JP3332834B2 - Lithium ion battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion battery, and more particularly to an improvement in an organic electrolyte for the purpose of improving storage characteristics and cycle characteristics.

[0002]

2. Description of the Related Art In recent years,
Coke, carbon material such as graphite, excellent in flexibility,
It has been proposed as a new negative electrode material for lithium ion batteries in place of conventional metal lithium because there is no risk of internal short circuit due to the growth of dendritic lithium.

As described above, it is known that battery characteristics using a carbon material as a negative electrode material greatly change depending on the type of organic electrolyte. In this case, when an asymmetric chain carbonate such as methyl ethyl carbonate is used as the organic electrolyte, the initial characteristics can be improved.

However, a carbon material (particularly, a graphite-based carbon material having a d value (d ₀₀₂ ) of less than 3.40 ° on a lattice plane (002) plane) is used as a negative electrode material, and methyl ethyl carbonate is used as an organic electrolyte solution. When used as a solvent, when a long-term storage or charge / discharge cycle is repeated, a passivation film is formed on the negative electrode surface because methyl ethyl carbonate causes a transesterification reaction on the negative electrode surface made of a carbon material. For this reason, there was a problem that storage characteristics and cycle characteristics were deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium ion battery capable of improving storage characteristics and cycle characteristics without deteriorating initial characteristics. .

[0006]

According to the present invention, there is provided a lithium-ion battery comprising a positive electrode and a graphite-based carbon having a d value (d ₀₀₂ ) of less than 3.40 ° on a lattice plane (002) plane. In a lithium ion battery including a negative electrode using a material as a negative electrode material and an organic electrolyte, as a solvent (excluding propylene carbonate) of the organic electrolyte, an asymmetric chain carbonate represented by the following chemical formula 3 and a chemical formula represented by the following chemical formula 4 are used. A cyclic carbonate having a double bond and ethylene carbonate are included, and a ratio of the cyclic carbonate having a double bond to the organic electrolytic solution excluding the cyclic carbonate having the double bond is 0.1 to 0.1. 5
% By weight.

[0007]

Embedded image Wherein R ¹ and R ² represent an alkyl group, and R ¹ ≠
R ² . ]

[0008]

Embedded image

As described above, if the organic electrolyte contains a cyclic carbonate having a double bond in addition to the asymmetric chain carbonate, the cyclic carbonate having a double bond and the negative electrode made of a carbon material have priority. , A good-quality film (Li ₂ CO ₃ ) is formed on the surface of the negative electrode. Therefore, the formation of a passive film on the negative electrode surface due to the presence of the asymmetric chain carbonate is suppressed, so that storage characteristics and cycle characteristics can be improved. Further, since the ratio of the cyclic carbonate having a double bond to the organic electrolytic solution excluding the cyclic carbonate having a double bond is regulated to 0.1 to 5% by weight, the proportion of the cyclic carbonate having a double bond is controlled. Does not lead to a decrease in storage characteristics and cycle characteristics due to an excessively small amount, and does not lead to a decrease in the initial capacity due to an excessively large proportion of the cyclic carbonate having a double bond (too little asymmetric chain carbonate).

Further, when a high-capacity carbon material having a d ₀₀₂ of less than 3.40 ° and high crystallinity is used, a transesterification reaction is particularly likely to occur, so that the effect of the present invention is sufficiently exhibited. Is done. Examples of such a highly crystalline carbon material include natural graphite and artificial graphite.

Further, the invention according to claim 2 is the invention according to claim 1, wherein R ¹ and R ² in the chemical formula ¹ are:
It is an alkyl group having 1 to 3 carbon atoms. As described above, when R ¹ and R ² in Chemical Formula 1 are alkyl groups having 1 to 3 carbon atoms, the above-described effect is further exhibited.

