JP2000340229A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery capable of having high capacity and high safety in over-charging, preventing gas generation under general use conditions, and having excellent storage characteristics at a high temperature. SOLUTION: This nonaqueous secondary battery comprises a positive electrode 1, a negative electrode 2, and electrolyte. The positive electrode 1 contains positive electrode active material of at least LixCoO2 (x is a value in assembling a battery, 1.01<=x<=1.10) and LiyNisCotMuO2 (M is at least one element selected from a group of B, Mg, Al, Si, P, V, Mn, Fe, Cu, Zn, Sr, In, Sn, and lanthanoid element, y is a value in assembling a battery, 1.01<=y<=1.10, 0.65<=s<=0.90, 0<t<=0.3, 0.01<=u<=0.2). An amount of LiyNisCotMuO2 contained is 10-45 wt.% of a total amount of LixCoO2 and LiyNisCotMuO2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery, and more particularly, to a high-capacity, high-overcharge safety, low gas generation under normal use conditions, and high-temperature storage. The present invention relates to a non-aqueous secondary battery having excellent characteristics.

[0002]

2. Description of the Related Art A demand for a secondary battery having a high energy density is increasing with the miniaturization of electronic equipment. At present, as a high-capacity secondary battery that meets this demand, a lithium ion secondary battery using Li _x CoO ₂ as a positive electrode active material and a carbon-based material as a negative electrode active material has been commercialized. This lithium ion secondary battery has an average driving voltage of 3.
It is as high as 6 V, about three times the average driving voltage of conventional nickel-cadmium batteries and nickel-metal hydride batteries, and uses a carbon-based material as a negative electrode active material, and the mobility involved in charging and discharging is lithium, which is a light metal. Therefore, it is possible to reduce the weight, and it has been attracting much attention.

On the other hand, while the capacity per unit weight is higher than that of the above-mentioned conventional battery, only the capacity per unit volume of about 60% of the nickel-metal hydride battery has been commercialized. Is required.
However, the theoretical discharge capacity of LiCoO ₂ is 274 mAh.
However, when deep charge / discharge is performed, LiCoO ₂ causes a phase change to affect the cycle life, so that a practical discharge capacity in an actual lithium ion secondary battery is in the range of 125 to 140 mAh / g. There was a problem that would be.

For this reason, when LiCoO ₂ is used for the positive electrode active material, it is conceivable to use a material having a small particle size, improve the filling property of the positive electrode active material, and increase the capacity. However, when a positive electrode is prepared using LiCoO ₂ as an active material as described above, a conductive additive, a binder, a solvent, and the like are added thereto, and mixed and dispersed to prepare a positive electrode mixture-containing paste, which is applied to a conductive substrate. Since the positive electrode is manufactured by drying and forming the positive electrode mixture layer to form the positive electrode mixture layer, in the positive electrode mixture layer having an improved packing density, the elasticity of the positive electrode mixture layer is lost and cracks may occur on the surface. Alternatively, there has been a problem that peeling from the conductive substrate occurs and the charge / discharge characteristics deteriorate.

[0005] Therefore, as a positive electrode active material in place of LiCoO _2, lithium manganese oxide of spinel structure, Li
Use of lithium nickelate such as NiO _2, lithium titanate such as LiTiO _{2, and the} like has been studied. Among these lithium-containing composite oxides, it is reported that LiNiO ₂ containing nickel as a constituent element, whose component element is inexpensive and whose supply is stable, is suitable as a positive electrode active material replacing LiCoO ₂ among these lithium-containing composite oxides ( JP-A-7-
37576, JP-A-7-307151, JP-A-6-231767, JP-A-8-31418, and the like.

[0006]

By the way, LiNiO
_TwoHas a theoretical discharge capacity of LiCoO_Two274mAh as well as
/ G, but the operating potential based on the Li electrode is LiCo
O_TwoLiNiO compared to _TwoIs lower in potential and LiNi
O_TwoThe voltage drop at the end of discharge of LiCoO_TwoSo steep
Because it is not intense, LiNiO_TwoIs 3.0 with respect to the Li pole.
LiCoO discharge capacity in the ~ 4.0V region_TwoLarger than
Kiku, LiNiO_TwoIs LiCoO_TwoMore practical electricity
In the range (3.0-4.3V region with respect to the Li pole)
Large electric capacity. 3.0 to 4.3 for the actual Li pole
The discharge capacity in the V region depends on the respective synthesis conditions.
Different but generally LiNiO_Two160 to 200 in case of
mAh / g. Therefore, LiCo as a positive electrode active material
O_TwoThan using LiNiO_TwoIt is better to use
It is expected that high capacity batteries can be manufactured.
You.

