RECHARGEABLE MANGANESE DIOXIDE ELECTRODE MATERIAL

Abstract: An improved manganese dioxide electrode material is disclosed. The improved electrode material is one which may be cycled between discharged and charged states at higher utilization of reactant and for a substantially greater number of cycles than previously known manganese di­ oxide electrode materials. The improved manganese di­ oxide electrode material is characterized in that a heavy me­ tal selected from the troup comprising of bismuth, lead, and mixtures of bismuth and lead is included in the electrode material.

Description: RECHARGEABLE MANGANESE DIOXIDE ELECTRODE MATERIAL-I TECHNICAL FIELD This specification is directed to a development in rechargeable manganese dioxide electrode materials. In particular, the development is- one which results in a rechargeable managanese dioxide electrode material making such material initially rechargeable up to about 90% of its theoretical two electron capacity. After 200 cycles, the electrode still retains above 40% of its theoretical two electron capacity. BACKGROUND ART AND PRIOR ART STATEMENT The manganese dioxide electrode has found wide application as a primary battery. One of the applications of such an electrode is in batteries used for a flashlight. The use of a flashlight is characteristic for an energy storage problem on a small scale: chemically stored energy is converted into electricity at will. We pay a high price for this conversion convenience. The throw-away battery may cost ten times the energy it stores simply to manufacture the battery. This is an important economic point of view considering that billions of these types of throw-away batteries are produced yearly throughout the world. It is already known that manganese dioxide cells of the alkaline version can be recharged a limited number of times so long as the cells are not discharged on their discharge cycle more than about 15% of their -two electron capacity. Normally these cells can be recharged at this very reduced fraction of their two electron capacity only about 50 cycles or so. Thus, it is known that certain manganese dioxide cells of the alkaline version can be recharged for approximately 50 cycles or so if the reactant (manganese dioxide) utilization does not exceed about 15%. Manganese dioxide electrodes of our invention can be discharged a substantially greater amount than known cells and may go through the discharge/recharge cycle a significant number of cycles more than the presently known cells. In a cell having a manganese dioxide electrode, the homogeneous reaction mechanism of the first step of the manganese dioxide discharge is unique. The introduction of protons in this discharge is largely reversible so long as the expansion of the structure can be kept small. If the depth of discharge is limited to about 10-15% of the two electron capacity of the manganese dioxide electrode, the electrode may be recharged to full capacity for approximately 50 cycles or so as has been stated above. This is technology which is known today. With the improved rechargeable manganese dioxide electrode material of our invention, we have built electrodes which can be initially discharged. up to 90% of their total two electron capacity. We have been able to cycle such electrode containing cells in excess of 200 cycles between a discharged and recharged condition before their capacity dropped to about 40% if we limit the depth of the theoretical two electron capacity. A search was conducted on the subject matter of this specification in the U.S. Patent and Trademark Office. As a result of that search, the following U.S. patents were cited as of interest: 3,066,179; 3,433,687; 3,615,833; 3,915,837; 4,009,052; 4,041,220; 4,049,887; 4,121,018; 4s125,687; and 4,286,589. After reviewing the patents, we were of the opinion that none of them disclosed the rechargeable manganese dioxide electrode material which is to be disclosed in this specification. U.S. patent 4,286,589 did disclose an alkaline manganese dioxide cell which can be repeatedly recharged from a discharged state. This cell is made by chemically contacting the manganese dioxide with free negative ions of at least one weak acid that does not, in conditions prevailing in the cell, form salts with the manganese, the crystals of which contain water of crystallization. The patent disclosed that suitable weak acids were silicic, carbonic, boric, cyanic and acidic acids and hydrogen sulfide. Although we are aware of what is going on in the development of rechargeable manganese dioxide electrode materials, we are unaware of any prior art which is relevant to the improved manganese dioxide electrode material of our invention. The utility and desirability of our improved manganese dioxide electrode material is set forth out in greater detail hereinbelow. DISCLOSURE OF THE INVENTION This invention relates to a rechargeable manganese dioxide electrode material. The improved manganese dioxide electrode material is a material which can be cycled to greater discharge depths while being recharged from such discharge depths many times more than any previously known manganese dioxide electrode material. In accordance with our invention, our improved manganese dioxide electrode material is characterized in that a heavy metal selected from the group comprising bismuth, lead, and mixtures of bismuth and lead, is included as an active element in the electrode material. The included bismuth, lead, and mixtures of bismuth and lead in the manganese dioxide electrode material is "active" within our definition in that the heavy metal vastly improves rechargeability and improves the depth from which the electrode material can be recharged as well as the number of times that the electrode material may be recharged. This new manganese dioxide electrode material leads tc a practical and efficient rechargeable cell when the electrode material is coupled with another electrode material to form such a cell. We have found that the introduction of bismuth, lead, and mixtures of bismuth and lead into the manganese dioxide electrode vastly improves not only the depth of discharge from which the electrode material may be recharged, but also the number of times that the electrode material may be discharged and thereafter recharged while retaining high capacity. Substantial improvement of the reactant utilization as well as of the number of times the cell can be cycled comes about on#ly when bismuth, lead, or mixtures of bismuth and lead are included as an active element in the electrode material. Materials such as potassium, sodium, calcium, manganese, copper, zinc, aluminum, and silver were tested and found not to be of any significant value in improving the rechargeability of a manganese dioxide electrode. According to a preferred, but not limiting, embodiment of the improved manganese dioxide electrode material of this invention, the material is characterized in the following manner. Prior to forming the manganese dioxide electrode material, a chemically reactable form of manganese dioxide is chemically reacted with a metal salt in which the metal is a heavy metal selected from the group of heavy metals consisting of bismuth, lead, and mixtures of bismuth and lead, thereby to form a heavy metal salt of manganese dioxide. The heavy metal salt of manganese dioxide is used with other materials such as graphite powder or carbon black to form the improved manganese dioxide electrode material having the heavy metal included as an active element thereof. This heavy metal containing manganese dioxide electrode material can be formed into a cell, the cell being one which may be discharged to a substantial extent of its two electron capacity for a substantial number of discharge/recharge cycles, the extent of discharge and number of discharge cycles being substantially in excess of those characteristics for presently known manganese dioxide electrode containing cells. Another, but not limiting, embodiment of an improved manganese dioxide electrode material is taught in this specification. In this embodiment, the improved manganese dioxide electrode material is characterized in that prior to forming the electrode material, an ion exchangeable form of manganese dioxide is ion exchanged with a solution containing a heavy metal ion selected from the group of heavy metal ions consisting of bismuth, lead, and mixtures of bismuth and lead. This ion exchange operation forms a heavy metal salt of manganese dioxide. The heavy metal salt of manganese dioxide is used with other materials such as graphite powder or carbon black to form the improved manganese dioxide electrode material having the heavy metal included as an active element thereof. As noted above, the heavy metal containing manganese dioxide electrode material is one which has significantly superior qualities with respect to the utilization of the reactant and number of cycles of discharge/recharge over known rechargeable manganese dioxide electrode containing cells. BRIEF DESCRIPTION OF THE DRAWING The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description and specific embodiments when read in connection with the accompanying drawing which is a graph of the Percent of Uilization of a Reactant In a Non-Optimized Electrode as a Function of Cycle Number. BEST MODE AND INDUSTRIAL APPLICABILITY The following description is what we consider to be a preferred embodiment of our improved manganese dioxide electrode material. The following description also sets forth what we contemplate to be the best mode of carrying out the manufacture of the improved manganese dioxide electrode material in a chemical reaction manner to form such an improved manganese dioxide electrode material. This description of the preferred embodiment is not intended in any manner to be a limitation upon the broader principles of this improved electrode material. As stated above, we have found that if a manganese dioxide electrode material is characterized in that a heavy metal selected from the group consisting of bismuth, lead, and mixtures of bismuth and lead is included as an active element therein, the manganese dioxide electrode has certain advantageous characteristics. These advantageous characteristics are that the number of cycles the electrode can undergo maintaining high reactant utilization is substantially greater than it was observed for any previously known manganese dioxide rechargeable electrode materials. Such advantages will be pointed in greater detail hereinbelow. In accordance with a preferred embodiment of this specification, a skilled artisan will be taught what we classify as a "chemical method" for preparing the improved manganese dioxide electrode material in accordance with our invention. Our copending U.S. patent application Serial No. ¯¯¯¯¯¯¯¯¯¯¯, , filefiled on even date herewith, sets forth what we classify as a "physical method" for preparing a manganese dioxide electrode material which is in accordance with the teachings of our invention. The present application contains the generic claims to the improved manganese dioxide electrode material along with claims directed to the chemical method for preparing the improved manganese dioxide electrode material. Examples 1. Lead-Manganese Dioxide Complex This example will show the invention in the improved manganese dioxide electrode material by illustrating a material in which lead is included as an active element in the manganese dioxide electrode material. The material illustrated is prepared by a chemical method. The precursor NaMnxOy.ZH2O was prepared according to the procedure given by Wadsley in JACS, Vol. 72, 1781 (1950), as follows. Solution A formed of 110 grams NaOH in 500 ml H2O was cooled in an ice bath before being added slowly into a solution B of 60g Mn(NO3)2.6 1120 in 400 ml of water that was held at 3-50C. The Mn(OH)2 that precipitated out was slowly oxidized by passing oxygen through a fritted glass tube into the solution still held at 3-50C for five hours with agitation followed by standing overnight. The solid was suction filtered and was washed 10 times with distilled water. It was dried over a warm plate at approximately 500C for one day. The product was analyzed by ICP-AES and found to contain 48% Mn and 7.5% Na. An x-ray diffraction pattern showed that the major corponcnts are (Na.Mn)4.Mnl2028 8H2ot Na4Mn14O27.9H2O, and a minor amount of Hausmanite. The surface area was determined by Krypton adsorption as 50 m2/g. The complex oxide, PbMnxOy.ZH2O, was prepared by an ion exchange method. This is the heavy metal (lead) containing manganese dioxide material to be used as the improved manganese dioxide electrode material. One gram of the precursor, as prepared above, was shaken in 10 ml of solution containing 1.9g Pb(NO3)2 (about five times of the stoichiometric amount required) for 16 hours. After exchange, the solid was filtered and repeatedly washed with distilled water. It was dried again at temperatures slightly above 500C. 20 milligrams of the lead manganese dioxide compound was ground for 18 hours in a pestle and mortar. This ground material was mixed for about 10 minutes with graphite (SP-1) powder in a spex-mixture mill. One gram of 9M KOB solution containing 4% by weight of an organic gelling agent was then added and a paste -prepared by shaking for an additional five minutes. Electrodes were prepared by sandwiching about 200 milligrams of the prepared paste between two platinum gauze current collectors, themselves being sandwiched between two sheets of Celgard No. 3401 separators. The paste electrode (0.75 inches in diameter) was further wrapped in two additional sheets of Celgard No. 3401 separator and epoxyed on one side with Epoweld 3673 cement. The electrode was inserted in a 0.75 inch diameter (ID) teflon tube, pressed at about 10 pounds per square inch, and allowed to cure for 24 hours at room temperature. The electrode was cycled at 0.5 mV/second in the range -0.6V to +0.2V (with respect to a Hg/HgO electrode). The results of this cycling are shown in the drawing as curve No. 1. This curve shows that when lead is used, the improved manganese dioxide electrode material may be recycled a substantial number of times in excess of 50 cycles and may be discharged in its highly cycled state to about 30% or more of its two electron capacity. This is substantially greater than known rechargeable manganese dioxide electrode materials which may be recycled at a maximum of only about 50 times with a discharge utilization of approximately 10-15% of its two electron capacity. 2. Bismuth Manganese Dioxide Complex This example will show the invention in the improved manganese dioxide electrode material by illustrating a material in which bismuth is included as an active element in the manganese dioxide electrode material. The material illustrated is also prepared by a chemical method. The precursor NaMnxOy.ZH2O complex was prepared in the same manner as discussed above in Example 1. This precursor was ion exchanged with bismuth in the following manner to form the heavy metal (bismuth) containing manganese dioxide electrode material to be used as the improved manganese dioxide electrode. A solution of 14.69 Bi(NO3)3.5H2O and 10 ml concentrated nitric acid in 100 ml of water was used for exchange. Dilute nitric acid instead of water was used to wash the filtered solid. The product contains 50% manganese, 12% bismuth, and less than .2% sodium. X-ray diffraction identified the product structure to be isomorphous to that of Mn7013.5H2O. 15 millig r aars of the bismuth/manganese dioxide compound was ground for 18 hours in a pestle and mortar and then was mixed with graphite (SP-1) powder for approximately 10 minutes in a spex-mixer mill. 125 mg of 9M KOH solution containing 4% by weight of an organic gelling agent was then added and a paste obtained by shaking for an additional five minutes. Approximately 0.020" thick by 0.75" in diameter modified manganese dioxide electrodes were prepared using about 200 mg of this paste according to the procedure described in Example 1. The results of cycling this electrode under the same conditions as in Example 1 are shown in the figure as curve 2. When bismuth is used as the heavy metal additive to the manganese dioxide electrode material, the graph of Figure 2 shows significant improvement is obtained over known commercial rechargeable electrode materials while very good improvements are also obtained over lead containing electrode material as depicted in curve No. 1. For example, at 100 cycles, the non-optimized bismuth containing electrode may still have a 55% or greater utilization based on its two electron capacity. 3. No Heavy Metal Addition-Manganese Dioxide By Itself The purpose of this example is to illustrate that when no heavy metal addition of the type described above is made to an International Sample No. 1 of manganese dioxide, the utilization and recharge capabilities of the cell are extremely poor. The procedure of Example '1 is carried out except that there is no need to react any elements in order to place bismuth or lead in conjunction with the manganese dioxide. Thus the manganese dioxide is used as described in the latter portion of Example 1 in order to manufacture an electrode which is subsequently made into a cell. The manganese dioxide used was a gamma manganese dioxide (#nternational Common Sample No. 1). A cell produced using this material resulted in the data shown in the drawing as curve No. 3. This curve shows that the material can be cycled very little, and that very little cycling causes a disastrous loss in the utilization of the material based upon the percentage discharge one can obtain on the two electron capacity of the material. 4. No Heavy Metal Addition-Manganese Dioxide By Itself The purpose of this example is to illustrate that when no heavy metal addition of the type described above is made to an International Sample No. 8 of manganese dioxide, the utilization and recharge capabilities of the cell are extremely poor. The procedure of Example 4 was repeated except that the gamma manganese dioxide used was an International Common Sample No. 8. The capacity of this electrode material as a function of cycles number is shown in the drawing as curve No. 4. Once again, curve No. 4 shows an extremely poor material with respect to its ability to be recharged for a number of discharge/recharge cycles. General Factors to be Taken Into Account In order to make the improved manganese dioxide electrode material, it is necessary to include in that material fine powdered carbon or graphite to aid in the electronic conductivity of the material. While the examples have talked of substituting either lead or bismuth into the manganese dioxide structure, mixtures of lead and bismuth may be substituted. An organic binder and/or gelling agent is also used in formation of the manganese dioxide electrode material. Normally the organic gelling agent is made up of 4% by weight of car box metal cellulose in 96% by weight of 9M SOH. It may be seen from the information reported above and the material presented graphically in the Figure that the inclusion of bismuth, lead, or mixtures of bismuth and lead in the manganese dioxide electrode brings about a rechargeability which is not seen in the manganese dioxide electrode by itself. This rechargeability enhancement is unique for the bismuth, lead, and bismuth/lead mixtures.

Claims: CLAIMS 1. An improved manganese dioxide electrode material characterized in that a heavy metal selected from the group consisting of bismuth, lead, and mixtures of bismuth and lead is included as an active element in said electrode material. 2. An improved manganese dioxide electrode material characterized in that prior to forming said electrode material a chemically reactable form of manganese dioxide is chemically reacted with a metal salt in which the metal is a heavy metal selected from the group of heavy metals consiting of bismuth, lead, and mixtures of bismuth and lead, thereby to form a heavy metal salt of manganese dioxide, said heavy metal of manganese dioxide beinn used with other materials such as graphite powder or carbon black to form said improved manganese dioxide electrode material having said heavy metal included as an active element thereof. 3. An improved manganese dioxide electrode material characterized in that prior to forming said electrode material an ion exchangeable form of manganese dioxide is ion exchanged with a solution containing a heavy metal ion selected from the group of heavy metal ions consisting of bismuth, lead, and mixture of bismuth and lead, thereby to form a heavy metal salt of manganese dioxide, said heavy metal salt of manganese dioxide being used with other materials such as graphite powder or carbon black to form said improved manganese dioxide electrode material having said heavy metal included as an active element thereof.

Inventors: GUPTA, NIRMAL KUMAR, KUMMER, JOSEPH TALBOT, WROBLOWA, HALINA STEFANIA, YU YAO, YUNG-FANG
Applicants: FORD FRANCE SOCIETE ANONYME, FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1984
Main classification: H01M4
IPC codes: C01G45, H01M4