WO2002071513A2

WO2002071513A2 - Aluminum anodes and method of manufacture thereof

Info

Publication number: WO2002071513A2
Application number: PCT/CA2002/000120
Authority: WO
Inventors: Alexander M. Iarochenko; Evgeny B. Kulakov; Valery V. Caronic
Original assignee: Aluminum-Power, Inc.
Priority date: 2001-03-02
Filing date: 2002-01-30
Publication date: 2002-09-12
Also published as: US20020148539A1; CA2339059A1; WO2002071513A3

Abstract

A process of making an aluminum alloy anodic material having improved electrochemical properties for use in an electrochemical cell and battery, the alloy consisting essentially of 95-99.5% w/w Al and 0.5-5.0 cumulative w/w additive metal selected from Group II - Group V metals of the Periodic Table, the process comprising heating 95 - 99.5% w/w A1 and 0.5 - 5.0 cumulative % w/w additive metal in admixture to a temperature to form a homogeneous matrix of melted alloy; cooling the melted alloy at a liquidus/solidius cooling rate to produce a solid, non-equilibrium alloy of a non-homogenous multiphase matrix comprising discrete, relatively large crystals of pure aluminum and relatively smaller crystals of the additive metal included at the interface with the aluminum crystals; rolling the solid alloy to reduce its thickness to a factor of 0.2 to 0.01 to produce a rolled sheet of the alloy having a microstructure comprising an aluminum matrix having elongate inclusions of the additive metal and small, satellite ovoidal inclusions of the additive metal dispersed in the matrix.

Description

ALUMINUM ANODES AND METHOD OF MANUFACTURE THEREOF

FIELD OF THE INVENTION This invention relates to improved aluminum alloy anodes, to batteries and fuel cells comprising said anodes and to methods of manufacture of said anodes.

BACKGROUND OF THE INVENTION Aluminum anode/metal-air cathode batteries and fuel cells require a combination of competing electrochemical properties to be of practical and, particularly, commercial value.

On one hand, the anode must be sufficiently highly active to provide high voltage and current, while on the other hand, the anode should not be active, i.e. corrode, when there is no power load requirement. The anode should also uniformly react at its surface without pitting or selective dissolution. Metals such as aluminum, zinc and magnesium in pure and technical grade form, i.e. greater than 99.5% purity do not provide a favourable balance of aforesaid electrochemical properties and, thus, are alloyed in admixture with suitable, but small amounts of additive metals to enhance electrochemical performance.

Metal alloying additives which improve the performance of the pure metals are known. For example, USP 4,098,606 discloses that the addition of indium, gallium or . thallium of 0.01 - 0.5% by weight, are beneficial for producing an active aluminum alloy.

USP 4,792,430 discloses that addition of 0.03 - 0.2% tin to aluminum is beneficial in which the benefit can be further enhanced by the addition of 0.03 - 0.07% gallium and/or 0.002 to 0.006% silicon. These beneficial alloys are produced by preparing a homogeneous mixture of the elements above their melting points and then subsequently cooling the mixture to produce a solid phase having the desired elements at their appropriate concentration.

The process of alloying aluminum, magnesium and zinc metals for modification of physical properties, such as strength or magnetic properties is well-known. For example, USP 4,294,625 discloses that aluminum may be given enhanced properties of strength, fatigue resistance and fracture toughness by the weight addition of 3.8-4.4%) copper, 1.2 - 1.8 % magnesium, 0.6 - 0.9% manganese, and less than 0.12% silicon, 0.15%) iron , 0.25% zinc, 0.15% titanium, 0.1% chromium and 0.05% other elements.

Other processes disclose the improvement of physical properties by providing specific cooling rates to the molten alloy. USP 4,126,486 discloses that an aluminum alloy containing 4-15% silicon may be strengthened by solidifying the molten alloy at a specific rate during casting and then further treating the alloy to a rolling process and finally an annealing process at 250-400°C.

