MXPA97009547A - An improved manganese dioxide for li batteries - Google Patents

Abstract

The present invention relates to: A process for treating manganese dioxide containing exchangeable cations to replace exchangeable cations present in manganese dioxide with lithium is disclosed by a process comprising first replacing the interchangeable cations present in manganese dioxide with hydrogen. This is easily accomplished by mixing the manganese dioxide in an aqueous acid solution. The resulting manganese dioxide is then neutralized with a basic solution of a lithium-containing compound, such as lithium hydroxide. This neutralization step serves to carry out the replacement of the previously introduced hydrogen, by ion exchange, with lithium. The manganese dioxide is then washed with water, dried and heat treated at a high temperature, convetionally, to convert manganese dioxide range to a mixture of gamma and beta forms, which is then used as the cathode component active in an electrochemical cell

Description

TITLE AN IMPROVED MANGANESE DIOXIDE FOR LITHIUM BATTERIES.

The present invention relates to an improved manganese dioxide, a method for preparing improved manganese dioxide, and the use of improved manganese dioxide in an electrochemical cell. In particular, the invention relates to an electrolytic manganese dioxide, and its Use in an electrochemical lithium battery. Electrochemical cells, like electric accumulators, commonly have a metallic anode and a cathode of an active material that can accept metal ions. An electrolyte is placed in contact with both the anode and the cathode and serves as a method to transmit ions. During the discharge of the battery, the metal ions leave the anode, enter the electrolyte and are then accepted by the active material of the cathode, resulting in the release of electrons from the cathode. A common type of electrochemical cell consists of an anode of a light alkaline metal, such as lithium and a cathode of active material which is the oxide of a transition metal, such as manganese dioxide. Manganese dioxide manufacturers generally use an electrolytic process whereby manganese sulfate undergoes electrolysis in a sulfuric acid solution. The resulting electrolytic manganese dioxide (EMD) has a residual acid surface by the sulfuric acid used in its preparation, which can be neutralized, then it can be used REF: 26375 effectively in electrochemical cells. Although other bases such as Ca (OH) 2 or NH4OH have been proposed for this use, a sodium hydroxide solution is most often used to effect this neutralization. Sodium hydroxide is preferred for cost, availability and environmental interest, also compatibility with the final product treated. The step of neutralization is inevitable in the introduction of cations within the MnO ?; The use of sodium hydroxide as the neutralizing base for the EMD product results in the introduction of sodium mainly on the surface of manganese dioxide. Now a hypothesis is formulated that when this neutralized EMD is used as the active material of the cathode, the residue, ion-exchangeable sodium can be released on the discharge of the battery. This represents that the changes of sodium with the lithium ion in the electrolyte of the stack, and thus is made available for the initiation of the main reactions for degradation of the lithium anode. The sodium ions of the electrolytic solution apparently deposited on the lithium anode; sodium is exchanged with lithium, and then metallic Na can react with the electrolyte. The metallic Li can also react with the electrolyte; the carbonates serve to inactivate the Li and prevent further reactions, but it is not effective to inactivate the Na. Therefore, the accumulation or storage life of the lithium cell has an adverse effect. To avoid this problem, a process has been developed to prepare an improved manganese dioxide. Now it has been found that the storage duration and charge voltage of a lithium electrochemical cell are increased if the exchangeable sodium ion content is reduced from the manganese dioxide electrode material. According to a preferred embodiment, the exchangeable sodium ion present in the electrolytic manganese dioxide is replaced with lithium, by means of this the sodium contamination of the anode of the lithium cell is prevented. The electrolytic manganese dioxide has a crystalline range structure It has been highly valued that gamma manganese dioxide can be used as material in the cathode in a lithium battery, the manganese dioxide must be treated with heat, to remove the water and to change the structure of the crystal from the gamma phase to the predominant beta phase For the manganese dioxide to have an adequate development as an active material of the cathode in a lithium battery, it has been found that the percentage of the crystalline beta form must be at least 30% but less than 90% outside this range, the utilization of the cathode is inferior to the use of the material within this range. According to the present invention, the exchangeable sodium ion present in the EMD is removed and replaced with lithium before the thermal conversion of the manganese dioxide from the gamma form to the predominantly beta form. Replace the exchangeable sodium ion present in the EMD with lithium it is carried out by a process that comprises first the replacement of the exchangeable sodium ion in the EMD with hydrogen. It is easily performed by mixing the EMD in an aqueous acid solution. The resulting acid EMD is then neutralized with a basic solution of a lithium-containing compound, such as lithium hydroxide. This neutralization step serves to perform the replacement of the previously introduced hydrogen, by ion exchange, with lithium. The EMD is then washed with water, dried, and heat treated at an elevated temperature, in a conventional manner, to convert the gamma EMD to a mixture of gamma and beta forms, this is then used as the active cathode element in a cell electrochemistry It should be used with care to avoid direct contact of manganese dioxide with a strong basic medium. This acts by destroying the EMD particle resulting in sub-micron size MnOj particles. Once the clustered crystals of Mn? 2 are broken, the sub-micron Mn02 becomes a difficulty in processing the silt which is not useful as electrochemically active material in piles. A difficult and expensive process is complicated to reconstitute MnC ^ into useful, large-sized particles. Contacting the EMD particle with a high pH LiOH solution can also serve to introduce the lithium into the crystal lattice of Mn02, by means of this transforming this crystal structure into a form which is not useful as a cathodic active material. In the current process, first treat the neutralized EMD with NaOH with various acids to replace the exchangeable sodium ion with hydrogen. Hydrogen can then be easily exchanged with lithium through the controlled addition of a solution of a lithium compound to the suspension of Mn02 increasing the pH of the suspension. This controlled neutralization minimizes the breaking of the clustered crystals of Mn? 2 which exhibit advantageous mechanical / physical properties.

