JP2569664B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a chargeable / dischargeable non-aqueous electrolyte secondary battery expected to be used as a power source for various small electronic devices.

[Summary of the Invention]

The present invention relates to a non-aqueous electrolyte secondary battery using lithium as a negative electrode active material, wherein MnO ₂ and lithium carbonate having a (110) plane diffraction X-ray peak near a diffraction angle 2θ = 36.3 ° in X-ray diffraction are formed. By using LiMn ₂ O ₄ obtained by firing at a predetermined temperature as a positive electrode active material, it is intended to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge characteristics and less deterioration in cycle capacity. is there.

[Conventional technology]

A so-called non-aqueous electrolyte battery using thylium as the negative electrode active material and an organic electrolyte as an electrolyte has advantages such as low self-discharge, high voltage, and excellent storage stability. In particular, it is widely used as a battery having a long-term reliability of 5 to 10 years, for example, as an electronic timepiece and a power supply for various memory backups.

However, the non-aqueous electrolyte battery conventionally used is a primary battery, and its service life is exhausted after one use, so that there is room for economical improvement. In recent years, with the remarkable progress of various electronic devices, the emergence of a rechargeable non-aqueous electrolyte secondary battery as a power source that can be used conveniently and economically for a long time has been awaited, and much research has been conducted. I have.

Generally, as a negative electrode active material of a non-aqueous electrolyte secondary battery,
Lithium metal, lithium alloy (for example, Li-Al alloy), conductive polymer doped with lithium ions (for example, polyacetylene or polypyrrole), and further, a layer-waiting compound in which lithium ions are mixed in the crystal, and the like are used. As the electrolyte, a non-aqueous electrolyte in which an electrolyte is dissolved in an organic solvent is used.

On the other hand, as a positive electrode active material, various materials have been proposed as a result of research, and typical ones include, for example, TiS ₂ , MoS ₂ ,
NbSe ₂ , V ₂ O _{5 and the} like can be mentioned.

The discharge reaction of a battery using these materials proceeds by intercalation of negative electrode lithium ions between layers of these materials that are the positive electrode active material, and when charged, lithium ions are discharged from the layers of the above materials. Deintercalate to the negative electrode. That is, charge and discharge can be repeated by repeating a reaction in which lithium ions of the negative electrode enter and exit between layers of the positive electrode active material.

However, the above-described positive electrode material has a disadvantage that lithium ions gradually become less likely to be deintercalated during repeated charge / discharge reactions, so that the discharge capacity gradually decreases and the cycle life is shortened.
In addition, since these positive electrode materials are very expensive, it is costly to manufacture a large number of batteries, which is economically disadvantageous as compared with nickel-cadmium batteries, which are the mainstream of secondary batteries. In addition, batteries using these cathode materials have a discharge voltage of 1.5 to 2.5 V, which is extremely low compared to the high voltage of 3.0 V of a general lithium primary battery (Li / MnO ₂ , Li / CF _X ). There is a problem that a high voltage, which is a feature of the battery used, cannot be obtained.

Therefore, as a positive electrode material that has less deterioration in discharge capacity due to charge / discharge cycles, has excellent cycle life characteristics, and is also economical, the applicant of the present invention has disclosed, for example, Japanese Patent Application No. 61-257479.
In the specification, a positive electrode material mainly composed of LiMn ₂ O ₄ was disclosed.

The battery reaction using this LiMn ₂ O ₄ is represented by the following equation.

[Problems to be Solved by the Invention] As described above, the development of LiMn ₂ O ₄ as a cathode material has resulted in significant improvements in discharge capacity, cycle life, and economy.

An object of the present invention is to further improve the cycle characteristics of a specific water electrolyte secondary battery using the above LiMn ₂ O ₄ as a positive electrode active material.

[Means for solving the problem]

The present inventors have made various studies to improve the charge / discharge characteristics and the deterioration of the cycle capacity of a specific water electrolyte secondary battery using LiMn ₂ O ₄ as a positive electrode active material. As a result, we recognized that manganese dioxide, which is a raw material of LiMn ₂ O ₄ , has various crystal phases, and among them, X-ray diffraction showed a diffraction X-ray peak of the (110) plane near diffraction angle 2θ = 36.3 ゜. Using MnO ₂ having, and using LiMn ₂ O ₄ obtained by firing this and lithium carbonate at 400 to 600 ° C. as a positive electrode active material, the cycle capacity deterioration of the non-aqueous electrolyte secondary battery will decrease. I got the knowledge. That is, the non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery comprising a negative electrode mainly composed of lithium or a lithium alloy, a positive electrode mainly composed of LiMn ₂ O ₄ , and a non-aqueous electrolyte. In the battery, the LiMn ₂ O ₄
Indicates that 400 to 600 MnO ₂ and lithium carbonate having a (110) plane diffraction X-ray peak near the diffraction angle 2θ = 36.3 ° by X-ray diffraction.
It is characterized by being LiMn ₂ O ₄ fired at ° C.

MnO ₂ used for obtaining LiMn ₂ O ₄ has a (110) plane diffraction X-ray peak near a diffraction angle 2θ = 36.3 ° in X-ray diffraction. This means, for example, that γ-phase MnO ₂
It is obtained by heat treatment in a temperature range of 0 to 500 ° C. The diffraction X-ray peak of the (110) plane of the γ-phase MnO ₂ shifts from the diffraction angle 2θ = around 28.2 ° to the vicinity of 36.3 ° toward a higher angle. Temperature conditions are important for the heat treatment. If the heat treatment temperature is 300 ° C. or lower, the diffraction X-ray peak of the (110) plane does not sufficiently shift, and it is difficult to obtain desired MnO ₂ . Conversely, when the heat treatment temperature is 500 ° C or higher, the diffraction X is further increased to higher angles.
The line peak shifts to MnO _{2 of} another phase (for example, α phase), and the desired MnO ₂ cannot be obtained.

MnO ₂ having a diffraction X-ray peak of (110) plane diffraction angle 2 [Theta] = 36.3 ° in the vicinity obtained X-ray diffraction by heat-treating γ-phase MnO ₂ as described above, has a tetragonal rutile-type crystal structure It is a very stable manganese dioxide. The γ-phase MnO ₂ used may be electrolytic manganese dioxide or manganese dioxide synthesized by chemical synthesis.

Thus, the predetermined value obtained by heat treatment of the γ phase MnO ₂ etc.
It is calcined at a temperature of 400 to 600 ° C. with lithium carbonate using MnO ₂ to obtain LiMn ₂ O ₄ . In the present invention, LiMn ₂ O ₄ obtained by the above operation is used as a positive electrode active material. The firing may be performed in the air or in an inert gas. It is also possible to use lithium iodide instead of lithium carbonate used in firing.

On the other hand, the negative electrode active material is mainly composed of metallic lithium, and lithium alone may be used as the negative electrode active material,
Alternatively, an alloy in which at least one of aluminum, lead, tin, bismuth, cadmium, copper, iron and the like is added to lithium may be used as the negative electrode active material. When an alloy of lithium and the other metal is used as the negative electrode active material, it is preferable that the other metal is added to such an extent that the original potential of lithium is not significantly changed.

As the electrolyte used for the non-aqueous electrolyte secondary battery, a non-aqueous electrolyte obtained by dissolving a lithium salt as an electrolyte in an organic solvent is used.

Here, examples of the organic solvent include esters, ethers, 3-substituted-2-thioxazolidinones, and a mixed solvent of two or more of these.

Examples of the esters include alkylene carbonates (ethylene carbonate, propylene carbonate, γ-butyl lactone, 2-methyl-γ-butyl lactone, and the like).

Examples of the ethers include diethyl ether, cyclic ethers, for example, ethers having a 5-membered ring [tetrahydrofuran; substituted (alkyl, alkoxy) tetrahydrofuran, for example, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2-ethyltetrahydrofuran, 2,2 '.
-Dimethyltetrahydrofuran, 2-methoxytetrahydrofuran, 2,5-dimethoxytetrahydrofuran and the like; dioxolane and the like], ether having a 6-membered ring [1,4-dioxane, pyran, dihydropyran, tetrahydropyran],
Dimethoxyethane and the like.

Examples of the 3-substituted-2-oxazolidinones include 3-alkyl-2-oxazolidinones (e.g., 3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone), 3-
Cycloalkyl-2-oxazolidinone (e.g., 3-cyclohexyl-2-oxazolidinone), 3-aralkyl-2
-Oxazolidinone (e.g., 3-benzyl-2-oxazolidinone), 3-aryl-2-oxazolidinone (3-
Phenyl) -2-oxazolidinone and the like.

