CA2044732A1 - Manganese oxide compound - Google Patents
Manganese oxide compoundInfo
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- CA2044732A1 CA2044732A1 CA002044732A CA2044732A CA2044732A1 CA 2044732 A1 CA2044732 A1 CA 2044732A1 CA 002044732 A CA002044732 A CA 002044732A CA 2044732 A CA2044732 A CA 2044732A CA 2044732 A1 CA2044732 A1 CA 2044732A1
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- Prior art keywords
- lithium
- compound
- reagent
- manganese oxide
- ymno2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G45/00—Compounds of manganese
- C01G45/12—Manganates manganites or permanganates
- C01G45/1221—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G45/00—Compounds of manganese
- C01G45/12—Manganates manganites or permanganates
- C01G45/1221—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof
- C01G45/1292—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof of the type [Mn5O12]n-
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/30—Three-dimensional structures
- C01P2002/32—Three-dimensional structures spinel-type (AB2O4)
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical Kinetics & Catalysis (AREA)
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- Engineering & Computer Science (AREA)
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- Inorganic Compounds Of Heavy Metals (AREA)
Abstract
ABSTRACT
A lithium manganese oxide compound Li2O.yMnO2 is provided in which y is >5 and the Mn cations are tetravalent. The compound, when coupled with lithium in an electrochemical cell provides an open circuit voltage of <3,5V. It is made by reacting together Li2O.yMnO2 reagent in which 2,5?y?4 and having a spinel-type structure with a manganese oxide reagent selected from A-Mno2 and electrolytically or chemically prepared manganese dioxide by mixing in finely divided form (?250µm) and heating to 150-450°C
for >8 hours. The invention also provides an electrochemical cell having a lithium anode coupled by an electrolyte to a cathode which is said lithium manganese compound Li2O.yMnO2 in which y>5 and provides the open circuit voltage of <3,5V when coupled with lithium.
A lithium manganese oxide compound Li2O.yMnO2 is provided in which y is >5 and the Mn cations are tetravalent. The compound, when coupled with lithium in an electrochemical cell provides an open circuit voltage of <3,5V. It is made by reacting together Li2O.yMnO2 reagent in which 2,5?y?4 and having a spinel-type structure with a manganese oxide reagent selected from A-Mno2 and electrolytically or chemically prepared manganese dioxide by mixing in finely divided form (?250µm) and heating to 150-450°C
for >8 hours. The invention also provides an electrochemical cell having a lithium anode coupled by an electrolyte to a cathode which is said lithium manganese compound Li2O.yMnO2 in which y>5 and provides the open circuit voltage of <3,5V when coupled with lithium.
Description
204~7~
THIS INVENTION relates to a lithium manganese oxide compound suitable for use as an electrode in an electrochemical cell; to a method of making such compound; and to an electrochemical cell employing such compound as its cathode.
According to one aspect of the invention there is provided a lithium manganese oxide compound having the general formula Li20 . yMnO2 in which:
y has a value which is >5; and the Mn cations are substantially all tetravalent, the compound, when coupled by a suitable electrolyte with lithium in an electrochemical cell, providing an open circuit voltage of <3,50V.
By 'substantially all tetravalent' is meant that the average valency of the manganese cations will ~e at least +3,7 and usually higher, eg 3,8-4,0.
The compound may have, as separate phases therein, a lithium manganese oxide component having a spinel-type structure, and a manganese oxide component. Instead, the compound may have an essentially single-phase spinel-type structure.
Preferably the compound is one ~Jhich, l.ihen coupled with lithium in a said cell, provides an open-circuit voltage of <3,40V, more preferably <3,35V.
Stoichiometric spinel compounds have structures that can be represented by the general formula A[B2]X4 in ~hich X atoms are arranged in a cubic-close-packed fashion to form a negatively charged anion array comprised of face-sharing and edge-sharing tetrahedra and octahedra. In the formula A[B2]X4 the A atoms are tetrahedral-site cations and the B atoms are octahedral-site cations, ie the A cations and B cations occupy tetrahedral and octahedral sites respectively. In the ideal spinel structure, with the origin of the unit cell at the centre (3m), the close-packed anions are located at the 32e positions of the space group Fd3m. Each unit cell contains 64 tetrahedral interstices situated at three crystallographically non-equivalent positions 8a, 8b and 48f, and 32 octahedral interstices situated at the crystallographically non-equivalent positions 16c and 16d. In an AtB2]X4 spinel the A cations reside in the 8a tetrahedral interstices and the B cations in the 16d octahedral interstices.
There are thus 56 empty tetrahedral and 16 empty octahedral sites per cubic unit cell.
Therefore, the B cations of the [B2]Xnn- host framework structure may be regarded as being located at the 16d octahedral positions and the X anions located at the 32e positions of the spinel structure. The tetrahedra defined by the 8a, 8b and 48f positions and octahedra defined by the l~c positions of the spinel structure thus form the interstitial spaces of the ~B2~X4n- framework structure.
For example, a lithium manganese oxide compound which has a spinel-type structure is Li[Mn2]O4 which is known to have been used as a cathode in primary and rechargeable cells and batteries with lithium as the active anode material. Li~Mn2]04 is typically made by reacting a lithium salt with a manganese oxide at temperatures above 700C. In its structure, half the Mn cations are tetravalent and half are trivalent. Lithium can be removed from the structure of Li[Mn2]O4 by means of a mineral acid such as 1 Molar H2S04 or HCl, ~ith associated oxidation of the trivalent Mn cations to form the manganese oxide phase known as l-MnO2, which has a defect spinel-type structure ~lhich can be represented in spinel notation by l O[Mn2]O4 (See Hunter -US
Patent 4 246 253). In l-MnO2 all the Mn cations are thus tetravalent.
` Another example of a lithium manganese oxide compound which has a spinel-type structure is Li4Mn5012, which has a more complex cation distribution which can be represented in spinel notation by Li[Li1/3Mn5/3]04. In this compound, as in A-Mno2, all the Mn cations are tetravalent.
It will be appreciated that, using the formula Li20.yMnO2, the stoichiometric ideal non-defect compound Li~MnsO12 can be represented by Li20.yMnO2 in which y is 2,5; and the defect non-stoichiometric spinel compound A-MnO2 can be represented by Li20.yMnO2 in which y is infinite (ie the concentration of Li2o is zero). The present invention concerns itself with compounds of formula Li2O.yMnO2 with y>5 and with a concentration of Li2o which is >0. The spinel-type compounds according to the invention are defect non-stoichiometric spinel-type co~pounds, and the expression 'spinel-type compounds' accordingly covers defect non-stoichiometric spinel-type compounds.
Thus, the compounds of the present invention are not stoichiometric spinel compounds, but are those in which defects are created by varying the quantity of Li ions at the A sites, such compounds being synthesized to have such defects by varying the quantity of Mn cations in the framework structure. The Li2O.yMnO2 compound in which y=5 can therefore be represented, instead, in spinel notation as Li1_x[Mn2_z]Og in which x=0,273 and y = 0,182. The compounds of the present invention, with y>5, can in turn be represented in spinel notation as Li1_x~Mn2_z]04 in which 0,273<x<1 and O~z<0,182.
