JPH0665030B2 - L-i alloy electrode for secondary battery and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a Li—Ai alloy electrode for a secondary battery and a method for producing the same.

[Prior Art] A conventional Li-Al alloy electrode for a secondary battery contains about 50% by weight of Li and has a thickness of millimeter unit. This Li-Al alloy is used as a negative electrode. In such a conventional Li-Al alloy electrode of a secondary battery, Li deposits on the surface of the electrode in a dendritic form during charging, which lowers the Coulomb efficiency of the battery and, at the same time, causes self-discharge, resulting in poor battery performance. Was there.

Therefore, it is necessary to use a Li-Al alloy having a Li content of 50% by weight or less as an electrode for a secondary battery.

However, when the amount of Li becomes small, the alloy becomes hard and brittle. This is due to the formation of the β layer shown in the Li-Al phase diagram. In Figure 2, Li
-A level diagram of an Al2 element alloy is shown. According to the figure, L
It can be seen that the β layer is formed when i is around 20% by weight. This β layer is a very hard and brittle layer, and cannot be assembled by a single layer. In a Li-Al alloy, Li
If the amount is decreased, the proportion of the β layer increases, and as a result, the Li-Al alloy becomes hard and brittle.

When the amount of Li decreases in this way, a thin electrode cannot be formed. As a result, the amount of Li could not be reduced, the weight of the secondary battery was increased, and the energy density could not be improved.

As an example of an electrode made of Li and Al, Japanese Patent Laid-Open No. 56-8646
No. 3, gazette discloses that Li is pressure-bonded on an Al thin film and the Li
An invention is described in which a thin film is electrodeposited and alloyed.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional example, since Li and Al are not alloyed at the atomic size, LA has a problem that the battery performance is insufficient because the LA first elutes and the Li precipitates. As a result, the battery life is also adversely affected.

In order to solve such a problem, the present invention aims to provide a Li alloy electrode having a low Li content, a high toughness, a thin film or a thin plate shape, and excellent battery performance, and a method for producing the same. And

[Means for Solving the Problems]

In order to achieve the above object, the first invention of the present application is Li1
A melt rapid solidification alloy consisting of 0 to 50% by weight, B0.0001 to 1.0% by weight, and the balance Al, with a plate thickness of 10 to 500 μm.
The lithium alloy electrode for a secondary battery, which is a thin plate.

The second invention of the present application is that Li of 10 to 50% by weight and B0.
A molten metal composed of 0001 to 1.0% by weight and the balance Al is jetted between a pair of high-speed rotating metal rolls to be rapidly cooled and solidified to have a plate thickness of 1
A method for producing a Li alloy electrode for a secondary battery, which comprises producing a thin plate of 0 to 500 μm.

[Action]

In the Li-Al alloy to which B is added, B enters the β layer and weakens the bonding force between crystal grains to cause grain boundary sliding.
As a result, the brittleness of the alloy is improved, and it is possible to manufacture a Li alloy electrode for a secondary battery having a toughness and a thin film or a thin film plate.

As shown in FIG. 1, if the B content is less than 0.0001% by weight, improvement in brittleness cannot be expected. On the other hand, even if the B content is increased, improvement in brittleness cannot be expected, so 1.0% by weight or less is desirable. On the other hand, if it exceeds 10% by weight, B precipitates between the crystal grains and forms a compound of B, resulting in deterioration of battery characteristics. That is, the reaction of Li ⁺ + E ⁻ → Li ... (1) is suppressed.

If the Li content is less than 10% by weight, the battery performance cannot be sufficiently exhibited. This is because if it exceeds 50% by weight, dendritic Li is generated on the electrode surface during battery charging, and the number of charge / discharge cycles of the battery is reduced. By adding B, L
Even if the i content is between 10 and 50% by weight, the toughness of the gold-containing material is maintained well.

Electrodes with a thickness of less than 10 μm have poor impact resistance,
If it exceeds 500 μm, a sufficient surface area cannot be secured, and high energy density cannot be achieved. The thinner the thickness, the better in order to reduce the size of the battery.