Among them, propylene carbonate, dimethoxyethane, and ethers having a 5-membered ring (particularly, tetrahydrofuran,
-Methyltetrahydrofuran, 2-ethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-methoxytetrahydrofuran), 3-methyl-2-oxazolidinone, and the like.

As the electrolyte, lithium perchlorate, lithium borofluoride, lithium phosphofluoride, lithium chloride aluminate,
Lithium halide, lithium trifluoromethanesulfonate and the like can be used, and lithium perchlorate and lithium borofluoride are preferred.

[Action]

For example, γ-phase MnO ₂ is heat-treated at a predetermined temperature,
By preparing LiMn ₂ O ₄ using manganese dioxide whose X-ray diffraction peak on the 0) plane is shifted to around 36.3 °, excellent LiMn ₂ O ₄ containing no impurities can be prepared. If this is used as the positive electrode active material of the non-aqueous electrolyte secondary battery, the deterioration of the cycle characteristics is extremely small.

〔Example〕

Hereinafter, the present invention will be described based on specific embodiments with reference to the drawings.

Example First, LiMn ₂ O which is a positive electrode active material of a non-aqueous electrolyte secondary battery
₄ was prepared.

In preparing LiMn ₂ O ₄ , first, MnO ₂ as a raw material was prepared. MnO _{2 as a} raw material was obtained by using a commercially available γ-type MnO ₂ and performing a heat treatment at 420 ° C. for 4 hours in an air atmosphere. FIG. 1 shows the X-ray diffraction pattern of commercially available γ-type MnO ₂ , and FIG. 2 shows the X-ray diffraction pattern of manganese dioxide obtained by heat treatment. As is clear from FIGS. 1 and 2, the heat treatment in an air atmosphere causes the (110) plane peak to move from the position (2θ = 28.2 °) shown in A of FIG. 1 (B in FIG. 2). Position (2θ =
It can be seen that the angle has shifted to the higher angle side to 36.3 ゜).

Manganese dioxide 86.9 obtained by heat treatment as described above
g (1 mol) and 18.5 g (0.25 mol) of commercially available lithium carbonate were sufficiently mixed while being ground in a mortar, and the resulting mixture was placed in an alumina boat and calcined at 460 ° C. for 1 hour in an air atmosphere. The obtained fired product was analyzed by X-ray diffraction. This X-ray diffraction was performed using FeKα radiation, and the measurement conditions were a tube voltage of 30 kV, a tube current of 15 mA, and a measurement range of 2000.
cps, scanning speed 1 mm / min, recording paper speed 5 mm / min, divergence slit width 1 mm, light receiving slit width 0.6 mm. The substance was identified by checking with the American Society for Testing and Materials (ASTM) card index, and it was confirmed that the calcined product was LiMn ₂ O ₄ . FIG. 3 shows an X-ray diffraction pattern of the obtained LiMn ₂ O ₄ .

Next, a non-aqueous electrolyte secondary battery as shown in a schematic sectional view in FIG. ₄ was produced using the LiMn ₂ O ₄ obtained as described above.

That is, 80 parts by weight of the above LiMn ₂ O ₄ , 15 parts by weight of graphite and 5 parts by weight of polytetrafluoroethylene (Teflon) as a binder were added thereto to obtain a positive electrode powder having a diameter of 10.2 mm at a pressure of 3 t / cm ^2. Then, it was press-molded to a thickness of 0.43 mm and vacuum dried at 300 ° C. for 3 hours to obtain a positive electrode pellet (5).

On the other hand, the negative electrode plate (1) is made of lithium foil 15.0 mm in diameter and thickness.
It was formed by punching out to 1.62 mm, and this was pressure-bonded to the negative electrode can (2).

Next, a propylene nonwoven fabric is stacked on the negative electrode plate (1) as a separator (3), and a mixed solution of propylene carbonate and 1,2-dimethoxyethane in which 1 mol / mol of lithium perchlorate is dissolved is used as an electrolyte. added. Further, the positive electrode pellet (5) previously prepared is stacked on the separator (3), a plastic gasket (4) is fitted therein, and then the positive electrode can (6) is covered, and the opening is sealed. Caulked and sealed, outer diameter 20 mm, thickness 2.5
A so-called button type sample battery with a positive electrode regulation of mm was fabricated.

