Research progress on solid polymer electrolytes

The conductivity of composite solid polymer electrolyte (SPE) made of different compositions of poly(ethylene oxide) (PEO), LiClO4 and fiber was investigated in this study. Results obtained through alternating current (AC) impedance measurements demonstrated that the conductivity of the SPE was much improved by blending fiber into it. Moreover, increasing the composition of fiber added leads, thereby increasing the conductivity of the composite SPE. The average conductivity of the composite SPE was 10−4 S/cm at 25 °C. Performance in thermal properties was also investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) experiments. Although the mechanical strength of the composite SPE was not better than that of other materials as expected, the fiber added made it more stable.

Lithium metal batteries (LMBs) have attracted significant interest as next-generation energy storage systems due to their high theoretical capacity (3860 mAh g⁻¹) and low electrochemical potential (-3.04 V vs. SHE).[1] However, practical applications using lithium metal to anode still have critical challenges. One is the formation of lithium dendrite, and the other is issues of liquid organic electrolytes. The formation of lithium dendrites comes from irregular lithium growth due to non-uniform active sites on the lithium surface, leading to issues such as dead lithium formation and volume expansion that pose internal short circuits and capacity fading.[2] Liquid organic electrolytes offer the advantage of high lithium salt dissolution and have excellent ionic conductivity. In contrast, their inherent flammability and leakage possibility pose significant safety and stability concerns.[3]. Therefore, the high energy density and long-term stability requirements such as transportations should be developed by addressing above limitations.The fabrication of solid polymer electrolytes demonstrates notable potential for suppressing lithium dendrites by physically restraining the interphase between lithium metal anode and electrolyte.[4] Also, there is no need for extra separators. These make battery cells possible to increase the thickness of the electrodes in order to reach high energy density while maintaining stability. Moreover, solid polymer electrolytes fabricated easily with liquid organic electrolyte, polymer materials, and initiator. The solid polymer electrolytes can reach non-leakage and non-flammable properties.To make batter solid polymer electrolytes, reducing crystallinity is important, because more amorphous areas in polymer electrolytes make better lithium ion transport and ion conductivity.[5] The other aspect is to increase mechanical properties to make batteries more stable and safe in long-term cycles. Some studies fillers can changes crystalline regions in polymer matrix to be more amorphous which have better lithium ion transport.[6] Especially, introducign inorganic nanofillers compensates for the polymer materials’ limitations such as mechanical strength.[7] Therefore, the development of inorganic nanofillers and polymer composite electrolytes is essential.In this study, a PMMA-based polymer electrolyte was developed to achieve stable operation at high voltages (> 4.2 V). LiFSI was selected as the lithium salt due to its superior ionic dissociation and high compatibility with high-voltage cathodes such as NCM811 and LFP. The solvent system was composed of EC and DEC to ensure optimized lithium-ion solvation and transport. To further enhance the electrochemical and mechanical properties of the polymer electrolyte, inorganic nanofillers were individually introduced. Their incorporation is expected to reduce polymer crystallinity, thereby increasing the amorphous content of the electrolyte matrix, which is favorable for lithium-ion conduction. Figure 1a shows the scheme of PMMA based solid polymer electrolytes and achieving free-standing solid polymer electrolytes. In experimental method, mix PMMA, LiFSI 1 M concentration in EC:DEC(1:1, v/v) solvents, TiO2 2 wt % and AIBN thermal initiator 1 wt % at first for the electrolyte precursor. Then, caste on the glass substrate, heat(<6 hours) 60 ℃ on hot plate, and finally dry(>12 hours) in vacuum.The effect of these inorganic nanofillers on the electrochemical performance and stability of the polymer electrolyte has been systematically investigated to test the influence of nanofillers on ionic conductivity by Li-Cu half cells (Figure 1b). Besides, mechanical strength, and lithium metal compatibility will be analyzed to determine their suitability for high-voltage lithium metal battery applications. Furthermore, characteriazations are important to certify the interphase of solid polymer electrolytes and compositions for mechanism studies. The Figure 1c shows the results of the fabricated polymer electrolyte samples. The xrd data prove the amorphousness of polymer electrolyte matrix and introduced TiO2 material presence. Figure 1d shows the SEM images of the sample surfaces, there are some ununiform surfaces caused nitrogen gas from the AIBN intiation mechanism that need to develop to retrain it. This study aims to provide fundamental insights into the role of inorganic nanofillers in polymer electrolyte systems and to develop a stable electrolyte platform for next-generation lithium metal batteries.

