U.S. patent application number 16/986320 was filed with the patent office on 2020-11-19 for positive electrode material and method for manufacturing the same, battery using the positive electrode material and method for manufacturing the same, and electronic device using the battery.
This patent application is currently assigned to FUJITSU LIMITED. The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to MASAHARU HIDA, Kenji Homma, jiyunichi iwata, Tomochika KURITA.
Application Number | 20200365894 16/986320 |
Document ID | / |
Family ID | 1000005022599 |
Filed Date | 2020-11-19 |
United States Patent
Application |
20200365894 |
Kind Code |
A1 |
KURITA; Tomochika ; et
al. |
November 19, 2020 |
POSITIVE ELECTRODE MATERIAL AND METHOD FOR MANUFACTURING THE SAME,
BATTERY USING THE POSITIVE ELECTRODE MATERIAL AND METHOD FOR
MANUFACTURING THE SAME, AND ELECTRONIC DEVICE USING THE BATTERY
Abstract
A positive electrode material has diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG., has a monoclinic crystal structure
belonging to a space group P2.sub.1/c, and is represented by a
composition formula Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2).
Inventors: |
KURITA; Tomochika;
(Kawasaki, JP) ; Homma; Kenji; (Atsugi, JP)
; HIDA; MASAHARU; (Atsugi, JP) ; iwata;
jiyunichi; (Sagamihara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
1000005022599 |
Appl. No.: |
16/986320 |
Filed: |
August 6, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2018/005102 |
Feb 14, 2018 |
|
|
|
16986320 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/0525 20130101;
H01M 2004/028 20130101; H01M 4/58 20130101 |
International
Class: |
H01M 4/58 20060101
H01M004/58; H01M 10/0525 20060101 H01M010/0525 |
Claims
1. A positive electrode material having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG., having a monoclinic crystal
structure belonging to a space group P2.sub.1/c, and represented by
a composition formula Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2).
2. The positive electrode material according to claim 1, wherein in
the crystal structure, the number of oxygen atoms coordinated to a
Co atom is 4 to 5.
3. The positive electrode material according to claim 1, wherein
a=8.2 .ANG., b=13.5 .ANG., c=9.7 .ANG., and .beta.=148.degree. are
satisfied as lattice constants.
4. A method for manufacturing a positive electrode material having
diffraction peaks at 2.theta.=13.1.degree..+-.0.2.degree.,
14.0.degree..+-.0.2.degree., and 18.4.degree..+-.0.2.degree. in
X-ray diffraction (2.theta.=5.degree. to 90.degree.) using
synchrotron radiation having a wavelength of 1 .ANG., having a
monoclinic crystal structure belonging to a space group P2.sub.1/c,
and represented by a composition formula
Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2), the
method comprising heat-treating a mixture of a lithium source, a
cobalt source, and a phosphoric acid source.
5. The method for manufacturing a positive electrode material
according to claim 4, wherein the heat treatment is performed at a
temperature of 420.degree. C. or higher and 520.degree. C. or
lower.
6. The method for manufacturing a positive electrode material
according to claim 4, wherein the heat treatment is performed in an
inert atmosphere.
7. A battery comprising: a positive electrode containing a positive
electrode material; a negative electrode; and an electrolyte
disposed between the positive electrode and the negative electrode,
wherein the positive electrode material has diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG., has a monoclinic crystal structure
belonging to a space group P2.sub.1/c, and is represented by a
composition formula Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of
International Application PCT/JP2018/005102 filed on Feb. 14, 2018
and designated the U.S., the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The present embodiment relates to a positive electrode
material and a method for manufacturing the same, a battery using
the positive electrode material and a method for manufacturing the
same, and an electronic device using the battery.
BACKGROUND
[0003] A secondary battery has been widely used as a storage
battery used for a mobile phone, a mobile personal computer, a
sensing device, an electric vehicle, or the like. Examples of the
secondary battery include a nickel-hydrogen battery, a
nickel-cadmium battery, and a lithium ion battery. Among these
batteries, a lithium ion battery is drawing attention because of
having a high energy density.
[0004] Related art is disclosed in International Publication
Pamphlet No. WO 2015/056412.
SUMMARY
[0005] According to an aspect of the embodiments, a positive
electrode material has diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG., has a monoclinic crystal structure
belonging to a space group P2.sub.1/c, and is represented by a
composition formula Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2).
[0006] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0007] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a schematic diagram illustrating a crystal
structure of Li.sub.2CoP.sub.2O.sub.7.
[0009] FIG. 2 is a schematic diagram illustrating a crystal
structure of a disclosed positive electrode material.
[0010] FIG. 3 is a part of an XRD spectrum of the disclosed
positive electrode material.
[0011] FIG. 4 is a schematic cross-sectional view illustrating an
example of a disclosed battery.
[0012] FIG. 5 illustrates XRD spectra of positive electrode
materials in Example 1(A) and Comparative Example 1(B).
[0013] FIG. 6 illustrates constant current charge/discharge curves
of half cells using positive electrode materials in Example 4 and
Comparative Example 4.
[0014] FIG. 7 illustrates a constant current charge/discharge curve
of a half cell using a positive electrode material in Example
6.
[0015] FIG. 8 is a schematic cross-sectional view illustrating an
example of a disclosed electronic device.
DESCRIPTION OF EMBODIMENTS
[0016] A battery includes a positive electrode active material that
performs a redox reaction in a positive electrode and includes a
negative electrode active material that performs a redox reaction
in a negative electrode. A lithium ion battery performs a redox
reaction when releasing or storing lithium ions (for example, WO
2015/056412). The lithium ion battery includes a positive electrode
active material capable of releasing or storing lithium ions in a
positive electrode. In the lithium ion battery, lithium ions move
back and forth between a positive electrode and a negative
electrode, which is a redox reaction. Electrons move in association
therewith, and electricity flows. By extracting this flowing
electricity from the lithium ion battery, the lithium ion battery
exhibits its function.
[0017] Examples of a positive electrode material currently in
practical use and an energy density thereof include LiCoO.sub.2
(570 Wh/kg), LiFePO.sub.4 (530 Wh/kg), and LiMn.sub.2O.sub.4 (590
Wh/kg). That is, the energy density of the positive electrode
material currently in practical use is within a range of 500 Wh/kg
to 600 Wh/kg. However, since these energy densities are not
sufficient for further downsizing a battery, development of a novel
positive electrode material having a higher energy density than
these materials is desired.
[0018] A positive electrode material having a high energy density
and a method for manufacturing the same, and a battery using the
positive electrode material and a method for manufacturing the same
may be provided.
[0019] (Positive Electrode Material)
[0020] An aspect of a disclosed positive electrode material is
represented by Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2).
[0021] The aspect of the positive electrode material has a
monoclinic crystal structure and belongs to a space group
P2.sub.1/c.
[0022] The aspect of the positive electrode material has
diffraction peaks at 2.theta.=13.1.degree..+-.0.2.degree.,
14.0.degree..+-.0.2.degree., and 18.4.degree..+-.0.2.degree. in
X-ray diffraction (2.theta.=5.degree. to 90.degree.) using
synchrotron radiation having a wavelength of 1 .ANG..
[0023] Another aspect of the disclosed positive electrode material
is represented by Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2).
[0024] The other aspect of the positive electrode material has a
monoclinic crystal structure and belongs to the space group
P2.sub.1/c.
[0025] The other aspect of the positive electrode material has
diffraction peaks at 2.theta.=13.1.degree..+-.0.2.degree.,
14.0.degree.+0.2.degree., and 18.4.degree..+-.0.2.degree. in X-ray
diffraction (2.theta.=5.degree. to 90.degree.) using synchrotron
radiation having a wavelength of 1 .ANG..
[0026] There have been various reports on a positive electrode
material so far, and one of the reports is a report on crystalline
Li.sub.2CoP.sub.2O.sub.7 (Kim, H. et al., Chemistry of Materials
2011, 23 (17), 3930-3937). The report describes that
Li.sub.2CoP.sub.2O.sub.7 theoretically has an energy density of
1,000 Wh/kg. This energy density is about twice the energy density
of a conventional positive electrode material. There are the
following two reasons why a large energy density is expected in
this way.
[0027] A voltage is as high as 4.9 V.
[0028] If it is assumed that all the lithium ions in a positive
electrode material are used for charge/discharge as in formula (I)
below, a capacity density is as large as 216 mAh/g.
Li.sub.2CoP.sub.2O.sub.7.revreaction.CoP.sub.2O.sub.7+2Li.sup.++2e.sup.-
(I)
[0029] However, at present, only a capacity density of 90 mAh/g,
which is about 40% of a theoretical capacity density, can be
verified.
[0030] Therefore, the present inventors assumed that there was a
problem in the crystal structure of Li.sub.2CoP.sub.2O.sub.7 (ICSD
#261899) reported above. This crystal structure is illustrated in
FIG. 1. In this crystal structure, a lithium atom or cobalt atom 1,
a lithium atom 2, an oxygen atom 3, and a phosphorus atom 4 are
arranged as illustrated in FIG. 1. Here, the lithium atom or cobalt
atom 1 indicates that a unit cell in which an atom at a
corresponding position is a lithium atom and a unit cell in which
an atom at a corresponding position is a cobalt atom are mixed.
Another feature of the crystal structure is that the lithium atom
or cobalt atom 1 composes MO4 (quadra-coordinated unit) or MO5
(penta-coordinated unit) with the surrounding oxygen atom 3.
[0031] In a lithium ion battery, lithium atoms (lithium ions) move
during charge or discharge. In a positive electrode, lithium ions
are inserted into or discharged from a positive electrode material
(positive electrode active material). Therefore, in order for a
crystal of the positive electrode material to function as the
positive electrode material (positive electrode active material),
the crystal of the positive electrode material needs to be in the
following state. Even if lithium atoms (lithium ions) that move
during charge or discharge are inserted into or discharged from the
crystal of the positive electrode material, it is necessary for the
crystal structure of the positive electrode material not to change
or to be able to reversibly change.
[0032] In Li.sub.2CoP.sub.2O.sub.7, when some of lithium atoms are
arranged at positions important for maintaining the crystal
structure of Li.sub.2CoP.sub.2O.sub.7, the lithium atoms are used
only for maintaining the crystal structure. Therefore, the lithium
atoms cannot be used for exchange between a positive electrode and
a negative electrode during charge/discharge, in other words, for a
redox reaction. This may be a reason why a theoretical capacity
value cannot be verified in the reported positive electrode
material.
[0033] Therefore, the present inventors studied
Li.sub.2CoP.sub.2O.sub.7 having different crystal structures. As a
result, the present inventors have found L.sub.2CoP.sub.2O.sub.7
having the crystal structure illustrated in FIG. 2 and have
completed the present invention.
[0034] Furthermore, the present inventors have found that
Li.sub.2FeP.sub.2O.sub.7 in which the cobalt atom is replaced with
an iron atom in the crystal structure illustrated in FIG. 2 can
also be used as the positive electrode material.
[0035] In the positive electrode material, the number of oxygen
atoms coordinated to a cobalt atom or an iron atom is preferably 4
to 5.
[0036] The number of oxygen atoms coordinated to the cobalt atom or
the iron atom can be calculated by estimating a distance between
the cobalt atom and each of the oxygen atoms or a distance between
the iron atom and each of the oxygen atoms in the crystal
structure. The distance between the cobalt atom and each of the
oxygen atoms or the distance between the iron atom and each of the
oxygen atoms can be calculated by simulation from the height of a
peak (peak intensity) in X-ray diffraction. For example, in the
crystal structure of the disclosed positive electrode material, an
ideal distance between the cobalt atom or the iron atom and each of
the oxygen atoms is 2.2 .ANG. to 2.8 .ANG.. From this fact, it is
possible to count the oxygen atoms located at a distance of 2.2
.ANG. to 2.8 .ANG. around the cobalt atom or the iron atom to count
the oxygen atoms coordinated to the cobalt atom or the iron
atom.
[0037] In FIG. 2, the polyhedron centered around the lithium or
cobalt atom 1 is a polyhedron representing oxygen atoms located at
a distance of 2.5 .ANG. away from the cobalt atom.
[0038] <Peak of X-Ray Diffraction>
[0039] Among the positive electrode materials of the present
invention, the positive electrode material represented by a
composition formula Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2) has diffraction peaks at the following
positions in X-ray diffraction (2.theta.=5.degree. to 90.degree.)
using synchrotron radiation having a wavelength of 1 .ANG..
[0040] 2.theta.=13.1.degree..+-.0.2.degree.,
14.0.degree..+-.0.2.degree., and 18.4.degree..+-.0.2.degree.
[0041] FIG. 3 illustrates a portion of 2.theta.=7.5.degree. to
20.5.degree. in the X-ray diffraction chart of the positive
electrode material (Li.sub.2CoP.sub.2O.sub.7) of the present
invention. As illustrated in FIG. 3, among the several peaks, peaks
with higher intensity than other peaks appear at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree.. Therefore, in X-ray diffraction,
having diffraction peak at 2.theta.=13.1.degree..+-.0.2.degree.,
14.0.degree..+-.0.2.degree., and 18.4.degree..+-.0.2.degree. means
that these peaks indicate extremely higher intensity than other
peaks.
[0042] Among the positive electrode materials of the present
invention, the positive electrode material represented by a
composition formula Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7
(-0.2.ltoreq.x.ltoreq.0.2) has diffraction peaks at the following
positions in X-ray diffraction (2.theta.=5.degree. to 90.degree.)
using synchrotron radiation having a wavelength of 1 .ANG..
[0043] 2.theta.=13.1.degree..+-.0.2.degree.,
14.0.degree..+-.0.2.degree., and 18.4.degree..+-.0.2.degree.
