JP2001222993A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte battery, equipped with flat wound electrode groups, excellent in a volume efficiency and productivity. SOLUTION: On at least one of the positive and negative strip, one-sided coated portion carrying the electrolyte layer on the one side in installed, and flat-shaped wound electrode groups are equipped, with one side thickness of 110 μm or less of the mixture layer at the electrode where one sided coated portion is installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery provided with a group of electrodes formed of a laminate of a band-shaped positive electrode, a separator and a band-shaped negative electrode, which are wound in a flat spiral shape.

[0002]

2. Description of the Related Art In recent years, portable devices for general users have been reduced in size and weight due to great progress in electronic technology. Along with this, high-capacity, small-size and light-weight batteries are required, and lithium ion batteries are widely used to meet these demands. Above all, prismatic and flat batteries are widely used as batteries having a small dead space when housed in equipment and having good volumetric efficiency.

In order to cope with high-rate discharge, a lithium ion battery generally employs a wound electrode group structure in which a strip-shaped electrode is formed in a spiral shape. In the wound electrode group structure, many attempts have been made to achieve high capacity by optimizing the thickness of the mixture layer of the positive electrode and the negative electrode.

Japanese Patent No. 2701347 discloses that
The thickness of the double-sided mixture layer of the positive electrode and the negative electrode is 80 to 250 μm,
It has been proposed that the thickness ratio of the mixture layer between the positive electrode and the negative electrode be 0.4 to 2.2. The publication states that providing a mixture layer on only one surface of the current collector causes warpage and is not practical. However, since the mixture layer on the inner surface of the innermost electrode and the outer surface of the outermost electrode, which is a surface not facing the counter electrode, does not contribute to the electromotive reaction, it causes a reduction in volume energy density and weight energy density. . In particular, in a battery provided with a flat-wound electrode group, the ratio of the non-facing surface to the band-shaped electrode increases, so that the mixture on the non-facing surface that does not contribute to the reaction has a large effect on the energy density. . Therefore, it is desired that the flat wound electrode group be provided with an electrode group provided with a mixture layer on only one surface on the innermost inner surface and the outermost surface.

However, when the mixture layer is provided only on one side, the strip-shaped electrode is warped as described above. In a battery having a circular winding surface, the effect of the warpage of the electrode on the manufacturing process is relatively small. It becomes difficult, and there is a possibility that a positional shift may occur or a separator may be damaged at an edge of the electrode to cause a short circuit.

Further, when the mixture layer is provided only on one side, there is a problem that a crack is easily formed at the boundary between the mixture part on both sides and the mixture part on one side after pressing the electrode.

[0007]

As described above, in a battery having a flat wound surface, a part having a mixture only on one side is provided in a part of the battery so that the electrode is not warped or cracked. Developing a suitable electrode is a critical factor. An object of the present invention is to provide a battery provided with a flat wound electrode group excellent in volume efficiency and excellent in productivity.

[0008]

In order to solve the above-mentioned problems, the present invention provides lithium cobaltate (LiCoO ₂ ),
A positive electrode mixture layer mainly composed of at least one transition metal oxide selected from lithium nickelate (LiNiO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) is supported on both surfaces of a positive electrode current collector. A battery comprising an electrode group obtained by flatly winding a laminate of a strip-shaped positive electrode, a strip-shaped separator, and a strip-shaped negative electrode in which a negative electrode material mixture layer containing graphite as a main component is supported on both surfaces of a negative electrode current collector. At least one electrode of the strip-shaped positive electrode and the strip-shaped negative electrode is provided with a single-sided coating portion in which a mixture layer is supported only on one side, and the single-sided coating portion has a single-sided thickness of the mixture layer of 110 μm. A battery characterized by the following. Further, the battery is characterized in that the volume ratio of the transition metal oxide in the positive electrode mixture layer is 60% or less, and the volume ratio of graphite in the negative electrode mixture layer is 75% or less. Further, a battery in which the thickness (t) of the flat wound electrode group is 4 mm or less.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing embodiments, but the present invention is not limited by the following description.

FIG. 1 is a plan view of the battery of the present invention. The electrode group is housed in the container 1. 5 is a negative electrode terminal. FIG. 2 is a cross-sectional view taken along line XX ′ of the battery of the present invention. It is drawn enlarged in the thickness direction for explanation. A laminate composed of the positive electrode 2, the negative electrode 3, and the separator 4 is wound into a flat shape to form an electrode group, and hermetically sealed in a metal container 1 also serving as a positive electrode terminal. The negative electrode terminal 5 is insulated from the container 1 by the insulating sealing material 6. FIG. 3 is a cross-sectional view of the battery of the present invention taken along line YY ′, in which the container 1 is omitted and only the electrode group is illustrated.
Further, for the sake of explanation, the drawing is enlarged in the thickness direction. t
Is the thickness of the pole group. FIG. 4 is a plan view and a cross-sectional view of the belt-shaped positive electrode used in the battery of the present invention. The numbers in the cross section are
The dimensional ratio of a double-sided coated part, a single-sided coated part, and a non-coated part is shown. FIG. 5 is a plan view and a cross-sectional view of the strip-shaped negative electrode used in the battery of the present invention. The numbers described in the cross-sectional views indicate the dimensional ratios of the double-sided coated part, the single-sided coated part, and the non-coated part.

