KR100813309B1 - Nonaqueous electrolyte for lithium secondary batteries having enhanced cycle performance and lithium secondary batteries comprising the same - Google Patents

Abstract

A nonaqueous electrolyte solution for a lithium secondary battery, and lithium secondary battery containing the nonaqueous electrolyte solution are provided to improve initial charge/discharge characteristics and high temperature lifetime characteristics. A nonaqueous electrolyte solution comprise a silane-based additive represented by X_n SiY_(4-n), wherein n is 1-3; X is CH2=CH-, CH2=(CH3)COOC3H6-, HN2C3H6-, NH2C2H4NHC3H6-, NH2COCHC3H6-, CH3COOC2H4NHC2H4NHC3H6-, NH2C2H4NHC2H4NHC3H6-, SHC3H6-, ClC3H6-, CH3-, CH2H5-, C2H5OCONHC3H6-, OCNC3H6-, C6H5-, C6H5CH2NHC3H6-, C3H5NC3H6-, H- or a halogen atom; and Y is an alkyl, alkoxy, acetoxy or cycloalkyl group capable of being substituted with a halogen atom, an aryl group, an aralkyl group or a phenyl group, a phenyl capable of being substituted with a halogen atom, -OC2H4OCH3, -Si(CH3)3, -OSi(CH3)3, -OSi(CH3)2H, -O(CH2CH2O)mCH3; -N(CH3)2 or a halogen atom; m is 1-10, but the case that X is CH2=CH- and Y is -OC2H4OCH3 is excluded.

Description

Nonaqueous electrolyte for lithium secondary battery having improved cycle performance and lithium secondary battery using the same {Nonaqueous electrolyte for lithium secondary batteries having enhanced cycle performance and Lithium secondary batteries comprising the same}

1 is a graph showing the experimental results of the high temperature charge and discharge characteristics of a unit cell to which a nonaqueous electrolyte according to the present invention is applied.

Figure 2 shows the results of measuring the surface morphology formed on the surface of the negative electrode after the charge and discharge of the unit cell to which the nonaqueous electrolyte according to the present invention is applied at high temperature (60 ° C.) 10 times by a scanning electron microscope.

The present invention relates to a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery comprising the same, and more particularly, to a non-aqueous electrolyte for lithium secondary batteries having an improved initial charge and discharge characteristics and high temperature life characteristics by forming a stable film during initial charge and discharge, and the same. It relates to a lithium secondary battery.

Recently, with the rapid advancement of information and communication technology, the demand for small secondary battery used as an essential power source for mobile IT (Information Technology) related electronic devices such as mobile phone, notebook PC, PDA, etc. is growing exponentially. There is a growing trend. The weight of the battery in various portable information and communication devices accounts for 10-20% for notebook PCs and 50% for mobile phones. The secondary battery not only affects the compactness and weight of the device, but also can be used continuously for a long time. Has become an important competitive factor for portable information and communication devices, and the development of small secondary batteries that can meet the demands of such devices will be a key factor in determining the competitiveness of not only the battery industry but also electronic information and communication products.

As the transmission speed of mobile communication systems increases, the existing secondary batteries (nickel-cadmium batteries, nickel-metal hydride batteries) are used to increase energy consumption due to the high functionalization of portable information communication devices and small electronic devices (wireless Internet and wireless data communication services). Since it cannot satisfy | fill, high energy density, high performance, and high stability of a small secondary battery are calculated | required. To this end, developed countries such as Japan and the United States have been actively promoting national-led R & D for a long time, and lithium secondary batteries are the most popular small secondary batteries in the world.

Lithium secondary battery system is one of the chemical energy conversion devices that can draw the change of free energy generated by electrochemical oxidation / reduction reaction into electrical energy. It consists of positive electrode, negative electrode and liquid electrolyte (organic solvent + salt). Thin film separators are being used to prevent physical contact.

In order to ensure high energy density, high performance, and high safety of lithium secondary batteries, development of high functional electrolyte materials as well as electrode materials is essential. A high functional electrolyte system that can supplement the existing electrolyte function is a non-aqueous electrolyte containing functional additives such as passivation film stabilizer, overcharge inhibitor, flame retardant.

