KR101664243B1 - A secondary battery - Google Patents

Abstract

A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution, wherein the separator comprises a porous substrate having pores, wherein the average diameter d of the pores is 50 nm or more, The diameter distribution (d75 / d25) of the pores is not less than 3, and the nonaqueous electrolyte has an ionic conductivity of not less than 10 mS / cm at 25 캜. It is possible to provide a lithium secondary battery in which cyclic characteristics and fine shots are generated and generation of unwanted by-products is minimized through controlling the value of the ionic conductivity of the non-aqueous electrolyte along the pores of the porous substrate.

Description

Lithium secondary battery {A SECONDARY BATTERY}

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having a nonaqueous electrolyte solution whose ion conductivity value is controlled in accordance with the average diameter of pores of a porous substrate of a separator.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. The electrochemical device is one of the most attracting fields in this respect, and development of a secondary battery such as a rechargeable lithium secondary battery has become a focus of attention.

The lithium secondary battery includes a positive electrode, a negative electrode, an electrolyte and a separator. Among these, the characteristics required of the separator are that the positive electrode and the negative electrode are separated and electrically insulated, and the lithium ion is permeated with high porosity. In such a separator, the cycle characteristics of the battery are improved as the base material having a large average pore diameter is used. However, there is a problem in that fine shots are generated and the production of unwanted byproducts is accelerated. Particularly, There is a problem that it is difficult to apply to a secondary battery.

A polyolefin (PO) film is used as a porous substrate of a separator generally used, or a nonwoven fabric can also be used. However, when the nonwoven fabric is used as a separator, the nonwoven fabric has a larger average diameter of pores than conventional polyolefin films, and thus there is a problem that the occurrence of fine shorts and the generation of by-products are accelerated.

Accordingly, there is a demand for a solution to the problem that occurs in the secondary battery when the average diameter of the pores of the porous base material is large or when the separator is used as a nonwoven fabric.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the aforementioned problems and it is an object of the present invention to provide a lithium secondary battery which can improve the cycle characteristics and reduce the occurrence of fine shorts and the formation of unwanted byproducts when using a separator comprising a porous substrate having a large average pore diameter, To provide a secondary battery.

According to one aspect of the present invention, there is provided a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the separator includes a porous substrate having pores And d75 / d75 which is a ratio of d25, which is the diameter located at the lower 25% and d75, which is located at the lower 75%, in the distribution of the average diameter (d) of the pores, d25 is 3 or more, and the non-aqueous electrolyte has an ionic conductivity at 25 DEG C of 10 mS / cm or more.

The non-aqueous electrolyte according to an embodiment of the present invention is a lithium salt dissolved in a nonaqueous solvent, the lithium salt is _{LiPF 6, LiAsF 6, LiBF 4} , LiClO 4, Lithium salts selected from LiBOB and LiFSI can be used.

The non-aqueous electrolyte in accordance with another embodiment of the present invention is a lithium salt dissolved in a nonaqueous solvent, the lithium salt is the lithium salt is _{LiPF 6, LiAsF 6, LiBF 4} , LiClO 4, The lithium salt selected from LiBOB and LiFSI may be contained in a molar number of 10% or more of the total number of moles of the lithium salt.

The nonaqueous electrolyte according to another embodiment of the present invention is a nonaqueous solvent in which a lithium salt is dissolved, and the nonaqueous solvent contains at least one of cyclic carbonate and linear carbonate to adjust the ratio of cyclic carbonate or linear carbonate The cyclic carbonate may be at least one selected from the group consisting of ethylene carbonate and propylene carbonate, and the linear carbonate may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate And may be at least one selected from the group consisting of

The porous substrate according to an exemplary embodiment of the present invention may include at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate ), Polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyether sulfone (also referred to as " polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide, polyvinyl alcohol, polyacrylic acid, polyethylene oxide (polyethylene) oxide, a polyethylene-polyvinyl alcohol copolymer, a polyethylene naphthalene lenenaphthalene) alone or a mixture of two or more thereof.

Also, the separator according to one embodiment of the present invention is characterized in that the porous substrate has an average diameter d of pores of 50 nm or more and a diameter distribution (d75 / d25) of the pores of 3 or more; And a mixture of inorganic particles and a binder polymer, wherein the inorganic particles are connected to and fixed to each other by the binder polymer, and at least one of the inorganic particles and the binder polymer is located in at least one of the at least one surface of the porous substrate and the at least one of the pores, and a porous coating layer having pores formed by interstitial volume.

The inorganic particles may be selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, and mixtures thereof.

The binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, But are not limited to, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate Cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, Cyanoethylsucc Agarose (cyanoethylsucrose), can be a pullulan (pullulan), and any one or a mixture of two or more of those selected from the group consisting of carboxyl methyl cellulose (carboxyl methyl cellulose).

According to the present invention, even if the average diameter of the pores of the porous base material of the separator is large and the diameter distribution is wide, even when the separator is used as the nonwoven fabric, the occurrence of fine short- A secondary battery may be provided. As a result, in the production of a lithium secondary battery, it is possible to use a non-woven fabric substrate having a small average pore diameter as a porous base material but inexpensive instead of a high-priced polyolefin film.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the constitutions described in the drawings are merely the most preferred embodiments, and not all of the technical ideas of the present invention are described. Therefore, various equivalents which can be substituted at the time of the present application It should be understood that variations can be made.

The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution in which a lithium salt is dissolved in a nonaqueous solvent, wherein the separator comprises a porous substrate having pores, (D75 / d25) of the pores is not less than 3, and the non-aqueous electrolyte has an ion conductivity of not less than 10 mS / cm at 25 DEG C .

The diameter distribution (d75 / d25) of the pores means a ratio of d25, which is the lower 25% of the average diameter d of the pores, and d75, which is the diameter of the lower 75%.

The ionic conductivity is characterized by an ionic conductivity of at least 10 mS / cm at 25 캜. The upper limit of the ionic conductivity can be as high as 15 mS / cm to maintain the performance of the lithium secondary battery.

에 비례한다. 여기서 N _A 및 e는 각각 아보가르도수와 전자의 전하량이다.In general, the ionic conductivity is a very important property because it is directly related to the performance of the battery such as the rate characteristic of the battery. The ionic conductivity of the electrolyte is determined by the number of charges z , concentration c and mobility of the ionic species i ,

. Where N _A And e are the charge amounts of the Abrogard number and the electron, respectively.

If the ionic conductivity of the electrolyte is too low, it is difficult to transfer the lithium ions generated from one electrode to the counter electrode during the charging / discharging process, making it difficult for the battery to operate normally. Generally, the ionic conductivity required for the lithium secondary battery electrolyte is 1.0 mS / cm or more.

However, when the average diameter of the pores of the porous substrate of the separator is large, there is a problem that the amount of the electrolyte to be permeated is greatly increased, and micro-shorts are generated and the production of by-products is accelerated. The present inventors have found that when the diameter of the pores is 50 nm or more and the diameter distribution (d75 / d25) of the pores is 3 or more, the ion conductivity of the non-aqueous electrolyte is 10 mS / cm or more. The relationship between the ion conductivity of such a nonaqueous electrolyte and the average diameter of the pores of the porous substrate can be solved by using a separator having a large average pore diameter or a nonwoven fabric as a separator due to a nonaqueous electrolyte having a high ionic conductivity It has its significance.

The reason for the relationship between the ion conductivity and the diameter of the pores of the electrolytic solution is as follows. According to Darcy's law, the flow rate (Q) is known to be proportional to the permeability (k) of the porous substrate (Q ~ k) at the same driving force. Also, according to the Hagen-Poiseuille equation, the permeability (k) is proportional to the square of the pore diameter (d) (k ~ d ² ). As a result, it can be predicted that the flow rate through the porous substrate is proportional to the square of the pore diameter (Q ~ d ² ), so that the diameter of the pore is sensitive to lithium ion transmission when the force is equal. Therefore, the present inventors have found that, in order to solve the problem that the average diameter of the pores is large and the diameter distribution of the pores is large, the lithium ion transfer is rapidly increased in the large diameter region, Directional lithium ion transmission force. Based on this, a relationship was established in which the ion conductivity of the non-aqueous electrolyte at 25 ° C was 10 mS / cm or more when the average diameter of the pores of the porous substrate was 50 nm or more and the diameter distribution (d75 / d25) was 3 or more.

The non-aqueous electrolyte according to one embodiment of the present invention will now be described in detail with reference to the ion conductivity of the non-aqueous electrolyte and the average diameter of the pores of the porous substrate of the separator. In the non-aqueous electrolyte according to the present invention, all of the non-aqueous electrolytes corresponding to the ion conductivity values according to the present invention can be used. More specifically, in the present invention, the kind, combination or respective contents of the lithium salt, The respective contents are adjusted to correspond to the ionic conductivity according to the present invention, and the following examples are given. The present invention is not limited to the following examples.