The positive electrode 2 has a positive electrode mixture layer formed by adding a conductive material such as carbon black and a resin binder to a composite oxide of lithium and a transition metal such as cobalt, nickel and manganese. It is carried on the surface of a positive electrode current collector made of aluminum foil of about 20 μm. The negative electrode 3 has a negative electrode mixture layer formed by adding a binder to a carbon material represented by graphite,
It is carried on a copper foil current collector having a thickness of about 10 μm.
A separator 4 made of a microporous resin film having a thickness of about 20 μm is laminated between the positive electrode 2 and the negative electrode 3. The electrolyte used for the electrodes and the separator may be, for example, an electrolytic solution in which lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate, or a gelled polymer electrolyte obtained by adding polyvinylidene fluoride thereto.

The thickness of one side of the mixture layer after pressing is 110 μm or less for both the positive electrode and the negative electrode.
９０90 μm or less. If the thickness of the mixture layer is less than 40 μm, the boundary between the double-sided coating portion and the single-sided coating portion receives a large force during pressing due to the step of the mixture, and the current collector is likely to crack. When the thickness is 40 μm or more, the shrinkage of the mixture layer is large, so that the force can be absorbed. Further, when the thickness of the mixture layer is less than 40 μm, the volume ratio of the mixture layer in the electrode group becomes small, so that there is a disadvantage that the volumetric efficiency of the battery becomes small. If the thickness of the mixture layer is larger than 110 μm, the electrode after pressing may be warped, which may hinder the winding step, or may cause cracks in the sakai between the double-sided mixture portion and the single-sided mixture portion. Table 1 shows the thickness of one side of the positive electrode mixture layer after pressing, the warpage of the electrode, and the occurrence of cracks.

[0013]

[Table 1]

In this embodiment, a single-sided coated portion having no mixture layer is disposed on the outermost peripheral surface of the positive electrode 2 and the innermost peripheral surface of the negative electrode 3. The composition of the positive electrode mixture was 90% by weight of lithium cobalt oxide having an average particle size of 15 μm, 5% by weight of acetylene black powder, and 5% by weight of polyvinylidene fluoride.
The mixture layer having the above composition is supported on an aluminum substrate having a thickness of 20 μm, and constitutes the positive electrode 2. The pressing pressure was adjusted so that the volume ratio of lithium cobalt oxide (LiCoO ₂ ) in the positive electrode mixture layer was about 55%.

Regarding the volume ratio of the metal oxide in the positive electrode mixture layer, the true density of the metal oxide is also a major factor. The true density of the lithium cobaltate is 4.9 g / cm.
³ The true density of lithium nickelate (LiNiO ₂ ) was also close to 4.7 g / cm ^3, and the same results as in Table 1 were obtained.

The true density of lithium manganate (LiMn ₂ O ₄ ) is rather low, at 4.2 g / cm ³ . Table 2 shows the results of experiments in which the LiCoO ₂ was replaced with LiMn ₂ O ₄ having an average particle size of 18 μm.

[0017]

[Table 2]

Table 3 shows the thickness of the negative electrode mixture layer after pressing, the warpage of the electrode, and the occurrence of cracks. The composition of the negative electrode mixture was 95% by weight of massive graphite particles having an average particle diameter of 25 μm, a true density of 2.1 g / cm ³ , and 5% by weight of polyvinylidene fluoride. The negative electrode mixture layer having the above composition is supported on a copper substrate having a thickness of 10 μm to form the negative electrode 4. The pressing pressure is such that the volume ratio of graphite in the negative electrode mixture layer is 65 to 75%.
It was adjusted to become. As the thickness decreases, the capacity of the battery decreases. To ensure the required discharge capacity,
The thickness of the mixture layer for both the positive electrode and the negative electrode is desirably 50 μm or more.

[0019]

[Table 3]

The volume ratio of the transition metal oxide in the positive electrode mixture layer is affected by the mixing ratio of the components constituting the mixture, the true density and particle size distribution of the powder constituting the mixture, and the degree of pressing of the electrode plate. Receive. However, the mixing ratio of the transition metal oxide in the components constituting the mixture is in a narrow range of 85 to 95% by weight, and the influence on the volume ratio is small. The true density of the metal oxide varies somewhat depending on the synthesis conditions, but the value is 4.6 to 4.6 for both LiCoO ₂ and LiNiO ₂ .
5.0 and 4.1 to 4.4 for LiMn ₂ O ₄ , which are not significantly different from each other, so that the influence on the volume ratio is small. Furthermore, the average particle size of the metal oxide used in the present invention is in a narrow range of 10 to 20 μm, and this also has a small effect on the volume ratio. on the other hand,
The degree of pressing of the electrode plate has a great influence on the volume ratio.

