JP3529750B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery using a lithium nickel cobalt composite oxide for a positive electrode, and more particularly to a non-aqueous electrolyte secondary battery with improved safety.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and VTRs have been reduced in size and demand has increased, there has been a demand for higher capacity secondary batteries serving as power supplies for these electronic devices. In addition, air pollution due to exhaust gas from automobiles has become a social problem, and it is expected that lightweight and high-performance secondary batteries will be used as power supplies for electric vehicles. As such a secondary battery, a non-aqueous electrolyte secondary battery in which a LiCoO ₂ positive electrode is combined with a carbon negative electrode has been developed and is currently used in large quantities.

However, in the positive electrode material of the secondary battery,
A certain LiCoO₂Is expensive because it contains Co, and
Due to resource constraints, LiNiO
₂Or LiNi in which part of Ni is replaced by Co_1-xCo_x
O₂Or LiMn₂O ₄Metal oxides such as
Compounds have been proposed and research is under way. In particular,
The positive electrode using the Ni-based active material is a conventional electrode material.
Compared with the case of using a Co-based positive electrode
Energy density can be increased, and the battery cost
Features that the capacitance characteristics are improved in addition to the
have. However, a charged Ni-based positive electrode
The material is thermally unstable compared to the Co-based active material.
External pressure when the battery is in a charged state
If an internal short circuit occurs due to
The Joule heat causes the battery temperature to rise, followed by the negative electrode and
The reaction between the positive electrode and the electrolyte solution generates heat, further generating
The active material itself decomposes. At this time, accompanied by oxygen generation
Further heating generates a combustion reaction of the electrolyte,
Cause thermal runaway (heat generation and gas release)
Ponds could burst or ignite.

As a countermeasure against such a problem, in a composite oxide containing lithium and nickel as main components,
It has been proposed that a battery excellent in safety can be realized by using a lithium nickel cobalt composite oxide in which a part of Ni is replaced with Co or Mn and further replaced with an element such as Al or Nb as a positive electrode active material. (JP 2000
-323143). According to this technique, by reducing the conductivity of the active material, a short-circuit current at the time of battery short circuit is prevented from penetrating into the active material particles, and the active material itself is thermally decomposed by Joule heat generated by the short-circuit current. It is considered that the temperature at which decomposition of the active material starts, that is, the thermal decomposition start temperature shifts to a higher temperature side. However, even if the short-circuit current does not penetrate the active material particles,
Since Joule heat is generated, the battery temperature rises, a reaction between the negative electrode and the positive electrode and the electrolytic solution occurs, further generating heat, and the positive electrode active material itself is eventually decomposed. As a result, a combustion reaction of the electrolytic solution is caused, and finally, a thermal runaway occurs. This phenomenon becomes remarkable when a battery has a high capacity, a high energy density, or a high output because a large current flows due to a short circuit.

[0005] As described above, even with the conventionally known means for improving safety, when the battery has a high capacity, a high energy density, or a high output, the safety of the battery is ensured. Therefore, non-aqueous electrolyte secondary batteries with high safety have not yet been put to practical use.

[0006]

As described above, in a non-aqueous electrolyte secondary battery using a conventional lithium nickel cobalt composite oxide as a positive electrode, when an internal short circuit occurs in a charged battery, the May rupture or ignite, and improving safety has been an issue. The present invention has been made in order to solve the above-mentioned problems of the prior art, and in a nonaqueous electrolyte secondary battery using a lithium nickel cobalt composite oxide for a positive electrode, even if an internal short circuit should occur, the battery could explode or ignite. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent safety.

[0007]

SUMMARY OF THE INVENTION The present invention provides LiNiO _2
0.8 NiC
o _0.2 O ₂ (hereinafter, referred to as Ni / Co-based positive electrode material) was used as a basic composition, and various Ni / Co-based positive electrode materials to which a different element was further added were prototyped and studied. In particular, the present invention solves the above-mentioned problems by including lithium niobate in a positive electrode active material mainly containing a lithium nickel cobalt composite oxide, thereby completing the present invention.

That is, the present invention comprises a positive electrode using a composite oxide mainly composed of lithium and nickel as a positive electrode active material, and a negative electrode using a material capable of occluding and releasing lithium ions as a negative electrode active material. In the nonaqueous electrolyte secondary battery, the positive electrode active material has a general formula: Li _{1 + Z} Ni
_{1-x-y Co x M} y O 2 ( where M may Al, M
at least one selected from n and Sn;
Are 0 <x ≦ 0.3, 0 ≦ y ≦ 0.1, 0 ≦ z ≦ 0.02
) As the first phase, and as the second phase, Li ₈ Nb ₂ O
₉ , lithium niobate represented by Li ₁₀ Nb ₂ O ₁₀
And the X-ray diffraction peak intensity of the (003) plane of the lithium-nickel-cobalt composite oxide of the positive electrode active material is I ₍₀₀₃₎ , and the X-ray diffraction peak intensity of the (104) plane is I _(104). When the maximum X-ray diffraction peak attributed to lithium _obate is _INb , these peak intensity ratios are I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧
1.6 and 0.01 ≦ _INb / I ₍₀₀₃₎ ≦ 0.
03 lithium nickel cobalt niobium composite
A non-aqueous electrolyte secondary battery using an oxide .

[0009]

Further, in the present invention, the general formula: Li _{1 + z} Ni which is a main component of the positive electrode active material is used.
In _1-x-y Co x lithium-nickel-cobalt composite oxide represented by M y _{O 2,} the value of the y, 0.03
It is preferable that ≦ y ≦ 0.08.

That is, the non-aqueous electrolyte secondary battery of the present invention
Corrects composite oxides containing lithium and nickel as main components.
Positive electrode as the active material and occludes and releases lithium ions
Anode with active material capable of non-aqueous electrolyte
In the secondary battery, the positive electrode active material has a general formula: Li
_{1 + z}Ni_1-xyCo_xM_yO₂(However, M is
At least one selected from the group consisting of Al, Mn, and Sn;
x, y, z are 0 <x ≦ 0.3, 0 ≦ y ≦ 0.1, 0 ≦ z
≦ 0.02) lithium-nickel-cobalt composite acid
And a general formula: Li_aNb_bO_c
(Where a, b, and c are positive integers, and 2.5 ≦ a
/B≦5.5, c = a / 2 + b × 5/2)
(003)
X-ray diffraction peak intensity of the surface₍₀₀₃₎, (104) plane
X-ray diffraction peak intensity of₍₁₀₄₎, Li₈Nb₂O
₉Or Li₁₀Nb₂O₁₀X-ray diffraction attributed to
Peak I _NbAnd the peak intensity ratio: I
₍₀₀₃₎/ I₍₁₀₄₎Satisfies ≧ 1.6, and
0.01 ≦ I_Nb/ I₍₀₀₃₎≤0.03
Having such a composition.
Lithium-nickel-cobalt-niobium composite oxide
Was obtained from differential scanning calorimetry (DSC) measurements
Heat generation during thermal decomposition is as small as 30 J / g or less, and thermal stability
In particular, nickel is partially replaced with Al, Mn, and S.
n-substituted lithium-nickel-cobalt composite oxide
The component containing lithium niobate as described above is
High thermal decomposition onset temperature and low calorific value of 30 J / g
And has particularly excellent thermal stability. Accordingly
Therefore, in the nonaqueous electrolyte secondary battery having such a configuration,
External pressure is applied when one battery is charged
Even if an internal short circuit occurs due to dropping, etc., the battery runs out of heat
A non-aqueous electrolyte secondary battery with excellent safety
It can be formed.

In the present invention, lithium niobate is
And represented by Li ₈ Nb ₂ O ₉ and Li ₁₀ Nb ₂ O ₁₀
The reason why lithium niobate is particularly selected is that such lithium niobate has a particularly large effect of suppressing heat generation during thermal decomposition.
This is because iNbO ₃ has a small effect of suppressing heat generation and no effect of improving battery safety was observed. Although the details of this reason are unknown, it is considered that lithium niobate such as Li ₈ Nb ₂ O ₉ or Li ₁₀ Nb ₂ O ₁₀ has a particularly large effect of stabilizing the crystal structure.

Further, a peak intensity ratio: I _Nb / I
₍₀₀₃₎ is 0.01 ≦ _INb / I _{(003 )} ≦ 0.0
The reason for specifying 3 is based on the following reasons. That is, the peak intensity ratio: I _Nb / I ₍₀₀₃₎ is 0.0
If it is larger than 3, it is not preferable because the discharge capacity is reduced, and if it is less than 0.01, the effect of improving safety according to the present invention is not exhibited. Peak intensity ratio:
A preferable range of I _Nb / I ₍₀₀₃₎ is 0.015 or more and less than 0.025.

Further, a peak intensity ratio: I₍₀₀₃₎/ I
₍₁₀₄₎Is defined as 1.6 or higher, as follows.
Based on reasons. Generally, the peak intensity ratio: I
₍₀₀₃₎/ I ₍₁₀₄₎Is the degree of layered structure development
Is used as an index indicating As the layered structure develops,
It has a large discharge capacity and is an excellent active material. This value is I
_{(003 )}/ I₍₁₀₄₎Larger if greater than ≦ 2
Very good. If this value is small, the layered structure will not develop.
Sufficient, Ni for lithium layer²⁺So-called rock mixed with
The discharge capacity becomes
Will drop. Therefore, in the present invention, in particular, I
₍₀₀₃₎/ I₍₁₀₄₎Lithium represented by ≧ 1.6
This is a nickel-cobalt composite oxide. What
Incidentally, the present invention relates to I_{(003 )}/ I₍₁₀₄₎≧ 1.6
And 0.01 ≦ I_Nb/ I₍₀₀₃₎≤0.03 simultaneously
And if either is outside this range,
No.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to embodiments. The present inventors attempted to improve the safety of a lithium nickel-based nonaqueous electrolyte secondary battery by using LiN
LiNi in which part of the Ni site of iO ₂ is replaced with Co
_0.8 Co _{0 . 2} O ₂ (hereinafter referred to as Ni / Co-based positive electrode material) was used as a basic composition, and various kinds of Ni / Co-based positive electrode materials to which different elements were further added were prototyped. The thermal stability of the prototype material was measured by differential scanning calorimetry (DSC) after charging to 4.4 V at Li potential. Also,
3. Various kinds of batteries are manufactured using the prototyped material for the positive electrode.
After charging to 4V, a nail penetration test simulating an internal short circuit in the battery was performed. The results were compared with the results of the differential scanning calorimetry to study the improvement of the battery safety. As a result, the following findings were obtained.

First, Ni.Co before adding a different element is used.
The starting temperature of thermal decomposition by DSC is 189 ° C.
(Exothermic peak temperature: 220 ° C.). As a result of a nail penetration test on a standard specification battery (18650 size) having a designed rated capacity of 1850 mAh, the battery burst or fired. next,
Part of the Ni site of the Ni / Co-based positive electrode material is further changed to Al.
_0.72 Co _0.2 Al _0.08 O substituted with
Sample No. ₂ has a thermal decomposition onset temperature of 228 ° C. (exothermic peak temperature: 250 ° C.) by DSC, and Ni before replacement with Al.
-The pyrolysis onset temperature shifted to a higher temperature side as compared with the Co-based positive electrode material. As a result of the nail penetration test of the prototype battery, the percentage of the battery that had burst or ignited was 50%. Then, a high-power specification battery (18650 size) having a designed rated capacity of 1700 mAh was manufactured using this material. When a nail penetration test was performed on this battery, the firing rate was 100%. Furthermore, a design rated capacity of 15 Ah (φ35 mm × 19
0 mm), similar results were obtained in a nail penetration test. From this, it was clarified that when a battery has a high capacity or a high output, a large current flows due to a short circuit, so that it is not possible to secure safety only by improving the thermal decomposition temperature of the material. .

The inventors of the present invention have focused on the calorific value at the time of thermal decomposition obtained from the DSC measurement, and have found the following. That is, the aforementioned LiNi
The thermal decomposition onset temperature of _0.72 Co _0.2 Al _0.08 O ₂ was 228 ° C., and the calorific value was about 60 J / g.
Those with a heating value larger than a predetermined value resulted in a burst or ignition in a nail penetration test when the battery was increased in capacity. On the other hand, even if the material does not necessarily have a high pyrolysis initiation temperature, a material that generates less heat during pyrolysis than a predetermined value may cause a burst or ignition in a nail penetration test when the battery capacity is increased. The percentage of batteries that had dropped was reduced. Furthermore, it was found that a material having a high thermal decomposition initiation temperature and a calorific value at the time of heat component smaller than a predetermined value significantly reduced the percentage of batteries that had burst or fired in a nail penetration test, The present invention has been completed.

With respect to the present invention completed based on the above findings, an embodiment of the nonaqueous electrolyte secondary battery of the present invention will be described in detail below with reference to FIGS.

(Method of Evaluating Thermal Stability of Material) The thermal stability of the material was evaluated using a differential scanning calorimeter (DSC) using the thermal decomposition onset temperature and the calorific value as indices. The evaluation method will be described below. 100 parts by weight of the positive electrode active material, 6 parts by weight of a conductive agent (acetylene black) and a binder (PTFE)
An electrode is prepared by mixing 3 parts by weight. Next, a three-electrode cell in which the reference electrode and the counter electrode are made of Li foil is assembled in an Ar atmosphere, and charged to 4.4 V at a constant current of 1 mA / cm ² . In the electrolyte, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 1: 1) was used.
The solution obtained by dissolving 1 mol / L of LiPF ₆ in 2) is used. The charged positive electrode is taken out in an Ar atmosphere, washed with EMC, vacuum-dried for 1 hour to remove the electrolytic solution, and sealed in a sealed aluminum pan to prepare a DSC measurement sample. In the DSC measurement, while flowing Ar at a flow rate of 50 ml / min, 2
The measurement is performed at a heating rate of 5 ° C./min from 0 ° C. to 450 ° C. One example of the DSC curve thus obtained is shown in FIG.
And FIG. As shown in FIG. 1, the thermal decomposition start temperature is determined by a tangential method from the first peak accompanying thermal decomposition of the positive electrode. Further, the calorific value is the integrated value of the peak (the area of the shaded area) as shown in FIG.

(Battery safety evaluation method-nail penetration test-)
A nail penetration test was performed as a test simulating an internal short circuit, and battery safety was evaluated. The method of the nail penetration test will be described below. First, the initially charged and sealed battery is charged within 24 hours. For the first charge, the current value for discharging the design rated capacity in one hour is 1C, and the current value of 0.3C is 4.2V.
After charging until it reaches, it is held at a constant voltage of 4.2V,
The total charging time is 8 hours. After the end of charging,
After a 0 minute pause, the battery voltage was 2.7 at a constant current of 0.2C.
Repeat until V is reached. Next, at a current value of 0.5 C, 4.2 V
A constant current-constant voltage charge (total charge time of 5 hours) is performed until the battery voltage reaches 2.7 V at a constant current of 0.5 C. Five charge / discharge cycles are performed. The battery after the completion of the charge / discharge cycle is subjected to constant current-constant voltage charging in which the battery is charged to 4.4 V at a current value of 0.5 C. The charging time is 5 hours. Take care that the test does not elapse for a long time from the end of charging to the test, and conduct the test within approximately one hour. The nail is made of stainless steel with a diameter of 2.5 mm, and the nail descent speed is 110 mm / sec. Monitor the terminal voltage and surface temperature when nailing.

(Form of Nonaqueous Electrolyte Secondary Battery According to the Present Invention) Next, a nonaqueous electrolyte secondary battery (for example, a cylindrical lithium ion secondary battery) according to the present invention will be described with reference to FIG. For example, a bottomed cylindrical container 1 made of nickel-plated iron has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1. The electrode group 3
Has a structure in which a belt-like material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound so that the negative electrode 6 is located outside. The separator 5
Is formed from, for example, a nonwoven fabric, a microporous polypropylene film, a microporous polyethylene film, or a microporous polyethylene-polypropylene laminated film. The container 1 contains an electrolytic solution. A safety valve 8 having a valve membrane 7 at the center and a hat-shaped positive terminal 9 disposed on the safety valve 8 are caulked and fixed to an upper opening of the container 1 via an insulating gasket 10. The positive electrode terminal 9 has a gas vent hole (not shown). One end of the positive electrode lead 11 is connected to the positive electrode 4, and the other end is connected to the safety valve 8. When the internal pressure of the battery increases, the valve membrane 7 swells and deforms, so that the welded portion is separated. The current is interrupted. The negative electrode 6 is connected to the container 1 serving as a negative electrode terminal via a negative electrode lead 12.

Next, the positive electrode 4, the negative electrode 6, and the electrolyte will be specifically described.

A) Positive electrode 4 The positive electrode 4 includes, for example, a positive electrode active material, a conductive agent, and a binder.
Of the positive electrode material paste obtained by dispersing
It is manufactured by applying it to one side or both sides of the conductor.
You. The positive electrode active material has a general formula: Li_{1 + z}Ni
_1-xyCo _xM_yO₂(However, M is Al, M
at least one selected from the group consisting of n and Sn;
Are 0 <x ≦ 0.3, 0 ≦ y ≦ 0.1, 0 ≦ z ≦ 0.0
2) Mainly lithium nickel cobalt composite oxide
Component, and further represented by the general formula: Li_aNb_bO_c(However,
A, b, and c are positive integers, and 2.5 ≦ a / b ≦
5.5, c = a / 2 + b × 5/2)
Containing (3) lithium X-ray
X-ray diffraction peak intensity₍₀₀₃₎X-ray on the (104) plane
Diffraction peak intensity I₍₁₀₄₎, The lithium niobate
The maximum X-ray diffraction peak attributed to_NbAnd when
Work strength ratio: I₍₀₀₃₎/ I₍₁₀₄₎Satisfies ≧ 1.6
And 0.01 ≦ I_Nb/ I₍₀₀₃₎≦ 0.0
Lithium-nickel-cobalt-niobium complex represented by 3
A composite oxide can be used. Specifically, (LiNi
_0.76Co_0.16Al_0.08O₂) + (Li₈N
b₂O₉), (LiNi_0.7Co_0.24Al
_0.06O₂) + (Li₁₀Nb₂O₁₀), (LiN
i_0.7Co_0.2Mn_0.1O₂) + (Li₈Nb₂
O₉), (LiNi_0.67Co_0.2Mn_0.1Al
_0.03O₂) + (Li ₈Nb₂O₉), (LiNi
_0.8Co_0.2O₂) + (Li₁₀Nb₂O₁₀),
(LiNi_0.75Co_0.25O₂) + (Li₁₀N
b₂O₁₀), (LiNi_0.7Co_0.3O₂) +
(Li₁₀Nb₂O₁₀) And the like.

Further, the positive electrode active material includes the lithium-nickel-cobalt-niobium composite oxide and LiC
Mixtures with oO ₂ can be used. As the conductive agent, for example, acetylene black, carbon black, artificial graphite, natural graphite and the like can be used. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), P
Modified PVdF in which at least one of hydrogen or fluorine of VdF is substituted with another substituent, a copolymer of vinylidene fluoride-6-propylene fluoride, polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride
An original copolymer or the like can be used. As the organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and the like are used. As the current collector, for example, a thickness of 10
Examples include aluminum foil, stainless steel foil, and titanium foil of 25 μm. The thickness of one side of the positive electrode active material layer is preferably 30 to 100 μm. When the thickness is in this range, large current discharge characteristics are improved. The preferred range of the thickness is 50 μm to 65 μm. In the positive electrode 4, the packing density of the active material layer after rolling is 2.
7 g / cm ³ or more is preferable. More preferably 3.0 g
/ Cm ³ or more. When the packing density is 3.0 g / cm ³ or more, the capacity of the battery can be increased. However, if the packing density is too high, the high-current discharge characteristics may be reduced. Therefore, the upper limit of the packing density is preferably 3.5 g / cm ³ or less.

B) Negative Electrode 6 The negative electrode 6 is made of, for example, a substance containing a carbonaceous substance or a chalcogen compound that absorbs and releases lithium ions, a light metal or the like. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved. Examples of the carbonaceous material that occludes and releases lithium ions include, for example, coke, carbon fiber, pyrolytic gas-phase carbonaceous material, graphite, fired resin, fired mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. . Among them, it is preferable to use mesophase pitch-based carbon fiber or mesophase spherical carbon which has been graphitized at 2500 ° C. or higher because the electrode capacity is increased. Examples of the chalcogen compound that stores and releases lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe ₂ ). When such a chalcogen compound is used for the negative electrode, the capacity of the secondary battery is improved because the capacity of the negative electrode is increased although the voltage of the secondary battery is reduced. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved. Examples of the light metal include aluminum, an aluminum alloy, a magnesium alloy, a lithium metal, and a lithium alloy.

The negative electrode (for example, a negative electrode made of carbon material)
Specifically, a negative electrode material paste obtained by dispersing the carbon material, the conductive agent and the binder in an appropriate solvent is applied to a current collector on one side or both sides. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) and the like can be used. As the current collector, for example, a copper foil, a nickel foil, or the like can be used, but a copper foil is most preferable in consideration of electrochemical stability, flexibility at the time of winding, and the like. At this time, the thickness of the foil is not less than 8 μm and not more than 15 μm.
The following is preferred. The thickness of one surface of the negative electrode active material layer is preferably 30 to 100 μm. When the thickness is in this range, large current discharge characteristics are improved.
The preferred range of the thickness is 50 μm to 65 μm.

In the negative electrode 6, the packing density of the active material layer after rolling is preferably 1.35 g / cm ³ or more. More preferably, it is 1.4 g / cm ³ or more. The packing density is 1.
When the amount is 4 g / cm ³ or more, the capacity of the battery can be increased. However, if the packing density is too high, the high-current discharge characteristics may be reduced. Therefore, the upper limit of the packing density is 1.5 g.
/ Cm ³ or less.

C) Electrolyte The electrolyte has a composition in which an electrolyte is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), such as dimethyl carbonate (DM).
C), linear carbonates such as methyl ethyl carbonate (MEC) and diethyl carbonate (DEC);
Chain ethers such as 2-dimethoxyethane (DME) and diethoxyethane (DEE), tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-Me
Cyclic ethers such as THF) and crown ethers;
At least one selected from fatty acid esters such as butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethylsulfoxide (DMSO) can be used.

Among them, those comprising at least one selected from EC, PC and γ-BL, EC, PC and γ-B
L, DMC, MEC, DE
It is desirable to use a mixed solvent comprising at least one selected from C, DME, DEE, THF, 2-MeTHF, and AN. Further, when a negative electrode containing a carbonaceous material that occludes and releases lithium ions is used, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC and γ-BL, and EC and PC And MEC, E
C and PC and DEC, EC and PC and DEE, EC and AN,
EC and MEC, PC and DMC, PC and DEC, or E
It is desirable to use a mixed solvent composed of C and DEC.

Examples of the electrolyte include lithium perchlorate.
(LiClO₄), Lithium hexafluorophosphate (Li
PF₆), Lithium borofluoride (LiBF₄), Six foot
Lithium arsenide (LiAsF)₆), Trifluorometas
Lithium sulfonate (LiCF ₃SO₃), Aluminum tetrachloride
Lithium (LiAlCl₄), Bistrifluoro
Lithium methylsulfonylimide [LiN (CF₃SO
₂)₂] And the like. Inside
Also LiPF₆, LiBF₄, LiN (CF₃SO₂)₂
Is preferred because conductivity and safety are improved.
No. The amount of the electrolyte dissolved in the non-aqueous solvent is 0.1.
It is preferred to be in the range of 5 mol / L to 2.0 mol / L.
No.

As described above in detail, in the nonaqueous electrolyte secondary battery according to the present invention, even if an internal short circuit occurs due to an external pressure or a fall when the battery is in a charged state, the positive electrode active material can be reduced. Since the calorific value during the thermal decomposition is small and the thermal stability is excellent, the battery does not run out of heat. Therefore, a non-aqueous electrolyte secondary battery having excellent safety can be formed.

[0032]

EXAMPLES Hereinafter, test examples and examples of the present invention will be described more specifically.

(Example 1) <Synthesis of lithium-nickel-cobalt-niobium composite oxide> Lithium nitrate (LiNO ₃ ), nickel nitrate [N
i (NO ₃ ) ₂ .6H ₂ O], cobalt nitrate [Co (N
_{O 3) 2 · 6H 2 O} ], aluminum nitrate [Al (NO
_{3) 2} · _{9H 2} O] were weighed in a predetermined amount to produce a concentration of 2 mol / L solution dissolved in water. Subsequently, niobium pentoxide (Nb ₂ O ₅ ) was added to the solution so as to have a desired composition to prepare a dispersion solution, and the dispersion solution was spray-dried to obtain a precursor. Next, this precursor was heated at 460 ° C. for 1 hour in an oxygen atmosphere.
It was kept for 0 hours, and then calcined at a temperature of 850 ° C. for 5 hours. Next, 0.1 mol of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to 1 mol of the calcined product, mixed well, and kept at 460 ° C. for 10 hours in an oxygen atmosphere. Heat treatment was performed at a temperature of 5 ° C. for 5 hours.

<Evaluation of Material Characteristics> With respect to the synthesized lithium nickel cobalt niobium composite oxide, powder X
A line diffraction measurement was performed. The X-ray source is CuKα and the output is 50
KV was performed at 300 mA. As a result, this fired product is L
It was found to be a layered compound containing i ₈ Nb ₂ O ₉ . As a result of composition analysis by ICP emission spectroscopy and atomic absorption spectroscopy, the main component was LiNi _0.76 Co
It was found to be _0.16 Al _0.08 O ₂ . Further, when the Nb distribution was examined by EPMA analysis,
It was found that b mainly exists at the primary particles and at the grain boundaries of the primary particles. The average particle size was 10 μm. From the results of the X-ray diffraction measurement, the diffraction peak intensity of the (003) plane and (10)
4) Ratio of peak intensity to diffraction peak intensity of plane: I
₍₀₀₃₎ / I ₍₁₀₄₎ was 1.65. Also,
(003) peak intensity ratio of the intensity of the diffraction peak intensity and the maximum X-ray diffraction peak attributed to _{Li 8 Nb 2 O 9 (2θ} = 23.8 °) _{of: I Nb / I (00 3} ) is 0 .03
Met.

Subsequently, the thermal stability of this material was evaluated by performing differential scanning calorimetry (DSC) based on the above method. As a result, the thermal decomposition onset temperature was 202 ° C., and the calorific value was 19 J / g. The exothermic peak temperature is 24
3 ° C. Next, the capacity per 1 g of this material was measured. The same sample electrode as that used in the DSC measurement was used. This was cut into a size of 1 cm × 1 cm, and a three-electrode cell having a reference electrode and a counter electrode made of Li foil was assembled in an Ar atmosphere, and 1 mA / cm ² (corresponding to 0.1 C).
After charging until reaching 4.2V at a constant current of 4.2V
, And the total charging time was 20 hours. As the electrolytic solution, a solution obtained by dissolving 1 mol / L of LiPF ₆ in a mixed solvent (volume ratio 1: 2) of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was used. Discharging is performed at 1 mA / cm ² after stopping for 30 minutes after charging is completed.
And the discharge termination voltage was 3 V. As a result, the discharge capacity was 175 mAh / g.

<Preparation of Positive Electrode> Polyvinylidene fluoride was converted to N
To a solution dissolved in -methyl-2-pyrrolidone, the above-mentioned lithium-nickel-cobalt-niobium composite oxide powder, acetylene black and graphite as a conductive agent were added, and mixed by stirring. A positive electrode mixture comprising 90% by weight of a composite oxide, 3% by weight of acetylene black, 3% by weight of graphite, and 4% by weight of polyvinylidene fluoride was prepared. This positive electrode mixture was applied to both surfaces of an aluminum foil (thickness: 20 μm), dried, and then pressed using a roller press to produce a 140 μm thick positive electrode.

<Preparation of Negative Electrode> Mesophase pitch carbon fibers made from mesophase pitch were carbonized at 1000 ° C. in an argon atmosphere, and the average fiber length was 30 μm.
After appropriately pulverizing so that 90% by volume exists with an average fiber diameter of 11 μm and a particle size of 1 to 80 μm, and particles having a particle size of 0.5 μm or less are reduced (5% or less), and then 3000 ° C. in an argon atmosphere. To produce a carbonaceous material. Polyvinylidene fluoride is converted to N-methyl-2
-The carbonaceous material and artificial graphite are added to a solution dissolved in pyrrolidone, and the mixture is stirred and mixed to prepare a negative electrode mixture having a composition of 86% by weight of carbonaceous material, 10% by weight of artificial graphite, and 4% by weight of polyvinylidene fluoride. did. This is a copper foil (thickness 12
μm), dried and then pressure-formed with a roller press to produce a negative electrode. At this time, the packing density and the electrode length were adjusted so that the ratio (capacity balance) of the designed capacity of the negative electrode to the designed capacity of the positive electrode after molding was 1.05 or more and 1.1 or less.

<Assembly of Battery> An aluminum positive electrode lead and a nickel negative electrode lead were welded to the positive electrode and the negative electrode, respectively, and then the positive electrode, a separator made of a microporous polyethylene film having a thickness of 25 μm, and the negative electrode were formed. Were laminated in this order, and spirally wound so that the negative electrode was located outside, to produce an electrode group. This electrode group is housed in a nickel-plated iron bottomed cylindrical container, and the negative electrode lead is placed at the bottom of the bottomed cylindrical container, and the positive electrode lead is placed at the opening of the bottomed cylindrical container. Each was welded to a safety valve having a current interruption function. Subsequently, 1 M of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio of 1: 2) in the bottomed cylindrical container. A non-aqueous electrolyte was injected, and the electrode group was sufficiently impregnated with the non-aqueous electrolyte. And after arranging the positive electrode terminal on the safety valve,
It was fixed by swaging. As described above, the design rated capacity 17
00 mAh cylindrical lithium ion secondary battery (1865)
0 size).

Example 2 In the same manner as in Example 1, lithium nitrate (LiNO ₃ ) and nickel nitrate [Ni (NO ₃ )
₂ · _{6H 2} O], cobalt nitrate _{[Co (NO 3) 2 ·} 6
H ₂ O], aluminum nitrate _{[Al (NO 3) 2 ·} 9H
₂ O] and niobium pentoxide (Nb ₂ O ₅ ) to prepare a dispersion solution, and this dispersion solution was spray-dried to obtain a precursor. Next, this precursor was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and subsequently calcined at a temperature of 850 ° C. for 5 hours. Subsequently, 0.05 mol of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to 1 mol of the calcined product, mixed well, and kept at 460 ° C. for 10 hours under an oxygen atmosphere.
Subsequently, heat treatment was performed at a temperature of 700 ° C. for 5 hours to obtain a lithium-nickel-cobalt-niobium composite oxide having an average particle size of 10 μm.

As a result of X-ray diffraction measurement, this lithium-nickel-cobalt-niobium composite oxide was found to be Li ₈ Nb ₂ O
₉ was found to be a layered compound. As a result of performing composition analysis by ICP emission spectroscopy and atomic absorption spectroscopy, the main component was LiNi _0.76 Co _0.16 Al
_0.08 O ₂ was found. (003) plane X
Intensity ratio of the X-ray diffraction peak intensity of the (104) plane to the X-ray diffraction peak intensity: I _{(003 )} / I ₍₁₀₄₎ is 1.
63. Further, the peak intensity ratio of the X-ray diffraction peak intensity of the (003) plane to the maximum X-ray diffraction peak (2θ = 23.8 °) attributed to Li ₈ Nb ₂ O ₉ : I _Nb /
I ₍₀₀₃₎ was 0.025. The thermal decomposition onset temperature was 204 ° C., and the calorific value was 26 J / g.
The discharge capacity was 173 mAh / g. Thereafter, in the same manner as in Example 1, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1700 mAh was assembled.

Example 3 In the same manner as in Example 1, lithium nitrate (LiNO ₃ ) and nickel nitrate [Ni (NO ₃ )
₂ · _{6H 2} O], cobalt nitrate _{[Co (NO 3) 2 ·} 6
H ₂ O], aluminum nitrate _{[Al (NO 3) 2 ·} 9H
₂ O] and niobium pentoxide (Nb ₂ O ₅ ) to prepare a dispersion solution, and this dispersion solution was spray-dried to obtain a precursor. Next, this precursor was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and subsequently calcined at a temperature of 850 ° C. for 5 hours. Subsequently, 0.03 mol of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to 1 mol of the calcined product, mixed well, and kept at 460 ° C. for 10 hours under an oxygen atmosphere.
Subsequently, a heat treatment is performed at a temperature of 700 ° C. for 5 hours, whereby lithium nickel cobalt having an average particle size of 10 μm is formed.
A niobium composite oxide was obtained.

