KR20130139555A - Metal-doped silicon oxide, anode material for secondary battery including the samme, and manufacturing method thereof - Google Patents

Abstract

An anode material for a secondary battery according to the present invention includes metal-doped silicon oxide represented by the chemical formula SiMxOy wherein Si represents silicon, x represents metal, y represents oxygen, and x and y satisfy that 0.1<=x<=1.0 and 0.01<=y<=2.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a metal-doped silicon oxide, an anode material for a secondary battery including the metal oxide, and a method for manufacturing the anode material.

The present invention relates to a negative electrode material for improving the energy density of a middle- or large-sized lithium secondary battery which requires a high output and a high voltage, and more particularly, to a negative electrode material for improving the energy density of SiMOx oxide doped with metal particles in silicon oxide having an oxygen content of less than 2, &Lt; / RTI &gt;

BACKGROUND ART [0002] Portable electronic devices have rapidly developed, and secondary batteries having high energy density, stability, small size, light weight, and long life have been demanded. The performance improvement of the lithium secondary battery is basically based on improvement of the performance of the three components of the anode, the cathode, and the electrolyte. Among them, the cathode material is being developed for the drastic increase of the capacity. Currently, commercialization of graphite, which is a negative electrode active material, is limited to a theoretical capacity of 372 mAh / g. Therefore, development of a negative electrode material using silicon, tin, and aluminum as a material to replace the graphite anode material has been studied.

Among them, silicon has a theoretical capacity of 4200 mAh / g, but cracks are generated in the electrode and the surface due to a high volume expansion rate in the process of alloying with lithium, and the cycle capacity is rapidly reduced due to deterioration of electrical contact There is a problem of degradation.

Silicon or tin-based high-capacity non-carbon based electrode materials are characterized in that the coulomb efficiency is low until the initial 10 to 20 cycles, and the cost increases in the process of lithium insertion and desorption according to cycling. Particularly, silicon oxide has an advantage that Li ₂ O is generated while lithium (Li) is inserted in the initial charging process, thereby alleviating the volume expansion of silicon, and at the same time, irreversible cost is generated, which is a problem in designing an actual battery . In addition, when the vapor phase method is used in the production of silicon nano-oxide, it is disadvantageous in that it is difficult to use commercially because of the increase in the price.

Many researchers have been studying the alloying of silicon, surface modification of silicon, and silicon composite as a way to overcome the problems of silicon. Alloying of silicon material can reduce excessive volume change during charging / discharging by controlling insertion reaction between lithium and silicon. Generally, iron, nickel, and copper are used as alloying material. However, And silicon alloying and surface modification for silicon are inevitable.

An object of the present invention is to provide metal oxide-doped silicon oxide as a negative electrode active material for a secondary battery, which is a high-capacity negative electrode active material for replacing existing graphite anode materials used in electric vehicles and energy storage systems, and a method of manufacturing the same.

It is another object of the present invention to provide a method for producing a silicon oxide doped with a metal which is simple and low-cost by doping a metal element through mechanical alloying with a silicon oxide having an oxygen content of less than 2.

The negative electrode material for a secondary battery according to the present invention comprises a silicon oxide doped with a metal element represented by the formula SiMxOy wherein Si represents silicon, x represents metal and y represents oxygen, and x and y satisfy 0.1? X? 1.0 And 0.01 < = y &lt; 2. The metal element is preferably a transition metal element that does not react with lithium, and at least one selected from the group consisting of Ni, Fe, Ti, Co, Ge, Ca and Al can be used. More preferably, the metal element is Ni.

In addition, a method of manufacturing a metal-doped silicon oxide according to the present invention includes a first step of preparing a mixed powder by mixing a silicon oxide powder represented by the general formula SiOx (0 <x <2) and a metal powder; And milling the mixed powder in an inert gas atmosphere to produce a silicon oxide doped with a metal element, wherein the silicon oxide doped with the metal element is represented by the formula SiMxOy, wherein Si is silicon, x is a metal and y represents oxygen, and x and y are characterized by being in the range of 0.1 ≦ x ≦ 1.0 and 0.01 ≦ y <2, respectively.

In the manufacturing method according to the present invention, the mixed powder is mixed with not less than 70 parts by weight and not more than 80 parts by weight of the silicon oxide powder, and not less than 20 parts by weight and not more than 30 parts by weight of the metal powder, . For example, the transition metal may be at least one selected from the group consisting of Ni, Fe, Ti, Co, Ge, Ca, and Al. In the first step, the metal powder is preferably a transition metal that does not react with lithium. Can be used. More preferably, the metal powder is Ni.

The silicon oxide powder represented by the formula SiOx (0 < x < 2) in the first step may be prepared by mixing (1) silicon chloride and a glycol, which is a dihydric alcohol, to form a porous material, and (2) And forming the silicon oxide by heat-treating the porous material in an inert gas atmosphere.

The metal oxide doped silicon oxide according to the present invention can be prepared by the above-described manufacturing method, in particular, when the metal oxide doped silicon represented by the formula SiMxOy, Si is silicon, x is a metal and y is oxygen X and y are in the range of 0.1 ≦ x ≦ 1.0 and 0.01 ≦ y <2, respectively.

According to the present invention, it is possible to provide a silicon oxide having an oxygen content of less than 2 as a negative electrode material, which is a negative electrode active material used in a middle- or large-sized secondary battery and a high capacity electric automobile. Particularly, according to the manufacturing method of the present invention, it is possible to manufacture a silicon oxide powder of a high capacity which can control the particle size organically and which can suppress the volume expansion upon charging and discharging, at low cost. In addition, the production method according to the present invention is very effective for the production of a metal-doped silicon oxide powder capable of drastically improving the characteristics of a material for energy storage.

1A, 2A, and 3A show electron micrographs of SiOx-metal [Ni, Fe, Ti] powders prepared according to the present invention.
Figures 1B, 2B and 3B show energy diffraction patterns of respective metal particles (i.e., Ni, Fe and Ti) in the silicon oxide produced according to the present invention.
4 shows an XRD diffraction pattern for confirming the crystal structure of a metal-doped silicon oxide powder produced by the present invention.
FIG. 5 shows electrochemical characteristics of metal-doped silicon oxide powders prepared according to the present invention.

Hereinafter, preferred embodiments of the metal-doped silicon oxide and the method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.

The silicon oxide doped with the metal element according to the present invention uses silicon oxide having an oxygen content of less than 2. That is, as expressed by the formula SiOx, x is a silicon oxide having a range of 0 < x < 2, which can be produced by using a chemical reaction between a silicon chloride and an alcohol compound. The silicon oxide thus produced is doped with a metal element in a silicon oxide crystal lattice by a mechanical alloying method as a solid phase reaction method to produce a metal-doped silicon oxide. The doped metal atoms serve as a transfer path of electrons to promote the diffusion of lithium ions. Therefore, the negative electrode material for a secondary battery manufactured using the metal-doped silicon oxide according to the present invention has an improved electrochemical property, .

Hereinafter, a method of manufacturing the above-described metal-doped silicon oxide will be described in more detail.

[Preparation of silicon oxide powder having an oxygen content of less than 2]

First, silicon chloride having a purity of 90% or more, if possible, is mixed with glycol, a divalent alcohol represented by the general formula R (OH) 2, to prepare a porous material. Examples of the silicon chloride having a purity of 90% or more include silicon tetrachloride (silicon tetrachloride), dialkyl dichlorosilane (RRSiCl2; Diacyldichlorosilane], and the like, and the glycol may include all alcohols represented by R (OH) 2, that is, ethylene glycol, propylene glycol, pinacol, and the like. The silicon chloride and glycols are rapidly mixed to prepare a porous material. In the case of adding silicon chloride to the glycol, a large amount of sponge-like porous material can be produced by a rapid reaction. Conversely, glycol may be added to the silicon chloride, in which case the porous material and the sol-state liquid material may be formed together. In the reaction of silicon chloride with glycol, the reaction rate can be controlled within a chemical weight ratio, and can be adjusted to have a reaction time of 1 minute to 60 minutes in consideration of rapid mixing time and weight ratio in real time mixing.

On the other hand, the mixing ratio of the silicon chloride and the glycol is controlled within the range of 0.1: 0.9 to 0.9: 0.1 in order to produce HCl by hydrogen reaction of chlorine and glycol in the silicon chloride so that the silicon oxide can be prepared easily . Here, when the weight ratio of the silicon chloride to the total mixture of silicon chloride and glycol is less than 10 wt%, the oxidation reaction in the silicon is not carried out smoothly and silicon oxide can not be formed. If the weight ratio of the silicon chloride to the whole mixture exceeds 90 parts by weight, the chlorine reaction in the glycol explosively increases and the silicon oxide can be dissolved.

