ANODE ACTIVE MATERIAL PARTICLES ENCAPSULATED IN PYROGENIC, NANOSTRUCTURED METAL OXIDES AND METHODS OF MAKING AND USING THE SAME

A process produces a coated active anode material, wherein a mixed anode material and a pyrogenically produced and nanostructured metal oxide of alumina, titania or a mixture thereof are subjected to dry mixing in a mixing unit. A coated mixed anode material obtainable by this process finds application in lithium-ion batteries, electric and/or electronic devices.

FIELD OF THE INVENTION

The invention relates to a method of producing encapsulated anode active material particles in which carbon and/or Si-based particles and fumed, nanostructured metal oxides are mixed dry under shearing conditions. The invention further relates to the fumed metal oxide coated anode material as well as to a battery cell containing the encapsulated carbon and/or Si-based anode particles and use thereof.

BACKGROUND OF THE INVENTION

Various energy storage technologies have recently attracted much attention of public and have been a subject of intensive research and development at the industry and in the academia. As energy storage technologies are extended to devices such as cellular phones, camcorders and notebook PCs, and further to electric vehicles, demand for high energy density batteries used as a source of power supply of such devices is increasing. Secondary lithium-ion batteries are one of the most important battery types currently used.

The secondary lithium-ion batteries are usually composed of an anode made of a carbon material or a lithium-metal alloy, a cathode made of a lithium-metal oxide, and an electrolyte in which a lithium salt is dissolved in an organic solvent. The separator of the lithium-ion battery provides the passage of lithium ions between the positive and the negative electrode during the charging and the discharging of the battery.

US2019/0393543 describes a lithium metal secondary battery, comprising a cathode, an anode, and a porous separator or electrolyte disposed between the cathode and the anode, wherein the anode comprises: (a) an anode active layer containing a layer of lithium or lithium alloy, in a form of a foil, coating, or multiple particles aggregated together, as an anode active material; and (b) an anode—protecting layer of a conductive sulfonated elastomer composite, disposed between the anode active layer and the separator/electrolyte.

US201363345 describes forming a protective coating of graphene on a negative lithium metal electrode, for lithium containing electrochemical cells, such as lithium-ion batteries. The graphene protective coating is said to reduce dendrite formation and growth.

WO2019215406A1 describes an anode for a lithium-ion battery, including at least one anode material which is binder-free, is pre-charged with lithium ions, and coated with a protective coating including a very long list of allegedly suitable materials, however none of the coatings employed in the present invention are disclosed in WO2019215406A1.

CN106025242A describes a composite anode material for a lithium-ion battery comprising a core layer of a porous silicon alloy nanowire with carbon nanotubes and a shell layer made of a conductive polymer film of a polypropylene oxide, polyethylene succinate, polyethylene succinate, or polyethylene glycol imine blended with graphene.

The coating of cathode materials of lithium-ion batteries with Al2O3, TiO2, ZrO2 for improving their cycling performance, is known.

Examples of use of metal oxide in cathode materials are provided in the following articles. In the article “mesoporous carbon material as cathode for high performance lithium-ion capacitor” published in Chinese Chemical Letters (2018), 29 (4) 620-623, by Zhang et al. Mg citrate was used as the precursor of the C mesoporous and the nano-sized metal oxide particles as template provided by the Mg citrate.

In the article “Improvement of cycling performance of lithium-sulfur batteries by using metal oxide as a functional additive for trapping lithium polysulfide” of Ponraj et al. published in ACS Applied Material Interfaces 2016, 8, 4000-4006, hydrophilic metal oxide was used as an additive on the surface of the active sulfur of positive electrodes to trap polysulfides.

Elements like carbon and its allotropes (graphene) have been used as anode materials in lithium-ion secondary batteries, however, there exist several issues with the structural stability of the graphene in the anode. In the article “An electrode comprising of graphene nano-powder inserted in an enclosed structure in anodic aluminum oxide coated with PANI by using low temperature hydrothermal process” of Sugam et al. published in 1942, 62nd DAE Solid State Physics Symposium, 2017, graphene nano-powder was inserted and confined on an anodic aluminum oxide coated using PANI (polyaniline).

In the article “An alumina-coated Fe3O4-Reduced graphene oxide composite electrode as a stable anode for lithium-ion battery” of Qi-Hui et al. published in Electrochimica Acta 2015, 156, 147-153, an Al2O3 coating was used on a Fe3O4-reduced graphene oxide composite anodic material.

Wu Xing et al. describe in “Electrochemical studies of MgFe2O4@TiO2 core-shell nanospheres as anode material for lithium battery applications” in Journal of Materials Science: Science in Electronics, vol. 29, no. 20 (2018), pages 17872-17880, ISSN: 0957-4522, a one-step hydrothermal method to produce core-shell-structures based on MgFe2O4 and TiO2.

