JP4530845B2 - 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.

  In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and non-aqueous electrolyte secondary batteries having high energy density and high capacity have been used as driving power sources. Widely used.

  Non-aqueous electrolyte secondary batteries that use a carbonaceous material that inserts and desorbs lithium as the negative electrode do not exist in a metallic state, and the precipitation of dendritic lithium is suppressed, so battery life and safety Excellent in properties. Of these, graphite is preferable because it can increase the battery capacity, but in recent years, there has been a demand for higher capacity of the battery. There are attempts to increase it.

  However, when lithium cobaltate (lithium-containing cobalt composite oxide), which has been 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. As a result, the cycle characteristics deteriorate.

  In order to solve this problem, it has been proposed to increase the stability at a high potential by adding a different metal such as zirconium or magnesium to lithium cobalt oxide. However, even this technique cannot sufficiently increase the thermal stability at a high potential.

  On the other hand, when a charge / discharge cycle is performed at a high potential, the electrolyte solution (nonaqueous electrolyte) is decomposed on the negative electrode surface, the electrolyte solution around the negative electrode becomes too small, and the charge / discharge reaction at the negative electrode is hindered. Even when a carbonaceous material is used as the active material, there is a problem that lithium is deposited on the negative electrode surface. The deposited lithium further proceeds the decomposition reaction of the electrolytic solution, and the amount of the electrolytic solution around the negative electrode is remarkably reduced (electrolytic solution dripping). For this reason, deposited lithium and electrolytic solution decomposition products are deposited on the negative electrode surface, and the negative electrode is deteriorated. However, when the amount of the electrolytic solution is increased in order to prevent liquid dripping, there is a problem that the energy density of the battery is lowered.

  Here, Patent Documents 1 and 2 have been proposed as techniques relating to the improvement of the negative electrode active material of the nonaqueous electrolyte secondary battery.

JP 2004-95426 A (Claims, paragraphs 0003-0009) JP-A-10-236809 (Claims, paragraphs 0004-0009)

Patent Document 1 discloses that the negative electrode material has a specific surface area of 0.5 to ² m ² / g, a total pore volume of 0.4 to 2.0 ml / g of pores in the range of 10 ¹ to 10 ⁵ nm, a tap density. Main particle graphite particles having a shape formed by assembling or bonding flat particles having a particle size of 0.5 to 1.2 g / cm ^{3 so} that a plurality of orientation planes are non-parallel, mesophase microsphere carbon, and vapor phase growth This is a technique using at least one compounding material selected from carbon fiber graphite. According to this technique, the formation of LiF and Li ₂ CO ₃ compounds on the negative electrode during the charge and discharge, and the formation of metallic lithium It is said that a battery with high capacity, long life and high safety can be obtained.

Patent Document 2 uses, as a negative electrode active material, graphite having a specific surface area of 8 m ² / g or less and a total pore volume of pores in the range of 10 ² to 10 ⁶ Å being 0.4 to 2.0 ml / g. According to this technology, a lithium secondary battery having a large battery capacity, a low self-discharge rate, excellent cycle characteristics, and high charge / discharge efficiency is obtained.

  However, none of the techniques according to the above two documents considers utilizing 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 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, 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 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 4.4 to 4.6 V based on lithium, and the negative electrode active material has a total pore volume of pores in the range of 10 ^{2 to} 10 ⁶ ０．４ of 0.4 to 2.0 ml / g per mass, 60% by mass or more of artificial graphite having a specific surface area of 8 m ² / g or less is included with respect to the total mass of the negative electrode active material.

  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.

Furthermore, as the negative electrode active material, the total pore volume of pores in the range of 10 ² -10 ⁶ Å is 0.4 to 2.0 ml / g per mass and the specific surface area is 8 m ² / g or less. Has graphite particles. This artificial graphite suitably holds the electrolytic solution in pores in the range of 10 ² -10 ⁶ Å by capillary action, so that the electrolytic solution does not spill even during charge / discharge cycles at a high potential. Therefore, the negative electrode does not deteriorate and the cycle characteristics are improved.

Here, since the size of pores smaller than 10 ²過 is too small, and the size of pores larger than 10 ⁶そ れ ぞ れ is too large, the electrolyte solution cannot be suitably held respectively.