The non-aqueous electrolyte according to an embodiment of the present invention for achieving the ionic conductivity is a non-aqueous solvent in which a lithium salt is dissolved, and the lithium salt is LiPF ₆ , LiAsF ₆ , LiBF _{4 ,} LiClO ₄ , The lithium salt may be at least one selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiBF _{4 ,} LiBF _{4 ,} LiBF _{4 ,} LiBF _{4 ,} LiBF _{4 ,} LiClO ₄ , The lithium salt selected from LiBOB (lithium (oxalorato) borate and LiFSI (lithium (fluorosulfonyl) imide) may be a moles of 10% or more of the total number of moles of the lithium salt.

The nonaqueous electrolyte according to another embodiment of the present invention is a nonaqueous solvent in which a lithium salt is dissolved. The nonaqueous solvent may have a high ionic conductivity corresponding to the present invention by adjusting the ratio of the cyclic carbonate or linear carbonate, The cyclic carbonate may be at least one selected from the group consisting of ethylene carbonate and propylene carbonate, and the linear carbonate may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

In the non-aqueous electrolyte used in the lithium secondary battery of the present invention, the lithium salt dissolved in the non-aqueous solvent may be any of those conventionally used in a lithium secondary battery in addition to the lithium salt described above. Typical examples of the lithium salt include LiSbF _{6 ,} LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ and LiBOB (LiC ₄ BO ₈ ). It goes without saying that compounds such as lactone, ether, ester, acetonitrile, lactam, and ketone may be further added to the non-aqueous electrolyte of the lithium secondary battery so long as the object of the present invention is not impaired.

The injection of the non-aqueous electrolyte in which the lithium salt is dissolved can be performed at an appropriate stage in the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

The ionic conductivity of the non-aqueous electrolyte according to the present invention and the average diameter of the separator pores will be described in detail below.

The separator according to the present invention comprises a positive electrode, a negative electrode, a porous substrate interposed between the positive electrode and the negative electrode, the porous substrate having an average diameter d of 50 nm or more and a diameter distribution d75 / d25) is 3 or more.

In particular, a porous substrate having pores having an average diameter of pores of 50 nm or more may be a porous nonwoven fabric. The nonwoven fabric is defined as having a fabric shape in which the fibrous aggregate is chemically bonded (e.g., by mixing the adhesive to the fibers) or by mechanical action or by appropriate moisture and heat treatment, without process by spinning, weaving or knitting . This nonwoven fabric is used in various fields including lithium secondary batteries due to its excellent air permeability, warmth and unfixed shape of the cut portion. Methods for producing such nonwoven fabrics include dry, wet, spun-lamination, and electrospray methods.

The nonwoven fabric according to the present invention may be formed of a material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, ), Polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene sulfide, polyphenylene sulfide, polyether sulfone, polyether sulfone, Polypropylene oxide, cyclic olefin copolymer, polyphenylenesulfide, polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyethylene-polypropylene oxide, Vinyl alcohol copolymer, polyethylene naphthalene (polyethylenenaphthalene) Or it may use a non-woven fabric formed of a mixture of two or more of these, to which is not limited to this.

Preferably, the separator according to the present invention has a porous substrate having an average diameter d of pores of 50 nm or more and a diameter distribution (d75 / d25) of the pores of 3 or more; And a mixture of inorganic particles and a binder polymer, wherein the inorganic particles are connected to and fixed to each other by the binder polymer, and the interstitial volume between the inorganic particles And a porous coating layer having formed pores.

The inorganic particles used for forming the porous coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied lithium secondary battery (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved.

For the reasons stated above, it is preferable that the inorganic particles include high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Nonlimiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT, 0 <x <1, 0 < y <1 _{Im), Pb (Mg 1/3} Nb 2/3) O 3 -PbTiO 3 (PMN-PT), hafnia _{(HfO 2), SrTiO 3,} SnO 2, CeO _{2, MgO, NiO, CaO,} ZnO, ZrO 2, Y 2 O 3, Al 2 O 3, TiO 2, SiC Or a mixture thereof.

As the inorganic particles, inorganic particles having a lithium ion transferring ability, that is, inorganic particles containing a lithium element but having a function of transferring lithium ions without storing lithium can be used. Non-limiting examples of inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li (LiAlTiP) _x O _y series glass (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5) such as _3.25 Ge _0.25 P _0.75 S ₄ , (Li _x N _y , 0 <x <4, 0 <y <2) such as Li ₃ N and Li ₃ PO ₄ -Li ₂ S-SiS ₂ SiS ₂ family, such as _{glass (Li x Si y S z} , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 There is P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof as such.

The average particle diameter of the inorganic particles is not limited. However, for the formation of the coating layer of uniform thickness and proper porosity, it is preferable that the average particle diameter is in the range of 0.001 to 10 탆. If it is less than 0.001 μm, the dispersibility may be lowered, and if it exceeds 10 μm, the thickness of the porous coating layer may increase.

The binder polymer constituting the porous coating layer is preferably a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C, which is preferably a mechanical property such as flexibility and elasticity of a finally formed porous coating layer. It is possible to improve the physical properties. Such a binder polymer serves as a binder for linking and stably fixing between inorganic particles or between inorganic particles and a porous substrate. The binder polymer may be a polymer commonly used in the art to form a porous coating layer on a porous substrate, and a polymer having superior heat resistance to a porous substrate is used.

The binder polymer does not necessarily have the ion conduction capability, but the performance of the lithium secondary battery can be further improved by using a polymer having ion conduction ability. Therefore, it is preferable that the binder polymer has a high permittivity constant. In fact, since the dissociation degree of the salt in the electrolyte depends on the permittivity constant of the electrolyte solvent, the higher the permittivity constant of the binder polymer, the better the salt dissociation in the electrolyte. The dielectric constant of such a binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), preferably 10 or more.

In addition to the functions described above, the binder polymer may be characterized by being capable of exhibiting a high degree of swelling of the electrolyte by being gelled upon impregnation with a liquid electrolyte. Accordingly, it is preferable to use a solubility parameter of 15 to 45 MPa ^1/2 of a polymer, and the more preferred solubility parameter of 15 to 25 MPa ^1/2, and 30 to 45 MPa ^1/2 range. Therefore, it is preferable to use hydrophilic polymers having many polar groups, rather than hydrophobic polymers such as polyolefins. If the solubility is more than 15 MPa ^1/2 and less than 45 MPa ^1/2, it is difficult to be impregnated with (swelling) by conventional liquid electrolyte batteries.

Non-limiting examples of such polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, But are not limited to, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, Cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylpyrrolidone, Cellulose (cyanoethylcellulose), City No-ethyl and the like sucrose (cyanoethylsucrose), pullulan (pullulan), carboxymethyl cellulose (carboxyl methyl cellulose).

According to an embodiment of the present invention, the composition ratio of the inorganic particles and the binder polymer in the porous coating layer coated on the porous substrate is preferably in the range of, for example, 50:50 to 99: 1, more preferably 70:30 to 95: to be. When the content ratio of the inorganic particles to the binder polymer is less than 50:50, the content of the polymer is increased, and the average diameter and porosity of the pores of the porous coating layer may be reduced. If the content of the inorganic particles exceeds 99 parts by weight, the fillerability of the porous coating layer may be weakened because the content of the binder polymer is small

The separator according to an embodiment of the present invention may further include other additives in addition to the above-mentioned inorganic particles and polymers as the porous coating layer component, so long as they do not impair the object of the present invention. The preferred thickness of the porous coating layer is 0.01 to 20 um.

The above-described separator can be produced by coating a solution of a binder polymer in which inorganic particles are dispersed on a porous substrate and drying it. As the coating method, a conventional coating method known in the art can be used, and various methods such as dip coating, die coating, roll coating, comma coating, Can be used. Further, the porous coating layer can be selectively formed on both or only one side of the porous substrate.

The separator according to an embodiment of the present invention is interposed between the positive electrode and the negative electrode. In this case, in the case of using a polymer capable of gelation upon impregnation with a liquid electrolyte as a binder polymer component, after the cell is assembled using the separator, the injected electrolyte may react with the polymer to gel.

The electrode (anode and cathode) to be used together with the separator is not particularly limited, and the electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof. The cathode active material may be a conventional cathode active material that can be used for a cathode of a conventional lithium secondary battery. It is preferable to use a lithium composite oxide. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of a lithium secondary battery can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

Hereinafter, embodiments of the present invention will be described in detail to facilitate understanding of the present invention. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

Example  One

An inorganic layer was coated on both sides of the substrate with an alumina slurry with a thickness of 5 mu m with a polyethylene / polypropylene nonwoven fabric (thickness 16 mu m) having an average pore diameter of 1,000 nm as a base material. The mean diameter of the prepared separator after coating was 60 nm. Then, the separator was interposed between a cathode made of a mixture of LiCoO ₂ and Li (Ni _{0 .53} Co _{0 .20} Mn _{0 .27} ) O ₂ in a _ratio of 2: 1 and a cathode made of artificial graphite, and EC / , 1.0 M LiBF ₄ was dissolved in a 1: 1 (v / v) solvent, and a nonaqueous electrolytic solution having an ion conductivity of 11.6 mS / cm at 25 ° C was injected to prepare a coin cell.

Example  2

Except that a nonaqueous electrolyte solution in which LiFSI and LiPF ₆ were mixed and dissolved at a ratio of 1: 1 (wt%) and the ion conductivity at 25 캜 was 13.1 mS / cm was used instead of the lithium salt of the nonaqueous electrolyte of Example 1 A coin cell was prepared in the same manner as in Example 1.

Example 3

Instead of the non-aqueous electrolyte of Example 1, LiPF ₆ was dissolved in a solvent in which PC / DMC was used at a ratio of 1: 1 (v / v) with a nonaqueous solvent to obtain a nonaqueous electrolyte solution having an ion conductivity of 11.0 mS / A coin cell was prepared in the same manner as in Example 1, except that it was used.

Comparative Example 1

1.0 M LiPF ₆ was dissolved in a solvent using EC / DEC of 1: 1 (v / v) as a nonaqueous solvent instead of the nonaqueous electrolyte of Example 1 to obtain a non-aqueous electrolyte solution having an ionic conductivity of 8.2 mS / cm at 25 캜 A coin cell was prepared in the same manner as in Example 1, except that the electrolytic solution was used.

Fine short evaluation

After 100 charge / discharge tests at room temperature, the coin cell was disassembled and observed. As a result, in Examples 1 to 3, there were no specificities on the surface of the negative electrode, but in Comparative Example 1, local fine shots were observed.

Claims (10)

A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,
Wherein the separator comprises a porous substrate having pores, wherein the average diameter (d) of the pores is 50 nm or more, the diameter distribution (d75 / d25) of the pores is 3 or more,
The nonaqueous electrolyte solution has an ionic conductivity of 10 mS / cm or more at 25 캜,
Wherein the non-aqueous electrolyte is a nonaqueous solvent in which a lithium salt is dissolved, and the lithium salt is a mixture of LiPF ₆ and LiFSI in which LiFSI is contained in a molar ratio of 10% or more of the total number of moles of the lithium salt. delete delete The method according to claim 1,
Wherein the non-aqueous electrolyte is a non-aqueous solvent in which a lithium salt is dissolved, and the non-aqueous solvent is at least one selected from the group consisting of cyclic carbonates and linear carbonates. 5. The method of claim 4,
Wherein the cyclic carbonate is at least one selected from the group consisting of ethylene carbonate and propylene carbonate. 5. The method of claim 4,
Wherein the linear carbonate is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The method according to claim 1,
The porous substrate may be formed of a material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, Polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide (polyetheretherketone), polyetheretherketone (polyetheretherketone), polyetheretherketone polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide, polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyethylene-polyvinyl alcohol Copolymer, polyethylene naphthalene (polyethylenenaphthalene) each alone Or a lithium secondary battery characterized in that the non-woven fabric formed of a mixture of two or more of these. The method according to claim 1,
Wherein the separator has a porous substrate having an average diameter d of pores of 50 nm or more and a diameter distribution (d75 / d25) of the pores of 3 or more; And a mixture of inorganic particles and a binder polymer, wherein the inorganic particles are connected to and fixed to each other by the binder polymer, and at least one of the inorganic particles and the binder polymer is located in at least one of the at least one surface of the porous substrate and the at least one of the pores, and a porous coating layer having pores formed by interstitial volume of the porous coating layer. 9. The method of claim 8,
Wherein the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, and mixtures thereof. 9. The method of claim 8,
The binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, But are not limited to, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate Cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, Cyanoethylsucc Agarose (cyanoethylsucrose), pullulan (pullulan) and carboxymethyl cellulose (carboxyl methyl cellulose), or any one group of lithium secondary battery, characterized in that a mixture of two or more of those selected from the consisting of.