JP2008300180A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with high capacity excellent in charging/discharging output characteristics and output balance. <P>SOLUTION: A nickel/cobalt/manganese composite oxide Li[Li<SB>a</SB>Ni<SB>x</SB>Co<SB>y</SB>Mn<SB>z</SB>]O<SB>2-b</SB>containing lithium is used in a transition metal site as a positive-electrode active material. The ratio n (negative electrode/positive electrode) in the initial charging capacity of the negative electrode to the positive electrode is 0.80≤n≤1.00 when charged until a potential in the positive electrode exceeds 4.45 V (Li/Li<SP>+</SP>), and initial charging is performed until the potential at the positive electrode exceeds 4.45 V (vs. Li/Li<SP>+</SP>). In the formula, the characters x, y, z, a and b satisfy the following relations: 0.1≤a≤0.3, 0<x<0.45, 0<y<0.45, 0.45≤z≤0.82, 0.1≤(x+y)/z≤1, a+x+y+z=1, and 0≤b≤0.25. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery using a lithium nickel cobalt manganese composite oxide containing lithium at a transition metal site as a positive electrode active material.

  In recent years, in order to solve environmental problems caused by exhaust gas, development of HEV (Hybrid Electric Vehicle) using both a gasoline engine and an electric motor of an automobile has been promoted at an international level. As a power source for HEV, a nickel hydride secondary battery has been conventionally used. However, a practical application of a higher voltage and higher capacity lithium ion secondary battery is expected.

  One of the important issues of lithium ion secondary batteries for HEV applications is cost reduction. A composite oxide containing Co is mainly used as a positive electrode active material for lithium-ion secondary batteries for power supplies such as portable electronic devices such as mobile phones, camcorders, and notebook computers that are already in practical use. In view of the above, in a large lithium secondary battery for HEV, a positive electrode material with a low content of expensive metal elements such as Co is desirable.

  Moreover, in the lithium ion secondary battery for HEV use, the recovery of brake regenerative energy is evaluated by the charge side output, and the output to the motor is evaluated by the discharge side output. That is, it is preferable that the values of the charge side output and the discharge side output are close to each other and the charge / discharge output balance is excellent.

However, lithium cobaltate LiCoO ₂ , lithium nickelate LiNiO ₂ , lithium manganese oxide LiMn ₂ O ₄ , Ni—Co—Mn ternary composite oxide, etc., which have been used as positive electrode active materials of lithium ion secondary batteries in the past Since the active material has a capacity region at a high potential in the potential range operating in the battery, there is a problem that the discharge side output is larger than the charge side output, resulting in a battery design with a poor output balance.

  One method for improving the balance between the charge and discharge outputs is to increase the charge side output by increasing the difference between the open circuit voltage of the battery and the upper limit voltage of the battery. For this reason, in the lithium ion secondary battery for HEV use, a battery with a low voltage is desired. In particular, in HEV applications, the entire battery capacity range is not used evenly, but is used mainly in the charging area near 50% depth of charge (SOC), so a battery design with a low charge / discharge voltage in this range is required. It is said.

  In order to solve such problems, as a positive electrode material for lithium ion secondary batteries for HEVs, in recent years, lithium-containing phosphates having an olivine structure, Ni-Mn composite oxides, composite oxidations with as little cobalt content as possible Things are being studied. As described above, active researches have been actively conducted on active materials in which elements that can be supplied at a relatively low cost are mainly used and the amount of expensive elements used is reduced.

In Patent Document 1 and Patent Document 2, a Li [LiNiCoMn] O ₂ composite oxide containing lithium at the transition metal site 3b is studied as a positive electrode material. However, when a lithium nickel cobalt manganese composite oxide containing lithium in the 3b site containing such a transition metal is used as the positive electrode active material, the capacity is high, and charge / discharge output characteristics and charge / discharge output balance are achieved. There are not enough studies to make an excellent battery.
JP 2004-6267 A JP 2006-253119 A

  An object of the present invention is to provide a high capacity and charge / discharge output characteristic in a non-aqueous electrolyte secondary battery using a lithium nickel cobalt manganese composite oxide containing lithium in the 3b site containing a transition metal as a positive electrode active material. And providing a non-aqueous electrolyte secondary battery excellent in charge / discharge output balance.

