KR20090082780A - Organic electrolytic solution and lithium battery employing the same - Google Patents

Abstract

An organic electrolytic solution, and a lithium battery employing the organic electrolytic solution are provided to improve initial charge/discharge efficiency. An organic electrolytic solution comprises a lithium salt; an organic solvent; and a compound represented by the formula 1, wherein R1 and R2 are independently hydrogen, an alkyl group of the carbon number 1 ~ 10 substituted or unsubstituted with a halogen atom, an alkenyl group of the carbon number 2 ~ 20 substituted or unsubstituted with a halogen atom, an alkynyl group of the carbon number 2 ~ 20 substituted or unsubstituted with a halogen atom, an aryl group of the carbon number 6 ~ 20 substituted or unsubstituted with a halogen atom, an alkylaryl group of the carbon number 7 ~ 20 substituted or unsubstituted with a halogen atom, or a heteroaryl group of carbon number 7 ~ 10; and R1 and R2 cannot be hydrogen at the same time.

Description

Organic electrolytic solution and lithium battery employing the same

The present invention relates to an organic electrolyte and a lithium battery employing the same, and more particularly, to an organic electrolyte including an additive to which a solvent phobic substituent is connected, and a lithium battery employing the same.

Batteries are used as power sources for portable electronic devices such as video cameras, mobile phones, and notebook computers. Rechargeable lithium batteries are more than three times higher in energy density per unit weight and can be charged faster than conventional lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries and nickel zinc batteries.

Lithium batteries operate at high drive voltages, so aqueous electrolytes cannot be used. The aqueous electrolyte reacts violently with lithium. In general, an organic electrolyte is used for a lithium battery. The organic electrolyte is prepared by dissolving lithium salt in an organic solvent. The organic solvent is preferably stable at high voltage, has high ion conductivity, high dielectric constant, and low viscosity.

When a polar carbonate-based non-aqueous solvent is used in a lithium battery, an irreversible reaction in which an excessive charge is used by a side reaction between an anode carbon and an electrolyte during initial charging proceeds. By the irreversible reaction, a passivation layer such as a solid electrolyte interface (SEI) is formed on the surface of the cathode. The SEI prevents decomposition of the electrolyte during charge and discharge and serves as an ion tunnel. The SEI passes only lithium ions during charging and discharging, and blocks the organic solvent that moves with the lithium ions in the electrolyte. Only lithium ions are intercalated into the carbon anode, and organic solvents are not cointercalated with lithium ions, thereby preventing the carbon anode structure from collapsing. However, organic solvents and lithium salts are prevented. The SEI produced only by is difficult to maintain the form and function of the initially generated SEI under high voltage conditions of 4V or more repeatedly applied during charging and discharging. As charging and discharging are repeated, cracks occur in the SEI, the solvent is continuously reduced, insoluble salts precipitate inside and outside the anode, and gas side reactions proceed. These side reactions again lead to SEI cracking. Due to the cracking of the anode, the resistance of the anode increases, so that the battery capacity decreases. In addition, the reduction of the electrolyte reduces the electrolyte, making ion transfer difficult.

US Pat. No. 5,352,548 discloses a technique in which an additive in the form of a vinylene carbonate derivative is injected into an electrolyte solution, and a film is formed on the surface of the negative electrode through a reduction / decomposition reaction of the additive to suppress the decomposition reaction of the solvent.

Lithium salts; Organic solvents; And it provides an organic electrolyte comprising a compound represented by the formula (1):

<Formula 1>

Where

R ₁ and R ₂ are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, unsubstituted or substituted with halogen, an alkenyl group having 2 to 10 carbon atoms, unsubstituted or substituted with halogen, and having 2 to 2 carbon atoms unsubstituted or substituted with halogen An alkynyl group of 10, an aryl group of 6 to 20 carbon atoms substituted or unsubstituted, an alkylaryl group of 7 to 20 carbon atoms substituted or unsubstituted with halogen, an arylalkyl group of 7 to 10 carbon atoms substituted or not substituted with halogen Or a heteroaryl group having 2 to 20 carbon atoms, which is unsubstituted or substituted with halogen, except that R ₁ and R ₂ are hydrogen at the same time.

