JP3448494B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having excellent cycle characteristics and storage characteristics. 2. Description of the Related Art In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable electronic devices and portable information terminals, small, lightweight and high-energy batteries have been required. There is a strong demand for the development of a secondary battery that can realize repeated charge and discharge for a longer period at a higher density. Above all,
Non-aqueous electrolyte secondary batteries such as lithium secondary batteries are the most promising secondary batteries that meet these requirements, compared to lead batteries and nickel cadmium batteries that use aqueous electrolytes. Have been. [0003] The electrolyte of a non-aqueous electrolyte secondary battery generally includes a mixed solvent of a high dielectric constant solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate or diethyl carbonate, such as LiPF ₆ or LiBF ₄ . What dissolved the electrolyte salt is used. Such an electrolytic solution is required to have high electric conductivity and excellent safety, and to be electrically and chemically stable. [0004] An electrolyte for a lithium battery needs to be stable to a lithium negative electrode, but it is said that there is no thermodynamically stable solvent for lithium. However, in practice, the electrolyte solution decomposes on the negative electrode during the initial charge, and the reaction product is deposited on the lithium surface as an ion-conductive protective film, a so-called SEI (Solid Elec).
It is considered that a reaction between the electrode and the electrolytic solution is suppressed to form a stable interface, thereby stabilizing the reaction. [0005] However, when the ionic conductivity of the SEI is not sufficient or when the SEI is not formed sufficiently, the internal resistance of the battery becomes high and the electrolytic process is required each time during the charging process. The liquid reacts with the electrode to repeat the formation of SEI, resulting in cycle deterioration. Therefore, forming a stable SEI is indispensable for maintaining good battery performance. Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to promote the formation of a good SEI, to have a high capacity retention rate, and to provide a non-volatile semiconductor device having excellent cycle characteristics and storage characteristics. An object of the present invention is to provide a water electrolyte secondary battery. [0007] That is, a nonaqueous electrolyte secondary battery according to the present invention comprises a positive electrode comprising a substance capable of occluding and releasing lithium ions, a carbon material, metallic lithium or a lithium alloy. And a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains 5-90 ppm of triethyl phosphate (OP (OCH ₃ ) ₃ ). As the positive electrode active material of the non-aqueous electrolyte secondary battery in the present invention, that is, a material mainly storing and releasing Li _x MO ₂ (where M is one or more transition metals). A single transition metal or a mixture of two or more transition metals can be used. In particular, it is desirable to use a transition metal selected from Co, Ni, and Mn as the transition metal M in view of the discharge voltage. Particularly, among them, those mainly composed of Co are more preferable. [0009] Host materials that occlude and release lithium ions, which are components of the negative electrode, include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, and metallic lithium. , Lithium alloy, polyacene, etc. can be used alone or as a mixture of two or more, but it is particularly preferable to use a carbonaceous material from the viewpoint of high safety. The solvent of the non-aqueous electrolyte includes ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, γ-valero Lactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran,
2-methyltetrahydrofuran, 3-methyl-1,3-
Dioxolan, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate,
Diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate,
Ethyl isopropyl carbonate, dibutyl carbonate and the like can be used alone or in combination of two or more. As the electrolyte salt as a solute of the non-aqueous electrolyte, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiB
F ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , L
iCF ₃ CF ₂ CF ₂ SO ₃ , LiN (CF ₃ SO ₂ )
₂ , LiN (C ₂ F ₅ SO ₂ ) _{2 and the} like can be used. It is preferable to use LiPF ₆ as the electrolyte salt. A solid ion-conductive polymer electrolyte can be used instead of or in addition to the above electrolyte salt. Of course, a plurality of types may be used. In this case, as a configuration of the non-aqueous electrolyte secondary battery, a combination of a positive electrode, a negative electrode, and a separator with an organic or inorganic solid electrolyte and a non-aqueous electrolyte (a solvent or a solvent and an electrolyte salt), or as a positive electrode, a negative electrode, and a separator And non-aqueous electrolytes (solvents or solvents and electrolyte salts). When the polymer electrolyte membrane is made of polyethylene oxide, polyacrylonitrile, polyethylene glycol, or a modified product thereof, it is lightweight and flexible, which is advantageous when used for a wound electrode plate. further,
In addition to the polymer electrolyte, an inorganic solid electrolyte or a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte can be used as the electrolyte. Further, the non-aqueous electrolyte secondary battery of the present invention comprises a combination of a positive electrode, a negative electrode and a separator with a non-aqueous electrolyte, a positive electrode, a negative electrode and a separator with an organic or inorganic solid electrolyte and a non-aqueous electrolyte. And a combination of a positive electrode, a negative electrode, and an organic or inorganic solid electrolyte with a non-aqueous electrolyte. The organic or inorganic solid electrolyte, when with ion conductivity, the electrolyte salt such as LiPF ₆ is also sufficient without using. Needless to say, the shape of the battery can be various shapes such as a cylinder, a square, a coin, a button, and a laminate. Hereinafter, an embodiment of the present invention will be described.
Details will be described with reference to the drawings. FIG. 1 is a schematic sectional view of a prismatic nonaqueous electrolyte secondary battery used in the present invention. The prismatic nonaqueous electrolyte secondary battery 1 has a positive electrode 3 formed by applying a positive electrode mixture containing a substance capable of absorbing and releasing lithium ions to an aluminum current collector, and a lithium current collector that stores lithium ions in a copper current collector. A battery case comprising: a flat electrode group 2 in which a negative electrode 4 formed by applying a negative electrode mixture containing a substance to be released is wound via a separator 5; and a non-aqueous electrolyte containing an electrolyte salt. 6
It is to be stored in. A battery cover provided with a safety valve 8 is attached to the battery case 6 by laser welding, a positive electrode terminal 9 is connected to the positive electrode 3 via a positive electrode lead 10, and the negative electrode 4 contacts the inner wall of the battery case 6. It is electrically connected. The positive electrode mixture is obtained by mixing 90 parts by weight of LiCoO _{2 as} an active material, 5 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder, and mixing N-methyl-2-pyrrolidone. Was added and dispersed to prepare a slurry. The slurry was uniformly applied to an aluminum current collector having a thickness of 20 μm, dried, and then compression-molded by a roll press to produce a positive electrode 3. The negative electrode mixture was prepared by mixing 90 parts by weight of a carbon material capable of inserting and extracting lithium ions and 10 parts by weight of polyvinylidene fluoride, adding N-methyl-2-pyrrolidone as needed, and dispersing the mixture to prepare a slurry. . The slurry was uniformly applied to a 10 μm-thick copper current collector, dried, and then compression-molded by a roll press to produce a negative electrode 4. For the separator 5, a microporous polyethylene film having a thickness of 25 μm was used. The solvent of the electrolytic solution is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 1.
1.0 mol / l of iPF ₆ was dissolved. Then, a predetermined amount of triethyl phosphate was added as shown in Table 1 to prepare an electrolytic solution. According to the above configuration and procedure, the design capacity 600
The battery of the present invention (Examples 1, 2, and 3) having mAh and comparative batteries (Comparative Examples 1, 2, 3, and 4) were produced. The difference between these batteries is that the amount of triethyl phosphate added is different. [Test] In the life test, the above-mentioned battery was charged at a current of 1 C at a constant current and a constant voltage of 3.5 V at 45 ° C. for 3 hours, and then discharged at a constant current of 1 C. 3
The ratio of the discharge capacity after 00 cycles was determined. In the storage test, the battery was charged at a constant current and a constant voltage of 1 C at a current of 4.1 V to 4.1 V for 3 hours, and stored at 45 ° C. for one month in the charged state. After storage, the discharge capacity relative to the initial capacity after discharging the battery was determined. The results of the life test and the storage test are shown in Table 1 (Examples and Comparative Examples). [Table 1] As shown in Examples 1 to 3 in Table 1, batteries using a non-aqueous electrolyte containing 5 to 90 ppm of triethyl phosphate were compared with Comparative Example 1 using a non-aqueous electrolyte containing none of these. It was clear that the capacity retention was higher and the cycle characteristics and storage characteristics were improved. Further, in Comparative Example 2 where the content is small, the effect of adding triethyl phosphate is not sufficiently obtained, so that the capacity retention is about the same as Comparative Example 1. Also,
In Comparative Examples 3 and 4 in which the content of triethyl phosphate is high, it is presumed that the discharge characteristics were deteriorated due to an increase in internal resistance and the like, and the capacity retention was lowered. According to the non-aqueous electrolyte secondary battery of the present invention,
When a specific amount of triethyl phosphate is contained in the electrolytic solution, a protective film having a high density and capable of suppressing a reaction between the negative electrode and the electrolytic solution and capable of maintaining sufficient ion conductivity is formed in a negative electrode shape. Therefore, a non-aqueous electrolyte secondary battery having excellent cycle characteristics and storage characteristics can be provided. Therefore, the industrial value is large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a prismatic battery according to one embodiment of the present invention. [Description of Signs] 1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Positive electrode 4 Negative electrode 5 Separator 6 Battery case 7 Cover 8 Safety valve 9 Positive electrode terminal 10 Positive electrode lead

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-223516 (JP, A) JP-A-61-284070 (JP, A) JP-A-1-1022862 (JP, A) JP-A-4- 184870 (JP, A) JP-A-8-88023 (JP, A) JP-A-10-189038 (JP, A) JP-A-10-255839 (JP, A) JP-A-2000-91161 (JP, A) JP-A-11-250919 (JP, A) JP-A-10-144344 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40

Claims (1)

(57) [Claim 1] A positive electrode composed of a substance that absorbs and releases lithium ions, a negative electrode composed of a carbon material, metallic lithium or a lithium alloy, and a non-aqueous electrolyte Wherein the non-aqueous electrolyte contains 5-90% triethyl phosphate.
A non-aqueous electrolyte secondary battery characterized by containing ppm .