The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte having lithium ion conductivity. Lithium nickel cobalt manganese composite oxide Li [Li _a Ni _x Co _y Mn _z ] O _2-b (wherein x, y, z, a and b are 0.1 ≦ a ≦ 0.3, 0 <x <0.45, 0 <y <0.45, 0.45 ≦ z ≦ 0.82, 0.1 ≦ (x + y) / z ≦ 1, a + x + y + z = 1, and 0 ≦ b ≦ 0.25 The ratio of the initial charge capacity of the negative electrode to the initial charge capacity of the positive electrode when charged until the potential of the positive electrode is 4.45 V (vs. Li / Li ⁺ ) or more (negative electrode / positive electrode) ) Is 0.80 ≦ n ≦ 1.00, and the potential of the positive electrode is 4 It is characterized in that the initial charge is carried out until 45V (vs.Li/Li ⁺⁾ or more.

  According to the present invention, in a nonaqueous electrolyte secondary battery using a lithium nickel cobalt manganese composite oxide containing lithium at a transition metal site as a positive electrode active material, the capacity is high, and charge / discharge output characteristics and charge / discharge output balance are high. The non-aqueous electrolyte secondary battery can be made excellent.

In the lithium nickel cobalt manganese composite oxide represented by Li [Li _a Ni _x Co _y Mn _z ] O _2-b of the present invention, the amount of Li contained in the 3b site of the transition metal is such that the potential of the positive electrode is 4 It is greatly involved in the charge capacity when charged to .45 V (vs. Li / Li ⁺ ) or higher. For this reason, from the viewpoint of a balance between increasing the battery capacity and decreasing the charge / discharge voltage of the battery, a indicating the amount of Li contained in the transition metal site is in the range of 0.1 ≦ a ≦ 0.3. It is preferable that it is in the range of 0.19 ≦ a ≦ 0.3.

In addition, regarding the ratio ((x + y) / z) of the Mn amount z to the sum of the Ni amount x and the Co amount y, the Ni amount and the Co amount are less than the positive electrode potential 4.45 V (vs. Li / Li ⁺ ). The amount of Mn must be increased in order to reduce costs and lower the charge / discharge voltage of the battery. Therefore, from the viewpoint of these balances, 0.1 ≦ (x + y) / z ≦ 1 It is preferable to be within the range. A, x, y, and z representing the amounts of Li, Ni, Co, and Mn at these 3b sites have a relationship of a + x + y + z = 1.

  Further, the Ni amount x is preferably in the range of 0 <x <0.45, and more preferably in the range of 0.09 <x <0.28. If the Ni amount x is too small, the output in the intermediate potential region is reduced, and if the Ni amount x is too large, the material price is expensive. The Co amount y is preferably in the range of 0 <y <0.45, and more preferably in the range of 0.09 <y <0.28. By containing Co, the charge / discharge output balance can be improved. Therefore, if y is too small, the charge / discharge output balance tends to be poor, and if y is too large, the material price becomes expensive. The Mn amount z is preferably in the range of 0.45 ≦ z ≦ 0.82, and more preferably in the range of 0.50 ≦ z ≦ 0.82. When z is too small, the effect of lowering the charge / discharge potential is reduced, and when z is too large, the electrochemical activity of the material is lowered and the output is lowered.

In addition, the lithium nickel cobalt manganese composite oxide represented by Li [Li _a Ni _x Co _y Mn _z ] O _2-b in the present invention can sufficiently exhibit the effects of the present invention even if there is an oxygen deficiency. it can. B indicating the oxygen deficiency is preferably in the range of 0 ≦ b ≦ 0.25. If b exceeds 0.25, the crystal structure may be greatly impaired, and the effects of the present invention may not be obtained.

  The Li amount a in the 3b site of the lithium nickel cobalt manganese composite oxide of the present invention can be measured using an X-ray diffraction method or a neutron diffraction method.

