as United States
`a2) Patent Application Publication co) Pub. No.: US 2002/0012830 A1
`
` Uemuraetal. (43) Pub. Date: Jan. 31, 2002
`
`
`US 20020012830A1
`
`(54) RECHARGEABLE LITHIUM BATTERY
`
`Publication Classification
`
`(75)
`
`Inventors: Ryuzo Uemura, Kanagawa-ken (JP);
`Toshihiro Takekawa, Kanagawa-ken
`(JP); Fumio Munakata, Kanagawa-ken
`(JP)
`
`Correspondence Address:
`McDERMOTT, WILL & EMERY
`600 13th Street, N.W.
`Washington, DC 20005-3096 (US)
`(73) Assignee: Nissan Motor Co., Ltd.
`(21) Appl. No.:
`09/917,745
`
`(22)
`
`Filed:
`
`Jul. 31, 2001
`
`(30)
`
`Foreign Application Priority Data
`
`Jul. 31, 2000
`
`(IP) nee eeeesneeseneeeeene P2000-230492
`
`Int. Ch?eee HOLM 4/48; HO1M 4/52;
`(1)
`HOIM 4/50
`.
`(52) U.S. Ch aceecscsctneee 429/60; 429/231.95; 429/224;
`429/231.1; 429/231.2; 429/231.3;
`429/231.5; 429/221
`
`(57)
`
`ABSTRACT
`
`Arechargeablelithium battery includes a negative electrode
`material having a total irreversible capacity of 45% orless
`of a total capacity of a positive electrode material. By
`adjusting the irreversible capacity of the negative electrode
`material
`in a wide range, a crystalline structure of the
`positive electrode material during charge-discharge is stably
`maintained, and cyclic resistance of the rechargeable lithium
`battery is improved. Moreover,
`the rechargeable lithium
`battery having a large capacity and high cyclic resistance at
`high temperature can be provided by the use of Li deficient
`type lithium manganese oxide of a layer structure as a
`
`1
`
`APPLE-1018
`
`positive electrode material.
`
`APPLE-1018
`
`1
`
`

`

`FIG.1
`
`2
`
`

`

`Patent Application Publication
`
`Jan. 31,2002 Sheet 2 of 4
`
`US 2002/0012830 Al
`
`FIG.2
`
` 250
`
`200
`
`150
`
`100
`
`50
`
`9
`
`80
`
`85
`
`90
`
`95
`
`100
`
`Content of Carbon[%]
`
`24
`
`&>3
`
`SY
`
`oO
`
`Ks)
`®
`
`© ~
`
`3
`
`

`

`Jan. 31, 2002
`
`Sheet 3 of 4
`
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`
`US 2002/0012830 Al
`
`Patent Application Publication
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`4
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`
`
`

`

`Patent Application Publication
`
`Jan. 31, 2002 Sheet 4 of 4
`
`US 2002/0012830 Al
`
`FIG.4
`
`awe
`
`ele|ee”
`hanged
`
`5
`
`

