JP2007188759A - Positive-electrode active material for nonaqueous electrolytic solution battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material for a non-aqueous electrolyte secondary battery which is excellent in a high synthetic rate and high filling properties, and its manufacturing method. <P>SOLUTION: The manufacturing method of the positive electrode active material for synthesizing lithium complex cobalt oxide represented as LiCoO<SB>2</SB>obtained by mixing tricobalt tetroxide (Co<SB>3</SB>O<SB>4</SB>) with Li<SB>2</SB>CO<SB>3</SB>, LiNO<SB>3</SB>, or LiOH is composed of a first heat treatment of progressing a synthetic reaction by 95% or more, and a second process of heating up from 850°C to 950°C, and shifted to the second process to manufacture the lithium complex cobalt oxide after 95% or more of a gas component formed by the synthetic reaction in the first process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium composite cobalt oxide that is a positive electrode active material for a non-aqueous electrolyte battery typified by a lithium secondary battery and a method for producing the same. It relates to a manufacturing method.

In recent years, consumer electronic devices have become increasingly portable and cordless. As these progress, demands for higher energy density, smaller size and lighter weight of secondary batteries serving as driving power sources are increasing. In recent years, it has been used as a power source for mobile phones, and it is desired to increase the talk time with the rapid expansion of the market, and there is a great demand for improvement of cycle life. Under such circumstances, a non-aqueous electrolyte secondary battery using a lithium composite transition metal oxide exhibiting a high charge / discharge voltage, such as LiCoO _2, as a positive electrode active material and utilizing insertion / extraction of lithium ions has been proposed. (For example, refer to Patent Document 1).

In the synthesis of LiCoO ₂ , when lithium carbonate, lithium nitrate, or lithium hydroxide is used as the lithium compound and tricobalt tetroxide is used as the cobalt compound, the specific surface area of the cobalt source must be increased in order to facilitate the synthesis reaction. It is necessary to carry out the synthesis at a temperature that does not decrease so that unreacted lithium compounds do not remain at the LiCoO ₂ grain boundaries.

When the LiCoO ₂ is treated at a high temperature with the unreacted lithium compound remaining, the LiCoO ₂ is accompanied by particle growth, reducing the reactivity between the cobalt compound and the lithium compound, resulting in a high synthesis rate, that is, LiCoO in which the reaction is complete. ₂ is difficult to obtain, and when this is used as a positive electrode active material, sufficient battery performance cannot be obtained.

Therefore, in order to synthesize LiCoO ₂ with a high synthesis rate, fine particle Co ₃ O ₄ is used, and LiCo _X O ₂ is synthesized with Li excess as X <1.0, and the particles are grown to increase the filling property. Has been proposed (see, for example, Patent Document 1).

However, when Li is excessive, it is difficult to obtain LiCoO ₂ having a high synthesis rate because reaction and particle growth tend to proceed simultaneously.
Japanese Patent Laid-Open No. 10-324522

The present invention has been made in view of the above-described problems, and aims to provide a LiCoO ₂ powder having a high synthesis rate and a high filling property, and a method for producing the same, by smoothly proceeding the reaction between the Li compound and the Co compound. And

Method of manufacturing a non-aqueous electrolyte secondary battery Seikatsu materials of the present invention, obtained by the Li ₂ CO _3, LiNO ₃ or at least one lithium compound of the group consisting of LiOH and Co ₃ O ₄ mixed, heated In the method for producing a positive active material for a non-aqueous electrolyte secondary battery for synthesizing a lithium composite cobalt oxide represented by the general formula LiCo _X O ₂ (where 1.0 <X ≦ 1.05), the heating The first step is to heat from room temperature to 600 to 800 ° C. while introducing oxygen or air, and the second step is to heat to 850 to 950 ° C., and 95% of the gas components generated by the synthesis reaction in the first step After the above occurs, the process proceeds to the second step. As a result, in LiCo _x O ₂ , 1.0 <X ≦ 1.05 is set to suppress particle growth caused by excess Li and promote the reaction. Also, in the process of synthesizing LiCoO ₂ by mixing and heating the Li compound and Co compound, the first step of the heat treatment is performed in a temperature range that does not reduce the specific surface area of Co ₃ O ₄ , and the progress of the process is checked. The gas component generated by the synthesis reaction is confirmed by the ratio of CO ₂ in the case of Li ₂ CO ₃ , NO _x in the case of LiNO ₃ , and H ₂ O in the case of LiOH. At that point, the process proceeds to the second step, where heat treatment is performed at 850 to 950 ° C., and the particles are grown, whereby the composite is sized.

