JP2010199077A - Non-aqueous electrolyte secondary battery and method of charging the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery which has a high capacity, superior cycle characteristics, and superior safety at high temperature. <P>SOLUTION: The non-aqueous electrolyte secondary battery has a structure in which a positive electrode active material is a mixture of a lithium cobalt composite oxide represented by Li<SB>a</SB>Co<SB>1-x-y-z</SB>Zr<SB>x</SB>Mg<SB>y</SB>M<SB>z</SB>O<SB>2</SB>(wherein M is at least one of Al, Ti, and Sn; 0<a≤1.1; 0.0001≤x; 0.0001≤y; and x+y+z≤0.03) with a lithium nickel manganese composite oxide having a lamellar structure represented by Li<SB>b</SB>Mn<SB>s</SB>Ni<SB>t</SB>Co<SB>u</SB>X<SB>v</SB>O<SB>2</SB>(wherein X is at least one of Zr, Mg, Al, Ti, and Sn; 0<b≤1.1; 0.1≤s≤0.5; 0.1≤t≤0.5; v=0 or 0.0001≤v≤0.03; and s+t+u+v=1), a potential of the positive electrode active material is 4.4 to 4.6 V based on lithium, an air permeability of a separator is ≥60 seconds/100 ml and ≤400 seconds/100 ml, and a porosity is less than 60%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in a non-aqueous electrolyte secondary battery intended to improve discharge capacity and cycle characteristics.

  Mobile information terminals such as mobile phones, notebook computers, and PDAs are rapidly becoming smaller and lighter, and non-aqueous electrolyte secondary batteries with high energy density and high capacity are widely used as drive power sources. Has been.

  In recent years, a further increase in capacity of a battery has been demanded, and attempts have been made to increase the utilization rate of the positive electrode active material by charging and using the battery until a higher potential is reached.

  However, when lithium cobaltate (lithium-containing cobalt composite oxide) conventionally used as a positive electrode active material is charged to a potential higher than 4.3 V on the basis of lithium, the stability as a compound is reduced. Deteriorates and the cycle characteristics deteriorate.

  In order to solve this problem, it has been proposed to increase the stability of a compound at a high potential by adding a different metal such as zirconium or magnesium to lithium cobalt oxide. However, this technique does not have sufficient thermal stability at high potential.

  As a separator for such a non-aqueous electrolyte secondary battery, a polyolefin microporous film having low reactivity with the non-aqueous electrolyte is used. As this separator, a separator having high lithium ion permeability is used in order to improve discharge characteristics.

  And, as an indicator of the ion permeability of the separator, air permeability (time required to allow 100 ml of air to permeate) and porosity (ratio of pore volume to separator unit volume) are used. The smaller the value of and the larger the porosity value, the better the ion permeability and the higher the discharge characteristics.

  Incidentally, Patent Documents 1 to 3 have been proposed as techniques relating to the separator of the nonaqueous electrolyte secondary battery.

JP 2000-348703 A (Claims, paragraphs 0011-0013) JP 2001-319695 A (claims, paragraphs 0005-0007) JP 2002-237330 A (claims, paragraphs 0004-0007)

  In Patent Document 1, the maximum pore diameter is 0.02 to 3 μm, the porosity is 30 to 85%, the film thickness is 5 to 100 μm, the air permeability is 30 to 2000 seconds / 100 cc, and the film width direction is treated at 105 ° C. for 2 hours. This technique uses a separator having a thermal shrinkage rate of + 3% or less, and according to this technique, it is said that the fuse function can be enhanced by rapidly closing the heat in a low temperature region.

  Patent Document 2 is a technique using a separator having an air permeability of 200 seconds / 100 cc or less at 25 ° C. According to this technique, output characteristics and high-rate discharge characteristics can be improved.

  Patent Document 3 is a technique using a separator having a thickness of 20 μm or less, an air permeability of 200 seconds or less, and an average pore diameter of 0.1 μm or more. According to this technique, safety during overcharge can be improved. Is done.

  In order to further increase the battery capacity of the nonaqueous electrolyte secondary battery, the present inventors have conducted intensive research on means for increasing the potential of the positive electrode active material to increase the utilization factor of the active material. As a result, it was found that a positive electrode having a positive electrode active material with a high potential should be combined with a separator having different characteristics from the conventional one.

  The present invention has been completed based on this finding, and an object thereof is to provide a non-aqueous electrolyte secondary battery having a high capacity, excellent cycle characteristics and high-temperature safety.

The present invention relating to a non-aqueous electrolyte secondary battery for solving the above problems includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt. In the non-aqueous electrolyte secondary battery provided, the positive electrode active material is Li _a Co _1-xy- Zr _x Mg _y M _z O ₂ (M is at least one of Al, Ti, Sn, and 0 <a ≦ 1.1,0.0001 ≦ x, and lithium-cobalt composite oxide of zirconium and magnesium are added, represented by 0.0001 ≦ y, x + y + z ≦ 0.03), Li b Mn s Ni t Co u X _v O ₂ (X is at least one of Zr, Mg, Al, Ti, Sn, 0 <b ≦ 1.1, 0.1 ≦ s ≦ 0.5, 0.1 ≦ t ≦ 0.5, v = 0 or 0.0001 ≦ v ≦ 0.03, s + t + u + v = 1) Lithium nickel manganese composite oxide having a layered structure represented by a mass ratio of 51:49 to 90:10, and the positive electrode active material has a potential of 4.4 to 4. 6 V, air permeability of the separator is 60 seconds / 100 ml or more and 400 seconds / 100 ml or less, and the porosity of the separator is less than 60%.

  In the said structure, it has lithium cobalt complex oxide with which zirconium and magnesium were added as a positive electrode active material, and this compound is excellent in stability in high potential (4.4-4.6V on lithium basis). . Furthermore, since the lithium nickel manganese composite oxide having a layered structure excellent in thermal stability at high potential is blended with this compound, thermal stability at high potential is also excellent.

The lithium cobalt composite oxide to which zirconium and magnesium are added is Li _a Co _1-xyz Zr _x Mg _y M _z O ₂ (M is at least one of Al, Ti, Sn, and 0 < a ≦ 1.1, 0.0001 ≦ x, 0.0001 ≦ y, x + y + z ≦ 0.03). Further, the layered lithium-nickel-manganese composite _{oxide, Li b Mn s Ni t Co} u X v O 2 (X is Zr, Mg, Al, Ti, at least one of Sn, 0 <b ≦ 1.1,0.1 ≦ s ≦ 0.5, 0.1 ≦ t ≦ 0.5, v = 0 or 0.0001 ≦ v ≦ 0.03, and s + t + u + v = 1). Since these compounds can increase the number of moles of lithium relative to the total number of moles of cobalt, nickel, manganese, etc., the amount of lithium contributing to charge / discharge can be sufficiently increased.

  In the above configuration, the air permeability of the separator is regulated to 60 seconds / 100 ml or more and 400 seconds / 100 ml or less. When the charge / discharge cycle is performed, the non-aqueous electrolyte reacts with the electrode and decomposes and polymerizes, but the product of this reaction closes part of the pores of the separator and reduces the ion permeability of the separator. . Here, when the air permeability is larger than 400 seconds / 100 ml (low ion permeability), this influence becomes extremely large, and the cycle characteristics are greatly deteriorated.

  Further, even when the air permeability of the separator is less than 60 seconds / 100 ml, cycle deterioration occurs. The reason for this is not clear, but the transition metal element is eluted from the layered lithium nickel manganese composite oxide, which is the positive electrode active material, by the charge / discharge cycle at a high potential, and the eluted transition metal element has low air permeability (ion It is considered that the charge / discharge reaction at the negative electrode is hindered by passing through the separator having high permeability and depositing on the negative electrode.

