JP2003303592A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having a high discharge capacity and excellent charging/discharging cycle characteristics. <P>SOLUTION: The nonaqueous electrolyte secondary battery 1 uses a positive electrode active material having a layered rock-salt structure. The positive electrode active material is a lithium-transition metal complex oxide represented by a general formula Li<SB>a</SB>Ni<SB>1-b-c</SB>Co<SB>b</SB>M<SB>c</SB>O<SB>2</SB>(wherein M is at least one element selected from the group consisting of Mg, Al, Ti, W, and Mo; and a, b, c and d respectively satisfy 0.2≤a≤1.05, 0.5≤1-b-c≤0.9, 0≤b≤0.47, and 0.03≤c≤0.1), in which the Ni concentration in the surface layer of the primary particle is lower than that in the inner layer of the primary particle. This allows the battery 1 to have a high discharge capacity and excellent charging/discharging cycle characteristics. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Among non-aqueous electrolyte secondary batteries which are composed of a positive electrode, a negative electrode and a non-aqueous electrolyte solution and can be repeatedly used by charging, they are capable of reversibly electrochemically reacting with lithium ions. A positive electrode containing a positive electrode active material, and a negative electrode containing a negative electrode active material capable of reversibly occluding and releasing lithium ions,
BACKGROUND ART A lithium ion battery including a solid polymer electrolyte and an electrolyte containing an organic solvent has a high voltage and a high energy density, and is therefore widely used as a power source for portable devices and the like.

Recently, LiNiO has been used as the positive electrode active material.
₂ has been widely studied because of its high voltage and high energy density.

However, since the crystal structure of LiNiO ₂ is unstable, there is a problem that the crystal structure changes during the charge / discharge cycle and the discharge capacity tends to decrease. Also, L
Since iNiO ₂ has a high reactivity with the electrolytic solution, there is a problem that heat escape easily occurs at the time of temperature rise and the internal resistance also increases during the charge / discharge cycle.

In order to solve the above problems, LiNiO ₂
Stabilization of crystal structure by adding different metals to
And an attempt to suppress reactivity with an electrolytic solution is disclosed in Japanese Patent Laid-Open No. 10-1
It is proposed in Japanese Patent No. 34811.

In Japanese Patent Laid-Open No. 10-134811, the coprecipitate of Ni and the third component is used as a starting material to uniformly disperse the third component in the crystal lattice of LiNiO _2. The structure is stabilized.

However, according to the above method, the crystal structure could be stabilized, but the reactivity with the electrolytic solution could not be sufficiently suppressed. This is considered to be due to the following reasons. That is, the discharge capacity is reduced by adding the third component. For this reason, since it was necessary to maintain the discharge capacity, it was not possible to increase the addition amount of the third component to such an extent that the reactivity with the electrolytic solution was sufficiently lowered.

[0008]

The present invention was completed in view of the above circumstances, and is a non-aqueous electrolyte secondary battery having a large discharge capacity and excellent charge / discharge cycle characteristics. The purpose is to provide.

[0009]

Means for Solving the Problems and Actions / Effects As a means for achieving the above object, the invention of claim 1 is a positive electrode containing a positive electrode active material comprising secondary particles in which primary particles are aggregated, In a non-aqueous electrolyte secondary battery including a negative electrode and a non-aqueous electrolyte, the positive electrode active material has a layered rock salt structure and has a general formula of Li _a Ni _1-b-c Co _b M _c O ₂ (however, M Is at least one element selected from Mg, Al, Ti, W, and Mo, and a, b, c, and d are 0.2 ≦ a ≦ 1.05 and 0.5 ≦ 1-b, respectively. −c ≦ 0.
9, 0 ≤ b ≤ 0.47, 0.03 ≤ c ≤ 0.1), wherein the concentration of Ni in the surface layer portion of the primary particles is from the inside of the primary particles. Is also low.

