KR20210082285A - Anode active material for secondary battery, manufacturing method of the same and manufacturing method of the secondary battery - Google Patents

Abstract

The present invention relates to a negative electrode active material for a secondary battery; a manufacturing method thereof; and a manufacturing method of a secondary battery using the same, wherein the negative electrode active material for a secondary battery is in a complex of a core-shell structure in which a TiO_2-xTiO_1-xN_x (0 < x < 1) complex coating layer surrounds silicon nano particles, and the TiO_2-xTiO_1-xN_x complex coating layer comprises TiO_2-x in an oxygen deficiency structure and TiO_1-xN_x (0 < x < 1) in a rock-salt structure. According to the present invention, in order to overcome a low electrical conductivity problem of silicon and volume expansion and structure change of the silicon generated in the process of repeated charging and discharging as problems caused by the silicon while containing the silicon having a high theoretical capacity, the TiO_2-xTiO_1-xN_x (0 < x < 1) complex coating layer is applied to obtain high ion/electrical conductivity and stable life characteristics.

Description

Anode active material for secondary battery with improved lifespan characteristics, manufacturing method thereof, and manufacturing method of secondary battery using same

The present invention relates to a negative active material for a secondary battery, a method for manufacturing the same, and a method for manufacturing a secondary battery using the same, and more particularly, to a problem of silicon including silicon having a theoretical capacity, low electrical conductivity, and repeated charging and discharging. Anode active material for secondary battery with high ion/electron conductivity and stable lifespan characteristics by applying _{TiO 2-x} -TiO _1-x N _x (0<x<1) composite coating layer to solve the volume expansion and structural change that occur. It relates to a method for manufacturing the same and a method for manufacturing a secondary battery using the same.

Lithium secondary batteries are composed of positive and negative active materials, separators, and electrolytes that generate electrical energy by a change in chemical potential during intercalation-deintercalation of lithium ions, and can be charged and discharged. to be. These lithium secondary batteries have advantages of high energy density, large electromotive force, and high capacity, and thus are being applied to various fields.

Recently, in order to reduce dependence on oil and solve environmental problems, the development of plug-in hybrid electric vehicles and hybrid vehicles has been actively carried out, and as the demand for medium and large-sized secondary batteries in various fields is increasing, the high energy density of lithium secondary batteries , R&D for a stable lifespan is being emphasized.

Carbon based meterials such as graphite and activated carbon are mainly used as anode active materials for lithium secondary batteries. However, the carbon-based active material has a theoretical capacity of about 400 mAh/g, which has a low capacity. To solve this problem, a lot of research on a high-capacity negative active material is being conducted. Among them, silicon having a high theoretical capacity is attracting attention.

Although silicon has a high theoretical capacity of 4200 mAh/g, it has low electrical conductivity and an unstable solid electrolyte interphase (SEI) is generated due to repeated volume expansion and structural change during charging and discharging, resulting in deterioration of lifespan characteristics. have.

Republic of Korea Patent Publication No. 10-0903610

The problem to be solved by the present invention is to solve the problem of low electrical conductivity and volume expansion and structural change that occurs during repeated charging and discharging as a problem of silicon while including silicon having a high theoretical capacity, TiO _2-x -TiO _{1 To provide a negative active material for a secondary battery having high ion/electron conductivity and stable lifespan characteristics by applying a -x} N _x (0<x<1) composite coating layer, a manufacturing method thereof, and a manufacturing method of a secondary battery using the same.

The present invention is a composite of TiO _2-x -TiO _1-x N _x (0<x<1) composite coating layer surrounding silicon nanoparticles and having a core-shell structure, and the TiO _2-x - TiO _1-x N _x composite coating layer is TiO _2-x (0<x<1) with _{oxygen deficiency structure and TiO 1-x} N _{x with} rock-salt structure (0<x<1) It provides an anode active material for a secondary battery, characterized in that it comprises a.

The TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles may have a weight ratio of 0.05:1 to 10:1.

The silicon nanoparticles preferably have a size of 10 to 200 nm.

The negative active material for secondary batteries preferably has a size of 15 to 500 nm.

In addition, the present invention, (a) _{using a TiO 2 precursor to TiO 2} to be coated on the surface of the silicon nanoparticles and (b) the Si-TiO ₂ composite particles _{coated with TiO 2 on the surface of the silicon nanoparticles nitrogen} By heat treatment in a reducing gas atmosphere containing components, a TiO _2-x -TiO _1-x N _x (0<x<1) composite coating layer surrounds the silicon nanoparticles to form a core-shell structure composite. wherein the TiO _2-x -TiO _1-x N _x composite coating layer has an oxygen deficiency structure of TiO _2-x (0<x<1) and a rock-salt structure of TiO It provides a method of manufacturing a negative active material for a secondary battery, characterized in that it contains _1-x N _{x (0<x<1).}

The silicon nanoparticles preferably have a size of 10 to 200 nm.

Wherein the step (a), and the method comprising: dispersing silicon nanoparticles in a solvent to form a silicon nano-particle dispersion comprising the steps of: mixing the TiO ₂ precursor to the silicon nano-particle dispersion, the TiO ₂ in the silicon nano-particle surface _{The coating and TiO 2} coating on the surface of the silicon nanoparticles may include selectively separating the _{Si-TiO 2 composite particles.}

The TiO ₂ precursor is composed of titanium tetramethoxide, titanium tetraethoxide, titanium tetraproposide, titanium tetraisoproposide, titanium tetrabutoxide, titanium tetraisobutoxide, titanium tetrapentoxide and titanium tetraisopentoxide. It may include one or more substances selected from the group.

It is preferable to mix the basic material with the solvent so that the pH of the silicon nanoparticle dispersion is 8 to 12.

The heat treatment is preferably performed at a temperature of 600 to 750 ℃.

The TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles may have a weight ratio of 0.05:1 to 10:1.

The negative active material for secondary batteries preferably has a size of 15 to 500 nm.

In addition, the present invention, 5 to 40 parts by weight of the conductive material with respect to 100 parts by weight of the negative active material for the secondary battery, the negative active material for the secondary battery, 5 to 40 parts by weight of the binder with respect to 100 parts by weight of the negative active material for the secondary battery, and for the secondary battery Preparing a composition for a negative electrode of a secondary battery by mixing 200 to 1000 parts by weight of a dispersion medium with respect to 100 parts by weight of an anode active material, and compressing the composition for a negative electrode of a secondary battery to form an electrode, or applying the composition for a negative electrode of a secondary battery to a metal foil Or by coating the current collector to form an electrode, or by pushing the composition for a negative electrode of a secondary battery with a roller to form a sheet and attaching it to a metal foil or a current collector to form an electrode, or casting to a metal current collector by a doctor blade method to electrode Forming into a shape, drying the resultant formed in the form of an electrode to form a negative electrode of a secondary battery, the negative electrode, a positive electrode comprising a positive electrode active material capable of inserting or deintercalating lithium ions, the positive electrode and the negative electrode It provides a method of manufacturing a secondary battery comprising disposing a separator therebetween to prevent a short circuit between the positive electrode and the negative electrode, and injecting an electrolyte in which a lithium salt is dissolved between the positive electrode and the negative electrode.

_{According to the present invention, TiO 2-x} to solve the problem of low electrical conductivity of silicon, volume expansion and structural change of silicon that occurs during repeated charging and discharging, as problems caused by silicon while including silicon having a high theoretical capacity. -TiO _1-x N _x (0<x<1) High ion/electron conductivity and stable lifespan characteristics can be obtained by applying a coating layer.

The oxygen-deficient TiO _{2-x surrounding the silicon nanoparticles forms a lithium conductive Li y} TiO _2-x phase during the initial insertion of lithium ions (activation step), which is trapped inside the structure even after the lithium ions are desorbed. Therefore, the conductivity of lithium ions can be greatly improved by acting as a scaffold. In addition, the rock-salt structure, TiO _1-x N _x is halite (rock-salt) there consists of a solid solution (solid solution) of TiO and TiN in the structure, these materials are silicon and the bulk modulus greater electrical conductivity is greatly superior to the TiO ₂ It can suppress the volume expansion and facilitate the movement of electrons. Accordingly, the TiO _2-x -TiO _1-x N _x composite coating layer can solve the problem of volume expansion of a high-capacity negative active material accompanied by volume expansion, such as silicon, and greatly improve electrochemical properties.

In addition, it is easy to commercialize because it can be easily manufactured through a simple coating process and a heat treatment process instead of an expensive chemical vapor deposition (CVD) or complicated process, which is mainly used as a method to solve the problems of existing silicon.

_{1 is a case of heat-treating TiO 2} according to Experimental Example 1 at 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C for 5 hours in an NH _{3 gas atmosphere, the heat treatment temperature} It is a diagram showing the results of X-ray diffraction (XRD) analysis of the star TiO _{2 particles.}
2 is a case in which TiO ₂ according to Experimental Example 1 was heat-treated for 5 hours at 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., and 950° C. in an NH _{3 gas atmosphere, the heat treatment temperature} It is a diagram showing the analysis result of the phase transformation yield (yield) to star TiO _x N _y.
Figure 3a is a field emission-scanning electron microscope (FE-SEM) image of the Si-TiO ₂ composite particles prepared according to Experimental Example 2, Figure 3b is a Si-TiO _{2 prepared according to Experimental Example 2} It is a transmission electron microscopy (TEM) image of the composite particle, and FIG. 3c is an enlarged image of the part 'A' boxed in yellow in FIG. 3b.
Figure 4a is a field emission scanning microscope (FE-SEM) image of the negative active material for a secondary battery prepared according to Experimental Example 3, Figure 4b is a transmission electron microscope (TEM) image of the negative active material for a secondary battery prepared according to Experimental Example 3 , FIG. 4C is an enlarged image of 'A' boxed in yellow in FIG. 4B.
5 is a TEM-EELS (electron energy loss spectroscopy) image of a negative active material for a secondary battery prepared according to Experimental Example 3. FIG.
6A and 6B are views showing the results of X-ray photoelectron spectroscopy of the negative active material for a secondary battery prepared according to Experimental Example 3;
7 is a graph showing the performance of the lithium secondary battery, and is a graph showing the first potential distribution at a current density of 0.1A/g at a voltage in the range of 0.01 to 1.5V.
8 is a graph showing the charging capacity and the coulombic efficiency according to 100 cycles at a current density of 1A/g.
9 is a graph showing changes in charge/discharge capacity as the current density changes to 0.1A/g, 0.5A/g, 1A/g, 2A/g, and 5A/g in order to examine the charging and discharging rates.
10 is an FE-SEM image of a cathode before and after 50 cycles at a current density of 1 A/g.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. However, the following examples are provided so that those of ordinary skill in the art can fully understand the present invention, and may be modified in various other forms, and the scope of the present invention is limited to the examples described below it's not going to be

When it is said that any one component "includes" another component in the detailed description or claims of the invention, it is not construed as being limited to only the component, unless otherwise stated, and other components are further added. It should be understood as being able to include

Hereinafter, 'nano-size' is used to mean a size in the range of 1 to 1000 nm as a size in nanometers (nm), and 'nanoparticle' is used to mean nano-sized particles.

The anode active material for a secondary battery according to a preferred embodiment of the present invention has a _{core-shell structure in which a TiO 2-x} -TiO _1-x N _x (0<x<1) composite coating layer surrounds silicon nanoparticles. of TiO _2-x -TiO _1-x N _x composite coating layer is TiO _2-x (0<x<1) having an _{oxygen deficiency structure and TiO 1- having a rock-salt structure contains x} N _x (0<x<1).

The TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles may have a weight ratio of 0.05:1 to 10:1.

The silicon nanoparticles preferably have a size of 10 to 200 nm.

The negative active material for secondary batteries preferably has a size of 15 to 500 nm.

The method for manufacturing a negative active material for a secondary battery according to a preferred embodiment of the present invention comprises the steps of (a) coating the surface of the silicon nanoparticles with TiO _{2 using a TiO 2 precursor, and (b) TiO 2 on the} surface of the silicon nanoparticles. A core-coated Si-TiO ₂ composite particle is heat-treated in a reducing gas atmosphere containing a nitrogen component to form a TiO _2-x -TiO _1-x N _x (0<x<1) composite coating layer surrounding the silicon nanoparticles- and forming a complex of a core-shell structure, wherein the TiO _2-x -TiO _1-x N _{x composite coating layer is TiO 2-x} (0<x<1) having an oxygen deficiency structure. _{) and TiO 1-x} N _x (0<x<1) in a rock-salt structure.

The silicon nanoparticles preferably have a size of 10 to 200 nm.

Wherein the step (a), and the method comprising: dispersing silicon nanoparticles in a solvent to form a silicon nano-particle dispersion comprising the steps of: mixing the TiO ₂ precursor to the silicon nano-particle dispersion, the TiO ₂ in the silicon nano-particle surface _{The coating and TiO 2} coating on the surface of the silicon nanoparticles may include selectively separating the _{Si-TiO 2 composite particles.}

The TiO ₂ precursor is composed of titanium tetramethoxide, titanium tetraethoxide, titanium tetraproposide, titanium tetraisoproposide, titanium tetrabutoxide, titanium tetraisobutoxide, titanium tetrapentoxide and titanium tetraisopentoxide. It may include one or more substances selected from the group.

It is preferable to mix the basic material with the solvent so that the pH of the silicon nanoparticle dispersion is 8 to 12.

The heat treatment is preferably performed at a temperature of 600 to 750 ℃.

The TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles may have a weight ratio of 0.05:1 to 10:1.

The negative active material for secondary batteries preferably has a size of 15 to 500 nm.

In the method of manufacturing a secondary battery according to a preferred embodiment of the present invention, 5 to 40 parts by weight of a conductive material based on 100 parts by weight of the negative active material for a secondary battery, the negative active material for a secondary battery, and a binder with respect to 100 parts by weight of the negative active material for a secondary battery Preparing a composition for a negative electrode of a secondary battery by mixing 200 to 1000 parts by weight of a dispersion medium with respect to 5 to 40 parts by weight and 100 parts by weight of the negative active material for a secondary battery, and pressing the composition for a negative electrode of a secondary battery to form an electrode, The composition for a negative electrode of a secondary battery is coated on a metal foil or a current collector to form an electrode, or the composition for a negative electrode of a secondary battery is pressed with a roller to form a sheet and attached to a metal foil or a current collector to form an electrode, or a metal collector The steps of casting the entirety by a doctor blade method to form an electrode, drying the resultant formed in the form of an electrode to form a negative electrode of a secondary battery, and the negative electrode and a positive electrode active material capable of inserting or deintercalating lithium ions. A secondary comprising: disposing a separator between the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode; and injecting an electrolyte in which lithium salt is dissolved between the positive electrode and the negative electrode A method for manufacturing a battery is provided.

Hereinafter, a negative active material for a secondary battery according to a preferred embodiment of the present invention will be described in more detail.

The negative active material for a secondary battery according to a preferred embodiment of the present invention is _{a composite (Si@TiO 2-} ) having a core-shell structure in which a _{TiO 2-x} -TiO _1-x N _{x composite coating layer surrounds silicon nanoparticles. x} -TiO _1-x N _x ), and the TiO _2-x -TiO _1-x N _x composite coating layer has an oxygen deficiency structure of TiO _2-x (0<x<1) and rock salt (rock- salt) structure of TiO _1-x N _x (0<x<1).

The TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles may have a weight ratio of 0.05:1 to 10:1.

The silicon nanoparticles preferably have a size of 10 to 200 nm.

The negative active material for secondary batteries preferably has a diameter of nano-size, more preferably 15 to 500 nm, and most preferably 20 to 300 nm.

_{TiO 2-x} -TiO _1-x to solve the problem of low electrical conductivity of silicon, volume expansion and structural change of silicon that occurs during repeated charging and discharging, as a problem caused by silicon while including silicon with high theoretical capacity. By _{applying the N x} composite coating layer, high ion/electron conductivity and stable lifespan characteristics can be obtained.

The oxygen-deficient TiO _{2-x surrounding the silicon nanoparticles forms a lithium conductive Li y} TiO _2-x phase during the initial insertion of lithium ions (activation step), which is trapped inside the structure even after the lithium ions are desorbed. Therefore, the conductivity of lithium ions can be greatly improved by acting as a scaffold.

In addition, the rock-salt structure, TiO _1-x N _x is halite (rock-salt) there consists of a solid solution (solid solution) of TiO and TiN in the structure, these materials are silicon and the bulk modulus greater electrical conductivity is greatly superior to the TiO ₂ It can suppress the volume expansion and facilitate the movement of electrons.

Accordingly, the TiO _2-x -TiO _1-x N _x composite coating layer can solve the problem of volume expansion of a high-capacity negative active material accompanied by volume expansion, such as silicon, and greatly improve electrochemical properties.

_{Hereinafter, a method of manufacturing a Si@TiO 2-x} -TiO _1-x N _x composite according to a preferred embodiment of the present invention will be described in more detail.

Silicon anode active material has a theoretical capacity of 4,200 mAh/g, which is almost 10 times higher than graphite, so it is being actively studied to overcome the limitations of lithium secondary batteries.

