 5 wt% loading of nanofillers as compared with pure PEO-LiClO4 electrolyte. The moduli of all the CPEs are much higher than pure PEO-LiClO4 electrolyte, and the CPE with TiO2-(SP-open) hybrid nanofiller yields the highest modulus of ca. 1 MPa at 1 Hz. There are two important points worthy of discussion here. First, the moduli of CPEs with the two kinds of TiO2-SP hybrid nanofillers are significantly higher than that of the CPE with untreated TiO2 nanoparticles. This result indicates that the protein-treatment of TiO2 significantly affects the mechanical properties by improving both the dispersion and interfaces, as demonstrated in Figure 2 (d) – (f). Second, the modulus for the CPE with TiO2-(SP-open) hybrid is slightly higher than that of the CPE with conventional TiO2-(SP-close) hybrid, which may indicate that the interface between TiO2-(SP-open) hybrid and PEO-LiClO4 matrix is much better than that for the CPE with conventional TiO2-(SP-close) hybrid. Figure 3 (e) summarizes both the ionic conductivities and moduli of all CPEs. It is well-known that there is always a trade-off between ion-conductivity and modulus in SPEs or CPEs due to the coupling effects between the ion-conduction and chain mobility of the matrix.5,39,61 However, for the CPEs with TiO2-(SP-close) hybrid and TiO2-(SP-open) hybrid, they show simultaneous improvement in both ionic conductivity and modulus as shown in


12

Page 13 of 30 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


Figure 3 (e). In particular, the CPE loaded with TiO2-(SP-open) hybrid shows the highest ionic conductivity and modulus among all the CPEs. We believe that the unique protein/TiO2 and protein/ PEO-LiClO4 interactions in the TiO2-(SP-open) hybrid CPE play critical roles in these properties. To further demonstrate the advantages of the TiO2-(SP-open) hybrid, Figure 3 (f) summarizes the room temperature ionic conductivity for the state-of-the-art solvent-free SPEs and CPEs based on PEO-Li+ system. Although the comparison of the ion-conductivity for these solid electrolytes is not rigorous since it is affected by many other factors and these factors are not the same for these studies, it can qualitatively show the unique advantages of the TiO2-(SP-open) hybrid for fabrication of advanced CPEs. In specific, Figure 3 (f) summarizes the ion-conductivity for three different modified systems based on PEO-Li+ solid electrolyte. The first category is the system with improved ion-conductivity via polymer blends and/or copolymers. The second category is the system by grafting conductive block (usually PEO-block) onto inorganic nanoparticles or molecules, which forms special ion-conductive hybrid materials. The third category, also the most common one, is the system by compositing the PEO-Li+ solid electrolyte with different types of nanofillers, including ion-conductive and non-conductive ones. Figure 3 (f) shows that the TiO2-(SP-open) hybrid nanofillers from our work give rise to the most improvement in ion-conductivity among various kinds of nanofillers reported for CPEs. As a result, the ionic conductivity of our CPE with TiO2-(SP-open) hybrid nanofillers reaches nearly the maximum value among all available SPEs and CPEs. More importantly, the mechanical property of our CPE is simultaneously improved.


13


Page 14 of 30

Figure 4. (a) Arrhenius plots of ionic conductivity of CPEs with the TiO2-SP hybrid nanofillers as compared with pure PEO-LiClO4 electrolyte; (b) Electrochemical stability studies of the CPEs as compared with pure PEO-LiClO4 electrolyte; (c) Discharge-charge profiles of LiCoO2/CPETiO2-(SP-open) hybrid/Li cells with varying C-rates tested at 65 °C; (d) Cycle performance and coulombic efficiency of LiCoO2/CPE- TiO2-(SP-open) hybrid/Li cells at 0.1 C tested at 65 °C. The ionic conductivity of the CPEs as a function of temperature is further studied and displayed in Figure 4 (a). For comparison, the ionic conductivity of PEO-LiClO4 electrolyte without nanofillers is also included in this figure. The ionic conductivity of the CPEs with TiO2-(SP-open) hybrid is found to be the highest throughout the temperature range. In specific,


