Description The present invention relates to a process for producing tin dioxide particles comprising elemental carbon, to tin dioxide particles comprising elemental carbon obtainable or obtained by the process of the invention, to electrodes for an electrochemical cell comprising said tin dioxide particles comprising elemental carbon and to electrochemical cells comprising said electrodes. Secondary batteries, accumulators or "rechargeable batteries" are just some embodiments by which electrical energy can be stored after generation and used when required. Owing to the significantly better energy density, there has in recent times been a move away from the water- based secondary batteries toward development of those batteries in which the charge transport in the electrical cell is accomplished by lithium ions.

In the lithium ion batteries currently being produced, the cathode typically comprises a lithium- transition metal compound, for example UC0O2 or LiFeP0 ₄ , and the anode typically comprises graphite into which Li° is intercalated in the charging operation. In order to increase the capacity of the graphite-based anodes, as described in Angew. Chem. 2008, 120, 2972-2989, anodes are being developed which comprise lithium-metal alloys, for example lithium-tin or lithium- silicon alloys. Tin and silicon can absorb large amounts of lithium forming alloys with the stoi- chiometry Li ₄₄ Sn and Li ₄₄ Si and therefore exhibit much higher capacities than a graphite electrode with intercalated Li°. Angew. Chem. 2008, 120, 2972-2989 states that "the consequence of accommodating such a large amount of lithium is large volume expansion-contraction that accompanies their electrochemical alloy formation. These changes lead rapidly to deterioration of the electrode (cracks, and eventually, pulverization), thus limiting its lifetime to only a few charge-discharge cycles."

Angew. Chem. 2008, 120, 2972-2989 discusses the following approach to a solution: "One of the earliest approaches involved replacing bulk material with nanostructured alloys. Reducing the metal particles to nanodimensions does not of course reduce the extent of volume change but does render the phase transitions that accompany alloy formation more facile, and reduces cracking within the electrode. Different synthetic routes have been used to fabricate nanostructured metals that can alloy with lithium, including sol-gel, ball-milling, and electrodeposition. Of these routes, electrodeposition is the most versatile, as it permits easy control of the electrode morphology by varying the synthesis conditions, such as current density and deposition time."

Angew. Chem. 2009, 121 , 1688-1691 proposes the production of SnO _x /C composites by CVD (chemical vapor deposition) and the subsequent conversion thereof to Sn/C materials, the pur- pose of the carbon skeleton being that of stabilization of the Sn particles. WO 2013/027157 describes electroactive materials comprising a carbon phase and a tin phase and/or tin oxide phase obtainable by carbonizing Sn(ll)-crosslinked novolac material and optionally partially or fully reducing Sn(ll) to Sn(0). Adv. Mater. 2005, 17, 2509 discloses a non-aqueous synthesis of tin oxide nanocrystals and their assembly into ordered porous mesostructures.

WO 201 1/045223 discloses a method of making re-dispersible metal oxide nanoparticles. Among other compounds the synthesis of antimony tin oxide nanoparticles is described.

Proceeding from this prior art, the object was to find a flexible and more efficient synthesis route to tin dioxide particles useful as anode material for lithium ion batteries, especially for lithium ion secondary batteries, and to find dioxide particles, which result in improved properties of the electrochemical cell comprising such dioxide particles in the anode. The electrochemical cells produced with these dioxide particles were to have a high capacity, cycling stability, efficiency and reliability, low self-discharge, good mechanical stability and low impedances.

This object is achieved by a process for producing tin dioxide particles comprising elemental carbon, comprising at least the process steps of preparation of a mixture comprising

(A) at least one liquid organic phase comprising at least one alcohol (A) comprising at least on hydroxyl group wherein the hydroxyl group is bound to a secondary, tertiary or ounsaturated carbon atom and

(B) at least one source of tin in the oxidation state +IV (B) which is at least partly soluble in the liquid organic phase, in a temperature range from -78 °C to 300 °C, further thermal treatment of the mixture formed in process step (a) in a temperature range from 40 °C to 300 °C, isolation and optionally further purification of the tin dioxide particles, which are formed in process step (b), and (d) calcination of the tin dioxide particles isolated in process step (c) in a temperature range from 200 °C to 650 °C in a non-oxidizing atmosphere.