At this time, the specific surface area of Co ₃ O ₄ is preferably 2.0 m ² / g or more.

  Moreover, after confirming that the reaction in the first step is almost completed, it is preferable to lower the temperature to room temperature and add pulverization. By adding this step, the sintered particles can be separated, the contact area with air or oxygen can be increased, and the synthesis can be easily advanced.

Further, the specific surface area of the lithium composite cobalt oxide represented by the general formula LiCo _X O ₂ (where 1.0 <X ≦ 1.05) obtained by these production methods is 0.4 m ² / g to 0.00. 9 m ² / g.

According to the present invention, the step of mixing and heating at least one lithium compound of the group consisting of Li ₂ CO ₃ , LiNO ₃ or LiOH and Co ₃ O ₄ is carried out from room temperature to 600 ° C. to 800 ° C. while introducing oxygen or air. The first step is heated to 850 ° C. to 950 ° C., and 95% or more of the gas components generated by the synthesis reaction in the first step are generated, and then transferred to the second step. The reaction between the compound and the Co compound can proceed smoothly, and the specific surface area of the lithium composite cobalt oxide represented by the general formula LiCo _x O ₂ (where 1.0 <X ≦ 1.05) is 0.00. 4m ² /g~0.9m was ² / g, it can be obtained LiCoO ₂ powder of high synthesis rate and high filling property.

  According to the present invention, the Co compound and the Li compound are mixed in an excess ratio of Co in the stoichiometric mixing, and it is confirmed that the synthesis reaction is completed by 95% or more in the first heat treatment step. Particles can be grown in the heat treatment step and the composite can be sized to preferred particles.

Co ₃ O ₄ is selected as the Co compound, and at least one member of the group consisting of Li ₂ CO ₃ , LiNO ₃ or LiOH is used as the Li compound, and a gas generated by a synthesis reaction in the first heat treatment step components, for example if the _{Li 2 CO 3 CO 2, LiNO} 3 and it if NOx, by check the amount of generation of H ₂ O, if LiOH, checks whether more synthesis which was how complete, high It becomes easy to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery with a synthesis rate.

At this time, in the case of Li ₂ CO ₃ , the maximum temperature during the synthesis is less than 600 ° C., the reaction between the solid phase and the solid phase of Li ₂ CO ₃ particles and Co ₃ O ₄ particles can easily proceed. However, when the temperature exceeds 800 ° C., the particles are easily sintered, the reaction is hardly completed, and the battery performance is poor. Therefore, the range of 600 ° C. to 800 ° C. at which the battery performance is good is preferable.

Thereafter, after the reaction is sufficiently completed, a second heat treatment is performed at 850 ° C. to 950 ° C. to finally obtain the target LiCoO ₂ . If the temperature is lower than 850 ° C. in the second heat treatment step, the capacity is reduced due to insufficient synthesis. If the temperature exceeds 950 ° C., the sintering of the particles proceeds or the crystal is decomposed, so that the battery performance is improved. The battery performance is improved because of the decrease 85
The range of 0 ° C to 950 ° C is preferred.

At this time, the specific surface area of Co ₃ O ₄ is preferably 2.0 m ² / g or more, and when it is less than 2.0 m ² / g, the reactivity between tricobalt tetroxide and the Li compound is lowered. However, since the synthesis rate in the primary heating is lowered and the specific capacity is lowered, it is not preferable. On the contrary, if the specific surface area exceeds 100 m ² / g, the tap density of the lithium cobalt oxide after the secondary heating is lowered due to the lightness, and the mixture filling property is lowered, which is not preferable.

  Then, after the first heat treatment step, by having the step of once cooling to room temperature and pulverizing, the agglomerated particles can be dispersed again and the reaction residue can be reliably reacted by contacting with air. This is preferable because it is possible.

The specific surface area of the lithium composite cobalt oxide represented by the general formula LiCo _X O ₂ (where 1.0 <X ≦ 1.05) obtained by such a production method is 0.4 to 0.9 m ² / g, and a LiCoO ₂ powder having a high synthesis rate and high filling property can be obtained.

When the specific surface area is less than 0.4 m ² / g, the battery performance deteriorates rate characteristics, which is not preferable. On the other hand, when it exceeds 0.9 m ² / g, it becomes light to secure the specific surface area, and LiCoO ₂ powder This is not preferable because the tap density is lowered and the mixture filling property is lowered.

  Next, a lithium secondary battery using the obtained lithium composite cobalt oxide as a positive electrode active material will be described with reference to FIG. FIG. 1 shows a longitudinal sectional view of a cylindrical lithium secondary battery as an example.

  The lithium secondary battery shown in FIG. 1 includes a positive electrode plate 11, a negative electrode plate 13, and an electrode plate group including a separator 15 disposed between the positive electrode plate 11 and the negative electrode plate 13, and an electric power generation including an electrolyte (not shown). A cylindrical battery case 16 having a bottom with the power generation element accommodated therein, a sealing body 28 for sealing the opening of the battery case 16, and an opening end of the battery case 16 and the sealing body. It consists of an insulating gasket 20.

  In addition, an upper insulating plate 21 and a lower insulating plate 22 are disposed above and below the electrode plate group, respectively.

  A grooving toward the inside is performed slightly below the upper end of the opening of the battery case 16, and an annular support portion 17 is formed to bulge toward the inside of the battery case 16. A sealing body 28 is fitted on the annular support portion 17. An insulating gasket 20 is disposed at the peripheral edge of the sealing body 28, whereby the battery case 16 and the sealing body 28 are insulated. Furthermore, the opening end of the battery case 16 is caulked by the insulating gasket 20, thereby sealing the battery case 16.

  The sealing body 28 includes a plate 18, a cap 19 serving as an external connection terminal, and an upper valve body 23 and a lower valve body 24 disposed between the plate 18 and the cap 19. Here, a filter 29 which is an insulator is sandwiched between the upper valve body 23 and the lower valve body 24. The upper valve body 23 and the lower valve body 24 are conductively connected at a welding point 25. The upper valve body 23 includes an annular easily breakable portion 23a, and the lower valve body 24 includes an annular easily breakable portion 24a. When the battery internal pressure rises, the easily breakable portion 24a of the lower valve body 24 breaks, and when the battery internal pressure rises further, the easily breakable portion 23a of the upper valve body 23 breaks and the cap 19 is discharged. The gas is released from the hole 26 to the outside. Thereby, it is possible to prevent the battery internal pressure from rising abnormally.

The plate 18 is connected with a positive electrode lead 12 drawn out from the positive electrode plate 11, and a negative electrode lead 14 drawn out from the negative electrode plate 13 is connected to the inner bottom of the battery case 16.

  Furthermore, in this cylindrical lithium ion secondary battery, the safety is further enhanced by disposing the PTC element 27 between the cap 19 and the upper valve body 23.

  The positive electrode plate 11 includes a positive electrode current collector and a positive electrode active material layer carried thereon. A positive electrode active material layer contains the positive electrode active material manufactured using the tricobalt tetroxide of this invention.

  The positive electrode plate 11 is produced, for example, by applying a positive electrode paste on both surfaces of a positive electrode current collector, drying, and rolling to form a positive electrode active material layer. The positive electrode plate is provided with a plain portion having no active material layer, and the positive electrode lead 12 is welded thereto.

  The positive electrode current collector is preferably made of aluminum or an aluminum alloy and has a thickness in the range of 10 μm to 60 μm. The surface of the positive electrode current collector may be subjected to lath processing or etching treatment.

  The positive electrode paste can be prepared by mixing a positive electrode active material produced using the tricobalt tetroxide of the present invention, a binder, and a conductive agent with a dispersion medium. Moreover, when preparing a positive electrode paste, you may add a thickener as needed.

  As the binder, the conductive agent, and the thickener added as necessary, the same materials as those used in the past can be used.

  For example, the binder is not particularly limited as long as it can be dissolved or dispersed in a paste dispersion medium. For example, a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (SBR), acrylic polymer, vinyl polymer, and the like can be used. These may be used alone or in combination of two or more.

  As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, polytetrafluoroethylene, and the like are preferable. These can be used as dispersions.

  As the conductive agent, acetylene black, graphite, carbon fiber, or the like can be used. These may be used alone or in combination of two or more.

  As the thickener, ethylene-vinyl alcohol copolymer, carboxymethyl cellulose, methyl cellulose and the like are preferable.

  As the dispersion medium used for the positive electrode paste, a dispersion medium in which the binder can be dispersed or dissolved is suitable. When using an organic binder, N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethyl sulfoxide, hexamethylsulfuramide, tetramethylurea, acetone, methyl ethyl ketone, etc. alone or It is preferable to use a mixture. Moreover, when using water-system binders, such as SBR, water and warm water are preferable.

A method for preparing a positive electrode paste by mixing a positive electrode active material, a binder, a conductive agent and a thickener added as necessary with a dispersion medium is not particularly limited. Examples include a method of mixing these components using a planetary mixer, a homomixer, a pin mixer, a kneader, a homogenizer, and the like. Moreover, the above apparatus may be used independently and may be used in combination of 2 or more type. Furthermore, various dispersants, surfactants, stabilizers, and the like can be added as necessary during kneading of the positive electrode paste.

  The positive electrode paste prepared as described above can be easily applied to the positive electrode current collector using, for example, a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater, dip coater, etc. can do. The positive electrode paste applied to the positive electrode current collector is preferably dried close to natural drying, but considering productivity, it is preferably dried at a temperature of 70 ° C. to 200 ° C. for 10 minutes to 5 hours.

  Rolling may be performed several times at a linear pressure of 1000 to 2000 kg / cm or by changing the linear pressure until the positive electrode plate has a predetermined thickness of 130 μm to 200 μm by a roll press.

  The negative electrode plate 13 is produced, for example, by applying a negative electrode paste on one or both sides of a negative electrode current collector, drying, and rolling to form a negative electrode active material layer. The negative electrode plate 13 is provided with a plain portion having no active material layer, and the negative electrode lead 14 is welded thereto.

  The negative electrode current collector is preferably made of a copper foil and has a thickness in the range of 10 μm to 50 μm. Further, the surface of the negative electrode current collector may be subjected to lath processing or etching treatment.

  The negative electrode paste is prepared by mixing a negative electrode active material, a binder, and a dispersion medium. Moreover, you may add a electrically conductive agent, a thickener, etc. to a negative electrode paste as needed.

  Although it does not specifically limit as a negative electrode active material, It is preferable to use the carbon material which can occlude / release lithium ion by charge / discharge. For example, carbon materials obtained by firing organic polymer compounds (phenolic resin, polyacrylonitrile, cellulose, etc.), carbon materials obtained by firing coke and pitch, artificial graphite, natural graphite, pitch-based carbon fibers, A PAN-based carbon fiber or the like is preferable, and the shape thereof can be a fibrous shape, a spherical shape, a scale shape, or a lump shape.

  As the binder, the conductive agent added as necessary, the thickener and the like, the same ones as in the past can be used. For example, the same binder, conductive agent, thickener and the like as those used for the positive electrode plate can be used.

  As the separator 15, a microporous film made of a polymer is preferably used. Examples of the polymer include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, and polyether (polyethylene oxide and polypropylene oxide). And at least one selected from the group consisting of cellulose (carboxymethylcellulose and hydroxypropylcellulose), poly (meth) acrylic acid, poly (meth) acrylic acid ester and the like. A multilayer film in which these microporous films are superposed can also be used. Among these, a microporous film made of polyethylene, polypropylene, polyvinylidene fluoride, or the like is preferable, and the thickness is preferably 15 μm to 30 μm.

  The battery case 16 may be made of copper, nickel, stainless steel, nickel plated steel, or the like. These materials can be subjected to drawing processing, DI processing, and the like to form a battery case shape. In order to improve the corrosion resistance of the case, the processed battery case 16 may be plated.

  Further, by using a battery case made of aluminum or an aluminum alloy, a square secondary battery having a light weight and a high energy density can be manufactured.

  As the non-aqueous electrolyte, a solution made of a non-aqueous solvent and a solute is used.

  As the non-aqueous solvent, those containing a cyclic carbonate and a chain carbonate as main components are preferable. For example, as the cyclic carbonate, it is preferable to use at least one selected from ethylene carbonate, propylene carbonate, and butylene carbonate. Further, as the chain carbonate, it is preferable to use at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like.

As the solute, for example, a lithium salt in which an anion has a functional group having a strong electron-withdrawing property is used. Examples of these include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ). ₃ etc. are mentioned. These solutes may be used alone or in combination of two or more. Further, these solutes are preferably dissolved at a concentration of 0.5 to 1.5M in the non-aqueous solvent.

  As the plate 18, a plate made of a material having an electrolytic solution resistance and a heat resistance can be used without particular limitation. Among them, those made of light aluminum or aluminum alloy having high electrolytic solution resistance and heat resistance are preferable.

  The upper valve body 23 and the lower valve body 24 are preferably made of a thin aluminum foil having flexibility.

  As the positive electrode lead 12 and the negative electrode lead 14, those known in the art can be used. For example, examples of the positive electrode lead include those made of aluminum. Examples of the negative electrode lead include those made of nickel.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but these do not limit the present invention.

Example 1
A method for synthesizing LiCoO ₂ of this example will be described.

FIG. 2 shows a schematic diagram of a first heat treatment furnace for synthesizing LiCoO ₂ . A ceramic container 3 filled with a mixture ₂ of Li ₂ CO ₃ and Co ₃ O ₄ , which is a material for synthesizing LiCoO ₂ , is disposed in the furnace body 1 and heated to a predetermined temperature by a heater 4. The air generated from the air pump 5 is inserted into the furnace through the air insertion port 6 and discharged from the generated gas disposal port 7 together with the gas components generated by the synthesis reaction in the furnace. _The CO ₂ gas which is a gas component generated by the synthesis reaction is measured by the _2- gas concentration measuring device 9.

As a mixture 2 of materials for synthesizing LiCoO ₂ , tricobalt tetroxide (Co ₃ O ₄ ) and lithium carbonate (Li ₂ CO ₃ ) were mixed so that the atomic molar ratio of Li and Co was 1: 1.01. . 2 kg of this mixture was put in a 5 L ceramic container 3, 2 L / min of air generated from the air pump 5 was inserted through the air insertion port 6, and the temperature in the furnace was A: 600 ° C., 65 in 2 hours.
The temperature was raised to 0 ° C., 700 ° C., and 800 ° C., and the temperature was held at temperature A for 5 hours after the temperature elevation, and then the heat treatment in the first step was performed to synthesize LiCoO ₂ to obtain compounds A1 to A4.

The reaction of Co ₃ O ₄ and Li ₂ CO ₃ is represented by the following formula (1).

4Co ₃ O ₄ + 6Li ₂ CO ₃ + O ₂ → 12LiCoO ₂ + 6CO ₂ (1)
At this time, the results of measuring the CO ₂ gas generation state (including gas generation at the time of temperature increase) with respect to the change with time at each temperature by the CO ₂ gas concentration measuring device 9 are shown in FIG.

Table 1 shows the result of calculating the amount of generated CO ₂ gas and converting it to the synthesis rate from this result and the above equation (1). It was confirmed that the synthesis rate calculated from the amount of CO ₂ gas and the synthesis rate measured from the decrease in mass were in agreement, and the synthesis rate of LiCoO ₂ could be evaluated by measuring the CO ₂ gas amount.

(Comparative Example 1)
Except that the temperature A was set to 400 ° C., 500 ° C., and 850 ° C., LiCoO ₂ was synthesized to produce compounds B1 to B3 and the CO ₂ gas concentration was measured in the same manner as in Example 1. 3 shows the synthesis rate of LiCoO ₂ .

(Comparative Example 2)
As a mixture 2 of materials for synthesizing LiCoO ₂ , cobalt oxide (Co ₃ O ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed so that the atomic molar ratio of Li and Co is 1: 0.99, and the temperature is increased. except that the a and 650 ° C., the same procedure as in example 1, to synthesize LiCoO _2, with making the compounds B4, the results of measurement of the CO ₂ gas concentration in FIG. 3, the synthesis rate of LiCoO ₂ Table 1 shows.

As is apparent from Table 1, a synthesis rate of 95% or higher is obtained when the temperature A of the heat treatment in the first step is 600 ° C., 650 ° C., 700 ° C., and 800 ° C., but when the compound B3 has a high temperature of 850 ° C., It was found that synthesis reached a peak at the initial stage of heating, and the total synthesis rate until the end of heating decreased. Further, when the compound B1 is 400 ° C. and the positive electrode active material B2 is 500 ° C., the reaction between the solid phase and the solid phase of the Li ₂ CO ₃ particles and the Co ₃ O ₄ particles does not easily proceed, and the synthesis rate decreases. .

By the way, when mixing so that the atomic molar ratio of Li and Co in the compound B4 is 1: 0.99, an excess of Li ₂ CO ₃ is required to sinter, resulting in sintering with Co ₃ O ₄ . The reaction is inhibited and the synthesis rate is lowered.

The compounds A1 to A4 and B2 to B4 thus obtained were heated in an electric furnace for 6 hours at a temperature B:
The heat treatment of the 2nd process was performed at 800 degreeC, 850 degreeC, 900 degreeC, 950 degreeC, and 1000 degreeC, and the obtained compound was grind | pulverized and classified and it was set as the positive electrode active material for batteries.

  Next, the cylindrical lithium secondary battery was comprised using the obtained positive electrode active material for batteries.

(Preparation of positive electrode plate)
The positive electrode active material for a battery obtained as described above, carbon black as a conductive agent, and polytetrafluoroethylene aqueous dispersion as a binder, in a mass of solids of 100: 3: Kneaded and dispersed at a rate of 10. This mixture was suspended in an aqueous solution of carboxymethyl cellulose to obtain a positive electrode mixture paste. This positive electrode mixture paste was applied to both surfaces of a current collector made of an aluminum foil having a thickness of 30 μm by a doctor blade method so that the total thickness was about 230 μm. Here, the total thickness refers to the total thickness of the current collector and the paste applied to both sides of the current collector.

  After drying, it was rolled to a thickness of 180 μm and cut to a predetermined size to obtain a positive electrode plate. An aluminum positive electrode lead was welded to a portion of the current collector where the positive electrode active material layer was not formed.

(Preparation of negative electrode plate)
A negative electrode mixture paste is prepared by kneading and dispersing a carbonaceous material (for example, natural graphite, artificial graphite, etc.) as a negative electrode active material and a styrene butadiene rubber binder in a mass ratio of 100: 5. Produced. This negative electrode mixture paste was applied to both surfaces of a current collector made of a copper foil having a thickness of 20 μm by a doctor blade method so that the total thickness was about 230 μm. The overall thickness is the same as described above.

  After drying, it was rolled to a thickness of 180 μm and cut to a predetermined size to obtain a negative electrode plate. A nickel negative electrode lead was welded to a portion of the current collector where the negative electrode active material layer was not formed.

(Battery assembly)
The positive electrode plate and the negative electrode plate produced as described above were spirally wound through a separator made of a microporous film made of polyethylene having a thickness of 25 μm to obtain an electrode plate group. This electrode plate group was housed in a battery case to produce a cylindrical lithium secondary battery as shown in FIG.

  In the battery, the non-aqueous electrolyte is 1 mol / L of lithium hexafluorophosphate as a solute in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a molar ratio of 1: 3. What was melt | dissolved by the density | concentration was used.

  The battery case was sealed by caulking the opening end of the battery case to the sealing body via the insulating gasket so that the compressibility of the insulating gasket was 30%.

  The obtained battery had a diameter of 18.0 mm, a total height of 65.0 mm, and a battery capacity of 2000 mAh.

The specific capacity of the positive electrode active material thus obtained was calculated as follows.
First, after charging to a battery voltage of 4.2 V at a constant current of 220 mAh at 20 ° C., the battery is paused for 1 hour, and then discharged to a battery voltage of 3.0 V at a constant current of 440 mAh. The charging / discharging was repeated 3 times by this method, and the third discharge capacity was set as the initial capacity. Table 2 shows the result of calculating the specific capacity of the positive electrode active material by dividing the initial capacity by the mass of LiCoO ₂ contained in the battery.

  From the results of Table 2, when the temperature A of the heat treatment in the first step is in the range of 600 to 800 ° C. and the temperature B of the heat treatment in the second step is 850 ° C. to 950 ° C., the specific capacity of the positive electrode active material is 140 g / It became more than mAh. At this time, at the end of the first step, 95% or more of gas components generated by the synthesis reaction in the first step were generated.

(Example 2)
As the specific surface area of ^{_{Co 3 O 4, 1.5m 2 /g,2.0m}} 2 / g, 50m 2 / g, 80m 2 / g, 100m 2 / g, those of 110m ² / g used in Example 1 In the same manner as above, LiCoO ₂ was synthesized to produce compounds A5 to A10, and the results of the synthesis rate, specific capacity, and active material tap density of LiCoO ₂ are shown in Table 3.

The active material tap density can be easily obtained by filling the measuring cylinder with 50 g of active material, tapping 1800 times with a stroke of 30 mm, measuring the volume, and calculating the mass per 1 cm ³ .

From Table 3, when the specific surface area of Co ₃ O ₄ is less than 2.0 m ² / g, tricobalt tetroxide and L
The reactivity with the i compound decreases, the synthesis rate in the primary heating decreases, the specific capacity decreases, and conversely, if the specific surface area exceeds 100 m ² / g, because of the lightness, reduced tap density of the lithium cobaltate, because the mixture filling property deteriorates, Co ₃ as a specific surface area of the O ₄ is 2.0m ² / g~100m ² / g range is clearly more preferable became.

(Example 3)
A method of synthesizing LiCoO ₂ in which the heat treatment in the _second step is performed after cooling and pulverization after the heat treatment in the first step of the present embodiment will be described.

  The compounds A1 to A4 and B2 to B4 according to Example 1 and Comparative Examples 1 and 2 were cooled to room temperature, pulverized with a crucible so that the average particle size was 5 μm to 10 μm, and then at 900 ° C. in the second step. The compound obtained when the heat treatment was performed and when the second step heat treatment was performed at 900 ° C. without cooling and pulverization was pulverized and classified to obtain a positive electrode active material. Table 4 shows the results of producing a battery in the same manner as in Example 1 and calculating the specific capacity.

  From Table 4, it was found that the specific capacity was further increased by adding a cooling and pulverization step after the first heat treatment step in the range of 600 ° C to 800 ° C.

  At 500 ° C., the specific capacity increases after the second heat treatment because the reaction in the first heat treatment is insufficient. On the other hand, in the case of 850 ° C. and the case where lithium is excessively mixed, sintering proceeds in the first heat treatment, so that the contact opportunity with the air by pulverization does not increase and the specific capacity does not increase greatly.

Example 4
In any of the manufacturing method of this embodiment 1-3, those having a specific surface area of raw materials Co ₃ O ₄ is different from 2.0m ² /g,30.0m ² /g,60.0m ² / g second heating step 900 ° C., it is heated to a specific surface area at ^{950 ℃ 0.3m 2 /g,0.4m 2 /g,0.6m 2} /g,0.8m 2 /g,0.9m 2 /g,1.0m ^An active material composed of ² / g LiCoO ₂ was synthesized, and the tap density was measured by the above method and tested under the following conditions to obtain a high-efficiency discharge capacity retention rate.

  First, the battery is charged at a constant current of 220 mA up to a battery voltage of 4.2 V at 20 ° C., then rested for 1 hour, and then discharged to a battery voltage of 3.0 V at a constant current of 440 mA. The charging / discharging was repeated 3 times by this method, and the third discharge capacity was set as the initial capacity. Next, a discharge test was conducted at a discharge current of 2200 mA, and the discharge capacity with respect to the initial capacity expressed in% was calculated as a high-efficiency discharge capacity retention rate. The results are shown in Table 5.

From Table 5, it was found that when the specific surface area was 0.3 m ² / g, the reaction area with the electrolytic solution was reduced, and the high-efficiency discharge capacity retention rate was reduced. Further, 1.0 m tap density decreases at ² / g or more, as the specific surface area of LiCoO ₂ was found to be more preferably in the range of 0.4m ² /g~0.9m ² / g.

In this example, a combination of tricobalt tetroxide (Co ₃ O ₄ ) and lithium carbonate (Li ₂ CO ₃ ) alone was used as a starting material for LiCoO ₂ , but tricobalt tetroxide, Li ₂ CO ₃ , and LiNO were used. ₃ , the same effect can be obtained even when at least one of LiOH is used in combination.

According to the production method of the present invention, it is possible to obtain a lithium composite cobalt oxide having a specific surface area of 0.4 to 0.9 m ² / g, and to synthesize LiCoO ₂ having a high synthesis rate and high filling property. It is possible and useful.

Vertical sectional view of a cylindrical lithium secondary battery of the present invention Schematic diagram of synthesis furnace and generated gas measuring device used in the present invention The figure which shows the generation condition of the gas at the time of this invention 1st heat processing

Explanation of symbols

1 furnace body 2 mixture 3 ceramic container 4 heater 5 air pump 6 air insertion opening 7 generated gas exhaust port 8 condenser 9 CO ₂ gas concentration measuring device 11 a positive electrode plate 12 cathode lead 13 negative electrode plates 14 negative electrode lead 15 separator 16 Upper insulating plate 17 Lower insulating plate 18 Battery case 19 Annular groove 20 Plate 21 Insulating gasket 22 Upper valve body 22a Upper valve body easily destructible portion 23 Lower valve body 23a Lower valve body easily destructible portion 24 Welding point 25 Cap (external connection terminal)
26 Discharge hole 27 PTC element 28 Sealing body 29 Filter

Claims (4)

General formula LiCo _X O ₂ (where 1.0 <X ≦ 1.05) obtained by mixing and heating at least one lithium compound of the group consisting of Li ₂ CO ₃ , LiNO ₃ or LiOH and Co ₃ O _4. In the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery for synthesizing a lithium composite cobalt oxide represented by the above formula), the heating step is performed at a temperature from 600 ° C. to 800 ° C. while introducing oxygen or air. The first step to be performed and the second step to be heated at 850 ° C. to 950 ° C., generating 95% or more of the gas component generated by the synthesis reaction in the first step, and then moving to the second step. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. ^{2. The} method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the specific surface area of the Co ₃ O ₄ is 2.0 m ² / g or more. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein 95% or more of the reaction product gas is generated in the first step, and then cooled, pulverized, and transferred to the second step. Manufacturing method. The specific surface area of the lithium composite cobalt oxide represented by the general formula LiCo _x O ₂ (where 1.0 <X ≦ 1.05) obtained by the production method according to claim 1 is 0.4 m ^2. /G-0.9 m < ² > / g The positive electrode active material for nonaqueous electrolyte secondary batteries characterized by the above-mentioned.

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