In the present invention, the A sites are partially occupied by Li cations, the B sites are partially occupied by Mn cations and the X anions are 0 anions. The frame;ork structure is thus a negatively charged [Mn2_zOz]04 structure wherein 0 represents a vacancy and may be regarded as part of the interstitial spaces, and said interstitial spaces are available for mobile Li cations, for diffusion therethrough during electrochemical discharge and charge reactions, as described hereunder.
20~47~
The aforegoing A[B2]X4 structure is known as a normal spinel structure. It is possible, however, for the cations to be rearranged into an arrangement wherein certain of the B cations occupy tetrahedral sites normally occupied by A cations and certain of the A cations occupy octahedral sites normally occupied by B cations. If the fraction of the B cations occupying tetrahedral sites is designated A, then in the normal spinel structure the value of A is 0. If the value of ~ is 0,5, then the spinel structure is known as an 'inverse spinel' structure, which can be represented by the general formula B~AB]X4. Intermediate values of l are common in compounds having spinel structures, and l is not necessarily constant for a particular compound, but can in some cases be altered by heat treatment under suitable conditions.
For the purpose of the present specification the expression 'spinel-type structure' refers to defect spinels and includes, in addition, normal spinel structures, also inverse spinel structures and intermediate structures wherein o<A<o,5.
Single-phase compounds in accordance with Li20.yMnO2 with 2,5sy<5 are known, eg said Li4Mn50l2, and Li2Mn409 which can be represented by Li20.yMnO2 in which y = 2,5 and y=4 respectively.
These compounds, and their manufacture and use in cells are described in published British Patent Application GB 2 221 213A
and South African Patent 89/5273. The Applicant has, however, been unable, using the techniques described therein, to obtain single-phase spinel phases of Li20.yMnO2 in which y is >5, and when y is >5 the Li20.y~nO2 produced by those techniques is contaminated with impurity phases, suspected to be ~ nO2 andtor Mn203 .
It should be noted that the compounds of the present invention, as described above, can have up to 20% of their manganese ions replaced by other metal ions, particularly transition metal cations such as cobalt, by doping with o~ides of such replacement metals, without affectin5 the properties of the compounds of the present invention as regards their utility 204~73~
in electrochemical cells of the type described hereunder. This doping can be effected by substituting said replacement metal oxides for a proportion of the manganese oxide reagent employed in the method, described hereunder, of making the compounds according to the invention. Accordingly, in the compounds of the present invention, at most 20% of the manganese cations may be replaced by other metal cations.
The lithium manganese oxide compounds of the present invention can be prepared by means of a solid state reaction whereby a lithium manganese oxide reagent is reacted at an elevated temperature with a suitable manganese oxide.
.
Thus, according to another aspect of the invention there is provided a method of making a lithium manganese oxide product which is a compound according to the present invention of the formula Li20.yMnO2 as defined above in which y is >5, the method comprising reacting together lithium manganese oxide reagent in which the ionic ratio of lithium to manganese is 21:2,5 with a manganese oxide reagent, the method comprising the steps of:
intimately mixing said reagents together in finely divided form having a particle size of at most 250~m; and heating the mixture so formed in an oxygen-containing oxidizing atmosphere to a temperature in the range 150 - 450C, for a period of at least 8 hours.
Naturally the proportions of the lithium manganese oxide reagent and the manganese oxide reagent will be selected on a stoichiometric basis so that the desired value of y is obtained in the product.
Preferably, the reagents have a particle size of at most 50 ~m, and a high specific surface of >20m2/g, the temperature being 240 - 400C, the heating being for a period of 8 -18 hours and the oxidizing atmosphere being selected from oxygen, air and mixtures thereof.
204~732 The lithium manganese oxide reagent preferably is of the formula Li20.yMnO2 in which 2,5sys4, having a spinel-type structure, the manganese oxide reagent being a manganese dioxide reagent selected from the group consisting of ~-MnO2, electrolytically prepared manganese dioxide (EMD), chemically prepared manganese dioxide (CMD) and mixtures thereof.
The manganese dioxide reagent may be A-Mno2~ the heating being carried out at a temperature of 240-400C to obtain a substantially single-phase product.
Instead, the manganese dioxide reagent may be selected from electrolytically prepared manganese dioxide, chemically prepared manganese dioxide and mixtures thereof, the heating being at a temperature of 350-400C to obtain a product which comprises, in addition to a component having a spinel-type phase, a component having a manganese dioxide phase.
Preferably, when the lithium manganese dioxide reagent is of the formula Li2O.yMnO2, the value of y is 2,5, so that the reagent can be represented by the formula Li4Mn5012.
The manganese dioxide reagent and said Li20.yMnO2 reagent in which 2,5sys4 need not be stoichiometric and the valency of the Mn therein need not be exactly +4 and may be <+4 depending on the temperature of preparation of the reagents. This valency may thus be 3-4, but is preferably 3.5-4, more preferably 4. In cases where the valency of the Mn is <4 the manganese dioxide reagent and Li20.yMnO2 will be oxygen-deficient.
The Li20.yMnO2 reagent in which 2,5<y<4 can be obtained by reacting together a lithium salt and a manganese salt according to the method described in published British Patent Application GB 2 221 213A and South African Patent 89/5273, and the lithium salt and manganese salt used to make this reagent are preferably anhydrous.
204~73~
The reaction between the Li2O.yMnO2 reagent and the manganese dioxide reagent is preferably, as indicated above, carried out at a temperature of 240 - 400C, for a period of eg 8 hrs - 1 weeX, preferably 8 - 18 hours, the heating period being, broadly, inversely related to the temperature. The heating temperature to an extent depends on the manganese dioxide reagent used. As A-Mno2 transforms in the absence of lithium to ~-MnO2 at 270C, a heating temperature of 240 - 270C is convenient therefor (although high temperature can be employed), whereas for electrolytically and/or chemically prepared manganese dioxides, temperatures of 375 - 400C are typically used.
By varying the mole ratio between the Li20.yMnO2 reagent and the manganese dioxide reagent, the value of y in the Li2O.yMnO2 product can be varied, frcm a value of 5 up to considerably higher values where the proportion of Li2o is extremely small, being a fraction of a percent or less. The method can thus be used to prepare high quality Li2O.yMnO2 in which y is 5 (which product is described in South African Patent 89/5273, but of substantially enhanced purity as regards its single-phase character), and the method is indeed the only method which the Applicant has found whereby said Li20.y~lnO2 can be made with y>5 and which provides said open circuit voltage of <3,5 when coupled electrochemically with lithium.
Conveniently the mixing is by dry milling, to obtain said particle size of at most 250~, preferably at most 50~. Instead, however the mixing may be by making up a slurry of said reagents in a suitable liquid by wet milling, which slurry can be dried to provide the mixture of said reagents which is heated.
If desired, the method may include the step, prior to the heating, of consolidating the mixture (after drying if necessary) by pressing it at a suitable pressure, eg 2-10 bars (ie 200 -1000 kPa), to form a green artifact which, after heating, forms a product in the form of a solid unitary artifact, as opposed to a powder.
20~732 - As indicated above, the lithium ~anganese oxide compounds of the present invention have utility as insertion electrodes in both primary and secondary electrochemical cells having lithium as their electrochemically active anode material.
