JPH09147861A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery which has sufficient charging and discharging capacity even in the case where lithium copper composite oxide, whose cost is lower than that of metal oxide containing lithium such as LiCoO2 or the like, is used as positive electrode material. SOLUTION: In a lithium secondary battery, metal lithium or material which can store and discharge lithium ions is used for a negative electrode 2, and simultaneously material which can store and discharge lithium ions is used for a positive electrode 1. One kind element or more selected out of B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Zr, Nb, Ru, Ag, Ta, Bi, In, Mo, W are compounded with Lithium copper composite oxide so as to be used as the material for the positive electrode 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery using a material capable of storing and releasing metallic lithium or lithium ions for the negative electrode and a material capable of storing and releasing lithium ions for the positive electrode. In particular, the present invention relates to a lithium secondary battery using a material for its positive electrode, which is inexpensive and has good lithium ion storage / release characteristics.

[0002]

2. Description of the Related Art In recent years, as one of new type secondary batteries having high output and high energy density, lithium secondary batteries which are charged and discharged by utilizing redox of lithium have come into use. .

Various materials have been conventionally used as materials for the positive electrode and the negative electrode in this lithium secondary battery. The material for the positive electrode is, for example, LiCoO 2 capable of absorbing and desorbing lithium ions. ₂ , LiNiO
₂ , lithium-containing metal oxides such as LiMnO ₂ have been commonly used.

However, these lithium-containing metal oxides generally have a problem of high cost, and new materials capable of inserting and extracting lithium ions have been investigated.

Here, as an inexpensive material capable of inserting and extracting lithium ions, lithium copper composite oxide Li _{2 is used.}
Although CuO _{2 and the} like have been known, this lithium-copper composite oxide has the above-mentioned LiCoO ₂ , LiNiO ₂ , and LiMnO ₂
Has a smaller capacity to store and release lithium ions than other lithium-containing metal oxides, and when used as a material for the positive electrode, a sufficient charge / discharge capacity as a lithium secondary battery cannot be obtained. was there.

[0006]

DISCLOSURE OF THE INVENTION The present invention uses a material capable of occluding and releasing metallic lithium or lithium ions for the negative electrode and a lithium secondary battery using a material capable of occluding and releasing lithium ions for the positive electrode. It is an object to solve the above problems in a battery, and L
An object of the present invention is to obtain a lithium secondary battery having a sufficient charge / discharge capacity even when using a lithium-copper composite oxide that is cheaper than a lithium-containing metal oxide such as iCoO ₂ , LiNiO ₂ , and LiMnO _2. It is what

[0007]

In the lithium secondary battery of the present invention, a material capable of storing and releasing metallic lithium or lithium ions is used for the negative electrode, and a material capable of storing and releasing lithium ions is used for the positive electrode. In the lithium secondary battery using, as the material of the positive electrode,
B, Na, Mg, Al, S in lithium copper composite oxide
i, K, Ca, Sc, Ti, V, Cr, Mn, Fe, C
o, Ni, Zn, Ga, Ge, Zr, Nb, Ru, A
A composite of one or more elements selected from g, Ta, Bi, In, Mo and W is used.

According to the consideration of the present inventors, when a lithium-copper composite oxide is used as a material for a positive electrode as in the lithium secondary battery of the present invention, the lithium copper composite oxide contains the above-mentioned elements. It is considered that when one or more of these are compounded, the redox of copper in this lithium-copper composite oxide will be carried out smoothly. Therefore, even if this lithium-copper composite oxide is used for this positive electrode. , LiCoO ₂ , LiNiO ₂ , LiMnO _{2 and the} like, a lithium secondary battery having a sufficient charge / discharge capacity similar to the case of using a lithium-containing metal oxide can be obtained.

If the amount of the above-mentioned element to be complexed with the lithium-copper composite oxide is small, the oxidation-reduction of copper in the lithium-copper composite oxide cannot be carried out smoothly, but the amount becomes too large. And the electrode activity in the positive electrode is reduced by the presence of the above elements alone, the charge and discharge capacity in the lithium secondary battery is reduced in any case, so that the complex with the lithium copper composite oxide The amount of element is C in the lithium-copper composite oxide.
It is preferably about 2 to 25 mol% with respect to u.

Therefore, as the material of the positive electrode used in the above lithium secondary battery, Lix Cu1-y My Oz (M is B, Na, Mg, Al, Si, K, Ca, Sc,
Ti, V, Cr, Mn, Fe, Co, Ni, Zn, G
a, Ge, Zr, Nb, Ru, Ag, Ta, Bi, I
One or more elements selected from n, Mo and W,
x, y, z are 0 <x ≦ 2.6, 0.02 ≦ y ≦ 0.
2, 1.8 ≦ z ≦ 2.2. It is preferable to use the material represented by the general formula (1).

Further, in the lithium secondary battery of the present invention, examples of the material capable of inserting and extracting lithium ions used for the negative electrode include carbon materials such as graphite, coke, and an organic fired body, Li-Al, Li-In, L
i-Sn, Li-Pb, Li-Bi, Li-Ga, Li
-Sr, Li-Si, Li-Zn, Li-Cd, Li-
A lithium alloy such as Ca or Li-Ba is used.

As the electrolyte in the lithium secondary battery of the present invention, a known non-aqueous electrolytic solution or a polymer solid electrolyte can be used, and a known solvent can also be used as the solvent in the non-aqueous electrolytic solution. It is possible to use, for example, organic solvents such as ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, and diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane in these organic solvents. It is possible to use a mixed solvent obtained by mixing a low boiling point solvent such as, and known solutes to be dissolved in this solvent, for example, LiPF ₆ , LiCF ₃ SO ₃ , LiCl.
O ₄ , LiBF ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl
₁₂ etc. can be used.

Also, when a polymer solid electrolyte is used, a known polymer can be used as the polymer constituting the polymer solid electrolyte, and in particular, a polymer having a high ionic conductivity for lithium ions is used. Preferably
For example, polyethylene oxide, polypropylene oxide, polyethyleneimine and the like are preferably used, and it is also possible to add the above solvent to the polymer together with the above solvent to form a gel.

[0014]

EXAMPLES Hereinafter, the lithium secondary battery according to the example of the present invention will be specifically described with reference to experimental examples, and it will be shown that the lithium secondary battery according to this example is excellent in charge and discharge characteristics. Make it clear. The lithium secondary battery according to the present invention is not limited to the examples shown below, and may be appropriately modified within the scope of the invention.

(Experimental Examples 1 to 6) In these experimental examples, the positive electrode, the negative electrode and the non-aqueous electrolyte prepared as described below were used to obtain a diameter of 24.0 mm and a thickness of 3.0 mm. A coin-type lithium secondary battery as shown in 1 was manufactured.

[Production of Positive Electrode] In the production of the positive electrode in these experimental examples, LiOH and CuO were used as raw materials in Experimental Example 1, and the molar ratio of Li and Cu was 2: 2.
1, so that LiOH was used in Experimental Examples 2 to 6.
And CuO, B ₂ O ₃ was used, and Li, Cu, and B were mixed so that the molar ratio was 2: 0.98: 0.02 in Experimental Example 2, and Li was mixed in Experimental Examples 3 to 6. The molar ratio of Cu and B was changed.

Then, these mixtures were respectively calcined in a dry air atmosphere at 850 ° C. for 20 hours to obtain Li ₂ CuO _{2 in} Experimental Example 1 and in the general formula Lix Cu1-y My Oz in Experimental Examples 2 to 6. M consists of B, y
A positive electrode material having a value shown in Table 1 below was obtained.

Then, each positive electrode material obtained in the above Experimental Examples 1 to 6 was crushed in an Ishikawa type raid mortar, and each powder thus obtained, acetylene black as a conductive agent, and fluororesin as a binder. The powder and the weight ratio of 90: 6:
4 to prepare a positive electrode mixture, and the positive electrode mixture was pressure-molded at a molding pressure of 2 ton / cm ^{2 into} a disk shape having a diameter of 20 mm, and thereafter, these were each mixed at 250 ° C. for 2 hours. Heat treatment was performed for a period of time to produce the positive electrode of each experimental example.

[Preparation of Negative Electrode] In these experimental examples, a negative electrode was prepared by punching a disc having a diameter of 20 mm from a lithium rolled plate having a predetermined thickness to prepare the negative electrode.

[Preparation of Non-Aqueous Electrolyte Solution] In these experimental examples, Li was added to a mixed solvent in which propylene carbonate and 1,2-dimethoxyethane were mixed at a volume ratio of 1: 1.
Cl ₄ was dissolved at a ratio of 1 mol / l to prepare a non-aqueous electrolytic solution.

[Production of Battery] Then, in producing each lithium secondary battery of Experimental Examples 1 to 6, as shown in FIG. 1, each positive electrode 1 and each negative electrode 2 produced as described above.
A separator 3 composed of a polypropylene microporous film (Hoechst Celanese Co., Ltd., Celgard) is sandwiched between the two, and the separator 3 is impregnated with the above non-aqueous electrolytic solution to form a positive electrode can 4a and a negative electrode. The positive electrode 1 is connected to the positive electrode can 4a via the positive electrode collector 5 while being housed in the battery case 4 formed by the can 4b, while the negative electrode 2 is connected to the negative electrode can 4b via the negative electrode collector 6. , And the positive electrode can 4a and the negative electrode can 4b were electrically insulated by the insulating packing 7 made of polypropylene to produce the lithium secondary batteries of Experimental Examples 1 to 6. Then, the chemical energy generated inside each lithium secondary battery was taken out as electric energy from both terminals of the positive electrode can 4a and the negative electrode can 4b.

Next, Experimental Example 1 produced as described above
In order to investigate the discharge characteristics of each of the lithium secondary batteries of Nos. 6 to 6, each lithium secondary battery was charged to a charge end voltage of 4.3 V at a charge current of 1 mA, and then discharged to a discharge end voltage of 2.0 V at a discharge current of 3 mA. The discharge capacities of the lithium secondary batteries of Experimental Examples 1 to 6 were examined, and the results are also shown in Table 1 below.

[0023]

[Table 1]

As is clear from these results, B was added in a predetermined ratio to Cu in the lithium-copper composite oxide, and particularly y in the general formula Lix Cu1-y My Oz was used.
In each of the lithium secondary batteries of Experimental Examples 2 to 5 in which the value was in the range of 0.02 ≦ y ≦ 0.2 as described above, compared with the lithium secondary battery of Experimental Example 1 in which B was not added. The discharge capacity was remarkably large.

(Experimental Examples 7 to 66) In these Experimental Examples, only the positive electrode in the lithium secondary batteries of Experimental Examples 1 to 6 was changed, and other than that, each lithium of Experimental Examples 1 to 6 was changed. A coin-type lithium secondary battery as shown in FIG. 1 was produced in the same manner as the secondary battery.

Here, in Experimental Examples 7 to 66,
In producing the positive electrode, as shown in Tables 2 to 4 below, the raw materials added to LiOH and CuO were changed, and the element of M and the y value in the general formula Lix Cu1-y My Oz were changed. The positive electrode was manufactured in the same manner as in Experimental Examples 1 to 6 except for the changes as shown in these tables.

Then, Experimental Example 7 produced in this way
For each of the lithium secondary batteries of No. 66 to No. 66, the discharge characteristics of each of the lithium secondary batteries were examined in the same manner as in the case of Experimental Examples 1 to 6 above, and the results are also shown in these tables.

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

As is clear from this result, the elements of M in the above-mentioned general formula Lix Cu1-y My Oz are replaced by B, N.
a, Mg, Al, Si, K, Ca, Sc, Ti, V, C
r, Mn, Fe, Co, Ni, Zn, Ga, Ge, Z
At least one element selected from r, Nb, Ru, Ag, Ta, Bi, In, Mo and W is used, and y
The discharge capacity was remarkably high in the lithium secondary battery of each experimental example having a value in the range of 0.02 to 0.2.

[0032]

As described above in detail, in the lithium secondary battery according to the present invention, when the lithium copper composite oxide is used as the material of the positive electrode, B, Na, Mg, Al, Si, K, Ca, S
c, Ti, V, Cr, Mn, Fe, Co, Ni, Zn,
Ga, Ge, Zr, Nb, Ru, Ag, Ta, Bi, I
Since one or more elements selected from n, Mo and W are compounded, the redox of copper in the lithium-copper composite oxide used for the positive electrode can be smoothly performed,
In particular, the amount of the element to be complexed with the lithium copper complex oxide is adjusted so that the y value of the element M represented by the general formula Lix Cu1-y My Oz becomes 0.02-0.2. In this case, a lithium secondary battery having a sufficient charge / discharge capacity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the internal structure of each lithium secondary battery of Experimental Examples 1 to 66.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Noma 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 in Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A lithium secondary battery using a material capable of occluding and releasing metallic lithium or lithium ions for the negative electrode and a material capable of occluding and releasing lithium ions for the positive electrode. As lithium copper composite oxide, B, Na, Mg, Al, Si, K, C
a, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,
Zn, Ga, Ge, Zr, Nb, Ru, Ag, Ta, B
A lithium secondary battery comprising a composite of one or more elements selected from i, In, Mo and W. 2. A lithium secondary battery using a material capable of absorbing and desorbing metallic lithium or lithium ions for the negative electrode and a material capable of absorbing and desorbing lithium ions for the positive electrode. As Lix Cu1-y My Oz (M is B, Na, Mg, Al, Si, K, Ca, Sc,
Ti, V, Cr, Mn, Fe, Co, Ni, Zn, G
a, Ge, Zr, Nb, Ru, Ag, Ta, Bi, I
One or more elements selected from n, Mo and W,
x, y, and z are 0 <x ≦ 2.6, 0.02 ≦ y ≦ 0.
2, 1.8 ≦ z ≦ 2.2. ) A lithium secondary battery characterized by using a material represented by the general formula (1).