U.S. patent application number 09/410072 was filed with the patent office on 2002-01-24 for process for producing a positive electrode active material for a nonaqueous secondary battery and a nonaqueous secondary battery using the active material.
Invention is credited to HAMANO, SHIGEYUKI, IIDA, TOYOSHI, INADA, TOMOHIKO, MAKINO, TETSUSHI, MITATE, TAKEHITO, TORATA, NAOTO.
Application Number | 20020009643 09/410072 |
Document ID | / |
Family ID | 17639108 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020009643 |
Kind Code |
A1 |
TORATA, NAOTO ; et
al. |
January 24, 2002 |
PROCESS FOR PRODUCING A POSITIVE ELECTRODE ACTIVE MATERIAL FOR A
NONAQUEOUS SECONDARY BATTERY AND A NONAQUEOUS SECONDARY BATTERY
USING THE ACTIVE MATERIAL
Abstract
A process for producing a positive electrode active material for
a nonaqueous secondary battery comprising the steps of: dissolving,
in an alcohol as a medium, a starting material which contains
metals necessary for giving a compound represented by the formula
LiNi.sub.1-xM.sub.xO.sub- .2, wherein 0.ltoreq.X<0.5 and M is at
least one metal selected from transition metals and 3B-, 4B- and
5B-group elements, as a positive electrode active material, and
which is soluble in the alcohol; adding a sufficient amount of
oxalic acid to the resulting solution to produce a precipitate
slightly soluble in the alcohol: separating the slightly soluble
precipitate from the solution: and calcining the precipitate to
obtain the positive electrode active material.
Inventors: |
TORATA, NAOTO;
(KASHIHARA-SHI, JP) ; MITATE, TAKEHITO;
(YAMATOTAKADA-SHI, JP) ; IIDA, TOYOSHI;
(FUKUI-SHI, JP) ; MAKINO, TETSUSHI; (FUKUI-SHI,
JP) ; HAMANO, SHIGEYUKI; (FUKUI-SHI, JP) ;
INADA, TOMOHIKO; (OSAKA-SHI, JP) |
Correspondence
Address: |
NIXON & VANDERHYE PC
1100 NORTH GLEBE ROAD
8TH FLOOR
ARLINGTON
CA
22201
|
Family ID: |
17639108 |
Appl. No.: |
09/410072 |
Filed: |
October 1, 1999 |
Current U.S.
Class: |
429/223 ;
423/594.4; 556/147 |
Current CPC
Class: |
C01P 2002/88 20130101;
C01G 53/42 20130101; C01P 2002/54 20130101; C01P 2006/40
20130101 |
Class at
Publication: |
429/223 ;
423/594; 556/147 |
International
Class: |
C01G 053/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 1998 |
JP |
HEI-10-281433 |
Claims
What is claimed is:
1. A process for producing a positive electrode active material for
a nonaqueous secondary battery comprising the steps of: dissolving,
in an alcohol as a medium, a starting material which contains
metals necessary for giving a compound represented by the formula
LiNi.sub.1-xM.sub.xO.sub- .2, wherein 0.ltoreq.X<0.5 and M is at
least one metal selected from transition metals and 3B-, 4B- and
5B-group elements, as a positive electrode active material, and
which is soluble in the alcohol; adding a sufficient amount of
oxalic acid to the resulting solution to produce a precipitate
slightly soluble in the alcohol: separating the slightly soluble
precipitate from the solution: and calcining the precipitate to
obtain the positive electrode active material.
2. A process according to claim 1, wherein the alcohol is a lower
aliphatic alcohol.
3. A process according to claim 2, wherein the alcohol is
ethanol.
4. A process according to claim 1, wherein the starting material
contains an inorganic or organic lithium compound such as lithium
nitrate, lithium chloride or lithium acetate and an inorganic or
organic nickel compound such as nickel nitrate, nickel chloride or
nickel acetate.
5. A process according to claim 1, wherein calcination is carried
out at a temperature of 650.degree. C. to 900.degree. C.
6. A process according to claim 1, wherein calcination is carried
out in air or in an atmosphere containing 21% to 100% by volume of
oxygen.
7. A process according to claim 1, wherein the alcohol Is separated
from the solution after the precipitate is separated and reused for
producing a positive electrode active material.
8. A process according to claim 1, wherein oxalic acid is added in
a molar ratio of 1.3 to 2.5:1 with respect to the sum of Ni and
M.
9. A process according to claim 1, wherein, in the case where X is
0, the nickel compound and the lithium compound are used in such
amounts that the molar ratio of nickel to lithium, Ni:Li, is 1:0.7
to 1:3.0.
10. A process according to claim 1, wherein a nickel compound, a
lithium compound and a starting compound giving M are used in such
amounts that the molar ratio of nickel and M to lithium, (Ni+M):Li,
is 1:0.7 to 1:3.0.
11. A nonaqueous secondary battery using a positive electrode
including a positive electrode active material produced by a
process as set forth in claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to Japanese application No. HEI
10-281433 filed on Oct. 2, 1998, whose priority is claimed under 35
USC .sctn.119, the disclosure of which Is incorporated by reference
in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a process for producing a
positive electrode active material for a nonaqueous secondary
battery and also relates to a nonaqueous secondary battery. More
particularly, the invention relates to a process for producing a
positive electrode active material for a nonaqueous secondary
battery, the active material being represented by the formula,
LiNi.sub.1-xM.sub.xO.sub.2 wherein 0.ltoreq.X<0.5 and M is at
least one element selected from transition metals, group 3B
elements, group 4B elements and group 5B elements, and a nonaqueous
secondary battery with use of a positive electrode including at
least one kind of positive electrode active material produced by
the process.
[0004] 2.Description of Related Art
[0005] With reduction of the size, the weight and the power
consumption of electronic equipment and like devices, progress has
been made in research and development of secondary batteries using
alkali metals such as lithium which are lightweight and able to
generate high voltage. Now lithium ion secondary batteries using
carbon or graphite for a negative electrode active material and
lithium cobalt oxide for the positive electrode active material are
in practical use.
[0006] In the case where lithium cobalt oxide is used for the
positive electrode active material, there is a problem that raw
material costs are high because cobalt resources are limited.
Accordingly, since John Banister Goodenough et al proposed lithium
nickel oxide (LiNiO.sub.2) using nickel whose resources are more
abundant than the cobalt resources and which is available at a
lower cost (see Japanese Patent Publication No. SHO
63(1988)-59507), active research have been made on positive
electrode active materials containing lithium nickel oxide.
[0007] The following processes have been reported for production of
lithium nickel oxide:
[0008] (1) A process of calcining anhydrous lithium hydroxide
together with a metal nickel in an atmosphere of oxygen (see
J.Am.Chem.Soc., 76, 1499(1954));
[0009] (2) A process of mixing LiOH.H.sub.2O and NiO, calcining the
mixture at 600.degree. C. in an atmosphere of air, pulverizing it,
and then calcining it again at 600.degree. C. to 800.degree. C.
(see Japanese Unexamined Patent Publication No. HEI
2(1990)-40861);
[0010] (3) A process of calcining a mixture of a compound as a
lithium source and a compound as a nickel source at 600.degree. C.
to 800.degree. C. (preferably at 800.degree. C. for six hours
twice) (see Japanese Unexamined Patent Publication No. HEI
4(1992)-181660);
[0011] (4) A process of mixing lithium peroxide (Li.sub.2O.sub.2)
and nickel oxide (NiO), allowing the mixture to react at a
temperature not higher than 750.degree. C. and then quenching the
mixture from that temperature (see Japanese Unexamined Patent
Publication No. HEI 5(1993)-205741); and
[0012] (5) A process of mixing lithium nitrate with at least one of
nickel hydroxide and nickel oxyhydroxide and calcining the mixture
at 500 to 1,000.degree. C. (see Japanese Unexamined Patent
Publication No. HEI 5(1993)-251079).
