KR20070019581A - Non-aqueous Electrolyte Secondary Battery - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte secondary battery suitable for secondary batteries for hybrid electric vehicles, which can exhibit uniform high power characteristics in a wide range of charge depths.

The first lithium-containing transition metal oxide Li _a Ni _x Mn _y O ₂ containing nickel and manganese as a transition metal and having a crystal structure belonging to the space group R3m, wherein a, x and y are 1 ≦ a ≦ 1.5, 0.5 ≦ x + y ≦ 1, satisfies the relationship of 0 <x <1 and 0 <y <1), and a crystal structure containing nickel, manganese and cobalt as transition metals and belonging to the space group R3m Secondary lithium-containing transition metal oxide with Li _b Ni _p Mn _q Co _r O ₂ (wherein b, p, q and r are 1 ≦ b ≦ 1.5, 0.5 ≦ p + q + r ≦ 1, 0 <p A mixture with <1, 0 <q <1 and 0 <r <1 is satisfied) or a mixture of a first lithium-containing transition metal oxide and lithium cobalt acid is used as a positive electrode active material.

Non-aqueous electrolyte secondary battery, positive electrode active material, lithium-containing transition metal oxide, R3m

Description

Non-aqueous Electrolyte Secondary Battery

1 is a view showing IV resistance and starting voltage of Examples 1 to 4 and Comparative Examples 1 to 2 according to the present invention.

FIG. 2 is a diagram showing the relationship between the mixing ratio and the output of the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide.

The present invention relates to a nonaqueous electrolyte secondary battery such as a lithium secondary battery.

In recent years, lithium ion batteries have attracted attention as batteries for hybrid electric vehicles because of their light weight and high output. As the required characteristics, it is required to exhibit not only high output characteristics but also relatively uniform output characteristics in a wide range of filling depths. This demand aims to reduce the system cost by simplifying the control algorithm for battery output.

Lithium-containing nickel-manganese composite oxides are attracting attention as inexpensive cathode materials because they use nickel and manganese, which are resource-rich than lithium cobalt oxide, which is conventionally used as a cathode active material. It is attracting attention as.

However, in the nonaqueous electrolyte secondary battery using lithium-containing nickel-manganese oxide as the positive electrode active material, there were problems such as low discharge capacity and high resistance and low output characteristics.

In order to solve the said problem, it is proposed by patent document 1 to mix lithium manganese oxide which has a spinel structure, and to improve low-temperature output characteristics. However, the use of lithium manganese oxide having a spinel structure with a discharge potential of about 4 V (vs Li / Li ⁺ ) causes a problem that not only the regenerative output characteristics cannot be obtained sufficiently but also that the battery capacity is not obtained sufficiently. In addition, many studies have been made on lithium-containing nickel-cobalt-manganese oxides, but since the increase in resistance at the end of the discharge is large, a uniform output cannot be obtained in a wide range of discharge depths, which makes them unsuitable for hybrid electric vehicle batteries. Was.

In addition, although Patent Document 2 describes that the discharge capacity is remarkably improved by using the Li (LiNiMn) O ₂ positive electrode material in which lithium is disposed at the transition metal position, the uniformity of the output characteristics described above is still insufficient.

Patent Document 1: Japanese Patent Application Laid-Open No. 2003-92108

Patent Document 2: US Patent Application Publication No. 2003/0108793

It is an object of the present invention to provide a nonaqueous electrolyte secondary battery suitable for secondary batteries for hybrid electric vehicles, which can exhibit uniform high power characteristics in a wide range of charge depths.

The present invention is a nonaqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode containing a negative electrode active material, and a nonaqueous electrolyte having lithium ion conductivity, containing nickel and manganese as transition metals, and further comprising a space group R3m. First lithium-containing transition metal oxide Li _a Ni _x Mn _y O ₂ having an attached crystal structure, wherein a, x and y are 1 ≦ a ≦ 1.5, 0.5 ≦ x + y ≦ 1, 0 <x <1 And 0 <y <1 is satisfied), and a second lithium-containing transition metal oxide Li _b Ni _p Mn having a crystal structure containing nickel, manganese and cobalt as transition metals and belonging to the space group R3m. _q Co _r O ₂ (where b, p, q and r are 1 ≦ b ≦ 1.5, 0.5 ≦ p + q + r ≦ 1, 0 <p <1, 0 <q <1 and 0 <r <1) And a mixture of a first lithium-containing transition metal oxide and lithium cobalt acid as the positive electrode active material.

