JPH04123769A - Nonaqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To transmit electric current without voltage loss by using Li-doped Li-Mn composite oxide which is prepared by doping a spinel-type LiMn2O4 with Li and has a specified formula as a cathode active mass and a carbonaceous material as an anode carrier. CONSTITUTION:A lithium-doped lithium-manganese composite oxide which is obtained by doping a spinel-type LiMn2O4 with lithium and has a formula; Li1+xMn2O4(x stands for the number within the range of 0.5<=X<=1) is used as a cathode active mass and a carbonaceous material is used as an anode carrier. The Li ion, with which the cathode is doped, is reversely comes in to and out of an anode and a cathode by charging and discharging of a battery and at that time the oxidation potential is low and thus the Li ion charging and discharging is carried out efficiently. Also, breaking of the crystal structure of the lithium-manganese composite oxide, which is a cathode, is suppressed to low level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to improvement of a positive electrode active material in a non-aqueous solvent secondary battery using a carbonaceous material as a negative electrode carrier.

E. Prior Art) In recent years, with the development of electronic devices, there has been a demand for the development of secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged.

This type of secondary battery uses lithium or lithium alloy as the negative electrode active material, and oxides, sulfides, etc. of molybdenum, vanadium, titanium, niobium, etc. as the positive electrode active material.
Those using selenide etc. are known.

Recently, spinel-type LiM, which improves and improves the cycle characteristics of manganese oxide with high energy density, has been developed.
Studies on na04 and other lithium manganese composite oxides are being actively conducted.

In battery systems in which lithium manganese oxide is used as a positive electrode active material and lithium is used as a negative electrode active material, by repeating the cycle, the dissolution and precipitation reactions of lithium, which is the negative electrode active material, are repeated, and eventually needles are formed on the lithium substrate. The problem arises of the formation of lithium dendrite precipitates.

Therefore, in battery systems, the battery life is determined by the gradual collapse of the crystal structure in the positive electrode active material, the formation of dendrites on the negative electrode side, and the decomposition reaction of the solvent, resulting in a lifespan of over 500 cycles and long-term reliability. It is extremely difficult to manufacture a battery with this property.

On the other hand, electrode active materials that utilize the intercalation or doping phenomenon of layered compounds, which have a different reaction form from these manganese oxides, are attracting attention. Since these electrode active materials do not cause complicated chemical reactions during charge and discharge reactions, they are expected to have extremely excellent charge and discharge cycles. Among these, those using carbonaceous materials as a carrier are attracting attention. This carbonaceous material was used as a negative electrode carrier, and LiCoO2/L i N was used as a positive electrode active material.
Battery systems using i O*, T i S t, and Mo5s have been proposed.

[Problem to be solved by the invention] However, when a carbonaceous material is used as a negative electrode active material, Ti
When a metal chalcogen compound such as Sz, MoS, etc. is used as a positive electrode active material, the electromotive force is small, and LiCo
o! , LiNiOa, etc. as the positive electrode active material, the electromotive force becomes very high at 3.9 to 4.3V, but this has the problem that decomposition of the solvent is likely to occur.

The present invention has been made to solve these problems, and does not cause decomposition of the solvent or collapse of the crystal structure of the positive electrode when using a carbon negative electrode active material, and also allows the material to move into the positive electrode during charging and discharging of the battery. The object of the present invention is to obtain a positive electrode active material containing Li ions.

[Means for Solving the Problems] That is, the non-aqueous solvent secondary battery of the present invention is obtained by doping lithium into spinel-type LiNiOa as a positive electrode active material. A lithium-doped lithium manganese composite oxide represented by a number in the range of 5≦X≦1 is used, and a carbonaceous material is used as the negative electrode support.

Spinel type L i M n 204 used in the present invention
For example, a manganese sulfate (MnSO4) solution is heated and condensed to obtain manganese sulfate crystals, which are then roasted at about 900°C in air to decompose the manganese sulfate. M n * 04 or M
A manganese oxide containing n*Os as a main component is synthesized. If the product is a manganese oxide mainly composed of Mn, 04, it is further roasted at about 800'C in a rotary kiln to obtain manganese oxide mainly composed of Mn20s.

The M n *Ox obtained in this way has an atomic ratio M
n: L 1 = 2: 1 nit! Mixing ratio TeL
It is mixed with i-COs and heated at a temperature of about 800'C to obtain spinel type LiMnt 04. Spinel-type LiMn*04 can also be obtained by the manufacturing method described in Japanese Patent Application Laid-Open No. 2-170354, Japanese Patent Application No. 1-135859, and Japanese Patent Application No. 1-246470.

This spinel type L i M n *Oa is immersed in an aqueous solution containing a lithium salt such as lithium sulfate, lithium nitrate, lithium iodide, lithium carbonate, and lithium hydroxide at a concentration of 1 to 20 mol/e. At this time, the ratio of the number of moles of manganese in the spinel type LiMn2O4 to the number of moles of lithium in the aqueous solution is preferably L i / M
L i so that n is in the range of 0.2 to 1.5
The amount of M n *04 and the concentration and volume of the lithium salt aqueous solution to be added are adjusted.

The aqueous solution containing this spinel-type L i M n t O4 powder is dehydrated using a dryer, vacuum dryer, etc., and then this material is heat-treated in a temperature range of 400 to 900°C to dope it with lithium. Li + ** M
Obtain ni 04 (0,5≦X≦1). At this time, the heating atmosphere is not particularly limited, and air, nitrogen, argon, etc. can be used. Here, the lithium doping amount X is 0
．． 5 ≦ This is because the amount of Li ions is limited and the battery capacity cannot be maintained. Also, even if the amount of lithium used for doping exceeds 1, the excess lithium is
This is because x is not doped into the O4 crystal and is merely physically adsorbed.

The carbonaceous material serving as the negative electrode carrier is preferably a carbonaceous material obtained by firing an organic compound in order to improve battery characteristics. The organic compound that serves as a raw material for this carbonaceous material is not particularly limited as long as it is commonly used, and for example, phenol resins, particularly novolak resins, polyacrylonitrile, and the like can be used. Moreover, as this carbonaceous material, patent application No.
Particularly preferred are those having the characteristics of an organic compound fired product as shown in No. 283086.

In the non-aqueous solvent secondary battery of the present invention, a binder may be used to form the positive electrode and the negative electrode.

Examples of the binder include a terpolymer of ethylene-problene-cyclic diene, polytetrafluoroethylene, polyacrylic acid, and polyacrylates.

Examples of the dispersion solvent in which the binder may be dissolved or dispersed include organic solvents such as hexane, toluene, and N-methylpyrrolidone, and water.

Examples of the electrolyte of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery of the present invention include L i P F s, LICI204,
Examples include lithium salts such as L i B F 4 and L iCF 3 So3. The solvent for the electrolyte is propylene carbonate (PC), ethylene carbonate (
EC), tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, and 1,2-dimethoxyethane (DME). One or two of these solvents
It can be used in a mixture of more than one species, and in particular, from the viewpoint of prolonging the charge/discharge cycle life, a mixed solvent of proplene carbonate and 1,2-dimethoxyethane, a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran, and ethylene can be used. A mixed solvent of carbonate and 1,2-dimethoxyethane and a mixed solvent of propylene carbonate and tetrahydrofuran are desirable.

[Example] Hereinafter, the present invention will be described in detail by way of Examples and Comparative Examples with reference to the drawings.

Example 1 60g of manganese sesquioxide (Mn*Os) obtained by roasting manganese sulfate (MnS04) at 900°C in air and 14g of Li2COs (Mn:Li=2 in molar ratio)
: Mix and crush 1), roast in air at 850℃ for 1 hour, cool, mix and crush again, and roast in air at 850℃ for 1 hour.
Roasted at 0°C for 2 hours. When examining the X-ray diffraction pattern of this reaction product, it was found that ASTM No. 18-736
It was consistent with the data of LiMntO4.

180 g of this spinel type L i M n t O4 was immersed in 1001 d of l Omof# aqueous solution of lithium iodide (Li/Mn = 0.5), while reducing the pressure with a vacuum pump equipped with a trap cooled with liquid nitrogen. Approximately 80
℃ to gradually evaporate water. The obtained powder was heated at 450° C. for 10 hours in an argon atmosphere to obtain the desired lithium-doped lithium manganese oxide.

90% by weight of the above lithium manganese oxide powder as a positive electrode active material, 7% by weight of acetylene black as a conductive material
and 3% by weight of an ethylene-propylene-cyclic diene terpolymer as a binder were kneaded in an organic solvent to prepare a slurry positive electrode mixture, and this positive electrode mixture was placed on a 15F+ thick stainless steel substrate. After coating and air drying, pressure was applied to give a constant thickness, followed by heating and drying at 200° C. for 10 hours to produce a plate-shaped positive electrode having a positive electrode mixture layer with a thickness of 0.26 mm.

On the other hand, the carbonaceous material that is the negative electrode carrier is made by baking the novolac resin at 950°C in a nitrogen atmosphere, and then heating it at 200°C.
It was produced by heating to 0° C. to carbonize it, and it was pulverized into a powder with an average particle size of 10P.

A terpolymer of ethylene-propylene-cyclic diene as a binder was dissolved in hexane, and carbonaceous material: binder = 97
: 3 to prepare a slurry-like negative electrode mixture. This slurry was applied onto a stainless steel substrate with a thickness of IOF and dried to form a negative electrode mixture layer with a thickness of 0.2 mm.

Using the positive and negative electrodes thus obtained, a non-aqueous solvent secondary battery of single cell (AA) size as shown in FIG. 1 was assembled. That is, the non-aqueous solvent secondary battery 1 has a bottomed cylindrical stainless steel container 3, which has an insulator 2 disposed at the bottom and also serves as a negative electrode terminal.

This container 3 houses an electrode group 4. This electrode group 4 has a structure in which a band-like material in which a negative electrode 5, a separator 6, and a positive electrode 7 are laminated in this order is spirally wound so that the negative electrode 5 is located on the outside. Said separator 6
is formed from a polypropylene porous film impregnated with an electrolyte. The electrolytic solution contains lithium hexafluorophosphate (LiPF) as an electrolyte in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (volume ratio 50:50) at a concentration of 0.5 molar. Inside the container 3, above the electrode group 4, there is an insulating plate 8 with an open center.
is located. An insulating sealing body 9 is hermetically caulked and fixed to the upper opening of the container 3. A positive electrode terminal 10 is fitted into the central opening of the insulating sealing plate 8 . This positive electrode terminal 10 is connected to the above-mentioned positive electrode 7 via a positive electrode lead 11. Note that the negative electrode 5 is connected to the container 3, which is a negative terminal, via a negative lead (not shown).

Example 2 Spinel type LI M was prepared by the same operation as in Example 1.
Synthesize n z O4. This LiMn1O4 was immersed in a 2 mol/1 aqueous solution of lithium nitrate in a 400° C. water solution, and most of the moisture was evaporated in a dryer kept at a temperature of 100.degree. This reactant was placed in an electric furnace under a nitrogen atmosphere,
The reaction was carried out at 400° C. for 10 hours to obtain the desired lithium manganese oxide.

Using this lithium manganese oxide, a positive electrode body similar to that in Example 1 was formed, and a carbonaceous negative electrode was wound to create a single cell size battery similar to that in Example 1.

Comparative Example A battery having exactly the same configuration as Example 1 was prepared except that metallic lithium was used for the negative electrode.

The nonaqueous solvent secondary batteries of Example 1.2 and Comparative Example thus created were charged and discharged at a constant discharge current of 100 mA at a room temperature of 20°C in a voltage range of 3.5 V to 2.0 ■. I did it. The results are shown in FIG. In the figure, A is the discharge capacity retention rate curve of the battery of Example 1, B is the battery of Example 2, and C is the discharge capacity retention rate curve of the battery of Comparative Example. As is clear from this figure, the non-aqueous solvent secondary battery of Example 1.2 shows little deterioration in the discharge capacity retention rate as the number of cycles increases, and has excellent charge-discharge reversibility. On the other hand, the battery of the comparative example is
After 200 cycles, the capacity retention rate decreases rapidly.
The differences in the characteristics of the negative electrode active materials are clearly visible.

In this way, spinel type Li doped with lithium on the positive electrode side
A battery having a long life can be obtained by using a carbon material obtained by firing an organic compound as a negative electrode with Mn2O4 active material.

[Effects of the Invention] The non-aqueous solvent secondary battery of the present invention is made by doping spinel-type LiMnx 04 as a positive electrode active material with lithium by immersing it in an aqueous lithium salt solution, evaporating water, and then heating and baking it. The method is characterized in that the obtained L l 1 *z M n 204 is used and carbon is used as the negative electrode active material. Li ions doped into the positive electrode reversibly move in and out between the negative and positive electrodes as the battery is charged and discharged, and the battery voltage at this time is approximately 2.0-3.7μ, so the oxidation potential is low and Li Good ion charging and discharging efficiency. In addition, low-viscosity solvents can be used without decomposition, and the carbonaceous material used as the negative electrode has almost no capacity deterioration due to charging and discharging.
The lithium-manganese composite oxide used as the positive electrode has also been improved so that its crystal structure is less likely to collapse. Therefore, according to the present invention, it was possible to obtain an excellent non-aqueous solvent secondary battery having long-term reliability and long life.

[Brief explanation of the drawing]

Figure 1 is a partial cross-sectional view showing the nonaqueous solvent secondary battery of Example 1, and Figure 2 is the change in discharge capacity with respect to the number of charge/discharge cycles in the nonaqueous solvent secondary batteries of Example 1.2 and Comparative Example. FIG. 1... Non-aqueous solvent secondary battery, 2... Insulator, 3...
Stainless steel container, 4... Electrode group, 5... Negative electrode, 6...
Separator, 7... Positive electrode, 8... Insulating plate, 9...
Insulating sealing plate, lO...positive electrode terminal, 11...positive electrode lead. A, B, C... Discharge capacity retention rate curve A of the following battery:
Example I B: Example 2 C: Comparative example

Claims (1)

[Claims] Lithium-doped lithium represented by the formula Li_1_+_xMn_2O_4 (wherein x represents a number in the range of 0.5≦x≦1) obtained by doping spinel-type LiMn_2O_4 with lithium as a positive electrode active material. A non-aqueous solvent secondary battery characterized by using a manganese composite oxide and using a carbonaceous material as a negative electrode carrier.