WO2016053031A1 - Anode active material for lithium secondary battery, method for manufacturing same, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to an anode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery comprising the same. The anode active material comprises a surface-treated silicon nanoparticle, wherein the surface-treated silicon nanoparticle comprises a silicon nanoparticle and a surface treatment layer which is positioned on the surface of the silicon nanoparticle and includes crystalline SiO₂, so that the anode active material, when being applied to a battery, can exhibit excellent lifespan and capacity characteristics as well as remarkably improved initial efficiency characteristics.

Description

Anode active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery comprising same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 2014-0133435 dated October 2, 2014 and Korean Patent Application No. 2015-0137455 dated September 30, 2015. The contents are included as part of this specification.

Technical Field

The present invention relates to a negative electrode active material for a lithium secondary battery, a method for preparing the same, and a lithium secondary battery including the same, which can exhibit a markedly improved initial efficiency characteristic with excellent life and capacity characteristics when applied to a battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used. In particular, as the market expands from small lithium secondary batteries used in portable devices to large secondary batteries used in automobiles, high capacity and high output technology of negative electrode active materials is required. Therefore, the development of non-carbon negative electrode active materials, such as silicon, tin, germanium, zinc, and lead, which has a higher theoretical capacity than the carbon-based negative electrode active materials, is being developed.

Among them, the silicon-based negative electrode active material has a capacity (4190 mAh / g) more than 11 times higher than the theoretical capacity (372 mAh / g) of the carbon-based negative electrode active material, has been spotlighted as a material for replacing the carbon-based negative electrode active material. However, when only silicon is used, since the volume expansion of the material is more than three times when lithium ion is inserted, the battery capacity tends to decrease as charging and discharging proceeds, and safety problems also occur, requiring much technical development to commercialize. do.

In addition, the silicon-based active material has a problem of high initial efficiency but low lifespan characteristics as compared to silicon oxide (SiO) -based active material. In order to improve this, a method of using nano-sized silicon has been studied. One of the most common methods for preparing nano-sized silicon is a method of crushing large silicon particles to produce nano-sized, specifically, tens of to 100 nm silicon particles. However, the method is susceptible to surface oxidation on the silicon surface during the grinding process, the initial efficiency is reduced by the amorphous SiO ₂ generated on the surface as a result of the oxidation.

The first technical problem to be solved by the present invention is to provide a negative electrode active material for a lithium secondary battery and a method of manufacturing the same, which can exhibit a significantly improved initial efficiency characteristics with excellent life and capacity characteristics when applied to a battery.

The second technical problem to be solved by the present invention is to provide a negative electrode, a lithium secondary battery, a battery module and a battery pack including the negative electrode active material.

In order to solve the above problems, the present invention comprises a surface-treated silicon nanoparticles, the surface-treated silicon nanoparticles are located on the surface of the silicon nanoparticles, and the silicon nanoparticles, comprising crystalline SiO ₂ It provides a negative electrode active material for a lithium secondary battery comprising a surface treatment layer.

The surface of the invention comprises heat-treating the silicon nano-particles including the amorphous SiO ₂ on the surface after mixing and alkali metal compounds by converting the amorphous SiO ₂ to a crystalline SiO _2, a crystalline SiO ₂ in the surface of the silicon nano-particles It provides a method for producing a negative electrode active material for a lithium secondary battery comprising the step of producing a surface-treated silicon nanoparticles formed with a treatment layer.

The present invention also provides a negative electrode for a lithium secondary battery including the negative electrode active material and a lithium secondary battery including the same.

In addition, the present invention provides a battery module including the lithium secondary battery as a unit cell.

Furthermore, the present invention provides a battery pack including the battery module.

The negative electrode active material for a lithium secondary battery according to the present invention may exhibit a markedly improved initial efficiency characteristic with excellent life and capacity characteristics when applied to a battery.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is a graph showing the results of X-ray diffraction (X-ray diffraction spectroscopy (XRD)) for the negative electrode active material prepared in Example 1.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Unless specifically limited herein, 'nanoparticles' means particles having an average particle diameter of several nanometers to hundreds of nanometers having an average particle diameter of less than 1 μm. In this case, the average particle diameter (D ₅₀ ) may be defined as the particle size at 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. For example, the method for measuring the average particle diameter (D ₅₀ ) of the silicon nanoparticles is, after dispersing the silicon nanoparticles in a solution, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) to about 28 after examining the kHz ultrasound of 60 W in output, it can be used to calculate the average particle diameter (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

In the present invention, the oxygen content in the active material is located on the surface of the silicon nanoparticles during the preparation of the silicon-based negative electrode active material, and by changing the amorphous SiO ₂ to the electrochemically inert crystalline SiO ₂ which decreases the initial efficiency by irreversible reaction during the initial charge Even without the change of the present invention can exhibit a markedly improved initial efficiency characteristics with excellent life and capacity characteristics in the battery application.