However, silicon anode active material deteriorates lifespan characteristics due to pulverization and formation of an unstable solid electrolyte interphase due to high volume expansion of 300% during lithium insertion and desorption. The reaction formula when lithium is inserted into silicon is as follows.

[Formula 1]

22Li + 5Si = Li ₂₂ Si ₅

To solve the problem of silicon, various studies on silicon nanostructure, porous silicon, silicon-carbon composite, silicon-metal oxide composite, etc. are being conducted, but there is a limit to effectively controlling the volume expansion problem of silicon, and most There are disadvantages in that an expensive chemical vapor deposition process and a complicated process must be used.

_{The present invention provides a TiO 2-x} -TiO _1-x N _x (0<x<1) composite coating layer with excellent performance while using a simple coating process to effectively control the volume expansion problem of silicon. , and a method for manufacturing the same and a method for manufacturing a secondary battery using the same.

To prepare an anode active material for a secondary battery, silicon nanoparticles and a TiO ₂ precursor are prepared.

The silicon nanoparticles are nanoparticles having a diameter. More preferably, the size of the silicon nanoparticles is preferably about 10 to 200 nm.

The TiO ₂ precursor is composed of titanium tetramethoxide, titanium tetraethoxide, titanium tetraproposide, titanium tetraisoproposide, titanium tetrabutoxide, titanium tetraisobutoxide, titanium tetrapentoxide and titanium tetraisopentoxide. It is preferred to include one or more substances selected from the group.

TiO _{2 The} surface of the silicon nanoparticle _{is coated with TiO 2} using a TiO 2 precursor to form the Si-TiO _{2 composite particle coated with TiO 2} on the surface of the silicon nanoparticle.

For the coating, a method such as a spray coating method, a sol-gel method, a chemical vapor deposition method, an immersion method, or a combination thereof may be used.

Hereinafter, an example of a method of forming the Si-TiO _{2 composite particles will be described.}

The silicon nanoparticles are dispersed in a solvent to form a silicon nanoparticle dispersion. The solvent may be alcohol or the like. The alcohol is preferably at least one selected from the group consisting of methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutanol and 2-butanol. The solvent is preferably used in an amount of 100 to 1000 parts by weight based on 100 parts by weight of the silicon nanoparticles.

In the dispersion of the silicon nanoparticles, a basic material may be added so that the reaction can occur locally only on the silicon surface. It is preferable to mix the basic material with the solvent so that the pH of the silicon nanoparticle dispersion is 8 to 12. The basic material may be aqueous ammonia (NH ₄ OH), but is not limited thereto.

The TiO ₂ precursor is mixed with the silicon nanoparticle dispersion, and TiO ₂ is coated on the surface of the silicon nanoparticle. The temperature of the coating process is preferably 25 to 80° C., and the reaction time is preferably in the range of 10 to 100 hours.

The Si-TiO ₂ composite particle (a composite coating on the TiO ₂ particle surface a silicon nanoparticles), which is TiO ₂ is coated on a silicon nanoparticle surface recall optionally isolated from the solvent. The selective separation may use a sedimentation method, a centrifuge method, a filtration method, etc., but is not limited thereto.

The Si-TiO _{2 composite particles coated with TiO 2} on the surface of the silicon nanoparticles were heat treated in a reducing gas atmosphere containing a nitrogen component to form a TiO _2-x -TiO _1-x N _x (0<x<1) composite coating layer of silicon. Forms a composite of a core-shell structure surrounding the nanoparticles.

The heat treatment is preferably performed at a temperature of about 600 to 750 °C, more preferably 600 to 700 °C in a reducing gas atmosphere containing nitrogen. At a heat treatment temperature higher than 750°C, a core-shell structure composite (Si@TiO _1-x N _x ) in which _{only the TiO 1-x} N _{x coating layer having the rock salt structure surrounds the silicon nanoparticles (Si@TiO 1-x N x )} can be formed. When heat-treated at 600~750℃, TiO _2-x (0<x<1) with _{oxygen deficiency structure and TiO 1-x} N _{x with} rock-salt structure (0<x<1) _{A composite coating layer of TiO 2-x} -TiO _1-x N _x (0<x<1) containing a core-shell structure (Si@TiO _2-x - TiO _1-x N _x complex) may be formed.

The reducing gas containing the nitrogen component may be ammonia gas (NH ₃ ), _{a mixed gas of H 2} and N ₂ , etc., and is preferably supplied into the furnace at a flow rate of 0.1 to 10 L/min.

As an example, during heat treatment, _{TiO 2} is _{reduced to TiO 2-x by NH 3} gas having a strong reducing power, and an oxygen-deficient structure is generated, and at a higher heat treatment temperature, one oxygen _{escapes from TiO 2} (rock salt) ) structure, a nitrogen atom can be substituted relatively easily in _{the TiO 1-x} N _{y structure formed. Therefore, the Si@TiO 2-x} -TiO _1-x N _x composite prepared through the control of their formation conditions has an oxygen-deficient structure of TiO _2-x and a rock salt structure of TiO _2-x -TiO _1-x N _x ( It has a composite coating layer of 0<x<1), and TiO _2-x can improve ionic and electronic conductivity by _{Li y} TiO _2-x formed by the following chemical formula.

[Formula 2]

TiO _2-x + Li ⁺ ↔ Li _y TiO _2-x

In addition, TiO _1-x N _x may improve electrical conductivity while increasing mechanical strength in a rock salt structure. Accordingly, due _{to the excellent output characteristics and lifespan characteristics of the Si@TiO 2-x} -TiO _1-x N _x composite, it can be effectively used as an anode active material for a secondary battery.

Hereinafter, Si@TiO _2-x -TiO _1-x N _x Composite (TiO _2-x -TiO _1-x N _x Composite having a core-shell structure in which a composite coating layer surrounds silicon nanoparticles) A method of manufacturing a secondary battery (eg, a lithium secondary battery) using as an anode active material will be described in detail.

