HK1214681B - Oxide shell formation on inorganic substrate via oxidative polyoxoanion salt deposition - Google Patents

Description

Formation of oxide shells on inorganic substrates via oxidized polyoxoanion salt deposition

Technical Field

The present invention relates to methods and compositions for forming metal oxide coatings on inorganic substrates. More particularly, the present invention relates to the formation of metal oxide, e.g., alumina, coatings on inorganic substrates, such as ceramic powders, by using quaternary ammonium metal compounds (metalates), e.g., aluminates, and peroxides. Most particularly, the invention relates to forming a metal oxide, such as alumina, coating on a lithium ion battery cathode material.

Background

Lithium ion battery cathode ceramic materials have been an attractive area of research for many years. Among the various cathode materials, lithium transition metal oxides represent the most successful class of cathode materials. The crystal structure of the lithium transition metal oxide may be of the formula LiMO₂(where M is, for example, Mn, Co and/or Ni) or a layered structure of the typical formula LiM₂O₄(M is, for example, Mn) of a three-dimensional spinel structure. Both the layered structure and the spinel structure include a framework of transition metal and oxygen, in which lithium ions are inserted.

Ceramic materials for the cathode of lithium ion batteries, such as lithium cobalt oxide, lithium nickel oxide or lithium cobalt nickel oxide, have excellent basic properties for energy storage. However, these materials also have disadvantages such as insufficient safety in terms of thermal stability and overcharge performance. To solve these problems, various safety methods have been introduced, which include a separator shutdown function, addition of additives to an electrolyte, a safety protection circuit, and a PTC (positive temperature coefficient) device. Unfortunately, all of these methods are designed for use under conditions where the charging capacity of the cathode active material is not too high. Therefore, when the charging ability of the cathode active material is increased to meet the increasing demand for high capacity in such batteries, it may cause deterioration in the safety of these systems.

On the other hand, the operation of electrochemical cells always creates an interfacial layer, called Solid Electrolyte Interface (SEI), between the active cathode material and the electrolyte. High pressure operation can easily break this interfacial layer, resulting in poor cycle performance and capacity loss. Therefore, controlling and stabilizing the formation and structure of SEI is still very important and of practical significance.

In addition, some active manganese-containing cathode materials (such as lithium manganese oxide), when in direct contact with the electrolyte, have the problem of manganese leaching into the electrolyte solution of the battery during battery operation. This may lead to capacity fade, i.e. capacity loss through repeated charge and discharge cycles.

To overcome the above disadvantages, core/shell structures have been proposed to improve cycle life and safety of lithium batteries. The formation of a passive shell on the surface (core) of the active cathode ceramic particles can provide structural and thermal stability in a highly delithiated (discharged) state, and thus cycle life and safety can be improved. There are various shells which have been described for the surface of the cathodic ceramic particles, including those made of, for example, barium titanate (BaTiO)₃) Lithium iron phosphate oxide, and gradient LiCoO₂The shell formed. Most of these shells are formed using expensive raw materials or using a complicated process, or both. In addition to the active material shells described above, there have been studies on inert metal oxide shells for a long time. The formation of the inert metal oxide shell is a relatively inexpensive process. Various inert metal oxide shells, such as TiO, have been prepared on the surface of ceramic particles by so-called heterogeneous nucleation wet chemistry₂、Al₂O₃MgO and ZnO. However, current heterogeneous nucleation to form an inert oxide shell is not controllable,in particular, the method comprises the following steps: the known processes do not provide any method of controlling the thickness of the shell with acceptable accuracy. The inert metal oxide shell is not electrochemically active per se by definition-meaning that it does not promote ionic or electronic transfer. At the same time, such a shell should not interfere with operation. If too thick and/or too dense inert shells are formed, the resistance of the shells can limit the charge and discharge rate capability of the electrodes, and cell performance can deteriorate. Current processes for depositing alumina (and other inert oxides) by heterogeneous nucleation using aluminum nitrate (or other aluminum salts) involve ion exchange between Li cations in the active ceramic material and Al ions in the process solution. It may cause loss of Li ions from the active ceramic material, generating waste and possibly cathode structural defects when the shell is deposited.

Thus, the problem of how to provide oxide coatings on inorganic substrates, such as active ceramic materials in the cathode of lithium ion batteries, has been present and has not been satisfactorily solved to date.

Disclosure of Invention

To address the above-mentioned problems, the present invention provides a method of forming an oxide shell, including metal oxides or certain non-metal oxides, on a ceramic or other inorganic substrate, wherein the oxide shell has a precisely controlled thickness. The thickness is precisely controlled by controlling the content of quaternary ammonium cations and polyoxoanions in the reaction composition and the deposition rate. The substrate may include an active cathode ceramic particle surface, such as a ceramic material used in a lithium ion battery cathode. The method uses an organic salt composed of a quaternary ammonium cation and a polyoxoanion as a source of shell-forming material. Organic salts can slowly form a conductive shell, semiconductive shell or insulating shell on such ceramic surfaces by the addition of an oxidizing agent, such as hydrogen peroxide. Thus, the deposition rate can be affected by the hydrogen peroxide content of the reactive composition.

Accordingly, in one embodiment, the present invention relates to a method for depositing an oxide coating onto an inorganic substrate, comprising:

providing an aqueous composition comprising a tetraalkylammonium polyoxoanion and hydrogen peroxide;

contacting the aqueous composition with an inorganic substrate for a time sufficient to deposit hydroxide derived from the polyoxoanion on the surface of the inorganic substrate, thereby forming an initially coated inorganic substrate; and

heating the initially coated inorganic substrate for a time sufficient to convert the hydroxide to an oxide to form an oxide coating derived from the polyoxoanion on the inorganic substrate.

In one embodiment, the tetraalkylammonium polyoxoanion comprises tetramethylammonium hydroxide.

In one embodiment, the tetraalkylammonium polyoxoanions comprise a compound having the general formula A_xO_y ^z-Wherein a represents one or more transition metals or other metals or metalloids capable of forming a polyoxoanion. In one embodiment, the atom A In the formula is selected from Al, Si, B, Ga, Ge, As, In, Sn, Sb, Tl, Pb and Bi, or a combination of any two or more thereof, O is an oxygen atom, the values of x, y and z depend on the valency of A In the polyoxoanion and y>x。

In one embodiment, the transition metal includes one or more of Ti, V, Zn, Ni, Co, Mn, Fe, and Cu.

In one embodiment, the inorganic substrate comprises a ceramic oxide. In one embodiment, the ceramic oxide comprises Li⁺And are suitable for use in ceramic cathode materials for lithium ion batteries.

In one embodiment, the inorganic substrate comprises a semiconductor material. In one embodiment, the semiconductor material comprises a semiconductor wafer, wherein optionally the semiconductor wafer comprises electronic circuitry.

In one embodiment, the tetraalkylammonium polyoxoanion is tetramethylammonium aluminate and the inorganic substrate is a ceramic material. In one embodiment, the ceramic material is a lithium ion battery cathode material.

In another more specific embodiment, the present invention relates to a method for depositing an alumina coating onto an inorganic substrate comprising:

providing an aqueous composition comprising tetraalkylammonium aluminate and hydrogen peroxide;

contacting the aqueous composition with an inorganic substrate for a time sufficient to deposit aluminum hydroxide onto the surface of the inorganic substrate, thereby forming an initially coated inorganic substrate; and

the initially coated inorganic substrate is heated for a sufficient time to convert the aluminum hydroxide to aluminum oxide.

In one embodiment, the inorganic substrate is a ceramic material. In one embodiment, the ceramic material is a lithium ion battery cathode material.

In one embodiment, the tetraalkylammonium aluminate is tetramethylammonium aluminate.

In one embodiment, the heating is performed at a temperature in the range of about 450 ℃ to about 1000 ℃ or at a temperature of about 500 ℃.

In one embodiment, the aqueous composition further comprises Li⁺Ions. Li in aqueous compositions⁺The presence of ions results in the inclusion of Li in the oxide shell⁺Ions.

The invention described herein is applicable not only to the formation of the core/shell structure of ceramic particles, but also to the formation of passive shells on the surface of inorganic materials in the form of flat plates or almost any other irregular form. Thus, for example, the invention may be applied to the formation of oxide layers on wafer surfaces of semiconductors such as silicon or silicon/germanium or on other inorganic surfaces such as glass surfaces as well as on semiconductor devices where electronic components already exist.

Advantages of the invention include one or more of (1) the process of the invention is a process at room temperature; (2) the method of the invention is a simple one-step method; (3) the method of the present invention provides predictable and controllable shell thickness; (4) the method of the invention is a homogeneous shell; (5) the method of the present invention is suitable for forming a thin film shell on a substrate; (6) the process of the invention is not an ion exchange process that can deplete ions from the substrate; (7) the method of the invention causes a shell to form on each individual crystal particle of the substrate; (8) the method of the invention can be widely applied to various substrates besides the ceramic material of the cathode of the Li-ion battery.

Brief description of the drawings

Fig. 1-5, 11-15, and 20 are X-ray diffraction (XRD) patterns of exemplary inorganic substrates with or without oxide coatings according to certain embodiments of the present invention.

Fig. 6-10, 16-19, and 21-23 are Scanning Electron Microscope (SEM) micrographs of exemplary inorganic substrates with and without an oxide coating, according to certain embodiments of the present invention.

The drawings are provided as non-limiting examples and comparative examples of embodiments of the present invention and are intended to facilitate the understanding of the present invention.

Detailed Description

As used herein, the term polyoxoanion is meant to have the general formula A_xO_y ^z-Wherein A represents a transition metal ion, As known In the periodic Table, such As Ti, V, Zn, Ni, Co, Mn, Fe and Cu, or a metal or metalloid comprising Al, Si, B, Ga, Ge, As, In, Sn, Sb, Tl, Pb and Bi, or any combination of two or more thereof, and O is an oxygen atom. X, y and z are dependent on the valence of the atom A in the polyoxoanion, and y>x. In most embodiments, atom a is in its highest oxidation (+) state. The atom A shall comprise an atom capable of forming a polyoxoanion.

As described previously, the present invention relates to the formation of an oxide shell such as a passivation shell on the surface of an inorganic material substrate. The invention is particularly applicable to ceramic particles for lithium ion battery cathodes. The method uses an organic salt consisting of a quaternary ammonium cation and a polyoxoanion, in combination with an oxidizing agent, such as hydrogen peroxide, which decomposes to produce H⁺Ions. The decomposition of hydrogen peroxide is as follows:

H₂O₂→O₂+2H⁺+2e^-

H₂O+(1/2)O₂+2e^-→2OH^-

when the inorganic oxide material is exposed to a hydrogen peroxide solution, it is considered that the following reaction occurs and OH is generated on the surface of the inorganic oxide material^-. Where M is an element forming a framework of inorganic material in the substrate, e.g. LiCo_0.2Ni_0.8O₂Ni or Co in (1) or Si in silicon wafers.

For oxide framework inorganic materials

H₂O₂→O₂+2H⁺+2e^-

-M-O-M-+2H₂O+(1/2)O₂+2e^-→2OH^-+2(-M-OH)

For semiconductor element inorganic materials (e.g. silicon)

H₂O₂→O₂+2H⁺+2e^-

-M-M-+2H₂O+O₂+2e^-→2OH^-+2(-M-OH)

Hereinafter, TMA (tetramethylammonium) aluminate is used as an example to show a possible mechanism of forming a shell on the surface of an inorganic material.

While not being bound by theory, it is believed that the process of the present invention proceeds as follows. When in useTMA aluminate is a compound which, when in solution with an oxidizing agent such as hydrogen peroxide, decomposes and slowly releases H with the hydrogen peroxide⁺Ion, believed to be H⁺The ions trap aluminate anions to gradually form an aluminum hydroxide layer (possibly crystallized) on the surface of the inorganic substrate by heterogeneous nucleation. The aluminum hydroxide layer is able to generate more H with continued decomposition from hydrogen peroxide⁺The ions grow until the aluminate ions in the solution are completely consumed. Thus, an aluminum hydroxide precursor of a nascent alumina shell is formed on the surface of the inorganic material. The inorganic material having the precursor aluminum hydroxide shell formed on its surface is then removed from the wet chemical solution and heated in an oven at an elevated temperature in the range of about 450 c to about 1000 c, or, for example, about 500 c, for several hours, for example, 5 hours. The hydroxyl group of the aluminum hydroxide bonded to the surface of the inorganic material, which is formed by the reaction with hydrogen peroxide, undergoes a condensation reaction with the aluminum hydroxide to form an-M-O-Al bond between the shell and the inorganic base material. Thus, the high temperature heating converts the aluminum hydroxide shell to an aluminum oxide (alumina) shell, removing the water of course. Thus, a very thin aluminum (or other atom as disclosed herein) oxide shell can be prepared that is chemically bonded to the substrate surface.

The invention described herein is applicable to the formation of a core/shell structure of particles of inorganic material, or to the formation of a passive shell on the surface of an inorganic material in the form of a flat plate or in any other regular or irregular form. That is, the present invention enables the formation of the disclosed oxide shells on those surfaces from fine ceramic particles (as used in forming lithium ion battery cathodes) to large flat surfaces (such as semiconductor wafers and devices) as well as on any type of irregular surface.

The inorganic material particles or substrates may be: oxides, ceramics, glass, silicon and any other inorganic material capable of forming a bond with a metal oxide through an atom such as an oxygen atom.

The shell material or passivation material may be any of transition metals such As Ti, V, Zn, Ag, Ni, Co, Mn, Fe, Cu and Au, As well As polyoxoanions of metals or metalloids including Al, Si, B, Ga, Ge, As, In, Sn, Sb, Tl, Pb and Bi. Accordingly, polyoxoanions useful in the present invention include all possible metallic and non-metallic elements that have or are capable of forming polyoxoanions, but do not include N, O, P, S, F, Cl, Br, I, etc., or alkali or alkaline earth metals.

The present invention thus provides a method for controlled deposition of an oxide coating onto an inorganic substrate, wherein the thickness of the oxide coating can be easily and predictably controlled.

The aqueous composition contains a tetraalkylammonium polyoxoanion and hydrogen peroxide. The aqueous composition contains tetraalkylammonium polyoxoanion at a concentration of from about 0.0001 weight percent to about 30 weight percent, and in one embodiment at a concentration of from about 0.011 weight percent to about 1.1 weight percent, based on the total weight of the aqueous composition. The content of the tetraalkylammonium polyoxoanion should be selected based on the amount of the inorganic substrate to be treated and the desired thickness of the oxide shell deposition layer. By adjusting the stoichiometry of the aqueous composition, different but controllable oxide shell thicknesses can be obtained, as shown in the examples.

In one embodiment, the aqueous composition contains hydrogen peroxide as the oxidizing agent. The hydrogen peroxide is provided in the aqueous composition at a concentration of about 0.0001 wt.% to about 30 wt.%, or at a concentration of 0.004 wt.% to about 5 wt.%, or at a concentration of 0.02 wt.% to about 1 wt.%, or at a concentration of about 0.35 wt.%, all based on the total content of the aqueous composition.

In one embodiment, the weight ratio of tetraalkylammonium polyoxoanion to inorganic substrate is from about 0.0001 to about 2, and in one embodiment from about 0.002 to about 0.5. As will be appreciated, this ratio depends on the surface area of the inorganic substrate and the desired thickness of the oxide shell to be deposited. As shown in the examples below, it was calculated to deposit an oxide shell of about 1nm to about 10nm on finely ground ceramic particles in a cathode material intended for use in a lithium ion battery at a rate of 0.01 to about 0.15. The above ranges are exemplary only, and the skilled person can calculate the desired ratio by relatively simple and straightforward calculations and some small but reasonable amount of experimentation based on the desired thickness of the oxide shell and the properties of the inorganic substrate. The embodiments set forth below provide a good starting point for such calculations.

In one embodiment, the aqueous composition further comprises lithium ion Li⁺Enabling the provision of oxide coatings with controlled content of lithium ions, which facilitates the use of the product of lithium ion battery cathode materials. When present, lithium ions are provided at a concentration of about 1ppm (parts per million) to about 1000ppm and in one embodiment about 90ppm to about 230 ppm. The content of lithium ions in the oxide shell should be 0 to about 50 wt%, and for the aluminum oxide shell, about 22 wt% is preferable. The amount of lithium ions added to the aqueous composition can be adjusted as desired to obtain the desired amount of lithium ions in the oxide shell.

When lithium is included in the aqueous composition, it will be included in the precursor shell. Upon heating, the lithium cations in the precursor shell can migrate into the inorganic substrate due to an intercalation (intercalation) reaction with the substrate, leaving the aluminate behind to form an aluminum oxide shell. The extent to which lithium ions migrate into the core depends on the lithium content of the core. Little or no migration may occur if the core is already saturated with lithium ions. If not all lithium ions are able to migrate into the core, some will remain in the shell. This provides the benefit of obtaining the desired alumina shell on the inorganic substrate core, while lithium ions are added to the core at the same time. This is particularly desirable for producing ceramic particles for lithium ion battery cathodes.

The step of contacting the aqueous composition with the inorganic substrate is carried out for a time sufficient to deposit the hydroxide derived from the polyoxoanion onto the surface of the inorganic substrate, thereby forming an initially coated inorganic substrate. The time for this deposition is generally from about 4 hours to about 24 hours, in one embodiment from about 6 hours to about 12 hours, and in one embodiment from about 8 to about 10 hours.

The contacting step is carried out by constant mixing of the ingredients in the mixture of the aqueous composition and the particles of the inorganic substrate. The actual method of mixing will, of course, depend on the volume of material being processed. On a small scale, a simple laboratory shaker may be used, while for larger scales, such as preparative or industrial scale, a suitable heavy duty mechanical mixing device may be used, which may be suitably selected by one of ordinary skill in the art.

The step of heating the initially coated inorganic substrate is conducted for a time sufficient to convert the hydroxide to an oxide. As described below, the time required for the oxide coating to be derived from the polyoxoanion and for the hydroxide to be converted to the oxide will depend to some extent on the identity (identity) and the central atom of the polyoxoanion, i.e., formula A_xO_y ^z-Element A in (1).

The tetraalkylammonium polyoxoanions can include alkyl groups of any desired size, but in most embodiments, the alkyl groups are each C₁-C₁₈Alkyl, or C₁-C₈Alkyl, or C₁-C₄Alkyl groups, any of which may be branched or unbranched. In general, it is believed that the size of the alkyl group is not critical, but the alkyl group should not be so long as to interfere with the solubility of the resulting tetraalkylammonium polyoxoanion in aqueous compositions. In one embodiment, the tetraalkylammonium polyoxoanion comprises tetramethylammonium hydroxide (TMAH). TMAH is generally the preferred quaternary ammonium compound because it is readily available and very soluble in aqueous compositions.

As mentioned above, the polyoxoanions of the tetraalkylammonium polyoxoanions have the general formula A_xO_y ^z-Wherein A represents a transition metal ion or a metal or metalloid capable of forming a polyoxoanion. In one embodiment, the atom A In the formula is selected from Al, Si, B, Ga, Ge, As, In, Sn, Sb, Tl, Pb and Bi, or a combination of any two or more thereof, O is an oxygen atom, and the values of x, y and z depend on the oxygen In which A is presentValence in the anion and y>x. Thus, if a is Al, x is 1, y is 3 and z is 1; if a is B, then x is 1, y is 3 and z is 3; if a is Mn, then x ═ 1, y ═ 4, and z ═ 1, and so on, as will be readily understood by those skilled in the art.

In one embodiment, the transition metal includes one or more of Ti, V, Zn, Ni, Co, Mn, Fe, and Cu.

In one embodiment, the inorganic substrate comprises a ceramic oxide. In one embodiment, the ceramic oxide comprises Li⁺Ionic and suitable for use in ceramic cathode materials for lithium ion batteries. The ceramic oxide may be, for example, one of the following:

lithium nickel manganese cobalt oxide, LiNi_0.33Mn_0.33Co_0.33O₂

Lithium nickel cobalt aluminum oxide, LiNi_0.8Co_0.15Al_0.05O₂

Lithium nickel cobalt aluminum oxide, LiNi_0.79Co_0.20Al_0.01O₂

Lithium nickel cobalt oxide, LiNi_0.8Co_0.2O₂

Lithium iron phosphate, LiFePO₄

Lithium nickel oxide, LiNiO₂

Lithium trivanadate, LiV₃O₈

Manganese Nickel carbonate, Mn_0.75Ni_0.25CO₃

Copper vanadium oxide, CuV₂O₆

Lithium cobalt phosphate, LiCoPO₄

Lithium manganese dioxide, LiMnO₂

Lithium manganese oxide, LiMn₂O₄

Lithium manganese nickel oxide, Li₂Mn₃NiO₈

Lithium iron oxide, LiFeO₂

Lithium cobalt oxide, LiCoO₂

Lithium molybdate, LiMoO₄

Lithium titanate, Li₂TiO₃

Lithium cobalt manganese oxide, LiCo_0.8Mn_0.2O₂

Lithium nickel manganese oxide, LiNi_0.85Mn_0.15O₂

Lithium cobalt nickel manganese oxide, LiCo_0.45Ni_0.45Mn_0.10O₂

Lithium nickel manganese oxide, LiNi_0.8Mn_0.2O₂

Lithium nickel cobalt boron oxide, LiNi_0.79Co_0.2B_0.01O₂

Lithium nickel cobalt tin oxide, LiNi_0.79Co_0.2Sn_0.01O₂

Lithium nickel cobalt aluminum oxide, LiNi_0.72Co_0.2B_0.08O₂。

In addition to ceramics (including the aforementioned exemplary materials suitable for use as cathodes in lithium ion batteries (this list does not include all such materials)), the inorganic substrate can be virtually any inorganic material, including ceramic materials and other inorganic materials such as silicon, glass, metals, dielectrics, and conductive materials. In one embodiment, the inorganic substrate comprises a semiconductor material. In one embodiment, the semiconductor material comprises a semiconductor wafer, wherein optionally the semiconductor wafer comprises electronic circuitry.

In one embodiment, the tetraalkylaluminum polyoxoanion is tetramethylammonium aluminate and the inorganic substrate is a ceramic material. In one embodiment, the ceramic material is a lithium ion battery cathode material. In a presently preferred embodiment, the present invention relates to a process for depositing an alumina coating onto a lithium ion battery cathode material as an inorganic substrate, comprising the steps described above, wherein the aqueous composition contains tetramethylammonium aluminate and hydrogen peroxide.

It should be noted that although the present invention provides a thin layer of an oxide derived from polyoxoanions on the surface of a target substrate, because the deposited layer is so thin that the X-ray diffraction (XRD) pattern of the resulting material should not change significantly. If an overly thick layer of polyoxoanion-derived oxide is deposited on the target substrate surface, the XRD pattern may change and it indicates that the deposited layer is thicker than needed or desired. The thickness, and particularly the excess thickness, can be observed and estimated via SEM by comparing SEM micrographs of the inorganic substrate taken before and after deposition of the oxide shell. See, for example, fig. 6-10 and the description of that figure in the following examples. For materials to be used as cathode materials for lithium ion batteries, the layer of oxide derived from polyoxoanions on the surface of the ceramic material should be sufficiently thin to allow Li⁺The ions pass during operation of the cell. If the layer is so thick that Li is suppressed⁺The free flow of ions, it is too thick. In one embodiment, the thickness of the polyoxoanion-derived oxide on the target substrate surface is from about 1nm to about 20nm, and in another embodiment from about 2nm to about 10 nm. Here, as well as elsewhere in the specification and claims of this application, finite values of the ranges may be combined, and all ranges are considered to include intervening integral (fractional) and fractional values. Thus, for example, although no specific mention is made of a thickness of 4nm, this value is included in the present disclosure as it falls within the disclosed range. Also, although no particular mention is made of a thickness of 3.5nm, it is also included in the present disclosure.

Examples

The quaternary ammonium polyoxoanions used in the present invention can be prepared using a two-step process involving precipitation and dissolution. The following examples use aluminum oxide as the polyoxoanion, but as mentioned above, this method is widely applicable to many metal and metalloid atoms. Preferably, the quaternary ammonium polyoxoanion used is tetramethylammonium aluminate.

Preparation of quaternary ammonium aluminates

To a 200ml flask with a magnetic stir bar was added 37.51g (0.1 mole) aluminum nitrate nonahydrate and 200g deionized water. The solution was stirred until a clear solution formed. To this solution was slowly added 114.04g (0.3 mole) of a 23.98 wt% solution of tetramethylammonium hydroxide (TMAH). A white precipitate appeared immediately. The resulting white precipitate was filtered and washed three times with 200ml of deionized water. The resulting white solid was freeze-dried to obtain dried aluminum hydroxide.

Then, 5.69g (0.073 mole) of the above aluminum hydroxide powder and 145.83g of deionized water were added to a 200ml flask having a magnetic stir bar. To this suspension 83.15g (0.22 mole) of a 23.98 wt% solution of TMAH was slowly added. When all the TMAH was added, the white aluminum hydroxide powder disappeared to form tetramethylammonium aluminate at a concentration of 0.311mmol/g, i.e., 9.24 wt%. Notably, stoichiometric TMAH should be used in both steps of the preparation, as excess TMAH inhibits the deposition of the oxide shell on the ceramic powder core, as discussed in more detail below.

With appropriate adjustment to take into account molecular weight, the same two-step process can be carried out to produce the corresponding quaternary ammonium polyoxoanions disclosed herein.

Ceramic powders to which the present invention can be applied include, but are not limited to, ceramic materials for lithium ion battery cathodes by having the formula LiCo_0.2Ni_0.8O₂The lithium nickel cobalt oxide of (a).The ceramic powders useful in the present invention are commercially available products or can be prepared according to methods found in the literature and/or known to those skilled in the art. LiCo_0.2Ni_0.8O₂The XRD pattern of the ceramic powder is shown in fig. 1, and the SEM micrograph thereof is shown in fig. 6.

Example 1(CS1P012) preparation of LiCo estimated to have a core-shell structure with a shell of 1nm_0.2Ni_0.8O₂Lithium nickel cobalt oxide

0.0594g of 0.311mmol/g TMA aluminate, 40g of DI water and 0.0594g of 30% by weight hydrogen peroxide were added to a 100ml plastic beaker. The total weight of the solution was increased to 50g by adding additional DI water. To the solution thus prepared, 0.5g of LiCo having an average crystal particle size of-3 μm was added_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours, resulting in a core-shell structured ceramic powder according to an embodiment of the present invention. The XRD pattern of the resulting product is shown in fig. 2 and the SEM micrograph is shown in fig. 7.

Example 2(CS2P012) preparation of LiCo with core-shell structure estimated to have a shell of 10nm_0.2Ni_0.8O₂Lithium nickel cobalt oxide

To a 100ml plastic beaker were added 0.594g of 0.311mmol/g TMA aluminate, 40g of DI water and 0.594g of 30% by weight hydrogen peroxide. The total weight of the solution was increased to 50g by adding additional DI water. To the solution thus prepared, 0.5g of LiCo having an average crystal particle size of-3 μm was added_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours. The XRD pattern of the resulting product according to an embodiment of the invention is shown in fig. 3 andthe SEM micrograph is shown in fig. 8.

Example 3(CS3P012) preparation of LiCo estimated to have a core-shell structure with a 20nm shell_0.2Ni_0.8O₂Lithium nickel cobalt oxide

To a 100ml plastic beaker were added 1.188g of 0.311mmol/g TMA aluminate, 40g of DI water and 1.188g of 30 wt% hydrogen peroxide. The total weight of the solution was increased to 50g by adding additional DI water. To the solution thus prepared, 0.5g of LiCo having an average crystal particle size of-3 μm was added_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours. The XRD pattern of the resulting product according to an embodiment of the present invention is shown in fig. 4 and the SEM micrograph is shown in fig. 9.

Example 4(CS4P012) preparation of LiCo with a core-shell structure estimated to have a shell of 30nm_0.2Ni_0.8O₂Lithium nickel cobalt oxide

To a 100ml plastic beaker were added 1.782g of 0.311mmol/g TMA aluminate, 40g of DI water and 1.50g of 30 wt% hydrogen peroxide. The total weight of the solution was increased to 50g by adding additional DI water. To the solution thus prepared, 0.5g of LiCo having an average crystal particle size of-3 μm was added_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours. The XRD pattern of the resulting product according to an embodiment of the present invention is shown in fig. 5 and the SEM micrograph is shown in fig. 10.

Example 5 preparation of LiCo with core-Shell Structure with addition of TMAH to the formulation_0.2Ni_0.8O₂Lithium nickel cobaltOxide compound

This experiment was used to determine the effect of the presence of TMAH in the reaction mixture on shell formation.

0.0594g, 0.594g, 1.782g, 4.158g and 5.94g of a solution consisting of 0.254mmol/g TMA aluminate and 0.153mmol/g TMAH, respectively, were added to each of five 100ml plastic beakers. The amount of Al in each solution was estimated to be sufficient under normal conditions to form shells of 1nm, 10nm, 30nm, 70nm and 100nm thickness on the ceramic particles. To each of the above solutions was added 40g of DI water and 1.5g of 30 wt% hydrogen peroxide. The total solution weight of each solution was increased to 50g by adding additional DI water. To each of the solutions thus prepared, 0.5g of LiCo having an average crystal particle diameter of-3 μm was added_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours. The filtrate thus obtained was filtered twice with a 0.2 μm filter. The obtained filtrate was subjected to elemental analysis to determine the Al content. The XRD patterns are shown in fig. 11 to 15. SEM micrographs of the resulting ceramic powder are shown in fig. 16 and 17. While some ceramic particles are coated according to the present invention, it is not preferred that an excess of TMAH, or other quaternary ammonium hydroxide, be present.

Example 6(CS7P114) preparation of LiCo with a core-shell structure estimated to have a shell of 10nm in the absence of a Hydrogen peroxide component_0.2Ni_0.8O₂Lithium nickel cobalt oxide

This experiment was used to show that the oxidant (H in this example)₂O₂) Importance for the formation of the core-shell structure.

To a 100ml plastic beaker were added 0.594g of 0.311mmol/g TMA aluminate, 0g of hydrogen peroxide, and DI water to increase the total weight of the solution to 50 g. To the solution thus prepared, 0.5g of LiCo having an average crystal particle size of-3 μm was added_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours. The product thus obtained was filtered twice through a 0.2 μm filter. The obtained filtrate was subjected to elemental analysis to determine the Al content. An SEM micrograph of the resulting ceramic powder is shown in fig. 18. This example is not an example according to the invention and is therefore a comparative example.

Discussion of the results of the foregoing examples

LiCo_0.2Ni_0.8O₂The XRD spectrum and SEM micrograph of the ceramic particles are shown in fig. 1 and 6, respectively. Examples 1 to 4 describe detailed methods for preparing the core-shell structures of the present invention, wherein LiCo_0.2Ni_0.8O₂Ceramic particles as core and Al₂O₃Serving as a shell. By mixing LiCo_0.2Ni_0.8O₂The ceramic particles are suspended in an aqueous solution containing tetramethylammonium aluminate and hydrogen peroxide to prepare a core-shell structure. Although some small amount of bubbles were generated from the prepared formulation solution, a large amount of bubbles were generated when the ceramic powder was added to the solution, which was accompanied with H₂O₂Is consistent with surface catalytic decomposition, as shown above for H₂O₂Described in the chemical equation of decomposition in the reaction sequence of the present invention. In the reaction of LiCo_0.2Ni_0.8O₂The ceramic powder is carefully ground in a mortar and pestle before it is added to the formulation solution used to prepare the shell so that there is no mechanical adhesion between the ceramic particles and the surface of all particles is available to be covered by the shell. After the shell forming process, the ceramic powder separated by centrifugation tends to agglomerate the particles again. However, the shell has been coated with attached aggregated ceramic particles.

The shell thickness can be controlled by manipulating the TMA aluminate concentration and can be designed with Al as in the examples₂O₃Shell thicknesses were estimated for 1nm, 10nm, 20nm, and 30nm formulations. LiCo of core-shell structure thus prepared_0.2Ni_0.8O₂XRD patterns of the ceramic particles are shown in fig. 2 to 5. Clearly, the shell formation process does not affect the ceramic crystal structure, and the shell thickness is small enough so as not to significantly affect the XRD pattern.

Prepared LiCo of core-shell structure_0.2Ni_0.8O₂SEM micrographs of the ceramic particles are shown in fig. 7 to 10. Pure LiCo with very sharp edges to the crystal faces_0.2Ni_0.8O₂In contrast to ceramic particles, LiCo prepared according to the invention_0.2Ni_0.8O₂The core-shell structure of the ceramic particles shows rounded (rounded) crystal edges. As the coating thickness increases, a thick shell can be observed based on a clear difference in appearance compared to uncoated ceramic particles such as shown in fig. 6.

The process solution after core-shell formation was analyzed to check for changes in residual aluminum content. The results are shown in Table 1. In table 1, the conversion of aluminum refers to the amount of aluminum deposited on the surface of the ceramic particles. It is evident that almost all of the aluminum in the solutions of examples 1 to 4 has been deposited on the surface of the ceramic particles. Accordingly, the present invention provides an effective method for controlling the shell thickness by controlling the aluminate concentration in the reaction liquid.

TABLE 1 transfer of aluminum from solution to ceramic particle surface

Example 5 demonstrates the effect of TMAH in a formulation. Shell formation is severely inhibited when TMAH is present in the process solution. Fig. 11 to 15 show XRD spectra of the processed ceramics, which indicate that the ceramic crystals are not affected. Table 2 shows the conversion of aluminum content from solution to ceramic particle surface transfer when TMAH is present in the reaction solution. It is clear that the shell formation was not very successful for the 1nm and 10nm cases; for the cases of 20nm, 30nm, 70nm and 100nm, shells could still be formed but did not show 100% conversion. Fig. 16 shows an SEM micrograph of ceramic particles, which should form a shell of 10nm on the surface according to the aluminum content in the reaction liquid. Obviously, no distinct shell is formed on the ceramic particles. FIG. 17 is an SEM micrograph of ceramic particles that should have a shell thickness of 100 nm. In this case the aluminium source is so excessive that a thick film is formed on the ceramic particles. Since the aluminate content is much higher than the TMAH content, it is clear that the inhibitory behavior of TMAH is completely suppressed in this example. Thus, excess TMAH appears to reduce the availability of aluminate, inhibiting the deposition of aluminum on the surface of the ceramic particles. As mentioned above, although the ceramic particles in the test with the higher TMA aluminate were coated according to the present invention, it is not preferred that there be an excess of TMAH or an excess of other quaternary ammonium hydroxide.

TABLE 2 transfer of aluminum from solution to ceramic particle surface

Example 6 was used to test the hydrogen peroxide requirements to achieve the desired shell deposition effect. It should generate a 10nm shell on the surface of the ceramic particles. In the absence of hydrogen peroxide, no obvious shell was observed, as shown by the SEM micrograph in fig. 18. Thus, example 6 is a comparative example.

OTHER EMBODIMENTS

Example 7(CS3P151) preparation of LiCo with core-shell structure estimated to have a 20nm silica shell_0.2Ni_0.8O₂Lithium nickel cobalt oxide

To a 100ml plastic beaker were added 0.0496g of 12.6 wt% TMA silicate, 40g of DI water and 1.5g of 30 wt% hydrogen peroxide. The total weight of the solution was increased to 50g by adding additional DI water. To the direction ofTo the solution thus prepared was added 0.5g of LiCo having an average crystal particle size of-3 μm_0.2Ni_0.8O₂. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours, thus obtaining a core-shell structure of the ceramic powder according to the present invention. The SEM micrograph is shown in fig. 19.

Example 8(CSXP151) preparation of LiMn with a core-shell structure with a silica shell₂O₄Lithium manganese oxide

To a 100ml plastic beaker were added 0.0496g of 12.6 wt% TMA silicate, 40g of DI water and 1.5g of 30 wt% hydrogen peroxide. The total weight of the solution was increased to 50g by adding additional DI water. To the solution thus prepared was added 0.5g of LiMn having an average crystal particle diameter of 1 to 2 μm₂O₄. The mixture was shaken vigorously overnight, and then the ceramic powder was separated by centrifugation. The collected ceramic powder was placed in an oven and heated at 500 ℃ for 5 hours to obtain a core-shell structure of the ceramic powder according to the present invention. Pure LiMn₂O₄XRD of is shown in fig. 20 and LiMn₂O₄The SEM micrograph of (a) is shown in fig. 21. LiMn of core-shell structure thus prepared₂O₄The SEM micrograph of (a) is shown in fig. 22.

Example 9(CSYP151) preparation of LiMn having a core-shell structure with an alumina shell₂O₄Lithium manganese oxide

To a 100ml plastic beaker were added 3.0g of 0.311mmol/g TMA aluminate, 40g of DI water and 1.5g of 30 wt% hydrogen peroxide. The total weight of the solution was increased to 50g by adding additional DI water. To the solution thus prepared was added 0.5g of LiMn having an average crystal particle diameter of 1 to 2 μm₂O₄. The mixture was vigorously allowed to stand overnight, and then the ceramic powder was separated by centrifugation. Collecting the ceramic powderThe powder was placed in an oven and heated at 500 ℃ for 5 hours to give a core-shell structure of ceramic powder. The SEM micrograph is shown in fig. 23.

It should be noted that numerical limits of ranges and ratios disclosed throughout the specification and claims may be combined and are considered to include all intermediate values. Moreover, all numbers are to be considered as modified by the word "about", whether or not specifically stated.

While the principles of the invention have been described in terms of certain specific embodiments and provided for purposes of illustration, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. It is, therefore, to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims. The scope of the invention is limited only by the scope of the claims.

Claims (14)

1. A method for depositing an oxide coating onto an inorganic substrate, comprising:

providing a catalyst containing tetra-C₁-C₈-an aqueous solution of an alkylammonium polyoxoanion and hydrogen peroxide, wherein the tetra-C₁-C₈The alkylammonium polyoxoanions contain tetra-C in a stoichiometric ratio of 3:1₁-C₈-alkylammonium and polyoxoanions;

contacting the aqueous solution with an inorganic substrate for a time sufficient to allow deposition of hydroxide derived from polyoxoanions onto the surface of the inorganic substrate by heterogeneous nucleation to form an initially coated inorganic substrate; and

heating the initially coated inorganic substrate for a time sufficient to convert the hydroxide to an oxide to form an oxide coating derived from the polyoxoanion on the inorganic substrate,

wherein said tetra-C₁-C₈The alkylammonium polyoxoanions comprise those of the formula A_xO_y ^z-Wherein A represents a transition metal, or a metal or metalloid selected from Al, Si, B, Ga, Ge, As, In, Sn, Sb and Pb, or a combination of any two or more thereof, O is an oxygen atom, and the x, y and z values depend on the valence of A In the polyoxoanion and y>x; and is

The hydrogen peroxide is present in a concentration of 0.02 to 1% by weight, based on the total content of the aqueous solution.

2. The method of claim 1, wherein the tetra-C is prepared from tetramethylammonium hydroxide₁-C₈-alkylammonium polyoxoanions.

3. The method of claim 1, wherein the transition metal comprises one or more of V, Zn, Mn, and Fe.

4. The method of any preceding claim, wherein the inorganic substrate comprises a ceramic oxide.

5. The method of claim 4, wherein the ceramic oxide comprises Li⁺And are suitable for use in ceramic cathode materials for lithium ion batteries.

6. The method of claim 1, wherein the inorganic substrate comprises a semiconductor material.

7. According to claim1, wherein said tetra-C₁-C₈-the alkylammonium polyoxoanion is tetramethylammonium aluminate and the inorganic substrate is a ceramic material.

8. The method of claim 7, wherein the ceramic material is a lithium ion battery cathode material.

9. A method for depositing an alumina coating onto an inorganic substrate, comprising:

providing a catalyst containing tetra-C₁-C₈-an aqueous solution of an ammonium alkyl aluminate and hydrogen peroxide, wherein the tetra-C₁-C₈The ammonium alkyl aluminate contains tetra-C in a stoichiometric ratio of 3:1₁-C₈-alkylammonium and aluminate salts;

contacting the aqueous solution with an inorganic substrate for a time sufficient for aluminum hydroxide to deposit by heterogeneous nucleation onto the surface of the inorganic substrate to form an initially coated inorganic substrate; and

heating the initially coated inorganic substrate for a time sufficient to convert the aluminum hydroxide to aluminum oxide.

10. The method of claim 9, wherein the inorganic substrate is a ceramic material.

11. The method of claim 10, wherein the ceramic material is a lithium ion battery cathode material.

12. The method of any one of claims 9 to 11, wherein the tetra-C₁-C₈The alkyl ammonium aluminate is tetramethyl ammonium aluminate.

13. The method of claim 1 or 9, wherein the heating is performed at a temperature in the range of 450 ℃ to 1000 ℃ or at a temperature of 500 ℃.

14. The method of claim 1 or 9, wherein the aqueous solution further comprises lithium ions.