WO2012117289A1

WO2012117289A1 - Lead electrode, method for its manufacturing and accumulator comprising the electrode

Info

Publication number: WO2012117289A1
Application number: PCT/IB2012/000374
Authority: WO
Inventors: Carmelo Sunseri; Salvatore Piazza; Rosalinda Inguanta; Germano Ferrara; Maria Chiara Mistretta; Francesco Gioacchino Vergottini
Original assignee: Cr Mobility Solution System S.R.L.
Priority date: 2011-02-28
Filing date: 2012-02-24
Publication date: 2012-09-07
Also published as: IT1404292B1; ITVI20110037A1

Abstract

A lead electrode designed to be applied to a device with an electric power circuit and an electrolyte (4) for transporting electric charges, which electrode comprising a current collector (5, 6) in a first material containing lead designed to be placed in electric contact with the power circuit for transferring electric charges thereto and a plurality of nanowires (7, 8) in a second material containing lead firmly coupled to the collector (5, 6) and adapted to chemically interact with the electrolyte (4) for transferring electric charges onto the collector (5, 6). An accumulator comprising the electrode and a method for the manufacturing of the electrode.

Description

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"LEAD ELECTRODE, METHOD FOR ITS MANUFACTURING AND ACCUMULATOR COMPRISING THE ELECTRODE"

DESCRIPTION

Technical field

The present invention finds its general application in the technical field of the electrical devices and in particular it relates with a lead electrode designed to be used in electrical devices, such as power accumulators.

The invention also relates to a method for manufacturing the electrode and an accumulator comprising the electrode.

Background art

As known, the lead-acid batteries are a kind of rechargeable accumulators having large use for feeding vehicles, as they allow high inrush other than they are relatively cost- effective.

Generally, the known lead-acid batteries comprise a positive electrode having lead dioxide as active material and a negative electrode wherein the active material is metallic lead.

Moreover, the two electrodes are immersed in an aqueous electrolytic solution containing sulphuric acid.

Typically, the electrodes are obtained by several manufacturing processes of the respective active materials starting from lead grid, the most common of which comprises the pressing of an active paste on the grid to fill all its meshes.

However, the batteries so obtained are affected by several drawbacks, one of which is represented by the rapid decay of the performances when the battery is subjected to high-current discharges.

This drawback is determined by the formation of passive surface layers of lead-sulphate that block the discharge reaction and convert into active materials with increasing difficulty.

Additionally, the use of the common sulphuric acid based electrolyte involves the formation of dendritic metallic lead, whose accumulation can cause short circuits between the electrodes, as well as a loss of metal due to the detachment of the dendrites.

Not least, the common processes for manufacturing the electrodes do not allow to modify their morphology to suit specific applications, for example diversifying them if the battery is of the high or low voltage type.

Disclosure of the invention

The object of the present invention is to overcome the above drawbacks realizing a lead electrode having high energy and power density.

A particular object is to realize a lead electrode whose morphology is suitable to the proper applications to which the electrode is designed.

Another object of the present invention is to realize an accumulator with lead electrodes having increased structural stability and high performances for a longer time than the common lead electrodes.

Another object of the present invention is to realize an accumulator comprising lead electrodes with nanometric structure which is particularly safe and has high durability. A further object is to provide a method for manufacturing a lead electrode with nanometric structure.

Yet another object is to provide a method for manufacturing a lead electrode with nanometric structure that does not needs tetrafluoroboric acid.

These and other objects, as better explained hereafter, are fulfilled by a lead electrode designed to be applied to an electrical device having an electric power circuit and an electrolyte for transporting electric charges, as claimed in claim 1 , which electrode comprises a current collector in a first material containing lead designed to be placed in electric contact with the power circuit for transferring electric charges thereto.

The electrode is characterized by comprising a plurality of nanowires in a second material containing lead, said nanowires being firmly coupled to said collector and adapted to chemically interact with the electrolyte for transferring electric charges onto said collector.

Thanks to this peculiarity, the electrode will have a large active surface which will allow to obtain accumulators with higher energy and power density .

According to a further aspect of the invention, an accumulator according to claim 5 is provided which comprises the electrode.

According to yet a further aspect of the invention, a method for manufacturing the electrode is provided according to claim 7.

Advantageous embodiments of the invention are defined by the dependent claims. Brief description of the drawings

Further characteristics and advantages of the invention will be more apparent upon reading the detailed description of preferred, non-exclusive embodiments of a lead electrode, an accumulator comprising the electrode and a method according to the present invention for manufacturing the electrode, which are described as non-limiting examples with the help of the annexed drawings, in which:

FIG. 1 is a schematic cross sectional view of an accumulator comprising a pair of electrodes according the invention;

FIGG. 2 to 4 represent schematic sequences of a method for manufacturing an electrode according to the invention ;

FIG. 5 is a schematic view of some embodiments of the electrode obtainable with the method of the invention;

FIGG. 6 to 9 are SEM images of the nanowires of an electrode of the invention obtained using different type of matrixes.

Detailed description of a preferred embodiment

With reference to the figures, a lead electrode of the invention may be used in electrical devices, not shown, having an electric power circuit and at least one electrolyte for transporting electric charges.

In particular, the electrode may be used as a cathode or as anode in any kind of accumulators, such as lead-acid batteries.

In Fig. 1 a preferred but non limiting embodiment of an accumulator, more particularly a lead-acid battery, generally referred with 1 , is shown which comprises a pair of electrodes 2, 3 according to the invention.

In particular, the accumulator 1 may comprise one or more active cells series or parallel connected and each formed by a pair of electrodes 2, 3 immersed in a respective electrolyte 4

Each electrode 2, 3 may essentially comprise a current collector 5, 6 in a first electrical active material containing lead and designed to be placed in electric contact with a power circuit, not shown, for transferring electric charges thereto.

According a peculiarity of the invention, each electrode 2, 3 further comprises a plurality of nanowires, generally referred 7, 8, in a second material containing lead.

In particular, the nanowires 7, 8 are firmly coupled to the respective collector 5, 6 for chemically interacting with the electrolyte 4 and transferring electric charges onto the collector 5, 6.

More precisely, the collectors 5, 6 may be substantially plate-like shaped with the nanometric wires 7, 8 having one end integral to a surface 9, 10 of the corresponding collector 5, 6 for obtaining a firm electric contact therewith and increasing the electric conductivity of the electrode 2, 3.

According an advantageous aspect of the invention, the nanowires 7, 8 may be realized by direct growing of the respective second material on the surface 9, 10 of the corresponding collector 5, 6.

For each electrode 2, 3, the first and second materials, respectively of the collector 5, 6 and of the nanowires 7, 8, may be substantially the same.

In particular, the positive electrode 2 may comprise or consist of a collector 5 and nanowires 7 in lead dioxide.

In turn the negative electrode 3 may comprise or consist of a collector 6 and nanowires 8 in metallic lead.

The described electrodes 2, 3 may be used for producing an accumulator 1 provided with a conventional electrolyte 4, i.e. sulphuric acid based, wound by an electrically insulated layer 11 and wherein the electrodes 2, 3 will be immersed.

However, according a particularly advantageous aspect of the invention, an accumulator 1 according to the invention may comprise an electrolyte 4 based on methanesulfonic acid.

As matter of fact, this latter will inhibit the formation of denditric metallic lead whose growing may cause short circuits between the electrodes 2, 3 other than loss of material due to the detachment of the dendrities.

Opportunely, the electrolyte 4 will be also supported by a polymer or co-polymer based hydrogel. As way of example the co-polymer may be selected into the group comprising PVA based co-polymers (polyvinyl alcohol), PAA (polyacrylic acid) or salt thereof, chitosan and the like.

Moreover, the hydrogel will allow an efficient electrolytic connection and will avoid the use of microporous separators.

