(12) United States Patent
`Bruce et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006214493Bl
`US 6,214,493 Bl
`Apr. 10, 2001
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) MANGANESE OXIDE BASED MATERIAL
`FOR AN ELECTROCHEMICAL CELL
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`(75)
`
`Inventors: Peter George Bruce, Newport-on-Tay;
`Anthony Robert Armstrong, St
`Andrews, both of (GB)
`
`(73) Assignee: The University Court of the
`University of St. Andrews, St.
`Andrews (GB)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.:
`
`09/101,870
`
`(22) PCT Filed:
`
`Jan. 8, 1997
`
`(86) PCT No.:
`
`PCT/GB97 /00031
`
`§ 371 Date:
`
`Aug. 9, 1999
`
`§ 102(e) Date: Aug. 9, 1999
`
`(87) PCT Pub. No.: W097/26683
`
`PCT Pub. Date: Jul. 24, 1997
`
`(30)
`
`Foreign Application Priority Data
`
`Jan. 15, 1996
`
`(GB) .................................................. 9600772
`
`Int. Cl? ...................................................... HOlM 4/50
`(51)
`(52) U.S. Cl. ................... 429/224; 429/231.9; 429/218.1;
`423/599; 423/179.5
`(58) Field of Search ................................. 429/224, 231.9,
`429/231.95, 218.1; 423/599, 179.5
`
`9/1996 Doeff ................................... 429/224
`5,558,961
`5,780,181 * 7/1998 Idota eta!. ........................... 429/194
`5,938,798 * 7/1999 Hanawa eta!. ..................... 29/623.1
`
`FOREIGN PATENT DOCUMENTS
`
`8/1993 (EP) .
`0 556 555
`2/1994 (EP) .
`0 581 290
`11/1994 (EP) .
`0 624 552
`6/1995 (EP) .
`0 656 667
`10/1991 (GB) .
`2 242 898
`* cited by examiner
`Primary Examiner-Maria Nuzzolillo
`Assistant Examiner-Raymond Alejandro
`(74) Attorney, Agent, or Firm-Lee, Mann, Smith,
`McWilliams, Sweeney & Ohlson
`ABSTRACT
`
`(57)
`
`A novel layered material for use in electrochemical cells is
`provided, together with a method for producing the layered
`material, and a cell having the layered material as the
`positive electrode. The material is of the form QqMnyMz0 2 ,
`where Q and M are each any element, y is any number
`greater than zero, and q and z are each any number greater
`than or equal to zero, and the material has a layered
`structure. Methods of preparing the manganese oxide mate(cid:173)
`rial are provided, using an ion exchange reaction or an ion
`removal reaction. Use of the material in an electrochemical
`cell is demonstrated.
`
`20 Claims, 4 Drawing Sheets
`
`•
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`•• •
`
`•• •
`
`•
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`•
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`•• •
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`•• •• •
`•• •
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`•
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`SONY EXHIBIT 1017
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`Page 1 of 9
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`

`
`U.S. Patent
`
`Apr. 10, 2001
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`Sheet 1 of 4
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`US 6,214,493 Bl
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`Page 2 of 9
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`U.S. Patent
`
`Apr. 10, 2001
`
`Sheet 2 of 4
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`US 6,214,493 Bl
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`

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`U.S. Patent
`
`Apr. 10, 2001
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`Sheet 3 of 4
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`US 6,214,493 Bl
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`•
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`Fig,3
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`Fig. 4
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`Page 4 of 9
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`Page 4 of 9
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`

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`U.S. Patent
`
`Apr. 10, 2001
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`Sheet 4 of 4
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`US 6,214,493 Bl
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`
`Page 5 of 9
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`Page 5 of 9
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`

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`US 6,214,493 Bl
`
`1
`MANGANESE OXIDE BASED MATERIAL
`FOR AN ELECTROCHEMICAL CELL
`
`FIELD OF THE INVENTION
`This invention concerns electrochemical cells and relates 5
`to a novel layered material for use in such cells, a method for
`producing the layered material, and a cell having the layered
`material as the positive electrode.
`
`10
`
`2
`Where z is not equal to zero, the element M is typically
`chosen from Group II elements, the transition elements or
`from Group III elements. Suitable elements include Be, Mg,
`Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, Ga, P.
