KR20190068371A - Dual-Crossliked aqueous binder for lithium secondary battery - Google Patents

Abstract

Disclosed is an electrode composition for a secondary battery, including: a binder composite which contains first polymer chains each of which has at least one negative ionic group, divalent or multivalent metal positive ions which fix the first polymer chains to each other by mutually interacting with the negative ionic groups of the first polymer chains, and second polymer chains connected to the first polymer chains having at least one negative ionic group through a covalent bond; and a crosslinking agent which connects the second polymer chains by being polymerized to the second polymer chains. The first polymer chains are crosslinked through the divalent or multivalent metal positive ions which are physical crosslinking agents, and the second polymer chains are crosslinked through a chemical crosslinking agent. Therefore, the electrode composition of the present invention is double-crosslinked and an electrode including the electrode composition has improved cycle, lifespan, and high rate properties.

Description

[0001] The present invention relates to a dual-cross-linked aqueous binder for a lithium secondary battery,

The present invention relates to an aqueous binder capable of imparting high-rate characteristics to a negative electrode for a lithium secondary battery and improving capacity, cycle and life characteristics, a negative electrode for a lithium secondary battery including the aqueous binder, and a lithium secondary battery having the negative electrode will be.

Attempts to utilize batteries as a power source for a variety of devices, from automobiles using existing fossil fuels to machine tools, are continuously expanding. This is because the use of electric energy is considered as an alternative to solve various problems caused by the use of fossil energy. However, in order to economically use a battery as a power source for an automobile, it is necessary to realize energy densification, and lithium secondary battery is considered to be the most likely candidate to meet the above-mentioned demand.

The lithium secondary battery includes a cathode, a cathode, and an electrolyte, and is characterized in that the lithium cations are reversibly intercalated or deintercalated into an electrode, and charging and discharging are performed. During the charging and discharging process, the lithium cation plays a role of neutralizing the electrons entering the electrode through the current collector and storing the electric energy in the electrode.

The cathode of the lithium secondary battery refers to an electrode into which lithium cations are inserted in the discharge process of the lithium secondary battery. The charge is transferred to the anode through the external conductor along with the insertion of the lithium cation, so that the anode is reduced in the discharge process. Typically, the positive electrode of a lithium secondary battery contains a transition metal oxide. The transition metal oxide included in the positive electrode is otherwise called a positive electrode active material, and the positive electrode active material generally has a repetitive and three-dimensional structure.

On the contrary, the anode of a lithium secondary battery refers to an electrode in which lithium cations are desorbed during the discharge process of the lithium secondary battery. The charge is discharged through the external lead along with the desorption of the lithium cation, so that the cathode is oxidized in the discharge process. Typically, a lithium metal, a carbon material, and a non-carbon material are included in a negative electrode of a lithium secondary battery, and a carbon material and the like contained in a negative electrode are called negative electrode active materials.

In order to maximize the performance of the lithium secondary battery, the essential conditions that the negative electrode active material should generally have are as follows. I) the amount of electricity that can be stored per unit weight is high, and ii) the density of the negative electrode active material per unit volume is high. And iii) the change in structure due to insertion and desorption of lithium ions should be small. In the case of a large change in the structure, as the charge and discharge proceed, the strain accumulates in the structure. As a result, irreversible insertion and desorption of lithium ions may be induced.

At present, a lithium secondary battery using a carbon material as a negative electrode active material is in a commercialized state. In particular, artificial graphite and natural graphite are frequently used because the electrochemical reaction potential with the lithium ion is very close to the lithium metal, and the crystal structure of the lithium ion is insufficiently changed during the insertion and desorption of lithium ions, Capacity and lifetime characteristics.

However, in order to meet the demand for higher densification of energy of the lithium secondary battery as described above, studies for using a material other than carbon materials as an anode active material have been continued. Particularly, silicon is a candidate for a negative electrode active material which is suitable for a lithium secondary battery having a high capacity and a high output at a theoretical capacity of 2000 mAh / cc or more. However, silicon and tin-based materials, when used alone, experience significant volume changes in the process of inserting and desorbing lithium ions and thus have a disadvantage in that cycle and lifetime characteristics are significantly degraded.

A binder is used to reduce the volume change of the active material. The binder prevents the separation of the electrode active material or between the electrode active material and the current collector during the production of the electrode, while suppressing the volume change of the active material during charging and discharging with strong binding force. The volume of the active material is kept constant despite the insertion and the desorption of lithium ions, so that the accumulation of strain in the active material due to the volume change is reduced, which results in improving the cycle and lifetime characteristics of the lithium secondary battery.

The types of binders are classified into two types: binder resins represented by polyvinylidene fluoride (PVdF) and aqueous binders represented by styrene-butadiene rubber (SBR). The oil binder means a binder dissolved in an organic solvent, and the aqueous binder means a binder dissolved in water. In particular, waterborne binders are more environmentally friendly and capable of producing slurries and coatings in the atmosphere, as compared with oilborne binders, and research on aqueous binders has been actively conducted.

For example, the results of a study on SBR / CMC binder, which is a kind of aqueous binder disclosed in Korean Patent No. 10-1077870, are as follows. CMC (Carboxy Methyl Cellulose) refers to a compound in which a hydroxyl group of cellulose is partially substituted with a carboxyl group. SBR is known to be uniformly dispersed in water in a particulate state. However, when SBR / CMC is used for silicon or tin-based anode active materials, It is known that the volume change of the city can not be sufficiently suppressed. It is believed that this is because the fine particles of the SBR exist in a water-dispersed state and only the spot contact with the negative electrode active material can be achieved. In the case where the volume of the silicon based negative active material expands rapidly, since it is possible to make only point contact with one negative active material, it is not possible to prevent the gap between the negative active materials from widening.

In light of the above, development of an aqueous binder capable of effectively suppressing the volume change of the silicon and tin-based anode active material caused by the insertion and desorption of lithium ions is essential in realizing a battery having a high capacity, high output and long life.

Patent Document 1: JP 10-1077870

The present invention has been developed in order to solve the above problems, and it is an object of the present invention to effectively suppress the volume change of the negative electrode active material by insertion and desorption of lithium ions when silicon is included as the negative electrode active material of the lithium secondary battery. A lithium secondary battery comprising the negative electrode for a lithium secondary battery comprising the electrode composition for a lithium secondary battery, the lithium secondary battery including the negative electrode for the lithium secondary battery, and the electronic device including the lithium secondary battery are provided. The purpose.

As a means for achieving the above object, the present invention relates to a polymer electrolyte membrane comprising first polymer chains each having at least one anion group, a divalent or more metal cation which interacts with the anion groups of the first polymer chains to fix the first polymer chains to each other And second polymer chains connected through a covalent bond with the first polymer chain having the at least one anion group; And a crosslinking agent polymerized on the second polymer chains to connect the second polymer chains.