That is, the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention includes surface treated silicon nanoparticles, and the surface treated silicon nanoparticles are silicon (Si) nanoparticles and the surface of the silicon nanoparticles. And a surface treatment layer comprising crystalline SiO ₂ .

In the surface-treated silicon nanoparticles, the silicon nanoparticles are nanoparticles containing silicon single particles, specifically, may have an average particle diameter (D ₅₀ ) of 150 nm or less. In this way, by including the nano-level silicon particles can exhibit a high initial efficiency and excellent life characteristics. In addition, in consideration of the remarkable improvement effect, the silicon nanoparticles may have an average particle diameter of 10nm to 100nm.

In addition, the silicon nanoparticles include a surface treatment layer containing crystalline SiO ₂ on the particle surface.

The surface treatment layer may be formed an amorphous SiO ₂ existing on the surface of the surface of the silicon oxide nano particles by pulverization is converted to SiO ₂ of a crystalline in the process of the basic substance, and formed to a uniform thickness on the surface of the silicon nano-particles Can be. Accordingly, the surface treatment layer may act as a buffering layer to control the volume expansion of the silicon nanoparticles, and as a result, to prevent the detachment of the active material from the electrode due to the volume expansion of silicon to improve the life characteristics of the battery Can be. In consideration of such a sufficient effect as the buffer layer, the surface treatment layer may be formed on the surface of the silicon nanoparticles with a thickness of 1 nm to 20 nm, thereby exhibiting excellent high rate charge and discharge efficiency as an effective control of the volume expansion of the silicon nanoparticles. have. When the thickness of the surface treatment layer is less than 1 nm, it is difficult to exhibit a sufficient buffering effect on the volume expansion of silicon, and when it exceeds 20 nm, there is a fear that battery characteristics are rather deteriorated. In addition, in consideration of the remarkable improvement effect, the surface treatment layer may be formed in a thickness of 2nm to 10nm more specifically.

In addition, since the crystalline SiO ₂ included in the surface treatment layer provides a channel of lithium ions during charge and discharge of the battery and is electrically inactive, it is possible to prevent a decrease in initial efficiency during initial charge and discharge. Specifically, the crystalline SiO ₂ is preferably included in 2 to 15% by weight based on the total weight of the surface-treated silicon nanoparticles. When the content of crystalline SiO ₂ is less than 2% by weight, the conversion rate of amorphous SiO ₂ present on the surface of the silicon nanoparticles to crystalline SiO ₂ is low, so that the decrease in initial efficiency is insignificant, and when the content exceeds 15% by weight. The initial efficiency is greatly increased, but there is a fear that the discharge capacity is reduced. In addition, in consideration of the remarkable improvement effect, the crystalline SiO ₂ is preferably included in 5 to 10% by weight relative to the total weight of the surface-treated silicon nanoparticles.

In addition, since the surface treatment layer is obtained by converting amorphous SiO ₂ present on the surface of the silicon nanoparticles into crystalline SiO ₂ , there is no change in oxygen content with the silicon nanoparticles containing amorphous SiO ₂ . Oxygen content contained in the surface-treated silicon nanoparticles may affect battery characteristics such as initial efficiency of the battery, the surface-treated silicon nanoparticles in the negative electrode active material according to the present invention is specifically 10 to 20% by weight It may have an oxygen content of%, even if it has an oxygen content in the range derived from the content of the crystalline SiO ₂ may exhibit an improved effect in terms of improving the initial efficiency of the battery.

In addition, the surface treatment layer may further include an alkali metal, in particular an alkali metal or an alkaline earth metal, which is unavoidably remaining due to the use of an alkali metal compound in the manufacturing process as an impurity content. Specifically, an alkali metal such as sodium (Na) or potassium (K) may be further included in an amount of 10 ppm or less based on the total weight of the silicon nanoparticles surface-treated.

In addition, the surface-treated silicon nanoparticles may be used alone, but may be used in combination with a conventional negative electrode active material.

Specific examples of the negative electrode active material include carbon-based materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, as the carbonaceous material, both amorphous carbon, low crystalline carbon, high crystalline carbon, and the like may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, mesocarbon microbeads. (mesocarbon microbeads), Kish graphite, graphitized mesoface spheres (MCMB), graphitized carbon fibers, liquid crystal pitch based carbon fibers, coke, pyrolytic carbon , High temperature calcined carbon such as meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

More specifically, considering the remarkable effect of improving the battery characteristics when used in combination with the surface-treated silicon nanoparticles, the negative electrode active material is capable of reversible intercalation and deintercalation of lithium ions and at the same time conductive carbon-based It may be a negative electrode active material. When used in conjunction with the carbon-based negative electrode active material, it is possible to improve the cycle characteristics by increasing the conductivity, in particular, when the carbon-based negative electrode active material is compounded, the electrical conductivity between the active material particles and the electrochemical properties of the electrolyte and silicon-based Reducing the volume expansion of the particles can increase cell life.

The carbon-based negative electrode active material may be preferably included in an amount of 10 to 90% by weight based on the total weight of the negative electrode active material, in consideration of the improvement in battery capacity characteristics and the control of volume expansion of the silicon-based negative electrode active material. If the content of the carbon-based negative electrode active material is less than 10% by weight, there is a fear that the electrical short circuit and volume expansion occurring during charging and discharging may not be effectively suppressed, and if it exceeds 90% by weight, the effect of improving the capacity increase due to the application of Si It can be insignificant.

In addition, when the carbon-based negative electrode active material is used together, the surface treatment is performed by a method such as surface coating by vapor deposition, coating or pressing, mechanical alloying, carbonization by firing organic materials, etc., in addition to simple mixing. It can be used in combination with silicon nanoparticles.

Specifically, when complexed with the surface-treated silicon nanoparticles, the negative electrode active material according to an embodiment of the present invention is the carbon-based negative electrode active material on the surface treatment layer containing crystalline SiO ₂ in the surface-treated silicon nanoparticles It may further include a coating layer comprising a.

In this case, the carbon-based negative electrode active material may be located over the entire surface of the silicon nanoparticles surface-treated within the above content range, or may be partially located. In consideration of the improvement effect of the formation of the coating layer including the carbon-based negative electrode active material, it is preferable to be formed throughout the surface-treated silicon nanoparticles surface, it may be more preferable to form a uniform thickness over the entire surface. .

In addition, when the carbon-based negative electrode active material is included in the form of a coating layer on the surface-treated silicon nanoparticle surface, under the conditions that satisfy the content range of the carbon-based negative electrode active material in the negative electrode active material, the thickness of the coating layer is 1nm to 20nm Can be. If the thickness of the coating layer is less than 1nm, the effect of improving the conductivity due to the coating layer is insignificant, and if it exceeds 20nm, there is a fear of deterioration of battery characteristics due to the formation of an excessively thick coating layer. In addition, in consideration of the remarkable improvement effect, the coating layer may be formed in a thickness of 2nm to 10nm more specifically.

In addition, when the carbon-based negative electrode active material forms a coating layer as described above, the carbon-based negative electrode active material is pyrolytic carbon formed by pyrolysis of a carbon raw material such as acetylene gas more specifically among the above-described materials. Can be.

In the case of complexing with the surface-treated silicon nanoparticles by another method, the negative electrode active material according to an embodiment of the present invention, the coating layer comprising the surface-treated silicon nanoparticles on the surface of the carbon-based negative electrode active material It may also be included in the form of. In this case, the surface-treated silicon nanoparticles may be located over the entire surface of the carbon-based negative electrode active material, or may be partially located, the composite layer with the carbon-based negative electrode active material and forming a coating layer including the surface-treated silicon nanoparticles In consideration of the excellent improvement effect according to, the coating layer including the surface-treated silicon nanoparticles can be formed in a uniform thickness over the entire surface of the carbon-based negative electrode active material.

In addition, when the silicon nanoparticles surface-treated with the carbon-based negative electrode active material is included in the form of a coating layer on the surface of the carbon-based negative electrode active material, under the conditions that satisfy the content range of the carbon-based negative electrode active material in the negative electrode active material, The thickness may be 1 nm to 20 nm. If the thickness of the coating layer is less than 1nm, the effect of improving the conductivity due to the coating layer is insignificant, and if it exceeds 20nm, there is a fear of deterioration of battery characteristics due to the formation of an excessively thick coating layer. In addition, in consideration of the remarkable improvement effect, the coating layer may be formed in a thickness of 2nm to 10nm more specifically.

In addition, when the carbon-based negative electrode active material is coated with the surface-treated silicon nanoparticles as described above, the carbon-based negative electrode active material is more specifically natural graphite, artificial graphite, mesocarbon microbeads (mesocarbon microbeads) Crystalline carbon, such as

In the negative electrode active material according to the embodiment of the present invention as described above, the silicon nanoparticles containing amorphous SiO ₂ on the surface of the silicon nanoparticles are mixed with an alkali metal compound and then heat treated to convert the amorphous SiO ₂ into crystalline SiO ₂ , It can be prepared by a manufacturing method comprising the step of forming a surface treatment layer comprising crystalline SiO ₂ on the surface of the particles. Accordingly, according to another embodiment of the present invention is provided a method for producing the negative electrode active material.

In the manufacturing method of the negative electrode active material, silicon nanoparticles containing amorphous SiO ₂ on the surface, it can be prepared by the surface oxidation on the silicon nanoparticles.

Specifically, the surface oxidation may be performed by dispersing the silicon nanoparticles in an alcohol solvent such as ethanol, and then grinding until the average particle diameter (D ₅₀ ) becomes 100 nm or less. The surface-oxidized silicon nanoparticles prepared as a result of the crushing process may have an oxygen content of 10 to 20% by weight in the silicon nanoparticles, and may exhibit an initial efficiency of 82% or more during an initial charge / discharge test.

In the method of preparing the negative electrode active material, the alkaline metal compound may be an alkali metal hydroxide such as LiOH, NaOH, KOH, Be (OH) ₂ , Mg (OH) or Ca (OH) ₂ , or a hydrate thereof. In consideration of reaction efficiency with surface-oxidized silicon nanoparticles, the alkaline metal compound may be NaOH.

In addition, the alkaline metal compound may be used in a solution phase. In this case, the solvent may be dissolved in the alkaline metal compound, and the solvent is not particularly limited as long as it is easy to remove. Specifically, a polar solvent such as water or an alcohol solvent (ethanol or methanol) can be used.

The mixing process of the surface oxidized silicon nanoparticles and the basic material may be carried out according to a conventional method.

In addition, the alkaline metal compound may be preferably used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the silicon nanoparticles including amorphous SiO ₂ on the surface. If the content of the alkali metal compound is less than 1 part by weight, the content of crystalline SiO ₂ generated after the subsequent heat treatment step is small, and as a result, the initial efficiency may be lowered, while the content of the alkali metal compound exceeds 10 parts by weight. In this case, the content of crystalline SiO ₂ formed after the heat treatment is too high, which may lower the capacity characteristics.

In addition, in the manufacturing method of the negative electrode active material, the heat treatment step may be carried out by heat treatment at 500 ℃ to 1000 ℃ in an inert atmosphere. If the temperature is less than 500 ℃ during heat treatment, the conversion efficiency of amorphous SiO ₂ to crystalline SiO ₂ is low, there is a risk that the initial efficiency and life characteristics may be lowered. When the temperature exceeds 1000 ℃ during heat treatment, a large amount of crystalline SiO ₂ is generated, And deterioration of the service life characteristics.

In addition, the heat treatment process may be preferably performed for 5 to 120 minutes under the above conditions. If the reaction time is less than 5 minutes, the conversion efficiency to crystalline SiO ₂ is low, there is a fear that the initial efficiency and life characteristics are lowered. If the reaction time is more than 120 minutes, enough time after the crystalline silicon dioxide is formed, energy efficiency It is not preferable in terms of.

As such, the formation of crystalline SiO ₂ may be promoted by heat treatment in the state where the alkaline metal compound is present on the surface of the silicon oxide nanoparticles surface-oxidized. Even if the heat treatment is performed at the same temperature, crystalline SiO ₂ is not produced when the alkali metal compound is not used. In addition, due to the mixing of the alkali metal compound, amorphous SiO ₂ grows into crystalline electrochemically inactive (inactive, no reaction with lithium), the initial coulombic efficiency (discharge capacity / charge capacity × 100, silicon-based compound for the first time The ratio of the amount of lithium first released to the amount of lithium) increases.

The method for preparing a negative electrode active material according to the present invention evaporates and removes a polar solvent present in a mixture of surface oxidized silicon nanoparticles and an alkali metal compound prepared before the heat treatment step, and as a result, crystalline SiO by subsequent heat treatment. ₂ may optionally further include a drying process for increasing the formation efficiency.

The drying process may be carried out according to a conventional method, specifically, may be carried out by heat treatment or hot air drying at 80 ℃ to 120 ℃.

In addition, the method of manufacturing the negative electrode active material may optionally further include a washing process for removing an alkaline metal compound present on the surface of the silicon oxide after the heat treatment process.

The washing process may be carried out according to a conventional method, specifically, it may be carried out by a method such as impregnation, rinsing using a washing liquid such as water.

In addition, the method for manufacturing a negative electrode active material according to an embodiment of the present invention, after forming a surface treatment layer on the surface of the silicon nanoparticles, to form a coating layer containing a carbon-based material on the surface treatment layer, or the surface treatment layer is The method may further include coating a surface of the carbonaceous material using the formed silicon nanoparticles.

Formation of the coating layer including the carbon-based material may be carried out by a conventional carbon-based coating layer forming method such as surface coating by vapor deposition, coating or pressing of carbon-based material, mechanical alloy, carbonization by firing organic materials, and the like. . In this case, the type and content of the carbonaceous material are the same as described above.

Specifically, the surface-treated silicon nanoparticles prepared above may be reacted with a carbon raw material under an inert gas atmosphere such as argon to form a coating layer containing a carbon-based material on the surface. In this case, a carbonaceous carbon material such as acetylene gas or the like may be used as the carbon raw material.

In addition, the reaction with the carbon raw material may be carried out at a temperature range of 700 ℃ to 1000 ℃.

