Conventional Polymer Electrolyte Research Articles

A Highly Compatible Deep Eutectic Solvent-Based Poly(ethylene) Oxide Polymer Electrolyte to Enable the Stable Operation of 4.5V Lithium Metal Batteries.

Insufficient ionic conductivity, limited Li+ transfer number (tLi+), and narrow electrochemical windows have heavily restricted the actual application of PEO （poly(ethylene) oxide）-based polymer electrolytes (PEs). Herein, a novel deep eutectic solvent (DES)-based PEO PE for stabilizing high voltage lithium metal battery (LMB) is designed. The DES reduces the crystallinity of PEO while promoting the dissociation of LiTFSI to release more free Li+, thus facilitating the transport of Li+ in the PEO matrix. In addition, the interaction between DES and the PEO, thereby improving the stability of the PEO-based PE under high voltage. Consequently, the PEO-DES-FEC (for short PDF) PE possesses satisfactory ionic conductivity, good mechanical properties, and high electrochemical stability. Meanwhile, PDF PE can build a robust/uniform LiF-rich solid electrolyte interface (SEI) to ensure electrode/electrolyte interface stability. As a concept proof, the Li symmetrical battery and Li||LiFePO4 LMBs of PDF PE exhibit good cycle stability. Applied to the high voltage Li||NCM811 LMBs, the PDF PE-based cell has excellent cycling performance at 4.3 and 4.5V. This tactic is one of the successful demonstrations of PEO-based electrolytes under 4.5V high voltage conditions, which breaks through the voltage constraint of conventional PEO-based PEs.

PTHF/LATP Composite Polymer Electrolyte for Solid State Batteries.

The novel crosslinked composite polymer electrolyte (CPE) was developed and investigated using polytetrahydrofuran (PTHF) and polyethyleneglycol diacrylate (PEGDA), incorporating lithium aluminum titanium phosphate (LATP) particles and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. Composite polymer electrolytes (CPEs) for solid-state lithium-ion batteries (LIBs) were synthesized by harnessing the synergistic effects of PTHF crosslinking and the addition of LATP ceramics, while systematically varying the film composition and LATP content. CPEs containing 15 wt% LATP (PPL15) demonstrated improved mechanical strength and electrochemical stability, achieving a high conductivity of 1.16 × 10-5 S·cm-1 at 80 °C, outperforming conventional PEO-based polymer electrolytes. The CPE system effectively addresses safety concerns and mitigates the rapid degradation typically associated with polyether electrolytes. The incorporation of PEGDA not only enhances mechanical stability but also facilitates lithium salt dissociation and ion transport, leading to a uniform microstructure free from agglomerated particles. The temperature-dependent ionic conductivity measurements indicated optimal performance at lower LATP concentrations, highlighting the impact of ceramic particle agglomeration onion transport pathways. These findings contribute to advancing solid-state battery systems toward practical application.

Design of Functional Gyroid Minimal Surfaces Transporting Proton Based Solely on Surface Hopping Conduction Mechanism.

Surface proton hopping conduction (SPHC) mechanisms is an important proton conduction mechanism in conventional polymer electrolytes, along with the Grotthuss and vehicle mechanisms. Due to the small diffusion coefficient of protons in the SPHC mechanism, few studies have focused on the SPHC mechanism. Recently, it has been found that a dense alignment of SO3 - groups significantly lowers the activation energy in the SPHC mechanism, enabling fast proton conduction. In this study, a series of polymerizable amphiphilic-zwitterions is prepared, forming bicontinuous cubic liquid-crystalline assemblies with gyroid symmetry in the presence of suitable amounts of bis(trifluoromethanesulfonyl) imide (HTf2N) and water. In situ polymerization of these compounds yields gyroid-nanostructured polymer films, as confirmed by synchrotron small-angle X-ray scattering experiments. The high proton conductivity of the films on the order of 10-2 S cm-1 at 40 °C and relative humidity of 90% is based solely on the SPHC mechanism.

Overview of Inorganic Electrolytes for All-Solid-State Sodium Batteries.

