AU665462B2 - Process for producing manganese dioxide - Google Patents

Abstract

The invention relates to the manufacture of manganese dioxide by a chemical process. The resulting manganese dioxide product takes the form of particles characterized by filament-like protrusions jutting out from its surface. The manganese dioxide particles having such surface features can be manufactured by reacting manganese sulfate with sodium peroxodisulfate in an aqueous solution. The process can be controlled to yield high density manganese dioxide. The manganese dioxide formed in the process can be deposited directly onto the surface of electrolytic manganese dioxide (EMD). The manganese dioxide product the is particularly suitable for use as a cathode active material in electrochemical cells.

Description

ANNOUNCEMENT OF ThE LATER PUBLICATION OF INTERNATIONAL SEARCH REPORTS 0tp

PCT

INTERNATIONAL APPLICAlION PUBLISHED UNDER IHE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 5 COIG 45/02 (1I) International Publication Number: A (43) International Publication Date: WO 94/08056 14 April 1994 (14.04.94) I (21) International Application Number: (22) International Filing Date: Priority data: 952,034 28 Septer PCT/US93/07333 4 August 1993 (04.08.93) nber 1992 (28.09.92) US (71) Applicant: DURACELL INC. [US/US]; Berkshire Corporate Park, Bethel, CT 06801 (US).

(72) Inventors: WANG, Enoch, 1. 70 Elizabeth Street No. 9, Attleboro, MA 02703 LIN, Lifun II Sunnyside Lane, Lincoln, MA 01773 BOWDEN, William, L.

28 Cathedral Circle, Nashua, NH 03063 (US).

(74) Agent: JOSEPHS, Barry. Duracell Inc., 255 Highland Ave., Needham, MA 02194 (US).

(81) Designated States: AU, BB, BG, BR, CA, CZ, FI, HU, JP, KP, KR, LK, MG, MN, MW, NO, NZ, PL, RO, RU.

SD, SK, UA, European patent (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OAPI patent (BF, BJ, CF, CG, Cl, CM, GA, GN, ML, MR.

NE, SN, TD, TG).

Published With international search report.

(88) Date of publication of the international search report: 27 July 1995 (27.07.95) 665462 (54)Title: PROCESS FOR PRODUCING MANGANESE DIOXIDE (57) Abstract The invention relates to the manufacture of manganese dioxide by a chemical process. The resulting manganese dioxide product takes the form of particles characterized by filament-like protrusions jutting out from its surface. The manganese dioxide particles having such surface features can be manufactured by reacting manganese sulfate with sodium peroxodisulfate in an aqueous solution. The process can be controlled to yield high density manganese dioxide. The manganese dioxide formed in the process can be deposited directly onto the surface of electrolytic manganese dioxi!! (EMD). The manganese dioxide product is particularly suitable for use as a cathode active material in electrochemical cells.

-1- PROCESS FOR PRODUCING MANGANESE DIOXIDE The invention relates to a process for production of manganese dioxide, particularly for use as a cathode active material in electrochemical cells.

Manganese dioxide is commonly employed as a cathode active material in commercial batteries. Such manganese dioxide has been derived from naturally occurring manganese dioxide (NMD) and synthetically produced manganese dioxide which includes electrolytic manganese dioxide (EMD) and chemical manganese dioxide (CMD). NMD has a high impurity content and cannot be employed in alkaline or lithium cells.

10 EMD is typically manufactured by direct electrolysis of manganese sulfate and sulfuric acid. It's high purity and high density make gamma manganese dioxide desirable for use as a cathode active material in alkaline and lithium cells.

According to a first aspect of the invention, there is provided a process for manufacture of gamma manganese dioxide comprising t& e steps of: 15 a) reacting MnSO 4 and Na 2

S

2 08 in a solution to produce a reaction product mixture comprising a precipitate of gamma Mn02 comprised of particles characterised by filament-like protrusions radiating outwardly from the surface of said particles; b) removing the gamma MnO 2 precipitate from said reaction product mixture; and c) drying said precipitate.

According to a second aspect of the invention, there is provided a hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of electrolytic manganese dioxide (EMD), wherein said gamma MnO 2 material has filament-like protrusions 17876.OO.DOCjmIn -laradiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 2,000 times actual size.

According to a third aspect of the invention, there is provided a hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of carbon material selected from the group consisting of graphite and carbon black, wherein said gamma MnO 2 material has filament-like protrusions radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 2,000 times actual size.

According to a fourth aspect of the invention, there is provided a hybrid MnO 2 10 material comprising gamma MnO 2 deposited on the surface of another material wherein said gamma MnO 2 material has filament-like protrusions radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 2,000 S• times actual size.

According to a fifth aspect of the invention, there is provided an electrochemical 15 cell having MnO 2 cathode active material in said cell, characterised in that at least of said MnO 2 material comprises gamma MnO 2 particles wherein said gamma MnO 2 particles have filament-like protrusions radiating outwardly from the surface of said particles, said filament-like protrusions being visible at a magnification of between 200 and 2,000 times actual size.

