GB2511743A

GB2511743A - Electrochemical cells

Info

Publication number: GB2511743A
Application number: GB1304302.1A
Authority: GB
Inventors: Craig Mclean-Anderson
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-03-11
Filing date: 2013-03-11
Publication date: 2014-09-17
Also published as: GB201304302D0

Abstract

A method of treating an electrochemical cell containing an electrolytic solution includes the step of dispersing particles of manganese dioxide within the electrolytic solution. Preferably the manganese particles are in fine powder form having a median diameter size of 10 to 110 microns. 0.5 to 3 mg/ml of electrolytic manganese dioxide may be added directly per ml of electrolyte or alternatively may be present in a dissolvable container such as gelatin for addition to the electrolyte. The electrolyte may further comprise filler such as sodium sulphate or potassium sulphate. The electrochemical cell may comprise a wet-cell lead-acid storage battery, such as a motor vehicle battery with multiple cells. In another embodiment the manganese dioxide particles may be added to a lead oxide paste to form an ingredient of a cathode of the battery. The manganese dioxide acts to react with the hydrogen ions and retard the dislodgement of lead oxide, thus increasing battery life and performance.

Description

ELECTROCHEMICAL CELLS

FIELD OF THE TNVENTTON

This invention relates to electrochemical cells and to methods of treating such cells.

BACKGROUND OF THE INVENTION

Electrochemical cells are used as a source of electrical energy. One of the most well known types of an electrochemical cell is the wet-cell lead-acid storage battery, commonly used to provide electrical energy to motor vehicles. A lead-acid storage battery conventionally comprises a plurality of anode plates typically of lead and a plurality of cathode plates typically of lead oxide immersed in an electrolytic solution which typically comprises 35% sulphuric acid and 651 water. Lead-acid batteries for motor vehicles generally have six galvanic cells in series, each cell typically providing 2 volts for a total of 12 volts at full charge.

During discharge of the battery, oxidation takes place at the anodes and reduction takes place at the cathodes, these reactions causing an electric current to flow between conductors to produce electricity to power inter alia the ignition and lighting systems of a motor vehicle.

One important advantage of a wet-cell lead-acid battery is that it can be recharged. A battery is recharged by applying an electric potential between the cathodes and anodes of the battery. A drawback with lead-acid batteries, especially if the battery is recharged rapidly, is that hydrogen gas tends to build up on the cathodes. This hydrogen gas build-up tends to reduce the surface area for ions in the electrolytic solution to come into contact with the cathode plates of the battery and this, in turn, leads to internal resistance within the battery. The presence of an internal resistance can cause heating or over-heating of the battery leading to a shortened battery life caused by, for example, warping of the anode lead plates of the battery. As a consequence, both the recharging process and the battery performance become less efficient.

Tt is also the case that as a lead-acid battery discharges, lead oxide (formed during discharge of the battery) can be dislodged from the electrode plates and precipitate to the bottom of the cell. This occurs narticularly when the battery is subject to internal resistance. In time the dislodged lead oxide can reach the electrodes where it forms a "dead short" that ends the life of the battery.

This is the primary limit to the life of a conventional lead-acid battery.

While the invention is described primarily in the context of lead-acid batteries, it is to be understood that the invention has broad application to all species of electrochemical cells and is not limited to lead-acid batteries. Thus, all references herein to "lead-acid" batteries apply equally to other species of electrochemical cells.

SUMMARY OF THE INVENTION

This invention sets out to address the issues raised above by reducing the build-up of hydrogen on the cathodes of an electrochemical cell and reducing the build-up of lead oxide within the cell.

Tn one aspect the invention provides a method of treating an electrochemlcal cell containing an electrolytic solution, the methcd including the step of dispersing particles of manganese dioxide within the electrolytic solution.

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Preferably, the manganese particles are in fine powder form, having a median diameter size of from 10 to 110 microns.

The manganese dioxide particles are preferably electrolytic manganese dioxide particles.

The electroohemical cell may comprise a wet-cell battery, preferably a wet-cell lead-acid storage battery. The battery preferably has multiple cells, typically (but not limited to) six cells. The electroohemioal cell could, however, comprise another species of battery.

In one arrangement, 0.5 to 3 mg per ml of electrolytic manganese dioxide per mIL of electrolyte is added to the electrolytic solutiou in each cell of the battery.

In an alternative arrangement, 2mg per ml of electrolytic manganese dioxide per ml of electrolyte is added to the electrolyte solution in each cell.

In a further alternative arrangement, 250mg of electrolytic manganese dioxide is added to each cell of the battery.

In another aspect, the invention provides an eleotrochemical cell treated by the method described in the preceding seven paragraphs.

The electrochemical cell may comprise a battery such as a wet-cell lead-acid storage battery.

In a further aspect, the invention provides an electrochemical cell additive, which comprises particulate manganese dioxide or a solution of particulate manganese dioxide present in a container for addition to the electrolyte solution of an electrochemical cell.

Preferably, the particles of manganese dioxide present in the container are particles of electrolytic manganese dioxide having a median diameter size of 10 to 110 microns (1x105 to 1,1 x104m).

Preferably, the container includes a predetermined amount of electrolytic manganese dioxide for treating a selected electrolytic cell. In a preferred arrangement the container includes 250 mq of electrolytic manganese dioxide for each cell of a six cell 12 volt lead cell motor vehicle battery, each cell of the battery including 120 ml electrolytic solution.

The container may comprise a capsule that is soluble in the electrolyte solution or a sachet made from a plastics material that can be emptied into the electrolyte solution of the lead-acid battery to which it is to be added. If the container is soluble it may be produced from gelatin.

In addition to manganese dioxide the container may include a filler which is soluble in the ie trolvoic rO±UnIH) The filler is preferably a sulphate, typically sodium or potassium sulphate.

In one arrangement, the sachet or capsule includes 250mg manganese dioxide and 250mg of filler.

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In another aspect, the invention provides a method of making a battery, said method including the step of adding electrolytic manganese dioxide particles to lead oxide paste which is to form a cathode in the battery.

The battery may comprise a lead-cell battery.

In a still further aspect, the invention provides a battery having one or more cathodes, the or each cathode including a lead plate which includes particles of manganese dioxide.

As mentioned previously, the invention concerns in one aspect an electrochemical cell which includes particles of manganese dioxide dispersed in the electrolytic solution of the cell. Typically, the manganese dioxide particles are in fine powder form and preferably have a median diameter size of between 10 and 110 microns (lxlcY5 tc 1,1 x l01m) The manganese dioxide particles are preferably electrolytic manganese dioxide particles, which disperse in the electrolytic solution of the electrochemical cell. These particles may initially be contained within a container which itself may be produced from a material which dissolves in the electrolytic solution of the chemical cell. Alternatively, the manganese dioxide particles may be present in the cathode plates of the electrochemical cell.

The particles of manganese dioxide are typically gamma type particles having a 92.65% purity and a median diameter size of 10 to 110 microns (lxlO to 1,1 x 10m) -Also as mentioned previously, eleotrochemioal cells in accordance with the invention include wet-cell lead-acid batteries including multiple cells, typically six cells, especially such batteries for motor vehicle use.

Where specific quantities are mentioned, it will be appreciated that the term substantially may be applied to these quantities to cover small variations.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described by way of example only with reference to the following embodiments of electrochernical cells in accordance with the invention and methods of treating such cells.

Tn a first embodiment of the invention, a six cell 12 volt wet-cell lead-acid storage battery containing an electrolytic solution of sulphuric acid and water was treated by adding to the electrolytic solution of each cell of the battery approximately 250 mg of electrolytic manganese dioxide in fine particulate powder form. This addition equated to 0.5 to 3mg per ml of electrolyte with the quantity of manganese dioxide added approximating to 2mg per ml of electrolyte for each battery cell. In this embodiment, the manganese dioxide was added through removable caps of the battery. For a sealed battery, the manganese dioxide can be added before sealing of the battery or by other means where the seal is broken and then resealed.