`

`US 2002/0012830 Al
`
`Jan. 31, 2002
`
`RECHARGEABLE LITHIUM BATTERY
`
`BACKGROUND OF THE INVENTION
`
`[0001]
`
`1. Ficld of the Invention
`
`[0002] The present invention relates to a non-aqucous
`electrolytic rechargeable lithium battery, more particularly,
`to a negative electrode material and a positive electrode
`material for improving cyclic resistance.
`
`[0003]
`
`2. Description of the Related Art
`
`In recent years, developmentof anelectric vehicle
`[0004]
`that is of zero emission has been strongly desired as interest
`in an environmental problem has been increased. As a power
`source for such an electric vehicle, a rechargeable lithium
`baltery among various
`secondary batteries has been
`expected as a secondary battery for an electric vehicle
`because it has a high charge-discharge voltage and a large
`charge-discharge capacity.
`
`In the rechargeable lithiumbattery, a carbon mate-
`[0005]
`rial such as graphite and hard carbon has been mainly
`employed as a negative electrode material. Also composition
`of the carbon material in which an irreversible capacity of a
`negative electrode material is suppressed has been employed
`so as to be as small as possible in order to improve a
`charge-discharge capacity of a battery.
`
`[0006] Meanwhile, as a positive electrode material, par-
`ticularly as a positive electrode active material, LiCoO, has
`been employed. However cobalt (Co) is high price and the
`LiCoO,is unstable under an environment where a battery is
`operated. Lithium manganese complex oxide (LiMn,O,) of
`spinel structure has been mainly employed as a positive
`electrode active material of the rechargeable lithium battery
`for an electric vehicle (Japanese Laid-Open Patent Publica-
`tions No. Hei 11-171550 (published in 1999) and No. Hei
`11-73962 (published in 1999)).
`
`[0007] Though LiMn,O, of spinel structure is good in
`cyclic resistance in comparison with the conventional
`LiCoO,, the cyclic resistance at high temperature is insuf-
`ficient, thus causing a problem that the positive material is
`dissolved in an electrolyte to cause deterioration of the
`negative electrode in performance. As meansfor solvingthis
`problem, a technique for substituting a part of Mn for a
`transition metal elementor a typical metal element has been
`tested. However, if Mn is substituted for various elements
`for the purpose of improving the cyclic resistance at high
`temperature, distortion is thereby brought into a crystalline
`structure, leading also to deterioration of the cyclic resis-
`tance at room temperature (Japanese Laid-Open Patent
`Publication No. Hei 11-71115 (published in 1999)). More-
`over,
`if substitution of a large quantity of elements is
`performed in order to stabilize the crystalline structure for
`the purpose of improving the cyclic resistance, lowering of
`a capacity is brought about.
`
`[0008] Furthermore, though both of a large capacity and
`high cyclic resistance are required for the positive electrode
`active material, the capacity of LiMn.O, of spinel structure
`is 100 mAh/g, which is lower than the capacity of 140
`mAh/g of the conventionally used LiCoO, based material.
`
`than
`is stabler
`though it
`the capacity thereof is small
`LiCoO,. Therefore, desired is development of a novel posi-
`tive electrode material provided with both of the large
`capacity and the high cyclic resistance.
`
`SUMMARY OF THE INVENTION
`
`In order to find a new positive electrode active
`[0010]
`material of high-capacity lithium complex oxide, research
`has been carried out based on a study in crystal chemistry
`(Japanese Patent Publication No. 2870741). In recent years,
`a LiMnO, based material of layer structure, which has a
`much larger capacity than the conventional LiCoO., based
`material, has been introduced (A. Robert and P. G. Buruce:
`Nature, vol. 381 (1996) p. 499). The capacity of the layered
`LiMnO,based material is about 270 mAh/g, which is more
`than twice the capacity of the conventional LiMn,O, of
`spinel structure.
`
`[0011] However, if the layered LiMnO, based material
`having a large capacity is employed as a positive electrode
`active material of the rechargeable lithium battery, a suffi-
`cient charge-discharge characteristic is obtained at,
`for
`example, 55° C., however, the capacity at room temperature
`is reduced to about one-third. Moreover, when charge and
`discharge are repeated at higher temperature than room
`temperature in order to ensure the sufficient charge-dis-
`charge characteristic, the capacity is gradually reduced, and
`the sufficient cyclic characteristic is not ensured.
`
`{0012] An object of the present invention is to provide a
`rechargeable lithium battery capable of improving the cyclic
`resistance, more particularly,
`to provide a rechargeable
`lithium battery structure capable of ensuring good cyclic
`resistance in the case of using a positive electrode material
`with a large capacity but unstable as described above.
`
`Inorder to achieve the above object, a rechargeable
`[0013]
`lithium battery of the present invention is characterized in
`that a negative electrode material having a total irreversible
`capacity of 45% or less of a total capacity of a positive
`electrode is employed.
`
`[0014] According to an aspect of the above rechargeable
`lithium battery of the present invention,
`the irreversible
`capacity of the negative electrode material can be adjusted
`in a wide range, and thus Li deficient quantity from the
`positive electrode material during charge can be adjusted.
`
`[0015] Therefore, as in the aspect of the present invention,
`if the layered lithium manganese complex oxide with a large
`capacity but without
`sufficient
`structural
`stability is
`employed as a positive electrode material, the total irrevers-
`ible capacity of the negative electrode material is adjusted so
`as to be larger thanthat of the conventional one, for example,
`in a range of about 10% to about 45%, preferably about 20%
`to about 36%, of the total capacity of the positive electrode
`material. Thus, the structure of the positive electrode mate-
`rial can be stabilized during charge-discharge, resulting in an
`increase of the cyclic resistance of the rechargeable lithium
`battery.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`
`[0009] As described above, LiCoO, is unstable though it [0016] FIG.1is a perspective view showing the structure
`has a large capacity. Meanwhile, LiMn,O, of spinel struc-
`example of a rechargeable lithium battery according to an
`ture cannot be said to be sufficient in cyclic resistance and
`embodiment of the present invention.
`
`6
`
`

