JP2000149950A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a discharge characteristic at high capacity and a high rate by covering each particle surface of a high-capacity positive electrode active material with magnesium-containing cobalt acid lithium that is excellent in electron conductivity and has a single layer structure. SOLUTION: Each particle surface of LiNi1-y-zCoyMzO2 (0<=y<=0.25, 0<=z<=0.15, M is a metal excluding Co and Ni) is provided with a positive electrode active material covered with magnesium containing cobalt acid lithium having a single layer structure. A coprecipitation method is used for the synthesis of the positive electrode active material, and an aqueous solution in which nickel nitrate and cobalt nitrate are dissolved is kept at 30 deg.C, a sodium hydroxide aqueous solution is dripped into it, and hydroxides of nickel and cobalt are produced by coprecipitating them. Then, the positive electrode active material is synthesized by adding water to the nickel-cobalt hydroxide to form a dispersed solution, by dripping a sodium hydroxide aqueous solution and an aqueous solution in which cobalt nitrate and magnesium nitrate are dissolved into it, and by depositing a magnesium-cobalt hydroxide on the surface of the nickel-cobalt hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art With the rapid reduction in size and weight of electronic equipment, there is an increasing demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. . In addition, due to environmental problems such as air pollution and an increase in carbon dioxide, early commercialization of electric vehicles is desired, and development of excellent secondary batteries having characteristics such as high efficiency, high output, high energy density, and light weight. Is required.

As a secondary battery satisfying these requirements, a secondary battery using a non-aqueous electrolyte has been put to practical use. This battery has several times the energy density of a battery using a conventional aqueous electrolyte solution. For example, a cobalt composite oxide, nickel composite oxide or spinel lithium manganese oxide is used for the positive electrode of a non-aqueous electrolyte secondary battery, and a carbon material or tin oxide capable of inserting and extracting lithium is used for the negative electrode. Long-life 4V-class non-aqueous electrolyte secondary batteries have been put to practical use.

[0004]

The non-aqueous electrolyte secondary battery, particularly a battery using a lithium nickel composite oxide as a positive electrode active material, is expected to have a higher capacity than a battery using a lithium cobalt composite oxide. it can. However, since the voltage drop due to polarization is remarkably large at the end of discharge, there is a problem that characteristics at the time of high-rate discharge are inferior. Then, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having high capacity and excellent discharge characteristics at a high rate.

[0005]

The non-aqueous electrolyte secondary battery according to the present invention comprises LiNi ₁ -yz Co _x M _z O ₂ (0 ≦ y ≦ 0.25, 0
≦ z ≦ 0.15, M is a positive electrode active material coated with a magnesium-containing lithium cobalt oxide having a single-layer structure with a particle surface of a metal other than Co and Ni). .

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to a preferred embodiment, but it goes without saying that the present invention is not limited to the following without departing from the spirit of the present invention. The non-aqueous electrolyte secondary battery according to the present invention is LiNi _1-yz Co _y
M _z O ₂ (0 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.15, M is Co, Ni
(A metal other than metal) is provided with a positive electrode active material coated with a magnesium-containing lithium cobalt oxide having a single-layer structure, and has a high capacity of LiNi _1-yz Co _y M _z O _2.
Magnesium-containing lithium cobaltate (LiCo _1-x Mg _x O ₂ ) with a single-layer structure with excellent electron conductivity on the surface of the particles of the positive electrode active material
By coating with, the electron conductivity of the positive electrode active material can be improved. As a result, the resistance between the particles of the active material can be reduced, and the discharge characteristics at a high rate can be improved. Table 1 shows the relationship between the Mg composition ratio (x) of single-layer magnesium-containing lithium cobalt oxide (LiCo _1-x Mg _x O ₂ ) and the electronic conductivity, discharge capacity, and capacity deterioration rate (after 20 cycles). Is shown. These electrochemical properties were measured using a three-terminal glass cell. In manufacturing the positive electrode, the positive electrode material is made of magnesium-containing lithium cobalt oxide (LiCo _1-x Mg _x O ₂ ; where X is 0,
0.01, 0.03, 0.05, 0.10, 0.15)
And the magnesium-containing lithium cobaltate (LiCo _1-x Mg _x O ₂ ; where X is 0, 0.01, 0.0
3, 0.05, 0.10, and 0.15) of powder, 7 parts by weight of carbon black as a conductive additive, and 5 parts by weight of polyvinylidene fluoride as a binder. -
A slurry was prepared by kneading while appropriately adding a methyl-2-pyrrolidone solution. Then, this slurry was applied to an aluminum foil as a positive electrode current collector by a doctor blade method, and this was vacuum-dried at 150 ° C. to produce each positive electrode. The positive electrode prepared above was used as a working electrode, and a lithium metal electrode was used as a counter electrode and a reference electrode. Lithium hexafluorophosphate LiPF ₆ was added to a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1.
A solvent dissolved at a rate of mol / l was used. The charge / discharge test was performed for each of the three-terminal glass cells prepared above. The charging current was set to 0.5 mA / cm ^2, and after charging to lithium metal to 4.3 V, the battery was discharged to lithium metal to 3.0 V at a discharge current of 0.5 mA / cm ² . Also,
The cycle test was performed by repeating this operation. The sample for electronic conductivity measurement was LiCo _1-x M synthesized above.
After pressing g _x O ₂ into a 4 mm x 5 mm x 20 mm prism, press
After sintering for a period of time, a gold paste was applied to both ends, and then the paste was dried and solidified to produce each. The electron conductivity was measured by a DC method under a dry atmosphere (dew point −60 ° C. or lower) by a two-terminal method.

[0007]

[Table 1]

From Table 1, it can be seen that the magnesium-containing lithium coating
The composition ratio X of Mg of um cobaltate is 0.01 or less in atomic ratio.
Less than 0.1, more preferably 0.01 or more and 0.03 or less
It turns out that it is desirable to make it below. In this range
If the electronic conductivity, discharge capacity and capacity deterioration rate (after 20 cycles)
It is evident that they show good performance. Next
Next, a positive electrode active material according to the present invention was synthesized. That is, Li
Co_0.99Mg_0.01O_TwoLiNi coated with_0.8Co_0.2O_TwoThe synthesis of
This was performed using a coprecipitation method. First, 0.8 mol / l nickel nitrate
Solution containing 0.2 mol / l cobalt nitrate dissolved in 30
° C and dropping aqueous sodium hydroxide solution.
PH of 10 to 13 and nickel and cobalt hydroxide
(Ni_0.8Co_0.2(OH)_Two) Was produced by coprecipitation. Next, this 2
Dispersion by adding water to mol / l nickel-cobalt hydroxide
And an aqueous solution of sodium hydroxide is added dropwise to the dispersion.
While maintaining the pH at 10-13, 0.99
mol / l cobalt nitrate and 0.01 mol / l magnesium nitrate
An aqueous solution in which is dissolved is dropped, and nickel-cobalt hydroxyl is added.
Of magnesium-cobalt hydroxide on the surface of the oxide
And coated with magnesium-cobalt hydroxide.
A nickel-cobalt hydroxide was synthesized. At this time, nitric acid
Drops of aqueous solution dissolving cobalt and magnesium nitrate
The lower amount is the amount of nickel-cobalt hydroxide added to the dispersion.
It was adjusted to 1 mol% based on the number of moles. Where water
The composition of the oxide is nickel nitrate, cobalt nitrate,
Adjust by adjusting the concentration of the gnesium solution.
And the coating amount is cobalt nitrate-magnesium.
Can be adjusted by adjusting the drop amount of the aqueous solution.
it can. Next, the synthesized hydroxide is washed with water and dried.
And then coated with this magnesium-cobalt hydroxide
Lithium hydroxide in nickel-cobalt hydroxide
Nickel-co coated with nesium-cobalt hydroxide
1 mole of lithium hydroxide per mole of Baltic hydroxide
Mixed in an oxidizing atmosphere such as oxygen or air
By firing at ~ 900 ° C for 24 hours, LiCo_0.99Mg_0.01O
_TwoLiNi coated with _0.8Co_0.2O_TwoWas synthesized. The third element
LiNi with elemental M added_1-yzCo_xM_zO_TwoWhen synthesizing
When synthesizing nickel-cobalt hydroxide,
It can be synthesized by adding M. above
LiCo synthesized by coprecipitation method_0.99Mg_0.01O_TwoLi coated with
Ni_0.8Co_0.2O_TwoThe electronic conductivity and discharge at high rate
Measure capacity and charge / discharge characteristics in the same way as above
Was performed. Also, LiCo_0.99Mg_0.01O_TwoLiNi coated with
_0.8Co_0.2O_TwoAbout LiCo_0.99Mg_0.01O_TwoOf LiCo
_0.99Mg_0.01O_Two: LiNi_0.8Co_0.2O_Two5:95, 10: 9 by molar ratio of
0, 20:80, 30:70, 40:60, 50:50 and above
Adjustment was performed in the same manner and a similar test was performed. As a result
Are shown in Table 2. The charging current is 0.5mA / cm^TwoAnd then
5mA / cm after charging to 4.3V^TwoDischarge electricity
The battery was discharged to 3.0 V against lithium metal. Also,
The cycle test is performed by repeating this operation.
Was.

[0009]

[Table 2]

From Table 2, it was found that coating with LiCo _0.99 Mg _0.01 O ₂ improves the electron conductivity. Further, the discharge capacity increases up to a molar ratio of the coating layer of up to 5%, but the discharge capacity decreases as the molar ratio of the coating layer further increases. This is because the proportion of LiCo _0.99 Mg _0.01 O ₂ having a small capacity increases. It was also found that the higher the rate of the coating layer, the higher the discharge characteristics at high rates. On the other hand, the cycle characteristics show good characteristics when the molar ratio of the coating layer is in the range of 5 to 20%. As described above, the coating amount of LiCo _0.99 Mg _0.01 O ₂ is LiNi _0.8 Co _0.2 O ₂
By controlling the molar ratio to 1% to 40%, an excellent effect can be obtained. More preferably 5
% To 20%. The coating method is not limited to the above method, and a known method can be used. Also, LiNi _1-yz Co _y M _z O ₂ (0 ≦ y ≦ 0.25, 0 ≦
z ≦ 0.15, M is the third element of metals other than Co and Ni)
M is not particularly limited as long as it is a metal that can co-precipitate with nickel-cobalt hydroxide, but is more preferably Al, Mg, Ti, Mn, Fe, Cr, or Cu. Also, Li
Ni _1-yz Co _y M _z O ₂ (0 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.1
5. M is a metal other than Co and Ni) and LiCo _1-x Mg _x O ₂ (0.01
≦ x <0.1), the same results are obtained with the composition shown. In addition, LiNi _1-yz Co _y M _z O
₂ (0.15 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.15, M is Co,
The particles of metal (other than Ni) may be primary or secondary particles, but primary particles are preferred. In addition, since the positive electrode active material according to the present invention has excellent electron conductivity, the amount of a conduction aid such as acetylene black and metal particles conventionally contained in the positive electrode mixture layer can be reduced. If the reduced amount is replaced with a positive electrode active material, it is possible to further increase the capacity. The shape of the battery may be any shape such as a square shape, a cylindrical shape, a coin shape or a paper shape, and the structure of the battery, and the structures and configurations of the positive electrode and the negative electrode are not limited. In the non-aqueous electrolyte secondary battery according to the present invention, as a configuration thereof, a combination of a positive electrode, a negative electrode and a separator with a non-aqueous electrolyte, or a positive electrode, an organic or inorganic solid electrolyte and a non-aqueous electrolyte as a negative electrode and a separator. A combination, or a combination of a positive electrode, a negative electrode and a separator, a combination of an organic or inorganic solid electrolyte and a non-aqueous electrolyte, or a combination of a positive electrode, a negative electrode and a separator of an organic or inorganic solid electrolyte and a non-aqueous electrolyte as a separator may be used. . Of course, a non-aqueous electrolyte is unnecessary if it is an ion conductive solid electrolyte. Further, as the separator or the organic or inorganic solid electrolyte as the separator, the non-aqueous electrolyte, the electrolyte salt, etc., any known one can be used.

Furthermore, the organic solvent is not fundamentally limited. The same effects as those of the present invention can be obtained as long as they are conventionally used for lithium batteries. For example, as a solvent, a low-viscosity solvent such as 1,2-dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl formate is mixed with a high dielectric constant solvent such as propylene carbonate, ethylene carbonate, γ-butyrolactone, and sulfolane. What was done can be used.

In the present invention, when applied to a non-aqueous electrolyte lithium ion secondary battery, the host material of the negative electrode may be any material as long as it can occlude and release lithium ions. For example, coke, carbon, amorphous carbon , SnO, SnO ₂ , Sn _1-x M _x O
(M = Hg, P, B, Si, Ge or Sb, provided that 0 ≦
_{X <1), Sn 1-} x M x O 2 (M = Hg, P, B, Si,
Ge or Sb, provided that 0 ≦ X <1), Sn ₃ O ₂ (OH)
₂ , Sn _3-x M _x O ₂ (OH) ₂ (M = Mg, P, B, S
i, Ge, Sb, As or Mn, provided that 0 ≦ X <3),
One or more selected from LiSiO ₂ , SiO _{2 and} LiSnO ₂ can be exemplified.

[0013]

According to the present invention, a non-aqueous electrolyte secondary battery having a high capacity and excellent discharge characteristics at a high rate can be provided. Therefore, the industrial value of the present invention is extremely high.

Claims (1)

[Claims] 1. The method according to claim 1, wherein LiNi _1-yz Co _y M _z O ₂ (0 ≦ y ≦ 0.25,
0 ≦ z ≦ 0.15, M is a positive electrode active material whose particle surface is coated with a single-layer LiCo _1-x Mg _x O ₂ (0.01 ≦ x <0.1) A non-aqueous electrolyte secondary battery comprising a substance.