14

Page 15 of 30 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


the ionic conductivity for the CPE with conventional TiO2-(SP-close) hybrid or the pure PEO-LiClO4 electrolyte is in the range of 10-5 – 10-4 S/cm when the temperature varies from 20 to 90 0C. However, for the CPE with TiO2-(SP-open) hybrid, the ion-conductivity increases to ca. 7 x 10-4 S/cm at 90 °C, which is close to the level of liquid electrolytes. In addition to ionic conductivity, the contribution of the nanofillers to the electrochemical stability was also characterized and the results are shown in Figure 4 (b). It is known that a wide electrochemical stability of the electrolytes is crucial for safety. As shown the pure PEO-LiClO4 electrolyte is electrochemically stabile below ca. 5.1 V, which is higher than that of organic liquid electrolytes (4.5 V)62,63. More importantly, for the two CPEs with TiO2-SP hybrid nanofillers, the electrochemical stability is evidently improved (5.2 V for TiO2-(SP-close)-CPE and 5.4 V for TiO2-(SP-open)-CPE). This result indicates that the addition of TiO2-SP hybrid can suppress the decomposition of PEO-LiClO4 electrolyte, which is consistent with other studies on nanofillers.64,65,66 To further investigate the electrochemical performance of the CPEs in a real device, the half cells containing the CPE with TiO2-(SP-open) hybrid nanofillers were assembled and tested at 65 °C. Figure 4 (c) presents the charge-discharge profiles for LiCoO2/CPE-TiO2-(SP-open)-hybrid/Li half cells at varying C-rates. As shown, typical LiCoO2 voltage profiles can be observed for the half cells, which suggests that the cells work very well and stably upon different C-rates (Also see Figure S5 (a) for C-rate performance). Figure 4 (d) displays the discharge capacity and coulombic efficiency versus cycle number at 0.1 C. Specifically, one can find that the capacity slightly decreased from 135 to 128 mAh/g after 24 cycles, and the Coulombic efficiency is slightly lower (about 95%) than traditional LCO system. This result indicates two points: firstly, it means that the new electrolyte can work simultaneously as separator and ion-conductor as


15


Page 16 of 30

designed; secondly, it means that there are some complicated factors contributing to the battery performance, such as, possible instable microstructures of the electrode, and the unknown SEI layer between the new solid electrolyte and lithium metal. At the same time, the improved interfacial property by adhesion can also be proved by electrochemical impedance spectra as shown in Figure S5 (b). The CPE loaded with 5 wt% TiO2-(SP-open) nanofillers shows much lower charger transfer resistance, as compared with the CPE with 5 wt% untreated TiO2. It indicates that the higher ionic conductivity and better interfacial property of CPE with TiO2-(SP-open) nanofillers can help to achieve faster charge transfer in the cell. 2. 3. Adhesion properties

Figure 5. Adhesion properties studies of the CPEs with TiO2-SP hybrid nanofillers. (a) – (c) Adhesion force mapping by AFM for the CPEs loaded with (b) TiO2 and (c) TiO2-(SP-open) hybrid compared with (a) pure PEO-LiClO4 electrolyte; (d) Comparison of the average adhesion


16

Page 17 of 30 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


force of the solid electrolytes; (e) Digital photo showing a strong adhesion between the CPE loaded with TiO2-(SP-open) hybrid and stainless steel; (f) Schematic of the possible mechanism for the TiO2-(SP-open) hybrid to improve the adhesion of the CPEs. In addition to the above contributions to electrochemical and mechanical properties, the TiO2-(SP-open) hybrid also improves the adhesion properties of CPEs. For SPEs, a strong adhesion of electrolyte allows stable contact between electrode and electrolyte.67,68 The adhesion force mappings of the electrolyte systems obtained by peak force QNM characterization via AFM are displayed in Figures 5 (a) – (c). For pure PEO-LiClO4 electrolyte as shown in Figure 5 (a), the adhesion force is between 6.9 and 10.5 nN. The force is contributed by amorphous structures of the PEO-Li+ complex as revealed by our previous studies42,43

the

from the

DSC characterization as well as optical microscopy images (See Figure S6, Supporting Info.). For the CPE with untreated TiO2 nanoparticles, the adhesion force decreases and ranges from 2.1 to 7.9 nN. However, interestingly the TiO2-(SP-open) hybrid can enhance the adhesion force as shown in Figure 5 (c), and the adhesion force ranges from 6.8 and 13.9 nN. Figure 5 (d) compares the average adhesion force for all these solid electrolyte samples. As shown, the average adhesion force of the CPE loaded with TiO2-(SP-open) hybrid is the highest among all the samples. (~ 11 nN). As demonstrated in Figure 5 (e), the CPE filled with TiO2-(SP-open) hybrid exhibits strong adhesion to a stainless steel. At the same time, it shows good mechanical properties (0.9 MPa at 5 HZ) and flexibility allowing stretching without fracture. Although the mechanisms for adhesion contribution may be complicated, we believe that the SP coating onto the TiO2 nanoparticles is the key for the improved adhesion properties since SP has been widely used as a class of adhesive for engineering applications.69 To illustrate this contribution, Figure 5 (f) lists the possible interactions at the interface contributed by the protein chain. The unique


17


Page 18 of 30

and richness of functional groups along with the protein chain may provide strong interactions to the substrate surface, including charge-charge interactions, hydrogen bonding, Van der Waals force, π-π interactions etc.59 2. 4. Simulation studies of the TiO2-SP hybrids

Figure 6. Molecular simulation studies of the soy-protein (SP) denaturation with or without TiO2. (a) – (b) Snapshot of the final state of denatured SP in mixture solvent of acetic acid (yellow) and H2O (red) under two conditions: w/o and w/ TiO2 (shown as plate), respectively; (c) Time evolution of the radius of gyration (Rg) of denatured SP under the two different conditions; (d) Illustration of adsorption of acid molecules on TiO2 surface; (e) Number density of acetic acid (oxygen atom on hydroxyl group) and water (oxygen atom) molecules along the Z direction.

Simulation studies on the soy-protein (SP) denaturation. As illustrated in Figure 1, careful control of the denaturation/mixing process may result in quite different protein configurations


18

Page 19 of 30 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


and protein/particle interactions, and eventually lead to different electrochemical and mechanical properties of the resulting CPEs. To uncover the underlying mechanisms, molecular dynamics (MD) simulations mimicking the experimental conditions have been carried out in this study (for details, See Experimental method). Our simulations have been divided into two parts. The first part is to study the protein denaturation process under two conditions as illustrated in Figure 1. In the first case, the SP was denatured in the AA/DI solvent at 95 oC without TiO2 nanoparticles. As shown by the snapshot in Figure 6 (a) and the time evolution of the radius of gyration (Rg) in Figure 6 (c), the protein structure quickly changes during the first 20 ns with a dramatic increase of Rg from 1.9 nm to 2.1 nm for the SP denatured without TiO2. Figure 6 (a) also reveals that only part of the protein has been unfolded, while the rest still keeps compact throughout the rest of the simulation with a relatively stable Rg fluctuates around 2.1 nm. Interestingly, for the SP denatured with the TiO2 nanoparticles, the SP undergoes much more dramatic structural changes. As shown in Figure 6 (c), the Rg of the protein increases from ~1.5 nm to ~2.5 nm during 200 ns simulations, and nearly all of the original structures have been destroyed (see the snapshot in Figure 6 (b)). The results clearly indicate that in the second case, the TiO2 nanoparticle strongly affect the protein denaturation process. Inspection of the TiO2 surface indicates a significant accumulation of the solvent molecules, including both acetic acid and water, due to the strong electrostatic interactions. As demonstrated in Figure 6 (d) and (e), this surface accumulation causes the depletion of solvent molecules in the bulk. The solvent molecules, such as water, in solution tend to stabilize the original protein structures through H-bonding, therefore a depletion of the water likely promotes the protein denaturation.


19


Page 20 of 30

Simulation studies on the TiO2/SP interactions. We have demonstrated above that TiO2 plays a critical role in denaturing protein. During the second part of our simulations we focus on the protein-particle interactions after protein denaturation. We first reduced the system temperatures to room temperature, then added TiO2 nanoparticle into the first case and carried out another 200 ns simulations. The initial and final states of protein-TiO2 configurations for both cases are illustrated in Figure 7. As shown in Figure 7 (a), for the first case a weak absorption of SP by the TiO2 was observed and the denatured SP chain with a more closed configuration jumped back and forth near the TiO2 surface. In contrast, for the second case we found a quite strong SP adsorption onto the nanoparticle surface throughout the 200 ns simulation as shown in Figure 7 (b). The denatured SP was locked onto the TiO2 surface throughout the entire process. Analysis of the individual energetic contributions from different residues indicates that the strong adsorption is dominated by the electrostatic interactions between the positively charged amino acids (such as Arg-30 and Arg-38 as illustrated in the inset of Figure 7 (b)) and the negatively charged oxygen atoms on TiO2 rutile surface. As shown in Figure 7 (b), the electrostatic interactions are strong enough such that the Arginine groups are able to penetrate the first solvent layer and direct contact with the rutile surface.


