JPH07105952A - Lithium secondary battery and its current collecting body - Google Patents

Abstract

PURPOSE:To provide a current collector which does not react with lithium and has a low electric resistivity and to offer a lithium secondary battery excellent in the electromotive force and the cycle characteristic. CONSTITUTION:A metallic material A is provided whose electric resistivity at 20 deg.C is below 5X10<-8>OMEGA.m while another metallic material B has a reactivity with lithium which is lower than that of the metal material A, and a current collector S for a lithium secondary battery is constructed by forming a layer consisting of the metallic material B on that surface of the metallic material A which is to be joined with a negative electrode. The collector S is joined with the negative electrode. Thereby deterioration of the lithium negative electrode and drop of the electromotive force are prevented, and a resultant lithium secondary battery is excellent in the cycle characteristic and is equipped with a high electromotive force and high capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode current collector for a lithium secondary battery using a negative electrode made of lithium or a lithium alloy, and a lithium secondary battery using the current collector.

[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 or a lithium alloy for the negative electrode, but when this lithium negative electrode is used, a current collector is usually used together to improve its conductivity. It This current collector has an electrical resistivity of 1.67 × 10 ⁻⁸ Ω at 20 ° C.
Cu of m or electric resistivity at 20 ° C. is 2.69 × 1
A metal material having a high conductivity such as Al of 0 ⁻⁸ Ω · m is used.

[0003]

The current collector is usually used by bonding it to an electrode in a battery. When the current collector made of Cu, Al or the like is bonded to a negative electrode made of lithium or a lithium alloy, An alloying reaction occurs between the current collector and lithium due to reaction diffusion even at room temperature. When this reaction progresses, the electric resistance of the current collector becomes large, and at the same time, lithium of the negative electrode is contaminated by Cu and Al of the current collector, and the electromotive force and cycle characteristics of the battery deteriorate.

For this reason, it is considered to use a metal whose reactivity with lithium is lower than that of Cu, Al or the like as the current collector. As such a metal, Ni, Fe, Cr, M is used.
o, W, Ta, etc., but these metals are 20
The electrical resistivity at ℃ is 5.5 × 10 ^-8 Ω at W
・ As m and Ta are 13.5 × 10 ^-8 Ω ・ m,
Both show high electrical resistivity of about 3 to 8 times that of Cu. Therefore, when these metals are used as a current collector, there is a problem that the internal resistance of the battery becomes large.

An object of the present invention is to solve the above problems and provide a current collector which does not react with lithium and has a low electric resistivity. Another object of the present invention is to provide a lithium secondary battery having excellent battery electromotive force and cycle characteristics.

[0006]

The present inventors have found that Cu, A
Inspired by the combination of high conductivity such as 1 and low reactivity with lithium such as Ni, Fe, Ta and W,
As a result of various studies on the method, the reactivity of a metal material having high conductivity such as Cu and Al with lithium such as Ni, Fe, Ta and W is low on the surface intended to be bonded to the negative electrode. When a current collector is formed by forming a layer made of a metal material, the internal resistance of the battery can be kept low due to the high conductivity of Cu, Al, etc., and the current collector is made of lithium due to the metal layer on the surface. The inventors have found that the reaction with is suppressed and have completed the present invention.

That is, the current collector for a lithium secondary battery of the present invention is used as a negative electrode of a metal material (hereinafter referred to as metal material A) having an electric resistivity of 5 × 10 ⁻⁸ Ω · m or less at 20 ° C. Is formed on the surface intended to be bonded with a metal material having a lower reactivity with lithium than the metal material A (hereinafter referred to as metal material B), and more preferably from the metal material B. The thickness of the layer is 0.05 to 5 μm. Further, the lithium secondary battery of the present invention is composed of a negative electrode made of lithium or a lithium alloy, a positive electrode, and an electrolyte, and the lithium secondary battery current collector is bonded to the negative electrode.
Desirably, the negative electrode is made of a lithium alloy having a lithium content of 80 atomic% or more.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing one embodiment of the current collector for a lithium secondary battery of the present invention. In the figure, S is a current collector for a lithium secondary battery, and a layer made of a metal material B is formed on the surface of the metal material A intended to be bonded to the negative electrode.

The metal material A is used to make the current collector S have high conductivity. The metal material A has an electrical resistivity of 5 × 10 ⁻⁸ Ω · m or less at 20 ° C., preferably 3 × 10 ⁻⁸ Ω · m or less, more preferably 2 × 10 ⁻⁸ Ω · m or less. Is used, specifically C
Examples include u, Al, Ag, and Cu-Ag alloy. Among them, Cu or Al is preferably used as a material exhibiting high conductivity.

