United States Patent [19J
`Thackeray et a!.
`
`[75]
`
`[54] LITHIUM MANGANESE OXIDE
`COMPOUND
`Inventors: Michael M. Thackeray; Margaretha
`H. Rossouw, both of Pretoria, South
`Africa
`[73] Assignee: CSIR, South Africa
`[21] Appl. No.: 558,816
`[22] Filed:
`Jul. 27, 1990
`[30]
`Foreign Application Priority Data
`Jul. 28, 1989 [ZA] South Africa ....................... 89/5789
`Apr. 12, 1990 [ZA] South Africa ....................... 90/2837
`[51]
`Int. CJ.S ....................... HOlM 6/16; HOlM 4/50;
`COlG 45/12
`[52] U.S. Cl ..................................... 429/194; 423/599;
`423/641; 429!224
`[58] Field of Search ....................... 423/605, 599, 641;
`429/224, 194
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`2.562, 705 7/1951 Ellestad et al. ..................... 423/599
`4,246,253 1/1981 Hunter ................................ 423/605
`4,277,360 7/1981 Mellors et al. ...................... 429/224
`4,758,484 7/1988 Furukawa et al. .................. 429/224
`4,828,834 5/1989 Nagaura et al. .................... 429/224
`4,959,282 9/1990 Dahn eta!. ......................... 423/605
`4,980,251 12/1990 Thackeray eta!. ................. 429/224
`
`FOREIGN PATENT DOCUMENTS
`
`009934 4/1980 European Pat. Off ..
`0265950 5/1988 European Pat. Off. .
`2221213A 1/1990 United Kingdom .
`
`OTHER PUBLICATIONS
`Goodenough, "Manganese Oxides as Battery Cath(cid:173)
`odes", in Proc. of the Symposium on Manganese Diox(cid:173)
`ide Electrode Theory and Practice for Electrochemical
`Applications Electrochemical Society, Battery Divi(cid:173)
`sion, Proceedings, vol. 85-4 (1986), pp. 77-96.
`Rossouw, M. H., et a!. "Structural Aspects of Lithi(cid:173)
`um-Manganese-Oxide Electrodes for Rechargeable
`Lithium Batteries", Materials Research Bulletin, vol. 25
`(1990), pp. 173-182.
`DeKock, A. et al. "Defect Spinels in the System Lith-
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US005153081A
`[II] Patent Number:
`[45] Date of Patent:
`
`5,153,081
`Oct. 6, 1992
`
`ium Oxide . y-Manganese Dioxide (y>2.5): A Neu(cid:173)
`tron-Diffraction Study and Electrochemical Charac(cid:173)
`terization of Li2Mn409", Mat. Res. Bull, vol. 25, (1990),
`p. 657.
`M. Jansen, "On the Knowledge of the Sodium Chlo(cid:173)
`ride-Type Structure Family: New Investigations on
`Li2Mn03", Zeitschrift fuer Anorg. Allgem. Chemie,
`vol. 397 (1973), pp. 279-289.
`J. C. Hunter. "Preparation of a New Crystal Form of
`Manganese Dioxide: t..-Mn02", Chemical Abstracts,
`vol. 95, #160312t (1981).
`Rossouw, M., et al. "Lithium Manganese Oxides from
`Li2Mn03 for Rechargeable Lithium Battery Opera(cid:173)
`tions", Mat. Res. Bull., vol. 26, pp. 463-473 (1991).
`David et al., "The Crystal Structure of Li2MN02",
`Revue de Chimie Minerale, 20, 1983, pp. 636-642.
`Wells, A. F., Structural Inorganic Chemistry, the passage
`"The y-MO.OH Structure" at pp. 527-528.
`Nohma, T., et al. "Manganese Oxides for a Lithium
`Secondary Battery-Composite Dimensional Manga(cid:173)
`nese Oxide (CDMO)", Journal of Power Sources, 26,
`389-396 (1989).
`Hunter, James C., "Preparation of a New Crystal Form
`of Manganese Dioxide: f..-Mn02," Journal of Solid State
`Chemistry, 39, 142-147 (1981).