All-solid-state sodium batteries (AS3B) emerged as a strong contender in the global electrochemical energy storage market as a replacement for current lithium-ion batteries (LIB) owing to their high abundance, low cost, high safety, high energy density, and long calendar life. Inorganic electrolytes (IEs) are highly preferred over the conventional liquid and solid polymer electrolytes for sodium-ion batteries (SIBs) due to their high ionic conductivity (∼10-2-10-4 S cm-1), wide potential window (∼5 V), and overall better battery performances. This review discusses the bird's eye view of the recent progress in inorganic electrolytes such as Na-β"-alumina, NASICON, sulfides, antipervoskites, borohydride-type electrolytes, etc. for AS3Bs. Current state-of-the-art inorganic electrolytes in correlation with their ionic conduction mechanism present challenges and interfacial characteristics that have been critically reviewed in this review. The current challenges associated with the present battery configuration are overlooked, and also the chemical and electrochemical stabilities are emphasized. The substantial solution based on ongoing electrolyte development and promising modification strategies are also suggested.

Polymer-based solid/semi-solid electrolytes in lithium ion batteries

Abstract The inception of lithium-ion batteries with liquid electrolytes can be traced back to the early 1980s. Nevertheless, the utilization of liquid electrolytes has many drawbacks, including its susceptibility to combustion, limited energy density, and very brief operational lifespan. Consequently, there is currently a concerted effort to substitute liquid electrolytes with solid compounds. This study investigates the electrochemical and mechanical features of solid/semi-solid electrolytes used in lithium ion batteries (LIBs) as well as their performance relative to conventional liquid electrolytes, with LIBs having unique challenges related to high flammability, electrochemical instability, and low mechanical stability posed by conventional liquid electrolytes versus solid polymer electrolytes (SPEs) which provide greater safety, mechanical stability but lower ionic conductivity than liquid counterparts. SPEs offer better safety but lack sufficient ionic conductivity which limits their potential. In order to overcome these obstacles, the implementation of gel-based and composite solid and semi-solid electrolytes is proposed as a means to improve ionic conductivity, electrochemical stability, and mechanical stability. The study suggests that a focus should be placed on solid composite electrolytes as they possess higher mechanical stability, which contributes to improved safety. Additionally, these electrolytes exhibit enhanced ionic conductivity within the range of 10−4 to 10−2 S/cm, hence enhancing the performance of LIBs.

Realizing highly conductive “polymer in salt” electrolytes through Li-ion-highway for room temperature all-solid-state Li-S batteries

“Polymer in salt” electrolytes (PISEs) have great application prospects because of their higher ionic conductivity than conventional solid polymer electrolytes (SPEs) at room temperature. However, it is still a challenge to realize both high ionic conduction and mechanical properties for PISEs. Here we address the issue by comprising interconnected ultra-long MnO2 nanowires modified with (3-Aminopropyl)trimethoxysilane (AMW) in PAN-LiTFSI-based PISEs. The presence of AMW reinforces the mechanical properties and aids Li-ion migration between ionic aggregates through a “hand-to-hand” mode. The resulting electrolyte (PIS-AMW) exhibits a high tensile strength of 2.77 MPa, ionic conductivity of 4.44 × 10−4 S cm−1 and Li-ion transference number of 0.61 at 25 °C. Li symmetric cells assembled with PIS-AMW demonstrate satisfactory cycling stability for up to 600 h. All-solid-state lithium‑sulfur batteries assembled with this electrolyte exhibit a capacity of 643 mAh g−1 at 0.05C and 25 °C after 80 cycles. The strategy effectively resolves the dilemma between long-range ionic conduction and mechanical properties in PISEs, which have potential applications in high-energy-density solid-state batteries.

Flexible High Lithium-Ion Conducting PEO-Based Solid Polymer Electrolyte with Liquid Plasticizers for High Performance Solid-State Lithium Batteries.

