MOFs Containing Solid-State Electrolytes for Batteries

Advances in poly(ethylene oxide)-based solid-state lithium-ion battery research

Solid-state lithium-ion batteries are increasingly recognized as a pivotal advancement for the next generation of energy storage technology, owing to their superior safety, high energy density, and extended cycle life. Among the various solid-state polymer materials for Li-ion batteries, poly(ethylene oxide) (PEO)-based solid-state electrolytes have garnered significant attention owing to their excellent interfacial affinity and high solubility for different lithium salts. However, PEO-based solid electrolytes continue to face obstacles, such as diminished ionic conductivity at ambient temperature, inadequate mechanical characteristics, and severe concentration polarization in practical applications. Researchers have proposed a series of modification strategies to enhance the room temperature ionic conductivity by exploring polymer copolymerization, blending, and hyperbranched methods. To optimize the mechanical properties, studies mainly focus on adding high-strength fillers, introducing cross-linking networks, and developing self-repairing materials. To mitigate the concentration polarization effect, a polyanionic configuration is introduced into the polymer backbone, accompanied by the addition of fillers having anionic receptor groups. In this review, the physicochemical properties and Li+ migration mechanisms of PEO-based solid polymer electrolytes are systematically described, focusing on the aforementioned modification strategies and their research progress. Additionally, it offers insights into future development trends.

Multiple Regulation of Electrolyte with Trace Amounts of Sodium Dehydroacetate Additives Enables High-Performance Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) draw much attention for low cost and high safety. However, hydrogen evolution reaction (HER) and uneven Zn2+ deposition shorten lifespan, hampering commercial use. In this study, sodium dehydroacetate (SD) containing carbonyl and keto-carbonyl is introduced as multifunctional electrolyte additives, which effectively modifies the solvent shell structure, achieving a Zn2+ transference number of up to 0.72. Acting as a hydrogen bond acceptor, SD disrupts the water network structure, thereby increasing the HER overpotential by 22 mV and the corrosion potential by 9 mV. The polar functional groups in SD can reversibly capture H⁺ ions and dynamically neutralize OH⁻ ions, maintaining interfacial pH balance on the zinc anode and suppressing HER. Notably, SD not only alters the electrolyte's kinetic but also induces uniform Zn2+ deposition along the (002) plane, inhibiting dendrite growth and minimizing side reactions. This phenomenon is demonstrated in both symmetric and full-cell configurations. The Zn//Zn symmetric cell achieves an ultra-long cycling lifespan of 2800 hours at 5 mA cm⁻2, and the Zn//VO2 full battery maintains a capacity retention rate of 73.09% after 2000 cycles with a high average coulombic efficiency of 99.98%, underscoring the effectiveness of this electrolyte additive in enhancing battery performance.

The enhancement of Li-ion conductivity in 2D metalloid organic frameworks via nodal element substitution

The development of solid-state electrolytes has become crucial for promoting the safety and performance of lithium-ion batteries. Herein, the substitution of nodal elements from Si to Ge significantly improved the lithium ionic conductivity in 2D metalloid organic frameworks, resulting in an enhancement of approximately one order of magnitude.

Amorphization engineering of Ni-cysteine coordination composition for urea electro-oxidation at large current density

Unavoidable oxygen evolution reaction (OER) and the relatively high potential to form real active sites of Ni3+ species severely decrease the efficiency of urea-assisted hydrogen generation facility. Herein, amorphization Ni-cysteine coordination (aNi-cys) is constructed as efficient urea electro-oxidation reaction (UOR) catalyst with highly capable of suppressing competitive OER and promoting the Ni2+ to Ni3+ in-situ electrochemical configuration through deliberately regulating the Ni/l-cysteine coordination environment. The abundant ligand atoms (N, S, and O) of l-cysteine considerably tuned the Ni electronic structure to the most suitable state while the amorphization thin lamellas increased the exposed active sites and befitting for the access of electrolyte to electrode surface, resulting improved UOR activity with a large peak current density of 263 mA cm-2, far exceeding crystalline Ni-cysteine coordination (cNi-cys) and long-term stability for 50 h working. Excitingly, only 41 kWh is required to produce 1 kg H2 (50 mA cm-2) from a home-made urea-assisted simulated seawater electrolysis apparatus, about 8 kWh energy saving from that of water splitting. This work gives a clue for preparing advanced electrocatalysts applicable to urea-related energy system with large current density.

