Synergistically Engineering Grains and Grain Boundaries toward Li Dendrite-Free Li7La3Zr2O12.

Cation-doped cubic Li7La3Zr2O12 is regarded as a promising solid electrolyte for safe and energy-dense solid-state lithium batteries. However, it suffers from the formation of Li2CO3 and high electronic conductivity, which give rise to an unconformable Li/Li7La3Zr2O12 interface and lithium dendrites. Herein, composite AlF3-Li6.4La3Zr1.4Ta0.6O12 solid electrolytes were created based on thermal AlF3 decomposition and F/O displacement reactions under a high-temperature sintering process. When the AlF3 is thermally decomposed, it leaves Al2O3/AlF3 meliorating the grain boundaries and F- ions partially displacing O2- ions in the grains. Due to the higher electronegativity of F- in the grains and the grain-boundary modification, these AlF3-Li6.4La3Zr1.4Ta0.6O12 deliver optimized electronic conduction and chemical stability against the formation of Li2CO3. The Li/AlF3-Li6.4La3Zr1.4Ta0.6O12/Li cell exhibits a low interfacial resistance of ∼16 Ω cm2 and an ultrastable long-term cycling behavior for 800 h under a current density of 200 µA/cm2, leading to Li//LiCoO2 solid-state batteries with good rate performance and cycling stability.

Tuning [VO6] Octahedron of Ammonium Vanadates via F Incorporation for High-Performance Aqueous Zinc Ion Batteries.

The electrochemical properties of vanadium-based materials as cathode materials for aqueous zinc ion batteries are still restricted by low conductivity, sluggish reaction kinetics, and poor structural stability. Herein, the [VO6] octahedron, as the basic unit of vanadium-oxide layer of ammonium vanadates (NH4V4O10, denoted as NVO), is incorporated by F atoms to regulate the coordinated environment of vanadium. Density functional theory (DFT) calculations and experimental results show that both physicochemical and electrochemical properties of NVO are improved by F-doping. The enhanced electronic conductivity accelerates the electron transfer and the expanded interlayer spacing expedites the diffusion kinetics of zinc ions. As a result, the F-doped NVO (F-NVO) electrode shows a high discharge capacity (465 mAh g-1 at 0.1 A g-1), good rate capability (260 mAh g-1 at 5 A g-1), and long-term cycling stability (88% capacity retention over 2000 cycles at 4 A g-1). The reaction kinetics and energy storage mechanism of F-NVO are further validated by in situ and ex situ characterizations.

Fluorinated Surface Engineering Towards High-Rate and Durable Potassium-Ion Battery.

Solid electrolyte interphase (SEI) crucially affects the rate performance and cycling lifespan, yet to date more extensive research is still needed in potassium-ion batteries. We report an ultra-thin and KF-enriched SEI triggered by tuned fluorinated surface design in electrode. Our results reveal that fluorination engineering alters the interfacial chemical environment to facilitate inherited electronic conductivity, enhance adsorption ability of potassium, induce localized surface polarization to guide electrolyte decomposition behavior for SEI formation, and especially, enrich the KF crystals in SEI by self-sacrifice from C-F bond cleavage. Hence, the regulated fluorinated electrode with generated ultra-thin, uniform, and KF-enriched SEI shows improved capacity of 439.3 mAh g-1 (3.82 mAh cm-2), boosted rate performance (202.3 mAh g-1 at 8.70 mA cm-2) and durable cycling performance (even under high loading of ~8.7 mg cm-2). We expect this practical engineering principle to open up new opportunities for upgrading the development of potassium-ion batteries.

Initiating Fluorine Chemistry in Polycyclic Aromatic Hydrocarbon-Derived Carbon for New Cluster-Mode Na Storage with Superhigh Capacity.

