JP4530843B2 - Nonaqueous electrolyte secondary battery and charging method thereof - Google Patents

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, there has been a demand for higher capacity of batteries, and attempts have been made to increase the active material utilization rate by charging and using the positive electrode active material to a higher potential.

  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 has a problem that thermal stability at a high potential is not sufficient, and the electrolytic solution (liquid non-aqueous electrolyte) is decomposed on the conductive agent contained in the positive electrode by a charge / discharge cycle, causing cycle deterioration. There is.

  Patent Documents 1 to 7 have been proposed as techniques relating to such a non-aqueous electrolyte secondary battery.

JP 2001-102055 A (Claim 1, paragraphs 0003-0006) JP 2001-283860 A (Claim 1, paragraphs 0006-0009) JP 2003-86174 A (Claim 1, paragraphs 0015 and 0016) JP 2004-207034 A (Claim 1, paragraphs 0007-0011) Japanese Patent Laying-Open No. 2004-71518 (Claim 1, paragraphs 0008 and 0009) JP-A-10-233205 (Claim 1, paragraphs 0006-0008) JP-A-10-284056 (Claim 1, paragraphs 0006-0014)

Patent Document 1 has a specific surface area of 500 m ² / g or less, P = D _SEM / D _BET [D _SEM : particle diameter observed with a scanning electron microscope (SEM), D _BET = 6 / (S × ρ), D _BET : specific surface area converted particle diameter, S: specific surface area ρ: density], and a technique using a conductive agent having a surface irregularity (P) of 1 ≦ P ≦ 3. It is said that the decomposition of can be suppressed.

Patent Document 2 is a technique using carbon black having an average particle diameter measured by SEM of 60 to 100 nm and a specific surface area measured by BET method of 20 to 30 m ² / g as a conductive agent. Suppresses the decrease in adhesion between the active material and the positive electrode current collector, prevents the electrolyte solution on the negative electrode side from gradually moving to the positive electrode side, prevents uneven charge / discharge reactions, improves cycle characteristics, It is said that deterioration of characteristics can be suppressed.

Patent Document 3 is a technology for adhering 0.5 to 6 wt% of a carbon material having a BET specific surface area of 29 m ² / g or more to the surface of the positive electrode active material. According to this technology, the carbon material is evenly distributed between the positive electrode active materials. It is said that the transfer of electrons between the active materials can be performed smoothly.

Patent Document 4 discloses a first acetylene black having a specific surface area of 35 m ² / g or more and 45 m ² / g or less as a conductive additive, and a ^second acetylene black having a specific surface area of 65 m ² / g or more and 75 m ² / g or less. Is a technology for containing 1% by mass to 2% by mass with respect to the mass of the positive electrode active material. According to this technology, the electron conductivity and the liquid absorbency of the electrolyte are improved, and sufficient load performance In addition, a nonaqueous electrolyte secondary battery having cycle performance can be provided.

Patent Document 5 is a technique that uses a conductive assistant of fine graphite having a specific area of 30 m ² / g or more and 300 m ² / g. According to this technique, when preparing a slurry or paste, dispersibility is good, When incorporated into a battery, it is said that the electrolyte solution can be held well on the particle surface.

Patent Document 6 discloses that a flaky graphite powder in which a graphite powder having an average particle diameter of 1 to 50 μm and a specific surface area of 5 to 50 m ² / g is formed into a flaky shape having a thickness of 1 μm or less is used as a conductive substance for a positive electrode mixture. It is a technique to be added within the range of 0.5 to 9.5% by weight, and according to this technique, it is said that the battery capacity and cycle characteristics of the nonaqueous electrolyte secondary battery can be greatly improved.

Patent Document 7 discloses that at least one of a positive electrode and a negative electrode has an electrode active material and a specific surface area (BET method) of 5 to 50 m ² / g, an average particle diameter of 1 to 50 μm, and an interplanar spacing in X-ray diffraction. Technology using natural scaly graphite or expanded graphite having d (002) of 0.333 to 0.340 nm, crystallite size of 40 to 500 nm in the c-axis direction (Lc), and 40 to 500 nm in the a-axis direction (La) According to this technique, even when the volume change of the electrode active material occurs, the electron conductivity can be secured between the electrode active material and the current collector, and the electrolyte decomposes on the surface of the carbonaceous material, so that carbon dioxide gas It can be said that generation of gas such as hydrocarbons and hydrocarbons and generation of a film such as hydrocarbons on the surface of the carbonaceous material can be suppressed.