Table 4 shows that lithium cobalt oxide was used as the metal oxide, and the thickness of one side of the positive electrode mixture layer was about 9% after pressing.
After determining the application amount so as to be 0μ, when the press pressure was changed, the volume ratio of lithium cobaltate in the positive electrode mixture, the warpage of the electrode plate, and the occurrence of cracks were shown. is there. Table 5 shows the results of a similar experiment performed on a positive electrode plate using lithium manganate as the metal oxide. From these results, the volume ratio of the metal oxide was 6%.
It must be 0% or less, and if it is too high, the electrode will be warped. However, as the temperature decreases, the electron conductivity of the mixture layer decreases, and the discharge capacity decreases. Preferred values are 40-6
0%.

[0022]

[Table 4]

[0023]

[Table 5]

On the other hand, in the negative electrode plate, although the true density of the graphite material slightly varies depending on the type, it is in a narrow range of 2.0 to 2.2, and greatly affects the volume ratio of graphite in the negative electrode mixture layer. Not something. The same applies even if the shape of graphite is different from flake, sphere, or lump. As the graphite material, graphite having an average particle size of 20 to 40 μm or a carbon material having properties close to graphite is generally used.

Table 6 shows experimental results when the volume ratio was changed by changing the degree of pressing of the negative electrode using a graphite material in the same manner as in the case of the positive electrode. The coating amount was adjusted so that the thickness of the mixture layer was about 90 μm. From this result, the volume ratio of the carbon material in the negative electrode mixture layer must be 75% or less. Preferred values are 50-75%.

[0026]

[Table 6]

The present invention is particularly effective in a battery provided with a flat wound electrode group in which the total thickness of the electrode group is 4 mm or less. When the thickness of the pole group is limited to 4 mm or less, effective utilization of the volume is particularly important. That is, the mixture layer that does not face the counter electrode does not contribute to power generation and wastes space. The smaller the pole group thickness, the larger the ratio of the wastefully occupied volume to the whole pole group. According to our calculations, both the positive electrode and the negative electrode have a mixture layer on both surfaces over the entire surface, and when the thickness of one surface of the mixture layer is 100 μm,
When the pole group thickness is 5 mm, the wasted space is only about 8%, but when the pole group thickness is 4 mm, about 15% is used.
% Volume is wasted.

On the other hand, the thickness of the pole group is preferably 1.5 mm or more. When the thickness of the pole group is less than 1.5 mm, the number of windings is one, and at most two times, and the number of parts is smaller than that of the lamination type, and the advantages unique to the winding type such as high productivity are not obtained. Also, since it has a curved part at the end,
The demerit that the volume efficiency is inferior to the stacked type is greatly exhibited.

According to the present invention, the occurrence of electrode warpage can be prevented, and a battery free from electrode displacement and internal short circuit can be produced. In addition, since the mixture layer on the non-opposing surface of the electrode is omitted, materials can be saved, and the internal volume of the battery can be effectively used, so that a battery having a large discharge capacity can be provided.

[0030]

As described above, the present invention provides an inexpensive flat sealed battery having high volumetric efficiency and low cost, and has high industrial value.

[Brief description of the drawings]

FIG. 1 is a plan view of a battery of the present invention.

FIG. 2 is a sectional view of the battery of the present invention.

FIG. 3 is a sectional view of a pole group of the battery of the present invention.

FIG. 4 is a plan view and a cross-sectional view of the belt-shaped positive electrode of the present invention.

FIG. 5 is a plan view and a cross-sectional view of a strip-shaped negative electrode of the present invention.

[Explanation of symbols]

 2 Positive electrode 3 Negative electrode 4 Separator

Continuing on the front page (72) Inventor Tatsuharu Nakagome 2-3-1, Kosobe-cho, Takatsuki-shi, Osaka F-term in Yuasa Corporation 5H029 AJ03 AJ14 AK03 AL07 AM00 AM03 AM07 BJ02 BJ14 DJ06 HJ01 HJ04 5H050 AA08 BA17 CA08 CA09 CB08 FA05 FA08 HA02 HA04

Claims (3)

[Claims] 1. Lithium cobaltate (LiCoO ₂ ),
A positive electrode mixture layer mainly composed of at least one transition metal oxide selected from lithium nickelate (LiNiO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) is supported on both surfaces of a positive electrode current collector. A battery comprising an electrode group obtained by flatly winding a laminate of a strip-shaped positive electrode, a strip-shaped separator, and a strip-shaped negative electrode in which a negative electrode material mixture layer containing graphite as a main component is supported on both surfaces of a negative electrode current collector. At least one electrode of the strip-shaped positive electrode and the strip-shaped negative electrode is provided with a single-sided coating portion in which a mixture layer is supported only on one side, and the single-sided coating portion has a single-sided thickness of the mixture layer of 110 μm. A battery characterized by the following. 2. The volume ratio of the transition metal oxide in the positive electrode mixture layer is 60% or less, and the volume ratio of graphite in the negative electrode mixture layer is 75% or less. battery. 3. The flat wound electrode group has a thickness (t) of 4 mm.
The battery according to claim 1, wherein: