JPH06290780A - Positive electrode material for lithium secondary battery and its synthesis and evaluation, and lithium secondary battery and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a stabilized synthesis method of a positive electrode material for a lithium secondary battery and its evaluation, and the construction and manufacturing method of a lithium secondary battery excellent in discharge capacity and discharge cycle characteristics. CONSTITUTION:A cobalt oxide as a starting material is baked in advance at between 910 deg.C-950 deg.C. This cobalt oxide and a lithium salt are then heattreated, so that a composition with LiCoO2, or LiCoO2 as its principal constituent is obtained. In this synthesis of a positive electrode material for a secondary battery, a furnace controlling thermocouple is inserted at the center of the baked powder, so that its two-stage baking is made with the upper limit temperature set at 900 deg.C. In this case, a spacer of 1mm or more in thickness is inserted to make gaps of 1mm-2mm between the press-molded material pieces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to LiCoO2 or a composition containing LiCoO2 as a main component, which is suitable for use as a positive electrode material for a lithium secondary battery, and a synthesis method and evaluation method thereof. The present invention relates to a structure and a manufacturing method of a lithium secondary battery using such a positive electrode material.

[0002]

2. Description of the Related Art Hitherto, LiCoO2 has been synthesized by mixing a cobalt compound and a lithium salt in an appropriate mixing ratio and firing at a relatively high temperature. For example, in the literature (Mat.
s. Bull. 15 (1980) 783 K. Mizushima
According to et al., CoCO3 and Li2CO3 are 900
After pre-firing in air at ℃ for 20 hours, firing is performed twice more (detailed temperature condition unknown) to obtain suitable LiCoO2.
Was being synthesized. The mixed CoCO3 and Li2CO3 are thermally decomposed at a high temperature to release CO2 gas and react with each other to produce LiCoO2. Given this reaction,
Probably it is considered to be represented by the following reaction formula.

[0003]

[Chemical 1]

In this reaction formula, (1) and (3) are characterized by requiring extra oxygen. If CoCO
If Co3O4 is used as a starting material from the beginning instead of 3, consideration for the reaction of the formula (1) becomes unnecessary. Therefore, it is considered that using Co3 O4 is more practically convenient than using CoCO3. In some cases, synthesis using a peroxide of lithium may be performed (for example, in literature (MGSR tho).
mas et al Mat. Res. Bull. , 20
(1985) 1137)).

As described above, there is a lot of know-how concerning the optimal synthesis method and the like, and patents have been applied for. However, basically, this composition has a high electric resistance value, and the literature (J, Phys, Chem, Solids, 48, 97 (1987)) 100Ω
・ It is cm. When a positive electrode is made using a positive electrode material having an essentially high electric resistance value, the disadvantage of large electron conduction resistance loss cannot be avoided. In addition, LiCoO2
There is a lack of oxygen. When the oxygen deficiency increases, it becomes difficult to maintain the layered structure.

On the other hand, in lithium secondary batteries, lithium metal alone was used as the negative electrode material before.
There was a problem such as an internal short circuit due to the dendritic deposition of lithium metal. Therefore, in recent years, a method of using carbon as a negative electrode material and inserting and desorbing lithium ions is becoming mainstream. By using this electrode, a battery having a voltage similar to that when using lithium metal and having high safety without dendrite was made possible. The negative electrode is composed of a carbon material such as pyrolytic carbon, carbon black, coke and graphite, and is bound by a binder for molding.

As a constituent material of the positive electrode, a positive electrode active material such as LiCoO 2 is used as a main component, graphite or the like is added to improve conductivity, and a binder is added in order to have moldability like the negative electrode. And glued.

These electrodes are formed into a film by a wet molding method, and then, in order to improve the charge / discharge capacity per unit volume, press compression is performed to increase the active material filling rate. There is.

In a conventional lithium secondary battery, a separator is interposed between both electrodes and a non-aqueous organic solvent is used as an electrolytic solution, and the battery structure is a coin type or a cylindrical type. Generally, when trying to obtain a large current in a battery, it has been attempted to make the electrode area as large as possible. Particularly in a lithium secondary battery, since an organic solvent having a relatively low conductivity is used as an electrolytic solution, increasing the area of the electrode is particularly important.

FIG. 38 shows a conventional coin type battery shown on page 124 of "Battery Handbook" (edited by Battery Handbook Editing Committee, published by Maruzen 1990). In the figure, 1 is a positive electrode active material layer, 2 is a negative electrode active material layer, 3 is a separator, and 10 is a sealing material. In the flat battery having such a structure, there is a limit in increasing the electrode area, and in fact, a cylindrical battery in which the electrode area is increased by winding up a strip electrode is made as a type of battery that takes a large current. . In order to obtain a large area by using a flat plate-shaped electrode, a conventional method has adopted a structure in which so-called strip-shaped electrodes are connected.

FIG. 39 shows the structure of the conventional clad lead-acid battery shown on page 188 of the "Battery Handbook" (edited by the Battery Handbook Editorial Committee, published by Maruzen 1990). Both the strip-shaped positive electrode 1 and the strip-shaped positive electrode 2 are connected like a comb by a current collecting tab and a connecting rod, arranged via a separator 3, and put in one container.

As a method of obtaining a large-area electrode, a folding battery structure as described in Japanese Patent Laid-Open No. 4-298973 has been proposed. A positive electrode plate in which a positive electrode active material is applied to one surface of a current collector base material made of a strip-shaped metal foil is folded into two with the active material facing each other, and a negative electrode plate is inserted between the two folded positive electrode plates with a separator interposed therebetween. Then, a strip-shaped electrode plate group is formed, and the electrode plate group is alternately bent with a constant width and folded to form a rectangular electrode structure.

Two important indexes in the development of a lithium secondary battery are discharge capacity and cycle life. Regarding the discharge capacity of the secondary battery, there are two ways of expressing the discharge capacity per active material weight and the discharge capacity per unit volume. A battery excellent in both performances is desired.
The discharge capacity per weight varies depending on how much carbon or inorganic oxide that is an electrode active material can be inserted or removed in the reaction of lithium ions. In addition, the composition and structure of each electrode are also affected by whether or not lithium is easily reacted.
On the other hand, the discharge capacity per unit volume depends on the amount of the electrode active material filled in the unit volume. That is, the filling rate of the electrode active material is greatly related to the discharge capacity per unit volume. Since the filling rate is affected by the particle size of the active material and the composition of the electrode, it may be considered that the discharge capacity per volume can be increased by studying these, but this study has not been conducted so far.

Another characteristic of the lithium secondary battery is an improvement in cycle life. As shown above,
Previously, lithium metal was used for the negative electrode of the lithium secondary battery, but by using carbon, the cycle life was significantly improved. However, since the capacity of carbon also decreases due to charge and discharge, it is necessary to improve the carbon material. Therefore, conventionally, the negative electrode has been formed by using carbon prepared by various raw materials and manufacturing conditions.

[0015]

As described above, the production and decomposition of LiCoO2 during the synthesis of LiCoO2 have not been explored so far. That is, there was no reply or report to the problem of how much the upper temperature limit can be allowed as the firing temperature condition.
Further, there has been no detailed report on the method of controlling or adjusting the Li / Co ratio of LiCoO2 or its stoichiometry (O / Co ratio). That is, what characteristics of LiCoO2
Regarding the positive electrode material for a lithium secondary battery, the evaluation means or the evaluation method has not been sufficiently established in terms of whether it is the most excellent composition.

Therefore, at present, under what kind of firing conditions, Li
The description focuses on the secondary battery characteristics of CoO2. Of course, powder X-ray diffraction is performed, and for example, the peak from the (104) plane with the highest intensity (CuKα
If a line is used, it has been performed to search for a firing condition such that the ratio of the peak having the second highest intensity (near 2θ = 45.2 degrees) (near 2θ = 18.8 degrees) becomes large.
However, such a method is necessary as a means for evaluating LiCoO2, as the inventors clarify,
I don't want to be enough.

Further, the inventors have found that the synthesis of LiCoO2 involves a considerably large exothermic reaction (about 40 cal / g), but if this exothermic amount is not sufficiently well dissipated, the temperature of the fired product is unexpectedly increased. Will cause. To detect the history of such undesired and unexpected temperature rises,
This was not possible with the powder X-ray diffraction method.

On the other hand, the high temperature firing is for LiCoO2,
Since it is adjacent to unfavorable thermal decomposition and a large amount of oxygen deficiency is generated, the possibility of low temperature synthesis is being studied. For example, the literature (Mat. Res. B
all. , 27 (1992) 327 Gummow) using CoCO3 and Li2CO3 at 400 ° C.
One week of low temperature synthesis has been attempted. However, it must be said that such an attempt is unreasonable because the thermal decomposition of carbonate requires a considerably high temperature. Li2C
The use of LiOH in place of O3, although there is a possibility of low temperature synthesis, LiOH always absorbs CO ₂ from the air, because it produces a Li2CO3, it must constantly monitors the mixed amount of Li2CO3 , Therefore, L in the fired product
It was difficult to maintain and control the i / Co ratio constant.

In some cases, it may be impossible to give finally desired characteristics only by the firing process. The possibility of giving desired characteristics by post-treatment has hardly been studied, but if it can be realized, LiCo
There is no doubt that it will be a great practical advance in the synthesis of O2.

In order to increase the low electric conductivity of the positive electrode material, it has been customary to add about 10% of graphite powder to LiCoO 2 to form a positive electrode. Since the addition of such a conductive material lowers the ratio of the original positive electrode material, there is a problem that the capacity of the battery is reduced.

A lithium secondary battery having a folding structure proposed so far is disclosed in, for example, the above-mentioned Japanese Patent Laid-Open No.
In order to realize this structure, the electrode and the separator are bent with an extremely small curvature, and in order to realize this workability, the member is extremely flexible. Had to be. The separator is a polymer porous body having a thickness of about 25 μm, and is relatively flexible and has high strength. However, the positive electrode layer and the negative electrode layer are formed by binding powders with a small amount of binder, and have relatively poor flexibility and low strength. For example, when the electrode plate formed on the current collector foil is folded, if the bending curvature becomes smaller than a certain value, cracks occur in the electrode active material layer, which not only poses a problem in production, but also increases the electrode capacity during battery operation. There was also a problem that I could not draw out enough.

At present, a lithium secondary battery is desired to have a large capacity, and in order to improve the capacity per cell, the active material layer is made thicker or the active material layer is compressed by pressing or the like. The active material filling rate is being studied. The thicker the active material layer is and the higher the active material filling rate is, the poorer the flexibility becomes, and the more difficult it is to assemble a folded battery that does not cause cracks in the active material layer.

Even if the folded battery can be assembled without cracks in the electrode active material layer, when carbon is used as the negative electrode active material and lithium cobalt oxide is used as the positive electrode active material, both of them swell during charging. Therefore, tensile stress is generated in the current collector foil that is in close contact with the electrode layer. In the case of the folded structure, this stress becomes larger at the bent portion, so that the current collector foil or the like may be broken and the current collection may become impossible when the charge and discharge are repeated.

In addition, when the positive electrode and the negative electrode are laminated facing each other via the separator to form a battery, the electrode performance cannot be sufficiently brought out unless the contact of each member is good. The contact problem becomes more serious as the battery area increases and the number of laminated members increases due to the folding structure.

One of the challenges in developing a lithium secondary battery is an increase in discharge capacity. As described above, regarding the discharge capacity per volume, improvement of the filling rate of the active material is a problem.
Conventionally, an electrode active material having a single average particle diameter was used, but if the average particle diameter is single, the close packing ratio of the active material is limited (Fig. 40). The smaller the diameter, the smaller the packing rate of the powder (FIG. 41). That is, it can be seen from FIG. 40 that the powder packing rate φ increases as the powder volume fraction (PVC) increases, but the powder packing rate becomes constant from a certain point (CPVC).

The positive electrode contains a conductive material and a molding aid together with the active material as a composition, and the negative electrode contains the active material and a molding aid. In this case, the filling rate of the active material varies depending on the ratio of the active material in the composition. However, the discharge capacity per volume was not always a satisfactory value in the closest packing at the composition ratio currently performed. Also, a binder that is a molding aid is added to bind the powder of the active material and the like. However, if the amount of this binder is too large, the thickness of the surface of the powder that is coated becomes thick, and the reaction of the active material occurs. It has become a problem.

Further, one of the problems in developing a lithium secondary battery is a decrease in cycle life. In particular, for the negative electrode, carbon having a long cycle life is studied by forming the negative electrode using various kinds of carbon materials.
However, carbon having a large discharge capacity has a problem that the capacity reduction rate during charge and discharge is large. It is considered that the cause of this is that in the case of carbon having a large capacity, the precipitation of lithium metal occurs when the potential of the electrode decreases. Since metalization of lithium ions causes loss of reactivity, the capacity is reduced due to lack of lithium ions and a short circuit occurs inside the battery, resulting in reduced cycle life.

The present invention has been made to solve the above-mentioned problems of lithium secondary batteries, and LiCoO2 or Li which is suitable as a positive electrode material for lithium secondary batteries.
A stable synthesis method of a composition containing CoO2 as a main component and its evaluation method are provided, and LiCoO2 or LiCo is provided.
To improve the electrical conductivity of a composition containing O2 as a main component, and to synthesize a composition suitable for such purpose,
It is an object of the present invention to provide a structure and a manufacturing method of a lithium secondary battery which is excellent in discharge capacity and discharge cycle characteristics while being established.

[0029]

The first invention of the present invention is as follows:
When synthesizing a positive electrode material for a lithium secondary battery composed of LiCoO2 or a composition containing LiCoO2 as a main component,
Cobalt oxide as a starting material is previously 910
It was baked at 950 ° C.

