Polymer-based Electrolytes Research Articles

Enhanced ionic conductivity and mechanical strength in nanocomposite electrolytes with nonlinear polymer architectures.

Solvent-free polymer-based electrolytes (SPEs) have gained significant attention to realize safer and flexible lithium-ion batteries. Among all polymers used for preparing SPEs electrolytes, poly(ethylene oxide), a biocompatible and biodegradable polymer, has been the most prevalent one mainly because of its high ionic conductivity in the molten state, the capability for the dissolution of a wide range of different lithium salts as well as its potential for the environmental health and safety. However, linear PEO is highly semicrystalline at room temperature and thus exhibits weak mechanical performance. Addition of nanoparticles enhances the mechanical strength and effectively decreases the crystallization of linear PEO, yet enhancement in mechanical performance often results in decreased ionic conductivity when compared to the neat linear PEO-based electrolytes; new strategies for decoupling ionic conductivity from mechanical reinforcement are urgently needed. Herein, we used lithium bis(trifluoromethane-sulfonyl)-imide (LiTFSI) salts dissolved in various nonlinear PEO architectures, including stars (4-arms and 8-arms) and hyperbranched matrices, and SiO2 nanoparticles (approximately equal to 50 nm diameter) as fillers. Compared to the linear PEO chains, the room temperature crystallinity was eliminated in the branched PEO architectures. The electrolytes with good dispersion of the nanoparticles in the nonlinear PEOs significantly enhanced ionic conductivity, specifically by approximately equal to 40% for 8-arm star, approximately equal to 28% for 4-arms star, and approximately equal to %16 for hyperbranched matrices, with respect to the composite electrolyte with the linear matrix. Additionally, the rheological results of the SPEs with branched architectures show more than three orders of magnitude enhancement in the low-frequency moduli compared to the neat linear PEO/Li systems. The obtained results demonstrate that the solvent-free composite electrolytes made of branched PEO architectures can be quite promising especially for irregularly shaped and environmentally benign battery applications suitable for medical implants, wearable devices, and stretchable electronics, which require biodegradability and biocompatibility.

Research Trends on Improvement of Physicochemical Properties of Sulfonated Hydrocarbon Polymer-based Polymer Electrolyte Membranes for Polymer Electrolyte Membrane Fuel Cell Applications

Research Trends on Improvement of Physicochemical Properties of Sulfonated Hydrocarbon Polymer-based Polymer Electrolyte Membranes for Polymer Electrolyte Membrane Fuel Cell Applications

Effect of Nanoparticles in LiFePO4 Cathode Material Using Organic/Inorganic Composite Solid Electrolyte for All-Solid-State Batteries.

Herein, we report the effect of using nanoparticles of LiFePO4 on the electrochemical properties of all-solid-state batteries (ASSBs) with a solid electrolyte. LiFePO4 (LFP) cathode materials are promising cathode materials in polymer-based composite solid electrolytes because of their limited electrochemical window range. However, LFP cathodes exhibit poor electric conductivity and sluggish lithium ion diffusion. In addition, there is a disadvantage in that the interfacial resistance increases due to poor contact between the LFP cathode material and the solid electrolyte when composing the composite cathode. The nano-sized LFP cathode material increases the contact area between solid electrolyte in the positive electrode and enhances lithium ion diffusion. Therefore, the structural differences and electrochemical performance of these nanoscale LFP cathode materials in the ASSB were studied by X-ray diffraction, scanning electron microscopy, and electrochemical analysis.

Insight into poly(1,3-dioxolane)-based polymer electrolytes and their interfaces with lithium Metal: Effect of electrolyte compositions

