KR20230098403A - Negative electrode for secondary battery containing water-soluble binder and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a secondary battery negative electrode containing a fibrin binder and a method for manufacturing the same, and more particularly, to an eco-friendly and highly efficient secondary battery negative electrode using a water-based binder using biomolecules and a method for manufacturing the same.

Description

Negative electrode for secondary battery containing water-soluble binder and method for manufacturing the same}

The present invention relates to a negative electrode for a secondary battery containing a water-soluble binder and a method for manufacturing the same, and more particularly, to a negative electrode for a secondary battery having an eco-friendly and high efficiency using a water-soluble binder including fibrin and a method for manufacturing the same.

Recently, technology for making electronic products smaller has attracted attention, and accordingly, demand for lithium ion batteries (LIBs) having higher energy density is increasing. In lithium-ion batteries, silicon has been attracting attention as an anode material for a long time because of its superior storage capacity compared to commercial graphite. However, the rapid failure caused by the expansion of silicon during cycling has limited its practical usefulness. Many routes based on silicon engineering have been proposed, either by providing usable free volume through nanostructures and pore engineering, or by adding buffer matrices through surface coatings to fabricate composite materials. Producing these materials at low cost or on a large scale remains challenging.

An emerging technology is one that utilizes new binders that are compatible with silicon powder. The weak van der Waals interaction between the hydroxylated polar silicon surface (Si-OH) and the non-polar binder (e.g. polyvinylidene fluoride) is one of the limiting factors for cycle life. Many polar binders, including polysaccharides, vinyl polymers, self-healing polymers and combinations thereof, have proven effective in improving cycling stability. Polar hydroxyl groups and/or carboxylate functional groups present in these binders form strong hydrogen bonds with the silicon surface. This enables a stable connection between the silicon and the conductive network that withstands the huge volume changes that occur in the silicon during cycling.

In addition to controlling intermolecular interactions, the mechanical properties of binders must be carefully designed for improved electrochemical performance. In general, stiff crosslinkers exhibit better capacity retention compared to non-crosslinked soft binders. The reason is that an appropriate level of stiffness can maintain electrode integrity and electrical connectivity. However, excessive stiffness has proven to be no longer beneficial to cycling performance. This is because stiff binders cannot effectively relieve the stress created by bulk cotton. Therefore, it is important to control the time-dependent mechanical response of the binder to determine the proper balance between stiffness and stress relaxation. Generalized but effective approaches to control the mechanical behavior include mixing two different binders, adjusting the crosslink density or changing the flexibility of the polymer chains.

Republic of Korea Patent Publication 10-2016-0011587

An object of the present invention is to provide a negative electrode for a secondary battery including a water-soluble binder.

Another object of the present invention is to provide a method for manufacturing a negative electrode for a secondary battery including a water-soluble binder.

According to one aspect of the present invention, embodiments of the present invention are a negative electrode active material; conductive material; and a water-soluble binder including fibrin and having a three-dimensional structure and binding the negative electrode active material and the conductive material.

The anode active material is at least one of Si, Li, SiO _x , Sn, Ge, Mg, P, Al, Zn, Pb, Pn, and As; Alternatively, it may include a composite of at least one of Si, Li, SiO _x , Sn, Ge, Mg, P, Al, Zn, Pb, Pn, and As and a carbon material.

The conductive material may include graphite-based materials such as natural graphite, artificial graphite, graphene, super P, and super C; activated carbon (active carbon) system; denka black, ketjen black, channel black, furnace black, thermal black, contact black, lamp black, acetylene carbon black systems such as acetylene black; carbon nanostructures such as carbon fibers, carbon nanotubes (CNTs), and fullerenes; And it may be one or more selected from the group consisting of combinations thereof.

The water-soluble binder may have a storage coefficient (G′) of 10 kPa to 70 kPa and a loss coefficient (G″) of 1 kPa to 20 kPa.

The water-soluble binder may have a creep strain (εc) of 10 ⁴ or less.

The water-soluble binder includes an amide group, a carboxyl group, a hydroxyl group, an amino group, lysine, histidine, aspartic acid, threonine ( threonine, serine, glutamic acid, glycine, arginine, proline, alanine, valine, isoleucine, leucine , At least one of tyrosine and phenylalanine as a reaction site, and the reaction site may hydrogen bond with the negative electrode active material.

The water-soluble binder may include at least one of fibrin, a fibrin-alginate complex, and a fibrin-alginate-cation complex.

The fibrin-alginic acid complex controls the rheological properties by adjusting the mixing ratio of fibrin and alginic acid, and the fibrin and alginic acid may be mixed in a weight ratio of 1:5 to 5:1.

The fibrin-alginate-cation complex controls the rheological properties by adjusting the mixing amount of fibrin, alginic acid and cations, the fibrin and alginic acid are mixed in a weight ratio of 1:5 to 5:1, and the cation is 0.01M to 1M can be added as

In the fibrin-alginate-cation complex, the fibrin and alginate may be physically entangled to form an interpenetrating network (IPN) or a semi-interpenetrating network.

In the fibrin-alginate-cation complex, the cation may be at least one of a divalent cation and a trivalent cation.

The negative electrode active material, the conductive material, and the water-soluble binder may have a weight ratio of 90:5:5 to 50:30:20.

The negative electrode for a secondary battery may expand by less than 50% in volume during charging and discharging.

Also, in one embodiment of the present invention, forming a water-soluble binder by mixing at least one of thrombin, alginic acid and cations with fibrinogen; preparing ink for an electrode by mixing a negative electrode active material and a conductive material with the water-soluble binder; and drying the ink for the electrode.

The fibrinogen may be mixed with thrombin, and the fibrinogen and thrombin may be mixed in a volume ratio of 2:1 to 1:2.

The fibrinogen is mixed with thrombin and alginic acid, the fibrinogen and thrombin are mixed in a volume ratio of 2:1 to 1:2, the fibrinogen and thrombin react to produce fibrin, and the fibrin and alginate are mixed in a volume ratio of 5:1 to 1 :5 by weight.

The fibrinogen is mixed with thrombin, alginic acid and cations, the fibrinogen and thrombin are mixed in a volume ratio of 2:1 to 1:2, the fibrinogen and thrombin react to produce fibrin, and the fibrin and alginate are mixed in a ratio of 5:1 to 1:5 by weight, and the cations may be mixed at 0.1M to 1M.

The cation may be at least one of a divalent cation and a trivalent cation.

The negative electrode active material, the conductive material, and the water-soluble binder may have a weight ratio of 85:15:5 to 50:30:20.

In addition, in one embodiment of the present invention, it is possible to provide a secondary battery including the negative electrode for the secondary battery.

According to the present invention, a negative electrode for a secondary battery including a water-soluble binder can be provided.

In addition, according to the present invention, it is possible to provide a method for manufacturing a negative electrode for a secondary battery including a water-soluble binder.