Next, the porous starting material produced by the above-described method is heat-treated to form a silicon oxide having an oxygen content of less than 2. More specifically, the produced porous initial material is heat-treated in an inert gas atmosphere using a mixed gas of hydrogen, nitrogen, argon, or a mixture of these three kinds of gases. The prepared porous starting material is subjected to heat treatment at 600 ° C to 900 ° C for 15 minutes to 6 hours in a vertical or horizontal or a heat treatment furnace including a conveyor belt. During the heat treatment, the chlorine gas is evaporated by the reaction of chlorine in the silicon chloride with carbon in the glycol, and by reaction of the silicon cluster in the silicon chloride with oxygen in the glycol, silicon oxide having an oxygen content of less than 2 is produced. The reason why the inert gas atmosphere is maintained during the heat treatment is that when an oxidizing gas or a reducing gas is included, an oxidizing atmosphere for oxide formation of less than 2 is not formed.

On the other hand, when the heat treatment temperature is less than 600 ° C., the reaction rate of chlorine and hydrogen is lowered, so that chlorine gas can not be removed as much as possible, and silicon oxide is not easily produced. If the temperature exceeds 900 ° C., the particle size of the produced silicon oxide grows, which may ultimately cause a secondary battery depletion problem. Also, due to the explosive generation of chlorine gas, Or more can be produced. If the heat treatment temperature is less than 15 minutes, silicon oxide formation is not easy, and if it exceeds 6 hours, particle growth may be caused. During the cooling after the heat treatment, it is preferable to perform air cooling or slow cooling to 20 deg. Or less per minute because excessive quenching may cause a problem that the electrochemical characteristics are lowered due to grain size growth.

The silicon oxide prepared by the above-mentioned method is composed of a bulk material as a porous material. The bulk of the bulk state is a state in which nanoparticles are aggregated and must be formed in powder form for application to a secondary cell and control of particle size. For this purpose, it is desirable to control the particle size of the bulk silicon oxide mass produced above through a ball mill. In the case of a ball mill, the particle size is extremely fine and electrochemical characteristics may be deteriorated. Therefore, it is preferable to control the rotation speed to 300 rpm or less and control the ball mill time to 12 hours or less.

[Synthesis of SiOx and metal dopant]

The silicon oxide produced by the above-described method has a normal concentration because the content of oxygen is less than 2. That is, the quasi-stable phase silicon oxide is not perfect in its crystal structure, so that doping can be performed smoothly. The prepared silicon oxide powder of SiOx (0 < x < 2) is mixed with a metal powder which provides a metal element to prepare a mixed powder. Here, it is preferable to mix at least 70 parts by weight and not more than 80 parts by weight of silicon oxide of SiOx (0 < x < 2) and not less than 20 parts by weight and not more than 30 parts by weight of the metal powder with respect to 100 parts by weight of the total mixed powder Do. The thus prepared mixed powder is ball-milled for 1 hour to 24 hours at a rotation speed of 100 to 500 rpm in an inert gas (e.g., argon) atmosphere using a ball milling machine to produce a metal-doped silicon oxide. At this time, when the weight ratio of the metal powder is less than 20 wt%, the metal elements are not uniformly doped in the crystal lattice, so that it is difficult to act as a movement path of electrons in the crystal lattice. In addition, when the weight ratio of the metal powder is more than 30 wt%, the metal element that is above the solubility limit that can be doped in the crystal lattice is doped so that the metal element can be eluted in a cluster state on the silicon oxide surface.

The average particle diameter of the silicon oxide having the oxygen number of 2 or less doped with the metal element thus prepared is preferably 50 nm to 30 탆, particularly preferably 85 nm to 15 탆.

On the other hand, the material of the metal powder is preferably selected from transition metals which do not react with lithium. In particular, at least one metal element selected from the group consisting of Ni, Fe, Ti, Co, Ge, Ca and Al can be used.

Ball milling machines that can be used for milling mixed powders include shaker milling machines, planetary milling machines, attritor milling machines, and magnetic milling machines used for high-energy ball milling. Ball milling vessels are made of stainless steel, zirconia Can be used. In case of ball milling, reactive ball milling may be used in which an inert gas such as nitrogen, hydrogen or argon is mixed or solely used to prevent oxidation of the metal elements, and then ball milling is performed after injection into the vessel.

In addition, powder having a particle size of 325 mesh or less can be used as the metal powder, and when using a metal element having a particle diameter exceeding 325 mesh, there is a problem of being eluted on the surface during ball milling.

