High-Performance All-Solid-State Polymer Electrolyte with Controllable Conductivity Pathway Formed by Self-Assembly of Reactive Discogen and Immobilized via a Facile Photopolymerization for a Lithium-Ion Battery

Lithium-ion batteries with fluorinated mesogen-based liquid-crystalline electrolytes: molecular design towards enhancing oxidation stability

Two-dimensional (2D) nanostructured liquid crystals containing fluorinated cyclohexylphenyl and cyclic carbonate moieties have been developed as quasi-solid-state self-organized electrolytes for safe lithium-ion batteries. We have designed lithium ion-conductive liquid-crystalline (LC) materials with fluorine substituents on mesogens for improved oxidation stability. Computational studies suggest that the fluorination of mesogens lowers the highest occupied molecular orbital (HOMO) level of LC molecules and improves their oxidation resistance as electrolytes. The LC molecule complexed with lithium bis(trifluoromethanesulfonyl)imide exhibits smectic A LC phases with 2D ion transport pathways over wide temperature ranges. Cyclic voltammetry measurements of the fluorinated mesogen-based LC electrolytes indicate that they are electrochemically stable above 4.0 V vs. Li/Li+. Lithium half-cells composed of fluorinated LC electrolytes show higher discharge capacity and coulombic efficiency than those containing non-fluorinated analogous LC molecules. Combining molecular dynamics simulations with the experimental results, it is revealed that the fluorination of the mesogen effectively enhances the electrochemical stability of the LC electrolytes without significantly disrupting ionic conductivities and the LC order.

Studies on Composite Solid Electrolytes with a Dual Selective Confinement Interface Structure of Anions for High-Performance Lithium Metal Batteries

Solid-state lithium batteries (SSLBs) have attracted much attention due to their good thermal stability and high energy density. However, solid-state electrolytes with low conductivity and prominent interfacial issues have hindered the further development of SSLBs. In this research, inspired from a selective confinement structure of anions, a novel HMOF-DNSE composite solid electrolyte with a dual selective confinement interface structure is proposed based on the semi-interpenetrating structure generated by poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), poly(di-n-butylmethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMATFSI), and a metal-organic frameworks MOF derivative (HMOF) as a filler. The dual-network structure of PVDF-HFP/PDADMATFSI combined with HMOF formed a dual selective confinement interface structure to confine out the movement of large anions TFSI-, thereby enhancing the transfer ability of Li+. Subsequently, the addition of HMOF further improves the transfer of Li+ by binding up TFSI- through its crystal structure. The results show that HMOF-DNSE possesses a high room-temperature ionic conductivity (0.7 mS cm-1), a wide electrochemical window (up to 4.5 V), and a high Li+ transfer number (tLi+) (0.56). LiFePO4/HMOF-DNSE/Li cell shows an excellent capacity of 141.5 mAh g-1 at 1C rate under room temperature, with a high retention of 80.1% after 500 cycles. The material design strategy, which is based on selective confinement interface structures of anions, offers valuable insights into enhancing the electrochemical performance of solid-state lithium batteries.

Highly elastic energy storage device based on intrinsically super-stretchable polymer lithium-ion conductor with high conductivity

Stretchable power sources, especially stretchable lithium-ion batteries (LIBs), have attracted increasing attention due to their enormous prospects for powering flexible/wearable electronics. Despite recent advances, it is still challenging to develop ultra-stretchable LIBs that can withstand large deformation. In particular, stretchable LIBs require an elastic electrolyte as a basic component, while the conductivity of most elastic electrolytes drops sharply during deformation, especially during large deformations. This is why highly stretchable LIBs have not yet been realized until now. As a proof of concept, a super-stretchable LIB with strain up to 1200% is created based on an intrinsically super-stretchable polymer electrolyte as the lithium-ion conductor. The super-stretchable conductive system is constructed by an effective diblock copolymerization strategy via photocuring of vinyl functionalized 2-ureido-4-pyrimidone (VFUpy), an acrylic monomer containing succinonitrile and a lithium salt, achieving high ionic conductivity (3.5 × 10-4 mS cm-1 at room temperature (RT)) and large deformation (the strain can reach 4560%). The acrylic elastomer containing Li-ion conductive domains can strongly increase the compatibility between the neighboring elastic networks, resulting in high ionic conductivity under ultra-large deformation, while VFUpy increases elasticity modulus (over three times) and electrochemical stability (voltage window reaches 5.3 V) of the prepared polymer conductor. At a strain of up to 1200%, the resulting stretchable LIBs are still sufficient to power LEDs. This study sheds light on the design and development of high-performance intrinsically super-stretchable materials for the advancement of highly elastic energy storage devices for powering flexible/wearable electronics that can endure large deformation.

Dendritic Solid Polymer Electrolytes: A New Paradigm for High-Performance Lithium-Based Batteries

Li-ions battery is widely used and recognized, but its energy density based on organic electrolytes has approached the theoretical upper limit, while the use of organic electrolytes also brings some safety hazards (leakage and flammability). Polymer electrolytes (PEs) are expected to fundamentally solve the safety problem and improve energy density. Therefore, Li-ions battery based on solid PE has become a research hotspot in recent years. However, low ionic conductivity and poor mechanical properties, as well as a narrow electrochemical window limit its further development. Dendritic PEs with unique topology structure has low crystallinity, high segmental mobility, and reduced chain entanglement, providing a new avenue for designing high-performance PEs. In this review, the basic concept and synthetic chemistry of dendritic polymers are first introduced. Then, this story will turn to how to balance the mechanical properties, ionic conductivity, and electrochemical stability of dendritic PEs from synthetic chemistry. In addition, accomplishments on dendritic PEs based on different synthesis strategies and recent advances in battery applications are summarized and discussed. Subsequently, the ionic transport mechanism and interfacial interaction are deeply analyzed. In the end, the challenges and prospects are outlined to promote further development in this booming field.

Polyzwitterion-SiO2 Double-Network Polymer Electrolyte with High Strength and High Ionic Conductivity

The key to developing high-performance polymer electrolytes (PEs) is to achieve their high strength and high ionic conductivity, but this is still challenging. Herein, we designed a new double-network PE based on the nonhydrolytic sol-gel reaction of tetraethyl orthosilicate and in situ polymerization of zwitterions. The as-prepared PE possesses high strength (0.75 Mpa) and high stretchability (560%) due to the efficient dissipation energy of the inorganic network and elastic characteristics of the polymer network. In addition, the highest ionic conductivity of the PE reaches 0.44 mS cm-1 at 30 °C owning to the construction of dynamic ion channels between the polyzwitterion segments and between the polyzwitterion segments and ionic liquids. Furthermore, the inorganic network can act as Lewis acid to adsorb trace impurities, resulting in a prepared electrolyte with a high electrochemical window over 5 V. The excellent interface compatibility of the as-prepared PE with a Li metal electrode is also confirmed. Our work provides new insights into the design and preparation of high-performance polymer-based electrolytes for solid-state energy storage devices.

Ultrathin Solid Polymer Electrolyte Design for High-Performance Li Metal Batteries: A Perspective of Synthetic Chemistry

Li metal batteries (LMBs) have attracted widespread attention in recent years because of their high energy densities. But traditional LMBs using liquid electrolyte have potential safety hazards, such as: leakage and flammability. Replacing liquid electrolyte with solid polymer electrolyte (SPE) can not only significantly improve the safety, but also improve the energy density of LMBs. However, till now, there is only limited success in improving the various physical and chemical properties of SPE, especially in thickness, posing great obstacles to further promoting its fundamental and applied studies. In this review, the authors mainly focus on evaluating the merits of ultrathin SPE and summarizing its existing challenges as well as fundamental requirements for designing and manufacturing advanced ultrathin SPE in the future. Meanwhile, the authors outline existing cases related to this field as much as possible and summarize them from the perspective of synthetic chemistry, hoping to provide a comprehensive understanding and serve as a strategic guidance for designing and fabricating high-performance ultrathin SPE. Challenges and opportunities regarding this burgeoning field are also critically evaluated at the end of this review.

Stimuli-Responsive Electrochemical Energy Storage Devices

Electrochemical energy storage (EES) devices have been swiftly developed in recent years. Stimuli-responsive EES devices that respond to different external stimuli are considered the most advanced EES devices. The stimuli-responsive EES devices enhanced the performance and applications of the EES devices. The capability of the EES devices to respond to the various external stimuli due to produced advanced EES devices that distinguished the best performance and interactions in different situations. The stimuli-responsive EES devices have responsive behavior to different external stimuli including chemical compounds, electricity, photons, mechanical tensions, and temperature. All of these advanced responsiveness behaviors have originated from the functionality and specific structure of the EES devices. The multi-responsive EES devices have been recognized as the next generation of stimuli-responsive EES devices. There are two main steps in developing stimuli-responsive EES devices in the future. The first step is the combination of the economical, environmental, electrochemical, and multi-responsiveness priorities in an EES device. The second step is obtaining some advanced properties such as biocompatibility, flexibility, stretchability, transparency, and wearability in novel stimuli-responsive EES devices. Future studies on stimuli-responsive EES devices will be allocated to merging these significant two steps to improve the performance of the stimuli-responsive EES devices to challenge complicated situations.

A dual-electrolyte system for highly efficient Al-air batteries

Herein, a brand-new dual-electrolyte consisting of porous polyacrylic acid (PAA) hydrogel and 4 M KOH aqueous electrolyte is put forward. The Al-air battery with this dual-electrolyte demonstrates well-suppressed self-corrosion and enhanced electrochemical performance.

Recent Advances in Flexible Zn-Air Batteries: Materials for Electrodes and Electrolytes

Flexible Zn-air batteries (ZABs) draw much attention due to the merits of high energy density, stability, and safety, and show potential applications for wearable devices. However, the development of flexible ZABs with great energy density, high round-trip efficiency, and long cycle life for practical applications is highly restricted by the lack of highly active oxygen catalysts, high ion-conducting solid-state electrolytes, appropriate Zn anodes, and advanced battery configuration. Promising oxygen catalysts should possess both, superior oxygen reduction reaction and oxygen evolution reaction performance and can be directly used as self-supporting cathodes without loading catalysts on support materials such as carbon cloth. In addition, electrolytes play an important role in ZABs; a good electrolyte should be in all-solid state with high ion conductivity. Moreover, for an excellent Zn anode, it is required to stably contact the electrolyte interface during the bending process. Therefore, in this review, recent advances in ZABs are summarized, including: i) the powder and 3D self-supporting oxygen catalysts, ii) the species of solid-state electrolytes, and iii) the rational design of Zn anodes. Finally, the challenges and opportunities of this promising field are presented.

Solvent-Free Synthesis of the Polymer Electrolyte via Photo-Controlled Radical Polymerization: Toward Ultrafast In-Built Fabrication of Solid-State Batteries under Visible Light

Thin solid polymer electrolytes (SPEs) with good processability, improved room-temperature ionic conductivity, and better interfacial compatibility are urgently needed to develop solid-state batteries without safety and leakage issues. In-built electrolyte polymerization has emerged as a novel and effective platform to obtain such electrolytes. However, existing in-built methods usually involve heat, UV, γ irradiation, and so forth to initiate the polymerization and often require the addition of solvents to avoid the concentrated active propagating species, which inevitably afford solvent residues that persist in the electrolyte matrix, leading to complex SPE preparation processes, safety hazards, and side reactions with the electrodes. Herein, a simple solvent-free preparation of the poly(mPEGAA)-based electrolyte film was achieved via the photo-controlled radical polymerization under visible light irradiation via an in-built manner, which resulted in 99% monomer conversion within 5 min to obtain the polymer electrolytes with a controlled molecular weight distribution. Thanks to the mild and green conditions, a thin, solvent-free, and cross-linked SPE electrolyte film was obtained efficiently yet in a well-regulated manner, which gave rise to good interfacial compatibility and an improved room-temperature ionic conductivity of 1.5 × 10^-4 S cm^-1 at 25 °C. As-prepared solid-state LiFePO₄|Li batteries based on the in-built thin SPE exhibited a high discharge areal capacity of 1.7 mA h cm^-2 (164.6 mA h g^-1) at an ambient temperature. Furthermore, the system displayed lithium dendrite suppression behavior and good long-term charge-discharge cycling in the Li symmetric battery for over 270 h, representing enhanced stability and capacities compared with ex-built systems.

Nanostructured liquid-crystalline Li-ion conductors with high oxidation resistance: molecular design strategy towards safe and high-voltage-operation Li-ion batteries

Nanostructured, uncharged liquid-crystalline (LC) electrolyte molecules having bicyclohexyl and cyclic carbonate moieties have been developed for application in Li-ion batteries as quasi-solid electrolytes, which suppress leakage and combustion. Towards the development of safe and high performance Li-ion batteries, we have designed Li-ion conductive LC materials with high oxidation resistance using density functional theory (DFT) calculation. The DFT calculation suggests that a mesogen with a bicyclohexyl moiety is suitable for the high-oxidation-resistance LC electrolytes compared to a mesogen containing phenylene moieties. A tri(oxyethylene) chain introduced between the cyclic carbonate and the bicyclohexyl moiety in the core part tunes the viscosity and the miscibility with Li salts. The designed Li-ion conductive LC molecules exhibit smectic LC phases over a wide temperature range, and they are miscible with added lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt up to 5 : 5 in molar ratio in their smectic phases. The resulting LC mixtures with LiTFSI show oxidation resistance above 4.0 V vs. Li/Li+ in cyclic voltammetry measurements. The enhanced oxidation resistance improves the performance of Li half-cells containing LC electrolytes.

Alkaline Double-Network Hydrogels with High Conductivities, Superior Mechanical Performances, and Antifreezing Properties for Solid-State Zinc-Air Batteries

For the development of advanced flexible and wearable electronic devices, functional electrolytes with excellent conductivity, temperature tolerance, and desirable mechanical properties need to be engineered. Herein, an alkaline double-network hydrogel with high conductivity and superior mechanical and antifreezing properties is designed and promisingly utilized as the flexible electrolyte in all-solid-state zinc-air batteries. The conductive hydrogel is comprised of covalently cross-linked polyelectrolyte poly(2-acrylamido-2-methylpropanesulfonic acid potassium salt) (PAMPS-K) and interpenetrating methyl cellulose (MC) in the presence of concentrated alkaline solutions. The covalently cross-linked PAMPS-K skeleton and interpenetrating MC chains endow the hydrogel with good mechanical strength, toughness, an extremely rapid self-recovery capability, and an outstanding antifatigue property. Gratifyingly, the entrapment of a concentrated alkaline solution in the hydrogel matrix yields an extremely high ionic conductivity (105 mS cm^-1 at 25 °C) and an excellent antifreezing capacity. The hydrogel retains comparable conductivity and eligible strength to withstand various mechanical deformations at -20 °C. The all-solid-state zinc-air batteries using PAMPS-K/MC hydrogels as flexible alkaline electrolytes exhibit comparable values of specific capacity (764.7 mAh g^-1), energy capacity (850.2 mWh g^-1), cycling stability, and mechanical flexibility. The batteries still possess competitive electrochemical performances even when the operating temperature drops to -20 °C.

Versatile Strategy for Realizing Flexible Room-Temperature All-Solid-State Battery through a Synergistic Combination of Salt Affluent PEO and Li6.75La3Zr1.75Ta0.25O12 Nanofibers

All-solid-state lithium metal batteries are highly attractive because of their high energy density and inherent safety. However, it is still a great challenge to design the solid electrolytes with high ionic conductivity at room temperature and good electrode/electrolyte interfacial compatibility simultaneously in a facile and scalable way. In this work, for the first time, the combination of salt affluent Poly(ethylene oxide) with Li_6.75La₃Zr_1.75Ta_0.25O₁₂ nanofibers was designed and intensively evaluated. The synergistic effect of each component in the electrolyte enhances the ionic conductivity to 2.13 × 10^-4 S cm^-1 at 25 °C and exhibits a high transference number of 0.57. The composite electrolyte possesses superior interfacial stability against Li metal for over 680 h in Li symmetric cells even at a relatively high current density of 2 mA cm^-2. The all-solid-state batteries employing the solid electrolytes exhibit excellent cycling stability at room temperature and superior safety performance. This work proposes a brand-new strategy to design and fabricate solid electrolytes in a versatile way for room-temperature all-solid-state batteries.

Long-Shelf-Life Polymer Electrolyte Based on Tetraethylammonium Hydroxide for Flexible Zinc-Air Batteries

Flexible zinc-air batteries (ZABs) have been considered as one of the most outstanding energy storage devices for flexible and portable electronics because of their superior energy density and environmental friendliness. As the "blood" of flexible ZABs, electrolytes play a significant role in determining their performance, such as discharge working time, cycling property, and shelf life. Herein, a novel polymer electrolyte based on quaternary ammonium hydroxides is first applied in flexible zinc-air batteries. Tetraethylammonium hydroxide (TEAOH) is innovatively used as the ionic conductor with poly(vinyl alcohol) (PVA) as the polymer host in the polymer electrolyte and exhibits a good water retention capability, resulting in not only a good shelf life but also a good working life of the flexible zinc-air batteries. The fabricated polymer electrolyte maintains its high ionic conductivity of 30 mS cm^-1 even after 2 weeks. In addition, the as-assembled zinc-air batteries based on the TEAOH-PVA electrolyte exhibit excellent discharge performance and cycling life compared to those based on the commonly used KOH-PVA electrolyte, and no notable degradation is observed after 2 weeks. Furthermore, flexible TEAOH-PVA-based zinc-air batteries can power a light-emitting diode (LED) electronic watch, a mobile phone, and an LED screen, indicating the very large potential of the high-performance zinc-air batteries that are safe, cost-effective, and remarkably flexible.

Poly(ethylene oxide)-Li10SnP2S12 Composite Polymer Electrolyte Enables High-Performance All-Solid-State Lithium Sulfur Battery

Composite polymer electrolyte membranes are fabricated by the incorporation of Li₁₀SnP₂S₁₂ into the poly(ethylene oxide) (PEO) matrix using a solution-casting method. The incorporation of Li₁₀SnP₂S₁₂ plays a positive role on Li-ionic conductivity, mechanical property, and interfacial stability of the composite electrolyte and thus significantly enhances the electrochemical performance of the solid-state Li-S battery. The optimal PEO-1%Li₁₀SnP₂S₁₂ electrolyte presents a maximum ionic conductivity of 1.69 × 10^-4 S cm^-1 at 50 °C and the highest mechanical strength. The possible mechanism for the enhanced electrochemical performance and mechanical property is analyzed. The uniform distribution of Li₁₀SnP₂S₁₂ in the PEO matrix inhibits crystallization and weakens the interactions among the PEO chains. The PEO-1%Li₁₀SnP₂S₁₂ electrolyte exhibits lower interfacial resistance and higher interfacial stability with the lithium anode than the pure PEO/LiTFSI electrolyte. The Li-S cell comprising the PEO-1%Li₁₀SnP₂S₁₂ electrolyte exhibits outstanding electrochemical performance with a high discharge capacity (ca. 1000 mA h g^-1), high Coulombic efficiency, and good cycling stability at 60 °C. Most importantly, the PEO-1%Li₁₀SnP₂S₁₂-based cell possesses attractive performance with a high specific capacity (ca. 800 mA h g^-1) and good cycling stability even at 50 °C, whereas the PEO/LiTFSI-based cell cannot be successfully discharged because of the low ionic conductivity and high interfacial resistance of the PEO/LiTFSI electrolyte.