JPH10308207A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the irreversible capacity of lithium in a negative electrode by using a mixture of an alloy powder and a carbon material powder, which can store and discharge lithium, as a main component, and using a mixture of a metal, which generates an alloying reaction with lithium, and a metal, which does not generate the alloying reaction with lithium, as an alloy powder. SOLUTION: As a negative electrode material, a mixture of a carbon material powder and an alloy powder composed of a metal, which generates an alloying reaction with lithium, and a metal, which does not generate the alloying reaction with lithium, is used. As a metal, which generates the alloying reaction with lithium, Su, Si, In, Bi, Al, Ga and Ag are preferable. As a metal, which does not generate the alloying reaction with lithium, Cu and Ni and preferable. Weight ratio of the metal, which does not generate the alloying reaction with lithium, to the metal, which generates the alloying reaction with lithium, is preferably set at 50-90 wt.%. Weight ratio of an alloy in relation to the carbon material is preferably 5-50 wt.%. With this composition, fining of metal to be used for negative electrode and loose-out thereof due to the fining can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a negative electrode thereof.

[0002]

2. Description of the Related Art As electronic devices have become smaller and lighter, there has been an increasing demand for smaller and lighter batteries as power sources. In particular, expectations are high for non-aqueous electrolyte lithium secondary batteries having high voltage and high energy density. Lithium secondary batteries using metallic lithium as the negative electrode active material have poor charging / discharging efficiency because the deposited lithium grows in dendrite shape, and are practically sufficient, such as the grown lithium penetrating through the separator and causing internal short-circuiting of the battery. No lithium secondary battery has been obtained.

On the other hand, in recent years, lithium has been absorbed,
A negative electrode using a releasable carbon material has been put to practical use.

[0004] In addition, as a configuration of a negative electrode, Japanese Patent Laid-Open No.
Japanese Patent No. 171678 discloses a negative electrode in which a carbon material powder capable of occluding and releasing lithium and a metal material powder which causes an alloying reaction with lithium are mixed. It is disclosed that a negative electrode side output terminal is formed from a layer using a metal element that forms an alloy with lithium and a layer using a metal element that does not form an alloy with lithium, and from a metal portion that does not form an alloy with lithium. . Japanese Patent Application Laid-Open No. 8-255610 discloses a clad material of a metal layer forming an alloy with lithium and a metal layer hardly forming an alloy with lithium.

[0005]

However, in a negative electrode in which a carbon material powder and a metal powder that causes an alloying reaction with lithium are mixed, the metal repeatedly expands and contracts during the reaction between the metal and lithium. As a result, the metal crystal powder was miniaturized and the metal was separated from the current collector and dropped off, and the charge-discharge cycle life characteristics of the battery were reduced.

When a negative electrode composed of a metal layer forming an alloy with lithium and a metal layer hardly forming an alloy with lithium is used, only the metal forming an alloy with lithium participates in the reaction, but the first charge. Sometimes, the difference between the amount of lithium alloyed with a metal and the amount of lithium involved in the reaction during discharge, that is, the irreversible capacity of lithium (hereinafter, retention) increases, and the discharge capacity of the battery itself decreases.

[0007] Further, in a metal which is easily alloyed with lithium, the metal itself expands and contracts, and the adhesion between the metal and the current collector or the other metal is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The present invention reduces the irreversible capacity of lithium in a negative electrode and prevents the metal used for the negative electrode from being finely divided and falling off due to the reduction in the discharge capacity and charge capacity. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent discharge cycle life characteristics.

[0009]

In order to solve these problems, a non-aqueous electrolyte secondary battery according to the present invention comprises, as a main constituent material, a mixture of an alloy powder and a carbon material powder capable of absorbing and storing lithium. The alloy uses a negative electrode composed of a metal that causes an alloying reaction with lithium and a metal that does not cause an alloying reaction with lithium.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is described in claim 1
As described above, a mixture of a carbon material powder and an alloy powder composed of a metal that causes an alloying reaction with lithium and a metal that does not occur is used for the negative electrode. Since the carbon material has a relatively low density, when forming a negative electrode, there is a disadvantage that the capacity density per volume is low, but there is an advantage that even if charge and discharge are repeated, there is almost no expansion, shrinkage or falling off due to this.

The carbon material used here is natural graphite or artificial graphite, and can be used without any particular restrictions such as flakes and spheres.