`

`US 2002/0012830 Al
`
`Jan. 31, 2002
`
`[0017] FIG.2is a graph showingthe relationship between
`trode material with a larger irreversible capacity than the
`carbon contents and irreversible capacities of carbon mate-
`conventional one are employed in combination,
`the Li
`rial employed as a negative electrode of the rechargeable
`deficient quantity of the positive electrode material, which is
`lithium battery.
`caused by the charge-discharge, can be substantially
`increased by increasing the irreversible capacity of the
`negative electrode material more than that of the conven-
`tional one. For example, if the negative electrode material
`with a total irreversible capacity of 10% or more, or 20% or
`more of a total capacity of the positive electrode material is
`used, the crystalline structure can be stabilized more, and the
`cyclic resistance of the rechargeable lithium battery can be
`improved.
`
`[0018] FIG. 3 is a table showing the composition of a
`positive electrode, the irreversible capacity of the negative
`electrode, the numberof cycles andthe like of each example
`and a comparison example of the present invention.
`
`[0019] FIG. 4 is a perspective view showingthe structure
`of a battery cell fabricated in the examples of the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`
`[0020]
`
`(1. Negative Electrode Material)
`
`lithium ions
`In a rechargeable lithium battery,
`{0021]
`partially escape from a positive electrode byinitial charge,
`pass through an electrolyte, and are doped onto a negative
`electrode. During discharge, the lithium ions doped onto the
`negative electrode return to the positive electrode. At this
`time, however, somelithium ions remainstill in the negative
`electrode, and do not contribute to the discharge. A quantity
`of Li
`ions remaining in the negative electrode without
`movingto the positive electrode during the discharge on and
`after the initial chargeis called an irreversible componentof
`the negative electrode, and a capacity thereof is called an
`irreversible capacity.
`
`[0022] The inventors of the present invention analyzed the
`irreversible capacity of a carbon material as a negative
`electrode of the rechargeable lithium battery. As a result, as
`shown in FIG.2, it has been found out that the irreversible
`capacity of the carbon material is inverscly proportional to
`a carbon content in the material, that is, purity of the carbon
`material, and that, as the carbon content
`in a negative
`electrode material is lowered,
`the irreversible capacity is
`increased. Specifically, it has been found out that the irre-
`versible capacity of the carbon material can be adjusted by
`the carbon content in the negative electrode material.
`
`type
`in the case where Li deficient
`[0026] Moreover,
`layered lithium manganese complex oxide, which is repre-
`sented by a general formula Li,_.Mn,_,M,O. (where M is a
`metal element, x>0, y>0),
`is used as a positive electrode
`material, the positive electrode already has a stable structure
`wherethe L1is deficient before the charge-discharge. There-
`fore, the cyclic resistance can be further improved.
`
`[0027] However, if the irreversible capacity of the nega-
`tive electrode material is increased too much,the discharge
`capacity of the rechargeable lithium battery is reduced to a
`great extent, and a merit of using the layered lithium
`manganese complex oxide material having high capacity as
`a positive material is lost. Therefore, the total irreversible
`capacity of the negative electrode material should be fixed at
`a range of about 45% orless, preferably about 36% orless,
`of the total capacity of the positive electrode material.
`
`Specifically, in the rechargeable lithium battery of
`[0028]
`this embodiment, the total irreversible capacity of the nega-
`tive electrode material should be fixed at a range of about
`10% or moreto about 45% orless, preferably about 20% or
`more to about 36% or less, of the total capacity of the
`positive electrode material.
`
`[0029] The negative electrode material described aboveis
`not limited to a carbon material, but various complex oxide
`or nitride can be also used. When these materials are
`employed as a negative electrode material,
`it
`is recom-
`mended to use a negative electrode material of weight
`obtained by dividing a capacity equivalent to 45% or less of
`the total capacity of the positive electrode material by an
`irreversible capacity of the negative electrode material per
`unit weight.
`
`Theirreversible capacity of the negative electrode
`[0023]
`material determines a quantity of Li ions coming in and out
`of the positive electrode material, that is, a discharge capac-
`ity on and after the second charge and discharge of the
`rechargeable lithium battery. When the irreversible capacity
`is increased, the discharge capacity is reduced. Therefore, in
`general, it is preferable to use a negative electrode material
`with an irreversible capacity as low as possible in order to
`increase the charge-discharge quantity of a battery. As with
`reference to the graph of FIG.2, the irreversible capacity of
`
`
`[0031] capacity)=-10.1x(carbon—con-(Irreversible
`the negative electrode can be suppressed by the use of a
`fent)(%)+(1006 to 1066)
`carbon material with the highest possible purity.
`
`It should be noted that, in the case where a carbon
`[0030]
`material is employed as the negative electrode material of
`the rechargeable lithium battery, the irreversible capacity of
`the negative electrode material is represented by the follow-
`ing formula with reference to the graph of FIG.2.
`
`[0024] Meanwhile, the inventors of the present invention
`found out that
`the Li deficient quantity of the positive
`electrode material, which is caused by the charge-discharge
`of the battery, can be adjusted by adjusting the irreversible
`capacity of the negative electrode material in a wider range,
`and thus the crystalline structure of the positive electrode
`material can be stabilized.
`
`(0025] For example, in the case where the layered lithium
`manganese complex oxide with a very large capacity but
`with an unstable crystalline structure and the negative elec-
`
`[0032] According to the above formula, a carbon content
`(%) of the carbon negative electrode material with a speci-
`fied irreversible capacity,
`that
`is, carbon purity can be
`determined.
`
`{0033] Furthermore, a capacity balance ratio B/A of the
`total capacity B of the negative electrode materialto the total
`capacity A of the positive electrode material is preferably
`fixed at a range of 1 to 1.5. If the capacity balance ratio B/A
`is below 1, lithium ion holding sites on the negative elec-
`trode material become insufficient. As the result, branch-
`
`7
`
`

