U.S. patent application number 14/272933 was filed with the patent office on 2014-08-28 for lithium composite metal oxide having layered structure.
This patent application is currently assigned to SUMITOMO CHEMICAL COMPANY, LIMITED. The applicant listed for this patent is SUMITOMO CHEMICAL COMPANY, LIMITED. Invention is credited to Cedric PITTELOUD, Yoshinari SAWABE, Satoshi SHIMANO.
Application Number | 20140242442 14/272933 |
Document ID | / |
Family ID | 42781092 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140242442 |
Kind Code |
A1 |
PITTELOUD; Cedric ; et
al. |
August 28, 2014 |
LITHIUM COMPOSITE METAL OXIDE HAVING LAYERED STRUCTURE
Abstract
A layered structure lithium mixed metal oxide obtained by a
method including a step of calcining a lithium mixed metal oxide
raw material containing a transition metal element and a lithium
element in a molar ratio of the lithium element to the transition
metal element of 1 or more and 2 or less, in the presence of an
inactive flux containing one or more compounds selected from the
group consisting of a carbonate of M, a sulfate of M, a nitrate of
M, a phosphate of M, a hydroxide of M, a molybdate of M, and a
tungstate of M, wherein M represents one or more elements selected
from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba.
Inventors: |
PITTELOUD; Cedric; (Muttenz,
CH) ; SAWABE; Yoshinari; (Tsukuba-shi, JP) ;
SHIMANO; Satoshi; (Tsukuba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO CHEMICAL COMPANY, LIMITED |
Tokyo |
|
JP |
|
|
Assignee: |
SUMITOMO CHEMICAL COMPANY,
LIMITED
Tokyo
JP
|
Family ID: |
42781092 |
Appl. No.: |
14/272933 |
Filed: |
May 8, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13257513 |
Sep 19, 2011 |
8758455 |
|
|
PCT/JP2010/055297 |
Mar 18, 2010 |
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14272933 |
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Current U.S.
Class: |
429/144 ;
429/231.1 |
Current CPC
Class: |
C01G 51/42 20130101;
H01M 4/5825 20130101; C01P 2004/62 20130101; Y10T 29/49108
20150115; C01G 53/42 20130101; Y02E 60/10 20130101; C01P 2004/03
20130101; C01G 53/006 20130101; H01M 4/366 20130101; H01M 4/525
20130101; H01M 10/052 20130101; C01P 2002/54 20130101; H01M 4/505
20130101; C01G 51/006 20130101; C01P 2002/76 20130101; C01P 2006/12
20130101; C01P 2006/40 20130101; C01P 2002/20 20130101 |
Class at
Publication: |
429/144 ;
429/231.1 |
International
Class: |
H01M 4/36 20060101
H01M004/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2009 |
JP |
2009-069547 |
Dec 7, 2009 |
JP |
2009-277248 |
Claims
1. A layered structure lithium mixed metal oxide obtained by a
method comprising: a step of calcining a lithium mixed metal oxide
raw material comprising a transition metal element and a lithium
element in a molar ratio of the lithium element to the transition
metal element of 1 or more and 2 or less, in the presence of an
inactive flux comprising one or more compounds selected from the
group consisting of a carbonate of M, a sulfate of M, a nitrate of
M, a phosphate of M, a hydroxide of M, a molybdate of M, and a
tungstate of M, wherein M represents one or more elements selected
from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba.
2. A positive electrode active material comprising the layered
structure lithium mixed metal oxide according to claim 1.
3. A positive electrode comprising the positive electrode active
material according to claim 2.
4. A nonaqueous electrolyte secondary battery comprising the
positive electrode according to claim 3.
5. The nonaqueous electrolyte secondary battery according to claim
4, further comprising a separator.
6. The nonaqueous electrolyte secondary battery according to claim
5, wherein the separator is made of a laminated film which has a
heat resistant porous layer and a porous film laminated to each
other.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of allowed U.S. application
Ser. No. 13/257,513, filed Sep. 19, 2011, which in turn is a
National Stage entry of International Application PCT/JP2010/055297
filed Mar. 18, 2010, claiming priority based on Japanese Patent
Application No. 2009-069547 filed Mar. 23, 2009, and Japanese
Patent Application No. 2009-277248 filed Dec. 7, 2009, the contents
of all of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method of producing a
layered structure lithium mixed metal oxide. More particularly, the
present invention relates to a method of producing a layered
structure lithium mixed metal oxide used in a positive electrode
active material for a nonaqueous electrolyte secondary battery.
BACKGROUND ART
[0003] A layered structure lithium mixed metal oxide is used as
positive electrode active materials in nonaqueous electrolyte
secondary batteries, such as a lithium secondary battery. The
lithium secondary battery has already been put into practical use
as a power source for portable telephones, notebook-sized personal
computers, and the like, and also attempted to be used in medium
and large size applications, such as applications of use for
automobiles or electric power storages.
[0004] A conventional method of producing a layered structure
lithium mixed metal oxide is described in JP-A-07-326356, which
describes a method of obtaining a layered structure lithium
nickelate as a layered structure lithium mixed metal oxide by
calcining a lithium mixed metal oxide raw material including a
mixture of nickel carbonate and lithium nitrate in the presence of
an active flux made of LiCl.
DISCLOSURE OF THE INVENTION
[0005] Incidentally, in nonaqueous electrolyte secondary batteries
used, for example, for automobile or for power tools, such as
electric tools, high output is required to be exhibited at a high
current rate. An object of the present invention is to provide a
method of producing a layered structure lithium mixed metal oxide,
by which a nonaqueous electrolyte secondary battery capable of
exhibiting high output at a high current rate can be provided.
[0006] The present invention provides the followings.
<1> A method of producing a layered structure lithium mixed
metal oxide, including a step of calcining a lithium mixed metal
oxide raw material containing a transition metal element and a
lithium element in a molar ratio of the lithium element to the
transition metal element of 1 or more and 2 or less, in the
presence of an inactive flux containing one or more compounds
selected from the group consisting of a carbonate of M, a sulfate
of M, a nitrate of M, a phosphate of M, a hydroxide of M, a
molybdate of M, and a tungstate of M, wherein M represents one or
more elements selected from the group consisting of Na, K, Rb, Cs,
Ca, Mg, Sr and Ba. <2> The method according to <1>,
wherein the lithium mixed metal oxide raw material is a mixture of
a compound of lithium and a compound of the transition metal
element. <3> The method according to <2>, wherein the
compound of the transition metal element includes Fe. <4> The
method according to <3>, wherein the compound of the
transition metal element further includes one or more elements
selected from the group consisting of Ni, Mn and Co. <5> The
method according to any one of <1> to <4>, wherein the
inactive flux is a carbonate of M, wherein M has same meaning as
defined above. <6> The method according to <5>, wherein
the carbonate of M is Na.sub.2CO.sub.3 or K.sub.2CO.sub.3 or both.
<7> The method according to any one of <1> to
<6>, wherein the inactive flux is present in an amount of 0.1
parts by weight or more and 100 parts by weight or less per 100
parts by weight of the lithium mixed metal oxide raw material at
the commencement of calcination. <8> The method according to
any one of <1> to <7>, wherein a temperature of the
calcination is in a range of from 200.degree. C. to 1050.degree. C.
<9> A layered structure lithium mixed metal oxide obtained by
the method according to any one of <1> to <8>.
<10> A positive electrode active material including the
layered structure lithium mixed metal oxide according to <9>.
<11> A positive electrode including the positive electrode
active material according to <10>. <12> A nonaqueous
electrolyte secondary battery including the positive electrode
according to <11>. <13> The nonaqueous electrolyte
secondary battery according to <12>, further including a
separator. <14> The nonaqueous electrolyte secondary battery
according to <13>, wherein the separator is made of a
laminated film which has a heat resistant porous layer and a porous
film laminated to each other.
MODE FOR CARRYING OUT THE INVENTION
[0007] The method of producing a layered structure lithium mixed
metal oxide of the present invention includes a step of calcining a
lithium mixed metal oxide raw material containing a transition
metal element and a lithium element in a molar ratio of the lithium
element to the transition metal element of 1 or more and 2 or less,
in the presence of an inactive flux including one or more compounds
selected from the group consisting of a carbonate of M, a sulfate
of M, a nitrate of M, a phosphate of M, a hydroxide of M, a
molybdate of M, and a tungstate of M, wherein M represents one or
more elements selected from the group consisting of Na, K, Rb, Cs,
Ca, Mg, Sr and Ba.
[0008] When the molar ratio of the lithium element to the
transition metal element is less than 1, the lithium mixed metal
oxide easily has a rock salt type structure or a spinel type
structure, and the output property of the obtained nonaqueous
electrolyte secondary battery at a high current rate (hereinafter,
referred to as a "rate property" in some cases) is not
satisfactory. On the other hand, when the above-mentioned molar
ratio is more than 2, the lithium mixed metal oxide includes much
excess lithium, which causes the generation of impurities, such as
lithium carbonate, and therefore the rate property of the obtained
nonaqueous electrolyte secondary battery is not satisfactory, and
it is difficult to obtain high discharge capacity. In the present
invention, from the viewpoint of enhancing the rate property of the
obtained battery, the molar ratio of the transition metal element
to the lithium element is preferably 1.05 or more and 1.5 or
less.
[0009] In the present invention, the lithium mixed metal oxide raw
material is not particularly limited as long as it is formed into a
layered structure lithium mixed metal oxide by calcination, but it
is preferably a mixture of a compound of lithium and a compound of
a transition metal element. Examples of the compound of a
transition metal element include an oxide, hydroxide (wherein, the
hydroxide also includes an oxyhydroxide. The same shall apply
hereinafter), chloride, carbonate, sulfate, nitrate, oxalate, and
acetate, of a transition metal element. These may be used in
combination of two or more of them. As the compound of lithium,
lithium hydroxide, lithium hydroxide monohydrate, or lithium
carbonate is preferably used, and these may be used in combination
of two or more of them. As the compound of a transition metal
element, a hydroxide of a transition metal element is preferably
used. Furthermore, the compound of a transition metal element
preferably contains two or more of transition metal elements. In
this case, the compound of a transition metal element may be one
using two or more of compounds each containing only one transition
metal element, but a compound containing two or more transition
metal elements is further preferred. The compound containing two or
more transition metal elements can be obtained by coprecipitation,
and the compound is preferably a hydroxide.
[0010] In the present invention, it is preferable that the compound
of a transition metal element contain Fe. The preferable amount of
Fe is in the molar ratio of the amount of Fe to the total amount of
the transition metal element is in the range of 0.01 or more and
0.5 or less, and more preferably in the range of 0.02 or more and
0.2 or less. Furthermore, from the viewpoint of enhancing the rate
property of the obtained nonaqueous electrolyte secondary battery,
it is preferable that the compound of a transition metal element
contain Fe and further contain one or more of elements selected
from the group consisting of Ni, Mn and Co, and it is more
preferable that the compound contain Fe and further contain Ni
and/or Mn. In the present invention, even if a Co raw material that
has conventionally been used in positive electrode active material
is not used, it is possible to obtain a layered structure lithium
mixed metal oxide, which gives a nonaqueous electrolyte secondary
battery having a high rate property.
[0011] In the present invention, the inactive flux does not easily
react with the lithium mixed metal oxide raw material in
calcination, and it is possible to use an inactive flux including
one or more compounds selected from the group consisting of a
carbonate of M, a sulfate of M, a nitrate of M, a phosphate of M, a
hydroxide of M, a molybdate of M and a tungstate of M (wherein, M
represents one or more elements selected from the group consisting
of Na, K, Rb, Cs, Ca, Mg, Sr and Ba).
[0012] Examples of the carbonate of M may include Na.sub.2CO.sub.3,
K.sub.2CO.sub.3, Rb.sub.2CO.sub.3, Cs.sub.2CO.sub.3, CaCO.sub.3,
MgCO.sub.3, SrCO.sub.3, BaCO.sub.3, and the melting points are
Na.sub.2CO.sub.3 (854.degree. C.), K.sub.2CO.sub.3 (899.degree.
C.), Rb.sub.2CO.sub.3 (837.degree. C.), Cs.sub.2CO.sub.3
(793.degree. C.), CaCO.sub.3 (825.degree. C.), MgCO.sub.3
(990.degree. C.), SrCO.sub.3 (1497.degree. C.), and BaCO.sub.3
(1380.degree. C.).
[0013] Furthermore, examples of the sulfate of M may include
Na.sub.2SO.sub.4, K.sub.2SO.sub.4, Rb.sub.2SO.sub.4,
Cs.sub.2SO.sub.4, CaSO.sub.4, MgSO.sub.4, SrSO.sub.4, and
BaSO.sub.4, and the melting points are Na.sub.2SO.sub.4
(884.degree. C.), K.sub.2SO.sub.4 (1069.degree. C.),
Rb.sub.2SO.sub.4 (1066.degree. C.), Cs.sub.2SO.sub.4 (1005.degree.
C.), CaSO.sub.4 (1460.degree. C.), MgSO.sub.4 (1137.degree. C.),
SrSO.sub.4 (1605.degree. C.), and BaSO.sub.4 (1580.degree. C.).
[0014] Examples of the nitrate of M may include NaNO.sub.3,
KNO.sub.3, RbNO.sub.3, CsNO.sub.3, Ca(NO.sub.3).sub.2,
Mg(NO.sub.3).sub.2, Sr(NO.sub.3).sub.2, and Ba(NO.sub.3).sub.2, and
the melting points are NaNO.sub.3 (310.degree. C.), KNO.sub.3
(337.degree. C.), RbNO.sub.3 (316.degree. C.), CsNO.sub.3
(417.degree. C.), Ca(NO.sub.3).sub.2 (561.degree. C.),
Sr(NO.sub.3).sub.2 (645.degree. C.), and Ba(NO.sub.3).sub.2
(596.degree. C.).
[0015] Examples of the phosphate of M may include Na.sub.3PO.sub.4,
K.sub.3PO.sub.4, Rb.sub.3PO.sub.4, Cs.sub.3PO.sub.4,
Ca.sub.3(PO.sub.4).sub.2, Mg.sub.3(PO.sub.4).sub.2,
Sr.sub.3(PO.sub.4).sub.2, and Ba.sub.3(PO.sub.4).sub.2, and the
melting points are K.sub.3PO.sub.4 (1340.degree. C.),
Mg.sub.3(PO.sub.4).sub.2 (1184.degree. C.),
Sr.sub.3(PO.sub.4).sub.2 (1727.degree. C.), and
Ba.sub.3(PO.sub.4).sub.2 (1767.degree. C.).
[0016] Examples of the hydroxide of M may include NaOH, KOH, RbOH,
CsOH, Ca(OH).sub.2, Mg(OH).sub.2, Sr(OH).sub.2, and Ba(OH).sub.2,
and the melting points are NaOH (318.degree. C.), KOH (360.degree.
C.), RbOH (301.degree. C.), CsOH (272.degree. C.), Ca(OH).sub.2
(408.degree. C.), Mg(OH).sub.2 (350.degree. C.), Sr(OH).sub.2
(375.degree. C.), and Ba(OH).sub.2 (853.degree. C.).
[0017] Examples of the molybdate of M may include
Na.sub.2MoO.sub.4, K.sub.2MoO.sub.4, Rb.sub.2MoO.sub.4,
Cs.sub.2MoO.sub.4, CaMoO.sub.4, MgMoO.sub.4, SrMoO.sub.4, and
BaMoO.sub.4, and the melting points are Na.sub.2MoO.sub.4
(698.degree. C.), K.sub.2MoO.sub.4 (919.degree. C.),
Rb.sub.2MoO.sub.4 (958.degree. C.), Cs.sub.2MoO.sub.4 (956.degree.
C.), CaMoO.sub.4 (1520.degree. C.), MgMoO.sub.4 (1060.degree. C.),
SrMoO.sub.4 (1040.degree. C.), and BaMoO.sub.4 (1460.degree.
C.).
[0018] Examples of the tungstate of M include Na.sub.2WO.sub.4,
K.sub.2WO.sub.4, Rb.sub.2WO.sub.4, Cs.sub.2WO.sub.4, CaWO.sub.4,
MgWO.sub.4, SrWO.sub.4, and BaWO.sub.4, and the melting point is
Na.sub.2WO.sub.4 (687.degree. C.).
[0019] Furthermore, two or more of these inactive fluxes may be
used. When two or more of these inactive fluxes are used, the
melting point may be lowered. Furthermore, among these inactive
fluxes, as an inactive flux for obtaining a particulate layered
structure lithium mixed metal oxide having a higher crystalline
property and having less aggregation between primary particles, a
carbonate of M is preferable, and particularly, Na.sub.2CO.sub.3 or
K.sub.2CO.sub.3 or both is preferable. Use of these inactive fluxes
makes it possible to obtain a layered structure lithium mixed metal
oxide that gives a nonaqueous electrolyte secondary battery having
a higher rate property. Furthermore, if necessary, inactive fluxes
other than the above-mentioned inactive fluxes may be used
together. Examples of such fluxes include chlorides, such as KCl
and NH.sub.4Cl, and fluorides, such as KF and NH.sub.4F.
[0020] In the present invention, it is preferable that the inactive
flux be present in an amount of 0.1 parts by weight or more and 100
parts by weight or less per 100 parts by weight of the lithium
mixed metal oxide raw material at the commencement of the
calcination. More preferably, the inactive flux is present in an
amount in the range of 0.5 parts by weight or more and 90 parts by
weight or less, and further preferably in an amount in the range of
1 part by weight or more and 80 parts by weight or less.
[0021] The calcination temperature is an important factor from the
viewpoint of adjusting the BET specific surface area of the
obtained layered structure lithium mixed metal oxide. Usually, the
higher the calcination temperature is, the smaller the BET specific
surface area tends to be. The lower the calcination temperature is,
the larger the BET specific surface area tends to be. The
calcination temperature is preferably in the range of 200.degree.
C. or more and 1050.degree. C. or less, and more preferably in the
range of 650.degree. C. or more and 1050.degree. C. or less. The
setting of the calcination temperature is depending upon the kinds
of inactive fluxes to be used. For example, the above-mentioned
melting point of the inactive flux may be taken into consideration,
and the calcination temperature is preferably set in the range of
from a temperature of the melting point minus 100.degree. C. or
more and a temperature of the melting point plus 100.degree. C. or
less. The calcination is usually carried out by allowing the
calcination temperature to be maintained at the above-mentioned
calcination temperature. The time during which the temperature is
maintained at the calcination temperature is usually 0.1 to 20
hours, and preferably 0.5 to 8 hours. The temperature rising rate
to the calcination temperature is usually 50 to 400.degree.
C./hour, and the temperature falling rate from the calcination
temperature to room temperature is usually 10 to 400.degree.
C./hour. Furthermore, calcination atmospheres include air, oxygen,
nitrogen, argon, or a mixed gas thereof, and air is preferable.
Furthermore, the inactive flux may remain in the layered structure
lithium mixed metal oxide, or may be removed by washing,
evaporation, and the like.
[0022] Furthermore, after calcination, the obtained layered
structure lithium mixed metal oxide may be pulverized using a ball
mill, a jet mill or the like. The pulverization may permit
adjusting the BET specific surface area of the layered structure
lithium mixed metal oxide. Furthermore, pulverization and
calcination may be conducted twice or more times repeatedly.
Furthermore, the layered structure lithium mixed metal oxide may be
washed or classified if necessary.
[0023] The layered structure lithium mixed metal oxide obtained by
the above-mentioned method of the present invention is useful as a
positive electrode active material of a nonaqueous electrolyte
secondary battery capable of exhibiting high output in a high
current rate.
[0024] It is preferable that the layered structure lithium mixed
metal oxide obtained by the method of the present invention include
a mixture of primary particles having a particle diameter (average
value) of 0.05 .mu.m or more 1 .mu.m or less, and secondary
particles formed by the aggregation of the primary particles and
having a particle diameter (average value) of 2 .mu.m or more and
100 .mu.m or less. The particle diameters (average values) of the
primary particles and the secondary particles can be measured by
observation with SEM. Specifically, the average value can be
obtained by calculating the average value of the values obtained by
measuring the maximum diameters of particles from 50 of primary
particles or secondary particles, which are photographed by SEM and
arbitrarily selected. From the viewpoint of enhancing the effect of
the present invention, the particle diameter (average value) of the
secondary particles is preferably 2 .mu.m or more and 50 .mu.m or
less, and further preferably 2 .mu.m or more and 10 .mu.m or less.
Furthermore, the particle diameter (average value) of the primary
particles is preferably 0.1 .mu.m or more and 0.5 .mu.m or less,
and further preferably 0.1 .mu.m or more and 0.3 .mu.m or less.
[0025] The crystal structure of the layered structure lithium mixed
metal oxide obtained by the method of the present invention has a
layered structure. From the viewpoint of the discharge capacity of
the obtained nonaqueous electrolyte secondary battery, the crystal
structure of the layered structure lithium mixed metal oxide is
preferably a crystal structure belonging to space group R-3m or
C2/m. The space group R-3m is included in a hexagonal type crystal
structure, and the hexagonal type crystal structure belongs to any
one of space groups selected from among P3, P3.sub.1, P3.sub.2, R3,
P-3, R-3, P312, P321, P3.sub.112, P3.sub.121, P3.sub.212,
P3.sub.221, R32, P3 m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c,
P-3m1, P-3c1, R-3m, R-3c, P6, P6.sub.1, P6.sub.5, P6.sub.2,
P6.sub.4, P6.sub.3, P-6, P6/m, P6.sub.3/m, P622, P6.sub.122,
P6.sub.522, P6.sub.222, P6.sub.422, P6.sub.322, P6mm, P6cc,
P6.sub.3cm, P6.sub.3mc, P-6m2, P-6c2, P-62m, P-62c, P6/mmm, P6/mcc,
P6.sub.3/mcm, and P6.sub.3/mmc. Furthermore, the space group C2/m
is included in a monoclinic type crystal structure, and the
monoclinic type crystal structure belongs to any one of space
groups selected from among P2, P2.sub.1, C2, Pm, Pc, Cm, Cc, P2/m,
P2.sub.1/m, C2/m, P2/c, P2.sub.1/c, and C2/c. The crystal structure
of the layered structure lithium mixed metal oxide can be
identified from a powder X-ray diffraction pattern obtained from
powder X-ray diffractometry using CuK.alpha. as a radiation
source.
[0026] Furthermore, in the present invention, when the transition
metal element of the layered structure lithium mixed metal oxide is
one or more transition metal elements selected from the group
consisting of Ni, Mn, Co and Fe, part of the transition metal
element may be substituted with other elements in the range where
the effect of the present invention is not remarkably impaired.
Herein, examples of the other elements may include B, Al, Ga, In,
Si, Ge, Sn, Mg, Sc, Y, Zr, Hf, Nb, Ta, Cr, Mo, W, Tc, Ru, Rh, Ir,
Pd, Cu, Ag, and Zn.
[0027] Furthermore, in the range where the effect of the present
invention is not remarkably impaired, a compound different from the
oxide may be attached onto the surface of the particles
constituting the layered structure lithium mixed metal oxide of the
present invention. Examples of the compound include a compound
containing one or more elements selected from the group consisting
of B, Al, Ga, In, Si, Ge, Sn, Mg and transition metal elements,
preferably a compound containing one or more elements selected from
the group consisting of B, Al, Mg, Ga, In and Sn, and more
preferably a compound of Al. Furthermore, specific examples of the
compound include oxides, hydroxides, oxyhydroxides, carbonates,
nitrates, and organic acid salts of the above-mentioned elements,
and the compound is preferably oxides, hydroxides, or
oxyhydroxides. Furthermore, a mixture of these compounds may be
used. Among these compounds, a particularly preferable compound is
alumina. Furthermore, after such compounds are attached, they may
be heated.
[0028] A positive electrode active material having the layered
structure lithium mixed metal oxide obtained by the method of the
present invention is suitable for a nonaqueous electrolyte
secondary battery. Furthermore, in the present invention, the
positive electrode active material may include only the layered
structure lithium mixed metal oxide of the present invention, and a
different compound may be attached to the surface of the particles
as mentioned above.
[0029] As a method of producing a positive electrode having the
positive electrode active material, the case of producing a
positive electrode for a nonaqueous electrolyte secondary battery
is described as an example hereinafter.
[0030] A positive electrode is produced by supporting a positive
electrode mixture containing a positive electrode active material,
a conductive material and a binder on a positive electrode current
collector. As the conductive material, carbonaceous materials can
be used. Examples of the carbonaceous materials include a graphite
powder, carbon black, acetylene black, and filamentous carbonaceous
materials. Since the carbon black and the acetylene black are
particulates and have a large surface area, with the addition of
small amount of such materials into the positive electrode mixture,
the conductivity inside the positive electrode is enhanced, and the
charge-discharge efficiency and the rate property can be improved.
However, when added in a too large amount, an adhesion property by
the binder between the positive electrode mixture and the positive
electrode current collector is lowered, leading to a cause for
increase in internal resistance. In general, the proportion of the
conductive material in the positive electrode mixture is 5 parts by
weight or more and 20 parts by weight or less per 100 parts by
weight of the positive electrode active material. In the case of
use of a filamentous carbonaceous material, such as graphitized
carbon fiber or carbon nanotube as the conductive material, it is
also possible to decrease this proportion.
[0031] As the above-described binder, a thermoplastic resin can be
used. Specific examples thereof include fluorine resins, such as
polyvinylidene fluoride (hereinafter, referred to as PVdF in some
cases), polytetrafluoroethylene (hereinafter, referred to as PTFE
in some cases), tetrafluoroethylene-propylene
hexafluoride-vinylidene fluoride copolymers, propylene
hexafluoride-vinylidene fluoride copolymers, and
tetrafluoroethylene-perfluoro vinyl ether copolymers; and
polyolefin resins, such as polyethylene and polypropylene.
Furthermore, two or more of these compounds may be used in
admixture. For example, a positive electrode mixture superior in
adhesion property with an electrode current collector can be
obtained by using a fluorine resin and a polyolefin resin as the
binder, and containing the fluorine resin and the polyolefin resin
so that the proportion of the fluorine resin relative to the
positive electrode mixture is from 1 to 10% by weight and the
proportion of the polyolefin resin relative to the positive
electrode mixture is from 0.1 to 2% by weight.
[0032] For the positive electrode current collector, Al, Ni,
stainless steel, and the like, can be used. Al is preferable
because it can be processed into a thin film easily and it is
cheap. Examples of a method of allowing the positive electrode
mixture to be supported on the positive electrode current collector
include a method of pressure molding; or a method of pasting the
positive electrode mixture using an organic solvent and the like,
applying the obtained paste on the positive electrode current
collector, drying thereof, and then carrying out pressing and the
like to attain fixation thereof. In the case of pasting, a slurry
including the positive electrode active material, the conductive
material, the binder and the organic solvent is produced. Examples
of the organic solvent include amine solvents, such as
N,N-dimethylaminopropylamine and diethylenetriamine; ether
solvents, such as tetrahydrofuran; ketone solvents, such as methyl
ethyl ketone; ester solvents, such as methyl acetate; amide
solvents, such as dimethylacetamide and N-methyl-2-pyrrolidone.
[0033] Examples of a method of applying a paste of the positive
electrode mixture onto the positive electrode current collector
include a slit die coating method, a screen coating method, a
curtain coating method, a knife coating method, a gravure coating
method, and an electrostatic spray method. By the above-mentioned
methods, a positive electrode for a nonaqueous electrolyte
secondary battery can be produced.
[0034] As a method of producing a nonaqueous electrolyte secondary
battery by using the above-mentioned positive electrode, the case
of producing a lithium secondary battery is described as an example
hereinafter. That is, an electrode group obtained by laminating or
laminating and winding a separator, a negative electrode, a
separator and the above-mentioned positive electrode in this order
is accommodated in a battery case, and the electrode group is
impregnated with an electrolytic solution, and thus a nonaqueous
electrolyte secondary battery can be produced.
