Electrochemical cell additive

Abstract

A method of treating an electrochemical cell, preferably a lead-acid storage battery, in which particles of manganese dioxide having a median particle diameter size, D50, of from 25-40µm, and a D10 of

Description

FIELD OF THE INVENTION This invention relates to a method of treating an electrochemical cell, an electrochemical cell treated by the method, and an additive for treating an electrochemical cell. 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, electric vehicles such as forklifts and golf buggies, the un-interruptible power supply (UPS) for technology and telecommunications networks, and solar and wind-farm power storage. The application to a motor vehicle is used by way of example as follows. 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 65% 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. It 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 particularly 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. The Applicant previously undertook research and development work to find a solution to these problems and discovered that adding manganese dioxide particles into the electrolyte solution of a lead acid battery, or to the cathode of such an electrochemical cell, unexpectedly resulted in an improvement in the life span of the battery, and reduced the unwanted side effects of discharging / recharging described above. The details of this initial discovery are in the UK patent application published under GB 2511743. Although this development proved to be a step forward in addressing the above-described problems, there is still a need to further improve the efficiency of lead acid batteries that undergo multiple charging / discharging cycles, and to further reduce the problems caused by hydrogen gas build-up. 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 The Applicants have undertaken a further research and development program to address the issues raised above by further reducing the build-up of hydrogen on the cathodes of an electrochemical cell and further reducing the build-up of lead oxide within the cell. According to a first aspect of the invention, there is provided a method of treating an electrochemical cell containing an electrolytic solution, the method comprising: (a) dispersing particles of manganese dioxide within the electrolytic solution; wherein the manganese dioxide particles have a median particle diameter size, D5o, of from 25 to 40 pm, and a Dw of from 2 to 8 pm, and wherein the manganese dioxide particles, before dispersal within the electrolytic solution, are substantially free of sulphate. Such a method has been found to give rise to unexpectedly advantageous effects on the electrochemical cell. In particular, such a particle size distribution of small D5o and D10 values (meaning a large surface area), resulted in a more efficient electrochemical cell after repeat discharge / charging cycles than manganese dioxide having larger D5o and Dw values. D5o and Dw values are measured using laser diffraction particle size analysis. The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. Preferably, the particles of manganese dioxide are dispersed within the electrolytic solution before the electrolytic solution is introduced into the electrochemical cell. Pre-mixing the manganese dioxide particles in electrolyte solution, and then adding the pre-mixed solution into the electrochemical cell allows for an easier addition of the additive to the electrochemical cell. Preferably, the manganese dioxide particles have a median diameter size, D5o, of from 26 to 36 pm. The manganese dioxide particles also preferably have a Dw of from 3 to 7 pm. These D5o and Dw values provide the optimum particle size distribution of the manganese dioxide to be able to most effectively reduce hydrogen gas build up and increase the life span of the electrochemical cell. Preferably, the manganese dioxide particles have a BET surface area of from 28 to 40 m2 / g, more preferably from 30 to 38 m2 / g. Such a large BET surface area is optimum for the manganese oxide to effectively increase the life span of the electrochemical cell and reduce hydrogen gas build up. Preferably, the electrolytic solution comprises sulphuric acid, preferably in a concentration of from 2 to 10 mol / L, more preferably from 3 to 8 mol / L, 3.5 to 6 mol / L, 4 to 5.5 mol / L, and most preferably from 4.2 to 5.0 mol / L Such a concentration of sulphuric acid is optimum for efficient operation of a lead acid battery. The electrochemical cell may comprise a wet-cell battery, preferably a wet-cell lead-acid storage battery. The battery preferably has multiple cells, preferably six cells. The electrochemical cell could, however, comprise another species of battery. Preferably, 0.5 to 3 mg per ml, or more preferably about 2.0 mg per ml, of the manganese dioxide per ml of electrolyte is added to the electrolytic solution in each cell. Preferably, about 250mg of the manganese dioxide is added to each electrochemical cell. Preferably, the manganese dioxide particles before dispersal within the electrolytic solution are free of sulphate. In a further aspect of the present invention, there is provided an electrochemical cell treated by the method of the first aspect of the invention. In a further aspect of the present invention, there is provided a wet-cell lead-acid storage battery treated by the method of the first aspect of the invention. In a further aspect of the present invention, there is provided an electrochemical cell additive, which comprises particulate manganese dioxide, preferably being present in a container for addition to the electrolyte solution of an electrochemical cell; wherein the particulate manganese dioxide has a median particle diameter size, D5o, of from 25 to 40 pm, and a Dio of from 2 to 8 pm, wherein the particulate manganese dioxide is substantially free of sulphate, and preferably has a BET surface area of from 28 to 40 m2 / g. Such an additive in a container ready for addition straight to an electrochemical cell is useful for increasing the life span of the cell and reducing the undesirable effects associated with repetitive discharging / re-charging cycles. When the additive is in a container, the container preferably comprises, or is made from, gelatin. Such a container is particularly useful for addition of the additive to an electrochemical cell as it can dissolve in the electrolyte solution. Preferably, the container includes about 250 mg of the manganese dioxide for each cell of a six cell 12 volt lead cell motor vehicle battery, each cell of the battery including about 120ml electrolytic solution. This is the preferred quantity of additive to achieve the desired effects. In addition to manganese dioxide the container may include a filler which is soluble in the electrolytic solution. Preferably the container includes 250 mg of filler. In one arrangement, the container is a sachet that includes 250mg manganese dioxide and 250mg of filler. In another aspect of the present invention, there is provided a method of making a battery, said method including the step of adding manganese dioxide particles to lead oxide paste which is to form a cathode in the battery, wherein the manganese dioxide particles are in powder form and have a median particle diameter size, D5o, of from 25 to 40 pm, and a Dm of from 2 to 8 pm; wherein the manganese dioxide particles are substantially free of sulphate, and preferably have a BET surface area of from 28 to 40 m2 / g. The battery may comprise a lead-cell battery. The use of manganese dioxide particles having this specific particle size distribution in the lead oxide of a cathode has proved to be particularly effective at reducing hydrogen gas production. In a further aspect of the present invention, there is provided a battery having one or more cathodes, wherein one or more of the cathodes includes a lead oxide plate which includes particles of manganese dioxide; wherein the manganese dioxide particles are in powder form and have a median particle diameter size, D5o, of from 25 to 40 pm, and a Dio of from 2 to 8 pm; wherein the manganese dioxide particles are substantially free of sulphate, and optionally have a BET surface area of from 28 to 40 m2 / g. As mentioned, the addition of such manganese dioxide particles with the recited particle size distribution to the cathode of a battery results in unexpectedly improved battery life and reduced hydrogen gas production. 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. The manganese dioxide particles have a median particle diameter size, D5o, of from 25 to 40 pm, and a Dw of from 2 to 8 pm; wherein the manganese dioxide particles, before being dispersed into the electrolytic solution, are substantially free of sulphate, and optionally have a BET surface area of from 28 to 40 m2 / g. 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. The particles of manganese dioxide have a median particle diameter size, D5o, of from 25 to 40 pm, and a Dw of from 2 to 8 pm; and are substantially free of sulphate before addition to an electrolyte solution. The manganese dioxide particles preferably have a BET surface area of from 28 to 40 m2 / g. Also as mentioned previously, electrochemical 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. The term “substantially free” of sulphate preferably means that the particles of manganese dioxide contain less than 1wt% sulphate, preferably less than 100 ppm of sulphate, more preferably less than 10 ppm and most preferably less than 1ppm of sulphate. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The invention will now be described by way of example only with reference to the following embodiments of electrochemical cells in accordance with the invention and method of treating such cells. The invention will also be described in relation to the following nonlimiting figures, in which: Figure 1 is a voltage vs time profile for the first to five consecutive charge / discharge cycles of two comparative batteries and one inventive battery. Figure 2 is a voltage vs time profile for the twentieth cycle / discharge cycle of two comparative batteries and one inventive battery. Figure 3 shows the voltammograms as potential vs current at a lead electrode in 1.28 s.g. sulphuric acid of two comparative and one inventive electrochemical cells. In 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, the manganese dioxide powder having a median particle diameter size, D50, of from 25 to 40 pm, and a Dw of from 2 to 8 pm; and being substantially free of sulphate before addition to an electrolyte solution. 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 charging powder. It could, alternatively be pre-mixed and added within a sulphuric acid solution or within distilled water. It has been established by the Applicant that the dispersion of particles of electrolytic manganese dioxide having a median particle diameter size, D5o, of from 25 to 40 pm, and a Dio of from 2 to 8 pm; and being substantially free of sulphate before addition to an electrolyte solution, 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 of the invention 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 overheat. 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 (having the recited particle size distribution) 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 (having the recited D5o and Dw values) retarded the dislodgment of lead oxide from the electrodes thereby significantly reducing or eliminating the formation of a “dead short” in the cell. The 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 each 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 the manganese dioxide having the recited particle size distribution 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 (having the recited particle size distribution, and being free of sulphate) were added to each of the six 25 electrolytic cells of a normal 12 volt lead-acid car 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 (PbO2). 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 battery contained 120ml of electrolytic solution (an aqueous solution containing sulphuric acid with a density of 1,250gcm-3). 250mg of electrolytic manganese dioxide particles in powder form (i.e. having a median particle diameter size, D5o, of from 25 to 40 pm, and a Dw of from 2 to 8 pm; and being substantially free of sulphate) 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. 