Molten Guest-Mediated Metal-Organic Frameworks Featuring Multi-Modal Supramolecular Interaction Sites for Flame-Retardant Superionic Conductor in All-Solid-State Batteries

The development of solid-state electrolytes (SSEs) with outstanding comprehensive performance is currently a critical challenge for achieving high energy density and safer solid-state batteries (SSBs). In this study, a strategy of nano-confined in situ solidification is proposed to create a novel category of molten guest-mediated metal-organic frameworks, named MGM-MOFs. By embedding the newly developed molten crystalline organic electrolyte (ML20) into the nanocages of anionic MOF-OH, MGM-MOF-OH, characterized by multi-modal supramolecular interaction sites and continuous negative electrostatic environments within nano-channels, is achieved. These nanochannels promote ion transport through the successive hopping of Li+ between neighbored negative electrostatic environments and suppress anion movement through the chemical constraint of the hydroxyl-functionalized pore wall. This results in remarkable Li+ conductivity of 7.1 × 10-4 S cm-1 and high Li+ transference number of 0.81. Leveraging these advantages, the SSBs assembled with MGM-MOF-OH exhibit impressive cycle stability and a high specific energy density of 410.5 Wh kganode + cathode + electrolyte -1 under constrained conditions and various working temperatures. Unlike flammable traditional MOFs, MGM-MOF-OH demonstrates high robustness under various harsh conditions, including ignition, high voltage, and extended to humidity.

From Liquid to Solid-State Batteries: Li-Rich Mn-Based Layered Oxides as Emerging Cathodes with High Energy Density

Li-rich Mn-based (LRMO) cathode materials have attracted widespread attention due to their high specific capacity, energy density, and cost-effectiveness. However, challenges such as poor cycling stability, voltage deca,y and oxygen escape limit their commercial application in liquid Li-ion batteries. Consequently, there is a growing interest in the development of safe and resilient all-solid-state batteries (ASSBs), driven by their remarkable safety features and superior energy density. ASSBs based on LRMO cathodes offer distinct advantages over conventional liquid Li-ion batteries, including long-term cycle stability, thermal and wider electrochemical windows stability, as well as the prevention of transition metal dissolution. This review aims to recapitulate the challenges and fundamental understanding associated with the application of LRMO cathodes in ASSBs. Additionally, it proposes the mechanisms of interfacial mechanical and chemical instability, introduces noteworthy strategies to enhance oxygen redox reversibility, enhances high-voltage interfacial stability, and optimizes Li+ transfer kinetics. Furthermore, it suggests potential research approaches to facilitate the large-scale implementation of LRMO cathodes in ASSBs.

Strategies Based on Nitride Materials Chemistry to Stabilize Li Metal Anode

Lithium metal battery is a promising candidate for high-energy-density energy storage. Unfortunately, the strongly reducing nature of lithium metal has been an outstanding challenge causing poor stability and low coulombic efficiency in lithium batteries. For decades, there are significant research efforts to stabilize lithium metal anode. However, such efforts are greatly impeded by the lack of knowledge about lithium-stable materials chemistry. So far, only a few materials are known to be stable against Li metal. To resolve this outstanding challenge, lithium-stable materials have been uncovered out of chemistry across the periodic table using first-principles calculations based on large materials database. It is found that most oxides, sulfides, and halides, commonly studied as protection materials, are reduced by lithium metal due to the reduction of metal cations. It is discovered that nitride anion chemistry exhibits unique stability against Li metal, which is either thermodynamically intrinsic or a result of stable passivation. The results here establish essential guidelines for selecting, designing, and discovering materials for lithium metal protection, and propose multiple novel strategies of using nitride materials and high nitrogen doping to form stable solid-electrolyte-interphase for lithium metal anode, paving the way for high-energy rechargeable lithium batteries.