JPH07296811A - Lithium secondary battery anode material and lithium secondary battery using same - Google Patents

Abstract

PURPOSE:To provide a lithium secondary battery anode material which provides a large charge and discharge capacity and a high energy density and which resists deterioration due to repeated charging and discharging and to provide a lithium secondary battery which has a high electromotive force, a high charge and discharge capacity, a high energy-density battery output and an excellent charge and discharge cycle life. CONSTITUTION:A lithium secondary battery, in which an Li-Ag-Te-(M1-M2) alloy composed of Li, Ag, Te, M1 and M2 in an atomic ratio of 80-150:1-20:0.001-10:1-50:1-30 (M1 is Zn and/or Si, M2 is one or two kinds or more of alloy components selected from Fe, Co, Mn, Mo, Ni and W) is used as anode material 3, is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode material having excellent charge / discharge cycle life and capable of forming a high output lithium secondary battery, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art Conventionally, as a secondary battery satisfying various characteristics such as high energy density battery output and high electromotive force, a non-aqueous electrolytic solution such as an organic solvent has been used as an electrolytic solution and a non-aqueous electrolyte using a pure lithium as a negative electrode. A water electrolyte type lithium secondary battery is known. However, according to the secondary battery, energetically active points are generated on the surface of the negative electrode during charging, and dendrite in which lithium grows in a tree shape is generated by electrodeposition from the site, and a positive-negative electrode is generated between the positive and negative electrodes. Short circuit,
There is a drawback in that the dendrites fall off from the negative electrode and become inactive, resulting in a decrease in efficiency or deterioration of the negative electrode, resulting in a shorter cycle life.

Therefore, there has been proposed a method of forming a negative electrode with a lithium alloy composed of an intermetallic compound of Al, Bi, Pb, Sn, In and the like and Li. That is, the alloying of lithium raises the electrode potential higher than that of pure lithium to lower the activity of the negative electrode, and reduces the rate of discharge reaction between lithium ions to suppress the growth of dendrite. . However, the decrease in the activity of the negative electrode due to the alloying reduces the electromotive force and the charge / discharge capacity, and the weakening due to the alloying causes the negative electrode to crack due to the expansion / contraction of the volume accompanying the absorption / release of lithium during charge / discharge. However, there is a problem in that the powder is eventually pulverized and a sufficient cycle life cannot be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention provides a negative electrode material for a lithium secondary battery, which overcomes the above-mentioned drawbacks, has a large charge / discharge capacity and a high energy density, and is less deteriorated by repeated charge / discharge. The aim is to develop and eventually obtain a lithium secondary battery with high electromotive force, high charge / discharge capacity, high energy density battery output, and excellent charge / discharge cycle life.

[0005]

Means for Solving the Problems As a result of further studies on the above-mentioned lithium alloy-based negative electrode, the present inventors have found that
It has been found that the above object can be achieved by constructing a negative electrode of a secondary battery with a lithium alloy having a specific composition range, and has completed the present invention. In the present invention, the composition based on the atomic ratio is Li: Ag: Te: M1: M2 = 80 to 150: 1.
˜20: 0.001 to 10: 1 to 50: 1 to 30 (M1 is Zn and / or Si, M2 is Fe, Co, M
A negative electrode material for a lithium-based secondary battery, comprising a Li-Ag-Te- (M1-M2) -based alloy, which is one or more alloy components selected from n, Mo, Ni, W), and such a negative electrode material The present invention provides a lithium secondary battery using the.

[0006]

In the negative electrode material of the present invention, the Li-Ag-Te based alloy component promotes the diffusion of lithium, and functions to smoothly insert and extract lithium during charge and discharge. Meanwhile (M
The 1-M2) -based alloy component is a stable intermetallic compound, and the binder effect of this intermetallic compound suppresses the deterioration of the negative electrode due to the expansion and contraction of the volume accompanying the occlusion and release of lithium, resulting in a cycle. Contributes to the prevention of life reduction.