Thus, according to a further aspect of the invention there is provided an electrochemical cell which comprises an anode selected from lithium-containing materials, a cathode and a suitable electrolyte whereby the anode is electrochemically coupled to the cathode, the cathode comprising a lithium manganese oxide compound in accordance~Jith the present invention and of formula Li20.yMnO2 in which y has a value of >5 as described above.
Such cells can accordingly be represented schematically by:
.
Li(anode)/electrolyte/Li20.yMnO2(cathode) Apart from lithium itself, suitable lithium-containing anodes which can be employed include suitable lithium-containing alloys with other metals or non-metallic elements, examples being lithium/aluminium alloys and lithium/silicon alloys wherein the lithium:aluminium and lithium:silicon ratios are those typically employed in the art, and lithium/carbon anodes in which lithium is intercalated into a carbonaceous structure, eg a graphite structure.
The electrolyte is conveniently a room-temperature electrolyte such as LiC104, LiAsF6 or LiBF4, dissolved in an organic solvent such as propylene carbonate, dimethoxyethane, mixtures thereof or the like.
Accordingly, the anode may be selecte~ from the group consisting of lithium metal, lithium alloys ~ith other metals, lithium alloys ~lith non-metals, lithium/caroon intercalation compounds and mixtures thereof, the electrolytes being a room temperature electrolyte and comprising a me~ber of the group consisting of LiC10~, LiAsF6, LiBF~ and miY.tures thereof, 2~732 dissolved in an organic solvent selected from the group consisting of propylene carbonate, dimethoxymethane and mixtures thereof.
The invention will now be described, by way o~ example, with reference to the following Example which describes the making and characterization of Li2O.y~nO2 according to the present invention, and with reference to the accompanying drawings, in which:
Figure 1 shows an X-ray diffraction pattern trace in counts per second plotted against 2~ for the 26 range 10-70 using CuKa radiation, for a A-MnO2 reagent used in the method of the present invention;
Figure 2 shows a similar trace, for a Li2Mn4Og (Li2O.yMnO2 in which y =~) reagent used in the method of the present invention to prepare a control compound;
Figure 3 shows a similar trace, for a Li4MnsOl2 (Li2O.yMn32 in which y = 2,5) reagent used in the method of the present invention to prepare product compounds according to the invention;
Figure ~ shows a similar trace, for a control Li2O.yMnO2 compound, made in accordance with the method of the present invention, in which y=5;
Figures 5 - 9 show similar traces, for various Li2O.yMnO2 product compounds, in accordance with the invention and made in accordance with the method of the invention, in which y varies from 7,5 - lO;
Figures 10 - 12 show discharge curves which are plots of voltage against capacity for control electrochemical cells operated at room temperature (20 - 25C) havi.ng lithium as anode material and respectively having y-MnO2, the l-Mno2 reagent whose trace is shown in Figure 1 and the control compound Li2O.yMnO2 in which y = 5, whose trace is shown in Figuxe ~, as their cathodes, the electrolyte being 1 Molar LiClO~ in propylene carbonate /dimethoxyethane mixed in a 1:1 volumetric ratio ; and Figures 13 - 17 show similar discharge curves for similar cells in accordance with the invention in which the cathodes 20~732 r~spectively are the lithium manganese oxide product compounds whose traces are shown in Figures 5 - 9.
Details of the various compounds whose traces are shown in these Figures are set forth in the follo~ing table, Table l. In each case, for each Figure it is indicated whether the compound is a reagent, a control compound or a lithium ~anganese oxide product compound in accordance with the invention; the value of y if that compound is eYpressed by the formula Li20.yMnO2; the manganese dioxide reagent from which it was made, if it was made from reagents in accordance with the method of the invention; and the mole ratio of the reagents used. Electrolytically prepared manganese dioxide is a~breviated to EMD, and chemically prepared manganese dioxide i~ abbreviated to CMD. The control employed Li2Mn409 as its lithium manganese oxide reagent, and the lithium manganese oxide product compounds according to the invention all employed Li4Mn50l2 as their lithium manganese dioxide reagent.
Mole Ratio (Lithium Manganese Manganese Figure No Reagent/Control Value of y in Dioxide re2gent Oxide Reagent:
/I nvention Li2O .yMnO2 used Manganese Dioxide Reagent) 1 Reagent ~
2 O 2 Reagent 4 .
THIS INVENTION relates to a lithium manganese oxide compound suitable for use as an electrode in an electrochemical cell; to a method of making such compound; and to an electrochemical cell employing such compound as its cathode.
According to one aspect of the invention there is provided a lithium manganese oxide compound having the general formula Li20 . yMnO2 in which:
y has a value which is >5; and the Mn cations are substantially all tetravalent, the compound, when coupled by a suitable electrolyte with lithium in an electrochemical cell, providing an open circuit voltage of <3,50V.
By 'substantially all tetravalent' is meant that the average valency of the manganese cations will ~e at least +3,7 and usually higher, eg 3,8-4,0.
The compound may have, as separate phases therein, a lithium manganese oxide component having a spinel-type structure, and a manganese oxide component. Instead, the compound may have an essentially single-phase spinel-type structure.
Preferably the compound is one ~Jhich, l.ihen coupled with lithium in a said cell, provides an open-circuit voltage of <3,40V, more preferably <3,35V.
Stoichiometric spinel compounds have structures that can be represented by the general formula A[B2]X4 in ~hich X atoms are arranged in a cubic-close-packed fashion to form a negatively charged anion array comprised of face-sharing and edge-sharing tetrahedra and octahedra. In the formula A[B2]X4 the A atoms are tetrahedral-site cations and the B atoms are octahedral-site cations, ie the A cations and B cations occupy tetrahedral and octahedral sites respectively. In the ideal spinel structure, with the origin of the unit cell at the centre (3m), the close-packed anions are located at the 32e positions of the space group Fd3m. Each unit cell contains 64 tetrahedral interstices situated at three crystallographically non-equivalent positions 8a, 8b and 48f, and 32 octahedral interstices situated at the crystallographically non-equivalent positions 16c and 16d. In an AtB2]X4 spinel the A cations reside in the 8a tetrahedral interstices and the B cations in the 16d octahedral interstices.
There are thus 56 empty tetrahedral and 16 empty octahedral sites per cubic unit cell.
Therefore, the B cations of the [B2]Xnn- host framework structure may be regarded as being located at the 16d octahedral positions and the X anions located at the 32e positions of the spinel structure. The tetrahedra defined by the 8a, 8b and 48f positions and octahedra defined by the l~c positions of the spinel structure thus form the interstitial spaces of the ~B2~X4n- framework structure.
For example, a lithium manganese oxide compound which has a spinel-type structure is Li[Mn2]O4 which is known to have been used as a cathode in primary and rechargeable cells and batteries with lithium as the active anode material. Li~Mn2]04 is typically made by reacting a lithium salt with a manganese oxide at temperatures above 700C. In its structure, half the Mn cations are tetravalent and half are trivalent. Lithium can be removed from the structure of Li[Mn2]O4 by means of a mineral acid such as 1 Molar H2S04 or HCl, ~ith associated oxidation of the trivalent Mn cations to form the manganese oxide phase known as l-MnO2, which has a defect spinel-type structure ~lhich can be represented in spinel notation by l O[Mn2]O4 (See Hunter -US
Patent 4 246 253). In l-MnO2 all the Mn cations are thus tetravalent.
