JPH06267543A - Collector for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain a collector which has a good adhesive property with an electrode and is low cost, and a battery using such a collector, by forming an uneven plane on the surface of the collector so as to increase the developed surface area. CONSTITUTION:In this lithium secondary battery D, a separator 3 is provided between a positive electrode body 1 and a negative electrode body 2. A positive electrode can 5 pressure-contacted to a collector 4a attached to the outer surface of the positive electrode body 1, and a negative electrode cap 6 pressure- contacted to a collector 4b attached to the outer surface of the negative electrode body 2, are sealed with an insulator 7. The collectors 4a and 4b improve the conductibility of the electrodes, and an uneven plane is formed on one side surface so as to increase the developed surface area. As a result, the adhesive property with the electrodes is improved, and the deterioration of the discharge capacity owing to a poor adhesion with the electrodes can be suppressed by using the collectors 4a and 4b. And the manufacturing cost is also reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having a high discharge capacity.

[0002]

2. Description of the Related Art Lithium secondary batteries are known as high energy density batteries which have various advantages such as wide operating temperature range, stable discharge voltage, and extremely low self-discharge rate. This lithium secondary battery generally uses lithium as the negative electrode, while the positive electrode is
It is known that a positive electrode active material such as MnO ₂ or LiCoO ₂ has a high electromotive voltage. When these electrodes are used, a current collector is usually used together in order to improve the conductivity thereof. As the current collector, a metal mesh such as nickel mesh or a metal sheet such as nickel sheet is used. Has been done.

[0003]

When a metal mesh is used as the current collector, the adhesion with the electrode is good, but there is a problem that the cost is high. On the other hand, when a metal sheet is used, Although the cost can be reduced, there is a problem that a defective product having a low discharge capacity is likely to occur because the adhesion with the electrode is likely to be poor.

An object of the present invention is to solve the above problems and provide a current collector which has good adhesion to electrodes and is inexpensive, and a lithium secondary battery using the current collector.

[0005]

As a result of various studies on the method for improving the adhesion between the current collector and the electrode, the present inventor formed unevenness on the surface of the current collector to reduce the spread surface area. It has been found that, when the amount is increased, it is possible to obtain a current collector having good adhesion to the electrode even if it is not a mesh-shaped one.
The present invention has been completed. That is, the current collector for a lithium secondary battery of the present invention has an expanded surface area by forming irregularities on the surface. The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode and an electrolyte, and the current collector is attached to at least one of the positive electrode and the negative electrode.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic view showing an embodiment of the lithium secondary battery of the present invention. In the figure, D is a lithium secondary battery, with a separator 3 interposed between the positive electrode body 1 and the negative electrode body 2, and a positive electrode can 5 press-contacted to a current collector 4a pressure-bonded to the outer surface of the positive electrode body 1. , The current collector 4 pressed onto the outer surface of the negative electrode body 2
The negative electrode cap 6 that is pressed against b is sealed with an insulator 7.

The current collectors 4a and 4b used in the present invention have the property of improving the conductivity of the electrodes. Specifically, the metals such as Al, Ni, Cu and Fe, stainless steel, etc. The alloy of can be used.

In the present invention, the developed surface area is increased by forming irregularities on at least one surface of the current collectors 4a and 4b. The irregularities on the surface are, for example, wire brushing, sand blasting, chemicals. It can be formed by performing a primer treatment such as etching.

In the treatment of the surface of the current collector, the developed surface area of the current collector is 30% or more, preferably 70% as compared with that before the treatment.
It is applied so as to increase above. If the expanded surface area of the current collector is less than 30%, the adhesion to the electrode becomes insufficient, which is not preferable.

The above-mentioned treatment of the surface of the current collector is performed by collecting the current collectors 4a and 4a.
It is preferable to apply it to both of b and b, but it may be applied to only one of them depending on the selection of the positive electrode material or the negative electrode material. As a method of attaching the electrode to the current collector, the current collector may be pressure-bonded to the electrode as shown in FIG. 1, but an active material prepared in a paste form is spray-coated, roll-formed, doctor blade. It is also possible to apply it on the surface of the current collector by a method such as a dipping method or a dipping method.

As the positive electrode body 1, a positive electrode material usually used for a positive electrode of a lithium secondary battery can be used. In the present invention, MnO ₂ , LiCoO ₂ or the like, which usually requires a current collector, is used as an active material. It is particularly effective when using a positive electrode body that The positive electrode active material is mixed with a conductive material such as acetylene black or Ketjen black, and a binder such as polytetrafluoroethylene or polyethylene.

As the negative electrode 2, a conventionally known negative electrode material for a lithium secondary battery can be used, and specifically, metallic lithium or an alloy thereof can be used. The negative electrode 2
Even if a carbon material, Nb ₂ O ₅ or the like is used as the material, the effect of the present invention can be obtained.

The positive electrode assembly and the negative electrode material are molded into an appropriate shape and size by any method such as casting, compression molding, roll molding and the like, and the positive electrode body 1 of the lithium secondary battery D of the present invention and Used as the negative electrode body 2.

In the present invention, an electrolytic solution obtained by dissolving salts in an organic solvent or a solid electrolyte can be used as the electrolyte. When the electrolyte is an electrolyte, the salts include LiClO ₄ and LiB.
F ₄ , LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , Li (CF ₃ SO ₂ ) ₂ N
Etc. can be used, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone, 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolane,
Dissolve it in an organic solvent such as 2-methyltetrahydrofuran, diethyl ether and a mixture thereof to give a concentration of 0.1
It is used by adjusting it to 3 mol / liter.

This electrolytic solution is used as an electrolyte by impregnating or filling a separator 3 such as a porous polymer or a glass filter.