20

Page 21 of 30 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


Figure 7. Simulation studies on the interactions between denatured SP and TiO2 nanoparticles. (a) Weak and unstable absorption of SP onto TiO2 nanoparticles in TiO2-(SP-close) hybrid; (b) Strong and stable absorption of SP onto TiO2 nanoparticles in TiO2-(SP-open) hybrid; (c) Schematics of fast ion-conduction channel formed in TiO2-(SP-open)


21


Page 22 of 30

hybrid and ion transport pathways in CPEs with TiO2-(SP-open) hybrid compared with TiO2-(SP-close) hybrid. Although it is still difficult to completely explain why the TiO2-(SP-open) hybrid nanofiller can notably outperform other nanofillers (i.e., TiO2-(SP-close) hybrid and untreated TiO2) as found in the experimental studies (see Figure 3), the above simulation studies bring critical clues for us to understand the mechanisms. Based on our experimental and simulation results, we propose a possible model as illustrated in Figure 7 (c) for explaining the unique contribution to ion-conduction in the CPE from the TiO2-(SP-open) hybrid. In this model, the presence of TiO2 promotes the denaturation of SP and the exposure of protein functional groups. As a result, the denatured SPs strongly bind to TiO2 surface and form a stable SP coating. The protein coating on TiO2 surface improves the dispersion of nanofillers in solution, meanwhile the functional groups on protein coating also actively interact with the polymer matrix (PEO in our experiments) leading to improved mechanical strength and flexibility. More importantly, during the fabrication of CPEs, the denatured SP can interact with lithium salts through strong electrostatic interaction between backbone oxygen of protein and Li+, and form anion clusters via strong electrostatic interactions between positive charge side groups (e.g. Lys. Arg.) of protein and anions (ClO4-), as revealed by our previous study39, creating ion conductive pathways and facilitating (see Figure 7(c)) fast Li+-transportation. This model indicates that manipulating the protein configuration by nanofillers will enable us to build novel ion channels for fast ion-conduction in solid polymer electrolytes. Meanwhile, we also propose a possible model to help us understand how the TiO2-(SP-open) hybrid nanofiller help the ion-transportation inside the CPEs. For the CPE with untreated TiO2 nanoparticles, the contribution from TiO2 to the ion-conduction is limited by the big


22

Page 23 of 30 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


agglomerates as revealed by SEM images shown in Figure 2 (a) and (d). In this situation, the transportation of lithium ions is mainly controlled by the polymer matrix, the TiO2 agglomerates do not help much and may even block the ionic transport.21,32 On the other hand, protein treatment can significantly reduce the particle aggregation41. At the same time, the denatured proteins on TiO2-SP hybrid may form unique ionic pathways for ion transport, depending on the protein configuration as revealed in this study. More specifically, even though the TiO2-(SP-close) sample shows similar nanofiller dispersion as that for TiO2-(SP-open) sample (see SEM images in Figure 2 (b, c, e, f)), the ion-transport is very different because of the difference in protein configuration structures on the TiO2 surfaces. For the TiO2-(SP-open) nanofillers, the completely unfolded configuration can help form effective ionic pathways to accelerate the ionic conduction,39 which explains the improved ion-conductivity as shown in Figure 3 (b). Other factors, such as protein/PEO-Li+ interactions may also significantly contribute the ion conduction, which will be studied in more details in our following work. 3. Conclusions In summary, we have demonstrated the fabrication of high-performance solvent-free composite polymer electrolytes (CPEs) with novel protein-ceramic hybrid nanofillers. The hybrid nanofillers can be fabricated by a simple biotechnology with a subtle control on the denaturation of soy-protein (SP) in the presence of TiO2 nanoparticles. We found that the ion-conduction of the TiO2-SP hybrid nanofillers was sensitive to the protein structures as revealed by both experimental and simulation studies. In specific, when TiO2 nanoparticles actively participate in protein denaturation, a more open and flexible structures of SP can be obtained. The elevated structural flexibility promotes protein-TiO2 interactions and helps to form ion conductive pathways. The ionic conductivity of the resultant CPEs has been significantly improved from 5 x


23


Page 24 of 30

10-6 to 6 x 10-5 S/cm at room temperature. In addition, other significant properties, such as electrochemical stability, mechanical properties and even adhesion properties, all are improved by the addition of the unique TiO2-(SP-open) hybrid nanofiller. The studies in this work bring a facile strategy based on controlling the structures and functions of natural proteins for design and fabrication of new organic-inorganic hybrid nanofillers to address the challenging issues in conventional solid polymer electrolytes. Supporting Information Experimental and simulation methods; SEM images of CPEs with different nanofillers; Agglomerate statistics; TGA curves of nanofillers; C-rate performance of half-cells with CPEs loaded with TiO2-(SP-open) hybrid nanofillers; Nyquist plots of half-cells; DSC curves and Polarized Optical Microscopy images of CPEs.

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support from USDA NIFA 2015-67021-22911, NSF CMMI 1463616 and NSF CBET 1604211. 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. Computational resources were provided in part by the Extreme Science and Engineering Discovery Environment (XSEDE) under Grant No. MCB170012.

REFERENCES (1)

Xue, Z.; He, D.; Xie, X. Poly(ethylene Oxide)-Based Electrolytes for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3 (38), 19218–19253.