`Primary Examiner-Michael Lewis
`Assistant Examiner-Peter DiMauro
`Attorney, Agent, or Firm-Richards, Medlock &
`Andrews
`
`ABSTRACT
`[57]
`The invention provides a novel lithium manganese
`oxide compound in which oxygen anions, lithium cati(cid:173)
`ons and manganese cations are arranged in layers, each
`layer of lithium cations being sandwiched between two
`layers of oxygen anions, each layer of manganese cati(cid:173)
`ons being sandwiched between two layers of oxygen
`anions and each layer of oxygen anions being sand(cid:173)
`wiched between a layer of lithium cations and a layer of
`manganese cations. The invention also provides a
`method of making the compound; and an electrochemi(cid:173)
`cal cell employing the compound as its cathode.
`
`10 Oaims, 7 Drawing Sheets
`
`SONY EXHIBIT 1018
`
`Page 1 of 13
`
`

`
`U.S. Patent
`
`Oct. 6, 1992
`
`Sheet 1 of 7
`
`5,153,081
`
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`Page 2 of 13
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`Page 2 of 13
`
`

`
`U.S. Patent
`
`Oct. 6, 1992
`
`Sheet 2 of 7
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`5,153,081
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`Page 3 of 13
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`Page 3 of 13
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`

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`U.S. Patent
`
`Oct. 6, 1992
`
`Sheet 3 of 7
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`5,153,081
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`

`
`U.S. Patent
`
`Oct. 6, 1992
`
`Sheet 4 of 7
`
`5,153,081
`
`FIG 4
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`Page 5 of 13
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`Page 5 of 13
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`

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`U.S. Patent
`
`Oct. 6, 1992
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`U.S. Patent
`
`Oct. 6, 1992
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`Sheet 6 of 7
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`

`
`U.S. Patent
`
`Oct. 6, 1992
`
`Sheet 7 of 7
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`5,153,081
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`Page 8 of 13
`
`

`
`1
`
`5,153,081
`
`LITHIUM MANGANESE OXIDE COMPOUND
`
`TECHNICAL FIELD OF THE INVENTION
`The invention relates to a layered lithium manganese
`oxide compound and to a method of making such a
`compound. The invention further includes an electro(cid:173)
`chemical cell employing the compound as the cathode.
`
`SUMMARY OF THE INVENTION
`This invention relates to a lithium manganese oxide
`compound. More particularly it relates to such com(cid:173)
`pound suitable for use as a cathode in an electrochemi(cid:173)
`cal cell. It also relates to a method of preparing such
`compound; and to an electrochemical cell having a 15
`cathode comprising such compound.
`According to one aspect of the invention there is
`provided an essentially layered lithium manganese
`oxide compound in which the average valency of the
`manganese ("Mn") cations is from +3 to +4, the com- 20
`pound having its oxygen ("0") anions arranged in lay(cid:173)
`ers in a substantially cubic-close-packed arrangement,
`with the lithium ("Li") cations being arranged in layers
`and the Mn cations occupying octahedral sites and
`being arranged in layers. Each layer of Li cations is 25
`sandwiched between two layers of 0 anions, each layer
`of Mn cations is sandwiched between two layers of 0
`anions and each layer of 0 anions is sandwiched be(cid:173)
`tween a layer of Li cations and a layer of Mn cations.
`Preferably, at least 75% of the Mn cations in the com- 30
`pound are located in the layers of Mn cations and the
`remainder of the Mn cations are located in the layers of
`Li cations.
`In other words, in said compound, the layers of Li
`cations will accordingly alternate with the layers ofMn 35
`cations, but will be separated therefrom by a layer of 0
`anions. While, as indicated above, the layers of Li cati(cid:173)
`ons may contain a minor proportion of the Mn cations
`of the compound, the layers of Mn cations in turn may
`contain a minor proportion of the Li cations of the 40
`compound. Preferably, at least 90% of the Mn cations in
`the compound are located in the layers of Mn cations.
`As the average valency of the Mn cations may be less
`than +4, the lithium manganese oxide compound of the
`invention may be somewhat oxygen-deficient. How- 45
`ever, the average valency of the Mn cations is prefera(cid:173)
`bly at least + 3.5 and more preferably close to +4 or
`equal thereto.
`Furthermore, particularly when the lithium manga(cid:173)
`nese oxide compound of the invention is prepared by a 50
`method involving acid leaching as described hereunder,
`its layers of Li cations may, in addition to containing Li
`cations, contain a proportion of H cations, which can be
`regarded as being Li cations replaced by H cations by
`ion exchange. Depending on the degree of cation ex- 55
`change, the relative proportions of Li and H cations in
`the structure can in principle vary from essentially
`100% Li cations and substantially no H cations, to es(cid:173)
`sentially 100% H cations and substantially no Li cati(cid:173)
`ons.
`When the layered lithium manganese oxide com(cid:173)
`pound is prepared, e.g., from LbMn03 as described
`hereunder, it can have the formula A2-2xMnOJ-x in
`which, neglecting any surface water or water occluded
`at grain boundaries, 0 < x ~ 1, A being a cation selected
`from Li cations and a mixture of Li cations and H cati(cid:173)
`ons. As the invention extends to said compound
`A2-2xMn03-x when xis 1, it includes a layered Mn02
`
`2
`compound in which each layer of Mn cations is sand(cid:173)
`wiched between two layers of 0 anions and each layer
`of 0 anions is sandwiched between a layer of Mn cati(cid:173)
`ons and a layer of 0 anions, so that a pair of layers of 0
`5 anions is sandwiched between two layers of Mn cations,
`as described hereunder. In this case, the structure of the
`compound may be stabilized by the presence of small
`numbers of stabilizing cations other than Li cations,
`between adjacent layers of 0 anions. The stabilizing
`10 cations may be H or Zn cations.
`According to another aspect of the invention, there is
`provided a method of preparing, as a product, a layered
`lithium manganese oxide compound as described above,
`which method comprises the steps of:
`synthesizing a LizMn03 precursor as defined herein
`by reacting together, at a temperature of 350°-800° C.,
`a manganese compound selected from the group con(cid:173)
`sisting of manganese salts, manganese oxides, manga(cid:173)
`nese hydroxides and mixtures thereof with a lithium
`compound selected from the group consisting oflithium
`salts, lithium oxide, lithium hydroxide and mixtures
`thereof, the reaction taking place by heating under a
`oxygen-containing oxidizing atmosphere with said com(cid:173)
`pounds intimately mixed in finely divided solid form,
`the mixture having an average particle size of at most
`250 1-t and the ratio of the Li cations to Mn cations in the
`mixture being in the range 1.8:1-2.2:1; and
`leaching LbO from the LbMn03 precursor by means
`of an aqueous mineral acid, to leave a product which
`comprises Mn02 combined together with a residual
`amount of Li20, the product comprising at most 50% of
`the Li cations originally present in said precursor.
`Preferably, the heating is for a time such that the
`reaction between the manganese compound and the
`lithium compound is substantially complete, i.e., to
`produce a substantially single-phase Li2Mn03 precur(cid:173)
`sor. The reaction time required for this is inversely
`related to the reaction temperature and the reaction
`temperature and reaction time will typically be selected
`by routine experimentation, taking into account practi(cid:173)
`cal and economic considerations. At 350° C. the reac(cid:173)
`tion time will be of the order of about 20 days and at
`800° c. it will be of the order of about 1 day.
`The LizMn03 precursor, whose formula may instead
`be written as Li20.Mn02, has a structure in which the
`oxygen anions are cubic-close-packed, but which is
`slightly distorted compared with an ideal cubic-close(cid:173)
`packed structure. The cations occupy all the octahedral
`sites of the structure, which are located in layers be(cid:173)
`tween cubic-close-packed oxygen planes. Alternate
`cation layers are filled respectively entirely with Li
`ions, and with Mn ions and Li ions in a 2:1 atomic ratio.