The transport properties and electrochemical stability of advanced lithiummetal batteries are severely constrained by the actual electrolyte compositions. Herein, for comprehensive atomistic insights and the development of electrolyte scientific theory, molecular dynamics technology is employed to investigate the electrochemical properties of recently attractive poly(1,3-dioxolane)-based electrolytes and their interfaces with lithium metal. This work elaborates on the characteristics of Li+ solvation environments and the effects of polymer chain length or plasticizer content on the experiment-concerned properties of bulk electrolytes, including solvation sheath structures, ionic diffusions, conductivities, transport numbers, etc. Meanwhile, to clarify the influence of polymer or salt concentration on the electrolyte/lithium metal interface, three distinctive interface models were proposed and analyzed based on different electrolyte compositions in this work: liquid-based, polymer-based, and highly-concentrated systems. Compared with the unfavorable liquid interface layer in the liquid-based system, the latter two systems have more electrochemically stable interfacial construction due to the appearance of polymer on the lithium metal surface. Besides, the Li+ solvation structure, which is related to the lithium electrodeposition, exhibits orientation, e.g., small organic liquid molecules in the liquid-based system are more likely to appear on the side that is accessible to the lithium metal surface. These small molecules are essentially excluded from the Li+ solvation structures in the polymer-based electrolyte, which is another important factor for stabilizing the interface. Furthermore, compared with the bulk electrolytes, it is found that ionic conductions at the interfaces are not attenuated in all systems. This work presents a comprehensive, profound view from bulk to interfacial properties, thus providing a theoretical cornerstone for the composition design and performance optimization of polymer electrolytes for lithium metal batteries.

Self-Repairable and Flexible Polymer Network Electrolyte with Enhanced Lithium-Ion Conduction for Lithium Metal Batteries.

Developing high-performance functional polymer-based electrolytes is important for realizing next generation safe lithium metal batteries. In this study, a new type of quasi-solid polymer network electrolyte (SIPH-x-y%) was prepared by combining synthesized polymer network (SIPH) containing urethane bond linked ionic liquids (ILs), polyethylene glycol (PEG), and disulfide bond moieties, lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI), and glyme type additive. It was found that SIPH-20-40% was mechanically flexible, self-healable, and showed high ionic conductivity of 2.67×10-4 S cm-1 . Also, SIPH-20-40% possesses a high lithium ion transference number of 0.43 and good electrochemical stability. These properties enabled the SIPH-20-40% electrolyte membrane to support Li/Li symmetrical cell to cycle stably during long term Li plating and stripping. The Li/SIPH-20-40%/LFP showed high delivered specific capacity and good stability (166.1 mAh g-1 after 106 cycles at 0.2 C). Such glyme doped polymer network electrolyte provides new experimental findings for developing polymer-based electrolyte with excellent mechanical integrity and battery related properties.

A room-temperature high performance all-solid-state lithium-sulfur battery enabled by a cross-linked copolymer@ceramic hybrid solid electrolyte

The use of solid electrolytes (SEs) is a key strategy for enabling the intrinsically safe operation of batteries comprising lithium metal anodes as they suppress the growth of lithium dendrites. Among the different types of SEs, polymer-based hybrid electrolytes (HEs) are highly promising due to their synergetic properties from the constituent polymer matrix and inorganic filler particles. However, the lithium-ion diffusion pathway in HEs is still dominated by the polymer, especially for polyethylene oxide (PEO)-based HEs. The main limitation of PEO is the strong temperature dependence of its ionic conductivity, preventing its use at room temperature (RT). Herein, a cross-linked polymer-based HE with a high ionic conductivity of 1.1 × 10-3 S cm-1 at RT is presented. The novel cross-linked copolymer, composed of pentaerythritol tetraacrylate (PETEA), tri(ethylene glycol) divinyl ether (TEG), and lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI), serves as a matrix to achieve satisfactory mechanical strength. Integrated Li7La3Zr2O12 (LLZO) particles are covalently bound to the copolymer by a prior surface modification step. To demonstrate the suitability of the developed HE for RT application in advanced battery systems, a solid-state lithium-sulfur cell is built which exhibits an initial specific capacity of 688 mA h g-1. The ability of this HE to operate at RT can be expected to boost the development of safe all-solid-state batteries for many applications.

