KR20130123831A - Electrode binder for lithium secondary battery, manufacturing method for the same, and electrode for lithium secondary battery - Google Patents

Abstract

An electrode binder for lithium secondary battery, a manufacturing method thereof, and an electrode for lithium secondary battery using the same are provided. According to an embodiment of the present invention, the electrode binder for lithium secondary battery comprises a polymer chain including a carboxyl group; and a material containing a catechol group conjugated to the carboxyl group of the polymer chain. According to the present invention, the property of an anode battery composed of silicon nanoparticles is improved using a new organism-derived binder. Especially, the silicon anode including an Alg-C polymer binder shows excellent specific capacity of 3,200 mAhg-1 and excellent cycling property of 200 cycles due to the rigid and adhesive property of the Alg-C binder.

Description

Lithium ion battery electrode binder and manufacturing method thereof, and lithium secondary battery electrode using the same {Electrode binder for lithium secondary battery, manufacturing method for the same, and electrode for lithium secondary battery}

The present invention relates to a lithium ion battery electrode binder, a manufacturing method thereof and a lithium secondary battery electrode using the same.

Lithium ion batteries (LIBs) are widely used in a wide range of applications, from general mobile small electronic devices to high-capacity devices such as electric vehicles or smart grid electric storage devices. In particular, the emergence of electric vehicles is considered to reduce the burden of fossil fuel exhaustion and the risk of carbon dioxide emissions. However, in practice, the performance of the currently developed lithium secondary battery should be individualized, and characteristics such as energy density, battery cycle, output capacity, and safety should be improved particularly for electric vehicle applications of lithium ion batteries. Among these properties, energy density is a very important factor in the use of lithium-ion batteries in electric vehicles because it relates to the distance traveled by the vehicle in one recharge.

In recent years, silicon has a weight capacity ten times more than lithium batteries based on existing graphite anodes. However, silicon electrodes have a relatively short life cycle due to the 300% level of expansion that occurs during full charge. As a result, silicon has the problem of being micronized by stresses formed during volume expansion. In an attempt to improve this problem, a method of reducing stress by using a material of a small size has been proposed. However, while the problem of micronization can be solved by the use of nano-sized materials, there is a problem of weakening the interfacial contact force (contact) between silicon and carbon conductors as a counterpart to the use of small sized materials, resulting in cycles. Performance improvement is weakened. In addition, the contact between the electrode film and the current collector is weakened, so that the electrode film can be easily peeled off during the cycle. Therefore, effective binder development and use are urgently needed to maintain excellent cycle characteristics.

Accordingly, the problem to be solved by the present invention is to provide a binder and a method of manufacturing the same that can be utilized in the electrode of a new lithium ion battery.

Another object of the present invention is to provide an electrode of a new lithium ion battery including the binder.

In order to solve the above problems, the present invention is an electrode binder of a lithium secondary battery, the binder is a polymer chain containing a carboxyl group; And it provides an electrode binder of a lithium secondary battery comprising a catechol group-containing material conjugated to the carboxyl group of the polymer chain.

In one embodiment of the invention, the polymer chain is alginate and the catechol group-containing material is dopamine.

According to an embodiment of the present invention, the binder has the following structural formula.

(Where l and k are positive real numbers and 0 <l, k <1 and l + k = 1)

The present invention, in order to solve the another problem, a method of manufacturing an electrode binder of a lithium secondary battery, the method comprising the steps of preparing an alginate solution; Preparing a mixed solution by adding a dopamine solution to the alginate solution; And it provides a method for producing an electrode binder of a lithium secondary battery comprising the step of reacting the mixed solution.

According to an embodiment of the present invention, the preparing of the alginate solution may include dissolving the alginate in a phosphate buffer solution; And activating the carboxyl group of the dissolved alginate. By the reaction, the carboxyl group of the algitate and the catechol group of the dopamine are conjugated.

The present invention also provides a lithium secondary battery negative electrode material, the material is a silicon material; A binder comprising a polymer chain comprising a carboxyl group and a catechol group-containing material conjugated to the carboxyl group of the polymer chain; And it provides a lithium secondary battery negative electrode material comprising a carbon conductor.

