Oxidation State Of Titanium Research Articles

Vacuum Ultraviolet Spectroscopic Analysis of Structural Phases in TiO2 Sol–Gel Thin Films

This study investigates the structural and electronic transitions of sol–gel derived titanium dioxide (TiO2) thin films using vacuum ultraviolet (VUV) spectroscopy, to elucidate the impact of annealing-induced phase evolution. As the annealing temperature increased from 400 °C to 800 °C, the films transitioned from amorphous to anatase, mixed anatase–rutile, and finally rutile phases. VUV spectroscopy revealed distinct absorption features: a high-energy σ → π* transition below 150 nm, associated with bonding to antibonding orbital excitations, and lower-energy absorption bands in the range 175–180 nm and near 280 nm, attributed to π → π* and t2g(π) → t*2g(π*) transitions, respectively. These spectral features highlight the material’s intrinsic electronic states and defect-related transitions. A slight redshift of the absorption band from 176 nm to 177 nm with annealing reflects bandgap narrowing, attributed to increased rutile content, crystallite growth, and defect-induced effects. Broadening and additional absorption features around 280 nm were attributed to oxygen vacancies and reduced titanium oxidation states (Ti3⁺), as corroborated by X-ray photoelectron spectroscopy (XPS). XPS further confirmed the presence of Ti3⁺ species and oxygen vacancies, providing complementary evidence of defect-mediated transitions observed in the VUV spectra. While complementary techniques such as X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed phase transitions and the reduction of hydroxyl groups, respectively, VUV spectroscopy uniquely captured the dynamic interplay between structural defects, phase evolution, and optical properties. This study underscores the utility of VUV spectroscopy as a powerful tool for probing the electronic structure of TiO2 films, offering insights critical for tailoring their functional properties in advanced applications.

Binary Mixtures (AlknAlCl3–n + Alk2Mg) as Catalyst Components for Ethylene Polymerization and the Role of Titanium Oxidation State in Their Catalytic Activity

Binary Mixtures (AlknAlCl3–n + Alk2Mg) as Catalyst Components for Ethylene Polymerization and the Role of Titanium Oxidation State in Their Catalytic Activity

Understanding the Non-Volatile Resistive Switching Behavior of Lithium Titanium Oxide during Spinel to Rock Salt Conversion for Neuromorphic Computing

Lithium based synaptic device research has been a growing new field in the last few years for enabling robust neuromorphic hardware systems. It can realize parallel analogue computation which is beyond the conventional von Neumann computing architecture which is slow, energy inefficient and expensive to execute complex tasks. In this study, we showcase the remarkable potential of Lithium Titanium Oxide (Li4Ti5O12) spinel, both computationally through Density of States (DoS) analysis using Density Functional Theory (DFT), and experimentally via direct current (DC) polarization investigation of electrochemically lithiated Li4Ti5O12 thin film, examining diverse states of discharge (SoD) in both in-plane and out-of-plane configurations. The observed conductivity jump spans up to six orders of magnitude, transitioning from the Li4Ti5O12 spinel phase to the fully lithiated Li7Ti5O12 rock salt phase. Raman Spectroscopy validates the transformation from the Li4Ti5O12 spinel phase to the Li7Ti5O12 rock salt phase. Moreover, the onset of increase in conductivity during this transformation is corroborated by changes in the oxidation state of Titanium (Ti), as explained with the help of X-Ray Photoelectron Spectroscopy. To actualize these findings, we engineered a three-terminal artificial synaptic device integrating Lithium Phosphorous Oxynitride (LiPON) solid-state electrolyte as the lithium ion source and conductor, while employing Lithium Titanium Oxide (Li4Ti5O12) spinel as the channel material. In device testing, we maintained a source-drain voltage (VSD) of 0.5 V, while sweeping the gate voltage (VG) from -3 V to 3 V, resulting in switching spanning up to 4 orders of magnitude, consistently replicable across multiple cycles. Widening the gate voltage window from ±3 V to ±7V induced an increase in conductance. Furthermore, non-volatile testing affirmed the sustained retention of the conductance state across all tested gate voltage windows, showcasing the device's stability over time. These compelling results portray a promising trajectory for the development of a robust synaptic device architecture reliant on lithium-based all solid-state materials, catalyzing the evolution of high-precision analogue neuromorphic computing systems.

