U.S. patent application number 12/512540 was filed with the patent office on 2009-11-26 for nonaqueous electrolyte battery containing a negative electrode of lithium-titanium composite oxide, battery pack and vehicle.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Hiroki INAGAKI, Norio Takami.
Application Number | 20090291354 12/512540 |
Document ID | / |
Family ID | 36177675 |
Filed Date | 2009-11-26 |
United States Patent
Application |
20090291354 |
Kind Code |
A1 |
INAGAKI; Hiroki ; et
al. |
November 26, 2009 |
NONAQUEOUS ELECTROLYTE BATTERY CONTAINING A NEGATIVE ELECTRODE OF
LITHIUM-TITANIUM COMPOSITE OXIDE, BATTERY PACK AND VEHICLE
Abstract
A nonaqueous electrolyte battery, containing a case and provided
in the case, a positive electrode, a negative electrode and a
nonaqueous electrolyte. The negative electrode comprises a
lithium-titanium composite oxide, wherein a crystallite diameter of
the lithium-titanium composite oxide is not larger than
6.9.times.10.sup.2 .ANG.. The lithium-titanium composite oxide
comprises: rutile TiO.sub.2; anatase TiO.sub.2; Li.sub.2TiO.sub.3;
and a lithium titanate having a spinel structure. A main peak
intensity relative to lithium titanate set at 100, as determined by
X-ray diffractometry, of each of lithium titanate having a spinel
structure, the rutile TiO.sub.2, the anatase TiO.sub.2 and
Li.sub.2TiO.sub.3 is not larger than 7.
Inventors: |
INAGAKI; Hiroki;
(Kawasaki-shi, JP) ; Takami; Norio; (Yokohama-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
36177675 |
Appl. No.: |
12/512540 |
Filed: |
July 30, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11228430 |
Sep 19, 2005 |
7595134 |
|
|
12512540 |
|
|
|
|
Current U.S.
Class: |
429/61 ;
252/182.1; 429/163 |
Current CPC
Class: |
C01G 23/005 20130101;
C01P 2006/40 20130101; C01P 2002/60 20130101; H01M 2300/004
20130101; H01M 4/364 20130101; C01G 53/50 20130101; H01M 4/485
20130101; H01M 4/525 20130101; H01M 4/5825 20130101; C01G 23/00
20130101; Y02T 10/70 20130101; H01M 4/505 20130101; C01G 45/1228
20130101; Y02P 70/50 20151101; H01M 2004/027 20130101; C01P 2002/32
20130101; C01P 2004/61 20130101; H01M 2004/021 20130101; C01G 51/50
20130101; C01P 2002/72 20130101; C01P 2002/74 20130101; H01M
10/0525 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
429/61 ; 429/163;
252/182.1 |
International
Class: |
H01M 2/02 20060101
H01M002/02; H01M 2/00 20060101 H01M002/00; H01M 4/86 20060101
H01M004/86 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2005 |
JP |
2005-141146 |
Claims
1. A nonaqueous electrolyte battery, comprising: a case; a positive
electrode provided in the case; a negative electrode provided in
the case; and a nonaqueous electrolyte provided in the case;
wherein the negative electrode comprises a lithium-titanium
composite oxide, a crystallite diameter of the lithium-titanium
composite oxide is not larger than 6.9.times.10.sup.2 .ANG., the
lithium-titanium composite oxide comprises: rutile TiO.sub.2;
anatase TiO.sub.2; Li.sub.2TiO.sub.3; and a lithium titanate having
a spinel structure; a main peak intensity relative to lithium
titanate set at 100, as determined by X-ray diffractometry, of each
of lithium titanate having a spinel structure, the rutile
TiO.sub.2, the anatase TiO.sub.2 and Li.sub.2TiO.sub.3 is not
larger than 7.
2. The battery according to claim 1, wherein the crystallite
diameter is not smaller than 1.5.times.10.sup.2 .ANG..
3. The battery according to claim 1, wherein the crystallite
diameter is not smaller than 2.6.times.10.sup.2 .ANG..
4. The battery according to claim 1, wherein a main peak intensity
relative to lithium titanate set at 100, as determined by X-ray
diffractometry, of each of lithium titanate having a spinel
structure, the rutile TiO.sub.2, the anatase TiO.sub.2 and
Li.sub.2TiO.sub.3 is not larger than 3.
5. The battery according to claim 1, wherein the nonaqueous
electrolyte comprises at least two solvents selected from the group
of solvents consisting of propylene carbonate, ethylene carbonate
and .gamma.-butyrolactone.
6. The battery according to claim 1, wherein the nonaqueous
electrolyte comprises .gamma.-butyrolactone.
7. The battery according to claim 1, wherein the positive electrode
contains a compound represented by
Li.sub.aNi.sub.bCo.sub.cMn.sub.dO.sub.2 wherein
0.ltoreq.a.ltoreq.1.1, 0.1.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.9, and 0.1.ltoreq.d.ltoreq.0.5.
8. A battery pack comprising a nonaqueous electrolyte battery
according to claim 1.
9. The battery pack according to claim 8 further comprising a
protective circuit which detects a voltage of the nonaqueous
battery.
10. A vehicle comprising a nonaqueous battery according to claim
1.
11. A lithium-titanium composite oxide comprising: rutile
TiO.sub.2; anatase TiO.sub.2; Li.sub.2TiO.sub.3; and a lithium
titanate having a spinel structure; wherein a crystallite diameter
is not larger than 6.9.times.10.sup.2 .ANG., and a main peak
intensity relative to lithium titanate set at 100, as determined by
X-ray diffractometry, of each of lithium titanate having a spinel
structure, the rutile TiO.sub.2, the anatase TiO.sub.2 and
Li.sub.2TiO.sub.3 is not larger than 7.
12. The lithium-titanium composite oxide according to claim 11,
wherein the crystallite diameter is not smaller than
1.5.times.10.sup.2 .ANG..
13. The lithium-titanium composite oxide according to claim 11,
wherein the crystallite diameter is not smaller than
2.6.times.10.sup.2 .ANG..
14. The lithium-titanium composite oxide according to claim 11,
wherein a main peak intensity relative to lithium titanate set at
100, as determined by X-ray diffractometry, of each of lithium
titanate having a spinel structure, the rutile TiO.sub.2, the
anatase TiO.sub.2 and Li.sub.2TiO.sub.3 is not larger than 3.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 11/228,430, filed Sep. 19, 2005, the
disclosure of which is incorporated herein by reference in its
entirety. The parent application claims priority to Japanese Patent
Application No. 2005-141146, filed May 13, 2005, the disclosure of
which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a nonaqueous electrolyte
battery, a lithium-titanium composite oxide, a battery pack and a
vehicle.
[0004] 2. Description of the Related Art
[0005] A vigorous research is being conducted on a nonaqueous
electrolyte battery having a high energy density in which lithium
ions are migrated between the negative electrode and the positive
electrode for charging and discharging the battery.
[0006] Various properties are required for the nonaqueous
electrolyte battery depending on the use of the battery. For
example, the discharge under a current of about 3 C is expected
when the nonaqueous electrolyte battery is used in a digital
camera, and the discharge under a current of at least about 10 C is
expected when the nonaqueous electrolyte battery is used in a
vehicle such as a hybrid electric automobile. Such being the
situation, the large current characteristics are particularly
required in the nonaqueous electrolyte battery used in the
technical fields exemplified above.
[0007] Nowadays, a nonaqueous electrolyte battery in which a
lithium-transition metal composite oxide is used as a positive
electrode active material and a carbonaceous material is used as a
negative electrode active material has been put to the practical
use. In general, Co, Mn or Ni is used as the transition metal
included in the lithium-transition metal composite oxide.
[0008] In recent years, a nonaqueous electrolyte battery in which a
lithium-titanium composite oxide having a high Li
absorption-release potential relative to the carbonaceous material
has been put to the practical use. Since the lithium-titanium
composite oxide is small in the change of volume accompanying the
charge-discharge of the battery, the lithium-titanium composite
oxide is expected to improve the charge-discharge cycle
characteristics of the secondary battery.
[0009] Among the lithium-titanium composite oxides, the Spinel type
lithium titanate is expected to be particularly useful. The Spinel
type lithium titanate can be synthesized by, for example, mixing
lithium hydroxide with titanium dioxide, followed by baking the
resultant mixture. If the baking is insufficient in this
synthesizing process, obtained are lithium-titanium composite
oxides containing an anatase type TiO.sub.2, a rutile type
TiO.sub.2, and Li.sub.2TiO.sub.3 as impurity phases in addition to
the Spinel type lithium titanate.
[0010] It is disclosed in Japanese Patent Disclosure (Kokai) No.
2001-240498 that lithium-titanium composite oxides containing the
Spinel type lithium titanate as a main component, having a small
amount of the impurity phases noted above, and also having a
crystallite diameter of 700 to 800 .ANG. can be used as the
negative electrode active material having a large capacity.