Reevaluating the Stability of the PEO-Based Solid-State Electrolytes for High Voltage Solid-State Batteries

Poly(ethylene oxide) (PEO) is a very popular polymer-based solid electrolyte material with relatively high ionic conductivity and dielectric constant1. However, many previous works mentioned that it could not be used in high voltage cells for its low oxidation potential (~3.9V vs. Li/Li+)2. However, only a handful of prior investigations evaluated the stability of the PEO-based solid-state electrolyte considering the contribution of the cathode surface chemistry to electrolyte oxidation and decomposition. Since most of the previous research exploring high voltage cathodes with PEO used LiCoO2, it could be possible the other cathode compositions will erode the PEO-based solid electrolyte in different and less extreme ways.Our work revisits the high voltage electrochemical stability of PEO-based solid state-electrolyte materials. Potentiodynamic and galvanostatic tests were performed in test cells using PEO electrolyte layers with either LiNixMnyCozO2 or LiCoO2 cathode materials. We found that the high voltage instability of PEO-based solid-state cells is profoundly affected by the instability of the cathode material used. Specifically, the LiCoO2 electrodes were observed to undergo an irreversible oxidation process where they shattered into small pieces, which then led to a rapid irreversible loss in capacity. In contrast, we found that the PEO-based solid-state electrolytes could be stably cycled with high-nickel content cathodes stably at a voltage up to 4.5V vs. Li/Li+ over many cycles with minimal capacity deterioration. K. Chrissopoulou, K. S. Andrikopoulos, S. Fotiadou, S. Bollas, C. Karageorgaki, D. Christofilos, G. A. Voyiatzis, and S. H. Anastasiadis, 44, 9710–9722 (2011).J. Qiu, X. Liu, R. Chen, Q. Li, Y. Wang, P. Chen, L. Gan, S.-J. Lee, D. Nordlund, Y. Liu, X. Yu, X. Bai, H. Li, and L. Chen, Adv. Funct. Mater., 30, 1909392 (2020).

Composite polymer electrolyte incorporating WO3 nanofillers with enhanced performance for dendrite-free solid-state lithium battery

All solid-state lithium batteries (ASS-LBs) with polymer-based solid electrolytes are a prospective contender for the next-generation batteries because of their high energy density, flexibility, and safety. Among all-polymer electrolytes, PEO-based solid polymer electrolytes received huge consideration as they can dissolve various Li salts. However, the development of an ideal PEO-based solid polymer electrolyte is hindered by its insufficient tensile strength and lower ionic conductivity due to its semi-crystalline and soft chain structure. In order to lower the crystallization and improve the performance of PEO-based solid polymer electrolyte, tungsten trioxide (WO3) nanofillers were introduced into PEO matrix. Herein, a PEO20/LiTFSI/x-WO3 (PELI-xW) (x = 0%, 2.5%, 5%, 10%) solid composite polymer electrolyte was prepared by the tape casting method. The solid composite polymer electrolyte containing 5 wt% WO3 nanofillers achieved the highest ionic conductivity of 7.4 × 10-4 S cm-1 at 60 °C. It also confirms a higher Li-ion transference number of 0.42, good electrochemical stability of 4.3V, and higher tensile strength than a PEO/LiTFSI (PELI-0W) fillers-free electrolyte. Meanwhile, the LiFePO4│PELI-xW│Li ASS-LBs demonstrated high performance and cyclability. Based on these findings, it can be considered a feasible strategy for the construction of efficient and flexible PEO-based solid polymer electrolytes for next-generation solid-state batteries.

A polydopamine-modified garnet–based polymer-in-ceramic hybrid solid electrolyte membrane for high-safety lithium metal batteries

Composite solid electrolyte (CSE) membranes combining the attractive properties of ceramic and polymer-based electrolytes have emerged as preferred electrolytes for all-solid-state lithium metal batteries (ASSLMBs). In this study, we used solution-casting to prepare a CSE membrane from a suspension of polydopamine (PDA)-modified Li6.28La3Zr2Al0.24O12 (LLZAO) filler (PDA@LLZAO), poly(vinylidene fluoride–co–hexafluoropropylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and succinonitrile (SN) as the middle layer and a matrix of PVDF-HFP, LiTFSI, and SN as both the top and bottom layers. The presence of PDA on the surface of LLZAO enabled the filler to percolate well within the polymer matrix. Consequently, a membrane based on PDA@LLZAO (CSE1) exhibited high ionic conductivity (4.01 × 10–4 S cm−1), a high lithium transference number (ca. 0.76), high tensile strength (29.09 MPa), and a stable electrochemical window (ca. 5.01 V vs Li/Li+) relative to those properties of a counterpart membrane (CSE0) having the same constituents as CSE1, but an unmodified LLZAO filler. The interfacial stability developed by the synergetic effect of the CSE1 membrane and Li metal anode enhanced the corresponding Li plating/stripping performance (2000 h) and critical current density (2.0 mA cm−2). Benefiting from this stable interfacial contact, an Al2O3@NCM811/CSE1/Li coin-type cell provided a discharge specific capacity of 136.46 mAh/g at a rate of 0.5C after 300 cycles, with a capacity retention of 86.22 % and a average coulombic efficiency of 99.16 % at 25 °C. Hence, our proposed strategy for preparing CSEs appears to be promising for use in ASSLMB applications.

Enhancement of the Electrochemical Performances of Composite Solid-State Electrolytes by Doping with Graphene.

With high safety and good flexibility, polymer-based composite solid electrolytes are considered to be promising electrolytes and are widely investigated in solid lithium batteries. However, the low conductivity and high interfacial impedance of polymer-based solid electrolytes hinder their industrial applications. Herein, a composite solid-state electrolyte containing graphene (PVDF-LATP-LiClO4-Graphene) with structurally stable and good electrochemical performance is explored and enables excellent electrochemical properties for lithium-ion batteries. The ionic conductivity of the composite electrolyte membrane containing 5 wt% graphene reaches 2.00 × 10−3 S cm−1 at 25 °C, which is higher than that of the composite electrolyte membrane without graphene (2.67 × 10−4 S cm−1). The electrochemical window of the composite electrolyte membrane containing 5 wt% graphene reaches 4.6 V, and its Li+ transference numbers reach 0.84. Assembling this electrolyte into the battery, the LFP/PVDF-LATP-LiClO4-Graphene /Li battery has a specific discharge capacity of 107 mAh g−1 at 0.2 C, and the capacity retention rate was 91.58% after 100 cycles, higher than that of the LiFePO4/PVDF-LATP-LiClO4/Li (LFP/PLL/Li) battery, being 94 mAh g−1 and 89.36%, respectively. This work provides a feasible solution for the potential application of composite solid electrolytes.

Dual Structure-Material Design of Separators toward Dendrite-Free Lithium Metal Anodes.

The practical applications of lithium metal anodes have been severely hindered by the Li dendrite issue. Herein, a dual structure-material design strategy was developed to fabricate a new type of separator using interconnected hollow porous polyacrylonitrile (PAN) nanofibers (HPPANF), which delivered controllable and dendrite-free Li depositions. The interconnected mesopores on HPPANF bridged the hollow interiors with the outside voids among the fibers, enabling outstanding electrolyte uptake capabilities for high ion conductivity, and nano-level wetted electrolyte/anode interface for uniform Li plating/stripping. In parallel, the HPPANF separator enriched with polar groups acted as an exceptional polymer-based solid-state electrolyte, providing 3D ion channels for the transport of Li ions. Benefiting from the dual structure-material design, the HPPANF separator induced uniform Li ion flux for dendrite-free Li depositions, which caused enhanced cycling stability (1300 h, 3 mA cm-2 ). This work demonstrates a new method to stabilize Li metal anodes through rational separator design.

Advanced polymer-based electrolytes in zinc–air batteries

Zinc–air batteries (ZABs) are expected to be some of the most promising power sources for wearable and portable electronic devices and have received widespread research interest. As an ion conductor connecting anodes and cathodes, the electrolyte is critical for the overall performance of ZABs (e.g., energy density, rechargeability, and operating voltage). Compared with liquid electrolytes, polymer-based electrolytes have superior characteristics for ZABs, such as negligible electrolyte leakage, three-phase interface stabilization, and dendrite suppression. In this perspective, we focus on recent progress in polymer-based electrolytes for ZABs. After a brief introduction to ZABs and electrolytes, we emphasize the development of polymer-based electrolytes in terms of their intrinsic properties and interfacial chemistry. Finally, challenges and viable strategies are proposed for polymer-based electrolytes in ZABs. We hope that this work will provide useful guidance to spur the development of high-performance ZABs based on advanced polymer-based electrolytes.