Further, the true density of LiCoO ₂ and LiNiO ₂ are, LiCoO ₂ is 4.9~5.1g / cm ^3, since LiNiO ₂ is 4.6~4.8g / cm ^3, approximately Since the same degree of packing can be obtained, LiCo
Even if O ₂ is replaced with LiNiO ₂ , there is almost no deterioration in the filling property during electrode fabrication.

Further, the irreversible capacity of LiNiO ₂ is Li
Since the irreversible capacity of CoO ₂ is larger than that of CoO ₂ , when a carbon-based material is used as the negative electrode active material, considering the irreversible capacity of the carbon-based material, the battery design becomes easier when LiNiO ₂ is used as the positive electrode active material. There are advantages. That is, when Li ions are inserted into the carbon-based material, some of the Li-ions are completely taken into the carbon-based material and do not participate in charging and discharging. When LiCoO ₂ is used as the positive electrode active material and a carbon-based material is used as the negative electrode active material, L
Since iCoO ₂ has almost no irreversible capacity, some Li ions of LiCoO ₂ are taken in as irreversible capacity of the carbon-based material in the first cycle, so that the amount of usable Li ions is reduced. That is, the amount of Li ions corresponding to the irreversible capacity of the negative electrode decreases from the amount of Li ions that can be extracted from LiCoO _{2 as} a lithium source, and as a result, the amount of Li ions that can be used for charging and discharging decreases. On the other hand, LiNiO ₂ is LiNiO ₂
Since the battery itself has a relatively large irreversible capacity, the balance between the irreversible capacity of LiNiO _{2 and} the irreversible capacity of the carbon-based material is controlled by controlling the amount of LiNiO _{2 and} the amount of the carbon-based material used in the production of the battery. When taking, without reducing the amount of Li ions that can be freely used for charge and discharge among Li ions that can be extracted from the positive electrode active material,
The amount of Li ions that no longer contributes to charging and discharging can be limited to the irreversible capacity of LiNiO ₂ itself.

[0009] However, LiNiO ₂ is Ni ²⁺ is easily mixed into the interlayer by synthetic conditions, the composition although Ni ²⁺ is mixed into the interlayer _{Li 1-x Ni 1 + x} O 2 , and the interlayer Ni ^{2 +} Has a smaller electrochemical capacity than stoichiometric LiNiO ₂ because it inhibits the transfer of Li ions. In addition, the synthesis of stoichiometric LiNiO ₂ must be performed carefully in an oxygen atmosphere, and the production cost is higher than that of LiCoO ₂ .

LiNiO ₂ undergoes a phase change between a hexagonal system and a monoclinic system during charging and discharging. When the Li content in LiNiO ₂ during charging and discharging decreases, N
A NiO ₂ phase having a short i-Ni interlayer distance is generated, and a two-phase coexistence state [LiNiO ₂ phase and Li _x
NiO ₂ (x≪1) phase]. Such a change puts stress on the active material itself, and adversely affects the cycle life as battery characteristics.

Furthermore, LiNiO_TwoIs LiCoO_TwoCompared to
Highly hygroscopic, LiNiO in air_TwoLeave
If it absorbs water, the electrochemical characteristics deteriorate. LiC
oO _TwoIs water content even after moisture absorption by vacuum drying or heat treatment.
The electrochemical properties are restored by removing
iNiO_TwoNow, even if the water removal operation is performed, the electrochemical characteristics
There is a problem that does not recover.

Therefore, L in which Ni is partially replaced by Co
i (NiCo) O ₂ has been proposed (JP-A-63-1).
24393, JP-A-7-142056, JP-A-7-129719), and among them, Li (NiCoM) O ₂ containing other elements (M is Ni,
Elements other than Co) generate a large amount of gas when overcharged,
Because of its excellent safety, it has been particularly noted (Japanese Patent Application Laid-Open No. 9-69363).

However, in a non-aqueous secondary battery, it is desirable to use an active material or an electrolyte which easily generates gas in order to ensure safety during overcharge. Unnecessary gas generation increases the rejection rate during battery manufacturing and must be avoided. on the other hand,
Under normal use environment, there is almost no gas generation, but when an abnormal voltage is applied to the battery and continuous current flows, gas is efficiently generated and the current cut-off mechanism is activated to prevent abnormal situations. It must be a battery that can be reliably avoided.

