JPH04160768A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To restrain the lowering of discharge capacity by using a positive plate in which a positive electrode mixture; composed by mixing manganese dioxide or lithium-manganese dioxide composite oxide, a conductive assistant, and a binding agent; is wrapped with nickel-or stainless-made gauze. CONSTITUTION:A battery is closedly sealed by inwardly caulking the opening end part of a battery case 1 doubling as a positive electrode terminal, and clamping the peripheral edge of a sealing plate 2 doubling as a negative electrode terminal via a gasket 4. In this case, acetylene black (conductive assistant) and ethylene polytetrafluoride (binding agent) are added to heat-treated manganese dioxide to be well kneaded, and then are hot-air dried to prepare a positive electrode mixture 6. The positive electrode mixture 6 is measured, wrapped with a nickel gauze and pressure-formed to be made a possitive electrode. This improves a capacity retaining characteristic following the progress of a charge and discharge cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a nonaqueous electrolyte secondary battery using manganese dioxide or lithium manganese dioxide composite oxide as a positive electrode active material.

BACKGROUND OF THE INVENTION Some secondary batteries using non-aqueous electrolytes include metal lithium, lithium alloys, or phosphorescent graphite for the negative electrode and T i S2, manganese dioxide, or lithium-manganese dioxide composite oxide for the positive electrode. Among these, non-aqueous electrolyte secondary batteries using TiS2 are superior in that they have a long cycle life of over 200 cycles.

On the other hand, those using manganese dioxide and lithium manganese dioxide composite oxide are T i S2
It is superior in that it has a high voltage and is abundant in resources, so it is inexpensive.

The positive electrode plate of conventional non-aqueous electrolyte secondary batteries is made of pellets made by press-molding a positive electrode mixture made of a mixture of an active material, a conductive additive, and a binder, or a positive electrode mixture coated on a metal mesh. The following was used.

Problems to be Solved by the Invention A non-aqueous electrolyte secondary battery using a conventional positive electrode plate as described above and using manganese dioxide or lithium manganese dioxide composite oxide as a positive electrode active material discharges as the charge/discharge cycle progresses. The problem was that the capacity was significantly reduced and the cycle life was short.

Means for Solving the Problems The present invention provides a positive electrode mixture having electrical conductivity and electrolyte permeability, which is obtained by mixing manganese dioxide or lithium manganese dioxide composite oxide, a conductive additive, and a binder. The above-mentioned problem is solved by providing a non-aqueous electrolyte secondary battery characterized by having a positive electrode plate housed in a compression holding case.

The main reason that the discharge capacity of non-aqueous electrolyte secondary batteries using manganese dioxide and lithium manganese dioxide composite oxides decreases as the charge/discharge cycle progresses is due to the change in crystal structure due to doping and dedoping of lithium ions. It has been said that it is in a state of collapse.

However, as a result of a detailed study of this decrease in capacity, it was found that the reason for the large decrease in discharge capacity was that the active material was electrically insulated in the positive electrode plate as described below rather than the collapse of the crystal structure. In the dual-layer manganese and lithium manganese dioxide composite oxides, the active material expands in volume with discharge. As a result, the electrical connection between the positive electrode active material and the conductive additive is likely to be partially lost. On the other hand, lithium mankanei (LiMn02), which is a discharge product, has very low electronic conductivity, so if the electrical connection on the surface of the active material is lost, subsequent charging becomes extremely difficult. This phenomenon is due to the unique properties of manganese dioxide and lithium manganese dioxide composite oxide, which change to electrically insulating properties as the discharge reaction progresses. That is, this phenomenon is not observed in T i S2, which similarly undergoes volumetric expansion due to discharge, but exhibits good electronic conductivity even after discharge.

Therefore, we fabricated a prototype nonaqueous electrolyte battery using a positive electrode plate in which a positive electrode mixture made of manganese dioxide or lithium manganese dioxide composite oxide, a conductive agent, and a binder was wrapped in a nickel or stainless wire mesh. When a life test was conducted, it was found that the decrease in discharge capacity was significantly suppressed, as shown in the later examples. This is because compressing and holding the mixture in a mixture case with excellent electronic conductivity and an electrolyte permeation layer has the effect of suppressing loss of electrical connection on the surface of the active material as a result of expansion and contraction of the active material. This is due to having.

A positive electrode plate in which the active material is wrapped in a wire mesh has traditionally been used in nickel-cadmium batteries, but is generally not used in non-aqueous electrolyte batteries. This is because the energy density of the battery decreases when a mixture case such as a wire mesh is used.
Another reason is that conventional batteries using TiS2 exhibited sufficient cycle life performance even without using a mixture case.