(2)

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

(3)

Wen, J.; Yu, Y.; Chen, C. A Review on Lithium-Ion Batteries Safety Issues: Existing


24

Page 25 of 30 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


Problems and Possible Solutions. Mater. Express 2012, 2 (3), 197–212. (4)

Agrawal, R. C.; Pandey, G. P. Solid Polymer Electrolytes: Materials Designing and All-Solid-State Battery Applications: An Overview. J. Phys. D. Appl. Phys. 2008, 41 (22), 223001.

(5)

Golodnitsky, D.; Strauss, E.; Peled, E.; Greenbaum, S. Review—On Order and Disorder in Polymer Electrolytes. J. Electrochem. Soc. 2015, 162 (14), A2551–A2566.

(6)

Wang, X.; Lu, X.; Liu, B.; Chen, D.; Tong, Y.; Shen, G. Flexible Energy-Storage Devices: Design Consideration and Recent Progress. Adv. Mater. 2014, 26 (28), 4763–4782.

(7)

Diddens, D.; Heuer, A.; Borodin, O. Understanding the Lithium Transport within a Rouse-Based Model for a PEO/LiTFSI Polymer Electrolyte. Macromolecules 2010, 43 (4), 2028–2036.

(8)

Guo, C.; Zhou, L.; Lv, J. Effect of Nano-TiO2 Dispersion on PEO Polymer Electrolyte Property. J. Appl. Polym. Sci. 2010, 118, 2976–2980.

(9)

Flora, X. H.; Ulaganathan, M.; Rajendran, S. Influence of Lithium Salt Concentration on PAN-PMMA Blend Polymer Electrolytes. Int. J. Electrochem. Sci. 2012, 7 (8), 7451– 7462.

(10)

Kuo, P.-L.; Wu, C.-A.; Lu, C.-Y.; Tsao, C.-H.; Hsu, C.-H.; Hou, S.-S. High Performance of Transferring Lithium Ion for Polyacrylonitrile-Interpenetrating Crosslinked Polyoxyethylene Network as Gel Polymer Electrolyte. ACS Appl. Mater. Interfaces 2014, 6, 3156–3162.

(11)

Zhang, J.; Zhao, J.; Yue, L.; Wang, Q.; Chai, J.; Liu, Z.; Zhou, X.; Li, H.; Guo, Y.; Cui, G.; Chen, L. Safety-Reinforced Poly(Propylene Carbonate)-Based All-Solid-State Polymer Electrolyte for Ambient-Temperature Solid Polymer Lithium Batteries. Adv. Energy Mater. 2015, 5 (24), 1–10.

(12)

Yu, X.-Y.; Xiao, M.; Wang, S.-J.; Zhoa, Q.-Q.; Meng, Y.-Z. Fabrication and Characterization of PEO/PPC Polymer Electrolyte for Lithium-Ion Battery. J. of Applied Polymer Sci. 2008, 115, 2718–2722.

(13)

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.

(14)

Varzi, A.; Raccichini, R.; Passerini, S.; Scrosati, B. Challenges and Prospects on the Role of Solid Electrolytes for the Revitalization of Lithium Metal Batteries. J. Mater. Chem. A 2016, 4, 17251–17259.

(15)

Suthanthiraraj, S. A.; Vadivel, M. K. Effect of Propylene Carbonate as a Plasticizer on (PEO)50AgCF3SO3:SnO2 Nanocomposite Polymer Electrolyte. Appl. Nanosci. 2012, 2, 239–246.

(16)

Qian, X.; Gu, N.; Cheng, Z.; Yang, X.; Wang, E.; Dong, S. Plasticizer Effect on the Ionic


25


Page 26 of 30

Conductivity of PEO-Based Polymer Electrolyte. Mater. Chem. Phys. 2002, 74 (1), 98– 103. (17)

Manuel Stephan, a. Review on Gel Polymer Electrolytes for Lithium Batteries. Eur. Polym. J. 2006, 42 (1), 21–42.

(18)

Long, L.; Wang, S.; Xiao, M.; Meng, Y. Polymer Electrolytes for Lithium Polymer Batteries. J. Mater. Chem. A Mater. energy Sustain. 2016, 4, 10038–10069.

(19)

Manuel Stephan, A.; Nahm, K. S. Review on Composite Polymer Electrolytes for Lithium Batteries. Polymer (Guildf). 2006, 47 (16), 5952–5964.

(20)

Zhang, J.; Huang, X.; Wei, H.; Fu, J.; Huang, Y.; Tang, X. Enhanced Electrochemical Properties of Polyethylene Oxide-Based Composite Solid Polymer Electrolytes with Porous Inorganic-Organic Hybrid Polyphosphazene Nanotubes as Fillers. J. Solid State Electrochem. 2012, 16 (1), 101–107.