According to a sixth aspect of the invention, there is provided an electrochemical cell having MnO 2 cathode active material in said cell, characterised by said electrochemical cell having an anode comprising lithium, and further characterised by A said MnO 2 material comprising gamma MnO 2 particles having filament-like protrusions 17876-00 DOC/mlm I lsu t~sl,~ III-L~;IP -Ibradiating outwardly from the surface of said particles, said filament-like protrusions being visible at a magnification of between about 200 and 2,000 times actual size.

According to a seventh aspect of the invention, there is provided a hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of electrolytic manganese dioxide (EMD), 1 herein said gamma MnOz material has filament-like protrusions radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 9,850 times actual size.

The features of the product of the invention will be better appreciated with reference to the following figures: 10 Fig. 1A is an electron photomicrograph showing the MnO 2 particles from the process of the invention carried out at slow rate of heating of reactants.

Fig. 1B is an electron photomicrograph of the particles in Fig. 1A enlarged to show the filament-like surface protrusions.

Fig. 2A is an electron photomicrograph showing smaller sized MnO 2 particles 0 15 from the process of the invention carried out at fast rate of heating of the reactants.

o••oo 17876-00 DOC/mlm I WO 94/08056 PCT/US93/07333 Fig. 2B is an electron photomicrograph of the particles in Fig. 2A enlarged to show the filament-like surface protrusions.

Fig. 3A is an electron photomicrograph of EMD particles (prior art).

Fig. 3B is an electron photomicrograph of the EMD particles in Fig. 3A enlarged to show the characteristically irregular particle shape and smooth surface structure.

Fig. 4A is an electron photomicrograph of EMD particles coated with MnO 2 produced by the process of the invention

(P-CMD).

Fig. 4B is an electron photomicrograph of coated EMD particles in Fig. 4A enlarged to show the filament-like surface protrusions.

Fig. 5A is an electron photomicrograph of prior art chemical manganese dioxide (CMD) particles.

Fig. 5B is an electron photomicrograph of the particles in Fig. 5A enlarged to show surface features.

Fig. 6A is a graphical plot of the voltage profile (voltage versus service hours) in an alkaline AA cell at 3.9 ohm constant load, comparing performance of the P-CMD with conventional EMD.

Fig. 6B is a graphical plot of the voltage profile (voltage versus milli amp-hour per gram MnO 2 in a flooded alkaline cell at 0.3 milli-amp/cm 2 current drain rate, comparing performance of the P-CMD with conventional EMD.

WO 94/08056 PCT/US93/07333 Fig. 7A is a graphical plot of the voltage profile (voltage versus milli amp-hour per gram MnO 2 in a lithium cell at 0.17 milli-amp/cm 2 current drain rate comparing performance of P-CMD with conventional EMD.

Fig. 7B is a graphical plot of the voltage profile (voltage versus milli amp-hour per gram MnO 2 in a lithium cell at milli-amp/cm 2 current drain rate, comparing performance of P-CMD with conventional EMD.

Fig. 8A is a graphical plot of the voltage profile (voltage versus milli amp-hour per gram MnO0) in a lithium cell at 0.17 milli-amp/cm 2 current drain rate, comparing performance of P-CMD with conventional CMD (WSLi).

Fig. 8B is a graphical plot of the voltage profile (voltage versus milli amp-hour per gram MnO 2 in a lithium cell at milli-amp/cm 2 current drain rate, comparing performance of the Mno, product of the invention (P-CMD) with conventional CMD (WSLi).

The present invention involves a process for production of battery grade chemical manganese dioxide (CMD). P-CMD when used in electrochemical cells, particularly alkaline and lithium cells, provides these cells with higher capacity and energy density per gram than are obtainable from the same cells employing electrolytic manganese dioxide (EMD). The process of the invention allows for greater control of properties such as density, surface area and particle size than is possible with present processes for the manufacture of conventional forms of EMD or CMD. The process of the invention therefore allows for production of high purity CMD which can be made to have properties more nearly optimal for a given electrochemical cell type. The high density of our MnO 2 product is comparable to WO 94/08056 PCT/US93/07333 that obtained from electrolytic manganese dioxide (EMD), yet the surface area of each MnO 2 particle is greater than that obtained from conventional EMD and CMD processes. The high useful surface area of each particle allows for better performance, particularly in lithium cells containing MnO 2 By "useful" surface area we refer to the surface area which is accessible to the electrolyte.

The process of the invention for production of battery grade manganese dioxide is carried out principally by reacting an aqueous solution of manganese sulfate with sodium peroxodisulfate.