Further, when the total pore volume of the pores in the range of 10 ² -10 ⁶ Å of the artificial graphite particles is less than 0.4 ml / g, the electrolyte solution holding performance is not sufficient. On the other hand, if the total pore volume is larger than 2.0 ml / g per mass, the binder is likely to be taken into the pores, so that the binding performance is lowered and the active material is collected by the charge / discharge cycle. Detach from the electric body, causing cycle deterioration. In this case, if the amount of the binder is increased in order to increase the binding force, the discharge reaction at the negative electrode is inhibited by the binder and the discharge capacity is lowered, which is not preferable.

Further, if the specific surface area is excessive, the irreversible capacity of the battery is increased, and the surface of the artificial graphite particles is easily covered with the binder, which is not preferable because the discharge capacity is reduced. Further, if the specific surface area is too small, the conductivity of the negative electrode may be lowered, which is not preferable. Therefore, the specific surface area is preferably 1.5 to 8 m ² / g, more preferably ² to 5 m ² / g.

  The battery voltage is indicated by the difference between the positive electrode potential and the negative electrode potential. By increasing the battery voltage, the capacity of the battery can be increased. Therefore, a battery having a high battery voltage and a high utilization rate of the positive electrode active material can be obtained.

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.

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 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.

  Further, in the above configuration, the artificial graphite is added to and mixed with a graphitizable aggregate and / or graphite, and a graphitizable binder, and a graphitization catalyst that volatilizes at a temperature lower than the firing temperature. It can be assumed that it is obtained after firing.

  In the above method, the graphitizable aggregate and / or graphite serves as a nucleus, and the graphitizable binder incorporating the graphitization catalyst surrounds it. Thereafter, when calcination is performed, the graphitization catalyst is volatilized and desorbed from the binder, so that pores can be formed in the graphite particles.

  Here, volatilization in the present specification means that the graphitization catalyst becomes a gas and desorbs, and its specific reaction such as boiling, sublimation, decomposition, etc. is not limited.

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

The addition of vinylene carbonate in the nonaqueous electrolyte, although the cycle characteristics are improved, whereas the addition amount is not obtained a sufficient effect to be too small, leading to swelling during lowering and high temperature in the initial capacity to be excessive. 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 the lithium-nickel-manganese composite oxide having a layered structure represented by, but a weight ratio 51: 49 to 90: is mixed with 10 ratio of it to the negative electrode active ^material, 10 2 -10 ⁶ Artificial graphite having a total pore volume of 0.4 to 2.0 ml / g per mass and a specific surface area of 8 m ² / g or less is 60 masses with respect to the total mass of the negative electrode active material. % Of the nonaqueous electrolyte secondary battery charging method, wherein the positive electrode active material is charged until the potential of the positive electrode active material becomes 4.4 to 4.6 V with respect to lithium.

  By adopting the above method, it is possible to provide a high energy density non-aqueous electrolyte secondary battery that has a high capacity and is charged and discharged at a high potential.

  As described above, the high-capacity, which functions stably at a high potential of 4.4 to 4.6 V on the basis of lithium, and can suppress the deterioration of the negative electrode and the electrolyte dripping even at a high potential. A non-aqueous electrolyte secondary battery excellent in cycle characteristics can be realized.

  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)
40 parts by mass of coke powder (average particle size 5 μm) as a graphitizable aggregate, 25 parts by mass of tar pitch and 20 parts by mass of coal tar as a graphitizable binder, and silicon carbide 5 as a graphitization catalyst Mass parts (average particle size 45 μm) were mixed, calcined at 2800 ° C. in a nitrogen atmosphere, and then pulverized to obtain artificial graphite having an average particle size of 20 μm. This artificial graphite particle has a total pore volume of 0.7 g / ml in the range of 10 ² to 10 ⁶に よ る by pore distribution measurement using a mercury intrusion method. The average particle size measured as D50 was 20 μm, and the specific surface area measured by the BET method was 4.1 m ² / g.

