JP3237071B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery using manganese dioxide or lithium manganese dioxide composite oxide as a positive electrode active material.

2. Description of the Related Art Some secondary batteries using a non-aqueous electrolyte use lithium metal, a lithium alloy or linear graphite for a negative electrode and use TiS ₂ , manganese dioxide, or a lithium manganese dioxide composite oxide for a positive electrode. Among these, the non-aqueous electrolyte secondary battery using TiS ₂ is excellent in having a long cycle life exceeding 200 cycles. On the other hand, the one using manganese dioxide and lithium manganese dioxide composite oxide is superior in that it has a higher voltage than TiS ₂ , is abundant in resources, and is inexpensive.

The positive electrode plate of a conventional nonaqueous electrolyte secondary battery is formed by pressing a positive electrode mixture obtained by mixing an active material, a conductive auxiliary agent, and a binder, or a positive electrode mixture is applied to a metal net. What was used was used.

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

Means for Solving the Problems The present invention comprises a positive electrode plate formed by wrapping a positive electrode mixture obtained by mixing manganese dioxide or lithium manganese dioxide composite oxide, a conductive auxiliary agent and a binder with a metal net, and press-molding. The above problem is solved by providing a non-aqueous electrolyte secondary battery characterized by the following.

The cause of the decrease in the discharge capacity of a nonaqueous electrolyte secondary battery using manganese dioxide and lithium manganese dioxide composite oxide with the progress of the charge / discharge cycle is mainly due to the crystal structure associated with doping and undoping of lithium ions. It has been said to be in collapse.

However, as a result of detailed examination of this capacity decrease,
It has been found that the fact that the active material is electrically insulated in the positive electrode plate rather than the collapse of the crystal structure causes a large decrease in the discharge capacity as described below. In the manganese dioxide and lithium manganese dioxide composite oxide, the active material expands in volume with discharge. As a result, the electrical connection between the positive electrode active material and the conductive additive tends to be partially lost. On the other hand, lithium manganate (LiMnO ₂ ), which is a discharge product, has extremely low electron conductivity, so that if the electrical connection on the surface of the active material is lost, the next charge becomes extremely difficult. Such a phenomenon is due to the unique properties of manganese dioxide and lithium manganese dioxide composite oxide, which change into electrical insulation as the discharge reaction proceeds. That is, the volume expansion accompanying the discharge occurs similarly, but is a phenomenon that is not observed in TiS ₂ which shows good electron conductivity even after the discharge.

Therefore, a non-aqueous electrolyte battery was prototyped by using a positive electrode plate in which a positive electrode mixture obtained by mixing manganese dioxide or lithium manganese dioxide composite oxide, a conductive additive and a binder was wrapped with a nickel or stainless steel wire mesh. When a life test was performed, it was found that a decrease in the discharge capacity was significantly suppressed as shown in Examples below. This is because holding the mixture in a mixture case excellent in electron conductivity and electrolyte penetration suppresses the loss of electrical connection on the active material surface as a result of expansion and contraction of the active material. It is due to having.

A positive electrode plate in which an active material is wrapped by a wire mesh has been used in a nickel cadmium battery, but is not generally used in a nonaqueous electrolyte battery. This is because the use of a mixture case such as a wire mesh lowers the energy density of the battery, and the conventional battery using TiS ₂ exhibited sufficient cycle life performance without using the mixture case.

Examples The present invention will be described using preferred examples. In the following examples, a button type battery as shown in FIG. 1 will be described. In the figure, reference numeral 1 denotes a case which also serves as a positive electrode terminal formed by pressing an organic electrolyte-resistant stainless steel sheet, and 2 denotes a sealing plate which also serves as a negative electrode terminal formed by processing the same kind of material. Alloy 3 is crimped. Reference numeral 5 denotes a separator impregnated with an organic electrolyte, and reference numeral 6 denotes a positive electrode mixture wrapped in a metal net and pressure-formed. The battery is hermetically sealed by caulking an opening end of the battery case 1 also serving as a positive electrode terminal inward and tightening a peripheral edge of a sealing plate 2 also serving 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 mm.

Example 1 γ-type manganese dioxide was reduced under reduced pressure of 50 mmHg or less.
After heat treatment at 375 ° C for 5 hours, 5 hours at 375 ° C in air.
Heat treated for hours.

After adding 5 parts by weight of acetylene black (conduction aid) and 2 parts by weight of polytetrafluoroethylene (binder) to 100 parts by weight of the heat-treated manganese dioxide, kneading the mixture at 120 ° C. The mixture was dried with warm air for an hour to prepare a positive electrode mixture. This positive electrode mixture was weighed 107 mg at a time and 180
The positive electrode was wrapped in a mesh nickel wire net and pressure-molded at 2 ton / cm ² to form a positive electrode. The dimensions of the positive electrode are 15.0 mm in diameter and thickness
It is about 0.6mm. Before incorporating this positive electrode into a battery, hot air drying treatment was performed again at 120 ° C. for 3 hours.

A 0.4mm thick lithium aluminum alloy plate (80wt% L
i) In a dry box in which argon has been replaced, the diameter is 16 mm.
Was used. The electrolytic solution used hexafluoride Kahisan lithium 2-methyltetrahydrofuran (2Me-THF) to (LiAsF ₆₎ obtained by dissolving 1.5 mol / l,
A microporous separator made of polypropylene (Celgard 2400) and a nonwoven fabric made of polypropylene were used as the separator. This battery is referred to as battery A1 of the example of the present invention.

Example 2 100 g of γ-type manganese dioxide and 25 g of lithium hydroxide were mixed in a mortar, and then heat-treated at 375 ° C. for 20 hours in air to obtain a lithium manganese dioxide composite oxide as a positive electrode active material. Except for the above, a battery similar to that in Example A1 was produced. This battery of the present invention is referred to as B1.

Comparative Example 1 A battery similar to that of Example 1 was made except that only the positive electrode mixture was pressure-molded at 2 ton / cm ² to form a positive electrode.
This comparative battery is designated as A2.

[Comparative Example 2] In such a manner that a nickel mesh comes at the contact portion between the positive electrode and the positive electrode
A 180 mesh nickel mesh having a diameter of 15.0 mm was inserted into the positive electrode mixture. Then, pressure molding was performed at 2 ton / cm ² to obtain a positive electrode. A battery similar to that of Example 1 was made except that this positive electrode was used. This comparative battery is designated as A3.

Comparative Example 3 A battery similar to Comparative Example 1 was made except that a lithium manganese dioxide composite oxide was used as the positive electrode active material. This comparative battery is designated as B2.

Comparative Example 4 A battery similar to that of Example 1 was made except that a lithium manganese dioxide composite oxide was used as a positive electrode active material. This comparative battery is designated as B3.

FIG. 2 and FIG. 3 are capacity retention characteristics diagrams as the charge / discharge cycle progresses when these batteries are charged / discharged in a thermostat at 20 ° C. under the following conditions. Charge end voltage 3.4
V, discharge end voltage 2.0V, charge / discharge current is 1.8mA (1.0mA / c
m ² ). As is clear from FIGS. 1 and 2, the batteries (A1) and (B1) of the present invention were compared with the comparative batteries (A2) (A3) (B2).
Compared with (B3), the capacity retention characteristics with the progress of the charge / discharge cycle are dramatically improved.

In the above embodiment, a nickel wire mesh is used. However, when a stainless steel wire mesh having higher strength is used, the compression holding performance is further increased, so that a better cycle life can be obtained. Also, excellent effects can be obtained when a mixture pressurization holding case made of a perforated plate is used.

Effect of the Invention As described above, the present invention can dramatically improve the capacity retention characteristics of a nonaqueous electrolyte secondary battery using manganese dioxide or lithium manganese dioxide composite oxide as a positive electrode active material as the charge / discharge cycle progresses. It is possible and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a battery in an example. FIGS. 2 and 3 are diagrams showing the relationship between the charge / discharge cycle and the discharge capacity. DESCRIPTION OF SYMBOLS 1 ... Battery case 2 ... Sealing plate 3 ... Lithium alloy 4 ... Gasket 5 ... Separator 6 ... Positive electrode mixture wrapped in a metal net and pressed

Continuation of the front page (56) References JP-A-63-121248 (JP, A) JP-A-50-45929 (JP, A) JP-A-64-81167 (JP, A) JP-A-63-261675 (JP, A) JP-A-4-51459 (JP, A) JP-A-64-35871 (JP, A) JP-A-63-150867 (JP, A) JP-A-63-138646 (JP, A) 2-256177 (JP, A) JP-A-2-114448 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02 H01M 4/04

Claims (1)

(57) [Claims] 1. A positive electrode plate comprising a positive electrode plate formed by wrapping a positive electrode mixture obtained by mixing a manganese dioxide or lithium manganese dioxide composite oxide, a conductive auxiliary agent and a binder in a metal net, and press-forming. Non-aqueous electrolyte secondary battery.