The Effect of Thermal Action on the Change in the Chemical Composition of the Surface Layers of a Titanium Alloy, with a Sprayed Carbon Film, after Irradiation with N<sup>+</sup> Ions

The effect of thermal exposure under high vacuum conditions on the chemical composition of the surface layers of the VT6 alloy with mixed implantation of N+ ions by a carbon film is investigated. It is shown that under the conditions of thermal exposure, the change in the concentration profiles of the distribution of elements is determined by the processes of chemical interaction, in which the diffusion of carbon and nitrogen into deeper layers does not occur. On the contrary, their concentration decreases and this is due to the formation of volatile compounds CO, CO2 or (CH)2 under thermal exposure. Titanium in the surface analyzed layer is in an oxidized state with various degrees of oxidation. Up to a depth of about 10 nm, the oxidation state of titanium is Ti4+ and Ti3+, and in the transition region of the film/substrate is Ti2+.

The oxidation state of titanium in silicate melts

The oxidation state of titanium in silicate melts

Copolymerization of Ethylene with Alpha-Olefins over Supported Titanium–Magnesium Catalysts Containing Titanium Compounds in Different Oxidation and Coordination States

Data were obtained on the copolymerization of ethylene with α-olefins over supported titanium–magnesium catalysts (TMC) prepared on the same magnesium dichloride support but differing in the composition and oxidation state of titanium. The copolymerization kinetics of ethylene with 1-hexene over TMC of different compositions were studied. Data on the composition of the produced ethylene–1-hexene copolymers, their molecular weight distribution, thermophysical characteristics, and branching distribution were presented. The constants of ethylene–1-hexene copolymerization over catalysts with different compositions were calculated. The TMC containing only Ti(II) compounds as the active component exhibited increased copolymerizing ability compared to the conventional TiCl4/MgCl2 catalyst containing Ti(III) compounds as the active component. In addition, TMC with Ti(II) as an active component produces copolymers with a more uniform branching distribution. It was shown that the TMC containing isolated Ti(II) ions could be used to produce X-ray amorphous ethylene-propylene elastomers with a high yield.

Effect of anodization time on the morphological, structural, electrochemical, and photocatalytic properties of anodic TiO2 NTs

Effect of anodization time on the morphological, structural, electrochemical, and photocatalytic properties of anodic TiO2 NTs

Enhancement of Hydrophilicity of Nano-Pitted TiO2 Surface Using Phosphoric Acid Etching.

Our research group developed a novel nano-pitted (NP) TiO2 surface on grade 2 titanium that showed good mechanical, osteogenic, and antibacterial properties; however, it showed weak hydrophilicity. Our objective was to develop a surface treatment method to enhance the hydrophilicity of the NP TiO2 surface without the destruction of the nano-topography. The effects of dilute and concentrated orthophosphoric (H3PO4) and nitric acids were investigated on wettability using contact angle measurement. Optical profilometry and atomic force microscopy were used for surface roughness measurement. The chemical composition of the TiO2 surface and the oxidation state of Ti was investigated using X-ray photoelectron spectroscopy. The ccH3PO4 treatment significantly increased the wettability of the NP TiO2 surfaces (30°) compared to the untreated control (88°). The quantity of the absorbed phosphorus significantly increased following ccH3PO4 treatment compared to the control and caused the oxidation state of titanium to decrease (Ti4+ → Ti3+). Owing to its simplicity and robustness the presented surface treatment method may be utilized in the industrial-scale manufacturing of titanium implants.

Metal Oxide Electrospun Nanofibrous Membranes for Effective Dye Degradation and Sustainable Photocatalysis

The fabrication of metal oxide nanofibers using (titanium (IV) isopropoxide) and (tin (IV) tert-butoxide) of weight ratio 1:1 precursor in presence of poly (vinyl pyrrolidone) as a binder using a well-known electrospinning technique is reported. The average diameter of TiO2, SnO2, and composite TiO2-SnO2 nanofibers were found to be in the range 75–110 nm. The nanofibers were characterized using thermogravimetric analysis (TGA) to understand the polymer evaporation temperature and further analyzed using scanning electron microscopy (SEM) to study the morphology of the nanofibers. The oxidation states of titanium (Ti) and tin (Sn) ions were analyzed using X-ray photoelectron spectroscopy (XPS), indicating that the TiO2 undergoes a change even after loading SnO2. The photocatalytic efficiency of the composite TiO2-SnO2 fibers was investigated to study the degradation capabilities under ultraviolet (UV) light towards industrial polluting dyes such as Alcian Blue, Alizarin Red S, Bilirubin, Brilliant Blue, Bromophenol Blue, and Rhodamine B ITC. Rhodamine B showed a significant degradation rate of about 0.0064 min−1 in comparison to the other dyes.

