United States Patent (19)
`Miyasaka
`
`USOO5871863A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,871,863
`Feb. 16, 1999
`
`54) LITHIUM ION SECONDARY BATTERY
`75 Inventor: Tsutomu Miyasaka, Kanagawa, Japan
`73 Assignee: Fuji Photo Film Co., Ltd., Kanagawa,
`Japan
`
`21 Appl. No. 709,034
`22 Filed:
`Sep. 6, 1996
`30
`Foreign Application Priority Data
`Sep. 6, 1995
`JP
`Japan .................................... T-228732
`Feb. 27, 1996
`JP
`Japan .................................... 8-0395.64
`(51) Int. Cl. ................................................ HO1 M 4/50
`52 U.S. Cl. ........................... 429/218; 429/223; 429/224
`58 Field of Search ..................................... 429/194, 197,
`429/218, 224, 223; 423/599
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,240,794 8/1993 Thackeray et al. ..................... 429/224
`5,370,710 12/1994 Nagaura et al. ....................... 29/623.1
`
`
`
`5,425,932 6/1995 Tarascon ................................. 423/599
`5,443,929 8/1995 Yamamoto et al.
`429/224
`5,597.664 1/1997 Ellgen ..................................... 429/224
`Primary Examiner Anthony Skapars
`Attorney, Agent, or Firm Sughrue, Mion, Zinn, Macpeak
`& Seas, PLLC
`ABSTRACT
`57
`In a lithium ion Secondary battery having a positive
`electrode, a negative electrode, non-aqueous electrolyte, and
`a container Sealing the electrodes anrd electrolyte therein,
`the positive electrode is formed of a positive electrode active
`material which is produced by electrochemically intercalat
`ing lithium ions into lithium manganese oxide in the con
`tainer to give a positive electrode active material precursor
`comprising lithium manganese oxide of which lithium ion
`contents are increased, and then releasing lithium ions from
`the positive electrode active material precursor in the
`container, and the negative electrode is formed of a negative
`electrode active material which is produced by intercalating
`the released lithium ions into a negative electrode active
`material precursor of a metal oxide in the container.
`17 Claims, 1 Drawing Sheet
`
`
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`1
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`APPLE 1011
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`U.S. Patent
`U.S. Patent
`
`Feb. 16, 1999
`
`5,871,863
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`APPLE 1011
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`1
`LITHIUM ION SECONDARY BATTERY
`FIELD OF THE INVENTION
`This invention relates to a lithium ion Secondary battery
`and a precursor for producing the lithium ion Secondary
`battery.
`
`BACKGROUND OF THE INVENTION
`A lithium ion Secondary battery is known as an advanta
`geous Secondary battery which is able to give a high Voltage
`of about 4 volts and a high discharge capacity. AS the
`positive electrode active material of the lithium ion Second
`ary battery, LiMnO, having the Spinel crystal Structure, as
`well as LiMnO, LiCoO, LiCo. NiO or LiNiO which
`has the rock Salt crystal Structure have been generally
`employed. The LiCoO having the rock Salt crystal Structure
`shows higher Voltage and higher discharge capacity than
`other oxides and therefore is advantageous. However, the
`LiCoO has Such drawbacks that cobalt is high in its cost and
`leSS available than other metals, and moreover may cause
`environmental pollution if battery wastes containing the
`lithium cobalt oxide are left outside
`Japanese Patent Provisional Publication H3(1991)-
`147276 proposes a lithium ion Secondary battery using
`LiMnO of the spinel crystal structure as the material for its
`positive electrode, that is, cathode. Manganese is leSS expen
`Sive and easily available, and moreover Scarcely causes
`environmental pollution. However, LiMnO, gives a charge
`capacity (corresponding to amount of releasable lithium
`ions) per unit volume less than LiCoO by 10 to 20%. This
`means that if the LiMnO is combined with a negative
`electrode active material of high capacity to prepare a
`Secondary battery, the Volume of the LiMnO (namely,
`positive electrode active material) to be used should be
`increased So as to balance its capacity with the high capacity
`of the negative electrode active material. As a result, the
`amout of the negative electrode active material encased in a
`container of a battery should be reduced, and then the battery
`capacity lowers.