`The LizMn03 precursor may be synthesized by react(cid:173)
`ing together the manganese compound and lithium
`compound at a temperature of 370°-450° C. under air,
`with the mixture having an average particle size of at
`most 100 1-t and the Li cation:Mn cation ratio being
`1.9:1-2.1:1, the leaching being by means of a concen-
`60 trated mineral acid selected from nitric acid, hydrochlo(cid:173)
`ric acid and sulfuric acid to leave a product comprising
`5-30% of the Li cations originally present in said pre(cid:173)
`cursor. Typically, the leaching is at room temperature
`(e.g., 15°-30° C.) and can be regarded as leaching out a
`65 LizO component from the LbMn03 precursor struc(cid:173)
`ture, leaving a Mn02 component of said structure, to(cid:173)
`gether with some residual Li20, the layered arrange(cid:173)
`ment of the Mn cations in the precursor being essen-
`
`Page 9 of 13
`
`Page 9 of 13
`
`

`
`3
`tially maintained. This can be expressed (when taken
`ideally to completion) by:
`
`5,153,081
`
`lithium manganese
`
`4
`Zn(anode)/electrolyte/layered
`oxide compound (cathode).
`In such cells. when the active anode material is lith(cid:173)
`ium, discharging such cells will involve insertion of Li
`5 cations into the cathode, with associated reduction or'
`the Mn cations, from a theoretical maximum average
`valency of +4 when the cathode is Az-2xMn03-x as
`described herein, to a theoretical average minimum
`valency of + 3. Although reduction of the Mn cations
`to an average valency of less than + 3 is in principle
`possible, the electrochemical reaction when the average
`valency drops to below + 3 will be associated with a
`drop in voltage from an open circuit value of approxi-
`mately 3 V to below 2 V, which limits its usefulness. In
`practice, the average valency of the Mn cations will be
`controlled during charging and discharging to be be(cid:173)
`tween suitable values, e.g., a value of +4 in the nomi(cid:173)
`nally fully charged state and a value of + 3 in the nomi-
`nally fully discharged state.
`While the cells of the invention, as indicated above,
`may be rechargeable storage cells, they may also, natu(cid:173)
`rally, be primary cells. Rechargeable cells can in princi(cid:173)
`ple be loaded at any convenient average valency of the
`Mn cations between its said average values in the nomi(cid:173)
`nally fully discharged, nominally fully charged states,
`i.e., at any value between +3 and +4.
`The cathode may comprise said lithium manganese
`oxide in particulate form compacted together with a
`suitable particular binder and a suitable electronically
`conductive particulate current collector to form a uni(cid:173)
`tary artifact. More particularly, the binder may be poly(cid:173)
`tetrafluoroethylene, the current collector being acety(cid:173)
`lene black, and said polytetrafluoroethylene and acety-
`35 lene black being mixed with the lithium manganese
`oxide of the cathode in the usual proportions employed
`in the art, e.g., a mass ratio of polytetrafluoroethylene(cid:173)
`:acetylene black ratio of 1:2 being used and the binder
`and particulate current collector together making up
`20% by mass of the artifact, the compaction being by
`pressing on to a stainless steel current collector at a
`pressure of 5-15 MPa.
`In one embodiment of the cell, the anode may be
`selected from lithium metal, lithium-containing alloys,
`lithium-containing compounds and mixtures thereof,
`the electrolyte being a room-temperature electrolyte
`comprising a salt having lithium as a cation thereof
`dissolved in an organic solvent. In this embodiment, the
`anode is preferably selected from lithium metal, lithium-
`/aluminum alloys, lithium/silicon alloys, lithium/car(cid:173)
`bon compounds and mixtures thereof, the electrolyte
`comprising a solution of a salt selected from LiCl04,
`LiAsF6, LiBF4 and mixtures thereof, dissolved in an
`organic solvent selected from propylene carbonate,
`dimethoxyethane and mixtures thereof. In these cells,
`the ratio of lithium to other constituents of the anodes
`may be those typically employed in the art. In these
`cells, it is believed that the layered lithium manganese
`oxide cathode will act essentially as a two-dimensional
`cathode of the solid solution type or the intercalation
`compound type. In the cathode during discharge, Li
`ions from the anode pass through the electrolyte and
`diffuse into two-dimensional lithium ion layers or planes
`in the cathode via face-sharing octahedra and tetrahe(cid:173)
`dra, the reverse taking place during charging. How(cid:173)
`ever, when the manganese layers contain lithium ions,
`then diffusion of lithium ions from one lithium layer to
`the next lithium layer is possible, resulting in three-di-
`
`10
`
`in which each layer of Mn cations is sandwiched be(cid:173)
`tween two layers ofO anions and each layer ofO anions
`is sandwiched between a layer of 0 anions and a layer
`of Mn cations, i.e., the 0 anion layers are arranged in
`pairs with each pair sandwiched between two layers of
`Mn cations, each Mn cation layer having a pair oflayers
`of 0 anions on each side thereof.