On the Use of Ti3C2 T x MXene as a Negative Electrode Material for Lithium-Ion Batteries.

The pursuit of new and better battery materials has given rise to numerous studies of the possibilities to use two-dimensional negative electrode materials, such as MXenes, in lithium-ion batteries. Nevertheless, both the origin of the capacity and the reasons for significant variations in the capacity seen for different MXene electrodes still remain unclear, even for the most studied MXene: Ti3C2 T x . Herein, freestanding Ti3C2 T x MXene films, composed only of Ti3C2 T x MXene flakes, are studied as additive-free negative lithium-ion battery electrodes, employing lithium metal half-cells and a combination of chronopotentiometry, cyclic voltammetry, X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy experiments. The aim of this study is to identify the redox reactions responsible for the observed reversible and irreversible capacities of Ti3C2 T x -based lithium-ion batteries as well as the reasons for the significant capacity variation seen in the literature. The results demonstrate that the reversible capacity mainly stems from redox reactions involving the T x -Ti-C titanium species situated on the surfaces of the MXene flakes, whereas the Ti-C titanium present in the core of the flakes remains electro-inactive. While a relatively low reversible capacity is obtained for electrodes composed of pristine Ti3C2 T x MXene flakes, significantly higher capacities are seen after having exposed the flakes to water and air prior to the manufacturing of the electrodes. This is ascribed to a change in the titanium oxidation state at the surfaces of the MXene flakes, resulting in increased concentrations of Ti(II), Ti(III), and Ti(IV) in the T x -Ti-C surface species. The significant irreversible capacity seen in the first cycles is mainly attributed to the presence of residual water in the Ti3C2 T x electrodes. As the capacities of Ti3C2 T x MXene negative electrodes depend on the concentration of Ti(II), Ti(III), and Ti(IV) in the T x -Ti-C surface species and the water content, different capacities can be expected when using different manufacturing, pretreatment, and drying procedures.

Water-rich conditions during titania atomic layer deposition in the 100 °C-300 °C temperature window produce films with TiIV oxidation state but large H and O content variations

Titania films prepared by atomic layer deposition attract great attention due to the widespread application of the oxide as a photocatalytic material, or more recently, as a promising charge storage material for lithium or proton batteries. We implement here advanced tools (Ion Beam Analysis and X-ray Photoelectron Spectroscopy, aided by Ellipsometry and X-ray Diffraction) to characterize films grown in the 100 °C-300 °C temperature window, using tetrakis(dimethylamino)titanium (TMDAT) as the metal precursor and water vapor as the oxidant. We examine the outcomes of the ALD process as a function of the deposition temperature, applying equal oxidant and precursor half-cycle time lengths, which contrasts with common deposition processes where the water half-cycle is considerably shorter than that of the metal precursor. Under the present ALD scheme, n-type conductive films are obtained where the oxidation state of titanium is overwhelmingly TiIV at all temperatures, while the hydrogen content (O/Ti ratio) varies considerably, from ∼ 15 at% (∼1.8) at 100 °C to ∼ 3 at% (∼2) at 300 °C. The ideality of the ALD process is discussed through the identification of nitrogen-containing molecules detected at the oxide surfaces. By extending the structural and compositional range of ALD titania films, new opportunities of application are expected to appear.

A novel and environmentally friendly NASICON-type material: Efficient catalyst for condensation of formaldehyde and acetic acid to acrylic acid and methyl acrylate

