EP2715843A1

EP2715843A1 - Electrode material for lithium and lithium ion batteries

Info

Publication number: EP2715843A1
Application number: EP11725660.2A
Authority: EP
Inventors: Elie Paillard; Dominic BRESSER; Martin Winter; Stefano Passerini; Marinella STRICCOLI; Enrico BINETTI; Roberto COMPARELLI; Maria Lucia CURRI
Original assignee: Westfaelische Wilhelms Universitaet Muenster; Consiglio Nazionale delle Richerche CNR
Current assignee: Westfaelische Wilhelms Universitaet Muenster; Consiglio Nazionale delle Richerche CNR
Priority date: 2011-06-01
Filing date: 2011-06-01
Publication date: 2014-04-09
Also published as: WO2012163426A1

Abstract

The present invention relates to a method for manufacturing electrode material particularly for lithium and lithium ion batteries comprising the following steps: a) providing nanoparticles of titanium dioxide, lithium titanate, silicon, silicon oxide or a transition metal oxide, coated with a monocarboxylic acid having a chain length of 7 to 26 carbon atoms; b) heat-treatment of the monocarboxylic acid coated nanoparticles of step a) for carbonization of the monocarboxylic acid coating.

Description

Electrode material for lithium and lithium ion batteries

The present invention relates to a method for manufacturing electrode material. In particular, the present invention relates to the use of a nanoparticle-carbon-composite prepared by the method as active material for electrodes used in lithium and lithium ion batteries. Due to their high energy density, long cycle life, and efficient energy storage, lithium ion batteries are currently being considered as the leading candidate to meet the demands of electrochemical energy storage for hybrid and electric vehicles and renewable energy sources. However, the up-scaling of the present chemistry, which is based on LiCo0₂ and graphite, raises issues on materials availability, costs, and safety. Focusing on the anode side, graphite and carbonaceous materials entail several disadvantages, especially in terms of safety, poor rate capability, and irreversible capacity loss in the first cycle, the latter being due to the initial decomposition of the electrolyte and formation of the solid electrolyte interface (SEI). This decomposition is caused by the lithium insertion in graphite electrodes taking place at a potential below the electrochemical stability window of the organic solvent-based electrolytes presently used.

Thus, there is a need for safe and effective anode materials particularly with improved high rate capability. Following the general tendency of downsizing, and by this taking advantage of typically shorter diffusion lengths for electrons and Li⁺ ions, higher electrode-electrolyte contact area, UD 40310 / SAM:AL better strain accommodation during lithium uptake/release, and extended solid solution domains, nano structured materials are currently studied as promising electrode materials.

However, nano structured materials have the disadvantage of agglomeration during the electrode preparation process. Thus, there is an ongoing demand for improvements in the preparation of nano structured electrode materials.

Therefore, the object underlying the present invention was to provide electrode material usable in lithium and lithium ion batteries

The problem is solved by a method for manufacturing electrode material particularly for lithium and lithium ion batteries comprising the following steps:

a) providing nanoparticles of titanium dioxide, lithium titanate, silicon, silicon oxide or a transition metal oxide, coated with a monocarboxylic acid having a chain length of 7 to 26 carbon atoms;

b) heat-treatment of the monocarboxylic acid coated nanoparticles of step a) for carbonization of the monocarboxylic acid coating.

The method of the invention using monocarboxylic acid for coating nanoparticles takes advantage of the organic capping as dispersing agent to avoid particle agglomeration during the preparation. Further, the monocarboxylic acid coating, upon thermally-induced conversion into carbon, can contribute to the electron conductive percolating network. Advantageously, the carbonization of the monocarboxylic acid provides the opportunity to create a coating on the electrode material.

Surprisingly, it was found that electrodes based on the nanoparticles prepared by the method taking advantage of the capping with monocarboxylic acids, showed improved high rate performance and cycling stability. Further, electrodes based on the nanoparticle-carbon- composite demonstrated improved results in terms of combined reversible capacity, long-term cycle performance, and safety, particularly for titanium based composite materials, wherein the operative potential window was within the electrochemical stability window of common electrolytes. Thus, the nanoparticle-carbon-composite prepared by the method of the invention provide an appealing anode material candidate for the realization of safe, high performance, large electrochemical energy storage devices that are strongly required for the development of sustainable electric vehicles and effective use of renewable energies.

Especially, the use of the nanoparticle-carbon-composite led to excellent high rate

performance and excellent cycle life performance of electrodes based on the nanoparticle- carbon-composite.

As used herein, the term "carbonization" refers to the conversion of an organic substance, particularly a monocarboxylic acid, into carbon or a carbon-containing residue. A

carbonization in the absence of oxygen is referred to as pyrolysis.

In a preferred embodiment, the heat-treatment of the monocarboxylic acid coated

nanoparticles in step b) is performed at a temperature in the range of > 250°C to < 850°C, preferably in the range of > 300°C to < 550°C, more preferably in the range of > 300°C to < 400°C.

Low temperatures can provide a gentle carbonization of the nanoparticles. Advantageously, low temperatures can prevent a phase transformation of nanoparticles. For example heat- treatment of anatase titanium dioxide nanoparticles at low temperatures can prevent a transformation to rutile titanium dioxide nanoparticles. It is especially advantageous that monocarboxylic acids provide the possibility to perform a carbonization at temperatures in the range of > 300°C to < 550°C, preferably in the range of > 300°C to < 400°C. The heat-treatment can be performed in an inert atmosphere. Advantageously, the heat- treatment can be performed in air. Performing the heat-treatment in air advantageously spares the need for an inert atmosphere and thus provides a cheaper and less complicated

preparation.

Preferably, a heat-treatment of the monocarboxylic acid coated nanoparticles in step b) is carried out for a time period in the range of > 3 h to < 24 h, preferably in the range of > 8 h to < 20 h, more preferably in the range of > 11 h to < 13 h. The method provides a cost-sensitive method for the preparation of electrode material by omitting the need for high reaction temperatures, the use of inert gases, long reaction times, and high number of reaction steps.

