Solid-state Polymer Electrolytes Research Articles

Solid-state polymer magnesium supercapacitor

The present article focuses on the development of a highly ion-conductive, solvent-free, solid-state polymer electrolyte membrane (PEM) via photopolymerization of polyethylene glycol diacrylate (PEGDA) network from its homogeneous melt mixtures containing succinonitrile (SCN) plasticizer and magnesium bis(trifluoromethane sulfonyl) imide Mg(TFSI)2 salt. The above solid-state Mg-PEM exhibits a Helmholtz electric double-layer capacitor (EDLC) behavior in its supercapacitive symmetric carbonaceous electrode configuration. The electrochemical stability for this PEM membrane (20/40/40 PEGDA/SCN/Mg (TFSI)2) was found to be approximately 3 V from linear sweep voltammetry with a specific capacitance of about 44 F/g from cyclic voltammetry and an energy density of approximately 17 Wh/kg in the 0–2 V range from the constant current density (CCD) experiment. Of particular interest is its excellent capacity retention of over 11,200 cycles, thus tested with the Coulombic efficiency of over 87%. Moreover, the energy density after extensive cycling for 11,200 has increased to approximately 56 Wh/kg at 10 mV/s in the potential range of 0–3 V relative to 17 Wh/kg in the potential range of 0–2 V at the same scan rate, attesting the excellent electrochemical stability and long life of the present Mg-PEM supercapacitor.

Polymers with Cyanoethyl Ether and Propanesulfonate Ether Side Chains for Solid-State Li-Ion Battery Applications

Two key challenges of solid-state polymer electrolytes (SPEs) are low ionic conductivity and low lithium transference number, which must be resolved in order to achieve satisfactory cycling performance for solid-state lithium batteries. Herein, we successfully substituted β-cyanoethyl ether [−O–(CH2)2–CN] and propanesulfonate ether [−O–(CH2)3–SO3–] groups for the −OH group in polyvinyl alcohol. SPEs were then prepared by mixing the resultant graft-polymer with various levels of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The SPE with an optimal concentration of LiTFSI (50 wt %) showed a maximum ionic conductivity of 5.4 × 10–4 S cm–1 with an activation energy of 31.6 kJ mol–1, an electrochemical stability window of 5.3 V (vs Li/Li+), and a lithium-ion transference number of 0.48 at room temperature (∼25 °C). The plating/stripping tests for a Li|SPE|Li cell demonstrated a steady voltage profile without short-circuiting issues for 500 cycles (i.e., 500 h). Furthermore, a solid-state Li|SPE|LiFePO4 battery was assembled with exceptional cycling stability at 25 °C. A discharge (DC) capacity of 159.1 mA h g–1 was attained at a 0.1 C-rate. In addition, the DC capacity at a 0.5 C-rate and capacity retention after 576 cycles are 138.0 mA h g–1 and 70%, respectively.

Conformational Regulation of Dielectric Poly(Vinylidene Fluoride)‐Based Solid‐State Electrolytes for Efficient Lithium Salt Dissociation and Lithium‐Ion Transportation

AbstractRestricted by the poor ability of polymers to dissociate lithium salts and transport ions, solid‐state polymer electrolytes (SPEs) show extremely low ionic conductivities (≈10−7–10−5 S cm−1) and transference number of lithium ions (tLi+ ≈0.2–0.4) at 25 °C. Here, a novel polymer matrix of SPEs that simultaneously promotes lithium salt dissociation and ion transportation based on a high dielectric poly(vinylidene fluoride‐trifluoroethylene‐chlorotrifluoroethylene) (TerP) and an all‐trans conformational poly(vinylidene fluoride‐trifluoroethylene) (CoP), is developed. The high dielectric constant increases the polarity of CH2CF2 polar groups; then, brings a strong electronegative end that dissociates Li+ from lithium salts. The all‐trans conformation assures all fluorine atoms locate on one side of the chain, constructing ion hopping highways. As a result, the TerP/CoP (TC) SPE exhibits a high ionic conductivity (2.37 × 10−4 S cm−1) and a quite large tLi+ of 0.61 at 25 °C. The Li/TC SPE/Li symmetric cells cycle stably for more than half a year (>4500 h) and the LiNi0.8Co0.1Mn0.1O2/TC SPE/Li cell cycles steadily for 1000 and 600 cycles at 1 C and 2 C at 25 °C, respectively. This work paves a new way to prepare high‐performance SPEs by simultaneously modulating dielectric constants and conformation of polymers.

Cold sintering-enabled interface engineering of composites for solid-state batteries

The cold sintering process (CSP) is a low-temperature consolidation method used to fabricate materials and their composites by applying transient solvents and external pressure. In this mechano-chemical process, the local dissolution, solvent evaporation, and supersaturation of the solute lead to “solution-precipitation” for consolidating various materials to nearly full densification, mimicking the natural pressure solution creep. Because of the low processing temperature (<300°C), it can bridge the temperature gap between ceramics, metals, and polymers for co-sintering composites. Therefore, CSP provides a promising strategy of interface engineering to readily integrate high-processing temperature ceramic materials (e.g., active electrode materials, ceramic solid-state electrolytes) as “grains” and low-melting-point additives (e.g., polymer binders, lithium salts, or solid-state polymer electrolytes) as “grain boundaries.” In this minireview, the mechanisms of geomimetics CSP and energy dissipations are discussed and compared to other sintering technologies. Specifically, the sintering dynamics and various sintering aids/conditions methods are reviewed to assist the low energy consumption processes. We also discuss the CSP-enabled consolidation and interface engineering for composite electrodes, composite solid-state electrolytes, and multi-component laminated structure battery devices for high-performance solid-state batteries. We then conclude the present review with a perspective on future opportunities and challenges.

Elastomeric Electrolyte for High Capacity and Long-Cycle-Life Solid-State Lithium Metal Battery.

High room-temperature ionic conductivity and good compatibility with lithium metal and cathode materials are prerequisites for solid-state electrolytes used in lithium metal batteries. Here, the solid-state polymer electrolytes (SSPE) are prepared by combining the traditional two-roll milling technology with interface wetting. The as-prepared electrolytes consisting of elastomer matrix and high-mole-loading of LiTFSI salt show a high room temperature ionic conductivity of 4.6×10-4 S cm-1 , a good electrochemical oxidationstability up to 5.08V, and improved interface stability. These phenomena are rationalized with the formation of continuous ion conductive paths based on sophisticated structure characterization including synchrotron radiation Fourier-transform infrared microscopy, wide- and small-angle X-ray scattering. Moreover, at room temperature, the Li||SSPE||LFP coin cell shows a high capacity (161.5 mAh g-1 at 0.1 C), long-cycle-life (retaining 50% capacity and 99.8% Coulombic efficiency after 2000 cycles), and good C-rate compatibility up to 5 C. This study, therefore, provides a promising solid-state electrolyte that meets both the electrochemical and mechanical requirements of practical lithium metal batteries.

Polyimide-Based Solid-State Gel Polymer Electrolyte for Lithium–Oxygen Batteries with a Long-Cycling Life

Metal-air batteries have attracted wide interest owing to their ultrahigh theoretical energy densities, particularly for lithium-oxygen batteries. One of the challenges inhibiting the practical application of lithium-oxygen batteries is the unavoidable liquid electrolyte evaporation accompanying oxygen fluxion in the semi-open system, which leads to safety issues and poor cyclic performance. To address these issues, we propose a solid-state polyimide based gel polymer electrolyte (PI@GPE), immobilizing and reserving a liquid electrolyte in the gelled polymer substrate. The liquid electrolyte uptake of PI@GPE is measured to be 842%, 6 times higher than that of the commercial glass fiber separator, contributing to a high ionic conductivity of 0.44 mS cm-1. Additionally, PI@GPE possesses an enhanced lithium transference number of 0.596 as well as superior interfacial compatibility with lithium metals. Under 0.1 mA cm-2 and 0.25 mA h cm-2, PI@GPE-based lithium-oxygen batteries demonstrate distinguished long-cycling stability of 366 cycles, 4 times more than that with a glass fiber separator and liquid electrolyte. Our work provides a unique solid-state gel polymer electrolyte to mitigate liquid electrolyte leakage, exhibiting promising potential application in highly safe lithium-oxygen batteries with a long-cycling life.