` Another example of a lithium manganese oxide compound which has a spinel-type structure is Li4Mn5012, which has a more complex cation distribution which can be represented in spinel notation by Li[Li1/3Mn5/3]04. In this compound, as in A-Mno2, all the Mn cations are tetravalent.
It will be appreciated that, using the formula Li20.yMnO2, the stoichiometric ideal non-defect compound Li~MnsO12 can be represented by Li20.yMnO2 in which y is 2,5; and the defect non-stoichiometric spinel compound A-MnO2 can be represented by Li20.yMnO2 in which y is infinite (ie the concentration of Li2o is zero). The present invention concerns itself with compounds of formula Li2O.yMnO2 with y>5 and with a concentration of Li2o which is >0. The spinel-type compounds according to the invention are defect non-stoichiometric spinel-type co~pounds, and the expression 'spinel-type compounds' accordingly covers defect non-stoichiometric spinel-type compounds.
Thus, the compounds of the present invention are not stoichiometric spinel compounds, but are those in which defects are created by varying the quantity of Li ions at the A sites, such compounds being synthesized to have such defects by varying the quantity of Mn cations in the framework structure. The Li2O.yMnO2 compound in which y=5 can therefore be represented, instead, in spinel notation as Li1_x[Mn2_z]Og in which x=0,273 and y = 0,182. The compounds of the present invention, with y>5, can in turn be represented in spinel notation as Li1_x~Mn2_z]04 in which 0,273<x<1 and O~z<0,182.
In the present invention, the A sites are partially occupied by Li cations, the B sites are partially occupied by Mn cations and the X anions are 0 anions. The frame;ork structure is thus a negatively charged [Mn2_zOz]04 structure wherein 0 represents a vacancy and may be regarded as part of the interstitial spaces, and said interstitial spaces are available for mobile Li cations, for diffusion therethrough during electrochemical discharge and charge reactions, as described hereunder.
20~47~
The aforegoing A[B2]X4 structure is known as a normal spinel structure. It is possible, however, for the cations to be rearranged into an arrangement wherein certain of the B cations occupy tetrahedral sites normally occupied by A cations and certain of the A cations occupy octahedral sites normally occupied by B cations. If the fraction of the B cations occupying tetrahedral sites is designated A, then in the normal spinel structure the value of A is 0. If the value of ~ is 0,5, then the spinel structure is known as an 'inverse spinel' structure, which can be represented by the general formula B~AB]X4. Intermediate values of l are common in compounds having spinel structures, and l is not necessarily constant for a particular compound, but can in some cases be altered by heat treatment under suitable conditions.
For the purpose of the present specification the expression 'spinel-type structure' refers to defect spinels and includes, in addition, normal spinel structures, also inverse spinel structures and intermediate structures wherein o<A<o,5.
Single-phase compounds in accordance with Li20.yMnO2 with 2,5sy<5 are known, eg said Li4Mn50l2, and Li2Mn409 which can be represented by Li20.yMnO2 in which y = 2,5 and y=4 respectively.
These compounds, and their manufacture and use in cells are described in published British Patent Application GB 2 221 213A
and South African Patent 89/5273. The Applicant has, however, been unable, using the techniques described therein, to obtain single-phase spinel phases of Li20.yMnO2 in which y is >5, and when y is >5 the Li20.y~nO2 produced by those techniques is contaminated with impurity phases, suspected to be ~ nO2 andtor Mn203 .
It should be noted that the compounds of the present invention, as described above, can have up to 20% of their manganese ions replaced by other metal ions, particularly transition metal cations such as cobalt, by doping with o~ides of such replacement metals, without affectin5 the properties of the compounds of the present invention as regards their utility 204~73~
in electrochemical cells of the type described hereunder. This doping can be effected by substituting said replacement metal oxides for a proportion of the manganese oxide reagent employed in the method, described hereunder, of making the compounds according to the invention. Accordingly, in the compounds of the present invention, at most 20% of the manganese cations may be replaced by other metal cations.
The lithium manganese oxide compounds of the present invention can be prepared by means of a solid state reaction whereby a lithium manganese oxide reagent is reacted at an elevated temperature with a suitable manganese oxide.
.
Thus, according to another aspect of the invention there is provided a method of making a lithium manganese oxide product which is a compound according to the present invention of the formula Li20.yMnO2 as defined above in which y is >5, the method comprising reacting together lithium manganese oxide reagent in which the ionic ratio of lithium to manganese is 21:2,5 with a manganese oxide reagent, the method comprising the steps of:
intimately mixing said reagents together in finely divided form having a particle size of at most 250~m; and heating the mixture so formed in an oxygen-containing oxidizing atmosphere to a temperature in the range 150 - 450C, for a period of at least 8 hours.
Naturally the proportions of the lithium manganese oxide reagent and the manganese oxide reagent will be selected on a stoichiometric basis so that the desired value of y is obtained in the product.
Preferably, the reagents have a particle size of at most 50 ~m, and a high specific surface of >20m2/g, the temperature being 240 - 400C, the heating being for a period of 8 -18 hours and the oxidizing atmosphere being selected from oxygen, air and mixtures thereof.
204~732 The lithium manganese oxide reagent preferably is of the formula Li20.yMnO2 in which 2,5sys4, having a spinel-type structure, the manganese oxide reagent being a manganese dioxide reagent selected from the group consisting of ~-MnO2, electrolytically prepared manganese dioxide (EMD), chemically prepared manganese dioxide (CMD) and mixtures thereof.
The manganese dioxide reagent may be A-Mno2~ the heating being carried out at a temperature of 240-400C to obtain a substantially single-phase product.
Instead, the manganese dioxide reagent may be selected from electrolytically prepared manganese dioxide, chemically prepared manganese dioxide and mixtures thereof, the heating being at a temperature of 350-400C to obtain a product which comprises, in addition to a component having a spinel-type phase, a component having a manganese dioxide phase.
Preferably, when the lithium manganese dioxide reagent is of the formula Li2O.yMnO2, the value of y is 2,5, so that the reagent can be represented by the formula Li4Mn5012.
The manganese dioxide reagent and said Li20.yMnO2 reagent in which 2,5sys4 need not be stoichiometric and the valency of the Mn therein need not be exactly +4 and may be <+4 depending on the temperature of preparation of the reagents. This valency may thus be 3-4, but is preferably 3.5-4, more preferably 4. In cases where the valency of the Mn is <4 the manganese dioxide reagent and Li20.yMnO2 will be oxygen-deficient.
The Li20.yMnO2 reagent in which 2,5<y<4 can be obtained by reacting together a lithium salt and a manganese salt according to the method described in published British Patent Application GB 2 221 213A and South African Patent 89/5273, and the lithium salt and manganese salt used to make this reagent are preferably anhydrous.
204~73~
The reaction between the Li2O.yMnO2 reagent and the manganese dioxide reagent is preferably, as indicated above, carried out at a temperature of 240 - 400C, for a period of eg 8 hrs - 1 weeX, preferably 8 - 18 hours, the heating period being, broadly, inversely related to the temperature. The heating temperature to an extent depends on the manganese dioxide reagent used. As A-Mno2 transforms in the absence of lithium to ~-MnO2 at 270C, a heating temperature of 240 - 270C is convenient therefor (although high temperature can be employed), whereas for electrolytically and/or chemically prepared manganese dioxides, temperatures of 375 - 400C are typically used.