The process of producing an alloy in which the alloying component is supersaturated has also been described. For example, USP 5,585,067 describes a process for mixing the molten alloy during the cooling stage such that a 2-phase dispersion of small-sized, well-dispersed inclusions is created. The supersaturated components were bismuth, cadmium, indium or lead. Other patents have described the benefits of keeping the additives in the aluminum phase by rapid cooling of the aluminum melt. United States RE 34,442 describes the production of an aluminum ingot having magnesium and silicon as strengthening agents, which are prevented from forming a separate phase by quick cooling of the melt. By keeping the additives in the aluminum matrix in a dissolved state, the extrudability of the alloy is improved. Other patents, such as USP 4,805,686 disclose that the rapid quenching is beneficial for producing a microeutectic microstructure which has high strength at elevated temperatures. The achievement of uniform, fine grain structure disclosed in USP 4,490,188 is important in the 2000 and 7000 class aluminum alloys because it allows cold rolling to be performed on the alloy without cracking of the aluminum sheet. The fine grained microstructure has also been achieved in USP 4,415,374 by heating an alloy which has been solidified with a second solid phase, to the melting point of the matrix, but below that of the second phase. Subsequent cooling of the melt yields a fine-grained microstructure. USP 5,009,844 discloses the processing of aluminum alloy with a hypoeutectic composition by heating at a finite (<20°C/min) rate such that partial dissolution of the second phase occurs. A more uniform and spherical second phase residue is left after treatment. A process of converting an alloy with a dendritic second phase into a uniformly dispersed second phase in a cast product is described in USP 5,91 1,843. The process uses thermal treatment which does not melt the alloy but allows the dendritic second phase to become dispersed. The processing of aluminum alloys by means of rolling to produce a sheet form is also known. Alloy composition and the hot and cold rolling conditions must be carefully controlled if a satisfactory rolled sheet product is to be produced. USP 5,080,728 discloses the conditions required for an aluminum alloy containing 0.7 - 1.15% iron plus 0.5 - 2.0%) manganese plus <0.6% silicon with the remainder being aluminum and inherent impurities (<0.03%). It is common to try to keep the second phase or intermetallics well dispersed and with small grain size i.e. <l lum, as seen in USP 5,1 16,428.

The aforesaid prior art has used composition and processing conditions to improve physical properties of the final alloy. However, none has disclosed that the electrochemical activity of an anode might also be improved by modifying the physical structure of the alloy. In general, it is believed that chemical activity is due to the chemical species present and not to their physical distinction.

There is a need, therefore, for an anodic material having improved electrochemical properties for use, particularly in batteries or fuel cells.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for producing an anodic material having improved electrochemical properties, such as, relatively higher current density, more efficient volt/ampere characteristics, and superior discharge properties.

It is a further object to provide an anodic material having aforesaid improved electrochemical properties.

It is a further object to provide said anodic material having aforesaid improved electrochemical properties made from so-called technical grade materials, particularly containing small amounts of Fe.

It is a further object to provide a battery having an anode formed of a material having aforesaid improved electrochemical properties.

The present invention provides that by a new physical process of homogeneous alloy melt formation with quenching at a rapid rate, followed by hot and/or cold rolling, improved electrochemical properties are achieved from alloys that would otherwise be considered to have low or no electrochemical property value. The improvement in electrochemical behavior, without being bound by theory is postulated to be the result of a two phase structure of inclusions and matrix developed by the new physical processing, which phase structure can be observed by optical and electron microscopy. Unexpectedly,, the preferred physical structure seen in the present invention is not the uniform, small inclusion size favoured for producing good physical strength characteristics noted in the prior art but that having two types of inclusions, viz, larger dendritic inclusions comprising the majority of the metal additive and a finely dispersed inclusion making up the remainder of the metal additive. A small amount of the metal additive ends up dissolved in the aluminum matrix. Characterization of the structures of conventional prior art alloys and processed alloy of the same composition according to the invention shows that there is substantial physical difference in the materials. The preferred performance is obtained when the alloy, according to the invention, has been processed to provide >80% of the metal additive inclusions in elongated dendritic form and the remainder of the inclusions as dispersed relatively very tiny particles.