• NASICON was used for acrylic acid production from formaldehyde and acetic acid. • Acrylic acid + methyl acrylate selectivity of 71% was successfully achieved. • Catalyst properties and structure–activity relationship has been explored in-depth. • Medium-strong basic and acid sites with moderate amount account for AA formation. The development of environmentally friendly and efficient catalysts for the production of essential chemicals has always been a desirable goal for technology in the chemical industry. In this paper, we fabricated a kind of sodium (Na) super ionic conductor (NASICON)-type materials (H 1-x Ti 2 (PO 4 ) 3-x (SO 4 ) x ) with different Ti/P ratios through tuning titanium content in synthetic mother liquor, and applied them to the aldol condensation reaction of acetic acid (HAc) and formaldehyde (FA) to acrylic acid (AA) and methyl acrylate (MA), which has never been not reported in previous researches. More importantly, these novel catalysts have showed their tremendous potential at the efficiency of AA + MA production, and over an optimized catalyst of NSC-Ti/P-0.53, the AA + MA selectivity being 71% (HAc input-based) was achieved at 360 ℃ when the reactant with FA/HAc molar ratio of 5:1 was fed; whereas, a highest space–time-yield (STY) of target products (∼37.2 μmol·g −1 ·min −1 ) was obtained with the FA/HAc molar ratio of 1:2.5, which is comparable to the best result reported previously. The detailed analysis of characterizations demonstrated that the change in the Ti/P ratio in the series NASICON catalysts led to the variation in the phase composition, the textural properties, surface titanium oxidation state, etc. thereby tuning the surface acid-base property, which is quite important for the present condensation reaction. More amounts of acidic sites and basic sites as well as their moderate distribution were proved to exert the promotional effects on the formation of AA and MA.

Regulating photocatalysis by the oxidation state of titanium in TiO2/TiO

The current research on the CO2RR process mainly focuses on the high selectivity of a single product and the material selectivity in the path process [1],[2] Guo et al ., 2019. There are relatively few studies on changes and causes. In this work, TiO2/TiO formed by in-situ oxidation was used as a photocatalyst for CO2 reduction. The structure of this semiconductor/metal-like heterojunction makes the internal electric field appear in the catalyst, which greatly improves the activity of the photocatalytic reaction. During the test, it was found that the hydrogenation product gradually appeared in the reaction product due to the appearance of TiO2. In the absence of a sacrificial agent, the catalyst exhibited a high HCOOH selectivity and obtained a considerable yield of 46.37μmolg-1h-1. After adding the sacrificial agent triethanolamine (TEOA), TiO2/TiO showed good CO production ability. As the reaction progressed, CH4 was gradually produced. DFT calculations confirmed that the structure of the heterojunction has lower workfunction for the CO2 hydrogenation option, and the energy band at the contact position is curved. The construction of this system has guiding significance for the construction of light-driven CO2 hydrogenation products in the future.

Nd3+-Doped TiO2 Nanoparticles as Nanothermometer: High Sensitivity in Temperature Evaluation inside Biological Windows.

TiO2 nanoparticles doped with different amounts of Nd3+ (0.5, 1, and 3 wt.%) were synthetized by the sol–gel method, and evaluated as potential temperature nanoprobes using the fluorescence intensity ratio between thermal-sensitive radiative transitions of the Nd3+. XRD characterization identified the anatase phase in all the doped samples. The morphology of the nanoparticles was observed with SEM, TEM and HRTEM microscopies. The relative amount of Nd3+ in TiO2 was obtained by EDXS, and the oxidation state of titanium and neodymium was investigated via XPS and NEXAFS, respectively. Nd3+ was present in all the samples, unlike titanium, where besides Ti4+, a significantly amount of Ti3+ was observed; the relative concentration of Ti3+ increased as the amount of Nd3+ in the TiO2 nanoparticles increased. The photoluminescence of the synthetized nanoparticles was investigated, with excitation wavelengths of 350, 514 and 600 nm. The emission intensity of the broad band that was associated with the presence of defects in the TiO2, increased when the concentration of Nd3+ was increased. Using 600 nm for excitation, the 4F7/2→4I9/2, 4F5/2→4I9/2 and 4F3/2→4I9/2 transitions of Nd3+ ions, centered at 760 nm, 821 nm, and 880 nm, respectively, were observed. Finally, the effect of temperature in the photoluminescence intensity of the synthetized nanoparticles was investigated, with an excitation wavelength of 600 nm. The spectra were collected in the 288–348 K range. For increasing temperatures, the emission intensity of the 4F7/2→4I9/2 and 4F5/2→4I9/2 transitions increased significantly, in contrast to the 4F3/2→4I9/2 transition, in which the intensity emission decreased. The fluorescence intensity ratio between the transitions and were used to calculate the relative sensitivity of the sensors. The relative sensitivity was near 3% K−1 for and near 1% K−1 for .

