JPH0244645A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase the cycle performance of a battery by forming a negative electrode with an alloy mainly comprising lithium and aluminum and having a specified characteristic. CONSTITUTION:A negative electrode is formed with an alloy mainly comprising lithium and aluminum. The half value width (beta1/2) on the face (400) of beta-phase Li-Al in the alloy at the X-ray diffraction peak measured with a copper tube is 0.45 deg. or more. The strain in beta-phase Li-Al is increased and forming of fine particles in the negative electrode or generation of its breakage caused by crystal deformation is difficult even if charge-discharge cycles are repeated. The cycle performance of a nonaqueous electrolyte secondary battery is increased.

Description

[Detailed Description of the Invention] Industrially and independently developed The present invention provides a negative electrode using lithium as an active material, and a positive electrode using manganese dioxide, vanadium pentoxide, titanium, or niobium sulfide, selenide, etc. as an active material. The present invention relates to a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte and a non-aqueous electrolyte.

The problem with this type of battery is that lithium, the negative electrode active material,
During charging, dendritic growth on the surface of the negative electrode can cause a short circuit inside the battery when it comes into contact with the positive electrode, or it can deposit in a mossy pattern and cause lithium to fall off, resulting in extremely short charge/discharge cycles. be. This is because when lithium turns into ions and elutes during discharging, the negative electrode surface becomes uneven, and during subsequent charging, lithium is deposited intensively on the convex portions.

As a countermeasure to this problem, as shown in Japanese Patent Laid-Open No. 52-5423, it has been proposed that the negative electrode be made of a lithium-aluminum alloy. Such a configuration has the advantage that lithium is restored to form an alloy with aluminum as a base during charging, and dendritic growth of lithium is suppressed. However, in this case,
Since the strength of the lithium-aluminum alloy is low, repeated charging and discharging causes cracking and micronization of the electric scraps, resulting in poor cycle characteristics.

Therefore, as shown in Japanese Patent Application Laid-open No. 63-131776, in order to improve the strength of lithium-aluminum alloy electrodes, lithium-aluminum alloy electrodes bonded with adhesive, aluminum alloys, ffJ, L. It has been proposed to create a stronger electrode by using alloys with metals such as nickel, manganese, cobalt, silicon, or zirconium as the base material and alloying these alloys with lithium. .

However, even with this configuration,
Practically satisfactory characteristics cannot be obtained. This is the β phase Li-Aj! in the aluminum alloy. When discharged, Li was released and became /l, while Li was released during charging.
is occluded and changes to β-phase-1,i-Al again. At this time, if the negative electrode has the above configuration, the initial β phase -Li-A
Since I has good crystallinity, distortion is reduced. Therefore, when the charge/discharge cycle is repeated, β phase -Li-A/ and A
This is due to the fact that the electrode becomes finer and crumbles due to crystal changes between I.

Therefore, the present invention aims to provide a non-aqueous electrolyte secondary battery with excellent cycle characteristics by suppressing the occurrence of fineness and collapse of the electrode even when charge/discharge cycles are repeated. It is something.

In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery comprising a negative electrode containing lithium as an active material, a positive electrode, and a nonaqueous electrolyte. consists of an alloy whose main components are lithium and aluminum, and the β phase in this alloy is
The X-ray diffraction peak of Li-Aj2 by copper tube method (400
) is characterized by a half width (βV2) of 0.45° or more.

As mentioned above, if the half width of the X-ray diffraction peak is 0.450 or more, β phase -Li-Aj! distortion increases. Therefore, even when charge/discharge cycles are repeated, the negative electrode is less likely to become fine or crumble due to crystal changes, so that the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

In addition, if the half-width in the (400) plane of the X-ray diffraction peak of β phase-Li-Al by the copper tube method exceeds 0.65°,
Because the electrode becomes brittle, the half width of the X-ray diffraction peak is 0.6
It is desirable that it is 5' or less.

Box 101 (Example I) A first example of the present invention will be described below with reference to FIGS. 1 to 11.

A negative electrode 2 made of a lithium alloy is pressed onto the inner surface of a negative electrode current collector 7, and this negative electrode current collector 7 is fixed to the inner bottom surface of a negative electrode can 5 made of stainless steel and having a substantially U-shaped cross section. The peripheral end of the negative electrode can 5 is fixed inside an insulating backing 8 made of polypropylene, and the outer periphery of the insulating banking 8 is a positive electrode can made of stainless steel and having a substantially U-shaped cross section in the opposite direction to the negative electrode can 5. 4 is fixed. A positive electrode current collector 6 is fixed to the inner bottom surface of the positive electrode can 4, and a positive electrode 1 is fixed to the inner surface of this positive electrode current collector 6. A separator 3 which also serves as a liquid retaining layer is provided between the positive electrode 1 and the negative electrode 2.
is interposed, and this separator 3 is impregnated with an electrolyte. The electrolyte is propylene carbonate and lithium perchlorate at 1 moj2/j! Additions are used. In addition, the battery dimensions are 25 mm in diameter and 3.0 mm in thickness.
It's a dragon.

Here, the positive electrode 1 is prepared by heat-treating a mixture of manganese dioxide and lithium hydroxide in a molar ratio of 2=1 at 375° C. for 20 hours, and uses this as an active material. Next, this active material, acetylene black W electrical material, and fluororesin binder were mixed in a weight ratio of 80:10:10 to create a mixture, and this mixture was pressure molded. Produced by drying.

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

First, aluminum and silver are mixed in a ratio of 97:23 and melted, and then cooled to create an ingot. Next, this ingot is subjected to homogenization treatment at 550° C. for 12 hours. Next, the surface layer of the ingot was cut off to remove the oxide film on the surface of the ingot, and rolling was repeated at room temperature to produce an aluminum-silver alloy plate having a thickness of 0.5 mm. After this, using the above alloy as a base,
In the non-aqueous electrolyte, preferably LiC10 or LiCF3SO
3. 1,3-dioxolane, 2-methyl-1 in which Li salt such as LiBF4, L+PF6, or LiSbF6 is dissolved
, 3-dioxolane, 4-methyl-1,3-dioxolane,
A lithium-aluminum alloy was prepared by immersing it in a cyclic ether such as tetrahydrofuran or 2-methyl-tetrahydrofuran and electrolyzing with Li as a counter electrode, and this was used as a negative electrode. The molar ratio of aluminum to lithium in this alloy was 65:35.

The battery thus produced is hereinafter referred to as (A1) battery.

(Examples ■ to ■) Batteries were produced in the same manner as in Example I above, except that aluminum and silver were mixed in the proportions shown in Table 1 below.

The batteries produced in this way are described below as (A2) batteries ~ (
A.) It is called a battery.

Table 1 (Comparative Example 1, ■) A battery was produced in the same manner as in Example ■ above, except that aluminum and silver were mixed in the proportions shown in Table 2 below.

The battery thus produced is hereinafter referred to as (Ul) battery, (
U2) It is called a battery.

[Margin below]

Table 2 Table 3 (Comparative Examples ■ to ■) Aluminum and silver are mixed and melted in the proportions shown in Tables 1 and 2 above, and then cooled to form an ingot. Next, this ingot is subjected to homogenization treatment at 550° C. for 12 hours. Next, after cutting off the surface layer of the ingot, the ingot is sliced to a thickness of 0.
A battery was produced in the same manner as in Example I above, except that a plate of aluminum-manganese alloy No. 51 was produced.

The batteries produced in this way are described below (■1) Battery ~ (
■7) It is called a battery.

In addition, (A1) battery to (A5) battery, (U,) battery, (U
2) The correspondence relationship (weight ratio of Ag to Ag) between the batteries and the above (V+) batteries to (V,) batteries is shown in Table 3 below.

(Comparative Examples X-XV) Aluminum, lithium, and aluminum were mixed and melted in the proportions shown in Table 4 below, and then cooled to form an ingot. Next, this ingot is homogenized at 550°C for 12 hours. Next, after cutting off the surface layer of the ingot, the ingot is sliced to a thickness of 0.
．． A 51-aluminum-manganese alloy plate was prepared,
This was used as a negative electrode. A battery was produced in the same manner as in Example I above, except that such a negative electrode was used.

The batteries produced in this way are described below as (WI) batteries ~ (
W5) It is called a battery.

[Margin below]

Table 4 (Experiment I) Battery (A1) of the present invention - negative electrode of (A,) battery, comparative example (U,) battery, (U2) battery and (■1) battery -
We investigated the half-value width (βlA) in the (400) plane of the X-ray diffraction peak of the β-phase LiA1 alloy using the copper tube method in the (7) battery and the negative electrode of the (W,) battery to (W5) battery. , the results are shown in FIGS. 2, 3, and 4.

As shown in FIGS. 2, 3, and 4, the negative electrodes of batteries (A1) to (A5) all have half widths of 0.45° or more, whereas (Ul) batteries, (U2) Battery, (V
,) Battery ~ (■7) Battery and (W+) Battery ~ (W5)
It is recognized that all of the negative electrodes of the batteries have half widths of 0.45' or less.

This is because Ag is not added in the (U,) battery and (U2) battery, or even if it is added, it is in a very small amount, and (■1) battery ~ (■,) battery is not cold rolled. It is difficult to increase the crystal strain of the lithium-aluminum alloy because it is not cold rolled and not alloyed in a non-aqueous electrolyte in the (Wl) battery ~ (W,) battery. For some reason.

