Method for preparing non-fluorine-based siloxane-polymer composite binder, non-fluorine-based siloxane-polymer composite binder prepared using same, and electrode comprising same

Abstract

The present invention relates to a non-fluorine-based siloxane-polymer composite binder and, specifically, to a method for preparing a non-fluorine-based siloxane-polymer composite binder having improved adhesion, and application, to an electrode and a secondary battery, of a non-fluorine-based siloxane-polymer composite binder prepared using the method. More specifically, the present invention provides a method for preparing a non-fluorine-based siloxane-polymer composite binder, comprising: a first step of adding, to a polymer solution prepared by dissolving a polymer having oxygen-containing functional groups in a solvent, a first silane compound that has an organic curing group and stirring same, thereby preparing a mixture in which the silane compound is uniformly dispersed in the polymer solution; and a second step of adding a second silane compound containing no organic curing groups and an acid catalyst or a base catalyst to the mixture and thermally stirring same, thereby inducing in situ condensation between the oxygen-containing functional groups of the polymer, the oxygen-containing functional groups of the first silane compound and the oxygen-containing functional groups of the second silane compound so that a siloxane resin is synthesized by binding of the polymer through a covalent bond, and thus a siloxane-polymer composite resin is prepared.

Description

Method for producing a non-fluorinated siloxane-polymer composite binder, a non-fluorinated siloxane-polymer composite binder produced thereby, and an electrode comprising the same

[0001] The present invention relates to a non-fluorinated siloxane-polymer composite binder, and more particularly, to a method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness, and to the application of the non-fluorinated siloxane-polymer composite binder produced by the method to electrodes and secondary batteries.

[0002] Lithium secondary batteries are widely used in various fields such as electric vehicles, energy storage systems (ESS), drones, and mobile phones. As the electric mobility market expands, the market demand for the development of high-capacity and high-durability lithium secondary batteries is increasing.

[0003] Lithium secondary batteries consist of a cathode, anode, separator, and electrolyte. Among these, polymer materials are actively used as electrode binders, along with separators and electrolytes. They are used not only to secure adhesive strength or bonding between the electrode active material and the current collector, but also to buffer the expansion and contraction of the active material due to the insertion and deintercalation of lithium ions. The basic requirements for polymers used as binders are that they should not chemically or electrochemically react with the organic electrolyte, and at the same time, they should maintain stable adhesive properties. Furthermore, since heating of up to 200℃ is required during electrode manufacturing, the binder must additionally have heat resistance to withstand this.

[0004] The most commonly known and used binder to date is the PVDF type. As shown in the chemical formula below, PVDF (polyvinylidene fluoride) binders have a higher dielectric constant than typical fluorine-containing polymers, excellent dispersibility and adhesion to electrode active material particles and conductive materials, and excellent oxidation resistance and electrochemical oxidation / reduction stability in organic electrolytes.

[0005]

[0006] Meanwhile, regulations on the use of per- and polyfluoroalkyl substances (PFAS) are emerging, led by Europe. PFAS are composed of multiple carbon atoms and fluorine atoms, making them difficult to break down. Because PFAS do not naturally decompose, they persist in the air, nature, and soil for long periods of time, accumulating in the human body and causing various adverse effects, including cancer and reproductive dysfunction. Accordingly, research is underway to find a replacement for PVDF, the binder used in lithium secondary batteries.

[0007] In this regard, Korean Patent Publication No. 10-2406884 (Organic-inorganic hybrid siloxane binder for secondary battery electrode slurry, preparation method thereof, and electrode slurry, secondary battery electrode, and secondary battery using the same) proposes a siloxane-based binder with improved electrochemical durability. However, the siloxane-based binder needs to be improved because its adhesive strength with the current collector is equivalent to or inferior to that of the currently used PFAS-based binder. Accordingly, there is a need for the development of new technologies for non-fluorinated binders that can improve the battery life by increasing the adhesive strength with the active material, conductive agent, and current collector of existing lithium secondary batteries while reducing environmental pollution by not containing PFAS.

[0008] Accordingly, in the present invention, taking into account the above-described technical requirements, a non-fluorinated siloxane-organic polymer composite binder for lithium secondary batteries was developed, which ensures electrochemical stability equivalent to or higher than that of existing PFAS-based binders through a siloxane-based resin with an organic-inorganic nanohybrid structure, and improves adhesive strength by introducing an organic polymer to increase the bonding strength of the electrode with the current collector, thereby improving the stability and lifespan of the lithium secondary battery, and the present invention was completed.

[0009] Accordingly, the present invention has as a technical problem a method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer.

[0010] In addition, the present invention has as another technical problem to be solved the non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer manufactured by the above method.

[0011] In addition, the present invention provides an electrode slurry including the non-fluorinated siloxane-polymer composite binder, an electrode including an electrode active layer formed by applying the electrode slurry, and a secondary battery including the electrode, as another technical problem to be solved.

[0012] In order to solve the above-described technical problem, the present invention,

[0013] A first step of preparing a mixture in which a first silane compound having an organic curing group is added to and stirred in a polymer solution prepared by dissolving a polymer having an oxygen-containing functional group in a solvent, and the silane compound is uniformly dispersed in the polymer solution; and

[0014] A second step of producing a siloxane-polymer composite resin by adding a second silane compound that does not contain an organic curing group to the mixture and an acid catalyst or a base catalyst and stirring the mixture under heat to cause an in situ condensation reaction between the oxygen-containing functional group of the polymer, the oxygen-containing functional group of the first silane compound and the oxygen-containing functional group of the second silane compound, thereby synthesizing a siloxane resin while the polymer is covalently bonded;

[0015] A method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer is provided, wherein the first silane compound comprises at least one of the following chemical formulas 1 and 2, and the second silane compound comprises at least one of the following chemical formulas 3, 4, and 5:

[0016]

[0017]

[0018] (However, R1 is at least one organic curing group selected from an epoxy group, an alicyclic epoxy group, an acrylic group, a methacrylic group, an amine group, a vinyl group, a cyan group, and a thiol group, and R2, R3, R4, and R5 are at least one functional group selected from an alkyl group, an aryl group, and a hydrogen group, respectively.)

[0019] In addition, in the present invention, in the first step, the polymer solution is prepared by dissolving 100 parts by weight of the polymer having the oxygen-containing functional group in 300 to 400 parts by weight of the solvent,

[0020] The first silane compound and the second silane compound added in the first and second steps are characterized in that they are added in an amount of 10 to 100 parts by weight, respectively, based on 100 parts by weight of the polymer.

[0021] In addition, in the present invention, the oxygen-containing functional group is characterized in that it is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, and a carbonyl group.

[0022] In addition, in the present invention, the polymer is characterized in that it has a molecular weight of at least 25,000.

[0023] In addition, in order to solve the above other technical problems, the present invention provides a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer, manufactured by the above-described method.

[0024] In addition, in order to solve the above-described further technical problem, the present invention provides an electrode slurry comprising the above-described non-fluorinated siloxane-polymer composite binder.

[0025] In addition, in order to solve the above-described further technical problem, the present invention provides an electrode including a current collector; and an electrode active layer formed by applying the above-described electrode slurry to the surface of the current collector.

[0026] In addition, in order to solve the above-mentioned further technical problem, the present invention provides a secondary battery including the electrode.

[0027] According to the present invention described above, there is an effect of being able to manufacture a siloxane-polymer composite resin that enables covalent bonding, i.e., primary bonding, between siloxane and polymer. In particular, when manufacturing a siloxane-polymer composite resin, oxygen-containing functional groups such as hydroxyl groups and carboxyl groups of a polymer side chain induce condensation with oxygen-containing functional groups such as alkoxy groups and hydroxyl groups of a silane compound to form a primary bond, and at the same time, a siloxane bond is formed, so that a uniform mixed compound can be obtained in situ, and there is an advantage of being able to manufacture a siloxane-polymer composite binder at once. In addition, the siloxane-polymer composite binder manufactured according to the present invention can improve the stability of a lithium secondary battery during charging and discharging by forming an interpenetrating polymer network microstructure through chemical bonding of electrochemically stable siloxane and polymer, and the introduction of an organic polymer having an oxygen-containing functional group improves the adhesive strength of the siloxane-organic polymer composite binder, thereby inducing a bonding strength with a current collector, thereby improving the stability of a lithium secondary battery.

[0028] Accordingly, while electrodes manufactured using conventional non-fluorinated polymers alone had low electrode durability due to the low electrochemical durability of the non-fluorinated polymer, the siloxane-polymer composite binder of the present invention can ensure the electrochemical stability of the electrode because the siloxane resin with excellent electrochemical durability is firmly bonded to the polymer through primary bonding, while also securing excellent adhesion to the current collector, which is characteristic of polymers. Furthermore, unlike existing PFAS-based binders, it does not contain a fluorine element, and has a higher solid content than existing PFAS-based binders, so that the amount of solvent used is less, thereby having the effect of reducing VOCs (volatile organic compounds).

[0029] Figure 1 is a flow chart showing a method for manufacturing a non-fluorinated siloxane-polymer composite binder according to the present invention.

[0030] Figure 2 illustrates the chemical bonding mechanism of the siloxane-polymer composite binder according to the present invention.