[0007]

EXAMPLES A negative electrode material for a lithium secondary battery of the present invention has a composition based on atomic ratio of Li: Ag: Te: M1: M2 =
80-150: 1-20: 0.001-10: 1-5
0: 1 to 30 (where M1 is Zn and / or Si, M2
Is one or more alloy components selected from Fe, Co, Mn, Mo, Ni and W), Li-Ag-Te-
It is composed of a (M1-M2) type alloy.

In the composition based on the above atomic ratio, if the Li content is less than 80, a sufficient electromotive force cannot be obtained.
If it exceeds, the dendrites cannot be sufficiently suppressed, probably because the activity of the negative electrode becomes high. Moreover, when Ag and Te are less than 1 and less than 0.001, respectively, Li-Ag-Te.
If the crystal grain refinement of the system alloy component is insufficient, and if it is 20 or more and 10 or more, respectively, it is difficult to process the sheet-like material required for making into a battery, or even if sheeting is possible, subsequent processing is not possible. It is not preferable because there is a disadvantage that it becomes extremely difficult, and further, the electrode potential increases and the battery electromotive force tends to decrease.

Further, if M1 and M2 are each 1 or less, the binder effect is not sufficiently exerted, and as a result, the cycle life of the battery is shortened, which is not preferable. On the other hand, when M1 exceeds 50, the attraction force for Li becomes too large and the discharge efficiency deteriorates, and when M2 exceeds 30, the battery electromotive force significantly decreases, resulting in low energy density of the battery. There is an inconvenience.

As a method for producing the negative electrode material of the present invention,
For example, an appropriate amount of (M1-M2) -based alloy powder is previously applied to or vapor-deposited on a flat metal foil, a metal mesh, or a metal porous body made of Ni, Al, Cu, Ag, or the like serving as a current collector, and then heat treated. Examples of the method include applying and then spraying, impregnating, or dipping the Li-Ag-Te alloy. These steps are to prevent deterioration of each component,
It needs to be performed in an inert gas atmosphere.

In the above production example, the Li-Ag-Te alloy is formed by a known alloying method such as a method of melting and reacting a predetermined ratio of Li, Ag and Te or a method of reacting by a vapor deposition method. Can be done at. By the way, in the above-mentioned melting method, alloying can be performed by heating and melting the alloy components in an inert gas atmosphere, and in that case, a method of heating to a temperature not lower than the melting point of Li to melt the alloy rapidly advances the alloying reaction. It is preferable in that

Another method for producing the negative electrode material of the present invention is an alloying method by vapor deposition. This method is achieved by evaporating the alloy components and solidifying them on the surface of a conductor made of another metal. In this case, even if all the alloy components are vapor-deposited, Li-Ag-
Only the Te-based alloy may be formed by vapor deposition. As the vapor deposition method, it is possible to adopt an appropriate method such as various sputtering methods such as ion beam sputtering, electron beam evaporation method, various ion plating methods, flash plasma evaporation method, pulse plasma evaporation method, CVD method, and the like. it can.

The Li secondary battery of the present invention can be appropriately formed by a conventionally known method except that the above alloy is used as the negative electrode material. For example, FIG. 1 shows a coin-type Li secondary battery. In the figure, 1 and 7 are battery cans, and 2,
Reference numeral 6 is a Ni current collector, 3 is a negative electrode, 4 is a separator (electrolyte layer), 5 is a positive electrode, and 8 is an insulating sealant.

Example 1 (Preparation of Negative Electrode) Li: Ag: Te = 90: 1 by atomic ratio in a high-purity Ar atmosphere (dew point -60 ° C. or lower).
What was weighed so as to be 0: 0.5 was heated to 500 ° C., and this was melted and alloyed. Also, in atomic ratio S
What was weighed so as to be i: Fe = 10: 20 (ratio to Li: Ag: Te) was heated to 1400 ° C. in the same atmosphere and alloyed. Obtained Si-F
The e-based alloy was crushed to -200 mesh, and this was pressed onto a long copper current collector (width 42 mm, thickness 10 micron) with a roll, and then heated at 800 ° C. for 3 hours to obtain a negative electrode substrate. . Then, the molten metal of the Li-Ag-Te alloy obtained above is kept at 250 ° C, and the negative electrode substrate is immersed therein,
A negative electrode plate was prepared by squeezing both sides of the substrate so that the thickness of the Li-Ag-Te alloy layer was 50 to 200 microns per side and cutting the length to 330 mm.