According to one embodiment of the invention, the silicon material is silicon particles of micrometer or less.

According to an embodiment of the present invention, in the negative electrode material, the silicon nanoparticle: binder and carbon conductor weight ratio is 60 to 70: 10 to 20: 10 to 20.

According to one embodiment of the invention, the carbon conductor is carbon black, and the polymer chain is alginate. In addition, the catechol group-containing material is dopamine.

According to an embodiment of the present invention, the binder has the following structural formula.

(Where l and k are positive real numbers and 0 <l, k <1 and l + k = 1)

The present invention is also a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, the negative electrode of the lithium secondary battery is made of the above-described negative electrode material, wherein the electrolyte may include vinylene carbonate (VC) as an additive.

According to the present invention, a novel bio-derived binder is used to improve the battery characteristics of a negative electrode made of silicon nanoparticles (NP). In particular, a silicon negative electrode comprising an alginate-catechol (Alg-C) polymer binder is an alginate-category. The hard, adhesive properties of the call binder have excellent specific capacities up to ˜3,200 mAh g ⁻¹ and excellent cycling characteristics over 200 cycles.

1 is a view illustrating an alginate-catechol (Alg-C) binder according to the present invention.
FIG. 2A is a spectroscopy (XPS) analysis demonstrating through peaks at 280 nm that dopamine was effectively conjugated to alginate sugar chains, and FIG. 2B shows peaks at 280 nm that dopamine was effectively conjugated to alginate (Alg) sugar chains. X-ray photoelectron spectroscopy (XPS) analysis proved through.
Figure 2c is a result of analyzing the binder-silicon interaction by combining the cantilever with the AFM after washing the cantilever binder is adsorbed with water, Figure 2d is a graph comparing the interaction force of alginate carbon and alginate to be.
3a is a lamella test results according to the experimental example of the present invention, Figure 3b is a lamella test results for the silicon-alginate-catechol (Si-Alg-C), Figure 3c is a lamella test picture according to the experimental example of the present invention to be.
4A is an experimental result of the voltage-specific capacity according to the experimental example of the present invention, FIG. 4B is an EIS analysis result, and FIG. 4C is a scanning electron microscope (SEM) image.
5a to 5c are cycle test results according to the experimental example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings. The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the width, length, thickness, etc. of components may be exaggerated for convenience. Like numbers refer to like elements throughout.

The present invention provides a novel bio-derived binder in order to solve the above problems, thereby improving the battery characteristics of the negative electrode made of silicon particles of less than a micro unit.

As a result of evolution, living organisms have very specific material properties. Among these materials, mussels have a surface property of exceptionally strong adhesion even in wet environments. Among the mussel-derived adhesive components, catechol plays a very important role in waterproof adhesive properties, and catechol-containing low molecules and polymers can be applied to various nano and biotechnology. In addition, alginate, a polysaccharide extracted from algae, is used as a biomaterial.

The present invention uses such a catechol-containing material in a polymer chain containing a carboxyl group or the like, and the polymer chain is mutually conjugated with the catechol-containing material having the above-described function. As an example of such a binder, the present inventors provide alginate-catechol (Alg-C), which is a new bio-derived binder, using alginate, a polymer chain, which binder is derived from mussels and algae. It can be prepared in a mixed-synthetic manner, and used in the silicon negative electrode of a lithium ion battery.

Silicon anodes comprising alginate-catechol (Alg-C) binding binders, due to the rigid, adhesive properties of alginate-catechol (Alg-C), have a high specific capacity of ~ 3,200 mAh g ^-1 and 200 cycles. It has excellent cycling characteristics in excess of.