A rather major general problem with anode materials, especially silicon-based anode materials, is the uncontrolled solid electrolyte interface (SEI) formation during initial charge-discharge processes of a battery. In addition, aging processes within the bulk of the material result in the loss of performance during cycling. This aging phenomenon is especially relevant for Si based anode active materials. During cycling the negative electrode material suffers from several electrochemical degradation mechanisms that may cause deactivation of the negative electrode material. Electrolyte induced surface transformations and unwanted side reactions with lithium species lead to the formation of SEI layers with increased thickness, finally resulting in a decreased performance and battery lifetime.

Surface coating has proven to be an extremely important method to address this aging problem by suppressing the direct contact between the active materials surfaces and the liquid electrolyte.

Although nano-sized metal oxide particles have been used as additives in lithium-ion batteries their effectiveness has been limited by poor dispersibility. Hence, practical ways to improve the long life of secondary lithium-ion batteries are often limited. Often times, the use of commercially available nano-sized metal oxides leads to inhomogeneous distribution and large agglomerated metal oxide particles on the surface of the anode materials. As a result, the anode material particles are not fully covered by the metal oxide particles and large non-dispersed metal oxide particles are present, located next to the anode particles, and are clearly visible by SEM elemental mapping.

The problem addressed by the present invention is that of providing a homogeneous coating layer of a metal oxide or a mixture of metal oxides around an anode active material comprising carbon and/or Si-based particles.

In the course of thorough experimentation, it was surprisingly found that pyrogenically produced, nanostructured metal oxide of alumina or titania (or mixed metal oxides of alumina and titania) may successfully be used for coating of anode materials including carbon and/or Si-based particles using a dry mixing process for coating the metal oxide on the anode materials. It was also surprisingly found that further surface modification of the pyrogenically produced, nanostructured metal oxide prior to the dry mixing may further improve the coverage and homogeneity of the coating significantly.

SUMMARY OF THE INVENTION

The invention provides a process for producing a coated active anode material, the coated active anode material, and the use of the coated active anode material in a lithium-ion battery. The lithium-ion battery of the present invention can be used in electronic and electric apparatuses including, for example, mobile phones, computers (lap top computers, desk top computers, computer pads), electronic watches, key fabs, electric appliances, power tools, vacuum cleaners, electric lawn mowers and electric vehicles.

According to a first aspect of the present invention there is provided a process for producing a coated active anode material. The process is characterized in that the coated active anode material is obtained by subjecting an active anode material and a pyrogenically produced metal oxide of alumina or titania to dry mixing in a mixing unit under shearing conditions, characterized in that the coated active anode material is in the form of particles, and the metal oxide has a BET surface area of 5-300 m2/g, a mono-modally and a narrow particle size distribution with a mean aggregate diameter d50 of 5-150 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

The pyrogenically produced metal oxide is hydrophilic. Preferably, in an embodiment, the pyrogenically produced metal oxide is subjected to a surface modification to become hydrophobic.

In an embodiment, the mixing unit has a specific electrical power of 0.05-1.5 KW per kg of the mixed anode material.

The coated active anode material is in the form of particles, and the metal oxide has a BET surface area of 5-300 m2/g, a mono-modally and narrow particle size distribution with a mean aggregate diameter d50 of 5-150 nm, more preferably 10-120 nm, even more preferably 20-100 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

SEM-EDX mapping of the coated active anode material provides a fully and homogeneous coverage of the metal oxide substantially around all anode particles, with no or only few larger metal oxide agglomerates.

In an embodiment, the process is characterized in that the specific electrical power of the mixing unit is 0.1-1000 KW, the volume of the mixing unit is 0.1 L to 2.5 m3, and the speed of a mixing tool in the mixing unit is 5-30 m/s.

The span (d90-d10)/d50 of particles of the metal oxide and/or of the mixed oxide comprising aluminum or titanium is 0.4-1.2, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

In an embodiment, the active anode material is in the form of powder and comprises carbon particles, silicon particles, or silicon oxide particles or any combinations thereof.

The active anode material comprises carbon and/or Si-based particles. Si-based particles as this term is used herein means silicon particles (e.g., pure silicon particles), silicon oxide (SiOx) particles, and any combinations of silicon, silicon oxide, and carbon particles including mixtures and composites thereof. Silicon oxide can be SiO and/or SiO2.

In an embodiment, the coated active anode material is further subjected to a heat treatment following the dry mixing.

In an embodiment, the proportion of the metal oxide in the coated active anode material is 0.05%-5% by weight, based on the total weight of the coated mixed anode material.

Another aspect of the present invention is directed to the coated active anode material obtainable by the above process.

According to yet another aspect of the present invention there is provided a coated active anode material comprising an active anode material and a coating of a pyrogenically produced, nanostructured metal oxide on the surface of the mixed anode material, wherein the coated active anode material is in the form of particles, and the metal oxide has a BET surface area of 5-300 m2/g, a mono-modally and a narrow particle size distribution with a mean aggregate diameter d50 of 5-150 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water and wherein the pyrogenically produced, nanostructured metal oxide is preferably surface treated to become hydrophobic may by reacting the hydroxyl groups of alumina or titania with a silane to form —O—Si—R groups. The metal oxide is hydrophilic or hydrophobic, preferably hydrophobic. The active anode material is carbon, silicon, silicon oxide (SiOx), or any combinations thereof, including mixtures and/or composites of carbon, silicon, and silicon oxide.

