JPH09139212A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain reducing of capacity or cycle characteristics, despite of a case where a nonaqueous electrolyte secondary battery, wherein a lithium containing composite oxide can be used as positive electrode active material, and carbon material capable of doping or dedoping lithium can be used as negative electrode active material, is preserved or used in a high-temperature environment. SOLUTION: In a nonaqueous electrolyte secondary battery, where a lithium containing composite oxide can be used as positive electrode active material, and carbon material, capable of doping and dedoping lithium, can be used as negative electrode active material; a compound, expressed in a formula Liw Nix Coy Mz O2 , is used as a lithium containing composite oxide. In the formula, M: at least one kind element selected from Zr and lanthanoid elements, w, x, y, and z: numbers satisfying all following expressions, 0.05<=w<=1.10, 0.5<=x<=0.995, y<=0.495, 0.005<=z<=0.20, x+y+z>=1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a lithium-containing composite oxide as a positive electrode active material and a carbon material capable of doping and dedoping lithium as a negative electrode active material. More specifically, it relates to a non-aqueous electrolyte secondary battery having a high energy density and excellent cycle characteristics under a high temperature environment.

[0002]

2. Description of the Related Art In recent years, due to advances in electronic technology, high performance, miniaturization, and portability of electronic devices have advanced, and the demand for high energy density batteries used in these portable electronic devices has increased. Conventionally, secondary batteries used in these electronic devices include nickel-cadmium batteries and lead batteries, but these batteries have low discharge potential, large battery weight and battery volume, and high energy density. The reality is that the demand for batteries has not been fully met.

Recently, as a battery system satisfying these requirements, a non-aqueous electrolyte secondary battery having a negative electrode made of metallic lithium or a lithium alloy has attracted attention and has been actively studied. However, in the case of non-aqueous electrolyte secondary batteries that use metallic lithium as the negative electrode, the cycle life and rapid charging characteristics are practically sufficient due to the dissolution of metallic lithium, the generation of dendrites at the time of cracking, and the miniaturization of precipitated lithium. There is a problem that it does not exhibit various characteristics.

[0004] In order to solve these problems,
Research and development of a lithium-ion non-aqueous electrolyte secondary battery in which a material capable of doping and de-doping with lithium ions, for example, a carbon material as a negative electrode is active. Non-aqueous electrolyte secondary battery using such a negative electrode, since lithium does not exist in the metal state, there is no problem related to deterioration of cycle characteristics and rapid charge characteristics due to the metal lithium negative electrode,
It exhibits excellent battery characteristics. Further, as compared with the nickel-cadmium battery, the low self-discharge property required for the secondary battery is also improved, and there is an advantage that there is no memory effect. Furthermore, by using a lithium-containing composite oxide having a high oxidation-reduction potential for the positive electrode, the voltage of the battery is increased, so that there is an advantage that a battery having a high energy density can be realized.

By the way, although such a lithium ion non-aqueous electrolyte secondary battery has been actually put into practical use as a power source for portable electronic equipment, the storage and use locations of such electronic equipment vary widely. It's another. Therefore, it is required for non-aqueous electrolyte secondary batteries to exhibit sufficient performance even when the environment changes, especially when stored in automobiles in the summer or in warehouses where the temperature and humidity are high. It is also necessary to assume that it will be used, and there is a demand for higher reliability (high temperature storability) in a high temperature atmosphere.

[0006] In order to meet such a demand, research has been conventionally conducted from various aspects of battery constituent elements, for example, a nonaqueous solvent of an electrolytic solution, a supporting electrolyte, or a positive electrode active material.

