JPH0679487B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvements in non-aqueous electrolyte secondary batteries.

Prior art and its problems Alkali metals such as lithium and sodium are used as a negative electrode active material, and propylene carbonate, ethylene carbonate,
A non-aqueous solution prepared by dissolving a solute such as lithium perchlorate or lithium borofluoride in a solvent such as tetrahydrofuran or dimethoxyethane is used as an electrolyte, and an oxide or sulfide of a transition metal such as manganese, molybdenum, or vanadium is used as a positive electrode active material. The development of the non-aqueous electrolyte secondary battery has been actively promoted.

However, many problems remain in the characteristics of the secondary battery. As one example, the most serious problem is the decrease in the electrochemical reversibility of each of the positive electrode and the negative electrode.

There are sulfides and oxides as the positive electrode active material, and the comparison is as follows.

Among sulfides, oxides are superior to sulfides in that free sulfur reacts with the negative electrode active material, and generally oxides are higher than sulfides because they have a higher capacity because they can take in more alkali metal ions. is there.

Oxides are also advantageous in terms of safety and synthesis method.

Much research has been done on vanadium oxides among the oxides. For example, there are V ₂ O ₅ , amorphous V ₂ O ₅ , V ₆ O _{13, and the} like. Batteries using these as the positive electrode active material all have high capacities, but have the drawbacks that the discharge characteristics are in multiple stages and that structural breakdown occurs during cycle progress.

In addition, V ₂ O ₅ and V ₆ O ₁₃ have a drawback in that the electrodes are likely to deteriorate due to overdischarge.

In order to improve these, it is a lithium vanadium oxide in which lithium is inserted in the crystal lattice in advance. LixV ₃ O ₈ was found to be a substance having excellent performances such as strong resistance to overdischarge, high capacity, and flat discharge characteristics. However, this product has the drawbacks that the characteristics are greatly influenced by the synthesis method, the voltage flatness is poor, and the cycle characteristics are deteriorated.

LixV ₃ O ₈ produced in large quantities by simple heat treatment synthesis has the above-mentioned properties remarkably.

The present invention is to solve the above-mentioned conventional problems, excellent in over-discharge resistance performance, high capacity, excellent flatness of discharge constant pressure,
An object is to provide a long-life non-aqueous electrolyte secondary battery.

Structure of the invention The present invention is, to achieve the above object, an alkali metal as a negative electrode active material, as a positive electrode active material of a battery using an alkali metal ion conductive non-aqueous electrolyte as an electrolyte, Li ₂ O liberated by aqueous solution treatment, LixV ₃ O, a lithiated vanadium oxide from which Li ₂ CO ₃ and vanadium oxide have been removed
_It is a non-aqueous electrolyte secondary battery characterized by using ₈ .

Example Hereinafter, details of the present invention will be described by way of an example.

Vanadium pentoxide, which is a commercially available special grade reagent, and lithium carbonate were used in a molar ratio of 5: 2, and were thoroughly mixed in a mortar.

Next, heat-synthesize this in air at about 700 ° C for 48 hours or longer, and
i _1.2 V ₃ O ₈ was obtained. Crush this Li _1.2 V ₃ O ₈ in an automatic mortar and
The particles were passed through a 00 mlsh sieve to an average particle size of 20 μm.

Li _1.2 V ₃ O ₈ whose particle size was adjusted was dissolved in an aqueous solution such as a buffer solution as an aqueous solution treatment, and liberated Li ₂ O, Li ₂ CO ₃ and vanadium oxide were removed by filtration. Then, it was washed several times with water, taken out from the paper, and dried at about 400 ° C. for 24 hours or more.

The active material, the conductive agent, acetylene black, and polytetrafluoroethylene as the binder were mixed in a weight ratio of 80: 1.
5: 5 was kneaded in a mortar. This is 0.8 with a roller press.
It was made into a sheet with a thickness of mm. Dried under vacuum at 200 ℃,
A positive electrode was obtained.

Next, a thin lithium plate having a thickness of 0.3 mm was punched out and used as a negative electrode.

The electrolyte was 1 mol concentration of LiClO _{4 in a} mixed solvent of equal volume of propylene carbonate (PC) and dimethoxyethane (DME).
Was dissolved.

A coin battery was prepared using the positive electrode, the negative electrode, the electrolytic solution and the separator to obtain the battery of the present invention.

For comparison, the conventional product was obtained by heat treatment synthesis on the positive electrode.
A similar coin-shaped battery was prepared using Li _1.2 V ₃ O ₈ and using the same negative electrode, electrolytic solution and separator.

A cycle life test was performed using the battery of the present invention and the conventional battery. The cut voltage at this time is the upper limit of 3.4V and the lower limit.
It was set to 2.0V. The results are shown in FIGS. 1 and 2.

FIG. 1 is a diagram showing a comparison of discharge pressure characteristics.

In cycle test FIG.

The battery of the present invention is extremely excellent in flatness of discharge voltage as compared with the conventional product.

FIG. 2 is a diagram showing the relationship between cycle life and capacity. Here again, it is understood that the battery of the present invention has a very small decrease in capacity during cycling.

Lithiumate vanadium oxide has less pore expansion and less structural destruction due to cycle progress because lithium ions do not accompany the solvent during intercalation compared to TiS _{2 and the} like. Since it has a capacity of accommodating 3 mol of lithium ions per mol, it has a high capacity and a theoretical energy density of 815 WH / kg. V ₆ O ₁₃ even for over discharge
It is stronger and more stable than other materials.

EFFECTS OF THE INVENTION As described above, the present invention provides a high capacity with excellent over-discharge resistance,
Since it is possible to provide a long-life non-aqueous electrolyte secondary battery having excellent flatness of discharge constant pressure, its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram comparing the discharge pressure characteristics of the battery of the present invention and a conventional product, and FIG. 2 is a diagram showing the relationship between the cycle life and the capacity of the present invention and the conventional product.

Claims (1)

[Claims] 1. Li liberated by treatment with an aqueous solution as a positive electrode active material of a battery using an alkali metal as a negative electrode active material and an alkali metal ion conductive non-aqueous electrolyte as an electrolyte.
A non-aqueous electrolyte secondary battery using LixV ₃ O ₈ which is a lithium vanadium oxide from which ₂ O, Li ₂ CO ₃ and vanadium oxide have been removed.