`Japanese Patent Provisional Publication H4(1992)-
`147573 describes a lithium ion secondary battery using
`LiMnO(x>0) as the positive electrode active material
`precursor in combination of a negative electrode active
`material precursor Such as carbonaceous material. Such
`positive electrode active material precursor-negative elec
`trode active material precursor combination in a container of
`a battery is electrochemically converted into a positive
`electrode active material-negative electrode active mate
`rial combination by electrically charging thus prepared
`battery So as to release lithium ions from the positive
`electrode active material precursor and intercalate the
`released lithium ions into the negative electrode active
`material precursor in the container.
`The LiMnO, having a lithium ion amount higher than
`LiMnO is advantageous because it gives a charge capacity
`higher than LiMn2O. In the lithium ion secondary battery
`described in the last Publication, the positive electrode
`active material of LiMn2O is produced electrochemi
`cally once in an electric cell or chemically in a known
`process outside an electric cell and then placed in a container
`of a final battery product. LiMn2O is known to be
`extremely unstable and easily oxidized. Therefore, this
`proceSS and the Secondary battery prepared by this proceSS
`may cause problems in industrial preparation and use.
`SUMMARY OF THE INVENTION
`It is a primary object of the present invention to provide
`a lithium ion Secondary battery which gives a high Voltage
`and high discharge capacity.
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`It is another object of the present invention to provide the
`lithium ion Secondary battery which is easily prepared
`without problems attached to the lithium ion Secondary
`battery of prior art.
`It is a further object of the invention to provide the lithium
`ion Secondary battery which is easily prepared with high
`reliability and reproductivity.
`It is a still further object of the invention to provide the
`lithium ion Secondary battery which is easily prepared with
`improved cost-perfomance.
`In one aspect, the present invention resides in a lithium
`ion Secondary battery comprising a positive electrode, a
`negative electrode, non-aqueous electrolyte, and a container
`Sealing the electrodes and electrolyte therein, wherein
`the positive electrode comprises a positive electrode
`active material which is produced by electrochemically
`intercalating lithium ions into lithium manganese oxide in
`the container to give a positive electrode active material
`precursor comprising lithium manganese oxide of which
`lithium ion contents are increased, and then releasing
`lithium ions from the positive electrode active material
`precursor in the container;
`and
`the negative electrode comprises a negative electrode
`active material which is produced by intercalating the
`released lithium ions into a negative electrode active mate
`rial precursor comprising a metal oxide in the container.
`In another aspect, the present invention resides in a
`lithium ion Secondary battery precursor comprising a posi
`tive electrode precursor, a negative electrode precursor,
`non-aqueous electrolyte, and a container Sealing the elec
`trode precursors and electrolyte therein, wherein
`the positive electrode precursor comprises a positive
`electrode active material precursor which is produced by
`electrochemically intercalating lithium ions into lithium
`manganese oxide in the container to increase the lithium ion
`content of the lithium manganese oxide;
`and
`the negative electrode precursor comprises a negative
`electrode active material precursor comprising a metal
`oxide.
`In a further aspect, the invention resides in a lithium ion
`Secondary battery precursor comprising a positive electrode
`precursor, a negative electrode precursor, non-aqueous
`electrolyte, and a container Sealing the electrode precursors
`and electrolyte therein, wherein
`the positive electrode precursor comprises lithium man
`ganese oxide, and has a lithium metal or a lithium alloy in
`the vicinity of the lithium manganese oxide under the
`condition that the lithium metal or lithium alloy is in electric
`contact with the lithium manganese oxide, and
`the negative electrode precursor comprises a negative
`electrode active material precursor comprising a metal
`oxide.