Preferably, the first polymer chains are polysaccharides, and the polysaccharide is selected from the group consisting of alginic acid, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl guar gum, guar gum, carboxymethyl xanthane gum, carboxymethyl tara gum, low methoxyl pectin, carrageenan, cellulose, amylose, , Chitosan, glucose, sucrose, maltose, lactose, starch, glycogen or a mixture thereof.

The first polymer chains may have at least one anion group, and the at least one anion group may include an oxygen anion. The anionic groups include the anionic oxygen is _{^{-CO 2 -, -SO 2 -,}} -SO 3 -, -OSO 3 -, -PO 3 2-, -OPO 3 2-, -OP (OH) O -, - And more preferably at least one selected from the group consisting of CS ₂ ^- or -OCO ₂ ^- _- .

On the other hand, it is preferable that the divalent or more metal cations are alkaline earth metal, divalent transition metal, or a cation of an alloy thereof. More preferably, the alkaline earth metal includes calcium, magnesium and barium, and the bivalent transition metal is selected from the group consisting of scandium, titanium, titanium, vanadium, chromium, manganese, iron, titanium, vanadium, chromium, manganese, iron, cobalt, nickel Or copper.

On the other hand, it is preferable that the second polymer chains include an acrylic polymer, and the acrylic polymer is selected from the group consisting of polyacrylamide, poly (methacrylic acid), poly (methyl acrylate) More preferably at least one polymer selected from the group consisting of poly (methyl acrylate), poly (methyl methacrylate), polyacrylic acid, and polyacrylonitrile Do.

On the other hand, the crosslinking agent may be a derivative of ethylene glycol di (meth) acrylate or a derivative of N, N'-Alkylenebisacrylamide And the derivative of N, N'-Alkylenebisacrylamide is preferably at least one selected from the group consisting of N, N'-methylenebisacrylamide, MBAA ) Is more preferable.

This specification describes details of the first polymer chains described above, details of the substituents substituted in the first polymer chain, details of the divalent metal ions, details of the second polymer chains, It should be noted that the details of the invention are also disclosed in connection with each other. In particular, the present specification discloses the invention in which the first polymer chain is alginic acid, the second polymer chain is polyacrylamide, the divalent metal ion is calcium, and the cross-linking agent is MBAA.

In addition, details of the first polymer chains, details of substituents substituted in the first polymer chain, details of the divalent metal ions, details of the second polymer chains, and details of the crosslinking agent A negative electrode for a secondary battery comprising an electrode composition for a secondary battery in which the negative electrode and the negative electrode are combined with each other. It is preferable that the negative electrode active material of the negative electrode contains silicon. The negative electrode may further include carbon as a negative electrode active material, and more preferably the mass ratio of the silicon to the carbon is 1: 3. Further, it is most preferable that the mass ratio of the electrode composition for a secondary battery to the negative active material containing silicon and carbon is 1: 5.

In addition, the present specification discloses, as means for solving the above-mentioned problems, the details of the first polymer chains, the details of the substituents substituted in the first polymer chain, the details of the divalent metal ions, A negative electrode for a secondary battery comprising an electrode composition for a secondary cell in which the details of the chain and the details of the cross-linking agent are combined with each other, wherein the negative electrode active material of the negative electrode is a lithium secondary battery And an electronic device including the lithium secondary battery.

By including the electrode composition for a secondary battery disclosed in the present specification in the negative electrode of a lithium secondary battery, the life span of the lithium secondary battery including the silicon negative active material is extended, the effect of increasing the capacity of the battery, Can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows a reaction formula for obtaining the electrode composition for a secondary battery of the present invention and a structural formula of the composition for the secondary battery.
2A is an IR spectrum of the electrode composition for a secondary battery of the present invention and comparative examples.
FIG. 2B is an IR spectrum of the electrode composition for a secondary battery of the present invention and a comparative example when added to a negative electrode active material containing Si. FIG.
3 is a graph comparing the amounts of electrolyte absorption of the electrode composition for a secondary battery of the present invention and Comparative Examples.
4 is a graph showing the binding force between the electrode composition for a secondary battery of the present invention and a comparative example and a negative electrode active material containing Si / C.
FIG. 5 shows a cyclic voltammetry result of a lithium secondary battery having a negative electrode including the electrode composition for a secondary battery of the present invention and Comparative Examples.
FIG. 6A is a graph comparing cell capacities of a lithium secondary battery having a negative electrode including the electrode composition for a secondary battery of the present invention and comparative examples according to charge and discharge.
FIG. 6B is a graph comparing the discharge characteristics of a lithium secondary battery having a negative electrode containing the electrode composition for a secondary battery of the present invention and Comparative Examples, respectively, at different current rates.
FIG. 7 is a graph comparing changes in the thickness of the negative electrode containing Si / C with each of the electrode composition and the comparative example of the secondary battery of the present invention during charging and discharging.

The terms used in the present application are used only to illustrate specific examples. Thus, for example, the expression " singular " includes plural expressions unless the context clearly dictates otherwise. In addition, the terms "comprise", "comprising" and the like used in the present application are used to specifically denote the presence of the features, steps, functions, elements, or combinations thereof described in the specification, And the like, are not used to preclude the presence of elements, steps, functions, components, or combinations thereof.

Unless defined otherwise, all terms used herein should be interpreted to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Thus, unless explicitly defined herein, certain terms should not be construed in an overly ideal or formal sense.

The binding aspect of the electrode composition for a secondary battery of the present invention

This specification discloses first and second polymer chains having at least one anion group and a divalent or higher metal cation that interacts with the anion groups of the first polymer chains to fix the first polymer chains to each other. An electrostatic attractive force is generated between the anion groups of the first polymer chain and the metal cations having a valence of two or more. By 'fixing to each other', it is meant that the bivalent or higher metal cation physically bridges the first polymer chains. Physical crosslinking will be described later in detail.

If the anion group of the first polymer chain is monovalent and the metal cation is divalent or more, an electrostatic attractive force (for example, ionic bonding) may occur between the metal cation and the second polymer chains of 2 equivalents or more It is obvious. In the above-mentioned case, the first polymer chains of two equivalents or more are physically bound via a bivalent or higher metal cation. For example, it can be said that the situation is similar to the case where a surfactant that forms an anion around the metal cation forms a micelle structure and bonds between the surfactants.

Also, the present specification discloses a binder composite comprising second polymer chains linked to the first polymer chain via covalent bonds. Since the second polymer chains are connected to the first polymer chain via a covalent bond, they may be chemically bonded to the first polymer chain. Preferably the first polymer chain and the second polymer chain are bonded through graft polymerization (Graft Polymerization), and a first polymer chain and the second polymer chain are bonded mainly by a σ bond _CO-mediated chemically.