Figg. 2 to 4 show some sequences of manufacturing the electrodes 2, 3 by means of the method of the invention. This method essentially comprises a step a) of providing a nano-porous matrix 12 having at least one active surface 13 and a plurality of substantially cylindrical pores 14 with diameter φ of nanometric size, a step b) of applying a layer of a first material containing lead on the active surface 13 of the matrix 12 to define a current collector 5, 6 having a surface 9, 10 into contact relationship with the active surface 13 and a step c) of depositing an electrically active second material containing lead into the pores 14 and into contact relationship with the surface 9, 10 of the collector 5, 6 to define a plurality of nanowires 7, 8.

Finally, a step d) is provided for removing the nano-porous matrix 12 to obtain an electrode 2, 3 having a collector 5; 6 firmly coupled with the nanowires 7, 8.

Before the step of application of the first material to realize the collector 5, a step of adhesion of a metallic film, not shown, on the active surface 13 of the matrix 12 may be provided to make this latter electrically conductive.

The conductive film may be distributed on the surface 13 of the matrix 12 by several chemicals or physical techniques, also in a substantially discontinuous manner.

By way of an example, the adhesion of the film may be carried out by means of a process selected into the group comprising the electroless deposition, the void metallization and the like.

The film may have nanometric or micrometric size or and may be made of any metal, preferably of the type with high electrical conductibility, such as gold, platinum, palladium, copper, tin.

For manufacturing the positive electrode 2 or anode both the first and the second material will comprise or consist of lead dioxide.

For manufacturing the negative electrode 3 or cathode both the first and the second material will comprise or consist of metallic lead.

In both cases, the application b) of the first material and the deposition c) of the second material may be carried out by respective electrolytic depositions of the first and of the second material starting from an electrolytic solutions containing a predetermined rates thereof.

For example, the electrolytic solutions may be of the conventional type and may also comprise tetrafluoroboric acid.

However, according an alternative embodiment of the method, schematized in Fig. 4, for growing the nanowires 8 in metallic lead designed to form the negative electrode 3 an indirect growing process may be carried out which avoid the use of tetrafluoroboric acid.

In particular, according this alternative embodiment, the deposition of the metallic lead on the collector 6 will be carried out by electrolytic deposition of lead dioxide on a collector 6' made of lead dioxide to obtain nanowires 8' of lead dioxide and a subsequent step e) of electrochemical reduction to metallic lead of the intermediate nanowires 8', other than of the lead dioxide of the collector 6.

By this way, it will be possible to avoid the use of tetrafluoboric acid, allowing the use of matrixes 12 made of anodic alumina, which otherwise could not be used because they would be subject to a quick chemical dissolution by means of the same acid.

As matter of fact, the use of anodic alumina has been shown to be particularly advantageous as this kind of matrixes 12 allows nanowires 7, 8 with parallel morphology to be obtained and thus more easily adapted to be modulated in the height. However, other materials may be also used for the matrix 12, both ceramic or polymeric, i.e. titanium, polycarbonates and the like, depending from the desired morphology for the nanowires 7, 8.

In Fig. 5 some possible embodiments for the nanowires 7, 8 are schematically shown. For example, other than the already cited parallel nanowires, parallel nanotubes and interconnected wires may be obtained.

These latter will have higher reciprocal distance which allows to follow more easily the change of the volume associated to the charge and discharge cycles. Moreover, the soaking of nanowires 7, 8 with the electrolyte 4 will be promoted.

Figg. 6 to 9 show some images taken with a scanning electron microscope (SEM) of the nanowires of an electrode of the invention obtained using several types of matrixes. In particular, Fig. 6 and Fig. 7 respectively show parallel nanowires and nanotubes made of lead dioxide, Fig. 8 shows interconnected nanowires in lead dioxide, while Fig. 9 shows lead nanowires obtained by the indirect method with reduction from lead dioxide.

Generally, using nanowires will allow to obtain a large active surface and a corresponding high power density for the accumulator.

Moreover, it will be possible to customize the morphology of the nanowires according the specific application, differentiating it, for example, when the battery is of the high power type or of the low power type.