Encapsulation of biomimetic nanozymes in MOF matrices as peroxidase mimetics for sensitive detection of L-cysteine

A metal-organic framework (MOF)-encapsulated nanozyme has been developed to detect L-cysteine (L-Cys) through a facile colorimetric sensing method in this study. This nanozyme was prepared by encapsulating Fmoc-histidine (FH) and hemin within ZIF-8 (FH/hemin@ZIF-8) and exhibited significantly enhanced catalytic activity and great stability because of its unique structure. FH/hemin@ZIF-8 oxidized colorless 3,3',5,5'-tetramethylbenzidine (TMB) to a distinct blue color with the assistance of H2O2. However, after the addition of L-Cys, this oxidation process was inhibited, resulting in the solution fading from blue to colorless. This change can be observed by the naked eyes and quantitatively analyzed using a UV-vis spectrophotometer. Additionally, this system demonstrated excellent resistance to interference and exceptional selectivity. In addition, this system showed a low detection limit of 23.1 nm (S/N = 3). Consequently, it is believed that the strategy of encapsulating biomimetic nanozymes within MOFs holds significant potential for applications in bioanalysis and the early diagnosis of L-Cys.

PEO-Based Solid-State Polymer Electrolytes for Wide-Temperature Solid-State Lithium Metal Batteries

Developing solid-state lithium metal batteries with wide operating temperature range is important in future. Polyethylene oxide (PEO)-based solid-state electrolytes are extensively studied for merits including superior flexibility and low glass transition temperature. However, ideal usage temperatures for conventional PEO-based solid-state electrolytes are between 60 and 65 °C, and unequable temperature degrades their electrochemical performances at low and high temperatures (≤25 °C and ≥80 °C). Herein, modification methods of PEO electrolytes for low, high especially wide-temperature applications are reviewed based on detailed analyses of mechanisms involved in its modification at different temperatures. First, shortcomings of PEO solid electrolytes due to influence of temperature are pointed out. Second, existing modification strategies are summarized in detail from three aspects of high, low especially wide temperatures, including application of PEO derivatives or chain segment modification treatment of PEO, addition of fillers, and other modification methods such as reasonable regulation of lithium salts, introduction of functional layers and addition of metal-organic frameworks (MOFs) or covalent organic frameworks (COFs). Finally, a summary and description of PEO-based solid electrolyte research and development trends for wide-temperature applications are provided. The review aims to offer some guidance for the creation of PEO solid batteries with wider working temperature ranges.

Tailoring Ce-Centered Metal-Organic Frameworks for Fast Li+ Transport in Composite Polymer Electrolyte

Regulating metal nodes to innovate the metal-organic framework (MOF) structure is of great interest to boost the performance of MOFs-incorporated composite solid electrolytes. Herein, Ce4+ with a low-lying 4f orbital is selected as metal center to coordinate with organic ligand to prepare MOF of Ce-UiO-66. The unsaturated open metal sites and defected oxygen vacancies furnish Ce-UiO-66 with strengthened Lewis acidity, which promotes Ce-UiO-66 interacting effectively with both poly(ethylene oxide) (PEO) and Li salt anions. Accordingly, Ce-UiO-66 as additive fillers can be uniformly dispersed in PEO matrix to form an advanced composite solid-state electrolyte (Ce-UiO@PEO) with accelerated Li+ transport. The optimized Ce-UiO@PEO displays a boosted ionic conductivity of 4.20 × 10-4 S cm-1 and an improved Li+ transference number of 0.39 at 60 °C, which are highly comparable to those of other MOFs@PEO electrolytes. Combined with the mechanical and thermal stabilities, such a Ce-UiO@PEO electrolyte enables Li/Li symmetric and Li/LiFePO4 full cells with superior cycling stability and rate performance. The Ce-UiO@PEO electrolytes are of great potential to be applied in high-performance lithium metal batteries.

Enhancing the performance of ionic conductivity for solid-state electrolytes: an effective strategy of injecting lithium ions within anionic metal-organic frameworks

Metal-organic frameworks (MOFs) are considered as potential solid-state electrolyte (SSE) materials due to their structural diversity and porosity. Adding lithium ions into the anionic frameworks of MOFs and then realizing single-ion transport is an efficient way to enhance the performance of ionic conductivity of SSE materials. Herein, an ionotropic MOF (Li+[Cu-BTC]-) with lithium ions in the pores of the lattice was synthesized through an ion exchange strategy, which exhibits outstanding lithium ionic conducting properties over a wide temperature range (ionic conductivity: 0.11-2.96 × 10-3 S cm-1 in the temperature range of -40 to 100 °C). The strategy of injecting Li+ within anionic metal-organic frameworks provides a new opportunity for exploring advanced SSEs.

