JP2011134730A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is prevented from swelling. <P>SOLUTION: By addition of a fluorinated compound to an electrolyte, generation of gas in a battery is suppressed. Therefore, swelling of the battery is suppressed even under a high temperature circumstance. When the amount of the fluorinated compound to add is determined to 5% or less based on the weight of the electrolyte, swelling of the battery can be suppressed while inhibiting the lowering of capacity of the battery due to a side reaction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Conventionally, batteries that charge and discharge by a reversible reaction in which lithium ions released between one and the other are occluded between the positive electrode and the negative electrode have high voltage and high energy density, and are widely used as power sources for consumer electronic devices. It has been. Since this type of battery has a high reactivity between lithium and water used in the electrode, a battery that does not contain water is used as the electrolyte, and is therefore referred to as a non-aqueous electrolyte secondary battery. (Hereinafter, simply referred to as “battery”).

  However, when such a non-aqueous electrolyte secondary battery is left in a high temperature environment for a long time, swelling may occur. If such a bulge is left unattended, it may lead to damage of the battery or performance degradation, and improvement has been demanded.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a nonaqueous electrolyte secondary battery capable of preventing swelling.

  The cause of the swelling of the battery in a high temperature environment is not clear, but it is considered that the electrolyte solution decomposes at the interface between the positive electrode and the separator to generate hydrogen gas when the temperature in the battery becomes high. . The present inventor has intensively studied to develop a non-aqueous electrolyte secondary battery capable of preventing this swelling, and by adding a carbamate compound containing a fluorinated alkyl group and an alkyl group as a side chain to the electrolytic solution, It was found that swelling can be suppressed.

  In particular, when a compound having a large molecular weight is added to the electrolytic solution, the viscosity of the electrolytic solution increases, which is not preferable. Therefore, it has been found that fluorinated alkyl groups and alkyl groups having 2 or less carbon atoms are preferable. Furthermore, it has been found that a trifluoroethyl group is most preferred as the fluorinated alkyl group.

  The present invention has been made on the basis of such novel findings. In the electrolyte solution, at least one of the fluorinated compounds represented by the following chemical formulas (1), (2), and (3) is an electrolyte solution. The nonaqueous electrolyte secondary battery is characterized by adding 0.01% or more and 5% or less based on the weight.

（なお、式中ｎは１〜２の整数を意味する）

(In the formula, n means an integer of 1 to 2)

  These fluorinated compounds may be used alone or as a mixture of two or more compounds.

  The solvent used in the electrolytic solution of the present invention is not particularly limited as long as it is usually used in non-aqueous electrolyte secondary batteries. For example, ethylene carbonate (EC), diethyl carbonate (DEC) dimethyl carbonate (DMC) , Propylene carbonate, γ-butyrolactone, dimethyl sulfoxide, tetrahydrofuran, dimethoxyethane, dimethylacetamide and the like.

The electrolyte used in the electrolytic solution of the present invention is not particularly limited as long as it is usually used in a nonaqueous electrolyte secondary battery. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₃ CF ₃ ), LiC ₄ F ₉ SO ₃ , LiC ₈ F ₁₇ SO _{3 and the} like. The electrolyte solution may contain additives such as an antioxidant, a flame retardant, a radical scavenger, and a surfactant.

  The amount of the fluorinated compound added to the electrolytic solution varies depending on the type of the fluorinated compound to be used, and is not generally limited, but is preferably 0.01% or more and 5% or less with respect to the weight of the electrolytic solution.

  The shape of the nonaqueous electrolyte secondary battery to which the present invention is applied is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a coin shape.

  By adding the fluorinated compound to the electrolytic solution, gas generation in the battery can be suppressed. For this reason, the swelling of the battery can be suppressed even in a high temperature environment. Further, by setting the addition amount of the fluorinated compound to 5% or less with respect to the weight of the electrolytic solution, it is possible to suppress the swelling of the battery while suppressing the decrease in the battery capacity due to the side reaction.

[Example]
Hereinafter, the present invention will be described in more detail with reference to examples.

<Example 1>
1. Production of Lithium Ion Secondary Battery (1) Production of Negative Electrode Graphite as an active material and polyvinylidene fluoride as a binder were mixed in a weight ratio of 86:14 to prepare a negative electrode mixture paste. . This paste was uniformly applied to both surfaces of a current collector made of a copper foil having a thickness of 10 μm, dried, pressed and then cut to prepare a strip-shaped negative electrode sheet.

(2) Production of positive electrode Lithium cobalt composite oxide as an active material, polyvinylidene fluoride as a binder with respect to the lithium cobalt composite oxide, and acetylene black as a conductive agent in a weight ratio of 87: 8: 5. The mixture was mixed to prepare a positive electrode mixture paste. This paste was uniformly applied to both surfaces of a current collector made of an aluminum foil having a thickness of 20 μm, and a strip-like positive electrode sheet was produced in the same manner as the negative electrode sheet.

(3) Preparation of electrolyte solution Ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 4/6. A predetermined amount of each of the fluorinated carbamate compounds shown in Table 1 was added to the mixture to prepare a non-aqueous solvent. To these nonaqueous solvents, LiPF ₆ as a lithium salt as an electrolyte was added at a concentration of 1.0 mol / l to prepare a nonaqueous electrolytic solution.

(4) Production of square battery A positive electrode sheet, a polyethylene separator, a negative electrode sheet, and a polyethylene separator were laminated in this order to produce a power generating element, which was stored in a square battery can. The battery can was filled with the electrolyte prepared in (3) above and sealed with a battery lid via an insulator, and a square battery was assembled by a well-known method. The battery can was manufactured from an aluminum plate having a thickness of 0.2 mm, and the assembled battery had a thickness of 5 mm and a width of 30 mm) and a height of 48 mm.

2. Leaving test The battery manufactured by the above method was charged under the conditions of a current density of 1 C and a charge end voltage of 4.2 V. After charging, the battery was left at 80 ° C. for 4 days. After the standing time, the thickness of the battery was measured at 25 ° C. Further, discharge was performed under the conditions of a current density of 1 C and a discharge end voltage of 2.5 V, and the remaining discharge capacity was measured.

<Comparative example>
Using the battery produced in the same manner as in Example 1 except that no fluorinated compound was added to the electrolytic solution, a standing test was conducted in the same manner as in Example 1.

<Results and discussion>
Table 2 shows the amount of each fluorinated compound added, the thickness of the battery after the standing test, and the retention rate of the discharge capacity. The retention rate is shown as a ratio of the remaining discharge capacity to the initial capacity. Table 3 shows the thickness of the battery after the standing test and the retention rate of the discharge capacity when no fluorinated compound is added to the electrolytic solution.

  From Table 2, when the fluorinated carbamate compound was added to the electrolytic solution, the swelling of the battery was suppressed in any compound compared to the case where it was not added (Table 3). When the addition amount was 0.01% and 5%, there was no significant difference in battery thickness and discharge capacity retention. However, when the addition amount was 10%, both the swelling suppression effect and the discharge capacity retention rate were reduced. Therefore, it was considered that the addition amount is preferably 0.01% to 5%.

  As is clear from the above results, the swelling of the battery can be suppressed in a high temperature environment by adding the fluorinated compound to the electrolytic solution. Further, by making the addition amount as small as possible within the range having the effect of preventing the swelling, it is possible to suppress the swelling of the battery while suppressing the decrease in the capacity of the battery due to the side reaction.

  The technical scope of the present invention is not limited by the above-described embodiment, but extends to an equivalent range.

Claims (1)

In the electrolytic solution, at least one of the fluorinated compounds represented by the following chemical formulas (1), (2), and (3) is added in an amount of 0.01% to 5% with respect to the weight of the electrolytic solution. A non-aqueous electrolyte secondary battery characterized by the above.

(In the formula, n means an integer of 1 to 2)