Lithium-ion secondary batteries (LIB) with high energy density have attracted much attention for electric vehicle (EV) applications. However, LIBs have a safety problem because these batteries contain a flammable organic electrolyte. As such, all-solid secondary batteries that are not flammable have been extensively reported recently. In this study, we have focused on polymer electrolytes, which is flexible and is expected to address the safety problem. However, the conventional polymer electrolytes have low electrial conductivity at room temperature. Various attempts have been made to solve this problem, such as the addition of inorganic fillers and ionic liquids; however, these composite polymer electrolytes have not yet reached a practical level of lithium-ion conductivity. In this study, high electrical conductivity and lithium dendrite formation-free PEO based composite electrolytes are developed with both a filler of Li6,4La3Zr1.4Ta0.6O12 and liquid plasticizers of tetraethylene glycol dimethyl ether and 1,2 dimethoxyethane. The proposed flexible polymer electrolyte shows a high electrical conduciviy of 6.01×10-4 S cm-1 at 25 °C.

SnCl4 initiated formation of polymerized solid polymer electrolytes for lithium metal batteries with fast ion transport interfaces

Solid-polymer-electrolytes (SPEs) are under active consideration for their high-energy and safe electrochemical energy storage. However, conventional polymer electrolytes are facing poor electrolyte/electrode interfacial contact and undesired lithium dendrite problems. Here, we report a polymerized-dioxolane (P-DOL) electrolytes created by in situ polymerization of DOL in the presence of tin tetrachloride (SnCl4), which enables ultra-conformal interfacial contact with all cell components. More importantly, SnCl4 plays a dual function by initiating ring-opening polymerization of DOL and simultaneously forming a LiCl/LixSn-based alloy composite protective layer on Li metal anodes. The robust Li-rich ion conductive alloys coupled with an electronically insulating surface component form fast ion transport channels. Using the SnCl4-initiated P-DOL SPEs exhibits a high ionic conductivity (>2 mS cm−1) and a wide electrochemical window (4.7 V) at room temperature. Applications of P-DOL SPEs in Li/Li symmetric and Li/LiFePO4 batteries further demonstrate low polarization and high capacity retention. This work provides a facile and practical approach to designing P-DOL SPEs for high-performance lithium metal batteries.

PVP/PEG polymer blend based electrolytes for quasi-solid-state dye-sensitized solar cells operating at low temperature

We investigated the performance of quasi-solid-state dye-sensitized solar cells (qs-DSSCs) employing Polyvinylpyrrolidone/Polyethylene glycol (PVP/PEG) blends over a wide temperature range. The photovoltaic performance of qs-DSSCs with conventional polymer electrolytes is very poor at low temperatures, mostly because of the significantly reduced ionic conductivity of the electrolyte. The PVP/PEG blend with a composition ratio of 20/80 exhibited low glass-transition temperature and high ionic conductivity, resulting in a power conversion efficiency (PCE) of 2.91% at a low temperature (−133 °C). This is 2.67 times higher than that of the device PCE (1.09%), with the most efficient and conventional gel-type polymer electrolyte. At ambient temperature, the qs-DSSC with PVP/PEG realized a device PCE of 6.13%, which is comparable to that of cells with conventional liquid electrolyte employing 3-methoxypropionitrile (6.36%) or a polymer electrolyte based on poly (vinylidene fluoride-co-hexafluoropropylene) (6.05%). In addition, the qs-DSSC with PVP/PEG exhibited excellent long-term stability during aging test, retaining approximately 88% of its initial PCE after 1000 h of light irradiation. The electrolyte developed in this study is not constrained by temperature factors and can be applied to solar cells that are viable for practical outdoor use (polar regions and space) with increased power output.

Anion Exchange Membrane Electrolyser Performance with Ni Ferrite Anodes Calcined at Different Temperatures

Hydrogen has a critical role in enabling European countries to achieve net-zero carbon targets. Hydrogen production via water splitting, using an electrolyser, is considered the "greenest" way because it does not produce any direct carbon emissions when powered by renewable sources. Among the different technologies of electrolysers (liquid alkaline, proton exchange membrane, etc.), there has been a recent surge in interest in that one based on anion-exchange membranes (AEMs). With respect to the state-of-the-art electrolysers that employ conventional acid polymer electrolyte separators (e.g., perfluorinated systems such as Nafion®), electrocatalysis with AEMs is much more promising. Accordingly, inexpensive catalysts can be used.In this work, NiFe2O4 catalysts are prepared by an "oxalate route". Nickel and iron nitrates in suitable stoichiometric ratios are added in successive steps to the oxalic acid solution. An oxidizing solution of hydrogen peroxide is then added. The obtained precipitate is first filtered and then dried. Different calcination temperatures (350, 450 and 550°C) are applied to obtain the Ni Ferrite with different surface and bulk characteristics. The catalysts are then deposited by a spray technique onto a commercial FAA3-50 (from FuMa-Tech) anion-exchange membrane, combined with a Pt-based cathode electrode, and investigated for the water electrolysis process in a single cell of 5 cm2 geometrical area. A comparison between the performance recorded with the different anode catalysts is reported and discussed. Acknowledgments The authors thank the Italian Ministry for University and Research (MUR) for funding through the FISR 2019 project AMPERE (FISR2019_01294).