The average particle size of the tin dioxide particles comprising elemental carbon, which are obtainable by the inventive process, can be varied in a wide range. Preferably the tin dioxide particles comprising elemental carbon have an average particle size in the range from 1 nm to 100 nm, more preferably in the range from 5 nm to 50 nm, in particular in the range from 10 nm to 20 nm. In one embodiment of the present invention the inventive process is characterized in that the tin dioxide particles comprising elemental carbon have an average particle size in the range from 1 nm to 100 nm, more preferably in the range from 5 nm to 50 nm, in particular in the range from 10 nm to 20 nm. The average particle size of the tin dioxide particles comprising elemental carbon throughout the present invention refers to a number-average d[1 ,0] value obtained by means of light scattering.

The tin dioxide particles comprising elemental carbon comprise crystallites of tin dioxide as primary particles wherein the crystallites (primary particles) preferably have an average particle size in the range froml nm to 10 nm, in particular in the range from 4 to 6 nm. The average par- tide size of the crystallites is determined by applying the Scherrer equation to X-ray diffraction data.

The carbon-content of the tin dioxide particles comprising elemental carbon can be varied in a wide range depending on isolation and optionally purification during process step (c) and de- pending on the calcination conditions during process step (d). It is possible to produce tin dioxide particles comprising elemental carbon, which have a carbon-content preferably in the range of from 0.1 to 15 %, particularly preferably in the range of from 2 to 10 %, in particular in the range of from 3 to 7 % by weight based on the total weight of the tin dioxide particles comprising carbon. The carbon content can be determined by elemental analysis or thermogravimetric analysis coupled with mass spectrometry.

In one embodiment of the present invention the inventive process is characterized in that the tin dioxide particles comprising elemental carbon have a carbon-content in the range of from 2 to 10 %, in particular from 3 to 7 % by weight based on the total weight of the tin dioxide particles comprising carbon.

The mixture prepared in process step (a) of the inventive process comprises as a first component at least one liquid organic phase comprising at least one alcohol (A) comprising at least on hydroxyl group wherein the hydroxyl group is bound to a secondary, tertiary or ounsaturated carbon atom, also referred to hereinafter as alcohol (A) for short, and as a second component at least one source of tin in the oxidation state +IV (B), also referred to hereinafter as tin source (B) for short, which is at least partly soluble in the liquid organic phase.

The liquid organic phase is preferably liquid in a temperature range from 0 °C to 400 °C, more preferable in a temperature range from 20 °C to 300 °C. In addition to alcohol (A) the liquid organic phase might also comprise at least one inert organic solvent that does not react with the tin source (B) but has the ability to dissolve alcohol (A) and tin source (B).

Examples of inert organic solvents are acetonitrile, dichloromethane, formamides, in particular Ν,Ν-dimethylformamide, sulfoxides, in particular dimethylsulfoxide, or substituted or unsubsti- tuted diphenylethers, in particular brominated diphenylethers.

Preferably alcohol (A) together with tin source (B) form a mixture that is liquid at 20 °C without the addition of an inert organic solvent. In this case the function of the alcohol (A) in the present invention is to serve as a source of oxygen for the formation of tin dioxide, as reaction medium and as a dispersing liquid (referred to as a solvent).

In principle, any alcohol (A) as defined above can be used provided it serves as a source of oxygen during the formation of the tin dioxide. It turned out to be advantageous to use alcohols in which the hydroxyl group is attached to an organic radical which is capable of forming stabilized carbocations.

Suitable alcohols (A) include substituted and unsubstituted arylmethanols such as benzyl alcohol or substituted benzyl alcohols such as 1 -phenylethanol or 4-methylphenylmethanol, sec- ondary alcohols such as isopropanol or higher homologues, and tertiary alcohols such as tert- butylalcohol, tert-amylalcohol or pinacol (1 ,1 ,2,2-tetramethylethylene glycol). The most preferred alcohol (A) is benzyl alcohol.

Preferred alcohols (A) are aliphatic alcohols, preferably with from 4 to 30 carbon atoms, with the hydroxyl group bound to a tertiary or benzylic carbon atom. Correspondingly alcohol (A) is advantageously a compound according to the formula R ¹ -OH, wherein R ¹ is selected from tertiary alkyl groups, preferably with from 4 to 20 carbons atoms, and benzylic groups, preferably with from 7 to 30 carbon atoms. In one embodiment of the present invention the inventive process is characterized in that alcohol (A) is a compound according to the formula R ¹ -OH, wherein R ¹ is selected from tertiary alkyl groups and benzylic groups.

The term "benzylic group" and correspondingly "benzylic carbon atom", in accordance to the lUPAC Compendium of Chemical Terminology 2nd Edition (1997), refers to aryl-methyl groups and their derivatives formed by substitution according to the general structure ArCR2- wherein each R independently represents hydrogen or a linear or branched aliphatic group or an aromatic group. Benzyl, C6H5CH2-, is the most preferred benzylic group.

It is particularly preferred to use benzyl alcohol as alcohol (A).

According to the invention at least one source of tin in the oxidation state +IV (B) (tin source (B)) which is at least partly soluble in the liquid organic phase is used. The term "tin source (B)" throughout the present invention refers to a tin compound which is convertible into tin dioxide by means of hydrolysis, solvolysis, and/or thermal treatment. Such tin sources (B) are known to the person skilled in the art. The term "tin dioxide" throughout the present invention refers to pure tin dioxide or mixtures of tin dioxide with other metal oxides, wherein the amount of tin dioxide is at least 50%, preferably at least 80% up to 100%, in particular between 90 and 99.9% by weight related to the sum of the metal compounds. The tin dioxide particles obtainable by the inventive process might not only comprise additional metal oxides like Sb203 or Ιη2θ3 but might also comprise tin oxide hydrates. It is known to the person skilled in the art that metal oxides may contain -OH and/or hbO-ligands in addition to oxygen, in particular on the surface.

Tin source (B) is at least partly soluble in liquid organic phase comprising alcohol (A). It is well known that the solubility of a compound increases in most cases when the temperature of the solvent is raised. Preferably tin source (B) is completely soluble in liquid organic phase, preferably at temperature below 40°C.

Tin source (B) can be chosen from a wide range of tin (IV) compounds. Appropriate tin sources (B) can be determined by simply testing the solubility of said tin source (B) in liquid organic phase. Preferably the tin source (B) is from tin(IV) nitrate, tin(IV) sulfate, tin(IV) fluoride, tin(IV) chloride, tin(IV) bromide and tin(IV) iodide, more preferably selected from the group of compounds consisting of tin(IV) chloride, tin(IV) bromide and tin(IV) iodide. A particularly preferred tin source (B) is tin(IV) chloride. In one embodiment of the present invention, the inventive process is characterized in that the source of tin in the oxidation state +IV (B) is selected from tin(IV) nitrate, tin(IV) sulfate, tin(IV) fluoride, tin(IV) chloride, tin(IV) bromide and tin(IV) iodide.

The mixture prepared in process step (a) is preferably a homogeneous mixture, in particular a solution.

The molar ratio of the sum of all tin sources (B) to the sum of all alcohols (A) in the mixture prepared in process step (a) can be varied in a wide range. Usually the molar ratio of reactive hy- droxyl groups to tin is at least 4 in order to replace all anions of tin source (B) by hydroxyl groups, which are converted under the reaction conditions to oxides by dehydration. In process step b) of the inventive process the mixture formed in process step (a) is further thermally treated in a temperature range from 40 °C to 300 °C, preferably in a temperature range from 80 °C to 150 °C. Depending on the boiling point of phase (A) the reaction can be done in an open or a closed system, in vacuum or under pressure. The reaction time can be varied in a wide range depending on the reaction rate.

In process step c) of the inventive process the tin dioxide particles, which are formed in process step (b), are isolated and optionally further purified. Methods for isolation of the tin dioxide particles in the form of a powder are known to those skilled in the art. Possible examples are decantation, filtration methods or centrifugation, wherein the isolated tin dioxide particles are optionally purified by further process steps, such as washing and drying steps. In process step d) of the inventive process the tin dioxide particles isolated in process step (c) are calcined in a temperature range from 200 °C to 650 °C, preferably in a temperature range from 350 °C to 450 °C, in particular in a temperature range from 375 °C to 425 °C in a non- oxidizing atmosphere, preferably in an inert gas atmosphere, in particular in an argon atmosphere.

In process step d) the remaining hydrocarbon residues originated from alcohol (A) and/or products thereof are converted to elemental carbon. Since a tin dioxide particle comprises a plurality of smaller tin dioxide crystallites (primary particles) and it is understood that the hydrocarbon residues are attached to the surface of these crystallites, elemental carbon is generated inside and outside of the tin dioxide particle.

In one embodiment of the present invention the inventive process is characterized in that in process step (a) alcohol (A) is benzylalkohol and the source of tin in the oxidation state +IV (B) is tin tetrachloride, and wherein in process step (d) the tin dioxide particles are calcined in a tem- perature range from 350 °C to 450 °C and the non-oxidizing atmosphere comprises at least one noble gas, in particular argon.