Regarding the non-aqueous solvent of the electrolytic solution, it has been proposed to use a mixed organic solvent of propylene carbonate and diethyl carbonate as the non-aqueous solvent of a lithium-ion non-aqueous electrolytic solution secondary battery, up to about 45 ° C. It has been realized that the storability is improved under high temperature environment (Japanese Patent Laid-Open No. 184872/1992). Further, as a supporting electrolyte dissolved in such a non-aqueous solvent, LiC (SO ₂ CF ₃ ) ₃ and LiC (SO ₂ C
F _{3) 2} F, it has been proposed to use a _{LiC (SO 2 CF 3) 2} SO 2 CH 1~3 amino methyl lithium compounds substituted with a trifluoromethyl sulfonyl group such as ₃ [Abstract
No.19, P33 in Extended Abstracts of the 184th Elec
Trochemical Society, New Orieans (1993)].

Regarding the positive electrode active material, it has been proposed to improve the cycle characteristics at high temperature by limiting the particle size distribution of the positive electrode active material to a specific range (Japanese Patent Laid-Open No. 151988/1993). Further, it has been proposed to use three kinds of elements of Li / Ni / Co as metal elements constituting the lithium composite oxide (Japanese Patent Laid-Open No. 3-49).
No. 155).

[0009]

However, when a mixed organic solvent of propylene carbonate and diethyl carbonate is used as a non-aqueous solvent of a non-aqueous electrolyte secondary battery, the battery is sufficiently high in a high temperature environment up to about 45 ° C. Although it is possible to realize the performance, there is a problem that the high temperature storability in a high temperature environment of 60 ° C. or higher that may actually occur is insufficient.

Further, in the case of using methyllithium substituted with a trifluoromethylsulfonyl group as a supporting electrolyte, a mass production method of these supporting electrolytes has not been established, and therefore, it is practically used at this stage. The reality is that it cannot be applied to batteries.

Further, when it is intended to limit the particle size distribution of the positive electrode active material to a specific range, it is technically difficult at present to grind the positive electrode active material to obtain the particle size distribution in the specific range. There is. In addition, 3 of Li / Ni / Co
A positive electrode active material using a lithium composite oxide composed of a kind of metal element and oxygen has an unstable hexagonal crystal structure when lithium is dedoped from the positive electrode active material at the time of charging, and particularly at high temperature. However, there is a problem in that the crystal structure of the positive electrode active material itself collapses when it is stored in, and it becomes difficult to dope and dedope lithium ions, resulting in a decrease in capacity.

As described above, a high energy density non-aqueous electrolyte secondary battery using a lithium-containing composite oxide as a positive electrode active material and a carbon material capable of doping and dedoping lithium as a negative electrode active material is used. At present, the technology for suppressing the deterioration of the capacity characteristics and the deterioration of the cycle characteristics of the battery when stored or used in is not established.

The present invention is intended to solve the above-mentioned problems of the prior art. A lithium-containing composite oxide is used as a positive electrode active material, and a carbon material capable of doping and dedoping lithium is used as a negative electrode active material. An object of the present invention is to make it possible to suppress deterioration of capacity characteristics and cycle characteristics even when the non-aqueous electrolyte secondary battery used as is stored or used in a high temperature environment.

[0014]

The present inventor has found that the above object can be achieved by using a specific lithium composite oxide as a positive electrode active material, and has completed the present invention.

That is, the present invention provides a non-aqueous electrolyte secondary battery in which a lithium-containing composite oxide is used as a positive electrode active material and a carbon material capable of doping and dedoping lithium is used as a negative electrode active material. The complex oxide has the formula (1)

[0016]

Embedded image Li _w Ni _x Co _y M _z O ₂ (1) (wherein, M is at least one element selected from Zr and lanthanoid elements. _W , x, y and z are represented by the following mathematical formulas) (i) ~ (v)

[0017]

2 ≦ 0.05 ≦ w ≦ 1.10 (i) 0.5 ≦ x ≦ 0.995 (ii) y ≦ 0.495 (iii) 0.005 ≦ z ≦ 0.20 (iv) x + y + z ≧ It is a number that satisfies 1 (v). And a non-aqueous electrolyte secondary battery.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the non-aqueous electrolyte secondary battery of the present invention, the lithium composite oxide of the formula (1) is used as the positive electrode active material. In this lithium composite oxide, some of the metal elements of the conventional lithium composite oxide containing three types of metal elements (Li / Ni / Co) are used as Zr and lanthanoid elements (for example, Ce, Sm, La, Dy, etc.). Corresponding to at least one element M selected from the above). By substituting with the element M in this way, it is possible to suppress deterioration of capacity characteristics and cycle characteristics even when the non-aqueous electrolyte secondary battery is stored or used in a high temperature environment.

