JPH06168722A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To restrict reduction of a charge capacity in case of a high-rate discharge, and reduce deterioration of a discharge capacity if high-rate charges and discharges are repeated in case of a secondary battery by displacing part of cobalt of LiCoO2 by magnesium. CONSTITUTION:LiMgxCo1-xO2-y (0<x<1, 0<y<0.5, x=2y) obtained by displacing part of cobalt in LiCoO by magnesium is used for positive electrode active material. In case of LiMg0.5Co0.95O1.75, for example, an electron conductivity is improved by about 1000 times compared to that of LiCoO2, and as a result of changing addition quantity of magnesium, the electron conductivity is improved in case that the value of (x) in LiMgxCo1-xO2-y (0<x<1, 0<y<0.5, x=2y) is 0.04 or more. Reduction of a charge/discharge capacity at the time of a high-rate discharge can thus be reduced, and reduction of the charge/ discharge capacity after repeating cycles can be restricted in case of a secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Along with the rapid reduction in size and weight of electronic equipment, there is a demand for small, lightweight batteries with high energy density. Non-aqueous electrolyte batteries are promising as batteries that meet these requirements. Among them, α-NaCrO _{2 is} used as the positive electrode active material.
Type non-aqueous electrolyte battery using layered LiCoO ₂ is 4V
It is expected to be used as a battery with high energy density because it shows extremely high voltage of the class.

However, LiCoO ₂ is an electrically insulating substance (J.
Since van Elp et al. (Physi. Rev. B., 44,6090 (1991)), there is a problem that the internal resistance of the battery increases and the discharge capacity decreases at the high rate discharge.

[0004]

The present invention provides a LiMg _x Co _1-x
The problem is solved by using a non-aqueous electrolyte battery using O _2−y (0 <x <1,0 <y <0.5, x = 2y) as the positive electrode active material.

[0005]

The present inventors have found that substituting a part of cobalt in LiCoO ₂ with magnesium significantly improves the electron conductivity of LiCoO ₂ . That is, as shown in FIG. 1, the new substance, LiMg _0.5 Co _0.95 O _1.75, had an electron conductivity improved about 1000 times at room temperature as compared with LiCoO ₂ . Moreover, as a result of studying various amounts of added magnesium, as shown in FIG. 2, the x value of LiMg _x Co _1-x O _2-y (0 <x <1,0 <y <0.5, x = 2y) It was found that the electron conductivity is improved when 0.04 or more.

As a result of the improved electronic conductivity of the active material itself, the lithium cobalt magnesium composite oxide LiMg _x Co _1-x O _2-y (0 <x <1,0 <y <0.5, x = 2y)
The non-aqueous electrolyte battery using as an active material, the decrease in the discharge capacity at the time of high rate discharge is suppressed as shown in the examples below, and in the case of a secondary battery, when high rate charge / discharge is repeated. Moreover, the decrease in discharge capacity is small.

[0007]

EXAMPLES The present invention will be described below with reference to preferred examples.

A positive electrode active material was synthesized as follows. Lithium carbonate, cobalt trioxide and magnesium carbonate having a lithium: cobalt: magnesium atomic ratio of 1: (1-x):
were mixed so that the x, active material lithium cobalt-magnesium composite oxide used in the non-aqueous electrolyte battery of the present invention is thermally decomposed in 16 hours in air at a temperature _{900 ℃ LiMg x Co 1-x} O 2- y
(0 <x <1,0 <y <0.5, x = 2y) was synthesized. In addition, lithium carbonate and cobalt tetraoxide are used in a lithium: cobalt atomic ratio.
Α-N, the active material used in conventional non-aqueous electrolyte batteries after being mixed in a 1: 1 ratio and pyrolyzed in air at 900 ℃ for 16 hours
aCrO ₂ type layered lithium cobalt composite oxide (LiC
oO ₂ ) was synthesized.

Carbon powder as a conductive agent and fluororesin powder as a binder were mixed with the above active material in a weight ratio of 90: 3: 7, and 0.165 g of this mixture was charged into an electrode molding die to obtain a diameter. It was formed into a disc with a thickness of 16 mm and a thickness of about 0.7 mm. This molded body was vacuum-dried at a temperature of 250 ° C. to obtain a positive electrode plate.

For the negative electrode plate, graphite and fluororesin powder as a binder were mixed in a weight ratio of 91: 9, and this mixture was made into a diameter of 16 mm and a thickness of 0.5 mm using the same mold as the positive electrode plate. It was obtained by pressure molding and then vacuum drying at a temperature of 250 ° C.

A button type battery as shown in FIG. 3 was manufactured by using the above positive electrode plate and negative electrode plate. The figure is a vertical cross-sectional view of a battery. In the figure, 1 is a case that also functions as a positive electrode terminal made by stamping a stainless steel (SUS304) steel plate, and 2 is a stainless steel (SUS 304)
U304) A sealing plate that also functions as a negative electrode terminal made by punching a steel plate, and the negative electrode plate 3 is in contact with the inner wall of the sealing plate. Reference numeral 5 is a separator made of polypropylene impregnated with an organic electrolyte, 6 is a positive electrode plate, and the opening end of the case 1 which also functions as a positive electrode terminal is swaged inward, and the outer periphery of the sealing plate 2 which also functions as a negative electrode terminal is inserted through a gasket 4. It is closed and sealed by tightening.

Ethylene carbonate (E
C), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 2: 2: 1, and lithium hexafluorophosphate was dissolved at a concentration of 1 mol / liter. Furthermore, 10 ppm of lithium perchlorate was added to the electrolytic solution.

LiMg _x Co _1-x O _2-y (0 <x <1,
0 <y <0.5, x = 2y) of the non-aqueous electrolyte battery of the present invention, where x = 0.03 is (A), x = 0.05 is (B), x =
The one with 0.08 is called (C) and the one with x = 0.1 is called (D). Another possible using LiCo _O2 as the positive electrode active material, referred to comparative battery was made to have the structure as a non-aqueous electrolyte battery of the present invention and (a).

Next, these batteries are connected to each other at a current density of 2 mA / cm.
^{In 2} , charge until the terminal voltage reaches 4.1V, then continue,
Similarly, a charge / discharge cycle life test was performed at room temperature for 100 cycles at ² mA / cm ² where the terminal voltage reached 2.75 V. ² mA / cm ² is a very high current density in a non-aqueous electrolyte battery. Table 1 shows the initial discharge capacity and the discharge capacity after 35 cycles of each battery.

[0015]

[Table 1] As is clear from Table 1, the batteries (A), (B) of the present invention,
(C) and (D) have a larger initial discharge capacity than the battery (A) for comparison, and the decrease in discharge capacity after 35 cycles is suppressed.

In the above examples, the carbon material was used as the negative electrode and the organic electrolytic solution was used as the electrolytic solution. However, in the non-aqueous electrolyte battery of the present invention, LiMg _x Co _1-x O _2-y (0 <x <1,
If 0 <y <0.5, x = 2y) is used for the positive electrode active material, the negative electrode active material and the electrolytic solution are basically not limited. That is, the negative electrode active material used in the conventional non-aqueous electrolyte battery, for example, pure lithium or lithium alloy, can be used as the negative electrode active material. In addition, other organic solvents such as cyclic esters such as ethylene carbonate and propylene carbonate and ethers such as tetrahydrofuran and dioxolane may be used alone or in combination in the electrolyte solution. Alternatively, an organic solid electrolyte or an inorganic solid electrolyte may be used as the electrolyte. Similarly, the materials for the supporting electrolyte, the separator, the electrode substrate, the battery case, etc. are not basically limited.

Although the batteries according to the above embodiments are button batteries, the same effect can be obtained by applying the present invention to cylindrical, prismatic or paper type batteries. Further, the effect of improving the high rate discharge performance is not limited to the secondary battery of the embodiment.
The same can be obtained in the non-aqueous electrolyte primary battery using LiMg _x Co _1-x O _2-y (0 <x <1,0 <y <0.5, x = 2y).

[0018]

As described above, the non-aqueous electrolyte battery of the present invention has a small decrease in discharge capacity during high rate discharge, and, in the case of a secondary battery, has a decrease in discharge capacity after repeated cycles. It has the effect of being suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a comparison of electron conductivity between a lithium cobalt magnesium composite oxide used in a non-aqueous electrolyte battery of the present invention and a conventional lithium cobalt composite oxide.

FIG. 2 is a diagram showing a change in electronic conductivity when the amount of added magnesium in a lithium cobalt magnesium composite oxide is changed.

FIG. 3 is a diagram showing an internal structure of a button battery which is an example of a non-aqueous electrolyte secondary battery.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Negative Electrode 4 Gasket 5 Separator 6 Positive Electrode

Claims (1)

[Claims] 1. LiMg _x Co _1-x O _2-y (0 <x <1,0 <y <0.5, x = 2y)
A non-aqueous electrolyte battery using as a positive electrode active material.