  The negative electrode active material slurry was prepared by mixing 95 parts by mass of the above artificial 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 artificial graphite is 0.1 V with respect to lithium. The active material filling amount of the positive electrode and the negative electrode is a charge capacity ratio of the positive electrode and the negative electrode (negative electrode charge capacity / positive electrode charge capacity) at a design voltage of 4.4 V (positive electrode potential is 4.5 V based on lithium). 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)
As a negative electrode active material, 40 parts by mass of coke powder (average particle size 5 μm) as aggregates capable of graphitization, 30 parts by mass of tar pitch and 20 parts by mass of coal tar as binders that can be graphitized, graphitization catalyst As in Example 1 except that 4 parts by mass of silicon carbide (average particle size 40 μm) was mixed, calcined at 2800 ° C. in a nitrogen atmosphere, and then pulverized artificial graphite was used. A non-aqueous electrolyte secondary battery according to Example 2 was produced. The artificial graphite has a total pore volume of 0.4 g / ml in the range of 10 ² to 10 ^{6 6} by pore distribution measurement using a mercury intrusion method, an average particle diameter of 20 μm, The specific surface area measured by the BET method was 4.1 m ² / g.

(Example 3)
As a negative electrode active material, 50 parts by mass of coke powder (average particle size: 5 μm) as aggregates capable of graphitization, 20 parts by mass of tar pitch and 20 parts by mass of coal tar as binders that can be graphitized, and graphitization catalyst As in Example 1 except that 8 parts by mass of silicon carbide (average particle size 45 μm) was mixed, calcined at 2800 ° C. in a nitrogen atmosphere, and then used to obtain artificial graphite obtained by pulverization. A non-aqueous electrolyte secondary battery according to Example 3 was produced. This artificial graphite has a total pore volume of 2.0 g / ml in the range of 10 ² to 10 ⁶ 〜１０ by pore distribution measurement using a mercury intrusion method, an average particle diameter of 20 μm, and BET The specific surface area measured by the method was 4.1 m ² / g.

(Comparative Example 1)
A non-aqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that artificial graphite (mesophase small spherical carbon) having an average particle size of 20 μm was used as the negative electrode active material. The mesophase carbon microbeads had a total pore volume of 0.3 g / ml in the range of 10 ² to 10 ⁶に よ る measured by pore distribution measurement using a mercury intrusion method, and were measured by the BET method. The specific surface area was 2.2 m ² / g.

(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 natural graphite having an average particle size of 20 μm was used as the negative electrode active material. This natural graphite has a total pore volume of 2.1 ml / g in the range of 10 ² to 10 ⁶に よ る by pore distribution measurement using a mercury intrusion method, and has a specific surface area measured by the BET method. It was 3.2 m ² / g.

(Comparative Example 3)
As a negative electrode active material, 40 parts by mass of coke powder (average particle size 5 μm) as aggregates capable of graphitization, 30 parts by mass of tar pitch and 20 parts by mass of coal tar as binders that can be graphitized, graphitization catalyst As in Example 1 except that 3 parts by mass of silicon carbide (average particle size: 45 μm) was mixed, calcined at 2800 ° C. in a nitrogen atmosphere, and then pulverized artificial graphite was used. Thus, a non-aqueous electrolyte secondary battery according to Example 3 was produced. This artificial graphite has a total pore volume of 0.9 g / ml in the range of 10 ² to 10 ^{6 6} by pore distribution measurement using a mercury intrusion method, an average particle diameter of 20 μm, The specific surface area measured by the BET method was 8.3 m ² / g.

[Cycle characteristic test]
A cycle characteristic test was performed on each of the batteries under the following conditions. The results are shown in Table 1 below.

Charging conditions: constant current 1 It (850 mA) up to 4.4 V, constant voltage 4.4 V up to 1/50 It (17 mA), 25 ° C.
Discharge conditions: constant current 1 It, final voltage 3.0 V, 25 ° C.
Cycle characteristics (%): (500th cycle discharge capacity / first cycle discharge capacity) × 100

From Table 1 above, in Examples 1 to 3, in which the total pore volume within the range of 10 ² to 10 ⁶ Å is 0.4 to 2.0 ml / g, the cycle characteristics are 78.5 to 80.2%. Compared with 30.2% of Comparative Example 1 where the total pore volume is 0.3 ml / g and 60.5% of Comparative Example 2 where the total pore volume is 2.1 ml / g I understand that.

  This is considered as follows. If the total pore volume is less than 0.4 ml / g, the pore volume is too small, and the amount of the electrolyte solution retained by the graphite particles is too small. Cycle degradation occurs. On the other hand, if the total pore volume is larger than 2.0 ml / g, the total pore volume is excessive, and the binder is taken into the pores, resulting in a decrease in binding performance. As a result, the graphite particles are detached from the current collector, resulting in cycle deterioration.

  On the other hand, when the total pore volume is 0.4 to 2.0 ml / g, the graphite particles can suitably hold the electrolytic solution, and the binder is hardly taken into the pores. Thereby, cycle characteristics are improved.

