Method for producing lithium carboxymethylcellulose salt and lithium secondary battery containing lithium carboxymethylcellulose salt produced by this method

Abstract

To provide a method of preparing a lithium salt of carboxymethyl cellulose that achieves high yield through a simple process, and a lithium secondary battery containing the lithium salt of carboxymethyl cellulose prepared by the method.SOLUTION: A method of preparing a lithium salt of carboxymethyl cellulose includes the steps for carrying out alkalization of cellulose and lithium hydroxide to generate an alkali product; and mixing the resulting alkalization product with a halogen-including acetic acid or a salt thereof to carry out etherification, wherein an amine derivative is added during at least one of the alkalization and etherification.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing lithium carboxymethylcellulose salt and a lithium secondary battery including the lithium carboxymethylcellulose salt produced by this method.

Background Art

[0002] Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small and lightweight but relatively high in capacity has been rapidly increasing. In particular, lithium secondary batteries have attracted attention as a driving power source for portable devices because they are lightweight and have a high energy density. As a result, research and development for improving the performance of lithium secondary batteries are actively underway.

[0003] Carboxymethylcellulose is one of the representative polymers used in lithium secondary batteries to increase viscosity. Carboxymethylcellulose is usually used in a form substituted with an alkali salt, and among these, the form substituted with sodium is suitable for aqueous systems and has been mainly used. However, sodium may cause an electrochemical side reaction in the battery, and recently, research has been actively conducted to use carboxymethylcellulose substituted with lithium instead of sodium.

[0004] However, the lithium salt of carboxymethylcellulose has the disadvantages of a complicated production process and being uneconomical.

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment provides a method for producing lithium carboxymethylcellulose salt capable of obtaining a high yield using a simple process.

[0006] Another embodiment provides a lithium secondary battery including a negative electrode, a positive electrode, and an electrolyte containing the lithium carboxymethylcellulose salt produced by the above method.

Means for Solving the Problem

[0007] One embodiment provides a method for producing lithium carboxymethyl cellulose, including: performing an alkalization reaction of cellulose and lithium hydroxide to produce an alkali product; and mixing the alkali product with haloacetic acid or its salts to perform an etherification reaction, wherein an amine derivative is added during at least one of the alkalization reaction and the etherification reaction.

[0008] The amine derivative may be represented by the following Chemical Formula 1 or Chemical Formula 2.

Chem.

Chem.

[0009] In one embodiment, the amine derivative may be dimethylamine, diethylamine, trimethylamine, triethylamine, chloroalkylamine, bromoalkylamine, bis(chloroalkyl)amine, tris(chloroalkyl)amine, ethylenediamine, diethylenetriamine, triethylenetetraamine, or a combination thereof.

[0010] The haloacetic acid may be chloroacetic acid, fluoroacetic acid, bromoacetic acid, iodoacetic acid, or a combination thereof.

[0011] The salt of the haloacetic acid may be a lithium salt of the haloacetic acid.

[0012] The addition amount of the amine derivative may be from 0.0001 parts by weight to 100 parts by weight with respect to 1 part by weight of the cellulose.

[0013] The haloacetic acid or its salts may be used in an amount of 0.1 parts by weight to 100 parts by weight with respect to 1 part by weight of the cellulose.

[0014] The degree of substitution of the carboxymethyl cellulose lithium salt may be 0.5 or more and 1.5 or less.

[0015] The alkalization reaction can be carried out in a solvent. At this time, the solvent may be water, alcohol, or a combination thereof.

[0016] Another embodiment provides a lithium secondary battery including a negative electrode containing the carboxymethyl cellulose lithium salt produced by the manufacturing method; a positive electrode; and an electrolyte.

Advantages of the Invention

[0017] The method for producing carboxymethyl cellulose lithium salt according to one embodiment has simple steps and can produce carboxymethyl cellulose lithium salt in a high yield.

Brief Description of the Drawings

[0018]

Figure 1

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims described later.

[0020] "These combinations" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0021] Terms such as "include", "comprise" or "have" are intended to specify the presence of implemented features, numbers, steps, components or combinations thereof, and it should be understood that the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof is not precluded in advance.

[0022] Throughout this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it can further include other components rather than excluding other components.

[0023] Also, throughout this specification, terms such as "about", "substantially", etc. are used to mean including the numerical value or a range close to the numerical value when manufacturing and material tolerances inherent in the mentioned meaning are presented, and are used to prevent unscrupulous infringers from improperly using the disclosed content where an exact or absolute numerical value is mentioned to assist in the understanding of the present application.

