JP2001126760A - Non-aqueous electrolyte type secondary battery - Google Patents

Abstract

(57) [Abstract] [Problem] To suppress the internal resistance and internal resistance rise rate of a battery,
Provide a high output and long life secondary battery. SOLUTION: A positive electrode 6 made of a lithium-containing compound capable of doping or undoping lithium, and a negative electrode 5 made of a non-graphitizable carbonaceous material capable of doping or undoping lithium.
And a non-aqueous electrolyte, wherein the non-aqueous electrolyte is a solution obtained by dissolving lithium hexafluorophosphate in a mixture of ethylene carbonate, propylene carbonate, and dimethyl carbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a positive electrode active material and a negative electrode active material which dope (occlude) and de-dope (release) lithium, and a non-aqueous electrolyte. Things.

[0002]

2. Description of the Related Art In recent years, interest in the pollution of the global environment and global warming has been increasing around the world, and high-performance electric vehicles and hybrid vehicles, which are expected to exert great effects, have been demanded as countermeasures. There is a demand for the development of high-performance secondary batteries for use in batteries.

Therefore, as a secondary battery having a high discharge voltage, a small self-discharge, and a long cycle life, recently, instead of a nickel-cadmium battery or a lead battery, the negative electrode is doped with lithium ions such as a carbon material. Non-aqueous electrolyte secondary batteries using lithium composite oxides of lithium and cobalt composite oxides for the positive electrode using substances that can be undoped and so-called lithium ion batteries have been actively researched and developed. ing.

[0004] The non-aqueous electrolyte secondary battery is lightweight and has a high capacity. Therefore, the non-aqueous electrolyte secondary battery has been put to practical use in portable electronic devices such as mobile phones and notebook computers, and has been widely used. It is also expected to be put to practical use as a secondary battery for hybrid vehicles. Secondary batteries for electric vehicles and hybrid vehicles are required to be lightweight and have a large capacity, and to have high durability and long life. In addition, since a very large current needs to be supplied to a motor for driving an automobile, it is particularly required that a secondary battery used for the motor be capable of discharging a large current, that is, has a high output.

[0005]

However, the conventional non-aqueous electrolyte secondary battery has a problem that the output gradually decreases because the internal resistance gradually increases when used for a long period of time. Although this decrease in output does not cause a great problem in practical use in portable electronic devices and the like, in electric vehicles and hybrid vehicles, it becomes impossible to supply a current necessary for driving the vehicle, which is a serious problem.

Accordingly, the present invention has been made in view of such conventional circumstances, and provides a non-aqueous electrolyte secondary battery suitable for electric vehicles and hybrid vehicles having high output and long life. It is intended to provide.

[0007]

That is, the present invention provides a positive electrode comprising a lithium-containing compound capable of doping or undoping lithium, a negative electrode comprising a non-graphitizable carbonaceous material capable of doping or undoping lithium, and A non-aqueous electrolyte, comprising: a solution obtained by dissolving lithium hexafluorophosphate in a mixture of ethylene carbonate, propylene carbonate, and dimethyl carbonate. It relates to a secondary battery.

According to the non-aqueous electrolyte secondary battery of the present invention,
By using the lithium hexafluorophosphate (lithium hexafluorophosphate) as a solute of the non-aqueous electrolyte, the internal resistance of the battery can be reduced, so that the battery has a high output and is suitable for electric vehicles and hybrid vehicles. Becomes

Further, by using ethylene carbonate, propylene carbonate, and dimethyl carbonate as the solvent, the initial internal resistance is reduced, and even when used for a long period of time, the rise in the internal resistance is small, the output is reduced, and the output is reduced. And a longer life can be achieved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the nonaqueous electrolyte secondary battery of the present invention, ethylene carbonate contains 5% by volume or more and 50% by volume or less.
It is preferable that a mixed solution in which propylene carbonate is mixed in a ratio of 10% by volume or more and 60% by volume or less and dimethyl carbonate is mixed in a ratio of 10% by volume or more and 60% by volume or less is used as the nonaqueous solvent.

It is preferable to have an electrode laminate in which a positive electrode and a negative electrode are wound via a separator.

Hereinafter, the present invention will be described in more detail by way of preferred embodiments with reference to the drawings as appropriate.

First, FIG. 2 shows a structure of a non-aqueous electrolyte secondary battery according to an embodiment. In this secondary battery, a negative electrode 5 and a positive electrode 6 are alternately wound integrally with current collectors 3 and 4 via a separator 7 between an inner wall of a cylindrical battery can 1 and a center pin 2. The electrode laminate 11 has a laminated structure, and is impregnated with a non-aqueous electrolyte (not shown). Insulating plates 8 are provided above and below the electrode laminate 11,
The lower part is closed by a battery can bottom 10 connected to the negative electrode lead 9, and the upper part is connected to the positive electrode lead 12
It is closed by a safety valve 13 that releases internal gas pressure at the time of discharge and a battery lid 14 that covers the safety valve 13. In addition,
In the figure, reference numeral 15 denotes a gasket for insulating between the positive and negative electrodes, and 16 denotes a PTC (Positive temperature coeffic) for preventing overdischarge.
ient) element.

This non-aqueous electrolyte secondary battery basically comprises a positive electrode 5 and a negative electrode 6 capable of doping and undoping lithium ions, and these electrodes are usually formed of a separator made of a porous material or the like. 7 are immersed in a non-aqueous electrolyte in which a lithium compound is dissolved in an organic solvent.

The positive electrode 6 is made of a positive electrode material such as a lithium composite oxide containing lithium and manganese, and the negative electrode 5 is made of a non-graphitizable carbonaceous material. While being held by the electric bodies 3 and 4,
Used as pole. Both the positive electrode active material and the negative electrode active material have a common molecular structure in that they have a layer structure in which lithium ions can be doped and dedoped.

The electrode material and the non-aqueous electrolyte hardly react with each other, and the principle is that lithium ions move in the electrolyte. At the time of discharge, lithium ions are released from the negative electrode 5 (de-doping). Then, the lithium ions move to the positive electrode 6 side through the separator 7, and on the contrary, at the time of charging, lithium ions are separated from the positive electrode 6 and enter the negative electrode 5 side (doping).

As described above, this non-aqueous electrolyte secondary battery accommodates a positive electrode made of a positive electrode active material, a negative electrode made of a negative electrode active material, and a non-aqueous electrolyte in, for example, a cylindrical iron battery can. The battery can and the battery lid are caulked and sealed. The positive electrode and the negative electrode are connected to the battery lid and the battery can, respectively, by the lead members, and are supplied with electricity from the outside via the battery lid or the battery can and the lead member. Further, as described above, when an abnormality such as overcharging occurs, a current cutoff mechanism that cuts off current in the battery system according to an increase in the internal pressure of the battery may be provided to improve safety.
The shape of the battery is not limited to a cylindrical shape, but may be a square shape or any other shape.

In the present embodiment, a non-aqueous electrolyte obtained by dissolving lithium hexafluorophosphate as a solute in a solvent containing ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) is used. Is used. First, by using lithium hexafluorophosphate as a solute, the internal resistance of the battery can be reduced, so that the battery has high output and is suitable for electric vehicles and hybrid vehicles. In addition, by using ethylene carbonate, propylene carbonate and dimethyl carbonate as solvents, the initial internal resistance is reduced, the internal resistance is not increased over a long period of use, the output is reduced, the output is increased, and the life is extended with high output Becomes possible.

The reason is that by mixing lithium hexafluorophosphate as a solute with ethylene carbonate, propylene carbonate, and dimethyl carbonate as solvents, a stable ion is formed on the surface of a positive electrode made of, for example, a lithium-manganese composite oxide. A conductive protective film is formed, thereby suppressing the reaction between the positive electrode and the electrolyte, and further suppressing the growth of the surface film accompanying the decomposition of the non-aqueous electrolyte on the surface of the negative electrode made of the non-graphitizable carbonaceous material. It is considered that the increase in the internal resistance is reduced by this.

In order to obtain such excellent results, the content of the above-mentioned ethylene carbonate (EC) is 5% by volume or more,
50% by volume or less (more preferably 10% by volume or more and 40% by volume or less, preferably 20% by volume or more and 40% by volume or less, more preferably 20% by volume or more and 30% by volume or less),
Propylene carbonate (PC) content is 10% by volume
Above, 60% by volume or less (more preferably, 20% by volume or more, 50% by volume or less, preferably 30% by volume or more, 50% by volume or less, more preferably 30% by volume or more, 40% by volume or less)
And the content of dimethyl carbonate (DMC) is 10% by volume or more and 60% by volume or less (furthermore, 20% by volume or more, 50% by volume or less, preferably 30% by volume or more,
50% by volume or less, more preferably 30% by volume or more, 40%
Volume% or less).

Next, the components of the solvent and solute of the non-aqueous electrolyte will be described in more detail.

As the solvent of the non-aqueous electrolyte, the above-mentioned ethylene carbonate, propylene carbonate and diethyl carbonate are indispensable, and in combination with these, other organic solvents such as carbonates, fatty acid esters or ethers may be used. A solvent may be added.

For example, butylene carbonate, 1,2-
Dimethoxyethane, 1,2-dimexethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like may be used. .

As the solute, the above-mentioned LiPF ₆ is indispensable, but together with this, LiClO ₄ , LiAs
F ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl,
A lithium salt having ionic conductivity such as lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate, or the like represented by LiBr, CH ₃ SOLi, CF ₃ SO ₃ Li, or the like may be added.

That is, the solvent to be used is not limited to the above-mentioned three types which are indispensable to the present invention, and can be adopted as long as three or more types produce the same effect as the present invention. This is also true for solutes.

Next, a non-graphitizable carbon material (hard carbon) is used as the negative electrode active material. The non-graphitizable carbon material can be obtained by heat treatment and carbonization by a method such as forming an organic polymer compound such as a phenol resin, an acrylic resin, and a furan resin. Alternatively, it can be obtained by introducing a functional group containing oxygen into petroleum pitch (so-called oxygen cross-linking) and heat-treating it to carbonize it. The carbonization temperature varies depending on the starting material, but is usually 500 to 3000 ° C. The non-graphitizable carbon material has, for example, d ₀₀₂ (degree of graphitization) of 0.37 to
It is preferably 0.38 nm.

This non-graphitizable carbon material has a small structural change due to a charge / discharge reaction, and therefore has a high cycle performance and is suitable for electric vehicles and high-bridged vehicles that require long-term durability as compared with portable electronic devices. It is particularly suitable as a negative electrode active material to be used.

Next, as the positive electrode active material, for example, a composite oxide containing lithium and manganese is used. Usable lithium-containing composite oxides include lithium cobalt composite oxide, lithium nickel composite oxide, and lithium manganese composite oxide, but are used for electric vehicles and hybrid vehicles that require a large amount of positive electrode active material. To do this, a lithium composite oxide containing manganese, which is rich in resources, is advantageous in terms of raw material costs.

Also, a battery using a lithium manganese composite oxide as a positive electrode active material has the characteristics that the temperature rise is small even during overcharge and the safety is high, and a large amount of the positive electrode active material is required. It is optimal to use a lithium manganese composite oxide as a positive electrode active material for electric vehicles and hybrid vehicles.

The lithium-manganese composite oxide is prepared by mixing carbonates and nitrates of lithium and manganese, oxides and hydroxides, etc., as starting materials, depending on the composition, and is usually 600 to 500 parts.
It is obtained by firing in a temperature range of 1000 ° C.
Note that the composite oxide containing lithium and manganese used in this embodiment may be one in which manganese is partially substituted with another metal.

Examples of the adhesive used for solidifying the negative electrode active material, the positive electrode active material, and the additives include polyvinylidene fluoride.

The shape of the battery as described above is not limited to a cylindrical shape, but may be a square shape or any other shape.

As described above, in the non-aqueous electrolyte secondary battery of the present embodiment, as the non-aqueous electrolyte, lithium hexafluorophosphate is used as a solvent, and ethylene carbonate, propylene carbonate, and dimethyl carbonate are used as a solvent. This makes it possible to reduce an increase in the internal resistance of the battery during long-term use.

Although the mechanism for suppressing the increase in internal resistance is not clear, a stable ionic conductive protective film is formed on the surface of the lithium manganese composite oxide of the positive electrode by ethylene carbonate, propylene carbonate, dimethyl carbonate and lithium hexafluorophosphate. By being formed, the reaction between the positive electrode and the electrolytic solution is suppressed, and the growth of the surface film accompanying the decomposition of the electrolytic solution on the surface of the non-graphitizable carbon material of the negative electrode is suppressed, so that the internal resistance rise is reduced. It is considered something.

[0035]

Embodiments of the present invention will be described below.

Example 1 The positive electrode 6 was produced as follows. Lithium carbonate and manganese oxide were mixed at a Li / Mn ratio of 1/1 and calcined in air at a temperature of 800 ° C. for 5 hours to obtain a LiMn ₂ O ₄ powder. Next, 90 parts by weight of LiMn ₂ O ₄ powder (positive electrode active material), 6 parts by weight of graphite powder (conductive additive), and polyvinylidene fluoride (binder) were placed on a 20 μm-thick aluminum foil (positive electrode current collector 3). A slurry in which 4 parts by weight of the mixture was dispersed in N-methyl-2-pyrrolidone (paste: the same applies hereinafter) was applied, dried, and then pressed with a roller press to obtain a belt-shaped positive electrode 6.

The negative electrode 5 was prepared as follows. After using a petroleum pitch as a starting material and introducing a functional group containing oxygen into it (oxygen crosslinking), the temperature is set to 1000 ° C. in an inert gas.
To obtain a non-graphitizable carbon powder (hard carbon). Next, a mixture of 90 parts by weight of non-graphitizable carbon powder (negative electrode active material) and 10 parts by weight of polyvinylidene fluoride (binder) was added to a 15-μm-thick copper foil (negative electrode current collector 4). The slurry dispersed in pyrrolidone was applied, dried, and then pressed by a roller press to obtain a belt-shaped negative electrode 5.

The positive electrode 6 and the negative electrode 5 formed as described above are laminated via a microporous polypropylene film having a thickness of 25 μm to be a separator 7, and are wound many times to form a spiral electrode body 11. Created.

Next, the insulating plates 8 are arranged on the upper and lower surfaces of the spirally wound electrode body 11, and are housed in the nickel-plated iron battery can 1, and the positive electrode 6 and the negative electrode 5 are collected. Therefore, the positive electrode lead 9 made of aluminum is
To the battery lid 14 and the nickel negative electrode lead 12 from the negative electrode current collector 4 and welded to the battery can 1.

Next, as shown in Table 1 below, ethylene carbonate, propylene carbonate, and dimethyl carbonate were placed in the battery can 1 at 40% by volume and 2%, respectively.
An electrolyte in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol was injected into a solvent mixed at a mixing ratio of 0% by volume and 40% by volume. And battery can 1
The battery cover 14 was fixed by caulking the battery cover 14 with a sealing gasket 15 to produce a cylindrical non-aqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm.

Example 2 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 30% by volume, the propylene carbonate (PC) at 30% by volume, and the dimethyl carbonate (DMC) at 40% by volume. A water electrolyte type secondary battery was prepared.

Example 3 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 20% by volume, the propylene carbonate (PC) at 40% by volume, and the dimethyl carbonate (DMC) at 40% by volume. A water electrolyte type secondary battery was prepared.

Example 4 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 10% by volume, the propylene carbonate (PC) at 50% by volume, and the dimethyl carbonate (DMC) at 40% by volume. A water electrolyte type secondary battery was prepared.

Example 5 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 30% by volume, the propylene carbonate (PC) at 20% by volume, and the dimethyl carbonate (DMC) at 50% by volume. A water electrolyte type secondary battery was prepared.

Example 6 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 10% by volume, the propylene carbonate (PC) at 40% by volume, and the dimethyl carbonate (DMC) at 50% by volume. A water electrolyte type secondary battery was prepared.

Example 7 The procedure of Example 1 was repeated, except that the ethylene carbonate (EC) was mixed at 30% by volume, the propylene carbonate (PC) at 40% by volume, and the dimethyl carbonate (DMC) at 30% by volume. A water electrolyte type secondary battery was prepared.

Example 8 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 40% by volume, the propylene carbonate (PC) at 40% by volume, and the dimethyl carbonate (DMC) at 20% by volume. A water electrolyte type secondary battery was prepared.

Example 9 The procedure of Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 30% by volume, the propylene carbonate (PC) at 50% by volume, and the dimethyl carbonate (DMC) at 20% by volume. A water electrolyte type secondary battery was prepared.

Example 10 The same procedure as in Example 1 was repeated except that the propylene carbonate (PC) was not contained, but the ethylene carbonate (EC) was mixed at 50% by volume and the dimethyl carbonate (DMC) at 50% by volume. An electrolyte secondary battery was prepared.

Example 11 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was not contained, but the propylene carbonate (PC) was mixed at 50% by volume and the dimethyl carbonate (DMC) was mixed at 50% by volume. An electrolyte secondary battery was prepared.

Example 12 The same procedure as in Example 1 was carried out except that the dimethyl carbonate (DMC) was not contained, and the ethylene carbonate (EC) was mixed at 50% by volume and the propylene carbonate (PC) at 50% by volume. An electrolyte secondary battery was prepared.

Example 13 The same procedure as in Example 1 was repeated except that 5% by volume of the ethylene carbonate (EC), 50% by volume of the propylene carbonate (PC) and 45% by volume of the dimethyl carbonate (DMC) were mixed. A water electrolyte type secondary battery was prepared.

Example 14 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 50% by volume, the propylene carbonate (PC) at 20% by volume, and the dimethyl carbonate (DMC) at 30% by volume. A water electrolyte type secondary battery was prepared.

Example 15 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 40% by volume, the propylene carbonate (PC) at 10% by volume, and the dimethyl carbonate (DMC) at 50% by volume. A water electrolyte type secondary battery was prepared.

Example 16 The procedure of Example 1 was repeated, except that the ethylene carbonate (EC) was mixed at 20% by volume, the propylene carbonate (PC) at 60% by volume, and the dimethyl carbonate (DMC) at 20% by volume. A water electrolyte type secondary battery was prepared.

Example 17 The procedure of Example 1 was repeated, except that the ethylene carbonate (EC) was mixed at 40% by volume, the propylene carbonate (PC) at 50% by volume, and the dimethyl carbonate (DMC) at 10% by volume. A non-aqueous electrolyte secondary battery was prepared.

Example 18 The same procedure as in Example 1 was repeated except that the ethylene carbonate (EC) was mixed at 20% by volume, the propylene carbonate (PC) at 20% by volume, and the dimethyl carbonate (DMC) at 60% by volume. A water electrolyte type secondary battery was prepared.

Example 19 30% by volume of the ethylene carbonate (EC), 40% by volume of the propylene carbonate (PC), and 30% by volume of the dimethyl carbonate (DMC) were mixed.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that LiCoO ₂ was used for the positive electrode.

Example 20 30% by volume of the ethylene carbonate (EC), 40% by volume of the propylene carbonate (PC), and 30% by volume of the dimethyl carbonate (DMC) were mixed.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that LiCoO ₂ was used for the positive electrode and LiBF ₄ was used for the solute.

Example 21 The above ethylene carbonate (EC) was mixed at 30% by volume, the propylene carbonate (PC) at 40% by volume, and the dimethyl carbonate (DMC) at 30% by volume.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the negative electrode was made of graphite.

<Evaluation of Battery Characteristics> With respect to the cylindrical battery prepared as described above, the initial internal resistance and the rate of increase in internal resistance after long-term use were evaluated as follows.

The batteries of each example were charged first.
For charging, the charging voltage is 4.2 V, the charging current is 1000 mA,
After performing the charging for 2.5 hours, the measured internal resistance was defined as the initial internal resistance.

After the measurement of the initial internal resistance, the battery was charged under the conditions of a charging voltage of 4.2 V, a charging current of 1000 mA, and a charging time of 2.5 hours.
000 mA, the discharge under the conditions of a final voltage of 2.75 V was repeated 1000 cycles, and the charging voltage was 4.2 V, the charging current was 1000 mA, and the charging time was 2.5.
After charging under the condition of time, the measured internal resistance was defined as the internal resistance after long-term use. The initial internal resistance was subtracted from the thus measured internal resistance after long-term use, and the internal resistance increase rate after long-term use was determined from this value.

The internal resistance was measured at 1 kHz using an LCR meter (KC-535C manufactured by Kokuyo Electric Industries Co., Ltd.).
This was done by measuring the impedance at the time.

The results are shown in Table 1 below. The ratings described in this table are represented by symbols as follows. Then, in the overall judgment, ◎ is the best, ○ is good, △ is acceptable, ×
Is not allowed.

FIG. 1 shows the correlation between the content of ethylene carbonate (EC), the content of propylene carbonate (PC) and the content of dimethyl carbonate (DMC) as a comprehensive evaluation.

[0067]

[0068]

[0069]

[0070]

[0071]

As apparent from these results, Examples 1 to
Nos. 9 and 13 to 18 contain ethylene carbonate, propylene carbonate, and dimethyl carbonate as solvents for the non-aqueous electrolyte, and have a small increase in internal resistance after long-term use. However, Example 11 containing no ethylene carbonate and Example 10 not containing propylene carbonate
Has a large internal resistance increase rate and a low-temperature internal resistance after long-term use. Example 12 containing no dimethyl carbonate
Has a large initial internal resistance and a large low-temperature internal resistance.

From the above, by using the three kinds of solvents of ethylene carbonate, propylene carbonate and dimethyl carbonate in combination, the initial internal resistance and the low-temperature internal resistance are low, and it is possible to suppress the rise of the internal resistance due to long-term use. It becomes clear that sufficient characteristics cannot be obtained if any of the three solvents is missing.

As in Example 19, the cathode material was LiC
The results were excellent when changed to oO ₂ . And example 2
0, LiCoO ₂ is used for the positive electrode, and the solute is LiB
If you F _4, the result was impossible. Furthermore, when graphite was used as the negative electrode as in Example 21, the cycle characteristics after 1000 cycles became poor (good in Example 7).

Accordingly, the positive electrode material may be a lithium-containing compound, the solute of the non-aqueous electrolyte is preferably lithium hexafluorophosphate, and the negative electrode material is preferably a non-graphitizable carbon material. Soft carbon) is not possible.

As is clear from FIG. 1, the content of ethylene carbonate (EC) is 5% by volume or more and 50% by volume or less (more preferably 10% by volume or more and 40% by volume or less, preferably 20% by volume or more, 40% by volume or less, more preferably 20% by volume or more and 30% by volume or less), and the content of propylene carbonate (PC) is 10% by volume or more and 6% by volume or less.
0% by volume or less (more preferably 20% by volume or more and 50% by volume or less, preferably 30% by volume or more and 50% by volume or less, more preferably 30% by volume or more and 40% by volume or less),
The content of dimethyl carbonate (DMC) is 10
Not less than 60% by volume (and more than 20% by volume,
50% by volume or less, preferably 30% by volume or more and 50% by volume or less, and more preferably 30% by volume or more and 40% by volume or less.

That is, as for the mixing ratio of the solvent, the region surrounded by line A in FIG. 1 is the usable range (△), the region surrounded by line B is the preferred range (○), and the region surrounded by line C is The region shown is a more preferable range (◎).

[0078]

As described above, the present invention provides a positive electrode comprising a lithium-containing compound capable of doping or undoping lithium, a negative electrode comprising a non-graphitizable carbonaceous material capable of doping or undoping lithium, and a non-aqueous Since the non-aqueous electrolyte comprises a solution obtained by dissolving lithium hexafluorophosphate in a mixture of ethylene carbonate, propylene carbonate, and dimethyl carbonate,
By using the lithium hexafluorophosphate (lithium hexafluorophosphate) as a solute of the non-aqueous electrolyte, the internal resistance of the battery can be reduced, and the battery is high in output and suitable for electric vehicles and hybrid vehicles. . Also,
By using ethylene carbonate, propylene carbonate, and dimethyl carbonate as the solvent, the initial internal resistance is reduced, and even when used for a long period of time, the increase in the internal resistance is small, the output is reduced, and the output is extended and the life is extended. It becomes possible.

[Brief description of the drawings]

FIG. 1 shows the content of ethylene carbonate (EC) in a non-aqueous electrolyte and propylene carbonate (P
FIG. 2 is a correlation diagram between the content of C) and the content of dimethyl carbonate (DMC).

FIG. 2 is a longitudinal sectional view of the cylindrical non-aqueous electrolyte secondary battery.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery can, 2 ... Center pin, 3, 4 ... Current collector, 5 ...
Negative electrode, 6 positive electrode, 7 separator, 8 insulating plate, 9, 1
2 ... lead, 10 ... bottom of battery can, 11 ... electrode laminate, 1
3: Safety valve, 14: Battery lid (positive electrode), 15: Gasket, 16: PTC element

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Claims (3)

[Claims] A positive electrode comprising a lithium-containing compound capable of doping or undoping lithium; a negative electrode comprising a non-graphitizable carbonaceous material capable of doping or undoping lithium;
A non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a solution obtained by dissolving lithium hexafluorophosphate in a mixture of ethylene carbonate, propylene carbonate, and dimethyl carbonate. Type secondary battery. 2. The method according to claim 1, wherein the content of the ethylene carbonate is 5% by volume or more and 50% by volume or less, and the content of the propylene carbonate is 1% by volume.
The mixed solution obtained by mixing 0% by volume or more and 60% by volume or less and the dimethyl carbonate in a ratio of 10% by volume or more and 60% by volume or less is used as a non-aqueous solvent.
2. The non-aqueous electrolyte secondary battery according to 1. 3. The non-aqueous electrolyte secondary battery according to claim 1, further comprising an electrode laminate in which the positive electrode and the negative electrode are wound with a separator interposed therebetween.