Cathode; Anode; And it provides a lithium battery comprising the organic electrolyte according to the above.

Hereinafter, an organic electrolyte solution and a lithium battery employing the same according to a preferred embodiment of the present invention will be described in more detail.

The organic electrolyte solution according to one embodiment of the present invention is a lithium salt; Organic solvents; And an additive compound represented by Formula 1 below:

<Formula 1>

Where

R ₁ and R ₂ are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, unsubstituted or substituted with halogen, an alkenyl group having 2 to 10 carbon atoms, unsubstituted or substituted with halogen, and having 2 to 2 carbon atoms unsubstituted or substituted with halogen An alkynyl group of 10, an aryl group of 6 to 20 carbon atoms substituted or unsubstituted, an alkylaryl group of 7 to 20 carbon atoms substituted or unsubstituted with halogen, an arylalkyl group of 7 to 10 carbon atoms substituted or not substituted with halogen Or a heteroaryl group having 2 to 20 carbon atoms, which is unsubstituted or substituted with halogen, except that R ₁ and R ₂ are hydrogen at the same time.

In the following, the working principle of the present invention will be described, which is intended to help the understanding of the present invention, but the scope of the present invention is not limited or limited to the following description.

In the compound of Formula 1, anionic polymerization may be initiated by an alkoxide anion generated from the compound and the polar solvent during initial charging of the battery, thereby forming a polymer film on the electrode surface. The polymerization can be represented, for example, by Scheme 1 below.

<Scheme 1>

In the above scheme, 5-phenyl-1,3-dioxolane-2,4-dione (5-phenyl-), wherein the alkoxide anion (RO ⁻ ) generated during initial charging of the battery is one of the compounds represented by Formula 1 above 1,3-dioxolane-2,4-dione) is attacked and carbon dioxide is separated to form an anionic intermediate. The intermediate again invades 5-phenyl-1,3-dioxolane-2,4-dione to form a dimer. This reaction may be repeated, resulting in a polymer coating.

In addition, the substituents represented by R ₁ and R ₂ in the compound of Formula 1 are nonpolar substituents and are solvent phobic functional groups having no affinity with a solvent. The functional groups have a high affinity with a carbon-based negative electrode surface such as graphite, thereby facilitating physical adsorption on the carbon-based negative electrode surface. Therefore, since a small solvent functional group such as a phenyl group exists in the repeating unit of the polymer produced as a result of the polymerization reaction, adsorption on the surface of the carbon-based negative electrode is easy.

The reduction potential of the compound of Formula 1 is preferably higher than that of the organic solvent. Since the reduction potential of the compound of Formula 1 is higher than that of the organic solvent, it is first reduced by the electrons provided from the anode upon charging.

The unsubstituted alkyl group having 1 to 20 carbon atoms in the above formula means a straight or branched alkyl group having 1 to 20 carbon atoms. More preferred is a straight or branched alkyl group having 1 to 12 carbon atoms. Specific examples are methyl, ethyl, propyl, isobutyl, n-butyl, sec-butyl, pentyl, iso-amyl, hexyl, heptyl, octyl, nonyl, dealkyl, dodecyl and the like.

The unsubstituted alkenyl group having 2 to 20 carbon atoms in the above formulas is a straight or branched aliphatic hydrocarbon group having 2 to 20 carbon atoms having a carbon-carbon double bond. Preferably it has 2 to 12 carbon atoms in the chain, more preferably 2 to 6 carbon atoms. Specific examples are vinyl, propvinyl, allyl, butenyl, orenyl and the like.

The unsubstituted alkynyl group having 2 to 20 carbon atoms in the above formulas is a straight or branched aliphatic hydrocarbon group having 2 to 20 carbon atoms having a carbon-carbon triple bond. Preferably it has 2 to 12 carbon atoms in the chain, more preferably 2 to 6 carbon atoms. Specific examples are ethynyl, propynyl, butynyl and the like.

An unsubstituted aryl group having 6 to 20 carbon atoms in the above formula means a carbocyclic aromatic system having 6 to 20 carbon atoms including at least one aromatic ring, wherein the at least one ring is fused to each other, a single bond, or the like. Can be connected via. As a specific example, it is a phenyl group, a naphthyl group, a biphenyl group.

The unsubstituted alkylaryl group having 7 to 20 carbon atoms in the formulas refers to an aryl group substituted with one of the hydrogen atoms of the alkyl group. For example, a benzyl group etc. are mentioned.

The unsubstituted arylalkyl group having 7 to 20 carbon atoms in the chemical formula of the present invention refers to an alkyl group substituted with one of the hydrogen atoms of the aryl group. For example, 4-tert-butylphenyl group, 4-ethylphenyl group, etc. are mentioned, but it is not limited to this.

In the formulas of the present invention, an unsubstituted heteroaryl group having 2 to 30 carbon atoms means a system composed of one or more aromatic rings containing one or more heteroatoms selected from N, O, P or S, and the remaining ring atoms being C. The one or more aromatic rings may be fused to each other or connected through a single bond or the like.

According to another embodiment of the present invention, the additive compound may be represented by the following Chemical Formulas 2 to 9.

<Formula 2> <Formula 3>

<Formula 4> <Formula 5>

<Formula 6> <Formula 7>

<Formula 8> <Formula 9>

According to another embodiment of the present invention, the content of the additive represented by the formula (1) is preferably 0.1 to 10% by weight based on the total weight of the organic electrolyte, but is not necessarily limited to this range, if necessary Appropriate amounts may be used. Additive content in the above range is suitable to achieve the object of the present invention.

The lithium salt may be used as long as it is commonly used in lithium batteries, LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiN (CF ₃ SO ₂ ), LiBF ₄ , LiC (CF ₃ SO ₂ ) ₃ , and Preference is given to at least one compound selected from the group consisting of LiN (C ₂ F ₅ SO ₂ ) ₂ .

In the organic electrolyte solution according to another embodiment of the present invention, the concentration of the lithium salt is preferably about 0.5 to 2M. When the concentration of the lithium salt is less than 0.5M, the conductivity of the electrolyte may be lowered, and thus the performance of the electrolyte may be lowered. When the viscosity of the electrolyte increases, the mobility of lithium ions may be reduced. However, it is also possible that the concentration of the lithium salt is used outside the range of 0.5 to 2M.

According to another embodiment of the present invention, the organic solvent is a high dielectric constant solvent, a low boiling point solvent or a mixed solvent thereof. The high dielectric constant solvent used in the present invention is not particularly limited as long as it is commonly used in the art, and cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, or gamma-butyrolactone may be used. Low boiling solvents are also commonly used in the art, such as dimethyl carbonate, ethylmethyl carbonate. Diethyl carbonate, chain carbonates such as dipropyl carbonate, dimethoxyethane, diethoxyethane or fatty acid ester derivatives and the like can be used.

In the mixed solvent in which the high dielectric constant solvent and the low boiling point solvent are mixed, the mixing volume ratio of the high dielectric constant solvent: low boiling point solvent is preferably 1: 1 to 1: 9, and when it is out of the range, it is preferable in terms of discharge capacity and charge and discharge life. It may not, but is not necessarily limited to this range.

According to another embodiment of the present invention, a lithium battery includes a cathode; Anode; And organic electrolytes according to the embodiments. The lithium battery is not particularly limited in form, and may be a lithium primary battery as well as a lithium secondary battery such as a lithium ion battery, a lithium ion polymer battery, a lithium sulfur battery, or the like.

The lithium battery may be manufactured as follows. First, a cathode active material, a conductive agent, a binder, and a solvent are mixed to prepare a cathode active material composition. The cathode active material composition is directly coated and dried on an aluminum current collector to produce a cathode electrode plate, or the cathode active material composition is cast on a separate support, and then a film obtained by peeling from the support is laminated on the aluminum current collector. It is also possible for the cathode electrode plate to be manufactured.

The cathode active material is a lithium-containing metal oxide, any one of those commonly used in the art can be used without limitation, for example, LiCoO ₂ , LiMn _x O _2x (x = 1, 2), LiNi _1-x Mn _x 0 ₂ (0 <x <1), LiNi _1-xy Co _x Mn _y O ₂ (0 ≦ _x ≦ 0.5, 0 ≦ _y ≦ 0.5), and the like.