Carbon materials are widely accepted as promising candidates for sodium-ion batteries (SIBs) anodes due to their chemical stability and conductivity, while the capacity is still unsatisfactory. Here, this work reports the superhigh capacity Na storage through initiating fluorine chemistry (CF bonds) in carbon synthesized by the dehydrogenation and fluorination of polycyclic aromatic hydrocarbon such as pitch. Experimental and theoretical investigations uncover that CF bonds exist at the form of dangling bonds (CFx ), which generates the coexistence of graphitic and defective nanodomains. It delivers a superhigh capacity of 450 mAh g-1 , far surpassing most of current SIBs carbon anodes. Theoretical calculation attributes this performance to a new Na storage mechanism that Na can be accommodated in the form of cluster rather than a single ion at each host site with F-doping. This work highlights the significance of carbon material chemistry in establishing the novel ion storage manner in SIBs and other batteries.

Recent Advances on F-Doped Layered Transition Metal Oxides for Sodium Ion Batteries.

With the development of social economy, using lithium-ion batteries in energy storage in industries such as large-scale electrochemical energy storage systems will cause lithium resources to no longer meet demand. As such, sodium ion batteries have become one of the effective alternatives to LIBs. Many attempts have been carried out by researchers to achieve this, among which F-doping is widely used to enhance the electrochemical performance of SIBs. In this paper, we reviewed several types of transition metal oxide cathode materials, and found their electrochemical properties were significantly improved by F-doping. Moreover, the modification mechanism of F-doping has also been summed up. Therefore, the application and commercialization of SIBs in the future is summarized in the ending of the review.

Stable Lead-Free Tin Halide Perovskite with Operational Stability >1200 h by Suppressing Tin(II) Oxidation.

Sn-based perovskites are the most promising alternative materials for Pb-based perovskites to address the toxicity problem of lead. However, the development of SnII -based perovskites has been hindered by their extreme instability. Here, we synthesized efficient and stable lead-free Cs4 SnBr6 perovskite by using SnF2 as tin source instead of easily oxidized SnBr2 . The SnF2 configures a fluorine-rich environment, which can not only suppress the oxidation of Sn2+ in the synthesis, but also construct chemically stable Sn-F coordination to hinder the electron transfer from Sn2+ to oxygen within the long-term operation process. The SnF2 -derived Cs4 SnBr6 perovskite shows a high photoluminescence quantum yield of 62.8 %, and excellent stability against oxygen, moisture, and light radiation for 1200 h, representing one of the most stable lead-free perovskites. The results pave a new pathway to enhance the optical properties and stability of lead-free perovskite for high-performance light emitters.

Boosting the Cycling Stability of Aqueous Flexible Zn Batteries via F Doping in Nickel-Cobalt Carbonate Hydroxide Cathode.

Cathodes of rechargeable Zn batteries typically face the issues of irreversible phase transformation, structure collapse, and volume expansion during repeated charge/discharge cycles, which result in an increased transfer resistance and poor long-term cycling stability. Herein, a facile F doping strategy is developed to boost the cycling stability of nickel cobalt carbonate hydroxide (NiCo-CH) cathode. Benefiting from the extremely high electronegativity, the phase and morphology stabilities as well as the electrical conductivity of NiCo-CH are remarkably enhanced by F incorporation (NiCo-CH-F). Phase interface and amorphous microdomains are also introduced, which are favorable for the electrochemical performance of cathode. Benefiting from these features, NiCo-CH-F delivers a high capacity (245 mA h g-1 ), excellent rate capability (64% retention at 8 A g-1 ), and outstanding cycling stability (maintains 90% after 10 000 cycles). Moreover, the quasi-solid-state battery also manifests superior cycling stability (maintains 90% after 7200 cycles) and desirable flexibility. This work offers a general strategy to boost the cycling stability of cathode materials for aqueous Zn batteries.

Enabling Ultrastable Co-Free Li-Rich Oxides via TbF3 Treatment.