  However, none of the techniques according to Patent Documents 1 to 7 consider use of the positive electrode active material at a high potential, and further improvements are required in this respect.

  This invention is made | formed in view of the above, Comprising: It aims at providing the high capacity | capacitance and the nonaqueous electrolyte secondary battery excellent in cycling characteristics.

The present invention related 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, 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, and 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, 0. 95 ≦ s / t ≦ 1.05, v = 0 or 0.0001 ≦ v 0.03, s + t + u + v = 1) and the lithium-nickel-manganese composite oxide having a layered structure represented by, but a weight ratio 51: 49 to 90: is mixed at 10 a rate of result, the potential of the positive electrode active material It is 4.4-4.6V on lithium basis, The said positive electrode further has 0.1-5 mass% of carbon materials whose specific surface area is 2-50 m < ² > / g as a electrically conductive agent, It is characterized by the above-mentioned.

  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, 0.95 ≦ s / t ≦ 1.05, v = 0 or 0.0001 ≦ v ≦ 0.03, s + t + u + v = 1) Is. 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.

Moreover, in the said structure, a positive electrode contains 0.1-5 mass% of carbon materials whose specific surface area is 2-50 m < ² > / g as a electrically conductive agent. When the specific surface area of the conductive agent is less than 2 m ² / g, the conductive path of the positive electrode is not satisfactorily formed. On the other hand, when the specific surface area is larger than 50 m ² / g, decomposition of the electrolytic solution on the conductive agent due to a charge / discharge cycle at a high potential cannot be sufficiently suppressed. By using a conductive agent made of a carbon material whose specific surface area is regulated within the above range, the decomposition reaction of the electrolytic solution on the positive electrode conductive agent can be suppressed, and the conductive path between the active materials can be kept good. A battery having excellent cycle characteristics can be realized.

  On the other hand, if the content of the conductive agent is less than 0.1% by mass, the conductive path becomes rough, so that the cycle characteristics are deteriorated. On the other hand, when the content of the conductive agent is more than 5% by mass, the amount of the positive electrode active material is decreased, so that the discharge capacity is decreased. For this reason, it is preferable that the content of the conductive agent is regulated within the above range.

  As the carbon material, acetylene black, thermal black, furnace black, natural graphite, artificial graphite, or a mixture of plural kinds thereof can be used.

In order to obtain the effect of the present invention sufficiently, the addition amount of zirconium, in _{Li a Co 1-x-y} -z Zr x Mg y M z O 2, and 0.0001 ≦ x. Further, in order to obtain the effect of the present invention sufficiently, the addition amount of magnesium, and at 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 and .1 ≦ t ≦ 0.5. In order to obtain high thermal stability, the ratio s / t of nickel and manganese 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.

Here, in the above configuration, the specific surface area of the carbon material can be 20 m ² / g or more.

When the specific surface area of the carbon material is 20 m ² / g or more, it is preferable in that the positive electrode has a large effect of improving the conductivity and the load characteristics are improved.

  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 decreases and the battery thickness swells particularly at a high temperature at a high temperature. 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, 0.95 ≦ s / t ≦ 1.05, v = 0 or 0.0001 ≦ v ≦ 0.03, + T + u + v = 1) and a lithium nickel manganese composite oxide having a layered structure represented by a mass ratio of 51:49 to 90:10, and the positive electrode further has a specific surface area as a conductive agent. A method for charging a non-aqueous electrolyte secondary battery having 0.1 to 5% by mass of a carbon material of ^{2 to} 50 m ² / g, wherein the potential of the positive electrode active material is 4.4 to 4.6 V based on lithium. It is characterized by charging up to.

  By adopting the above method, it is possible to provide a nonaqueous electrolyte secondary battery having a high capacity and excellent discharge performance at a high potential.

  According to the present invention, the stability of the positive electrode active material at a high potential is high, and the decomposition of the electrolyte solution at a high potential can be suppressed, thereby realizing a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics. be able to.

  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 acetylene black having a specific surface area of 40 m ² / g as a conductive agent, and a binder As a positive electrode active material slurry, 3 parts by mass of polyvinylidene fluoride (PVdF) and N-methylpyrrolidone were mixed. 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 active material potential (designated as 4.4 V on the lithium basis and 4.3 V battery voltage in this example), and the positive and negative electrode charge capacities. The ratio (negative electrode charge capacity / positive electrode charge capacity) was adjusted to 1.1.

