NL1015886C2 - Mixed oxide material with high electron conductivity, used in production of electrode for electrochemical cell, does not contain metals from platinum group - Google Patents

Abstract

A mixed oxide material with high electron conductivity does not contain metals from platinum group. A mixed oxide material with a high electron conductivity has an empirical formula of ABOy. y = not equal to 3; A = sodium (Na), potassium (K), rubidium (Rb), calcium (Ca), barium (Ba), lanthanum (La), praseodymium (Pr), strontium (Sr), cerium (Ce), niobium (Nb), lead (Pb), neodymium (Nd), samarium (Sm), and/or gadolinium (Gd), and B is copper (Cu), magnesium (Mg), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), niobium, molybdenum (Mo), tungsten (W), and/or zirconium (Zr). A and B cannot both be Nb, and compound SrVO2.5 is excluded. Independent claims are also included for: (A) a method for producing an electrode for an electrochemical cell, comprising: (a) forming a cohesive layer of a mixed oxide on a substrate by applying a mixture of the above mixed oxide material, binder(s) and solvent(s), (b) removing the solvent, and optionally (c) heat treatment; and (B) an electrochemical cell comprising at least two electrodes and an electrolyte.

Description

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Electrode for an electrochemical cell

The present invention relates to an electrode for an electrochemical cell. Electrochemical cell electrode is here understood to mean, in the broadest sense, the use of an electrode in combination with an electrolyte and other electrodes. That is, the invention relates to electrodes for electrochemical conversion and storage of electricity as they occur in electrochemical capacitors, also referred to as super capacitors or ultra capacitors, batteries, in particular also rechargeable batteries of the alkaline type or the metal / air type , fuel cells such as the polymer electrolyte fuel cell, electrolysis devices and sensors.

An electrochemical capacitor (or super-capacitor or ultra-capacitor) is a device in which electricity can be stored and subsequently withdrawn from it, in particular with high power density (in W / kg and W / l), by using electric double layer capacity and or so-called pseudo-capacity which is linked to Faraday processes such as redox reactions or intercalation processes. Applications include the (short-term) storage and / or delivery of peak powers and the reduction of “duty cycles” of batteries, such as those that occur in battery, hybrid or fuel cell vehicles, installations or equipment that ensure central or local electricity networks or power supplies, and in electronic or portable equipment such as laptops and mobile phones. Such an electrochemical capacitor has two electrodes, an anode and a cathode, to which electrons are released and received, respectively. Furthermore, the capacitor contains an electrolyte, for example an aqueous or an organic solution, and a separator, and the whole can be built into a metal or plastic housing. At least one of the two electrodes can now be an electrode according to the invention. The charge, positive at one electrode and negative at the other, is stored in the electric double layer capacity at the electrode and electrolyte interface, in the pseudo-capacity resulting from highly reversible redox reactions or intercalation processes at this interface, or in a combination thereof. Important properties here are the specific capacity (in pF / cm2) which is determined by the nature of the electrode material and the λ electrolyte used, the specific surface area of the electrode material (in cm / g) and the effective capacity resulting therefrom in (F / g). Furthermore, the nature of the electrolyte is of importance for the allowable potentials on the electrodes. In the case of pseudo-capacitance together with the potential range of the related reactions or processes, these determine the operational voltage range of the capacitor which should preferably be as large as possible. The composition and the microstructure of the electrode materials, the microstructure of the separator and the composition of the electrolyte also determine, but not only, the internal resistance Rj (in Ω) of the capacitor, which should preferably be as low as possible. The quantities described also determine, but not only, the energy density of the capacitor (in Wh / kg and Wh / 1) and the power density (in W / kg and W / l). For known technologies, these are typically a few Wh / kg and a few thousand W / kg, respectively. For the energy E (in J) and the power P (in W) of the capacitor with capacitance C (in F) and charged to the voltage V (in V), the approximate E = CV2 / 2 and P = V2 / 4Ri.

Known are, inter alia, electrochemical capacitors with electrodes that have activated carbon as their most important component and which mainly make use of electric double layer capacity. It is important that the activated carbon forms a porous structure with a high surface area accessible to the electrolyte to form the highest possible capacity, and with the highest possible conductivity for electrons to achieve the lowest possible resistance 20 and as much electrode material as possible. to utilize. In this way the highest energy and power densities are obtained which is required for most applications. Carbon electrodes which mainly utilize double layer capacity can be used as an anode and as a cathode; symmetrical capacitors can be made in this way. Carbon electrodes can be used in combination with an aqueous electrolyte, the permissible capacitor voltage being a maximum of approximately 1.2 V and a low internal resistance is obtained, or in combination with an organic electrolyte in which the maximum voltage is approximately 2.4 V but generally a less low internal resistance can be obtained.

