Electrochemical Stability Window Research Articles

High Na‐ion conductivity and mechanical integrity of anion‐exchanged polymeric hydrogel electrolytes for flexible sodium ion hybrid energy storage

AbstractThe polymeric gel electrolytes are attractive owing to their higher ionic conductivities than those of dry polymer electrolytes and lowered water activity for enlarged potential window. However, the ionic conductivity and mechanical strength of the Na‐ion conducting polymeric gel electrolytes are limited by below 20 mS cm−1 and 2.2 MPa. Herein, we demonstrate Na‐ion conducting and flexible polymeric hydrogel electrolytes of the chemically coupled poly(diallyldimethylammonium chloride)‐dextrin‐N,N′‐methylene‐bis‐acrylamide film immersed in NaClO4 solution (ex‐DDA‐Dex + NaClO4) for flexible sodium‐ion hybrid capacitors (f‐NIHC). In particular, the anion exchange reaction and synergistic interaction of ex‐DDA‐Dex with the optimum ClO4− enable to greatly improve the ionic conductivity up to 27.63 mS cm−1 at 25°C and electrochemical stability window up to 2.6 V, whereas the double networking structure leads to achieve both the mechanical strength (7.48 MPa) and softness of hydrogel electrolytes. Therefore, the f‐NIHCs with the ex‐DDA‐Dex + NaClO4 achieved high specific and high‐rate capacities of 192.04 F g−1 at 500 mA g−1 and 116.06 F g−1 at 10 000 mA g−1, respectively, delivering a large energy density of 120.03 W h kg−1 at 906 W kg−1 and long cyclability of 70% over 500 cycles as well as demonstrating functional operation under mechanical stresses.

Aliphatic Hyperbranched Polycarbonates Solid Polymer Electrolytes with High Li-Ion Transference Number for Lithium Metal Batteries.

In this work, hyperbranched polycarbonate-poly(ethylene oxide) (PEO)-based solid polymer electrolytes (HBPC-SEs) are successfully synthesized via a straightforward organo-catalyzed "A1"+"B2"-ring-opening polymerization approach. The temperature-dependent ionic conductivity of HBPC-SEs, composed of different polycarbonate linkages and various LiTFSI concentrations, is investigated. The results demonstrate that HBPC-SE with an ether-carbonate alternating structure exhibits superior ionic conductivity, attributed to the solubility of Li salts in the polymer matrix and the mobility of the polymer segments. The HBPC1-SE with 30 wt% LiTFSI presents the highest ionic conductivities of 2.15 × 10-5, 1.78 × 10-4, and 6.07 × 10-4 Scm-1 at 30, 60, and 80 °C, respectively. Compared to traditional PEO-based electrolytes, the incorporation of polycarbonate segments significantly enhances the electrochemical stability window (5V) and Li+ transference number (0.53) of HBPC-SEs. Furthermore, the LiFePO4/HBPC1-SE-3/Li cell exhibits exceptional rate capability and long-cycling performance, maintaining a discharge capacity of 130 mAh g-1 at 0.5C with a capacity retention of 95% after 300 cycles.

Borate-containing triblock copolymer electrolytes for improved lithium-ion transference number and interface stability

The electrolytes with high lithium-ion transference number (tLi+) can reduce the formation of concentration polarization during charge/discharge process and improve the electrochemical performance of lithium-ion batteries (LIBs). Herein, we report triblock copolymer electrolytes (PBOEE) containing borate. The sp2 hybridized boron atoms acting as Lewis acids can anchor the anions of lithium salts, enabling PBOEE to achieve high tLi+ of up to 0.53. Also, the borate groups can promote the formation of stable organic-rich solid electrolyte interphase (SEI) film, which enables the Li symmetric cell to cycle stably at 0.1 mA cm−2/0.1 mAh cm−2 for more than 3100 h with a low overpotential of 0.08 V under 50 °C. The optimized PBOEE_24 has an ionic conductivity of 1.41 × 10−4 S cm−1 and electrochemical stability window of 4.8 V vs. Li+/Li at 50 °C. Combining these advantages, the LiFePO4/PBOEE_24/Li cell exhibits an initial discharge specific capacity of 157.3 mA h g−1 at 0.5C with a capacity retention of 85 % after 600 cycles under 50 °C. At a higher current density of 1C, the discharge capacity maintains at 128.0 mA h g−1 after 400 cycles with a capacity retention of 84.88 %. These results suggest that block copolymer containing sp2 hybridized boron atoms is a promising all-solid-state polymer electrolyte.