`In practice, the Applicant has found usually that, 15
`during the leaching, not all the lithium ions can easily be
`removed from the structure. However, the degree of
`removal of lithium ions can, within limits, be controlled
`by the degree of leaching which is allowed to take
`place, to ensure that a suitable residual small proportion 20
`(at most 50% as indicated above and typically 5-30%)
`of the lithium cations originally present in the precursor
`remain in the layered product to stabilize the layered
`structure provided by the Mn02 in the product. Al(cid:173)
`though, with sufficient leaching, it is, in principle, possi- 25
`ble to leach substantially all the LizO therefrom to leave
`the layered Mn02 product described above. In this
`regard, it is also to be noted that, if the Li2Mn03 precur(cid:173)
`sor is synthesized at higher temperatures, it is more
`difficult to leach out the Li20 component from the 30
`structure by means of a mineral acid, than when it is
`synthesized at lower temperatures. For the leaching,
`hydrochloric acid or sulfuric acid will typically be used,
`and they may be found at a Molarity of 10-15, e.g.,
`about 14.
`The product, after said leaching, can contain in addi(cid:173)
`tion to said H cations, some surface water and some
`occluded water associated with grain boundaries in its
`interior. For use in electrochemical cells, as described
`hereunder, which have lithium as an active anode mate- 40
`rial, the product should be anhydrous, as the presence
`of water is undesirable and because it can react with
`said lithium. The surface water and occluded water can
`be removed, at least partially, by drying, e.g., heating to
`80' C. to remove surface water and heating up to 200' 45
`C. or more to remove said occluded water. Accord(cid:173)
`ingly, the method may include the step, after the leach(cid:173)
`ing, of drying the product by heating to remove surface
`water therefrom and to remove at least some occluded 50
`water from grain boundaries therein. The drying is
`preferably by heating under air to a temperature of at
`least 80' C. However, for use in aqueous cells in which
`zinc is the active anode material, as described hereun(cid:173)
`der, no heat treatment or drying of the product to re- 55
`move water is necessary_
`According to another aspect of the invention, there is
`provided an electrochemical cell having a cathode com.(cid:173)
`prising a layered lithium manganese oxide compound as
`described above, a suitable anode which comprises, as 60
`its active anode substance, a metal selected from lithium
`and zinc, and a suitable electrolyte whereby the anode
`and cathode are ·electrochemically coupled together.
`Such cells can accordingly be represented schemati(cid:173)
`cally (and ignoring any H cations in the layered lithium 65
`manganese oxide compound) by:
`Li(anode)/electrolyte!layered lithium manganese oxide
`(cathode); or
`
`Page 10 of 13
`
`Page 10 of 13
`
`

`
`5
`mensional diffusion pathways for the mobile lithium
`ions.
`In another embodiment of the cell, the anode may be
`selected from metallic zinc and zinc alloys, the electro(cid:173)
`lyte being a room-temperature electrolyte comprising 5
`an aqueous solution. In these cells, the electrolyte may
`be a compound selected from NH4Cl, ZnCl2 and KOH.
`In these cells, as indicated above, the electrolytes may
`accordingly be of the type used in the art for Leclanche
`cells, ZnC]z cells or KOH cells. In these cells it is con- 10
`templated that, during discharge, cations from the elec(cid:173)
`trolyte (e.g., H cations or Zn cations) will diffuse into
`the cathode structure, the reverse taking place during
`charging; and it is contemplated that said cations from
`the electrolyte will stabilize the layered structure of the 15
`cathode. Accordingly, the layered lithium manganese
`oxide of the cathode may, after cycling and in the
`charged state, contain, in addition to Li and H cations,
`a minor proportion of Zn cations which stabilize the
`charged cathode.
`
`20
`
`6
`lithium in the LiOH and the manganese in the y-Mn02
`was 2:1.