BRIEF SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a
nonaqueous electrolyte battery, a lithium-titanium composite oxide,
a battery pack and a vehicle, which are excellent in the large
current characteristics.
[0012] According to a first aspect of the present invention, there
is provided a nonaqueous electrolyte battery, comprising:
[0013] a case;
[0014] a positive electrode provided in the case;
[0015] a negative electrode provided in the case and containing a
lithium-titanium composite oxide comprising a crystallite diameter
not larger than 6.9.times.10.sup.2 .ANG., the lithium-titanium
composite oxide including a rutile type TiO.sub.2, an anatase type
TiO.sub.2, Li.sub.2TiO.sub.3 and a lithium titanate having a spinel
structure, the rutile type TiO.sub.2, the anatase type TiO.sub.2
and Li.sub.2TiO.sub.3 each having a main peak intensity not larger
than 7 on the basis that a main peak intensity of the lithium
titanate as determined by the X-ray diffractometry is set at 100;
and
[0016] a nonaqueous electrolyte provided in the case.
[0017] According to a second aspect of the present invention, there
is provided a battery pack comprising nonaqueous electrolyte
batteries,
[0018] each of the nonaqueous electrolyte batteries comprising:
[0019] a case;
[0020] a positive electrode provided in the case;
[0021] a negative electrode provided in the case and containing a
lithium-titanium composite oxide comprising a crystallite diameter
not larger than 6.9.times.10.sup.2 .ANG., the lithium-titanium
composite oxide including a rutile type TiO.sub.2, an anatase type
TiO.sub.2, Li.sub.2TiO.sub.3 and a lithium titanate having a spinel
structure, the rutile type TiO.sub.2, the anatase type TiO.sub.2
and Li.sub.2TiO.sub.3 each having a main peak intensity not larger
than 7 on the basis that a main peak intensity of the lithium
titanate as determined by the X-ray diffractometry is set at 100;
and
[0022] a nonaqueous electrolyte provided in the case.
[0023] Further, according to a third aspect of the present
invention, there is provided a lithium-titanium composite oxide
comprising a crystallite diameter not larger than
6.9.times.10.sup.2 .ANG., the lithium-titanium composite oxide
including a rutile type TiO.sub.2, an anatase type TiO.sub.2,
Li.sub.2TiO.sub.3 and a lithium titanate having a spinel structure,
the rutile type TiO.sub.2, the anatase type TiO.sub.2 and
Li.sub.2TiO.sub.3 each having a main peak intensity not larger than
7 on the basis that a main peak intensity of the lithium titanate
as determined by the X-ray diffractometry is set at 100.
[0024] According to a fourth aspect of the present invention, there
is provided a vehicle comprising a battery pack comprising
nonaqueous electrolyte batteries,
[0025] each of the nonaqueous electrolyte batteries comprising:
[0026] a case;
[0027] a positive electrode provided in the case;
[0028] a negative electrode provided in the case and containing a
lithium-titanium composite oxide comprising a crystallite diameter
not larger than 6.9.times.10.sup.2 .ANG., the lithium-titanium
composite oxide including a rutile type TiO.sub.2, an anatase type
TiO.sub.2, Li.sub.2TiO.sub.3 and a lithium titanate having a spinel
structure, the rutile type TiO.sub.2, the anatase type TiO.sub.2
and Li.sub.2TiO.sub.3 each having a main peak intensity not larger
than 7 on the basis that a main peak intensity of the lithium
titanate as determined by the X-ray diffractometry is set at 100;
and
[0029] a nonaqueous electrolyte provided in the case.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1A is a cross sectional view schematically showing as
an example the construction of a unit cell according to a first
embodiment of the present invention;
[0031] FIG. 1B is a cross sectional view schematically showing the
construction of the circular portion A shown in FIG. 1A;
[0032] FIG. 2 is an oblique view showing in a dismantled fashion
the construction of a battery pack according to a second embodiment
of the present invention;
[0033] FIG. 3 is a block diagram showing the electric circuit of
the battery pack according to the second embodiment of the present
invention;
[0034] FIG. 4 is a graph showing the X-ray diffraction pattern of
the lithium-titanium composite oxide for the Example of the present
invention;
[0035] FIG. 5 is an oblique view, partly broken away, schematically
showing the construction of another unit cell according to the
first embodiment of the present invention; and
[0036] FIG. 6 is a cross sectional view showing in a magnified
fashion the construction of the circular portion B shown in FIG.
5.
DETAILED DESCRIPTION OF THE INVENTION
[0037] As a result of an extensive research, the present inventors
have found that the lithium-titanium composite oxide exhibits a
relatively low lithium ion conductivity. For example, it has been
found that the lithium ion conductivity of the lithium-titanium
composite oxide is much lower than that of lithium-cobalt composite
oxide. To be more specific, the lithium ion conductivity of the
lithium-titanium composite oxide is one-several hundredth of that
of lithium-cobalt composite oxide. As a result, in the nonaqueous
electrolyte battery comprising both lithium-titanium composite
oxide and lithium-cobalt composite oxide, the diffusion of the
lithium ions in the lithium-titanium composite oxide provides the
rate-determining step and thus, the nonaqueous electrolyte battery
is made poor in its large current characteristics.
[0038] Under the circumstances, the present inventors have found
that the diffusion rate of the lithium ions is increased with
decrease in the crystallite diameter of the lithium-titanium
composite oxide so as to improve the ionic conductivity of the
lithium-titanium composite oxide.
[0039] The present inventors have also found that the diffusion
rate of lithium ions is increased with decrease in the amount of
the impurity phases contained in the lithium-titanium composite
oxide. It is considered reasonable to understand that the impurity
phases impair the diffusion of lithium ions so as to lower the
diffusion rate of the lithium ions.
[0040] However, where the baking is performed sufficiently in the
manufacturing process, the lithium-titanium composite oxide has a
large crystallite diameter and the amount of the impurity phases is
decreased in the manufactured lithium-titanium composite oxide. On
the other hand, where the baking is suppressed in the manufacturing
process, the lithium-titanium composite oxide has a small
crystallite diameter and contains a large amount of the impurity
phases. Such being the situation, it was difficult to manufacture a
lithium-titanium composite oxide having a small crystallite
diameter and containing a small amount of the impurity phases so as
to make it difficult to improve the ionic conductivity of the
lithium-titanium composite oxide.
[0041] The present inventors have found that the ionic conductivity
of the lithium-titanium composite oxide can be improved by allowing
the crystallite diameter and the amount of the impurity phases of
the lithium-titanium composite oxide to satisfy the conditions
described herein later, thereby improving the large current
discharge characteristics of the nonaqueous electrolyte
battery.
[0042] Each embodiment of the present invention will now be
described with reference to the accompanying drawings.
Incidentally, in the accompanying drawings, the common constituents
of the embodiment are denoted by the same reference numerals so as
to omit the overlapping description. Also, the accompanying
drawings are schematic drawings that are simply intended to
facilitate the understanding of the present invention. The
accompanying drawings may include portions differing from the
actual apparatus in the shape, size and ratio. However, the design
of the apparatus may be changed appropriately in view of the
following description and the known technologies.
First Embodiment
[0043] The construction of the unit cell as an example according to
the first embodiment of the present invention will now be described
with reference to FIGS. 1A and 1B. Specifically, FIG. 1A is a cross
sectional view schematically showing the construction of a
flattened type nonaqueous electrolyte secondary battery according
to the first embodiment of the present invention, and FIG. 1B is a
cross sectional view showing in detail the construction of a
circular region A shown in FIG. 1A.
[0044] A positive electrode terminal 1 is electrically connected to
a positive electrode 3, and a negative electrode terminal 2 is
electrically connected to a negative electrode 4. The positive
electrode 3, the negative electrode 4 and a separator 5 interposed
between the positive electrode 3 and the negative electrode 4
collectively form a flattened wound electrode 6. Since the
separator 5 is interposed between the positive electrode 3 and the
negative electrode 4, the negative electrode 4 and the positive
electrode 3 are positioned spatially apart from each other. The
wound electrode 6 is housed in a case 7 having a nonaqueous
electrolyte loaded therein.
[0045] As shown in FIG. 1A, the flattened wound electrode 6 is
housed in the case 7 having the nonaqueous electrolyte loaded
therein. The negative electrode 2 is electrically connected to the
outside and the positive electrode terminal 1 is electrically
connected to the inside in the vicinity of the outer
circumferential edge of the wound electrode 6. The wound electrode
6 has a laminate structure comprising the negative electrode 4, the
separator 5, the positive electrode 3 and the separator 5, which
are laminated one upon the other in the order mentioned, though the
laminate structure is not shown in FIG. 1A.