By varying the mole ratio between the Li20.yMnO2 reagent and the manganese dioxide reagent, the value of y in the Li2O.yMnO2 product can be varied, frcm a value of 5 up to considerably higher values where the proportion of Li2o is extremely small, being a fraction of a percent or less. The method can thus be used to prepare high quality Li2O.yMnO2 in which y is 5 (which product is described in South African Patent 89/5273, but of substantially enhanced purity as regards its single-phase character), and the method is indeed the only method which the Applicant has found whereby said Li20.y~lnO2 can be made with y>5 and which provides said open circuit voltage of <3,5 when coupled electrochemically with lithium.
Conveniently the mixing is by dry milling, to obtain said particle size of at most 250~, preferably at most 50~. Instead, however the mixing may be by making up a slurry of said reagents in a suitable liquid by wet milling, which slurry can be dried to provide the mixture of said reagents which is heated.
If desired, the method may include the step, prior to the heating, of consolidating the mixture (after drying if necessary) by pressing it at a suitable pressure, eg 2-10 bars (ie 200 -1000 kPa), to form a green artifact which, after heating, forms a product in the form of a solid unitary artifact, as opposed to a powder.
20~732 - As indicated above, the lithium ~anganese oxide compounds of the present invention have utility as insertion electrodes in both primary and secondary electrochemical cells having lithium as their electrochemically active anode material.
Thus, according to a further aspect of the invention there is provided an electrochemical cell which comprises an anode selected from lithium-containing materials, a cathode and a suitable electrolyte whereby the anode is electrochemically coupled to the cathode, the cathode comprising a lithium manganese oxide compound in accordance~Jith the present invention and of formula Li20.yMnO2 in which y has a value of >5 as described above.
Such cells can accordingly be represented schematically by:
.
Li(anode)/electrolyte/Li20.yMnO2(cathode) Apart from lithium itself, suitable lithium-containing anodes which can be employed include suitable lithium-containing alloys with other metals or non-metallic elements, examples being lithium/aluminium alloys and lithium/silicon alloys wherein the lithium:aluminium and lithium:silicon ratios are those typically employed in the art, and lithium/carbon anodes in which lithium is intercalated into a carbonaceous structure, eg a graphite structure.
The electrolyte is conveniently a room-temperature electrolyte such as LiC104, LiAsF6 or LiBF4, dissolved in an organic solvent such as propylene carbonate, dimethoxyethane, mixtures thereof or the like.
Accordingly, the anode may be selecte~ from the group consisting of lithium metal, lithium alloys ~ith other metals, lithium alloys ~lith non-metals, lithium/caroon intercalation compounds and mixtures thereof, the electrolytes being a room temperature electrolyte and comprising a me~ber of the group consisting of LiC10~, LiAsF6, LiBF~ and miY.tures thereof, 2~732 dissolved in an organic solvent selected from the group consisting of propylene carbonate, dimethoxymethane and mixtures thereof.
The invention will now be described, by way o~ example, with reference to the following Example which describes the making and characterization of Li2O.y~nO2 according to the present invention, and with reference to the accompanying drawings, in which:
Figure 1 shows an X-ray diffraction pattern trace in counts per second plotted against 2~ for the 26 range 10-70 using CuKa radiation, for a A-MnO2 reagent used in the method of the present invention;
Figure 2 shows a similar trace, for a Li2Mn4Og (Li2O.yMnO2 in which y =~) reagent used in the method of the present invention to prepare a control compound;
Figure 3 shows a similar trace, for a Li4MnsOl2 (Li2O.yMn32 in which y = 2,5) reagent used in the method of the present invention to prepare product compounds according to the invention;
Figure ~ shows a similar trace, for a control Li2O.yMnO2 compound, made in accordance with the method of the present invention, in which y=5;
Figures 5 - 9 show similar traces, for various Li2O.yMnO2 product compounds, in accordance with the invention and made in accordance with the method of the invention, in which y varies from 7,5 - lO;
Figures 10 - 12 show discharge curves which are plots of voltage against capacity for control electrochemical cells operated at room temperature (20 - 25C) havi.ng lithium as anode material and respectively having y-MnO2, the l-Mno2 reagent whose trace is shown in Figure 1 and the control compound Li2O.yMnO2 in which y = 5, whose trace is shown in Figuxe ~, as their cathodes, the electrolyte being 1 Molar LiClO~ in propylene carbonate /dimethoxyethane mixed in a 1:1 volumetric ratio ; and Figures 13 - 17 show similar discharge curves for similar cells in accordance with the invention in which the cathodes 20~732 r~spectively are the lithium manganese oxide product compounds whose traces are shown in Figures 5 - 9.
Details of the various compounds whose traces are shown in these Figures are set forth in the follo~ing table, Table l. In each case, for each Figure it is indicated whether the compound is a reagent, a control compound or a lithium ~anganese oxide product compound in accordance with the invention; the value of y if that compound is eYpressed by the formula Li20.yMnO2; the manganese dioxide reagent from which it was made, if it was made from reagents in accordance with the method of the invention; and the mole ratio of the reagents used. Electrolytically prepared manganese dioxide is a~breviated to EMD, and chemically prepared manganese dioxide i~ abbreviated to CMD. The control employed Li2Mn409 as its lithium manganese oxide reagent, and the lithium manganese oxide product compounds according to the invention all employed Li4Mn50l2 as their lithium manganese dioxide reagent.
Mole Ratio (Lithium Manganese Manganese Figure No Reagent/Control Value of y in Dioxide re2gent Oxide Reagent:
/I nvention Li2O .yMnO2 used Manganese Dioxide Reagent) 1 Reagent ~
2 O 2 Reagent 4 .
3 Reagent 2,5 4 Control 5 1 MnO2 1:1 Invention 8,25 ~.-MnO2 1:11,5 6 Invention 7,5 EMD 1:10 7 Invention 8,75 EMD 1:12,5 8 Invention 7,5 CMD 1:10 9 Invention 10 CMD 1:15 ~ _ _ _ In the follo~ing table, Table 2, further details are set forth for the co~pounds T~hose traces are shoT~in in Figures 1 - 9.
The control compound and product compounds according to the invention were prepared in accordance with the methods given 20~4732 respectively in Examples 1 and 2 - 6 hereunder. In Table 2 are given the reaction temperatures for making the control compound and product compounds according to the invention of Figure 4 and Figures 5 - 9; the initial open circuit voltage of the compounds in question when loaded, as cathodes into cells of the type whose discharge curves are shown in Figures 10 -17; and the theoretical capacity of the compounds as cathodes in such cells. Table 2 also shows values for EMD and CMD (both of which are ~-MnO2) reagent compounds for comparative purposes, the EMD and CMD being heated in air at 400C, for about 8 hours beforehand; and it is to be noted that the reagent compound of Figure 1 was dried in air at 120C for about 8 hours. It is to be noted that a number of tests were repeated, the repeat values also being shown in Table 2.
