JP3213459B2 - Non-aqueous electrolyte secondary 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 non-aqueous electrolyte secondary battery, and more particularly to an improvement in a non-aqueous electrolyte for the purpose of improving 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 a non-aqueous electrolyte secondary battery in place of conventional metallic lithium because there is no risk of internal short circuit due to the growth of dendritic lithium.

As described above, it is known that in a battery using a carbon material as a negative electrode material, the battery characteristics greatly change depending on the type of the non-aqueous electrolyte. In this case, when a carbonate such as ethylene carbonate, dimethyl carbonate, or vinylene carbonate is used for the non-aqueous electrolyte, the electrochemical characteristics of the negative electrode made of a carbon material can be sufficiently exhibited.

However, when a carbon material is used as a negative electrode material and a carbonate is used as a solvent for the non-aqueous electrolyte, the non-aqueous electrolyte generates gas on the carbon negative electrode as the charge / discharge cycle progresses. As a result, the battery capacity gradually decreases. That is, when a carbon material and a carbonic acid ester are used in combination, there is an advantage that the capacity can be increased, but there is a disadvantage that the non-aqueous electrolyte is easily decomposed and the cycle characteristics are not good. Such a defect tends to occur particularly when a carbon material having high crystallinity, that is, a high degree of graphitization is used for the negative electrode material.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the cycle characteristics of a nonaqueous electrolyte secondary battery using a carbon material as a negative electrode material.

[0006]

In order to achieve the above object, a nonaqueous electrolyte secondary battery according to the present invention (hereinafter referred to as "battery of the present invention") has a positive electrode and a lattice (002) plane. You
A negative electrode made of a carbon material having a d value (d ₀₀₂ ) of 3.37 ° C. or less, and ethylene carbonate and dimethyl carbonate.
-Selected from the group consisting of carbonate and vinylene carbonate
A nonaqueous electrolyte secondary battery comprising at least one type of carbonated nonaqueous electrolyte, wherein the nonaqueous electrolyte contains a vinylene carbonate derivative represented by Chemical Formula 2. I do.

[0007]

Embedded image [However, R ¹ and R ² each independently represent an alkyl group having 1 to 3 carbon atoms. ]

Specific examples of the vinylene carbonate derivative represented by Chemical formula 2 include 3,4-dimethylvinylene carbonate, 3,4-diethylvinylene carbonate, and 3,4-dipropylvinylene carbonate.

When the non-aqueous electrolyte contains a vinylene carbonate derivative, the derivative is stable with respect to lithium and easily exists near the negative electrode. Is suppressed.

In the present invention, d ₀₀₂ is a negative electrode material.
Limited to high-capacity carbon materials with high crystallinity of 3.37 ° or less
The reason is that when this negative electrode material is used,
This is because decomposition degradation of the lysate is a particular problem. Such a conclusion
Graphite (natural graphite and artificial graphite)
In addition to graphite, increase the crystallinity by high pressure treatment, for example.
Modified coke having a d ₀₀₂ value of 3.37 ° or less is mentioned.
It is.

In the present invention, the solvent of the non-aqueous electrolyte is
And a vinylene carbonate derivative shown in Chemical formula 2
Carbonate, dimethyl carbonate and vinyleneca
At least one charcoal selected from the group consisting of carbonates
A mixed solvent containing an acid ester is used. Shown in Chemical formula 2
The solvent mixed with the vinylene carbonate derivative is
In the case of decomposable carbonate, vinyleneca shown in Chemical formula 2
The carbonate derivative in the non-aqueous electrolyte.
Cycle characteristic improvement effect is particularly pronounced.
is there.

Furthermore, if restricting the percentage of non-aqueous electrolyte bi two alkylene carbonate derivative 5 to 50% by volume,
The effect of the present invention will be further exhibited. This is because, when the proportion is less than 5% by volume, the amount of the vinylene carbonate derivative present in the vicinity of the negative electrode is small, so that the decomposition of the non-aqueous electrolyte on the surface of the carbon material cannot be sufficiently suppressed, and the cycle characteristics are deteriorated. On the other hand, if the proportion exceeds 50% by volume, the conductivity of the non-aqueous electrolyte decreases, the smoothness of the charge / discharge reaction is slightly impaired, and the cycle characteristics deteriorate. It is because it falls.

The present invention relates to a crystal having d ₀₀₂ of 3.37 ° or less.
High-capacity carbon material with a high capacity as the negative electrode material, and
As a non-aqueous electrolyte, a readily decomposable carbonate (ethylene
Carbonate, dimethyl carbonate and vinylene car
Decomposition and degradation of the non-aqueous electrolyte, which has been a problem when using a solvent containing (carbonate), can be easily performed in the non-aqueous electrolyte by adding the vinylene carbonate derivative shown in Chemical formula 2 to the non-aqueous electrolyte. It is intended to suppress the decomposition of the decomposable carbonate and thereby to improve the cycle characteristics. Therefore, with respect to the positive electrode material, the solute of the non-aqueous electrolyte, and the like, it is possible to use various materials which are conventionally proposed or practically used for the non-aqueous electrolyte secondary battery without any particular limitation.

As a positive electrode material (active material), LiCoO
The _{2, LiNiO 2, LiMnO 2,} LiFeO 2 and the like, also the solute of the non-aqueous electrolyte solution, LiPF _6,
LiClO ₄ and LiCF ₃ SO ₃ are exemplified.

[0015]

In the battery of the present invention , a mixed solvent containing a vinylene carbonate derivative represented by Chemical Formula 2 and a readily decomposable carbonate ester is used as the non-aqueous electrolyte. Easy to be nearby
Therefore, the easily decomposable carbonate ester hardly approaches the negative electrode, and as a result, the degradation of the easily decomposable carbonate ester is suppressed.

Incidentally, even in a non-aqueous electrolyte secondary battery using lithium metal as a negative electrode material, as the charge / discharge cycle progresses, the lithium metal reacts with the non-aqueous electrolyte to form a coating composed of a reaction product (organic substance). Are formed on the surface of lithium metal, and the formation of this coating increases the electrode plate reaction resistance, resulting in a problem that the cycle characteristics deteriorate. However, when lithium metal is the negative electrode material, even if the vinylene carbonate derivative is contained in the nonaqueous electrolyte, the formation of a reactant film between the lithium metal and the nonaqueous electrolyte cannot be suppressed, so that the cycle characteristics are improved. It will not be done. Therefore, the effect of improving the cycle characteristics by adding the vinylene carbonate derivative to the non-aqueous electrolyte can be said to be an effect recognized only when the negative electrode material is a highly crystalline carbon material.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(Example 1) AA type (AA size) non-aqueous electrolyte secondary batteries (batteries of the present invention) were prepared.

[Positive electrode] LiNiO ₂ as a positive electrode active material
A mixture obtained by mixing the graphite and artificial graphite 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 to prepare a slurry. After applying to both sides of aluminum foil as a positive electrode current collector by doctor blade method, 15
Vacuum drying was performed at 0 ° C. for 2 hours to produce a positive electrode.

[Anode] Graphite powder (d ₀₀₂ = 3.35 °,
Lc = 2000 °) is dispersed in a 5 wt% NMP solution of polyvinylidene fluoride as a binder to prepare a slurry, and this slurry is applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method. And vacuum drying at 150 ° C. for 2 hours to produce a negative electrode.

[Non-aqueous electrolyte] The volume mixing ratio is 30:70.
In a mixed solvent of 3,4-dimethylvinylene carbonate (3,4-dimethylVC; R ¹ and R ² are both methyl groups in the above formula 2) and dimethyl carbonate (DMC), 1M of LiPF ₆ was added. (Mol / liter) to prepare a non-aqueous electrolyte.

[Preparation of Battery] AA type battery BA1 of the present invention was prepared using the positive and negative electrodes and the nonaqueous electrolyte described above. As the separator, a microporous polypropylene membrane (manufactured by Hoechst Celanese Co., Ltd., trade name "Celgard") was used, and this was impregnated with the above nonaqueous electrolyte.

FIG. 1 is a cross-sectional view schematically showing a manufactured battery BA1 of the present invention. The illustrated battery BA1 of the present invention includes a positive electrode 1, a negative electrode 2, a separator 3 separating these two electrodes, a positive electrode lead 4, and a negative electrode. Lead 5, positive external terminal 6, negative can 7
Etc. 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.

Comparative Example 1 Example 1 was repeated except that a mixed solvent of ethylene carbonate and DMC having a volume mixing ratio of 30:70 was used instead of the mixed solvent of 3,4-dimethylvinylene carbonate and DMC. A non-aqueous electrolyte was prepared in the same manner as described above. Next, the AA comparative battery BC1 was manufactured in the same manner as in Example 1 except that this non-aqueous electrolyte was used.
Was prepared.

Comparative Example 2 Example 1 was repeated except that a mixed solvent of vinylene carbonate and DMC having a volume mixing ratio of 30:70 was used in place of the mixed solvent of 3,4-dimethylvinylene carbonate and DMC. A non-aqueous electrolyte was prepared in the same manner as described above. Then, the AA type comparative battery BC2 was manufactured in the same manner as in Example 1 except that this non-aqueous electrolyte was used.
Was prepared.

[Cycle Characteristics] The battery BA1 of the present invention and the comparative batteries BC1 and BC2 (the discharge capacity at the beginning of the cycle is 600 mAh) were charged at 200 mA to a charge end voltage of 4.2 V and then stopped at 200 mA. The battery was discharged to a voltage of 2.75 V, and the cycle characteristics of each battery were examined. The results are shown in FIG.

FIG. 2 is a graph showing the cycle characteristics of each battery, the vertical axis showing the discharge capacity (mAh), and the horizontal axis showing the number of cycles (times). As shown in FIG. The discharge capacity at the 1000th cycle of the battery BA1 is 550 m
The discharge capacity at the 1000th cycle of the comparative batteries BC1 and BC2 is as small as 420 mAh (capacity deterioration rate: 30%), whereas the Ah is large (capacity deterioration rate: 8%). From this, the decrease in the discharge capacity due to the decomposition of the non-aqueous electrolyte during the charge / discharge cycle is significantly suppressed by including 3,4-dimethylvinylene carbonate in the solvent of the non-aqueous electrolyte. I understand.

<Relationship between volume mixing ratio of 3,4-dimethylvinylene carbonate and cycle characteristics> LiCoO ₂ is used as a positive electrode active material, and the volume mixing ratio of 3,4-dimethylvinylene carbonate and DMC is 0: 10
0, 5:95, 10:90, 20:80, 30:70,
40:60, 50:50, 60:40, 70:30, 8
A battery of the present invention and a comparative battery were produced in the same manner as in Example 1 except that 0:20, 90:10 or 100: 0 was used. Next, a charge / discharge cycle test was performed under the same conditions as above to determine the capacity deterioration rate at the 1000th cycle of each battery.
The relationship between the volume mixing ratio of 3,4-dimethylvinylene carbonate and DMC and the cycle characteristics was examined. The results are shown in FIG.

In FIG. 3, the vertical axis represents the discharge capacity (mAh), and the horizontal axis represents 3,4-dimethylvinylene carbonate and DMH.
5 is a graph showing the volume mixing ratio with C, and as shown in the figure, when the ratio of 3,4-dimethylvinylene carbonate to the nonaqueous electrolyte is 5 to 50% by volume, the capacity deterioration rate It can be seen that the non-aqueous electrolyte secondary battery exhibiting excellent cycle characteristics can be obtained.

[0031]

[0032]

[0033]

[0034]

[0035]

In the embodiments described above, the case where the present invention is applied to an AA battery is described as an example. However, the shape of the battery of the present invention is not particularly limited. Which can be applied to non-aqueous electrolyte secondary batteries of various shapes.

In the above embodiment, 3,4-dimethylvinylene carbonate was used as the vinylene carbonate derivative.
While the case of using the door has been described as an example, 3,4-diethyl
It is possible to obtain a non-aqueous electrolyte secondary battery that exhibits similar excellent cycle characteristics even when other vinylene carbonate derivatives are used in addition to tylvinylene carbonate, 3,4-dipropylvinylene carbonate, and the like. .

[0038]

Since the decomposition of the non-aqueous electrolyte on the surface of the carbon material is suppressed, the battery of the present invention has a unique characteristic that the battery has a small capacity deterioration rate along with the progress of the charge / discharge cycle and excellent cycle characteristics. Has the effect of

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an AA battery of the present invention.

FIG. 2 is a graph showing cycle characteristics of the battery of the present invention and a comparative battery.

FIG. 3: 3,4-dimethylvinylene carbonate and DM
6 is a graph showing a relationship between a volume mixing ratio with C and a discharge capacity.

[Explanation of symbols]

 BA1 Battery of the present invention 1 Positive electrode 2 Negative electrode 3 Separator

──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Nishio, inventor 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Toshihiko Saito 2-18-18 Keihanhondori, Moriguchi-shi, Osaka (56) References JP-A-62-90863 (JP, A) JP-A-2-215059 (JP, A) JP-A-63-121260 (JP, A) JP-A-4-169075 (JP JP, A) JP-A-2-172162 (JP, A) JP-A-5-13088 (JP, A) JP-A-6-52887 (JP, A) JP-A-6-275271 (JP, A) JP JP-A-4-95362 (JP, A) JP-A-5-211070 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/58 H01M 4/02

Claims (2)

(57) [Claims] 1. A d value in a positive electrode and a lattice plane (002) plane
A negative electrode using a carbon material (d ₀₀₂ ) of 3.37 ° or less as a negative electrode material; ethylene carbonate and dimethyl carbonate;
And vinylene carbonate.
A non-aqueous electrolyte secondary battery comprising at least one non-aqueous electrolyte solution containing a carbonate ester , wherein the non-aqueous electrolyte solution contains a vinylene carbonate derivative represented by Chemical Formula 1. Non-aqueous electrolyte secondary battery. Embedded image [However, R ¹ and R ² each independently represent an alkyl group having 1 to 3 carbon atoms. ] 2. The method of claim 1, wherein the vinylene carbonate derivative is
The non-aqueous electrolyte secondary battery according to claim 1 , wherein the proportion of the non-aqueous electrolyte in the aqueous electrolyte is 5 to 50% by volume .