a2) United States Patent
`US 6,506,518 Bl
`(10) Patent No.:
`Kobayashietal.
`(45) Date of Patent:
`Jan. 14, 2003
`
`
`US006506518B1
`
`(54) LITHIUM SECONDARY BATTERY
`
`(75)
`
`Inventors: Koutaro Kobayashi, Okayama GIP);
`Yoshimasa Koishikawa, Honjou(JP);
`-
`‘
`.
`Kensuke Hironaka, Pukaya(JP)
`(73) Assignee: Shin-Kobe Electric Machinery Co.,
`Ltd., Tokyo (JP)
`Subject to any disclaimer, the term of this
`
`(*) Notice:
`
`ee. 154by0 faye under 35
`
`6,083,644 A *
`7/2000 Watanabeetal. ........ 429/231.1
`
`6,146,791 A * 11/2000 Loutfy ot al. wu... 423/445 B
`
`........... 429/231.4
`6,156,457 A * 12/2000 Takamiet al.
`
`"0D5L8
`eee BI
`73001 on e a ”
`ao etal...
`.
`265,
`.
`6,306.542 B1 * 10/2001 Nakanoet al.0.0... 429/24
`Eo
`0334°993 Bt * wy5002 quatanabect al. — S390
`
`5/2002 Kobayashi et al.
`......... 429/221
`2002/0055041 Al *
`FOREIGN PATENT DOCUMENTS
`
`pp
`
`0528557 Al
`
`2/1993
`
`EP 0 808 798 A2=11/1997
`
`EP
`0 917 223 Al
`5/1999
`JP
`10321225
`4/1998
`(21) Appl. No.: 09/525,264
`JP
`11-185822
`7/1999
`.
`
`
`(22) Filed:=Mar. 14, 2000 Jp 11-214042 8/1999
`
`
`Eo
`(0)
`Forsgn Appleton Peoity Dat
`Wo
`WORRDEE AT TN
`Apr. 27, 1999
`JP)
`ieeecesceecseccccccee see cee ee eeeeeeeeenees 11-118961
`:
`:
`Nov. 15, 1999 Py esssssseessvussssuessssueesssectanieesvaee 11323502
`“ited by examiner
`(51)
`Inte Ch? vacccccccssesseeecsee HOLM 4/58; HOIM 4/74;
`Primary Examiner—om Dunn
`HOIM 6/00
`Assistant Examiner—L. Edmondson |
`(52) US. Cle cacescssessscssssseeesee 429/231.1; 429/231.8,
`(74) Attorney, Agent, or Firm—Olill & Berridge, PLC
`429/244; 29/623.1; 29/623.5
`(57)
`ABSTRACT
`.
`.
`.
`(58) Field of Search .....0..00 429/231.1, 231.4,
`a
`429/231.8, 218, 218.1, 244; 29/623.1-623.5
`A lithium secondary battery capable of improving high
`temperature cycle life characteristic effectively without
`decreasing discharge capacity. Amorphous carbon powder
`with a specific surface area of 10.0 m/g and a meanparticle
`diameter of 7.0 wm is uscd as negative clectrode active
`material and lithium manganate with a Li/Mnratio of 0.58
`is used as positive electrode active material. Since a surface
`area of the negative electrode active material layer is made
`large by setting the meanparticle diameter of the amorphous
`carbon powder to 10 wm or less, the surface area of the
`negative electrode active material layer is sufficiently large
`that, even wheninert coating is formed onthe surface of the
`negative electrode due to manganese deposition caused by
`manganese elution from the positive electrode, high tem-
`perature cycle life characteristic can be improved without
`high temperature deterioration.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,069,683 A * 12/1901 Fong et al. vessccssssseee 29/623.
`ae 429/192
`5,219,680 A *
`6/1993 Fauteux .......
`
`7/1995 Ohtsuka et al...
`429/194
`5,436,092 A *
`
`......
`... 29/623.5
`5,443,601 A *
`8/1995 Doeff et al.
`5,571,638 A * 11/1996 Satoh et al. wu. 429/248
`5,601,952 A *
`2/1997 Dsgupta etal.
`5,629,112 A
`5/1997 Davidsonctal.
`9,056,394 A :
`8/1997 Koksbangetal. ......... 429/218
`ae ‘ ‘ 71008 Wane. Ct AL aes 5500
`
`5,856.043 A *
`1/1999 Ohsakietal. ........ 420/218
`5,907,899 A *
`6/1999 Dahnet al. cscs 252/182.1
`6,030,726 A *
`2/2000 Takeuchiet al.
`......... 429/231.8
`6,053,953 A *
`4/2000 Tomiyamaetal.
`........ 29/623.1
`
`4 Claims, No Drawings
`
`APPLE-1019
`
`APPLE-1019
`
`1
`
`

`

`US 6,506,518 B1
`
`1
`LITHIUM SECONDARY BATTERY
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`
`invention relates to a lithium secondary
`The present
`battery, and in particular relates to a lithium secondary
`battery using lithiummanganate as positive electrode active
`matcrial and amorphous carbon material as negative clec-
`trode active material.
`
`10
`
`15
`
`2
`In the lithium manganate whose manganese site is
`replaced with the dissimilar metal, the manganese elution
`amount at the high temperature is decreased definitely, but
`there are drawbacksin that the manganese elution into the
`electrolytic solution is not only prevented completely but
`also discharge capacity is decreased.
`SUMMARY OF THE INVENTION
`
`inventors have studicd and analyzed the
`The present
`causes of the cycle deterioration at the high temperature in
`the battery using the lithium manganate as the positive
`electrode material and the amorphous carbon material as the
`negative electrode material. As a result, the inventors have
`found outthat the cycle deterioration at the high temperature
`is caused by formation of inert coating on a surface of the
`negative electrode because of the manganese eluted from the
`positive electrode acting as cores of the inert coating.
`In view of the above drawbacks and based upon the
`findings, a first object of the present invention is to provide
`a lithium secondary battery capable of improving cycle
`characteristic effectively without decreasing discharge
`capacity.
`A second object of the invention is to provide a lithium
`secondary battery capable of improving charging/
`discharging cycle lite and preservation life under a high
`temperature.
`In order to achieve the first object, a first aspect of the
`present invention is a lithium secondary battery, comprising
`a positive electrode having a positive electrode collector to
`which mixture containing lithium manganate as positive
`electrode active material is applied; and a negative electrode
`having a negative electrode collector to which mixture
`containing amorphouscarbon material as negative electrode
`active material is applied, wherein a mean particle diameter
`of the amorphous carbon material is 10 wm or less. In this
`aspect, since the mean particle diameter of the amorphous
`carbon material is made to be 10 xm orless, surface area of
`the amorphous carbon material becomes large. Therefore,
`even whenthe inert coating is formed on the surface of the
`negative electrode due to the manganese elution from the
`positive electrode/the manganese deposition on the negative
`electrode, as a total surface area of the amorphous carbon
`material is large, the high temperature cycle characteristic of
`the secondary battery can be improved without decreasing
`discharge capacity.
`In this aspect, the specific surface area of the amorphous
`carbon material having the mean particle diameter of 10 um
`is about 5 m*/g, and when the specific surface area is less
`than 5 m?/g, an effect of a surface area increase is hardly
`obtained. The specific surface area of the amorphous carbon
`material with the mean particle diameter of 3.5 amts about
`20 m?/g, and when the specific surface area is 20 m?/g or
`more, the specific surface area is made excessively large so
`that deterioration in other performances such as an irrevers-
`ible capacity increase and the like occurs. Therefore, it is
`preferable that the mean particle diameter of the amorphous
`carbon material is in the range of 3.5 wm or more and 10 wm
`or less. Further, when a Li/Mnratio in the lithium manganate
`is in a range of more than 0.5 and 0.6 or less, a manganese
`elution amount can be reduced without decreasing the
`discharge capacity extremely as compared with the reduc-
`tion in a case of the stoichiometric composition (0.5).
`In order to achieve the second object, a second aspect of
`the invention is a lithium secondarybattery, comprising a
`positive electrode having a positive electrode collector to
`which mixture containing lithium manganate as positive
`
`2. Description of the Related Art
`Conventionally, in a field of a rechargeable secondary
`battery, an aqueoussolution type battery such as a lead-acid
`battery, a nickel-cadmium battery, a nickel-hydrogen battery
`and the like was in a main trend. In recent years, however,
`in view of such problemsas global warming and exhaustible
`fuel, attention has beenpaid to an electric vehicle (EV) and
`a hybrid electric vehicle (HEV) whose driving force is
`assisted with an electric motor, and a secondarybattery with
`higher capacity and higher power (output) for such vehicles
`has been required. As a power source to meet such a need,
`a non-aqueous solution type lithium secondary battery
`which has high voltage has lately drawn attention.
`Carbon material which lithium ions can be inserted
`in/departed from (occluded in/released from) is generally 5
`used as negative electrode material (negative electrode
`active material) for the lithium secondary battery. As such
`carbon material, for example, graphite system material such
`as natural graphite, scale-shaped or massive-shapedartificial
`graphite, mesophase pitch system; graphite or the like, or
`amorphous (noncrystalline) carbon material prepared by
`calcinating such furan resin as furfuryl alcohol or the like
`can belisted up. In the graphite system material, while there
`are advantages in that irreversible capacity is small, voltage
`characteristic is flat and capacity is high, but there is a
`disadvantage in that cycle characteristic is inferior. Also, in
`the amorphous carbon prepared bycalcinating the synthetic
`resin, while there are advantages in that a capacity value
`exceeding a theoretical capacity value of the graphite can be
`obtained and the cycle characteristic is superior, but there are
`disadvantagesin that the irreversible capacity is large and it
`is difficult to increase battery capacity.
`Meanwhile, lithium transition metallic oxide is used as
`positive electrode material (positive electrode active
`material) for the lithium secondary battery. As the positive
`electrode material, lithium cobaltate is generally used in
`view of balances of capacity, cycle characteristic and the
`like. In a secondary battery using lithium cobaltate for the
`positive electrode material, since the quantity of cobalt
`resourcesas its raw material is small and the cobaltis costly,
`lithium manganate has been regarded as promising material
`for the EV or HEV battery, and the development has been
`advanced for the battery.
`However, in the battery using the lithium manganate as
`the positive electrode material, since the lithium manganate
`causes elution at a high temperature of 50° C. or so, the
`battery is inferior to the battery using the lithium cobaltate
`for the positive electrode material in cycle characteristic
`under the high temperature. Thus, there is a drawback in a
`case in which the lithium manganate is assumed to be
`applied to the EV or HEV.
`In order to overcome the
`drawback, there have been various proposals that manga-
`nese site of the lithium manganate is replaced with dissimi-
`lar metal such as cobalt (Co), chromium (Cr) or the like so
`as to decrease the manganese elution even under the high
`temperature and to improve the high temperature character-
`istic of the battery.
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`2
`
`

`

`US 6,506,518 B1
`
`4
`ductive material and 5 weight parts of PVDFas binder, and
`it is added and mixed with N-methylpyrrolidone as disper-
`sion solvent to produce slurry. The slurry thus obtained is
`applied to both surfaces of an aluminumfoil serving as a
`positive electrode collector with a thickness of 20 um and
`subsequently the aluminum foil applied is dried. Thereafter,
`the positive clectrode collector on which mixture layers
`containing the positive electrode active material are formed
`is pressed and then cut to obtain a positive electrode with a
`thickness of 70 um.
`<Assembly of Battery>
`The negative electrode and the positive electrode thus
`obtained are wound with two sheets of polyethylene-made
`separators each having a thickness of 25 um through which
`lithium ions can pass and interposed therebetween to manu-
`facture a winding group or winding body. After the winding
`group is inserted into a cylindrical battery container or can,
`a predetermined amount of electrolytic solution is poured
`into the battery container, and an upper opening portion of
`the battery container is caulked with a lid disposed inside the
`upper portion of the battery container so that a cylindrical
`lithium secondary battery is assembled. The electrolytic
`solution is prepared previously in the following manner.
`Lithium hexafluorophosphate (LiPE,) is dissolved at 1 mole/
`liter into mixed solution of ethylene carbonate (EC) and
`dimethyl carbonate (DMC). The design capacity of the
`cylindrical lithium secondary battery is 4.0 Ah.
`EXAMPLES
`
`Next, batteries of examples manufactured by changing the
`mean particle diameter and specific surface area of the
`amorphous carbon powder, and the Li/Mn ratio of the
`lithium manganate in various manners will be explained. It
`should be noted that batteries: of controls (comparative
`examples) assembled for comparison with the batteries of
`the examples will also be described.
`
`Example 1-1
`
`in Example 1-1,
`As shown in the following Table 1,
`according to the above first embodiment, a cylindrical
`lithium secondary battery (hereinafter, referred to as a bat-
`tery of Example 1-1) was assembled using amorphous
`carbon powder with a mean particle diameter of 7.0 um and
`a specific surface area of 10.0 m?/g and lithium manganate
`with Li/Mnratio of 0.58.
`
`TABLE1
`
`3
`electrode active material is applied; and a negative electrode
`having a negative electrode collector to which mixture
`containing amorphous carbon material as negative electrode
`active material is applied, wherein irreversible capacity of
`the amorphous carbon material is in a range of 5% or more
`and 25% orless of initial charge capacity, and a discharge
`capacity ratio (-/+ ratio) of the negative clectrode to the
`positive electrode after the initial charge is in a range of 1.3
`or more and 1.8 or less. In this aspect, since the depth of
`discharge in the positive electrode becomes small as much
`as the irreversible capacity of the negative electrode
`increases by making the amount of the negative electrode
`active material in the lithium secondary: battery excessive so
`as to make the discharge capacity ratio of the negative
`electrode to the positive electrode large, deterioration of the
`positive electrode can be suppressed. Since the utilization
`factor of the negative electrode also becomes small due to
`the excess in the negative electrode active material, dete-
`rioration of the negative electrode can be suppressed. When
`the -/+ ratio is less than 1.3, an effect obtained by increasing
`the ratio is small, and whenthe —/+ ratio exceeds 1.8, as the
`load of the positive electrode becomes large and the battery
`capacity is reduced in spite of increasing the ratio.
`Accordingly,it is necessary to set the —/+ ratio in the range
`of at least 1.3 and at most 1.8. According to the present
`invention, since the deterioration of the positive and nega-
`tive electrodes can be suppressed, the charging/discharging
`cycle life and preservation life can be improved.
`In this aspect, when a Li/Mnratio in the lithium manga-
`nate is set to at least 0.55 and at most 0.6, the amount of
`manganese elution can be reduced without decreasing the
`battery capacity extremely as compared with the stoichio-
`metric composition (0.5). Thus, the above rangeis desirable
`for improvementin discharge cycle life and preservationlife
`even under the high temperature.
`The present invention will become more obvious with
`reference to the following prefcrred embodiments.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`(First Embodiment)
`A first embodiment where the present invention is applied
`to a cylindrical lithium secondary battery for a vehicle will
`be explained hereinafter. First, manufacturing procedure of
`the cylindrical lithium secondary battery according to the
`present embodiment will be described in order of a negative
`electrode, a positive electrode and assembly of the battery.
`<Negative Electrode>
`90 weight parts of amorphous carbon powderserving as
`negative electrode active material having a mean particle
`diameter of 3.5 um to 10 wm and a predetermined specific
`surface area described later is added with 10 weightparts of
`polyvinylidene fluoride (PVDF) as binder, and it is added
`and mixed with N-methylpyrrolidone as dispersion solvent
`to produceslurry. The slurry thus obtainedis applied to both
`surfaces of a rolled copper foil with a thickness of 10 wm
`serving as a negative electrode collector and subsequently
`the rolled copper foil applied is dried. Thereafter, the nega-
`tive electrode collector on which mixture layers containing
`the negative electrode active material are formed is pressed
`and then cul to obtain a negative electrode with a thickness
`of 70 um.