Comparative Example 86.9 g (1 mol) of commercially available γ-type MnO ₂ and 18.5 g (0.25 mol) of commercially available lithium carbonate were thoroughly mixed in a mortar, and the resulting mixture was placed in an alumina boat at 460 ° C. in an air atmosphere. The firing was performed for one hour. The obtained fired product was analyzed by X-ray diffraction. This X-ray diffraction
The measurement conditions were as follows: tube voltage 30 kV, tube current 15 mA, measurement range 2000 cps, scanning speed 1 mm / min, recording paper speed 5 mm / min, divergence slit width 1 mm, light receiving slit width 0.6 m.
m. Material identification is American Society for Testing and Materials (ASTM)
The calcined product was confirmed to be LiMn ₂ O ₄ . L obtained
The X-ray diffraction pattern of iMn ₂ O ₄ is shown in FIG. When FIG. 5 is compared with FIG. 3 showing the X-ray diffraction pattern of LiMn ₂ O ₄ produced in the example, the main peaks indicating LiMn ₂ O ₄ appear similarly, but FIG. As shown by middle a and b, some peaks not appearing in FIG. 3 are seen.

Next, using LiMn ₂ O ₄ obtained as described above, a sample battery as shown in a schematic sectional view in FIG. 4 was produced in the same manner as in the example.

Using the sample battery of the example and the sample battery of the comparative example,
At a discharging current density of 0.5 mA / cm ² until the discharge end voltage 2.0V was discharged, charge voltage in the subsequent charge current density 0.5 mA / cm ² 4.0
Charged to V. This charge / discharge is repeated several times, and the results are shown in FIG. 6 as the cycle capacity retention. Sixth
In the figure, the discharge capacity at the second cycle is set to 100%, and the cycle capacity retention for each cycle is shown. As is clear from FIG. 6, even when the number of cycles is increased, the cycle capacity of the sample battery of the present invention is small. In contrast, it can be seen that the cycle capacity of the comparative sample battery gradually deteriorates as the number of cycles increases. As shown in FIG. 5, a peak which seems to be an impurity appears in LiMn ₂ O ₄ used as the positive electrode active material, and this acts as a substance which inhibits a reaction at the time of charging and discharging, thereby deteriorating the cycle capacity. Is considered to be large.

〔The invention's effect〕

As is clear from the above description, in the present invention, as the positive electrode active material, MnO ₂ having a (110) plane diffraction X-ray peak near the diffraction angle 2θ = 36.3 ° by X-ray diffraction and lithium carbonate are specified. Since it uses LiMn ₂ O ₄ that is obtained by firing at a temperature of and does not contain impurities etc., it has excellent charge / discharge characteristics and a non-aqueous electrolyte secondary battery with very little cycle capacity deterioration. be able to.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing an X-ray diffraction pattern of commercially available γ-type MnO ₂ . FIG. 2 is a characteristic diagram showing an X-ray diffraction pattern of manganese dioxide obtained by heat treatment. FIG. 3 is a characteristic diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ used in Examples. FIG. 4 is a schematic sectional view showing a configuration example of a non-aqueous electrolyte secondary battery. FIG. 5 is a characteristic diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ used in the comparative example. FIG. 6 is a characteristic diagram showing the cycle capacity retention of the sample battery of the example in comparison with that of the sample battery of the comparative example. DESCRIPTION OF SYMBOLS 1 ... Negative electrode plate 2 ... Negative electrode can 3 ... Separator 4 ... Gasket 5 ... Positive electrode pellet 6 ... Positive electrode can

Claims (1)

(57) [Claims] A non-aqueous electrolyte secondary battery comprising a negative electrode mainly composed of lithium or a lithium alloy, a positive electrode mainly composed of LiMn ₂ O ₄ , and a non-aqueous electrolyte, wherein the LiMn ₂ O ₄ is X Diffraction angle 2θ = around 36.3 ゜ (1
10) A non-aqueous electrolyte secondary battery comprising LiMn ₂ O _{4 obtained} by calcining MnO ₂ and lithium carbonate having a plane diffraction X-ray peak at 400 to 600 ° C.