Composition for modifying electrode active material comprising cellulose or functionalized cellulose, electrode active material modified with cellulose or functionalized cellulose, and secondary battery comprising same

Abstract

The present invention relates to: a composition for modifying the surface of an electrode active material for a secondary battery, wherein the composition comprises cellulose, modified cellulose, or a mixture thereof; an electrode active material for a secondary battery, wherein the electrode active material is coated with cellulose, modified cellulose, or a mixture thereof; and a secondary battery comprising same. According to the present invention, a dry electrode can be manufactured by excluding the use of a fluorine-based binder or reducing the amount of the used fluorine-based binder, and excellent dispersibility and adhesion are achieved without using a PTFE binder conventionally used as a dry electrode binder, thereby enabling the production of a high-capacity thick film electrode.

Description

Composition for modifying electrode active material including cellulose or functionalized cellulose, electrode active material modified with cellulose or functionalized cellulose, secondary battery including the same

[0001] The present invention relates to a composition for modifying an electrode active material including cellulose or functionalized cellulose, an electrode active material modified with cellulose or functionalized cellulose, a secondary battery including the same, and the like.

[0002] With the advent of the Battery of Things (BoT) era, where everything from smart devices, electric vehicles, drones, home appliances, and robots runs on batteries, demand for rechargeable secondary batteries is exploding. In particular, the rapid growth of the electric vehicle market and the expansion of energy storage systems (ESS) driven by global renewable energy expansion policies are driving the growth of the secondary battery market.

[0003] With this market expansion, the importance of cathode materials, among the four core materials of lithium secondary batteries—category A, anode materials, separators, and electrolytes—is increasingly highlighted. Cathode materials serve as a source of lithium in secondary batteries and are a key component determining battery capacity. In particular, mid- to large-sized batteries require high energy density, leading to active development of high-capacity active materials, particularly NCM and NCA, which have high nickel (Ni) content.

[0004] These active materials have lower cobalt (Co) content than conventional LCO, making them price-competitive. Furthermore, their large surface area offers superior power density. However, due to high technological barriers to manufacturing, Korean and Japanese companies are currently leading the development process, while Chinese companies tend to focus on low-cost materials like LFP.

[0005] Cathode materials, along with anode materials, are key components that determine the capacity, output, and safety of secondary batteries. They store lithium ions released from the anode. Accordingly, as anode capacity increases, anode capacity also accelerates.

[0006] Currently, active research is underway to increase the capacity of existing graphite anode materials by adding silicon to them, or to develop anodes based solely on silicon. This reflects efforts to increase battery energy density while optimizing charge / discharge performance.

[0007] In addition, beyond the development of positive and negative electrode materials, high-capacity technologies utilizing thick-film electrodes, which increase the thickness of the electrode active material layer, have recently been attracting attention. Thick-film electrodes can replace conventional multi-layer thin-film electrodes, significantly reducing the volume of secondary batteries. They also reduce the use of high-density current collectors and relatively expensive separators, making them a highly promising technology in terms of weight and cost. However, their performance and manufacturing process have not yet been sufficiently secured compared to conventional thin-film electrodes.

[0008] Current secondary battery manufacturing processes predominantly utilize wet electrode processes. However, wet processes exhibit limitations in achieving thick-film electrodes due to deteriorated structural and electrochemical performance.

[0009] In wet processes, a process solvent must be used to uniformly disperse the electrode components (active material, conductive agent, and binder) and apply them to the current collector as a slurry. However, during the drying process of the electrode slurry, the binder tends to concentrate and aggregate on the upper layer of the electrode. This disrupts the lithium ion conduction path and weakens the adhesion between the electrode and the current collector.

[0010] This limits electrode thickness increases and increases internal battery resistance, making it difficult to improve battery performance. To address these issues, dry electrode manufacturing technologies that do not use process solvents have recently been attracting attention.

[0011] The limitations of the wet electrode process are mainly due to the low adhesiveness and dispersibility of the PVDF binder, and the current dry electrode also has problems of electrode structure instability and performance degradation due to the use of PTFE binder.

[0012] In particular, as the European Chemicals Agency (ECHA) pursues restrictions on the use of nearly all perfluorinated compounds (PFAS), PTFE, used as a binder in dry electrodes, is now subject to regulation. Consequently, the development of new dry electrode manufacturing technologies that eliminate or reduce the use of fluorinated binders has become an urgent task.

[0013] [Prior Art Literature]

[0014] [Patent Document]

[0015] (Patent Document 1) 1. Korean Patent No. 10-1198295

[0016] (Patent Document 2) 2. Chinese Publication Patent No. 112467141

[0017] [Non-patent literature]

[0018] (Non-patent Document 1) 1. Imidazolium functionalized cellulose filter paper derived from waste newspaper and its application in removal of chromium(VI), Reactive and Functional Polymers, Volume 157, December 2020, 104776

[0019] (비특허문헌 2)2. Cellulosic poly(ionic liquid)s: synthesis, characterization and application in the cycloaddition of CO2 to epoxides, RSC Adv., 2015, 5, 44598

[0020] (비특허문헌 3)3. Phosphorylation of the cellulose surface with PCl3 and P(O)Cl3, Phosphorus, Sulfur, and Silicon and the Related Elements, Volume 197, Issues 5-6, 2022, Pages 634-638

[0021] (비특허문헌 4)4. Sulfonic acid functionalized cellulose-derived (nano)materials: Synthesis and application, Advances in Colloid and Interface Science, Volume 328, June 2024, 103158

[0022] (비특허문헌 5)5. Synthesis of amino-functionalized nanocellulose by guanidine based deep eutectic solvent and its application in fine fibers retention, International Journal of Biological Macromolecules, Volume 260, Part 1, March 2024, 129473

[0023] The purpose of the present invention is to solve the above problems, and to provide a surface-modified electrode active material that enables the manufacture of a dry electrode by eliminating or minimizing the use of a binder such as a fluorine-based binder, and has excellent dispersibility and adhesiveness without using a binder such as PTFE, which is commonly used as a conventional dry electrode binder, thereby enabling the manufacture of a high-capacity thick-film electrode.

[0024] Another object of the present invention is to provide an electrode including a surface-modified electrode active material, which can form a stable electrode-electrolyte interface by configuring an electrode including a surface-modified active material, thereby improving life characteristics, suppressing collapse of the active material structure, and consequently implementing high energy density, and a secondary battery including the same.

[0025] According to one aspect of the present invention, a composition for modifying the surface of an electrode active material for a secondary battery is provided, which comprises cellulose or cellulose functionalized to have a functional group bound thereto or a mixture thereof.

[0026] According to another aspect of the present invention, an electrode active material is provided that is surface-modified with cellulose or cellulose functionalized to have a functional group bound thereto or a mixture thereof.

[0027] According to another aspect of the present invention, there is provided an electrode for a secondary battery comprising a surface-modified electrode active material of cellulose or a functionalized cellulose or a mixture thereof to which a functional group is bound, a secondary battery comprising the same, or a device selected from among a portable electronic device, a mobile unit, a power device, and an energy storage device comprising the same.

[0028] According to another aspect of the present invention, a method for producing a positive electrode active material or a negative electrode active material surface-modified with cellulose or cellulose functionalized to have a functional group bonded thereto or a mixture thereof is provided.

[0029] Another aspect of the present invention provides a method for manufacturing an electrode comprising an active material surface-modified with cellulose or functionalized cellulose or a mixture thereof to bind functional groups.

[0030] The electrode active material for a secondary battery of the present invention is modified by coating the surface of the electrode active material with cellulose or cellulose functionalized to have a functional group bonded thereto, or a mixture thereof, thereby eliminating the use of a fluorine-based binder or reducing the amount used, thereby enabling the manufacture of a dry electrode, and has excellent dispersibility and adhesiveness without using a PTFE binder used as a conventional dry electrode binder, thereby enabling the manufacture of a high-capacity thick-film electrode.

[0031] Furthermore, secondary batteries containing active materials surface-modified with cellulose or functionalized cellulose or a mixture thereof, such as those bonded with functional groups, can form a stable electrode-electrolyte interface through the interaction between the electrolyte and the functional cellulose, thereby improving cycle life characteristics and suppressing the structural collapse of the active material, thereby achieving high energy density.

[0032] Figure 1 is a conceptual diagram of surface modification of a positive electrode active material using functionalized cellulose of the present invention and a dry electrode based on the surface-modified positive electrode active material.

[0033] Figure 2 is a schematic diagram of a surface modification process of a positive electrode active material according to Manufacturing Example 2-2.

[0034] Figure 3 shows a dispersion of cellulose (a) and a microscope image of cationic cellulose (b) before and after modification according to Experimental Example 1.

[0035] Figure 4 is an SEM image comparing the positive electrode active material before and after surface modification according to Experimental Example 2.

[0036] Figure 5 is a photograph comparing the electrode mixtures of Example 1 and Comparative Example 1 according to Experimental Example 3.

[0037] Figure 6 is a photograph comparing the adhesive strength of a functionalized cellulose film and a PTFE binder film according to Experimental Example 4.

[0038] Figure 7 is a graph comparing photographs of dry electrodes manufactured in examples, adhesive strength according to the presence or absence of active material modification, and charge / discharge profiles. (Surface modification) Active material: conductive material: PTFE weight ratio = 98:1:1.

[0039] Figure 8 shows the results of electrochemical life characteristics analysis according to Experimental Example 5.

[0040] Figure 9 is a SEM image of an NCM cathode active material surface-modified by combining cationic cellulose (c-CNF) and a conductive material (CNT) without a PTFE binder. (c-CNF+CNT) Surface-modified active material: conductive material weight ratio 98:2 vs. surface-unmodified active material: conductive material: PTFE weight ratio 96:2:2

[0041] Figure 10 is an SEM photograph of a negative electrode active material surface-modified with cationic cellulose (c-CNF), anionic cellulose (a-CNF), and polar cellulose (p-CNF).

[0042] Figure 11 shows a photograph of a surface-modified negative active material and the electronic conductivity of the composite layer of the electrode.

[0043] Hereinafter, various aspects and various implementation examples of the present invention will be described in detail with reference to examples and the attached drawings so that those skilled in the art can easily implement the present invention.

[0044] However, the following description is not intended to limit the present invention to only the specific implementation examples, and if it is determined that a specific description of a known technology mentioned in the course of explaining the present invention may obscure the gist of the present invention, the detailed description will be omitted.

[0045] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, or combinations thereof.

[0046] One aspect of the present invention relates to a composition for modifying the surface of an electrode active material for a secondary battery, the composition comprising cellulose, functionalized cellulose, or a mixture thereof.

[0047] In the present invention, functionalized cellulose or modified cellulose means at least one selected from cellulose modified to bind a cationic functional group, cellulose modified to bind an anionic functional group, and cellulose modified to bind a polar functional group, unless otherwise described in the relevant part.

[0048] Another aspect of the present invention relates to a modified electrode active material for a secondary battery, comprising (a) an active material core layer selected from among a positive electrode active material and a negative electrode active material, and (b) an active material coating layer coating the active material core layer.

[0049] Here, the electrode is a cathode or an anode, and the active material coating layer comprises cellulose, functionalized cellulose, or a mixture thereof.

[0050] A conceptual diagram of surface modification of a positive electrode active material using cellulose or functionalized cellulose of the present invention and a dry electrode based on the surface-modified positive electrode active material is presented in Fig. 1.

[0051] In the present invention, cellulose or functionalized cellulose performs the function of improving the dispersibility between materials constituting the electrode, such as an electrode active material or a conductive material, and also improving the adhesive strength between the electrode material and the current collector, which can be realized by combining an ionic or polar functional group capable of hydrogen bonding or ionic bonding.

[0052] According to the present invention, the positive or negative active material surface-modified with cellulose or functionalized cellulose can be used not only for dry electrode production but also for wet electrode production. When applied to a wet process, it has the advantage of solving the problem of ion transport being hindered and current collectors and electrodes being detached due to the presence of a conductive material and binder in the upper layer and an active material in the lower layer.

[0053] Among these, in particular, when functionalized cellulose is used, it can be applied to the production of dry electrodes, and can have the effect of eliminating the use of PTFE binder, which was conventionally used in the production of dry electrodes, or significantly reducing the amount used.

[0054] As such, the cellulose used to modify the surface of the electrode active material in the present invention is an environmentally friendly polymer extracted from trees and possesses a fibrous structure with a high aspect ratio. This cellulose is easily amenable to functional group substitution, and the following properties can be expected through functional group design.

[0055] First, the adhesion and dispersibility can be maximized by modifying the surface properties through the introduction of functional groups. Specifically, the surface energy (γ) of cellulose can be increased by introducing various ionic or polar functional groups. Binder ) and work of adhesion (W CA-Binder ) can be used to improve adhesion and dispersibility.

[0056] In addition, by introducing functional groups capable of dynamic covalent bonding, such as amine, imine, and ester, it is possible to secure thermal processability, which is an important characteristic for the dry electrode manufacturing process.

[0057] Moreover, unlike hydrophobic PTFE, which is conventionally used as a binder for dry electrodes, the introduction of polar or ionic functional groups can promote interaction with ions within the electrolyte. This can enhance the wettability of polar electrolytes and contribute to changes in the electrolyte solvation structure within the electrode pore structure, thereby forming a stable protective layer (cathode-electrolyte interphase, CEI) on the surface of the active material, thereby improving electrode performance.

[0058] In this way, the present invention includes as one of its technical features the ability to simultaneously achieve low electrolyte swelling and high electrolyte wettability by coating the surface of an electrode active material using cellulose or functionalized cellulose.

[0059] However, the cellulose usable in the present invention does not necessarily mean only natural polymer cellulose extracted from trees. Examples of cellulose usable in the present invention include, but are not limited to, cellulose nanofibers (CNF), cellulose nanocrystals (CNC), microfibrillated cellulose (MFC), microcrystalline cellulose (MCC), bacterial cellulose, and the like.

[0060] Among these celluloses, cellulose nanofibers or cellulose nanocrystals are preferred, and among them, cellulose nanofibers are particularly preferred.

[0061] The above cellulose nanofibers may have a diameter of 1 nm to 100 μm, preferably 5 to 100 nm, more preferably 10 to 50 nm. In addition, the cellulose nanofibers may have a length of 50 nm to 500 μm, preferably 1 to 300 μm, more preferably 10 to 100 μm.

[0062] Additionally, the diameter of the cellulose nanocrystals may be 1 nm to 100 μm, preferably 5 to 100 nm, and more preferably 10 to 50 nm.

[0063] When the diameter and length of cellulose are within the above range, the dispersibility and binding force can be maximized, and when the diameter and length of cellulose are below the lower limit, the binding force can be reduced, and when the diameter and length of cellulose exceed the above upper limit, the dispersibility can be reduced.

[0064] According to one embodiment of the present invention, the functionalized cellulose has a degree of substitution (DS) of 0.03 to 3, where the degree of substitution means the number of substituted or modified functional groups per cellulose monomer (anhydroglucose unit, AGU).

[0065] For example, in the case of cellulose modified with quaternary (or quaternary) ammonium functional groups, which is an example of cationic cellulose, the DS value can be derived in the range of 0.1 to 0.5 through the substitution of quaternary ammonium. In the case of TEMPO-oxidized cellulose nanofibers, which is an example of anionic cellulose, the amount of carboxylate functional groups introduced is on the order of 0.2 to 2 mmol / g, and the corresponding DS value can be calculated to be in the range of about 0.03 to 0.32. In addition, in the case of 2-hydroxyethyl cellulose (HEC), which is an example of polar cellulose, the DS value has been reported to range from 0.8 to 3.0 depending on the amount of hydroxyethyl functional groups introduced, and may vary depending on the physical properties and use of the product. Therefore, the DS value of the polar and ionic cellulose applicable in the present invention can be adjusted within a range of 0.03 or more and 3 or less.

[0066] According to another embodiment of the present invention, the active material coating layer further comprises a conductive material. That is, the conductive material can be used to surface-modify a positive electrode active material or a negative electrode active material as a composite material together with cellulose or functionalized cellulose.

[0067] Examples of conductive materials that can be used in this manner include, but are not limited to, one or more selected from conductive polymers, carbon nanotubes, MXenes, graphene, metal nanowires, conductive ceramics, and metal or alloy powders.

[0068] Examples of the conductive polymer include, but are not limited to, polyacetylene, polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene) (PEDOT).

[0069] Carbon nanotubes include, but are not limited to, single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof.

[0070] Maxine is a titanium-based maxine (Ti3C2T x ), vanadium-based MXene (V2CT) x ), niobium-based MXene (Nb2CT x ), or mixtures thereof, including but not limited to.

[0071] According to another embodiment of the present invention, the functional group introduced to modify cellulose is at least one selected from a cationic functional group, an anionic functional group, and a polar functional group, and when two or more functional groups are introduced, the introduced functional groups may be all the same, all different, or only some of them may be the same and the rest may be different.

[0072] The above cationic functional group is ammonium (-NH4 + ), primary to quaternary ammonium (-NH3R + , -NH2R2 + , -NHR3 + , -NR4 + ), pyridinium (-Py + ), imidazolium (-Im + ), triazolium(-Trz + ), thiazolium (-Thz + ), phosphonium (eg -PR4 + ), sulfonium (eg -SR3 + ), hydrazonium(-N2H5 + ), or ammonium peroxide (-N(O2)R3 + ) may be one or more selected from the functional groups of the series, but is not limited thereto.

[0073] The above anionic functional group is carboxylate (-COO - ), sulfonate (-SO3 - ), sulfate (SO4 2- ), sulfite (SO3 2- ), phosphonate (-PO3 2- ), borate (-BO3 2- ), sulfinate (-SO2 - ), phosphate (-PO4 3- ), heteropolyanion (-PMo12 O 40 3- , -PW 12 O 40 3- ), perfluoroalkylsulfonic acid (-CF3SO3 - ), bis(trifluoromethanesulfonyl)imide (TFSI) - ), triplet (-OTf - ), tetrafluoroborate (BF4 - ), phenylborate (-BPh4 - ), hydroxamate (-C(O)NHO - ), or perchlorate (ClO4 - ) may be one or more selected from the functional groups of the series, but is not limited thereto.

[0074] The above polar functional group may be any one selected from a carboxyl group (-COOH), a cyanide group (-C≡N), an amino group (-NH2), a secondary or tertiary amine group (-NHR, -NR2), a thiol group (-SH), -O-(C=O)OH, O=C-NH2, an ether group (-O-), an ester group (-C(O)O-), an amide group (-C(O)NH-), a carbonate group (-OC(O)O-), a urea group (-NHC(O)NH), a urethane group (-OC(O)NH-), and an imide group (-C(O)NH-C(O)-).

[0075] Unless otherwise stated in the relevant section, the substituent R in the present invention may be an alkyl group, an aryl group, an acetonyl group, an acyl group, an alkenyl group, an alkynyl group, a benzyloxycarbonyl group, a tert-butoxycarbonyl group (Boc), a carboxyl group, etc., and preferably means a lower alkyl group having C1 to C6.

[0076] According to another embodiment of the present invention, the cationic functional group may include a counter anion.

[0077] Examples of such counter anions include halogen ions, sulfone ions, phosphate ions, borate ions, sulfite or sulfate ions, nitrate ions, and perchlorate (ClO4 -), hydroxamate (-C(O)NHO - ), sulfate ion (SO4 2- ) includes, but is not limited to, one or more selected from the following.

[0078] Also, examples of halogen ions include chloride ion (Cl - ), bromide ion (Br - ), fluoride ion (F - ), iodide ion (I - ) include, but are not limited to, triflate ions (OTf - ), methylsulfonic acid ion (CHSO3 - ), bis(trifluoromethanesulfonyl)imide (TFSI) - ) include, but are not limited to. Examples of phosphate ions include hexafluorophosphate (PF6 - ), phosphate (PO4 3- ), phosphonate (PO3 2- ) include, but are not limited to. Examples of borate ions include tetrafluoroborate (BF4 - ), borate (BO3) 2- ), phenylborate (BPh4 - ) includes, but is not limited to.

[0079] The functionalized cellulose of the present invention may be (i) a cellulose modified by introducing a functional group to bond to all or part of the hydroxyl groups (-OH) present in the cellulose (type 1), (ii) a cellulose modified by substituting all or part of the hydroxyl groups present in the cellulose with nitrogen (type 2), (iii) a cellulose modified by modifying all or part of the hydroxymethyl groups present in the cellulose (type 3), or (iv) a cellulose modified by ring-opening all or part of the cellulose ring (type 4).

[0080] Therefore, according to another embodiment of the present invention, the functionalized cellulose is a modified cellulose in which a functional group is introduced to bond to all or part of the hydroxyl groups (-OH) present in the cellulose, and may be a functionalized cellulose of type 1 represented by the following structural formula 1.

[0081] [Structural formula 1]

[0082]

[0083] In structural formula 1, n1 is the number of repeating units, which is an integer from 100 to 10,000,

[0084] R 1 Inland R 6 are each independently a hydrogen atom, R 8 , or And,

[0085] n2 and n3 are each independently integers from 1 to 4, and are repeating unit numbers,

[0086] R 7 is a hydrogen atom, a hydroxyl group, or a C1 to C4 alkyl group,

[0087] R 8 silver P(=O)HOH, P(=O)(OH)2, S(=O)2OH, CH2CH2O - , CH2CH2OH, COOH, CO-CH2C(COOH)(OH)CH2COOH, ,

[0088] R 9 Inland R 11 are each independently a hydrogen atom or a C1 to C4 alkyl group,

[0089] R 12 is a hydrogen atom or a C1 to C4 alkyl group,

[0090] R 13 Inland R 19are each independently a hydrogen atom or a C1 to C4 alkyl group.

[0091] In the present invention, when the functionalized cellulose has the structure of structural formula 1, it can maintain a particularly low electrolyte swelling degree while simultaneously maintaining high electrolyte wettability, thereby lowering the electrolyte swelling degree while simultaneously lowering the electrolyte wettability. However, when the functionalized cellulose of the present invention does not have the structure of structural formula 1, it is undesirable in that it may not have such an effect.

[0092] In addition, according to another embodiment of the present invention, the functionalized cellulose is a cellulose modified by substituting all or part of the hydroxyl groups present in the cellulose with nitrogen, and may be a functionalized cellulose of type 2 represented by the following structural formula 2.

[0093] [Structural formula 2]

[0094]

[0095] In structural formula 2, n1 is the number of repeating units, which is an integer from 100 to 10,000,

[0096] T 1 and T 2 are each independently a hydroxyl group, -NH2(CH2) n4 NH 2, , And,

[0097] Here, n4 is an integer from 1 to 5, and R 12 is a hydrogen atom or a C1 to C4 alkyl group,

[0098] V 1 Inland V 4 are each independently a hydroxyl group or a C1 to C4 alkoxy group.

[0099] In addition, according to another embodiment of the present invention, the functionalized cellulose is a cellulose modified so that all or part of the hydroxymethyl groups present in the cellulose are modified, and may be a functionalized cellulose of type 3 represented by the following structural formula 3.

[0100] [Structural formula 3]

[0101]

[0102] In structural formula 3, n1 is the number of repeating units, which is an integer from 100 to 10,000,

[0103] W 1 and W 2 are each independently a hydroxymethyl group, COOH or COO - And,

[0104] X 1 Inland X 4 are each independently a hydroxyl group or a C1 to C4 alkoxy group.

[0105] In addition, according to another embodiment of the present invention, the functionalized cellulose is a cellulose modified so that all or part of the cellulose ring is ring-opened, and may be a functionalized cellulose of type 4 represented by the following structural formula 4.

[0106] [Structural formula 4]

[0107]

[0108] In structural formula 3, n1 is the number of repeating units, which is an integer from 100 to 10,000,

[0109] Y 1 and Y 2 are each independently C(=O)H, (C=O)OH, CH-NH-(CH2)n5-Y 3 , C=N-NH-C(=N + H2)-NH-NH2, or Y1 and Y 2 are connected to each other C=N=NH-C(=N + H2)-NH-N=C It can be,

[0110] Y 3 Is or and here R 12 is a hydrogen atom or a C1 to C4 alkyl group.

[0111] According to a specific embodiment of the present invention, specific examples of the functionalized cellulose include, but are not limited to, materials having the following structures.

[0112]

[0113]

[0114]

[0115] The functionalized cellulose of the present invention can be modified to introduce functional groups into cellulose by a conventionally known method, and based on the disclosure of the present invention, it is clear that a person skilled in the art will be able to manufacture or purchase the functionalized cellulose of the present invention without difficulty based on current common sense.

[0116] However, the following provides an example of a manufacturing method for some of the functionalized cellulose of the present invention, but is not limited to the following method or structure.

[0117] First, the functionalized cellulose of type 1 represented by the above structural formula 1 is a cellulose modified by introducing a functional group to bond to all or part of the hydroxyl groups (-OH) present in the cellulose, and includes, for example, a functionalized cellulose that can be manufactured by the following method, but is not limited to the following method or structure.

[0118] (1) Ammonium series functional group (e.g. -N + H3, -N+ H2R -N + HR2, -N + R3, -CH2CH(OH)CH2N + R3)

[0119]

[0120] (2) Phosphonium or phosphorate functional groups (e.g. -P + H3, -P + H2R, -P + HR2, -P + R3, -P(=O)HOH, -P(=O)(OH)2)

[0121]

[0122] (3) Sulfonium or sulfonate functional groups (e.g. -S) + H2), -S + HR, -S + R2, -S(=O)2OH, -S(=O)OH, -S(=O)2H)

[0123]

[0124] (4) Carboxyl group functional group

[0125]

[0126] (5) Phosphate series functional group (e.g. -P + (=O)(OH)2)

[0127]

[0128] (6) Sulfate series functional group (e.g. -SO3) - )

[0129]

[0130] (7) Hydroxyethyl series functional group (e.g. -CH2CH2OH)

[0131]

[0132] (8) Triazine series functional group

[0133]

[0134] Next, the functionalized cellulose of type 2 represented by the above structural formula 2 is a cellulose modified by substituting all or part of the hydroxyl groups present in the cellulose with nitrogen, and includes, for example, a functionalized cellulose that can be manufactured by the following method, but is not limited to the following method or structure.

[0135] (1) Imidazolium (-Im + ) series functional group

[0136]

[0137] (2) Amine (-NH2, -NHR, -NR2, -NH2(CH2)2NH2) series functional groups

[0138]

[0139] In addition, the functionalized cellulose of type 3 represented by the above structural formula 3 is a cellulose modified so that all or part of the hydroxymethyl groups present in the cellulose are transformed into carboxylate or the like, and includes, for example, a functionalized cellulose that can be manufactured by the following method, but is not limited to the following method or structure.

[0140] - Carboxyl group series functional group (TEMPO-oxidation)

[0141]

[0142] Finally, the functionalized cellulose of type 4 represented by the above structural formula 4 is a cellulose modified so that all or part of the cellulose ring is ring-opened, and includes, for example, a functionalized cellulose that can be produced by the following method, but is not limited to the following method or structure.

[0143] (1) Aldehyde group (e.g. -CHO) series functional group

[0144]

[0145] (2) Imidazolium group (-Im+ ) series functional group

[0146]

[0147] (4) Carboxyl group functional group

[0148]

[0149] According to a preferred embodiment of the present invention, the functionalized cellulose has a structure of structural formula 1 as described above,

[0150] Here, n1 is the number of repeating units, which is an integer between 100 and 10,000,

[0151] R 1 Inland R 6 are each independently a hydrogen atom, or And,

[0152] n2 and n3 are each independently the number of repeating units of 1 or 2,

[0153] R 7 is a hydrogen atom or a hydroxyl group,

[0154] R 8 silver is a cationic group,

[0155] R 9 Inland R 11 are each independently a hydrogen atom or a methyl group.

[0156] In the present invention, when the functionalized cellulose has a structure represented by structural formula 1 and satisfies the conditions of the above preferred embodiments, the problem of transition metal dissolution occurring during high-voltage operation of a high-nickel cathode material can be solved through the interaction between the functionalized functional group of the cellulose and the transition metal ion. However, when the functionalized cellulose of the present invention does not have a structure represented by structural formula 1, or when it has a structure represented by structural formula 1 but does not satisfy the conditions of the above preferred embodiments, it is undesirable in that it may not have such an effect.

[0157] Another aspect of the present invention relates to an electrode for a secondary battery comprising a modified electrode active material for a secondary battery according to various embodiments of the present invention.

[0158] According to one embodiment of the present invention, the secondary battery electrode is a dry electrode, and the secondary battery electrode is a secondary battery electrode that does not include a binder. According to the present invention, when an electrode active material modified with cellulose or functionalized cellulose or the like is used as a positive electrode active material and a positive electrode is manufactured by a dry method, there is an advantage in that a binder such as a fluorinated binder is not included or a smaller amount of binder is required than in the prior art in order to exhibit electrode performance equivalent to or higher than that of a conventional positive electrode using a binder.

[0159] Another aspect of the present invention relates to a secondary battery comprising an electrode for a secondary battery according to various embodiments of the present invention.

[0160] Another aspect of the present invention relates to devices such as portable electronic devices, mobile units, power devices, and energy storage devices comprising secondary batteries according to various embodiments of the present invention.

[0161] Another aspect of the present invention relates to a method for manufacturing a modified electrode active material for a secondary battery, comprising the step of coating an active material core layer on an active material core layer selected from among a positive electrode active material and a negative electrode active material.

[0162] Here, the electrode is a cathode or an anode, and the active material coating layer comprises cellulose, functionalized cellulose, or a mixture thereof.

[0163] According to one embodiment of the present invention, the coating step can be performed by a non-solvent inducing phase separation (NIPS) method.

[0164] That is, the coating step can be performed by introducing and mixing the positive electrode active material or the negative electrode active material into a mixed solution containing the cellulose, functionalized cellulose, or a mixture thereof, a solvent, and a non-solvent.

[0165] According to another embodiment of the present invention, the weight ratio of the cellulose component, which is cellulose, functionalized cellulose, or a mixture thereof, and the active material during the mixing process is 1:400 to 1:600.

[0166] Another aspect of the present invention relates to a method for manufacturing a secondary battery electrode, comprising the steps of: manufacturing an electrode mixture comprising a modified electrode active material and a conductive material according to various embodiments of the present invention; and coating the electrode mixture on a current collector to form an electrode.

[0167] According to one embodiment of the present invention, the electrode mixture contains 1 to 3 parts by weight of the conductive material based on 100 parts by weight of the modified electrode active material for the secondary battery.

[0168] According to another embodiment of the present invention, the electrode mixture does not include a solvent and a binder.

[0169] Hereinafter, a method for manufacturing a surface-modified active material according to the present invention and a method for manufacturing an electrode using the same will be described in detail.

[0170] First, a cellulose solution is prepared by adding a non-solvent to an aqueous solution of cellulose or cellulose functionalized to have ionic or polar functional groups (step a).

[0171] The above non-solvent may be selected from dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), acetonitrile (ACN), methyl ethyl ketone (MEK), isopropanol (IPA), ethanol, acetone, supercritical CO₂, and mixtures thereof.

[0172] The functional groups and functionalized cellulose that can be used here are as described above.

[0173] Next, an electrode active material is mixed into a solution of the cellulose or functionalized cellulose, and the surface of the electrode active material is coated with cellulose or functionalized cellulose by a non-solvent inducing phase separation (NIPS) method to manufacture a surface-modified electrode active material (step b).

[0174] In mixing the electrode active material into the above cellulose or functionalized cellulose solution, the weight ratio of cellulose or functionalized cellulose: electrode active material is preferably 1:400 to 1:600, and more preferably 1:450 to 1:550. The surface-modified electrode active material of the present invention enables the manufacture of a dry electrode having high adhesive strength by inducing hydrogen bonds and ionic bonds due to the polar functional groups of cellulose even when a relatively very small amount of cellulose is used.

[0175] By coating cellulose or functionalized cellulose on the electrode active material using the non-solvent-induced phase separation (NIPS) method, a porous structure of the cellulose coating layer can be formed so that charge transfer of the electrode active material is not hindered.

[0176] Thereafter, an electrode mixture including the surface-modified electrode active material and conductive material is prepared (step c).

[0177] The above electrode mixture can be used for manufacturing wet or dry electrodes, and when used for manufacturing dry electrodes, the fluorine-based binder can be excluded.

[0178] The above electrode mixture can be prepared by mixing 1 to 3 parts by weight of a conductive agent based on 100 parts by weight of an electrode active material. If the conductive agent is included in an amount less than the above content, the electrical conductivity may be lowered, which may result in deterioration of electrochemical performance. If the amount exceeds the upper limit, the conductive agent may clump together or the energy density of the battery may be reduced.

[0179] The above electrode active material can be used as a positive electrode active material or a negative electrode active material, and preferably can be used as a positive electrode active material for a lithium secondary battery.

[0180] The above positive electrode active material for lithium secondary batteries is Li x Mn 1-y M y A2, Li x Mn2O 4-z X z , Li x Mn 2-y M y M' z A4, Li x Co 1-y M y A2, Li x Co 1-y M y O 2-z X z , Li x Ni 1-y M y O 2-z X z , Li x Ni 1-y Co y O 2-z X z , Li x Ni 1-y-z Co y M z Aα , Li x Ni 1-y-z Co y M z O 2-α X α , Li x Ni 1-y-z Mn y M z A α , Li x Ni 1-y-z Mn y M z O 2-α X α It may include any one of the positive electrode active materials. Here, 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, and M and M' are each independently any one selected from Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, and V, A may be any one selected from O, F, S, and P, and X may be any one selected from F, S, and P. The positive electrode active material is not limited to those described above.

[0181] The conductive material may be a dot-shaped carbon-based conductive material, a linear carbon-based conductive material, a plate-shaped carbon-based conductive material, a metal fiber, a metal powder, a conductive metal oxide, etc. The dot-shaped carbon-based conductive material may be any one selected from acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon black, the linear carbon-based conductive material may be any one selected from carbon nanotubes and conductive carbon fibers, and the plate-shaped carbon-based conductive material may be graphene. The conductive material is not limited to the above range, and any conductive material that can be typically used in a positive electrode of a lithium ion battery can be applied.

[0182] Next, the electrode mixture is coated on a current collector to form an electrode (step b).

[0183] It is preferable that the above coating be a dry coating performed by rolling or pressing.

[0184] Hereinafter, the present invention will be described in more detail through examples and the like. However, the scope and content of the present invention should not be construed as being limited or reduced by the examples and the like. Furthermore, based on the disclosure of the present invention, including the following examples, it is clear that those skilled in the art can easily implement the present invention, even though specific experimental results are not presented. It is also natural that such variations and modifications fall within the scope of the appended claims.

[0185] In addition, the experimental results presented below only describe representative experimental results of the above examples and comparative examples, and the effects of each of the various implementation examples of the present invention that are not explicitly presented below will be specifically described in the relevant section.

[0186] Example

[0187] Manufacturing Example 1: Preparation of cellulose nanofibers (CNF)

[0188] Cellulose nanofibers (CAS Number 9004-34-6, average diameter 50 nm) were purchased from Maine and used in the present invention without any separate pretreatment.

[0189] Manufacturing Example 1-2: Preparation of cationic cellulose nanofibers (cationic CNF, c-CNF)

[0190] (2) The trimethylamine group, which is a cationic group, is bonded to the cellulose nanofibers prepared above according to the reaction scheme 1 below, and the counter anion is TFSI. - Cationic cellulose nanofibers modified to be (bis(trifluoromethanesulfonyl)imide) were prepared.

[0191] [Reaction Formula 1]

[0192]

[0193] Manufacturing Example 1-3: Preparation of anionic cellulose nanofibers (anionic CNF, a-CNF)

[0194] TEMPO-oxidized cellulose nanofibers (carboxylate level 0.2 to 2 mmol / g) were purchased from Maine and used as anionic cellulose nanofibers.

[0195] Manufacturing Example 1-4: Preparation of polar cellulose nanofibers (polar CNF, pCNF)

[0196] Hydroxyethyl cellulose (CAS number: 9004-62-0) was purchased from Aldrich and used as polar cellulose nanofibers.

[0197] Manufacturing Example 2-1: Manufacturing of a positive electrode active material surface-modified with cellulose

[0198] Cathode active material LiNi 0.8 Mn 0.1 Co 0.1 The positive electrode active material and cellulose solution were mixed so that O2 (NCM811) and cellulose had a weight ratio of 500:1 (w / w) and were mixed using an ultrasonic mixer (Thinky TM The surface of the positive electrode active material was coated with cellulose by non-solvent induced phase separation (NIPS) by treating it at 2,000 rpm for 5 minutes in a mixer. Afterwards, the active material surface-modified with cellulose was manufactured by drying it at 80°C for 5 minutes.

[0199] Manufacturing Example 2-2: Manufacturing of a positive electrode active material surface-modified with cationic cellulose

[0200] A 0.5 wt% solution was prepared by adding dimethylacetamide (DMAc) as a non-solvent to the cationic cellulose aqueous solution prepared above. At this time, water and DMAc in the solution were present in a 1:1 (w / w) ratio. The cathode active material LiNi 0.8 Mn0.1 Co 0.1 The cationic cellulose solution was mixed with the cationic active material at a weight ratio of 500:1 (w / w) for O2 (NCM811) and the cationic cellulose, and the surface of the cationic cellulose was coated with the cationic cellulose using a non-solvent induced phase separation (NIPS) method by treating the mixture in an ultrasonic mixer (THINKY mixer) at 2000 rpm for 5 minutes. Then, the cationic cellulose was dried at 80°C for 5 minutes to produce a cationic cellulose-surface-modified cationic cellulose-surfaced ...

[0201] Manufacturing Example 2-3: Manufacturing of a positive electrode active material surface-modified with anionic cellulose

[0202] A positive electrode active material surface-modified with anionic cellulose was prepared in the same manner as above, except that the anionic cellulose prepared above was used instead of the cationic cellulose.

[0203] Manufacturing Example 2-4: Manufacturing of a positive electrode active material surface-modified with polar cellulose

[0204] A positive electrode active material surface-modified with polar cellulose was prepared in the same manner as above, except that the polar cellulose prepared above was used instead of the cationic cellulose.

[0205] Manufacturing Examples 3-1 to 3-4: Manufacturing of negative electrode active material surface-modified with cellulose

[0206] Cathode active material (LiNi) 0.8 Mn 0.1 Co 0.1Except for using graphite as the negative active material instead of O2, NCM811, surface-modified negative active materials were manufactured using cellulose (Preparation Example 3-1), cationic cellulose (Preparation Example 3-2), anionic cellulose (Preparation Example 3-3), and polar cellulose (Preparation Example 3-4) in the same manner as above.

[0207] Manufacturing Example 4-1: Manufacturing of a composite cathode active material surface-modified with a composite material of carbon nanotubes and one selected from cellulose, cationic cellulose, anionic cellulose, and polar cellulose.

[0208] The cationic cellulose and conductive material (carbon nanotubes) prepared above were placed in an ultrasonic mixer (sonicator) at a weight ratio of 1:1 and treated for 30 minutes to obtain an aqueous dispersion. DMAc was added as a nonsolvent to the aqueous dispersion to prepare a 0.5 wt% solution (cationic cellulose 0.25 wt%, carbon nanotube 0.25 wt%). At this time, the weight ratio of water and DMAc was 1:1. The cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2, NCM811) and cationic cellulose and carbon nanotubes were mixed in a weight ratio of 100:0.5:0.5 and mixed using an ultrasonic mixer (Thinky TM The positive electrode active material surface was treated at 2,000 rpm for 5 minutes in a mixer. The positive electrode active material surface was coated with cationic cellulose and carbon nanotubes using this non-solvent inducing phase separation (NIPS) method. Afterwards, the positive electrode active material surface-modified with cationic cellulose and carbon nanotubes was manufactured by drying at 80°C for 5 minutes.

[0209] In this manner, a composite cathode active material can be manufactured by surface-modifying one selected from cellulose, anionic cellulose, and polar cellulose with a composite material of carbon nanotubes.

[0210] Manufacturing Example 4-2: Manufacturing of a composite negative electrode active material surface-modified with a composite material of carbon nanotubes and one selected from cellulose, cationic cellulose, anionic cellulose, and polar cellulose.

[0211] Cathode active material (LiNi) 0.8 Mn 0.1 Co 0.1 A composite negative electrode active material surface-modified with a composite material of carbon nanotubes and one selected from cellulose, cationic cellulose, anionic cellulose, and polar cellulose was manufactured in the same manner as above, except that the negative electrode active material (graphite) was used instead of O2, NCM811.

[0212] Example 1: Preparation of a binder-free dry-modified cathode (using a surface-modified cathode active material)

[0213] A cathode mixture was prepared by dry mixing the cationic cellulose-surface-modified cathode active material (NCM811) and the conductive agent (Super P) at a weight ratio of 98:2. Next, the cathode mixture was applied to an Al current collector in a titanium mold, and a dry cathode with a coating thickness of approximately 150 μm was prepared by rolling at a high temperature of 120°C so that the electrode composite density was approximately 3-3.5 g / cc.

[0214] At this time, since the weight ratio of the surface-modified positive electrode active material (NCM811) and cationic cellulose was 500:1, the final manufactured positive electrode was manufactured as a dry-modified positive electrode (binder-free) with a weight ratio of positive electrode active material (NCM811): cationic cellulose: conductive material (Super P) of 97.804:0.196:2.

[0215] Example 2: Preparation of a binder-containing dry-modified cathode (using surface-modified cathode active material)

[0216] Instead of dry mixing the cationic cellulose surface-modified cathode active material (NCM811) and the conductive material (Super P) at a weight ratio of 98:2, a dry-modified cathode (including the binder) was manufactured in the same manner as above, except that the cationic cellulose surface-modified cathode active material and the conductive material (Super P) and the binder (polytetrafluoroethylene, PTFE) were dry mixed at a weight ratio of 98:1:1.

[0217] Example 3: Preparation of a binder-containing wet-modified cathode (using surface-modified cathode active material)

[0218] The cathode active material (NCM811), surface-modified with cationic cellulose, conductive agent (Super P), and binder (polyvinylidene fluoride, PVDF) were dissolved in a solvent (1-methyl-2-pyrrolidinone, NMP) at a weight ratio of 96:2:2 and mixed to prepare a cathode mixture. The cathode mixture was applied to an Al current collector in a titanium mold and vacuum-dried at 120°C to prepare a wet-modified cathode (including the binder).

[0219] Example 4: Preparation of binder-free dry composite reformed cathode (composite cathode active material)

[0220] A dry composite-modified positive electrode (binder-free) was manufactured in the same manner as above, except that a composite positive electrode active material surface-modified with a composite material of cationic cellulose and a conductive material was used instead of the positive electrode active material surface-modified with cationic cellulose.

[0221] Comparative Example 1: Manufacturing of a dry-mixed cathode without a binder (using a mixture of a non-surface-modified cathode active material and cationic cellulose)

[0222] A dry-mixed positive electrode (binder-free) was manufactured in the same manner as in Example 1, except that instead of dry-mixing the positive electrode active material (NCM811) surface-modified with cationic cellulose and the conductive material (Super P) at a weight ratio of 98:2, the non-surface-modified positive electrode active material (NCM811) and the cationic cellulose and conductive material (Super P) manufactured above were dry-mixed at a weight ratio of 97.804:0.196:2.

[0223] Comparative Example 2: Preparation of a dry-mixed anode containing a binder (using a mixture of surface-unmodified cathode active material and cationic cellulose)

[0224] Instead of dissolving and mixing the cationic cellulose surface-modified cathode active material (NCM811, conductive agent (Super P), and binder (polyvinylidene fluoride, PVDF) in a weight ratio of 96:2:2 in a solvent (1-methyl-2-pyrrolidinone, NMP), a mixture of the cationic cellulose surface-modified cathode active material (NCM811) and the cationic cellulose prepared above in a weight ratio of 500:1, the conductive agent (Super P), and the binder (polyvinylidene fluoride, PVDF) in a weight ratio of 96:2:2 in a solvent (1-methyl-2-pyrrolidinone, NMP) was prepared in the same manner as in Example 2, except that a dry-mixed cathode (including the binder) was prepared.

[0225] Comparative Example 3: Preparation of a binder-containing wet-mixed cathode (using a mixture of surface-unmodified cathode active material and cationic cellulose)

[0226] A wet mixed positive electrode (including binder) was manufactured in the same manner as in Example 3, except that instead of dissolving and mixing the positive electrode active material (NCM811) surface-modified with cationic cellulose, the conductive agent (Super P), and the binder (polyvinylidene fluoride, PVDF) in a solvent at a weight ratio of 96:2:2, a mixture of 500:1 and the conductive agent (Super P) and the binder (polyvinylidene fluoride, PVDF) was dissolved and mixed in a solvent at a weight ratio of 96:2:2.

[0227] Example 5: Preparation of a binder-free dry-modified negative electrode (using a surface-modified negative electrode active material)

[0228] A surface-modified dry-modified negative electrode was manufactured using the cationic cellulose-surface-modified negative electrode active material (c-CNF coated graphite), the anionic cellulose-surface-modified negative electrode active material (a-CNF coated graphite), and the polar cellulose-surface-modified negative electrode active material (p-CNF coated graphite), respectively.

[0229] Thinky surface-modified graphite (c-CNF coated graphite, a-CNF coated graphite, p-CNF coated graphite) and conductive material (Super P) were mixed at a weight ratio of 95:5. TM After mixing using a mixer, the cathode mixture was applied to a carbon-coated Cu foil in a titanium mold, and a dry cathode was manufactured by rolling at a high temperature of 60°C so that the electrode composite density was approximately 1-1.5 g / cc.

[0230] At this time, the weight ratio of the surface-modified negative electrode active material graphite and the modified cellulose was 500:1, so the final negative electrode had a weight ratio of graphite, modified cellulose, and conductive material of 94.81:0.19:5.

[0231] In Fig. 11, the photograph of the electrode and the electronic conductivity of the electrode composite layer are compared. When compared to the negative electrode having a weight ratio of 90:5:5 of graphite / conductive agent (Super P) / binder (PTFE) without surface modification, the use of surface-modified graphite showed an electronic conductivity of the electrode composite layer that was equivalent or higher, confirming that the dry negative electrode operates with high performance even without the binder (PTFE).

[0232] Device Example 1: Manufacturing of Lithium Secondary Battery

[0233] A 2032-type coin cell (manufactured positive electrode / PE separator (thickness = 20 μm, Toray-Tonen) / Li metal negative electrode (200 μm)) containing a liquid electrolyte was manufactured using the positive electrode manufactured according to Example 3 to evaluate electrochemical performance. The liquid electrolyte used was 1 M LiPF6 in EC / DEC = 1 / 1 (w / w) + 10 wt% FEC + 1 wt% VC. The cell was assembled in an argon-filled glove box.

[0234] Device Comparison Example 1: Manufacturing of Lithium Secondary Battery

[0235] A lithium secondary battery was manufactured under the same conditions as in Device Example 1, except that the positive electrode of Comparative Example 3 was used instead of the positive electrode of Example 3.

[0236] Experimental Example 1: Comparative Analysis of Dispersibility and Shape of Cellulose and Cationic Cellulose

[0237] In order to compare the dispersibility of cationic cellulose manufactured according to Manufacturing Example 1-2 and unmodified nanocellulose, dispersions were manufactured using water as a solvent, and a photograph of the aqueous solution (a) and an image of the cationic cellulose of Manufacturing Example 1-2 observed under a microscope (b) are shown in Fig. 3.

[0238] According to this, the cationic cellulose dispersion of Manufacturing Example 1-2 showed high dispersibility and appeared transparent, but the unmodified cellulose dispersion appeared cloudy and showed low dispersibility.

[0239] Experimental Example 2: Comparison of the Shapes of Positive Electrode Materials with and without Surface Modification

[0240] The SEM images of the cationic cellulose (c-CNF), anionic cellulose (a-CNF), and polar cellulose (p-CNF) surface-modified positive electrode active material of Manufacturing Example 2-2 and the non-modified positive electrode active material are compared and shown in Fig. 4. According to this, the surface of the cationic cellulose-modified positive electrode active material NCM811 according to the method of Manufacturing Example 2-2 was coated with cationic cellulose, and compared to the surface of the non-modified NCM811, it was confirmed that the modified component was evenly covered on the active material particles.

[0241] Experimental Example 3: Preparation of dry electrodes without fluorine-based binders

[0242] In order to verify whether a dry electrode can be manufactured without using a fluorinated binder, the electrode mixture (a) manufactured in Example 1 using modified ionic cellulose and the electrode mixture (b) manufactured in Comparative Example 1 using unmodified cellulose were compared, and the photograph thereof is shown in Fig. 5. According to this, in Comparative Example 1 using unmodified cellulose, the electrode mixture was scattered in a powder state in the absence of a fluorinated binder, making it impossible to manufacture a dry electrode. In contrast, in the electrode mixture of Example 1 using ionic cellulose, only the NCM811 active material and the conductive agent were mixed in a weight ratio of 98:2 (w / w), and it was confirmed that the bonding between the components was well formed, making it possible to manufacture a dry electrode, even though the fluorinated binder was excluded.

[0243] That is, the present invention confirms that it is possible to manufacture a dry electrode using only a small amount of ionic cellulose without using a fluorine-based binder, which is a material subject to future PFAS regulations.

[0244] Experimental Example 4: Electrode Adhesion Analysis

[0245] First, the adhesion of ionic cellulose and the common dry binder PTFE was compared. Films were manufactured using the cationic cellulose nanofibers prepared according to Manufacturing Example 1-2, and PTFE, a commonly used binder for dry electrodes, was also prepared into films of the same thickness. Each film was rolled at 120°C, adhered to aluminum foil, and then bent to a radius of 4 cm to observe the film's adhesion. The experimental results are shown in photographs in Figure 6.

[0246] According to this, the film (a) manufactured using cationic cellulose nanofibers manufactured according to Manufacturing Example 1-2 maintained adhesion even after banding, but the PTFE binder film (b) was detached and showed lower adhesion than the modified cellulose nanofiber film.

[0247] To quantitatively express this, the adhesion between Al foil and binder film was evaluated. PTFE, cationic cellulose (c-CNF), anionic cellulose (a-CNF), and polar cellulose (p-CNF) samples were cut to a size of 1.5 cm × 3.5 cm, and the electrode surfaces were adhered to slide glasses with double-sided tape to prepare four samples for peel tests. The samples for peel tests were loaded into a UTM for measuring adhesion, and a 180° peel test was performed to measure the peel resistance (N / cm) and calculate the adhesion of each electrode. The propagation speed was 300 mm / min. The results of the adhesion measurement are shown in Fig. 6.

[0248] Meanwhile, in order to compare the adhesive strength of electrodes depending on the presence or absence of surface modification of the active material, the side SEM images of the dry electrode (a) with the non-surface-modified active material of Comparative Example 2 and the fluorine-based binder added and the dry electrode (b) with the surface-modified active material of Example 2 and the fluorine-based binder added, adhered to an aluminum current collector, are shown in FIG. 7.

[0249] According to this, the dry electrode including the active material surface-modified with ionic cellulose of Example 2 was in close contact with the surface of the current collector and had good adhesion, whereas the dry electrode including the active material without surface modification of Comparative Example 2 had poor adhesion as a space where the electrode material was lifted from the current collector adhesion surface was observed.

[0250] In addition, the electrochemical performance of the cathode surface-modified with cationic cellulose (c-CNF), anionic cellulose (a-CNF), and polar cellulose (p-CNF) and the non-surface-modified cathode (bare NCM) was evaluated. 30 mg / cm 2 When the positive electrode was manufactured and the charge / discharge current density was set to 0.2C / 0.2C, the surface-modified positive electrode showed a higher charge / discharge capacity than the non-surface-modified positive electrode (bare NCM). This is because the adhesive strength and dispersibility within the electrode were improved when the surface-modified active material was used.

[0251] Experimental Example 5: Electrochemical Characteristics Analysis

[0252] The constant current charge / discharge life characteristics of lithium secondary batteries manufactured according to Device Example 1 and Device Comparative Example 1 were tested under conditions of 3.0-4.5 V and 1 C / 1 C, and the results are shown in Fig. 8.

[0253] According to this, the lithium secondary battery of Device Example 1 showed a capacity retention rate of about 75% with a specific capacity of 150 mAh / g even after 100 cycles, but the lithium secondary battery of Device Comparative Example 1 showed a capacity retention rate of about 65% with a specific capacity of 130 mAh / g even after 50 cycles, and was found to no longer function.

[0254] According to these results, high anode interface stability due to active material surface modification was confirmed under high voltage conditions of 4.5 V or higher.

[0255] Experimental Example 6: Analysis of a Cellulose / Conductive Material Composite Dry Electrode

[0256] An NCM cathode surface-modified by combining cationic cellulose (c-CNF) and a conductive material, CNT, was manufactured without a PTFE binder, and the results are shown in Fig. 9.

[0257] As shown in the SEM image, c-CNF and CNT are evenly coated on the surface of the NCM cathode. To verify whether electrode fabrication is possible using only the modified active material, the cathode mixture was applied to an Al current collector in a titanium mold, and a dry cathode was manufactured by rolling at a high temperature of 120°C to a thickness of approximately 150 μm so that the electrode composite density was approximately 3-3.5 g / cc.

[0258] When the electronic conductivity of the electrode composite layer of a binder-free composite-modified cathode and a cathode manufactured with surface-unmodified NCM: Super P: PTFE = 96:2:2 (w / w / w) was compared, the surface-modified cathode showed superior electronic conductivity. The results are shown in Fig. 9.

[0259] Experimental Example 7: Preparation of a cellulose surface-modified negative electrode active material

[0260] SEM images of the cathode surface-modified with cationic cellulose (c-CNF), anionic cellulose (a-CNF), and polar cellulose (p-CNF) are shown in Fig. 10. As shown in Fig. 10, it can be confirmed that cellulose is evenly coated on the surface of the graphite cathode.

[0261] Experimental Example 8: Fabrication of a cellulose surface-modified cathode dry electrode

[0262] Each of cationic cellulose (c-CNF), anionic cellulose (a-CNF), and polar cellulose (p-CNF) surface-modified cathodes was dry mixed with Super P at a weight ratio of 95:5, and the cathode mixture was applied to a carbon-coated Cu foil in a titanium mold, and a dry-coated cathode was manufactured by rolling at a high temperature of 60°C so that the electrode composite density was approximately 1-1.5 g / cc.

[0263] At this time, since the weight ratio of the surface-modified negative electrode active material (graphite) and each modified cellulose was 500:1, the final negative electrode was made so that the weight ratio of graphite and each modified ionic cellulose and conductive agent (Super P) was 94.81:0.19:5. In Fig. 11, the photograph of the electrode and the electronic conductivity of the composite layer of the electrode were compared. When compared to the negative electrode having a weight ratio of 90:5:5 of graphite without surface modification, conductive agent (Super P), and binder (PTFE), the case where surface-modified graphite was used showed an electronic conductivity of the electrode composite layer of an equivalent or higher level, confirming that the dry negative electrode operates with high performance even without the binder (PTFE).

[0264] Above, embodiments of the present invention have been described, but those of ordinary skill in the art will be able to modify and change the present invention in various ways by adding, changing, deleting or adding components, etc., within the scope that does not depart from the spirit of the present invention described in the claims, and this will also be considered to be included within the scope of the rights of the present invention.

Claims

1. A composition for modifying the surface of an electrode active material for a secondary battery, comprising cellulose, functionalized cellulose, or a mixture thereof, A composition for surface modification of an electrode active material for a secondary battery, wherein the functionalized cellulose is at least one selected from among cellulose modified to have a cationic functional group bonded thereto, cellulose modified to have an anionic functional group bonded thereto, and cellulose modified to have a polar functional group bonded thereto.

2. A modified electrode active material for a secondary battery, comprising (a) an active material core layer selected from among a positive electrode active material and a negative electrode active material, and (b) an active material coating layer coating the active material core layer, The above electrode is a cathode or an anode, The above active material coating layer comprises cellulose, functionalized cellulose, or a mixture thereof, A modified electrode active material for a secondary battery, wherein the functionalized cellulose is at least one selected from among cellulose modified to have a cationic functional group bonded thereto, cellulose modified to have an anionic functional group bonded thereto, and cellulose modified to have a polar functional group bonded thereto.

3. In the second paragraph, the functionalized cellulose has a degree of substitution of 0.03 to 3, The above substitution degree is the number of substituted or modified functional groups per cellulose monomer, and is a modified electrode active material for a secondary battery.

4. In the second paragraph, the active material coating layer additionally includes a conductive material, A modified electrode active material for a secondary battery, wherein the conductive material is at least one selected from conductive polymers, carbon nanotubes, MXene, graphene, metal nanowires, conductive ceramics, metal or alloy powders.

5. In the second paragraph, the cationic functional group is ammonium (-NH4 + ), primary to quaternary ammonium (-NH3R + , -NH2R2 + , -NHR3 + , -NR4 + ), pyridinium (-Py + ), imidazolium (-Im + ), triazolium(-Trz + ), thiazolium (-Thz + ), phosphonium (eg -PR4 + ), sulfonium (eg -SR3 + ), hydrazonium(-N2H5 + ), or ammonium peroxide (-N(O2)R3 + ) is at least one selected from the functional groups of the series, The above anionic functional group is carboxylate (-COO - ), sulfonate (-SO3 - ), sulfate (SO4 2- ), sulfite (SO3 2- ), phosphonate (-PO3 2- ), borate (-BO3 2- ), sulfinate (-SO2 - ), phosphate (-PO4 3- ), heteropolyanion (-PM O12 O 40 3- , -PW 12 O 40 3- ), perfluoroalkylsulfonic acid (-CF3SO3 - ), bis(trifluoromethanesulfonyl)imide (TFSI) - ), triplet (-OTf - ), tetrafluoroborate (BF4 - ), phenylborate (-BPh4 - ), hydroxamate (-C(O)NHO - ), or perchlorate (ClO4 - ) is at least one selected from the functional groups of the series, A modified electrode active material for a secondary battery, wherein the polar functional group is at least one selected from a carboxyl group (-COOH), a cyanide group (-C≡N), an amino group (-NH2), a secondary or tertiary amine group (-NHR, -NR2), a thiol group (-SH), -O-(C=O)OH, O=C-NH2, an ether group (-O-), an ester group (-C(O)O-), an amide group (-C(O)NH-), a carbonate group (-OC(O)O-), a urea group (-NHC(O)NH), a urethane group (-OC(O)NH-), and an imide group (-C(O)NH-C(O)-).

6. In the second paragraph, the cellulose modified to bind the cationic functional group includes a counter anion to the cation, The above counter anions are halogen ions, sulfone ions, phosphate ions, borate ions, sulfite or sulfate ions, nitrate ions, perchlorate (ClO4 - ), hydroxamate (-C(O)NHO - ), sulfate ion (SO4 2- ) A modified electrode active material for a secondary battery, wherein at least one selected from the group consisting of:

7. In the second paragraph, the functionalized cellulose is a modified electrode active material for a secondary battery represented by the following structural formula 1: [Structural formula 1] In structural formula 1, n1 is the number of repeating units, which is an integer from 100 to 10,000, R 1 Inland R 6 are each independently a hydrogen atom, R 8 , or And, n2 and n3 are each independently integers from 1 to 4, and are repeating unit numbers, R 7 is a hydrogen atom, a hydroxyl group, or a C1 to C4 alkyl group, R 8 silver P(=O)HOH, P(=O)(OH)2, S(=O)2OH, CH2CH2O - , CH2CH2OH, COOH, CO-CH2C(COOH)(OH)CH2COOH, , R 9 Inland R 11 are each independently a hydrogen atom or a C1 to C4 alkyl group, R 12 is a hydrogen atom or a C1 to C4 alkyl group, R 13 Inland R 19 are each independently a hydrogen atom or a C1 to C4 alkyl group.

8. In the second paragraph, the functionalized cellulose is a modified electrode active material for a secondary battery represented by the following structural formula 2: [Structural formula 2] In structural formula 2, n1 is the number of repeating units, which is an integer from 100 to 10,000, T 1 and T 2 are each independently a hydroxyl group, -NH2(CH2) n4 NH 2, , And, n4 is an integer from 1 to 5, and R 12 is a hydrogen atom or a C1 to C4 alkyl group, V 1 Inland V 4 are each independently a hydroxyl group or a C1 to C4 alkoxy group.

9. In the second paragraph, the functionalized cellulose is a modified electrode active material for a secondary battery represented by the following structural formula 3: [Structural formula 3] In structural formula 3, n1 is the number of repeating units, which is an integer from 100 to 10,000, W 1 and W 2 are each independently a hydroxymethyl group, COOH or COO - And, X 1 Inland X 4 are each independently a hydroxyl group or a C1 to C4 alkoxy group.

10. In the second paragraph, the functionalized cellulose is a modified electrode active material for a secondary battery represented by the following structural formula 4: [Structural formula 4] In structural formula 3, n1 is the number of repeating units, which is an integer from 100 to 10,000, Y 1 and Y 2 are each independently C(=O)H, (C=O)OH, CH-NH-(CH2)n5-Y 3 , C=N-NH-C(=N + H2)-NH-NH2, or Y 1 and Y 2 are connected to each other C=N=NH-C(=N + H2)-NH-N=C It can be, Y 3 Is or and here R 12 is a hydrogen atom or a C1 to C4 alkyl group.

11. In the second paragraph, the functionalized cellulose is a modified electrode active material for a secondary battery, wherein the functionalized cellulose is at least one selected from functionalized cellulose having the following structure.

12. In the second paragraph, in the structural formula 1, n1 is the number of repeating units which is an integer from 100 to 10,000. R 1 Inland R 6 are each independently a hydrogen atom, or And, n2 and n3 are each independently the number of repeating units of 1 or 2, R 7 is a hydrogen atom or a hydroxyl group, R 8 silver is a cationic group, R 9 Inland R 11 A modified electrode active material for a secondary battery, each independently representing a hydrogen atom or a methyl group.

13. In the second paragraph, the cellulose is at least one selected from among cellulose nanofibers (CNF), cellulose nanocrystals (CNC), microfibrillated cellulose (MFC), microcrystalline cellulose (MCC), and bacterial cellulose. A modified electrode active material for a secondary battery.

14. In the 13th paragraph, the cellulose nanofiber has a diameter of 1 nm to 100 μm and a length of 50 nm to 500 μm, The above cellulose nanocrystals are modified electrode active materials for secondary batteries having a diameter of 1 nm to 100 μm.

15. A secondary battery electrode comprising a modified electrode active material for a secondary battery according to any one of claims 2 to 14.

16. In the 15th paragraph, the electrode for the secondary battery is a dry electrode, The above secondary battery electrode is a secondary battery electrode that does not contain a binder.

17. A secondary battery comprising an electrode for a secondary battery according to Article 15.

18. In the 17th paragraph, the secondary battery is a secondary battery selected from among a lithium secondary battery, a sodium secondary battery, a zinc secondary battery, an aluminum secondary battery, a magnesium secondary battery, a calcium secondary battery, a lithium-sulfur secondary battery, a lithium-air secondary battery, a sodium-air secondary battery, a zinc-air secondary battery, an aluminum-air secondary battery, a magnesium-air secondary battery, and a calcium-air secondary battery.

19. In the 17th paragraph, the material of the electrode or electrode active material is selected from among excess layered oxide (LLO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt manganese (NCM), lithium nickel cobalt aluminum (LNCA), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium lithium manganese iron phosphate (LMFP), lithium nickel oxide (LNO), lithium manganese phosphate (LMP), lithium iron manganese phosphate (LFMP), lithium vanadium phosphate (LVP), and lithium iron fluorosulfate (LFSF), or a secondary battery selected from among lithium metal, silicon-carbon composite, tin-based alloy, silicon, lithium titanate (LTO), soft carbon, hard carbon, and graphite.

20. Any one device selected from among portable electronic devices, mobile units, power devices, and energy storage devices containing the secondary battery of Article 17.

21. A method for manufacturing a modified electrode active material for a secondary battery, comprising a step of coating an active material core layer on an active material core layer selected from among a positive electrode active material and a negative electrode active material, The above electrode is a cathode or an anode, The above active material coating layer comprises cellulose, functionalized cellulose, or a mixture thereof, A method for producing a modified electrode active material for a secondary battery, wherein the functionalized cellulose is at least one selected from among cellulose modified to have a cationic functional group bonded thereto, cellulose modified to have an anionic functional group bonded thereto, and cellulose modified to have a polar functional group bonded thereto.

22. A method for producing a modified electrode active material for a secondary battery, wherein the coating step is performed by at least one method selected from the group consisting of non-solvent inducing phase separation (NIPS), spray coating, dip coating, blade coating, and roll coating.

23. A method for producing a modified electrode active material for a secondary battery, wherein the coating step is performed by introducing and mixing the positive electrode active material or the negative electrode active material into a mixed solution containing the cellulose, functionalized cellulose, or a mixture thereof, a solvent, and a non-solvent.

24. In paragraph 23, the weight ratio of the cellulose component and the active material is 1:400 to 1:600, The above cellulose component is cellulose, functionalized cellulose, or a mixture thereof, A method for producing a modified electrode active material for a secondary battery, wherein the above active material is the positive electrode active material or the negative electrode active material.

25. A step of preparing an electrode mixture comprising a modified electrode active material and a conductive material for a secondary battery according to any one of claims 2 to 14; and A method for manufacturing a secondary battery electrode, comprising the step of forming an electrode by coating the electrode mixture on a current collector.

26. A method for manufacturing an electrode for a secondary battery, wherein the electrode mixture in paragraph 25 contains 1 to 3 parts by weight of the conductive material based on 100 parts by weight of the modified electrode active material for a secondary battery.

27. A method for manufacturing a secondary battery electrode in claim 25, wherein the electrode mixture does not contain a solvent or binder.

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