(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0012830 A1
`(43) Pub. Date:
`Jan. 31, 2002
`Uemura et al.
`
`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 (JP).................................... P2000-2304.92
`
`
`
`(51) Int. Cl." ............................ H01M 4/48; H01 M 4/52;
`HO1 M 4/50
`(52) U.S. Cl. ...................... 429/60; 429/231.95; 429/224;
`429/231.1; 429/2312; 429/231.3;
`429/231.5; 429/221
`
`ABSTRACT
`(57)
`A rechargeable lithium battery includes a negative electrode
`material having a total irreversible capacity of 45% or less
`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
`positive electrode material.
`
`1
`
`APPLE 1009
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`

`

`FIG. 1
`
`2
`
`

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`Patent Application Publication Jan. 31, 2002 Sheet 2 of 4
`FIG.2
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`US 2002/0012830 A1
`
`250
`
`
`
`t
`G a 200
`E.
`D g 150
`g
`
`100
`
`()
`
`s
`g 50
`
`0.
`80
`
`85
`
`90
`
`95
`
`100
`
`Content of Carbon%
`
`3
`
`

`

`Patent Application Publication
`
`Jan. 31, 2002. Sheet 3 of 4
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`US 2002/0012830 A1
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`
`
`4
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`

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`Patent Application Publication Jan. 31, 2002. Sheet 4 of 4
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`US 2002/0012830 A1
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`FIG.4
`
`
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`5
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`

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`US 2002/0012830 A1
`
`Jan. 31, 2002
`
`RECHARGEABLE LITHIUM BATTERY
`
`BACKGROUND OF THE INVENTION
`0001) 1. Field of the Invention
`0002 The present invention relates to a non-aqueous
`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
`0004.
`In recent years, development of an electric vehicle
`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
`battery 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.
`0005. In the rechargeable lithium battery, a carbon mate
`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 (LiMnO) 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 LiMnO 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 means for Solving this
`problem, a technique for Substituting a part of Mn for a
`transition metal element or 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 LiMnO of Spinel Structure
`is 100 mAh/g, which is lower than the capacity of 140
`mAh/g of the conventionally used LiCoO based material.
`0009. As described above, LiCoO is unstable though it
`has a large capacity. Meanwhile, LiMnO of Spinel Struc
`ture cannot be said to be Sufficient in cyclic resistance and
`
`the capacity thereof is Small though it is stabler than
`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
`0010. In order to find a new positive electrode active
`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 LiMnO 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.
`0013 In order to achieve the above object, a rechargeable
`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 than that 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
`0016 FIG. 1 is a perspective view showing the structure
`example of a rechargeable lithium battery according to an
`embodiment of the present invention.
`
`6
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`
`Jan. 31, 2002
`
`0017 FIG. 2 is a graph showing the relationship between
`carbon contents and irreversible capacities of carbon mate
`rial employed as a negative electrode of the rechargeable
`lithium battery.
`0.018
`FIG. 3 is a table showing the composition of a
`positive electrode, the irreversible capacity of the negative
`electrode, the number of cycles and the like of each example
`and a comparison example of the present invention.
`0.019
`FIG. 4 is a perspective view showing the structure
`of a battery cell fabricated in the examples of the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`0020 (1. Negative Electrode Material)
`0021. In a rechargeable lithium battery, lithium ions
`partially escape from a positive electrode by initial 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, Some lithium ions remain Still in the negative
`electrode, and do not contribute to the discharge. A quantity
`of Li ions remaining in the negative electrode without
`moving to the positive electrode during the discharge on and
`after the initial charge is called an irreversible component of
`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 inversely 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.
`0023 The irreversible capacity of the negative electrode
`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
`the negative electrode can be Suppressed by the use of a
`carbon material with the highest possible purity.
`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.
`0.025
`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
`
`trode material with a larger irreversible capacity than the
`conventional one are employed in combination, the Li
`deficient quantity of the positive electrode material, which is
`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.
`0026. Moreover, in the case where Li deficient type
`layered lithium manganese complex oxide, which is repre
`sented by a general formula Li-MiniMO (where M is a
`metal element, XZ0, y >0), is used as a positive electrode
`material, the positive electrode already has a Stable structure
`where the Li is 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% or less, preferably about 36% or less,
`of the total capacity of the positive electrode material.
`0028 Specifically, in the rechargeable lithium battery of
`this embodiment, the total irreversible capacity of the nega
`tive electrode material should be fixed at a range of about
`10% or more to about 45% or less, 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 above is
`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.
`0030. It should be noted that, in the case where a carbon
`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.
`capacity)=-10.1 x(carbon
`0031) (Irreversible
`tent)(%)+(1006 to 1066)
`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 material to 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
`
`con
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`US 2002/0012830 A1
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`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)
`0.035 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-MnO,
`LiMn, MO, or Li, Mn, M.O.s, 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.
`0036). In typical NaCl type MO crystal (where M is metal
`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-Lilayer-oxygen layer
`Mn layer-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 LiOMO 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 Na2MnO2
`is considered by applying the block Structure described
`above, Na-MnO can be written as Na2OMnO). 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 NaOMO
`blocks. If this consideration is applied to LiOMO 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 Lisites 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 IMO blocks similarly.
`0.038 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 is important in the cyclic charge-discharge,
`is desirably as much as possible in the crystalline Structure.
`For this reason, M of the IMO blocks cannot be simply
`made deficient.
`0039) Meanwhile, as in Japanese Patent No. 2870741,
`when a positive electrode active material represented by a
`
`chemical formula LiMn-MOs (where M is a substituted
`element, y is a rational number of 0 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 Mn sites, 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 employed as 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
`LiOMnO). 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 /2, /3, 73, 4, /s, 2/5, /6, . . .
`/s, . . . . Moreover, in order to maintain the durability and the
`Stability at high temperature, a block structure of LiO
`Mn, MO) is enabled, in which the Mn sites are regularly
`substituted for other metal elements. For example, when
`x=/3 and y=%, a block structure Li. OIMn, MO is
`enabled, and Li,Mn,NiO is obtained as a compound
`possible when M=Ni.
`0042 Specifically, the preferable positive electrode mate
`rial according to this embodiment is the Li deficient type
`layered lithium manganese complex oxide represented by
`the general formula Li-Mn-MO.
`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
`tendency that a Sufficient capacity cannot be Secured. There
`fore, the lithium deficient quantity X is desirably fixed at a
`rational number range of 0<x<1, preferably 0.03<Xs 0.5 or
`O.1X0.33.
`0044) Moreover, the substitution quantity y of the Mn
`sites for the metal element M is desirably fixed at a rational
`number range of 0<y<1, preferably 0.03<ys 0.5. 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.
`
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`Jan. 31, 2002
`
`0.045. 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 number range of 1 to 30, and
`that a relation of azb is 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 deficiency is not sufficiently exerted, and thus the
`cyclic resistance is not ensured. And also when the relation
`ofa-b is not Satisfied, the cyclic resistance is not Sufficiently
`Secured.
`0.046
`Still further, when the Substitution quantity y of the
`Mn sites for the metal element M is represented as c/d, it 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
`reason is 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 not Sufficiently 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.
`0047 Yet further, composition variation ranges of the
`lithium deficient quantity X and of the Substitution quantity
`y of the Mn sites for the metal element M are desirably set
`within +5%. The cyclic resistance is not sufficiently ensured
`if the variation ranges exceed its%.
`0.048 And, the quantity of oxygen deficiency 8 is desir
`ably set as: Ös 0.2. If 6 is larger than 0.2, there occurs a
`tendency in which the crystalline Structure becomes unstable
`and deteriorated.
`0049. It should be noted that the substitution metal ele
`ment M is desirably at least one or more of metals selected
`from the transition metal elements and the typical metal
`elements excluding Mn. For 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.
`0050 (3. Structure and Manufacturing Method of the
`Rechargeable Lithium Battery)
`0051
`FIG. 1 shows a representative structure example of
`the rechargeable lithium battery according to the embodi
`ment of the present invention. As shown in 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
`collector, a negative electrode 3 Similarly obtained by coat
`ing a negative electrode active material on both Surfaces of
`a metal foil collector, and Separator 3 interposed between the
`both electrodes are wound in a roll fashion, is accommo
`dated in a Sealing can 4, and an electrolyte (electrolytic
`solution) is filled therein.
`0.052
`(1) Negative Electrode Material
`0.053 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-aqueous electrolytic 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
`
`obtain a predetermined total 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 embodiment is 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.
`0056 First, a manganese compound, a lithium compound
`and a metal compound are mixed. AS the manganese com
`pound, electrolytic manganese dioxide, chemosynthetic
`manganese dioxide, dimanganese trioxide, Y-MnOOH, man
`ganese carbonate, manganese nitrate, manganese acetate or
`the like can be employed. Moreover, an average diameter of
`manganese compound powder is appropriately fixed at a
`range of 0.1 to 100 um, preferably 20 um or less. This is
`because, in the case where an average size of the manganese
`compound is large, reaction of the manganese compound
`and the lithium compound becomes significantly slow, and
`it becomes difficult 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 um or less.
`0.058 As the metal compound, nitrate, acetate, citrate,
`chloride, hydroxide, oxide or the like of transition 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 compound and 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 compound and the transition metal
`compound by a coprecipitation method by the use of citric
`acid, ammonium bicarbonate and the like. The most Suitable
`method for obtaining a homogeneous product is the one, in
`which a mixed Solution obtained by completely dissolving
`the manganese compound and the transition metal com
`pound into ion-exchange water in advance is dropped into a
`lithium hydroxide Solution to obtain a coprecipitation prod
`uct, and then the coprecipitation product and the lithium
`compound of 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 Such as nitrogen,
`argon and carbon dioxide. And in this case, a partial pressure
`of oxygen is set equal to 1000 ppm or less, preferably 100
`ppm or less.
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`
`Baking temperature is fixed equal to 1100° C. or
`0061
`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.
`0.062. It should be noted that the partial pressure of
`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, purity of 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, LiCIO, LiASF, LiPF, LiBF,
`LiCFSO, Li(CFSO)N or the like can be employed.
`0065. The organic solvent is not particularly limited.
`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.
`0.066
`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 body can 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 preventing a short
`circuit between the positive electrode and the negative
`electrode, a Separator can be provided. As a separator, a
`porous sheet, a nonwoven fabric or the like made of a
`material Such as polyethylene, polypropylene and cellulose
`is employed.
`
`EXAMPLES
`0068 Examples of the present invention and a compara
`tive example will be described.
`0069. The positive electrode materials of the recharge
`able lithium batteries in examples 1 to 9 were prepared by
`the use of a coprecipitation method described below. The
`positive electrode materials in examples 10 to 17 were
`prepared by the use of a Solid-phase mixing method. More
`over, Sealed-type non-aqueous Solvent battery cells were
`assembled with the positive electrode materials obtained in
`the examples and the comparison example together with the
`
`carbon negative electrode materials and the electrolytes.
`And, the performances of the batteries were evaluated.
`0070 Synthesis of Positive Electrode Material by
`Coprecipitation Method
`0071. A mixed solution with a specified mol ratio
`between Mn and the transition metal M was prepared by the
`use of manganese nitrate and a compound of the transition
`metal M as shown in Table 1 of FIG. 3