In this regard, the selection of the matrix 12 will be important as the features thereof will determine the diameter of the nanowires 7, 8 and, through the change of the time of electrodeposition, their height.

The selection of a matrix 12 of anodic alumina will also allow to have higher surface density than the other solutions and a better control of the diameter φ of the pores 14. For example, diameters between 20 nm and 200 nm may be obtained anodizing the aluminum in a solution containing 1.5 M of sulfuric acid, 0.5 M of oxalic acid, 0.4 M of phosphoric acid.

Further, the diameter may be controller by anodizing in mixed electrolytes containing aluminum hydroxide with concentration of 0.04 M, 0.095 M, 0.13 M.

The above disclosure clearly shows that the invention fulfills the intended objects and particularly the provision of an electrode for producing lead-acid batteries having high energy density and with increased performance, as a method for manufacturing an electrode using nanowires firmly connected to the charge collector in such a manner to increase its performance, in particular in term of electric capacity.

The electrode, the accumulator and the method according to the invention are susceptible to numerous modifications and variants, all falling within the inventive concept expressed in the enclosed claims. All details can be substituted by technically equivalent elements, and the materials can differ as required, without departing from the scope of the invention.

Even if the electrode, the accumulator and the method have been described with particular reference to the enclosed figures, the reference numbers are used for improving the comprehension of the invention and do not constitute any limitation of the claimed protective scope.

Claims

1. A lead electrode designed to be applied to a device with an electric power circuit and an electrolyte (4) for transporting electric charges, which electrode comprising a current collector (5, 6) in a first material containing lead designed to be placed in electric contact with the power circuit for transferring electric charges thereto;

characterized by comprising a plurality of nanowires (7, 8) in a second material containing lead, said nanowires (7, 8) being firmly coupled to said collector (5, 6) for chemically interacting with the electrolyte (4) and transferring electric charges onto said collector (5, 6).

2. Electrode as claimed in claim 1 , characterized in that said nanowires (7, 8) are realized by direct growing of said second material on said collector (5, 6).

3. Electrode as claimed in claim 2, characterized in that said first and said second material both comprise lead dioxide.

4. Electrode as claimed in claim 2, characterized in that said first and said second material both comprise metallic lead.

5. An accumulator, comprising:

- at least one positive electrode (2) made of a first electrically active material;

- at least one negative electrode (3) made of a second electrically active material;

- an electrolyte (4) for electrically connecting said electrodes (2, 3);

characterized in that said electrodes (2, 3) are according one or more of the preceding claims.

6. Accumulator as claimed in claim 5, characterized in that said electrolyte (4) comprises methanesulfonic acid supported by a polymer or co-polymer based hydro gel.

7. A method for manufacturing a lead electrode in accordance with any claims 1 to 4, comprising the following steps:

a) providing a nano-porous matrix (12) having at least one active surface (13) and a plurality of substantially cylindrical pores (14) with diameter (<f>) of nanometric size;

b) applying a layer of a first material containing lead on said active surface (13) of said matrix (12) to define a current collector (5, 6) having a surface (9, 10) into contact relationship with said active surface (13);

c) depositing an electrically active second material containing lead into said pores (14) and into contact with said surface (9, 10) of said collector (5, 6) to define a plurality of nanowires (7, 8);

d) removing said nano-porous matrix (12) to obtain an electrode (2, 3) having a collector (5, 6) firmly coupled with said nanowires (7, 8).

8. Method as claimed in claim 7, characterized in that step (b) of said application of a layer of a first material and said step (c) of deposition of said second material are carried out by respective electrolytic depositions of said first and said second material having predetermined rates in respective electrolytic solutions.

9. Method as claimed in claim 7, characterized in that said second material is metallic lead, said step (c) of deposition of said second material being carried out by electrolytic deposition of lead dioxide on said collector (6) and subsequent electrochemical reduction (e) to metallic lead of the electrodeposited lead dioxide.

10. Method as claimed in any claim 7 to 9, characterized by comprising, before said step (b) of application of said first material, a step of adhesion of a metallic film on said active surface (13) of said matrix (12).