Since the first polymer chain and the cations having two or more cations are physically bonded and the first polymer chain and the second polymer chain are chemically bonded, the binder composite itself has considerable durability. However, in the binder composite, there is a limit in that the bonding between the first polymer chains is possible only through physical bonding mediated by cations having two or more cations.

Therefore, the electrode composition for a secondary battery, which further comprises a crosslinking agent polymerized on the second polymer chains and connecting the second polymer chains, exhibits improved durability as compared with the binder composite. The crosslinking agent is chemically bonded to the second polymer chains and serves as a bridge linking the second polymer chains. As a result, a structure is obtained in which a first polymer chain chemically connected to one second polymer chain and another first polymer chain connected to another one second polymer chain are chemically connected through a crosslinking agent. Therefore, the electrode composition for a secondary battery of the present invention shows a more compact connection between the polymer chains than the binder composite.

Examples of the electrode composition for a secondary battery of the present invention

≪ First polymer chain and metal cation >

The first polymer chains may be polysaccharides, but are not limited thereto. Since the polysaccharide contains a large amount of hydoxyl group, it can be strongly bound through chemical bonding with the silicon-based and tin-based negative electrode active materials.

For example, the bond dissociation energy of the _Si-O bond σ is a value greater than the normal σ _CC coupled to approximately 150 Kcal / mol level. However, since the hydroxyl group is a weak acid with a pKa of about 16, it becomes an anion group only through strong base conditions and through acid-base reaction. Therefore, it is expected that a substituent containing oxygen which can strongly bond with silicon is preferable, and a substituent which is stronger than a hydroxyl group can form a stronger ionic bond with a divalent or higher metal cation. Thus, one or more of the hydroxyl groups of the polysaccharide is ^{_{-CO 2 -, -SO 2 -,}} -SO 3 -, -OSO 3 -, -PO 3 2-, -OPO 3 2-, -OP (OH) O ^- , -CS ₂ ^-, or -OCO ₂ ^- _- .

The first polymer chains may be exemplified by polysaccharides such as alginic acid, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl guar gum, carboxymethyl cellulose, Carboxymethyl tartarum, carboxymethyl tararum, low methoxyl pectin, carrageenan, cellulose, amylose, chitosan, glucose, sucrose, , Maltose, lactose, starch, glycogen or a mixture thereof.

However, as described above, alginic acid, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl guar gum, carboxymethyl cellulose, carboxymethyl cellulose, It is more preferable that the first polymer chain is carboxymethyl xanthan gum, carboxymethyl tara gum, low methoxyl pectin, carrageenan, and the like.

On the other hand, the hydroxyl group of the polysaccharide also plays a crucial role in chemically linking with the second polymer chain through graft polymerization. In particular, graft polymerization by hydroxyl groups exposed to the outside of the first polymer chain among several hydroxyl groups is important. In general, it is known that graft polymerization of hydroxyl groups and second polymer chains located in the axial direction is easy, but it is not impossible that graft polymerization of the second and third polymer chains located in the equatorial direction is possible.

Further examples of the first polymer chain include alginic acid, carboxymethyl guar gum, low methoxyl pectin, etc. substituted with hydroxyl groups in the axial direction Most preferred is the first polymer chain. However, the graft polymerization by the hydroxyl group located in the equatorial direction is not impossible, so it is not limited thereto.

The anion groups of the first polymer chains are bonded to the metal cations having a valence of two or more through electrostatic attraction. Particularly, the metal cation is preferably two or more valent. The divalent metal cation is theoretically capable of ionic bonding with two or more anionic groups. Two equivalents of the first polymer chains per metal cation having one equivalent of divalent or more can be combined. This means that the first polymer chains can bind to each other through the metal cations having the divalent or higher valency. In other words, the divalent metal cations physically cross-link the first polymer chains.

As the bivalent or higher metal cation, an alkaline earth metal, a divalent transition metal, or a cation of an alloy thereof is preferable. More preferably, the alkaline earth metal includes calcium, magnesium and barium, and the bivalent transition metal is selected from the group consisting of scandium, titanium, titanium, vanadium, chromium, manganese, iron, titanium, vanadium, chromium, manganese, iron, cobalt, nickel , Zinc, or copper. Particularly, a structure similar to a crown structure can be formed with four monomers of an alginate anion, which is one kind of calcium 2 cations and one kind of first polymer chains.

An aspect similar to the above crown structure includes, for example, an aspect in which four alginic acid anionic monomers are arranged symmetrically around a calcium cation. The alginic acid anionic monomer is derived from two different first polymer chains. That is, two of the alginic acid anionic monomers are derived from the first first polymer chain, and the other two are derived from the second first polymer chain. The first first polymer chain and the second first polymer chain are concentrated around the calcium cation. In other words, it is the same as that in which the first polymer chains are cross-linked centered on the calcium cation.

The above-described crosslinking pattern is a weak crosslinking pattern in which the first polymer chains are crosslinked through covalent bonding because two first polymer chains are connected to each other via electrostatic attraction. However, the covalent bond can not be recovered once it is lost, while the cation-mediated crosstalk can be recovered even if it is lost.

≪ Second Polymer Chain >

The second polymer chains of the present invention may include an acrylic polymer. However, the acrylic polymer is not necessarily included. The acrylic polymer has an advantage that it can easily perform graft polymerization with the hydroxyl group of the first polymer chain. Any of the first polymer chain and the graft polymerizable polymer may be included in the second polymer chain. By graft polymerization is meant polymerization in the form of addition of side branches to the main chain structure. For example, when the first polymer chain is referred to as a main chain, the second polymer chain includes side chains of the first polymer chain and side chains of the second polymer chain. On the other hand, when the second polymer chain is referred to as a main chain, the first polymer chain may be bonded to the side of the second polymer chain to form a side chain of the first polymer chain.

In addition, since the acrylic polymer essentially contains a carbonyl group, it has an advantage that it can form a σ _Si-O bond or a σ _Si-N bond with the _silicon- based negative active material separately from the hydroxyl group of the first polymer chain . More specifically, the acrylic polymer may be selected from the group consisting of polyacrylamide, poly (methacrylic acid), poly (methyl acrylate), poly (methyl methacrylate) It is preferable to include at least one polymer selected from the group consisting of poly (methyl methacrylate), polyacrylic acid, and polyacrylonitrile.

(Methacrylic acid), poly (methyl acrylate), poly (methyl methacrylate), poly (methyl methacrylate), poly Polyacrylic acid can form a _Si-O bond with a _silicon- based negative active material, and polyacrylonitrile can form a _Si-N bond with a _silicon- based negative active material. Therefore, the second polymer chain is fixed to the negative electrode active material separately from the first polymer chain.

The SBR-based water dispersion (in which the second polymer chain connected to the first polymer chain and the first polymer chain via graft polymerization is linearly connected to the silicon anode active material through chemical bonding, water-dispersed binder can be overcome. The first polymer chain and the second polymer chain are in line contact with the negative electrode active material.