As mentioned above, in this embodiment of the invention, the manganese dioxide was added as a fine particulate powder. It could, alternatively be added within a sulphuric acid solution or within distilled water.

It has been established by the Applicant that the dispersion of particles of electrolytic dioxide into the electrolytic solution of a lead-acid battery treats the battery by alleviating heating of the battery during charging and rapid charging and thus increases battery life and performance. The electrolytic manganese dioxide (gamma type) used in this embodiment had a 92.65% purity.

After addition of the fine particulate manganese dioxide to the electrolytic solution, electrolytic manganese dioxide was found to be deposited onto the cathodes (the negative plates) of each cell of the battery. This deposited electrolytic manganese dioxide reacted with positive hydrogen ions in the electrolytic solution converting them to water, thereby preventing hydrogen gas from forming or significantly reducing the amount of hydrogen gas formed.

The consequence was that very little hydrogen gas was produced even during rapid charging of the battery thereby severely limiting internal resistance within the battery cells caused by hydrogen gas build-up and ensuring that the battery did not over heat.

This limit on the amount of hydrogen gas build up is especially important for sealed batteries where a valve would otherwise need to be fitted to release any significant build-up of hydrogen gas.

Thorough testing of the treated battery, established that the dispersion of particles of electrolytic manganese dioxide added to the electrolytic solution of the battery alleviated heating of the battery during charging and rapid charging thus leading to increased battery life and performance.

This testing also established that the presence of electrolytic manganese dioxide retarded the dislodgement of lead oxide from the electrodes thereby significantly reducing or eliminating the formation of a "dead short" in the cell.

Applicant has established that the amount of electrolytic manganese dioxide to be added to each electrolytic cell of a lead cell battery depends on the size of the battery (the volume of electrolyte in each cell, and the number of plates in eaoh cell) . Battery sizes generally range from a small battery for a car, which has 120 ml of electrolyte and 7 plates per cell, to a large battery for a truck that has 350 ml of electrolyte and up to 29 plates per cell.

The applicant has established that 250 mg of manganese dioxide is adequate for cells ranging from 120 ml to 350 ml. If necessary, more manganese dioxide may be added to cells having a greater volume than 350 ml.

In a second embodiment of the invention, electrolytic manganese dioxide particles were added to each of the six electrolytic cells of a normal 12 volt lead-acid oar battery. Each cell contained seven lead plates separated by isolators. The anodes within the cells were in the form of lead plates while the cathodes were formed by lead grills filled with lead oxide (Pb02) . Each electrolytic cell had a potential of 2 volts and the six cells were connected in series to generate 12 volts.

Each cell of the bactery contained 120m1 of electrolytic solution (an agueous solution containing sulphuric acid

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with a density of 1,250 gcm3) . 250mg of electrolytic manganese dioxide particles in powder form (i.e. having a median diameter of 10 to 110 microns (1 xlO to 1,1 x 1o 1m) ), was added to each cell so that the particles dispersed in the solution. Accordingly, 2,1 mg of electrolytic manganese dioxide was added per ml of electrolytic solution in the lead cells of the battery.

After the electrolytic manganese dioxide particles were added to the electrolytic solution, the clear electrolytic solution turned a muddy colour. The electrolytic solution then became clear again within about 24 hours of adding the electrolytic manganese dioxide indicating that the electrolytic manganese dioxide particles had settled on the cathode of each cell.

The treated lead-acid cell car battery was charged at a rapid rate for six to seven hours, with the temperature remaining 4 to 5 degrees centigrade cooler than would have been the case for an untreated battery. In tests conducted by the applicant, the treated battery charged at a rapid rate reached temperatures of 38 to 43 degrees centigrade during charging, while an untreated battery charged at the same rate, reached temperatures of 45 to 50 degrees centigrade.

