KR20170122378A - A silicon electrode comprising guar gum and a method of manufacturing the same - Google Patents

Abstract

The present invention relates to a silicon electrode comprising guar gum and to a manufacturing method thereof, wherein the manufacturing method comprises the following steps: preparing slurry by mixing a binder composed of a polymer including an electrode active material, a conductive material, guar gum, and a carboxyl group with a solvent; applying the slurry to a metal current collector; and cross-linking the guar gum and the polymer applied to the metal current collector. Therefore, by forming a dense network structure through cross-linking between the guar gum and the polymer comprising the carboxyl group, a volume change of the electrode during charging and discharging of lithium ions can be reduced to obtain an effect of improving mechanical performance of the electrode.

Description

TECHNICAL FIELD The present invention relates to a silicon electrode including guar gum and a method of manufacturing the same.

The present invention relates to a silicon electrode containing guar gum and a method for producing the same. More particularly, the present invention relates to a silicon electrode which comprises a guar gum and a polymer containing a carboxyl group to form a dense network structure, To a silicon electrode containing guar gum which can improve the mechanical performance of the electrode, and a method of manufacturing the same.

In order to achieve miniaturization and long-term continuous use of portable electronic devices in accordance with the improvement of industrial development and living standards, there is a need for a lightweight and low power consumption part and a high performance energy storage device capable of realizing a compact and high capacity. Recently, a lithium ion battery (LIB) has been used as a small-sized, high-performance energy source such as an electric vehicle, a large-capacity power storage battery such as a battery power storage system, and a portable electronic device such as a mobile phone, a camcorder and a notebook.

In particular, lithium ion batteries have advantages of high energy density, large capacity per area, low self-discharge rate and long life. In addition, since there is no memory effect, it is convenient for the user to use and has a characteristic that the life is long. The structure of the lithium ion battery is composed of an anode and a cathode capable of inserting and removing lithium ions, a lithium salt and a non-aqueous electrolytic solution. The reason why the non-aqueous liquid electrolyte is used is that lithium (Li) is highly reactive with respect to water and can not exist stably when an aqueous electrolyte is used. Typical lithium-ion battery cathode active materials include lithium transition metal compounds such as LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ , and these materials can intercalate / deintercalate lithium ions into the crystal structure . Lithium metal, carbon or graphite is mainly used for the negative electrode active material. In contrast to the positive electrode active material, the electrochemical reaction potential is low. The electrolyte is mainly composed of LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN ((LiPF ₄ ) ₂ ) in a polar organic solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, SO ₂ C ₂ F ₅ ) _2, and the like.

Although such a lithium ion battery is a secondary battery having the highest performance, it requires a secondary battery having higher performance than the current performance in terms of electronic devices. Improvement in the performance of the lithium ion battery plays an important role in improving the properties of the positive electrode active material and the negative electrode active material, and development of a high performance negative electrode active material is an important task. Silicon, a representative material of the anode active materials currently being developed, is one of high capacity anode active materials having a theoretical capacity of 4200 mAh / g by reaction with lithium ions. Such a silicon anode active material, together with a strong polymeric binder, prevents the mechanical cracking of the cathode during charging and discharging cycles, thereby regulating the electrochemical performance of the battery. However, in the case of a silicon anode active material, there is a disadvantage that the capacity is reduced very quickly due to loss of the anode active material due to extreme volume expansion of 400% or more of the existing volume during lithium ion charging and discharging.

In recent years, attempts have been made to form a coating layer on the surface of an anode active material as in Korean Patent No. 10-2012-0136131 in order to suppress the volume expansion of the anode active material. However, such an attempt tends to complicate the process and increase the manufacturing cost, thereby raising the unit price of the lithium ion battery.

Korean Patent Application Publication No. 10-2012-0136131 Korean Patent Application Publication No. 10-2014-0134954 Korean Patent Application Publication No. 10-2016-0037334

Accordingly, an object of the present invention is to provide a method for manufacturing a lithium ion battery, which comprises forming a dense net structure through cross-linking of a polymer containing guar gum and a carboxyl group to reduce the volume change of the electrode during charging and discharging lithium ions, And a method of manufacturing the same.