`

`US 2002/0012830 Al
`
`Jan. 31, 2002
`
`shaped or needle-shaped crystal (dendrite crystal) tends to
`occur during the charge to cause a short circuit phenomenon
`between the positive electrode and the negative electrode. If
`the capacity balance ratio B/A exceeds 1.5, negative elec-
`trode sites that do not contribute to the charge-discharge are
`increased, leading to the wasteful use of materials.
`[0034]
`(2. Positive Electrode Material)
`[0035] A type of the positive electrode material used in
`combination with the negative electrode material described
`above is not particularly limited, but Li deficient
`type
`lithium manganese complex oxide of a layer structure,
`which is represented by a general formula Li,,Mn0O,,
`Li,Mn,.,M,O, or Li,,Mn,.,M,O,.5,
`is desirably used.
`This layered lithium manganese complex oxide is a novel
`material found by the inventors of the present invention,
`which has been introduced from a designing concept
`described below.
`
`In typical NaCl type MO crystal (where M is metal
`[0036]
`element, O is oxygen), for example, oxide such as NiO has
`a crystalline structure in which Ni layers and O (oxygen)
`layers are alternately arrayed in a <111> orientation of the
`crystal. Moreover,
`in the conventional LIMO, complex
`oxide of a layer structure (where M is Ni, Co or Mn), the
`lithium manganese complex oxide of a layer structure taken
`as an example has a crystalline structure described below.
`Here, specifically, oxygen planes and metal planes are
`alternately and repeatedly arrayed in such a manner as:
`oxygen layer-Mn layer-oxygen layer-Li layer-oxygen layer-
`Mnlayer-oxygen layer, and further, planes (layers) having
`metal elements thereon are laminated regularly and alter-
`nately.
`[0037] As described above,it is conceived that the NaCl
`type MO crystal and the layered LIMO, complex oxide have
`structures very similar to each other. When the layered
`LiMO, complex oxide is conceived as one obtained by
`repeatedly laminating MO crystal blocks with focusing on
`the regular structure described above,
`the layered LIMO,
`complex oxide is conceived as one obtained by repeatedly
`arraying [LiO ][MO] blocks, in which MO blocks [MO] and
`LiO blocks [LiO] are laminated alternately and repeatedly.
`In this connection, when a crystalline structure of the
`conventionally known sodium manganese oxide Na,,MnO,,
`is considered by applying the block structure described
`above, Naz,MnO, can be written as [Na,,O]MnO]. This
`suggests that
`it will be possible to create novel sodium
`manganese oxide of a layer structure by reducing the Na
`occupation ratio of the [NaO] blocks in the [NaO][MO]
`blocks. If this consideration is applied to [TiO ][MO] blocks,
`it
`is possible to create novel
`layered lithium manganese
`oxide by regularly reducing the Li occupation ratio of the
`[LiO] blocks. It should be noted that the Li sites and the Mn
`sites originally differ little from each other in terms of the
`crystal chemistry, and the consideration described above can
`be also applied to the [MO] blocks similarly.
`[0038] However, if such as layered manganese oxide is
`employed as the positive electrode material of the recharge-
`able lithium battery, a quantity of Mn causing valence
`variation, which ts important in the cyclic charge-discharge,
`is desirably as muchas possible in the crystalline structure.
`For this reason, M of the [MO] blocks cannot be simply
`made deficient.
`
`[0039] Meanwhile, as in Japanese Patent No. 2870741,
`when a positive electrode active material represented bya
`
