U.S. patent application number 14/063436 was filed with the patent office on 2014-05-01 for active material.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. The applicant listed for this patent is Kabushiki Kaisha Toshiba. Invention is credited to Yasuhiro Harada, Hiroki Inagaki, Norio Takami, Wen Zhang.
Application Number | 20140120380 14/063436 |
Document ID | / |
Family ID | 50547522 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140120380 |
Kind Code |
A1 |
Inagaki; Hiroki ; et
al. |
May 1, 2014 |
ACTIVE MATERIAL
Abstract
According to one embodiment, an active material is provided. The
active material includes orthorhombic system oxide represented by
the following formula: Li.sub.xM1M2.sub.2O.sub.6. In this formula,
0.ltoreq.x.ltoreq.5, M1 is at least one selected from the group
consisting of Fe and Mn, and M2 is at least one selected from the
group consisting of Nb, Ta and V.
Inventors: |
Inagaki; Hiroki;
(Yokohama-shi, JP) ; Zhang; Wen; (Sagamihara-shi,
JP) ; Harada; Yasuhiro; (Yokohama-shi, JP) ;
Takami; Norio; (Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba |
Minato-ku |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Toshiba
Minato-ku
JP
|
Family ID: |
50547522 |
Appl. No.: |
14/063436 |
Filed: |
October 25, 2013 |
Current U.S.
Class: |
429/7 ;
252/182.1; 429/149; 429/160; 429/221; 429/224; 429/231.95 |
Current CPC
Class: |
H01M 10/48 20130101;
C01P 2006/40 20130101; C01P 2004/61 20130101; H01M 10/425 20130101;
C01G 23/005 20130101; C01G 33/00 20130101; H01M 10/486 20130101;
H01M 4/505 20130101; C01G 45/00 20130101; H01M 4/485 20130101; H01M
4/131 20130101; C01G 33/006 20130101; H01M 4/525 20130101; C01P
2002/32 20130101; C01P 2006/12 20130101; Y02E 60/10 20130101; C01G
49/0018 20130101; C01G 49/0072 20130101 |
Class at
Publication: |
429/7 ;
429/231.95; 429/221; 429/224; 429/149; 429/160; 252/182.1 |
International
Class: |
H01M 4/505 20060101
H01M004/505; H01M 4/525 20060101 H01M004/525 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2012 |
JP |
2012-239487 |
Claims
1. An active material comprising an orthorhombic system oxide
represented by the following formula: Li.sub.xM1M2.sub.2O.sub.6
wherein 0.ltoreq.x.ltoreq.5, M1 is at least one selected from the
group consisting of Fe and Mn, and M2 is at least one selected from
the group consisting of Nb, Ta and V.
2. The active material according to claim 1, wherein the
orthorhombic system oxide is represented by the formula
Li.sub.xFeNb.sub.2O.sub.6, the formula Li.sub.xFeV.sub.2O.sub.6,
the formula Li.sub.xFe.sub.0.5Mn.sub.0.5Nb.sub.2O.sub.6, the
formula Li.sub.xMnNb.sub.2O.sub.6, or the formula
Li.sub.xMnTa.sub.2O.sub.6.
3. The active material according to claim 1, wherein the
orthorhombic system oxide is represented by the formula
Li.sub.xFeNb.sub.2O.sub.6 or the formula
Li.sub.xFeV.sub.2O.sub.6.
4. The active material according to claim 1, wherein the
orthorhombic system oxide has a BET specific surface area of 1
m.sup.2/g or more but 50 m.sup.2/g or less.
5. A nonaqueous electrolyte battery, comprising: a negative
electrode comprising the active material according to claim 1; a
positive electrode; and a nonaqueous electrolyte.
6. The nonaqueous electrolyte battery to claim 5, wherein the
negative electrode further comprising niobium titanium composite
oxide comprising monoclinic-system oxide.
7. The nonaqueous electrolyte battery to claim 6, wherein the
niobium titanium composite oxide is selected from the group
consisting of Li.sub.xNb.sub.2TiO.sub.7,
Li.sub.xNb.sub.10Ti.sub.2O.sub.29, Li.sub.xNb.sub.14TiO.sub.37, and
Li.sub.xNb.sub.24TiO.sub.62.
8. A battery pack comprising the nonaqueous electrolyte battery
according to claim 5.
9. The battery pack according to claim 8, comprising a plurality of
the nonaqueous electrolyte battery.
10. The battery pack according to claim 9, wherein the plurality of
the nonaqueous electrolyte battery are electrically connected to
each other in series, in parallel or in the combination
thereof.
11. The battery pack according to claim 8, further comprising: a
protective circuit configured to detect the voltage of the
nonaqueous electrolyte battery.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2012-239487, filed Oct. 30, 2012, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to an active
material, a nonaqueous electrolyte battery and a battery pack.
BACKGROUND
[0003] Recently, a nonaqueous electrolyte battery such as a lithium
ion battery has been actively researched and developed as a high
energy density battery. The nonaqueous electrolyte battery is
expected to be used as a power source for hybrid electric vehicles,
electric vehicles or uninterruptible power supplies for base
stations for mobile phone. For this, the nonaqueous electrolyte
battery is desired to have other performances such as rapid
charge/discharge performance and long-term reliability, in addition
to high energy density. For example, a nonaqueous electrolyte
battery enabling rapid charge/discharge not only remarkably
shortens the charging time but also makes it possible to improve
performances of the motive force of a hybrid vehicle and to
efficiently use the regenerative energy of them as power.
[0004] In order to enable rapid charge/discharge, it is necessary
that electrons and lithium ions can migrate rapidly between the
positive electrode and the negative electrode. When a nonaqueous
electrolyte battery using a carbon-based negative electrode repeats
rapid charge/discharge, dendrite precipitation of metal lithium is
occurred on the electrode, raising the fear as to heat generation
and fires caused by internal short circuits.
[0005] In light of this, a nonaqueous electrolyte battery using a
metal composite oxide for a negative electrode in place of a
carbonaceous material has been developed. Particularly, in a
nonaqueous electrolyte battery using titanium oxide for the
negative electrode, rapid charge/discharge can be performed stably.
Such a battery also has a longer life than those using a
carbonaceous material.
[0006] However, titanium oxide has a higher (i.e., nobler)
potential than the carbonaceous material relative to metal lithium.
Further, titanium oxide has a lower capacity per weight. Thus, a
nonaqueous electrolyte battery using titanium oxide for the
negative electrode has a problem such that the energy density is
low.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of a flat-shaped nonaqueous
electrolyte battery according to a second embodiment;
[0008] FIG. 2 is an enlarged sectional view of a A portion of FIG.
1;
[0009] FIG. 3 is a partially cut perspective view schematically
showing another flat-shaped nonaqueous electrolyte battery
according to the second embodiment;
[0010] FIG. 4 is an enlarged sectional view of a B section of FIG.
3;
[0011] FIG. 5 is an exploded perspective view of a battery pack
according to a third embodiment;
[0012] FIG. 6 is a block diagram showing the electric circuit of
the battery pack shown in FIG. 5; and
[0013] FIG. 7 is the first charge (Li insertion) curve of the
electrode produced in Example 1.
DETAILED DESCRIPTION
[0014] In general, according to one embodiment, an active material
for a battery is provided. The active material comprises
orthorhombic system oxide represented by the following formula:
Li.sub.xM1M2.sub.2O.sub.6. In this formula, 0.ltoreq.x.ltoreq.5, M1
is at least one selected from the group consisting of Fe and Mn,
and M2 is at least one selected from the group consisting of Nb, Ta
and V.
[0015] The embodiments will be explained below with reference to
the drawings. In this case, the structures common to all
embodiments are represented by the same symbols and duplicated
explanations will be omitted. Also, each drawing is a typical view
for explaining the embodiments and for promoting the understanding
of the embodiments. Though there are parts different from an actual
device in shape, dimension and ratio, these structural designs may
be properly changed taking the following explanations and known
technologies into consideration.
First Embodiment
[0016] According to the first embodiment, there is provided an
active material which comprises an orthorhombic system oxide
represented by the formula: Li.sub.xM1M2.sub.2O.sub.6. In this
formula, 0.ltoreq.x.ltoreq.5, M1 is at least one selected from the
group consisting of Fe and Mn, and M2 is at least one selected from
the group consisting of Nb, Ta and V.
[0017] The content of lithium ions in the orthorhombic system oxide
represented by the formula: Li.sub.xM1M2.sub.2O.sub.6
(0.ltoreq.x.ltoreq.5) may vary depending on the charge and
discharge state and the maximum content of Li ions per 1 mole of
the oxide may be 5 mol. The electrode containing the active
material containing the oxide can increase the absorption/release
amount of lithium ions per mass. Accordingly, the nonaqueous
electrolyte battery comprising the electrode containing the active
material containing the oxide can realize high energy density.
[0018] The orthorhombic system oxide represented by the formula
Li.sub.xM1M2.sub.2O.sub.6 (0.ltoreq.x.ltoreq.5) has a gradual
change in electrical potential (from 0.5 V (vs. Li/Li.sup.+) to 2.5
V (vs. Li/Li.sup.+)) due to the absorption and release reaction of
lithium. Thus, the nonaqueous electrolyte battery comprising the
electrode containing the active material containing the
orthorhombic system oxide can absorb and release lithium at a
potential nobler than the potential during electrocrystallization
of metal lithium. The nonaqueous electrolyte battery can reduce or
eliminate the electrocrystallization of metal lithium, resulting in
rapid charge and discharge.
[0019] The orthorhombic oxide contained in the active material
according to the embodiment is more preferably represented by
Li.sub.xFeNb.sub.2O.sub.6 or Li.sub.xFeV.sub.2O.sub.6
(0.ltoreq.x.ltoreq.5). Since the orthorhombic system oxide resented
by Li.sub.xFeNb.sub.2O.sub.6 or Li.sub.xFeV.sub.2O.sub.6
(0.ltoreq.x.ltoreq.5) has a crystal lattice advantageous to the
conduction of lithium ions, it is possible to achieve an
improvement in rapid charge/discharge performance of the nonaqueous
electrolyte battery and an improvement in electrode
capacitance.
[0020] The orthorhombic system oxide represented by the formula:
Li.sub.xM1M2.sub.2O.sub.6 (0.ltoreq.x.ltoreq.5) may be represented
by the formula: Li.sub.xM1M2.sub.2O.sub.6-.delta.
(0.ltoreq.x.ltoreq.5, 0.ltoreq..delta..ltoreq.0.3).
[0021] During the preparation of the orthorhombic system oxide,
oxygen deficiency may occur in a raw material or an intermediate
product. Further, inevitable impurities contained in the raw
material and impurities which have been mixed in during the
preparation may be present in the prepared orthorhombic system
oxide. Therefore, the active material according to the embodiment
may contain an orthorhombic system oxide having the composition
deviated from the stoichiometric ratio represented by the formula
Li.sub.xM1M2.sub.2O.sub.6 (0.ltoreq.x.ltoreq.5) because of, for
example, the above inevitable factor. For example, the oxygen
deficiency generated during the preparation of the orthorhombic
system oxide may cause an orthorhombic system oxide having the
composition represented by the formula:
Li.sub.xM1M2.sub.2O.sub.6-.delta. (0.ltoreq.x.ltoreq.5,
0<.delta..ltoreq.0.3) to be prepared.
[0022] However, even in the case of the orthorhombic system oxide
having the composition deviated from the stoichiometric ratio
because of the above inevitable factor, the absorption/release
amount of lithium ions per mass is high, and the absorption and
release reaction of lithium is generated within a range of 0.5 V
(vs. Li/Li.sup.+) to 2.5 V (vs. Li/Li.sup.+)). Accordingly, an
active material which contains the orthorhombic system oxide having
the composition deviated from the stoichiometric ratio because of
the above inevitable factor exerts the same effect as an active
material which contains an orthorhombic system oxide having the
composition represented by the formula Li.sub.xM1M2.sub.2O.sub.6
(0.ltoreq.x.ltoreq.5).
[0023] For the above reason, the active material according to the
embodiment encompasses the active material which contains the
orthorhombic system oxide having the composition deviated from the
stoichiometric ratio represented by the formula
Li.sub.xM1M2.sub.2O.sub.6 (0.ltoreq.x.ltoreq.5) because of the
above inevitable factor.
[0024] <Particle Diameter and BET Specific Surface Area>
[0025] The average particle diameter of the orthorhombic system
oxide contained in the active material according to this embodiment
is not particularly limited and it may be changed according to
desired battery characteristics.
[0026] The BET specific surface area of the orthorhombic system
oxide contained in the active material according to this embodiment
is not particularly limited and it is preferably 1 m.sup.2/g or
more and less than 50 m.sup.2/g.
[0027] The term "BET specific surface area" means a specific
surface area determined by the BET method. The specific surface
area of the particles is generally measured using a method in which
molecules whose adsorption occupied area is known are allowed to
adsorb to the plane of powder particles at the temperature of
liquid nitrogen to find the specific surface area of the sample
from the amount of the adsorbed molecules. Among them, the most
frequently used method is a BET method based on the low
temperature/low humidity physical adsorption of an inert gas. This
method is a method in which the Langmuir theory as a monolayer
adsorption theory is extended to multilayer adsorption and is the
best-known method as a calculation method of the specific surface
area of a solid such as a powder or particles.
[0028] In the case of a battery comprising a negative electrode
containing an active material containing an orthorhombic system
oxide having a specific surface area of 1 m.sup.2/g or more, the
contact area between the negative electrode active material and the
electrolyte solution can be sufficiently ensured, and excellent
discharge rate characteristics are easily obtained. Further, the
charging time can be reduced.
[0029] On the other hand, in the case of a negative electrode
containing an active material containing an orthorhombic system
oxide having a specific surface area of less than 50 m.sup.2/g, it
is possible to prevent the reactivity with the electrolyte solution
from being too high. Thus, lifetime characteristics of a nonaqueous
electrolyte battery comprising the above negative electrode can be
improved. Further, the active material containing an orthorhombic
system oxide having a specific surface area of less than 50
m.sup.2/g can improve coating properties of a slurry containing an
active material to be used in the following production of an
electrode.
[0030] <Production Method>
[0031] The active material according to this embodiment can be
produced by, for example, the following method.
[0032] First, an oxide or a salt containing at least one selected
from the group consisting of Fe and Mn, i.e., M1 and an oxide or a
salt containing at least one selected from the group consisting of
Nb, Ta, and V, i.e., M2 are mixed at a molar ratio so as to obtain
an orthorhombic system oxide represented by M1M2.sub.2O.sub.6. The
above salt is preferably a salt such as a carbonate and nitrate,
which is decomposed at a relatively low temperature to form an
oxide.
[0033] Next, the obtained mixture is ground and blended as
uniformly as possible and is then sintered. The sintering is
performed at a temperature range from 800 to 1500.degree. C. for a
total of 1 to 100 hours.
[0034] When the sintering temperature is raised to a temperature
range from 900 to 1300.degree. C., an active material with low
impurity phase content can be obtained.