`Accordingly in a particularly preferred material according
`to the invention, Q is an alkali metal ion, such as Rb, K or
`Li, and M is a transition metal ion.
`Preferably Q is chosen to be Li, so that the material is of
`the form LiwMnyMz0 2 , where w is any number greater than
`zero.
`The layered structure preferably possesses a crystal sym(cid:173)
`metry lower than rhombohedral. A preferred symmetry for
`the layered structure is monoclinic. The monoclinic struc(cid:173)
`ture possesses one 2-fold axis and/or one plane of symmetry,
`its unit cell possessing three unequal axes, one axis being
`perpendicular to the other two axes which are inclined at an
`oblique angle, ~· In such a structure the Mn ions are not
`equally spaced from all nearest neighbour oxide ions, i.e. the
`three oxide ions in the adjacent upper layer and the three
`oxide ions in the adjacent lower layer, but rather are dis(cid:173)
`torted from equal spacing so that the Mn-0 bond distance
`varies. An equivalent view of this is that the layered struc(cid:173)
`ture comprises layers of Mn0 6 polyhedra separated by
`layers of other ions, for example lithium ions.
`Preferably the material is LiMn0 2 , having a layered
`monoclinic structure.
`In a simple alternative the material may be of the form
`MnY0 2 , where the layers order as a layer of oxide ions, a
`layer of Mn ions; this being repeated throughout the struc(cid:173)
`ture. The layered structure of this material is rhombohedral,
`with the Mn ions being equally spaced from all nearest
`neighbour oxide ions, i.e. the three oxide ions in the adjacent
`upper layer and the three oxide ions in the adjacent lower
`layer, so that the Mn-0 bond distance is constant. An
`equivalent view of this is that the layered structure com-
`prises successive layers of Mn0 6 octahedra.
`According to a further aspect of the invention, there is
`provided a method of preparing a manganese oxide material
`of the invention, comprising processing an intermediate
`material XxMnyMz0 2 , where X is a Group I element not
`being lithium, M is any element, x and y are each any
`number greater than zero, and z is any number greater than
`or equal to zero, by an ion exchange reaction with a reactant
`45 containing lithium ions, so as to replace X with lithium and
`produce a material of the form LiwMnyMz0 2 , where w is any
`number greater than zero, and the material has a layered
`structure.
`Preferably X is chosen to be Na, so that the intermediate
`50 material is of the form NaxMnyMz0 2 .
`More preferably y is equal to one and z is equal to zero,
`so that the intermediate material is of the form N aMn0 2 . The
`use of such an intermediate material results in production of
`55 a layered material of the form LiMn0 2 , having a layered
`monoclinic structure as described above.
`The reactant may be any suitable lithium salt, such as
`LiBr or LiCl. Preferably the ion exchange reaction is
`achieved by heating the reactant and intermediate material
`60 under reflux. Typically n-pentanol, n-hexanol or n-octanol
`are used as the reflux agent, with the reflux period being 6-8
`hours.
`According to a further aspect of the invention, there is
`provided a method of preparing a manganese oxide material
`65 of the invention, comprising processing a precursor material
`QqMnyMz0 2 , where Q and M are each any element, q and
`y are each any number greater than zero, and z is any number
`
`35
`
`40
`
`Electrochemical cells generally have a negative electrode,
`a positive electrode, and an electrolyte placed between the
`electrodes. The electrolyte is chosen so that transfer of ions
`between the two electrodes occurs, thus producing an elec(cid:173)
`trical current. One example of an electrochemical cell is a 15
`rechargeable battery. The use of non-layered LiMn0 2 in
`secondary batteries is proposed in JP 6036799. The use of
`layered materials such as lithium cobalt oxide, LiCo0 2 , as
`the positive electrode in such a rechargeable battery is well
`established. The layered material LiCo0 2 consists of sheets 20
`of oxygen ions stacked one on top of the other. Between the
`first and second layers of oxygen are located the cobalt ions,
`with the lithium ions being located between the second and
`third oxygen layers. Use ofLiCo02 in rechargeable batteries
`allows greater energy storage per unit weight and volume 25
`than is possible in conventional rechargeable batteries such
`as nickel-cadmium. However LiCo0 2 has disadvantages in
`that it is somewhat toxic, has limited energy storage
`capacity, and the cobalt containing materials from which it
`is produced are expensive and scarce.