In situ formed self-healable quasi-solid hybrid electrolyte network coupled with eutectic mixture towards ultra-long cycle life lithium metal batteries

The exploration of high-performance polymer-based electrolyte have great promise for the development of next-generation lithium metal batteries. In this study, a self-healable quasi-solid hybrid electrolyte network coupled with deep eutectic solvent (X-PPS-D4) was prepared by polyaddition reaction, photo-initiated free-radical crosslinking, and physical blending. X-PPS-D4 not only possessed high ionic conductivity (σ) of 2.03✗10−4 S cm−1 at 30 ℃ but also wide electrochemical stability window (0∼5.0 V vs. Li+|Li). The enhanced lithium ion transference number (tLi+= 0.44) for X-PPS-D4 resulted from reduction of anion mobility that was proved by spectral analysis together with nuclear magnetic resonance study and theoretical calculation. Under testing temperature of 30 ℃, X-PPS-D4 could support stable long-term (>1300 h) plating/stripping tests of lithium symmetrical cell at current density of 0.1 mA cm−2. More importantly, the in situ formed X-PPS-D4 on LiFePO4 cathode within the coin cell facilitated excellent cell performance with specific capacity over 100 mA h g−1 at 5 C and ultra-long cycle life (>1000 cycles) with high delivered specific capacity at 1 C (>116.1 mA h g−1 after 1000 cycle). X-PPS-D4 also supported coin cells with high voltage cathode to perform decently. This research provides new insights into structure-property relationship of quasi-solid hybrid electrolyte with eutectic mixture and offered an effective way to develop high-performance polymer-based electrolytes for LMBs.

Characteristics of Methyl Cellulose Based Solid Polymer Electrolyte Inserted with Potassium Thiocyanate as K+ Cation Provider: Structural and Electrical Studies

The attention to a stable and ionic conductive electrolyte is driven by the limitations of liquid electrolytes, particularly evaporation and leakage, which restrain their widespread use for electrochemical device applications. Solid polymer electrolyte (SPE) is considered to be a potential alternative since it possesses high safety compared to its counterparts. However, it still suffers from low device efficiency due to an incomplete understanding of the mechanism of ion transport parameters. Here, we present a simple in situ solution casting method for the production of polymer-based electrolytes using abundantly available methylcellulose (MC) doped at different weight percentages of potassium thiocyanate (KSCN) salt. Fourier transform infrared (FTIR), and electrochemical impedance spectroscopy (EIS) methods were used to characterize the prepared samples. Based on EIS simulation and FTIR deconvolution associated with the SCN anion peak, various ion transport parameters were determined. The host MC medium and KSCN salt have a strong interaction, which was evident from both peak shifting and intensity alteration of FTIR spectra. From the EIS modeling, desired electric circuits correlated with ion movement and chain polarization were drawn. The highest ionic conductivity of 1.54 × 10−7 S cm−1 is determined from the fitted EIS curve for the film doped with 30 wt.% of KSCN salt. From the FTIR deconvoluted peak, free ions, ions in contact with one another, and ion aggregates were separated. The extracted ion transport parameters from the EIS method and FTIR spectra of the SCN anion band confirm that both increased carrier concentration and their mobility were crucial in improving the overall conductivity of the electrolyte. The dielectric investigations were further used to understand the conductivity of the films. High dielectric constants were observed at low frequencies for all MC:KSCN systems. The dispersion with a high dielectric constant in the low-frequency band is ascribed to the dielectric polarization. The wide shift of M″ peak towards the high frequency was evidenced by the MC-based electrolyte impregnated with 30 wt.% of KSCN salt, revealing the improved ionic movement assisted with chain segmental motion. The AC conductivity pattern was influenced by salt concentration.

Study of MC:DN-Based Biopolymer Blend Electrolytes with Inserted Zn-Metal Complex for Energy Storage Devices with Improved Electrochemical Performance.