Example  One

Electrode binder

The bio-derived binder according to an embodiment of the present invention combines the biological specificities of two living organisms, namely algae such as green algae and mussels (FIGS. 1A and 1B). Double alginates are natural polymers extracted from algae, such as green algae, which constitute hard sugar chains (polymer chains), which are very important in silicon electrode binders. Polymers with high Young's modulus, such as polyacrylic acid (PAA) or carboxymethylcellulose (CMC), are much more likely to maintain the capacity of silicon electrodes than polymers that are widely used such as poly (vinylidene fluoride) (PVDF). It is advantageous. In addition, catechol, an adhesive moiety found in mussels, is covalently bonded to the alginate sugar chain, providing a wet-resistant adhesive. By utilizing bio-derived binders, the present invention significantly improved the performance of silicon anodes using silicon nanoparticles to achieve high specific capacities (˜3,200 mAh g ⁻¹ ). Further, in one embodiment of the present invention, silicon nanoparticles were selected as a component of the negative electrode material because of their ease of production.

Furthermore, the silicon nanoparticle cycle life of the negative electrode according to the present invention was markedly improved compared to the life achieved by other binders, and the specific amount was maintained completely for 200 cycles. This result means that the binder according to the present invention provides a very effective solution in energy storage technology. In one embodiment of the present invention, the alginate (Alg) which is a sugar chain is (1-4) -linked β-D-mannuronic acid (M) and α-L-gluronic acid (α-L- guluronic acid (G)) (see FIG. 1A). Alg contains a carboxyl group and obtains mussel-derived adhesive properties by conjugating dopamine (see FIGS. 1B and 1C).

Example  2

Manufacturing method

Alginate  refine

Alginate sodium salts contain impurities and have a pale yellow color. Therefore, the purification was carried out by dialysis five or more times before the yellow color of the alginate sodium salt disappeared before catechol binding. The white powder of the purified alginate was obtained through the freeze-drying process, and it was confirmed by UV-Vis measurement that impurities were removed.

Alginate-Catechol (Alg-C) Synthesis

Using a conventional EDC-NHS coupling method, the catechol moiety was conjugated (covalently bonded) to the carboxylate functional group of the alginate sugar chain. The purified alginate (1 g) was dissolved in 100 mL of phosphate buffer (PBS, pH 6.0) with stirring. EDC (1.63 g) and NHS (0.98 g) were dissolved in the PBS buffer and added to the alginate solution again to activate the carboxylic acid groups of the alginate. The resulting mixture was stirred at room temperature for 20 minutes, and then a dopamine solution (0.50 g in PBS solution) was added to the alginate solution. The mixed solution was reacted at room temperature for 9 hours, and then the obtained product was purified by dialysis (MWCO = 25 kDa) twice in tertiary distilled water (DDW). The final product was lyophilized and stored in the refrigerator before use. The amount of catechol-conjugation was monitored at 280 nm using a UV-Vis spectrometer (HP8453, Agilent). Dopamine standard curves were determined using serially diluted dopamine solutions (0.125-0.015 mgmL ^-1 ), thereby measuring the degree of dopamine conjugation to alginate. Dopamine conjugated to the alginate sugar chains according to one embodiment of the present invention was about 3.4 ± 0.4%.

Experimental Example  One

Ultraviolet-visible light ( UV - Vis ) Spectrocopy  analysis

UV-Vis spectroscopy analysis demonstrated that dopamine was effectively conjugated to alginate (Alg) sugar chains through a peak at 280 nm (red in FIG. 2A). That is, the absorption peak at 280 nm means the amount of catechol conjugated (covalently bonded) to the carboxylic acid of the alginate (Alg) sugar chain.

By comparing the dopamine solution at the standard concentration, we found that 3.4 ± 0.4% of the alginate (Alg) carboxylic acid was conjugated with dopamine. Furthermore, dopamine conjugation was confirmed through the nitrogen 1s peak (XB) of X-ray photoelectron spectroscopy (XPS), resulting from amide bonds (see FIG. 1C) appearing at 399 eV. In contrast, no N1s peak detected means Alg unmodified.

Mussel-derived adhesive catechol in alginate-catechol (Alg-C), the binder material according to the present invention, exhibits excellent interaction properties on the silicon surface. This alginate-catechol (Alg-C) / silicon (Si) interaction was quantitatively analyzed via AFM.

For this purpose, a silicon nitride cantilever having a spring constant of ~ 250 pNnm ^-1 alginate - were each immersed in catechol (Alg-C) and Alg (0.5 mgmL ^-1) solution. After the binder-adsorbed cantilever was washed with water, the cantilever was combined with AFM to measure the binder-silicon interaction (see FIG. 2C). Catechol-silicon interaction forces at the monomolecular level were observed for alginate-catechol (Alg-C) (arrows, red spectra), but no measurable peaks were observed in Alg itself (black spectra). ). It can also be seen that a plurality of catechols were conjugated to the alginate sugar chains (middle, red). Average force values were 370 pN (n = 272) for alginate-catechol (Alg-C) and 73 pN (n = 52) for Alg (see FIG. 2D). This interaction between Alg and silicon is believed to be the result of hydrogen bonding with a force of less than 100 pN.

Consistent with the results on the monomolecular scale, the excellent adhesion properties of alginate-catechol (Alg-C) were also demonstrated in bulk-level peeling mechanics (see FIG. 3). This experiment is a universal experiment to evaluate the adhesion properties of silicon electrodes, the initial flake force increased by 100% as the binder was changed from alginate (Alg) to alginate-catechol (Alg-C) (Alg: ~ 0.3 N , Alginate-catechol (Alg-C): ˜0.6 N).

In addition, sharp, discontinuous peaks, indicated by arrows, are frequently observed in the force-displacement curves of silicon electrodes containing binders according to the present invention. However, this property was not observed in alginate (Si-Alg) and PVDF (Si-PVDF) in which the binder according to the present invention was not used. However, sharp peaks in silicon-alginate-catechol (Si-Alg-C) are more clearly observed in the enlarged force-displacement curve (see Figure 3b).

This observation indicates that many of the catechol groups have detached from the silicon surface collectively. In addition, the adhesion of the improved silicon-alginate-catechol (Si-Alg-C) can be immediately seen through the flake interface between the detached electrode film and the copper foil. At this interface, silicon-alginate-catechol (Si-Alg-C) represents a stretched binder bridge, which is more tensile than the observed silicon-alginate (Si-Alg) and silicon-PVDF (Si-PVDF). It became. All of the above results demonstrate that the binder according to the present invention has improved adhesive properties.

Experimental Example  2

Electrical characterization

The effect of improving the electrostatic properties of mussel-derived alginate-catechol (Alg-C) binders, especially silicon nanoparticle cells, was measured by electrostatic measurements of coin-type half-cells using lithium as the reference and counter electrodes. Lithium hexafulurophosphate (LiPF ₆ , 1 M) was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (1: 1 volume ratio) to prepare an electrolyte solution. The experiment consists of preliminary cycling at C / 10 speed followed by bone cycling at various speeds above C / 10. It should be noted that achieving excellent cell performance in electrodes made from silicon nanoparticles has been considered a very difficult challenge. The reason is that the silicon nanoparticles have a low specific capacity and difficult to maintain capacity according to the cycle. However, since the binder according to the present invention has a hard sugar chain and a carboxylic acid functional group capable of coordinating with silicon oxide, it produces an excellent cell performance improvement effect compared to conventional binders such as CMC and PVDF. Furthermore, in the present invention, active silicon accounts for at least 60% compared to the prior art used at a 1: 1 level, and furthermore, the silicon nanoparticles do not need to be coated by a carbon layer.

Through galvano electrostatic measurements in the potential region of 0.005-2.0 V (Li / Li +), charge-discharge occurred at +0.15 and +0.4 V, respectively. In addition, silicon nanoparticle cells with different binders showed significantly different specific capacities during the pre-cycling process. Silicon-Alginate-Catechol (Si-Alg-C), Silicon-Alginate (Si-Alg), Silicon-PVDF (Si-PVDF), Silicon-PAA (Si-PAA), and Silicon-CMC (Si-CMC) Represents specific capacities of 3,190, 2,640, 2,050, 2,590, and 2,710 mAh g- ¹ , respectively. Among them, silicon-alginate-catechol (Si-Alg-C) showed the highest specific capacity, which proves the importance of the catechol group in the contact between the silicon nanoparticle and the carbon conductor.

In the case of silicon-alginate-catechol (Si-Alg-C), effective contact has created an efficient electrical induction path in the electrode, which minimizes the amount of inactivated silicon.

Experimental Example  3

Adhesive Properties Analysis of Binder

PVDF is known to bind to silicon oxide surfaces by weak van der Waals interactions. CMC and PAA, on the other hand, are known to have hydrogen bonds between the hydroxide groups on the silicon oxide surface and the carboxylic acid groups of the binder. On the other hand, the binder according to the present invention utilizes a double adhesion mechanism of catechol interactions and coordination bonds with silicon nanoparticle surfaces. In particular, as confirmed by the adhesion test in FIG. 2, catechol interactions at both monomolecular scale and bulk scale proved to be much stronger than other binding mechanisms. The high dose of silicon-alginate-catechol (Si-Alg-C) clearly demonstrates the importance of the adhesive properties by the binder, thereby providing the important properties of the new silicone binder design through the present invention.

Electrochemical impedance spectroscopy (EIS) measurements were performed after preliminary cycling. EIS data is shown in FIG. 4B. Referring to FIG. 4B, it can be seen that the interfacial resistance is lowered from PVDF to Alg and alginate-catechol (Alg-C). The observed interfacial resistance tendency can be understood as the improved bonding properties between silicon nanoparticles and the carbon conductors in the case of silicon-alginate-catechol (Si-Alg-C). The film structure can be maintained as it is. Thus, a relatively thin SEI layer can be formed between nanoparticles. Despite the dense film properties, the permeability of the electrolyte in the electrode was not reduced, which can also be proved with high specific capacity.

The scanning electron microscope (SEM) shown in FIG. 4 illustrates all the mechanical and electrochemical results and the excellent catechol adhesion of the alginate-catechol (Alg-C) binder.

After five cycles at the C / 2 rate, the film stability of the Si-PVDF is significantly worse, which can be seen in the micrometer-sized majority of cracks. Between sulfur-alginate-catechol (S-Alg-C) and Si-Alg, the catechol effect of the alginate-catechol (Alg-C) binder causes a change in the nanostructure of the surface, before the charge-discharge cycle , Very little difference was observed between the two samples (upper part of Figure 4c). However, after five cycles, silicon-alginate-catechol (Si-Alg-C) shows fewer nanometer cracks and gentle surface properties compared to silicon-alginate (Si-Alg) (bottom of Figure 4c). part).

Experimental Example  4

Cycle life measurement

Since the cycle life (Fig. 5) is a very important factor in the use of the silicon electrode in all kinds of batteries, this experiment was tested.

When more silicon is used (weight ratio of silicon: carbon black: binder = 75: 17: 8), a battery having silicon-alginate-catechol (Si-Alg-C) and another carboxylic acid binder is Si-PVDF. Rather, it shows better capacity retention characteristics. However, all cells with catechol and non-catechol binders showed some level of capacity reduction after 5-10 cycles. This reduction in capacity can be explained by the fact that because the silicon nanoparticle density is too high, it is difficult to maintain the bonding of these nanoparticles and cannot promote a stable SEI layer during a large number of cycles. In addition, the high density of the silicon nanoparticles may promote the aggregation phenomenon of the nanoparticles, thereby promoting unavoidable micronization, and the high density silicon nanoparticles may induce mechanical stress on the SEI layer. Furthermore, the mechanically unstable SEI layer induces electrolyte consumption and promotes disordered SEI layer growth.

Therefore, the present inventors lowered the density of the silicon nanoparticles in order to improve the cycling performance (silicon: carbon black: binder = weight ratio of 60:20:20). As a result, the cycling performance was significantly improved (FIG. 5B). When measured at a rate of 1 C, silicon-alginate-catechol (Si-Alg-C) and silicon-alginate (Si-Alg) maintained 75.3% and 68% of their original capacity even after 200 cycles. In contrast, Si-PVDF lost most of its original capacity after 10 cycles. Therefore, the cathode according to the present invention preferably has a silicon: carbon black: binder weight ratio of 60 to 70:10 to 20:10 to 20.

To further analyze cycling performance, we tested silicon-alginate-catechol (Si-Alg-C) and silicon-alginate (Si-Alg) using an additive-containing electrolyte. The additive in this test was vinylene carbonate (VC, 5% by weight) known to form a stable SEI layer on the silicon electrode. Through the addition of the additive, the capacity maintenance was significantly improved and at the same time the capacity also remained the same during the 200 cycle charge-discharge, rather the capacity increase was observed. This gradual increase in specific capacity is associated with improved kinetics of lithium insertion / extraction during the cycle.

The above specific capacity improvement results demonstrate the importance of forming a stable SEI layer in silicon cathode operation. In addition, Fig. 5b shows the coulombic efficiencies (CEs) for cycling data. The CE analyzed in this experimental example is a very important factor in long-term battery operation.

Referring to FIG. 5B, the silicon-alginate-catechol (Si-Alg-C) of the present invention in which vinylene carbonate (VC) is used together shows superior CE results compared to other cells.

The above experimental results demonstrate that the binder plays a very important role in the operation of the silicon cathode. In addition, it can be seen that bio-derived binders having specific waterproof adhesive properties can contribute significantly to improving cycle life and capacity of silicon nanoparticle anodes. In addition, the bio-induced binder according to the present invention can be used for any other type of cell in which the volume of the cycle changes.

So far I looked at the center of the preferred embodiment for the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments are to be regarded in an illustrative rather than a restrictive sense, and all differences within the equivalent scope should be construed as being included in the present invention.

Claims (16)

As an electrode binder of a lithium secondary battery, the binder
A polymer chain containing a carboxyl group; And
An electrode binder of a lithium secondary battery comprising a catechol group-containing material conjugated to a carboxyl group of the polymer chain. The method of claim 1,
The polymer chain is an electrode binder of a lithium secondary battery, characterized in that the alginate. The method of claim 2,
The catechol group-containing material is a dopamine electrode binder, characterized in that the. The method of claim 1,
The binder has the following structural formula, the electrode binder of a lithium secondary battery, characterized in that.

(Where l and k are positive real numbers and 0 <l, k <1 and l + k = 1)
Method of manufacturing an electrode binder of a lithium secondary battery, the method
Preparing an alginate solution;
Preparing a mixed solution by adding a dopamine solution to the alginate solution; And
Method of manufacturing an electrode binder of a lithium secondary battery comprising the step of reacting the mixed solution. The method of claim 5, wherein preparing the alginate solution
Dissolving alginate in phosphate buffer solution; And
Method of manufacturing an electrode binder of a lithium secondary battery comprising the step of activating the carboxyl group of the dissolved alginate. The method according to claim 6,
The reaction method for producing an electrode binder of a lithium secondary battery, characterized in that the carboxyl group of the algitate and the catechol group of the dopamine is conjugated by the reaction. Lithium secondary battery negative electrode material, the material is
Silicone materials;
A binder comprising a polymer chain comprising a carboxyl group and a catechol group-containing material conjugated to the carboxyl group of the polymer chain; And
Lithium secondary battery negative electrode material comprising a carbon conductor. The method of claim 8,
The silicon material is a lithium secondary battery negative electrode material, characterized in that the silicon particles of less than micrometer. The method of claim 9, wherein in the negative electrode material,
The silicon nanoparticles: binder and carbon conductor weight ratio is 60 to 70: 10 to 20: 10 to 20, characterized in that the lithium secondary battery negative electrode material. The method of claim 10,
The carbon conductor is a lithium secondary battery negative electrode material, characterized in that the carbon black. The method of claim 8,
The polymer chain is a lithium secondary battery negative electrode material, characterized in that the alginate. 13. The method of claim 12,
The catechol group-containing material is a dopamine lithium secondary battery negative electrode material, characterized in that. The method of claim 8,
The binder has the following structural formula, the lithium secondary battery negative electrode material.

(Where l and k are positive real numbers and 0 <l, k <1 and l + k = 1) A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode of the lithium secondary battery is made of a negative electrode material according to any one of claims 8 to 14. 16. The method of claim 15,
The electrolyte is a lithium secondary battery comprising vinylene carbonate (VC) as an additive.

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