As a result of the X-ray diffraction measurement,
Kel cobalt niobium composite oxide is Li₈Nb₂O
₉It turned out that it is a layered compound containing. ICP emission
Results of composition analysis by spectroscopy and atomic absorption
As a result, the main component is LiNi_0.76Co_0.16Al
_0.08O₂It turned out to be. (003) plane X
-Ray diffraction peak intensity and (104) plane X-ray diffraction peak intensity
And peak intensity ratio: I_{(003 )}/ I₍₁₀₄₎Is 1.
6, the (003) plane X-ray diffraction peak intensity and Li₈Nb
₂O₉X-ray diffraction peak (2θ = 23.8)
°) Peak intensity ratio with intensity: I_Nb/ I₍₀₀₃₎Is
0.024. The thermal decomposition start temperature is 203
° C, calorific value is 30 J / g, discharge capacity is 170 mA
h / g. Hereinafter, in the same manner as in the first embodiment,
Cylindrical lithium-ion secondary with a total rated capacity of 1700 mAh
A battery (18650 size) was assembled.

(Example 4) In the same manner as in Example 1, lithium-nickel-cobalt-metal having an average particle size of 10 µm was used.
A niobium composite oxide was obtained. As a result of X-ray diffraction measurement, this lithium-nickel-cobalt-niobium composite oxide
It was found to be a layered compound containing i ₁₀ Nb ₂ O ₁₀ . As a result of composition analysis by ICP emission spectroscopy and atomic absorption spectroscopy, the main component was LiNi _0.7 Co
It was found to be _0.24 Al _0.06 O ₂ . (0
Peak intensity ratio between the X-ray diffraction peak intensity of the 03) plane and the X-ray diffraction peak intensity of the (104) plane: I ₍₀₀₃₎ / I
₍₁₀₄₎ is 1.68, and the peak intensity ratio between the X-ray diffraction peak intensity of the (003) plane and the maximum X-ray diffraction peak (2θ = 22.2 °) attributed to Li ₁₀ Nb ₂ O ₁₀ is I:
_Nb / I ₍₀₀₃₎ was 0.023.

The thermal decomposition onset temperature was 215 ° C., and the calorific value was 22 J / g. The exothermic peak temperature is 227.
At ° C, the discharge capacity was 178 mAh / g. Hereinafter, in the same manner as in the first embodiment, the design rated capacity is 1700 mAh.
Cylindrical lithium ion secondary battery (18650 size)
Was assembled.

(Example 5) Nickel hydroxide powder [Ni _0.7 Co _{0.2. 2} Mn
_0.1 (OH) ₂ ] and lithium hydroxide monohydrate (LiO
H.H ₂ O) were blended so that the atomic ratio of Li to Ni (Li / Ni) was 1.05. After adding niobium pentoxide powder (Nb ₂ O ₅ ) to the mixture and pulverizing and mixing the mixture, the mixture was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and then maintained at 850 ° C.
For 5 hours. Next, 0.1 mol of lithium hydroxide monohydrate (LiO
_H · H 2 O) were mixed thoroughly by adding, under oxygen atmosphere 46
The lithium-nickel-cobalt-niobium composite oxide having an average particle size of 7 μm was obtained by maintaining the temperature at 0 ° C. for 10 hours and then performing a heat treatment at a temperature of 700 ° C. for 5 hours. This lithium-nickel-cobalt-niobium composite oxide
It turned out to be a layered compound containing Li ₈ Nb ₂ O ₉ . As a result of composition analysis by ICP emission spectroscopy and atomic absorption spectroscopy, the main component was LiNi _0.7 Co _0.2 M
n _0.1 O ₂ was found. (003) plane X
Intensity ratio of the X-ray diffraction peak intensity of the (104) plane to the X-ray diffraction peak intensity: I ₍₀₀₃₎ / I ₍₁₀₄₎ is 1.
63. Further, the peak intensity ratio of the X-ray diffraction peak intensity of the (003) plane to the maximum X-ray diffraction peak (2θ = 23.8 °) attributed to Li ₈ Nb ₂ O ₉ : I _Nb /
I ₍₀₀₃₎ was 0.025. The thermal decomposition onset temperature was 213 ° C., and the calorific value was 16 J / g.
The exothermic peak temperature was 232 ° C., and the discharge capacity was 171 ° C.
mAh / g. Thereafter, in the same manner as in Example 1, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1700 mAh was assembled.

(Example 6) Ni was partially replaced with Co.
Nickel hydroxide powder [Ni_0.8Co_0.2(O
H)₂] And lithium hydroxide monohydrate (LiOH.H
₂O) and tin oxide (SnO)₂) With the atomic ratio of Li to Ni (L
(i / Ni) was adjusted to 1.05. This mixture
Niobium pentoxide powder (Nb₂O₅) And crush and mix
After being combined, it is kept at 460 ° C. for 10 hours in an oxygen atmosphere,
And calcined at a temperature of 850 ° C. for 5 hours. Next, this firing
0.1 mol of lithium hydroxide 1 water per 1 mol of product
Japanese (LiOH ・ H₂O), mix well and add oxygen
Hold at 460 ° C. for 10 hours in the atmosphere, then at 700 ° C.
By performing the heat treatment at a temperature for 5 hours, the average particle size becomes 7 μm.
m lithium-nickel-cobalt-niobium composite oxide
Got. As a result of X-ray diffraction measurement, this lithium nickel
・ Cobalt-niobium composite oxide is Li₁₀Nb₂O
₁₀It turned out that it is a layered compound containing. ICP departure
Composition analysis by optical spectroscopy and atomic absorption
As a result, the main component is LiNi_0.776Co_0.194Sn
_0.03O₂It turned out to be. (003) plane X
-Ray diffraction peak intensity and (104) plane X-ray diffraction peak intensity
And peak intensity ratio: I₍₀₀₃₎/ I₍₁₀₄₎Is 1.
At 77, the X-ray diffraction peak intensity of the (003) plane and Li₁₀
Nb₂O₁₀X-ray diffraction peak (2θ = 2
2.2 °) Ratio of peak intensity to intensity: I_Nb/ I
₍₀₀₃₎Was 0.023.

The thermal decomposition onset temperature is 207 ° C.
The calorific value was 14 J / g. Exothermic peak temperature is 229
At C, the discharge capacity was 174 mAh / g. Hereinafter, in the same manner as in the first embodiment, the design rated capacity is 1700 mAh.
Cylindrical lithium ion secondary battery (18650 size)
Was assembled.

(Example 7) Nickel hydroxide powder [Ni _0.8 Co _0.2 (O
H) ₂ ] and lithium hydroxide monohydrate (LiOH · H
₂ O) with an atomic ratio of Li to Ni (Li / Ni) of 1.0
5 was added. After niobium pentoxide powder (Nb ₂ O ₅ ) was added to this mixture and ground and mixed, the mixture was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and then calcined at 850 ° C. for 5 hours. Next, 0.1 mol of lithium hydroxide monohydrate (LiOH.H
₂ O), mixed well, kept at 460 ° C. for 10 hours in an oxygen atmosphere, and then heat-treated at 700 ° C. for 5 hours to obtain lithium nickel cobalt niobium having an average particle size of 7 μm. A composite oxide was obtained.

As a result of the X-ray diffraction measurement,
Kel cobalt niobium composite oxide is Li₁₀Nb₂
O₁₀It turned out that it is a layered compound containing. ICP
Composition analysis was performed by emission spectroscopy and atomic absorption spectrometry.
As a result, the main component is LiNi_{0. 8}Co_0.2O₂Is
I understood. (003) plane X-ray diffraction peak intensity
Peak intensity ratio to the X-ray diffraction peak intensity of the (104) plane:
I₍₀₀₃₎/ I_{(10 4)}Is 1.82, and (003)
X-ray diffraction peak intensity and Li₁₀Nb₂O₁₀Belong to
X-ray diffraction peak (2θ = 22.2 °) intensity
Peak intensity ratio: I _Nb/ I₍₀₀₃₎Is 0.018
Was. The thermal decomposition onset temperature is 185 ° C,
Was 14 J / g. The exothermic peak temperature is 213.
At ° C, the discharge capacity was 172 mAh / g. Following
Cylindrical with a rated capacity of 1700 mAh in the same manner as in Example 1.
Assembled lithium-ion secondary battery (18650 size)
I was

(Example 8) Ni was partially replaced with Co.
Nickel hydroxide powder [Ni_0.75Co_0.25(O
H)₂] And the average particle size in the same manner as in Example 6.
Is 7μm lithium-nickel-cobalt-niobium composite
An oxide was obtained. As a result of X-ray diffraction measurement, this lithium ni
The nickel-cobalt-niobium composite oxide is Li₁₀Nb
₂O₁₀It was found to be a layered compound containing IC
Perform composition analysis by P emission spectroscopy and atomic absorption spectrometry
As a result, the main component was LiNi_{0. 75}Co_0.25O₂so
I found it. X-ray diffraction peak intensity of (003) plane
Intensity of the X-ray diffraction peak intensity of (104) plane
Ratio: I₍₀₀₃₎/ I_{( 104)}Is 1.88 and (00
3) X-ray diffraction peak intensity of surface and Li₁₀Nb₂O ₁₀To
Assigned maximum X-ray diffraction peak (2θ = 22.2 °) intensity
And peak intensity ratio: I_Nb/ I₍₀₀₃₎Is 0.01
there were. The thermal decomposition onset temperature was 199 ° C,
The amount was 15 J / g. The exothermic peak temperature is 22
At 1 ° C., the discharge capacity was 165 mAh / g. Less than,
In the same manner as in the first embodiment, the design rated capacity is 1700 mA.
h cylindrical lithium ion secondary battery (18650 size)
) Was assembled.

(Example 9) Ni was partially replaced with Co.
Nickel hydroxide powder [Ni_0.8Co_0.2(O
H)₂] And lithium hydroxide monohydrate (LiOH.H
₂O) and the atomic ratio of Li to Ni (Li / Ni) is 1.1.
It was blended so that Add niobium pentoxide powder to this mixture
(Nb₂O₅), Pulverize and mix, then add oxygen atmosphere
Hold at 460 ° C. for 10 hours, then at 850 ° C.
It was baked for 5 hours. Next, for 1 mol of this fired product
0.1 mol of lithium hydroxide monohydrate (LiOH.H
₂O) and mix well, at 460 ° C under oxygen atmosphere
Hold for 10 hours, then heat treat at 700 ° C. for 10 hours
By the treatment, the lithium particle having an average particle diameter of 7 μm
A nickel-cobalt-niobium composite oxide was obtained. X-ray diffraction
As a result of the measurement, this lithium nickel cobalt
Composite oxide is Li₁₀Nb₂O₁₀Layered compound containing
Turned out to be a thing. ICP Emission Spectroscopy and Hara
As a result of a composition analysis by a proton absorption method, the main component was Li
_1.02Ni_0.8Co_0.2O₂It turns out that
Was. X-ray diffraction peak intensity of (003) plane and (104) plane
Ratio of X-ray diffraction peak intensity to X-ray diffraction peak intensity: I₍₀₀₃₎
/ I₍₁₀₄₎Is 1.85, X-ray diffraction of (003) plane
Peak intensity and Li₁₀Nb ₂O₁₀X-rays belonging to
Peak intensity with diffraction peak (2θ = 22.2 °) intensity
Ratio: I_Nb/ I₍₀₀₃₎Was 0.015. Ma
The thermal decomposition onset temperature was 188 ° C, and the calorific value was 17J.
/ G. The exothermic peak temperature was 212 ° C,
The electric capacity was 180 mAh / g. The same as in Example 1 below
And cylindrical lithium with a rated capacity of 1700 mAh
An ion secondary battery (18650 size) was assembled.

(Example 10) Nickel hydroxide powder [Ni _0.77 Co _{0 . 2}
Al _0.03 (OH) ₂ ] and lithium hydroxide monohydrate (LiOH · H ₂ O) are converted to Li / (Ni + Co + Al).
Was 1.1. After adding niobium pentoxide powder (Nb ₂ O ₅ ) to the mixture and pulverizing and mixing the mixture, the mixture was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and then maintained at 850 ° C.
For 5 hours. Next, 0.1 mol of lithium hydroxide monohydrate (LiO
_H · H 2 O) were mixed thoroughly by adding, under oxygen atmosphere 46
By maintaining the temperature at 0 ° C. for 10 hours and then performing a heat treatment at a temperature of 700 ° C. for 10 hours, a lithium-nickel-cobalt-niobium composite oxide having an average particle size of 7 μm was obtained.

As a result of the X-ray diffraction measurement, this lithium-nickel-cobalt-niobium composite oxide was found to be Li ₁₀ Nb ₂
It proved to be layered compound containing O _10. ICP
As a result of composition analysis by emission spectroscopy and atomic absorption spectroscopy, the main component was Li _1.02 Ni _0.77 Co _0.2 A.
It was found to be l _0.03 O _2. The peak intensity ratio of the (003) plane X-ray diffraction peak intensity to the (104) plane X-ray diffraction peak intensity: I ₍₀₀₃₎ / I ₍₁₀₄₎ is 1.79, and the (003) plane X-ray diffraction Peak intensity and Li
X-ray diffraction peak (2θ) attributable to ₁₀ Nb ₂ O ₁₀
= 22.2 °) Ratio of peak intensity to intensity: I _Nb / I
₍₀₀₃₎ was 0.02. The thermal decomposition onset temperature was 210 ° C., and the calorific value was 20 J / g. The exothermic peak temperature was 225 ° C., and the discharge capacity was 178 m.
Ah / g. Thereafter, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1700 mAh was assembled in the same manner as in Example 1.

Reference Example Nickel hydroxide powder [Ni _0.77 Co _0.2 Al _0.03 (OH) ₂ ] in which a part of Ni was replaced with Co and Al, and lithium hydroxide monohydrate (LiOH)・ H ₂ O) and Li
/ (Ni + Co + Al) was adjusted to 1.05. After niobium pentoxide powder (Nb ₂ O ₅ ) was added to this mixture and ground and mixed, the mixture was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and then calcined at 850 ° C. for 5 hours. Next, 0.05 mol of lithium hydroxide monohydrate (LiOH.H ₂ O) was added to 1 mol of the calcined product, mixed well, and kept at 460 ° C. for 10 hours under an oxygen atmosphere. By performing a heat treatment at a temperature of 10 ° C. for 10 hours, a lithium nickel cobalt niobium composite oxide having an average particle size of 7 μm was obtained. As a result of the X-ray diffraction measurement, this lithium nickel cobalt niobium composite oxide was found to be Li ₃ NbO
It was found to be a layered compound containing ₄ . As a result of composition analysis by ICP emission spectroscopy and atomic absorption spectroscopy, the main component was LiNi _0.77 Co _0.2 Al _0.03.
It was found to be O _2. The peak intensity ratio between the X-ray diffraction peak intensity of the (003) plane and the X-ray diffraction peak intensity of the (104) plane: I ₍₀₀₃₎ / I ₍₁₀₄₎ was 1.71,
The peak intensity ratio between the X-ray diffraction peak intensity of the (003) plane and the maximum X-ray diffraction peak (2θ = 14.8 °) attributed to Li ₃ NbO ₄ : I _Nb / I ₍₀₀₃₎ is 0.021.
Met. The thermal decomposition onset temperature was 211 ° C., and the calorific value was 30 J / g. The exothermic peak temperature is 2
At 25 ° C., the discharge capacity was 171 mAh / g. Thereafter, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1700 mAh was assembled in the same manner as in Example 1.

(Comparative Example 1) Ni was partially replaced with Co.
Nickel hydroxide powder [Ni_0.8Co_0.2(O
H)₂] And lithium hydroxide monohydrate (LiOH.H
₂O) and the atomic ratio of Li to Ni (Li / Ni) is 1.0
5 was added. This mixture is placed in an oxygen atmosphere 4
Hold at 60 ° C. for 10 hours, then at 700 ° C. for 10 hours
Fired for hours. As a result of X-ray diffraction measurement, this fired product
Turned out to be a phase. Also, X-ray diffraction of (003) plane
The peak intensity and the peak intensity of the (104) plane X-ray diffraction peak
Work strength ratio: I ₍₀₀₃₎/ I₍₁₀₄₎Is 1.93
there were. In this way, lithium particles having an average particle size of 7 μm
Nickel cobalt oxide: LiNi_0.8Co_0.2
O₂Got. Differential scanning calorimetry (DS
C) was performed to evaluate the thermal stability of the material. As a result, heat
The decomposition start temperature is 189 ° C and the calorific value is 60 J / g.
there were. The discharge capacity was 193 mAh / g.
Hereinafter, the design rated capacity 170
0 mAh cylindrical lithium ion secondary battery (18650
Size) assembled.

Comparative Example 2 Lithium nitrate (LiN
O _3), nickel nitrate _{[Ni (NO 3) 2 ·} 6H
₂ O], cobalt nitrate _{[Co (NO 3) 2 ·} 6H
₂ O], aluminum nitrate _{[Al (NO 3) 2 ·} 9H 2
O] was weighed in a predetermined amount and dissolved in water to prepare a 2 mol / L solution. This solution was spray-dried in the same manner as in Example 1 to obtain a precursor. This precursor was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and subsequently calcined at a temperature of 750 ° C. for 5 hours. As a result of X-ray diffraction measurement, it was found that the fired product had a single phase. The peak intensity ratio of the (003) plane X-ray diffraction peak intensity to the (104) plane X-ray diffraction peak intensity: I ₍₀₀₃₎ / I ₍₁₀₄₎ was 1.76.
Thus, the lithium-nickel-cobalt-aluminum composite oxide having an average particle size of 10 μm: LiNi
_0.72 Co _0.2 Al _0.08 O ₂ was obtained. The thermal decomposition onset temperature of this material is 228 ° C, and the calorific value is 61 J /
g. The exothermic peak temperature was 250 ° C. The discharge capacity was 168 mAh / g. Thereafter, in the same manner as in Example 1, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1700 mAh was assembled.

(Comparative Example 3) Nickel hydroxide powder in which a part of Ni was replaced with Co and Al [Ni _0.77 Co _{0 . 2} A
l _0.03 (OH) ₂ ] and lithium hydroxide monohydrate (L
iOH.H ₂ O) was mixed so that Li / (Ni + Co + Al) became 1.03, and pressed at 1 t / cm ² to obtain a molded body. The molded body is heated at 700 ° C.
It was baked for 0 hours. Next, niobium pentoxide powder (Nb ₂ O ₅ ) was added to the calcined product, pulverized and mixed, dispersed in a lithium nitrate (LiNO ₃ ) solution, and the dispersion was spray-dried to prepare a precursor. . This was baked at 800 ° C. for 2 hours in an oxygen atmosphere, and was crushed using a crusher (high-speed rotating pin mill). As a result of X-ray diffraction measurement, it was found that the fired product was a single phase. The composition was analyzed by ICP emission spectroscopy and atomic absorption spectroscopy. As a result, Li _1.02
Ni _0.76 Co _0.2 Al _0.03 Nb _{0.0 1} O ₂
Turned out to be. Further, the ratio of the peak intensity between the X-ray diffraction peak intensity of the (003) plane and the X-ray diffraction peak intensity of the (104) plane: I ₍₀₀₃₎ / I ₍₁₀₄₎ was 1.58. The thermal decomposition onset temperature of this material is 215 ° C,
The calorific value was 47 J / g. The exothermic peak temperature was 230 ° C., and the discharge capacity was 185 mAh / g. The average particle size was 10 μm. Thereafter, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1700 mAh was assembled in the same manner as in Example 1.

Comparative Example 4 In the same manner as in Example 1, lithium nitrate (LiNO ₃ ) and nickel nitrate [Ni (NO ₃ )
₂ · _{6H 2} O], cobalt nitrate _{[Co (NO 3) 2 ·} 6
H ₂ O], aluminum nitrate _{[Al (NO 3) 2 ·} 9H
₂ O] and niobium pentoxide (Nb ₂ O ₅ ). This dispersion was spray-dried in the same manner as in Example 1 to obtain a precursor. This precursor was placed in an oxygen atmosphere 46
It was kept at 0 ° C. for 10 hours and subsequently calcined at a temperature of 850 ° C. for 5 hours. As a result of X-ray diffraction measurement, this calcined product was LiNb
It turned out to be a layered compound containing O ₃ . ICP emission spectroscopy, as well as a result of composition analysis by atomic absorption spectrometry, the main component is _LiNi 0.72 _Co 0.2 _{Al 0.0 8}
It was found to be O _2. The peak intensity ratio of the X-ray diffraction peak intensity of the (003) plane and the X-ray diffraction peak intensity of the (104) plane: I ₍₀₀₃₎ / I ₍₁₀₄₎ is 1.4.
2, the X-ray diffraction peak intensity of the (003) plane and LiNbO
Maximum X-ray diffraction peak belonging to ₃ (2θ = 23.7 °)
Peak intensity ratio with intensity: _INb / I _{( 003)} is 0.0
It was 31. The thermal decomposition onset temperature of this material is 22
The temperature was 2 ° C, and the calorific value was 51 J / g. The exothermic peak temperature was 240 ° C. The discharge capacity is 148 mA
h / g. The average particle size was 9 μm. Less than,
A cylindrical lithium ion secondary battery (18650 size) having a high output specification was assembled in the same manner as in Example 1. The design rated capacity was 1450 mAh.

Comparative Example 5 Nickel hydroxide powder [Ni _0.8 Co _0.2 (O
H) ₂ ] and lithium hydroxide monohydrate (LiOH · H
₂ O) with an atomic ratio of Li to Ni (Li / Ni) of 1.0
5 was added. After niobium pentoxide powder (Nb ₂ O ₅ ) was added to this mixture and ground and mixed, the mixture was kept at 460 ° C. for 10 hours in an oxygen atmosphere, and then calcined at 850 ° C. for 5 hours. This was crushed and subjected to X-ray diffraction measurement. As a result, it was found that the fired product was a layered compound containing LiNbO ₃ . As a result of composition analysis by ICP emission spectroscopy and atomic absorption spectroscopy, the main component was LiNi
_0.8 Co _0.2 O ₂ . Further, the peak intensity ratio of the X-ray diffraction peak intensity of the (003) plane and the X-ray diffraction peak intensity of the (104) plane: I _{(003 )} / I ₍₁₀₄₎ is 1.35, and the X-ray diffraction intensity of the (003) plane is X-ray diffraction peak intensity and Li
The maximum X-ray diffraction peak attributed to NbO ₃ (2θ = 23.
7 °) Peak intensity ratio to intensity: I _Nb / I ₍₀₀₃₎ was 0.033. The thermal decomposition onset temperature of this material is 18
The temperature was 7 ° C, and the calorific value was 55 J / g. Further, the discharge capacity was 157 mAh / g. Average particle size is 11 μm
Met. Thereafter, in the same manner as in Example 1, a cylindrical lithium ion secondary battery (18650 size) having high output specifications was assembled. The design rated capacity was 1500 mAh.

Comparative Example 6 A part of Ni was replaced with Co.
Nickel hydroxide powder [Ni_0.75Co_0.25(O
H)₂] And lithium hydroxide monohydrate (LiOH.H
₂O) and the atomic ratio of Li to Ni (Li / Ni) is 1.0
5 was added. Add niobium pentoxide powder to this mixture
End (Nb₂O₅), Pulverize and mix in an oxygen atmosphere
Hold at 460 ° C. for 10 hours, followed by 850 ° C.
For 5 hours. This is crushed and X-ray diffraction measurement is performed.
As a result, the fired product was LiNbO₃Layered compounds containing
It turned out to be. ICP emission spectroscopy and atoms
As a result of composition analysis by the absorption method, the main component was LiNi.
_0.75Co_0.25O₂Met. Also, (003)
-Ray diffraction peak intensity of X-ray plane and X-ray diffraction peak of (104) plane
Ratio of peak intensity to peak intensity: I ₍₀₀₃₎/ I₍₁₀₄₎
Is 1.51, the X-ray diffraction peak intensity of the (003) plane and L
iNbO₃X-ray diffraction peak (2θ = 2
3.7 °) Ratio of peak intensity to intensity: I_Nb/ I
₍₀₀₃₎Was 0.027. Thermal decomposition of this material
The starting temperature was 205 ° C, and the calorific value was 52 J / g.
Was. Further, the discharge capacity was as low as 139 mAh / g. flat
The average particle size was 10 μm. Hereinafter, the same as the first embodiment
And high-output cylindrical lithium-ion rechargeable battery
(18650 size) was assembled. Design rated capacity is
It was 1400 mAh.