  Further, even when the porosity of the separator is 60% or more, cycle deterioration occurs. The reason for this is also not clear, but is considered to be due to the same reason as when the air permeability of the separator is less than 60 seconds / 100 ml. For this reason, the porosity of the separator is preferably less than 60%.

In order to sufficiently obtain the effects of the present invention, the amount of zirconium is set to 0.0001 ≦ x in Li _a Co _1-xyz Zr _x Mg _y M _z O ₂ . In order to sufficiently obtain the effects of the present invention, the amount of magnesium added is 0.0001 ≦ y. Further, in addition to zirconium and magnesium, Al, Ti, and Sn may be added in a ratio of 0.0002 ≦ z. However, if the total x + y + z of the added metals is larger than 0.03, the battery capacity is decreased, which is preferable. Absent.

Further, in order to obtain the effect of the present invention _{sufficiently, Li b Mn s Ni t Co} u X v in _{O 2,} the nickel content was set to 0.1 ≦ s ≦ 0.5, the manganese content is 0 .1 ≦ t ≦ 0.5. Further, in order to obtain high thermal stability, it is preferable that the ratio s / t of nickel to manganese is in the range of 0.95 to 1.05. Further, in order to further increase the thermal stability of the compound, a different element such as Zr, Mg, Al, Ti, or Sn may be added at a ratio of 0.0001 ≦ v ≦ 0.03.

  In addition, when the content of the lithium cobalt composite oxide in the positive electrode active material is less than 51% by mass, the battery capacity, cycle characteristics, and storage characteristics may be deteriorated, and the lithium nickel manganese composite oxide having a layered structure may be deteriorated. When the content is less than 10% by mass, the effect of improving the thermal stability of the positive electrode active material at a high potential cannot be sufficiently obtained. For this reason, the mass ratio of the lithium cobalt composite oxide and the layered lithium nickel manganese composite oxide is 51:49 to 90:10, and more preferably 70:30 to 80:20.

  In the above configuration, the negative electrode active material may be made of a carbonaceous material.

  The battery voltage is indicated by the difference between the positive electrode potential and the negative electrode potential. By increasing the battery voltage, the battery capacity can be increased, but the negative electrode active material is a low-potential carbonaceous material (lithium reference). About 0.1 V), a battery having a high battery voltage and a high utilization rate of the positive electrode active material can be obtained.

  As the carbonaceous material, natural graphite, artificial graphite, carbon black, coke, glassy carbon, carbon fiber, or one or a mixture of these fired bodies can be used.

  Moreover, in the said structure, 0.5-5 mass% of vinylene carbonate can further be included in the said nonaqueous electrolyte.

  When vinylene carbonate is added to the nonaqueous electrolyte, cycle characteristics are improved. However, if the added amount is too small, a sufficient effect cannot be obtained. On the other hand, if the added amount is too large, the initial capacity is lowered and the battery thickness swells particularly at a rectangular battery. For this reason, the addition amount is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass with respect to the total mass of the nonaqueous electrolyte.

  Moreover, in the said structure, the said lithium nickel manganese complex oxide shall contain cobalt in the crystal structure.

  When cobalt is contained in the crystal structure of the lithium nickel manganese composite oxide, this cobalt is preferable in that it acts to improve discharge characteristics. The amount added is preferably 0.1 ≦ u ≦ 0.8 in the above chemical formula.

Further, the present invention relating to a method for charging a non-aqueous electrolyte secondary battery for solving the above-described problem is a non-aqueous electrolyte having a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a non-aqueous solvent, and an electrolyte salt. A positive electrode active material, wherein Li _a Co _1-xy- Zr _x Mg _y M _z O ₂ (M is at least one of Al, Ti, and Sn, and 0 <a ≦ 1) .1, 0.0001 ≦ x, 0.0001 ≦ y, x + y + z ≦ 0.03), and a lithium cobalt composite oxide to which zirconium and magnesium are added, and Li _b Mn _s N _t Co _u X _v O ₂ (X is at least one of Zr, Mg, Al, Ti, Sn, 0 <b ≦ 1.1, 0.1 ≦ s ≦ 0.5, 0.1 ≦ t ≦ 0.5, v = 0 or 0.0001 ≦ v ≦ 0.03, layer represented by s + t + u + v = 1) Lithium nickel manganese composite oxide having a structure is mixed at a mass ratio of 51:49 to 90:10, and the air permeability of the separator is 60 seconds / 100 ml or more and 400 seconds / 100 ml or less, A method for charging a non-aqueous electrolyte secondary battery in which the porosity of the separator is less than 60%, wherein charging is performed until the potential of the positive electrode active material is 4.4 to 4.6 V based on lithium. To do.

  By adopting the above method, it is possible to charge a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics at a high potential.

  As described above, according to the present invention, it is possible to stably function at a high potential of 4.4 to 4.6 V on the basis of lithium and to suppress high-temperature cycle deterioration at a high potential, and to have a high capacity and safety. It is possible to provide a non-aqueous electrolyte secondary battery that is excellent in performance.

  The best mode for carrying out the present invention will be described in detail with reference to examples. In addition, this invention is not limited to the following form, In the range which does not change the summary, it can change suitably and can implement.

Example 1
<Preparation of positive electrode>
Co-precipitation of 0.2 mol% of zirconium (Zr) with respect to cobalt (Co) and 0.5 mol% of magnesium (Mg) with respect to cobalt, followed by thermal decomposition reaction, gave zirconium and magnesium-containing trioxide. Cobalt was obtained. This tricobalt tetroxide and lithium carbonate are mixed, calcined in an air atmosphere at 850 ° C. for 24 hours, and then pulverized in a mortar until the average particle size becomes 14 μm. A positive electrode active material A) was obtained.

Lithium carbonate and a coprecipitated hydroxide represented by Ni _0.33 Mn _0.33 Co _0.34 (OH) ₂ are mixed, baked at 1000 ° C. for 20 hours in an air atmosphere, and then ground in an mortar until the average particle size becomes 5 μm. Thus, a cobalt-containing lithium nickel manganese composite oxide (positive electrode active material B) was obtained. In addition, when the X-ray crystal structure diffraction of this positive electrode active material B was performed, it was confirmed that it is a layered structure.

  94 parts by mass of a positive electrode active material obtained by mixing the positive electrode active material A and the positive electrode active material B at a mass ratio of 7: 3, 3 parts by mass of carbon powder as a conductive agent, and polyvinylidene fluoride (PVdF) 3 as a binder Mass parts and N-methylpyrrolidone were mixed to obtain a positive electrode active material slurry. This positive electrode active material slurry was applied on both sides of an aluminum positive electrode current collector (thickness 15 μm), dried and rolled to produce a positive electrode.

<Preparation of negative electrode>
A negative electrode active material slurry was prepared by mixing 95 parts by mass of graphite as a negative electrode active material, 3 parts by mass of carboxymethyl cellulose as a thickener, 2 parts by mass of styrene butadiene rubber as a binder, and water. This negative electrode active material slurry was applied to both sides of a copper negative electrode current collector (thickness 8 μm), dried and rolled to produce a negative electrode.

  The potential of graphite is 0.1 V with respect to lithium. The positive electrode and negative electrode active material filling amounts are the positive electrode and negative electrode charge capacities at the potential of the positive electrode active material which is a design standard (in this example, 4.4 V based on lithium and the battery voltage is 4.3 V). The ratio (negative electrode charge capacity / positive electrode charge capacity) was adjusted to 1.1.

<Preparation of separator>
The polyethylene mixture, the inorganic fine powder, and the plasticizer were formed into a sheet shape while kneading and heating and melting, and then the inorganic fine powder and the plasticizer were extracted and removed, and then dried. Thereafter, the separator was stretched to produce a separator having an air permeability of 60 seconds / 100 ml and a porosity of 50%.

(Measurement of air permeability)
The air permeability was measured by measuring the time (seconds) for 100 ml of air to pass according to JIS P-8117, using a Toyo Seiki Gurley Densometer.

[Measurement of porosity]
The separator was cut into 10 cm square, and its thickness t and weight W were measured. And the density (%) of the separator material was set to p, and porosity (%) was computed by the following formula. (In the case of polyethylene, p = 0.95 g / cm ³ )

  Porosity (%) = {1- (W / p) / (10 × 10 × t)} × 100

<Production of electrode body>
An electrode body was produced by winding the positive electrode and the negative electrode through the separator.

<Adjustment of non-aqueous electrolyte>
Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC) as a nonaqueous solvent are mixed at a volume ratio of 20:30:50 (25 ° C.), and LiPF ₆ as an electrolyte salt is mixed with 1 M (mol). / Liter) to prepare an electrolyte solution. 2 parts by mass of vinylene carbonate was added to 100 parts by mass of this electrolytic solution to obtain a nonaqueous electrolyte.

<Assembly of battery>
After the electrode body is inserted into the outer can, the nonaqueous electrolyte is injected, and the opening of the outer can is sealed, whereby the nonaqueous electrolyte secondary battery according to Example 1 (width 34 mm × height 43 mm × A thickness of 5 mm and a discharge capacity of 800 mAh) were produced.

(Example 2)
A nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same manner as in Example 1 except that a separator having an air permeability of 200 seconds / 100 ml and a porosity of 44% was used.

(Example 3)
A nonaqueous electrolyte secondary battery according to Example 3 was produced in the same manner as in Example 1 except that a separator having an air permeability of 400 seconds / 100 ml and a porosity of 45% was used.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that a separator having an air permeability of 50 seconds / 100 ml and a porosity of 55% was used.

(Comparative Example 2)
A nonaqueous electrolyte secondary battery according to Comparative Example 2 was produced in the same manner as in Example 1 except that a separator having an air permeability of 500 seconds / 100 ml and a porosity of 48% was used.

(Comparative Example 3)
A nonaqueous electrolyte secondary battery according to Comparative Example 3 was produced in the same manner as in Example 1 except that the positive electrode active material A alone was used as the positive electrode active material.

(Comparative Example 4)
A nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same manner as in Example 2 except that the positive electrode active material A alone was used as the positive electrode active material.

(Comparative Example 5)
A nonaqueous electrolyte secondary battery according to Comparative Example 5 was produced in the same manner as in Example 3 except that the positive electrode active material A alone was used as the positive electrode active material.

(Comparative Example 6)
A nonaqueous electrolyte secondary battery according to Comparative Example 6 was produced in the same manner as Comparative Example 1 except that the positive electrode active material A alone was used as the positive electrode active material.

(Comparative Example 7)
A nonaqueous electrolyte secondary battery according to Comparative Example 7 was produced in the same manner as Comparative Example 2 except that the positive electrode active material A alone was used as the positive electrode active material.

(Comparative Example 8)
A nonaqueous electrolyte secondary battery according to Comparative Example 8 was produced in the same manner as in Example 1 except that a separator having an air permeability of 60 seconds / 100 ml and a porosity of 60% was used.

(Comparative Example 9)
A nonaqueous electrolyte secondary battery according to Comparative Example 9 was produced in the same manner as Comparative Example 8 except that the positive electrode active material A alone was used as the positive electrode active material.

  The physical properties of the separator were controlled by changing the addition amount / particle size of the fine inorganic powder and stretching conditions.

[Battery characteristics test]
About each said battery, the high temperature cycling characteristic test and the heating test were done on condition of the following. The results are shown in Table 1 below.

[High-temperature cycle characteristics test]
Charging conditions: Constant current 1 It (800 mA) up to 4.4 V, constant voltage 4.4 V up to 1/50 It (16 mA), 25 ° C.
Discharge conditions: constant current 1 It, end voltage 3.0 V, 45 ° C.
High temperature cycle characteristics (%): (200th cycle discharge capacity / 1st cycle discharge capacity) × 100

[Heating test]
Charging conditions: Constant current 1 It (800 mA) up to 4.4 V, constant voltage 4.4 V up to 1/50 It (16 mA), 25 ° C.
Heating conditions: From 25 ° C. to 150 ° C. at a rate of 5 ° C./min in an oven, then left at 150 ° C. for 10 minutes Evaluation: Impossible to burn all batteries (x), good not to burn all (○)
n (number of specimens) = 3.

  From Table 1 above, in Comparative Examples 3 to 7 and Comparative Example 9 using only zirconium and magnesium-added lithium cobalt composite oxide (positive electrode active material A) as the positive electrode active material, all the heating test results are not possible. In Examples 1 to 3, Comparative Example 1, Comparative Example 2, and Comparative Example 8 using a mixture of the positive electrode active material A and the layered lithium nickel manganese composite oxide (positive electrode active material B) as the positive electrode active material, heating is performed. It turns out that all the test results are good.

  This is considered as follows. Zirconium and magnesium-added lithium-cobalt composite oxides do not have sufficient thermal stability at high potential, and the active material deteriorates due to storage at an abnormally high temperature of 150 ° C at a high potential (4.5 V on a lithium basis). To do. Thereby, reaction with a nonaqueous electrolyte and a positive electrode is accelerated | stimulated, the emitted-heat amount inside a battery increases, and the battery which concerns on Comparative Examples 3-7 and Comparative Example 9 burns.

  On the other hand, when the lithium nickel manganese composite oxide (positive electrode active material B) having a layered structure is included in the positive electrode active material, this compound acts to drastically improve the thermal stability at a high potential. For this reason, in Examples 1-3, Comparative Example 1, Comparative Example 2, and Comparative Example 8, the active material does not deteriorate, heat generation inside the battery is suppressed, and combustion does not occur.

  In Comparative Examples 3 to 7 using only the positive electrode active material A and using a separator with a porosity of less than 60%, the cycle characteristics may tend to improve as the air permeability of the separator decreases. Recognize.

  On the other hand, in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 using a mixture of positive electrode active material A and positive electrode active material B as a positive electrode active material and a separator having a porosity of 55% or less In the range of 60 to 500 seconds / 100 ml of air permeability, the same tendency as in Comparative Examples 3 to 7 is observed, but when the air permeability becomes 50 seconds / 100 ml, the high temperature cycle characteristics are 43% (Comparative Example). It can be seen that 1) and the air permeability is inferior to 63 to 68% (Examples 1 to 3 and Comparative Example 2) in the range of 60 to 400 seconds / 100 ml.

  This is considered as follows. Zirconium and magnesium-containing lithium cobalt composite oxides are difficult to elute transition metal elements from the crystals due to high-temperature charge / discharge cycles at high potentials. , Transition metal elements (Co, Ni, Mn) are easily removed from the crystal. Here, when the air permeability of the separator is 50 seconds / 100 ml, since the air permeability is low and the ion permeability is high, the eluted transition metal element also passes through the pores of the separator and moves to the negative electrode to move to the negative electrode surface. It precipitates in. As a result, the charge / discharge reaction is hindered and cycle deterioration occurs.

  In Example 1, Comparative Example 4, Comparative Example 8, and Comparative Example 9 using a separator having an air permeability of 60 seconds / ml, a mixture of positive electrode active material A and positive electrode active material B as the positive electrode active material Example of using only positive electrode active material A as a separator and / or positive electrode active material having a high temperature cycle characteristic of 32% and a porosity of 50% or less in Comparative Example 8 using a separator having a porosity of 60% 1, Comparative Example 4 and Comparative Example 9 are found to be degraded more than 68-79%.

  This is because, in the layered lithium nickel manganese composite oxide, the air permeability is 50 seconds / 100 ml or less even when the porosity of the separator is 60% or more due to a high temperature charge / discharge cycle at a high potential. Similarly, it is considered that the transition metal element easily escapes from the crystal and causes the above-described problem.

(Other matters)
In the present invention, since the battery shape is not limited, a cylindrical outer can, a coin outer body, and a laminated outer body can be used in addition to the rectangular outer can.

  In addition to diethyl carbonate (DEC), propylene carbonate, γ-butyrolactone, dimethyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, 1,3-dioxolane, 2-methoxytetrahydrofuran, diethyl ether and the like are used as the nonaqueous solvent. be able to.

As the electrolyte salt, in addition to the above LiPF ₆ , one kind or a mixture of plural kinds such as LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiClO ₄ , LiBF ₄ can be used.

  Moreover, in the said Example, although polyethylene was used as a separator material, you may use another olefin type material (for example, polypropylene). Further, a polymer alloy or a laminate of a plurality of types of polymers may be used.

  As described above, according to the present invention, it is possible to realize a nonaqueous electrolyte secondary battery in which the positive electrode active material is highly stable at a high potential and has excellent cycle characteristics. Therefore, industrial applicability is great.

Claims (5)

In a nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt,
The positive electrode active material is Li _a Co _1-xy- Zr _x Mg _y M _z O ₂ (M is at least one of Al, Ti, and Sn, and 0 <a ≦ 1.1, 0.0001 ≦ x, 0.0001 ≦ y, x + y + z ≦ 0.03), a lithium cobalt composite oxide to which zirconium and magnesium are added,
_{Li b Mn s Ni t Co u} X v O 2 (X is Zr, Mg, Al, Ti, at least one of Sn, 0 <b ≦ 1.1,0.1 ≦ s ≦ 0.5,0.1 ≦ lithium nickel manganese composite oxide having a layered structure represented by t ≦ 0.5, v = 0 or 0.0001 ≦ v ≦ 0.03, s + t + u + v = 1),
Are mixed at a mass ratio of 51:49 to 90:10,
The positive electrode active material has a potential of 4.4 to 4.6 V based on lithium,
The air permeability of the separator is 60 seconds / 100 ml or more and 400 seconds / 100 ml or less,
The separator has a porosity of less than 60%,
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1,
The non-aqueous electrolyte contains 0.5 to 5% by mass of vinylene carbonate,
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1 or 2,
The negative electrode active material is made of a carbonaceous material,
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1, 2 or 3,
The lithium nickel manganese composite oxide contains cobalt in its crystal structure,
A non-aqueous electrolyte secondary battery. A positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt,
The positive electrode active material is Li _a Co _1-xy- Zr _x Mg _y M _z O ₂ (M is at least one of Al, Ti, and Sn, and 0 <a ≦ 1.1, 0.0001 ≦ x, 0.0001 ≦ y, x + y + z ≦ 0.03), a lithium cobalt composite oxide to which zirconium and magnesium are added,
_{Li b Mn s Ni t Co u} X v O 2 (X is Zr, Mg, Al, Ti, at least one of Sn, 0 <b ≦ 1.1,0.1 ≦ s ≦ 0.5,0.1 ≦ lithium nickel manganese composite oxide having a layered structure represented by t ≦ 0.5, v = 0 or 0.0001 ≦ v ≦ 0.03, s + t + u + v = 1),
Are mixed at a mass ratio of 51:49 to 90:10,
The air permeability of the separator is 60 seconds / 100 ml or more and 400 seconds / 100 ml or less,
A method for charging a non-aqueous electrolyte secondary battery, wherein the porosity of the separator is less than 60%,
Charging until the potential of the positive electrode active material is 4.4 to 4.6 V with respect to lithium;
A non-aqueous electrolyte secondary battery charging method.