JPH05326016A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To improve reliability and lessen the capacity decrease of a nonaqueous electrolytic secondary battery by using a mixed solute consisting of LiXFm and LiZ(CF3SO2)n in a prescribed range of the mixing ratio as an electrolytic solution. CONSTITUTION:Regarding a nonaqueous electrolytic secondary battery having a positive electrode corrector made of aluminum or an aluminum alloy, as a solution for the nonaqueous electrolytic solution, a mixed solution consisting of LiXm and LiZ(CF3SO2)n in a mole ratio (1:9)-(9:1) is used wherein X stands for As, Sb, B, Bi, A, Ga or In: in the case X is P, As, or Sb, m is 6: in the case X is B, Bi, A, Ga, or In, m is 4: Z stands for o, N, or C: in the case Z is O, n is 1: in the case Z is N, n is 2: and in the case Z is C, n is 3.

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 improvement of a non-aqueous electrolyte solution for the purpose of improving reliability (safety).

[0002]

2. Description of the Related Art In recent years,
A non-aqueous electrolyte secondary battery using aluminum or an aluminum alloy as a positive electrode current collector and a solution in which LiPF ₆ (lithium hexafluorophosphate) as an electrolyte solute is dissolved in a non-aqueous solvent as an electrolyte is proposed. ing.

However, in this type of battery, the electrolytic solution solvent violently reacts and decomposes on the positive electrode during overcharging, and decomposed gas such as hydrogen is generated at that time, and the internal pressure of the battery rises. There was a problem of lacking. For this reason,
As an electrolyte solute that replaces LiPF ₆ , LiCF ₃ SO ₃ (lithium trifluoromethanesulfonate), which does not cause the above-mentioned problems, has been temporarily studied.

However, since LiCF ₃ SO ₃ has a low dissolution potential with respect to an electrolytic solution containing aluminum as a solute of LiCF ₃ SO ₃ , aluminum in the positive electrode current collector is charged in the electrolytic solution during charging when the positive electrode has a high potential. There was a problem in that the battery was not sufficiently charged due to the elution to the battery, and a battery having a practically usable capacity could not be obtained. Since aluminum does not dissolve in the electrolyte solution containing LiPF ₆ ,
This problem does not occur with LiPF ₆ .

Thus, LiPF ₆ and LiCF ₃ S
Since O ₃ has merits and demerits in terms of reliability and battery characteristics, improvement of the electrolytic solution has been desired.

Then, as a result of intensive studies, the present inventors have found that when LiPF ₆ and LiCF ₃ SO ₃ are used in combination, the dissolution potential of aluminum changes depending on the mixing ratio of both.

The present invention has been made on the basis of such findings, and the purpose thereof is to have high reliability,
Moreover, it is another object of the present invention to provide a non-aqueous electrolyte secondary battery in which the reduction in capacity due to the dissolution of aluminum is small.

[0008]

In the non-aqueous electrolyte secondary battery according to the present invention (hereinafter, referred to as "the battery of the present invention") for achieving the above object, the positive electrode current collector is aluminum or aluminum alloy. In a non-aqueous electrolyte secondary battery comprising LiXF _m (X is P
(Phosphorus), As (arsenic), Sb (antimony), B (boron), Bi (bismuth), Al (aluminum), G
a (gallium) or In (indium), when X is P, As or Sb, m is 6, X is B, Bi, Al,
When Ga or In, m is 4. ) And LiZ (CF ₃
SO ₂ ) _n (Z is O, N or C, and when Z is O, n
Is 1, n is 2 when Z is N, and n is 3 when Z is C. Mixed solute with a molar ratio of 1: 9 to 9: 1).

In the battery of the present invention, a mixed solute having a molar ratio of LiXF _m and LiZ (CF ₃ SO ₂ ) _n within the range of 1: 9 to 9: 1 is used as the solute of the non-aqueous electrolyte solution. .. The reason that the solute molar ratio is regulated within the above range is that the dissolution potential of aluminum is lower than the decomposition potential of the electrolytic solution and higher than the positive electrode potential during normal charging.

That is, as shown in Examples described later, when the molar ratio value of LiXF _m and LiZ (CF ₃ SO ₂ ) _n is less than 1/9, LiZ (CF ₃ SO ₂ ) _n
Since it is too large, charging becomes insufficient and a battery having a practically usable discharge capacity cannot be obtained. Further, when the molar ratio exceeds 9/1, LiXF _m is too much and gas is generated during overcharge (during abnormal charge) to increase the internal pressure of the battery, which may cause damage or rupture of the battery. There is.