Anti‐Polyelectrolyte Effect of Zwitterionic Hydrogel Electrolytes Enabling High‐Voltage Zinc‐Ion Hybrid Capacitors

AbstractTo date, the exploration of zwitterionic application is confined to the function of electrolyte's additives to improve the properties of the electrolytes. However, reports on the unique properties of zwitterions, namely the anti‐polyelectrolyte effect (APE), as the regulators of the electrochemical stability windows (ESWs) of the zwitterionic electrolytes are scarce. Herein, a zwitterionic electrolyte system is designed and study the relationship between the APE and the ESWs of the zwitterionic electrolytes. The hydrogen/oxygen evolution in the zwitterionic electrolytes is significantly inhibited under the action of the APE. On this basis, the ESWs of zwitterionic electrolytes can be expanded, ultimately achieving an effective improvement in the energy density of zinc‐ion hybrid capacitors (ZHCs). The sulfonic‐based zwitterionic hydrogel electrolytes prepared based on this strategy achieve a wide ESW of 2.58 V and high ionic conductivity of 29.3 mS cm−1. Meanwhile, the corresponding ZHCs possess a high working voltage of 2.1 V (1.6 V for the traditional ZHCs), a high capacity of 188.9 mAh g−1 and a high energy density of 110 Wh kg−1. The way utilizing the APE of zwitterions to expand the ESWs opens up a new avenue to improve the energy density of energy storage devices.

Fine Tuning Water States in Hydrogels for High Voltage Aqueous Batteries.

Hydrogels are widely used as quasi-solid-state electrolytes in aqueous batteries. However, they are not applicable in high-voltage batteries because the hydrogen evolution reaction cannot be effectively suppressed even when water is incorporated into the polymer network. Herein, by profoundly investigating the states of water molecules in hydrogels, we designed supramolecular hydrogel electrolytes featuring much more nonfreezable bound water and much less free water than that found in conventional hydrogels. Specifically, two strategies are developed to achieve this goal. One strategy is adopting monomers with a variety of hydrophilic groups to enhance the hydrophilicity of polymer chains. The other strategy is incorporating zwitterionic polymers or polymers with counterions as superhydrophilic units. In particular, the nonfreezable bound water content increased from 0.129 in the conventional hydrogel to >0.4 mg mg-1 in the fabricated hydrogels, while the free water content decreased from 1.232 to ∼0.15 mg mg-1. As a result, a wide electrochemical stability window of up to 3.25 V was obtained with the fabricated hydrogels with low concentrations of incorporated salts and enhanced hydrophilic groups or superhydrophilic groups. The ionic conductivities achieved with our developed hydrogel electrolytes were much higher than those in the conventional highly concentrated salt electrolytes, and their cost is also much lower. The designed supramolecular hydrogel electrolytes endowed an aqueous K-ion battery (AKIB) system with a high voltage plateau of 1.9 V and contributed to steady cycling of the AKIB for over 3000 cycles. The developed supramolecular hydrogel electrolytes are also applicable to other batteries, such as aqueous lithium-ion batteries, hybrid sodium-ion batteries, and multivalent-ion aqueous batteries, and can achieve high voltage output.