1 is a diagram schematically showing the structure of fibrin in vivo and the structure of a negative electrode for a secondary battery including a water-soluble binder prepared including fibrin according to an embodiment of the present invention.
2 is an FTIR measurement result of single binders.
3 is an image showing the three-dimensional structures of fibrin and alginic acid and their actual behavior.
4 and 5 are results of evaluating the electrochemical properties of single binders.
6 is a peel force test result of a single binder.
7 schematically shows the shape of the three-dimensional network structure of the mixed binder.
8 is an FTIR measurement result for mixed binders.
9 is a result of measuring cycle stability and speed performance of a mixed binder.
10 shows the measurement of capacity according to cycles of a battery by using F4A1-10Ca as a binder and varying the weight ratio of Si anode active material:binder:Super P.
11 is a result of measuring cycle stability and speed performance of a mixed binder.
12 is a comparative plot of Coulombic efficiency (CE) versus cycle number for each sample.
13 is a measurement result of electrochemical impedance spectroscopy (EIS).
14 is a peel force test result for a mixed binder.
15 and 16 are the results of measuring the mechanical properties of the mixed binder.
17 is a cross-sectional image of FIB milling before and after 100 cycles of each electrode.
18 to 20 are surface SEM images of each electrode before/after cycling.
21 to 23 are analysis results of the SEI layer of each electrode.

Details of other embodiments are included in the detailed description and drawings.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and unless otherwise specified in the following description, components, reaction conditions, and content of components are expressed in the present invention. All numbers, values and/or expressions are to be understood as being qualified in all cases by the term "about" as such numbers are inherently approximations that reflect, among other things, various uncertainties of measurement that arise in obtaining such values. . Also, when numerical ranges are disclosed herein, such ranges are contiguous and include all values from the minimum value of such range to the maximum value inclusive, unless otherwise indicated. Furthermore, where such a range refers to an integer, all integers inclusive from the minimum value to the maximum value inclusive are included unless otherwise indicated.

Further, in the present invention, where ranges are stated for a variable, it will be understood that the variable includes all values within the stated range inclusive of the stated endpoints of the range. For example, a range of "5 to 10" includes values of 5, 6, 7, 8, 9, and 10, as well as any subrange of 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like. inclusive, as well as any value between integers that fall within the scope of the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5 and 6.5 to 9, and the like. For example, the range of “10% to 30%” could range from 10% to 15%, 12% to 18%, as well as values such as 10%, 11%, 12%, 13%, and all integers up to and including 30%. %, 20% to 30%, etc., and any value between reasonable integers within the scope of the stated range, such as 10.5%, 15.5%, 25.5%, etc. It will be understood to include.

1 shows the structure of fibrin in vivo, the structure of a negative electrode for a secondary battery including a water-soluble binder prepared using fibrin according to an embodiment of the present invention, and the volume when the negative electrode of the secondary battery is lithiated/delithiated It is a diagram schematically showing the change.

According to one aspect of the present invention, embodiments of the present invention are a negative electrode active material; conductive material; and a water-soluble binder including fibrin and having a three-dimensional structure and binding the negative electrode active material and the conductive material.

The negative electrode active material may include a material having a property of expanding in volume according to charging/discharging of the battery. The anode active material may have characteristics of high capacity and high output compared to conventional graphite anodes. For example, the anode active material is at least one of Si, Li, SiO _x , Sn, Ge, Mg, P, Al, Zn, Pb, Pn, and As; Alternatively, it may include a composite of at least one of Si, Li, SiO _x , Sn, Ge, Mg, P, Al, Zn, Pb, Pn, and As and a carbon material.

The conductive material may include a material containing carbon. For example, the conductive material may include graphite-based materials such as natural graphite, artificial graphite, graphene, super P, and super C; activated carbon (active carbon) system; denka black, ketjen black, channel black, furnace black, thermal black, contact black, lamp black, acetylene carbon black systems such as acetylene black; carbon nanostructures such as carbon fibers, carbon nanotubes (CNTs), and fullerenes; And it may be one or more selected from the group consisting of combinations thereof.

The water-soluble binder may include fibrin and bind the negative electrode active material and the conductive material with a three-dimensional structure. The water-soluble binder has a water-soluble reaction site and is soluble in water, so it may be environmentally friendly compared to conventional organic binders.

The water-soluble binder itself may have a three-dimensional structure. The three-dimensional structure of the water-soluble binder may mean that fibrin included in the water-soluble binder is agglomerated to form a three-dimensional shape. Accordingly, the water-soluble binder can three-dimensionally bind the negative electrode active material and the conductive material due to the three-dimensional structure, and even form a hydrogen bond with the negative electrode active material to bind them more firmly.

The water-soluble binder may have rheological properties, particularly strain-stiffening properties. The rheological properties of the water-soluble binder can be formed by appropriately balancing the stiffness and stress relaxation ability of the material. The water-soluble binder binds the negative electrode active material so that it can be elongated as the negative electrode active material expands, but can return to its original length due to elasticity. can Therefore, when the anode active material expands according to charge/discharge of the electrode, the water-soluble binder binds the anode active material to prevent excessive expansion. Therefore, excessive expansion of the electrode by the water-soluble binder can be prevented.

The water-soluble binder may have a storage modulus (G') of 10 kPa to 70 kPa.

The water-soluble binder may have a loss factor (G") of 1 kPa to 20 kPa. Also preferably, the water-soluble binder may have a loss factor (G") of 2 kPa to 17 kPa.

The water-soluble binder may have a creep strain (ε _c ) of 10 ⁴ or less.

The ranges of the storage coefficient, loss coefficient, and creep strain may be within a range in which the water-soluble binder can effectively bind the negative electrode active material by appropriately balancing stiffness and stress relaxation ability.

The water-soluble binder may have a water-soluble reaction site and hydrogen bond with other functional groups on the surface of the negative electrode active material. By the hydrogen bond, the water-soluble binder can be more firmly bound by three-dimensionally bonding with the negative electrode active material and the conductive material. The water-soluble reaction site may be a functional group present in fibrin. The water-soluble reaction site of the water-soluble binder is, for example, an amide group, a carboxyl group, a hydroxyl group, an amino group, lysine, histidine, or aspartic acid. (aspartic acid), threonine, serine, glutamic acid, glycine, arginine, proline, alanine, valine, isoleucine ( isoleucine), leucine, tyrosine, and phenylalanine.

The water-soluble binder may have a water-soluble reaction site and include fibrin. This may mean that the water-soluble binder may be formed of only fibrin, may be formed by combining fibrin and other substances, and may also mean that it has a water-soluble reaction site in all applicable cases. Specifically, the water-soluble binder may include fibrin, a fibrin-alginate complex, or a fibrin-alginate-cation complex.

The water-soluble binder includes fibrin, and the fibrin may be formed by mixing fibrinogen and thrombin in a volume ratio of 1:2 to 2:1.

Rheological properties of the water-soluble binder including the fibrin-alginic acid complex can be adjusted by adjusting the mixing ratio of fibrin and alginic acid. Here, fibrin may be formed by mixing fibrinogen and thrombin in a volume ratio of 1:2 to 2:1. In addition, the fibrin and alginic acid may be mixed and polymerized in a weight ratio of 1:5 to 5:1 to form a composite, and preferably mixed and polymerized in a weight ratio of 4:1 to form a composite. When the weight ratio of fibrin to alginic acid is less than 1:5 or greater than 5:1, cycle stability of the battery may deteriorate.

The fibrin-alginate-cation complex can adjust the rheological properties by adjusting the mixing amount of fibrin, alginic acid, and cation. Here, fibrin may be formed by mixing fibrinogen and thrombin in a volume ratio of 1:2 to 2:1. In addition, the fibrin and alginic acid may be mixed and polymerized in a weight ratio of 1:5 to 5:1 to form a composite, and preferably mixed and polymerized in a weight ratio of 4:1 to form a composite. In addition, the cation may be added at 0.01M to 1M to form a complex, preferably at 0.1M. Here, as in the fibrin-alginic acid complex, the ratio of fibrin to alginic acid affects the cycle stability of the battery, and in addition, when the amount of added cation is less than 0.01M or exceeds 1M, the cycle stability is higher than when no cation is added. It may deteriorate and affect the performance of the battery.