(21)

Lin, D.; Liu, W.; Liu, Y.; Lee, H. R.; Hsu, P. C.; Liu, K.; Cui, Y. High Ionic Conductivity of Composite Solid Polymer Electrolyte via in Situ Synthesis of Monodispersed SiO2 Nanospheres in Poly(ethylene Oxide). Nano Lett. 2016, 16 (1), 459–465.

(22)

Yuan, C.; Li, J.; Han, P.; Lai, Y.; Zhang, Z.; Liu, J. Enhanced Electrochemical Performance of Poly(ethylene Oxide) Based Composite Polymer Electrolyte by Incorporation of Nano-Sized Metal-Organic Framework. J. Power Sources 2013, 240, 653–658.

(23)

Kumar, B.; Scanlon, L.; Marsh, R.; Mason, R.; Higgins, R.; Baldwin, R. Structural Evolution and Conductivity of PEO:LiBF4-MgO Composite Electrolytes. Electrochim. Acta 2001, 46 (10–11), 1515–1521.

(24)

Kumar, R.; Subramania, A.; Sundaram, N. T. K.; Kumar, G. V.; Baskaran, I. Effect of MgO Nanoparticles on Ionic Conductivity and Electrochemical Properties of Nanocomposite Polymer Electrolyte. J. Memb. Sci. 2007, 300 (1–2), 104–110.

(25)

Tambelli, C. C.; Bloise, A. C.; Rosário, A. V.; Pereira, E. C.; Magon, C. J.; Donoso, J. P. Characterisation of PEO-Al2O3 Composite Polymer Electrolytes. Electrochim. Acta 2002, 47 (11), 1677–1682.

(26)

Lim, Y.-J.; An, Y.-H.; Jo, N.-J. Polystyrene-Al2O3 Composite Solid Polymer Electrolyte for Lithium Secondary Battery. Nanoscale Res. Lett. 2012, 7 (1), 19.

(27)

Kumar, B.; Rodrigues, S. J.; Koka, S. The Crystalline to Amorphous Transition in PEO-Based Composite Electrolytes: Role of Lithium Salts. Electrochim. Acta 2002, 47 (25), 4125–4131.

(28)

Zhao, X. G.; Jin, E. M.; Park, J. Y.; Gu, H. B. Hybrid Polymer Electrolyte Composite with SiO2 Nanofiber Filler for Solid-State Dye-Sensitized Solar Cells. Compos. Sci. Technol. 2014, 103, 100–105.

(29)

Zhu, Z.; Hong, M.; Guo, D.; Shi, J.; Tao, Z.; Chen, J. All-Solid-State Lithium Organic


26

Page 27 of 30 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


Battery with Composite Polymer Electrolyte and Pillar[5]quinone Cathode. J. Am. Chem. Soc. 2014, 136 (47), 16461–16464. (30)

Ni’Mah, Y. L.; Cheng, M. Y.; Cheng, J. H.; Rick, J.; Hwang, B. J. Solid-State Polymer Nanocomposite Electrolyte of TiO2/PEO/NaClO4 for Sodium Ion Batteries. J. Power Sources 2015, 278, 375–381.

(31)

Scrosati, B.; Croce, F.; Persi, L. Impedance Spectroscopy Study of PEO-Based Nanocomposite Polymer Electrolytes. J. Electrochem. Soc. 2000, 147 (5), 1718.

(32)

Cao, J.; Wang, L.; He, X.; Fang, M.; Gao, J.; Li, J. In Situ Prepared Nano-Crystalline TiO2–poly (Methyl Methacrylate) Hybrid Enhanced Composite Polymer Electrolyte for Li-Ion Batteries. J. Mater. Chem. A 2013, 1 (19), 5955-5961.

(33)

Shim, J.; Kim, D. G.; Kim, H. J.; Lee, J. H.; Lee, J. C. Polymer Composite Electrolytes Having Core-Shell Silica Fillers with Anion-Trapping Boron Moiety in the Shell Layer for All-Solid-State Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2015, 7 (14), 7690– 7701.

(34)

Ma, C.; Zhang, J.; Xu, M.; Xia, Q.; Liu, J.; Zhao, S.; Chen, L.; Pan, A.; Ivey, D. G.; Wei, W. Cross-Linked Branching Nanohybrid Polymer Electrolyte with Monodispersed TiO2 Nanoparticles for High Performance Lithium-Ion Batteries. J. Power Sources 2016, 317, 103–111.

