JP2567674B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a negative electrode using lithium as an active material, and a positive electrode using manganese dioxide, vanadium pentoxide, titanium, or a sulfide or selenide of niobium as an active material. , A non-aqueous electrolyte secondary battery including a non-aqueous electrolyte.

2. Description of the Related Art The problem with this type of battery is that the negative electrode active material, lithium, grows in a dendritic manner on the negative electrode surface during charging, resulting in a short circuit inside the battery in contact with the positive electrode, or in the form of mossy deposition. Lithium is lost, and as a result, the charge / discharge cycle becomes extremely short. this is,
This is because the surface of the negative electrode becomes uneven when lithium is turned into ions and eluted during discharging, and lithium is concentrated on the convex portions during subsequent charging.

As a countermeasure against this, as shown in JP-A-52-5423,
It has been proposed to construct the negative electrode with a lithium-aluminum alloy. With such a configuration, lithium is restored so as to form an alloy with aluminum as a base during charging, and thus there is an advantage that dendritic growth of lithium is suppressed. However, in this case, since the strength of the lithium-aluminum alloy is weak, cracking and miniaturization of the electrode occur due to repeated charging / discharging, and thus the cycle characteristics are also not good.

Therefore, as shown in JP-A-63-131776, in order to improve the strength of the lithium-aluminum alloy electrode,
A lithium-aluminum alloy adhered with an adhesive or an alloy of aluminum and a metal such as copper, iron, nickel, manganese, cobalt, silicon, or zirconium is used as a base material, and these alloys and lithium are used. There is proposed a method of forming an electrode having higher strength by alloying and.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, even with such a configuration, it is not possible to obtain practically satisfactory characteristics. This is because the β phase-Li-Al in the aluminum alloy releases Li to become Al by discharge, while it occludes Li during charging and changes to β phase-Li-Al again. At this time, in the case of the negative electrode having the above-described structure, the initial β-phase-Li-Al crystallinity is good, and thus the strain is reduced. Therefore, this is because when the charge and discharge cycles are repeated, the crystal change between β-phase-Li-Al and Al causes miniaturization and collapse of the electrode.

Therefore, the present invention aims to provide a non-aqueous electrolyte secondary battery having excellent cycle characteristics by suppressing the miniaturization or collapse of the electrodes even when the charge / discharge cycle is repeated. It is a thing.

Means for Solving the Problems The present invention, in order to achieve the above object, a negative electrode using lithium as an active material, a positive electrode, and a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, wherein the negative electrode is It consists of an alloy containing lithium and aluminum as its main components, and the half-value width (β 1/2) on the (400) plane of the β-phase-Li-Al copper tube in the alloy is 0.45 ° or more. It is characterized by being less than 0.65 °.

Action As described above, when the half width of the X-ray diffraction peak is 0.45 ° or more, the strain of β-phase-Li-Al becomes large. Therefore,
Even when the charge-discharge cycle is repeated, the negative electrode is less likely to be miniaturized or collapsed due to the crystal change, so that the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

If the full width at half maximum of the X-ray diffraction peak of the β-phase-Li-Al copper tube at the (400) plane exceeds 0.65 °, the electrode becomes brittle, so the width of the X-ray diffraction peak is set to 0.65 ° or less. It is necessary.

First Example (Example I) A first example of the present invention will be described below with reference to FIGS. 1 to 11.

The negative electrode 2 made of a lithium alloy is pressure-bonded to the inner surface of the negative electrode current collector 7, and the negative electrode current collector 7 is fixed to the inner bottom surface of the negative electrode can 5 made of stainless steel and having a substantially U-shaped cross section.
A peripheral end of the negative electrode can 5 is fixed inside an insulating packing 8 made of polypropylene, and an outer periphery of the insulating packing 8 is made of stainless steel and has a substantially U-shaped cross section in a direction opposite to the negative electrode can 5. 4 is fixed. The positive electrode current collector 6 is fixed to the inner bottom surface of the positive electrode can 4, and the positive electrode 1 is fixed to the inner surface of the positive electrode current collector 6. A separator 3, which also functions as a liquid retaining layer, is interposed between the positive electrode 1 and the negative electrode 2, and the separator 3 is impregnated with an electrolytic solution. As this electrolyte, propylene carbonate containing 1 mol / liter of lithium perchlorate was used. The battery dimensions are 25 mm in diameter and 3.0 mm in thickness.