The reaction may be represented as follows: MnSO 4 Na 2

S

2 gO 2H 2 0 MnOg Na 2

SO

4 2H 2 S0 4

(I)

When an aqueous solution of manganese sulfate (MnS04) is reacted with sodium peroxodisulfate (Na 2

S

2 8 a gamma crystal structure of MnO 2 is directly obtainable as a reaction product in the form of a precipitate. The MnO 2 precipitate tends to form spherical particles having filament-like protrusions emanating outwardly from each particle surface and are substantially uniformly distributed over the particle surface. The term "filament-like" as used herein shall be construed as including thin, elongated, protruding structures such as but not limited to filaments, hairs, needles and fibers. The "filament-like" protrusions are characterized by a length to width ratio between about 2:1 and 20:1, typically between about 3:1 and 10:1, wherein the width and length refer to those portions of the protrusions which are visible from the particle surface. The average length of the "filament-like" protrusions is typically between 0.3 to 1 micron and the average width is typically between 0.1 to 0.3 micron.

These dimensions are measurable at a magnification of about 40,000 times actual size. The "filament-like" protrusions resul-fin high surface area of the MnO 2 particle. The MnO 2 WO 94/08056 PCT/US93/07333 particles of the invention as above described may be referred to in the specification drawings and claims as P-CMD.

Unlike the well known Sedema process as disclosed in U.S patent 2,956,860, the present invention permits the average particle size and density of the MnO 2 product to be altered by regulating the rate of the above reaction This can be accomplished by simply controlling the amount or rate of heat supplied to the reaction. Unlike the Sedema process the present reaction does not require a catalytic MnO 2 substrate for receiving the MnO 2 product. In fact no catalyst is required and the MnO 2 product forms into dense, discrete particles without the need of a substrate material. However, it has been discovered that the reaction mixture can be seeded with almost any nonreactive solid material including metals and such material will act as a substrate for the P-CMD. That is, the MnO, reaction product will precipitate directly on the solid material.

*auc It has been discovered that the above reaction mixture can be seeded with particles of electrolytic manganese dioxide (EMD) and the MnO 2 reaction product will deposit directly on the EMD.

This results in a very high der sity hybrid gamma MnO 2 whose outer surface comprises a P-CMD coating having filament-like protrusions and high surface area, while the overall particle shape and interior structure is that characteristic of EMD.

This hybrid form of MnO 2 can advantageously be used as cathode active material in electrochemical cells, particularly alkaline or lithium cells. It is especially attractive for use in lithium cells, since the exposure of the EMD particles to H 2 SO4 during the reaction of the invention, leaches out small amounts of sodium that is trapped within the EMD particles. This r ces the amount of sodium impurity in the P-CMD product, w, h is particularly advantageous if it is to be used as 7 kabJ A$s'Z IlrCI'F~ WO 94/08056 PCI/US93/07333 cathode active material in lithium cells. It has also been discovered that the reaction mixture can advantageously be seeded with graphite or carbon black particles. In such case the MnO 2 reaction product will deposit directly onto the surface of these particles to form a hybrid particulate material which may also be used as cathode active material in electrochemical cells.

The above reaction may typically be carried out in a temperature range between about 30 and 1000 C, preferably between and 900 C. The reaction is preferably carried out in a temperature range between about 700 C and 800 C when the intended use of the P-CMD is as a cathode active material in an alkaline cell, and between about 80 and 900 C when the intended use is as a cathode active material in a lithium cell. (For end application of the P-CMD in alkaline cells it is preferable to keep the final temperature below 850 C in order to obtain a gamma MnO 2 product with higher running voltage and capacity than EMD.) After the reaction is complete, the MnO 2 precipitate is collected and rinsed with distilled water until it has a pH of 7. It may then be dried at room temperature if its intended use is as a cathode active material in an alkaline cell. Alternatively, it may be dried at elevated temperature for more thorough drying, if its intended use is as cathode active material in a lithium cell. The resulting dry gamma MnO 2 has a high purity and low sodium content of less than about 500 ppm. The dry P-CMD contains at least 95% gamma MnO 2 in particulate form. (No other crystalline forms of MnO 2 have been detected in the dry P-CMD of the invention, but 95% is the limit of resolution of the xray diffraction analysis employed for MnO 2 Every MnO 2 particle made by the process of the invention, when observed between 200 and 2000 times actual size, appears to have filament-like protrusions radiating outwardly from the particle surface and these protrusions appear to be uniformly distributed around the WO 94/08056 PCT/US93/07333 particle surface. The P-CMD so produced may subsequently be heat treated in conventional manner to convert it to a gammabeta variety, if desired. This treatment is preferred if the end use of the MnO, is as cathode active material in lithium cells. The heat treatment is well known, a suitable heat treatment process being disclosed in U.S. patent 4,921,689.

It has been determined that various properties of the MnO, 2 product can be altered and controlled by controlling the rate at which the reaction mixture is heated. In general a denser P-CMD is obtained if the reaction is carried out at a slower rate, if the reaction temperature is increased at a slower rate. In a slower reaction individual particles of MnO 2 have time to grow to form larger, more compact particles. In a faster reaction, e.g. produced by faster increase of the reaction temperature, the individual particles of the P-CMD do not have sufficient time to grow to form larger particles.