`<Positive Electrode>
`
`100 weight parts of lithium manganate serving as positive
`electrode active material with a ratio of lithium to manga-
`nese (Li/Mnratio) of more than 0.5 and at most 0.6 is added
`with 10 weight parts of scale-shaped graphite as electrocon-
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Negative Electrode
`MeanParticle
`Diameter (um)
`
`Example 1-1
`Example 1-2
`Example 1-3
`Example 1-4
`Example 1-5
`Example 1-6
`Example 1-7
`Example 1-8
`Control 1-1
`
`Control 1-2
`
`7.0
`2.0
`3.5
`10.0
`7.0
`7.0
`7.0
`7.0
`15.0
`
`15.0
`
`Specific Surface
`Area (m7/g)
`10.0
`25.0
`20.0
`5.0
`10.0
`10.0
`10.0
`10.0
`3.0
`
`3.0
`
`Positive Electrode
`Li/Mn Ratio
`
`0.58
`0.58
`0.58
`0.58
`0.55
`0.60
`0.50
`0.62
`0.50
`(replaced)
`0.58
`
`Example 1-2 to Example 1-4
`
`As shown in Table 1, the negative electrodes of Example
`1-2 to Example 1-4 were manufactured by changing the
`
`3
`
`

`

`US 6,506,518 B1
`
`6
`
`TABLE 2-continued
`
`Test Results
`
`Discharge
`Capacity (Ah)
`
`High Temp. Cycle
`Life (Cycle)
`
`10
`
`Example 1-5
`Example 1-6
`Example 1-7
`Example 1-8
`Control 1-1
`Control 1-2
`
`4.2
`4.0
`4.2
`3.8
`3.5
`4.1
`
`215
`250
`180
`250
`50
`75
`
`5
`mean particle diameter and the specific surface area of the
`amorphous carbon powderin the range of 2.0 to 10.0 wm and
`in the range of 5.0 to 25.0 m?/g, respectively. The batteries
`(referred to as batteries of Examples 1-2 to 1-4) were
`assembled using the samepositive electrode, separators and
`electrolytic solution as those of Example 1-1 except for the
`negative clectrode.
`
`Example 1-5 to Example 1-8
`
`As shownin Table 1, the positive electrodes of Examples
`1-5 to 1-8 were manufactured by changing the Li/Mnratio
`of the lithium manganate in the range of 0.50 to 0.62. The
`batteries (referred to as batteries of Examples 1-5 to 1-8)
`were assembled using the same negative electrode, separa-
`tors and electrolytic solution as those of Example 1-1 except
`for the positive electrode.
`<Control 1-1>
`
`As shown in Table 1, in Control (Comparative Example)
`1-1, amorphous carbon powder (specific surface area: 3.0
`m*/g) having a meanparticle diameter of 15 yam and lithium
`manganate (Li/Mn ratio: 0.50) whose manganesesite is
`partially replaced with Cr (replacement amount: 5%) were
`used. The battery (hereinafter, referred to as a battery of
`Control 1-1) was assembled using the same separators and ,
`electrolytic solution as those of Example 1-1 except for the
`negative and positive electrodes.
`<Control 1-2>
`
`As shown in Table 1, in Control 1-2, amorphous carbon
`powder (specific surface area: 3.0 m?/g) having a mean
`particle diameter of 15 wm was used. The battery
`(hereinafter, referred to as a battery of Control 1-2) was
`assembled using the samepositive clectrode, separators and
`electrolytic solution as those of Example 1-1 except for the
`amorphous carbon powder. (Test)
`Next, a discharge capacity test and a high temperature
`cycle life test were carried out about the respective batteries
`of the Examples and Controls thus assembled.
`In the discharge capacity test, after constant voltage
`constant current charge (upper limit voltage=4.1 V) at a 2
`hour rate (1/2C) was performed for 5 hours, and discharge
`was performed at a 2 hourrate (1/2C) until final voltage=2.7
`Vv.
`
`In the high temperature cycle life test, observation was
`made under the condition that, after an initial capacity test
`was carried out and charging/discharging behavior became
`stable, under the atmosphere of 50° C., constant voltage
`constant current charge (upper limit=4.1 V) at a 1 hour rate
`(1C) was performed for 4 hours and then discharge was
`performed at a 1 hour rate (1C) until the depthof a is charge
`(DOD)=40% (24 minutes) Life of each battery was deter-
`mined as the number of cycles that the battery capacity
`reached 80% ofthe initial capacity.
`Test results in the discharge capacity test and the high
`temperature cycle life test are shownin the following Table
`
`TABLE 2
`Test Results
`
`Discharge
`Capacity (Ah)
`
`High Temp. Cycle
`Life (Cycle)
`
`Example 1-1
`Example 1-2
`Example 1-3
`Example 1-4
`
`41
`41
`41
`41
`
`250
`150
`300
`205
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`(Evaluation)
`As shownin Tables 1 and 2,as the discharge capacity test
`results, all of the batteries of Examples 1-1 to 1-7 where the
`mean particle diameter of the amorphous carbon powder
`was 10 um or less demonstrated excellent discharge capacity
`characteristic of 4.0 Ah or more. The battery of Example 1-8
`where the Li/Mnratio in the lithium manganate wasaslarge
`as 0.62 was slightly reduced in the discharge capacity.
`Meanwhile,
`in the battery of Control 1-1,
`its discharge
`capacity was reduced by 10% or more. It is considered that
`the discharge capacity of the positive electrode became
`small and the discharge capacity of the battery was reduced
`due to using the lithtum manganate whose manganesesite
`was replaced with Cr. Therefore, it will be understood that
`the Li/Mnratio of the lithium manganate is desirable to be
`0.6 or less.
`
`As the high temperature cycle life test results, all of the
`batteries of Examples 1-1 to 1-8 using the amorphous carbon
`powder with the mean particle diameter of 10 um or less
`were greatly improved in the cycle life. However,
`the
`batteries of Controls 1-1 and 1-2 using the amorphous
`carbon powderwith the meanparticle diameter of 15 um and
`with the specific surface area of 3.0 m?/g were poorin the
`high temperature cycle life characteristic because of 75
`cycles or less. In the battery of Example 1-2 using the
`amorphous carbon powder with the specific surface area of
`25 m*/g which wasslightly larger than those of the other
`examples, since its specific surtace area wastoo large, the
`reaction area with the electrolytic solution increased and
`deterioration of the negative electrode active material itself
`advanced so that the improvementin the high temperature
`cycle life was relatively small because of 150 cycles.
`Therefore,
`it will be understood that
`the mean particle
`diameter of the amorphous carbon powder should be in the
`range of 3.5 wm or more and 10 um orless.
`Further, as the high temperature cycle life test results, in
`the battery of Example 1-7, since the Li/Mnratio in the
`lithium manganate wasset to 0.5, the numberof cycles was
`180. Thus,
`in this battery,
`the improvement in the high
`temperature cycle characteristic wasrelatively small next to
`the battery of Example 1-2, as compared with the other
`examples where the number of cycles is more than 200.
`Taking the above-mentioned discharge capacity test results
`into consideration,it is preferable that the Li/Mnratio in the
`lithium manganate is in the range of more than 0.5 and 0.60
`or less.
`
`(Second Embodiment)
`Next, a second embodiment where the present invention
`is applied to a cylindrical lithium secondary battery for a
`vehicle will be described hereinafter. In this embodiment,
`the same components or elements as the first embodiment
`are denoted by the same names, and explanation thereof is
`omitted and only different portions will be explained.
`
`4
`
`

`

`US 6,506,518 B1
`
`7
`
`<Negative Electrode>
`As a negative electrode in this embodiment, amorphous
`carbon powderis used of whichirreversible capacity is 5%
`to 25% of initial charge capacity.
`<Positive Electrode>
`
`For a positive electrode, lithium manganate with Li/Mn
`ratio of 0.55 to 0.60 was uscd, and in the same manneras the
`first embodimentslurry is produced with the mixture. The
`slurry obtained was applied to both surfaces of the alumi-
`num foil (positive electrode collector) and subsequently
`dried. Thereafter, the positive electrode collector on which
`mixture layers were formed was pressed and then cut to
`obtain a positive electrode with a thickness of 90 um.
`Further, in this embodiment, an application amountof the
`slurry on the positive electrode (thickness of the positive
`electrode mixture layer) was adjusted so that a discharge
`capacity ratio (hereinafter, referred to as —/+ ratio) of the
`negative electrode to the positive electrode after initial
`charge wasset to 1.3 to 1.8.
`Next, batteries of examples manufactured by variously
`changing the Li/Mnratio of the lithium manganate and the
`-/+ ratio will be explained. Batteries of controls manufac-
`tured for comparison will also be explained.
`
`Example 2-1
`
`in Example 2-1,
`As shown in the following Table 3,
`according to the second embodiment, a cylindrical lithtum
`secondary battery (hereinafter, referred to as a battery of
`Example 2-1) was assembled by using lithium manganate
`with Li/Mnratio of 0.55, adjusting the application amount of
`slurry onthe positive electrode collector to obtain —/+ ratio
`of 1.3, and using amorphous carbon powder where irrevers-
`ible capacity was 20% ofinitial capacity.
`
`TABLE3
`
`-/+ Ratio
`
`Li/MnRatio
`
`Example 2-1
`Example 2-2
`Fxample 2-3
`Example 2-4
`Example 2-5
`Control 2-1
`Control 2-2
`Control 2-3
`Control 2-4
`
`13
`15
`18
`18
`18
`1.0
`1.2
`19
`1.3
`
`0.55
`0.55
`0.55
`0.58
`0.60
`0.55
`0.55
`0.55
`0.50
`
`Examples 2-2 and 2-3
`
`As shown in Table 3, in Example 2-2 a battery of which
`-/+ ratio was 1.5 was manufactured, and in Example 2-3 a
`battery of which —/+ ratio was 1.8 was manufactured. The
`batteries (hereinafter, referred to as batteries of Examples
`2-2 and 2-3) were assembled in the same procedure as
`Example 2-1 by using the same positive electrode, negative
`electrode, separators and electrolytic solution as those in
`Example 2-1 except for the application amount of the
`positive electrode slurry.
`
`Examples 2-4 and 2-5
`
`in Example 2-4 a battery was
`As shown in Table 3,
`manufactured by using lithium manganate of which Li/Mn
`ratio was 0.58, and in Example 2-5 a battery was manufac-
`tured by using lithium manganate of which Li/Mnratio was
`0.60. The batteries (hereinafter, referred to as batteries of
`Examples 2-4 and 2-5) were assembled in the same proce-
`dure as Example 2-3 by using the same positive electrode,
`
`8
`negative electrode, separators and electrolytic solution as
`those in Example 2-3 except for the Li/Mnratio.
`<Controls 2-1 to 2-3>
`As shownin Table 3, batteries of Controls 2-1 to 2-3 were
`manufactured by using lithium manganate of which Li/Mn
`ratio was 0.55, and changing the application amountof the
`positive electrode slurry to set -/+ ratio to 1.0, 1.2 and 1.9,
`respectively. The batteries (hereinafter, referred to as batter-
`ies of Controls 2-1 to 2-3) were assembled in the same
`procedure as Example 2-1 by using the same positive
`electrode, negative electrode, separators and electrolytic
`solution as those in Example 2-1 except for the Li/Mnratio
`and -/+ ratio.
`<Control 2-4>
`in Control 2-4 a battery was
`As shown in Table 3,
`manufactured by using lithium manganate of which Li/Mn
`ratio was 0.50. The battery (hereinafter, referred to as a
`battery of Control 2-4) was assembled in the same procedure
`as Example 2-1 by using the same positive electrode,
`negative electrode, separators and electrolytic solution as
`those in Example 2-1 except for the Li/Mnratio.
`(Test)
`Next, regarding the respective batteries of Examples and
`Controls manufactured, their battery capacities (discharge
`capacities) were measured, and after measured, their high
`temperature cycle life tests were conducted.
`In the measurementof the battery capacity, after an initial
`capacity stabilizing operation, under the atmosphere of 25°
`C., constant voltage constant current charge (upper limit
`voltage: 4.1V) at a 1 hour rate (1C) was performed for 4
`hours, and then discharge capacity where the battery was
`discharged by constant current at a 1 hour rate (1C) down to
`2.7 V was determined as the battery capacity.
`In the high temperature cycle life test, the same test as the
`high temperature cycle life test shown in the first embodi-
`ment was implemented. That is, the observation was made
`under the condition that, under the atmosphere of 50° C., the
`constant voltage constant current charge (upper limit=4.1 V)
`at the 1 hour rate (1C) was performed for 4 hours and then
`discharge was performed at the 1 hour rate (1C) until the
`depth of discharge (DOD)=40% (24 minutes). The life of
`each battery was determined as the numberof cyclesthat the
`battery capacity reached 80% of the initial capacity.
`Test results of measuring the battery capacities (discharge
`capacities) and the high temperature cycle life tests are
`shown in the following Table 4.
`
`TABLE 4
`
`Discharge
`Capacity (Ah)
`
`High Temp. Cycle
`Life (Cycle)
`
`Example 2-1
`Example 2-2
`Example 2-3
`Example 2-4
`Example 2-5
`Control 2-1
`Control 2-2
`Control 2-3
`Control 2-4
`
`4.0
`3.6
`3.2
`3.1
`3.0
`47
`4.2
`3.1
`42
`
`250
`270
`290
`300
`310
`110
`150
`200
`150
`
`(Evaluation)
`As shown in Tables 3 and 4, in each of the batteries of
`Examples 2-1 to 2-3 where the -/+ ratio was in the range of
`1.3 to 1.8 and the lithium manganate with the Li/Mnratio
`=0.55 wasused, an excellent cycle life of 250 cycles or more
`wasobtained evenat the high temperature of 50° C. Also, in
`each of the batteries of Examples 2-4 and 2-5 where the —/+
`ratio was 1.8 and the lithium manganate with the Li/Mn
`ratio=0.58 or 0.60 was used, excellent cycle life of 300
`cycles or more was obtained.
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`5
`
`

`

`US 6,506,518 B1
`
`9
`Meanwhile, in each of the batteries of Controls 2-1 and
`2-2, the battery capacity was large, but the cycle life was
`inferiorto that of each battery of Examples.In the battery of
`Control 2-3, though the -/+ ratio was made large (-/+ ratio:
`1.9), the cycle life was hardly improved and on the contrary
`the battery capacity became small. Also, in the battery of
`Control 2-4 using the lithtum manganate with the Li/Mn
`ratio of 0.50, though the -/+ ratio was 1.3, the improvement
`in the cycle life could not be observed.
`From the above results, in the case of each of Examples
`2-1 to 2-5 where the -/+ ratio wasin the rangeof atleast 1.3
`and at most 1.8, it was found that the battery capacity was
`slightly reduced but the cycle characteristic was largely
`improved. In this case, it was also found that it was prefer-
`able that the Li/Mn ratio in the positive electrode active
`material was in the range of 0.55 to 0.60.
`Generally, as compared with the room temperature, the
`cycle life of the lithium secondary battery using the lithium
`manganate as the positive electrode active material
`is
`extremely shortened at the high temperature of 50° C. or so
`like the battery being mounted inside an engine room.
`However,
`in the lithium battery according to this
`embodiment, even whenthe battery is mounted inside: the
`EV or HEV engine room,sutficient cycle life can be secured,
`as demonstrated in the results of the high temperature cycle
`life test.
`
`the examples
`in the second embodiment,
`Incidentally,
`have been shownthat the —/+ ratio is changed in the range
`of 1.3 to 1.8 by changing the application amount of the
`mixture containing the positive electrode active material, but
`the —/+ratio maybeset in the range of 1.3 to 1.8 by changing
`the application amount of the mixture containing the nega-
`tive electrode active material.
`
`Further, in this embodiment, though the same amorphous
`carbon as that in the first embodiment was used, the mean
`particle diameter and the specific surface area are notlimited
`to the ranges specified in the first embodiment as the
`preferable ranges.
`in the examples according to this
`Furthermore,
`embodiment, the amorphous carbon powderwheretheirre-
`versible capacity was 20% ofthe initial capacity was used,
`but the same effects can be obtained even when ones where
`the irreversible capacity is in the range of 5% to 25% are
`used as the amorphous carbon powder.
`In the above embodiments,as the electrolytic solution, the
`electrolytic solution wherelithium hexafluorophosphate was
`dissolved in the mixed solution of ethylene carbonate and
`dimethyl carbonate at 1 mole/liter was used, but the elec-
`trolytic solution is not particularly limited to this one, and
`even when the electrolytic solution being used by ordinary
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`10
`is used, the same effects as in the above embodiments can be
`obtained. Namely, even whenthe electrolytic solution where
`ordinary lithium salt used as electrolyte is dissolved in
`organic solvent, the present invention is applicable to the
`batteries using such electrolytic solution, and the lithiumsalt
`and the organic solvent to be used are not limited in this
`invention. For example, as the electrolyte, LiclO,, LiAsF.,
`LiBF,, LiB(CsH;)4,, CH,;S03Li, CF,;SO,Li or the like, or
`mixture thereof can be used. Also, as the organic solvent,
`polypropylene carbonate, ethylene carbonate, 1,2-
`dimethoxyethane, 1,2-diethoxyethane, y-butyrolactone,tet-
`rahydrofuran 1,3-dioxolane, 4-methy-1,3-dioxolane, diethyl
`ether, sulfolane, methylsulfolane, acetonitrile, propionitrile
`or the like, or mixture of two kinds or more thereof can be
`used.
`In the forgoing, the case