3D Printing of Gel Polymer Electrolytes for Sodium-Ion Batteries

In order to maximize the capabilities of existing battery chemistries, a big effort has been recently focused on manufacturing more complex battery structures, which promotes 3D lithium ion diffusion resulting in an increase in power density.1-3 The current limitation is still the manufacturing part, which is often complex and expensive for mainstream production. 3D printing appears in this context as an exceptional tool to fill the gaps for 3D battery manufacturing. Among the 3D printing processes, vat photopolymerization is especially interesting thanks to its high printing resolution through a layer-by-layer curing approach that solidifies a UV-photocurable resin. Multiple examples of functional 3D printed batteries manufactured by various methods have been reported in the literature.4-7 Most of the recent works have been focused on half-cells where only one electrode is printed, or complete cells containing printed electrodes but using a non-printed conventional separator-electrolyte couple in between. Among the alternatives to replace this couple for a functional and printable material, gel polymer electrolytes appear as an appropriate option because they possess the advantages of a liquid electrolyte, without severely compromising the mechanical integrity. In addition, they exhibit competitive ionic conductivity and enhanced safety in comparison to liquid electrolytes, and they do not require a thermal post-processing step to be manufactured. Combining the knowledge in this topic with the design freedom that 3D printing allows will certainly contribute to obtaining the next generation of 3D printed batteries. In a first instance, this work will show a brief overview about suitable UV-photocurable resin compositions that can be employed as gel polymer electrolytes in sodium-ion batteries, with a view to employ them as material feedstock in the high-resolution vat photopolymerization process. The freedom of design that 3D printing allows will be then shown through a variety of printed items that transcend the well-known tape casting method to produce conventional gel polymer electrolytes. Finally, a variety of electrochemical tests to prove stability, ionic conductivity and performance within sodium-ion batteries will be shown. Talin, A. A. et al. Fabrication, Testing, and Simulation of All-Solid-State Three-Dimensional Li-Ion Batteries. ACS Appl. Mater. Interfaces 8, 32385–32391 (2016).Liu, Y. et al. Transforming from planar to three-dimensional lithium with flowable interphase for solid lithium metal batteries. Sci Adv 3, eaao0713 (2017).Long, J. W., Dunn, B., Rolison, D. R. & White, H. S. 3D architectures for batteries and electrodes. Adv. Energy Mater. 10, 2002457 (2020).Cheng, M., Deivanayagam, R. & Shahbazian-Yassar, R. 3D printing of electrochemical energy storage devices: A review of printing techniques and electrode/electrolyte architectures. Batter. supercaps 3, 130–146 (2020).Pang, Y. et al. Additive manufacturing of batteries. Adv. Funct. Mater. 30, 1906244 (2020).Zeng, L. et al. Recent progresses of 3D printing technologies for structural energy storage devices. Materials Today Nano 12, 100094 (2020).Maurel, A. et al. Toward High Resolution 3D Printing of Shape-Conformable Batteries via Vat Photopolymerization: Review and Perspective. IEEE Access 9, 140654–140666 (2021).

Benchmarking and Simulation of Solid-Oxide Steam Electrolysis for Propellant Production in a Vacuum Chamber-Simulated Lunar Environment

NASA and other space agencies have prioritized the development of in-situ resource utilization (ISRU) technology for producing critical materials such as propellants in space. Electrolysis to split water found in lunar, asteroid, and Martian environments provides a pathway for liquid H2 and O2 production, but the challenges of deploying such technology in extraterrestrial environments put an extreme emphasis on minimizing specific energy (measured in kWhelec/kgH2) and system specific mass (system kg/(kgH2/h)). High-temperature, solid oxide electrolysis cell (SOEC) systems have the potential to achieve lower specific energy than conventional liquid-phase alkaline and polymer electrolyte membrane (PEM) electrolysis systems, but this requires efficient thermal integration and minimization of balance of plant loads in order to take advantage of the lower electrolysis voltages for steam (vs. liquid H2O). The high operating temperatures of SOECs, however, require significant system mass for steam generators, heat exchangers for recuperation, and insulation of the electrolysis stack, particularly for space applications where ambient temperatures may be extremely low.This NASA-sponsored collaboration between OxEon Energy and Colorado School of Mines explored the feasibility of a lunar-based SOEC system, which was modeled and demonstrated at the lab-scale by operating a breadboard system, consisting of a SOEC stack and associated balance of plant BOP) in a cryogenic vacuum chamber in order to simulate a lunar environment. The combined »2.5-kWelec SOEC stack and BOP achieved a specific energy < 50 kWhelec/kgH2 at an H2 production rate of > 0.075 kgH2/h operating in the cryo-vacuum chamber.This study has benchmarked system-level models of the lab-scale SOEC stack based on doped-zirconia electrolytes fabricated at OxEon and designed to operate near thermoneutral voltage (1.28 V/cell) at 800°C. The stack BOP includes a steam generator, an oil-free scroll compressor, cathode and anode exhaust recuperators, and a H2 dryer, which uses cold incoming liquid water feeds to cool the cathode exhaust and condense most of the excess H2O in the H2 product stream out. Operation of this demonstration system provides a basis for designing scaled-up lunar fuel production systems of 40 kgH2/h. The success of the lab-scale tests in terms of thermal integration and the benchmarked models suggest a pathway to such a full-scale SOEC system that can achieve < 46 kWhelec/kgH2 with much lower specific mass.Both the modeling and the lab-scale demonstration tests revealed that system specific energy was most sensitive to stack steam utilization, and that achieving < 50 kWhelec/kgH2 required stack steam utilization > 75%. In addition, effective thermal integration that limited the electrical heating primarily to steam generation is critical to minimizing the SOEC-system BOP loads. The stack was shown to run reliably at steam utilizations > 90% with a single pass feed. Efforts will be presented on how to simulate such high utilization at larger scales for full lunar deployment. Additional testing of the lab-scale system in larger cryo-vacuum chambers at NASA during 2023 will allow for further confirmation of thermal management strategies to ensure reliable SOEC operation for lunar production of H2/O2 propellants.

Bikitaite composite polymer electrolyte for high-performance solid-state lithium metal battery

Ceramic-polymer hybrids promise to form composite electrolytes with high ionic conductivity, good stability, and electrode compatibility that conventional ceramic or polymer electrolytes cannot achieve. Using ceramic fillers in polymer electrolytes frequently results in significantly improved ion conduction. This study employs a representative composite electrolyte based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), Li zeolite Li2(Al2Si4O12) (bikitaite, BKT) ceramics, and an ether-based dual salt containing Li nitrate (EDSN) electrolyte as a plasticizer. The resulting composite electrolyte composed of PVdF, EDSN, and BKT has a superior ionic conductivity of 1.03 × 10–3 S cm−1, a broader electrochemical window of 4.8 V, and a high Li transference number of 0.61. The assembled solid-state LiFePO4/Li metal battery demonstrates a long lifespan, with an outstanding capacity retention of 86% after 450 cycles at 0.3C. The developed electrolyte with long cycling stability may serve as a model for developing solid electrolytes for Li metal secondary battery applications.

