JPH0869818A - Nonaqueous solvent system lithium secondary battery - Google Patents

Abstract

PURPOSE: To obtain a lithium secondary battery which has a long life of charging and discharging and a proper safety. CONSTITUTION: An electrolyte in which lithium ions are used as a negative electrode active material that can be discharged and charged and vanadium oxide is used as a positive electrode active material, and at least one kind of lithium salt is dissolved in an organic solvent is used. The organic solvent mixes three kinds of solvents; ethylene carbonate(EC), propylene carbonate(PC), and 2-methil tetrahydrofuran(2MeTHF) at the following volume ratio: EC(x)PC (y)2MeTHF(z). x, y, z: solvent volume mixing ratio, x+y+z=100, x<y, z<y, x+y>50 (or z<50). By this result, a lithium secondary battery whose discharge life is long and that is in a good safe condition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery having a negative electrode capable of charging and discharging lithium ions, a positive electrode capable of charging and discharging lithium ions, and an electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent. .

[0002]

2. Description of the Related Art Lithium secondary batteries are secondary batteries that have hitherto been commercially available (for example, lead storage batteries, nickel cadmium).
It is expected as a battery with a higher energy density compared to. A small lithium secondary battery such as a coin type is already on the market. In addition, carbon containing lithium ions in the negative electrode,
AA and similar-sized secondary batteries using cobalt oxide for the positive electrode are commercially available, but the discharge capacity is smaller than that of nickel-cadmium batteries. Therefore, single 5-single 1
A high-energy lithium secondary battery of a size has not yet been put into practical use. This is mainly due to the following two reasons. The first reason is that the charge / discharge efficiency of lithium in the non-aqueous solvent electrolyte is low. The second reason is a problem that the safety of the battery is reduced as the battery becomes larger. If the lithium secondary battery is upsized, a large amount of gas may be generated from the battery if the battery is mistakenly used as a secondary battery at extremely high temperatures, or in extreme cases there is a risk of ignition or explosion. . The safety problem of the lithium secondary battery is closely related to the combination of the positive electrode, the negative electrode and the electrolytic solution.

While lithium is capable of high energy batteries, the high chemical reactivity of lithium poses the risk of making the battery unsafe. The lithium and the non-aqueous solvent react thermodynamically, and the decomposition products of the electrolytic solution are usually solids and gases remaining on the lithium surface. This exothermic reaction can raise the battery temperature to the melting point of lithium (180 ° C.).
When the lithium melts, it reacts violently with the electrolytic solution and the positive electrode, further raising the internal temperature of the battery and accelerating these exothermic reactions. Some reaction products are highly flammable. Furthermore, when the battery is repeatedly charged and discharged,
It tends to be less secure. This is interpreted that the precipitation form of lithium is not flat, the surface area is increased, and the reactivity of charged and discharged lithium is increased. Therefore, when an electrolyte solution having a high charge / discharge efficiency of lithium is used, on the other hand, the reaction activity of lithium has a high risk, and the electrolyte solution used in the practical battery has practical safety assurance and practical lithium The charge and discharge efficiency must be compromised at a high level. In other words, there is a danger that the safety of the battery cannot be actually ensured with an electrolyte solution having a high lithium charge / discharge efficiency. Of course, the charge and discharge performance and safety of the battery are as described above for the negative electrode, positive electrode, electrolytic solution,
All combinations affect. In other words, a practical electrolytic solution suitable for the positive electrode is required.

In order to improve the charge / discharge efficiency of lithium,
Various electrolytes have been studied up to now, but their safety is hardly mentioned. At present, it is considered possible to use an electrolytic solution containing 2-methyltetrahydrofuran (2MeTHF) as a solvent component in order to obtain the highest lithium charge / discharge efficiency. For example, it has been reported in an experiment using a lithium half cell (no positive electrode) that an electrolyte solution using a single solvent of 2MeTHF exhibits high charge / discharge efficiency of lithium (US Pat. No. 4,118,550 (1978). ). When 2-methylfuran is added to 2MeTHF alone or a mixture of 2MeTHF and ethers such as THF, TiS ₂
It has been reported that a lithium battery using a cathode as a positive electrode has a long charge / discharge life (US Pat. No. 4,489,145 (1).
988)). Further, when ethylene carbonate (EC) is added to 2MeTHF, a lithium battery using V ₂ O ₅ as a positive electrode tends to show a long charge / discharge life, and 2MeT
It is also reported that the volume mixing amount of HF is required to be 50% or more (US Pat. No. 4,737,424 (198).
8)). In the case of Li / TiS ₂ battery, in order to obtain a long cycle life, EC / 2MeTHF (10/9)
0) is also effective (proceedingon
the symposium on "Rechargeable Lithium Batterie
s ", proceeedings volume 90-5, the Electrochemical
Society Inc., pp. 114-126, 1990). Also, 2MeT
HF has a similar structure to EC as propylene carbonate (P
It has been reported that a mixture of C) shows a high lithium charge / discharge efficiency in a half-cell experiment of lithium.
Not as effective (Electrochimica Acta, vol. 29, N
o. 10, pp. 1471-1476. (1984)). Furthermore, for charging / discharging lithium batteries using VO ₂ as a positive electrode, EC / PC / 2MeT
An electrolytic solution using HF (12.5 / 12.5 / 75) has been reported to be effective (US Pat. No. 4,96).
5,150 (1990)). All of these reports of electrolytes using 2MeTHF state that 50% or more of 2MeTHF is required to obtain the best charge / discharge life. However, from a practical point of view, we
It has been found that the use of 50% or more of F in large quantities is problematic.
2MeTHF has a low flash point of -11 ° C, is volatile (boiling point is about 80 ° C), and easily burns. Also, it is easily oxidized,
Easy to make explosive peroxides. Although a large amount of 2MeTHF improves the charge / discharge efficiency of lithium, it has a serious practical problem of reducing the safety of the battery. Therefore, considering the combination with the positive electrode, 2
The amount of MeTHF used must be optimized.

On the other hand, a mixed solvent of EC and PC, which is a mixed solvent of ester and ester, has been proposed as an electrolytic solution solvent for a lithium secondary battery using MoS ₂ as a positive electrode (Jo
unalof Power Sources, vol.24, pp.195-206 (1988)).
EC and PC have high boiling points (238 and 241 respectively)
C) and a high flash point (160 and 132 C).
In the case of a lithium battery using V ₂ O ₅ as the positive electrode or a half cell of lithium, using EC / PC results in EC / 2MeTH.
It has been reported that the charge / discharge cycle life is shorter than that of the F mixed system (Jounal of Power Sources, vol.20, pp.293-
297 (1987)), EC / PC is considered to have higher battery safety than EC / 2MeTHF. And NbSe
_In order to extend the charge / discharge life of the lithium secondary battery using ₃ as the positive electrode and improve the battery safety, EC / P
It has also been reported that glymes are added to C (US Pat. No. 4,753,859 (1988)). However, the electrolyte solution material and its composition must be determined in consideration of the balance between the charge / discharge life and safety of the lithium battery.

Many compounds have been investigated as positive electrode active materials for lithium secondary batteries. Among these compounds, vanadium oxide is expected from the viewpoint of energy and cycle life. For example, crystalline V ₂ O ₅ , amorphous V ₂ O ₅ , and V ₆ O ₁₃ are expected to have high energy and a long lithium charge / discharge life. Further, a lithium compound of vanadium oxide (for example, LiαV ₃ O ₈ , 1.0 ≦ α
≦ 1.2) is also expected as a positive electrode active material with excellent performance. EC / 2Me as an electrolytic solution for improving the charge / discharge life of a lithium secondary battery using vanadium oxide for the positive electrode
Although a THF mixed solvent-based electrolytic solution has been proposed, there is a safety problem from a practical viewpoint.

The main object of the present invention is to provide an electrolytic solution for realizing a lithium secondary battery having a long charge / discharge life and good safety.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, lithium is used as an anode active material capable of discharging and charging lithium ions, vanadium oxide as a cathode active material, and an electrolytic solution prepared by dissolving at least one lithium salt in an organic solvent. In the secondary battery, the organic solvent is a mixture of three kinds of solvents of ethylene carbonate (EC), propylene carbonate (PC) and 2-methyltetrahydrofuran (2MeTHF) in the following volume ratio. A battery is provided.

EC (x) PC (y) 2MeTHF (z) x, y, z: solvent volume mixing ratio, x + y + z = 100, x <y, z <y, x + y> 50
(Or z> 50)

As the negative electrode active material capable of discharging and charging lithium ions, metallic lithium, an alloy capable of charging and discharging lithium ions, or a compound capable of charging and discharging lithium ions can be used. As the positive electrode active material, it is possible to use vanadium. Vanadium oxide, which has a molar ratio of oxygen of 2-3 and undergoes a reversible electrochemical reaction with lithium ions, can be used, and the electrolytic solution contains at least one lithium salt EC, P
A mixture of 3 solvents of C and 2MeTHF in the above volume ratio can be used. Particularly preferably, 2
The mixing amount of MeTHF is 35% or less, and the mixing ratio of EC to PC is 5/9 when the total of EC and PC is 100.
5 to 45/55.

The present invention will be described in more detail.

The electrolyte for lithium secondary batteries is required to have high lithium charge / discharge efficiency. As described above, lithium reacts with the electrolytic solution to form a solid film on the surface of lithium. The charge / discharge performance of lithium is affected by various properties of this film. For example, properties such as the generation rate of the film, ionic conductivity, electronic conductivity, porosity, mechanical strength, and flexibility of the film influence. From this viewpoint, EC and 2MeTHF are required to improve the charge / discharge performance of lithium. However, the use of a large amount of 2MeTHF risks reducing the safety of the battery. If EC / 2Me
Decreasing the mixing amount of 2MeTHF in the rTHF binary mixed solvent system causes other problems. The melting point of EC is 36
Even if EC is used as a mixed solvent, the characteristics at a low temperature of the battery are significantly deteriorated when the mixed amount of EC exceeds 50%. If PC is used instead of EC, the charge / discharge performance of lithium is lowered. From the measurement result of the charge and discharge efficiency of lithium using the lithium half cell (Electr
ochimica Acta, vol.29, No.2, pp.267-271 (1984))
It has been reported that, in the EC / PC mixed system, the charge / discharge efficiency of lithium improves as the amount of EC mixed increases. However, we have found that the charge / discharge life of a lithium battery using a vanadium compound depends on the amount of PC mixed.
It has been found that the improvement is achieved with more EC / PC mixed systems.

The present invention is capable of making lithium batteries of various shapes and sizes. FIG. 1 shows an example of a battery structure. The battery structure of FIG. 1 is called a cylindrical battery structure having a spiral electrode. This cell contains four layers. That is, the negative electrode 1 (for example, lithium metal foil), the separator 2, the positive electrode 3 (for example, vanadium oxide), and the other separator 4. These layers are wound in a cylindrical shape and housed in a cylindrical battery can 5. The battery can 5 has suitable electrode tabs 6 and 7, which are connected to the positive electrode 3 and the negative electrode 1, respectively. The battery can 5 has a safety valve 8 at the bottom so that the generated gas is released in order to prevent an explosion during operation of the battery. Cap 9 is battery can 5
Used to seal the upper end of the. An insulating disk 10 is provided between the cap 9 and the cylindrical battery structure. The battery can 5 is filled with an electrolytic solution so that an electrochemical reaction is possible.

In the present invention, the composition of the electrolytic solution is shown below.

EC (x) PC (y) 2MeTHF (z) x, y, z: solvent volume mixing ratio, x + y + z = 100, x <y, z <y, x + y> 50
(Or z <50)

Preferably, the mixing amount of 2MeTHF is 35%.
Below, assuming that the sum of EC and PC is 100, EC / P
The mixing ratio of EC / PC in C / 2MeTHF is 5 /
95-45 / 55.

As is clear from the examples below, x: 5
-30%, y: 40-80%, z: 15-30%, x +
It is particularly preferable that y + z = 100.

The lithium salt used in the present invention is LiPF
₆ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiCF
₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ S
O ₂ ) ₃ , LiCF ₃ CO ₂ , LiBF ₄ , LiAlCl ₄ ,
At least one compound selected from LiBr or LiB (C ₆ H ₅ ) ₄ can be used, and the concentration thereof can be used in the range of 0.5 to 2.0 mol / l. If the solute concentration is out of this range, the charge / discharge performance of lithium will be significantly deteriorated.

Examples of the negative electrode active material used in the lithium secondary battery of the present invention include metallic lithium, an alloy capable of charging and discharging lithium ions, and a compound capable of charging and discharging lithium ions. Examples of alloys that can be charged and discharged with lithium ions include Li-Al alloys and Li-Sn. Examples of the compound capable of charging and discharging lithium ions include various carbon materials and compounds capable of inserting lithium ions such as tungsten oxide and niobium oxide. A preferable negative electrode active material is one having an electrode potential as close as possible to lithium metal and capable of inserting and releasing as many lithium ions as possible, and as a result, a battery having a higher energy density has better performance. Will be.

The positive electrode active material used in the lithium secondary battery of the present invention is a vanadium oxide that undergoes an electrochemically reversible reaction with lithium ions and has a molar ratio of oxygen to vanadium in the range of 2-3. . For example, mainly V
Amorphous vanadium oxide made of ₂ O _5, crystalline V ₂ O _5, V
₆ O ₁₃ or these lithium compounds, or L
iαV ₃ O ₈ (1.0 ≦ α ≦ 1.2) and the like. It is also possible to add a small amount of a metal element or compound other than lithium or vanadium to the positive electrode if necessary to improve the battery performance. For example, in the case of amorphous V ₂ O _5, a small amount of a compound called a network former can be added in order to stabilize the amorphous state during repeated charging and discharging (for example, V ₂ O ₅ -P ₂ O _5, the molar ratio is 9
5: 5). Further, in order to improve the conductivity of the positive electrode, crystalline V ₂ O _{5 is used.}
There is also an example of adding a small amount of copper oxide to.

Various polymer compounds can be used for the separator used in the lithium secondary battery of the present invention. A microporous polymer membrane is preferred. As the polymer material, for example, one or more kinds of polyolefin such as polyethylene and polypropylene can be used.

Basically, practical batteries are required to have electrical stability and thermal stability. Thermal stability is mainly determined by the combination of battery constituent materials. Since the upper limit of the operating temperature of a lithium battery is usually 60 ° C., the thermal stability of the battery must be ensured up to a minimum of 60 ° C. Preferably, thermal stability must be ensured up to 100 ° C. The external short circuit of the battery is the most likely misuse of the battery, but it is an item of electrical stability that must be considered.

The effects of the present invention will be shown below using examples.

[0024]

Example 1 Amorphous V ₂ O ₅ —P ₂ O ₅ (V ₂
O ₅ : P ₂ O ₅ = 95: 5 molar ratio) was used, and the cylindrical battery shown in FIG. 1 was prepared using lithium as the negative electrode active material.

In order to compare and examine the charge / discharge characteristics and safety of the battery, the following four kinds of electrolytic solutions (electrolytic solution (A)-
(D)) was used.

Electrolyte solution (A): 1M LiAsF ₆ -EC /
PC / 2MeTHF (30/40/30)

Electrolyte solution (B): 1M LiAsF ₆ -EC /
PC / 2MeTHF (15/70/15)

Electrolyte solution (C): 1M LiAsF ₆ -EC /
2MeTHF (50/50)

Electrolyte solution (D): 1M LiAsF ₆ -EC /
PC (50/50)

The electrolytic solutions (C) and (D) are reference examples for showing the effects of the present invention. The electrolytic solution (C) is an electrolytic solution that is known to have a high lithium charging / discharging efficiency. The electrolytic solution (D) is an electrolytic solution showing relatively high charge-discharge efficiency and safety of lithium, and is an electrolytic solution used in a lithium battery that has been commercially available.

In the battery charge / discharge test, the discharge current was 600 m.
A, the charging current is 100 mA, and the end-of-charge voltage is 3.5.
V, the discharge end voltage was 1.8V. The charge / discharge life of a battery is defined by the following formula: FOM (Figure of Meri)
t).

FOM = [cumulative discharge capacity] / [discharge capacity of charged lithium in battery]

The value of this FOM has a correlation with the charge / discharge efficiency (E) of lithium according to the following equation.

FOM = 1 / (1-E)

When evaluating the FOM, the initial discharge capacity of 5
The number of charge / discharge cycles at which the discharge capacity of the battery decreased to 0% was defined as the charge / discharge life of the battery. The values of these FOMs are
In this specification, FOM-R was used for comparison. FOM-R
Is a relative value of FOM when the value of the electrolytic solution (D) represented by the following formula is 1.

FOM-R = [FO of the electrolyte of interest
M value] / [FOM value of electrolyte (D)]

As shown in Table 1, the electrolytic solution (C) can charge and discharge the lithium battery using vanadium oxide for the positive electrode for the longest time. The electrolytic solution (A) and the electrolytic solution (B) of the present invention
The FOM values of the electrolytic solution (C) were 93% and 90%, respectively. Further, the FOM values of the electrolytic solution (A) and the electrolytic solution (B) of the present invention were about twice those of the electrolytic solution (D). The known electrolytic solution (C) has better characteristics as far as the charge / discharge performance of the battery is limited. However, the performance difference from the electrolytic solution of the present invention is very small.

Table 1 Electrolyte solution FOM-R (A) 1.9 (B) 1.8 (C) 2.0 (D) 1.0

In order to investigate the thermal stability of the battery, a heating test was conducted on the manufactured battery. Further, in order to examine the electrical stability of the battery, an external short circuit test of the battery was also conducted.

The heating test of the battery was conducted on the batteries having the above-mentioned four kinds of electrolytic solutions (electrolytic solutions (A), (B), (C) and (D)). Batteries are heated to 130 ° C and 2
The temperature was maintained at 130 ° C for the time. Table 2 shows the results.
In the battery using the electrolytic solution (C), the safety valve was opened and intense gas generation was observed. No batteries using the electrolytes (A), (B) and (D) occurred. In other words, abnormal temperature rise, voltage drop, safety valve opening, explosion,
No phenomenon such as ignition was observed. From these results, it is understood that the battery using the electrolytic solution (C) has a problem in safety in practical use.

Table 2 Results of Electrolyte Heating Test (A) Safety valve did not open, no voltage drop, no ignition, no rupture. (B) Without opening the safety valve, no voltage drop, no ignition, no explosion. (C) The safety valve was opened and a large amount of gas was generated. (D) Without opening the safety valve, no voltage drop, no ignition, no rupture.

A battery using the electrolytic solutions (A) and (B) charged and discharged 50 times under the above-mentioned battery charging and discharging conditions was subjected to a heating test at 130 ° C. and an external short circuit test for the battery at 21 ° C. and 55 ° C. I did. The results are shown in Tables 3 and 4.

Table 3 Results of Electrolyte Heating Test (A) Safety valve did not open, no voltage drop, no ignition, no rupture. (B) Without opening the safety valve, no voltage drop, no ignition, no explosion.

Table 4 Results of external short-circuit test at 21 ° C. and 55 ° C. (A) The safety valve did not open, did not ignite and burst. (B) The safety valve did not open, did not ignite, and did not burst.

[0045]

Example 2 A battery was manufactured in the same manner as in Example 1.
The following two types were used as the electrolytic solution (electrolytic solution (E)
And electrolyte (F)).

Electrolyte solution (E): 1M LiPF ₆ -EC / P
C / 2MeTHF (15/70/15)

Electrolyte solution (F): 1M LiN (CF ₃ SO ₂ )
_2- EC / PC / 2MeTHF (15/70/15)

A heating test at 130 ° C. and an external short-circuit test were conducted on the battery which was charged and discharged 50 times under the same battery charging and discharging conditions as described in Example 1. The results are shown in Table 5. L
It is known that the electrolytic solution using iPF ₆ easily decomposes at a temperature of higher than 70 ° C., but the battery of the present invention was stable as shown in Table 5.

Table 5 Electrolyte Results of external short-circuit test and heating test at 21 ° C. and 55 ° C. (E) Safety valve did not open, did not ignite, and did not burst. (F) The safety valve did not open, did not ignite, and did not burst.

[0050]

Example 3 Amorphous V ₂ O ₅ —P ₂ O as a positive electrode active material
_A battery was prepared in the same manner as in Example 1, except that lithium metal was used as No. ₅ as the negative electrode active material. About the battery using the electrolytic solution (B), the heating test at 130 ° C and 21 ° C
And an external short circuit test at 55 ° C. was performed. Before this test, the battery had a discharge current of 60 mA and a charge current of 60 mA, a discharge end voltage of 1.8 V and a charge end voltage of 3.3 V.
The battery was cycled 10 times. When the discharge current value decreases,
Not only does the lithium deposit during charging have poor smoothness, the surface area increases, and the lithium reactivity becomes high, but lithium deposits in the form of needles. It is known that not only the battery performance deteriorates due to a short circuit, but also the safety of the battery decreases.

Table 6 shows the results. As shown in Table 6, the battery was stable. Furthermore, when a test was conducted to examine the charge / discharge cycle life of the battery, no internal short circuit of the battery occurred until the end of the charge / discharge test of the battery. In the case of a battery using a conventionally known electrolytic solution such as the electrolytic solution (D), an internal short circuit occurred before the battery reached the charge / discharge life, which made it unusable. As shown in Table 7, due to the internal short circuit of the battery, the battery using the conventional electrolytic solution (D) exhibited only about half the charge / discharge cycle life of the battery using the electrolytic solution (B) of the present invention. It was

Table 6 Electrolyte Results of external short-circuit test and heating test at 21 ° C. and 55 ° C. (E) Safety valve did not open, did not ignite, and did not burst.

Table 7 Electrolyte solution cycle charge / discharge life, FOM-R (B) 1.8 (D) 1.0

[0054]

Example 4 A compound obtained by lithiating amorphous V ₂ O ₅ —P ₂ O ₅ (the molar ratio of lithium: V ₂ O ₅ was 1: 1) was used as the positive electrode active material and shown in FIG. A battery was prepared and a charge / discharge test was performed. As the electrolytic solution, electrolytic solutions (A) and (D) were used. Discharge current is 600mA and charge current is 100m
A, discharge end voltage is 1.8V, charge end voltage is 3.5V
Is. The results are shown in Table 8. The battery using the electrolytic solution (A) of the present invention is about 2 times as large as the battery using the electrolytic solution (D) of the comparative example.
It showed a double charge / discharge cycle life. After the battery using the electrolytic solution (A) was charged and discharged 50 times, a heating test at 130 ° C. and an external short circuit test were performed. The results are shown in Table 9.

Table 8 Electrolyte solution cycle charge / discharge life, FOM-R (A) 1.8 (D) 1.0

Table 9 Results of Electrolytic Solution External Short-Circuit Test and Heating Test at 21 ° C. and 55 ° C. (E) Safety valve did not open, did not ignite, and did not burst.

The content of 2MeTHF in the electrolytic solution is 50v.
EC, PC and 2MeTH as long as it is less than ol%
The safety of the battery is the same even when the mixing ratio of F changes, and the factor that most strongly affects the safety of the battery is the 2MeTHF content.

[0058]

Example 5 Using the crystal V ₂ O ₅ as the positive electrode active material and the Li—Al alloy as the negative electrode, the battery shown in FIG. 1 was prepared and a charge / discharge test was conducted. The electrolyte is EC with a different solvent mixture ratio.
/ PC / 2MeTHF ternary mixed system electrolyte was used.
The discharge current is 600 mA, the charge current is 100 mA, the discharge end voltage is 1.8 V, and the charge end voltage is 3.5 V.
Among the electrolytic solutions used, four kinds (electrolytic solution (B), electrolytic solution (G), electrolytic solution (H) and electrolytic solution (I)) are shown below as examples.

Electrolyte solution (B): 1M LiAsF ₆ -EC /
PC / 2MeTHF (15/70/15)

Electrolyte solution (G): 1M LiAsF ₆ -EC /
PC / 2MeTHF (5/80/15)

Electrolyte solution (H): 1M LiAsF ₆ -EC /
PC / 2MeTHF (30/55/15)

Electrolyte solution (I): 1M LiAsF ₆ -EC /
PC / 2MeTHF (42.5 / 42.5 / 15)

Table 10 shows an example of the charge / discharge test results. FOM-R shown in Table 10 is shown as a relative value when the FOM of the battery using the electrolytic solution (I) is 1.0.
It was found that the EC content must be lower than the PC content in order to improve the charge / discharge life. Table 1
After the charge and discharge test was completed for the battery shown in 0, 1
All batteries were stable when subjected to a heating test at 30 ° C. This is 2 Me in the electrolyte solution shown in Table 10.
This is because the THF content is less than 50%.

Table 10 Electrolyte solution cycle charge / discharge life, FOM-R (B) 1.6 (G) 1.5 (H) 1.4 (I) 1.0

[0065]

As is apparent from the above description, according to the present invention, a non-aqueous solvent type lithium secondary battery excellent in charge / discharge characteristics and safety can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a cylindrical battery as an example of the present invention.

[Explanation of symbols]

 1 Negative electrode 2 Separator 3 Positive electrode 4 Electrode tab 5 Battery cap 6 Insulator ring 7 Battery can

Front Page Continuation (72) Inventor Shinichi Tobishima Buoy, Canada 6 pp 1 E8 British Columbia, Vancouver City West 51 51 Avnu 2335 (72) Inventor Kunio Moriya Canada Buoy 52 1 E8 British Columbia Vancouver Vancouver City Bailey Street 5410

Claims (8)

[Claims] 1. A lithium secondary battery using an electrolytic solution in which lithium ions are used as a negative electrode active material that can be discharged and charged, vanadium oxide is used as a positive electrode active material, and at least one lithium salt is dissolved in an organic solvent. The lithium secondary battery, wherein the organic solvent is a mixture of three kinds of solvents of ethylene carbonate (EC), propylene carbonate (PC) and 2-methyltetrahydrofuran (2MeTHF) in the following volume ratio. EC (x) PC (y) 2MeTHF (z) x, y, z: solvent volume mixing ratio, x + y + z = 100, x <y, z <y, x + y> 50
(Or z <50) 2. When z is 35% or less and x + y = 100, the ratio of EC to PC is 5: 95-45:
55. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is 55. 3. The lithium secondary battery according to claim 1, wherein the vanadium oxide has a ratio of oxygen to vanadium of more than 2 and less than 3. 4. The lithium secondary battery according to claim 3, wherein the vanadium oxide is an amorphous vanadium oxide mainly composed of V ₂ O ₅ . 5. The lithium secondary battery according to claim 4, wherein the vanadium oxide is an amorphous vanadium oxide composed of V ₂ O ₅ —P ₂ O ₅ . 6. The lithium secondary battery according to claim 1, wherein the negative electrode active material is metallic lithium, an alloy capable of charging and discharging lithium ions, or a compound capable of charging and discharging lithium ions. Next battery. 7. The lithium salt is LiPF ₆ , LiAsF ₆ ,
LiSbF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN
(CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃
7. The lithium secondary battery according to claim 1, wherein at least one compound selected from CO ₂ , LiBF ₄ , LiAlCl ₄ , LiBr or LiB (C ₆ H ₅ ) ₄ is used. 8. Vanadium is obtained by electrochemically reversibly reacting metallic lithium, an alloy capable of charging / discharging lithium ions, or a compound capable of charging / discharging lithium ions as a negative electrode active material with lithium ions as a positive electrode active material. The vanadium oxide having a molar ratio of oxygen to oxygen in the range of 2-3 is used as an electrolytic solution for LiPF ₆ , LiAsF ₆ , and LiS.
bF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃
SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃ CO ₂ ,
LiBF ₄ , LiAlCl ₄ , LiBr or LiB
At least one lithium salt selected from the group consisting of (C ₆ H ₅ ) ₄ at a concentration of 0.5-2.0M, EC, PC and 2M.
3. A solution obtained by dissolving three kinds of eTHF solvents in an organic solvent mixed in the following volume ratio is used.
The lithium secondary battery according to any one of 1 to 7. EC (x) / PC (y) / 2MeTHF (z), x: 5-30%, y: 40-80%, z: 15-30
%, X + y + z = 100