The lithium nickel cobalt manganese composite oxide in the present invention needs to be charged for the first time until the potential of the positive electrode becomes 4.45 V (vs. Li / Li ⁺ ) or higher. This causes a structural change in the lithium nickel manganese composite oxide. As a battery voltage when a carbon material is used as the negative electrode active material, it is desirable to charge at 4.35 V or more. After the structural change is caused at the first charge, it is not necessary to perform the subsequent charge so that the potential of the positive electrode is 4.45 V (vs. Li / Li ⁺ ) or more, and the influence of the decomposition of the electrolytic solution For example, the effects of the present invention can be obtained even when the battery voltage is about 4.2V.

  In addition, the composition of the lithium nickel cobalt manganese composite oxide of the present invention is a composition before the first charge / discharge, and is different from the composition after the structure change at the first charge. However, the composition before the charge / discharge and the composition after the structure change are uniquely related. Therefore, the composition after the structure change is performed by performing X-ray diffraction method, neutron diffraction method, elemental analysis, etc. Therefore, the composition before charging / discharging can be determined.

  The lithium nickel cobalt manganese composite oxide used in the present invention may contain one or more metal elements other than Li, Ni, Co, and Mn. Specifically, B, Mg, Al, Si, P, Ca, Sc, Ti, Cr, Fe, Cu, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh , Pd, In, Sn, Sb, Te, Ba, lanthanoid elements, Hf, Ta, W, Re, Os, Ir, Pt, Pb, Bi, Ra, actinoid elements, and the like may be further included. From the viewpoint of securing the weight energy density (Wh / kg) of the active material, the content of these metal elements is 0.1 or less in terms of molar ratio with respect to the transition metal element contained in the 3b site. Preferably, it is 0.001 or more and 0.05 or less. For the same reason, one or more kinds of halogen elements or chalcogen elements may be contained. Specifically, F, Cl, Br, I, At, S, Se, Te, Po, or the like may be included. From the viewpoint of securing the weight energy density (Wh / kg) of the active material, the content of the halogen element or chalcogen element is 0.1 or less in terms of molar ratio with respect to O contained in the 6c site. And more preferably 0.001 or more and 0.05 or less.

  In the present invention, a positive electrode active material other than the lithium nickel cobalt manganese composite oxide may be mixed as the positive electrode active material. The other positive electrode active material to be mixed is not particularly limited as long as it is a compound capable of reversibly inserting and desorbing Li, but it is a layered structure capable of inserting and desorbing Li while maintaining a stable crystal structure. A positive electrode active material having a rock salt structure, a spinel structure, or an olivine structure is preferable.

As the supporting salt used in the present invention, a lithium salt generally used as an electrolyte of a nonaqueous electrolyte secondary battery can be used. Such a lithium salt preferably contains one or more elements of P, B, F, O, S, N, and Cl. Specifically, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO _{4 and the} like and mixtures thereof can be used. Furthermore, in addition to these salts, it is preferable that a lithium salt having an oxalato complex as an anion is contained, and more preferably lithium-bis (oxalato) borate that suppresses an increase in resistance after high-temperature storage.

  Moreover, as a solvent of the non-aqueous electrolyte used in the present invention, those conventionally used as an electrolyte solvent for non-aqueous electrolyte secondary batteries can be used. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, and chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate can be used. In particular, a mixed solvent of cyclic carbonate and chain carbonate having high lithium ion conductivity is preferable. An ionic liquid can also be used as a solvent for the electrolyte. The cationic species and the anionic species are not particularly limited, but from the viewpoint of obtaining low viscosity, electrochemical stability, and hydrophobicity, the cation is a pyridinium cation, an imidazolium cation, or a quaternary ammonium cation as an anion. Is particularly preferably a combination using a fluorine-containing imide anion.

The negative electrode active material used in the present invention is not particularly limited as long as it can reversibly occlude and release lithium, and a carbon material, an alloy, a metal oxide, or the like can be used. In particular, from the viewpoint of cost, it is preferable to use a carbon material. Specific examples of the carbon material include natural graphite, artificial graphite, mesophase pitch-based carbon fiber (MCF), mesocarbon microbeads (MCMB), coke, and hard carbon. , Fullerenes, carbon nanotubes and the like. Among these, a graphitic carbon material is particularly preferably used because of a small potential change accompanying lithium insertion / extraction. By using a graphitic carbon material, the potential of the positive electrode is maintained at 4.45 V (vs. Li / Li ⁺ ) or more during the first charge, causing a structural change of the lithium nickel manganese composite oxide in the battery. Can be made easier.

  The separator used in the present invention is not particularly limited as long as it is a material that prevents a short circuit due to contact between the positive electrode and the negative electrode and that can obtain lithium ion conductivity by impregnating with an electrolytic solution. For example, a polypropylene, polyethylene, a polypropylene-polyethylene multilayer separator, etc. are mentioned.

The initial charge capacity ratio n in the present invention can be measured using a three-electrode test cell in which a positive electrode or a negative electrode to be used is a working electrode and lithium metal is a counter electrode and a reference electrode. That is, n = (negative electrode initial charge capacity) / (positive electrode initial charge capacity), and n is calculated from the positive electrode initial charge capacity measured using a three-electrode test cell and the negative electrode initial charge capacity. Can do. The initial charge capacity of the positive electrode is charged until the potential of the positive electrode becomes 4.45 V (vs. Li / Li ⁺ ) or higher. That is, in the present invention, as described above, since it is necessary to charge the initial charge so that the potential of the positive electrode is 4.45 V (vs. Li / Li ⁺ ) or higher, the positive electrode during the actual initial charge is required. The initial charge capacity of the positive electrode is measured with a three-electrode test cell.

  By setting the initial charge capacity ratio n within the range of 0.80 ≦ n ≦ 1.00, a non-aqueous electrolyte secondary battery having high discharge capacity and excellent charge / discharge output characteristics and charge / discharge output balance is obtained. be able to.

  When n is less than 0.80, the amount of lithium involved in the reaction in the negative electrode active material out of the lithium desorbed from the positive electrode during the first charge exceeds the limit amount of lithium obtained by the negative electrode active material, Lithium may be deposited on the surface, which may greatly impair the safety and reliability of the battery. On the other hand, if n is less than 0.80, the output characteristics deteriorate due to precipitated lithium. Further, when n exceeds 1.00, the charge / discharge capacity is greatly reduced. In particular, the charge / discharge capacity at the time of designing a 18650 battery (cylindrical battery having a diameter of about 18 mm and a height of about 65 mm) is greatly reduced.

  Moreover, it is thought that the lithium contained in the transition metal site of the lithium nickel cobalt manganese composite oxide is irreversible lithium. Therefore, the ratio of reversible lithium to the total amount of lithium is represented by 1 / (1 + a). For this reason, the initial charge capacity ratio n is preferably in the range of 1 / (1 + a) ≦ n ≦ 1.00.

In accordance with the present invention, when a specific lithium nickel cobalt manganese composite oxide containing lithium at the transition metal site is used as the positive electrode active material, and charging is performed until the positive electrode potential is 4.45 V (vs. Li / Li ⁺ ) or higher. The ratio n of the initial charge capacity of the negative electrode to the initial charge capacity of the positive electrode is set in the range of 0.80 ≦ n ≦ 1.00, and the first time until the potential of the positive electrode is 4.45 V (vs. Li / Li ⁺ ) or more. By performing charging / discharging, a non-aqueous electrolyte secondary battery having high capacity and excellent charge / discharge output characteristics and charge / discharge output balance can be obtained.

  Hereinafter, the present invention will be described in detail on the basis of examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without departing from the scope of the present invention. is there.

Example 1
[Preparation of positive electrode active material]
A 1M aqueous solution in which Ni (CH ₃ COO) ₂ , Co (CH ₃ COO) ₂ and Mn (CH ₃ COO) ₂ are dissolved is prepared so that the molar ratio of Ni: Co: Mn is 13:13:54. Then, a 0.1 M (mol / liter) NaOH aqueous solution was added to the aqueous solution, and Ni, Co, and Mn hydroxides were coprecipitated to obtain a Ni—Co—Mn composite hydroxide. Using this Ni—Co—Mn composite hydroxide, the Li ₂ CO ₃ and Ni—Co—Mn composite hydroxide were converted to a Li: Ni: Co: Mn element molar ratio of 1.20: 0.13: 0. .13: 0.54, and the mixture was calcined at 500 ° C. for 10 hours in an air atmosphere, and then calcined at 1000 ° C. for 20 hours to obtain Li [LiNiCoMn] O ₂ composite oxidation. A product was made. The composition of the obtained Li [LiNiCoMn] O ₂ composite oxide was Li [Li _0.20 Ni _0.13 Co _0.13 Mn _0.54 ] O ₂ .

[Production of positive electrode]
The positive electrode active material produced as described above, carbon as a conductive agent, and an N-methyl-2-pyrrolidone solution in which polyvinylidene fluoride as a binder is dissolved, the positive electrode active material, the conductive agent, and the binder The weight ratio was adjusted to 90: 5: 5 and then kneaded to prepare a positive electrode slurry. The produced positive electrode slurry was applied on an aluminum foil as a current collector and then dried to obtain a positive electrode plate. Thereafter, the obtained positive electrode plate was cut into a size of 30 mm × 37 mm, and the 7 mm coated part was peeled off, rolled using a rolling roller, and the coated part was peeled off and exposed on an aluminum foil. A positive electrode was produced by attaching a current collecting tab.

(Production of negative electrode)
An aqueous solution in which graphite as a negative electrode active material, styrene butadiene rubber as a binder, and carboxymethyl cellulose as a thickener are dissolved, and the weight ratio of the active material, the binder, and the thickener is 97.5: 1. 5: 1.0, and then kneaded to prepare a negative electrode slurry. The prepared negative electrode slurry was applied to a copper foil as a current collector with the application amount adjusted so that the initial charge capacity ratio n (negative electrode / positive electrode) was 0.80 with respect to the positive electrode capacity, and then dried. A negative electrode plate was obtained. Thereafter, the obtained negative electrode plate was cut out to a size of 31 mm × 37.5 mm, and the 6.5 mm coated part was peeled off, rolled using a rolling roller, and the coated part was peeled off and exposed on the copper foil. A negative electrode was prepared by attaching a current collecting tab made of nickel.

The initial charge capacity of the positive electrode and the negative electrode was measured by separately preparing a three-electrode test cell. Note that the positive electrode was charged until the potential was 4.6 V (vs. Li ^/ Li ⁺ ).

[Production of winding electrode body]
A wound electrode body was fabricated by winding the positive electrode and the negative electrode fabricated as described above facing each other through a polyethylene separator.

(Preparation of electrolyte)
1 mol / liter of LiPF ₆ as a supporting salt is dissolved in a solvent prepared by mixing ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) in a volume ratio of 3: 3: 4, An electrolytic solution was prepared by dissolving 1% by weight of vinylene carbonate (VC) as a film forming agent.

[Production of battery]
After inserting the wound electrode body produced as described above into a battery can, drying under reduced pressure, pouring the electrolyte solution in a glove box under an argon (Ar) atmosphere, and sealing the non-water An electrolyte secondary battery A was produced.

(Charge / discharge test)
The battery was charged at 1.1 mA at 25 ° C. for 5 hours, and allowed to stand at 25 ° C. for 5 days for stabilization. Thereafter, constant current charging to 4.5 V at 4.4 mA was performed at 25 ° C., constant voltage charging to 0.44 mA at 4.5 V, and then discharging to 2.4 V at 2.2 mA. The charge capacity and discharge capacity at this time were defined as initial charge capacity and initial discharge capacity, respectively.

[Output measurement test]
From the result of the initial discharge capacity obtained from the above charge / discharge test, after adjusting to SOC 50%, the following measurement was performed to plot each current value on the horizontal axis and voltage on the vertical axis, and to approximate each point linearly The DC resistance and open circuit voltage were obtained from the slope, and the charge / discharge output balance was calculated from these values.

(1) 1 mA charge (10 seconds) → pause (5 minutes) → 1 mA discharge (10 seconds) → pause (5 minutes)
(2) 5 mA charge (10 seconds) → pause (5 minutes) → 1 mA discharge (50 seconds) → pause (5 minutes)
(3) 10 mA charge (10 seconds) → pause (5 minutes) → 1 mA discharge (100 seconds) → pause (5 minutes)
(4) 20 mA charge (10 seconds) → pause (5 minutes) → 1 mA discharge (200 seconds) → pause (5 minutes)
(5) 1 mA discharge (10 seconds) → pause (5 minutes) → 1 mA charge (10 seconds) → pause (5 minutes)
(6) 5 mA discharge (10 seconds) → pause (5 minutes) → 1 mA charge (50 seconds) → pause (5 minutes)
(7) 10 mA discharge (10 seconds) → pause (5 minutes) → 1 mA charge (100 seconds) → pause (5 minutes)
(8) 20 mA discharge (10 seconds) → pause (5 minutes) → 1 mA charge (200 seconds) → pause (5 minutes)

  At room temperature, the charge / discharge tests of (1) to (8) are performed in order, the voltage after 10 seconds at the time of each discharge is measured, and the voltage of the current value is measured using the results of (1) to (4). The charging side DC resistance was determined from the slope of the change, and the charging side open circuit voltage was determined from the intercept. Similarly, the discharge side DC resistance and the discharge side open circuit voltage were obtained from the results of (5) to (8).

  By substituting the obtained value into the following formula, the charge side output, the discharge side output, and the charge / discharge output balance were calculated.

Charge side output (W) = ((4.5 [V] −Charge side open circuit voltage [V] / Charge side DC resistance [Ω] × 4.5 [V]
Discharge side output (W) = ((discharge side open circuit voltage [V] −2.4 [V] / discharge side DC resistance [Ω] × 2.4 [V]
Charge / discharge output balance = charge side output / discharge side output

[Estimation of 18650 battery capacity]
From the results of each battery used in the above test, the capacity when a 18650 battery was produced was estimated. The design of the 18650 battery is such that the mixture filling density of the positive electrode and the negative electrode used in the battery, the thickness of the electrode plate, the amount of mixture applied per unit area is constant, and the thickness of the separator is taken into consideration. The proportion of the positive electrode, the negative electrode, and the separator in the battery can was 94%. From the obtained design, the amount of the positive electrode active material in the 18650 battery can was obtained, and the estimated capacity of the 18650 battery was obtained from the relationship between the initial discharge capacity and the amount of the positive electrode active material of the battery used in this test by the following formula.

  18650 battery estimated capacity [mAh] = initial discharge capacity × (amount of positive electrode active material / amount of positive electrode active material in 18650 battery)

(Example 2)
In Example 1, a nonaqueous electrolyte secondary battery B was similarly produced except that n = 0.87, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Example 3)
In Example 1, a nonaqueous electrolyte secondary battery C was prepared in the same manner except that n = 0.92, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

Example 4
In Example 1, a nonaqueous electrolyte secondary battery D was prepared in the same manner except that n = 1.00, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 1)
In Example 1, a nonaqueous electrolyte secondary battery E was produced in the same manner except that n = 0.49, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 2)
In Example 1, a nonaqueous electrolyte secondary battery F was prepared in the same manner except that n = 0.61, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 3)
In Example 1, a nonaqueous electrolyte secondary battery G was prepared in the same manner except that n = 0.75, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 4)
In Example 1, a nonaqueous electrolyte secondary battery H was similarly manufactured except that n = 1.06, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 5)
In Example 1, a nonaqueous electrolyte secondary battery I was prepared in the same manner except that n = 1.11, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 6)
In Example 1, a nonaqueous electrolyte secondary battery J was prepared in the same manner except that n = 1.20, and the results of 18650 battery trial capacity and charge / discharge output balance were obtained by the same measurement.

(Comparative Example 7)
In Example 1, a non-aqueous electrolyte secondary battery K is similarly used except that Li [Ni _0.4 Co _0.3 Mn _0.3 ] O ₂ is used as the positive electrode active material and n = 0.97. The result of charge / discharge output balance was obtained by the same measurement.