By a carbonization of the monocarboxylic acid coating of the nanoparticles a carbon-based coating layer can be formed on the surface of the nanoparticles. The obtained nanoparticle- carbon-composite thus can comprise a carbonaceous coating.

The nanoparticle-carbon-composite, for example Ti0₂-nanorod-carbon-composite, preferably comprises a weight ratio of nanoparticle to carbon, for example Ti0₂/C, in the range of > 50 : 50 to < 98 : 2, more preferably in the range of > 75 : 25 to < 90 : 10, and most preferred in a weight ratio of 85 : 15.

The nanoparticle-carbon-composite advantageously provides an active electrode material which can be deposited on a substrate to form battery electrodes. The nanoparticle-carbon- composite particularly provides an electrode material for use in lithium and lithium ion batteries. Advantageously, no additional carbon needs to be used for the electrode

preparation. Advantageously, the carbon-based coating can increase the electronic conductivity and inhibit particle agglomeration during the subsequent electrode preparation process. By this, higher capacities, enhanced high rate capability, and better cycling stability of the resulting electrodes can be obtained.

Advantageously, an oleic acid-coating on the nanoparticles is sufficient for providing a sufficient carbon-based coating of the nanoparticles after carbonization. However, conductive carbon can be added to further contribute to the electron conducting carbonaceous percolating network. Adding carbonaceous material further can increase the electronic conductivity of the electrode material.

In a preferred embodiment, the method further comprises, particularly before the heat- treatment of step b), adding carbonaceous material to the monocarboxylic acid coated nanoparticles. Preferably, carbonaceous material can be added to the monocarboxylic acid coated nanoparticles in a weight ratio of monocarboxylic acid coated nanoparticles to carbonaceous material in the range of > 1 : 1 to < 40 : 1, more preferably in the range of > 7 : 3 to < 20 : 1 , and most preferred in a weight ratio of 9 : 1.

The mixture of carbonaceous material and coated nanoparticles can be homogenized, for example using a planetary ball mill. The carbonaceous material can be added to the nanoparticles coated with a monocarboxylic acid which can either be dried or dispersed in an organic liquid compound for example selected from the group comprising dichloromethane, chloroform, alkanes, and monocarboxylic acids. If the carbonaceous material is added to the coated nanoparticles dispersed in an organic liquid compound, the mixture can be allowed to dry before heat-treatment. The carbonaceous material preferably is selected from the group comprising carbon black, synthetic or natural graphite, graphenes, carbon nanotubes, carbon wires, carbon fibres, and fullerenes. Any one or combinations of two or more thereof may be used. A usable carbon black for example commercially is available under the tradename

Ketjenblack®. A preferably usable conductive carbon black commercially is available under the tradenames Super P® and Super P® Li. Of these, SuperP® conductive carbon is especially preferred. Illustrative examples of usable electrically conductive graphite include flake graphite, lump graphite, artificial graphite, cashew graphite, amorphous carbon, and expanded graphite .

The carbonaceous material preferably is a carbonaceous powder. It is desirable for the conductive carbonaceous powder to have an average particle size within a range of 1 nm to 500 μιη, preferably 5 nm to 1 um. Especially preferred is the use of a conductive

carbonaceous powder having an average particle size in a range of 10 nm to 50 nm.

In further embodiments, the average particle diameter may be 20 μιη or smaller, preferably 15 μιη or smaller, more preferably 10 μιη or smaller, especially in a range of 10 nm to 50 nm. The average particle diameter refers to the median diameter (50% particle diameter) in a volume-based particle diameter distribution for example obtained with a laser diffraction type particle diameter distribution analyzer.

The carbonaceous powder may be subjected to size reduction and other suitable particle preparation operations so as to bring the average particle size into a usable range. Particularly, fine conductive carbonaceous powder can be obtained by pulverizing a conductive

carbonaceous powder using a known pulverizer, e.g., a ball mill, pin mill, homogenizer or the like. Further, a commercially marketed fine powders can be used. In a further preferred embodiment, the method further comprises adding carbonaceous material to the nanoparticle-carbon-composite obtained in step b), particularly after the heat- treatment of step b). In a further embodiment, the method can comprise adding carbonaceous material to the monocarboxylic acid coated nanoparticles before the carbonization and to the nanoparticle- carbon-composite obtained in step b).

The term "monocarboxylic acid" as used herein refers to organic acids having one carboxylic function, the hydrocarbon chain being the saturated or unsaturated, branched or not branched, aliphatic or aromatic. The term "fatty acid" as used herein refers to medium to long-chain saturated and unsaturated monocarboxylic acids, with an even number of carbons.

In preferred embodiments, the monocarboxylic acid is an aliphatic straight-chain saturated or unsaturated monocarboxylic acid. The monocarboxylic acid can be an aliphatic straight-chain saturated acid having a chain length of 8 to 20 carbon atoms, preferably selected from the group of octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, and eicosanoic acid. In preferred embodiments, the monocarboxylic acid is a saturated fatty acid selected from the group comprising capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid. Preferably, the monocarboxylic acid is an aliphatic straight-chain saturated acid having a chain length of 8 to 14 carbon atoms. Most preferred the aliphatic straight-chain saturated monocarboxylic acid is decanoic or capric acid. Advantageously, the hydrocarbon chain length can influence the size of the nanoparticles.

In further preferred embodiments, the monocarboxylic acid is a mono or polyunsaturated fatty acid having a chain length of 8 to 20 carbon atoms, preferably selected from the group comprising oleic acid, palmitoleic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, and arachidonic acid. Preferably, the monocarboxylic acid is a monounsaturated fatty acid selected from the group of oleic acid and palmitoleic acid. Palmitoleic acid also is denoted (Z)-9-hexadecenoic acid according to the IUPAC nomenclature. Most preferred the monocarboxylic acid is oleic acid which also is denoted (9Z)-Octadec-9-enoic acid according to the IUPAC nomenclature.

Preferably, the nanoparticles are rod-shaped. As used herein, the term "rod-shaped nanoparticles" refers to nanosized cylindrical structures, particularly nanorods, nanowires, nanotubes, and nano fibers. These nanosized cylindrical structures are also referred to as one- dimensional nano structures.

