KR102154194B1 - A graft copolymer, a method for producing the same, a binder for a silicon anode including the same, a silicon anode including the binder for the silicon anode, and a lithium ion battery including the silicon anode - Google Patents

Abstract

The present invention relates to a graft copolymer, a method for preparing the same, a binder for a silicon anode including the same, a silicon anode including the binder for a silicon anode, and a lithium ion battery including the silicon anode. The graft copolymer according to the present invention can be used as a binder for a silicon anode, which reduces a change in volume of a silicon anode through the graft polymerization of chitosan having high mechanical strength with an aniline-based polymer having high electrical conductivity, and provides excellent battery performance. In addition, chitosan can be extracted from crustacean shells, which are waste materials, at low costs. Therefore, the graft copolymer can be obtained by using radical polymerization with high cost-efficiency and high reproducibility through a simple process.

Description

A graft copolymer, a method for producing the same, a binder for a silicon negative electrode including the same, a silicon negative electrode including the binder for the silicon negative electrode, and a lithium ion battery including the silicon negative electrode for a silicon anode including the same, a silicon anode including the binder for the silicon anode, and a lithium ion battery including the silicon anode}

The present invention relates to a graft copolymer, a method for preparing the same, a binder for a silicon negative electrode including the same, a silicon negative electrode including the binder for the silicon negative electrode, and a lithium ion battery including the silicon negative electrode.

Lithium-ion batteries (LIB) are widely used in portable energy storage devices, electric vehicles, and the like because of their high energy density, low cost, long cycle life, and safety. The development of lithium-ion batteries having high energy density and long life is attracting attention. Although graphite is one of the most commonly used negative electrode materials, its low theoretical capacity serves as a limiting factor in the performance of lithium-ion batteries. Silicon, which has a relatively low lithium ion intercalation potential, and a high theoretical capacity (4200 mAh g ⁻¹ ), is considered the cathode of the next generation lithium ion battery.

However, the silicon negative electrode has not been commercialized due to the enormous volume change occurring during the charging/discharging process of the battery. The volume change occurring in the charging/discharging process creates cracks in the electrode material, and ultimately leads to collapse of the electrically conductive network formed between the silicon particles and the conductive carbon and metal-based current collectors. This deterioration of the electrode causes a rapid loss of capacity by separating electrical contact between the silicon particles and the current collector. In order to mitigate the volume change of silicon, studies such as nano-sized silicon, porous silicon spheres, thin films, or fusion with conductive polymers are being conducted, but these methods significantly increase the cost, expand the lower surface, and lower energy density per volume. There is a problem of reducing the efficiency by.

Another method is to use a polymeric binder material with high mechanical strength. In general, the binder used for the battery electrode must maintain the adhesive strength between the entire composite structure in order to obtain high electrochemical performance 1) to prevent excessive volume change during the charging/discharging process, and 2) suitable for the active material and the conductive material. It is required to provide an interaction to provide a stable electrical path, 3) to form a thin and stable SEI layer, and 4) to properly swell in the electrolyte. Traditionally used polyvinylidene fluoride (PVdF) and styrene butadiene rubber (SBR) have a weak van der Waals interaction with silicon particles, so they are not effective in alleviating large volume changes of silicon particles. In addition, in order to dissolve PVdF, there is a problem in that it is toxic and requires the use of N-methylpyrrolidinone, an expensive organic solvent.

Korean Patent Publication No. 2016-0036988

Accordingly, the present invention is to provide a graft copolymer that is strongly bonded to a silicon negative electrode and has excellent mechanical strength and electrical conductivity, and a method for producing the same.

In addition, to provide a binder for a silicon negative electrode including the graft copolymer, a silicon negative electrode including the binder for the silicon negative electrode, and a lithium ion battery including the silicon negative electrode.

One aspect of the present invention relates to a graft copolymer comprising a main chain containing chitosan and a side chain containing an aniline-based polymer bonded to the main chain.

Another aspect of the present invention relates to a binder for a silicon negative electrode comprising the graft copolymer.

Another aspect of the present invention relates to a silicon negative electrode comprising the binder for the silicon negative electrode.

Another aspect of the present invention relates to a lithium ion battery including the silicon negative electrode.

Another aspect of the present invention is to prepare a chitosan solution by dissolving chitosan in an acidic solution; And adding an aniline monomer to the chitosan solution and polymerizing in the presence of an initiator to prepare a graft copolymer.

The graft copolymer of the present invention can be used as a binder for a silicon negative electrode to have excellent battery performance while reducing the volume change of the silicon negative electrode by graft polymerization of chitosan having strong mechanical strength and an aniline-based polymer having excellent electrical conductivity. . In addition, the chitosan has the advantage of being economical because it can be extracted from the shells of crustaceans, which are wastes, inexpensively, and has the advantage of producing a graft copolymer through radical polymerization, which has high reproducibility and a simple production process.

1 is a schematic diagram showing a method of manufacturing a graft copolymer according to an embodiment of the present invention.
2 is a graph showing the results of ¹ H NMR analysis of a binder according to an embodiment of the present invention.
3A and 3B are graphs showing FT-IR analysis results of a binder according to an embodiment of the present invention.
4 is a graph showing a result of TGA analysis of a binder according to an embodiment of the present invention.
5A and 5B are results of a Peel-off test of a binder according to an embodiment of the present invention.
6A to 6C are results of measuring electrochemical properties of a lithium ion battery including a silicon electrode according to an exemplary embodiment of the present invention. Figure 6a is a first galvanostatic charge-discharge curve, Figure 6b is a life characteristic, Figure 6c is a result of measuring the rate control characteristics.
7A to 7E are EIS measurement results of a lithium ion battery including a silicon electrode according to an embodiment of the present invention.
8A to 8E are CV measurement results of a lithium ion battery including a silicon electrode according to an embodiment of the present invention.
9A is an SEM-EDS mapping analysis image of silicon actives according to an embodiment of the present invention, and FIG. 9B is an SEM analysis image of a silicon electrode according to an embodiment of the present invention.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

One aspect of the present invention provides a graft copolymer comprising a main chain including chitosan and a side chain including an aniline-based polymer bonded to the main chain. Chitosan is one of the most abundant organic compounds in marine resources. Chitosan is a biodegradable natural compound and has excellent mechanical strength and adhesion. The graft copolymer of the present invention includes a chitosan main chain and a side chain containing an aniline polymer bonded to the chitosan main chain, and has excellent mechanical strength and adhesion by the chitosan main chain, and at the same time, excellent electrical conductivity resulting from the aniline polymer side chain. It features. The graft copolymer is used as a binder for a silicon negative electrode of a lithium-ion battery that undergoes extreme volume changes during the insertion/desorption process of lithium ions using this property, and not only mitigates the volume change of the silicon negative electrode, but also exhibits excellent electrochemical performance. I can.

The aniline-based polymer may be polyaniline, and the chitosan and the aniline-based polymer may be included in the graft copolymer in a weight ratio of 1:0.3 to 0.9. The polyaniline is a polymer having excellent electrical conductivity, but it is unreasonable to be used alone as a binder for a silicon negative electrode due to insufficient mechanical performance. When polyaniline is graft-polymerized on chitosan, insufficient mechanical performance can be greatly improved, and electrical conductivity required as a binder can be satisfied. The chitosan and the aniline polymer may be included in the graft copolymer in a weight ratio of 1: 0.3 to 0.9, preferably 1: 0.4 to 0.6, more preferably 1: 0.45 to 0.55. . As can be seen in the examples to be described later, the best battery performance (specific capacity, cycle performance, rate-limiting characteristics) of a silicon negative electrode using a graft copolymer containing chitosan and polyaniline in a weight ratio of 1:0.45 to 0.55 as a binder It is preferable in that it was seen.

The aniline-based polymer may be represented by Formula 1 below.

[Formula 1]

In Formula 1, the R ₁ , R ₂ , R ₃ and R ₄ are the same as or different from each other, and each independently H or COOH, and at least one of the R ₁ , R ₂ , R ₃ and R ₄ is COOH. , Wherein n and m are the mole fractions in the repeating unit, respectively, and are 0.1≦n≦0.9, 0.1≦m≦0.9, and n+m=1.

Since the polymer of Formula 1 can significantly mitigate the volume change of the silicon negative electrode through the characteristic of having electrical conductivity and the interaction with silicon through -COOH, which is a polar functional group in the molecule, when polyaniline is graft-copolymerized with chitosan Compared to that, it can be used as a more excellent silicon negative electrode binder.

More preferably, in Formula 1, n and m may be 0.45<n<0.55 and 0.45<m<0.55, because electrical conductivity and mechanical properties are balanced in the above range to show the most improved performance.

The chitosan and the aniline polymer represented by Chemical Formula 1 may be included in the graft copolymer in a weight ratio of 1:0.05 to 1:10. Synthesis is possible in the ratio of 1:0.05 to 1:10, and particularly, when included in the range of the ratio of 1:0.1 to 1:1, it is preferable in that the conductivity and adhesive properties are particularly excellent in the silicon negative electrode binder.

The chitosan may be extracted from the shell of crustaceans. Chitosan is abundantly present in the shells of crustaceans, but the shells of crustaceans are generally discarded without any special use. Since discarded shells of crustaceans can be purchased at low prices, there is an advantage in that a graft copolymer can be economically manufactured using shells of crustaceans and is eco-friendly. In addition, as can be seen in the examples to be described later, the graft copolymer prepared using the shell of a crustacean crab is preferable in that it is used as a binder for a silicon negative electrode to produce a battery that exhibits the best performance.

Another aspect of the present invention provides a binder for a silicon negative electrode comprising the graft copolymer.

Another aspect of the present invention provides a lithium ion battery including the silicon negative electrode binder.

Another aspect of the present invention is to prepare a chitosan solution by dissolving chitosan in an acidic solution; And adding an aniline monomer to the chitosan solution and polymerizing in the presence of an initiator to prepare a graft copolymer. Since the method for preparing the graft copolymer is performed by radical polymerization, the manufacturing process is very simple and has the advantage of high reproducibility.

The solvent of the chitosan solution is preferably an acidic solution, and the acidic solution may be any one or a mixture of two or more selected from HCl, sulfonic acid, camposulfonic acid, and toluensulfonic acid. . Most preferably, the acidic solution may be 0.1 to 5 M HCl at 70 to 200°C.

In the chitosan solution, chitosan and aniline monomers may be included in a weight ratio of 1: 0.3 to 0.9, preferably 1: 0.4 to 0.6, more preferably 1: 0.45 to 0.55. As can be seen in the examples described below, the best battery performance (specific capacity, cycle performance) of a silicon negative electrode using a graft copolymer containing chitosan and polyaniline in a weight ratio of 1: 0.45 to 0.55 as a binder was shown. It is preferable in

The initiator may be any one or a mixture of two or more selected from ammonium persulfate, hydroperoxide, and copper(II) chloride.

The chitosan is obtained by pulverizing the shells of crustaceans, adding to 1 to 5 M NaOH aqueous solution, and heating to 100 to 200 °C to obtain chitin; And adding the chitin to a 1 to 5 M NaOH solution and heating at 100 to 200° C. for 1 to 12 hours to obtain chitosan. It may be obtained by a method comprising. As described above, when chitosan is extracted from the shell of crustaceans and used, a graft copolymer can be produced very economically and is environmentally friendly. In addition, as can be seen in Examples to be described later, it is preferable in that it shows the best battery performance when using chitosan extracted from crustacean shells by the above method.

In the step of preparing a graft copolymer by adding an aniline monomer to the chitosan solution and polymerizing in the presence of an initiator, an anthranilic acid monomer may be additionally added to the chitosan solution along with the aniline monomer. When an anthranilic acid monomer is additionally used, a copolymer in which a copolymer of aniline and anthranilic acid is grafted to chitosan can be prepared. Since anthranilic acid exhibits more excellent mechanical performance by interacting with silicone nanoparticles having a -COOH functional group, a more excellent binder can be prepared than a copolymer in which polyaniline is graft-polymerized on chitosan.

The aniline monomer and the anthranilic acid monomer are preferably added in a molar ratio of 0.45:0.55 to 0.55:0.45.

A mixed solution in which an anthranilic acid monomer is additionally added together with an aniline monomer to the chitosan solution is cooled to 1 to 10°C, and then an initiator may be added. When the mixed solution is cooled to 1 to 10° C. and then an initiator is added, it is preferable in that there is an advantage that the position of polymerization can be selected. If polymerization occurs at high temperature, there is a possibility of ortho and para aniline polymerization, but these variables can be eliminated by lowering the temperature.

Although not explicitly described in the following Examples or Comparative Examples, etc., in the method for producing a graft copolymer according to the present invention, a graft copolymer was prepared by varying various conditions of the manufacturing method, and each graft copolymer was used as a binder. Was used to prepare a silicon negative electrode. A peel-off test was performed on the silicon negative electrode of the prepared graft copolymer, and a 2032 coin cell using the prepared silicon negative electrode and lithium metal as a counter electrode was manufactured, through which electrochemical performance was measured.

As a result, unlike in other conditions and numerical ranges, when all of the following conditions were satisfied, even though the aniline-based polymer was included, it had an adhesive strength of 0.78 N or more in the peel-off test, and was similar or superior to pure chitosan. It was confirmed that the chemical performance measurement also showed the best specific capacity, life characteristics, and rate-limiting characteristics. In addition, it was confirmed that the graft yield of the aniline polymer to chitosan significantly increased by 20% or more, unlike other conditions.

(I) the acidic solution is 0.5 to 2 M HCl at 70 to 110°C, (ii) chitosan and aniline monomers in the chitosan solution are contained in a weight ratio of 1: 0.45 to 0.55, (iii) the initiator is ammonium persulfate, ( Iv) the chitosan is obtained by pulverizing the shells of crustaceans, adding to 1 to 3 M aqueous NaOH solution, and heating to 100 to 200°C to obtain chitin; And adding the chitin to a 1 to 3 M NaOH solution and heating at 100 to 200° C. for 2 to 6 hours to obtain chitosan; obtained by a method comprising, (v) aniline in the chitosan solution An anthranilic acid monomer is additionally added with the monomer, (vi) the aniline monomer and an anthranilic acid monomer are added in a molar ratio of 0.45: 0.55 to 0.55: 0.45, (vii) an anthranilic acid monomer is additionally added to the chitosan solution together with an aniline monomer. After cooling one mixed solution to 3 to 7 °C, an initiator was added.

However, if any of the above conditions were not satisfied, the results in the long-term cycle test were not good, the initial capacity efficiency decreased, and the electrochemical performance decreased. In addition, there is a problem that the yield is reduced by more than 20% and the electrode cannot be manufactured from the obtained material.

Hereinafter, a preferred embodiment is presented to aid the understanding of the present invention. However, these examples are for describing the present invention in more detail, and the scope of the present invention is not limited thereto, and various changes and modifications are possible within the scope and spirit of the present invention. It will be self-evident to those of knowledge

Manufacturing example. Chitosan extraction from crab skin

Chitin extraction from crab skin

The crab shells were washed several times with distilled water and dried in an oven at 40° C. for 48 hours. 2 g of dried crab skin was powdered using a mortar, and minerals were removed by heating at 80° C. for 24 hours in 2 M HCl. Thereafter, the protein was removed by heating at 110° C. in 20 ml of 2 M NaOH aqueous solution to obtain chitin, and washed with acetone. The sample was filtered, washed with distilled water, and dried in an oven at 40° C. for 48 hours.

Production of chitosan from chitin extracted from crab skin

The extracted chitin was deacetylated by heating at 150° C. for 4 hours with 20 ml of 2 M NaOH solution. After deacetylation, the sample was filtered and washed with distilled water until the pH became neutral. Then, it was dried in an oven at 40° C. for 48 hours to obtain chitosan.

Example 1. Preparation of CS-g-PANi binder

Materials used

Apart from the prepared chitosan, chitosan was purchased from TCI. Aniline, anthranilic acid, and ammonium persulfate (APS) were purchased from Sigma-Aldrich. Hydrochloric acid and N-methylpyrrolidon (NMP) were purchased from Daejung Chemicals & Metals, and silicon nanoparticles (50 nm) were purchased from Alfa-Aesar. Electrolyte (1 M LiPF ₆ in ethylene carbonate/ethyl methyl carbonate (EC: EMC=1:2 v/v)) with 10 wt.% fluoroethylene carbonate (FEC)) was purchased from Panax Etec.

Preparation of polyaniline graft-polymerized chitosan (CS-g-PANi)

To prepare chitosan (CS-g-PANi) in which polyaniline was graft-polymerized, the weight ratio of chitosan and aniline was adjusted to 1:0.3.

The biodegradable and conductive chitosan-g-polyaniline copolymer was synthesized by radical polymerization, and the synthesis procedure is schematically shown in Figure 1 below.

[Figure 1] Synthesis procedure of chitosan-g-polyaniline

A chitosan solution was prepared by dissolving 2.0 g of chitosan in 200 mL of 1 M HCl solution. At room temperature, 0.98 mL of aniline monomer was added dropwise to the chitosan solution to prepare a chitosan-polyaniline solution. After completely dissolving the aniline, a 1 M HCl solution was added dropwise to the chitosan-polyaniline solution so as to have a molar ratio of 1:1 with an aniline monomer. APS was used as an initiator for the graft polymerization. The mixture was stirred for 24 hours in a nitrogen atmosphere. The reaction mixture was neutralized with 5 M NaOH solution, and the graft polymerized polymer was precipitated with an excess of ethanol. The resulting precipitate was washed with N-methylpyrrolidinone to remove the homopolymer PANi from the copolymer, washed with acetone, and dried at 40°C in vacuum. The graft yield and percentage (grafting percentage) of polyaniline for chitosan were calculated by the following calculation formula 1.

[Calculation 1]

Grafting percentage =

Name of the binder

In the same manner as in the above example, a binder was prepared by adjusting the weight ratio of chitosan and aniline. In the case of a binder prepared in a 1:0.3 weight ratio of chitosan and aniline, CS-g-PANi-0.3, a binder prepared in a 1:0.5 weight ratio is CS-g-PANi-0.5, and a binder prepared in a weight ratio of 1: 0.9 is CS Named each as -g-PANi-0.9.

Example 2. Preparation of CS-g-PAAA and EC-g-PAAA binders

To prepare a copolymer of chitosan and poly(aniline-g-anthrannylic acid) (CS-g-PAAA), aniline and anthranilic acid were adjusted in a molar ratio of 1:1, and the weight ratio of chitosan and aniline was 1:0.125. Adjusted. The synthesis procedure is schematically shown in Figure 2 below.

[Picture 2]

1.0 g of chitosan was dissolved in 100 ml, 90° C., 1 M HCl to prepare a chitosan solution. 0.125 g of aniline monomer and 0.184 g of anthranilic acid monomer were added dropwise to the chitosan solution at room temperature. After 0.5 hours, the solution was cooled to 5°C, and then 0.613 g of ammonium persulfate was mixed with 10 ml, 1 M HCl solution, and the prepared initiator solution was added to the chitosan-aniline solution in a molar ratio of aniline monomer and ammonium persulfate of 1:1. It was added drop by drop so as to be. The mixture was stirred for 24 hours in a nitrogen atmosphere, and a dark green product was obtained. The reaction was neutralized with a 5 M NaOH solution, and the copolymer was precipitated with an excess of ethanol. The unpolymerized PANi homopolymer present in the precipitate was removed by washing with N-methyl pyrrolidone (NMP). Finally, it was washed with acetone and dried at 40° C. for 24 hours in vacuum.

In the case of a binder prepared using chitosan extracted by the above preparation example, EC-g-PAAA-0.125, and a binder prepared using chitosan purchased from TCI, were designated as CS-g-PAAA-0.125.

Example 3. Preparation of silicon nanoparticle electrode

In order to prepare a silicon nanoparticle electrode, the binders prepared in Examples 1 and 2 were dissolved in 1 M acetic acid solution and sonicated for 45 minutes to prepare a binder solution. Silicon nanoparticles and carbon black were pulverized together, and then the binder solution was added to prepare a uniform slurry having a controlled viscosity. The mass ratio of the silicon nanoparticles, the carbon black and the binder was 60:20:20. In the case of the electrode without the conductive material added, the mass ratio of the silicon nanoparticles and the binder was 75:25. The working electrode was prepared by coating the slurry on a 15 mm thick copper foil, drying in a vacuum oven at 80° C. for 30 minutes, and further drying at 120° C. for 3 hours. The loading amount relative to the total electrode mass was fixed at 0.7 to 0.9 mg cm ^-1 .

For convenience, each electrode manufactured with a different binder was named the same as the binders named in Examples 1 and 2.

Comparative Example 1. Silicon anode using chitosan (CS) as a binder

It was carried out in the same manner as in the manufacturing part of the silicon nanoparticle electrode of Example 3, but chitosan was used as a binder.

Comparative Example 2. Silicon anode using polyvinylidene fluoride (PVDF) as a binder

It was carried out in the same manner as in the manufacturing part of the silicon nanoparticle electrode of Example 3, but PVDF was used as a binder.

Test Example 1. ^One H NMR analysis

¹ H NMR analysis of Example 1, chitosan and polyaniline was performed. ^{For 1} H NMR spectrum, an Agilent-D2 MHz NMR device was used and DMSO-d6 was used as a reference material. 2 is a graph showing the results of ¹ H NMR analysis of Example 1 of the present invention, chitosan and polyaniline. In the case of Example 1 from FIG. 2, it was confirmed that polyaniline was successfully polymerized in chitosan.

Test Example 2. FT-IR analysis

FT-IR analysis of the above Examples 1 and 2, chitosan and polyaniline was performed. The FT-IR spectrum is in the range of 4000-400 cm ^-1 Recorded using Perking Elmer Spectrum Two ATR spectrometer. 3A is a graph showing the results of FT-IR analysis of Example 1, chitosan and polyaniline of the present invention. As can be seen in FIG. 3A, it is clear that CS-g-PANi, which is a graft copolymer, exhibits characteristic peaks of chitosan and PANi, and it was confirmed that aniline was successfully graft-polymerized on chitosan.

3B is a result of FT-IR measurement in Example 2 of the present invention. As can be seen in Figure 3b, it can be confirmed that the CS-g-PAAA of Example 2 including the characteristic peaks of chitosan and PAAA, poly(aniline-g-anthranylic acid) was successfully graft-polymerized on chitosan. there was.

Test Example 3. TGA (Thermogravimetric Analysis) analysis

TGA analysis of Example 1, chitosan and polyaniline was performed. 4 is a graph showing the TGA analysis curve of Example 1, chitosan and polyaniline of the present invention.

The weight loss at 30-150 °C was due to the decrease in moisture, and the second weight loss at 256-342 °C was caused by the breakdown of the chain and the decomposition of the ether bond of the chitosan structure. At 600° C., the amount of chitosan residue was 31%. The decrease in weight of polyaniline at 168-299°C is due to the generation of oligomers of small dopant chains, and the second decrease in weight at 201-336°C is the removal of the dopant anion and the ether bond of the CS-g-PANi chain. It was caused by decomposition. The residue was 40% at 600° C., which can contribute to the thermal stability of CS-g-PANi, which is due to hydrogen bonds formed by the hydroxy group and amine group of chitosan in the copolymer structure.

As can be seen from FIG. 4, as the ratio of the aniline monomer increased, the thermal stability also increased. This means that the adhesion properties changed with the decrease of the chitosan ratio, and it was confirmed that the conductivity also increased with the increase of aniline.

Test Example 4. Measurement of mechanical properties of a binder in a silicon electrode

The silicon electrodes of Example 3 and Comparative Examples 1 and 2 were coated and the physical properties of each electrode were analyzed. The adhesive strength of each binder was measured through a 180° peel test. The 180° peeling test was measured using a Universal Testing Machine (UTM, Shimadzu EZ-L), and after cutting the electrode of Example 3 into a rectangular shape, attaching a 12 mm wide 3M tape to the tape 30 mm/min. Pulled at the separation speed of.

5A and 5B are 180° peeling test results of Example 3 and Comparative Examples 1 and 2 of the present invention. As can be seen in FIGS. 5A and 5B, since chitosan of Comparative Example 1 has a large amount of hydroxy groups and amine groups, it has stronger adhesion than PVDF of Comparative Example 2. The PVDF electrode of Comparative Example 2 showed weak adhesion compared to the CS-g-PANi electrode of Example 3 due to weak Van der Waals interaction. The adhesion of chitosan was 0.765 N, and CS-g-PAAA-0.125 was 0.719 N, which was higher than that of CS-g-PANI, and the result of high adhesion was not significantly different even compared to chitosan. The results were 0.640N for CS-g-PANi-0.3, 0.509N for CS-g-PANi-0.5, and 0.399N for CS-g-PANi-0.9.

In Example 3, as the polymerization rate of chitosan increased, it was confirmed that the adhesive strength increased, and it was confirmed that all of Example 3 had much stronger adhesion than PVDF of Comparative Example 2.

Test Example 5. Measurement of electrochemical performance

Electrochemical performance was measured using a silicon electrode containing the binders of Example 3 and Comparative Examples 1 and 2 and a 2032 coin cell using lithium metal as a counter electrode. 6 is a result of measuring the electrochemical properties of Example 3 and Comparative Examples 1 and 2, FIG. 6A is a first galvanostatic charge-discharge curve, FIG. 6B is a life characteristic, and FIG. 6C is a measurement result of rate-limiting characteristics.

As can be seen from FIGS. 6A to 6D, when the chitosan of Comparative Example 1 and the PVDF binder of Comparative Example 2 were used, not only showed very low specific capacity but also collapsed within several cycles. PVDF is a binder material widely used in electrode manufacturing due to its high electrical and thermal stability, but it was confirmed that it was not suitable to accommodate the volume change of silicon.

On the other hand, the electrode prepared using CS-g-PANi, CS-g-PAAA and EC-g-PAAA of Example 3 exhibited a much higher specific capacity than the case of using PVDF by conductive aniline,- It was confirmed that the OH and -NH ₂ functional groups exhibited excellent mechanical performance, thereby withstanding changes in the volume of silicon and exhibiting excellent stability.

The CS-g-PANi-0.90 electrode of Example 3 exhibited a high initial capacity due to a high content of aniline, but the content of chitosan was low and the electrode rapidly deteriorated in 40 charge/discharge cycles. Although reduced compared to the initial capacity, 554 mAh g ^-1 was maintained until 200 cycles by chitosan. This showed remarkably improved performance compared to the conventional PVDF whose capacity was rapidly decreased after 10 cycles.

The CS-g-PANi-0.30 electrode of Example 3 has a higher chitosan content, so that the binder binds to the silicon much more strongly. The initial specific capacity was slightly lower than that of CS-g-PANi-0.50 and CS-g-PANi-0.90 of Example 3 because the content of conductive aniline was small. After 40 charge/discharge cycles, the specific capacity rapidly decreased, but the capacity was maintained thereafter. Even after 200 cycles, the capacity of 677 mAh g ^-1 was maintained, which corresponds to superior performance compared to the case of using the chitosan of Comparative Example 1 as a binder.

The CS-g-PANi-0.50 electrode of Example 3 showed the best overall performance during the charging and discharging process. At 200 cycles, the specific capacity had a 1086 mAh g ^-1 corresponding to 42.31% of the initial specific capacity, and the Coulomb efficiency was 99.52%. This was an improved value compared to the CS-g-PANi-0.30 and CS-g-PANi-0.90 of Example 3, which showed a 30% level of specific capacity maintenance in the initial specific capacity.

In addition, the results of CS-g-PAAA-0.125 showed a capacity retention of 1643 mAh/g at 200 cycles, and the capacity retention was very high at 54.0%. In addition, the initial efficiency was 75.3% at EC-g-PAAA-0.125, 1731 mAh/g at 200 cycles and capacity retention at 56.9% at 200 cycles.

That is, among the electrodes prepared according to Example 3, CS-g-PANI-0.50 and CS-g-PAAA showed particularly excellent electrochemical properties.

Test Example 6. Electrochemical Impedance Spectroscopy (EIS) measurement

EIS measurements of Example 3 and Comparative Examples 1 and 2 were performed. 7 is a graph showing the EIS measurement results of Example 3 and Comparative Examples 1 and 2 of the present invention, FIG. 7A is CS-g-PANI-0.50 of Example 3, and FIG. 7B is CS-g- of Example 3 PANI-0.30, Figure 7c shows the CS-g-PANI-0.90 of Example 3, Figure 7d is Comparative Example 1, Figure 7e shows the EIS measurement results of Comparative Example 2.

As can be seen in FIGS. 7A to 7E, the presence of polyaniline in the main chain of chitosan, as in Example 3, improved Li ion transport and effectively reduced the overall charge transfer resistance of the silicate negative electrode. In addition, it was confirmed that there was no significant change in resistance even after several charge/discharge cycles.

On the other hand, in the case of Comparative Examples 1 and 2, the resistance increased as the number of cycles increased, because the performance of the electrode was not maintained during cycling and electron transfer decreased.

Test Example 7. CV (Cyclic Voltammetry) Measurement

CV measurements of Example 3 and Comparative Examples 1 and 2 were performed. CV was performed between 0.01 and 2.5 V with a scanning speed of 0.1 mV/s. 8 is a graph showing the CV measurement results of Example 3 and Comparative Examples 1 and 2 of the present invention, and FIG. 8A is CS-g-PANI-0.50 of Example 3, and FIG. 8B is CS-g- of Example 3 PANI-0.30, FIG. 8C shows the CS-g-PANI-0.90 of Example 3, FIG. 8D shows the CV measurement results of Comparative Example 1 and FIG. 8E.

As can be seen in FIGS. 8A to 8E, two lithium desorption peaks observed at 0.33 and 0.49 V in the first cycle in all electrodes used for CV appeared in the cathode scan, corresponding to lithium insertion at about 0.21 V. A broad anodic peak appeared. Except for PVdF, the intensity of the lithium desorption/insertion peaks increased significantly even after the first cycle, and CS-g-PANI and chitosan electrodes showed excellent stability and high reproducibility for Si anodes. A broad peak of 1.5 V appeared on the first anode scan and disappeared in the next cycle due to SEI formation due to electrolyte decomposition. This tendency disappeared as the cycle was repeated, and it means that a new SEI layer was not formed on the Si surface. In addition, the intensity of the peak continuously increased as cycling progressed, indicating a gradual activation process.

On the other hand, in the case of the PVdF binder electrode, two broad peaks appeared at 1.13 V and 0.48 V in the first anode scan and disappeared by the SEI layer formation in the next cycle, and no other peaks appeared. However, a lithium peak was observed at 0.18 V in the second cycle, and changed to 0.11 V in the sixth cycle. In addition, the intensity of the desorption peak decreased remarkably after several cycles.

Test Example 8. SEM (Scanning Electron Microscopy) analysis

CS-g-PANI-0.50 of Example 3, Comparative Examples 1 and 2 The shape and structural stability of the electrodes before and after cycling were observed through FE-SEM. 9A is a SEM-EDS mapping analysis image of CS-g-PANI-0.50 in Example 3, and FIG. 9B is a CS-g-PANI-0.50 in Example 3, chitosan in Comparative Example 1, and PVdF in Comparative Example 2. This is an SEM analysis image before and after cycling the electrode.

As can be seen from FIG. 9A, it was confirmed that Si nanoparticles, carbon black, and binder were uniformly dispersed from the initial Si electrode.

In addition, as can be seen from FIG. 9B, it was confirmed that the PVDF electrode of Comparative Example 2 did not maintain its initial shape after 50 cycles and was separated from the current collector, and was enough to be confirmed with the naked eye.

On the other hand, it was confirmed that the CS-g-PANI-0.50 electrode of Example 3 maintained its surface due to the excellent mechanical properties of chitosan.

Therefore, the graft copolymer of the present invention can be used as a binder for a silicon negative electrode to have excellent battery performance while mitigating the volume change of the silicon negative electrode by graft polymerization of chitosan having strong mechanical strength and an aniline-based polymer having excellent electrical conductivity. I can. In addition, the chitosan has the advantage of being economical because it can be extracted from the shells of crustaceans, which are wastes, inexpensively, and has the advantage of being able to manufacture a graft copolymer through radical polymerization, which has high reproducibility and a simple production process.

The above-described Examples and Comparative Examples are examples for explaining the present invention, and the present invention is not limited thereto. Since those of ordinary skill in the art to which the present invention pertains will be able to implement the present invention by various modifications therefrom, the technical protection scope of the present invention should be determined by the appended claims.

Claims (18)

A main chain containing chitosan and a side chain containing an aniline-based polymer bonded to the main chain,
The aniline-based polymer is a graft copolymer represented by the following formula (1):
[Formula 1]

In Formula 1,
The R ₁ , R ₂ , R ₃ and R ₄ are the same as or different from each other, and each independently H or COOH,
At least one of the R ₁ , R ₂ , R ₃ and R ₄ is COOH,
Wherein n and m are the mole fractions in the repeating unit, respectively, 0.1≦n≦0.9, 0.1≦m≦0.9, and n+m=1.
delete delete delete The method of claim 1,
In Formula 1, wherein n and m are 0.45<n<0.55 and 0.45<m<0.55.
The method of claim 1,
The chitosan and the aniline-based polymer are graft copolymers contained in the graft copolymer in a weight ratio of 1:0.05 to 1:10.
The method of claim 1,
The chitosan is a graft copolymer that is extracted from the shell of crustaceans.
A binder for a silicone negative electrode comprising the graft copolymer of any one of claims 1 and 5 to 7.
A silicon negative electrode comprising the binder for a silicon negative electrode of claim 8.
A lithium ion battery comprising the silicon negative electrode of claim 9.
Dissolving chitosan in an acidic solution to prepare a chitosan solution; And
A method for producing a graft copolymer comprising: adding an anthranilic acid monomer together with an aniline monomer to the chitosan solution and polymerizing in the presence of an initiator to prepare a graft copolymer.
The method of claim 11,
The acidic solution is a method of producing a graft copolymer of 0.1 to 5 M HCl at 70 to 200°C.
delete The method of claim 11,
The initiator is ammonium persulfate (ammonium persulfate), hydroperoxide (hydroperoxide), and any one or a mixture of two or more selected from copper (II) chloride method for producing a graft copolymer.
The method of claim 11,
The chitosan is obtained by pulverizing the shells of crustaceans, adding to 1 to 5 M NaOH aqueous solution, and heating to 100 to 200 °C to obtain chitin; And
Injecting the chitin into a 1 to 5 M NaOH solution and heating at 100 to 200 °C for 1 to 12 hours to obtain chitosan; a method for producing a graft copolymer obtained by a method comprising.
delete The method of claim 11,
The aniline monomer and the anthranilic acid monomer are added in a molar ratio of 0.45: 0.55 to 0.55: 0.45.
The method of claim 11,
A method for producing a graft copolymer in which an initiator is added after cooling a mixed solution in which an anthranilic acid monomer is additionally added together with an aniline monomer to the chitosan solution to 1 to 10°C.

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