JPS63318070A - Lithium secondary cell - Google Patents

Abstract

PURPOSE:To improve the charging and discharging efficiency and the cyclic lifetime of a cell by constructing the aluminum alloy for the electrode with an alloying metal having a specified bond length between atoms of the same element and metallic aluminum. CONSTITUTION:A cell is constructed with the positive electrode 2 and the electrolytic solution 3 containing at least lithium ions and the negative electrode 1 made of an aluminum alloy, and the said aluminum alloy consists of an alloying metal having a bond length between atoms of the same element different from that of aluminum more than 0.3Angstrom (Angstron) and metalic aluminum. Desirable examples of such a metal having difference of the bond length more than 0.3Angstrom are silicon, copper and magnesium, and desirable fractional amount to be added is 5-15% and more preferably 5-10%. And any electrolytic solution containing dissolved lithium ions can be used. Thereby the charging and the discharging efficiency and the cyclic lifetime can be improved and the precipitation of dendrite and the micro-powdering of the electrode can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a lithium battery of a non-aqueous electrolyte secondary battery, and particularly relates to an improvement of a negative electrode.

[Prior Art] Conventional lithium secondary batteries have a negative electrode that uses lithium metal (Japanese Patent Application Laid-Open No. 61-4164), or uses aluminum metal or an aluminum-lithium alloy (Japanese Patent Application Laid-Open No. 61-203562). ), lithium alloy containing cadmium (JP-A-60-170172)
, and lithium and aluminum as well as magnesium, calcium, potassium, indium, silicon, germanium,
A method using an alloy with at least one metal selected from tin (Japanese Unexamined Patent Publication No. 61-66369) is known.

[Problems to be Solved by the Invention] When the above-mentioned negative electrode active material is lithium metal, a short circuit between the positive and negative electrodes occurs due to precipitation of lithium during charging. In the case of aluminum or an aluminum-lithium alloy, dendrite precipitation can be suppressed, but the alloy becomes finely pulverized as lithium is inserted and released, resulting in a decrease in discharge capacity and a decrease in cycle life. In addition, in the case of lithium alloys containing cadmium, puntolite precipitation and fine powdering of the electrode hardly occur, but
There are problems in that the electromotive force is lower than that of lithium metal, that the discharge voltage decreases linearly with time, resulting in a capacitor-like discharge, and that it contains cadmium, which is harmful to the human body.

Therefore, the present invention provides a lithium secondary battery that improves the efficiency of occlusion and desorption and the cycle life of the battery by preventing lithium dendrite precipitation and fine powder formation of the electrode. be.

[Means for Solving the Problems] The lithium secondary battery of the present invention is a lithium secondary battery comprising a positive electrode, an electrolytic solution containing at least lithium ions, and a negative electrode formed of an aluminum alloy, In this aluminum alloy, the bond length between the same elements is 0.3 angstroms (angstroms) longer than the bond length between aluminum elements.
It is characterized by being composed of alloy constituent metals and aluminum metal having the above-mentioned differences.

The lithium secondary battery of the present invention is the same as a normal battery 3
It is uniformly composed of a positive electrode, a negative electrode, an electrolyte, and a separator.

The positive electrode active material is not particularly limited as long as it can be used as a positive electrode active material of a secondary battery.

Activated carbon is preferably used, and fibers are preferable in the form. Others include polyacetylene, polypyrrole, polythiophene, polyaniline, -dimensional graphite, titane disulfide, vanadium pentoxide, manganese dioxide, molybdenum disulfide, molybdenum trisulfide, iron disulfide, and zirconium sulfide. , zirconium disulfide, niobium disulfide, nickel phosphorous trisulfide, vanadium selenide, etc.

Any electrolytic solution that dissolves and retains lithium ions can be used. For example, as an organic electrolyte, 1.2-
1-Hexyethane, 1,2-di-oxyethane, propylene carbonate, γ-butyrolactone, dimethyl sulfoxide (DMSO), dimethylborumamide (DMF), acetonitrile, tetrahydrofuran, 2
-Methyltetrahydrofuran, 1,3-dioxolane,
Single or double 4-methyl-1,3-dioxolane etc.
A solution obtained by dissolving a salt compound that forms lithium ions in a mixed solution of more than one species is used. Lithium ion forming compounds include LiCIO4, l1PFe, LiBF4
, L+ASF6. I tB (Cel15)4 or the like is used.

The negative electrode active material used in the negative electrode of the present invention is an aluminum alloy. The metals constituting the alloy are selected from metals in which the bond length between the same elements is different from the bond length between aluminum elements by 0°3 Å or more. Examples of metal elements having a bond length difference of 0.3 or more are shown in Table 1. In Table 1, manganese, zinc, and lithium are elements outside the range. Particularly preferable examples of the alloy constituent metals shown in Table 1 include silicon, copper, and magnesium. The amount of this alloy constituent metal added can be up to 20% by weight.

For example, when the alloy constituent metal is silicon, an increase in the amount of silicon added increases the electrical resistance of the silicon, increases the voltage during charging, and deteriorates the performance of the battery, which is not preferable. ;1 On the contrary, as shown in Table 1, if the amount of silicon added is reduced, the effect of the addition will not be realized, which is not preferable for improving battery performance. Therefore, the amount of alloy constituent metal added is 5 to 15%, more preferably 5%.
~10%.

The separator has the role of separating the positive electrode and the negative electrode and allowing ions to pass therethrough, and may be made of polypropylene nonwoven fabric, glass fiber cloth, ceramic cloth, nylon cloth, or the like.

[Operations and Effects of the Invention] The lithium secondary battery of the present invention uses an electrolyte containing lithium ions and uses a specific alloy constituent metal and an aluminum alloy for the negative electrode active material, thereby achieving excellent charge/discharge efficiency and cycle cycle performance. Not only does the lifespan become longer, but there is no dendrite precipitation, and pulverization of the electrode can be suppressed. Furthermore, since the voltage during charging can be kept low, decomposition of the electrolyte can be suppressed. It is also an excellent secondary battery that does not contain substances harmful to the human body.

The battery of the present invention can be used as a memory backup power source for various paper-type devices including those for cars, and can also be used for small radios,
It can be used as a power source for televisions, communication devices, headphone stereos, etc. in place of Nil-Cd (N1-Cd) batteries or lead-acid batteries.

[Example] The present invention will be explained below with reference to Examples.

FIG. 1 shows the basic configuration of the battery of the present invention. This battery is
The positive electrode 2 and the negative electrode 1 are immersed in an electrolytic solution 3 with a separator 4 sandwiched therebetween so as not to short-circuit the positive electrode 2 and the negative electrode 1.

The negative electrode active material is an aluminum alloy containing 7.5% by weight of silicon. This aluminum alloy is formed by adding silicon as it is to molten aluminum and alloying it. The shape is a sheet of 40 x 35 x 0.1 mm.

The positive electrode active material 2 is an activated carbon fiber (ACC507-20 manufactured by Nippon Kynol Co., Ltd.) obtained by heat treatment and activation of a cloth-like weave of novolak resin fibers obtained by reacting phenol and formaldehyde with an acid catalyst. . The specific surface area of this activated carbon fiber is 2000 m2/Q and the dimensions are 4
It is 0x35x0°4mm.

Electrolyte 3 is a solution of lithium perchlorate dissolved in propylene carbonate at a concentration of 1 mol/dm3.

The separator 4 used was a polypropylene nonwoven fabric with dimensions of 50 x 50 x 0 and 2 mm, which were larger than the electrodes.

(Example 1) A charge/discharge test was conducted using the above battery.

Charging was performed for 40 minutes at a constant current of 4.2 mA.

Discharge was carried out at a constant current of 4.2 mA, and the final voltage was set to 2. A charging/discharging test was conducted with this charging/discharging as one cycle.

Figure 2 shows the charge/discharge efficiency, and Figure 3 shows the test results for the maximum charging N voltage.

Charging and discharging efficiency - 100X shows cycle change in discharge capacity/charging capacity. In this case, the charging capacity is 2.8mAh (4,2
mAX 40 minutes/60 minutes).

In FIG. 2, the horizontal axis shows the number of charge/discharge cycles, and the vertical axis shows the percentage of charge/discharge efficiency calculated by the formula shown above. The charge/discharge efficiency of Example 1, in which the negative electrode active material was an aluminum-silicon alloy, was 9 even after 400 cycles.
More than 0%. As a comparative example, when pure aluminum was used as the negative electrode active material, the charge/discharge efficiency was 70 to 60%, and the charge/discharge cycle also rapidly decreased after 350 times. Therefore, the aluminum-silicon alloy of the example is more than 30% more efficient than pure aluminum, and the cycle life is also improved by about 20%.

As a reference example, the charge/discharge efficiency and maximum charging pressure of a battery using titanium and cadmium alloy as negative electrode active materials are
It is shown in conjunction with FIG. The cadmium alloy contains bismuth, lead, and cadmium in a ratio of 52:/1. An alloy containing O: at a ratio of 8 was used. In both cases, the charge/discharge efficiency was low, lower than that of pure aluminum, and the charge/discharge cycle was 40 times or less, which was less than 10% of that in this example. In the aluminum-silicon of this example, dendrite growth of lithium, which is observed in the case of titanium, was not observed, and the phenomenon of the electrode becoming fine and spilling into the electrolyte was also less pronounced than in the case of pure aluminum. I was able to keep it low.

Furthermore, performance was improved without using substances that are harmful to the human body, such as cadmium.