(Experiment ■) (A1) battery to (A,) battery of the present invention and (U
, ) battery, (U2) battery, (Vl) battery to (V7) battery, and (W+) battery to (W5) battery.The results are shown in Figures 5, 6, and 7th
As shown in the figure. The experimental conditions were that the battery was discharged and charged for 10 hours each at a current of 2 mA, and when the voltage dropped to 2 V or less at the end of discharge, the cycle life of the battery was determined.

As shown in FIGS. 5, 6, and 7, (
Ul ) battery, (U2) battery, (V,) battery ~ (■,)
Batteries and (W,) batteries to (W5) batteries are all 300
In contrast to the lifespan of the present invention (A,
) Batteries to (A5) All of the batteries were found to have a lifespan of 400 cycles or more.

A battery was prepared 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 form an aluminum alloy.

The battery thus produced is hereinafter referred to as a (B,) battery.

(Examples ■ to ■) Batteries were prepared 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 form an aluminum alloy.

The batteries produced in this way are described below as (B2) batteries ~ (
B5) It is called a battery.

Table 5 (Comparative Example I, ■) A battery was produced in the same manner as in Example ■ above, except that aluminum and silver were mixed in the proportions shown in Table 6 below.

The battery thus produced is hereinafter referred to as (Xl) battery (
x2) It is called a battery.

Table 6 (Experiment I) β in the negative electrodes of the (B1) batteries to (B,) batteries of the present invention and the negative electrodes of the (X,) batteries and (X2) batteries of the comparative examples
The half width (β2) of the X-ray diffraction peak in the (400) plane of the phase-Li-Aj2 alloy using a copper tube was investigated, and the results are shown in FIG.

As shown in Figure 8, the negative electrodes of batteries (B1) to (B5) all have half widths of 0.45° or more, whereas (
The half width of the negative electrodes of X, ) battery and (×2) battery are all 0.4.
It is recognized that the angle is 5° or less.

(Experiment ■) (B1) battery to (B,) battery of the present invention and (X
, ) battery, and (X2) battery, as we investigated the cycle characteristics of the battery.
The results are shown in FIG. The experimental conditions were the same as those in Experiment (2) of the first example.

As shown in FIG. 9, the comparative example (Xl) battery, (X2)
While both batteries have a lifespan of 300 cycles or less, batteries (B1) to (B5) of the present invention all have a lifespan of 300 cycles or less.
It is recognized that the product has a lifespan of 0 cycles or more.

First Example (Example ■) A battery was prepared in the same manner as in Example 1 of the first example except that an aluminum alloy was prepared by mixing aluminum and rhenium in a ratio of 98:3.

The battery thus produced is hereinafter referred to as a (C1) battery.

(Examples ■ to ■) Batteries were produced in the same manner as in Example 1 of the first embodiment, except that aluminum and rhenium were mixed in the proportions shown in Table 7 below to produce an aluminum alloy.

The batteries produced in this way are described below as (C2) batteries ~ (
C1) It is called a battery.

[Margin below]

Table 7 (Comparative Examples ■, ■) A battery was produced in the same manner as in Example I above, except that aluminum and rhenium were mixed in the proportions shown in Table 8 below.

The batteries produced in this way are hereinafter referred to as (Y,) battery, (
Y2) It is called a battery.

Table 2 (Experiment I) β in the negative electrodes of the (C3) batteries to (C5) batteries of the present invention and the negative electrodes of the (Y,) batteries and (Y2) batteries of the comparative examples.
Phase-Li-A4 alloy X-ray diffraction peak (
The half width (β2) in the 400) plane was investigated, and the results are shown in FIG.

As shown in Fig. 10, the half width of the negative electrodes of batteries (C1) to (C3) are all 0.45° or more, whereas
The negative electrodes of the (Yl) battery and (Y2) battery all have half widths of 0.
It is recognized that the number is 456 or less.

(Experiment ■) Batteries (C1) to (C5) of the present invention and (Y
, ) battery, (Y2) battery, we investigated the cycle characteristics of the battery.
The results are shown in FIG. The experimental conditions were the same as those in Experiment (2) of the first example.

As shown in FIG. 11, the comparative example (Yl) battery, (Y2
) batteries have a service life of 300 cycles or less, whereas the (C4) to (C,) batteries of the present invention all have a lifespan of 300 cycles or less.
It is recognized that the product has a lifespan of 00 cycles or more.

As mentioned above, it is not possible to improve the cycle characteristics in a battery using Lithium-Aluminum alloy for the negative electrode, which has a half-value width of the (400) plane of β-phase-Li-A1 alloy of 0.45° or more (large strain). can.

In this way, in order to increase the strain of aluminum or aluminum alloy, a negative electrode may be manufactured as in the above embodiment. This is summarized below.

■The metal bond radius in aluminum is 1.23 Å or more1.
Add a metal of 63 Å or less to form an alloy.

When alloyed in this way, lattice defects are created during crystallization, which causes a lot of strain in the crystal, and the β phase-Li
-It becomes possible to increase the strain of the AA gold alloy. Such metals include, in addition to Ag, W, and Re shown in the first to third embodiments, Mg, Ca, Sc, Ti, V,
Cr, Mn, FeCo, Ni, Cu, Zn, Zr, Nb
, Mo, Ru, Rh, Pd, Cd, In, Ta, etc. Note that when a metal outside the above range is added to aluminum, it is difficult to increase the crystal strain of aluminum because such a metal is difficult to form a solid solution with aluminum.

■ Cold rolling aluminum. When cold rolling is performed in this way, the aluminum crystals extend in the rolling direction, but because the process is carried out at a low temperature, atoms within the metal do not diffuse sufficiently.
Many strains occur within the crystal.

Therefore, if such aluminum is alloyed with lithium, it becomes possible to increase the β-phase-Li-AA gold alloy strain. In particular, by adding a metal such as the above-mentioned Ag, it becomes possible to generate more strain within the crystal.

(2) Alloy lithium and aluminum by short-circuiting or electrolyzing in a non-aqueous electrolyte at a temperature around room temperature. this is,
When a lithium-aluminum alloy is produced by metallurgy or by electrolysis in molten salt, - Because it is produced at high temperatures of over 300°C during boat fishing, the atoms in the metal diffuse quickly and become distorted. Although it is difficult to produce a lithium-aluminum alloy, if alloying is performed by electrolysis in a non-aqueous electrolyte at a temperature around room temperature, the β phase-Li - The distortion of the A1 alloy increases.

In addition, in the aluminum alloy, the content of metals other than aluminum is preferably 0.1 weight percent or more and 5 weight percent or less. This means that if the addition effect is less than 0.1% by weight, the effect of addition will not appear much, but if the addition is less than 0.1% by weight,
This is due to the aluminum base becoming brittle and becoming finer when the weight percentage is higher than that.

As described above, according to the present invention, the distortion of the β-phase-Li-AA increases, so even when repeated charge/discharge cycles are performed, the negative electrode becomes finer and crumbles due to crystal changes. becomes less likely to occur. As a result, it is possible to dramatically improve the cycle characteristics of the non-aqueous electrolyte secondary battery.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery of the present invention, and FIG.
, ) battery and (U2) β phase -Li- of the negative electrode in the battery
A graph showing the half-value width of the (400) plane of the A2 alloy, FIG. 3, shows the β-phase -Li-Ajl! of the negative electrode in the comparative examples (■1) to (■7) batteries. A graph showing the half-width of the (400) plane of the alloy, Figure 4 shows the (400) β phase of the negative electrode in the comparative example (WI) battery to (W,) battery of the Li-A42 alloy.
A graph showing the half-width of the surface, Figure 5 is (A,) battery ~ (A
s) A graph showing the cycle characteristics of the battery, the (U,) battery, and the (U2) battery. Figure 6 is a graph showing the cycle characteristics of the (Vl) battery to (■,) battery. Figure 7 is the (Wl) battery. ~
(W5) A graph showing the cycle characteristics of the battery, Figure 8 shows the (B,) battery of the present invention ~ (B,) battery and the comparative example (Wl)
β-phase -Li-A of negative electrode in batteries and (WZ) batteries
A graph showing the half-width of the (400) plane of the 42 alloy, Fig. 9 is a graph showing the cycle characteristics of (B.) battery to (B,) battery, (WI) battery, and (W2) battery, Fig. 10 is (C) of the present invention
, ) battery ~ (C3) battery and comparative example (Yl) battery and (
Figure 11 is a graph showing the half-width of the β-phase-Li A/gold alloy surface of the negative electrode in the Y2) battery. It is a graph.■...Positive electrode, 2...Negative electrode, 3...Separator.

Claims (1)

[Claims] (1) In a non-aqueous electrolyte secondary battery comprising a negative electrode using lithium as an active material, a positive electrode, and a non-aqueous electrolyte, the negative electrode is made of an alloy mainly composed of lithium and aluminum, and the negative electrode is made of an alloy mainly composed of lithium and aluminum. Half width (β1/2) of the X-ray diffraction peak in the (400) plane of the β phase-Li-Al in the copper tube
A non-aqueous electrolyte secondary battery characterized in that the angle is 0.45° or more.