`Attempts have been made to use other compounds with a
`similar layered structure to that of LiCo0 2 , such as LiNi0 2 ,
`and LiFe0 2 . EP 0 017 400 discloses a range of compounds
`having layers of the a-NaCr0 2 structure and GB 2242898
`discloses a range of compounds with a layering intermediate
`that of a AB0 2 structure and a spinel-type structure A(B 2 )
`0 4 . However, preparation of the materials according to the
`present invention is not taught and could not be achieved;
`see for example E. Rossen, C. D. W. Jones, and J. R. Dahn,
`"Structure and electrochemistry of LixMnYNi1 _Y0 2 ", Solid
`State Ionics, 57 (1992), 311-318.
`It is one aim of the present invention to provide a novel
`layered manganese oxide material which can be used in
`electrochemical cells.
`
`30
`
`BACKGROUND OF THE INVENTION
`
`SUMMARY OF THE INVENTION
`According to one aspect of the present invention, there is
`provided a manganese oxide material, wherein the material
`is of the form Q~nyMz02, where Q is any Group I element,
`i.e. K, Li, Rb, M is any element, y is any number greater than
`zero, q and z are each any number greater than or equal to
`zero, and the material has a layered structure.
`A layered structure is one in which the ions are arranged
`in a series of generally planar layers, or sheets, stacked one
`on top of another. In general, each layer contains ions of one
`particular element, although the layer of Mn ions may
`contain M ions if present. Thus, when z is equal to zero and
`q is greater Man zero, the layering will consist of sheets of
`oxide ions which are separated by alternating layers of Q
`ions and Mn ions, i.e. the layers order as a layer of oxide
`ions, a layer of Mn ions, a layer of oxide ions, a layer of Q
`ions and a layer of oxide ions; this is repeated throughout the
`structure.
`Where z is not equal to zero, y+z is preferably chosen to
`equal one. In such a material, the M ions will occupy sites
`in the Mn layers.
`
`Page 6 of 9
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`Page 6 of 9
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`

`
`US 6,214,493 Bl
`
`3
`greater than or equal to zero, by carrying out an ion If
`removal reaction, so as to remove Q and produce a material
`of the form MNyMz0 2 , with a layered structure.
`Ion removal is conveniently achieved by electrochemical
`extraction, using the precursor material as the working
`electrode in an electrochemical cell. This is of particular
`advantage in preparation of materials of the form MnY0 2 .
`For preparation of these materials, Q is preferably chosen
`from the Group I elements, such as Na, K, Rb. The MnY0 2
`may be subsequently processed to insert lithium so as to
`produce LiwMny0 2 .
`According to another aspect of the invention, there is
`provided an electrochemical cell, wherein the positive elec(cid:173)
`trode is of the form LiqMnyMz0 2 , where M is any element,
`y is any number greater than zero, and q and z are each any 15
`number greater than or equal to zero. The use of the
`manganese in the electrode avoids the need for use of cobalt
`or nickel which is of advantage as manganese is less toxic,
`more abundant and cheaper than cobalt and nickel.
`Preferably y and q are equal to one, and z is equal to zero, 20
`with the preferred electrode material being LiMn0 2 .
`A rechargeable battery is an example of an electrochemi(cid:173)
`cal cell with which the invention may be used.
`The invention will now be described by way of example,
`and with reference to the accompanying Figures in which:
`FIG. 1 shows the observed diffraction data of the material
`obtained from the method according to the invention, and
`the fit of a theoretical diffraction pattern assuming a layered
`monoclinic model;
`FIG. 2 shows the observed diffraction data of the material
`obtained from the method according to the invention, and
`the fit of a theoretical diffraction pattern assuming a tetrago(cid:173)
`nal spinel model;
`FIG. 3 shows a representation of LiMn0 2 assuming a 35
`monoclinic layered model;
`FIG. 4 shows a representation of LiMn0 2 assuming a
`tetragonal spinel model;
`FIG. 5 shows the voltage response of an electrolytic cell
`using Li1_xMn0 2 , as 1-x varies; and
`FIG. 6 shows the percentage of initial discharge capacity
`on successive discharge cycles of the cell.
`
`30
`
`4
`After heating the sample is furnace cooled and then
`removed from the furnace. Phase purity of the resulting
`NaMn0 2 was confirmed by powder X-ray diffraction. Mate(cid:173)
`rials of the form NaMnyMz0 2 (where M=Be, Mg, Ca, Sc, Ti,
`5 V, Cr, Fe, Co, Ni, Cu, Zn, Al, Ga, P etc) may be prepared by
`using the appropriate oxide to replace some of the Mn2 0 3 .
`In stage 2), a 10 to 15 fold excess of lithium chloride,
`LiCl, i.e. 5 g., or lithium bromide, LiBr, i.e 10 g, is added to
`a round bottomed flask containing 100 ml of either
`10 n-pentanol, n-hexanol, or n-octanol. 1 g of the previously
`prepared NaMn0 2 is added to the mixture in the flask, a
`condenser attached and the mixture heated under reflux for
`a period of 6 to 8 hours. Refluxing temperatures are around
`130° C. for n-pentanol, 145-150° C. for n-hexanol and
`180-185° C. for n-octanol. After cooling to room
`temperature, the product is filtered under suction, washed
`firstly with the appropriate alcohol and then with ethanol,
`and finally dried. Phase purity of the resulting product
`material was confirmed by powder X-ray diffraction.
`The structure of the product produced according to the
`method was then determined by neutron diffraction. Deter(cid:173)
`mination of the structure by this method requires the
`observed diffraction data from a representative sample of the
`product to be compared to theoretical diffraction data for a
`25 variety of structural models. The correct structural model
`produces the best fit between theoretical and observed data.
`Typically trial models are selected by looking at the struc(cid:173)
`tures of similar families of compounds, or from the struc-
`tures of the compounds that formed the product.
`To analyse the structure of the material formed from the
`above described method, two models were tested. The first
`assumed that the layered monoclinic structure of the parent
`NaMn0 2 was retained after the ion exchange reaction. The
`second model assumed a tetragonal spinel structure as
`adopted by Li2Mn2 0 4 , i.e. not a layered structure like the
`cobalt or nickel compounds discussed above but rather a
`completely different three dimensional structure. It should
`be understood that other compounds with the LiMn0 2
`composition have been prepared in the past but with com-
`40 pletely different structures. It is known that orthorhombic
`LiMn0 2 , low temperature "orthorhombic" LiMn0 2 and
`tetragonal spinel Li2 Mn2 0 4 may be produced.
`Time-of-flight powder neutron diffraction data were col(cid:173)
`lected on the POLARIS high intensity, medium resolution
`45 diffractometer at the ISIS pulsed source at the Rutherford
`Appleton Laboratory. Data from the highest resolution back(cid:173)
`scattering bank of detectors were used for structural analy(cid:173)
`sis.
`The observed diffraction data were compared with thea-
`50 retical data for each of the two models. The fit of the real and
`theoretical data for the monoclinic layered structure is
`shown in FIG.l. FIG. 3 shows a representation of this model
`as it is thought to relate to LiMn0 2 ; Mn0 6 polyhedra shown,
`with Li ions as circles. The structure shown in FIG. 3 is
`55 layered and related to the structure of LiCo0 2 , described
`above. However due to the presence of the Jahn-Teller active
`ion Mn3
`+, the structure is distorted from that of LiCo0 2 . The
`main difference is that the crystal symmetry is lowered from
`rhombohedral (LiCo0 2 )
`to monoclinic (LiMn0 2 ). The
`Mn0 6 polyhedra have a lower symmetry that of the Co0 6
`polyhedra as the Mn0 6 polyhedra are considerably distorted
`compared with those of Co0 6 . The Co0 6 polyhedra are
`octahedral. Table 1 below shows relative site occupancies
`and positions of the atoms within this material when using
`the monoclinic structure.
`The fit of the real and theoretical data in the case of the
`tetragonal (Li2Mn2 0 4 spinel) structure is shown in FIG. 2.
`
`DESCRIPTION
`
`EXAMPLE 1
`A material LiMn0 2 , being a preferred embodiment of the
`invention will now be described by way of example. The
`preparation of the material LiMn0 2 and the experimental
`verification of its structure and its properties as an electrode
`for an electrochemical cell will be described.
`Preparation of LiMn0 2
`Preparation of LiMn0 2 required two stages:
`1) The preparation of the intermediate material, sodium
`manganese oxide, NaMn0 2 ; and
`2) Ion exchange reaction.
`Stage 1) is largely known from the literature, see Fuchs
`and Kemmler-Sack, Solid State Ionics 68, 279, 1994. Sto(cid:173)
`ichiometric quantities of sodium carbonate, Na2 C03 , and
`manganese (III) oxide, Mn2 0 3 , are weighed out, intimately 60
`mixed and ground under acetone in an agate mortar and
`pestle until a homogeneous mixture is obtained. The acetone
`is allowed to evaporate and the mixture transferred to a
`crucible and heated in a tube furnace at 700-730° C. for
`18-72 hours under flowing argon. The optimal heating time 65
`to ensure the best density and homogeneity of the resulting
`material is 48 hours.
`
`Page 7 of 9
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`US 6,214,493 Bl
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`6
`As a variant of this, sodium can be electrochemically or
`chemically extracted from this NaMn0 2 yielding a material
`with a layered structure and the formula Mn0 2 . Typically
`this involves an electrochemical cell in which NaMn0 2 is
`the working electrode and passing a constant current through
`the cell. Such a cell may be a cell such as that described
`above for LiMn0 2 , but using sodium counter and reference
`electrodes and a solution of NaClO 4 in propylene carbonate.
`The electrode material is thus oxidised, removing sodium
`and converting Mn3 + to Mn4+, producing Mn0 2 . An alter-
`native synthesis of LiMn0 2 may then be carried out by
`insertion of lithium into the Mn0 2 .
`EXAMPLE 2
`
`5
`
`10
`
`15
`
`5
`FIG. 4 shows a representation of the model applied to
`LiMn0 2 ; Mn0 6 polyhedra are shown, with Li ions as light
`circles and Mn ions as dark circles. Table 2 below shows the
`relative site occupancies and positions of the atoms if this
`model applied.
`
`TABLE 1
`
`Results obtained on fitting a layered monoclinic structure
`to the observed data. space group C2/m (no. 12).
`
`Atom
`
`Li1/
`Mn1
`Li2/
`Mn2
`01
`
`Wyckoff
`symbol x
`
`y
`
`z
`
`Site
`Occupancy
`
`2d
`
`2a
`
`4i
`
`0
`
`0
`
`0.5 0.5
`
`2.4(2)
`
`0.91/0.09(4)
`
`0
`
`0.0
`
`0.72(6) 0.10/0.90(3)
`
`0.2723(3) 0
`
`0. 7706(2) 0.68( 4)
`
`a ~ 5.4387(7), b ~ 2.80857(4), c ~ 5.3878(6) A, 13 ~ 116.006(3t
`x2~ 11.83 (R,xp ~ 0.60%, ~ ~ 1.86%, Rwp ~ 2.06%, R 1 ~ 3.98%)
`
`TABLE 2
`
`Results obtained on fitting a tetragonal structure to the
`observed data. space group !4,/amd (no. 141).
`
`Wyckoff
`symbol X
`
`Atom
`
`y
`
`z
`
`Li
`Mn
`0
`
`8c
`8d
`16h
`
`0
`0
`0.0
`
`0
`0
`0.5
`0
`0.4826(5) 0.2552(3)
`
`B,q
`
`3.6(5)
`0.12(5)
`0.39(5)
`
`Site
`Occupancy
`
`a ~ 5.66632(6), b ~ 5.66632, c ~ 9.1852(2) A
`X2 ~ 63.50 (Rexp ~ 0.60%, ~ ~ 4.00%, ~P ~ 4.79%, R1 ~ 6.58%)
`
`25
`
`30
`
`Two methods were used to prepare compounds of the
`form NaMn1 -xMx0 2 . The first preparation involved weigh(cid:173)
`ing stoichiometric quantities of sodium carbonate (Na2 C03 )
`(or a slight Na2 C03 excess) and managanese (III) oxide
`(Mn2 0 3 ) and the appropriate other metal oxide e.g. cobalt
`20 oxide (Co3 0 4), nickel (II) oxide (NiO), iron (III) oxide
`Fe2 0 3 ) and intimately mixing and grinding under acetone in
`an agate mortar and pestle until a homogeneous mixture was
`obtained. Once the acetone had evaporated the mixture was
`transferred to a crucible and heated in a furnace at 650--750°
`C. for 10-72 hours in air. The sample was cooled to below
`200° C. before removal from the furnace. Phase purity was
`confirmed by powder X-ray diffraction.
`The second preparation involved weighing out appropri(cid:173)
`ate quantities of manganese (II) acetate
`(Mn(CH3 C00)2 .4H2 0) and the other metal salt e.g. cobalt
`(II) acetate (Co(CH3 C00)2 .4H2 0) or nickel (II) acetate
`(Ni(CH3 C00)2 .4H2 0) and dissolving them in distilled
`water. A stoichiometric quantity of sodium carbonate
`(Na2 C03 ), or a slight Na2 C03 excess, was weighed out into
`35 a separate vessel and dissolved in distilled water. The two
`solutions were then mixed and stirred. The water was then
`removed on a rotary evaporator. The resulting solid was
`transferred to a crucible and heated in a furnace at 180--300°
`C. for 2-24 hours in air. The sample was cooled to below
`100° C. before removal from the furnace; it was then ground
`in an agate mortar and pestle, transferred to a crucible with
`a lid and heated in a furnace at 500-850° C. for 1-60 hours
`in air. Samples were removed from the furnace at this
`temperature or after cooling. Phase purity was confirmed by
`powder X-ray diffraction.
`Subsequent processing of either preparation was as
`described in Example 1 above.
`What is claimed is:
`1. A manganese oxide material wherein the material is of
`the form QqMnyMz02 , where Q is a group I element, M is
`another element, Y is a number greater than zero, q and z are
`each a number greater than or equal to zero, wherein the
`material comprises a layered structure of ions, which ions
`are arranged in a series of generally planar layers stacked
`one on top of another with successive layers of oxide ions
`separated by alternating layers of Q ions, the layers thereby
`being arranged in a repeating sequence comprising a layer of
`Q ions, a layer of oxide ions, a layer of Mn ions and a further
`layer of oxide ions.
`2. A manganese oxide material according to claim 1,
`wherein y+z is chosen to equal one.
`3. A manganese oxide material according to claim 1,
`wherein Q is an alkali metal ion and M is a transition metal
`lOll.
`4. A manganese oxide material according to claim 1,
`wherein Q is chosen to be Li, so that the material is of the
`form LwMnyMz0 2 , where w is any number greater than zero.
`
`It can be seen from the analysis presented in Tables 1 and
`2, and FIGS. 1 and 2, that the best fit, i.e. that with least error,
`see x2 value and R values, is obtained for the monoclinic
`structure. The method according to the invention has thus
`produced monoclinic layered LiMn0 2 .
`The performance of the monoclinic LiMn0 2 in an elec(cid:173)
`trochemical cell was then investigated. Investigation into the
`properties of LiMn0 2 was undertaken using a three elec- 40
`trade cell composed of lithium metal counter and reference
`electrodes. The working electrode. i.e. the positive electrode
`was fabricated by compressing powdered LiMn0 2 (80%),
`carbon black (13.3%) and PTFE (6.7%) on to a metal grid.
`The electrolyte was LiCl0 4 dissolved in propylene carbon- 45
`ate. LiCl0 4 was rigorously dried by heating under vacuum
`at 150° C. and the solvent was distilled using a Fischer HMS
`500C distillation apparatus with 90 theoretical plates. The
`cell with an electrolyte solution of 1M LiCl0 4 in propylene
`carbonate was subjected to charging at a current of 10 50
`,uAcm-2
`.
`The resulting voltage of this cell as a function of lithium
`content is shown in FIG. 5. Two voltage plateaux are visible;
`one at 3.4V, the other at 4V vs. Li+(1 M)/Li. The maximum
`voltage of 4.1 V is obtained for 1-x=O, i.e. for Mn0 2 . The 55
`cell was cycled at a constant current of 0.5 mAcm- 2 between
`the potential limit 3.4 and 4.3 V to simulate the behaviour of
`a rechargeable battery. This cycling data is shown in FIG. 6,
`with the percentage of initial discharge capacity shown for
`successive cycles. It will be seen that capacity declines on 60
`cycling. However the voltage range has not been optimised
`and includes both plateaux. FIG. 6 demonstrates that lithium
`can be chemically or electrochemically extracted from
`LiMn0 2 and reinserted into this compound, i.e. it is an
`intercalation/insertion electrode.