The present invention further also provides tin dioxide particles comprising elemental carbon having an average particle size in the range from 1 nm to 100 nm and a carbon-content in the range of from 2 to 10 %, in particular 3 to 7 % by weight, obtainable by a process for producing tin dioxide particles comprising elemental carbon as described above. This process comprises the above-described process steps (a), (b), (c) and (d), especially also with regard to preferred embodiments thereof. The present invention likewise also provides tin dioxide particles comprising elemental carbon having an average particle size in the range from 1 nm to 100 nm and a carbon-content in the range of from 2 to 10 %, in particular 3 to 7 % by weight, wherein the tin dioxide particles are prepared by a process comprising at least the process steps of

(a) preparation of a mixture comprising

(A) at least one liquid organic phase comprising at least one alcohol (A) comprising at least on hydroxyl group wherein the hydroxyl group is bound to a secondary, tertiary or ounsaturated carbon atom and

(B) at least one source of tin in the oxidation state +IV (B) which is at least partly soluble in the liquid organic phase, in a temperature range from -78 °C to 300 °C,

(b) further thermal treatment of the mixture formed in process step (a) in a temperature range from 40 °C to 300 °C, (c) isolation and optionally further purification of the tin dioxide particles, which are formed in process step (b), and (d) calcination of the tin dioxide particles isolated in process step (c) in a temperature range from 200 °C to 650 °C in a non-oxidizing atmosphere.

The process steps a), b), c) and d) have been described above. In particular, preferred embodiments of the process steps have been described above.

The tin dioxide particles comprising elemental carbon, which are obtainable or obtained by the inventive process, have an average particle size in the range from 1 nm to 100 nm, preferably in the range from 5 nm to 50 nm, in particular in the range from 10 nm to 20 nm, and a carbon- content in the range of from 2 to 10 %, in particular 3 to 7 % by weight based on the total weight of the tin dioxide particles comprising carbon.

As described above the tin dioxide particles comprising elemental carbon comprise crystallites of tin dioxide as primary particles wherein the crystallites (primary particles) preferably have an average particle size in the range froml nm to 10 nm, in particular in the range from 4 to 6 nm with low polydispersity. Due to its composition, the inventive tin dioxide particles comprising elemental carbon are particularly suitable as a material for anodes in electrochemical cells, preferably in Li ion cells, especially in Li ion secondary cells or batteries. More particularly, in the case of use in anodes of Li ion cells and especially of Li ion secondary cells, the inventive tin dioxide particles are notable for high capacity and good cycling stability, and ensures low impedances in the cell. In addition anodes comprising the above described tin dioxide particles show high coulombic efficiency. Moreover, the inventive tin dioxide particles can be produced in a simple manner and with reproducible quality. The present invention further also provides for the use of the inventive tin dioxide particles as described above as part of an electrode for an electrochemical cell.

The present invention likewise accordingly also provides an electrode for an electrochemical cell comprising the inventive tin dioxide particles as described above. This electrode is typically incorporated and used as the anode in an electrochemical cell. Therefore, the electrode which comprises the inventive tin dioxide particles is also referred to hereinafter as the anode.

In addition to the inventive tin dioxide particles comprising elemental carbon, the anode generally comprises at least one suitable binder for consolidation of the inventive tin dioxide particles comprising elemental carbon, and optionally further electrically conductive or electroactive constituents. In addition, the anode generally has electrical contacts for supply and removal of charges. The amount of inventive tin dioxide particles comprising elemental carbon, based on the total mass of the anode material, minus any current collectors and electrical contacts, is generally at least 5% by weight, frequently at least 50% by weight and especially at least 60% up to 97.5% by weight.

Useful further electrically conductive or electroactive constituents in the inventive anodes include carbon black (conductive black), graphite, carbon fibers, carbon nanofibers, carbon nano- tubes or electrically conductive polymers. Typically about 2.5 to 40% by weight of the conduc- tive material are used in the anode together with 50 to 97.5% by weight, frequently with 60 to 95% by weight, of the inventive tin dioxide particles comprising elemental carbon, the figures in percent by weight being based on the total mass of the anode material, minus any current collector and electrical contacts. Useful binders for the production of an anode using the inventive tin dioxide particles comprising elemental carbon include especially the following polymeric materials: polyethylene oxide, cellulose, carboxymethylcellulose, polyvinyl alcohol, polyvinylidene fluoride, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylonitrile-methyl methacrylate co- polymers, styrene-butadiene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinyli- dene fluoride-chlorotrifluoroethylene copolymers, ethylene-chlorofluoroethylene copolymers, polyacrylic acid or ethylene-acrylic acid copolymers, optionally at least partly neutralized with alkali metal salt or ammonia, ethylene-methacrylic acid copolymers, optionally at least partially neutralized with alkali metal salt or ammonia, ethylene-(meth)acrylic ester copolymers, polyi- mides and/or polyisobutene, and mixtures thereof.