Figure No Temperature of Initial Open Circuit Theore~ical Capacity . reaction ( C) Voltage (V)(mAh/g) I I
EMD 3,56 308 (reagent) 3,56 308 CMD . 3,62 308 (reagent) ~ ; ~ a 4 400 3,37 231 ~ 400 3,41 260 6 375 3,40 256 . 7 380 3,34 263 8 400 3,42 256 9 350 3,43 268 Table 2 illustrates that Li20.y~nO2 compounds can be made with y>5 in accordance with the present in~ention, which compounds give initial voltages of <3,5V when coupled with Li/Li+
in an electrochemical cell of the type in question.
With regard to the discharge curves shown in Figures 10- 17, it is to be noted that the cells in question were operated at a discharge current of 500 ~A/cm2 down to a cut-off voltage of 2V, and in the following table, Table 3, cell capacity down to said cut-off voltage of 2V is shown for the cells whose discharge curves are shown in Figures 10-17.
Figure No Capacity (to a 2V cut off at 500~A discharge current (mAh/s) Ir1~3 ~ 211~8~362 1 1s 26 EXAMPLE 1 (CONTROL) In this example a Li2O.yMnO2 reagent compound was init.ially prepared in accordance with the formula Li2Mn4Og (ie Li2O.yMnO2 in which y=4) by milling together Li2co3 and MnCO3 in a suitable mole ratio of Li2CO3:MnCO3 to obtain a mixture with an atomic ratio of Li:Mn of 1:2, and a particle size O.c <50~. The : mixture was heated at 420C for 5 hours in air to produce the Li2Mn4Og which had an essentially single~
phase spinel-type structure (see Figure 2).
Separately, a A~MnO2 reagent was made by reacting stoichiometric LiMn2O4 with 1 Molar HCl at 25C for 24 hours (see Figure 1).
.
The Li2Mn4Og and i.-MnO2 were intimately mixed by milling to a particle size of <50~ followed by heating at 240C in air for 16 hours. The Li2Mn~os:A-Mno2 mole ratio was selected to give a Li:Mn atomic ratio of 2:5 to obtain Li2O.yMnO2 in which y=5 (see Figure 4).
EXAMPLE 2 (INVENTION) Example 1 was repeated except that the I.i2O.yMnO2 reagent compound initially prepared was Li2O.yMnO2 in 2~732 which y = 2,5 (ie Li4Mn5O12). The Li4Mn5O12 and 1-MnO2 were heated together at 400C for 10 hours, in a mole ratio of 1:11,5 to obtain a Li2O.yMnO2 product compound in which y is 8,25 ~see Figure 5).
The Li4MnsOl2 was prepared in the same fashion as said Li2Mn4O9 reagent of Example 1 but using a starting mixture of Li2Co3 and MnCO3 in which the molar ratio was such as to obtain, in the mixture, a Li:Mn atomic ratio of 4:5, the heating being at 420C for a period of 5 hours.
EXAMPLE 3 (INVENTION) Example 2 was repeated using EMD instead of A-Mno2, the reaction of the Li4Mn5O12 and EMD being at 375C
for 48 hours to obtain a Li2O.yMnO2 prsduct compound in which y was 7,5, the mole ratio of LiAMnsOi2:EMD being 1:10 (see Figure 6).
EX.~MPLE 4 (INVENTION) Example 3 was repeated, the reaction of the Li4Mn5O12 and EMD being at 350~C for 16 hours in a mole ratio of Li4Mn5O12:EMD of 1:12,5, to obtain a Li20.y~.-InO2 product compound in which y was 8,75 (see Figure 7).
EXAMPLE 5 (INVENTION) Example 3 was repeated, usiny C;~3 in5tead of EMD, except that the reaction of the Li~Mn;012 with CMD was at 400C for 24 hours (see Figure ~).
EXAMPLE 6 iINVENTION) Example 5 was repeated, except tna the reaction of the Li4Mn5O12 with the CMD took place at 350C for a period of 3 days with a mole ratio or Li~Mr5Ol2:CMD of 1:15 (see Figure.9).
20~732 X-ray diffraction traces were prepared from the aforegoing and are shown in the accompanying drawings as set forth in the tables above.
Figures 1 to 3 respectively demonstrates the essentially 5single-phase character of the A-Mno2~ Li2Mn4Og and Li4Mn5O12 in question.
Figure 4 shows that the control Li2O.5MnO2 prepared in accordance with the method of the present invention also has a single-phase character, in which only negligible traces of Mn2O3 10impurlty are discernible.
Figure 5 shows that the Liz0~8~25MnO2 of the invention, prepared according to the method of the invention, has a .
predominantly spir.el-type character, in which no more than acceptably small traces of ~-MnO2, ~-MnO2 and Mn2O3 are discernable as impurities.
Figures 6, 7, 8 and 9 show that the products of the invention, Li2O.yMnO2 with y >5 contain a significant component having a spinel-type structure, and, in addition, a y-MnO2-related phase that it believed to contain a minor proportion of lithium ions.
An advantage of the invention is that the Li2O.yMnO2 product compounds according to the present invention, as electrodes in cells wherein they are coupled with Li/Li~ anodes, can have significantly high electrode capacities - see Table 2 which shows that the compounds of particularly Figure S (y = 8,2S) and Figure 9 (y = 10) can have significantly higher capacities than the Li2O.yMnO2 reagents with y=4 and y = 2,5 respectively, (Figures 2 and 3) and the control (Figure 4 in which y = 5). It should be noted, however, that the relatively low capacities obtained using A-Mno2 reagents (see Figures 12 and 13) are attributed to the low surface area of this reagent (less than 10 m2/g). Higher capacities can be expected if A-MnO2 reagents with higher specific surfaces are used.
.
.
' ,, 2~73~
While cells according to the invention have shown particularly high capacities during the first or initial discharge cycles thereof, cell capacities in excess of 140 mA-h/g have also been achieved on repeated charge/discharge cycling of these cells, as illustrated by Figure 14 which shows the first 6 discharge cycles of the cell in question, it should be noted that the initial open circuit voltage of the cell was 3,40 Vl but for the cycling experiments shown in Figure 14 the upper and lower voltage limits were set at 3,8 V and 2lO V respectively.
This confirms that the product compounds of the present invention can have utility in both primary and rechargeable (secondary) electrochemical cells.
It is a further advantage that the initial open circuit voltages of <3,5 V of the cells of the present invention are substantially less then those of known cells employing EMD, CMD
or A-MnO2 as cathodes, all of which are >3,5V (see Table 2). For example, Table 2 shows that A-Mno2 cathodes deliver an initial open circuit voltage against lithium of 4,12 V and EMD and CMD
deliver initial open circuit voltages of 3,56 V and 3l62 V
respectively. However, after reaction with a Li20.yNnO2 reagent such as Li2O.2,5MnO2 (y = 2,5) as described hereinbefore, the open circuit voltages drop to below 3,5 V. Cells according to the present invention, as contrasted with said known cells, can thus be made which do not need to be partially predischarged by the manufacturer before they are stored, to resist self-discharge and promote an acceptable shelf-life.
