KR20050062211A - Non-aqueous electrolyte for lithium battery - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte solution for lithium batteries, and more particularly, to a lithium battery prepared by adding 0.1 to 10 parts by weight of a compound represented by the following Formula 1 to 100 parts by weight of an organic solvent in which lithium salt is dissolved in 0.8 to 2.0 M. The present invention relates to a nonaqueous electrolyte solution, and when the nonaqueous electrolyte solution for a lithium battery of the present invention is used, a lithium battery having excellent charge and discharge cycle characteristics can be produced without reducing the thickness expansion at a high temperature without affecting the original characteristics of the battery.

[Formula 1]

Wherein R ₁ and R ₂ are simultaneously ClCOO—, CH ₃ COO— or CH ₂ CCH ₃ COO—.

Description

Non-aqueous electrolyte for Lithium battery

The present invention relates to a non-aqueous electrolyte for lithium ion batteries, and more particularly to bisphenol A bis (chloroformate) and bisphenol 100 parts by weight of an organic solvent in which lithium salt is dissolved in 0.8 to 2.0 M. The present invention relates to a nonaqueous electrolyte solution for lithium batteries prepared by adding 0.1 to 10 parts by weight of A diacetate or bisphenol A dimethacrylate.

As the rapid miniaturization and diversification of portable information terminals such as mobile phones and portable electronic devices are rapidly progressing, not only the miniaturization and weight reduction are required for the battery, but also a high energy density for a long time. It is desired to be capable of discharge and to have excellent high rate characteristics. Since lithium ion batteries have an average discharge voltage of about 3.6 to 3.7 V, they have higher power than other alkaline batteries or Ni-MH or Ni-Cd batteries, and thus are promising as secondary batteries that meet the above requirements. It has been going on. However, in order to achieve such a high driving voltage, electrochemically stable in the charge and discharge voltage range of 0 to 4.2V, and stable electrolyte composition is necessary even in the temperature range of -20 ° C to 60 ° C. Due to these characteristics, EC (ethylene carbonate) , A mixture consisting of a combination of carbonates such as DMC (dimethyl carbonate) or DEC (diethyl carbonate) is used. However, the electrolyte of the composition of the electrolyte may act as a very unfavorable cause in high rate charge and discharge because the ion conductivity is significantly lower than the aqueous electrolyte used in Ni-MH or Ni-Cd batteries.

The basic principle of a lithium battery is to move lithium ions from a lithium metal compound used as an anode during initial charging to a graphite (crystalline or amorphous) electrode used as a cathode, and to insert current between layers of the graphite electrode. At this time, since lithium has a high reactivity, the electrolyte and the carbon constituting the cathode react on the surface of the graphite anode to generate compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of ion conductive protective film, or SEI (Solid Electrolyte Interface), on the surface of the graphite cathode. Once formed, the SEI film acts as an ion tunnel and passes only lithium ions. Suppresses the reaction of The SEI film solvates lithium ions by the effect of such an ion tunnel, and together with lithium ions in an electrolyte, a large molecular weight organic solvent molecule such as ethylene carbonate (EC), dimethyl carbonate (DMC) or diethyl carbonate (DEC), etc. The graphite cathode is inserted together to prevent the structure of the graphite cathode from being collapsed. The amount of charge once consumed to form the SEI film has a property of not reversibly reacting upon discharging at an irreversible capacity. Therefore, no further decomposition of the electrolyte occurs and the amount of lithium ions around the electrolyte is reversibly maintained to maintain stable charge and discharge.

In the thin rectangular battery, (J. Power Sources, 72 (1998) 66-70), such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ , generated by decomposition of carbonate-based organic solvents in the SEI formation reaction When the battery is expanded, the SEI film is subjected to increased electrochemical and thermal energy over time when the battery is expanded and stored at a high temperature (for example, 4 days at 85 ° C after 4.2V 100% charge). It slowly decays, causing continuous side reactions that react with the exposed new cathode surface. However, the increase in the pressure varies depending on the characteristics of the solvent or additives included in the electrolyte, and as a result, it is known as one of the main factors that determine the performance change of the battery, in particular, the charge-discharge cycle characteristics. Therefore, experiments have been conducted to change the SEI formation reaction by adding an additive to the electrolyte in order to suppress such an increase in internal pressure. As an example, Japanese Patent Application Laid-Open No. 95-176323A discloses a technique for adding CO ₂ to an electrolyte solution, and Japanese Patent Application Laid-Open Publication No. 95-320779A discloses a technique for suppressing decomposition of an electrolyte solution by adding a sulfide-based compound to the electrolyte solution.

The present invention is to solve the problems of the prior art as described above by adding an additive to the conventional non-aqueous electrolyte, as well as the initial full charge, as well as a low thickness expansion during high temperature standing after full charge and excellent charge-discharge cycle characteristics It is to provide.

That is, one aspect of the present invention is to provide a non-aqueous electrolyte solution for a lithium battery prepared by adding 0.1 to 10 parts by weight of the compound represented by Formula 1 to 100 parts by weight of an organic solvent in which lithium salt is dissolved in 0.8 to 2.0M.

[Formula 1]

Wherein R ₁ and R ₂ are simultaneously ClCOO—, CH ₃ COO— or CH ₂ CCH ₃ COO—.

Hereinafter, the present invention will be described in more detail.

The nonaqueous electrolyte of the present invention is composed of an organic solvent, a lithium salt and an additive.

The organic solvent may be used by mixing a cyclic carbonate organic solvent and a linear carbonate organic solvent. Specific examples of the cyclic carbonate organic solvent used in the present invention include ethylene carbonate, propylene carbonate or a mixture thereof. In addition, the linear carbonate organic solvent is exemplified by dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or a mixture thereof. More preferably, a mixture of ethylene carbonate and dimethyl carbonate or a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is used. As the mixed organic solvent, one or two or more compounds selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate and fluorobenzene may be further mixed and used as necessary. . The mixing ratio of the organic solvent selected from each group is not particularly limited as long as the object of the present invention is not impaired.

The lithium salt may be selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, and LiN (CF ₃ SO ₂ ) ₂ . Use more than one species. The lithium salt is added at a concentration of 0.8 ~ 2.0M. If the salt concentration is less than 0.8M, the conductivity of the electrolyte is lowered and the performance of the electrolyte is lowered. If the salt concentration is higher than 2.0M, the mobility of lithium ions due to the increase in viscosity at low temperature may decrease, resulting in a problem of low temperature performance. to be.

In the nonaqueous electrolyte, bisphenol A bis (chloroformate), bisphenol A diacetate, or bisphenol A dimethacrylate represented by Chemical Formula 1 is lithium. It is prepared by adding 0.1 to 10 parts by weight, more preferably 1 to 5 parts by weight based on 100 parts by weight of the basic nonaqueous electrolyte solution including a salt. If the amount of the additive is less than 0.1 parts by weight, there is a problem that does not suppress the swelling action, if more than 10 parts by weight disadvantageous battery life occurs.

Wherein R ₁ and R ₂ are simultaneously ClCOO—, CH ₃ COO— or CH ₂ CCH ₃ COO—.

When the additive of the present invention uses, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, or the like as the positive electrode active material at the time of supercharging, the solvent in the nonaqueous electrolyte is locally oxidatively decomposed at the time of charging, and this decomposed product is used to charge the battery. It is intended to prevent chemical reactions from ultimately degrading the performance of the cell. In other words, the additive inhibits the oxidative decomposition of the electrolyte by oxidatively decomposing the positive electrode active material, thereby contributing to the formation of a passivation film on the surface of the positive electrode active material material, thereby impairing the normal reaction of the battery.