Other aspects of the present invention, are directed to an active negative electrode material for a lithium-ion battery comprising the coated active anode material, also to a lithium-ion battery comprising the coated active anode material, and also to the use of the coated active anode material in an active negative electrode material of a lithium-ion battery.

Yet another aspect of the present invention is directed to an apparatus powered by the lithium-ion battery.

The nanostructured metal oxide made by the flame process has a mono-modally and narrow particle size distribution in combination with an excellent dispersibility during the dry coating process of the anode material. These particles lead to an excellent interaction and proper adhesion to the anode active material.

Furthermore, the additional surface modification of these particles leads to further improvements in interaction and adhesion to the anode active material. This results in a complete de-agglomeration of the metal oxide agglomerates and finally provide a fully and homogenously covered anode active material particles by fumed, nanostructured and surface modified metal oxide.

It has been found that by using a high intensity dry coating process in combination with the pyrogenic, nanostructured metal oxide particles, the present invention method results in significantly improved dispersibility of the metal oxide particles and homogeneous coating. During the dry mixing the applied shear forces (mixing) decompose any metal oxide agglomerates into tiny aggregates which have a very high tendency to settle down on the surface of the anode active material particles powder resulting in very good interaction and adhesion which in turn results in a homogeneous coating. In contrast, conventional metal oxide particles, which are not pyrogenically produced and nanostructured, are composed of isolated, spherical particles (which are the result of milling coarser metal oxide particles) and do not show such behaviour.

These and other features and advantages of the invention will become better understood from the following detailed description in conjunction with the following figures.

DETAILED DESCRIPTION OF THE INVENTION

According to a first aspect of the invention there is provided a method of producing encapsulated active anode material particles in which an active anode material and fumed, nanostructured metal oxide are mixed dry under shearing conditions. The fumed, nanostructured metal oxide is preferably also surface modified to become hydrophobic prior to the dry mixing. A second aspect of the invention relates to the fumed metal oxide coated anode material, and a third aspect of the invention relates to a battery cell containing the encapsulated carbon and/or Si-based anode particles.

Process for Producing the Coated Anode Active Material

According to a first aspect of the present invention, there is provided a process for producing a coated active anode material, wherein active anode material particles such as carbon, and/or Si-based anode particles and a pyrogenically produced, nanostructured, and/or a pyrogenically produced mixed oxide comprising at least two metals are subjected to dry mixing under shearing conditions. Si-based anode particles includes silicon particles, silicon oxide particles, and any combinations of silicon, silicon oxide, and carbon particles.

The fumed, nanostructured metal oxide is preferably also surface modified to become hydrophobic prior to the dry mixing.

The active anode material may be referred to also as the core active anode material or the substrate active anode material or particles. The pyrogenically produced, nanostructured and, preferably, surface modified metal oxide may also be referred as the coating. The coated active anode material refers to the mixed active anode material with the coating produced by dry mixing. Once the dry mixing is completed the carbon and/or Si-based particles are covered with said metal oxide.

Dry Mixing

Dry mixing may be performed, for example, in a mixing unit having a specific electrical power of 0.05-1.5 KW per kg of the mixed anode material. Dry mixing is understood to mean that no liquid is added or used during the mixing process, that is e.g., substantially dry powders are mixed together. However, it is possible that there are trace amounts of moisture or some other than water liquids present in the mixed feedstocks or that these include crystallization water.

If the used specific electrical power is less than 0.05 KW per kg of the mixed anode material, this gives an inhomogeneous distribution of the metal oxide on top of the anode active material particles, which may be not firmly bonded to the core material of the anode active material particles. A specific electrical power of more than 1.5 KW per kg of the mixed anode material leads to poorer electrochemical properties. In addition, there is the risk that the coating will become brittle and prone to fracture. The nominal electrical power of the mixing unit can vary in a wide range, e.g., from 0.1 kW to 1000 kW. Thus, it is possible to use mixing units on the laboratory scale with a nominal power of 0.1-5 KW or mixing units for the production scale with a nominal electrical power of 10-1000 KW. The nominal electrical power is the nameplate, maximal absolute electrical power of the mixing unit.

The volume of the mixing unit may vary in a wide range. For example, the volume of the mixing unit may range from 0.1 L to 2.5 m3. For example, mixing units on a laboratory scale may have a volume of 0.1-10 L or mixing units for the production scale may have a volume of 0.1-2.5 m3.

Preferably, in the process according to the invention, forced action mixers are used in the form of intensive mixers with high-speed mixing tools. It has been found that a speed of the mixing tool of 5-30 m/s, more preferably of 10-25 m/s, gives the best results. Examples of commercially available mixing units which are suitable for the process of the invention include Henschel mixers and Eirich mixers. The Eirich mixers may be, for example, high intensity Eirich mixers.

The mixing time may vary and may be preferably from 0.1 to 120 minutes, more preferably from 0.2 to 60 minutes, and most preferably from 0.5 to 10 minutes.

The mixing may be followed by a thermal treatment of the mixture for improved binding of the coating to the anode active material particles. However, this treatment is optional in the process according to the invention since in this process, the pyrogenically produced, nanostructured and surface modified metal oxide adheres with sufficient firmness to the core anode active material particles, i.e., the carbon and/or Si-based particles. Hence, a preferred embodiment of the process according to the invention may not include a thermal treatment after the mixing.

It has been found that the best results regarding the adhesion of the metal oxides to the core anode active material particles are obtained when the metal oxide has a BET surface area of 5 m2/g-300 m2/g, more preferably of 10 m2/g-200 m2/g and most preferably of 15-150 m2/g. The BET surface area can be determined according to DIN 9277:2014 by nitrogen adsorption according to the Brunauer-Emmett-Teller procedure.

Pyrogenic Formation

The metal oxide used in the process, i.e., the aluminum oxide or the titanium oxide, according to the invention is produced pyrogenically, i.e., by a pyrogenic method. A pyrogenic method is also referred to as a “fumed” method. Such “pyrogenic” or “fumed” method involves the reaction of the corresponding metal precursor in a flame hydrolysis or a flame oxidation in an oxyhydrogen flame to form the metal oxide. This reaction initially forms highly disperse approximately spherical primary metal oxide particles, which in the further course of the reaction coalesce to form aggregates. The aggregates can then accumulate into agglomerates. In contrast to the agglomerates, which as a rule can be separated into the aggregates relatively easily by introduction of energy, the aggregates are broken down further, if at all, only by intensive introduction of energy. Said metal oxide powder may be partially destructed and converted into nanometre (nm) range particles advantageous for the present invention by suitable grinding.

The preparation of pyrogenic metal oxides is further described in WO2004108595A2. The fumed metal oxides of the present invention include aluminum oxide (Al2O3) also called alumina and titanium oxide (TiO2) also called titania. Preferably, the fumed alumina and fumed titania are further subjected to a surface treatment to become hydrophobic. An example of a fumed alumina commercially available is the AEROXIDE® Alu C from Evonik Operations GmbH. Another example of a fumed hydrophobic alumina is the AEROXIDE® Alu C 805 commercially available from Evonik Operations GmbH. An example of a fumed hydrophobic titania is the AEROXIDE® TiO2 T 805, commercially available from Evonik Operations GmbH. The BET surface area as well as other characteristics of these materials are provided in Table 1.

More specifically, the pyrogenically, especially flame-hydrolytically produced aluminum oxide or titanium oxide powder can be produced starting from a metal halide, preferably a metal chloride such as aluminum chloride or titanium chloride, respectively. The metal chloride precursor and if applicable, other metal precursors, can be evaporated, the resulting vapor is mixed alone or together with a carrier gas, e.g., nitrogen, in a mixing unit in a burner with other gases; i.e., air, oxygen, nitrogen and hydrogen. The gases are caused to react with each other in a flame in a closed combustion chamber to produce the metal oxide (or mixed metal oxides) and waste gases. Then the hot waste gases and the metal oxide are cooled off in a heat-exchanger unit, the waste gases are separated from the metal oxide and any halide remnants adhering to the metal oxide obtained are removed by a heat treatment with moistened air.

The flame spray pyrolysis (FSP) process suitable for preparing the metal oxide may comprise the following steps: 1) a solution containing the metal precursor (e.g., the alumina chloride, or titanium chloride) is atomized, e.g., by means of air or an inert gas, preferably using a multi-substance nozzle, and 2) mixed with a combustion gas, preferably hydrogen and/or methane, and air, and 3) the mixture is allowed to burn in a flame into a reaction chamber surrounded by a casing, 4) the hot gases and the solid products are cooled, and then the solid product is removed from the gases.

Suitable other aluminum oxide or titanium oxide metal precursors used for producing the aluminum oxide or the titanium oxide by flame spray pyrolysis process may include either inorganic compounds, such as nitrates, chlorides, or organic compounds, such as carboxylates of aliphatic acids having 6 to 9 carbon atoms, for example, aluminum 2-ethylhexanoate or titanium 2-ethylhehanoate. The used metal oxide precursors may be atomized dissolved in water or an organic solvent. Suitable organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, 2-propanone, 2-butanone, diethyl ether, tert-butyl methyl ether, tetrahydrofuran, C1-C8-carboxylic acids, ethyl acetate, toluene, petroleum and mixtures thereof.

The pyrogenically produced, nanostructured and surface modified metal oxide used in the process according to the invention, is in the form of aggregated primary particles, preferably with a numerical mean aggregate diameter of 5-150 nm, more preferably 10-120 nm, even more preferably 20-100 nm, as determined by transition electron microscopy (TEM). This numerical mean diameter can be determined by calculating the average size of at least 500 particles analysed by TEM.

The mean diameter of the agglomerates is usually 1-2 μm. These mean numerical values can be determined in a suitable dispersion, e.g., in an aqueous dispersion, by a static light scattering (SLS) method. The agglomerates and partly the aggregates can be destroyed e.g., by grinding or ultrasonic treatment of the particles to result in particles with a smaller particle size.

The mean aggregate diameter d50 of the metal oxide is 5-150 nm, more preferably 10-120 nm, even more preferably 20-100 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

Thus, the pyrogenically produced, nanostructured and surface modified metal oxide used in the process of the present invention is preferably characterized by high dispersibility, that is, the ability to form relatively small particles under mild ultrasonic treatment. It is believed, that dispersion under such mild conditions correlates with the conditions during the dry coating process. That means, the agglomerates of the metal oxide are destroyed in the mixing process of the present invention in a similar way as under the ultrasonic treatment and are able to form a homogeneous coating of the anode active material particles.

The span (d90-d10)/d50 of particles of the metal oxide and/or of the mixed oxide comprising metal is preferably 0.4-1.2, more preferably 0.5-1.1, and even more preferably 0.6-1.0, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

Thus, the pyrogenically produced, nanostructured metal oxide used in the process of the present invention is preferably characterized by a relatively narrow particle size distribution. This helps to achieve a high-quality metal oxide coating on the surface of the transition metal oxide.

The d values d10, d50 and deo are commonly used for characterizing the cumulative particle diameter distribution of a given sample. For example, the d10 diameter is the diameter at which 10% of a sample's volume is comprised of smaller than dio particles, the d50 is the diameter at which 50% of a sample's volume is comprised of smaller than d50 particles. The d50 is also known as the “volume median diameter” as it divides the sample equally by volume; the doo is the diameter at which 90% of a sample's volume is comprised of smaller than doo particles.

The pyrogenically produced metal oxide (alumina and/or titania) is hydrophilic. Through surface modification of the pyrogenically produced metal oxide, a hydrophobic metal oxide is then produced. The surface treatment may include using any of many suitable hydrophobic reagents, such as silanes. Both the hydrophilic and the hydrophobic forms of the fumed, nanostructured metal oxide may be used as coatings using the process of the present invention via dry mixing with the substrate active anode material. However, the fumed, nanostructured, and surface modified hydrophobic metal oxide is preferred because it shows a more homogeneous coverage of the substrate active anode material and a full coverage of the substrate active anode material.

Surface Treatment of the Pyrogenically Produced Metal Oxide

The pyrogenically produced alumina or titania without any further surface treatment is hydrophilic because it is naturally covered with hydroxyl (—OH) groups. However, through surface modification of the pyrogenically produced alumina or titania, hydrophobic alumina or titania can be produced. For example, hydrophobization of the alumina or titania may be performed by reacting the hydroxyl groups with a silane to form —O—Si—R groups. Thus, preferably, the alumina or titania is surface modified, meaning that the surface of the alumina or titania is at least partially covered by silanes.

The pyrogenically produced alumina or titania may be used in its hydrophilic and hydrophobic forms. The use of the hydrophilic alumina or titania does not require any further treatment after synthesis by the pyrogenic process. However, by further treatment with a hydrophobic reagent, such as silanes, after synthesis by the pyrogenic process the alumina or titania particles can become hydrophobic. For example, in an embodiment, an octyl silane is covalently bound to the surface of the alumina or titania particles. Both the hydrophilic and the hydrophobic forms of the fumed, nanostructured alumina or titania may be used effectively as coatings using the process of the present invention via dry mixing with the substrate active anode material. The fumed, nanostructured and surface modified alumina or titania is preferred because it shows more homogeneous coverage of the substrate active anode material.

Accordingly, the pyrogenically prepared alumina or titania is sprayed with a surface modifying agent at room temperature and the mixture is subsequently treated thermally at a temperature of 50 to 300° C., preferably 80-180° C., over a period of 0.5 to 3 h.

In an alternative embodiment, surface modification of the pyrogenically prepared alumina or titania can be carried out by treating the pyrogenic metal oxide with a surface modifying agent in vapor form and subsequently treating the mixture thermally at a temperature of 50 to 800° C. over a period of 0.5 to 6 h.

An alternative method for surface modification of the pyrogenically prepared alumina or titania can be carried out by treating the pyrogenic alumina or titania with a surface modifying agent in vapor form and subsequently treating the mixture thermally at a temperature of 50 to 800° C. over a period of 0.5 to 6 h.

The thermal treatment can be conducted under protective gas, such as, for example, nitrogen. The surface treatment can be carried out in heatable mixers and dryers with spraying devices, either continuously or batchwise. Suitable devices can be, for example, plowshare mixers or plate, cyclone, or fluidized bed dryers.