Structurally integrated asymmetric polymer electrolyte with stable Janus interface properties for high-voltage lithium metal batteries

Solid-state polymer electrolytes are outstanding candidates for next-generation lithium metal batteries in the realm of high specific energy densities, high safeties and tight contact with electrodes. However, their applications are still hindered by the limitations that no single polymer is electrochemically stable with the oxidizing high-voltage cathode and the highly reductive Li anode, simultaneously. Herein, a bilayer asymmetric polymer electrolyte (SL-SPE) without accessional interface resistance that using poly (ethylene glycol) diacrylate (PEGDA) as a “bridge” to connect the sulfonyl (OS = O)-contained oxidation-tolerated layer and polyether-derived reduction-tolerated layer (SPE), is proposed and synthesized by sequential two-step UV polymerizations. SL-SPE can provide widened electrochemical stability window up to 5 V, while simultaneously deploying a stable Janus interface property. Eventually, the superior high-voltage (4.4 V) cycling durability can be displayed in LiNi0.6Co0.2Mn0.2O2|SL-SPE|Li batteries. This finding provides a bran-new idea for designing multifunctional polymer electrolytes in the application of solid-state batteries.

Pendant Length-Dependent Electrochemical Performances for Conjugated Organic Polymers as Solid-State Polymer Electrolytes in Lithium Metal Batteries.

The development of solid-state polymer electrolytes (SPEs) has been plagued by poor ionic conductivity, low ionic transference number, and limited electrochemical potential window. The exploitation of ionized SPEs is a feasible avenue to solve this problem. Herein, conjugated organic polymers (COPs) with excellent designability and rich pore structures have been selected as platforms for exploration. Three cationic COPs with different chain lengths of quaternary ammonium salts (CbzT@Cx, x = 4, 6, 9) are designed and applied to SPEs for the first time. Meanwhile, the effects of chain lengths on their electrochemical performances are compared. Especially, CbzT@C9 shows the most attractive electrochemical performance due to its high specific surface area of 212.3 m2 g-1. The larger specific surface area allows more exposure of the long-chain quaternary ammonium cation groups, which is more favorable for the dissociation of lithium salts. Moreover, the flexible long-chain structure increases the compatibility with poly(ethylene oxide) (PEO) and reduces the crystallinity of PEO to some extent. The richer pore structure can accommodate more PEO, further disrupting the crystallinity of PEO and creating more channels for the ether-oxygen chain to transport lithium ions. At 60 °C, the SPE (CbzTM@C9) presents an excellent ionic conductivity (σ) of 8.00 × 10-4 S cm-1. CbzTM@C9 has a lithium-ion transference number (tLi+) of 0.48. Thus, the assembled Li/CbzTM@C9/LiFePO4 battery provides a good discharge capacity of 158.8 mAh g-1 at 0.1C. After 70 cycles, the capacity retention rate is 93.8% with a Coulombic efficiency of 98%. The excellent flexibility brings stable power supply capability under various bending angles to the assembled Li/CbzTM@C9/LiFePO4 soft-packed battery. The project uses conjugated organic polymers in SPEs and creates an avenue to develop flexible energy storage equipment.

Novel quasi-solid-state composite electrolytes boost interfacial Li+ transport for long-cycling and dendrite-free lithium metal batteries

