JP3263466B2 - 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 LiCF ₃ SO ₃ , LiN (CF
_The present invention relates to an improvement in an aluminum molded body as a positive electrode current collector for making ₃ SO ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ practically usable as an electrolyte solute of a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Unlike a nonaqueous electrolyte secondary battery, a lithium secondary battery, which is a typical nonaqueous electrolyte secondary battery, does not need to consider the decomposition voltage of water. In many cases, the positive electrode potential is about 4.0 V during charging. A material such as stainless steel (SUS) that reacts with and dissolves in the electrolytic solution during charging cannot be used for the positive electrode current collector having such a high potential.

For this reason, conventionally, an aluminum molded body (a plate, a foil, or the like) is generally used as a positive electrode current collector of a nonaqueous electrolyte secondary battery. Aluminum can be used for LiPF ₆ , LiBF ₄ , L even when the positive electrode potential becomes 4.0 V or more.
This is because iAsF _{6 and the} like (hereinafter, these may be collectively referred to as “lithium hexafluorophosphate and the like”) are not dissolved in an electrolytic solution having an electrolytic solution solute.

[0004] However, aluminum is LiCF
₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiC (CF
₃ SO ₂ ) ₃ (hereinafter sometimes collectively referred to as “lithium trifluoromethanesulfonate”)
When the positive electrode potential becomes 3.5 V or more, it reacts and dissolves.

For these reasons, lithium hexafluorophosphate and the like cannot be used as an electrolyte solute of a non-aqueous electrolyte secondary battery using aluminum as a positive electrode current collector material, and lithium trifluoromethanesulfonate and the like cannot be used. That is the fact.

Accordingly, in order to make lithium trifluoromethanesulfonate and the like practically usable as an electrolyte solute for batteries of this type, a result of intensive studies on why aluminum does not dissolve when lithium hexafluorophosphate or the like is used is shown. The present inventors have found that a specific passivation film is electrochemically formed on the surface of the aluminum molded body during charging.

The present invention has been made based on such knowledge, and an object of the present invention is to use lithium trifluoromethanesulfonate or the like which has been considered to be impractical in a conventional non-aqueous electrolyte secondary battery. An object of the present invention is to provide a nonaqueous electrolyte secondary battery having excellent cycle characteristics, which is used as a solute.

[0008]

In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention (hereinafter referred to as "battery of the present invention") comprises LiCF ₃ SO ₃ , LiN (C
A non-aqueous electrolyte secondary battery using F ₃ SO ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ as an electrolyte solute, wherein an aluminum molded article having an AlF ₃ coating formed on the surface as a positive electrode current collector Will be used.

The battery (target battery) to which the present invention is directed is:
This is a non-aqueous electrolyte secondary battery using lithium trifluoromethanesulfonate or the like as an electrolyte solute. An object of the present invention is to make aluminum, which has been conventionally impractical in batteries of this type, practically usable as a positive electrode current collector material. Therefore, a non-aqueous electrolyte secondary battery using lithium hexafluorophosphate or the like as an electrolyte solute is outside the scope of the present invention.

In the battery of the present invention, an aluminum molded body having an AlF ₃ (aluminum fluoride) film formed on its surface is used as the positive electrode current collector of the above-mentioned target battery.

The reason why the AlF ₃ coating was formed on the surface of the aluminum molded body was that the passive coating formed by the electrochemical reaction of lithium hexafluorophosphate or the like with aluminum showed that AlF ₃ was mainly formed as a result of analysis. It is because it turned out that it is a component.

[0012] As a method for forming the AlF ₃ coating on the surface of an aluminum molded product, the lithium hexafluorophosphate or the like and the electrolyte solute, a method of forming an electrochemically AlF ₃ coating of aluminum moldings as an anode, the aluminum molding A method of forming aluminum oxide by anodic oxidation on the surface of the body and reacting it with hydrogen fluoride or silicon tetrafluoride under heating to form an AlF ₃ coating,
CVD method and the like can be mentioned. Among them, the above method is advantageous because an AlF ₃ coating having a desired thickness can be easily obtained by changing the amount of aluminum oxide formed by anodic oxidation.

The preferred thickness of the AlF ₃ coating is 10 to 50
0 °. As shown in the examples described later, the thickness is 10
When the thickness is less than Å, the effect of suppressing the dissolution of aluminum by the passivation film is not sufficiently exhibited, and the thickness is 500 Å.
If it exceeds, the resistance of the AlF ₃ coating increases,
This is because in any case, the capacity is reduced.

[0014] As described above, the present invention is an aluminum molded product which has been a conventional practice not in the non-aqueous electrolyte secondary battery and the electrolyte solute of lithium trifluoromethanesulfonate and the like, the AlF ₃ coating on the surface thereof It has the greatest feature in that it can be made practical by forming. Therefore, other members in the battery of the present invention, such as a positive electrode material, a negative electrode material, a negative electrode current collector, and an electrolyte solvent, are not particularly limited.

For example, as the positive electrode active material, LiCo
O ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ are exemplified. As the negative electrode material, a carbon material such as graphite and coke, a lithium metal, and a lithium alloy are exemplified. Further, as the electrolyte solvent, various solvents which have been conventionally proposed or used for non-aqueous electrolyte secondary batteries, such as ethylene carbonate, dimethyl carbonate, or a mixed solvent thereof, can be used.

[0016]

In the battery of the present invention, since the AlF ₃ coating is formed on the surface of the aluminum molded body, the aluminum does not react with lithium trifluoromethanesulfonate and the like even after repeated charging and discharging, so that aluminum dissolution occurs. Absent.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be carried out by appropriately changing the scope of the present invention. Is possible.

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

[Positive electrode] LiCoO ₂ as positive electrode active material
And acetylene black as a conductive agent and a fluororesin dispersion as a binder in a weight ratio of 90:
The mixture was mixed at 6: 4 to obtain a positive electrode mixture. Next, this positive electrode mixture was applied to an aluminum foil as a positive electrode current collector having an AlF ₃ film having a thickness of 50 ° formed on the surface, and then applied to an aluminum foil.
A positive electrode was prepared by performing a vacuum heat treatment at 2 ° C. for 2 hours.

[Negative Electrode] A 400 mesh pass graphite powder was mixed with a fluororesin dispersion as a binder at a weight ratio of 95: 5 to obtain a negative electrode mixture. Next, after applying this negative electrode mixture to a copper foil as a current collector, 250
Vacuum heat treatment was performed at 2 ° C. for 2 hours to produce a negative electrode.

[Electrolyte] A nonaqueous electrolyte was prepared by dissolving LiN (CF ₃ SO ₂ ) ₂ as an electrolyte solute at a rate of 1 mol / l in an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate. .

[Preparation of Battery] AA type batteries of the present invention were prepared using the positive and negative electrodes and the non-aqueous electrolyte described above. In addition,
As a separator, a microporous film made of polypropylene (manufactured by Polyplastics, trade name "Celgard 3401")
Was used.

FIG. 1 is a cross-sectional view schematically showing a battery BA1 of the present invention produced. The battery BA1 shown has 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. , 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.

Example 2 LiN was used as the electrolyte solute.
(CF ₃ SO _{2) 2} in place of LiC (CF ₃ SO _{2) 3}
A battery BA2 of the present invention was made in the same manner as in Example 1 except that was used.

Example 3 LiN was used as an electrolyte solute.
The battery BA of the present invention was prepared in the same manner as in Example 1 except that LiCF ₃ SO ₃ was used instead of (CF ₃ SO ₂ ) _2.
3 was produced.

Comparative Example 1 A comparative battery BC1 was produced in the same manner as in Example 1 except that an aluminum foil having no AlF ₃ coating was used as a positive electrode current collector.

Comparative Example 2 A comparative battery BC2 was produced in the same manner as in Example 2 except that an aluminum foil on which no AlF ₃ coating was formed was used as the positive electrode current collector.

Comparative Example 3 A comparative battery BC3 was produced in the same manner as in Example 3, except that an aluminum foil having no AlF ₃ coating was used as a positive electrode current collector.

Comparative Example 4 Comparative Example 4 was repeated in the same manner as in Example 1 except that an aluminum foil without an AlF ₃ coating was used as a positive electrode current collector and LiPF ₆ was used as an electrolyte solute. Battery BC4 was produced.

[Discharge Characteristics of Each Battery] After the battery was charged at 200 mA to a charge end voltage of 4.1 V, the battery was discharged at 200 mA to a discharge end voltage of 2.75 V, and the discharge characteristics of each battery were examined. The results are shown in FIG.

FIG. 2 is a graph showing the discharge characteristics of each battery, with the vertical axis representing battery voltage (V) and the horizontal axis representing discharge capacity (mAh).

As can be seen from the figure, the comparative batteries BC1, BC2 and BC3 using lithium trifluoromethanesulfonate or the like as the electrolyte solute and using an aluminum foil whose surface is not passivated as the positive electrode current collector were charged. The battery voltage suddenly drops to 2.75 V after the start of discharge due to the fact that aluminum dissolution sometimes occurs and charging is hardly possible, whereas aluminum whose surface has been passivated by forming an AlF ₃ coating. Inventive battery BA using foil
It can be seen that 1, BA2 and BA3 do not dissolve aluminum and thus are sufficiently charged and have excellent discharge characteristics which are not different from those of the comparative battery BC4 using LiPF ₆ as an electrolyte solute.

[Cycle Characteristics] With respect to the battery BA1 of the present invention and the comparative battery BC4, the end-of-charge voltage at 200 mA.
After charging to 1 V, the discharge end voltage was 2.7 mA at 200 mA.
A cycle test was performed in which the process of discharging to 5 V was one cycle, and the cycle characteristics of both batteries were examined. The results are shown in FIG.

FIG. 3 is a graph showing the cycle characteristics of each battery, the discharge capacity (mAh) on the vertical axis, and the number of cycles (times) on the horizontal axis.

From the figure, it can be seen that the battery BA1 of the present invention has a more gradual decrease in the discharge capacity with the passage of the cycle than the comparative battery BC4, and has excellent cycle characteristics. Thus, the cycle characteristics of the comparative battery BC2 are slightly inferior because LiPF ₆ causes a side reaction with the graphite of the negative electrode.

(Examples 4 to 9) As a positive electrode current collector, Al
The thickness of the F ₃ coating is 1Å, 5Å, 10Å, 100Å, 50
Batteries BA4 to BA9 of the present invention were produced in the same manner as in Example 1 except that six types of aluminum foils different from 0 ° and 1000 ° were used.

[Discharge capacity of each battery] After charging at 200 mA to a charge end voltage of 4.1 V, the battery was discharged at 1000 mA to a discharge end voltage of 2.75 V, and the discharge capacity of each battery was examined. FIG. 4 shows the results.

FIG. 4 is a graph showing the discharge capacity of each battery, the vertical axis shows the discharge capacity (mAh), and the horizontal axis shows the thickness (Å) of the AlF ₃ coating.

As shown in the figure, the preferable range of the thickness of the AlF ₃ coating in the present invention is 10 to 500 as described above.
It turns out that it is Å.

In the above embodiments, the present invention has been described by taking as an example a case where the present invention is applied to a non-aqueous electrolyte secondary battery using graphite for the negative electrode and LiCoO ₂ for the positive electrode active material. If it is a non-aqueous electrolyte secondary battery in which the positive electrode potential becomes higher than the decomposition potential of aluminum (about 3.5 V) during charging,
Similar results are obtained for batteries using other materials.

[0041]

According to the battery of the present invention, AlF ₃
Since the aluminum molded body in which the film is formed and passivated is used as the positive electrode current collector, the aluminum is not dissolved even after repeated charging and discharging, and the present invention is excellent in that it has excellent cycle characteristics. Has a unique effect.

[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 discharge characteristics of each battery prepared in Examples 1 to 3 and Comparative Examples 1 to 4.

FIG. 3 is a graph showing the cycle characteristics of the batteries manufactured in Example 1 and Comparative Example 4.

FIG. 4 is a graph showing the relationship between the thickness of the AlF ₃ coating and the 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, the 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-2-86074 (JP, A) JP-A-2-265167 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10 / 40 H01M 4/66 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A method according to claim 1, wherein LiCF ₃ SO ₃ , LiN (CF ₃ S
A non-aqueous electrolyte secondary battery using O ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ as an electrolyte solute, wherein an aluminum molded body having an AlF ₃ coating formed on the surface is used as a positive electrode current collector Non-aqueous electrolyte secondary battery characterized in that: 2. The AlF ₃ coating has a thickness of 10 to 500 °.
The non-aqueous electrolyte secondary battery according to claim 1, wherein