[0031] FIG. 3 shows a solution photograph of a siloxane-polymer composite binder manufactured in-situ and ex-situ according to one embodiment of the present invention.

[0032] Figure 4 shows the adhesive strength of an electrode to which a siloxane-polymer composite binder is applied according to a preferred embodiment of the present invention.

[0033] FIG. 5 shows electrochemical evaluation data of a lithium secondary battery half-cell using a siloxane-polymer composite binder according to a preferred embodiment of the present invention.

[0034] The present invention is described in detail below.

[0035] The present invention is susceptible to various modifications and embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0036] The terminology used herein is solely for the purpose of describing specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. Furthermore, throughout the specification, when a part is said to "include" a component, unless otherwise specifically stated, this does not exclude other components but rather implies the inclusion of additional components.

[0037]

[0038] FIG. 1 is a flow chart showing a method for manufacturing a non-fluorinated siloxane-polymer composite binder according to the present invention, and FIG. 2 shows a chemical bonding mechanism of a siloxane-polymer composite binder according to the present invention, and the present invention will be described in detail with reference to these.

[0039] In one aspect, the present invention relates to a method for producing a non-fluorinated siloxane-polymer composite binder, comprising: a first step (S10) of adding and stirring a first silane compound having an organic curing group to a polymer solution prepared by dissolving a polymer having an oxygen-containing functional group in a solvent, thereby producing a mixture in which the silane compound is uniformly dispersed in the polymer solution; and a second step (S20) of adding a second silane compound not including an organic curing group and an acid catalyst or a base catalyst to the mixture, and thermally stirring the mixture to cause an in situ condensation reaction between the oxygen-containing functional group of the polymer, the oxygen-containing functional group of the first silane compound, and the oxygen-containing functional group of the second silane compound, thereby synthesizing a siloxane resin while the polymer is covalently bonded, thereby producing a siloxane-polymer composite resin.

[0040] Preferably, the first silane compound comprises at least one of the following chemical formulas 1 and 2, and the second silane compound comprises at least one of the following chemical formulas 3, 4, and 5:

[0041]

[0042]

[0043] (However, R1 is at least one organic curing group selected from an epoxy group, an alicyclic epoxy group, an acrylic group, a methacrylic group, an amine group, a vinyl group, a cyan group, and a thiol group, and R2, R3, R4, and R5 are at least one functional group selected from an alkyl group, an aryl group, and a hydrogen group, respectively.)

[0044] In the present invention, the non-fluorinated siloxane-polymer composite binder refers to a form in which a polymer and a siloxane are bonded together. Referring to FIG. 2, it can be confirmed that the oxygen-containing functional group of the polymer is covalently bonded to the oxygen-containing functional group of the siloxane through a condensation reaction to form a composite binder. At this time, the oxygen-containing functional group may be at least one selected from the group consisting of a hydroxy group (-OH), a carboxy group (-COOH), and a carbonyl group (-C(=O)-).

[0045] More specifically, the first step (S10) is a step of preparing a mixture in which a first silane compound having an organic curing group is uniformly dispersed in a polymer solution. At this time, the mixture is prepared by adding and stirring the first silane compound having an organic curing group to a polymer solution prepared by dissolving the polymer having the oxygen-containing functional group in a solvent. Preferably, the polymer solution may use various conventional polymers having a molecular weight of at least 25,000. For example, epoxy-based, acrylic-based, polyimide-based, polyamide-imide-based, polyolefin-based, urethane-based, phenoxy-based, polyphenylene sulfide-based, polyketone-based, polyester-based, etc. may be used. If the molecular weight of the polymer is less than 25,000, the durability of the polymer itself is significantly reduced, and even if a composite binder is formed with a siloxane having excellent durability, the electrochemical durability may be reduced during the manufacture of an electrode.

[0046] In addition, the solvent used in the preparation of the polymer solution may be a typical organic solvent used in the preparation of secondary batteries. For example, it may be at least one of a protic solvent, an aprotic solvent, and a non-polar solvent, and specific examples thereof include N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, 2-ethoxyethanol, isopropyl alcohol, toluene, and the like. Preferably, the solvent may be added in an amount of 100 to 400 parts by weight based on 100 parts by weight of the polymer.

[0047] In addition, the first silane compound is a mixture of organic crosslinking silanes, (RSiO 3 / 2 ) T unit of the structure, (R2SiO 2 / 2 ) may include a D unit of the structure. The T unit has a structure represented by the following chemical formula 1, and the D unit has a structure represented by the following chemical formula 2.