In FIG. 3, the horizontal axis shows the number of charge/discharge cycles, and the vertical axis shows the maximum charging voltage in V. In Fig. 3, the voltage during charging in Example 1 can be kept lower than that in the case of pure aluminum after the 150th cycle, which prevents the generation of gas due to decomposition of the electrolytic solution and the reduction in charging and discharging efficiency. Can be done. In the case of the titanium and cadmium alloy of the reference example, an abnormality occurs after 50 charge/discharge cycles, and the performance is inferior to that of the present invention.

(Example 2) A battery having the same configuration as in Example 1 was prepared using an alloy of copper (4·Qwt%) and aluminum as the negative electrode active material, and the same cycle characteristic test as in the example was conducted. The results are shown in Figure 4.
It is shown in FIG.

The charge/discharge efficiency shown in FIG. 4 was higher than that of the silicon-aluminum alloy of Example 1, and the cycle life was improved by more than 40%. In other words, the charging/discharging efficiency is 90% or more and 600 times →
He had a J-Ikuru blue life.

Also, the cycle life is 70% longer than that of pure aluminum.
This has improved. The maximum charging voltage in Fig. 5 is 4V up to 6001 Nokle for the aluminum-copper alloy of this example.
It is an excellent battery that does not rise like pure aluminum.

(Example 3) A battery having the same configuration as in Example 1 was created using an alloy of magnesium (2.5 wt%) and aluminum as the negative electrode active material. A Nigel characteristic test was conducted in the same manner as in Example 1. The results are shown in FIGS. 6 and 7. Both the charge/discharge efficiency and cycle life shown in FIG. 6 were comparable to those of Example 1, and were maintained at 90% for 500 cycles. The maximum charging voltage in Figure 7 is approximately 0.2V higher overall than in Example 1, but the maximum voltage of 4cm is about the same as in the case of pure aluminum.
The cycle was maintained.

(Comparative Example 1) A battery having the same configuration as in Example 1 was created except that an alloy of manganese (0.2 wt%) and aluminum was used as the negative electrode active material.

Compared to silicon, copper, and magnesium, manganese is an element that does not cause much strain on the crystal structure in alloys because the bond length between elements is closer to that of aluminum. That is, the difference in bond length is -0,132, which is smaller than 0.3 people.

As shown in Figure 8, the charge/discharge efficiency is higher than that of pure aluminum, but the cycle or life is 40% lower than that of pure aluminum.
It is short, less than 150 cycles at 0%.

Further, the maximum charging voltage shown in FIG. 9 is also higher overall by 0.5 to 0.7 V than that of pure aluminum, and the life span is only 150 cycles or less, which is not preferable.

(Comparative Example 2) A battery having the same configuration as Example 1 was created except that an alloy of zinc (4.0 wt%) and aluminum was used as the negative electrode active material. The test conditions were also the same as in Example 1.

Similar to manganese, zinc also does not cause much strain on the crystal structure when the alloy is made with a difference between the bond length of the aluminum element and the bond length of -0,194 and less than 0.3. Efficiency as a negative electrode active material cannot be expected.

As shown in Figure 10, the charging and discharging efficiency is higher than that of pure aluminum, but it does not show stable charging and discharging efficiency and the cycle life is 32.
It was short, 0 times. Moreover, as shown in FIG. 11, the maximum charging voltage is generally 0.2 to 0.3 V higher than that of pure aluminum, and the cycle life is short at 320 times. Further, the charge/discharge cycle was only 90% that of pure aluminum. Therefore, zinc is not preferred.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing the structure of the battery of the present invention.
Fig. 11 is a graph showing the charge/discharge test results, Fig. 2 is the charge/discharge efficiency of Example 1, Fig. 3 is the maximum charging voltage of Example 1, Fig. 4 is the charge/discharge efficiency of Example 2, Fig. 5 shows the maximum charging voltage of Example 2, Fig. 6 shows the charging/discharging efficiency of Example 3, Fig. 7 shows the maximum charging voltage of Example 3, Fig. 8 shows the charging/discharging efficiency of Comparative Example 1, and Fig. 9 shows the charging/discharging efficiency of Example 3. 10 is a graph showing the maximum charging voltage of Comparative Example 1, FIG. 10 is a graph showing the charging/discharging efficiency of Comparative Example 2, and FIG. 11 is a graph showing the maximum charging voltage of Comparative Example 2. 1... Negative electrode 2... Positive electrode 3... Electrolyte 4... Separator patent applicant
Nippondenso Co., Ltd. Agent Patent Attorney Hiroshi Okawa = 15 - Figure 1

Claims (2)

[Claims] (1) A lithium secondary battery consisting of a positive electrode, an electrolyte containing at least lithium ions, and a negative electrode formed of an aluminum alloy, in which the bond length between the same elements is 1. A lithium secondary battery comprising an alloy constituent metal having a bond length difference of 0.3 Å (angstrom) or more from that of an aluminum metal and an aluminum metal. (2) The lithium secondary battery according to claim 1, wherein the alloy constituent metal is at least one of silicon, copper, and magnesium.