As described above, the gamma manganese dioxide produced by the acid electrolysis of manganese sulfate with sulfuric acid is typically washed with aqueous sodium hydroxide to neutralize the acidity of the surface of the EMD product. This neutralization introduces the exchangeable sodium ion in Mn02, mainly in this surface. The amount of sodium ion present in the EMD generally has ranges of about 800 ppm. to approximately 3000 ppm.; if the EMD is thermally converted to the beta form for use in a lithium battery, this sodium content is retained even by the Mn? 2. According to the present invention, it has been found that for the use of a lithium cell, it is preferred that the gamma / beta MnO2 contains approximately less than 1000 ppm. of Na, preferably less than 800 ppm. and the greater preference less than 400 ppm. In addition, the sodium content of the EMD generally needs to be reduced. In one embodiment of the currently found process, the EMD particles have an average size ranging from 10 to 50 microns, and have a sodium content with range from 800 ppm. up to 8000 ppm. (after neutralizing the NaOH) is mixed in an aqueous acid solution for a sufficient time to replace the exchangeable sodium ion in the EMD with hydrogen. The EMD is formed in a medium of sulfuric acid and generally contains about 1% sulfate by weight. The mixture of sulfuric acid is allowed to settle and the mother liquid is removed. Any strong acid can be used for the acid treatment, such as f sf acid, nitric acid and sulfuric acid. Sulfuric acid is the preferred acid, because it is relatively inexpensive, it is easily obtained and generally free of adverse contaminants.

An aqueous solution of a lithium compound is then gradually introduced into a mixture of the acid-treated, to exchange the hydrogen ions for lithium ions of the exchanged EMD. The lithium compound can be any lithium salt soluble in water includes lithium hydroxide, lithium carboxylate, lithium carbonate, lithium benzoate, lithium sulfate, lithium nitrate and the like. The lithium hydroxide is preferred. As the lithium cation replaces the hydrogen in Mn02, the acidity of the mixture gradually decreases. Therefore, if an alkaline solution contains lithium the cation is used for ion exchange of hydrogen, the ion exchange progress can be conveniently monitored by indication of the pH of the solution. Once the Mn02 is exchanged to a convenient degree, the EMD containing lithium is then washed with de-ionized water to remove the remaining excess lithium salt on the particles. As indicated before, it is advantageous to reduce the sodium content of MnO? , although a certain level of sodium content can be tolerated without significant adverse effects on the development of the electrochemical cell in which Mn02 is used. According to, the current process to reduce the sodium content to a desirable level, adapts the use of economic, commercial grades of reagents which may include some sodium contents, are not previously tolerated as contaminants. If, for example, the commercial grade of sulfuric acid and / or lithium hydroxide is used in the ion exchange process, the degree of ion exchange can be adjusted to compensate for any additional sodium introduced with the reagents.

If manganese dioxide is used in a lithium battery, the EMD range needs to be converted to the beta crystalline form. The Mn02 range is only partially converted, less than 30% by weight of the Mn? 2 range is converted to the beta form. It is preferred that, from 60% to 90% by weight of gamma MnO2 be converted to the beta form, it is known from experience in the art, and as taught, for example, commonly indicated in US Pat. No. 4, 921,689. Following the thermal conversion of the EMD to convert the Mn02 range to the beta form, a cathode can be prepared from the Mn? 2 using conventional formulation techniques. For example, Mn? 2 is combined with a conductive reagent, such as carbon, with a binder reagent throughout, such as PTFE, to form a mixture, and then the Mn? 2 mixture is formed into a cathode structure. Typically Mn0 converted to beta is used as the electrochemically active cathode component for electrochemical cells having a non-aqueous electrolyte. For example, in a standard button cell, the mixture of Mn02 is pressed into a disk shape; in a spirally wound stack, the mixture is applied to the smaller side of a compatible substrate. The substrate may or may not be porous, depending on the particular design of the stack A type of spiral wound stack is manufactured using the commonly known "gelled roll" construction type, characterized in that a group of electrodes comprises a roll of a structure such as tape having alternating layers of a positive electrode, a separator, and negative electrode wound in a spiral to place the negative electrode on the outside of it. The separator, designed to separate approaches of the positive and negative electrodes against each other, is typically microporous polypropylene. The stack comprises a stainless steel cylinder with an electrically insulating member inside the surface of the button. The cell also contains a non-aqueous electrolyte comprising one or more lithium salts dissolved in a non-aqueous solvent. As is known in the art, suitable lithium salts include LiAsEj, LiBF, iCF3 SO3, LiC104, LiN (CF3 SO2) 2, LiPFfi, mixtures thereof and the like; Suitable non-aqueous solvents include dimethoxyethane, diethyl carbonate, diethoxyethane, dimethylcarbonate, ethylene carbonate, propylene carbonate, mixtures thereof, and the like. The positive electrode is a Mn02 converted to beta pressed on a compatible substrate; The negative electrode is a sheet of lithium metal. An insulating layer is placed over the electrode assembled to the top of the stack, and the top of the stack is sealed with a plastic sealing member through which a positive terminal was placed and electrically connected to the positive electrode. The negative electrode is in electrical contact with the container, which is the negative terminal In a typical "button" type lithium electrochemical cell a metal container that serves as the positive terminal has a metal cap that serves as the negative terminal , with a plastic insulator and the sealing member that seals the lid against the container which separates the lid of the container. The negative electrode is lithium metal in electrical contact with the cap via a collector layer. A manganese dioxide disc converted to beta pressured serves as a positive electrode in electrical contact with the positive metal terminal of the container through another collector layer. Manganese dioxide converted to beta, exchanged with lithium that was found, according to the present invention, in particular, is an improved material cathode for a lithium battery, the range Mn02 exchanged with lithium (prior to the conversion to the beta form) it is also useful as an electrochemically active cathode component for other types of cells including those cells that employ an aqueous electrolyte. As alkaline zinc batteries and others. Alkaline zinc batteries, as is commonly known in the art, comprise a cylindrical metal container, closed on one side, and sealed on the other side by means of an assembly seal. This cell contains a zinc powder gel as the electrochemically active anodic component, Mn02 as the electrochemically active cathode component, and an alkaline solution of potassium hydroxide as the electrolyte. Mn02 is in physical and electrical contact with the metal which may constitute the positive terminal of the cell, and a metal current collector, typically referred to as a "tip", is in physical and electrical contact with the gelled zinc anode, and also with the metal of the lid The end of the metal lid serves as the negative terminal of the stack The following examples are provided to illustrate the invention and demonstrate the improved properties of the Mn02 encountered when used as a cathode member in a stack lithium-manganese dioxide electrochemistry.

EXAMPLE 1. An electrolytic manganese dioxide exchanged with lithium was prepared as follows: For one kg. of commercial grade, the EMD (Mn02 range) neutralized with NaOH, has an average particle size around 50 microns and contains approximately 2200 ppm. of sodium, mixed in a flask containing two liters of sulfuric acid one molar. The mixture was stirred for two hours at room temperature after which the EMD particles were allowed to settle out of suspension. The liquid in the flask was then siphoned out. A fresh two liter portion of sulfuric acid one molar was added; the solids of MnO? they were again mixed by stirring for another two hours, then the solids were again allowed to settle and the liquid was siphoned out. The remaining solids, the treated acid, the exchanged hydrogen ion or protonated EMD, were rinsed off by mixing these in three liters of shameful water shaking for about an hour After the solids were allowed to settle, the liquid was siphoned off, and the washed solids were remixed in two liters of de-ionized fresh water. The lithium hydroxide was then slowly added to the agitated suspension, the pH of the mixture was monitored The portions of lithium hydroxide were continued adding until the pH of the mixture was established between about 7 and 7.5. The pH is indicative that the exchangeable hydrogen ion in the manganese dioxide has been replaced by the lithium ion.

The mixture was then vacuum filtered through an agglomerated funnel with glass powder, and the collected solids were rinsed three times allowing proportions of 100 milliliters of de-ionized water to be filtered under vacuum through the solids in the funnel. The rinsed solids were put to dry under ambient conditions in the agglomerated funnel with glass powder for 16 hours, then transferred into a beaker and dried at 125 ° C in vacuum for about 24 hours. The M11O2 range exchanged with dry lithium was then partially converted to the beta form, by heating to 400 ° C for about 6 hours, followed by lowering the temperature to room temperature for another 6 hour period. The MnO was converted to beta, then a weighed mixture was made by total preparation of 90% by weight of Mn? 2, 4% of black acetylene, and 2% of graphite using a tubular mixer, and then 4% of PTFE and alcohol to make the paste The paste was passed through a sheet of nickel and assembled as cathodes for lithium batteries of size 2/3 A of the gelled roll type, generally described above, using a lithium sheet as the anode material. The piles were filled with an electrolyte comprising 30% propylene carbonate and 70% dimethoxyethane with 0.5 M LiCF salt? SO3.

COMPARATIVE EXAMPLE A In this example, the initial EMD material neutralized with NaOH had neither acid treatment, nor wash, nor neutralized as outlined in example 1. The non-exchanged EMD was directly thermally converted to the beta form of Mn02 and incorporated as cathode material in lithium batteries as described in the example.

COMPARATIVE EXAMPLE B. In the same general way as outlined in the example 1, a sample of EMD was prepared in which the EMD neutralized with NaOH was washed with water The washed EMD was then converted to the beta form and processed into the cathode material which was incorporated into the piles as in example 1 .

COMPARATIVE EXAMPLE C. In the same general manner as outlined in the example 1, a sample of EMD was prepared in which the EMD was acid treated and washed, was neutralized with Ca (OH) 2, instead of LiOH. The result was the Ca-exchanged, the? LnO? The range was then converted to the beta form and processed into the cathode material for electrochemical cells as in example 1.

COMPARATIVE EXAMPLE D. In the same general manner as large traits were exposed in Example 1, a sample of EMD was prepared in which the EMD was acid treated and washed, neutralized with NH4OH, instead of LiOH. The result was NH-interchangeable, the Mn02 range was then converted to the beta form and processed into the cathode material for electrochemical cells as in example 1.

COMPARATIVE EXAMPLE E. In the same general manner as outlined in Example 1, a sample of EMD was prepared in which the EMD was acid treated and washed, neutralized with IO N NaOH, instead of LiOH. The result was MnO2 with Na re introduced, then it was converted to the beta form and processed into the cathode material for piles as in example 1. The Mn02 samples were taken during each of the examples described above, and analyzed the content of the cation. Samples were taken from the processing stage after the material started treatment, at EMD with neutralized NaOH the acid was washed, and the base neutralized, washed with water The sample of Comparative Example A represents that the initial EMD material was not treated, since in this example, Mn? 2 is not washed the acid or neutralized the base. The sample of Comparative Example B was taken after washing the acid and rinsing with water since neutralization of the base was not applied. Table 1 shows the determined contents of the cation from analysis .TABLA 1 The batteries prepared according to the examples above were tested by a charging voltage The batteries were then discharged in a high-speed test (1.8 A for 3 seconds, the rest for 7 seconds) shortened to 1.7V. The results are summarized in Table 2. The batteries were tested at an intermittent storage rate (50 pulses 1.8A for 3 seconds, 7 seconds the rest for a week with storage at 60 ° C). This aggressive test evaluated the stability of the battery. The results are reported in table H TABLE 2 HIGH-SPEED PULSE TEST TABLE 3 Although the invention has been described with reference to the specific embodiment thereof, it is intended that everything contained in the description above or shown in the accompanying drawings be interpreted and not limited in clarity. Various modifications of the discussed embodiments, as well as other Embodiments of the invention may clarify those specializations in the art in reference to this description, or may be made without departing from the scope and the essence of the invention defined in the appended claims.