In Examples 1 to 3 having a specific surface area of 4.1 m ² / g, and the cycle characteristics are 78.5 to 80.2 and a specific surface area of Comparative Example 3 is 8.3 m ² / g 62.3 It turns out that it is excellent compared with%.

This is considered as follows. When the specific surface area is excessive, the binder covers the surface of the negative electrode active material, the binding performance is lowered, and the graphite particles are detached from the current collector, resulting in cycle deterioration. Therefore, the specific surface area is preferably less than 8.3 m ² / g, more preferably 8.0 m ² / g or less.

  In addition, in the battery which concerns on Comparative Examples 1-3, compared with the battery which concerns on Examples 1-3, the internal resistance value measured by the alternating current method (1 kHz) after a cycle characteristic test was rising significantly. This confirms the above consideration.

(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 order to obtain the effects of the present invention, the content of the artificial graphite having specific physical properties is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. Preferably it is 90 mass% or more. A plurality of artificial graphites satisfying the above physical property values may be mixed and used. Furthermore, the average particle diameter of the artificial graphite is preferably 10 to 50 μm.

  In addition, natural graphite as a negative electrode active material, artificial graphite other than the above physical properties, carbon black, coke, glassy carbon, carbon fiber, or one or a mixture of these calcined products are added to artificial graphite having specific physical properties. May be. Among these, it is preferable to use natural graphite or artificial graphite.

  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 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.

<Matters related to artificial graphite production>
The blending amount of the binder is preferably 5 to 80% by mass, more preferably 10 to 80% by mass, and further preferably 15 to 80% by mass with respect to the total mass of the graphitizable aggregate and graphite.

  The addition amount of the graphitization catalyst is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, and further preferably 5 to 30% by mass with respect to the mass of the resulting artificial graphite particles.

  As the aggregate that can be graphitized, a powder material that can be graphitized is preferably used, more preferably, coke or resin carbide powder is used, and more preferably, coke powder that is easily graphitized such as needle coke is used. As the graphite, natural graphite powder and artificial graphite powder can be used. Further, the particle size of graphitizable aggregate or graphite is preferably smaller than the particle size of the artificial graphite particles to be produced.

  In addition, as the graphitizable binder, organic materials such as tar, pitch, thermosetting resin and thermoplastic resin are used. The mixing of the aggregate and the like, the binder, and the catalyst is preferably performed at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar, etc., 50 to 300 ° C. is preferable. When is a thermosetting resin, 20-100 degreeC is preferable.

  Examples of the graphitization catalyst that can be used include metals such as iron, nickel, titanium, silicon, and boron, and carbides and oxides thereof. Of these, silicon or boron carbides or oxides are preferred. The volatilization temperature of the graphitization catalyst is preferably 2800 ° C. or lower.

  As the firing atmosphere, firing is preferably performed under conditions that do not oxidize the mixture. For example, firing is performed in a nitrogen atmosphere, an argon gas atmosphere, or a vacuum. The firing temperature is preferably a temperature at which the binder or the like can be sufficiently graphitized and higher than the volatilization temperature of the graphitization catalyst. Specifically, it is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher, and further preferably 2800 ° C. to 3200 ° C. If the firing temperature is too high, the graphite sublimates and the productivity is lowered.

  In addition, the physical property of artificial graphite can be adjusted by changing each said material, the change of a particle size, and baking conditions.

As described above, according to the present invention, a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics at a high potential can be provided. 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-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,
Artificial graphite in which the negative electrode active material has a total pore volume of 0.4 to 2.0 ml / g per mass and a specific surface area of 8 m ² / g or less in a range of 10 ^{2 to} 10 ⁶ Å. 60% by mass or more based on the total mass of the negative electrode active material,
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1,
The artificial graphite is obtained by mixing and calcining a graphitizable aggregate and / or graphite, a graphitizable binder, and a graphitization catalyst that volatilizes at a temperature lower than the firing temperature. is there,
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1 or 2,
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 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-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,
Artificial graphite in which the negative electrode active material has a total pore volume of 0.4 to 2.0 ml / g per mass and a specific surface area of 8 m ² / g or less in the range of 10 ^{2 to} 10 ⁶ Å. Is a charging method for a non-aqueous electrolyte secondary battery containing 60% by mass or more based on the total mass of the negative electrode active material,
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.