[0035] As the particle diameter of the raw powder is smaller, an
active material having a uniform phase is obtained within a shorter
time for sintering. The active material prepared by sintering for a
short time has a small particle diameter and is excellent in
crystallinity. The nonaqueous electrolyte battery comprising the
negative electrode containing the active material is excellent in
output characteristics.
[0036] Lithium ions can be inserted by charging the orthorhombic
system oxide synthesized in the above manner. Further, the use of a
compound containing lithium such as lithium carbonate as a
synthetic raw material allows an orthorhombic system oxide
containing lithium in advance to be obtained.
[0037] <Powder X-Ray Diffraction Measurement>
[0038] The crystal state of the orthorhombic oxide in the active
material can be observed using, for example, powder X-ray
diffractometry (XRD).
[0039] A scattering angle 2.theta. is determined from the position
of the diffraction peak obtained by the XRD measurement, and a
crystal spacing d is calculated by the Bragg's law. The analysis
allows the crystal structure (crystal system) to be identified.
Further, known substances can be identified by referring to
diffraction data of standard substances such as cards of the Joint
Committee on Powder Diffraction Standards (JCPDS).
[0040] The powder X-ray diffraction measurement of the active
material can be performed, for example, as follows:
[0041] First, a target sample is ground to an average particle
diameter of about 5 .mu.m. The average particle diameter thereof
can be determined by the laser diffractometry. At this time, in
order to check whether or not the grinding influences on the
crystallizability of the sample, it is conformed whether or not a
half-width value of the main peak in the X-ray chart is changed
before and after the grinding.
[0042] Alternatively, particles having an average particle diameter
of about 5 .mu.m or less are selected using a sieve from the target
sample.
[0043] A holder portion with a depth of 0.2 mm formed on a glass
sample plate is filled with the sample ground or the sample
subjected to the particle size selection. In this case, a care must
be taken to fill the holder with the sample sufficiently. In order
to prevent the occurrence of cracks and voids, a further care must
be taken to apply the right amount of the sample.
[0044] Then, another glass plate is pressed against the sample and
the surface of the sample with which the holder portion is filled
is smoothed. In this case, a care must be taken to prevent the
generation of parts which depress or protrude from the standard
level of the holder due to an excess or a deficiency amount of the
sample to be filled.
[0045] Then, the glass plate filled with the sample is placed in a
powder X-ray diffractometer and a diffraction pattern is obtained
using Cu--K.alpha. rays.
[0046] Incidentally, there is a case an orientation of the
particles becomes high depending on the particle shape of the
sample. When the orientation of the sample is high, the position of
a peak may be shifted or the intensity ratio may be changed
depending on the way of filling the sample. In such a case, the
same sample is filled in a Lindemann glass capillary and the
measurement is performed using a rotary sample stand, whereby the
influence of the orientation can be determined. If there is a
difference in the intensity ratio exceeding the device tolerance on
a specific surface comparing the X-ray charts obtained, a
measurement result obtained by using the rotary sample stand can be
used as the measurement result of the sample.
[0047] When the powder X-ray diffraction measurement is performed
on the active material contained in the electrode, it can be
performed, for example, as follows:
[0048] First, in order to analyze the crystal state of the active
material, the active material is put into a state in which lithium
ions are perfectly released from the orthorhombic system oxide. For
example, when the active material is used in the negative
electrode, the battery is put into a fully discharged state.
However, there is a case where lithium ions still remain even in a
discharged state.
[0049] Next, the battery is disintegrated in a glove box filled
with argon. Then, the electrode is taken out and washed with an
appropriate solvent. As the appropriate solvent, for example, ethyl
methyl carbonate may be used. If the electrode is washed
insufficiently, it may sometimes be contaminated with an impurity
phase of lithium carbonate or lithium fluoride due to the influence
of the lithium ions remaining in the electrode. In such a case, it
is better to use an airtight container in which the measurement can
be performed in an inert gas atmosphere. The washed electrode is
cut into a size having almost the same area of the holder of the
powder X-ray diffractometer and used as a measurement sample. This
sample is attached directly to the glass holder, followed by
measurement of the sample. At this time, a peak corresponding to
the metal of the metallic foil included in the electrode substrate
is previously measured using XRD to obtain the peak position
derived from the electrode substrate. Further, peak positions of
other components such as a conductive auxiliary agent and a binder
are previously measured in the same manner as above to obtain the
positions. When the peak of the substrate material is overlapped on
the peak of the active material, it is desired to separate the
active material from the substrate prior to the measurement. This
is performed in order to separate the overlapped peaks in the
quantitative measurement of the peak intensity. Needless to say,
the procedure can be omitted if these data have been obtained in
advance. Although the electrode may be subjected to a physical
separation, the separation can be easily performed by applying
ultrasonic wave to the electrode in a solvent. When the ultrasonic
treatment is performed in order to separate the active material
from the substrate, the electrode powder (including the active
material, the conductive auxiliary agent and the binder) can be
recovered by volatilizing the solvent. The electrode powder
recovered is filled in, for example, a Lindemann glass capillary
and the measurement is performed, whereby the powder X-ray
diffraction of the active material can be measured. The electrode
powder recovered in the ultrasonic treatment may be subjected to
various analyses other than the powder X-ray diffraction.
[0050] The active material according to the first embodiment as
described above contains the orthorhombic system oxide represented
by the formula: Li.sub.xM1M2.sub.2O.sub.6 (0.ltoreq.x.ltoreq.5) (M1
is at least one selected from the group consisting of Fe and Mn,
and M2 is at least one selected from the group consisting of Nb, Ta
and V.). The electrode containing the active material containing
the oxide can increase the absorption/release amount of lithium
ions per mass. Accordingly, the nonaqueous electrolyte battery
comprising the electrode containing the active material containing
the oxide can realize high energy density. Further, the nonaqueous
electrolyte battery comprising the electrode containing the active
material containing the orthorhombic system oxide can absorb and
release lithium at a potential nobler than the potential during
electrocrystallization of metal lithium. The nonaqueous electrolyte
battery can reduce or even eliminate the electrodeposition of metal
lithium, resulting in rapid charge and discharge.
[0051] In other words, according to the first embodiment, there can
be provided an active material which can realize a nonaqueous
electrolyte battery having excellent rapid charge/discharge
performance and high energy density.
Second Embodiment
[0052] According to the second embodiment, there is provided a
nonaqueous electrolyte battery which comprises a negative
electrode, a positive electrode, and a nonaqueous electrolyte. The
active material in the first embodiment is used for the negative
electrode active material, the positive electrode active material,
or both of the negative electrode active material and the positive
electrode active material.
[0053] The nonaqueous electrolyte battery according to the second
embodiment may comprise a separator disposed between the positive
electrode and the negative electrode and a container which houses
the positive electrode, the negative electrode, the separator, and
the nonaqueous electrolyte.
[0054] Hereinafter, the negative electrode, the positive electrode,
the nonaqueous electrolyte, the separator, and the container will
be described in detail.
[0055] 1) Negative Electrode
[0056] The negative electrode comprises a current collector and a
negative electrode layer (negative electrode active material
containing layer). The negative electrode layer is formed on one
side or both sides of the current collector. The layer comprises
the active material and arbitrarily comprises the conductive agent
and the binder.
[0057] The active material according to the first embodiment, i.e.,
the orthorhombic oxide represented by the formula:
Li.sub.xM1M2.sub.2O.sub.6 (0.ltoreq.x.ltoreq.5) is used for the
negative electrode active material. Here, M1 is at least one
selected from the group consisting of Fe and Mn, and M2 is at least
one selected from the group consisting of Nb, Ta, and V.