Conducting Composite Polymer-Based Solid-State Electrolyte with High Ion Conductivity via Amorphous Condensed Structure and Multiple Li+ Transport Channels

Traditional PEO electrolyte has high crystallinity which hinders the transmission of Li+, resulting in poor ion conductivity and complicated processing technology. Herein, a polymer electrolyte (p-electrolyte) with a wide electrochemical window and high ionic conductivity is designed, which possesses an amorphous condensed structure. The amorphous structure provides fast transport channels for Li+, so the p-electrolyte possesses an electrochemical window of 4.2 V, and high ionic conductivity of 1.58 × 10-5 S cm-1 at room temperature, which is 1-2 orders of magnitude higher than that of traditional PEO electrolyte. By using the designed polymer electrolyte as the foundation, an in situ curable composite polymer electrolyte (CPE-L) with multiple Li+ transport channels is elaborately constructed. The Cu-BTC MOF stores abundant Li+, which is introduced into the p-electrolyte. The rich unsaturated Cu2+ coordination sites of Cu-BTC can anchor TFSI- to release Li+, and the pore structure of Cu-BTC MOF cooperates with LLZTO nanoparticles to provide multiple fast transport channel for Li+, resulting in remarkable ionic conductivity (1.02 × 10-3 S cm-1) and Li+ transference number (0.58). The Li||CPE-L||Li symmetric battery cycles stably for more than 700 h at 0.1 mA cm-2, while the specific capacity of full battery is ≈153 mAh g-1 (RT, 0.2 C).

Bimetal Fluorides with Adjustable Vacancy Concentration Reinforcing Ion Transport in Poly(ethylene oxide) Electrolyte

The poor ambient ionic transport properties of poly(ethylene oxide) (PEO)-based SPEs can be greatly improved through filler introduction. Metal fluorides are effective in promoting the dissociation of lithium salts via the establishment of the Li-F bond. However, too strong Li-F interaction would impair the fast migration of lithium ions. Herein, magnesium aluminum fluoride (MAF) fillers are developed. Experimental and simulation results reveal that the Li-F bond strength could be readily altered by changing fluorine vacancy (VF) concentration in the MAF, and lithium salt anions can also be well immobilized, which realizes a balance between the dissociation degree of lithium salts and fast transport of lithium ions. Consequently, the Li symmetric cells cycle stably for more than 1400 h at 0.1 mA cm-2 with a LiF/Li3N-rich solid electrolyte interphase (SEI). The SPE exhibits a high ionic conductivity (0.5 mS cm-1) and large lithium-ion transference number (0.4), as well as high mechanical strength owing to the hydrogen bonding between MAF and PEO. The corresponding Li//LiFePO4 cells deliver a high discharge capacity of 160.1 mAh g-1 at 1 C and excellent cycling stability with 100.2 mAh g-1 retaining after 1000 cycles. The as-assembled pouch cells show excellent electrochemical stability even at rigorous conditions, demonstrating high safety and practicability.

Advances in nanoporous materials for next-generation battery applications

In recent years, nanoporous materials, mainly represented by metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have shown unparalleled potential in critical applications such as energy storage, gas separation and catalysis. The integration of MOFs/COFs into battery technology has garnered substantial research attention since it was found that such materials also play important roles in batteries. The highly controllable nanoporous features of MOFs/COFs enable the regulation of the solvation environment of lithium ions, thereby significantly improving the performance of lithium metal batteries. Moreover, the selective adsorption features of MOFs/COFs make them particularly useful for stabilising high nickel cathodes and sulfur cathodes. This review provides an overview of the application of MOFs/COFs in batteries, and explores potential future directions and challenges in this rapidly evolving interdisciplinary field.

Toward Enhancing Low Temperature Performances of Lithium-Ion Transport for Metal-Organic Framework-Based Solid-State Electrolyte: Nanostructure Engineering or Crystal Morphology Controlling

Metal-organic frameworks (MOFs) have emerged as attractive candidates for Li+ conducting electrolytes due to their regular channels and controllable morphology, making their presence prominent in the field of solid-state lithium batteries. However, most MOF-based electrolytes are researched at or near room temperature, which poses a challenge to their practical applications at low temperatures. Herein, a thin layer flower-shaped 2D Cu-MOF (CuBDC-10)-based solid-state electrolytes (SSEs) for lithium-ion batteries (LIBs) are developed for facilitating Li+ transport at lower temperatures, which achieve an ion conductivity of 10-4 S cm-1 at -30 °C. The CuBDC-10-based SSE exhibits outstanding ionic conductivity over a wide temperature range of -40 to 100 °C (0.073-3.68 × 10-3 S cm-1). This work provides strategies for exploring MOF-based SSEs with high ionic transport performances at low temperatures.

Vitrified Metal-Organic Framework Composite Electrolyte Enabling Dendrite-Free and Long-Lifespan Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (LMBs) are still plagued with low ionic conductivity and inferior interfacial contact, which hinder their practical implementation. Herein, a quasi-solid-state composite electrolyte, poly(1,3-dioxolane) (PDOL)/glassy ZIF-62 (PGZ) with fast ion transport and intimate interface contact, is fabricated via in situ polymerization. The in situ polymerization of DOL in an electrolyte matrix not only improves the exterior interface between electrolyte/electrode but also optimizes the inner interfaces among glassy particles, rendering PGZ as an uninterrupted ionic conductor. Moreover, PGZ inherits the superior ionic conductivity and the robust dendrite prohibition of glassy MOFs originating from their grain-boundary-free nature, isotropy, and abundant groups containing N species. As expected, our proposed PGZ exhibits a prominent ionic conductivity of 6.3 × 10-4 S cm-1 at 20 °C. Li|PGZ|LiFePO4 delivers an outstanding rate performance (103 mAh g-1 at 4C) and a stable cycling capacity (118 mAh g-1 at 1C over 1000 cycles). PGZ also presents excellent low-temperature cycling performance with 75 mAh g-1 for 480 cycles at -20 °C and excellent flame retardance. Even at a high loading of 12.1 mg cm-2, it can still discharge at 140 mAh g-1 for 100 cycles. Hence, PGZ prepared via in situ polymerization holds enormous prospects as a solid-state electrolyte for high-performance and safe LMBs.

Imparting Stable and Ultrahigh Proton Conductivity to a Layered Rare Earth Hydroxide via Ion Exchange

Proton conductors are essential functional materials with a wide variety of potential applications in energy storage and conversion. In order to address the issues of low proton conductivity and poor stability in conventional proton conductors, a simple and valid ion-exchange method was proposed in this study for the introduction of stable and ultrahigh proton conductivity in layered rare earth hydroxides (LRHs). Test analyses by solid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, and powder X-ray diffraction revealed that the exchange of H2PO4- not only does not disrupt the layered structure of LRHs, but also creates more active proton sites and channels necessary for proton transport, thereby creating a high-performance proton conductor (LRH-H2PO4-). By utilizing this ion-exchange method, the proton conductivity of LRHs can be significantly enhanced from a low level to an ultrahigh level (>10-2 S·cm-1), while maintaining excellent long-term stability. Moreover, through methodically manipulating the guest ions and molecules housed within the interlayers of LRHs, a comprehensive explanation has been presented regarding the proficient mechanism of proton conduction in LRH-H2PO4-. As a result, this investigation presents a feasible and available approach for advancing proton conductor.

Processing mechanism synergizing surface and intercalation pseudocapacitance engineering fast-charging Li-based anode materials

Pseudocapacitive material can achieve rapid charge and discharge response. In this study, a vanadium-based conductive network hydrate (Na0.13Mg0.02)V2O5·0.98H2O (NMVO) was designed. The Na+ and Mg2+ in NMVO are sandwiched between two layers of vacancy-ordered prisms and monoclinic nanonetwork V3O7 (VO2:V2O5 = 1:1) to form a conductive network with a layer spacing of up to 11.67 Å, this structure facilitates rapid interlayer diffusion of cations and enhanced conductivity. Reduction-NMVO (r-NMVO) with hierarchical heterostructures was prepared via an in-situ electrochemical process to generate interlayer vanadium-based active sites (LiV3O8, LiV2O5, Na3V3O8, MgVO3) with multi-electron reaction, which enhanced the generation of surface redox pseudocapacitance. The interlayer heterostructure is integrated with the core of the precursor V3O7 to form an active site-rich conductive network with strong pulse impact resistance, which promotes the generation of intercalated pseudocapacitance and increases the cycle stability of the electrode. This intercalation-surface redox pseudocapacitive mechanism was confirmed by first-principles, in-situ, and ex-situ characterization analysis. The r-NMVO|Li battery still maintains a capacity of 95.5 % after 65,500 cycles at a current density of 50 A g-1. These results contribute directly to the realization of stable, fast charge and discharge material design.