Efficient transformation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system over single-site titanium BEA zeolite

Ti x SiBEA zeolites prepared by a two-step post-synthesis method are applied in the liquid-phase Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system. Such method of ε-caprolactone synthesis offers the application of milder reaction conditions with the catalytic system which transforms cyclic ketones into lactones in the presence of molecular oxygen and aldehyde. They are the source of in situ peracid formation. The Ti incorporation into SiBEA involves the formation of Ti(IV) (OSi) 4 as main species and small numbers of Ti(III) (OSi) 3 –O(H)–Si sites having Brønsted and Lewis acid properties. The acidity is a key factor for efficient transformation of cyclohexanone to ε-caprolactone in the BV oxidation depending on the titanium oxidation state and environment. Among all of the studied catalysts, the highest catalytic activity is observed for Ti 2.0 SiBEA zeolite. The active catalyst of the studied BV oxidation reaction is bi-functional, possessing both the acidic and redox properties, catalyzing different reaction stages. • The incorporation of Ti into the SiBEA framework evidenced by FTIR and NMR. • DR UV–vis and XPS showed the presence of framework tetrahedral Ti(IV). • Ti(IV) (OSi) 4 sites appeared as main redox centres. • Ti(III) (OSi) 3 –O(H)–Si sites possessed both Brønsted and Lewis acid properties. • The Ti x SiBEA catalysts applied in BV oxidation reaction have bifunctional character.

Rapid synthesis of TiO2 nanocrystal in aqueous solution at room temperature

In the presented work, we develop an original simple, green, and rapid protocol to prepare anatase titanium dioxide (TiO2) nanocrystal in aqueous solution at room temperature. The secret of this chemical process is the use of ammonium persulfate ((NH4)2S2O8) as initiator in the presence of titanium butoxide (Ti(C4H9O)4) as precursor. The reaction was conducted at room temperature which make this protocol very useful and efficient. The high crystallinity of the obtained TiO2 nanocrystal was confirmed by X-ray diffraction and high-resolution microscopy, both size and shape were observed by transmission electron microscopy. The average particle size of TiO2 nanocrystal was found to be 7 nm with quasi-spherical shape. X-ray photoelectron spectroscopy technique was performed to confirm the purity of the final product and the oxidation state of titanium. The optical property of the as-prepared TiO2 nanocrystal was studied using UV-visible spectroscopy. The thermal stability was measured using differential thermal analysis combined with thermogravimetric analysis. The decrease of TiO2 nanocrystal size affects well the absorption spectrum of TiO2 (UV absorption peak shift from 340 to 325 nm) and therefore affects their photocatalytic activity. This chemical process offers many advantages compared to previous works especially the soft synthesis condition (room temperature, reaction occurs instantly and the aqueous medium) which make it a very promising fast wet chemical process.

Density Functional Theory Driven Analysis of the Interplay among Structure, Composition, and Oxidation State of Titanium in Hibonite, Spinel, and Perovskite

Hibonite (CaAl12O19), spinel (MgAl2O4), and perovskite (CaTiO3) represent oxides that occur in primitive meteorites and are among some of the first phases to have condensed from the early solar nebula. Hibonite and spinel can contain 3d transition metals such as titanium that substitute at cation sites. The substituted titanium can occur in multiple oxidation states, which are in turn linked to the redox conditions under which the material formed or last equilibrated. Similarly, in perovskite, the oxidation state of titanium can also vary but depends on the extent of nonstoichiometry that can arise because of the presence of oxygen vacancies. Here we present density functional theory-based calculations that provide a fundamental understanding on the interplay among changes in composition, structure, and the oxidation state of titanium in spinel, perovskite, and hibonite, with an added emphasis on characterizing the underlying role of oxygen vacancies. Single-site substitution by titanium for aluminum and coupled substitution in conjunction with divalent cations such as magnesium were examined for hibonite and spinel. In addition, the crystal-chemical effects of a single oxygen vacancy were examined in all three systems. Our results show that in hibonite, the M2 cation site is preferred for single titanium substitution, where the titanium oxidation state corresponds to 3+. For the coupled substitution system, the M4 and M3 sites are energetically favorable for titanium and magnesium, respectively, with the oxidation state of titanium corresponding to 4+. In the case of spinel, the substitution of titanium in any of the octahedral aluminum sites are equivalent, and interestingly, substituted titanium is more reduced in spinel as compared with hibonite for both single as well as coupled substitution cases. Further, the oxidation state and Ti–O bonding of couple-substituted titanium in spinel is similar to the titanium cations in the phase-pure perovskite structure. For hibonite and spinel with an oxygen vacancy, we restricted our examination to mono- and di-coupled substitution with the choice motivated by available experimental data. Our results suggest that the oxidation state and the chemical bonding of the substituted titanium cations is directly influenced by their spatial location with respect to the oxygen vacancy.

Nanoscale TiO2 and Ta2O5 as efficient antireflection coatings on commercial monocrystalline silicon solar cell

In this paper, we report the enhancement of photon to electron conversion efficiency of commercial monocrystalline silicon solar cells after deposition of nanoscale TiO2 and Ta2O5 as an antireflection coating. The nanoscale TiO2 and Ta2O5 ARC’s remarkably enhanced PEC efficiency of m-Si solar cells from 17.18% to 17.87% and 18.8% respectably. The enhancement in PEC efficiency is predominantly attributed to the increase in fill factor from 36.8% to 36.9% and 37.2% after deposition of nanoscale TiO2 and Ta2O5 as ARCs respectively. The reflectance of nanoscale TiO2 ARCs increased from 27% to 43% within the wavelength range from to 530 nm and decreases to 34% with increasing wavelength. However, for Ta2O5 the reflectance was 11% at 370 nm and increased up to 29% in the studied wavelength range. The reduced magnitude of reflectance for Ta2O5 throughout the studied wavelength resulted in notable improvement of PEC efficiency compared to TiO2. The phase formation of nanoscale TiO2 characterized by x-ray diffraction reviles the presence of both anatase and rutile phase TiO2 whereas Ta2O5 displays amorphous nature. The oxidation state of titanium (Ti) and tantalum (Ta) was evaluated from x-ray photon emission spectroscopy and observed to be in the form of Ti4+ and Ta5+ chemical state. The nanoscale thickness of both TiO2 and Ta2O5 ARCs was acquired by variable angle spectroscopic ellipsometry and found to be 55.2 nm and 70.8 nm respectively, and the same was confirmed by measuring cross-section thickness of ARCs using a scanning electron microscope.

Substoichiometric Tuning of the Electronic Properties of Titania

Reduced titania phases such as Ti2O3, Ti3O5, and TixO2x-1 (the magńeli phase, 4 ≤ x ≤10) are collectively a promising class of materials due to the stoichiometric tunability of their electronic structure. This flexibility, combined with their relatively high electrical conductivity, high corrosion resistance, and photostability makes reduced titania a candidate for many applications. In this work, stable reduced titania films were synthesized on silicon substrates via pulsed laser deposition (PLD) under a forming gas environment at elevated temperatures. The atomic/electronic structure and the electrical properties of the PLD reduced titania films were investigated using four-point probe, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy (XAS), and ultraviolet photoelectron spectroscopy (UPS). The PLD films demonstrated a notable decrease in resistivity compared to those of stoichiometric TiO2 films reported in the literature. Raman spectroscopy and XAS revealed that the observed resistivities in these films are correlated to substoichiometric titania phases (Ti2O3 between 400-600 °C and the Ti3O5-like at 700 °C) present in them. UPS measurements on the sub-stoichiometric titania indicated a decrease in the work functions with a decrease in the titanium oxidation state. The ability to tune such electrical properties with careful control of preparation is key to using reduced titania as a flexible platform for material design.

New Li0.8M0.1Ti2(PO4)3 (M=Co, Mg) Electrode Materials for Lithium‐Ion Batteries: In Operando X‐Ray Diffraction and Ex Situ X‐ray Photoelectron Spectroscopy Investigations

AbstractPure Li0.8M0.1Ti2(PO4)3 (M: Co, Mg) phosphates with the NASICON‐type structure were synthesized using a solid‐state reaction. Depending on the cation, M, the synthesis temperature and the annealing duration were optimized. The electrochemical performances of Li0.8M0.1Ti2(PO4)3 were evaluated as negative electrode materials for Li‐ion batteries over two different voltage ranges, 1.5–3.0 V and 1.0–3.0 V. The best electrochemical results were obtained for the voltage range 1.5–3.0 V with discharge capacities of 100 mAh g−1 and 80 mAh g−1 for Li0.8Co0.1Ti2(PO4)3 and Li0.8Mg0.1Ti2(PO4)3, respectively, over 20 cycles with capacity retentions exceeding 80 %. Raman spectroscopy was used to confirm the formation of the carbon layer after the carbon‐coating procedure. In operando XRD was performed to investigate the structural changes upon the first discharge/charge cycle, showing the progressive evolution of Li‐poor and Li‐rich phase fractions. Ex situ XPS analysis was conducted to follow the oxidation state of titanium during the insertion/de‐insertion of lithium ions, demonstrating that the redox couple (Ti4+/Ti3+) is reversibly active during the electrochemical cycling.