For many applications, but in particular for use in vehicles, a higher energy density is desirable than is known in the prior art when using carbon electrodes. Particularly for this pursuit of higher energy density, the use of pseudo-capacity is useful, since it generally achieves much higher specific values than with double-layer capacity. The use of ruthenium oxide RuO2 and hydrated ruthenium oxide R.UO2.XH2O is known, inter alia from U.S. Patent Nos. 5,550,706, 5,851,506, 5,875,092 and 6,025,020. This compound, in combination with aqueous electrolytes such as, for example, KOH solutions, has a high effective capacity in F / g based on redox reactions and can be used as an anode and as a cathode. It also has a good electrical conductivity. Disadvantages of this connection when used in (symmetrical) electrochemical capacitors are the limited allowable voltage and the very high cost of material of the desired purity. A lot of research is being done into alternative pseudo-capacity materials that can meet these drawbacks while still allowing the desired higher capacity and energy density.

It is generally assumed in the prior art that the use of compounds with noble metal elements, such as for example noble metal oxides, is necessary to obtain sufficiently high storage capacity, or sufficiently high conversion speed or catalytic activity of the electrode, and a sufficiently high electrical conductivity.

However, it will be understood that the costs of such connections are high. It has therefore been proposed to reduce the amount of noble metal in such compounds by using compositions consisting partly of inexpensive, non-noble metals. Examples are compounds with the pyrochlore structure such as PI52RU2O7 and the addition of Sr to ruthenium oxide. With the first-mentioned group of materials, only a limited reduction in the required amount of the expensive ruthenium is achieved; no reduction is achieved at all in the second class of compounds. Furthermore, the use of metal hydroxides has been proposed, which can become metal oxy-hydroxides, such as in particular Ni (OH) 2. This connection is attractive because of the low costs, the high specific capacity and the favorable potential range, but it has a low and charge-dependent conductivity. The reversible charge / discharge reaction at an electrode of this material in an alkaline electrolyte can be represented by Ni (OH) 2 + OH 10 O NiOOH + H 2 O + e, where Ni (OH) 2 conducts poorly and NiOOH has a significant electrical conduction if it is in the right phase (the β phase). These limitations in electrical conductivity necessitate the use of additives, such as, for example, graphite, and the use of conductive matrices, such as, for example, metal foams or metal mats, to enclose the material with additive. This limits the useful electrode thickness and entails additional costs, weight and volume. This also makes the manufacture of electrodes more complicated and more expensive. The occurrence of Ni (OH) 2 in more phases (α, β, γ) limits the allowable operational conditions for the electrode to those conditions where the desired β phase is stable ". Furthermore, Ni (OH) 2 electrode can only be used as an anode, so that symmetrical capacitors cannot be made and, for example, a carbon counter electrode is needed. This limits the improvements in capacity and energy density that are achievable with respect to the symmetrical carbon capacitor. Ni (OH) 2, but in particular the nickel component and optionally the nickel required for the preparation, are also attributed adverse environmental and health properties. As a result, requirements and regulations regarding processing and processing apply, which entail additional costs. This also means that there are 15 restrictions on applicability, for example to those applications and markets for which collection and / or reuse has been arranged.

A (rechargeable) battery is a known device. Electricity can be stored in it and then extracted again, in particular with a high energy density (in Wh / kg and Wh / 1), by making use of electrochemical conversion of electrical energy to chemical energy and vice versa. The construction of such batteries corresponds to the previously described construction of electrochemical capacitors, although the construction and operation may differ. Known are, inter alia, (rechargeable) batteries of the nickel-cadmium type, nickel-zinc, and nickel-iron, of the nickel-hydrogen type, of the nickel-metal hydride type, and of the metal / air type such as iron / air , zinc / air, aluminum / air and lithium / air. At least one of the two electrodes of such batteries can now be profitably replaced by an electrode according to the invention. The nickel electrodes, the cadmium electrode and the air electrodes in particular, but not only, are eligible for this.

NiCd, NiZn, NiFe, N1H2 and NiMH batteries are known, among others, where the "nickel electrode" consists of the same Ni (OH) 2 compound and has the same effect as for electrochemical capacitors above. I 0 1 5 8 β r "5. The same disadvantages also apply as a result of the limitations in electrical conductivity.