One polymer chain may be connected to a plurality of negative electrode active materials through a sigma bond, or a single polymer chain may be connected to a negative active material through a plurality of sigma bonds. The first polymer chain may be connected to a plurality of negative electrode active materials and the second polymer chain may be connected to a plurality of negative electrode active materials. There may be a negative electrode active material included in the intersection between the negative electrode active material connected to the first polymer chain and the negative electrode active material connected to the second polymer chain and there may be no negative electrode active material included in the intersection.

Among the acrylic polymer chains, polyacrylamide, poly (methyl acrylate), polyacrylic acid, and polyacrylonitrile are more preferable. The σ _CH bond is present in the alpha-position of the carbonyl group contained in the acrylic polymer so that polymerization with the crosslinking agent through the radical mechanism is possible. This will be described later.

<Cross-linking agent>

The crosslinking agent means a compound in which the terminal of the crosslinking agent is connected to one second polymer chain via a covalent bond and the other terminal of the crosslinking agent is connected to the other second polymer chain through a covalent bond. By including the cross-linking agent, the different second polymer chains are chemically cross-linked.

When considering the radical mechanism in which the crosslinking agent is polymerized, it is preferable that Enone is included as a functional group of the crosslinking agent. The polymerization mechanism is briefly described as follows. Hydrogen located at the alpha position of the carbonyl group contained in the second polymer chain is equally decomposed to form radicals. The radical located at the alpha position is stabilized through the resonance structure with the carbonyl group. The radicals are connected to the crosslinking agent through radical addition (Radical Conjugate Addition, 1,4-addition). Especially, Enone is conjugated with Alkene and Carbonyl group included in Enone, so that LUMO is low, so that conjugated addition as described above occurs rapidly.

As examples of the crosslinking agent included in Enone, a derivative of ethylene glycol di (meth) acrylate or a derivative of N, N'-Alkylenebisacrylamide Derivatives thereof, and the like. Particularly preferred are derivatives of N, N'-Alkylenebisacrylamide which are thermally stable and are not chemically decomposed under aqueous conditions.

Further, the derivative of N, N'-Alkylenebisacrylamide is more preferably N, N'-Methylenebisacrylamide. This is because the shorter the length of the cross-linking agent, the closer the second polymer chain becomes. Accordingly, it is more preferable that N, N'-Methylenebisacrylamide is used in which only one carbon is contained between the two Enone functional groups.

The first polymer chains connected to the respective second polymer chains are also chemically connected by chemically connecting the second polymer chains having different crosslinking agents. Further, a first polymer chain and a second polymer chain capable of line-contacting with the silicon-based anode active material and another group of first polymer chains and second polymer chains capable of making line contact with the second polymer chain and the silicon- By chemically connecting, the line contact becomes a net contact that is close to the surface contact. The volume change of the silicon-based negative electrode active material due to the insertion and desorption of lithium ions through the net contact can be more effectively suppressed.

In addition, it should be noted that the first polymer chains are physically weakly cross-linked via metal cations. Physical crosslinking through the metal cation, which is the weakest bond, is lost when the volume expansion of the silicon based negative active material due to the insertion of lithium ions is interrupted. The weak bond mediated by the metal cation is lost and the volume expansion pressure can be solved once, thereby preventing the covalent bond between the polymer chains from being damaged due to the volume expansion.

 Further, the weak bonding mediated by the metal cation is restored again when the volume of the silicon based negative electrode active material is reduced through the elimination of lithium ions. This is one of the most important advantages of the present invention. That is, the crack of the electrode composition that may occur during the process of volume expansion of the negative electrode active material is self-healed again in the volume reduction process. The electrode composition for a secondary battery of the present invention has a property of effectively suppressing the volume expansion of a negative electrode active material and extending its lifetime as a volume expansion inhibiting material as compared with a normal binder by restoring the weak bonding again.

A negative electrode for a secondary battery comprising the electrode composition of the present invention

The electrode composition for a secondary battery of the present invention may be directly connected to the carbon-based active material through a? _CO bond or a? _CN bond. Or may be directly connected to the silicon-based active material through a sigma _SiO bond or a sigma _SiN bond. In particular, in the case of a silicon-based active material, as described above, it is possible to form a strong sigma bond and theoretically, at most two sigma _SiO bonds can be formed per one silicon atom, so that the electrode composition of the present invention is particularly strong can do.

When a part of silicon is contained as the negative electrode active material, it is collectively referred to as a silicon-based active material. Specifically, the mass ratio of carbon to silicon contained as the negative electrode active material is preferably 3: 1. When the ratio of carbon is 3 or more, the effect of increasing the capacity of the battery through silicon content is insignificant. When the ratio of carbon is 3 or less, a considerable amount of electrode composition must be contained in order to suppress the volume change of silicon. And the mass ratio of the catalysts is decreased.

As described above, the ratio of the negative electrode active material having a mass ratio of carbon to silicon of 3: 1 and the electrode composition of the present invention (the following formula) is preferably 5: 1. When the ratio of the electrode composition is 1, the electrode composition can effectively suppress the volume expansion of the negative electrode active material and increase battery life while maximizing the battery capacity. That is, when the above ratio is satisfied, an increase in the capacity characteristics and lifetime characteristics of the battery reaches an appropriate equilibrium point.

The binding force between the electrode composition for a secondary battery of the present invention and the silicon-based active material increases in the following order. One electrode composition contains only the first polymer chain, and one electrode composition exhibits the weakest adhesion force. This case is a case where a crosslinking agent is added to the first polymer chain, and the adhesion force with the electrode active material is slightly improved as compared with the one electrode composition. Third, the second polymer chains are connected to the first polymer chain through graft polymerization, and the adhesion strength is improved as compared with the first to the second electrode compositions. In the case of No. 4, the second polymer chains are connected to the first polymer chains through graft polymerization, and the second polymer chains are connected to each other through the crosslinking agent. Finally, the oval number is the case where Ca ²⁺ is added to the above-mentioned four times, and shows an improved binding force as compared with the four electrode compositions. In addition, the electrode composition of the fifth electrode has a characteristic that defects on the electrode composition caused by the volume change of the active material are self-healed.

As the electrode composition containing the electrode composition having a strong binding property with the silicon-based active material is included in the electrode, the volume change of the active material due to insertion and desorption of lithium ions is reduced. As the volume change of the active material decreases, the lifetime of the electrode including the active material increases. This is because the greater the change in the volume of the active material, the greater the elution of the active material and the irreversible insertion and desorption of lithium ions occur. Therefore, as the volume change is suppressed, reversible insertion and desorption of lithium ions can be continuously performed, and dissolution of the active material can be prevented, so that the battery capacity can be kept constant.

In addition, as the electrode composition containing a strong binding force with the silicon-based active material is included in the electrode, the high-rate characteristics of the battery are increased. This is because, as the binding force of the electrode composition is stronger, it is possible to enjoy the effect of suppressing the volume change of the active material, which is improved compared to the conventional binder, with only a small amount of the electrode composition. It is possible to increase the amount of simultaneous insertion and desorption of lithium ions by decreasing the addition ratio of the electrode composition and increasing the ratio of the electrode active material.

In addition, the electrode composition of the present invention has the most improved binding power as compared with the conventional binder, and can effectively suppress the volume expansion of the active material even in the smallest amount. In addition, the electrode composition of the present invention has a self-restoring property, and permanent damage to the electrode composition due to the volume expansion of the active material is minimized. Therefore, the electrode composition of the fifth electrode not only improves the capacity of the battery and imparts high-rate characteristics, but also has an improved lifetime characteristic compared with the conventional binder.

An electronic device comprising a lithium secondary battery comprising the electrode composition of the present invention and the lithium secondary battery.

&Lt; Lithium Secondary Battery Containing a Negative Electrode for a Secondary Battery of the Present Invention &

The lithium secondary battery of the present invention includes all conventional lithium secondary batteries such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The lithium secondary battery of the present invention can be produced by a conventional method known in the art. For example, a porous separator may be placed between the anode and the cathode, and a non-aqueous electrolyte may be added. The electrode of the lithium secondary battery can be manufactured by a conventional method known in the art. For example, a slurry is prepared by mixing and stirring a solvent, an optional binder, a conductive material, and a dispersing material in an electrode active material, and then applying (coating) the electrode to a current collector of a metal material, have.

LiCoO ₂ (LCO) having a layered structure, LiMn ₂ O ₄ - (LMO) having a spinel structure, LiFePO ₄ (LFP) having an olivine structure, vanadium oxide having various phases and a crystal structure LVO) may be used, but the present invention is not limited thereto.

The lithium secondary battery may further include a non-aqueous liquid electrolyte as the electrolyte, and the non-aqueous liquid electrolyte may include a non-aqueous electrolyte and a lithium salt.

Examples of the nonaqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, Nitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives , Aprotic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate and ethyl propionate may be used.

In addition, the lithium salt may be dissolved in the non-aqueous liquid electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO _{2 , LiAsF 6, LiSbF 6, LiAlCl} 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, such as chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate, may be used .

In some cases, a solid electrolyte may also be used. Examples of the solid electrolytes include organic solid electrolytes such as polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer including an acid dissociation group, and the like can be considered. Examples of the solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be considered.

In addition, for the purpose of improving the charge-discharge characteristics, the flame retardancy and the like, the lithium-containing battery may further contain an additive. N-substituted oxazolidinones such as pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylenediamine, glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may further be added. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (Propenesultone), FEC (Fluoro-Ethylene carbonate), and the like.

<Electronic equipment>

Since the lithium secondary battery having the negative electrode of the present invention has improved charging characteristics, cycle characteristics, and high rate characteristics, it can be used as a power source for various electronic apparatuses. Examples of electronic devices include air conditioners, washing machines, TVs, refrigerators, freezers, air conditioners, laptops, tablets, smart phones, PC keyboards, PC displays, desktop PCs, CRT monitors, printers, TV, music recorder, music player, oven, range, toilet with washing function, warm air heater, car component, car navigation system, car navigation system, PC peripherals, iron, clothes dryer, window pan, transceiver, blower, ventilation fan Coffee maker, kotatsu, copier, disc changer, radio, razor, juicer, shredder (shredder), coffee maker, coffee maker, coffee maker, air purifier, air purifier, mobile phone, emergency light, flashlight, humidifier, portable karaoke machine ), A water purifier, a lighting device, a dehumidifier, a dish dryer, an electric cooker, a stereo, a stove, a speaker, a trouser press, a vacuum cleaner, Electric toothbrushes, electric feet, electric toothbrushes, electrical appliances, electronic games, electronic games, electronic dictionaries, electronic cookers, electric cookers, electronic calculators, electric carts, electric wheelchairs, electric power tools VCR, facsimile, food processor, air conditioner, air conditioner, air conditioner, hot plate, toaster, hair dryer, electric drill, hot water heater, panel heater, grinder, soldering iron, A mattress, a mixer, a sewing machine, a rice cracker, a floor heating panel, a lantern, a remote control, a cold water heater, a water cooler, a chiller, a word processor, a blower, an electronic musical instrument, a motorcycle, a toy, a lawn mower , Fishing tackle, bicycle, car, hybrid car, plug-in hybrid car, electric car, railroad, ship, airplane, emergency battery have.

The secondary battery according to the present invention is particularly useful for a notebook computer, a tablet, a smart phone, an electric cart, an electric wheelchair, a motorcycle car, a hybrid car, a plug-in hybrid car, an electric car, a railroad, , An emergency battery, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, reference will be made to the specification in more detail with reference to the accompanying drawings and embodiments. It should be understood, however, that the drawings and examples set forth herein may be modified in various ways by those of ordinary skill in the art, and the description herein is not intended to limit the invention to the specific forms disclosed It is to be understood that the invention includes all equivalents and substitutions that fall within the spirit and scope of the present invention. The accompanying drawings are included to provide a further understanding of the present invention to those skilled in the art, and may be exaggerated or reduced in size.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows a reaction formula for obtaining the electrode composition for a secondary battery of the present invention and a structural formula of the composition for the secondary battery. TEMED (Tetra-methyl-ethylene-diamine) is a substance added to stabilize free radicals and increase polymerization reaction rate. APS (Ammonium Persulfate) is used as a polymerization initiator by free radicals. Lt; / RTI &gt; The structural formula represented by Alg is a form in which 3 equivalents of alginate anion is polymerized, and the polymerization pattern is β-anomer. The alginic acid anionic monomer is polymerized to become an example of the first polymer chain of the present invention. AAm (Acryl amide) is polymerized as a monomer of polyacrylamide and is an example of the second polymer chain of the present invention.

It shall collectively refer to Alg, AAm, and Alg- g -PAAm the precursor to obtain the electrode compositions of the present invention. When Alg and AAm are heated at 50 ° C for 3 hours under the APS / TEMED addition condition, Alg- g- PAAm having a structure in which polyacrylamide is graft-polymerized on an alginate anion polymer chain can be obtained. And the inclined g is a graft polymerization. Adding a chemical cross-linker MBAA (N, N'-Methylenebisacrylamide) and physical cross-linking agent Ca ²⁺ in Alg- g -AAm and, when heated to 70 to the reaction conditions in the APS of one example of the electrode composition of the present invention c -Alg- g -PAAm can be obtained. The slanted c means cross-linked.

As can be seen from the general structural formula of c-Alg-g-PAAm, the axial hydroxyl group of the first polymer chain and the second polymer chain were graft-polymerized via the σ _CO- bond Can be confirmed. However, graft polymerization between the equatorial hydroxyl group and the second polymer chain is not impossible.