Hereinafter, a specific example of a method for producing a silicon oxide having a metal-doped oxygen number of less than 2 according to the present invention will be described.

[Example]

First, a silicon oxide having an oxygen content of less than 2 was prepared. To prepare the porous material as an initial material, silicon tetrachloride [SiCl4, 98%] and ethylene glycol [99%] were mixed at a weight ratio of 1: 1. At this time, ethylene glycol was first placed on the base, and then silicon tetrachloride was mixed. When the reaction time of silicon tetrachloride and ethylene glycol was prolonged for a long time, the porous material was not prepared but proceeded to a sol state in a liquid state. Therefore, after the reaction, the porous material in the form of sponge was immediately collected and transferred to zirconia paul. During the mixing, the mixture was reacted while mixing through a stirrer so that the reaction proceeded smoothly.

The porous material thus formed was transferred to zirconia paul and then charged into a vertical tubular furnace maintained with nitrogen gas as an inert gas, and heat treatment was performed at 750 ° C. for 2 hours. At this time, the temperature was maintained at 5 to 25 ° C per minute in the heat treatment to 750 ° C. When the rate of temperature rise is less than 5 ° C per minute, the reaction rate due to the heat of reaction is not favorable, so that the oxidation-reduction reaction in the porous material does not proceed smoothly. When the rate of temperature increase exceeds 25 ° C, the oxidation reaction is accelerated by rapid heat treatment Silicon oxide is not produced. A more preferable heating rate is 5 ° C per minute.

After the heat treatment, the material was cooled through air cooling to obtain a bulk lump material, followed by pulverization through a mortar or ball mill. At this time, the rotation speed of the ball miller was controlled to 300 rpm or less and the ball mill time was controlled to be 12 hours or less. More preferably, the rotational speed is set to 100 rpm and the ball mill time is limited to 30 minutes or less.

The silicon oxide having an oxygen number of less than 2 and the metal powder (Ni, Fe and Ti metal powder) produced by the above method were mixed at a weight ratio of 75:25, and then charged into a ball milling container charged with argon gas. Then, Milled for 6 hours at a rotational speed of 30 DEG C to obtain a silicon oxide of less than 2 in which metal elements were doped.

The anode electrode was fabricated using the doped silicon oxide thus obtained. That is, 5 g of each of the anode active materials obtained in the above (namely, Ni-doped SiOx, Fe-doped SiOx and Ti-doped SiOx), 0.2 g of carbon black conductive material and 0.1 wt% of carboxymethyl cellulose (CMC) 7.5 g of an aqueous solution containing 40% by weight of styrene butadiene rubber (SBR) was mixed and adjusted to a viscosity of 1,000 cP (centi-poise), which is easy to apply to a copper thin film. Lt; / RTI &gt; The stirred slurry was coated on copper foil having a thickness of 10 mu m to a thickness of 100 mu m using a doctor blade method, followed by drying and rolling to prepare an anode plate. Then, it was cut into a predetermined size (3 × 4 cm) and dried in a vacuum oven at 80 ° C. for 24 hours before assembling the cell.

In the case of a half-cell, a lithium metal electrode is laminated as a counter electrode. A polypropylene (PP) separator is inserted between the two electrodes, and a mixture of ethyl carbonate (EC) And an electrolytic solution in which 1 M of LiPF ₆ was dissolved in an organic solvent having a volume ratio of 1: 1: 1 mixed with EMC / dimethyl carbonate (DMC) was injected into the aluminum pouch battery. In the case of a full battery, a positive electrode plate using lithium cobalt oxide as a positive electrode active material as a counter electrode was prepared, and then the same structure as that of the above half cell was constructed.

The results of electron microscopy, X-ray diffraction analysis and electrochemical characteristics evaluation of the metal-doped silicon oxide prepared according to the present invention are as follows.

1A, 2A and 3A are electron micrographs of SiOx-metal [Ni, Fe, Ti] powders prepared according to the present invention. 1A, 1A), Fe-doped SiOx (Example 2; FIG. 2A), and Ti-doped SiOx (Example 3; 3A), it can be seen that the particle size is in the range of 5 to 10 mu m, and that the metal particles are uniformly distributed in the SiOx. 1B, 2B, and 3B show the energy diffraction patterns of the respective metal particles (i.e., Ni, Fe, and Ti) in the silicon oxide produced according to the respective embodiments, It can be confirmed that the elements are uniformly doped.

FIG. 4 shows an XRD diffraction pattern for confirming the crystal structure of the metal-doped silicon oxide powder produced by the present invention. As shown in FIG. 2, it can be seen that Examples 1 to 3 have a crystal structure of silicon oxide having an oxygen content of less than 2, which is different from the diffraction pattern of SiO ₂ , which is a stable oxide of silicon. As a result, it was confirmed that the diffraction pattern of the doped metal elements did not appear through the XRD diffraction analysis of FIG. 4, indicating that the elution of the doped metal elements did not occur.

FIG. 5 shows electrochemical characteristics of metal-doped silicon oxide powders prepared according to the present invention. As shown in FIG. 3, it can be seen that the metal oxide-doped silicon oxide maintains a high capacity and lifetime of 1210-1600 mAh / g. Particularly, in the case of Ni-doped silicon oxide (Example 1; denoted by "Ni-doped SiOx" in FIG. 5), it was confirmed that the charge-discharge capacity and charge-discharge efficiency were as high as 84% or more. In addition, in the case of Fe and Ti (denoted by "Fe doped SiOx" and "Ti doped SiOx" in FIG. 5, respectively), it was confirmed that a high capacity and easy charge and discharge efficiency were shown. The reason for the improvement in capacity and lifetime of the silicon oxide anode material due to the doping of the metal element is that the metal element is doped in the crystal lattice of the silicon oxide to form a sufficient crystal lattice interval for allowing lithium to diffuse, And the capacity was increased. Also, in the case of Ni, Fe, and Ti, there is an advantage that the electric conductivity is improved because it is a conductive material having electric conductivity. Further, the lifetime is improved to 15 cycles or more in the embodiments according to the present invention because the doped metal elements are not oxidized to SiO ₂ in the crystal lattice in the crystal lattice, and the volume expansion of the anode material does not occur.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. It is therefore to be understood that the embodiments of the invention described herein are to be considered in all respects as illustrative and not restrictive, and the scope of the invention is indicated by the appended claims rather than by the foregoing description, Should be interpreted as being included in.

Claims (11)

A silicon oxide doped with a metal element represented by the formula SiMxOy, wherein Si represents silicon, x represents a metal and y represents oxygen, and x and y are in the range of 0.1 ≦ x ≦ 1.0 and 0.01 ≦ y <2, respectively. A negative electrode material for a secondary battery, characterized in that.
The method of claim 1,
The metal element is a negative electrode material for a secondary battery, characterized in that the transition metal element does not react with lithium.
3. The method of claim 2,
Wherein the transition metal element is at least one selected from the group consisting of Ni, Fe, Ti, Co, Ge, Ca and Al.
The method of claim 1,
The metal element is a negative electrode material for a secondary battery, characterized in that Ni.
A first step of preparing a mixed powder by mixing a silicon oxide powder represented by the general formula SiOx (0 < x < 2) and a metal powder; And
And a second step of milling the mixed powder in an inert gas atmosphere to produce a silicon oxide doped with a metal element,
When the silicon oxide doped with the metal element is represented by the formula SiMxOy, Si represents silicon, x represents metal and y represents oxygen, and x and y are in the range of 0.1≤x≤1.0 and 0.01≤y <2, respectively. Method for producing a metal oxide doped silicon.
The method of claim 5, wherein
In the first step, the mixed powder is formed by mixing 70 parts by weight or more and 80 parts by weight or less of the silicon oxide powder, 20 parts by weight or more and 30 parts by weight or less of the metal powder, &Lt; / RTI &gt; wherein the metal-doped silicon oxide is doped.
The method of claim 5, wherein
Wherein the metal powder is a transition metal that does not react with lithium in the first step.
The method of claim 7, wherein
Wherein the transition metal is at least one selected from the group consisting of Ni, Fe, Ti, Co, Ge, Ca and Al.
The method of claim 5, wherein
Wherein the metal powder is Ni. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
The method of claim 5, wherein
In the first step, the silicon oxide powder represented by the formula SiO x (0 <x <2) may include (1) mixing a silicon chloride and a glycol which is a dihydric alcohol to form a porous material, and (2) the porous A method of producing a metal-doped silicon oxide, characterized in that the material is prepared through the step of forming a silicon oxide by heat treatment in an inert gas atmosphere.
A metal oxide doped with a metal produced by the manufacturing method according to any one of claims 5 to 10, wherein the silicon oxide is represented by the formula SiMxOy, Si is silicon, x is metal and y is oxygen. And x and y are in the ranges of 0.1 ≦ x ≦ 1.0 and 0.01 ≦ y <2, respectively.

Images