EP3221909A1

EP3221909A1 - Nanometric anatase lattice stabilised by cation vacancies, methods for the production thereof, and uses of same

Info

Publication number: EP3221909A1
Application number: EP15861644.1A
Authority: EP
Inventors: Damien Dambournet; Wei Li; Henri Groult; Sandrine LECLERC; Christian Julien; Karim Zaghib
Original assignee: Hydro Quebec; Centre National de la Recherche Scientifique CNRS; Universite Pierre et Marie Curie Paris 6
Current assignee: Hydro Quebec; Centre National de la Recherche Scientifique CNRS; Universite Pierre et Marie Curie Paris 6
Priority date: 2014-11-20
Filing date: 2015-11-20
Publication date: 2017-09-27
Also published as: CA2963732A1; US20180277840A1; JP6692810B2; CN107210430B; WO2016077933A1; CA2963732C; US10680241B2; KR102411459B1; KR20170084311A; EP3221909A4; JP2017536320A; CN107210430A

Abstract

The invention relates to a method for producing titanium-containing compounds having an anatase-type structure with cation vacancies resulting from a partial substitution of oxygen atoms with fluorine atoms and hydroxyl groups. The invention also relates to electrochemically active materials comprising titanium-containing compounds for use in lithium-ion battery electrodes.

Description

NANOM ANATASE NETWORK STABILIZED BY CATIONIC GAPS, PROCESSES FOR THEIR PREPARATION AND THEIR

USES

PRIORITY APPLICATION This application claims priority, under the applicable law, of US Provisional Application No. 62 / 082,345 filed on November 20, 2014, the contents of which are hereby incorporated by reference in its entirety and for all purposes.

TECHNICAL FIELD The invention relates to a chemical process which allows the preparation of anatase nanoparticles containing a controllable quantity of cationic vacancies by the partial substitution of oxygen by fluorine atoms and / or hydroxyl groups, and their uses in electrodes for lithium batteries. CONTEXT

Energy supply is one of the greatest challenges of the 21st century. Concomitant climatic changes to future limited fossil fuel resources are pushing towards the use of clean energy sources. It is expected that the storage of electrochemical energy will play a major role in the decarbonization of our energy. Batteries, which are devices capable of storing energy through electrochemical reactions, are considered one of the most promising technologies to meet future societal challenges such as electrical transport and storage systems. Stationary energy that can be used, for example, to support wind or solar energy.

With regard to negative electrodes, the use of carbon electrodes is limited, due to safety concerns and low capacity. In contrast, titanium-based compounds are considered very good candidates as safe negative electrodes for lithium batteries. Indeed, the operating voltage of this class of materials is in the zone of stability of the electrolyte, that is to say> 0.8V. This imparts improved safety features to the battery, as well as the desirability of a thermally unstable electrolyte-solid interface (SEI) layer and lithium plating on the anode.

Another interesting feature of titanium-based compounds is their ability to sustain high charge / discharge rates, which is necessary for high power applications, such as electric vehicles. A commonly used approach to achieving an improved capacity rate is the reduction of particle size. A complementary approach involves modifying the structural arrangement through ionic substitutions.

In the family of titanium dioxide, the anatase form (tetragonal, space group: I4i / amd) has been extensively studied because of its particular properties. Based on the Ti ⁴⁺ / Ti ³⁺ reducing-oxidant pair, a capacity of 335 mAh / g can be obtained. The anatase structure is built from octahedron units Τ \ 0 ₆ linked by common edges. This three-dimensional structure has suitable vacant sites for lithium intercalation via a first-order reversible transition, i.e. from a tetragonal system to an orthorhombic system. This phase transition behavior is characterized by a plateau region in the potential / capacitance curve. Nevertheless, a solid solution property over the full range of lithium compositions is preferred for practical applications. Indeed, this generally avoids a high rate nucleation process and easier monitoring of the state of charge of the battery compared to first-order transition materials. SUMMARY

According to a first aspect, the invention relates to a method for preparing a titanium-based compound having anatase-like structure with cationic vacancies resulting from a partial substitution of oxygen atom (s) by one or more fluorine atom (s) and hydroxyl group (s). For example, the method comprises the steps of: a) preparing a solution containing a titanium precursor, a fluorinating agent and a solvent; and

b) precipitation of a titanium compound having the general chemical formula Tii- _x- yDx ₊ yF x (OH) yO2 _-4 (x + y), where □ represents a cationic gap and wherein x and y are numbers such as 0.01 <(x + y) <0.5, or such that 0.04 <(x + y) <0.5.