Construction of High-Strength Flame-Retardant Li-SPEEK-Modified PEG Gel Polymer Electrolytes for Lithium Batteries

The low mechanical performance and high flammability of gel polymer electrolytes limit their application. Here, we prepare a high-strength and nonflammable polymer Li-SPEEK (lithium sulfonated polyetheretherketone) to modify PEG (polyethylene glycol) and construct a PEG-Li-SPEEK cross-linked network as a polymer electrolyte matrix, with an overall improvement in electrochemical performance, mechanical properties, and flame retardancy. The PEG-Li-SPEEK-ls (PEG-Li-SPEEK cross-linked network after gelation of the liquid electrolyte) electrolyte achieves a conductivity of 1.62 × 10–4 S·cm–1 at 30 °C, a wider electrochemical window of 4.5 V vs Li+/Li, and a higher lithium-ion transference number compared to the PEG-ls electrolyte. The excellent mechanical properties allow the symmetric cell-containing PEG-Li-SPEEK-ls electrolyte to exhibit better cycling performance for over 300 h at a current density of 0.2 mA·cm–2. The LFP/PEG-Li-SPEEK-ls/Li cells deliver a maximum discharge capacity of 142.1 mAh·g–1 with a capacity retention of 98.1% after 50 cycles at 0.5 C and the Coulombic efficiency remains above 99.5% throughout the cycling process. In addition, the good carbon formation properties of Li-SPEEK give the electrolyte matrix satisfactory flame-retardant properties. Thus, we validate the excellent performance of Li-SPEEK for modifying conventional polymer electrolytes and improving their mechanical, electrochemical, and flame-retardant properties.

Open-source Computational Model for Polymer Electrolyte Fuel Cells

Open-source fuel cell models outmatch commercial codes in many important aspects. By providing the source code, reuse, modification and extension of the model and comparison with other codes becomes possible. With this motivation, we present a three-dimensional, steady-state, non-isothermal proton exchange membrane fuel cell model, implemented in the open-source finite volume library OpenFOAM® . At every stage of implementation, special care was taken to ensure a well documented, organised, and modular structure of the software. The resulting model suite can, and should, be extended with new sub-modules by the user. The main field of application, modelling of fuel cells from an engineering perspective, is demonstrated by simulating two different conventional polymer electrolyte fuel cells, operated at CIEMAT and Forschungszentrum Jülich, respectively.

A Charge Equalizer in Accordion—MXene‐Modified Layer Leading to Spherical Lithium Deposition

Lithium‐ion batteries with polymer electrolytes (PEs) are promising candidates for high safety performance batteries. However, conventional PEs suffer from poor compatibility and high impedance of electrolyte–electrode interfaces. Herein, we present a method of the interfacial modification for PEs to inhibit lithium dendrites based on the solution to the interfacial compatibility. Our strategy is to improve the interfacial properties and inhibit the dendrite generation by coating a modified layer on PEs of the anode side with acetylene black (AB) and MXene. The mixed conductive layer (MCL) can promote the generation of Li3N and LiF with a uniform arrangement of electrons to form a dense solid electrolyte interphase layer and the even lithium‐ion deposition for improving the performance and stability of the battery during cycling. After adding the MCL, the discharge capacity of solid lithium‐ion batteries (SLIBs) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/organic modified montmorillonite (OMMT)/soybean isolate protein (SPI)/poly(vinylidene fluoride) (PVDF) (LOSP) PE from 74.2 mAh g−1 up to 111.1 mAh g−1 (AB‐LiTFSI/OMMT/SPI/PVDF (AB‐LOSP)) and 111.6 mAh g−1 (AB/MXene‐LiTFSI/OMMT/SPI/PVDF (AB/MXene‐LOSP)). The polarization voltage dropped by 0.06 and 0.12 V, respectively. This work represents a milestone in the dendrite‐free SLIBs with good performances.

Functionalized methyl cellulose/LiClO4 composite as an environmentally friendly quasi-solid polymer electrolyte for solid-state electrochromic devices and cellulose-based supercapacitors

Electrochemical devices, including energy storages and modulators, are expected to play key roles in creating a sustainable future. However, to achieve the technological break-through in electrochemical technologies, the development of solid electrolytes applicable in various electrochemical devices seem necessary. In this study, an environmentally friendly fluorine-free quasi-solid polymer electrolyte derived from a functionalized cellulose composited with LiClO4 is synthesized. The synthesized quasi-solid polymer electrolyte, LiClO4–sulfonated methyl cellulose incorporating lithium ion (LiSMC), exhibits a high conductivity exceeding 1 mS/cm with negligible electron leakage. The LiClO4–LiSMC electrolyte also exhibits high optical transparency and mechanical flexibility, thus it can be applied in various solid-state electrochemical systems including electrochromic devices and energy storages. The applicability of the LiClO4-LiSMC electrolyte in quasi-solid-state electrochromic devices and cellulose-based supercapacitor is demonstrated, from which reduction of the operating voltage and enhancement in performances compared with the similar devices with conventional polymer electrolytes are demonstrated. The cellulose-based supercapacitor demonstrates an excellent stability against mechanical bending and charge–discharge cycling (up to 30,000 cycles) as well. Considering the natural abundance and low environmental impacts of cellulose and its derivatives, this work may open a path to the truly sustainable future through the development of an environmentally friendly material for environmentally friendly applications.

