JP2561556B2 - Positive electrode active material for lithium secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a positive electrode active material for a lithium secondary battery, which uses lithium or a lithium alloy as a negative electrode active material.

[Conventional technology]

Conventionally, for example, vanadium pentoxide and titanium disulfide with low superpower, and manganese dioxide with relatively low electronic conductivity are used as positive electrode active materials for non-aqueous electrolyte secondary batteries such as lithium secondary batteries. There is.

[Problems to be Solved by the Invention]

By the way, when vanadium pentoxide and titanium disulfide as described above are used as the positive electrode active material, the material cost becomes bulky and the battery becomes expensive, or the super power such as titanium disulfide is low and the battery is low. Since manganese dioxide is not preferable in terms of characteristics, the manganese dioxide is generally used because it is inexpensive and can obtain good superpower.

However, this manganese dioxide positive electrode active material has a relatively low electronic conductivity as described above, which increases the internal resistance of the battery and also causes an electrode reaction (MnO ₂ + Li ⁺ + e ⁻
→ LiMnO ₂ ) did not progress sufficiently and the utilization rate was decreasing.

It is an object of the present invention to provide a positive electrode active material for a lithium secondary battery, which can reduce the internal resistance and improve the utilization rate by improving the electronic conductivity of the positive electrode containing manganese.

[Means for solving the problem]

The present invention relates to a positive electrode active material for a lithium secondary battery, which uses lithium or a lithium alloy as a negative electrode active material, is represented by the following composition formula (I), and the atomic ratio of Mn, Co, and Ni is shown in FIG. Point A (x = 0.95, y = 0.05, z = 0), point B (x = 0.05, y = 0.95, z = 0), point C (x = 0, y)
= 0.95, z = 0.05), point D (x = 0, y = 0.66, z = 0.
34), point E (x = 0.66, y = 0, z = 0.34), point F (x
= 0.95, y = 0, z = 0.05) (however,
a range of z = 0, and y = 0, and x is 0.75 to
The present invention provides a positive electrode active material for a lithium secondary battery, which is an oxide of 0.95 and z is in the range of 0.05 to 0.25) and is sintered in an oxygen atmosphere.

LiMn _x Co _y Ni _z O ₂ (I) (x + y + z = 1) In the positive electrode active material of the present invention, the atomic ratio of Mn, Co, and Ni is A → B → C → D → E → F → A. Within a range surrounded by (where z = 0, and y = 0, x
Except 0.75 to 0.95 and z is 0.05 to 0.25)
In addition, when Mn is larger than on the points A to F, the electrical conductivity is lowered and the utilization rate is the same as that of MnO _2, and when Co is larger than on the points B to C, the cycle stability is significantly deteriorated. Further, when the amount of Ni is larger than that on the lines D to E, the discharge capacity is remarkably reduced, which is not preferable.

In the present invention, the atomic ratio of the range of points A to F (excluding the range where z = 0 and the range where y = 0 and x is 0.75 to 0.95 and z is 0.05 to 0.25) The use of the oxide can improve the electronic conductivity of the positive electrode containing manganese, which can reduce the internal resistance and improve the utilization rate of the lithium secondary battery.

When a positive electrode is manufactured using this positive electrode active material, the particle size of the positive electrode active material is not necessarily limited, but the average particle size is 5 μm.
A high-performance positive electrode can be produced by using a resin having a thickness of m or less. In this case, to these powders, a conductive agent such as acetylene black or a binder such as fluororesin powder is added and mixed, kneaded with an organic solvent, rolled with a roll, and dried by a method such as a positive electrode. Can be produced. The conductive agent may be mixed in an amount of 5 to 50 parts by weight, particularly 7 to 10 parts by weight, based on 100 parts by weight of the positive electrode active material. In the present invention, the conductivity of the positive electrode active material is good. Therefore, the amount of conductive agent used can be reduced. Further, the compounding amount of the binder is preferably 5 to 10 parts by weight with respect to 100 parts by weight of the positive electrode active material.

The positive electrode active material of the present invention, for example, an organic solvent such as ethanol is added to a mixture of lithium carbonate, manganese carbonate and cobalt carbonate, crushed by a crushing means such as a ball mill, and after drying, a temperature of 750 to 950 in an oxygen atmosphere. It can be produced by firing at 2 ° C. for about 2 to 6 hours, further adding the organic solvent, pulverizing with a ball mill, and drying.

The non-aqueous electrolyte used in the secondary battery using the positive electrode active material of the present invention is chemically stable with respect to the positive electrode active material and the negative electrode active material, and the lithium ions are electrically stable with the positive electrode active material. Any non-aqueous substance that can move in order to undergo a chemical reaction can be used, in particular, a compound composed of a combination of a cation and an anion, such as Li ⁺ as a cation and P as an example of an anion.
_{^{F 6 -, AsF 6 -,}} SbF 6 - halide anion of halogen group elements Va group element, such _{^{as, I - (I 3 -)}} , Br -, Cl - halogen anion such as, ClO ₄ ^- like a perchlorate _{^{anion, HF 2 -, CF 3 SO}} 3 -, SCN - and the like can be mentioned compounds having an anion such as, but not necessarily limited to these anions. Such a cation,
Specific examples of electrolytes having anions include LiPF ₆ and LiAsF
₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ , LiI, LiBr, LiCl, LiAlC
l ₄ , LiHF ₂ , LiSCN, LiSO ₃ CF _{3 and the} like.

Among these, especially LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiCl
O ₄ , LiSbF ₆ and LiSO ₃ CF ₃ are preferred.

The non-aqueous electrolyte is usually used in a state of being dissolved in a solvent. In this case, the solvent is not particularly limited, but a solvent having a relatively large polarity is preferably used. Specifically, propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, glymes such as diethylene glycol dimethyl ether, lactones such as r-butyrolactan, phosphate esters such as triethyl phosphate, boro One or more of boric acid esters such as triethyl acid, sulfur compounds such as sulfolane and dimethylsulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, dimethyl sulfate, nitromethane, nitrobenzene and dichloroethane. Can be mentioned. Of these, one or a mixture of two or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane and γ-butyrolactone is particularly preferable.

Further, as the non-aqueous electrolyte, the non-aqueous electrolyte is, for example, polyethylene oxide, polypropylene oxide, an isocyanate cross-linked product of polyethylene oxide, an organic solid electrolyte impregnated with a polymer such as a phosphazene polymer having an ethylene oxide oligomer in the side chain, Inorganic ion derivatives such as Li ₃ N and LiBCl ₄ , Li ₄ SiO ₄ , L
It is also possible to use an inorganic solid electrolyte such as lithium glass such as i ₃ BO ₃ .

A lithium secondary battery using the positive electrode active material of the present invention will be described in more detail with reference to the drawings.

That is, in the lithium secondary battery using the positive electrode active material of the present invention, the opening 10a has the negative electrode cover plate 20 as shown in FIG.
The inside of the button-shaped positive electrode case 10 sealed with is partitioned by the separator 30 having fine holes, and the positive electrode 50 in which the positive electrode current collector 40 is arranged on the positive electrode case 10 side is housed in the partitioned positive electrode side space. The negative electrode 70 in which the negative electrode current collector 60 is arranged on the negative electrode cover plate 20 side is housed in the negative electrode side space.

As the negative electrode active material used for the negative electrode 70, for example, lithium or a lithium alloy capable of absorbing and releasing lithium is used. In this case, as the lithium alloy, a lithium-containing IIa, IIb, IIIa, IVa, Va group metal or an alloy of two or more thereof can be used, but particularly lithium-containing Al, In, Sn, Pb, Bi, Cd, Zn or an alloy of two or more of these is preferable.

As the separator 30, for example, a non-woven fabric or knitted fabric made of a synthetic resin such as polytetrafluoroethylene, polypropylene or polyethylene, which is porous and capable of passing or containing an electrolytic solution, can be used.

Reference numeral 80 is a polyethylene insulating packing that is provided around the inner peripheral surface of the positive electrode case 10 and insulates and supports the negative electrode cover plate 20.

〔Example〕

Hereinafter, an example of the present invention will be described, but the present invention is not necessarily limited to this example.

Comparative Example 1 Li ₂ CO ₃ , M so that the atomic ratio is Li: Mn: Co = 1: 0.5: 0.5.
nCO ₃ and CoCO ₃ were weighed, 25 wt% of ethanol was added and mixed in a ball mill for 2 hours, then dried, and heat-treated in an oxygen atmosphere at 750 ° C. for 2 hours, and then again. 50% by weight of ethanol was added, followed by pulverizing for 12 hours with a ball mill to obtain a powdered positive electrode active material (LiMn _1/2 Co _1/2 O ₂ ).

The obtained positive electrode active material has a carrier concentration in the bulk lower than that of Example 1 described later, as shown by the line a in the graph of FIG. 3, and as a result, the high conductivity of Example 1 was obtained. There wasn't. In addition, regarding the electronic conductivity of the positive electrode,
Inferior to the above, the internal resistance of the lithium secondary battery was higher, and the utilization rate as in Example 1 was not obtained. To 100 parts by weight of this positive electrode active material, 10 parts by weight of acetylene black as a conductive agent and After adding 10 parts by weight of Teflon binder as an adhesive and mixing, kneading with ethanol as an organic solvent, rolling to about 200 μm with a rolling roll, vacuum drying at 150 ° C, and punching to a specified diameter It was used as the positive electrode.

For the negative electrode, an aluminum plate punched out to a predetermined size was pressure-bonded with lithium, and an aluminum-lithium alloy was used in the electrolytic solution. Also, a solvent of propylene carbonate and diethylene glycol dimethyl ether containing 1 mol / mol of LiClO ₄ was used. The battery shown in FIG. 1 was assembled using the electrolyte.

This battery was repeatedly charged and discharged at a discharge end voltage of 2 V and a charge end voltage of 4 V at a charge and discharge of 5 mA, and the discharge capacity at the 50th cycle was 98 Ahr / kg, which was not as high as that of Example 1.

Example 1 Li: Mn: Ni: Co = 1: 0.3 in atomic ratio as a material for the positive electrode active material
3: 0.17: 0.5 of Li ₂ CO ₃ , MnCO ₃ , CoCO ₃ , NiCO ₃ Ni (OH)
_A positive electrode active material (LiMn _1/3 Ni _1/6 Co _1/2 O ₂ ) was obtained in the same manner as in Comparative Example 1 except that 2.4H ₂ O was used.

The obtained positive electrode active material, as shown by the line B in the graph of FIG. As a result, the internal resistance and the utilization rate of the lithium secondary battery have been further reduced.

When a battery was prepared in the same manner as in Comparative Example 1 using this positive electrode active material, the discharge capacity of this battery was 10
A better result was obtained with 3 Ahr / kg.

Comparative Example 2 Li ₂ C with an atomic ratio of Li: Mn = 1: 1 as a material for the positive electrode active material
Comparative Example 1 and Example 2 except that O ₃ and MnCO ₃ were used
A positive electrode active material (LiMnO ₂ ) was obtained in the same manner as in.

The obtained positive electrode active material had a low carrier concentration in the bulk as shown by the line C in the graph of FIG. 3 and only low conductivity was obtained. The internal resistance was high and the utilization rate was low.

Further, when a battery was provided using this positive electrode active material in the same manner as in Comparative Example 1 and Example 2, the discharge capacity of this battery was 90 Ahr / kg, which was a low capacity result.

〔The invention's effect〕

Since the present invention is such, by improving the electronic conductivity of the positive electrode containing manganese, it is possible to obtain an effect that the internal resistance can be reduced and the utilization rate can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the atomic ratio of Mn, Co and Ni in the positive electrode active material for a lithium secondary battery of the present invention, and FIG. 2 is a lithium secondary battery using the positive electrode active material for a lithium secondary battery of the present invention. Fig. 3 is a front view including a partial sectional view of Fig. 3, and Fig. 3 is a graph showing the electrical conductivity of the positive electrode active material for a lithium secondary battery. 50; Positive electrode

Claims (1)

(57) [Claims] 1. A positive electrode active material for a lithium secondary battery, which uses lithium or a lithium alloy as a negative electrode active material, is represented by the following composition formula (I), and the atomic ratio of Mn, Co and Ni is shown in FIG. Point A (x = 0.95, y = 0.05, z = 0), point B (x = 0.05, y = 0.95, z = 0), point C (x = 0, y)
= 0.95, z = 0.05), point D (x = 0, y = 0.66, z = 0.
34), point E (x = 0.66, y = 0, z = 0.34), point F (x
= 0.95, y = 0, z = 0.05) (however,
a range of z = 0, and y = 0, and x is 0.75 to
A positive electrode active material for a lithium secondary battery, which is an oxide of 0.95 and z is in the range of 0.05 to 0.25) and is baked in an oxygen atmosphere. LiMn _x Co _y Ni _z O ₂ (I) (x + y + z = 1)