Accordingly, in one aspect, the invention provides a process of making an aluminum alloy anodic material having improved electrochemical properties for use in an electrochemical cell, said alloy consisting essentially of 95-99.5%) w/w Al and 0.5-5.0 cumulative w/w additive metal selected from Group II - Group V metals of the Periodic Table, said process compromising heating 95-99.5%) w/w Al and 0.5 - 5.0 cumulative % w/w addictive metal in admixture to a temperature to form a homogeneous matrix of melted alloy; cooling said melted alloy at a liquidus/solidus cooling rate to produce a solid, non-equilibrium alloy of a non-homogenous multiphase matrix comprising discrete relatively large crystals of pure aluminum and relatively smaller crystals of said additive metal included at the interface with said aluminum crystals; rolling said solid alloy to reduce its thickness to a factor of 0.2 to 0.01 to produce a rolled sheet of said alloy having a microstructure comprising an aluminum matrix having elongate inclusions of said additive metal and small, satellite ovoidal inclusions of said additive metal dispersed in said matrix.

Preferably, the additive metal is selected from Ga, In, Tl, Cd, Sn, Pb, Mn, Fe, and Mg; and more preferably, Mn, In, Sn and Fe. In the alloy cooling step according to the invention, a non-equilibrium multiphase structure having large pure Al crystals of all shapes as one phase up to 5 cm long is produced and wherein the additive metal(s) are occluded at the Al periphery as one or more phases if one of more additive metals are present. The aluminum crystals or grains in the pre-rolled alloy, thus, preferably, have an average length selected from about 1-5 cm.

It is known that when solidification of a melted homogeneous aluminum alloy is carried out slowly, equilibrium conditions can be maintained during solidification. However, equilibrium conditions are not attained in commercial casting techniques, and so-called "non-equilibrium" or meta-stable alloys are produced. The term "non- equilibrium" is understood in the art and reference is made to the treatise: Aluminum: Technology, Applications and Environment - "A Profile of a Modern Metal", Aluminum from Within - the Sixth Edition by Dietrich G. Althenpohl, The Aluminum Association, Inc. 900 19^th Street, Suite 300, Washington, D.C. and The Minerals, Metals and Materials Society (TMS), 420 Commonwealth Drive, Warrendale, Pennsylvania.

In commercial casting processes, solidification rates and cooling of the solidified structure are closely tied together by the rapid heat removal per unit of time. Especially in direct chill or strip casting techniques, solidification and cooling after solidification is so rapid that, in addition to the grain segregation, a considerable supersaturation of the alloying elements occurs.

The term "liquidus/solidus cooling rate" in this specification means the cooling rate of about 10kg of a 3cm thick alloy matrix in a rectangular mould when cooled over the liquidus/solidus stage, i.e. from the temperature at which solidification of the melted alloy commences to the temperature at which it has completely solidified. This solidification temperature range is, for example, typically, about 20-30°C for alloy compositions of use in the practice of the invention, which commence to solidify at about 660°C and are essentially solid at about 640°C.

A preferred cooling rate is selected from about 1° to 10°C per minute, and more preferably selected from 2° to 5°C per minute. The alloy cooling step in the practice of the present invention may be suitably and readily achieved, preferably, for example by air cooling. The melted admixture is cooled at such a rate as to produce a non-equilibrium, solid alloy, multi-phase matrix, as hereinabove defined. If the melt is cooled too quickly, a homogeneous multi-metallic phase having no or little discrete crystals is obtained. If the cooling rate is too slow, multi-phases of the different metals, each as relatively large inclusions, non-uniformly distributed throughout the thickness of the mass is undesirably obtained. The melted alloy may be readily melted and transferred to a typical mould for cooling at the aforesaid desired rate. An essentially rectangularly shaped, mould of internal dimensions selected, for example, from 3-5 cm, wide, 5-20 cm long and 10-50 cm high to accommodate 1-10 Kg alloy may be used.