Although the reason why such an effect is obtained is not clear, it is considered as follows.

That is, three conventional metal elements (Li / N
When lithium is dedoped from the positive electrode active material at the time of charging by substituting at least one element M selected from Zr and lanthanoid elements for part of the metal elements of the lithium composite oxide containing i / Co) However, the hexagonal crystal structure of the lithium composite oxide is stabilized, the collapse of the crystal structure of the positive electrode active material itself is suppressed even when stored at high temperature, so that lithium ion doping and dedoping are easily performed, and the battery It is considered that the deterioration of the capacitance characteristic of is suppressed.

In the present invention, as mentioned above, at least one selected from Zr and lanthanoid elements is used as M. The use of other elements as M is not preferable because it is difficult to synthesize a hexagonal crystal structure.

If the amount of substitution of the element M is too small, the effect of stabilizing the crystal structure is hardly recognized, and the capacity characteristics of the battery are deteriorated. If the amount of the element M is substituted too much, the crystal structure is deteriorated. However, since the charge / discharge performance of the positive electrode active material itself is lowered and the battery capacity is lowered, z indicating the content ratio of the element M is set to a number of 0.005 or more and 0.20 or less. Moreover, w showing the content rate of Li is 0.
The number is from 05 to 1.10. Further, x, which indicates the content ratio of Ni, is 0.5 or more, since the battery capacity becomes small when Ni is too small, and the crystal structure stabilizing effect of the active material due to the substituting element cannot be sufficiently exhibited. 9
The number is 95 or less, preferably 0.6 or more and 0.995 or less. Further, y representing the content ratio of Co is set to 0.495 or less, preferably 0.295 or less, because the effect of the substitutional element to stabilize the crystal structure of the active material cannot be sufficiently exhibited when Co is too much. In this case, y may be 0. That is, all of Co may be replaced with the element M.

Such lithium composite oxides include, for example, a lithium salt, a cobalt salt, a nickel salt and a salt of the substituting element M such as carbonate, nitrate, sulfate, oxide, hydroxide,
It can be produced using a halide or the like as a raw material. For example, according to a desired composition, raw materials of a lithium salt, a nickel salt, a cobalt salt and an element M salt are weighed, sufficiently mixed, and then heated and calcined in a temperature range of 600 ° C. to 1000 ° C. in an oxygen existing atmosphere. It can be manufactured. In this case, the mixing method of each component is not particularly limited, and powdery salts may be mixed as they are in a dry state, or powdery salts may be dissolved in water and mixed in an aqueous solution. You may.

As the negative electrode active material constituting the non-aqueous electrolyte secondary battery of the present invention, a carbon material capable of doping and dedoping lithium is used, and such a carbon material has a relatively low temperature of 2000 ° C. or lower. A low crystalline carbon material obtained by firing at a low temperature or a raw material that is easily crystallized is 3000 ° C.
It is possible to use a highly crystalline carbon material or the like that has been treated at a high temperature nearby. For example, pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), artificial graphites, natural graphites, glassy carbons, organic polymer compound fired bodies (fired furan resin, etc. at an appropriate temperature) Carbonized), carbon fiber, activated carbon and the like can be used. Among them, a low crystalline carbon material having a (002) plane spacing of 3.70 angstroms or more, a true density of less than 1.70 g / cc, and having no exothermic peak at 700 ° C. or more in a differential thermal analysis in an air stream, A highly crystalline carbon material having a high negative electrode mixture filling property and a true specific gravity of 2.10 g / cc or more can be preferably used.

As the electrolytic solution, a non-aqueous electrolytic solution prepared by dissolving a lithium salt as a supporting electrolyte in an organic solvent is used.
Here, the organic solvent is not particularly limited, but propylene carbonate, ethylene carbonate,
Butylene carbonate, 1,2-dimethoxyethane, γ
-Butyrolactone, sulfolane, tetrahydrofuran,
2-Methyl-tetrahydrofuran, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate and the like can be mentioned.
You may use these individually or in mixture of 2 or more types.
In particular, a mixed solvent of cyclic carbonic acid esters and chain carbonic acid esters can be preferably used.

As the supporting electrolyte, LiClO ₄ , LiAsF ₆ and Li which are generally used for lithium batteries are used.
PF ₆ , LiBF ₄ , LiCl, LiBr, CH ₃ SO ₃ L
i, CF ₃ SO ₃ Li and the like can be mentioned. You may use these individually or in mixture of 2 or more types.

The non-aqueous electrolyte used in the present invention is not limited to a liquid state, and may be solid or gel as long as the supporting electrolyte is dissolved in the non-aqueous organic solvent. May be.

In order to obtain a more safe sealed non-aqueous electrolyte secondary battery, it is desirable to provide a means for interrupting the current in response to an increase in the battery internal pressure when an abnormality occurs during overcharging.

The battery type is not particularly limited and may be a cylindrical type, a square type, a coin type, a button type or a paper type.

[0030]

EXAMPLES Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail with reference to examples.

Example 1 A specific description will be given with reference to the sectional view of the battery shown in FIG.

(Production of Positive Electrode (2)) First, lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and zirconium oxide (Zr).
O ₂ ) and the molar ratio of Li / Ni / Co / Zr is 1 /
The mixture was mixed so as to be 0.60 / 0.395 / 0.005, and the mixture was heated in an oxygen atmosphere at 750 ° C. for 5 hours to obtain a lithium composite oxide (LiNi
_0.6 Co _0.395 Zr _0.005 O ₂ ) was obtained.

An X-ray diffraction diagram of the obtained positive electrode active material using Cu-Kα radiation is shown in FIG. This X-ray diffraction pattern is
It closely resembled the X-ray diffraction pattern of LiCoO ₂ registered in JCPDS 16-427 and LiNiO ₂ registered in 9-63. Therefore, it was confirmed that the positive electrode active material synthesized in this example had the same layered hexagonal crystal structure as LiCoO ₂ and LiNiO ₂ . This indicates that Zr, which is the substituting element, is in solid solution in the oxide.

Next, 91% by weight of the positive electrode active material (LiNi
_0.6 Co _0.395 Zr _0.005 O ₂ ), 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture, which was added to N-methyl-2-pyrrolidone. Dispersed into a slurry. Further, this slurry was applied to both sides of an aluminum foil as the positive electrode current collector (11), dried and then compression molded with a roller press machine to obtain a positive electrode (2).

(Preparation of Negative Electrode (1)) After introducing a functional group containing oxygen into petroleum pitch in an amount of 10 to 20% (oxygen cross-linking), it is fired at 1000 ° C. in an inert gas to approximate a glassy carbon material. A non-graphitizable carbon material having properties was obtained. next,
90% by weight of the obtained carbon material and 10% by weight of polyvinylidene fluoride as a binder are mixed to prepare a negative electrode mixture,
This was dispersed in N-methyl-2-pyrrolidone to form a slurry. Furthermore, this slurry was added to the negative electrode current collector (1
Negative electrode (1) was obtained by applying it to both surfaces of the copper foil which is 0), drying and then compression molding with a roller press.

(Preparation of Non-Aqueous Electrolyte Secondary Battery for Test) Strip-shaped negative electrode (1) and positive electrode (2) prepared as described above,
A center pin (1) is formed by sequentially laminating a separator (3) made of a microporous polyethylene film having a thickness of 25 μm.
By making many turns around 4), a spirally wound electrode body was produced as shown in FIG.