Also known are batteries of the type Fe / air, Zn / air, Al / air and Li / air, wherein during discharge at the air electrode oxygen is consumed by electrochemical reduction; such batteries are "mechanically recharged" by renewing the anode. Also known are bi-directional air electrodes; which, in addition to reducing oxygen, can also evolve oxygen in the reverse process and thus enable electrically rechargeable metal / air batteries. The previously known compounds only allow moderate performance due to limited conductivity and catalytic activity, and are often expensive.

It is the object of the present invention to provide an electrode which does not have the above disadvantages, i.e. is inexpensive to manufacture, has no limitations on the useful thickness, and has no environmental problems.

This object can be achieved in an electrode for an electrochemical cell by a compound comprising a perovskite of the ABO3 type wherein A comprises a metal selected from the group Na, K, Rb, Ca, Ba, La, Pr, Sr, Ce, Nb, Pb, Nd, Sm and Gd, and B comprises a metal selected from the group Cu, Mg, Ti, V, Cr, Mn, Fe, Co, Nb, Mo, W and or Zr and wherein no metal from the group Pt, Ru, Ir, Rh, Ni and Pd is present. It has surprisingly been found that when such a perovskite of the ABO3 type is used in which no noble metals are present nor nickel is present, particularly good storage capacity, or conversion speed or catalytic activity, and also a very high electrical conductivity are obtained. It should be understood that perovskites of the type ABO3 25 are also understood to mean perovskites of the type ABC> 3_5 or A1A2B03_ $ or AB1B2C> 3_8 or A1A2B1B2C> 3_6 where δ can be between approximately - 0.2 and approximately + 0.5. It has been found that such perovskites used in an electrode comprise a surprisingly high electrical conductivity (S / cm), a high conversion speed or catalytic activity and a high storage capacity (in F / g or Ah / kg).

Examples are, but the invention is not limited to, Smo ^ SrosCoOs ^,

Ndo.sSro.5Co03-5 and Ndo.4Sro..6Coo.8Feo.203 ^. By applying this connection it is possible to obtain electrodes with desired properties at low 101588; 6 material costs and via a simple manufacturing process. Furthermore, the invention makes it possible to use electrodes up to large thicknesses in a useful manner, without the need for additions of additional materials or components, for example for electrical conduction or current collection. Preferably, such electrodes 5 have considerable porosity to increase the effective surface with the electrolyte. Such an electrode preferably consists at least near the surface of a porous structure which consists of at least 30% and preferably more than 70% of one or more of the above compounds. In an electrochemical capacitor, it has surprisingly been found that such electrodes have a high pseudo-capacitance. For example, when used as an anode in an asymmetric electrochemical capacitor with a carbon cathode and with KOH electrolyte, a high electrode capacity was found which, due to the effective surface, cannot be attributed to double layer capacity. A high capacity of the total cell was also found, with a low internal resistance and a favorable usable voltage range. This results in high energy and power densities for the cell. Individual measurements demonstrated high electrical conductivity of the said electrodes. A comparison with the properties of electrodes known from the prior art is given in Table 1. In particular, the electrical conductivity is of the same high level as that of PI72RU2O7 and the capacitance in pF / cm2 is of the same high level as that of Ni (OH) 2. In addition to the expensive ruthenium, an electrode according to the invention can also, but not necessarily, avoid the heavy lead.

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Table 1. Comparison of properties between electrodes ** according to the prior art and a Smo.sSro.sCoOa-g electrode ** according to the invention. C is capacity; σ is electrical conductivity.

Property Active Ru02.xH20 Pb2Ru207 SrRu03 Ni (OH) 2 Sm05Sro5CoO · carbon C (pF / cm2) 10 ... 40 60 2200 2200 A (m2 / g) <1200 120 10 ... 150 70 120 5 {0) C (F / g) <100 <720 72 20..200 95> 130 <0) σ (S / cm) <1 ·· 500 .. ..> 300 V (V) 1> 2 1.3 .. 1 , 2 1.6 1.6 Δ V (V) 1.0 0.9 0.7 0.8 1.2 K (Euro / kg) 2> 25 (1) 3000 (2) ... 1000 (2). ..> 3000 6 ... 10 (5) 20 (2 * ...

5000 (3) 23,000 (4) (2) 1200 (6) 5 *) as a working electrode in a super capacitor with carbon counter electrode and KOH electrolyte.

Maximum voltage V and voltage drop Δ V apply to the entire cell.

(0)> 400 F / g with> 20 m2 / g (1) purchase price on a 1000 kg basis 10 (2) raw material price (3) purchase price on a 25 kg basis and depending on purity (4) chemically pure and based on 5 grams ( 5) based on NiO raw material price for> 1000 kg (6) purchase price of a one-off batch of 1 kg 15

In addition to the aforementioned perovskites, the electrodes may, in addition to one or more of these compounds, also, but not necessarily, contain a binder to form a coherent structure. Such a structure can, but does not have to, be arranged in a matrix. Also, but not necessarily, the electrodes may have undergone a heat treatment or calcination treatment or sintering treatment.

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Figure 1 shows results of measurements on electrochemical capacitors with a carbon electrode and, respectively, a Ni (0H) 2 electrode known from the prior art and a Smo.sSro.sCoOa-g electrode according to the present invention. With the Ni (OH) 2 electrode, graphite was added in different percentages to improve the electrical conductivity, while with the Smo.5Sro.5Co03.5 electrode no addition was used. It is clear that the electrode according to the invention can be used to greater thicknesses without loss of effective capacity. It is thus possible to utilize electrodes according to the invention to greater thicknesses without the use of additives, such as, for example, graphite, or conductive matrices, such as, for example, metal foams. This makes cells and stacks of cells possible with less inactive material and therefore with higher energy and power density. Due to the high conductivity, it is also possible to use a matrix which conducts less well than, for example, a metal foam, for example a matrix of a conductive plastic or a conductive polymer, and with which reductions in weight and costs are also achieved. It is also possible to form independent, relatively thick electrode layers, for example by printing, printing, casting or dipping, whether or not on other (electrical or electronic) components, and which have a high capacity and do not use expensive noble metal elements.

All this does not alter the fact that electrodes according to the invention can also be made as thin layers, for example by printing, printing, casting, dipping, painting or spraying, and applied.

The electrodes according to the invention are not limited in their design and application to asymmetrical capacitors or to capacitors according to the construction described; They can also be advantageously used in symmetrical electrochemical capacitors, in batteries and in fuel cells, reversible fuel cells, electrolysis devices and sensors.

An electrode according to the invention is characterized by the complete or complete avoidance of noble metal elements, in particular ruthenium and irridium, by a high pseudo-capacity (of the same level as with Ni (OH) 2) and or high catalytic activity and or high conversion speed, due to a high electrical conductivity (of the same level as with Pb2 Ru207), practically independent of the charge state or polarization, due to a high stability due to the absence of undesired phases and due to a favorable voltage range. In an electrode according to the invention, the use of environmentally harmful elements, such as nickel and lead, occurring in electrodes according to the prior art can also be avoided. As a result of the properties mentioned, an electrode according to the invention, compared to what is known in the state of the art, can be cheaper, have a higher round-trip efficiency, in particular at higher currents, can be manufactured more easily, used in the in the form of a thin layer or thick layer, and may or may not be enclosed in a matrix which may also consist of a light, inexpensive and moderately conductive plastic. In this way an electrode according to the invention also allows other concepts than those known in the prior art for capacitors, super capacitors, batteries, fuel cells, electrolysers and sensors. For example, it is now possible to print the electrode as a layer on another component and in this way add a function to that component. That component can for instance be part of a photovoltaic solar cell or an electro-15 chrome window.

The present invention will be described in more detail below with reference to a number of examples.

Example 1 Electrode according to the invention manufactured by applying a layer of suspension, ink or paste to a substrate. The substrate can be, for example, a metal foil or a plastic foil. The suspension, ink or paste comprises one or more perovskite compounds according to the invention, a solvent and possibly auxiliaries such as dispersants, surfactants, wetting agents and the like. The perovskite compounds can be added in the form of a powder with a high specific surface area. The suspension, ink or paste can optionally also contain a binder. Application is by means of lubrication, painting, spraying, dipping, printing, casting, sludge casting, rolling or rolling. After application, the layer can first be dried, with solvent and auxiliaries wholly or partially withdrawn. A heat treatment, calcination or sintering can optionally be used, after drying, or as a substitute for drying. Subsequently, the substrate with the layer, which can have characteristic thicknesses between approximately 2 μηι and approximately

t 0 1 5 8 $ fc 10 1000 µm, and which may be between about 5% and about 40% porous, used in a super capacitor or battery.