Therefore the individual particles are smaller and less compact.

They have a fluffier appearance and lower average density than particles obtained from a slower rate of heating.

A sufficiently slow reaction rate to provide a P-CMD product bulk density of about 15 to 32 g/in 3 (0.9 and 2 g/cm 3 SAD (Scott Apparent Density) is obtained if the aqueous reaction mixture of MnSO, and Na 2

S

2

O

8 is maintained at an initial temperature of about 500 C for about 18 hours and then slowly increased at nearly constant rate for between about 5 and 10 hours until a final temperature of between about 70 to 900 C is obtained. The reaction mix may then be left to stand for about 1 hour at this final reaction temperature, to obtain a maximum yield, typically about 70% of the stoichiometric amount of MnSO 4 converted to P- CMD. In this manner battery grade P-CMD can be obtained having densities comparable to or even higher than the density of electrolytic manganese dioxide (EMD) which typically is at a WO 94/08056 PCT/US93/07333 level of about 25 to 28 g/in 3 (1.5 to 1.7 g/cm 3 SAD (Scott Apparent Density). In general a bulk density of the P-CMD between about 15 and 32 g/in 3 (0.9 and 2 g/cm 3 can be achieved by heating the aqueous solution of MnSO 4 and Na 2

S,

2 0 from an initial temperature between about 400 C and 700 C for a period during reaction at an average rate of less than about 70 C per hour for at least 5 hours, typically between about 10 C per hour and 70 C per hour for at least 5 hours.

A sufficiently fast reaction rate to achieve a P-CMD product bulk density of between about 8 to 15 g/cm 3 (0.5 to 0.9 g/cm 3 (Scott Apparent Density) is obtained if the aqueous reaction mixture of MnSO 4 and Na 2

S

2 0 8 is heated at about constant rate from room temperature so that a final temperature of between 70 and 900 C is achieved in about one to two hours. The reaction mixture may be left to stand for about one hour at this final temperature, to obtain a maximum yield, typically about of the stoichiometric amount of manganese in MnSO 4 converted to MnO 2 In general a bulk density of the MnO 2 product between about 8 g/in 3 and 15 g/in 3 (0.5 and 0.9 g/cm 3 can be achieved by heating the aqueous solution of MnS04 and Na 2

S

2 0g from an initial temperature between about 300 C and 1000 C for a period during reaction at an average rate greater than 70 C per hour for less than about 5 hours, typically between about 70 C and 200 C per hour for less than about 5 hours.

It has been determined that the stoichiometric yield of MnO 2 can be dramatically increased to about 95% by slowly adding a suitable alkaline base slowly to the reaction mixture. As the reaction proceeds the base reacts with the H 2 SO, as it forms, thereby improving the reaction kinetics and ultimate yield of MnO 2 A preferred base is Li 2

CO

3 Alternative bases can be employed to react with the H 2 S0 4 to produce the same increase in yield of MnO 2 Such compounds include Na 2

CO

3 LiOH, NaOH and MgO.

WO 94/08056 PCT/US93/07333 For ultimate use of the MnO 2 product in lithium cells it would be preferred to add compounds such as Li 2

CO

3 and LiOH to the re.,sgtion mixture to increase yield. For ultimate use of the MnO 2 product in alkaline cells it would be preferred to add Na 2

CO

3 or NaOH to the reaction mixture. If such compounds are added, they should be added slowly to the reaction mixture to prevent the pH of the mixture from abruptly increasing to a pH greater than about 3.

The MnO 2 reaction product of the invention takes the form of discrete particles having a spherical shape and gamma crystalline structure.- The particle size of the P-CMD can also be controlled by varying the rate at which the reaction mixture is heated. If the reaction mixture is heated to produce a constant rate of increase in temperature then the MnO 2 particle size distribution will be uniform, that is, there will not be much variance in the diameter of individual MnO 2 particles. If the reaction mixture is slowly heated at constant rate, of between about 10 C and 70 C for at least 5 hours, the MnO, product will take the form of relatively large uniform spherical particles as above mentioned. If the reaction mixture is rapidly heated at a fast constant rate, between about C per hour and 200 C per hour for less than about 5 hours, the P-CMD product will tend to take the form of relatively small spherical particles. If the reaction mixture is initially heated at a slow constant rate of temperature increase and later at a fast constant rate of temperature increase, the reaction product will contain a distribution of both large and small MnO 2 particles.

The following examples illustrate the method of preparation of battery grade MnO 2 by the the process of the invention. All parts are parts by weight unless specified otherwise.

WO 94/08056 PCT/US93/07333 Example 1: High density gamma MnO 2 is prepared by the process of the invention as follows: 120 g of MnSO 4

H

2 0 is dissolved in 1800 ml of distilled water.

Then, stoichiometric amount of Na 2

S

2 08 (169 g) is added to the clear pinkish solution to form a reactant solution. While stirring, the temperature of the solution is raised over a period of about 2 hours from room temperature (200 C) to 500 c and is maintained at a temperature of 500 C overnight (about 18 hrs) while continually stirring. This enhances the nucleation process. The reaction proceeds according to reaction above referenced. The clear pinkish solution slowly turns brown and then eventually turns a black color as more MnO 2 is precipitated.

After the 18 hour period the solution is heated from about 500 C to produce a constant rate of temperature increase of about 250 C per hour for about 1 hour to a temperature of about 750 C and is maintained at 750 C for about 3 hours. The solution is then heated at constant rate of about 100 C per hour for about 1 hour to a temperature of 850 C and maintained at 850 C for 1 hour. The solution is again heated at a constant rate 300 C per hour for about 1/2 hour to a temperature of about 1000 C and maintained at 1000 C for about 1 1/2 hours at which time the run is ended. The pH of the solution at the end of the run is less than 0.5. The solution is then cooled to room temperature (200 C) in about one hour. The solution is filtered and the solid MnO z is continually rinsed with distilled water until the filtrate stream has a neutral pH of about 7. The resulting black powder is dried at 1000 C to drive off surface water. The ovzeall yield of P-CMD is 41 g or 67% of theoretical yield.

The resulting product is battery grade MnO 2 at least 95% of which is verified by x-ray diffraction to be of the gamma crystalline structure. (No other type MnO 2 crystalline structure was detected, the 95% threshold being the limit of resolution of the x'ray diffraction analysis.) The P-CMD product has a high WO 94/08056 PCT/US93/07333 bulk density of about 23 g/in 3 (1.4 g/cm 3 SAD (Scott Apparent Density). An electron photomicrograph representative of this MnO 2 product is shown in Figs. 1A and lB. The uniform spherical structure of the P-CMD particles particle 10) is shown in Fig. 1A taken at 199X magnification. The filament-like (e.g.

hair-like) protrusions 15 emanating from the surface of each spherical particle are clearly visible in Fig. 1B, which shows an individual particle at 2,030X magnification. By comparison the electron photomicrographs of the commercial battery grade CMD (WSLi) particles are shown in Figs. 5A and 5B, which are taken at 202X and 2060X magnification, respectively. (The WSLi brand of CMD is available from Sedema, a division of Sadacem, Terte, Belgium.) It is clear from Figs. A and 5B that representative particles 70 do not exhibit filament-like protrusions characteristic of the MnO 2 product of the invention (Figs lA and 1B).

Example 2: Lower density gamma MnO 2 is prepared by the process of the invention as follows: The P-CMD is made in a similar manner as described in example 1, except that rate of heating is faster leading to smaller size and less dense particles. Specifically, the same method of preparation and conditions as in example 1 are employed except the reactant solution is heated from 500 C to 1000 C at rate of about about 170 C per hour for a period of less than 5 hours, namely about 3 hours. Figures 2A and 2B are electron photomicrographs of the resulting MnO 2 product. The product sample represented in Figs. 2A and 2B had a bulk density of about 8.7 g/in 3 (0.53 g/cm 3 (Scott Apparent Density) and is at least 95% gamma MnO 2 The filament-like hair-like) surface protrusions 20 and of the individual particles may be seen in Figs. 2A and 2B, respectively. The P-CMD particles as described in this example WO 94/08056 PCT/US93/07333 may be used as cathode active material in electrochemical cells, particularly alkaline and lithium cells. If intended for use in lithium cells the gamma MnO 2 may be heated at a temperature between about 300-4000 C, typically for about 6 hours at 3500 C or 32 hours at 3000 C to convert the gamma MnO 2 to gamma-beta crystalline structure and to evaporate any residual moisture entrapped within the MnO 2 particles.

Example 3: P-CMD is produced in a manner similar to that described in Example 1 except that Li 2

CO

3 is added to the reaction mixture in order to increase the yield of MnO 2 583 g of MnSO 4

H

2 0 is first dissolved in 8 liter of distilled water in a 12 liter round bottom flask. Then stoichiometric amount of Na 2

S

2 0 (822 g) is added to the slightly pinkish solution. The solution is heated at a constant slow rate for 6 hours from room temperature (200 C) to 55 Then 23 g of Li 2

CO

3 is then slowly added and the solution is maintained at a temperature of about 550 C for 18 hours while continually mixing. An additional 69 g of Li 2

CO

3 is added after the 18 hour period and the solution is heated at a constant rate of about 60 C per hour for about 2.5 hours up to a temperature of 700 C. Another 36 g of Li 2

CO

3 is then added and the solution is heated at a constant rate of about 50 C per nour for 2 hours up to a temperature of about 800 C. The solution is then heated at a reduced constant rate of about 3.30 C per hour for 3 more hours up to a temperature of 900 C. The solution temperature is held for about 18 lhurs and then cooled in about 1 hour to room temperature (200 P-CMD is recovered and dried in the manner described in example 1. The yield of MnO 2 is 270 g or 90% of the theoretical yield. At least 95% of the MnO, product is verified by x-ray diffraction to be gamma MnO 2 The bulk density of the P-CMD is measured as 20 g/in 3 (1.2 cm 3 (Scott Apparent Density). This P-CMD product can be heat treated as in Example 1 whereupon it becomes particularly WO 94/08056 PCT/US93/07333 suitable for use as a cathode active material in lithium cells.

Example 4: This example demonstrates the use of EMD particles as a substrate for the precipitation of MnO 2 made in accordance with the invention.

120 g of MnSO 4 HO0 is dissolved in 1.6 liter of distilled water in a 2 liter beaker by stirring. 120 g of Na 2

S

2 O, and g of EMD (from Kerr-McGee) are then added to the slightly pinkish clear solution.

The heating regimen is as follows. The whole mixture is fir heated from room temperature (200 C) to 550 C in about 2 hours and held at this temperature for 18 hours while continually mixing. The whole mixture is then heated slowly at constant rate for about 5.5 hours to a temperature of 750 C. Then the whole mixture is heated for another hour at constant rate to a temperature of 1000 C. Thereupon the mixture is cooled to room temperature (200 C) in about 1 hour.

The hybrid MnO 2 product is rinsed with distilled water until neutral. Then it is filtered and dried at 1000 C to remove surface water. The total yield of hybrid MnO 2 product is 60 g and its bulk density is 24 g/in 3 (1.5 g/cm 3 (Scott Apparent Density). The hybrid MnOg product contains about 67 wt% of the deposited gamma MnO 2 and 33 wt% EMD.

The MnO 2 product consists of gamma MnO 2 deposited uniformly over the surface of the individual EMD particles to form a hybrid MnO 2 product. Each particle of the hybrid MnO 2 product retains the overall irregular shape of the EMD particle, but exhibits a surface formed of uniformly distributed filament-like protrusions characteristic of the gamma MnO 2 made in accordance with the process of the invention. Representative electron photomicrographs of the hybrid MnOz particles are shown in Figs.

4A and 4B. By way of comparison Figs. 3A and 3B are electron photomicrographs of the EMD particles. These figures clearly WO 94/08056 PCT/US93/07333 show the irregular shape and smooth surface of each EMD particle. Fig. 4A shows the overall shape of each hybrid particle, particle 60 (at a magnification of 450 times actual), as resembling the shape of the EMD particles, e.g.

particle 50 (Fig 3A). However, as may be seen from Fig. 4B, the surface features of each hybrid MnO 2 particle exhibit filamentlike protrusions, e.g. protrusions 65, emanating from and uniformly covering the surface of each hybrid particle. This is the result of the deposition of the gamma MnO 2 of the present process onto the BMD particles. An advantage of this hybrid is that it has higher surface area than EMD, but yet also has high bulk density. It is also cheaper to manufacture than an equivalent weight of gamma MnO 2 produced by the process of the invention. The hybrid MnO 2 so produced can be used as cathode active material in electrochemical cells. If heat treated before application, e.g. as in Example 1, it can be employed as cathode active material in lithium cells.

Example This example demonstrates the preparation of high density P- CMD specifically for use as cathode active material in alkaline cells.

583 g of MnSO 4 HO are dissolved in 8000 ml of distilled water contained in a 12 liter round bottom flask. Then, stoichiometric amount of Na 2

S

2 0 8 (822 g) is added to the clear pinkish solution. The solution is heated from room temperature (200 C) to 50° C in about 2 hours. The solution is then slowly heated from 50° C to 650 C over a period of eight hours and maintained at a temperature of 650 C for 18 hours while continually stirring. The reaction proceeds according to reaction above referenced. The clear pinkish solution slowly turns to a brown and then eventually black color as more MnO 2 is deposited. Following the 18 hour period the solution is then finally heated slowly at about a constant rate from 650 C WO 94/08056 PCT/US93/07333 to 800 C over a period of eight hours. The solution is cooled to room temperature (200 C) in about 1 hour. The gamma MnO 2 product is recovered by filtering the final solution and continually rinsing with distilled water until the filtrate has a neutral pH of about 7. The resulting black powder is dried as in the preceeding examples to drive off surface water. The resulting product is battery grade MnO 2 which is verified by xray diffraction to be of the gamma crystalline structure. The MnO 2 product has a high bulk density of about 28 g/in 3 (1.7 g/cm 3 SAD (Scott Apparent Density). (For usage in an alkaline cell, the Mn02 product of the invention preferably should exhibit a high SAD, preferably of at least 25 g/in 3 (1.5 g/cm 3 which in turn has bean found to result in a high load voltage and capacity.) Performance Tests: Example 6: The P-CMD product of the invention (P-CMD) is evaluated for its electrochemical performance in an AA cell. The performace of the P-CMD as cathode active material in an alkaline AA cell is shown in figure 6A and compared to conventional EMD cathode active material (from Kerr-McGee Corp.) for the same type cell.

It is clear that P-CMD exhibits a slightly higher running voltage and a gr:eater capacity (amp-hrs) than obtainable for the same cell using EMD as cathode material. The P-CMD produc.. is believed to be the first CMD that exhibits better performance in alkaline cells than EMD.

Example 7: P-CMD is evaluated for its performance in a flcnded alkaline cell. This cell utilizes conventional zinc an-<de and KOH electrolyte and paper separator as employed in commercial alkaline cells. The flooded cell is in the shape of a disk of same diameter as that of a Duracell AA cell. The flooded cell is cathode limited, thus excess electrolyte (1.5 g) and excess zinc (5.6 g) are used in order to evaluate the intrinsic _C WO 94/08056 PCT/US93/07333 performance of the MnO 2 product (0.17 g) as cathode active material. The flooded cell is fabricated by first pouring a mixture of MnO 2 powder, graphite and KOH (60 wt% MnO 2 34.5 wt% graphite and 5.5 wt% KOH) intm the bottom of an empty AA size nickel coated stainless steel can which is open at one end and closed at the other. The MnO 2 powder is then compacted into a disk-like shape. A paper separator is then placed on top of the MnO 2 disk. The separator is then filled with the KOH electrolyte and the remaining volume of the can then filled with a zinc slurry. The open end of the can is covered with a stainless steel cap. The cap is in electrical contact with the zinc slurry through a nail penetrating from the cap into the slurry.

Two flooded cells are made as above described, but with one containing P-CMD as cathode material and the other containing conventional battery grade EMD (from Kerr-McGee Co.) as cathode material. The performance of the two cells are compared at a current drain rate of 0.3 milli-amp/cm 2 and the results shown in Figure 6B. It may be seen from the voltage profiles reported in Figure 6B that the performance of the flooded alkaline cell utilizing P-CMD is superior to that employing the EMD.

Example 8: The P-CMD product obtained by the process described in example 3 is heated at about 3500 C for about six hours to convert the gamma MnO 2 to a gamma-beta phase.

A coin shaped cell is fabricated utilizing a cathode active material prepared by mixing MnO 2 graphite and polytetrafluoroethylene binder in a weight ratio of 6:3:1. The cathode mixture is compacted by press molding it onto a stainless steel mesh and spot welding it onto a steel case which forms the positive electrode. The positive electrode containing the cathode material is immersed in a conventional lithium salt electrolyte composed of lithium hexafluorophosphate (LiPF 6 dissolved in propylene carbonate and dimethoxyethane organic WO 94/08056 PCT/US93/07333 solvents. Other conventional lithium salt electrolytes such as lithium perchlorate and organic solvents such as propylene carbonate, ethylene carbonate, dimethoxyethane and mixtures thereof can also be used. Excess amount of lithium is employed for the negative electrode. The negative electrode is formed by press molding a lithium foil onto a stainless steel mesh which in turn is spot welded to a steel case. A separator composed of a non-woven cloth is applied over the lithium foil. The positive electrode is assembled over the negative electrode with the separator therebetween. The assembly is performed in an argon filled dry chamber. The entire assembly is filled with the liquid electrolyte and then sealed by crimping the edge of the cell.

Two lithium coin-shaped cells made in the above manner are discharged down to 1.2 volts with current drain rates of 0.17 and 1 milliamp/cm 2 respectively. The resulting voltage profiles for these cells using P-CMD are shown in figures 7A and 7B for drain rates at 0.17 and 1 milliamp/cm 2 respectively. Each figure also shows -comparative voltage profiles obtained for a like cell at same current drain rates, but instead using conventional EMD cathode active material (from Kerr-McGee Corp.) which is heat treated and press molded for use in the lithium cell. As may be seen from the figures, P-CMD exhibits a greater capacity (milliamp-hr/g) than the EMD. The capacity improvement of the P-CMD over that of EMD at current drain rates of 0.17 and 1 milliamp/cm 2 are about 20% and 28%, respectively. The P-CMD, thus, shows performance improvement over EMD in lithium cells, particularly at the higher current rates.

Example 9: The same tests are performed as in example 8 using the coinshaped lithium cells assembled, as above described, except that the performance of the P-CMD is compared to that of CMD. The WO 94/08056 PCrUS93/07333 CMD chosen is a commercially available CMD from Sedema intended for specific use in lithium cells.

Two coin-shaped lithium cells are prepared as in example 8 but with one cell containing Sedema CMD and the other containing the P-CMD as cathode active material. The voltage profiles for these two cells are given at current drain rates of 0.17 and milliamp/cm 2 as illustrated in figures 8A and 8B, respectively.

As can be sL-n from these figures, the P-CMD has significantly greater capacity (milliamp-hr/g) than the Sedema CMD at the current drain rates tested.

Although the present invention has been reference to specific embodiments, it should be variations are possible within the scope of Therefore, the invention is not intended to specific embodiments, but rather is defined uy equivalents thereof.

described with recognized that the invention.

be limited to the claims and

Claims (4)

1. A process for manufacture of gamma manganese dioxide comprising the steps of: a) reacting MnSO 4 and Na 2 S 2 0 8 in a solution to produce a reaction product mixture comprising a precipitate of gamma MnO 2 comprised of particles characterised by filament-like protrusions radiating outwardly from the surface of said particles; b) removing the gamma MnO 2 precipitate from said reaction product mixture; and c) drying said precipitate.

2. The process of claim I wherein the filament-like protrusions are visible at a magnification between about 200 and 2,000 times actual size.

3. The process of claim 1 or 2 wherein the solution is characterised by an aqueous p I solution and said aqueous solution during step a) is heated to a temperature between to* about 30° C and 1000 C.

4. The process of claim 3 and further characterised by bringing the temperature of S S: said aqueous solution to between 40 and 70° C and then raising the temperature thereof during a period of at least 5 hours at an average rate of less than 70 C per hour, whereby S the bulk density of the resulting gamma MnO 2 will be between 15 and 32 g/in (0.9 and 2 g/cm 3 The process of claim 3 and further characterised by bringing the temperature of said aqueous solution to between 30 and 1000 C and then raising the temperature thereof during a period of less than 5 hours at an average rate of greater than 70 C per hour, whereby the bulk density of the resulting gamma MnO 2 will be between 8 and 15 g/in 3 and 0.9 g/cm 3

17876.00 DOC/mtm 6. The process of any one of claims 1 to 5 further comprising adding a compound reactive with H 2 S0 4 to said solution during or prior to step a) to increase the yield of MnO 2 wherein said compound is selected from the group consisting of Li 2 CO 3 Na 2 CO 3 LiOH, NaOH and MgO. 7. The process of any one of claims 1 to 6 further comprising adding carbon particles to said solution daring or prior to step wherein the carbon particles are selected from the group consisting of graphite and carbon black and wherein the MnO 2 precipitate deposits on the surface of the carbon particles. 8. The process of anyone of claims 1 to 7 further comprising adding electrolytic 10 MnO 2 (EMD) particles to said solution during or prior to step wherein the MnO 2 precipitate deposits on the surface of the EMD particles. 9. A hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of electrolytic manganese dioxide (EMD), wherein said gamma MnO 2 material has filament-like protrusions radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 2,000 times actual size. 10. A hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of carbon material selected from the group consisting of graphite and carbon black, wherein said gamma MnO 2 material has filament-like protrusions radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 2,000 times actual size. 11. A hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of another material wherein said gamma MnO 2 material has filament-like protrusions 17876.M.DOC/mlm -21- radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 2,000 times actual size. 12. An electrochemical cell having MnO 2 cathode active material in said cell, characterised in that at least 95% of said MnO 2 material comprises gamma MnO 2 particles wherein said gamma MnO 2 particles have filament-like protrusiors radiating outwardly from the surface of said particles, said filament-like protrusions being visible at a magnification of between 200 and 2,000 times actual size. 13. An electrochemical cell having MnO 2 cathode active material in said cell, characterised by said electrochemical cell having an anode comprising lithium, and 10 further characterised by said MnO 2 material comprising gamma MnO 2 particles having i S° filament-like protrusions radiating outwardly from the surface of said particles, said filament-like protrusions being visible at a magnification of between about 200 and 2,000 times actual size. 14. The electrochemical cell of claim 13 wherein the gamma MnO 2 particles comprise S 15 at least 95% of said MnO 2 material. 15 The electrochemical cell of claim 13 or 14 characterised by the filament-like protrusions being substantially uniformly distributed over the surface of said particles and the filament-like protrusions having a length to width ratio between about 2:1 and 20:1. 16. A hybrid MnO 2 material comprising gamma MnO 2 deposited on the surface of electrolytic manganese dioxide (EMD), wherein said gamma MnO 2 material has filament-like protrusio radiating outwardly from its surface, said protrusions being visible at a magnification between about 200 and 9,850 times actual size. 17876-OO.DOC/mtm -22- 17. A process for the manufacture of gamma manganese dioxide, substantially as herein described with reference to any one of the Examples or any one of Figs. 1A, 1B, 2A, 2B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A and 8B but excluding any comparative examples therein. 18. A hybrid MnO 2 material, substantially as herein described with reference to any one of the Examples or any one of Figs. 1A, 1B, 2A, 2B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A or 8B but excluding any comparative examples therein. DATED this 1st day of November, 1995 a DURACELL INC 10 Attorney: RUTH M. CLARKSON SFellow Institute of Patent Attorneys of Australia of SHELSTON WATERS ti oa• ola o a 17876.00 DOC/mim