JPH0676823A - Non-aqueous electrolyte secondary battery and positive electrode active material thereof - Google Patents

Abstract

PURPOSE:To obtain a battery having a high capacity and the excellent cycle characteristic and a high discharge characteristic by limiting the apparent density of lithium compound cobalt oxide as the positive electrode active material by the standing method or the tapping method. CONSTITUTION:As the positive electrode active material, lithium compound cobalt oxide at 0.35-1.5g/cm<3>, and furthermore at 0.5-1.5g/cm<3> of apparent density by the standing method and at 1.0-3.3g/cm<3>, and furthermore at 1.4-3.3g/cm<3> of the apparent density by the tapping method is used. A battery having the excellent cycle characteristic and a high discharge characteristic can be realized by using this positive electrode active material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a lithium composite cobalt oxide as a positive electrode active material and a positive electrode active material for a non-aqueous electrolyte battery, and more particularly to improving battery characteristics thereof. It is a thing.

[0002]

2. Description of the Related Art In recent years, portable electronic devices for consumer use,
Cordless is rapidly progressing. Currently, nickel-cadmium batteries or sealed small lead-acid batteries play a role as driving power sources for these electronic devices, but with the progress of portable and cordless development, it has become established.
There is an increasing demand for higher energy density, smaller size and lighter weight of the secondary battery as a driving power source. Further, in recent years, a battery capable of high-rate charging / discharging has been demanded as represented by the rapid expansion of the market of small camcorders.

Under such circumstances, a non-aqueous electrolyte secondary battery has been proposed which uses a lithium composite cobalt oxide showing a high charge / discharge voltage, for example, LiCoO _2, as a positive electrode active material and utilizes insertion / extraction of lithium ions. (See, for example, JP-A-63-59507).

In order to realize high-rate charging / discharging, such a battery is devised to maximize the electrode area by, for example, forming a spiral structure in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween. ing.

For example, as an example of the method for producing the electrode, in the method disclosed in JP-A-3-244508, first, 100 parts by weight of LiCoO ₂ powder as a positive electrode active material, 3 parts by weight of acetylene black, 4 parts by weight of graphite powder and 7 parts by weight of a fluororesin binder are mixed and suspended in carboxymethyl cellulose and an aqueous solution to form a paste. Apply this paste to both sides of aluminum foil,
After drying, it is rolled to obtain a positive electrode plate.

In order to increase the battery capacity, the positive electrode plate manufactured by such a method has a weight of lithium composite cobalt oxide per unit volume in the positive electrode active material layer (hereinafter referred to as active material density). It is necessary to increase the size, but it is known that a low active material density is preferable for high rate discharge in which a large current is discharged.

For example, active material densities of 2.0, 2.5, and 3.0 are formed on both sides of an aluminum foil having a thickness of 0.03 mm.
Width 35 mm as 4.0, 4.5 and 5.0 g / cm ³ .
A positive electrode plate having a positive electrode active material layer having a length of 240 mm and a thickness of 0.07 mm and a negative electrode plate having a carbon agent obtained by heat treatment of coke as an active material are combined to form a battery, and a diameter is formed. The battery was housed in a battery case having a height of 13.8 mm and a height of 50 mm and subjected to constant current charging / discharging at a charge end voltage of 4.1 V and a discharge end voltage of 3.0 V.

As is apparent from FIG. 1, when the active material density of the positive electrode plate is 2.0 g / cm ³ or less, the high rate discharge characteristics are good, but the capacity of the battery itself is 300 AA size batteries.
It is not practical because it becomes smaller than mAh. Further, when the active material density is 5.0 g / cm ³ or more, although the capacity is high at a low rate discharge, the porosity of the electrode plate is decreased due to the increase of the active material density and the positive electrode plate with respect to the electrolyte solution is reduced. Since the wettability is deteriorated, the high rate discharge rate is significantly deteriorated.

As can be seen from this, the active material density of the positive electrode plate is usually set to 2.5 to 4.5 g / cm ³ .

[0010]

However, even in the battery constructed by using the electrode plate having the active material density of the electrode plate in the range of 2.5 to 4.5 g / cm ³ as described above, a large current is required. When high-rate charging and discharging is performed, the active material density is 3.5 g /
A battery using an electrode plate having a size of ³ cm ³ or more still has a problem of capacity reduction.

A battery using such a positive electrode plate is
It was also clarified that the capacity deterioration with the repetition of charge and discharge cycles was large.

As a result of thorough investigations by the present inventors, it has been found that such characteristic deterioration is caused by the following.

In a battery having such a spiral structure, it is desirable that the electrode plate area be as large as possible in order to enable charging and discharging at a high rate. However, conversely, as the area of the electrode plate increases, the proportion of the separator in the battery unit volume increases, so that the amount of the active material decreases and it becomes difficult to maintain the high capacity of the battery. Therefore, in order to secure the capacity, it is necessary to increase the amount of the active material filled per unit volume of the electrode plate.

In order to satisfy such characteristics, for example, in the battery disclosed in Japanese Unexamined Patent Publication No. 3-244508,
As described above, a method in which the active material paste is applied to a current collector such as an aluminum foil, dried, and then rolled by a roller press or the like is applied. When making an electrode plate by such a method, in order to increase the active material filling amount per unit area, increase the thickness of the paste applied to the current collector such as aluminum foil, and press with a pressing machine such as a roller pressing machine. It is necessary to roll to a predetermined electrode plate thickness.

However, when a battery is constructed by using the positive electrode plate prepared by such a method and charging and discharging with a large current is carried out, it becomes clear that the potential of the positive electrode plate is polarized and the capacity is lowered. It was As described above, the potential of the positive electrode is remarkably polarized because the positive electrode plate is smoothly rolled when the active material density of the positive electrode plate is increased by rolling several times with a roller press machine or the like, and therefore the vicinity of the surface of the positive electrode plate is increased. This is because the porosity is remarkably reduced and the substantial surface area of the electrode plate is reduced.

Further, in a battery utilizing such ion insertion and desorption, the positive electrode plate expands and contracts due to charge and discharge. Therefore, when such a strongly rolled electrode plate is used, the charge and discharge cycle is repeated. As a result, it was revealed that the active material fell off from the electrode plate, showing a significant capacity deterioration.

[0017]

The present invention relates to a non-aqueous electrolyte secondary battery comprising a negative electrode plate and a positive electrode plate having a lithium composite cobalt oxide as a main active material with a separator interposed between them. , The apparent density of the lithium composite cobalt oxide powder as the positive electrode active material by the static method (Appa
rent Bulk Density: hereinafter referred to as ABD) is 0.35
What is set to be ~ 1.5 g / cm ³ is used. ABD of the lithium composite cobalt oxide is 0.5 to
More preferably, it is 1.5 g / cm ³ .

The present invention also provides an apparent density (Apparent T) of the lithium composite cobalt oxide powder obtained by the tap method.
ap Density: hereinafter referred to as ATD), 1.0 to 3.3 g
It is an / cm ^3. The apparent density of the lithium composite cobalt oxide powder by the tap method is 1.4 to
More preferably, it is 3.3 g / cm ³ .

The lithium composite cobalt oxide may be lithium carbonate and a cobalt salt, for example, one synthesized from tricobalt tetraoxide, cobalt carbonate, cobalt monoxide, cobalt hydroxide, cobalt nitrate or a mixture thereof. . As the cobalt source, among the above examples, tricobalt tetraoxide powder has a large apparent density, and it is easy to synthesize a lithium composite cobalt oxide having a large apparent density.

ABD of lithium composite cobalt oxide powder
Alternatively, the ATD changes synthesis conditions such as the apparent density of the cobalt salt, the mixing ratio of the lithium source and the cobalt source, the pressure treatment of the mixture of the lithium source and the cobalt source, and the heat treatment temperature and heat treatment time in the synthesis. It is possible to obtain the lithium composite cobalt oxide which is set to the predetermined ABD or ATD by these methods.