Here, for the positive electrode 1, a mixture of manganese diacid and lithium hydroxide in a molar ratio of 2: 1 is heat-treated at 375 ° C. for 20 hours, and this is used as an active material. Next, the active material, the acetylene black conductive material, and the fluororesin binder are mixed at a weight ratio of 80:10:10 to prepare a mixture, and then the mixture is pressure-molded. It is prepared by drying.

 On the other hand, the negative electrode 2 is manufactured as follows.

First, aluminum and silver are mixed and melted at a ratio of 97: 3, and then this is cooled to prepare an ingot (base alloy). Next, the base alloy consisting of this ingot is homogenized at 550 ° C. for 12 hours. Then
After cutting off the surface layer of the ingot to remove the oxide film on the surface of the ingot, repeatedly rolling at room temperature
A 0.5 mm aluminum-silver alloy plate (cold rolled base alloy) is made. Then, using this cold-rolled base alloy as a substrate, in a non-aqueous electrolyte, preferably LiCl
1.3-dioxolane, 2-methyl-1.3-dioxolane, 4-methyl-1.3-dioxolane, tetrahydrofuran, or 2-methyl-tetrahydrofuran in which Li salt such as O ₄ , LiCF ₃ SO ₃ , LiBF ₄ , LiPF ₆ , or LiSbF ₆ is dissolved It was immersed in a cyclic ether such as the above, electrolysis was performed using Li as the counter electrode, and a lithium-aluminum alloy was prepared, which was used as the negative electrode. The molar ratio of aluminum to lithium in this alloy was 65:35.

The battery thus manufactured is hereinafter referred to as (A ₁ ) battery.

(Examples II to V) A battery was produced in the same manner as in Example I except that aluminum and silver were mixed in the proportions shown in Table 1 below.

The battery produced in this way is referred to as (A ₂ ) battery-
(A ₅ ) Battery.

(Comparative Examples I and II) A battery was prepared in the same manner as in Example I except that aluminum and silver were mixed in the proportions shown in Table 2 below.

The battery produced in this way is referred to below as (U ₁ ) battery,
(U ₂ ) Battery.

(Comparative Examples III to IX) Aluminum and silver are mixed at a ratio shown in Tables 1 and 2 above and melted, and then cooled to prepare an ingot. Next, this ingot is homogenized at 550 ° C. for 12 hours. Then, after cutting off the surface layer of the ingot, this ingot is sliced to a thickness of 0.5 mm.
A battery was prepared in the same manner as in Example I above, except that the aluminum-silver alloy plate was prepared.

The battery produced in this way is referred to as (V ₁ ) battery to
(V ₇ ) Battery.

The correspondence between (A ₁ ) battery to (A ₅ ) battery, (U ₁ ) battery, (U ₂ ) battery and the above (V ₁ ) battery to (V ₇ ) battery (Al and Ag
The weight ratio) is shown in Table 3 below.

(Comparative Examples X to XV) Aluminum, lithium and silver are mixed at a ratio shown in Table 4 below and melted, and then cooled to prepare an ingot. Next, this ingot is homogenized at 550 ° C. for 12 hours. Then, after cutting off the surface layer of the ingot, this ingot is sliced to a thickness of 0.5 mm.
Of aluminum-lithium-silver alloy plate was prepared and used as a negative electrode. A battery was made in the same manner as in Example I except that such a negative electrode was used.