Advantagegously, nanometer-sized particles with a one-dimensional structure, such as nanotubes, nanorods, and nanowires, particularly in lithium ion batteries can provide easy Li⁺ ion diffusion into the host structure caused by their high specific surface area and low particle size.

In preferred embodiments, the nanoparticles are rod-shaped nanoparticles having an average diameter in the range of > 2 nm to < 35 nm and an average length in the range of > 5 nm to < 200 nm. Preferably, rod-shaped nanoparticles have an average diameter in the range of > 2 nm to < 20 nm and an average length in the range of > 10 nm to < 100 nm, more preferably an average diameter in the range of > 3 nm to < 5 nm and an average length in the range of > 25 nm to < 35 nm. In further preferred embodiments, the rod- shaped nanoparticles have an average diameter in the range of > 3 nm to < 4 nm and an average length in the range of > 25 nm to < 35 nm. Advantageously, embodiments wherein the nanoparticles are rod-shaped nanoparticles were characterized as very good Li-insertion material and electrodes based on rod-shaped nanoparticles were able to deliver at high rates high reversible capacities. In an alternative embodiment, the nanoparticles are sphere-shaped nanoparticles. As used herein, the term "sphere-shaped nanoparticles" refers to nanosized spherical structures, particularly nanospheres and nanodots. Preferably, sphere-shaped nanoparticles have an average diameter in the range of > 2 nm to < 100 nm, preferably an average diameter in the range of > 5 nm to < 50 nm, more preferably an average diameter in the range of > 7 nm to < 25 nm. Also sphere-shaped nanoparticles can exhibit good Li- insertion capability and electrodes based on sphere-shaped nanoparticles were able to deliver high rate reversible capacities.

In preferred embodiments, the nanoparticles are titanium dioxide nanoparticles.

Advantageously, titanium oxides (Ti0₂) in lithium ion batteries provides the ability to reversibly insert considerable amounts of lithium within the electrochemical stability window of common organic electrolytes. Beside this, Ti0₂ offers several other advantages as being biocompatible, environmentally friendly, abundant and inexpensive. For example, the high lithium insertion potential, compared to graphite, prohibits the risk of electrolyte

decomposition and/or metallic lithium deposition in normal operating conditions and upon moderate overcharges

In preferred embodiments, titanium dioxide has a polymorph selected from the group comprising rutile, anatase, brookite and titanium dioxide (B). Preferably, the polymorph of titanium dioxide is anatase. Anatase and rutile are tetragonal, brookite is orthorhombic and titanium dioxide(B) is monoclinic. In all four polymorphs, titanium is coordinated octahedrally by oxygen, but the position of the octahedra differs between polymorphs. Advantageously, the use of anatase titanium dioxide nanoparticles led to improved results of lithium ion electrodes in terms of high rate capability, rate and cycling stabilities as well as higher capacities. In an alternative embodiment, the nanoparticles are lithium titanate nanoparticles. Preferably, the lithium titanate has a formula Li_xTi_y0₄, wherein 0.8 < x < 1.4 and wherein 1.6 < y < 2.2, preferably the lithium titanate is I^TisO^.

In a further embodiment, the nanoparticles are silicon oxide nanoparticles, wherein preferably the silicon oxide has a formula SiO_x, wherein 0 < x < 1.8.

In a further embodiment, the nanoparticles are transition metal oxide nanoparticles.

Preferably, the transition metal oxide is selected from the group comprising transition metal oxides of the formula MO_x wherein the transition metal M is selected from the group comprising Sn, Zn, Cu, Co, Ni, Mn, and Fe, and x is in the range of > 1 to < 2, and mixtures thereof, and transition metal oxides comprising at least one transition metal oxide of MO_x, Fe₃0₄, Mn₃0₄, Co₃0₄, and mixtures thereof.

Transition metal oxides of the formula MO_x, wherein the transition metal M is selected from the group comprising Sn, Zn, Cu, Co, Ni, Mn, and Fe, and x is in the range of > 1 to < 2, are for example ZnO, CoO, CuO, Fe₃0₄, Mn₃0₄, Co₃0₄, and Sn0₂. Mixtures of transition metal oxides of the formula MO_x wherein the transition metal M is selected from the group comprising Sn, Zn, Cu, Co, Ni, Mn, and Fe, and x is in the range of > 1 to < 2 for example are oxides of the formula Cu_xSni__xO wherein 0 < x < 1, ZnCo₂0₄, CoFe₂0₄, and ZnFe₂0₄.

Transition metal oxides comprising at least one transition metal oxide of MO_x, Fe₃0₄, Mn₃0₄, and Co₃0₄ are for example MgCo₂0₄ and CdFe₂0₄. Also a use of transition metal oxide nanoparticles can provide electrodes for lithium and lithium ion batteries.

Chemical approaches for the preparation of nanoparticles, particularly one-dimensional nanoparticles of titanium dioxide, include several methods comprising sol-gel methods, surfactant-directed methods, and hydrothermal methods. Preferably, the nanoparticles are prepared by a low-temperature synthesis. A preferred preparation of nanoparticles is a one- step, low-temperature method. In a preferred embodiment the nanoparticles coated, or capped, with a monocarboxylic acid in step a) are prepared by hydrolysis of an alkoxide of titanium, lithium, silicon, a transition metal, or mixtures thereof solved in the monocarboxylic acid at a temperature in the range of > 80°C to < 100°C using tertiary amines or quaternary ammonium hydroxides as catalysts. Preferably, the molar ratio of the monocarboxylic acid to the alkoxide is in the range of > 15 : 1 to < 130 : 1.

This method provides the advantage of the preparation of well-crystallized nanoparticles of controlled size and shape. Without being bound to a specific theory, it is assumed that the monocarboxylic acid functions as a shape-controller for the formation of the nanoparticles.

Preferred tertiary amines and quaternary ammonium hydroxides are selected from the group comprising trimethylamino-N-oxide dihydrate, anhydrous trimethylamino-N-oxide, trimethylamine, tetramethylammonium-hydroxide, tetrabutylammonium-hydroxide, triethylamine, and tributylamine.

