JPH04215251A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous electrolyte secondary battery with a high discharge capacity, high voltage and excellent charge/discharge cycle characteristics. CONSTITUTION:In a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode which can adsorb or desorb lithium, and a nonaqueous electrolyte containing lithium ions, a lithium-vanadium composite oxide expressed by LixV2O5 (0.03<=x<=0.15) and having main peaks at 2theta=17.0 deg.+ or -0.5 deg., 20.2+ or -0.5 deg., 21.7 deg.+ or -0.5 deg. respectively in the X-ray diffraction by CrKalpha rays as shown by C-E in the figure.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte secondary battery that is high voltage, has excellent charge/discharge cycle characteristics, and is highly stable and reliable.

0002

BACKGROUND OF THE INVENTION Conventionally, it has been proposed to use metal oxides, halides, or sulfides as positive electrode active materials in non-aqueous electrolyte batteries using alkali light metals such as lithium and sodium as negative electrode active materials. Currently, primary batteries that mainly use manganese dioxide or carbon fluoride as positive electrode active materials are in practical use.

In addition, for rechargeable and dischargeable secondary batteries, such as lithium secondary batteries, positive electrode active materials include titanium, sulfides such as molybdenum, and oxides such as vanadium, which have good cycle characteristics for occluding and releasing lithium ions. , or use a conductive polymer material such as polyaniline, or use an alloy of lithium and a metal such as aluminum that can be easily alloyed with lithium for the negative electrode active material. Various methods have been proposed to suppress short circuit problems caused by dendrite growth, and some secondary batteries that combine these positive and negative electrodes have begun to be commercialized.

Under these circumstances, there are various materials suitable for the positive electrode active material, but among these, batteries using vanadium pentoxide as the positive electrode active material have relatively high voltage, excellent chemical stability, and It is highly anticipated that it will be applied to secondary batteries because of its relatively good cycle characteristics.

[0005]

[Problems to be Solved by the Invention] However, non-aqueous electrolyte batteries using vanadium pentoxide for the positive electrode have been described in the literature (W.B. Ehner and W.C. Mer).
z, 28th Power Sources Sym
p. June 1978, p. 214), there are many application examples, but there are various problems. For example, when we examine the discharge behavior using Li metal as a negative electrode, we find that there are flat parts at about 3.3 V and about 2.4 V above 2 V, and in both parts, about 1 mole of lithium atoms interact with vanadium pentoxide electrochemically. react to. However, the potential gap between the two is very large, 1V, and the potential changes occur rapidly. Repeating the charge/discharge cycle through both flat areas causes destruction of the crystal structure, resulting in a decrease in discharge capacity. It tends to become more pronounced.

As one method to solve this problem, it has been proposed to melt vanadium pentoxide and rapidly cool it to make it amorphous and use it as a positive electrode active material (for example, Solid State Ioni
cs 9 & 10 649-657 (198
3)) Although the reversibility is improved, the discharge voltage generally decreases, and the advantage of high voltage is lost.

From this point of view, it is preferable to use vanadium pentoxide with Li as the counter electrode and to utilize the flat part of the first stage where the voltage is 2.5 V or more.
It is possible to realize a discharge capacity of 0 mAH/g, and therefore,
It can be fully used as a positive electrode active material for secondary batteries.

However, there is a problem with this usage, for example, when charging and discharging between 3.8 and 2.5V, the capacity is only 80 to 90% of the initial capacity after the second cycle. However, the disadvantage is that the voltage is slightly lower.

That is, this vanadium pentoxide positive electrode absorbs lithium ions between its layers as it discharges, forming LixV2O.
5, and at a potential of 3.8 to 2.5 V, it is possible to incorporate up to 1 mole of lithium ions per 1 mole of V2O5. During charging, a reaction is triggered to release lithium ion atoms, but the occluded lithium atoms cannot be completely released in this reaction, and 10 to 20% of the occluded lithium remains, and a vanadium pentoxide layer is formed. The diffusion resistance inside is also large,
This results in a decrease in discharge voltage. In addition, although the cycle characteristics are relatively good, the limit is about 100 cycles, and the performance is inferior to conventional storage batteries such as NiCd batteries.

The present invention was made in view of the above circumstances, and
By using a lithium-vanadium composite oxide, which contains vanadium pentoxide with a small amount of lithium to strengthen the layered structure of vanadium pentoxide, as the positive electrode active material, it has high voltage and excellent charge-discharge cycle characteristics. Stability,
The purpose is to provide a non-aqueous electrolyte secondary battery with excellent reliability.

[0011]

[Means and effects for solving the problem] As a result of intensive studies to achieve the above object, the inventor has discovered that LixV
2O5 (0.03≦x≦0.15, preferably 0.07
≦x≦0.12), and 2θ=17.0°±0.5°, 20.2°±0.5° in X-ray diffraction using CuKα rays.
The lithium vanadium composite oxide, which has main peaks at 21.7°±0.5°, has a stable structure, and a secondary battery using this as a positive electrode active material exhibits good charge-discharge cyclability. It was discovered that the material has very favorable properties as a positive electrode active material for non-aqueous electrolyte secondary batteries.

To further explain this point, according to the study of the present inventor, vanadium pentoxide is used as a Li counter electrode.
．． Even after discharging to 5 V and further charging to 3.7 to 3.8 V to desorb Li, the peak shift to the lower angle side is clearly seen in the results of X-ray diffraction analysis, which is due to the This shows that Li ions remain in vanadium oxide and the lattice remains expanded. On the other hand, Li
In the substance LixV2O5 to which a small amount of
No shift of the line diffraction peak was observed after charging and discharging, indicating that the diffusivity and reversibility of Li ions in the crystal structure are very high, and as a result, the average voltage changes by approximately 0.
An increase of 1 V was observed, and it was also found that high durability was obtained even after 400 to 500 charge/discharge cycles.

[0013] The present inventor constructed a positive electrode using the above lithium vanadium composite oxide as an active material, a negative electrode using a material capable of intercalating and releasing lithium as an active material, and a non-containing material containing lithium ions. The present invention was completed based on the finding that a nonaqueous electrolyte secondary battery having high discharge capacity, high voltage, and excellent charge/discharge cycle characteristics can be obtained by combining the present invention with an aqueous electrolyte.

Therefore, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte containing lithium ions, in which, as the active material of the positive electrode, LixV2O5(0.03≦x≦
0.15) and 2θ by X-ray diffraction using CuKα rays.
=17.0°±0.5°, 20.2°±0.5° and 2
Provided is a nonaqueous electrolyte secondary battery characterized in that it uses a lithium vanadium composite oxide having main peaks at 1.7°±0.5°.

[0015] To explain the present invention in more detail below, the positive electrode of the non-aqueous electrolyte secondary battery of the present invention is represented by LixV2O5 (0.03≦x≦0.15) as described above,
As shown in C to E in Figure 1, 2θ = 17.0° ± 0.5°, 20.2° ± 0.5° in X-ray diffraction using CuKα rays.
The active material is a lithium vanadium composite oxide having main peaks at 21.7°±0.5°.

Here, x in LixV2O5 is 0.
03 to 0.15, particularly preferably 0.07 to 0.12. When x is less than 0.03, the above-mentioned structure cannot be achieved, while when x exceeds 0.15, although the cycle characteristics are good, the discharge capacity is reduced and the practicality as a positive electrode active material is poor.

In order to obtain the above lithium vanadium composite oxide, the amount of lithium atoms is 0.03 to 0.15 mol, preferably 0.07 to 0.15 mol, per 1 mol of vanadium pentoxide.
Add and mix a lithium salt with a low melting point in an amount of 12 moles, and heat at a temperature near the melting point of the lithium salt (300 to 5
It is effective to perform the firing treatment at a temperature of 00°C. In this case, examples of the lithium salt include lithium iodide, lithium oxalate, lithium nitrate, and the like. In addition, as an electrochemical method, after discharging vanadium pentoxide to 2.2 to 2.0 V at a Li counter electrode (in this case, 1.7 to 2 moles of lithium atoms are inserted into vanadium pentoxide). A lithium vanadium composite oxide having an optimal structure can also be obtained by subsequently performing a charging treatment.

When producing a positive electrode using the above lithium vanadium oxide as a positive electrode active material, the particle size is not necessarily limited, but it is more preferable to use one having an average particle size of 5 to 10 μm. In this case, conductive agents such as graphite and acetylene black,
A positive electrode can be produced by a method such as adding and mixing a binder such as fluororesin powder, kneading with an organic solvent, and rolling with a roll. The amount of the conductive agent mixed is 3 to 25 parts per 100 parts (parts by weight, same hereinafter) of the positive electrode active material.
In particular, it is preferably 5 to 15 parts. Further, the amount of the binder mixed is preferably 5 to 15 parts with respect to 100 parts of the positive electrode active material.

The negative electrode active material capable of intercalating and deintercalating lithium used in the battery of the present invention includes lithium metal, alloys of lithium and metals that can be easily alloyed with lithium such as aluminum and low melting point alloys, carbonaceous materials, In particular, a material in which a graphitized layered compound is doped with lithium can be used.

[0020] The non-aqueous electrolyte used in the secondary battery of the present invention is one containing lithium ions, and specifically, lithium salts, particularly LiClO4, LiBF4, L
One or more selected from iPF6, LiCF3SO3, and LiAsF6 are preferred. These electrolytes are usually used in a state dissolved in a solvent. In this case, the solvent is not particularly limited, but is selected from propylene carbonate, 2-methyltetrahydrofuran, tetrahydrofuran, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, dioxolane, butylene carbonate, acetonitrile, and dimethylformamide. Type 1 or 2
A mixed solvent of more than one species is suitable.

The nonaqueous secondary battery of the present invention is usually constructed by interposing an electrolyte between the positive and negative electrodes, but in this case, a separator is interposed between the positive and negative electrodes in order to prevent current short-circuiting due to contact between the two electrodes. be able to. As a separator, use a material that can reliably prevent contact between the two electrodes and allow the electrolyte to pass through or contain it, such as nonwoven fabrics made of synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene, porous woven fabrics, and nets. Among these, a microporous film made of polypropylene or polyethylene having a thickness of about 20 to 50 μm is particularly preferably used.

[0022] Furthermore, in the electrolyte of the present invention, the above electrolyte solution may be used as a solid electrolyte, such as polyethylene oxide,
Organic solid electrolytes impregnated with polymers such as polypropylene oxide and phosphazene polymers having ethylene oxide oligomers in their side chains, Li3N, LiBCl4, L
An inorganic solid electrolyte such as lithium glass such as i4SiO4 or Li3BO3 may also be used.As for other constituent members of the non-aqueous electrolyte secondary battery of the present invention, commonly used materials can be used without any problem. . Further, the form of the battery is not particularly limited, and can take various forms such as a coin type, button type, paper type, or spiral-structured cylindrical battery.

[0023]

[Examples] The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example] After adding lithium iodide powder to vanadium pentoxide powder,
The mixture was thoroughly mixed and fired at a temperature of 300° C. for about 10 hours to obtain lithium vanadium oxide. At this time, depending on the amount of lithium iodide, the added lithium concentration, that is, LixV
By changing the x value in 2O5, A to E as shown in Table 1
Five types of oxides were prepared.

Obtained lithium vanadium oxides A to E
X-ray diffraction using CuKα rays was performed on the sample. The chart is shown in Figure 1. It can be seen from FIG. 1 that the peak around 17° becomes more prominent as the amount of lithium added increases.

Next, 15 parts of acetylene black as a conductive agent and 10 parts of fluororesin powder as a binder were added to 100 parts of each of the above positive electrode active materials, and after thorough mixing, kneaded with an organic solvent and rolled to a thickness of about 500 μm. Rolled to 150
After vacuum drying at °C, a positive electrode was produced by punching out a piece with a diameter of 15 mm.

On the other hand, a 300 μm thick lithium metal sheet punched to the same diameter as the positive electrode was used as the negative electrode, and as the electrolyte, LiPF6 dissolved in propylene carbonate at 1 mol/l was used. The coin cell battery shown was assembled.

Here, in FIG. 2, the positive electrode 1 and the positive electrode current collector 2 made of aluminum are spot welded to the inner surface of the positive electrode can 3, and the negative electrode 4 is spot welded to the inner surface of the negative electrode can 6. is press-fitted into the Further, a separator 7 made of a nonwoven polypropylene fabric is impregnated with the electrolyte. Note that 8 is an insulating packing. Further, the battery dimensions are 20.0 mm in diameter and 1.6 mm in thickness.

For each of the five batteries manufactured as described above, at a charge/discharge current of 1 mA, the discharge end voltage was 2.
．． Charging and discharging were repeated under the conditions of 5V and a charging end voltage of 3.8V, and the cycle characteristics were measured up to 200 cycles.

Table 1 shows the average discharge voltage, the initial discharge capacity per gram of active material, and the discharge capacity in the second cycle. Further, FIG. 3 shows the change in capacity per gram of active material up to 200 cycles.

[0031]

[Table 1]

From the results shown in Table 1, although the initial discharge capacity of the battery of the present invention is slightly lower than that of untreated vanadium pentoxide, the decrease in capacity in the second cycle is small, and the average discharge voltage is improved. was seen.

Furthermore, from the results shown in FIG. 3, it was confirmed that the battery using the positive electrode active material of the present invention had good cycle characteristics.

[0034]

[Effects of the Invention] As explained above, the nonaqueous electrolyte secondary battery of the present invention uses lithium vanadium oxide, which has an optimal structure as a positive electrode active material, and therefore has a high discharge capacity, high voltage, and Has excellent charge/discharge cycle characteristics.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction chart using CuKα rays of lithium vanadium oxides of Examples of the present invention and Comparative Examples.

FIG. 2 is a sectional view showing a coin-type battery according to an embodiment of the present invention.

FIG. 3 is a graph showing characteristics of battery cycles according to Examples and Comparative Examples of the present invention.

[Explanation of symbols]

1 Positive electrode 2 Positive electrode current collector ３　　　　Positive electrode can 4 Negative electrode 5 Negative electrode current collector 6 Negative electrode can 7 Separator 8 Insulating packing

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte containing lithium ions, wherein LixV2O5 (0. 03≦x≦0.15), and 2θ=17.0°± by X-ray diffraction using CuKα rays.
0.5°, 20.2°±0.5° and 21.7°±0.
A nonaqueous electrolyte secondary battery characterized by using a lithium vanadium composite oxide having main peaks at 5 degrees.