Carbon black may be used as the conductive agent, and vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, A mixture or a styrene butadiene rubber-based polymer may be used, and as the solvent, N-methylpyrrolidone, acetone, water, or the like may be used. The amount of the cathode active material, the conductive agent, the binder, and the solvent is at a level commonly used in lithium batteries.

Next, as in the case of the cathode electrode plate described above, the anode active material, the conductive agent, the binder and the solvent are mixed to prepare the anode active material composition. The anode active material composition is directly coated and dried on a copper current collector to prepare an anode electrode plate, or an anode active material film cast on a separate support and peeled from the support is laminated to a copper current collector to prepare an anode electrode plate. The amount of the anode active material, the conductive agent, the binder, and the solvent is at a level generally used in lithium batteries. As the anode active material, silicon metal, silicon thin film, lithium metal, lithium alloy, carbon material, or graphite may be used. . In the anode active material composition, the same conductive agent, binder, and solvent may be used as in the case of the cathode. A plasticizer may be added to the cathode electrode active material composition and the anode electrode active material composition to form pores in the electrode plate. As the anode active material, graphite is preferable.

Next, the cathode and the anode may be separated by a separator, and the separator may be used as long as it is commonly used in lithium batteries. It is desirable to have low resistance to the ion migration of the electrolyte and excellent electrolytic solution-wetting ability. For example, a material selected from glass fiber, polyester, teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof may be in the form of a nonwoven fabric or a woven fabric. More specifically, a rollable separator such as polyethylene or polypropylene is used in a lithium ion battery, and a separator having excellent organic electrolyte impregnation ability is used in a lithium ion polymer battery.

The separator may be manufactured according to the following method. After the polymer resin, the filler, and the solvent are mixed to prepare a separator composition, the separator composition is directly coated and dried on an electrode to form a separator film, or the separator composition is cast and dried on a support, and then peeled off from the support. The separator film may be formed by being laminated on the electrode.

The polymer resin is not particularly limited, and any polymer can be used as long as it is a material used as a binder of the electrode plate. For example, vinylidene fluoride / hexafluoro propylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate or mixtures thereof can be used. Preference is given to using vinylidene fluoride / hexafluoropropylene copolymers having a hexafluoropropylene content of 8 to 25% by weight.

The battery structure is formed by disposing a separator between the cathode electrode plate and the anode electrode plate described above. When the battery structure is wound or folded to be accommodated in a cylindrical battery case or a rectangular battery case, and then an organic electrolyte solution is injected according to the embodiment, a lithium ion battery is completed.

After the battery structure is stacked in a bi-cell structure, the stacked structure is impregnated with the organic electrolyte according to the embodiment, and the impregnated structure is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

Hereinafter, the present invention will be described in more detail with reference to preferred examples, but the present invention is not limited thereto.

(Production of electrolyte)

Example 1

5-phenyl-1,3-dioxolane-2,4-dione, an additive to the propylene carbonate solvent, was added in an amount of 5% by weight based on the total weight of the organic electrolyte solution. Was added in an amount, and 1.0M LiClO ₄ was used as the lithium salt to prepare an organic electrolyte solution.

Comparative Example 1

In the same manner as in Example 1, except that 5-phenyl-1,3-dioxolane-2,4-dione (additive) was not added. An organic electrolyte was prepared.

Comparative Example 2

1,3-dioxolane-2,4-dione (instead of 5-phenyl-1,3-dioxolane-2,4-dione) An organic electrolyte was prepared in the same manner as in Example 1, except that 1,3-dioxolane-2,4-dione) was added.

(Manufacture of Lithium Battery)

Example 2

A binder containing 5 wt.% Of polyvinylidene fluoride (PVdF) dissolved in graphite powder (MCMB (mesocarbon microbeads), Osaka gas Chemicals Company) and N-methylpyrrolidone (NMP) at 95: 5 weight ratio The slurry was prepared by addition and mixing well. The slurry was cast on a doctor blade with a thickness of 100 μm on a copper foil having a thickness of 15 μm, then placed in a 90 ° C. oven, and firstly dried for NMP to evaporate for about 2 hours, and secondly dried for 2 hours in a 120 ° C. vacuum oven. NMP was dried to complete evaporation. Next, the electrode was rolled to obtain an anode having an electrode thickness of 50 μm.

A 2016 standard coin cell was manufactured using the anode, the lithium metal as the counter electrode, the polyethylene separator as the separator and the organic electrolyte obtained in Example 1 as the electrolyte.

Comparative example  3 to 4

Coin cells were manufactured in the same manner as in Example 2, except that the organic electrolyte solutions prepared in Comparative Example 1 and Comparative Example 2 were used instead of the organic electrolyte solution obtained in Example 1.

Evaluation Example 1 Initial Charging / Discharging Characteristics Evaluation

Cells with a theoretical cell capacity of 1.05 mAh prepared in Example 2 and Comparative Examples 3 to 4 were then charged with a constant current until they reached 0.001 V for the Li electrode at a current of 0.1 C rate for each, followed by 0.001 V Constant voltage charging was performed until the current was lowered to 0.05C rate with respect to the cell capacity while maintaining the voltage of. Then, the charge and discharge capacity was obtained by performing constant current discharge at a current of 0.1 C rate of the cell capacity until the voltage reached 1.5V. From this, the charge and discharge efficiency was calculated. Charge and discharge efficiency is represented by the following equation (1). Charge and discharge results for the first cycle are shown in Figure 1 and Table 1 below.

<Equation 1>

Initial charge and discharge efficiency (%) = 1 ^st cycle discharge capacity / 1 ^st cycle charge capacity

TABLE 1

1 ^st cycle discharge capacity [mAh] 1 ^st cycle charge capacity [mAh] Initial charge and discharge efficiency (%) Comparative Example 3 - - - Comparative Example 4 2.81 0.79 28 Example 2 1.00 0.85 85

As shown in Table 1 and Figure 1, the battery of Example 2 containing the additive of the present invention is improved initial charging and discharging efficiency compared to the battery of Comparative Example 4 does not contain the additive of the present invention. In addition, in the coin cell of Comparative Example 3, the solvent was decomposed and the capacity was not measured.

1 is a graph showing the charge and discharge test results of the lithium battery according to Example 2 and Comparative Examples 3 to 4 of the present invention.

Claims (8)

Lithium salts; Organic solvents; And An organic electrolyte containing a compound represented by the following formula (1): <Formula 1>

Where R ₁ and R ₂ are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, unsubstituted or substituted with halogen, an alkenyl group having 2 to 10 carbon atoms, unsubstituted or substituted with halogen, and having 2 to 2 carbon atoms unsubstituted or substituted with halogen An alkynyl group of 10, an aryl group of 6 to 20 carbon atoms substituted or unsubstituted, an alkylaryl group of 7 to 20 carbon atoms substituted or unsubstituted with halogen, an arylalkyl group of 7 to 10 carbon atoms substituted or not substituted with halogen Or a heteroaryl group having 2 to 20 carbon atoms, which is unsubstituted or substituted with halogen, except that R ₁ and R ₂ are hydrogen at the same time. The organic electrolyte of claim 1, wherein the compound is any one of Formulas 2 to 8. <Formula 2> <Formula 3>

<Formula 4> <Formula 5>

<Formula 6> <Formula 7>

<Formula 8> <Formula 9>

The organic electrolyte solution of claim 1, wherein the compound is present in an amount of about 0.1 wt% to about 10 wt% based on the total weight of the organic electrolyte solution. The organic electrolyte solution according to claim 1, wherein the lithium salt has a concentration of 0.5 to 2.0 M. The organic electrolyte of claim 1, wherein the organic solvent comprises at least one solvent selected from the group consisting of a high dielectric constant solvent and a low boiling point solvent. The organic electrolyte of claim 5, wherein the high dielectric constant solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, and gamma butyrolactone. 6. The organic electrolyte of claim 5, wherein the low boiling point solvent is at least one selected from the group consisting of dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, dipropyl carbonate, dimethoxyethane, diethoxyethane and fatty acid ester derivatives. Cathode; Anode; And A lithium battery comprising the organic electrolyte solution according to any one of claims 1 to 7.

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