[0024] Throughout this specification, the description of "A and / or B" means "A or B or all of these".

[0025] In this specification, unless otherwise defined, the particle size means the average particle size (D50), which refers to the diameter of the particle with a cumulative volume of 50% in the particle size distribution. The measurement of the average particle size (D50) can be carried out by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. As another method, it can be measured using a measuring device that uses the dynamic light-scattering method, and after performing data analysis to count the number of particles for each particle size range, the average particle size (D50) value can be calculated therefrom.

[0026] A method for producing lithium carboxymethyl cellulose according to an embodiment includes performing an alkalization reaction between cellulose and lithium hydroxide to produce an alkali product, and mixing the alkali product with haloacetic acid or its salts to perform an etherification reaction. At this time, an amine derivative is added during at least one of the alkalization reaction and the etherification reaction.

[0027] The following will explain each step in detail.

[0028] First, the alkalization reaction between cellulose and lithium hydroxide is carried out. This can be carried out by mixing cellulose and lithium hydroxide, and this mixing step can be carried out by physically mixing or by ultrasonic treatment.

[0029] The alkalization reaction can be carried out in a solvent. This solvent may be water, alcohol, or a combination thereof. The alcohol may be ethanol, isopropyl alcohol, methanol, butanol, or a combination thereof.

[0030] At this time, the usage amount of the lithium hydroxide may be 0.01 to 100 parts by weight, or may be 0.1 to 10 parts by weight with respect to 1 part by weight of the cellulose. When the usage amount of the lithium hydroxide is included in the above range, the reaction of the cellulose can be facilitated, and the lithium salt of carboxymethyl cellulose can be produced in a higher yield.

[0031] Next, the obtained product is mixed with haloacetic acid or salts thereof to carry out an etherification reaction.

[0032] In one embodiment, at least one of the alkalization reaction or the etherification reaction can be carried out by adding an amine derivative. For example, the alkalization reaction can be carried out by mixing cellulose, lithium hydroxide and an amine derivative, and the etherification reaction can also be carried out by mixing the product, haloacetic acid or salts thereof, and an amine derivative. Of course, the amine derivative can also be used in both the alkalization reaction and the etherification reaction.

[0033] Thus, when an amine derivative is used in the manufacturing process, the lithium salt of carboxymethyl cellulose can be produced.

[0034] Generally, the alkali salt of carboxymethyl cellulose is produced by dispersing cellulose and an alkali hydroxide compound in an alcohol solvent such as a mixture of ethanol and water and carrying out an alkalization reaction, and then carrying out an etherification reaction with haloacetic acid or salts thereof. When the alkali salt is a sodium salt, it can be easily produced by this method. However, when the alkali salt is a lithium salt, since lithium hydroxide has low solubility in the alcohol solvent and the cellulose is not activated, the etherification reaction does not occur, so it has been difficult to produce by the above method. Therefore, conventionally, the lithium salt of carboxymethyl cellulose has been produced by producing sodium carboxymethyl cellulose, then subjecting it to acid treatment and reacting it with lithium hydroxide again.

[0035] On the reverse side, in the manufacturing method according to an embodiment of the present invention, the step of manufacturing sodium carboxymethyl cellulose using an amine derivative is omitted, and lithium carboxymethyl cellulose can be immediately manufactured. This is because even if lithium hydroxide has low solubility in an alcohol-based solvent, the amine derivative can serve as a catalyst in the etherification reaction, so that the etherification reaction of unactivated cellulose can easily occur regardless of whether it is used in the alkalization reaction or the etherification reaction.

[0036] In one embodiment, the amine derivative can be represented by the following Chemical Formula 1 or the following Chemical Formula 2.

Chemical Formula

Chemical Formula

[0037] In the above Chemical Formula 1 or the above Chemical Formula 2, the alkyl group may be linear, branched or cyclic. In one embodiment, at least one of R 1 to R 9 may be an alkyl group having 1 to 12 carbon atoms, and in another embodiment, R 1 to R 9may each independently be an alkyl group having 1 to 12 carbon atoms. R 1 ~R 9 When at least one of them is an alkyl group having 1 to 12 carbon atoms, it is possible to have a more appropriate basicity for producing lithium carboxymethylcellulose salt, and side reactions during the reaction can be more effectively suppressed.

[0038] In one embodiment, the alkyl group may have 1 to 4 carbon atoms.

[0039] The amine derivative according to one embodiment may be dimethylamine, diethylamine, trimethylamine, triethylamine, chloroalkylamine, bromoalkylamine, bis(chloroalkyl)amine, tris(chloroalkyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, or a combination thereof. In the bis(chloroalkyl)amine and tris(chloroalkyl)amine, the alkyl may be methyl, alkyl, propyl or butyl.

[0040] In one embodiment, the addition amount of the amine derivative may be 0.0001 to 100 parts by weight, or 0.001 to 10 parts by weight, based on 1 part by weight of the cellulose. When the addition amount of the amine derivative is within the above range, a lithium carboxymethylcellulose salt having a lithium substitution degree suitable for a battery can be produced. When the amine derivative is used in an amount less than 0.0001 parts by weight based on 1 part by weight of the cellulose, the lithium carboxymethylcellulose salt cannot be effectively produced.

[0041] The haloacetic acid used in the etherification reaction may be chloroacetic acid, fluoroacetic acid, bromoacetic acid, or iodoacetic acid. Also, the salt of the haloacetic acid may be a lithium salt thereof.

[0042] The usage amount of the haloacetic acid or salts thereof may be 0.1 to 100 parts by weight, or may be 1 to 20 parts by weight with respect to 1 part by weight of the cellulose. When the content of the haloacetic acid or salts thereof is within the above range, a lithium carboxymethylcellulose salt having a lithium substitution degree suitable for use in a battery can be produced.

[0043] The lithium substitution degree means the substitution degree described below.

[0044] The degree of substitution (DS) of the lithium carboxymethylcellulose salt produced by the production method of one embodiment may be 0.5 or more and 1.5 or less, or may be 0.7 to 1.3. The degree of substitution means the average number of substituents substituted for cellulose per cellulose repeating unit. Therefore, the lithium carboxymethylcellulose salt according to one embodiment can have 3 or less CH2COOLi per cellulose repeating unit, that is, per unit unit, and the average number may be 0.5 or more and 1.5 or less.

[0045] The weight average molecular weight (Mw) of the lithium carboxymethylcellulose salt may be 10,000 g / mol to 10,000,000 g / mol, or may be 100,000 g / mol to 3,000,000 g / mol. When the weight average molecular weight (Mw) of the lithium carboxymethylcellulose salt is within the above range, it can show a suitable viscosity during the production of a slurry-type composition for manufacturing a negative electrode, thereby improving workability.

[0046] Further, the viscosity of the lithium carboxymethylcellulose salt may be 100 mPas or more and 5000 mPas or less in a 1 wt% aqueous solution. The viscosity is a value at a normal temperature of 20°C to 25°C.

[0047] Such lithium carboxymethyl cellulose can be usefully used in a lithium secondary battery, and in particular, it can be usefully used as a thickener for a negative electrode and also as a binder.

[0048] The negative electrode includes a negative electrode active material layer and a current collector that supports the negative electrode active material layer.

[0049] The lithium carboxymethyl cellulose according to one embodiment may be included in the negative electrode active material layer. In this case, the amount of the lithium carboxymethyl cellulose may be 0.5% by weight or more and less than 3% by weight based on 100% by weight of the entire negative electrode active material layer.

[0050] The negative electrode active material layer contains a negative electrode active material, may contain a binder, and may further contain a conductive material.

[0051] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0052] Examples of the material capable of reversibly intercalating / deintercalating lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0053] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0054] As the substance capable of doping and undoping with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a Si-C composite, SiO x (0 < x < 2), a Si-Q alloy (wherein Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), etc. can be mentioned. As the Sn-based negative electrode active material, Sn, SnO2, a Sn-R alloy (wherein R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. can be mentioned. Also, at least one of these and SiO2 can be mixed and used. As the elements Q and R, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and those selected from the group consisting of combinations thereof can be used.

[0055] In one embodiment, the Si-C composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles assembled from primary silicon particles and an amorphous carbon coating layer located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. Also, the silicon-carbon composite may include a core in which silicon particles are dispersed in an amorphous carbon matrix and an amorphous carbon coating layer coating the surface of the core.

[0056] Since the secondary particles are located at the center of the Si-C composite, they can be referred to as the core or the central part. Also, the amorphous carbon coating layer can be referred to as the outer part or the shell.

[0057] The silicon particles may be nanosilicon particles. The particle size of the nanosilicon particles may be 10 nm to 1,000 nm, and according to another embodiment, may be 20 nm to 900 nm, 20 nm to 800 nm, 20 nm to 500 nm, 20 nm to 300 nm, or 20 nm to 150 nm. When the average particle size of the silicon particles is within the above range, it is possible to suppress the excessive volume expansion generated during charge and discharge, and prevent the interruption of the conductive path due to particle crushing during charge and discharge.

[0058] At this time, the mixing ratio of nanosilicon and amorphous carbon may be 1:99 to 60:40 by weight.

[0059] In one embodiment, the secondary particles or the core may further contain crystalline carbon. When the silicon-carbon composite further contains crystalline carbon, the Si-C composite may include silicon primary particles and secondary particles assembled with crystalline carbon, as well as an amorphous carbon coating layer located on the surface of the secondary particles.

[0060] Also, when the Si-C composite contains silicon particles, crystalline carbon, and amorphous carbon, the content of the amorphous carbon may be 30 wt% to 70 wt% based on 100 wt% of the entire Si-C composite, and the content of the crystalline carbon may be 1 wt% to 20 wt% based on 100 wt% of the entire Si-C composite. Also, the content of the silicon particles may be 20 wt% to 70 wt% based on 100 wt% of the entire Si-C composite, and according to one embodiment, may be 30 wt% to 60 wt%.

[0061] If the particle size of the Si-C composite is appropriately adjusted, there is no need for special limitation.

[0062] When the amorphous carbon is located while surrounding the surface of the secondary particles, its thickness can be appropriately adjusted, and for example, it may exist with a thickness of 5 nm to 100 nm.

[0063] In one embodiment, the Si-C composite may be included as the first negative electrode active material, and crystalline carbon may be included as the second negative electrode active material. At this time, the mixing ratio of the first negative electrode active material and the second negative electrode active material may be a weight ratio of 1:99 to 50:50. More specifically, the first negative electrode active material and the second negative electrode active material may be included as the negative electrode active material at a weight ratio of 5:95 to 20:80.

[0064] The binder serves to well adhere the negative electrode active material particles to each other and also to well adhere the negative electrode active material to the current collector. The binder may be an aqueous binder.

[0065] Examples of the aqueous binder include styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polypropylene, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0066] The content of the aqueous binder may be 0.5% by weight or more and less than 3% by weight with respect to 100% by weight of the entire negative electrode active material layer. According to one embodiment, the total content of the carboxymethyl cellulose lithium salt and the aqueous binder may be included in the range of 1% to 3% by weight with respect to 100% by weight of the entire negative electrode active material layer.

[0067] The conductive material is used to impart conductivity to the electrode, and in the battery thus formed, any electron-conductive material that does not cause a chemical change can be used. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof can be used.

[0068] As the current collector, those selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0069] The lithium secondary battery according to one embodiment includes a positive electrode and an electrolyte together with the negative electrode.

[0070] The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

[0071] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium can be used. More specific examples include compounds represented by any one of the following chemical formulas: Li a A 1-b X b D 1 2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5); Li a A 1-b X b O 2-c1 D 1 c1 (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c1 ≦ 0.05); Li a E1-b X b O 2-c1 D 1 c1 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c1 ≤ 0.05); Li a E 2-b X b O 4-c1 D 1 c1 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c1 ≤ 0.05); Li a Ni 1-b-c Co b X c D 1 α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤ 2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni 1-b-c Co b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c D 1 α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤ 2); Li a Ni 1-b-c Mn b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni b E c G dO2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c L 1 d G e O2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 0.1); Li a NiG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4 (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3 (0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3 (0 ≤ f ≤ 2); Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0072] In the above chemical formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D 1is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof; L 1 is selected from the group consisting of Mn, Al, and combinations thereof.

[0073] Of course, those having a coating layer on the surface of this compound can also be used, or the compound and a compound having a coating layer can be mixed and used. This coating layer can contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline. As the coating elements contained in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof can be used. In the coating layer forming step, any coating method may be used as long as such elements are used for the compound and it does not adversely affect the physical properties of the positive electrode active material (for example, spray coating, dipping method, etc.). Since this is well understood by those skilled in the art, detailed description is omitted.

[0074] In the positive electrode, the content of the positive electrode active material may be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

[0075] In one embodiment, the positive electrode active material layer may further contain a binder and a conductive material. At this time, the contents of the binder and the conductive material may each be 1% to 5% by weight based on the total weight of the positive electrode active material layer.

[0076] The binder serves to well adhere the positive electrode active material particles to each other and also to well adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0077] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0078] Al can be used as the current collector, but is not limited thereto.

[0079] The electrolytic solution contains a non-aqueous organic solvent and a lithium salt.

[0080] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0081] As the non-aqueous organic solvent, carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents can be used.

[0082] As the carbonate solvents, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, caprolactone, etc. can be used. As the ether solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as the ketone solvent, cyclohexanone, etc. can be used. Also, as the alcohol solvents, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvents, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, etc. can be used.

[0083] The organic solvent(s) can be used alone or in a mixture of one or more. When used in a mixture of one or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which should be widely understood by those skilled in the art.

[0084] In the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed and used at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte is excellent.

[0085] The organic solvent may further contain an aromatic hydrocarbon organic solvent in the carbonate solvent. At this time, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed at a volume ratio of about 1:1 to about 30:1.

[0086] As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound of the following Chemical Formula 3 can be used.

Chemical Formula

[0087] Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and those selected from the group consisting of combinations thereof.

[0088] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate compound represented by the following Chemical Formula 4 as a life improvement additive in order to improve battery life. [Chemical formula]

[0089] (In the above Chemical Formula 4, R 15 and R 16 are the same as or different from each other and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2) and a fluorinated alkyl group having 1 to 5 carbon atoms, and the R 15 and R 16At least one of them is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R 15 and R 16 are not all hydrogen.)

[0090] Typical examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When such a life-improving additive is further used, its usage amount can be appropriately adjusted.

[0091] The lithium salt is a substance that is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of such lithium salts are LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1(SO2) (where x and y are natural numbers, for example, integers from 1 to 20), lithium difluoro(bisoxalato) phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato) borate; LiBOB), and lithium difluoro(oxalato) borate (LiDFOB), and includes one or more selected from the group as a supporting electrolyte salt. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

[0092] Depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator can be used.

[0093] Fig. 1 shows an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. Although a lithium secondary battery according to an embodiment is described by taking a rectangular shape as an example, the present invention is not limited thereto, and it can be applied to batteries in various forms such as a cylindrical shape and a pouch shape.

[0094] Referring to Fig. 1, a lithium secondary battery 100 according to an embodiment can include an electrode assembly 40 wound between a positive electrode 10 and a negative electrode 20 via a separator 30, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown).

[0095] Examples and comparative examples of the present invention will be described below. Such examples below are merely one embodiment of the present invention, and the present invention is not limited to the following examples.

Examples

[0096] (Example 1) Using a mechanical stirrer, cellulose and lithium hydroxide were mixed in an aqueous solvent to carry out an alkalization reaction to produce an alkali product.

[0097] Chloroacetic acid and triethylamine were added to the alkali product to carry out an etherification reaction.

[0098] In the above process, the weight ratio of cellulose, chloroacetic acid, and triethylamine was used to be 1:1:5. Also, the amount of lithium hydroxide used was 5 parts by weight with respect to 1 part by weight of the cellulose.

[0099] In this process, lithium carboxymethylcellulose salt with a degree of substitution of 0.5 was produced (yield: 98%). The viscosity (25 °C) of a 1 wt% aqueous solution of the produced product was 5000 mPas, and the weight average molecular weight (Mw) of the lithium carboxymethylcellulose salt was 100,000 g / mol to 1,000,000 g / mol.

[0100] (Example 2) The same procedure as in Example 1 was carried out except that the weight ratio of cellulose, chloroacetic acid, and triethylamine was changed to 1:2:5 to produce lithium carboxymethylcellulose salt with a degree of substitution of 0.9 (yield: 98%).

[0101] The viscosity (25 °C) of a 1 wt% aqueous solution of the produced product was 3000 mPas, and the weight average molecular weight (Mw) of the lithium carboxymethylcellulose salt was 100,000 g / mol to 1,000,000 g / mol.

[0102] (Example 3) Except for changing the weight ratio of cellulose, chloroacetic acid, and triethylamine to 1:5:5, the procedure was the same as in Example 1 to produce lithium carboxymethylcellulose with a degree of substitution of 1.2 (yield: 94%).

[0103] The viscosity (25 °C) of a 1 wt% aqueous solution of the produced product was 1500 mPas, and the weight-average molecular weight (Mw) of lithium carboxymethylcellulose was 100,000 g / mol to 1,000,000 g / mol.

[0104] (Example 4) Except for changing the weight ratio of cellulose, chloroacetic acid, and triethylamine to 1:5:10, the procedure was the same as in Example 1 to produce lithium carboxymethylcellulose with a degree of substitution of 1.5 (yield: 91%).

[0105] The viscosity (25 °C) of a 1 wt% aqueous solution of the produced product was 100 mPas, and the weight-average molecular weight (Mw) of lithium carboxymethylcellulose was 100,000 g / mol to 1,000,000 g / mol.

[0106] (Comparative Example 1) Using a mechanical stirrer, cellulose and lithium hydroxide were mixed to carry out an alkalization reaction to produce an alkaline product.

[0107] Chloroacetic acid was added to the alkaline product to carry out an etherification reaction to produce lithium carboxymethylcellulose with a degree of substitution of 0.4 (yield: 5%).

[0108] In the above process, the weight ratio of cellulose and chloroacetic acid was used to be 1:10. The produced lithium carboxymethylcellulose had an excessively low solubility in water and viscosity measurement was impossible.

[0109] Experimental Example 1) Measurement of degree of substitution The lithium substitution degrees of the lithium carboxymethyl cellulose salts produced by the above Examples 1 to 4 and Comparative Example 1 were measured through ICP (Inductively-coupled plasma) analysis, and the results are shown in Table 1 below.

[0110] Experimental Example 2) Lithium content measurement The lithium contents contained in the lithium carboxymethyl cellulose salts produced by the above Examples 1 to 4 and Comparative Example 1 were measured through ICP analysis. The results are shown in Table 1 below.

[0111] The weight ratios, yields, and viscosities of the cellulose, chloroacetic acid (CA), and triethylamine (TEA) of the above Examples 1 to 4 and Comparative Example 1 were also tabulated and shown in Table 1 below.

[0112] [Table 1]

[0113] As shown in Table 1 above, in the case of Examples 1 to 4 in which lithium carboxymethyl cellulose salts were produced using an amine derivative, it can be seen that lithium carboxymethyl cellulose salts having an appropriate substitution degree were produced in a high yield. On the contrary, in the case of Comparative Example 1 in which no amine derivative was used, a lithium carboxymethyl cellulose salt having a low substitution degree was produced in a very low yield.

[0114] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made and implemented within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that this also belongs to the scope of the present invention.

Description of reference numerals

[0115] 10 ··· Positive electrode 20 ··· Negative electrode 30 ··· Separator 40 ··· Electrode assembly 50 ··· Case 100... Lithium secondary battery

Claims

1. Performing an alkalization reaction of cellulose and lithium hydroxide; and Mixing the product obtained in the above step with haloacetic acid or its salts to perform an etherification reaction A method for producing lithium carboxymethylcellulose salt, comprising: Adding an amine derivative during at least one of the alkalization reaction and the etherification reaction, The amine derivative is represented by the following Chemical Formula 1 or Chemical Formula 2, a method for producing lithium carboxymethylcellulose salt: 【Chemical 1】 (In the above chemical formula (1), R １ , R ２ and R ３ are the same as or different from each other, and are hydrogen, or an alkyl group or haloalkyl group having 1 to 12 carbon atoms, provided that at least one of R1 to R3 is an alkyl group having 1 to 12 carbon atoms). [Chemical Formula 2] (In the above chemical formula 2, R ４ , R ５ , R ７ , R ８ and R ９ are the same as or different from each other, and are hydrogen, or an alkyl group or haloalkyl group having 1 to 12 carbon atoms, R ６ is an alkylene group having 1 to 12 carbon atoms, W １ and W ２ are the same as or different from each other and are alkylene groups having 1 to 12 carbon atoms, a is an integer from 0 to 2).

2. The amine derivative is dimethylamine, diethylamine, trimethylamine, triethylamine, chloroalkylamine, bromoalkylamine, bis(chloroalkyl)amine, tris(chloroalkyl)amine, ethylenediamine, diethylenetriamine, triethylenetetraamine or a combination thereof. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

3. The haloacetic acid is chloroacetic acid, fluoroacetic acid, bromoacetic acid, iodoacetic acid or a combination thereof. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

4. The salt of the haloacetic acid is a lithium salt of the haloacetic acid. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

5. The addition amount of the amine derivative is 0.0001 parts by weight to 100 parts by weight based on 1 part by weight of the cellulose. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

6. The haloacetic acid or its salts is 0.1 parts by weight to 100 parts by weight based on 1 part by weight of the cellulose. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

7. The degree of substitution of the lithium carboxymethylcellulose salt is 0.5 or more and 1.5 or less. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

8. The alkalization reaction is carried out in a solvent. The method for producing lithium carboxymethylcellulose salt according to Claim 1.

9. The solvent is water, alcohol or a combination thereof. The method for producing lithium carboxymethylcellulose salt according to Claim 8.

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