On the other hand, if only a metal that causes an alloying reaction with lithium is easily expanded and contracted during charge and discharge, alloying is performed with a metal that does not cause an alloying reaction with lithium. Accordingly, the metal that does not alloy with lithium forms a skeleton, so that it is possible to prevent the alloy from being miniaturized during charging and thereby exfoliating and falling off the current collector.

The metals which cause alloying include Sn, Si,
In, Bi, Al, Ga, and Ag are preferable, and Cu and Ni are preferable as the metal that does not cause alloying.

[0014] In addition, while a metal that forms an alloy with lithium alone has a large retention, by combining with a carbon material, it is possible to reduce the retention of the metal and increase the amount of lithium that can participate in charge and discharge. Capacity can be improved.

Further, the ratio of the metal which forms an alloying reaction with lithium to the metal which does not form an alloy with lithium in the alloy is preferably 50 to 90% by weight, particularly preferably 60 to 8% by weight.
0% by weight is preferred. The ratio of alloy to carbon material is
The content is preferably 5 to 50% by weight, particularly preferably 5 to 30% by weight.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) FIG. 1 is a sectional view of a coin-type battery for evaluating the negative electrode of the present invention. In the figure,
1 is a stainless steel case, 2 is a disc spring. The test electrode No. 3 was prepared by mixing styrene-butadiene rubber (SBR) as a binder at a weight ratio of 95: 3.5 with the main constituent material of the negative electrode, applying the mixture to a copper foil core material, drying, After rolling,
It is punched to a predetermined size. The mixing ratio of the binder SBR is calculated based on the solid content. Lithium is used for the counter electrode of No. 4 and pressed against a stainless steel sealing plate No. 5. 6 is a gasket, 7 is a separator made of a microporous film made of polypropylene. The electrolytic solution was prepared by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3.
And a solution prepared by dissolving lithium hexafluorophosphate at 1.5 mol / dm ³ is used. Battery size is 20m in diameter
m, height 1.6 mm.

(Example 1) Sn-Cu alloy powder having an average particle size of 15 µm and an average particle size of 6 µm
Was mixed at a weight ratio of 20:80, and the mixture was uniformly dispersed by stirring with a mill to prepare the test electrode, thereby forming a coin-type battery. Here, the ratio of Sn in the Sn—Cu alloy is 30% by weight, 50% by weight,
Batteries having 60% by weight, 80% by weight, 90% by weight and 95% by weight were replaced with batteries A1, A2, A3, A4 and A, respectively.
5, A6.

These batteries were subjected to a charge / discharge cycle test under test conditions at a charge / discharge current density of 0.5 mA / cm ² , a charge upper limit potential of 1.0 V, and a discharge lower limit potential of 0 V.

Example 2 Lithium was used as a negative electrode active material.
Does not cause alloying reaction with metal Si that causes alloying reaction
The composition of the alloy with metal Cu makes the weight ratio of Si 30 wt.
%, 50 wt%, 60 wt%, 80 wt%, 90 wt%
%, 95% by weight of Si-Cu alloy powder having a particle size of 6 μm.
m spheroidal graphite powder at a weight ratio of 20:80 wt%
Then, the mixture was uniformly dispersed by stirring with a mill. This
The particle size of the alloy used here was 10 μm. This
A coin-type battery was prepared in the same manner as in Example 1, and each of the batteries B
1, B2, B3, B4, B5, and B6. These
About pond, 0.5mA / cm ^TwoCharge by constant current charge / discharge
Test strip with an upper limit potential of 1.0 V and a lower discharge limit of 0 V
Charge / discharge cycle test was conducted.

Comparative Example 1 A Sn powder having an average particle size of 15 μm and a spheroidal graphite powder having an average particle size of 6 μm were in a weight ratio of 20:80.
A coin-type battery was prepared in the same manner as in Example 1 except that the mixture was mixed at a ratio of wt%, and a charge / discharge cycle test was performed in the same manner as a comparative battery A.

Comparative Example 2 A weight ratio of Si powder having an average particle diameter of 10 μm to spherical graphite powder having an average particle diameter of 6 μm was 20:80.
A coin-type battery was prepared in the same manner as in Example 1 except that the mixture was mixed at a ratio of% by weight, and a charge / discharge cycle test was performed in the same manner as a comparative battery B.

Comparative Example 3 A coin-type battery was prepared in the same manner as in Example 1 except that only spherical graphite having an average particle size of 6 μm was used, and a charge / discharge cycle test was performed in the same manner as in Example 1 as Comparative Battery C. Was done. Table 1 shows the charge / discharge capacity at the first cycle and the maintenance ratio of the discharge capacity at the 30th cycle to the discharge capacity at the first cycle of the battery of the present invention and the comparative battery.

[0024]

[Table 1]

As can be seen from Table 1, batteries A2, A3, A4, A5, or Si, in which a Sn-Cu alloy having a Sn weight ratio of 50% by weight to 90% by weight and spheroidal graphite are mixed.
Batteries B2, B3, B4, and B5 in which a weight ratio of 50% to 90% by weight of the Si—Cu alloy and the spheroidal graphite were mixed, had a significantly improved capacity retention ratio as compared with the comparative batteries.

However, in the batteries A1 and B1 in which the metal which reacts with lithium in the alloy, that is, the ratio of Si to Sn was 30% by weight, the capacity of the negative electrode was reduced and the battery capacity was reduced.

A battery A in which a ratio of a metal which does not react with lithium in the alloy, that is, Cu, is 5% by weight.
In B6 and B6, the amount of Cu serving as the skeleton of the alloy during charge and discharge was small, so that the alloy powder was refined and the battery capacity was reduced.

Example 3 In order to examine the ratio of the alloy to the carbon material, the weight ratio of Sn was 70% by weight.
2% by weight of n-Cu alloy powder based on spheroidal graphite powder;
A battery was prepared in the same manner as in Example 1 except that the weight was changed to 20% by weight, 20% by weight, 50% by weight, and 80% by weight.
1, D2, D3, D4, and D5, and the same charge / discharge cycle test was performed.

(Example 4) The same batteries as in Example 3 were used except that the Sn-Cu alloy was changed to the Si-Cu alloy, and the batteries E1, E2, E3, E4, and E5 were respectively formed. The test was performed.

Table 2 shows the batteries D1 to D5 and E1 to E5.
Of the first cycle charge / discharge capacity and the maintenance rate of the 30th cycle discharge capacity with respect to the first cycle discharge capacity.

[0031]

[Table 2]

As a result, when the mixing ratio of the alloy to the carbon material is 2% by weight, a high capacity cannot be obtained because it is insufficient to obtain the capacity of the alloy. The difference in the discharge capacity in the first cycle, that is, the retention is large. Therefore, the mixing ratio of the alloy to the effective carbon material was 5% by weight to 50% by weight.

Next, evaluation was made on a cylindrical battery. FIG.
Figure 2 shows a cross-sectional view of a cylindrical battery. In the figure, the positive electrode 1 uses LiCoO ₂ as an active material, carbon black as a conductive material, and an aqueous dispersion of polytetrafluoroethylene as a binder in a weight ratio of 100: 2.5: 7.5.
Is coated on both sides of an aluminum foil core, dried and rolled, cut into a predetermined size, and a titanium positive electrode lead 2 is spot-welded thereto. Negative electrode 3
The main constituent material is a mixture of Sn-Cu alloy powder containing 70% by weight of Sn and 20% by weight with respect to a spherical graphite powder having a particle diameter of 6 μm, and a styrene-butadiene rubber-based binder (SBR) is added to the material. The mixture was mixed at a ratio of 95: 3.5, applied to a copper foil core material, dried, rolled, cut into a predetermined size, and spotted with a copper negative electrode lead of 4. 5
Is a separator made of a microporous film made of polypropylene, and a positive electrode 1 and a negative electrode 2 are spirally wound through a separator 5 to form an electrode plate group. Insulating plates 6 and 7 made of polypropylene resin are arranged above and below the electrode plate group, respectively, and inserted into a nickel-plated iron case 8. The positive electrode lead 2 is inserted into a titanium sealing plate 10, and the negative electrode lead 4 is inserted into the case 8. After spot welding to the bottom, respectively, an electrolytic solution is injected and the battery is sealed via the gasket 9 to obtain a completed battery. The dimensions of this battery are 17 mm in diameter and 50 mm in height. Reference numeral 11 denotes a positive electrode terminal, and the negative electrode terminal is also used by the battery case. The electrolyte used was a mixture of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 3, and lithium hexafluorophosphate dissolved at 1.5 mol / dm ³ . This battery was designated as battery d of the present invention.

A battery having the same composition and composition as described above except that the Sn—Cu alloy was replaced with a Si—Cu alloy was fabricated, and this was designated as Battery e of the present invention.

Further, Comparative Battery A,
A battery similar to the above was prepared except that the batteries used for the comparative batteries B and C were used, and the comparative batteries a and
Comparative battery b and comparative battery c were used.

Using these batteries, a charge / discharge cycle test was performed at a constant current of 0.2 C. The charging upper limit potential is 4.2
V and the lower discharge limit potential were 3.0 V.

FIG. 3 shows the charge / discharge cycle life characteristics of batteries d and e of the present invention and comparative batteries a, b and c. In each of the batteries of the present invention, results were obtained in which the capacity was higher and the charge / discharge cycle characteristics were better than the comparative battery.

The present invention is not limited to this embodiment. As a metal that causes an alloying reaction with lithium, S
n, Si, In, Bi, Al, Ga,
Similar results were obtained with Ag and two or more of them.

Although Cu has been described as a metal that does not cause an alloying reaction with lithium, similar results were obtained with Ni.

Although spheroidal graphite was used as the carbon material, similar results were obtained with other carbons, artificial graphite, natural graphite, non-graphitizable carbon, and graphitizable carbon.

Although LiCoO 2 was used for the positive electrode of the cylindrical battery, other lithium-containing transition metal compounds such as L
iNiO 2, LiMn 2 O 4, or a material in which part of a transition metal thereof is replaced with another element may be used.

In addition, although a solution obtained by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and ethyl methyl carbonate was used for the electrolytic solution, other materials used for ordinary lithium secondary batteries, such as solutes, were used. Lithium borofluoride, lithium hexafluoroarsenate, etc., and solvents such as carbonates such as propylene carbonate, diethyl carbonate, dimethyl carbonate, and aliphatic carboxylic esters and ethers such as methyl propionate and ethyl propionate. Can be.

[0043]

As described above, in the present invention, a negative electrode is used in which an alloy powder composed of a metal that causes an alloying reaction with lithium, a metal that does not cause an alloying reaction with lithium, and a carbon material powder are mixed. In addition, the irreversible capacity of lithium in the negative electrode material can be reduced and the negative electrode material can be prevented from falling off from the negative electrode plate, so that a non-aqueous electrolyte lithium secondary battery having high capacity and excellent charge / discharge cycle characteristics can be obtained. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a coin-type battery.

FIG. 2 is a longitudinal sectional view of a cylindrical battery.

FIG. 3 is a diagram showing charge / discharge cycle life characteristics of a battery of the present invention and a battery of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode lead 3 Negative electrode 4 Negative electrode lead 5 Separator 6 Upper insulating plate 7 Lower insulating plate 8 Case 9 Gasket 10 Sealing plate 11 Positive electrode terminal

Claims (5)

[Claims] 1. A negative electrode comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is mainly composed of a mixture of an alloy powder and a carbon material powder capable of occluding and releasing lithium, and the alloy undergoes an alloying reaction with lithium. A non-aqueous electrolyte secondary battery comprising a resulting metal and a metal that does not cause an alloying reaction with lithium. 2. The metal which causes an alloying reaction with lithium is S
The metal selected from the group consisting of n, Si, In, Bi, Al, Ga, and Ag, and the metal that does not cause an alloying reaction with lithium is a metal selected from the group consisting of Cu and Ni. 2. The non-aqueous electrolyte secondary battery according to 1. 3. The non-aqueous electrolyte secondary solution according to claim 1, wherein the metal that causes an alloying reaction with lithium is 50 wt% to 90 wt% with respect to the metal that does not alloy with lithium. battery. 4. The negative electrode according to claim 1, wherein a mixing ratio of an alloy composed of a metal that causes an alloying reaction with lithium and a metal that does not cause an alloying reaction with lithium is 5 wt% to 5 wt% with respect to the carbon material.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the content is 50 wt%. 5. A positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the negative electrode uses a mixture of an alloy powder and a carbon material powder capable of occluding and releasing lithium, wherein the alloy is a Sn—Cu alloy or a Si— A non-aqueous electrolyte secondary battery that is one of Cu alloys.