A Fluoride-Rich Solid-Like Electrolyte Stabilizing Lithium Metal Batteries

Defect-Tailoring Metal-Organic Frameworks for Highly Fast-Charging Quasi-Solid-State Electrolytes Lithium Metal Batteries

Metal-organic frameworks (MOFs) show revolutionary potential in quasi-solid-state electrolytes (QSSEs) designed for high-energy-density batteries, owing to their tunable nanoporous structures and open metal sites (OMSs). However, their application is hindered by insufficient Li+ dissociation and low ionic conductivity, attributed to limited metal active sites. This study employed defect engineering to modulate hafnium-based MOFs, increasing OMS density while optimizing the pore microenvironment. The engineered defects improve the Lewis acid strength of OMSs, driving lithium salt dissociation and establishing strong chemisorption of TFSI- anions. By synergistically optimizing defect density, Lewis acidity, and structural stability, the defect-engineered Hf-MOF-QSSE achieved an ionic conductivity of 1.0 mS cm-1 at 30 °C and delivered a critical current density of 2 mA cm-2, surpassing previously reported MOF-QSSEs, underscoring the pivotal role of defect engineering in electrolyte optimization. Furthermore, Li||LiFePO4 cells exhibited excellent cycling stability and ultrahigh rate capability, retaining 93% of their capacity after 1500 cycles at 10C, while Li||NCM811 cells maintained a specific capacity of 85 mAh g-1 after 600 cycles at 5C.

Anthraquinone substituents modulate ionic hydrogen-bonded organic frameworks to achieve high ionic conductivity for alkali metal ions

Herein, we report two charge-assisted hydrogen-bonded organic frameworks (iHOF-24 and iHOF-25) with 3D/2D hydrogen-bonding networks, which exhibit high ionic conductivity for alkali metal ions. Among them, the conductivity of Li+ is higher than that of Na+ and K+, and the ionic conductivities of Li@iHOF-24 and Li@iHOF-25 at 30 °C were 9.44 × 10-5 and 9.85 × 10-5 S cm-1. This change is attributed to the distance between neighboring carbonyl groups in iHOF-24 and iHOF-25, as well as the radius of the loaded alkali metal ions.

Hopping-Phase Ion Bridge Enables Fast Li+ Transport in Functional Garnet-Type Solid-State Battery at Room Temperature

Composite polymer electrolytes (CPEs) containing Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is widely regarded as leading candidate for high energy density solid-state lithium-metal batteries due to its exceptional ionic conductivity and environmental stability. However, Li2CO3 and LiOH layers at LLZTO surface greatly hinder Li+ transport between LLZTO-polymer and the electrode-electrolyte interface. Herein, the surface of LLZTO is boronized to obtain functionalized LLZTO, and its conversion mechanism is clarified. By dissolving the crystal structure of cellulose to obtain hopping-phase ion bridge (HPIB), which release the Li+ transport activity of its oxygen-containing polar functional group (─OH, ─O─). Therefore, a high-throughput ion transporter (HTIT-37) with high ion transfer number (0.86) is prepared by introducing the HPIB into functionalized LLZTO and polyvinylidene fluoride interface by intermolecular hydrogen bond interaction, and it is demonstrated that the HPIB acts as a "highway" for the Li+ across this heterogeneous interface. Moreover, the HPIB is found to self-adsorb on the SEI surface, leading to fast Li+ transport kinetics at anode-CPE interface. Thus, the lifespan of Li|HTIT-37|Li is over 8000 h, and the critical current density exceeds 2.3 mA cm-2. The LiNi0.5Co0.2Mn0.3O2|Li and Li1.2Ni0.13Co0.13Mn0.54O2|Li battery remains stable with the HPIB-enhanced electrode process, proving the application potential of LLZTO-based CPE in high energy density SSLMB.

A Gradient Solid-like Electrolyte Stabilizing Zn Anodes by In Situ Formation of a ZnSe Interphase

Rechargeable aqueous Zn-ion batteries are renowned for their safety, cost-effectiveness, environmental friendliness, and high capacity. However, critical issues, such as restricted electrode kinetics and uncontrolled dendrite growth of Zn anodes, have hindered their practical applications. Here, we propose a gradient solid-like electrolyte (GSLE) to enhance the overall performance of Zn anodes and Zn-ion batteries. It shows a high room-temperature conductivity of 13.3 mS cm-1 with an enhanced Zn2+ transference number of 0.67. With its negatively charged network, the GSLE establishes a Zn2+-rich region at the Zn|electrolyte interface, thereby boosting the interfacial charge transfer and accelerating electrode kinetics. Moreover, the GSLE in situ establishes a ZnSe-containing interphase on the surface of Zn anodes during cycling. Such an interphase effectively guides uniform Zn deposition and inhibits side reactions. As a result, symmetric cells using the GSLE demonstrate stabilized Zn plating/stripping cycling over 1400 h and tolerate a high critical current of 15 mA cm-2. Furthermore, the assembled vanadium-based full cells deliver a remarkable capacity of 125.4 mAh g-1 at 4 A g-1 and achieve a 90% capacity retention after 1000 cycles.

Significantly promoting the lithium-ion transport performances of MOFs-based electrolytes via a strategy of introducing fluoro groups in the crystal frameworks

Metal-organic frameworks (MOFs) with well-ordered channels are considered ideal solid-state electrolytes (SSEs) for lithium ionic conductors and are expected to be utilized in all-solid-state Li-ion batteries. However, the outstanding Li+ conductivity of MOFs, especially the properties at low temperatures, has become a crucial problem to overcome. Herein, a breakthrough is first realized to cope with this challenge via a strategy of introducing fluoro-substituted bridging ligands in MOFs. Benefiting from the fluorinated strategy in MOFs (Cu-MOF-F4), an outstanding Li+ conductivity of 1.16 × 10-3 S cm-1 at room temperature, a low activation energy of 0.15 eV, and a high transference number of 0.84 are achieved. In particular, Cu-MOF-F4 shows high conductivities of (0.15-2.99) × 10-3 S cm-1 in the temperature range of -40 to 110 °C. The proposed novel fluoro-substituted strategy of bridging ligands in MOFs is of great significance for developing high-performance SSEs for solid-state lithium batteries.

A triflate porous layer stabilizing Zn anodes for high-performance Zn-ion batteries

We meticulously designed a triflate porous layer on Zn anodes to enhance the overall performance of Zn-ion batteries. During battery operation, it stabilizes the surface pH of Zn anodes and facilitates the formation of a ZnF2-containing interphase. Therefore, both the reversibility and reaction kinetics of Zn anodes are effectively promoted.

Fast-Charging Solid-State Li Batteries: Materials, Strategies, and Prospects

The ability to rapidly charge batteries is crucial for widespread electrification across a number of key sectors, including transportation, grid storage, and portable electronics. Nevertheless, conventional Li-ion batteries with organic liquid electrolytes face significant technical challenges in achieving rapid charging rates without sacrificing electrochemical efficiency and safety. Solid-state batteries (SSBs) offer intrinsic stability and safety over their liquid counterparts, which can potentially bring exciting opportunities for fast charging applications. Yet realizing fast-charging SSBs remains challenging due to several fundamental obstacles, including slow Li+ transport within solid electrolytes, sluggish kinetics with the electrodes, poor electrode/electrolyte interfacial contact, as well as the growth of Li dendrites. This article examines fast-charging SSB challenges through a comprehensive review of materials and strategies for solid electrolytes (ceramics, polymers, and composites), electrodes, and their composites. In particular, methods to enhance ion transport through crystal structure engineering, compositional control, and microstructure optimization are analyzed. The review also addresses interface/interphase chemistry and Li+ transport mechanisms, providing insights to guide material design and interface optimization for next-generation fast-charging SSBs.

High-Strength MOF-Based Polymer Electrolytes with Uniform Ionic Flow for Lithium Dendrite Suppression

The uneven formation of lithium dendrites during electroplating/stripping leads to a decrease in the utilization of active lithium, resulting in poor cycling stability and posing safety hazards to the battery. Herein, introducing a 3D continuously interconnected zirconium-based metal-organic framework (MOF808) network into a polyethylene oxide polymer matrix establishes a synergistic mechanism for lithium dendrite inhibition. The 3D MOF808 network maintains its large pore structure, facilitating increased lithium salt accommodation, and expands anion adsorption at unsaturated metal sites through its diverse large-space cage structure, thereby promoting the flow of Li+. Infrared-Raman and synchrotron small-angle X-ray scattering results demonstrate that the transport behavior of lithium salt ion clusters at the MOF/polymer interface verifies the increased local Li+ flux concentration, thereby raising the mobility number of Li+ to 0.42 and ensuring uniform Li+ flux distribution, leading to dendrite-free and homogeneous Li+ deposition. Furthermore, nanoindentation tests reveal that the high modulus and elastic recovery of MOF-based polymer electrolytes contribute to forming a robust, dendrite-resistant interface. Consequently, in symmetric battery systems, the system exhibits minimal overpotential, merely 35 mV, while maintaining stable cycling for over 1800 h, achieving low-overpotential lithium deposition. Moreover, it retains redox stability under high voltages up to 5.3 V.

A "Zn2+ in Salt" Interphase Enabling High-Performance Zn Metal Anodes

Zinc metal is a promising anode candidate for aqueous zinc ion batteries due to its high theoretical capacity, low cost, and high safety. However, its application is currently restricted by hydrogen evolution reactions (HER), by-product formation, and Zn dendrite growth. Herein, a "Zn2+ in salt" (ZIS) interphase is in situ constructed on the surface of the anode (ZIS@Zn). Unlike the conventional "Zn2+ in water" working environment of Zn anodes, the intrinsic hydrophobicity of the ZIS interphase isolates the anode from direct contact with the aqueous electrolyte, thereby protecting it from HER, and the accompanying side reactions. More importantly, it works as an ordered water-free ion-conducting medium, which guides uniform Zn deposition and facilitates rapid Zn2+ migration at the interface. As a result, the symmetric cells assembled with ZIS@Zn exhibit dendrite-free plating/striping at 4500 h and a high critical current of 14 mA cm-2. When matched with a vanadium-based (NVO) cathode, the full battery exhibits excellent long-term cycling stability, with 88% capacity retention after 1600 cycles. This work provides an effective strategy to promote the stability and reversibility of Zn anodes in aqueous electrolytes.

A fluorinated metal-organic framework-based quasi-solid electrolyte for stabilizing Li metal anodes

A fluorinated quasi-solid electrolyte (QSE) with a high conductivity of 2.3 mS cm-1 is meticulously designed for Li metal batteries. It facilitates the formation of a LiF-rich solid electrolyte interface that effectively enhances the reversibility of Li anodes. The assembled Li|QSE|LiFePO4 batteries exhibit 92.3% capacity retention after 1500 cycles and an impressive capacity of up to 45 mA h g-1 at 20C.

Super-Ionic Conductor Soft Filler Promotes Li+ Transport in Integrated Cathode-Electrolyte for Solid-State Battery at Room Temperature

Composite polymer solid electrolytes (CPEs), possessing good rigid flexible, are expected to be used in solid-state lithium-metal batteries. The integration of fillers into polymer matrices emerges as a dominant strategy to improve Li+ transport and form a Li+-conducting electrode-electrolyte interface. However, challenges arise as traditional fillers: 1) inorganic fillers, characterized by high interfacial energy, induce agglomeration; 2) organic fillers, with elevated crystallinity, impede intrinsic ionic conductivity, both severely hindering Li+ migration. Here, a concept of super-ionic conductor soft filler, utilizing a Li+ conductivity nanocellulose (Li-NC) as a model, is introduced which exhibits super-ionic conductivity. Li-NC anchors anions, and enhances Li+ transport speed, and assists in the integration of cathode-electrolyte electrodes for room temperature solid-state batteries. The tough dual-channel Li+ transport electrolyte (TDCT) with Li-NC and polyvinylidene fluoride (PVDF) demonstrates a high Li+ transfer number (0.79) due to the synergistic coordination mechanism in Li+ transport. Integrated electrodes' design enables stable performance in LiNi0.5Co0.2Mn0.3O2|Li cells, with 720 cycles at 0.5 C, and 88.8% capacity retention. Furthermore, the lifespan of Li|TDCT|Li cells over 4000 h and Li-rich Li1.2Ni0.13Co0.13Mn0.54O2|Li cells exhibits excellent performance, proving the practical application potential of soft filler for high energy density solid-state lithium-metal batteries at room temperature.

Recent progress and perspectives on metal-organic frameworks as solid-state electrolytes for lithium batteries

Solid-state electrolytes (SSEs) are the key materials in the new generation of all-solid-state lithium ion/metal batteries. Metal-organic frameworks (MOFs) are ideal materials for developing solid electrolytes because of their structural diversity and porous properties. However, there are several significant issues and obstacles involved, such as lower ion conductivity, a smaller ion transport number, a narrower electrochemical stability window and poor interface contact. In this review, a comprehensive analysis and summary of the unique ion-conducting behavior of MOF-based electrolytes in rechargeable batteries are presented, and the different design principles of MOF-based SSEs are classified and emphasized. Accordingly, four design principles for achieving these MOF-based SSEs are presented and the influence of SSEs combined with MOFs on the electrochemical performance of the batteries is described. Finally, the challenges in the application of MOF materials in lithium ion/metal batteries are explored, and directions for future research on MOF-based electrolytes are proposed. This review will deepen the understanding of MOF-based electrolytes and promote the development of high-performance solid-state lithium ion/metal batteries. This review not only provides theoretical guidance for research on new MOF-based SSE systems, but also contributes to further development of MOFs applied to rechargeable batteries.