A composition for a negative electrode of a secondary battery is formed by mixing the negative electrode active material, the conductive material, the binder and the dispersion medium prepared as described above.

The conductive material is not particularly limited as long as it is an electronically conductive material that does not cause chemical change, and examples include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, Super-P black, carbon fiber, copper, nickel. , a metal powder such as aluminum, silver, or a metal fiber, etc. are possible. The conductive material is preferably mixed in an amount of 5 to 40 parts by weight based on 100 parts by weight of the negative electrode active material.

The dispersion medium may be an organic solvent such as ethanol (EtOH), acetone, isopropyl alcohol, N-methylpyrrolidone (NMP), propylene glycol (PG), or water. The dispersion medium is preferably mixed with 200 to 1000 parts by weight based on 100 parts by weight of the negative electrode active material.

The binder is polytetrafluoroethylene (PTFE), polyvinylidenefloride (PVDF), carboxymethylcellulose (CMC), polyvinyl alcohol (polyvinyl alcohol; PVA), polyvinylbutyral (polyvinylidenefloride) vinyl butyral (PVB), polyvinyl pyrrolidone (PVP), styrene butadiene rubber (SBR), polyamide-imide, polyimide, or mixtures thereof, etc. can be used The binder is preferably mixed in an amount of 5 to 40 parts by weight based on 100 parts by weight of the negative electrode active material.

For uniform dispersion of the negative electrode active material and the conductive material, a slurry suitable for manufacturing an electrode (cathode) can be obtained by stirring for a predetermined time (eg, 1 minute to 24 hours) using a high-speed mixer. The stirring is preferably performed at a rotation speed of about 100 to 4,000 rpm.

The composition for a negative electrode of a secondary battery prepared in this way is in a slurry state.

The composition for a negative electrode of a secondary battery in which the negative electrode active material, binder, conductive material and dispersion medium are mixed is compressed to form an electrode, or the composition for a negative electrode of a secondary battery is coated on a metal foil or a current collector to form an electrode, or the secondary battery The negative electrode composition is pressed with a roller to form a sheet state, is attached to a metal foil or a current collector to form an electrode, and the resultant formed in the electrode form is dried at a temperature of 100°C to 350°C to form the negative electrode of the secondary battery. . A negative electrode can be formed using a metal (alloy) current collector, for example, by casting a metal (alloy) current collector such as a copper current collector by a doctor blade method to form an electrode. It may be dried to form the negative electrode of the secondary battery.

More specifically, an example of forming the negative electrode of the secondary battery can be molded by pressing the composition for the secondary battery negative electrode using a roll press molding machine. The roll press molding machine aims to improve the electrode density and control the thickness of the electrode through rolling, and a controller that can control the thickness and heating temperature of the upper and lower rolls and rolls, and a winding that can unwind and wind the electrode. made up of wealth As the rolled electrode passes through the roll press, the rolling process proceeds and it is wound again in the roll state. At this time, the pressing pressure of the press is preferably 5 to 20 ton/cm 2 and the temperature of the roll is preferably 0 to 150°C. The composition for a negative electrode of a secondary battery that has been subjected to the press compression process as described above is subjected to a drying process. The drying process is carried out at a temperature of 100°C to 350°C, preferably 150°C to 300°C. In this case, when the drying temperature is less than 100° C., it is not preferable because evaporation of the dispersion medium is difficult, and when drying at a high temperature exceeding 350° C., oxidation of the conductive material may occur. Therefore, it is preferable that a drying temperature is 100 degreeC or more, and does not exceed 350 degreeC. And the drying process is preferably carried out for about 10 minutes to 6 hours at the same temperature as above. This drying process dries the molded composition for a negative electrode of a secondary battery (evaporating the dispersion medium) and at the same time binds powder particles to improve the strength of the negative electrode of the secondary battery.

In addition, looking at another example of forming the negative electrode of the secondary battery, the composition for the secondary battery negative electrode is a titanium foil (Ti foil), an aluminum foil (Al foil), an aluminum etching foil (Al etching foil), a copper foil (Cu foil) It may be coated on a metal foil, such as, or the composition for a negative electrode of a secondary battery may be pressed with a roller to form a sheet (rubber type) and attached to a metal foil to form a negative electrode. The aluminum etching foil means that the aluminum foil is etched in a concave-convex shape. A drying process is performed on the negative electrode shape that has been subjected to the above process. The drying process is carried out at a temperature of 100°C to 350°C, preferably 150°C to 300°C. At this time, when the drying temperature is less than 100 ℃, it is not preferable because evaporation of the dispersion medium is difficult, and when drying at a high temperature exceeding 350 ℃, oxidation of the conductive material may occur. Therefore, it is preferable that a drying temperature is 100 degreeC or more, and does not exceed 350 degreeC. And the drying process is preferably carried out for about 10 minutes to 6 hours at the same temperature as above. Such a drying process dries the composition for a negative electrode of a secondary battery (evaporation of the dispersion medium) and at the same time binds the powder particles to improve the strength of the negative electrode of the secondary battery.

The secondary battery negative electrode prepared as described above may be usefully applied to a secondary battery of a desired type, such as a coin cell.

A negative electrode manufactured by using the negative electrode active material as described above, a positive electrode including a positive electrode active material capable of intercalating or deintercalating lithium ions, and a separator for preventing a short circuit between the positive electrode and the negative electrode between the positive electrode and the negative electrode ( seperator) and injecting an electrolyte in which lithium salt is dissolved between the positive electrode and the negative electrode to manufacture a secondary battery.

The positive electrode may include at least one positive electrode active material selected from lithium metal, lithium alloy, crystalline carbon, amorphous carbon, carbon composite material, and carbon fiber, but is not limited thereto. The positive electrode may also be manufactured by the same or similar method to the method for manufacturing the negative electrode.