Solid-state composite electrolytes (SCEs) have received wide attention due to their advantages of both solid-state polymer electrolytes and inorganic ceramic electrolytes. However, poor interfacial compatibility in SCEs still limits their practical applications in lithium metal batteries. Herein, a lotus pod-inspired flexible PC-g-PMT/LL-g-PMT20 membrane composed of zero-dimensional LLZTO-g-PVIM+TFSI− (denoted as LL-g-PMT) hairy nanoparticle, one-dimensional PVDF-CTFE-g-PVIM+TFSI− (denoted as PC-g-PMT) comb polymer, and lithium salt LiTFSI (LLZTO = Li6.4La3Zr1.4Ta0.6O12; PVDF-CTFE = poly(vinylidene fluoride-co-chlorotrifluoroethylene); PVIM+TFSI− = poly(1-butyl-3-vinylimidazolium bis(trifluoromethylsulphonyl)imide); LiTFSI = lithium bis(trifluoromethylsulphonyl)imide) is designed and prepared. Our PC-g-PMT/LL-g-PMT20 membrane facilitates molecular-level homogeneous lithium ion (Li+) flux, provides fast transmission pathways for Li+ by the three-dimensional well-developed porous framework, and improves interfacial stability via molecular engineering. The quasi-solid-state composite electrolytes (QSCEs) can be further obtained facilely via introducing plasticizer into PC-g-PMT/LL-g-PMT20 membrane. The as-obtained QSCEs (e.g., PC-g-PMT/LL-g-PMT20/P) integrate features of LLZTO-enhanced Li+ conducting and mechanical properties, PVDF-CTFE backbone-induced flexibility, and PVIM+TFSI− side-chain-strengthened interfacial compatibility. As a result, our PC-g-PMT/LL-g-PMT20/P has a membrane thickness as low as 22 µm, but still delivers an ionic conductivity as high as 6.03 × 10−4 S cm−1 at room temperature. Furthermore, Li/LFP full cell with PC-g-PMT/LL-g-PMT20/P exhibits excellent rate and cycling performance.

Novel PEO-based composite electrolyte for low-temperature all-solid-state lithium metal batteries enabled by interfacial cation-assistance

Non-flammable succinonitrile (SN) is a promising plasticizer for lowering the working temperature of poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes. However, its application is greatly impeded by the inherent instability interface toward the Li anode. Here, we report a novel PEO/SN-based composite solid-state electrolyte with a durable interface and high room-temperature ionic conductivity of 6.74×10−4 S cm−1. By taking advantage of cation-assistance between La3+ cation in LLZTO and N atom in SN, reducing the active -CN groups or converting them to less reactive -C = N- groups, preventing the corrosion of lithium anode from SN. As a result, PEO/SN-based electrolyte displays highly stable Li plating/stripping cycling for over 1000 h at 0.1 mA cm−2 at RT. Furthermore, the all-solid-state lithium metal batteries (ASSLBs) based on LiFePO4 cathode deliver admirable cycling stability with a discharge capacity of 133 mAh g−1 and high-capacity retention of 92.6% after 240 cycles at 0.5C at RT. Even at -10 °C, the batteries still can achieve excellent electrochemical performance. The unique Li+ ion conduction pathway is investigated by tracer-exchange 6Li NMR. This work proposes new insight via cation assistance to build a durable interface for the real application of PEO/SN-based electrolytes system in ASSLBs.

Spatially isolating Li+ reduction from Li deposition via a Li22Sn5 alloy protective layer for advanced Li metal anodes.

A Li alloy based artificial coating layer can improve the cyclic performance of Li metal anodes. However, the protective mechanism is not well clarified due to multiple components of the artificial layer and complicated interface in liquid electrolytes. Herein, a single-component Li22Sn5 alloy layer buffered Li anode is paired with a solid-state polymer electrolyte, where a metallic Sn film is sputtered onto the Li anode and the subsequent alloying reaction leads to the formation of a Li22Sn5 phase. During the striping/plating process, the thickness and composition of the Li-Sn alloy passivation layer remain unchanged. Meanwhile, Li+ ions are reduced on the top surface of the Li22Sn5 layer, then the reduced Li atoms immediately pass through the alloy layer, and finally dense Li deposition occurs beneath the protective layer, realizing spatial isolation of the electrochemical reduction of Li+ from Li nucleation/growth. This unique protection mechanism can principally avoid the formation of Li dendrites and efficiently mitigate irreversible reactions between the Li anode and the polymer electrolyte. The synergistic effects lead to a clean and flat surface of the protected Li electrode, enabling a prolonged cycle lifetime over 1300 h at 25 °C at 0.1 mA cm-2 and 0.1 mA h cm-2 in a configuration of symmetrical cells.

A PEG-borate ester solid-state polymer electrolyte to fabricate a Li6PS5Cl-rich composite for a Li metal battery.

