JPS6313266A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To increase charge-discharge cycle performance by alloying lithium with an aluminium alloy obtained by adding titanium and boron to aluminium, and using in a negative electrode. CONSTITUTION:Two lithium sheets and an aluminium-titanium-boron alloy containing 0.2wt% titanium and 0.05wt% boron are used as negative material. A lithium sheet 3a, an aluminium-titanium-boron alloy sheet 3b, and a lithium sheet 3c are placed in order inside a negative can 1, and a battery is assembled in a regular way. The lithium sheets 3a, 3c and the aluminium-titanium-boron alloy sheet 3b are alloyed under the existence of electrolyte to form a negative electrode 3. Thereby, a lithium secondary battery having excellent chargedischarge performance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lithium secondary battery, and more particularly to improvement of its negative electrode.

[Conventional technology]

Conventionally, lithium secondary batteries used metallic lithium alone as the negative electrode, but due to repeated charging and discharging cycles,
There was a problem that the negative electrode deteriorated. This is because lithium precipitates in a dendrite shape during charging, and this dendrite lithium is very active and reacts with the electrolyte, making it unusable for charging and discharging reactions, or the dendrite lithium is repeatedly charged and discharged. grow by,
This is because it breaks off from its base and falls off, making it unusable for charging and discharging reactions. There was also the problem that dendrite-like lithium, which had grown through repeated charging and discharging, penetrated the separator separating the positive and negative electrodes and came into contact with the positive electrode, causing an internal short circuit and causing the battery to lose its function.

Therefore, it has been proposed to prevent deterioration of the negative electrode and improve charge/discharge cycle characteristics by using a lithium-aluminum alloy for the negative electrode (for example, US Pat. No. 4,002,492, Book III).

The proposal to use a lithium-aluminum alloy for the negative electrode as described above utilizes an electrochemical alloying reaction between lithium and aluminum during charging to diffuse lithium into the aluminum and cause the precipitated lithium to react with the electrolyte. However, the electrochemical alloying reaction between lithium and aluminum during charging is not fast enough, and it is not possible to improve charge/discharge cycle characteristics to a satisfactory level. I couldn't.

Therefore, the present inventors made the crystals finer by using aluminum as the base material and adding small amounts of boron (CB) and titanium (Ti) (however, each was added alone). We have discovered that by increasing the presence of many boundaries and diffusing lithium at grain boundaries, we can speed up the electrochemical alloying of lithium and aluminum and improve the charge/discharge cycle characteristics, and have already filed a patent application for this. No. 60-159723, patent application No. 60-259335)
.

As mentioned above, by alloying boron or titanium with aluminum, the electrochemical alloying reaction between lithium and aluminum during charging becomes faster than when aluminum is used alone, resulting in active precipitated lithium. The amount of time the precipitated lithium remains in the aluminum layer is reduced, and dendrite growth of precipitated lithium is suppressed, resulting in significantly improved charge-discharge cycle characteristics compared to when aluminum is used alone.

However, from the standpoint of using the battery, it is desirable for the battery to have higher charge-discharge cycle characteristics, and the improvements in charge-discharge cycle characteristics provided by the prior art described above are not necessarily satisfactory.

[Problem that the invention seeks to solve]

The present invention solves the problems of the prior art as described above, and also aims to provide a lithium secondary battery with improved charge/discharge cycle characteristics than the prior art for which the present applicant previously filed a patent application. purpose.

[Means for solving problems]

The present invention uses aluminum as a base material and alloys it with titanium and boron, which enables the electrochemical alloying reaction with lithium during charging to be performed not only with aluminum alone but also with aluminum-titanium alloys. It has improved charge-discharge cycle characteristics and is faster than aluminum-boron alloys.

In other words, when small amounts of titanium and boron are added to aluminum, titanium diboride (Ti82) is formed in the aluminum, and in aluminum alloys in which TiB2 is present, the crystal grains continue to become finer even after repeated charging and discharging. The advantage of fast electrochemical alloying reaction with lithium during charging is maintained over a long period of time, and the charge/discharge cycle characteristics are improved compared to aluminum-titanium alloys and aluminum-boron alloys.

Alloying of aluminum, titanium, and boron is usually carried out by so-called metallurgical alloying, in which powders of these materials are mixed and heated and melted, but alloying of this aluminum-titanium-boron alloy with lithium is In addition to metallurgical alloying, it is also possible to carry out electrochemical alloying in the presence of an electrolyte, which makes the alloying operation extremely easy.

Usually, this electrochemical alloying is carried out inside the battery, but it can also be carried out outside the battery.

The amount of titanium and boron in the aluminum alloy is 0.01 to 2.0% by weight for titanium and 0.005 to 2.0% for boron.
It is preferable to set the amount to 0.3% by weight, because if the amount of titanium or boron is less than the above range, the amount of grain boundaries formed will be reduced and the electrochemical alloying reaction with lithium will be accelerated during charging. If the effect decreases, and if the amount of titanium or boron exceeds the above range, uniform alloying with aluminum will be difficult to proceed, and titanium and boron will remain in the aluminum as they are, resulting in a foil-like, In other words, it becomes difficult to form the material into a thin plate shape, and it becomes difficult to perform electrochemical alloying with lithium within the battery, which is the easiest method for forming the negative electrode. The slight difference between the amount of titanium and the amount of boron is basically based on the fact that the stoichiometry required to produce Ti82 is expressed in terms of weight percent. In the present invention, TiB
As long as 2 is formed, a small amount of excess titanium or boron may be present, and both the amount of titanium and the amount of boron can be appropriately selected within the above ranges.

The amount of lithium to be alloyed with this aluminum-titanium-boron alloy, the so-called lithium charge amount, can be varied depending on the purpose of the battery.
) is preferable.

In the battery of the present invention, the lithium ion conductive organic nonaqueous electrolyte includes, for example, 1,2-dimethoxyethane, 1
．． 2-jethoxyethane, ethylene carbonate, propylene carbonate, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3
- For example, LiClO4, LiPF6, LiAsF6, L
i5bFs, LiBFa, LiB (C6Hc+)
A solution obtained by dissolving one or more electrolytes such as No. 4 is used. Furthermore, in order to stabilize the electrolyte such as LiPF5 in the electrolytic solution, it is also preferably employed to add a stabilizer such as hexamethylphosphoric triamide to the electrolytic solution.

Examples of positive electrode active materials constituting the positive electrode include titanium disulfide (Ti32) and molybdenum disulfide (MnS2).
), molybdenum trisulfide (MnS2), iron disulfide (FeS
2), zirconium sulfide (ZrS2), niobium disulfide (
Chalcogen compounds of transition metals such as NbS2), nickel phosphorous trisulfide (NiPS3), and vanadium selenide (VSe2) are used. In particular, titanium disulfide has a layered crystal structure, and the diffusion constant of lithium ions within it is large (When titanium disulfide is used as a positive electrode active material, the charge/discharge reaction on the positive electrode side proceeds smoothly, It is preferred because lithium has good reversibility.

(Example〕 Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Thickness: 0.1 mm, diameter: 7. Two lithium plates of hm, thickness 0.3sN, diameter 7. An aluminum-titanium-boron alloy plate containing 0.2% by weight of titanium and 0.05% by weight of boron was used as the negative electrode material, and as explained later based on FIG. 2, one side was placed in the negative electrode can. The lithium plate, the aluminum-titanium-boron alloy plate, and the other lithium plate are placed in this order, and then the battery is assembled according to the usual method, and the lithium and aluminum-titanium-alloy are combined in the presence of an electrolyte.
It was alloyed with a boron alloy to form a negative electrode.

A battery having the above negative electrode is shown in Figure 1. In Figure 0, 1 is a negative electrode can made of stainless steel with nickel plating on the surface.
2 is a negative electrode current collector made of a stainless steel mesh welded to the inner surface of the negative electrode can 1.

Reference numeral 3 denotes a negative electrode, and as shown in FIG.
Aluminum-titanium-boron alloy plate containing 3% by weight
b and the lithium plate 3C are placed in the negative electrode can 1,
It is formed by alloying in the presence of an electrolyte. 4 is a separator made of a microporous polypropylene film, and 5 is an electrolyte absorber made of a polypropylene nonwoven fabric. 6 is a positive electrode that is pressure-molded using titanium disulfide as an active material and polytetrafluoroethylene as a binder. It has a disc shape with a thickness of 0.5 am and a diameter of 7.0 ffim, and one side is covered with stainless steel. A positive electrode current collector 7 made of steel mesh is provided. 8 is a positive electrode can made of stainless steel with a nickel-plated surface, and 9 is a gasket made of polypropylene. And this battery has 4
-Methyl-1,3-dioxolane 60% by volume, 1,2-
1.0 mo! of LiPF5 was added to a mixed solvent consisting of 34.8% by volume of dimethoxyethane and 5.2% by volume of hexamethylphosphoric triamide. /1 An organic non-aqueous electrolyte is used. The composition of lithium in the negative electrode of this battery is approximately 38 at%, and the theoretical amount of electricity in the negative electrode is approximately 20 m
Ah, and the theoretical amount of electricity of the positive electrode is about 8 mAh. Hexamethylphosphoric triamide in the electrolyte is a stabilizer for stabilizing l,1PF6.

Example 2 In place of the aluminum-titanium-boron alloy plate in Example 1, an aluminum-titanium-boron alloy plate with a titanium content of 1.0% by weight and a boron collection amount of 0.1% by weight was used. A lithium secondary battery having the same configuration as in Example 1 was manufactured.

Example 3 In place of the aluminum-titanium-boron alloy plate in Example 1, an aluminum-titanium-boron alloy plate with a titanium content of 1.5% by weight and a boron content of 0.2% by weight was used. A lithium secondary battery having the same configuration as in Example 1 was produced.

Example 4 In place of the aluminum-titanium-boron alloy plate in Example 1, an aluminum cam titanium-boron alloy plate with a titanium content of 0.01% by weight, a boron collection amount of Q, and 01i11% was used. A lithium secondary battery having the same configuration as in Example 1 was produced.

Comparative Example 1 Two lithium plates with a thickness of 0.1+m and a diameter of 7.81 and a hard aluminum plate with a thickness of 0.311I11 and a diameter of 7.8t+g (more grain boundaries than the soft aluminum plate, electrochemical alloy with lithium) lithium plate, aluminum plate, and the other lithium plate are placed in the negative electrode can in this order, and the lithium and aluminum are alloyed in the presence of an electrolyte. A lithium secondary battery having the same configuration as in Example 1 except for the use of a negative electrode was produced.

Reference Example 1 Lithium secondary having the same structure as Example 1 except that an aluminum-titanium alloy plate with a titanium content of 1.7% by weight was used in place of the aluminum-titanium-boron alloy plate in Example 1. A battery was created.

Reference Example 2 Lithium secondary having the same configuration as Example 1 except that an aluminum-boron alloy plate with a boron content of 0.3% by weight was used in place of the aluminum-titanium-boron alloy plate in Example 1. A battery was created.

The batteries of Examples 1 to 4, the batteries of Comparative Example 1, and the batteries of Reference Examples 1 to 2 were charged and discharged at 2 mAh at a constant current of Q, 5 mAh, and cycled in a voltage range of 1.5 to 2.5 ■. The number of cycles capable of discharging 2 mAh at 1.5 V was investigated, and the results are shown in Table 1.

Table 1 As shown in Table 1, the batteries of Examples 1, 2, 3 and 4 using aluminum alloy plates containing titanium and boron are different from those of Comparative Example 1 using aluminum containing no titanium or boron. The number of charge/discharge cycles that can be discharged at 2 mAh is greater than that of the batteries described above, and the charge/discharge cycle characteristics are excellent. They also had excellent charge-discharge cycle characteristics.

〔Effect of the invention〕

As explained above, in the present invention, by alloying an aluminum-titanium-boron alloy, which is made of aluminum as a base material and alloyed with titanium and boron, and lithium to form a negative electrode, the charging/discharging cycle can be improved. We were able to provide a lithium secondary battery with excellent characteristics.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a lithium secondary battery according to the present invention, and FIG. 2 shows an alloy of lithium and aluminum-titanium-boron alloy used as the negative electrode material of the battery shown in FIG. FIG. 3... Negative electrode, 3a, 3c... Lithium plate, 3b
...Aluminum-titanium-boron alloy plate, 6.
positive electrode

Claims (4)

[Claims] (1) In a lithium secondary battery comprising a positive electrode, a lithium ion conductive organic non-aqueous electrolyte, and a negative electrode, the negative electrode is an alloy of lithium and an aluminum alloy made of aluminum as a base material and titanium and boron added thereto. A lithium secondary battery characterized by using a lithium alloy. (2) The amount of titanium in the aluminum alloy is 0.0
The lithium secondary battery according to claim 1, wherein the amount of boron is 1 to 2.0% by weight, and the amount of boron is 0.005 to 0.3% by weight. (3) The lithium secondary battery according to claim 1 or 2, wherein the lithium alloy used for the negative electrode contains 20 to 48 at.% of lithium. (4) The lithium secondary battery according to claim 1, 2, or 3, wherein the positive electrode active material is titanium disulfide.