[0058] According to a negative electrode using such a negative
electrode active material, there can be provided a nonaqueous
electrolyte battery having excellent rapid charge/discharge
performance and high energy density.
[0059] As the negative electrode active material, the orthorhombic
oxide represented by the formula: Li.sub.xM1M2.sub.2O.sub.6
(0.ltoreq.x.ltoreq.5) may be used alone or as a mixture with other
active materials. Examples of other active materials include
niobium titanium composite oxide comprising monoclinic-system oxide
(Li.sub.xNb.sub.2TiO.sub.7, Li.sub.xNb.sub.10Ti.sub.2O.sub.29,
Li.sub.xNb.sub.14TiO.sub.37, Li.sub.xNb.sub.24TiO.sub.62), titanium
dioxide having an anatase structure or a monoclinic system
.beta.-type structure (TiO.sub.2), lithium titanate having a
ramsdellite structure (e.g., Li.sub.2Ti.sub.3O.sub.7), and lithium
titanate having a spinel structure (e.g.,
Li.sub.4Ti.sub.5O.sub.12).
[0060] The conductive agent is added to improve the current
collection performance and suppress the contact resistance with the
current collector. Examples of the conductive agent include
carbonaceous substances such as acetylene black, carbon black, and
graphite.
[0061] The binder is added to fill gaps of the dispersed negative
electrode active material and bind the active material to the
current collector. Examples of the binder include
polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF),
fluorine-based rubber, and styrene butadiene rubber.
[0062] Preferably, blending rates of the active material, the
conductive agent, and the binder in the negative electrode layer
are 68 to 96 mass %, 2 to 30 mass %, and 2 to 30 mass %,
respectively. If the amount of the conductive agent is set to 2
mass % or more, the current collection performance of the negative
electrode layer can be improved. When the amount of the binder is
set to 2% by mass or more, the binding property of the negative
electrode layer and the current collector is sufficient and
excellent cycle characteristics can be expected. On the other hand,
the amounts of the conductive agent and the binder are preferably
set to 28 mass % or less from the viewpoint of high capacity
performance.
[0063] A material which is electrochemically stable at the lithium
absorption and release potential of the negative electrode active
material is used for the current collector. The current collector
is preferably formed of copper, nickel, stainless steel or an
aluminium, or an aluminium alloy containing at least one element
selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the
current collector is preferably from 5 to 20 .mu.m. The current
collector having such a thickness can achieve a good balance
between the strength and lightweight of the negative electrode.
[0064] The negative electrode may be produced by a method
comprising suspending the negative active material, the binder, and
the conductive agent in a widely used solvent to prepare a slurry,
applying the slurry to the negative electrode current collector,
drying to form a negative electrode layer, and pressing it. The
negative electrode may also be produced by forming a pellet
comprising the active material, the binder, and the conductive
agent to produce a negative electrode layer and placing the layer
on the current collector.
[0065] 2) Positive Electrode
[0066] The positive electrode comprises a current collector and a
positive electrode layer (positive electrode active material
containing layer). The positive electrode layer is formed on one
side or both sides of the current collector. The layer comprises
the active material and arbitrarily includes the conductive agent
and the binder.
[0067] Usable examples of the active material include oxides or
sulfides. Examples of the oxides and sulfides include manganese
dioxide capable of absorbing lithium (MnO.sub.2), iron oxide,
copper oxide, nickel oxide, a lithium manganese composite oxide
(e.g. Li.sub.xMn.sub.2O.sub.4 or Li.sub.xMnO.sub.2), 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. LiNi.sub.1-yCo.sub.yO.sub.2), a lithium
manganese cobalt composite oxide (e.g.
Li.sub.xMn.sub.yCo.sub.1-yO.sub.2), a lithium-manganese-nickel
composite oxide having a spinel structure (e.g.
Li.sub.xMn.sub.2-yNi.sub.yO.sub.4), a lithium phosphorus oxide
having an olivine structure (e.g. Li.sub.xFePO.sub.4,
Li.sub.xFe.sub.1-yMn.sub.yPO.sub.4, Li.sub.xCoPO.sub.4), iron
sulfate (Fe.sub.2(SO.sub.4).sub.3), a vanadium oxide (e.g.
V.sub.2O.sub.5), and a lithium nickel cobalt manganese composite
oxide. In the above formula, x is more than 0 and 1 or less and y
is more than 0 and 1 or less. As the active material, these
compounds may be used alone or in combination with a plurality of
compounds.
[0068] Examples of a more preferred active material include a
lithium manganese composite oxide having a high positive electrode
voltage (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. LiNi.sub.1-yCo.sub.yO.sub.2), a lithium-manganese-nickel
composite oxide having a spinel structure (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), lithium
iron phosphate (e.g. Li.sub.xFePO.sub.4), and a lithium nickel
cobalt manganese composite oxide. In the above formula, x is more
than 0 and 1 or less and y is more than 0 and 1 or less.
[0069] When the ordinary temperature molten salt is used as the
nonaqueous electrolyte of the battery, examples of a preferred
active material include lithium iron phosphate, Li.sub.xVPO.sub.4F
(0.ltoreq.x.ltoreq.1), a lithium manganese composite oxide, a
lithium nickel composite oxide, and a lithium nickel cobalt
composite oxide. Since these compounds have low reactivity with an
ordinary temperature molten salt, the cycle life can be
improved.
[0070] The primary particle diameter of the positive electrode
active material is preferably 100 nm or more and 1 .mu.m or less.
In the case of the positive electrode active material having a
primary particle diameter of 100 nm or more, the handling in the
industrial production is easy. In the case of the positive
electrode active material having a primary particle diameter of 1
.mu.m or less, diffusion in solid of lithium ions can be smoothly
proceeded.
[0071] The specific surface area of the active material is
preferably 0.1 m.sup.2/g or more and 10 m.sup.2/g or less. In the
case of the positive electrode active material having a specific
surface area of 0.1 m.sup.2/g or more, the absorption and release
site of lithium ions can be sufficiently ensured. In the case of
the positive electrode active material having a specific surface
area of 10 m.sup.2/g or less, the handling in the industrial
production is made easy and good charge discharge cycle performance
can be ensured.
[0072] The binder is added to bind the active material to the
current collector. Examples of the binder include
polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and
fluorine-based rubber.
[0073] The conductive agent is added, if necessary, to improve the
current collection performance and suppress the contact resistance
between the active material and the current collector. Examples of
the conductive agent include carbonaceous substances such as
acetylene black, carbon black, and graphite.
[0074] In the positive electrode layer, the active material and
binder are preferably formulated in a ratio of 80% by mass or more
and 98% by mass or less and in a ratio of 2% by mass or more and
20% by mass or less respectively.
[0075] When the amount of the binder is 2% by mass or more,
sufficient electrode strength is obtained. Further, when the amount
of the binder is 20% by mass or less, the amount of the insulating
material of the electrode can be reduced, leading to reduced
internal resistance.
[0076] When the conductive agent is added, the active material,
binder, and conductive agent are added in amounts of 77% by mass or
more and 95% by mass or less, 2% by mass or more and 20% by mass or
less and 3% by mass or more and 15% by mass or less respectively.
When the amount of the conductive agent is 3% by mass or more, the
above effect can be exerted. Further, when the amount of the
conductive agent is 15% by weight or less, the decomposition of the
nonaqueous electrolyte on the surface of the positive electrode
conductive agent during storage at high temperatures can be
reduced.