A Li6PS5Cl-rich composite is prepared using a PEG-borate ester solid-state polymer electrolyte (BSPE). BSPE is a highly accessible compound with high ionic conductivity and excellent electrochemical stability against Li metal. Thereby, the stability of the Li6PS5Cl-rich composite with BSPE improved significantly.

High voltage stable cycling of all-solid-state lithium metal batteries enabled by top-down direct fluorinated poly (ethylene oxide)-based electrolytes

Poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes (SPEs) show prospects in all-solid-state lithium metal batteries. However, they suffer from low ionic conductivity at room temperature and interfacial instability with high voltage cathodes for long-term cycling. In this work, top-down fluorinated PEOs (F-PEOs) for the all-solid-state electrolytes, which are scalable and cost-effective, are developed to improve the battery performance. We demonstrate, that by enhancing the disordering of the F-PEO matrix, the SPE achieves a maximum Li+ conductivity of 1.1 × 10−4 S cm−1 at 40 °C, which is 20 times higher than the baseline. By forming robust cathode/SPE and Li/SPE interfaces, the F-PEO-based SPEs demonstrate stable cycling in the LiFePO4/Li and LiNi0·8Mn0·1Co0·1O2/Li (3–4.4 V, 500 cycles, capacity retention of 91.6%) based all-solid-state batteries at 40 °C. Furthermore, our work highlights the significance of “disordering engineering” for energy storage materials.

In Situ Constructing Ultrathin, Robust-Flexible Polymeric Electrolytes with Rapid Interfacial Ion Transport in Lithium Metal Batteries.

Safety of lithium metal batteries (LMBs) has been improved by using the solid-state polymer electrolytes, but the performance of LMBs is still troubled by the poor interface of solid electrolytes/electrodes, leading to insufficient interfacial Li+ transport. Here, a novel ultrathin, robust-flexible polymeric electrolyte is achieved by in situ polymerization of 1,3-dioxolane in soft nanofibrous skeleton at room temperature without any extra initiator or plasticizer, leading to the electrolyte with rapid interfacial ion transport. This facilitated Li+ transportation is demonstrated by molecular dynamics simulation. Consequently, the as-prepared electrolyte exhibits excellent cycling performance. The results indicate that the electrolyte works well in the LiFePO4 //Li cell at elevated temperature up to 90°C, and further matches with the high-voltage LiNi0.8 Mn0.1 Co0.1 O2 cathode. This study provides an effective approach to constructing a practical polymeric electrolyte for fabrication of safe, high performance LMBs.

(General Student Poster Award Winner - 2nd Place) Analyzing the Soret Coefficient Using Time Resolved Fourier Transform Infrared Spectroscopy (FTIR)

This study varies salt concentrations of lithium bis-trifluoromethanesulfonylimide (LiTFSI) in the block copolymer polystyrene-poly(ethylene oxide) (SEO), at different temperature gradients, analyzing the effect these parameters have on the magnitude of the Soret coefficient. The Soret Coefficient is the phenomena resulting in a concentration gradient via a temperature gradient. It is quantified by the ratio of thermal diffusion to mutual diffusion. The Soret effect can be utilized in thermogalvanic cells, by re-harvesting wasted heat from most power generating systems. Thermogalvanic cells, are a way to utilize a heat sink to create electrical energy, having the temperature gradient drive the system. Specifically, solid state polymer electrolytes are of interest in these cells as they offer benefits such as low flammability, high safety, and improved energy density, compared to common liquid electrolytes. Thus, application of the Soret effect in thermogalvanic cells is a clear way to greatly increase global energy efficiency, saving money for companies, and decreasing the global environmental footprint. To gain insight as to direction of diffusion in solid-state polymer electrolytes, and make this cell a reality, time resolved Fourier Transform Infrared spectroscopy (FTIR-ATR) measurements provide an unprecedented data accuracy for modeling. The FTIR makes the correlation between the infrared absorbance of the presented salt and its boundary concentration in the polymer through the Beer Lambert law, which has been proven true for salts in previous work. This technique overcomes many previous limitations to experimental techniques measuring the Soret Coefficient, making the FTIR-ATR an effective and repeatable instrument to use for collecting diffusion coefficients.

