Fluorine-containing Electrolyte Research Articles

Comprehensive study on physicochemical properties of materials based on titanium suboxides

This study focuses on the surface structures and microstructural changes of titanium dioxide nanotubes, when electrochemically coated with platinum and/or palladium. Ti samples anodized in a fluorine-containing electrolyte exhibit self-organized nanotubes of varying diameters with open pores. Annealing at 773 K led to compaction of the porous layer, the formation of cracks, and the appearance of corrugation in the nanotubes. The deposition of platinum produced a transition from a nanotubular surface structure to a microcrystalline structure consisting of rutile crystallites. The palladium-coated samples showed fused blocks characteristic of titanium suboxides. The tubular structure was preserved, even after crystallization. SEM images revealed a comb-like pattern in coatings with varying metal content. XRPD analysis confirmed the presence of anatase and elemental titanium. PdO was detected on the surface of the thermally treated samples. For samples co-treated with Pd and Pt, mutual diffusion of the two metals took place during the heat treatment. The findings reveal surface characteristics, metal deposition effects, and phase composition of titania nanotubes, providing valuable insights for further research.

Highly Ordered Nanotube-Like Microstructure on Titanium Dental Implant Surface Fabricated via Anodization Enhanced Cell Adhesion and Migration of Human Gingival Fibroblasts.

Titanium (Ti) surface with nanotubes array via anodization has been used in dental implants to enhance bone regeneration but little research was carried out to evaluate whether the presence of highly ordered or disorderly distributed nanotubes array on titanium surface would have an effect on cell behaviors of gingival fibroblasts. The present study fabricated nanotubes arrays with varied topography under different constant voltage of electrochemical anodization in fluorine-containing electrolyte. Human gingival fibroblasts (HGFs) from extracted third molar were harvested and co-cultured with titanium disks with different nanotubes topography. Then cell behaviors of gingival fibroblasts including cell proliferation, adhesive morphology and cell migration were estimated to investigate the influence of titanium nanotubes on cell biology. Besides, gene and protein expression of adhesion molecule (integrin β1/β4/α6, fibronectin, intracellular adhesion molecule-1 and collagen type I) were detected to evaluate the influence of different surfaces on cell adhesion. Highly ordered arrays of nanotubes with pore diameter of 60 nm and 100 nm were fabricated under 30 and 40 V of anodization (TNT-30 and TNT-40) while disorderedly distributed nanotube arrays formed on the titanium surface under 50 V of anodization (TNT-50). Our results demonstrated that compared with raw titanium surface and disorderly nanotubes, surface with orderly nanotubes array increased cell area and aspect ratio, as well as cell migration ability in the early phase of cell adhesion (p<0.05). Besides, compared with raw titanium surface, gene and protein expression of adhesion molecules were upregulated in nanotubes groups to different extents, no matter whether in an orderly or disorderly array. Within the limitations of our study, we conclude that compared with raw titanium surface, the presence of nanotubes array on titanium surface could enhance cells adhesion and cell migration in the early phase. And compared with disorderly distributed nanotubes, highly ordered nanotubes array might provide a much more favorable surface for gingival fibroblasts to achieve a tight adhesion on the materials.

Prolonged lifespan of initial-anode-free lithium-metal battery by pre-lithiation in Li-rich Li2Ni0.5Mn1.5O4 spinel cathode.

Anode-free lithium metal batteries (AF-LMBs) can deliver the maximum energy density. However, achieving AF-LMBs with a long lifespan remains challenging because of the poor reversibility of Li+ plating/stripping on the anode. Here, coupled with a fluorine-containing electrolyte, we introduce a cathode pre-lithiation strategy to extend the lifespan of AF-LMBs. The AF-LMB is constructed with Li-rich Li2Ni0.5Mn1.5O4 cathodes as a Li-ion extender; the Li2Ni0.5Mn1.5O4 can deliver a large amount of Li+ in the initial charging process to offset the continuous Li+ consumption, which benefits the cycling performance without sacrificing energy density. Moreover, the cathode pre-lithiation design has been practically and precisely regulated using engineering methods (Li-metal contact and pre-lithiation Li-biphenyl immersion). Benefiting from the highly reversible Li metal on the Cu anode and Li2Ni0.5Mn1.5O4 cathode, the further fabricated anode-free pouch cells achieve 350 W h kg-1 energy density and 97% capacity retention after 50 cycles.

Morphology evolution of the aluminum surface in a fluorine-containing environment.

The interaction between aluminum (Al) and F and O atoms is essential to understand the etching process of Al and alumina (Al2O3) by fluorine-containing gases. In addition, it also has an influence on the corrosion behavior of Al devices, e.g., the Al collector in lithium-ion batteries operates in fluorine-containing electrolytes. However, the understanding of the structural evolution of the Al surface by fluorination at the atomistic level still remains elusive. Here, the thermodynamic and kinetic behaviors of F adatoms as well as co-adsorbed F and O adatoms on typical Al surfaces have been systematically investigated by combining density functional theory (DFT) calculations, canonical Monte Carlo (CMC) simulations and reactive molecular dynamics (RMD) simulations. The results of DFT calculations indicate that there is a repulsion (about 0.07 eV on Al(111) and Al(110), and 0.7 eV on Al(100)) between the first nearest neighboring (1NN) F adatoms, while an attraction of 0.14 eV on Al(111) exists within a 1NN F-O pair. CMC simulations reveal that the configurations of co-adsorbed F and O adatoms on the Al(111) surface at medium to low temperature (<600 K) and low total coverage (<0.2 monolayer, ML) have F adatoms dispersed in the hexagonal islands of O adatoms due to the attraction within the O-O and F-O pairs and the repulsion between F adatoms. As the coverage increases, the surface undergoes serious deformation. The average 1NN coordination numbers (1st CN) of O-to-O, F-to-O and F-to-F are six, three and zero, respectively. As the temperature increases, the interactions among adsorbates begin to be disrupted: the 1st CNs of O-to-O and F-to-O decrease, while that of F-to-F increases. The O-F hexagonal pattern remains until above the Al melting temperature (>1200 K). For F adatoms, both their migration on the surface and the penetration into the subsurface are easier than those of O adatoms, confirmed by both the DFT and RMD simulations. Our study on the co-adsorbates with opposite lateral interactions is instructive for understanding the thermal etching of Al and Al2O3 by fluorine-containing compounds.

Микро/наноструктурированные анодно-оксидные покрытия на монокристаллах ниобия

The paper discusses the results of studying of the growth of anodic oxide films (AOFs) by anodizing of niobium single crystals in a fluorine-containing electrolyte (aqueous solution of 10 % H2SO4 + 1 % HF), as well as the effect of saturation of the niobium surface with oxygen on the structure and properties of AOF.

Locking Active Li Metal through Localized Redistribution of Fluoride Enabling Stable Li-Metal Batteries.

The creation of fluorinated interphase has emerged as an effective strategy for improving Li-metal anodes for rechargeable high-energy batteries. In contrast to the introduction of fluorine-containing species through widely adopted electrolyte engineering, a Li-metal composite design is reported in which LiF can locally redistribute on the Li-metal surface in liquid electrolytes via a dissolution-reprecipitation mechanism, and enable the formation of a high-fluorine-content solid electrolyte interphase (SEI). For validation, a Li/Li22 Sn5 /LiF ternary composite is investigated, where the as-formed LiF-rich SEI locks the active Li metal from corrosive electrolyte. The Li/Li22 Sn5 /LiF anode displays an impressive average Coulombic efficiency (ACE, ≈99.2%) at 1mA cm-2 and 1 mAh cm-2 in a carbonate electrolyte and a remarkable cycling life of over 1600h at 1mA cm-2 and 2 mAh cm-2 . Applied to a LiCoO2 full cell with a high cathode areal capacity of 4.0 mAh cm-2 , a high capacity retention of ≈91.1% is realized for 100 cycles at 0.5 C between 2.8 to 4.5V with a low negative/positive (N/P) ratio of 2:1. This design is conceptually different from the design employing the widely used fluorine-containing electrolyte additive and provides an alternative approach to realize reliable Li-metal batteries.

Recovery of spent LiCoO2 lithium-ion battery via environmentally friendly pyrolysis and hydrometallurgical leaching

LiCoO2 (LCO) lithium-ion battery (LIB) is rich in valuable metals (cobalt and lithium), which has high recycling value. The existing process has basically realized the extraction of cobalt, but there are still shortcomings in harmless disposal of fluorine-containing electrolyte, binder and other organic matters, selective extraction of lithium and low-cost extraction of cobalt. In this context, a novel process was developed to realize the full-component recovery of spent LiCoO2 battery via environmentally friendly pyrolysis and hydrometallurgical leaching. The organic matters were recovered in the form of pyrolytic oil and gas, in which the harmful fluorine element was absorbed by Ca(OH)2 solution. The current collectors (copper and aluminum) were recovered after the easy separation of electrode materials due to the degradation of binders. During pyrolysis the cathode material was deconstructed and reduced under the synergistic effect of pyrolytic gas and anode graphite. Selective recovery of lithium and cobalt was achieved through carbonated water leaching and reductant-free acid leaching. The leaching efficiencies of lithium and cobalt were respectively 87.9% and 99.1% under the optimal conditions. Lithium carbonate and cobalt sulfate were obtained by evaporative crystallization, respectively. The remaining residue was only graphite without impurity entrainment. The results in this research suggest that the process consisting of pyrolysis and hydrometallurgical leaching is inexpensive, efficient, and eco-friendly for full-component recycling of spent LiCoO2 battery.

Bridging role of ethyl methyl carbonate in fluorinated electrolyte on ionic transport and phase stability for lithium-ion batteries

Developing electrolytes with a higher oxidation potential is essential to the performance of lithium-ion batteries (LIBs). Fluorine-containing solvent (1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether (TTE)) is a promising candidate for high-voltage use; however, its weak interaction with lithium hexafluorophosphate (LiPF6) containing electrolyte results in phase separation and causes concerns in practical applications. In this work, ethyl methyl carbonate (EMC) is selected to resolve the phase separation. The solvation structure, oxidation stability, and transport property of 1 M LiPF6 in fluoroethylene carbonate (FEC)/TTE and FEC/TTE/EMC (3:7 and 3:5:2 by vol., respectively) are investigated. The solvation energy of TTE in LiPF6 can be greatly increased by the inclusion of EMC and achieve improved thermodynamic stability. Upon adding EMC, the solvation structure is altered from Li+(FEC)2(PF6−) to Li+(FEC)(EMC)(PF6−) and confirmed by the Raman spectroscopy result. The transference number of Li+ in the improved electrolyte also evidently increases, as confirmed both theoretically and experimentally. Besides, 1 M LiPF6 in EFC/TTE/EMC (3:5: 2 by vol.) exhibits high oxidation potential ~ 5.31 V (vs. Li/Li+) and significantly enhances the transference number of Li+. This work offers a fluorine-containing electrolyte with a stable phase and high oxidation potential for LIB's practical application.

Research progress of fluorine-containing electrolyte additives for lithium ion batteries

The construction of Solid Electrolyte Interface (SEI) film in Li-ion batteries with functional electrolyte additives is able to passivate the active material surface and inhibit the decomposition of the electrolyte continuously. In addition, safety issue is also an important factor restricting the large scale application of present lithium-ion batteries. Therefore, the additives for film-forming and safety enhancement are a class of cost-effective components that promote the application and development of batteries. Fluorine is a kind of “bipolar” element, which has strong electronegativity and weak polarity. Fluorine-containing electrolyte additives have excellent kinetic reactivity, which can preferentially generate stable SEI films and uniform Cathode-Electrolyte Interface (CEI) films to effectively improve the electrochemical performance of the batteries. Meanwhile, fluorine-containing electrolyte additives can also be used as flame-retardants to improve safety performance. In this review, we summarize the research status of fluorine-containing additives in recent years and elaborate its reaction mechanisms of improving battery performance. Finally, a personal perspective on the future of the development of fluorine-containing additives is presented.

Molecular Simulations of the Microstructure Evolution of Solid Electrolyte Interphase during Cyclic Charging/Discharging.

Lithium (Li) metal is regarded as one of the most promising anode materials for use in next-generation high-energy-density rechargeable batteries because of its high volumetric and gravimetric specific capacity, as well as low reduction potential. Unfortunately, uncontrolled dendritic Li growth during cyclic charging/discharging leads to low columbic efficiency and critical safety issues. Hence, comprehensive understanding of the formation mechanism for Li-dendrite growth, particularly at the onset of dendrite formation, is essential for developing Li-metal anode batteries. In this study, reactive molecular dynamics (MD) simulations in combination with the electrochemical dynamics with implicit degrees of freedom (EChemDID) method were performed to investigate the formation and evolution of solid electrolyte interphase (SEI) films for a Li-metal anode under cyclic charging/discharging processes in two distinct dimensions, namely, electrolyte compositions and initial surface morphologies. Our simulations indicated that regardless of the electrolyte compositions and initial anode morphologies, inhomogeneous Li reduction, namely, the formation of Li-reduction "hotspots" during cyclic charging cycles, took place and could serve as the seed for subsequent dendrite growth. The fluorine-containing electrolyte additives could notably mitigate the Li-anode roughening processes by forming dense-SEI-layer products or suppressing electrolyte decomposition. A series of Li-ion-drifting simulations suggest that Li ions navigate through the SEI layer via pathways composed of low-density atoms and become reduced at these reduction hotspots, promoting inhomogeneous deposition and subsequent dendrite growth. The present study reveals atomistic details of the early stage of dendrite growth during cyclic loadings under different electrolyte compositions and anode morphologies, thereby providing insights for designing artificial SEI layers or electrolytes for long-life, high-capacity Li-ion batteries.

Oriented porous anodic oxide layers on Ti-50Al with outstanding oxidation resistance at 800 °C

A fluoride-containing anodic oxide layer with oriented porous structure coated Ti-50Al intermetallic can be fabricated by anodizing in sulfuric acid (H2SO4) solution containing a small quantity of hydrofluoric acid (HF). X-ray photoelectron spectroscopy (XPS) analysis reveals that the porous anodic oxide layer consists mainly of TiO2, Al2O3, titanium fluoride and aluminum fluoride. Cyclic oxidation tests indicate that all Ti-50Al samples anodized in fluorine-containing electrolyte exhibit outstanding oxidation resistance with little or even no scale spallation at 800 °C. The improvement of oxidation resistance is mainly attributed to the fluorine effect and the oriented porous structure of anodic oxide layer.

A further insight into coating-substrate interface of TiUnite implant by a novel coating detachment method

This work reports the development of a novel method to treat a commercially TiUnite® implant to detach its tightly bonded surface oxide layer. The implant was anodized in a fluorine-containing electrolyte (usually for TiO2 nanotubes preparation) at 50 V for 2 h, which resulted in detachment of the coating. High-quality coating cross-sectional samples were prepared with detached coating fragments. Both the exposed titanium substrate and the detached coating were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). It was interesting to find that the coating-substrate interface exhibited a specific “mortise-tenon” anchorage structure. For comparison, focused ion beam (FIB) method was also conducted and the results revealed uneven bonding interface, specific internal pores distribution and varied coating thickness of the oxide coating. EDX results reported to existence of Ga+ ion in the coating after FIB treatment while the novel method would increase the O element content. The novel method gave a brand new angle for detection of TiUnite implant and enhanced the understanding of its coating-substrate interface features unprecedentedly. It provides a novel and economy method for research, development and evaluation of coated titanium-based implant.

Fe-Ti alloy layer plasma deposition – Monitoring of plasma parameters and properties of deposited alloys, anodization and photoelectrochemical characterization

Metallic Fe-Ti alloy thin films were deposited by high-power impulse magnetron sputtering (HiPIMS) on a glass substrate with an FTO electrode. Two-component alloys were prepared by sputtering of a single target, which was composed from two sectors made from different elements: iron disc and titanium ring. Chemical composition of alloy thin films was controlled by the width of titanium ring that partially covered iron target. These alloy thin films were anodized in fluorine-containing electrolyte with the aim to create mixed oxide nanostructures. Anodized layers were amorphous and transparent. After calcination, the layers consisted of crystalline Fe2O3 although TiO2 was still amorphous. Photoelectrochemical characterization show that increasing amount of titanium in the alloy results in the fabrication of Fe2O3/TiO2 nanostructures with higher photocurrent compared to those prepared from pure iron by the same anodization technique.

Fluorine-Induced Superhydrophilic Ti Foam with Surface Nanocavities for Effective Oil-in-Water Emulsion Separation

Recently, oil/water separation has attracted intensive attention because of frequent crude oil spill accidents and the increasing amount of industrial wastewater. Ti-based materials are nontoxic and environment-friendly for oil/water separation; however, there is little attention focused on this field. In the present work, we introduce, for the first time, surface −O–Ti–F groups onto Ti foam by a simple anodization in a fluorine-containing electrolyte to form a superhydrophilic membrane for oil-in-water emulsion separation, which was proven to be excellent with the assistance of surface nanocavities. The water permeability of anodized Ti foam is elevated by about 10 times as compared to that of the original one, and the oil/water separation efficiency is above 99% with good anticorrosive properties. In addition, this fluorine-induced superhydrophilicity can be applied to metals and semimetals for many other applications such as self-cleaning, surface modification of catalysts, removal of heavy metal ions,...

Tracking the morphology and phase transformations of anodic iron oxide nanotubes using X-ray spectroscopy

X-ray spectroscopic techniques have been employed to investigate highly ordered iron oxide nanotubes (NTs) prepared by iron anodization in a fluorine-containing electrolyte followed with annealing at elevated temperatures. NTs undergo morphology and phase evolutions from amorphous NTs to single crystalline nanoplates, then nanoflakes, and finally to a polycrystalline film. X-ray diffraction and X-ray absorption near edge structure have been used for the investigation. We show that fluorine incorporation can be used as an effective morphology tailoring tool for the engineering of efficient iron oxide nanostructures.

Influence of annealing on the structure of nanoporous oxide films on the surface of titanium‒aluminum powder alloy

Oxide films obtained during anodization of Ti‒40% Al sintered powder samples in fluorine-containing electrolytes are investigated. With scanning electron microscopy and X-ray phase analysis, it is demonstrated that an X-ray amorphous nanoporous anodic oxide film is formed on the surface of the powder microparticles under optimal anodization conditions. After annealing at T = 1093 K in air and vacuum (10‒2 Pa), the oxide films are revealed to crystallize with its regular porous structure retained. The composition of the polycrystalline anodic-oxide films annealed in air is a mixture involving TiO2 (anatase and rutile) and α- and γ-Al2O3 phases and Ti2O3 and Al2TiO5 traces. The vacuum annealing process makes it possible to identify TiO2, in which anatase is the main phase, α- and γ-Al2O3, and Ti2O3 and TiO traces. However, rutile is not revealed. The presented results indicate that the application of the anodic nanostructuring of Ti‒40% Al powders is promising for the obtainment of new photocatalytic active nanomaterials.

Superhydrophilic Nickel Nanoparticles with Core–Shell Structure To Decorate Copper Mesh for Efficient Oil/Water Separation

Recently, oil/water separation has attracted intensive attention due to the frequent crude oil spill accidents and the increasing amount of industrial wastewater. Thousands of outstanding achievements have been reported on the basis of membranes with superhydrophilicity and underwater superoleophobicity. However, a universal approach combining cheaper reagents with easier operations to fabricate superhydrophilic materials for effective oil/water separation is still a challenge and greatly encouraged. In the present work, we fabricate the superhydrophilic copper mesh decorated with nickel nanoparticles (Ni-NPs) via electrodeposition in fluorine-containing electrolyte. The size of Ni-NPs that consists of a metal Ni core and a polar NiO/Ni(OH)2 shell is about 300 nm; what’s more, the Ni-NPs combine with each other to form treelike nickel crystals by varying the experimental parameters. This optimized mesh exhibits remarkable oil/water separation performance. The oil content in separated water is lower than 3...

Surface and sorption properties of TIO2 nanotubes, synthesized by electrochemical anodization

Electrochemical anodizing of titanium metal in the fluorine-containing electrolyte was used for production of nanotubes of titanium dioxide. The surface morphology of the films was investigated by scanning electron microscopy. It was found that with increasing anodizing voltage the inner diameter, growth rate and nanotubes interporous distance is increasing. The distribution of pore volume studied by the method of adsorption and desorption of nitrogen. The specific surface area of titanium dioxide films was measured for determine the conditions of anodizing on their changes. The sorption capacity of the films was studied.

Fabrication of Well-Aligned TiO2 Nanotube Arrays with Outstanding Light-Induced Hydrophilicity Performance

TiO2 nanotube arrays (TiO2-NTAs) were respectively fabricated using traditional one-step oxidation and re-oxidation method on a titanium surface in fluorine-containing electrolytes. Microstructures, optical properties of specimen were characterized by X-ray diffractometer, digital microscope, field-emission scanning electron microscope and ultraviolet-visible spectroscope. Compared with the one-step oxidation, the resulted samples showed more uniform surface, longer tube length and statistical higher absorption in visible light region. Importantly, a new growth mechanism named template-induced growth model is proposed to explain the growth of TiO2-NTAs prepared by re-oxidation approach in present work. Besides, water contact angles of samples before and after irradiated by UV light were measured and discussed in detail. It is confirmed that samples obtained from re-oxidation method have more hydroxyl groups can be formed when irradiated by UV light, which lead to more sensitive light-induced hydrophilicity finally. The light-induced hydrophilic performance of TiO2-NTAs would be favorable to improve the likelihood of electrolyte contacting of the surface, which is useful in many realistic application instances.

Исследование поверхностных свойств пленок TiO2 –NTs при изменении условии анодирования

Electrochemical anodizing titanium metal in the fluorine-containing electrolyte to produce nanotubes of titanium dioxide. The surface morphology of the films was investigated by scanning electron microscopy. It was found that with increasing anodizing voltage increasing inner diameter growth rate and distance interporous nanotubes. The method of adsorption and desorption of nitrogen studied the distribution of pore volume. Measured by a specific surface area of titanium dioxide films for determine the conditions of anodizing on their changes.