`In a still further aspect, the invention resides in a lithium
`ion Secondary battery precursor comprising a positive elec
`trode precursor, a negative electrode precursor, non-aqueous
`electrolyte, and a container Sealing the electrode precursors
`and electrolyte therein, wherein
`the positive electrode precursor comprises lithium man
`ganese oxide, and
`the negative electrode precursor comprises a negative
`electrode active material precursor comtprising a metal
`oxide, and has a lithium metal or a lithium alloy in the
`
`3
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`APPLE 1011
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`5,871,863
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`1O
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`vicinity of the negative electrode active material precursor
`under the condition that the lithium metal or lithium alloy is
`brought into electric contact with the lithium manganese
`oxide through an externally Set electric circuit.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a Schematic Section of a typical lithium ion
`Secondary battery according to the invention.
`PREFERRED EMODIMENTS OF THE
`INVENTION
`The preferred emments of the lithium ion secondary
`battery of the invention and the lithium ion secondary
`battery precursor (which is converted into the lithium ion
`Secondary battery of the invention by electrochemical
`processing) are set forth below
`1) The positive electrode active material precursor has a
`tetragonal crystal Structure and is represented by the formula
`of LiMnO, under the condition of 0.3<x<1, and the
`positive electrode active material has a cubic crystal Struc
`ture and is represented by the formula of Li,Mn2O, under
`the condition of 0<y<0.3.
`2) The positive electrode contains, as a Sub-active
`material, lithium cobalt oxide having the formula of Li
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`CoO under the condition of 0.5-Xs 1, or lithium nickel or
`cobalt-nickel oxide having the formula of LiCo, NiO.
`under the conditions of 0.5<Xs 1,0sys 1, and 0s 1.
`3) The positive electrode active material precursor is
`produced in the container by electrochemical Self-discharge
`between lithium manganese oxide and a lithium metal or a
`lithium alloy.
`4) The positive electrode active material precursor is
`produced in the container by electrochemical discharge
`between lithium maganese oxide and a lithium metal or a
`lithium alloy which is placed near the negative electrode
`active material precursor, utilizing an externally Set electric
`circuit.
`5) The negative electrode active material precursor com
`prises an amorphous mtal oxide which has a tin atom and at
`40
`least one other metal atom and into which the lithium ions
`have been intercalated.
`6) The negative electrode active material precursor com
`prises an amorphous metal oxide which has a tin atom and
`at least one other metal atom and which is represented by the
`formula of SnLO in which L is at least one atom Selected
`from the group consisting of Al, B, P, Si, Li, Na, K, Rb, Cs,
`Be, Mg, Ca, Sr., Ba, Sc, Y, lanthanides, and halogens, and k
`and Z are numbrS Satisfying the conditions of 0.2sks 2 and
`1s ZS 6, respectively, or the formula of SnOLO in
`which Q is a transition metal atom, L is at least one atom
`Selected from the group consisting of Al, B, P, Si, Li, Na, K,
`Rb, CS, Be, Mg, Ca,Sr., Ba, Sc, Y, lanthanides, and halogens,
`and d, k and Z are numbers Satisfying the conditions of
`0.1sds 0.9, 0.2sks2, and 1s Zs 6, respectively.
`7) The ratio of the amout of lithium ions to be released
`from the negative electrode active material until the dis
`charge Voltage of the battery lowers to 3V in a discharge
`Step, to the amnount of lithium ions intercalated into the
`negative electrode active material precursor is lower than
`1/(1+x) wherein X is as defined in 1) above.
`8) The positive electrode active material precursor is
`produced in the container by electrochemical Self-discharge
`between lithium manganese oxide and a lithium metal or a
`lithium alloy.
`9) The positive electrode active material precursor is
`produced in the container by electrochemical discharge
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`between lithium manganese oxide and a lithium metal or a
`lithium alloy which is placed near the negative electrode
`active material precursor, utilizing an externally Set electric
`circuit.
`10) The lithium manganese oxide has a spinel crystal
`Structure.
`11) The lithium manganese oxide has a spinel crystal
`Structure and is represented by the formula of LiMn
`O under the condition of 0s x<1.7 and 0sy<0.7, or the
`formula of Li-LMn-IO, under the condition of 0<x<1.0
`and 0sy<0.5.
`12) The positive electrode precursor contains, as a Sub
`active material, lithium cobalt oxide having the formula of
`LiCoO under the condition of 0.5<Xs 1, or lithium nickel
`or cobalt-nickel oxide having the formula of LiCo, NiO,
`under the condition of 0.5<Xs 1, and 0<Zs 1.
`The lithium ion secondary battery of the invention and the
`lithium ion Secondary battery precursor of the invention, as
`well as processes for the preparation of the battery and its
`precursor are described below.
`The lithium ion secondary battery of the invention
`employs a positive electrode active material (i.e., an active
`material of cathode) prepared from lithium manganese
`oxide. The lithium manganese oxide preferably is that
`having the Spinel crystal Structure, which give a high Volt
`age. The oxide of Spinel type has a crystal Structure of
`A(B)O, in which oxygen anions are arranged at the tops of
`tetragonal and hexagonal planes of the cubic close-packed
`Structure. Based on the arrangements of the cation “A”, the
`spinel structures are classified into a regular (or normal)
`spinel, that is, A(B)O, and a reverse spinel, that is,
`A(A,B)O. There is an intermediate spinel structure, that is,
`A,B,CA.B.)O4. A representative lithium manganese
`oxide of the regular spinel is LiMn2O. In this structure, a
`half of Macations are trivalent and another half are tetrava
`lent. 2-MnO, that is a known active material, has the crystal
`structure of LiMnO, from which lithium is removed, that is
`called a defective spinel Structure. In this crystal Structure,
`Mn cations are all tetravalent. The lithium manganese oxide
`employed in the invention can have any spinel Structures,
`Such as regular Spinel, reverse Spinel, intermediate Spinel,
`and defective Spinel including a spinel of non-Stoichiometric
`composition.
`An example of the lithium manganese oxide (i.e., lithium
`containing manganese oxide) employable in the invention is
`represented by the formula of Li,Mn2O, (0sx<1.7,
`0sy<0.7). Examples of the oxides include LiMnO
`(which is described by LiMnsO in the manner of
`representation for spinel structure). The examples also
`include the following oxides in which the subscripts
`attached to the formulas can be equally multiplied or
`divided: LiMnOo, LiMnO, Lis MnO, and Li MnO2.
`Another example of the lithium manganese oxide employ
`able in the invention can be described by the formula of
`Li-IMn2O (0s x<1.0, 0sy<0.5). Preferred is an oxide
`having the formula of Li-IMn2O (0.20<x<1.0,
`0<y<0.2). Examples of the oxides of the formula include
`LiMns O (which is described by Li-IMn2-O.
`(x=0.273, y=0.182) in the mamner of representation for
`spinel Structure) which is a non-stoichiometric spinel and
`described in Japanese Patent Provisional Publication
`H4(1992)-240117. Also preferred is an oxide having the
`formula of Li, MnO, (0<xs 0.20, 0<y<0.4) such as an
`oxide of LiMnO. The examples further include the fol
`lowing oxides in which the Subscripts attached to the for
`mulas can be equally multiplied or divided: LiMnOs,
`LiMn-7sO16, and Lio, MnO.
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`The lithium manganese oxide can be produced by a
`conventional method Such as a Solid-phase reaction of a
`lithium Salt and a manganese Salt or a manganese oxide at an
`elevated temperature. If lithium carbonate and manganese
`dioxide are employed, the reaction is performed at a tem
`perature of 350° to 900° C., preferably 350° to 500° C., for
`a period of 8 to 48 hours. If lithium nitrate (having a low
`melting temperature of 261 C.) is employed, the reaction
`temperature is in the range of 300 to 900 C., preferably
`300 to 500 C. Examples of employable manganese oxides
`include 2-MnO, MnO produced by electrolytic synthesis
`(EMD), chemically produced MnO (CMD), and their mix
`tures. As a raw material for the lithium component, a lithium
`manganese oxide (Such as LiMnO) also can be employed.
`The lithium manganese oxide can be mixed with a manga
`nese compound Such as manganese dioxide and fired at a
`temperature of 350° to 500° C.
`The above-described lithium manganese oxide can be
`employed in combination with one or more of other lithium
`manganese oxides Such as LiMnO of the rock Salt crystal
`Structure and LiMn2O (OsXs 0.5, which is produced by
`chemically inserting Li ion into LiMn2O), and Li Mn2O
`(0sXs 0.5, which is produced by chemically removing Li
`ion from LiMnO).
`The lithium manganese oxide can be employed further in
`combination with a lithium-containing transition metal
`oxide which Serves as Sub-active material. An preferred
`example of the Sub-active material is lithium cobalt oxide
`(LiCoO, 0.5sXs 1, which gives a high voltage and high
`electric capacity). Also preferred is lithium cobalt-nickel
`oxide (LiCo, NiO2, 0.5<xs 1,0sys 1, 0<zs 1). The sub
`active material may be a Solid Solution made of cobalt, other
`transition metal elements, non-transition metal elements, an
`alkali metal, and/or lanthanides.
`The Sub-active material can be employed in combination
`with the lithium manganese oxide in the weight ratio of 2/8
`to /6 (former/latter), preferably % to 7/3.
`The lithium manganese oxide preferably is crystalline but
`may be amorphous or a mixture of a crystalline material and
`an amorphous material.
`The negative electrode active material (i.e., anode active
`material) preferably employed in the lithium ion Secondary
`battery of the invention is a lithium-containing metal oxide
`of low electric potential which is produced in the container
`of the final battery product by intercalating lithium ions into
`a metal oxide containing almost no lithium ion in the
`container. The term of “metal oxide containing almost no
`lithium ion” means “metal oxide containing almost no
`movable lithium ion'. Such negative electrode active mate
`rial can give a lithium ion Secondary battery of high battery
`capacity when it is employed in combination with the
`positive electrode active material of the invention.
`The negative electrode active material is, as described
`above, produced by intercalating lithium ions into a negative
`electrode active material precursor of a metal oxide in the
`container of the final battery product. The metal oxide
`preferably contains a tin atom and one or more other atoms.
`Preferred are metal oxides having one of the following two
`formulas:
`
`(1)
`SnL.O.
`In the formala, L represents at least one atom Selected
`from the group consisting of Al, B, P, Si, elements of Groups
`1 to 3 of Periodic Table (such as Li, Na, K, Rb, Cs, Be, Mg,
`Ca,Sr., Ba, Sc, Y, and lanthanides) and halogen atoms. k and
`
`6
`Z are numbers Satisfying the conditions of 0.2sks 2 and
`1s ZS 6, respectively.
`Among the tin-containing metal oxides of the formula (1),
`a compound of SnT.R.O. (in which T is at least one atom
`Selected from the group consisting of Al, B, P, element of
`Groups 1 to 3 of Periodic Table, and halogens, and h, i and
`Z are numbers Satisfying the conditions of 0.2s his 2,
`0.01s is 1, 0.2sh--is 2, and 1s Zs 6, respectively) is par
`ticularly preferred.
`
`(2)
`Sn/QL.O.
`In the formula, Q is a transition metal atom, L is at least
`one atom Selected from the group consisting of Al, B, P, Si,
`elements of Groups 1 to 3 of Periodic Table (such as Li, Na,
`K, Rb, Cs, Be, Mg, Ca, Sr., Ba, Sc, Y, and lanthanides), and
`halogens, and d, k and Z are numbers Satisfying the condi
`tions of 0.1sds 0.9, 0.2sks2, and 1s Zs 6, respectively.
`The metal oxide for the preparation of the negative
`electrode active material preferably is amrphous material
`when it is placed in the container of the final battery product.