A lithium-containing nickel-manganese oxide Li _a Ni _x Mn _y O ₂ , which is the first lithium-containing transition metal oxide according to the present invention, wherein a, x and y are 1 ≦ a ≦ 1.5, 0.5 ≦ x + y ≦ 1 , 0 <x <1 and 0 <y <1 are satisfied.) The lithium-containing nickel-manganese-cobalt oxide Li _b Ni _p Mn _q Co _r O ₂ (wherein, b, p, q and r satisfy the relation of 1 ≦ b ≦ 1.5, 0.5 ≦ p + q + r ≦ 1, 0 <p <1, 0 <q <1 and 0 <r <1) or cobalt acid By mixing lithium and using it as a positive electrode active material, not only the output characteristic is remarkably improved, but also the uniform output characteristic can be obtained in a wide charge depth range.

In the present invention, the mixing ratio of the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide (first lithium-containing transition metal oxide: second lithium-containing transition metal oxide) and first lithium-containing The mixing ratio of the transition metal oxide and lithium cobalt acid (first lithium-containing transition metal oxide: lithium cobalt acid) is preferably in the range of 1: 9 to 9: 1 by weight ratio, more preferably 2: 8 to It is in the range of 8: 2, More preferably, it is in the range of 6: 4-4: 6. By mixing within these ranges, the effect of the present invention that the output characteristics are high and uniform output characteristics can be obtained over a wide range of filling depths can be obtained more effectively.

In the first lithium-containing transition metal oxide Li _a Ni _x Mn _y O ₂ , more preferable ranges of x and y are 0 <x ≦ 0.5 and 0.5 ≦ y <1. In addition, it is preferable that the molar ratio (x / y) of Ni / Mn in a 1st lithium containing transition metal oxide is less than 1, and x + y <1. In the second lithium-containing transition metal oxide, it is preferable that cobalt is contained in a molar ratio of 0.2 or more with respect to the total content of the transition metal. More preferred ranges of p, q and r in Li _b Ni _p Mn _q Co _r O ₂ are 0 <p ≦ 0.8, 0.5 ≧ r ≧ 0.2 and 0 <q ≦ 0.5.

In the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide, at least one element selected from B, Mg, Al, Ti, Cr, V, Nb, Zr, Sn, and Mo is a metal other than lithium. 0.1 or less may be contained in molar ratio with respect to the total.

Moreover, also in lithium cobalt acid, 1 or more types of elements chosen from B, Mg, Al, Ti, Cr, V, Nb, Zr, Sn, Mo, W, and P may be contained. As content, it is preferable that it is 0.1 or less in molar ratio with respect to the total metals other than lithium.

In the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide in the present invention, part of lithium may be contained at the 3b position of the transition metal. In this case, it is preferable to set the initial charge end potential to 4.45 V or more and 4.65 V or less from the viewpoint of improving the output characteristics. Moreover, it is preferable that the particle diameters of these oxides exist in the range of 1-20 micrometers, and it is preferable that BET specific surface area exists in the range of 0.1-3 m <^2> / g.

Both the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide of the present invention have a crystal structure belonging to the space group R3m. Such crystal structure can be confirmed by X-ray diffraction measurement. In addition, lithium cobalt acid also has a crystal structure belonging to the space group R3m.

The negative electrode active material used in the present invention is not particularly limited as long as it is a negative electrode active material that can be used for a nonaqueous electrolyte secondary battery, but a carbon material can be preferably used.

As the solute (supporting salt) of the nonaqueous electrolyte solution which can be used in the present invention, a lithium salt that can be generally used as a solute of a nonaqueous electrolyte secondary battery can be used. Such lithium salts include 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 ) , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof. . In addition to these salts, a lithium salt containing an oxalate complex as an anion may be included. Examples of such lithium salts include lithium bis (oxalate) borate.

As a solvent of the nonaqueous electrolyte used by this invention, what is generally used as a solvent of the electrolyte of a nonaqueous electrolyte secondary battery can be used. Among these, the mixed solvent of cyclic carbonate and linear carbonate can use especially preferable. Ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc. are mentioned as cyclic carbonate. Examples of the linear carbonates include dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate.

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example, It is possible to change suitably and to implement in the range which does not change the summary.

Example 1 :

[Production of Anode Active Material]

The first lithium-containing transition metal oxide, lithium-containing nickel of the present invention the manganese oxide was 1.1 in the Li ₂ CO ₃ and _{(Ni 0 .5 Mn 0 .5)} 3 O 4 molar ratio, and mixed so that the first, and the mixture It produced by baking for 20 hours at 900 degreeC in air atmosphere. The resulting lithium-containing nickel-manganese oxide of the composition is Li was _{1 .1 Ni 0 .5 Mn 0 .5} O 2.

The lithium containing nickel-cobalt-manganese oxide which is the 2nd lithium containing transition metal oxide of this invention was produced as follows. The Li ₂ CO ₃ and _{(Ni 0 .4 Co 0 .3 Mn} 0 .3) 3 O 4 in a molar ratio of 1.15: 1 so that the mixture, and the mixture was manufactured by 20 hours and baked at 900 ℃ in air atmosphere. The composition of the obtained lithium-containing nickel-cobalt-manganese oxide was Li _1.15 Ni _0.4 Co _0.3 Mn _0.3 O ₂ .

The particle size of the obtained lithium-containing nickel-manganese oxide was 10 µm, and the BET specific surface area was 1.0 m ² / g. In addition, the particle size of the lithium-containing nickel-cobalt-manganese oxide was 10 µm, and the BET specific surface area was 1.0 m ² / g. In addition, it was confirmed by X-ray diffraction measurement that all of them had a crystal structure attributed to the space group R3m.

[Production of anode]

The first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide prepared as described above are mixed in a weight ratio (first lithium-containing transition metal oxide: second lithium-containing transition metal oxide) to 8: 2. The N-methyl-2-pyrrolidone solution in which the carbon material as the conductive agent and the polyvinylidene fluoride as the binder is dissolved, is mixed so that the weight ratio of the active material and the conductive agent and the binder is 90: 5: 5, and the positive electrode slurry is mixed. Produced. The produced slurry was applied onto aluminum foil as a current collector, dried, then rolled using a rolling roller, and a positive electrode was produced by providing a current collector tab.

[Production of electrolyte]

An electrolyte solution was prepared by dissolving LiPF ₆ as a solute to 1 mol / liter in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7.

[Production of 3-electrode beaker cell]

The above-mentioned electrolyte solution was injected using the above-mentioned anode as a working electrode, lithium metal as a counter electrode and a reference electrode, and a three-electrode beaker cell A1 was produced.

Example 2 :

A test cell A2 was prepared in the same manner as in Example 1 except that the mixing ratio of the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide was mixed so as to be 6: 4 (weight ratio).

Example 3 :

A test cell A3 was prepared in the same manner as in Example 1 except that the mixing ratio of the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide was mixed so that it was 4: 6 (weight ratio).

Example 4 :

A test cell A4 was prepared in the same manner as in Example 1 except that the mixing ratio of the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide was 2: 8 (weight ratio).

Comparative Example 1 :

A test cell B was prepared in the same manner as in Example 1 except that only the first lithium-containing transition metal oxide was used as the positive electrode active material.

Comparative Example 2 :

A test cell C was prepared in the same manner as in Example 1 except that only the second lithium-containing transition metal oxide was used as the positive electrode active material.

Comparative Example 3 :

A test cell D was prepared in the same manner as in Example 1 except that the first lithium-containing transition metal oxide and lithium manganate (Li _1.1 Mn _1.9 O ₄ ) were mixed to be 8: 2 (weight ratio) as the positive electrode active material. .

The following charge and discharge tests and IV resistance measurement tests were performed on the test cells of Examples 1 to 4 and Comparative Examples 1 to 3.

[Charge / discharge test]

Each cell was charged to 4300 mV (vs Li / Li ⁺ ) at 1 mA at room temperature and then rested for 10 minutes, and then discharged to 2000 mV (vs Li / Li ⁺ ) at 1 mA to calculate the rated discharge capacity.

IV resistance measurement test

After charging to 2000mV (vs Li / Li ⁺ ) in the above charge and discharge test conditions, and charged to 10% and 50% of the rated discharge capacity at 1mA, respectively, the following test was performed.

(1) 5mA charge (10 seconds) → pause (10 minutes) → 5mA discharge (10 seconds) → pause (10 minutes)

(2) 10mA charge (10 seconds) → pause (10 minutes) → 10mA discharge (10 seconds) → pause (10 minutes)

(3) 20mA charge (10 seconds) → pause (10 minutes) → 20mA discharge (10 seconds) → pause (10 minutes)

The charge and discharge tests of (1) to (3) were carried out sequentially at room temperature, and the highest reached potential at each charge was measured to calculate the IV resistance from the slope of the potential change with respect to the current value. The output value was calculated from the IV resistance and starting voltage V ₀ at the start of the test of (1) using the following formula.

Output (W) = (4300-V ₀ ) / IV Resistance × 4300

The rated discharge capacity, starting voltage V ₀ , IV resistance and output measured for each cell are shown in Table 1 (output characteristics at 50% SOC) and Table 2 (output characteristics at 10% SOC).

Table 1 :

Cell _{Li 1 .1 Ni 0 .5 Mn 0} .5 O 2 mixing ratio (% by weight) Rated Discharge Capacity (mAh / g) Start voltage V ₀ (mV vs Li / Li ⁺ ) IV resistance (mΩ) Output (W) Example 1 A1 80 124 3902 3845 444 Example 2 A2 60 133 3881 2914 617 Example 3 A3 40 139 3866 2492 748 Example 4 A4 20 145 3847 2085 933 Comparative Example 1 B 100 116 3927 6655 240 Comparative Example 2 C 0 149 3830 2082 969 Comparative Example 3 D 80 (mixed with lithium manganate) 133 3930 2333 681

Table 2 :

Cell _{Li 1 .1 Ni 0 .5 Mn 0} .5 O 2 mixing ratio (% by weight) IV resistance (mΩ) Output (W) Output difference at SOC50% time-SOC10% time Example 1 A1 80 4424 527 83 Example 2 A2 60 3614 698 81 Example 3 A3 40 3800 634 114 Example 4 A4 20 3783 606 327 Comparative Example 1 B 100100 7607 292 52 Comparative Example 2 C 0 4007 585 384 Comparative Example 3 D 80 (mixed with lithium manganate) 6670 389 292

In addition, IV resistance and starting voltage of Examples 1-4 and Comparative Examples 1-2 are shown.

Further, Fig. 2 shows the relationship between a first lithium-containing transition metal oxide is Li _{1 .1} Ni _{0 .5 0 .5} O ₂ mixing ratio of Mn to the output of. As is apparent from FIGS. 1 and 2, the IV resistance and output are specific from the weighting calculation at a simple mixing ratio by mixing the second lithium-containing transition metal oxide with the first lithium-containing transition metal oxide according to the present invention. It can be seen that the improvement. In addition, by mixing the second lithium-containing transition metal oxide, the starting voltage V ₀ is decreased, and the output characteristics are improved. Manganese oxide having a spinel structure, lithium _{(Li 1 .1 Mn 1 .9 O} 4) can not be obtained a sufficient output characteristics by the Comparative Example 3 in which increase of the starting voltage V ₀ in the resulting high discharge potential of the mixture .

In addition, as shown in Table 2, Comparative Example 2 using only lithium-containing nickel-cobalt-manganese oxide has the largest difference in output between SOC at 50% and SOC at 10%. On the other hand, in Examples 1 to 4 in which the lithium-containing nickel-manganese oxide and the lithium-containing nickel-cobalt-manganese oxide according to the present invention were mixed, the SOC 50% output and the SOC 10% output were compared with those of Comparative Example 2. Since the difference is small, a relatively large output can be obtained. Therefore, according to the present invention, it can be seen that not only uniform but also high output can be obtained in a wide range of filling depths.

Although the details of the mechanism of action of the effects of the present invention are not clear, the electrochemical activity of lithium-containing nickel-cobalt-manganese oxide is improved by adding lithium-containing nickel-cobalt-manganese oxide to lithium-containing nickel-manganese oxide; At the same time, the electrochemical activity of lithium-containing nickel-cobalt-manganese oxide can be enhanced, and the charge-discharge depth dependence of the output characteristics is considered to be reduced.

Example 5 :

Li ₂ Co ₃ and _{(Ni 0 .1 Mn 0 .6)} 3 O 4 in the molar ratio 1.3: 0.7, and by mixing so that the 20 hours calcining the mixture at 1000 ℃ in air atmosphere, lithium-containing nickel-manganese oxide Li _1.3 Ni _0.1 Mn _0.6 O ₂ was prepared and used as the first positive electrode active material, except that the mixing ratio of the second positive electrode active material Li _1.15 Ni _0.4 Co _0.3 Mn _0.3 O ₂ was 1: 1 in weight ratio. In the same manner, test cell A5 was produced.

Example 6 :

A test cell A6 was prepared in the same manner as in Example 5 except that lithium cobalt lithium LiCo _0.99 Zr _0.005 Mg _0.005 O ₂ containing another element was used as the second positive electrode active material.

Comparative Example 4 :

As a cathode active material, Li _{1 .3 .1} Mn Ni _{0 0 .6} O ₂ except that using only the same manner as in Example 1 to prepare a test cell E.

Comparative Example 5 :

As a cathode active material, in the same manner as in Example 1 except that using only a lithium cobaltate _{LiCo 0 .99 Zr 0 .005 Mg 0} .005 O 2 containing the other elements to prepare a test cell F.

[Charge / discharge test]

Each cell was charged to 4600 mV (vs Li / Li ⁺ ) at 1 mA at room temperature and then rested for 10 minutes, and then discharged to 2000 mV (vs Li / Li ⁺ ) at 1 mA to calculate the rated discharge capacity.

IV resistance measurement test

After charging to 2000mV (vs Li / Li ⁺ ) in the above charge and discharge test conditions, and charged to 30% and 70% of the rated discharge capacity at 1mA, respectively, the following test was performed.

(1) 5mA charge (10 seconds) → pause (10 minutes) → 5mA discharge (10 seconds) → pause (10 minutes)

(2) 10mA charge (10 seconds) → pause (10 minutes) → 10mA discharge (10 seconds) → pause (10 minutes)

(3) 20mA charge (10 seconds) → pause (10 minutes) → 20mA discharge (10 seconds) → pause (10 minutes)

The charge and discharge tests of (1) to (3) were carried out sequentially at room temperature, and the highest reached potential at each charge was measured to calculate the IV resistance from the slope of the potential change with respect to the current value. The output value was calculated from the IV resistance and starting voltage V ₀ at the start of the test of (1) using the following formula.

Output (W) = (4300-V ₀ ) / IV Resistance × 4300

Table 3 shows the output and output difference measured for each cell.

Table 3 :

Cell Positive electrode active material SOC 70% Output (W) SOC 30% Output (W) SOC30-70% Output (W) Example 5 A5 _{Li 1 .3 Ni 0 .1 Mn 0} .6 O 2 _{+ Li 1 .15 Ni 0 .4 Co} 0 .3 Mn 0 .3 O 2 1: 1 mixing 420 463 43 Example 6 A6 _{Li 1 .3 Ni 0 .1 Mn 0} .6 O 2 + LiCo _0.99 Zr _0.005 Mg _0.005 O ₂ 1: 1 Mix 167 174 6.8 Comparative Example 4 E _{Li 1 .3 Ni 0 .1 Mn 0} .6 O 2 Exclusive 110 230 120 Comparative Example 5 F LiCo _{0 .99} Zr _{0 .005} Mg _{0 .005} O ₂ Exclusive 408 658 250

As it is apparent from the test results shown in Table 3, SOC change by mixing a Li _1.3 Ni _0.1 Mn _0.6 O ₂ and _{Li 1.15 Ni 0.4 Co 0.3 Mn 0.3} O 2 or _{LiCo 0 .99 Zr 0 .005 Mg 0} .005 O 2 It is possible to significantly reduce the output change with respect to the battery, and to produce a battery having a small dependency on the charging depth of the output.

Although the mechanism of action of the effect of the present invention is not known in detail, the lithium-containing nickel-manganese oxide positive electrode material having a high manganese ratio has low electron conductivity, so the electrochemical activity of lithium-containing nickel-manganese oxide by mixing other positive electrode active materials It is thought that this effect is improved, and the effect of reducing the filling depth dependency of the output is more remarkable.

According to the present invention, by mixing the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide or lithium cobalt acid as a positive electrode active material, the output characteristics can be dramatically improved and a wide range of filling depths can be achieved. Uniform output characteristics can be obtained. Therefore, by using the nonaqueous electrolyte secondary battery of the present invention in a secondary battery for a hybrid electric vehicle, the control algorithm in the hybrid electric vehicle can be simplified, and the system can be reduced in cost.

Claims (3)

A nonaqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode containing a negative electrode active material, and a nonaqueous electrolyte having lithium ion conductivity, The first lithium-containing transition metal oxide Li _a Ni _x Mn _y O ₂ containing nickel and manganese as a transition metal and having a crystal structure belonging to the space group R3m, wherein a, x and y are 1 ≦ a ≦ 1.5, 0.5 ≦ x + y ≦ 1, satisfies the relationship of 0 <x <1 and 0 <y <1), and a crystal structure containing nickel, manganese and cobalt as transition metals and belonging to the space group R3m Secondary lithium-containing transition metal oxide with Li _b Ni _p Mn _q Co _r O ₂ (wherein b, p, q and r are 1 ≦ b ≦ 1.5, 0.5 ≦ p + q + r ≦ 1, 0 <p A mixture of <1, 0 <q <1 and 0 <r <1 is satisfied) or a mixture of the first lithium-containing transition metal oxide and lithium cobalt acid is used as the positive electrode active material. Nonaqueous electrolyte secondary battery. The method of claim 1, And said mixture is a mixture of said first lithium-containing transition metal oxide and said second lithium-containing transition metal oxide. The method according to claim 1 or 2, A nonaqueous electrolyte secondary battery, wherein the molar ratio (x / y) of Ni / Mn in the first lithium-containing transition metal oxide is less than 1 and x + y <1.

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