[0021]

The paste prepared by suspending the lithium composite cobalt oxide according to the present invention in an aqueous solution of carboxymethyl cellulose has a large specific gravity after drying, so that the paste can be applied in a predetermined unit without being thickly applied to the collector metal. The active material filling amount per area can be obtained.

Therefore, it is possible to remarkably reduce the pressure and the number of times of rolling by a pressing machine or the like when forming into a predetermined electrode plate size.

Therefore, the weight of the active material per unit area can be increased without decreasing the porosity of the surface of the electrode plate.

As a result, not only low rate charging / discharging but also high rate charging / discharging in which a large current is passed can maintain a high capacity.

Further, since it is not rolled firmly, the active material does not fall off from the electrode plate even after repeated charge and discharge cycles.
The cycle life of the battery is significantly improved.

Furthermore, since the paste application pressure can be made thin, the paste can be dried easily, and the electrode plate production efficiency is greatly improved.

[0027]

【Example】

(Embodiment 1) An embodiment of the present invention will be described with reference to the drawings.
In this Example 1, lithium cobalt composite oxides having different apparent densities were prepared by changing the apparent density of tricobalt tetroxide as a raw material.

FIG. 2 shows a vertical sectional view of the cylindrical battery used in the first embodiment. In FIG. 2, reference numeral 1 is a battery case formed by processing an organic electrolytic solution resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which the positive electrode plate 5 and the negative electrode plate 6 are spirally wound a plurality of times via the separator 7 and housed in the case. A positive electrode lead 5a is drawn out from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6a is drawn out from the negative electrode plate 6 and connected to the bottom of the battery case 1. 8
Are insulating rings provided on the upper and lower portions of the electrode plate group 4, respectively.

The positive electrode plate 5, the negative electrode plate 6, the electrolytic solution and the like will be described in detail below. The negative electrode plate 6 was made into a paste by mixing 100 parts by weight of carbon powder obtained by heat-treating coke with 10 parts by weight of a fluororesin-based binder and suspending the mixture in an aqueous carboxymethyl cellulose solution. Then, this paste is applied to the surface of a copper foil having a thickness of 0.015 mm, and after drying 0.2 m
It was rolled into a size of m and cut into a size of width 37 mm and length 280 mm to obtain a negative electrode plate.

The positive electrode plate was prepared by adding 100 parts by weight of powder of active material LiCoO ₂ (detailed later) to acetylene black 3
By weight, 7 parts by weight of a fluororesin-based binder were mixed and suspended in an aqueous carboxymethyl cellulose solution to form a paste. This paste was applied on both sides of an aluminum foil in various thicknesses so that the amount of active material present per unit area was constant, dried, and then dried with a roll press machine to a thickness of 0.17.
The positive electrode plate 5 was obtained by rolling into a width of 35 mm and cutting into a width of 35 mm and a length of 250 mm. Then, the leads 5a and 6a were attached to the positive and negative electrodes, respectively, and they were spirally wound with a separator interposed therebetween and housed in a battery case having a diameter of 13.8 mm and a height of 50 mm.

The electrolytic solution was prepared by mixing 1 volume / l of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume.
After injecting into the electrode plate group 4 using the one dissolved at a ratio of
The battery was sealed and used as a test battery.

The synthesis of the positive electrode active material and the production of the positive electrode plate will be described in detail below. In the present invention, ABD and ATD are measured according to JIS K 5101 20.1.
And 20.2 are the same as the method for determining the apparent density of pigments.

The ABD has an opening of 0.
5 mm sieve 9, funnel 10, container 30 cm ³ in capacity
1. Using a container equipped with a container receiver 12 and a funnel stand 13, place the sample on a sieve, wipe the entire surface of the sieve evenly and lightly with a brush until the sample that has passed through the sieve becomes heaped up on the receiver. receive. Next, the mountain portion was scraped off using a spatula, the content of the receiver was weighed, and the apparent density was calculated.