The above object can be accomplished by a method for producing a slurry by mixing a binder comprising a polymer comprising an electrode active material, a conductive material, a guar gum and a carboxyl group in a solvent; Applying the slurry to a metal current collector; And a step of cross-linking the guar gum and the polymer applied to the metal current collector.

In the step of preparing the slurry, the guar gum and the polymer are mixed at a weight ratio of 1: 1 to 1: 4, and the step of cross-linking the guar gum and the polymer comprises mixing the hydroxy group -OH) and the carboxyl group (-COOH) of the polymer are crosslinked to form a crosslinking binder.

The step of cross-linking the guar gum and the polymer may include heating the metal current collector at 80 to 110 ° C to dry the solvent; And raising the heating temperature to 130 to 170 DEG C to crosslink the guar gum and the polymer in the metal current collector in a vacuum atmosphere to form a crosslinking binder.

The polymer may be selected from the group consisting of polyacrylic acid, polymaleic acid, polymethacrylic acid, polypropylacrylic acid, polyacrylic acid- co-maleic acid) and mixtures thereof.

The conductive material may be at least one selected from the group consisting of carbon black, carbon nano tube (CNT), carbon nano fiber (CNF), activated carbon, graphite, graphene, Wherein the metal current collector is selected from the group consisting of soft carbon, hard carbon, modified carbon, carbon composite, and mixtures thereof, and the metal current collector is selected from the group consisting of copper (Cu), aluminum ), Platinum (Pt), gold (Au), nickel (Ni), titanium (Ti), iron (Fe), molybdenum (Mo), and mixtures thereof.

The above-mentioned object can also be achieved by a method for producing a conductive paste, which comprises mixing a binder composed of a polymer containing an electrode active material, a conductive material, a guar gum and a carboxyl group in a solvent to apply a slurry to a metal current collector, Is cross-linked with the silicon electrode.

According to the structure of the present invention described above, it is possible to reduce the volume change of the electrode during charge and discharge of lithium ions by forming a dense net structure through crosslinking of the polymer containing guar gum and carboxyl group, thereby improving the mechanical performance of the electrode Can be obtained.

1 is a flowchart of a method of manufacturing a silicon electrode including guar gum according to the present invention,
2 is a state diagram showing cross-linking of a polymer containing guar gum and a carboxyl group,
3 is a graph showing the battery capacity retention rate according to the type of the binder,
4 is a graph showing the capacity retention rate according to the mixing weight ratio of the cross-linked polyacrylic acid-guar gum binder.

Hereinafter, a silicon electrode including guar gum according to an embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the drawings.

First, as shown in FIG. 1, a slurry is prepared (S1).

The slurry prepared for forming the silicon electrode is prepared by putting the electrode active material, the conductive material and the binder into a solvent and then performing stirring so as to uniformly mix the same. Here, it is preferable that the solvent should be capable of dissolving the binder, and that the active material and the conductive material can be smoothly mixed and dispersed. The most preferred solvent can be, but is not limited to, water, distilled water or n-methyl-2-pyrrolidonem NMP.

The electrode active material is made of silicon or a silicon alloy and can be applied to both the negative electrode active material and the positive electrode active material, but in the case of the electrode active material including silicon, it is generally applied to the negative electrode active material. When constituting an electrode active material containing silicon, it can be a high capacity anode active material having a theoretical capacity of 4200 mAh / g by reaction with lithium ions. In some cases, a carbon material may be added to silicon or a silicon alloy to form an electrode active material.

The conductive material is one of the basic materials constituting the electrodes, and is a fine powdered carbon added in small quantities to improve the conductivity between the electrode active material particles or the metal current collector. The conductivity of the electrode varies depending on the kind of the conductive material. The conductive material may be selected from the group consisting of carbon black, carbon nano tube (CNT), carbon nano fiber (CNF), activated carbon, graphite, graphene, soft It is preferably selected from the group consisting of soft carbon, hard carbon, modified carbon, carbon composite, and mixtures thereof.

The binder of the present invention uses a binder to prevent the cycle characteristics of the lithium ion battery from deteriorating due to the volume expansion of silicon while the silicon electrode is repeatedly charged and discharged. The binder of the present invention uses a binder capable of cross-linking a polymer containing guar gum and a carboxyl group (-COOH). Guar gum (GG) is a polysaccharide obtained from seeds of cyamopsis tetragonolobus and has a relatively linear structure. It also contains a large number of hydroxyl groups (-OH) with high polarity in the molecule and is known to be conductive to lithium ions.

Herein, the polymer containing a carboxyl group may be selected from the group consisting of polyacrylic acid, polymaleic acid, polymethacrylic acid, polypropylacrylic acid, polyacrylic acid-poly maleic acid copolymer acrylic acid-co-maleic acid) and mixtures thereof.

In the present invention, it is preferable that the active material, the conductive material and the binder are mixed in an amount of 90 parts by weight or more, 5 parts by weight or less of the conductive material and 5 parts by weight or less of the binder, respectively. When the active material is used in an amount of less than 90 parts by weight, the energy density of the battery is lowered, which is not suitable for battery applications. When the conductive material is more than 5 parts by weight, there is a problem that the battery life characteristic is reduced. When the binder is more than 5 parts by weight, the content of the active material and the conductive material is lowered to thereby decrease the battery characteristics. The weight ratio of the most preferable active material, conductive material, and binder is 96.9: 0.1: 3.

The slurry is applied to the metal current collector (S2).

A slurry composed of a mixture of an electrode active material, a conductive material, a binder and a solvent is applied to an upper portion of the metal current collector having conductivity. Here, the metal current collector is made of copper (Cu), aluminum (Al), platinum (Pt), gold (Au), nickel (Ni), titanium (Ti), iron (Fe), molybdenum . ≪ / RTI > In the case of a slurry applied to a metal current collector, a mixture of guar gum and a polymer containing a carboxyl group is used in a weight ratio of 1: 1 to 1: 4. When the amount of guar gum is increased from 1: 1, May result in a residual hydroxy group, which reacts with the electrolyte and adversely affects battery life. Also, when the mixing ratio of the polymer containing carboxyl groups is increased from 1: 4, there is a problem that the content of guar gum is not sufficient enough to form a dense net structure. Therefore, the mixing ratio of the guar gum and the polymer containing a carboxyl group is most preferably 1: 1 to 1: 4 by weight.

The slurry-coated metal current collector is dried and cross-linked with a polymer including a guar gum and a carboxyl group (S3).

The slurry-coated metal current collector is first heated through a drier to dry the solvent present in the slurry. In this case, the heating temperature is preferably 80 to 110 ° C. If the temperature is lower than 80 ° C., the solvent is not dried. If the temperature is lower than 110 ° C., crosslinking of some guar gum and polymer may occur. In the case of cross-linking, the solvent should not be heated to a temperature exceeding 110 占 폚 in the step of drying the solvent since it must be carried out under a vacuum atmosphere. The heating temperature is then increased to crosslink the guar gum and polymer in the slurry to form a crosslinking binder. At this time, it is preferable that the heating temperature is increased to 130 to 170 ° C and crosslinking is performed in a vacuum atmosphere. When the temperature is less than 130 ° C, complete crosslinking is not effected and some crosslinked guar gum and polymer remain. When the temperature is higher than 170 ° C, adverse reaction may occur due to high temperature.

In the case of carboxymethyl cellulose (CMC), alginate, xanthan gum, etc., which are made of a structure similar to guar gum and currently being studied as a binder, not only a hydroxyl group (-OH) but also a carboxyl group -COOH). Methyl cellulose, alginate, xanthan gum, etc., contain complex structures and carboxyl groups, and these structures are intertwined to each other to form a complicated net structure, thereby suppressing volume expansion. More specifically, when a hydroxyl group contained in methyl cellulose, alginate or xanthan gum is combined with a carboxyl group contained in the polymer, a water is formed and a hydroxyl group and a carboxyl group are esterified (-COO- ) Cross-linking. Through such a process, the binder forms a dense net structure to suppress the volume expansion of the electrode.

On the other hand, it does not contain a guar black carboxyl group but contains only a hydroxyl group. As shown in FIG. 2, the hydroxyl group of guar gum crosslinks with the carboxyl group of the polymer to form a crosslinked binder. The crosslinked binder of the present invention formed through guar gum has a greater degree of suppression of volume expansion than methyl cellulose, alginate and xanthan gum which have been studied in the past, thereby improving the performance of the electrode. This is possible because guar gum contains a hydroxyl group but does not contain a carboxyl group such as methyl cellulose, alginate and xanthan gum. Since guar gum contains only hydroxyl groups, there is no binding between guar gums, and the whole amount of guar gum crosslinks with the polymer to form a dense net structure. On the other hand, since not only methyl cellulose, alginate and xanthan gum black hydroxyl groups but also carboxyl groups reacting with hydroxyl groups are included together, there arises a problem that some of them are not entirely crosslinked with the polymer and some of them are bonded to each other. Therefore, when a carboxyl group is contained, the effect of inhibiting the volume expansion is somewhat less than the amount used. In addition, since the carboxyl group is also reacted with silicon, a problem may occur that the polymer is partially crosslinked with silicon used as an electrode active material, thereby preventing cross-linking of the polymer. In this case, it is difficult to form a dense net structure, and it is not easy to suppress the volume expansion.

In addition, guar black is formed as a linear structure which is not complicated and has less branching than other molecules, and when formed into a linear structure, the hydroxyl group easily binds to the carboxyl group of the polymer, Do. When formed into a complex structure rather than a linear structure, the hydroxyl group and the carboxyl group are difficult to meet with each other because of the fact that they are clustered together, which makes it difficult to cross-link. Therefore, it is most suitable to apply guar gum having a linear structure to a binder.

Hereinafter, embodiments of the present invention will be described more clearly.

<Examples>

A mixture of graphite and a silicon alloy is used as a negative electrode active material, a carbon nano tube is used as a conductive material, and guar gum and polyacylic acid are mixed in a ratio of 1: 1 By weight to prepare a slurry containing n-methyl-2-pyrrolidone as a solvent. At this time, the weight ratio of active material: conductive material: binder is 96.9: 0.1: 3.

The slurry in a mixed state at this weight ratio is coated on top of a copper (Cu) foil to be a metal current collector, and then heated at 100 DEG C to dry the solvent in the slurry. Then, the mixture is heated again in a vacuum atmosphere at 150 ° C for 2 hours so that the guar gum and the polyacrylic acid binder can form cross-linking.

The prepared electrode was assembled into a coin cell half cell having a lithium metal foil as a counter electrode, and charge and discharge tests were conducted at a potential window of 0.005 to 1.5V. As a comparative example, in place of guar gum, carboxymethyl cellulose (CMC), alginate and xanthan gum were added at a weight ratio of 1: 1, respectively, and crosslinked with polyacrylic acid, . In addition, the electrode was manufactured using a binder in which carboxymethylcellulose and styrene butadiene rubber (SBR) were mixed only without cross-linking, and tested.

FIG. 3 is a graph showing the capacity retention rate of the battery after 100 cycles after the electrodes and the electrodes of the examples and the comparative examples are formed. FIG. 3 is a graph showing the capacity retention rate of the battery after styrene butadiene rubber-carboxymethyl cellulose (SBR-CMC) , The capacity retention rate was 11.5%, and the capacity retention ratio of the cross-linked polyacrylic acid-carboxymethyl cellulose (c-PAA-CMC) was found to be 15.8%. (C-PAA-GG) exhibited a very high capacity retention ratio of 37.9%, and the cross-linked polyacrylic acid-alginate (c-PAA-Alg) and cross- The retention capacity of acrylic acid-xanthan gum (c-PAA-XG) was 28.6% and 30.4%, respectively, but it was lower than that of guar gum.

