WO2019145181A1

WO2019145181A1 - Electrode material comprising carbon-coated titanium dioxide particles

Info

Publication number: WO2019145181A1
Application number: PCT/EP2019/050831
Authority: WO
Inventors: Jun Wang; Jie Li; Xin He; Xiaofei Zhang; Elie Paillard; Tobias PLACKE; Martin Winter
Original assignee: Westfälische Wilhelms-Universität Münster; Forschungszentrum Jülich GmbH
Priority date: 2018-01-23
Filing date: 2019-01-14
Publication date: 2019-08-01
Also published as: EP3743954A1; DE102018101484A1

Abstract

The invention relates to an electrode material having a porous agglomeration of carbon-coated titanium dioxide particles, titanium dioxide particles being coated with carbon and forming spherical TiO2/C particles, which agglomerate to form a porous three-dimensional structure, the average diameter of the pores between the TiO2/C particles lying in the range of ≥ 50 nm to ≤ 200 nm. The invention further relates to electrodes produced therefrom.

Description

Electrode material comprising carbon-coated titanium dioxide particles

Description

The invention relates to an electrode material comprising carbon-coated

Titanium dioxide particles, a process for their preparation and its use as

Anode material in lithium ion batteries, sodium ion batteries and

Supercapacitors.

Climate change and the decreasing availability of fossil fuels make the demand for sustainable and renewable energy resources more and more important. Therefore, it is of paramount importance to have a renewable energy production based on

Developing solar energy, water and wind as well as mobility concepts such as electric vehicles or hybrid electric vehicles with low CCh emissions. Without

Energy storage systems, such as rechargeable batteries and electrochemical

However, capacitors (ECs) will hardly be feasible for such applications.

Lithium ion rechargeable batteries (LIBs) were commercially introduced in 1991 by Sony. The high energy density of LIBs has transformed portable electronics in the last two decades. Due to the much higher sodium deposits are also Rechargeable sodium ion batteries (NIBs) are considered as promising candidates for large-scale production.

Electrochemical capacitors are power devices that can be fully charged or discharged in seconds; as a result, their energy density (about 5 Wh kg ¹ ) is lower than in batteries, but much higher power output (about 10 kW kg ¹ ) can be achieved within a shorter time, for example a few seconds. Electrochemical capacitors therefore play an important role in supplementing or replacing batteries in the field of power supply such as uninterruptible power supplies (backup accessories to protect against power supply disruptions) and load balancing.

The performance of these storage systems is closely related to the properties of their materials. Innovative materials are at the heart of the advances made in the

Energy conversion and storage have already been achieved, and further breakthroughs in materials are key to new generations of energy storage and storage

Energy conversion systems. Among the various suitable ones

Transition metal oxides became titanium dioxide (Ti0 ₂ ) because of its exceptional stability as a potential active material for lithium and sodium ion batteries as well

extensively studied electrochemical capacitors. A disadvantage of using pure titanium dioxide are its low electronic conductivity and slow

Ion diffusion.

In addition, carbon films are known to be a successful strategy for improving electrochemical performance. For example, Vinod Mathew et al. in Journal of The Electrochemical Society, 162 (7) A1220-A1226 (2015) an anode of porous titanium dioxide prepared by a polyol-based pyrosynthetic process. However, known methods of carbon coating lead to a phase separation or agglomeration of TiCh nanoparticles and / or an inhomogeneous distribution of Carbon layer, which leads to a relatively low electronic conductivity, slow ion diffusion and low electrochemical performance.

There is therefore a continuing need for carbon-based electrode material

coated titanium dioxide particles. It is an object of the present invention to provide such a material and method of making the material suitable for use as an electrode material in a lithium-ion battery.

This object is achieved by an electrode material with a porous agglomeration of carbon-coated titanium dioxide particles, wherein titanium dioxide particles are coated with carbon and form spherical Ti0 ₂ / C particles, which agglomerate into a porous three-dimensional structure, wherein the average diameter of the Pore between the TiCh / C particles in the range of> 50 nm to <200 nm.

Surprisingly, it has been found that electrodes which are porous according to the invention

Contain agglomeration or structure of carbon-coated titanium dioxide particles as electrode material, have a very high capacity. In particular, the electrodes demonstrated a stable cycle capacity of over 500 cycles in lithium and sodium ion batteries and over 2000 cycles in lithium and sodium ion based

Supercapacitors.

It is believed that these results are based in particular on the structure of the porous active material. The agglomerated particles form a three-dimensional structure in which small, primary TiCh nanoparticles are coated with carbon and thereby form spherical TiCh / C secondary particles, which in turn agglomerate into a three-dimensional structure. In particular, the agglomerated structure has a platelike morphology. Without being bound to a particular theory, it is believed that in addition to the surface properties such as pore size and pore volume and the Particle size, in particular the morphology of the electrode material for the promising electrochemical properties provides.

