KR20150040141A - Negative electrode material for secondary battery and method for manufacturing the same - Google Patents

Abstract

In the present invention, provided are a negative electrode, which has negative electrode active materials and accordingly improves stability and performance, and a lithium secondary battery including the same. The present invention relates to a negative electrode active material, comprising a core which has silicon particles or a silicon based compound particle; and a polydopamine layer formed on the core, a manufacturing method thereof and a negative electrode including the same.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material for a secondary battery and a method for manufacturing the negative electrode active material for a secondary battery,

The present invention relates to a negative electrode active material for a secondary battery having improved dispersibility, a method for producing the negative electrode active material, and a negative electrode including the same.

Recently, miniaturization and weight reduction of electronic equipment and general use of portable electronic devices have led to active research on lightweight lithium secondary batteries having high energy density as their power source.

The lithium secondary battery generates electrical energy by oxidation and reduction reactions in which lithium ions are inserted and removed from the cathode and the anode.

Recently, a silicon-based material having a maximum capacity of about 4020 mAh / g (9800 mAh / cc, specific gravity: 2.23) as the negative electrode material is used in combination with a carbonaceous material, Researches for realizing a battery are emerging.

However, when the above-mentioned silicon based material is used as a negative electrode material, an extreme volume change occurs during charging and discharging, resulting in an increase in electrical resistance, a decrease in battery efficiency, and a shortened battery cycle life. This phenomenon is further exacerbated as the silicon content is increased in order to produce a cell having a high energy density.

In order to overcome such disadvantages, SiO ₂ nano-domains, which are inactive materials, are distributed around the silicon-based material to minimize particle cleavage, and a carbon coating layer is additionally introduced into the surface of the negative electrode active material (SiO 2 / C negative electrode active material) And a method of improving electrical conductivity.

However, when the carbon coating layer is introduced, the electrical conductivity is improved, but the chemical functionalization of the surface is originally blocked due to the chemical inertness of the carbon layer, and the dispersibility of the active material in the slurry is lowered There are disadvantages.

As a result, the binder, the conductive material, and the like that are mixed together at the time of manufacturing the electrode are not uniformly mixed with the negative electrode active material, so that a partial coagulation region is generated on the electrode, thereby increasing the internal resistance of the electrode, And deterioration of the secondary battery is promoted.

Accordingly, in order to produce a high-capacity high-capacity secondary battery, it is urgently required to develop a negative electrode active material having a novel structure with improved dispersibility.

The present invention provides a negative active material for a secondary battery having improved dispersibility and a method for producing the same.

Also, the present invention provides a negative electrode having improved stability and performance characteristics by including the negative active material, and a lithium secondary battery having the negative electrode.

Specifically, the present invention provides

A core comprising silicon particles or silicon-based compound particles; And

And a polypopamine layer formed on the surface of the core.

At this time, the silicon particles or the silicon compound particles may include a carbon layer.

The present invention also relates to a method for producing a negative electrode active material for a secondary battery, comprising the step of mixing a dopamine compound and a core containing silicon particles or silicon compound particles in the presence of a weak basic buffer solution based on distilled water to form a polypopamine layer on the surface of the core .

The present invention also provides a negative electrode comprising the negative active material.

In addition, the present invention provides a negative electrode comprising: the negative electrode; Separation membrane; And a non-aqueous electrolyte.

According to the present invention, it is possible to provide a negative electrode active material for a secondary battery having improved dispersibility by coating a surface of a negative electrode active material containing a core containing silicon particles or silicon compound particles with a polydodamine compound to modify the surface. Therefore, it is possible to manufacture a negative electrode having reduced internal resistance and a secondary battery having improved cycle efficiency by including it.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description of the invention serve to further the understanding of the technical idea of the invention, But is not limited to.
1 is a photograph showing the result of measurement of dispersibility according to Experimental Example 1 of the present invention.
2 is a graph showing a TGA measurement result of a secondary battery according to Experimental Example 2 of the present invention.
3 is a graph showing the results of measurement of powder resistance of a secondary battery according to Experimental Example 4 of the present invention.
FIG. 4A is a graph showing the results of capacitance measurement during charging and discharging of the secondary battery according to Experimental Example 4 of the present invention. FIG.
4B is a graph showing a cycle measurement result of the secondary battery according to Experimental Example 4 of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

First, according to an embodiment of the present invention,

A core comprising silicon particles or silicon-based compound particles; And

And a polypopamine layer formed on the surface of the core.

