WO2015189282A1

WO2015189282A1 - Thin film coated battery electrode and method for producing the same

Info

Publication number: WO2015189282A1
Application number: PCT/EP2015/062960
Authority: WO
Inventors: Patrick Ginet; Shingo Okubo
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2014-06-13
Filing date: 2015-06-10
Publication date: 2015-12-17
Also published as: JP2016003340A

Abstract

Method for producing a battery electrode which comprises the following steps: A first step during which a substrate (1), either made of an electrode material, comprising at least on its surface, a layer of an electrode material, is introduced in a reaction vessel; A vapor deposition step during which a metal precursor, that is a metal raw material, is fed with a carrier gas in said reaction vessel, either simultaneously or separately, with an oxidizing agent that includes ozone and/or oxygen, to obtain said substrate (1) coated with a thin film (2) of at least one oxide of said metal precursor; wherein said vapor deposition step is repeating several times, in order to reach a predetermined thickness of said film (2), greater or equal to 0.1nm and less or equal to 100nm, said battery electrode; and said battery comprising said battery electrodes.

Description

Thin film coated battery electrode and method for producing the same

The present invention relates to a battery electrode that is suitable as an electrode used for a battery such as a metal-air battery or a fuel cell, a method for producing the same and a battery comprising it.

An electrochemical catalyst for an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) is important for an electrode used for a battery such as a metal-air battery or a fuel cell.

Oxides of transition metals such as manganese, cobalt, and nickel have been extensively studied in connection with such a catalyst. These oxides of transition metals can be produced in a liquid phase or a gas phase. A chemical vapor deposition (CVD) method and an atomic layer deposition (ALD) method have been studied to produce such oxides in a gas phase. For example, JP-A-2011 -071210 discloses a method for producing a metal oxide film that utilizes the ALD method.

It has been considered that high-temperature annealing is necessary when producing oxides of transition metals in order to improve catalytic activity. Therefore, oxides of transition metals have been normally produced using an annealing step. For example, K. L. Pickrahn et al. (K. L. Pickrahn et al. Adv. Ener. Mater. 201200230, 2012) teaches that an excellent electrochemical catalytic activity can be achieved by heating a film of manganese oxide formed on glassy carbon using the ALD method at 480°C in air for a long time.

However, the inventors of the invention found that it is difficult to obtain sufficient catalytic activity when performing annealing (see the above documents) if the thickness of the layer is less than a certain thickness.

When using a layer of a metal oxide as an electrochemical catalyst, it is considered that the surface of the layer of a metal oxide achieves a catalytic effect. Since a layer of a metal oxide formed using the methods disclosed in the above documents has been subjected to annealing, and has a relatively large thickness, the ratio of the active surface to the mass of the metal oxide is not necessarily high. Therefore, it takes time to form the layer of metal oxide, and the cost of the raw material (e.g., precursor) for forming the metal oxide increases.

According to the above documents that utilize annealing, the amount of carbon may decrease due to burning when a layer of a metal oxide is formed on carbon, and electrical/mechanical contact between carbon and the metal oxide may be insufficient.

An object of several aspects of the invention is to provide battery electrode that includes a thin film of a metal oxide that exhibits excellent catalytic activity, and makes it possible to efficiently utilize the raw material, methods for producing the same.

The invention was conceived in order to solve at least some of the above problems, and may be implemented as described below (see the following aspects or application examples).

According to one embodiment, the invention relates to a method for producing a battery electrode which comprises the following steps:

- A first step during which a substrate 1 , either made of an electrode material or comprising at least partly on its surface, a layer of an electrode material, is introduced in a reaction vessel;

- A vapor deposition step during which a metal precursor, that is a metal raw material, is fed with a carrier gas in said reaction vessel, either simultaneously or separately, with an oxidizing agent that includes ozone and/or oxygen, to obtain said substrate 1 coated with a thin film 2 of at least one oxide of said metal precursor; wherein said vapor deposition step is repeated several times, in order to reach a predetermined thickness of said film 2, greater or equal greater or equal to 0.1 nm and less or equal to 100nm, preferably greater or equal to 1 nm and less or equal to 50nm, more preferably greater or equal to 1.5nm to 30nm and more preferably greater or equal to 2nm to 20nm.

Implementing the abovementioned method, the inventors found that the thin film exhibits excellent catalytic activity, and makes it possible to efficiently utilize the raw material.

Examples of the vapor deposition method used during said vapor deposition step, include a chemical vapor deposition (CVD) method, an atomic layer deposition (ALD) method, a physical vapor deposition (PVD) method, a resistance heating deposition method, an electronic beam deposition method, a molecular beam epitaxy method, an ion-plating method, an ion beam deposition method, a sputtering method, a thermal CVD method, a catalytic CVD method, a photo-CVD method, a plasma CVD method, and a metal organic chemical vapor deposition (MOCVD) method.

According to a preferred embodiment, said vapor deposition step is chosen from an atomic layer deposition (ALD) method or a chemical vapor deposition (CVD) method.

Both methods are indeed preferable from the viewpoint of the uniformity of the material, and a capability to easily form a thin film 2 that exhibits excellent undercoat (electrode material) coverage.

When using an ALD method or a CVD method as the vapor deposition method, the thin film 2a is formed by introducing the electrode material into a reaction vessel of a vapor deposition device, and feeding a metal oxide raw material and an oxidizing agent to the reaction vessel either simultaneously or separately.

Since the ALD method and the CVD method vaporize the raw material, and deposit the raw material on the electrode material using the resulting gas (vapor), the vapor pressure of said metal raw material at 80°C is preferably 1 .33Pa (0.01 Torr) or more, and more preferably 13,33Pa (0.1 Torr) or more. Such a metal precursor makes it possible to form a thin film 2a that includes a specific metal oxide while setting the pressure inside the reaction vessel at 1 .33Pa to 1 .01 x10⁵Pa (0.01 to 760Torr), for example. A compound that includes a metal species that forms a specific metal oxide may be used as the raw material. A commercially available reagent or the like may be appropriately used as the metal precursor corresponding to each metal.

In the method as hereinabove defined, said electrode material is a material which exhibits electrical conductivity. Examples of such materials are conductive carbon such as glassy carbon or carbon nanofibers, a metal such as platinum, gold, copper, nickel, iron, an alloy such as stainless steel, a metal oxide such indium tin oxide (ITO) or zinc oxide (ZnO) or mixtures thereof.

In the method as hereinabove defined, said substrate 1 may be formed of the electrode material only. If said substrate 1 comprises a material other than said electrode material, said electrode material is preferably located on the external surface of said substrate in order to allow the thin film 2 may be formed on said electrode material.

A titanium layer or the like (not illustrated in Figure 1 ) may be provided between the substrate 1 (electrode material) and the thin film 2 in order to improve adhesion, for example. According to this particular embodiment the titanium is brought before the use of the herein above defined method.

In the method as hereinabove defined, said substrate may have a flat shape, a curved shape, or a combination thereof. The substrate surface on which the thin film is formed may have irregularities.

In the method as hereinabove defined, said metal raw material (hereinafter may be referred to as "metal precursor") is an organometallic compound that includes a specific metal element, an organometallic complex that includes a specific metal element, an inorganic metal compound that includes a specific metal element, an inorganic metal complex that includes a specific metal element, and the like. Said specific metal element is namely selected among the elements that belong to Groups 3 to 11 in the periodic table and is preferably a transition metal oxide. Specific examples of said metal element includes manganese (Mn), cobalt (Co), (Ni), iron (Fe), copper (Cu), tantalum (Ta), titanium (Ti), niobium (Nb), zirconium (Zr), hafnium (Hf), zinc (Zn), lanthanum (La), cerium (Ce), vanadium (V), molybdenum (Mo), tin (Sn), tungsten (W), or mixtures thereof.