[0048]

[0049] In Chemical Formula 1 and Chemical Formula 2, R1 may be at least one organic curing group selected from an epoxy group, an alicyclic epoxy group, an acrylic group, a methacrylic group, an amine group, a vinyl group, a cyan group, and a thiol group. Preferably, in the case of the first silane compound, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyldimethoxymethylsilane, N-(3-acryloxy-2-hydroxypropyl)-3-aminopropyltrimethoxysilane, N-(3-acryloxy-2-hydroxypropyl)-3-aminopropyltriethoxysilane, N-(3-acryloxy-2-hydroxypropyl)-3-aminopropyltripropoxysilane, 3-acryloxypropylmethylbis(trimethoxy)silane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-acryloxypropyltripropoxysilane, 3-acryloxypropyldimethoxymethylsilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(Meth)acryloxypropyldimethoxymethylsilane, 3-(Meth)acryloxypropyltriethoxysilane, 3-(Meth)acryloxypropyltripropoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-(2,3-epoxypropoxypropyl)methyldimethoxysilane, 3-(2,3-epoxypropoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-cyanopropyltrimethoxysilane, 3-cyanopropyldimethoxymethylsilane, N-(aminoethyl-3-aminopropyl)trimethoxysilane, N-(2-aminoethyl-3-aminopropyl)triethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, chloropropyltrimethoxysilane, chloropropyltriethoxysilane, 3-mercapdopropyltrimethoxysilane, 3-mercapdopropyldimethoxymethylsilane, 3-glycidoxypropyldimethoxymethylsilane, 3-glycidoxypropyldiethoxymethylsilane, or a mixture thereof.

[0050] At this time, the first silane compound including an organic curing group may be added in an amount of 10 to 100 parts by weight based on 100 parts by weight of the polymer. If the first silane compound is mixed in an amount of less than 10 parts by weight, the synthesis of the siloxane binder is not easy, which has the disadvantage of not being able to properly connect the polymer and siloxane, and if it exceeds 100 parts by weight, the ratio of siloxane becomes too large, which may reduce the adhesive strength of the binder, which is not preferable.

[0051]

[0052] Next, the second step (S20) is a step for manufacturing a siloxane-polymer composite resin, which is manufactured by adding a second silane compound that does not contain an organic curing group and an acid catalyst or a base catalyst to a mixture of the first silane compound and the polymer solution and thermally stirring the mixture. In this step, the addition of the catalyst causes the silane compounds to form a siloxane resin, and at this time, an in situ condensation reaction occurs between the oxygen-containing functional group of the polymer and the oxygen-containing functional group of the second silane compound. Accordingly, the polymer is covalently bonded to synthesize a siloxane resin, thereby manufacturing a siloxane-polymer composite resin.

[0053] At this time, the second silane compound not containing an organic curing group can be added in an amount of 10 to 100 parts by weight per 100 parts by weight of the polymer. If the second silane compound is mixed in an amount of less than 10 parts by weight, there is a disadvantage in that the miscibility with the first silane compound is poor and the binding role between the polymer and siloxane cannot be sufficiently performed. On the other hand, if the second silane compound is mixed in an amount exceeding 100 parts by weight, the molecular weight of the siloxane-polymer composite resin increases, resulting in transformation into a gel form, which is not preferable.

[0054] Preferably, the second silane compound is a mixture of non-crosslinking silanes that do not contain an organic curing group, (R2SiO 2 / 2 ) D unit of the structure, (R3SiO 1 / 2) M unit of structure, (SiO 4 / 2 ) includes at least one Q unit of the structure, and the D unit, the M unit and the Q unit have structures represented by the following chemical formulas 3, 4 and 5. R3, R4 and R5 in chemical formulas 3 and 4 may each be at least one functional group selected from an alkyl group, an aryl group and a hydrogen group.

[0055]

[0056] In particular, it is preferable to use a second silane compound including a silane having a Q unit as the second silane compound. This is because a siloxane resin binder manufactured by including a silane having a Q unit can generate a greater number of hydroxyl groups per unit molecule compared to a siloxane resin binder using silanes having M, D, and T units, thereby facilitating a condensation reaction with the polymer. However, if the silane having a Q unit exceeds 100 parts by weight based on 100 parts by weight of the polymer, as mentioned above, the molecular weight of the siloxane resin binder excessively increases, which is not preferable because there is a high possibility that a gel will be formed.

[0057] More preferably, the second silane compound is methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, trichlorooctadecylsilane, trichlorohexadecylsilane, trichlorododecylsilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenylsilanediol, triphenylmethoxysilane, 3,3,3-trifluorotrimethoxysilane, 3,3,3-Trifluorotriethoxysilane, perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorododecyltrimethoxysilane, perfluorododecyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraphenoxysilane, tetraacetoxysilane, trimethoxysilane, triethoxysilane, tri-n-propoxysilane, triisopropoxysilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, or a mixture thereof.

[0058] For reference, if we organize the chemical formulas 1 to 5 of the first silane compound and the second silane compound mentioned above, the T unit is (RSiO 3 / 2 ) means the unit represented by (R2SiO 2 / 2 ) means the unit indicated by (R3SiO 1 / 2 ) means the unit represented by (SiO 4 / 2 ) refers to a unit represented by R. Here, R refers to a functional group bonded to each silicon (Si).

[0059] The chemical bonding mechanism of the siloxane-polymer composite resin binder manufactured through the second step is shown in Fig. 2. Referring to this, a more detailed description will be given. In the first step (S10), an acid or base catalyst is added to a mixture composed of a polymer and a first silane compound, and then heat and stir to cause condensation, thereby inducing an in-situ condensation reaction to manufacture a siloxane resin. The siloxane resin is bonded to a polymer having an oxygen-containing functional group, so that the siloxane and the polymer are chemically bonded. That is, as shown in Fig. 2, the siloxane-polymer composite resin is covalently and ionicly bonded by the condensation reaction between the hydroxyl group, which is an oxygen-containing functional group of the siloxane resin, and the hydroxyl group, which is an oxygen-containing functional group on the surface of the polymer, and the condensation reaction is generated and bonded in an in-situ manner.

[0060] In addition, the above siloxane-polymer composite resin is a condensation reaction that occurs with a siloxane bond having a Si-O-Si structure using a sol-gel synthesis method based on a first silane compound and a second silane compound. At this time, if the reaction starts in the presence of a polymer having an oxygen-containing functional group, an in-situ heterometal condensation reaction can be generated between the oxygen-containing functional group of the polymer, such as a hydroxyl group or a carboxyl group, and the oxygen-containing functional group of the first silane compound and the second silane compound, such as an alkoxy group. This is expressed by the following reaction formula.

[0061] [Reaction Formula 1]

[0062] R'-OH + RO-Si → RO-Si + ROH

[0063] [Reaction Formula 2]

[0064] R'-OOH + RO-Si → RO-Si + ROOH

[0065] [Reaction Formula 3]

[0066] R'-OH + OH-Si → RO-Si + H2O

[0067] In the above reaction formulas 1, 2, and 3, R' represents a polymer having an oxygen-containing functional group. Referring to the above reaction formulas, when a silane compound is added together with a polymer having an oxygen-containing functional group, an in-situ condensation reaction occurs between a hydroxyl group of the polymer side chain and an alkoxy group or hydroxyl group of the silane compound through a heat-stirring reaction, thereby forming a primary bond rather than a secondary bond. In other words, the siloxane-polymer composite resin can be provided as a binder for secondary batteries, and can be applied as a binder material that can improve the durability and stability of electrodes.

[0068] In addition, the catalyst added in the second step may be an acid or base catalyst. At this time, the catalyst is added in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the silane compound including the first silane compound and the second silane compound. If the catalyst is added in an amount less than 0.1 parts by weight, the reactivity decreases, which has the disadvantage of lowering the degree of condensation of the siloxane resin. On the other hand, if it is added in an amount exceeding 0.5 parts by weight, the reactivity increases too much, which may result in the synthesis of a siloxane-polymer composite resin in the form of particles or gels.

[0069] At this time, an acidic aqueous solution or a base aqueous solution may be used as the acid catalyst or base catalyst. The acidic aqueous solution may be an aqueous solution containing at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, iodic acid, hydrofluoric acid, and chlorosulfonic acid. The base aqueous solution may be an aqueous solution containing at least one of imidazole, potassium hydroxide, barium hydroxide, ammonium hydroxide, and sodium hydroxide. In some cases, an ion exchange resin such as Amberite IRA-400 or IRA-67 may also be used as a catalyst.

[0070] Additionally, a pH regulator may be added to control the pH of the siloxane-polymer composite resin at this stage, and the type of pH regulator used is not limited.

[0071] In addition, in the second step, the thermal stirring is performed at a temperature ranging from 10 to 80°C and a speed of 100 to 2,000 RPM for 4 to 48 hours to in-situ condense and synthesize the siloxane resin while simultaneously allowing the siloxane resin to bind to the polymer, thereby producing a siloxane-polymer composite resin.

[0072] At this time, if the temperature is less than 10℃ during the above heat stirring, it cannot be considered that heat has been applied, and if it exceeds 80℃, the time required for synthesizing the siloxane-polymer composite resin is reduced, but there is a problem that heat-induced deformation may occur in the siloxane resin that is combined with the polymer.

[0073] In addition, if stirring is performed at a speed of less than 100 RPM, it takes more than 48 hours for the siloxane resin to completely bind with the polymer, which results in poor productivity, and if the stirring speed exceeds 2,000 RPM, the sample is pumped out of the container, which results in a high sample loss rate.

[0074] In addition, there is a disadvantage that chemical bonding between the siloxane resin and the polymer is not completely achieved under conditions of thermal stirring of less than 4 hours, and if it exceeds 48 hours, there is a disadvantage that it becomes difficult to control the viscosity of the siloxane-polymer composite resin.

[0075]

[0076] According to the method described above, it is characterized in that it is possible to manufacture a siloxane-polymer composite resin that enables covalent bonding between the siloxane and the polymer, i.e., primary bonding. In particular, when manufacturing the siloxane-polymer composite resin, the oxygen-containing functional groups such as hydroxyl groups and carboxyl groups of the polymer side chain induce condensation with the oxygen-containing functional groups such as alkoxy groups and hydroxyl groups of the silane compound to form a primary bond, and at the same time, a siloxane bond is formed, so that a siloxane-polymer composite binder can be manufactured in situ at once. If it is not manufactured in situ, as shown in FIG. 3, phase separation of the siloxane and the polymer will occur, which will ultimately result in layer separation. Therefore, if it is manufactured in situ according to the method of the present invention described above, the polymer and siloxane will chemically bond to form a uniform compound, so that layer separation will not occur.

[0077] Accordingly, the electrode manufactured using a conventional non-fluorinated polymer alone had a low electrode durability due to the low electrochemical durability of the non-fluorinated polymer, whereas the siloxane-polymer composite binder of the present invention can ensure the electrochemical stability of the electrode because the siloxane resin with excellent electrochemical durability is firmly bonded to the polymer through a primary bond, and can also secure excellent adhesion to the current collector, which is unique to the polymer. According to a preferred embodiment of the present invention, compared to an electrode using a PVDF resin, which is a conventional fluorinated binder, an electrode using the siloxane-polymer composite resin of the present invention as a binder showed an adhesive strength that was more than twice as improved (see Fig. 4), and it was confirmed that the output efficiency and lifespan stability of a battery using the electrode were improved because the siloxane with excellent durability and the polymer were chemically bonded, thereby improving the electrochemical stability (see Fig. 5).

[0078]

[0079] Accordingly, in another aspect, the present invention relates to a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer and manufactured by the above-described method.

[0080] In another aspect, the present invention relates to an electrode slurry comprising the above-described non-fluorinated siloxane-polymer composite binder. Preferably, the electrode slurry may comprise an electrode active material; and the above-described binder. If necessary, a solvent, a conductive agent, etc. may be further included. Specifically, the slurry according to one embodiment of the present invention may comprise 1 to 5 wt% of the binder based on 100 wt% of the total slurry. If the binder is included in an amount less than the above range, the adhesive strength between the active material and the electrode may be reduced, and if the content of the included binder exceeds the above range, the resistance of the battery may be increased.

[0081] In addition, the electrode active material may be a positive electrode active material or a negative electrode active material, and any material commonly used in the art may be used without limitation. For example, the positive electrode active material may be at least one compound oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof, and the negative electrode active material may include at least one selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

[0082] In addition, carbon black, graphite particles, etc. may be used as the conductive material, but are not limited thereto, and any material that can be used as a conductive material in the relevant technical field may be used.

[0083] In another aspect, the present invention relates to an electrode for a lithium secondary battery, characterized by including a current collector and an electrode active layer formed by applying an electrode slurry containing the siloxane-polymer composite binder to the surface of the current collector. The electrode active layer may include a conventional positive or negative electrode active material used in a lithium secondary battery, and a conventional conductive material may be used. The electrode of the present invention to which the siloxane-polymer composite binder is applied can obtain an effect of improving adhesive strength with the current collector. That is, whereas an electrode manufactured using a conventional non-fluorinated polymer alone had a reduced electrode durability due to the low electrochemical durability of the non-fluorinated polymer, when the siloxane-polymer composite binder of the present invention is applied, the siloxane resin having excellent electrochemical durability is firmly bonded to the polymer through primary bonding, thereby ensuring the electrochemical stability of the electrode and also securing excellent adhesive strength with the current collector that is characteristic of the polymer.

[0084] In another aspect, the present invention relates to a lithium secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized by including an electrode to which the above-described siloxane-polymer composite binder is applied. The lithium secondary battery can improve physical properties equivalent to or greater than those of a conventional lithium secondary battery by applying the siloxane-polymer composite binder of the present invention to an electrode active layer.

[0085]

[0086] Hereinafter, embodiments of the present invention will be described in more detail. However, the following embodiments are provided merely to aid understanding of the present invention, and the scope of the present invention is not limited thereby.

[0087]

[0088] <Example 1>

[0089] 1-1. Preparation of an epoxy siloxane-EVOH composite binder using a siloxane binder having an epoxy group as an organic curing group and an EVOH polymer.

[0090] 100 parts by weight of EVOH pellets (Kurary, F171B) and 400 parts by weight of NMP solvent were added to a two-necked flask and dissolved at 60°C. 70 parts by weight of a first silane compound composed of 80 parts by weight of 3-glycidoxypropyltrimethoxysilane and 20 parts by weight of 3-glycidoxypropyldimethoxymethylsilane was added to the polymer solution and stirred at 60°C for 2 hours.

[0091] Afterwards, based on 100 parts by weight of EVOH polymer, 50 parts by weight of a second silane compound composed of 50 parts by weight of tetramethoxysilane and 50 parts by weight of dimethoxydimethylsilane and 0.5 parts by weight of 0.05N ammonium hydroxide were added, and the mixture was stirred at 60°C for an additional 8 hours to prepare an epoxy siloxane-EVOH polymer composite binder.

[0092] To the manufactured composite binder, 0.5 parts by weight of cationic initiator (diphenylmethylsulfonium tetrafluoroborate) was added per 100 parts by weight of the binder, and the mixture was stirred at room temperature.

[0093] 1-2. Manufacturing of the anode

[0094] The epoxy siloxane-EVOH polymer composite binder manufactured in Example 1-1 was mixed with NCM811 active material and MWCNT conductive material to manufacture a positive electrode slurry (binder:active material:conductive material mixed in a weight ratio of 3:95:2). The manufactured positive electrode slurry was applied to aluminum foil using a doctor blade, and then dried at 120°C for 4 hours to induce evaporation of the NMP solvent and thermal curing, thereby manufacturing a positive electrode.

[0095]

[0096] <Example 2>

[0097] 2-1. Preparation of a methacrylic siloxane-phenoxy polymer composite binder using a siloxane binder having a methacrylic group as an organic curing group and a phenoxy polymer.

[0098] 100 parts by weight of phenoxy pellets (Gabriel, PKHH) and 300 parts by weight of NMP solvent were added to a two-necked flask and dissolved at room temperature. 100 parts by weight of a first silane compound composed of 50 parts by weight of 3-(meth)acryloxypropyltrimethoxysilane and 50 parts by weight of 3-(meth)acryloxypropyldimethoxymethylsilane based on 100 parts by weight of the total phenoxy polymer was added and mixed.

[0099] 0.5 parts by weight of a 0.03 N aqueous hydrochloric acid solution was added to 100 parts by weight of the phenoxy polymer, and the mixture was stirred at 60°C for 6 hours. Thereafter, 50 parts by weight of a second silane compound composed of 20 parts by weight of tetramethoxysilane and 80 parts by weight of dimethyldiethoxysilane was additionally added to 100 parts by weight of the phenoxy polymer, and the mixture was stirred at 60°C for an additional 12 hours to produce a methacrylic siloxane-phenoxy polymer composite binder.

[0100] To the manufactured complex, 0.5 parts by weight of radical initiator (tert-butyl peroxide) was added to 100 parts by weight of phenoxy polymer, and the mixture was stirred at room temperature.

[0101] 2-2. Manufacturing of the cathode

[0102] The methacrylic siloxane-phenoxy polymer composite binder manufactured in Example 2-1 was mixed with the negative electrode active material (carbon) and the conductive material (Super P) to manufacture a negative electrode slurry (the weight ratio of binder:active material:conductive material was 5:90:5). The mixed negative electrode slurry was applied onto copper foil using a doctor blade and dried at 150°C for 4 hours to manufacture a negative electrode.

[0103]

[0104] <Example of an exam>

[0105] Adhesion test

[0106] The electrode manufactured in Example 1 was cut to a certain size and fixed to a slide glass using 3M double-sided tape. Then, the current collector was peeled off and the 180° peel strength was measured, and the results are shown in Fig. 4. The evaluation was determined by measuring the peel strength of five or more and taking the average value.

[0107] As a comparative example, a positive electrode was manufactured using the same method as Example 1 using a PVDF binder and a siloxane binder, and an adhesion test was performed in the same manner.

[0108]

[0109] Referring to Fig. 4, it can be confirmed that the siloxane-polymer composite resin of the present invention has significantly improved adhesive strength compared to the electrode using PVDF, a conventional fluorinated binder, and the electrode using a siloxane-only resin. The electrode using PVDF, a conventional fluorinated binder, showed an adhesive strength of 25 gf / 20mm on average, but the electrode using the siloxane-polymer composite binder of the present invention showed an adhesive strength value that was more than twice as improved as that of the PVDF binder, at approximately 60 gf / 20mm or more.

[0110] Charge and discharge test of half-cell

[0111] A half-cell was fabricated using NCM811 (Ni:Cr:Mn=8:1:1) as the active material as the positive electrode, Li metal as the negative electrode, 1M LiPF6 dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate (v:v=1:1) as the electrolyte, and Celgard 2400 as the separator. A charge / discharge test was performed on the half-cell under the following measurement conditions, and the voltage and capacity (Capacity / mAh g-1) were measured. The measurement conditions are shown in Table 1 below.

[0112] In addition, as a comparative example, half-cells using different binders were manufactured and measured using the same method as above.

[0113] C-rate measurement conditions - Charge: 0.33C (CC) - Discharge: 0.33C, 0.5C, 1C, 2C, 3C, 4C, 5C (CC) - 1 hour rate (1C rate) = 230mA / g - Voltage range: 3-4.35V vs Li / Li+ - Temperature: 45℃ Cycle test measurement conditions - 0.33C / 0.33C(CC / CC) 2 cycles 0.5C / 0.5C(CC / CC) 2 cycles 0.5C / 1C(CC / CC) 200 cycles - 1 hour rate (1C rate) = 230mA / g - Voltage range: 3-4.35V vs Li / Li+ - Temperature: 45℃

[0114] The results of measuring the output efficiency and life stability of the above half-cell are shown in Fig. 5. Referring to this, the cell to which the polymer-only binder was applied showed the lowest output efficiency and life stability. On the other hand, when the siloxane-polymer composite binder of the present invention was applied, results equivalent to those of the existing siloxane-only binder were observed, and somewhat improved output efficiency and life stability were observed compared to when PVDF, a fluorinated binder, was applied. This is believed to be the result of the improved electrochemical stability due to the chemical bonding of the durable siloxane and polymer in the binder of the present invention.

[0115]

[0116] Thus, according to the present invention, an interpenetrating polymer network microstructure is formed through chemical bonding of electrochemically stable siloxane and polymer, thereby improving the stability of a lithium secondary battery during charge and discharge, and it is confirmed that the introduction of an organic polymer having an oxygen-containing functional group improves the adhesive strength of a siloxane-polymer composite binder, thereby inducing a bonding strength with a current collector, thereby improving the stability of a lithium secondary battery.

Claims

1. A first step of preparing a mixture in which a first silane compound having an organic curing group is added and stirred into a polymer solution prepared by dissolving a polymer having an oxygen-containing functional group in a solvent, thereby uniformly dispersing the silane compound in the polymer solution; and A second step of producing a siloxane-polymer composite resin by adding a second silane compound that does not contain an organic curing group to the mixture and an acid catalyst or a base catalyst and stirring the mixture under heat to cause an in situ condensation reaction between the oxygen-containing functional group of the polymer, the oxygen-containing functional group of the first silane compound and the oxygen-containing functional group of the second silane compound, thereby synthesizing a siloxane resin while the polymer is covalently bonded; A method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer, characterized in that the first silane compound comprises at least one of the following chemical formulas 1 and 2, and the second silane compound comprises at least one of the following chemical formulas 3, 4, and 5: (However, R1 is at least one organic curing group selected from an epoxy group, an alicyclic epoxy group, an acrylic group, a methacrylic group, an amine group, a vinyl group, a cyan group, and a thiol group, and R2, R3, R4, and R5 are at least one functional group selected from an alkyl group, an aryl group, and a hydrogen group, respectively.) 2. In paragraph 1, A method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer, characterized in that the oxygen-containing functional group is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, and a carbonyl group.

3. In paragraph 1, In the first step, the polymer solution is prepared by dissolving 100 parts by weight of the polymer having the oxygen-containing functional group in 100 to 400 parts by weight of the solvent. A method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer, characterized in that the first silane compound and the second silane compound added in the first and second steps are each added in an amount of 10 to 100 parts by weight based on 100 parts by weight of the polymer.

4. In paragraph 1, A method for producing a non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer, wherein the polymer has a molecular weight of at least 25,000.

5. A non-fluorinated siloxane-polymer composite binder having improved adhesiveness by a binding polymer, characterized in that it is manufactured according to any one of claims 1 to 4.

6. An electrode slurry comprising a non-fluorinated siloxane-polymer composite binder according to Article 5.

7. The entire house; and An electrode comprising an electrode active layer formed by applying an electrode slurry according to claim 6 to the surface of the above-mentioned collector.

8. A secondary battery comprising an electrode according to Article 7.

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