<Production of electrode body>
The positive electrode and the negative electrode were wound through a separator made of a polypropylene microporous film to produce an electrode body.

<Adjustment of 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 obtain an electrolytic solution.

<Assembly of battery>
After the electrode body is inserted into the outer can, the electrolyte solution 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 × thickness). 5 mm).

(Example 2)
The above examples except that the potential of the positive electrode active material as a design standard was changed to 4.5 V, and the active material filling amount of the positive electrode and the negative electrode was adjusted so that the charge capacity ratio of the positive electrode and the negative electrode was 1.1. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery according to Example 2 was produced.

(Example 3)
The above examples except that the potential of the positive electrode active material serving as the design standard is changed to 4.6 V and the active material filling amount of the positive electrode and the negative electrode is adjusted so that the charge capacity ratio between the positive electrode and the negative electrode is 1.1. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery according to Example 3 was produced.

Example 4
A nonaqueous electrolyte secondary battery according to Example 4 was produced in the same manner as in Example 2 except that acetylene black having a specific surface area of 15 m ² / g was used as the conductive agent.

(Example 5)
A nonaqueous electrolyte secondary battery according to Example 5 was produced in the same manner as in Example 2 except that acetylene black having a specific surface area of 18 m ² / g was used as the conductive agent.

(Example 6)
As a conductive agent, except that the specific surface area of acetylene black was used a 20 m ² / g, in the same manner as in Example 2, was used to fabricate a non-aqueous electrolyte secondary cell according to example 6.

(Example 7)
A nonaqueous electrolyte secondary battery according to Example 7 was produced in the same manner as in Example 2 except that acetylene black having a specific surface area of 32 m ² / g was used as the conductive agent.

(Example 8)
A nonaqueous electrolyte secondary battery according to Example 8 was produced in the same manner as in Example 2 except that acetylene black having a specific surface area of 50 m ² / g was used as the conductive agent.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 2 except that acetylene black having a specific surface area of 53 m ² / g was used as the conductive agent.

(Comparative Example 2)
As a conductive agent, the specific surface area, except for using acetylene black as a 67m ² / g, in the same manner as in Example 2, was used to fabricate a non-aqueous electrolyte secondary cell according to comparative example 2.

(Comparative Example 3)
Except that the positive electrode active material potential as a design standard was changed to 4.3 V and the active material filling amount of the positive electrode and the negative electrode was adjusted so that the charge capacity ratio between the positive electrode and the negative electrode was 1.1. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery according to Comparative Example 3 was produced.
(Comparative Example 4)
Except that the positive electrode active material potential as a design standard was changed to 4.7 V and the active material filling amount of the positive electrode and the negative electrode was adjusted so that the charge capacity ratio between the positive electrode and the negative electrode was 1.1. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced.

  The specific surface area of the conductive agent was controlled by changing the average particle size or modifying the surface.

[Relationship between potential and charge capacity per gram of positive electrode active material]
A tripolar cell (counter electrode: lithium metal, reference electrode: lithium metal) using the positive electrode prepared in Example 1 was prepared, and the positive electrode charge capacity per gram of active material at each charging potential at 25 ° C. was measured. The results are shown in Table 1 below.

  In the said Examples 1-8 and Comparative Examples 1-4, the positive electrode charge capacity in the electric potential used as a design standard was computed from the said Table 1, and the negative electrode charge capacity was computed from the theoretical capacity | capacitance of graphite.

<Battery characteristics test>
The above battery was tested for battery characteristics under the following conditions. The results are shown in Table 2 below.

[High temperature storage test]
Charging conditions: constant current 1 It (battery capacity divided by 1 hour), constant voltage (battery voltage of each battery), total 3 hours, 25 ° C
Storage conditions: 100 ° C., 72 hours Discharge conditions: constant current 1 It, final voltage 3.0 V, 25 ° C.
Storage characteristics (%): (discharge capacity after storage / discharge capacity before storage) × 100

[Cycle characteristic test]
Charging conditions: constant current 1 It (battery capacity divided by 1 hour), constant voltage (battery voltage of each battery), total 3 hours, 25 ° C
Discharge conditions: constant current 1 It, final voltage 3.0 V, 25 ° C.
Cycle characteristics (%): (300th cycle discharge capacity / first cycle discharge capacity) × 100

[Load characteristic test]
Load discharge conditions: constant current 2.5 It (battery capacity / value expressed by 1 hour × 2.5), final voltage 3.0 V, 25 ° C.
Load characteristics (%): (Load discharge capacity / 1 It discharge capacity) × 100

  From Table 2 above, in Examples 1 to 3 where the battery voltage is 4.3 to 4.5 V, the battery capacity is 820 to 910 mAh, compared to 770 mAh of Comparative Example 3 where the battery voltage is 4.2 V. It can be seen that is increased by 50 to 140 mAh.

