KR20170031337A - Core-shell silicon composite, method for preparaing the same, and negative electrode active material for rechargeable lithium battery comprising the same - Google Patents

Abstract

The present invention relates to a core-shell silicon composite, a method for preparing the same, and a negative electrode active material for a lithium secondary battery including the same. The core-shell silicon composite includes: a core including a carbon matrix and silicon (Si) nanoparticles located in a carbon matrix; and a shell surrounding the core. The core-shell silicon composite effectively controls volume expansion of Si due to charging and discharging so as to form a stable SEI layer on an outer side of the core-shell silicon composite when the core-shell silicon composite is applied as the negative electrode active material of the lithium secondary battery, and accordingly, a lifespan characteristic of the battery is improved. In addition, high mechanical strength and optimum filling density are provided, so that durability of the electrode and performance of the battery are improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a core-shell silicone composite, a core-shell silicon composite, a method for producing the same, and a negative electrode active material for a lithium secondary battery comprising the same. BACKGROUND ART [0002] CORE- SHELL SILICON COMPOSITE, METHOD FOR PREPARATION THE SAME, AND NEGATIVE ELECTRODE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY COMPRISING THE SAME

The present invention relates to a core-shell silicone composite, a process for producing the same, and a negative electrode active material for a lithium secondary battery comprising the same.

2. Description of the Related Art Lithium secondary batteries (for example, lithium ion batteries), nickel metal hydride batteries, and other secondary batteries are becoming increasingly important as power sources for vehicle-mounted power supplies and portable terminals such as notebook computers. Particularly, a lithium secondary battery capable of obtaining a light energy with a high energy density can be preferably used as a high output power source for mounting on a vehicle, and it is expected that there will be an increase in demand in the future.

The lithium secondary battery is manufactured by using a material capable of inserting and desorbing lithium ions as an active material of a negative electrode, providing a porous separator between the positive electrode and the negative electrode, injecting a liquid electrolyte, Electricity is generated or consumed by the redox reaction by insertion and desorption.

Specifically, various types of carbon-based materials including artificial graphite, natural graphite, hard carbon, and soft carbon capable of inserting and separating lithium have been applied to the negative electrode active material in lithium secondary batteries. The graphite used as the negative electrode active material of the carbon series exhibits a high discharge voltage of 3.6 V as well as an advantage in terms of the energy density of the lithium secondary battery and the long life of the lithium secondary battery Widely used. However, since the density of graphite (theoretical density 2.2 g / cc) is low in the production of the graphite active material, the capacity is low in terms of the energy density per unit volume of the electrode plate, and a side reaction with the organic electrolyte used tends to occur at high voltage. There has been a problem of capacity reduction.

In order to solve such a problem of the carbon-based negative electrode active material, a Si-based negative electrode active material having a very high capacity relative to graphite has been developed and studied. However, a high-capacity Si-based anode material is accompanied by a severe volume change during charging and discharging, resulting in particle cleavage and poor lifetime characteristics. Specifically, a silicon or silicon oxide (SiO _x , 0 < x < 2) -type anode active material alloyable with a lithium ion and capable of de-alloying has a volume expansion up to 300%. During such volume expansion and contraction, the SiO _x -based anode active material is physically subjected to severe stress and pulverization. As a result, the existing SEI layer is destroyed and a new interface is formed and a new SEI layer is formed. This causes continuous decomposition of the electrolytic solution and consumption of lithium ions, thereby deteriorating the cycle characteristics of the battery. In addition, during the continuous charging / discharging, the conductive structure is destroyed by the volume expansion / contraction of the SiO _x based negative electrode active material, the durability of the electrode is lowered, and the battery life is deteriorated.

To solve this problem, a composite containing voids capable of buffering the volume expansion has been proposed. However, in the case of a composite including a void structure, the composite tends to be crushed during the rolling process during the production of the electrode, and it is difficult to manufacture an electrode with a high loading amount because the density is low.

In order to solve this problem, a nanotube type SiO _x has been developed, but it has a problem that it is difficult to manufacture due to its difficult manufacturing process and high unit cost.

Korean Patent Publication No. 2008-0018737 (published on February 28, 2008)

It is an object of the present invention to provide a negative active material for a lithium secondary battery which can effectively control the volume expansion of Si due to charging and discharging and form a stable SEI layer on the outer side of the core- Shell silicone composite having excellent filling density and capable of improving durability and cell performance of an electrode, and a method for manufacturing the same.

Still another object of the present invention is to provide a negative electrode active material for a lithium secondary battery, a negative electrode and a lithium secondary battery which can improve the durability of the electrode and the life of the battery including the core-shell silicone composite.