A preferred preparation of titanium dioxide nanoparticles coated or capped with a

monocarboxylic acid, preferably oleic acid, is performed by hydrolysis of a titanium alkoxide solved in the monocarboxylic acid at a temperature in the range of > 80°C to < 100°C using tertiary amines or quaternary ammonium hydroxides as catalysts. The molar ratio of the monocarboxylic acid to the titanium alkoxide preferably is in the range of > 15 : l to < 130 : 1. Advantageously, a temperature in the range of > 80°C to < 100°C can yield anatase polymorphs of titanium dioxide. A preferred titanium alkoxide for the preparation of titanium dioxide nanoparticles is titanium tetraisopropoxide.

A preferred preparation of rod-shaped titanium dioxide nanoparticles coated or capped with a monocarboxylic acid, preferably oleic acid, is performed using an aqueous solution of tertiary amines or quaternary ammonium hydroxides selected from the group comprising

trimethylamino-N-oxide dihydrate, anhydrous trimethylamino-N-oxide, trimethylamine, tetramethylammonium-hydroxide, and tetrabutylammonium-hydroxide, or the use of triethylamine or tributylamine and the addition of water. For the preparation of rod-shaped titanium dioxide nanoparticles, the solution of titanium tetraisopropoxide, monocarboxylic acid and catalyst preferably is reacted over a time period in the range of > 4 h to < 12 h, preferably in the range of > 6 h to < 12 h. Advantageously, rod- shaped well-crystallised anatase titanium dioxide nanoparticles are obtainable using a fast hydrolysis in an aqueous solution of tertiary amines or quaternary ammonium hydroxides.

A preferred preparation of spherical titanium dioxide nanoparticles coated or capped with a monocarboxylic acid, preferably oleic acid, is performed using a solution of tertiary amines or quaternary ammonium hydroxides selected from the group comprising anhydrous

trimethylamino-N-oxide, triethylamine, or tributylamine in ethylene glycol without the addition of water. For the preparation of spherical titanium dioxide nanoparticles, the solution of titanium tetraisopropoxide, monocarboxylic acid and catalyst preferably is reacted over a time period up to 60 h, preferably up to 48 h. Advantageously, using a slow hydrolysis in a non-aqueous solution spherical well-crystallised anatase titanium dioxide can be obtained. The nanoparticles coated with a monocarboxylic acid, for example oleic acid-coated anatase Ti0₂-nanorods, can contain in the range of > 10 wt.-% to < 50 wt.-%, preferably in the range of > 20 wt.-% to < 35 wt.-%, more preferably in the range of > 22 wt.-% to < 26 wt.-%, of a monocarboxylic acid, based on the total weight of the coated nanorods.

By the carbonization of the monocarboxylic acid coating of the nanoparticles a carbon-based coating layer can be formed on the surface of the nanoparticles. Thus, a nanoparticle-carbon- composite can be obtained by the heat-treatment.

The nanoparticle-carbon-composite advantageously provides an active electrode material which can be deposited on a substrate to form battery electrodes. The nanoparticle-carbon- composite particularly provides an electrode material for use in lithium and lithium ion batteries. Advantageously, no additional carbon needs to be used for the electrode preparation.

In a preferred embodiment, the method further comprises the step of depositing the nanoparticle-carbon-composite of step b) on a conductive substrate for an electrode, particularly for a lithium or lithium ion battery.

The conductive substrate can serve as current collector in the electrode. A preferred conductive substrate is a copper foil. Further possible conductive substrates are nickel and aluminum foil, as well as alloys containing these metals, as well as stainless steel, titanium, graphite, as well as carbon, as well as conductive glasses or carbonaceous compounds in general.

For depositing the nanoparticle-carbon-composite on a conductive substrate the composite, for example Ti0₂-nanorod-carbon-composite, can be mixed with a binder, for example poly(vinylidenedifluoride-hexafluoropropylene) (PVDF-HFP) copolymer. Further usable binders comprise simple polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), or sodium carboxymethyl cellulose (Na-CMC), or poly(tetrafluoroethylene) (PTFE). The weight ratio of nanoparticle-carbon-composite, for example Ti0₂-nanorod-carbon- composite, and binder preferably is in the range of > 70 : 30 to < 97 : 3, more preferably in the range of > 80 : 20 to < 95 : 5. Most preferred the weight ratio of the nanoparticle-carbon- composite, for example Ti0₂-nanorod-carbon-composite, and binder is 88: 12. Based on the total weight of the mixture, a mixture of nanoparticle-carbon-composite, binder, and conductive carbonaceous material can comprise in the range of > 50 to wt.-% < 95 wt.-% nanoparticle-carbon-composite, in the range of > 2 to wt.-% < 45 wt.-% conductive carbonaceous material, and in the range of > 2 to wt.-% < 20 wt.-% binder, respectively, wherein the total amount of the mixture will not exceed 100 wt.-%. In some embodiments, the dry weight of a mixture of nanoparticle-carbon-composite, for example Ti0₂-nanorod-carbon- composite, and binder comprises 75 wt.-% nanoparticles, 13 wt.-% carbon and 12 wt.-% binder, for example PVDF-HFP, based on the total weight of the mixture.

In preferred embodiments, the nanoparticle-carbon-composite of step b) is deposited on a conductive substrate for a battery electrode, particularly for a lithium or lithium ion battery, with a wet film thickness in the range of > 50 μιη to < 300 μιη, preferably in the range of > 90 μιη to < 150 μιη, more preferably in the range of > 110 μιη to < 130 μιη.

In other preferred embodiments, the nanoparticle-carbon-composite of step b) is deposited on a conductive substrate for a battery electrode, particularly for a lithium or lithium ion battery, with a mass loading in the range of > 0.2 mg cm^"2 to < 30 mg cm^"2, preferably in the range of > 1 mg cm^"2 to < 10 mg cm^"2, more preferably in the range of > 1.5 mg cm^"2 to < 1.7 mg cm^"2. Advantageously, such a wet film thickness and/or mass loading can provide a good performance of electrochemical energy storage devices, especially lithium or lithium ion batteries. In other embodiments a method for preparing an electrode based on nanoparticle-carbon- composite, for example Ti0₂-nanorod-carbon-composite, comprises the steps of admixing the nanoparticle-carbon-composite with carbon black, binder, and a solvent, e.g. N- methylpyrrolidinone (NMP), acetone, or water, or without in case of PTFE as binder, stirring the admixture, depositing the admixture onto a surface of conductive substrate for an electrode preparation and obtaining electrodes from the spread particulate admixture, and drying the obtained electrodes.

Another aspect of the invention refers to an electrode material for electrochemical energy storage devices particularly for lithium and lithium ion batteries prepared by the method according to the invention.

It was found that the electrode material manufactured by the method according to the invention provides improved high rate performance and cycling stability of the resulting electrodes.

The method for manufacturing electrode material comprises to the following steps:

b) heat-treatment of the monocarboxylic acid coated nanoparticles of step a) for carbonization of the monocarboxylic acid coating. Preferably, the heat-treatment of the monocarboxylic acid coated nanoparticles in step b) is performed at a temperature in the range of > 250°C to < 850°C, preferably in the range of > 300°C to < 550°C, more preferably in the range of > 300°C to < 400°C. Another aspect of the invention refers to an electrode comprising electrode material, particularly a nanoparticle-carbon-composite, prepared by the method according to the invention.

Preferably, the electrode comprising the nanoparticle-carbon-composite is an anode for a lithium or lithium ion battery. A lithium- ion battery for example comprises a first electrode of a cathodic material, a second electrode of an anodic material and an electrolyte.

Surprisingly, it was found that electrodes based on the nanoparticles prepared by the method taking advantage of the capping with monocarboxylic acids, showed improved high rate performance and cycling stability. Further, electrodes based on the nanoparticle-carbon- composite demonstrated improved results in terms of combined reversible capacity, long-term cycle performance, and safety, particularly for titanium based composite materials, wherein the operative potential window was within the electrochemical stability window of common electrolytes. Especially, the use of the nanoparticle-carbon-composite led to excellent high rate performance and excellent cycle life performance of electrodes based on the nanoparticle- carbon-composite.

Especially, anatase Ti0₂-nanorod electrodes showed excellent electrochemical performance in terms of reversible capacity, cycling stability, faradic efficiency and high rate capability.

Preferably, the nanoparticles for the electrode material are rod-shaped. In preferred embodiments, the nanoparticles are rod-shaped nanoparticles having an average diameter in the range of > 2 nm to < 35 nm and an average length in the range of > 5 nm to < 200 nm. Preferably, rod-shaped nanoparticles have an average diameter in the range of > 2 nm to < 20 nm and an average length in the range of > 10 nm to < 100 nm, more preferably an average diameter in the range of > 3 nm to < 5 nm and an average length in the range of > 25 nm to < 35 nm. In further preferred embodiments, the rod- shaped nanoparticles have an average diameter in the range of > 3 nm to < 4 nm and an average length in the range of > 25 nm to < 35 nm.

In an alternative embodiment, the nanoparticles for the electrode material are sphere-shaped nanoparticles. As used herein, the term "sphere-shaped nanoparticles" refers to nanosized spherical structures, particularly nanospheres and nanodots. Preferably, sphere-shaped nanoparticles have an average diameter in the range of > 2 nm and < 100 nm, preferably an average diameter in the range of > 5 nm to < 50 nm, more preferably an average diameter in the range of > 7 nm to < 25 nm. In preferred embodiments, the nanoparticles for the electrode material are titanium dioxide nanoparticles. In preferred embodiments, titanium dioxide has a polymorph selected from the group comprising rutile, anatase, brookite and titanium dioxide (B). Preferably, the polymorph of titanium dioxide is anatase. In an alternative embodiment, the nanoparticles are lithium titanate nanoparticles. Preferably, the lithium titanate has a formula Li_xTi_y0₄, wherein 0.8 < x < 1.4 and wherein 1.6 < y < 2.2, preferably the lithium titanate is I^TisO^.

In a further embodiment, the nanoparticles are silicon or silicon oxide nanoparticles, wherein preferably the silicon oxide has a formula SiO_x, wherein 0 < x < 1.8.

Transition metal oxides of the formula MO_x, wherein the transition metal M is selected from the group comprising Sn, Zn, Cu, Co, Ni, Mn, and Fe, and x is in the range of > 1 to < 2, are for example ZnO, CuO, CoO, Fe₃0₄, Mn₃0₄, Co₃0₄, and Sn0₂. Mixtures of transition metal oxides of the formula MO_x wherein the transition metal M is selected from the group comprising Sn, Zn, Cu, Co, Ni, Mn, and Fe, and x is in the range of > 1 to < 2 for example are oxides of the formula Cu_xSni__xO wherein 0 < x < 1, ZnCo₂0₄, CoFe₂0₄, and ZnFe₂0₄.

Transition metal oxides comprising at least one transition metal oxide of MO_x, Fe₃0₄, Mn₃0₄, and Co₃0₄ are for example MgCo₂0₄ and CdFe₂0₄. By a carbonization of the monocarboxylic acid coating of the nanoparticles a carbon-based coating layer can be formed on the surface of the nanoparticles. The nanoparticle-carbon- composite can comprise a carbonaceous coating. Preferably, the nanoparticle-carbon- composite can comprise a carbon-based coating layer on the surface of the nanoparticles. The carbonized nanoparticles, for example carbonized Ti0₂-nanorods, preferably comprise a weight ratio of nanoparticle to carbon, for example Ti0₂/C, in the range of > 50 : 50 to < 98 : 2, more preferably in the range of > 75 : 25 to < 90 : 10, and most preferred in a weight ratio of 85: 15. Another aspect of the invention refers to the use of nanoparticle-carbon-composite prepared by the method according to the invention as electrode material for electrochemical energy storage devices, particularly as active material for electrodes used in lithium and lithium ion batteries. Preferably, the carbonized nanoparticles comprise a carbonaceous coating. Further possible applications for electrochemical energy storage devices for example are hybrid supercapacitors, for example comprising activated carbon as cathode and Ti0₂ as anode.

Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The examples which follow serve to illustrate the invention in more detail but do not constitute a limitation thereof. While at least one exemplary embodiment is presented, it should be appreciated that a vast number of variations exist.

In the figures show:

Figure 1 A powder X-ray diffraction (XRD) pattern of the carbonized Ti0₂-nanorods (Ti0₂- NRs/C) after thermal treatment at 350°C in air. The anatase Ti0₂ reference ICSD 172914 is shown in the bottom.

Figure 2 Voltammograms of a Ti0₂-nanorods electrode. The scan rate was 0.05 mV sec^"1.

The voltammograms of cycles 1 to 5 are shown in figures a) to c). a) Between 3.0 V and 1.2 V. The cut-off potential was 1.2 V. b) Between 3.0 V and 1.0 V. The cut-off potential was 1.0 V. c) Between 3.0 V and 0.1 V. The cut-off potential was 0.1 V. The voltammograms were taken after one day rest after assembling.

Figure 3 HRSEM images of aTi0₂-nanorod electrodes a) pristine and b) after 50 cycles. The cut-off voltage was 1.0 V.

Figure 4 Galvanostatic charge discharge tests at different C rates. The lower cut-off potential was 1.2 V. Figure 5a): Voltage profile versus specific capacity of a Ti0₂-nanorods electrode. Figure 5b) Specific capacity of a Ti0₂-nanorods electrode. The I^s cycle is not shown.

Figure 5 Specific capacity of Ti0₂-nanorod electrodes subjected to continuous galvanostatic charge discharge tests at different C rates. The lower cut-off potential was 1.2 V. a) Increasing discharge rates (C/5, C/2, 1C, 2C, 5C, IOC), constant charge rate: C/5. b)

Increasing charge rates (C/5, C/2, 1C, 2C, 5C, IOC), constant discharge rate: C/5. c) Increasing charge and discharge rates (C/5, C/2, 1C, 2C, 5C, IOC), d) Constant charge and discharge rate: 1C. The 1^st cycle is not shown. Example 1

Preparation of oleic acid-capped anatase Ti0₂-nanorods

The synthesis of oleic acid (OLEA) capped anatase Ti0₂ nanorods (NRs) was performed by using an airless technique using standard Schlenk technique. Technical grade oleic acid was degassed and titanium tetraisopropoxide (TTIP) was added under nitrogen flow at 100°C to the degassed oleic acid. The anhydrous environment prevented the titanium tetraisopropoxide from premature hydrolysis. Subsequently, an aqueous solution of trimethylamine-N-oxide (TMAO) dehydrate was rapidly injected. The injection started the fast hydrolysis, by which the formation of oleic acid-capped anatase Ti0₂-nanorods was obtained.

Characterization of the morphology as well as particle size and shape were carried out by transmission electron microscopy (TEM), which was carried out on samples deposited on a carbon-coated 400 mesh copper grid, using a JEOL TEM microscope operating at an accelerating voltage of 100 kV. It could be seen that the single particles of the prepared anatase Ti0₂-nanorods were well separated. It is assumed that this is due to the oleic acid capping agent. The nanorods in average were 3 nm to 4 nm in diameter and 25 nm to 30 nm in length. The obtained anatase Ti0₂-nanorods contained 24.5% of organic material (oleic acid), as was determined by thermogravimetric analysis (TGA) under 0₂, using a TA instruments Q5000.

Example 2

Heat-treatment of the oleic acid-capped anatase Ti0₂-nanorods

The oleic acid-capped anatase Ti0₂-nanorods obtained in example 1 were mixed with Super P conductive carbon (TIMCAL) in a 90: 10 Ti0₂/C-weight ratio in CH₂C1₂. The mixture was then homogenized using a planetary ball mill (Vario-Planetary Mill Pulverisette 4, Fritsch) set at 800 rpm for 3 hours. The composite was allowed to dry overnight at ambient temperature (20 ± 2°C) and then was heat-treated at 350°C in air for 12 hours by placing the sample in a quartz boat, which was subsequently placed in a tubular furnace and heated up by 3°C/minute.

Thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD) characterizations showed that such a thermal treatment did not result in any weight loss for Super P or phase transformation of the Ti0₂-nanorods, but allowed the carbonization of the oleic acid. A TGA performed after this step revealed an 85: 15 weight ratio of Ti0₂/C for the carbonized Ti0₂- nanorods, showing that a carbonaceous residue was remaining within the composite, probably forming a carbonaceous surface layer.

The preservation of single-phase anatase crystal structure of the Ti0₂-nanorods was confirmed by powder X-ray diffraction (XRD) on a Bruker D8 Advance (Cu-Κα radiation, λ = 0.154 nm). As shown in Figure 1, all observed diffraction peaks in the XRD pattern could be clearly indexed as belonging to the anatase phase (ICSD 172914) with the space group. The peaks showed in Figure 1 are broad, as expected considering the small crystallite size of the nanorods. This confirmed that the anatase phase was preserved after the

preparation of the composite and the following heat treatment and did not undergo any phase transformation to the thermodynamically favored rutile phase. Example 3

Preparation of Ti0₂-nanorods electrodes The Ti0₂-nanorods-carbon-composite (Ti0₂-NRs/C composite) was mixed with PVDF-HFP copolymer (Kynarflex 2801, Arkema), as the binder, in an 88: 12 weight ratio. No additional carbon was used for the electrode preparation. N-methylpyrrolidone (Aldrich) was used as the solvent. The dry composition of the slurry was 75 wt.-% Ti0₂-nanorods, 13 wt.-% carbon and 12 wt.-% PVDF-HFP. The slurry was homogenized using planetary ball milling at 800 rpm for 1 hour (Vario-Planetary Mill Pulverisette 4, Fritsch). The resulting slurry was then casted on dendritic copper foil (Schlenk) by using a laboratory doctor blade, with a wet film thickness of 120 μιη. The electrodes were dried in air for 1 hour at 80°C then 12 hours at ambient temperature (20 ± 2°C). Disk electrodes of 12 mm diameter were then punched and dried for 12 hours at 120°C under vacuum. The active material mass loading was comprised between 1.5 and 1.7 mg cm^"2. The active material mass loading was determined by weighting the electrodes, in a dry room or a glove box at room temperature, then the weight was divided by the area of the coated copper foil.

Example 4

Electrochemical characterization

Electrochemical studies were carried out in three-electrodes Swagelok™-type cells, with lithium metal foils (Chemetall, lithium battery grade) used as counter and reference electrodes. The cells were assembled in an MBraun glove box with oxygen and water contents below 0.5 ppm. A stack of polypropylene fleeces (Freudenberg FS 2226) drenched with a 1 M solution of LiPF₆ in the 3:7 weight mixture of ethylene carbonate and diethyl carbonate was used as the electrolyte. Since lithium foil was used as counter and reference electrode, all the potential values given are referring to the Li⁺/Li reference couple. All electrochemical studies were performed at 20°C ± 2°C. For galvanostatic cycling, a Maccor Battery Tester 4300 was used. Cyclic voltammetry experiments were performed by mean of a Solartron 1287 potentiostat (Ametek) and a VMP3 potentiostat (BioLogic).

Galvanostatic cycling and cyclic voltammetry were performed in three different potential ranges ranging from 3.0 V (cathodic limit) and either 0.1, 1.0 and 1.2 V (anodic limit). For the galvanostatic measurements a charge/discharge rate of 1C corresponds to a current density of 168 mA g^"1, considering x = 0.5 as the reference limit of the insertion reaction: Ti0₂ + x(Li⁺ + e^")→ Li_xTi0₂. For the cyclic voltammetry a scan rate of 0.05 mV sec^"1 was applied.

Ex situ, high resolution scanning electron microscope (HRSEM) analysis was carried out on a ZEISS Auriga® microscope on pristine and cycled (50 cycles with 1.0 V as the lower cut-off potential) electrode.

Example 4.1

Cyclic voltammetry experiments

Cyclic voltammetry was carried out with different cathodic potential limits, namely 0.1, 1.0 and 1.2 V. The anodic limit was in all experiments set to 3.0 V. The recorded voltammograms during the initial 5 cycles are shown in Figure 2 a) - c). All three figures show the

characteristic couple of cathodic and anodic peaks at about 1.7 V and 2.0 V, respectively.

For micrometer-sized anatase Ti0₂ only this peak couple is observed, which corresponds to the Li insertion/extraction processes into the Ti0₂ host structure. During lithium insertion, anatase Ti0₂ undergoes a separation in two phases, the Li-poor Lio.₀iTi0₂ phase (space group with maintained anatase structure and tetragonal symmetry, and the Li-rich

Lio.55Ti0₂ phase (space group Imma) with lithium titanate structure and orthorhombic symmetry. These two phases coexist up to a Li mol fraction of 0.55. In nanometer- sized particles, a second phase transformation (Lio.ssTiC^-^ LiTi0₂) takes place during lithium insertion, leading to anatase LiTi0₂ (space group: I4]/amd). The appearance of this new phase is confirmed by the peak couple seen in Figures 2 a) and b) at 1.45 V and 1.8 V, respectively for the lithium insertion and extraction processes. This peak couple is never observed in micro-sized particles.

During the first anodic scan (delithiation), the behavior of the Ti0₂-nanorod electrodes appeared to be strongly affected by the cathodic potential limit. For a reversing cathodic voltage limit of 0.1 V, in fact, a much larger irreversibility was observed, as can be seen in Figure 2 c. A large background current was observed below 1.2 V without any corresponding anodic feature. In addition, both the cathodic and anodic peaks sharply decreased during the following cycles. This behavior is explained by an extensive electrolyte decomposition favored by the large surface area of the nanorods that lead to the formation of the Solid Electrolyte Interphase (SEI) layer. Electrolyte decomposition was already observed during the voltammetric test performed with a cathodic limit of 1.0 V as confirmed by high resolution scanning electron microscope HRSEM analysis of a pristine and a cycled electrode, as can be seen in Figure 3. The comparison of these two HRSEM images of Figure 3a) and Figure 3b) shows that a Solid Electrolyte Interphase (SEI) film was formed on the cycled electrode. Solid Electrolyte Interphase denotes an electrodeposited layer originating from the decomposition products of the electrolyte. Favorably, an SEI passivates the electrode, preventing further decomposition of the electrolyte, while allowing the transport of lithium ions to the active material.

Example 4.2

Galvanostatic tests

To evaluate the charge/discharge performance of the Ti0₂-nanorod electrodes galvanostatic cycling tests were carried out between 3 V (charge limit) and a discharge cut-off voltage of 1.2 V. The results are shown in Figures 4 a) and b). As can be seen in the charge profile of Figure 4a), setting the cut-off potential at 1.2 V and the rate at C/10, wherein a C rate of 1C corresponds to an applied current density of 168 mA g^"1, resulted in the electrode reversible capacity in the first cycle to be 245 mAhg^"1, corresponding to 0.73 Li⁺ per Ti0₂. The delivered capacity at 1C rate was as high as 210 mAh g^"1 with a faradic efficiency higher than 99%. At even higher C rates the electrodes still delivered high reversible capacities, namely 194 mAh g^"1 at 2C, 165 mAh g^"1 at 5C (this capacity

corresponds to 0.5 mole of Li⁺ per mole of Ti0₂) and 130 mAh g^"1 at IOC, thus demonstrating the high rate capability of the investigated nanorods.

The Figure 4b) shows the performance of a Ti0₂-nanorods electrode subjected to continuous charge/discharge tests at different rates within 3.0 V and 1.2 V cut-off limits. The overall stability of delivered capacity upon cycling at different rates demonstrates the highly stable cyclability of the investigated nanorods for a potential range of 1.2 to 3.0 V. The high reversibility of the lithium insertion/extraction processes in the Ti0₂-nanorods electrode after the first cycle is demonstrated by the recovery of the delivered specific capacity when the discharge/charge rate is set back to 1C.

The galvanostatic cycle tests evidenced that the nanorods showed the best balance between delivered reversible capacities and cycling stability at a cut-off limit 1.2 V.

Example 4.3

Power rate tests

The investigation of the electrochemical properties of the nanorods for increasing discharge or/and charge rates were carried out with the cut-off limit set at 1.2 V, as is shown in Figure 5. It can be seen that lithium insertion is the limiting factor. As can be seen from figure 5, an excellent reversibility of lithium insertion/extraction into the anatase Ti0₂-nanorods electrode material was demonstrated, by retrieving the former specific capacity for lower current densities. It should be pointed out that in a real battery the achievable capacity at IOC discharge (charge for Li half cell) is 184 mAh g^"1.

The electrochemically investigations show that dispersed anatase Ti0₂-nanorods prepared by low-temperature synthesis using capping with oleic acid, led to improved high rate performance and cycling stability of the synthesized nanorods. The Ti0₂-nanorods based electrodes showed very good results in terms of combined reversible capacity, long-term cycle performance, and safety, while the operative potential window was within the electrochemical stability window of common electrolytes. The Ti0₂-nanorods appear as an appealing anode material candidate for the realization of safe, high performance, large electrochemical energy storage devices that are strongly required for the development of sustainable electric vehicles and effective use of renewable energies.

Claims

1. A method for manufacturing electrode material particularly for lithium and lithium ion batteries comprising the following steps:

2. The method according to claim 1, wherein the heat-treatment of the monocarboxylic acid coated nanoparticles in step b) is performed at a temperature in the range of > 250°C to < 850°C, preferably in the range of > 300°C to < 550°C, more preferably in the range of > 300°C to < 400°C.

3. The method according to claim 1 or 2, wherein the method further comprises adding carbonaceous material to the monocarboxylic acid coated nanoparticles, preferably in a weight ratio of monocarboxylic acid coated nanoparticles to carbonaceous material in the range of > 1 : 1 to < 40 : 1, more preferably in the range of > 7 : 3 to < 20 : 1, and most preferred in a weight ratio of 9 : 1.

4. The method according to any of the preceding claims, wherein the method further comprises adding carbonaceous material to the nanoparticle-carbon-composite obtained in step b).

5. The method according to any of the preceding claims, wherein the monocarboxylic acid is an aliphatic straight-chain saturated or not saturated monocarboxylic acid, preferably a saturated fatty acid selected from the group comprising capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid, or a mono or polyunsaturated fatty acid, preferably selected from the group comprising oleic acid, palmitoleic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, and arachidonic acid, most preferred the

monocarboxylic acid is oleic acid.

6. The method according to any of the preceding claims, wherein the nanoparticles are rod-shaped nanoparticles having an average diameter in the range of > 2 nm to < 35 nm and an average length in the range of > 5 nm to < 200 nm, preferably an average diameter in the range of > 2 nm to < 20 nm and an average length in the range of > 10 nm to < 100 nm, more preferably an average diameter in the range of > 3 nm to < 5 nm and an average length in the range of > 25 nm to < 35 nm.

7. The method according to any of the preceding claims, wherein the nanoparticles are sphere-shaped nanoparticles having an average diameter in the range of > 2 nm to < 100 nm, preferably an average diameter in the range of > 5 nm to < 50 nm, more preferably an average diameter in the range of > 7 nm to < 25 nm.

8. The method according to any of the preceding claims, wherein the nanoparticles are of titanium dioxide, wherein titanium dioxide preferably has a polymorph selected from the group comprising rutile, anatase, brookite and titanium dioxide (B), preferably the polymorph of titanium dioxide is anatase.

9. The method according to any of the preceding claims, wherein

- the lithium titanate has a formula Li_xTi_y0₄ wherein 0.8 < x < 1.4 and wherein 1.6 < y < 2.2, preferably the lithium titanate is I^TisO^; and/or

- wherein the silicon oxide has a formula SiO_x wherein 0 < x < 1.8; and/or

- wherein the transition metal oxide is selected from the group comprising transition metal oxides of formula MO_x wherein the transition metal M is selected from the group comprising Sn, Zn, Cu, Co, Ni, Mn, and Fe, and x is in the range of > 1 to < 2, such as ZnO, CoO, CuO, Fe₃0₄, Mn₃0₄, Co₃0₄, or Sn0₂, and mixtures thereof such as Cu_xSni__xO wherein 0 < x < 1 , ZnCo₂0₄, CoFe₂0₄ or ZnFe₂0₄, and transition metal oxides comprising at least one transition metal oxide of MO_x, Fe₃0₄, Mn₃0₄, Co₃0₄, and mixtures thereof such as MgCo₂0₄ or CdFe₂0₄.

10. The method according to any of the preceding claims, wherein the method further comprises the step of depositing the nanoparticle-carbon-composite of step b) on a conductive substrate for an electrode, particularly for a lithium or lithium ion battery.

1 1. The method according to any of the preceding claims, wherein the nanoparticle- carbon-composite of step b) is deposited on a conductive substrate for a battery electrode, particularly for a lithium or lithium ion battery, with a wet film thickness in the range of > 50 μιη to < 300 μιη, preferably in the range of > 90 um to < 150 μιη, more preferably in the range of > 1 10 μι ίο < 130 um.

12. The method according to any of the preceding claims, wherein the nanoparticle- carbon-composite of step b) is deposited on a conductive substrate for a battery electrode, particularly for a lithium or lithium ion battery, with a mass loading in the range of > 0.2 mg cm^"2 to < 30 mg cm^"2, preferably in the range of > 1 mg cm^"2 to < 10 mg cm^"2, more preferably in the range of > 1.5 mg cm^"2 to < 1.7 mg cm^"2.

13. Electrode material for electrochemical energy storage devices particularly for lithium and lithium ion batteries prepared by the method according to any of the preceding claims.

14. Electrode comprising electrode material prepared by the method according to any of the preceding claims.

15. Use of a nanoparticle-carbon-composite prepared by the method according to any of the preceding claims as electrode material for electrochemical energy storage devices, particularly as active material for electrodes used in lithium and lithium ion batteries.