Recyclable, Self-Healing Solid Polymer Electrolytes by Soy Protein-Based Dynamic Network

In Situ Integration of a Flame Retardant Quasisolid Gel Polymer Electrolyte with a Si-Based Anode for High-Energy Li-Ion Batteries

Silicon (Si) stands out as a promising high-capacity anode material for high-energy Li-ion batteries. However, a drastic volume change of Si during cycling leads to the electrode structure collapse and interfacial stability degradation. Herein, a multifunctional quasisolid gel polymer electrolyte (QSGPE) is designed, which is synthesized through the in situ polymerization of methylene bis(acrylamide) with silica-nanoresin composed of nanosilica and a trifunctional cross-linker in cells, leading to the creation of a "breathing" three-dimensional elastic Li-ion conducting framework that seamlessly integrates an electrode, a binder, and an electrolyte. The silicon particles within the anode are encapsulated by buffering the QSGPE after cross-linking polymerization, which synergistically interacts with the existing PAA binder to reinforce the electrode structure and stabilize the interface. In addition, the formation of the LiF- and Li3N-rich SEI layer further improves the interfacial property. The QSGPE demonstrates a wide electrochemical window until 5.5 V, good flame retardancy, high ionic conductivity (1.13 × 10-3 S cm-1), and a Li+ transference number of 0.649. The advanced QSGPE and cell design endow both nano- and submicrosized silicon (smSi) anodes with high initial Coulombic efficiencies over 88.0% and impressive cycling stability up to 600 cycles at 1 A g-1. Furthermore, the NCM811//Si cell achieves capacity retention of ca. 82% after 100 cycles at 0.5 A g-1. This work provides an effective strategy for extending the cycling life of the Si anode and constructing an integrated cell structure by in situ polymerization of the quasisolid gel polymer electrolyte.

Biodegradable Solid Polymer Electrolytes from the Discarded Cataractous Eye Protein Isolate

The protein extracted from the discarded eye lenses postcataract surgery, referred to as the cataractous eye protein isolate (CEPI), is employed as a polymer matrix for the construction of solid polymer electrolyte species (SPEs). SPEs are expected to be inexpensive, conductive, and mechanically stable in order to be economically and commercially viable. Environmentally, these materials should be biodegradable and nontoxic. Taking these factors into account, we investigated the possibility of using a discarded protein as a polymer matrix for SPEs. Natural compounds sorbitol and sinapic acid (SA) are used as the plasticizer and cross-linker, respectively, to tune the mechanical as well as electrochemical properties. The specific material formed is demonstrated to have high ionic conductivity ranging from ∼2 × 10-2 to ∼8 × 10-2 S cm-1. Without the addition of any salt, the ionic conductivity of sorbitol-plasticized non-cross-linked CEPI is ∼7.5 × 10-2 S cm-1. Upon the addition of NaCl, the conductivity is enhanced to ∼8 × 10-1 S cm-1. This study shows the possibility of utilizing a discarded protein CEPI as an alternative polymer matrix with further potential for the construction of tunable, flexible, recyclable, biocompatible, and biodegradable SPEs for flexible green electronics and biological devices.

Practical Applications of Self-Healing Polymers Beyond Mechanical and Electrical Recovery

Self-healing polymeric materials, which can repair physical damage, offer promising prospects for protective applications across various industries. Although prolonged durability and resource conservation are key advantages, focusing solely on mechanical recovery may limit the market potential of these materials. The unique physical properties of self-healing polymers, such as interfacial reduction, seamless connection lines, temperature/pressure responses, and phase transitions, enable a multitude of innovative applications. In this perspective, the diverse applications of self-healing polymers beyond their traditional mechanical strength are emphasized and their potential in various sectors such as food packaging, damage-reporting, radiation shielding, acoustic conservation, biomedical monitoring, and tissue regeneration is explored. With regards to the commercialization challenges, including scalability, robustness, and performance degradation under extreme conditions, strategies to overcome these limitations and promote successful industrialization are discussed. Furthermore, the potential impacts of self-healing materials on future research directions, encompassing environmental sustainability, advanced computational techniques, integration with emerging technologies, and tailoring materials for specific applications are examined. This perspective aims to inspire interdisciplinary approaches and foster the adoption of self-healing materials in various real-life settings, ultimately contributing to the development of next-generation materials.

Hybrid Dynamic Covalent Network-Based Protecting Layer for Stable Li-Metal Batteries

Metallic lithium (Li) is considered as the "Holy Grail" anode material for next-generation energy storage systems due to its extremely high theoretical capacity and low electrochemical potential. Before the commercialization of the Li electrode, dendritic Li growth and the unstable solid electrolyte interphase layer should be conquered. Herein, a hybrid covalent adaptable polymer network (HCAPN) is prepared via the random copolymerization of poly(ethylene glycol) methyl ether methacrylate and -acetoacetoxyethyl methacrylate, followed by chemical cross-linking with polyethylenimine (PEI) and amine-modified silicon dioxide (SiO2). Such a hybrid network, where PEI and amine-modified SiO2 formed a vinylogous urethane-based dynamic covalent bond with the copolymer, respectively, shows improved mechanical properties, solvent resistance, and excellent healability/recyclability. As the protecting layer on the Li electrode, the assembled HCAPN@Li||HCAPN@Li symmetric cell shows a long cycle life of 800 h with low overpotential at a current density of 1 mA cm-2, and superior electrochemical performance can be achieved in the HCAPN@Li||LiFePO4 full cell (capacity retention of 77% over 400 cycles at 1.5 C) and HCAPN@Li||NCM811 cell (capacity retention of 79% after 300 cycles). Surface morphology analysis is also performed for physical insight into their role as protecting layer. This work provides a new perspective for constructing a hybrid dynamic covalent network-based polymer protecting layer for inhibiting Li dendrite growth.

Simultaneous High Ionic Conductivity and Lithium-Ion Transference Number in Single-Ion Conductor Network Polymer Enabling Fast-Charging Solid-State Lithium Battery

Developing solid-state electrolyte with sufficient ionic conduction and flexible-intimate interface is vital to advance fast-charging solid-state lithium batteries. Solid polymer electrolyte yields the promise of interfacial compatibility, yet its critical bottleneck is how to simultaneously achieve high ionic conductivity and lithium-ion transference number. Herein, single-ion conducting network polymer electrolyte (SICNP) enabling fast charging is proposed to positively realize fast lithium-ion locomotion with both high ionic conductivity of 1.1 × 10-3 S cm-1 and lithium-ion transference number of 0.92 at room temperature. Experimental characterization and theoretical simulations demonstrate that the construction of polymer network structure for single-ion conductor not only facilitates fast hopping of lithium ions for boosting ionic kinetics, but also enables a high dissociation level of the negative charge for lithium-ion transference number close to unity. As a result, the solid-state lithium batteries constructed by coupling SICNP with lithium anodes and various cathodes (e.g., LiFePO4 , sulfur, and LiCoO2 ) display impressive high-rate cycling performance (e.g., 95% capacity retention at 5 C for 1000 cycles in LiFePO4 |SICNP|lithium cell) and fast-charging capability (e.g., being charged within 6 min and discharged over than 180 min in LiCoO2 |SICNP|lithium cell). Our study provides a prospective direction for solid-state electrolyte that meets the lithium-ion dynamics for practical fast-charging solid-state lithium batteries.

Structure and dynamics of dynamic covalent cross-linked PEOs and PEO/LiPF6 electrolytes: a coarse-grained simulation study

The incorporation of dynamic covalent bonds has been an attractive strategy to synthesize adaptive solid polymer electrolytes (SPEs). Here, we present molecular dynamics results concerning the relationship between ion transport and segmental dynamics for dynamic covalent cross-linked PEO-Li⁺ SPEs. To dissolve LiPF₆ into PEO, a 1/r⁴-form approximation of ion-dipole interactions is employed as the solvation potential. Its parameters are estimated with the assistance of the Bayesian optimization algorithm and validated by comparing the resulting behaviors of PEO/LiPF₆ with experimental observations. The dynamic associations of EO with Li⁺ and PF₆^- significantly reduce the segmental mobility of PEO, verifying the coupling of PEO segmental dynamics with ion transport. In order to reproduce the unique behaviors of associative covalent adaptive networks (CANs), the bond-exchange reaction is controlled by the collision probability and the user-defined activation energy (E_a ≥ 0) based on a hybrid of molecular dynamics and Monte Carlo methods. The dynamics of network topology, facilitated by the reshuffling of dynamic covalent bonds, is analyzed using graph theory. The network mesh size varies with time, which can be considered as one of the characteristics for associative CANs. The reshuffling of dynamic bonds releases the constraint from cross-linked structures, and enhances the long-range segmental mobility as well as the mobilities of Li⁺ and PF₆^-. By drawing comparisons with its conventionally cross-linked counterpart, the effect of dynamic-bond reshuffling on ion transport is studied for the dynamic covalent cross-linked PEO₁₆-LiPF₆ electrolyte in terms of self-diffusivities, cation transference number, and ionic conductivity.

Metal Coordination in Polyimine Covalent Adaptable Networks for Tunable Material Properties and Enhanced Creep Resistance

Covalent adaptable networks (CANs) can replace classical thermosets, as their unique dynamic covalent bonds enable recyclable crosslinked polymers. Their creep susceptibility, however, hampers their application. Herein, an efficient strategy to enhance creep resistance of CANs via metal coordination to dynamic covalent imines is demonstrated. Crucially, the coordination bonds not only form additional crosslinks, but also affect the imine exchange. This dual effect results in enhanced glass transition temperature (T_g ), elasticmodulus (G') and creep resistance. The robustness of metal coordination is demonstrated by varying metal ion, counter anion, and coordinating imine ligand. All variations in metal or anion significantly enhance the material properties. The T_g and G' of the CANs are correlated to the coordination bond strength, offering a tunable handle by which choice of metal can steer material properties. Additionally, large differences in T_g and G' are observed for materials with different anions, which are mostly linked to the anion size. This serves as a reminder that for coordination chemistry in the bulk, not only the metal ion is to be considered, but also the accompanying anion. Finally, the reinforcing effect of metal coordination is proved insensitive to the metal-ligand ratio, emphasizing the robustness of the applied method.

Self-Healing Polymer Electrolytes for Next-Generation Lithium Batteries

The integration of polymer materials with self-healing features into advanced lithium batteries is a promising and attractive approach to mitigate degradation and, thus, improve the performance and reliability of batteries. Polymeric materials with an ability to autonomously repair themselves after damage may compensate for the mechanical rupture of an electrolyte, prevent the cracking and pulverization of electrodes or stabilize a solid electrolyte interface (SEI), thus prolonging the cycling lifetime of a battery while simultaneously tackling financial and safety issues. This paper comprehensively reviews various categories of self-healing polymer materials for application as electrolytes and adaptive coatings for electrodes in lithium-ion (LIBs) and lithium metal batteries (LMBs). We discuss the opportunities and current challenges in the development of self-healable polymeric materials for lithium batteries in terms of their synthesis, characterization and underlying self-healing mechanism, as well as performance, validation and optimization.

Current Self-Healing Binders for Energetic Composite Material Applications

Energetic composite materials (ECMs) are the basic materials of polymer binder explosives and composite solid propellants, which are mainly composed of explosive crystals and binders. During the manufacturing, storage and use of ECMs, the bonding surface is prone to micro/fine cracks or defects caused by external stimuli such as temperature, humidity and impact, affecting the safety and service of ECMs. Therefore, substantial efforts have been devoted to designing suitable self-healing binders aimed at repairing cracks/defects. This review describes the research progress on self-healing binders for ECMs. The structural designs of these strategies to manipulate macro-molecular and/or supramolecular polymers are discussed in detail, and then the implementation of these strategies on ECMs is discussed. However, the reasonable configuration of robust microstructures and effective dynamic exchange are still challenges. Therefore, the prospects for the development of self-healing binders for ECMs are proposed. These critical insights are emphasized to guide the research on developing novel self-healing binders for ECMs in the future.

Rapid Self-Healing Gel Electrolyte Based on Deep Eutectic Solvents for Solid-State Lithium Batteries

A deep eutectic solvent (DES) is a promising electrolyte choice for lithium metal batteries. However, the DES liquid electrolyte causes safety concerns and side reactions with the lithium anode. Therefore, it is necessary to solidify the DES-based electrolyte and enhance its electrochemical stability. Herein, we present a novel DES-based rapid self-healing gel electrolyte, which is able to self-smooth its surface cracks in only 30 min. The electrolyte exhibits noncombustibility (SET = 4 s g-1), high ionic conductivity (1.1 × 10-3 S cm-1 at 25 °C), and a wide electrochemical voltage window (4.5 V vs Li/Li+). As a result, the solid-state lithium batteries coupling the gel electrolyte with the Li anode and LiFePO4 cathode deliver a high specific capacity of 135.4 mA h g-1 with durable cyclic stability (>1200 h). This work provides valuable insights for design of fire-resistant and high-energy solid-state lithium batteries.

Concepts and Emerging Trends for Structural Battery Electrolytes

The structural battery is a multifunctional energy storage device that aims to address the weight and volume efficiency issues that conventional batteries face, especially in electric transportation. By combining the functions of mechanical load bearing and energy storage, structural batteries can reduce the reliance on, or even eventually replace the main power source in an electric vehicle or a drone. However, one of the key challenges to be addressed before achieving multifunctionality in structural batteries would be the design of a suitable multifunctional structural battery electrolyte. The structural battery electrolyte is the constituent that provides mechanical integrity under flexural loads or impact and hence determines the electrochemical and much of the mechanical performance of a structural battery device. This concept paper aims to cover the key considerations and challenges facing the design of structural battery electrolytes. In addition, the main approaches to surmount these challenges are highlighted, keeping design aspects like sustainability and recyclability in view.