Single-Ion Conducting Polymeric Protective Interlayer for Stable Solid Lithium-Metal Batteries

With many reported attempts on fabricating single-ion conducting polymer electrolytes, they still suffer from low ionic conductivity, narrow voltage window, and high cost. Herein, we report an unprecedented approach on improving the cationic transport number (tLi+) of the polymer electrolyte, i.e., single-ion conducting polymeric protective interlayer (SIPPI), which is designed between the conventional polymer electrolyte (PVEC) and Li-metal electrode. Satisfied ionic conductivity (1 mS cm-1, 30 °C), high tLi+ (0.79), and wide-area voltage stability are realized by coupling the SIPPI with the PVEC electrolyte. Benefiting from this unique design, the Li symmetrical cell with the SIPPI shows stable cycling over 6000 h at 3 mA cm-2, and the full cell with the SIPPI exhibits stable cycling performance with a capacity retention of 86% over 1000 cycles at 1 C and 25 °C. This incorporated SIPPI on the Li anode presents an alternative strategy for enabling high-energy density, long cycling lifetime, and safe and cost-effective solid-state batteries.

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.

Biphasic Solid Electrolytes with Homogeneous Li-Ion Transport Pathway Enabled By Metal-Organic Frameworks

Solid-state batteries based on nonflammable inorganic solid electrolytes provide a promising technical solution that can resolve the safety issues of current lithium-ion batteries. Biphasic solid electrolytes comprising Li7La3Zr2O12 (LLZO) garnet and polymer have been attracting significant interest for solid-state Li batteries because of their mechanical robustness and enhanced Li+ conductivity, compared to conventional polymer electrolytes. Furthermore, the hybridization allows for the fabrication of thin and large-area electrolyte membranes without the need for high-temperature sintering of LLZO. However, the non-uniform distribution of LLZO particles and polymer species in biphasic electrolytes may cause uneven Li+ conduction, which results in poor interfacial stability with electrodes during repeated charge–discharge cycling.In this study, we report a biphasic solid electrolyte with homogeneous Li+ transport pathway achieved by a metal–organic framework (MOF) layer. To regulate and homogenize the Li+ flux across the interface between the electrolyte and electrode, a free-standing, biphasic solid electrolyte membrane is integrated with the MOF nanoparticle layer. A mixture of plastic crystal (PC) and polymeric phase is infused into porous networks of the MOF-integrated electrolyte membrane, producing the percolating Li+ conduction pathways. The MOF-integrated electrolyte membrane is found to form the smooth and uniform interface with nanoporous channels in contact with the electrodes, effectively facilitating homogeneous Li+ transport. A solid-state battery with the MOF-integrated electrolyte membrane shows the enhanced rate-capability and cycling stability in comparison to the battery with the unmodified biphasic electrolyte. This study demonstrates that the proposed electrolyte design provides an effective approach to improving the interfacial stability of biphasic electrolytes with electrodes for long-cycling solid-state batteries.[1] H.-S. Shin, W. Jeong, M.-H. Ryu, S.W. Lee, K.-N. Jung, J.-W. Lee, Electrode-to-electrode monolithic integration for high-voltage bipolar solid-state batteries based on plastic-crystal polymer electrolyte, Chem. Eng. J, published online.[2] T. Jiang, P. He, G. Wang, Y. Shen, C.-W. Nan, L.-Z. Fan, Solvent-free synthesis of thin, flexible, nonflammable garnet-based composite solid electrolyte for all-solid-state lithium batteries, Adv. Energy Mater. 10 (2020) 1903376.