According to a third aspect of the present invention, in the first or second aspect, the ratio of the asymmetric chain carbonate in the organic electrolyte is 10 to 80% by volume. . The reason for this restriction is that the ratio of the asymmetric chain carbonate in the organic electrolyte is 10%.
If the amount is less than volume%, the effect of the addition is insufficient, leading to a decrease in the initial capacity.
This is also because the initial capacity is reduced.

[0013]

[0014]

[0015] The invention described in claim 4 is based on claim 1,
4. The invention according to 2 or 3, wherein the asymmetric chain carbonate is methyl ethyl carbonate or methyl propyl carbonate, and the cyclic carbonate having a double bond is vinylene carbonate.
However, the present invention is not limited to these. In addition, examples of the asymmetric chain carbonate include ethyl propyl carbonate, and examples of the cyclic carbonate having a double bond include propene carbonate.

[0016] Further, the invention according to claim 5 is based on claim 1,
5. The invention according to 2, 3, or 4, wherein the proportion of the ethylene carbonate in the organic electrolyte solution excluding the cyclic carbonate having a double bond is 20 to 90% by volume. The reason for this restriction is that if the proportion of ethylene carbonate in the organic electrolyte deviates from the above range, the battery capacity after high-temperature storage and the battery capacity after charge / discharge cycles are reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. [Positive electrode] A mixture obtained by mixing LiCoO ₂ as a positive electrode active material and carbon as a conductive agent at a weight ratio of 9: 1 was dispersed in a 5% by weight N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride. A slurry was prepared by applying the slurry to both surfaces of an aluminum foil as a positive electrode current collector by a doctor blade method, and then vacuum-dried at 150 ° C. for 2 hours to produce a positive electrode.

[Anode] Graphite powder (d ₀₀₂ = 3.37 °)
5% by weight of polyvinylidene fluoride as binder
A slurry was prepared by dispersing the slurry in a P solution, and this slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, and then dried under vacuum at 150 ° C. for 2 hours to prepare a negative electrode.

[Organic electrolyte solution] The volume mixing ratio is 30:70.
To ethylene carbonate (EC) and methyl ethyl carbonate (MEC) mixed at a ratio of 1% by weight of vinylene carbonate (VC) with respect to the total weight of ethylene carbonate and methyl ethyl carbonate, and the mixed solvent was added. Then, LiPF ₆ was added at 1 M (mol / mol).
Liter) to prepare an organic electrolyte solution.

[Preparation of Battery] The battery of the present invention (cylindrical, diameter: 18 mm,
(Height: 65 mm). In addition, as a separator, a microporous film made of polypropylene was used, and this was impregnated with the organic electrolytic solution.

FIG. 1 is a cross-sectional view schematically showing a manufactured battery of the present invention.
Separator 3, positive electrode lead 4, separating these two electrodes,
It comprises a negative electrode lead 5, a positive electrode external terminal 6, a negative electrode can 7, and the like. The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 in a state of being spirally wound through a separator 3 into which a non-aqueous electrolyte is injected. The terminal 6 and the negative electrode 2 are connected to a negative electrode can 7 via a negative electrode lead 5, so that chemical energy generated inside the battery can be taken out as electric energy.

In the present invention, the transesterification reaction on the surface of the negative electrode, which has been a problem when a carbon material is used as the negative electrode material, comprises causing the organic electrolytic solution to contain a cyclic carbonate having a double bond. Thus, the storage characteristics and the cycle characteristics are improved. Therefore, as for the positive electrode material, the solute of the organic electrolyte, and the like, it is possible to use various materials that have been conventionally proposed or practically used for lithium ion batteries without any particular limitation.

As the positive electrode material (active material), the above LiC
In addition to oO ₂ , LiNiO ₂ , LiMnO ₂ , LiFe
O ₂ is exemplified. In addition to the above-mentioned LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃
Is exemplified.

[0024]

EXAMPLES [First Example] (Example 1) As Example 1, the battery described in the embodiment of the present invention was used. The battery fabricated in this way is
Hereinafter, the battery is referred to as Battery A1 of the invention.

(Examples 2 to 5) Except that the addition ratio of vinylene carbonate was 0.05% by weight, 0.1% by weight, 5% by weight and 10% by weight, respectively, in the same manner as in Example 1 above. A battery was manufactured. The battery fabricated in this way is
Hereinafter, these batteries are referred to as present invention batteries A2 to A5, respectively.

Comparative Example 1 A battery was manufactured in the same manner as in Example 1 except that vinylene carbonate was not added. The battery fabricated in this manner is hereinafter referred to as Comparative Battery X
No. 1.

(Experiment 1) For the batteries A1 to A5 of the present invention and the comparative battery X1, the initial battery capacity and after storage at high temperatures (60
(For 20 days at 20 ° C.) and the battery capacity after 500 cycles of charging and discharging. The results are shown in Table 1. The charge and discharge conditions are shown below. Charging conditions: After charging to a charge end voltage of 4.1 V with a predetermined current, the current value was gradually reduced while maintaining the voltage at 4.1 V, and charging was terminated when the current value reached 27 mA. However, if the current value exceeded 27 mA even after 3 hours, charging was completed in 3 hours. Discharge conditions: Discharge was performed at a predetermined current to a discharge end voltage of 2.75V.

[0028]

[Table 1]

As is clear from Table 1, the battery A1 of the present invention
A5 has substantially the same initial capacity as the comparative battery X1, but it is recognized that the battery capacity after high-temperature storage and the battery capacity after charging and discharging for 500 cycles are significantly larger. Therefore, it can be confirmed that it is desirable that vinylene carbonate be contained in the solvent of the organic electrolyte.

However, the battery A2 of the present invention in which the ratio of vinylene carbonate to the organic electrolytic solution excluding vinylene carbonate (hereinafter, simply referred to as the ratio of vinylene carbonate) is less than 0.1% by weight, and the ratio of vinylene carbonate is 5% by weight. The battery A5 of the present invention has a vinylene carbonate content of 0.1 to 5% by weight.
Battery capacity after high-temperature storage compared to A3 and A4, and 500
It is recognized that the battery capacity after cycle charge / discharge is slightly reduced. Therefore, the ratio of vinylene carbonate is desirably 0.1 to 5% by weight.

Comparative Example 2 A battery was manufactured in the same manner as in Example 1 except that dimethyl carbonate (DMC) was used instead of methyl ethyl carbonate. The battery fabricated in this manner is hereinafter referred to as Comparative Battery X2.

Comparative Example 3 A battery was prepared in the same manner as in Comparative Example 2 except that vinylene carbonate was not added. The battery fabricated in this manner is hereinafter referred to as Comparative Battery X
No. 3.

Comparative Example 4 A battery was produced in the same manner as in Example 1 except that diethyl carbonate (DEC) was used instead of methyl ethyl carbonate. The battery fabricated in this manner is hereinafter referred to as Comparative Battery X4.

Comparative Example 5 A battery was prepared in the same manner as in Comparative Example 4 except that vinylene carbonate was not added. The battery fabricated in this manner is hereinafter referred to as Comparative Battery X
No. 5.

(Experiment 2) For the comparative batteries X2 to X5, the initial battery capacity, the battery capacity after high-temperature storage, and 50
Table 2 shows the results of examining the battery capacity after 0 cycles of charging and discharging. The charge and discharge conditions were the same as those in Experiment 1. Table 2 also shows the results of the battery A1 of the present invention for easy comparison.

[0036]

[Table 2]

As is clear from Table 2, the comparative battery X2,
X4 has a larger battery capacity after high-temperature storage and a larger battery capacity after 500 cycles of charging and discharging than the comparative batteries X3 and X5, but both battery capacities are smaller than the battery A1 of the present invention. Is recognized. Therefore, it can be confirmed that the effect of the present invention is not sufficiently exhibited when a symmetric chain carbonate such as dimethyl carbonate or diethyl carbonate is used in place of an asymmetric chain carbonate such as methyl ethyl carbonate.

Example 6 As an organic electrolytic solution, ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate mixed at a volume mixing ratio of 30:40:30, and vinylene carbonate in an amount of 1 wt. A battery was fabricated in the same manner as in Example 1, except that the battery was added at a ratio of 0.1%. The battery fabricated in this manner is hereinafter referred to as Battery A6 of the invention.

Comparative Example 6 A battery was manufactured in the same manner as in Example 6 except that vinylene carbonate was not added. The battery fabricated in this manner is hereinafter referred to as Comparative Battery X
No. 6.

(Experiment 3) For the battery A6 of the present invention and the comparative battery X6, the initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after charging and discharging for 500 cycles were examined. 3 is shown. The charge and discharge conditions were the same as those in Experiment 1. Table 3 also shows the results of the battery A1 of the present invention for easy comparison.

[0041]

[Table 3]

As is clear from Table 3, the battery A6 of the present invention
Indicates that the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charge / discharge are larger than the comparative battery X6, and it is recognized that the battery has substantially the same performance as the battery A1 of the present invention. Therefore, it can be confirmed that the effects of the present invention can be sufficiently exerted when the organic electrolyte solution contains a symmetric chain carbonate such as dimethyl carbonate, but also contains an asymmetric chain carbonate such as methyl ethyl carbonate.

Examples 7 to 13 The volume ratios of ethylene carbonate and methyl ethyl carbonate were 10:90, 20:80, 50:50, 70:30 and 8 respectively.
A battery was fabricated in the same manner as in Example 1 except that 0:20, 90:10, and 95: 5 were set. The batteries fabricated in this manner are hereinafter referred to as Batteries A7 to A13 of the invention, respectively.

(Experiment 4) For the batteries A7 to A13 of the present invention, the initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after 500 charge / discharge cycles were examined.
Table 4 shows the results. The charge and discharge conditions were the same as those in Experiment 1. Table 4 also shows the results of the battery A1 of the present invention.

[0045]

[Table 4]

As is clear from Table 4, the battery A of the present invention
1 and A8 to A12 show that the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charge / discharge were larger than those of the batteries A7 and A13 of the present invention. Therefore, the volume ratio between ethylene carbonate and methyl ethyl carbonate is from 20:80 to 90:10.
Can be confirmed to be desirable.

Example 14 A battery was fabricated in the same manner as in Example 1 except that a graphite-based carbon material having a d value (d ₀₀₂ ) of 3.35 ° in the lattice plane (002) was used as a negative electrode material. Produced. The battery fabricated in this manner is hereinafter referred to as Battery A14 of the invention.

(Comparative Examples 7 and 8) As the negative electrode material, the d value (d ₀₀₂ ) on the lattice plane (002) plane was 3.4, respectively.
A battery was manufactured in the same manner as in Example 1 except that a graphite-based carbon material of 0 ° and 3.45 ° was used. The batteries fabricated in this manner are hereinafter referred to as comparative batteries X7 and X8, respectively.

(Experiment 5) The initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after 500 cycles of charging and discharging were examined for the battery A14 of the present invention and the comparative batteries X7 and X8. Are shown in Table 5. The charge and discharge conditions were the same as those in Experiment 1. Table 5 also shows the results of the battery A1 of the present invention.

[0050]

[Table 5]

As is clear from Table 5, the battery A of the present invention
1 and A13, the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charging and discharging are larger than those of the comparative batteries X7 and X8. Therefore, the d value (d ₀₀₂ ) on the lattice plane (002) plane is
It can be confirmed that it is desirable that the angle is less than 3.40 °.

[Second Embodiment] (Example 1) A battery was manufactured in the same manner as in Example 1 of the first embodiment except that methylpropyl carbonate (MPC) was used instead of methyl ethyl carbonate.
The battery fabricated in this manner is hereinafter referred to as Battery B1 of the invention.
Called.

(Examples 2 to 5) Except that the addition ratio of vinylene carbonate was 0.05% by weight, 0.1% by weight, 5% by weight and 10% by weight, respectively, in the same manner as in Example 1 above. A battery was manufactured. The battery fabricated in this way is
Hereinafter, these batteries are referred to as present invention batteries B2 to B5, respectively.

Comparative Example 1 A battery was manufactured in the same manner as in Example 1 except that vinylene carbonate was not added. The battery fabricated in this manner is hereinafter referred to as Comparative Battery Y.
No. 1.

(Experiment 1) For the batteries B1 to B5 of the present invention and the comparative battery Y1, the initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after 500 charge / discharge cycles were examined. It is shown in Table 6. The charging and discharging conditions are the same as those in Experiment 1 of the first embodiment.

[0056]

[Table 6]

As is clear from Table 6, the battery B1 of the present invention
B5 has substantially the same initial capacity as the comparative battery Y1, but it is recognized that the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charge / discharge are significantly larger. Therefore, it can be confirmed that it is desirable to include vinylene carbonate in the solvent of the organic electrolyte.

However, when the ratio of vinylene carbonate to the organic electrolyte solution excluding vinylene carbonate (hereinafter, simply referred to as the ratio of vinylene carbonate) is less than 0.1% by weight, the battery B2 of the present invention and the ratio of vinylene carbonate are 5% by weight. Inventive battery B5 having a vinylene carbonate ratio of 0.1 to 5% by weight,
Battery capacity after high temperature storage compared to B3 and B4, and 500
It is recognized that the battery capacity after cycle charge / discharge is slightly reduced. Therefore, the ratio of vinylene carbonate is desirably 0.1 to 5% by weight.

Example 6 As an organic electrolytic solution, ethylene carbonate, methyl propyl carbonate and dimethyl carbonate mixed at a volume mixing ratio of 30:40:30, and vinylene carbonate in an amount of 1 wt. A battery was fabricated in the same manner as in Example 1, except that the battery was added at a ratio of 0.1%. The battery fabricated in this manner is hereinafter referred to as Battery B6 of the invention.

Comparative Example 2 A battery was fabricated in the same manner as in Example 6 except that vinylene carbonate was not added. The battery fabricated in this manner is hereinafter referred to as Comparative Battery Y.
No. 2.

(Experiment 3) With respect to the battery B6 of the present invention and the comparative battery Y2, the initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after 500 charge / discharge cycles were examined. FIG. The charge and discharge conditions were the same as those in Experiment 1. Table 3 also shows the results of the battery B1 of the present invention for easy comparison.

[0062]

[Table 7]

As is clear from Table 7, the battery B6 of the present invention
Indicates that the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charging and discharging are larger than those of the comparative battery Y6, and it is recognized that the battery has substantially the same performance as the battery B1 of the present invention. Therefore, it can be confirmed that the effects of the present invention can be sufficiently exerted even if the organic electrolyte solution contains a symmetric chain carbonate such as dimethyl carbonate, but also contains an asymmetric chain carbonate such as methyl propyl carbonate.

Examples 7 to 13 The volume ratios of ethylene carbonate and methyl propyl carbonate were 10:90, 20:80, 50:50, 70:30,
A battery was fabricated in the same manner as in Example 1 except that the batteries were 80:20, 90:10, and 95: 5. The batteries fabricated in this manner are hereinafter referred to as Batteries B7 to B13 of the invention, respectively.
Called.

(Experiment 4) For the batteries B7 to B13 of the present invention, the initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after 500 charge / discharge cycles were examined.
Table 8 shows the results. The charge and discharge conditions were the same as those in Experiment 1. Table 8 also shows the results of the battery B1 of the present invention.

[0066]

[Table 8]

As is clear from Table 8, the battery B of the present invention
1 and B8 to B12 show that the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charging and discharging are larger than those of the batteries B7 and B13 of the present invention. Therefore, the volume ratio of ethylene carbonate to methyl propyl carbonate is from 20:80 to 90: 1.
It can be confirmed that 0 is desirable.

Example 14 A battery was fabricated in the same manner as in Example 1 except that a graphite-based carbon material having a d-value (d ₀₀₂ ) of 3.35 ° in the lattice plane (002) was used as a negative electrode material. Produced. The battery fabricated in this manner is hereinafter referred to as Battery B14 of the invention.

(Comparative Examples 3 and 4) As the negative electrode material, the d value (d ₀₀₂ ) on the lattice plane (002) plane was 3.4, respectively.
A battery was manufactured in the same manner as in Example 1 except that a graphite-based carbon material of 0 ° and 3.45 ° was used. The batteries fabricated in this manner are hereinafter referred to as comparative batteries Y3 and Y4, respectively.

(Experiment 5) With respect to the battery B14 of the present invention and the comparative batteries Y3 and Y4, the initial battery capacity, the battery capacity after high-temperature storage, and the battery capacity after 500 cycles of charging and discharging were examined. Are shown in Table 9. The charge and discharge conditions were the same as those in Experiment 1. Table 9 also shows the results of the battery B1 of the present invention.

[0071]

[Table 9]

As is clear from Table 9, the battery B of the present invention
1 and B13, it is recognized that the battery capacity after high-temperature storage and the battery capacity after 500 cycles of charging and discharging are larger than those of the comparative batteries Y7 and Y8. Therefore, the d value (d ₀₀₂ ) on the lattice plane (002) plane is
It can be confirmed that it is desirable that the angle is less than 3.40 °.

[0073]

As described above, according to the present invention, the formation of a passivation film on the surface of the negative electrode can be suppressed, so that the storage characteristics and the cycle characteristics can be improved without lowering the initial characteristics. It has an excellent effect that it can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a battery of the present invention.

[Explanation of symbols]

 1 positive electrode 2 negative electrode 3 separator

Continuation of the front page (56) References JP-A-9-147910 (JP, A) JP-A-8-22839 (JP, A) JP-A-8-96852 (JP, A) JP-A-11-67266 (JP) JP-A-11-162510 (JP, A) JP-A-7-220756 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40

Claims (5)

(57) [Claims] 1. A positive electrode and d in a lattice plane (002) plane
In a lithium ion battery including a negative electrode using a graphite-based carbon material having a value (d ₀₀₂ ) of less than 3.40 ° as a negative electrode material and an organic electrolyte, the solvent (excluding propylene carbonate) of the organic electrolyte is as follows: The asymmetric chain carbonate shown in FIG. 1, the cyclic carbonate having a double bond shown in the following chemical formula 2, and ethylene carbonate are included, and the organic electrolyte solution except for the cyclic carbonate having the double bond is used. A lithium ion battery, wherein the proportion of the cyclic carbonate having a double bond is 0.1 to 5% by weight. Embedded image Wherein R ¹ and R ² represent an alkyl group, and R ¹ ≠
R ² . [Chemical formula 2] 2. The lithium ion battery according to claim 1, wherein R ¹ and R ² in Chemical Formula 1 are alkyl groups having 1 to 3 carbon atoms. 3. The lithium ion battery according to claim 1, wherein the proportion of the asymmetric chain carbonate in the organic electrolyte is 10 to 80% by volume. 4. The lithium ion battery according to claim 1, wherein the asymmetric chain carbonate is methyl ethyl carbonate or methyl propyl carbonate, and the cyclic carbonate having a double bond is vinylene carbonate. 5. The lithium ion battery according to claim 1, wherein the proportion of the ethylene carbonate in the organic electrolyte except for the cyclic carbonate having a double bond is 20 to 90% by volume.