The selection of the binder is often made with consideration of the properties of any solvent used for production. For example, polyvinylidene fluorides are suitable when N-ethyl-2- pyrrolidone is used as the solvent while polyvinyl alcohol can be processed in aqueous solution. The binder is generally used in an amount of 1 to 20% by weight, based on the total mass of the anode material. Preference is given to using 2 to 15% by weight, especially 7 to 10% by weight.

The inventive electrode comprising the inventive tin dioxide particles comprising elemental carbon, also referred to above as anode, generally comprises electrical contacts for supply and removal of charges, for example an output conductor, which may be configured in the form of a metal wire, metal grid, metal mesh, expanded metal, a metal foil and/or a metal sheet. Suitable metal foils are especially copper foils.

In one embodiment of the present invention, the anode has a thickness in the range from 15 to 200 μηη, preferably from 30 to 100 μηη, based on the thickness excluding output conductor.

The anode can be produced in a manner customary per se by standard methods as known from relevant monographs. For example, the anode can be produced by mixing the inventive tin dioxide particles comprising elemental carbon, optionally using an organic solvent (for example N-methylpyrrolidinone, N-ethyl-2-pyrrolidone or a hydrocarbon solvent), with the optional further constituents of the anode material (electrically conductive constituents and/or organic binder), and optionally subjecting it to a shaping process or applying it to an inert metal foil, for example Cu foil. This is optionally followed by drying. This is done, for example, using a temperature of 80 to 150°C. The drying operation can also take place under reduced pressure and lasts generally for 3 to 48 hours. Optionally, it is also possible to employ a melting or sintering process for the shaping.

The present invention further provides an electrochemical cell, especially a lithium ion secondary cell, comprising at least one electrode which has been produced from or using tin dioxide particles comprising elemental carbon as described above.

Such cells generally have at least one inventive anode, a cathode, especially a cathode suitable for lithium ion cells, an electrolyte and optionally a separator. With regard to suitable cathode materials, suitable electrolytes, suitable separators and possible arrangements, reference is made to the relevant prior art (see, for example, Wakihara et al.: Lithium Ion Batteries, 1 st edition, Wiley VCH, Weinheim (1998); David Linden: Handbook of Batteries, 3rd edition, McGraw-Hill Professional, New York (2008); J. O. Besenhard: Handbook of Battery Materials, Wiley-VCH (1998)).

Useful cathodes include especially those cathodes in which the cathode material comprises lithium transition metal oxide, e.g. lithium cobalt oxide, lithium nickel oxide, lithium cobalt nickel oxide, lithium manganese oxide (spinel), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide or lithium vanadium oxide, or a lithium transition metal phosphate such as lithium iron phosphate. If the intention, however, is to use those cathode materials which comprise sulfur and polymers comprising polysulfide bridges, it has to be ensured that the an- ode is charged with Li° before such an electrochemical cell can be discharged and recharged.

The two electrodes, i.e. the anode and the cathode, are connected to one another using a liquid or else solid electrolyte. Useful liquid electrolytes include especially nonaqueous solutions (water content generally less than 20 ppm) of lithium salts and molten Li salts, for example solu- tions of lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethylsulfonate, lithium bis(trifluoromethylsulfonyl)imide or lithium tetrafluoroborate, especially lithium hexafluorophosphate or lithium tetrafluoroborate, in suitable aprotic solvents such as ethylene carbonate, propylene carbonate and mixtures thereof with one or more of the following solvents: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, dimethoxyethane, methyl propionate, ethyl propionate, butyrolactone, acetonitrile, ethyl acetate, methyl acetate, toluene and xylene, especially in a mixture of ethylene carbonate and diethyl carbonate. The solid electrolytes used may, for example, be ionically conductive polymers. A separator impregnated with the liquid electrolyte may be arranged between the electrodes. Examples of separators are especially glass fiber nonwovens and porous organic polymer films, such as porous films of polyethylene, polypropylene etc.

Particularly suitable materials for separators are polyolefins, especially porous polyethylene films and porous polypropylene films.

Polyolefin separators, especially composed of polyethylene or polypropylene, may have a porosity in the range from 35 to 45%. Suitable pore diameters are, for example, in the range from 30 to 500 nm.