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 particular 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 (having the required particle size distribution, and being free of sulphate) for each cell of the battery. In a fourth embodiment, the invention provides a method of manufacturing a lead-acid battery, this method including the step of adding electrolytic manganese dioxide particles having a median particle diameter size, D5o, of from 25 to 40 pm, and a Dio of from 2 to 8 pm; and being substantially free of sulphate before addition to an electrolyte solution to lead oxide paste which defines part of the cathode plates of the battery. In a fifth aspect, the invention provides for a lead-acid battery whose cathode plates contain particles of manganese dioxide having a median particle diameter size, D5o, of from 25 to 40 pm, and a Dw of from 2 to 8 pm; and being substantially free of sulphate before addition to an electrolyte solution. 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. 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. When required, a capsule or sachet is simply added to each cell of the battery. Also as mentioned above, electrolytic manganese dioxide particles having the required particle size distribution and being free of sulphate may be added to the lead oxide 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. The smaller particle size and larger particle size distribution has shown to provide an unexpectedly improved life and performance of the battery compared to manganese dioxide particles having a larger particle size distribution and containing sulphate before addition to the electrochemical cell. 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. 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. EXAMPLES The invention will now be described further in relation to the following non-limiting examples. Two manganese dioxide additives were tested: - Additive 1 - manganese dioxide having a D5o greater than 40 pm, and a Dio greater than 8 pm, and containing approximately 50wt.% sulphate. - Additive 2 - manganese dioxide having a median particle diameter size, D5o, of between 25 and 40 pm, and a Dw of between 2 and 8 pm; and being substantially free of sulphate. Example 1 - Battery Cycling Each additive was added to the electrolyte solution in a lead acid battery. These were compared with an untreated battery (having no additive at all). The batteries were subjected to charge / discharge cycling using current densities between C / 14 (0.5 A) and 1.5C (10.5 A). During cycling, the voltage and efficiency was monitored along with cell temperature and volume of gas evolved. Measurements were obtained using a Basytec batter analyser operating with associated software. The batteries were cycled using the following parameters: charge at C / 14 rate to 15 V cut-off followed by discharge at C / 3 rate for 30 minutes. The batteries were subjected to 20 full cycles. In addition, charges at C / 7, C / 3 and 1.5C rates were performed. On addition of each additive (comparative, 1, and inventive, 2) a spike in temperature was observed and the initial charge / discharge cycle was significantly shortened. However, following the initial cycle the batteries showed more typical voltage vs. time profiles. The voltages were slightly lower during both charging and discharging periods. Reference is made to Figure 1, which shows the voltage vs. time profiles for the first five consecutive cycles of the three types of batteries (the untreated battery, and the batteries treated with comparative additive 1, and inventive additive 2). Figure 2 shows the 20’th cycle of each battery type. As shown in Figure 2, over a period of 20 discharge / charge cycles, in comparison to the untreated battery, the battery treated with inventive additive 2 showed a 5% increase in Whr efficiency, compared to an increase in Whr efficiency of 4% for the battery treated with comparative additive 1. Both batteries treated with additive 1 and additive 2 showed an average 2% reduction in volume of gas evolved during the charging periods. The temperature of the batteries was measured during the charge and discharge cycling experiments using a Fluke dual input temperature probe. At the highest charge rate used (1.5C), the largest temperature difference of 6°C (over the untreated battery) was observed, which was for inventive additive 2. Thus, Example 1 shows that the inventive additive is able to reduce the temperature of the battery more than the comparative additive, provide a good reduction in gas evolution, and provide an increased efficiency of the battery compared to the comparative additive. Example 2 - Cyclic Voltammetry The same 3 additive samples as used in Example 1 were tested by cyclic voltammetry (i.e. comparative additive 1, inventive additive 2, and a comparative sample without any additive). Linear sweep voltammograms were recorded using a standard three-compartment glass electrochemical cell. A metallic lead working electrode, platinum counter electrode and saturated calomel reference electrode were fitted into the cell, which was filled with 1.28 s.g. sulphuric acid. Voltammetric measurements were carried out using a Princeton Applied Research model 263A potentiostat / galvanostat. The potential was swept at 100 mV s-1 from 0.0 V vs. SCE to -1.5 V vs. SCE. This potential range corresponds to the voltages associated with the negative electrode in a lead acid battery. Separate scans were performed using standard acid (comparative untreated example) and with the inclusion of one of two separate additives (i.e. comparative additive 1 and inventive additive 2) in the electrolyte. Figure 3 shows the voltammograms for each of the three electrolytes. The x-axis shows the applied potential, E vs SCE in V, and the y-axis shows the current, I, in A. At zero volts, a layer of lead sulphate will be present on the surface of the lead electrode. Moving towards negative potentials, with each electrolyte there is a reduction wave at circa -0.7 V vs. SCE which corresponds to conversion of lead sulphate to metallic lead. This is equivalent to the charging reaction in a lead acid battery. At negative potentials, the current increases rapidly as hydrogen evolution begins. It can be seen from the voltammograms in Figure 3 that the onset of bulk hydrogen evolution occurs at negative potentials when the additives are present. This indicates the inhibition of hydrogen evolution by the additives.