In one embodiment, the titanium precursor is selected from titanium C ₂ -C ₁₀ alkoxides and titanium tetrachloride. In another embodiment, the fluorinating agent is an agent that provides fluoride anions, preferably hydrogen fluoride (HF), ammonium fluoride (NH ₄ F), or ammonium difluoride and difluoride. hydrogen (NH HF ₂ ). In another embodiment, the solvent of the solution of step (a) is an organic solvent or a mixture of organic solvent and water, for example a mixture in which the organic solvent is the major component, such as an organic solvent containing traces of water. For example, the organic solvent is selected from C1-C10 alcohols (such as methanol, ethanol, isopropanol, butanol, and octanol), dialkyl ketones (e.g., acetone), ethers, esters or a combination thereof. In one embodiment, step (b) of the method further comprises a heat treatment (e.g., in a sealed container) which comprises, for example, heating the solution of step (b) to a temperature in the range of about 50 ° C to about 220 ° C, or about 90 ° C to about 160 ° C. According to one embodiment, the degree of cationic vacancies (□) is controlled by adjusting the temperature of the heat treatment.

The invention also relates to a compound based on titanium of general chemical formula: _-X- Til YDX yF ₊ ₄ x (OH) ₄ y02- ₄ (x + y)

in which,

□ represents a cationic gap; and

x and y are numbers and have the formula 0.01 <(x + y) <0.5, or the formula 0.04 <(x + y) <0.5. In one embodiment, the titanium compound is prepared according to the method of the invention. In another embodiment, the titanium compound is TiO _. 78no.22Fo.4 (OH) o _{. 8} Oi _. i ₂ .

The invention also relates to an electrochemically active material comprising a titanium compound prepared according to the process of the invention or a titanium-based compound as defined herein; an electrode comprising the electrochemically active material and a current collector; and lithium-ion batteries comprising them.

Other features and advantages of the present invention will be better understood on reading the description below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a powder X-ray diffraction pattern of a phase prepared according to Example 1. The diagram has been indexed using quadratic symmetry, characteristic of the anatase network. FIG. 2 illustrates a high resolution transmission electron micrograph (TEM) obtained from the phase prepared according to Example 1. Figure 3 shows the Ti2p XPS ring spectrum obtained from the phase prepared according to Example 1.

Figure 4 shows a ¹⁹ F NMR spectrum by magic angle rotation of the phase prepared according to Example 1. Figure 5 shows the correlation between the synthesis temperature and the chemical composition of T11- _x- yDx ₊ y0 _2-4 (x + y ₎ F x (OH) y. The occupancy of the Ti (4a) site was determined by the structural analysis of the diffraction data.

Figure 6 shows the potential as a function of the capacity of a Li / Tio.78no.22Fo.4o (OH) o cell. ₄ 80i.i2 cycled between 1 and 3V at 20 mA / g. Insert: Voltage profile of a Li / Ti0 ₂ cell.

Figure 7 demonstrates the quasi-equilibrium potential obtained by the intermittent galvanostatic titration technique. The Li / Ti ₀ cell. ₇ 8no.22Fo. ₄ o (OH) o. ₄ 80i.i2 was discharged intermittently at a rate of C C / 10 (33.5 mA / g) for 20 min followed by 20 hours of relaxation. The x axis refers to the number of Li ions inserted into the Tio electrode. ₇ 8no.22Fo. o (OH) o. ₄₈ Oi.i2.

Figure 8 shows the capacity rate of a Li / Tio.78no.22Fo cell. ₄ o (OH) o. 80i.i2. For comparison purposes, the data obtained for a Li / TiO ₂ cell at 335 mA / g are also indicated.

DETAILED DESCRIPTION The present invention relates to methods for the preparation of titanium-based compounds having anatase-like structure with cationic vacancies resulting from substitution of oxygen atoms by fluorine / hydroxyl groups. The degree of cationic vacancies can be controlled by the amount of fluorine / OH groups substituting the oxygen atoms within the anatase network. The general chemical formula of the compound prepared is T _-X- yDx ₊ yF _x (OH) y o _2-4 (x + y), where □ represents a cationic gap and x and y are such that their sum is between 0.01 and 0.5, or between 0.04 and 0.5, the upper limit being excluded.

The presence of cationic gaps within the network provides additional vacant sites to accommodate lithium ions and increase ion mobility, thus potentially contributing to higher energy / power density.

The invention further relates to electrochemical cells utilizing the titanium compounds herein prepared as an electrode with a structural arrangement / chemical formula allowing a lithium storage mechanism contributing to high power and high energy density obtainable . The modification of the structural arrangement by the control of the chemical composition induces a variation in the electrochemical response when tested as a negative electrode in lithium batteries. Indeed, the presence of cationic vacancies and fluorine atoms within the lattice induces a reversible solid solution behavior at the time of lithium intercalation as opposed to the reversible first-order transition observed with stoichiometric an2 anatase. . In addition, a significant improvement in capacity ratio, compared to pure ΤΊΟ2, can be achieved with the present material, when used as an electrode, being suitable for high power applications.

The present invention describes the preparation of titanium-based compounds having anatase-like structure with cationic vacancies induced by the partial substitution of oxygen by fluorine and hydroxyl groups, and their uses in negative electrodes for lithium-ion batteries. ion. In certain embodiments, this application describes a method of preparation using, but not limited to, the following steps: a) preparing a solution containing a titanium precursor and a fluorinating agent; and b) Precipitation of a titanium compound having the general chemical formula Τίι _-χ-γ _{+ γ} θ2 _{-4 (} χ + _γ) Ρ _χ (ΟΗ) _γ , where □ represents a cationic gap and wherein x and y are numbers such that 0.01 <(x + y) <0.5, or such that 0.04 <(x + y) <0.5, for example, 0.1 <(x + y) <0.3, where x can not be zero .

For example, the titanium precursor of step (a) is selected from C ₂ -C ₁₀ alkoxides of titanium and titanium chloride. For example, the C ₂ -C ₁₀ alkoxide of titanium may be selected from ethoxide, propoxide, isopropoxide and / or titanium butoxide. The fluorinating agent is an agent acting as a source of fluoride anion including, for example and without limitation, hydrogen fluoride (HF), ammonium fluoride (NH ₄ F), and ammonium difluoride and difluoride. hydrogen (NH ₄ HF ₂ ). The fluorinating agent may be in the form of a solution, for example, of an aqueous solution, such as a concentrated solution of hydrofluoric acid. For example, the solvent used in the solution of step (a) is an organic solvent or a mixture of organic solvent and water. The organic solvent is chosen from C1-C10 alcohols, dialkyl ketones (for example, acetone), ethers and esters. Examples of C1-C10 alcohols include methanol, ethanol, isopropanol, butanol, and octanol.

In one embodiment, a solution containing a titanium alkoxide, an alcohol and a fluoride ion source is used. The molar ratio of fluoride and titanium preferably varies from 0.1 to 4, preferably the molar ratio is 2.0. Typically, a solution containing titanium alkoxide, fluoride and organic solvent is prepared and then transferred to a sealed container, for example, a sealed Teflon ^® -contaminated container. The sealed container is then placed in an oven and subjected to a temperature, for example, in the range of from about 50 ° C to about 200 ° C, or from about 90 ° C to about 160 ° C, or the temperature is set at about 90 ° C. The duration of the heat treatment is preferably between 1 and 300 hours, preferably about 12 hours. After filtration, the precipitate is then washed and degassed overnight at a temperature of from 50 to 400 ° C, preferably at 150 ° C.

Several fluorinated anatase compounds, having different chemical compositions, have been prepared for exemplary purposes by the preparation method of the present application. For comparison purposes, a fluorine-free compound was prepared by heat treating a fluorinated compound at 450 ° C for 4 hours under an air atmosphere.

EXAMPLES

The following non-limiting examples illustrate the invention. These examples and the invention will also be better understood with reference to the appended figures.

Example 1

Fluorinated anatase was obtained by treating a solution containing 13.5 mmol of titanium isopropoxide (4 mL) and 27 mmol of aqueous HF (40%) in 25 mL of isopropanol in a sealed container at 90 ° C. for 12 hours. Figure 1 shows the X-ray powder diffraction pattern (CuKa) recorded on the sample obtained according to this example. The corresponding diagram was indexed using the quadratic structure with the space group 14 amd, which is characteristic of the anatase network. The sample is well crystallized and an enlargement of x-ray lines has been observed, indicating small domains of coherence.

High resolution transmission electron microscopy (HRTEM) (Figure 2) revealed that the morphology of the solid consists of agglomerates of particles ranging in size from 5 to 8 nm. In addition, broadening of hkl-dependent x-ray lines and HRTEM indicate the formation of faceted crystals, i.e., platelets, in accordance with a recent article (HG Yang et al., 2008, Nature, Vol 453, pp. 638-641) which emphasizes the role of fluorine atoms in the stabilization of metastable surfaces. The specific surface, determined by nitrogen adsorption on the sample prepared according to this example, was about 180 m ² / g.

The oxidation state of the titanium within the sample was determined using X-ray photoelectron spectroscopy. Figure 3 shows the XPS core spectrum of Ti2p with the Ti 2p _3/2 ring. located at 458.9 eV, characteristic of tetravalent titanium.

The fluorine atom content in the prepared sample was evaluated using Solid State Nuclear Magnetic Resonance of the fluorine ring ( ¹⁹ F). The estimation of the molar ratio F / Ti was performed using a reference (NaF) and led to a ratio of 0.5. The chemical composition of the sample was Tio _. 78no.22 o.4 (OH) o.4eOi .i 2. For information, the three signals observed in the ¹⁹ F MAS NMR spectra (Figure 4) have been assigned to various modes of fluorine coordination within the anatase network. The peak centered at -85 ppm was assigned to a coordinated fluorine with three titanium ions. The most intense peak near 0 ppm is characteristic of a bridged fluorine and has therefore been attributed to fluoride ions located near a gap. Finally, the broad signal detected at about 90 ppm was assigned to fluoride ions located near two gaps, i.e., coordinated once. From the relative intensity, it was concluded that the fluoride ions preferentially adopted a coordination of 2, which is close to a gap.

Synchrotron diffraction was also used to obtain the crystallographic data from the sample. The results were compared to those of a fluorine free TiO ₂ compound and are summarized in Table 1. ableau 1. Structural parameters obtained by diffraction data analysis.

Both compounds showed values close to unit cell parameters and interatomic distances. The refinement of the fluorine-free Ti0 ₂ occupancy rates led to a 100% occupancy rate confirming the stoichiometric composition. On the other hand, the fluorinated compound has a Ti (4a) occupancy of 78%. Thus, the combination of different techniques, including elemental and thermal analyzes, makes it possible to determine a chemical composition of Ti _0.78 no.22Fo _.4 (OH) _0.4 80i _. i ₂ for the sample prepared in this example. Example 2

The content of cationic vacancies in Ti _{1 -x-} yDx ₊ yF ₄ x (OH) ₄ _y o _2- (x _{+ y} ) can be controlled synthetically. Different cationic concentrations were obtained by adjusting the reaction temperature under the conditions of Example 1. Solutions containing 13.5 mmol of titanium isopropoxide (4 mL) and 27 mmol of aqueous HF (40%) in 25 mL of isopropanol, placed in sealed containers, were treated at various temperatures ranging from 90 to 160 ° C. for 12 hours. The cationic content of the prepared samples was determined by the analysis of the diffraction data. The results presented in FIG. 5 showed a linear variation of the cationic content as a function of the reaction temperature.

Example 3

The Tio _. 78no.22Fo _.4 (OH) o _.4 80i _. i ₂ prepared according to Example 1 was tested in a cell Li / Ti _0.78 no.22Fo _.4 (OH) o _.4 _80i. i ₂ . The electrochemical cell is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode consists of a mixture of 80% (by weight) of Ti0.78n0.22F0.88O1.12 powder, 10% (by weight) of carbon, and 10% (by weight) of binder. PVDF, coated on a copper foil. The negative electrode was metallic lithium and served as a reference. A commercial solution of LP30 was used as the non-aqueous electrolyte. It contains LiPF ₆ dissolved in a solvent mixture ethylene carbonate (EC) and dimethyl carbonate (DMC).

Figure 6 shows potential curves as a function of the capacity of a Li cell / Tio _.78 _.22 No Fo _.4 (OH) _{o. 8} Oi _. i ₂ at 20 mA / g for the first three cycles. The voltage window has been set between 1 and 3V. The first discharge capacity far exceeded the theoretical capacity, reaching 490 mAh / g. A large irreversible capacity is observed during charging, with a load capacity of up to 230 mAh / g. Such a phenomenon is commonly observed for materials based on nanometric titanium and is attributed to lithium reacting with surface species (H ₂ 0, OH groups, etc.). The most striking point here is the shape of the discharge (reduction) and charge (oxidation) curves showing a continuous evolution of the potential with respect to the capacitance, which indicates that the fluorinated anatase Ti _0.78 No. ₂₂ Fo _{. 4} (OH) _{O. 8} Oi _. i ₂ inserts lithium topotactic manner by a process in a single phase, that is to say a solid solution behavior. This is in contrast with the TiO ₂ anatase which inserts lithium by a two-phase process (first-order transition) according to a quadratic phase transition (14 amd) to orthorhombic (Imma) characterized by the presence of a Li plateau. at 1.78V (inset in Figure 6).

To confirm that the reaction with lithium proceeds via a solid solution behavior, the near-equilibrium potential (Figure 7) was obtained by the technique of intermittent galvanostatic titration (GITT). The GITT graph shows a smooth curve underlining that lithium is inserted into the Tio _. 78no _.22 Fo _.4 (OH) o _.48 Oi _. i ₂ via solid solution behavior.

Figure 8 shows the evolution of the capacity as a function of the number of cycles for a cell Li / Tio.78no.22Fo.88Oi.i2. Excellent capacity retention has been achieved under high current density. The cell Li / Ti ₀ .78no.22Fo.88Oi .i2 can indeed support a capacity of 135 mAh / g after 50 cycles under 3335 mA / g. This corresponds to discharging 135 mAh / g in 4 minutes, which is equivalent to a rate of 15C. For comparison purposes, the Li / TiO ₂ cell cycled at 335 mA / g achieved 165 mAh / g after 10 cycles, demonstrating the higher capacity rate of the fluorinated anatase vis-à-vis the fluorine-free sample.

Many modifications could be made to one or other of the embodiments described above without departing from the scope of the invention as envisaged. References, patents, or scientific literature referred to herein are hereby incorporated by reference in their entirety and for all purposes.

Claims

1. A method of preparing a titanium-based compound having anatase-like structure with cationic vacancies resulting from a partial substitution of oxygen atoms by fluorine atoms and hydroxyl groups.

The method of claim 1 comprising the steps of:

a) preparing a solution containing a titanium precursor, a fluorinating agent and a solvent; and

b) precipitating the titanium-based compound having the general chemical formula Tii- _x- yDx ₊ yF x (OH) yO2 _-4 (x + y), wherein □ represents a cationic gap and wherein x and y are numbers such that 0.01 <(x + y) <0.5, or such that 0.04 <(x + y) <0.5.

3. Method according to claim 2, wherein the titanium precursor is selected from titanium C2-Cioalkoxides and titanium chloride.

4. The method of claim 2 or 3, wherein the fluorinating agent is an agent which provides fluoride anions, preferably hydrogen fluoride (HF), ammonium fluoride (NH F), or difluoride d ammonium and hydrogen (NH ₄ HF ₂ ).

The method of any one of claims 2 to 4, wherein the solvent of the solution of step (a) comprises an organic solvent or a mixture of organic solvent and water.

6. The method of claim 5, wherein the organic solvent is selected from C1-C10 alcohols, dialkylketones, for example, acetone, ethers, esters or a combination thereof.

The method of claim 5 or 6, wherein the organic solvent is methanol, ethanol, isopropanol, butanol, octanol or a combination thereof.

The method of any one of claims 2 to 7 wherein step (a) or (b) further comprises a heat treatment.

The method of claim 8, wherein the heat treatment comprises heating the solution of step (a) to a temperature in the range of about 50 ° C to about 220 ° C, or about 90 ° C to about 160 ° C.

The method of claim 8 or 9, wherein the degree of cationic vacancies (□) is controlled by adjusting the temperature of the heat treatment.

1 1. Compound based on titanium of general chemical formula:

Til _-X- y --- lx + yF ₄ x (OH) ₄ y02 _-4 (x + y)

in which,

□ represents a cationic gap; and

x and y are numbers and correspond to the formula 0.01 <(x + y) <0.5, or 0.04 <(x + y) <0.5.

A titanium compound prepared by a process according to any one of claims 1 to 10, wherein said compound is of general chemical formula:

Til _-X- y --- lx ₊ y02 _{-4 (} x ₊ y) F ₄ x (OH) ₄ y

in which,

□ represents a cationic gap; and

13. titanium-based compound according to claim 1 1 or 12, which is Τίο.78Πθ.22Ρο.4 (ΟΗ) ο.48θι .ΐ 2-

An electrochemically active material comprising a titanium compound prepared according to the method as defined in any one of the Claims 1 to 10 or a titanium-based compound as defined in any one of Claims 1 to 13.

An electrode comprising the electrochemically active material of claim 14 on a current collector.

16. A lithium-ion battery comprising the electrode of claim 15, a counter-electrode and an electrolyte between the electrode and the counter-electrode.