The metal material A is formed into a shape corresponding to the shape of the lithium secondary battery. For example, in the case of a button type battery as shown in FIG. 2, a sheet type (disc-shaped) battery is formed, and as shown in FIG. 3, an electrode and a separator are spirally wound. It is shaped like a tape.

On the other hand, in the metal material B, the current collector and lithium undergo an alloying reaction to increase the electrical resistance of the current collector, or the negative electrode lithium is contaminated with Cu or Al of the current collector. This is for suppressing that. This metal material B
As those having a reactivity with lithium lower than that of the metal material A, desirably having a solubility in lithium at 700 ° C. of 1% by weight or less, preferably 0.5% by weight or less, and more preferably 0.2% by weight or less. The above materials are used, and specific examples thereof include one kind of metal selected from Ni, Fe, Cr, Mo, W, and Ta, or an alloy composed of two or more kinds of metals.

The current collector S is obtained by forming a layer of the metal material B on the surface of the metal material A intended to be bonded to the negative electrode. The method for forming the layer is as follows. ,
It is appropriately selected from among physical vapor deposition methods such as electroplating, vacuum deposition, sputtering, and ion plating, and methods of combining rolling with methods such as electroplating and thermal spraying.

The thickness of the layer made of the metal material B is 0.0
The thickness is preferably about 5 to 5 μm, more preferably about 0.1 to 1 μm. When the thickness of this layer is less than 0.05 μm, it becomes difficult to form the layer uniformly, while when it exceeds 5 μm, the electric resistance of the layer becomes large, which is not preferable.

FIG. 2 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, and a separator 3 is provided between the negative electrode body 1 and the positive electrode body 2.
Collector 4 which is pressure-bonded to the outer surface of the negative electrode body 1 with the interposition of
A negative electrode cap 5 that is in pressure contact with a and a positive electrode can 6 that is in pressure contact with a current collector 4b that is pressure bonded to the outer surface of the positive electrode body 2 are sealed with an insulator 7.

As the current collector 4a joined to the negative electrode body 1, a current collector in which a layer of the metal material B is formed on the surface of the metal material A is used. In addition, in this embodiment, the current collector 4a is formed into a sheet shape. In addition, in the current collector 4 a, the layer made of the metal material B is formed on the joint surface with the negative electrode body 1.

On the other hand, as the current collector 4b joined to the positive electrode body 2, usually used Al, Cu or the like is used.

As a method of joining the current collectors 4a and 4b to the electrodes, for example, in the case of a sheet-shaped current collector as shown in FIG. 1, the current collectors are pressure-bonded to the electrodes. In the case of a tape-shaped current collector, it is preferable that the negative electrode active material or the positive electrode active material is coated on the surface of the current collector by a method such as roll molding, spray coating, or reduced pressure plasma spraying.

As the negative electrode body 1, metallic lithium or an alloy thereof can be used, but it is preferable to use a lithium alloy from the viewpoint of cycle characteristics and safety. However,
When using this lithium alloy, high electromotive force of lithium,
The lithium content in the alloy is preferably 80 atomic% or more in order to prevent the characteristics such as high discharge capacity from being impaired as much as possible. The metallic lithium or its alloy is used as a negative electrode material in the form of powder, sheet, or the like.

As the positive electrode body 2, MnO ₂ , LiCoO ₂ and Li which are usually used for positive electrodes of lithium secondary batteries are used.
Co _0.5 P _0.5 O ₂ , LiCo _0.3 Ni _0.3 P
A positive electrode material whose main component is an oxide, sulfide, or the like such as _0.4 O ₂ , MoS ₂ , or TiS ₂ can be used. 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.

The above-mentioned positive electrode constituent and the above-mentioned negative electrode material are formed into an appropriate shape and size by any method such as casting, compression molding, roll molding, or coated on the surface of the current collector as described above. Then, it is used as the negative electrode body 1 and the positive electrode body 2 of the lithium secondary battery D of the present invention.

In the present invention, salts are used as electrolytes in organic solvents.
An electrolytic solution or solid electrolyte dissolved in can be used. Electrolytes
If the electrolyte is electrolyte, LiClO_Four ， LiB
F_Four， LiPF₆， LiF ₆, LiAlCl_Four , Li (CF₃SO₂)₂N etc.
Can be used, ethylene carbonate, propylene carbon
, Dimethyl sulfoxide, sulfolane, γ-butyro
Lactone, 1,2-dimethoxyethane, N, N-dimethylform
Amide, tetrahydrofuran, 1,3-dioxolane, 2-me
Cyltetrahydrofuran, diethyl ether and this
When dissolved in an organic solvent such as a mixture of
It is adjusted to 1 / liter before use.

The 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, etc. or their derivatives, mixtures, complexes and the like. This solid electrolyte also serves as a separator 3 for the negative electrode body 1 and the positive electrode body 2.

In the present invention, the negative electrode body 1, the separator (or the solid electrolyte) 3, the positive electrode body 2 and the like are formed into a tape shape and wound into a spiral structure to form a lithium secondary battery having a higher electric capacity. Can be manufactured. FIG. 3 is a schematic diagram showing an embodiment of a lithium secondary battery in which the electrode and the separator are spirally wound. In the figure, D is a lithium secondary battery, which is a negative electrode tape 1, a separator 3 and a positive electrode tape 2.
The spiral body obtained by winding the stacked ones is loaded into the battery can 5, and the current collector tape 4a in the negative electrode tape 1 is
Is connected to the bottom of the battery can 5 while the current collector tape 4b in the positive electrode tape 2 is connected to the positive electrode cap 6. An electrolytic solution is injected into the battery can 5, and the battery can 5 and the positive electrode cap 6 are sealed with an insulator 7.

[0025]

The current collector for the lithium secondary battery comprises a metal material A having an electric resistivity of 5 × 10 ⁻⁸ Ω · m or less at 20 ° C.
A layer made of a metal material B having a reactivity with lithium lower than that of the metal material A is formed on the surface intended to be bonded to the negative electrode, and the layer made of the metal material B serves as a collector for lithium. The reaction is suppressed, and the high electrical conductivity of the metal material A keeps the electrical resistance of the current collector low.

[0026]

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 Current Collector) Width 41 mm, Length 250 mm, Thickness 10 μ
Thickness of 1μ by electroless plating on the entire surface of Cu tape of m
A Ni layer of m was formed to prepare a current collector tape.

(Preparation of Negative Electrode Body) A powder of Li-Ag-Te alloy (having an atomic ratio of Li: Ag: Te = 95: 10: 3) was used as a raw material and was subjected to reduced pressure plasma spraying in an Ar atmosphere. 50μ thick on both sides of the current collector tape
An alloy layer of m was formed to prepare a negative electrode tape.

(Production of Positive Electrode) Lithium carbonate, basic cobalt, and an aqueous phosphoric acid solution having a phosphoric acid content of 85%, in an atomic ratio of Li: Co: P = 2: 1.5: 0.5. Were weighed and thoroughly mixed, then placed in an alumina crucible and heat-treated in an electric furnace at 900 ° C. for 24 hours to prepare an oxide substance. The oxidant is a mixture of lithium phosphate, lithium cobalt phosphate and cobalt oxide. Then, this oxide is crushed with a ball mill and sieved to a particle size of 20μ.
m powdered positive electrode active material was prepared. Then, 46 parts by weight of the positive electrode active material, 4 parts by weight of acetylene black, 2 parts by weight of polyvinylidene fluoride and 5 parts of n-methylpyrrolidone.
Mix 0 parts by weight, and mix this mixture with a width of 38 mm and a length of 240
mm, 20 μm thick Al tape is applied and vacuum dried,
A positive electrode tape having a thickness of 150 μm was prepared.

(Preparation of Separator) A porous polypropylene film having a thickness of 20 μm was formed with a width of 44 mm and a length of 250 mm.
To prepare a separator.

(Preparation of Electrolyte Solution) An electrolyte solution was prepared by dissolving 1 mol / liter of lithium perchlorate in propylene carbonate having a water content of 50 ppm or less.

(Production of Lithium Secondary Battery) The above separator, negative electrode tape, separator and positive electrode tape were superposed in this order and wound so that the positive electrode tape was on the inside to obtain a spiral body. This spiral body was loaded into a Ni-plated Fe battery can 5 having a diameter of 15 mm and a height of 50 mm, as shown in FIG. At that time, the lead wire 8a connected to the current collector tape 4a in the negative electrode tape 1 is connected to the battery can 5 described above.
The lead wire 8b connected to the Al tape 4b in the positive electrode tape 2 was welded to the positive electrode cap 6 made of Ni, respectively, at the bottom of the. Then, the electrolytic solution 3 is placed in the battery can 5.
After injecting ml, the battery can 5 was covered with the positive electrode cap 6, sealed with the gasket 7, and caulked to prepare a cylindrical lithium secondary battery D.

(Charge / Discharge Test of Lithium Secondary Battery) After leaving the above lithium secondary battery for 100 hours, a current density of 0.
It was charged at 4 mA / cm ² until the electromotive force increased to 4.2 V, and then discharged at the same current density until the electromotive force dropped to 2.0 V. In this charging / discharging, the battery electromotive force and the discharging time after charging were as shown in Table 1.

[0033]

[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 Ni layer was not formed on the Cu tape and used as a current collector tape. The battery electromotive force after discharge and the discharge time were as shown in Table 1.

Example 2 A lithium secondary battery was prepared in the same manner as in Example 1 except that a Ta layer having a thickness of 0.8 μm was formed on the entire surface of the Cu tape by sputtering to prepare a current collector tape. A charging / discharging test was conducted in the same manner as in Example 1 except that the battery was manufactured and allowed to stand for 500 hours, and the battery electromotive force and the discharging time after charging were as shown in Table 1.

Comparative Example 2 A lithium secondary battery was manufactured and a charge / discharge test was conducted in the same manner as in Example 2 except that the Ta layer was not formed on the Cu tape and used as a current collector tape. The battery electromotive force after discharge and the discharge time were as shown in Table 1.

Example 3 In Example 1, the Li-Ag-Te alloy powder (average particle size: 10 μm) was hot-rolled at 120 ° C. on a current collector tape having a Ni layer so that the thickness was 80 μm. A lithium secondary battery was manufactured and a charge / discharge test was conducted in the same manner except that the negative electrode tape was prepared by pressure bonding with a press. The battery electromotive force and the discharge time after charging were as shown in Table 1.

Comparative Example 3 A lithium secondary battery was manufactured and a charge / discharge test was conducted in the same manner as in Example 3 except that the Ni layer was not formed on the Cu tape and used as a current collector tape. The battery electromotive force after discharge and the discharge time were as shown in Table 1.

Examples 4 to 7 A lithium secondary battery was prepared in the same manner as in Example 1 except that the current collector tape was prepared by varying the thickness of the Ni layer on the Cu tape as shown in Table 1. Was manufactured and a charge / discharge test was conducted. The battery electromotive force and the discharge time after charging were as shown in Table 1.

[0040]

As described in detail above, the current collector for a lithium secondary battery of the present invention has an electric resistivity of 5 × at 20 ° C.
Since a metal material B having a reactivity with lithium lower than that of the metal material A is formed on the surface of the metal material A having a resistance of 10 ⁻⁸ Ω · m or less, which is intended to be bonded to the negative electrode. The reaction of the current collector with lithium is suppressed by the layer made of the metal material B, and the high electrical conductivity of the metal material A suppresses the electrical resistance of the current collector to a low level. Therefore, a lithium secondary battery using the current collector for a lithium secondary battery described above is a lithium secondary battery with high electromotive force and high capacity, which is excellent in cycle characteristics, in which deterioration of the lithium negative electrode and decrease in battery electromotive force are prevented. Has become.

[Brief description of drawings]

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

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

FIG. 3 is a perspective sectional view of a lithium secondary battery showing another embodiment of the present invention.

[Explanation of symbols]

A metal material having an electric resistivity of 5 × 10 ⁻⁸ Ω · m or less at 20 ° C. B metal material having lower reactivity with lithium than metal material A S current collector for lithium secondary battery

Claims (7)

[Claims] 1. The electrical resistivity at 20 ° C. is 5 × 10 ^−8.
A lithium secondary battery in which a layer of a metal material having a reactivity with lithium lower than that of the metal material (A) is formed on the surface of the metal material (A) of Ω · m or less intended to be bonded to the negative electrode. Current collector. 2. The lithium secondary battery according to claim 1, wherein the metal material having a lower reactivity with lithium than the metal material (A) has a solubility in lithium at 700 ° C. of 1% by weight or less. Current collector. 3. The current collector for a lithium secondary battery according to claim 1, wherein the metal material (A) is Cu or Al. 4. The metal material having a lower reactivity with lithium than the metal material (A) is a metal selected from Ni, Fe, Cr, Mo, W and Ta or an alloy composed of two or more metals. The current collector for a lithium secondary battery according to claim 1. 5. The current collector for a lithium secondary battery according to claim 1, wherein the layer made of a metal material having a lower reactivity with lithium than the metal material (A) has a thickness of 0.05 to 5 μm. 6. A negative electrode made of lithium or a lithium alloy, a positive electrode, and an electrolyte, wherein
5. A lithium secondary battery, which is obtained by joining the current collector for a lithium secondary battery according to any one of 5 above. 7. The lithium secondary battery according to claim 6, wherein the negative electrode is made of a lithium alloy having a lithium content of 80 atomic% or more.