JP2001351614A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high energy density, long life and improved safety in a lithium secondary battery. SOLUTION: The lithium secondary battery 10 comprises a positive electrode 4 having a positive electrode active material which is provided through a separator 6, a negative electrode 5 having a negative electrode active material and an electrolyte. In this, the negative electrode or the negative electrode current collector contains a substance which compensates the capacity deterioration of the negative electrode active material. This substance is a mixture of an amorphous substance which does not react with lithium and a substance which reacts with lithium. As an amorphous substance which does not react with lithium, silicon dioxide is preferable and as a substance which reacts with lithium, silver, aluminum, silicon or the like are preferable. With the above structure, a lithium secondary battery is realized which has an excellent charge and discharge cycle and high energy density as well as superior safety.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode active material for a secondary battery, and more particularly to a lithium secondary battery having a large charge / discharge energy, an excellent cycle life, and a high safety.

[0002]

_2. Description of the Related Art Conventionally, as a positive electrode active material of a non-aqueous electrolyte secondary battery, metal chalcogenides such as TiS ₂ , MoS ₂ and NbSe ₃ and simple oxides such as MnO ₂ , MoO ₃ and V ₂ O ₅ have been used. Or LiCoO ₂ , LiNiO ₂ ,
Lithium-containing metal oxides such as LiMn ₂ O ₄ have been proposed. In addition, alloy materials such as Al, which can occlude and release lithium metal and lithium,
Alternatively, materials using tin oxide as an occlusion substance such as a carbon-based material that occludes Li ions between layers have been proposed,
Some of them are already in practical use.

[0003]

In the above-mentioned negative electrode material, among the materials other than lithium metal, in particular, when an alloy based on which a high capacity can be expected is used, the efficiency of use of lithium during charge and discharge is reduced. There is a problem that the electrode material is low and cracks and the like are apt to occur in the electrode material at the time of charge / discharge cycles. This has been a factor of significantly shortening the cycle life of the battery.

[0004] Among the above, when a lithium intercalation compound such as a carbon material is used, the crystal structure is destroyed at the time of overcharge or overdischarge, or an irreversible substance at the time of inserting and extracting lithium. There is a problem that the active material is degraded due to the generation of slag. In particular, in the case of a lithium metal anode,
Dendritic crystals are easily formed on the surface of the negative electrode, which poses a problem in the safety of the battery. For this reason, high-capacity, long-life, and safe materials have not yet been realized in the above-mentioned negative electrode materials. It is.

The present invention has been made to solve the above problems, and has as its object to provide a highly safe lithium secondary battery having a high energy density and excellent charge / discharge cycles.

[0006]

Means for Solving the Problems Normally, in a secondary battery, repeated charging / discharging causes cycle deterioration, and a phenomenon in which the battery capacity gradually decreases is observed. We found that this problem can be solved by devising it.

[0007] That is, a lithium secondary battery according to claim 1 has a positive electrode provided with a positive electrode active material, a negative electrode provided with a negative electrode active material, and an electrolyte provided through a separator. , Wherein the negative electrode or the negative electrode current collector contains a material for compensating for capacity deterioration of the negative electrode active material.

Further, the lithium secondary battery according to the present invention is characterized in that the material for compensating for the capacity deterioration is a mixture of an amorphous material which does not react with lithium and a material which reacts with lithium.

Further, in the lithium secondary battery according to the present invention, the amorphous substance which does not react with lithium is silicon dioxide, and the substance which reacts with lithium is silver, aluminum, or silicon. It is characterized by:

[0010] The lithium secondary battery according to a fourth aspect is characterized in that the mixture is produced by a sputtering method.

As described above, by adding a substance whose reversible capacity increases as the charge / discharge cycle progresses,
A secondary battery that can maintain stable battery capacity while suppressing cycle deterioration can be realized. For example, when amorphous silicon dioxide is used as a target and sputtering is performed on a copper current collector with a silver chip placed on the target, the resulting sputtered film increases in battery capacity as charge and discharge cycles are repeated. I found out. Although the reason is not clear, it is considered that, by repeating charge and discharge, the number of lithium conduction paths inside the sputtered film increases, and the amount of silver used for charge and discharge increases. The capacity of the sputtered film and its increase ratio can be adjusted by the number of silver chips to be put on the target, the substrate temperature during sputtering, the sputtering atmosphere, the firing temperature after sputtering, and the firing atmosphere.

When the negative electrode material of the present invention is used,
Lithium ion can be reversibly inserted and removed as a positive electrode active material.
Transition metal oxides and the like can be used.
oO ₂ , LiNiO₂ , LiMn₂O₄Etc.
However, the present invention is not necessarily limited to these.
In addition, non-aqueous electrolytes, polymer electrolytes, inorganic
Solid electrolytes and the like are preferred. Normally, non-aqueous electrolytes are
And a salt that dissolves in the solvent of the non-aqueous solvent and
Including chain esters and cyclic ethers
Various solvents can be used.
Carbonate, propylene carbonate, dimethical
Carbonate, diethyl carbonate, 1,2-dimethoate
Xyethane, etc., but of course other than these
You may use it. Also, as the electrolyte, usually used
Any one can be used, for example, LiBF
₄ , LiPF₆ , LiClO₄ , CF₃SO₃Li
And so on. In addition, other, solid electrolyte and polymer electrolyte,
Alternatively, a polymer electrolyte or the like may be used.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A lithium secondary battery according to the present invention will be described below with reference to FIGS.

FIG. 1 is a view showing the internal structure of a coin-type lithium secondary battery to which the present invention is applied.

A coin-type lithium secondary battery 10 shown in FIG.
, Reference numeral 1 denotes a battery case formed by processing a stainless steel plate having resistance to organic electrolyte into a disc shape, reference numeral 2 denotes a sealing plate made of the same material as the battery case 1, reference numeral 3 denotes a current collector, and reference numeral 4 denotes metallic lithium. Reference numeral 5 is a mixture containing the active material of the present invention, 6 is a microporous separator made of polypropylene, and 7 is a gasket made of polypropylene. Incidentally, the coin-type lithium secondary battery 10 has a thickness of 5 mm and a diameter of 24 m.
It is a size such as m.

[0016]

EXAMPLES In order to evaluate the active material of the present invention, a coin-type lithium secondary battery for evaluation was prepared in the following manner.

Example 1 The above active material was produced as follows. First, alkali aluminosilicate glass (composition, N
a ₂ O: MgO: Al ₂ O ₃ : SiO ₂ : K ₂ O: trace component = 12: 6: 12: 65: 3: 2 mol%) using a pulverizer to grind to a particle size of about 20 μm or less. The powder was ion-exchanged in a high-purity alumina crucible while stirring about 100 g of AgNo ₃ and about 10 g of glass powder in an electric furnace at 300 ° C. for 24 hours. Then, the solidified Ag
NO ₃ was dissolved and filtered in pure water to separate the ion-exchanged powder, and washed with pure water to produce a composite oxide glass.

To 46% by weight of the composite oxide glass thus obtained, 50% by weight of graphite as a conductive material and 4% by weight of polytetrafluoroethylene as a binder were mixed, and the active material mixture was mixed. Obtained. A predetermined amount of this mixture is pressure-formed on the negative electrode current collector 3 and is heated to 120 ° C. using a vacuum dryer.
And dried under reduced pressure for 6 hours.

Further, in addition to this active material mixture, 12 silver chips each having a size of 5 mm square are arranged on an amorphous silicon dioxide target, and the thickness thereof is formed on a copper foil under the conditions of RF power of 200 W and argon gas of 2.7 Pa. A sputtered film of about 8 μm was formed, and the mixture was hit on the sputtered film on the copper foil to assemble the coin-type lithium secondary battery of the present invention shown in FIG. In addition, a 1 N solution in which LiPF ₆ was dissolved in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate was used as the electrolytic solution.

(Comparative Example 1) A cell was fabricated in the same procedure using only the same active material mixture as in Example 1 without using a sputtered film, and a coin type lithium secondary battery for comparison was assembled. .

(Comparative Example 2) A cell was manufactured in the same procedure using only the sputtered film without using the active material mixture of Example 1, and a coin type lithium secondary battery for comparison was assembled. .

(Example 2) Instead of the alkali aluminosilicate glass used in Example 1, an alkali aluminoborosilicate glass (composition, Na ₂ O: Al ₂ O ₃ : Si) was used.
O ₂ : B ₂ O ₃ = 15: 16: 64: 5 mol%)
A cell was manufactured in the same procedure as in Example 1 except that silicon was used as a chip for sputtering, and a coin-type lithium secondary battery of the present invention was assembled.

(Comparative Example 3) A cell was fabricated in the same procedure using the same active material mixture as in Example 2 without using a sputtered film, and a coin-type lithium secondary battery was assembled.

Comparative Example 4 A coin-type lithium secondary battery for comparison was prepared by using the sputtered film of Example 2 but not using the active material mixture of Example 2 and forming cells in the same procedure. Was assembled.

After the coin-type lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4 were aged at room temperature for about one week, a charge / discharge cycle test was performed.
The capacity characteristics of each battery were investigated, and the results are shown in FIGS. The charge / discharge test was performed with a current of 0.2 mA / cm ² , a charge end voltage of 2.0 V, and a discharge end voltage of 0.005 V. The number of cycles performed was 2 in each case.
It was set to 0 times. Here, the characteristic A in FIG.
3 indicates Comparative Example 1, characteristic C indicates Comparative Example 2, characteristic D in FIG. 3 indicates Example 2, characteristic E indicates Comparative Example 3, and characteristic F indicates Comparative Example 4.

According to FIGS. 2 and 3, active materials whose battery capacity deteriorates as the charge / discharge cycle progresses (characteristics B and E correspond to these) are substances (characteristics corresponding to the deterioration). C, characteristic F is equivalent to this)
It can be seen that a battery having stable characteristics without cycle deterioration (characteristics A and D correspond thereto) can be manufactured.

[0027]

As described above, according to the lithium secondary battery of the present invention, a substance whose reversible capacity increases as the charge / discharge cycle progresses is added to the negative electrode material, whereby the charge / discharge cycle is excellent. In addition, a lithium secondary battery having high energy density and excellent safety can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an internal structure of a coin-type lithium secondary battery to which the present invention is applied.

FIG. 2 is a diagram showing charge / discharge cycle characteristics of a battery.

FIG. 3 is a diagram showing charge / discharge cycle characteristics of a battery different from that of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Current collector 4 Metal lithium 5 Active material mixture 6 Separator 7 Gasket 10 Coin-type lithium secondary battery

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) CB12 DA03 DA04 DA09 EA02 EA05 EA12 FA20 GA10 GA24

Claims (4)

[Claims] 1. A lithium secondary battery comprising: a positive electrode provided with a positive electrode active material, a negative electrode provided with a negative electrode active material, and an electrolyte provided through a separator; wherein the negative electrode or the negative electrode current collector is a negative electrode A lithium secondary battery including a substance that compensates for capacity deterioration of an active material. 2. The lithium secondary battery according to claim 1, wherein the material that compensates for the capacity deterioration is a mixture of an amorphous material that does not react with lithium and a material that reacts with lithium. 3. The lithium according to claim 2, wherein the amorphous material that does not react with lithium is silicon dioxide, and the material that reacts with lithium is silver, aluminum, or silicon. Rechargeable battery. 4. The lithium secondary battery according to claim 2, wherein the mixture is formed by using a sputtering method.