The Li alloy electrode is manufactured by a rapid solidification method in which a molten metal is jetted onto a rotating body that rotates at high speed to rapidly solidify it. The rapid solidification can reduce the crystal grain size and increase the amount of crystal grain boundaries, and in such a state, B can be present in the grain boundaries. As a result, the toughness of the Li alloy electrode can be significantly improved. Rapid solidification is generally performed by solidifying a molten metal at a cooling rate of 10 ² K / sec or more. As an example of this rapid solidification method, a liquid rapid solidification method such as a twin roll method or a single roll method can be used.

It should be noted that another rapid solidification method such as a thermal spraying method may be used.

In manufacturing the above Li alloy electrode, the cooling rate was 10 ²
It is desirable to set it to K / sec or more. Cooling rate is 10 ² K /
If it is less than sec, the degree of refinement of crystal grains of the Li alloy will be low, and as a result, the effect of B for improving brittleness may not be sufficiently obtained.

〔Example〕

 Next, examples of the present invention will be described.

A ductility test was carried out on an alloy electrode having a thickness of 100 μm, a parallel portion length of 5 mm, and a width of 2 mm, in which the amount of Li was kept constant at 10 wt% and 20 wt%.

The alloy electrode was manufactured by the twin roll method with a cooling rate of 10 ² K / sec.

The ductility test was a room temperature tensile test at a strain rate of 0.001 / s.

The results of the above tests are shown in FIG. As is clear from FIG. 1, an alloy electrode containing 0.0005% by weight of B (Li1
It can be seen that 0 wt%) shows elongation of 10% or more. After that, the ductility gradually decreases, and if the B content exceeds 10% by weight, the ductility cannot be improved so much. If the amount of B exceeds 10% by weight, the B compound is generated in the crystal grain boundaries, which adversely affects the battery characteristics. Thickness 1
In order to obtain a Li alloy electrode for a secondary battery having a thickness of 0 to 500 μm, it is necessary that the B content be at least 0.0001% or more.

Next, Li-Al containing 1% by weight of B and 20% by weight of Li
A charge / discharge cycle test was performed on the alloy electrode. In this test, for comparison, Li100% by weight, Al-6
A charge / discharge cycle test was similarly performed for each electrode of 0 wt% Li and Al-50 wt% Li.

The thickness of the electrode is 100 μm, and Li, LiAl, LiA
The 1B metal was held on the Ni substrate. Electrode size is 1
It was set to cm ² or more.

The electrolyte used was a 1 mol LiBF ₄ propylene carbonate solution. The counter electrode was Li and the reference electrode was Li. The test method uses a test electrode as a cathode and a current density of ² mA / cm ²
It was energized for 1 hour.

On the other hand, the test electrode was used as the anode, and the current density was 2 mA / cm.
^{At 2} , the electrodes were energized until the electrode potential became 1 V (vs Li / Li ⁺ ). The cycle of (1) and (2) above was repeated, and the Coulombic efficiency at that time was obtained. The results are shown in FIG. As can be seen from FIG. 3, Al-20 wt% L
The electrode of i-1 wt% B can be charged and discharged without depositing Li on the electrode. It is also found that the addition of B does not have a great influence on the battery performance.

On the other hand, 50% by weight or more of Li containing no B
It can be seen that in the electrode including, the efficiency decreases at a low cycle number. In addition, when the amount of Li is 5% by weight or less, the energy density of the battery is lowered and it is not suitable as a secondary battery.

Next, one embodiment of the secondary battery according to the present invention will be described with reference to the accompanying drawings. FIG. 4 is a perspective view of the electrode portion. FIG. 5 is a plan view of FIG. FIG. 6 shows a cross-sectional view of one embodiment of the secondary battery. In FIGS. 4 to 6, an alloy electrode 1 composed of 15 wt% Li, 84 wt% Al, and 1 wt% B is used.
Is used as the negative electrode, and the positive electrode 3 via the separator 5.
And these are formed into a roll shape. A positive electrode terminal 4 and a negative electrode terminal 2 are provided at the ends of the roll-shaped electrode portion. The negative electrode terminal 2 is connected to the alloy electrode 1, and the positive electrode terminal 4 is connected to the positive electrode 3.

These electrodes are made of SUS case 6 as shown in FIG.
Held in.

The alloy electrode is prepared by the twin roll method as described above. A thickness of about 200 μm was cut out into a size of width 20 mm and length 200 mm, and the negative electrode terminal 2 was attached. Negative electrode 1 was obtained by stacking these on a SUS wire mesh.

As the positive electrode 3, 4 g of titanium disulfide powder and 0.4 g
The acetylene black powder (1) was mixed and applied onto a SUS wire net having a width of 20 mm and a length of 180 mm using polytetrafluoroethylene as a binder. A positive electrode terminal 4 was attached to the positive electrode 3. The positive electrode material is V
It is also possible to use ₂ O ₅ , CoO _2, or the like.

The positive electrode 3 and the negative electrode 1 were wound with a polypropylene nonwoven fabric separator having a thickness of about 100 μm interposed therebetween. The electrode after winding was put in an SUS case 6 having an inner diameter of 20 mm and a height of 30 mm, and the negative electrode terminal 2 and the SUS case 6 were spot-welded.

About 4 ml of a propylene carbonate solution of LiBF _{4 having} a concentration of 1 mol was injected as an electrolytic solution, a battery lid connected to the positive electrode terminal 4 was covered, and the battery was sealed by caulking.

In this embodiment, since the alloy electrode can be about 200 μm, the battery can be downsized and at the same time,
The energy density of the battery can be increased.

When the charge / discharge test of the secondary battery as described above was performed, the battery voltage was 2.0 V and the battery capacity was 1000 mA.
indicated h. Furthermore, charging / discharging with an electric quantity of 50% of the maximum capacity could be repeated 50 times or more.

〔The invention's effect〕

As described above, according to the Li alloy electrode for a secondary battery according to the present invention, the toughness is improved by adding B, and the electrode thickness becomes thin even when the amount of Li is small. Therefore, in a secondary battery using such an alloy electrode, it is possible to make the battery compact and achieve high energy density.

Further, according to the method for producing a Li alloy electrode for a secondary battery according to the present invention, the crystal grain size can be reduced by the molten metal rapid solidification method, and as a result, the toughness of the alloy can be improved.
Li alloy electrodes for secondary batteries can also be manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing the results of a ductility test based on changes in the amount of B in the Al-Li alloy, FIG. 2 is a state diagram of the Li-Al alloy, and FIG. 3 is a graph showing the relationship between the cycle number and the battery efficiency. FIG. 4 is a perspective view of a Li—Al alloy electrode according to the present invention, FIG. 5 is a plan view thereof, and FIG. 6 is a Li—Al alloy of FIG.
It is a cross-sectional block diagram of the secondary battery in which the alloy electrode was accommodated in the case. 1 ... Negative electrode, 2 ... Negative electrode terminal, 3 ... Positive electrode, 4 ... Positive electrode terminal, 5 ... Separator, 6 ... SUS case.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuki Fujita 4026 Kujimachi, Hitachi City, Hitachi, Ibaraki Prefecture, Hitachi Research Institute, Ltd. (72) Tetsuro Kuroda 4026 Kujicho, Hitachi City, Ibaraki, Hitachi Corporation Hitachi Research Laboratory (72) Inventor Hiroshi Fukui 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP 61-66369 (JP, A) JP 61-23751 (JP) , A) JP-A-61-32953 (JP, A)

Claims (2)

[Claims] 1. A Lithium alloy for a secondary battery, which is a melt-quenched and solidified alloy comprising 10 to 50% by weight of Li, 0.0001 to 1.0% by weight of B, and the balance of Al, and having a plate thickness of 10 to 500 μm. Alloy electrode. 2. A molten metal composed of 10 to 50% by weight of Li, 0.0001 to 1.0% by weight of B, and the balance of Al is ejected between a pair of metal rolls rotating at a high speed and rapidly solidified to obtain a plate thickness of 10 to 500 μm.
A method for producing a Li alloy electrode for a secondary battery, which comprises producing a thin plate of m.