(35)

Kim, S.; Park, S. J. Preparation and Electrochemical Behaviors of Polymeric Composite Electrolytes Containing Mesoporous Silicate Fillers. Electrochim. Acta 2007, 52 (11), 3477–3484.

(36)

Wang, Y.-J.; Pan, Y.; Kim, D. Conductivity Studies on Ceramic Li1.3Al0.3Ti1.7(PO4)3-Filled PEO-Based Solid Composite Polymer Electrolytes. J. Power Sources 2006, 159 (1), 690–701.

(37)

Liu, W.; Lee, S. W.; Lin, D.; Shi, F.; Wang, S.; Sendek, A. D.; Cui, Y. Enhancing Ionic Conductivity in Composite Polymer Electrolytes with Well-Aligned Ceramic Nanowires. Nat. Energy 2017, 2, 17035.

(38)

Tang, C.; Hackenberg, K.; Fu, Q.; Ajayan, P.; Ardebili, H. High Ion Conducting Polymer Nanocomposite Electrolytes Using Hybrid Nanofillers. Nano Lett. 2012, 12, 1152–1156.

(39)

Fu, X.; Jewel, Y.; Wang, Y.; Liu, J.; Zhong, W.-H. Decoupled Ion Transport in a Protein-Based Solid Ion Conductor. J. Phys. Chem. Lett. 2016, 4304–4310.

(40)

Ji, J.; Lively, B.; Zhong, W. Soy Protein-Assisted Dispersion of Carbon Nanotubes in a Polymer Matrix. Mater. Express 2012, 2 (1), 76–82.

(41)

Jewel, Y.; Liu, T.; Eyler, A.; Zhong, W. H.; Liu, J. Potential Application and Molecular Mechanisms of Soy Protein on the Enhancement of Graphite Nanoplatelet Dispersion. J. Phys. Chem. C 2015, 119 (47), 26760–26767.

(42)

Wang, Y.; Zhong, W. H.; Schiff, T.; Eyler, A.; Li, B. A Particle-Controlled,


27


Page 28 of 30

High-Performance, Gum-like Electrolyte for Safe and Flexible Energy Storage Devices. Adv. Energy Mater. 2015, 5 (2), 1–9. (43)

Wang, Y.; Gozen, A.; Chen, L.; Zhong, W.-H. Gum-Like Nanocomposites as Conformable, Conductive, and Adhesive Electrode Matrix for Energy Storage Devices. Adv. Energy Mater. 2017, 7, 1601767.

(44)

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

(45)

Ji, J.; Li, B.; Zhong, W. H. An Ultraelastic Poly(ethylene Oxide)/soy Protein Film with Fully Amorphous Structure. Macromolecules 2012, 45 (1), 602–606.

(46)

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

(47)

Diebold, U. The Surface Science of Titanium Dioxide. Surf. Sci. Rep. 2003, 48 (5–8), 53– 229.

(48)

Köppen, S.; Langel, W. Simulation of the Interface of (1 0 0) Rutile with Aqueous Ionic Solution. Surf. Sci. 2006, 600 (10), 2040–2050.

(49)

Ohler, B.; Ohler, B.; Langel, W.; Langel, W. Molecular Dynamics Simulations on the Interface between Titanium Dioxide and Water Droplets: A New Model for the Contact Angle. J. Phys. Chem. C 2009, 113 (23), 10189–10197.

(50)

Cao, J.; Wang, L.; Yuming, S.; Fang, M.; Deng, L.; Gao, J.; Li, J.; Chen, H.; He, X. Dispersibility of Nano-TiO2 on Performance of Composite Polymer Electrolytes for Li-Ion Batteries. Electrochim. Acta 2013, 111, 674–679.

(51)

Ju, S. H.; Lee, Y.-S.; Sun, Y.-K.; Kim, D.-W. Unique Core–shell Structured SiO2 (Li+) Nanoparticles for High-Performance Composite Polymer Electrolytes. J. Mater. Chem. A 2013, 1, 395–401.

(52)

Bouchet, R.; Phan, T. N. T.; Beaudoin, E.; Devaux, D.; Davidson, P.; Bertin, D.; Denoyel R. Charge Transport in Nanostructured PS−PEO−PS Triblock. Macromolecules 2014, 47, 2659–2665.

(53)

Noor, S. A. M.; Ahmad, A.; Talib, I. A.; Rahman, M. Y. A. Morphology, Chemical Interaction, and Conductivity of a PEO-ENR50 Based on Solid Polymer Electrolyte. Ionics (Kiel). 2010, 16 (2), 161–170.

(54)

Sengwa, R. J.; Dhatarwal, P.; Choudhary, S. Role of Preparation Methods on the Structural and Dielectric Properties of Plasticized Polymer Blend Electrolytes: Correlation between Ionic Conductivity and Dielectric Parameters. Electrochim. Acta 2014, 142, 359– 370.

(55)

Shim, J.; Kim, D.-G.; Lee, J. H.; Baik, J. H.; Lee, J.-C. Synthesis and Properties of Organic/inorganic Hybrid Branched-Graft Copolymers and Their Application to


28

Page 29 of 30 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


Solid-State Electrolytes for High-Temperature Lithium-Ion Batteries. Polym. Chem. 2014, 5, 3432. (56)

Kim, D. G.; Shim, J.; Lee, J. H.; Kwon, S. J.; Baik, J. H.; Lee, J. C. Preparation of Solid-State Composite Electrolytes Based on Organic/inorganic Hybrid Star-Shaped Polymer and PEG-Functionalized POSS for All-Solid-State Lithium Battery Applications. Polymer (Guildf). 2013, 54 (21), 5812–5820.

(57)

Kao, H. M.; Chao, S. W.; Chang, P. C. Multinuclear Solid-State NMR, Self-Diffusion Coefficients, Differential Scanning Calorimetry, and Ionic Conductivity of Solid Organic-Inorganic Hybrid Electrolytes Based on PPG-PEG-PPG Diamine, Siloxane, and Lithium Perchlorate. Macromolecules 2006, 39 (3), 1029–1040.

(58)

Zhao, Y.; Huang, Z.; Chen, S.; Chen, B.; Yang, J.; Zhang, Q.; Ding, F.; Chen, Y.; Xu, X. A Promising PEO/LAGP Hybrid Electrolyte Prepared by a Simple Method for All-Solid-State Lithium Batteries. Solid State Ionics 2016, 295, 65–71.

(59)

Wang, X.; Fu, X.; Wang, Y.; Zhong, W. A Protein-Reinforced Adhesive Composite Electrolyte. Polym. (United Kingdom) 2016, 106, 43–52.

(60)

Bresser, D.; Passerini, S.; Scrosati, B. Recent Progress and Remaining Challenges in Sulfur-Based Lithium Secondary Batteries--a Review. Chem. Commun. (Camb). 2013, 49 (90), 10545–10562.

(61)

Agapov, A. L.; Sokolov, A. P. Decoupling Ionic Conductivity from Structural Relaxation: A Way to Solid Polymer Electrolytes? Macromolecules 2011, 44 (11), 4410–4414.

(62)

Li, Q.; Chen, J.; Fan, L.; Kong, X.; Lu, Y. Progress in Electrolytes for Rechargeable Li-Based Batteries and beyond. Green Energy Environ. 2016, 1, 1–25.

(63)

Xu, K. Electrolytes and Interphases in Li-Ion Batteries and beyond. Chem. Rev. 2014, 114 (23), 11503–11618.

(64)

Liu, W.; Lin, D.; Sun, J.; Zhou, G.; Cui, Y. Improved Lithium Ionic Conductivity in Composite Polymer Electrolytes with Oxide-Ion Conducting Nanowires. ACS Nano 2016, 10, 11407−11413.

(65)

Liu, W.; Liu, N.; Sun, J.; Hsu, P. C.; Li, Y.; Lee, H. W.; Cui, Y. Ionic Conductivity Enhancement of Polymer Electrolytes with Ceramic Nanowire Fillers. Nano Lett. 2015, 15 (4), 2740–2745.

(66)

Lee, K.-P.; Gopalan, A. I.; Manesh, K. M.; Santhosh, P.; Kim, K. S. Influence of Finely Dispersed Carbon Nanotubes on the Performance Characteristics of Polymer Electrolytes for Lithium Batteries. IEEE Trans. Nanotechnol. 2007, 6 (3), 362–367.

(67)

Wang, Y.; Li, B.; Ji, J.; Eyler, A.; Zhong, W. H. A Gum-like Electrolyte: Safety of a Solid, Performance of a Liquid. Adv. Energy Mater. 2013, 3 (12), 1557–1562.

(68)

Porcarelli, L.; Gerbaldi, C.; Bella, F.; Nair, J. R. Super Soft All-Ethylene Oxide Polymer Electrolyte for Safe All-Solid Lithium Batteries. Sci. Rep. 2016, 6, 19892.


29


(69)

Page 30 of 30

Kumar, R.; Choudhary, V.; Mishra, S.; Varma, I. K.; Mattiason, B. Adhesives and Plastics Based on Soy Protein Products. Ind. Crops Prod. 2002, 16 (3), 155–172.

TOC GRAPHICS


30

Building Ion-Conduction Highways in Polymeric Electrolytes by

Recommend Documents