`As demonstrated in the above preparation of LiMn0 2 , it
`is possible to ion exchange sodium for lithium in NaMn0 2 .
`
`65
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`US 6,214,493 Bl
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`7
`5. A manganese oxide material according to claim 1,
`wherein the layered structure possesses a crystal symmetry
`lower than rhombohedral.
`6. A manganese oxide material according to claim 1,
`wherein the material has a layered monoclinic structure.
`7. A manganese oxide material according to claim 1,
`wherein the material is LiMn0 2 , having a layered mono(cid:173)
`clinic structure.
`8. A manganese oxide material according to claim 1,
`wherein the material is of the form MnY0 2 .
`9. A method of preparing a manganese oxide material,
`comprising processing an intermediate material
`XxMnyMz0 2 , where X is a Group I element not being
`lithium, M is an element, x and y are each a number greater
`than zero, and z is a number greater than or equal to zero, by 15
`an ion exchange reaction with a reactant containing lithium
`ions, so as to replace X with lithium and produce a material
`of the form LiwMnyMz0 2 , where w is a number greater than
`zero, and the material has a layered structure of ions, which
`ions are arranged in a series of generally planar layers 20
`stacked one on top of another with successive layers of oxide
`ions separated by alternating layers of X ions, the layers
`thereby being arranged in a repeating sequence comprising
`a layer of X ions, a layer of oxide ions, a layer of Mn ions
`and a further layer of oxide ions.
`10. A method according to claim 9, wherein X is chosen
`to be Na, so that the intermediate material is of the form
`NaxMnyMz0 2 .
`11. A method according to claim 9, wherein y is equal to
`one and z is equal to zero, so that the intermediate material 30
`is of the form NaMn0 2 .
`12. A method according to claim 9, wherein the reactant
`is a lithium salt.
`13. A method according to claim 9, wherein the ion
`exchange reaction is achieved by heating the reactant and
`intermediate material under reflux.
`14. A method of preparing a manganese oxide material,
`comprising processing a precursor material QqMnyMn0 2 ,
`where Q is a Group I element, M is an element, x and y are
`
`10
`
`8
`each a number greater than zero, and z is a number greater
`or equal to zero, by carrying out an ion removal reaction, so
`as to remove Q and produce a material of the form
`MnyMn0 2 of ions, which ions are arranged in a series of
`5 generally planar layers stacked one on top of another with
`successive layers of oxide ions separated by alternating
`layers of Q ions, the layers thereby being arranged in a
`repeating sequence comprising a layer of Q ions, a layer of
`~xide ions, a layer of Mn ions and a further layer of oxide
`lOllS.
`15. A method according to claim 14, wherein the ion
`removal reaction is achieved by an electrochemical cell
`having a working electrode constituted by the precursor
`material.
`16. A method according to claim 14, wherein the material
`is of the form MnY0 2 .
`17. An electrochemical cell, wherein the positive elec(cid:173)
`trode is of the form LiwMnyMz0 2 , where M is an element,
`y is a number greater than zero, and q and z are each a
`number greater than or equal to zero, and the material has a
`layered structure of ions, which ions are arranged in a series
`of generally planar layers stacked one on top of another with
`successive layers of oxide ions separated by alternating
`25 layers of Li ions, the layers thereby being arranged in a
`repeating sequence comprising a layer of Li ions, a layer of
`~xide ions, a layer of Mn ions and a further layer of oxide
`lOllS.
`18. An electrochemical cell according to claim 17,
`wherein y and q are equal to one, and z is equal to zero, with
`the electrode being of the form LiMn0 2 .
`19. A rechargeable battery, comprising an electrochemical
`cell according to claim 17.
`20. An electrochemical cell having a positive electrode of
`35 manganese oxide material according to claim 1, a negative
`electrode and electrolyte placed between the positive and
`negative electrodes.
`
`* * * * *
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