The separator is a polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, polyacrylonitrile porous separator, poly(vinylidene fluoride) hexafluoropropane copolymer porous separator, cellulose porous separator, kraft paper or rayon fiber, etc. in the battery field. If it is a commonly used separation membrane, it is not particularly limited.

As the electrolyte of the electrolyte to be charged in the secondary battery, a lithium salt dissolved therein may be used. The lithium salt is not particularly limited as a lithium salt commonly used in secondary batteries, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , Li(CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiSbF ₆ , LiAsF ₆ or a mixture thereof, and the like. The lithium salt is preferably contained in the electrolyte at a concentration of 0.1 to 3M.

The solvent constituting the electrolyte is not particularly limited, and for example, a cyclic carbonate solvent, a chain carbonate solvent, an ester solvent, an ether solvent, a nitrile solvent, an amide solvent, or a mixture thereof may be used. . Ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc. may be used as the cyclic carbonate-based solvent, and dimethyl carbonate, methylethyl carbonate, diethyl carbonate, etc. may be used as the chain carbonate-based solvent, and the As the ester solvent, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, etc. can be used, and as the ether solvent, 1,2-dimethoxyethane, 1,2-diethane Toxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran, etc. may be used, and the nitrile solvent may include acetonitrile, and the amide solvent may include dimethylformamide, etc. can be used

Hereinafter, experimental examples according to the present invention are specifically presented, and the present invention is not limited by the experimental examples presented below.

<Experimental Example 1>

Germany Degussa (Degussa) TiO ₂ Using NH ₃ gas atmosphere 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃ each was heat-treated for 5 hours. The flow rate of the NH ₃ gas was 0.5 L/min. The structural change of _{TiO 2-x} -TiO _1-x N _x according to the heat treatment temperature was monitored.

_{1 is a case of heat-treating TiO 2} according to Experimental Example 1 at 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C for 5 hours in an NH _{3 gas atmosphere, the heat treatment temperature} It is a diagram showing the results of X-ray diffraction (XRD) analysis of the star TiO _{2 particles.}

Referring to FIG. 1, as the heat treatment temperature increases, the _{Anatase and Rutile structures representing the structure of TiO 2} disappear, and it can be observed that _{TiO 1-x} N _x having a rock salt structure is formed at a heat treatment temperature of 600° C. or higher. , it can be observed that as the heat treatment temperature increases, more _{TiN-rich phases are formed in the crystal structure of TiO 1-x} N _x of the rock salt structure formed, and the phenomenon that 2-Theta shifts to a lower value can be observed. there was.

2 is a case in which TiO ₂ according to Experimental Example 1 was heat-treated for 5 hours at 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., and 950° C. in an NH _{3 gas atmosphere, the heat treatment temperature} It is a diagram showing the analysis result of the phase transformation yield (yield) to star TiO _x N _y.

Referring to FIG. 2 , at a heat treatment temperature of 750° C. or less, _{TiO 2-x} region having many oxygen defect structures before phase transformation into _{TiO 1-x} N _x and TiO _1-x N _{x having a rock salt structure.} It can be seen that they exist together.

For functionalization of the material coated on the surface of silicon nanoparticles, _{650° C., in which the TiO 2-x} region and the TiO _1-x N _x region coexist, was set as the heat treatment temperature and applied to Experimental Example 3.

<Experimental Example 2>

Silicon nanoparticles having a diameter of about 50 nm and TiO _{2 As a} precursor, titanium tetraisoproposide was prepared.

0.5 g of the silicon nanoparticles and 8 ml of aqueous ammonia were added to a solvent of 666 ml of absolute ethanol, followed by ultrasonic dispersion for about 30 minutes to obtain a silicon nanoparticle dispersion.

After slowly dropping 7.6 ml of the TiO ₂ precursor into the silicon nanoparticle dispersion, the mixture was stirred at 40° C. for 40 hours to allow TiO ₂ to be coated on the silicon nanoparticle surface through a sol-gel method.

After repeating the process of removing the supernatant by centrifugation at 11000 rpm for 1 hour to remove unreacted substances 3 times, Si-TiO ₂ composite particles (TiO ₂ coated composite particles on the surface of silicon nanoparticles) are recovered did.

<Experimental Example 3>

Silicon nanoparticles having a diameter of about 50 nm and TiO _{2 As a} precursor, titanium tetraisoproposide was prepared.

0.5 g of the silicon nanoparticles and 8 ml of aqueous ammonia were added to a solvent of 666 ml of absolute ethanol, followed by ultrasonic dispersion for about 30 minutes to obtain a silicon nanoparticle dispersion.

After slowly dropping 7.6 ml of the TiO ₂ precursor into the silicon nanoparticle dispersion, the mixture was stirred at 40° C. for 40 hours to allow TiO ₂ to be coated on the silicon nanoparticle surface through a sol-gel method.

After repeating the process of removing the supernatant by centrifugation at 11000 rpm for 1 hour to remove unreacted substances 3 times, Si-TiO ₂ composite particles (TiO ₂ coated composite particles on the surface of silicon nanoparticles) are recovered did.

The Si-TiO ₂ composite particles were _{heat-treated in an NH 3} gas atmosphere to obtain a negative active material for a secondary battery (Si@TiO _2-x -TiO _1-x N _x composite). The heat treatment was performed at 650° C. for 3 hours, and _{the flow rate of NH 3} gas was 0.5 L/min. The negative active material for secondary batteries is a composite (Si@TiO _2-x -TiO _1-x N _{) of a core-shell structure in which a TiO 2-x} -TiO _1-x N _{x composite coating layer surrounds silicon nanoparticles. x} ).