The second invention is LiCoO2 or Li
When synthesizing a positive electrode material for a lithium secondary battery, which comprises a composition containing CoO2 as a main component, Li2 is added to cobalt oxide.
The above composition is synthesized using a mixed salt of CO3 and LiHCO3.

A third aspect of the present invention is the heat treatment using a cobalt compound and a lithium salt to obtain LiCoO2 or Li
When synthesizing a positive electrode material for a secondary battery comprising a composition containing CoO2 as a main component, a thermocouple for controlling a furnace temperature was inserted in the most central part of the calcined powder, and the upper limit of the calcining temperature was set to 900 ° C. is there.

A fourth aspect of the present invention is the heat treatment using a cobalt compound and a lithium salt to form LiCoO2 or Li
When synthesizing a positive electrode material for a secondary battery composed of a composition containing CoO2 as a main component, the firing temperature range of the first stage of the second stage firing is 735 to 785 ° C, and the firing temperature range of the second stage is
A temperature of 785 to 850 ° C is selected.

The fifth aspect of the present invention is the heat treatment using a cobalt compound and a lithium salt to form LiCoO2 or Li
When synthesizing a positive electrode material for a secondary battery composed of a composition containing CoO2 as a main component, 100 kg / c of mixed raw material powder was used.
m ² to 1000 kg / cm ² , preferably 500 kg /
While press-molding with a pressure of cm ² , the thickness of the molded body is set to 2 to 10 mm, preferably about 5 mm, and a spacer having a thickness of 1 mm or more is sandwiched and baked so that the gap between the molded bodies is 1 to 2 mm. It is a thing.

A sixth aspect of the present invention is to prepare cesium iodide pellets of calcined powder, measure the infrared absorption spectrum in the wave number range (10 to 50 μm) of 1000 to 200 cm ⁻¹ , and use the baseline for the infrared absorption spectrum. Approximately 600 cm
Co-O stretch absorption band with a peak at ^-1 is 600 cm ^-1
A symmetric region A around the splits in the other remaining region B disordered, from both the area ratio B / A, with the evaluation of the stoichiometry, the baseline method, about 247cm ^{chromatography From} the ratio of the absorbance of the O-Co-O bending angle absorption band of ¹ to the absorbance of the absorption band of about 600 cm ^-1 ,
-To evaluate the degree of perfection of O6 bond.

In the seventh invention, based on the result of the infrared absorption spectrum, the firing temperature is 500 to 900 ° C., the oxygen partial pressure of the atmosphere is any value from air to pure oxygen, and the post-treatment is carried out. Thus, the degree of perfection of stoichiometry and Co-O6 bond was readjusted.

The eighth invention is the main component LiCoO2.
When synthesizing cobalt from a cobalt oxide and a lithium salt, sodium salt or potassium salt is added to
Add more than 1% and less than 30mol%, and add Li1-xNaxCoO
2-y (x≤0.3, y≤0.3) or Li1-xKxCo
O2-y or Li1-x Nax1Kx2CoO2-y (x = x1 +
x2) composition.

In a ninth aspect of the present invention, the sodium salt or potassium salt is a carbonate, a hydrogen carbonate, a mixed salt of a carbonate and a hydrogen carbonate, or a eutectic hydrogen carbonate, and the upper limit of temperature rise is 900 ° C. or less. The thermocouple for controlling the furnace temperature was inserted in the most central part of the calcined powder.

A tenth aspect of the present invention is that a mixture of cobalt oxide and lithium salt is mixed with a metal oxide, such as Ag ₂ O, which decomposes in a temperature range up to the firing temperature to produce a metal powder.
It is obtained by adding 30 mol% to 30 mol% and baking.

The eleventh invention is one in which an oxide semiconductor such as Cu ₂ O is added in an amount of 5 mol% to 30 mol% to a mixture of cobalt oxide and a lithium salt, and the mixture is fired.

[0040] A twelfth aspect of the present invention is cobalt oxide and a mixture of a lithium salt, a metal oxide capable of forming a spinel structure by reacting with lithium, for example by adding 30 mol% of MnO ₂ from 5 mol%, is obtained by calcining .

The thirteenth invention is the area B / A ratio of the Co—O stretchable absorption band (peak approximately 600 cm ⁻¹ ) (non-normal part /
Normal part) is from 0.5 to 3.0, and about 247
The ratio of the absorbance of ^cm-1 absorption band and ~600cm ^-1 absorption band is in the 4.0 to 0.5 LiCoO2 or LiCo
A lithium secondary battery is constructed by using a composition containing O2 as a main component as a positive electrode material.

A fourteenth aspect of the present invention is one in which a folding battery has two or more electrode active material layers, which are folded by bending and then contact-molded.

A fifteenth aspect of the invention is one in which an electrode active material layer of a folding battery is provided only on a flat portion, an electrode active material layer on a curved portion is removed, and adjacent electrode active material layers folded by a collector foil are connected. is there.

The sixteenth invention is such that two or more electrode pairs are stacked in parallel and folded.

The seventeenth invention is one in which two or more electrode pairs are stacked at a right angle and are alternately stacked and folded.

In the eighteenth invention, the electrode active material layer is folded in an unpressed state and then pressed.

A nineteenth invention is a lithium secondary battery using an inorganic oxide as a positive electrode active material and carbon as a negative electrode active material, wherein the inorganic oxide is a positive electrode active material,
Alternatively, the carbon as the negative electrode active material has an average particle size of at least two kinds, and when the particle size of the large particles is 1, the particle size ratio of the small particles is 0.3 or less.

A twentieth aspect of the present invention is a lithium secondary battery in which the negative electrode active material is carbon, in which carbon, which is the negative electrode active material, has different raw materials, manufacturing conditions or characteristics.
It is composed of at least two types.

A twenty-first aspect of the invention is a lithium secondary battery in which the positive electrode composition comprises an inorganic oxide as a positive electrode active material, graphite as a conductive agent, and a binder as a molding aid, and the positive electrode active material is a powder. When the surface of the substance and the conductive agent are coated, the average coating thickness t _{B of the} binder is 3 ≦ t _B ≦
It is in the range of 16.

A twenty-second aspect of the present invention is a lithium secondary battery in which the positive electrode composition comprises an inorganic oxide which is a positive electrode active material, graphite which is a conductive agent, and a binder which is a molding aid, and the active material is the closest packing. When the material volume fraction is x _AC , the graphite volume fraction x _G is in the range of (1-x _AC ) / 3 ≦ x _G ≦ 1-x _AC .

The twenty-third invention is a lithium secondary battery in which an inorganic oxide is used as a positive electrode active material and carbon is used as a negative electrode active material, and the porosity P (%) in the electrode is 1
It is in the range of 0 ≦ P ≦ 30.

[0052]

According to the first aspect of the present invention, since cobalt oxide as a starting material is previously fired at a temperature of 910 to 950 ° C, the composition of the cobalt oxide is unified to Co3O4, and a positive electrode active material having a stable composition is obtained. To be

According to the second invention, cobalt oxide is added to L.
Since the composition is synthesized using a mixed salt of i2CO3 and LiHCO3, the cobalt oxide and the lithium salt react at a low temperature, the Li / Co ratio is easily controlled, and a positive electrode active material having a stable composition is obtained. .

According to the third aspect of the invention, the thermocouple for controlling the furnace temperature is inserted in the most central part of the fired powder, and the upper limit of the firing temperature is set to 900.
Since the temperature is set to ℃, the firing temperature can be easily controlled, an accidental temperature rise more than necessary can be appropriately prevented, and the inclusion of decomposition products can be avoided.

According to the fourth aspect of the present invention, 735 to 785 ° C. is selected as the first stage baking temperature range and 785 to 850 ° C. is selected as the second stage baking temperature range. A positive electrode active material having a uniform and stable composition can be obtained.

According to the fifth invention, the mixed raw material powder is
Press molding is performed at a pressure of 00 kg / cm ² to 1000 kg / cm ² , and the thickness of the molded body is set to 2 to 10 mm, and a spacer having a thickness of 1 mm or more is sandwiched so that the gap between the molded bodies is 1 to 2 mm and baked. Because
The reaction proceeds rapidly, and a positive electrode active material having a uniform and stable composition is obtained.

According to the sixth aspect of the present invention, cesium iodide pellets such as calcined powder are prepared and infrared absorption spectra are measured in the wave number region (10 to 50 μm) of 1000 to 200 cm ⁻¹ to evaluate stoichiometry. Since the completion of the Co-O6 bond is evaluated, the quality of the fired active material can be judged quickly and easily, which is useful for quality control.

According to the seventh aspect of the invention, the heat treatment temperature is 500 to 900 ° C. and the oxygen partial pressure of the atmosphere is between air and pure oxygen depending on the stoichiometry and the value of the degree of perfection of the Co--O 6 bond. The stoichiometry and the degree of perfection of the Co-O6 bond were readjusted by post-treatment after selecting an arbitrary value of, so that even if the active material is insufficiently fired due to a process failure, it should be re-fired properly. Can be done without waste.

According to the eighth invention, when LiCoO 2 is synthesized from cobalt oxide and lithium salt, sodium salt or potassium salt is added in an amount of 5 mol% of the lithium salt.
More than 30mol% and added, Li1-xNaxCoO2-y
(X ≦ 0.3, y ≦ 0.3) or Li1−xKxCoO2
-Y or Li1-x Nax1Kx2CoO2-y (x = x1 + x2)
Since the composition is set to K, Na ions are Li
It is incorporated into the structure of CoO2 and becomes a highly conductive active material.

According to the ninth aspect of the present invention, the sodium salt or potassium salt is a carbonate salt, a hydrogen carbonate salt, a mixed salt of a carbonate salt and a hydrogen carbonate salt, or a eutectic hydrogen carbonate salt. Ion is LiCo
It is taken into the structure of O2 and replaced with Li, and an active material having high conductivity is obtained by a low temperature reaction.

According to the tenth aspect of the invention, a mixture of cobalt oxide and lithium salt is decomposed in a temperature range up to the firing temperature to produce a metal powder, for example Ag ₂ O.
By adding the above, an active material in which metal particles having extremely fine and high electric conductivity are uniformly dispersed in the positive electrode active material can be obtained.

According to the eleventh invention, a mixture of cobalt oxide and lithium salt is added to an oxide semiconductor such as Cu ₂
Since O and the like are added, a positive electrode active material in which semiconductive particles are uniformly dispersed can be obtained, and an active material having high conductivity can be obtained.

According to the twelfth invention, since a metal oxide capable of forming a spinel structure by reacting with lithium, such as MnO _2, is added to a mixture of cobalt oxide and a lithium salt, LiCoO 2 and spinel having a layered structure are added. An oxide composite having a structure is obtained, and a positive electrode active material having a high battery capacity is obtained.

According to the thirteenth invention, since the composition having the optimum value of the stoichiometry and the perfectness of Co--O6 bond is used as the positive electrode material, a positive electrode active material having a uniform composition and a large capacity is used. A battery is obtained.

In the fourteenth invention, since the folding battery has two or more electrode active material layers, which are folded by bending and then adhered to each other, the single layer of the electrode active material layer becomes thin, so that it is flexible against bending. It is possible to assemble the battery without increasing cracking properties in the electrode layer. Further, when the electrode manufacturing method is wet molding, the film thickness becomes thin, so that the drying time is shortened even if the number of molded sheets is increased, which leads to a reduction in manufacturing energy.

In the fifteenth invention, since the electrode active material layer of the folding battery is only the flat portion, the electrode active material layer of the curved portion is removed, and the adjacent electrode active material layers folded by the collector foil are connected. The electrode layer is treated as a flat plate only,
Since there is no need to bend, battery assembly is possible without cracking. Further, since the material such as the active material can be used without waste, the material yield of the electrode active material is improved. Further, the portion of the curved portion where the electrode is removed may be a cavity, but if a separator material or the like is inserted as a semi-cylindrical spacer corresponding to the curvature of the current collecting foil, a function as an electrolyte reservoir can also be expected. Not only that, even if the electrode expands or contracts during charge / discharge of the battery, the spacer at the bent portion relaxes the stress applied to the current collector foil, so that a stable charge / discharge cycle can be expected without breakage.

According to the sixteenth invention, since two or more electrode pairs are stacked in parallel and folded, the curvature of the electrode on the outside of the folding is larger than that on the inside.
The probability of cracking during battery assembly is reduced. Further, although the electrode in the inner portion has a small curvature, since it is supported by the outer member, the strength is improved, and thus the generation of cracks can be avoided. Further, even during charging / discharging of the battery, the stress on the current collector foil due to the swelling / shrinkage of the electrode layer is relatively small in the portion having a large curvature, so that the breakage of the current collector foil is suppressed.

In the seventeenth invention, since two or more pairs of electrodes are folded at right angles and are alternately overlapped with each other, the curvature of folding the electrode layers can be designed to be larger than the breaking curvature of the electrodes, so that the electrodes are not cracked. The layers are easier to fold and the manufacturing yield is improved. Further, even when the battery is charged / discharged, since the curvature is large, the stress on the current collector foil due to the swelling / shrinkage of the electrode layer is relatively small, so that the current collector foil is prevented from breaking.

According to the eighteenth aspect, since the electrode active material layer having a relatively high porosity is folded in an unpressed state and then pressed, the electrode active material layer is easily bent, and the contact between the battery constituent members is improved, and the contact resistance is improved. Is reduced and battery characteristics are improved.

According to the nineteenth invention, by mixing at least two kinds of powders having different particle sizes in the positive electrode and the negative electrode active material, the filling rate of the active material can be improved. As a result, the discharge capacity per unit volume can be increased and the battery performance can be improved.