(Digital Presentation) Post-Treatment Study on Blended Polymer for Solid-State Lithium Batteries

The widely used Li batteries (LiBs) is the most established rechargeable energy storage device. Therefore, the development of new electrode and electrolyte materials is essential for improving battery performance. Solid polymer electrolytes (SPEs) have been presented as safer alternatives for liquid electrolytes as they tend to be non-flammable, have enough mechanical strength to resist dendrite growth, and do not leak. However, these materials tend to be less conductive than liquid electrolytes. This problem can be solved by solid-state gel polymer electrolytes (GPEs), which have lately received more attention. In fact, present a possible solution to this dilemma as they combine the ionic conductivity of liquid electrolytes with the increased safety of SPE to develop of electrolytes with high ionic conductivity and good mechanical stability.1 This work presents a preparation of in-situ GPE from SPE which produce by dry process in order to take advantage of the easy processability of SPE and the higher ionic conductivity of GPE.2, 3 The initial SPE was prepared by combining two polymers with LiTFSI (bis(trifluorormethanesulfonyl)imide) via extrusion mixing. This method of GPE processing was also found to improve other aspects of the electrolyte such as thermal and electrochemical properties which were characterized using cycling voltammetry, electrochemical impedance spectroscopy, and thermal gravimetric analysis. Additionally, the salt-polymer interaction in the GPE was characterized using FTIR, NMR, and the homogeneity of the polymer blend study by SEM-EDX. The cell of LFP/electrolyte/ Li metal showed a high capacity near to the theoretical one at C/20 at temperature 60 C. Additionally, the ionic conductivity of the electrolyte is around 10-5 S/cm. These first results confirmed that this blend of the polymers is a good electrolyte candidate for lithium batteries. Verdier, N.; Lepage, D.; Zidani, R.; Prebe, A.; Ayme-Perrot, D.; Pellerin, C.; Dolle, M.; Rochefort, D., Cross-linked polyacrylonitrile-based elastomer used as gel polymer electrolyte in Li-ion battery. ACS Applied Energy Materials 2019, 3 (1), 1099-1110.Ma, C.; Cui, W.; Liu, X.; Ding, Y.; Wang, Y., In situ preparation of gel polymer electrolyte for lithium batteries: Progress and perspectives. InfoMat 2021.Verdier, N.; Foran, G.; Lepage, D.; Prébé, A.; Aymé-Perrot, D.; Dollé, M., Challenges in Solvent-Free Methods for Manufacturing Electrodes and Electrolytes for Lithium-Based Batteries. Polymers 2021, 13 (3), 323.

3D spiny AlF3/Mullite heterostructure nanofiber as solid-state polymer electrolyte fillers with enhanced ionic conductivity and improved interfacial compatibility

Lithium metal batteries assembled with solid-state electrolyte can offer high safety and volumetric energy density compared to liquid electrolyte. The polymer solid-state electrolytes of poly(ethylene oxide) (PEO) are widely used in lithium metal solid-state batteries due to their unique properties. However, there are still some defects such as low ionic conductivity at room temperature and weak inhibition of lithium dendrite growth. Herein, the spiny inorganic nanofibers heterostructure with mullite whiskers grown on the surface of aluminum fluoride (AlF3) nanofibers are introduced into the PEO-LiTFSI electrolytes for the first time to prepare composite solid-state electrolytes. The AlF3 as a strong Lewis acid can adsorb anions and promote the dissociation of Li salts. Besides, the specially three-dimensional (3D) structure enlarges the effective contacting interface with the PEO polymer, which allows the lithium ions to be transported not only along the large aspect ratio of AlF3 nanofibers, but also along the mullite phase in the transmembrane direction rapidly. Thereby, the transport channel of lithium ions at the spiny inorganic nanofibers-polymer interface is further improved. Benefiting from these advantages, the obtained composite solid-state electrolyte has a high ionic conductivity of 1.58 × 10−4 S cm−1 at 30 °C and the lithium ions transfer number of 0.53. In addition, the AlF3 has strong binding energy with anions, low electronic conductivity and wide electrochemical stability window, and reduced nucleation overpotential of lithium during cycling, which is positive for lithium dendrite suppression in solid-state electrolytes. Thus, the assembled symmetric Li/Li symmetric batteries exhibit stable cycling performance at different area capacities of 0.15, 0.2, 0.3 and 0.4 mA h cm−2. More importantly, the LiFePO4 (LFP)/Li battery still has 113.5 mA h g−1 remaining after 400 cycles at 50 °C and the Coulomb efficiency is nearly 100% during the long cycle. Overall, the interconnected structure of 3D spiny inorganic heterostructure nanofiber constitutes fast and uninterrupted lithium ions transport channels, maximizing the synergistic effect of interfacial transport of inorganic fillers and reducing PEO crystallinity, thus providing a novel approach to high performance solid-state electrolytes.

