JP2001351623A - Lithium secondary battery negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for making a lithium secondary battery that has an excellent charge and discharge cycle characteristics. SOLUTION: The negative electrode is amorphous in substance and made of aluminum alloy foil manufactured by liquid quenching roll method as expressed in the composition formula Al100-xMx (wherein M is at least one kind of element selected from the group of Ce, La, Y, Yb, Gd, Nd, Sm, Pr, Er, Ni, Co, Cu, Fe, and Cr; 1<=x<=20).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a lithium secondary battery comprising an aluminum alloy foil, and more particularly, to provide a negative electrode having a good charge / discharge cycle characteristic. It relates to improvement of the aluminum alloy foil.

[0002]

2. Description of the Related Art When a lithium metal plate is used as a negative electrode of a lithium secondary battery,
Active dendritic lithium precipitates during charging, and the precipitated lithium reacts with the electrolytic solution to reduce the capacity of the negative electrode, or grow by repeated charge and discharge to cause an internal short circuit. In place of the lithium metal plate, if a lithium-aluminum alloy plate prepared by electrochemically alloying lithium and crystalline aluminum is used, a dendritic shape accompanying the repetition of the reaction between lithium and the electrolytic solution and charge / discharge is provided. The growth of lithium is suppressed, and the charge / discharge cycle characteristics are improved. However, since the rate of the electrochemical reaction (alloying reaction) between lithium and crystalline aluminum is slow, the charge / discharge cycle characteristics are not significantly improved.

Therefore, as a negative electrode of a lithium secondary battery,
Instead of the above-mentioned lithium-aluminum alloy plate, a thickness of 0.3 mm (300 μm) obtained by lithium and a liquid quenching method was used.
It has been proposed to use a lithium-aluminum alloy plate produced by electrochemically alloying about m) amorphous aluminum or an aluminum alloy (JP-A-63-13267). According to the publication, the electrochemical reaction between lithium and amorphous aluminum or an aluminum alloy proceeds more rapidly than the electrochemical reaction at the time of charging lithium and crystalline aluminum. It is said that the characteristics are greatly improved.

However, the above-mentioned amorphous aluminum or aluminum alloy has a low level of amorphization.
This is because, in the liquid quenching method, when the thickness of the alloy is large, the cooling rate (solidification rate) decreases, and the level of amorphization inevitably decreases. It is difficult to obtain a lithium secondary battery having good charge / discharge cycle characteristics with aluminum and aluminum alloy which have a low level of amorphization and are not substantially amorphous. Aluminum and aluminum alloys having a low level of amorphization are easily pulverized due to a volume change accompanying insertion / desorption of lithium during charge / discharge,
This is because, when the powder is pulverized, the contact resistance between the negative electrode active material particles increases and the current collecting property decreases.

Accordingly, an object of the present invention is to provide a negative electrode which provides a lithium secondary battery having good charge / discharge cycle characteristics.

[0006]

The negative electrode for a lithium secondary battery (the electrode of the present invention) according to the present invention is substantially amorphous and has a composition formula of Al _100-x M _x [where M is Ce , La, Y, Y
b, Gd, Nd, Sm, Pr, Er, Ni, Co, C
at least one selected from the group consisting of u, Fe and Cr
Seed element: 1 ≦ x ≦ 20], which is an aluminum alloy foil produced by a liquid quenching roll method.

[0007] The use of a substantially amorphous aluminum alloy foil is generally based on the fact that a crystalline aluminum alloy foil is pulverized due to a volume change accompanying insertion and desorption of lithium during charge and discharge. While the contact resistance between alloy particles increases due to the formation of the alloy, the charge-discharge cycle characteristics tend to decrease because the current collecting property decreases.However, the amorphous aluminum alloy foil has high ductility and is hardly pulverized. is there. In this specification, a substantially amorphous aluminum alloy foil means that a halo portion is observed in a powder X-ray diffraction profile and the degree of amorphization A defined by the following formula is 0.3 or more. Shall say something. The higher the degree of amorphization A, the more amorphization is performed.

Amorphization degree A = maximum peak intensity of halo portion profile / maximum peak intensity of all profiles

The substantially amorphous aluminum alloy foil in the present invention is produced by a liquid quenching roll method (single roll method and twin roll method). The liquid quenching roll method is a rapid solidification method in which an alloy is heated and melted to form a molten metal, and the obtained molten metal is injected onto a high-speed rotating roll.

The thickness of the aluminum alloy foil is 100 μm
The following is preferred. Aluminum alloy foil thickness is 100μ
If it exceeds m, the utilization rate of the negative electrode decreases. On the other hand, when the foil thickness is larger than 100 μm, the cooling rate in the liquid quenching roll method becomes slow, so that the degree of amorphization A decreases, and it becomes difficult to obtain a substantially amorphous aluminum alloy foil. . When the electrode of the present invention is used as a negative electrode of a cylindrical battery or a card type battery which is wound or bent together with the positive electrode in a state where a separator is interposed between both electrodes and is housed in a battery can, the thickness is 10 to 100 μm. preferable. 1 foil thickness
If the thickness is less than 0 μm, the aluminum alloy peels off during winding or bending, making it difficult to produce a negative electrode.
If the thickness exceeds 00 μm, the utilization rate of the negative electrode decreases, and it becomes difficult to perform winding or bending.
Since the electrode of the present invention is different from a negative electrode obtained by applying a powdery negative electrode active material to a current collector (core) using a binder, the entire electrode is made of a negative electrode active material having current collecting properties. No electrical conductor is required, and therefore the active material loading can be increased by that volume.

A substantially amorphous aluminum alloy according to the present invention.
Alloy foil has a composition formula of Al_100-xM _x[Wherein M is C
e, La, Y, Yb, Gd, Nd, Sm, Pr, Er,
Selected from the group consisting of Ni, Co, Cu, Fe and Cr
At least one element; 1 ≦ x ≦ 20].
M increases the degree of amorphization A.

In order to obtain a lithium secondary battery having good charge / discharge cycle characteristics, it is necessary to use the electrode of the present invention for the negative electrode and an active material having good electrochemical reversibility for the positive electrode. Specific examples of such a positive electrode active material include lithium cobaltate (such as LiCoO ₂ ), lithium nickelate (such as LiNiO ₂ ), lithium manganate (LiM
nO ₂ etc.) and mixtures thereof.

[0013]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(Experiment 1) Negative electrodes having different compositions of aluminum alloy foil were prepared, and a lithium secondary battery was prepared using each negative electrode, and charge / discharge cycle characteristics of each battery were examined.

[Preparation of positive electrode] LiC having an average particle size of 20 μm
NMP (N-methyl-2-pyrrolidone) comprising 90 parts by weight of oO ₂ powder (positive electrode active material), 5 parts by weight of artificial graphite powder (conductive agent), and 5 parts by weight of polyvinylidene fluoride (binder)
A slurry was prepared by mixing the mixture with a solution, and the slurry was applied to both surfaces of an aluminum foil by a doctor blade method to form an active material layer. The active material layer was vacuum-dried at 150 ° C. for 2 hours, and a 40 mm × 300 mm positive electrode ( (Thickness: about 60 μm).

[Preparation of Negative Electrode] Al and an element M shown in Table 1 (Al and M are both 99.9% pure) were prepared at an atomic ratio of 9
After weighing at 5: 5, mixing in a mortar, and press molding, an ingot was produced by the arc melting method. After the ingot was melted, the distance between the rolls was adjusted by a twin-roll method and the mixture was rapidly solidified to produce an aluminum alloy foil having a thickness of 20 μm, and then cut to produce a negative electrode. The size of the negative electrode using Ce as the element M is 40 mm × 300 m
m, and the other negative electrodes were cut to the same weight as the negative electrodes. Emission analysis (ICP) confirmed that all aluminum alloys were represented by the composition formula Al ₉₅ M ₅ .

[Preparation of Electrolyte Solution] LiPF was added to an equal volume mixed solvent of ethylene carbonate and diethyl carbonate.
₆ was dissolved at 1 mol / liter to prepare an electrolytic solution.

[Preparation of Lithium Secondary Battery]
Using the negative electrode and the electrolytic solution, lithium secondary batteries A1 to A15 of AA size (diameter 14 mm, height 50 mm) were produced. A polypropylene microporous film was used as a separator.

FIG. 1 is a cross-sectional view of a manufactured lithium secondary battery. The lithium secondary battery A shown in FIG.
It comprises a negative electrode 2, a separator 3 separating them, a positive electrode lead 4, a negative electrode lead 5, a positive electrode cover 6, a negative electrode can 7, and the like.
The positive electrode 1 and the negative electrode 2 are spirally wound with the separator 3 interposed between the two electrodes and housed in the negative electrode can 7. The positive electrode 1 is inserted into the positive electrode lid 6 via the positive electrode lead 4,
The negative electrode 2 is connected to a negative electrode can 7 via a negative electrode lead 5, and has a structure capable of charging and discharging.

<Charge / Discharge Cycle Characteristics>
At 25 ° C., a charge / discharge cycle test was performed in which a charge / discharge cycle in which the battery was charged at 200 mA to 4.2 V and then discharged at 200 mA to 2.75 V as one cycle was performed.
The cycle up to 80% of the discharge capacity at the cycle was determined. Table 1 shows the results. Table 1 also shows the degree of amorphousness A of the aluminum alloy foil used for each battery. The cycle shown in Table 1 corresponds to the cycle of the battery A1 for 10 cycles.
The relative index is set to 0.

[0021]

[Table 1]

Table 1 shows that a lithium secondary battery having good charge / discharge cycle characteristics can be obtained by using a substantially amorphous aluminum alloy foil as the negative electrode.

(Experiment 2) The relationship between the thickness of the aluminum alloy foil and the charge / discharge cycle characteristics was examined.

Al and Ce (both having a purity of 99.9%) were weighed at an atomic ratio of 95: 5, mixed in a mortar, pressed and molded, and an ingot was produced by an arc melting method. . After the ingot was melted, it was rapidly solidified at various roll distances by a twin-roll method, and the thickness was 5 μm.
Five types of aluminum alloy foils of 10 μm, 50 μm, 100 μm or 120 μm were prepared, and cut to a size that would be the same as the weight of the negative electrode used for the battery A1 to prepare a negative electrode. The thinner the foil, the higher the cooling rate. Emission analysis confirmed that each of the aluminum alloys was an alloy represented by the composition formula Al ₉₅ Ce ₅ .

Except that the above-mentioned negative electrode was used, the same procedure as in Experiment 1 was carried out, and only the negative electrode was different from the lithium secondary battery B.
1 to B5 were prepared, and a charge / discharge cycle test was performed under the same conditions as those performed in Experiment 1, and the cycle until the discharge capacity was reduced to 80% of the first cycle discharge capacity was obtained. However, for the lithium secondary battery B1, the strength of the aluminum alloy foil having a thickness of 5 μm was low and the aluminum alloy foil was pulverized in several cycles, so the charge / discharge cycle test was terminated at that point.
Table 2 shows the results. Table 2 also shows the degree of amorphousness A of the aluminum alloy foil used for each battery. Table 2
Also shows the result of battery A1 transcribed from Table 1.
The cycle shown in Table 2 is a relative index when the cycle of the battery A1 is set to 100.

[0026]

[Table 2]

From Table 2, the thickness of the aluminum alloy foil is:
It turns out that 10-100 micrometers is preferable. The reason why the charge / discharge cycle characteristics of the lithium secondary battery B5 is not good is that the pulverization of the aluminum alloy foil progressed in a short cycle because the degree of amorphousness A was small.

(Experiment 3) The relationship between _x in the composition formula Al _100-x M x and charge / discharge cycle characteristics was examined.

As the negative electrode, an alloy foil having a thickness of 20 μm and represented by the composition formula shown in Table 3 was used.
The lithium secondary batteries C1 to C6 different from No. 1 were produced. The weight of the negative electrode was the same as the weight of the negative electrode used for the battery A1. The batteries C2 to C4 are batteries using the electrode of the present invention, and the other batteries are batteries using the reference electrode. For each battery, a charge / discharge cycle test was performed under the same conditions as those performed in Experiment 1, and the cycle until the discharge capacity was reduced to 80% of the discharge capacity in the first cycle was determined. Table 3 shows the results
Shown in Table 3 shows the negative electrode active materials (Al
_100-x M amorphous degree of _x alloy) A Aru be shown. Also,
Table 3 also shows the results of Battery A1 transcribed from Table 1. In the cycle shown in Table 3, the cycle of the battery A1 is 10 cycles.
The relative index is set to 0.

[0030]

[Table 3]

As shown in Table 3, the electrodes using the electrode of the present invention
The ponds A1 and C2 to C4 are used for other batteries using the reference electrode.
In comparison, the charge / discharge cycle characteristics are better. From this result,
Negative electrode providing lithium secondary battery with good discharge cycle characteristics
In order to obtain, the composition formula Al _100-xM_xX is 1-2
0 aluminum alloy foil must be used
You. Regarding other elements M, the composition formula Al_100-xM_xIn
It is necessary to use aluminum alloy foil with x in the above range
Confirmed that there is.

(Experiment 4) A positive electrode active material was examined.

As the positive electrode active material, LiNiO ₂ , LiMnO ₂ , LiCoO ₂ and LiCoO ₂ are used instead of LiCoO _2.
Using a mixture with NiO ₂ at a weight ratio of 1: 1 or TiS ₂ , only the positive electrode active material was changed to lithium secondary battery A1 in order.
And lithium secondary batteries D1 to D4 different from. The initial capacity of the positive electrode of each battery was made equal by adjusting the filling amount of the positive electrode active material. For each battery, a charge / discharge cycle test was performed under the same conditions as those performed in Experiment 1, and the cycle until the discharge capacity was reduced to 80% of the discharge capacity in the first cycle was determined. Table 4 shows the results. In Table 4, the results of Battery A1 are also transcribed from Table 1. The cycles shown in Table 4 are relative indices with the cycle of battery A1 as 100.

[0034]

[Table 4]

As shown in Table 4, batteries A1 and D1-D
The battery No. 3 has better charge / discharge cycle characteristics than the battery D4.
The reason why the charge / discharge cycle characteristics of the lithium secondary battery D4 is not good is that the reversibility of TiS ₂ used as the positive electrode active material at the time of charge / discharge is not good. From these results, in order to obtain a lithium secondary battery having good charge / discharge cycle characteristics, while using the electrode of the present invention for the negative electrode, as a positive electrode active material,
It is understood that it is necessary to use at least one lithium / transition metal composite oxide selected from the group consisting of lithium cobaltate, lithium nickelate and lithium manganate.

[0036]

The present invention provides a negative electrode which provides a lithium secondary battery having good charge / discharge cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a lithium secondary battery manufactured in an example.

[Explanation of symbols]

 A lithium secondary battery 1 positive electrode 2 negative electrode 3 separator 4 positive electrode lead 5 negative electrode lead 6 positive electrode lid 7 negative electrode can

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 1/02 503 C22C 1/02 503J (72) Inventor Hiroshi Nakamura 2-5 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Yasuhiko Ito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 5H029 AJ05 AK03 AL11 AL12 AM03 AM04 AM05 AM07 BJ02 BJ14 CJ00 CJ02 CJ28 DJ18 HJ02 HJ04 5H050 AA07 BA16 CA08 CA09 CB11 CB12 EA09 EA24 FA20 GA00 GA02 HA02 HA04

Claims (4)

[Claims] A substantially amorphous, compositional composition Al _100-x M _x
[Wherein, M is Ce, La, Y, Yb, Gd, Nd, S
at least one element selected from the group consisting of m, Pr, Er, Ni, Co, Cu, Fe and Cr; 1 ≦ x ≦ 2
0], a negative electrode for a lithium secondary battery comprising an aluminum alloy foil produced by a liquid quenching roll method. 2. The thickness of the aluminum alloy foil is 100 μm.
The negative electrode for a lithium secondary battery according to claim 1, wherein m is not more than m. 3. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode comprises at least one lithium selected from the group consisting of lithium cobaltate, lithium nickelate and lithium manganate. Having a transition metal composite oxide as an active material, wherein the negative electrode is substantially amorphous, and has a composition formula of Al _100-x M _x [wherein
M is Ce, La, Y, Yb, Gd, Nd, Sm, P
at least one element selected from the group consisting of r, Er, Ni, Co, Cu, Fe, and Cr; 1 ≦ x ≦ 20], and an aluminum alloy foil produced by a liquid quenching roll method. A lithium secondary battery, characterized in that: 4. The aluminum alloy foil has a thickness of 100 μm.
The lithium secondary battery according to claim 3, which is not more than m.