In addition, it can be confirmed that the α-carbon of the carbonyl group of the second polymer chain and the MBAA as the chemical crosslinking agent form a new σ _CC- bond. This is because the radical located at the alpha -position of the carbonyl group has a stable resonance structure as described above. However, the polymerization site with the crosslinking agent is not necessarily limited to the α-position of the above-mentioned carbonyl group (Carbonyl group). It can be formed by chemical equilibrium with relatively unstable forms of radicals.

Further, as shown in the structural formula of FIG. 1, the alginic acid anion has a symmetrical structure centered on Ca ²⁺ which is a physical crosslinking agent. The Ca ²⁺ and alginate anions are bound by electrostatic attraction, indicating that different alginate anions derived from separate first polymer chains can be physically crosslinked via the Ca ²⁺ .

On the other hand, it is possible to check visually the degree c -Alg- g -PAAm that has a greater density than the reference when a picture of 1, Alg- g -AAm. This is an evidence that by adding a crosslinking agent was added to the structural changes in Alg- g -AAm occurs, it is possible to guess that hageondae Alg- g -AAm indirect evidence has been successfully cross-linked.

The overall structure of c- Alg- g- PAAm, which is an example of the electrode composition of the present invention, is not simple linear as described above. On the c- Alg- g- PAAm, graft polymerization of the first polymer chain and the second polymer chain, physical crosslinking between the first polymer chain and another first polymer chain, between the second polymer chain and another second polymer chain Chemical cross-linking, and so on. By repeating and crossing the above-described various binding modes, the electrode composition of the present invention has a meshed, complicated structure. Such a characteristic of the present invention is not a simple line contact with an active material but also a structural reason for enabling a net contact.

2A is an IR spectrum of the electrode composition for a secondary battery of the present invention and comparative examples. Alg- g- PAAm is a simple mixture of an Alg polymer chain and PAAm, and Alg- mix- PAAm is a simple mixture of an Alg polymer chain and PAAm, in the order from the top of the spectrum, c -Alg is the IR spectrum when only the physical crosslinking agent Ca ²⁺ is added to the Alg polymer chain, and c -Alg- g- PAAm is the IR spectrum when the Alg polymer chain and PAAm are graft-polymerized and physically chemically crosslinked.

IR Spectrum provides indirect information on whether a particular compound contains a specific functional group. For example, it is compared with the vicinity of 3500cm ^-1 absorption of Alg -Alg c and c -Alg- g -PAAm vicinity of 3500cm ^-1 absorption is confirmed that made wider. This is evidence that a strong bond is formed between the Ca ²⁺ added as a physical crosslinking agent and the carboxylate anion (hydroxyl group) of the alginate anion. Further, there is absorbed a c -Alg- g -PAAm spectral absorption of 3195cm ^-1 and 3400cm ^-1 on a comprises as by expansion and contraction of a σ bond _NH derived from the MBAA, the amine groups in the c -Alg- g -PAAm It becomes indirect evidence. Therefore, it can be inferred from the above evidence that both physical and chemical crosslinking are included in the structure of c- Alg- g- PAAm.

FIG. 2B is an IR spectrum of the electrode composition for a secondary battery of the present invention and a comparative example when added to a negative electrode active material containing Si. FIG. Alg- g -PAAm is a precursor of the electrode composition of the present invention the first and second polymer chains between polymer chains but grafting polymerization is formed, as a composition that does not include a physical cross-linking agent and a chemical cross-linker. c- Alg- g- PAAm is an example of the electrode composition of the present invention in which graft polymerization is formed between the first polymer chain and the second polymer chain, and also includes a physical crosslinking agent and a chemical crosslinking agent.

In the spectrum of FIG. 2B, the spectrum of a pure silicon-based anode active material containing no electrode composition exhibits strong absorption particularly at around 1150 cm ^-1 . It is believed to be absorption by Si-O-Si bond. The absorption at about 1150 cm ^-1 is observed to be reduced by adding the electrode composition of the present invention and the precursor of the electrode composition. This is because the new σ _SiO bond formed between the electrode composition such as a silicon-based negative active material is being lost some binding existing SiO. Further, if included the Alg-g-PAAm and c -Alg- g -PAAm has to observe a large absorption in the vicinity of 3500cm ^-1, which can be so much as the absorption of hydroxide groups to amine groups. In addition, the sharp absorption near 1400 cm ^{-1 in} the absorption of c- Alg- g- PAAm is due to the expansion and contraction of the sigma _CN bond, suggesting the presence of a chemical crosslinking agent.

Therefore, in view of the above, not only the physical crosslinking agent and the chemical crosslinking agent are included in the c- Alg- g- PAAm which is an example of the electrode composition of the present invention, but also the c- Alg- g- It can be deduced that a new chemical bond (σ _SiO ) is formed between the anode active materials.

{Example}

Example 1: c -Alg- g -PAAm Electrode composition

2.8 g of Na-Alg and 10 g of AAm were dissolved in 80 ml of distilled water, APS (0.06 g) / TEMED (0.055 g) was added, and the mixture was heated at 50 ° C for 3 hours to obtain Alg- g- PAAm. Alg- g -PAAm is an exemplary one first polymer chain (Alg) and second polymer chains (PAAm) the graft-polymerization. The melting Alg- -PAAm g of distilled water and stirred at room temperature to prepare a solution of 5 wt%. Then, CaCl2, MBAA, and APS were added to the solution and stirred for 30 minutes. As a result of the stirring, a viscous hydrogel was obtained. The hydrogen was allowed to stand at 80 for 4 hours to obtain an electrode composition crosslinked physically and chemically.

Example 2: c -Alg- g -PAAm and a silicon-based negative electrode active material,

The melting Alg- -PAAm g of distilled water and stirred at room temperature to prepare a solution of 5 wt%. The above solution was mixed with silicon, graphite, water-dispersed CNT as a conductive agent, and heated to prepare an electrode slurry. The mass ratio of silicon to graphite was about 20 wt% to 60 wt%. Alg- g -PAAm the conductive agent was included approximately 13wt%, 7wt%. A small amount of CaCl2 and MBAA was added to the electrode slurry, stirred, applied to a copper foil, and heated in an oven at 70 for 3 hours. After heating, it was dried at 70 캜 under vacuum for 12 hours. At this time, care was taken so that the loading mass could be between 1.2 mg / cm ^-2 and 1.4 mg / cm ^-2 .

Example 3: A lithium secondary battery including the negative electrode of Example 2

A CR2032 type coin half cell was prepared, including the negative electrode obtained through the method described in Example 2 above. 0.4 wt% LiBF ₄ was contained as an electrolyte, and a polypropylene film was used as a separator.