[0044] As lattice constants of the positive electrode material,
a=8.2 .ANG., b=13.5 .ANG., c=9.7 .ANG., and .beta.=148.degree. are
preferably satisfied.
[0045] The lattice constants of the positive electrode material can
be calculated from the X-ray diffraction data described above.
[0046] (Method for Manufacturing Positive Electrode Material)
[0047] A disclosed method for manufacturing a positive electrode
material is not particularly limited and can be appropriately
selected depending on a purpose, but the following method for
manufacturing a positive electrode material is preferable.
[0048] An aspect of the disclosed method for manufacturing a
positive electrode material includes a step of heat-treating a
mixture of a lithium source, a cobalt source, and a phosphoric acid
source, and further includes another step such as a mixing step, if
necessary.
[0049] The aspect of the method for manufacturing a positive
electrode material is a method for manufacturing a positive
electrode material, satisfying the following (1) to (3).
[0050] (1) Represented by a composition formula
Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0051] (2) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0052] (3) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0053] Another aspect of the disclosed method for manufacturing a
positive electrode material includes a step of heat-treating a
mixture of a lithium source, an iron source, and a phosphoric acid
source, and further includes another step such as a mixing step, if
necessary.
[0054] The other aspect of the method for manufacturing a positive
electrode material is a method for manufacturing a positive
electrode material, satisfying the following (4) to (6).
[0055] (4) Represented by a composition formula
Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0056] (5) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0057] (6) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0058] <Mixing Step>
[0059] The mixing step is not particularly limited as long as being
a step of mixing a lithium source, a cobalt source, and a
phosphoric acid source to obtain a mixture thereof, and can be
appropriately selected depending on a purpose. For example, the
mixing step can be performed using a planetary ball mill. When this
mixing step is used, a positive electrode material represented by a
composition formula Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7 is
obtained.
[0060] The mixing step is not particularly limited as long as being
a step of mixing a lithium source, an iron source, and a phosphoric
acid source to obtain a mixture thereof, and can be appropriately
selected depending on a purpose. For example, the mixing step can
be performed using a planetary ball mill. When this mixing step is
used, a positive electrode material represented by a composition
formula Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7 is obtained.
[0061] Examples of the lithium source include a lithium salt.
[0062] An anion constituting the lithium salt is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the anion include a hydroxide ion, a carbonate ion, an
oxalate ion, an acetate ion, a nitrate anion, a sulfate anion, a
phosphate ion, a fluorine ion, a chlorine ion, a bromine ion, and
an iodine ion.
[0063] These anions may be used singly or in combination of two or
more types thereof.
[0064] Furthermore, the lithium salt is not particularly limited
and can be appropriately selected depending on a purpose. Examples
of the lithium salt include lithium hydroxide (LiON), lithium
carbonate (Li.sub.2CO.sub.3), lithium nitrate (LiNO.sub.3), lithium
sulfate (Li.sub.2SO.sub.4), lithium perchlorate (LiClO.sub.4),
lithium hexafluorophosphate (LiPF.sub.6), lithium tetrafluoroborate
(LiBF.sub.4), and the like. These salts may be hydrates or
anhydrides. Among these salts, lithium carbonate and lithium
nitrate are preferable because lithium carbonate and lithium
nitrate do not cause a side reaction.
[0065] Examples of the cobalt source include a cobalt salt or the
like.
[0066] An anion constituting the cobalt salt is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the anion include a carbonate ion, an oxalate ion, an
acetate ion, a nitrate anion, a sulfate anion, a phosphate ion, a
fluorine ion, a chlorine ion, a bromine ion, an iodine ion, and the
like. These anions may be used singly or in combination of two or
more types thereof.
[0067] Furthermore, the cobalt salt is not particularly limited and
can be appropriately selected depending on a purpose. Examples of
the cobalt salt include cobalt oxalate, cobalt nitrate, cobalt
sulfate, cobalt chloride, and the like. These salts may be hydrates
or anhydrides.
[0068] Examples of the iron source include an Iron salt or the
like.
[0069] An anion constituting the iron salt is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the anion include an oxide ion, a carbonate ion, an
oxalate ion, an acetate ion, a nitrate anion, a sulfate anion, a
phosphate ion, a fluorine ion, a chlorine ion, a bromine ion, an
iodine ion, and the like.
[0070] These anions may be used singly or in combination of two or
more types thereof.
[0071] Furthermore, the iron salt is not particularly limited and
can be appropriately selected depending on a purpose. Examples of
the iron salt include ferrous oxide, iron oxalate (II), iron
nitrate (II), iron sulfate (II), iron chloride (II), and the like.
These salts may be hydrates or anhydrides.
[0072] Examples of the phosphoric acid source include phosphoric
acid, a phosphate, and the like.
[0073] A cation constituting the phosphate is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the cation include an ammonium ion or the like.
[0074] Examples of the phosphate include ammonium phosphate,
ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and
the like.
[0075] Furthermore, instead of the lithium source and the
phosphoric add source, lithium phosphate, dilithium hydrogen
phosphate, lithium dihydrogen phosphate, or the like may be used as
a compound serving as the lithium source and the phosphoric acid
source.
[0076] A ratio among the lithium source, the cobalt source, and the
phosphoric acid source at the time of mixing is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the ratio include Li:Co:P=1.6 to 2.4:0.8 to 1.2:2.0
(element ratio) or the like.
[0077] A ratio among the lithium source, the iron source, and the
phosphoric add source at the time of mixing is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the ratio include Li:Fe:P=1.6 to 2.4:0.8 to 1.2:2.0
(element ratio) or the like.
[0078] <Heat Treatment Step>
[0079] The heat treatment step is not particularly limited as long
as the above-described mixture is heat-treated, and can be
appropriately selected depending on a purpose.
[0080] The number of times for performing the heat treatment step
is not particularly limited and can be appropriately selected
depending on a purpose, but is preferably two.
[0081] A first heat treatment step is performed in order to remove
carbon dioxide and ammonia generated from the lithium source, the
phosphoric add source, the cobalt source, the iron source, and the
like.
[0082] The temperature of the first heat treatment is not
particularly limited and can be appropriately selected depending on
a purpose, but is preferably 500.degree. C. or higher and
720.degree. C. or lower.
[0083] The time of the first heat treatment is not particularly
limited and can be appropriately selected depending on a purpose,
but is preferably one hour or more and 24 hours or less, more
preferably two hours or more and 18 hours or less, and particularly
preferably three hours or more and 15 hours or less.
[0084] A second heat treatment is performed in order to bring the
mixture into a desired crystal structure. When the heat treatment
is performed only once, the following conditions for the second
heat treatment are used as heat treatment conditions.
[0085] The temperature of the second heat treatment is not
particularly limited and can be appropriately selected depending on
a purpose, but is preferably 420.degree. C. or higher and
520.degree. C. or lower, and more preferably 450.degree. C. or
higher and 510.degree. C. or lower. When the heat treatment
temperature is lower than 420.degree. C. or higher than 520.degree.
C., the desired crystal structure cannot be necessarily
obtained.
[0086] The time of the heat treatment is not particularly limited
and can be appropriately selected depending on a purpose, but is
preferably one hour or more and 24 hours or less.
[0087] The heat treatment is preferably performed in an inert
atmosphere. Examples of the inert atmosphere include an argon
atmosphere or the like.
[0088] (Battery)
[0089] A disclosed battery includes a positive electrode containing
a positive electrode material, a negative electrode, and an
electrolyte disposed between the positive electrode and the
negative electrode, and further includes other members, if
necessary.
[0090] An aspect of the battery includes a positive electrode
containing a positive electrode material satisfying the following
(1) to (3).
[0091] (1) Represented by a composition formula
Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0092] (2) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0093] (3) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0094] The battery uses the disclosed positive electrode material
having a high energy density. Therefore, the disclosed battery is a
battery having a high energy density.
[0095] Another aspect of the battery includes a positive electrode
containing a positive electrode material satisfying the following
(4) to (6).
[0096] (4) Represented by a composition formula
Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0097] (5) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0098] (6) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0099] The battery includes, for example, at least a positive
electrode, and further includes other members such as a negative
electrode, an electrolyte, a separator, a positive electrode case,
and a negative electrode case, if necessary.
[0100] <<Positive Electrode>>
[0101] The positive electrode contains at least the disclosed
positive electrode material, and further contains another part such
as a positive electrode current collector, if necessary.
[0102] In the positive electrode, the positive electrode material
functions as a so-called positive electrode active material.
[0103] The content of the positive electrode material in the
positive electrode is not particularly limited and can be
appropriately selected depending on a purpose.
[0104] In the positive electrode, the positive electrode material
may be mixed with a conductive material and a binder to form a
positive electrode layer.
[0105] The conductive material is not particularly limited and can
be appropriately selected depending on a purpose. Examples of the
conductive material include a carbon-based conductive material or
the like. Examples of the carbon-based conductive material include
acetylene black, carbon black and the like.
[0106] The binder is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
binder include polytetrafluoroethylene (PTFE), polyvinylidene
fluoride (PVDF), ethylene-propylene-butadiene rubber (EPBR),
styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and
the like.
[0107] The material, size, and structure of the positive electrode
are not particularly limited and can be appropriately selected
depending on a purpose.
[0108] The shape of the positive electrode is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the shape include a rod shape, a disk shape, and the
like.
[0109] --Positive Electrode Current Collector--
[0110] The shape, size, and structure of the positive electrode
current collector are not particularly limited and can be
appropriately selected depending on a purpose.
[0111] The material of the positive electrode current collector is
not particularly limited and can be appropriately selected
depending on a purpose. Examples of the material include stainless
steel, aluminum, copper, nickel, and the like.
[0112] The positive electrode current collector is used for
favorably conducting a positive electrode layer to a positive
electrode case that is a terminal.
[0113] <<Negative Electrode>>
[0114] The negative electrode contains at least a negative
electrode active material, and further contains another part such
as a negative electrode current collector, if necessary.
[0115] The size, and structure of the negative electrode are not
particularly limited and can be appropriately selected depending on
a purpose.
[0116] The shape of the negative electrode is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the shape include a rod shape, a disk shape, and the
like.
[0117] --Negative Electrode Active Material--
[0118] The negative electrode active material is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the negative electrode active material include a
compound containing an alkali metal element.
[0119] Examples of the compound containing an alkali metal element
include a metal simple substance, an alloy, a metal oxide, a metal
nitride, and the like.
[0120] Examples of the alkali metal element include lithium or the
like.
[0121] Examples of the metal simple substance include lithium or
the like.
[0122] Examples of the alloy include an alloy containing lithium or
the like. Examples of the alloy containing lithium include a
lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy,
a lithium silicon alloy, and the like.
[0123] Examples of the metal oxide include a metal oxide containing
lithium or the like. Examples of the metal oxide containing lithium
include lithium titanium oxide or the like.
[0124] Examples of the metal nitride include a metal nitride
containing lithium, or the like. Examples of the metal nitride
containing lithium include lithium cobalt nitride, lithium iron
nitride, and lithium manganese nitride, and the like.
[0125] The content of the negative electrode active material in the
negative electrode is not particularly limited and can be
appropriately selected depending on a purpose.
[0126] In the negative electrode, the negative electrode active
material may be mixed with a conductive material and a binder to
form a negative electrode layer.
[0127] The conductive material is not particularly limited and can
be appropriately selected depending on a purpose. Examples of the
conductive material include a carbon-based conductive material or
the like. Examples of the carbon-based conductive material include
acetylene black, carbon black and the like.
[0128] The binder is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
binder include polytetrafluoroethylene (PTFE), polyvinylidene
fluoride (PVDF), ethylene-propylene-butadiene rubber (EPBR),
styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and
the like.
[0129] --Negative Electrode Current Collector--
[0130] The shape, size, and structure of the negative electrode
current collector are not particularly limited and can be
appropriately selected depending on a purpose.
[0131] The material of the negative electrode current collector is
not particularly limited and can be appropriately selected
depending on a purpose. Examples of the material include stainless
steel, aluminum, copper, nickel, and the like.
[0132] The negative electrode current collector is used for
favorably conducting a negative electrode layer to a negative
electrode case that is a terminal.
[0133] <<Electrolyte>>
[0134] The electrolyte is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
electrolyte include a non-aqueous electrolytic solution, a solid
electrolyte, and the like.
[0135] --Non-Aqueous Electrolytic Solution--
[0136] Examples of the non-aqueous electrolytic solution include a
non-aqueous electrolytic solution containing a lithium salt, an
organic solvent, and the like.
[0137] --Lithium Salt--
[0138] The lithium salt is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
lithium salt include lithium hexafluorophosphate, lithium
tetrafluoroborate, lithium perchlorate, lithium
bis(pentafluoroethanesulfone) imide, lithium
bis(trifluoromethanesulfone) imide, and the like. These lithium
salts may be used singly or in combination of two or more types
thereof.
[0139] The concentration of the lithium salt is not particularly
limited and can be appropriately selected depending on a purpose,
but is preferably 0.5 mol/L to 3 mol/L in the organic solvent from
a viewpoint of ionic conductivity.
[0140] --Organic Solvent--
[0141] The organic solvent is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
organic solvent include ethylene carbonate, dimethyl carbonate,
propylene carbonate, diethyl carbonate, ethyl methyl carbonate, and
the like. These organic solvents may be used singly or in
combination of two or more types thereof.
[0142] The content of the organic solvent in the non-aqueous
electrolytic solution is not particularly limited and can be
appropriately selected depending on a purpose, but is preferably
75% by mass to 95% by mass, and more preferably 80% by mass to 90%
by mass.