The present invention solves the problems and future requirements of the conventional nonaqueous secondary battery as described above, and has a high capacity, a high safety at the time of overcharge, and a gas under a normal use condition. An object of the present invention is to provide a non-aqueous secondary battery which is less likely to be generated and has excellent high-temperature storage characteristics.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, at least Li _x CoO ₂ (x is a value at the time of battery assembly and 1 .01 ≦ x ≦ 1.10) and Li _y Ni _s Co _t
M _u O ₂ (M is, B, Mg, Al, Si , P, V, M
n, at least one element selected from the group consisting of Fe, Cu, Zn, Sr, In, Sn and a lanthanoid element, y is a value at the time of battery assembly, and is 1.01 ≦
y ≦ 1.10, 0.65 ≦ s ≦ 0.90, 0 <t ≦ 0.
3, 0.01 ≦ u ≦ 0.2) and the above Li
_y Ni _s Co _t M _u content of O ₂ and Li _x CoO ₂ and L
i _y Ni _s Co _t M 10~ in a total amount in the _u O ₂
When the content is 45% by weight, the capacity is high, the safety at the time of overcharging is high, and the gas generation is small under normal use conditions.
The inventors have found that a nonaqueous secondary battery having excellent high-temperature storage characteristics can be obtained, and have solved the above-mentioned problems.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, Li _x CoO ₂ has a smaller capacity that can be actually charged and discharged than the theoretical capacity. Therefore, the present inventors have studied Li (NiCoM) O ₂ which can be expected to have a high capacity as a positive electrode active material. The capacity of this Li (NiCoM) O ₂ is Ni, Co
And M are known to be affected by the composition ratio.
Then, the present inventors, together with various elements M, Ni,
Li (NiCoM) with various composition ratios of Co and M
When O ₂ was examined, M, B, Mg, A
1, Si, P, V, Mn, Fe, Cu, Zn, Sr, I
n, with use of at least one element selected from the group consisting of Sn and lanthanoid elements, Li-rich composition, especially when expressed in _{Li y Ni s Co t M u} O 2, 1.01 ≦ y ≦ 1. 10, 0.65 ≦ s ≦ 0.9
It has been found that when the range is 0, 0 <t ≦ 0.3, and 0.01 ≦ u ≦ 0.2, high capacity can be achieved.

[0017] However, the above-mentioned Li _y Ni _s Co _t
When using M _u O _2, although Li _x CoO ₂ gas generating a large amount of current interruption mechanism during overcharge as compared with to operate at lower temperatures, the discharge potential is lowered was found.

Therefore, the present inventors have proposed Li_xCoO_Two
Part of the above Li_yNi_sCo_tM _uO_TwoAnd replace both
A positive electrode active material system that uses
When a polar active material is used, Li_yNi_sCo_tM_uO_Twoof
As the mixing ratio increases, the current interruption mechanism during overcharge
Operates at lower temperatures and has a higher discharge capacity, but
It was found that the surface and discharge potential decreased. This is Li
_yNi_sCo_tM_uO_TwoWith the increase of Li_yNi_sC
o_tM_uO_TwoBecause the nature of will appear stronger
is there.

Therefore, the present inventors have proposed Li_xCoO_TwoTo
Capacity reduction and Li_yNi_sCo_tM_uO_TwoBased on
For the lowering of the discharge potential and the increase of the calorific value,_y
Ni _sCo_tM_uO_TwoWas studied by changing the replacement amount of
As a result, Li_yNi_sCo_tM _uO_TwoThe amount of Li_xCoO
_TwoAnd Li_yNi_sCo_tM_uO_TwoAnd in the total amount
When the content is 10 to 45% by weight, the discharge capacity is large,
It was found that the electric potential was slightly reduced. Sand
Chi, Li_yNi_sCo_tM_uO_TwoContent of Li _xCo
O_TwoAnd Li_yNi_sCo_tM_uO_TwoAnd in the total amount
If less than 10% by weight, current interruption mechanism at overcharge
Will not operate at a sufficiently low temperature, and the discharge capacity
If the improvement of the discharge cannot be achieved and it is more than 45% by weight,
The decrease in potential is large. And this Li_yNi_sC
o_tM_uO_TwoThe content of Li_xCoO_TwoAnd Li
_yNi_sCo_tM_uO_Two10 to 3 in the total amount of
Particularly preferred is 5% by weight.

Next, the present inventors have found that the Li _x CoO ₂ and _{Li y Ni s Co t M u} O 2 combined in a ratio within the above range, was investigated safety by gas generation during overcharging , Li amount in Li _x CoO ₂ and _{Li y Ni s Co 1-s} O 2 (i.e., values of and y of x) 1.
When the pressure is set to 01 to 1.10, gas is generated particularly efficiently, and the current cutoff mechanism incorporated in the battery sealing portion is activated by the time the thermal runaway occurs to improve safety. It has been found that the generation of gas from the powder can be reduced and the high-temperature storage characteristics can be improved.

That is, when the Li amount is less than 1.01, the gas generation speed becomes slow, and the time required for the current interrupting mechanism to operate during overcharging becomes long. Therefore, when the current interrupting mechanism operates, the battery becomes hot. However, if the Li content exceeds 1.10, the amount of gas generated increases even during normal use, and gas is generated during high-temperature storage. The shut-off mechanism operates to increase the battery failure rate.

[0022] In the _{Li y Ni s Co t M u} O 2, as the composition ratio of Ni and Co, for high capacity,
It is necessary that 0.65 ≦ s ≦ 0.90 and 0 <t ≦ 0.3, especially 0.70 ≦ s ≦ 0.80 and 0.10 ≦
It is preferable that t ≦ 0.20. In addition, as the composition ratio of M, in order to increase the capacity by Ni and Co and to reduce the calorific value, the crystal form of the solid solution does not significantly change based on the reasons described below, and the active material having a non-stoichiometric composition is used. In this case, the contact between the decomposition product and the electrolytic solution is prevented, but the amount must not affect the charge / discharge reaction.
It is necessary that 01 ≦ u ≦ 0.2, especially 0.0
It is preferable that 5 ≦ u ≦ 0.20. The lanthanoid elements include Y, La, Ce, Nb, and Yb.
And the like, and may be a misch metal which is a mixture thereof.

In the present invention, the above Li_yNi_sCo_t
M_uO_TwoContains M in addition to Ni and Co,
This is because by containing M, Li (NiCo) O
_TwoHeat generation can be reduced as compared with, and safety can be improved
Because it can be. In order to contain such M
The reason why the calorific value can be further reduced is not always
Although it is not clear, it can be considered as follows. That is, the book
The inventors have detailed the heat generated by the positive electrode active material.
As a result of examination, the above heat was generated by the positive electrode active material alone.
Instead of the reaction between the positive electrode active material and the electrolyte, especially the positive electrode active material
It is thought to be due to the reaction between the decomposition product of the electrolyte and the electrolyte.
It is. From such a viewpoint, in order to reduce the calorific value,
Cathode active material that does not generate decomposition products that easily react with the electrolyte
Quality or contact of electrolytes with such decomposition products
The positive electrode active material must have a surface property that prevents
is there. Therefore, the above Li_yNi_sCo_tM_uO_Twosmell
Is a solid solution in which the element M partially replaces Ni and Co.
In the case, Li (NiCo) O_TwoCrystal form is more stable than
And the generation of decomposition products can be suppressed._yNi _sC
o_tM_uO_TwoIs Li (NiCo) O_TwoAdd element M to
If the active material has a non-stoichiometric composition, the element M
Exists on the surface of the substance to prevent direct contact between the decomposition product and the electrolyte
This is probably due to the fact that

Next, the fabrication of the non-aqueous secondary battery of the present invention will be described.

In the present invention, Li_xCoO_TwoAnd Li_y
Ni_sCo_tM_uO_TwoAnd non-aqueous
To produce a positive electrode for a secondary battery, for example,
If necessary, for example, flaky graphite, acetylene
Conductive additives such as racks and polytetraflu
Binders such as polyethylene and polyvinylidene fluoride
Is added and mixed, and the obtained positive electrode mixture is molded by an appropriate means.
do it. For example, pressure molding of the positive electrode mixture,
Alternatively, the above positive electrode mixture is dispersed in a solvent to form a paste.
(In this case, dissolve the binder in the solvent beforehand
May be mixed with the positive electrode active material, etc.)
Apply paste containing electrode mixture to conductive base material as current collector
And drying to form a positive electrode mixture layer.
Thus, a positive electrode is manufactured. However, the method of manufacturing the positive electrode is described above.
The present invention is not limited to the illustrated method, but may be performed by other methods.
No. In the positive electrode, the active material Li_xCoO_TwoPair of
When x ≦ 1.03, gas is generated at the time of overcharging.
May be added. The above lithium compound
Gas from the positive electrode active material
Adjustment becomes easier. As such a lithium compound
Is, for example, Li_TwoCO _ThreeAnd the like.
The amount of the lithium compound added may be Li_xCoO_Two
And Li_yNi_sCo_tM_uO_Two100 parts by weight
0.1 to 2 parts by weight, preferably 0.1 to 2 parts by weight.
It is particularly preferred to use 2 to 1 part by weight. The present invention
When the positive electrode active material is used, the packing density of the positive electrode mixture layer is increased.
2.8-3.5 g / cm for capacity^ThreeAnd raised place
In this case, the present invention has high capacity
It is particularly useful in the production.