Stable and ionic conducting electrolytes are needed to make supercapacitors more feasible, because liquid electrolytes have leakage problems and easily undergo solvent evaporation. Polymer-based electrolytes meet the criteria, yet they lack good efficiency due to limited segmental motion. Since metal complexes have crosslinking centers that can be coordinated with the polymer segments, they are regarded as an adequate method to improve the performance of the polymer-based electrolytes. To prepare plasticized proton conducting polymer composite (PPC), a simple and successful process was used. Using a solution casting process, methylcellulose and dextran were blended and impregnated with ammonium thiocyanate and zinc metal complex. A range of electrochemical techniques were used to analyze the PPC, including transference number measurement (TNM), linear sweep voltammetry (LSV), cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The ionic conductivity of the prepared system was found to be 3.59 × 10−3 S/cm using the EIS method. The use of glycerol plasticizer improves the transport characteristics, according to the findings. The carrier species is found to have ionic mobility of 5.77 × 10−5 cm2 V−1 s−1 and diffusion coefficient of 1.48 × 10−6 cm2 s−1 for the carrier density 3.4 × 1020 cm−3. The TNM revealed that anions and cations were the predominant carriers in electrolyte systems, with an ionic transference value of 0.972. The LSV approach demonstrated that, up to 2.05 V, the film was stable, which is sufficient for energy device applications. The prepared PPC was used to create an electrical double-layer capacitor (EDLC) device. The CV plot exhibited the absence of Faradaic peaks in the CV plot, making it practically have a rectangular form. Using the GCD experiment, the EDLC exhibited low equivalence series resistance of only 65 Ω at the first cycle. The average energy density, power density, and specific capacitance values were determined to be 15 Wh/kg, 350 W/kg, and 128 F/g, respectively.

A review on nano composite polymer electrolytes for high-performance batteries

Polymer electrolytes (PEs) are lightweight, flexible, non-flammable solutions and provide a feasible way to replace organic liquid electrolytes because of the safety issues faced by energy storage devices. Inorganic nanofillers are vital in enhancing ionic conductivity by creating additional pathways in polymer-based nanocomposite solid electrolytes. The advances in polymer electrolytes play an essential role in developing the energy storage devices such as batteries. This article briefly summarises the preparation techniques of different polymer electrolytes, developing and focusing on fundamental properties such as surface morphology, electrolyte phases, and the influence of dopants, fillers, and plasticizers on the ionic charge transfer, ionic conductivity, dielectric properties, and transport properties using impedance spectroscopy. We anticipate that gives clear direction for developing energy storage devices.

Organic sensitizer with azine π-conjugated architecture as co-sensitizer and polymer-based electrolyte for efficient dye-sensitized solar cell

The donor-π-acceptor architecture of a novel organic sensitizer (NHC) is synthesized and used in dye-sensitized solar cells (DSSCs). An azine-spacer (=N-N=) is employed to connect the 3-nitrobenzene anchor unit with the carbazole donor in the sensitizer. Photophysical, electrochemical, and photovoltaic performances of the synthesized dye are studied in depth. Further, polymer-based electrolytes were prepared by doping 1-n-hexyl-3-methylimidazolium iodide (HMIm+I−) to the polyvinylidene fluoride electrolyte solution and studied their conductivity and dielectric properties. DSSC fabricated with NHC dye and HMIm+I−-20% electrolyte displayed an efficiency of 1.24%. In addition, NHC co-sensitization with bis(isothiocyanato)(2,2′-bipyridyl-4,4′-dicarboxylato)(4,4′-dinonyl-2,2′-bipyridyl)ruthenium(II) (Z907) is investigated. As a result, the co-sensitized device exhibit greater photovoltaic performance, with an efficiency of 4.76% compared to the cell with Z907 (4.17%) alone, owing to higher short-circuit current density in conjunction with higher open-circuit voltages.

Are Polymer-Based Electrolytes Ready for High-Voltage Lithium Battery Applications? An Overview of Degradation Mechanisms and Battery Performance

Are Polymer-Based Electrolytes Ready for High-Voltage Lithium Battery Applications? An Overview of Degradation Mechanisms and Battery Performance

Utilizing an Oxygen-Rich Interface by Hydroxyapatite to Regulate the Linear Diffusion for the Stable Solid-State Electrolytes.

Improving dissociation and diffusion of lithium ions is the key to solving the practical application of polymer-based solid-state electrolytes (SSE). Here, a low-cost three-dimensional hydroxyapatite (HAP) nanowire is used in polyethene oxide to obtain an enhanced lithium-ion electrolyte. The oxygen-rich interface of HAP provides an integrated dissociation-diffusion platform for lithium salts. The TFSI- anions tend to coordinate with calcium ions, which makes it easier for lithium ions to escape and stay in a free state. The lateral nucleus in the HAP polyethene electrolyte regulates the diffusion from spherical diffusion into linear planar diffusion, which is confirmed by chronoamperometry curves and in situ observation. The stability of the electrolyte at high voltages is improved by inhibiting the superoxide radicals of polyethene oxide chains, which is demonstrated by nuclear magnetic resonance and electron paramagnetic resonance spectroscopy methods. The initial specific charge capacity of the Li/SPE/LiFePO4 cell with HAP-modified polyethene oxide at 2 C is 148.8 mA h/g, and its initial Coulombic efficiency is 95.17%. After 100 cycles, the specific discharge capacity is 125.5 mA h/g with 99.91% retention per cycle. This oxygen-rich interface strategy would guide the discovery of novel materials for polymer-based SSE.

Role of Agent Molecules for Low-Temperature Activation of Lithium-Ion Transport for Solid-State Polymer Electrolytes

The realization of all-solid-state lithium-ion batteries (LIBs) is often considered as the final challenge in the development of LIBs. Replacing Li-ion conductive liquid electrolytes with high-performance solid-state electrolytes is indispensable for the development of all-solid-state LIBs. Solid-state electrolytes under development fall into three classes: polymers, oxides, and sulfides. Polymer-based electrolytes have advantages over oxides and sulfides, such as formation of low-resistance electrolyte/electrode interfaces, good processability, and high energy-density owing to low density. Therefore, polymer-based solid-state electrolytes are being developed in both industry and academia as a practical route for realizing high-capacity LIBs.[1]For application in commercial LIBs, the electrolyte should have an ionic conductivity higher than 10-4 S/cm at room temperature. Conventional solid polymer electrolytes, such as polyethylene oxide (PEO)-based electrolytes, do not meet the performance requirements due to insufficient ionic conductivity in the range of 10-6 to 10-5 S/cm. Recently, polyphenylene sulfide (PPS)-based polymer electrolytes have been reported to yield ion conductivities as high as those of liquid electrolytes over a wide temperature range (> 1.0 × 10-4 S/cm at 25 °C, > 1.0 × 10-3 S/cm at 80 °C, and > 1.0 × 10-3 S/cm at −40 °C).[2] These electrolytes consist of base polymer chains containing PPS, Li salts that can dissociate into cations and anions, and neutral agent molecules. However, the detailed Li-ion transport mechanism in terms of the respective roles of the molecular components of PPS electrolytes is yet to be determined. This limited understanding hinders the further improvement of PPS-based electrolytes.In this study, we perform a series of first-principle calculations and demonstrate that certain types of neutral molecules (so-called agent molecules) accelerate solid-state lithium-ion migration when mixed with lithium salts.[3] We find that the intermolecular interaction in a selected agent-molecule/lithium-salt binary system is governed by the strong coupling between lithium and oxygen atoms. Upon the addition of agent molecules, the anionic species surrounding the lithium of lithium salts is replaced by the agent molecules. The resulting weakened Coulomb energy coupling between lithium and oxygen atoms is determined to be a key factor in enabling fast lithium-ion migration via facile dissociation of lithium salts and subsequent formation of ion-hopping sites in the form of lithium-free oxygen-cages. The structure-based interpretation of agent molecules suggests that neutral molecules with functional groups which enhance chemical resonance can be selected as potential agent molecules. We believe that the results obtained in this study serve as a theoretical basis for the future development of solid-state polymer electrolytes, particularly toward mitigating the dependence of lithium-ion transport on the movement of polymer chains.