Mixing ratios of each component in the fibrin-alginate complex and the fibrin-alginate-cation complex may be pre-calculated by assuming a reaction of each component. Specifically, when fibrinogen and thrombin are mixed in a volume ratio, and it is assumed that fibrinogen and thrombin completely react to form fibrin, the weight is calculated from the density of the fibrin, and alginate is expressed as a weight ratio with respect to the calculated weight of fibrin. can be mixed. The weight of fibrin may be calculated differently depending on the concentrations of fibrinogen and thrombin.

In the fibrin-alginate-cation complex, the fibrin and alginate may be physically entangled to form an interpenetrating structure or a semi-interpenetrating structure. The interpenetrating structure or semi-interpenetrating structure may refer to a structure in which fibrin and alginic acid are entangled at a molecular level due to cross-linking without chemical bonding between fibrin and alginic acid. A Young's modulus of the water-soluble binder may be further increased by forming the interpenetrating structure or the semi-interpenetrating structure. Therefore, expansion of the negative electrode active material can be more effectively controlled.

In addition, the water-soluble binder can improve the cycle life of the battery by forming a better solid electrolyte interphase layer (SEI) during the cycle of the battery. When the water-soluble binder is included, the SEI layer is formed thinly and stably, so that the resistance of the battery is reduced and the performance of the battery itself can be improved.

In the fibrin-alginate-cation complex, the cation may be at least one of a divalent cation, a trivalent cation, and a cation having a higher charge. The cation may form a cross-linking bond between alginic acid and fibrin, and may form an interpenetrating structure between alginate and fibrin. As a result, the stiffness of fibrin and the stress relieving ability of alginic acid complement each other, so that the performance and stability of the electrode can be further improved compared to a binder in which cations are not added. For example, the cation may be any one of Ca ²⁺ , Ba ²⁺ , Zn ²⁺ and Mn ²⁺ .

In the negative electrode for a secondary battery, the negative electrode active material, the conductive material, and the water-soluble binder may have a weight ratio of 90:5:5 to 50:30:20, preferably 70:15:15 to 50:30:20. can have Here, the negative electrode active material may be in an amount capable of securing sufficient battery capacity, and the water-soluble binder may be in an amount capable of sufficiently binding the negative electrode active material and the conductive material. When the water-soluble binder is included in a smaller amount, the anode active material and the conductive material cannot be sufficiently bound, and expansion of the anode active material cannot be effectively suppressed. On the other hand, when more is included, the amount of the negative electrode active material and the conductive material is reduced, so that a sufficient level of secondary battery capacity cannot be obtained.

When the water-soluble binder having the above characteristics is included, volume expansion during charging/discharging of the battery can be effectively suppressed. When the change in the thickness of the secondary battery before the cycle (t _before ) and the thickness after the cycle (t _after ) is defined by [Equation 1], the change in thickness may be less than 50%.

[Equation 1]

Also, in one embodiment of the present invention, forming a water-soluble binder by mixing at least one of thrombin, alginic acid and cations with fibrinogen; preparing ink for an electrode by mixing a negative electrode active material and a conductive material with the water-soluble binder; and drying the ink for the electrode.

The water-soluble binder may be formed by selecting at least one of thrombin, alginic acid, and cations, mixing with the fibrinogen, and polymerizing the mixture.

For example, when only thrombin is selected from the group, a water-soluble binder containing only fibrin may be formed by polymerizing thrombin and fibrinogen. At this time, the fibrinogen and thrombin may be mixed in a volume ratio of 2:1 to 1:2.

Also, for example, when thrombin and alginic acid are selected from the group, a water-soluble binder including a fibrin-alginate complex may be formed by mixing the fibrinogen and alginic acid and then mixing and polymerizing the thrombin. Here, fibrin may be formed by mixing fibrinogen and thrombin in a volume ratio of 1:2 to 2:1. In addition, the fibrin and alginic acid may be mixed and polymerized in a weight ratio of 1:5 to 5:1 to form a composite, and preferably mixed and polymerized in a weight ratio of 4:1 to form a composite.

In addition, for example, when thrombin, alginic acid, and cations are selected from the group, the fibrinogen and alginic acid are mixed, and then the thrombin is mixed and polymerized, and the cation is added thereto to form a fibrin-alginate-cation complex. can form Here, fibrin may be formed by mixing fibrinogen and thrombin in a volume ratio of 1:2 to 2:1. In addition, the fibrin and alginic acid may be mixed and polymerized in a weight ratio of 1:5 to 5:1 to form a composite, and preferably mixed and polymerized in a weight ratio of 4:1 to form a composite. The cation may be mixed with 0.1M to 1M.

In the fibrin-alginate-cation complex, the cation may be at least one of a divalent cation, a trivalent cation, and a cation having a higher charge. The cation may form a cross link between alginic acid and alginic acid or between alginic acid and fibrin, and may form an interpenetrating structure between alginate and fibrin. As a result, the stiffness of fibrin and the stress relieving ability of alginic acid complement each other, so that the performance and stability of the electrode can be further improved compared to a binder in which cations are not added. For example, the cation may be any one of Ca ²⁺ , Ba ²⁺ , Zn ²⁺ and Mn ²⁺ .

In the negative electrode for a secondary battery, the negative electrode active material, the conductive material, and the water-soluble binder may have a weight ratio of 90:5:5 to 50:30:20, preferably 70:15:15 to 50:30:20. can have Here, the negative electrode active material may be in an amount capable of securing sufficient battery capacity, and the water-soluble binder may be in an amount capable of sufficiently binding the negative electrode active material and the conductive material. When the water-soluble binder is included in a smaller amount, the anode active material and the conductive material cannot be sufficiently bound, and cycle stability is reduced, so expansion of the anode active material cannot be effectively suppressed. On the other hand, when more is included, the amount of the negative electrode active material and the conductive material is reduced, so that a sufficient level of secondary battery capacity cannot be obtained.

In addition, in one embodiment of the present invention, it is possible to provide a secondary battery including the negative electrode for the secondary battery.

Examples and comparative examples of the present invention are described below. However, the following examples are only preferred embodiments of the present invention, and the scope of the present invention is not limited by the following examples.

Si nanoparticles (˜100 nm, 99%) and CaCl ₂ (97%) used in the following examples were purchased from Alfa Aesar (USA). Alginate sodium salt (Alg) was purchased from Sigma-Aldrich (USA). Bovine fibrinogen (without plasminogen and fibronectin) and thrombin were purchased from Enzyme Research Laboratories (USA) and stored at -80°C to maintain activity. Both samples were thawed at -37 °C before use.

[Example 1]

1. Preparation of water-soluble binder

In order to prepare a water-soluble binder according to an embodiment of the present invention, first, fibrinogen and thrombin were diluted to 12.8 mg/ml and 3.0 U/ml, respectively, using Type 1 water (18.2 MΩcm at 25° C.). The final concentration of fibrinogen was adjusted to 6.4 mg/ml, and the final concentration of thrombin was adjusted to 1.5 U/ml. Diluted phytriinogen and thrombin solutions were mixed at a volume ratio of 1:1 to form a fibrin hydrogel. They were reacted for 1 hour to complete their polymerization.