The term "particles" is used synonymously with "particles" in the sense of the present invention. The term "average diameter" is understood to mean the average value of all diameters or the arithmetically averaged diameters relative to the respective particles or pores. The pore size or pore diameter can be evaluated using field emission scanning electron microscopy (SEM). The pore volume of the electrode material was measured using

Nitrogen adsorption measurements determined by nitrogen adsorption isotherms.

In preferred embodiments, the average diameter of the pores between the spherical TiO ₂ / C particles is in the range of> 50 nm to <200 nm. The average diameter of the pores between the primary titanium dioxide particles is preferably in the range of> 2 nm to < 10 nm, preferably in the range of> 3 nm to <6 nm. The pore structure provides the electrode material with outstanding capacitive performance for both lithium ion and sodium ion batteries and supercapacitors, as demonstrated by electrochemical studies.

It is assumed that in particular pore volume and BET surface area influence the electrochemical properties. In preferred embodiments, the average pore volume of the porous agglomeration is in the range of> 0.05 cm ³ / g to <0.2 cm ³ / g, preferably in the range of> 0.06 cm ³ / g to <0.14 cm ³ /G. The middle one

Pore volume may for example be 0.1 cm ³ / g. The high pore volume can contribute to a high capacity of an electrochemical cell. In preferred

Embodiments, the BET surface area of the porous agglomeration is in the range of> 60 m ² / g to <100 m ² / g, preferably in the range of> 65 m ² / g to <70 m ² / g. The BET surface area can be, for example, 68 m ² / g. The BET surface can through

Determination of the specific surface area of solids by gas adsorption after Brunauer-Emmett-Teller (BET) method can be determined by means of the adsorption of nitrogen, for example using a porosimeter. The electrode material advantageously has a high pore volume and a large Brunauer-Emmett-Teller (BET) surface. It is believed that the large pore volume and large BET surface area lead to the high measured capacities of about 300 mAh g ¹ in lithium ion cells and about 280 mAh g ¹ in sodium ion cells.

Preferably, the titanium dioxide particles have a size in the nanometer range. In preferred embodiments, the titanium dioxide particles have an average

Diameter in the range of> 1 nm to <50 nm, preferably in the range> 1 nm to <10 nm, more preferably in the range of> 2 nm to <10 nm, on. A small size of the primary TiCh particles enables the electrochemical performance of the

Electrode material. Titanium dioxide is a stable and abundant and

largely biocompatible material. In addition, titanium dioxide is chemically resistant. Titanium dioxide (TiO ₂ ) is understood as meaning titanium-valent oxides of titanium. Titanium dioxide forms a polymorphic oxide which, in addition to the three naturally occurring modifications, rutile, anatase and brookite, are synthetically engineered modifications. Useful polymorphic modifications are selected from fluorite, pyrite, rutile, anatase, hollandite, brookite, ramsdellite, columbite, cotunnite, modified fluorite, bronze, baddeleyite, the Fe ₂ P-type hexagonal phase, and mixtures thereof. Preferred polymorphic

Modifications are selected from the types rutile, anatase and brookite.

The carbon-coated titanium dioxide particles, also referred to as TiO ₂ / C particles, have a spherical or spherical shape. Spherical or spherical particles have the advantage of allowing good contact as electrode material. In preferred embodiments, the spherical TiO ₂ / C particles have an average diameter in the range of> 10 nm to <1 pm, preferably in the range of> 50 nm to <500 nm. Advantageously, spherical particles, in particular with a size in the nanometer range, can provide a high specific surface area put. This allows a large contact surface of the particles with the electrolyte and thus a high number of possible reaction sites with those contained in the electrolyte

Charge-bearing ions, in particular Li ⁺ - or nations.

The spherical Ti0 ₂ / C secondary particles agglomerate into a three-dimensional structure. In preferred embodiments, the porous three-dimensional structure comprises platelet-shaped particles, wherein the platelet-shaped particles preferably have an average diameter in the range of> 1 gm to <100 gm, preferably in the range of> 2 pm to <50 pm. The free volume between the platelet-shaped particles can in the

Range from> 500 nm to <10 pm, preferably in the range of> 500 nm to <5 pm. It is believed that the platelet-like morphology of the agglomerate, and particularly the large intervening volume, promotes the advantageous electrochemical properties of the electrode material.

The carbon coating of the titanium dioxide particles advantageously increases the electronic conductivity of the material. In preferred embodiments, the proportion of carbon, based on the total weight of the porous agglomeration, in the range of 0.1 wt .-% to <30 wt .-%, preferably in the range of 2 wt .-% to <10 wt. %. The proportion of carbon can be determined gravimetrically as shown in the examples.

The carbon may be formed of amorphous carbon, carbon nanotubes, graphene and mixtures thereof.