  This is considered as follows. In Examples 1 to 3, since the positive electrode is charged to a higher potential than that of Comparative Example 3, and the utilization rate of the positive electrode active material is increased, the battery capacity is increased.

  Moreover, in the comparative example 4 whose battery voltage is 4.6V, cycling characteristics are 68% and deteriorated much more than 84-85% of Examples 1-3 whose battery voltage is 4.3-4.5V. I understand that.

  This is considered as follows. When the battery voltage is as high as 4.6 V, the stability of the positive electrode active material is lowered and the active material is deteriorated. For this reason, cycle deterioration becomes large. On the other hand, when the battery voltage is in the range of 4.3 to 4.5 V, the active material does not deteriorate. In addition, when each battery after a cycle characteristic test was decomposed | disassembled, although deterioration of the active material was not seen in Examples 1-3, it was confirmed in Comparative Example 4 that the active material has deteriorated greatly.

In Comparative Examples 1 and ² where the specific surface area of the conductive agent is 53 to 67 m ² / g, the storage characteristics are 72% and 73%, the cycle characteristics are 74% and 63%, and the specific surface area of the conductive agent is It turns out that it is deteriorated more than 83-85% of Example 2 and Examples 4-8 which are 15-50 m < ² > / g, 88-92%.

This is considered as follows. If the specific surface area of the conductive agent is larger than 50 m ² / g, the decomposition reaction of the electrolytic solution on the conductive agent cannot be suppressed, so that the cycle deterioration becomes large. On the other hand, when the specific surface area of the conductive agent is 50 m ² / g or less, the decomposition reaction of the electrolytic solution can be sufficiently suppressed, so that cycle deterioration does not occur. In addition, when each battery after the cycle characteristic test was disassembled, in Examples 2 and 4 to 7, the electrolyte solution was not deteriorated, but in Comparative Examples 1 and 2, the electrolyte solution was decomposed. It was confirmed that

In Examples 4 and 5 where the specific surface area of the conductive agent is 15 to 18 m ² / g, the load characteristics are 75% and 78%, and the specific surface area of the conductive agent is 20 to 50 m ² / g. It turns out that it deteriorates slightly from 83-85% of Example 2 and Examples 6-8.

This is considered to be because when the specific surface area of the conductive agent is less than 20 m ² / g, the effect of improving the conductivity of the positive electrode is reduced and the load characteristics are reduced.

(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.

  Nonaqueous solvents include diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, 1,3-dioxolane, 2-methoxytetrahydrofuran, diethyl ether, etc. Can be used.

As the electrolyte salt, in addition to the above LiPF ₆ , one 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.

As described above, according to the present invention, the high capacity capable of stably functioning at a high potential of 4.4 to 4.6 V on the basis of lithium and suppressing the decomposition of the electrolytic solution even at a high potential. Thus, a non-aqueous electrolyte secondary battery having excellent cycle characteristics can be provided. Therefore, industrial applicability is great.

Claims (6)

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-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), 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, 0.95 ≦ s / t ≦ 1.05, v = 0 or 0.0001 ≦ v ≦ 0.03, and s + t + u + v = 1) When,
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 positive electrode further has 0.1 to 5% by mass of a carbon material having a specific surface area of ² to 50 m ² / g as a conductive agent.
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1,
The specific surface area of the carbon material is 20 m ² / g or more,
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 non-aqueous electrolyte further includes 0.5 to 5% by mass of vinylene carbonate.
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1, 2, 3 or 4,
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-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), 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, 0.95 ≦ s / t ≦ 1.05, v = 0 or 0.0001 ≦ v ≦ 0.03, and s + t + u + v = 1) When,
Are mixed at a mass ratio of 51:49 to 90:10,
The positive electrode is a method for charging a non-aqueous electrolyte secondary battery further comprising 0.1 to 5% by mass of a carbon material having a specific surface area of ² to 50 m ² / g as a conductive agent,
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.