[0077] The collector is preferably an aluminum foil or an aluminum
alloy foil containing at least one element selected from Mg, Ti,
Zn, Ni, Cr, Mn, Fe, Cu, and Si.
[0078] The thickness of the aluminum foil or aluminum alloy foil is
preferably 5 .mu.m or more and 20 .mu.m or less, more preferably 15
.mu.m or less. The purity of the aluminum foil is preferably 99% by
mass or more. The content of transition metals such as iron,
copper, nickel, and chromium contained in the aluminum foil or
aluminum alloy foil is set to, preferably 1% by mass or less.
[0079] The positive electrode may be produced by a method
comprising suspending the active material, the binder, and the
conductive agent to be added, if necessary in an appropriate
solvent to prepare a slurry, applying the slurry to the positive
electrode collector, drying to form a positive electrode layer, and
pressing it. The positive electrode may also be produced by forming
a pellet comprising the active material and binder and optionally
the conductive agent to produce a positive electrode layer, which
is then placed on the collector.
[0080] (Nonaqueous Electrolyte)
[0081] The nonaqueous electrolyte may be, for example, a liquid
nonaqueous electrolyte prepared by dissolving an electrolyte in an
organic solvent or a gel-like nonaqueous electrolyte prepared by
forming a composite of a liquid electrolyte and a polymer
material.
[0082] The liquid nonaqueous electrolyte is preferably one which is
prepared by dissolving an electrolyte in an organic solvent at a
concentration of 0.5 to 2.5 mol/L.
[0083] Examples of the electrolyte include lithium perchlorate
(LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium
tetrafluoroborate (LiBF.sub.4), arsenic lithium hexafluoride
(LiAsF.sub.6), lithium trifluoromethasulfonate
(LiCF.sub.3SO.sub.3), a lithium salt such as lithium
bis(trifluoromethylsulfonyl)imide [LiN(CF.sub.3SO.sub.2).sub.2],
and the mixtures thereof. The electrolyte is preferably one which
is not easily oxidized even at a high potential and LiPF.sub.6 is
the most preferable.
[0084] Examples of the organic solvent include cyclic carbonates
such as propylene carbonate (PC), ethylene carbonate (EC), and
vinylene carbonate; linear carbonates such as diethyl carbonate
(DEC), dimethyl carbonate (DMC), and methylethyl carbonate (MEC);
cyclic ethers such as tetrahydrofuran (THF),
2-methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); linear
ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and
.gamma.-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL).
These organic solvents can be used alone or as a mixed solvent.
[0085] Examples of the polymer material include polyvinylidene
fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide
(PEO).
[0086] Alternatively, an ordinary temperature molten salt
containing lithium ions (ionic melt), polymer solid electrolyte,
inorganic solid electrolyte and the like may be used as the
nonaqueous electrolyte.
[0087] The ordinary temperature molten salt (ionic melt) means
compounds which can exist in a liquid state at normal temperature
(15 to 25.degree. C.) among organic salts constituted of
combinations of organic cations and anions. Examples of the
ordinary temperature molten salt include those which solely exist
in a liquid state, those which are put into a liquid state when
mixed with an electrolyte, and those which are put into a liquid
state when dissolved in an organic solvent. The melting point of
the ordinary temperature molten salt to be usually used for the
nonaqueous electrolyte battery is 25.degree. C. or less. Further,
the organic cation has generally a quaternary ammonium
skeleton.
[0088] The polymer solid electrolyte is prepared by dissolving an
electrolyte in a polymer material and by solidifying the
mixture.
[0089] The inorganic solid electrolyte is a solid material having
lithium ion-conductivity.
[0090] 4) Separator
[0091] The separator may be formed from a porous film including a
material such as polyethylene, polypropylene, cellulose, or
polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven
fabric. Particularly, a porous film formed of polyethylene or
polypropylene can melt at a constant temperature and can block
electric current, and thus it is preferred from the viewpoint of
improvement in safety.
[0092] 5) Container
[0093] As the container, a container formed of a laminate film
having a thickness of 0.5 mm or less or a container formed of metal
having a thickness of 1 mm or less can be used. The thickness of
the laminate film is preferably 0.2 mm or less. The thickness of
the metal container is more preferably 0.5 mm or less, still more
preferably 0.2 mm or less.
[0094] The shape of the container may be flat-type (thin-type),
square-type, cylindrical-type, coin-type, button-type or the like.
The container may be, for example, a container for a small battery
which is loaded into a portable electronic device or a container
for a large battery which is loaded into a two- or four-wheeled
vehicle depending on the size of the battery.
[0095] As the laminate film, a multilayer film in which a metal
layer is intervened between resin layers is used. The metal layer
is preferably aluminum foil or aluminum alloy foil in order to
reduce the weight. Polymer materials such as polypropylene (PP),
polyethylene (PE), nylon, and polyethylene terephthalate (PET) can
be used for the resin layer. The laminate film can be formed into a
shape of the container by heat sealing.
[0096] The metal container is formed from aluminium or an aluminium
alloy. It is preferable that the aluminium alloy contains elements
such as magnesium, zinc, and silicon. When transition metals such
as iron, copper, nickel, and chromium are contained in the alloy,
the content is preferably 1% by mass or less.
[0097] Subsequently, examples of the nonaqueous electrolyte battery
according to the second embodiment will be more specifically
described with reference to the drawings.
[0098] FIG. 1 is a cross-sectional view of a flat-shaped nonaqueous
electrolyte battery according to a second embodiment; FIG. 2 is an
enlarged sectional view of a portion A of FIG. 1.
[0099] A battery 10 shown in FIGS. 1 and 2 comprises a flat-shaped
wound electrode group 1. The flat-shaped wound electrode group 1
comprises a negative electrode 3, a separator 4, and a positive
electrode 5. In the negative electrode 3, the separator 4, and the
positive electrode 5, the separator 4 is intervened between the
negative electrode 3 and the positive electrode 5. The flat-shaped
wound electrode group 1 can be formed by stacking the negative
electrode 3, the separator 4, and the positive electrode 5 so that
the separator 4 is intervened between the negative electrode 3 and
the positive electrode 5 to form a laminate, spirally winding the
laminate so that the negative electrode 3 faces the outside as
shown in FIG. 2, and subjecting it to press-molding.
[0100] The negative electrode 3 comprises a negative electrode
current collector 3a and a negative electrode layer 3b. The
above-mentioned negative electrode active material is contained in
the negative electrode layer 3b. As shown in FIG. 4, the negative
electrode 3 on the outermost shell has a configuration in which the
negative electrode layer 3b is formed at only one side of the inner
plane of the negative electrode current collector 3a. In other
negative electrodes 3, the negative electrode layer 3b is formed at
both sides of the negative electrode current collector 3a.
[0101] In the positive electrode 5, the positive electrode layer 5b
is formed at both sides of the positive electrode current collector
5a.
[0102] As shown in FIG. 3, in a vicinity of a peripheral edge of
the wound electrode group 1, a negative electrode terminal 6 is
connected to the negative electrode current collector 3a of the
negative electrode 3 of the outermost shell, and a positive
electrode terminal 7 is connected to the positive electrode current
collector 5a of the positive electrode 5 at the inside. The
negative electrode terminal 6 and the positive electrode terminal 7
are extended outwardly from an opening of the bag-shaped container
2. For example, the liquid nonaqueous electrolyte is injected from
the opening of the bag-shaped container 2. The wound electrode
group 1 and the liquid nonaqueous electrolyte can be completely
sealed by heat-sealing the opening of the bag-shaped container 2
with the negative electrode terminal 6 and the positive electrode
terminal 7.
[0103] The negative electrode terminal 6 is formed from a material
which is electrically stable in Li absorption-release potential of
the negative electrode active material and has conductivity.
Specific examples thereof include copper, nickel, stainless steel,
and aluminium. It is preferable that the negative electrode
terminal 6 is formed of a material similar to that of the negative
electrode current collector 3a in order to reduce the contact
resistance with the negative electrode current collector 3a.
[0104] The positive electrode terminal 7 is formed of, for example,
a material which is electrically stable in a potential range of 3
to 5 V to lithium ion metal and has conductivity. Specifically, it
is formed of aluminium or an aluminium alloy containing elements
such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the
positive electrode terminal 7 is formed of the same material as
that of the positive electrode current collector 3a in order to
reduce the contact resistance with the positive electrode current
collector 5a.
[0105] The nonaqueous electrolyte battery according to the second
embodiment may have not only the configurations shown in FIGS. 1
and 2, but also the configurations shown in FIGS. 3 and 4.
[0106] FIG. 3 is a partially cut perspective view schematically
showing another flat-shaped nonaqueous electrolyte secondary
battery according to the second embodiment. FIG. 4 is an enlarged
sectional view of a portion B of FIG. 3.
[0107] A battery 10' shown in FIGS. 3 and 4 comprises a
lamination-type electrode group 11.
[0108] The lamination-type electrode group 11 is housed in a
container 12 which is formed of a laminate film in which a metal
layer is intervened between two resin films. As shown in FIG. 6,
the lamination-type electrode group 11 has a structure in which a
positive electrode 13 and a negative electrode 14 are alternately
stacked while a separator 15 is intervened between the both
electrodes. A plurality of the positive electrodes 13 are present
and they comprise the current collector 13a and a positive
electrode active material containing layer 13b formed at both sides
of the current collector 13a. A plurality of the negative
electrodes 14 are present and each of them comprises a negative
electrode current collector 14a and a negative electrode active
material containing layer 14b formed at both sides of the negative
electrode current collector 14a. In each of the negative electrode
current collectors 14a of the negative electrodes 14, a side is
protruded from the negative electrode 14. The protruded negative
electrode current collector 14a is electrically connected to a
belt-like negative electrode terminal 16. The distal end of the
negative electrode terminal 16 is externally drawn from the
container 12. In the positive electrode current collector 13a of
the positive electrode 13, not illustrated, one side located at the
opposite side of the protruded side of the negative electrode
current collector 14a is protruded from the positive electrode 13.
The positive electrode current collector 13a protruded from the
positive electrode 13 is electrically connected to a belt-like
positive electrode terminal 17. The distal end of the belt-like
positive electrode terminal 17 is located at the opposite side of
the negative electrode terminal 16 and externally drawn from the
container 12.
[0109] The nonaqueous electrolyte battery according to the second
embodiment comprises a negative electrode containing the active
material according to the first embodiment. Therefore, according to
the second embodiment, there can be provided a nonaqueous
electrolyte battery having excellent rapid charge/discharge
performance and high energy density.
Third Embodiment
[0110] The battery pack according to the third embodiment comprises
the nonaqueous electrolyte battery (unit cell) according to the
second embodiment.
[0111] The battery pack according to the third embodiment may
comprise one or a plurality of nonaqueous electrolyte batteries.
When the battery pack according to the third embodiment comprises
the nonaqueous electrolyte batteries, each of the unit cells may be
electrically connected each other in series or in parallel.
[0112] Subsequently, on example of the battery pack according to
the third embodiment will described with reference to the
drawings.
[0113] FIG. 5 is an exploded perspective view of a battery pack
according to a third embodiment; FIG. 6 is a block diagram showing
the electric circuit of the battery pack shown in FIG. 5.
[0114] A battery pack 20 shown in FIGS. 5 and 6 comprises a
plurality of flat-type batteries 10 having the structures shown in
FIGS. 1 and 2 as unit cells.
[0115] A battery module 23 is configured by stacking the unit cells
10 so that the negative electrode terminal 6 extended outside and
the positive electrode terminal 7 are arranged in the same
direction and fastening them with an adhesive tape 22. The unit
cells 10 are electrically connected in series with one another as
shown in FIG. 6.
[0116] A printed wiring board 24 is arranged opposed to the side
plane where the negative electrode terminal 6 and the positive
electrode terminal 7 in each of the unit cells 10 are extended. A
thermistor 25, a protective circuit 26, and an energizing terminal
27 to an external instrument are mounted on the printed wiring
board 24 as shown in FIG. 6. An electric insulating plate (not
shown) is attached to the surface of the printed wiring board 24
facing the battery module 23 to avoid unnecessary connection of the
wiring of the battery module 23.
[0117] A positive electrode-side lead 28 is connected to the
positive electrode terminal 7 in each of the unit cells 10 located
at the bottom layer of the battery module 23 and the distal end of
the positive electrode-side lead 28 is inserted into a positive
electrode-side connector 29 of the printed wiring board 24 so as to
be electrically connected. A negative electrode-side lead 30 is
connected to the negative electrode terminal 6 in each of the unit
cells 10 located at the top layer of the battery module 23 and the
distal end of the negative electrode-side lead 30 is inserted into
an negative electrode-side connector 31 of the printed wiring board
24 so as to be electrically connected. The connectors 29 and 31 are
connected to the protective circuit 26 through wirings 32 and 33
formed in the printed wiring board 24.
[0118] The thermistor 25 detects the temperature of the unit cells
10 and transmit a signal of the detected temperature to the
protective circuit 26. The protective circuit 26 can shut down a
plus-side wiring 34a and a minus-side wiring 34b between the
protective circuit 26 and the energizing terminal 27 to an external
instrument under a predetermined condition. An example of the
predetermined condition indicates when a signal showing that the
temperature of the unit cells 10 is a predetermined temperature or
more is received from the thermistor 25. Further, the predetermined
condition indicates when the over-charge, over-discharge, and
over-current of the unit cells 10 are detected. The over-charge
detection may be performed on each of the unit cells 10 or the
whole of the unit cells 10. When each of the unit cells 10 is
detected, the cell voltage may be detected, or positive electrode
potential or negative electrode potential may be detected. In the
case of the latter, a lithium electrode to be used as a reference
electrode is inserted into each of the unit cells 10. In the
battery packs of FIGS. 5 and 6, wirings 35 for voltage detection
are connected to the unit cells 10 and a signal of the detected
voltage are transmitted to the protective circuit 26 through the
wirings 35.
[0119] Protective sheets 36 comprised of rubber or resin are
arranged on three side surfaces of the battery module 23 except the
side surface in which the positive electrode terminal 7 and the
negative electrode terminal 6 are protruded.
[0120] The battery module 23 is housed in a housing container 37
together with each of the protective sheets 36 and the printed
wiring board 24. That is, the protective sheets 36 are arranged on
both internal surfaces in a long side direction of the housing
container 37 and on one of the internal surface at the opposite
side in a short side direction. The printed wiring board 24 is
arranged on the other internal surface in a short side direction.
The battery module 23 is located in a space surrounded by the
protective sheets 36 and the printed wiring board 24. A lid 38 is
attached to the upper surface of the housing container 37.
[0121] In order to fix the battery module 23, a heat-shrinkable
tape may be used in place of the adhesive tape 22. In this case,
the battery module is bound by placing the protective sheets on the
both sides of the battery module, revolving a heat-shrinkable tube,
and thermally shrinking the heat-shrinkable tube.
[0122] The battery pack 20 shown in FIG. 5 or FIG. 6 is configured
to comprise the unit cells 10 which are connected to each other in
series. In the battery pack according to the third embodiment, the
unit cells 10 may be connected in parallel in order to increase the
battery capacity. Alternatively, the battery pack according to the
third embodiment may comprise a plurality of unit cells 10 which
are connected in combination of series and parallel connections.
The assembled battery pack 20 can be further connected in series or
in parallel.
[0123] The battery pack 20 shown in FIG. 5 or FIG. 6 comprises a
plurality of the unit cells 10, however the battery pack according
to the third embodiment may comprise one unit cell 10.
[0124] The form of the battery pack is appropriately changed
according to the use. The battery pack according to this embodiment
is used suitably for the application which requires the excellent
cycle characteristics when a high current is taken out.
Specifically, it is used as the battery pack for power sources for
digital cameras, the battery pack for vehicles such as two- or
four-wheel hybrid electric vehicles, two- or four-wheel electric
vehicles, and assisted bicycles or the like. Particularly, it is
suitably used as a battery for automobile use.
[0125] The battery pack according to the third embodiment comprises
the battery according to the second embodiment. As described above,
the battery according to the second embodiment is a nonaqueous
electrolyte battery which can have excellent rapid charge/discharge
performance and high energy density. Therefore, according to the
third embodiment described above, there can be provided a battery
pack having excellent rapid charge/discharge performance and high
energy density.
EXAMPLES
[0126] Hereinafter, the embodiments will be described in detail
based on examples. The identification of the crystal phase and
estimation of crystal structure of the synthesized orthorhombic
system oxide were performed by powder X-ray diffractometry using
Cu--K.alpha. rays.
Example 1
Synthesis
[0127] As starting materials, commercially available oxide reagents
FeO and Nb.sub.2O.sub.5 were used. Powders of these starting
materials were weighed to have a molar ratio of 1:1 and mixed in a
mortar. Then, the obtained mixture was put into an electric furnace
and sintered in a nitrogen stream at 900.degree. C. for a total of
10 hours. The sintered powder was subjected to a ball mill
treatment using zirconia beads as media. As a result, a sample
having an average particle diameter of 1.8 .mu.m and a BET specific
surface area of 12 m.sup.2/g was obtained.
[0128] (Powder X-Ray Diffraction Measurement)
[0129] The powder X-ray diffraction measurement was performed on
the obtained sample as follows. First, a sample is ground until the
average particle diameter becomes about 10 .mu.m. A holder portion
with a depth of 0.2 mm formed on a glass sample plate was filled
with the ground sample. Then, using a separate glass plate, the
glass plate was sufficiently pressed against the sample from the
outside to smooth the surface of the sample. Then, the glass plate
filled with the sample was placed in a powder X-ray diffractometer
and a diffraction pattern was obtained using Cu--K.alpha. rays. The
JCPDS cards were used to confirm the obtained diffraction patterns.
The obtained sample was identified as an orthorhombic system oxide
FeNb.sub.2O.sub.6 of the JCPDS card 34-0426.
[0130] (Production of Negative Electrode)
[0131] Acetylene black as a conductive agent was added to the above
synthesized orthorhombic complex oxide at 10 parts by weight based
on the weight of the oxide. The mixture was dispersed in
N-methyl-2-pyrrolidone (NMP) and a polyvinylidene fluoride (PVdF)
as a binder was added to the mixture at 10 parts by weight based on
the weight of the oxide. The slurry was applied to a current
collector 3a made of an aluminum foil by using a blade. The slurry
was dried at 130.degree. C. for 12 hours in vacuo to obtain a
negative electrode 3.
Example 2
[0132] An orthorhombic oxide FeV.sub.2O.sub.6 was prepared in the
same manner as described in Example 1 except that commercially
available oxide reagents FeO and V.sub.2O.sub.5 were used as
starting materials. The average particle diameter of the obtained
sample was 1.9 .mu.m, and the BET specific surface area was 12
m.sup.2/g. The sample was used to produce a negative electrode in
the same manner as described in Example 1.
Example 3
[0133] An orthorhombic oxide Fe.sub.0.5Mn.sub.0.5Nb.sub.2O.sub.6
was prepared in the same manner as described in Example 1 except
that commercially available oxide reagents FeO, MnO.sub.2, and
Nb.sub.2O.sub.5 were used as starting materials. The average
particle diameter of the obtained sample was 1.6 .mu.m, and the BET
specific surface area was 14 m.sup.2/g. The sample was used to
produce a negative electrode in the same manner as described in
Example 1.
Example 4
[0134] An orthorhombic oxide MnNb.sub.2O.sub.6 was prepared in the
same manner as described in Example 1 except that commercially
available oxide reagents MnO.sub.2 and Nb.sub.2O.sub.5 were used as
starting materials. The average particle diameter of the obtained
sample was 2.0 .mu.m, and the BET specific surface area was 12
m.sup.2/g. The sample was used to produce a negative electrode in
the same manner as described in Example 1.
Example 5
[0135] An orthorhombic oxide MnTa.sub.2O.sub.6 was prepared in the
same manner as described in Example 1 except that commercially
available oxide reagents MnO.sub.2 and Ta.sub.2O.sub.5 were used as
starting materials. The average particle diameter of the obtained
sample was 2.4 .mu.m, and the BET specific surface area was 10
m.sup.2/g. The sample was used to produce a negative electrode in
the same manner as described in Example 1.
Comparative Example 1
[0136] Commercially available TiO.sub.2 and Li.sub.2CO.sub.3 were
used as starting materials. Powders of these starting materials
were weighed to have a molar ratio of 5:2 and mixed in a mortar.
Then, the obtained mixture was put into an electric furnace and
sintered in the air at 850.degree. C. for a' total of 24 hours. The
sintered powder was subjected to a ball mill treatment using
zirconia beads as media to obtain a cubic system oxide
Li.sub.4Ti.sub.5O.sub.12 having an average particle diameter of 1.1
.mu.m and a BET specific surface area of 12 m.sup.2/g. The sample
was used to produce a negative electrode in the same manner as
described in Example 1.
Comparative Example 2
[0137] A negative electrode was produced in the same manner as
described in Example 1 except that a commercially available cubic
system oxide Fe.sub.3O.sub.4 having an average particle diameter of
0.3 .mu.m and a BET specific surface area of 10 m.sup.2/g was
used.
Comparative Example 3
[0138] A negative electrode was produced in the same manner as
described in Example 1 except that a commercially available cubic
system oxide FeO having an average particle diameter of 0.3 .mu.m
and a BET specific surface area of 10 m.sup.2/g was used.
[0139] <Electrochemical Measurement>
[0140] An electrochemical measuring cell was produced using each
negative electrode produced in Examples 1 to 5 and Comparative
examples 1 to 3, a metal lithium foil as a counter electrode, and a
nonaqueous electrolyte. As the nonaqueous electrolyte, a solution
obtained by dissolving 1 M of lithium hexafluorophosphate in a
mixed solvent of ethylene carbonate and diethyl carbonate (volume
ratio: 1:1) was used.
[0141] The capacity at the first cycle of each measuring cell of
Examples 1 to 5 and Comparative examples 1 to 3 was confirmed at a
potential range of 0 V to 3.0 V (vs. Li/Li.sup.+) relative to metal
lithium electrode and at a charge/discharge current of 0.2 C
(hourly discharge rate). Then, the rapid charge/discharge test was
similarly carried out in an environment of 25.degree. C. The rapid
charge/discharge test was carried out at a potential range of 0.8 V
to 3.0 V (vs. Li/Li.sup.+) relative to metal lithium electrode and
at a charge/discharge current of 2 C (hourly discharge rate).