The coating of the titanium oxide particles with carbon can be achieved and controlled by calcining a carbonaceous compound and a titanium compound. A preferred carbonaceous compound is graphene oxide. Under

"Graphene oxide" is understood to mean an oxidized and oxygenated functional grouped, single-ply or low-lathing graphene derivative. Graphene oxide can be prepared by reacting naturally occurring graphite with strong oxidants and provides a starting material for the recovery of graphene in high yields Available. Graphene oxide decomposes already at temperatures around 100 ° C to graphene and C0 / C0 ₂ . In particular, it was found that during calcination by decomposition of graphene oxide, an advantageously homogeneous distribution of the carbon coating on the simultaneously produced titanium oxide particles could be achieved.

The superior electrochemical performance is overall the structure of the

Attributed to electrode material that combines the advantages of a small primary particle size, large voids between the agglomerated platelet particles, and a homogeneous carbon coating.

Another object of the present invention relates to a method for producing a porous agglomeration of carbon-coated titanium dioxide particles, comprising the following steps:

a) preparing a solution (I) comprising a titanium compound and optionally a

Contains chelating agent;

b) preparing a solution (II) containing a reducing agent, a carbon source and optionally a surfactant;

c) combining solutions (I) and (II) to form a slurry;

d) mixing the slurry obtained from step c);

e) isolating a precipitate of a precursor compound obtained from the slurry of step d);

f) freeze-drying the precipitate of the precursor compound obtained from step e); g) calcining the precursor obtained from step f) to produce the porous agglomeration of carbon-coated titanium dioxide particles.

The method is in particular a method for producing an electrode material, in particular for lithium and sodium ion-based energy storage and

Supercapacitors, in particular lithium and sodium ion-based supercapacitors, containing a porous agglomeration of carbon-coated titanium dioxide particles. First, a solution (I) containing a titanium compound is prepared. The titanium compound may be an organic or inorganic titanium (IV) salt. The salt may be, for example, a sulfate, acetate, carbonate, nitrate, chloride, oxalate, an alkyl titanate, or a mixture thereof. The solution (I) may contain a chelating agent. Preferably, the chelating agent is selected from the group comprising glutamic acid, histidine,

Methylamine, ethylenediamine, acetic acid, ethylenediaminetetraacetic acid, phytochelatin, malate and mixtures thereof. The weight ratio of the chelating agent to the titanium compound in the solution (I) may be in the range of 0: 1 to 1: 1.

The solvent may be selected from water, an alcohol or a mixture thereof. Preference is given to an alcoholic solvent. Preferably, the solvent for solution (I) is selected from methanol, ethanol, propanol, butanol or mixtures thereof. Preferably, the weight ratio of the solvent to the titanium compound and the chelating agent in step a) is in the range of> 1: 1 to <999: 1, preferably in the range of> 2: 1 to <99: 1.

Furthermore, a solution (II) containing a reducing agent and a carbon source is prepared. Preferably, the reducing agent is selected from formic acid, oxalic acid, ascorbic acid and mixtures thereof. Preferably, the carbon source is selected from organic carbon compounds, carbon nanotubes, graphene and

Graphene oxide, or mixtures thereof. Preferably, the carbon source is graphene oxide. The solution (II) may contain a surfactant. Preferably, the surfactant is selected from

Disodium monolauryl sulfosuccinate (disodium 4-dodecyl-2-sulfonato succinate),

Disodium laureth-3-sulfosuccinate, disodium cocoyl monoethanolamide sulfosuccinate, sodium dodecylbenzene sulfonate, anionic phosphate ester-based diethyl salicylates such as lauryl alcohol phosphate ester and potassium salts of lauryl alcohol phosphoric esters, lauramidopropylamine oxide and mixtures thereof. The solvent may be selected from water, an alcohol or a mixture thereof. Preferably, the solvent for solution (II) is a mixture of alcohol and water. The alcohol is preferably selected from methanol, ethanol, propanol, butanol or mixtures thereof.

Preferably, the weight ratio of the alcohol to water in step b) is in the range of> 1: 99 to <99: 1, preferably in the range of> 1: 9 to <9: 1.

Preferably, the weight ratio of the reducing agent to the solvent in step b) is in the range of> 1: 999 to <1: 9.

Preferably, the weight ratio of the carbon source to the solvent in step b) is in the range of> 1: 99 to <1: 1, preferably in the range of> 1: 99 to <1: 2. Preferably, the weight ratio of the surfactant to the solvent in Step b) in the range of> 1: 999 to <1: 9, preferably in the range of> 1: 999 to <1: 99.

The solutions (I) and (II) are combined in step c) to form a slurry. The reaction temperature in step c) may be in the range of 0 ° C to 100 ° C. The slurry is mixed in step d), in particular mixed homogeneously. This can be assisted by stirring, especially for several hours, for example for 6 to 12 hours, and aging of the slurry. Subsequently, in step e), a precipitate obtained from the slurry from step d) is obtained

Isolated precursor compound. This can be achieved in particular by repeated washing and centrifuging. It is believed that the precipitate is formed from a precursor compound of the carbon-coated particles to be formed, with the carbon source depositing on the titanium compound. The precipitate of the precursor compound obtained from step e) is freeze-dried in step f).

Subsequently, the precursor obtained from step f) is calcined to produce the porous agglomeration of carbon-coated titanium dioxide particles. For the purposes of the present invention, the term "calcining" is understood as meaning the heating of a material in order to produce a state of thermal decomposition. The calcining For example, a titanium hydroxide or other titanium compound converts to titanium oxide. The calcination is preferably carried out under a protective gas atmosphere, for example in a reaction atmosphere of argon, a mixture of hydrogen and argon,

Nitrogen, or mixtures thereof. Preferably, the reaction temperature of the calcining is in the range of> 400 ° C to <1000 ° C. Preferably, the reaction time for calcining is in the range of 1 to 100 hours.

The titanium dioxide particles of the porous agglomeration obtained are coated with carbon and form spherical TiO ₂ / C particles which agglomerate into a porous three-dimensional structure, the average diameter of the pores between the TiO ₂ / C particles in the range of> 50 nm to <200 nm. For the further description of the porous agglomeration of carbon-coated titanium dioxide particles, reference is made to the above description. The resulting porous agglomeration of carbon-coated titanium dioxide particles is particularly useful as electrode material for lithium ion and sodium ion batteries and supercapacitors, particularly lithium and sodium ion based supercapacitors.

Another object relates to a porous agglomeration of carbon-coated titanium dioxide particles obtainable by the process according to the invention. This material can be used in particular for the production of electrodes, in particular anodes.

Another object of the invention relates to an electrode containing a

Inventive electrode material with a porous agglomeration of carbon-coated titanium dioxide particles or a porous agglomeration of carbon-coated titanium dioxide particles obtainable by the process according to the invention. The titanium dioxide particles are coated with carbon and form spherical TiO ₂ / C particles, which agglomerate into a porous three-dimensional structure, wherein the middle

Diameter of the pores between the Ti0 ₂ / C particles in the range of> 50 nm to <200 nm lies. For the further description of the electrode material is based on the above

Description Reference.

The porous agglomeration of carbon-coated titanium dioxide particles form the material, commonly referred to as "active material", of an electrode capable of reversibly receiving and releasing lithium or sodium ions. An electrode containing an electrode material according to the invention can advantageously be a very good

Show capacity behavior and a very good cycle stability.

In addition to the active material, an electrode usually still contains binder and conductive carbon. These are usually applied to a metal foil, such as a copper or aluminum foil, as a current conductor. Such an electrode is

commonly referred to as a composite electrode. In preferred embodiments, the electrode is a composite electrode comprising an electrode material according to the invention with a porous agglomeration of carbon-coated titanium dioxide particles. It can be provided to add further carbon for the production of an electrode.

Preferred carbonaceous materials are, for example, carbon black, synthetic or natural graphite, graphene, carbon nanoparticles, fullerenes, or mixtures thereof. A usable carbon black is, for example, carbon black. Leitruß is understood to mean a carbon black which has small primary particles and widely branched aggregates, and thus enables good electronic conductivity. A preferred carbon black is available, for example, under the trade designation Super C65 (Imerys). Furthermore, the composite electrode may comprise a binder. Suitable binders are, for example

Polyvinylidene difluoride (PVdF) or sodium carboxymethylcellulose (Na-CMC).

For example, the dry weight of a mixture of the porous agglomeration of carbon-coated titanium dioxide particles, binder and conductive carbon may be 80% by weight of the agglomerate, 10% by weight carbon black and 10% by weight of binder, for example PVdF, based on the total dry weight the mixture. The production of The electrode may include the steps of mixing the porous agglomeration with carbon black, mixing the solid mixture with a binder dissolved in a solvent, applying the slurry to an electronically conductive substrate, and drying the resulting electrode.

Another object relates to an electrochemical energy store, in particular a lithium or sodium ion-based electrochemical energy store or a supercapacitor, in particular a lithium and sodium ion-based

Supercapacitor containing an electrode according to the invention. The electrode contains an electrode material with a porous agglomeration of carbon-coated

Titanium dioxide particles. The titanium dioxide particles are coated with carbon and form spherical TiO ₂ / C particles, which agglomerate into a porous three-dimensional structure, wherein the average diameter of the pores between the TiCh / C particles in the range of> 50 nm to <200 nm , For the further description of the electrode material, reference is made to the above description.

The term "energy storage" in the context of the present invention includes primary and secondary electrochemical energy storage devices and energy storage systems, ie batteries (primary storage) and accumulators (secondary storage). In general

Spoken language, accumulators are often referred to by the term commonly used as a generic term "battery". Thus, the term lithium-ion battery is used synonymously with lithium-ion accumulator, unless otherwise specified. The term "electrochemical energy storage" for the purposes of the present invention also includes electrochemical capacitors or supercapacitors (English: electrochemical (super) capacitors). Electrochemical capacitors, also known in the literature as

Double-layer capacitors, or supercapacitors, are electrochemical energy storage devices that stand out from batteries by a significantly higher power density, compared to conventional capacitors by a orders of magnitude higher

Distinguish energy density. Electrochemical energy stores are preferably selected from the group comprising lithium ion batteries, lithium ion accumulators,

Sodium ion batteries and sodium ion accumulators. Preferably, the

Energy storage a lithium-ion battery or a lithium-ion battery. More preferably, the electrochemical energy store is a supercapacitor, in particular a lithium and sodium ion-based supercapacitor.

In preferred embodiments, the electrochemical energy store is a lithium or sodium ion battery comprising a positive electrode, a negative electrode, an electrolyte between the electrodes, the negative electrode containing the

comprises electrode material according to the invention. In further preferred embodiments, the electrochemical energy storage is a supercapacitor comprising a working electrode, a counter electrode, a reference electrode and an electrolyte, wherein the

Working electrode comprises the electrode material according to the invention. In further preferred embodiments, the electrochemical energy store is a lithium- and sodium-ion-based supercapacitor comprising a positive electrode, a negative electrode, and an electrolyte between the electrodes, the negative electrode comprising the electrode material according to the invention.

In principle, all electrolytes, solvents, conductive salts and counterelectrodes known to those skilled in the art, which are commonly used in lithium and sodium ion batteries and supercapacitors, can be used for the electrochemical energy store.

Preferred conducting salts are LiPF _ö and NaCl0. ₄ As the solvent of the electrolyte, mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC) or ethylene carbonate (EC) and propylene carbonate (PC) are particularly preferred.

Examples and figures which serve to illustrate the present invention are given below.

Here are the figures: Figure 1 in Figure la) and lb) Scanning electron micrographs of a porous

Agglomeration of carbon-coated titanium dioxide particles according to a first embodiment of the invention.

FIG. 2 shows the X-ray diffractogram of the carbon-coated titanium dioxide particles obtained.

Figure 3 shows the thermogravimetric analysis of the obtained carbon-coated

Titanium dioxide particles.

Figure 4 shows the Raman spectrum of the porous agglomeration of carbon-coated

Titanium dioxide particles.

FIG. 5 shows the X-ray diffractogram of a porous agglomeration of carbon

coated titanium dioxide particles according to a second embodiment of the invention.

FIG. 6 shows the results of the cyclization of a lithium-ion cell using a porous agglomeration of carbon-coated titanium dioxide particles as electrode material. Figure 6a) shows a plot of voltage versus capacitance for the first five cycles, Figure 6b) shows the capacitance of the electrode at various C rates plotted against the number of charge / discharge cycles, and Figure 6c) shows the charge capacity (left ordinate axis). and Coulomb efficiency (right ordinate axis) of the electrode plotted against the number of charge / discharge cycles at an applied current density of 85 mA g ¹ .

FIG. 7 shows the results of the cyclization of a sodium ion cell using a porous agglomeration of carbon-coated titanium dioxide particles as electrode material. Figure 7a) shows a plot of voltage versus capacitance for the first five cycles, Figure 7b) shows the capacitance of the electrode at various C rates plotted against the number of charge / discharge cycles, and Figure 7c) shows the charge capacity (left ordinate axis). and Coulomb efficiency (right ordinate axis) of the electrode plotted against the number of charge / discharge cycles at an applied current density of 85 mA g ¹ . FIG. 8 shows the results of the cyclization of a lithium-ion-based supercapacitor. Figure 8a) shows a plot of voltage vs. time for different current densities, Figure 8b) shows capacitance retention of the electrode versus scan rate, and Figure 8c) shows capacitance retention versus number of cycles.

FIG. 9 shows the results of the cyclization of a sodium ion-based supercapacitor.

Figure 9a) shows a plot of potential versus time for different current densities, Figure 9b) shows capacitance retention of the electrode plotted against current density, and Figure 9c) shows capacitance retention versus number of cycles.

example 1

Production of a porous agglomeration of carbon-coated titanium dioxide particles with anatase structure

For the synthesis of carbon-coated titanium dioxide particles with anatase structure, initially 120 ml of ethanol solution containing 20 g of tetrabutyl titanate (Ti (OC ₄ H 9) ₄ ) and 1.2 g of acetic acid were prepared. These were added dropwise to 240 ml of a 3: 1 by volume water / ethanol solution containing 8 grams of oxalic acid, 0.8 grams of sodium dodecylbenzenesulfonate (SDBS) and 28 grams of an aqueous slurry of graphene oxide (nanosheets, 1 weight percent) by WS Hummers and RE Offeman, J. Am. Chem. Soc., 1958, 80, 1339, added with stirring in an ice bath. The resulting light brown slurry was stirred for a further 12 hours and additionally aged for one hour. The precipitate was collected by centrifugation, washed repeatedly with ethanol and distilled water, and then freeze-dried. The resulting freeze-dried nanocomposite was then calcined at 450 ° C for 5 hours in a tube furnace under argon atmosphere. After cooling, the morphology and particle size of the particles obtained were determined. The crystal structure was determined by X-ray diffraction (XRD) with Cu-Ka radiation on a Bruker D8 Advance (Germany) in the 2Q range of 10 ° to 90 °. The morphology was determined by high-resolution scanning electron microscopy (SEM, microscope EVO MA 10, Zeiss). Transmission electron microscopy (TEM) images, high-resolution transmission electron microscopy (HRTEM) images and

"Selected-area electron diffraction (SAED) patterns were taken with an FEI Tecnai G2 F20 electron microscope at an acceleration voltage of 200 kV. Raman spectra were recorded with a SENTERRA Raman Microscope (Bruker Optics) with a 532 nm laser. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer Pyris Diamond Thermogravimetry / Differential Thermal Analyzer.

The nanocomposite obtained had a three-dimensional morphology, as shown in FIG. FIG. 1 a shows a representative scanning electron micrograph of the resulting composite. As can be seen from Figure la, the composite comprises platelet-like particles. The plate-like particles have a length of several micrometers. Between the platelets large cavities can be seen. These are particularly advantageous for electron transport and electrolyte wetting. It can be seen from the enlarged image of FIG. 1b that the platelet-like particles are composed of agglomerated, spherical secondary particles which are formed from graphene-coated TiO ₂ primary particles. In particular, a homogeneous carbon coating can be seen. HRTEM images showed that the Ti0 ₂ primary particles had a mean diameter smaller than 10 nm. The X-ray diffractometry signals shown in FIG. 2 showed that the signals of the obtained TiO ₂ coincide with those of the anatase phase.

The content of graphene was determined by thermogravimetric analysis (TGA). FIG. 3 shows the signal of the thermogravimetric analysis of the obtained TiO ₂ graph Composite. As can be seen from Figure 3, a major weight loss of 8.5% by weight was observed between 300 ° C and 600 ° C. This is attributed to the combustion of carbon into C0 ₂ and CO, suggesting that the content of

Graphene in the composite about 8.5 wt .-% was. The first weight loss of about 3.5% within the range of room temperature to about 300 ° C becomes elimination

attributed to physically adsorbed water molecules.

The Raman spectrum of the TiO ₂ graphite composite shown in FIG. 4 shows typical bands from the anatase phase at 150, 390, 510 and 635 cm ^1, respectively. The characteristic bands of graphene are visible at 1343 cm ¹ (D band) and 1597 cm ¹ (G band).

This shows the successful carbon coating of the Ti0 ₂ particles.

The BET surface area was determined by determining the specific surface area of solids by gas adsorption by the Brunauer-Emmett-Teller (BET) method using a Micromeritics ASAP-2020 M apparatus using nitrogen adsorption isotherms. The BET surface area of the produced carbon-coated spherical Ti0 ₂ / C secondary particles was calculated to be 67.9 m ² g ¹ . The result of the pore size distribution calculated from the desorption isotherm using the Barrett-Joyner-Halenda (BJH) method showed the presence of nanopores with an average pore diameter of 5 nm. The average diameter of the pores between the TiO ₂ / C secondary particles was at 128 nm.

Example 2

Production of a porous agglomeration of carbon-coated titanium dioxide particles with brookite structure

For the synthesis of carbon-coated titanium dioxide particles with brookite structure, 120 ml of ethanol solution containing 20 g of tetrabutyl titanate (Ti (OC ₄ H 9) ₄ ) and 1.2 g of acetic acid were first prepared. These were added dropwise to 240 ml of a water / ethanol solution (im 3: 1 by volume) containing 8 g of oxalic acid, 0.8 g of sodium dodecylbenzenesulfonate (SDBS) and 120 g of an aqueous slurry of graphene oxide (nanosheets, 1% by weight) prepared as described by WS Hummers and RE Offeman, J. Am. Chem. Soc., 1958, 80, 1339, added with stirring in an ice bath. The resulting light brown slurry was stirred for a further 12 hours and additionally aged for one hour. The precipitate was collected by centrifugation, washed repeatedly with ethanol and distilled water, and then freeze-dried. The resulting freeze-dried nanocomposite was then calcined at 450 ° C for 5 hours.

The X-ray diffractometry signals shown in FIG. 5 showed that the resulting TiO _{2 had} a brookite structure. The content of carbon was determined by thermogravimetric analysis (TGA) to be 28% by weight based on the total weight of the composite.

Example 3

Electrochemical investigation of the TiO ₂ / C composite prepared according to Example 1 in a lithium ion cell

For the electrode fabrication, the TiO ₂ / C composites of anatase-structure carbon-coated titanium dioxide particles prepared according to Example 1 together with a conductive carbon (Super C65, Imerys) and polyvinylidene difluoride (PVdF, ARKEMA KYNAR) as a binder were in a weight ratio of 80:10:10 in 1-methyl-2-pyrrolidinone (NMP, ACROS Organics). The slurry was applied to a copper foil. After drying, round electrodes with a

Die cut diameter of 12 mm, pressed with a hydraulic press, and dried at 120 ° C under vacuum. The mass loading of the active material was 0, 8-1.0 mg cm ² .

The electrochemical examination was carried out in a three-electrode arrangement

(Swagelok ™ cells) with lithium metal foil as counter and reference electrodes. The 2032-type button cells were assembled in a dry room. As electrolyte was a Solution of 1 M LiPF _{ö used} in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in the volume ratio 1: 1. The separator used was an electrolyte-impregnated glass fiber filter (Whatman, GF / D). The cells were galvanostatically charged and discharged between 1.0 V and 3.0 V against Li / Li ⁺ using a Maccor Series 4000 battery test system at various C rates (rated current 1 C = 170 mA g ¹ ).

The cells were activated at a current density of 0.1 C corresponding to 17 mA g ¹ for the first cycle and then cycled at 0.5 C for 50 cycles in a voltage range of 1.0-3.0 V against lithium.

Figure 6 shows the results of the cyclization. Figure 6a) shows a plot of voltage versus capacitance for the first five cycles, Figure 6b) shows the specific capacitance of the electrode at different C rates plotted against the number of charge / discharge cycles and Figure 6c) shows the charge and discharge Capacitance (left ordinate axis) and efficiency (right ordinate axis) of the electrode plotted against the number of charge / discharge cycles at an applied current density of 85 mA g ¹ over 500 cycles. As can be seen from Figure 6, the cell provided a very high charge capacity of about 310 mAh g ¹ and had a constant capacity over 500 cycles.

Example 4

Electrochemical investigation of the TiO ₂ / C composite prepared according to Example 1 in a sodium ion cell

The electrochemical examination of the sodium ion battery was carried out using a TiO ₂ / C composite electrode prepared according to Example 3 as an anode in three-electrode Swagelok ™ cells with sodium metal foil as counter and reference electrodes. The 2032-type button cells were assembled in a dry room. The electrolyte used was a solution of 1 M NaClO ₄ in a mixture of EC and propylene carbonate (PC) in the volume ratio 1: 1. The separator was an electrolyte-soaked Glass fiber filter (Whatman, GF / D) used. The cells were galvanostatically charged and discharged between 0.05V and 2.0V against Na / Na ⁺ using a Maccor Series 4000 battery test system at various C rates (rated current 1 C = 170mA g ¹ ).

The cells were activated at a current density of 0.1 C corresponding to 17 mA g ¹ for the first cycle and then cycled at 0.5 C for 50 cycles in a voltage range of 0.05-2.0 V versus sodium.

Figure 7 shows the results of the cyclization of the sodium ion cell. Figure 7a) shows a plot of voltage versus capacitance for the first five cycles, Figure 7b) shows the capacitance of the electrode at various C rates plotted against the number of charge / discharge cycles, and Figure 7c) shows the charge and discharge Capacity (left

Ordinate axis) and efficiency (right ordinate axis) of the electrode plotted against the number of charge / discharge cycles at an applied current density of 85 mA g ¹ over 500 cycles. As can be seen from Figure 7, the cell provided a very high charge capacity of about 280 mAh g ¹ and had a constant capacity over 500 cycles.

Example 5

Electrochemical investigation of the TiO ₂ / C composite prepared according to Example 1 in a lithium-ion-based supercapacitor

The electrochemical examination of a lithium-ion supercapacitor was carried out in three-electrode Swagelok ™ cells using a TiO ₂ / C composite electrode prepared according to Example 3 as the anode and commercial activated carbon as the cathode. The preparation of the cathode was analogous to the production of the anode, wherein 90 wt .-% activated carbon, 5 wt .-% Super C65 and 5 wt .-% sodium carboxymethyl cellulose (Na CMC) were used. The mass loading was between 2, 4-3.0 mg cm ² .

Lithium metal foil served as the third electrode for the pre-lithiation. The lithium ion supercapacitor was assembled in a dry room. As electrolyte was a Solution of 1 M LiPF _{ö used} in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in the volume ratio 1: 1. The separator used was an electrolyte-impregnated glass fiber filter (Whatman, GF / D).

The working electrode was first pre-lithiated by the third electrode at a current density of 10 mA g ¹ for the first discharge. Subsequently, the lithium ion capacitor was cycled at various different C rates between 1.0V and 3.0V.