Advances in energy storage (ES) devices have the potential to transform nearly every aspect of society, from transportation to communication to electricity delivery, national defense and domestic security. Among the various prevalent energy storage devices, the most prominent to date are related to electrochemical energy storage (EES) technologies. Several EES technologies are either in existence or have evolved over the years. Among the various systems studied, lithium battery technologies (LBs) have emerged in the forefront as a panacea to the high energy and high power problems facing portable electronics, electric powered vehicle, military applications as well as stand-alone stationary power systems integrated into the electric grid. Despite advances in the anode arena, lithium metal anodes due to the inherent dendrite formation limitations have never attained commercial status. Overcoming these barriers would be a major breakthrough in the search for high energy density anode systems due to its extremely high theoretical specific capacity (~3860 mAh/g) and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode). Similarly, pursuit of high energy density rechargeable lithium metal battery (LMB) cathodes have led to sulfur (for a Li-S battery), air electrode (for a Li-air battery) or intercalation compounds (e.g. NbSe3, V2O5) to realize high voltage LMBs exhibiting high energy densities. Li-S batteries, owing to their high theoretical energy density (2600 Wh kg-1)1, is considered as one of the most promising Li metal-based batteries. However, the liquid organic electrolytes, S cathodes and Li metal in current LMBs could not be commercialized globally for high energy applications due to low cycle life and safety issues. The low cycle life, low coulombic efficiency (CE) and safety issue of rechargeable LMBs mainly arises due to the uncontrolled cellular and dendritic growth of Li metal during repeated lithium plating/stripping and formation of unstable solid electrolyte interphase (SEI) and the continuous growth of thick SEI during repeated cycling at the solid liquid interface of organic electrolyte based LMBs. In addition, the large volume expansion (~80%)3 of sulfur accompanying the electrochemical cycling, the low utilization of sulfur resulting from poor room-temperature electronic conductivity of sulfur (~10-15 S/cm) 4 , combined with the shuttle effect of highly soluble polysulfide species in the organic ether-based electrolytes has limited the use of Li-S batteries. To address these challenges facing sulfur cathodes, significant efforts have been made to demonstrate advanced composite cathodes using various carbon materials5, polymers6 and metal-organic framework (MOF) materials7. In addition, solid polymer electrolytes8 and electrolytes additives have also been studied to develop a viable Li-S battery system. Thin-film solid-polymer electrolyte batteries offer the potential for improved safety because of the reduced activity of lithium with the solid electrolyte, flexibility in design as the cell can be fabricated in various sizes and shapes, and high energy density. In this work, we demonstrate the use of a composite polymer electrolyte (CPE) with modified physical and chemical properties in Li-S batteries. These CPEs exhibits superior mechanical properties, excellent room-temperature lithium ion conductivity and low electrolyte: sulfur (E:S) ratio. These CPEs, when used as electrolytes for Li-S batteries, helps prevent both polysulfide dissolution and dendrite formation, in addition to providing very high energy density (~750 Wh/kg). Structural, chemical, physical and electrochemical characterization results validating these properties of the CPEs will be presented and discussed. Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0006825 and DE-EE-0008199, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM). References V. S. Kolosnitsyn and E. V. Karaseva, Russian Journal of Electrochemistry, 2008, 44, 506-509.Y. Sun, G. Li, Y. Lai, D. Zeng and H. Cheng, Scientific Reports, 2016, 6, 22048.B. Dunn, H. Kamath and J.-M. Tarascon, Science, 2011, 334, 928-935.M. Edeling, R. W. Schmutzler and F. Hensel, Philosophical Magazine Part B, 1979, 39, 547-550.J. Jin, Z. Wen, G. Ma, Y. Lu and K. Rui, Solid State Ionics, 2014, 262, 170-173.P. J. Hanumantha, B. Gattu, O. Velikokhatnyi, M. K. Datta, S. S. Damle and P. N. Kumta, Journal of The Electrochemical Society, 2014, 161, A1173-A1180.P. M. Shanthi, P. J. Hanumantha, B. Gattu, M. Sweeney, M. K. Datta and P. N. Kumta, Electrochimica Acta, 2017, 229, 208-218.B. A. Boukamp, I. D. Raistrick, C. Ho, Y.-W. Hu and R. A. Huggins, in Superionic Conductors, eds. G. D. Mahan and W. L. Roth, Springer US, Boston, MA, 1976, DOI: 10.1007/978-1-4615-8789-7_65, pp. 417-417.E. Peled, C. Menachem, D. Bar‐Tow and A. Melman, Journal of The Electrochemical Society, 1996, 143, L4-L7.

Electric vehicles (EVs) have become the dominant choice in the automotive industry, displacing internal combustion engine vehicles (ICEVs) to some extent. The development of high-efficiency batteries is essential to meet these market demands. Conventional lithium-ion batteries (LIBs), which consist of a cathode, anode, separator, and liquid electrolyte (such as 1M LiPF6 in carbonate solvents), have been widely utilized in portable electronic devices, hybrid electric vehicles (HEVs), and EVs. This popularity is attributed to their relatively high energy density and extended cycle life [1]. However, LIBs with energy density exceeding 240 Wh kg-1 face challenges in terms of thermal stability, potentially leading to fire and explosions by overcharging or accidental cell penetration. This drawback significantly hinders their application in automotive settings [2, 3]. In response to these safety concerns, there is a shift towards incorporating solid-state electrolytes (SSEs) as a replacement for liquid electrolytes. SSEs include solid polymer electrolyte (SPE), inorganic solid electrolyte (ISE), and composite polymer electrolyte (CPE).Solid-state lithium metal batteries (SSLMBs) incorporating SPE hold significant promise for advancing energy storage technologies due to their high energy density and improved safety features. However, the low ionic conductivity and ionic transference number of SPEs present challenges in their application for solid-state batteries. This work focuses on designing novel copolymers with polar soft unit and zwitterionic unit to address these challenges.In this study, poly(ethylene glycol) methyl ether acrylate (PEGMEA) and sulfobetaine methacrylate (SBMA) were selected as the polar soft segment and zwitterionic unit, respectively. Various ratios of PEGMEA/SBMA in copolymers were synthesized and characterized, and the resultant SPEs consisting of resultant copolymers and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were prepared. Subsequently, their electrochemical, thermal, mechanical, and morphological properties were systematically investigated. The copolymers-based SPEs exhibited improved electrochemical properties. The optimized SPE comprising the copolymer with the molar ratio of PEGMEA/SBMA = 1/3 and 50 wt% LiTFSI exhibited the ionic conductivity of approx. 2×10–4 S cm–1, lithium-ion transference number of approx. 0.3, Li+ diffusion coefficient of 15×10-12 cm² s-1, and oxidation stability of 5.2 V (vs. Li/Li+) at 25 oC. Additionally, the mechanical properties of such SPEs were assessed, showing improved tensile strength (up to approx. 6 MPa) and Young’s modulus (up to approx. 83 MPa) with increasing SBMA content. The selected SPE with the best electrochemical properties was sandwiched between a Li metal electrode and a LiFePO4 electrode to assemble a SSLMB. As a result, the discharge capacity (DC) at 0.1 C-rate and room temperature was approx. 170 mA h g–1. Furthermore, the DC at a 0.5 C-rate was approx. 146 mA h g–1, and the capacity retention of 70% obtained after 470 cycles. In summary, this work demonstrates the potential of tailored copolymers with zwitterionic moiety-based SPEs for SSLMB. The comprehensive characterization and performance assessments provide valuable insights into the design and optimization of polymer electrolytes for next-generation energy storage systems.The copolymers and corresponding SPEs underwent characterization through various techniques such as DSC, SEM, XRD, and FTIR. The Ionic conductivity of the SPEs was determined by analyzing the results obtained from EIS measurement. The lithium-ion diffusion coefficient (DLi+) for SPE in a symmetric SSLMB cell, Li/SPE/Li, was also calculated based on the EIS results [4]. The oxidation stability window of the SPE was measured using the linear sweep voltammetry technique, and the ion transfer number was determined using the Evans-Vincent-Bruce method [5].