`chemical formula LiMn,_,M,O._3 (where M is a substituted
`element,y is a rational numberof0 to 0.25) is employed,the
`capacity of the battery can be increased and the resistance
`thereof can be improved in comparison with a typical active
`material of spinel structure. However, particularly in a low
`temperature range below room temperature, a sufficient
`operational characteristic cannot be ensured. Specifically,
`since the distortion and the chemical bond in the crystal
`cannot be stabilized only by substitution of the Mnsites, the
`good operation in a low temperature range cannot be
`ensured. As a result of examination for the effect of making
`positive ions deficient as described above, the inventors of
`the present invention obtained a guideline for the material
`designing described below.
`[0040]
`Specifically, making the positive ions deficient at
`the same time selecting a regular quantity of substituted
`elements can lessen distortion or strengthen the chemical
`bond to stabilize the crystal structure. If such a complex
`oxide designed under the guideline is employedas a positive
`electrode active material, reaction with an electrolytic solu-
`tion during the charge-discharge can be suppressed and
`cyclic stability, durability and stability of the rechargeable
`lithium battery can be improved.
`[0041] When the positive electrode active material of
`complex oxide with manganese layers is considered by
`applying, the above-described block structure in accordance
`with the designing guideline, the NaCl type complex oxide
`with Li deficient type layered Li,,.MnO, can be written as
`[Li,_,O][MnO]. In this case,
`the deficient quantity x is
`regularly varied, the crystalline structure can be stabilized,
`and thus the cyclic resistance can be improved. For example,
`as a value of x, there may be %, 3, %, 4, V5, 75, %,.
`¥s,.... Moreover, in order to maintain the durability and the
`stability at high temperature, a block structure of [Li,_.O]
`[Mn,_,M,O]is cnabled, in which the Mnsites are regularly
`substituted for other metal elements. For example, when
`x= and y=, a block structure [Li,,O]/Mn,,M,,0] is
`enabled, and Li.,Mni,Ni,,0, is obtained as a compound
`possible when M=Ni.
`[0042]
`Spccifically, the preferable positive clectrode mate-
`rial according to this embodiment is the Li deficient type
`layered lithium manganese complex oxide represented by
`the general formula Li,_,.Mn,,M,0,.
`[0043] Moreover, when the above-described lithium defi-
`cient quantity x is small, the quantity of lithium deficient
`from a congruent composition of the lithium-containing
`complex oxide is reduced, leading to a tendency of deterio-
`ration of the battery during the charge-discharge by Li ion
`movement, which is not preferable. When the lithium defi-
`cient quantity is too much, the quantity of lithium deficient
`from the congruent composition is increased, leading to a
`tendencythat a sufficient capacity cannot be secured. There-
`fore, the lithium deficient quantity x is desirably fixed at a
`rational number range of O<x<1, preferably 0.03<x30.5 or
`0.1<x<0.33.
`
`[0044] Moreover, the substitution quantity y of the Mn
`sites for the metal element M is desirably fixed at a rational
`number range of O<y<1, preferably 0.03<y30.5. If the
`substitution quantity for the metal element M is small, there
`occurs a tendency of deterioration of the battery during the
`discharge by Li ion movement. And on the contrary, when
`the substitution quantity is increased, there occurs a ten-
`dency in which a sufficient capacity cannot be secured.
`
`8
`
`