[0035] Examples of the shape of the above-mentioned electrode group
include a shape having a cross-section when the electrode group is
cut in a direction perpendicular to the winding of the electrode
group is circle, ellipse, rectangle, and rounded rectangle.
Furthermore, examples of the shape of the battery may include a
paper shape, a coin shape, a cylindrical shape, and a rectangular
shape.
[0036] The above-mentioned negative electrode is not particularly
limited as long as it is capable of being doped and dedoped with a
lithium ion at an electric potential that is lower than that of the
positive electrode, and examples thereof may include an electrode
formed by allowing a negative electrode mixture containing a
negative electrode material to be supported by a negative electrode
current collector, or an electrode consisting of a single negative
electrode material. Examples of the negative electrode material may
include a carbonaceous material, a chalcogen compound (an oxide, a
sulfide, and the like), a nitride, metal or an alloy, which are
materials capable of being doped and dedoped with a lithium ion at
an electric potential that is lower than that of the positive
electrode. Furthermore, such negative electrode materials may be
mixed and used.
[0037] The above-mentioned negative electrode material is
exemplified hereinafter. Specific examples of the above-mentioned
carbonaceous material may include graphite, such as natural
graphite and artificial graphite, cokes, carbon black, pyrolytic
carbons, carbon fiber, and a calcined product of an organic polymer
compound. Specific examples of the oxide may include oxides of
silicon represented by the formula SiO.sub.x (wherein x denotes a
positive real number), such as SiO.sub.2 and SiO; oxides of
titanium represented by the formula TiO.sub.x (wherein x denotes a
positive real number), such as TiO.sub.2 and TiO; oxides of
vanadium represented by the formula VO.sub.X (wherein x denotes a
positive real number), such as V.sub.2O.sub.5 and VO.sub.2; oxides
of iron represented by the formula FeO.sub.x (wherein x denotes a
positive real number), such as Fe.sub.3O.sub.4, Fe.sub.2O.sub.3,
and FeO; oxides of tin represented by the formula SnO.sub.x
(wherein x denotes a positive real number), such as SnO.sub.2 and
SnO; oxides of tungsten represented by the formula WO.sub.x
(wherein x denotes a positive real number), such as WO.sub.3 and
WO.sub.2; mixed metal oxides containing lithium and titanium and/or
vanadium, such as Li.sub.4Ti.sub.5O.sub.12, LiVO.sub.2, and
Li.sub.1.1V.sub.0.9O.sub.2. Specific examples of the sulfide may
include sulfides of titanium represented by the formula TiS.sub.x
(wherein x denotes a positive real number), such as
Ti.sub.2S.sub.3, TiS.sub.2, and TiS; sulfides of vanadium
represented by the formula VS.sub.x (wherein x denotes a positive
real number), such as V.sub.3S.sub.4, VS.sub.2, and VS; sulfides of
iron represented by the formula FeS (wherein x denotes a positive
real number), such as Fe.sub.3S.sub.4, FeS.sub.2, and FeS; sulfides
of molybdenum represented by the formula MoS.sub.x (wherein x
denotes a positive real number), such as Mo.sub.2S.sub.3 and
MoS.sub.2; sulfides of tin represented by the formula SnS.sub.x
(wherein x denotes a positive real number), such as SnS.sub.2 and
SnS; sulfides of tungsten represented by the formula WS.sub.x
(wherein x denotes a positive real number), such as WS.sub.2;
sulfides of antimony represented by the formula SbS.sub.x (wherein
x denotes a positive real number), such as Sb.sub.2S.sub.3; and
sulfides of selenium represented by the formula SeS.sub.x (wherein
x denotes a positive real number), such as Se.sub.5S.sub.3,
SeS.sub.2, and SeS. Specific examples of the nitride may include
lithium-containing nitrides, such as Li.sub.3N, and
Li.sub.3-xA.sub.xN (wherein, A denotes Ni and/or Co, x satisfies
0<x<3). These carbonaceous materials, oxides, sulfides, and
nitrides may be used together, and may be crystalline or amorphous.
Furthermore, these carbonaceous materials, oxides, sulfides, and
nitrides are supported on mainly a negative electrode current
collector and used as an electrode.
[0038] Furthermore, specific examples of the metal may include
lithium metals, silicon metals, and tin metals. Examples of the
alloy may include lithium alloys, such as Li--Al, Li--Ni, and
Li--Si; silicon alloys, such as Si--Zn; tin alloys, such as Sn--Mn,
Sn--Co, Sn--Ni, Sn--Cu, and Sn--La; and alloys, such as Cu.sub.2Sb
and La.sub.3Ni.sub.2Sn.sub.7. These metals and alloys are, in most
cases, used singly as an electrode (for example, used in the form
of foil).
[0039] Among the negative electrode materials, carbonaceous
materials made of graphite, such as natural graphite and artificial
graphite, for a main component are preferably used from the
viewpoint of high potential flatness, low average discharge
potential, good cyclic performance, and the like. As the shape of
the carbonaceous material, for example, any of flake such as
natural graphite, sphere such as mesocarbon microbeads, fiber such
as graphitized carbon fiber, and aggregate of fine powder, may be
used.
[0040] The negative electrode mixture may contain a binder if
necessary. Examples of the binder may include thermoplastic resins,
and specific examples thereof may include PVdF, thermoplastic
polyimide, carboxymethylcellulose, polyethylene, and
polypropylene.
[0041] Examples of the negative electrode current collector may
include Cu, Ni, and stainless steel, and from the viewpoint of
difficulty of making an alloy with lithium and easiness of
processing into a thin film, Cu may be used. A method for allowing
a negative electrode mixture to be supported on the negative
electrode current collector is the same as in the case of the
positive electrode, and includes a method of pressure molding, a
method of pasting the negative electrode mixture using a solvent
and the like, and applying this on the negative electrode current
collector and drying thereof, and then performing pressing to
attain press bonding thereof, and the like.
[0042] As the separator, materials having the form of a porous
film, a nonwoven fabric, a woven fabric or the like, may be used.
Examples of the material of the separator may include polyolefin
resins, such as polyethylene and polypropylene, fluorine resins,
and nitrogen-containing aromatic polymers. Two or more of such
materials may be formed into a separator, and the separator
materials may be laminated. Examples of the separator may include
separators described in JP-A-2000-30686, JP-A-10-324758 and the
like. It is advantageous that the thickness of the separator is
thinner as long as the mechanical strength is maintained, from the
viewpoint of increase in the volume energy density of a battery and
decrease in internal resistance thereof, and it is usually around
from 5 to 200 .mu.m, and preferably around from 5 to 40 .mu.m.
[0043] The separator preferably includes a porous film containing a
thermoplastic resin. A nonaqueous electrolyte secondary battery
usually has a function by which, when an abnormal current flows in
the battery because of short circuit between a positive electrode
and a negative electrode and the like, the current is interrupted
to block (shutdown) the flow of excessive current. Herein, the
shutdown is carried out by obstructing micropores of the porous
film in the separator when the temperature exceeds the usual
temperature for use. Then, after the shutdown, it is preferable
that even if the temperature in the battery is increased to some
extent, film destruction due to the temperature should not occur,
and the shutdown state is maintained. Examples of such a separator
include a laminated film which has a heat resistant porous layer
and a porous film laminated to each other. When such a film is used
as a separator, the heat resistant property of a secondary battery
in the present invention can be enhanced. In the laminated film,
the heat resistant porous layer may be laminated onto both surfaces
of the porous film.
[0044] Hereinafter, the laminated film obtained by laminating the
heat resistant porous layer and the porous film is described.
[0045] In the laminated film, the heat resistant porous layer is a
layer having higher heat resistant property than the porous film.
The heat resistant porous layer may be formed from an inorganic
powder, and may contain a heat resistant resin. Because the heat
resistant porous layer contains a heat resistant resin, the heat
resistant porous layer can be formed by an easy technique, such as
coating. Examples of the heat resistant resin may include
polyamide, polyimide, polyamide-imide, polycarbonate, polyacetal,
polysulfone, polyphenylene sulfide, polyether ketone, aromatic
polyester, polyether sulfone, and polyether imide. From the
viewpoint of enhancing the heat resistant property, polyamide,
polyimide, polyamide-imide, polyether sulfone, and polyether imide
are preferable, and polyamide, polyimide, and polyamide-imide are
more preferable. Nitrogen-containing aromatic polymers, such as
aromatic polyamide (para-oriented aromatic polyamide, meta-oriented
aromatic polyamide), aromatic polyimide, and aromatic
polyamide-imide are furthermore preferable. Aromatic polyamide is
particularly preferable. In production aspect, para-oriented
aromatic polyamide (hereinafter, referred to as "para-aramide" in
some cases) is more particularly preferable. Furthermore, examples
of the heat resistant resin may include poly-4-methyl pentene-1 and
cyclic olefin polymer. Use of such heat resistant resins makes it
possible to enhance the heat resistant property of a laminated
film, that is, the thermal film breaking temperature of a laminated
film. When the nitrogen-containing aromatic polymer is used among
such heat resistant resins, compatibility with an electrolytic
solution, that is, a liquid retaining property in the heat
resistant porous layer may also be improved, possibly due to
polarity in its molecule, and also the rate of impregnation of an
electrolytic solution in the production of a nonaqueous electrolyte
secondary battery is high, and also the charge and discharge
capacity of a nonaqueous electrolyte secondary battery is further
enhanced.
[0046] The thermal film breaking temperature of such a laminated
film is dependent upon the kind of the heat resistant resin, and is
selected and used according to places for use and purposes for use.
More specifically, the thermal film breaking temperature can be
controlled to around 400.degree. C. when the above-mentioned
nitrogen-containing aromatic polymer is used as the heat resistant
resin, to around 250.degree. C. when poly-4-methyl pentene-1 is
used, and to around 300.degree. C. when cyclic olefin polymer is
used, respectively. Furthermore, the thermal film breaking
temperature can also be controlled to, for example, around
500.degree. C. or more when the heat resistant porous layer is
formed from an inorganic powder.
[0047] The above-mentioned para-aramide is obtained by condensation
polymerization of para-oriented aromatic diamine and para-oriented
aromatic dicarboxylic acid halide, and consists substantially of a
repeating unit in which an amide bond is linked at a para-position
or orientation position according to the para-position of an
aromatic ring (for example, orientation position extending
coaxially or parallel toward the reverse direction, such as
4,4'-biphenylene, 1,5-naphthalene, and 2,6-naphthalene). Specific
examples thereof include para-aramides having a para-orientation
type structure or a structure according to the para-orientation
type, such as poly(para-phenylene terephthalamide),
poly(para-benzamide), poly(4,4'-benzanilide terephthalamide),
poly(para-phenylene-4,4'-biphenylene dicarboxylic acid amide),
poly(para-phenylene-2,6-naphthalene dicarboxylic acid amide),
poly(2-chloro-para-phenylene terephthalamide), and para-phenylene
terephthalamide/2,6-dichloro para-phenylene terephthalamide
copolymer.
[0048] The aromatic polyimide is preferably a wholly aromatic
polyimide produced by condensation polymerization of aromatic
dianhydride and diamine. Specific examples of the dianhydride may
include pyromellitic acid dianhydride, 3,3',4,4'-diphenylsulfone
tetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone
tetracarboxylic acid dianhydride,
2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane, and
3,3',4,4'-biphenyltetracarboxylic acid dianhydride. Specific
examples of the diamine may include oxydianiline,
para-phenylenediamine, benzophenone diamine,
3,3'-methylenedianiline, 3,3'-diaminobenzophenone,
3,3'-diaminodiphenyl sulfone, and 1,5'-naphthalene diamine.
Furthermore, polyimide soluble in a solvent can be suitably used.
Examples of such a polyimide may include a polyimide of a
polycondensate of 3,3',4,4'-diphenylsulfone tetracarboxylic acid
dianhydride and an aromatic diamine.
[0049] Examples of the aromatic polyamide-imide may include a
product obtained by condensation polymerization using aromatic
dicarboxylic acid and aromatic diisocyanate, and a product obtained
by condensation polymerization using aromatic dianhydride and
aromatic diisocyanate. Specific examples of the aromatic
dicarboxylic acid may include isophthalic acid, and terephthalic
acid. Specific examples of the aromatic dianhydride may include
trimellitic anhydride. Specific examples of the aromatic
diisocyanate may include 4,4'-diphenylmethane diisocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
ortho-tolylane diisocyanate, and m-xylene diisocyanate.
[0050] Furthermore, from the viewpoint of enhancing ion
permeability, it is preferable that the thickness of the heat
resistant porous layer be thin, and the thickness is preferably 1
.mu.m or more and 10 .mu.m or less, further preferably 1 .mu.m or
more and 5 .mu.m or less, and particularly preferably 1 .mu.m or
more and 4 .mu.m or less. Furthermore, the heat resistant porous
layer has micropores, and the pore size (diameter) thereof is
usually 3 .mu.m or less, and preferably 1 .mu.m or less.
Furthermore, when the heat resistant porous layer contains the heat
resistant resin, the heat resistant porous layer further can also
contain the below-mentioned filler.
[0051] In the laminated film, it is preferable that the porous film
have micropores and have a shutdown function. In this case, the
porous film contains a thermoplastic resin. The size of the
micropore in the porous film is usually 3 .mu.m or less, and
preferably 1 .mu.m or less. The porosity of the porous film is
usually 30 to 80 vol %, and preferably 40 to 70 vol %. In the
nonaqueous electrolyte secondary battery, when the temperature
exceeds the usual temperature for use, the porous film containing a
thermoplastic resin can obstruct the micropores by the softening of
the thermoplastic resin constituting the porous film.
[0052] As the thermoplastic resin, any thermoplastic resin can be
selected as long as it is not dissolved in an electrolytic solution
in the nonaqueous electrolyte secondary battery. Specific examples
thereof may include polyolefin resins, such as polyethylene and
polypropylene, and thermoplastic polyurethane resins, and two or
more thereof may be used. From the viewpoint of being softened and
shut down at lower temperatures, it is preferable that the resin
contain polyethylene. Specific examples of the polyethylene may
include polyethylenes, such as low-density polyethylene,
high-density polyethylene, and linear polyethylene, and also
include ultra high molecular weight polyethylene having a molecular
weight of 1,000,000 or more. From the viewpoint of enhancing the
puncture strength of the porous film, the thermoplastic resin
constituting the film preferably contains at least ultra high
molecular weight polyethylene. Furthermore, from the aspect of
manufacturing a porous film, the thermoplastic resin may preferably
contain wax made of polyolefin having a low molecular weight
(weight-average molecular weight: 10,000 or less).
[0053] Furthermore, the thickness of the porous film in the
laminated film is usually from 3 to 30 .mu.m, and further
preferably from 3 to 25 .mu.m. Furthermore, in the present
invention, the thickness of the laminated film is usually 40 .mu.m
or less and preferably 20 .mu.m or less. It is preferable that the
value of A/B be 0.1 or more and 1 or less, where the thickness of
the heat resistant porous layer is A (.mu.m) and the thickness of
the porous film is B (.mu.m).
[0054] Furthermore, when the heat resistant porous layer contains
the heat resistant resin, the heat resistant porous layer may
contain one or more fillers. The material of the filler may be
selected from any of an organic powder, an inorganic powder or a
mixture thereof. Particles constituting the filler preferably have
an average particle diameter of 0.01 .mu.m or more and 1 .mu.m or
less.
[0055] Examples of the organic powder may include powders made of
organic substances, such as copolymers of single or two or more of
styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl
methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl
acrylate; fluorine-based resins, such as polytetrafluoroethylene,
ethylene tetrafluoride-propylene hexafluoride copolymer, ethylene
tetrafluoride-ethylene copolymer and polyvinylidene fluoride;
melamine resins; urea resins; polyolefins; and polymethacrylates.
The organic powders may be used singly, or in admixture of two or
more thereof. Among these organic powders, polytetrafluoroethylene
powder is preferable from the viewpoint of chemical stability.
[0056] Examples of the inorganic powder may include powders made of
inorganic substances, such as metal oxide, metal nitride, metal
carbide, metal hydroxide, carbonate, and sulfate. Among these
substances, powders made of inorganic substances having low
conductivity are preferably used. Specific examples thereof include
powders made of alumina, silica, titanium dioxide, or calcium
carbonate. The inorganic powders may be used singly or in mixture
of two or more thereof. Among these inorganic powders, from the
viewpoint of chemical stability, alumina powder is preferable.
Herein, it is preferable that all the particles constituting the
filler be alumina particles. A more preferable embodiment is that
all the particles constituting the filler are alumina particles,
and part or all of them are substantially spherical alumina
particles. When the heat resistant porous layer is formed from an
inorganic powder, the above-exemplified inorganic powders may be
used, and a binder may be mixed therewith and used if
necessary.
[0057] The content of the filler when the heat resistant porous
layer contains the heat resistant resin depends upon the specific
gravity of the material of the filler. For example, the weight of
the filler is usually 5 or more and 95 or less, preferably 20 or
more 95 or less, and more preferably 30 or more and 90 or less,
when the total weight of the heat resistant porous layer is made to
be 100, in the case where all the particles constituting the filler
are alumina particles. Such ranges can be appropriately set
according to the specific gravity of the material of the
filler.
[0058] The shape of the particles constituting the filler includes
a substantially spherical shape, a plate shape, a columnar shape, a
needle-like shape, a whisker shape, a fiber shape, and the like,
and any of shapes may be used. From the viewpoint that uniform
pores can be formed easily, the particles constituting the filler
are preferably substantially spherical particles. The substantially
spherical particles may include particles having an aspect ratio
(particle major axis/particle minor axis) is in the range of 1 or
more and 1.5 or less. The particle aspect ratio can be measured by
an electron micrograph.
[0059] In the present invention, from the viewpoint of ion
permeability, the separator has an air permeability according to
the Gurley method of from preferably 50 to 300 second/100 cc, and
further preferably from 50 to 200 second/100 cc. Furthermore, the
porosity of the separator is usually 30 to 80 vol %, and preferably
40 to 70 vol %. The separator may be a laminate of separators
having different porosities.