[0046] FIG. 1B shows more in detail the construction of the wound
electrode 6. As shown in the drawing, the positive electrode 3, the
negative electrode 4 and the separator 5 interposed between the
positive electrode 3 and the negative electrode 4 are laminated one
upon the other in the order mentioned. The negative electrode 4
constituting the outermost circumferential region comprises a
negative electrode current collector 4a forming the outer layer and
a negative electrode layer 4b positioned inside the negative
electrode current collector 4a. Each of the other negative
electrodes 4 comprises the negative electrode layer 4b, the
negative electrode current collector 4a and the additional negative
electrode layer 4b, which are laminated one upon the other in the
order mentioned. Likewise, the positive electrode 3 comprises a
positive electrode layer 3b, a positive electrode current collector
3a and another positive electrode layer 3b, which are laminated one
upon the other in the order mentioned.
[0047] The negative electrode, the nonaqueous electrolyte, the
positive electrode, the separator, the case, the positive electrode
terminal, and the negative electrode terminal included in the
nonaqueous electrolyte battery will now be described in detail.
[0048] 1) Negative Electrode
[0049] The negative electrode comprises a negative electrode
current collector and a negative electrode layer supported on one
surface or both surfaces of the negative electrode current
collector and containing a negative electrode active material, a
negative electrode conductive agent, and a binder.
[0050] The negative electrode active material comprises a
lithium-titanium composite oxide having the crystallite diameter
not larger than 6.9.times.10.sup.2 .ANG. and containing a lithium
titanate having a spinel structure (hereinafter referred to a
Spinel type lithium titanate) as the main component and low in the
impurity phase content. The Spinel type lithium titanate can be
represented by the chemical formula
Li.sub.4+xTi.sub.5O.sub.12(0.ltoreq.x.ltoreq.3).
[0051] To be more specific, the crystallite diameter of the
lithium-titanium composite oxide, which is obtained by the Scherrer
formula from the half value width of the X-ray diffraction peak, is
not larger than 6.9.times.10.sup.2 .ANG.. Also, the
lithium-titanium composite oxide contains a rutile type TiO.sub.2,
an anatase type TiO.sub.2 and Li.sub.2TiO.sub.3 each having the
main peak intensity not larger than 7 on the basis that the main
peak intensity of the Spinel type lithium titanate as determined by
the X-ray diffractometry is set at 100. Incidentally, the situation
that the main peak intensity of any of the rutile type TiO.sub.2,
the anatase type TiO.sub.2 and Li.sub.2TiO.sub.3 is not larger than
7 covers the case where the main peak intensity is zero (0) in some
of the main peak intensity of the rutile type TiO.sub.2, the main
peak intensity of the anatase type TiO.sub.2 and the main peak
intensity of Li.sub.2TiO.sub.3, and the case where the main peak
intensity is zero in all of the rutile type TiO.sub.2, the anatase
type TiO.sub.2 and Li.sub.2TiO.sub.3. Where the main peak intensity
is lower than the detection limit, the main peak intensity is
regarded as being zero (0).
[0052] The main peak of the Spinel type lithium titanate denotes
the peak in the case where the lattice spacing d in the X-ray
diffraction pattern is 4.83 .ANG.. Also, the main peak of the
anatase type TiO.sub.2, the main peak of the rutile type TiO.sub.2
and the main peak of Li.sub.2TiO.sub.3 denote the peaks in the
cases where the lattice spacing d is 3.51 .ANG., 3.25 .ANG. and
2.07 .ANG., respectively.
[0053] The lithium-titanium composite oxide in this embodiment of
the present invention makes it possible to increase the diffusion
rate of the lithium ions and to improve the ionic conductivity. In
addition, it is possible to improve the large current
characteristics of the nonaqueous electrolyte battery.
Incidentally, the diffusion rate noted above includes both the
transgranular diffusion and the grain boundary diffusion. It is
considered reasonable to understand that the effect produced by the
lithium-titanium composite oxide according to this embodiment of
the present invention is produced by the situation that the lithium
ion diffusion rate at the crystal grain boundary is higher than
that inside the crystal grain.
[0054] It is desirable for the crystallite diameter of the
lithium-titanium composite oxide to be not larger than
5.3.times.10.sup.2 .ANG.. If the crystallite diameter is not larger
than 5.3.times.10.sup.2 .ANG., the ionic conductivity and the large
current characteristics can be further improved. It is more
desirable for the crystallite diameter to be not larger than
4.4.times.10.sup.2 .ANG..
[0055] It is desirable for the crystallite diameter of the
lithium-titanium composite oxide to be not smaller than
1.5.times.10.sup.2 .ANG.. If the crystallite diameter is not
smaller than 1.5.times.10.sup.2 .ANG., it is possible to form
easily the lithium-titanium composite oxide low in the contents of
the impurity phases such as the rutile type TiO.sub.2, the anatase
type TiO.sub.2 and Li.sub.2TiO.sub.3. It is more desirable for the
crystallite diameter to be not smaller than 2.6.times.10.sup.2
.ANG..
[0056] It is desirable for the main peak intensity of any of the
rutile type TiO.sub.2, the anatase type TiO.sub.2 and
Li.sub.2TiO.sub.3 to be not higher than 3, more desirably not
higher than 1.
[0057] The diffusion rate of the lithium ions can be further
improved with decrease in the amount of the impurity phases noted
above. Also, the ionic conductivity and the large current
characteristics can be improved with decrease in the amount of the
impurity phases noted above.
[0058] It is desirable for the lithium-titanium composite oxide to
be in the form of particles having the average particle diameter
not smaller than 100 nm and not larger than 1 .mu.m. If the average
particle diameter is not smaller than 100 nm, the lithium-titanium
composite oxide can be handled easily in the industrial manufacture
of the nonaqueous electrolyte battery.
[0059] Also, if the average particle diameter is not larger than 1
.mu.m, the diffusion of the lithium ions within a particle can be
performed smoothly.
[0060] It is desirable for the lithium-titanium composite oxide to
have a specific surface area not smaller than 5 m.sup.2/g and not
larger than 50 m.sup.2/g. If the specific surface area is not
smaller than 5 m.sup.2/g, it is possible to secure sufficiently the
absorption-release sites of the lithium ions. On the other hand, if
the specific surface area is not larger than 50 m.sup.2/g, the
lithium-titanium composite oxide can be handled easily in the
industrial manufacture of the nonaqueous electrolyte battery.
[0061] Incidentally, it is possible for the lithium-titanium
composite oxide to contain Nb, Pb, Fe, Ni, Si, Al, Zr, etc. in an
amount of 1,000 ppm or less.
[0062] An example of the manufacturing method of the
lithium-titanium composite oxide will now be described.
[0063] In the first step, prepared is a lithium salt used as a
lithium source such as lithium hydroxide, lithium oxide or lithium
carbonate. Also prepared are a sodium hydroxide as the sodium
source and potassium hydroxide as the potassium source. Prescribed
amounts of the lithium source and at least one of the sodium source
and potassium source are dissolved in a pure water so as to obtain
an aqueous solution. Desired addition amounts of the sodium source
and the potassium source will be described herein later.
[0064] In the next step, titanium oxide is put in the resultant
solution such that lithium and titanium have a prescribed atomic
ratio. For example, in the case of synthesizing the
lithium-titanium composite oxide having the spinel structure and
the chemical formula of Li.sub.4Ti.sub.5O.sub.12, titanium oxide is
added to the solution such that Li and Ti have an atomic ratio of
4:5.
[0065] In the next step, the solution thus obtained is dried while
stirring the solution so as to obtain a baking precursor. The
drying method employed in this stage includes, for example, a spray
drying, a granulating drying, a freeze drying, and a combination
thereof. The baking precursor thus obtained is baked so as to form
a lithium-titanium composite oxide for this embodiment of the
present invention. It suffices to perform the baking under the air
atmosphere. It is also possible to perform the baking under an
oxygen gas atmosphere or an argon gas atmosphere.
[0066] It suffices to perform the baking under temperatures not
lower than 680.degree. C. and not higher than 1,000.degree. C. for
about 1 hour to about 24 hours. Preferably, the baking should be
carried out under temperatures not lower than 720.degree. C. and
not higher than 800.degree. C. for 5 hours to 10 hours.
[0067] If the baking temperature is lower than 680.degree. C., the
reaction between titanium oxide and the lithium compound is
rendered insufficient so as to increase the amount of the impurity
phases such as the anatase type TiO.sub.2, the rutile type
TiO.sub.2 and Li.sub.2TiO.sub.3, with the result that the electric
capacity is decreased. On the other hand, if the baking temperature
exceeds 1,000.degree. C., the sintering of the Spinel type lithium
titanate proceeds so as to cause the crystallite diameter to be
increased excessively and, thus, to lower the large current
performance.
[0068] The lithium-titanium composite oxide manufactured by the
manufacturing method described above contains Na or K. Each of Na
and K performs the function of suppressing the crystal growth of
the Spinel type lithium titanate. Such being the situation, it is
possible to suppress the growth of the crystallite of the Spinel
type lithium titanate even if the baking is performed under high
temperatures in an attempt to prevent the phases such as the
anatase type TiO.sub.2, the rutile type TiO.sub.2 and
Li.sub.2TiO.sub.3 from remaining unreacted. As a result, it is
possible to obtain the lithium-titanium composite oxide having a
small crystallite diameter and low in the impurity phase content.
