DE19547445A1 - Electrochemical cell - Google Patents

Abstract

A method of manufacturing a positive electrode active mass precursor comprises reacting a transition metal halide aqueous solution with an alkali metal hydroxide and, optionally, a metal-free base, to produce an alkali metal halide-containing precipitate. The alkali metal halide-containing precipitate is separated from residual liquid by removing residual liquid to a degree which adjusts, or allows adjusting of, the proportions of soluble and insoluble reaction products. The precipitate may be washed to adjust the content of soluble reaction products therein. If necessary, the water content of the precipitate can be adjusted to render it suitable for shaping. The precipitate is dried and reduced at temperatures up to the melting point of the alkali metal halide, to form an intimate mixture of transition metal and alkali metal halide having a mean particle size of less than 2 mu m.

Description

The present invention relates to an electrochemical cell. It also affects a method of making a positive active mass precursor Electrode, the precursor of the active mass of a positive electrode, and a Process for producing a shaped article, the shaped counter stood and the precursor of a positive electrode for an electrochemical Cell.

According to a first aspect of the invention, there is provided a method of producing the positive electrode active mass precursor which consists of
reacting the aqueous solution of a transition metal halide with an alkali metal hydroxide and optionally a metal-free base to form an alkali metal halide-containing precipitate;
separating the alkali halide-containing precipitate from the remaining liquid by removing the remaining liquid to an extent which adjusts or allows the amount of soluble and insoluble reaction products to be added;
optionally washing this precipitate to adjust the content of soluble reaction products therein;
if necessary, adjust the water content of the precipitation to make it suitable for deformation; and
drying the precipitate and reducing it at temperatures up to the melting point of the alkali halide to form an intimate mixture of transition metal and alkali halide with an average particle size of less than 2 microns.

According to a second aspect of the invention, a precursor to the active Ground of a positive electrode provided when following the procedure can be produced according to the first aspect of the invention.

According to a third aspect of the invention there is provided a method of making a shaped article which consists in
reacting the aqueous solution of a transition metal halide with an alkali metal hydroxide and optionally a metal-free base in order to form an alkali metal halide-containing precipitate,
to separate the alkali halide-containing precipitate from the remaining liquid by removing the remaining liquid to an extent which adjusts or permits the proportions of soluble and insoluble reaction products,
optionally washing this precipitate in order to adjust the content of soluble reaction products therein,
if necessary, adjust the water content of the precipitation to make it suitable for deformation,
deforming the precipitate into a shape suitable for insertion into a cathode compartment of the housing of an electrochemical cell, and
drying the precipitate and reducing it at temperatures up to the melting point of the alkali halide to form an intimate mixture of transition metal and alkali halide with an average particle size of less than 2 microns.

According to a fourth aspect of the invention, a molded article provided if it is according to the method according to the third aspect of Invention can be produced.

The molded article is thus suitable for use as a precursor positive electrode or cathode of an electrochemical cell as still be is written.  

According to a fifth aspect of the invention, the precursor becomes positive An electrode provided comprising a shaped article according to the fourth aspect of the invention or the precursor of the active mass of a positi ven electrode according to the second aspect of the invention.

The cathodic precursor or the precursor of the active mass of the positive Electrode therefore has no final shape, which differentiates it from the precursor of one distinguishes positive electrode, which has a defined shape and space occupies the ready for a cathode in the housing of an electrochemical cell is posed. The precursor for the positive electrode or cathode can thus be charged to form the cathode of the obtained cell.

According to a sixth aspect of the invention, an electrochemical cell provided which comprises a cell housing which has an anode and a cathode, wherein the cathode is at least initially the precursor to a positive electrode according to the fifth aspect of the invention.

The cell can thus be a rechargeable electrochemical alkali metal / metal be halide cell, which also contains a molten salt electrolyte, wherein this molten salt electrolyte contains at least one salt of the alkali metal points. The electrolyte may have melted and at the cell operating temperature the alkali metal in the cathode can be replaced by an alkali metal alloy. Especially when the alkali metal melted at the cell operating temperature is, the cell further comprises a solid electrolyte separator, which is the liquid Separates alkali metal from the molten salt electrolyte, this solid electrolyte is an ion conductor for ions of this alkali metal or in the case of an alkali metal alloy for ions of at least one of these alkali metals.

A typical example of these cells is the so-called ZEBRA cell, the one Sodium metal anode and a cathode comprising a transition metal chloride contains, e.g. B. iron chloride or nickel chloride.  

In general, the precursor to an active mass is therefore a chemical one Compound or a mixture of compounds after further treatment or workup, e.g. B. by chemical or electrochemical redox reaction, which can be effected by charging, give the active mass, the electroche is active for the discharge of the electrode of the cell or battery.