Claims (15)

18 CLAIMS What is claimed is:

1. A process for treating manganese dioxide containing exchangeable cations comprises introducing a basic aqueous solution containing lithium ions into an aqueous acid mixture of said manganese dioxide to neutralize said mixture and replacing at least a portion of said interchangeable cations with said lithium.

2. A process for treating manganese dioxide containing exchangeable cations comprises contacting said manganese dioxide with an aqueous acid solution to replace at least a portion of said cations with hydrogen, followed by the introduction of an aqueous basic solution containing ions lithium to an acid mixture of said manganese dioxide to neutralize said mixture and replace at least a part of said hydrogen contained by said manganese dioxide with said lithium.

3. The process of claim 2, characterized in that said manganese dioxide contains interchangeable sodium cations.

4. The process of claim 3, characterized in that said manganese dioxide is a gamma manganese dioxide produced electrolytically neutralized by sodium hydroxide.

5. The process of claim 2, characterized in that the basic aqueous solution includes a lithium compound selected from the group consisting of lithium hydroxide, lithium carboxylate, lithium carbonate, lithium benzoate, lithium sulfate, lithium nitrate and the like.

6. The process of claim 5, characterized in that the basic aqueous solution contains lithium hydroxide.

7. The process of claim 4 includes a thermal treatment, said dioxide containing lithium at a temperature of at least about 350 ° C for a sufficient time to convert at least 30% by weight of said manganese dioxide from the gamma form to the beta

8. A process for producing an active cathode material for a lithium electrochemical cell comprises: a) contacting a neutralized gamma electrolytic manganese dioxide with sodium hydroxide with an aqueous acid solution to replace at least a portion of said sodium with hydrogen; b. ) forming an aqueous mixture of manganese dioxide containing hydrogen; c. ) introducing a basic aqueous solution of lithium hydroxide to said mixture to neutralize said mixture and replace at least a part of said hydrogen with lithium; and d.) the heat treatment of the manganese dioxide contains lithium at a temperature of at least 350 ° C for a sufficient time to convert at least 30% by weight of said manganese dioxide from the gamma form to the beta form

9. A manganese dioxide material made by the process of claim 1.

10. A manganese dioxide material made by the process of claim 2.

11. A cathode of manganese dioxide-active material for a lithium electrochemical cell made by the process of claim 8.

12. An electrochemical cell comprises a lithium anode, an electrolyte, and a cathode made of a manganese dioxide as claimed in claim 9.

13. An electrochemical cell comprises a lithium anode, an electrolyte, and a cathode made of a manganese dioxide as claimed in claim 10.

14. A primary element of the electrochemical cell comprises a lithium anode and the electrolyte, and a cathode made an active manganese dioxide cathode is claimed in claim 11.

15. A process for increasing the storage duration and charging voltage of a primary element of the lithium electrochemical cell comprises the steps of contacting the manganese dioxide containing exchangeable cations with an aqueous acid solution to replace at least a portion of said cations with hydrogen, followed by introducing a basic aqueous solution containing lithium ions into an acid mixture of said manganese dioxide to neutralize said mixture and replacing at least a portion of said hydrogens contained by said manganese dioxide with lithium salts, to form a electrode of said manganese dioxide, and employ the electrode as a cathode in a primary element of an electrochemical cell TITLE AN IMPROVED MANGANESE DIOXIDE FOR LITHIUM BATTERIES. SUMMARY A process for treating manganese dioxide containing interchangeable cations to replace exchangeable cations present in manganese dioxide with lithium is disclosed by a process comprising first replacing the interchangeable cations present in manganese dioxide with hydrogen. This is easily accomplished by mixing the manganese dioxide in an aqueous acid solution. The resulting acid manganese dioxide is then neutralized with a basic solution of a lithium containing compound, such as lithium hydroxide. This neutralization step serves to carry out the replacement of the previously introduced hydrogen, by ion exchange, with lithium. The manganese dioxide is then washed with water, dried and heat treated at a high temperature, in a conventional manner, to convert manganese dioxide gamma to a mixture of the gamma and beta forms, which is then used as the cathodic component active in an electrochemical cell