Examples The present invention will be explained using preferred examples. In the following examples, a button type battery as shown in FIG. 1 will be described. In the figure, 1 is a case that doubles as a positive electrode terminal, which is made by pressing an organic electrolyte-resistant stainless steel plate, and 2 is a sealing plate that also serves as a negative electrode terminal, which is made of the same material. Alloy 3 is crimped.

5 is a separator impregnated with an organic electrolyte, and 6 is a positive electrode mixture housed in a mixture compression holding case. The battery is installed by caulking the open end of the battery case 1, which also serves as the positive terminal, inward.
Hermetically sealed sealing is achieved by tightening the periphery of a sealing plate 2, which also serves as a negative electrode terminal, via a gasket 4. The outer diameter of the battery is 20.0 mm and the height is 2.0 mgw.

[Flow-through side 1] γ-type manganese dioxide was heat-treated at 375° C. for 5 hours under reduced pressure of 50 mml (g or less), and then heat-treated at 375° C. for 5 hours in air.

To 100 parts by weight of this heat-treated manganese dioxide, 5 parts by weight of acetylene black (conductivity aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added, kneaded well, and heated to 120°C for 5 parts by weight. A positive electrode mixture was prepared by drying in hot air for a period of time. Weigh out 107 mg of this positive electrode mixture and
．． It was wrapped in a 0 mm 180 mesh nickel wire gauze and press-molded at 2 tons/cm' to form a positive electrode. The dimensions of the positive electrode are approximately 15.0 mm in diameter and 0.6 mm in thickness. Before assembling this positive electrode into the battery, heat it again at 120"C for 3 seconds.
A hot air drying process was performed for a period of time.

The negative electrode is a lithium aluminum alloy plate with a thickness of 0.4 m + n < 8
0 wt
A polypropylene microporous separator (Celguard 2) was used as the separator.
400) and a non-lined polypropylene cloth were used in layers.

This battery is referred to as battery A1 of the embodiment of the present invention.

[Example 2] A lithium manganese dioxide composite oxide obtained by mixing 100 g of γ-type manganese dioxide and 25 g of lithium hydroxide in a mortar and then heat-treating the mixture at 375° C. for 20 hours in air was used as a positive electrode active material. Except for this, a battery similar to Example AI was produced. This invention battery is designated as 81.

[Comparative Example 1] A battery similar to Example 1 was prepared except that only the positive electrode mixture was pressure-molded at 2 tons/cm 2 to form a positive electrode. This comparison battery is designated as A2.

[Comparative Example 2] A 180-mesh nickel mesh with a diameter of 15.0 mm was inserted into the positive electrode mixture so that the nickel mesh was located in the contact area between the positive electrode and the positive electrode can. Then, it was press-molded at 2 tons/cm2 to form a positive electrode. A battery similar to that of Example 1 was produced except for using this positive electrode. This comparison battery is designated as A3.

[Comparative Example 3] A battery similar to Comparative Example 1 was produced except for using lithium manganese dioxide composite oxide as the positive electrode active material. This comparison battery is designated as B2.

[Comparative Example 4] A battery similar to Example 1 was produced except for using lithium manganese dioxide composite oxide as the positive electrode active material. This comparison battery is designated as 83.

Figures 2 and 3 are capacity retention characteristics as the charge/discharge cycle progresses when these batteries are charged and discharged in a constant temperature bath at 20°C under the following conditions. Charging end voltage 3.
4V, discharge end voltage 2. Ov, and the charging/discharging current is 1.8
mA (1.0 mA/cm. In comparison, the capacity retention characteristics as the charge/discharge cycle progresses are dramatically improved.

In the above-mentioned embodiment, a nickel wire mesh is used, but if a stronger stainless steel wire mesh is used, the compression holding performance will further increase, and a more excellent cycle life will be obtained. Further, excellent effects can also be obtained when a mixture compression holding case made of a perforated plate is used.

Effects of the Invention As described above, the present invention dramatically improves the capacity retention characteristics of a nonaqueous electrolyte secondary battery that uses manganese dioxide or lithium manganese dioxide composite oxide as a positive electrode active material as the charge/discharge cycle progresses. The industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a battery in an example. FIGS. 2 and 3 are diagrams showing the relationship between charge/discharge cycles and discharge capacity. l - - Battery case 2 - Sealing plate 3 - Lithium alloy 4 - Gasket 5 - Separator 6-1 Positive electrode mixture stored in the mixture compression holding case

Claims (1)

[Claims] A positive electrode plate is made by storing a positive electrode mixture made by mixing manganese dioxide or lithium manganese dioxide composite oxide, a conductive additive, and a binder in a positive electrode mixture compression holding case that has conductivity and electrolyte permeability. A non-aqueous electrolyte secondary battery comprising: