KR102003301B1 - Lithium electrode comprising polymer protecting layer and lithium secondary battery employing thereof - Google Patents

Abstract

The present invention relates to a lithium electrode and a lithium secondary battery comprising the same, and more particularly, to form a polymer protective film on the electrode containing lithium, a high concentration in a polyalkylene glycol diacrylate network crosslinked with the polymer protective film The present invention relates to a lithium electrode and a lithium secondary battery including the same, by using polyethylene oxide together with a lithium salt to inhibit lithium dendrite growth and to prevent electrolyte decomposition at an electrode surface, thereby improving battery performance.

Description

Lithium electrode comprising polymer protective layer and lithium secondary battery comprising same

The present invention relates to an electrode capable of improving battery performance, including a high-strength polymer protective film, and a lithium secondary battery including the same.

With the rapid development of the electronics, telecommunications and computer industries, the application of energy storage technology is expanding to camcorders, mobile phones, notebook PCs and even electric vehicles. Accordingly, the development of small sized secondary batteries with high performance, light weight and long life, and high reliability is underway.

Lithium secondary batteries are in the spotlight as batteries which satisfy these requirements.

The lithium secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is stacked or wound, and the electrode assembly is embedded in a battery case and a nonaqueous electrolyte is injected into the inside. do. The lithium secondary battery produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.

As the negative electrode of the lithium secondary battery, lithium metal, carbon, and the like are used as active materials, and as the positive electrode, lithium oxide, transition metal oxide, metal chalcogenide compounds, conductive polymers, and the like are used as active materials.

In this case, when the lithium electrode is used as the negative electrode, a lithium electrode formed by attaching a lithium foil to a planar current collector has been generally used. When the battery is driven, electrons moving to the lithium foil through the current collector are unidirectional. Go to the flow of. As a result, non-uniformity of electron density occurs on the surface of lithium, whereby lithium dendrite may be formed. Such lithium dendrites may eventually cause damage to the separator and may cause short circuits of the lithium secondary battery.

Accordingly, various methods for stabilizing lithium have been proposed, and among them, a method of forming a protective layer in contact with an electrode has been proposed.

In Korean Patent Registration No. 10-0425585, a crosslinked polymer protective film is formed on a surface of a lithium electrode using a diacryl monomer represented by CH ₂ = CH-CO _2- (CH ₂ ) ₈ -CO ₂ -CH = CH ₂ . It is mentioned that the life of the battery can be increased by improving the interface property between the electrode and the polymer electrolyte.

However, in addition to these effects, the crosslinked polymer protective film becomes harder and more fragile as the crosslinking reaction proceeds, resulting in a new problem that the protective film is damaged by the volume change of the surface of the lithium cathode during charging / discharging.

On the other hand, the electrolyte of the lithium secondary battery serves to quickly transport lithium ions, and usually contains a lithium salt and a non-aqueous organic solvent. The performance of the battery varies depending on the concentration of lithium salt, which is usually used at a concentration in the range of 0.1 to 2.0M at maximum.

Recently, the use of a high concentration of lithium salt of 2.0M or more, for example 4M or more, has been proposed, and a technique has been reported that the high concentration of the electrolyte solution can prevent the decomposition of the electrolyte solution on the surface of the lithium electrode to improve battery performance.

However, the high concentration of lithium salt is usually 2 to 5 times higher than the concentration of the electrolyte, and the viscosity is high to use as an electrolyte, it is difficult to inject the electrolyte when manufacturing a battery, difficult to manufacture a battery larger than a coin cell or a battery stack It is difficult to apply to an actual battery process.

Republic of Korea Patent Registration No. 10-0425585, "Lithium polymer secondary battery with a cross-linked polymer protective thin film and its manufacturing method"

In order to solve the above problem, the present inventors have formed a polymer protective film to prevent direct contact between the lithium electrode and the electrolyte, but the polymer protective film has been variously studied to reduce the reactivity of the electrolyte even when the electrolyte contacts some electrode surfaces. By using polyethylene oxide with a high concentration of lithium salt, it was confirmed that the prevention of electrolyte decomposition at the electrode and thereby suppressing the performance degradation of the battery was completed.

Accordingly, an object of the present invention is to provide a lithium secondary battery electrode that suppresses lithium dendrite growth formed on the electrode and prevents direct decomposition of the electrolyte solution.

In addition, another object of the present invention is to provide a lithium secondary battery having improved battery performance, including the lithium secondary battery electrode.

In order to achieve the above object, the present invention is an electrode current collector; An electrode mixture layer formed on one or both surfaces of the electrode current collector and including lithium; And a polymer protective film formed on the electrode mixture layer,

The polymer protective film provides a lithium secondary battery electrode comprising a high concentration of lithium salt and polyethylene oxide in the crosslinked polyalkylene glycol diacrylate network.

At this time, the lithium salt is characterized in that the concentration is a high concentration salt of 2M to 10M.

In addition, the present invention is a lithium secondary battery comprising a separator and an electrolyte interposed between a positive electrode, a negative electrode, a positive electrode, any one or more of the positive electrode, negative electrode or positive electrode is a lithium secondary battery electrode Provide a battery.

The electrode for a lithium secondary battery according to the present invention forms a network structure crosslinked with a polymer protective film on one side to physically inhibit free growth of lithium dendrites on the electrode surface and at the same time increases the strength of the electrolyte and the polymer protective film. To prevent the polymer film from dissolving upon contact.

In addition, the polymer protective film can increase battery performance by using a high concentration of lithium salt, and the polymer protective film does not act as a resistance layer due to high ion conductivity, so that overvoltage is not applied during charge and discharge. Accordingly, there is no deterioration in battery performance due to the use of the polymer protective film, and it can be used even during rapid charge and discharge.

Therefore, the lithium secondary battery having the polymer protective film can be applied to various fields because the battery performance and life is improved.

1 is a graph showing a change in E / V (efficiency / voltage) characteristics with time of the battery prepared in Examples and Comparative Examples, wherein (a) is Comparative Examples 1, (b) is Comparative Examples 2, (c ) Shows Examples 1 and (d) comparing the batteries prepared in Comparative Example 1 and Example 1.
Figure 2 is a graph comparing the efficiency of the battery prepared in Example 1, Comparative Example 1 and Comparative Example 2.

Hereinafter, the present invention will be described in detail.

Lithium secondary batteries use lithium as an electrode active material. At this time, lithium is consumed by contact between lithium and electrolyte and side reactions occur, resulting in a decrease in lifespan. In order to control the reaction at the interface between lithium and the electrolyte, a polymer protective film is placed between them, and a high concentration of lithium salt and a polyethylene oxide for transport thereof in a network structure in which the polymer is crosslinked with the material of the polymer protective film , Called 'PEO').

Lithium salt is used to improve the lithium ion conductivity, it is used in a high concentration in the present invention. Preferably, the lithium salt is used in the range of 2M or more, more preferably 2M to 10M, most preferably 4M to 6M.

Through the use of such a high concentration of lithium salt can be obtained a number of advantages.

First, the use of high concentrations of lithium salts can improve battery performance.

Next, the primary role of the polymer protective film is to act as a protective layer to prevent direct contact between the electrode and the electrolyte as a primary coating film on the surface of the lithium electrode, even though the electrolyte penetrates into the polymer protective film and the electrolyte contacts the electrode surface. Coordination bonds with a high concentration of lithium ions present in the protective film prevents the introduction of the electrolyte solution into the electrode layer, thereby lowering the reactivity of the electrolyte solution. As a result, it is possible to effectively solve the problem caused by the conventional contact between the electrolyte and the electrode.

In addition, since a polymer membrane in which a high concentration of lithium salt is dissociated is used, the polymer membrane does not act as a resistance layer because of high ion conductivity, and does not take overpotential during charging and discharging, thereby preventing the battery from deteriorating and thus rapidly charging. It can be used more advantageously at the time of discharge.

At this time, the lithium salt may be any one used as the lithium salt in the battery field, typically LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, Li (FSO ₂ ) ₂ N (Lithium bis (fluorosulfonyl) imide, hereinafter referred to as 'LiFSI') LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN ( SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carbonate, 4 phenyl lithium borate imide And one selected from the group consisting of a combination thereof, and preferably LiFSI. Lithium salts have different ionic conductivity depending on their type, and the interaction between lithium ions and polymer chains can lead to strong or weak ionic mobility, which is optimal when PEO and LiFSI are used together. Can be.

PEO is known as a polymer electrolyte, and in the present invention, a weight average molecular weight of 1,000,000 to 5,000,000 is used. If the molecular weight is less than the above range, the polymer protective film may have a low strength and may dissolve upon contact with the electrolytic solution. On the contrary, if the molecular weight exceeds the above range, lithium ions may be inhibited from moving to lower the performance of the battery. use.

Conventionally, lithium salt and PEO are known as solid electrolytes, and when they are introduced into a polymer protective film, battery performance can be expected by increasing the transfer rate of lithium ions. However, the polyethylene oxide alone has a problem that the strength of the polymer protective film is low, so that physical properties (eg, strength) are easily degraded by the electrolyte, thereby shortening the electrode life.

Accordingly, in the present invention, the lithium salt and the PEO are present in the crosslinked network as the polymer protective film, thereby increasing the strength of the polymer protective film.

The polymer protective film is positioned between the electrode and the electrolyte, and reduces direct contact therebetween, thereby physically inhibiting the growth of lithium dendrites. However, a part of the solvent in the electrolyte solution penetrates into the polymer protective film, so that the polymer protective film is partially dissolved or swelled, thereby reducing the physical properties of the protective film, thereby not fully exhibiting its function. Accordingly, in the present invention, a network structure crosslinked with a polymer is introduced into the polymer protective film, thereby fundamentally preventing a problem caused by contact between the electrolyte and the polymer protective film.

The crosslinked network structure increases the strength of the polymer protective film, and the higher the strength, the more physically it can suppress the generation of lithium dendrites on the electrode surface, the electrolyte penetrates into the polymer film more effectively to dissolve the polymer film, etc. You can prevent it. However, if the strength is increased too much, the polymer protective film becomes harder and more fragile, causing a problem that the polymer protective film is damaged by the volume change of the surface of the lithium cathode during charging / discharging. Therefore, in the present invention, a flexible polymer is used, and a specific polymer is selected and used so that lithium ions can move smoothly.

This crosslinked network structure may be a bifunctional or more than one multifunctional monomer for crosslinking, preferably using an alkylene glycol diacrylate monomer.

That is, the alkylene glycol diacrylate has a polymerizable vinyl group at both ends, and the vinyl group acts as a crosslinking point to form a crosslinking network structure made of polyalkylene glycol diacrylate through a polymerization process. do.

In this case, the polyalkylene glycol diacrylate may be one selected from the group consisting of polyethylene glycol diacrylate, polypropylene glycol diacrylate, polybutylene glycol diacrylate, and combinations thereof, and preferably polyethylene glycol diacryl. Use rate.

The polyalkylene glycol diacrylate forming the crosslinked network structure is limited in consideration of the damage of the above-mentioned polymer protective film and battery characteristics. Preferably, polyalkylene glycol diacrylate is used in an amount of 5 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of PEO. If the content exceeds the above range, the strength of the polymer protective film may be excessively increased and the density may be increased to inhibit the movement of lithium ions, thereby degrading battery performance.

The thickness of the polymer protective film having the above composition is not limited in the present invention, and has a range that does not increase the internal resistance of the battery while securing the above effects, and may be, for example, 2 to 10 μm. If the thickness is less than the above range, it may not function as a protective film. On the contrary, if the thickness exceeds the above range, stable interfacial properties may be imparted, but initial interface resistance may increase, resulting in an increase in internal resistance during battery manufacturing.

Preparation of the polymer protective film is not particularly limited in the present invention, but may be prepared by adding a lithium salt, PEO, alkylene glycol diacrylate monomer and initiator in a solvent, and then coating the electrode and performing a curing reaction.

The solvent can be any solvent as long as it can dissolve lithium salt and PEO, and preferably a non-aqueous organic solvent is used. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move, and a known carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent can be used. For example, the non-aqueous organic solvent may be N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2 Dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, Diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolane derivatives, sulfolane, methylsulforane, 1,3- Aprotic organic solvents such as dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

The coating may use a method used in a conventional wet process such as spin coating, spray coating, doctor blade coating, dip coating and the like. However, it may be desirable to perform spin coating for uniformity of coating and ease of coating thickness control.

If necessary, drying is carried out after coating. The drying may be appropriately selected at temperatures above the boiling point of the solvent and below the Tg of the polymer material of the protective layer. The drying process may remove the solvent remaining on the surface of lithium and at the same time improve the adhesion of the polymer protective film.

The curing reaction is carried out by UV or heat, through which the crosslinking of the alkylene glycol diacrylate monomer occurs.

The initiator depends on the UV / thermal polymerization method, and any known photoinitiator or thermal initiator can be used. For example, the photoinitiator is benzoin, benzoin ethyl ether, benzoin isobutyl ether, alphamethylbenzoin ethyl ether, benzoin phenyl ether, acetophenone, dimethoxyphenylacetophenone, 2,2-diethoxyacetophenone , 1,1-dichloroacetophenone, trichloroacetophenone, benzophenone, p-chloro benzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy- 2-methyl propiophenone, benzyl benzoate, benzoyl benzoate, anthraquinone, 2-ethylanthraquinone, 2-chloroanthraquinone, 2-methyl-1- (4-methylthiophenyl) -morpholinopropanone- 1, 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocure 1173 from CIba Geigy), Darocure 1116, Irgacure 907, 2-benzyl-2-dimethylamino-1- ( 4-morpholinophenyl) -butanone-1, 1-hydroxycyclohexylphenyl ketone (Irgacure 184 from CIba Geigy), Mikler ketone, benzyl dimethyl ketal, thio Santone, isopropyl thioxanthone, chlorothioxanthone, benzyl, benzyl disulfide, butanedione, carbazole, fluorenone, and alpha acyl oxime ester may be used, and as the thermal initiator, peroxide (-OO-) series Benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, cumyl hydroperoxide, etc. may be used, and azobisisobutyronitrile of the azo compound (-N = N-) series , Azobisisovaleronitrile and the like can be used.

The content of the initiator is not particularly limited to the present invention, and preferably has a range that does not affect the physical properties and the electrode and the electrolyte as the polymer protective film, for example, 1 to 15% by weight relative to 100 parts by weight of the alkylene glycol diacrylate monomer. Use as a negative range.

The polymer protective film produced by this method can be preferably introduced into a lithium secondary battery electrode because a high concentration of lithium ions and PEO are simultaneously present in the crosslinked network structure.

The lithium secondary battery electrode includes an electrode current collector and an electrode mixture layer formed on one or both surfaces of the electrode current collector and including lithium. At this time, the polymer protective film as described above is positioned on the electrode mixture layer, thereby suppressing side reactions between lithium and the electrolyte and delaying consumption of lithium.

In this case, the electrode may be an anode, a cathode, or both of these electrodes.

The electrode current collector is a positive electrode current collector when the electrode is a positive electrode, and a negative electrode current collector when the electrode is a negative electrode.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, carbon, nickel on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with titanium, silver, or the like can be used. In this case, the positive electrode current collector may use various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric having fine irregularities formed on a surface thereof so as to increase the adhesion with the positive electrode active material.

In addition, the negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, carbon on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel , Surface-treated with nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like can be used. In addition, the negative electrode current collector, like the positive electrode current collector, may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric having fine irregularities formed on a surface thereof.

When the electrode according to the present invention is a positive electrode, the electrode mixture layer includes a positive electrode active material, and in the case of a negative electrode, a negative electrode active material. At this time, each electrode active material can be any active material applied to a conventional electrode, and is not particularly limited in the present invention.

The positive electrode active material is any one lithium transition metal selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium copper oxide, vanadium oxide, lithium nickel oxide and lithium manganese composite oxide, and lithium-nickel-manganese-cobalt oxide include oxides and, more specifically, _{Li 1 + x Mn 2 - x} O 4 ( where, x is from 0 to 0.33), LiMnO _3, the lithium manganese oxide such as LiMn ₂ O _3, LiMnO _2; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Lithium nickel oxide represented by LiNi _{1 - x} M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; LiMn _{2 - x} MxO ₂ , where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Ni, Cu Or lithium manganese composite oxide represented by Zn, Li (Ni _a Co _b Mn _c ) O ₂ , where 0 <a <1, 0 <b <1, 0 <c <1, a + b + c Lithium-nickel-manganese-cobalt oxide etc. which are represented by = 1) are mentioned, It is not limited only to these.

In addition, the negative electrode active material may be one selected from the group consisting of lithium metal, lithium alloy, lithium metal composite oxide, lithium-containing titanium composite oxide (LTO), and combinations thereof. At this time, the lithium alloy may be an alloy consisting of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn. In addition, the lithium metal composite oxide is any one metal (Me) oxide (MeO _x ) selected from the group consisting of lithium and Si, Sn, Zn, Mg, Cd, Ce, Ni, and Fe, for example, LixFe ₂ O ₃ ( 0 = x = 1) or LixWO ₂ (0 <x = 1).

In addition, the negative electrode active material is SnxMe _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, Metal complex oxides such as halogen, 0 <x = 1, 1 = y = 3, 1 = z = 8); SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO _{2 2} , Bi ₂ O ₃ , Bi ₂ O ₄ and An oxide such as Bi ₂ O ₅ may be used, and a carbon-based negative active material such as crystalline carbon, amorphous carbon or a carbon composite may be used alone or in combination of two or more thereof.

In this case, the electrode mixture layer may further include a binder resin, a conductive material, a filler and other additives.

The binder resin is used for bonding the electrode active material and the conductive material and the current collector. Examples of such binder resins include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetra Fluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

The said conductive material is used in order to improve the electroconductivity of an electrode active material further. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives and the like can be used.

The filler is optionally used as a component for inhibiting the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The production of the lithium secondary battery electrode according to the present invention is not particularly limited, and follows a conventional electrode manufacturing process.

For example, the electrode mixture layer and the polymer protective film are sequentially stacked on an electrode current collector.

In this case, the electrode mixture layer may be prepared in the form of a lithium metal foil or a lithium metal powder coated on a support in the case of a lithium metal electrode.

The present invention also provides a lithium secondary battery including a separator interposed between a positive electrode, a negative electrode, and a positive electrode and an electrolyte, and provides a lithium secondary battery in which the positive electrode, the negative electrode, or the positive electrode is an electrode as described above.

The lithium secondary battery may extend the life of the lithium secondary battery by preventing the consumption of lithium and suppressing or minimizing side reactions between the lithium and the electrolyte due to the polymer protective layer formed in the electrode.

Preferably, the lithium secondary battery according to the present invention may be a lithium metal battery whose negative electrode is lithium metal.

In this case, the separation membrane may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate that is typically used in an electrochemical device. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is specifically limited thereto. It is not.

The separator is polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, It may be a porous substrate composed of any one selected from the group consisting of polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate or a mixture of two or more thereof.

The lithium secondary battery electrolyte is a non-aqueous electrolyte consisting of a non-aqueous organic solvent electrolyte and a lithium salt as a lithium salt-containing electrolyte, and may include, but are not limited to, an organic solid electrolyte or an inorganic solid electrolyte.

The non-aqueous organic solvent is, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2 Dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, Diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolane derivatives, sulfolane, methylsulforane, 1,3- Aprotic organic solvents such as dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, Li (FSO ₂ ) ₂ N LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiC At least one lithium salt selected from the group consisting of (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carbonate, lithium phenyl borate imide, and combinations thereof Can be.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

Lithium secondary battery according to the present invention, in addition to the winding (winding) which is a general process, the lamination (stacking) and folding (folding) process of the separator and the electrode is possible. The battery case may be cylindrical, square, pouch type, or coin type.

Hereinafter, preferred examples are provided to help the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and various changes and modifications within the scope and spirit of the present invention are apparent to those skilled in the art. It goes without saying that changes and modifications belong to the appended claims.

EXAMPLE

Example  1: Manufacturing of Lithium Secondary Battery

In order to evaluate battery performance according to the use of the polymer protective film according to the present invention, a lithium / lithium battery (symmetric cell) using both lithium and negative electrodes was prepared.

A negative electrode was prepared by laminating a lithium metal foil on a copper foil and forming a polymer protective film thereon. At this time, the lithium metal foil was used as the positive electrode.

To prepare a polymer protective film, polyethylene oxide (MV: 4,000,000) and lithium bis (fluorosulfonyl) imide (LiFSI, Li (FSO ₂ ) ₂ N) were added to an acetonitrile solvent in EO: Li = 5: 1 (EO : A repeating unit of PEO) to prepare a polymer electrolyte solution. To the solution was added 10 parts by weight of polyethylene glycol diacrylate and 1 part by weight of BPO (benzoyl peroxide) as an initiator with respect to 100 parts by weight of the polymer electrolyte, followed by solution casting (by solution casting method) on a free-standing film (3 μm). Was prepared. The film was cured in a vacuum oven at 100 ° C. for 24 hours to prepare a polymer protective film having a crosslinked network, and then laminated on a lithium negative electrode.

After inserting an electrode assembly having a polyolefin-based porous membrane between the prepared negative electrode and the positive electrode in a pouch-type battery case, a non-aqueous electrolyte (1M LiFSI, DOL: DME = 1: 1 (volume ratio)) was injected into the battery case. After that, a lithium secondary battery was manufactured by completely sealing.

Comparative example  1: Manufacturing of Lithium Secondary Battery

A battery was manufactured in the same manner as in Example 1, except that the polymer protective layer was not formed.

Comparative example  2: Manufacturing of Lithium Secondary Battery

A battery was manufactured by performing the same method as Example 1 without forming a crosslinked network structure as a polymer protective film.

As the polymer protective film, polyethylene oxide (Mw: 4,000,000) and LiFSI were mixed with EO: Li = 5: 1 (EO: PEO repeating unit) in an acetonitrile solvent to prepare a polymer electrolyte solution, followed by solution casting on PTFE. A free-standing film (3 μm) was prepared. The film was dried in a vacuum oven at 100 ° C. for 24 hours to prepare a polymer protective film in which no crosslinked network was formed, and then laminated on a lithium negative electrode.

Experimental Example  1: Lithium Secondary Battery Performance Evaluation

The electrochemical characteristics of the lithium secondary batteries prepared in Examples and Comparative Examples were measured, and the results are shown in FIGS. 1 and 2.

1 is a graph showing a change in E / V (efficiency / voltage) characteristics with time of the battery prepared in Examples and Comparative Examples, wherein (a) is Comparative Examples 1, (b) is Comparative Examples 2, (c ) Shows Examples 1 and (d) comparing the batteries prepared in Comparative Example 1 and Example 1.

Referring to FIG. 1, it can be seen that the case (c) having the electrode having a network structure crosslinked according to the present invention has a greatly improved lifespan characteristic compared to the case of Comparative Examples 1 (a) and 2 (b). Can be. In particular, it can be seen that the difference is more clearly seen in FIG. In addition, comparing (b) and (c) of FIG. 1, it can be seen that the battery characteristics are significantly improved in the crosslinked network structure even when the polymer protective film is formed.

These results show that in the case of the battery of Example 1, the oxidation and reduction reaction of lithium occurs uniformly on the electrode surface for a long time during the charge / discharge process of the battery, and the polymer protective film suppresses the growth of lithium dendrite and the electrolyte according to the present invention. It can be seen indirectly that decomposition of is suppressed.

Figure 2 is a graph comparing the efficiency of the battery prepared in Example 1, Comparative Example 1 and Comparative Example 2, the case of the battery of Example 1 of the present invention that the efficiency is further improved compared to the batteries of Comparative Examples 1 and 2 Able to know.

Claims (12)

Electrode current collectors;
An electrode mixture layer formed on one or both surfaces of the electrode current collector and including lithium; And
It includes a polymer protective film formed on the electrode mixture layer,
The polymer protective film is a lithium secondary battery electrode comprising a high concentration of lithium salt and polyethylene oxide of 4M to 6M in the crosslinked polyalkylene glycol diacrylate network. delete The method of claim 1,
The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, Li (FSO ₂ ) ₂ N LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ An electrode for a lithium secondary battery comprising at least one member selected from the group consisting of NLi, chloroborane lithium, lower aliphatic lithium carbonate, lithium 4-phenyl borate imide, and combinations thereof. The method of claim 1,
The polyethylene oxide is a lithium secondary battery electrode, characterized in that the weight average molecular weight of 1,000,000 to 5,000,000. The method of claim 1,
The polyalkylene glycol diacrylate is a lithium secondary battery electrode, characterized in that it comprises one selected from the group consisting of polyethylene glycol diacrylate, polypropylene glycol diacrylate, and combinations thereof. The method of claim 1,
The polymer protective film is a lithium secondary battery electrode, characterized in that it comprises polyalkylene glycol diacrylate at 50 parts by weight or less based on 100 parts by weight of polyethylene oxide. The method of claim 1,
The electrode is a lithium secondary battery electrode, characterized in that the positive electrode, the negative electrode or these positive electrode. The method according to claim 1 or 7,
When the electrode for a lithium secondary battery is a negative electrode,
The electrode mixture layer is a lithium secondary battery electrode, characterized in that it comprises one selected from the group consisting of lithium metal alone or alloys thereof, lithium-containing oxide, lithium-containing titanium composite oxide and combinations thereof. The method according to claim 1 or 7,
When the electrode for a lithium secondary battery is a positive electrode,
The electrode mixture layer is in the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium copper oxide, vanadium oxide, lithium nickel-based oxide and lithium manganese composite oxide, lithium-nickel-manganese-cobalt-based oxide, and combinations thereof Lithium secondary battery electrode, characterized in that it comprises one selected. The method of claim 1,
The lithium secondary battery electrode is a lithium secondary battery electrode, characterized in that the negative electrode of the lithium metal battery electrode. In a lithium secondary battery comprising a separator and an electrolyte interposed between a positive electrode, a negative electrode or these positive electrodes,
Any one of the positive electrode, the negative electrode or the positive electrode comprises a lithium secondary battery electrode according to claim 1. The method of claim 11,
The lithium secondary battery is a lithium secondary battery, characterized in that the lithium metal battery.

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