Co-free Li-rich Mn-based cathode materials (Co-free LRMOs) have become one of the most promising cathode materials in lithium-ion batteries for the next generation due to their low cost, high capacity, and environmental friendliness. Under high voltage, redox reactions involving anions can easily lead to various issues, including oxygen release, dissolution of transition metal elements (TMs), and structural collapse in these materials. The absence of the Co element further exacerbates this issue. Here, a simple one-step solid-phase reaction strategy is proposed to achieve nanoscale dual modification of the Co-free LRMOs with F and Tb doping. The dual modification has a relatively small impact on the cell parameters and Li+ diffusion ability of the LRMOs, leading to no significant improvement in its rate performance. The modified LRMOs only exhibited discharge capacities of 220.7, 200.1, 140.0, 115.5, and 90.9 mAh·g-1 at 0.1, 0.2, 1.0, 2.0, and 5.0 C, respectively. However, the modified Co-free LRMOs exhibit extremely strong structural stability and retain 95.1% of the initial capacity after 300 cycles, so far, the highest capacity retention rates among all Ni/Mn-based Li-rich materials. Mechanism studies have shown that the enhancement in structural stability of the Co-free LRMOs is attributed to the increased concentration of oxygen vacancies and Ni3+ ions through F doping. Furthermore, Tb doping not only hinders the release of O2 but also enhances the Li+ migration and electronic conductivity coefficient of the LRMOs.

Robust Solid-State Na-CO2 Battery with Na2.7Zr2Si2PO11.7F0.3-PVDF-HFP Composite Solid Electrolyte and Na15Sn4/Na Anode.

Solid-state Na-CO2 batteries are a kind of energy storage devices that can immobilize and convert CO2. They have the advantages of both solid-state batteries and metal-air batteries. High-performance solid electrolyte and electrode materials are important for improving the performance of solid-state Na-CO2 batteries. In this work, we investigate the influence of fluorine doping on the structure and ionic conductivity of Na3Zr2Si2PO12 (NZSP). An ionic conductive solid electrolyte membrane was prepared by compositing the inorganic solid electrolyte Na2.7Zr2Si2PO11.7F0.3 (NZSPF3) with poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP). It shows an ionic conductivity of up to 2.17 × 10-4 S cm-1 at room temperature, a high sodium ionic transfer number of ∼0.70, a broad electrochemical window of ∼5.18 V, and better mechanical strength. Furthermore, we studied the Na15Sn4/Na composite foil with the ability to inhibit dendrite as the anode for solid-state Na-CO2 batteries. Through density functional theory (DFT) calculations, the Na15Sn4 particle has been verified with a strong sodiophilic property, which reduces the nucleation barrier during the deposition process, leading to a lower overpotential. The symmetric cell assembled with the composite solid-state electrolyte NZSPF3-PVDF-HFP and Na15Sn4/Na composite anode can inhibit the growth of Na dendrites effectively and maintain the stability of the whole cell structure. Solid-state Na-CO2 batteries assembled with Ru-carbon nanotube (Ru-CNTs) as cathode catalysts exhibit a high discharge capacity of 6371.8 mAh g-1 at 200 mA g-1, excellent cycling stability for 1100 h, and good rate performance. This work provides a promising strategy for designing high-performance solid-state Na-CO2 batteries.

F-doping-Enhanced Carrier Transport in the SnO2/Perovskite Interface for High-Performance Perovskite Solar Cells.

SnO2 is widely used as the electron transport layer (ETL) in n-i-p perovskite solar cells. However, the deep-level defects at the interface between SnO2 and the perovskite film will lead to energy loss, reducing the open-circuit voltage. Therefore, the interface optimization is essential to raise the efficiency and enhance the stability of perovskite solar cells. In this work, we introduce NH4F into the SnO2 electron transport layers, and the optimized SnO2 films reduce the interface defect density, improve the charge extraction, and reveal a better energy-level arrangement. Compared to the conventional SnO2 perovskite solar cell, the average Voc is improved by 70 mV with the champion efficiency up to 22.12%. Moreover, the unencapsulated F-doped SnO2 perovskite solar cells show better thermal stability (maintained 86.2%) and humidity stability (maintained 80.8%) after 35 days.

"Two Birds with One Stone": F Doping Ni-Co Hydroxide as High-Performance Cathode Material for Aqueous Zn Batteries.