Figure 8 shows the results of the cyclization of the lithium ion-based

Supercapacitor. Figure 8a) shows a plot of voltage versus time for different current densities, Figure 8b) shows capacitance retention of the electrode versus scan rate, and Figure 8c) shows capacitance retention versus number of cycles. As can be seen from FIG. 8, the lithium-ion-based supercapacitor provided a good one

Capacity retention under high current densities and good cycle performance.

Example 6

Electrochemical investigation of the TiO ₂ / C composite prepared according to Example 1 in a sodium ion-based supercapacitor

The electrochemical examination of a sodium ion supercapacitor was carried out in three-electrode Swagelok ™ cells using a TiCh / C composite electrode prepared according to Example 3 as the anode and commercial activated carbon as the cathode. The preparation of the cathode was analogous to the production of the anode, wherein 90 wt .-% activated carbon, 5 wt .-% Super C65 and 5 wt .-% sodium carboxymethyl cellulose (Na CMC) were used. The mass loading was between 2, 4-3.0 mg cm ² .

Sodium metal foil served as the third electrode for the pre-sodiation. The supercapacitor was assembled in a dry room. The electrolyte used was a solution of 1 M NaClO ₄ in a mixture of EC and PC in a volume ratio of 1: 1. The separator used was an electrolyte-impregnated glass fiber filter (Whatman, GF / D). The working electrode was first pre-natriumzed by the third electrode at a rate of 0.1C for the first discharge. Subsequently, the sodium ion capacitor was cycled at various different C rates between 1.0V and 3.8V.

FIG. 9 shows the results of the cyclization of the sodium ion supercapacitor. Figure 9a) shows a plot of potential versus time for different current densities, Figure 9b) shows capacitance retention of the electrode versus current density, and Figure 9c) shows capacitance retention versus number of cycles. As can be seen from Fig. 9, the sodium ion-based supercapacitor provided good capacity retention under high current densities and good cycle performance.

Overall, the results of the electrochemical investigations show that electrodes based on a porous agglomeration of carbon-coated titanium dioxide particles show very good results in terms of high charge capacity, capacity retention and cycle stability. Thus, the results show that the porous

Agglomerations of carbon-coated titanium dioxide particles can represent a favorable anode material with high cycle stability.

Claims

Patent claims

An electrode material having a porous agglomeration of carbon-coated titanium dioxide particles, wherein

Titanium dioxide particles are coated with carbon and form spherical Ti0 ₂ / C particles, which agglomerate into a porous three-dimensional structure, wherein the average diameter of the pores between the Ti0 ₂ / C particles in the range of> 50 nm to <200 nm ,

2. electrode material according to claim 1, characterized in that the middle

Pore volume of the porous agglomeration in the range of> 0.05 cm ³ / g to <0.2 cm ³ / g, preferably in the range of> 0.06 cm ³ / g to <0.14 cm ³ / g.

3. electrode material according to claim 1 or 2, characterized in that the BET surface area of the porous agglomeration in the range of> 60 m ² / g to <100 m ² / g, preferably in the range of> 65 m ² / g to <70 m ² / g.

4. electrode material according to any one of the preceding claims, characterized

characterized in that the titanium dioxide particles have an average diameter in the range of> 1 nm to <50 nm, preferably in the range> 1 nm to <10 nm, more preferably in the range of> 2 nm to <10 nm.

5. electrode material according to any one of the preceding claims, characterized

characterized in that the spherical Ti0 ₂ / C particles have an average diameter in the range of> 10 nm to <1 pm, preferably in the range> 50 nm to <500 nm.

6. electrode material according to any one of the preceding claims, characterized

characterized in that the porous three-dimensional structure is platelet-shaped particles wherein the platelet-shaped particles preferably have a mean

Diameter in the range of> 1 pm to <100 pm, preferably in the range> 2 pm to <50 pm.

7. electrode material according to any one of the preceding claims, characterized

characterized in that the proportion of carbon, based on the total weight of the porous agglomeration, in the range of 0.1 wt .-% to <30 wt .-%, preferably in the range of 2 wt .-% to <10 wt .-% , lies.

8. Method for producing a porous agglomeration of carbon

coated titanium dioxide particles, comprising the following steps:

a) preparing a solution (I) comprising a titanium compound and optionally a

Contains chelating agent;

c) combining solutions (I) and (II) to form a slurry;

d) mixing the slurry obtained from step c);

9. An electrode containing an electrode material having a porous agglomeration of carbon-coated titanium dioxide particles according to any one of claims 1 to 7 or a porous agglomeration of carbon-coated titanium dioxide particles obtainable by the method according to claim 8.

10. Electrochemical energy storage, in particular lithium or sodium-based electrochemical energy storage or supercapacitor, comprising an electrode according to claim 9.