Comparative Example 1: Electrode composition which is Alg

Alg polymer chain was added to distilled water and stirred to prepare a 5 wt% solution

Comparative Example 2: A negative electrode comprising an electrode composition of Alg and a silicon-based negative electrode active material

A negative electrode was prepared in the same manner as in Example 2 except that a solution containing 5 wt% of Alg was added.

Comparative Example 3: A lithium secondary battery including a negative electrode of Comparative Example 2

A lithium secondary battery was prepared in the same manner as in Example 3 except that the negative electrode of Comparative Example 2 was included.

Comparative Example 4: Alg- g -PAAm Electrode composition

Except that a physical crosslinking agent and a chemical crosslinking agent were additionally added, the remaining steps were carried out in the same manner as in Example 1 to prepare an electrode composition which is an electrode composition of Alg- g- PAAm.

Comparative Example 5: Synthesis of Alg- g -PAAm and a silicon-based negative electrode active material,

A negative electrode was prepared in the same manner as in Example 2 except that a solution containing 5 wt% of Alg- g- PAAm was added.

Comparative Example 6: A lithium secondary battery including a negative electrode of Comparative Example 5

A lithium secondary battery was prepared in the same manner as in Example 3 except that the negative electrode of Comparative Example 5 was included.

Comparative Example 7: c -Alg electrode composition

Except that the step of allowing the second polymer chain (PAAm) to be graft-polymerized to the first polymer chain was omitted and the chemical crosslinking agent (MBAA) was not added, the same procedure as in Example 1 was repeated to prepare c -Alg. &Lt; / RTI &gt;

Comparative Example 8: c -Alg &lt; / RTI &gt; and a silicon-based negative active material,

A negative electrode was prepared in the same manner as in Example 2 except that a solution containing 5 wt% of c- Alg was added.

Comparative Example 9: A lithium secondary battery including a negative electrode of Comparative Example 8

A lithium secondary battery was prepared in the same manner as in Example 3 except that the negative electrode of Comparative Example 8 was included.

Interaction between electrode composition and electrolyte

3 is a graph comparing the amounts of organic electrolytes absorbed by the electrode composition for a secondary battery of the present invention and Comparative Examples. The black bar labeled Alg on the X-axis shows the amount of electrolyte absorption of the electrode composition of Comparative Example 1. [ The red bar labeled Alg indicates the electrolyte uptake of the electrode composition of Comparative Example 3. [ Black bars shown Alg- g -PAAm d on the X-axis indicates the absorption of the electrolyte of the electrode composition of the Comparative Example 2. Alg- g -PAAm la shown red bar indicates the electrolyte absorption of the electrode composition according to the first embodiment.

The electrode composition of Example 1 showed an electrolyte uptake of less than 2% on average, but the electrode composition of the comparative example showed up to 12% of electrolyte uptake. This is presumably because the electrode composition of Example 1 has a more compact structure and there is no void space in the electrode composition. The fact that the amount of electrolyte absorption is small indicates that the interaction with the electrolyte is small, and the electrode composition of Example 1 is a factor having strong binding force with the negative electrode active material.

Interaction between the electrode composition and the negative electrode active material

4 is a graph showing the binding force between the electrode composition for a secondary battery of the present invention and a comparative example and a negative electrode active material containing Si / C. A black bar labeled Si / C-Alg on the X-axis indicates the binding force between the electrode composition of Comparative Example 1 and the Si / C negative active material. The red bar labeled Si / C-Alg on the X-axis indicates the binding force between the electrode composition of Comparative Example 3 and the Si / C negative active material. A black bar labeled Si / C-Alg- g -PAAm on the X-axis indicates the binding force between the electrode composition of Comparative Example 2 and the Si / C negative active material. The red bar labeled Si / C-Alg- g -PAAm on the X-axis indicates the binding force between the electrode composition of Example 1 and the Si / C negative active material.

The binding force between the electrode composition and the negative active material can be estimated by measuring the force required to peel off the electrode by 180 ^° . The average force required for peeling was 20 times or more higher when the electrode composition of Example 1 was included than when the electrode composition of Comparative Example 1 was included. When the electrode composition of Example 1 was contained in comparison with Comparative Example 2, it was confirmed that the bonding force was increased by about 1 Newton per unit area.

Comparison of battery characteristics

<Cycle characteristics of battery>

FIG. 5 shows a cyclic voltammetry result of a lithium secondary battery having a negative electrode including the electrode composition for a secondary battery of the present invention and Comparative Examples. The red line represents Example 3, the black line represents Comparative Example 3, the blue line represents Comparative Example 6, and the green line represents Comparative Example 9.

Referring to FIG. 5, it can be seen that the maximum and minimum currents are the same in all four cases, so that lithium is inserted and removed in the batteries of Example 3 and Comparative Example through the same mechanism. Further, it can be confirmed that the battery of Example 3 exhibits improved cycle characteristics as compared with the battery of Comparative Example. In particular, it can be seen that the battery of Example 3 has an increased current value in the overall range from 0 V to 2 V as compared to the batteries of the comparative example. This fact suggests that the electrode composition of Example 1 suppresses the volume change of the negative electrode active material most effectively, and the reversible insertion and desorption of lithium ions can occur quickly and quickly.

&Lt; Life characteristics of battery &

FIG. 6A is a graph comparing cell capacities of a lithium secondary battery having a negative electrode including the electrode composition for a secondary battery of the present invention and comparative examples according to charge and discharge. The red dot represents Example 3, the black dot represents Comparative Example 3, the blue dot represents Comparative Example 6, and the green dot represents Comparative Example 9.

It can be confirmed that the battery of Example 3 has a higher discharge capacity than that of the batteries of the comparative example from the beginning. This is an observation result that is consistent with the fact observed in FIG. Further, when the charging and discharging were repeated 100 times, the discharge capacity of the battery of Example 3 was reduced by only about 10%, while the batteries of Comparative Example were reduced to as much as 50% (the battery of Comparative Example 3) have. It can be deduced that the electrode composition of Example 1 effectively suppresses the change in the volume of the negative electrode active material and most effectively prevents irreversible deformation of the negative electrode active material from the point of view that the life of the battery is not reduced even after repeated charging and discharging. The fact that the cell of Example 3 exhibits the highest Coulomb efficiency also supports this fact.

&Lt; High-rate characteristics of battery &

FIG. 6B is a graph comparing the discharge characteristics of a lithium secondary battery having a negative electrode containing the electrode composition for a secondary battery of the present invention and Comparative Examples, respectively, at different current rates. The red dot represents Example 3, the black dot represents Comparative Example 3, the blue dot represents Comparative Example 6, and the green dot represents Comparative Example 9.

Referring to FIG. 6B, the battery of Example 3 not only exhibits the highest discharge capacity even when the non-end current is 0.1 C, but also exhibits the highest discharge capacity even at 10 C. The ratio of the discharge capacity at a discharge capacity of 0.2 C at 10 C in the battery of Example 3 is 83%, which is much larger than that of batteries of the comparative example. The batteries of the comparative examples were 24% (Comparative Example 3), 61% (Comparative Example 6) and 15% (Comparative Example 9), respectively.

This means that the battery of Example 3 has the most stable cycle characteristics and has a high rate characteristic. Due to the strong binding force between the electrode composition of Example 1 and the Si / C negative active material, volume change is limited even when sudden lithium ion insertion and desorption occurs, and volume change is limited, so that a larger amount of lithium ions can be stably moved .

&Lt; Variation of Thickness of Cathode &

FIG. 7 is a graph comparing changes in the thickness of the negative electrode containing Si / C with each of the electrode composition and the comparative example of the secondary battery of the present invention during charging and discharging. The red dot and the red line represent Example 2, the black dot and black line represent Comparative Example 2, the blue dot and blue line represent Comparative Example 4, the green dot and the green line represent Comparative Example 6.

Referring to FIG. 7, lithium ions are inserted into the cathode while the voltage falls to about 5 mV in the vicinity of about 3 V. The volume of the Si / C cathode increases from about 10 hours. It can be confirmed that the change in the volume of the cathode including the electrode composition of Example 1 is delayed most and occurs only in the vicinity of 25 hours. It can be confirmed that the thickness of the negative electrode including the electrode composition of Example 1 was increased by only 97% even in the vicinity of about 40 hours where the insertion of lithium ions was the maximum. The measurement result of the change in the cathode volume is a direct basis that the electrode composition of the embodiment 1 can suppress the volume change of the silicon-based cathode most effectively as compared with the comparative examples.

In addition, after 40 hours, the lithium ions are released from the cathode and the voltage is kept constant. It should be noted that the volume change of the negative electrode appears before and after insertion and desorption of lithium ions. The negative electrode containing the electrode composition of Example 1 showed only a 4% change in thickness before and after one charge / discharge cycle. In the case of the negative electrode containing the electrode composition of Comparative Example 7 showing the best performance among the comparative examples, when the change in thickness before and after charging and discharging reaches 83%, the thickness of the negative electrode including the electrode composition of Example 1 Of only 4% shows a remarkable performance of the electrode composition of the present invention.

It is believed that the negative electrode containing the electrode composition of Example 1 exhibits a thickness variation of only 4% before and after a single charge / discharge operation because the reversibility of insertion and desorption of lithium ions is maintained when the electrode composition of Example 1 is included . Reduction shows that the irreversible structural change of the silicon-based cathode and the accumulation of strain are remarkably small. From the above characteristics, it can also be rationalized that the negative electrode comprising the electrode composition of Example 1 exhibits improved cycle characteristics.

Claims (16)

A first polymer chain having at least one anion group, a second polymer chain having two or more metal cations interacting with the anion groups of the first polymer chains to fix the first polymer chains to each other, and a first polymer having the at least one anion group A second polymer chain linked through a covalent bond with the chain; And
And a crosslinking agent polymerized on the second polymer chains to connect the second polymer chains.
The method according to claim 1,
Wherein the first polymer chains are polysaccharides.
3. The method of claim 2,
The first polymer chains include alginic acid, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl guar gum, carboxymethyl xanthane gum, carboxymethyl starch, Carboxymethyl tara gum, low methoxyl pectin, carrageenan, cellulose, amylose, chitosan, glucose, sucrose, maltose, lactose, starch, and glycogen And at least one polymer selected from the group consisting of the following.
3. The method of claim 2,
The at least one anionic group is _{^{-CO 2 -, -SO 2 -,}} -SO 3 -, -OSO 3 -, -PO 3 2-, -OPO 3 2-, -OP (OH) O -, -CS 2 - or -OCO &lt; _{2 &gt;} ^{- &lt;} _{- &} gt ;.
The method of claim 3,
Wherein the bivalent or higher metal cation is a cation of an alkaline earth metal, a bivalent or higher transition metal, or an alloy thereof.
The method according to claim 1,
Wherein the second polymer chains include an acrylic polymer.
The method according to claim 6,
The acrylic polymer may be selected from the group consisting of polyacrylamide, poly (methacrylic acid), poly (methyl acrylate), poly (methyl methacrylate) Wherein the polymer composition comprises at least one polymer selected from the group consisting of polyacrylic acid, polyacrylic acid, and polyacrylonitrile.
6. The method of claim 5,
Wherein the second polymer chains include an acrylic polymer.
9. The method of claim 8,
The acrylic polymer may be selected from the group consisting of polyacrylamide, poly (methacrylic acid), poly (methyl acrylate), poly (methyl methacrylate) Wherein the polymer composition comprises at least one polymer selected from the group consisting of polyacrylic acid, polyacrylic acid, and polyacrylonitrile.
10. The method of claim 9,
The crosslinking agent may be selected from the group consisting of ethylene glycol di (meth) acrylate and derivatives thereof, or N, N'-Alkylenebisacrylamide and derivatives thereof And at least one selected from the group consisting of a metal oxide and a metal oxide.
11. The method of claim 10,
Wherein the N, N'-Alkylenebisacrylamide is N, N'-Methylenebisacrylamide. 10. The electrode composition for a secondary battery according to claim 1, wherein the N, N'-alkylenebisacrylamide is N, N'-methylenebisacrylamide.
A first polymer chain having at least one anion group, a second polymer chain having two or more metal cations interacting with the anion groups of the first polymer chains to fix the first polymer chains to each other, and a first polymer having the at least one anion group A second polymer chain linked through a covalent bond with the chain; And
And a crosslinking agent polymerized on the second polymer chains to connect the second polymer chains,
The first polymer chains include alginic acid, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl guar gum, carboxymethyl xanthane gum, carboxymethyl starch, Carboxymethyl tara gum, low methoxyl pectin, carrageenan, cellulose, amylose, chitosan, glucose, sucrose, maltose, lactose, starch, and glycogen At least one polymer selected from the group consisting of:
The divalent or more metal cations are alkaline earth metals, transition metals having a valence of 2 or more, or cations of alloys thereof,
The second polymer chains may be selected from the group consisting of polyacrylamide, poly (methacrylic acid), poly (methyl acrylate), poly (methyl methacrylate) methyl methacrylate), polyacrylic acid, and polyacrylonitrile. In the present invention,
Wherein the crosslinking agent comprises N, N'-methylenebisacrylamide (N, N'-methylenebisacrylamide), and the negative electrode active material comprises silicon.
13. The method of claim 12,
Wherein the negative electrode further comprises carbon as a negative active material, and the mass ratio of the silicon to the carbon is 1: 3.
14. The method of claim 13,
Wherein the mass ratio of the electrode composition for a secondary battery and the negative electrode active material is 1: 5.
A lithium secondary battery comprising the negative electrode for the secondary battery according to claim 12.
An electronic device comprising the lithium secondary battery of claim 15.

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