Rational Lithium Salt Molecule Tuning for Fast Charging/Discharging Lithium Metal Battery.

The electrolytes for lithium metal batteries (LMBs) are plagued by a low Li+ transference number (T+) of conventional lithium salts and inability to form a stable solid electrolyte interphase (SEI). Here, we synthesized a self-folded lithium salt, lithium 2-[2-(2-methoxy ethoxy)ethoxy]ethanesulfonyl(trifluoromethanesulfonyl) imide (LiETFSI), and comparatively studied with its structure analogue, lithium 1,1,1-trifluoro-N-[2-[2-(2-methoxyethoxy)ethoxy)]ethyl]methanesulfonamide (LiFEA). The special anion chemistry imparts the following new characteristics: i) In both LiFEA and LiETFSI, the ethylene oxide moiety efficiently captures Li+, resulting in a self-folded structure and high T+ around 0.8. ii) For LiFEA, a Li-N bond (2.069 Å) is revealed by single crystal X-ray diffraction, indicating that the FEA anion possesses a high donor number (DN) and thus an intensive interphase "self-cleaning" function for an ultra-thin and compact SEI. iii) Starting from LiFEA, an electron-withdrawing sulfone group is introduced near the N atom. The distance of Li-N is tuned from 2.069 Šin LiFEA to 4.367 Šin LiETFSI. This alteration enhances ionic separation, achieves a more balanced DN, and tunes the self-cleaning intensity for a reinforced SEI. Consequently, the fast charging/discharging capability of LMBs is progressively improved. This rationally tuned anion chemistry reshapes the interactions among Li+, anions, and solvents, presenting new prospects for advanced LMBs.

Asymmetric Trihalogenated Aromatic Lithium Salt Induced Lithium Halide Rich Interface for Stable Cycling of All-Solid-State Lithium Batteries.

Solid polymer electrolytes (SPEs) are the key components for all-solid-state lithium metal batteries with high energy density and intrinsic safety. However, the low lithium ion transference number (t+) of a conventional SPE and its unstable electrolyte/electrode interface cannot guarantee long-term stable operation. Herein, asymmetric trihalogenated aromatic lithium salts, i.e., lithium (3,4,5-trifluorobenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiFFF) and lithium (4-bromo-3,5-difluorobenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiFBF), are synthesized for polymer electrolytes. They exhibit higher t+ values and better compatibility with Li metal than conventional lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Due to the trihalogenated aromatic anions, LiFFF- and LiFBF-based electrolytes are prone to generate an LiF- and LiBr-rich solid electrolyte interphase (SEI), therefore increasing the stability of the solid electrolyte/anode interface. Particularly, LiFBF could induce a LiF/LiBr hybrid SEI, where LiF shows a high Young's modulus and high surface energy for homogenizing Li ion flux and LiBr exhibits an extremely low Li ion diffusion barrier in the SEI layer. As a result, the Li/Li symmetric cells could remain stable for more than 1200 h without a short circuit and the LiFePO4/Li batteries showed superb electrochemical performance over 1200 cycles at 1 C. This work provides valuable insights from the perspective of lithium salt molecular structures for high-performance all-solid-state lithium metal batteries.

Tuning and Balancing the Donor Number of Lithium Salts and Solvents for High-Performance Li Metal Anode.

The low reversibility of Li deposition/stripping in conventional carbonate electrolytes hinders the development of lithium metal batteries. Herein, we proposed a combination of solvents with a moderate donor number (DN) and LiNO3 as the sole salt, which has rarely been attempted due to its low solubility or dissociation degree in common solvents. It is found that the DN value of solvents is highly correlated to the reversibility of Li deposition behavior when LiNO3 is applied as the sole salt. The combination of LiNO3 and solvents with moderate DN behaves like a quasi-concentrated electrolyte even at a common or moderate concentration, while neither the solvents with poor solubility and low dissociation for LiNO3 (which usually corresponds to a low DN) nor the solvents with high dissociation for LiNO3 (which usually corresponds to an overly high DN) can achieve a high reversibility for low conductivity or excessive solvent decomposition. As a result, a Coulombic efficiency as high as 99.6% for Li deposition/stripping is achieved with the optimized combination. We believe this work will give a better understanding of the role of anions and solvents in the regulation of the solvation structure, and DN can be utilized as an important guideline to sieve suitable solvents for LiNO3 as the main salt to exhibit intriguing properties beyond traditional cognition.

Fluorinated Carbamate-Based Electrolyte Enables Anion-Dominated Solid Electrolyte Interphase for Highly Reversible Li Metal Anode.

Li metal is regarded as the most promising battery anode to boost energy density. However, being faced with the hostile compatibility between the Li anode and traditional carbonate electrolyte, its large-scale industrialization has been in a distressing circumstance due to severe dendrite growth caused by unsatisfying solid electrolyte interphase (SEI). With this regard, accurate control over the composition of the SEI is urgently desired to tackle the electrochemical and mechanical instability at the electrolyte/anode interface. Herein, we report a rationally designed fluorinated carbamate-based electrolyte employing LiNO3 as one of the main salts to induce the preferable anion decomposition to achieve a homogeneous and inorganic (LiF, Li3N, Li2O)-rich SEI. Thus, this electrolyte achieves a high Coulombic efficiency of 99% of the Li metal anode, a stable cycling over 1000 h for Li|Li symmetric cells, more than 100 cycles in 40-µm-thin Li|high-loading-NCM811 full batteries, and >50 cycles in Cu|LiFePO4 pouch cells, which is a promising electrolyte for highly reversible Li metal batteries.

Tuning the Li+ Solvation Structure by a "Bulky Coordinating" Strategy Enables Nonflammable Electrolyte for Ultrahigh Voltage Lithium Metal Batteries.

In battery electrolyte design principles, tuning Li+ solvation structure is an effective way to connect electrolyte chemistry with interfacial chemistry. Although recent proposed solvation tuning strategies are able to improve battery cyclability, a comprehensive strategy for electrolyte design remains imperative. Here, we report a solvation tuning strategy by utilizing molecular steric effect to create a "bulky coordinating" structure. Based on this strategy, the designed electrolyte generates an inorganic-rich solid electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI), leading to excellent compatibility with both Li metal anodes and high-voltage cathodes. Under an ultrahigh voltage of 4.6 V, Li/NMC811 full-cells (N/P = 2.0) hold an 84.1% capacity retention over 150 cycles and industrial Li/NMC811 pouch cells realize an energy density of 495 Wh kg-1. This study provides innovative insights into Li+ solvation tuning for electrolyte engineering and offers a promising path toward developing high-energy Li metal batteries.

Towards ambient temperature operation of Li metal batteries using UV-Crosslinked single-ion electrospun electrolytes.

In spite of the fact that lithium metal batteries (LMBs) facilitate the diversification of energy storage technologies, their electrochemical reversibility and stability have long been constrained by side reactions and lithium dendrite problems. While single-ion conducting polymer electrolytes (SICPEs) possess unique advantages of suppressing Li dendrite growth, they deal with difficulties in practical applications due to their slow ion transport in general application scenarios at âˆ¼25 °C. In this study, we develop novel bifunctional lithium salts with negative sulfonylimide (-SO2N(-)SO2-) anions mounted between two styrene reactive groups, which is capable of constructing 3D cross-linked networks with multiscale reticulated ion nanochannels, resulting in the uniform and rapid distribution of Li+ ions in the crosslinked electrolyte. To verify the feasibility of our strategy, we designed PVDF-HFP-based SICPEs and the obtained electrolyte exhibits high thermal stability, outstanding Li+ transference number (0.95), pleasing ionic conductivity (0.722 mS cm-1), and broad chemical window (greater than5.85 V) at ambient temperature. As a result of the electrolyte structural merits, the Li||LFP cells displayed excellent cycling stability (96.4% reversible capacities after 300 cycles at 0.2C) without additional auxiliary heating. This ingenious strategy is expected to providing a new perspective for advanced performance and high safety LMBs.

A Fluorinated Covalent Organic Framework with Accelerated Oxygen Transfer Nanochannels for High-Performance Zinc-Air Batteries.

The establishment of abundant three-phase interfaces with accelerated mass transfer in air cathodes is highly desirable for the development of high-rate and long-cycling rechargeable zinc-air batteries (ZABs). Covalent organic frameworks (COFs) exhibit tailored nanopore structures, facilitating the rational tuning of their specific properties. Here, by finely tuning the fluorinated nanopores of a COF, a novel air cathode for rechargeable ZABs is unprecedentedly designed and synthesized. COF nanosheets are decorated with fluorinated alkyl chains, which shows high affinity to oxygen (O2 ), in its nanopores (fluorinated COF). The fluorinated COF nanosheets are stacked into well-defined O2 -transport channels, which are then assembled into aerophilic "nano-islands" on the hydrophilic FeNi layered-double-hydroxide (FeNi LDH) electrocatalyst surface. Therefore, the mass-transport "highway" for O2 and water is segregated on the nanoscale, which significantly enlarges the area of three-phase boundaries and greatly promotes the mass-transfer therein. ZABs based on the COF-modified air cathode deliver a small charge/discharge voltage gap (0.64 V at 5 mA cm-2 ), a peak power density (118 mW cm-2 ), and a stable cyclability. This work provides a feasible approach for the design of the air cathodes for high-performance ZABs, and will expand the new application of COFs.

Nanoemulsion-Coated Ni-Fe Hydroxide Self-Supported Electrode as an Air-Breathing Cathode for High-Performance Zinc-Air Batteries.

To improve the energy conversion efficiency and durability of zinc-air batteries (ZABs) for large-scale implementations, here we propose an "air-breathing" strategy to significantly enlarge triple-interfaces with intensified mass transfer. By dip-coating the aerophilic perfluorochemical compounds (PFC) and amphiphilic ionomers into the self-supported electrodes, (1) the high solubility of O2 in the PFC nanoemulsions greatly increases triple-phase boundaries and facilitates the efficient supply/removal of O2 from the electrolyte; (2) the ionomers with hydrophobic and hydrophilic functionalities enable fast gas, water, and ion transport to the triple-phase boundaries; and (3) the self-supported electrode without binder ensures fast electron transfer while the firm integration prevents catalyst shedding. By applying this strategy, the ZABs show a high power density of 115 mW cm-2 and a narrow discharge/charge gap of 0.64 V at 10 mA cm-2 and a long-cycling durability (over 1000 h). This work provides a universal approach to promote gas-evolving reactions for electrochemical applications.

Strategies for the application of metal-organic frameworks in catalytic reactions.

Efficient catalysts play crucial roles in various organic reactions and polymerization. Metal-organic frameworks (MOFs) have the merits of ultrahigh porosity, large surface area, dispersed polymetallic sites and modifiable linkers, which make them promising candidates for catalyzation. This review primarily summarizes the recent research progress on diverse strategies for tailoring MOFs that are endowed with excellent catalytic behavior. These strategies include utilizing MOFs as nanosized reaction channels, metal nodes decorated as catalytic active sites and the modification of ligands or linkers. All these make them highly attractive to various applications, especially in catalyzing organic reactions or polymerizations and they have proven to be effective catalysts for a wide variety of reactions. MOFs are still an evolving field with tremendous prospects; therefore, through the research and development of more modification and regulation strategies, MOFs will realize their wider practical application in the future.

Revealing the Sole Impact of Acceptor's Molecular Conformation to Energy Loss and Device Performance of Organic Solar Cells through Positional Isomers.

Two new fused-ring electron acceptor (FREA) isomers with nonlinear and linear molecular conformation, m-BAIDIC and p-BAIDIC, are designed and synthesized. Despite the similar light absorption range and energy levels, the two isomers exhibit distinct electron reorganization energies and molecular packing motifs, which are directly related to the molecular conformation. Compared with the nonlinear acceptor, the linear p-BAIDIC shows more ordered molecular packing and higher crystallinity. Furthermore, p-BAIDIC-based devices exhibit reduced nonradiative energy loss and improved charge transport mobilities. It is beneficial to enhance the open-circuit voltage (VOC ) and short-current current density (JSC ) of the devices. Therefore, the linear FREA, p-BAIDIC yields a relatively higher efficiency of 7.71% in the binary device with PM6, in comparison with the nonlinear m-BAIDIC. When p-BAIDIC is incorporated into the binary PM6/BO-4Cl system to form a ternary system, synergistic enhancements in VOC , JSC , fill factor (FF), and ultimately a high efficiency of 17.6% are achieved.

Unprecedented Application of Covalent Organic Frameworks for Polymerization Catalysis: Rh/TPB-DMTP-COF in Polymerization of Phenylacetylene and Its Functional Derivatives.

Covalent organic frameworks (COFs) are applied widely in organic catalysis; however, no precedent has been reported in polymerization catalysis. Herein, we report the new application of COFs for polymerization catalysis. Different amounts of homogeneous Rh catalyst are incorporated into the COF via post-treatment to give a series of TPB-DMTP-COF-X wt % Rh (b-e) containing varying amounts of Rh from 2.74 to 11.38 wt %. In contrast to the known Rh catalysts, TPB-DMTP-COF-X wt % Rh (b-e) display an uncommon synergistic effect and exceptional steric confinement effect of nanochannels. Therefore, they possess the advantages of both homogeneous catalysts in high activity and selectivity and heterogeneous catalysts in stability and recyclability with extremely high activity up to 1.3 × 107 g·molRh-1·h-1 and cis-selectivity up to 99% and can be readily recycled and reused five times in the polymerization of phenylacetylene and its derivatives, affording cis-transoidal polyphenylacetylene and its derivatives having helical structures, aggregation-induced emission properties, or fluorescence properties with narrow molecular weight distributions.