`The LiOH and y-Mn02 were mixed with a mortar
`and pestle until substantially homogeneous to form a
`mixture which was a powder with an average particle
`size of less than 50 JL· The reaction was effected by
`heating in air at 400' C. for 18 days to obtain a substan(cid:173)
`tially single-phase Li2Mn03 precursor powder.
`The precursor was leached with 14 Molar sulfuric
`acid at 25' C. for 48 hours to obtain an essentially lay(cid:173)
`ered product of formula Az-z.xMn03-x in accordance
`with the present invention in which the atomic ratio of
`Li:Mn was 0.15:1.00.
`The LizMn03 precursor and the A2-2xMn03-x
`product were subjected to X-ray diffraction using
`CuKa radiation and over the 28 range of 10' -70' . The
`diffraction pattern trace of the precursor is shown in
`FIG. 1 at (a), a similar trace for the A2-2xMn03-x
`product being shown at (b) in FIG. 1.
`
`5,153,081
`
`EXAMPLE2
`BRIEF DESCRIPTION OF THE DRAWINGS
`Example 1 was repeated in identical fashion, except
`that the heating in air was at 700' C. for 24 hours. X-ray
`FIG. 1 shows a trace of an X-ray diffraction pattern
`diffraction traces for the LizMn03 precursor and the
`of (a) a LizMn03 precursor when prepared by reacting
`y-MnOz with LiOH at 400' C., and of (b) said LizMn03 25 Az-z.xMn03-x product are shown respectively at (a)
`and (b) in FIG. 2. A schematic representation of the
`after delithiation thereof by acid treatment to remove
`Li20 to obtain an A2-2xMn03-x product in accor-
`Li2Mn03 precursor is shown in FIG. 4.
`dance with the present invention, for the 28 range of
`By way of comparison, similar X-ray diffraction
`10' -70' using CuKa radiation;
`traces for a standard (control) LiMn204 reference sam-
`FIG. 2 shows similar traces to those of FIG. 1 of (a) 30 pie and a standard (control) t..-Mn02 reference sample
`LizMn03 when prepared in the same fashion from the
`are shown in FIG. 3 at (a) and (b), respectively. It is to
`same reagents but at 700' C. instead of 400' C., and of
`be noted that the X-ray diffraction patterns for the
`(b) this LizMn03 after delithiation in the same fashion to
`A2-2xMn03-xproduct made at 400' C. [shown at (b) in
`FIG. 1] in accordance with the present invention is
`obtain an A2-2xMn03-x product according to the in-
`vention;
`35 broadly similar to that of the reference samples of FIG.
`3; and it is to be noted that the LiMn204 reference sam-
`FIG. 3 shows a trace, similar to FIG. 1, of (a) a stan-
`dard (control) LiMn204 reference sample and (b) of a
`pie has a spinel structure, and that the t..-Mn02[eference
`standard (control) f..-Mn02 reference sample;
`sample has a defect spinel structure, i.e., D1.o[Mn2]04,
`FIG. 4 shows a schematic representation of the struc-
`obtained by delithiating Li[Mnz]04 in 1 Molar sulfuric
`ture of the Li2Mn03 precursor whose trace is shown in 40 acid at 25' C. There are, however, significant differ-
`ences between the pattern at (b) in FIG. 1 and the pat-
`FIG. 2 at (a);
`FIG. 5 shows a schematic representation of an elec-
`terns at (a) and (b) in FIG. 3; and between these patterns
`((b) in FIG. 1 and (a) and (b) in FIG. 3) on the one hand
`trochemical cell according to the present invention,
`employing the A2-2xMn03-x whose trace is shown in
`and the pattern of the LbMn03 precursor shown at (a)
`FIG. 1 at (b) as its cathode;
`45 in FIG. 1 (which has a rock-salt structure) on the other
`FIG. 6 shows electrochemical discharge curves for
`hand.
`the 1st and 8th cycles, in terms of plots of cell voltage
`The pattern shown at (a) in FIG. 1 shows that the
`(V) against capacity (mAh/g), for the cell of FIG. 5;
`LizMn03 precursor made at 400' C. is significantly less
`FIG. 7 shows curves, similar to these of FIG. 6, of the
`crystalline than the Li2Mn03 precursor made at 700' C.