Stable sodium anodes for sodium metal batteries (SMBs) enabled by in-situ formed quasi solid-state polymer electrolyte

A high-performance quasi-solid polymer electrolyte for sodium metal batteries (SMBs) based on in-situ polymerized poly(1,3-dioxolane) (DOL) with 20% volume ratio of fluoroethylene carbonate (FEC), termed “PDFE-20”, is proposed in this work. It is demonstrated PDFE-20 possesses a room-temperature ionic conductivity of 3.31 × 10−3 S cm−1, an ionic diffusion activation energy of 0.10 eV, and an oxidation potential of 4.4 V. SMBs based on PDFE-20 and Na3V2(PO4)3 (NVP) cathodes were evaluated with an active material mass loading of 6.8 mg cm−2. The cell displayed an initial discharge specific capacity of 104 mA h g−1, and 97.1% capacity retention after 100 cycles at 0.5 C. In-situ polymerization conformally coats the anode/cathode interfaces, avoiding geometrical gaps and high charge transfer resistance with ex-situ polymerization of the same chemistry. FEC acts as a plasticizer during polymerization to suppress crystallization and significantly improves ionic transport. During battery cycling FEC promotes mechanical congruence of electrolyte–electrode interfaces while forming a stable NaF-rich solid electrolyte interphase (SEI) at the anode. Density functional theory (DFT) calculations were also performed to further understand the role FEC in the poly(DOL)–FEC electrolytes. This work broadens the application of in-situ prepared poly(DOL) electrolytes to sodium storage and demonstrates the crucial role of FEC in improving the electrochemical performance.

19.1: Invited Paper: Electrochromic Display Based on Semiconducting Polymer

19.1: <i>Invited Paper:</i> Electrochromic Display Based on Semiconducting Polymer

Effect of oligo(ethylene glycol) length on properties of poly(oligoethylene glycol terephthalate)s and their cyclic oligomers

We present here the effect of oligo(ethylene glycol) (OEG) segmental length on properties of cyclic oligo(oligoethylene glycol terephthalate)s (COEGTs) and their corresponding polymer counterparts, poly(oligoethylene glycol terephthalate)s (POEGTs). COEGT monomers were synthesized from terephthaloyl chloride with corresponding diethylene glycol, triethylene glycol, and tetraethylene glycol under pseudo-high-dilution conditions. As those large ring cyclic monomers are hard to be polymerized via traditional ring-opening polymerization, a cascade polycondensation-coupling ring-opening polymerization method is utilized to obtain high molecular weight POEGTs. The cascade polymerization mechanism is confirmed by the kinetics study. The structures of COEGTs and POEGTs were well characterized and their properties were studied to reveal the structure-property relationship. With the increment of OEG length in repeating units, the chain flexibility of POEGT and COEGTs is enhanced. As a result, the melting temperatures of COEGTs and glass transition temperatures of POEGTs decrease. On the other hand, the thermal degradation temperature of POEGTs and COEGTs increases due to the enhanced ether fraction and reduced ring strain. Solid-state polymer electrolytes based on POEGTs was prepared by blending with lithium bis(trifluoromethanesulfonyl)imide. The measured ionic conductivity increased with the OEG length in POEGT repeating units. Our results revealed the effect of OEG length on the structure-property relationship in cyclic oligo(ether ester)s and copoly(ether ester)s, providing a facile way to tune their properties.