(Comparative Example 7) A part of Ni was replaced with Co.
Nickel hydroxide powder [Ni_0.8Co_0.2(O
H)₂] And lithium hydroxide monohydrate (LiOH.H
₂O) and the atomic ratio of Li to Ni (Li / Ni) is 1.0
5 was added. Add niobium pentoxide powder to this mixture
End (Nb₂O₅), Pulverize and mix in an oxygen atmosphere
Hold at 460 ° C. for 10 hours, followed by 850 ° C.
For 5 hours. Next, for 1 mol of this fired product
0.05 mol of lithium hydroxide monohydrate (LiOH.
H₂O) and mix well, 675 ° C under oxygen atmosphere
Heat treatment at a temperature of 10 hours, the average particle size becomes
7μm lithium-nickel-cobalt-niobium complex acid
Compound was obtained. As a result of the X-ray diffraction measurement,
Kel cobalt niobium composite oxide is Li₃NbO₄
It turned out that it is a layered compound containing. ICP emission
As a result of composition analysis by optical method and atomic absorption method,
Main component is LiNi_0.8Co _0.2O₂I know
won. X-ray diffraction peak intensity of (003) plane and (10)
4) Ratio of peak intensity to X-ray diffraction peak intensity of the surface: I
₍₀₀₃₎/ I₍₁₀₄₎Is 1.76, (003) face
X-ray diffraction peak intensity and Li₃NbO₄Maximum attributed to
Peak intensity with X-ray diffraction peak (2θ = 14.8 °) intensity
Degree ratio: I_Nb/ I_{(0 03)}Was 0.009. Ma
The thermal decomposition onset temperature was 185 ° C and the calorific value was 46J.
/ G. The exothermic peak temperature was 212 ° C,
The capacitance was 178 mAh / g. The same as in Example 1 below
And cylindrical lithium with a rated capacity of 1700 mAh
An ion secondary battery (18650 size) was assembled.

Comparative Example 8 Niobium pentoxide (Nb)₂O₅)
Is twice the weight (weight ratio) of Examples 1 to 3.
Except that the average particle size was 10 μm in the same manner as in Example 3.
m lithium-nickel-cobalt-niobium composite oxide
Got. As a result of X-ray diffraction measurement, this lithium nickel
・ Cobalt-niobium composite oxide is Li₈Nb₂O₉To
It was found to be a layered compound containing. ICP emission spectroscopy
As a result of composition analysis by the
The component is LiNi_0.76Co_0.16Al_0.08O₂
It turned out to be. X-ray diffraction peak of (003) plane
Intensity between peak intensity and X-ray diffraction peak intensity of (104) plane
Degree ratio: I₍₀₀₃₎/ I₍₁₀₄₎Is 1.56 and (0
03) X-ray diffraction peak intensity of plane and Li₈Nb ₂O₉Return to
Maximum X-ray diffraction peak (2θ = 23.8 °) intensity
Peak intensity ratio: I_Nb/ I₍₀₀₃₎Is 0.031
there were. The thermal decomposition onset temperature was 202 ° C. and the calorific value was 1
It was 4 J / g. The discharge capacity is 151 mAh / g.
Was low. Hereinafter, in the same manner as in the first embodiment, a high output
Specification cylindrical lithium ion secondary battery (18650 size)
) Was assembled. Design rated capacity is 1500mAh
there were.

A predetermined number of the lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 8 obtained as described above were prepared, and a capacity confirmation test was performed. In the capacity confirmation test, when charging was performed at 20 ° C. and the current value when the designed rated capacity was discharged in one hour was 1 C, the battery was charged until it reached 4.2 V at a current value of 0.3 C, and then 4.2 V. , And the total charging time was 8 hours. The discharge is performed at a constant current of 0.2 C, and the discharge end voltage is 2.7 V
And The rest time after charging and discharging was 30 minutes each. As a result, the discharge capacities of Examples 1 to 11 and Comparative Examples 1 to 8 were all equal to the design rated capacities. Next, the output characteristics of each of the batteries of Examples 1 to 11 and Comparative Examples 1 to 8 were evaluated. Here, as a method of defining this output characteristic,
A method of defining the ratio of each discharge capacity obtained when discharging at two current values was adopted. That is, the discharge capacity at the time of discharging at 0.2C (0.2C) and the discharge capacity at the time of discharging at 5C (5C) were measured, and the ratio of the two discharge capacities, discharge capacity (5C) / discharge capacity The value of (0.2C) was taken as the large current discharge capacity ratio. As a result, Examples 1 to 1
1 and Comparative Example 1 to Comparative Example 8 each had a large current discharge capacity ratio of 90% or more, which confirmed that the output characteristics were excellent.

Next, an internal short circuit of the battery was simulated, and a nail penetration test was carried out with the battery charged at 4.4 V according to the method described above. Table 1 shows the results. As an evaluation rank, 100 test samples were prepared for each example, and as a result of the overcharge test, the safety valve was normally operated and represented as a percentage of 100 batteries that did not burst or ignite. % To 98% or more, B rank is less than 98%, 80%
As described above, the rank C is less than 80%. As is clear from Table 1 below, none of the batteries of Examples 1 to 11 burst or fired. On the other hand, in the batteries of Comparative Examples 1 to 7, a large number of batteries that burst or ignited were found. In addition, in the battery of Comparative Example 8, although no battery that ruptured or ignited was observed, the discharge capacity per unit mass of the positive electrode active material (that is, the discharge capacity per unit weight of the positive electrode active material) was reduced. I have.

[0065]

[Table 1]

(Comparative Examples 9 to 11) Batteries were produced in the same manner as in Example 1 except that the substances shown in Table 2 were used as the nickel-cobalt composite oxide. The discharge capacity and safety tests of these batteries were measured in the same manner as in Example 1. The results are also shown in Table 2. As is evident from the results in Table 2, in the comparative example 9 in which the nickel-cobalt composite oxide was a substance having a composition range different from that of the present invention, the safety test was inferior to the battery of the present invention. . In Comparative Examples 10 and 11, the discharge capacity was inferior to that of the battery of the present invention.

[0067]

[Table 2]

As described in detail above, the non-aqueous electrolyte secondary battery of the present invention can be used even if an internal short circuit occurs due to external pressure or drop when the battery is in a charged state.
Since the calorific value at the time of thermal decomposition of the positive electrode active material is small and the thermal stability is excellent, the battery does not undergo thermal runaway and has excellent safety. Therefore, the non-aqueous electrolyte secondary battery of the present invention is useful not only as a power source for electric tools and cordless cleaners but also as a power source for electric vehicles.

[0069]

According to the non-aqueous electrolyte secondary battery of the present invention, the calorific value during thermal decomposition of the positive electrode active material is small and the thermal stability is excellent, so that a non-aqueous electrolyte secondary battery excellent in safety can be formed. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a thermal decomposition starting temperature.

FIG. 2 is a diagram showing a calorific value;

FIG. 3 is a diagram showing an example of a non-aqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

1 ... Battery container 2 ... insulator 3 ... electrode group 4 ... Positive electrode 5 ... Separator 6 ... negative electrode 7 ... Valve part 8 ... Safety valve 9 ... Positive electrode terminal 10 ... Gasket 11 ・ ・ ・ Positive electrode lead 12 ... Negative electrode lead

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2000-315502 (JP, A) JP-A-2002-151011 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4 / 00-4/04 H01M 4/36-4/62 H01M 10/40

Claims (2)

(57) [Claims] 1. A non-aqueous electrolyte comprising a positive electrode using a composite oxide mainly composed of lithium and nickel as a positive electrode active material, and a negative electrode using a material capable of inserting and extracting lithium ions as a negative electrode active material. In the secondary battery, the positive electrode active material has a general formula: Li _{1 + Z} Ni _1-xy
Co _x M _y O ₂ (provided that at least one M may Al, Mn, selected from Sn, the x, y, z is 0 <x ≦
0.3, 0 ≦ y ≦ 0.1 and 0 ≦ z ≦ 0.02) as the first phase, and further, as the second phase, Li ₈ Nb ₂ O ₉ , Li ₁₀ N
b ₂ O ₁₀ , wherein the X-ray diffraction peak intensity of the (003) plane of the lithium nickel cobalt composite oxide of the positive electrode active material is I ₍₀₀₃₎ , (104) plane X-ray diffraction peak intensity of
_(104), and when the maximum X-ray diffraction peak attributed to lithium _niobate is _INb , these peak intensity ratios are I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.6 and 0 Using a lithium nickel cobalt niobium composite oxide having a relationship of 0.01 ≦ _INb / I ₍₀₀₃₎ ≦ 0.03 .
Non-aqueous electrolyte secondary battery characterized in that there. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the value of y satisfies 0.03 ≦ y ≦ 0.08.