(Comparative Example 8)
In Example 1, a non-aqueous electrolyte secondary battery L is similarly used except that Li [Li _0.22 Ni _0.17 Mn _0.61 ] O ₂ is used as the positive electrode active material and n = 0.99. The result of charge / discharge output balance was obtained by the same measurement.

  The measurement results of Examples 1 to 4 and Comparative Examples 1 to 8 are shown in Table 1 below. FIG. 1 shows the relationship between the negative electrode / positive electrode initial charge capacity ratio n, the charge side output, the discharge side output, and the estimated capacity of the 18650 battery. Moreover, the charge / discharge output balance of the cell D (Example 4), the cell K (Comparative Example 7), and the cell L (Comparative Example 8) is shown in FIG.

  As shown in Table 1 and FIG. 1, the estimated capacity of the 18650 battery is high when the initial charge capacity ratio n is 1.00 or less, but suddenly increases when n exceeds 1.00. Has fallen. The reason why the high capacity is obtained by reducing the capacity ratio n is considered to be that the amount of the negative electrode not involved in charge / discharge decreases and the amount of the positive electrode active material in the battery increases in terms of battery design. Further, although the detailed cause of the decrease in the capacity when the capacity ratio n exceeds 1.00 is not clear, the excess negative electrode active material increases, so that the SEI (Solid Electrolyte) formed on the negative electrode surface at the time of the initial charge is formed. Since the amount of (Interface) also increases, the battery initial efficiency is considered to decrease.

  Further, both the charging side output and the discharging side output are greatly reduced when n is less than 0.80. Although the detailed cause for this phenomenon is unknown, if n is too small, lithium desorbed from the positive electrode active material is deposited on the surface of the negative electrode active material. It seems that the output characteristics deteriorate due to blocking.

  In Comparative Example 7, lithium nickel cobalt manganese oxide containing no lithium at the transition metal site is used as the positive electrode active material. In Comparative Example 8, lithium is contained in the transition metal site, but cobalt is contained. Lithium nickel manganese oxide is used as the positive electrode active material. As is clear from comparison between these Comparative Examples 7 and 8 and Examples 1 to 4, Examples 1 to 4 according to the present invention are more satisfactory than Comparative Examples 7 and 8 using these conventional positive electrode active materials. Excellent discharge output balance.

  As is clear from the above, according to the present invention, a nonaqueous electrolyte secondary battery having a high capacity and excellent charge / discharge output characteristics and charge / discharge output balance can be obtained. Therefore, it can be set as a suitable battery as a lithium ion secondary battery for HEV use.

The figure which shows the relationship between the initial charge capacity ratio n in an Example and a comparative example, charge side output, discharge side output, and 18650 battery trial calculation capacity. The figure which shows the charging / discharging output balance of the cell D (Example 4), the cell K (comparative example 7), and the cell L (comparative example 8).

Claims (4)

In a non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte having lithium ion conductivity,
As the positive electrode active material, lithium nickel cobalt manganese composite oxide Li [Li _a Ni _x Co _y Mn _z ] O _{2 -b} containing lithium at the transition metal site, where x, y, z, a and b are 0.1 ≦ a ≦ 0.3, 0 <x <0.45, 0 <y <0.45, 0.45 ≦ z ≦ 0.82, 0.1 ≦ (x + y) / z ≦ 1, a + x + y + z = 1 and 0 ≦ b ≦ 0.25 are satisfied)
The ratio n (negative electrode / positive electrode) of the initial charge capacity of the negative electrode to the initial charge capacity of the negative electrode when charged until the potential of the positive electrode is 4.45 V (vs. Li / Li ⁺ ) or more is 0.80 ≦ n ≦ 1.00,
The non-aqueous electrolyte secondary battery is characterized in that the first charge is performed until the potential of the positive electrode becomes 4.45 V (vs. Li / Li ⁺ ) or more.   The non-aqueous electrolyte secondary battery according to claim 1, wherein a in the formula is 0.19 ≦ a ≦ 0.3.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a carbon material is used as the negative electrode active material. 4. The non-aqueous electrolyte secondary according to claim 1, wherein the initial charge capacity ratio n (negative electrode / positive electrode) is 1 / (1 + a) ≦ n ≦ 1.00. battery.

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