The lithium battery can be manufactured according to a conventional method using the nonaqueous electrolyte solution for lithium batteries of the present invention, and the mixing ratio of the organic solvent selected from each group is not particularly limited as long as the object of the present invention is not impaired. The mixing ratio at the time of preparation of the nonaqueous electrolyte solution for ion batteries is followed.

Hereinafter, the present invention will be described in more detail with reference to the following examples, which are intended to explain the present invention in detail and are not intended to limit the present invention.

Example 1

In the embodiment of the present invention, the basic nonaqueous electrolyte solution was an electrolyte solution in which 1.0 M of LiPF ₆ was dissolved as a solute in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 1: 1. Bisphenol A bis (chloroformate) was added 1.0 parts by weight based on parts by weight to prepare a rectangular 423048 cell. The battery negative electrode was constructed using graphite as an active material and polyvinylidene fluoride (hereinafter referred to as “PVDF”) as a binder. The positive electrode was composed of LiCoO ₂ as an active material, PVDF as a binder, and acetylene black as a conductive agent. The produced batteries were charged under a CC-CV condition at 4.2 V charging voltage with a current of 0.2 C, and then discharged to 2.75 V with a current of 0.2 C for 1 hour after being left for 1 hour. After repeating this process three times, it was charged with 4.2V charging voltage for 3 hours at a current of 0.5C. After the initial assembly at this time, the thickness change after the charge versus the thickness of the battery was compared in Table 1. In addition, it is shown in Figure 1 the thickness change when fully charged and left for 4 days at 84 ℃.

Example 2

A battery was manufactured in the same manner as in Example 1, except that 1.0 part by weight of bisphenol A diacetate was added to the basic electrolyte solution.

Example 3

A battery was manufactured in the same manner as in Example 1, except that 1.0 part by weight of bisphenol A dimethacrylate was added to the basic electrolyte solution.

Comparative example

The same procedure as in Example 1 was conducted except that only the basic electrolyte solution was used.

Compared with the comparative example without addition of the additive, Examples 1 to 3 in which bisphenol A bis chloroformate, bisphenol A diacetate or bisphenol A dimethacrylate were added showed that the initial thickness expansion decreased by about 3 to 8%. Can be.

In addition, after 4.2V 100% full charge, when left at 85 ℃, 4 days, when the thickness increase rate compared to the initial, as shown in Figure 1, the thickness increase rate of Examples 1 to 3 using the additive is about 5 to 20% It can be seen that the thickness increase rate is smaller in the high temperature leaving characteristic than in the comparative example.

As a result of using the non-aqueous electrolyte solution for batteries of the present invention, the thickness expansion during initial full charge of the battery is reduced and the thickness change during high temperature standing is not only improved to improve the reliability of SET installability, but also shows good capacity retention characteristics in life characteristics. Can be.

1 shows the thickness expansion characteristics at high temperatures of the batteries prepared in Comparative Examples and Examples 1 to 3.

Claims (5)

A non-aqueous electrolyte solution for lithium batteries prepared by adding 0.1 to 10 parts by weight of a compound represented by Formula 1 to 100 parts by weight of an organic solvent in which lithium salt is dissolved in 0.8 to 2.0 M: [Formula 1] Wherein R ₁ and R ₂ are simultaneously ClCOO—, CH ₃ COO— or CH ₂ CCH ₃ COO—. The non-aqueous electrolyte solution for lithium batteries according to claim 1, wherein the organic solvent is a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. According to claim 2, wherein the cyclic carbonate organic solvent is ethylene carbonate, propylene carbonate or a mixture thereof, the linear carbonate organic solvent is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or It is a mixture of these, The nonaqueous electrolyte solution for lithium batteries. The nonaqueous electrolyte solution for lithium batteries according to claim 1, wherein the organic solvent further comprises at least one member selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate. . The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, and LiN (CF ₃ SO ₂ ) ₂ . Non-aqueous electrolyte solution for lithium batteries, characterized in that at least one selected from the group consisting of.