JP2001006673A - Nonaqueous electrolyte lithium secondary battery and its positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery causing small drop of the battery capacity even through repetitive charge and discharge for a long period of time, and excellent in the cyclic characteristics, in particular in a high-temp. environment and offer spinel type lithium manganate for positive electrode active material to be used in such a lithium secondary battery. SOLUTION: A compound is formed from lithium hydroxide and at least one of the doping elements M including Ti, Co, Ni, Fe, Cr, V, Al and Mg, and this compound and manganese dioxide are mixed together in a solvent consisting of aliphatic alcohol having the carbon umber 1-3 so that a homogeneous mixture is prepared, and the mixture is dried and baked so that intended spinel type lithium manganate for a positive electrode active material is produced, wherein the 2Li/(Mn+M) atomic ratio ranges between 1.01 and 1.30 and the content of the doping element M ranges between 0.01-10.0 mol% relative to the manganese atom. A non-aqueous electrolyte lithium secondary battery is formed using this spinel type lithium manganate as the positive electrode active material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte lithium secondary battery and a positive electrode active material therefor.
In particular, the present invention relates to a non-aqueous electrolyte lithium secondary battery having significantly improved cycle characteristics and a positive electrode active material comprising spinel-type lithium manganate therefor. The present invention also relates to a method for producing such a spinel-type lithium manganate.

[0002]

2. Description of the Related Art A non-aqueous electrolyte (organic electrolyte) lithium secondary battery has a high discharge potential and a high energy density, has less self-discharge than conventional secondary batteries, and has excellent cycle characteristics. In addition to being widely used as a power source for various portable cordless electronic devices, it has recently been put to practical use as a power source for driving electric vehicles from the viewpoint of protecting the global environment. Hitherto, lithium cobalt oxide (LiCoO ₂ ) having a layered structure has been put to practical use as a positive electrode active material of such a nonaqueous electrolyte secondary battery because a high discharge potential and a high energy density are easily obtained. .

[0003] However, since lithium cobaltate has a small amount of cobalt as a natural resource and is expensive,
In recent years, lithium nickel oxide (LiNiO ₂ ) has attracted attention. Although lithium nickelate is relatively inexpensive as compared with lithium cobaltate, there are still various obstacles to practical use from the viewpoint of price and performance.

Therefore, recently, a manganese-based oxide has been expected as a positive electrode active material that provides a low-cost, small-sized, light-weight, and high-energy-density lithium secondary battery. Among various manganese oxides, in particular, L
Attention has been paid to a spinel-type lithium manganate represented by iMn ₂ O ₄ , and research is proceeding.

However, a lithium secondary battery using spinel-type lithium manganate as a positive electrode active material has a lower discharge capacity due to charge and discharge than a lithium secondary battery using lithium cobalt oxide as a positive electrode active material. Remarkable. That is, the cycle characteristics are poor. In particular, this tendency is remarkable at a battery temperature exceeding 45 ° C., and at 55 ° C., the discharge capacity rapidly decreases. In order for a lithium secondary battery using spinel-type lithium manganate as a positive electrode active material to be a practical power source for automobiles, it is important to suppress the deterioration of discharge capacity under such a high-temperature environment.

In order to solve such a problem, conventionally,
Various methods have been proposed. For example, JP-A-10-1
Japanese Patent Application Publication No. 06561 proposes that the lithium content in the spinel-type lithium manganate be excessive in a certain range than the stoichiometric amount. Has not been improved enough.

Japanese Patent Application Laid-Open No. 9-35712 discloses that
Spinel-type lithium manganate whose surface has been replaced with a transition metal such as cobalt, iron and nickel has been proposed.
JP-A-10-172571 discloses that lithium manganate particles have a two-layer structure including a central layer and a surface layer,
It has been proposed that one is made of lithium manganate and the other is made of a composite oxide containing one selected from cobalt, nickel, chromium, iron, titanium, vanadium, molybdenum or boron together with manganese. However, none of these lithium manganates has sufficiently improved cycle characteristics even at room temperature.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in a lithium secondary battery using spinel-type lithium manganate as a positive electrode active material. The reduction in battery capacity is small even when repeated, and in particular, even under a high-temperature environment, aims to provide a lithium secondary battery with excellent cycle characteristics, and the present invention provides a positive electrode in such a lithium secondary battery. An object of the present invention is to provide a spinel-type lithium manganate for an active material. Another object of the present invention is to provide a method for producing such a spinel-type lithium manganate.

[0009]

According to the present invention, lithium hydroxide and Ti, Co, Ni, Fe, Cr, V, Al and Mg are dissolved in a solvent comprising an aliphatic alcohol having 1 to 3 carbon atoms. At least one doping element M selected from
Is mixed with manganese dioxide to form a homogeneous mixture, which is dried and calcined to obtain 2Li / (M
n + M) The atomic ratio is in the range of 1.01 to 1.30 and the doping element M is 0.01 to manganese atom.
A positive electrode active material for a non-aqueous electrolyte lithium secondary battery comprising spinel-type lithium manganate having a content of 10.0 mol% is provided.

Further, according to the present invention, there is provided a non-aqueous electrolyte lithium secondary battery using the above spinel-type lithium manganate as a positive electrode active material.

Further, according to the present invention, lithium hydroxide and at least one selected from the group consisting of Ti, Co, Ni, Fe, Cr, V, Al and Mg are used in a solvent comprising an aliphatic alcohol having 1 to 3 carbon atoms. 2Li / (Mn +) comprising mixing a compound of one kind of doping element M and manganese dioxide to form a homogeneous mixture, drying and calcining the mixture.
M) The atomic ratio is in the range of 1.01 to 1.30, and the doping element M is 0.01 to 10.0 with respect to manganese atoms.
A method for producing spinel-type lithium manganate having a molar percentage in the range is provided.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A positive electrode active material for a non-aqueous electrolyte lithium secondary battery according to the present invention comprises lithium hydroxide and Ti, C in a solvent comprising an aliphatic alcohol having 1 to 3 carbon atoms.
o, a compound of at least one doping element M selected from Ni, Fe, Cr, V, Al and Mg and manganese dioxide are mixed to form a homogeneous mixture, which is dried and fired, 2Li / (Mn + M) atomic ratio is
A spinel type having a doping element M in a range of 0.01 to 10.0 mol% in a range of 1.01 to 1.30;
That is, it is made of lithium manganate having a spinel crystal structure.

Such a spinel-type lithium manganate has an atomic ratio of 2Li / (Mn + M) in the range of 1.01 to 1.30 and a doping element M of 0.01 to 10.0 with respect to manganese. In a range of mol%, lithium hydroxide, the compound of the doping element M, and manganese dioxide are mixed in a solvent composed of an aliphatic alcohol having 1 to 3 carbon atoms to form a homogeneous mixture. Dry,
It can be obtained by firing.

In the present invention, the 2Li / (Mn + M) atomic ratio indicates an excess ratio from the stoichiometric ratio (1.00) of lithium atoms in spinel-type lithium manganate;
The substitution amount of the manganese atom by the doping element M is:
It is defined by [M / (Mn + M)] × 100 (mol%).

As the above-mentioned aliphatic lower alcohol having 1 to 3 carbon atoms, for example, methanol, ethanol, n-propanol, isopropanol and the like can be used. Of these, methanol is particularly preferable. In the present invention, the most preferred solvent is 50
Said aliphatic alcohols which may contain up to 20% by weight of water, preferably up to 20% by weight of water, particularly preferably those having a water content of 5% by weight or less (including anhydrous). Especially methanol.

The amount of the solvent to be used is not particularly limited, but is usually 0.1 to 1 kg of manganese dioxide.
A range of 2L to 1L is preferred. As described above, when lithium hydroxide, manganese dioxide, and the compound of the doping element are mixed in the solvent, a homogeneous mixture can be usually obtained within one hour.

More specifically, first, a compound of manganese dioxide and the doping element M, preferably an oxide, is added to the above-mentioned solvent in the above-mentioned ratio to prepare a suspension. And add lithium hydroxide
With mixing and stirring, lithium hydroxide is reacted with an alcohol solvent, dissolved in the solvent, and the lithium ions thus generated are impregnated into manganese dioxide, which is porous particles,
The mixture thus obtained is dried and calcined.

In the method of the present invention, lithium hydroxide is considered to dissolve quickly in the above-mentioned alcoholic solvent by synergistic action with manganese dioxide in the above-mentioned alcoholic solvent to form a homogeneous mixture. In other words, lithium hydroxide is formed in the presence of manganese dioxide by a complex physical action including adsorption on manganese dioxide particles and a complex chemical reaction including exothermic chemical reaction between manganese dioxide and the alcohol. It dissolves readily and quickly in alcohol as an ion, and the lithium ions thus formed diffuse into the pores of the porous manganese dioxide particles, producing a homogeneous paste-like mixture. In particular, according to a preferred embodiment, while the lithium hydroxide is dissolved in the alcohol, the heat largely evaporates the alcohol, and by the time the reaction is completed, a paste-like homogeneous mixture can be obtained. .

As manganese dioxide, electrolytic manganese dioxide is particularly preferably used. As the doping element, at least one element selected from titanium, cobalt and aluminum is preferably used. In particular, titanium is preferably used alone in the form of titanium dioxide or in combination with cobalt and / or aluminum.

Therefore, such a paste-like mixture is
If necessary, after heating and drying, baking is carried out at a high temperature in an oxidizing atmosphere, usually at a temperature in the range of 650 to 950 ° C., whereby the intended spinel-type lithium manganate can be obtained. The sintering time depends on the sintering means such as an electric furnace or a microwave and the sintering temperature, but is usually in the range of 5 minutes to 15 hours.

In the production of the spinel-type lithium manganate according to the present invention, the 2Li / (Mn + M) atomic ratio is 1.0.
When it is smaller than 1, even if a part of the manganese atom is replaced with the doping element M, the retention of the discharge capacity of the nonaqueous electrolyte lithium secondary battery using this as the positive electrode active material is not significantly improved. Here, the retention rate of the discharge capacity is the ratio of the discharge capacity to the initial discharge capacity when charging and discharging of the obtained nonaqueous electrolyte lithium secondary battery are repeated. However, when the 2Li / (Mn + M) atomic ratio exceeds 1.30,
Such a nonaqueous electrolyte lithium secondary battery using spinel-type lithium manganate as a positive electrode active material is excellent in cycle characteristics, but is not preferable because the battery capacity is reduced.

Further, in the production of the spinel-type lithium manganate according to the present invention, even if the doping element is used in a proportion of less than 0.01 mol% with respect to manganese atoms,
The retention rate of the discharge capacity of the obtained lithium secondary battery is not significantly improved. On the other hand, if the doping element is more than 10.0 mol% with respect to manganese atoms, not only the retention of the discharge capacity is saturated, but also the production cost of such a spinel-type lithium manganate is undesirably increased. Absent.

In particular, in the present invention, 2Li / (Mn
+ M) The atomic ratio is preferably in the range from 1.02 to 1.25, and particularly preferably in the range from 1.03 to 1.20.
Further, the ratio of the doping element M to the manganese atom is preferably in the range of 0.1 to 5.0 mol%, more preferably in the range of 0.2 to 4.0 mol%, and most preferably. , 0.25 to 3.5 mol%.

According to the present invention, as described above, the manganese atom is replaced with the doping element M in a limited range, and the lithium atom is replaced with the manganese atom and the doping element M in a limited range. By using the spinel-type lithium manganate obtained in excess as the positive electrode active material, the cycle characteristics are remarkably improved.
A lithium secondary battery with significantly improved cycle characteristics at high temperatures can be obtained. It is considered that such improvement of the cycle characteristics is due to the synergistic effect in the above-described manufacturing stage and, as described above, the synergistic effect due to the presence of excess lithium and the addition of the doping element in the obtained spinel-type lithium manganate.

In particular, in the present invention, titanium is used as a doping element, the 2Li / (Mn + Ti) atomic ratio is set to 1.05 to 1.15, and the ratio of titanium to manganese is set to 0.3 to 3. When the content is in the range of 0.5 mol%, a nonaqueous electrolyte lithium secondary battery having extremely excellent cycle characteristics can be obtained not only at normal temperature (25 ° C.) but also at high temperature (65 ° C.).

The lithium secondary battery according to the present invention comprises a positive electrode, a negative electrode made of a carbonaceous material capable of occluding and releasing lithium, a lithium alloy or lithium ions, and a separator disposed between the positive electrode and the negative electrode. , A lithium ion conductive organic electrolyte. Such a lithium secondary battery is already well known.

For example, when the positive electrode is used in a coin-type battery, a positive electrode active material, a conductive agent and a binder are mixed, and this mixture (positive electrode mixture) is pressure-formed to form a disc. A positive electrode can be obtained. As the conductive agent, for example, graphite is used, and as the binder, for example, polytetrafluoroethylene or the like is used. On the other hand, the negative electrode is made of a carbonaceous material capable of occluding and releasing lithium metal, a lithium alloy or lithium ions, and has a shape of
It is determined appropriately according to the positive electrode. Further, the positive electrode and the negative electrode may be used together with a current collector, if necessary.

As the separator provided between the positive electrode and the negative electrode, for example, a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene, a porous film made of a polyolefin, or the like is used.

As the lithium ion conductive organic electrolyte, for example, an electrolytic solution obtained by dissolving an electrolyte in a non-aqueous solvent is preferably used, but is not limited to this. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone,
Sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and the like are used. These are used alone or as a mixture of two or more.

Examples of the lithium ion conductive electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and lithium arsenide hexafluoride (LiAsF).
₆ ), lithium trifluoromethanesulfonate (LiC
F ₃ SO ₃ ), lithium aluminum chloride (LiAlC)
l) and the like. Such an electrolyte is generally used in the non-aqueous solvent so as to have a concentration of 0.5 to 1.5 mol / L.

Further, in the present invention, instead of using the combination of the organic electrolyte solution and the separator as described above, a lithium ion conductive solid electrolyte which also serves as the separator can be used. Various types of such solid electrolytes are already known.

FIG. 1 shows an example of a coin-type lithium secondary battery. That is, in this battery, for example, a positive electrode current collector 2 is disposed on the bottom surface of a positive electrode can 1 made of stainless steel, a disk-shaped positive electrode 3 is laminated thereon, and further, The separator 4 is laminated. The disk-shaped negative electrode 5 is provided on the separator, and the negative electrode current collector 6 is provided on the negative electrode. Further, the negative electrode can 7
A negative electrode can 7 having the negative electrode current collector on the bottom surface is provided via an insulating packing 8 so as to liquid-tightly seal the opening of the positive electrode can. The negative electrode can 7 is made of, for example, stainless steel. Further, the lithium ion conductive electrolyte is usually impregnated and supported on a separator.

[0033]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples.

Electrolytic manganese dioxide 1.0 L in 3 L of methanol
0 kg, a predetermined amount of lithium hydroxide monohydrate and titanium dioxide were added, mixed and stirred to obtain a paste-like mixture. After drying to a powder, the powder is dried in air at 85
Heating and baking at 0 to 900 ° C. for 10 hours gave spinel-type lithium manganate.

To 85 parts by weight of the spinel-type lithium manganate thus obtained, 10 parts by weight of graphite as a conductive agent and 5 parts by weight of polytetrafluoroethylene as a binder were mixed to form a positive electrode mixture. It was molded to prepare a disk-shaped positive electrode. Disc-shaped lithium was used as the negative electrode. The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / L in a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 2. The coin-type lithium secondary battery shown in FIG. 1 was assembled using a microporous polypropylene film as a separator.

Here, 1 mol% of manganese atoms is replaced by titanium atoms, and the 2Li / (Mn + Ti) atomic ratio is 1.3.
FIG. 2 shows an X-ray diffraction diagram of the spinel-type lithium manganate obtained as 0, 1.20, 1.10, or 1.00. FIG. 3 shows a charge / discharge curve at 25 ° C. of a lithium secondary battery provided with a positive electrode using these lithium manganate as a positive electrode active material.

Further, as described above, as shown in Table 1, the manganese atoms were replaced with the doping elements at various ratios, and the 2Li / (Mn + M) atomic ratios were changed at various ratios to obtain the spinel-type lithium manganate. A non-aqueous electrolyte lithium secondary battery using this as a positive electrode active material was assembled, and charge and discharge were repeated at 25 ° C. or 60 ° C. to evaluate the cycle characteristics. That is, the current density is 1 m
The battery was charged at A / cm ^{2 to an} upper limit voltage of 4.3 V, discharged at a current density of ² mA / cm ^{2 to a} lower limit voltage of 3.0 V, and charging and discharging were repeated in this manner.

When titanium is used as a doping element, 2Li / (Mn + Ti) atomic ratio and 1 to titanium amount
FIG. 4 shows the retention rate (25 ° C.) of the discharge capacity at the 00th cycle. Table 1 shows the retention ratio of the discharge capacity of the battery at 25 ° C. or 60 ° C. In the retention rate of discharge capacity,
Numbers in parentheses indicate the number of cycles (actually measured values).
The inside shows the retention rate of the discharge capacity at the 100th cycle (actually measured value or extrapolated value therefrom).

[0039]

[Table 1]

In the batteries J, K and L (comparative examples),
Since the 2Li / (Mn + Ti) atomic ratio is the stoichiometric ratio of spinel-type lithium manganate, even if a part of the manganese atoms is replaced with the doping element Ti, the discharge capacity retention rate at the 100th cycle is at most 85%. It's just Battery G,
In H and I, the 2Li / (Mn + Ti) atomic ratio is
1.05, that is, an excess amount of lithium with respect to manganese and titanium was set to 5%, and a part of the manganese atoms was replaced with a doping element titanium to obtain an ordinary temperature (25%).
C.), the retention rate of the discharge capacity at the 100th cycle is 9
It is raised to about 0%.

In the battery F-1 (comparative example), 2Li
/ (Mn + Ti) atomic ratio was 1.10, that is, the excess amount of lithium to manganese was 10%. However, since manganese atoms were not replaced by doping elements, normal temperature (25
° C) and high temperature (60 ° C), the cycle characteristics are poor. On the other hand, according to the batteries F-2 and F-3, lithium is made excessive with respect to manganese and the doping element, and a part of the manganese atoms is replaced with aluminum atoms. At 25 ° C.).

Batteries A, B-1, B-2, C, D and E
Means that the 2Li / (Mn + Ti) atomic ratio is from 1.10 to 1.14.
And the capacity retention of a non-aqueous electrolyte lithium secondary battery using a spinel-type lithium manganate obtained as a positive electrode active material by using titanium (partially in combination with cobalt) as a doping element. A remarkable improvement in cycle characteristics at not only 25 ° C.) but also at a high temperature (60 ° C.) has been achieved. According to battery A, 1 at room temperature
99.3% retention of discharge capacity at the 00th cycle, 94.6% retention of discharge capacity at 800 cycles, 10% at 60 ° C.
The discharge capacity retention rate at the 0th cycle is 94.7%, and the discharge capacity retention rate at the 148th cycle is as high as 92.1%.
Similarly, according to Battery B-2, the discharge capacity retention at the 100th cycle at room temperature was 99.4%, the discharge capacity retention at the 145th cycle was 99.2%, and the discharge capacity at the 100th cycle at 60 ° C. was 99.2%. The retention rate of the discharge capacity reached 95.5%, and the retention rate of the discharge capacity at 150 cycles reached 93.2%.

[0043]

As described above, the spinel-type lithium manganese oxide according to the present invention can be used in a solvent composed of an aliphatic alcohol having 1 to 3 carbon atoms in a limited amount of excess water relative to manganese dioxide. Lithium oxide and a compound of a doping element in a limited range are mixed with manganese dioxide to form a homogeneous mixture, which is dried and fired.

A lithium secondary battery using such a spinel-type lithium manganate as a positive electrode active material has a high battery capacity and excellent cycle characteristics, and is particularly useful not only at room temperature but also under a high temperature environment. Also, the cycle characteristics are much better than those of conventional lithium secondary batteries.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a lithium secondary battery.

FIG. 2 shows that the substitution ratio of titanium to manganese atoms is 1 mol%, and the atomic ratio of 2Li / (Mn + Ti) is 1.30 and 1.2.
It is an X-ray-diffraction figure of the spinel type lithium manganate obtained as 0, 1.10, and 1.00.

FIG. 3 shows that the substitution ratio of titanium to manganese atoms is 1 mol%, and the atomic ratio of 2Li / (Mn + Ti) is 1.30 and 1.2.
It is a charge / discharge curve at 25 degreeC of the lithium secondary battery provided with the positive electrode which uses the spinel type lithium manganate obtained as 0, 1.10, and 1.00 as a positive electrode active material.

FIG. 4 shows the substitution amount of titanium to manganese atom and 2
4 is a graph showing the relationship between the Li / (Mn + Ti) atomic ratio and the discharge capacity at the 100th cycle at room temperature.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode can, 2 ... Positive electrode collector, 3 ... Positive electrode, 4 ... Separator, 5 ... Negative electrode, 6 ... Negative electrode collector, 7 ... Negative electrode can, 8 ... Insulating packing.

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[Procedure amendment]

[Submission date] July 9, 1999 (1999.7.9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction contents]

[0039]

[Table 1]

Continuing on the front page (72) Inventor Kazuhiko Hirao 3-4-2, Miyahara, Yodogawa-ku, Osaka-shi Inside Honjo Chemical Co., Ltd. F term in the company (reference) 5H003 AA04 BB05 BC01 BC06 BD03 5H014 AA01 AA06 EE01 EE10 HH01 5H029 AJ05 AK03 AL06 AL12 AM03 AM04 AM05 AM07 BJ03 DJ16 HJ01

Claims (2)

[Claims] In a solvent comprising an aliphatic alcohol having 1 to 3 carbon atoms, lithium hydroxide and Ti, Co, Ni, F
at least one selected from e, Cr, V, Al and Mg
A compound of the kind of doping element M and manganese dioxide are mixed to form a homogeneous mixture, which is dried and calcined to obtain a 2Li / (Mn + M) atomic ratio of 1.01 to 1.3.
A positive electrode active material for a non-aqueous electrolyte lithium secondary battery, comprising a spinel type lithium manganate having a doping element M in a range of 0.01 to 10.0 mol% with respect to manganese atoms while being in a range of 0. 2. A positive electrode, a negative electrode made of a substance capable of occluding and releasing lithium, a lithium alloy or lithium ions, a separator disposed between the positive electrode and the negative electrode, and a lithium ion conductive organic electrolyte. In a lithium secondary battery including, in a solvent composed of an aliphatic alcohol having 1 to 3 carbon atoms, lithium hydroxide and Ti, Co, Ni, Fe,
2Li / (Mn + M) atoms obtained by mixing a compound of at least one doping element M selected from Cr, V, Al and Mg with manganese dioxide to obtain a homogeneous mixture, drying and calcining the mixture. A non-aqueous solution comprising a spinel-type lithium manganate as a positive electrode active material having a ratio in the range of 1.01 to 1.30 and having the doping element M in the range of 0.01 to 10.0 mol% based on manganese atoms. Electrolyte lithium secondary battery.