The present invention has the advantage that commercially available silanes can be used to modify the metal oxide (i.e., the alumina, or titania) and thus individually adapt the properties of the alumina or titania, depending on the desired properties and intended purposes.

As surface modifying agent, it is possible to employ the following compounds and mixtures of the following compounds:

The metal oxide particles produced via the pyrogenic process usually have a purity of at least 96% by weight, preferably at least 98% by weight, more preferably at least 99% by weight. The metal oxide used in the inventive process preferably contains the elements Cd, Ce, Fe, Na, Nb, Pin proportions of <10 ppm and the elements Ba, Bi, Cr, K, Mn, Sb in proportions of <5 ppm, where the sum of the proportions of all of these elements is <100 ppm. The content of chloride is preferably less than 0.5% by weight, more preferably 0.01 to 0.3% by weight, based on the mass of the metal oxide powder. The proportion of carbon in hydrophilic, non surface-modified metal oxides is preferably less than 0.2% by weight, more preferably 0.005%-0.2% by weight, even more preferably 0.01%-0.1% by weight, based on the mass of the metal oxide powder.

Active Anode Material

The substrate anode particles which are encapsulated or coated with the fumed metal oxide may include any suitable material used as anode active material in secondary lithium-ion batteries, capable of reversible intercalating/deintercalating lithium ions and/or reversible reaction with lithium species. Examples thereof are carbonaceous materials including crystalline carbon such as natural or artificial graphite in the form of plate-like, flake, spherical or fibrous type graphite; amorphous carbon, such as soft carbon, hard carbon, mesophase pitch carbide, fired coke and the like, or mixtures thereof. In addition, Si-based particles can be used as anode active materials. Preferred anode active materials are carbon and/or Si-based particles. Si-based particles includes silicon particles (e.g., pure silicon particles), silicon oxide (SiOx) particles, and any combinations of silicon, silicon oxide, and carbon particles including mixtures and composites thereof. Silicon oxide can be SiO and/or SiO2. In an embodiment, the active anode material may be a nanostructured porous silicon material. In an embodiment, the anode material is SiOx where x can vary from 0 to about 2, such as, Si, SiO, SiO2 or any combinations thereof.

Preferred anode active materials are carbon and/or Si-based particles, including a composite material of C and Si-based particles. “Composite material” refers to a composition comprising both carbon material and silicon material. The carbon and silicon material may be a mixture of a carbon powder and a silicon powder of nano sized particles. In an embodiment the composite material may comprise individual particles of carbon and silicon which are chemically bonded. In another embodiment, the composite material may comprise porous, nanosized silicon particles with carbon impregnated within the silicon porous structure.

The active anode material which is mixed and coated with the metal oxide may comprise carbon and/or Si-based particles. In some embodiments, the active anode material may comprise a composite SiOx/C material wherein x can vary from 0 to about 2, made of 60-99% carbon and 40-1% silicon oxide, preferably 70-95% carbon and 30-5% silicon oxide, and more preferably 80-90% carbon and 20-10% silicon oxide. The composite SiOx/C material may be in the form of powder or particles.

In an embodiment, the active anode material may comprise a composite SiO/C material, made of 60-99% carbon and 40-1% SiO, preferably 70-95% carbon and 30-5% SiO, and more preferably 80-90% carbon and 20-10% SiO. The composite SiO/C material may be in the form of powder or particles.

In some embodiments, the active anode material may comprise a composite Si/C material, made of 60-99% carbon and 40-1% silicon, preferably 70-95% carbon and 30-5% silicon, and more preferably 80-90% carbon and 20-10% silicon. The composite Si/C material may be in the form of powder or particles.

The coated active anode material has a numerical mean particle diameter of 1-50 μm, preferably of 1-40 and more preferably of 2-20 μm. A numerical mean particle diameter can be determined according to ISO 13320:2009 by laser diffraction particle size analysis.

The active anode material may be referred to also as the core active anode material or the substrate active anode material or particles. The titanium oxide or the aluminum oxide may also be referred as the coating and the mixed active anode material with the coating may also be referred to as the coated active anode material or particles.

The proportion of the metal oxide in the coated mixed anode material is preferably 0.05%-5% by weight, more preferably 0.1%-2% by weight, based on the total weight of the coated mixed anode material. If the proportion of the metal oxide is less than 0.05% by weight, no beneficial effect of the coating can usually be observed yet. In the case of more than 5% by weight thereof, no beneficial effect of the additional quantity of the metal coating of more than 5% by weight is usually observed.

The coated mixed anode material preferably has a coating layer thickness of 10-200 nm, as determined by TEM analysis.

The present invention further provides a coated mixed anode material obtainable by the process according to the invention. The invention further provides a coated mixed anode material containing a pyrogenically produced, nanostructured and surface modified metal oxide coating on the surface of the anode active material particles.

The further preferred features of the coated mixed anode material, of the pyrogenically produced, nanostructured and surface modified metal oxide described above in the preferred embodiments of the process according to the present invention are also the preferred features of the coated mixed anode material, the pyrogenically produced, nanostructured and surface modified metal oxide, in respect to the coated mixed anode material according to the present invention, independent on whether it is produced by the inventive process or not.

The invention further provides an active negative electrode material for a lithium-ion battery comprising the coated anode material according to the invention or the coated anode material obtainable by the process according to the invention.

The negative electrode, i.e., the anode of the lithium-ion battery includes a current collector and the coated active anode material particles formed over or on the current collector. The current collector may be an aluminium foil, copper foil, a nickel foil, a stainless-steel foil, a titanium foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The invention also provides a lithium-ion battery comprising the coated anode material or the coated anode material obtainable by the process according to the invention.

The lithium-ion battery of the invention, apart from the anode, may also comprise a cathode, optionally a separator and an electrolyte comprising, for example, a lithium salt or a lithium compound.

The cathode of the lithium-ion battery may comprise any suitable material, commonly used in secondary lithium-ion batteries, capable of reversible intercalating/deintercalating lithium ions.

The cathode material used with preference in the process according to the invention is selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel- cobalt oxides, lithium-nickel-manganese-cobalt oxides, lithium-nickel-cobalt-aluminium oxides, lithium-nickel-manganese oxides, or a mixture thereof.

The electrolyte of the lithium-ion battery can be in the liquid, gel or solid form. The liquid electrolyte of the lithium-ion battery may comprise any suitable organic solvent commonly used in the lithium-ion batteries, such as anhydrous ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate, methylethyl carbonate, diethyl carbonate, gamma butyrolactone, dimethoxyethane, fluoroethylene carbonate, vinylethylene carbonate, or a mixture thereof.

The gel electrolytes include gelled polymers. Any suitable gelled polymers may be used.

The solid electrolyte of the lithium-ion battery may comprise oxides, e.g., lithium metal oxides, sulfides, phosphates, or solid polymers.

The electrolyte of the lithium-ion battery can contain a lithium salt. Examples of such lithium salts include lithium hexafluorophosphate (LiPF6), lithium bis 2-(trifluoromethylsulfonyl) imide (LiTFSI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), Li2SiF6, lithium triflate, LIN(SO2CF2CF3)2and mixtures thereof.

The invention further provides use of the coated anode material in an active negative electrode material of a lithium-ion battery.

Even without further explanations, it is assumed that a person skilled in the art can fully use the above description. The preferred embodiments and examples are therefore to be understood only as a descriptive, by no means as a limiting in any way.

In the following, the present invention is explained in more detail using examples. Alternative embodiments of the present invention are available in an analogous manner.

EXAMPLES

Determination of the Physical-Chemical Characteristic Data

In the context of the present invention the following measurement methods for evaluating the characteristics for the different materials were used:

A) BET Surface Area

Apparatus for Tamped Density Determination

Carrying Out the Tamped Density Determination

Evaluation of the Tamped Density Determination

C) pH Value

Working Procedure for the Determination of the pH Value

D) Drying Loss

The result is given to within one decimal place.

E) Loss on Ignition

Carrying Out the Loss on Ignition

Evaluation of the Determination of the Loss on Ignition

F) Carbon Content

Starting Materials

Dry Coating Additives

Fumed alumina (AEROXIDE® Alu C) with a BET surface area of 85-115 m2/g, commercially available by Evonik Operations GmbH. The AEROXIDE® Alu C is a fine-particulate material, pure aluminum oxide (Al2O3) with high specific surface area.

Fumed hydrophobic alumina (AEROXIDE® Alu C 805) with a BET surface area of 75-105 m2/g, commercially available by Evonik Operations GmbH. The AEROXIDE® Alu C 805 is highly hydrophobized with an organosilane.

Fumed hydrophobic titania (AEROXIDE® TiO2T 805) with a BET surface area of 35-55 m2/g, commercially available by Evonik Operations GmbH. The AEROXIDE® TIO2 T 805 is a fine particulate, fumed titanium oxide (TiO2) that is highly hydrophobized with an organosilane.

Non-fumed alumina (ADMAFINE® AO-802) with a BET surface area of approximately 6 m2/g, commercially available by Admatechs Company Limited. The ADMAFINE® AO-802 consists of microscopic spherical aluminum oxide particles with a diameter of 0.2 to 10 μm produced by oxidizing metal aluminum powder using an original technique known as the VMC method.

Table 1 shows the full properties of these materials.

dispersion

Drying loss [%]
Less than 5
Less than 5
Less than 1.0

based on

ignited material

Carbon content

based on

ignited material

based on

based on

Anode Active Material

Composite Si/C material, made of 86% carbon and 14% silicon (DXB8), purchased via Shandong Gelon Lib Co., Ltd., China, and artificial graphite powder (SAG20) purchased via MTI Corporation, USA were used.

The composite Si/C material made of 86% by weight carbon and 14% by weight silicon is commercially available under the trademark DXB8 Shandong Gelon Lib Co., Ltd., China, and is hereinafter referred to as the Si86/C14 substrate anode active material (“Si86/C14_AAM”) powder or particles. The Si86/C14_AAM is a mixture of SiOx and carbon as shown by SEM analysis, and has the following characteristics.