In the case of a lithium ion secondary battery, during initial charging, lithium ions from the lithium metal oxide, which is a positive electrode, move to a graphite electrode, which is a negative electrode, and are inserted into graphite. At this time, decomposition products such as lithium ions and nonaqueous electrolytes or anions of salts react to form a thin film on the graphite surface. Such a film is referred to as a solid electrolyte interface layer (SEI layer). The passivation film allows lithium ions to pass but prevents electrons from moving. In addition, the lithium ion is inserted into the graphite negative electrode together with the organic solvent reduction by-product of the large molecular weight electrolyte to prevent the graphite structure from decaying. Thus, after the passivation film is formed, lithium ions are prevented from further side reactions with other organic solvents or anions of salts, thereby helping to maintain the discharge capacity even during long charge and discharge. That is, the components and morphology of the passivation film formed on the surface of the negative electrode active material particles during initial charging of the battery determine the stability and charge / discharge characteristics of the battery. If the passive film, which can expect such a positive effect, is not formed stably unlike the original intention, it may lead to further decomposition of the organic solvent. This reduces the number of lithium ions reversibly moving, decreases the charge and discharge capacity and decreases the efficiency. This tendency is more severe when charging and discharging at high temperatures. Therefore, in order to implement a high performance secondary battery, a functional material that can decompose first at a lower potential than a mixed organic solvent component to form a stable passivation film is required. If no functional substance is added, lithium ions and electrons are consumed by the reductive decomposition reaction of the organic solvent used in the initial charging of the battery, increasing irreversible capacity, and the formed resistance layer decreases the battery continuously during repeated charging and discharging. Will cause.

In order to minimize the deterioration of battery performance due to the reduction decomposition reaction of the organic solvent, Japanese Patent Laid-Open No. 7-176323 discloses a method of adding CO ₂ to the electrolyte, and Japanese Patent Laid-Open No. 7-320779 discloses sulfide in the electrolyte. A method of suppressing decomposition of an electrolyte by adding a system compound is described. In addition, Korean Patent No. 10-0412527 attempted to make a stable passivation film by making an electrolyte solution containing a vinyl ester compound. As described above, by adding a small amount of organic or inorganic substances, it has been tried to form a more stable film on the surface of the negative electrode by reducing decomposition at a lower potential than the organic solvent during initial charging. However, depending on the nature of the compound added, rather than increasing the irreversible capacity, and interacted with the carbon as the negative electrode to form a decomposed or unstable coating, this tendency was more severe at high temperatures.

The present invention has been made to solve the problems of the prior art as described above, the object is to form a stable film during the initial charge and discharge to provide a non-aqueous electrolyte for lithium secondary battery improved initial charge and discharge characteristics and high temperature life characteristics have.

Another object of the present invention is to provide a lithium secondary battery having improved initial charge and discharge characteristics and high temperature life characteristics by forming a stable film during initial charge and discharge.

In order to achieve the above object, the present invention provides a nonaqueous electrolyte solution for a lithium secondary battery including a silane-based additive.

The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and a silane-based additive included in the nonaqueous electrolyte.

Hereinafter, the content of the present invention in more detail as follows.

The nonaqueous electrolyte solution for lithium secondary batteries according to the present invention contains a passivation film stabilizer composed of a silane compound in an organic solvent in which lithium salt is dissolved.

Organic solvents that can be used in the present invention are ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), gamma butyrolactone (γ BL), ethyl methyl carbonate (EMC), dimethicone 1 type, or 2 or more types of mixed solvent chosen from methoxyethane (DME), diethoxy ethane (DEE), 2-methyl tetrahydrofuran (2-MeTHF), and dimethyl sulfoxide. The mixing ratio of the organic solvent is not particularly limited as long as the object of the present invention is not impaired, and the mixing ratio of the non-aqueous electrolyte solution for normal lithium batteries is followed.

The lithium salt may be selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiSCN, LiC (CF ₃ SO ₂ ) ₃ , LiBOB Or 2 or more types of mixed salts. The lithium salt is added in a concentration of 0.5 ~ 2.0M, when the salt concentration is less than 0.5M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, if it exceeds 2.0M of lithium ions due to the increase in viscosity at low temperatures There is a fear that the problem of low temperature performance is reduced due to reduced mobility.

The silane-based passivation coating additive which can be used in the present invention includes a compound represented by the following formula.

X _n SiY _4-n (n = 1 ~ 3)

X = CH ₂ = CH-, CH ₂ = (CH ₃ ) COOC ₃ H _6- , HN ₂ C ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₃ H _6- , NH ₂ COCHC ₃ H _6- , CH ₃ COOC ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , SHC ₃ H _6- , ClC ₃ H _6- , CH _3- , CH ₂ H _5- , C ₂ H ₅ OCONHC ₃ H _6- , OCNC ₃ H _6- , C ₆ H _5- , C ₆ H ₅ CH ₂ NHC ₃ H _6- , C ₃ H ₅ NC ₃ H _6- , H- and Selected from halogen.

Y = -H, alkyl, alkoxy, acetoxy and cycloalkyl which can be substituted by a functional group selected from the group consisting of halogen, aryl, aralkyl and allyl groups, phenyl which can be substituted by halogen, -OC ₂ H ₄ OCH ₃ ,- Si (CH ₃ ) ₃ , -OSi (CH ₃ ) ₃ , -OSi (CH ₃ ) ₂ H, -O (CH ₂ CH ₂ O) _m CH ₃ (m = 1-10), -N (CH ₃ ) ₂ and halogen, except when X = CH ₂ = CH- and at the same time Y = -OC ₂ H ₄ OCH ₃ . The functional group which can be substituted in the above is not specifically limited, For example, the number of the aromatic rings which contain a phenyl group, a naphthyl group, etc. as an aryl group is 1-3, and an aralkyl group and an allyl group have a C1-C10 thing can be used.

The said alkyl, alkoxy, and acetoxy group is not specifically limited, A C1-C10 thing and a cycloalkane are C3-C12.

The silane additive may be added in an amount of 0.1 to 10%, preferably 1 to 5%, based on the total weight of the organic solvent including the lithium salt. If the amount of the additive is less than 0.1%, it is difficult to form a stable passivation film, and if it exceeds 10%, there is a concern that a problem of degrading the performance of the battery occurs.

The silane-based compound contained in the non-aqueous electrolyte according to the present invention mentioned above is decomposed before the general non-aqueous electrolyte during charge and discharge, thereby controlling the film formation, thereby improving initial charge and discharge characteristics and life characteristics.

The present invention includes a lithium secondary battery containing the nonaqueous electrolyte. The lithium secondary battery includes a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte according to the present invention.

In the lithium secondary battery electrode, an electrode active material such as a positive electrode active material or a negative electrode active material is mixed with a conductive agent and / or a binder to prepare each electrode slurry, the prepared electrode slurry is applied to each electrode current collector, and then a solvent or a dispersion medium is dried. It removes and binds an electrode active material to an electrical power collector, and simultaneously binds between each electrode active material, and manufactures it.

The positive electrode active material of the electrode active material constituting the present invention may be used without limitation as long as it is a material capable of occluding and releasing lithium. For example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCoPO ₄ , LiNi _(1-X) Co _X M _Y O ₂ , where M = Al, Ti, Mg or Zr, 0 <x _{≤1, 0≤y≤0.2), LiNi x Co} y Mn (1-xy) O 2 ( where, 0 <x≤0.5, 0 <y≤0.5 ) and _{LiM x M 'y Mn (2} -xy) _{O 4 (M, M '=} V, Cr, Fe, Co, Ni or Cu, 0 <X≤1, 0 < Y≤1) , but the complex metal oxides such as, but not the type is not limited thereto. These may be used alone or in combination.

The negative electrode active material of the electrode active material of the present invention is a non-limiting example of lithium alloy, carbon (carbon), coke (activation carbon), graphite (graphite), silicon (Si) that can occlude and release lithium And metals such as tin (Sn) and / or alloys may be used.

Since the conductive material is for imparting conductive contact between electrode materials, any material having high electrical conductivity and having a very large specific surface area can be used without limitation. Typical examples include carbon blacks such as acetylene black, ketjen black, farnes black and thermal black; Natural graphite, artificial graphite, etc. can be used.

As the binder, any one of a thermoplastic resin and a thermosetting resin may be used, or a combination thereof may be used. Representative examples include polyvinylidene fluoride (PVdF) or copolymers thereof, polytetrafluoroethylene (PTFE), and SBR (Styrene-Butadiene Rubber).

Representative examples of the dispersion medium include isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water.

As the current collector, a metal having high conductivity is generally used, and any metal may be used as long as the electrode slurry is a metal that can be easily bonded as long as it is not reactive in the voltage range of the battery. Representative examples include meshes or foils made of aluminum, copper, nickel, stainless steel, and the like.

The lithium secondary battery of the present invention may be prepared by adding a nonaqueous electrolyte according to the present invention through a separator between a positive electrode and a negative electrode by a conventional method known in the art.

In preparing the lithium secondary battery of the present invention, a polyolefin-based separator such as polyethylene or polypropylene may be used without limitation.

The lithium secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type, or coin type using a can.

Hereinafter, the content of the present invention will be described in detail through examples. However, these are intended to explain the present invention in more detail, and the scope of the present invention is not limited thereto.

<Example 1>

1M LiPF ₆ was added to a non-aqueous organic solvent in which ethylene carbonate / dimethyl carbonate (EC / DMC) was mixed in a 1: 1 volume ratio, and tris (2-ketoxyethoxy) (vinyl) silane was used as a silane-based passivation film stabilizer. 1 wt% phosphorus was added to the electrolyte to prepare an electrolyte.

<Example 2>

An electrolyte solution was prepared in the same manner as in Example 1, and 3 wt% of tris (2-ketoxyethoxy) (vinyl) silane was added to the basic electrolyte solution.

<Example 3>

An electrolyte solution was prepared in the same manner as in Example 1, and 5% by weight of tris (2-methoxyethoxy) (vinyl) silane was added to the basic electrolyte solution.

Comparative Example

An electrolyte was prepared in the same manner as in Example 1, except that vinyl silane was not added.

<Test Example 1>

A unit cell was prepared for measuring the irreversible capacity of the functional nonaqueous electrolyte prepared by Comparative Example 1 and Examples 1 to 3. The battery negative electrode was composed of graphite as the active material and polyvinylidene fluoride as the binder, and the positive electrode was composed of LiCoO ₂ as the active material, polyvinylidene fluoride as the binder and acetylene black as the conductive agent. The unit cell prepared above was charged under a CC condition with a current of C / 10 and a charging voltage of 4.2V, and then discharged to 3.0V with a current of C / 10, thereby measuring irreversible capacity. The results are shown in Table 1 below.

TABLE 1

Comparative example Example 1 Example 2 Example 3 Irreversible capacity 28% 25% 22% 19%

<Test Example 2>

In order to determine the degree to which the functional nonaqueous electrolyte prepared by Comparative Example 1 and Examples 1 to 3 were decomposed during initial charging, the change in bulk resistance was investigated using impedance. The results are shown in Table 2 below.

TABLE 2

<Test Example 3>

In order to determine the high temperature charge / discharge characteristics of the functional nonaqueous electrolytes prepared by Comparative Examples 1 and 2, the unit cell was configured in the same manner as in Test Example 1, and the C / 2 current and the 4.2 V charge voltage were used at 60 ° C. After charging under CC-CV conditions, the battery was discharged 10 times to 3.0V with a current of C / 2. The capacity change according to the number of charge and discharge cycles is shown in FIG. 1, and the morphology change of the cathode surface is shown in FIG. 2.

As can be seen in Table 1, in the case of Examples 1 to 3 in which the additive is introduced, as compared with the comparative example in which the additive of the present invention is not introduced, the irreversible capacity decreases as the content thereof increases. In addition, it can be seen from Table 2 that the additive of the present invention suppresses the increase in the bulk resistance after the initial charge, thereby effectively suppressing the decomposition of the organic solvent.

When the nonaqueous electrolyte solution of Example 2 according to the present invention is introduced from FIG. 2, it can be seen that the initial negative electrode morphology is well maintained even after charge and discharge compared to the comparative example which is not introduced.

According to the present invention, by forming a stable film during the initial charge and discharge of the battery to improve the initial charge and discharge characteristics and high temperature life characteristics. In addition, even when used in an electrolyte solution containing a lithium salt, such as lithium hexafluorophosphate, which is weak in heat, it exhibits excellent charge and discharge characteristics during high temperature charge and discharge, and also improves charge and discharge characteristics at high rates.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and modified within the scope of the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be appreciated that it can be changed.

Claims (12)

Non-aqueous electrolyte solution for lithium secondary batteries containing a silane-based additive represented by the following formula. X _n SiY _4-n (n = 1 ~ 3) X = CH ₂ = CH-, CH ₂ = (CH ₃ ) COOC ₃ H _6- , HN ₂ C ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₃ H _6- , NH ₂ COCHC ₃ H _6- , CH ₃ COOC ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , SHC ₃ H _6- , ClC ₃ H _6- , CH _3- , CH ₂ H _5- , C ₂ H ₅ OCONHC ₃ H _6- , OCNC ₃ H _6- , C ₆ H _5- , C ₆ H ₅ CH ₂ NHC ₃ H _6- , C ₃ H ₅ NC ₃ H _6- , H- and Selected from halogen. Y = -H, alkyl, alkoxy, acetoxy and cycloalkyl which can be substituted by a functional group selected from the group consisting of halogen, aryl group, aralkyl group and phenyl group; Phenyl which is substituted with halogen; -OC ₂ H ₄ OCH ₃ , -Si (CH ₃ ) ₃ , -OSi (CH ₃ ) ₃ , -OSi (CH ₃ ) ₂ H, -O (CH ₂ CH ₂ O) _m CH ₃ (m = 1 ~ 10), -N (CH ₃ ) ₂ and halogen, except when X = CH ₂ = CH- and at the same time Y = -OC ₂ H ₄ OCH ₃ . delete The nonaqueous electrolyte of claim 1, wherein the silane-based additive comprises 0.1 to 10% of the total weight of the organic solvent including lithium salt. The nonaqueous electrolyte solution according to claim 1, wherein the nonaqueous electrolyte is an organic solvent, such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, ethyl methyl carbonate, dimethoxyethane, diethoxyethane, 2-methyltetrahydrofuran, and dimethyl. A nonaqueous electrolyte solution for lithium secondary batteries, which is one or two or more mixed solvents selected from sulfoxides. The method of claim 1, wherein the lithium salt is LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiSCN, LiC (CF ₃ SO ₂ ) ₃ , LiBOB Non-aqueous electrolyte solution which is 1 type, or 2 or more types of mixed salt selected from the group. It includes a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, the non-aqueous electrolyte is a lithium secondary battery containing a silane-based additive represented by the following formula X _n SiY _4-n (n = 1 ~ 3) X = CH ₂ = CH-, CH ₂ = (CH ₃ ) COOC ₃ H _6- , HN ₂ C ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₃ H _6- , NH ₂ COCHC ₃ H _6- , CH ₃ COOC ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , SHC ₃ H _6- , ClC ₃ H _6- , CH _3- , CH ₂ H _5- , C ₂ H ₅ OCONHC ₃ H _6- , OCNC ₃ H _6- , C ₆ H _5- , C ₆ H ₅ CH ₂ NHC ₃ H _6- , C ₃ H ₅ NC ₃ H _6- , H- and Selected from halogen. Y = -H, alkyl, alkoxy, acetoxy and cycloalkyl which can be substituted by a functional group selected from the group consisting of halogen, aryl group, aralkyl group and phenyl group; Phenyl which is substituted with halogen; -OC ₂ H ₄ OCH ₃ , -Si (CH ₃ ) ₃ , -OSi (CH ₃ ) ₃ , -OSi (CH ₃ ) ₂ H, -O (CH ₂ CH ₂ O) _m CH ₃ (m = 1 ~ 10), -N (CH ₃ ) ₂ and halogen, except when X = CH ₂ = CH- and at the same time Y = -OC ₂ H ₄ OCH ₃ . delete The lithium secondary battery of claim 6, wherein the silane-based additive comprises 0.1 to 10% of the total weight of the organic solvent containing lithium salt. The lithium secondary battery according to claim 6, wherein the electrode active material constituting the positive electrode and the negative electrode is selected from the following materials. (A) positive electrode active material LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCoPO ₄ , LiNi _(1-X) Co _X M _Y O ₂ (where M = Al, Ti, Mg or Zr, 0 <x≤1, 0 _{≤y≤0.2), LiNi x Co y Mn} (1-xy) O 2 ( where, 0 <x≤0.5, 0 <y≤0.5 ) and _{LiM x M 'y Mn (2} -xy) O 4 (M , M '= V, Cr, Fe, Co, Ni or Cu, 0 <X ≤ 1, 0 <Y ≤ 1) at least one selected from the group consisting of. (B) negative electrode active material At least one selected from the group consisting of lithium alloy, carbon, coke, activated carbon, graphite, silicon, metal or alloy. The lithium secondary battery according to claim 6, wherein the conductive material constituting the positive electrode and the negative electrode is at least one selected from the group consisting of carbon black, natural graphite, and artificial graphite. The lithium secondary battery according to claim 6, wherein the binder constituting the positive electrode and the negative electrode is at least one selected from the group consisting of polyvinylidene fluoride or a copolymer thereof, polytetrafluoroethylene, and styrenebutadiene rubber. The lithium secondary battery according to claim 6, wherein the current collector constituting the battery is a mesh or a foil.

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