It should also be noted that since the lithium-titanium composite
oxide contains an element X consisting of at least one of Na and K,
the stability of the crystal structure is enhanced so as to improve
the charge discharge cycle characteristics of the nonaqueous
electrolyte battery. Also, it is possible to improve the ionic
conductivity of the lithium-titanium composite oxide.
[0069] It is desirable for the lithium-titanium composite oxide to
contain the element X, i.e., (Na+K), in an amount not smaller than
0.10% by weight and not larger than 3.04% by weight based on the
amount of the lithium-titanium composite oxide. If the amount of
(Na+K) contained in the lithium-titanium composite oxide is smaller
than 0.10% by weight, it is difficult to obtain a sufficient effect
of suppressing the crystal growth. It is also difficult to obtain a
sufficient effect of stabilizing the crystal structure and of
improving the ionic conductivity. On the other hand, if the amount
of (Na+K) is larger than 3.04% by weight, it is possible for the
Spinel type lithium titanate containing Na and K to form an
impurity phase so as to lower the electric capacity of the
nonaqueous electrolyte battery. It should be noted in this
connection that the phenomenon noted above is brought about because
Li is possibly substituted by the element X and the element X can
be positioned in the sites of Li of the Spinel type lithium
titanate.
[0070] It is possible for each of Na and K to be positioned in the
Li sites of the Spinel type lithium titanate. This can be confirmed
by applying an X-ray diffraction measurement to the
lithium-titanium composite oxide so as to perform the Rietveld
analysis. For performing the Rietveld analysis, it is possible to
use, for example, RIETAN (trade name of an analytical soft ware).
If Na or K is positioned in the Li site of the Spinel type lithium
titanate, the stability of the crystal structure can be further
improved and, at the same time, the segregation can be
suppressed.
[0071] It is desirable for the lithium-titanium composite oxide to
contain K in an amount larger than that of Na because K produces a
higher effect of promoting the crystallization and, thus, permits
shortening the sintering time.
[0072] Incidentally, it is possible to use titanium oxide
containing a prescribed amount of Na or K as the raw material in
the manufacturing process in place of allowing sodium hydroxide
and/or potassium hydroxide to be dissolved in water.
[0073] It is possible to use, for example, acetylene black, carbon
black, graphite, etc. as the negative electrode conductive agent
for enhancing the current collecting performance and for
suppressing the contact resistance between the current collector
and the active material.
[0074] It is possible to use, for example, polytetrafluoroethylene
(PTFE), polyvinylidene fluoride (PVdF), a fluorinated rubber, a
styrene-butadiene rubber, etc. as the binder for bonding the
negative electrode active material to the negative electrode
conductive agent.
[0075] Concerning the mixing ratio of the negative electrode active
material, the negative electrode conductive agent, and the binder,
it is desirable for the negative electrode active material to be
used in an amount not smaller than 70% by weight and not larger
than 96% by weight, for the negative electrode conductive agent to
be used in an amount not smaller than 2% by weight and not larger
than 28% by weight, and for the binder to be used in an amount not
smaller than 2% by weight and not larger than 28% by weight. If the
mixing amount of the negative electrode conductive agent is smaller
than 2% by weight, the current collecting performance of the
negative electrode layer may be lowered so as to possibly lower the
large current characteristics of the nonaqueous electrolyte
battery. Also, if the mixing amount of the binder is smaller than
2% by weight, the bonding between the negative electrode layer and
negative electrode current collector may be lowered so as to
possibly lower the charge-discharge cycle characteristics of the
nonaqueous electrolyte battery. On the other hand, it is desirable
for the mixing amount of each of the negative electrode conductive
agent and the binder to be not larger than 28% by weight in view of
the improvement in the capacity of the nonaqueous electrolyte
battery.
[0076] It is desirable for the negative electrode current collector
to be formed of an aluminum foil that is electrochemically stable
within the potential range nobler than 1.0 V or an aluminum alloy
foil containing an element such as Mg, Ti, Zn, Mn, Fe, Cu, or
Si.
[0077] The negative electrode can be prepared by, for example,
coating a negative electrode current collector with a slurry
prepared by suspending a negative electrode active material, a
negative electrode conductive agent and a binder in a solvent,
followed by drying the coated slurry so as to form a negative
electrode layer on the negative electrode current collector and
subsequently pressing the current collector having the negative
electrode layer formed thereon. Alternatively, it is also possible
to form a mixture of a negative electrode active material, a
negative electrode conductive agent and a binder into pellets for
forming a negative electrode layer.
[0078] 2) Nonaqueous Electrolyte
[0079] The nonaqueous electrolyte includes a liquid nonaqueous
electrolyte that is prepared by dissolving an electrolyte in an
organic solvent and a gel-like nonaqueous electrolyte that is
prepared by using a composite material containing a liquid
nonaqueous electrolyte and a polymer material.
[0080] The liquid nonaqueous electrolyte can be prepared by
dissolving an electrolyte in an organic solvent in a concentration
not lower than 0.5 mol/L and not higher than 2.5 mol/L.
[0081] The electrolyte includes, for example, lithium salts such as
lithium perchlorate (LiCl.sub.4), lithium hexafluoro phosphate
(LiPF.sub.6), lithium tetrafluoro borate (LiBF.sub.4), lithium
hexafluoro arsenate (LiAsF.sub.6), lithium trifluoro metasulfonate
(LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonyl imide lithium
[LiN(CF.sub.3SO.sub.2).sub.2], and a mixture thereof. It is
desirable to use an electrolyte that is unlikely to be oxidized
under a high potential. Particularly, it is most desirable to use
LiPF.sub.6 as the electrolyte.
[0082] The organic solvent includes, for example, cyclic carbonates
such as propylene carbonate (PC), ethylene carbonate (EC) and
vinylene carbonate; linear carbonates such as diethyl carbonate
(DEC), dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC);
cyclic ethers such as tetrahydrofuran (THF), 2-methyl
tetrahydrofuran (2Me THF) and dioxolane (DOX); linear ethers such
as dimethoxy ethane (DME), and diethoxy ethane (DEE); as well as
.gamma.-butyrolactone (GBL), acetonitrile (AN) and sulfolane (SL).
These solvents can be used singly or in the form of a mixed
solvent.
[0083] The polymer materials include, for example, polyvinylidene
fluoride (PVdF), polyacrylonitrile (PAN) and polyethylene oxide
(PEO).
[0084] It is desirable to use a mixed solvent prepared by mixing at
least two organic solvents selected from the group consisting of
propylene carbonate (PC), ethylene carbonate (EC) and
.gamma.-butyrolactone (GBL). Further, it is more desirable to use
the organic solvent containing .gamma.-butyrolactone (GBL).
[0085] It should be noted that the lithium-titanium composite oxide
permits absorbing-releasing lithium ions in the potential region in
the vicinity of 1.5V (vs. Li/Li.sup.+). However, in the potential
region noted above, the nonaqueous electrolyte is unlikely to be
decomposed by reduction, and a film consisting of the reduction
product of the nonaqueous electrolyte is unlikely to be formed on
the surface of the lithium-titanium composite oxide. Such being the
situation, if the nonaqueous electrolyte battery is stored under
the state that lithium ions have been inserted, i.e., under the
charged state, the lithium ions inserted in the lithium-titanium
composite oxide are gradually diffused into the liquid electrolyte
so as to bring about a so-called "self-discharge". The
self-discharge is rendered prominent with increase in the
temperature of the storing environment of the battery.
[0086] As described above, the lithium-titanium composite oxide in
this embodiment of the present invention has a small crystallite
diameter so as to increase the crystal boundary area per unit
weight. As a result, the self-discharge is rendered somewhat
prominent in the lithium-titanium composite oxide, compared with
the conventional material.
[0087] It should be noted in this connection that
.gamma.-butyrolactone is likely to be reduced, compared with the
linear carbonate or the cyclic carbonate. To be more specific, the
organic solvents are likely to be reduced in the order of
.gamma.-butyrolactone >>> ethylene carbonate >
propylene carbonate >> dimethyl carbonate > methyl ethyl
carbonate > diethyl carbonate. Incidentally, the degree of
difference in the reactivity between the solvents is denoted by the
number of signs of inequality (>).
[0088] Such being the situation, in the case where the liquid
electrolyte contains .gamma.-butyrolactone, a good film can be
formed on the surface of the lithium-titanium composite oxide even
under the operable potential region of the lithium-titanium
composite oxide. As a result, the self-discharge can be suppressed
so as to improve the storage characteristics of the nonaqueous
electrolyte battery under high temperatures. This is also the case
with the mixed solvents referred to above.
[0089] In order to form a better protective film, it is desirable
for .gamma.-butyrolactone to be contained in an amount not smaller
than 40% by volume and not larger than 95% by volume of the organic
solvent.