Ultrafast Ion Transfer of Metal-Organic Framework Interface for Highly Efficient Energy Storage

Flexible supercapacitors are favorable for wearable electronics. However, their high-rate capability and mechanical properties are limited because of unsatisfactory ion transfer kinetics and interfacial modulus mismatch inside devices. Here, we develop a metal-organic framework interface with superior electrical and mechanical properties for supercapacitors. The interfacial mechanism facilitates ultrafast ion transfer with an energy barrier reduction of 43% compared with that of conventional transmembrane transport. It delivers high specific capacity at a wide rate range and exhibits ultrastability beyond 30000 charge-discharge cycles. Furthermore, meliorative modulus mismatch benefited from ultrathin interface design that improves mechanical properties of flexible supercapacitors. It delivers a stable energy supply under various mechanical conditions like bending and twisting status and displays ultrastable mechanical properties with performance retention of 95.5% after 10 000 bending cycles. The research paves the way for interfacial engineering for ultrastable electrochemical devices.

Composite poly(ethylene oxide)-based solid electrolyte with consecutive and fast ion transport channels constructed by upper-dimensional MIL-53(Al) nanofibers

Novel structural designs for metal organic frameworks (MOFs) are expected to improve ion-transport behavior in composite solid electrolytes. Herein, upper-dimensional MIL-53(Al) nanofibers (MNFs, MIL-53 belongs to the MIL (Material Institute Lavoisier) group) with flower-like nanoflake structures have been designed and constructed via modified hydrothermal coordination. The optimized MNFs with high surface area and porosity can form abundant interfaces with poly(ethylene oxide) (PEO) matrix. The plasticization of MNFs to the PEO matrix will facilitate segmental movement of PEO chains to facilitate Li+ conduction. The unsaturated open metal centers of MNFs can effectively capture bis(trifluoromethanesulfonyl)imide anions (TFSI-) to deliver more free lithium ions for transfer. Moreover, the upper-dimensional nanofiber structure endows lithium ions with a long-range and consecutive transport pathway. The obtained composite solid electrolyte (MNFs@PEO) presents a high ionic conductivity of 4.1 × 10-4 S cm-1 and a great Li+ transference number of 0.4 at 60 °C. The electrolyte also exhibits a stable Li plating/stripping behavior over 1000 h at 0.1 mA cm-1 with inhibited Li dendrite growth. Furthermore, the Li/LiFePO4 and Li/LiNi0.8Mn0.1Co0.1O2 batteries with MNFs@PEO as electrolytes both display great cycling stabilities with high-capacity retention, indicating their potential applications in lithium metal batteries. The study will put forward new inspirations for designing advanced MOF-based composite solid electrolytes.

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.

Metal-Organic Frameworks for the Enhancement of Lithium-Based Batteries: A Mini Review on Emerging Functional Designs

Metal-organic frameworks (MOFs) have played a crucial role in recent advancements in developing lithium-based battery electrolytes, electrodes, and separators. Although many MOF-based battery components rely on their well-defined porosity and controllable functionality, they also boast a myriad of other significant properties relevant to battery applications. In this mini-review, the distinct advantages of MOFs in battery applications are discussed, including using MOFs to 1) scavenge impurities to increase cycling stability, 2) widen the operation temperature range of conventional electrolytes, 3) widen the operation voltage range of common electrolytes, and 4) employ as artificial solid-electrolyte interphases to prevent lithium dendrite growth. Furthermore, subsisting challenges of developing these emerging MOF-based battery technologies are discussed and guidance for shaping the future of this field is given.

MOF-derived Co-C composites with 3D star structure for enhanced microwave absorption

The demand of microwave absorption materials (MAMs) with unique morphologies and electromagnetic (EM) balance has become necessary in recent years. Due to the ease of synthesis and tunable structure, metal-organic frameworks (MOFs) are widely used for this special MAMs. In this study, a new three-dimensional hybrid MOF is proposed that is co-doped with six equally branched star morphologies. The Co-C composite has the same six-branched morphology as that of the precursor. When the EM wave is incident, this special structure makes it easier for the EM wave to enter the material vertically due to the expansion of the incident surface, which is effective in adjusting the transmission path of the electron and the reflection and distribution of the EM wave. Because of the special morphology and magneto-dielectric synergy, the Co-C composite shows a minimum reflection loss (RLmin) of -48.5 dB at 11.0 GHz at an absorption thickness of 3.0 mm, with a microwave absorption bandwidth (EAB) of 6.1 GHz. This research provides a practical guidance for preparing the MAMs of special star structure.