Next, the spiral electrode body was housed in a nickel-plated iron battery can (5). Insulating plates (4) are arranged on the upper and lower surfaces of the spirally wound electrode body, and a positive electrode lead (13) made of aluminum is connected from the positive electrode current collector (11) to collect the positive electrode (2) and the negative electrode (1). It was led out and connected to the battery lid (7) through a safety valve device (8) equipped with a PTC element (9) as a current cutoff device. Further, a negative electrode lead (12) made of nickel was led out of the negative electrode current collector (10) and was welded to the battery can (5).

Next, 50 vol% of propylene carbonate and 50 vo of diethyl carbonate were placed in the battery can (5).
An electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 mol / l was injected into a mixed solvent with 1%. The battery lid (7) was fixed by caulking the battery lid (7) and the battery can (5) through the gasket (6) coated with asphalt.
This gives a diameter of 18 mm and a height of 6 as shown in FIG.
A 5 mm cylindrical battery was prepared.

Example 2 Li / Ni / Co / Zr mol of lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and zirconium oxide (ZrO ₂ ). A positive electrode active material made of a lithium composite oxide was obtained by mixing and firing so that the ratio was 1 / 0.60 / 0.20 / 0.20. The X-ray diffraction diagram of the obtained positive electrode active material by Cu-Kα ray is shown in FIG. As a result, it was found that the positive electrode active material of Example 1 had a layered hexagonal crystal structure.

A cylindrical battery was manufactured in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Comparative Example 1 As a positive electrode active material to which no substituting element was added, lithium hydroxide, nickel oxide and cobalt oxide were used as Li / Ni.
A positive electrode active material made of a lithium composite oxide was obtained by mixing and firing so that the ratio of / Co was 1 / 0.60 / 0.40. An X-ray diffraction diagram of the obtained positive electrode active material by Cu-Kα ray is shown in FIG. As a result, it was found that the positive electrode active material of Example 1 had a layered hexagonal crystal structure.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Comparative Example 2 Lithium hydroxide, nickel oxide, cobalt oxide and zirconium oxide were used, and the ratio of Li / Ni / Co / Zr was 1 /.
A positive electrode active material made of a lithium composite oxide was obtained by mixing and firing so as to be 0.60 / 0.15 / 0.25. An X-ray diffraction diagram of the obtained positive electrode active material by Cu-Kα ray is shown in FIG. As a result, a peak considered to be an impurity was observed.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Example 3 Lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and cerium oxide (CeO ₂ ) were added in a molar ratio of Li / Ni / Co / Ce. By mixing and firing so that the ratio becomes 1 / 0.60 / 0.35 / 0.05, M is a kind of lanthanoid element C
A positive electrode active material composed of the lithium composite oxide of e was obtained. An X-ray diffraction diagram of the obtained positive electrode active material by Cu-Kα ray is shown in FIG. As a result, it was found to have a layered hexagonal crystal structure as in Example 1.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Example 4 Li / Ni / Co / Sm was prepared by adding lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and samarium oxide (Sm ₂ O ₃ ). M is a kind of lanthanoid element by mixing and firing so that the molar ratio of S becomes 1 / 0.60 / 0.35 / 0.05.
A positive electrode active material composed of a lithium composite oxide of m was obtained. FIG. 6 shows an X-ray diffraction diagram of the obtained positive electrode active material by Cu-Kα radiation. As a result, it was found to have a layered hexagonal crystal structure as in Example 1.

A cylindrical battery was manufactured in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Example 5 Li / N was added to lithium hydroxide (LiOH.H ₂ 0), nickel oxide (NiO) and cerium oxide (CeO ₂ ).
A positive electrode active material made of a lithium composite oxide was obtained by mixing and firing so that the molar ratio of i / Ce was 1 / 0.995 / 0.005. Cu of the obtained positive electrode active material
The X-ray diffraction diagram by -Kα ray is shown in FIG. 7. As a result, it was found to have a layered hexagonal crystal structure as in Example 1.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Example 6 Lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and zirconium oxide (ZrO ₂ ) were mixed in a molar ratio of Li / Ni / Co / Zr. The positive electrode active material made of the lithium composite oxide was obtained by mixing and firing so that the ratio was 1 / 0.70 / 0.295 / 0.005. Cu-K of the obtained positive electrode active material
An X-ray diffraction diagram of α rays is shown in FIG. As a result, it was found to have a layered hexagonal crystal structure as in Example 1.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Example 7 Li / Ni / Co / Zr was mixed with lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and zirconium oxide (ZrO ₂ ). The positive electrode active material made of a lithium composite oxide was obtained by mixing and firing so that the ratio was 1 / 0.50 / 0.495 / 0.005. Cu-K of the obtained positive electrode active material
An X-ray diffraction diagram of α rays is shown in FIG. As a result, it was found to have a layered hexagonal crystal structure as in Example 1.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Comparative Example 3 Lithium hydroxide (LiOH.H ₂ O), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and zirconium oxide (ZrO ₂ ) were added in a molar ratio of Li / Ni / Co / Zr. The positive electrode active material made of a lithium composite oxide was obtained by mixing and firing so that the ratio was 1 / 0.40 / 0.595 / 0.005. Cu-K of the obtained positive electrode active material
An X-ray diffraction diagram of α rays is shown in FIG.

A cylindrical battery was produced in the same manner as in Example 1 except that the obtained positive electrode active material was used.

(Evaluation of Battery Performance) Cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 thus produced were subjected to the cycle life test shown below. It was

First, charging was performed under the conditions of a charging voltage of 4.20 V and a charging current of 1000 mA for a charging time of 2.5 h,
Subsequently, the initial capacity was measured under charge / discharge conditions in which discharge was performed at a discharge current of 500 mA and a final voltage of 2.75 V, and then
A cycle life test was performed 300 times in a 60 ° C. high temperature environment atmosphere.

In Table 1, the Ni ratio, the Co ratio, and the ratio of the substituting elements are 1 for Li in the positive electrode active material.
The atom (mol) ratio of each element to the atom (mol) is shown. The capacity retention ratio means the ratio (%) of the discharge capacity in the 300th cycle to the discharge capacity in the second cycle.

[0060]

[Table 1] Substitution element Initial capacity Capacity retention ratio Ni ratio Co ratio Type ratio (mAh) (%) Comparative example 1 0.60 0.40 None None 1080 68 Example 1 0.60 0.395 Zr 0.005 1060 85 Example 2 0.60 0.20 Zr 0.20 1050 87 Comparative example 2 0.60 0.15 Zr 0.25 890 75 Example 3 0.60 0.35 Ce 0.05 1070 86 Example 4 0.60 0.35 Sm 0.05 1050 85 Example 5 0.995 0 Zr 0.005 1130 84 Example 6 0.70 0.295 Zr 0.005 1100 88 Example 7 0.50 0.495 Zr 0.005 1050 89 Comparative Example 3 0.40 0.595 Zr 0.005 1050 66

From the results of Examples 1 and 2 and Comparative Examples 1 and 2 in Table 1, when the ratio of Co and Zr in the positive electrode active material was changed, the higher the ratio of Zr as the substituting element, the higher the temperature environment. It can be seen that the capacity retention ratio below improves. It is considered that this is because Zr has a function of stabilizing the crystal structure of the lithium composite oxide that is the positive electrode active material.

However, according to the result of Comparative Example 2, when the ratio of Zr is too large, Zr cannot be completely dissolved in the positive electrode active material and an impurity peak appears in the X-ray diffraction pattern. This means that the hexagonal crystal structure is disordered, and this reduces the initial capacity of the battery.

From the results of Comparative Example 1, the initial capacity was not reduced unless Zr was added, but the positive electrode active material could not be stabilized, and the capacity retention ratio in a high temperature environment was significantly decreased. You can see that

Examples 3 and 4 using lanthanoid elements (Ce, Sm) in place of Zr in Examples 1 and 2.
It can be seen that the battery of No. 1 shows a good capacity retention rate even in a high temperature environment without impairing the initial capacity, as in the case of Examples 1 and 2. Therefore, Ce or Sm is L
It is considered that the solid solution in the i / Ni / Co composite oxide has the effect of stabilizing the crystal structure of the positive electrode active material even in a high temperature atmosphere.

From the results of Examples 5 to 7 and Comparative Example 3 in which the ratio of Ni and Co was changed by fixing the ratio of Zr in the positive electrode active material and the result of Example 1, it was found that It can be seen that the capacity retention ratio under high temperature environment changes depending on the ratio of Ni and Co. That is, it can be seen that when the Ni ratio is smaller than 0.50 and the Co ratio is larger than 0.495, the capacity retention ratio decreases.

Although the detailed reason for this is not clear, it is considered that the effect of stabilizing the crystal structure of the Zr positive electrode active material does not appear at a composition ratio with a large Co ratio.

[0067]

According to the present invention, a lithium-containing composite oxide is used as a positive electrode active material, and a carbon material capable of doping and dedoping lithium is used as a negative electrode active material. The high temperature storability (cycle characteristics) of the secondary battery can be improved.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of the positive electrode active material of Example 1.

2 is an X-ray diffraction diagram of the positive electrode active material of Example 2. FIG.

FIG. 3 is an X-ray diffraction diagram of the positive electrode active material of Comparative Example 1.

FIG. 4 is an X-ray diffraction diagram of the positive electrode active material of Comparative Example 2.

5 is an X-ray diffraction diagram of the positive electrode active material of Example 3. FIG.

6 is an X-ray diffraction diagram of the positive electrode active material of Example 4. FIG.

7 is an X-ray diffraction diagram of the positive electrode active material of Example 5. FIG.

8 is an X-ray diffraction diagram of the positive electrode active material of Example 6. FIG.

9 is an X-ray diffraction diagram of the positive electrode active material of Example 7. FIG.

FIG. 10 is an X-ray diffraction diagram of the positive electrode active material of Comparative Example 3.

FIG. 11 is a cross-sectional view of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 1 Negative electrode 2 Positive electrode 3 Separator 4 Insulating plate 5 Battery can 6 Gasket 7 Battery lid 8 Safety valve device 9 PTC element 10 Negative electrode current collector 11 Positive electrode current collector 12 Negative electrode lead 13 Positive electrode lead 14 Center pin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoyuki Kato No. 1 Shimosugishita, Takakura, Hiwata-cho, Koriyama-shi, Fukushima Prefecture Sony Energy Tech Co., Ltd. (72) Inventor Yoshikatsu Yamamoto, Koriyama-shi, Fukushima Prefecture 1 in Shimo-Sugishita, Takakura, Wada-machi 1) Sony Energy Tech Co., Ltd. (72) Inventor Shuhito Yoshikawa 2-26 Kitahama, Chuo-ku, Osaka City, Osaka Shodo Chemical Industry Co., Ltd. (72) Invention Person Miyuki Imai 1-226 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture Shodo Chemical Co., Ltd. (72) Inventor Yumiko Kawagoe 2-1-2, Kitahama, Chuo-ku, Osaka City, Osaka

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery using a lithium-containing composite oxide as a positive electrode active material, and using a carbon material capable of doping and dedoping lithium as a negative electrode active material. Formula (1) embedded image Li _w Ni _x Co _y M _z O ₂ (1) (In the formula, M is at least one element selected from Zr and lanthanoid elements. _W , x, y and z are , The following equations (i) to (v): 0.05 ≦ w ≦ 1.10 (i) 0.5 ≦ x ≦ 0.995 (ii) y ≦ 0.495 (iii) 0.005 ≦ z ≦ 0.20 (iv) x + y + z ≧ 1 (v), which is a number satisfying the following condition.) A non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing composite oxide is a hexagonal crystal.