2. Manufacture of 2-electrode coin cell (CR2032)

In order to measure the electrochemical properties of the electrode containing the prepared water-soluble binder, a two-electrode coin cell was prepared in an Ar-filled glove box. A metallic Li foil (99.9%, Sigma-Aldrich, USA) and a polypropylene membrane (Celgard 2400, Celgard, USA) were used as a counter electrode and separator, respectively. Contains 10 wt% of fluoroethylene carbonate (FEC) as an additive, and ethylene carbonate (EC, diethyl carbonate), diethyl carbonate (DEC), and dimethyl carbonate (DMC) are 1:1: 1M LiPF ₆ was dissolved in a solution mixed at 1 (w/w/w) and used as an electrolyte. The working electrode was fabricated by casting an aqueous 60:15:20 (w/w/w) slurry of Si nanoparticles, binder and Super P on Cu foil, followed by drying at 70 °C in a vacuum oven. The mass loading of the Si nanoparticles used was ~1.0 mg/cm.

[Example 2]

Example 2 was prepared by changing the water-soluble binder manufacturing process of Example 1 as follows and the rest being the same.

2 g of alginate sodium salt was added to 50 ml of Type 1 water to prepare an alginate aqueous solution (4% by weight). For uniform dispersion, the alginate aqueous solution was stirred with a stirrer for at least 12 hours. An appropriate amount of fibrinogen and an aqueous solution of alginic acid were mixed for 3 minutes using a vortex mixer to prepare a mixture of fibrinogen and alginic acid. Thereafter, thrombin was added to the mixed solution in order to initiate fibrinogen polymerization, and then waited for 1 hour until the reaction was completed. Fibrin and alginic acid were polymerized to prepare a water-soluble binder including a fibrin-alginate complex. Example 2 was prepared in five ways as shown in [Table 1] below by varying the ratio of fibrin and alginic acid.

show drawing fibrin:alginic acid (weight ratio) Example 2-1 F1A1 1:1 Example 2-2 F2A1 2:1 Example 2-3 F3A1 3:1 Example 2-4 F4A1 4:1 Example 2-5 F5A1 5:1

[Example 3]

Example 3 was prepared by changing the water-soluble binder manufacturing process of Example 1 as follows and remaining the same.

In the process of preparing the water-soluble binder of Example 2, 0.1 M aqueous solution of CaCl ₂ was added after polymerization of fibrin and alginic acid. A water-soluble binder including a fibrin-alginate-cationic complex was prepared by forming interchain bridges by Ca ²⁺ cations. Example 3 was prepared by polymerizing the weight ratio of fibrin and alginic acid to 4:1, and then varying the ratio of cations to prepare 4 types as shown in [Table 2] below.

show drawing amount of cation Example 3-1 5 μl 5 μl Example 3-2 10μl (10Ca) 10 μl Example 3-3 20 μl 20 μl Example 3-4 40 μl 40 μl

[Example 4]

In the process of preparing the water-soluble binder of Example 3, the F4A1-10Ca binder was prepared, and Example 4 was prepared by adjusting the amounts of the Si negative electrode active material and Super P.

bookbinder Si:binder:Super P (weight ratio) Example 4-1 F4A1-10Ca 65:15:20 Example 4-2 F4A1-10Ca 80:10:10 Example 4-3 F4A1-10Ca 90:5:5

[Comparative example]

A comparative example was prepared by using alginate as a binder instead of the water-soluble binder in Example 1 and the rest being the same.

Hereinafter, the characteristics of the water-soluble binder and the electrode including the same were evaluated using the prepared examples and comparative examples.

1. Comparison of properties of fibrin and alginic acid as binders

(1) Identification of water-soluble reaction sites

FT-IR spectrum (Infrared absorbance spectra) was analyzed to confirm the presence of water-soluble reaction sites of each material. Total reflection Fourier-transform infrared spectroscopy (ATR-FTIR; Cary 630, Agilent, USA) attenuated in the range of 4000 to 650 cm ^-1 with a resolution of 2 cm ^-1 was measured.

2 is an FT-IR spectrum result for confirming the interaction between silicon used as an anode active material and a binder. Fib (fibrin), Si / Fib (silicone / fibrin), Alg (alginic acid) and Si / Alg (silicone / alginic acid) were measured.

The spectral results of Fib and Si/Fib are shown in FIG. 2b, and all are ~3264 cm ^-1 (NH bending: amide A and hydrogen bond OH stretch), ~2943 cm ^-1 (CH stretch), ~1620 cm ^-1 (C=O Stretch: amide ), ˜1521 cm ⁻¹ (NH bending: amide Ⅱ) and ˜1392 cm ⁻¹ (CH bending). The difference between the Fib and Si/Fib samples is that in the Si/Fib sample, after fiphrine is bonded to Si, the peaks corresponding to the C=O stretch (amide ) and NH bending (amide II) are 5 cm ^-1 and 8 cm ^-1 , respectively. It is red-shifted by (Fig. 2b). This indicates that a hydrogen bond is formed between the hydroxyl group (Si-OH) on the Si surface and the peptide bond (amide) of fibrin.

Conversely, the Alg and Si/Alg samples (above Fig. 2a) show ∼3193 cm ⁻¹ (hydrogenated OH stretch), ∼2921 cm ⁻¹ (CH stretch and CO stretch of the pyranose ring), ∼1589 cm ⁻¹ (carboxyl OCO asymmetric stretch of rate), ˜1405 cm ⁻¹ (OCO symmetric stretch of carboxylate) and ˜1024 cm ⁻¹ (COC asymmetric stretch). When alginate is also bonded to Si, a red-shift of 5 cm ^-1 for OCO asymmetric stretch and 3 cm ^-1 for OCO symmetric stretch appears due to the hydrogen bond between Si-OH and the carboxylate of alginic acid (FIG. 2c) .

These results indicate that fibrin and alginic acid can hydrogen bond with silicon and bind silicon.

(2) 3D network structure

3 is a diagram showing the three-dimensional structure of fibrin and alginic acid. 3a and b are SEM images showing a 3D network structure of fibrin and a 3D network structure of alginate, respectively. Fibrin is formed when factor XIII present in fibrinogen is activated by thrombin and forms an active transglutaminase enzyme (factor XIIIa) to form α-α, γ-γ, and α-γ in adjacent fibril. induces covalent cross-links between the γ chains. Accordingly, a three-dimensional network entangled like a net can be formed as shown in FIG. 3A. On the other hand, alginate is difficult to form a fibrous network as shown in FIG. 3B. Instead, when alginate is 4 wt% (the concentration used in this experiment), it behaves as a physically entangled, uncharged polymer in a salt-free aqueous solution. As a result, at the same concentration, fibrin is a non-flowing viscoelastic hydrogel, whereas alginate is a flowing viscous solution (Fig. 3c). FIG. 3d shows a slurry prepared by mixing each of fibrin and alginic acid with Si nanoparticles and Super P using the properties of fibrin and alginic acid, and then applied to a 5×5 cm ² Cu foil.

(3) Evaluation of electrochemical properties

The electrochemical properties of the Si/Fib and Si/Alg electrodes were evaluated against Li/Li+ in a half-cell configuration. Galvanostatic charge/discharge and cyclic voltammetry (CV) measurements were performed using a WBCS 3000 battery cycle (WBCS 3000 battery cycle, WonATech, Korea) to measure 0.01 ~ 1.0 vs. Measured over the voltage window of Li/Li ⁺ .

Figure 4a shows a cyclic voltammetry (CV) curve, which was scanned at a rate of 0.1 mV/s during the 1st, 2nd, 3rd, 5th, and 10th cycles for each electrode. The behavior of these electrodes in the first discharge/charge cycle was similar with a thin anodic peak at ~0.01 V. This result is the result of inserting Li into crystalline Si to form amorphous Li _x Si _y (a-Li _x Si _y ). The two cathodic peaks starting to appear at ~0.34 V and ~0.52 V correspond to the Li-extraction phase transformation from a-Li ₁₄ Si ₃ to a-Li ₇ Si ₃ and aL ₇ Si ₃ to a-LiSi, respectively. In subsequent cycles, both Si/Fib and Si/Alg show anodic peaks at higher potentials (~0.18 V) during discharge, which is due to intercalation of Li into amorphous Si. During charging, the two negative peaks remained separate until the third cycle in both cases. Si/Alg followed this behavior in all cycles while Si/Fib deviated from this pattern. From the 5th cycle, the a-Li ₇ Si ₃ delithiation peak (~0.52 V) started to shift to a lower potential, and the a-Li ₁₄ Si ₃ delithiation peak (~0.34 V) appeared. Since a lower cathodic potential is generally a result of lower polarization resistance, the inclusion of fibrin may increase the transfer of electrons and/or ions with respect to a-Li ₇ Si ₃ delithiation and increase the efficiency of the cell. can make it

Figure 4b shows the galvanostatic primary discharge/charge voltage curves of Li/Li ⁺ versus 0.01V and 1.0 at 0.1C (1C=4200mAh/g) for Si/Fib and Si/Alg. The characteristic lithiation/delithiation plateau of Si is found at 0.08/0.45 V for Si/Fib and at 0.11/0.44 V for Si/Alg. The initial Coulombic efficiencies (ICEs) of Si/Fib and Si/Alg were ~71% and ~70%, respectively. The ICE of Si/Fib appeared similar to that of Si/Alg, indicating that fibrin can effectively ensure reversibility by forming a stable solid electrolyte interphase (SEI) layer during the first cycle.

15/65)였고, 이는 0.33(

20/60) 보다 ~1.4배 낮은 것이었으며, Si 음극에서 바인더로서 매우 우수한 바인더임을 나타낸다.Figure 4c shows that Si/Fib exhibits better cycling efficiency than Si/Alg. When subjected to 100 cycles at 0.1C, Si/Fib maintained ~69% capacity, showing much higher cycle stability than Si/Alg (16%). The same result was found even when 150 cycles were run at a faster rate of 0.5C, and Si/Fib maintained 58% (728mAh/g) of the initial delithiation capacity, which was 30% ( 381 mAh/g) showed higher cycle stability than Si/Alg, which was maintained (FIG. 5). In the electrode used in this experiment, the quantitative ratio between the binder and the Si nanoparticles was 0.23 (

15/65), which was 0.33 (

20/60), indicating that it is a very good binder as a binder in Si anodes.

4D shows the result of evaluating the speed performance while gradually increasing the cycle speed and then decreasing it again. Unlike Si/Alg, Si/Fib shows capacities of 2262(0.05C), 2097(0.1C), 1832(0.2C), 1210(0.5C) and 723mAh/g(1C), recovering when the cycle rate slows down. capacity was found to be good. Except for 0.05C, the rate performance of Si/Fib was superior to that of Si/Alg.

Combining these electrochemical properties, it can be seen that Si / Fib exhibits superior performance and stability than Si / Alg in almost all aspects.

2. Peel force test of single binder

Si/Fib's improved electrochemical properties over Si/Alg may be due to its higher bulk-scale mechanical stability. To confirm this, the peeling force of the electrode on the Cu foil was measured using a universal tester (UTM; Instron 5844, Instron, USA). A 3M tape was attached to the entire surface of the 2x8 cm ² electrode and peeled 180° at a speed of 100 μm/s, and the peel force was recorded as a function of displacement. The test results are shown in FIG. 6 .

Figure 6a is an image of the appearance of the peel force test.

The peel force for each electrode is shown in FIG. 6B. As expected, the adhesion of Si/Fib (average 4.2 N) was 6 times stronger than that of Si/Alg (average 0.7 N). This difference can be confirmed by optical microscope images of the two samples before and after the peel force test (Fig. 6c, d). Si/Alg revealed more Cu after exfoliation than Si/Fib. One major reason for this result is that, unlike alginate, fibrin forms a continuous three-dimensional network structure with abundant side chains of amino acids, which hydrogen bonds with Si and Cu to allow more contact. Since the adhesive force of the electrode is governed by the number density and bond strength of bonding sites in Si-binder attachment and Si-binder-Cu attachment, these features form stronger adhesive force. In addition, mechanical stress can be more effectively relieved through such a three-dimensional continuous network than individual linear polymer chains. Another reason is the large difference in stiffness between fibrin and alginic acid. Fibrin has high rigidity to form a viscoelastic hydrogel with covalent crosslinking, whereas alginate has very low rigidity to form a viscous solution (4 wt% in this experiment) without crosslinking. It can be seen that the rigid cross-linked binder (fibrin binder here) tends to show stronger adhesive strength than the soft binder without it, and this is due to the improved mechanical robustness by cross-linking.

3. Characterization of mixed binders

Fibrin has excellent electrochemical performance and rigidity, but rather lacks stress relaxation ability due to these characteristics. Therefore, after forming a binder by mixing fibrin with alginate and/or proton so that stiffness and stress relaxation ability are appropriately balanced, the properties thereof were tested.

(1) Analysis of the shape of the binder

7a schematically shows the three-dimensional shape of Fib/Alg (fibrin and alginate mixed without cations), and 7b shows the three-dimensional shape of Fib/Alg/Ca ²⁺ (fibrin, alginate, and Ca ²⁺ mixed with cations). It is a schematic representation of the shape.

Both fibrinogen and alginic acid are hydrophilic and negatively charged in Type 1 water (pH ~7). Also, since Type 1 water has very low ionic strength, these two substances are miscible by constitutive entropy and stabilized by electrostatic repulsion. Therefore, the alginate chain can be uniformly dispersed in the three-dimensional network of fibrin after complete conversion of fibrinogen to fibrin, and is not dispersed to fibrinogen and thrombin because of its inactivity to proteins. Fib/Alg binders were prepared with varying weight ratios of fibrin and alginic acid (5:1, 4:1, 3:1, 2:1 and 1:1), while the total weight of the binder was varied to give it a wide range of mechanical properties. was kept constant.

The Fib/Alg/Ca ²⁺ binders formed ionic bridges between entangled alginate chains with small additions of Ca ²⁺ ions (5, 10, 20, and 40 μl). This forms a structure in which the covalent cross-linked fibrin network and the ionic cross-linked alginate network are entangled with each other but do not chemically bond, forming a three-dimensional interpenetrating network (IPN). IPN hydrogels are known to have superior mechanical, chemical and biophysical properties than those exhibited by individual polymers. Ionic cross-links take advantage of weaker and looser points than covalent cross-links to precisely control the amount of Ca ²⁺ to produce a binder that is soft enough to relieve stress. You can expect to bind effectively.

(2) Identification of water-soluble reaction sites

When amino acids and polysaccharides are mixed in an aqueous medium, the ideal situation is that the two polymers do not undergo a chemical reaction and are kept apart by electrostatic repulsion. In order to confirm this, the IR absorbance spectrum of the mixed binder was measured and shown in FIG. 8 . The types of binders were measured for Fib, Alg, F4A1 (mixing fibrin and alginic acid in a 4:1 weight ratio) and F4A1-10Ca (mixing fibrin and alginate in a 4:1 weight ratio and adding 10 μl of Ca ²⁺ ), F4A1 and F4A1-10Ca were also measured when an electrode was formed by mixing with Si. In the spectra of F4A1 and F4A1-10Ca, the fibrin and alginate spectra were combined, and no additional peaks appeared (FIG. 8a). This means that no chemical bond has occurred between fibrin and alginic acid.

In addition, it can be seen in FIG. 8b that two peaks of C=O stretch (amide ) and N-H bending (amide II) are maintained even after the F4A1 and F4A1-10Ca mixtures are formed. This means that there are no strong supramolecular interactions between fibrin and alginic acid, but instead, it was confirmed that there is a repulsion between negative charges at pH ~7.

In addition, in FIGS. 8c and d, after the mixed binders are bonded to Si, it can be seen that the two peaks opposing amide and amide II are red-shifted for both F4A1 and F4A1-10Ca, which means that a hydrogen bond is formed.

(3) Measurement of electrode efficiency of mixed binder

9 is a result of measuring the rate performance of the Si electrode by varying the mixing ratio of the mixed binder components. The electrode applied to each graph is indicated as Si-FxAy, and x:y is the weight ratio of fibrin to alginic acid.

In Figure 9a, the weight ratio of fibrin was increased from 1 to 5, respectively, and the rate was measured at 1C. Si-F4A1 showed the best rate performance with 1013 mAh/g, followed by Si-F5A1 with 762 mAh/g, Si-F3A1 with 691 mAh/g, Si-F2A1 with 652 mAh/g, and Si-F1A1 with 618 mAh/g. showed the speed performance of Si-F4A1 and Si-F5A1 showed better performance than the rate performance (723 mAh/g at 1C) when only fibrin was used as a binder, and the electrochemical performance improved when an appropriate amount of alginate was included in the fibrin network. means to become

In addition, the rate performance of the binder at 1C was measured while varying the addition ratio of cations to Si-F4A1, which is the most efficient in the fibrin-alginic acid mixed binder, and the results are shown in FIG. 9B. Ca ²⁺ was added as a cation, and 5, 10, 20, and 40 μl were added, respectively. When 10 μl of cation was added, the highest rate performance was shown at 1103 mAh/g, and when no cation was added, when 5, 20, or 40 μl was added, the performance was slightly lower than when 10 μl was added.

In addition, based on the above results, the cycle stability of Si-F4A1 and Si-F4A1-10Ca, which showed excellent speed performance by running 500 cycles at 0.5 C, was measured, and the results are shown in FIG. 9c. In order to compare with the mixed binder, the same experiment was performed on a single binder made of fibrin or alginic acid and Si-F1A1. The worst cycle characteristics were observed for Si-Alg and Si-F1A1, which resulted from either no fibrin or too little fibrin. On the other hand, in Si-F4A1 in which fibrin was added 4 times more, it was confirmed that the capacity was significantly increased compared to the fibrin single binder. In addition, when 10 μl of positive ions were added here, the capacity of 740 mAh/g was maintained even after 500 cycles, confirming that 53% of the capacity was maintained.

10 shows the measurement of capacity according to cycles of a battery by using F4A1-10Ca as a binder and varying the weight ratio of Si anode active material:binder:Super P. In the graph, the best capacity efficiency is shown when prepared at a weight ratio of 65:15:20 (in the drawing, the weight ratio of Si:Super P:binder is 65:20:15). When the amount of binder was reduced to 10 wt%, the capacity retention was 33% after 500 cycles, which was 1.6 times lower than that of 65:15:20 (53%). When the amount of binder was reduced to 5 wt%, the capacity retention was lowered to 17%.

Also, the rate performance and cycle stability for each electrode showed similar trends. In FIG. 9b, the cycle stability according to the amount of each cation added was the highest when 10 μl was added (FIG. 11a), and the rate performance for each electrode in FIG. 9c was also the highest in Si-F4A1-10Ca (FIG. 11b). ).

These results confirm that the higher the stiffness, the higher the electrochemical properties are not necessarily improved. This is because a binder obtained by mixing alginic acid or alginic acid with cations in fibrin shows better rate performance and cycle stability than fibrin, which is a material with high stiffness. In addition, this is because the network formed by mixing fibrin and alginic acid or fibrin, alginic acid and cations balances stiffness and stress relaxation and provides a path to improve electrochemical performance.

12 shows a comparative plot of C.E. versus cycle number for each sample. In all samples, C.E reached almost 90% after 1 cycle and reached 99% after 100 cycles, indicating high lithiation/delithiation reversibility.

(4) Electrochemical impedance spectroscopic measurement of mixed binders

Electrochemical impedance spectroscopy (EIS) was measured to confirm the factors of electrochemical performance for Si-F4A1-10Ca, which showed the best performance in the results of measuring the electrochemical properties of the mixed binder, and the results It is shown in Figure 13.

Electrochemical impedance spectroscopy (EIS; Ivium-n-Stat, Ivium Technologies, Netherlands) was performed by applying a 5 mV alternating current (AC) voltage over a frequency range of 1 MHz to 0.01 Hz. EIS spectra were collected at two different states of charge (0.01 V for lithiation and 1.0 V for delithiation) over the course of a cycle.

For Si-F4A1-10Ca, the Nyquist plot was measured at the initial open rotation voltage, and then the lithiation and delithiation states were measured at the 1st, 10th, 30th, 50th and 100th cycles, shown in Fig. 13a, b, and comparison In order to do so, the same experiment was performed for Si-Alg and is shown in FIGS. 13c and d. 11e and f are extracted by fitting the resistance of the SEI layer (R _SEI ) and the resistance to charge transfer (R _ct ) into the spectrum for an equivalent circuit (inserted in FIG. 13a) at each stage.

13e and f, it can be seen that Si-F4A1-10Ca has smaller R _SEI and R _ct values than Si-Alg in all cases during 100 cycles. Such a small resistance can support the excellent performance of Si-F4A1-10Ca in the experimental results for the speed performance and cycle stability. It also means that the movement of lithium ions in the SEI layer and the movement of charges at the interface have a great influence on the properties of the binder.

4. Peel Force Test for Mixed Binders

The stronger the adhesion to the electrode plate, the better the mechanical integrity of the electrode, which affects the electrochemical performance such as cycle stability and rate performance. As with the single binder, the peel force of the mixed binder was tested and shown in FIG. 15A, and an image of the test result is shown in FIG. 14. The experiment was conducted in the same way as for a single binder.

The experiment was conducted with respect to the same electrode as in FIG. 9c, and it can be seen that the peel force test results follow a similar trend to the experimental result of FIG. 9c. The highest value of 6.9N was measured for Si-F4A1-10Ca, followed by 6.1N for Si-F4A1, 4.2N for Si-Fib, 1.3N for Si-F1A1, and 0.7N for Si-Alg. This difference can be confirmed again in the optical microscope image of the peel force test result. In Si-F4A1-10Ca and Si-F4A1, the surface of the copper substrate is barely exposed, whereas in Si-F1A1, a large portion is exposed.

Through this peel force test, it can be confirmed that the electrode containing the fibrin-alginic acid mixed binder at an appropriate ratio has excellent electrode integrity and supports the electrochemical performance tested above.

5. Measurement of mechanical properties of mixed binders

(1) Measurement of rolling shear strain

In order to examine the relationship between electrode integrity and mechanical properties of the binder, the storage (G′) and loss (G″) moduli of each binder were measured using oscillatory shear rheology, and are shown in FIG. 15B.

In this measurement, the mechanical properties of the water-soluble binder were measured using an advanced rheometric expansion system (ARES, TA Instruments. USA). _Storage modulus (G') and dissipation modulus (G ") were collected.

At the highest measured angular frequency (ω), alginate behaves like a viscous fluid, which means that the loss coefficient (G") is larger than the storage modulus (G'). In contrast, in fibrin, F4A1-10Ca and F4A1, The storage modulus dominates the dissipation factor at all angular frequency values, which means that it is more like an elastic solid.

However, if you look closely, there are some differences. At ω = 1 rad/s, fibrin shows the highest stiffness (G' = 29 kPa) and the lowest stress relaxation (G" = 5.4 kPa). When fibrin is mixed with alginate in a weight ratio of 4:1 (F4A1), the stiffness (G"=26kPa) decreased by only ~12%, but the stress relaxation ability (G"=8.6kPa) was improved by ~60%. In addition, G' of F4A1-10Ca with cations added was 28 kPa, similar to fibrin, but G" was 7.9 kPa, similar to F4A1. As a result, in the Si electrode, F4A1-10Ca can bind electrode components firmly and effectively relieve stress at the same time.

These results can also be factors that improve adhesion and electrochemical performance. The reason why the decrease in G" is not as large as the increase in G' when cations are added is not clear, but it is probably because ionic cross-links are less restrictive than covalent cross-links in polymer chain motion. Figure 15c shows each binder. Plots of adhesion force (left axis) and 500th cycle capacity (right axis) as a function of the ratio between G' and G" at 1 rad/s (G'/G") are shown to visualize the relationship between G'/G" = 1/tan(δ) and δ is the phase shift). Here, alginate with low G'/G" (0.3) and high δ (73˚) is too soft to bind and fix the position of the components of the electrode, whereas with high G'/G" (5.3) and low δ ( 10˚) is too stiff to relieve stress. On the other hand, when fibrin and alginate are mixed in an appropriate ratio to form cross-links, stress relaxation ability is obtained, and as a result, the F4A1-10Ca binder has G'/G"=3.5 (~34% reduction compared to fibrin) and δ=16 F1A1 has G'/G"(5.1) and δ(11˚) values, similar to fibrin, but has excellent adhesion and capacity retention. Stability has a lower value than fibrin because the G' of F1A1 has a very low value (~3.6 times less than fibrin at 8.1 kPa).

This tendency for each binder is similarly shown in FIG. 16 where the angular frequency ω is set and measured differently.

These results confirm that the balance between stiffness and stress relaxation ability is very important.

(2) Creep strain measurement

Also, the change in volume of Si during cycling generates a significant amount of mechanical stress enough to deform the binder. Therefore, in order to test the mechanical properties of these electrodes, a constant stress of 70 kPa was applied and the creep strain was monitored as a function of time, and the results are shown in FIG. 15D.

Due to the viscous nature of alginate, the creep strain (ε _с ) increased very significantly within a few seconds after exposure to stress. Fibrin initially showed a small creep strain, but suddenly increased at ~25 sec because of its high stiffness. The ideal viscoelastic behavior appeared in F4A1-10Ca and part of F4A1. Creep strain of F4A1-10Ca increased rapidly at the beginning, but not as much as that of alginate, and after a certain increase, it showed a gentle increasing slope. Since then, no sharp increase in creep strain has been observed. This behavior confirms once again that the optimal balance between the storage modulus (G') and the dissipation modulus (G") greatly affects the properties of the binder, and for fibrin and alginate, F4A1-10Ca Compared to the case of fibrin alone, which has semi-flexibility, it shows that the mixed binder can better distribute the stress by freely transforming the flexible alginate structure. F1A1 initially showed a similar trend to F4A1-10Ca, but increased rapidly at ∼5 s, likely due to its low storage modulus.

The creep measurement results are also consistent with the results observed in rheology, and show that the balance between elastic and viscous properties is very important.

6. Electrode thickness measurement before/after electrode cycle

The change of the electrode before and after cycling shows the binding ability of the binder. In order to observe the thickness change before and after the cycle of the electrode, the thickness was measured in the cross-sectional SEM image of the milled sample using a focused ion beam (FIB; Tescan Anber, Tescan Brno s.r.o., Czech Republic) and shown in FIG. 17.

17 sequentially shows cross sections of FIB milling before and after 100 cycles of Si-Fib, Si-F4A1, Si-F4A1-10Ca, and Si-Alg, respectively. The change in thickness (t) was defined by [Equation 1].

[Equation 1]

The change in thickness for each electrode calculated by [Equation 1] was the smallest at 25% for Si-F4A1-10Ca, followed by 30% for Si-F4A1, 44% for Si-Fib, and 76% for Si-Alg. percent change in thickness.

These results confirm that F4A1-10Ca is most effective in buffering the Si volume change and preserving electrode integrity, and is consistent with the characteristics of the electrodes tested above.

7. Morphology analysis after cycling of electrodes

In order to evaluate the binding performance of each binder, the surface of the electrode before and after cycling was observed. In order to analyze the shape of the surface before/after the cycle of the electrode, the shape of the sample was observed using a scanning electron microscope (SEM; CX-200, COXEM, Korea), and is shown in FIGS. 18 to 20.

FIG. 18 sequentially shows plane-view images of Si-Fib, Si-F4A1, Si-F4A1-10Ca, and Si-Alg before and after 100 cycles, respectively. FIG. 19 is the analysis of the SEM image of FIG. 18 to calculate the crack density for each electrode, and FIG. 20 is another sample having the same configuration of the electrode as in FIG. 18 manufactured and the same experiment performed and the crack density calculated. In all three images, it can be observed that the crack depth and the number of cracks are small in Si-F4A1 and Si-F4A1-10Ca, and the calculated crack density also supports this. The crack densities (Φ _c ) calculated in FIG. 19 were Si-Fib (8.2%), Si-F4A1 (6.4%), Si-F4A1-10Ca (4.8%), and Si-Alg (13%), respectively. . In addition, the crack density (Φ _c ) calculated in FIG. 20 was Si-Fib (4.4%), Si-F4A1 (1.8%), Si-F4A1-10Ca (1.1%), and Si-Alg (11.1%), respectively. appear.

Similar to the result of measuring the thickness change, it can be seen that the least amount of cracks is observed in F4A1 and F4A1-10Ca after cycling, which means that these binders have an optimal ratio of stiffness and stress relaxation ability, thereby strongly binding the electrode while reducing deformation It means that it doesn't happen very well.

This morphological stability is also consistent with adhesion and electrochemical performance.

8. Analysis of the SEI layer of the electrode

Since a thin and stable SEI layer is a determining factor for long cycle life and high coulombic efficiency, the SEI layer was analyzed for each electrode. The stability of the SEI layer formed in the initial state, after 1 cycle, and after 100 cycles was evaluated for Si-Alg, Si-Fib and Si-F4A1-10Ca. It was evaluated using X-ray photoelectron spectroscopy (XPS; X-TOOL, ULVAC-PHI, Japan) and scanning transmission electron microscopy (STEM; JEM-2100F, JEOL, Japan). 21 is an XPS result for C 1s and FIG. 22 is an XPS result for F 1s.

In FIG. 21, peaks appeared at ~286 (CO) and ~288 eV (C=O) for all three electrodes after 1 cycle, indicating that lithium alkyl carbonate (ROCOOLI) and/or lithium carbonate (Li ₂ CO ₃ ) in the SEI layer. will represent The integrated intensity ratio (r) of the two peaks (IC-O+IC=O) for CC/CH at ~286 eV (IC-C/CH) after 100 cycles is Si-Alg (~0.43) and Si-Fib (~ 0.45) remained almost constant. However, after 100 cycles in Si-F4A1-10Ca, the two peaks for ROCOOLi and Li ₂ CO ₃ were greatly reduced, confirming that r was only ~0.27. The peak in Si-F4A1-10Ca means that a thinner and denser SEI layer is formed, which is consistent with the fact that the R _SEI value of Si-F4A1-10Ca is small in the EIS measurement. This result is because the F4A1-10Ca binder accommodates a large range of volume expansion/contraction of Si and prevents continued exposure of the electrolyte to the Si surface.

In addition, this tendency also appears in FIG. 22 as well. Li _x PF _y O _z , a decomposition product of LiPF6 in the SEI film, is a helpful material for cycling stability. In the case of Si-F41-10Ca, the ratio between the integrated intensity (ILPFO/ILF) of the Li _x PF _y O _z peak at ~687eV and the LiF peak at ~685eV was ~0.2, which is equivalent to that of Si-Alg (~0.12). It is a higher value than the ratio of Si-Fib (~0.17). Therefore, when F4A1-10Ca is used as a binder, it is confirmed that it has high cycling stability.

23 shows STEM images (a-f) and fast Fourier transform (FFT, g-i) pattern images after 100 cycles for Si-Alg, Si-Fib and Si-F4A1-10Ca, which are also consistent with the XPS results. . In particular, in the high-magnification images (d to f) of STEM, the thickness of the SEI layer of Si-F4A1-10Ca was measured as 10 nm, confirming that it was formed much thinner than Si-Fib (18 nm) and Si-Alg (33 nm). In addition, the FFT pattern shows the blue square part of d to f for each sample. The point where the Si reflection starts to disappear in the FFT pattern is where the SEI layer begins.

Those skilled in the art to which the present invention pertains will understand that the present invention can be embodied in other specific forms without changing its technical spirit or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. The scope of the present invention is indicated by the claims to be described later rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present invention. should be interpreted

Claims (20)

negative electrode active material;
conductive material; and
A water-soluble binder containing fibrin and binding the negative electrode active material and the conductive material with a three-dimensional structure,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The anode active material is
at least one of Si, Li, SiO _x , Sn, Ge, Mg, P, Al, Zn, Pb, Pn, and As; or
At least one of Si, Li, SiO _x , Sn, Ge, Mg, P, Al, Zn, Pb, Pn, and As and a composite of a carbon material,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The conductive material,
Graphite systems such as natural graphite, artificial graphite, graphene, super P, and super C;
activated carbon (active carbon) system;
denka black, ketjen black, channel black, furnace black, thermal black, contact black, lamp black, acetylene carbon black systems such as acetylene black;
carbon nanostructures such as carbon fibers, carbon nanotubes (CNTs), and fullerenes; and
At least one selected from the group consisting of combinations thereof,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The water-soluble binder has a storage modulus (G ') of 10 kPa to 70 kPa,
With a loss factor (G") of 1 kPa to 20 kPa,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The water-soluble binder has a creep strain (ε _c ) of 10 ⁴ or less
A negative electrode for a secondary battery comprising a water-soluble binder.
According to claim 1,
The water-soluble binder includes an amide group, a carboxyl group, a hydroxyl group, an amino group, lysine, histidine, aspartic acid, threonine ( threonine, serine, glutamic acid, glycine, arginine, proline, alanine, valine, isoleucine, leucine , has at least one reaction site of tyrosine and phenylalanine,
The reaction site hydrogen bonds with the negative electrode active material,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The water-soluble binder includes at least one of fibrin, a fibrin-alginate complex, and a fibrin-alginate-cation complex.
An anode for a secondary battery containing a water-soluble binder.
According to claim 7,
The fibrin-alginate complex controls the rheological properties by adjusting the mixing ratio of fibrin and alginic acid,
The fibrin and alginic acid are mixed in a weight ratio of 1:5 to 5:1,
An anode for a secondary battery containing a water-soluble binder.
According to claim 7,
The fibrin-alginate-cation complex controls the rheological properties by adjusting the mixing amount of fibrin, alginic acid, and cations,
The fibrin and alginic acid are mixed in a weight ratio of 1:5 to 5:1,
The cation is added at 0.01M to 1M,
An anode for a secondary battery containing a water-soluble binder.
According to claim 7,
In the fibrin-alginate-cation complex,
The fibrin and alginate are physically entangled to form an interpenetrating structure or a semi-interpenetrating structure,
An anode for a secondary battery containing a water-soluble binder.
According to claim 7,
In the fibrin-alginate-cation complex, the cation is at least one of a divalent cation and a trivalent cation,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The negative electrode active material, the conductive material and the water-soluble binder have a weight ratio of 90:5:5 to 50:30:20,
An anode for a secondary battery containing a water-soluble binder.
According to claim 1,
The negative electrode for the secondary battery,
When the secondary battery is charged and discharged, the volume expands to less than 50%.
A negative electrode for a secondary battery comprising a water-soluble binder.
Forming a water-soluble binder by mixing at least one of thrombin, alginic acid, and cations with fibrinogen;
preparing ink for an electrode by mixing a negative electrode active material and a conductive material with the water-soluble binder; and
Including the step of drying the ink for the electrode,
A method of manufacturing a negative electrode for a secondary battery according to any one of claims 1 to 13.
According to claim 14,
The fibrinogen is mixed with thrombin,
The fibrinogen and thrombin are mixed in a volume ratio of 2: 1 to 1: 2,
A method for manufacturing a negative electrode for a secondary battery.
According to claim 14,
The fibrinogen is mixed with thrombin and alginic acid,
The fibrinogen and thrombin are mixed in a volume ratio of 2:1 to 1:2,
The fibrinogen and thrombin react to produce fibrin,
The fibrin and alginic acid are mixed in a weight ratio of 5: 1 to 1: 5,
A method for manufacturing a negative electrode for a secondary battery.
According to claim 14,
The fibrinogen is mixed with thrombin, alginic acid and cations,
The fibrinogen and thrombin are mixed in a volume ratio of 2:1 to 1:2,
The fibrinogen and thrombin react to produce fibrin,
The fibrin and alginic acid are mixed in a weight ratio of 5:1 to 1:5,
The cation is mixed at 0.1M to 1M,
A method for manufacturing a negative electrode for a secondary battery.
According to claim 14,
The cation is at least one of a divalent cation and a trivalent cation,
A method for manufacturing a negative electrode for a secondary battery.
According to claim 14,
The negative electrode active material, the conductive material and the water-soluble binder have a weight ratio of 90:5:5 to 50:30:20,
A method for manufacturing a negative electrode for a secondary battery.
A secondary battery comprising a negative electrode for a secondary battery comprising the water-soluble binder according to any one of claims 1 to 13.

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