According to one embodiment of the present invention, there is provided a core-shell silicone composite comprising a core comprising a carbon matrix and silicon (Si) nanoparticles located in the carbon matrix, and a shell surrounding the core.

The core may include a plurality of silicon nanoparticles, and the silicon nanoparticles may be aggregated through the carbon matrix.

The core-shell silicone composite may include an internal void within the shell.

The core-shell silicone composite may include an internal cavity formed between the core and the shell.

The carbon matrix may include internal voids within the carbon matrix.

The inner cavity and the silicon nanoparticles may be included in the core-shell silicon composite at a volume ratio of 1: 1 to 6: 1.

The core-shell silicon composite may satisfy the following condition (1).

[Equation 1]

1? R / x? 1.8

(Where r is the radius of the internal space of the core-shell silicon composite other than the shell and x is the radius of the virtual particle having the same volume as all the silicon particles in the core)

The shell may comprise silicon oxide.

The silicon oxide may be SiO _x where x is a real number between 1 and 2, and the silicon oxide may be SiO ₂ .

The shell may be included in an amount of 10 to 150 parts by weight based on 100 parts by weight of the silicon nanoparticles.

The average particle diameter (D50) of the core-shell silicone composite may be 50 nm to 50 탆.

The average particle diameter (D50) of the silicon nanoparticles may be 10 nm to 5 mu m.

According to another embodiment of the present invention, there is provided a method of manufacturing a carbon nanotube, comprising: preparing a core precursor by mixing a carbon matrix precursor and silicon (Si) nanoparticles; preparing a shell surrounding the core precursor; Shell silicon composite comprising the steps of:

In the step of carbonizing the carbon matrix precursor, the carbon matrix precursor may be carbonized and shrunk to form an internal gap between the core and the shell.

Also, in the step of carbonizing the carbon matrix precursor, the carbon matrix precursor may be carbonized, and an internal void may be formed in the carbon matrix.

The temperature for carbonizing the carbon matrix precursor may be 200 to 1000 ° C.

The carbon matrix precursor may be any one selected from the group consisting of a heterocyclic aromatic compound, polyphenol, polydodamine, monosaccharide, disaccharide, dicyanodiamide, urea, and mixtures thereof.

The silicon nanoparticles may be mixed in an amount of 5 to 90 parts by weight based on 100 parts by weight of the carbon matrix precursor.

The precursor for forming the shell may be used in an amount of 10 to 300 parts by weight based on 100 parts by weight of the core precursor.

According to another embodiment of the present invention, there is provided a negative active material for a lithium secondary battery comprising the core-shell silicon composite.

According to another embodiment of the present invention, there is provided a negative electrode comprising the negative active material.

According to another embodiment of the present invention, a lithium secondary battery including the negative electrode is provided.

The core-shell silicon composite according to the present invention is characterized in that, when a core-shell silicon composite having a core-shell structure is manufactured, a structure containing voids capable of buffering against the volume expansion of Si is formed inside the shell containing Si And forming a coating layer having a high mechanical property on the outer surface of the shell so that the volume expansion of Si proceeds into the interior of the composite body. Thus, the volume of Si due to charging / discharging when applied as an anode active material of a lithium secondary battery It is possible to form a stable SEI layer on the outer side of the core-shell silicon composite by effectively controlling the expansion, and it has high mechanical strength and high packing density, thereby improving the durability of the electrode and the battery performance.

1 is a schematic cross-sectional view illustrating volume change of a core-shell silicon composite according to an embodiment of the present invention during charging / discharging.
2 is a schematic cross-sectional view illustrating a method of manufacturing a core-shell silicon composite according to another embodiment of the present invention.
3 is a schematic view illustrating a structure of a lithium secondary battery according to another embodiment of the present invention.
4 and 5 are photographs of the core-shell silicon composite prepared in Production Examples 1 and 2 of the present invention by scanning electron microscopy (SEM).
6 is a graph showing the capacity retention characteristic measured in Experimental Example 2 of the present invention.
FIGS. 7 and 8 are SEM photographs of the core-shell silicon composite measured before and after charge-discharge as measured in Experimental Example 3 of the present invention. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as "comprises" or "having" are used to designate the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

The core-shell silicon composite according to an embodiment of the present invention includes a core including a carbon matrix and silicon (Si) nanoparticles located in the carbon matrix, and a shell surrounding the core.

At this time, the core-shell silicone composite may include an inner cavity in the shell. The inner cavity may be formed between the core and the shell, or may include an inner cavity formed inside the carbon matrix as the carbon matrix is made of porous carbon.

The inner cavity formed between the core and the shell may be a space which is completely continuous between the core and the shell to completely or partially separate the core from the shell, The core and the shell are partially in contact with each other and are formed only in a portion where the core and the shell are not in contact with each other by the rugged surface of the core. But it is to be understood that the present invention is not limited to these examples and includes any form including a void space between the core and the shell.

