JPH03225756A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To obtain a high discharge capacity and excellent charge and discharge characteristic by using a lithium manganese oxide having main peaks at specified angles in X-ray diffraction by FeKalpha ray and a maximum strength peak within a specified range as a positive electrode active material. CONSTITUTION:As a positive electrode active material, a lithium manganese oxide obtained by mixing manganese dioxide with a lithium compound followed by baking is used. Further, this compound has main peaks at 2theta=23 deg.+ or -1 deg., 27.5 deg.+ or -1 deg., 40 deg.+ or -1 deg., 47 deg.+ or -1 deg., 53 deg.+ or -1 deg., 68 deg.+ or -1 deg., respectively, in X-ray diffraction by FeKalpha ray and a value in which the main peak strength of 2theta=23 deg. is divided by the main peak strength at 2theta=27.5 deg. is within the range of 0.5 to 1.2. By optimizing the maximum strength peak of the lithium manganese oxide in which trivalent and tetravalent manganese atoms are included, a nonaqueous electrolytic secondary battery having a high discharge capacity and excellent charge and discharge cycle characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nonaqueous electrolyte secondary battery having high discharge capacity, high voltage, and excellent charge/discharge cycle characteristics.

Conventionally, in nonaqueous electrolyte batteries that use alkaline light metals such as lithium and sodium as negative electrode active materials, metal oxides, halides, or sulfides can be used as positive electrode active materials. This has been proposed, and currently, batteries using manganese dioxide or fluorinated carbon as positive electrode active materials are mainly put into practical use.

In addition, for rechargeable and dischargeable secondary batteries, such as lithium secondary batteries, titanium, which has good cycle characteristics for intercalating and deintercalating lithium ions, is used as the positive electrode active material.

Sulfides such as molybdenum, oxides such as vanadium, or conductive polymer materials such as polyaniline are used, and lithium and metals that can be easily alloyed with lithium such as aluminum and fusible metals are used as negative electrode active materials. Various methods have been proposed using alloys to suppress the short-circuit problem caused by dendrite growth when metallic lithium is used alone, and some secondary batteries that adopt these positive and negative electrode combinations have also begun to be commercialized. ing.

Under these circumstances, there are various materials suitable for positive electrode active materials, but among these, manganese dioxide is not suitable for non-aqueous electrolyte secondary batteries due to economic efficiency, chemical stability, high voltage, etc. as a positive electrode active material. Of course, it is also expected to be applied to secondary batteries.

However, manganese dioxide has the following problems when used as a positive electrode active material of a secondary battery.

In other words, in a lithium secondary battery, the manganese dioxide positive electrode absorbs lithium ions between its layers as it discharges, resulting in L
It changes into a substance called izMnoz (0≦X≦1), and Mn
It is possible to incorporate up to 1 mole of lithium ions per 0.1 mole. During charging, a reaction occurs that releases lithium atoms, but in this reaction, the lithium atoms occluded by discharge cannot be completely released from manganese dioxide, and 0.3 to 0.5 moles of lithium remain. That is, 0.3 to 0.5 moles of dead lithium atoms that cannot be electrochemically charged are present, and in terms of cycle characteristics, the capacity retention rate in the second cycle compared to the initial stage is greatly reduced. Furthermore, in the second cycle and beyond, inactive lithium gradually increases, so-called coulombic efficiency deteriorates, and the capacity decreases further, which raises questions about its suitability as a secondary battery.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having high discharge capacity, high voltage, and excellent charge/discharge cycle characteristics.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary comprising a positive electrode, a negative electrode using lithium metal or an alloy containing lithium as an active material, and a non-aqueous electrolyte containing alkali metal ions. In the battery, as the active material of the positive electrode, a lithium-manganese oxide obtained by mixing and firing manganese dioxide and a lithium compound is used, which is
By line diffraction, 2θ=23°±1'27.5"±1s4
0'+1@,47"+1'53"fl'68°±
Each has a main peak at 1°, and 2θ = 23°
A nonaqueous electrolyte secondary battery characterized in that the value obtained by dividing the main peak intensity of ±1″ by the main peak intensity of 2θ=27.51±1° is in the range of 0.5 to 1.2. I will provide a.

That is, the present applicant first mixed lithium nitrate or lithium hydroxide in powder form with manganese dioxide having a large specific surface area, and then fired it, thereby bonding lithium in manganese dioxide in advance and forming a crystal structure. By expanding the glabella of manganese dioxide, we can obtain lithium-manganese oxide that has the function of reducing diffusion resistance during charging and discharging of lithium ions, and we propose to use this as a positive electrode active material for lithium secondary batteries. (Special application 1986-
No. 103366, Japanese Patent Application No. 127359/1983).

The present inventor conducted various analyzes on such lithium-manganese oxide and further investigated its characteristics as an electrode active material, and found that 2
The peak that appears near θ=23'' has important meaning for cycle characteristics and discharge capacity, and the existence of this peak indicates that MnO
, the diffusivity of lithium ions in the lithium ions, that is, is essential for obtaining cycle durability, but on the contrary, it has been found that in cases where this peak is extremely prominent, the discharge capacity tends to decrease. Therefore, lithium-manganese oxide is suitable as a positive electrode active material for lithium secondary batteries.
As a result of further investigation into the relationship between peak characteristics by X-ray diffraction using eKa rays and electrode characteristics, we found that 2θ=23°±
1″27.5″±1″, 40″±1″, 47°±1′
It has main peaks at 53"±1' and 68°±1', and the value obtained by dividing the main peak intensity at 2θ=23"±1° by the main peak intensity at 2θ=27.5°±1°. The present invention was completed based on the discovery that a material having a value in the range of 0.5 to 1.2 has a high discharge capacity and excellent charge/discharge cycle characteristics, and is particularly suitable as a positive electrode active material for lithium secondary batteries. .

It is not clear why the lithium-manganese oxide having the above-mentioned peak characteristics exhibits excellent discharge capacity and cycle characteristics, but according to the inventor's estimation,
The peak at 2θ=23°±1@ in linear diffraction correlates with the oxidation state of existing manganese atoms, and if this peak is high, it is thought that there is a lot of trivalent manganese (Mn 3 + ) in the fired product, and this The position of the diffraction angle (2θ) is Mn”, M
This coincides with the maximum intensity peak of LiMn11O, in which n'+ is mixed, and it is thought that the amount thereof is increasing. Here, the discharge reaction of manganese dioxide in a lithium battery at a high potential of around 3V is based on a reduction reaction in which the manganese atom changes from tetravalent to trivalent, as expressed by the following formula (A). Therefore, in order to obtain a high discharge capacity, an important point is how many manganese atoms having a valence of four can be present in the active material. Therefore, by optimizing the peak at 2θ = 23° ± 1°, which indicates the amount of trivalent manganese atoms and is the maximum intensity peak of LiMn, ○, where Mn■Mn'+ is mixed, according to the above regulations, It is believed that a secondary battery having this lithium-manganese oxide positive electrode exhibits excellent discharge capacity and cycle characteristics.

The present invention will be explained in more detail below.

As described above, the non-aqueous electrolyte secondary battery of the present invention mixes manganese dioxide and a lithium compound.

A lithium-manganese oxide obtained by firing, which contains Fe
By X-ray diffraction using Ka rays, 2θ=23'±1''27.5
'±1',40°±1",47"±1"53°±
1”, with main peaks at 68°±1′, respectively,
And the main peak intensity of 2θ=23°±1° is 2θ=2
The value divided by the main peak intensity of 7.5°±1″ is 0.5
The positive electrode active material has a molecular weight in the range of 1.2 to 1.2.