Cathode materials have impeded the development of aqueous Zn batteries (AZBs) for a long time due to their low capacity and poor cycling stability. Here, a "two birds with one stone" strategy is devised to optimize the Ni-Co hydroxide cathode material (NCH) for AZBs, which plays an essential role in both composition adjustment and morphology majorization. The F-doped Ni-Co hydroxide (FNCH) exhibits a unique nanoarray structure consisting of the 2D flake-like unit, furnishing abundant active sites for the redox reaction. A series of analyses prove that FNCH delivers improved electrical conductivity and enhanced electrochemical activity. Contributing to the unique morphology and adjusted characteristics, FNCH presents a higher discharge-specific capacity, more advantageous rate capability and competitive cycling stability than NCH. As a result, an aqueous Zn battery assembled with a FNCH cathode and Zn anode exhibits a high capacity of 0.23 mAh cm-2 at 1 mA cm-2, and retains 0.10 mAh cm-2 at 10 mA cm-2. More importantly, the FNCH-Zn battery demonstrates no capacity decay after 3000 cycles with a conspicuous capacity of 0.15 mAh cm-2 at 8 mA cm-2, indicating a superior cycling performance. This work provides a facile approach to develop high-performance cathodes for aqueous Zn batteries.

Flexible construct of N vacancies and hydrophobic sites on g-C3N4 by F doping and their contribution to PFOA degradation in photocatalytic ozonation.

N vacancies, hydrophobic sites and electron rich zone were simply regulated by doping F into g-C3N4 (CN) to accelerate photocatalytic ozonation of PFOA. Activity of F-CN was superior to that of CN, with 74.3% PFOA removal by F-CN/Vis/O3 but only 57.1% by CN/Vis/O3. Experimental results and theory simulations suggested that the photogenerated hole (hvb+) oxidation with the help of N vacancies was vital for PFOA degradation. N vacancies on both CN and F-CN would trap O atom of PFOA and seize electron from α -CF2 group, which made PFOA more easily to be oxidized. Doping of F narrowed band gap, lowered the valence band position and enhanced the oxidation potential of hvb+. The hydrophobic sites would accelerate the mass transfer of O3 and PFOA, enhance O3's single electron reduction with ecb- to generate hydroxyl radicals (•OH) and reduce the recombination of hvb+-ecb-. Under the joint function of hvb+, N vacancies and •OH, PFOA degradation in F-CN/Vis/O3 proceeded through the gradually shortening of perfluoroalky chain and loss of CF2 unit. The acute and chronic toxicity of generated short-chain perfluorocarboxylic acid toward fish, green algae daphnid were predicted by ECOSAR. And the toxicity change of solutions was examined by luminescent bacteria.

Investigation of optical properties for N- and F-doped triangular shaped carbon molecules.

Optical properties of N- and F-doping triangular-shaped carbon molecules have been investigated in theory and experiment. The theoretical results showed that carbon molecules with impurity F and Cl have the same characters with pure carbon. Doping N into pure carbon molecule would change the optical rotation at 589 nm. For doping N replacing hydrogen atom structures (N-doping 1 and N-doping 2 molecules), the absorption spectra of them are similar to pure carbon molecule. However, for molecules with impurity N atom in benzene ring (N-doping 3 and N-doping 4 molecules), the peaks of wavelength of absorption spectra shift to long wavelength compared to that of pure carbon molecule. Moreover, the delocalization of molecular orbital (MO) is different from pure carbon molecule, which is caused by the impurity N changing the electrons distribution of benzene ring. We have calculated 3 without H and 4 without H molecules which are removing hydrogen atom in nitrogen atom from N-doping 3 and 4. 3 without H and 4 without H molecules have similar optical properties with pure carbon molecule. The results testified that the impurity N and F would not change the optical properties of carbon molecule if impurity did not change the delocalization of all benzene rings. Optical properties of nitrogen- and fluorine-doping carbon molecules investigating in theory and experiment.

Promoting Oxygen Evolution by Deep Reconstruction via Dynamic Migration of Fluorine Anions.

Promoting the reconstruction of electrocatalysts during the oxygen evolution reaction (OER) is generally regarded as a promising strategy for enhanced activity. F anions with strong electronegativity are predicted to enhance this transformation. Herein, a fluorine-anion doping route is proposed to convert the well-latticed NiMoO4@MNF to amorphous F-NiMoO4@MNF by a facile and versatile molten salt strategy. The well-defined nanorod arrays guarantee abundant exposed active sites, rapid mass transfer, and fast gas bubble release. Moreover, the emerged loose amorphous structure is conducive to the dynamic migration of F species and effective penetration of the electrolyte; therefore, the resulting exchange between F and hydroxide anions induces the formation of an active oxy(hydroxide) layer, thus finally optimizing the electronic structure and absorption/desorption energy on the surface of F-NiMoO4@MNF. The boosted OER performance of reconstructed F-NiMoO4@MNF is reliably confirmed by a low overpotential of 188 mV at 50 mA cm-2, a small Tafel slope of 33.8 mV dec-1, and favorable long-term stability. In addition, accelerated hydrogen evolution is observed, which is ascribed to the finely tuned electron distribution. This work would provide a new reconstruction route assisted by F-anion doping to the development of high-performance catalysts.

F-doped ZnO nano- and meso-crystals with enhanced photocatalytic activity in diclofenac degradation.

Diclofenac (DCF), a non-steroidal anti-inflammatory drug, is considered one of the most widespread emerging contaminants. Its incidence in water can favor the growth of drug-resistant bacteria and harm aquatic organisms endangering both the human health and the ecosystem. Advanced oxidation processes (AOPs) based on the action of reactive oxygen species are very effective technologies for the removal of this contaminant from water. In this context, ZnO is one of the most studied semiconductors for photocatalytic water treatment. In this work, the photocatalytic activity of fluorine-doped ZnO nano- and meso-crystals synthesized by a hydrothermal approach is reported, exploring the role of a low F atomic concentration (0.25, 0.5 and 1 at. %) on the degradation of DCF in comparison with bare ZnO. All doped samples show high rates of DCF degradation and mineralization, which were realized primarily thanks to their high efficiency in the generation of hydroxyl radicals (OH). The property-structure-function relationships of the materials are investigated by complementary techniques, such as SEM, XRD, EPR, UV-vis DRS and PL, with the aim to evaluate the role of fluorine in determining their morphological, electronic and optical properties.

Tunable Electrochemical Activity of P2-Na0.6Mn0.7Ni0.3O2-xFx Microspheres as High-Rate Cathodes for High-Performance Sodium Ion Batteries.

As an important cathode candidate for the high-performance sodium ion batteries (SIBs), P2-type oxides with layered structures are needed to balance the specific capacities and cycling stability. As a result, a cation and anion codoped strategy has been adopted to tune the electrochemical activity of the redox centers and modulate the structure properties. Herein, a series of P2-Na0.6Mn0.7Ni0.3O2-xFx (x = 0, 0.03, 0.05, and 0.07) cathodes with microsphere structures are synthesized, using a solid-state reaction in the presence of MnO2 microsphere self-templates. Compared with the cation-doped Na0.6Mn0.7Ni0.3O2, additional F-doping can affect the lattice parameters and redox centers of Na0.6Mn0.7Ni0.3O2-xFx. Comprehensively considering the specific capacities, cycling stability, and rate capability, the optimized x value in Na0.6Mn0.7Ni0.3O2-xFx is determined to be 0.05. In the half cells, Na0.6Mn0.7Ni0.3O1.95F0.05 (F-0.05) maintains a capacity of 90.5 mA h g-1 in the first cycle at 1.0 A g-1, giving a capacity retention of 78% within 900 cycles. The superior rate capability of F-0.05 is guaranteed by the larger diffusion coefficient of Na+ (DNa) combined with higher charge transfer speed. In addition, when coupled with MoSe2/PC anodes, the full cells also exhibit impressive electrochemical performance.

Robust Li6PS5I Interlayer to Stabilize the Tailored Electrolyte Li9.95SnP2S11.95F0.05/Li Metal Interface.