[0090] It is also possible to use an ionic liquid containing
lithium ions, a polymer solid electrolyte, and an inorganic solid
electrolyte as the nonaqueous electrolyte.
[0091] The ionic liquid denotes a compound, which can be present in
the form of a liquid material under room temperature (15.degree. C.
to 25.degree. C.) and which contains an organic cation and an
organic anion. The ionic liquid noted above includes, for example,
an ionic liquid that can be present singly in the form of a liquid
material, an ionic liquid that can be converted into a liquid
material when mixed with an electrolyte, and an ionic liquid that
can be converted into a liquid material when dissolved in an
organic solvent. Incidentally, the ionic liquid, which is used in
the nonaqueous electrolyte battery, can have a melting point not
higher than 25.degree. C. Also, the organic cation forming the
ionic liquid in question can have a quaternary ammonium
skeleton.
[0092] The polymer solid electrolyte is prepared by dissolving an
electrolyte in a polymer material, followed by solidifying the
resultant solution.
[0093] Further, the inorganic solid electrolyte denotes a solid
material exhibiting a lithium ion conductivity.
[0094] 3) Positive Electrode
[0095] The positive electrode comprises a positive electrode
current collector and a positive electrode layer formed on one
surface or both surfaces of the positive electrode current
collector and containing a positive electrode active material, a
positive electrode conductive agent and a binder.
[0096] The positive electrode active material includes, for
example, an oxide and a polymer.
[0097] The oxides include, for example, manganese dioxide
(MnO.sub.2) absorbing Li, iron oxide, copper oxide, nickel oxide, a
lithium-manganese composite oxide such as Li.sub.XMn.sub.2O.sub.4
or Li.sub.xMnO.sub.2, a lithium-nickel composite oxide such as
Li.sub.xNiO.sub.2, a lithium-cobalt composite oxide such as
Li.sub.xCoO.sub.2, a lithium-nickel-cobalt composite oxide such as
LiNi.sub.1-yCo.sub.yO.sub.2, a lithium-manganese-cobalt composite
oxide such as LiMn.sub.yCo.sub.1-yO.sub.2, the Spinel type
lithium-manganese-nickel composite oxide such as
Li.sub.xMn.sub.2-yNi.sub.yO.sub.4, a lithium phosphate oxide having
an olivine structure such as Li.sub.xFePO.sub.4,
Li.sub.xFe.sub.1-yMn.sub.yPO.sub.4, or Li.sub.xCoPO.sub.4, an iron
sulfate such as Fe.sub.2(SO.sub.4).sub.3, and vanadium oxide such
as V.sub.2O.sub.5.
[0098] The polymer includes, for example, a conductive polymer
material such as polyaniline or polypyrrole, and a disulfide series
polymer material. It is also possible to use sulfur (S), a
fluorocarbon, etc. as the positive electrode active material.
[0099] The positive electrode active material that is desirable
includes, for example, a lithium-manganese composite oxide (e.g.,
Li.sub.xMn.sub.2O.sub.4), a lithium-nickel composite oxide (e.g.,
Li.sub.xNiO.sub.2), a lithium-cobalt composite oxide (e.g.,
Li.sub.xCoO.sub.2), a lithium-nickel-cobalt composite oxide (e.g.,
Li.sub.xNi.sub.1-yCo.sub.yO.sub.2), the Spinel type
lithium-manganese-nickel composite oxide (e.g.,
Li.sub.xMn.sub.2-yNi.sub.yO.sub.4), a lithium-manganese-cobalt
composite oxide (e.g., Li.sub.xMn.sub.yCo.sub.1-yO.sub.2), a
lithium-nickel-cobalt-manganese composite oxide (e.g.,
Li.sub.xNi.sub.1-y-zCo.sub.yMn.sub.zO.sub.2) and lithium iron
phosphate (e.g., Li.sub.xFePO.sub.4). The positive electrode active
materials exemplified above make it possible to obtain a high
positive electrode voltage. Incidentally, it is desirable for each
of the molar ratios x, y and z in the chemical formulas given above
to fall within a range of 0 to 1.
[0100] It is also desirable to use a compound represented by
Li.sub.aNi.sub.bCo.sub.cMn.sub.dO.sub.2, where the molar ratios a,
b, c and d are 0.ltoreq.a.ltoreq.1.1, 0.1.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.9, and 0.1.ltoreq.d.ltoreq.0.5). Incidentally,
Li and Co are optional components of the compound given above. It
is more desirable for the molar ratios b, c and d in the structural
formula given above to fall with the ranges of:
0.3.ltoreq.b.ltoreq.0.4, 0.3.ltoreq.c.ltoreq.0.4, and
0.3.ltoreq.d.ltoreq.0.4.
[0101] Since the positive electrode active materials exemplified
above exhibit a high ionic conductivity, the diffusion of the
lithium ions within the positive electrode active material is
unlikely to provide the rate-determining step when the positive
electrode active material is used in combination with the negative
electrode active material specified in this embodiment of the
present invention so as to make it possible to further improve the
large current characteristics.
[0102] It is desirable for the positive electrode active material
to have the primary particle diameter not smaller than 100 nm and
not larger than 1 .mu.m. If the primary particle diameter is not
smaller than 100 nm, the positive electrode active material can be
handled easily in the industrial manufacture of the nonaqueous
electrolyte battery. On the other hand, if the primary particle
diameter is not larger than 1 .mu.m, the diffusion of the lithium
ions within the particle can be proceeded smoothly.
[0103] It is desirable for the positive electrode active material
to have a specific surface area not smaller than 0.1 m.sup.2/g and
not larger than 10 m.sup.2/g. If the specific surface area of the
positive electrode active material is not smaller than 0.1
m.sup.2/g, it is possible to secure sufficiently the
absorption-release sites of the lithium ions. On the other hand, if
the specific surface area of the positive electrode active material
is not larger than 10 m.sup.2/g, the positive electrode active
material can be handled easily in the industrial manufacture of the
nonaqueous electrolyte battery, and it is possible to secure a
satisfactory charge-discharge cycle life of the nonaqueous
electrolyte battery.
[0104] The positive electrode conductive agent permits enhancing
the current collecting performance and also permits suppressing the
contact resistance between the current collector and the active
material. The positive electrode conductive agent includes, for
example, a carbonaceous material such as acetylene black, carbon
black and graphite.
[0105] The binder for bonding the positive electrode active
material to the positive electrode conductive agent includes, for
example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride
(PVdF) and a fluorinated rubber.
[0106] Concerning the mixing ratio of the positive electrode active
material, the positive electrode conductive agent, and the binder,
it is desirable for the mixing amount of the positive electrode
active material to be not smaller than 80% by weight and not larger
than 95% by weight, for the mixing amount of the positive electrode
conductive agent to be not smaller than 3% by weight and not larger
than 18% by weight, and for the mixing amount of the binder to be
not smaller than 2% by weight and not larger than 17% by weight. If
the positive electrode conductive agent is mixed in an amount not
smaller than 3% by weight, it is possible to obtain the effects
described above. On the other hand, if the mixing amount of the
positive electrode conductive agent is not larger than 18% by
weight, it is possible to suppress the decomposition of the
nonaqueous electrolyte on the surface of the positive electrode
conductive agent during storage of the nonaqueous electrolyte
battery under high temperatures. Further, where the binder is used
in an amount not smaller than 2% by weight, it is possible to
obtain a sufficient electrode strength. On the other hand, where
the mixing amount of the binder is not larger than 17% by weight,
it is possible to decrease the mixing amount of the insulator in
the electrode so as to decrease the internal resistance of the
nonaqueous electrolyte battery.
[0107] It is desirable for the positive electrode current collector
to be formed of an aluminum foil or an aluminum alloy foil
containing at least one element selected from the group consisting
of Mg, Ti, Zn, Mn, Fe, Cu, and Si.
[0108] The positive electrode can be prepared by coating a positive
electrode current collector with a slurry prepared by, for example,
suspending a positive electrode active material, a positive
electrode conductive agent and a binder in a suitable solvent,
followed by drying the coated slurry so as to form a positive
electrode layer, and subsequently pressing the positive electrode
current collector having the positive electrode layer formed
thereon. Alternatively, it is also possible to form a mixture of a
positive electrode active material, a positive electrode conductive
agent and a binder into pellets, which are used for forming the
positive electrode layer.
[0109] 4) Separator
[0110] The separator includes, for example, a porous film including
polyethylene, polypropylene, cellulose and/or polyvinylidene
fluoride (PVdF), and an unwoven fabric made of a synthetic resin.
Particularly, it is desirable in view of the improvement in safety
to use a porous film made of polyethylene or polypropylene because
the particular porous film can be melted under a prescribed
temperature so as to break the current.
