JP2001118599A - Secondary cell of nonaqueous electroyte solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide prolonged of service life of a secondary cell of nonaqueous electrolyte solution. SOLUTION: In a secondary cell 1 of nonaqueous electrolyte solution is constituted by dissolving electrolyte salt in nonaqueous solvent comprising a positive pole 2 consisted of combination, including lithium and negative pole 3 consisted of a carbon material that can dope or de-dope lithium, and alcohol is added as an added agent agent to the nonaqueous electrolyte solution.

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.

[0002]

2. Description of the Related Art In recent years, interest in global environmental pollution and global warming has been increasing around the world. One of the countermeasures is the widespread use of high-performance electric vehicles, which are thought to exert a significant effect on such problems, and the spread of so-called hybrid vehicles, which run as appropriate by switching between a gasoline-powered engine and an electric-powered motor as a drive source. Has been requested. In response to such demands, the development of high-performance secondary batteries used for motors serving as these driving sources has been promoted.

The above-mentioned secondary battery includes a non-aqueous electrolyte secondary battery in which a lithium-containing compound is used for a positive electrode and a negative electrode material capable of doping and undoping lithium is used for a negative electrode. . Because of its light weight and high capacity, it has been put to practical use as a power supply for driving portable electronic devices such as mobile phones and notebook personal computers.
Widespread. Therefore, it is expected to be put to practical use as a drive power source for high-performance electric vehicles and hybrid vehicles.

A secondary battery used as a power source for driving an electric vehicle or a hybrid vehicle is required to be lightweight, have a high capacity, and have high durability and a long life. Also, driving a car requires supplying a very large current to the motor as a drive source, so the secondary battery used as the power source must be capable of discharging a large current, that is, it must have a high output. Desired.

[0005]

However, when the conventional non-aqueous electrolyte secondary battery is used for a long time,
Since the internal resistance gradually increases, there is a problem that the output gradually decreases. Such a decrease in the output of the non-aqueous electrolyte secondary battery does not pose a significant problem in practical use when used as a drive power source for portable electronic devices, but high output is required for electric vehicles and hybrid vehicles. When used as a drive power supply in applications, there is a serious problem that a necessary current cannot be supplied to the motor. Therefore, when a non-aqueous electrolyte secondary battery is used as a power source for driving an electric vehicle or a hybrid vehicle, the internal resistance is suppressed from rising in order to maintain a high output and to be usable for a long time. It is necessary.

Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that suppresses an increase in internal resistance that occurs when the battery is used for a long time.

[0007]

A non-aqueous electrolyte secondary battery according to the present invention has a positive electrode made of a lithium-containing compound and a negative electrode made of a carbon material capable of doping and undoping lithium. And a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent. The non-aqueous electrolyte contains a polyhydric alcohol as an additive.

According to the non-aqueous electrolyte secondary battery of the present invention, a compound such as Li alcoholate is formed on the surface layer of the negative electrode by adding a polyhydric alcohol as an additive to the non-aqueous electrolyte. This suppresses the formation of lithium carbonate and suppresses an increase in internal resistance that occurs when used for a long time.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a non-aqueous electrolyte secondary battery according to the present invention will be described with reference to an example.
It is not limited to the examples shown below. That is, the non-aqueous electrolyte secondary battery of the present invention is not limited to a battery having a cylindrical shape as described below, but a battery having another shape, for example, a square shape, a coin shape, a button shape, or the like. It may be. Further, the non-aqueous electrolyte secondary battery of the present invention has a structure for improving safety by providing a current interrupting mechanism for interrupting current in the battery in response to an increase in internal pressure of the battery when an abnormality such as overcharge occurs. May be used.

FIG. 1 is a schematic perspective view of an example of the non-aqueous electrolyte secondary battery 1 of the present invention. As shown in FIG. 1, a nonaqueous electrolyte secondary battery 1 includes a positive electrode 2 coated with a positive electrode paint containing a positive electrode active material, and a negative electrode 3 coated with a negative electrode paint containing a negative electrode active material. The separator 4 interposed between the positive electrode 2 and the negative electrode 3 is stacked and spirally wound and stored in a cylindrical metal battery can 5 together with the non-aqueous electrolyte. The battery can 5 is sealed by caulking a metal lid 6 to the opening.

In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the positive electrode 2 and the negative electrode 3 are connected to a battery can 5 or a lid 6 by a positive electrode lead 7 and a negative electrode lead 8, respectively. Conduction is conducted from outside through the body 6 and the positive electrode lead 7 or the negative electrode lead 8.

In the non-aqueous electrolyte secondary battery 1, the positive electrode 2
Lithium-containing compounds are used as the positive electrode active material used in the above. As the lithium-containing compound, Li _x MO
₂ (where M represents one or more transition metals, and x represents 0.
05 ≦ x ≦ 1.10. )), Among which LiCoO ₂ , L
iNiO ₂ and LiMn ₂ O ₄ are preferred. Such lithium transition metal composite oxides, for example, lithium, cobalt, nickel, manganese carbon salts, nitrates, oxides,
A hydroxide or the like is used as a starting material, these are mixed in an amount according to the composition, and the mixture is fired in a temperature range of 600 ° C to 1000 ° C.

As the negative electrode active material used for the negative electrode 3, a carbon material is used. Any carbon material may be used as long as it is capable of doping and undoping lithium. A low-crystalline carbon material obtained by firing at a relatively low temperature of 2000 ° C. or less,
A highly crystalline carbon material such as artificial graphite that has been treated at a high temperature close to ℃ is used. As the carbon material, in addition to those described above, for example, pyrolytic carbons, cokes, graphites, glassy carbons, and organic polymer compound fired bodies (furan resins and the like are fired and carbonized at an appropriate temperature). ), Carbon fiber, activated carbon, etc.

The non-aqueous electrolyte is prepared by adding an organic solvent, an electrolyte dissolved in the organic solvent, and a polyhydric alcohol as additives.

The organic solvent is not particularly restricted but includes, for example, cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate and diethyl carbonate;
Examples thereof include cyclic esters such as butyrolactone and γ-valerolactone, chain esters such as ethyl acetate and methyl propionate, and ethers such as tetrahydrofuran and 1,2-dimethoxyethane. One of the above organic solvents may be used alone, or two or more of them may be used as a mixture.

The electrolyte dissolved in the above-mentioned organic solvent is
Lithium dissolved in a solvent and exhibiting ionic conductivity
The salt is not particularly limited as long as it is, for example, Li
PF ₆, LiBF_Four, LiClO_Four, LiCF_ThreeS
O_Four, LiN (CF_ThreeSO_Two)_Two, LiC (CF_ThreeSO
_Two)_ThreeAnd the like. The above-mentioned electrolyte is 1
The seeds can be used alone or as a mixture of two or more.
You may.

Further, polyhydric alcohols selected as additives include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol,
Glycerin, pentaerythritol and the like can be mentioned. In addition, the polyhydric alcohol as an additive applied to the nonaqueous electrolyte secondary battery of the present invention is not limited to the above example, and a conventionally known polyhydric alcohol can be appropriately used.

The non-aqueous electrolyte preferably contains the above-mentioned additive polyhydric alcohol in an amount of 0.01 to 0.5% by weight based on the non-aqueous electrolyte. Is more preferably contained in an amount of 0.03 [% by weight] to 0.2 [% by weight].

The non-aqueous electrolyte secondary battery 1 of the present invention contains the above-mentioned polyhydric alcohol as an additive in the non-aqueous electrolyte, thereby suppressing an increase in internal resistance due to long-term use. A longer life of the output secondary battery is achieved. This is because a compound such as Li alcoholate is formed on the surface layer of the negative electrode by adding the polyhydric alcohol, thereby suppressing the formation of lithium carbonate and suppressing an increase in internal resistance.

With respect to the non-aqueous electrolyte secondary battery according to the present invention, specific examples (Examples 1 to 9) and (Comparative Example 1)
6) will be described. The present invention is not limited to the following examples.

First, a positive electrode was prepared as follows.
90 parts by weight of a LiMn ₂ O ₄ powder as a positive electrode active material, 6 parts by weight of a graphite powder as a conductive additive, and polyvinylidene fluoride as a binder, on a 20 μm thick aluminum foil as a positive electrode current collector 4 parts by weight of the mixture are mixed with N-methyl-
After applying the slurry dispersed in 2-pyrrolidone and drying,
A belt-shaped positive electrode was formed by pressing with a roller press.

Further, a negative electrode was produced as follows.
A mixture of 90 parts by weight of graphite powder as a negative electrode active material and 10 parts by weight of polyvinylidene fluoride as a binder was added to a 15-μm-thick copper foil as a positive electrode current collector.
The slurry dispersed in pyrrolidone was applied, dried, and then pressed by a roller press to obtain a strip-shaped negative electrode.

The positive electrode and the negative electrode produced as described above were mixed with microporous polypropylene having a thickness of about 25 μm,
A spiral electrode body was formed by laminating and interposing as a separator and winding a number of times. Insulating plates are placed on the upper and lower surfaces of this spiral electrode body, housed in a nickel-plated iron battery can, and an aluminum positive electrode lead is derived from the positive electrode current collector to collect the positive and negative electrodes. Then, a nickel negative electrode lead was led out from the negative electrode current collector to an iron lid, and was welded to a battery can.

The battery can contains LiP as a non-aqueous electrolytic solution.
F ₆ was dissolved in ethylene carbonate / diethyl carbonate (1/1 [vol%]) dissolved at a concentration of 1 [M],
The various additives shown in (Table 1) were added so as to have the content of (Table 1). Then, the battery can and the lid were each caulked via a sealing gasket to fix the lid, thereby producing a cylindrical battery having a diameter of 18 mm and a height of 65 mm.

The polyhydric alcohol to be added to the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery of the present invention is not limited to the examples shown in the following (Table 1).
It can be applied instead of these, or a mixture thereof. At this time, when two or more polyhydric alcohols are used as additives, the total weight%
The value needs to be 0.01 to 0.5 [% by weight].

[0026]

[Table 1]

(Examples 1 to 5) Diethylene glycol as an additive was added to a non-aqueous electrolyte.
0.1% by weight, 0.01% by weight, 0.1% by weight, respectively.
03 [% by weight], 0.2 [% by weight], 0.5 [% by weight]
And a cylindrical battery was produced by the above method. Example 6 0.1% by weight of ethylene glycol was added to a non-aqueous electrolyte as an additive, and a cylindrical battery was manufactured in the same manner as in Example 1. (Example 7) Triethylene glycol was added as an additive to a non-aqueous electrolyte at 0.1% by weight, and a cylindrical battery was manufactured in the same manner as in Example 1. (Example 8) To a non-aqueous electrolyte, propylene glycol was added as an additive in an amount of 0.1% by weight, and a cylindrical battery was manufactured in the same manner as in Example 1. Example 9 A cylindrical battery was manufactured in the same manner as in Example 1 except that 0.1% by weight of glycerin was added as an additive to the nonaqueous electrolyte.

Comparative Example 1 A cylindrical battery was manufactured in the same manner as in Example 1 except that no additive was added to the nonaqueous electrolyte. Comparative Example 2 0.1-% by weight of 1-propanol was added as an additive to a non-aqueous electrolyte, and a cylindrical battery was manufactured in the same manner as in Example 1. Comparative Example 3 0.1% by weight of 2-ethoxyethanol was added as an additive to a non-aqueous electrolyte, and a cylindrical battery was manufactured in the same manner as in Example 1. Comparative Example 4 0.1% by weight of 2- (2-ethoxyethoxy) ethanol as an additive was added to a non-aqueous electrolyte solution, and a cylindrical battery was manufactured in the same manner as in Example 1. (Comparative Example 5) To a non-aqueous electrolyte, 0.005 [wt%] of diethylene glycol was added as an additive, and a cylindrical battery was produced in the same manner as in Example 1. Comparative Example 6 0.8% by weight of diethylene glycol was added as an additive to a non-aqueous electrolyte, and a cylindrical battery was manufactured in the same manner as in Example 1.

Fabricated as described above (Examples 1 to 3)
For the cylindrical batteries of 9) and (Comparative Examples 1 to 6), the initial capacity [mAh], the initial internal resistance [mΩ], and the increase in internal resistance [mΩ] after long-term use were measured.

The initial capacity was determined by charging the cylindrical batteries of each example and each comparative example with a charge voltage of 4.2 [V] and a charge current of 1000 [V].
After charging the battery under the conditions of [mA] and a charging time of 2.5 [hours], a discharging current of 500 [mA] and a cut-off voltage of 2.75 were obtained.
The discharge was performed under the condition [V], and the capacity at the time of discharge was defined as the initial capacity.

The initial internal resistance is as follows: charge voltage of 4.2 [V], charge current of 1000 [mA] and charge time of 2.5 [hour] for the cylindrical batteries of each of the examples and comparative examples after the measurement of the initial capacity. After charging under the conditions, the measured internal resistance was defined as the initial internal resistance.

The amount of increase in the internal resistance after long-term use was determined by measuring the charging voltage of 4.2 [V], the charging current of 1000 [mA], and the charging time of the cylindrical batteries of each of the examples after the initial internal resistance measurement and the comparative examples. Charge and discharge current 50 under the condition of 2.5 [hours]
Under the conditions of 0 [mA] and a final voltage of 2.75 [V], the discharge was repeated 1000 cycles, and the charging voltage was further increased to 4.
2 [V], charging current 1000 [mA], charging time 2.5
After charging under the condition of [time], the measured internal resistance was taken as the internal resistance after long-term use. The initial internal resistance was subtracted from the thus measured internal resistance after long-term use to obtain the amount of increase in internal resistance after long-term use.

The internal resistance was measured using an LCR meter (KC-523C manufactured by Kokuyo Electric Industries Co., Ltd.).
The measurement was performed by measuring the impedance at [kHz]. The measurement results are as shown in (Table 1).

As shown in Table 1, (Example 1)
(Example 9) That is, a polyhydric alcohol such as diethylene glycol, ethylene glycol, triethylene glycol, propylene glycol, or glycerin was
In the cylindrical battery used as an additive in the non-aqueous electrolyte, the additive was not used (Comparative Example 1), or compared with the case where a monohydric alcohol was used (Comparative Example 2) to (Comparative Example 4). Thus, the internal resistance increase after long-term use is small, indicating that there is an excellent internal resistance increase suppression effect. That is, no additive was added to the non-aqueous electrolyte (Comparative Example 1).
Has a large increase in internal resistance, and also in the case of using a monohydric alcohol as an additive (Comparative Example 2) to (Comparative Example 4), the internal resistance rise amount is relatively large, and the internal resistance rise suppression effect is It turns out that it is small.

Further, (Example 1) to (Example 9), that is, polyhydric alcohols such as diethylene glycol, ethylene glycol, triethylene glycol, propylene glycol, and glycerin were added to the non-aqueous electrolyte as additives. In the cylindrical battery to which 0.01 to 0.5 [% by weight] is added, the internal resistance rise after long-term use is small,
It can be seen that the initial capacity [mAh] is high and the battery has excellent battery characteristics. On the other hand, in the cylindrical battery (Comparative Example 5) to which 0.005% by weight of diethylene glycol, which is a polyhydric alcohol, was added as an additive, the internal resistance increase was relatively large, and the internal resistance increase was suppressed. It can be seen that the effect is not sufficiently obtained. As an additive, diethylene glycol, which is a polyhydric alcohol, is added in an amount of 0.8%.
It can be seen that the initial capacity of the cylindrical battery (Comparative Example 6) to which [wt%] was added was lower than that of (Example 1) to (Example 9). Therefore, in a non-aqueous electrolyte secondary battery, excellent battery characteristics can be obtained by adding a polyhydric alcohol to the non-aqueous electrolyte as an additive in an amount of 0.01 to 0.5% by weight. all right.

Next, FIG. 2 shows that 0.01 to 0.8% by weight of diethylene glycol, 0.1% by weight of ethylene glycol, and 0.1% by weight of propylene glycol were added to the nonaqueous electrolyte as additives. [Wt%], triethylene glycol 0.1 [wt%], glycerin 0.1 [wt%], propanol 0.1 [wt%], ethoxyethanol 0.1 [wt%], ethoxyethoxy When the internal resistance rise [mΩ] was measured under the same conditions as above for the cylindrical batteries in which 0.1% by weight of ethanol was added, and the case where no additive was added, respectively. The figure of the value was shown. Based on this measurement result, in the nonaqueous electrolyte secondary battery, a polyhydric alcohol is added to the nonaqueous electrolyte as an additive in an amount of 0.01 to 0.5% by weight, more preferably, 0.03-0.2
[Weight%] It has become clear that excellent battery characteristics can be obtained by the addition.

[0037]

According to the non-aqueous electrolyte secondary battery of the present invention,
By including a polyhydric alcohol as an additive in the non-aqueous electrolyte, an increase in internal resistance that occurs when the non-aqueous electrolyte is used for a long time was suppressed, and the life of the battery was prolonged.

According to the present invention, the initial capacity is large and the nonaqueous electrolyte is used for a long time by adding 0.01 to 0.5% by weight of a polyhydric alcohol as an additive to the nonaqueous electrolyte. A non-aqueous electrolyte secondary battery having excellent battery characteristics in which a rise in internal resistance caused in such a case was suppressed was obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an example of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a graph showing the relationship between the amount of additive added to a non-aqueous electrolyte and the amount of increase in internal resistance.

[Explanation of symbols]

1 Non-aqueous electrolyte secondary battery, 2 positive electrode, 3 negative electrode, 4 separator, 5 battery can, 6 lid, 7 positive electrode lead, 8
Negative electrode lead

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Claims (3)

[Claims] 1. A non-aqueous electrolyte having a positive electrode made of a lithium-containing compound and a negative electrode made of a carbon material capable of being doped with and dedoped with lithium, wherein an electrolyte salt is dissolved in a non-aqueous solvent. A non-aqueous electrolyte secondary battery comprising: a non-aqueous electrolyte secondary battery comprising: a polyhydric alcohol as an additive. 2. The amount of the polyhydric alcohol added is 0.0
2. The method according to claim 1, wherein the amount is 1 to 0.5% by weight.
3. The non-aqueous electrolyte secondary battery according to 1. 3. The non-aqueous solution according to claim 1, wherein the polyhydric alcohol contains at least one of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, glycerin, and pentaerythritol. Electrolyte secondary battery.