FIG. 4 is a graph showing the effect of the weight ratio of polyacrylic acid and guar gum in the cross-linked polyacrylic acid-guar gum (c-PAA-GG) according to the present invention. C-PAA-GG as a binder were mixed at 1: 1, 1.5: 1, 2: 1, 3: 1 and 4: 1 and crosslinked. As a result of confirming the polyacrylic acid and guar gum as a single without cross-linking, it can be confirmed that the capacity retention ratio is as low as 23.1% and 15.7%.

When the mixture was mixed at a weight ratio of 1: 1, the capacity retention rate was 37.9%. When the mixture was mixed at a weight ratio of 1.5: 1, 54.1%, 49.4% 1, the capacity retention rate of 42.8% can be confirmed. Therefore, it is found that the capacity retention ratio is excellent when a binder obtained by crosslinking polyacrylic acid and guar gum is used. In particular, it can be seen that the weight ratio of polyacrylic acid: guar gum is the most excellent when the weight ratio is 1.5: 1. It can be predicted that this is the optimum ratio of crosslinking with polyacrylic acid without leaving guar gum.

That is, unlike the methyl cellulose, alginate and xanthan gum which have been studied in the prior art, guar gum does not contain a carboxyl group but contains only a hydroxy group, so that the degree of volume expansion is largely suppressed, Polymer network to form a dense net structure, thereby reducing the volume change of the electrode during the charging and discharging of lithium ions, thereby improving the mechanical performance of the electrode.

Claims (8)

Preparing a slurry by mixing a binder composed of a polymer including an electrode active material, a conductive material, a guar gum, and a carboxyl group in a solvent;
Applying the slurry to a metal current collector;
And cross-linking the guar gum and the polymer applied to the metal current collector. The method according to claim 1,
The step of preparing the slurry may comprise:
Wherein the guar gum and the polymer are mixed in a weight ratio of 1: 1 to 1: 4. The method according to claim 1,
The step of cross-linking the guar gum and the polymer comprises:
Wherein the hydroxy group (-OH) of the guar gum is cross-linked with the carboxyl group (-COOH) of the polymer to form a crosslinking binder. The method according to claim 1,
The step of cross-linking the guar gum and the polymer comprises:
Heating the metal current collector at 80 to 110 DEG C to dry the solvent;
And raising the heating temperature to 130 to 170 占 폚 to crosslink the guar gum and the polymer in the metal current collector in a vacuum atmosphere to form a crosslinking binder. The method according to claim 1,
Preferably,
Polyacrylic acid, polymaleic acid, polymethacrylic acid, polypropylacrylic acid, poly (acrylic acid-co-maleic acid) ), And mixtures thereof. &Lt; Desc / Clms Page number 19 &gt; The method according to claim 1,
The conductive material may be at least one selected from the group consisting of carbon black, carbon nano tube (CNT), carbon nano fiber (CNF), activated carbon, graphite, graphene, A method of manufacturing a silicon electrode comprising the steps of: forming a conductive layer on a substrate; forming a conductive layer on the conductive layer; forming a conductive layer on the conductive layer; The method according to claim 1,
Wherein the metal current collector is made of copper (Cu), aluminum (Al), platinum (Pt), gold (Au), nickel (Ni), titanium (Ti), iron (Fe), molybdenum &Lt; / RTI &gt; wherein the silicon dioxide is selected from the group consisting of silicon dioxide and silicon dioxide. A slurry is applied to a metal current collector by mixing a binder composed of a polymer containing an electrode active material, a conductive material, a guar gum, and a carboxyl group in a solvent, and the slurry is formed by crosslinking the guar gum and the polymer applied to the metal current collector Wherein the silicon electrode is a silicon oxide film.

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