`

`US 2002/0012830 Al
`
`Jan. 31, 2002
`
`[0045] Furthermore, when the lithium deficient quantity x
`is represented as a/b,
`it
`is desirable that a and b are
`respectively fixed at a rational numberrange of 1 to 30, and
`that a relation of a<bis satisfied. If each of a and b is smaller
`
`than 1 or larger than 30, there occurs a tendency in which the
`effect of Li deficiencyis not sufficiently exerted, and thus the
`cyclic resistance is not ensured. And also whenthe relation
`of a<bis notsatisfied, the cyclic resistanceis not sufficiently
`secured.
`
`obtain a predeterminedtotal irreversible capacity. Further-
`more, the predetermined irreversible capacity can be also
`obtained by adjusting weight of the carbon material.
`[0054]
`(2) Positive Electrode Material
`[0055] As described above,the positive electrode material
`of the rechargeable lithium battery of this embodimentis not
`particularly limited. However, the Li deficient type lithium
`manganese complex oxide of a layer structure is preferably
`used. In order to prepare this Li deficient
`type layered
`lithium manganese complex oxide, the following process is
`used.
`
`[0052]
`
`(1) Negative Electrode Material
`
`[0053] As a negative electrode material of the recharge-
`able lithium battery of this embodiment, complex oxide,
`nitride or the like can be employed. However, a carbon
`material for use in a typical non-aqueouselectrolytic sec-
`ondary battery is preferably employed. Such a carbon mate-
`rial can include, for example, coke, natural graphite, artifi-
`cial graphite and hard carbon. As described above,
`the
`irreversible capacity of the carbon material can be basically
`controlled by the carbon content in the material. Moreover,
`since the irreversible capacity characteristic is varied in each
`carbon material, the carbon materials can be mixed so as to
`
`[0046] Still further, when the substitution quantity y of the
`Mnsites for the metal element M is represented as c¢/d, il is
`desirable that c and d be respectively set in a rational number
`range of 1 to 30, and that a relation of c<d be satisfied. The
`reasonis as follows. If each of c and d is smaller than 1 or
`
`larger than 30,the effect of substitution for the metal element
`M is notsufficiently exerted, and thus the cyclic resistance
`at high temperature is not ensured. And also when the
`relation of c<d is not satisfied, the cyclic resistance at high
`temperature is not secured.
`
`‘Yet further, composition variation ranges of the
`[0047]
`lithium deficient quantity x and of the substitution quantity
`y of the Mnsites for the metal element M are desirably set
`within +5%. The cyclic resistanceis not sufficiently ensured
`if the variation ranges exceed 45%.
`
`[0048] And, the quantity of oxygen deficiency 6 is desir-
`ably set as: 620.2. If 6 is larger than 0.2, there occurs a
`tendency in whichthe crystalline structure becomesunstable
`and deteriorated.
`
`It should be noted that the substitution metal ele-
`[0049]
`ment M is desirably at least one or more of metals selected
`from the transition metal elements and the typical metal
`elements excluding Mn. lor example, as the substitution
`metal element M, at least one selected from Co, Ni, Fe, Al,
`Ga, In, V, Nb, Ta, Ti, Zr and Ce or the one including at least
`Cr is desirable.
`
`(3. Structure and Manufacturing Method of the
`[0050]
`Rechargeable Lithium Battery)
`
`{0051] FIG. 1 showsa representative structure example of
