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"Fluorination"
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Contemporary synthetic strategies in organofluorine chemistry
This PrimeView describes novel fluorination and fluoroalkylation techniques and the key considerations for their use, and highlights the range of applications for fluorinated molecules in society.
Journal Article
Tetramethylammonium Fluoride: Fundamental Properties and Applications in C-F Bond-Forming Reactions and as a Base
Nucleophilic ionic sources of fluoride are essential reagents in the synthetic toolbox to access high added-value fluorinated building blocks unattainable by other means. In this review, we provide a concise description and rationale of the outstanding features of one of these reagents, tetramethylammonium fluoride (TMAF), as well as disclosing the different methods for its preparation, and how its physicochemical properties and solvation effects in different solvents are intimately associated with its reactivity. Furthermore, herein we also comprehensively describe its historic and recent utilization, up to December 2021, in C-F bond-forming reactions with special emphasis on nucleophilic aromatic substitution fluorinations with a potential sustainable application in industrial settings, as well as its use as a base capable of rendering unprecedented transformations.
Journal Article
Over 16% efficiency organic photovoltaic cells enabled by a chlorinated acceptor with increased open-circuit voltages
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency.
Halogenation has proved an effective strategy to improve the power conversion efficiencies of organic solar cells but it usually leads to lower open-circuit voltages. Here, Cui et al. unexpectedly obtain higher open-circuit voltages and achieve a record high PCE of 16.5% by chlorination.
Journal Article
Fluorinated ether electrolyte with controlled solvation structure for high voltage lithium metal batteries
The development of new solvents is imperative in lithium metal batteries due to the incompatibility of conventional carbonate and narrow electrochemical windows of ether-based electrolytes. Whereas the fluorinated ethers showed improved electrochemical stabilities, they can hardly solvate lithium ions. Thus, the challenge in electrolyte chemistry is to combine the high voltage stability of fluorinated ethers with high lithium ion solvation ability of ethers in a single molecule. Herein, we report a new solvent, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane (DTDL), combining a cyclic fluorinated ether with a linear ether segment to simultaneously achieve high voltage stability and tune lithium ion solvation ability and structure. High oxidation stability up to 5.5 V, large lithium ion transference number of 0.75 and stable Coulombic efficiency of 99.2% after 500 cycles proved the potential of DTDL in high-voltage lithium metal batteries. Furthermore, 20 μm thick lithium paired LiNi
0.8
Co
0.1
Mn
0.1
O
2
full cell incorporating 2 M LiFSI-DTDL electrolyte retained 84% of the original capacity after 200 cycles at 0.5 C.
The development of lithium-metal batteries is limited by the low thermodynamic and/or low voltage stability of conventional electrolytes. Here, the authors combined the high voltage stability of fluorinated ethers with high Li
+
solvation ability of ethers in a single molecule and realized highly stable lithium-metal batteries.
Journal Article
Orientated crystallization of FA-based perovskite via hydrogen-bonded polymer network for efficient and stable solar cells
Incorporating mixed ion is a frequently used strategy to stabilize black-phase formamidinum lead iodide perovskite for high-efficiency solar cells. However, these devices commonly suffer from photoinduced phase segregation and humidity instability. Herein, we find that the underlying reason is that the mixed halide perovskites generally fail to grow into homogenous and high-crystalline film, due to the multiple pathways of crystal nucleation originating from various intermediate phases in the film-forming process. Therefore, we design a multifunctional fluorinated additive, which restrains the complicated intermediate phases and promotes orientated crystallization of α-phase of perovskite. Furthermore, the additives in-situ polymerize during the perovskite film formation and form a hydrogen-bonded network to stabilize α-phase. Remarkably, the polymerized additives endow a strongly hydrophobic effect to the bare perovskite film against liquid water for 5 min. The unencapsulated devices achieve 24.10% efficiency and maintain >95% of the initial efficiency for 1000 h under continuous sunlight soaking and for 2000 h at air ambient of ~50% humid, respectively.
Formamidinum lead iodide perovskite solar cells commonly suffer from photoinduced phase segregation and humidity instability. Here, the authors design a multifunctional fluorinated additive to promote orientated crystallization of α-phase, and achieve maximum efficiency of 24.1% and T95 over 1000 h.
Journal Article
Efficient Stereo-Selective Fluorination on Vitamin Dsub.3 Side-Chain Using Electrophilic Fluorination
Our research regarding side-chain fluorinated vitamin D[sub.3] analogues has explored a series of efficient fluorination methods. In this study, a new electrophilic stereo-selective fluorination methodology at C24 and C22 positions of the vitamin D[sub.3] side-chain was developed using N-fluorobenzenesulfonimide (NFSI) and CD-ring imides with an Evans chiral auxiliary (26,27,30).
Journal Article
Electrolyte engineering via ether solvent fluorination for developing stable non-aqueous lithium metal batteries
Fluorination of ether solvents is an effective strategy to improve the electrochemical stability of non-aqueous electrolyte solutions in lithium metal batteries. However, excessive fluorination detrimentally impacts the ionic conductivity of the electrolyte, thus limiting the battery performance. Here, to maximize the electrolyte ionic conductivity and electrochemical stability, we introduce the targeted trifluoromethylation of 1,2-dimethoxyethane to produce 1,1,1-trifluoro-2,3-dimethoxypropane (TFDMP). TFDMP is used as a solvent to prepare a 2 M non-aqueous electrolyte solution comprising bis(fluorosulfonyl)imide salt. This electrolyte solution shows an ionic conductivity of 7.4 mS cm
–1
at 25 °C, an oxidation stability up to 4.8 V and an efficient suppression of Al corrosion. When tested in a coin cell configuration at 25 °C using a 20 μm Li metal negative electrode, a high mass loading LiNi
0.8
Co
0.1
Mn
0.1
O
2
-based positive electrode (20 mg cm
–2
) with a negative/positive (N/P) capacity ratio of 1, discharge capacity retentions (calculated excluding the initial formation cycles) of 81% after 200 cycles at 0.1 A g
–1
and 88% after 142 cycles at 0.2 A g
–1
are achieved.
Fluorination of solvents, useful for non-aqueous lithium-based batteries, improves the electrochemical stability but decreases the ionic conductivity. Here, the authors report a targeted functionalization of an ether solvent to balance the electrolyte ionic conductivity and oxidative stability.
Journal Article
Methylation enables the use of fluorine-free ether electrolytes in high-voltage lithium metal batteries
Lithium metal batteries represent a promising technology for next-generation energy storage, but they still suffer from poor cycle life due to lithium dendrite formation and cathode cracking. Fluorinated solvents can improve battery longevity by improving LiF content in the solid–electrolyte interphase; however, the high cost and environmental concerns of fluorinated solvents limit battery viability. Here we designed a series of fluorine-free solvents through the methylation of 1,2-dimethoxyethane, which promotes inorganic LiF-rich interphase formation through anion reduction and achieves high oxidation stability. The anion-derived LiF interphases suppress lithium dendrite growth on the lithium anode and minimize cathode cracking under high-voltage operation. The Li
+
-solvent structure is investigated through in situ techniques and simulations to draw correlations between the interphase compositions and electrochemical performances. The methylation strategy provides an alternative pathway for electrolyte engineering towards high-voltage electrolytes while reducing dependence on expensive fluorinated solvents.
Lithium metal batteries are an attractive energy storage technology, but their development relies on the complex interplay between the components’ chemical, physical and mechanical properties. Now, selective methylation of dimethoxyethane ether electrolytes is shown to improve electrolyte, electrode and solid–electrolyte interphase stabilities to enable high-performance 4.3 V lithium metal batteries.
Journal Article
Durable superhydrophobic coatings for prevention of rain attenuation of 5G/weather radomes
Superhydrophobic coatings are expected to solve the rain attenuation issue of 5G radomes. However, it is very challenging to design and construct such superhydrophobic coatings with good impalement resistance, mechanical robustness, and weather resistance, which remains as one of the main bottlenecks hindering their practical applications. Here, we report the design of superhydrophobic coatings with all these merits mentioned above by spray-coating a suspension of adhesive/fluorinated silica core/shell microspheres onto substrates. The core/shell microspheres are formed by phase separation of the adhesive and adhesion between the adhesive and fluorinated silica nanoparticles. The coatings have an approximately isotropic three-tier hierarchical micro-/micro-/nanostructure, a dense but rough surface at the nanoscale, and chemically inert composition with low surface energy. Consequently, the coatings show excellent impalement resistance, mechanical robustness and weather resistance compared with previous studies, and the mechanisms are revealed. Furthermore, we realize large-scale preparation, extension, and practical application of the coatings for efficiently preventing rain attenuation of 5G/weather radomes. By taking these advantages, we believe that the superhydrophobic coatings have great application potential and market prospect. The findings here will boost preparation and real-world applications of superhydrophobic coatings.
Good impalement resistance, mechanical robustness and weather resistance are essential for applications of superhydrophobic coatings. Here, the authors achieve scalable preparation and practical application of robust superhydrophobic coatings for preventing rain attenuation of 5G/weather radomes.
Journal Article