Such a precursor can also contain components that are not in the active Mass itself are transferred, but are otherwise functional, z. B., by providing metallic conduits, mechanical support for the Deliver active mass, pore formers, spreading agents, load reserve, getters and form other additives in this area to improve the electrodes are well known.

Thus, a positive active mass precursor is for the above type of Cells known, which has at least one transition metal with an alkali metal halogen nid combined, which is capable of in the chemical composition of the ge molten salt electrolyte to enter, for. B. by combining nickel or iron with sodium chloride and a reducing agent such as aluminum. At the The precursor mixture is loaded into the metal halide or the metal halides converted, d. H. the actual positive active mass and the reduc tion agent is halogenated in situ to z. B. to form aluminum chloride combined with excess sodium chloride to make the sodium aluminum chloride to form molten salt electrolytes and an equivalent amount of alkali metal, like sodium on the negative electrode.

The present invention thus provides a new method for producing the Precursor of positive active mass for such cells. In the process must the alkali metal hydroxide used can be selected so that the alkali metal cations are able to in the composition of the molten salt electrolytes to enter when he is in an electrochemical cell, like before described, is used.  

The precursor may contain a compound that is reduced upon heating initiates conditions for the reduction stage and / or under reducing Atmosphere becomes or remains electronically conductive.

Thus, the invention provides an electrode precursor and a shaped counter was of controllable porosity and pore size distribution, consisting of finely divided metal particles in an intimate mixture with at least one alkali logenide and, where appropriate, additives known in the art that they improve the electrode behavior.

According to a preferred version of the invention, the metal component is made of the precursor from finely divided particles of iron and / or nickel and up to 50 mol% of at least one element from the group As, Sb and Bi and possibly a smaller proportion of aluminum. The finely divided alkali ha logenide consists of sodium chloride with minor additions of sodium fluoride, Sodium bromide and any other dopants based on this Area are known. All additives from As, Sb and Bi to aluminum and doping the halides can already be present during the precipitation stage or can be used individually or together during a stage before forming ben provided that an intimate, uniform mixture is produced.

The preferred application of the electrode precursor of the invention is thus in the production of positive electrodes in discharged or over-discharged State in sodium / nickel chloride or sodium / iron chloride batteries. The intimate Distribution of the metal and the metal halide components is intended for this and capable of delivering a large reaction surface area as well as a con Continuous electronic conductive matrix to achieve high reaction rates to allow d. H. high energy density of the electrochemical cell.

So far, the precursors to positive electrodes of such cells have become common produced by physically mixing the metallic components in particulate form with the alkali halides in particulate form. Consequently  was the smallest primary particle size of the metallic component due to the Available work and the pyrophoric nature of fine metal powders limited.

In the case of iron, the metal is caused by superficial oxidation processes deactivated or passivated when handled in air and even faster, if it comes into contact with sodium halides during processing. Deactivation is a deterioration in the electrochemical behavior to understand the loading capacity, which leads to a reduced capacity yield during unloading. It can be seen that the metal, e.g. B. iron, is converted into metal halide during loading in this type of cell. Because of this passivation of fine metal powders in air, one has so far Heat treatment performed in a reducing environment to oxide layers to eliminate from the metal surfaces and the specific resistance of the Reduce electrode. A reduction stage similar to that of the Process for the preparation of the active mass precursor according to the Erfin be necessary in the manufacturing process of the prior art, despite the formation of the precursor from a metal powder.

To prepare the active mass precursor according to the invention Solutions of transition metal chloride used from the Recycli Decorative process of sodium / iron chloride and / or sodium / nickel chloride cells are preserved.

In a preferred version of the invention, an acidic aqueous solution of the Transition metal salt, especially the transition metal chlorides FeCl₃ and NiCl₂ can be neutralized in up to two stages during the reaction stage:

In a first stage, up to the stoichiometric amount of aqueous sodium hydroxide solution can be added to the metal chloride solution with agitation. The Reaction of the sodium hydroxide provides a mixture of sodium chloride in sus pension with a precipitate of metal oxyhydroxides and / or hydroxides and / or -oxychlorides and / or -hydroxychlorides, depending on the course of the Reaction.  

If the ratio of sodium hydroxide to metal chloride is chosen so that it is less than stoichiometric, residual metal chloride anions can be in one second stage to be neutralized to a pH of about 7 by adding aqueous ammonia solution or an organic base, e.g. B. alkyl ammonium ver bonds. In addition to the metal hydroxides and / or oxychlorides and / or -hydroxychlorides, which are formed in the first stage of hydrolysis the hydrolysis product enriched by dissolved and / or suspended Ammonium chloride or organic base chloride, which forms a base to to obtain a modified pore structure, like this in more detail is performed. Therefore, this second precipitation step can be carried out to modify the pore structure of the product.

