JPS6049573A - Solid thin film secondary battery and its manufacture - Google Patents

Abstract

PURPOSE:To provide a secondary battery having high energy density and good charge-discharg performance by successively stacking a positive electrode using molybdenum trisulfide as active material, an organic polymer electrolyte layer, and a negative electrode using lithium as active electrode on an electroconductive substrate. CONSTITUTION:A positive electrode 2 is formed in such a manner that ammonium thiomolybdate added with a binder is press-bonded on an electroconductive substrate 1 such as stainless steel plate and molybdenum trisulfide is formed by thermal decomposition. Solvent solution containing electrolyte and organic polymer such as polyethylene oxide is spreaded on the positive electrode 2, and solvent is removed by drying to form an orgainic polymer electrolyte layer 3. A negative electrode 4 comprising lithium or lithium alloy is formed on the electrolyte layer 3 by vapor deposition. This solid thin film secondary battery has large discharge capacity and good charge-discharge performance.

Description

[Detailed description of the invention] This invention relates to a secondary battery and its manufacturing method.

Conventionally, few battery systems using lithium or lithium alloys as negative electrodes had sufficient charge/discharge characteristics. In recent years, only lithium/titanium disulfide systems have received attention.

However, titanium disulfide (TiS2) contains only one lithium atom during discharge, and the energy density is 48Hh/k.
g, and is not suitable for battery systems that require a large energy density. Furthermore, it is preferable to form a titanium disulfide positive electrode with good characteristics by a chemical vapor deposition method, which also has the drawback of increasing manufacturing costs.

Therefore, there is a desire for a secondary battery that is easy to manufacture, has high energy density, and has excellent charging and discharging characteristics.

The present invention was made in response to such demands.
This objective was achieved by constructing a battery using molybdenum trisulfide as the positive electrode active material, an organic polymer electrolyte as the electrolyte, and lithium or a lithium alloy as the negative electrode active material.

Molybdenum trisulfide as a positive electrode active material in the present invention has a chemical formula of M o S 3, and about 4 lithium atoms can enter and exit during charge/discharge reactions, and therefore has an energy density of 717 Wh/kg, which is about It is possible to create a solid thin film secondary battery with twice the energy density and higher performance than ever before.

This molybdenum trisulfide is obtained, for example, by thermal decomposition of ammonium thiomolybdate ((NH4)2MO34). To form a battery positive electrode, ammonium thiomolybdate is mixed with a binder such as polytetrafluoroethylene in a weight ratio of 100 to prevent chipping or cracking.
About 1 to 10% of the ammonium thiomolybdate is added, and this is pressed onto a conductive substrate such as a stainless steel plate, and heat treated in a stream of an inert gas such as argon to thermally decompose the ammonium thiomolybdate and form a molybdenum trisulfide layer. Heat treatment) When heat-treated at a heating temperature of 270 to 380° C. for 1 to 10 hours, the resulting molybdenum trisulfide becomes amorphous and has good electrical properties as described below.

The organic polymer electrolyte can be prepared by mixing an organic polymer such as polyethylene oxide (hereinafter referred to as "F, PEO") or polymethyl methacrylate with an electrolyte such as LjC104 or LiBF4, or by dissolving the polymer and electrolyte in a common solvent for both. After mixing in solution state,
Those with the solvent removed are used. In addition, cyclic monomers such as ethylene oxide are used as LiBF4', Li
It is also possible to use ring-opening polymerization in the presence of an electrolyte such as C104 to support or chemically bond the electrolyte in a polymer matrix.

Lithium, lithium, and alloys are used as negative electrode active materials, and lithium alloys include alloys of lithium and aluminum, mercury, zinc, cadmium, etc., for example.

The battery is formed, for example, as shown below.

As mentioned above, ammonium thiomolybdate added with a binder is pressure-bonded onto a conductive substrate, and heat treated in an argon stream at a temperature of 270 to 380°C for 1 to 10 hours to heat ammonium thiomolybdate. Decomposition to form molybdenum trisulfide, then e.g. PEO and LiBF4
(4.5:1 in molar ratio) dissolved in acetonitrile is impregnated into the gaps in the thin layer of molybdenum trisulfide by vacuum impregnation, and the acetonitrile is removed by vacuum drying. Thereafter, the above PE0-'LiBF4 is applied and dried to form an electrolyte layer, and then a thin film of lithium or a lithium alloy is formed on the electrolyte layer by vapor deposition, or a thin film of lithium or a lithium alloy is pressed onto the electrolyte layer. to form a negative electrode.

According to the above manufacturing method, the positive electrode and the electrolyte layer can be formed without using conventional chemical paper deposition or sputtering methods, so the cost for the apparatus is low. Moreover, according to such a manufacturing method, a positive electrode,
Since both the electrolyte and the negative electrode can be formed with a thickness of about 10 μm each, a very thin battery can be obtained. Furthermore, by obtaining amorphous molybdenum trisulfide as described above and impregnating the gap with an organic polymer electrolyte, a positive electrode with a large reaction area in which the electrolyte is well dispersed can be obtained, and the current during charging and discharging can be increased. A secondary battery with lower density and better charge/discharge characteristics can be obtained.

Next, the present invention will be explained with reference to Examples.

Example A mixture of ammonium thiomolybdate and polytetrafluoroethylene powder (mixing ratio 100:4 by volume) was placed on a stainless steel plate with a thickness of 100 μm in an amount of about 10 μm.
The film was pressed to a thickness of m and heat treated at 330° C. for 6 hours in an argon gas stream to thermally decompose ammonium thiomolybdate and form an amorphous film of molybdenum trisulfide.

Next, PEO and LiBF4 (molar ratio: 4.541. Coat it to a thickness of about 10,100 m, and after coating, dry it to form an electrolyte layer.
Next, lithium was formed to a thickness of about 10 μm by vapor deposition to form a battery.

The structure of this battery is shown in FIG. In FIG. 1, ▪ is a stainless steel plate as a conductive substrate, 2 is a positive electrode made of molybdenum trisulfide, 3 is an electrolyte layer made of PE0-LiBF4, and 4 is a negative electrode made of lithium.

The charging and discharging characteristics of this battery were investigated at 20 DEG C. and at a constant current of 5 .mu.A/cTA from charging 2.degree.

Comparative Example A mixture of titanium disulfide and polytetrafluoroethylene at a volume ratio of 100:4 was crimped to a thickness of about 10 μm on a 100 μm thick stainless steel plate, and then PE0-Li
BF4 about 10. The electrolyte layer was coated to a thickness of 10 μm and dried to form an electrolyte layer, and then lithium was formed to a thickness of about 10 μm by vapor deposition to manufacture a battery. This battery was heated at 20°C in the same manner as in the previous example.
, Charge 2.5V to discharge 1. with a constant current of 5μΔ/cJ. O
Figure 2 shows the characteristics when charging and discharging to V.

As shown in FIG. 2, the battery of the example of the present invention has a larger discharge capacity and better charge/discharge characteristics than the battery of the comparative example, making it an excellent secondary battery.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the solid thin film secondary battery of the present invention, and FIG. 2 is a chart of charging and discharging characteristics of the battery of the embodiment of the present invention and a conventional battery.

Claims (1)

[Scope of Claims] fil A solid thin film secondary battery comprising a positive electrode using molybdenum trisulfide as a positive electrode active material, an organic polymer electrolyte layer, and a negative electrode using lithium or a lithium alloy as a negative electrode active material. (2) A mixture of ammonium thiomolybdate and a binder is pressure-bonded onto a conductive substrate, and ammonium thiomolybdate is thermally decomposed to generate molybdenum trisulfide to form a positive electrode. A solid thin film dielectric characterized in that a solvent solution of an organic polymer electrolyte is applied to the substrate, the solvent is removed by drying to form an organic polymer electrolyte layer, and then a negative electrode using lithium or a lithium alloy as a negative electrode active material is formed. Method of manufacturing next battery.