Here, the above-mentioned manganese dioxide is not particularly limited, but it is preferable to use a manganese dioxide which has a large reaction surface area during the firing process because a higher discharge capacity can be obtained. In particular, it is preferable to use a material having a specific surface area of 601/g or more as measured by the BET method, and specifically, chemically synthesized manganese dioxide is suitable.

Further, the lithium compound is not particularly limited, but lithium nitrate, lithium hydroxide, or lithium carbonate is preferably used.

Lithium from the above manganese dioxide and lithium compound
The method for obtaining manganese oxide is not particularly limited, but it is preferable to add an oxidizing agent such as hydrogen peroxide when mixing and firing the two, or to treat both in an oxygen atmosphere. .

The mixing ratio of manganese dioxide and lithium compound is
It is preferable that the molar ratio of the lithium compound is 0.3 to 0.8.

When creating a positive electrode using the above lithium manganese oxide as a positive electrode active material, the particle size of the lithium manganese oxide is not necessarily limited, but if the average particle size is 3 or less, a higher performance positive electrode can be obtained. can be made. In this case, conductive agents such as graphite or acetylene black, binders such as fluororesin powder, etc. are added and mixed to these powders, pressed, kneaded with an organic solvent, rolled with rolls, and dried. A positive electrode can be created by the method. The amount of the conductive agent mixed is preferably 3 to 25 parts by weight, particularly 5 to 15 parts by weight, based on 100 parts by weight of the positive electrode material.

As the negative electrode of the non-aqueous electrolyte secondary battery of the present invention, high voltage,
A lithium metal that exhibits high energy capacity or a lithium alloy such as a lithium-aluminum alloy that has good charge and discharge characteristics is used. Note that lithium alloys are not limited to lithium-aluminum alloys, and include, for example, lithium and magnesium, indium, mercury, zinc,
An alloy of one or more of cadmium, manganese, lead, bismuth, tin, antimony, etc. is preferably used.

Furthermore, the electrolyte constituting the battery of the present invention is also appropriately selected,
Any ordinary battery electrolyte can be used, but in the battery of the present invention using lithium or lithium alloy as the negative electrode, LiCΩO, LiBF4tLiAsF, Li5
One or more of O, CF, LiPF, etc. are preferably used.

These electrolytes are usually used in a state dissolved in a solvent, and in this case, a relatively polar solvent is preferably used as the solvent. Specifically, propylene carbonate and ethylene carbonate.

Glymes such as diethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, diethylene glycol dimethyl ether, lactones such as γ-butyrolactone, phosphoric acid esters such as triethyl phosphate, boric acid esters such as triethyl borate Examples include sulfur compounds such as sulfolane and dimethyl sulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, dimethyl sulfate, nitromethane, nitrobenzene, and dichloroethane, or a mixture of two or more thereof. .

Among these, especially ethylene carbonate.

Propylene carbonate, diethyl carbonate.

Butylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane.

One or more mixed solvents selected from dioxolane and γ-butyrolactone are suitable.

Further, in the battery of the present invention, as a solid electrolyte.

An organic solid electrolyte obtained by impregnating a polymer such as polyethylene oxide, polypropylene oxide, an isocyanate crosslinked product of polyethylene oxide, or a phosphazene polymer having an ethylene oxide oligomer in its side chain with the above electrolyte solution.

LL, N, LiBCQ4. LL, 5in4. Li, B.O.
An inorganic solid electrolyte such as lithium glass such as , etc. can also be used.

The battery of the present invention is constructed by interposing an electrolyte between the positive and negative electrodes, but in this case, a separator can be interposed between the positive and negative electrodes to prevent short circuiting of current due to contact between the two electrodes. As the separator, it is possible to use porous materials that allow the electrolyte to pass through or contain them, such as nonwoven fabrics, woven fabrics, porous bodies, and nets made of synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene. can.

Summary of the Invention The nonaqueous electrolyte secondary battery of the present invention has high discharge capacity, high voltage, and excellent charge/discharge cycle characteristics.

EXAMPLES Hereinafter, the present invention will be specifically explained by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Example, comparative example]

Adding lithium glass wax powder to manganese dioxide powder with a specific surface area of 7 Onf/g by the BET method relative to manganese dioxide
．． 4 mol was added, mixed and fired to obtain lithium-manganese oxide. At this time, four types of lithium-manganese compounds A to D were obtained under the firing atmosphere and firing temperature conditions shown in Table 1.

Table 1: Fe for these A-D lithium-manganese oxides
X-ray diffraction using Ka rays was performed. The second chart
As shown in the figure.

Next, 15 parts by weight of acetylene black as a conductive agent and 10 parts by weight of fluororesin powder as a binder were added to 100 parts by weight of each of the above positive electrode active materials, and after thorough mixing, the mixture was kneaded with an organic solvent and rolled to about 400 parts by weight. After vacuum drying at 150° C., the positive electrode was punched out to a predetermined diameter.

On the other hand, lithium was pressed onto an aluminum plate punched to a predetermined size, and a lithium-aluminum alloy with a thickness of about 400mm (lithium content 30 at%) was made into an electrolyte containing lithium salt, and used as a negative electrode. 1 mol/Q of lithium barchlorate (LiCQO4) in a mixed solvent with dimethoxyethane (volume ratio 1:1)
Using each solution dissolved in the above as an electrolyte, the secondary battery shown in FIG. 1 was assembled.

Here, in FIG. 1, 1 is a positive electrode, 2 is a positive electrode current collector made of stainless steel, and the positive electrode 1 and current collector 2 are integrated, and the current collector 2 is attached to the inner surface of the positive electrode can 3. Spot welded. Further, 4 is a negative electrode, 5 is a negative electrode current collector, and the negative electrode 4 is spot-welded to the current collector 5 fixed to the inner surface of the negative electrode can 6.

Furthermore, 7 is a separator made of a polypropylene nonwoven fabric, which is impregnated with the electrolytic solution.
8 is an insulating backing. Also, the battery dimensions are 20mm in diameter.
．． The thickness is 1.6 mm.

Using the batteries prepared as described above, the end-of-discharge voltage was 1.5 V and the end-of-charge voltage was 3 at a charge/discharge current of 1 mA.
．． Charging and discharging was repeated at 2 ■, and the charging and discharging characteristics up to 100 cycles were confirmed.

Table 2 shows the initial discharge capacity per gram of active material, and Figure 3 shows the initial discharge capacity per gram of active material.
The capacity change up to 00 cycles is shown.

From the results shown in Table 2, it was confirmed that all the batteries of the present invention exhibited high initial discharge capacity.

Further, from the results shown in FIG. 3, it was confirmed that the battery of the present invention exhibited good cycle characteristics.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of the present invention, Fig. 2 is an X-ray diffraction chart using FaKa rays of each lithium-manganese oxide, and Fig. 3 shows the cycle characteristics of batteries according to the example and comparative example. This is a graph showing.

Claims (1)

[Claims] 1. In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode using lithium metal or an alloy containing lithium as an active material, and a non-aqueous electrolyte containing alkali metal ions, manganese dioxide and manganese dioxide are used as the active material of the positive electrode. A lithium-manganese oxide obtained by mixing with a lithium compound and firing it, and according to X-ray diffraction using FeKα rays, 2θ = 23° ± 1°,
27.5°±1°, 40°±1°, 47°±1°, 53
It has main peaks at ゜±1゜ and 68゜±1゜, and the main peak intensity at 2θ: 23゜±1゜ is 2θ=
The value divided by the main peak intensity of 27.5°±1° is 0.
A non-aqueous electrolyte secondary battery characterized in that a non-aqueous electrolyte secondary battery having an electrolyte in the range of 5 to 1.2 is used.