Example 2 Electrode manufactured by applying a suspension, ink or paste to a matrix. The matrix can be a metal foam, or a metal mat, metal mesh, polymer foam, polymer mesh, or other porous structure. The suspension, ink or paste comprises one or more perovskite compounds according to the invention, and may further contain components as described in Example 1. The perovskite compounds 10 can be added in the form of a powder with a high specific surface area. The application of the suspension, ink or paste can take place according to the methods described in Example 1, and in particular by means of pressure filtration. After application, the steps as in example 1 can follow. Typical thicknesses of the formed electrode structure will now be between approximately 100 µm and approximately 1500 µm.

Example 3

Electrode manufactured by applying a layer of suspension, ink or paste to a substrate. The suspension, ink or paste comprises one or more perovskite compounds according to the invention, a solvent and possibly auxiliaries such as dispersants, surfactants, wetting agents and the like. The perovskite compounds can be added in the form of a powder with a high surface area. The suspension, ink or paste can optionally also contain a binder. The substrate is a smooth surface. The suspension is distributed over the surface by means of smearing, painting, printing or pouring and is dried. The tape formed is then removed from the smooth surface as an independent electrode layer. If appropriate, heat treatments, calcination or sintering can be applied to the tape for use in a capacitor, battery, fuel cell, electrolyser or sensor.

Example 4

Electrode produced by applying a suspension, ink or paste comprising one or more perovskites according to the invention, on a substrate or in a matrix, wherein this substrate or matrix forms part of another component or device , such as a photovoltaic solar cell or electro-chrome window.

Example 5 One or more perovskites according to the invention are packed in powder form in an envelope of porous plastic material, inert to the electrolyte to be used and electrically insulating. For closing the envelope, powder material, envelope and a wire or strip of metal are compressed in such a way that contact occurs between the powder particles and between the wire or the strip and the powder. The structure created in this way is used as an electrode in an electrochemical cell.

Due to the characteristic use of perovskites in the electrodes according to the invention, there are many possibilities compared to known materials and electrodes for influencing the properties and adapting them to specific application requirements.

Although the invention has been described above with reference to preferred embodiments, it is to be understood that after reading the above description, those skilled in the art will immediately come up with variants that are obvious and are within the range of the appended claims.

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Claims (15)

An electrode for an electrochemical cell, comprising a perovskite of the type ABC> 3_8 wherein δ is between approximately -0.2 and approximately +0.5 and wherein A comprises a metal selected from the group Na, K, Rb, Ca , Ba, La, Pr, Sr, Ce, Nb, Pb, Nd, Sm and Gd, and B comprises a metal selected from the group Cu, Mg, Ti, V, Cr, Mn, Fe, Co, Nb, Mo, W and or Zr and wherein no metal from the group Pt, Ru, Ir, Rh, Ni and Pd is present. The electrode of claim 1, wherein A and or B comprises a metal doped with a further metal. The electrode of any one of the preceding claims, wherein A comprises SmxSr (i.x) with x between about 0.4 and about 0.6. 15 The electrode of any one of the preceding claims, wherein A comprises NdxSr (i.x) with x between about 0.4 and about 0.6. The electrode of any one of the preceding claims, wherein B comprises Co. 20 The electrode of any one of the preceding claims, wherein B comprises Fe. The electrode of any one of the preceding claims, wherein B comprises Co (i.X) Fex with x between about 0.2 and about 0.6. 25 An electrode according to any one of the preceding claims, comprising at least 30 wt. % of one or more of those perovskites. 9. Method for manufacturing an electrode according to any of the preceding claims, comprising providing a substrate and applying a layer comprising said perovskite thereon. 1. i 8 b w t A method for manufacturing an electrode according to any one of the preceding claims, comprising providing a matrix and applying said perovskite therein. A method for manufacturing an electrode according to any one of the preceding claims, comprising manufacturing an independent tape or structure comprising said perovskite. 12. Method for manufacturing an electrode layer according to any of the preceding claims, comprising integrating said electrode layer into a component or device and comprising said perovskite. An electrochemical cell comprising an electrode according to any one of the preceding claims, as well as an electrolyte and a further electrode. 15 An electrochemical cell according to claim 10, wherein said further electrode comprises a carbon electrode, or a RuC> 2 electrode, or a RuC ^ xflbO electrode. 15. An electrochemical cell comprising two electrodes, each according to one of claims 1 to 11 and possibly different from each other, and an electrolyte. 1 0 1 b 8 8 r