[0143] When the content of the organic solvent is less than 75% by
mass, the viscosity of the non-aqueous electrolytic solution
increases, and the wettability to an electrodes decreases.
Therefore, the internal resistance of the battery may increase.
When the content of the organic solvent is more than 95% by mass,
the ionic conductivity may decrease, and an output of the battery
may decrease. Meanwhile, when the content of the organic solvent is
within the above-described more preferable range, high ionic
conductivity can be maintained, the viscosity of the non-aqueous
electrolytic solution can be suppressed, and the wettability to an
electrode can be thereby maintained advantageously.
[0144] --Solid Electrolyte--
[0145] The solid electrolyte is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
solid electrolyte include an inorganic solid electrolyte, an
intrinsic polymer electrolyte, and the like.
[0146] Examples of the inorganic solid electrolyte include a
LISICON material, a perovskite material, and the like.
[0147] Examples of the intrinsic polymer electrolyte include a
polymer or the like having an ethylene oxide bond.
[0148] The content of the electrolyte in the battery is not
particularly limited and can be appropriately selected depending on
a purpose.
[0149] <<Separator>>
[0150] The material of the separator is not particularly limited
and can be appropriately selected depending on a purpose. Examples
of the material include paper, cellophane, polyolefin nonwoven
fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and
the like. Examples of the paper include kraft paper, vinylon mixed
paper, synthetic pulp mixed paper, and the like.
[0151] The shape of the separator is not particularly limited and
can be appropriately selected depending on a purpose. Examples of
the shape include a sheet shape or the like.
[0152] The structure of the separator may be a single layer
structure or a laminated structure.
[0153] The size of the separator is not particularly limited and
can be appropriately selected depending on a purpose.
[0154] <<Positive Electrode Case>>
[0155] The material of the positive electrode case is not
particularly limited and can be appropriately selected depending on
a purpose. Examples of the material include copper, stainless
steel, and a metal of stainless steel or iron plated with nickel or
the like.
[0156] The shape of the positive electrode case is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the shape include a dish shape with a warped-up
periphery and a shallow bottom, a bottomed cylinder shape, a
bottomed prismatic column shape, and the like.
[0157] The structure of the positive electrode case may be a single
layer structure or a laminated structure. Examples of the laminated
structure include a three-layer structure of nickel, stainless
steel, copper, and the like.
[0158] The size of the positive electrode case is not particularly
limited and can be appropriately selected depending on a
purpose.
[0159] <<Negative Electrode Case>>
[0160] The material of the negative electrode case is not
particularly limited and can be appropriately selected depending on
a purpose. Examples of the material include copper, stainless
steel, and a metal of stainless steel or iron plated with nickel or
the like.
[0161] The shape of the negative electrode case is not particularly
limited and can be appropriately selected depending on a purpose.
Examples of the shape include a dish shape with a warped-up
periphery and a shallow bottom, a bottomed cylindrical shape, a
bottomed prismatic shape, and the like.
[0162] The structure of the negative electrode case may be a single
layer structure or a laminated structure. Examples of the laminated
structure include a three-layer structure of nickel, stainless
steel, copper, and the like.
[0163] The size of the negative electrode case is not particularly
limited and can be appropriately selected depending on a
purpose.
[0164] The shape of the battery is not particularly limited and can
be appropriately selected depending on a purpose. Examples of the
shape include a coin shape, a cylindrical shape, a rectangular
shape, a sheet shape, and the like.
[0165] An example of the disclosed lithium ion secondary battery
will be described with reference to a drawing. FIG. 4 is a
schematic cross-sectional view illustrating a lithium ion secondary
battery which is an example of the disclosed battery.
[0166] The lithium ion secondary battery illustrated in FIG. 4 is a
coin type lithium ion secondary battery. The coin type lithium ion
secondary battery includes a positive electrode 10 including a
positive electrode current collector 11 and a positive electrode
layer 12, a negative electrode 20 including a negative electrode
current collector 21 and a negative electrode layer 22, and an
electrolyte layer 30 interposed between the positive electrode 10
and the negative electrode 20. In the lithium ion secondary battery
of FIG. 4, the positive electrode current collector 11 and the
negative electrode current collector 21 are fixed to a positive
electrode case 41 and a negative electrode case 42 via a current
collector 43, respectively. A gap between the positive electrode
case 41 and the negative electrode case 42 is sealed with a packing
material 44, for example, made of polypropylene. The current
collector 43 is used for filling a gap between the positive
electrode current collector 11 and the positive electrode case 41
and a gap between the negative electrode current collector 21 and
the negative electrode case 42 and achieving conduction.
[0167] Here, the positive electrode layer 12 is manufactured using
the disclosed positive electrode material.
[0168] (Method for Manufacturing Battery)
[0169] A disclosed method for manufacturing a battery is a method
for obtaining the above-described battery.
[0170] The disclosed method for manufacturing a battery is a method
for manufacturing a battery including a positive electrode
containing a positive electrode material, a negative electrode, and
an electrolyte disposed between the positive electrode and the
negative electrode.
[0171] An aspect of the method for manufacturing a battery includes
a step of heat-treating a mixture of a lithium source, a cobalt
source, and a phosphoric add source to obtain a positive electrode
material, and further includes another step such as a step of
assembling a positive electrode, a negative electrode, and the like
into a desired structure, if necessary.
[0172] In the aspect of the method for manufacturing a battery, the
positive electrode material satisfies the following (1) to (3).
[0173] (1) Represented by a composition formula
Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0174] (2) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0175] (3) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0176] The disclosed battery uses the disclosed positive electrode
material having a high energy density. In addition, the disclosed
battery then is a battery having a high energy density. Therefore,
the disclosed method for manufacturing a battery is a method for
obtaining a battery having a high energy density.
[0177] Another aspect of the method for manufacturing a battery
includes a step of heat-treating a mixture of a lithium source, an
iron source, and a phosphoric acid source to obtain a positive
electrode material, and further includes another step such as a
step of assembling a positive electrode, a negative electrode, and
the like into a desired structure, if necessary.
[0178] In the other aspect of the method for manufacturing a
battery, the positive electrode material satisfies the following
(4) to (6).
[0179] (4) Represented by a composition formula
Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0180] (5) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0181] (6) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2.degree.,
and 18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0182] (Electronic Device)
[0183] A disclosed electronic device includes a battery and an
electronic circuit, and further includes other members, if
necessary.
[0184] <Battery>
[0185] The battery includes a positive electrode containing a
positive electrode material, a negative electrode, and an
electrolyte disposed between the positive electrode and the
negative electrode, and further includes other members, if
necessary.
[0186] The negative electrode, the electrolyte, and the other
members are not particularly limited and can be appropriately
selected depending on a purpose, but the above-described ones are
preferably used.
[0187] An aspect of the a battery includes a positive electrode
containing a positive electrode material satisfying the following
(1) to (3).
[0188] (1) Represented by a composition formula
Li.sub.2-2xCo.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0189] (2) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0190] (3) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2, and
18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0191] The battery uses the disclosed positive electrode material
having a high energy density. Therefore, the disclosed battery is a
battery having a high energy density. In addition, the disclosed
electronic device includes a battery having a high energy
density.
[0192] Another aspect of the battery includes a positive electrode
containing a positive electrode material satisfying the following
(4) to (6).
[0193] (4) Represented by a composition formula
Li.sub.2-2xFe.sub.1+xP.sub.2O.sub.7 (-0.2.ltoreq.x.ltoreq.0.2).
[0194] (5) Having a monoclinic crystal structure belonging to a
space group P2.sub.1/c.
[0195] (6) Having diffraction peaks at
2.theta.=13.1.degree..+-.0.2.degree., 14.0.degree..+-.0.2, and
18.4.degree..+-.0.2.degree. in X-ray diffraction
(2.theta.=5.degree. to 90.degree.) using synchrotron radiation
having a wavelength of 1 .ANG..
[0196] The shape and size of the battery are not particularly
limited and can be appropriately selected depending on a
purpose.
[0197] The number of batteries included in the electronic device is
not particularly limited and can be appropriately selected
depending on a purpose. For example, a battery pack including a
plurality of batteries may be incorporated into the electronic
device.
[0198] <Electronic Circuit>
[0199] The electronic circuit is electrically connected to the
positive electrode and the negative electrode.
[0200] The material, shape, and size of the electronic circuit are
not particularly limited and can be appropriately selected
depending on a purpose.
[0201] The electronic circuit may include, for example, a central
processing unit (CPU), a peripheral logic unit, an interface unit,
and a storage unit, and may control the entire electronic
device.
[0202] The electronic device is not particularly limited and can be
appropriately selected depending on a purpose. Examples of the
electronic device include the following devices. Examples of the
electronic device include a notebook personal computer, a tablet
computer, a mobile phone (such as a smartphone), a personal digital
assistant (PDA), an imaging device (such as a digital still camera
or a digital video camera), an audio device (such as a portable
audio player), a game device, a cordless phone handset, an
electronic book, an electronic dictionary, a radio, a headphone, a
navigation system, a memory card, a pacemaker, a hearing aid, a
lighting device, a toy, a medical device, and a robot.
[0203] An example of the disclosed electronic device will be
described with reference to a drawing. FIG. 8 is a schematic
cross-sectional view illustrating an example of the disclosed
electronic device. An electronic device 001 includes an electronic
circuit 002 which is a main body of the electronic device and a
battery pack 003. The battery pack 003 is electrically connected to
the electronic circuit 002 via a positive electrode terminal 003a
and a negative electrode terminal 003b. The electronic device 001
has, for example, a configuration in which a user can attach and
detach the battery pack 003. Note that the configuration of the
electronic device 001 is not limited to this configuration, and may
be a configuration in which the battery pack 003 is built in the
electronic device 001 such that a user cannot remove the battery
pack 003 from the electronic device 001.
[0204] The battery pack 003 includes an assembled battery 004 and a
charge/discharge circuit 005. The assembled battery 004 is
configured by connecting a plurality of secondary batteries 004a to
each other in series and/or in parallel. The plurality of batteries
004a is connected to each other, for example, such that n batteries
are arranged in parallel and m batteries are arranged in series (n
and m are positive integers). As the battery 004a, the battery
described above or a modification thereof is used. Instead of the
assembled battery 004, only one secondary battery 004a may be
included.
[0205] The electronic circuit 002 includes, for example, a central
processing unit (CPU), a peripheral logic unit, an interface unit,
and a storage unit, and controls the entire electronic device
001.
[0206] When the battery pack 003 is charged, the positive electrode
terminal 003a and the negative electrode terminal 003b of the
battery pack 003 are connected to a positive electrode terminal and
a negative electrode terminal of a charger (not illustrated),
respectively. Meanwhile, when the battery pack 003 is discharged
(when the electronic device 001 is used), the positive electrode
terminal 003a and the negative electrode terminal 003b of the
battery pack 003 are connected to a positive electrode terminal and
a negative electrode terminal of the electronic circuit 002,
respectively.
[0207] During charge, the charge/discharge circuit 005 controls
charge of the assembled battery 004. Meanwhile, during discharge
(that is, when the electronic device 001 is used), the
charge/discharge circuit 005 controls discharge of the electronic
device 001.
EXAMPLES
[0208] Hereinafter, Examples of the disclosed technology will be
described, but the disclosed technology is not limited to the
following Examples.
[0209] The following raw materials used in Examples and Comparative
Examples were obtained from each of the following companies for
use.
[0210] Lithium carbonate: Kojundo Chemical Lab. Co., Ltd.
[0211] Cobalt oxalate dihydrate: Junsei Chemical Co., Ltd.
[0212] Iron oxalate dihydrate: Junsei Chemical Co., Ltd.
[0213] Diammonium hydrogen phosphate: Wako Pure Chemical
Industries, Ltd.
[0214] Cobalt oxide: Sigma-Aldrich Japan Co., Ltd.
Example 1
[0215] <Preparation of Positive Electrode Material>
[0216] Lithium carbonate (2.96 g), cobalt oxalate dihydrate (7.32
g), and diammonium hydrogen phosphate (10.56 g) were put in a
planetary ball mill container. Thereafter, the planetary ball mill
container was disposed in a ball mill device, and the ball mill
device was driven to mix the raw materials. The resulting mixture
was fired at 600.degree. C. for 12 hours in an argon atmosphere.
The resulting fired product was pulverized with the planetary ball
mill to obtain amorphous Li.sub.2CoP.sub.2O.sub.7. The amorphous
Li.sub.2CoP.sub.2O.sub.7 was further annealed at 500.degree. C. for
30 minutes in an argon atmosphere to obtain
Li.sub.2CoP.sub.2O.sub.7 having a crystal structure, which is a
positive electrode material.
[0217] (A) of FIG. 5 illustrates a synchrotron radiation
diffraction (X-ray diffraction) spectrum of the resulting positive
electrode material at a wavelength of 1 .ANG.. The obtained
spectrum had diffraction peaks with large intensity at
2.theta.=13.1.degree., 14.0.degree., and 18.4.degree.. The crystal
structure of Li.sub.2CoP.sub.2O.sub.7 was analyzed using this
spectrum. As a result, it was found that the crystal structure had
a monoclinic crystal phase belonging to a space group P2.sub.1/c.
The lattice constants are as follows.
[0218] [Lattice Constant]
[0219] a=8.2 .ANG.
[0220] b=13.5 .ANG.
[0221] c=9.7 .ANG.
[0222] .beta.=148.degree.
Example 2
[0223] Lithium carbonate (3.55 g), cobalt oxalate dihydrate (5.86
g), and diammonium hydrogen phosphate (10.56 g) were put in a
planetary ball mill container. Thereafter, the planetary ball mill
container was disposed in a ball mill device, and the ball mill
device was driven to mix the raw materials. The resulting mixture
was fired at 600.degree. C. for 12 hours in an argon atmosphere.
The resulting fired product was pulverized with the planetary ball
mill to obtain amorphous Li.sub.2.4Co.sub.0.8P.sub.2O.sub.7. The
amorphous Li.sub.2.4Co.sub.0.8P.sub.2O.sub.7 was further annealed
at 500.degree. C. for 30 minutes in an argon atmosphere to obtain
Li.sub.2.4Co.sub.0.8P.sub.2O.sub.7 having a crystal structure,
which is a positive electrode material.
[0224] The obtained positive electrode material was measured for
synchrotron radiation diffraction (X-ray diffraction) at a
wavelength of 1 .ANG.. As a result, a diffraction pattern similar
to that of (A) of FIG. 5 was obtained, and it was found that the
crystal lattice was similar to that of the positive electrode
material in Example 1.
Example 3
[0225] Lithium carbonate (2.37 g), cobalt oxalate dihydrate (8.78
g), and diammonium hydrogen phosphate (10.56 g) were put in a
planetary ball mill container. Thereafter, the planetary ball mill
container was disposed in a ball mill device, and the ball mill
device was driven to mix the raw materials. The resulting mixture
was fired at 600.degree. C. for 12 hours in an argon atmosphere.
The resulting fired product was pulverized with the planetary ball
mill to obtain amorphous Li.sub.1.6Co.sub.1.2P.sub.2O.sub.7. The
amorphous Li.sub.1.6Co.sub.1.2P.sub.2O.sub.7 was further annealed
at 500.degree. C. for 30 minutes in an argon atmosphere to obtain
Li.sub.1.6Co.sub.1.2P.sub.2O.sub.7 having a crystal structure.
[0226] The obtained positive electrode material was measured for
synchrotron radiation diffraction (X-ray diffraction) at a
wavelength of 1 .ANG.. As a result, a diffraction pattern similar
to that of (A) of FIG. 5 was obtained, and it was found that the
crystal lattice was similar to that of the positive electrode
material in Example 1.
Comparative Example 1
[0227] Lithium carbonate (2.96 g), cobalt oxalate dihydrate (7.32
g), and diammonium hydrogen phosphate (10.56 g) were put in a
planetary ball mill container. Thereafter, the planetary ball mill
container was disposed in a ball mill device, and the ball mill
device was driven to mix the raw materials. The resulting mixture
was fired at 600.degree. C. for 12 hours in an argon atmosphere to
obtain L.sub.2CoP.sub.2O.sub.7 having a crystal structure, which is
a positive electrode material.
[0228] (8) of FIG. 5 illustrates a synchrotron radiation
diffraction experiment spectrum of the resulting positive electrode
material at a wavelength of 1 .ANG.. The obtained spectrum had
diffraction peaks with large intensity at 2.theta.=9.3.degree.,
10.7.degree., 16.3.degree., 17.1, 18.7.degree., 21.3.degree., and
21.6.degree.. The crystal structure of Li.sub.2CoP.sub.2O.sub.7 was
analyzed using this spectrum. As a result, it was found that the
crystal structure had a monoclinic crystal phase belonging to a
space group P2.sub.1/c. The lattice constants are as follows.
[0229] [Lattice Constant]
[0230] a=9.8 .ANG.
[0231] b=9.7 .ANG.
[0232] c=11.0 .ANG.
[0233] .beta.=102.degree.
Comparative Example 2
[0234] Lithium carbonate (2.96 g), cobalt oxalate dihydrate (7.32
g), and diammonium hydrogen phosphate (10.56 g) were put in a
planetary ball mill container. Thereafter, the planetary ball mill
container was disposed in a ball mill device, and the ball mill
device was driven to mix the raw materials. The resulting mixture
was fired at 600.degree. C. for 12 hours in an argon atmosphere.
The resulting fired product was pulverized with the planetary ball
mill to obtain amorphous Li.sub.2CoP.sub.2O.sub.7. The amorphous
Li.sub.2CoP.sub.2O.sub.7 was further annealed at 550.degree. C. for
30 minutes in an argon atmosphere to obtain
Li.sub.2CoP.sub.2O.sub.7 having a crystal structure, which is a
positive electrode material.
[0235] The obtained positive electrode material was measured for
synchrotron radiation diffraction (X-ray diffraction) at a
wavelength of 1 .ANG.. As a result, a diffraction spectrum similar
to that in Comparative Example 1 was obtained ((B) of FIG. 5). The
crystal structure of Li.sub.2CoP.sub.2O.sub.7 was analyzed using
this spectrum. As a result, it was found that the crystal structure
had a monoclinic crystal phase belonging to a space group
P2.sub.1/c. The lattice constants are as follows.
[0236] [Lattice Constant]
[0237] a=9.8 .ANG.
[0238] b=9.7 .ANG.
[0239] c=11.0 .ANG.
[0240] .beta.=102.degree.
Comparative Example 3
[0241] Li.sub.2CO.sub.3 (1.1084 g), Co.sub.3O.sub.4 (2.4080 g), and
(NH.sub.4).sub.2HPO.sub.4 (7.9234 g) weighed according to a
stoichiometric ratio were put in a planetary ball mill container.
Thereafter, the planetary ball mill container was disposed in a
ball mill device, and the ball mill device was driven to mix the
raw materials. The resulting mixture was fired at 1,100.degree. C.
in an argon atmosphere to obtain LiCoP.sub.2O.sub.7 which is a
positive electrode material.
[0242] The obtained positive electrode material was measured for
synchrotron radiation diffraction (X-ray diffraction) at a
wavelength of 1 .ANG.. Crystal analysis was performed using the
obtained spectrum. As a result, it was found that the mixture was
not a single phase mixture but a multiphase mixture of
Li.sub.2CoP.sub.2O.sub.7 and LiCo.sub.2P.sub.3O.sub.10 (ICSD
#82382), having a known structure.
Example 4
[0243] <Preparation of Half Cell>
[0244] A half cell was prepared using the positive electrode
material (positive electrode active material) prepared in Example
1.
[0245] A mixed agent containing the positive electrode material,
conductive carbon (Ketjen Black, Lion Co., ECP600JD), and
polyvinylidene fluoride (Kureha Co., Ltd., KF #1300) at a mass
ratio (positive electrode active
material:conductivecarbon:polyvinylidene fluoride) of 85:10:5 was
used as a positive electrode.
[0246] As an electrolytic solution, a 1 M solution obtained by
dissolving lithium bis(trifluorosulfonyl) imide (LiTFSI) in
1-methyl-1-propylpyrrolidinium bis(trifluorosulfonyl) imide
(MPPyr-TFSI) (purchased from Kishida Chemical Co., Ltd.) was
used.
[0247] Metallic lithium was used as a negative electrode.
[0248] <Constant Current Charge/Discharge Test>
[0249] A constant current charge/discharge test was performed on
the prepared half cell. Conditions of the constant current
charge/discharge test are as follows.
[0250] Both charge and discharge were terminated at a voltage
value. Charge was terminated at 5.7 V. Discharge was terminated at
2.0 V.
[0251] A discharge capacity of 160 mAh/g was obtained from the
prepared half cell.
[0252] FIG. 6 illustrates a constant current charge/discharge
curve.
Comparative Example 4
[0253] <Preparation of Half Cell and Constant Current
Charge/Discharge Test>
[0254] A half cell was prepared in a similar manner to Example 4
except that the positive electrode material in Example 4 was
replaced with the positive electrode material prepared in
Comparative Example 1.
[0255] A constant current charge/discharge test was performed on
the prepared half cell. Conditions of the constant current
charge/discharge test are as follows.
[0256] Both charge and discharge were terminated at a voltage
value. Charge was terminated at 5.5 V. Discharge was terminated at
3.0 V.
[0257] A discharge capacity of 75 mAh/g was obtained from the
prepared half cell.
[0258] FIG. 6 illustrates a constant current charge/discharge
curve.
[0259] A discharge capacity of 160 mAh/g was obtained in Example 4,
and a discharge capacity of 75 mAh/g was obtained in Comparative
Example 4. The discharge capacity in Example 4 is about 74% of a
theoretical capacity. This indicates that not all the lithium atoms
are used for charge/discharge but the ratio of lithium atoms that
can be used for charge/discharge has increased as compared with the
conventional positive electrode material in Comparative Example
1.
[0260] Furthermore, from the results of Example 4, it was found
that the energy density was 860 Wh/kg, and the energy density about
1.5 times that of the conventional positive electrode material was
obtained.
[0261] In the positive electrode material of the present invention,
the valence of Co changes with charge/discharge. Here,
consideration will be given based on the result of Example 1
(discharge capacity 160 mAh/g) in a case of x=0.
[0262] A redox reaction of Li.sub.2CoP.sub.2O.sub.7 during
charge/discharge is expressed by the following formula.
[0263] Li.sub.2CoP.sub.2O.sub.7.revreaction.Li.sub.0.52
CoP.sub.2O.sub.7+1.48Li.sup.++1.48e.sup.- This indicates that an
average valence of Co changes within a range of 2 to 3.48 during
charge/discharge.
[0264] Here, similarly, by assuming that the average valence of
cobalt changes within a range of 2 to 3.48 during charge/discharge
in a case of -0.2.ltoreq.x.ltoreq.0.2, a charge/discharge reaction
and a capacity thereof in a case of x=-0.2 (Example 2) or +0.2
(Example 3) are simulated.
[0265] In a case of x=-0.2,
[0266] reaction formula:
Li.sub.2.4Co.sub.0.8P.sub.2O.sub.7.revreaction.Li.sub.1.22Co.sub.0.8P.sub-
.2O.sub.7.sup.++1.18Li.sup.++1.18e.sup.- is satisfied.
[0267] From this formula, a capacity was calculated to be 133
mAh/g.
[0268] In a case of x=+0.2,
[0269] reaction formula:
Li.sub.1.6Co.sub.1.2P.sub.2O.sub.7.revreaction.Co.sub.1.2P.sub.2O.sub.7+1-
.6Li.sup.++1.6e.sup.- is satisfied.
[0270] From this formula, a capacity was calculated to be 168
mAh/g.
[0271] From the above results, it is estimated that each of the
cases of x=-0.2 (Example 2) and +0.2 (Example 3) has a high
discharge capacity. In addition, it can also be estimated that each
of the cases of x=-0.2 (Example 2) and +0.2 (Example 3) has a high
energy density because it is estimated that each of the cases has a
high discharge capacity.
[0272] (Note that in a case of x=+0.2, the capacity is
rate-determined by the content of lithium in the positive electrode
material. Furthermore, in this case, an average valence of cobalt
is within a range of 2 to 3.33.)
Example 5
[0273] Lithium carbonate (2.96 g), iron oxalate dihydrate (7.21 g),
and diammonium hydrogen phosphate (10.56 g) were put in a planetary
ball mill container. Thereafter, the planetary ball mill container
was disposed in a ball mill device, and the ball mill device was
driven to mix the raw materials. The resulting mixture was fired at
600.degree. C. for 12 hours in an argon atmosphere. The resulting
fired product was pulverized with the planetary ball mill to obtain
amorphous Li.sub.2FeP.sub.2O.sub.7. The amorphous
Li.sub.2FeP.sub.2O.sub.7 was further annealed at 500.degree. C. for
30 minutes in an argon atmosphere to obtain
Li.sub.2FeP.sub.2O.sub.7 having a crystal structure, which is a
positive electrode material.
[0274] The obtained positive electrode material was measured for
synchrotron radiation diffraction (X-ray diffraction) at a
wavelength of 1 .ANG.. As a result, a diffraction pattern similar
to that of (A) of FIG. 5 was obtained, and it was found that the
positive electrode material had a single phase. The obtained
spectrum had diffraction peaks with large intensity at
2.theta.=13.1.degree., 14.0.degree., and 18.4.degree.. The crystal
structure of Li.sub.2FeP.sub.2O.sub.7 was analyzed using this
spectrum. As a result, it was found that the crystal structure had
a monoclinic crystal phase belonging to a space group P2.sub.1/c.
The lattice constants are as follows.
[0275] [Lattice Constant]
[0276] a=8.3 .ANG.
[0277] b=13.6 .ANG.
[0278] c=9.7 .ANG.
[0279] =148.degree.
Example 6
[0280] A half cell was prepared in a similar manner to Example 4
except that the positive electrode material in Example 4 was
replaced with the positive electrode material prepared in Example
5.
[0281] A constant current charge/discharge test was performed on
the prepared half cell. Conditions of the constant current
charge/discharge test are as follows.
[0282] Both charge and discharge were terminated at a voltage
value. Charge was terminated at 4.5 V. Discharge was terminated at
2.0 V. As a result, a discharge capacity of 89 mAh/g was obtained.
FIG. 7 illustrates a constant current charge/discharge curve.
Example 7
[0283] Using the half cell prepared in Example 4, a battery pack in
which two half cells were arranged in parallel and three half cells
were arranged in series was prepared. At this time, each of the
half cells was fully charged by being connected to a charger in
advance. When a constant current discharge test (terminated at 6.0
V) was performed on this battery pack, a plateau appeared in a
region near 14 V.
[0284] All examples and conditional language provided herein are
intended for the pedagogical purposes of aiding the reader in
understanding the invention and the concepts contributed by the
inventor to further the art, and are not to be construed as
limitations to such specifically recited examples and conditions,
nor does the organization of such examples in the specification
relate to a showing of the superiority and inferiority of the
invention. Although one or more embodiments of the present
invention have been described in detail, it should be understood
that the various changes, substitutions, and alterations could be
made hereto without departing from the spirit and scope of the
invention.
* * * * *