`the rechargeable lithium battery according to the embodi-
`mentof the present invention. As shownin FIG.1, a device,
`in which a positive electrode 1 obtained by coating a positive
`electrode active material on both surfaces of a metal foil
`
`First, a manganese compound,a lithium compound
`[0056]
`and a metal compound are mixed. As the manganese com-
`pound, clectrolytic manganese dioxide, chcmosynthctic
`manganese dioxide, dimanganesetrioxide, y-MnOOH,man-
`ganese carbonate, manganese nitrate, manganese acetate or
`the like can be employed. Moreover, an average diameter of
`manganese compound powderis appropriately fixed at a
`range of 0.1 to 100 um, preferably 20 wm or less. This is
`because, in the case where an average size of the manganese
`compoundis large, reaction of the manganese compound
`and the lithium compound becomessignificantly slow, and
`it becomesdifficult to obtain a uniform product.
`(0057] As
`the lithium compound,
`lithium carbonate,
`lithium hydroxide, lithium nitrate,
`lithium oxide, lithium
`acetate or the like can be employed. Lithium carbonate or
`lithium hydroxide is preferably employed, and an average
`diameter thereof is desirably 30 xm orless.
`[0058] As the metal compound, nitrate, acetate, citrate,
`chloride, hydroxide, oxide orthe like oftransition metal can
`be employed.
`[0059] A mixing method of the above-described materials
`includes a dry or wet mixing method of the manganese
`compound, the lithium compoundand the transition metal
`compound, a dry or wet mixing method of the lithium
`compound and manganese-transition metal complex oxide
`obtained by synthesizing the manganese compound and the
`transition metal compound, a dry or wet mixing method of
`LiMnO, and the transition metal compound, a method of
`obtaining a product from a solution of the lithium com-
`pound, the manganese compoundandthe transition metal
`compound by a coprecipitation method bythe use ofcitric
`acid, ammonium bicarbonate and the like. The most suitable
`method for obtaining a homogeneous productis the one, in
`collector, a negative electrode 3 similarly obtained by coat-
`which a mixed solution obtained by completely dissolving
`ing a negative electrode active material on both surfaces of
`the manganese compound and the transition metal com-
`a metal foil collector, and separator 3 interposed between the
`pound into ion-exchange water in advance is dropped into a
`both electrodes are wound inaroll fashion, is accommo-
`lithium hydroxide solution to obtain a coprecipitation prod-
`dated in a sealing can 4, and an electrolyte (electrolytic
`uct, and then the coprecipitation product and the lithium
`solution) is filled therein.
`compoundof a quantity short for the target composition ratio
`are mixed by dry or wet mixing. The coprecipitation product
`obtained by the above-described method may be employed
`by adding the lithium compound of a quantity short for the
`target composition ratio thereto, after it is made to be a
`manganese-transition complex metal compound by baking.
`[0060] Next,
`the mixture thus obtained is baked. The
`baking must be performed in an atmosphere with a low
`oxygen density. Preferably, the baking is performed in an
`atmosphere of gas containing no oxygen suchas nitrogen,
`argon and carbon dioxide. Andin this case, a partial pressure
`of oxygen is set equal to 1000 ppm orless, preferably 100
`ppm orless.
`
`9
`
`

`

`US 2002/0012830 Al
`
`Jan. 31, 2002
`
`[0061] Baking temperature is fixed equal to 1100° C. or
`less, preferably 950° C. or less. This is because the product
`is decomposed if the temperature exceeds 1100° C. Baking
`time is fixed at a range of 1 to 48 hours, preferably 5 to 24
`hours. As the baking method, one-step baking may be
`employed. Also a multi-step baking performed by varying a
`baking temperature may be performed according to needs.
`
`the partial pressure of
`It should be noted that
`[0062]
`oxygen in the baking atmosphere can be efficiently reduced
`by adding a carbon-containing compound,preferably carbon
`powder such as carbon black and acetylene black, or an
`organic material such as citric acid to the mixture of the
`lithium compound and the manganese compound. A content
`of such additive is fixed at a range of 0.05 to 10%, preferably
`0.1 to 2%. If the quantity of additive is small, an effect
`thereof is small. On the contrary, if the quantity is large, a
`by-product tends to be generated, and therefore, purityof the
`target product is reduced due to the residual carbon-con-
`taining compound added.
`
`[0063]
`
`(3) Non-aqueous Electrolyte
`
`[0064] As a non-aqueous electrolyte (non-aqueous elec-
`trolytic solution), the one obtained by dissolving a lithium
`salt as a supporting electrolyte into a non-aqueous organic
`solvent. As a lithium salt, LiclO,, LiAsF,, LiPF,, LiBF,,
`LiCF,SO,;, Li(CF,SO,),N or the like can be employed.
`
`is not particularly limited.
`[0065] The organic solvent
`However, it includes a carbonate group, a lactone group, an
`ether group and the like. For example, a solvent such as
`ethylene carbonate, propylene carbonate, diethyl carbonate,
`dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy
`ethane, 1-2-diethoxy ethane, tetrahydrofuran,1,3-dioxolane,
`y-buthyrolactone can be employed singly or in mixture of
`two or more. Concentration of the electrolyte dissolved in
`such a solvent can be fixed at a range of 0.5 to 2.0 mol/l.
`
`[0066] Besides the above solvent, a solid or viscous body
`having a lithium salt dispersed evenly in a high molecular
`matrix or the one obtained by immersing a non-aqueous
`solvent in such a solid or viscous bodycan be also used. As
`a high molecular matrix, for example, polyethylene oxide,
`polypropylene oxide, polyacrylonitrile, polyvinylidene fluo-
`ride or the like can be used.
`
`[0067] Moreover, for the purpose of preventi