In the present invention, the negative electrode active material only needs to be capable of doping and undoping lithium ions. Specific examples of such a negative electrode active material include graphite,
Examples include pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, carbon-based materials such as mesocarbon microbeads, carbon fibers, and activated carbon, as well as lithium or lithium-containing compounds. As the lithium-containing compound, there are a lithium alloy and others, and as the lithium alloy, for example, lithium-
Aluminum, lithium-lead, lithium-indium,
Lithium-gallium, lithium-indium-gallium and the like, and examples of the lithium-containing compound other than the lithium alloy include, for example, tin oxide, silicon oxide, nickel-silicon alloy, magnesium-silicon alloy, tungsten oxide, Indium oxide, lithium iron composite oxide and the like can be mentioned. Some of these exemplified lithium-containing compounds do not contain lithium at the time of production, but when they act as a negative electrode active material, they contain lithium. Each of these negative electrode active materials can be used alone, or two or more of them can be used in combination.

Further, the present inventors have proposed the above-mentioned anode active material.
That is, when the above-mentioned positive electrode active material is used, the
-The rise of dance can be suppressed and efficient gas generation is possible.
After examining the combination with the negative electrode active material,
(002) Distance between planes (d ₀₀₂) Is 0.338 nm or less
Lower, preferably 0.336 nm or less, crystallite in c-axis direction
Has a size (Lc) of 35 to 57 nm, preferably 40 to 57 nm.
45 nm, aspect ratio (major axis diameter / minor axis diameter) 2-2
0, preferably 5 to 15, having an average particle diameter of 20 μm or less,
Preferably, a flaky carbon-based material of 6 μm or less is used.
Found that the above characteristics can be improved by
did. By using such a carbon-based material,
The reason why the characteristics can be improved at present is always
Although it is not clear, the layer where these carbon-based materials have developed
Lithium ion doped from the positive electrode
The anode is smoothly inserted into the carbon-based material,
Doping and undoping of lithium ions into a substance
Slides with the expansion and contraction of the positive electrode active material
Keeps contact and maintains conductivity,
Due to the fact that a smooth charge / discharge reaction is possible
it is conceivable that.

As such a carbon-based material, for example,
In addition to natural graphite, those obtained by pyrolysis of various organic compounds, carbonization by calcining, and the like, for example, carbon-based materials obtained by gas phase pyrolysis of carbon compounds such as benzene, methane, and carbon monoxide, and the like. The temperature at the time of the thermal decomposition is preferably from 2000 ° C. to 3300 ° C. Other examples include pitch-based carbon-based materials, and examples of such pitches include petroleum pitch, asphalt pitch, coal tar pitch, crude oil cracking pitch, petroleum such as petroleum sludge pitch, Pitch obtained by thermal decomposition of coal, pitch obtained by thermal decomposition of organic low molecular weight aromatic compounds, and the like are included. Still another example is a calcined carbide of a polymer containing acrylonitrile or the like as a main component.

The negative electrode is mixed with the above-mentioned negative electrode active material, if necessary, by adding the same binder and conductive assistant as in the case of the above-mentioned positive electrode active material, and then molding the obtained negative electrode mixture by an appropriate means. It is produced by For example, pressure-forming the negative electrode mixture, or dispersing the negative electrode mixture in a solvent to form a paste (the binder may be dissolved in the solvent in advance and then mixed with the negative electrode active material),
The negative electrode is prepared by applying the negative electrode mixture-containing paste to a conductive substrate serving as a current collector, and drying the paste to form a negative electrode mixture layer. However, the method for producing the negative electrode is not limited to the method exemplified above, and may be another method.

As a method of applying the positive electrode mixture-containing paste and the negative electrode mixture-containing paste to the conductive substrate, for example, various coating methods such as an extrusion coater, a reverse roller, and a doctor blade are employed. be able to. In addition, as the conductive substrate serving as a current collector for electrodes such as a positive electrode and a negative electrode, for example, a metal mesh such as aluminum, stainless steel, titanium, and copper, punched metal, expanded metal, foam metal, and foil are used. However, aluminum foil is particularly suitable for the conductive substrate of the positive electrode, and copper foil is particularly suitable for the conductive substrate of the negative electrode.

The ratio of the amount of the active material in the positive electrode to the amount of the active material in the negative electrode depends on the type of the negative electrode active material used in combination with the positive electrode active material. It is preferable to set it to 1.0 to 3.5 (weight ratio).

In the non-aqueous secondary battery using the positive electrode active material of the present invention, the electrolyte is usually a liquid electrolyte (hereinafter, referred to as a liquid electrolyte).
This is referred to as “electrolyte solution”). As the electrolyte, a non-aqueous solvent-based electrolyte in which a lithium salt as a solute is dissolved in an organic solvent is used. The organic solvent that is a constituent solvent of the non-aqueous solvent-based electrolytic solution is not particularly limited, but it is particularly suitable to use a chain ester as a main solvent. Examples of such a chain ester include organic solvents having a chain COO-bond such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, and methyl propionate. The fact that the chain ester is the main solvent of the electrolytic solution means that the chain ester has a volume of more than 50% by volume in the total electrolyte solvent, and in particular, that the chain ester is It is preferred that 65% by volume or more in the liquid solvent, especially the chain ester accounts for 70% by volume or more in the total electrolyte solution solvent, and that the chain ester occupies 75% by volume or more in the total electrolyte solution solvent. preferable.