According to a particular embodiment of the invention said metal element of said metal raw material is manganese (Mn) and said metal raw material used in said vapor deposition step, is a compound selected from a compound of the formula (1 ):

L¹L²Mn (1 ),

and/or from a compound of the formula (2):

L¹L²L³Mn (2),

said formulas (1 ) and/or (2) wherein L¹, L², and L³ are bonded to the Manganese atom via a covalent bond, a coordination bond, or an ionic bond, and are independently selected from a hydrogen atom, a carbonyl group a group or a ligand having a skeleton selected from the group consisting of a substituted or unsubstituted alkyl, preferably having from one to six carbon atoms, a substituted or unsubstituted allyl, a substituted or unsubstituted allylalkyl preferably having from three to nine carbon atoms, a substituted or unsubstituted diketone, a substituted or unsubstituted cycloalkyl preferably having from five to eight carbon atoms, a substituted or unsubstituted cycloalkenyl preferably having from five to eight carbon atoms, a substituted or unsubstituted silyl, a substituted or unsubstituted amino, a substituted or unsubstituted silylamino, a substituted or unsubstituted cydopentadienyl, and a substituted or unsubstituted phenyl, or a mixture thereof.

According to a more particular embodiment of the invention said metal element of said metal raw material is manganese (Mn) and said metal raw material worked in said vapor deposition step, is a compound selected from a compound of the formula (3):

Cp(R¹R²R³R⁴R⁵)MnCp(R⁶R⁷R⁸R⁹R¹⁰)(3)

wherein Cp is a cydopentadienyl group, and R¹ to R¹⁰ are a substituent that substitutes Cp, and are independently an hydrogen atom, or a group or a ligand having a structure selected from the group consisting of a substituted or unsubstituted alkyl preferably having from one to six carbon atoms, a substituted or unsubstituted allyl, a substituted or unsubstituted allylalkyl preferably having from three to nine carbon atoms, , a substituted or unsubstituted cydopentadienyl, and a substituted or unsubstituted phenyl or a mixture thereof.

As examples of compounds of the formulas (1 ), (2) or (3), mention may be done of bis(ethyl cydopentadienyl) manganese (EtCp)₂Mn _^ bis(cyclopentadienyl) manganese (Cp₂Mn) „ bis(methyl cydopentadienyl) manganese (MeCp)₂Mn, bis(isopropyl cydopentadienyl) manganese (iPrCp)₂Mn, [bis(methyl cydopentadienyl) manganese tri carbonyl] [MeCpMn(CO)₃], bis(tert-butyl cydopentadienyl) manganese, [(t-BuCp)₂Mn, bis(ethyl cydopentadienyl) manganese 2,4-dimethylpentanedione] [(DMPD)(EtCp)Mn], bis(pentamethyl cydopentadienyl) manganese [(CH₃)₅Cp)₂Mn] or tris(2,2,6,6-tetramethyl heptane-3,5-dione) manganese [(thd)₃Mn] or a mixture thereof.

The choice of a manganese precursor allows the thin film 2 to be easily produced, and said film 2 exhibits high electrochemical catalytic activity.

According to another particular embodiment of the method hereinabove defined, said vapor deposition step is achieved using a metal precursor of the formula (3). According to this embodiment, a high vapor pressure and high reactivity are achieved.

In the vapor deposition step (film forming step), of the hereinabove defined process, said oxidizing agent used when forming the thin film 2a by the CVD method or the ALD method includes water, oxygen, ozone, oxygen plasma, nitrogen dioxide, and the like. These oxidizing agents may be used in combination, or may be used in combination with another gas (e.g., nitrogen, air, or inert gas). The oxidizing agent may be fed to the reaction vessel together with the metal precursor when using the CVD method, and may be fed to the reaction vessel separately from the metal precursor when using the ALD method, for example. It is expected that a high deposition rate can be achieved when using the CVD method. It is expected that a thin film 2a having a uniform thickness can be formed when using the ALD method (e.g., when the substrate 1 has a complex structure).

According to a particular embodiment, of the hereinabove defined method, said oxidizing agent comprises ozone.

According to another particular embodiment, the method as hereinbefore defined does not comprises any annealing step of said substrate 1 coated with said porous thin film 2.

In the vapor deposition step of the hereinabove defined process, nitrogen is generally first introduced into the reaction vessel to set the pressure inside the reaction vessel 20 to about 1 .33Pa to 1 .01 x10⁵Pa (0.01 to 760Torr), preferably about 13,33Pa to 1 .33x10⁴Pa (0.1 to 100Torr), and more preferably about 1 .33x10²Pa to 1 .33x10³Pa (1 to 10Torr). The reaction vessel is then is heated in order that the temperature of said electrode material during said vapor deposition step is about 20°C to 300°C, preferably 25°C to 200°C, and more preferably about 50°C to 150°C.