Implementation of solid polymer electrolytes (SPEs) is believed to be one pathway forward in the development of lithium-metal batteries (LMBs) that are both safe and possesses high capacities. This combination is possible since the free-standing SPE maintains its mechanical integrity during electrochemical and thermal exposure while utilizing lithium metal as the negative electrode, thus accessing the extremely high theoretical capacity of lithium metal. The main drawback for SPEs are however the poor ionic conductivity compared to the liquid electrolytes used in lithium-ion batteries today.[1] The low ionic conductivity for SPEs stems from the conduction mechanism of the ions, which is a slower process in SPEs compared to in liquid electrolytes. In general, the conductivity in SPEs are confined to the amorphous regions, where segmental motion of the polymer chains facilitates the ion transport; while the crystalline regions restrict the movements of the polymer chains and impairs the ion transport.[2] The highly crystalline polyketone poly(1-oxoheptamethylene) (POHM) is a material that has shown interesting characteristics for implementation as a SPE in batteries. In earlier studies, the polyketone revealed an extensive improvement of the ionic conductivity upon increasing the salt concentration, although the crystallinity remained with a high melting point.[3] Herein this study, the effect of the crystallinity on the characteristics and the performance was investigated further. To understand its effect, a second less hydrogenated version of POHM was synthesized, POHM-75, which is fully amorphous at high salt concentrations. The characteristics of the polyketones were in addition also compared with the more well-studied SPEs, that is polyethylene oxide (PEO) and poly(trimethylene carbonate) (PTMC). Focus of the presentation is on the interplay between the ionic conductivity and mechanical stability for the polyketones, for which something different to the normally observed tradeoff between the two properties is observed. The electrochemical performance of the polyketones are furthermore evaluated when implemented as SPEs in LMBs at extreme temperature environments, a possible application area for mechanically stable SPEs.[1] D. Zhou, D. Shanmukaraj, A. Tkacheva, M. Armand, G. Wang, Chem 2019, 5, 2326-2352.[2] M. A. Ratner, P. Johansson, D. F. Shriver, MRS Bulletin 2011, 25, 31-37.[3] T. Eriksson, H. Gudla, Y. Manabe, T. Yoneda, D. Friesen, C. Zhang, Y. Inokuma, D. Brandell, J. Mindemark, Macromolecules 2022, 55, 10940-10949. Figure 1

Nanoscale Mapping of Extrinsic Interfaces in Hybrid Solid Electrolytes

As a high-efficiency energy storage and conversion device, lithium-ion batteries have high energy density, and have received widespread attention due to their good cycle performance and high reliability. However, currently commercial lithium batteries usually use organic solutions containing various lithium salts as liquid electrolytes. In practical applications, liquid electrolytes have many shortcomings and shortcomings, such as poor chemical stability, flammability, and explosion. Therefore, the liquid electrolyte has a great safety hazard. The use of solid electrolyte ensures the safety of lithium-ion batteries, and has the advantages of high energy density, good cycle performance, long life, and wide electrochemical window, making the battery safer and more durable, with higher energy density and simple battery Structural design. Solid electrolytes mainly include inorganic solid electrolytes and organic polymer solid electrolytes. Although both inorganic solid electrolytes and polymer solid electrolytes have their own advantages, as far as the existing research work is concerned, whether it is an inorganic system or a polymer system, a single-system solid electrolyte can never achieve the full performance of an ideal solid electrolyte. The composite solid electrolyte composed of active or passive inorganic filler and polymer matrix is considered as a promising candidate electrolyte for all-solid-state lithium batteries. Among many polymer systems, PEO-based is considered to be the most ideal polymer substrate. In this review article, we first introduced the structure, properties, and preparation methods of PEO-based polymer electrolytes. Furthermore, the researches related to the modification of PEO-based polymer solid electrolytes in recent years are summarized. The contribution of polymer structural modification and the introduction of additives to the ionic conductivity, electrochemical stability and mechanical properties of PEO-based solid electrolytes is described. Examples of different composite solid electrolyte design concepts were extensively discussed, such as inorganic inert nanoparticles/PEO, oxide/PEO, and sulfide/PEO. Finally, the future development direction of composite solid electrolytes was prospected.