It is preferred that the chain ester be used as the main solvent as the solvent of the electrolytic solution because the chain ester exceeds 50% by volume in the total solvent of the electrolyte, and the battery characteristics, especially the low temperature characteristics Is improved.

However, as the electrolyte solvent, an ester having a high dielectric constant (an ester having a dielectric constant of 30 or more) is used as the above-mentioned chain ester in order to improve the battery capacity as compared with the case of using only the above-mentioned chain ester. It is preferable to use a mixture. The amount of such an ester having a high dielectric constant in the total electrolyte solvent is 10% by volume or more, particularly 20% by volume.
The above is preferred. That is, when the amount of the ester having a high dielectric constant is 10% by volume or more in the total electrolyte solvent, the improvement in capacity is clearly exhibited, and when the amount of the ester having a high dielectric constant becomes 20% by volume or more in the total electrolyte solution. The improvement in capacity is more clearly expressed. However, if the proportion of the ester having a high dielectric constant in the total solvent of the electrolyte is too large, the discharge characteristics of the battery tend to be reduced. As described above, the content is preferably 10% by volume or more, more preferably 20% by volume or more, preferably 40% by volume or less, more preferably 30% by volume or less, and still more preferably 25% by volume or less.

Examples of the ester having a high dielectric constant include ethylene carbonate, propylene carbonate,
Examples thereof include butylene carbonate, γ-butyrolactone, and ethylene glycol sulphite. Particularly, those having a cyclic structure such as ethylene carbonate and propylene carbonate are preferable, and cyclic carbonates are particularly preferable. Specifically, ethylene carbonate is most preferable.

Examples of the solvent which can be used in combination with the ester having a high dielectric constant include 1,2-dimethoxyethane, 1,3-dioxolan, tetrahydrofuran,
-Methyl-tetrahydrofuran, diethyl ether and the like. In addition, an amine-based or imide-based organic solvent, a sulfur-containing or fluorine-containing organic solvent, and the like can also be used.

As a lithium salt to be a solute of the electrolytic solution,
For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , Li
AsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄
F ₉ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO
₃ ) ₂ , LiN (CF ₃ SO ₂ ), LiC (CF ₃ SO
₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2) or the like is used alone or in combination of two or more. Particularly, LiPF ₆ and LiC ₄ F ₉ SO ₃ are preferable because of good charge / discharge characteristics. The concentration of the lithium salt as a solute in the electrolyte is not particularly limited, but may be 0.3 to 1.
7 mol / l, particularly preferably about 0.4 to 1.5 mol / l.

In the present invention, a solid or gel electrolyte can be used as the electrolyte in addition to the above-mentioned electrolyte. Examples of such electrolytes include, besides inorganic solid electrolytes, organic solid electrolytes and organic gel electrolytes mainly composed of polyethylene oxide, polypropylene oxide or derivatives thereof.

The separator is not particularly limited, but preferably has sufficient strength and can hold a large amount of electrolyte.
m, and a microporous film or nonwoven fabric made of polypropylene, polyethylene, or a copolymer of propylene and ethylene having a porosity of 30 to 70% is preferable.

As a method for producing the battery of the present invention, for example, an electrode assembly produced by laminating or winding the positive electrode and the negative electrode produced as described above via a separator is inserted into a battery case, And then sealed with a sealing body having a cleavage vent. As the cleavage vent, in order to ensure high safety, 20 to 40 at
m, especially those having an irreversible vent structure operating at 25-35 atm. In addition, the non-aqueous secondary battery of the present invention preferably has a current cut-off mechanism in the above-mentioned sealing portion. In particular, when the positive electrode active material of the present invention is used, the amount of gas generated during overcharge is increased to increase the In order to ensure safety in the event of a change, the operating pressure of the current interrupt mechanism should be 5-20.
atm, preferably 8 to 15 atm.

[0041]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples. In the following, “parts” means “parts by weight”.

Examples 1 to 6 and Comparative Examples 1 to 4 Li having the composition shown in Table 1 below was used as a positive electrode active material._xCoO
_TwoAnd Li_yNi_sCo _tM_uO_TwoIs shown in Table 2
Quantitative ratio), 91 parts of those positive electrode active materials in total amount,
4 parts of natural graphite as a conductive additive, as a binder
Mix polyvinylidene fluoride in a ratio of 4 parts
Was. However, mixing should be done with polyvinylidene fluoride in advance.
Dissolved in N-methylpyrrolidone,
The active material and natural graphite are added to the solution, and
Add lidon, disperse well, adjust viscosity and mix positive electrode
A containing paste was prepared. Example 4 and Example 4
In the paste containing the positive electrode mixture of No. 5, Li_TwoCO_Three0.5 parts
Was added.