`1st and 8th charge curves of the cell of FIG. 5; and
`50 [shown at (a) in FIG. ,2], as reflected by the significantly
`FIG. 8 shows a cyclic voltammogram trace of the
`broader peaks shown at (a) in FIG. 1, compared with
`cell of FIG. 5, for the first three cell cycles, when the
`those at (a) in FIG. 2.
`cell is cycled at a scan rate of 1 mV /s between the
`The trace at (b) in FIG. 1 shows retention, in the
`voltage limits of 4.6 V and 1.1 V, in terms of plots of
`Az-z.xMn03-xproduct, of a strong, well resolved peak
`55 at about 19' 28, and this is indicative of the retention in
`current (rnA) against voltage (V).
`this product of the layering of the cubic-close-packed
`oxygen anion array of the Li2Mn03 precursor whose
`trace is shown at (a) in FIG. 1. The significant shift
`towards the right of this peak in the trace for the prod(cid:173)
`uct compared with the trace for the precursor (i.e., an
`increase in the 28 value at which it occurs) is also indic(cid:173)
`ative of a contraction of the layers of the lattice, which
`is an expected consequence of the delithiation. The
`overall patterns remain sufficiently unchanged, despite
`a loss of crystallinity, which indicates that the layered
`structure from the LizMn03 precursor has remained
`substantially intact in the A2-2xMn03-x product, both
`when the precursor is made at 400' C. and when it is
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`The invention will now be described, by way of non(cid:173)
`limiting illustrative example, with reference to tests 60
`which the Applicant has conducted, and with reference
`to the accompanying diagrammatic drawings.
`
`EXAMPLE 1
`A sample of lithium manganese oxide of formula 65
`Az_z.xMn03-x in accordance with the present inven(cid:173)
`tion was made by reacting together LiOH and y-Mn02
`in proportions such that the atomic ratio between the
`
`Page 11 of 13
`
`Page 11 of 13
`
`

`
`7
`made at 700• C. However, changes in intensity of peaks
`from (a) to (b) in FIG. 1 (see e.g., the peaks at about 45•
`20) indicate that some of the manganese cations may be
`displaced during the delithiation, probably into vacan(cid:173)
`cies created by the removal of lithium cations from the 5
`lithium layers of the precursor during the delithiation.
`In a spinel such as LiMn204, or in the defect spinel
`A.-Mn02, the manganese cations occupy octahedral sites
`in alternate layers in a 3:1 ratio, and it is to be noted that
`the trace shown at (b) in FIG. 1 also resembles, but is 10
`not identical to, the traces of the LiMn204 and A-Mn02
`spinel reference samples shown respectively in FIG. 3
`at (a) and (b). Thus, a doublet peak at about 64 • -66• 20
`in the trace at (a) in FIG. 1 of LbMn03 is reflected by
`a single peak in FIG. 3 at (a) and (b) respectively for 15
`LiMn204 and A-Mn02. At (b) in FIG. 1 the peak at
`about 66. 20 is a broad singlet, which implies that the
`symmetry of the A2-2xMn03-x phase is closer to the
`cubic symmetry of LiMn204 or /,-Mn02 (in which the
`separation of oxygen layers is identical from layer-to- 20
`layer, than to that of LbMn03, which is monoclinic
`symmetry, in which only alternate oxygen layers have
`the same interplanar d-spacings.
`It is therefore believed that the A2-2xMn03-x prod(cid:173)
`uct of the present invention has a layered structure 25
`intermediate that of an ideal layered structure in which
`the manganese cations are restricted to alternate cation
`layers, and that of LiMn204, so that more than 75% of
`the manganese cations of the product are present in the
`Mn layers, less than 25% of said Mn cations being pres- 30
`ent in the Li cation layers. Furthermore, it has been
`shown that when Li20 has been leached out of the
`structure such that the Li:Mn atomic ratio is 0.5, then
`heat treatment to 350• C. or more transforms the deli(cid:173)
`thiated compound to a spinel structure, i.e., LiMn204, 35
`or an oxygen-rich spinel structure, i.e., LiMn204+o• in
`which 0~8~0.5.