[0013] In these processes, a lithium source compound and a nickel
source compound are mixed in the state of solid and then
calcined.
[0014] As another process, there is proposed a process of
dissolving nickel acetate and lithium acetate in ethylene glycol
with heating, further heating the mixture to set it up, thermally
treating the resulting substance at 400.degree. C. in air,
pulverizing it, calcining it in an oxidizing flow at 700.degree. C.
and then calcining it at 800.degree. C. in an oxidizing flow (see
Japanese Unexamined Patent Publication No. HEI 6(1994)-203834).
[0015] Further, known are the following processes for uniformly
mixing a lithium compound and a nickel compound to facilitate the
production of the positive electrode active material:
[0016] (a) A process of equimolarly mixing an aqueous solution of
lithium hydroxide of 4.5 mol/L and an aqueous solution of nickel
nitrate of 1.0 mol/L at 60%, stirring the resulting mixture, drying
it under reduced pressure, pulverizing the resulting matter,
preliminarily calcining the pulverized matter at 300.degree. C. and
thereafter subjected to a major calcination at 800.degree. C. (see
Chemistry Express, 6, 161(1991));
[0017] (b) A process of obtaining LiCo.sub.xNi.sub.1-xO.sub.2
(0.ltoreq.X.ltoreq.0.5)by dissolving a nickel salt, a lithium salt
and an optional cobalt in a solvent and wet-mixing the resulting
mixture, followed by calcination (see Japanese Unexamined Patent
Publication No. HEI 5(1993)-325966);
[0018] (c) A process of mixing a water-soluble nickel salt and a
water-soluble lithium salt in an aqueous solution, solidifying by
drying the resulting mixture and calcining the resulting cake-like
matter at 600.degree. C. to 800.degree. C.;
[0019] (d) A process of kneading by stirring a powdery nickel
compound slightly soluble or insoluble in water with an aqueous
solution of a water-soluble lithium salt, solidifying by drying the
resulting mixture and calcining the resulting cake-like matter at
600 to 800.degree. C. (see Japanese Unexamined Patent Publication
No. HEI 6(1994)-44971);
[0020] (e) A process of weighing a lithium source and a nickel
source In a molar ratio of 1:1 in terms of nickel and lithium,
sufficiently mixing them with a little amount of water as a
dispersant, followed by drying, and calcining the resulting mixture
at 650.degree. C. in an atmosphere (see Japanese Unexamined Patent
Publication No. HEI 6(1994)-96768);
[0021] (f) A process of dispersing a nickel compound in a solution
of lithium nitrate, volatilizing the solvent, and calcining the
resulting mixture of lithium nitrate and the nickel compound In an
atmosphere containing oxygen (see Japanese Unexamined Patent
Publication No. HEI 7(1995)-307165);
[0022] (g) A process of weighing a powdery nickel oxide and a
lithium compound, i.e., either lithium hydroxide or lithium
nitrate, in a molar ratio of 1:1 in terms of lithium and nickel,
melting the lithium compound at a temperature of its melt
temperature or higher and 500.degree. C. or lower, allowing the
powdery nickel oxide to soak into the melted lithium compound, and
calcining the resulting matter in the presence of oxygen or a gas
containing oxygen in a high content (see Japanese Unexamined Patent
Publication No. HEI 9(1997)-156931):
[0023] (h) A process of dissolving a nickel compound and a lithium
compound in an aqueous solution, adding oxalic acid to produce a
nickel salt and a lithium salt as precipitates at a time, and
calcining the precipitates (see Japanese Unexamined Patent
Publication No. HEI 10(1998)-106564).
[0024] In the case of the above-mentioned processes (1) to (5),
there is a problem that the mixture before calcination is not
uniform.
[0025] In the case where ethylene glycol is used as a solvent,
there are problems that reaction time period is long and that the
production process is complicated.
[0026] In the case of the above-mentioned processes (a) to (c), the
mixed state of nickel and lithium is somewhat improved compared
with cases where they are mixed in a solid state. However, the
uniformity of the mixture is still insufficient.
[0027] In the case of the above-mentioned processes (d) to (f),
there is a problem that the mixture is not uniform when water or a
solvent as a dispersant is removed. Further, uniformity is
insufficient even though a melted salt is mixed as in the above
described (g).
[0028] Also, a positive electrode active material produced by any
of the above-mentioned processes has a problem that, when it is
used for producing a positive electrode, the active material
deteriorates rapidly and good cycle characteristics cannot be
obtained.
[0029] In the case of the above-mentioned process (h), since
lithium and nickel are precipitated as composite oxalates, a
slightly soluble precipitate in which lithium and nickel are
uniformly mixed is obtained. However, since lithium oxalate is more
soluble in water than other oxalates, the reproducibility of the
mixed state is not sufficient. Accordingly, although a positive
electrode containing lithium nickel oxide obtained by calcining
this precipitate exhibits improved initial electrode
characteristics and good cycle characteristics, there is a problem
that an active material having stable characteristics cannot be
obtained.
[0030] Also every time when the slightly soluble precipitate is
prepared, the lithium salt as a raw material is required in an
amount about several times to about ten times larger than the
amount of lithium finally contained in the slightly soluble
precipitate. Accordingly, there are problems that raw material
costs are high and the lithium salt is wastefully used from the
viewpoint of resources.
SUMMARY OF THE INVENTION
[0031] During study for solving the above problems, the inventors
of the present invention have found that a precipitate comprised of
oxalates containing a composite oxalate in which the ratio of Li:Ni
is close to that of starting compounds and lithium and nickel are
uniformly mixed and which Is slightly soluble in an alcohol is
produced by a co-precipitation process wherein a lithium compound
and a nickel compound as starting compounds are dissolved and then
oxalic acid is added to the resulting mixture, and have achieved
the present invention.
[0032] Accordingly, the present invention provides a process for
producing a positive electrode active material for a nonaqueous
secondary battery comprising the steps of: dissolving, in an
alcohol as a medium, a starting material which contains metals
necessary for giving a compound represented by the formula
LiNi.sub.1-xM.sub.xO.sub.2, wherein 0.ltoreq.X<0.5 and M is at
least one metal selected from transition metals and 3B-, 4B- and
5B-group elements, as a positive electrode active material, and
which is soluble in the alcohol; adding a sufficient amount of
oxalic acid to the resulting solution to produce a precipitate
comprised of oxalates including a composite oxalate slightly
soluble in the alcohol: separating the precipitate comprised of
oxalates including the composite oxalate slightly soluble in the
alcohol from the solution: and calcining the precipitate thereby to
obtain the positive electrode active material.
[0033] The production of the precipitate comprised of oxalates
including the slightly soluble composite oxalate improves
uniformity of a mixed state of the substance before calcination and
facilitates control of the ratio of lithium to nickel, Li:Ni, in
the precipitate comprised of oxalates containing the slightly
soluble composite oxalate. Furthermore, since lithium oxalate is
slightly soluble in an alcohol, it is easy to produce the
precipitate comprised of oxalates including the slightly soluble
composite oxalate containing lithium and nickel, from starting
compounds. Thus, it has been found that the process of the present
invention is excellent also from the viewpoint of stability of
manufacturing process and costs.