[0060] In a secondary battery, an electrolytic solution usually
contains an electrolyte and an organic solvent. Examples of the
electrolyte include lithium salts, such as LiClO.sub.4, LiPF.sub.6,
LiAsF.sub.6, LiSbF.sub.6, LIBF.sub.4, LiCF.sub.3SO.sub.3,
LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2,
LiN(SO.sub.2CF.sub.3)(COCF.sub.3), Li(C.sub.4F.sub.9SO.sub.3),
LiC(SO.sub.2CF.sub.3).sub.3, Li.sub.2B.sub.10Cl.sub.10, LiBOB
(herein, BOB denotes bis(oxalato)borate), lower aliphatic
carboxylic acid lithium salts, and LiAlCl.sub.4, and a mixture of
two or more thereof may be used. Among them, as the lithium salt, a
salt containing at least one selected from the group consisting of
LiPF.sub.6, LiAsF.sub.6, LiSbF.sub.6, LiBF.sub.4,
LiCF.sub.3SO.sub.3, LiN(SO.sub.2CF.sub.3).sub.2 and
LiC(SO.sub.2CF.sub.3).sub.3, which contain fluorine, is usually
used.
[0061] Furthermore, examples of the organic solvent to be used in
the electrolytic solution may include carbonates, such as propylene
carbonate, ethylene carbonate, dimethyl carbonate, diethyl
carbonate, ethyl methyl carbonate,
4-trifluoromethyl-1,3-dioxolane-2-on, and
1,2-di(methoxycarbonyloxy)ethane; ethers, such as
1,2-dimethoxyethane, 1,3-dimethoxy propane, pentafluoropropyl
methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether,
tetrahydrofuran, and 2-methyltetrahydrofuran; esters, such as
methyl formate, methyl acetate, and .gamma.-butyrolactone;
nitriles, such as acetonitrile and butyronitrile; amides, such as
N,N-dimethylformamide and N,N-dimethylacetamide; carbamates, such
as 3-methyl-2-oxazolidone; sulfur-containing compounds, such as
sulfolane, dimethyl sulfoxide, and 1,3-propanesultone, and
substances in which a fluorine substituent is introduced into the
above-mentioned organic solvent. Two or more thereof may be mixed
and used. Among them, a mixed solvent containing carbonates is
preferable, and a mixed solvent of cyclic carbonate and non-cyclic
carbonate, or a mixed solvent of cyclic carbonate and ethers are
further preferable. As the mixed solvent of cyclic carbonate and
non-cyclic carbonate, a mixed solvent of ethylene carbonate,
dimethyl carbonate and ethyl methyl carbonate is preferable from
the viewpoint that the solvent has a wide operational temperature
range, a superior load property, and a persistent property even if
graphite materials, such as natural graphite and artificial
graphite are used as the negative electrode active material.
Furthermore, from the viewpoint that it is capable of obtaining a
particularly superior effect of improving safety, an electrolytic
solution including a lithium salt containing fluorine, such as
LiPF.sub.6, and an organic solvent having a fluorine substituent is
preferably used. A mixed solvent containing ethers having a
fluorine substituent, such as pentafluoropropyl methyl ether and
2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl
carbonate is further preferable because of its discharge property
with a large electric current.
[0062] Instead of the above-mentioned electrolytic solution, a
solid electrolyte may be used. Examples of the solid electrolyte
may include organic polymer electrolytes, such as a polyethylene
oxide polymer compound, and a polymer compound having at least one
or more of a polyorganosiloxane chain and a polyoxyalkylene chain.
Furthermore, an electrolyte in which a nonaqueous electrolyte
electrolytic solution is supported on a polymer compound, that is,
a gel type electrolyte may also be used. Furthermore, an inorganic
solid electrolyte including sulfides, such as Li.sub.2S--SiS.sub.2,
Li.sub.2S--GeS.sub.2, Li.sub.2S--P.sub.2S.sub.5,
Li.sub.2S--B.sub.2S.sub.3, Li.sub.2S--SiS.sub.2--Li.sub.3PO.sub.4,
and Li.sub.2S--SiS.sub.2--Li.sub.2SO.sub.4 may be used. Use of such
solid electrolytes may further enhance the safety. Furthermore,
when the solid electrolyte is used in the nonaqueous electrolyte
secondary battery of the present invention, the solid electrolyte
may play a role as a separator. In such a case, a separator may not
be needed.
EXAMPLE
[0063] Next, the present invention will be described in more detail
with reference to examples. The evaluation of a layered structure
lithium mixed metal oxide (positive electrode active material), a
charge-discharge test, and a discharge rate test were carried out
as follows.
1. Charge-Discharge Test
[0064] To a mixture of a positive electrode active material and a
conductive material (a mixture of acetylene black and graphite in
the weight ratio of 1:9), a solution of PVdF in
N-methyl-2-pyrrolidone (hereinafter, referred to as "NMP" in some
cases) as a binder was added so that the resultant mixture had a
composition of positive electrode active material:conductive
material:binder=86:10:4 (weight ratio), and the mixture was kneaded
so as to obtain a paste. The paste was applied on an Al foil having
the thickness of 40 .mu.m as a current collector and dried in
vacuum at 150.degree. C. for 8 hours to obtain a positive
electrode.
[0065] The obtained positive electrode, a solution as an
electrolytic solution obtained by dissolving LiPF.sub.6 in a mixed
solution of ethylene carbonate (hereinafter, referred to as "EC" in
some cases), dimethyl carbonate (hereinafter, referred to as "DMC"
in some cases) and ethyl methyl carbonate (hereinafter, referred to
as "EMC" in some cases) in the ratio of 30:35:35 (volume ratio) so
that the concentration of LiPF.sub.6 was 1 mol/liter (hereinafter,
referred to as "LiPF.sub.6/EC+DMC+EMC" in some cases), a
polypropylene porous membrane as a separator, and metallic lithium
as a negative electrode are assembled to produce a coin type
battery (R2032).
[0066] A discharge rate test was carried out by using the
above-mentioned coin type battery while maintaining the battery at
25.degree. C. under the below-mentioned conditions. In the
discharge rate test, discharge capacity was measured by varying a
discharge current at the time of discharging, and the discharge
capacity retention ratio was calculated as follows.
<Discharge Rate Test>
[0067] Charge maximum voltage: 4.3 V, Charge time: 8 hours, Charge
current: 0.2 mA/cm.sup.2
[0068] During discharging, the discharge minimum voltage was made
to be a constant voltage of 3.0 V, and discharge was carried out by
varying a discharge current in each cycle as follows. Higher
discharge capacity by discharge at the following 10 C (high current
rate) means high output.
[0069] Discharge in the first and second cycles (0.2 C): Discharge
current 0.2 mA/cm.sup.2
[0070] Discharge in the third cycle (1 C): Discharge current 1.0
mA/cm.sup.2
[0071] Discharge in the fourth cycle (5 C): Discharge current 5.0
mA/cm.sup.2
[0072] Discharge in the fifth cycle (10 C): Discharge current 10
mA/cm.sup.2
<Discharge Capacity Retention Ratio>
[0073] Discharge capacity retention ratio (%)=Discharge capacity in
predetermined cycle/Initial discharge capacity.times.100
2. Measurement of BET Specific Surface Area of Layered Structure
Lithium Mixed Metal Oxide
[0074] One gram of a powder was dried in a nitrogen atmosphere at
150.degree. C. for 15 minutes, and then the BET specific surface
area thereof was measured using FlowSorb 112300 manufactured by
Micromeritics.
3. Composition Analysis of Layered Structure Lithium Mixed Metal
Oxide
[0075] A powder was dissolved in hydrochloric acid, and then the
composition was determined using an inductively coupled plasma
atomic emission spectroscopy (SPS3000, hereinafter referred to as
"ICP-AES" in some cases).
4. Powder X-ray Diffractometry of Layered Structure Lithium Mixed
Metal Oxide
[0076] The powder X-ray diffractometry of a layered structure
lithium mixed metal oxide was carried out using RINT 2500 TTR-type
manufactured by Rigaku Corporation. The layered structure lithium
mixed metal oxide was filled on a dedicated substrate, and then the
measurement was carried out in the range of a diffraction angle 20
of from 10.degree. to 90.degree. using a CuK.alpha. radiation
source, to obtain a powder X-ray diffraction pattern.
Example 1
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0077] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.07 g of nickel(II) chloride hexahydrate, 11.38 g of
manganese(II) chloride tetrahydrate, and 2.49 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0078] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.00 g of the coprecipitate,
1.16 g of lithium hydroxide monohydrate and 1.16 g of
K.sub.2CO.sub.3 (the amount of the inactive flux was 36 parts by
weight per 100 parts by weight of the lithium mixed metal oxide raw
material) were dry mixed to obtain a mixture. Next, the mixture was
placed in an alumina calcination container, calcined by maintaining
it in an air atmosphere at 900.degree. C. for 6 hours using an
electric furnace and then cooled to room temperature to obtain a
calcined article. The calcined article was pulverized to obtain a
pulverized article, and the pulverized article was washed with
distilled water by decantation and filtered to obtain a solid, and
then the resultant solid was dried at 100.degree. C. for 8 hours to
obtain a powder B.sup.1.
[0079] As a result of the composition analysis of the powder
B.sup.1, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.12:0.44:0.46:0.10. Furthermore, the powder B.sup.1 had a BET
specific surface area of 7.9 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.1 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.1 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0080] A coin type battery was produced by using the powder B.sup.1
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 119, 102, 79,
and 63, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 86, 66 and 53, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 2
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0081] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0082] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.85 g of the coprecipitate,
1.51 g of lithium carbonate and 0.40 g of K.sub.2CO.sub.3 (the
amount of the inactive flux was 9 parts by weight per 100 parts by
weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 900.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
and the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.2.
[0083] As a result of the composition analysis of the powder
B.sup.2, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.15:0.47:0.48:0.05. Furthermore, the powder B.sup.2 had a BET
specific surface area of 8.2 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.2 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.2 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0084] A coin type battery was produced by using the powder B.sup.2
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 140, 133, 116
and 104, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 95, 83, and 74, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 3
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0085] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0086] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.85 g of the coprecipitate,
1.51 g of lithium carbonate, 0.40 g of K.sub.2CO.sub.3, and 0.60 g
of KCl (the amount of the inactive flux K.sub.2CO.sub.3 was 9 parts
by weight and the amount of the inactive flux KCl was 14 parts by
weight per 100 parts by weight of the lithium mixed metal oxide raw
material) were dry mixed to obtain a mixture. Next, the mixture was
placed in an alumina calcination container, calcined by maintaining
it in an air atmosphere at 930.degree. C. for 6 hours using an
electric furnace and then cooled to room temperature to obtain a
calcined article. The calcined article was pulverized to obtain a
pulverized article, and the pulverized article was washed with
distilled water by decantation and filtered to obtain a solid, and
then the resultant solid was dried at 100.degree. C. for 8 hours to
obtain a powder B.sup.3.
[0087] As a result of the composition analysis of the powder
B.sup.3, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.21:0.47:0.48:0.05. Furthermore, the powder B.sup.3 had a BET
specific surface area of 2.4 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.3 was
0.3 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.3 was a
layered crystal structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0088] A coin type battery was produced by using the powder B.sup.3
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 130, 116, 92,
and 79, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 89, 71, and 61, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 4
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0089] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0090] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 4.00 g of the coprecipitate,
2.14 g of lithium carbonate, 0.30 g of K.sub.2CO.sub.3, and 0.36 g
of K.sub.2SO.sub.4 (the amount of the inactive flux K.sub.2CO.sub.3
was 5 parts by weight and the amount of the inactive flux
K.sub.2SO.sub.4 was 6 parts by weight per 100 parts by weight of
the lithium mixed metal oxide raw material) were dry mixed to
obtain a mixture. Next, the mixture was placed in an alumina
calcination container, calcined by maintaining it in an air
atmosphere at 900.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
and the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.4.
[0091] As a result of the composition analysis of the powder
B.sup.4, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.11:0.47:0.48:0.05. Furthermore, the powder B.sup.4 had a BET
specific surface area of 8.5 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.4 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.4 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0092] A coin type battery was produced by using the powder B.sup.4
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 141, 132, 115,
and 99, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 94, 82, and 70, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 5
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0093] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0094] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 4.00 g of the coprecipitate,
2.14 g of lithium carbonate, and 0.47 g of Na.sub.2CO.sub.3 (the
amount of the inactive flux was 8 parts by weight per 100 parts by
weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 900.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
and the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.5.
[0095] As a result of the composition analysis of powder B.sup.5,
it was found that the molar ratio of Li:Ni:Mn:Fe was
1.14:0.47:0.48:0.05. Furthermore, the powder B.sup.5 had a BET
specific surface area of 9.2 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.5 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.5 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0096] A coin type battery was produced by using the powder B.sup.5
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 145, 136, 120
and 96, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 94, 83, and 66, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 6
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0097] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0098] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 4.00 g of the coprecipitate,
2.14 g of lithium carbonate, 0.31 g of K.sub.2CO.sub.3, and 0.39 g
of K.sub.3PO.sub.4 (the amount of the inactive flux K.sub.2CO.sub.3
was 5 parts by weight and the amount of the inactive flux
K.sub.3PO.sub.4 was 6 parts by weight per 100 parts by weight of
the lithium mixed metal oxide raw material) were dry mixed to
obtain a mixture. Next, the mixture was placed in an alumina
calcination container, calcined by maintaining it in an air
atmosphere at 900.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
and the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.6.
[0099] As a result of the composition analysis of powder B.sup.6,
it was found that the molar ratio of Li:Ni:Mn:Fe was
1.09:0.47:0.48:0.05. Furthermore, the powder B.sup.6 had a BET
specific surface area of 8.5 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.6 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.6 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0100] A coin type battery was produced by using the powder B.sup.6
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 144, 135, 118,
and 106, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 94, 82, and 74, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 7
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0101] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0102] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.87 g of the coprecipitate,
1.44 g of lithium carbonate, 0.32 g of Na.sub.2CO.sub.3, and 0.43 g
of Na.sub.2SO.sub.4 (the amount of the inactive flux
Na.sub.2CO.sub.3 was 7 parts by weight and the amount of the
inactive flux Na.sub.2SO.sub.4 was 10 parts by weight per 100 parts
by weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 950.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
and the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.7.
[0103] As a result of the composition analysis of the powder
B.sup.7, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.09:0.47:0.48:0.05. Furthermore, the powder B.sup.7 had a BET
specific surface area of 6.4 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.7 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.7 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0104] A coin type battery was produced by using the powder B.sup.7
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 140, 125, 118,
and 106, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 89, 84, and 76, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 8
K.sub.2MoO.sub.4 Flux
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0105] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0106] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.00 g of the coprecipitate,
1.05 g of lithium carbonate, and 0.27 g of K.sub.2MoO.sub.4 (the
amount of the inactive flux was 9 parts by weight per 100 parts by
weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 870.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.8.
[0107] As a result of the composition analysis of the powder
B.sup.8, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.19:0.46:0.49:0.05. Furthermore, the powder B.sup.8 had a BET
specific surface area of 4.5 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.8 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.8 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0108] A coin type battery was produced by using the powder B.sup.8
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 148, 135, 117,
and 103, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 92, 80, and 70, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 9
Na.sub.2MoO.sub.4 Flux
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0109] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0110] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.00 g of the coprecipitate,
1.05 g of lithium carbonate, and 0.27 g of Na.sub.2MoO.sub.4 (the
amount of the inactive flux was 9 parts by weight per 100 parts by
weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 870.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.9.
[0111] As a result of the composition analysis of the powder
B.sup.9, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.11:0.46:0.49:0.05. Furthermore, the powder B.sup.9 had a BET
specific surface area of 5.4 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.9 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.9 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0112] A coin type battery was produced by using the powder B.sup.9
as a positive electrode active material, and a discharge rate test
of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 145, 134, 116,
and 101, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 92, 80, and 70, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 10
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0113] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0114] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.87 g of the coprecipitate,
1.53 g of lithium carbonate, 0.17 g of Na.sub.2CO.sub.3, and 0.46 g
of Na.sub.2WO.sub.4 (the amount of the inactive flux
Na.sub.2CO.sub.3 was 4 parts by weight and the amount of the
inactive flux Na.sub.2WO.sub.4 was 10 parts by weight per 100 parts
by weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 900.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
the pulverized article was washed with distilled water by
decantation and filtered to obtain a solid, and then the resultant
solid was dried at 100.degree. C. for 8 hours to obtain a powder
B.sup.10.
[0115] As a result of the composition analysis of the powder
B.sup.10, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.21:0.47:0.48:0.05. Furthermore, the powder B.sup.10 had a BET
specific surface area of 8.0 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.10 was
0.2 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.10 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0116] A coin type battery was produced by using the powder
B.sup.10 as a positive electrode active material, and a discharge
rate test of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 144, 136, 121,
and 108, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 94, 84, and 75, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 11
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0117] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0118] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.87 g of the coprecipitate,
1.53 g of lithium carbonate, 0.22 g of Na.sub.2CO.sub.3, and 0.52 g
of K.sub.2WO.sub.4 (the amount of the inactive flux
Na.sub.2CO.sub.3 was 5 parts by weight and the amount of the
inactive flux K.sub.2WO.sub.4 was 12 parts by weight per 100 parts
by weight of the lithium mixed metal oxide raw material) were dry
mixed to obtain a mixture. Next, the mixture was placed in an
alumina calcination container, calcined by maintaining it in an air
atmosphere at 900.degree. C. for 6 hours using an electric furnace
and then cooled to room temperature to obtain a calcined article.
The calcined article was pulverized to obtain a pulverized article,
the pulverized article was washed with distilled water by
decantation and filtered, and was then dried at 100.degree. C. for
8 hours to obtain a powder B.sup.11.
[0119] As a result of the composition analysis of the powder
B.sup.11, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.26:0.47:0.48:0.05. Furthermore, the powder B.sup.11 had a BET
specific surface area of 5.9 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.11 was
0.1 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.11 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0120] A coin type battery was produced by using the powder
B.sup.11 as a positive electrode active material, and a discharge
rate test of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 145, 136, 120,
and 108, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 94, 82, and 74, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Example 12
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0121] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.96 g of nickel(II) chloride hexahydrate, 11.87 g of
manganese(II) chloride tetrahydrate, and 1.24 g of iron(II)
chloride tetrahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0122] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.87 g of the coprecipitate,
1.72 g of lithium hydroxide monohydrate and 2.69 g of NaNO.sub.3
(the amount of the inactive flux NaNO.sub.3 was 59 parts by weight
per 100 parts by weight of the lithium mixed metal oxide raw
material) were dry mixed to obtain a mixture. Next, the mixture was
placed in an alumina calcination container, calcined by maintaining
it in an air atmosphere at 300.degree. C. for 6 hours using an
electric furnace and then cooled to room temperature to obtain a
calcined article. The calcined article was pulverized to obtain a
pulverized article, the pulverized article was washed with
distilled water by decantation and filtered to obtain a solid, and
then the resultant solid was dried at 100.degree. C. for 8 hours to
obtain a powder B.sup.12.
[0123] As a result of the composition analysis of the powder
B.sup.12, it was found that the molar ratio of Li:Ni:Mn:Fe was
0.52:0.47:0.48:0.05. Furthermore, the powder B.sup.12 had a BET
specific surface area of 74.5 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder B.sup.12 was
0.05 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder B.sup.12 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0124] A coin type battery was produced by using the powder
B.sup.12 as a positive electrode active material, and a discharge
rate test of the battery was carried out to find that the discharge
capacities (mAh/g) at 0.2 C, 1 C, 5 C and 10 C were 110, 86, 40,
and 22, respectively, and the discharge capacity retention ratios
(%) thereof were 100, 79, 36, and 20, respectively. The discharge
capacity and the discharge capacity retention ratio in 10 C of the
battery were respectively higher than the discharge capacity and
the discharge capacity retention ratio in 10 C of a coin type
battery using a powder A.sup.1 in the below-mentioned Comparative
Example 1 as a positive electrode active material.
Comparative Example 1
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0125] In a polypropylene beaker, 83.88 g of potassium hydroxide
was added to 200 ml of distilled water and then potassium hydroxide
was dissolved while stirring to obtain an aqueous potassium
hydroxide solution (aqueous alkali solution). In a glass beaker,
13.90 g of nickel(II) chloride hexahydrate, 13.95 g of
manganese(II) chloride tetrahydrate, and 4.05 g of iron(II)
chloride hexahydrate were added to 200 ml of distilled water, and
dissolved while stirring to obtain an aqueous nickel-manganese-iron
mixed solution. While stirring the aqueous potassium hydroxide
solution, the aqueous nickel-manganese-iron mixed solution was
added dropwise thereto to generate a coprecipitate, and thus a
coprecipitate slurry was obtained.
[0126] Next, the coprecipitate slurry was filtered, and washed with
distilled water, and then the resultant solid was dried at
100.degree. C. to obtain a coprecipitate (hydroxide of a transition
metal element). Using an agate mortar, 2.00 g of the coprecipitate
and 1.16 g of lithium hydroxide monohydrate were dry mixed to
obtain a mixture (no inactive flux is contained in the mixture).
Next, the mixture was placed in an alumina calcination container,
calcined by maintaining it in an air atmosphere at 900.degree. C.
for 6 hours using an electric furnace and then cooled to room
temperature to obtain a calcined article. The calcined article was
pulverized to obtain a pulverized article, the pulverized article
was washed with distilled water by decantation and filtered to
obtain a solid, and then the resultant solid was dried at
100.degree. C. for 8 hours to obtain a powder A.sup.1.
[0127] As a result of the composition analysis of the powder
A.sup.1, it was found that the molar ratio of Li:Ni:Mn:Fe was
1.30:0.41:0.49:0.10. Furthermore, the powder A.sup.1 had a BET
specific surface area of 0.3 m.sup.2/g, and the particle diameter
of primary particles in SEM observation of the powder A.sup.1 was
0.7 .mu.m in average. As a result of the powder X-ray diffraction
measurement, the crystal structure of the powder A.sup.1 was a
layered structure belonging to the R-3m space group.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0128] A coin type battery was produced by using the powder A.sup.1
as a positive electrode active material, and a discharge rate test
was carried out to find that the discharge capacities (mAh/g) at
0.2 C, 1 C, 5 C and 10 C were 76, 51, 22, and 14, respectively, and
the discharge capacity retention ratios (%) thereof were 100, 67,
29, and 18, respectively. The discharge capacity and the discharge
capacity retention ratio in 10 C of the coin type battery using the
powder A.sup.1 were not satisfactory.
Comparative Example 2
1. Production of Layered Structure Lithium Mixed Metal Oxide
[0129] By using a coprecipitate obtained by the same method as in
Comparative Example 1 (hydroxide of a transition metal element),
2.85 g of the coprecipitation, 2.32 g of lithium carbonate, 0.13 g
of lithium chloride (the amount of lithium chloride is 2.5 parts by
weight per 100 parts by weight of the lithium mixed metal oxide raw
material) are dry mixed by using an agate mortar to obtain a
mixture (no inactive flux is contained in the mixture). Next, as in
Comparative Example 1, the mixture was calcined, and from the
resultant calcined product, powder A.sup.2 is obtained as in
Comparative Example 1.
[0130] Similar to the powder A.sup.1, the BET specific surface area
of the powder A.sup.2 is smaller than that in the powder obtained
in each of Examples 1 to 12, and the average value of the particle
diameter of the primary particles in the powder A.sup.2 is larger
than that in the powder obtained in each of Examples 1 to 12.
2. Discharge Rate Test of Nonaqueous Electrolyte Secondary
Battery
[0131] When a coin type battery is produced by using the powder
A.sup.2 as a positive electrode active material and a discharge
rate test of the battery is carried out, the discharge capacity and
the discharge capacity retention ratio in 10 C of the battery are
smaller as compared with the discharge capacity and the discharge
capacity retention ratio in 10 C of the battery in Examples 1 to
12, which is similar to Comparative Example 1.
Production Example 1
Production of Laminated Film
(1) Production of Coating Fluid
[0132] Calcium chloride (272.7 g) was dissolved in 4200 g of NMP,
and then 132.9 g of para-phenylenediamine was added and dissolved
completely. To the resultant solution, 243.3 g of terephthalic acid
dichloride was gradually added and polymerization thereof was
carried out to obtain a para-aramide, and this was diluted further
with NMP to obtain a para-aramide solution (A) having a
concentration of 2.0% by weight. To 100 g of the resultant
para-aramide solution, 2 g of an alumina powder (a) (manufactured
by Nippon Aerosil Co., Ltd., Alumina C, average particle diameter:
0.02 .mu.m) and 2 g of an alumina powder (b) (Sumicorandom AA03
manufactured by Sumitomo Chemical Co., Ltd., average particle
diameter 0.3 .mu.m) were added as a filler in a total amount of 4
g, and these were mixed and treated three times by a nanomizer, and
further, filtered through a 1000 mesh wire netting, and defoamed
under reduced pressure to produce a slurry-formed coating fluid
(B). The weight of the alumina powders (filler) with respect to the
total weight of the para-aramide and the alumina powders was 67% by
weight.
(2) Production and Evaluation of Laminated Film
[0133] A polyethylene porous film (thickness: 12 .mu.m, air
permeability: 140 second/100 cc, average pore size: 0.1 .mu.m,
porosity: 50%) was used as the porous film. On a PET film having
the thickness of 100 .mu.m, the above-mentioned polyethylene porous
film was fixed, and the slurry-form coating fluid (B) was applied
on the porous film by a bar coater manufactured by Tester Sangyo
Co., Ltd. The PET film integrated with the applied porous film was
immersed into water that was a poor solvent to allow a para-aramide
porous layer (heat resistant porous layer) to precipitate, and then
the solvent was dried to yield a laminated film 1 which has a heat
resistant porous layer and a porous film laminated to each other.
The thickness of the laminated film 1 was 16 .mu.m, and the
thickness of the para-aramide porous film (heat resistant porous
layer) was 4 .mu.m. The laminated film 1 had an air permeability of
180 second/100 cc, and a porosity of 50%. The cross section of the
heat resistant porous layer in the laminated film 1 was observed by
a scanning electron microscope (SEM) to find that relatively small
micropores of around from 0.03 .mu.m to 0.06 .mu.m and relatively
large micropores of around from 0.1 .mu.m to 1 .mu.m were present.
The evaluation of the laminated film was carried out as
follows.
<Evaluation of Laminated Film>
(A) Measurement of Thickness
[0134] The thickness of the laminated film and the thickness of the
porous film were measured according to JIS standard (K7130-1992).
As the thickness of the heat resistant porous layer, a value
obtained by subtracting the thickness of the porous film from the
thickness of the laminated film was used.
(B) Measurement of Air Permeability by Gurley Method
[0135] The air permeability of the laminated film was measured by
digital timer mode Gurley type Densometer manufactured by Yasuda
Seiki Seisakusho Ltd., according to JIS P8117.
(C) Porosity
[0136] A sample of the resultant laminated film was cut into a
square having a side length of 10 cm, and the weight W (g) and the
thickness D (cm) thereof were measured. The weights (Wi (g)) of the
respective layers in the sample were measured, and the volumes of
the respective layers were calculated from Wi and the true specific
gravities (true specific gravity i (g/cm.sup.3)) of the materials
of the respective layers, and the porosity (vol %) was calculated
according to the following formula.
Porosity (vol %)=100.times.{1-(W1/true specific gravity 1+W2/true
specific gravity 2+ . . . +Wn/true specific gravity
n)/(10.times.10.times.D)}
[0137] In each of the above-mentioned examples, a lithium secondary
battery capable of increasing thermal film breaking temperature can
be obtained when the laminated film produced in the Production
Example 1 is used as a separator.
INDUSTRIAL APPLICABILITY
[0138] According to the present invention, it is possible to obtain
a layered structure lithium mixed metal oxide having particulates
and high crystalline property. Use of the layered structure lithium
mixed metal oxide can give a nonaqueous electrolyte secondary
battery capable of exhibiting high output at a high current rate.
The secondary battery is useful for applications of use in which
high output at a high current rate is required, that is, a
nonaqueous electrolyte secondary battery for automobile or for
power tools, such as electric tools.
* * * * *