[0111] 5) Case
[0112] The case is formed of a laminate film having a thickness of,
for example, 0.2 mm or less, or a metal sheet having a thickness
of, for example, 0.5 mm or less. It is more desirable for the metal
sheet to have a thickness of 0.2 mm or less. Also, the case has a
flattened shape, an angular shape, a cylindrical shape, a coin
shape, a button shape or a sheet shape, or is of a laminate type.
The case includes a case of a large battery mounted to, for
example, an electric automobile having two to four wheels in
addition to a small battery mounted to a portable electronic
device.
[0113] The laminate film includes, for example, a multi-layered
film including a metal layer and a resin layer covering the metal
layer. For decreasing the weight of the battery, it is desirable
for the metal layer to be formed of an aluminum foil or an aluminum
alloy foil. On the other hand, the resin layer for reinforcing the
metal layer is formed of a polymer material such as polypropylene
(PP), polyethylene (PE), Nylon, and polyethylene terephthalate
(PET). The laminate film case can be obtained by bonding the
periphery of superposed laminate films by the thermal fusion.
[0114] It is desirable for the metal case to be formed of aluminum
or an aluminum alloy. Also, it is desirable for the aluminum alloy
to be an alloy containing an element such as magnesium, zinc or
silicon. On the other hand, it is desirable for the amount of the
transition metals, which are contained in the aluminum alloy, such
as iron, copper, nickel and chromium, to be not larger than 100
ppm.
[0115] 6) Negative Electrode Terminal
[0116] The negative electrode terminal is formed of a material
exhibiting an electrical stability and conductivity within the
range of 1.0 V to 3.0 V of the potential relative to the lithium
ion metal. To be more specific, the material used for forming the
negative electrode terminal includes, for example, aluminum and an
aluminum alloy containing Mg, Ti, Zn, Mn, Fe, Cu or Si. In order to
lower the contact resistance relative to the negative electrode
current collector, it is desirable for the negative electrode
terminal to be formed of a material equal to the material used for
forming the negative electrode current collector.
[0117] 7) Positive Electrode Terminal
[0118] The positive electrode terminal is formed of a material
exhibiting an electrical stability and conductivity within the
range of 3.0 V to 4.25 V of the potential relative to the lithium
ion metal. To be more specific, the material used for forming the
positive electrode terminal includes, for example, aluminum and an
aluminum alloy containing Mg, Ti, Zn, Mn, Fe, Cu or Si. In order to
lower the contact resistance relative to the positive electrode
current collector, it is desirable for the positive electrode
terminal to be formed of a material equal to the material used for
forming the positive electrode current collector.
[0119] The construction of the nonaqueous electrolyte battery
according to the first embodiment of the present invention is not
limited to that shown in FIGS. 1A and 1B. For example, it is
possible for the nonaqueous electrolyte battery according to the
first embodiment of the present invention to be constructed as
shown in FIGS. 5 and 6. To be more specific, FIG. 5 is an oblique
view, partly broken away, schematically showing the construction of
another flattened type nonaqueous electrolyte secondary battery
according to the first embodiment of the present invention, and
FIG. 6 is a cross sectional view showing in a magnified fashion the
construction in the circular portion B shown in FIG. 5.
[0120] As shown in FIG. 5, a laminate type electrode group 9 is
housed in a case 8 formed of a laminate film. As shown in FIG. 6,
the laminate type electrode group 9 comprises a positive electrode
3 and a negative electrode 4, which are laminated one upon the
other with a separator 5 interposed between the positive electrode
3 and the negative electrode 4. Each of a plurality of positive
electrodes 3 includes a positive electrode current collector 3a and
positive electrode layers 3b formed on both surfaces of the
positive electrode current collector 3a and containing a positive
electrode active material. Likewise, each of a plurality of
negative electrodes 4 includes a negative electrode current
collector 4a and negative electrode layers 4b formed on both
surfaces of the negative electrode current collector 4a and
containing a negative electrode active material. One side of the
negative electrode current collector 4a included in each negative
electrode 4 protrudes from the positive electrode 3. The negative
electrode current collector 4a protruding from the positive
electrode 3 is electrically connected to a band-like negative
electrode terminal 2. The distal end portion of the band-like
negative electrode terminal 2 is withdrawn from the case 8 to the
outside. Also, one side of the positive electrode current collector
3a included in the positive electrode 3 is positioned on the side
opposite to the protruding side of the negative electrode current
collector 4a and is protruded from the negative electrode 4, though
the particular construction is not shown in the drawing. The
positive electrode current collector 3a protruding from the
negative electrode 4 is electrically connected to a band-like
positive electrode terminal 1. The distal end portion of the
band-like positive electrode terminal 1 is positioned on the side
opposite to the side of the negative electrode terminal 2 and is
withdrawn from the side of the case 8 to the outside.
Second Embodiment
[0121] A battery pack according to a second embodiment of the
present invention comprises the nonaqueous electrolyte battery
according to the first embodiment of the present invention as a
unit cell, and a plurality of unit cells are included in the
battery pack according to the second embodiment of the present
invention. The unit cells are arranged in series or in parallel so
as to form a battery module.
[0122] The unit cell according to the first embodiment of the
present invention is adapted for the preparation of the battery
module. Also, the battery pack according to the second embodiment
of the present invention is excellent in its charge-discharge cycle
characteristics as described in the following.
[0123] In the lithium-titanium composite oxide, the phase having an
irregular crystal structure is increased with decrease in the
crystallite diameter. As a result, the variation of the negative
electrode potential at the charge-discharge terminal and, thus, the
variation of the battery voltage at the charge-discharge terminal,
is rendered small so as to decrease the nonuniformity in the
battery voltage in the battery module. It follows that the battery
pack according to the second embodiment of the present invention
can control the battery voltage easily to make it possible to
improve the charge-discharge cycle characteristics. The
nonuniformity in the battery voltage in the battery module is
brought about due to the difference in capacity among the
individual batteries and tends to be rendered large when the
battery module of a series connection is fully charged.
[0124] An example of the battery pack according to the second
embodiment of the present invention will now be described with
reference to FIGS. 2 and 3.
[0125] FIG. 2 is an oblique view showing in a dismantled fashion
the construction of the battery pack according to the second
embodiment of the present invention.
[0126] As shown in FIG. 2, a plurality of plate-like unit cells 11,
e.g., 8 unit cells 11, are laminated one upon the other so as to
form a parallelepiped laminate body 20 forming a battery module. As
described previously, each of the unit cells 11 is constructed such
that the positive electrode terminal 13 and the negative electrode
terminal 14 connected to the positive electrode and the negative
electrode, respectively, are withdrawn to the outside of the case.
A printed wiring board 12 is arranged on the side toward which the
positive electrode terminal 13 and the negative electrode terminal
14 are allowed to protrude.
[0127] The positive electrode terminal 13 is electrically connected
to a connector 16 on the side of the positive electrode via a
wiring 15 on the side of the positive electrode. Likewise, the
negative electrode terminal 14 is electrically connected to a
connector 18 on the side of the negative electrode via a wiring 17
on the side of the negative electrode. The connectors 16, 18 on the
side of the positive electrode and the negative electrode,
respectively, are connected to the counterpart connectors mounted
to the printed wiring board 12.
[0128] The laminate body 20 of the unit cells 11 is fixed by
adhesive tapes 19. Protective sheets 21 each formed of rubber or a
resin are arranged to cover the three side surfaces of the laminate
body 20 except the side toward which protrude the positive
electrode terminal 13 and the negative electrode terminal 14. Also,
a protective block 22 formed of rubber or a resin is arranged in
the clearance between the side of the laminate body 20 and the
printed wiring board 12.
[0129] The laminate body 20 is housed in a housing vessel 23
together with the protective sheets 21, the protective block 22 and
the printed wiring board 12. Also, a lid 24 is mounted to close the
upper open portion of the housing vessel 23.
[0130] Each constituent of the battery pack according to the second
embodiment of the present invention will now be described in
detail.
[0131] As shown in FIG. 3, a thermistor 25, a protective circuit
26, and a terminal 27 for the current supply to the external
apparatus are mounted to the printed wiring board 12.
[0132] The thermistor 25 serves to detect the temperature of the
unit cell 11. The signal denoting the detected temperature is
transmitted to the protective circuit 26.
[0133] As shown in FIG. 3, the protective circuit 26 is capable of
breaking under prescribed conditions wirings 28a and 28b stretched
between the protective circuit 26 and the terminal 27 for the
current supply to the external apparatus. The prescribed conditions
noted above include, for example, the case where the temperature
detected by the thermistor 25 is higher than a prescribed
temperature and the case of detecting, for example, the
over-charging, the over-discharging and the over current of the
unit cell 11. In the case of detecting the individual unit cells
11, it is possible to detect the battery voltage, the positive
electrode potential or the negative electrode potential.
Incidentally, in the case of detecting the electrode potential, a
lithium electrode used as a reference electrode is inserted into
the unit cell 11. In the case of FIG. 3, the protective circuit 26
is provided with a battery voltage monitoring circuit section. Each
of the unit cells 11 is connected to the battery voltage monitoring
circuit section via a wiring 29. According to the particular
construction, the battery voltage of each of the unit cells 11 can
be detected by the protective circuit 26. Incidentally, FIG. 3
covers the case of applying the detection to the individual unit
cells 11. However, it is also possible to apply the detection to
the battery module 20. Further, in the case shown in FIG. 3, all
the unit cells 11 included in the battery module 20 are detected in
terms of voltage. Although it is particularly preferable that the
voltages of all of the unit cells 11 of the battery module 20
should be detected, it may be sufficient to check the voltages of
only some of the unit cells 11.
[0134] The battery pack according to the second embodiment of the
present invention is excellent in the control of the positive
electrode potential or the negative electrode potential by the
detection of the battery voltage and, thus, is particularly adapted
for the case where the protective circuit detects the battery
voltage.
[0135] It is possible to use a thermally shrinkable tape in place
of the adhesive tape 19. In this case, the protective sheets 21 are
arranged on both sides of the laminate body 20 and, after the
thermally shrinkable tube is wound about the protective sheets 21,
the thermally shrinkable tube is thermally shrunk so as to bond the
laminate body 20.
[0136] Incidentally, FIG. 2 shows that the unit cells 11 are
connected in series. However, it is also possible to connect the
unit cells 11 in parallel so as to increase the capacity of the
battery pack. Of course, it is also possible to connect the
assembled battery packs in series and in parallel.
[0137] The unit cell 11 used in the battery pack shown in FIGS. 2
and 3 is formed of the flattened type nonaqueous electrolyte
battery shown in FIG. 1. However, the unit cells constituting the
battery pack are not limited to the nonaqueous electrolyte battery
shown in FIG. 1. For example, it is also possible to use the
flattened type nonaqueous electrolyte battery shown in FIGS. 5 and
6 for forming the battery pack according to the second embodiment
of the present invention.
[0138] The construction of the battery pack can be changed
appropriately depending on the use of the battery pack.
[0139] It is desirable for the battery pack according to the second
embodiment of the present invention to be used in the field
requiring the large current characteristics and the
charge-discharge cycle characteristics. To be more specific, it is
desirable for the battery pack according to the second embodiment
of the present invention to be used in the power source for a
digital camera and for the vehicles such as the hybrid electric
automobiles having two to four wheels, electric automobiles having
two to four wheels, and the assist bicycles.
[0140] Incidentally, where the nonaqueous electrolyte contains
.gamma.-butyrolactone (GBL) or a mixed solvent containing at least
two organic solvents selected from the group consisting of
propylene carbonate (PC), ethylene carbonate (EC) and
.gamma.-butyrolactone (GBL), it is desirable for the battery pack
to be used in the field requiring the high temperature
characteristics, i.e., for the battery pack mounted to a
vehicle.
[0141] The present invention will now be described with reference
to Examples of the present invention. Needless to say, the
technical scope of the present invention is not limited to the
following Examples as far as the subject matter of the present
invention is not exceeded.
Rapid Charging Test
Example 1
Preparation of Positive Electrode
[0142] In the first step, a slurry was prepared by adding 90% by
weight of a lithium-cobalt composite oxide (LiCoO.sub.2) used as a
positive electrode active material, 5% by weight of acetylene black
used as a conductive agent, and 5% by weight of polyvinylidene
fluoride (PVdF) used as a binder to N-methylpyrrolidone (NMP),
followed by coating the both surfaces of an aluminum foil having
thickness of 15 .mu.m with the resultant slurry and subsequently
drying and, then, pressing the current collector coated with the
slurry so as to obtain a positive electrode having an electrode
density of 3.3 g/cm.sup.3.
[0143] <Preparation of Lithium-Titanium Composite Oxide>
[0144] In the first step, an anatase type titanium oxide was put in
a solution prepared by dissolving lithium hydroxide, 0.0112 g of
sodium hydroxide and 0.1336 g of potassium hydroxide in a pure
water, followed by stirring and drying the reaction system.
Further, the dried reaction system was baked under the air
atmosphere at 780.degree. C. for 10 hours so as to obtain a
lithium-titanium composite oxide having a spinel structure and a
chemical formula of Li.sub.4Ti.sub.5O.sub.12 and containing 0.03%
by weight of Na and 0.42% by weight of K. The crystallite diameter
of the lithium-titanium composite oxide thus obtained was found to
be 582 .ANG..
[0145] <Measurement of Crystallite Diameter and Strength Ratio
of Main Peaks>
[0146] In the first step, the X-ray diffraction pattern using
Cu-K.alpha. of the lithium-titanium composite oxide was obtained by
using XRD (type number M18XHF.sup.22-SRA, manufactured by Mac
Science Inc.). FIG. 4 exemplifies the X-ray diffraction pattern of
the lithium-titanium composite oxide for this Example.
Incidentally, the X-ray diffraction pattern having the background
and the K.alpha..sub.2 line removed therefrom was used in the
subsequent analysis.
[0147] The crystallite diameter was obtained by formula (1) given
below (Scherrer formula) by calculating the half value width of the
X-ray diffraction peak of the (111) plane of the diffraction angle
(2.theta.) of 18.degree.. Incidentally, for calculating the half
value width of the diffraction peak, it is necessary to correct the
line width that varies by the change of the optical system of the
diffraction apparatus. A standard silicon powder was used for this
correction.
D.sub.hkl=(K.lamda.)/(.beta.cos .theta.) (1)
[0148] where D.sub.hkl denotes the crystallite diameter (.ANG.),
.lamda. denotes the wavelength (.ANG.) of the X-ray used for the
measurement, .beta. denotes the broadening of the diffraction
angle, .theta. denotes the Bragg angle of the diffraction angle;
and K denotes a constant (0.9).
[0149] The intensity ratio of main peaks of the anatase type
TiO.sub.2, the rutile type TiO.sub.2 and Li.sub.2TiO.sub.3,
respectively, was calculated from the X-ray diffraction pattern on
the basis that the peak intensity of main peak of
Li.sub.4Ti.sub.5O.sub.12 was set at 100. Incidentally, the main
peak of Li.sub.4Ti.sub.5O.sub.12 was a peak at 4.83 .ANG.
(2.theta.:18.degree.). The main peak of the anatase type TiO.sub.2
was a peak at 3.51 .ANG. (2.theta.:25.degree.). The main peak of
the rutile type TiO.sub.2 was a peak at 3.25 .ANG.
(2.theta.:27.degree.). The main peak of Li.sub.2TiO.sub.3 was a
peak at 2.07 .ANG. (2.theta.:43.degree.).
[0150] <Manufacture of Negative Electrode>
[0151] A slurry was prepared by adding 90% by weight of the
obtained lithium-titanium composite oxide powder, which was used as
the negative electrode active material, 5% by weight of coke baked
at 1,200.degree. C. (the layer spacing d.sub.002 of 0.3465 nm and
the average particle diameter of 3 .mu.m), which was used as the
negative electrode conductive agent, and 5% by weight of
polyvinylidene fluoride (PVdF) used as a binder to
N-methylpyrrolidone (NMP), followed by coating the both surfaces of
an aluminum foil having thickness of 15 .mu.m, which was used as a
negative electrode current collector, with the resultant slurry,
and subsequently drying and, then, pressing the aluminum foil
having the dried slurry layers formed thereon so as to obtain a
negative electrode having an electrode density of 2.0
g/cm.sup.3.
[0152] Incidentally, the lithium-titanium composite oxide powder
was found to have an average particle diameter of 0.82 .mu.m. The
average particle diameter of the lithium-titanium composite oxide
powder was measured as follows.
[0153] Specifically, about 0.1 g of a sample, a surfactant, and 1
to 2 mL of a distilled water were put in a beaker, and the
distilled water was sufficiently stirred, followed by pouring the
stirred system in a stirring water vessel. Under this condition,
the light intensity distribution was measured every 2 seconds and
measured 64 times in total by using SALD-300, which is a Laser
Diffraction Particle Size Analyzer manufactured by Shimadzu
Corporation, so as to analyze the particle size distribution
data.
[0154] <Manufacture of Electrode Group>
[0155] A laminate structure was prepared by disposing a positive
electrode, a separator formed of a porous polyethylene film having
a thickness of 25 .mu.m, a negative electrode and another separator
one upon the other in the order mentioned, followed by spirally
winding the laminate structure thus prepared. The wound laminate
structure was pressed under heat of 90.degree. C. so as to obtain a
flattened electrode group having a width of 30 mm and a thickness
of 3.0 mm. The electrode group thus prepared was housed in a pack
formed of a laminate film having a thickness of 0.1 mm and
including an aluminum foil having a thickness of 40 .mu.m and a
polypropylene layer formed on each surface of the aluminum foil.
The electrode group housed in the pack was subjected to a vacuum
drying at 80.degree. C. for 24 hours.
