KR102038546B1 - Separator for lithium secondary battery and lithium secondary battery employing the same - Google Patents

Abstract

The present invention relates to a separator having a multilayer structure for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a separator having a multilayer structure prepared by stacking and bonding two or more kinds of separator sheets oriented with lithium ion channels. As a result of the introduction into a lithium secondary battery by using as a separator capable of being stored, the performance and lifespan of the battery are increased since the phenomenon in which the aqueous or non-aqueous electrolytes used for both electrodes do not mix with each other does not occur.

Description

Separator for lithium secondary battery and lithium secondary battery comprising same {Separator for lithium secondary battery and lithium secondary battery employing the same}

The present invention relates to a separator having a multilayer structure in which a separator sheet is stacked 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 has been in progress, and lithium secondary batteries have been in the spotlight as batteries that 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 laminated or wound, and the electrode assembly is built in a battery case and an electrolyte is injected therein. The charging and discharging of electrical energy occurs by oxidation and reduction reaction when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.

Separation membrane is one of the core materials of the battery, and it is located between the positive and negative electrodes of the battery, so that lithium oxide, a highly active positive electrode material, reacts directly with the negative electrode and separates it so that it does not lead to explosion. In addition, since the electrodes are positioned between the two electrodes, the pores are developed to smoothly move lithium ions between the electrodes.

In addition, secondary batteries including high energy density and large capacity lithium ion secondary batteries, lithium ion polymer batteries, and supercapacitors (electric double layer capacitors and similar capacitors) must have a relatively high operating temperature range and continuously maintain high rate charge and discharge conditions. Since the temperature rises when used, the separators used in these batteries are required to have higher heat resistance and thermal stability than those required for ordinary separators. In addition, it should have excellent battery characteristics such as high ion conductivity that can cope with rapid charging and discharging and low temperature.

The separator is positioned between the anode and the cathode of the battery to insulate it, maintains the electrolyte to provide a path for ion conduction, and when the temperature of the battery becomes too high, a part of the separator melts to block pores in order to block the current. Have

On the other hand, various battery types have been proposed in the meantime in order to improve characteristics such as capacity, lifespan, and stability of lithium secondary batteries.

For example, as lithium secondary batteries, batteries in which electrode materials such as lithium-sulfur batteries, lithium air batteries, and zinc air batteries are converted have been proposed, and when a single electrolyte is used during repeated charging / discharging of lithium secondary batteries, either side of the battery is driven. In order to improve the problem that the battery performance is not exhibited by continuously eluting the electrode, it is proposed to use two electrolytes that are most effective for each of the positive electrode and the negative electrode.

In 2010, the H. Zhou group proposed a lithium-air battery using this multilayer electrolyte.

The proposed lithium-air battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator, and two kinds of electrolytes are used to distinguish the positive and negative electrolytes.

That is, an organic electrolyte is used to prevent precipitation reaction of lithium oxide and the like from the positive electrode (air electrode) as the positive electrode electrolyte, and an aqueous alkali solution such as KOH is used as the negative electrode electrolyte, and lithium ion has conductivity between the two electrolytes. Solid electrolyte separator is used.

Through such a system, it is disclosed that there is no deposition of lithium oxide at the anode and high discharge capacity is achieved.

However, new problems have arisen due to the miscibility of the aqueous or non-aqueous electrolytes used as the positive and negative electrolytes, respectively.

In other words, the positive and negative electrolytes are separated by a separator, but the respective electrolytes are mixed with each other in and outside the separator, and in some cases, the negative electrolyte contacts the positive electrode and vice versa, resulting in the performance of the lithium secondary battery. As a result of the problem of shortening the lifespan, it is necessary to solve the structural problem of the separator which can separate the two electrolytes from each other.

International Publication No. 2014-0141726 "Novel cathode for use in battery" Japanese Laid-Open Patent Publication No. 2008-004500 "Polar membrane for fuel cell electrolyte and its manufacturing method"

In order to solve the above problems, the present inventors have conducted various studies to manufacture a separator having a new structure, and when the lithium ion conductive separators are laminated to each other and thermally compressed, the present inventors can control the direction of internal pores and channels of the separator. As a result of introducing a separator of a layer by layer arranged by crossing the directions of the lithium ionic channel as a separator of a lithium secondary battery, two electrolytes and by-products do not mix without a decrease in lithium ion conductivity. It was confirmed that the performance and life of the battery is increased to complete the present invention.

Accordingly, an object of the present invention is to provide a separator having a multilayer by layer in which a separator sheet having lithium ionic channels of different orientations is stacked and a lithium secondary battery including the same. The solution is to improve the performance and life of the battery.

In order to achieve the above object, the present invention includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode, the separator has a structure in which the separator sheet is laminated in a multi-layer, wherein the separator sheet is the orientation of the lithium ion channel The lithium secondary battery is provided so that the directions are the same or different from each other.

In this case, the multilayer structure may be two layers or two or more layers, and preferably two to three layers.

In addition, the multi-layered structure is characterized in that the orientation direction of the lithium ion channel by pressing and stretching the separator sheet for each layer is laminated differently.

At this time, the lithium secondary battery is characterized by using an electrolyte of different composition as the electrolyte contacting the positive electrode and the negative electrode.

The lithium secondary battery according to the present invention is selected according to the characteristics of the positive electrode and the negative electrode when driving the battery so that the two electrolytes used in both electrodes are not mixed with each other (immiscible) increases the performance and life of the battery.

1 is a cross-sectional view showing a lithium secondary battery according to an embodiment of the present invention.
2 is an image showing a separator according to an embodiment of the present invention.
3 is an image showing the structure of a separator according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The lithium secondary battery according to the present invention has a structure in which two different electrolytes are separated by a multilayer membrane.

Referring to FIG. 1, the lithium secondary battery 100 includes a positive electrode 11 and a negative electrode 12, and has a structure in which electrolytes 13 and 14 and a separator 15 are disposed therebetween.

The electrolytes 13 and 14 include a cathode electrolyte 13 in contact with the anode 11 and a cathode electrolyte 14 in contact with the cathode 12, and these electrolytes prevent decomposition of the electrodes 11 and 13. Alternatively, a specific composition may be used to prevent side reactions caused by the materials of the electrodes 11 and 13.

The separator 15 functions to prevent direct contact between the positive electrode 11 and the negative electrode 12, and selectively transfers only lithium ions present in the electrolyte. However, when the battery is charged / discharged, a compound generated in the positive electrode (positive / negative electrode) and each electrolyte are mixed with each other inside or outside the separator 15 or cross with both poles.

This problem does not need to be greatly considered when the electrolyte is used in one type, but when an effective electrolyte is independently used for each electrode to improve battery performance, the composition of each electrolyte or crossover occurs at both poles. The problem that the battery performance deteriorates occurs. For example, in the case of a lithium-sulfur battery, a problem such as by-products such as lithium polysulfide generated at the positive electrode is passed through the separator to the negative electrode.

Accordingly, in the present invention, in the lithium secondary battery using different electrolytes, a structure of the separator 15 having a multilayer structure that prevents mixing or crossover of electrolytes and selectively delivers only lithium ions while driving the battery is provided.

Preferably, the separator 15 according to the present invention is formed of an ion channel in the membrane structure, a material having lithium ion conductivity, and more preferably lithium ion conductor (lithium ionic conducting), It is made of a polymer having a lithium ionic channel, or a lithium ionic transfer channel, which may be a porous membrane including pores in the membrane structure.

Channels and internal pores in which lithium ions are present in each of the separators 15 are transferred to control the thermal fusion or thermocompression process in the manufacturing process to have alignment directions of the internal pores and the channels. In this case, when the multilayer membrane 15 is manufactured, the alignment directions of the lithium ion channels present in the individual separators 15 are arranged to be the same or different from each other. Lithium ions move between the separator and the separator by hopping and selectively block the movement of electrolytes and by-products located at each electrode, thereby fundamentally preventing, delaying, or reducing the exchange or crossing of electrolytes. .

2 is an image showing the separator 15 according to an embodiment of the present invention, Figure 3 is an image showing the structure of the separator 15 according to another embodiment of the present invention. In FIG. 2, a separator having a two-layer structure is provided for convenience, but each separator may have a multilayer structure having two or more layers.

As shown in Figures 2 and 3, the separator 15 according to the present invention has a multilayer structure in which two or more separator sheets are stacked in multiple layers, wherein the separator sheet has a lithium ion channel therein. When the multilayer structure is formed, the lithium ion channel is laminated by thermal fusion or thermal compression to change the orientation direction of the lithium ion channel. As a result, the separator 15 can control the orientation direction of the ion channels in the different separators 15 without reducing the lithium ion conductivity due to the multilayer structure, through which the two electrolytes 13 and 14 are mixed. Characterized in that can block the phenomenon.

The separator 15 according to the present invention serves as a reservoir of the electrolyte so that the electrolytes 13 and 14 are separated by the separator 15 so that the mixing phenomenon of the conventional electrolytes 13 and 14 does not occur. Increases its performance and lifespan.

The separator 15 may be any polymer substrate that is usually manufactured by an stretching process, which is a separator material of an electrochemical device. More specifically, polyethylene (high density polyethylene, low density polyethylene, linear low density polyethylene, high molecular weight polyethylene, etc.), polypropylene, polybutylene, polypropylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, Polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidenedifluoride, cellulose, polyvinylchloride And one or two or more selected from the group consisting of a combination thereof is possible, and commercially available products include Lithiated Nafion.

The thickness of the separator 15 is not particularly limited, but is preferably in the range of about 1 to about 100 μm, more preferably in the range of about 5 to about 30 μm. It is also desirable to have a porosity of about 10 to about 80%.

The separation membrane 15 according to the present invention is characterized in that two or more sheets of the separator sheet are stacked and bonded to each other in a structure in which two or more sheets of the separator sheet are arranged or crossed in the same direction in two different directions including the same direction or an orthogonal direction.

Hereinafter, a method of manufacturing the separator 15 according to the present invention will be described. This is to aid the understanding of the present invention, the scope of the present invention is not limited thereto, and the present invention should be understood to cover all ranges equivalent to the following contents.

The method of manufacturing the separator 15 according to the present invention comprises the steps of stacking two or more sheets of separator sheets in a structure in which two or more sheets of separator sheets are arranged or crossed in two different directions including the same direction or an orthogonal direction and the stacked separator sheets. It characterized in that it comprises at least a step of bonding.

In the present invention, the resin material serving as the starting material of the separation membrane 15 may be a resin material used as a conventional electrolyte membrane. Preferably, it is easy to form lithium ion channels due to excellent orientation of molecular structure by stretching. One resin material is particularly preferred.

A separator sheet is manufactured using such a resin material, and the preparation of the separator sheet is not particularly limited in the present invention, and may be manufactured through a known method. For example, the separator sheet may be prepared by dissolving a resin material in a solvent to prepare a coating solution, followed by a casting method of drying the substrate after wet coating, or by preparing a coating solution after forming the sheet. The wet coating may include gravure coating, curtain coating, dip coating, slot-die coating, spray coating, continuous nozzle coating, and doctor. Methods such as doctor blade coating may be used, but are not limited to such.

In particular, the present invention performs a pressing or stretching process to control the orientation of the micropores and / or lithium ion channels.

Pressurization uses a press device, and a separator is mounted between a pair of hot plates or a press plate, and then compressed and fastened to orient the lithium ion channel in the separator 15 in one direction. At this time, the pressure or heat applied to the hot plate or the press plate is adjusted to facilitate the orientation of the lithium ion channel. For example, 1.02 to 10 times the predetermined length unit (width) of the separator 15, preferably 1.1 to 5 times. If the extension is less than the above range, it is impossible to secure the orientation of the lithium ion channel in one direction, and if the extension exceeds the range, the thickness of the separator 15 is reduced, making it difficult to use the battery. In addition, when pressurized by a hot plate, it is preferable to perform at a temperature below Tg so that thermal fusion or deformation of the material of the separator 15 may not be made in consideration of the material of the separator 15. As an example, 10 seconds to 1 hour, preferably 30 seconds to 30 minutes, more preferably 1 minute to 15 at a pressure of 1 to 50 MPa, preferably 2 to 30 MPa, more preferably 3 to 20 MPa. Apply pressure for minutes.

In addition, pore alignment is possible through the stretching process, it is preferable to perform uniaxial stretching to proceed in one direction, and stretching in the biaxial direction in consideration of mechanical properties can be used without limitation. The stretching process is not limited in the present invention and may be a dry stretching or wet stretching method known in the art, for example, 1.01 to 15 times, preferably 1.1 to 5 times stretching at a temperature of 20 ℃ to 80 ℃ It may also be carried out by dry stretching at magnification.

The separator sheet in which the lithium ion channel is oriented by the pressurization or stretching is usually converted from a sheet having a transparency of 70% or more to a less opaque sheet, and the change of the transparency confirms that the lithium ion channel is oriented in one direction. Can be.

The separator 15 according to the present invention is produced by stacking two or two sheets of the separator sheets so as to cross each other, and bonding the sheets together by a suitable method such as thermocompression bonding. In this case, the angle of crossing the separator sheet may be greater than 0 ° and 180 ° or less, preferably 45 ° to 135 °, in the orientation direction of the lithium ion channel of the separator sheet adjacent to the lithium ion channel direction reference of one separator sheet. More preferably 75 ° to 105 °, most preferably 90 ° ± 10 °.

Bonding of the laminated separator sheets is preferably thermally fused at a temperature equal to or higher than the melting point of the laminated separator sheets, but is not limited thereto, and may be achieved by crimping by hot pressing or by interfacial fiberization by stretching in a sheet laminated state. Due to the flexibility of the bonding method, or the separator sheet, a wet adhesion method such as adding a liquid phase between the sheets may also be employed. Here, the method of increasing the adhesion of an interface may be more preferable by thermocompression bonding at the temperature below melting | fusing point before extending | stretching.

The separator 15 manufactured by the above method exhibits high heat resistance and thermal stability, and electrolytes 13 and 14 contacting the positive electrode 11 and the negative electrode 12 are separated from the separator 15 without reducing ion conductivity when the battery is driven. Mixing with each other does not occur through the battery, which increases battery performance and lifespan.

Since the process of drawing the separation membrane 15 and the bonding process between the sheets is well known in the art, a description thereof will be omitted herein.

On the other hand, the positive electrode 11, the negative electrode 12, the electrolyte 13, 14 constituting the lithium secondary battery 100 is not limited in the present invention, including the contents described below, what is known in the art Follow.

The electrode may be a positive electrode 11, a negative electrode 12, or both positive electrodes, and has a structure in which a positive electrode active material or a negative electrode active material is stacked on an electrode current collector.

The electrode current collector is a positive electrode current collector when the electrode is a positive electrode 11, 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 changes in the battery. Examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon or nickel on the surface of aluminum or stainless steel. Surface treated with titanium, silver, or the like can be used. In this case, 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, etc., in which fine unevenness is formed on the surface so as to increase the adhesive strength 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. Examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and carbon on the surface of 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 includes any one lithium transition metal oxide selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium copper oxide, lithium nickel oxide, lithium manganese composite oxide, and lithium-nickel-manganese-cobalt oxide. More specifically, lithium manganese oxides such as Li _{1+ x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; 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 , wherein 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. Among cathode materials of lithium air batteries or lithium sulfur batteries known as next-generation batteries, sulfur-based sulfur and carbon-based conductive materials may be included or polymeric sulfur.

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, Li _x Fe ₂ O ₃ (0 ≦ x ≦ 1) or Li _x WO ₂ (0 <x ≦ 1).

In addition, the negative electrode active material is Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, group 1, 2, 3 of the periodic table) Metal complex oxides such as an element, a 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 , 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.

Here, 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. Examples of the conductive material 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 that inhibits 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. For example, olefinic polymers such as polyethylene and polypropylene, and fibrous materials such as glass fibers and carbon fibers are used.

In particular, in the lithium secondary battery 100 of the present invention, the electrolytes 13 and 14 in contact with the positive electrode 11 and the negative electrode 12 have different compositions.

That is, when driving the lithium secondary battery 100, a different kind of problem occurs in each of the positive electrode 11 and the negative electrode 12 depending on the material of each electrode. Accordingly, when the electrolytes 13 and 14 optimized for the positive electrode 11 and the negative electrode 12 are selected and used, problems occurring in each of the positive electrode 11 and the negative electrode 12 can be solved. In this case, although there is a problem of mixing or crossing the electrolytes 13 and 14, the problem may be fundamentally blocked due to the use of the separator 15 as described above.

Specifically, the electrolytes 13 and 14 may be aqueous or non-aqueous electrolytes as lithium salt-containing electrolytes, and preferably non-aqueous electrolytes consisting of an organic solvent electrolyte and a lithium salt. In addition, an organic solid electrolyte or an inorganic solid electrolyte may be included, but is not limited thereto.

The non-aqueous electrolyte includes a non-aqueous organic solvent and a lithium salt.

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, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2 One or more aprotic organic solvents such as imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

In this case, an ether solvent is used as the non-aqueous organic solvent to be similar to the electrode protective layer of the present invention. Specifically, tetrahydrofuran, ethylene oxide, 1,3-dioxolane, 3,5-dimethyl isoxazole, 2,5- Dimethylfuran, furan, 2-methylfuran, 1,4-oxane, 4-methyldioxolane and the like are used.

Lithium salt is a good material to dissolve in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, chloroborane lithium, Pyridinium, imidazolium, pyrrolidinium, ammonium, with lower aliphatic lithium carbonate, lithium tetraphenyl borate, lithium imide, N, P, S, etc. An ionic liquid electrolyte composed of organic cations such as phosphonium and sulphonium, and inorganic or organic anions may be used.

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

As the inorganic solid electrolyte, for example, 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 , Li Nitrides, halides, sulfates, and the like of Li, such as ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ , may be used.

In addition, for the purpose of improving charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, 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 and the like can be added. have. 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.

According to a preferred embodiment of the present invention, the lithium secondary battery may be a lithium-sulfur battery including a negative electrode of lithium metal and a positive electrode of sulfur.

Specifically, the negative electrode 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.

The anode may include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof, and these compounds are applied in combination with a conductive material because sulfur material alone is not electrically conductive. Specifically, the sulfur-based compound may be Li ₂ S _n (n ≧ 1), an organic sulfur compound, or a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≧ 2), or the like.

Lithium-sulfur battery produces lithium polysulfide (Li ₂ S _x , x = 2 ~ 8) during discharge by reduction reaction of sulfur at positive electrode during battery operation, which dissolves in electrolyte and diffuses to negative electrode causing various side reactions do. In the case of using the separator 15 according to the present invention, only lithium ions are selectively moved by lithium ion channels, and diffusion of lithium polysulfide from the positive electrode to the negative electrode is prevented.

As the separator 15 for preventing diffusion of the lithium polysulfide, a separator 15 having a two-layer structure in which a separator sheet is stacked in two layers is used. In this case, the separator sheet may be made of Nafion, and the separator sheet may be disposed such that lithium ion channels cross at 90 ° to prepare a separator 15.

In this case, as the electrode electrolytes 13 and 14, a non-aqueous solvent as described above or a one-component, two-component or ternary mixed solvent containing a cyclic ether / linear ether selected from known bars is used.

For example, 1,3-dioxolane may be disposed on the negative electrode and 1,2-dimethoxyethane on the positive electrode, or a binary system in which the two are mixed may be disposed on the negative electrode and the positive electrode, respectively. At this time, when used as a two-component system can be used by varying the volume ratio of each solvent, for example, freely used within the volume ratio range of 1:10 to 10: 1.

In the lithium-sulfur battery having such a configuration, when a separator having a two-layer structure is used, lithium ions are selectively moved and the lithium polysulfide is prevented from moving, thereby increasing the cycle efficiency of the battery.

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

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example  One

In order to limit the movement of the electrolyte and by-products except for lithium ions, a lithium ion conductive separator was applied to the lithium ion conductive separator by applying temperature and pressure, respectively.

First, a Nafion separator, a typical membrane, was prepared by heating a 3 wt% hydrogen peroxide solution and heating at 80 ° C. for 1 hour, and then boiled in a 1 M sulfuric acid solution using the same temperature and time. Subsequently, the resultant was washed with distilled water, and the Nafion membrane was taken out to remove water, and then placed in 1M aqueous LiOH solution and stirred for 1 day to carry out lithiation.

Then, after the water was removed, it was left in the desiccator overnight to remove residual moisture. Next, each of the membranes were put in a pressing machine set at 112 ° C. and pressurized at 8 M Pa pressure for 10 minutes. The transparent membrane finally prepared by this pressurization was turned into an opaque membrane, and the membranes were prepared by applying pressure once again by crossing each of the changed membranes by 90 °.

Comparative example  One

Nafion membrane was prepared by heating a 3 wt% hydrogen peroxide solution at 80 ℃ boiled for 1 hour, and then boiled in 1M sulfuric acid solution using the same temperature and time. Subsequently, after washing with distilled water, the Nafion membrane was taken out to remove water, and then placed in a 1M LiOH aqueous solution and stirred for 1 day to carry out lithiation.

Subsequently, after removing water, the resultant was allowed to stand overnight in a desiccator to remove residual moisture to prepare a transparent membrane.

Experimental Example  One

The electrical conductivity of the separator prepared in Example 1 and Comparative Example 1 was measured by using an electrical conductivity tester (Electric Conductivity Tester), the results obtained are shown in Table 1 below.

Example 1 Comparative Example 1 Conductivity (S / cm) 0.076 0.083

According to Table 1, in the case of Example 1 in which the lithium ion channel is oriented in one direction, the electrical conductivity tended to decrease slightly compared to the separator of Comparative Example 1, but it had a sufficient level of electrical conductivity to be used as the separator. Able to know.

Experimental Example  2

After separating the two membranes prepared in Example 1 by 90 degrees, a separator (diameter 14 mm) was prepared by applying pressure. In addition, two separators prepared in Comparative Example 1 were punched out in the same manner.

Each prepared membrane was assembled into a cell for permeability experiment, and one side was injected with DOL / DME (1: 1 mixed volume ratio) electrolyte and one side with lithium polysulfide and DOL / DME (1: 1 mixed volume ratio).

As a result of leaving the assembled permeate cell at 25 ° C. for 3 hours, in the case of the cell with the separator of Comparative Example 1, a phenomenon in which the transparent electrolyte became red due to the movement of lithium polysulfide was observed. It can be seen that it is moved.

In comparison, in the case of the cell having the separator of Example 1, no change was observed, and thus, lithium polysulfide was not moved.

Experimental Example  3

In order to confirm the battery characteristics of the lithium secondary battery provided with a separator of the present invention, a lithium symmetric cell was manufactured.

After the separators prepared in Example 1 and Comparative Example 1 were interposed between lithium foils having a thickness of about 40 μm, an electrolyte solution in which 1M LiFSI salt was dissolved in DOL / DME (1: 1 mixed volume ratio) solvent was prepared. Injected to produce a lithium symmetric cell.

The cycle efficiency in the battery prepared above was measured. Cycle efficiency was 1C rate and depth of discharge (DOD: depth of discharge) to calculate the cycle efficiency by repeating charging and discharging 50 times at 83% condition, the results are summarized in Table 2 below.

Example 1 Comparative Example 1 Cycle efficiency 98.5% 97.0%

Referring to Table 2, in the case of a battery having a separator in which lithium ion channels are oriented according to the present invention, it can be seen that high battery efficiency is maintained for 50 cycles.

In comparison, it can be seen that the battery efficiency of the battery with the separator of Comparative Example 1 is lower than that of the battery with the separator of Example 1.

11: anode 12: cathode
13, 14 electrolyte 15 membrane
100: lithium secondary battery

Claims (10)

A positive electrode, a negative electrode, and a separator and an electrolyte interposed therebetween,
The electrolyte is composed of a cathode electrolyte in contact with the anode, a cathode electrolyte in contact with the cathode, the cathode electrolyte and the cathode electrolyte has a different composition,
The separator has a structure in which a lithium ionized Nafion separator sheet is thermally compressed at a temperature below Tg to convert transparency to less than 70% to laminate a separator sheet in which lithium ion channels are oriented in multiple layers, wherein the separator sheet is lithium ion. The lithium secondary battery, characterized in that the orientation of the channels are arranged differently, to prevent mixing or crossing of the electrolyte and to selectively transfer only lithium ions. The method of claim 1,
The separator is a lithium secondary battery, characterized in that the orientation of the lithium ion channel direction of the separator sheet adjacent to the lithium ion channel direction of one separator sheet so as to have a 45 ° to 135 °. The method of claim 1,
The separator is a lithium secondary battery, characterized in that the separator sheet is laminated in two layers or two or more layers. delete delete delete The method of claim 1,
The separator is a lithium secondary battery, characterized in that the thickness of 0.1 to 100 ㎛. delete delete The method of claim 1,
The electrolyte is a lithium secondary battery, characterized in that the aqueous or non-aqueous electrolyte.

Images