The ATD has a capacity of 1 as shown in FIG.
00 cm ³ graduated cylinder, rubber stopper for graduated cylinder, device for dropping graduated cylinder from height of 50 mm, and spring specified in JIS K 6301 5.2 (spring hardness test) with a thickness of 3 to 5 mm. Using a type A type with a rubber plate having a hardness of 60 to 80, put a sample of a constant mass (for example, 50 grams) in a graduated cylinder, put a rubber stopper on the graduated cylinder, and apply a rubber from a height of 50 mm. Tap on the plate 200 times. After tapping, the sample volume in the graduated cylinder is read and the apparent density is calculated.

It should be noted that tricobalt tetroxide absorbs AB when it absorbs moisture.
Since the values of D and ATD fluctuate, the apparent density was measured after sufficiently drying by heat treatment at 650 ° C. for 10 hours.

The positive electrode active material in the present invention was prepared as follows. ABD 0.31g / cm ³ , ATD 0.8
Tricobalt tetroxide of g / cm ³ and lithium carbonate were mixed at a ratio of Co to Li of 1: 1 and baked in an air atmosphere at 900 ° C. for 5 hours to obtain a lithium composite cobalt oxide. . This lithium composite cobalt oxide is referred to as sample A. Measurement of the ABD and ATD of the lithium composite cobalt oxide synthesized in this manner were respectively 0.37 g / cm ³ and 1.02 g / cm ^3.

Similarly, the ABD at the time of drying is 0.44,
A lithium composite cobalt oxide was synthesized in the same manner as in Sample A except that 0.64, 0.88, and 1.21 g / cm ³ of tricobalt tetraoxide were used as the cobalt source. (Samples B to E) Table 1 shows the values of ABD and ATD of tricobalt tetroxide and lithium composite cobalt oxide, which are raw materials of the lithium composite cobalt oxides (Samples A to E) thus synthesized.

[0038]

[Table 1]

(Example 2) As Example 2, A at the time of drying
BD is 1.21 g / cm ³ , ATD is 2.53 g / cm
³ were mixed tricobalt tetraoxide and lithium carbonate, 100
Sample F was a lithium composite cobalt oxide obtained by pressurizing into pellets at kgf / cm ² and then firing under the same conditions. The ABD and ATD of sample F are shown in Table 1.
Also described in.

Comparative Example 1 As Comparative Example 1, A at the time of drying was used.
BD is 0.22 g / cm³, ATD 0.40g / cm
³Of tricobalt tetroxide and lithium carbonate
The lithium composite cobalt oxide obtained by firing under the conditions
This is Sample G. AB of the obtained lithium composite oxide
D and ATD are each 0.26 g / cm³, 0.5
3 g / cm ³Met.

Comparative Example 2 As Comparative Example 2, A at the time of drying was used.
BD is 1.21 g / cm ³ , ATG is 2.53 g / cm
³ were mixed tricobalt tetraoxide and lithium carbonate, 500
Sample H was a lithium composite cobalt oxide obtained by pressurizing into pellets at kgf / cm ² and then firing under the same conditions. The ABD and ATD of sample H are 1.
It was 63 and 3.72 g / cm ³ .

100 parts by weight of the powders of the above samples A to H (LiCoO ₂ ) were mixed with 3 parts by weight of acetylene black and 7 parts by weight of a fluororesin binder and suspended in an aqueous carboxymethylcellulose solution to form a paste. . This paste was applied to both sides of an aluminum foil having a thickness of 30 μm while changing the coating thickness so that 0.05 g of the active material was present per cm ² and dried.

The obtained electrode plate was rolled using a roller press machine to a thickness of 0.17 mm and cut into a width of 35 mm and a length of 250 mm to prepare a positive electrode plate.

The active material densities of the positive electrode plates prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were all 3.57 g / cm ³ .

The thus prepared electrode plate was spirally wound with a separator interposed between the electrode plates and the electrode plate, which was then housed in a battery case. After injection of the electrolyte, the battery was sealed and a test battery was prepared. These are batteries A to H.