The positive electrode active material has a layered rock salt structure and has the general formula
Li_aNi_1-bcCo_bM_cO _Two(However, M is M
At least one selected from g, Al, Ti, W, and Mo
A, b, c, and d are each 0.2
≦ a ≦ 1.05, 0.5 ≦ 1-bc−0.9, 0 ≦ b
≦ 0.47, 0.03 ≦ c ≦ 0.1)
Since it is a transition metal complex oxide,
Obtaining a non-aqueous electrolyte secondary battery with a large discharge capacity
You can

1 showing the composition ratio of Ni in the positive electrode active material
-Bc is preferably 0.5≤1-bc≤0.9. If 1-bc is less than 0.5, the discharge capacity is reduced, which is not preferable. If 1-bc exceeds 0.9, the stability of the crystal structure is not maintained, and as a result, the charge / discharge cycle characteristics deteriorate, which is not preferable.

B representing the composition ratio of Co in the positive electrode active material
Is preferably 0 ≦ b ≦ 0.47. b is 0.
When it exceeds 47, the Ni concentration relatively decreases, and as a result, the discharge capacity decreases, which is not preferable.

It is preferable that c representing the composition ratio of the third component M in the positive electrode active material is 0.03≤c≤0.1. When c is less than 0.03, the thermal stability of the positive electrode active material decreases, which is not preferable. When c exceeds 0.1,
It is not preferable because the discharge capacity is significantly reduced.

Since the concentration of Ni in the surface layer portion of the primary particles is lower than that in the inside of the primary particles, the decomposition reaction of the electrolytic solution due to charging and discharging is suppressed. As a result, an increase in internal resistance of the battery is suppressed, so that charge / discharge cycle characteristics are improved.

Further, since only the Ni concentration in the surface layer portion is reduced, it is possible to minimize the reduction in discharge capacity that is inevitably caused by the reduction in Ni concentration.
The charge / discharge cycle characteristics can be improved while maintaining the discharge capacity.

The invention of claim 2 is characterized in that the positive electrode active material has an average particle size of 5 μm or more and 30 μm or less.

The positive electrode active material has an average particle size of 5 μm or more 30
When the thickness is less than or equal to μm, a non-aqueous electrolyte secondary battery having a large discharge capacity and charge / discharge cycle characteristics can be obtained.

When the average particle diameter of the positive electrode active material is less than 5 μm, the reactivity of the positive electrode active material is excessively improved, and the reactivity between the positive electrode active material and the electrolytic solution is also increased, resulting in deterioration of charge / discharge cycle characteristics. Is not preferred. When it exceeds 30 μm, the reactivity of the positive electrode active material is lowered and the packing density of the active material is also lowered, so that the discharge capacity is lowered, which is not preferable.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of a prismatic non-aqueous electrolyte secondary battery 1 according to one embodiment of the present invention. In FIG. 1, 1 is a prismatic non-aqueous electrolyte 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, and 9 is a negative electrode terminal. Reference numeral 10 is a positive electrode lead, and 11 is a negative electrode lead.

In this prismatic non-aqueous electrolyte secondary battery 1, a positive electrode 3 is formed by applying a positive electrode mixture to a current collector made of aluminum foil, and a negative electrode mixture is applied to a current collector made of copper foil. The negative electrode 4 and a non-aqueous electrolyte (not shown) 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 container 6 via the positive electrode lead 10.

The positive electrode active material in the present invention is a layered material.
It has a rock salt structure and has the general formula Li_aNi _1-bcCo_bM
_cO_Two(However, M is selected from Mg, Al, Ti, W, and Mo.
At least one element, a, b, c, and
d is 0.2 ≦ a ≦ 1.05 and 0.5 ≦ 1-b, respectively.
-C≤0.9, 0≤b≤0.47, 0.03≤c≤0.
Use the lithium-transition metal composite oxide shown in 1).
You can

The positive electrode active material in the present invention can be prepared as follows. First, a mixed aqueous solution of a water-soluble nickel compound, a water-soluble cobalt compound, and a water-soluble compound of the third component is prepared, and this is reacted with an aqueous solution of an alkali compound to form a co-precipitated compound of nickel and the third component. Let Next, this coprecipitate is dried, the powder of the lithium compound is added to the obtained powder or the powder obtained by firing the powder, and the powder is fired at 600 ° C. to 850 ° C. in an oxygen atmosphere. The surface of the powder thus obtained is coated with a lithium-transition metal composite oxide containing the same constituents as the powder and having a low Ni concentration, and this is coated in an oxygen atmosphere at 600 ° C to 8 ° C.
By baking again at 50 ° C., it is possible to obtain a positive electrode active material in which the nickel concentration on the surface of the primary particles is lower than that in the inside of the primary particles.

As the water-soluble nickel compound, for example,
Examples thereof include nickel hydroxide, nickel oxide, nickel carbonate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate and nickel oxyhydroxide.

As the water-soluble cobalt compound, for example,
Examples thereof include cobalt hydroxide, cobalt oxide, cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, and cobalt oxyhydroxide. These may be used alone or in combination.

As the water-soluble compound as the third component, its nitrate, sulfate, hydrochloride, carbonate or the like can be used. These may be used alone or in combination.

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. These may be used alone or in combination.

As the alkali compound, hydroxide, carbonate or the like of potassium, sodium or ammonia can be used. When sodium or potassium is used, it is necessary to filter and wash sodium salt or potassium salt from the coprecipitate. On the other hand, when using ammonia, it is not necessary to filter and wash the coprecipitate, but since nickel forms complex ions and is partially dissolved in the solution, it is necessary to dry at once by spray drying or the like.

1 mol of lithium carbonate and nickel hydroxide
0.7 mol, 0.28 mol of cobalt hydroxide, and sodium sulfate.
Mixed with 0.01 mol of tan and 0.01 mol of niobium hydroxide.
And mix this mixture in air at a temperature of 750 ° C. for 15 hours.
By firing, LiNi _0.7Co_0.28Ti
_0.01Nb_0.01O_TwoInferred lithium transition gold
A metal complex oxide can be obtained.

1 mol of lithium carbonate, 0.7 mol of nickel hydroxide, 0.28 mol of cobalt hydroxide, 0.01 mol of molybdenum oxide and 0.01 mol of tungsten oxide were mixed, and this mixture was mixed. By firing in air at a temperature of 850 ° C. for 15 hours, LiNi _0.7 Co
A lithium transition metal composite oxide estimated to be _0.28 Mo _0.01 W _0.01 O ₂ can be obtained.

The lithium-transition metal 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 current collector made of a metal foil. The positive electrode can be manufactured by applying it to the 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 type of binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolytic solution used in the production of electrodes. 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.

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.

Examples of the positive electrode current collector include Al, Ta and 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 can be 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 electrolyte 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)
_Two, And LiC (CF_ThreeSO_Two)_ThreeFluorine-containing organic such as
Examples thereof include lithium salts. These solutes are
You may select and use only one type, or use two or more types.
You may use it in combination.

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 membrane 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.

With respect to these batteries, at a temperature of 25 ° C., charging was performed at a constant current of 1 CmA up to 4.1 V, and a constant voltage of 4.1 V was further applied for a total of 3 hours, and discharge was performed at a constant current of 1 CmA with a final voltage of 2.75 V. By doing so, a charge / discharge cycle test can be performed.

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

Example 1 Nickel hydroxide Ni (OH)
_Two1.14 mol and cobalt hydroxide Co (OH) _Two0.
78 mol and dissolved in water (atomic ratio Ni: Co = 0.5
7: 0.39) 2 liters of nickel hydroxide and hydroxide
A mixed aqueous solution (liquid A) with cobalt was prepared. On the other hand, N
a_TwoCO_ThreeDissolve 3.0 moles in water and add 1.8 liters
An aqueous sodium carbonate solution (solution B) was prepared. Solution A and solution B
And in 1 liter of hot water at 80 ° C under stirring at the same time.
It was added at a constant rate. At this time, keep the temperature of the solution at 80 ° C.
It was After the addition of the solution is completed, the mixture is stirred at 80 ° C for 60 minutes.
During that period, the precipitate was aged. The precipitate thus obtained
Was filtered and washed with water. Then dried at 120 ° C for 16 hours
The basic carbon dioxide of nickel and cobalt
A salt co-precipitate was obtained. This powder was heated to 400 ° C in an air stream.
CO_TwoAnd oxidize
It was a thing. 88.5 parts by weight of this oxide powder and aluminum sulfate
Ni Al_Two(SO_Four)_Three6.8 parts by weight and LiOH2
3.9 parts by weight (mixed in atomic ratio: Ni: Co: A
l: Li = 0.57: 0.39: 0.04: 1), which
Is baked in an oxygen stream at 700 ° C. for 10 hours to obtain LiNi._0.57
Co_0.39Al_0.04O_TwoGot Of the obtained particles
The average particle size was 10 μm.

LiNi obtained as described above_0.57C
o_0.39Al_0.04O_Two100 parts by weight and lithium hydroxide
3.78 parts by weight of um and 1.46 parts by weight of nickel hydroxide
And 11.90 parts by weight of cobalt hydroxide and aluminum sulfate
After mixing with 0.09 part by weight of um, in an oxygen flow, 700
After firing at ℃ for 8 hours, the surface layer of the primary particles and the inside
Positive electrode active material with different average concentration and particle size of 10.5 μm
LiNi_0.50Co _0.45Al_0.05O_TwoGot
It was

Positive electrode active material 92 obtained as described above
Parts by weight, 3 parts by weight of acetylene black as a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder are mixed, and N-
Methyl-2-pyrrolidone was appropriately added and dispersed to prepare a slurry. After uniformly applying the slurry to both surfaces of a positive electrode current collector made of aluminum having a thickness of 20 μm and drying the slurry,
The positive electrode 4 was produced by compression molding with a roll press.

90 parts by weight of graphite and 10 parts by weight of polyvinylidene fluoride were mixed and N-methyl-2-pyrrolidone was appropriately added and dispersed to prepare a slurry. The slurry was uniformly applied to a copper negative electrode current collector having a thickness of 10 μm, dried, and compression-molded with a roll press to prepare a negative electrode 3.

For the separator 5, a microporous polyethylene film having a thickness of 25 μm was used.

Using the above components, a rated capacity of 100
Width 34 mm, Height 67 mm, Thickness 6.2 mm at 0 mAh
A prismatic non-aqueous electrolyte secondary battery was manufactured.

As the non-aqueous electrolyte, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 4: 6, and LiPF ₆ was dissolved in this solution at 1.0 mol / liter.

Examples 2 to 7 LiNi _0.57 Co _0.39 Al _0.04 O constituting the inside of the positive electrode active material particles
The composition of the surface layer portion of the positive electrode active material particles was changed as shown in Table 1 by using the lithium-transition metal composite oxide shown in Table 1 instead of ₂ , and changing the addition amount of lithium hydroxide or the like. Except for the above, nonaqueous electrolyte secondary batteries of Examples 2 to 7 were produced in the same manner as in Example 1. Table 1 also shows the composition of the whole positive electrode active material and the average particle size.

<Examples 8 to 11> Of positive electrode active material particles
LiNi forming the inside_0.57Co_0.39Al_0.04
O_TwoInstead of lithium, lithium transition metal composite oxides shown in Table 1
Was used, and the amount of lithium hydroxide added was changed.
Table 1 shows the composition of the surface layer of the positive electrode active material particles.
The inside of the positive electrode active material particles
Lithium having average particle size as shown in Table 1 as particles
Example 1 except that the transition metal complex oxide was used.
Similarly, non-aqueous electrolyte secondary batteries of Examples 8 to 11
Was produced. In addition, the composition of the entire positive electrode active material and the average particle size
The results are also summarized in Table 1.

Comparative Example 1 Ni (OH) ₂ was pulverized with a wet pulverizer using water as a solvent to obtain particles having an average particle size of 1 μm. Dry this particle slurry with a spray dryer,
Granulation was performed to obtain particles having an average particle size of 10.5 μm. This Ni
75.7 parts by weight of (OH) ₂ and 23.9 parts by weight of LiOH were mixed (atomic ratio Ni: Li = 1: 1), and the mixture was fired in an oxygen flow at 700 ° C. for 10 hours to obtain LiNi.
O ₂ was obtained.

<Comparative Example 2> LiNi_0.57Co_0.39A
l_0.04O_TwoInstead of LiNi_0.70Co
_0.25Al_0.05O_TwoTable of positive electrode active material particles
As in Example 1 except that the layer-forming material was not added.
Similarly, a non-aqueous electrolyte secondary battery of Comparative Example 2 was prepared.
It was The average particle size of the positive electrode active material is 10.5 μm, and the composition
Is LiNi_0.70Co_0.25Al_0.05O_TwoWas
It was

Comparative Example 3 The lithium transition metal composite oxide shown in Table 1 was used in place of LiNi _0.57 Co _0.39 Al _0.04 O ₂ forming the inside of the positive electrode active material particles, and water was used. Non-aqueous electrolyte secondary battery of Comparative Example 3 in the same manner as in Example 1 except that the composition of the surface layer portion of the positive electrode active material particles was changed as shown in Table 1 by changing the addition amount of lithium oxide or the like. Was produced.

[0059]

[Table 1]

<Measurement> (X-ray microanalysis) The state of the coating of the positive electrode active material was measured by X-ray microanalysis (XMA). After mixing the positive electrode active material and the epoxy resin, the epoxy resin was cured and an arbitrary surface was polished to expose the cross section of the active material. X-ray microanalysis was performed on the cross section. Ni in the surface layer and inside of the positive electrode active material
The concentrations are summarized in Table 2 as the ratio of Ni atoms to the sum of the numbers of Ni, Co and M atoms.

(Measurement of Particle Diameter) The average particle diameter of the powder was measured by a laser diffraction / scattering method using Nikkiso Microtrac UPA and HRA.

(Charge / Discharge Cycle Characteristics Measurement Test) Example 1
11 to 11 and the non-aqueous secondary batteries of Comparative Examples 1 to 3, the charge / discharge cycle characteristics were measured using a potentiogalvanostat. Charging is up to 4.10V at a constant current of 1000mA, and at a constant voltage of 4.10V, a total of 3
I went on time. The discharge was performed at a constant current of 1000 mA, and the final voltage was 2.75V. The average discharge capacity in the 1st to 5th cycles is defined as the initial discharge capacity, and the discharge capacity is 8 times the initial discharge capacity.
The results are summarized in Table 2 with the cycle life when the number of cycles when it decreased to 0%.

(Discharge Capacity Measurement Test) Examples 1 to 1
1 and the non-aqueous secondary batteries of Comparative Examples 1 to 3,
The discharge capacity was measured using a potentiogalvanostat. Charging up to 4.10V at 1000mA constant current,
Further, it was carried out at a constant voltage of 4.10 V for a total of 3 hours. The discharge was performed at a constant current of 1000 mA, and the discharge capacity was calculated from the discharge time up to a final voltage of 2.75 V and summarized in Table 2.

[0064]

[Table 2]

<Results> (X-ray microanalysis) As a result of X-ray microanalysis, in Examples 1 to 11 obtained by the present invention, the Ni concentration in the surface layer portion of the primary particles constituting the positive electrode active material was 0.
While it was 33 or less, the internal Ni concentration was 0.57 or more. Thus, Examples 1 to 1
In No. 1, a significant difference was found in the Ni concentration between the surface layer part and the inside of the particle.

On the other hand, in Comparative Example 1, Ni in the surface layer portion was
The concentration was 1.00 and the internal Ni concentration was 1.00, and no significant difference was observed between the two. Also in Comparative Example 2, the Ni concentration in the surface layer portion was 0.70 and the Ni concentration in the inside was 0.70 as well, and no significant difference was observed.

(Discharge Capacity and Charging / Discharging Cycle Characteristics) First, regarding charging / discharging cycle characteristics, in Comparative Example 2, 3
In contrast to 23 cycles, in Example 2, it was 5
It showed a remarkably high value of 03 cycles. This is because in Example 2, since the Ni concentration in the surface layer portion of the primary particles was lower than that in the inside, the decomposition reaction of the electrolytic solution due to charge / discharge was suppressed, and as a result, the increase in internal resistance of the battery was suppressed. it is conceivable that.

(Influence of Average Particle Diameter) Average particle diameter is 5 μm
In Examples 2, 9 and 10 in which the thickness is 30 μm or less,
In Example 8 in which the average particle size was 0.9 μm, while the charge / discharge cycle characteristics were 450 cycles or more,
It was 400 cycles. It is considered that this is because in Example 8, the average particle size was less than 1 μm, so the reactivity with the electrolytic solution increased and the internal resistance increased.

On the other hand, in Examples 2, 9 and 10, the discharge capacity was 1100 mAh or more, whereas in Example 11 in which the average particle size was 43 μm, it was 1010 mAh. It is considered that this is because the reactivity of the positive electrode active material with the lithium ions was lowered because the average particle diameter exceeded 30 μm.

From the above, in the non-aqueous electrolyte secondary battery,
The positive electrode active material has a layered rock salt structure and has the general formula Li _a Ni
_{1-b-c Co b M} c O 2 ( where M is, Mg, Al, T
i, W, and Mo are at least one element selected from a, b, c, and d, and 0.2 ≦ a ≦ 1.
05, 0.5 ≦ 1-bc−0.9, 0 ≦ b ≦ 0.4
7, 0.03 ≤ c ≤ 0.1), and by setting the concentration of Ni in the surface layer portion of the primary particles to be lower than that in the interior of the primary particles, a large discharge capacity and It is possible to obtain a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics.

The above results show that the inside 100 of the positive electrode active material particles are
Regarding the case where 15.8 parts by weight of the surface layer of the positive electrode active material particles were added to the parts by weight, in another test, 100 parts by weight of the inside of the positive electrode active material particles were added to the positive electrode active material particles. Similar results were confirmed when 33.1 parts by weight of the surface layer was added.

<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-described embodiment, the prismatic non-aqueous electrolyte 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.

[0074]

According to the present invention, a non-aqueous electrolyte secondary battery having a large discharge capacity and excellent charge / discharge cycle characteristics can be obtained.

[Brief description of drawings]

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

[Explanation of symbols]

1. Square non-aqueous electrolyte 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

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Claims (2)

[Claims] 1. A nonaqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material composed of secondary particles in which primary particles are aggregated, a negative electrode, and a nonaqueous electrolytic solution, wherein the positive electrode active material is layered rock salt. Having a structure of the general formula Li _a Ni _1-bc Co _b
M _c O ₂ (where M is at least one element selected from Mg, Al, Ti, W and Mo, and a, b, c,
And d are 0.2 ≦ a ≦ 1.05 and 0.5 ≦ 1 respectively.
−b−c ≦ 0.9, 0 ≦ b ≦ 0.47, 0.03 ≦ c ≦
0.1) The lithium-transition metal composite oxide represented by 0.1), wherein the concentration of Ni in the surface layer portion of the primary particles is lower than that in the interior of the primary particles. 2. A non-aqueous electrolyte secondary battery, wherein the secondary particles of the positive electrode active material have an average particle size of 5 μm or more and 30 μm or less.