In another embodiment of the present invention, separators composed of polyethylene tereph- thalate nonwovens filled with inorganic particles may be present. Such separators may have a porosity in the range from 40 to 55%. Suitable pore diameters are, for example, in the range from 80 to 750 nm.

Inventive electrochemical cells further comprise a housing which may be of any shape, for example cuboidal, or the shape of a cylinder. In another embodiment, inventive electrochemical cells have the shape of a prism. In one variant, the housing used is a metal-plastic composite film elaborated as a pouch.

The cells may have, for example, a prismatic thin film structure, in which a solid thin film electro- lyte is arranged between a film which constitutes an anode and a film which constitutes a cathode. A central cathode output conductor is arranged between each of the cathode films in order to form a double-faced cell configuration. In another embodiment, a single-faced cell configuration can be used, in which a single cathode output conductor is assigned to a single anode/separator/cathode element combination. In this configuration, an insulation film is typically arranged between individual anode/separator/cathode/output conductor element combinations.

The inventive electrochemical cells have high capacity, cycling stability, efficiency and reliability, and low impedances leading to high possible charge and discharge rates. The inventive electrochemical cells can be combined to form lithium ion batteries.

Accordingly, the present invention further also provides for the use of inventive electrochemical cells as described above in lithium ion batteries. The present invention further provides lithium ion batteries comprising at least one inventive electrochemical cell as described above. Inventive electrochemical cells can be combined with one another in inventive lithium ion batteries, for example in series connection or in parallel connection. Series connection is preferred. Inventive electrochemical cells are notable for particularly high capacities, high power even after repeated charging, and significantly delayed cell death. Inventive electrochemical cells are very suitable for use in devices. The use of inventive electrochemical cells in devices also forms part of the subject matter of the present invention. Devices may be stationary or mobile devices. Mobile devices are, for example, vehicles which are used on land (preferably particularly automobiles and bicycles/tricycles), in the air (preferably particularly aircraft) and in water (preferably particularly ships and boats). In addition, mobile devices are also mobile appliances, for example cellphones, laptops, digital cameras, implanted medical appliances and power tools, especially from the construction sector, for example drills, battery-powered screwdrivers and battery- powered tackers. Stationary devices are, for example, stationary energy stores, for example for wind and solar energy, and stationary electrical devices. Such uses form a further part of the subject matter of the present invention.

The present invention further provides for the use of inventive electrochemical cells as described above in motor vehicles, bicycles operated by electric motor, aircraft, ships or stationary energy stores. The use of inventive electrochemical cells in devices gives the advantage of prolonged run time before recharging and a smaller loss of capacity in the course of prolonged run time. If the intention were to achieve an equal run time with electrochemical cells with lower energy density, a higher weight for electrochemical cells would have to be accepted.

The present invention therefore also further provides for the use of inventive electrochemical cells in devices, especially in mobile devices. Examples of mobile devices are vehicles, for example automobiles, bicycles, aircraft, or water vehicles such as boats or ships. Other examples of mobile devices are those which are portable, for example computers, especially laptops, tel- ephones or electrical power tools, for example from the construction sector, especially drills, battery-driven screwdrivers or battery-driven tackers.

The present invention further provides a device comprising at least one electrochemical cell as described above.

The invention is illustrated by the examples which follow, but these do not restrict the invention. Figures in percent are each based on % by weight, unless explicitly stated otherwise. I. Preparation of tin dioxide particles

1.1 Preparation of inventive tin dioxide particles Sn02-C

1 ml. (2.23 g) SnCU was injected into 20 ml. benzyl alcohol using a syringe under vigorous stir- ring at 1 15 °C. After 1 hour, the reaction temperature was lowered to 105 °C and kept there for further 17 hours. The reaction mixture was then allowed to cool down to room temperature and the white precipitate was washed two times with acetone and collected by centrifugation. Further purification was carried out by washing with THF and precipitation with acetone and, lastly, by dispersing in a mixture consisting of 10 mL THF and several drops of concentrated aqueous hydrochloric acid. Residues of non-dispersible solid were removed by centrifugation and the clear dispersion afterwards dried under ambient conditions in a petri dish.

The resulting white to slightly yellow solid was ground to a powder and heated under argon atmosphere to 400 °C using a heating ramp of 10 °C/min and a subsequent 5 minute soak. After cooling to room temperature, the gray powder referred to as Sn02-C was used as active mate- rial for preparing lithium ion battery anodes.

To demonstrate the improvements by the inventive process according to example 1.1 , the following examples are given for reference 1.2 Preparation of comparative tin dioxide particles Sn02-air (calcination in air)

1 ml. (2.23 g) SnCU was injected into 20 ml. benzyl alcohol using a syringe under vigorous stirring at 1 15 °C. After 1 hour, the reaction temperature was lowered to 105 °C and kept there for further 17 hours. The reaction mixture was then allowed to cool down to room temperature and the white precipitate was washed two times with acetone and collected by centrifugation. Further purification was carried out by washing with THF and precipitation with acetone and, lastly, by dispersing in a mixture consisting of 10 mL THF and several drops of concentrated aqueous hydrochloric acid. Residues of non-dispersible solid were removed by centrifugation and the clear dispersion afterwards dried under ambient conditions in a petri dish.

The resulting white to slightly yellow solid was ground to a powder and heated under ambient atmosphere to 400 °C using a heating ramp of 10 °C/min and a subsequent 5 minute soak. After cooling to room temperature, the powder referred to as Sn02-air was used as active material for preparing lithium ion battery anodes.

1.3 Preparation of comparative tin dioxide particles Sn02-RT (omitting heat treatment)

1 mL (2.23 g) SnCU was injected into 20 mL benzyl alcohol using a syringe under vigorous stirring at 1 15 °C. After 1 hour, the reaction temperature was lowered to 105 °C and kept there for further 17 hours. The reaction mixture was then allowed to cool down to room temperature and the white precipitate was washed two times with acetone and collected by centrifugation. Further purification was carried out by washing with THF and precipitation with acetone and, lastly, by dispersing in a mixture consisting of 10 mL THF and several drops of concentrated aqueous hydrochloric acid. Residues of non-dispersible solid were removed by centrifugation and the clear dispersion afterwards dried under ambient conditions in a petri dish.

The resulting white to slightly yellow solid referred to as Sn02-RT was ground to a powder and was used as active material for preparing lithium ion battery anodes.

1.4 Preparation of comparative a Sn02 C composite Ref-C comprising commercially available Sn02 nanoparticles

1 g commercially available Sn02 nanopowder (Sigma Aldrich, < 100 nm) was dispersed in a solution of 120 mg sucrose in 2 mL water. The mixture was dried under ambient conditions, ground to a powder and heated under argon atmosphere to 400 °C using a heating ramp of 10 °C/min and a subsequent 5 minute soak. After cooling to room temperature, the gray powder referred to as Ref-C was used as active material for preparing lithium ion battery anodes

II. Preparation of anodes comprising tin oxide particles 11.1 Preparation of inventive anode Sn02-C-PVA (use of polyvinyl alcohol as binder) 450 mg tin dioxide particles containing elemental carbon (Sn02-C) were mixed with 90 mg carbon black (Super C65) and 60 mg polyvinyl alcohol) binder (Selvol 425, used as 6% aqueous solution). After dispersing using a planetary mixer, the resulting slurry was cast onto copper foil acting as current collector using a doctor blade. The electrode tape was dried under vacuum at 100 °C over night. The resulting electrodes were designated as Sn02-C-PVA

11.2 Preparation of inventive anode Sn02-C-PAA (use of polyacrylic acid as binder)

450 mg tin dioxide particles comprising elemental carbon (Sn02-C) were mixed with 90 mg car- bon black (Super C65) and 60 mg poly(acrylic acid) binder (M=450.000 g/mol, used as 5% aqueous solution). After dispersing using a planetary mixer, the resulting slurry was cast onto copper foil using doctor blade technique. The electrode tape was dried under vacuum at 100 °C over night. The resulting electrodes were designated as Sn02-C-PAA 11.3 Preparation of inventive anode Sn02-C-PVDF (use of polyvinylidene fluoride as binder)

450 mg tin dioxide particles comprising elemental carbon (Sn02-C) were mixed with 90 mg carbon black (Super C65) and 60 mg polyvinylidene fluoride binder (used as 10% solution in N- ethyl pyrrolidone). After dispersing using a planetary mixer, the resulting slurry was cast onto copper foil using doctor blade technique. The electrode tape was dried under vacuum at 120 °C over night. The resulting electrodes were designated as Sn02-C-PVDF

I I.4 Preparation of comparative anodes Sn02-air-PVA, Sn02-RT-PVA and Ref-C-PVA, comprising reference materials Sn02-air, Sn02-RT and Ref-C

450 mg tin dioxide particles used for reference (Sn02-air, Sn02-RT, Ref-C) were mixed with 90 mg carbon black (Super C65) and 60 mg polyvinyl alcohol) binder (Selvol 425, used as 6% aqueous solution). After dispersing using a planetary mixer, the resulting slurry was cast onto copper foil acting as current collector using a doctor blade. The electrode tape was dried under vacuum at 100 °C over night. The resulting electrodes were designated as Sn02-air-PVA, Sn02-RT-PVA and Ref-C-PVA, respectively.

