JPH0644493B2 - Lithium secondary battery - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a lithium secondary battery containing an organic solvent as an electrolyte component and having a lithium-strontium alloy negative electrode.

[Background of the Invention]

A battery using an electrolyte material containing an organic solvent and lithium as a negative electrode active material has been studied as a battery having a small size and a high energy density, but its secondary formation has been a serious problem.

Many compounds have been investigated as positive electrode active materials that can be secondaryized. For example, batteries using titanium, zirconium, hafnium, niobium, tantalum, vanadium sulfides, selenides, tellurides (US Pat. No. 408905).
No. 2) is disclosed.

However, research on the charge and discharge characteristics of the Li electrode is not sufficient compared to research on such positive electrode active materials for secondary batteries, and in order to realize lithium secondary batteries, charge and discharge efficiency, cycle life, etc. The production of a lithium electrode having good charging characteristics has become a serious problem.

As an attempt to improve the charge and discharge characteristics of the Li electrode,
Attempts to use Li treated with gas such as O ₂ and CO ₂ for the negative electrode [J. Electrochem. Soc., Vol. 125, pages 1371 to 1377] and Li
To use an alloy of Al and Al as a negative electrode [J. Electrochem.
c., Vol. 127, pp. 2100 to 2104], but this is not always sufficient, and it is required to prepare a Li negative electrode having further excellent characteristics.

[Outline of Invention]

The present invention has been made in view of such a current situation,
It is an object of the present invention to provide a lithium secondary battery having an electrolyte containing an organic solvent having excellent discharge and charge characteristics as a constituent element.

To outline the present invention, the negative electrode active material is lithium, the positive electrode active material is a substance that reversibly electrochemically reacts with lithium ions, the electrolyte substance contains an organic solvent,
It is a substance that is chemically stable to the positive electrode material and lithium and that moves so that lithium ions can undergo an electrochemical reaction with the positive electrode active material. An alloy of Li and Sr is used as a negative electrode used in a lithium secondary battery containing an organic solvent.

By using the negative electrode for a lithium secondary battery according to the present invention, there is an advantage that a lithium secondary battery having excellent charge / discharge characteristics can be manufactured.

[Specific Description of the Invention]

 The present invention will be described in more detail.

The metal forming an alloy with Li used in the negative electrode for a lithium secondary battery according to the present invention is Sr.

Generally, as the lithium negative electrode, a metal plate is often used, but in this case, when the discharge or charging current increases, the lithium negative electrode is punctured due to local reaction promotion,
At the time of charging, dendrite-like lithium is deposited, which causes a phenomenon such as detachment from the negative electrode. In addition, lithium has a high electron donating property and has a drawback that it reductively decomposes an organic solvent. These are the causes of lowering the charge / discharge efficiency of the lithium electrode.

Therefore, by alloying lithium with an appropriate metal, that is, Sr, the precipitation form of lithium is smoothed and the reaction activity with an organic solvent is lowered, so that the charge and discharge efficiency of the lithium negative electrode is improved.

The amount of Li in this Sr-Li alloy is preferably 47 mol%
It should be above. This is because Li ⁺ ions, which are less than 47 mol%, are hard to be released.

The method of alloying lithium is not fundamentally limited in the present invention. Any method may be used as long as it is an alloy of lithium and strontium. For example, 1) a method of electrochemically attaching lithium to Sr in a solution containing Li ⁺ ions, 2) a method of electrochemically attaching lithium to Sr metal in a molten salt, and 3) a molten liquid of lithium metal. A method of immersing Sr metal in it, 4) a method of reacting Sr metal with n-butyllithium, and 5) a method of depositing lithium on Sr metal can be used.

Examples of the present invention will be described below.

Example Using Li ₂ Sr ₆ as a Li—Sr alloy, first, it was investigated how electrochemically Li contained in Li ₂ Sr ₆ can be discharged as Li ⁺ .

In the experiment, a button-type battery having a disc-shaped Li _{2 3} Sr ₆ (diameter 15 mm, weight 0.144 g) as a negative electrode, Li _{2 3} Sr ₆ as a positive electrode, and a polypropylene separator as a bipolar ring (thickness 2 mm) was prepared. ,
The outer diameter was 23 mm) and a constant current discharge of 1 mA was performed. The discharge curve at this time is shown in FIG.

As is clear from Fig. 1, the discharge capacity until the voltage stability is disturbed is 99.3 mAhr, which is about 70% of that of Li in Li _{2 3} Sr _6.
% Can be discharged, and calculated Li _5.5 Sr ₆ (Li content is about 47 mol
%) Or more, it has been found that it can withstand use as a negative electrode for a Li battery.

Next, the same battery as above was manufactured except that it had Li _{2 3} Sr ₆ on both electrodes, and it was charged and discharged at a constant current of 1 mA with a charge and discharge capacity of 24.8 mAhr (1/4 of the dischargeable Li amount). I went. In this case, the charge / discharge cycle life is
(Figure of Merit)

Formula (1) In the above formula (1), Qps is the charge / discharge capacity (24.8mAhr), Qd
Is the amount of Li that can be discharged (99.3 mAhr), and n is the number of cycles that apparently shows 100% efficiency.

At the same time, the same battery as above was manufactured except that both electrodes were made of disc-shaped Li (thickness 0.43 mm, diameter 17 mm, dischargeable Li amount 201.2 mA 1 hr), and constant current charge / discharge at 15 mAhr charge / discharge capacity of 1 mA. A cycle test was performed. The results of these cycle tests are shown in Table 1.

As is clear from Table 1, by using a Li-Sr alloy, a lithium negative electrode having better charge / discharge efficiency than Li can be obtained.

[Effects of the Invention] As is clear from the above description, according to the present invention, by using an alloy of lithium and Sr as the negative electrode, there is an advantage that a lithium secondary battery having excellent charge and discharge characteristics can be realized. .

[Brief description of drawings]

FIG. 1 is a diagram showing a discharge curve in an example according to the present invention.

Claims (1)

[Claims] 1. A method comprising: (A) a negative electrode made of an alloy of lithium and strontium; (B) a positive electrode having a positive electrode active material that reversibly electrochemically reacts with lithium ions; and (C) an organic solvent. A lithium secondary battery comprising an electrolyte, which is a substance that is contained and is chemically stable to the positive electrode material and lithium, and that moves due to an electrochemical reaction of lithium ions with the positive electrode active material.