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

Specifically, the negative electrode is formed on the negative electrode current collector and the negative electrode current collector, and includes a negative electrode active material layer containing the negative electrode active material.

The negative electrode having the structure as described above may be prepared according to a conventional negative electrode manufacturing method, specifically, after applying a negative electrode mixture including a binder, and optionally a conductive agent with a negative electrode active material on the negative electrode current collector, It can be prepared by drying.

In this case, the negative electrode current collector may be used without particular limitation as long as it has high conductivity without causing chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, or the like on the surface of the steel, aluminum-cadmium alloy and the like can be used.

The negative electrode current collector as described above may have various forms, and specifically, may be in the form of a film, a sheet, a foil, a net, a porous body, a foam, or a nonwoven fabric.

In addition, the negative electrode current collector may have a thickness of 3 to 500 μm, and fine concavities and convexities or patterns may be formed on the surface of the current collector so as to enhance the bonding force of the negative electrode active material.

In addition, the negative electrode mixture may be prepared by dissolving and dispersing a negative electrode active material, a binder, and optionally a conductive agent in a solvent.

The negative electrode active material is the same as described above.

In addition, the binder serves to improve the binding between the negative electrode active material and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene- Diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluorine-based rubber or various copolymers thereof, and the like, and one or a mixture of two or more thereof may be used. Can be.

Of these, the aqueous binder is preferable in view of the remarkable improvement effect, and in particular, the styrene-butadiene rubber is more preferable in view of the remarkable improvement effect, the adhesive ability of the binder itself, and the high temperature drying process in the manufacturing process of the negative electrode. can do.

Such a binder may be included in the negative electrode mixture in an amount such that it can be included in 1 to 20% by weight based on the total weight of the negative electrode active material layer.

In addition, the conductive material is selectively used to impart conductivity to the negative electrode, and in the battery constituted, any conductive material can be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Needle or branched conductive whisker such as zinc oxide whisker, calcium carbonate whisker, titanium dioxide whisker, silicon oxide whisker, silicon carbide whisker, aluminum borate whisker, magnesium borate whisker, potassium titanate whisker, silicon nitride whisker, silicon carbide whisker, alumina whisker Whisker; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used.

Among these, a carbon-based material such as carbon black may be more preferable in consideration of the remarkable improvement effect of the use of the conductive agent and the high temperature drying process in the negative electrode manufacturing process.

The conductive material may be included in the negative electrode mixture in an amount such that 0.5 to 5% by weight based on the total weight of the negative electrode active material layer.

In addition, the solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone ) Or water, and one kind alone or a mixture of two or more kinds thereof may be used.

In addition, the negative electrode mixture may further include a thickener together with the above components. Specifically, the thickener may be a cellulose compound such as carboxymethyl cellulose (CMC). The thickener may be included in the negative electrode mixture in an amount such that the thickener is included in an amount of 1 to 10% by weight based on the total weight of the negative electrode active material layer.

The negative electrode mixture having the above configuration can be applied to one surface of the negative electrode current collector using a conventional slurry coating method.

Examples of the slurry coating method may include bar coating, spin coating, roll coating, slot die coating, or spray coating, and one or two or more of these methods may be mixed.

In addition, when the negative electrode mixture is applied, it may be preferable to apply the negative electrode mixture to an appropriate thickness in consideration of the loading amount and thickness of the active material in the final negative electrode active material layer.

Thereafter, a drying process is performed on the coating film of the negative electrode mixture formed on the negative electrode current collector.

At this time, the drying process may be carried out by a method such as heating treatment, hot air injection, etc. at a temperature capable of removing the moisture contained in the negative electrode with the evaporation of the solvent in the negative electrode mixture as much as possible, and at the same time increasing the binding force of the binder.

Specifically, the drying process may be carried out at a temperature below the boiling point of the solvent or less than the melting point of the binder, more specifically, may be carried out at 100 ℃ to 150 ℃. More preferably, it may be carried out for 1 to 50 hours at a temperature of 100 ℃ to 120 ℃ and a pressure of 10torr or less.

In addition, the rolling step after the drying step may be carried out according to a conventional method, and if necessary, a vacuum drying step may be optionally further performed.

In another method, the negative electrode active material layer is prepared by applying the negative electrode mixture on a separate support and then drying to prepare a film, and peeling the formed film from the support, then laminating and rolling on the negative electrode current collector. May be

At this time, the negative electrode mixture, the negative electrode current collector, the coating, drying and rolling processes are the same as described above.

The negative electrode manufactured according to the manufacturing method as described above, by including the negative electrode active material or negative electrode material can exhibit excellent life characteristics without fear of lowering the initial efficiency.

Accordingly, according to another embodiment of the present invention, a lithium secondary battery including the negative electrode manufactured by the above-described manufacturing method is provided.

Specifically, the lithium secondary battery includes a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode manufactured by the manufacturing method described above and a nonaqueous electrolyte. In the lithium secondary battery, the negative electrode is the same as described above.

In addition, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing a positive electrode active material.

In this case, the positive electrode current collector may be used without particular limitation as long as it has conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum may be used on the surface of stainless steel. The surface-treated with carbon, nickel, titanium, silver, etc. can be used.

In addition, the positive electrode current collector may have a thickness of 3 to 500㎛, and may form fine irregularities on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In the cathode active material layer, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used as the cathode active material. Specifically, one or more of complex oxides of metal and lithium of cobalt, manganese, nickel or a combination thereof may be used, and as a specific example, a lithium metal compound represented by the following Chemical Formula 1 may be used.

[Formula 1]

Li _x M _y M ' _z O ₂

(In Formula 1, M and M 'are each independently Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and combinations thereof And x, y, and z are atomic fractions of independent oxide composition elements, and 0 <x≤1, 0 <y≤1, 0 <z≤1, and 0 <x + y. + z≤2.)

Among these, the positive electrode active material is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (eg, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ , or LiNi _{0 . 8} Mn _{0 . 1} Co _{0 . 1} O _2), or lithium nickel cobalt aluminum oxide (for _{example, LiNi 0. 8 Co 0.} 15 Al 0. 05 O 2 , etc.), and it may be preferably selected from the group consisting of a mixture thereof.

The positive electrode as described above may be manufactured according to a conventional positive electrode manufacturing method. Specifically, the positive electrode mixture prepared by dissolving a conductive agent and a binder in a solvent together with the positive electrode active material may be prepared by applying a positive electrode current collector on a positive electrode current collector, followed by drying and rolling.

In addition, the binder and the conductive agent included in the active material layer of the positive electrode may be the same as described above in the negative electrode.

In addition, as the solvent, a solvent generally used in the art may be used, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone ( acetone), water, and the like, and one kind alone or a mixture of two or more kinds thereof may be used.

After the coating, drying and rolling process for the positive electrode current collector may be carried out in the same manner as described in the manufacturing method of the negative electrode.

In addition, the positive electrode may also be prepared by applying the positive electrode mixture on a separate support and then peeling the film for forming the positive electrode active material layer prepared by drying from the support and laminating on the positive electrode current collector.

On the other hand, in the lithium secondary battery, the separator can be used without particular limitation as long as it is usually used as a separator in a lithium secondary battery, it is particularly preferable that the resistance to the ion migration of the electrolyte, while excellent in the electrolyte solution moisture-absorbing ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used.

In the lithium secondary battery, the nonaqueous electrolyte contains an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC) and fluoroethylene carbonate (FEC).

Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable.

In addition, the lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 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 . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The lithium salt is preferably included at a concentration of approximately 0.6 mol% to 2 mol% in the electrolyte.

In addition to the electrolyte components, the electrolyte includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. -Glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2 One or more additives such as -methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.

The lithium secondary battery having the above configuration may be manufactured by manufacturing an electrode assembly through a separator between a positive electrode and a negative electrode, placing the electrode assembly inside a case, and then injecting an electrolyte solution into the case.

As described above, since the lithium secondary battery including the negative electrode manufactured by the manufacturing method according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, laptop computers, digital cameras, And electric vehicle fields such as hybrid electric vehicles.

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

[ Example  One]

Step 1: Preparation of Silicon Nanoparticles with Amorphous SiO ₂ on the Surface

0.1mm the Si particles of the ZrO ₂ particles, an average particle size 3㎛ 10 having a size ball (ball) in the form of: milling (milling) for 2 hours and then mixed in an ethanol solvent in a weight ratio of 1, the amorphous SiO ₂ particles on the surface Silicon nanoparticles having an average particle diameter (D ₅₀ ) of 100 nm were prepared.

As a result of oxygen analysis of the prepared silicon nanoparticles using infrared absorption spectrometry, it was confirmed that the oxygen content was 10% by weight based on the total weight of the particles.

Step 2: Preparation of Cathode Active Material of Silicon Nanoparticles with Crystallized SiO ₂ Layer

Into the sodium hydroxide solution prepared by dissolving 30 mg of sodium hydroxide in 100 ml of ethanol, 1 g of silicon nanoparticles having amorphous SiO ₂ was prepared on the surface thereof, and stirred for 10 minutes or more to prepare a mixed solution including silicon nanoparticles.

The mixed solution containing the silicon nanoparticles was put in an alumina boat heated to 80 ° C to 120 ° C, and ethanol was evaporated. When the solvent evaporation is completed, the alumina boat containing the resulting reactant is placed in a quartz tube furnace, heat treated at 800 ° C. for 30 minutes while flowing argon gas, and the quartz tube furnace is cooled to room temperature (20 ˜25 ° C.) to prepare silicon nanoparticles comprising crystallized SiO ₂ on the surface.

The negative electrode active material was obtained by dipping the silicon nanoparticles containing the prepared crystallized SiO ₂ in distilled water for 2 hours and then removing sodium hydroxide adhering to the surface.

Example 2

20 g of the negative electrode active material prepared in Example 1 was added to a rotary tubular furnace, argon gas was flowed at 0.3 L / min, and the temperature was raised to 800 ° C. at a rate of 10 ° C./min. While rotating the rotary tubular furnace at a speed of 15 rpm / min, argon gas was flowed at 1.8 L / min and acetylene gas at 0.5 L / min, followed by heat treatment for 5 hours to prepare a negative electrode active material having a conductive carbon coating layer formed on the surface of the particle. At this time, the conductive carbon coating layer was included in 10% by weight relative to the total weight of the negative electrode active material.

Example 3

10 g of a powder mixed with 15 wt% of the negative electrode active material prepared in Example 1 and 85 wt% of spherical natural graphite having an average particle diameter of 16 μm was dispersed in 1000 mL of ethanol, and then spray dried. The negative electrode active material prepared in Example 1 was coated on the natural graphite surface. The resulting composite was carried out in the same manner as in Example 2 to form a conductive carbon coating layer on the surface. At this time, the conductive carbon coating layer was included in 10% by weight relative to the total weight of the negative electrode active material.

Comparative Example 1

Silicon nanoparticles having amorphous SiO ₂ on the surface prepared in Step 1 of Example 1 were used as a negative electrode active material.

Comparative Example 2

90% by weight of silicon nanoparticles having an average particle diameter of 100 nm and 10% by weight of crystalline SiO ₂ powder having an average particle diameter of 100 nm having no surface oxidized were used as a negative electrode active material.

Experimental Example 1

X-ray diffraction spectroscopy (XRD) was performed on the anode active material of silicon nanoparticles containing crystallized SiO ₂ on the surface prepared in Example 1. The results are shown in FIG.

As a result of the analysis, it was confirmed that crystalline SiO ₂ (near 22 degrees) was formed in addition to Si (near 28 degrees).

In addition, to confirm the content of crystalline SiO ₂ contained in the negative electrode active material prepared in Example 1, after mixing the crystalline MgO with the negative electrode active material prepared in Example 1, XRD analysis was performed.

As a result, the content of crystalline SiO ₂ contained in the negative electrode active material prepared in Example 1 was 10% by weight.

Experimental Example 2

The structures of the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were analyzed.

Specifically, the type and content of the surface treatment layer forming material in the negative electrode active material were mixed with crystalline MgO with each negative electrode active material in the same manner as in Experimental Example 1, XRD analysis was performed, and confirmed from the results.

In addition, the thickness of each surface treatment layer was confirmed through the scanning electron microscope observation.

		Example 1	Example 2	Example 3	Comparative Example 1	Comparative Example 2
core	Kinds	Silicon nanoparticles	Silicon nanoparticles	Spherical natural graphite with an average particle diameter of 16㎛	Silicon nanoparticles	Silicon Nanoparticles + Crystalline SiO 2
Surface treatment layer	Kinds	Crystalline SiO 2	Crystalline SiO 2	Silicon nanoparticles with a surface treatment layer of crystalline SiO 2	Amorphous SiO 2	-
	Content (% by weight)	10	10	13.5	10	-
	Average thickness (nm)	5	5	5	5	-
Coating layer	Kinds	-	carbon	carbon	-	-
	Content (% by weight)	-	10	10	-	-
	Average thickness (nm)	-	5	5	-	-
Average particle size of active material (nm)		100	100	16010	100	100/100

Content table in Table 1 is a value based on the total weight of the negative electrode active material.

Experimental Example 3

After the half battery was manufactured using the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2, initial efficiency, capacity, and lifespan characteristics were evaluated, respectively. The results are shown in Table 2.

Specifically, each of the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2, 5% by weight of carbon black, a binder of styrene butadiene rubber (SBR) and carboxymethyl cellulose were used as the conductive material. After mixing in distilled water at a weight ratio of 5:10 to prepare a composition for forming a negative electrode active material layer, it was applied to a copper current collector and dried to prepare a negative electrode. In addition, as an electrolyte, 1M concentration of lithium hexafluorophosphate (LiPF ₆ ) and an additive in an organic solvent composed of ethylene carbonate (EC) / diethyl carbonate (DEC) (mixing volume ratio of EC / DEC = 3/4/3) It was prepared by dissolving 1% by weight of vinylene carbonate and 5% by weight of fluoethylene carbonate relative to the total weight of the electrolyte solution. A half cell (using Li metal as a counter electrode) was manufactured using the negative electrode and electrolyte solution prepared above.

After charging and discharging the prepared half-cell at 0.1 C / 0.1 C at room temperature (25 ° C.), the discharge capacity and the initial efficiency were measured, and the initial charge and discharge characteristics were evaluated therefrom.

In addition, charging / discharging was performed 50 times under the condition of 0.5C / 0.5C, and the life characteristics were confirmed from the capacity retention rate up to 50 cycles.

	Example 1	Example 2	Example 3	Comparative Example 1	Comparative Example 2
Discharge Capacity (mAh / g)	2250	2186	630	2268	1952
Initial Efficiency (%)	89.7	90.2	91.6	81.7	84.1
Capacity maintenance rate (%)	83	94	98	81	56

As a result of the measurement, the batteries of Examples 1 and 2 including the negative electrode active material according to the present invention showed an equivalent level of discharge capacity compared to Comparative Examples 1 and 2, but significantly improved in terms of initial efficiency and lifetime characteristics. It was. On the other hand, the negative electrode active material of Example 3, which contains 85% by weight of graphite, exhibited significantly lower discharge capacities than those of Examples 1 and 2 and Comparative Examples 1 and 2. Indicated.

Claims (21)

1. Surface-treated silicon nanoparticles,

   The surface-treated silicon nanoparticles are silicon nanoparticles, and is located on the surface of the silicon nanoparticles, including a surface treatment layer containing crystalline SiO ₂ that the lithium active battery negative electrode active material.
2. The method of claim 1,

   The crystalline SiO ₂ is a negative active material for a lithium secondary battery that is contained in 2 to 15% by weight based on the total weight of the surface-treated silicon nanoparticles.
3. The method of claim 1,

   The silicon nanoparticles have an average particle diameter (D ₅₀ ) of less than 150nm lithium secondary battery negative electrode active material.
4. The method of claim 1,

   The surface treatment layer is a negative electrode active material for a lithium secondary battery having a thickness of 1nm to 20nm.
5. The method of claim 1,

   A negative electrode active material for a lithium secondary battery further comprising a carbon-based negative electrode active material.
6. The method of claim 5,

   The carbon-based negative electrode active material is a lithium active battery negative electrode active material that is contained in 10 to 90% by weight based on the total weight of the negative electrode active material.
7. The method of claim 1,

   A negative electrode active material for a lithium secondary battery further comprising a coating layer comprising a carbon-based negative electrode active material on the surface treatment layer.
8. The method of claim 1,

   Further comprising a carbon-based negative electrode active material,

   The surface-treated silicon nanoparticles are located on the surface of the carbon-based negative electrode active material negative electrode active material for a lithium secondary battery.
9. Silicon nanoparticles containing amorphous SiO ₂ on the surface are mixed with an alkali metal compound and then heat treated to convert amorphous SiO ₂ to crystalline SiO ₂ , thereby forming a surface treatment layer including crystalline SiO ₂ on the surface of the silicon nanoparticles. Method of producing a negative electrode active material for a lithium secondary battery comprising the step of manufacturing the treated silicon nanoparticles.
10. The method of claim 9,

    Silicon nanoparticles containing amorphous SiO ₂ on the surface is prepared by dispersing silicon nanoparticles in an alcohol solvent and then pulverized.
11. The method of claim 9,

    Method for producing a negative active material for a lithium secondary battery that the average particle diameter of the silicon nanoparticles containing amorphous SiO ₂ on the surface is 150nm or less.
12. The method of claim 9,

    Wherein the alkaline metal compound is LiOH, NaOH, KOH, Be (OH) ₂ , Mg (OH), Ca (OH) ₂ and one or more selected from the group consisting of hydrates thereof Lithium secondary battery negative electrode active material Manufacturing method.
13. The method of claim 9,

    The alkaline metal compound is a method for producing a negative electrode active material for a lithium secondary battery that is used in 1 to 10 parts by weight based on 100 parts by weight of silicon nanoparticles containing amorphous SiO ₂ on the surface.
14. The method of claim 9,

    The heat treatment is a method for producing a negative electrode active material for a lithium secondary battery that is carried out at 500 ℃ to 1000 ℃ under an inert atmosphere.
15. The method of claim 9,

    After the preparation of the surface-treated silicon nanoparticles, further forming a coating layer including a carbon-based negative electrode active material on the surface treatment layer of the surface-treated silicon nanoparticles; Or mixing with a carbon-based negative electrode active material to form a coating layer including the surface-treated silicon nanoparticles on the surface of the carbon-based negative electrode active material.
16. A negative electrode for a lithium secondary battery comprising the negative electrode active material according to any one of claims 1 to 8.
17. A lithium secondary battery comprising the negative electrode according to claim 16.
18. A battery module comprising the lithium secondary battery according to claim 17 as a unit cell.
19. A battery pack comprising the battery module according to claim 18.
20. The method of claim 19,

    Battery pack that is used as a power source for medium and large devices.
21. The method of claim 20,

    The medium-to-large device is a battery pack that is selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

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