Claims

1. A method of treating an electrochemical cell containing an electrolytic solution, the method comprising:(a) dispersing particles of manganese dioxide within the electrolytic solution;wherein the manganese dioxide particles have a median particle diameter size, D50, of from 25 to 40 pm, and a D10 of from 2 to 8 pm, and wherein the manganese dioxide particles, before dispersal within the electrolytic solution, are substantially free of sulphate.

2. The method according to claim 1, wherein the particles of manganese dioxide are dispersed within the electrolytic solution before the electrolytic solution is introduced into the electrochemical cell.

3. The method of claim 1 or claim 2 wherein the manganese dioxide particles have a median diameter size, D50, of from 26 to 36 pm.

4. The method of any preceding claim, wherein the manganese dioxide particles have a D10 of from 3 to 7 pm.

5. The method of any preceding claim, wherein the manganese dioxide particles have a BET surface area of from 28 to 40 m2 / g, preferably from 30 to 38 m2 / g.

6. The method of any preceding claim, wherein the electrolytic solution comprises sulphuric acid, preferably in a concentration of from 2 to 10 mol / L.

7. The method of any one of the preceding claims wherein the electrochemical cell comprises a wet-cell battery, preferably a wet-cell lead-acid storage battery.

8. The method of claim 7 wherein the battery is a motor vehicle battery having multiple cells, preferably six cells.

9. The method of any one of the preceding claims wherein 0.5 to 3mg per ml of the manganese dioxide per ml of electrolyte is added to the electrolytic solution in each electrochemical cell.

10. The method of claim 9 wherein about 2 mg per ml of the manganese dioxide per ml of electrolyte is added to the electrolyte solution in each electrochemical cell.

11. The method of any one of the preceding claims wherein about 250 mg of the manganese dioxide is added to each electrochemical cell.

12. The method of any one of the preceding claims, wherein the manganese dioxide particles before dispersal within the electrolytic solution are free of sulphate.

13. An electrochemical cell treated by the method of any one of claims 1 to 11.

14. A wet-cell lead-acid storage battery treated by the method of any one of claims 1to 11.

15. An electrochemical cell additive which comprises particulate manganese dioxide; wherein the particulate manganese dioxide has a median particle diameter size, D5o, of from 25 to 40 pm, and a Dio of from 2 to 8 pm, wherein the particulate manganese dioxide is substantially free of sulphate, and preferably has a BET surface area of from 28 to 40 m2 / g.

16. An additive as claimed in claim 15 wherein the particulate manganese dioxide is present in a container for addition to the electrolyte solution of an electrochemical cell, preferably wherein the container comprises, or is made from, gelatin.

17. An additive as claimed in any one of claims 15 to 16 wherein the container includes about 250 mg of the manganese dioxide for each cell of a six cell 12 volt lead cell motor vehicle battery, each cell of the battery including about 120 ml electrolytic solution.

18. An additive as claimed in any one of claims 15 to 17 wherein in addition to manganese dioxide the container includes a filler which is soluble in a electrolytic solution, preferably wherein the container includes 250 mg of filler.

19. A method of producing a battery which includes the step of adding manganese dioxide particles to lead oxide paste which is to form an ingredient of a cathode of the battery;wherein the manganese dioxide particles are in powder form and have a median particle diameter size, D50, of from 25 to 40 pm, and a D10 of from 2 to 8 pm; wherein the5 manganese dioxide particles are substantially free of sulphate, and preferably have a BET surface area of from 28 to 40 m2 / g.

20. A battery having one or more cathodes, wherein one or more of the cathodes includes a plate which includes particles of manganese dioxide;10 wherein the manganese dioxide particles are in powder form and have a medianparticle diameter size, D50, of from 25 to 40 pm, and a D10 of from 2 to 8 pm; wherein the manganese dioxide particles are substantially free of sulphate, and optionally have a BET surface area of from 28 to 40 m2 / g.17

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