(Preparation of positive electrode) LiC as a positive electrode active material
46 parts by weight of oO2, 4 parts by weight of acetylene black as a conductivity-imparting material, 1 part by weight of PVDF as a binder,
And 49 parts by weight of N-methylpyrrolidone were mixed sufficiently to prepare a long aluminum foil (width 42 mm, thickness 1
The thickness of one side is 10 by the doctor blade method.
Both sides are coated so that it becomes 0 micron, and temporary drying is performed at 200 ° C for 1 minute, followed by rolling. This is cut into a length of 300 mm, and main drying is performed in vacuum at 120 ° C for 3 hours.
A positive electrode plate was created.

(Preparation of Separator) Propylene carbonate having a water content of 20 ppm or less and 1,2-dimethoxyethane were mixed at a volume ratio of 1: 1 and 1 was added to the mixture.
Mol / l lithium perchlorate was dissolved to prepare an electrolyte. A polypropylene film having a porosity of 43% and a thickness of 25 μm was impregnated with this to prepare a separator. The negative electrode plate and the positive electrode plate obtained as described above were wound with the separator interposed, and the resulting product was housed in a nickel-plated iron battery can to prepare an AA-type Li secondary battery. .

Example 2 Instead of the Si—Fe alloy used in the negative electrode of Example 1, the alloy was weighed so that the atomic ratio was Zn: Ni = 10: 10 (ratio to Li: Ag: Te). A Li secondary battery was produced in the same manner as in Example 1 except that the alloyed one was heated to 1000 ° C. in the same atmosphere.

Example 3 Instead of the Si—Fe alloy used in the negative electrode of Example 1, the alloy was weighed so that the atomic ratio was Si: Ni = 20: 10 (ratio to Li: Ag: Te). A Li secondary battery was prepared in the same manner as in Example 1 except that the alloyed one was heated to 1200 ° C. in the same atmosphere.

Comparative Example 1 Li: Ag = 9 in atomic ratio in a high-purity Ar atmosphere.
Example 1 except that the alloy was weighed to 0:10, heated to 500 ° C., melted, and alloyed to be used as the negative electrode.
A Li secondary battery was prepared in the same manner as in.

Comparative Example 2 Li: Ag: Te in atomic ratio in a high-purity Ar atmosphere.
= 90: 10: 0.5, heated to 500 ° C., melted and alloyed to be used as the negative electrode,
A Li secondary battery was prepared in the same manner as in Example 1.

Evaluation Test Using the Li secondary batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2, the upper limit voltage was 4.2 V and the lower limit voltage was 2.7 V, and charging and discharging were repeated. Then, the energy density and charge / discharge efficiency at the time of 50 cycles were measured. The energy density and charge / discharge efficiency of the negative electrode of the Li secondary battery obtained as a result of these tests were as shown in Table 1.

[0022]

[Table 1]

[0023]

As described above, according to the present invention, it is possible to obtain a negative electrode in which dendrite is hard to grow, the charge / discharge capacity is large, the energy density is high, and the deterioration due to repeated charge / discharge is small. It is possible to obtain a Li secondary battery having excellent cycle life, high energy density, high electromotive force, and high discharge capacity that can be used for a long period of time.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a coin-type Li secondary battery according to the present invention.

[Explanation of symbols]

 1,7 Battery can 2,6 Ni current collector 3 Negative electrode 4 Separator 5 Positive electrode 8 Insulation sealant

Claims (2)

[Claims] 1. A composition based on atomic ratio is Li: Ag: T.
e: M1: M2 = 80 to 150: 1 to 20: 0.001
-10: 1 to 50: 1 to 30 (where M1 is Zn and /
Alternatively, Si and M2 are one or more alloy components selected from Fe, Co, Mn, Mo, Ni, W) Li-
A negative electrode material for a lithium-based secondary battery, comprising an Ag-Te- (M1-M2) -based alloy. 2. A lithium secondary battery comprising the negative electrode material according to claim 1.