All-solid-state lithium-metal batteries (ASSLMBs) with sulfide electrolytes have attracted attention owing to their superior safety and high energy density. However, interfacial instability of sulfide electrolytes against Li metal still hinders their applications. Herein, F-doping is adopted to optimize the structure of Li10SnP2S12. It is demonstrated that the Li9.95SnP2S11.95F0.05 (LSPSF) electrolyte exhibits a high ionic conductivity of 6.4 mS cm-1 because of F-doping, which can reduce the impurity Li2SnS3 and generate Li+ vacancies. In addition, the Li6PS5I (LPSI) glass-ceramic interlayer is employed to enhance the interfacial stability between the sulfide electrolyte and Li metal by restraining the reduction of Sn4+ cations, as indicated by X-ray photoelectron spectroscopy (XPS). As a result, the assembled ASSLMBs with the LPSI interlayer deliver high initial discharge capacity and remarkable cycling stability. This work provides a new design route for manufacturing high-performance ASSLMBs.

F-Doped NaTi2(PO4)3/C Nanocomposite as a High-Performance Anode for Sodium-Ion Batteries.

We are presenting a sol-gel method for building novel nanostructures made of nanosized F-doped Na1-2 xTi2(PO4)3- xF x (NTP-F x, x = 0, 0.02, 0.05, and 0.10) particles embedded in three-dimensional (3D) carbon matrices (NTP-F x/C). This technique combines advantages of both zero-dimensional materials and 3D-carbon networks. Proper fluorine doping stabilizes the NTP structure and greatly enhances ion/electron transportation, leading to superhigh-rate electrochemical performance and ultralong cycle life. The composite electrode delivers high specific capacities of 121, 115, 112.2, 110.1, 107.7, 103.1, 85.8, and 62.5 mA h g-1 at 0.2, 0.5, 1, 2, 5, 10, 20, and 30 C, respectively. It retains an unbelievable ∼70% capacity after a thousand cycles at a rate as high as 10 C. Electroanalytical results reveal that fluorine doping significantly enhances Na+ diffusion kinetics. Meanwhile, density functional theory calculations demonstrate F-doped NTPs' own outstanding electrochemical properties, which is due to the enhanced intrinsic ionic/electronic conductivity. The results show that anion doping is an efficient way to make high-performance NTP anodes for sodium-ion batteries.

Effects of Fluorine Doping on Structural and Electrochemical Properties of Li6.25Ga0.25La3Zr2O12 as Electrolytes for Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) are promising technologies with great potential in improving safety and energy density, compared with the traditional liquid based lithium ion batteries. However, the bottleneck of SSLBs lies in the issues of poor interface contact and low electrolyte conductivity. In this work, the crystal structure of garnet-type Li6.25Ga0.25La3Zr2O12 (LGLZO) was engineered more rigidly with subdued atoms displacement by fluorine doping and thus smoother and faster lithium ion diffusion paths are formed. The ionic conductivity of garnet-type electrolyte is significantly increased from 5.43 × 10-4 S/cm to 1.28 × 10-3 S/cm at 25 °C and the activation energy is reduced from 0.33 to 0.28 eV. The solid-state symmetric cell consisting of F doped Li6.25Ga0.25La3Zr2O12 electrolyte and lithium metal has lower resistance and displays stable lithium plating/stripping for over 650 h with smaller overpotentials than those on LGLZO electrolyte. Moreover, the all solid-state lithium battery with F-LGLZO electrolyte and LiFePO4 composite electrode exhibits an improved rate capability, which can still keep 132.9 mAh/g at 1 C. Fluorine substitution in garnet-type electrolyte opens new avenues to design new solid-state electrolytes for practical applications of SSLBs.

Effects of F-Doping on the Electrochemical Performance of Na2Ti3O7 as an Anode for Sodium-Ion Batteries.

The effects of fluorine (F) doping on the phase, crystal structure, and electrochemical performance of Na2Ti3O7 are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. F-doping does not change the crystal structure of NTO, although it has an effect on the morphology of the resultant product. As an anode material for sodium-ion batteries, the specific capacity of Na2Ti3O7 exhibits a 30% increase with F-doping owing to the improved sodium ion diffusion coefficient. F-doped Na2Ti3O7 also displays an enhanced rate capability and favourable cycling performance for more than 800 cycles.