`It is apparent from trace (b) in FIG. 2 that it is more
`difficult to leach out the LhO component from the
`LbMn03 precursor of Example 2 than from that of 40
`Example 1, which precursor was made at a higher tem(cid:173)
`perature than that of FIG. 1. However, the onset of
`A2-2xMn03-x formation by leaching is clearly appar(cid:173)
`ent from the peaks at about 19• 20 and at about 38• 20
`as indicated in trace (b) of FIG. 2.
`The compound A2-2xMn03-x. particularly as de(cid:173)
`scribed above With reference to examples 1 and 2, has
`good electrochemical activity in primary and recharge(cid:173)
`able cells of the type:
`
`45
`
`Li(anode)/electrolyte/ A2-2xMn03-x (cathode)
`
`50
`
`as described hereunder.
`Turning to FIG. 5 of the drawings, a cell in accor(cid:173)
`dance with the invention is shown schematically and is
`designated by reference numeral 10. The cell is of the 55
`type:
`
`Lithium metal (anode)/electrolyte/ A2-2xMn03-x
`(cathode)
`
`60
`
`the electrolyte being 1 Molar LiCI04 in propylene car(cid:173)
`bonate.
`The cell is designated 10 and the anode, electrolyte
`and cathode are respectively designated 12, 14 and 16,
`being contained in an insulating housing 18 with the 65
`anode separated from the cathode by the electrolyte
`and suitable terminals (not shown) being provided in
`electronic contact respectively with the anode and the
`
`5,153,081
`
`8
`cathode. In the cathode, the A2-2xMn03-x in powder
`form is mixed with polytetrafluoroethylene and acety(cid:173)
`lene black.
`In the cathode, the polytetrafluoroethylene is a
`binder and the acetylene black is a current collector.
`The A2- 2xMn03-x in powder form is mixed in a mass
`proportion of 80% A2-2xMn03-x with 20% by mass
`polytetrafluoroethylene and acetylene black, with the
`polytetrafluoroethylene and acetylene black being in a
`mass ratio of I :2, and compacted at 5-10 MPa pressure,
`onto a stainless steel current collector.
`the A2-2xMn03-x used was that produced by Exam(cid:173)
`ple 1 above and heated in air at so· c. for 48 hours to
`remove water and at least some of any water occluded
`at grain boundaries therein, prior to use.
`The cell10 was subjected to a number of charge/dis(cid:173)
`charge cycles, the initial cycle being a discharge cycle,
`and in FIGS. 6 and 7 are shown respectively the 1st and
`8th discharge cycles, on the one hand, and the 1st and
`8th charge cycles, on the other hand, with cell voltage
`(V) being plotted against cell capacity (mAh/g).
`Cyclic voltammetry tests were carried out on a simi(cid:173)
`lar cell and FIG. 8 shows a voltammogram in which
`current (rnA) is plotted against voltage (V), between
`voltage limits of 4.6 V and 1.1 V for the first three cell
`cycles. The scan rate was 1 m V /s. From this voltammo(cid:173)
`gram it can be seen that lithium can be inserted into and
`extracted from the product Az-2xMn03-x in question,
`at voltages which correspond to typical reduction of
`Mn4+ and oxidation Mn3 +. It thus follows that the
`A2-2xMn03-x product contains Mn with an average
`valency between 3+ and 4+, i.e., a mixed 3+/4+
`valency during charging and discharging.
`The cell10, during its first 8 charge/discharge cycles
`was discharged at a rate of 200 ILA/cm 2 and charged at
`a rate of 100 ILA/cm2, between voltage limits of 2.40 V
`and 3.80 V at room temperature. The cathode com(cid:173)
`prised 40 mg of active cathode material (A2-2xM(cid:173)
`n03-x), mixed with said 20% by mass ofpolytetrafluo(cid:173)
`roethylene and acetylene (carbon) black in a mass ratio
`of 1:2 of polytetrafluoroethylene:acetylene black.
`Results are set forth in the following Table:
`TABLE
`
`Discharge Capacity
`Data Capacity (mAh/g)
`
`Cycle No.
`
`Charge Capacity
`Data Capacity