The microstructures may be viewed by optical and electron microscopy. The rolling step of use in the practice of the invention may comprise either hot rolling or cold rolling techniques or, preferably, conventional hot rolling at a temperature selected from 200-560°C, followed by cold rolling. Reductions by hot rolling to 10-20% of the original thickness, followed by further reductions to 2-10% of the original thickness by cold rolling is most preferred. The resulting thickness of the rolled plate, sheet, film, foil and the like of the order of 0.2 - 2 mm, preferably, about 0.5 mm is of particular value as an anodic material in the practice of one aspect of the invention, in batteries, and have been found to provide enhanced current density activity.

Without being bound by theory, we believe that the cold rolling step, in particular, causes the aluminum crystals to merge under the shearing action to form a bulk matrix, and the relatively large additive metal occlusions to elongate as occlusions within the aluminum matrix, which occlusions are surrounded by a plurality of much smaller, fragmented satellite additive metal occlusions dispersed in the matrix. The rolling steps are beneficially enhanced by use of lubricating oils.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be better understood, preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings wherein

Figs 1A - ID represent electron microscopic images of an aluminum/indium cast alloy according to the invention;

Figs 2A - 2D represent electron microscopic images in cross-section perpendicular to the direction of rolling of the alloy of Example 1 after rolling as described therein; Fig 3 represents a sketch of a test cell used to determine anode potentials and corrosion rates of anode alloys according to the invention;

Fig 4 represents graphs of the polarization characteristics Pa (anode) as a function of current density of test anodes of 99.4% w/w (Al 99.95% pure) + 0.6% In, manufactured by different methods;

Fig 5 represents graphs of the discharge characteristics Pa (anode) of the anode materials manufactured as described with reference to Fig. 4;

Fig 6 represents curves showing the dependency of the corrosion current density I(corr.) on the relative amount of additive in anode materials manufactured as described with reference to Fig 4;

Fig 7 shows comparative graphs of the polarization characteristics Pa(anode) in volts as a function of current density of several test anodes with various additive metals manufactured by different methods;

Fig 8 represents graphs of the discharge characteristics Pa(anode) volts of various anode alloy materials as described with reference to Fig 7; and

Fig 9 represents graphs showing comparative corrosion current densities against anode current densities for the alloys described with reference to Figs 7 and 8, manufactured according to the invention.

DETAILED DESCRIPTON OF PREFERRED EMBODIMENTS

EXAMPLE 1

Al (9.5Kg. 99.95%) purity) and In (0.5Kg.) were melted in admixture to just above its melting point at about 660°C and forced air-cooled in a carbon-lined, rectangularly- shaped chamber having a width of 3 cm, over a period of 30 minutes, and a crystallization liquidus/solidus temperature range of about 20°C to achieve the aforesaid non-equilibrium, homogeneous, crystal-forming conditions distinct from non- heterogeneous amorphous solidification.

The resultant alloy plate was hot-rolled at 500°C to a thickness of about 3 mm and cold rolled to a thickness of about 0.5 mm.

EXAMPLE 2 Example 1 was repeated wherein a 10cm thick amount of the melted alloy of Example 1 was air-cooled over a period of 10 hours.

EXAMPLE 3 Example 1 process conditions were repeated with a 99.1% aluminum/0.3% indium alloy.

With reference to Fig 1, this shows electron microscopic structures of the aluminum/indium alloy cast according to Example 1 prior to hot/cold rolling. Figs 1A and IB, enlarged x200 and x400, respectively, show large aluminum crystals of 1.5 cm length having indium colonies on the periphery of the aluminum grains. Fig IC at an enlargement of x4000 shows indium colonies as spherical bodies of approximately 1.6 micron diameter or elongated occlusions of approximately 10 microns in length. Fig ID shows the internal structure of the indium colony at a magnification of xl0,000.

Fig 2 shows the rolled alloy wherein Figs 2A and 2C represent a strip, foil and the like of thickness 1 mm at a magnification of x2600 and x6000, respectively, while

Figs 2B and 2D are 3mm thick and at a magnification of x2000 and x6000, respectively.

Satellite indium inclusions of not larger than 0.1-0.2 micron diameter can be seen to be interspersed among the larger elongate indium crystals.

Fig 3 shows generally as 10 the test cell used to determine anode potentials and rates of corrosion of the aluminum alloys under test.