DXB8
TEST INSTRUMENT

% by weight
Carbon 86
Silicon 14
AND METHOD

tracker

SSA testing instrument

TAP density testing

instrument

Half cell testing

Half cell testing

efficiency

The artificial graphite powder (SAG20) of MTI Corporation, USA has the following characteristics.

Comparative Example 11

The particle size distribution for the hydrophilic aluminum oxides was measured to visualize the dispersibility behavior during applying shear forces to the alumina agglomerates.

FIG. 1 shows the particle size distribution of AEROXIDE® Alu C (a) and ADMAFINE® AO-802 (b), analyzed by a laser diffraction particle size analyzer. The samples were dispersed in distilled water and treated for 5 minutes in an external ultrasonic bath (160W).

For AEROXIDE® Alu C, a mono-modally and very narrow particle size distribution was detected with small aggregate sizes of D10=60 nm, D50=81 nm, D90=120 nm.

In the case of ADMAFINE® AO-802 a broader, wide-spread and partially bimodal distribution was detected with aggregate sizes of D10=78 nm, D50=176 nm, D90=1770 nm, revealing the presence of larger, non-dispersed particles.

FIG. 2 shows the SEM-EDX mapping of the different coating additives on the composite Si/C anode active material DXB8 (a: AEROXIDE® Alu C 805, b: AEROXIDE® Alu C, c: ADMAFINE® AO-802, d: AEROXIDE® TiO2 T 805). On the left side of each of 2a, 2b, 2c, and 2d, the mapping of Si is shown to visualize the silicon distribution within the anode active material (mixture of carbon with silicon). This information helps when comparing with the Al/Ti distribution of the coating additives on the right side and nicely shows the interaction of the coating additives with the anode material surface.

The mappings of DXB8 coated by fumed hydrophobic alumina (a) and fumed hydrophobic titania (d) show a fully and homogeneous coverage of Al/Ti substantially around all anode particles (silicon rich as well as carbon rich). No larger metal oxide agglomerates were detected, showing that the dispersion of nanostructured fumed, hydrophobic metal oxides was successful. Additionally, no free unattached Al2O3/TiO2 particles next to the anode particles were found, indicating the strong interaction of the surface modified metal oxide particles with the AAM particle surface and therefore an excellent adhesion between coating layer and substrate.

In comparison to the surface modified and therefore hydrophobic alumina, the hydrophilic material (AEROXIDE® Alu C) shows a good dispersibility of the agglomerates as well, but preferably interacts with the Si-rich particles instead of the carbon-rich particles. Hence, the alumina coating is more pronounced on the surfaces of the Si-rich particles.

In contrast, by using coarser alumina particles (ADMAFINE® AO-802) as coating for AAM particles (c), only a minor amount of the finer-sized Al2O3 particles is attached to the anode material surface. The larger, non-dispersed and therefore unattached Al2O3 particles are located next to the anode particles. As a result, the AAM particles are not fully covered by this coarser, non-surface modified alumina particles.

FIG. 3 shows the SEM-EDX mapping of the alumina coating additives on the

The mapping of graphite coated by fumed hydrophobic alumina AEROXIDE® Alu C 805 shows the best dispersibility behavior and the most homogeneous coverage of the AAM particles with alumina, in direct comparison to the hydrophilic alumina materials. This phenomenon is again related to the excellent interaction of the hydrophobic surface modification of AEROXIDE® Alu C 805 with the surface of the graphite anode particles.

FIG. 4 shows a lithium-ion battery generally designated with numeral 10 inside an apparatus 100 powered by the lithium-ion battery 10 according to an embodiment of the present invention. The apparatus may be any electronic device such as, for example, a mobile phone, an electronic watch, a key fab, a laptop computer, a desktop computer, a computer pad and the like. The apparatus may also be an electric apparatus such as a power tool, a vacuum cleaner, an electric lawn mower, an electric appliance, and the like. The lithium-ion battery 10 may be packaged in modules as is well-known, each module comprising a plurality of lithium batteries 10, and used to power electric vehicles or hybrid electric vehicles. The lithium-ion battery 10 comprises negative and positive current collectors 14, and 12, a cathode 18 adjacent to the positive current collector 12, an anode adjacent to the negative current collector 14, an electrolyte 20 and a separator 22 disposed between the anode 16 and cathode 18. The anode 16 comprises a coated active anode material obtained by subjecting an active anode material and a pyrogenically produced, nanostructured metal oxide of titanium or aluminum to dry mixing in a mixing unit. The active anode material is in the form of powder and comprises carbon particles, silicon particles, silicon oxide particles or any combinations thereof.

Although the present invention has been described in reference to specific examples it should be understood that the invention is not limited to these examples only and many variations thereof will fall within the scope of the invention as defined by the accompanying claims.

LIST OF REFERENCE NUMERALS