[0156] <Preparation of Liquid Nonaqueous Electrolyte>
[0157] A liquid nonaqueous electrolyte was prepared by dissolving
LiBF.sub.4 used as an electrolyte in a mixed solvent prepared by
mixing ethylene carbonate (EC) with .gamma.-butyrolactone (GBL) in
a mixing ratio by volume of 1:2. The electrolyte was dissolved in
the mixed solvent in an amount of 1.5 mol/L.
[0158] After the liquid nonaqueous electrolyte was poured into a
laminate film pack having the electrode group housed therein, the
pack was perfectly closed by the heat seal so as to manufacture a
nonaqueous electrolyte secondary battery constructed as shown in
FIG. 1 and having a width of 35 mm, a thickness of 3.2 mm and a
height of 65 mm.
Examples 2 to 14 and Comparative Example 1
[0159] A nonaqueous electrolyte secondary battery was manufactured
as in Example 1, except that the addition amounts of Na and K were
set as shown in Table 1, and that used was a lithium-titanium
composite oxide having the crystallite diameter shown in Table
1.
Examples 15 to 19
[0160] A nonaqueous electrolyte secondary battery was manufactured
as in Example 1, except that the baking temperature was set as
shown in Table 1, and that used was a lithium-titanium composite
oxide having the crystallite diameter shown in Table 1.
Comparative Examples 2 to 8
[0161] A nonaqueous electrolyte secondary battery was manufactured
as in Example 1, except that the baking temperature was set as
shown in Table 1, and that used was a lithium-titanium composite
oxide having the crystallite diameter shown in Table 1.
Examples 20 to 25
[0162] A nonaqueous electrolyte secondary battery was manufactured
as in Example 1 and Examples 15 to 19, except that used was
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 as the positive electrode
active material.
[0163] A rapid charging performance was evaluated in respect of the
nonaqueous electrolyte battery for each of Examples 1 to 25 and
each of Comparative Examples 1 to 8. To be more specific, the
battery discharged to reach the rated discharge voltage of 1.5 V
under the current of IC was charged for 3 hours under the constant
voltage of 2.8 V. The obtained charging capacity was regarded as
the standard charging capacity. Tables 1 and 2 show the 80%
charging time (seconds) required for charging 80% of the standard
charging capacity.
[0164] Also, the electric capacity of the negative electrode was
measured by a half cell test in which a lithium metal was used as
the counter electrode. To be more specific, lithium ions were
absorbed (charging) in the negative electrode under the current
value of 0.1 mA/cm.sup.2 to reach 1V (Li/Li+) with a lithium metal
used for forming the counter electrode, followed by releasing the
lithium ions (discharge) under the current value of 0.1 mA/cm.sup.2
to reach 2V (Li/Li+) with the counter electrode. The discharge
capacity in this stage was converted into the capacity per unit
weight of the negative electrode active material. The converted
value is also shown in Tables 1 and 2 as the negative electrode
capacity.
[0165] The following description is based on the values obtained by
applying an appropriate effective numeral to the numeral values
shown in each of Tables 1 and 2.
[0166] The 80% charging time for Examples 1 to 19 is shorter than
that for Comparative Examples 1 to 8. The experimental data clearly
support that the nonaqueous electrolyte battery according to the
embodiment of the present invention is excellent in the rapid
charging performance, i.e., in the large current
characteristics.
[0167] The 80% charging time for Examples 12 to 19 is shorter than
that for Examples 1 to 11. The experimental data clearly support
that, if the crystallite diameter of the lithium-titanium composite
oxide is not larger than 5.3.times.10.sup.2 .ANG., the nonaqueous
electrolyte battery is made more excellent in the rapid charging
performance, i.e., in the large current characteristics.
[0168] The 80% charging time for Examples 15 to 19 is shorter than
that for Examples 1 to 14. The experimental data clearly support
that, if the crystallite diameter of the lithium-titanium composite
oxide is not larger than 4.4.times.10.sup.2 .ANG., the nonaqueous
electrolyte battery is made furthermore excellent in the rapid
charging performance, i.e., in the large current
characteristics.
[0169] The 80% charging time for Example 17 is shorter than that
for Examples 18 to 19. The experimental data clearly support that,
if the main peak intensity of each of the rutile type TiO.sub.2,
the anatase type TiO.sub.2 and Li.sub.2TiO.sub.3 is not larger than
3, the nonaqueous electrolyte battery is made more excellent in the
rapid charging performance, i.e., in the large current
characteristics.
[0170] Further, the crystallite diameter for Examples 1 to 19 is
smaller than that for Comparative Example 1. The experimental data
clearly support that, if the amount of (Na+K) is not smaller than
0.10% by weight and not larger than 3.04% by weight based on the
amount of the lithium-titanium composite oxide, the
lithium-titanium composite oxide having the crystallite diameter
not larger than 6.9.times.10.sup.2 .ANG. and small in the amount of
the impurity phase can be baked easily.
[0171] The 80% charging time for Example 20 is shorter than that
for Example 1. The experimental data clearly support that, in the
case of using a compound represented by
Li.sub.aNi.sub.bCo.sub.cMn.sub.dO.sub.2 (where
0.ltoreq.a.ltoreq.1.1, 0.1.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.9, and 0.1.ltoreq.d.ltoreq.0.5) as the positive
electrode active material, the nonaqueous electrolyte battery is
rendered more excellent in the rapid charging performance, i.e., in
the large current characteristics.
[0172] This is also the case with each of Examples 21 to 25, as
apparent from the comparison with Examples 15 to 19.
High Temperature Storage Test
Examples 26 to 29
[0173] A nonaqueous electrolyte secondary battery was manufactured
as in Example 1, except that the solvent of the liquid electrolyte
had a composition shown in Table 3.
[0174] The nonaqueous electrolyte secondary battery for each of
Example 1 and Examples 26 to 29 was stored under the fully charged
state in a constant temperature vessel maintained at 45.degree. C.,
i.e., a constant temperature vessel type No. EC-45 MTP manufactured
by Hitachi Ltd. so as to measure the remaining capacity after the
storage for one month. Table 3 shows the ratio of the remaining
capacity of the nonaqueous electrolyte secondary battery to the
discharge capacity before the storage.
TABLE-US-00001 TABLE 3 Remaining Solvent capacity/ First Second
ratio discharge solvent/A solvent/B (A:B) capacity (%) Example 1 EC
GBL 1:2 97 Example 26 EC PC 1:2 80 Example 27 EC DMC 1:2 74 Example
28 EC MEC 1:2 72 Example 29 EC DEC 1:2 70
[0175] The remaining capacity for each of Examples 1 and 26 is
larger than that for any of Examples 27 to 29. The experimental
data clearly support that, in the case of using a mixed solvent
containing at least two organic solvents selected from the group
consisting of propylene carbonate (PC), ethylene carbonate (EC) and
.gamma.-butyrolactone (GBL), it is possible to improve the high
temperature storage characteristics of the nonaqueous electrolyte
secondary battery.
[0176] The remaining capacity for Example 1 is larger than that for
any of Examples 26 to 29. The experimental data clearly support
that, in the case of using a solvent containing
.gamma.-butyrolactone (GBL), it is possible to improve further the
high temperature storage characteristics of the nonaqueous
electrolyte secondary battery.
Examples 30 to 33
[0177] A nonaqueous electrolyte secondary battery was manufactured
as in Example 1, except that the solvent of the liquid electrolyte
had a composition shown in Table 4. Incidentally, the solvent ratio
shown in Table 4 denotes the volume ratio of the solvent. The
abbreviation EC shown in Table 4 denotes ethylene carbonate, GBL
denotes .gamma.-butyrolactone, PC denotes propylene carbonate, and
VC denotes vinylene carbonate.
[0178] The nonaqueous electrolyte secondary battery for each of
Example 1, Example 26 and Examples 30 to 33 was stored under the
fully charged state in a constant temperature vessel maintained at
60.degree. C., i.e., a constant temperature vessel type No. EC-45
MTP manufactured by Hitachi Ltd., so as to measure the remaining
capacity after the storage for one month. Table 4 shows the ratio
of the remaining capacity of the nonaqueous electrolyte secondary
battery to the discharge capacity before the storage.
[0179] As shown in Table 3 given previously, the high temperature
storage characteristics of the nonaqueous electrolyte secondary
battery under the temperature of about 45.degree. C. can be
improved in Examples 1 and 26 using two kinds of solvents selected
from the group consisting of PC, EC and GBL. However, when it comes
to the storage characteristics of the nonaqueous electrolyte
secondary battery under a further higher temperature of 60.degree.
C., the secondary battery for Examples 30 to 33 using at least
three kinds of solvents selected from the group consisting of PC,
EC, GBL and VC is superior to the secondary battery for Examples 1
and 26, as apparent from Table 4. The experimental data clearly
support that, in order to obtain a sufficient high temperature
storage characteristics, it is desirable to use at least three
kinds of solvents selected from the group consisting of PC, EC, GBL
and VC.
[0180] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *