JP2003223887A - Nonaqueous system secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous system accumulator provided with superior safety, high energy density and a sufficient charge and discharge cycle characteristic. <P>SOLUTION: In the nonaqueous system accumulator 1, lithium nickel cobalt manganese composite oxide is used as active positive electrode substance, a thickness of a positive electrode 3 is ≥160 μm and ≤240 μm, and the mass of the lithium nickel cobalt manganese composite oxide coated on the positive collector is ≥38 mg/cm<SP>2</SP>and ≤65 mg/cm<SP>2</SP>per unit area of both sides of the positive collector. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous secondary battery.

[0002]

2. Description of the Related Art A non-aqueous secondary battery, which comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte such as an organic solvent or a solid polymer electrolyte, and which can be repeatedly used by charging, has been widely used as a power source for portable devices in recent years. Being researched. Among the non-aqueous secondary batteries, a positive electrode containing a positive electrode active material capable of reversibly electrochemically reacting with lithium ions, a negative electrode containing a negative electrode active material capable of reversibly inserting and releasing lithium ions, and a lithium salt Lithium ion batteries composed of a non-aqueous electrolyte containing is widely used as a power source for mobile phones, portable personal computers, video cameras, etc. because of their high energy density. As the positive electrode active material of this lithium ion battery,
LiCoO ₂ has already been put to practical use because it has a high energy density and is easy to synthesize.

However, LiCoO ₂ has a problem in that heat is generated and becomes unstable due to a change in crystal structure during overcharge.

With respect to this point, various safety devices are provided in the lithium ion batteries currently in practical use. However, when considering not only power supply applications for mobile devices that are required to be further downsized but also power applications for electric vehicles and hybrid vehicles that are required to be upsized, lithium ion batteries are Further improvement of safety is required.

Therefore, in recent years, attempts have been made to use LiMn ₂ O _4, which is excellent in safety during overcharge, as a positive electrode active material. However, LiMn ₂ O ₄ has a lower capacity than LiCoO _2, and when repeatedly charged and discharged, the capacity is deteriorated due to the change in the crystal structure, so that there is a problem that the charge and discharge cycle characteristics are inferior.

[0006]

The present invention has been made in view of the above circumstances, and an object thereof is to have excellent safety, high energy density, and sufficient charge / discharge cycle characteristics. It is to provide a non-aqueous secondary battery.

[0007]

According to a first aspect of the present invention, a positive electrode is obtained by applying a positive electrode mixture containing a positive electrode active material to both surfaces of a positive electrode current collector made of a metal foil, and a non-containing positive electrode containing lithium salt. In a non-aqueous secondary battery composed of a water electrolyte and a negative electrode containing a negative electrode active material capable of inserting and extracting lithium ions, a lithium nickel cobalt manganese composite oxide is used as the positive electrode active material, and the thickness of the positive electrode is Is 160 μm or more and 240 μm or less, and the mass of the lithium nickel cobalt manganese composite oxide applied to the positive electrode current collector is 38 mg / cm ² or more and 65 mg / cm ² or less per unit area of both surfaces of the positive electrode current collector. It is characterized by being.

First, by using the lithium nickel cobalt manganese composite oxide as the positive electrode active material, it has high energy density and stable charge / discharge cycle characteristics, and is equivalent to LiMn ₂ O ₄ having a spinel type crystal structure. It is possible to obtain a non-aqueous secondary battery having high safety.

Next, if the thickness of the positive electrode is less than 160 μm, the amount of the positive electrode active material is insufficient, the discharge capacity is reduced, and as a result, the energy density is reduced, which is not preferable. If the thickness exceeds 240 μm, the positive electrode mixture layer becomes too thick, so that the amount of the positive electrode active material that can be accommodated in the battery case having a predetermined size is substantially reduced. As a result,
It is not preferable because the discharge capacity is lowered and the energy density is lowered. Therefore, in the present invention, the thickness of the positive electrode needs to satisfy the relationship of 160 μm or more and 240 μm or less.

Further, as a result of intensive studies by the inventors, it was found that the energy density and charge / discharge cycle characteristics were significantly influenced by the amount of the active material of the positive electrode.

That is, when the amount of the positive electrode active material per unit area of the positive electrode is 38 mg / cm ² or more and 65 mg / cm ² or less, a non-aqueous electrolyte secondary battery having high energy density and excellent charge / discharge cycle characteristics can be obtained. Was found.

Although the clear reason is not clear, it is considered as follows. That is, if the amount of the positive electrode active material per unit area of the positive electrode is less than 38 mg / cm ² , the energy density will decrease.

On the other hand, when the amount of the positive electrode active material is more than 65 mg / cm ² , the charge / discharge cycle characteristics deteriorate.

This is considered as follows. Sanawa
The amount of positive electrode active material is 65 mg / cm ^TwoMore, positive electrode
While the proportion of the positive electrode active material in the active material layer increases,
The ratio of the part formed by the binder etc. decreases.
It And, the electrolyte is almost immersed in the positive electrode active material itself.
Part that is not transparent and is formed by a porous binder, etc.
Penetrate mainly into. Therefore, the amount of positive electrode active material is 65 mg.
/ Cm^TwoNon-aqueous electrolyte that penetrates into the positive electrode active material layer when there is more
The amount of will decrease. As a result, during charging and discharging, the active material layer
The electrolyte is an active material because the crystal structure of
Due to so-called liquid withdrawal phenomenon that exudes from the stratum corneum
It is greatly affected by the decrease in discharge capacity, and
It is thought that the wheel characteristics will deteriorate.

For these reasons, the amount of the positive electrode active material per unit area of the positive electrode is 38 mg / cm ² or more and 65 m.
When it is g / cm ² or less, it is considered that high energy density and excellent charge / discharge cycle characteristics are secured.

According to a second aspect of the invention, in the non-aqueous secondary battery according to the first aspect, the positive electrode has a thickness of 180.
and the mass of the lithium nickel cobalt manganese composite oxide applied to the positive electrode current collector is 45 m per unit area on both sides of the positive electrode current collector.
g / cm ² or more and 55 mg / cm ² or less.

In the invention of claim 2, the positive electrode has a thickness of 180 μm or more and 210 μm or less, and the mass of the lithium nickel cobalt manganese composite oxide applied to the positive electrode current collector is equal to both surfaces of the positive electrode current collector. 45 m / cm ² or more and 55 mg / cm ² or less per unit area, it is possible to obtain a non-aqueous secondary battery having both energy density and charge / discharge cycle characteristics at a higher level than the invention of claim 1. .

This is because when the thickness of the positive electrode is 180 μm or more and 210 μm or less, the effect of improving the discharge capacity and thus the energy density is remarkable, and the mass of the lithium nickel cobalt manganese composite oxide is large. This is because the charge / discharge cycle characteristics are remarkably improved when the surface area of the positive electrode current collector is 45 mg / cm ² or more and 55 mg / cm ² or less per unit area.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, LiNi _a C
_{o b Mn c O 2 (0} <a <1,0 <b <1,0 <c <
1, a + b + c = 1), which is a layered structure of lithium nickel cobalt manganese composite oxide is used as a positive electrode active material. This composite oxide is produced by heat-treating a lithium compound, a nickel compound, a cobalt compound, and a manganese compound in an oxidizing atmosphere in the range of 400 ° C to 900 ° C. The crystal structure of the composite oxide can be analyzed by X-ray diffraction. For example, Rigaku Denki, X-Ray Diffractometer, RI
It can be measured by using NT2000 and CuKα ray.

Examples of the lithium compound include lithium nitrate, lithium sulfate, lithium chloride, lithium bromide,
Lithium iodide, lithium hydroxide, lithium oxide, lithium peroxide, lithium carbonate, lithium formate, lithium acetate, lithium benzoate, lithium citrate, lithium oxalate, lithium pyruvate, lithium stearate,
Examples thereof include lithium tartrate.

Examples of the nickel compound include nickel hydroxide, nickel oxide, nickel carbonate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate, nickel oxyhydroxide and the like.

Examples of the cobalt compound include cobalt hydroxide, cobalt oxide, cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, and cobalt oxyhydroxide.

Examples of manganese compounds include manganese carbonate, manganese acetate, manganese hydroxide, manganese oxide, manganese oxyhydroxide and the like.

The lithium nickel cobalt manganese composite oxide obtained as described above is mixed with a conductive agent and a binder to prepare a positive electrode mixture, and this positive electrode mixture is used as a positive electrode collector made of a metal foil. A positive electrode can be manufactured by applying to an electric body.

The type of conductive agent is not particularly limited, and may be a metal or a nonmetal. As a metal conductive agent,
Examples thereof include materials composed of metal elements such as Cu and Ni. Examples of the non-metal conductive agent include carbon materials such as graphite, carbon black, acetylene black and Ketjen black.

The binder is not particularly limited in its kind as long as it is a material which is stable to the solvent and the electrolytic solution used at the time of manufacturing the electrode. Specifically, polyethylene, polypropylene,
Resin-based polymers such as polyethylene terephthalate, aromatic polyamide, cellulose, styrene-butadiene rubber,
Rubber-like polymers such as isoprene rubber, butadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymers and hydrogenated products thereof, styrene-ethylene-butadiene-styrene block copolymers and hydrogenated products thereof, styrene -Isoprene-styrene block copolymer and thermoplastic elastomeric polymers such as hydrogenated products thereof, syndiotactic 1,2-polybutadiene, ethylene-vinyl acetate copolymer, propylene-α-olefin (having 2 to 12 carbon atoms) ) A soft resin-like polymer such as a copolymer, a fluoropolymer such as polyvinylidene fluoride, polytetrafluoroethylene, a polytetrafluoroethylene-ethylene copolymer, or the like can be used.

Further, as the binder, a polymer composition having an alkali metal ion conductivity such as lithium ion can also be used. Examples of the polymer having such ion conductivity include polyether polymer compounds such as polyethylene oxide and polypropylene oxide, cross-linked polymer compounds of polyether, polyepichlorohydrin,
Polyphosphazene, polysiloxane, polyvinylpyrrolidone, polyvinylidene carbonate, a system in which a lithium salt or an alkali metal salt mainly composed of lithium is combined with a polymer compound such as polyacrylonitrile, or propylene carbonate, ethylene carbonate,
A system containing an organic compound having a high dielectric constant such as γ-butyrolactone can be used. These materials may be used in combination.

The positive electrode current collector includes, for example, Al, Ta, N
Examples thereof include b, Ti, Hf, Zr, Zn, W, Bi, and alloys containing these metals. These metals form a passivation film on the surface by anodic oxidation in an electrolytic solution. Therefore, it is possible to effectively prevent the non-aqueous electrolyte from oxidatively decomposing at the liquid contact portion between the positive electrode current collector and the electrolytic solution. As a result, the cycle characteristics of the non-aqueous secondary battery can be effectively improved. Among the above metals, Al, Ti, Ta and alloys containing these metals can be preferably used. In particular, Al and its alloys have a low density, so that the mass of the positive electrode current collector can be reduced as compared with the case of using other metals. for that reason,
Since the energy density of the battery can be improved,
Particularly preferred.

When the positive electrode mixture obtained as described above is applied to the positive electrode current collector, it can be carried out by a known means. When the mixture is in the form of a slurry, it can be applied onto the current collector using, for example, a doctor blade. When the mixture is in the form of paste, it can be applied onto the current collector by, for example, roller coating. If a solvent is used, the electrode can be prepared by drying to remove the solvent.

As the negative electrode active material, lithium metal, lithium
Lithium-aluminium, a substance that can inhale and release um
Um alloy, lithium-lead alloy, lithium-tin alloy, etc.
Lithium alloy, Li₅(Li_ThreeN) Lithium nitride
Carbon materials such as aluminum, graphite, coke, and organic fired materials, W
O_Two, MoO_Two, SnO_Two, SnO, TiO_Two, NbO
_ThreeTransition metal oxides such as these
Only one type of negative electrode active material may be selected and used.
However, two or more kinds may be used in combination.

The material of the negative electrode current collector is preferably a metal such as copper, nickel or stainless steel. Among them, a copper foil is more preferable because it is easily processed into a thin film and is inexpensive.

The method for producing the negative electrode is not particularly limited, and the negative electrode can be produced by the same method as the above-mentioned method for producing the positive electrode.

Examples of the non-aqueous solvent for the non-aqueous electrolytic solution include:
Cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, methyl acetate and methyl propionate. Chain esters such as tetrahydrofuran, 2-methyltetrahydrofuran, cyclic ethers such as tetrahydropyran, chain ethers such as dimethoxyethane and dimethoxymethane, ethylene methyl phosphate, cyclic phosphate such as ethyl ethylene phosphate,
Chain phosphoric acid esters such as trimethyl phosphate and triethyl phosphate, and halides of these compounds can be used. Only one kind of these organic solvents may be selected and used, or two or more kinds thereof may be used in combination.

The solute of the non-aqueous electrolyte is LiCl
O_Four, LiPF₆, LiBF_FourInorganic lithium salts such as
LiCF_ThreeSO_Three, LiN (CF_ThreeSO_Two)_Two, Li
N (CF _ThreeCF_TwoSO_Two )_Two , LiN (CF_ThreeCO)
And LiC (CF_ThreeSO_Two ) _ThreeFluorine-containing organic
Examples thereof include thium salt. These solutes are
You may select and use only one type, or combine two or more types.
You may use it together.

As the electrolyte, a solid or gel electrolyte can be used in addition to the above-mentioned electrolyte solution. Examples of such an electrolyte include an inorganic solid electrolyte, polyethylene oxide, polypropylene oxide, or a derivative thereof.

As the separator, an insulating polyethylene microporous film impregnated with an electrolytic solution, a polymer solid electrolyte, or a gel electrolyte in which a polymer solid electrolyte contains an electrolytic solution can be used. Also, an insulating microporous membrane and a polymer solid electrolyte may be used in combination. Furthermore, when a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the electrolytic solution contained in the polymer may be different from the electrolytic solution contained in the pores.

The present invention will be described in detail below based on examples. The present invention is not limited to the following examples.

Examples 1 to 8 and Comparative Examples 1 to 5
Then, the prismatic nonaqueous electrolyte secondary battery 1 shown in FIG. 1 was produced. 1, 1 is a prismatic non-aqueous secondary battery, 2 is an electrode group, 3 is a positive electrode, 4 is a negative electrode, 5 is a separator, 6 is a battery case, 7 is a battery lid, 8 is a safety valve, 9 is a negative electrode terminal, 10 Is a positive electrode lead, and 11 is a negative electrode lead.

This prismatic non-aqueous secondary battery 1 is formed by applying the following positive electrode 3 formed by applying a positive electrode mixture to a current collector made of aluminum foil, and by applying a negative electrode mixture to a current collector made of copper foil. The following negative electrode 4 and a non-aqueous electrolyte are housed in a battery case 6.

A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, and a negative electrode terminal 9 is attached.
Is connected to the negative electrode 4 via the negative electrode lead 11, and the positive electrode 3 is electrically connected to the battery case 6 via the positive electrode lead 10.

<Example 1> Compositional formula LiNi _0.5 Co
Lithium nickel cobalt manganese composite oxide represented by _0.2 Mn _0.3 O ₂ (hereinafter referred to as composite oxide A)
To 91 parts by weight, 6 parts by weight of polyvinylidene fluoride as a binder and 3 parts by weight of acetylene black as a conductive agent were mixed. N-methylpyrrolidone was appropriately added to this to prepare a paste, and this paste was applied to both sides of a current collector made of an aluminum foil having a width of 26 mm, a length of 590 mm and a thickness of 20 μm. This is dried at 150 ° C. and then pressed to make the mixture layer on one side of the aluminum foil have a thickness of 70.
A positive electrode having a thickness of 160 μm, which is the total thickness of the mixture layer on both sides of the aluminum foil and the thickness of the aluminum foil (hereinafter, referred to as the total thickness of the positive electrode), was manufactured. The mass of the positive electrode active material per unit area on both surfaces of the current collector in the positive electrode mixture was 40 mg / cm ² .

92 parts by weight of graphite as a negative electrode host material and 8 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was appropriately added thereto to prepare a paste form. The paste thus obtained was applied to both sides of a current collector made of copper foil having a width of 27 mm, a length of 610 mm and a thickness of 10 μm. After drying this at 150 ° C., pressure was applied, and the thickness of the mixture layer applied to one side of the copper foil was 70 μm, the total thickness of the mixture layer thickness on both sides of the copper foil and the copper foil thickness (hereinafter, negative electrode). (Called total thickness) is 150 μm
The negative electrode of was produced.

The separator has a thickness of 25 μm and a width of 30 mm.
The polyethylene microporous membrane of was used.

The positive electrode and the negative electrode obtained as described above were laminated with a separator interposed therebetween, and by winding this, a ticket-type power generating element of 47 mm × 30 mm × 6 mm was produced.

The solute in the electrolytic solution had a concentration of 1 mol / l.
Using LiPF ₆ in a volume ratio as a solvent 4: 6 was used in the mixed solvent of ethylene carbonate and diethyl carbonate.

A prismatic nonaqueous secondary battery 1 of Example 1 was manufactured using the above-mentioned components.

Example 2 Using the composite oxide A, the length of the aluminum foil was 505 mm, the thickness of the mixture layer on one side of the aluminum foil was 85 μm, and the total thickness of the positive electrode was 190 μm.
A positive electrode was produced in the same manner as in Example 1 except that the mass of the positive electrode active material per unit area on both surfaces of the aluminum foil in the positive electrode mixture was 48 mg / cm ² .

The length of the copper foil is 525 mm, the thickness of the mixture layer on one side of the copper foil is 85 μm, and the total thickness of the negative electrode is 180 μm.
The negative electrode of was produced.

Using the positive electrode and negative electrode thus obtained, a non-aqueous secondary battery of Example 2 was obtained in the same manner as in Example 1.

Example 3 Using the composite oxide A, the length of the aluminum foil was 480 mm, the thickness of the mixture layer on one side of the aluminum foil was 90 μm, and the total thickness of the positive electrode was 200 μm.
A positive electrode was produced in the same manner as in Example 1 except that the mass of the positive electrode active material per unit area on both sides of the current collector plate in the positive electrode mixture was 51 mg / cm ² .

Further, the length of the copper foil is 500 mm, the thickness of the mixture layer on one side of the copper foil is 90 μm, and the total thickness of the negative electrode is 190 μm.
The negative electrode of was produced.

Using the positive electrode and negative electrode thus obtained, a non-aqueous secondary battery of Example 3 was obtained in the same manner as in Example 1.

Example 4 Using the composite oxide A, the length of the aluminum foil was 410 mm, the thickness of the mixture layer on one side was 110 μm, the total thickness of the positive electrode was 240 μm, and both sides of the current collector plate in the positive electrode mixture were used. A positive electrode was prepared in the same manner as in Example 1 except that the mass of the positive electrode active material per unit area was 62 mg / cm ² .

A negative electrode having a length of the copper foil of 430 mm, a thickness of the mixture layer on one side of 110 μm and a total thickness of the negative electrode of 230 μm was prepared.

Using the positive electrode and the negative electrode thus obtained, a non-aqueous secondary battery of Example 3 was obtained in the same manner as in Example 1.

Example 5 Compositional formula LiNi _0.6 Co
Lithium nickel cobalt manganese composite oxide represented by _0.2 Mn _0.2 O ₂ (hereinafter referred to as composite oxide B)
A positive electrode was produced in the same manner as in Example 1 except that was used, and the nonaqueous secondary battery of Example 5 was obtained in the same manner as in Example 1 using this positive electrode.

Example 6 A positive electrode was prepared in the same manner as in Example 2 except that the composite oxide B was used, and this positive electrode was used in the same manner as in Example 1 to prepare the non-aqueous secondary liquid of Example 6. I got a battery.

<Example 7> A positive electrode was prepared in the same manner as in Example 3 except that the composite oxide B was used. Using this positive electrode, a battery of Example 7 was obtained in the same manner as in Example 1. It was

<Example 8> A positive electrode was prepared in the same manner as in Example 4 except that the composite oxide B was used, and this positive electrode was used in the same manner as in Example 1 to prepare the non-aqueous electrolyte of Example 8. The next battery was obtained.

Comparative Example 1 A positive electrode was prepared in the same manner as in Example 1 except that LiCoO ₂ having a layered rock salt structure was used instead of the composite oxide A. Using this positive electrode, Example 1
A non-aqueous secondary battery of Comparative Example 1 was obtained in the same manner as in.

Comparative Example 2 A positive electrode was prepared in the same manner as in Example 1 except that LiMn ₂ O ₄ having a spinel structure was used in place of the composite oxide A, and this positive electrode was used in the same manner as in Example 1. A non-aqueous secondary battery of Comparative Example 2 was obtained by the above method.

Comparative Example 3 Using the composite oxide A,
Minium foil length 620mm, aluminum foil on one side
The thickness of the mixture layer is 70 μm, the total thickness of the positive electrode is 160 μm,
Unit area equivalent of both sides of the aluminum foil in the positive electrode mixture
The mass of the positive electrode active material is 35 mg / cm ^TwoOther than
A positive electrode was manufactured in the same manner as in Example 1.

A negative electrode having a copper foil length of 640 mm, a mixture layer thickness of 60 μm on one side, and a total negative electrode thickness of 130 μm was prepared.

Using the positive electrode and negative electrode thus obtained, a non-aqueous secondary battery of Comparative Example 3 was obtained in the same manner as in Example 1.

Comparative Example 4 Using the composite oxide A, the length of the aluminum foil was 470 mm, the thickness of the mixture layer on one side of the aluminum foil was 115 μm, and the total thickness of the positive electrode was 250 μm.
m, a positive electrode was prepared in the same manner as in Example 1 except that the mass of the positive electrode active material per unit area on both surfaces of the aluminum foil in the positive electrode mixture was 40 mg / cm ² .

A negative electrode having a copper foil length of 490 mm, a mixture layer thickness of 70 μm on one side, and a total negative electrode thickness of 150 μm was prepared.

A non-aqueous secondary battery of Comparative Example 4 was obtained in the same manner as in Example 1 using the positive electrode and negative electrode thus obtained.

Comparative Example 5 Using the composite oxide A,
Minium foil length 670mm, aluminum foil one side
The thickness of the mixture layer is 60 μm, the total thickness of the positive electrode is 140 μm,
Unit area equivalent of both sides of the aluminum foil in the positive electrode mixture
The mass of the positive electrode active material is 34 mg / cm ^TwoOther than
A positive electrode was manufactured in the same manner as in Example 1.

A negative electrode having a copper foil length of 690 mm, a mixture layer thickness of 60 μm on one side, and a total negative electrode thickness of 130 μm was prepared.

Using the positive electrode and negative electrode thus obtained, a non-aqueous secondary battery of Comparative Example 5 was obtained in the same manner as in Example 1.

Table 1 shows the ratio of the number of transition metal atoms other than lithium in the lithium nickel cobalt manganese composite oxide. In addition, the thickness of the positive electrode and the mass of the active material per unit area are also shown.

[0072]

[Table 1]

<Measurement> Examples 1 to 8 and Comparative Example 1
Nos. 5 to 5 were charged at a constant current of 500 mA to 4.2 V, and at a constant voltage of 4.2 V for a total of 3 hours, and for discharging, the voltage dropped to 2.75 V at a constant current of 500 mA. The discharge capacity was measured at the end of the time point. The energy density (Wh / kg) was calculated by multiplying the discharge capacity thus obtained by the average voltage during discharge and dividing this value by the mass of the battery.

Examples 1 to 8 and Comparative Examples 1 to 5
The initial discharge capacity and charge / discharge cycle characteristics of the non-aqueous secondary battery of were measured using a potentiogalvanostat. First, charging was performed at a constant current of 500 mA up to 4.2 V, and further at a constant voltage of 4.2 V for a total of 3 hours. Next, discharging was performed at a constant current of 500 mA until the voltage dropped to 2.75V. The charging / discharging cycle was performed 300 times, the average discharge capacity of the 1st to 5th cycles was defined as the initial discharge capacity, and the discharge capacity at the 300th cycle relative to the initial discharge capacity was defined as the capacity retention rate (%).

Examples 1 to 8 and Comparative Examples 1 to 5
3CmA as a safety test for the non-aqueous secondary battery of
An overcharge test was performed under the condition of / 10V.

The results of these tests are summarized in Table 2.

[0077]

[Table 2]

<Results> In the safety test, in Examples 1 to 8 in which the lithium nickel cobalt manganese composite oxide was used as the positive electrode active material, the crystal structure of the positive electrode active material did not change, so that no sudden heat generation occurred. As a result, the safety valve did not work. On the other hand, in Comparative Example 1 using the lithium cobalt composite oxide as the positive electrode active material,
The safety valve was activated by the sudden heat generation due to the change in the crystal structure of the positive electrode active material. From this, by using a lithium nickel cobalt manganese composite oxide as the positive electrode active material, a non-aqueous secondary material having the same level of safety as when using a spinel structure lithium manganese composite oxide as the positive electrode active material. It turns out that a battery can be obtained.

In Examples 1 to 8 using the lithium nickel cobalt manganese composite oxide as the positive electrode active material, the energy density was 317 Wh / kg or more, and the charge / discharge cycle characteristics were 80%. On the other hand, in Comparative Example 2 in which the lithium manganese composite oxide was used as the positive electrode active material, the energy density was 218 Wh / kg and the charge / discharge cycle characteristics were 70%. From this, it was found that by using a lithium nickel cobalt manganese composite oxide as the positive electrode active material, a non-aqueous secondary battery having high energy density and stable charge / discharge cycle characteristics can be obtained.

In Examples 1 to 8 in which the mass of the positive electrode active material was 38 mg / cm ² or more and 65 mg / cm ² or less per unit area of the positive electrode current collector, the energy density was 317 Wh.
/ Kg or more. On the other hand, in Comparative Example 3 in which the mass of the positive electrode active material was 35 mg / cm ² per unit area of the positive electrode current collector, the energy density was 296 Wh / kg. From this, in order to obtain a non-aqueous secondary battery having a high energy density, the mass of the lithium nickel cobalt manganese composite oxide per unit area on both sides of the current collector may be within the range defined in claim 1. It is understood that it is mandatory.

Further, the positive electrode thickness is 160 μm or more and 240 μm or more.
In Examples 1 to 8 in which the energy density is 3 or less, the energy density is 3
It was 17 Wh / kg or more. On the other hand, in Comparative Example 4 in which the positive electrode thickness was 250 μm, it was 257 Wh / kg. From this, it is understood that it is essential that the thickness of the positive electrode is within the range defined in claim 1 in order to obtain a non-aqueous secondary battery having a high energy density.

Examples 1 to 8 in which the positive electrode thickness and the mass of the positive electrode active material per unit area of the positive electrode current collector are within the scope of claim 1, and the positive electrode thickness is 140 μm and the unit area of the positive electrode current collector is The positive electrode active material has a mass of 34 mg / cm ² , and by comparing with Comparative Example 5 in which both are out of the range of claim 1, a high energy density and a sufficient charge / discharge cycle characteristic are obtained. In order to obtain an aqueous secondary battery, the positive electrode thickness is within the range defined in claim 1, and the mass of lithium nickel cobalt manganese composite oxide per unit area on both sides of the current collector is defined in claim 1. It turns out that it is essential to be in range.

The positive electrode thickness is 180 μm or more and 210 μm or less, and the mass of the positive electrode active material is 4 per unit area of the positive electrode current collector.
In 5 mg / cm ² or more 55 mg / cm ² or less is Examples 2 and 3, the energy density of 335Wh / kg or more,
The charge / discharge cycle characteristic was 81%. On the contrary,
In Example 1, the energy density was 322 Wh / kg, and in Example 4, the charge / discharge cycle characteristic was 80%. From this result, when the positive electrode thickness and the mass of the lithium nickel cobalt manganese composite oxide per unit area on both surfaces of the current collector are within the ranges defined in claim 2,
Compared with the case where these are in the range limited in claim 1,
It can be understood that a non-aqueous secondary battery having a high level of both energy density and charge / discharge cycle characteristics can be obtained.
A similar tendency was found in Examples 5 to 8.

LiNi _0.5 Co as the positive electrode active material
Examples 1 to 4 using _0.2 Mn _0.3 O ₂ and LiNi _0.6 Co _0.2 Mn _0.2 O as the positive electrode active material
By comparing Examples 5 to 8 in which No. ₂ was used, the composition ratio of the metal elements contained in the lithium nickel cobalt manganese composite oxide was appropriately changed to achieve a high balance between energy density and charge / discharge cycle characteristics. It is understood that changes can be made while maintaining the standard.

<Other Embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition to the above, various modifications can be made without departing from the scope of the invention.

In the above-mentioned embodiment, the prismatic non-aqueous secondary battery 1 has been described, but the battery structure is not particularly limited, and needless to say, it may be a cylindrical, bag-shaped, lithium polymer battery or the like.

[0087]

According to the present invention, a non-aqueous secondary battery having excellent safety and high energy density and having sufficient charge / discharge cycle characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a prismatic non-aqueous secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

1. Square non-aqueous secondary battery 2 ... Electrode group 3 ... Positive electrode 4 ... Negative electrode 5 ... Separator 6 ... Battery case 7 ... Battery lid 8 ... Safety valve 9 ... Negative electrode terminal 10 ... Positive electrode lead 11 ... Negative electrode lead

Continued front page    F-term (reference) 5H017 AA03 AS02 AS10 CC01 HH01                       HH03                 5H029 AJ03 AJ05 AK03 AL01 AL02                       AL06 AL12 AM03 AM04 AM05                       AM07 BJ02 BJ14 HJ01 HJ04                 5H050 AA07 AA08 BA17 CA08 CA09                       CB01 CB02 CB07 CB12 HA01                       HA04

Claims (2)

[Claims] 1. A positive electrode obtained by applying a positive electrode mixture containing a positive electrode active material on both sides of a positive electrode current collector made of a metal foil, a non-aqueous electrolyte containing lithium ions, and capable of inserting and extracting lithium ions. In a non-aqueous secondary battery including a negative electrode, a lithium nickel cobalt manganese composite oxide is used as the positive electrode active material, and the positive electrode has a thickness of 16
It is 0 μm or more and 240 μm or less, and the mass of the lithium nickel cobalt manganese composite oxide applied to the positive electrode current collector is 38 per unit area on both surfaces of the positive electrode current collector.
A non-aqueous secondary battery characterized by having a content of not less than mg / cm ^{2 and not} more than 65 mg / cm ² . 2. The non-aqueous secondary battery according to claim 1, wherein the positive electrode has a thickness of 180 μm or more and 210 μm or less, and the lithium nickel cobalt manganese composite oxide is applied to the positive electrode current collector. The mass is 45 mg / cm ² or more and 55 mg / cm ² per unit area on both sides of the positive electrode current collector.
A non-aqueous secondary battery having a size of not more than cm ² .