In the negative electrode active material for a secondary battery according to the present invention, the silicon particles or the silicon-based compound particles may be at least one selected from the group consisting of Si, SiOx (0 <x? 2) and Si-Z alloy (Z is Mg, Ca, Sr, Ba, , La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, , One or more elements selected from the group consisting of Cd, B, Ge, P, As, Sb, Bi, S, Se, Te, Po, (SiOx) (0 < x &lt; = 2).

In the negative electrode active material of the present invention, the total content of the polypodamine is preferably 5.5 to 30 wt%, more preferably about 10 to 25 wt%, based on the total weight of the negative electrode active material. If the dopamine content is greater than 30 wt%, the resistance of the negative electrode active material is increased. If the dopamine content is less than 5.5 wt%, a portion where the polypodamine layer is not formed may occur on the surface of the negative electrode active material.

At this time, in the negative electrode active material of the present invention, the polydopamine layer may be coated along the core surface in a curved shape with a thickness of at least 10 nm to a thickness of at most about 60 nm.

In addition, it is preferable that the total average particle diameter of the negative electrode active material of the present invention in which the polypodamine layer is formed is about 1 탆 to about 20 탆.

On the other hand, the above-mentioned polydodamine is a polymer substance obtained by polymerizing a dopamine compound which is a catecholamines-based compound having a catechol group represented by the following general formula (1) It is known to impart hydrophilicity and excellent adhesion to all the substrates regardless of the surface properties of the resin or resin. Moreover, it is known that the surface-modified substrate is capable of a second-order surface modification through covalent bonding between catechol functional groups and amine functional groups and thiol functional groups ((1) BP Lee et al., Annu. Rev. Mater. Res. 41, 99 (2011) and (2) Lee et al., Science 318, 426 (2007)).

[Chemical Formula 1]

As described above, in the present invention, by introducing a polycondopamine layer containing a large amount of a catechol group on the surface of carbon-coated silicon particles or silicon compound particles, it is possible to produce a negative electrode active material having improved surface hydrophilicity and improved dispersibility. Accordingly, when the electrode is manufactured using the negative electrode active material, the effect of improving the negative electrode performance for the secondary battery can be obtained by minimizing the intergranular agglomeration.

Further, in the negative electrode active material of the present invention, the silicon particles or the silicon based compound particles may include a carbon layer.

At this time, the carbon layer is not particularly limited as long as it can absorb and desorb lithium ions, and may be formed of a crystalline carbon-based compound, an amorphous carbon-based compound, or a mixture thereof.

In the negative electrode active material of the present invention, the carbon content may be about 20 parts by weight or less, for example about 1 to 20 parts by weight, based on 100 parts by weight of the total of the negative electrode active material, taking into account the appropriate electrical conductivity. If the carbon content is less than 1 part by weight, it does not have a sufficient conduction path. If the carbon content is more than 20 parts by weight, the battery capacity may decrease.

At this time, the carbon layer preferably has a thickness of 1 to 50 nm or less.

In an embodiment of the present invention,

Mixing a dopamine compound with a core containing silicon particles or silicone compound particles in the presence of a weak basic buffer solution based on distilled water to form a polypodamine layer on the surface of the core.

At this time, in the method of the present invention, the carbon layer is not particularly limited, but may be formed using a crystalline carbon-based compound, an amorphous carbon-based compound, or a mixture thereof as a precursor.

In addition, the carbon layer forming step may be formed by a conventional dry coating method or a liquid coating method, and is not limited thereto.

Examples of the dry coating method include vapor deposition or chemical vapor deposition (CVD), and the liquid coating method includes an impregnation or spray method. If a liquid coating method is used, DMSO, THF, or the like may be used as a solvent.

Specifically, the carbon layer forming step may be performed by coating a carbon precursor on the surface of a core including silicon particles or silicon compound particles, followed by heat treatment in an inert atmosphere such as argon or nitrogen. At this time, the heat treatment process may be performed by heating at a temperature of about 400 ° C to about 1200 ° C for about 1 hour to about 10 hours. That is, the carbon precursor may be carbonized by the heat treatment to form a carbon coating layer on the core surface.

In addition, in the method for manufacturing an anode active material of the present invention, the step of forming the polydopamine layer may be carried out by stirring at room temperature for 3 to 10 hours. If the stirring time is less than 3 hours, a portion where the polypopamine layer is not formed on the surface of the anode active material may occur. If the stirring time is more than 10 hours, the thickness of the polypodamine coating layer may increase and the resistance may increase.

The pH of the weakly basic buffer solution based on the distilled water is preferably 8.5.

Specifically, the step of forming the polydopamine layer may be performed by sequentially adding a dopamine compound and a core coated with a carbon layer while stirring a weakly basic (pH 8.5) buffer solution (Tris-HCl) based on distilled water at room temperature . At this time, during the stirring process, the weakly basic solvent is used as a catalyst, and a spontaneous polymerization reaction occurs between the dopamine compounds to form a polypopamine layer on the surface of the core. At this time, the coating thickness of the polypodamine layer can be controlled by controlling the agitation time.

As described above, in the method of manufacturing the anode active material of the present invention, since the weakly basic water is used as the reaction solvent in the step of forming the polypodamine layer, it is environmentally friendly and can be coated on various surfaces regardless of the organic / inorganic substrate. Particularly, when the polypodamine layer having high chemical stability is additionally formed on the surface of the negative electrode active material as in the present invention, the surface of the negative electrode active material is effectively converted into hydrophilic property without any side effect such as internal resistance or physical damage of the negative electrode active material, The dispersibility of the negative electrode active material can be improved.

In addition, the method of the present invention for producing a negative electrode active material may further include washing and drying a negative electrode active material on which a polydopamine layer formed by filtering after forming a polypodamine layer is formed.

In addition, in the method of manufacturing an anode active material of the present invention, a secondary surface modification reaction such as a Michael addition or a schiff-base reaction is further performed on the anode active material on which the polydopamine layer is formed By introducing various functional groups or the like, the physical properties and the like of the surface of the negative electrode active material can be further modified.

Also, an embodiment of the present invention provides a negative electrode for a secondary battery comprising the negative active material of the present invention. At this time, the negative electrode for a secondary battery may be manufactured by applying an anode active material containing a polydopamine layer of the present invention and an anode active material slurry further comprising a conductive material, a binder or a filler on the anode current collector, followed by drying .

At this time, the negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the negative electrode current collector is made of at least one of stainless steel, nickel, copper, titanium and alloys thereof Can be used, and generally has a thickness of 3 to 500 mu m.

The conductive material is used for imparting conductivity to the electrode. Any conductive material may be used without causing any chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And a conductive material such as a polyphenylene derivative may be mixed and used. The conductive material is a component for further improving the conductivity of the electrode active material, and may be contained in an amount of 1 to 10% by weight based on the total weight of the electrode active material.

The binder may be an organic binder, an aqueous binder, or a combination thereof as a component that assists in bonding between the negative electrode active material and the conductive material using the transition metal oxide and bonding to the current collector. The organic binder means a binder dissolved or dispersed in an organic solvent, particularly N-methylpyrrolidone (NMP), and the aqueous binder means a binder in which water is used as a solvent or a dispersion medium.

Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyimide, poly But are not limited to, amide imide, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber and fluorine rubber.

The binder may include 1 to 20% by weight based on the total weight of the negative electrode active material. If the binder content is less than 1 wt%, the adhesive force between the electrode active material and the current collector may be insufficient. If the binder content is more than 20 wt%, the content of the electrode active material may be decreased to increase the battery capacity and resistance.

On the other hand, the filler is not particularly limited as long as it is a fibrous material without causing chemical change in the battery, and is used selectively as a component for suppressing the expansion of the electrode. For example, the filler may be an oligomeric polymer such as polyethylene, My; Fibrous materials such as glass fibers and carbon fibers are used.

At this time, the content of the conductive material, the binder, the filler, and the like may be appropriately and optionally included within a range that does not deteriorate the performance of the electrode.

In still another embodiment of the present invention, there is provided a negative electrode comprising the negative active material of the present invention; A cathode comprising a cathode active material; And a non-aqueous electrolyte, thereby providing a lithium secondary battery having improved cycle characteristics.

In addition, the present invention can provide a middle- or large-sized battery pack including a plurality of the lithium secondary batteries electrically connected to each other. The middle- or large-sized battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicle; Or a power storage system, as shown in FIG.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It should be noted, however, that the examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Example

( Anode active material  Produce)

The dopamine compound and silicon compound particles (SiO ₂ ) were added sequentially in the amounts shown in Table 1 while stirring the weakly basic (pH 8.5) buffer solution (tris-HCl) based on distilled water at room temperature, To prepare a negative electrode active material comprising a core containing silicon-based particles (SiO ₂ ) and a polydopamine layer formed in a curved shape with an average thickness of 50 nm on the core surface. The negative electrode active material thus obtained was washed three times through a filtering process and then dried in an oven at 85 캜 for 24 hours.

(Example 3: Production of secondary battery)

The anode active material having the respective polypodamine layers prepared in Example 1, the polyamideimide binder, and the carbon black conductive material were mixed in an N-methylpyrrolidone solvent in an 8: 1: 1 weight ratio to prepare a negative electrode active material slurry Examples 4 to 6), respectively. A negative electrode was prepared by a conventional electrode manufacturing process in which each of the negative electrode active material slurries was applied to a Cu-foil current collector.

Next, LiCoO ₂ cathode active material, polyvinylidene fluoride binder and carbon black conductive material were mixed in N-methylpyrrolidone solvent to prepare a cathode active material slurry. The mixing ratio of the cathode active material, the binder and the conductive material was 94: 3: 3 by weight. The positive electrode was prepared by a conventional electrode manufacturing process in which the positive electrode active material slurry was applied to an Al-foil current collector.

A coin-type secondary battery was fabricated by a conventional process using the positive electrode, the negative electrode, and the non-aqueous electrolyte. As the non-aqueous electrolyte, a mixed solvent of ethylene carbonate and ethyl methyl carbonate (3: 7 by volume) in which 1.0 M of LiPF ₆ was dissolved was used.

( Example  4: manufacture of secondary battery)

Except that the anode active material prepared in Example 2 was used instead of the anode active material prepared in Example 1, the negative electrode and the secondary battery including the same were manufactured in the same manner as in Example 3 Respectively.

( Comparative Example  2: Manufacture of secondary battery)

Except that the anode active material prepared in Comparative Example 1 was used instead of the anode active material formed with the polydopamine layer prepared in Example 1, the negative electrode and the secondary battery including the negative electrode active material were manufactured in the same manner as in Example 3 Respectively.

( Experimental Example  One. Negative active material  Dissolution test)

The negative electrode active material including the polydodamine coating layer of Example 1 and the negative active material (SiOx / C) containing commercially available silicon particles were put into distilled water and the sedimentation rate was measured. After 10 minutes, the sedimentation rate was measured. As a result, a considerable amount of the negative electrode active material including the polypodamine coating layer of Example 1 was precipitated, but the negative active material of Comparative Example was found to have a poor degree of precipitation (see FIG. 1). These results show that the present invention improves the surface hydrophilicity and improves the dispersibility by including the poly dopamine coating layer in the case of the negative electrode active material.

( Experimental Example  2. Experiment to measure loss ratio of negative electrode active material)

A TGA 2050 thermogravimetric analysis (TGA) of TA Instruments Co., Ltd. was loaded on the balance and the negative electrode active material formed with the polydopamine layer prepared in Examples 1 and 2 and the negative electrode active material prepared in Comparative Example 1 were loaded on balance. The loss rate was measured by varying the weight of the sample as a function through the temperature change process for 12 hours while flowing the gas.

2, the negative electrode active material of Comparative Example 1 in which the polypodamine layer was formed to have a thin thickness had little loss of the mass at a temperature of 650 degrees or less, whereas the negative electrode of Examples 1 and 2, in which the polypodamine layer was formed, In the case of the active material, it can be confirmed that the mass loss is caused by burning of polypodamine.

( Experimental Example  3. Negative active material Powder  Resistance comparison experiment)

The negative electrode active material prepared in Example 1 and the negative electrode active material prepared in Comparative Example 1 were placed in a measuring container having a predetermined volume and then the powder resistance was measured according to the change in density while the pressure was applied. 3, the powder resistances of the negative active material of Example 3 and the negative active material of Comparative Example 2 were found to be similar to each other.

That is, in the case of the negative electrode active material coated with the organic material, polypodamine, as in the present invention, it is confirmed that the resistance does not increase sharply, and thus it is understood that the surface modification is possible.

( Experimental Example  4. Performance test of secondary battery

The charging, discharging capacity and life span of the coin-type secondary battery manufactured in Example 3 and the coin-type secondary battery prepared in Comparative Example 2 were measured using a conventional coin cell measuring method (charging 0.1C and discharging 0.1C) (0.5C / 1C) was measured. 4A and 4B, it was confirmed that the secondary battery of Example 6 and the secondary battery of Comparative Example 4 had similar charge, discharge capacity, and 50 cycle life characteristics.

Claims (13)

A core comprising silicon particles or silicon-based compound particles; And
And a polypopamine layer formed on the surface of the core. The method according to claim 1,
The silicon particles or the silicon-based compound particles may be at least one selected from the group consisting of Si, SiOx (0 <x? 2) and Si-Z alloy (Z is Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ti, Zr, , Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, , An element selected from the group consisting of Sb, Bi, S, Se, Te, Po, and combinations thereof, and is not Si). Active material. The method according to claim 1,
Wherein the total content of polypodamine in the negative electrode active material is from 5.5 to 30% by weight based on the total weight of the negative electrode active material. The method according to claim 1,
Wherein the polydopamine layer is coated along the surface of the core in a curved shape with a thickness of at least 10 nm to a thickness of at most 60 nm. The method according to claim 1,
Wherein the anode active material having the polydopamine layer formed thereon has a total average particle diameter of 1 占 퐉 to 20 占 퐉. The method according to claim 1,
Wherein the silicon particles or the silicon based compound particles comprise a carbon layer. Mixing a dopamine compound with a core containing silicon particles or silicon compound particles in the presence of a weak basic buffer solution based on distilled water to form a polypodamine layer on the surface of the core. The method of claim 7,
Wherein the step of forming the polypodamine layer is performed by stirring at room temperature for 3 to 10 hours. The method of claim 7,
Wherein the distilled water-based weak basic buffer solution has a pH of 8.5. The method of claim 7,
Wherein the method further comprises, after the step of forming the polypodamine layer, washing and drying the negative electrode active material on which the recovered polypodamine layer is formed. The negative electrode current collector,
And a negative electrode active material according to claim 1 formed on the negative electrode current collector. The method of claim 11,
Wherein the negative electrode active material further optionally comprises a conductive material, a binder or a filler. A negative electrode according to claim 12;
anode;
A separator interposed between the cathode and the anode, and
A lithium secondary battery comprising a non-aqueous electrolyte.

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