[0034] In another aspect, the present invention provides a
nonaqueous secondary battery with use of a positive electrode
including a positive electrode active material produced by the
above-described process.
[0035] It has been found that the above-mentioned nonaqueous
secondary batter has improved initial electrode characteristics and
good cycle characteristics.
[0036] These and other objects of the present application will
become more readily apparent from the detailed description given
hereinafter. However, it should be understood that the detailed
description and specific examples, while indicating preferred
embodiments of the invention, are given by way of illustration
only, since various changes and modifications within the spirit and
scope of the invention will become apparent to those skilled in the
art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a graphical representation illustrating the
relationship between an initial discharge capacity and calcination
temperatures in Examples 5 to 13 in accordance with the present
invention;
[0038] FIG. 2 is a graphical representation illustrating the
relationship between an initial discharge capacity and calcination
temperatures in Examples 14 to 22 in accordance with the present
invention;
[0039] FIG. 3 is a graphical representation illustrating a
relationship between an initial discharge capacity and
concentrations of oxygen in calcining atmosphere in Examples 23 to
29 in accordance with the present invention;
[0040] FIG. 4 is a schematic sectional view illustrating a
coin-shape battery used in Example 31 in accordance with the
present invention;
[0041] FIG. 5 is a schematic sectional view illustrating a
cylinder-shape battery used in Example 32 in accordance with the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] The present invention is now explained along its production
steps.
[0043] First, the starting material which contains metals necessary
for giving a compound represented by the formula
LiNi.sub.1-xM.sub.xO.sub.2 wherein 0.ltoreq.X<0.5 and M is at
least one metal selected from transition metals and 3B-, 4B- and
5B-group elements as a positive electrode active material and which
is soluble in a alcohol is dissolved in the alcohol as a
medium.
[0044] The alcohol is not particularly limited provided that it
dissolves the starting material for a positive electrode active
material. In the alcohol, lower aliphatic alcohol is preferable. As
more preferable alcohols, primary alcohols such as methanol and
ethanol may be mentioned. Particularly, ethanol is preferred from
the view point of safety. As regards the purity of the alcohol, it
is preferable to use an alcohol which is anhydrous or substantially
does not contain any water (e g., having a purity of 98% or more).
However, in the case where the positive electrode active material
is produced in an industrial scale, the alcohol may contain about
20 wt % or less of water provided that the characteristics of the
positive electrode active material to be obtained is not adversely
affected.
[0045] As the starting material, inorganic or organic nickel and
lithium compounds may be mentioned.
[0046] As the nickel compound, it is preferable to use a nickel
compound having a high solubility In the above-described alcohol.
Examples thereof include nickel chloride, nickel perchlorate,
nickel bromide, nickel Iodide, nickel nitrate, nickel acetate and
hydrates of these compounds. Especially, where ethanol is used,
nickel nitrate, nickel chloride and nickel acetate are
preferable.
[0047] As the lithium compound, it is preferable to use a lithium
compound having a high solubility in the above-described alcohol.
Examples thereof include lithium chloride, lithium bromide, lithium
iodide, lithium chlorate, lithium perchlorate, lithium sulfide,
lithium hydrogensulfide, lithium nitrate, lithium acetate and
hydrates of these compounds. Especially, lithium nitrate, lithium
chloride and lithium acetate are preferable since they are unlikely
to remain as impurities after the final calcination.
[0048] Besides the above nickel and lithium compounds, a compound
containing a transition metal or a 3B-, 4B- or 5B-group element
(referred to as a third compound herein after) is optionally
dissolved as the starting compound in the alcohol. For example, the
third compound is preferably a compound of Mn, Fe, Co, Cu, Zu, Y,
La, Al or Sn, from the viewpoint of performance of a battery.
Particular examples include manganese chloride, manganese nitrate,
manganese acetate, iron chloride, iron bromide, iron iodide, iron
nitrate, cobalt chloride, cobalt bromide, cobalt iodide, cobalt
nitrate, cobalt acetate, copper nitrate, copper acetate, zinc
chloride, zinc bromide, zinc iodide, zinc nitrate. zinc acetate,
yttrium chloride, yttrium bromide, yttrium iodide, yttrium nitrate,
lanthanum chloride, lanthanum bromide, lanthanum nitrate, lanthanum
acetate, aluminum chloride, tin chloride, tin bromide and hydrates
of these compounds.
[0049] In the case where only the nickel compound and the lithium
compound are used, they are dissolved in the alcohol so that the
molar ratio of nickel to lithium, Ni:Li, is 1:0.7 to 1:3.0,
preferably. If the ratio of lithium is smaller than 1:0.7, the
amount of lithium in the precipitate comprised of oxalates
containing a slightly soluble composite oxalate becomes smaller,
and 10 it becomes impossible to obtain LiNiO.sub.2 after
calcination.
[0050] Therefore, it is not preferable. If the ratio of lithium is
larger than 1:3.0, LiNiO.sub.2 can be obtained after calcination
but a lot of impurities are also generated. Therefore, it is not
preferable. More preferably, the molar ratio of nickel to lithium
is 1:1 to 1:1:5 for obtaining better characteristics.
[0051] In the case where the third compound is also used, the third
compound is dissolved in the alcohol so that the molar ratio of the
sum of the transition metal or the 3B-, 4B- or 5-B element and
nickel in the third compound and the nickel compound with respect
to lithium in the lithium compound, i.e., (Ni+M):Li, is 1:0.7 to
1:3.0, i.e., Li/(Ni+M) is 0.7 to 3.0, preferably. If the amount of
lithium is smaller, it is difficult to obtain
LiNi.sub.1-xM.sub.xO.sub.2 after calcination. Therefore, it is not
preferable. If the amount of lithium is larger,
LiNi.sub.1-xM.sub.xO.sub.2 can be obtained after calcination but a
lot of impurities are also generated. Therefore, it is not
preferable. More preferably, the molar ratio of (Ni+M):Li may be
1:1 to 1:1.5, i.e., Li/(Ni+M) is 1 to 1.5, for obtaining better
characteristics. If the amount of M is large, it becomes difficult
to obtain crystals. Therefore, it is not preferable.
[0052] Next, a sufficient amount of oxalic acid is added to the
resulting solution in which the starting compounds are dissolved,
thereby to produce a precipitate comprised of oxalates containing a
composite oxalate slightly soluble in the alcohol as a solvent.
Here, the sufficient amount may be set as appropriate depending
upon the solubility of the starting compounds in the alcohol.
However, this amount is preferably set as small as possible for
reducing a production time period. More particularly, oxalic acid
is preferably added in a molar ratio of 1.3 to 2.5 with respect to
the sum of nickel and the transition metal or 3B-, 4B- or 5B-group
element of the third compound dissolved in the alcohol. If the
ratio of oxalic acid is smaller than 1.3, it becomes difficult to
control the ratio of lithium to nickel and the transition metal or
the 3B-, 4B- or 5B-group element in the precipitate comprised of
oxalates containing a slightly soluble composite oxalate and to
obtain LiNi.sub.1-xM.sub.xO.sub.2 after calcination. Therefore, it
is not preferable. If the ratio of oxalic acid is larger than 2.5,
LiNi.sub.1-xM.sub.xO.sub.z can be obtained after calcination but a
lot of impurities are also generated. Therefore, it is not
preferable.
[0053] The precipitate is considered to be composed of oxalates of
nickel, lithium and the transition metal or the 3B-, 4B- or
5B-group element, a composite oxalate of nickel, lithium and the
transition metal or the 3B-, 4B- or 5B-group element, and mixtures
of these oxalates.
[0054] Oxalic acid may be added either in a solid sate or in the
form of a solution. In the case of solid oxalic acid, it is easy to
control the production of the precipitate composed of oxalates
containing a slightly soluble composite oxalate. In the case of the
solution, it is possible to obtain finer particles of the
precipitate by adding a solution of oxalic acid in an alcohol.
[0055] Next, the precipitate composed of oxalates containing a
slightly soluble composite oxalate Is separated and calcined to
obtain a positive electrode active material.
[0056] The precipitate composed of oxalates containing a slightly
soluble composite oxalate may be separated, for example, by
filtration, centrifugation or the like. Besides, the alcohol may be
separated by distillation from the solution after the
above-mentioned separation of the precipitate and recycled for use
in the production of a positive electrode active material, thereby
to reduce production costs.
[0057] Further, the precipitate composed of oxalates containing a
slightly soluble composite oxalate, after being separated but
before being calcined, may be subjected to a drying process for
substantially removing the alcohol.
[0058] Subsequently, the precipitate composed of oxalates
containing a slightly soluble composite oxalate is subjected to
calcination. Calcining temperature is preferably within the range
of 650.degree. C. to 900.degree. C., more preferable 700.degree. C.
to 800.degree. C. The calcination is preferably carried out in air
(volume fraction of oxygen is about 20%) or in an atmosphere having
a higher volume fraction of oxygen than air. The atmosphere having
a higher volume fraction of oxygen than air means an atmosphere
having a volume fraction of oxygen of 21% to 100%, preferably 50%
to 100%.
[0059] In the above-described calcination, if it is carried out at
a temperature below 650%, development of crystals slows. On the
other hand, if it is carried out at a temperature above 900.degree.
C., generated crystals decompose. Therefore both cases are not
preferable since the discharge capacity declines. Further, if the
calcination temperature is 700 to 850.degree. C., still better
characteristics can be obtained.
[0060] If the calcination is carried out in an atmosphere having a
lower oxygen concentration than air, reaction slows and crystals
become difficult to develop. Accordingly, the discharge capacity
declines, and therefore, it is not preferable. Where the
calcination is carried out in an atmosphere of 50% to 100% of
oxygen, better electrode characteristics can be obtained.
[0061] Here, before the above-mentioned calcination, it is
preferable to carry out a preliminary calcination. Hereinafter, the
calcination described in the foregoing paragraphs is referred to as
a major calcination. Where the preliminary calcination is
conducted, the crystallinity of the obtained positive electrode
active material improves compared with the case without the
preliminary calcination, and as a result, the electrode
characteristics thereof can be improved further.
[0062] Preferably, the preliminary calcination is carried out at a
temperature of 300.degree. C. to 550.degree. C. , more preferably
350.degree. C. to 450.degree. C. A temperature below 300.degree. C.
is not preferable because it is lower than a pyrolytic temperature
of the precipitate composed of oxalates containing a slightly
soluble composite oxalate.
[0063] Further, it is preferable to pulverize the precipitate after
the preliminary calcination but before the major calcination. By
pulverization, reaction efficiency with oxygen at the major
calcination is improved, and crystals of the positive electrode
active material become more ready to develop than In the case where
pulverization is not conducted. Therefore, better electrode
characteristics can be obtained by pulverization.
[0064] The nonaqueous secondary battery of the present invention
usually comprises a positive electrode, a negative electrode and an
ion conductor.
[0065] The positive electrode may be formed by use of a mixture of
LiNi.sub.1-xM.sub.xO.sub.2 (0.ltoreq.X<5) (a positive electrode
active material) produced as described, an electric conductor, a
binder and optionally, a solid electrolyte and the like.
[0066] Materials for the electric conductor are not particularly
limited, and any material known in this field of art may be used.
Examples thereof include carbons such as carbon black, acetylene
black, Ketchen black, graphite powder (natural graphite and
artificial graphite), metal powder and metallic fibers.
[0067] Materials for the binder are not particularly limited, and
any materials known in the field of art may be used. Examples
thereof include fluoropolymers such as polytetrafluoroethylene and
polyvinylidene fluoride, polyolefins such as polyethylene,
polypropylene and ethylene-propylene-diene terpolymer, and
styrenebutadiene rubber.
[0068] As regards a mix ratio, the mixture preferably contains 1 to
50 parts by weight of the electric conductor and 1 to 30 parts by
weight of the binder with respected to 100 parts by weight of the
positive electrode active material. It the electric conductor is
less than 1 part by weight, the resistance and polarization of the
electrode rise. As a result, the discharge capacity decreases and
it becomes impossible to prepare a practical secondary battery.
Therefore, it is not preferable. If the electric conductor is more
than 50 parts by weight, the amount of the active material in the
electrode decreases. As a result, the discharge capacity of the
positive electrode declines. Therefore, it is not preferable. If
the binder is less than 1 part by weight, the mixture loses its
binding power. Therefore, it is not preferable. If the binder is
more than 30 parts by weight, the amount of the active material in
the electrode decreases, and the resistance and polarization of the
electrode rise, as in the case of the electric conductor. As a
result, the discharge capacity of the positive electrode declines.
Therefore, it is impractical. It is noted that the above-mentioned
mix ratio may be adjusted as appropriate depending upon the kinds
of the electric conductor and binder to be used.
[0069] The positive electrode may be produced by forming the
above-described mixture. How to form the electrode is not
particularly limited, but the mixture may be compressed into a
pellet; or the mixture may be formed in an electrode by adding a
proper solvent to the mixture to produce a paste, applying the
paste onto a collector described below, drying and compressing it
into a sheet.
[0070] Electrons are sent to and received by the positive electrode
preferably through the collector. As collectors, usable are metals
themselves, alloys, carbons and the like. More particularly,
examples thereof include titanium, aluminum, stainless steel;
copper, aluminum and stainless steel whose surface is treated with
carbon, titanium and silver; and the surface-treated materials
whose surface is further oxidized. The positive electrode may be in
the form of a foil, film, sheet, net, punched form, lath or foam,
in a perforated or porous form, in a form of fibers, or the like.
The thickness is not particularly limited, but may usually be about
1 .mu.m to about 1 mm.
[0071] As an active material contained In the negative electrode,
usable is metallic lithium, a lithium alloy and/or a material
capable of intercalating or deintercalating lithium. For example,
metallic lithium and lithium alloys such as lithium/aluminum alloy,
lithium/tin alloy, lithium/lead alloy and Wood's alloys may be
mentioned. In addition to the above mentioned, usable are materials
capable of electrochemically doping/dedoping lithium ion, for
example, conductive polymers such as polyacetylene, polythiophene
and polyparaphenylene; pyrolyzed carbons such as a carbon pyrolyzed
in a gas phase in the presence of a catalyst: carbons produced by
burning pitch, coke, tar and the like; carbons produced by burning
polymers such as cellulose and a phenol resin; graphites (natural
graphites, artificial graphites, expanded graphites and the like)
capable of intercalating/deintercalating lithium ion; and inorganic
compounds capable of doping/dedoping lithium ion such as WO, and
MoO.sub.2. These active materials may be used singly or as a
composite of two or more thereof.
[0072] Of the above-mentioned negative electrode active materials,
the pyrolyzed carbons, the carbons produced by calcining pitch,
coke, tar and the like, the carbons produced by calcining polymers
and graphites (natural graphites, artificial graphites, expanded
graphites and the like) may be used for preparing secondary
batteries preferable in battery characteristics (especially in
safety).
[0073] Of the above-mentioned negative electrode active materials,
where the negative electrode is formed of a conductive polymer,
carbon, graphite or inorganic compound, the negative electrode may
be formed by use of a mixture containing the negative electrode
active material, an electric conductor and a binder.
[0074] Materials for the electric conductor are not particularly
limited, and any material known in this field of art may be used.
Examples thereof include carbons such as carbon black, acetylene
black and Ketchen black, graphite powder (a natural graphite, an
artificial graphite), metal powder and metallic fibers.
[0075] Materials for the binder are not particularly limited, and
any material known in the field of art may be used. Examples
thereof include fluoropolymers such as polytetrafluoroethylene and
polyvinylidene fluoride, polyolefins such as polyethylene,
polypropylene and ethylene-propylene-diene terpolymer, and
styrenebutadiene rubber.
[0076] As the ion conductor, usable is an organic electrolyte
liquid, a solid electrolyte (an inorganic or organic solid
electrolyte), or a molten salt. Of these ion conductors, the
organic electrolyte liquid may be used aptly.
[0077] The organic electrolyte liquid is composed of an organic
solvent and an electrolyte.
[0078] The organic solvent is not particularly limited and any
organic solvent known in the field of art may be used. Examples
thereof include esters such as propylene carbonate, ethylene
carbonate, butylene carbonate, diethyl carbonate, dimethyl
carbonate, methylethyl carbonate, .gamma.-butyrolactone, methyl
formate and methyl acetate, tetrahydrofuran, substituted
tetrahydrofurans such as 2-methyltetrahydrofuran, ethers such as
dioxolane, diethyl ether, dimethoxyethane, diethoxyethane and
methoxyethoxyethane, and aprotic organic solvents such as
dimethylsulfoxide, sulfolane, methylsulfolane and acetonitrile.
These organic solvents may be used singly or as a mixture of two or
more thereof.
[0079] The electrolyte is not particularly limited, and any
electrolyte known in the field of art may be used. Examples thereof
include lithium salts such as lithium perchlorate, lithium
borofluoride, lithium phosphofluoride, arsenic lithium
hexafluoride, lithium trifluoromethanesulfonate, a lithium halide
and lithium chloroaluminate. These electrolytes may be used singly
or as a mixture of two or more thereof.
[0080] The electrolyte liquid may be prepared by dissolving the
electrolyte in the above-described organic solvent.
[0081] The inorganic solid electrolyte is not particularly limited,
and any one known in this field of art may be used. For example,
nitride, halides and oxygen acid salts of lithium are known. More
particularly, Li.sub.3N, LiI, Li.sub.3N--LiI--LiOH,
Li.sub.4SiO.sub.4, Li.sub.4SiO.sub.4--LiI--LiOH,
Li.sub.3PO.sub.4--Li.sub.4SiO.sub.4, phosphorus sulfide compounds
and Li.sub.2SiS.sub.3 may be mentioned.
[0082] The organic solid electrolyte is not particularly limited,
and any one known in this field of art may be used. For example, a
material composed of the above-described electrolyte and a polymer
acting to dissociate the electrolyte and a material wherein a
polymer carries an ion dissociation group are known. Examples of
the polymer acting to dissociate the electrolyte include
derivatives of polyethylene oxide, polymers containing such
derivatives, derivatives of polypropylene oxide, polymers
containing such derivatives and phosphate polymers. In addition, a
polymeric matrix material containing the above-mentioned aprotic
polar solvent, a mixture of a polymer containing an ion
dissociation group with the above mentioned aprotic electrolyte,
and an electrolyte liquid to which polyacrylonitrile is added may
also be mentioned.
[0083] The inorganic solid electrolyte and the organic solid
electrolyte may be used together.
[0084] Usually the organic electrolyte liquid is preferably
retained by a separator. As materials for the separator, nonwoven
fabrics, woven fabrics and microporous materials of electrically
insulative synthetic resin fibers, glass fibers, natural fibers and
the like and formed pieces of alumina powder may be mentioned.
Among these, nonwoven fabrics and microporous materials of
synthetic resins such as polyethylene. polypropylene and the like
are preferable because they are stable in quality. Some of these
nonwoven fabrics and microporous materials of synthetic resins have
an additional function of, when the battery abnormally heats, being
melted by heat and making a block between the positive electrode
and the negative electrode. Such fabrics and materials may be
suitably used from the viewpoint of safety. The thickness of the
separator is not particularly limited provided that it can retain a
sufficient amount of the electrolyte liquid and prevent the
positive electrode and the negative electrode from
short-circuiting. It may usually be about 0.01 mm to about 1 mm,
preferably about 0.02 mm to about 0.05 mm, for example.
[0085] The nonaqueous secondary battery of the present invention
may have any of a coin shape, a button shape, a sheet shape, a
cylindrical shape, a cubic shape and the like. In the case where
the battery has a coin or button shape, the battery is produced, in
general, by forming the positive electrode and the negative
electrode in pellets, putting them in a can, and sealing the can by
caulking with intervention of an insulative packing.
[0086] In the case where the battery has a cylindrical or cubic
shape, the battery is formed, in general, by inserting a sheet-form
positive electrode and a sheet-form negative electrode in a can,
electrically connecting the can and the sheets, pouring an Ion
electrolyte and sealing the can with a sealing plate with
intervention of an insulative packing or with insulation by a
hermetic seal At this time, a safety valve provided with a safety
device may be used as the sealing plate. As the safety device, an
overcurrent prevention element such as a fuse, a bimetal, a PTC
element may be mentioned. Also, as measures for preventing rise of
inner pressure of the battery can, adopted are methods of making a
crack on a gasket, the sealing plate and the battery can. Further,
an external circuit may be used which has an Integrated
countermeasure against overcharge and overdischarge.
[0087] When the above-described battery is formed, the positive and
negative electrode in the pellet or sheet form are preferably dried
and dehydrated beforehand. As a drying and dehydrating method, a
common method may be used. For example, a method of blowing heated
air or low-moisture air to the positive and negative electrode, a
method of exposing them under vacuum and a method of irradiating
them with infrared, far-infrared and an electron beam may be
mentioned. These methods may be used singly or as a combination.
Temperature at drying and dehydration is preferably within the
range of 50 to 380.degree. C.
EXAMPLES
[0088] The present invention is now described in detail by way of
example thereof. It is noted that ethanol used in the following
examples had a purity of 99.5%.
Example
[0089] Preparation of LiNiO.sub.2
[0090] Starting compounds comprised of 0.03 moles of lithium
nitrate and 0.03 moles of nickel nitrate hexahydrate (molar ratio
of lithium to nickel is 1:1) were dissolved in 100 ml of ethanol
and stirred. To the mixture, 0.045 moles of oxalic acid dehydrate
in a powdery state was added and stirred at room temperature for
two hours, thereby to produce a precipitate comprised of oxalates
including a composite oxalate slightly soluble in alcohol from the
starting compounds. The mixture was filtered off to isolate the
precipitate, which was then dried. The resulting precipitate
comprised of oxalates containing the slightly soluble composite
oxalate was subjected to the major calcination at 700% in an
atmosphere of 100% oxygen for 10 hours The resulting calcined
matter was pulverized to obtain a positive electrode active
material, LiNiO.sub.2.
[0091] Production of Positive Electrode
[0092] The above-mentioned positive electrode active material,
LiNiO.sub.2, was mixed with acetylene black and
polytetrafluoroethylene in a mix ratio of 100:10:10 (by weight) in
a mortar. Subsequently, the resulting mixture was pressure-formed
into a pellet having a diameter of 20 mm and containing 0.01 g of
the active material. At that pressure-formation, a mesh of titanium
which would act as a collector was also included in the mixture. A
wire of titanium was taken out of the mesh of titanium and
spot-welded to evaluation means, thereby to obtain a positive
electrode for evaluation.
[0093] Evaluation of Positive Electrode Evaluation was carried out
by a three electrode method in which lithium was used as a counter
electrode and a reference electrode. As an electrolyte, used was 1
mol/L of lithium perchlorate (LiClO.sub.4) dissolved in a mixture
solvent of 1:1 of ethylene carbonate and ethylmethyl carbonate.
Lithium of the reference electrode was charged to 4.2V at a current
density of 27.4 mA/g and then discharged to 2.7V at the same
current density. Charge and discharge are repeated a number of
times within the same potential range at the same current
density.
[0094] As a result, an initial discharge capacity was 174
mAh/g.
Comparative Example 1
[0095] Preparation of LiNiO.sub.2
[0096] Lithium hydroxide and Nickel oxyhydroxide (NiOOH) were
weighed so that the molar ratio of lithium to nickel, Li:Ni, was
1.1:1, and mixed in a mortar. The mixture was formed into a pellet
at a pressure of 100 kg/cm.sup.2. This pellet was subjected to the
major calcination at 800.degree. C. in an atmosphere of 100% oxygen
for two hours. The resulting calcined matter was pulverized to
obtain a positive electrode active material, LiNiO.sub.2.
[0097] Production and Evaluation of Positive Electrode
[0098] A positive electrode was produced and evaluated in the same
manner as in Example 1. As a result, the initial discharge capacity
was 124 mAh/g.
Comparative Example 2
[0099] Preparation of LiNiO.sub.2
[0100] Lithium hydroxide, 0.20 moles, and nickel chloride, 0.20
moles, were weighed (the molar ratio of lithium to nickel, Li:Ni,
was 1:1) and each dissolved in 100 ml of water to obtain aqueous
solutions. The aqueous solution of lithium hydroxide was added to
the aqueous solution of nickel chloride in five hours with stirring
at 30.degree. C. The resulting aqueous solution was dried at 90 to
100%, and the resulting solid was pulverized and formed at a
pressure of 100 kg/cm.sup.2, thereby to produce a pellet. The
pellet was subjected to the major calcination at 800.degree. C. in
an atmosphere of 100% oxygen for two hours. The resulting calcined
matter was pulverized to obtain a positive electrode active
material, LiNiO.sub.2.
[0101] Production and Evaluation of Positive Electrode
[0102] A positive electrode was produced and evaluated in the same
manner as in Example 1. As a result, the initial discharge capacity
was 120 mAh/g.
Comparative Example 3
[0103] Preparation of LiNiO.sub.2
[0104] Lithium hydroxide and nickel hydroxide were weighed so that
the molar ratio of lithium to nickel, Li:Ni, was 1:1, and mixed
with a small amount of water as a dispersant in a mortar. The
resulting mixture was dried at 90 to 100.degree. C. to obtain a
solid. The solid was pulverized and formed at a pressure of 100
kg/cm.sup.2 into a pellet. The pellet was subjected to the major
calcination at 800% in an atmosphere of 100% oxygen for two hours.
The resulting calcined matter was pulverized to obtain a positive
electrode active material, LiNiO.sub.2.
[0105] Production and Evaluation of Positive Electrode
[0106] A positive electrode was produced and evaluated in the same
manner as in Example 1. As a result, the initial discharge capacity
was 110 mAh/g.
Comparative Example 4
[0107] Preparation of LiNiO.sub.2
[0108] Lithium chloride, 0.20 moles, and nickel oxide (NiO), 0.20
moles, were weighed (the molar ratio of lithium to nickel, Li:Ni,
was 1:1) and lithium chloride was dissolved in 100 ml of water to
obtain an aqueous solution. The aqueous solution of lithium
chloride was added to nickel oxide in five hours while kneading
nickel oxide at 30.degree. C. The resulting mixture was dried at 90
to 100.degree. C. to obtain a solid. The solid was pulverized and
formed at a pressure of 100 kg/cm.sup.2 into a pellet. The pellet
was subjected to the major calcination at 800.degree. C. in an
atmosphere of 100% oxygen for two hours. The resulting calcined
matter was pulverized to obtain a positive electrode active
material, LiNiO.sub.2.
[0109] Production and Evaluation of Positive Electrode
[0110] A positive electrode was produced and evaluated in the same
manner as in Example 1. As a result, the initial discharge capacity
was 127 mAh/g.
Comparative Example 5
[0111] Preparation of LiNiO.sub.2
[0112] Lithium hydroxide anhydride, 0.60 moles, and nickel nitrate
hexahydrate, 0.03 moles, were dissolved in 100 ml of water and
stirred. To the resulting mixture, 0.045 moles of oxalic acid in a
powdery state were added and stirred at room temperature for two
hours with co-precipitation. The resulting precipitate was filtered
off and dried. The resulting precipitate was subjected to the major
calcination at 700.degree. C. in an atmosphere of 100% oxygen for
10 hours. The resulting calcined matter was pulverized to obtain a
positive electrode active material, LiNiO.sub.2.
[0113] Production and Evaluation of Positive Electrode
[0114] A positive electrode was produced and evaluated in the same
manner as in Example 1. As a result, the initial discharge capacity
was 158 mAh/g.
[0115] Comparison of Example 1 with Comparative Examples 1 to 5
showed that according to the process of Example 1, a positive
electrode active material having excellent initial discharge
characteristics was able to be obtained.
Example 2
[0116] Precipitate comprised of oxalates containing a slightly
soluble composite oxalate were obtained in substantially the same
manner as in Example 1 except that lithium nitrate and nickel
nitrate were weighed so that the molar ratio of lithium to nickel,
Li:Ni, was 0.5:1, 1.0:1, 1.1:1, 1.5:1 and 2.5:1. The molar ratio of
lithium to nickel in the resulting precipitates comprised of
oxalates containing a slightly soluble composite oxalate was
determined with an ICP emission spectroscopy. The respective molar
ratios of lithium to nickel, Li:Ni, were 0.48:1, 1.02:1, 1.10:1,
1.46:1 and 2.47:1. The results showed that the resulting
precipitates comprised of oxalates containing a slightly soluble
composite oxalate had molar ratios close to those of the starting
material.
Example 3
[0117] The production of the precipitate comprised of oxalates
containing a slightly soluble composite oxalate of Example 1 was
repeated three times. The resulting precipitates comprised of
oxalates containing a slightly soluble composite oxalate were
determined with regard to the molar ratio of lithium to nickel with
the ICP emission spectroscopy. The molar ratios in the precipitates
were 0.98:1, 1.02:1 and 1.01:1.
[0118] The above precipitates comprised of oxalates containing a
slightly soluble composite oxalate were subjected to the major
calcination as in Example 1, to produce positive electrode active
materials. Positive electrodes were produced from the active
materials and evaluated as in Example 1. The initial discharge
capacities of the positive electrodes were 176 mAh/g, 175 mAh/g and
173 mAh/g.
Example 4
[0119] Filtrate which was obtained when the precipitate comprised
of oxalates containing a slightly soluble composite oxalate of
Example 1 was filtered off was distilled to separate ethanol.
Ethanol thus obtained was used for producing a positive electrode
active material and a positive electrode as in Example 1 and the
positive electrode was evaluated. The initial discharge capacity
was 176 mAh/g.
[0120] Examples 2 to 4 showed that it became easy to control the
ratio of lithium to nickel in the precipitate comprised of oxalates
containing a slightly soluble composite oxalate, that the
uniformity of the precipitate was improved, and that the initial
discharge characteristic of the positive electrode active material
after calcination was able to be stabilized. It was also found that
the alcohol obtained from the filtrate could be used again and
therefore that the production costs could be reduced.
Examples 5 to 13
[0121] Preparation of LiNiO.sub.2
[0122] Starting compounds composed of 0.33 moles of lithium nitrate
and 0.30 moles of nickel nitrate hexahydrate (the molar ratio of
lithium and nickel, Li:Ni, was 1.1:1) were dissolved in 1000 ml of
ethanol and stirred. To the mixture, added were 0.465 moles of
oxalic acid dehydrate in a powdery state and the resulting mixture
was stirred at room temperature for two hours, thereby to produce a
precipitate comprised of oxalates containing a composite oxalate
slightly soluble in alcohol from the starting compounds. The
mixture was filtered off to isolate the precipitate, which was then
dried. The precipitate was subjected to the major calcination for
five hours in an atmosphere of 100% oxygen at varied temperatures
of 600, 650, 700, 750, 800, 850, 900, 940 and 980.degree. C. The
resulting calcined matters were pulverized to obtain positive
electrode active materials, LiNiO.sub.2. These active materials are
referred to as Examples 5 to 13, respectively.
[0123] Production and Evaluation of Positive Electrodes
[0124] Positive electrodes were produced in substantially the same
manner as in Example 1 except that the ratio of the positive
electrode active materials, acetylene black and
polytetrafluoroethylene was 100:8:10.
[0125] The positive electrodes were evaluated in substantially the
same manner as in Example 1 except that the electrolyte was 1 mol/L
of lithium perchlorate (LiClO.sub.4) dissolved in a mixture solvent
of 1:1 of ethylene carbonate and diethylcarbonate.
[0126] FIG. 1 is a graphical representation illustrating
relationship between the initial discharge capacity and the major
calcination temperature. FIG. 1 shows that the major calcination
temperature is preferably within the range of 650 to 900.degree.
C., more preferably 700 to 850.degree. C.
Examples 14 to 22
[0127] Preparation of LiNi.sub.0.8Al.sub.0.2O.sub.2
[0128] Starting compounds comprised of 0.30 moles of lithium
nitrate, 0.24 moles of nickel nitrate hexahydrate and 0.06 moles of
aluminum nitrate nonahydrate (the molar ratio of lithium, nickel
and aluminum, Li:Ni:Al, was 1:0.8:0.2) were dissolved in 1000 ml of
ethanol and stirred. To the mixture, added was oxalic acid in a
powdery state and the resulting mixture was stirred at room
temperature for two hours. thereby to produce a precipitate
comprised of oxalates containing a composite oxalate slightly
soluble in alcohol from the starting compounds. The mixture was
filtered off to isolate the precipitate, which was then dried. The
resulting precipitate was subjected to the major calcination for 10
hours in an atmosphere of 100% oxygen at temperatures of 600, 650,
700, 750, 800, 850, 900, 940 and 980.degree. C. The resulting
calcined matters were pulverized to obtain positive electrode
active materials, LiNi.sub.0.8Al.sub.0.2O.sub.2.
[0129] These positive electrode active materials are referred to as
Examples 14 to 22, respectively.
[0130] Production and Evaluation of Positive Electrodes
[0131] Positive electrodes were produced in substantially the same
manner as in Example 1 except that the ratio of the positive
electrode active materials, acetylene black and
polytetrafluoroethylene was 100:8:10.
[0132] The positive electrodes were evaluated in substantially the
same manner as in Example 1 except that the electrolyte was 1 mol/L
of lithium perchlorate (LiClO.sub.4) dissolved in a mixture solvent
of 1:1 of ethylene carbonate and diethylcarbonate.
[0133] FIG. 2 is a graphical representation illustrating
relationship between the initial discharge capacity and the major
calcination temperature.
[0134] FIG. 2 shows that the major calcination temperature is
preferably within the range of 650 to 900.degree. C., more
preferably 700 to 850.degree. C.
Examples 23 to 29
[0135] Preparation of LiNiO.sub.2
[0136] Starting compounds comprised of 0.10 moles of lithium
acetate dehydrate and 0.10 moles of nickel acetate hexahydrate (the
molar ratio of lithium to nickel, Li:Ni, was 1:1) were dissolved in
1000 ml of ethanol and stirred. To the mixture, added was oxalic
acid which was dissolved in an alcohol and the mixture was stirred
at room temperature for two hours, thereby to produce a precipitate
comprised of oxalates containing a composite oxalate slightly
soluble in alcohol from the starting compounds. The mixture was
filtered off to isolate the precipitate, which was then dried. The
resulting precipitate was subjected to the major calcination at
700.degree. C. for eight hours in atmospheres of nitrogen and
oxygen having oxygen concentrations of 10, 30, 50, 70, 80 and 100%
and in an atmosphere of air (the oxygen concentration was about
20%). The resulting calcined matters were pulverized to obtain
positive electrode active materials, LiNiO.sub.2.
[0137] The active materials are referred to as Examples 23 to 29,
respectively.
[0138] Production and Evaluation of Positive Electrodes
[0139] Positive electrodes were produced in substantially the same
manner as in Example 1 except that the ratio of the positive
electrode active materials, acetylene black and
polytetrafluoroethylene was 100:15:8.
[0140] The positive electrodes were evaluated in substantially the
same manner as in Example 1 except that the electrolyte was 1 mol/L
of lithium phosphofluoride (LiPF.sub.6) dissolved in a mixture
solvent of 1:1 of ethylene carbonate and diethylcarbonate.
[0141] FIG. 3 is a graphical representation illustrating
relationship between the initial discharge capacity and
concentrations of oxygen in calcining atmosphere.
[0142] FIG. 3 shows that the concentration of oxygen in the
calcining atmosphere is preferably that in air or within the range
of 21 to 100%, which is higher than the ratio by volume of oxygen
in the atmosphere, more preferably within the range of 50 to
100%
Example 30
[0143] Preparation of Positive Electrode Active Material and
Production of Positive Electrode
[0144] A positive electrode active material, LiNiO.sub.2, and a
positive electrode in a pellet form of is mm diameter containing 50
mg of the active material were produced in the same manner as in
Example 1.
[0145] Production of Negative Electrode
[0146] A substrate of nickel (having a surface area of 4 cm.sup.2)
was used as a collector. A negative electrode was produced by
depositing a pyrolyzed carbon as a negative electrode active
material on the collector, the pyrolyzed carbon being obtained from
propane as a starting material by an atmospheric gas-phase
pyrolysis. The pyrolyzed carbon was deposited under a temperature
of 750.degree. C. for two hours. The pyrolyzed carbon was found by
X-ray diffractometry to have an interpolar distance d.sub.002 of
0.337 nm on plane (002) and a thickness of crystallite Lc of 15 nm
in the direction of the plane (002) and by argon laser Raman
spectroscopy to have an R value of 0.45. The R value is a ratio of
intensity of a peak around 1360 cm.sup.-1 to intensity of a peak
around 1580 cm.sup.-1. A wire of nickel was spot-welded to the
substrate of nickel for taking out collected electricity. The
substrate was dried at 200.degree. C. under vacuum for removing
moisture, thereby to obtain a negative electrode. The weight of the
active material in the negative electrode was 35 mg.
[0147] Evaluation of Battery
[0148] For evaluation of a battery, a beaker-form cell was used and
the positive and negative electrodes produced as above were used.
The electrolyte was 1 mol/L of lithium perchlorate dissolved in a
mixture solvent of 1:1 of propylene carbonate and diethyl
carbonate. For a charge/discharge test, the battery was first
charged to 4.4V at a current of 0.2 mA and then discharged to 2.5 V
at the same current. Charge and discharge was repeated over and
over within the same range of voltage and at the same current
density from the second charge and discharge in order to evaluate
the battery.
[0149] The first discharge capacity of the battery was 8.0 mAh, and
the 100th discharge capacity of the battery was 7.3 mAh.
Example 31
[0150] Preparation of Positive Electrode Active Material and
Production of Positive Electrode
[0151] A positive electrode active material, LiNiO.sub.2, and a
positive electrode in a pellet form of 15 mm diameter and 0.75 mm
thickness which contained 0.2 g of the active material were
produced in the same manner as in Example 1.
[0152] Production of Negative Electrode
[0153] Natural graphite from Madagascar (in a scale form: particle
diameter was 11 .mu.m; d.sub.002 was 0.337 nm; Lc was 27 nm; La was
17 nm, R value was 0; specific surface area was 8 m.sup.2/g) was
used as a negative electrode active material. The negative
electrode active material was mixed with polytetrafluoroethylene in
a mixing ratio of 10:1. The mixture was pressure-formed into a
pellet of 15 mm diameter and-0.59 mm thickness which contained 0.1
g of the active material. At the pressure-formation, a mesh of
nickel which would act as a collector was included. The pellet was
dried at 200.degree. C. under vacuum for removing moisture, thereby
to obtain a negative electrode.
[0154] Assembly of Battery
[0155] As shown in FIG. 4, the positive electrode containing a
positive electrode collector 2 was contact-bonded to a positive
electrode can 1 provided with an insulating packing 8.
Subsequently, a separator 7 of nonwoven polypropylene was placed
thereon. The separator was impregnated with an electrolyte
comprised of 1 mol/L of an electrolytic salt LiPF.sub.6 dissolved
in a mixture solvent of ethylene carbonate, propylene carbonate and
diethyl carbonate in a mixing ratio of 2:1:3 by volume. On the
other hand, for contact-bonding the negative electrode 6 containing
a negative electrode collector 5 to the inside surface of a
negative electrode can 4, the negative electrode 6 was placed on
the separator 7. Then the positive electrode can 1 and the negative
electrode can 4 were caulked with intervention of the insulating
packing 8 and sealed. Thus a coin-type battery was produced.
[0156] Evaluation of Battery
[0157] The produced coin-type battery was charged up to an upper
charge limit of 4.4 V at a charge/discharge current of 1 mA and
subsequently discharged to a lower discharge limit of 2.5V. For
evaluation, the battery was tested on its discharge capacity. This
charge and discharge were repeated over and over within the same
range of voltage at the same current density from the second charge
and discharge in order to evaluate the battery.
[0158] The discharge capacity at the first cycle was 28.4 mAh and
the discharge capacity at the 100th cycle was 25.7 mAh.
Example 32
[0159] A cylindrical battery as shown in FIG. 5 was produce as
follows.
[0160] For a positive electrode, 100 parts by weight of a positive
electrode active material LiNiO.sub.2 produced as in Example 1, 7
parts by weight of powdery acetylene black as a conductor and 10
parts by weight of polyvinylidene fluoride as a binder were mixed
with N-methyl-2-pyrrolidone as a dispersant, to obtain a paste for
forming the positive electrode. The paste for forming the positive
electrode was applied onto both faces of a collector of aluminum
foil of 20 .mu.m thickness, followed by drying. The aluminum foil
was subjected to rolling and cut into strips. A tab of aluminum as
a positive electrode lead was spot-welded to an end portion of the
separate strip. Thus a positive electrode 16 was obtained. The
positive electrode active material was contained in the positive
electrode in a ratio of 40 mg/cm.sup.2.
[0161] For a negative electrode, 100 parts by weight of an
artificial graphite (particle diameter was 8 .mu.m; d.sub.002 was
0.337 nm; Lc was 25 nm; La was 13 nm; R value was 0; specific
surface area was 12 m.sup.2/g) as a negative electrode active
material and 10 parts by weight of polyvinylidene fluoride as a
binder were mixed with N-methyl-2-pyrrolidone as a dispersant, to
obtain a paste for forming the negative electrode. The paste for
forming the negative electrode was applied onto both faces of a
collector of copper foil of 18 .mu.m thickness, followed by drying.
The copper foil was subjected to rolling and cut into strips. A tab
of nickel as a negative electrode lead was spot-welded to an end
portion of the separate strip. Thus a negative electrode 15 was
obtained. The negative electrode active material was contained in
the negative electrode in a ratio of 20 mg/cm.sup.2.
[0162] The positive electrode 16 and the negative electrode 15 were
arranged in an opposed relation with intervention of a porous
separator 14 of polyethylene and spirally wound to form a wound
element. This wound element was placed in a battery can 13 (of 17
mm diameter and 50 mm height, made of stainless steel) with the
positive electrode lead and the negative electrode lead upward and
downward, respectively. The negative electrode lead was spot-welded
to the bottom of the battery can 13 and the positive electrode lead
was spot-welded to a positive electrode cap 11 with a safety valve.
A center pin 17 (a tube of stainless steel of 3.4 mm diameter and
40 mm length) was inserted in the center of the wound element for
preventing wind shifting. Subsequently, an electrolyte of lithium
phosphofluoride dissolved in a ratio of 1 mol/L in a mixture
solvent of 1:1 of ethylene carbonate and diethyl carbonate was
poured into the battery can, and the positive electrode cap 11 was
caulked with intervention of an insulating packing 12. Thus
produced was cylindrical battery.
[0163] The charge/discharge test was carried out in a constant
temperature bath at 25.degree. C. by charging in a constant current
and constant method at a discharge current of 500 mA and at an
upper limit voltage of 4.2 V for three hours and discharging in a
constant current method at a discharge current of 100 mA and at a
lower limit voltage of 2.75 V.
[0164] As a result, the initial discharge capacity was 916 mAh and
the battery capacity after 50 cycles was 810 mAh.
[0165] According to the process for producing a positive electrode
active material of the present invention, obtainable is a
precipitate comprised of oxalates containing a slightly soluble
composite oxalate in which lithium and nickel are uniformly mixed.
As a result, a positive electrode active material produced by use
of the precipitate comprised of oxalates containing the slightly
soluble composite oxalate exhibits a discharge capacity of about
175 mAh/g while at the same time exhibiting excellent
charge/discharge characteristics and cycle characteristics.
Further, since alcohol used for producing the precipitate comprised
of oxalates containing the slightly soluble composite oxalate can
be recycled for use, a large effect can be expected from the
viewpoint of costs.
[0166] Further, anonaqueous secondary battery using the positive
electrode active material obtained by the process of the present
invention has an improved performance compared with a battery
obtained by the conventional process, and also reduction of costs
is possible.
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