Rechargeable lithium ion batteries become an very important technology in the contemporary society. They are expanding their application in electric vehicles and power grids. However, current lithium ion batteries with liquid electrolyte have been suffering from potential safety crisis mainly due to their highly flammable organic liquid carbonate organic electrolyte and explosion hazards. These potential risks (combustion and explosion) would retard the commercialization of electric vehicles or hybrid electric vehicles. Thus, the safety issue of lithium ion battery merits further study. Solid electrolytes have attracted ever-increasing interest owing to their enhanced safety issue and higher energy density of lithium battery. Solid electrolyte materials mainly include inorganic solid electrolytes (ISEs) and solid polymer electrolytes (SPEs). The ISEs are classified into oxide-based, sulfide-based and etc. However, in spite of the presence of highly ion conductive ISEs, there are still many undergoing issues that limit the practical application at the present stage, like the large interface impedance between electrode and ISEs and the difficulty of processing. More attention has been paid to solid polymer electrolytes due to their superior flexibility and processability, which are also subjected to thermal expansion at elevated temperature. Poly(ethylene oxide) (PEO) solid polymer electrolyte has undergone a sort of renaissance in the past few decades. However, the quintessential frailty of PEO solid polymer electrolyte is low ionic conductivity (in the order of 10(-7) S cm(-1)) at room temperature with a relatively narrow electrochemical window. Hence, it is essential to develop new solid polymer electrolytes with comprehensive performance in terms of high ionic conductivity, wide electrochemical window, superior mechanical strength, excellent thermal stability as well as good interfacial compatibility. In this review, a series of polycarbonate-based solid polymer electrolytes (such as PEC, PPC, PTMC and PVC et al.) are summarized. In addition, we also present a brief review on preparation, electrochemical property, modification, ionic transportation mechanism and future development direction for each of these solid polymer electrolytes.

Solid electrolytes are critical for structural batteries, combining energy storage with structural strength for applications like electric vehicles and aerospace. However, achieving high ionic conductivity remains challenging, compounded by a lack of standardized testing methodologies. This study examines the impact of experimental setups and data interpretation methods on the measured ionic conductivities of solid polymer electrolytes (SPEs). SPEs were prepared using a polymer-induced phase separation process, resulting in a bi-continuous microstructure for improved ionic transport. Eight experimental rigs were evaluated, including two- and four-electrode setups with materials like stainless steel, copper, and aluminum. Ionic conductivity was assessed using electrochemical impedance spectroscopy, with analysis methods comparing cross-sectional and surface-area-based approaches. Results showed that the four-electrode stainless steel setup yielded the highest ionic conductivity using the cross-sectional method. However, surface-area-based methods provided more consistent results across rigs. Copper setups produced lower conductivities but exhibited less data variability, indicating their potential for reproducible measurements. These findings highlight the critical influence of experimental design on conductivity measurements and emphasize the need for standardized testing protocols. Advancing reliable characterization methods will support the development of high-performance solid electrolytes for multifunctional energy storage applications.

Functionalized siloxane-based solid polymer electrolytes were synthesized using a platinum-catalyzed silylation reaction. The ionic conductivities of these solid polymer electrolytes were measured as a function of the concentration of lithium bis(trifluoromethylsulfonyl)imide (LiTFSi) salt. The highest ionic conductivity and lowest activation energy of solid polymer electrolytes were observed to be 1.15 × 10−4 S cm−1 (25 °C) and 3.85 kJ mol−1, respectively. The interface property between electrolyte and electrode and thermal stability of the polymer electrolytes were found to enhance after they were functionalized with acrylate, and the functionalized electrolytes were observed to maintain a glass transition temperature as low as that of other siloxane compounds. Thus, modifications involving acrylate with ethylene oxide group substitution provide a route for carrier ions and enhance both the ionic conductivity and mechanical properties of the siloxane structure.

Currently, electrolytes used in lithium-ion batteries are flammable and leaky, causing safety problems when used under high temperatures or extreme conditions. Solid electrolytes can fundamentally avoid the occurrence of such issues, at the same time, it can significantly increase the energy density of solid state lithium batteries. Solid electrolytes are classified into inorganic solid electrolytes and solid polymer electrolytes. Although inorganic solid electrolytes have the high mechanical strength and room temperature ionic conductivity, it has poor flexibility and complicated preparation process. In contrast, solid polymer electrolyte has good elasticity and good interface contact, which can overcome many disadvantages of the inorganic solid electrolyte. Among them, polyethylene oxide (PEO) is first proposed as a polymer electrolyte. Due to its excellent mechanical properties, electrochemical stability and thermal stability, it has been a hot topic for polymer solid electrolytes for decades. However, its low room temperature ionic conductivity limits practical application. Given the problems existing in PEO-based polymer electrolytes, several methods for improving ionic conductivity have been proposed. The primary methods include plasticization, the organic-inorganic composite, and polymer blending. Comparing these methods, it can be seen that adding plasticizers to the polymer can effectively increase the conductivity of the electrolyte, but at the same time it will cause a decrease in the mechanical properties, and the safety issues limit its application in lithium-ion batteries. Inorganic fillers can balance the problems of ionic conductivity and mechanical properties, but the construction of a good filler-polymer dispersion system is complicated in preparing such composite electrolytes, design a new type of multi-dimensional the ion transport network also face tremendous challenges. Undoubtedly, in the future research, inorganic fillers will be the dominant means in the modification of composite electrolytes. Compared with the former two modification methods, polymer blending is easy to operate and friendly to industry, but low ionic conductivity at room temperature still exist. To give full play to the advantages of polymer blending, using it as an auxiliary means to improve the performance of composite electrolytes will be the primary development direction of such modification methods. PEO is the most widely studied polymer electrolyte. Even though a large number of modification methods have emerged in its development history, the ionic conductivity at room temperature is still limited to a relatively low level. To meet the needs of the application in lithium-ion batteries, a high operating temperature (50−70℃) is still needed, the biggest problem remains exist. To solve the problems in polymer solid electrolytes, the research directions in the future may mainly focus on: Expanding the modification method of PEO to other polymer electrolyte host materials, broadening the scope of research, and finding the available polymer electrolytes at room temperature. Concerned about the preparation of ultra-thin polymer electrolytes, reducing the ion transmission path to increase the transmission efficiency of lithium ions between positive and negative electrodes. Effectively combines inorganic solid electrolytes and solid polymer electrolytes to give full play to their advantages. In addition, exploring the effect of inorganic filler morphology on the conductivity of the composite electrolyte will also deserve attention. Many one-dimensional, two-dimensional materials can build ion transport networks so that lithium ions can travel rapidly along the path. With the deepening of research, it is expected that PEO-based polymer electrolytes may replace liquid electrolytes and become an essential cornerstone for building the next generation of safe and reliable lithium-ion batteries.

Following the COP26 Summit in November 2021, more than hundred countries pledged to reach zero-emission by 2070 at the latest and the major car manufacturers committed to selling only electric vehicles by 2040. Currently, lithium-ion batteries (LIBs) are among the most widely used storage systems because of their high energy and power densities and long lifespan.1 The early LIBs are composed of intercalation electrodes, electronically isolated by an ion-conducting organic liquid electrolyte. However, the use of liquid electrolytes presents some disadvantages – especially in regard to consumer safety – related to short-circuits and potential leakages of the flammable liquid solvent. Moreover, in the case of lithium metal batteries, the combination of a liquid electrolyte and a high-capacity lithium metal anode leads to the uncontrolled deposition of lithium during the reduction, forming dendrites between the electrodes. A promising way to avoid this instability and improve battery safety is to replace the liquid electrolyte with an ion-conducting solid electrolyte.2 Among them, solid polymer electrolytes (SPEs) represent one of the most attractive alternatives due to their capacity to effectively conduct ions and higher mechanical resistance than their liquid counterparts.3 An important criterion for selecting polymers for use in SPEs is their ability to dissolve lithium salts through polar functional groups. Salt dissolution results in the replacement of ion-ion interactions in the lithium salt, with ion-dipole interactions in the polymer. The transport mechanisms of these ion-conducting materials differ from those of liquid electrolytes. Cation transport in polymer involves two steps which are considered to be dissociated or not, depending on the model chosen (Arrhenius or Vogel-Tamman-Fulcher, respectively). The application of one of these models provides interesting information on the ionic mobility dynamics in SPEs and, in particular, on the interplay between ionic jumps and polymer chain mobility. According to previous studies, higher segmental motions in the amorphous phase of polymers mainly provide ionic transport, which explains the limited ionic conductivity of SPEs at ambient temperature (less than 10-5 S/cm).Another major limitation of SPEs is primarily related to their dual role as electrolyte and binder in composite electrodes, which requires contradictory requirements to be met. Indeed, SPEs must have both sufficient flexibility to allow good interfacial contact between the electrode components and sufficient rigidity to limit short circuits.Polymer blending has emerged as an economic and effective technique to develop new SPEs which may simultaneously combine properties of each polymer and control the intrinsic properties of the resulting blend by adjusting the formulation.4 Moreover, polymer blends can be obtained by a solvent-free processing method, which reduce SPE toxicity and production time and cost. However, polymer blending makes both the salt dissociation processes and the ionic transport more difficult to understand as both polymers can dissolve lithium salts with their polar groups. Each polymer has different ionic transport properties depending on its architecture and thermal properties. Currently, no systematic survey comparing the ability of polymers with various functional groups to dissolve lithium salts in blends has thus far been conducted.In this presentation, we will discuss the salt dissociation ability of polar functional groups in various polymer blend SPEs. These groups are limited to those that are most commonly present in SPEs : ether, nitrile, carbonate, ester, alcohol and amide.5 The blends presented have been obtained by extrusion, which allows the effect of solvents on salt/polymer interactions to be neglected. Coupled FTIR, EDX and 7Li NMR analyses allow the interactions between LiTFSI and the polymer blends to be determined with a good degree of certainty. Our original study combines experimental and theoretical approaches to determine effects of polymers’ lithium salt solvating ability on blend electrolyte properties. Finally, this survey highlights an ideal polymer couple with the most promising and complementary properties, usable as SPE for LIBs. Indeed, this blend presents encouraging properties, compared to single-polymer SPEs, such as higher ionic conductivities over a wide temperature range, as well as improved mechanical and thermal stability properties and cycling performances. References Xie, W., Liu, X., He, R., Li, Y., Gao, X., Li, X., Peng, Z., Feng, S., Feng, X. and Yang, S. Journal of Energy Storage 2020, 32, 101837.Chen, R., Qu, W., Guo, X., Li, L. and Wu, F. Materials Horizons 2016, 3, 487-516.Gray, F. M. Solid polymer electrolytes, VCH New Tork 1991.Caradant, L., Lepage, D., Nicolle, P., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2020, 4943-4951.Caradant, L., Verdier, N., Foran, G., Lepage, D., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2021. Figure 1

The development of high-performance solid polymer electrolytes is crucial for producing all-solid-state lithium metal batteries with high safety and high energy density. However, the low ionic conductivity of solid polymer electrolytes and their unstable electrolyte/electrode interfaces have hindered their widespread utilization. To address these critical challenges, a strong Lewis acid (aluminum fluoride (AlF3)) with dual functionality is introduced into polyethylene oxide) (PEO)-based polymer electrolyte. The AlF3 facilitates the dissociation of lithium salt, increasing the iontransfer efficiency due to the Lewis acid-base interaction; further the in-situ formation of lithium fluoride-rich interfacial layer is promoted, which suppresses the uneven lithium deposition and continuous undesired reactions between the Li metal and PEO matrix. Benefiting from our rational design, the symmetric Li/Li battery with the modified electrolyte exhibits much longer cycling stability (over 3600 h) than that of the pure PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte (550 h). Furthermore, the all-solid-state LiFePO4 full cell with the composite electrolyte displays a much higher Coulombic efficiency (98.4% after 150 cycles) than that of the electrolyte without the AlF3 additive (63.3% after 150 cycles) at a large voltage window of 2.4–4.2 V, demonstrating the improved interface and cycling stability of solid polymer lithium metal batteries.

Solid polymer electrolytes (SPEs) are well known for their excellent mechanical properties and high safety. It will be significant to develop advanced SPEs for substituting currently used organic liquid electrolytes. However, determined by their ion-transport coupled with mobility of polymer segments, SPEs usually exhibit low ionic conductivity (10-8 ~ 10-6 S/cm) at room temperature, which severely limits their practical applications. Thus far, efforts on enhancing the ionic conductivity of SPEs have been primarily focusing on reducing crystallinity degree of the polymer hosts via introducing plasticizers, advanced nanofillers, other polymers, etc. while there have not existed effective ways to the control of the ion-transport pathways inside the SPEs. In our work, we discovered that by manipulating the configuration of denatured soy protein, the transportation of Li+ can be significantly promoted, which is of great interest for fabricating high-performance SPEs. Via carefully controlling critical factors, including denaturation of soy protein, loading level of lithium salt and temperature for the evaporation process of the electrolyte preparation, a protein-based solid electrolyte with high ionic conductivity (ca. 10-5 S/cm at room temperature) and modulus (ca. 1 GPa) was achieved, which has never been realized in any conventional SPEs. Meanwhile, the soy-protein-based SPE presents high lithium ion transference number of ca. 0.94. Molecular dynamic simulation results indicate that evaporation temperature for electrolyte preparation plays a critical role in controlling the configuration of protein. As a result, a more flexible protein configuration allows strong interactions between anions of lithium salts with the backbone oxygen and negative charge side groups of protein to form anion clusters that can facilitate the transportation of Li+. It is therefore speculated that this unique ion-transport mechanism is ceramic-like and is decoupled with mobility of protein chains. In addition, by introducing ceramic nanoparticles into denaturation of soy protein, the configuration of the protein was dramatically changed to result in a type of highly efficient nanofiller that enables fast ion-transport. A composite polymer electrolyte based on poly(ethylene oxide) (PEO) loaded with such hybrid nanofillers shows one order of magnitude improvement in ionic conductivity at room temperature, as compared with the one with untreated nanofillers. Moreover, the composite polymer electrolyte was demonstrated improved mechanical properties, and importantly improved adhesion properties that greatly benefit interfacial properties with the electrodes. The studies may open a new avenue for developing high-performance SPEs with promoted ion-transport by manipulating the configuration of the protein.

In this study, a dry type conducting polymer actuator was prepared. Nitrile rubber (NBR) containing ionic liquid, 1-butyl-3-methyl imidazolium bis(trifluoromethyl sulfonyl)imide (BMITFSI), was utilized as the solid polymer electrolyte exhibiting high ionic conductivity as well as electrical stability. Various grades of NBRs having different amounts of acrylonitrile (ACN), viz. 23, 35 and 40 mol%, were found to be well compatible with BMITFSI. The thermomechanical property and ionic conductivity of the solid polymer electrolyte were characterized by dynamic mechanical analysis and impedance analysis, respectively. A maximum conductivity of 2.54 × 10−4 S cm−1 at 20 °C was achieved in the NBR sample containing 40 mol% ACN activated in BMITFSI. A conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), was synthesized on the surface of the solid polymer electrolyte by chemical oxidative polymerization to yield the structure of solid polymer actuator. The effect of the NBR composition on the actuation behavior was examined.