The control compound and product compounds according to the invention were prepared in accordance with the methods given 20~4732 respectively in Examples 1 and 2 - 6 hereunder. In Table 2 are given the reaction temperatures for making the control compound and product compounds according to the invention of Figure 4 and Figures 5 - 9; the initial open circuit voltage of the compounds in question when loaded, as cathodes into cells of the type whose discharge curves are shown in Figures 10 -17; and the theoretical capacity of the compounds as cathodes in such cells. Table 2 also shows values for EMD and CMD (both of which are ~-MnO2) reagent compounds for comparative purposes, the EMD and CMD being heated in air at 400C, for about 8 hours beforehand; and it is to be noted that the reagent compound of Figure 1 was dried in air at 120C for about 8 hours. It is to be noted that a number of tests were repeated, the repeat values also being shown in Table 2.
Figure No Temperature of Initial Open Circuit Theore~ical Capacity . reaction ( C) Voltage (V)(mAh/g) I I
EMD 3,56 308 (reagent) 3,56 308 CMD . 3,62 308 (reagent) ~ ; ~ a 4 400 3,37 231 ~ 400 3,41 260 6 375 3,40 256 . 7 380 3,34 263 8 400 3,42 256 9 350 3,43 268 Table 2 illustrates that Li20.y~nO2 compounds can be made with y>5 in accordance with the present in~ention, which compounds give initial voltages of <3,5V when coupled with Li/Li+
in an electrochemical cell of the type in question.
With regard to the discharge curves shown in Figures 10- 17, it is to be noted that the cells in question were operated at a discharge current of 500 ~A/cm2 down to a cut-off voltage of 2V, and in the following table, Table 3, cell capacity down to said cut-off voltage of 2V is shown for the cells whose discharge curves are shown in Figures 10-17.
Figure No Capacity (to a 2V cut off at 500~A discharge current (mAh/s) Ir1~3 ~ 211~8~362 1 1s 26 EXAMPLE 1 (CONTROL) In this example a Li2O.yMnO2 reagent compound was init.ially prepared in accordance with the formula Li2Mn4Og (ie Li2O.yMnO2 in which y=4) by milling together Li2co3 and MnCO3 in a suitable mole ratio of Li2CO3:MnCO3 to obtain a mixture with an atomic ratio of Li:Mn of 1:2, and a particle size O.c <50~. The : mixture was heated at 420C for 5 hours in air to produce the Li2Mn4Og which had an essentially single~
phase spinel-type structure (see Figure 2).
Separately, a A~MnO2 reagent was made by reacting stoichiometric LiMn2O4 with 1 Molar HCl at 25C for 24 hours (see Figure 1).
.
The Li2Mn4Og and i.-MnO2 were intimately mixed by milling to a particle size of <50~ followed by heating at 240C in air for 16 hours. The Li2Mn~os:A-Mno2 mole ratio was selected to give a Li:Mn atomic ratio of 2:5 to obtain Li2O.yMnO2 in which y=5 (see Figure 4).
EXAMPLE 2 (INVENTION) Example 1 was repeated except that the I.i2O.yMnO2 reagent compound initially prepared was Li2O.yMnO2 in 2~732 which y = 2,5 (ie Li4Mn5O12). The Li4Mn5O12 and 1-MnO2 were heated together at 400C for 10 hours, in a mole ratio of 1:11,5 to obtain a Li2O.yMnO2 product compound in which y is 8,25 ~see Figure 5).
The Li4MnsOl2 was prepared in the same fashion as said Li2Mn4O9 reagent of Example 1 but using a starting mixture of Li2Co3 and MnCO3 in which the molar ratio was such as to obtain, in the mixture, a Li:Mn atomic ratio of 4:5, the heating being at 420C for a period of 5 hours.
EXAMPLE 3 (INVENTION) Example 2 was repeated using EMD instead of A-Mno2, the reaction of the Li4Mn5O12 and EMD being at 375C
for 48 hours to obtain a Li2O.yMnO2 prsduct compound in which y was 7,5, the mole ratio of LiAMnsOi2:EMD being 1:10 (see Figure 6).
EX.~MPLE 4 (INVENTION) Example 3 was repeated, the reaction of the Li4Mn5O12 and EMD being at 350~C for 16 hours in a mole ratio of Li4Mn5O12:EMD of 1:12,5, to obtain a Li20.y~.-InO2 product compound in which y was 8,75 (see Figure 7).
EXAMPLE 5 (INVENTION) Example 3 was repeated, usiny C;~3 in5tead of EMD, except that the reaction of the Li~Mn;012 with CMD was at 400C for 24 hours (see Figure ~).
EXAMPLE 6 iINVENTION) Example 5 was repeated, except tna the reaction of the Li4Mn5O12 with the CMD took place at 350C for a period of 3 days with a mole ratio or Li~Mr5Ol2:CMD of 1:15 (see Figure.9).
20~732 X-ray diffraction traces were prepared from the aforegoing and are shown in the accompanying drawings as set forth in the tables above.
Figures 1 to 3 respectively demonstrates the essentially 5single-phase character of the A-Mno2~ Li2Mn4Og and Li4Mn5O12 in question.
Figure 4 shows that the control Li2O.5MnO2 prepared in accordance with the method of the present invention also has a single-phase character, in which only negligible traces of Mn2O3 10impurlty are discernible.
Figure 5 shows that the Liz0~8~25MnO2 of the invention, prepared according to the method of the invention, has a .
predominantly spir.el-type character, in which no more than acceptably small traces of ~-MnO2, ~-MnO2 and Mn2O3 are discernable as impurities.
Figures 6, 7, 8 and 9 show that the products of the invention, Li2O.yMnO2 with y >5 contain a significant component having a spinel-type structure, and, in addition, a y-MnO2-related phase that it believed to contain a minor proportion of lithium ions.
An advantage of the invention is that the Li2O.yMnO2 product compounds according to the present invention, as electrodes in cells wherein they are coupled with Li/Li~ anodes, can have significantly high electrode capacities - see Table 2 which shows that the compounds of particularly Figure S (y = 8,2S) and Figure 9 (y = 10) can have significantly higher capacities than the Li2O.yMnO2 reagents with y=4 and y = 2,5 respectively, (Figures 2 and 3) and the control (Figure 4 in which y = 5). It should be noted, however, that the relatively low capacities obtained using A-Mno2 reagents (see Figures 12 and 13) are attributed to the low surface area of this reagent (less than 10 m2/g). Higher capacities can be expected if A-MnO2 reagents with higher specific surfaces are used.
.
.
' ,, 2~73~
While cells according to the invention have shown particularly high capacities during the first or initial discharge cycles thereof, cell capacities in excess of 140 mA-h/g have also been achieved on repeated charge/discharge cycling of these cells, as illustrated by Figure 14 which shows the first 6 discharge cycles of the cell in question, it should be noted that the initial open circuit voltage of the cell was 3,40 Vl but for the cycling experiments shown in Figure 14 the upper and lower voltage limits were set at 3,8 V and 2lO V respectively.
This confirms that the product compounds of the present invention can have utility in both primary and rechargeable (secondary) electrochemical cells.
It is a further advantage that the initial open circuit voltages of <3,5 V of the cells of the present invention are substantially less then those of known cells employing EMD, CMD
or A-MnO2 as cathodes, all of which are >3,5V (see Table 2). For example, Table 2 shows that A-Mno2 cathodes deliver an initial open circuit voltage against lithium of 4,12 V and EMD and CMD
deliver initial open circuit voltages of 3,56 V and 3l62 V
respectively. However, after reaction with a Li20.yNnO2 reagent such as Li2O.2,5MnO2 (y = 2,5) as described hereinbefore, the open circuit voltages drop to below 3,5 V. Cells according to the present invention, as contrasted with said known cells, can thus be made which do not need to be partially predischarged by the manufacturer before they are stored, to resist self-discharge and promote an acceptable shelf-life.
Claims (15)
1. A lithium manganese oxide compound having the general formula:
Li2O.yMnO2 in which:
y has a value of >5; and the Mn cations are substantially all tetravalent, the compound, when coupled by a suitable electrolyte with lithium in an electrochemical cell, providing an open circuit voltage of <3,50 V.
Li2O.yMnO2 in which:
y has a value of >5; and the Mn cations are substantially all tetravalent, the compound, when coupled by a suitable electrolyte with lithium in an electrochemical cell, providing an open circuit voltage of <3,50 V.
2. A compound as claimed in claim 1, which has, as separate phases therein, a lithium manganese oxide component having a spinel-type structure, and a manganese oxide component.
3. A compound as claimed in claim 2, which has an essentially single-phase spinel-type structure.
4. A compound as claimed in claim 1, which, when coupled with lithium in a said cell, provides an open circuit voltage of <3,40 V.
5. A compound as claimed in claim 4, in which said open circuit voltage is <3,35 V.
6. A compound as claimed in claim 1, in which at most 20% of the manganese cations are replaced by other metal cations.
7. A method of making a lithium manganese oxide product which is a compound having the general formula Li2O.yMnO2 as claimed in claim 1, the method comprising reacting together a lithium manganese oxide reagent in which the ionic ratio of lithium to manganese is ?1:2,5 with a manganese oxide reagent, the method comprising the steps of:
intimately mixing said reagents together in finely divided form having a particle size of at most 250µm; and heating the mixture so formed in an oxygen-containing oxidizing atmosphere to a temperature in the range 150-450°C for a period of at least 8 hours.
intimately mixing said reagents together in finely divided form having a particle size of at most 250µm; and heating the mixture so formed in an oxygen-containing oxidizing atmosphere to a temperature in the range 150-450°C for a period of at least 8 hours.
8. A method as claimed in claim 7, in which the reagents have a particle size of at most 50µm and a specific surface of >20 m2/g, the temperature being 240-400°C, the heating being for a period of 8 -18 hours, and the oxidizing atmosphere being selected from air, oxygen and mixtures thereof.
9. A method as claimed in claim 7, in which the lithium manganese oxide reagent is of the formula Li2O.yMnO2 in which 2,5?y?4, having a spinel-type structure, the manganese oxide reagent being a manganese dioxide reagent selected from the group consisting of .lambda.-MnO2, electrolytically prepared manganese dioxide, chemically prepared manganese dioxide and mixtures thereof.
10. A method as claimed in claim 9, in which the manganese dioxide reagent is .lambda.-MnO2, the heating being carried out at a temperature of 240-400°C to obtain a substantially single-phase product.
11. A method as claimed in claim 9, in which the manganese dioxide reagent is selected from electrolytically prepared manganese dioxide, chemically prepared manganese dioxide and mixtures thereof, the heating being at a temperature of 350-400°C
to obtain a product which comprises, in addition to a component having a spinel-type phase, a component having a manganese dioxide phase.
to obtain a product which comprises, in addition to a component having a spinel-type phase, a component having a manganese dioxide phase.
12. A method as claimed in claim 9, in which the value of y in the Li2Q.yMnO2 reagent is 2,5.
13. A method as claimed in claim 7, which includes the step, prior to the heating, of consolidating the mixture by pressing it at a pressure of 2 - 10 bars (200 - 1000 kPa) to form a green artifact which, after heating, forms a product in the form of a solid unitary artifact.
14. An electrochemical cell which comprises an anode selected from lithium-containing materials, a cathode and an electrolyte whereby the anode is electrochemically coupled to the cathode, the cathode comprising a lithium manganese oxide compound as claimed in claim 1.
15. A cell as claimed in claim 14, in which the anode is selected from the group consisting of lithium metal, lithium alloys with other metals, lithium alloys with non-metals, lithium/carbon intercalation compounds and mixtures thereof, the electrolyte being a room temperature electrolyte and comprising a member of the group consisting of LiClO4, LiAsF6, LiBF6 and mixtures thereof, dissolved in an organic solvent selected from the group consisting of propylene carbonate, dimethoxyethane and mixtures thereof.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA904713 | 1990-06-18 | ||
| ZA90/4713 | 1990-06-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2044732A1 true CA2044732A1 (en) | 1991-12-19 |
Family
ID=25580173
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002044732A Abandoned CA2044732A1 (en) | 1990-06-18 | 1991-06-17 | Manganese oxide compound |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH04240117A (en) |
| CA (1) | CA2044732A1 (en) |
| DE (1) | DE4119944A1 (en) |
| FR (1) | FR2663468B1 (en) |
| GB (1) | GB2245264B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2251119B (en) * | 1990-12-20 | 1995-06-07 | Technology Finance Corp | Electrochemical cell |
| ZA936168B (en) * | 1992-08-28 | 1994-03-22 | Technology Finance Corp | Electrochemical cell |
| ZA94750B (en) | 1993-09-02 | 1994-09-29 | Technology Finance Corp | Electrochemical cell |
| CN1049529C (en) * | 1994-11-03 | 2000-02-16 | 北京有色金属研究总院 | Cathode material for lithium secondary battery and method of manufacturing the same |
| GB9512971D0 (en) | 1995-06-26 | 1995-08-30 | Programme 3 Patent Holdings | Electrochemical cell |
| WO1998035400A1 (en) | 1997-02-06 | 1998-08-13 | Aabh Patent Holdings Societe Anonyme | Electrochemical cell |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4959282A (en) * | 1988-07-11 | 1990-09-25 | Moli Energy Limited | Cathode active materials, methods of making same and electrochemical cells incorporating the same |
| CA1331506C (en) * | 1988-07-12 | 1994-08-23 | Michael Makepeace Thackeray | Method of synthesizing a lithium manganese oxide |
| JPH02207460A (en) * | 1989-02-06 | 1990-08-17 | Otsuka Chem Co Ltd | Fully solid state lithium battery |
| GB2234233B (en) * | 1989-07-28 | 1993-02-17 | Csir | Lithium manganese oxide |
-
1991
- 1991-06-17 DE DE4119944A patent/DE4119944A1/en not_active Withdrawn
- 1991-06-17 CA CA002044732A patent/CA2044732A1/en not_active Abandoned
- 1991-06-17 FR FR9107385A patent/FR2663468B1/en not_active Expired - Fee Related
- 1991-06-17 GB GB9113020A patent/GB2245264B/en not_active Expired - Fee Related
- 1991-06-18 JP JP3146152A patent/JPH04240117A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2663468B1 (en) | 1994-03-25 |
| GB9113020D0 (en) | 1991-08-07 |
| DE4119944A1 (en) | 1991-12-19 |
| GB2245264B (en) | 1994-06-15 |
| GB2245264A (en) | 1992-01-02 |
| JPH04240117A (en) | 1992-08-27 |
| FR2663468A1 (en) | 1991-12-20 |
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Effective date: 19941219 |