Distinct roles: Co-solvent and additive synergy for expansive electrochemical range and low-temperature aqueous batteries

The present study addresses the challenges encountered by aqueous lithium-ion batteries (ALiBs), specifically the limited electrochemical stability window and inadequate low-temperature energy retention. We propose a binary solvent electrolyte system comprising N,N-Dimethylformamide (DMF) as a co-solvent and 3-sulfolene (3SF) as an additive (5 wt.% 3SF in 9 M LiTFSI H2O/DMF with a molar ratio of 1:1). The H2O solvent ensures non-flammability and high safety, while DMF reduces the freezing point and enhances low-temperature conductivity. Additionally, DMF actively solvates Li+ ions, thereby reducing interfacial H2O content. Moreover, through the incorporation of the 3SF additive along with LiTFSI, a stable bilayer interphase film is formed on the anode surface effectively expanding the electrochemical stability window to 4.37 V. By leveraging the distinct roles played by solvents and additive, exceptional performance at both room temperature and low-temperature is achieved for the LiMn2O4/Li4Ti5O12 cell. Specifically, at room temperature, the cell demonstrates an initial coulombic efficiency reaching 90 %. Moreover, even after undergoing 300 cycles at 1 C, the capacity remains as high as 156.3 mAh g−1 (with a remarkable capacity retention rate of 96 %). Notably, in extremely low-temperatures of -30 °C, the cell exhibits excellent cycling performance which can still maintain a capacity retention rate of 98.8 % after 50 cycles. The proposed electrolyte design strategy, which takes into account both the bulk electrolyte and interfacial chemistry, presents a practical and feasible approach for the development of safe, low-temperature, and high-energy density ALiBs.

Water‐based Supercapacitors with Amino Acid Electrolytes: A Green Perspective for Capacitance Enhancement

AbstractState‐of‐the art Electrochemical Double‐Layer Capacitors (EDLCs) usually extend their operating electrochemical stability window (ESW) by means of organic electrolytes, or highly concentrated aqueous (water‐in‐salt) electrolytes hindering parasitic water splitting reactions. Unfortunately, organic solvents and high concentrations of ions penalize the dielectric constant of the electrolyte, hence the capacitive performance. We suggest here a new concept of cost‐effective and sustainable aqueous electrolytes based on concentrated amino acid water solutions with a dielectric permittivity much higher than pure water, unlocking the capacitive performance of aqueous EDLC references. Amino acids are natural zwitterionic molecules with a large separation between the positive and negative moiety, leading to huge dipoles with excellent dielectric properties. Some of them (e. g., lysine and proline), have a solubility 10 m at ambient temperature. With an experimental characterization we prove that aqueous EDLCs based on electrolytes obtained with L‐ lysine or L‐proline added to 2 M NaNO3 solution have +50 % of gravimetric capacitance enhancement at low specific currents (0.1 A/g) compared to a reference device based on 2 M NaNO3 electrolyte without amino acids. A theoretical model suggests that this performance may be further enhanced by increasing the ionic accessibility of commercially available active materials, with porosity optimized to the size of amino acid ions.

Inhibition of hydrogen evolution in proton battery by sulfamic acid-caprolactam electrolyte and its electrochemical study

Proton batteries are expected to be used in large-scale energy storage systems in the future because of their reliability, safety, non-toxicity, and low cost. However, the hydrogen evolution reaction in the electrolyte of a proton battery limits the development of a high-voltage proton battery, and it is difficult to study the anode materials with lower charge and discharge potential. In this study, a novel sulfamic acid-caprolactam based electrolytes for inhibiting hydrogen evolution in the proton batteries was investigated. Aminosulfonic acid was used as a proton source in the proton batteries for the first time. In addition, caprolactam cosolvent with double hydrogen bond site was added to the electrolyte to help H3O+ de-solvent into H+, which effectively inhibited the hydrogen evolution behavior in the electrolyte of proton battery. The MoO3 electrode showed good cycling stability in the SA-H2O-CPL electrolyte. After 300 cycles, the capacity retention rate was 83.3%, and the average CE value was 99.7%. After adding caprolactam to the electrolyte, the hydrogen evolution potential is reduced to -1.7 V, and the electrochemical stability window of the electrolyte is greatly widened, which will help to develop anode materials with lower redox potential and be of great significance to the realization of high voltage proton batteries.

Kinetics Conditioning of (Electro) Chemically Stable Zn Anode with pH Regulation Toward Long-Life Zn-Storage Devices.

