JPH0644485B2 - Negative electrode for lithium battery - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to lithium negative electrodes for use in lithium primary and secondary batteries.

[Background of the Invention]

A battery using 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 become 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.

In an attempt to improve the charge and discharge characteristics of the Li electrode, Li was replaced with O ₂ ,
An attempt to use a gas treated with CO ₂ etc. for the negative electrode [J. Ele
ctrochem.Soc., Vol. 125, pages 1371 to 1377] and an attempt to use an alloy of Li and Al as a negative electrode [J. Electrochem. Soc., Vol. 1
27 pages 2100 to 2104], etc., but it is not always sufficient, and it is required to produce a Li negative electrode having more excellent characteristics.

[Outline of Invention]

The present invention has been made in view of such a current situation,
The purpose is to provide a lithium negative electrode having excellent discharge and charge characteristics.

To outline the present invention, the negative electrode active material is lithium, the positive electrode active material is a material that reversibly electrochemically reacts with lithium ions, the electrolyte material is chemically stable to the positive electrode material and lithium, In addition, lithium and IVa in an organic solvent containing a lithium salt are used as a negative electrode used in lithium primary and secondary batteries, which is a substance that transfers lithium ions to cause an electrochemical reaction with a positive electrode active material.
It is characterized by using an electrochemically alloyed alloy of one or more of the group elements.

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

[Specific Description of the Invention]

 The present invention will be described in more detail.

Examples of the group IVa element used in the negative electrode for a lithium battery according to the present invention include one or more of Ti, Zr, and Hf.

Generally, a lithium metal plate is often used as a lithium negative electrode, but in this case, if discharge or charging current increases, local reaction acceleration may cause holes in the lithium negative electrode, or dendrite-like lithium may be deposited during charging. However, a phenomenon such as falling off from the negative electrode occurs. 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.

So by alloying lithium with a suitable metal,
The lithium deposition is smoothed, the reaction activity with an organic solvent is reduced, and the charge / discharge efficiency of the lithium negative electrode is improved.

As a method for alloying lithium, lithium can be electrochemically attached to a group IVa metal in an organic solvent containing lithium ions to form an alloy.

Example 1 A battery using a Li plate (size 1 cm ² , thickness 0.25 mm) as a negative electrode and a Ti plate (size 1 cm ² , thickness 0.05 mm) as a positive electrode was assembled in 1M LiC10 ₄ -propylene carbonate, 0.
Discharged at 5 mA / cm ² for 80 minutes to prepare a Li-Ti alloy. The electrochemical amount of Li in this alloy was 2.4 C / cm ² .

A battery using the Li—Ti alloy produced as described above as a working electrode, Li as a negative electrode and Li as a reference electrode was assembled, and a charge / discharge test of the Li—Ti alloy was performed. The electrolytic solution, 1MLiC10 ₄ - using propylene carbonate.

Measurements First, part of the Li-Ti alloy (0.6C / cm ²⁾ was discharged as Li ⁺ ions with a constant current of 0.5 mA / cm ^2, again 0.6 C / cm
^The cycle test of discharging at a capacity of ² was repeated. The average charging / discharging efficiency E per cycle is obtained from the potential change of the Li-Ti electrode, and the number of cycles that apparently shows 100% efficiency is n.
When it is repeated, E is obtained from the equation (1).

Formula (1) The results are shown as A in Table 1 below. In addition, in Table 1,
B is a comparative example for showing the effect of the present invention, and shows the result of performing the same experiment using a Cu plate of the same size instead of the Ti plate [Cu is difficult to alloy with Li. (J. Electrochem. Soc., 118, 1547, 19)
71)).

From Table 1 below, by using a Li-Ti alloy, Li
It can be seen that the charging / discharging efficiency of is significantly improved.

Example 2 The charge-discharge efficiency of the Li-Zr alloy was measured in the same manner as in Example 1 except that Li-Zr was used as the Li alloy.

The results are shown as C in Table 1 below. It was found that the charge and discharge efficiency was remarkably improved by using the Li-Zr alloy as compared with the case of using the Cu plate (B in Table 1).

Example 3 In the same manner as in Example 1 except that 1 mol / 1 of LiC10 ₄ was dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 1 as an electrolytic solution. , Li-Ti alloy was measured for charge / discharge efficiency.

The results are shown as D in Table 1 below. For reference, the case where a Cu plate was used under the same conditions is shown as E.

As is clear from Table 1, it was found that the use of Li-Ti alloy significantly increased the charge / discharge efficiency.

Example 4 The charge / discharge efficiency of the Li—Zr alloy was measured in the same manner as in Example 3 except that Li—Zr was used as the Li alloy. The results are shown as F in Table 1 below.

It was found that the charge / discharge efficiency was remarkably improved by using the Li-Zr alloy as compared with the case of using the Cu plate (E in Table 1).

Example 5 The charge / discharge efficiency of the Li—Hf alloy was measured in the same manner as in Example 1 except that Li—Hf was used as the Li alloy. The results are shown as G in Table 1 below.

It was found that the charge / discharge efficiency was remarkably improved by using the Li-Hf alloy as compared with the case of using the Cu plate (B in Table 1).

Example 6 The charge-discharge efficiency of a Li-Ti alloy was measured in the same manner as in Example 1 except that 1 mol / 1 of LiC10 ₄ dissolved in γ-butyrolactone was used as the electrolytic solution.

The results are shown as H in Table 1 below. For reference, the case where a Cu plate was used under the same conditions is shown as I.

As is clear from Table 1, it was found that the use of Li-Ti alloy significantly increased the charge / discharge efficiency.

Comparative Example Table 2 shows the Li- by the same experimental method as the example of the present invention.
The charge and discharge efficiencies of the Al alloy and the Li-Ti alloy are shown for comparison.

Li-Al alloy is the most known lithium alloy negative electrode. The advantage is that the initial charge / discharge efficiency is high.
However, (1) the diffusion rate of the alloy crystal lattice width of Li ions is slow, so a large current cannot flow, and (2) the electrode expands and contracts during charge and discharge, causing the electrode to physically break, which is long. L and L cannot be charged and discharged, and (3) Li is strongly alloyed with Al after repeated charge and discharge.
i-ion cannot be discharged, and the charge / discharge efficiency deteriorates.
There are drawbacks such as.

Here, a cycle test was performed until Li could not be charged / discharged, and the average charge / discharge efficiency per one time was obtained.

As shown in Table 2 below, the Li-Al alloy has a high initial charge / discharge efficiency only, but a high average charge / discharge efficiency cannot be obtained. On the other hand, the Li-Ti alloy of the present invention shows no breakage of the electrode due to repeated charging / discharging, and shows a high charge / discharge efficiency even at a large current value, which is superior to the Li-Al alloy. It was

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

Claims (1)

[Claims] 1. A negative electrode for a lithium battery, which comprises an alloy formed by electrochemically alloying with a metal of one or more group IVa elements in an organic solvent containing a lithium salt.