In order to improve the reliability of the battery of the present invention without lowering the battery capacity of the conventional non-aqueous electrolyte secondary battery, which used LiPF ₆ alone as the electrolyte solute, as described above, As the electrolyte solute, a mixed solute in which LiPF ₆ or a solute of the same type (LiXF _m ) and LiCF ₃ SO ₃ or a solute of the same type (LiZ (CF ₃ SO ₂ ) _n ) were mixed at a specific ratio was used. It is characterized by points. Therefore, it is possible to use various materials without limitation for other members constituting the battery such as the positive electrode active material, the electrolytic solution solvent, and the separator.

For example, as the positive electrode active material, any material can be used without particular limitation as long as it is a material capable of inserting and extracting lithium. Examples of the substance capable of inserting and extracting lithium include oxides having tunnel-shaped holes such as Li ₂ FeO ₃ , TiO ₂ and V ₂ O ₅ , and metal chalcogenides having a layered structure such as TiS ₂ and MoS _2. The composition formula Li _x MO ₂ or Li _y M ₂ O ₄ (however,
M is preferably a transition element, and a complex oxide represented by 0 ≦ x ≦ 1 and 0 ≦ y ≦ 2). The complex oxides represented by these composition formulas include LiCoO ₂ , LiMnO ₂ , and LiNi.
O ₂ , LiCrO ₂ , and LiMn ₂ O ₄ are exemplified. The above positive electrode active materials are acetylene black,
Conductive agents such as carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVd)
It is used as a positive electrode mixture by kneading with a binder such as F).

Further, as the negative electrode material, a substance capable of inserting and extracting lithium such as lithium metal, lithium alloy, and carbon material is used. Powdered substances such as carbon materials,
It is used as a negative electrode mixture by kneading with a binder and, if necessary, a conductive agent.

Further, as the solvent for preparing the electrolytic solution, ethylene carbonate, dimethyl carbonate, a mixed solvent thereof or the like, as well as various solvents conventionally used or proposed for non-aqueous electrolytic solution secondary batteries are proposed. A non-aqueous solvent can be used.

[0015]

In the battery of the present invention, as the electrolyte solute, the dissolution potential of aluminum is lower than the decomposition potential of the electrolyte,
In addition, LiXF _m and LiZ (CF ₃ mixed with each other in a ratio within a predetermined range so as to be higher than the positive electrode potential during normal charging.
Since a mixed solute consisting of SO ₂ ) _n is used,
At the time of overcharge, aluminum elutes and the positive electrode potential is kept lower than the decomposition potential, which suppresses the generation of gas, while at the time of normal charging, aluminum hardly elutes into the electrolytic solution, which is good. Charging is done.

[0016]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications can be made without departing from the scope of the invention. Is possible.

(1) Relation between molar ratio of solute and dissolution potential of aluminum In an equal volume mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC), LiPF ₆ (lithium hexafluorophosphate) and / or LiCF. ₃ SO ₃
(Lithium trifluoromethanesulfonate) was dissolved at a predetermined ratio to prepare 12 kinds of electrolytic solutions A to L shown in Table 1.

[0018]

[Table 1]

Then, an aluminum electrode (+ electrode) and a lithium electrode (-electrode: reference electrode) are immersed in each of the above-mentioned electrolytic solutions (immersion potential is about 2.5 V), and continuously at a rate of 100 mV / min. Then, the potential of the aluminum electrode with respect to the lithium electrode was increased, and the relationship between the potential of the aluminum electrode and the dissolution current (current flowing due to the dissolution of aluminum) was investigated.

FIG. 1 shows the relationship between the dissolution current and the potential of the aluminum electrode for the three types of electrolytes A, H and L.
6 is a graph in which the vertical axis represents the dissolution current density (μA / cm ² ) and the horizontal axis represents the potential of the aluminum electrode (V vs. Li ^/ Li ⁺ ).

Further, FIG. 2 shows the above twelve kinds of electrolytic solutions A to L.
It is a graph for all, melting current density is 10μA
/ Cm ² shows the relationship between the potential of the aluminum electrode and the molar ratio of the solute, the vertical axis shows the potential of the aluminum electrode (V vs. Li ^/ Li ⁺ ) and the horizontal axis shows the molar ratio of the solute. It is a thing.