[0043]

[Table 1]

[0044]

[Table 2]

Each of the positive electrode mixture-containing pastes of Examples 1 to 6 and Comparative Examples 1 to 4 was uniformly coated on a 20 μm-thick aluminum foil as a conductive substrate in a uniform amount, dried and dried. A mixture layer was formed. Similarly, the positive electrode mixture-containing paste is applied to the back surface of the aluminum foil, dried to form a positive electrode mixture layer, and then rolled under a pressure change by a roll press, cut, and cut into a strip-shaped positive electrode. Was prepared. The packing density of the positive electrode mixture layer is 3.0 to 3.0.
It was 2 g / cm ³ .

A binder solution (a binder solution obtained by dissolving polyvinylidene fluoride in N-methylpyrrolidone) similar to that of the above positive electrode was prepared, and graphite [as a negative electrode active material] was added to the binder solution. Distance (d ₀₀₂ ): 0.336 nm, crystallite size in the c-axis direction (Lc): 42 nm, aspect ratio: 10, average particle diameter: 10 μm] 180 parts were added and mixed to obtain a negative electrode mixture-containing paste. Prepared. This negative electrode mixture-containing paste is uniformly applied to both sides of a copper foil having a thickness of 18 μm as a conductive substrate, dried to form a negative electrode mixture layer, rolled by a roll-press, and then cut. Thus, a strip-shaped negative electrode was produced. The weight ratio between the positive electrode active material and the negative electrode active material was 2.1: 1 [positive electrode active material / negative electrode active material = 2.1 (weight ratio)].

Next, a separator made of a microporous polyethylene film having a thickness of 25 μm was arranged between the strip-shaped positive electrode and the strip-shaped negative electrode of each of the above-mentioned Examples and Comparative Examples, and wound spirally to form a spiral electrode body. After that, outer diameter 18mm, height 6
The battery was inserted into a 7 cm bottomed cylindrical battery case, and the positive electrode lead body and the negative electrode lead body were welded.

After that, 1.0 mol / l in the battery case
Electrolyte solution composed of LiPF ₆ / EC + EMC (volume ratio 1: 3) [that is, LiPF ₆ was added to a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3.
Was dissolved in 1.0 mol / l].

Then, the opening of the battery case was sealed in a conventional manner, and the structure shown in FIG.
A 5 mm cylindrical non-aqueous secondary battery was produced.

The battery shown in FIG. 1 will be described briefly. 1 is the positive electrode and 2 is the negative electrode. However, FIG. 1 does not show the substrates used for producing the positive electrode 1 and the negative electrode 2 in order to avoid complication.
The positive electrode 1 and the negative electrode 2 are spirally wound with a separator 3 interposed therebetween, and are accommodated in a stainless steel battery case 4 together with an electrolytic solution having the above composition as a spiral electrode body.

The battery case 4 also serves as a negative electrode terminal, and an insulator 5 is disposed at the bottom thereof, and an insulator 6 is also disposed on the spiral electrode body. And battery case 4
The opening 8 is provided with a sealing body 8 through an annular insulating packing 7.
Are arranged, and the inside of the battery is sealed by tightening the open end of the battery case 4 inward.

However, the sealing member 8 has a current cut-off mechanism for preventing a current from flowing inside the battery when a decomposition reaction of the electrolyte occurs inside the battery when an abnormal situation such as overcharging occurs and gas is generated. And, when the gas generated inside the battery rises to a certain pressure, an irreversible vent mechanism is built in to prevent the battery from bursting under high pressure by discharging to the outside of the battery, and the current interruption mechanism is The gas pressure inside is 1
The irreversible vent that operates when the pressure becomes 3 atm or more and operates under high pressure is activated when the gas pressure in the battery becomes 30 atm or more.

With respect to the batteries of Examples 1 to 5 and Comparative Examples 1 to 4 prepared as described above, the discharge capacity and the average discharge voltage were measured, and a storage test and an overcharge test were performed. Table 3 shows the results. The discharge capacity of each battery was 0.2 at 20 ° C.
It was measured by discharging the battery to a final voltage of 3.0 V at a current density of 2 C, and was indicated by an index when the capacity of the battery of Comparative Example 1 was 100. The average discharge voltage was constant current and constant voltage charging at 20 ° C and 1C up to 4.2V, then the voltage at a discharge depth of 50% when discharging at a final voltage of 3V at 0.2C was measured. Voltage.

In the storage test, 1.5 A under an environment of 20 ° C.
After charging to 4.2 V at a constant current of 2.5 V, charging was performed by a constant voltage method, and charging was performed so that the total charging time was 2.5 hours. 2.75
After 5 charge / discharge cycles of discharging to V, 2
After charging to 4.2 V at a constant current of 1.5 A in an environment of 0 ° C., charging was performed by a constant voltage method, and the total charging time was 2.
After charging for 5 hours, the battery was stored in an environment of 60 ° C. Then, by measuring the impedance of the battery after storage at 60 ° C. for 20 days, it was checked whether or not the current interrupting mechanism was activated.

Further, in the overcharge test, the battery was charged at a constant current of 1.5 A to 4.2 V in an environment of 20 ° C., and then charged by a constant voltage method, for a total charging time of 2.5 hours. Then, the battery was stored at 0 ° C. for 4 hours, and the presence or absence of ignition was examined at a charging current of 3 A.

[0056]

[Table 3]

[0057] batteries of Examples 1-6, as shown in Table _{2, Li x CoO 2 / Li} y Ni s Co t M u O 2 ( weight ratio) in the range of 90 / 10-55 / 45 [ That is,
_{Li y Ni s Co t M u} O 2 content is Li _x CoO ₂
1 in the total amount of the _{Li y Ni s Co t M u} O 2 and
0 to 45% by weight (Example 1 is 20% by weight, Example 2 is 1% by weight)
0% by weight, Example 3 has 35% by weight, Example 4 has 20% by weight, Example 5 has 20% by weight, and Example 6 has 45% by weight). As shown in Table 3, the battery of Comparative Example 1 was used as a reference for comparison (the positive electrode active material of the battery of Comparative Example 1 was Li as shown in Table 1).
₍ Using only _1.00 CoO ₂ ), and the average discharge voltage was slightly lower than that of Comparative Example 1, but was 3.65 V, which was a sufficiently high voltage.

The batteries of Examples 1 to 6 do not ignite at the time of overcharging and can ensure safety. However, even when stored at 60 ° C. for 20 days, the current cutoff mechanism does not operate, and the battery is operated under normal operating conditions. It has become clear that the current interruption mechanism does not operate and the battery cannot be used, and that the current interruption mechanism does not operate at the time of battery production and the defect rate does not increase. That is, the batteries of Examples 1 to 6 had high capacity, high safety during overcharge, low gas generation under normal use conditions, and excellent high-temperature storage characteristics.

On the other hand, the battery of Comparative Example 1 had a smaller capacity than the batteries of Examples 1 to 6, and had a problem of ignition at the time of overcharging, and lacked safety at the time of overcharging. .

The battery of Comparative Example 2 is shown in Table 1.
In addition, Li as a positive electrode active material_1.02Ni _0.82C_0.08Mg
_0.1O_TwoBattery that uses only
Although the operating temperature of the disconnection mechanism is low and the capacity is high,
The voltage has dropped.

Further, lithium (L) in Li _x CoO ₂
Comparative Example Ratio of i) is having a high lithium compound as a cathode active material 3 and _{Li y Ni s Co t M u} O cell of Comparative Example 4 using the ratio of lithium in ₂ high lithium compound as a cathode active material However, there is a problem in that the current cutoff mechanism operates during storage at 60 ° C. for 20 days, and lacks high-temperature storage characteristics.

[0062]

As described above, according to the present invention, a non-aqueous secondary battery having a high capacity, high safety at the time of overcharging, low gas generation under normal use conditions, and excellent high-temperature storage characteristics. Could be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view schematically illustrating an example of a non-aqueous secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery case 5 Insulator 6 Insulator 7 Insulation packing 8 Sealing body

Continued on the front page F-term (reference)

Claims (1)

[Claims] 1. A non-aqueous electrolyte comprising a positive electrode, a negative electrode, and an electrolyte.
In the secondary battery, the positive electrode has a small amount as a positive electrode active material.
And Li_xCoO_Two(X is a value at the time of battery assembly,
1.01 ≦ x ≦ 1.10) and Li_yNi_sCo_tM_uO
_Two(M is B, Mg, Al, Si, P, V, Mn, F
e, Cu, Zn, Sr, In, Sn and lanthanoid
At least one element selected from the group consisting of
Where y is a value at the time of battery assembly, and 1.01 ≦ y ≦
1.10, 0.65 ≦ s ≦ 0.90, 0 <t ≦ 0.3,
0.01 ≦ u ≦ 0.2) and the above Li_yNi_sC
o_tM _uO_TwoContent of Li_xCoO_TwoAnd Li_yNi_s
Co_tM_uO_Two10 to 45% by weight in the total amount of
Non-aqueous secondary battery characterized by the following.