III. Electrochemical testing Test cells (coin-type cells) containing the electrodes mentioned above and lithium foil as counter electrode were assembled in an argon-filled glove box using a solution of 1 M LiPF6 in FEC/EMC (fluoroethylene carbonate) as electrolyte and glass fiber discs (Whatman GF/D) as separator. The cycling experiments were conducted in the potential range of 50 - 900 mV vs. Li/Li ⁺ if not stated otherwise For the first cycle, a rate of 0.05 C was used and the subsequent cycles were conducted either at a constant rate of 0.5 C or with varying currents in the range of 0.1 C to 2 C, namely 0.1 C, 0.2 C, 0.5 C, 1 C, 2C for 5 cycles in each case. For the example 111.1 additional testing in the potential range of 10 - 1200 mV and 10 - 1500 mV vs. Li/Li ⁺ was carried out, respectively and in example 111.4 the comparative cell was additionally tested in the potential range of 10 - 1200 mV.

111.1 Inventive cells comprising inventive anode Sn02-C-PVA

Table 1 : Lithiation and delithiation capacity of test cells comprising inventive anode Sn02-C- PVA cycled in the potential range of 50 - 900 mV vs. Li/Li ⁺ .

25

Table 2: Lithiation and delithiation capacity of test cells comprising inventive anode Sn02-C- PVA cycled in the potential range of 10 - 1200 mV vs. Li/Li ⁺ .

Table 3: Lithiation and delithiation capacity of test cells comprising inventive anode Sn02-C- PVA cycled in the potential range of 10 - 1500 mV vs. Li/Li ⁺ . C-Rate Lithiation capacity

0.1 C 576

0.2 C 560

0.5 C 526

1 C 468

2 C 359

Table 4: Lithiation capacity of test cells comprising inventive anode Sn02-C-PVA cycled in the potential range of 50 - 900 mV vs. Li/Li ⁺ as a function of cycling rate

III.2 Inventive cells comprising inventive anode Sn02-C-PAA

Table 5: Lithiation and delithiation capacity of test cells comprising inventive anode Sn02-C- PAA

Table 6: Lithiation capacity of test cells comprising inventive anode Sn02-C-PAA as a function of cycling rate III.3 Inventive cells comprising inventive anode Sn02-C-PVDF

Table 7: Lithiation and delithiation capacity of test cells comprising inventive anode Sn02-C- PVDF

Table 8: Lithiation capacity of test cells comprising inventive anode Sn02-C-PVDF as a function of cycling rate III.4 Comparative cells comprising comparative anode Sn02-air-PVA

Table 9: Lithiation and delithiation capacity of test cells comprising comparative anode Sn02- air-PVA cycled in the potential range of 50 - 900 mV vs. Li/Li ⁺ Cycle no. Lithiation capacity Delithiation capacity

[mAh/gsn02] [mAh/gsn02]

1 1658 590

2 530 453

10 447 444

50 434 433

100 418 417

Table 10: Lithiation and delithiation capacity of test cells comprising comparative anode Sn02- air-PVA cycled in the potential range of 10 - 1200 mV vs. Li/Li ⁺

Table 1 1 : Lithiation capacity of test cells comprising comparative anode Sn02-air-PVA cycled in the potential range of 50 - 900 mV vs. Li/Li ⁺ as a function of cycling rate

III.5 Comparative cells comprising comparative anode Sn02-RT-PVA

Table 12: Lithiation and delithiation capacity of test cells comprising comparative anode Sn02- RT-PVA C-Rate Lithiation capacity

0.1 C 51 1

0.2 C 440

0.5 C 352

1 C 267

2 C 133

Table 13: Lithiation capacity of test cells comprising comparative anode Sn02-RT-PVA as a function of cycling rate

111.6 Comparative cells comprising comparative anode Ref-C-PVA

Table 14: Lithiation and delithiation capacity of test cells comprising comparative anode Ref-C- PVA

Table 15: Lithiation capacity of test cells comprising comparative anode Ref-C-PVA as a function of cycling rate