Tests have also shown that the performance of a lead cell oar battery treated with manganese dioxide particles in accordance with this invention is better than that of a battery that has not been so treated. Applicant's tests further show that a battery treated in accordance with the invention took 1,5 hours longer to reach a full charge than an untreated battery but obtained a capacity of approximately 2,5 Ah (50 hours) greater than the untreated C) battery -In a third embodiment of the invention, particles of manganese dioxide for use in treating an electrolytic cell by the method described above were retained prior to use in a sealed container, the amount of manganese particles being predetermined for any particilar electrochemical cell such as a wet-cell lead-acid battery.

For example, for a cell of a six cell 12 volt lead-acid motor vehicle battery containing 120 ml of electrolytic solution, the container would contain 250 mg of electrolytic manganese dioxide particles for each cell of the battery.

Tn one arrangement, the container comprised a capsule made from a plastics material. The capsule may also contain a filler which may be soluble in sulphuric acid, such as a sulphate. Preferred sulphates are sodium and potassium sulphate but could also be magnesium sulphate.

The capsule will typically contain 250 mg manganese dioxide and 250 mg of the filler described above.

The container may be produced from gelatin, this dissolving when added to the electrolytic solution of the battery.

This is the preferred delivery method.

Specifically, a preferred capsule comprises 100 mg gelatin and contains 250 mg manganese dioxide and 250 mg of a filler described above.

Tn a fourth embodiment, the invention provides a method of manufacturing a lead-acid battery, this method including I0 the step of adding electrolytic manganese dioxide particles to lead oxide paste which defines part of the cathode plates of the battery.

Tn a fifth aspect, the invention provides for a lead-acid battery whose cathode plates contain particles of manganese dioxide.

As mentioned previously, electrolytic manganese dioxide for treating electrochemical cells (particularly lead-acid batteries) can conveniently be sold in capsules containing the required amount of electrolytic manganese dioxide for the cell of a particular battery. A customer may then purchase, for example, six capsules, open each capsule in turn and empty the contents of each capsule into a different cell of a normal six cell car battery. Typically, each capsule will contain 250 mg of manganese dioxide and 250 mg of a filler. The filler should be inert and preferably dissolve in the elecrrolytic solution. A preferred filler that dissolves in the electrolytic solution is a soluble sulphate such as potassium or sodium sulphate. The preferred filler is potassium sulphate.

Alternatively, the electrolytic manganese dioxide is contained in capsules that dissolve in a sulphuric acid solution (i.e. the electrolytic solution of a battery), thus releasing the electrolytic manganese dioxide particles to disperse in the electrolytic solution.

capsules in accordance with the invention are typically produced from gelatin, this dissolving in the electrolytic solution of a lead-acid battery; the presence of the gelatin has the added benefit of increasing the specific gravity of the electrolyte. A filler, typically 250 mg of

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potassium sulphate may also be included in the capsule. A preferred capsule is made from 100 mg of gelatine and contains 250 mg manganese dioxide and 250 mg potassium sulphate. When required, a capsule or sachet is simply added to each cell of the battery.

These capsules can readily be marketed to vehicle users in packs each containing an individual capsule for each cell of any given battery. it)

Also as mentioned above, electrolytic manganese dioxide particles may be added to the lead paste content of each cathode plate of a lead-acid battery during manufacture of the battery. Those added manganese dioxide particles present on the outer surface of the cathode plates reduce the formation of hydrogen gas in the same manner as described above leading to improved life and performance of the battery.

Advantages of electrochemical cells in accordance with the invention include an increased cell life and the fact that they can be charged more rapidly than presently known chemical cells without overheating. A further advantage is manganese dioxide is a surface attached particle which nay be separated from lead in the re-melting/recovery of lead from used batteries.

It will be appreciated that the foregoing is merely exemplary of chemical cells in accordance with the invention, and that modifications can readily be made without departing from the scope of the invention as set out in the appended claims.