Si, normally used as an anode active material, reacts with lithium to exhibit a theoretical maximum capacity of about 4000 mAh / g. However, when the volume expansion of the Si causes the SEI layer attached to the Si surface to be removed, a new Si interface is exposed, or a crack is generated or broken in the Si particles to expose a new Si interface, and the exposed interface and the electrolyte And the process of generating a new SEI layer is repeated. As the reaction is repeated, a thick SEI layer is formed to increase the impedance and deplete the electrolyte, thereby deteriorating battery life characteristics.

On the other hand, in the present invention, a shell, which is a coating layer of silicon oxide having an excellent strength characteristic as compared with Si, is formed on the outer surface of the core containing Si so that the volume expansion of Si is directed to the inside of the core- The core-shell silicon composite is formed so as to include internal voids capable of exhibiting a buffering action by absorbing stress generated during volume expansion of Si between the core and the shell. Thus, when applied as an anode active material of a lithium secondary battery, It is possible to form a stable SEI layer on the outer side of the core-shell silicon composite by effectively controlling the volume expansion of the Si due to the high mechanical strength and high filling density to improve the durability of the electrode and the battery performance .

In the core-shell composite, the core includes a carbon matrix and silicon nanoparticles located in the carbon matrix. Specifically, the core may be a plurality of the silicon nanoparticles aggregated through the carbon matrix. The core may have a roughly spherical shape, but the present invention is not limited thereto, and the silicon nanoparticles may protrude from the surface of the core in a rugged manner as a plurality of the silicon nanoparticles are aggregated through the carbon matrix.

The carbon matrix may be formed by carbonizing the carbon matrix precursor, and the carbon matrix precursor may be any carbon precursor that is generally used. For example, the carbon matrix precursor may be a heteroaromatic compound, , Polycaprolactone, polydipamine, monosaccharide, disaccharide, dicyanodiamide, urea, and mixtures thereof. Specifically, the heterocyclic aromatic compound may be melamine or the like, and the disaccharide may be sucrose or the like , But the present invention is not limited thereto. Further, in addition to the above-mentioned dicyanodiamide or urea, any of N-doped carbon containing nitrogen may be used.

The carbon matrix may include voids formed in the carbon matrix as the carbon matrix precursor is formed of carbonized porous carbon. The internal voids formed inside the carbon matrix may further buffer the volume expansion of the silicon nanoparticles with internal voids formed between the core and the shell.

The average particle diameter (D50) of the silicon nanoparticles may be 10 nm to 5 mu m, and preferably 50 to 500 nm. When the average particle diameter of the silicon nanoparticles is less than 10 nm, the dispersion of the silicon nanoparticles may not be smoothly performed in the production of the core-shell silicon composite, resulting in the formation of agglomerated silicon nanoparticles, which may be difficult to form an effective conductive path, The size of the core-shell silicon composite increases to several tens of micrometers, which is not suitable for the production of a battery, and the breakdown of the silicon nanoparticles is continuously generated to generate particles having no electrical contact with the carbon matrix in the core- .

On the other hand, in the core-shell silicone composite, a shell is located on the outer surface of the core. The shell may be made of a material having high strength properties to direct the volume expansion of the silicon nanoparticles of the core toward the interior of the core-shell silicone composite. The shell may be any material such as an oxide or a sulfide capable of transferring lithium ions while having high strength characteristics. As a specific example, the shell may include silicon oxide, but the present invention is not limited thereto. The silicon oxide may specifically be SiO _x (where x is a real number of 1 to 2), more specifically SiO or SiO ₂ .

The shell may be 10 to 150 parts by weight based on 100 parts by weight of the silicon nanoparticles. When the shell is less than 10 parts by weight based on 100 parts by weight of the silicone nanoparticles, it is difficult to control the stress due to the volume expansion of the silicon nanoparticles toward the outer surface of the shell. When the shell is in excess of 150 parts by weight, The initial efficiency may be lowered or the movement of lithium ions may be disturbed and the rate characteristic may be deteriorated or the capacity of the active material may be difficult to manifest.

When the average particle diameter (D50) of the core-shell silicone composite is 50 nm to 50 占 퐉, the specific surface area is reduced and a small amount of binder and conductive material are required, so that the amount of active material in the electrode can be increased.

The core-shell silicone composite should have a porosity capable of sufficiently absorbing the stress generated upon volume expansion of the silicon nanoparticles of the core.

The inner cavity and the silicon nanoparticles contained in the core-shell silicon composite may be in the range of 1: 1 to 6: 1, preferably 1: 1 to 5: 1, in consideration of the volume expansion of the silicon nanoparticles, 1 &lt; / RTI &gt; by volume. Wherein the volume of the silicon nanoparticles is the sum of the volumes of all the silicon nanoparticles contained within the core-shell silicon composite. When the volume ratio of the internal voids is less than 1, the volume of the voids is so small that the volume expansion of the silicon nanoparticles can not be effectively mitigated. When the volume ratio of the internal voids is more than 6, the mechanical strength of the core- Or the core-shell silicone composite may be fractured in the slurry preparation step.

Accordingly, it is preferable that the core-shell silicon composite satisfies the following formula (1).

[Equation 1]

1? R / x? 1.8

In Equation (1), r is the radius of the internal space of the core-shell silicon composite other than the shell, and x is the radius of a virtual particle having a volume equal to the volume of all the silicon particles in the core. On the other hand, the porosity of the core-shell silicone composite can be measured substantially by mercury porosimetry.

1 is a schematic cross-sectional view illustrating volume change of a core-shell silicon composite according to an embodiment of the present invention during charging / discharging.

1, a core-shell silicon composite according to an embodiment of the present invention includes a core 110 having a plurality of silicon nanoparticles 111 interposed between the carbon matrix 112, And a shell 120 surrounding the core 110 and containing silicon oxide. At this time, an inner space 130 is formed between the core 110 and the shell 120 for buffering the expansion of the silicon nano-particles 111. Meanwhile, internal voids may also be formed in the carbon matrix 112.

When the silicon nanoparticles 111 of the core 110 expand due to a change in volume due to charging and discharging, the silicon nanoparticles 111 are separated by the shell 120 located on the outer surface of the core 110 111 is limited within the core-shell silicone composite 100, and as a result, expansion pressure is absorbed by the inner cavity 130 of the core-shell silicon composite 100, and exhibits a buffering action.

The core-shell silicon composite having the above structure is obtained by mixing a carbon matrix precursor and silicon (Si) nanoparticles to prepare a core precursor, preparing a shell surrounding the core precursor, And then carbonizing the mixture.

Describing each step in detail, Step 1 is a step of producing a core precursor.

Specifically, the core precursor may be prepared by removing the solvent by spray-drying a solution prepared by mixing the carbon matrix precursor and the silicon nanoparticles, or by adding the precursor of the carbon matrix precursor And polymerizing the polymer.

The carbon matrix precursor may be any of those generally used as a carbonizable precursor, and examples thereof include heterocyclic aromatic compounds, polyphenols, polycondensates, monosaccharides, disaccharides, dicyanodiamides, ureas, and mixtures thereof And the heterocyclic aromatic compound may be melamine or the like, and the disaccharide may be sucrose or the like, but the present invention is not limited thereto. Further, in addition to the above-mentioned dicyanodiamide or urea, any of N-doped carbon containing nitrogen may be used.

Since the silicon nanoparticles are as described above, repetitive description thereof will be omitted.

However, the content of the silicon nanoparticles may be 5 to 90 parts by weight, preferably 15 to 50 parts by weight, based on 100 parts by weight of the carbon matrix precursor. When the amount of the silicon nanoparticles is less than 5 parts by weight based on 100 parts by weight of the carbon matrix precursor, the amount of the active material in the core-shell silicone composite may be small and the capacity per weight may be small. The volume of pores in the shell silicon composite is small and the volume expansion of the silicon nanoparticles can not be effectively mitigated and can be broken.

Step 2 is then the step of forming a shell on the core precursor.

As described above, the shell may be any material such as an oxide or a sulfide capable of transferring lithium ions while having high strength characteristics, and specific examples thereof may include silicon oxide. Hereinafter, the case where the shell is a silicon oxide will be described in detail, but the present invention is not limited thereto.

The shell may be formed by applying a composition containing a silicon oxide precursor such as TEOS (tetraethyl orthosilicate) or the like onto the particles of the core precursor prepared in the step 1 by coating, spraying or impregnation, -gel &lt; / RTI &gt; reaction.

Alternatively, when the chemical vapor deposition growth method is used, the step may be carried out by mixing the core precursor particles prepared in the above step 1 with a gas-phase silicon-containing compound mixed with an oxidizing gas and then depositing the mixture.

The oxidizing gas may be oxygen, chlorine, carbon dioxide, air, or the like.

In addition, the gas phase silicon-containing compound gas and the oxidizing gas are preferably mixed in a volume ratio of 0.5: 1 to 2: 1, more preferably 1: 1 to 1.5: 1.

The silicon oxide precursor for forming the shell may be used in an amount of 10 to 300 parts by weight based on 100 parts by weight of the core precursor. When the content of the silicon oxide precursor is less than 10 parts by weight based on 100 parts by weight of the core precursor, it is difficult to control the stress due to the volume expansion of the silicon nanoparticles toward the outer surface of the shell. When the amount exceeds 300 parts by weight, There is a possibility that the initial efficiency is greatly lowered due to the irreversible reaction between SiO _x and lithium ions.

Finally, step 3 is a step of carbonizing the carbon matrix precursor to prepare the core precursor as a core.

The carbon matrix precursor shrinks when carbonized, wherein an internal void is formed between the core and the shell.

Specifically, the temperature for carbonizing the carbon matrix precursor may be 200 to 1000 캜, and preferably 400 to 800 캜. If the carbonization temperature is less than 200 ° C, the carbon matrix precursor may be incompletely carbonized. If the carbonization temperature exceeds 1000 ° C, the carbon matrix precursor may be economically unnecessary. More specifically, it is preferable that the carbonization is carried out in three stages of 200 to 500 ° C, 500 to 700 ° C, and 700 to 1000 ° C in that the carbon matrix precursor can completely carbonize and form the voids.

2 is a schematic cross-sectional view showing a method of manufacturing the core-shell silicon composite.

Referring to FIG. 2, a core precursor is prepared by mixing the carbon matrix precursor 113 and the silicon nanoparticles 111, and a shell 120 containing silicon oxide is formed to surround the core precursor The carbon matrix precursor 113 is carbonized so that the carbon matrix 112 and the core 110 are formed and an internal cavity 130 is formed between the core 110 and the shell 120.

The core-shell silicon composite produced by the above-described production method has a specific structure to suppress the volume change of Si due to charging / discharging of the battery when it is applied as an anode active material of a lithium secondary battery, A stable SEI layer can be formed. As a result, lifetime characteristics of the battery can be improved. Moreover, it is possible to improve the durability of the electrode and the battery performance by having an optimal packing density with high mechanical strength.

Accordingly, according to another embodiment of the present invention, there is provided a negative electrode comprising the above-mentioned core-shell silicon composite as a negative electrode active material.

The negative electrode may be prepared by mixing a negative electrode active material, a binder and optionally a conductive material in a solvent to prepare a composition for forming a negative electrode active material layer, and then coating the composition on an anode current collector.

In the composition for forming the negative electrode active material layer, the negative electrode active material is the same as that described above. The negative electrode active material may be contained in the composition in an amount of 1 to 99% by weight based on the total weight of the negative electrode active material layer, more preferably 10 to 98% by weight. If the content is out of the above range, there is a fear that the binding force with the current collector is lowered due to the reduction of the capacity or the relative amount of the binder.

In addition, the binder serves to adhere the electrode active material particles to each other and to adhere the electrode active material to the current collector well. Specific examples include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, There can be mentioned polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber or copolymers thereof and one or a mixture of two or more thereof have. The binder is preferably contained in the composition for forming an anode active material layer, more preferably in an amount of 2 to 10 wt%, in an amount such that the binder is 1 to 20 wt% based on the total weight of the anode active material layer.

The conductive material is used for imparting conductivity to the electrode and serving as a lubricant between the active material particles to improve the expansion and lifetime characteristics of the electrode plate. In the battery constituted by the electroconductive material, Available. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; And conductive polymers such as polyphenylene derivatives. Of these, one type or a mixture of two or more types may be used.

The conductive material is preferably contained in an amount such that the conductive material is 20% by weight or less based on the total weight of the anode active material layer, more preferably 1 to 10% by weight. If the content of the conductive material exceeds 20% by weight, the energy density in the electrode may be lowered.

As the solvent, a solvent such as water, dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP) or acetone may be used.

The negative electrode current collector may be any metal selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be carbon, nickel , Titanium or silver. The alloy may be preferably an aluminum-cadmium alloy. In addition, a non-conductive polymer surface-treated with a conductive material, a conductive polymer, or the like may be used.

The method of applying the prepared composition for forming a negative electrode active material layer to the negative electrode current collector may be selected from known methods in consideration of the characteristics of materials and the like or may be carried out by a new suitable method. For example, it is preferable that the composition for forming the negative electrode active material layer is dispersed on the negative electrode current collector and uniformly dispersed using a doctor blade or the like. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, methods such as die casting, comma coating, and screen printing may be used.

According to another embodiment of the present invention, there is provided a lithium secondary battery comprising the core-shell silicon composite produced according to the above-described production method as a negative electrode active material.

Specifically, the lithium secondary battery includes a positive electrode including a positive electrode active material disposed opposite to each other, a negative electrode including a negative active material, and a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution. Do.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery and a lithium polymer battery according to the type of the separator and the electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type.

3 is an exploded perspective view of a lithium secondary battery according to another embodiment of the present invention. 3 is an illustration for illustrating the present invention, but the present invention is not limited thereto.

3, the lithium secondary battery 1 includes a separator 7 disposed between a cathode 3, an anode 5, the cathode 3, and an anode 5 to form an electrode assembly 9 And placing it in the case 15 and injecting an electrolyte (not shown) so that the negative electrode 3, the positive electrode 5 and the separator 7 are impregnated into the electrolyte.

Conductive lead members 10 and 13 for collecting a current generated during a battery operation can be attached to the cathode 3 and the anode 5 respectively and the lead members 10 and 13 are respectively connected to the anode 5, And the current generated in the cathode (3) can be led to the positive electrode terminal and the negative electrode terminal.

The positive electrode 5 is prepared by mixing a positive electrode active material, a conductive material and a binder in the same manner as the negative electrode 3 to prepare a composition for forming a positive electrode active material layer. The composition for forming the positive electrode active material layer is then applied to a positive electrode current collector Followed by rolling. It is also possible to produce the positive electrode plate by casting the positive electrode active material composition on a separate support, then peeling the film from the support, and laminating the film on the metal current collector.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Specifically, a lithium-containing transition metal oxide may be preferably used. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 < 0 <b <1, 0 < c <1, a + b + c = 1), LiNi 1 -y Co y O 2, LiCo 1 - y Mn y O 2, LiNi 1 - y Mn y O 2 (O≤ y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O ₄ , LiMn _{2 - z} Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more thereof. In addition to these oxides, sulfide, selenide and halide may be used.

The conductive material and the binder are the same as those described above for the cathode.

On the other hand, the electrolyte includes an organic solvent and a lithium salt.

The organic solvent may be any organic solvent that can act as a medium through which ions involved in an electrochemical reaction of a battery can move. Specifically, examples of the organic solvent include an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a carbonate solvent, etc. These solvents may be used singly or in combination of two or more.

Specific examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, But are not limited to, ethyl propionate,? -Butyrolactone, decanolide,? -Valerolactone, mevalonolactone,? -Caprolactone (? -caprolactone, 隆 -valerolactone, 竜 -caprolactone, and the like.

Specific examples of the ether solvent include dibutyl ether, tetraglyme, 2-methyltetrahydrofuran, tetrahydrofuran, and the like.

Specific examples of the ketone-based solvents include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, xylene, (xylene), and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane and diethoxy ethane.

Specific examples of the carbonate solvent include dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate (EPC) , Methyl ethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC) And fluoroethylene carbonate (FEC).

The lithium salt can be used without any particular limitation as long as it is a compound capable of providing lithium ions. Specifically, the lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) _{2 , LiN (C 2 F 5 SO} 2) 2, LiN (CF 3 SO 2) 2, LiN (C a F 2a + 1 SO 2) (C b F 2b + 1 SO 2) ( However, a and b is a natural number , Preferably 1? A? 20 and 1? B? 20), LiCl, LiI, LiB (C ₂ O ₄ ) ₂ and mixtures thereof.

When the lithium salt is dissolved in the electrolyte, the lithium salt functions as a source of lithium ions in the lithium secondary battery 1 and can accelerate the movement of lithium ions between the anode 5 and the cathode 3. Accordingly, it is preferable that the lithium salt is contained in the electrolyte at a concentration of approximately 0.6M to 2M. If the concentration of the lithium salt is less than 0.6M, the ion conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If the concentration exceeds 2M, the viscosity of the electrolyte may be increased and the lithium ion mobility may be lowered. Considering the conductivity of the electrolyte and the mobility of lithium ions, it is more preferable that the lithium salt is controlled to be approximately 0.7 M to 1.6 M in the electrolyte.

The electrolyte further includes an additive (hereinafter, referred to as "other additive") which can be generally used for an electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing the decrease of battery capacity, and improving the discharge capacity of the battery in addition to the electrolyte components can do.

Examples of the other additives include vinylene carbonate (vinylenecarbonate, VC), metal fluoride (metal fluoride, for example, LiF, RbF, TiF, AgF , AgF2, BaF 2, CaF 2, CdF 2, FeF 2, HgF ₂ , Hg ₂ F ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF _{3, GdF 3, FeF 3,} HoF 3, InF 3, LaF 3, LuF 3, MnF 3, NdF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3, _{YbF 3, TIF 3, CeF 4} , GeF 4, HfF 4, SiF 4, SnF 4, TiF 4, VF 4, ZrF4 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6 , WF ₆ , CoF ₂ , CoF ₃ , CrF ₂ , CsF, ErF ₃ , PF ₃ , PbF ₃ , PbF ₄ , ThF ₄ , TaF ₅ and SeF ₆ ), glutaronitrile Succinonitrile (SN), adiponitrile (AN), 3,3'-thiodipropionitrile (TPN), vinylethylene carbonate (VEC) Fluoroethylene carbo Fluoroethylene carbonate (FEC), difluoroethylenecarbonate, fluorodimethylcarbonate, fluoroethylmethylcarbonate, lithium bis (oxalato) borate, LiBOB ), Lithium difluoro (oxalate) borate, LiDFOB, lithium (malonato oxalato) borate, LiMOB) and the like. Of these, 1 Or a mixture of two or more species. The other additives may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

The separator 7 is not particularly limited as long as it is used as a separator in a lithium secondary battery. In particular, it is preferable that the separator 7 is low in resistance against ion movement of the electrolyte and excellent in electrolyte wettability. Specifically, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer may be used alone Or they may be laminated. Alternatively, nonwoven fabrics made of conventional porous nonwoven fabrics such as glass fibers of high melting point, polyethylene terephthalate fibers and the like may be used, but the present invention is not limited thereto.

Although the cylindrical lithium secondary battery 1 has been described as an example in the present embodiment, the present invention is not limited to the cylindrical lithium secondary battery 1, and any shape can be used as long as it can operate as a battery.

As described above, since the lithium secondary battery including the negative electrode active material according to the present invention stably exhibits excellent discharge capacity, cycle life characteristics and rate characteristics, it can be used for a mobile phone, a notebook computer, a digital camera, a camcorder (HEVs), plug-in HEVs (PHEVs) and the like, as well as medium to large-sized energy storage systems.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[Production example: Production of silicone composite]

(Production Example 1)

Melamine and formaldehyde were added to water at a weight ratio of 1: 1 and heated to 100 占 폚 and stirred. And 50 parts by weight of silicon nanoparticles (average particle size (D50): 250 nm) were added to a stirred solution of a solution of pluronic F127 in water at the same weight ratio as that of melamine and 100 parts by weight of melamine, followed by addition of 2 ml of hydrochloric acid Lt; / RTI &gt; and stirred for a period of time to prepare a core precursor.

Next, the prepared core precursor was put into a mixed solvent of ethanol and water (ethanol: water = 4: 1 by volume), and TEOS and ammonia water were added to form a SiO ₂ shell surrounding the surface of the core precursor.

(Average particle diameter (D50): 2.5 mu m) was prepared by carbonizing the melamine of the core precursor by heat treatment at 400 DEG C, 600 DEG C and 800 DEG C for 2 hours each.

(Production Example 2)

20 parts by weight of TEOS and ammonia water were added to 100 parts by weight of the core precursor (ethanol: water = 4: 1 by volume) in the solvent mixture of ethanol and water prepared in Preparation Example 1 to prepare the core precursor The core-shell silicone composite was prepared in the same manner as in Example 1, except that the SiO ₂ shell was formed to surround the surface of the core-shell silicon composite.

[Example: Preparation of half cell]

(Example 1)

(CNT) as a conductive material and polyvinylidene fluoride (PVDF) as a binder were added to NMP (N-methylpyrrolidone) at a weight ratio of 8: 1: 1 And mixed to prepare an anode active material slurry. The slurry was coated to a thickness of 50 탆 on a copper foil having a thickness of 20 탆 (tape coating) and dried in a vacuum oven at 120 캜 for 24 hours to prepare a working electrode.

A coin half cell was fabricated using Li foil (150 mu m) as the working electrode and the counter electrode. A battery was constructed by using an electrolytic solution in which a polyethylene porous film was interposed between a working electrode and a counter electrode and 1M LiPF ₆ was dissolved in DEC / FEC as an electrolyte. The inside of the coin half cell was argon atmosphere and sealed to block the air.

(Comparative Example 1)

A half cell was fabricated in the same manner as in the above example, except that silicon (Si) powder was used as the negative electrode active material.

[Experimental Example 1: Observation of shape of core-shell silicon composite]

The core-shell silicon composites prepared in Preparation Examples 1 and 2 were observed with a scanning electron microscope (SEM), and the results are shown in FIGS. 4 and 5. FIG.

4 and 5, the core-shell silicon composite prepared in Preparation Example 1 is somewhat irregular in shape, while the core-shell silicon composite produced in Production Example 2 has a spherical composite Can be confirmed.

[Experimental Example 2: Measurement of Capacity Retention Ratio of Half Cells]

The capacity retention characteristics were measured for the half cells prepared in the above Examples and Comparative Examples.

Specifically, the half cells prepared in the above example were charged / discharged at a current density of 0.5 C at a room temperature (25 캜) within a range of 1 to 0.05 V, and repeatedly carried out 50 times, And the results are shown in Table 1 and FIG. 6 below.

Normalized retention (@ 50 ^th cycle) Example 1 88% Comparative Example 1 67%

Referring to Table 1 and FIG. 6, it can be seen that the half cell of the embodiment including the core-shell silicon composite of the present invention as a negative electrode active material has a better capacity retention ratio than the half cell of the comparative example.

[Experimental Example 3: Observation of shape of core-shell silicon composite after charge / discharge]

In Experimental Example 2, after 50 cycles of charging / discharging, the core-shell silicon composite used in Example 1 was observed with a scanning electron microscope (SEM), and the results are shown in FIGS. FIG. 7 is a scanning electron microscope photograph before charging / discharging, and FIG. 8 is a scanning electron microscopic photograph after 50 cycles of charging / discharging.

Referring to FIGS. 7 and 8, it can be seen that almost all of the composites maintain the same shape as the first embodiment even after 50 cycles of charging and discharging the core-shell silicone composite used in Example 1. That is, it can be seen that the shell is not broken due to the volume expansion of the silicon nanoparticles at the time of charging and discharging. It can be seen that the core-shell silicon composite has a stable SEI layer at the outer periphery of the composite.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

1: Lithium secondary battery
3: cathode
5: anode
7: Separator
9: Electrode assembly
10, 13: lead member
15: Case
100: core-shell silicone composite
110: Core
111: Silicon nanoparticles 112: Carbon matrix
113: Carbon matrix precursor
120: Shell
130: Internal clearance

Claims (23)

A core comprising a carbon matrix and silicon (Si) nanoparticles located in the carbon matrix, and
The shell surrounding the core
&Lt; / RTI &gt; The method according to claim 1,
Wherein the core comprises a plurality of silicon nanoparticles,
Wherein the silicon nanoparticles are agglomerated via the carbon matrix. The method according to claim 1,
Wherein the core-shell silicon composite comprises an interior void within the shell. The method of claim 3,
Wherein the core-shell silicone composite comprises an inner cavity formed between the core and the shell. The method of claim 3,
Wherein the carbon matrix comprises an interior void within the carbon matrix. The method of claim 3,
Wherein the internal voids and the silicon nanoparticles are contained in the core-shell silicon composite in a volume ratio of 1: 1 to 6: 1. The method of claim 3,
Wherein the core-shell silicon composite meets the conditions of the following formula (1).
[Equation 1]
1? R / x? 1.8
(Where r is the radius of the internal space of the core-shell silicon composite other than the shell and x is the radius of the virtual particle having the same volume as all the silicon particles in the core) The method according to claim 1,
Wherein the shell comprises silicon oxide. 9. The method of claim 8,
Wherein the silicon oxide is SiO _x where x is a real number between 1 and 2. 10. The method of claim 9,
The core of the silicon oxide is an SiO ₂ - the shell of silicon composite. The method according to claim 1,
Wherein the shell is contained in an amount of 10 to 150 parts by weight based on 100 parts by weight of the silicon nanoparticles. The method according to claim 1,
Wherein the core-shell silicon composite has an average particle size (D50) of 50 nm to 50 [mu] m. The method according to claim 1,
Wherein the average particle diameter (D50) of the silicon nanoparticles is 10 nm to 5 占 퐉. Preparing a core precursor by mixing a carbon matrix precursor and silicon (Si) nanoparticles,
Fabricating a shell surrounding the core precursor, and
Carbonizing the carbon matrix precursor
&Lt; / RTI &gt; 15. The method of claim 14,
Wherein the carbon matrix precursor is carbonized and contracted to form an inner cavity between the core and the shell in the step of carbonizing the carbon matrix precursor. 15. The method of claim 14,
Wherein the step of carbonizing the carbon matrix precursor carbonizes the carbon matrix precursor to form an inner cavity in the carbon matrix. 15. The method of claim 14,
Wherein the temperature for carbonizing the carbon matrix precursor is 200 to 1000 ° C. 15. The method of claim 14,
Wherein the carbon matrix precursor is any one selected from the group consisting of a heterocyclic aromatic compound, polyphenol, polydodamine, monosaccharide, disaccharide, dicyanodiamide, urea, and mixtures thereof. 15. The method of claim 14,
Wherein the silicon nanoparticles are mixed in an amount of 5 to 90 parts by weight based on 100 parts by weight of the carbon matrix precursor. 15. The method of claim 14,
Wherein the precursor for forming the shell is used in an amount of 10 to 300 parts by weight based on 100 parts by weight of the core precursor. A negative electrode active material for a lithium secondary battery comprising the core-shell silicone composite according to claim 1. An anode comprising the anode active material according to claim 21. 23. A lithium secondary battery comprising a negative electrode according to claim 22.

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