<Experimental Example 4>

Silicon nanoparticles having a diameter of about 50 nm and TiO _{2 As a} precursor, titanium tetraisoproposide was prepared.

0.5 g of the silicon nanoparticles and 8 ml of aqueous ammonia were added to a solvent of 666 ml of absolute ethanol, followed by ultrasonic dispersion for about 30 minutes to obtain a silicon nanoparticle dispersion.

After slowly dropping 7.6 ml of the TiO ₂ precursor into the silicon nanoparticle dispersion, the mixture was stirred at 40° C. for 40 hours to allow TiO ₂ to be coated on the silicon nanoparticle surface through a sol-gel method.

After repeating the process of removing the supernatant by centrifugation at 11000 rpm for 1 hour to remove unreacted substances 3 times, Si-TiO ₂ composite particles (TiO ₂ coated composite particles on the surface of silicon nanoparticles) are recovered did.

The Si-TiO ₂ composite particles were _{heat-treated in an NH 3} gas atmosphere to obtain a negative active material for a secondary battery (Si@TiO _1-x N _{x composite).} The heat treatment was performed at 800° C. for 3 hours, and _{the flow rate of NH 3} gas was 0.5 L/min. The anode active material for a secondary battery is a composite (Si@TiO _1-x N _x ) having a _{core-shell structure in which a TiO 1-x} N _{x coating layer surrounds silicon nanoparticles.} This can also be predicted from FIG. 2 , and looking at FIG. 2 , _{it can be seen that only the TiO 1-x} N _x region of the rock salt structure exists at a heat treatment temperature higher than 750° C., according to Experimental Example 2, 800° C. In the case of heat treatment, _{a composite (Si@TiO 1-x} N _x ) having a core-shell structure in which only _{the TiO 1-x} N _{x coating layer surrounds the silicon nanoparticles is formed.}

A negative electrode was prepared using the negative active material for secondary batteries prepared according to Experimental Examples 3 and 4. More specifically, a composite as an anode active material, Super-P carbon black as a conductive material, and poly(acrylic acid) as a binder are mixed in a weight ratio of 80:10:10 and added to a solvent. to prepare a slurry. Distilled water was used as the solvent. The slurry was applied to a copper foil current collector to prepare a negative electrode.

A 2032 coin-type half cell was prepared using the negative electrode and lithium metal (counter electrode). As the electrolyte, _{a mixed solvent of EC:DEC (ethylene carbonate:diethylene carbonate) in which 1M LiPF 6} was dissolved (volume ratio = 1:1) and 5wt% of FEC (fluoroethylene carbonate) additive were used. A polyolefin separator was used as a separator between the negative electrode and the counter electrode.

Figure 3a is a field emission-scanning electron microscope (FE-SEM) image of the Si-TiO ₂ composite particles prepared according to Experimental Example 2, Figure 3b is a Si-TiO _{2 prepared according to Experimental Example 2} It is a transmission electron microscopy (TEM) image of the composite particle, and FIG. 3c is an enlarged image of the part 'A' boxed in yellow in FIG. 3b.

3A to 3C, the Si-TiO ₂ composite particles prepared according to Experimental Example 2 (composite particles _{coated with TiO 2} on the surface of the silicon nanoparticles) have an amorphous TiO ₂ coating layer of about 3.5 nm on the surface of the silicon nanoparticles. It could be confirmed that this was formed.

Figure 4a is a field emission scanning microscope (FE-SEM) image of the negative active material for a secondary battery prepared according to Experimental Example 3, Figure 4b is a transmission electron microscope (TEM) image of the negative active material for a secondary battery prepared according to Experimental Example 3 , FIG. 4C is an enlarged image of 'A' boxed in yellow in FIG. 4B.

4A to 4C , the anode active material for a secondary battery prepared according to Experimental Example 3 (TiO _2-x -TiO _1-x N _x composite coating layer surrounds the silicon nanoparticles core-shell structure) The composite (Si@TiO _2-x -TiO _1-x N _x )) is formed by forming a coating layer _{of TiO 1-x} N _{x with a rock salt structure and TiO 2-x} with an amorphous structure on the surface of silicon nanoparticles. could confirm that there was

5 is a TEM-EELS (electron energy loss spectroscopy) image of a negative active material for a secondary battery prepared according to Experimental Example 3;

Referring to FIG. 5, a composite of a core-shell structure in which a negative active material for a secondary battery (TiO _2-x -TiO _1-x N _{x composite coating layer surrounds silicon nanoparticles) prepared according to Experimental Example 3 (} In Si@TiO _2-x -TiO _1-x N _x )), it was confirmed that Ti, O, and N were uniformly coated on the surface of the silicon nanoparticles.

6A and 6B are views showing the results of X-ray photoelectron spectroscopy of the negative active material for a secondary battery prepared according to Experimental Example 3;

7 is a graph showing the performance of the lithium secondary battery, and is a graph showing the first potential distribution at a current density of 0.1A/g at a voltage in the range of 0.01 to 1.5V.

Referring to FIG. 7, when a negative electrode was prepared using the negative active material for a secondary battery prepared according to Experimental Example 3, and a 2032 coin-type half battery (lithium secondary battery) was manufactured using the negative electrode (Si@TiO in FIG. 7) Represented by _{2-x -TiO 1-x} N _x )), a negative electrode was prepared using the negative active material for secondary batteries prepared according to Experimental Example 4, and a 2032 coin-type half battery (lithium secondary battery) was prepared using the negative electrode. It was confirmed that the performance was superior to that of _{one case (represented by Si@TiO 1-x} N _x in FIG. 7 ).

8 is a graph showing the charging capacity and the coulombic efficiency according to 100 cycles at a current density of 1A/g.

Referring to FIG. 8 , in the case of commercial silicon nanoparticles, the initial capacity decrease is large due to the volume expansion of silicon, and in the case of Si-TiO ₂ composite particles (Si@TiO ₂ composite), the volume expansion of silicon can be suppressed to some extent. However, it showed a sharp decrease in capacity after 20 cycles. On the other hand, in the case of the Si@TiO _2-x -TiO _1-x N _x composite (anode active material for secondary batteries prepared according to Experimental Example 3), due to the composite coating layer having high mechanical strength, stable lifespan characteristics of 85% and High capacity (1332mAh/g) was confirmed.

9 is a graph showing changes in charge/discharge capacity as the current density changes to 0.1A/g, 0.5A/g, 1A/g, 2A/g, and 5A/g in order to examine the charging and discharging rates.

Referring to FIG. 9 , the Si@TiO _2-x -TiO _1-x N _x composite (anode active material for a secondary battery prepared according to Experimental Example 3) is _{a Li conductive Li y} TiO _{in which TiO 2-x} is formed by an electrochemical reaction. _{Due to the formation of 2-x and the characteristics of TiO 1-x} N _x with high electrical conductivity, the charge/discharge rate efficiency was superior to that of Si@TiO _2-x or Si@TiO _1-x N _{x composites.}

10 is an FE-SEM image of a cathode before and after 50 cycles at a current density of 1 A/g.

Referring to FIG. 10, in the case of commercial silicon nanoparticles or Si-TiO ₂ composite particles (Si@TiO ₂ composite), the structure collapsed due to volume expansion and micronization of silicon after 50 cycles, but Si@TiO _2-x - In the case of the TiO _1-x N _x composite (anode active material for secondary batteries prepared according to Experimental Example 3), the initial shape was maintained by effectively suppressing the volume expansion of Si with the high mechanical strength characteristics of _{TiO 1-x} N _{x even after 50 cycles.} showed

As mentioned above, although preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various modifications are possible by those skilled in the art.

Claims (13)

TiO _2-x -TiO _1-x N _x (0<x<1) The composite coating layer is a composite having a core-shell structure surrounding the silicon nanoparticles,
The TiO _2-x -TiO _1-x N _x composite coating layer has an oxygen deficiency structure of TiO _2-x (0<x<1) and a rock-salt structure of TiO _1-x N _x ( A negative active material for a secondary battery, characterized in that it contains 0<x<1).
The negative active material of claim 1, wherein the TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles have a weight ratio of 0.05:1 to 10:1.
The negative active material of claim 1, wherein the silicon nanoparticles have a size of 10 to 200 nm.
The negative active material for secondary batteries according to claim 1, wherein the negative active material for secondary batteries has a size of 15 to 500 nm.
(a) Step using a TiO ₂ precursor which causes the TiO ₂ coating on the silicon nano-particle surfaces; and
_{(b) TiO 2} -TiO _{1 -x} N _x (0<x<1) _{by heat-} treating the Si-TiO _{2 composite particles coated with TiO 2} on the surface of the silicon nanoparticles in a reducing gas atmosphere containing a nitrogen component A composite coating layer comprising the step of forming a composite of a core-shell structure surrounding the silicon nanoparticles,
The TiO _2-x -TiO _1-x N _x composite coating layer has an oxygen deficiency structure of TiO _2-x (0<x<1) and a rock-salt structure of TiO _1-x N _x ( A method of manufacturing a negative active material for a secondary battery, characterized in that it contains 0<x<1).
The method of claim 5, wherein the silicon nanoparticles have a size of 10 to 200 nm.
According to claim 5, wherein the step (a),
dispersing the silicon nanoparticles in a solvent to form a silicon nanoparticle dispersion;
_{mixing the TiO 2} precursor into the silicon nanoparticle dispersion;
_{TiO 2} coating the surface of the silicon nanoparticles; and
The method for producing a negative active material for a secondary battery, comprising the step of selectively separating the Si-TiO _{2 composite particles coated with TiO 2} on the surface of the silicon nanoparticles.
The method of claim 7, wherein the TiO ₂ precursor is titanium tetramethoxide, titanium tetraethoxide, titanium tetraproposide, titanium tetraisoproposide, titanium tetrabutoxide, titanium tetraisobutoxide, titanium tetrapentoxide and titanium A method for producing a negative active material for a secondary battery, comprising at least one material selected from the group consisting of tetraisopentoxide.
The method according to claim 7, wherein a basic material is mixed with the solvent so that the pH of the silicon nanoparticle dispersion is 8 to 12.
The method of claim 5, wherein the heat treatment is performed at a temperature of 600 to 750°C.
The method of claim 5, wherein the TiO _2-x -TiO _1-x N _x composite coating layer and the silicon nanoparticles have a weight ratio of 0.05:1 to 10:1.
The method of claim 5, wherein the negative active material for secondary batteries has a size of 15 to 500 nm.
5 to 40 parts by weight of the conductive material based on 100 parts by weight of the negative active material for a secondary battery according to claim 1, 5 to 40 parts by weight of a binder based on 100 parts by weight of the negative active material for a secondary battery, and the negative active material for a secondary battery preparing a composition for a negative electrode of a secondary battery by mixing 200 to 1000 parts by weight of a dispersion medium with respect to 100 parts by weight;
The composition for a negative electrode of a secondary battery is compressed to form an electrode, or the composition for a negative electrode of a secondary battery is coated on a metal foil or a current collector to form an electrode, or the composition for a negative electrode of a secondary battery is pressed with a roller to form a sheet Forming in the form of an electrode by attaching it to a metal foil or a current collector, or casting to a metal current collector by a doctor blade method to form an electrode;
drying the resultant formed in the form of an electrode to form a negative electrode of a secondary battery;
disposing a separator for preventing a short circuit between the anode and the cathode, the cathode comprising a cathode active material capable of intercalating or deintercalating lithium ions, and between the cathode and the anode; and
and injecting an electrolyte in which a lithium salt is dissolved between the positive electrode and the negative electrode.

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