The battery produced in this way is referred to below as (W ₁ ) battery
(W ₅ ) Battery.

(Experiment I) The negative electrodes of the (A ₁ ) battery to the (A ₅ ) battery of the present invention, the (U ₁ ) battery, the (U ₂ ) battery, and the (V ₁ ) battery to the (V ₇ ) battery of Comparative Examples, And (W ₁ ) battery to (W ₅ ) battery negative electrode and β phase-Li-Al alloy X-ray diffraction peak (400) of the steel tube
The full width at half maximum (β 1/2) was examined, and the results are shown in FIGS. 2, 3, and 4.

As shown in FIG. 2, FIG. 3, and FIG. 4, the half widths of the negative electrodes of the (A ₁ ) battery to the (A ₅ ) battery are all 0.45 ° or more, whereas the (U ₁ ) battery is , (U ₂ ) battery, (V ₁ ) battery ~
It is recognized that the full width at half maximum of the negative electrodes of the (V ₇ ) battery and the (W ₁ ) battery to the (W ₅ ) battery is 0.45 ° or less.

This means that Ag is not added to the (U ₁ ) battery and (U ₂ ) battery, or the amount is very small even if Ag is added,
(V ₁₎ cell ~ (V ₇₎ that is not cold rolled in battery, not alloyed with (W ₁₎ cell ~ (W ₅₎ that is not cold rolled in battery and the nonaqueous electrolytic solution By
This is because it is difficult to increase the strain of crystals of the lithium-aluminum alloy.

(Experiment II) (A ₁ ) Battery to (A ₅ ) Battery of the Present Invention and (U ₁ ) of Comparative Example
The cycle characteristics of the battery, the (U ₂ ) battery, the (V ₁ ) battery to the (V ₇ ) battery, and the (W ₁ ) battery to the (W ₅ ) battery were examined. The results are shown in FIGS. It is shown in FIG.
The experimental condition was that discharge and charge were performed at a current of 2 mA for 10 hours each, and when the discharge reached 2 V or less at the end of discharge, the cycle life of the battery was defined.

As shown in FIGS. 5, 6, and 7, (U ₁ ) battery, (U ₂ ) battery, (V ₁ ) battery to (V ₇ ) battery, and (W ₁ ) battery of Comparative Examples ~ It is recognized that all of the (W ₅ ) batteries have a life of 300 cycles or less, while the (A ₁ ) batteries of the present invention to (A ₅ ) have a life of 400 cycles or less. .

Second Example (Example I) A battery was produced in the same manner as in Example 1 of the first example except that aluminum and tungsten were mixed at a ratio of 98: 2 to produce an aluminum alloy.

The battery thus manufactured is hereinafter referred to as a (B ₁ ) battery.

(Examples II to V) A battery was produced in the same manner as in Example 1 of the first example except that aluminum and tungsten were mixed in the proportions shown in Table 5 below to produce an aluminum alloy.

The battery produced in this way is referred to as (B ₂ ) battery to
(B ₅₎ is referred to as a battery.

(Comparative Examples I and II) A battery was prepared in the same manner as in Example I except that aluminum and tungsten were mixed in the ratios shown in Table 6 below.

The battery prepared in this manner is referred to as (X ₁ ) battery,
(X ₂ ) Battery.

(Experiment I) β-phase-Li in the negative electrodes of the (B ₁ ) battery to the (B ₅ ) battery of the present invention and the negative electrodes of the (X ₁ ) battery and the (X ₂ ) battery of Comparative Examples.
The full width at half maximum (β 1/2) on the (400) plane of the X-ray diffraction peak of the copper tube of the -Al alloy was investigated.
Shown in the figure.

As shown in FIG. 8, the half-widths of the negative electrodes of the (B ₁ ) battery to the (B ₅ ) battery are all 0.45 ° or more, whereas the negative electrodes of the (X ₁ ) battery and the (X ₂ ) battery are It is recognized that the full width at half maximum is 0.45 ° or less.

