KR20160079634A - Separator for lithium ion secondary battery and preparation method thereof - Google Patents

Abstract

Provided is a separator for a lithium ion secondary battery to realize good battery performance (cycle property) without preventing the movement of lithium ions between electrodes. The separator for a lithium ion secondary battery is a separator for a lithium secondary battery made of modified micro cellulose fiber having carboxyl radicals on a surface. The counter lithium ions of carboxyl radicals include lithium ions. In the counter ions, the weight of residual counter ions to all the lithium ions is 10 wt% or less. The average void diameter is 0.05μm to 1μm.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator for a lithium ion secondary battery, and a separator for a lithium ion secondary battery,

The present invention relates to a separator for a lithium ion secondary battery and a method for producing the same.

Secondary batteries are widely used in mobile electronic devices, electric vehicles, hybrid vehicles, and the like. Particularly, a lithium ion secondary battery has been actively developed due to its high energy density.

At present, as a separator of a lithium ion secondary battery, a polyolefin-based microporous membrane which is chemically stable at low cost and excellent in mechanical characteristics is used. However, since the polyolefin-based microporous membrane has a problem in heat resistance, a method of applying ceramic particles or chemical crosslinking has been studied to supplement it. However, in this method, there is a problem that the cost is increased because a step of applying the coating on the microporous film is added.

For this reason, the use of a material having high heat resistance has been studied. Particularly, cellulose has attracted attention because it is a material derived from wood that is thermally stable up to about 300 캜 and can be regenerated.

When conventional pulp is used as the cellulose, there is a problem that it is difficult to reduce the thickness of the separator. There has been proposed a method of finely physically defibrating cellulosic fibers (microfibrillated cellulose, MFC) (see, for example, Patent Document 1).

However, by merely defibrating the cellulose fibers, the fiber diameters do not become uniform. Further, since large fibers are mixed, there is a problem that large pores are partially formed. In addition, there is a problem in that the strength is lowered because the number of contacts contacting by cellulose bonds between the cellulose fibers by hydrogen bonding is reduced.

Therefore, in order to solve such a problem, a separator using cellulose fibers having unified fiber length has been proposed. More specifically, a separator using microcellulose fibers having a constant fiber diameter is disclosed by oxidizing cellulose having an I-form crystal structure using an N-oxyl compound (see, for example, Patent Document 2 ).

Patent Document 1: Japanese Patent Publication No. 5445885

Patent Document 2: JP-A-2013-251236

However, in the separator described in Patent Document 2, the counter ion in the case where the surface of the microcellulose is oxidized to a carboxyl group is sodium ion. Therefore, in the lithium ion secondary battery, the sodium ion is an inhibiting factor when the lithium ion moves.

In addition, since water is used as a solvent and cellulose is dispersed in such water to form a film, the cellulose is coagulated by hydrogen bonding at the time of drying to form a dense film. As a result, good ion migration (for example, lithium The movement of ions) is hindered.

Accordingly, one aspect of the present invention has been made in consideration of this point, and it is an object of the present invention to provide a lithium ion secondary battery separator capable of realizing good cell performance (for example, cycle characteristics) without inhibiting the movement of lithium ions between electrodes The purpose is to provide.

According to one embodiment,

A lithium battery separator comprising modified microfibrillated cellulose having a carboxyl group on its surface,

Wherein the counter ion of the carboxyl group comprises lithium ion,

The weight of other metal ions relative to the total lithium ion is 10 wt% or less with respect to the counter ion,

There is provided a separator for a lithium ion secondary battery having an average pore diameter of 0.05 mu m to 1 mu m or less.

According to another embodiment,

anode; cathode; And

And a separator according to the above, which is disposed between the positive electrode and the negative electrode.

According to another embodiment,

Preparing a solution containing a modified microcellulose fiber having a carboxyl group on its surface, a hydrophilic solvent having a boiling point of 100 to 160 DEG C, and water;

Applying the solution onto a substrate;

Drying a solution applied on the substrate to prepare a paint film; And

And separating the film from the base material.

According to one aspect, by using the new separator for a lithium battery, good battery performance can be realized without inhibiting the movement of lithium ions between the electrodes.

1 is a schematic diagram of a lithium battery according to an exemplary embodiment.
Description of the Related Art
1: Lithium battery 2: cathode
3: anode 4: separator
5: Battery case 6: Cap assembly

Hereinafter, a separator for a lithium ion secondary battery according to exemplary embodiments and a method of manufacturing the separator will be described in more detail.

The separator for a lithium battery according to an embodiment is formed by modified (i.e., chemically treated) microcellulose fibers (cellulose nanofiber).

Wherein the separator for a lithium battery is a separator for a lithium battery including modified microfibrillated cellulose having a carboxyl group on its surface, wherein counter ions of the carboxyl group include lithium ions, and in the counter ion, The weight of the metal ion other than lithium relative to the total ion is 10 wt% or less, and the average pore diameter is 0.05 탆 to 1 탆 or less.

The heat resistance is improved by the modified microcellulose fiber of the separator for a lithium battery, and the lithium ion conductivity is improved by mainly containing lithium ions as counter ions of the carboxyl group, and the average pore diameter is 0.05 탆 to 1 탆, It is easy to move the electrolyte including ions.

Hereinafter, the lithium battery separator will be described in more detail.

(Modified microcellulose fiber)

In one embodiment, modified microfibrillated cellulose (MFC) is used as the material forming the separator. Such a modified microcellulose fiber is a cellulose having an I-form crystal structure in which the molecular chain (hydroxyl group) on the surface of cellulose is oxidized to a carboxyl group by oxidation treatment.

That is, in one embodiment, cellulose microsized by oxidizing the surface of the natural cellulose having the I-form crystal structure is used.

Also, in one embodiment, such an oxidation treatment may be carried out, for example, using an N-oxyl compound (for example, 2,2,6,6-tetramethylpiperidine- 6-tetramethylpiperidine-1-oxyl) radical (hereinafter referred to as "TEMPO").

By performing such an oxidation treatment, it becomes possible to selectively oxidize only the crystal surface of the cellulose fiber while maintaining the crystal structure, and thereafter, by defibrating treatment, the minimum of the natural high crystalline cellulose Unit of cellulose fibers can be obtained.

Further, since it has an I-form crystal structure, it is possible to prevent the cellulose fiber from lowering its strength and dissolving it.

The cellulose used as a raw material for the modified microcellulose fibers is not particularly limited. For example, the natural cellulose is not particularly limited and may be an isolate from the biosynthesis of plants, animals, For example, nonwoven pulp such as softwood pulp, hardwood pulp, cotton linter, invisible pulp such as straw pulp or bagasse pulp, bacterial cellulose or sea squirts , Cellulose isolated from seaweed, and the like.

Examples of the counter ion of the carboxyl group of the modified microcellulose fiber include alkali metals such as lithium ion and sodium ion, ammonium ion and quaternary ammonium ion. And lithium ion as a counter ion of the carboxyl group.

In one embodiment, in the counter ion, the weight of the other metal ion relative to the total lithium ion is 10 wt% or less. For example, for counter ions, the weight of other metal ions relative to the total lithium ion may be 8 wt% or less. For example, for a counter ion, the weight of other metal ions relative to the total lithium ion may be 6 wt% or less. For example, for a counter ion, the weight of other metal ions relative to the total lithium ion may be 4 wt% or less. For example, for a counter ion, the weight of other metal ions relative to the total lithium ion may be less than or equal to 2 wt%. For example, for counter ions, the weight of other metal ions relative to the total lithium ion may be less than or equal to 1 wt%. The reason why the content is limited to 10% by weight or less is that when the content is 10% by weight or more, ion migration of lithium ions is inhibited.

Therefore, since most of the counter ions are lithium ions, and lithium ions can be bonded to the carboxyl groups of the modified microcellulose fibers, unlike the case where the counter ions are ions other than lithium ions (for example, sodium ions) The lowering of the movement of lithium ions between the electrodes is suppressed. As a result, good battery performance (for example, cycle characteristics) can be realized.

Further, in one embodiment, the mean pore diameter of the separator formed by the modified microcellulose fibers is set to be 0.05 탆 or more and 1 탆 or less. For example, the average pore diameter of the separator formed by the modified microcellulose fibers may be 0.1 탆 to 1 탆. For example, the average pore diameter of the separator formed by the modified microcellulose fibers may be 0.1 탆 to 0.8 탆. For example, the average pore diameter of the separator formed by the modified microcellulose fibers may be 0.1 탆 to 0.6 탆. For example, the average pore diameter of the separator formed by the modified microcellulose fibers may be 0.1 탆 to 0.5 탆. With this configuration, the diameter of the pores of the separator through which lithium ions migrate becomes sufficiently large. Therefore, in the step of drying and forming a sheet, which will be described later, deterioration of lithium ion migration caused by agglomeration of the cellulose can be prevented. Particularly, by setting the average pore diameter to be 1 mu m or less, generation of dendrites of lithium ions can be effectively suppressed.

In the present specification, "average pore diameter" means the median diameter of a mercury porosity meter.

The content of the carboxyl group (amount of carboxyl group) in the modified microcellulose fiber is, for example, from 0.1 to 2.5 mmol / g, for example, from 0.3 to 2.0 mmol / g, for example, from 0.5 to 2.0 mmol / Lt; / RTI > This is because when the content of the carboxyl group is less than 0.1 mmol / g, the electrostatic repulsion at the time of defibration is small and the fibrillation property is deteriorated. When the content of the carboxyl group is less than 2.5 mmol / g If it is large, the water solubility of the cellulose may become too large.

The number average fiber length of the modified microcellulose fiber is preferably 0.2 mu m or more to 3 mu m or less, more preferably 0.5 mu m or more to 3 mu m or less, and particularly preferably 1 mu m or more to 3 mu m or less. When the number average fiber length is less than 0.2 m, the fibers may be too short and the mechanical strength of the separator may become weak. When the number average fiber length is more than 3 m, the viscosity of the dispersion becomes too high, It is because there are times when things become worse.

The term "number average fiber length" in the present specification is a value obtained by measuring the number of fibers of the modified microcellulose fiber by thinly casting the modified microcellulose fiber on the substrate, drying the fiber, observing the fiber using an atomic force microscope (AFM) Means the average value of the fiber length.

The number average fiber diameter of the modified microcellulose fibers may be 100 nm or less. For example, the number average fiber diameter of the modified microcellulose fibers may be 50 nm or less. For example, the number average fiber diameter of the modified microcellulose fibers can be 20 nm or less. For example, the number average fiber diameter of the modified microcellulose fibers may be 10 nm or less. For example, the number average fiber diameter of the modified microcellulose fibers may be 5 nm or less. When the number average fiber diameter is larger than 100 nm, the pore diameter distribution of the separator may become large.

The term "number average fiber diameter" in the present specification means a number average fiber diameter obtained by thinly casting a dispersion of modified microcellulose fibers on a substrate, drying the same, observing the resultant using an atomic force microscope (AFM) Means the average value of the fiber diameters.

The tensile strength of the separator may be 100 to 140 MPa. For example, the tensile strength of the separator may be 100 to 130 MPa. For example, the tensile strength of the separator may be between 100 and 120 MPa. For example, the tensile strength of the separator may be 100 to 110 MPa. The separator having the above tensile strength range can maintain excellent durability and can effectively accommodate the expansion and the like of the electrode. The method of measuring the tensile strength is specifically disclosed in Evaluation Example 2 below.

A lithium battery according to another embodiment includes a positive electrode; cathode; And the aforementioned separator for a lithium battery disposed between the positive electrode and the negative electrode. By including the separator, the heat resistance of the lithium battery can be improved and excellent battery characteristics can be provided.

For example, the lithium battery may be a lithium ion battery.

The lithium ion battery can be manufactured, for example, in the following manner.

First, a cathode is prepared.

For example, a negative electrode active material composition in which a negative electrode active material, a conductive material, a binder and a solvent are mixed is prepared. The negative electrode active material composition is directly coated on the metal current collector to produce a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then the film peeled off from the support may be laminated on the metal current collector to produce a negative electrode plate. The negative electrode is not limited to the above-described form, but may be in a form other than the above-described form.

The negative electrode active material may be a non-carbon-based material. For example, the negative electrode active material includes at least one selected from the group consisting of a metal capable of forming an alloy with lithium, an alloy of a metal capable of forming an alloy with lithium, and an oxide of a metal capable of forming an alloy with lithium can do.

For example, the lithium-alloysable metal may be selected from the group consisting of Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloys (Y is an alkali metal, an alkaline earth metal, a Group 13-16 element, (The Y is an alkali metal, an alkaline earth metal, a Group 13 to 16 element, a transition metal, a rare earth element, or a combination element thereof, but not Sn), or the like . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0 <x <2), or the like.

The anode active material may include at least one selected from the group consisting of Si, Sn, Pb, Ge, Al, SiOx (0 <x? 2), SnOy (0 <y? 2), Li ₄ Ti ₅ O ₁₂ , TiO ₂ , LiTiO ₃ , Li ₂ Ti ₃ O ₇ , but it is not limited thereto, and any negative electrode active material used in the technical field can be used.

Also, a composite of the non-carbon based negative active material and the carbon-based material may be used, and in addition to the non-carbon based material, a carbon-based negative active material may be additionally included.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as natural graphite or artificial graphite in the form of non-shaped, flake, flake, spherical or fibrous type, and the amorphous carbon may be a soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, calcined coke, and the like.

As the conductive material, metal powders such as acetylene black, Ketjen black, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, copper, nickel, aluminum and silver, metal fibers, In addition, one or more conductive materials such as polyphenylene derivatives may be used in combination, but the present invention is not limited thereto, and any conductive material may be used as long as it can be used as a conductive material in the related art. In addition, the above-described crystalline carbon-based material can be added as a conductive material.

Examples of the binder include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene and mixtures thereof, and styrene butadiene rubber-based polymers May be used, but are not limited thereto and can be used as long as they can be used as bonding agents in the art.

As the solvent, N-methylpyrrolidone, acetone, water or the like may be used, but not limited thereto, and any solvent which can be used in the technical field can be used.

The content of the negative electrode active material, the conductive material, the binder and the solvent is a level commonly used in a lithium battery. Depending on the application and configuration of the lithium battery, one or more of the conductive material, the binder and the solvent may be omitted.

Next, the anode is prepared.

For example, a cathode active material composition in which a cathode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated on the metal current collector and dried to produce a positive electrode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then the film peeled from the support may be laminated on the metal current collector to produce a cathode plate.

The positive electrode active material may include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide. However, May be used.

For example, Li _a A _1-b B _b D ₂ , wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5; Li _a E _1-b B _b O _{2 -c} D _c wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1); Li _a CoG _b O ₂ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); In the formula of LiFePO ₄ may be used a compound represented by any one:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise an oxide, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a coating element compound of the hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method which does not adversely affect the physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

For example, LiNiO ₂ , LiCoO ₂ , LiMn _x O ₂ x (x = 1, 2), LiNi _1-x Mn _x O ₂ (0 <x <1), LiNi _1-xy Co _x Mn _y O ₂ ? 0.5, 0? Y? 0.5), LiFeO ₂ , V ₂ O ₅ , TiS, MoS and the like can be used.

As the conductive material, the binder and the solvent in the positive electrode active material composition, the same materials as those for the negative electrode active material composition may be used. It is also possible to add a plasticizer to the cathode active material composition and / or the anode active material composition to form pores inside the electrode plate.

The content of the cathode active material, the conductive material, the general binder, and the solvent is a level commonly used in a lithium battery. Depending on the use and configuration of the lithium battery, one or more of the conductive material, general binder, and solvent may be omitted.

Next, the aforementioned separator is inserted between the positive electrode and the negative electrode.

The separator is a separator for a lithium battery comprising modified microfibrillated cellulose having a carboxyl group on its surface as described above, wherein the counter ion of the carboxyl group contains lithium ions, The weight of other metal ions relative to the total lithium ion is 10 wt% or less, and the average pore diameter is 0.05 탆 to 1 탆 or less.

Next, the electrolyte is prepared. The electrolyte may be in a liquid or gel state.

For example, the electrolyte may be an organic electrolyte.

The organic electrolytic solution can be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be any organic solvent that can be used in the art. Examples of the solvent include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , N, N-dimethylformamide, dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, tetrahydrofuran, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or mixtures thereof.

Lithium salts may also be used as long as they can be used in the art as lithium salts. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

Alternatively, the electrolyte may be a solid. For example, boron oxide, lithium oxynitride, and the like, but not limited thereto, and any of them can be used as long as they can be used as solid electrolytes in the art. The solid electrolyte may be formed on the cathode by a method such as sputtering.

Finally, the electrolytic solution is injected between the positive electrode, the negative electrode and the separator disposed therebetween to prepare the lithium ion electromagnetic.

For example, as shown in FIG. 1, the lithium battery 1 includes an anode 3, a cathode 2, and a separator 4. The anode 3, the cathode 2 and the separator 4 described above are wound or folded and housed in the battery case 5. Then, an organic electrolytic solution is injected into the battery case 5 and is sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may have a cylindrical shape, a rectangular shape, a thin film shape, or the like. For example, the lithium battery may be a thin film battery. For example, the lithium battery may be a lithium ion polymer battery.

A separator may be disposed between the anode and the cathode to form a battery structure. The cell structure is laminated or wound in a bi-cellular structure, then impregnated with an organic electrolytic solution, and the resulting product is received in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery assemblies may be stacked to form a battery pack, and such battery pack may be used for all devices requiring high capacity and high output. For example, a notebook, a smart phone, an electric vehicle, and the like.

Particularly, the lithium battery is suitable for an electric vehicle (EV) because it has excellent thermal stability and provides good battery characteristics. For example, it is suitable for a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV).

Alternatively, the lithium battery may be a lithium air battery.

The lithium air cell can be prepared, for example, as follows.

First, an air electrode is prepared as an anode. For example, the air electrode may be manufactured as follows. As the electrode member, a conductive material and a binder are mixed and then an appropriate solvent is added or a solvent is not added to prepare an air electrode slurry. Then, the air electrode slurry is coated and dried on the current collector surface, For example, by compression molding. The current collector may be a gas diffusion layer. Alternatively, the air electrode slurry may be coated and dried on the surface of a separator or a solid electrolyte membrane, or alternatively, compression-molded into a separator or a solid electrolyte membrane to improve electrode density.

The conductive material contained in the air electrode slurry may be porous. Accordingly, any material having porosity and conductivity can be used without limitation, and for example, a carbon-based material having porosity can be used. Examples of such carbon-based materials include carbon blacks, graphites, graphenes, activated carbons, and carbon fibers.

Catalysts for oxidation / reduction of oxygen may be added to the air electrode slurry. Examples of such catalysts include noble metal catalysts such as platinum, gold, silver, palladium, ruthenium, rhodium and osmium, manganese oxides, iron oxides, cobalt oxides, nickel Oxides and the like, or organometallic catalysts such as cobalt phthalocyanine may be used. However, the present invention is not limited thereto, and any catalyst that can be used as an oxidation / reduction catalyst for oxygen in the related art can be used.

In addition, the catalyst may be supported on the carrier. The carrier may be an oxide, zeolite, clay minerals, carbon, or the like. The oxide may include one or more oxides such as alumina, silica, zirconium oxide, and titanium dioxide. Or an oxide comprising at least one metal selected from Ce, Pr, Sm, Eu, Tb, Tm, Yb, Sb, Bi, V, Cr, Mn, Fe, Co, Ni, Cu, . The carbon may be carbon black such as Ketjen black, acetylene black, tan black, lamp black, graphite such as natural graphite, artificial graphite and expanded graphite, activated carbon, carbon fiber and the like, Anything that can be used as a carrier in the field is possible.

The air electrode slurry may comprise a binder. The binder may include a thermoplastic resin or a thermosetting resin. For example, it is possible to use polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride- Vinylidene fluoride copolymer, fluoroethylene copolymer, fluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, Ethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene- Acrylic acid copolymer and the like can be used singly or in combination, but they are not limited to these, Anything that can be used as a binder in the technical field is possible.

The current collector may use a porous material such as a mesh or mesh in order to accelerate the diffusion of oxygen, and a porous metal plate such as stainless steel, nickel, or aluminum may be used. However, the present invention is not limited thereto, As long as it can be used as an electronic device. The current collector may be coated with an oxidation-resistant metal or alloy coating to prevent oxide.

The air electrode slurry may optionally include conventional conventional oxygen oxidation / reduction catalysts and conductive materials. In addition, the air electrode slurry may optionally include lithium oxide.

Next, a cathode is prepared.

The cathode may be, for example, a lithium metal thin film. Examples of the lithium metal-based alloy include aluminum, tin, magnesium, indium, calcium, titanium, vanadium and the like and lithium alloys.

Next, the lithium battery separator described above is disposed between the air electrode and the cathode.

The separator is a separator for a lithium battery comprising modified microfibrillated cellulose having a carboxyl group on its surface as described above, wherein the counter ion of the carboxyl group contains lithium ions, The weight of other metal ions relative to the total lithium ion is 10 wt% or less, and the average pore diameter is 0.05 탆 to 1 탆 or less.

Further, as the separator, other separator besides the microcellulose fiber separator described above may be additionally disposed. The additional separator is not limited as long as it can withstand the use range of the air cell. For example, the separator may be a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, an olefinic resin such as polyethylene or polypropylene And a combination of two or more of them may be used.

In addition to the separator, an oxygen barrier film impervious to oxygen may be additionally disposed between the air electrode and the cathode. The oxygen barrier layer may serve as a protective layer for protecting impurities such as oxygen contained in the air electrode from directly reacting with the lithium metal anode, as a lithium ion conductive solid electrolyte membrane. Examples of the lithium ion conductive solid electrolyte membrane impermeable to oxygen as described above include, but are not limited to, lithium ion conductive glass, lithium ion conductive crystals (ceramics or glass-ceramics), or inorganic materials containing a mixture thereof Otherwise, any solid electrolyte membrane having lithium ion conductivity, impermeable to oxygen, and capable of protecting the cathode can be used as long as it can be used in the art. On the other hand, in consideration of chemical stability, the lithium ion conductive solid electrolyte membrane may be exemplified by an oxide.

Examples of the lithium ion conductive crystals include crystals having a perovskite structure having lithium ion conductivity such as Li ₃ N, LISICON and La _0.55 Li _0.35 TiO ₃ , crystals having a perovskite structure such as LiTi ₂ P ₃ O ₁₂ having a NASICON structure , Or a glass-ceramics for precipitating these crystals can be used.

Examples of lithium ion conductive crystals include lithium-aluminum-germanium-phosphate (LAGP), lithium-aluminum-titanium-phosphate (LATP) and lithium-aluminum-titanium-silicon-phosphate (LATSP).

For example, the oxygen barrier film containing lithium ion conductive crystals may include Li _{1 + x + y} Al _x (Ti, Ge) _2-x Si _y P _3-y O _1, 0-x-2, 0- ), And is, for example, a solid electrolyte membrane containing LATP (Li _1.4 Ti _1.6 Al _0.4 P ₃ O ₁₂ ).

Next, an electrolytic solution is injected between the air electrode and the cathode. The electrolytic solution may be the same as that used for the lithium ion battery. The electrolytic solution can be impregnated into the separator and the anode (air electrode).

The shape of the lithium air battery is not particularly limited and may be, for example, a coin shape, a button shape, a sheet shape, a laminate shape, a cylindrical shape, a flat shape, a horn shape or the like. It can also be applied to large-sized batteries used in electric vehicles and the like.

As used herein, the term "air" is not meant to be limited to atmospheric air, but may include a combination of gases containing oxygen, or pure oxygen gas. The broad definition of this term "air" can be applied to all applications, such as air cells, air air poles, and the like.

A method of manufacturing a separator for a lithium battery according to another embodiment will be described.

The method for producing a separator according to another embodiment includes a step of modifying cellulose, a step of purifying the modified cellulose, a step of finely dispersing the purified cellulose in a dispersion medium, and a step of drying and finely chopping the cellulose to form a sheet do.

Preparing a solution comprising a modified microcellulose fiber having a carboxyl group on its surface, a hydrophilic solvent having a boiling point of 100 to 160 ° C, and water; Applying the solution onto a substrate; Drying the applied solution on the substrate to prepare a film; And peeling the film from the substrate. The solution may be a dispersion.

The pore size of the separator can be easily controlled by using a solution containing both water and a hydrophilic solvent at a predetermined temperature range.

(Cellulose reforming step)

First, by oxidizing the surface of a natural cellulose fiber having an I-form crystal structure, the molecular chain (hydroxyl group) of the cellulose is oxidized to a carboxyl group to modify the cellulose fiber.

More specifically, in one embodiment, the reaction is carried out under alkaline conditions using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) The modified cellulose fibers are prepared by oxidation.

In this method, the bleached softwood pulp is first suspended in water, and the above-mentioned TEMPO and sodium bromide (NaBr) are added to the suspension and stirred. Subsequently, a small amount of sodium hypochlorite (NaClO) aqueous solution is added to this solution to initiate the oxidation reaction.

Then, during the oxidation reaction, an aqueous solution of sodium hydroxide (NaOH) at a predetermined concentration is dropped, the pH is maintained at a predetermined value, and the reaction is terminated at the point when no change in pH is observed, thereby obtaining a modified cellulose fiber.

For example, the content of carboxyl groups in the obtained modified microcellulose fibers may be 0.1 to 2.5 mmol / g.

For example, the number average fiber length of the obtained modified microcellulose fibers may be 0.2 탆 to 3 탆.

For example, the modified microcellulose fibers may have a number average fiber diameter of 100 nm or less.

(Cellulose purification step)

After the oxidation reaction is completed, an acid (for example, hydrochloric acid) of a predetermined concentration is added dropwise with stirring until the pH is stabilized. Then, filtration and washing with pure water are carried out, and filtration and washing are repeated until the pH of the pure water used for washing and the pH of the solution become the same value.

Then, an alkaline solution (for example, an aqueous solution of lithium hydroxide) containing pure water and a predetermined concentration of lithium ions is added to the solution containing the obtained modified cellulose fibers until the pH becomes a predetermined value, and while the solution is neutralized, At the same time as the fiber is purified, a suspension of the modified cellulose fiber of a predetermined concentration is prepared.

At this time, the counter ion of the carboxyl group on the surface of the modified cellulose can be changed to lithium ion in order to neutralize the solution containing the modified cellulose fiber with an aqueous alkali solution (for example, an aqueous solution of lithium hydroxide) containing lithium ions.

By such a change to lithium ion, the weight of the metal ion other than lithium in the total lithium ion among the counter ions of the carboxyl group can be 10% by weight or less.

(Cellulose finely dispersing step)

Next, the suspension of the modified cellulose fibers is treated for a predetermined number of times using a dispersing machine (for example, a high-pressure homogenizer), and then the dispersion medium is added and sufficiently stirred, To obtain a dispersion of cellulose fibers (modified microcellulose fibers).

The dispersing machine can be dispersed by a known dispersing machine such as a propeller type mixer, a paddle type mixer, a disper type mixer, a turbine type mixer and the like. In addition, a strong beating such as a homomixer, a high pressure homogenizer, an ultrasonic dispersion treatment, a beater, a disk type refiner, a conical type refiner, a double disk type refiner, ), It is possible to obtain a finer dispersion of nanofibers.

As the dispersion liquid, a modified microcellulose fiber is used in an amount of 0.1 to 10% by weight and a solvent having a boiling point of 100 to 160 ° C and a hydrophilic solvent in an amount of 1 to 50% by weight with respect to the entire dispersion.

When the content of the modified microcellulose fibers is less than 0.1% by weight, the content of the solid content is too small, so that a large amount of time is required for drying. Therefore, . When the content of the modified microcellulose fibers is more than 10% by weight, the viscosity of the dispersion becomes excessively high, resulting in a problem in workability.

In addition, the use of a hydrophilic solvent containing 1 to 50% by weight of the hydrophilic solvent is preferable because the amount of the solvent contributing to the control of the pore diameter of the separator is too small when the content of the hydrophilic solvent is less than 1% , And there is a possibility that the cellulose fibers aggregate. When the content of the hydrophilic solvent is more than 50% by weight, the dispersion of the modified microcellulose fibers becomes insufficient, and the modified microcellulose fibers may aggregate and precipitate.

In addition, the dispersion may further contain a binder. The content of the binder additionally contained may be 1 to 50 wt% of the content of the binder relative to the entire modified microcellulose fibers. The binder used in the dispersion is not particularly limited, and any binder that can be used in the art can be used.

By using such a dispersion, a solvent having a boiling point higher than the boiling point of water is used. Therefore, by evaporating water, it becomes possible to dry while inhibiting hydrogen bonding of cellulose. Therefore, it is possible to control the average pore diameter of the separator.

In addition, in one embodiment, as the dispersion medium, water can be used, and at the same time, hydrocarbons such as hexane, benzene and toluene, methanol, ethanol, iso-propanol, iso-butanol, sec- Alcohols such as butanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol and glycerin, ethers such as ethylene glycol dimethyl ether, 1,4-dioxane and tetrahydrofuran, acetone, methyl ethyl ketone Organic solvents such as ketones, N, N-dimethylformamide, N, N-dimethylacetamide, and dimethylsulfoxide may also be used.

(Drying step)

Next, the obtained dispersion of the modified microcellulose fibers is cast, for example, in Chararele, and sufficiently dried to produce a separator for a lithium ion secondary battery having a predetermined thickness.

As a drying method, a suitable method such as, for example, hot air drying, infrared drying, hot plate drying, vacuum drying and the like can be selected. First, a first drying step of evaporating water by keeping the temperature of the liquid below 100 ° C . Subsequently, the water is evaporated and then a second drying step is carried out in which the hydrophilic solvent is dried at a boiling point of the hydrophilic solvent other than water, that is, in the range of 100 to 160 ° C. Further, by evaporating water in advance, it is possible to dry while inhibiting hydrogen bonding between cellulose fibers. When the hydrogen bonding between the cellulose fibers is increased, the cellulosic fibers are bound to each other by hydrogen bonding, and the pores of the separator are not obtained.

[Example]

Hereinafter, this inventive idea will be described based on the embodiment. In addition, this inventive idea is not limited to these examples, and it is possible to modify and modify these embodiments based on the purpose of this inventive idea, and do not exclude them from the scope of this creative idea.

Example 1

(Preparation of separator)

After 2 g of the bleached softwood pulp was suspended in 150 ml of water, 0.025 g of TEMPO and 0.25 g of sodium bromide were added and sufficiently stirred.

Next, an aqueous 13% by weight sodium hypochlorite solution was added to 1 g of the pulp so that the amount of sodium hypochlorite was 1.6 mmoll / g to initiate the oxidation reaction. During the reaction, an aqueous 0.5 N sodium hydroxide solution was added dropwise, the pH was kept at 10.5, and the oxidation reaction was terminated when no change in pH could be observed.

Next, 0.5 N hydrochloric acid was added dropwise with stirring until it became stable at pH 1, and then filtration and washing with pure water were carried out. The pH of the pure water used for washing and the pH of the solution were the same And repeatedly purified.

Further, 60 ml of a 0.5-1 weight% dispersion liquid was adjusted from the cellulose sample in which the dry weight was precisely measured with respect to the carboxyl group content of the modified cellulose fiber, and the pH was adjusted to 2.5 with 0.1 M hydrochloric acid aqueous solution. Aqueous sodium hydroxide solution was added dropwise to measure the electric conductivity. The measurement was continued until the pH reached 11. Then, the carboxyl group content was determined from the amount of sodium hydroxide consumed in the neutralization step of the weak acid whose change in electrical conductivity was gentle, using the following equation (1). The results are shown in Table 1.

&Quot; (1) &quot;

Content of carboxyl group (mmoll / g) = [sodium hydroxide content (ml) x 0.05 / weight of cellulose (g)]

Next, the solution containing the modified cellulose fibers was neutralized by adding pure water and a 0.1 N aqueous solution of lithium hydroxide until the pH became 10, and the modified cellulose fibers were purified, and 2 wt% A modified cellulose fiber suspension was prepared.

Next, 10 parts by mass of dimethylformamide (boiling point: 153 占 폚) was added thereto, and the mixture was treated five times at 100 MPa using an ultrahigh pressure homogenizer (Sugino Machine Co., Ltd., trade name: Starburst) , And sufficiently stirred to obtain a microcellulose dispersion.

Then, the resulting microcellulose dispersion was cast on a glass chaery, dried at 100 ° C for 2 hours, and further dried at 160 ° C for 2 hours to prepare a separator having a thickness of 20 μm .

Example 2

A separator having a thickness of 20 탆 was produced in the same manner as in Example 1 except that dimethylformamide was changed to pyridine (boiling point: 115 캜).

Comparative Example 1

A separator having a thickness of 20 占 퐉 was produced in the same manner as in Example 1 except that dimethylformamide was not used.

Comparative Example 2

Except that a 0.1 N aqueous sodium hydroxide solution was used in place of the 0.1 N lithium hydroxide aqueous solution to prepare a suspension of modified cellulose fibers having a concentration of 2% by weight, a 20 mu m thick Was prepared.

Comparative Example 3

A separator having a thickness of 20 占 퐉 was obtained in the same manner as in Example 1 except that dimethylformamide was changed to triethylene glycol butyl methyl ether (boiling point: 261 占 폚) and the second drying temperature was changed to 270 占 폚. Respectively.

Comparative Example 4

A separator having a thickness of 20 占 퐉 was obtained in the same manner as in Example 1 except that dimethylformamide was changed to dipropylene glycol dimethyl ether (boiling point: 171 占 폚) and the second drying temperature was changed to 170 占 폚 Respectively.

Evaluation Example 1: Measurement of number average fiber length and number average fiber length

Each of the cellulose dispersions in Examples 1 and 2 and Comparative Examples 1 to 4 was diluted with pure water to 0.001% (concentration of the modified cellulose fiber with respect to the entire solvent), and then cleaved mica After casting and drying on the substrate, observation was made with an atomic force microscope (AFM, Hitachi High Tech Science Co., Ltd.), and the average value at 20 points was defined as the number average fiber diameter and number average fiber length. The above results are shown in Table 1 below.

Evaluation Example 2: Measurement of tensile strength

Each separator manufactured in Examples 1 and 2 and Comparative Examples 1 to 4 was pulled at a moving speed of 5 mm / min using a tensilon meter with a strip having a width of 15 mm, The stress was regarded as the tensile strength. The above results are shown in Table 1 below.

Evaluation Example 3: Thickness measurement

Each of the separators produced in Examples 1 and 2 and Comparative Examples 1 to 4 was cut with a razor and the cross section was observed under an optical microscope (KYES) to measure the thickness of the separator. The above results are shown in Table 1 below.

Evaluation Example 4: Measurement of average pore diameter

For each of the separators prepared in Examples 1 and 2 and Comparative Examples 1 to 4, the average pore diameter was measured by mercury intrusion porosimetry (Micromeritics), and the median diameter was measured as the average pore diameter Respectively. The above results are shown in Table 1 below.

Evaluation Example 5: Evaluation of lithium ion secondary battery performance

(EC) / diethyl carbonate (DEC) obtained by dissolving LiCoO ₂ in an anode, graphite in a cathode, and LiPF ₆ in an amount of 1 mol / L as an electrolyte using the separator prepared in Examples 1 and 2 and Comparative Examples 1 to 4 ) (3: 7 by volume), a lithium ion secondary battery was fabricated. Then, the battery characteristics were compared by charging the batteries at 4.2 V and 0.1 C. The battery characteristics were evaluated according to the following criteria.

○ ... When the battery is charged to 4.2V, battery characteristics are good.

× ... If not charged to 4.2V, the battery characteristics are poor.

Evaluation Example 6: Measurement of metal ion content

The metal ion content of the separator fabricated in Examples 1 and 2 and Comparative Examples 1 to 4 was measured using an Electron Probe Microanalyzer (EPMA method, JEOL, JEOL Ltd.) The contents of other metals were measured. The above results are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Counter ion Li Li Li Na Li Li Other metals
Ion content
[weight%] 8 8 8 100 8 8 Average pore diameter
[Mu m] 0.4 0.2 0.01 or less 0.3 Not measurable 0.6 Carboxyl group content
[mmoll / g] 1.6 1.6 1.6 1.6 1.6 1.6 Number average fiber length
[Mu m] 0.8 0.8 0.7 0.8 0.8 0.8 Number average fiber diameter
[nm] 3.5 3.4 3.6 3.5 3.5 3.5 Boiling point of solvent
[° C] 153 115 - 153 261 171 Second drying step temperature [캜] 160 160 160 160 270 170 The tensile strength
[MPa] 110 100 140 100 Not measurable 50 Battery characteristics ○ ○ × × Not measurable ×

As shown in Table 1, the lithium ion secondary batteries of Examples 1 and 2 are superior to the lithium ion secondary batteries of Comparative Examples 1 to 4 in battery characteristics.

In other words, in Examples 1 and 2, the counter ion of the carboxyl group is lithium ion, and the weight of other ions relative to the counter ion is 10% by weight or less, and the average pore diameter is 0.05 - 1 占 퐉. Therefore, as described above, good cell performance can be realized without inhibiting the movement of lithium ions between the electrodes.

Although one exemplary embodiment has been described in detail, the inventive idea is not limited to this example. Those skilled in the art will recognize that various changes or modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims, .

Claims (20)

A lithium battery separator comprising modified microfibrillated cellulose having a carboxyl group on its surface,
Wherein the counter ion of the carboxyl group comprises lithium ion,
In the counter ion, the weight of the metal ion other than lithium relative to the total lithium ion is 10% by weight or less,
Wherein the average pore diameter is 0.05 占 퐉 to 1 占 퐉 or less. The separator for a lithium battery according to claim 1, wherein the modified microcellulose fibers have a cellulose type I crystal structure. The separator for a lithium battery according to claim 1, wherein the modified microcellulose fiber has a carboxyl group content of 0.1 to 2.5 mmol / g. The lithium cell separator according to claim 1, wherein the modified microcellulose fibers have a number average fiber length of 0.2 mu m to 3 mu m. The separator for a lithium battery according to claim 1, wherein the modified microcellulose fibers have a number average fiber diameter of 100 nm or less. The lithium battery separator according to claim 1, wherein the separator has a tensile strength of 100 to 140 MPa. anode; cathode; And
The lithium battery according to any one of claims 1 to 6, which is disposed between the positive electrode and the negative electrode. The lithium battery according to claim 7, wherein the lithium battery is a lithium ion battery. The lithium battery according to claim 7, wherein the lithium battery is a lithium air battery. Preparing a solution containing a modified microcellulose fiber having a carboxyl group on its surface, a hydrophilic solvent having a boiling point of 100 to 160 DEG C, and water;
Applying the solution onto a substrate;
Drying the applied solution on the substrate to prepare a film; And
And peeling the film from the base material. The method of claim 10, wherein the step of drying the coated solution to prepare a film
A first drying step of performing drying at less than 100 캜; And
And a second drying step of performing drying at 100 to 160 ° C. The process for producing a lithium battery separator according to claim 10, wherein the content of the hydrophilic solvent in the solution is 1 to 50% by weight. The process for producing a lithium battery separator according to claim 10, wherein the hydrophilic solvent comprises at least one selected from the group consisting of dimethylformamide and pyridine. The process for producing a lithium battery separator according to claim 10, wherein the content of the modified microcellulose fibers in the solution is 0.1 to 10% by weight. The process for producing a separator for a lithium battery according to claim 10, wherein the solution further contains a binder, and the content of the binder relative to the entire modified microcellulose fibers is 1 to 50% by weight. 11. The method according to claim 10, wherein the counter ion of the carboxyl group contains lithium ions,
Wherein the counter ion has a weight of a metal ion other than lithium with respect to the total lithium ion of 10% by weight or less. The process for producing a separator for a lithium battery according to claim 10, wherein the modified microcellulose fibers have a cellulose I-form crystal structure. The process for producing a lithium battery separator according to claim 10, wherein the modified microcellulose fiber has a carboxyl group content of 0.1 to 2.5 mmol / g. The process for producing a separator for a lithium battery according to claim 10, wherein the modified microcellulose fibers have a number-average fiber length of 0.2 mu m to 3 mu m. The process for producing a separator for a lithium battery according to claim 10, wherein the modified microcellulose fibers have a number-average fiber diameter of 100 nm or less.

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