According to the twentieth aspect, at least two kinds of carbons having different potential characteristics are mixed as the negative electrode carbon of the lithium secondary battery to raise the average potential and suppress the precipitation of lithium metal due to the reduction of the potential. You can Therefore, loss due to metalization of lithium ions can be eliminated, reduction in capacity can be reduced, short circuit inside the battery can be prevented, and reduction in cycle life due to charge / discharge can be reduced.

According to the twenty-first aspect, when the binder in the positive electrode composition is coated on the surfaces of the powdery positive electrode active material and the conductive agent, the average coating thickness t _B of the binder is set to an appropriate value. As a result, the reaction of lithium with the active material can be made smooth, and the discharge capacity per weight of the active material can be increased.

According to the twenty-second aspect, by optimizing the graphite concentration in the positive electrode composition, the filling rate of the positive electrode active material can be increased and the discharge capacity per unit volume can be increased, thereby improving the battery performance. Can be improved.

According to the twenty-third aspect, by optimizing the porosity in the electrode, the reaction of lithium ions between the active material and the electrolytic solution can be made smooth and the discharge capacity per weight is increased. be able to.

[0075]

【Example】

Example 1. First, the invention according to claims 1 to 7 will be described. 1 kg of commercially available Co3 O4 powder was placed in an alumina crucible, placed in an electric furnace set at a temperature of 925 ° C., and fired in air for 3 hours. Cobalt oxide is always undecomposed basic cobalt carbonate (2CoCO3 ・ 3Co (OH) 3)
However, it is decomposed by firing in air at 910 to 950 ° C., and the composition is unified into Co3O4. 1 (a) and 1 (b) show the X-ray diffraction results before and after the heat treatment of cobalt oxide (at 925 ° C. for 1 hour in air), respectively, in which ◯ indicates LiCoO 2 and X indicates basic cobalt carbonate. Indicates. From the figure, it can be seen that this heat treatment completely eliminates the basic cobalt carbonate, resulting in a pure Co3O4 composition.

722.4 g of this baked powder was mixed with Li2CO3.
332.52 g was taken and thoroughly mixed and pulverized in a dry ball mill for 5 hours. Next, the mixed powder is 50m in diameter
m, thickness 5 mm, press pressure 500 kg / cm ²
Press-molding with 1 mm thick, insert 1mm thick pieces of alumina spacers into the press-molded body at appropriate places, and press for 5 minutes for 1 minute.
Temperature from room temperature to 740 ° C in air
It was baked at 740 ° C. for 10 hours. After that, the temperature was raised to 820 ° C. at a heating rate of 5 ° C. for 1 minute and then 20
Held for hours. After that, the power of the electric furnace was turned off and the system was cooled to room temperature as it was. The fired powder taken out was pulverized for 2 hours using a dry ball mill, and then 20 times by a mechanical sieve.
Large particles larger than micron m were removed.

By press molding, LiCoO 2
In addition to facilitating the synthesis reaction, the press-molded body was thinly molded, and an appropriate gap was provided between the molded bodies to easily dissipate the heat generated by the LiCoO2 synthesis reaction. Moreover, by performing the two-stage firing, L
The heat generated during iCoO2 synthesis was dissipated, and the temperature rise during firing was kept below 900 ° C, effectively preventing an unexpected temperature rise.

That is, the inventors have obtained the following findings as a result of earnest research using thermal analysis as to the production and decomposition during LiCoO 2 synthesis. FIG. 2 shows the measurement results of TG-DTA showing the decomposition of LiCoO2. The solid line is DT
A, the dotted line is the change in TG. LiCoO2 itself decomposes at 1130 ° C. and again produces Co3O4 (X-ray diffraction data omitted). Decomposition heat is about 82 cal /
It is g. It is therefore self-evident that the synthesis temperature of LiCoO2 should not exceed this temperature. Furthermore, as shown in FIG. 3, the inventors have confirmed from the X-ray diffraction results of the samples with different firing temperatures that there is an unclear decomposition temperature range between 930 and 1030 ° C. This decomposition temperature range is also confirmed from the infrared absorption spectrum shown in FIG.
FIG. 4A shows the infrared absorption spectrum of the heat-treated sample, the horizontal axis represents wavelength (microns), and the vertical axis represents transmittance. Numbers indicate peak wavenumbers (cm ^-1 ). (B) is the absorbance ratio of the sample (to 247 cm ⁻¹ absorption band / to 600 cm ⁻¹ absorption band). The horizontal axis represents the wave number (cm ^-1 ) and the vertical axis represents the absorbance ratio.
From this, it is clear that in the synthesis of LiCoO2, the temperature should not be raised above this decomposition temperature range (930 ° C to 1030 ° C). It can be understood from FIG. 4 that when the temperature is raised to 1000 ° C., it is transformed into a foreign substance.

However, when synthesizing LiCoO 2,
To prevent the temperature from rising above 00 ° C, set the furnace temperature to 9
It is not enough to keep it at 00 ° C. There is a problem of the exothermic amount of the synthetic reaction, which the inventors found out, which will be described below.

FIG. 5 shows the result of thermal analysis (TG-DTA), and Table 1 shows the amount of heat.

[0081]

[Table 1]

The samples had Li / Co ratios of 0.6, 0.8,
There are four types, 1.0 and 1.2. Co3O4 and Li2CO3 were used in this experiment. Speaking of the composition of Li / Co = 1, the endothermic peak (endothermic amount 48.4c from 675C).
Al / g) starts and ends at 735 ° C. After that, an exothermic reaction immediately starts and ends before 900 ° C. The calorific value ΔH is 38.5 cal / g. Since the specific heat of the sample is about 0.2 cal / g ° C, LiC
Considering that the amount of heat generated during the synthesis of oO2 is generated in an adiabatic state, it is large enough to raise the temperature of the sample by about 200 degrees.
In other words, if you do not dissipate this heat generation sufficiently well,
It can be assumed that the sample temperature easily exceeds 900 ° C.
In fact, if a large amount of the sample is fired, the furnace temperature will be 90%.
Even if it was kept at 0 ° C, it was unavoidable to raise the temperature above 900 ° C.

In order to sufficiently dissipate the heat generation and prevent an accidental temperature rise exceeding 900 ° C., two-step firing was carried out. 735-785 degreeC is suitable as a baking temperature range of the 1st step. As a result, a considerable part of the calorific value from 735 ° C. can be diffused on the low temperature side. afterwards,
The temperature is raised from 785 ° C. to 850 ° C., and the second stage firing is performed. At this time, most of the exothermic heat of the LiCoO2 synthesis reaction is dissipated first, so that an unexpected temperature rise is unlikely to occur. It should be noted that this object can be reliably achieved by inserting the furnace temperature control thermocouple into the most central portion of the fired powder.

[0084] To further promote the synthesis reaction of LiCoO2, a powder from 100kg / cm ² 1000kg / cm ²
Mold at the pressure of. The suitable pressure range may be determined in consideration of the size of the die used and the performance of the handheld press. At this time, the thickness of the molded body is preferably 2 to 10 mm in order to dissipate the heat generation of the LiCoO2 synthesis reaction sufficiently quickly. If it is 10 mm or more, reaction heat tends to stay inside the molded body, and if it is 2 mm or less, it is difficult to take out the molded body from the mold.

By stacking the compacts at the time of firing with a gap of 1 to 2 mm, it is possible to dissipate the reaction heat and improve the filling rate. Table 2 shows the X-ray diffraction intensities of the powder sample and the pressed sample.
It can be seen that the synthesis reaction proceeds easily.

The evaluation of the calcined LiCoO 2 can be roughly performed by the powder X-ray diffraction method as described above. For example, as shown in Table 2,

[0087]

[Table 2]

Three strong diffraction lines (45.2, 37.3,
18.8) absolute intensity, or their ratio 18.8 / 45.2 or 18.8 / 37.3. However, as explained earlier, the X-ray diffraction findings do not give detailed information.

Next, the evaluation method by infrared absorption according to the present invention will be described in detail. FIG. 6 shows the portion of the Co—O stretchable absorption band with the baseline drawn. The shaded area centered at about 600 cm ^-1 is Co-O6 (C in LiCoO2).
o is surrounded by 6 oxygens, and Li is also surrounded by 6 oxygens), and the rest of the tail portion is due to Co—O 6 -x (a portion where oxygen is partially removed). It is considered to be a thing. The former is called the normal part (A) and the latter is called the non-normal part (B).
Taking the (non-normal part / normal part), it became clear that this ratio was related to the stoichiometry (O / Co) of LiCoO2 (FIG. 7). The area is measured with a planimeter. Therefore, by mixing a few mg of the sample powder with 0.3 g of cesium iodide powder, preparing a tablet sample, and measuring with an infrared spectroscope, the stoichiometry can be easily evaluated.

Further, FIG. 8 shows an infrared absorption spectrum in the case of replacing Li7 in LiCoO2 by Li6.
The absorption band at 279 cm ^-1 is 292 cm due to Li6 substitution.
To ^{over 1,} the absorption band of ^229cm-1 since it is clear that the shift to ^239cm-1, the absorption band of the two can conclude that is based on Li over O vibrations. Compared to the theoretical value of the shift ratio (square root of 7/6) of 1.08, both shift ratios are slightly smaller, 1.04. In addition, two of the absorption band ^247cm-1 and ^224cm-1, which does not shift, O-
It is considered that this is due to Co—O bending vibration. It was previously shown in FIG. 4 that the absorbance ratio between the 247 cm ⁻¹ absorption band and the 598 cm ⁻¹ absorption band greatly changed above the X-ray diffraction intensity, reflecting the firing conditions. Therefore, this absorbance ratio can be regarded as the completeness of the Co-O6 bond. This is because the O—Co—O bending vibration reflects the degree of perfection of the omnidirectional crystal structure.

As is clear from the above description, 10
From the infrared absorption spectrum of 00-200 cm ^-1 , LiC
oO2 stoichiometry (O / Co) and Co-
It was possible to evaluate the degree of perfection of the O6 bond. The degree of perfection of the Co—O6 bond is a strong indicator of the degree of perfection of the layered structure of the LiCoO2 crystal, and the inventors have confirmed that a sufficiently high value has excellent properties as a positive electrode material. It is self-evident that compositions with better stoichiometry have better properties in terms of lithium ingress and egress. Therefore, these two parameters are LiCoO2
Since it largely reflects the characteristics of the positive electrode material of LiCoO2 or LiC
It can be used as a criterion for judging the quality of the composition containing oO2 as a main component. Above, from the infrared absorption spectrum, LiC
It was revealed that two important parameters of oO2 can be evaluated.

The powders 1 to 1 prepared in Example 1 above
After taking 2 mg and mixing well with 0.3 g of cesium iodide powder, the mixture was molded into a tablet having a diameter of 13 mm by a press (molding pressure is 2 ton / cm ² ), and an infrared spectrometer 883 manufactured by Perkin Elmer Co. 1000cm ^-1 to 200cm ^-1
When the infrared absorption spectrum was measured, the area ratio of (non-normal part / normal part) was found to be 0.7, or 247 cm ^-1 / 600 cm, as an index of the O / Co ratio.
The absorbance ratio of ^-1 was 1.5.

Example 2. The calcined powder does not always have the desired parameters, and it may be necessary to adjust the X-ray diffraction intensity and the like by appropriate post-treatment. In such a case, according to the values of the two parameters of the sample, the heat treatment temperature is set to 500 to 900 ° C., and the oxygen partial pressure is set to an appropriate value between air and pure oxygen, and the heat treatment is performed to obtain the desired parameter value. Can be changed to.
This is because during the post-treatment, the LiCoO2 powder adjusts the amount of oxygen according to the post-treatment conditions to complete the crystal structure. Table 3 shows examples of three samples (A, B, C).

[0094]

[Table 3]

The sample A can be increased in intensity at the 18.8 degree peak by firing in O ₂ . Sample B can be fired in air to increase the intensity of the peak at 37.3 degrees and the peak at 45.2 degrees in O ₂ . Sample C is 1 even if fired in air
The intensity of the 8.8 degree peak can be increased.

Example 3. Make a cesium iodide tablet of commercially available LiCoO2 powder, 1000 cm-1 to 200 cm
The infrared absorption spectrum between -1 was measured. As a result, B
The / A area ratio was 0.7, and the completeness of the Co-O6 bond was 0.64. This powder was calcined in air at 900 ° C. for 2 hours and cooled in a furnace. After the heat treatment, a cesium iodide tablet was prepared, and the infrared absorption spectrum was measured and evaluated in the same manner. As a result, the B / A area ratio increased to 1.15.
6 Bond integrity was unchanged at 0.69. Using this powder after the heat treatment, a positive electrode was prepared, a lithium battery was manufactured, and the charge / discharge characteristics were measured. As a result, the characteristics were significantly improved compared to the powder before the heat treatment.

Example 4. Co3O4 240.8g (1m
ol), 88.67 g (1.2 mo) of Li2CO3
1) and 40.76 g (0.6 mol) of LiHCO3 were weighed and mixed well with a ball mill. In Example 1, the case was described in which the powder to be fired was press-molded and then was fired in two stages. However, the powder was not press-molded, and the thermocouple for controlling the furnace temperature was placed at the most central portion of the powder in the powder state. After being inserted, it was baked in air at 900 ° C. for 25 hours. Since the heat generated by the synthetic reaction accumulates inside the fired powder,
If a thermocouple for controlling the furnace temperature is inserted in the most central part of the calcined powder, the input to the electric furnace can be finely controlled according to the temperature rise inside the powder, so the temperature rises above 900 ° C. Don't worry. Since the most central part of the powder tends to have the highest temperature, inserting the thermocouple in the most central part can always detect the maximum temperature of the fired powder. When evaluated by an infrared spectroscope, the B / A ratio was 1.0, and Co-O6
The bond perfection was 2.0.

Example 5. In Example 1, LiC
When synthesizing oO2, Li3CO3 was mixed with Co3O4 to synthesize Li3CO3 and LiHCO3.
Synthesis may be performed using a mixed lithium salt of 3. That LiHCO3 is easily decomposed at a temperature lower than the Li2 CO3, also unlike LiOH, it without absorbing the CO ₂ in air, it is easy to manage the Li / Co ratio.

Example 6. Next, the invention according to claim 8 will be described. Co3O4 (8.023 g) was mixed with Li2CO3 (3.283 g) and NaHCO3 (2.511 g) in an automatic mortar for 2 hours (Na addition amount: 10 mol%). This mixed powder was fired in an electric furnace in air at 850 ° C. for 20 hours. When the electric resistance value was measured, it was 20 KΩ. This value is about 1/5 of the value of 1 MΩ when Na is not added.
00, it can be seen that the active material has high conductivity.

The sample in which Na is replaced will be further described. The addition amount of Na is 10, 20, 30 mol%,
As used in here is the Co3O4 and Li2CO3, Na ₂ CO3, was thoroughly pulverized in a mortar. In FIG. 9, Na-added Li
TG-D on thermal behavior and Na addition amount during CoO2 synthesis
The TA measurement result is shown. The horizontal axis represents temperature (° C.) and the vertical axis represents heat quantity. Samples were added at concentrations of 10, 20, 30 mol% and 4
It is a seed. TG-DTA measurement result Temperature rising rate 10K / mi
n) is shown. Regardless of the amount of Na added, it shows one broad endothermic peak from around 350 ° C to around 460 ° C. Since there is no heat change other than this, it can be inferred that Na sufficiently replaces Li. FIG. 10 shows the X of this sample.
The change in line diffraction intensity was shown. All the three peaks having high intensity show a linear relationship with the amount of Na added. Figure 11
(A), (b) and (c) are the addition amounts of Na of 10 and 2, respectively.
The X-ray-diffraction result at the time of scanning at a diffraction angle 2 (theta) = 70-10 in 0,30 mol% is shown. Diffraction pattern is that of essentially LiCoO2, those marked with v marked with a small diffraction peak NaCo ₂ O ₂ (ASTM2
7-682), α-Na0.75CoO ₂ (ASTM3
2-1068), β-Na0.6CoO ₂ (ASTM3
0-1181) and so on.

The addition of Na to LiCoO 2 is described in the literature (J. Power Sources, 39 (1992)).
313 Bludska et al.) And reported that using each carbonate up to 20 mol% Na, 4
Samples are prepared by firing at 00 ° C. for 30 hours, 650 ° C. for 8 hours, and 900 ° C. for 8 hours. It is concluded that the addition of Na increases the mobility of Li, and the Na concentration of 5 mol% is the best. According to our experimental results, it was found that the optimum amount of Na added is more than 5 mol% and 30 mol% or less. That is, when the amount of Na added exceeds 30 mol% and the amount of Li further decreases, the capacity of the battery decreases. On the other hand, if it is less than 5 mol%, the mobility of Li decreases and the resistance decreases.

Example 7. Next, a sample in which K is replaced will be described. The amount of K added is 10, 20, 30 mol%
, And the was used Co3O4, Li2CO3, K ₂ CO3
Is. Explaining the K addition amount of 20 mol%, C
o3O4, 8.023 g, Li2CO3 3.283 g,
2.002 g of KHCO3 was mixed in an automatic mortar for 2 hours. This powder was fired in an electric furnace in air at 850 ° C. for 20 hours. When the electric resistance was measured, it was 43Ω.

As described above, in the sixth and seventh embodiments,
As a result of substituting a part of lithium with sodium or potassium, Li ₁ -x Na x CoO ₂ or Li ₁ -x was obtained as a firing composition.
KxCoO ₂ or Li1-xNax1Kx2 (x1 + x2 =
x) is obtained, and K ion or Na ion is Li
When incorporated into the structure of CoO2, it becomes a highly conductive active material.

Example 8. Next, the invention according to claim 9 will be described. The sodium salt or potassium salt is used as a carbonate, a hydrogen carbonate, a mixed salt of a carbonate and a hydrogen carbonate, or a eutectic hydrogen carbonate, because the thermal decomposition temperature is lowered and low temperature firing becomes possible.
It is possible to obtain a calcined powder having a less disordered crystal structure. Such an example is shown. Co3O4, 8.023g, Li2CO3 3.283g, NaHCO3, 0.837g, KHCO
3, 0.501 g were mixed in an automatic mortar for 2 hours (Na added amount: 10 mol%, K added amount: 10 mol%), and this powder was fired in an electric furnace in air at 850 ° C. for 20 hours. When the electric resistance of the fired product was measured, it was 100Ω. 12
The measurement results of TG-DTA of this sample are shown in FIG. 36
The endothermic peak around 0 to 500 ° C. tends to become smaller as the amount of K added increases, but the endothermic peak near 850 ° C. (data not collected) has a reverse tendency. The small endothermic peak around 850 ° C is observed when the added amount does not replace Li quickly (temporarily Li / Co
This is because <1 and Li becomes insufficient. ), Ag ₂ O
It is also seen when Cu and Cu ₂ O are added. Figure 1
3 shows the relationship between the K concentration and the diffraction intensities of the three diffraction peaks. Refraction only at the 18.8 degree peak is different from the case of adding Na. In FIG. 14, 2θ = 70 to 10
It showed diffraction peaks between degrees. The small peaks marked with X are unidentified, but the strong peaks are of LiCoO2 structure. In addition, such NaHCO3,
Addition of Na ₂ CO 3, KHCO 3, and K ₂ CO 3 alone or in combination not only causes a large decrease in the thermal decomposition temperature of the lithium mixed salt, but also a decrease in the melting point, so the possibility of further low-temperature synthesis is greatly increased. It is a thing.

Example 9. Next, the invention according to claim 10 will be described. Li3CO3 on Co3O4, 8.023g
Was mixed with 3.694 g, Ag2O, and 11.587 g in an automatic mortar for 2 hours (Ag addition amount: 10 mol%). This mixed powder was fired in an electric furnace in air at 850 ° C. for 20 hours. Since it decomposes during the firing to form a metal powder, LiCoO2, which is extremely fine and in which the metal powder is uniformly dispersed, can be obtained. When Ag ₂ O is used, a part of Ag is Li
, So that the composition is Li1−xAgxCo.
O ₂ : Agy (x + y = added amount). Since the metal powder has high electric conductivity, a composition having high electric conductivity can be obtained as a result. When the electric resistance value was measured, it was 52 KΩ.

In FIG. 15, Ag ₂ O is set to Ag and 1
0,20,30Mol% added sample (Co3O4: Li ₂
The TG-DTA measurement result (in air) of C03) is shown.
The endothermic peak P1 from around 250 ° C. increases as the amount of Ag added increases. This is because Ag ₂ O contains Ag and O ₂
It is based on the reaction that decomposes into, and weight loss is observed in this temperature range (data not collected). Therefore, in the temperature range above this temperature, LiCoO2 is present in the presence of metallic Ag.
It is clear that the synthetic reaction of is progressing. 400
The endothermic peak P2 from around ℃ does not change so much depending on the added amount of Ag, but the endothermic peak on the high temperature side from 850 ° C. tends to increase as the added amount of Ag increases (data not collected).

FIG. 16 shows X-ray diffraction peaks between 2θ = 70 to 10. Basically, there are two diffraction peaks of LiCoO2 and metallic silver (indicated by a star). FIG. 17 shows the relationship between the added amount of Ag and the diffraction intensity. The diffraction intensity from metallic silver increases with Ag concentration,
It can be seen that the diffraction intensity from LiCoO2 decreases conversely.

Although silver oxide was added in the above-mentioned examples, other metal oxides which decompose in the temperature range up to the firing temperature to produce metal powder, namely gold oxide, platinum oxide, iridium oxide, osmium oxide, Alternatively, palladium oxide or the like has the same effect.

Example 10. Next, the invention according to claim 11 will be described. Li3C on Co3O4, 8.023g
3.694 g of O3 and 7.154 g of Cu2O were mixed in an automatic mortar for 2 hours (Cu addition amount 10 mol%). This mixed powder was fired in an electric furnace in air at 850 ° C. for 20 hours. When the electric resistance value was measured, it was 13 KΩ (1 MΩ before addition).

As a result of the oxide semiconductor having high electric conductivity being uniformly dispersed in the produced LiCoO 2 powder, a composition having high electric conductivity can be obtained. In particular, when Cu ₂ O is used, a part of the added Cu replaces Li, so that Li1-xC
A composition such as uxCoO ₂ : (Cu ₂ O) y (x + y = added amount) can be obtained. Cu ₂ O does not thermally decompose at 900 ° C. In addition to Cu ₂ O, NiO, FeO, Cr ₂ O 3,
Since MoO ₂ is a type of semiconductor that is sufficiently fired in air and its electrical conductivity increases as oxidation progresses, L
Oxidation during the synthesis reaction of the composition containing iCoO2 or LiCoO2 as the main component further improves the electric conductivity, which is preferable.

Further, NiO, FeO and Cr ₂ O 3 are Li
CoO2 has the possibility of substituting with Co instead of substituting during the synthesis reaction. Thus, for example the addition of NiO, LiCo1-xNixO _2: composition of NiOy (x + y = amount) will be obtained. The same applies to the addition of FeO and Cr ₂ O.

FIG. 18 shows a Cu-added sample (Cu = 10,
The TG-DTA measurement results (in air) of 20 and 30 mol%) are shown. Endothermic peak P1 from 370 ℃ to 470 ℃
Does not change depending on the Cu concentration, but the endothermic peak P2 above 480 ° C. and the endothermic peak P3 from 810 ° C. (enlarged view in the figure) tend to increase as the Cu concentration increases. FIG. 19 shows the X-ray diffraction result. The star is Cu ₂ O
However, it is basically LiCoO2. The amount of added Cu is 10 mol% and 30 mol% is Co.
A diffraction peak of 3O4 can be seen, but this is a baking time of 30.
Since it was a minute sample, it was not observed in the sample fired for a longer time.

20A and 20B show three diffraction peaks (2θ = 45.2) of the Cu-added sample and the Ag-added sample, respectively.
, 37.3 degrees, 18.8 degrees). C
Since the u-added sample has a wider concentration range in which the linearity is established, it can be inferred that Cu has a wider concentration range in which it can be replaced with Li than Ag.

Example 11. Next, the invention according to claim 12 will be described. Co3O4, MnO on 8.023g
2,8.181 g and 3.694 g of Li2CO3 were mixed in an automatic mortar for 2 hours (Mn content 30 mol%). This mixed powder was fired in an electric furnace in air at 850 ° C. for 20 hours.

The LiCoO 2 synthesis reaction is a reaction requiring an extra oxygen as shown in the following chemical formula.

[0116]

[Chemical 2]

Usually, LiCoO 2 synthesized at high temperature is deficient in oxygen. That is, LiC
The composition is represented by oO2-y (0 <y <0.3).
Oxygen generated from the oxide decomposed during the synthesis of LiCoO2 has an effect of compensating the above-mentioned insufficient oxygen amount and improving the stoichiometry.

There is also a synthetic method (M, G, S, R, T) using a lithium peroxide in order to reduce the oxygen deficiency.
homeset al. , Mat. Res. Bul
l. , 20 (1985) 1137).

A sample in which Co replaces Mn will be described. The amount of Mn added is 10, 20 and 30 mol%,
Co3O4, MnO2 and Li2CO3 were used. FIG. 21 shows the TG-DTA measurement result when MnO _{2 was} added. 48 from around 360 ° C regardless of the amount of Mn added
It shows one endothermic peak up to around 0 ° C. Since there is no other heat change than this, it is considered that Mn undergoes lithiation to the same extent as Co.

FIG. 22 shows the X-ray diffraction results measured at diffraction angles 2θ = 70 to 10. The amount of lithium manganese oxide increases as the amount of Mn added increases. FIG. 23 shows the infrared absorption spectrum of MnO2 added. The peak at the wave number of 660 cm ⁻¹ indicated by the arrow is a peak peculiar to the spinel structure. Therefore, from the infrared absorption spectrum, it can be said that in the sample to which Mn is added, the layered structure of LiCoO2 and the spinel structure of lithiated manganese oxide coexist, and the crystal structure is composite. Lithiated manganese oxide having a spinel structure is used as a positive electrode material for high-performance lithium secondary batteries in LiCo.
It is a strong candidate material comparable to O2. Since the spinel structure has many tunnel structures capable of accommodating Li, the Mn-added composition having a composite crystal structure has an excellent lithium accommodating capacity. That is, a secondary battery having a high capacity can be obtained.

Table 4 shows that Na, which has been explained so far,
K, Ag, Cu2O and MnO2 were added to 5, 10, 20, 3
The electric resistance measurement result of the sample added with 0 mol% is shown.

[0122]

[Table 4]

The electric resistance of the fired powder was measured by the following procedure. Take 1g of finely crushed powder in an agate mortar and press the press to ² ton / cm ^{2 on a} 13mm disk.
Was molded under pressure. Both sides of this molded body were sandwiched between copper plates, and the electrical resistance was measured with a digital voltmeter.

The results in Table 4 are first compared with the above-mentioned literature values for LiCoO 2. The electric resistance value of LiCoO2 is 26.5 Ω when the above-mentioned literature value of 100 Ωcm is converted into this measurement disk size. In Table 4, our value is 1 MΩ. The reason for this difference may be the difference in particle size of the powder or the difference in pressing pressure. Incidentally, since these concrete numerical values have not been raised, further consideration is impossible.