`The term of “amorphous material”, in the invention means
`a material which gives a broad Scattered band having its
`main peak in the range of 20 to 40° (in terms of 20) in X-ray
`diffraction using Cu-K C. rays. In the Scattered band, a
`diffraction line may be present. The diffraction line in the
`range of 40 to 70° (in term of 20) preferably has a strength
`as much as 500 times or less (more preferably as much as
`100 times or less, and moreover as much as 5 times or less)
`than the diffraction line in the range of 20° to 40° (in term
`of 20). Most preferably, there appears no diffraction lines
`representing a crystalline Structure.
`Examples of the tin-containing metal oxides for the
`negative electrode active material precursor include the
`following
`compounds:
`Sn Sios Po2O3,
`SnSios Alo BoPo2O10s, SnSios Bo02.9, SnSios.Alo2O2.0,
`Sn Sio. 6 Alo.1 Bo. 2 O16s, Sn Sio. Aloi Po. 6 O2.2 s,
`SnSio BoPo. O2.1, SnSio.6Alo Bois02.1, SnBois Pos Os,
`Snalos Bois Po2O2.7, Snko.2PO3.6, SnRbo2Alolos PosC-2s,
`Sn A lot a Bo. 7 O2 is Sn Bao. A los P. as O 7,
`Sn Lao. Alo. Polo Oass, Sn Nao. Aloos Boas Ois,
`Sn Lio.2 Bos Pos O 31, Sno so.1 Bo. 4 Po. 4 O2.6s,
`SnBao. Bo. Po. O2.7, SnCao. Alois Boas PossOslo,
`Snyo. Alois Bo. 6 Po. 6 O4, SnRbo.2 Alo.1 Bos Po. O2.7,
`SnCso.2 Alo.1 Bois Po. O2.7, SnCso. Alo. Bo. Po. O2.s,
`Sn Ko.1 Cso. Bo Po. O2.7, SnBao.1 Cso. Bo. Po. O2.7s,
`SnMgo. Ko Bo Po. O27s, SnCao Ko Bo Pos O,
`SnBa0.1KO.1A10.1 B0.31P0.4O2.75SnMgCs. Alo Bo
`Po. 4 O2. 7s, Sn Cao. 1 Ko. 1 Alo.1 Bois Po. 4 O27s,
`SnMgo. Rbo. Alo BosPo. O2.7s, SnCao. Bo.2 Po2Fo2O2.6,
`S in M g o
`1 C S o
`Bo Po Fo 2 O a ,
`SnMgo. Alo.2Bo Po. FoC)2.0, Snos Minos Mgo. BooC)2.4s,
`Snos Minos Cao. 1 Po. oO3.3s, Snos Geo.5Mgo. 1 Po. oO3.3s,
`Snos Feos Bao. 1 Polo Cass, Snos Feo.s Alo.1 Bo. oO2.s,
`Snos Feo.2 Cao. 1 Polo Osas, Sno.3 Feo. 7 Bao. 1 Po.oO 3.3s,
`Snoo Mino. Mgo. PooCsas, Sno.2Mnos Mgo. PooCsas,
`Sno.7Pbo.3 Cao. 1 Po. oO3.35, Sno. 2 Geos Bao. 1 Po.oO 3.3s,
`Sn 1.0 Alo.1 Bois Pos O3.35, Sn 1.oCso.1 Bois Pos Osos,
`Sn 1.0Cso.1 Alo.1 Bos PosC3.20, Sn 1.0Cso.1 Alo.3 Bos Posos.so,
`Sn 1.oC So. 1 Geo.os Alo.1 Bois Pos Osso,
`and
`SnoCso. Geolos AloisBospois0s.go.
`The negative electrode active material of the lithium ion
`Secondary battery of the invention is produced by interca
`lating lithim ions electrochemically into the negative elec
`trode active material precursor Such as those described
`above. The intercalation is performed by electrically charg
`ing a battery precursor which comprises a positive electrode
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`active material precursor, a negative electrode active mate
`rial precursor, and a nonaqueous electrolyte containing
`lithium ions. The negative electrode active material prefer
`ably shows the ratio of the amount of lithium ions to be
`released from the negative electrode active material until the
`discharge Voltage of the battery lowers to 3V in a discharge
`Step, to the amount of lithium ions intercalated into the
`negative electrode active material precursor is lower than
`1/(1+x) wherein X is “X” of the formula of LiMnO.