From FIG. 1, in the case of the electrolytic solution using only one kind of LiCF ₃ SO ₃ , a large melting current flows when the voltage exceeds about 4 V, whereas LiPF ₆ and LiCF ₃ SO ₃ flow.
It can be seen that in the case of the electrolytic solution using the mixed solute with ₃ , only a small amount of dissolution current flows up to around 5V. From this, in the electrolytic solution using only one kind of LiCF ₃ SO ₃ , the charge potential of the positive electrode in a normal state (usually 4.2 to 4.3 V
It is a degree. ), The elution of aluminum occurs violently, whereas it is understood that the electrolytic solution using the mixed solute hardly elutes aluminum at the charging potential under normal conditions, and good charging can be performed. .. Further, from the figure, it is understood that when only one kind of LiPF ₆ is used, only a small current flows and the elution of aluminum does not occur during overcharge as well as during normal operation. The minute current is a current that flows when a passive film is formed on the surface of aluminum.

Further, from FIG. 2, LiPF ₆ and LiCF ₃
It is understood that when the value of the molar ratio with SO ₃ is 1/9 or more, the elution of aluminum during normal charging is significantly suppressed.

(2) Relationship between solute molar ratio and discharge capacity of battery (2-1) 13 kinds of non-aqueous electrolyte batteries using electrolytic solutions having different molar ratios of LiPF ₆ and LiCF ₃ SO ₃ Was prepared and the discharge capacity of each battery was examined.

[Production of Positive Electrode] LiC as Positive Electrode Active Material
In oo ₂ , acetylene black as a conductive agent and a fluororesin dispersion as a binder were added in a weight ratio of 9
After kneading at a ratio of 0: 5: 5 to form a positive electrode mixture, this was applied to both surfaces of an aluminum foil as a positive electrode current collector and dried to prepare a positive electrode.

[Preparation of Negative Electrode] PV as a binder on graphite
dF was mixed in a weight ratio of 95: 5, dispersed in a solvent (N-methylpyrrolidone) to form a slurry, and then applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, It was dried to prepare a negative electrode.

[Preparation of Electrolytic Solution] LiPF ₆ and / or LiCF ₃ SO ₃ as an electrolytic solution solute was dissolved in an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate at a predetermined ratio shown in Table 2 to obtain 13 kinds. The electrolytic solution of was prepared.

[0028]

[Table 2]

[Production of Non-Aqueous Electrolyte Secondary Battery] Thirteen types of cylindrical non-aqueous electrolyte secondary batteries BA1 to BA9 (invention batteries) and BC1 using the positive and negative electrodes and the electrolyte described above.
BC4 (comparative battery) was produced (battery size: diameter 14.
2 mm; length 50.0 mm). As the separator, an ion-permeable polypropylene microporous thin film was used.

FIG. 3 is a schematic cross-sectional view of the produced battery. The battery BA shown in FIG. 3 includes a positive electrode 1 and a negative electrode 2, a separator 3 separating these electrodes, a positive electrode lead 4, a negative electrode lead 5, and a positive electrode outside. The terminal 6, the negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are housed in the negative electrode can 7 in a state of being spirally wound via the separator 3 into which the nonaqueous electrolytic solution is injected, and the positive electrode 1 is connected to the positive electrode external terminal via the positive electrode lead 4. 6, and the negative electrode 2 is connected to the negative electrode can 7 via the negative electrode lead 5 so that the chemical energy generated inside the battery BA can be taken out as electric energy to the outside.

For each of the above batteries, 4.1 at 200 mA
The discharge capacity was measured when the battery was charged to V and then discharged to 200 V at 2.75 V. The result is shown in Figure 4.
Is plotted with ●.

In FIG. 4, the vertical axis on the right side shows the discharge capacity (mAh).
Is a graph in which the abscissa represents the molar ratio of the solute in each battery, and from the graph, LiPF ₆ : LiCF ₃
Comparative battery BC1 having a molar ratio of SO ₃ smaller than 1/9
It can be seen that the discharge capacities of BC and BC2 are extremely smaller than those of the batteries BA1 to BA9 of the present invention having the same molar ratio of 1/9 or more. It should be noted that this result perfectly matches the result described in (1) above.

(2-2) LiCoO ₂ as a positive electrode active material
In place of LiNiO ₂ , an electrolytic solution solvent in which an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate is replaced with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate (DEC), and an electrolytic solution solute of LiPF ₆ and / or Or, instead of LiCF ₃ SO ₃ , Li
Ten kinds of cylindrical batteries were produced in the same manner as in the above (2-1) except that BF ₄ and / or LiN (CF ₃ SO ₂ ) ₂ was used at the predetermined ratios shown in Table 3, and each battery was prepared. Discharge capacity was measured. The results are shown in Table 3.

[0034]

[Table 3]

(2-3) LiCoO ₂ as a positive electrode active material
In place of LiMnO ₂ , an electrolyte solution solvent in which an equal volume solvent mixture of ethylene carbonate and dimethyl carbonate is replaced by a vinylene carbonate (VC) and an equivalent volume solvent mixture in dimethyl carbonate, and an electrolyte solution solute of LiPF ₆ and / or Or LiA instead of LiCF ₃ SO ₃
Ten kinds of cylindrical batteries were produced in the same manner as in the above (2-1) except that sF ₆ and / or LiC (CF ₃ SO ₂ ) ₃ was used at a predetermined ratio shown in Table 4. Discharge capacity was measured. The results are shown in Table 4.

[0036]

[Table 4]

(2-4) Lithium metal is used as the negative electrode material in place of graphite, and LiPF ₆ and / or electrolyte solute is used.
Or LiCF ₃ the place of the SO ₃ LiSbF ₆ and / or LiCF ₃ SO ₃ except for using a predetermined ratio shown in Table 5, prepared 10 kinds of cylindrical batteries in the same manner as in the above (2-1) Then, the discharge capacity of each battery was measured. The results are shown in Table 5.

[0038]

[Table 5]

From Table 3 to Table 5, LiXF _m : LiZ (C
Comparative batteries BC5, BC6, BC9, BC10, BC13 and B having a molar ratio of F ₃ SO ₂ ) _n smaller than 1/9
It can be seen that C14 has an extremely small discharge capacity as compared with the batteries BA10 to BA27 of the present invention in which the value of the same molar ratio is 1/9 or more.

(3) Relationship between molar ratio of solute and amount of gas generated during overcharge For each battery produced in the same manner as in (2-1) to (2-4) above, the battery was charged at 5V for 1 hour (overcharge). The amount of gas generated (cc) when charged) was measured. The results for the battery manufactured in the same manner as in the above (2-1) are shown by plotting with a circle in FIG. 4 above, and for each battery manufactured in the same manner as in the above (2-2) to (2-4). The results are shown in Tables 3 to 5 above. In addition, in FIG. 4, the vertical axis on the left side of the gas generation amount is shown as a coordinate axis.

From FIG. 4 and Tables 3 to 5, LiXF _m : L
Comparative batteries BC3, BC4, BC7, BC8, BC1 in which the molar ratio of iZ (CF ₃ SO ₂ ) _n is greater than 9/1
It can be seen that 1, BC12, BC15, and BC16 have an extremely large amount of gas generation as compared with the batteries BA1 to BA27 of the present invention in which the value of the same molar ratio is 9/1 or less.

In the above embodiment, a specific example in which the present invention is applied to a cylindrical battery is explained, but the shape of the battery is not particularly limited, and the present invention has various shapes such as a flat shape and a square shape. It is applicable to a lithium secondary battery.

[0043]

In the battery of the present invention, there is no problem that a large amount of aluminum is eluted in the electrolytic solution during charging, so there is no decrease in battery capacity due to this, and the amount of gas generated during overcharging is small. Therefore, the present invention has excellent unique effects such as high reliability.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a melting current of aluminum and a potential of an aluminum electrode.

FIG. 2 is a graph showing the relationship between the aluminum electrode potential and the solute molar ratio when the dissolution current density is 10 μA / cm ² .

FIG. 3 is a cross-sectional view of a cylindrical battery manufactured in an example.

FIG. 4 is a graph showing the relationship between the molar ratio of solute and the discharge capacity and the amount of gas generated during overcharge.

[Explanation of symbols]

 BA cylindrical battery 1 positive electrode 2 negative electrode 3 separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Takahashi 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Hiroshi Watanabe 2-18-2 Keihanhondori, Moriguchi-shi, Osaka Sanyo Denki Incorporated (72) Inventor Atsue Suemori 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. In a non-aqueous electrolyte secondary battery in which the positive electrode current collector is made of aluminum or an aluminum alloy, LiXF _m (X is P, As, S) as a solute of the non-aqueous electrolyte solution.
b, B, Bi, Al, Ga or In, and X is P, A
When s or Sb, m is 6, and when X is B, Bi, Al, Ga or In, m is 4. ) And LiZ (CF ₃ S
O ₂ ) _n (Z is O, N or C, n is 1 when Z is O, n is 2 when Z is N, and n is 3 when Z is C). : A non-aqueous electrolyte secondary battery, wherein a mixed solute of 9 to 9: 1 is used.