When K is added, the amount becomes 1 / 100,000 at 20 mol% or more, and when Ag is added, the amount becomes 1 / 100,000 at 30 mol% or more. With addition of Cu, it is one thousandth above 20 mol%
In addition, when Na is added, the amount becomes one thousandth at 30 mol% or more. It should be noted that no decrease in electrical resistance was observed with the addition of Mn.

As described above, by adding K, Ag, Cu, and Na, LiCoO 2 having an essentially high electric resistance value can have a low resistance, and the internal resistance of the positive electrode can be reduced. In particular, it is remarkable in the K additive and the Ag additive.
A considerable effect can be expected with Cu additive and Na additive.

Example 12. Next, the invention according to claim 13 will be described. First, the infrared absorption spectrum (1000
From 200 cm-1) will be described. As described above, the Co-O6 stretchable absorption band (600 cm) is divided into the normal part (A) and the non-normal part (B), and the calculated area ratio (B / A) is related to stoichiometry (O / Co). It is a parameter to do. The smaller the B / A ratio, the more Li
The lower the oxygen deficiency in CoO2 and the higher the B / A ratio, the greater the oxygen deficiency. As shown in FIG. 24, in the relationship between B / A and the diffusion coefficient of lithium ions in the positive electrode active material, the B / A value has a maximum in the vicinity of 2. The diffusion coefficient of lithium ions was measured by a cyclic voltammetry method which is a general electrochemical measurement method. The diffusion coefficient of lithium ions is related to the current at the time of battery reaction, and the reaction current is large when the diffusion coefficient is large. A diffusion coefficient of 10 ^-12 or more is desirable, and therefore B /
The range of A is preferably 0.5 to 3.0.

As described above, the absorption band (Co--O6) at 247 cm ^-1 is used. The bending ratio of the bond) and the absorption band at 600 cm ^-1 is Co-O6 It is considered to indicate the degree of perfection of the bond. The smaller this value, the lower the degree of perfection, and the larger this value, the higher the degree of perfection. As shown in FIG. 25, Co-O
6 until the ratio of the absorbance of the absorption band of the absorption band and 600 cm ^-1 of 247cm ^-1 which is considered an indicator of binding of perfection is 4,
The discharge capacity per active material weight increases. Since the discharge capacity suitable for practical use is considered to be 70 mAh / g or more, the absorbance ratio is preferably 0.5 to 4.0.

As described above, the evaluation of these two points is very important that can never be obtained from the X-ray diffraction results. Table 5 shows a summary of the additives from infrared absorption.

[0130]

[Table 5]

Of the additive elements, only Na and Mn are B / A.
It is clear that it has the effect of reducing the ratio. That is, the addition of Na and Mn makes oxygen deficiency less likely to occur.
On the contrary, K, Ag and Cu do not have such a special effect, and give the same B / A ratio as in the case of no addition.

Next, Co-related to the degree of perfection of the crystal structure
Looking at the effect of additional elements on the degree of perfection of O6 bonds, Na and K have similar effects, and it seems that Na is slightly superior. Ag, Cu, and Mn are not so different and do not seem to have a particularly excellent effect as compared with Na and K.

Example 13 Next, the invention according to claim 14 will be described. In this example, a secondary battery using the above positive electrode material and a method for manufacturing the same will be described. FIG. 26 is a cross-sectional configuration diagram of the lithium secondary battery according to this example, and the wet method was used as the method for forming the electrode layer. The positive electrode is
3 parts by weight of PVdF as a binder were dissolved in 33 parts by weight of an NMP solution as a solvent to prepare a binder solution, and 58 parts by weight of LiCoO2 powder as a positive electrode active material 1 and 6 parts by weight of graphite powder as a conductive agent were dispersed in the solution for coating. A liquid was created. This coating liquid is a current collector, thickness 2
After coating and drying on a 0 μm aluminum foil 4, a long electrode sheet having a width of 30 cm and a thickness of about 150 μm was prepared. Furthermore, the width is 30 cm and the thickness is about 1 on the coated base material coated with silicon in the same manner.
After coating and drying so as to have a thickness of 50 μm, a positive electrode independent film sheet was prepared by peeling from the coating substrate.

The negative electrode was prepared by dissolving 3 parts by weight of PVdF as a binder in 33 parts by weight of an NMP solution as a solvent to prepare a binder solution, and 62 parts by weight of carbon powder of mesophase microbeads and 2 parts by weight of lithium carbonate as the negative electrode active material 2 in this solution. A coating liquid was prepared by dispersing. This coating solution was applied on a copper foil 5 having a thickness of 20 μm, which is a current collector, and dried, and an electrode sheet having a width of 31 cm and a thickness of about 150 μm was prepared. Further, similarly, a negative electrode independent film sheet was prepared by drying the coating on a coating base material coated with silicon so as to have a width of 31 cm and a thickness of about 150 μm, and then peeling the sheet from the coating base material.

As shown in FIG. 26, a two-layer positive electrode and a negative electrode body, in which an electrode independent film sheet is stacked on the collector foil integrated electrode body prepared for the separator 3, are opposed to each other, and 30c is formed in the length direction.
A battery element structure was created by folding it four times every m. About 3 cm of the separator 3 was made to protrude from the positive electrode and the negative electrode at the beginning and the end of folding, respectively. After that, these battery element structures were pressed together to improve the contact of each member.

The prepared battery element of about 30 cm square was fitted in a polyethylene frame, connected to the separator and the reservoir protruding from the battery element, further sandwiched by two 0.1 mm-thick stainless steel plates, while pressing the periphery. Heat fusion,
A quadrangular flat cell was prepared.

The entire battery was placed in a vacuum container and placed under vacuum (-75
(0 mmHg or less), and then 1: 1 of ethylene carbonate and dimethoxyethane to the injection port provided in advance.
An electrolytic solution in which 1 mol / l of lithium perchlorate was dissolved was poured into the mixed solvent. The injection was performed in a dry box in a dry carbon dioxide atmosphere, and after the injection was completed, the injection port was welded and sealed.

The battery assembled in this manner was charged to a voltage of 4.2 V for the first time and then charged to a voltage of 3.6 V,
An output of 162 W was obtained. In addition, in the present example, the folding battery has two or more electrode active material layers, which are folded by bending and then contact-molded. In addition, it has become possible to assemble batteries without causing cracks in the electrode layers. Further, when the electrode manufacturing method is wet molding, the film thickness becomes thin, so that the drying time is shortened even if the number of molded sheets is increased, which leads to a reduction in manufacturing energy.

Example 14. Next, the invention according to claim 15 will be described. In this example, a positive electrode coating liquid was prepared in the same manner as in Example 13. This coating liquid is a current collector, thickness 2
After coating on a 0 μm aluminum foil and drying, a long electrode sheet having a width of 30 cm and a thickness of about 300 μm was prepared. Also, a negative electrode coating solution was prepared in the same manner as in Example 13. This coating solution was applied onto a copper foil having a thickness of 20 μm, which is a current collector, and dried to prepare several long electrode sheets having a width of 31 cm and a thickness of about 300 μm.

As shown in FIG. 27, as a battery assembly preparation process for the prepared positive and negative electrodes, slits 8 were formed in the active material layers 1 and 2 in the folded battery, which corresponded to the bent portions having a curvature of 0. The active materials 1 and 2 corresponding to the bent portions 9 having a curvature were removed from the current collector foils 4 and 5 to prepare electrode bodies. Porous polypropylene film (thickness 5
0 μm) so that the active material layers face each other, and the semi-cylindrical porous polypropylene material is inserted into the folded portion as spacers 6 every 30 cm in the lengthwise direction as shown in FIG. A battery element structure was created.

The following battery assembly was performed in the same manner as in Example 13 and a battery test was conducted. The battery assembled in this manner obtained outputs of battery voltages of 3.5 V and 158 W after being charged to the initial single battery voltage of 4.2 V. Further, no significant deterioration in characteristics was observed even after a long-term charge / discharge cycle. As described above, in this embodiment, the electrode active material layer in the curved portion is removed, so that the electrode layer is treated as a flat plate only and does not need to be bent, so that battery assembly can be performed without cracks. Further, since the material such as the active material can be used without waste, the material yield of the electrode active material is improved. In addition, since the semi-cylindrical spacer is inserted in the part of the curved part where the electrode has been removed, not only can it be expected to function as an electrolyte reservoir, but even if the electrode expands and contracts during battery charging and discharging, the bent part Since the spacer of 1 relaxes the stress applied to the current collector foil, a stable charge / discharge cycle can be expected without breaking.

Example 15. Next, the invention according to claim 16 will be described. In this embodiment, similar to Embodiment 13,
Several long electrodes having a continuous active material layer with a thickness of about 300 μm were prepared. After that, as shown in FIG. 29, three batteries (electrode pairs) were stacked in parallel, a folding battery was assembled in the same manner as in Example 13, and a battery test was conducted. The lead wire 7 was taken out from the internal battery current collector foil and wired so that the three layers of batteries would form a parallel circuit. After that, the battery assembled in the same manner as in Example 13 was charged to the initial cell voltage of 4.2 V,
A battery voltage of 3.7 V and an output of 500 W were obtained. Further, no significant deterioration in characteristics was observed even after a long-term charge / discharge cycle.

As described above, in this embodiment, since two or more batteries are stacked in parallel and folded, the curvature of the outer electrode of the folded part is larger than that of the inner part.
The probability of cracking during battery assembly is reduced. Further, although the electrode in the inner portion has a small curvature, since it is supported by the outer member, the strength is improved, and thus the generation of cracks can be avoided. Further, even during charging / discharging of the battery, the stress on the current collector foil due to the swelling / shrinkage of the electrode layer is relatively small in the portion having a large curvature, so that the breakage of the current collector foil is suppressed.

Example 16. Next, the invention according to claim 17 will be described. In this example, similar to Example 15, several continuous electrodes having a thickness of about 300 μm and having a continuous active material layer were prepared. Then, a folded battery element structure was assembled while alternately stacking orthogonal battery layers as shown in FIGS. A semi-cylindrical spacer 6 was inserted inside the bent portion. Thereafter, a battery was assembled and a battery test was conducted in the same manner as in Example 13. The battery assembled in this manner obtained an output of 666 W at a battery voltage of 3.7 V after being charged to the initial single battery voltage of 4.2 V. Further, no significant deterioration in characteristics was observed even after a long-term charge / discharge cycle. As described above, in this embodiment, two or more batteries are stacked at right angles and folded while being alternately stacked. Therefore, the curvature of folding the electrode layer can be designed to be larger than the breaking curvature of the electrode, so that the electrode layer can be folded without cracks. It becomes easy and the manufacturing yield is improved. Further, even when the battery is charged / discharged, since the curvature is large, the stress on the current collector foil due to the swelling / shrinkage of the electrode layer is relatively small, so that the current collector foil is prevented from breaking.

Example 17: Next, the invention according to claim 18 will be described. In this example, according to the method of Example 13, an electrode coating solution was prepared and then applied on a silicon-coated substrate, and a positive electrode and negative electrode independent film sheet was prepared so that the thickness was about 300 μm after drying. This is the battery plane area 30 cm
28, the battery element was configured to have the configuration of FIG. 28, and the battery element structure was integrally pressed in the same manner as in Example 13 to improve the contact of each member. The battery assembled in this manner obtained outputs of battery voltages of 3.5 V and 158 W after being charged to the initial single battery voltage of 4.2 V. Also,
No significant deterioration in characteristics was observed even after a long-term charge / discharge cycle.

Comparative Example 1 ... An electrode coating liquid was prepared in the same manner as in Example 13, coated on a collector foil and dried to give a thickness of 300 μm.
A single-layer coating film sheet of m was prepared and pressed to prepare positive and negative electrode sheets having a relatively high active material filling rate. The sheet size is the same as in Example 13. In the same manner as in Example 13, the positive electrode and the negative electrode in which the electrode independent film sheets were stacked on the collector foil-integrated electrode body prepared for the separator were made to face each other, and were separated every 30 cm in the length direction as shown in FIG. A battery element structure was created that was folded in a zigzag shape. During this step, the electrode layer was sometimes cracked at the bent portion and the electrode active material layer was peeled off from the current collector foil, but a battery element structure was prepared in the same manner as in Example 13. After this, Example 1 was repeated except that the pressing process of the battery components was omitted.
A battery was assembled in the same manner as 3 and a battery test was conducted. The battery assembled in this manner obtained outputs of a battery voltage of 3.3V and 148W after being charged to the initial single battery voltage of 4.2V. In addition, when a long-term charge / discharge cycle was performed, the rate of deterioration of characteristics was relatively large.

COMPARATIVE EXAMPLE 2 An electrode coating liquid was prepared in the same manner as in Comparative Example 1, coated on the collector foil and dried to a thickness of about 300 μm.
m single-layer coating film sheet was prepared. Using this unpressed sheet, a battery element structure was prepared in the same manner as in Example 13, and after the battery was assembled, the battery test was conducted in the same manner.
An output of V, 153 W was obtained. In addition, when a long-term charge / discharge cycle was performed, the rate of deterioration of characteristics was relatively large.

As described above, it was revealed that the battery characteristics are improved by folding and pressing the electrode active material layer having a relatively high porosity in the unpressed state.

Example 18. Next, an invention according to claim 19 will be described. In this example, in a lithium secondary battery in which an inorganic oxide is used as the positive electrode active material and carbon is used as the negative electrode active material, the average particle size of the inorganic oxide that is the positive electrode active material or the carbon that is the negative electrode active material is different. The purpose is to increase the filling rate by mixing powders of different particle sizes. That is, in a powder having a single average particle diameter, if the particles are spherical, the close-packed structure has a cubic close-packed structure and a hexagonal close-packed structure. The filling rate is about 0.75, and it cannot be filled any more, resulting in voids. However, it is possible to further increase the packing rate by mixing particles having a small particle size that fit into the voids between the particles with the particles having a large particle size.

33 parts by weight of NMP solution as a coating solvent,
As a binder, 3 parts by weight of PVdF was dissolved to obtain a binder solution. Lithium cobalt oxide powder as a positive electrode active material was added to this solution as a large particle size powder having an average particle size of 10 μm and a small particle size powder having a particle size ratio of 0.05 as a weight ratio of the small particle size to the large particle size of 0.1. It was added so that it might become 2 so that it might become 58 weight parts in total. A coating liquid was prepared by dispersing 6 parts by weight of graphite powder as a conductive agent. This coating solution was applied onto an aluminum foil having a thickness of 20 μm, which is a current collector, and dried to prepare an electrode sheet of about 150 μm. The filling rate of the electrode was obtained by measuring the weight and volume of this electrode. As a result, the filling rate was increased by about 20% as compared with the case of the active material powder having a single average particle size shown in Comparative Example 3.

Comparative Example 3 An electrode sheet was prepared in the same manner as in Example 18 except that only the active material having an average particle size of 10 μm was used, and the same evaluation was performed. The filling rate is 0.61
Met.

By thus mixing at least two kinds of powders having different particle sizes in the positive electrode and negative electrode active materials, the filling rate of the active material can be improved. As a result, the discharge capacity per unit volume can be increased and the battery performance can be improved. In the above-mentioned examples, the particle size of the small particles is 0.05 when the particle size of the large particles is 1, but the particle size ratio of the small particles is 0.3 or less. Has the effect of.

Example 19 Next, the invention according to claim 20 will be described. The purpose of this example is to mix at least two kinds of carbons having different potential characteristics in the negative electrode carbon to raise the negative electrode potential and suppress the precipitation of lithium metal in the negative electrode.
It has been known that carbon has greatly different powder characteristics depending on starting materials, firing temperature, and firing time. Therefore, the carbon used for the negative electrode also has different electrode characteristics depending on the type of carbon, resulting in large differences in capacity, potential and the like. Therefore, by mixing carbon powders having different characteristics, carbon electrodes having different potential characteristics can be prepared.

45 parts by weight of NMP solution as a coating solvent,
As a binder, 5 parts by weight of PVdF was dissolved to obtain a binder solution. In this solution, carbon powder as a negative electrode active material having a single electrode potential of about 0 V and about 0.2 V
Was added in a weight ratio of 1: 1 so that the total amount was 50 parts by weight to prepare a coating solution. This coating solution was applied onto a copper foil having a thickness of 20 μm, which is a current collector, and dried to prepare an electrode sheet having a thickness of about 100 μm. The filling rate of the electrode was obtained by measuring the weight and volume of this electrode. Further, a battery test was conducted in a coin-type cell using lithium cobalt oxide as the positive electrode and a mixed solution of ethylene carbonate / dimethoxyethane / lithium perchlorate as the electrolytic solution. As a result, it was possible to suppress the decrease in average potential and suppress the precipitation of lithium metal as compared with the case of using alone.

Comparative Example 4 An electrode sheet was prepared and evaluated in the same manner as in Example 19 except that only carbon having an average electrode potential of about 0 V was used.
The average electrode potential became 0 V or less, and lithium metal deposition was observed after the battery was disassembled.

Example 20. Next, the invention according to claim 21 will be described. In this example, the discharge capacity was improved by optimizing the composition of the positive electrode. Since both electrodes of the lithium secondary battery use powder, it is necessary to add a binder for molding. The binder exerts an effect on the formability and electrode structure in the production of electrodes, but it is desirable that it does not exist in terms of electrode characteristics and battery characteristics.
Therefore, when the amount of the binder is increased, the moldability is improved, but the electrode reaction is adversely affected. As described above, when the amount of the binder is large, the filling rate of the active material may be affected. Therefore, as a result of studying the appropriate value in consideration of the moldability of the slurry, the degree of freedom of the electrode structure, the filling rate of the active material, and the electrode reaction, the binder is coated on the surface of the positive electrode active material which is powder and the conductive agent. The average coating thickness t _{B of the} binder
However, the range of 3 ≦ t _B ≦ 16 is considered to be an appropriate value for the binder.

As a coating solvent, 30 parts by weight of NMP solution was added,
As a binder, 1.5 to 4 parts by weight of PVdF was dissolved to prepare binder solutions having different concentrations. 60 parts by weight of lithium cobalt oxide powder as a positive electrode active material and 6 parts by weight of graphite powder as a conductive agent were dispersed in this solution to prepare a coating solution. This coating liquid is used as a current collector with a thickness of 20.
Approximately 1 by coating on aluminum foil of μm and drying
A 50 μm electrode sheet was prepared. A battery test was carried out on these electrodes by using a carbon electrode as a negative electrode and a mixed solution of ethylene carbonate / dimethoxyethane / lithium perchlorate as an electrolytic solution in a coin cell. The result is shown in FIG. As a result, it was found that when the composition of the binder increased and the coating thickness on the powder surface increased, the discharge capacity sharply decreased after 16 times. Further, the coating thickness is preferably 3 or more in view of strength and formability.

Example 21. Next, the invention according to claim 22 will be described. The present example relates to improvement of the filling rate by optimizing the positive electrode composition. Since the positive electrode active material is an inorganic oxide and has poor electron conductivity, graphite is added as a conductive agent. When the graphite concentration in the electrode increases, the electronic resistance of the electrode decreases, but the filling rate of the active material decreases. For this reason, an appropriate value was investigated for the filling factor of the active material and the electrode resistance, and the appropriate value for the graphite concentration was determined. This density range will be described with reference to FIG. The horizontal axis the volume fraction of the active material x _A of FIG. _{(= V A / (V A} + V G), V A active material volume, V _G graphite volume), and the active material packing ratio on the vertical axis phi _A The graph shows the graphite filling rate φ _G. From this figure, it can be seen that the active material filling rate increases as the active material volume fraction increases. However, it can be seen that the filling factor is saturated at a certain concentration. When the value of this closest packing is φ _AC and the volume fraction of the active material at this time is x _AC , the graphite concentration at this time is 1-x _AC . Therefore, if the concentration is less than this concentration, the active material filling rate is the closest packing. However, since the resistance increases as the graphite concentration decreases, the lower limit of the concentration was determined by the amount of voltage loss due to the resistance increase. That is, the graphite volume fraction x _G (= V _G /
(V _A + V _G)) is optimal in the range of less. (1-x _AC ) / 3 ≤ x _G ≤ 1-x _AC

30 parts by weight of NMP solution as a coating solvent,
PVdF as a binder with a binder coating thickness of 12
The binder solution was dissolved to have a thickness of nm. 60 parts by weight of lithium cobalt oxide powder as a positive electrode active material and 3 to 8 parts by weight of graphite powder as a conductive agent were dispersed in this solution to prepare a coating solution. This coating solution was applied onto an aluminum foil having a thickness of 20 μm, which is a current collector, and dried to prepare an electrode sheet of about 150 μm. The filling rate of the electrode was obtained by measuring the weight and volume of this electrode. The electronic resistance of this electrode was measured with a milliohm meter. Also, in a coin-type cell, the negative electrode is a carbon electrode,
A battery test was conducted using a mixed solution of ethylene carbonate / dimethoxyethane / lithium perchlorate as an electrolytic solution. The results are shown in FIGS. 34 to 35. As a result, it was found that the filling rate of the active material was saturated at a certain graphite concentration when the graphite concentration was lowered, and the filling rate of the active material becomes the highest value when the electrode is formed at this concentration, that is, x _G ≦ 13. You can see (Fig. 34). However, since graphite is a conductive agent, it can be seen that the electronic resistance of the electrode increases as the composition ratio decreases (Fig. 3
5). Therefore, it is preferable that 5 ≦ x _G.

Example 22. Next, the invention according to claim 23 will be described. The present embodiment relates to the improvement of discharge capacity by optimizing the electrode composition. The electrode is porous, and the electrolytic solution enters between the electrodes to react with the active material. Therefore, it is necessary that there be an appropriate amount of voids into which the electrolytic solution enters. The proper value of porosity P (%) is 10 ≦ P
The range of ≦ 30 is preferable.

That is, the porosity of the positive electrodes prepared in Examples 18 to 21 was measured, and the relationship between this value and the discharge capacity per weight is shown in FIG. As a result, it was found that the discharge capacity decreased sharply when the porosity was 10% or less. Also,
It was found that the discharge capacity per volume was reduced when the content was 30% or more.

FIG. 37 is a diagram showing the rate of increase in discharge capacity when the filling rate is increased by improving the electrode structure.
Shown in. From this figure, it can be seen that the discharge capacity increases as the filling rate increases.

In the electrodes of the lithium secondary batteries shown in Examples 18 to 22, the ratio of the coating solvent in the preparation of the electrodes was 5 to 3 parts by weight of the binder.
It is desirable that the amount is 0 parts by weight, preferably 8 to 20 parts by weight. As an example of the production method, there is a method in which the binder is dissolved in a coating solvent to prepare a binder solution, and an active material and the like are dispersed in the solution to be molded on a substrate or an electrode current collector. The binder is not particularly limited, but a fluororesin is particularly preferable, and examples thereof include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). The solvent is not particularly limited as long as it can dissolve the binder, but one example is N-methylpyrrolidone (NM
P), N, N dimethylformamide (DMF) and the like. The negative electrode active material is not particularly limited,
Examples thereof include carbon materials such as graphite, glassy carbon, carbon black, coke, pyrolytic carbon, and carbon fiber. The positive electrode active material is not particularly limited, but examples thereof include TiS ₂ , MoS ₂ , and Mn.
O ₂ , V ₂ O ₅ , V ₆ O ₁₃ , LiCoO 2, LiNiO ₂ , L
Inorganic compounds such as iMn ₂ O ₄ are listed. Examples of the current collector include foils such as copper, aluminum, nickel, iron, and stainless steel, mesh, expanded metal, and the like. When the electrode prepared as described above using the binder is used in a non-aqueous electrolyte battery, it can also be used as a negative electrode or a positive electrode, and the electrolyte or electrolytic solution of such a battery is not particularly limited, and it is conventional. The same as can be used.

[0164]

As described above, according to the first invention, L
When synthesizing a positive electrode material for a lithium secondary battery, which comprises a composition containing iCoO 2 or LiCoO 2 as a main component, cobalt oxide as a starting material is preliminarily 910-9
Since it was baked at 50 ° C., a positive electrode active material having a stable composition can be obtained.

According to the second invention, since the composition is synthesized by using a mixed salt of Li2CO3 and LiHCO3 for cobalt oxide, low temperature synthesis is possible.

Further, according to the third invention, since the thermocouple for controlling the furnace temperature is inserted in the most central part of the calcined powder and the upper limit of the calcining temperature is set to 900 ° C., the temperature is not raised to the decomposition temperature range of LiCoO 2. Therefore, a high quality positive electrode material having excellent charge / discharge characteristics and charge / discharge efficiency can be obtained with good reproducibility.

Further, according to the fourth invention, 735 to 785 ° C. is selected as the first stage baking temperature range and 785 to 850 ° C. is selected as the second stage baking temperature range. A positive electrode active material having a uniform and stable composition which can be avoided is obtained.

According to the fifth invention, the mixed raw material powder is press-molded at a pressure of 100 kg / cm ² to 1000 kg / cm ^{2 and} the thickness of the molded body is 2 to 10 m.
Since m is used and a spacer having a thickness of 1 mm or more is sandwiched and baked so that the gap between the formed bodies is 1 to 2 mm, the reaction proceeds rapidly, and a positive electrode active material having a uniform and stable composition is obtained.

According to the sixth aspect of the invention, the infrared absorption spectrum is measured, stoichiometry is evaluated, and Co-
Since the degree of completion of the O6 bond is evaluated, the quality of the fired active material can be judged quickly and easily, which is useful for quality control.

According to the seventh aspect of the present invention, the completion of the stoichiometry and Co--O6 bond is readjusted by post-processing according to the values of the completion of the stoichiometry and Co--O6 bond. Therefore, even if an active material is insufficiently fired due to a process failure, it can be redone properly and no waste occurs.

According to the eighth invention, when LiCoO 2 is synthesized from cobalt oxide and lithium salt,
Sodium salt or potassium salt, lithium salt 5m
Add more than 30% by mol of more than ol% and add Li1-xNaxCo
O2-y (x≤0.3, y≤0.3) or Li1-xKxC
oO2-y or Li1-x Nax1Kx2CoO2-y (x = x1 +
Since the composition of x2) is adopted, K ions or Na ions are taken into the structure of LiCoO2 and become an active material having high conductivity.

According to the ninth aspect of the invention, the sodium salt or potassium salt is a carbonate, a hydrogen carbonate, a mixed salt of a carbonate and a hydrogen carbonate, or a eutectic hydrogen carbonate. Highly active material is obtained by low temperature reaction.

According to the tenth aspect of the invention, a mixture of cobalt oxide and lithium salt is decomposed in a temperature range up to the firing temperature to produce a metal powder, for example, Ag.
_{Since 2} O and the like are added, an active material in which metal particles having high electric conductivity are uniformly dispersed in the positive electrode active material can be obtained.

According to the eleventh invention, since an oxide semiconductor such as Cu ₂ O is added to the mixture of cobalt oxide and lithium salt, an active material having high conductivity can be obtained.

According to the twelfth aspect of the invention, since a metal oxide capable of reacting with lithium to form a spinel structure, such as MnO _2, is added to the mixture of cobalt oxide and lithium salt, the positive electrode having a high battery capacity can be obtained. An active material is obtained.

Further, according to the thirteenth invention, since the composition having the optimum value of the stoichiometry and the perfectness of Co--O6 bond is used as the positive electrode material, the capacity using the positive electrode active material having a uniform composition is obtained. A large battery can be obtained.

According to the fourteenth aspect of the invention, the folding battery has two or more electrode active material layers, which are folded by bending and then contact-molded, so that the folding battery does not cause cracks in the electrodes. Can be easily manufactured.

Further, in the fifteenth invention, the electrode active material layer of the folding battery has only the flat surface portion, the electrode active material layer at the curved portion is removed, and the adjacent electrode active material layers folded by the collector foil are connected. Therefore, the electrode layer is treated as a flat plate only and does not need to be bent, so that battery assembly is possible without causing cracks.

In the sixteenth and seventeenth inventions, a large area electrode can be obtained with a small number of folds by stacking and folding a plurality of battery layers, and as a result, a large capacity battery manufacturing capability is improved.

Further, in the eighteenth invention, since the contact between the respective members is improved by pressing after the battery element is constructed, the contact resistance is reduced, and the high battery characteristics are obtained even if the area is increased and the stacking is increased. Can be expected.

According to the nineteenth invention, in a lithium secondary battery using an inorganic oxide as the positive electrode active material and carbon as the negative electrode active material, the inorganic oxide or the negative electrode active material as the positive electrode active material is used. A lithium secondary battery electrode structure in which the average particle size of a certain carbon is composed of at least two kinds and the ratio of the particle size of the small particles is 0.3 or less when the particle size of the first particle is 1. As a result, an electrode having a higher active material filling rate than before can be obtained, the discharge capacity per unit volume can be increased, and the performance of the lithium secondary battery can be improved.

According to the twentieth invention, in the lithium secondary battery in which the negative electrode active material is made of carbon, the raw material of carbon as the negative electrode active material or the manufacturing conditions or characteristics are different, and at least two or more kinds are constituted. With the existing lithium secondary battery electrode structure, the decrease in the potential of the negative electrode could be suppressed. For this reason, it was possible to prevent the precipitation of lithium metal due to the decrease in the potential in the negative electrode carbon, and it was possible to extend the cycle life by suppressing the capacity decrease due to the metalization of lithium ions and the internal short circuit of the electrode.

According to the twenty-first aspect of the invention, the positive electrode composition is a molding auxiliary agent in a lithium secondary battery comprising an inorganic oxide which is a positive electrode active material, graphite which is a conductive agent, and a binder which is a molding auxiliary. When the binder coats the surfaces of the positive electrode active material which is powder and the conductive agent, a lithium secondary battery electrode structure is prepared in which the average coating thickness t _B (nm) of the binder is within the range of 3 ≦ t _B ≦ 16. By so doing, it was possible to prevent the binder from inhibiting the reaction of lithium ions on the surface of the active material, and to increase the discharge capacity per weight.

According to the twenty-second aspect of the invention, in the lithium secondary battery in which the positive electrode composition is composed of the inorganic oxide as the positive electrode active material, the graphite as the conductive agent, and the binder as the molding aid, the active material is most densely packed. When the active material volume fraction to be filled is x _AC , it is possible to create an electrode having a high active material filling rate by adopting a lithium secondary battery electrode structure in which the graphite volume fraction x _G is in the following range. it can. (1-x _AC ) / 3 ≤ x _G ≤ 1-x _AC Therefore, an electrode having a large discharge capacity per unit volume could be prepared, and the electrode resistance could be set to an appropriate value.

According to the twenty-third aspect of the invention, in a lithium secondary battery in which an inorganic oxide is used as the positive electrode active material and carbon is used as the negative electrode active material, the porosity P in the electrode is
By making the lithium secondary battery electrode structure in which (%) is within the range of 10 ≦ P ≦ 30, the reaction of lithium ions between the active material and the electrolytic solution becomes smooth, and the discharge capacity per weight is increased. I was able to.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing X-ray diffraction results before and after heat treatment of a cobalt oxide according to Example 1 of the present invention.

FIG. 2 is an explanatory diagram showing a measurement result of TG-DTA showing decomposition of LiCoO2.

FIG. 3 is a characteristic diagram showing an X-ray diffraction intensity of a heat-treated sample.

FIG. 4 is a characteristic diagram showing an infrared absorption spectrum and an absorbance ratio of a heat-treated sample.

FIG. 5 is an explanatory diagram showing the results of TG-DTA regarding the Li / Co ratio.

FIG. 6 is an explanatory diagram showing a Co—O stretchable absorption band.

FIG. 7 is an explanatory diagram showing stoichiometry and B / A area ratio of LiCoO 2.

FIG. 8 is a characteristic diagram showing infrared absorption spectra of Li (7) CoO ₂ and Li (6) CoO ₂ .

FIG. 9: Na-added LiCoO 2 according to Example 6 of the present invention
2 It is an explanatory view showing the TG-DTA measurement result regarding the thermal behavior during synthesis and the amount of Na added.

FIG. 10 is a characteristic diagram showing changes in X-ray diffraction intensity according to Example 6 of the present invention.

FIG. 11 is a characteristic diagram showing changes in X-ray diffraction intensity according to Example 6 of the present invention.

FIG. 12: K-added LiCoO 2 according to Example 8 of the present invention
2 It is an explanatory diagram showing the TG-DTA measurement results regarding the thermal behavior and the K addition amount during the synthesis.

FIG. 13 is a characteristic diagram showing changes in X-ray diffraction intensity according to Example 8 of the present invention.

FIG. 14 is a characteristic diagram showing changes in X-ray diffraction intensity according to Example 8 of the present invention.

FIG. 15: Ag-added LiCo according to Example 9 of the present invention
TG-DTA on thermal behavior and Ag addition amount during O2 synthesis
It is explanatory drawing which shows a measurement result.

FIG. 16 is a characteristic diagram showing a change in X-ray diffraction intensity according to Example 9 of the present invention.

FIG. 17 is a characteristic diagram showing changes in X-ray diffraction intensity according to Example 9 of the present invention.

FIG. 18: Cu-added LiC according to Example 10 of the present invention
TG-DT on thermal behavior and Cu addition amount during oO2 synthesis
It is explanatory drawing which shows A measurement result.

FIG. 19 is a characteristic diagram showing a change in X-ray diffraction intensity according to Example 10 of the present invention.

FIG. 20 is a characteristic diagram showing changes in X-ray diffraction intensity according to Example 10 and Example 9 of the present invention.

FIG. 21: Mn-added LiC according to Example 11 of the present invention
TG-DT concerning thermal behavior and Mn addition amount during oO2 synthesis
It is explanatory drawing which shows A measurement result.

FIG. 22 is a characteristic diagram showing a change in X-ray diffraction intensity according to Example 11 of the present invention.

FIG. 23 is a characteristic diagram showing an infrared absorption spectrum according to Example 11 of the present invention.

FIG. 24 is an explanatory diagram showing the relationship between B / A and the diffusion coefficient of lithium ions according to Example 12 of the present invention.

FIG. 25 is an explanatory diagram showing the relationship between the absorbance ratio and the discharge capacity according to Example 12 of the present invention.

FIG. 26 is a sectional configuration diagram showing a lithium secondary battery according to Example 13 of the present invention.

FIG. 27 is an explanatory diagram showing the method for manufacturing the lithium secondary battery according to the fourteenth embodiment of the present invention.

FIG. 28 is a sectional configuration diagram showing a lithium secondary battery according to Example 14 of the present invention.

FIG. 29 is a structural diagram showing a lithium secondary battery according to Example 15 of the present invention.

FIG. 30 is a configuration diagram showing a lithium secondary battery according to Example 16 of the present invention.

FIG. 31 is a configuration diagram showing a conventional foldable lithium secondary battery.

FIG. 32 is a characteristic diagram showing the relationship between the coating thickness of the binder on the powder and the discharge capacity per weight of the positive electrode according to Example 20 of the present invention.

FIG. 33 is an explanatory diagram showing the geometry of the active material / graphite system.

FIG. 34 is a characteristic diagram showing a positive electrode active material filling rate when the graphite volume fraction according to Example 21 of the present invention is changed.

FIG. 35 is a characteristic diagram showing the specific resistance of the positive electrode when the graphite volume fraction according to Example 21 of the present invention is changed.

FIG. 36 is a characteristic diagram showing the relationship between the porosity in the positive electrode and the discharge capacity according to Example 22 of the present invention.

FIG. 37 is a characteristic diagram showing discharge capacity per unit volume when the active material filling rate is changed.

FIG. 38 is a configuration diagram showing a structure of a conventional coin-type battery.

FIG. 39 is a configuration diagram showing a structure of a conventional clad lead-acid battery.

FIG. 40 is an explanatory diagram showing a powder / binder geometry.

FIG. 41 is an explanatory diagram showing the relationship between the average particle size of powder and the filling rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Separator 4 Positive electrode current collector foil 5 Negative electrode current collector foil 6 Folding battery bent part spacer 7 Current collecting lead wire 8 Electrode active material layer slit position 9 Electrode active material layer release part 10 Seal material

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[Procedure amendment]

[Submission date] July 7, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

Therefore, at present, under what kind of firing conditions, Li
The description focuses on the secondary battery characteristics of CoO2. Of course, powder X-ray diffraction is performed, and for example, the peak from the (104) plane with the highest intensity (CuKα
If a line is used, it has been performed to search for a firing condition such that the ratio of the peak having the second highest intensity (near 2θ = 45.2 degrees) (near 2θ = 18.8 degrees) becomes large.
However, such a method is necessary as a means for evaluating LiCoO2, as the inventors clarify,
It wasn't enough .

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[0029]

The first invention of the present invention is as follows:
When synthesizing a positive electrode material for a lithium secondary battery composed of LiCoO2 or a composition containing LiCoO2 as a main component,
Cobalt oxide as a starting material is 900-
It was baked at 950 ° C.

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[Correction target item name] 0049

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A twenty-first aspect of the invention is a lithium secondary battery in which the positive electrode composition comprises an inorganic oxide as a positive electrode active material, graphite as a conductive agent, and a binder as a molding aid, and the positive electrode active material is a powder. When coated on the surface of the substance and the conductive agent, the average coating thickness t _B (nm) of the binder is
The range is 3 ≦ t _B ≦ 16.

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[Correction target item name] 0052

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[0052]

According to the first aspect of the invention, since cobalt oxide as a starting material is preliminarily fired at a temperature of 900 to 950 ° C, the composition of the cobalt oxide is unified to Co3O4, and a positive electrode active material having a stable composition is obtained. To be

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[Correction target item name] 0075

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[0075]

EXAMPLES Example 1. First, the invention according to claims 1 to 7 will be described. 1 kg of commercially available Co3 O4 powder was placed in an alumina crucible, placed in an electric furnace set at a temperature of 925 ° C., and fired in air for 3 hours. Cobalt oxide is always undecomposed basic cobalt carbonate (2CoCO3 ・ 3Co (OH) 3)
However, it is decomposed by firing in air at 900 to 950 ° C., and the composition is unified to Co3O4. 1 (a) and 1 (b) show the X-ray diffraction results before and after the heat treatment of cobalt oxide (at 925 ° C. for 1 hour in air), respectively, in which ◯ indicates LiCoO 2 and X indicates basic cobalt carbonate. Indicates. From the figure, it can be seen that this heat treatment completely eliminates the basic cobalt carbonate, resulting in a pure Co3O4 composition.

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That is, the inventors have obtained the following findings as a result of earnest research using thermal analysis as to the production and decomposition during LiCoO 2 synthesis. FIG. 2 shows the measurement results of TG-DTA showing the decomposition of LiCoO2. The solid line is DT
A, the dotted line is the change in TG. LiCoO2 itself decomposes at 1130 ° C. and again produces Co3O4 (X-ray diffraction data omitted). Decomposition heat is about 82 cal /
It is g. It is therefore self-evident that the synthesis temperature of LiCoO2 should not exceed this temperature. Furthermore, as shown in FIG. 3, the inventors have confirmed from the X-ray diffraction results of the samples with different firing temperatures that there is an unclear decomposition temperature range between 930 and 1030 ° C. This decomposition temperature range is also confirmed from the infrared absorption spectrum shown in FIG.
FIG. 4A shows the infrared absorption spectrum of the heat-treated sample, the horizontal axis represents wavelength (microns), and the vertical axis represents transmittance. Numbers indicate peak wavenumbers (cm ^-1 ). (B) is the same as above Sample absorbance ratio
(Absorption band of the absorption band / ~600cm ^-1 of 2 47cm ^-1).
The horizontal axis represents the wave number (cm ^-1 ) and the vertical axis represents the absorbance ratio. From this, in the decomposition of LiCoO2 (9
It is also clear that the temperature should not rise above 30 ° C to 1030 ° C. It can be understood from FIG. 4 that when the temperature is raised to 1000 ° C., it is transformed into a foreign substance.

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[0087]

[Table 2]

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Example 6. Next, the invention according to claim 8 will be described. Co3O4 (8.023 g) was mixed with Li2CO3 (3.283 g) and NaHCO3 (2.511 g) in an automatic mortar for 2 hours (Na addition amount: 10 mol%). This mixed powder was fired in an electric furnace in air at 850 ° C. for 20 hours. When the electric resistance value was measured, it was 20 KΩ. This value is about 1/5 of the value of 1 MΩ when Na is not added.
It is 0 , which means that the active material has high conductivity.

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[Correction target item name] 0111

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Further, NiO, FeO and Cr ₂ O 3 are Li
Instead of substituting with Li during CoO2 synthesis reaction, CoO2
With the possibility of replacing. Thus, for example the addition of NiO, LiCo1-xNixO _2: composition of NiOy (x + y = amount) will be obtained. The same applies to the addition of FeO and Cr ₂ O.

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As described above, by adding K, Ag, Cu, and Na, LiCoO 2 having an essentially high electric resistance value can have a low resistance, and the internal resistance of the positive electrode can be reduced. In particular, it is remarkable in the K additive and the Ag additive.
A considerable effect can be expected with Cu additive and Na additive.

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[0130]

[Table 5]

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Example 18. Next, an invention according to claim 19 will be described. In this example, in a lithium secondary battery in which an inorganic oxide is used as the positive electrode active material and carbon is used as the negative electrode active material, the average particle size of the inorganic oxide that is the positive electrode active material or the carbon that is the negative electrode active material is different. The purpose is to increase the filling rate by mixing powders of different particle sizes. That is, the close-packed structure is a cubic close-packed structure.
Structure and hexagonal close-packed structure
If the particles are spherical, the packing factor is about
It is 0.76. However, it is possible to further increase the packing rate by mixing particles having a small particle size that fit into the voids between the particles with the particles having a large particle size.

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By thus mixing at least two kinds of powders having different particle sizes in the positive electrode and negative electrode active materials, the filling rate of the active material can be improved. As a result, the discharge capacity per unit volume can be increased and the battery performance can be improved. Incidentally, when the particle size of the small particles was between 1 and particle size of the large particles in the above embodiment, an example of 0.05, the particle size of the small particle ratios similar if not more than 0.3 effective.

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[Name of item to be corrected] 0156

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Example 20. Next, the invention according to claim 21.
Will be described. In this example, in order to optimize the positive electrode composition
This is related to the improvement of discharge capacity. Lithium secondary battery
Since both electrodes of the pond use powder, in order to perform molding
It is necessary to add a binder.But the excess
It may interfere with the electrode reaction.Binder as above
-A large amount may affect the active material filling rate. This
Therefore, the moldability of the slurry and the degree of freedom of the electrode structure and the active material
The optimum value considering the filling rate and electrode reaction was examined.
As a result, the positive electrode active material in which the binder is powder and the conductive agent
The average coating thickness t of the binder when coated on the surface_B
(Nm)Is 3 ≦ t_BThe range of ≦ 16 is appropriate for the binder
It was assumed to be a value.

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[Correction target item name] 0157

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As a coating solvent, 30 parts by weight of NMP solution was added,
As a binder, 1.5 to 4 parts by weight of PVdF was dissolved to prepare binder solutions having different concentrations. 60 parts by weight of lithium cobalt oxide powder as a positive electrode active material and 6 parts by weight of graphite powder as a conductive agent were dispersed in this solution to prepare a coating solution. This coating liquid is used as a current collector with a thickness of 20.
Approximately 1 by coating on aluminum foil of μm and drying
A 50 μm electrode sheet was prepared. A battery test was carried out on these electrodes by using a carbon electrode as a negative electrode and a mixed solution of ethylene carbonate / dimethoxyethane / lithium perchlorate as an electrolytic solution in a coin cell. The result is shown in FIG. As a result, it was found that when the binder composition increased and the coating thickness on the powder surface exceeded 16 (nm), the discharge capacity sharply decreased. In addition, the coating thickness is preferably 3 (nm) or more from the viewpoint of strength and formability.

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30 parts by weight of NMP solution as a coating solvent,
PVdF as a binder with a binder coating thickness of 12
The binder solution was dissolved to have a thickness of nm. 60 parts by weight of lithium cobalt oxide powder as a positive electrode active material and 3 to 8 parts by weight of graphite powder as a conductive agent were dispersed in this solution to prepare a coating solution. This coating solution was applied onto an aluminum foil having a thickness of 20 μm, which is a current collector, and dried to prepare an electrode sheet of about 150 μm. The filling rate of the electrode was obtained by measuring the weight and volume of this electrode. The electronic resistance of this electrode was measured with a milliohm meter. Also, in a coin-type cell, the negative electrode is a carbon electrode,
A battery test was conducted using a mixed solution of ethylene carbonate / dimethoxyethane / lithium perchlorate as an electrolytic solution. The results are shown in FIGS. 34 to 35. As a result, it was found that when the graphite concentration was lowered, the filling rate of the active material was saturated at a certain graphite concentration, and if the electrode was formed below this concentration, that is, x _G ≦ 0.13 , the filling rate of the active material becomes the highest value. It can be seen (Fig. 34). However, since graphite is a conductive agent, it can be seen that the electronic resistance of the electrode increases as the composition ratio decreases (FIG. 35). Therefore, it is preferable that 0.05 ≦ x _G.

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FIG. 23

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Nishimura 8-1-1 Tsukaguchihonmachi, Amagasaki City Central Research Laboratory, Mitsubishi Electric Corporation (72) Inventor Hisashi Shioda 8-1-1 Tsukaguchihonmachi, Amagasaki Mitsubishi Electric Central Research Institute Co., Ltd. (72) Inventor Akira Shirakami 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Central Research Institute

Claims (23)

[Claims] 1. When synthesizing a positive electrode material for a lithium secondary battery comprising LiCoO2 or a composition containing LiCoO2 as a main component, a cobalt oxide as a starting material is preliminarily calcined at 910 to 950 ° C., and then the above composition is used. A method for synthesizing a positive electrode material for a lithium secondary battery, which comprises synthesizing a product. 2. When synthesizing a positive electrode material for a lithium secondary battery comprising LiCoO2 or a composition containing LiCoO2 as a main component, the above composition is synthesized by using a mixed lithium salt of Li2CO3 and LiHCO3 in Co3O4. A method for synthesizing a positive electrode material for a lithium secondary battery, which comprises: 3. A thermocouple for controlling a furnace temperature when a positive electrode material for a secondary battery comprising LiCoO2 or a composition containing LiCoO2 as a main component is synthesized by heat treatment using a cobalt compound and a lithium salt. The method for synthesizing a positive electrode material for a lithium secondary battery, characterized in that the upper limit of temperature rise is 900 ° C. 4. When synthesizing a positive electrode material for a secondary battery composed of LiCoO2 or a composition containing LiCoO2 as a main component by heat treatment using a cobalt compound and a lithium salt, the firing temperature of the first step is 735 to 785. C. and the subsequent second-stage firing temperature was 785 to 850.degree. C. A method for synthesizing a positive electrode material for a lithium secondary battery, which is characterized in that. 5. When synthesizing a positive electrode material for a secondary battery comprising LiCoO2 or a composition containing LiCoO2 as a main component by heat treatment using a cobalt compound and a lithium salt, 100 kg / cm ² to 1000 kg of mixed powder is used.
Of a positive electrode material for a lithium secondary battery, characterized by being press-molded at a pressure of / cm ² and having a thickness of the press-molded body of 2 to 10 mm and a gap of the press-molded body of 1 mm or more and laminating and firing. Synthetic method. 6. A cesium iodide disk made of LiCoO2 or a composition containing LiCoO2 as a main component,
Obtain the infrared absorption spectrum in the wave number range of 0 to 200 cm ^-1 ,
Draw a baseline on the above infrared absorption spectrum to obtain about 60
Co-O stretching absorption band with a peak at 0 cm ^-1 is 600
It is divided into a symmetrical area A centered at cm ^-1 and a remaining area B other than that which is disturbed, and the stoichiometry is evaluated from the area ratio B / A of both, and by the baseline method, from the ratio of approximately absorbance O over Co-O bending absorption band at ^247cm-1 and the absorbance of the absorption band of about ^600cm-1, the lithium secondary, characterized in that to evaluate the completeness of Co-O6 bond Evaluation method for positive electrode materials for batteries. 7. LiCoO 2 according to the evaluation method according to claim 6.
2 or a composition containing LiCoO2 as a main component was evaluated, and the heat treatment temperature was 500 to 900 ° C, and the oxygen partial pressure of the atmosphere was adjusted to be pure from air depending on the value of the completeness of stoichiometry and Co-O6 bond. A method for synthesizing a positive electrode material for a lithium secondary battery, characterized in that the stoichiometry and the degree of perfection of the Co--O6 bond are readjusted by selecting an arbitrary value up to oxygen and performing post-treatment. 8. L from a cobalt oxide and a lithium salt
When synthesizing iCoO2, sodium salt or potassium salt is added in an amount of more than 5 mol% and 30 mol% of lithium salt.
In addition, Li1−xNaxCoO2−y (x ≦ 0.3, y ≦
0.3) or Li1−xKxCoO2−y or Li1−x
A positive electrode material for a lithium secondary battery, which has a composition of Nax1Kx2CoO2-y (x = x1 + x2). 9. The sodium salt or potassium salt according to claim 8 is a carbonate salt, a hydrogen carbonate salt, a mixed salt of a carbonate salt and a hydrogen carbonate salt, or a eutectic hydrogen carbonate salt, and the upper limit of temperature rise is 900 ° C. A method for synthesizing a positive electrode material for a lithium secondary battery, characterized in that a thermocouple for controlling a furnace temperature is inserted in the most central part of the fired powder as follows. 10. When synthesizing LiCoO2 from cobalt oxide and a lithium salt by firing, a metal oxide that decomposes in a temperature range up to the firing temperature to produce a metal powder, that is, silver oxide, gold oxide, platinum oxide. , Iridium oxide, osmium oxide, or palladium oxide is added to a composition containing LiCoO2 or LiCoO2 as a main component at a concentration of 5 to 30 mol% as a metal,
A method for synthesizing a positive electrode material for a lithium secondary battery, which comprises firing at 900 ° C. or lower. 11. L from cobalt oxide and lithium salt
When synthesizing iCoO2, an oxide semiconductor, that is, C
u2O, NiO, FeO, Cr2O3, MoO2, etc. are added to Li
A method for synthesizing a positive electrode material for a lithium secondary battery, which comprises adding 5 mol% to 30 mol% to a composition containing CoO2 or LiCoO2 as a main component and firing the mixture at 900 ° C or lower. 12. A cobalt oxide and a lithium salt to form Li
When synthesizing CoO2, a metal oxide capable of forming a spinel structure by reacting with lithium, that is, MnO2, Mn2O
3, Fe2O3, Cr2O3, etc. to LiCoO2 or Li
A method for synthesizing a positive electrode material for a lithium secondary battery, comprising adding 5 mol% to 30 mol% to a composition containing CoO2 as a main component and firing the mixture at 900 ° C or lower. 13. The area B / A ratio of the Co—O stretching absorption band obtained by the evaluation method according to claim 6 is 0.5 to 3.0.
And a composition containing LiCoO2 or LiCoO2 as a main component, which has an absorbance ratio between the 247 cm ^-1 absorption band and the 600 cm ^-1 absorption band of 0.5 to 4.0, is used as a positive electrode material. Lithium secondary battery. 14. A lithium secondary battery characterized in that a positive electrode and a negative electrode each having two or more electrode active material layers are opposed to each other with a separator interposed therebetween, and the electrodes are bent by bending and then contact-molded. Manufacturing method. 15. A lithium secondary battery comprising a positive electrode and a negative electrode made of an electrode active material layer, which are opposed to each other via a separator and are folded, and the electrode active material layer is provided only on a flat plate portion, and a collector foil is provided. The rechargeable lithium secondary battery is characterized in that the adjacent electrode active material layers are connected together. 16. A lithium secondary battery comprising a positive electrode and a negative electrode opposed to each other with a separator interposed therebetween, and the electrode pair being folded, wherein two or more of the electrode pairs are stacked in parallel and folded. Lithium secondary battery. 17. A lithium secondary battery constituted by facing a positive electrode and a negative electrode with a separator interposed therebetween, and folding the electrode pair, wherein two or more electrode pairs are stacked at a right angle and are alternately stacked. A lithium secondary battery characterized in that 18. A lithium secondary battery comprising a positive electrode and a negative electrode made of an electrode active material layer, which are opposed to each other with a separator interposed therebetween, and is folded. In the lithium secondary battery, the electrode active material layer is folded in an unpressed state and then pressed. A method of manufacturing a lithium secondary battery, comprising: 19. An inorganic oxide is used as a positive electrode active material,
In a lithium secondary battery using carbon as the negative electrode active material, the average particle diameter of the inorganic oxide that is the positive electrode active material or the carbon that is the negative electrode active material is composed of at least two types, and the particle diameter of the large particles is The lithium secondary battery is characterized in that the ratio of the particle size of the small particles is 0.3 or less when set to 1. 20. A lithium secondary battery using carbon as a negative electrode active material, wherein the negative electrode active material carbon is composed of at least two or more different raw materials, manufacturing conditions, or characteristics. And a lithium secondary battery. 21. A lithium secondary battery having a positive electrode composition comprising an inorganic oxide as a positive electrode active material, graphite as a conductive agent, and a binder as a molding aid, wherein the positive electrode active material in which the binder is powder and the above A lithium secondary battery characterized in that the average coating thickness t _B (nm) of the binder is in the following range when coated on the surface of the conductive agent. 3 ≦ t _B ≦ 16 22. A lithium secondary battery having a positive electrode composition comprising an inorganic oxide as a positive electrode active material, graphite as a conductive agent, and a binder as a molding aid, wherein the positive electrode active material is the closest packing. A lithium secondary battery, wherein the graphite volume fraction x _G is in the following range when the volume fraction is x _AC . (1-x _AC ) / 3 ≤ x _G ≤ 1-x _AC 23. An inorganic oxide is used as the positive electrode active material,
A lithium secondary battery using carbon as a negative electrode active material, wherein the porosity P (%) in the electrode is within the following range. 10 ≦ P ≦ 30