(Experiment II) (B ₁ ) Battery to (B ₅ ) Battery of the Present Invention and (X ₁ ) of Comparative Example
The cycle characteristics of the battery and the (X ₂ ) battery were examined, and the results are shown in FIG. 9. The experimental conditions were the same as those of Experiment II of the first embodiment.

As shown in FIG. 9, both the (X ₁ ) battery and the (X ₂ ) battery of the comparative example have a life of 300 cycles or less.
It is recognized that the batteries (B ₁ ) to (B ₅ ) of the present invention all have a life of 300 cycles or more.

Third Example (Example I) Example 1 of the first example except that aluminum and rhenium were mixed at a ratio of 98: 3 to form an aluminum alloy.
A battery was prepared in the same manner as in.

The battery thus manufactured is hereinafter referred to as a (C ₁ ) battery.

(Examples II to V) A battery was produced in the same manner as in Example 1 of the first example except that aluminum and rhenium were mixed in the ratios shown in Table 7 below to produce an aluminum alloy.

The battery prepared in this way is referred to as (C ₂ ) battery
(C ₅₎ is referred to as a battery.

(Comparative Examples I and II) A battery was produced in the same manner as in Example I except that aluminum and rhenium were mixed in the proportions shown in Table 8 below.

The battery produced in this way is referred to below as (Y ₁ ) battery,
(Y ₂ ) battery.

(Experiment I) Of the β-phase-Li-Al alloy in the negative electrodes of the (C ₁ ) battery to the (C ₅ ) battery of the present invention and the negative electrodes of the following (Y ₁ ) batteries and (Y ₂ ) batteries of Comparative Examples. X-ray diffraction peak of copper tube (400)
The full width at half maximum (β 1/2) was examined, and the results are shown in FIG.

As shown in FIG. 10, the negative electrodes of the (C ₁ ) battery to the (C ₅ ) battery all have a half width of 0.45 ° or more, whereas the negative electrodes of the (Y ₁ ) battery and the (Y ₂ ) battery are It is recognized that the full width at half maximum is 0.45 ° or less.

(Experiment II) (C ₁ ) Battery to (C ₅ ) Battery of the Present Invention and (Y ₁ ) of Comparative Example
The cycle characteristics of the battery and (Y ₂ ) battery were examined. The results are shown in FIG. 11. The experimental conditions were the same as those of Experiment II of the first embodiment.

As shown in FIG. 11, both the (Y ₁ ) battery and the (Y ₂ ) battery of the comparative example have a life of 300 cycles or less.
It is recognized that the (C ₁ ) battery to the (C ₅ ) battery of the present invention all have a life of 400 cycles or more.

As described above, the cycle characteristics can be improved in the battery using the lithium-aluminum alloy in which the half-value width of the (400) plane of the β-phase-Li-Al alloy is 0.45 ° or more (large strain) as the negative electrode. As described above, in order to increase the strain of aluminum or aluminum alloy, the negative electrode may be manufactured as in the above embodiment. This procedure will be described below.

First, the metal bond radius is 1.23Å or more in aluminum
Prepare a base alloy by alloying by adding a metal of 1.63Å or less. When the base alloy is prepared in this manner, lattice defects are generated during crystallization, so that many strains occur in the crystal. Examples of such metals include Mg, Ca, Sc, Ti, V, Cr, Mn and F in addition to Ag, W and Re shown in the first to third embodiments.
There are e, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Cd, In and Ta.
When a metal other than the above range is added to aluminum, such a metal is difficult to form a solid solution with aluminum,
It is difficult to increase the crystal strain of aluminum in the base alloy.

Next, the base alloy containing aluminum is cold-rolled. If cold rolling is performed in this way, the aluminum crystal extends in the rolling direction, but since it is carried out at a low temperature, the atoms in the metal are not sufficiently diffused, and many strains occur in the crystal. Such aluminum is alloyed with lithium by the following procedure.