When the electrolyte is a solid electrolyte, the above-mentioned salts are mixed with polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide and the like, their derivatives, mixtures and composites. This solid electrolyte also serves as a separator 3 for the positive electrode body 1 and the negative electrode body 2.

In the present invention, as shown in FIG. 2, if the positive electrode body 1, the separator (or the solid electrolyte) 3, the negative electrode body 2 and the like are formed into a sheet shape and they are wound to form a spiral structure, it is further improved. A lithium secondary battery having an electric capacity can be manufactured.

[0018]

Since the current collector for a lithium secondary battery having the above-mentioned structure has unevenness on the surface to increase the developed surface area, the adhesion with the electrode is good. Therefore, since the lithium secondary battery of the present invention uses the above current collector, the reduction in discharge capacity due to poor adhesion with the electrode is suppressed.

[0019]

EXAMPLES Hereinafter, the present invention will be described more specifically by showing examples. Needless to say, the present invention is not limited to this. Example 1 (Production of Positive Electrode Constituent) Lithium carbonate, basic cobalt carbonate, and 85% phosphoric acid aqueous solution were used at an atomic ratio of Li: Co :.
P = 2: 1: 1 was weighed and mixed well, then put in an alumina crucible and placed in an electric furnace for 24 hours.
Heat treatment at 900 ° C for
A phosphorus complex oxide was produced. Further, this was pulverized by a ball mill to produce a positive electrode active material having a particle size of 20 μm or less. Then, to a mixture of 2 parts by weight of EPDM (ethylene-propylene-diene-terpolymer) and 198 parts by weight of cyclohexane, 90 parts by weight of the positive electrode active material and 8 parts by weight of acetylene black were added and thoroughly mixed, A positive electrode paste was manufactured.

(Surface treatment of current collector) Thickness 20 μm, width 4
A 0 mm aluminum sheet was wound on a bobbin through a twin roller with a wire brush. The expansion of the developed surface area on both sides of the aluminum sheet by this treatment is 230%
Met.

(Production of Positive Electrode Body) The above-mentioned surface-treated aluminum sheet was cut into a length of 250 mm, the positive electrode paste was applied to both sides of the sheet, dried, and then passed through a roller to be molded to a thickness of 150 μm. A positive electrode sheet 1 was produced.

(Production of negative electrode body) Thickness 10 μm, width 42 m
On both sides of a nickel sheet of m, 270 mm in length, a thickness of 0.
A lithium sheet having a width of 1 mm, a width of 41 mm and a length of 250 mm was pressure-bonded to produce a negative electrode sheet 2.

(Preparation of Separator) A porous polypropylene film having a thickness of 25 μm was formed with a width of 45 mm and a length of 350 mm.
To prepare a sheet-shaped separator 3.

(Preparation of Electrolyte Solution) 1 mol / liter of lithium perchlorate was dissolved in a mixture of propylene carbonate and 1,2-dimethoxyethane having a water content of 50 ppm or less at a volume ratio of 1: 1. An electrolytic solution was prepared.

(Preparation of lithium secondary battery) The separator 3, the negative electrode sheet 2, the separator 3 and the positive electrode sheet 1
Were superposed in this order, and were wound so that the positive electrode sheet 1 was on the inner side to obtain a spiral body S. This spiral body S
2 was loaded into a nickel-plated iron negative electrode can 6 having a diameter of 14 mm and a height of 50 mm, as shown in FIG. that time,
The lead wire 8b connected to the nickel sheet in the negative electrode sheet 2 is attached to the bottom of the negative electrode can 6, and the lead wire 8a connected to the aluminum sheet in the positive electrode sheet 1 is nickel-plated iron positive electrode. Each was welded to the cap 5. Then, after injecting the electrolytic solution into the negative electrode can 6, the negative electrode can 6 was covered with the positive electrode cap 5 and sealed with a gasket 7 to be caulked, whereby a cylindrical lithium secondary battery D was produced.

(Charge / Discharge Test of Lithium Secondary Battery) Ten lithium secondary batteries were manufactured (Sample Nos. 1 to 10).
, And a charge / discharge test was performed for each of them.
In this charge / discharge test, after setting the initial current to 80 mA and performing constant voltage charging with the upper limit voltage of 4.3 V for 8 hours, the lower limit voltage of 3 V was applied.
The constant current discharge of 80 mA was carried out by setting to, and this charging and discharging was repeated. When the discharge capacity at the 10th charging / discharging was measured, the results shown in Table 1 were obtained.

[0027]

[Table 1]

Comparative Example 1 A lithium secondary battery was manufactured and a charge / discharge test was conducted in the same manner as in Example 1 except that the aluminum sheet was used as a current collector without surface treatment. The results shown in are obtained.

Examples 2 to 4 A lithium secondary battery was manufactured and a charge / discharge test was conducted in the same manner as in Example 1 except that the increase in the developed surface area of the aluminum sheet due to the surface treatment was varied as shown in Table 1. As a result, the results shown in Table 1 were obtained.

[0030]

As described in detail above, since the current collector for a lithium secondary battery of the present invention has unevenness on the surface to increase the developed surface area, the adhesion with the electrode becomes good. ing. Therefore, the lithium secondary battery of the present invention is a collector produced by using the above-mentioned current collector, in which a decrease in discharge capacity is suppressed and a performance defect rate is reduced, and a relatively expensive metal mesh is not used. Since the electric body can be used, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a lithium secondary battery showing an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a lithium secondary battery showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4a, 4b Current collector 5 Positive electrode can 6 Negative electrode cap 7 Insulator D Lithium secondary battery

Claims (2)

[Claims] 1. A current collector for a lithium secondary battery, which has an expanded surface area by forming irregularities on the surface. 2. A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the current collector according to claim 1 is attached to at least one of the positive electrode and the negative electrode.