Cell 10 has a cylindrical body 12 hermetically sealed between removable end covers 14 against gaskets 16. Body 12 at an upper part has a side tube 18 for release of hydrogen under test. Coaxial within body 12 is a reference electrode 20 adjacent disc 22 of specimen anode under test. Terminals 24, 26 are located at upper and lower covers 14, respectively for contact with electrode 20 and disc 22, respectively, for measuring Pr (reference) and Pa (anode), respectively. Cell 10 contains aqueous potassium hydroxide (4 mol/L) electrolyte with 0.6% w/w potassium stannate additive, 28. The temperature was controlled to that specified by the testing requirements.

With reference to Fig 4, this shows the polarization characteristics Pa (anode) as a function of current density of test anode alloys comprising 99.4% Al and 0.6% In, wherein the alloy is made as follows. Curve 1 is for the aforesaid alloy made according to the present invention, comprising the general steps of a. casting and quick crystallization of the non-equilibrated alloy (fast quenching); b. multi stage hot rolling; and subsequent c. cold rolling as a finishing stage. Curve 2 is as far as step a., only.

Curve 3 is cast and hot and cold rolled according to conventional prior art manufacturing methods. The polarization characteristics were measured at a temperature of T=60°C

(333°C). Curves 1, 2 and 3 show that the polarization characteristics are not much different up to the current density of J=300-400 ma/cm². With further increase of the current density, the difference between the polarization characteristics rapidly increases. For example, for current density of J=500ma/cm², the potential Pa (anode), curve 1 is about -1.50 V, for curve 2 it is -1.25 V, and for curve 3 it is -1.3 V. For the current density of J=550 ma/cm² the difference in the potentials on curves 1 and 3 is about 0.4 V; i.e. for the invention anode curve 1, Pa (anode) is about -1.37 V, while for the traditional technology, curve 3, it is about -0.93 V.

Accordingly, the efficiency of the anode electrode manufactured according to the invention is superior for nominal and large current loadings of the anode as compared to the regular anode alloys made using the method according to the prior art.

Fig 5 shows the discharge characteristics against time for the three anode materials manufactured as described with reference to Fig 4, in the same electrolyte composition and at the same temperature of 60°C, and a discharge current density of 100 ma cm², using the cell described in Fig 3.

The results show that for the extended discharge cycles, the anode electrode according to the invention (curve 1) is superior over prior art alloy anode material (curve 3), in part related to the energy capacity, of approximately by 30-40%. The longer the discharge cycle, the better the electrochemical property of an anode material. Fig 6 shows corrosion current density I(corr.) curves for materials made by each of the three methods of manufacture described with reference to Fig 4, using the test cell described in Fig 3 under the same conditions of temperature in the same electrolyte. The curves of Fig 6 show that the anode alloy according to the invention (curve

1) provides the most advantageous values of corrosion current density from 10 to 20 ma/cm² within the range of from 0.05 to 1.4% w/w of the additive In. The maximum value of the corrosion current density of about 20 ma/cm² falls within the range of 0.5 - 0.8% w/w In.

It is worth noting that with the reduction of the concentration of In in the alloy from 0.2 to 0.05% w/w, the corrosion current rapidly increases from 10 ma/cm² to 20 ma/cm².

For prior art anode alloy (curve 3), the character dependency of the corrosion current density is about the same. However, the magnitude of the corrosion density is about an order larger i.e. from 130 ma/cm² to 160 ma/cm². Gentle, but noticeable maximum corrosion current density in the range 0.5 to 0.8% w/w In was observed.

" For the non-rolled anode of alloy (curve 2) the character dependency of the corrosion current density is significantly inferior. Longer-term measurements were conducted to obtain the mass-volumetric characteristics of the corrosion reaction of the aforesaid alloys having 0.6% In, according to the invention, in the aforesaid cell at an electrolyte temperature of 20°C (293°K).

The results of multiple measurements showed that, on average, the rate of hydrogen generation H₂ during the corrosion reaction is about 0.66mL/hr/cm², which corresponds to a corrosion current density of 1.3-1.5 ma/cm².

With reference to Fig 7, this shows a series of curves obtained under the same conditions and manner as described with reference to Fig 4, representing the polarization characteristics as a function of current density of test anode alloys comprising as follows:- In: 99.4%A1 + 0.6% In; Sn: 99.85%AI + 0.15%Sn; Mn: 99.97%A1 + 0.03%Mn;

Fe: 99.99%AI + 0.01% Fe; and wherein in each trio of curves:- Lines 1 denote the respective aforesaid alloy made according to the invention; Line 2 denote the respective aforesaid alloy made according to the pre-rolled invention process step only; and Lines 3 denote the respective aforesaid alloy made according to a conventional prior art cast and hot and cold rolled manufacturing method.

The series of comparative curves show in each case for each alloy, that the efficiency of the anode material made according to the invention is superior to the same anode composition made according to the prior art, and, indeed, when only the fast quenching step process used in the two- step process of the invention is used.

Fig 8 shows discharge characteristics against time for the four different metal compositions, of anode materials manufactured as described with reference to Fig 7 in the same electrolyte composition, at the same temperature of 60°C, and a discharge current density of 100 ma/cm², using the cell described in Fig 3.

The results show that for the extended discharge cycles, the anode electrodes according to the invention (curves 1) are superior over corresponding composition prior art alloy anode material (curves 3) and pre-rolled only materials (curves 2). The longer the discharge cycle, the better the electrochemical property of an anode material. With reference to Fig 9 this shows comparative graphs of different alloys made according to the method of manufacture according to the invention, as follows:

1. 99.4%A1 + 0.6% In;

2. 99.85%Al + 0.15%Sn;

3. 99.97%A1 + 0.03%Mn; 4. 99.99%A1 + 0.01 % Fe (technical Al) EXAMPLE 4

The anode material according to the invention as described under Example 1 was subjected to subsequent additional thermal treatment of different temperatures and time periods. The additional treatment steps included, for example, tempering, annealing, and cooling as given in Table 1. Also given in Table 1 are the electrochemical values obtained from the test cell described with reference to Fig 3 operated at 60°C. Values of the anode potentials, corrosion rates and effective activation energy - which is related to the corrosion current and temperature by the Arrhenius Equation. The relative errors of the measurements were as follows:- - 2.8%) for the anode potential Pa (anode)

6.3%) for the corrosion current density I(corr.) 1 1.1 % for the effective activation energy E_a. TABLE 1

+ Anode potential at the end of the tests (for 2.16 x 10⁴ sec.) Annealing at 340°C. Tempering at 500°C. Water Cooling at 37°C.

The results in Table 1 show several secondary thermal treatment features. The first is that even though the alloy composition is fixed for all of the tests, the electrochemical behavior can be modified to some minor degree by changing the cooling rates for the alloy. In the prior art, it has always been assumed that alloying by addition of certain specific elements to the base material is sufficient to provide adequate electrochemical properties. From the results in Table 1 it is clear that the electrochemical kinetic parameters, such as the effective activation energy, can be modified by processing to provide additional good properties. From the processing results in Table 1 , it can be seen that a small activation energy 40.6 kJ/mole results in a relatively large corrosion current of 276 A/m2 while a high activation energy value of 47.2 kJ/mole results in a smaller corrosion rate of 231 A/m2. The unexpected aspect of the results is that processing affects such a fundamental electrochemical characteristic as activation energy. Tempering for 25 minutes cooling in water^' produces an improved electrochemical property independent of the effect of alloy composition. Interestingly, this process condition also produces the best initial and final voltage. Thus, the physical processing method described, has the ability to substantially improve the performance characteristics of aluminum anode materials. By way of comparison, an alloy of similar composition produced conventionally, has an undesirable corrosion current of 1700 A/m2 as shown in Fig 6. The processing set forth clearly demonstrates a method to produce an anode material that has superior electrochemical properties; initially (high initial voltage see Table 1); during discharge (high voltage during discharge at high currents, see Fig. 4); and at end of discharge by way of greater capacity (smaller corrosion rates see Fig. 5).

In conclusion, the results show that anode alloys according to the invention have about one order lower corrosion current density relative to the alloy of the same composition made according to the prior art, while having more efficient volt-ampere characteristics when used at medium and particularly high anode current densities; and also has a relatively larger energy capacity to provide superior discharge characteristics.

Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.

Claims

1. A process of making an aluminum alloy anodic material having improved electrochemical properties for use in an electrochemical cell, said alloy consisting essentially of 95-99.5%) w/w Al and 0.5-5.0 cumulative w/w additive metal selected from Group II - Group V metals of the Periodic Table, said process compromising heating 95 - 99.5%) w/w Al and 0.5 - 5.0 cumulative % w/w additive metal in admixture to a temperature to form a homogeneous matrix of melted alloy; cooling said melted alloy at a liquidus/solidus cooling rate to produce a solid, non-equilibrium alloy of a multiphase matrix comprising discrete, relatively large crystals of pure aluminum and relatively smaller crystals of said additive metal included at the interface with said aluminum crystals; rolling said solid alloy to reduce its thickness to a factor of 0.2 to 0.01 to produce a rolled sheet of said alloy having a microstructure comprising an aluminum matrix having elongate inclusions of said additive metal and small, satellite ovoidal inclusions of said additive metal dispersed in said matrix.

2. A process as defined in claim 1 wherein said cooling rate of said melted alloy is selected from 1° to 10°C per minute.

3. A process as defined in claim 2 wherein said cooling rated is selected from 2-5°C per minute.

4. A process as defined in claim 1 wherein about 80-90%> w/w of said additive metal in said rolled alloy is in the form of said elongate inclusions and about 10-20%) w/w is in the form of said ovoidal inclusions.

5. A process as defined in claim 1 wherein said elongate inclusion has a length selected from 2-30 microns, a width selected from 0.4-3 microns; and said ovoidal inclusion has a diameter selected from 0.1-0.3 microns.

6. A process as defined in claim 1 wherein said additive metal is selected from Ga, In, Tl, Cd, Sn, Pb, Mn, Fe, and Mg.

7. A process as defined in claim 6 wherein said additive metal is selected from Sn, In, Mn and Fe.

8. A process as defined in claim 6 wherein said alloy consists essentially of 99.4% w/w Al and 0.6% w/w In.

9. A process as defined in claim 1 wherein said solid alloy is hot rolled to 10-20% of original thickness and subsequently cold rolled to 2-10% of original thickness.

10. A process as defined in claim 1 wherein said solid alloy is rolled to a thickness selected from 0.2- lmm.

1 1. A process as defined in claim 1 wherein said aluminum crystals in said pre-rolled solid alloy have an average length selected from up to 5cm and a width of 0.2 - 1 mm.

12. An aluminum alloy having improved electrochemical properties for use as an anode in an electrochemical cell consisting essentially of 95-99.5% w/w aluminum and 0.5-5.0 cumulative % w/w additive metal selected from Group II -

Group V metals of the Periodic Table, and having a microstructure comprising an aluminum matrix having elongate inclusions of said additive metal and smaller, satellite ovoidal inclusions of said additive metal dispersed in said matrix.

13. An alloy as defined in claim 12 wherein about 80-90% w/w of said additive metal is in the form of said elongate inclusions dispersed in said matrix.

14. An alloy as defined in claim 12 wherein said elongate inclusion has a length selected from 2-30 microns and a width selected from 0.4-3 microns; and said ovoidal inclusions has a diameter selected from 0.1-0.3 microns.

15. An alloy as defined in claim 12 wherein said additive metal is selected from Ga, In, Tl, Cd, Sn, Pb, Mn, Fe, and Mg.

16. An alloy as defined in claim 12 wherein said additive metal is In at a concentration of about 0.5% w/w.

17. An electrochemical cell comprising an anode, a cathode, and an electrolyte, wherein said anode is formed of an alloy as defined in claim 12.

18. A battery comprising an anode, a gas-diffusion cathode, and an alkali metal electrolyte; wherein said anode is formed of an alloy as defined claim 12 and is in the form of a tape, foil or sheet having a thickness selected from 0.05mm - 2 cm.