Then, using this cold-rolled base alloy,
Short-circuit or electrolyze in a non-aqueous electrolyte solution at a temperature of about room temperature to alloy with lithium to obtain an alloy containing lithium and aluminum as main components. In addition, when metallurgically or when a lithium-aluminum alloy is produced by electrolysis in a molten salt, it is generally produced at a high temperature of 300 ° C or higher, so that diffusion of atoms in the metal is accelerated. However, it is difficult to produce a lithium-aluminum alloy with a large amount of strain. Then, as described above, when electrolysis or the like is performed in a non-aqueous electrolytic solution at a temperature of about room temperature to alloy, the β-phase-Li-Al alloy has a large strain due to a crystal change at the time of alloying.

In the aluminum alloy, the content of metals other than aluminum is preferably 0.1% by weight or more and 5% by weight or less. This is because when the content is less than 0.1% by weight, the effect of addition is not significant, whereas when the content is more than 5% by weight, the aluminum substrate becomes brittle and becomes fine.

As described above, according to the present invention, since the β-phase-Li-Al strain becomes large, even when the charge / discharge cycle is repeatedly performed, miniaturization or collapse of the negative electrode due to crystal change occurs. It will be difficult. As a result, it is possible to dramatically improve the cycle characteristics of the non-aqueous electrolyte secondary battery.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery of the present invention, and FIG. 2 is a (A ₁ ) battery to (A ₅ ) battery of the present invention and (U ₁ ) battery and (U ₂ ) of a comparative example. Fig. 3 is a graph showing the full width at half maximum of the (400) plane of the β-phase-Li-Al alloy of the negative electrode in the battery.
₁ ) A graph showing the full width at half maximum of the (400) plane of the β-phase-Li-Al alloy of the negative electrode in the battery to the (V ₇ ) battery, and FIG. 4 shows the (W ₁ ) battery to the (W ₅ ) battery of the comparative example. Fig. 5 is a graph showing the full width at half maximum of the (400) plane of the negative electrode β-phase-Li-Al alloy, (A ₁ )
Batteries to (A ₅ ) battery, (U ₁ ) battery and (U ₂ ) battery showing cycle characteristics, FIG. 6 shows (V ₁ ) battery to (V ₇ ) battery showing cycle characteristics, _7th battery The illustration shows (W ₁ ) battery ~
(W ₅ ) A graph showing the cycle characteristics of the battery, and FIG. 8 is a β phase of the negative electrode in the (B ₁ ) battery to (B ₅ ) battery of the present invention and the (W ₁ ) battery and (W ₂ ) battery of Comparative Example. -Li-Al alloy (400)
Fig. 9 is a graph showing the full width at half maximum of the surface. Fig. 9 shows (B ₁ ) battery to (B ₅ )
FIG. 10 is a graph showing cycle characteristics of the battery, the (W ₁ ) battery and the (W ₂ ) battery, and FIG. 10 shows the (C ₁ ) battery to the (C ₅ ) battery of the present invention and the (Y ₁ ) battery and (Y) of the comparative example. ₂ ) β phase of negative electrode in battery −
A graph showing the full width at half maximum of the (400) plane of the Li-Al alloy, and Fig. 11 is a graph showing the cycle characteristics of the (C ₁ ) battery to the (C ₅ ) battery and the (Y ₁ ) battery and the (Y ₂ ) battery. is there. 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator.

Claims (1)

(57) [Claims] 1. A negative electrode using lithium as an active material, a positive electrode,
In a non-aqueous electrolyte secondary battery provided with a non-aqueous electrolyte, the negative electrode is made of an alloy containing lithium and aluminum as main components, and X-rays from a β-phase-Li-Al copper tube in the alloy. Full width at half maximum on the (400) plane of the diffraction peak (β 1/2)
Is 0.45 ° or more and 0.65 ° or less, a non-aqueous electrolyte secondary battery.