Said metal precursor raw is optionally heated, and fed to the reaction vessel 20 together with the carrier gas, such as nitrogen or other inert gases.

Said oxidizing agent is also fed to the reaction vessel, optionally together with the carrier gas.

At the end of said film forming step, said thin film 2 is formed on said substrate 1 .

Said thin film 2 generally includes organic substance and/or volatile substance derived from said metal precursor, oxygen derived from said oxidizing agent and the like, since the deposition temperature is relatively low. Said organic and/or volatile substances, oxygen and the like can be removed from the film through the pore-forming step to obtain the porous thin film 2. Said thin film 2a can also be formed so that no organic substance and/or volatile substance are present in the thin film 2a by choosing the appropriate raw material, oxidizing agent, and deposition conditions.

The material for forming the thin film 2 may have a composition represented by the formula (4):

M_xOyC_zX_n (4)

wherein

M is a metal atom such as manganese, cobalt, nickel, iron, copper, tantalum, titanium, niobium, zirconium, hafnium, zinc, lanthanum, cerium, vanadium, molybdenum, tin, tungsten,

O is an oxygen atom,

C is a carbon atom, and

X is at least one atom selected from the group consisting of nitrogen (N), silicon (Si), (P) and (S).

According to a preferred embodiment of the method as hereinbefore defined, the metal oxide included in said thin film 2 of said battery electrode obtained by the hereinabove defined method, is manganese oxide, cobalt oxide, or nickel oxide and more preferably manganese oxide, or a mixture of a plurality of manganese oxides, selected from the group consisting of dimanganese trioxide (Mn₂0₃), trimanganese tetraoxide (Mn₃0₄) (manganese(ll ,ll l) oxide), dimanganese trioxide (Mn₂0₃) (manganese(l ll) oxide), manganese dioxide (Mn0₂) (manganese(IV) oxide), and manganese monoxide (manganese(l l) oxide) (MnO) ; and particularly preferably trimanganese tetraoxide (Mn₃0₄) (manganese(ll ,l ll) oxide). Said thin film 2 need not necessarily have a uniform thickness over the entirety thereof. It may have a thickness distribution. Its average thickness of the thin film 2 can be estimated by microscopic observation, ellipsometry. The thickness of the thin film 2 is generally between 0.01 nm and 100nm, preferably between 1 nm and 50nm, and more preferably between 1 .5nm and 30nm and particularly preferably 2 to 20nm.

The hereinbefore defined method can also optionally comprise some auxiliary steps such as a preliminary cleaning of the reaction vessel, optionally some cooling steps or replacing the gas inside the reaction vessel with another gas, or some pore forming steps to create some porosity on said film 2.

According to another aspect, the invention relates to a battery electrode which is produced by the method for producing a battery electrode, as hereinbefore defined.

According to a last embodiment, the invention relates to a battery comprising as electrodes, at least one battery electrode, as hereinbefore defined.

The advantages of the methods are the following:

- Said battery electrode that exhibits excellent electrochemical catalytic activity. It can efficiently catalyze an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER). Therefore, said battery electrode is suitable as an electrode used for a battery such as a metal-air battery or a fuel cell. Moreover, the discharge voltage can be increased while decreasing the charge voltage, and energy can be efficiently utilized.

Figure 1 is a schematic cross-sectional view illustrating a battery electrode 10 produced by the method for producing a battery electrode according to one embodiment of the invention. The battery electrode 10 illustrated in Figure 1 has a configuration in which a thin film 2 is formed on a substrate 1 . The substrate 1 and the thin film 2 form the battery electrode 10. The thin film 2 is formed on the substrate 1 .

Figure 2 is a non limitative schematic illustration of the method according the invention. The vapor deposition device 100 includes a quartz tube (reaction vessel 20) into which the substrate 1 (electrode material) can be introduced, an exhaust means 30 that can evacuate (decompress) the quartz tube (decompress the quartz tube), a furnace (heating means 40) that can externally heat the quartz tube, a precursor feeding section 50 that feeds a metal precursor to the quartz tube, an oxidizing agent feeding section 60 that feeds an oxidizing agent, and a carrier gas feeding means 70 that circulates a carrier gas for introducing the metal precursor and the oxidizing agent into the quartz tube, each section being connected via an appropriate tube. The vapor deposition device 100 also includes a plurality of valves that can open and close each tube (pipe) (not illustrated on Figure 2). The exhaust means 30 and the heating means 40 may be implemented by an appropriate pump, heater, or the like. The vapor deposition device 100 may further include a pressure measurement means, a flow rate measurement means, a temperature measurement means, a control means, and the like (not illustrated on Figure 2). The substrate 1 is introduced into the reaction vessel 20 (quartz tube) of the vapor deposition device 100. Note that at least the surface of the substrate 1 is formed of the electrode material. The quartz tube is decompressed to about 1 .33Pa to 1 .33x10³Pa (0.01 to 10Torr) by operating the exhaust means 30 to remove residual gas such as air from the quartz tube. Nitrogen is introduced into the reaction vessel 20 from the carrier gas feeding means 70 to set the pressure inside the reaction vessel 20 to about 1 .33Pa to 1 .01 x10⁵Pa (0.01 to 760Torr), preferably about 13.33Pa to 1 .33x10⁴Pa (0.1 to 100Torr), and more preferably about 1 .33x10²Pa to 1 .33x10³Pa (1 to 10Torr). The quartz tube is heated using the heating means 40 to heat the substrate 1 (electrode material). The quartz tube is heated so that the temperature of the substrate 1 is about 23°C to 600°C, preferably about 80°C to 300°C, and more preferably about 50°C to 150°C. The metal precursor contained in the precursor feeding section 50 is optionally heated, and fed to the reaction vessel 20 together with the carrier gas fed from the carrier gas feeding means 70. In the example illustrated in Figure 2, the metal precursor is fed from the precursor feeding section 50 merges with the flow of the carrier gas. Optionally, the carrier gas may be bubbled into the precursor feeding section 50 to feed the metal compound to the reaction vessel 20.

After optionally removing excess metal precursor from the quartz tube, the oxidizing agent contained in the oxidizing agent feeding section 60 is fed to the reaction vessel 20 together with the carrier gas fed from the carrier gas feeding means 70. The oxidizing agent feeding section 60 may be optionally configured to pass oxygen gas through an ozonizer.

The thin film 2 can thus be formed on the substrate 1. Note that the thickness of the thin film 2a can be increased by performing the raw material feeding step that feeds the metal oxide raw material (metal precursor) to the reaction vessel 20, and/or the oxidizing agent feeding step that feeds the oxidizing agent to the reaction vessel 20 for a longer time, or repeating the raw material feeding step and the oxidizing agent feeding step a plurality of times. The deposition time and/or the repetition count are adjusted so that the thin film 2a has a predetermined thickness. The thin film 2a thus formed normally includes an organic substance and a volatile substance derived from the metal precursor, oxygen derived from the oxidizing agent, and the like, since the deposition temperature is relatively low. The organic substance, the volatile substance, oxygen, and the like can be removed from the film through the pore-forming step to obtain the porous thin film 2. The thin film 2a can also be formed so that an organic substance and a volatile substance are not present in the thin film 2a by changing the raw material, the oxidizing agent, and deposition conditions. In such a case, the porous thin film 2 is similarly formed by performing the pore-forming step. The details thereof are described below.

According to the above method for producing the battery electrode 10 (thin film 2), since a thin film is formed at 600°C or less by at least the raw material feed step and the oxidizing agent feeding step, and an annealing step is not performed, a thin film having excellent properties can be formed even when a material having low heat resistance is used as the material for forming the substrate 1 . For example, even when a carbon material is used as the material for forming the substrate 1 (electrode material), it is possible to prevent a situation in which the amount of carbon decreases due to burning, and electrical/mechanical contact between carbon and the metal oxide becomes insufficient.

The invention is described in more detail below by way of Examples.

Example 1

A thin film of manganese oxide was formed using the ALD method. Specifically, a thin film was formed by the ALD method using (EtCp)₂Mn as a metal precursor, and using gas including ozone as an oxidizing agent.

Glassy carbon (electrode material) (diameter: 5 mm, thickness: 4 mm) was introduced into a quartz reaction vessel (diameter: 48 mm, length: 100 cm). After decompressing the reaction vessel using a vacuum pump, nitrogen was introduced into the reaction vessel at a flow rate of 0.34Pa.m³/s (200 seem) to adjust the pressure inside the reaction vessel to 2.66x10²Pa (2Torr). The electrode material was heated to 120°C by heating the reaction vessel. (EtCp)₂Mn at 80°C was fed to the reaction vessel by bubbling with nitrogen (carrier gas) (0.08Pa.m³/s = 50 seem). Oxygen (0.08Pa.m³/s = 50 seem) was passed through an ozonizer to produce ozone, which was used as the oxidizing agent. The metal precursor and the oxidizing agent were successively fed by operating the corresponding valve. The feeding operation was performed using a computer-controlled pneumatic valve.

Figure 3 illustrates the metal precursor/oxidizing agent feeding scheme employed in Example 1 :

(1 ) - (EtCp)₂Mn is introduced into the reaction vessel for 5 seconds at a flow rate of

1 .69x10^"3Pa.m³/s (1 sccm).

(2) - Nitrogen gas was introduced into the reaction vessel for 30 seconds at a flow rate of 0.42Pa.m³/s (250sccm) to remove excess (EtCp)₂Mn.

(3) - The oxidizing agent (including ozone) was introduced into the reaction vessel for 10 seconds at a flow rate of 1 .69x10^"3Pa.m³/s (1 seem).

(4) Nitrogen gas was introduced into the reaction vessel for 30 seconds at a flow rate of 0.42Pa.m³/s (250sccm) to remove excess oxidizing agent.

The above steps were repeated a given number of times to deposit a thin film of manganese oxide having a given thickness on the electrode material. After completion of deposition, the atmosphere inside the reaction vessel was replaced with nitrogen, and cooled to room temperature, and the substrate (electrode material) and the thin film (battery electrode) were removed.

Twenty battery electrode samples including a thin film having a thickness of about 0.36 to 75 nm were produced by the above operation. In Example 1 , the flow rate and the introduction time of each raw material were fixed. Note that the flow rate and the introduction time of each raw material may be appropriately changed.

Each sample was observed using a scanning electron microscope (SEM) to measure the thickness of the thin film, and the deposition rate of the thin film was calculated, and found to be about 0.36 nm/cycle. Note that the invention is not limited to the above deposition rate.

Figure 4 illustrates the XRD (X-ray diffraction pattern) of the sample including a thin film having a thickness of about 7 nm. As illustrated in FIG. 4, it was found that Mn₃0₄ was included in the thin film of manganese oxide obtained in Example 1 .

Example 2

Samples obtained in Example 1 including a thin film having a thickness of about 0.36 to 75 nm were subjected to an annealing treatment. The sample was heated to 480°C in the air, and held at 480°C for 2 hours.

Example 3

The electrochemical catalytic activity of the samples obtained in Examples 1 and 2 was determined. The battery electrode in which the thin film of manganese oxide was formed was used as a work electrode, and connected to a rotating electrode-type electrochemical analyzer ("WaveDriver 20, AFMSRCE" manufactured by Pine Research Instrumentation).

The work electrode, the counter electrode (platinum), and the reference electrode

(mercury/mercury oxide) were immersed in an electrolyte solution (0.1 mol/l potassium hydroxide aqueous solution).

Oxygen gas was bubbled through the electrolyte solution for about 10 minutes to effect saturation. A voltage scan operation was performed while rotating the work electrode at 1600 rpm to measure the ORR/OER activity.

The ORR activity was measured while performing the voltage scan operation from 0V to -0.9V(vs. Hg/HgO). The current value at a voltage of -0.47V (vs. Hg/HgO) or 0.4V (vs. RHE) was recorded as an index of the ORR performance.

The OER activity was measured while performing the voltage scan operation from 0V to 2V(vs. Hg/HgO). The current value at a voltage of 1 .03V (vs. Hg/HgO) or 1 .9V (vs. RHE) was recorded as an index of the OER performance. Note that RHE is an abbreviation for "reversible hydrogen electrode".

Figures. 5A and 5B includes graphs showing the ORR/OER activity of the samples obtained in each of the examples (the thickness was changed by changing the number of ALD cycles). Figure 5A shows the OER activity measurement results, and Figure 5B shows the ORR activity measurement results.

As illustrated in Figure 5A, the samples obtained in Example 1 that were not subjected to the annealing treatment showed a rapid increase in OER activity when the thickness of the thin film was more than 2 nm (corresponding to about 6 ALD cycles). On the other hand, the samples obtained in Example 2 that were subjected to the annealing treatment showed a small increase in OER activity with respect to an increase in the thickness of the thin film.

It was thus found that the samples obtained in Example 1 exhibited high OER activity when the thickness of the thin film was small as compared with the samples subjected to the annealing treatment.

As illustrated in Figure 5A, the samples obtained in Example 1 showed the highest OER activity when the thickness of the thin film was about 7 nm. The OER activity was maintained when the thickness of the thin film was about 20 nm or less, but decreased when the thickness of the thin film exceeded about 20 nm. On the other hand, the OER activity of the samples obtained in Example 2 was saturated when the thickness of the thin film was 20 nm or more. It was thus found that the samples obtained in Example 1 exhibited high OER activity when the thickness of the thin film was about 2 to 20 nm, and exhibited good OER activity as compared with the samples obtained in Example 2 when the thickness of the thin film was about 2 to 8 nm.

As illustrated in Figure 5B, the samples obtained in Example 1 exhibited sufficient ORR activity when the thickness of the thin film was about 0.36 to 20 nm (corresponding to about 1 to 20 ALD cycles). The samples obtained in Example 1 exhibited insufficient ORR activity when the thickness of the thin film exceeded 20 nm. On the other hand, the samples obtained in Example 2 exhibited good ORR activity when the thickness of the thin film was within a relatively wide range.

It was thus confirmed that the samples obtained in Example 1 exhibited OER activity and ORR activity in a well-balanced manner when the thickness of the thin film was about 2 to 20 nm, and the OER activity and the ORR activity are remarkably balanced as compared with the samples obtained in Example 2 when the thickness of the thin film was about 2 to 8 nm. Therefore, it was confirmed that the battery electrode (thin film) according to the invention exhibits excellent electrochemical catalytic activity as compared with a known thin film when the thickness of the thin film is small.

The invention includes configurations that are substantially the same as the configurations described in the above embodiments (e.g., in function, method and effect, or objective and effect). The invention also includes a configuration in which an unsubstantial element of the above embodiments is replaced by another element. The invention also includes a configuration having the same effects as those of the configurations described relating to the above embodiments, or a configuration capable of achieving the same object as those of the above-described configurations. The invention further includes a configuration obtained by adding known technology to the configurations described in the above embodiments.

Claims

1 . Method for producing a battery electrode which comprises the following steps:

- A vapor deposition step during which a metal precursor, that is a metal raw material, is fed with a carrier gas in said reaction vessel, either simultaneously or separately, with an oxidizing agent that includes ozone and/or oxygen, to obtain said substrate 1 coated with a thin film 2 of at least one oxide of said metal precursor; wherein said vapor deposition step is repeated several times, in order to reach a predetermined thickness of said film 2, greater or equal to 0.1 nm and less or equal to 100nm, preferably greater or equal to 1 nm and less or equal to 50nm, more preferably greater or equal to 1 .5nm to 30nm and more preferably greater or equal to 2nm to 20nm.

2. Method according to Claim 1 , wherein said vapor deposition step is chosen from an atomic layer deposition (ALD) method or a chemical vapor deposition (CVD) method.

3. Method according to anyone of Claim 1 or 2, wherein, said electrode material is selected from glassy carbon or carbon nanofibers, platinum, gold, copper, nickel, iron, stainless steel, indium tin oxide (ITO) or zinc oxide (ZnO).

4. Method according to anyone of Claims 1 to 3, wherein said metal raw material used in said vapor deposition step, is a compound selected from a compound of the formula (1 ):

L¹L²Mn (1 ),

and/or from a compound of the formula (2):

L¹L²L³Mn (2),

said formulas (1 ) and/or (2) wherein L¹, L², and L³ are bonded to the Manganese atom via a covalent bond, a coordination bond, or an ionic bond, and are independently selected from a hydrogen atom, a group or a ligand having a skeleton selected from the group consisting of a substituted or unsubstituted alkyl, a substituted or unsubstituted allyl, a substituted or unsubstituted allylalkyi, a substituted or unsubstituted diketone, a substituted or unsubstituted cycloalkyl, a substituted or unsubstituted cycloalkenyl, a substituted or unsubstituted silyl, a substituted or unsubstituted amino, a substituted or unsubstituted silylamino, a substituted or unsubstituted cyclopentadienyl, and a substituted or unsubstituted phenyl or a mixture thereof.

5. Method according to Claim 4, wherein said metal raw material used in said vapor deposition step, is a compound selected from a compound of the formula (1 ):

L¹L²Mn (1 ),

and/or from a compound of the formula (2):

L¹L²L³Mn (2),

said formulas (1 ) and/or (2) wherein L¹, L², and L³ are bonded to the Manganese atom via a covalent bond, a coordination bond, or an ionic bond, and are independently selected from a hydrogen atom, a carbonyl group a group or a ligand having a skeleton selected from the group consisting of a substituted or unsubstituted alkyl, having from one to six carbon atoms, a substituted or unsubstituted allyl, a substituted or unsubstituted allylalkyi having from three to nine carbon atoms, a substituted or unsubstituted diketone, a substituted or unsubstituted cycloalkyl having from five to eight carbon atoms, a substituted or unsubstituted cycloalkenyl having from five to eight carbon atoms, a substituted or unsubstituted silyl, a substituted or unsubstituted amino, a substituted or unsubstituted silylamino, a substituted or unsubstituted cyclopentadienyl, and a substituted or unsubstituted phenyl or a mixture thereof.

6. Method according to anyone of Claims 4 or 5, wherein said metal raw material used in said vapor deposition step, is a compound selected from a compound of the formula (3):

Cp(R¹R²R³R⁴R⁵)MnCp(R⁶R⁷R⁸R⁹R¹⁰)(3)

wherein Cp is a cyclopentadienyl group, and R¹ to R¹⁰ are a substituent that substitutes Cp, and are independently an hydrogen atom, or a group or a ligand having a structure selected from the group consisting of a substituted or unsubstituted alkyl, a substituted or unsubstituted allyl, a substituted or unsubstituted allylalkyi, a substituted or unsubstituted cyclopentadienyl, and a substituted or unsubstituted phenyl or a mixture thereof.

7. Method according to Claim 6, wherein said metal raw material used in said vapor deposition step, is a compound selected from a compound of the formula (3):

Cp(R¹ R²R³R⁴R⁵)MnCp(R⁶R⁷R⁸R⁹R¹⁰)(3)

wherein Cp is a cyclopentadienyl group, and R¹ to R¹⁰ are a substituent that substitutes Cp, and are independently an hydrogen atom, or a group or a ligand having a structure selected from the group consisting of a substituted or unsubstituted alkyl having from one to six carbon atoms, a substituted or unsubstituted allyl, a substituted or unsubstituted allylalkyl having from three to nine carbon atoms, a substituted or unsubstituted cyclopentadienyl, and a substituted or unsubstituted phenyl or a mixture thereof.

8. Method according to anyone of Claims 4 to 7, wherein said compounds of the formulas (1 ), (2) or (3), are selected from bis(ethyl cyclopentadienyl) manganese, bis(cyclopentadienyl) manganese, bis(methyl cyclopentadienyl) manganese, bis(isopropyl cyclopentadienyl) manganese, [bis(methyl cyclopentadienyl) manganese tricarbonyl], bis(tert-butyl cyclopentadienyl) manganese, [bis(ethyl cyclopentadienyl) manganese 2,4-dimethylpentanedione], bis(pentamethyl cyclopentadienyl) manganese, and [(CH₃)₅Cp)2Mn], tris(2,2,6,6-tetramethylheptane-3,5-dione) or a mixture thereof.

9. Method according to anyone of Claims 1 to 8, wherein said oxidizing agent comprises ozone.

10. Method according to anyone of Claims 1 to 9, characterized in that it does not comprising any annealing step of said substrate 1 coated with said porous thin film 2.

11 . Battery electrode which is produced by the method for producing a battery electrode, according to anyone of Claims 1 to 10.

12. Battery comprising as electrodes at least one battery electrode obtained by the method according to anyone of Claims 1 to 10.