The safety, low cost, and high power density of aqueous Zn-based devices (AZDs) appeal to large-scale energy storage. Yet, the presence of hydrogen evolution reaction (HER) and chemical corrosion in the AZDs leads to local OH- concentration increasement and the formation of Znx SOy (OH)z •nH2 O (ZHS) by-products at the Zn/electrolyte interface, causing instability and irreversibility of the Zn-anodes. Here, a strategy is proposed to regulate OH- by introducing a bio-sourced/renewable polypeptide (ɛ-PL) as a pH regulator in electrolyte. The consumption of OH- species is evaluated through in vitro titration and cell in vivo in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy at a macroscopic and molecular level. The introduction of ɛ-PL is found to significantly suppress the formation of ZHS and associated side reactions, and reduce the local coordinated H2 O of the Zn2+ solvation shell, widening electrochemical stable window and suppressing OH- generation during HER. As a result, the inclusion of ɛ-PL improves the cycle time of Zn/Zn symmetrical cells from 15 to 225h and enhances the cycle time of aqueous Zn- I2 cells to 1650h compared to those with pristine electrolytes. This work highlights the potential of kinetical OH- regulation for by-product and dendrite-free AZDs.

Printable Single‐Ion Polymer Nanoparticle Electrolytes for Lithium Batteries

New material solutions are searched for the manufacturing and safety of current batteries. Herein, an extrusion printable polymer separator for lithium batteries based on single‐ion polymer electrolytes is presented. The polymer electrolytes are based on methacrylic polymeric nanoparticles (NPs) functionalized with a lithium sulfonamide group combined with different organic plasticizers such as sulfolane and carbonates. The synthesis of the polymer NPs is carried out by emulsion copolymerization of methyl methacrylate and lithium sulfonamide methacrylate in the presence of a crosslinker, resulting in particle sizes of less than 30 nm, as shown by electron microscopy. Then polymer electrolytes are prepared by mixing polymer NPs with varying lithium sulfonamide content and different plasticizers such as carbonates and sulfolane. The polymer electrolytes show ionic conductivities between 2.9 × 10−4 and 2.3 × 10−5 S cm−1 at 85 °C with the highest values for the small‐sized NPs with the highest lithium content. As a proof‐of‐concept application, layer‐by‐layer printing of a sulfolane‐based polymer electrolyte is evaluated via direct ink writing directly onto classic battery electrodes. The electrochemical characterization of the printed solid electrolyte indicates favorable properties, ionic conductivity, lithium transfer number, electrochemical stability window, and cyclability in lithium symmetrical cells, to be used in lithium batteries.

Indolocarbazole‐Based Small Molecule Cathode‐Active Material Exhibiting Double Redox for High‐Voltage Li‐Organic Batteries

Most organic electrode materials (OEMs) for rechargeable batteries employ n‐type redox centers, whose redox potentials are intrinsically limited <3.0 V versus Li+/Li. However, p‐type materials possessing high redox potentials experience low specific capacities because they are capable of only a single redox reaction within the stable electrochemical window of typical electrolytes. Herein, we report 5,11‐diethyl‐5,11‐dihydroindolo[3,2‐b]carbazole (DEICZ) as a novel p‐type OEM, exhibiting stable plateaus at high discharge potentials of 3.44 and 4.09 V versus Li+/Li. Notably, the second redox potential of DEICZ is within the stable electrochemical window. The mechanism of the double redox reaction is investigated using both theoretical calculations and experimental measurements, including density functional theory calculations, ex situ electron spin resonance, and X‐ray photoelectron spectroscopy. Finally, hybridization with single‐walled carbon nanotubes (SWCNT) improves the cycle stability and rate performance of DEICZ owing to the π–π interactions between the SWCNT and co‐planar molecular structure of DEICZ, preventing the dissolution of active materials into the electrolyte. The DEICZ/SWCNT composite electrode maintains 70.4% of its initial specific capacity at 1‐C rate and also exhibits high‐rate capability, even performing well at 100‐C rate. Furthermore, we demonstrate its potential for flexible batteries after applying 1000 bending stresses to the composite electrode.