However, in order to confirm the capacity at the first cycle, the
test using the measuring cell of Comparative Example 1 was carried
out at a potential range of 0.8 V to 3.0 V (vs. Li/Li.sup.+) to
protect the crystal structure.
[0142] <Results>
[0143] The first cycle discharge (Li discharge) capacity and the
capacity-maintenance ratio regarding the examples and the
comparative examples are shown in Table 1. The capacity-maintenance
ratio was a ratio (%) of the discharge capacity at the 30th cycle
to the discharge capacity at the first cycle.
[0144] The measured discharge (Li discharge) curve at the first
cycle in the sample obtained in Example 1 is shown in FIG. 7.
TABLE-US-00001 TABLE 1 Initial Capacity General capacity retention
formula (mAh/g) (%) Example 1 FeNb.sub.2O.sub.6 510 88 Example 2
FeV.sub.2O.sub.6 600 80 Example 3
Fe.sub.0.5Mn.sub.0.5Nb.sub.2O.sub.6 500 87 Example 4
MnNb.sub.2O.sub.6 500 85 Example 5 MnTa.sub.2O.sub.6 440 80
Comparative Li.sub.4Ti.sub.5O.sub.12 160 100 Example 1 Comparative
Fe.sub.3O.sub.4 460 <10 Example 2 Comparative FeO 520 <10
Example 3
[0145] From the results shown in FIG. 7, it is found that the
capacity of an electrode using an orthorhombic system oxide of
Example 1 as an active material is about 400 mAh/g when releasing
lithium at a range of 2.5 V (vs. Li/Li.sup.+) to 0.5 V (vs.
Li/Li.sup.+). The measured discharge (Li discharge) curve at the
first cycle in each sample obtained in Examples 2 to 5 was the same
as the curve of the sample of Example 1 shown in FIG. 7. In other
words, the obtained results show that in nonaqueous electrolyte
batteries of Examples 1 to 5 comprising a negative electrode
containing an orthorhombic system oxide, a high capacity can be
obtained by absorbing and releasing lithium at a potential nobler
than the potential during electrocrystallization of metal
lithium.
[0146] Further, from the results shown in Table 1, it is found that
nonaqueous electrolyte batteries of Examples 1 to 5 comprising a
negative electrode containing an orthorhombic system oxide did not
exhibit a significantly decreased capacity, even if the rapid
charge/discharge test was carried out at a charge/discharge current
of 2 C (hourly discharge rate) 30 times. In other words, the
obtained results show that in electrodes of the examples using an
orthorhombic system oxide as an active material, it is possible to
realize a nonaqueous electrolyte battery having a high capacity and
excellent charge/discharge cycle performance even in rapid
charging/discharging.
[0147] On the other hand, from the results shown in Table 1, it is
found that the electrode of Comparative example 1 using a cubic
system oxide has excellent rapid charge/discharge cycle
performance, but has a low capacity.
[0148] From the results shown in Table 1, it is found that
electrodes of Comparative examples 2 and 3 using a cubic system
oxide have a high capacity. However, in electrodes of Comparative
examples 2 and 3 using a cubic system oxide, the charge/discharge
operation was repeated at a charge/discharge current of 2 C (hourly
discharge rate) 30 cycles. As a result, the capacity was
significantly reduced as shown in Table 1. In other words, the
obtained results show that nonaqueous electrolyte batteries of
Comparative examples 2 and 3 comprising an electrode using a cubic
system oxide are poor in charge/discharge cycle performance during
rapid charge and discharge, and thus they are not suitable for
rapid charge and discharge.
Example 6-1
[0149] In Example 6-1, a negative electrode was produced in the
same manner as described in Example 1 using a mixture obtained by
mixing the orthorhombic system oxide FeNb.sub.2O.sub.6 obtained in
Example 1 and a monoclinic system oxide Nb.sub.2TiO.sub.7 in a
mixing ratio of 10:1.
[0150] The monoclinic system Nb.sub.2TiO.sub.7 was prepared by
mixing Nb.sub.2O.sub.5 and TiO.sub.2 as starting materials in a
molar ratio of 1:1, and then sintering the mixture at 1200.degree.
C. for 12 hours.
Examples 6-2 and 6-3
[0151] A negative electrode was produced in the same manner as
described in Example 6-1 except that the mixing ratio of the
orthorhombic system oxide FeNb.sub.2O.sub.6 obtained in Example 1
to the monoclinic system Nb.sub.2TiO.sub.7 was 1:1 or 1:10.
Examples 7-1 to 7-3
[0152] Negative electrodes were produced respectively in the same
manner as described in Examples 6-1 to 6-3 except that the spinel
system Li.sub.4Ti.sub.5O.sub.12 described in Comparative example 1
was used instead of the monoclinic system Nb.sub.2TiO.sub.7.
[0153] <Electrochemical Measurement>
[0154] Electrochemical measurement of each negative electrode
produced in Examples 6-1 to 6-3 and Examples 7-1 to 7-3 was
performed in the same manner as described in that of each negative
electrode produced in Examples 1 to 5 and Comparative examples 1 to
3. The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Initial Capacity Mixing ratio capacity
retention (w:w) (mAh/g) (%) Example 6-1
FeNb.sub.2O.sub.6:Nb.sub.2TiO.sub.7 = 10:1 483 90 Example 6-2
FeNb.sub.2O.sub.6:Nb.sub.2TiO.sub.7 = 1:1 375 93 Example 6-3
FeNb.sub.2O.sub.6:Nb.sub.2TiO.sub.7 = 1:10 267 98 Example 7-1
FeNb.sub.2O.sub.6:Li.sub.4Ti.sub.5O.sub.12 = 10:1 475 90 Example
7-2 FeNb.sub.2O.sub.6:Li.sub.4Ti.sub.5O.sub.12 = 1:1 263 94 Example
7-3 FeNb.sub.2O.sub.6:Li.sub.4Ti.sub.5O.sub.12 = 1:10 195 99
[0155] From the results shown in Table 2, it is found that the
electrodes in Examples 6-1 to 6-3 and Examples 7-1 to 7-3, in which
the active material different from the orthorhombic system oxide
FeNb.sub.2O.sub.6 obtained in Example 1 is combined, show better
cycle performance than that in Example 1. It is further found that
the electrodes in Examples 6-1 to 6-3 and Examples 7-1 to 7-3 show
the initial capacity higher than that in Comparative example 1.
[0156] The cell for electrochemical measurement produced in each of
Examples and Comparative examples described above has the lithium
metal as a counter electrode, and the potential of the negative
electrode produced in each of Examples and Comparative examples is
nobler than the counter electrode. As a result, the negative
electrode produced in each Examples and Comparative examples acts
as a positive electrode in the cell for the electrochemical
measurement described above. Here, in order to avoid confusions, in
Examples described above, a direction of inserting lithium ions
into the negative electrode produced in each of Examples and
Comparative examples is uniformly referred to as "charging" and a
direction of releasing the ions from the negative electrode is
uniformly referred to as "discharging."
[0157] On the other hand, the negative electrode produced in each
of Examples and Comparative examples can act as the negative
electrode in a battery produced combining with a conventionally
known positive electrode material. In the battery produced in this
way, a direction of inserting lithium ions into the negative
electrode produced in each Examples and Comparative examples is a
discharging direction, and a direction of releasing the ions from
the negative electrode is a charging direction.
[0158] Hence, according to at least one of the embodiments and the
examples as described above, there can be provided an active
material which can realize a nonaqueous electrolyte battery having
excellent rapid charge/discharge performance and high energy
density.
[0159] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *