JPH11185821A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery that can realize high power and is excellent in discharging characteristics, life cycle characteristics and heavy load characteristics while using lithium manganese oxide for its positive electrode active material. SOLUTION: This secondary battery is equipped with a positive electrode 1 using lithium manganese oxide as its active material, a negative electrode 2 formed from a material that can dope or undope a lithium metal, a lithium alloy or lithium, and a nonaqueous electrolytic solution; the thickness of the mix layer of the positive electrode 1 is not more than four times as large as the thickness of a collector 10 and 50% cumulative particle diameter of its lithium manganese oxide is in the range of 5-15 μm. In addition, the negative electrode 2, the thickness of the mix of which is not more than four times as large as the thickness of a collector 11, is formed from a carbonaceous material having 50% cumulative particle diameter in the range of 5-15 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonaqueous electrolyte secondary battery using lithium manganese oxide as a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, with the advance of electronic technology, high performance, miniaturization, and portability of electronic devices have been advanced, and secondary batteries with high energy density have been required for these electronic devices. Conventionally, as a secondary battery used in these electronic devices, a nickel-cadmium secondary battery, a lead-acid battery, a nickel-metal hydride battery, a lithium ion secondary battery, and the like are exemplified. In particular, lithium ion secondary batteries are the most promising batteries that have high battery voltage, high energy density, low self-discharge, excellent cycle characteristics, and can be adapted to small and lightweight batteries.

As a cathode material of such a lithium ion secondary battery, LiCoO ₂ and LiNiO ₂ are used. However, cobalt compounds and nickel compounds are rare metal materials worldwide and are expensive. Therefore, batteries using them are in a very disadvantageous situation for mass production, and are particularly unsuitable as materials for large batteries.

For this reason, the use of lower-cost lithium manganese oxides such as LiMn ₂ O ₄ has been studied as a positive electrode material of a lithium ion secondary battery. Research for improving the charge / discharge capacity, life characteristics, storage characteristics, and the like by variously changing the heat treatment temperature conditions and the like has been actively conducted.

[0005]

However, in reality, satisfactory characteristics have not yet been obtained.
For example, it has been proposed to mix a dissimilar metal, particularly a transition metal, with a spinel-type lithium manganese oxide. By adding a dissimilar metal, the spinel crystal structure can be stabilized, and the life characteristics can be improved. However, since a sufficient lithium passage cannot be ensured due to insertion / desorption of lithium, the charge / discharge capability is reduced, and the material is not a practical material.

Various synthesis conditions for lithium manganese oxide have been proposed. In a method of obtaining an oxide of lithium and manganese by decomposing a compound such as a carbonate or a nitrate, a powder having an extremely fine particle shape can be obtained, and a powder having excellent charge / discharge characteristics can be obtained. it can. However, there is a problem that the filling property of the battery is low and the battery capacity is small.

On the other hand, in a method of obtaining an oxide of lithium and manganese by mixing a commercially available electrolytic manganese dioxide powder with a lithium compound and heat-treating the powder, the powder can be filled at a high density, but the charge and discharge capacity is low. There is a problem that it is low and the life characteristics are short. In particular, the capacity of lithium manganese oxide synthesized from electrolytic manganese dioxide is reduced under large current discharge conditions, and the performance is significantly reduced as the cycle life elapses.

[0008] Further, from the viewpoint of the battery configuration, the optimum conditions for the combination of the positive electrode material and the negative electrode material have been studied. However, in reality, an effective method of a secondary battery using a combination of a lithium manganese oxide and a carbonaceous material has not yet been achieved.

Accordingly, the present invention provides a non-aqueous electrolyte secondary battery which achieves high output while using lithium manganese oxide as a positive electrode active material and has excellent charge / discharge characteristics, cycle life characteristics, and heavy load characteristics. The purpose is to do.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, by using lithium manganese oxide having a predetermined particle size,
It has been found that the thickness of the mixture layer can be set to five times or less, which has been impossible so far, and that a high-output battery system is made possible.

That is, the non-aqueous electrolyte secondary battery according to the present invention comprises: a positive electrode comprising lithium manganese oxide as an active material;
Doped with lithium metal, lithium alloy, or lithium
The negative electrode comprises a non-aqueous electrolyte and a non-aqueous electrolyte. The positive electrode has a thickness of the mixture layer that is four times or less the thickness of the current collector.
% Integrated particle diameter is 5 to 15 μm.

In addition to the positive electrode, the negative electrode has a thickness of the mixture layer that is four times or less the thickness of the current collector.
It is preferable that the carbonaceous material has a% integrated particle diameter of 5 to 15 μm.

In the non-aqueous electrolyte secondary battery according to the present invention, since the thickness of the electrode can be extremely thin, particularly high output can be achieved, and the electrode structure can be flexibly adapted to various electrodes. can do.

Further, in the nonaqueous electrolyte secondary battery according to the present invention, since the reaction electrode area can be increased by reducing the thickness of the electrode, the difference in the reaction potential distribution in the electrode thickness direction can be obtained. Can be reduced, that is, the polarization between the layer on the surface side of the electrode and the layer on the current collector side can be reduced, and an extremely efficient electrode reaction can be performed. As a result, it is possible to follow the large current discharge, and it is possible to reduce the performance deterioration of the large current discharge even after the lapse of the cycle.

Further, by regulating the particle size,
Polarization in large current discharge can be reduced, lithium can be rapidly diffused into the electrode, and it can contribute to stabilization of particles.
Even after the lapse of the cycle, non-uniformity inside the electrode can be suppressed, and performance degradation can be reduced.

As described above, by regulating the thickness and the particle size of the electrode, a high output can be achieved, and the charge / discharge characteristics and the cycle life characteristics are excellent, and the heavy load characteristics comparable to those of the aqueous secondary battery. Non-aqueous electrolyte secondary battery having

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a non-aqueous electrolyte secondary battery according to the present invention will be described in detail.

A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode using lithium manganese oxide as an active material, a negative electrode capable of doping and undoping lithium, and a non-aqueous electrolyte. ing.

The above-mentioned positive electrode is coated with a positive electrode mixture obtained by adding a conductive agent, a binder, a solvent and the like in addition to lithium manganese oxide as an active material to one or both surfaces of a current collector, and dried. It is produced by pressure molding.

The present invention is characterized in that the thickness of the mixture layer of the positive electrode is four times or less the thickness of the current collector. Furthermore, the lithium manganese oxide in the positive electrode mixture is 50%
It is characterized in that the integrated particle diameter is 5 to 15 μm. This lithium manganese oxide has a particle size distribution of 1 to 40 μm.
m, the maximum particle diameter is 20 to 40 μm, and the primary constituent particles are composed of pseudo-agglomerated particles of 0.1 to 1 μm.

Here, the lithium manganese oxide is represented by the general formula Li _x MnO _y , for example, LiMn ₂ O ₄ , Li
_{1 + z} Mn _2-z O ₄ , Li ₄ Mn ₅ O ₁₂ , or LiM _w Mn
_2-w O ₄ (where M is a transition metal) can be used.

The manganese compounds used as raw materials for these lithium manganese oxides include, in addition to electrolytic manganese dioxide, chemically synthesized manganese dioxide, dimanganese trioxide, trimanganese tetroxide, manganese oxyhydroxide, manganese sulfate,
Manganese carbonate, manganese nitrate and the like can be used. In addition, as a lithium compound serving as a raw material of lithium manganese oxide, lithium nitrate, lithium carbonate, lithium hydroxide,
Lithium acetate, lithium oxalate and the like can be used.

On the other hand, as the negative electrode, metallic lithium, a lithium alloy (for example, lithium-aluminum alloy), or a material capable of doping and undoping lithium can be used. Materials capable of doping and undoping lithium include pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites,
Glassy carbons, organic polymer compound fired bodies (phenol resin, furan resin, etc. fired at appropriate temperature and carbonized), carbonaceous materials such as carbon fiber and activated carbon, and other polymers such as polyacetylene and polypyrrole Can be used.

In particular, as the negative electrode, as in the case of the above-described positive electrode, a carbonaceous material in which the thickness of the mixture layer is four times or less the thickness of the current collector and the 50% cumulative particle diameter is 5 to 15 μm. It is preferable to use This carbonaceous material has a particle size distribution of 1 to 40 μm and a maximum particle size of 20 to 40 μm.
It is preferred that

Materials having various plane spacings, such as graphite powder, mesophase microbeads, pyrolytic carbon fibers, mesophase pitch-based carbon fibers, and high-temperature treated pitch carbon, have been obtained. It is preferable that the spacing between the (002) planes is 0.38 nm or less in order to improve the charge / discharge characteristics. in this way,
The thickness of the mixture of the positive electrode is set to four times or less the thickness of the current collector, and the 50% integrated particle diameter of lithium manganese oxide is 5 to 15 μm.
By this, the thickness of the electrode can be made extremely thin, the difference in the reaction potential distribution in the thickness direction of the electrode can be made small, and an extremely efficient electrode reaction becomes possible. As a result, it is possible to follow the large current discharge, and it is possible to reduce the performance deterioration of the large current discharge even after the lapse of the cycle. As a result, a heavy load characteristic comparable to that of an aqueous secondary battery can be obtained even when used at a large current discharge, which has not been suitable for a conventional nonaqueous electrolyte secondary battery.

Furthermore, 50% of the lithium manganese oxide
By regulating the cumulative particle size, the polarization of large current discharge can be reduced, lithium diffusion into the electrode can be performed quickly, and it can contribute to the stabilization of the particles. Can be suppressed, and performance degradation can be reduced.

In the present invention, by regulating the electrode thickness and the particle diameter of the negative electrode in addition to the above-mentioned positive electrode,
A higher performance battery can be obtained. In particular, the thickness of the mixture layer is four times or less the thickness of the current collector,
By using a carbonaceous material having an integrated particle diameter of 5 to 15 μm, a higher-performance battery can be obtained.

As the electrolytic solution, a non-aqueous electrolytic solution obtained by dissolving a lithium salt as an electrolyte in an organic solvent at a concentration of 0.5 to 2.0 mol / l is used. Here, the organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl formate, ethyl formate, formic acid Propyl, acetate compounds, propionate compounds, dimethoxyethane, diethoxyethane, diethoxypropane, dioxolan, ether compounds such as dioxane, γ-butyrolactone, cyclic esters such as δ-hexyllactone,
Organic sulfur compounds such as sulfolane and dimethylsulfolane can be used. These may be single solvents or 2
It can be used as a mixed solvent of more than one kind.

As the electrolyte, lithium hexafluorophosphate,
Lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium tetrafluoroborate, lithium trifluoride methanesulfonate, lithium trifluoroacetate, or the like can be used.

Further, the shape of the non-aqueous electrolyte secondary battery according to the present invention is not particularly limited, and coin type batteries, paper type batteries, cylindrical spiral type batteries, flat rectangular type batteries, inside-out batteries, The present invention can be applied to any battery such as a cylindrical battery.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. FIG. 1 shows a cylindrical secondary battery manufactured in this example.

Example 1 First, a positive electrode 1 was produced as follows.

Manganese dioxide having a particle size distribution of 1 to 29 μm and a 50% cumulative particle size of 7 μm, and lithium carbonate having an average particle size of 2 μm are mixed with Li / Mn ratio of 0.5.
3 and weighed in a mortar. Then, this mixture was put on an alumina board, heat-treated at 700 ° C. for 12 hours, cooled to room temperature, and then mixed again in a mortar. Further, this mixture was put on an alumina board, heat-treated at 800 ° C. for 12 hours, and cooled to obtain a lithium manganese oxide.

As a result of X-ray diffraction measurement, a peak corresponding to the spinel type LiMn ₂ O ₄ was obtained from the obtained lithium manganese oxide. Furthermore, as a result of measuring the particle size distribution of this lithium manganese oxide, the 50% particle size was 8 μm, and the particle size distribution was 1 to 29 μm.

90% by weight of this lithium manganese oxide, 6% by weight of graphite as a conductive agent, 4% by weight of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone as a solvent were added to form a positive electrode. Agent.
Then, the positive electrode mixture was uniformly applied to both surfaces of a current collector 10 made of an aluminum foil having a thickness of 20 μm, dried, and then pressed and formed with a roller press to obtain a positive electrode 1. The thickness of the mixture layer of the positive electrode 1 was 52 μm.

Next, the negative electrode 2 was manufactured as follows.

The petroleum pitch is heat-treated at 1000 ° C. in an oxygen atmosphere (crosslinked with oxygen) to obtain non-graphitizable carbon, which is then pulverized, and has a 50% integrated particle diameter of 7 μm and 1-2 μm.
A carbonaceous material having a distribution of 4 μm was obtained.

90% by weight of this carbonaceous material and 10% by weight of polyvinylidene fluoride as a binder were mixed, and N-methyl-2-pyrrolidone was added as a solvent to form a negative electrode mixture. After uniformly applying and drying both surfaces of the current collector 11 to be formed, the resultant was subjected to pressure molding with a roller press machine to obtain a negative electrode 2. The mixture thickness of the negative electrode 2 is 46 μ
m.

Next, after cutting the positive electrode and the negative electrode into a predetermined width, a positive electrode lead 13 made of aluminum is attached to one end of the positive electrode 1.
Negative electrode lead 1 made of nickel at the end of negative electrode 2
2 was welded. Then, the positive electrode 1 and the negative electrode 2 were laminated with a microporous polyethylene separator 3 interposed therebetween, and wound many times to produce a spiral electrode element. The polypropylene insulating plate 4 was placed above and below the electrode element, placed in an iron battery can 5, the negative electrode lead 12 was welded to the bottom of the battery can 5, and the positive electrode lead 13 was welded to the aluminum safety valve 7. Thereafter, a solution obtained by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of equal amounts of propylene carbonate and dimethyl carbonate was injected as an electrolyte, and the safety valve 7 and the PTC element 9 (Positive Tempe
After the rature coefficiency (manufactured by Raychem) and the top cover 8 were placed in this order, they were caulked with the gasket 6 to produce a cylindrical battery having an outer diameter of 18 mm and a height of 65 mm.

Example 2 As a positive electrode material, the 50% integrated particle diameter was 13 μm,
Manganese dioxide having a particle size distribution of 2 to 30 μm and lithium carbonate having an average particle size of 2 μm were weighed so that the Li / Mn ratio became 0.53, and lithium manganese oxide was obtained in the same manner as in Example 1. I got

As a result of X-ray diffraction measurement, a peak corresponding to the spinel type LiMn ₂ O ₄ was obtained from the obtained lithium manganese oxide. Furthermore, as a result of measuring the particle size distribution of this lithium manganese oxide, the 50% particle size was 13 μm, and the particle size distribution was 2 to 34 μm.

As a negative electrode material, non-graphitizable carbon was pulverized to obtain a carbonaceous material having a 50% integrated particle diameter of 9 μm and a distribution of 1 to 30 μm.

Using the positive electrode material and the negative electrode material, a positive electrode 1 having a positive electrode mixture thickness of 54 μm, and a negative electrode mixture having a thickness of 4 μm.
A cylindrical secondary battery was produced in the same manner as in Example 1, except that a negative electrode having a thickness of 7 μm was produced.

Examples 3 to 6 and Comparative Examples 1 to Comparative Examples
2 Example 1 was repeated except that a material having a 50% integrated particle diameter and a particle diameter distribution shown in Table 1 was used as a positive electrode material and a negative electrode material, and a positive electrode 1 and a negative electrode 2 having a mixture thickness shown in Table 1 were used. In the same manner as described above, a cylindrical secondary battery was produced.

[0045]

[Table 1]

[0046] Characterization Examples and using the produced non-aqueous electrolyte secondary battery in Comparative Example First, a current density of 0.3 mA / cm ^2, was charged for 8 hours at the upper limit voltage 4.2 V, the current density 1mA / Cm ² to a cut-off voltage of 2.5 V, and thereafter, at a current density of 1 A, between the upper limit voltage of 4.2 V and the cut-off voltage of 2.5 V, respectively.
The charge / discharge cycle was repeated five times at a time, and the following discharge load test and cycle test were performed.

Using the above battery, a current density of 1 mA / cm
^2. Charged at an upper limit voltage of 4.2 V for 3 hours and a current density of 0.2
A discharge load test was performed in which the discharge voltage was changed to a final voltage of 2.5 V while changing to 10 mA / cm ² .

Further, using another battery, a current density of 1
mA / cm ^2, was charged for 3 hours at the upper limit voltage 4.2 V, was performed 200 times the charging and discharging cycle of discharging to a final voltage of 2.5V at a current density of 0.5 mA / cm ^2.

The results are shown in FIGS.

From the results shown in Table 1 and FIGS. 2 to 4, the thickness of the mixture layer was made four times or less the thickness of the current collector, and a positive electrode having a lithium manganese oxide having a 50% integrated particle diameter of 5 to 15 μm was provided. In the batteries (Examples 1 to 7), superior heavy-load discharge characteristics can be obtained, the deterioration after the lapse of the cycle is small, and the battery is excellent as compared with the battery (Comparative Example 1) having a large particle diameter and a large electrode thickness. It can be seen that improved cycle life characteristics can be obtained.

In particular, in the battery of the embodiment, even when used at a large current, which was not suitable for the conventional lithium secondary battery, it is possible to bring out a performance comparable to that of the aqueous secondary battery. Heavy load charge / discharge characteristics can be obtained. This is because the reaction polarization resistance between the layer on the surface side of the electrode and the layer on the current collector side is extremely small, and there is almost no reaction delay or resistance delay. This is because it can be done.

In Examples 1 to 6, the thickness of the mixture layer is not more than four times the thickness of the current collector not only in the positive electrode but also in the negative electrode, and the 50% integrated particle diameter is 5 to 15 μm.
Therefore, superior heavy load characteristics and cycle life characteristics can be obtained as compared with the seventh embodiment.

[0053]

As is apparent from the above description, according to the present invention, the thickness of the mixture layer and the particle size are regulated to the optimum ranges, so that the electrode thickness can be extremely reduced and the height can be reduced. An output battery system becomes possible. Furthermore, according to the present invention, it has both discharge characteristics and life cycle characteristics,
It is possible to provide a non-aqueous electrolyte secondary battery that is more excellent in heavy load characteristics than a conventional non-aqueous electrolyte secondary battery.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical secondary battery of the present embodiment.

FIG. 2 is a characteristic diagram showing a relationship between a discharge current and a discharge capacity in the cylindrical secondary battery of this example.

FIG. 3 is a characteristic diagram showing the relationship between the battery capacity and the number of cycles in the cylindrical secondary battery of this example.

FIG. 4 is a characteristic diagram showing a relationship between a discharge current and a discharge capacity in the cylindrical secondary battery of the present embodiment.

[Explanation of symbols]

1 positive electrode, 2 negative electrode, 3 separator, 4 insulating plate, 5
Battery can, 6 gasket, 7 safety valve, 8 top cover, 9 PTC element, 10 positive electrode current collector, 11 negative electrode current collector, 12 negative electrode lead, 12 positive electrode lead

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masashi Kumakawa 1-1-1 Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture Sony Energy Tech Co., Ltd.

Claims (2)

[Claims] 1. A positive electrode comprising: a positive electrode using a lithium manganese oxide as an active material; a negative electrode made of lithium metal, a lithium alloy, or a material capable of doping / dedoping lithium; and a non-aqueous electrolyte. Is a non-aqueous electrolyte secondary battery characterized in that the thickness of the mixture layer is four times or less the thickness of the current collector, and the 50% integrated particle diameter of lithium manganese oxide is 5 to 15 μm. . 2. The negative electrode, wherein the thickness of the mixture layer is four times or less the thickness of the current collector, and the 50% integrated particle diameter is 5 to 1
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is a carbonaceous material having a thickness of 5 µm.