Tungsten Oxide Coated Liquid Metal Electrodes via Galvanic Replacement as Heavy Metal Ion Sensors.

Gallium liquid metals (LMs) like Galinstan and eutectic Gallium-Indium (EGaIn) have seen increasing applications in heavy metal ion (HMI) sensing, because of their ability to amalgamate with HMIs like lead, their high hydrogen potential, and their stable electrochemical window. Furthermore, coating LM droplets with nanopowders of tungsten oxide (WO) has shown enhancement in HMI sensing owing to intense electrical fields at the nanopowder-liquid-metal interface. However, most LM HMI sensors are droplet based, which show limitations in scalability and the homogeneity of the surface. A scalable approach that can be extended to LM electrodes is therefore highly desirable. In this work, we present, for the first time, WO-Galinstan HMI sensors fabricated via photolithography of a negative cavity, Galinstan brushing inside the cavity, lift-off, and galvanic replacement (GR) in a tungsten salt solution. Successful GR of Galinstan was verified using optical microscopy, SEM, EDX, XPS, and surface roughness measurements of the Galinstan electrodes. The fabricated WO-Galinstan electrodes demonstrated enhanced sensitivity in comparison with electrodes structured from pure Galinstan and detected lead at concentrations down to 0.1 mmol·L-1. This work paves the way for a new class of HMI sensors using GR of WO-Galinstan electrodes, with applications in microfluidics and MEMS for a toxic-free environment.

Unconventional PEO-PPC quasi-solid state blend polymer electrolyte for high efficiency solid-state Li-metal batteries

Polymer electrolytes represent a safer alternative over traditional liquid electrolytes, enabling the use of higher energy density active materials as electrodes for batteries. Among the wide variety of different polymeric matrix that are currently been proposed, polyethylene oxide (PEO) is considered one of the most promising. In this work, a PEO-based quasi-solid polymer electrolyte (QSPE) was produced by easily scalable solution casting technique, optimized with addition of plasticizers and blended with polypropylene carbonate (PPC). The resulting polymer electrolyte was ultimately supported to glass fiber separator. Improvement of ionic conductivity, transfer number and electrochemical stability window of the different formulations was confirmed through electrochemical impedance spectroscopy and linear sweep voltammetry. Plating and stripping tests in symmetric LiLi cells and charge–discharge tests in half-cell configuration (Li vs LFP) were performed to evaluate the cyclability and stability of the QSPEs. The PEO-PPC polymer electrolyte showed improved efficiency and stability during charge–discharge cycles, at room temperature, suggesting the positive effect of the presence of carbonate groups in the polymer matrix. The promising results demonstrate that the as-prepared QSPE could represent a feasible and viable alternative to conventional liquid electrolytes and could accelerate the adoption of high energy density storage systems, like Li-metal batteries.

MXene nanofiller doped ion conducting polyethylene oxide for electrochemical devices

AbstractNanofiller‐doped polymer electrolyte‐based electrochemical devices are now emerged as a novel material for electrochemical devices. This paper reports a solid polymer electrolyte film doped with a new nanofiller synthesized by the solution casting technique. Electrical, optical, and photoelectrochemical characterization are presented in detail. Electrochemical impedance spectroscopy (EIS) shows with the dispersion of nanofillers conductivity increases attains maxima and decreases. The maximum conductivity was at 0.04 wt% nanofiller concentration of 2.05 × 10−4 S/cm. The calculated ionic transference value was 0.92 which shows the dormancy of the system as ionic. The linear sweep voltammetry confirms a high electrochemical stability window (ESW) of 4.01V. Sandwitched electrical double‐layer capacitors (EDLC) have been developed using carbon‐based electrodes and sandwitched nanofiller dispersed polymer electrolyte, showing a high specific capacitance value of ~200 F/g.

A Low‐Cost Moderate‐Concentration Hybrid Electrolyte of Introducing CaCl2 and Ethylene Glycerol Enables Low‐Temperature and High‐Voltage Micro‐Supercapacitors

AbstractHigh‐concentration electrolyte effectively improves the energy density and anti‐freezing property of aqueous micro‐supercapacitors (MSCs), endowing them the opportunity serving as power sources for miniaturized electronics. However, the excessive usage of salt significantly increases the cost of the electrolyte. Herein, a cost‐effective moderate‐concentration hybrid electrolyte is designed by introducing CaCl2 and ethylene glycerol (EG) additives for low‐temperature and high‐voltage MSCs. The results manifest that the introduction of CaCl2 minimizes the number of water molecules with strong hydrogen bonds while the addition of EG can reduce the amount of H2O molecules in the primary solvation shell sheath of Ca2+ ion and strengthen the hydrogen bonds between EG and water molecules, thus endowing the optimal electrolyte with a wide electrochemical stability window of 3.5 V and a freezing point lower than −120 °C. Furthermore, the resulting hybrid MSCs offer a high voltage of 1.6 V, and realize 62% capacitance retention at −40 °C compared to that at room temperature. Moreover, The MSCs can endure 20000 cycles with 98.5% capacitance retention at −40 °C. This work provides a meaningful guidance for designing low‐cost moderate‐concentration hybrid electrolyte with wide electrochemical stability window and anti‐freezing property for intrinsically safe and environmentally adaptable devices.

In Situ/Operando Techniques for Unraveling Mechanisms of Ionic Transport in Solid-State Lithium Indium Halide Electrolyte

Over the past years, lithium-ion solid-state batteries have demonstrated significant advancements regarding such properties as safety, long-term endurance, and energy density. Solid-state electrolytes based on lithium halides offer new opportunities due to their unique features such as a broad electrochemical stability window, high lithium-ion conductivity, and elasticity at close to melting point temperatures that could enhance lithium-ion transport at interfaces. A comparative study of lithium indium halide (Li3InCl6) electrolytes synthesized through a mechano-thermal method with varying optimization parameters revealed a significant effect of temperature and pressure on lithium-ion transport. An analysis of Electrochemical Impedance Spectroscopy (EIS) data within the temperature range of 25–100 °C revealed that the optimized Li3InCl6 electrolyte reveals high ionic conductivity, reaching 1.0 mS cm−1 at room temperature. Herein, we present the utilization of in situ/operando X-ray Photoelectron Spectroscopy (XPS) and in situ X-ray powder diffraction (XRD) to investigate the temperature-dependent behavior of the Li3InCl6 electrolyte. Confirmed by these methods, significant changes in the Li3InCl6 ionic conductivity at 70 °C were observed due to phase transformation. The observed behavior provides critical information for practical applications of the Li3InCl6 solid-state electrolyte in a broad temperature range, contributing to the enhancement of lithium-ion solid-state batteries through their improved morphology, chemical interactions, and structural integrity.

Recent Advances in Graphene-Based Materials for Zinc-Ion Batteries.

Zinc-ion batteries (ZIBs) are a promising alternative for large-scale energy storage due to their advantages of environmental protection, low cost, and intrinsic safety. However, the utilization of their full potential is still hindered by the sluggish electrode reaction kinetics, poor structural stability, severe Zn dendrite growth, and narrow electrochemical stability window of the whole battery. Graphene-based materials with excellent physicochemical properties hold great promise for addressing the above challenges foe ZIBs. In this review, the energy storage mechanisms and challenges faced by ZIBs are first discussed. Key issues and recent progress in design strategies for graphene-based materials in optimizing the electrochemical performance of ZIBs (anode, cathode, electrolyte, separator and current collector) are then discussed. Finally, some potential challenges and future research directions of graphene-based materials in high-performance ZIBs are proposed for practical applications.

Electrospun gel composite electrolyte of solvent-free SiO2 nanofluids coupled polyacrylonitrile nanofibers for high-rate lithium-metal batteries

Composite polymer electrolytes (CPEs) are considered as one of the most promising electrolytes for the next generation of solid-state lithium metal batteries (LMBs) because of their good flexibility, favorable interface contact, easy large-scale processing and improved safety. To address the severe agglomeration of inorganic nanofillers at the high-level loading, a new gel polymer electrolyte (GPE) was fabricated by electrospun membranes adopting polyacrylonitrile (PAN) as the host matrix and solvent-free SiO2 nanofluids (NFs) as nanofillers, presenting low crystallinity, high electrolyte uptake, superior flexibility, and large porosity. The as-prepared PAN/SiO2 GPEs containing 20 % SiO2 NFs show the optimum mechanical and thermal properties, the maximum ionic conductivity (3.44 x 10−4 S cm−1) and Li+ transfer number (0.73), and the widest electrochemical stable window (4.99 V). Benefiting from multiple advantages, the percolated 3D Li+ transport networks are well-established to suppress the electrode polarization and Li dendrite growth. Further, the abundant ester groups on the SiO2 NFs shell and Lewis acid-based sites on SiO2 cores are favored to dissociate lithium salts and produce more free Li+. Accordingly, the assembled solid-state LiFePO4/Li cell exhibits superior cycling stability (132.7 mAh/g after 500 cycles at 3C with a retention of 90.8 %) and rate capability (80.4 mAh/g at 25C) at ambient temperature. This work provides a facile strategy to fabricate GPEs by incorporating solvent-free NFs containing inorganic cores for LMBs with high-rate capability, good cycling stability, and high safety.

Controlling the Supramolecular Architecture Enables High Lithium Cationic Conductivity and High Electrochemical Stability for Solid Polymer Electrolytes

AbstractSolid polymer electrolytes (SPEs) are long sought after for versatile applications due to their low cost, light weight, flexibility, ease of scale‐up, and low interfacial impedance. However, obtaining SPEs with high Li+ conductivity (σ+) and high voltage stability to avoid concentrated polarization and premature capacity loss has proven challenging. Here a stretchable dry‐SPE is reported with a semi‐interpenetrating, supermolecular architecture consisting of a cross‐linked polyethylene oxide (PEO) tetra‐network and an alternating copolymer poly(ethylene oxide‐alt‐butylene terephthalate). Such a unique supermolecular architecture suppresses the formation of Li+/PEO intermolecular complex and enhances the oxidation stability of PEO‐based electrolyte, thus maintaining high chain segmental motion even with high salt loading (up to 50 wt%) and achieving a wide electrochemical stability window of 5.3 V. These merits enable the simultaneous accomplishment of high ionic conductivity and high Li+ transference number (t+) to enhance the energy efficiency of energy storage device, and electrochemical stability.

On the Na+ transport and electrochemical stability window in NaTFSI:NMA deep eutectic solvent

Deep eutectic solvents (DES), such as the ▪:▪ (sodium bistrifluoromethane sulfonyl imide - N-methyl acetamide) system, have been considered as promising electrolytes for sodium-ion (▪) batteries. However, our current atomistic understanding of those systems is still in a state of evolution and remains incomplete. In this context, we combined classical force field molecular dynamics (MD) simulations and periodic density functional theory (DFT) calculations to enhance our atomistic understanding on the ▪ transport mechanisms, DES structure organization, hydrogen-bond network formation, and electrochemical stability windows (ESWs). Firstly, we obtained a substantial improvement in the description of the DES transport and structural properties using self-consistent MD/DFT calculations to assign effective charges on all atoms, while the remaining OPLS parameters were kept constant. From our analyses, an increasing in the ▪ mole fraction leads to different chemical environments, reflecting an electrolyte with larger aggregates, low conductivity, and high viscosity. The liquid structure seems to remain unchanged as a function of temperature. However, higher temperatures reduce the lifetime of ionic pairs and increase the mobility of ▪ ions. The disruption of the hydrogen-bonds formed between the ▪ species increases with the ▪ concentration. In addition, our periodic DFT calculations reveals the substitution of atomic sites from ▪ to ▪ during the reduction process. Furthermore, the ESW results provided evidence supporting the safeguarding of the solvent from degradation at higher salt concentrations.