After the precipitation stage or stages, the liquid is essentially chen a more or less saturated alkali salt solution and the invention before, the solution by filtration, centrifugation or other mechanical doors Removal measures known in this field Extent that the salinity of the remaining solid / liquid residue or "Cake" approximates the intended proportions as much as possible approximates. An optional washing step with water can be used to to further reduce the salt content of the residue after this separation.

After these operations, the wet raw product contains the intended ones Amounts of transition metal compounds and alkali halides intimately Mixture, but it may not yet be suitable for deformation. Therefore the water content of the mixture can be adjusted by suitable measures need to be, e.g. B. by evaporation or by adding water in one Kneader or a compulsory mixer or clay kneader to get the appropriate consistency to achieve. According to the invention, the paste or powder mixture thus formed is then formed into a body suitable for use as an electrode. Depending on the viscosity of the material can extrude the molding, uniaxial pressing or compacting by sintering in a mold.  

Suitable forms include particulate agglomerates, granules and Pellets as well as solidified bodies that are released in the form of a film or an extrudate can stand, or an electronically conductive matrix or a current collector included.

After the deformation process, the objects thus formed are made Powder or paste of heating and a reduction process at temperatures below the melting point of the alkali salt mixture or of sodium chloride pulled. It is known from thermal analysis that the tempera obtained rise leads to a loss of physically bound water (Drying), followed by loss of chemically bound water (dehydroxy lation) before the reduction occurs, and thus the heating and the Reduction can be split into the above levels or sections if this is should appear useful, and various equipment and atmospheres can be used for these levels. Thus, the drying and the Dehydroxylation can be carried out in streams of air while the Reduk tion is carried out in a reducing atmosphere. The procedural conditions Conditions for the individual stages depend on the particular chemistry of the Mix existing compounds and can be obtained from the literature will.

This process produces water vapor and small amounts of hydrogen chloride acid (HCl) according to the oxychloride content and ammonia produced by the optionally used second precipitation stage, and the release these gases make the resulting product porous. The type of porosity of the Object after reduction can be controlled by the combination setting of the hydrolysis mixture formed in the neutralization stage, as above indicated, namely by adding a second precipitation stage with ammonia or organic base.

The reduction can be induced by heating to about 300 ° C when that Metal is nickel or at about 500 ° C if the metal is iron, in  a hydrogen atmosphere. The precursor exists after the reduction stage product of a solid porous body, which consists of an intimate mixture of:

Sodium chloride and metal
and optionally dopants known in this field,
and optionally a component that imparts improved electronic conductivity
is constructed.

It is within the scope of the invention to add a component that is heated to temperatures below the melting point of sodium chloride under reduced decorative atmosphere remains or will be an electronically conductive material. Preferably, this material can be the same metal as the metal used in the Reduction stage of the preparation of the precursor is formed, or it can be high-melting carbide compound of a transition metal with at least a Group B, C, N, Si and P non-metal. The electronically conductive Component can have a relatively small surface area if it does so is intended to function as an at least partially adjacent current collector kidneys, e.g. B. take the form of a fiber network, an expanded one Metal foil and similar forms used in this field for electricity collectors are known, or they can have a relatively large surface area, such as Carbon powder and fibers, also in this field as the conductivity increasing additives are known and are either prefabricated or in situ generated by pyrolysis of suitable compounds such as furfuryl alcohol will. Depending on their nature, this conductivity-improving com component before or during the precipitation or at any other stage before the mixture loses its formability by drying.

The invention will now, without limitation, refer to FIG following non-limiting examples explained.  

example 1

A mole of a 40 wt .-% solution of FeCl₃ (Fluka, Buchs / Switzerland) was brought to the boil and 0.924 mol of a 50 wt .-% sodium hydroxide solution (Hoechst AG, Frankfurt / Main, Germany) were added dropwise with stirring . The solution was allowed to cool to 25 ° C and was then neutralized with 2.076 mol aqueous ammonia solution. After lowering the temperature to 5 ° C, the brownish slurry obtained was allowed to drip into liquid nitrogen. The solid material that formed was separated from the liquid nitrogen and dried at a temperature below -30 ° C. for 2 days under reduced pressure. The agglomerated particles thus obtained were compressed by uniaxial pressing at 2.55 kilobar. By sintering under hydrogen at 610 ° C for 1 hour (1.5 hours at temperatures of more than 500 ° C) at an oxygen partial pressure of 2 · 10 ^-22 bar, both the volatilization of NH₄Cl and the reduction of the iron oxide were achieved. The material was not pyrophoric, which is probably a consequence of the dispersion of fine iron powder in NaCl.

Electron microscopic photographs of the chemically generated Fe / NaCl Mixtures showed that the size of the spherical Fe- (<1 µm) and cubic NaCl particles (<2µm) considerably due to this chemical production method was reduced compared to mixtures of commercially available powders. In such powder mixtures, the particle size of iron is typically in the Range from 5 µm to 30 µm.

The loading of the finely divided powder mixture was in an elec trochem cell with an iron / sodium chloride mixture tested as Cathode was used and an aluminum plate as the anode, being cathode and anode separated by a porous glass sheet and melted into NaAlCl₄ were immersed at 260 ° C. The cathode material was Felt and Ni powder (Inco W 201) brought into contact and between 0.4 and 0.9 V cyclized, measured against an aluminum reference electrode, whereby a con  constant current of 20 mA to a pellet with a cross section of 1 cm² and a thickness of 2 mm was created. The theoretical capacity of the pellet was based on the content of NaCl limited to 21.01 mAh. The measured load was 20.07 mAh.

Thus, more than 95% of the NaCf introduced was consumed accordingly 45% of iron, which were converted into FeCl₂.

Example 2

One mole of a 40% by weight aqueous solution of NiCl₂ (OMG Europe GmbH, Düsseldorf / Germany) was mixed with 2 moles of a 50% by weight aqueous NaOH Solution (Hoechst AG, Frankfurt / Main, Germany) neutralized. The received green slurry contained Ni (OH₂) precipitate and NaCl in solution. Then 1 mol of NaCl, i.e. H. half of the sodium chloride, from the remaining Cake separated by filtration. The drying of the wet cake and the Dehydroxylation, i.e. H. the conversion of Ni (OH) ₂ into NiO were by led by slowly increasing the temperature in flowing air to 300 ° C has been. The average size of the primary NiO particles was 0.2 µm by electron microscopy. The reduction with hydrogen at temperatures up to 500 ° C produced nickel and sodium chloride as a finely divided mixture.

Claims (9)

1. A method for producing the precursor of the active mass of a positive electrode, characterized in that
reacting the aqueous solution of a transition metal halide with an alkali metal hydroxide and optionally a metal-free base to form an alkali halide-containing precipitate,
separating the alkali halide-containing precipitate from the remaining liquid by removing the remaining liquid to an extent
which adjusts or permits the proportions of soluble and insoluble reaction products,
optionally washing this precipitate in order to adjust the content of soluble reaction products therein,
if necessary, adjust the water content of the precipitation to make it suitable for deformation, and
dries the precipitate and reduces it at temperatures up to the melting point of the alkali halide to form an intimate mixture of transition metal and alkali halide with an average particle size of less than 2 μm. 2. The method according to claim 1, characterized in that the transition metal is selected from the group consisting of iron (Fe), nickel (Ni) and mixtures thereof, the alkali metal is sodium (Na) and the halogen of the halide is chlorine, the reaction of the solution with the Hydroxide the addition of up to the stoichiometric amount of aqueous Sodium hydroxide solution to dissolve the transition metal chloride under Moving involves, and neutralizing any remaining Matellchoridanio to a pH of about 7 by adding aqueous ammonia solution or an organic base.   3. The method according to claim 1 or 2, characterized in that the Separation is effected by mechanical separation measures, whereby the water setting, if applied, vaporizing or adding water in a kneader or a clay mixer. 4. Precursor for the active mass of a positive electrode, characterized thereby indicates that it is obtainable by the method of any of claims 1 to 3. 5. Forerunner according to claim 4, characterized in that the Metallkom component of the precursor of finely divided particles of iron and / or Nickel and up to 50 mol% of at least one element from the Group As, Sb and Bi and possibly a smaller proportion of aluminum, the finely divided alkali halide from Natri umchloride with minor additions of sodium fluoride and / or sodium bromide exists. 6. A process for the production of a shaped article, characterized in that it comprises:
the reaction of the aqueous solution of a transition metal halide with an alkali metal hydroxide and optionally a metal-free base to produce a precipitate containing alkali metal halide,
Separation of the alkali halide-containing precipitate from the remaining liquid by removing the remaining liquid to an extent which adjusts or permits the proportions of soluble and insoluble reaction products,
optionally washing the precipitate to adjust the content of soluble reaction products therein,
if necessary, adjusting the water content of the precipitation to make it suitable for deformation,
Shaping the precipitate into a shape suitable for insertion into a cathode compartment of the housing of an electrochemical cell, and
Drying the precipitate and reducing it at temperatures up to the melting point of the alkali halide to form an intimate mixture of transition metal and alkali halide with an average particle size of less than 2 µm. 7. Shaped object, characterized in that it after Ver drive according to claim 6 is available. 8. precursor for a positive electrode, characterized in that it a molded article according to claim 7 or the precursor an active mass of a positive electrode according to claim 4 or 5. 9. Electrochemical cell, characterized in that it is a cell housing comprises an anode and a cathode, the cathode at least initially the precursor of a positive electrode according to An saying 8 includes.