The battery thus prepared was subjected to a cycle test in which the charge / discharge current was 100 mA and the end-of-charge voltage was 4.1.
Constant-current charging / discharging was performed under the conditions of V and discharge end voltage of 3.0V. Further, a high rate discharge test was conducted at a discharge current of 1A.

The results of the cycle test are shown in FIG.
From these test results, batteries (Batteries A to F, H) using the lithium composite cobalt oxide according to the present invention as a positive electrode active material.
It is recognized that the cycle characteristics are improved as compared with the battery G made of LiCoO ₂ having a small ABD and ATD, and the ABD is 0.5 or more and the ATD is 1.
It can be seen that the batteries B to F and H using LiCoO ₂ of 45 or more have further improved cycle characteristics.

The reason why the cycle characteristics are improved is that
Even if the expansion and contraction of the active material caused by the insertion and desorption of lithium ions due to charging and discharging occurs, the electrode plate is not rolled firmly, so the space volume in the electrode plate is large and the expansion and contraction of the active material itself The space in the electrode plate can absorb. Therefore, the shape of the electrode plate itself hardly changes even if the charge / discharge cycle is repeated, so that the active material does not fall off from the electrode plate, and good cycle characteristics are exhibited.

However, in the sample H shown in Comparative Example 2, even if acetylene black and a fluororesin-based binder were mixed and suspended in an aqueous carboxymethyl cellulose solution, the active material precipitated due to its large apparent density, Dispersibility in the paste becomes poor. Therefore, when the paste is applied to the surface of the aluminum foil, uneven coating is likely to occur, and when rolled after drying, the electrode plate structure is difficult, such as meandering. As a result, the density of the active material varied, and the discharge capacity of the battery of Sample H using this positive electrode plate was smaller than that of the other batteries.

From these results, the ABD and ATD of the lithium composite cobalt oxide were 1.5 g / cm 2 respectively.
³ , 3.5 g / cm ³ or less is preferable.

Further, a high rate discharge test was conducted at a discharge current of 1 A to obtain a high rate charge / discharge rate (discharge capacity at 1 A / discharge capacity at 100 mA × 100 (%)).

The results of the high rate discharge test are shown in FIG. Figure 6
As is clear from the above, batteries using the lithium composite cobalt oxide according to the present invention as a positive electrode active material (Batteries A to F,
H) shows that the high rate discharge rate and the ward administration are improved compared with the result (76%) in the battery G made from LiCoO ₂ having a small ABD and ATD.
BD is 0.5 g / cm ³ or more, ATD is 1.45 g / c
In the batteries B to F and H using LiCoO _{2 of} m ³ or more, it is recognized that the high-rate discharge rate is 90% or more, which is clearly improved. In this way, the high rate discharge rate was improved because the active material filling amount per unit area when applied with a paste was large in the electrode plate making process, so the rolling pressure or the number of times of rolling in the rolling process after drying was increased. This is because the porosity of the positive electrode plate is increased and the polarization does not increase even when discharging at a high rate.

As described above, the ABD in the present invention is 0.
35-1.5 g / cm ³ , ATD 1.0-3.3 g /
When using the lithium composite cobalt oxides cm ³ charge-discharge cycle characteristics and high-rate discharge characteristics of the battery can be significantly improved.

ABD is 0.5 to 1.5 g / c
m³, ATD 1.4-3.3 g / cm ³Is Richiu
The composite cobalt oxide has a high charge / discharge cycle characteristic.
And high rate discharge characteristics are good, and more preferable.

Also, ABD and ATD are 0.
3~1.2g / cm ^3, was mixed with tricobalt tetroxide lithium carbonate 0.8~2.5g / cm ^3, the cycle characteristics, good active materials high rate discharge characteristics can be obtained by calcining It became clear.

In Example 1, tricobalt tetraoxide was used as the cobalt source, but cobalt salts such as cobalt carbonate, cobalt monoxide, cobalt nitrate and cobalt hydroxide, or a mixture of these cobalt salts was used. Even if the synthesized lithium composite cobalt oxide A
Similar effects were obtained when BD and ATD were within the scope of the present invention.

(Third Embodiment) A third embodiment of the present invention will be described with reference to the drawings. In Example 3, lithium cobalt composite oxides having different apparent densities were prepared by changing the mixing ratio of the raw material cobalt carbonate and lithium carbonate.

Cobalt carbonate having an ATD of 1.20 g / cm ³ when dried, lithium carbonate, and the ratio of Co to Li are C
The mixture was mixed at a ratio of o / Li = 1.05 and fired at 900 ° C. for 5 hours in an air atmosphere. (Sample I) The ABD and ATD of the lithium composite cobalt oxide (Sample I) thus synthesized were measured and found to be 0.52 and 1.41 g / cm ³ , respectively. Similarly, the ratio of Co to Li is Co / Li = 1.00, 0.
Mix in a ratio of 95 and at 900 ° C in an air atmosphere for 5
Burned for hours.

Table 2 shows the ABD and ATD of the lithium composite cobalt oxide (Samples I to K) obtained by the above method.

[0060]

[Table 2]

Comparative Example 3 As Comparative Example 3, A after drying was used.
Cobalt carbonate having a TD of 1.20 g / cm ³ and lithium carbonate were mixed at a ratio of Co and Li of Co / Li = 1.10 and fired at 900 ° C. for 5 hours in an air atmosphere.

A of the obtained lithium composite cobalt oxide
BD and ATD were 0.33 g / cm ³ , 0.
It was 96 g / cm ³ . (Sample L) (Comparative Example 4) As Comparative Example 4, the ATD during drying was 1.2.
Cobalt carbonate of 0 g / cm ³ and lithium carbonate as C
The ratio of o and Li was mixed at a ratio of Co / Li = 0.9, and the mixture was baked at 900 ° C. for 5 hours in an air atmosphere.

A of the obtained lithium composite cobalt oxide
BD and ATD are 1.86 g / cm ³ , 3.
It was 58 g / cm ³ . (Sample M) A battery was prepared in the same manner as in Example 1 except that Samples I to M above were used. (Batteries I to M) As a cycle test, the batteries thus produced were subjected to constant current charge / discharge under the conditions of a charge / discharge current of 100 mA, a charge end voltage of 4.1 V, and a discharge end voltage of 3.0 V. Further, a high rate charge / discharge test was conducted at a discharge current of 500 mA.

The results of the cycle test are shown in FIG.
From this test result, ABD was 0.33 g / cm³, AT
D is 0.96 g / cm ³Lithium composite cobalt oxide
In the battery L using, cobalt oxide is excessively mixed.
Therefore, the initial capacity is small and the electrode plate is rolled firmly.
Therefore, the battery capacity decreases greatly with the cycle.

On the other hand, a battery using the lithium composite cobalt oxide according to the present invention as the positive electrode active material (Batteries I to I
In K), it can be seen that the cycle characteristics are remarkably improved.

In the sample M in which lithium carbonate was mixed in a very excessive amount, the lithium composite cobalt oxide was easily sintered, the primary particles were very large, and the lithium composite cobalt oxide having a large ABD and ATD was obtained. .

However, when such a powder is suspended in an aqueous carboxymethylcellulose solution, the active material precipitates due to the large apparent density as in Sample H of Comparative Example 2, and the dispersibility in the paste deteriorates. Therefore, when the paste is applied to the surface of the aluminum foil, uneven coating is likely to occur, variation in the active material density occurs, or meandering occurs after rolling after drying, which causes a problem that the electrode plate configuration is difficult, The discharge capacity also decreased because the active material density in the electrode plate varied.

Furthermore, in such a lithium composite cobalt oxide having a very large primary particle, when the charge / discharge cycle is repeated, the particles are made finer due to the expansion and contraction of the particles accompanying the insertion and desorption of lithium ions. , The active material falls off from the electrode plate, causing capacity deterioration.

As described in Example 1, the ABD of the lithium composite cobalt oxide synthesized by changing the Co / Li ratio was 0.35 to 1.5 g / c.
It can be seen that the cycle characteristics are improved by using the active material having m ³ and ATD of 1.0 to 3.3 g / cm ³ .

ABD is 0.5 to 1.5 g / c
m³, ATD 1.4-3.3 g / cm ³The lithium compound
Compound cobalt oxide is more preferred.

The batteries (I to M) produced in Example 3 and Comparative Examples 3 and 4 were subjected to a high rate discharge test at a discharge current of 1 A to obtain a high rate charge / discharge rate (discharge capacity at 1 A / discharge at 100 mA). The capacity x 100 (%) was determined.

The results of the high rate discharge test are shown in FIG. Figure 8
As is clear from the above, the ABD according to the present invention is 0.5 to
1.5 g / cm ³ , ATD 1.4-3.3 g / cm ³
The batteries (I to K) using the above lithium composite cobalt oxide as a positive electrode active material are batteries L (68%) made from lithium composite cobalt oxide having a small ABD and ATD,
And ABD is 1.5 g / cm ³ , ATD is 3.3 g /
It is recognized that the high rate discharge rate characteristics are 90% or more, which is clearly improved, as compared with the result in the battery M (85%) made from the lithium composite cobalt oxide exceeding cm ³ .

The high rate of discharge is improved as described above because the amount of the active material filled per unit area when applied with the paste is large in the electrode plate producing process, and therefore, the rolling pressure in the rolling process after drying is high. Alternatively, since the rolling pressure can be remarkably reduced, the porosity of the positive electrode plate becomes large, and the polarization does not become large even when discharging at a high rate.

The high rate discharge characteristic of the battery M is as bad as 85% because the primary particles are large and the surface area (specific surface area) in contact with the electrolytic solution per unit weight of the active material is small.

Regarding the lithium composite cobalt oxide synthesized by changing the Co / Li ratio in this way,
The high rate discharge rate is improved by using the lithium composite cobalt oxide within the range specified in the present invention.

In Example 3, cobalt carbonate was used as the cobalt source, but cobalt cobalt such as tricobalt tetraoxide, cobalt monoxide, cobalt hydroxide, cobalt nitrate, or a mixture thereof may be used instead of cobalt carbonate. Even if there was, the same effect was obtained.

In Examples 1 to 3, the active material density was set to 3.
Although it was set to 5 g / cm ³ , the same effect was obtained if it was 4.5 g / cm ³ or less. However, the active material density is 4.
If it is 4 g / cm ³ or more, it is indispensable to strongly roll the electrode plate, and the same effect cannot be obtained.

There is a method of designing a battery by regulating the particle size distribution, which is one of the powder characteristics of such a positive electrode active material, but when filling such an active material into an electrode plate Since the shape is more affected by the particle shape than the particle size, it is rather affected by the apparent density by the stationary method or the tap method. Therefore, by regulating the apparent density, more rigorous battery design becomes possible.

In the above examples, the evaluation was performed using a cylindrical battery, but the same effect can be obtained even when the battery shape is different, such as a prismatic battery.

Further, although the carbonaceous material is used for the negative electrode in the above embodiment, the same effect can be obtained by using lithium metal or lithium alloy as the negative electrode.

Although lithium hexafluorophosphate was used as the electrolyte in the above examples, other lithium-containing salts such as lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and hexafluorofluoride were used. Similar effects were obtained with lithium arsenate and the like.

Furthermore, although a mixed solvent of ethylene carbonate and diethyl carbonate was used in the above examples, other non-aqueous solvents such as cyclic esters such as propylene carbonate, cyclic ethers such as tetrahydrofuran, chain ethers such as dimethoxyethane, Similar effects were obtained using a non-aqueous solvent such as a chain ester such as methyl propionate or a multi-component mixed solvent thereof.

[0083]

EFFECT OF THE INVENTION ABD 0.35 to 1.5 g according to the present invention
/ Cm ³ , ATD 1.0 ~ 3.3 g / cm ³ or more by using a lithium composite cobalt oxide as a positive electrode active material, good cycle characteristics, excellent non-aqueous electrolyte secondary battery of high rate discharge characteristics. Can be provided.

Furthermore, ABD 0.5 to 1.5 g / c
m ^3, by using a lithium composite cobalt oxide ATD1.4~3.3g / cm ^3, excellent productivity, capacity variation is small, the cycle characteristics, superior non-aqueous electrolyte solution of the high-rate discharge characteristic two A secondary battery can be provided.

ABD 0.3 to 1.2 g / cm ³ ,
A positive electrode active material having excellent cycle characteristics and high rate discharge characteristics can be provided by mixing a tricobalt tetraoxide powder having an ATD of 0.8 to 2.5 g / cm ³ and a lithium carbonate powder and firing the mixture.

[Brief description of drawings]

FIG. 1 Relationship between active material density and high discharge rate in electrode plate

FIG. 2 is a vertical sectional view of a cylindrical battery according to this embodiment.

FIG. 3 is a diagram of an apparent density measuring device by a stationary method in this example.

FIG. 4 is a diagram of an apparent density measuring device by a tap method in this embodiment.

FIG. 5 is a diagram showing cycle characteristics in Examples 1 and 2 and Comparative Examples 1 and 2.

6 is a diagram showing high rate discharge characteristics in Examples 1 and 2 and Comparative Examples 1 and 2. FIG.

FIG. 7 is a diagram showing cycle characteristics in Example 3 and Comparative Examples 3 and 4.

FIG. 8 is a diagram showing high rate discharge characteristics in Example 3 and Comparative Examples 3 and 4.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Insulating Packing 4 Electrode Plate Group 5 Positive Electrode Plate 5a Positive Electrode Lead 6 Negative Electrode Plate 6a Negative Lead 7 Separator 8 Insulating Ring 9 Sieve 10 Funnel 11 Receiver 12 Receiver Stand 14 Messy Cylinder 15 Rubber Plug 16 rubber plate

Claims (7)

[Claims] 1. A negative electrode plate formed by forming a layer of a carbonaceous material on the surface of a metal current collector, or a negative electrode plate made of lithium or a lithium alloy, and a lithium composite cobalt oxide powder on both surfaces of the metal current collector. In a positive electrode plate having a positive electrode active material layer formed mainly of a positive electrode active material, and a non-aqueous electrolyte secondary battery having a separator between the negative electrode plate and the positive electrode plate, the positive electrode active material of the positive electrode plate The density of the lithium composite cobalt oxide is in the range of 2.5 to 4.5 g / cm ³ , and the apparent density by the standing method of the lithium composite cobalt oxide powder is 0.35 to 1.5 g / cm ³ . What is used is a non-aqueous electrolyte secondary battery. 2. The apparent density of the lithium composite cobalt oxide powder according to a stationary method is 0.5 to 1.5 g / c.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery has a m ^{3 value} . 3. The apparent density by the tap method as the lithium composite cobalt oxide powder is 1.0 to 3.3 g /
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery has a size of ³ cm ³ . 4. The apparent density of the lithium composite cobalt oxide powder as measured by the tap method is 1.4 to 3.3 g /
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery has a size of ³ cm ³ . 5. The lithium composite cobalt oxide powder, wherein the composition ratio of Co and Li at the time of its synthesis is expressed as Co / Li, Co / Li = 1.05 to 0.95 is used. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, which is characterized in that. 6. A lithium composite cobalt oxide synthesized by mixing tricobalt tetraoxide powder (Co ₃ O ₄ ) and lithium carbonate powder and heat-treating the mixture, wherein the tricobalt tetraoxide powder is allowed to stand. Apparent density is 0.3
A positive electrode active material for a non-aqueous electrolyte battery, wherein the positive electrode active material has a content of up to 1.2 g / cm ³ . 7. The positive electrode active material for a non-aqueous electrolyte battery according to claim 6, wherein the apparent density of the cobalt tetraoxide powder by a tap method is 0.8 to 2.5 g / cm ^3. .