`There is no specific limitation on the amount of lithium
`ions to be intercalated into the negative electrode active
`material. For example, the lithium ion is preferably interca
`lated into the material So as to show 0.05 volt, more
`preferably 0.1 volt, most preferably 0.15V, against Li-Al
`alloy (80-20 wt.%). In these cases, the amount of the
`intercalated lithium ion becomes to correspond to 3 to 10
`equivalent amounts depending on the electric potential. The
`electric capacity resulting from the intercalation generally
`reaches a high value Such as about 500 mAh/g. In consid
`eration of the desired electric capacity on the negative
`electrode active material, the amounts of the lithium man
`ganese oxide (material for preparing the positive electrode
`active material precursor) and a lithium metal (or lithium
`alloy) to be placed on the positive electrode side are deter
`mined. For instance, the total equivalents of lithium ion
`releasable from the lithium manganese oxide and the lithium
`metal (or lithium alloy) preferably is in the range of 0.5 to
`2 as much as the equivalent of lithium ion to be intercalated
`into the negative electrode active material precursor.
`The positive electrode active material (and its precursor,
`and the lithium manganese oxide for the preparation of the
`precursor) and the negatic electrode active material (and its
`precursor) preferably are in the form of particles having a
`mean diameter of 0.03 to 50 lum, more preferably 0.1 to 20
`tim. The mean diameter corresponds to a mode diameter
`representing the maximum frequency point which is
`determined, for instance, by preparing an average value of
`values determined by microscopic observation or by mea
`Surement utilizing an apparatus for measuring particle size
`distribution. The active materials preferably have a specific
`surface area of 0.1 to 50 m/g. The positive electrode active
`material and its precursor preferably has a specific Surface
`area of 1 to 10 m/g.
`The preparation of the positive electrode active material
`precursor from the lithium manganese oxide or a composi
`tion comprising the lithium manganese oxide is described
`below.
`The positive electrode active material precursor is pre
`pared by activation of the lithium manganese oxide or its
`composition in the container of the final battery product. The
`term of “activation' is performed by electric charging to
`give electrode active material having a high discharge
`energy and an electric potential capable of performing
`repeated charge-discharge cycles. The activation of the
`positive electrode material means the material placed on the
`positive electrode Side is charged So as to acquire high electric
`potential to show a high discharge energy enough for the
`desired repeatable charge-discharge cycles. For the lithium
`manganese oxide of LiMn2O, or its composition placed on
`the positive electrode Side, the enough high electric potential
`is more than 3.8 volts, more Specifically 4.2 volts, against the
`Li ion. Under the condition of electric potential of more than
`4.2 volts, more than 0.9 equivalent, Specifically more than
`0.95 equivalent for 4.3 volets, of the lithium ion in the matrix
`of LiMnO is released. However, the amount of the releas
`able lithium ion (which corresponds to charge capacity)
`from LiMnO, perse is lower thin LiCoO by 10 to 20%,
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`when is compared under the same weight level. Because the
`metal oxide which requires an increased amount of lithium
`ion (which means to have a large capacity for electric
`charging) for activation is employed as the negative elec
`trode active material in the Secondary battery of the
`invention, the amount of lithium ion releasable from the
`positive electrode active material precursor should be larger.
`Accordingly, the LiMn2O, which has an increased
`amount of lithium ion is required to increase the amount of
`releasable lithium ion So as to allow intercalation of an
`increased amount of lithium ion into the negative electrode
`active material precursor.
`In the present invention, the LiMnO, which is a
`precursor of the positive electrode active material should be
`produced in the container of the final battery product to be
`actually employed for the repeated discharge-charge cycles.
`According to the invention, the positive electrode active
`material precursor is produced in the container by electro
`chemical Self-discharge between lithium manganese oxide
`and a lithium metal or a lithium alloy. Otherwise, the
`positive electrode active material precursor is produced in
`the container by electrochemical discharge between lithium
`manganese oxide and a lithium metal or a lithium alloy
`which is placed near the negative electrode active material
`precursor, utilizing an externally Set electric circuit. Details
`are described below.
`(1) Use of lithium metal or alloy arranged on positive
`electrode Side
`This process can be performed by one of the following
`proceSSeS.
`1) The lithium metal or its alloy is deposited on a collector
`of positive electrode having the lithium manganese oxide
`thereon to give an electric contact between the lithium metal
`or alloy and the lithium manganese oxide. Thus arranged
`electrode material is then Subjected to Self discharging
`reaction in the presence of an electrolytic Solution.
`2) The lithium metal or its alloy in the form of film is
`deposited directly on the Surface of the lithium manganese
`oxide provided on the collector. Thus arranged electrode
`material is then Subjected to Self discharging reaction in the
`presence of an electrolytic Solution.
`3) The lithium metal or its alloy in the form of film is
`deposited on a Surface protective layer of the lithium man
`ganese oxide provided on the collector. The Surface protec
`tive layer is made of electroconductive material. Thus
`arranged electrode material is then Subjected to Self dis
`charging reaction in the presence of an electrolytic Solution.
`The processes 2) and 3) are preferred. Mst preferred is the
`process 3), because the electroconductive protective layer
`can releave progreSS of quick exothamic reaction.
`(2) Use of lithium metal or alloy arranged on negative
`electrode Side
`This process can be performed by one of the following
`proceSSeS.
`1) The lithium metal or its alloy is deposited on a collector
`of negative electrode having the negative electrode active
`material precursor thereon, preferably, to give an electric
`contact between the lithium metal or alloy and the precursor.
`Thus arranged electrode material is then Subjected to dis
`charging reaction in the presence of an electrolytic Solution
`utilizing an externally Set electric circuit to produce lithium
`ions from the lithium metal or alloy and intercalate them into
`the lithium manganese oxide on the positive electrode Side.
`2) The lithium metal or its alloy in the form of film is
`deposited directly on the Surface of the negative electrode
`active material precursor provided on the collector. Thus
`arranged electrode material is then Subjected to discharging
`
`6
`
`APPLE 1011
`
`

`

`5,871,863
`
`reaction in the presence of an electrolytic Solution utilizing
`an externally Set electric circuit to produce lithium ions from
`the lithium metal or alloy and intercalate them into the
`lithium manganese oxide on the positive electrode Side.
`3) The lithium metal or its alloy in the form of film is
`deposited on a Surface protective layer of the negative
`electrode active material precursor provided on the collector.
`The Surface protective layer is made of electroconductive
`material. Thus arranged electrode material is then Subjected
`to discharging reaction in the presence of an electrolytic
`Solution utilizing an externally Set electric circuit to produce
`lithium ions from the lithium metal or alloy and intercalate
`them into the lithium manganese oxide on the positive
`electrode Side.
`The processes 2) and 3) are preferred. Most preferred is
`the process 3), because the electroconductive protective
`layer can releave progreSS of quick exothamic reaction.
`In the positive electrode active material precursor of
`LiMnO of the invention, X preferably is under the
`condition of 0.3<x<1. More preferably is 0.5<Xs 0.9, if the
`lithium ion Secondary battery of the invention is to give a
`higher charge capacity per Volume than LiCoO which is
`known as a positive electrode active material to have a high
`charge capacity.
`The positive electrode active material precursor is pref
`erably converted into a positive electrode active material of
`the formula of Li,Mn2O, under the condition of 0<y<0.3,
`more preferably 0<y<0.2 for increaing the discharge capac
`ity.
`In the lithium ion secondary battery of the invention, the
`lithium manganese oxide in the positive electrode active
`material preferably keeps the formula of Li,Mn2 er the
`condition of 0<y<1, more preferably 0<y<0.9, in the
`r