KR20160125330A - Anode active material for secondary battery and method of manufacturing the same - Google Patents

Abstract

Provided is a negative electrode active material for a secondary battery, which provides high capacity and high efficiency charging/discharging characteristics. The negative electrode active material for a secondary battery includes a silicon single phase, and a silicon-metal alloy phase interfaced with the silicon single phase and distributed around the silicon single phase. The negative electrode active material includes 0-30 atomic percent (at%) of iron (Fe), 0-10 at% of first additive element, and 60-90 at% of silicon. The first additive element is one element selected from a group consisting of boron, carbon, phosphorous, titanium, chrome, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, and tin. The negative electrode active material has a first peak and a second peak which are originated from the silicon-metal alloy phase in an X-ray diffraction analysis, wherein the first peak is located at 49.1+/-0.5 degrees and the second peak is located at 38.0+/-0.5 degrees, and the diffraction intensity of the first peak is less than or equal to two times that of the second peak.

Description

[0001] The present invention relates to an anode active material for secondary batteries,

TECHNICAL FIELD The present invention relates to a secondary battery, and more particularly, to a negative electrode active material for a secondary battery capable of providing high capacity and high efficiency charging / discharging characteristics, and a method of manufacturing the secondary battery.

Recently, the lithium secondary battery has been used as a power source for portable electronic products including mobile phones and notebook computers, as well as being used as a medium and large power source for hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (plug-in HEV) Applications are rapidly expanding. As the application field is expanded and demand is increased, the external shape and size of the battery are variously changed, and capacity, lifetime, and safety are demanded more than those required in conventional small batteries.

The lithium secondary battery is generally manufactured by using a material capable of intercalating and deintercalating lithium ions as a cathode and an anode, providing a porous separator between the electrodes, and then injecting an electrolyte. And electricity is generated or consumed by the redox reaction by insertion and desorption of lithium ions in the anode.

Graphite, which is a negative electrode active material widely used in conventional lithium secondary batteries, has a layered structure and is very useful for insertion and desorption of lithium ions. Theoretically, graphite has a capacity of 372 mAh / g, but with the recent increase in demand for high capacity lithium batteries, a new electrode capable of replacing graphite is required. Accordingly, researches for commercialization of electrode active materials such as silicon (Si), tin (Sn), antimony (Sb), aluminum (Al) and the like that form an electrochemical alloy with lithium ion as a high capacity negative electrode active material are actively conducted . However, silicon, tin, antimony, and aluminum have the characteristics of increasing / decreasing the volume during charging / discharging through the formation of an electrochemical alloy with lithium. The volume change due to such charging / , The electrode cycle characteristics are deteriorated in an electrode in which an active material such as aluminum is introduced. Also, such a change in volume causes cracks on the surface of the electrode active material, and continuous crack formation causes undifferentiation of the surface of the electrode, thereby deteriorating cycle characteristics.

1. Korean Patent Publication No. 2009-0099922 (Published September 23, 2009) 2. Korean Patent Publication No. 2010-0060613 (Published on Jun. 7, 2010) 3. Korea Patent Publication No. 2010-0127990 (Dec. 07, 2010)

SUMMARY OF THE INVENTION The present invention provides a negative electrode active material for a secondary battery capable of providing a high capacity and high efficiency of charge / discharge characteristics.

According to another aspect of the present invention, there is provided a method for manufacturing a negative electrode active material for a secondary battery.

According to an aspect of the present invention, there is provided a negative active material for a secondary battery, comprising: a silicon single phase; And a silicon-metal alloy phase forming an interface with the silicon single phase and surrounding the silicon single phase, wherein the negative active material comprises 0 to 30 atomic% Fe, 0 to 10 atomic% Wherein the first additive element is selected from the group consisting of boron, carbon, phosphorus, titanium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum , And tin, wherein the anode active material has a first peak and a second peak of the silicon-metal alloy phase represented by the silicon-metal alloy phase in an X-ray diffraction analysis, and the first active material The peak has a peak of 49.1 +/- 0.5 degrees ([deg.]), The second peak is 38.0 +/- 0.5 degrees ([deg.]), And the diffraction intensity of the first peak is twice or less .

In an exemplary embodiment, the first peak on the silicon-metal alloy is a diffraction peak by crystallographic (102) face on ferrosilicon (FeSi2) and the second peak on the silicon- (101) plane on the ferrosilicon (FeSi ₂ ).

In exemplary embodiments, the diffraction intensity of the first peak relative to the diffraction intensity of the second peak may be 1.8 to 1.9 times.

In the exemplary embodiments, the negative active material further has a third peak on the silicon-metal alloy phase represented by the silicon-metal alloy phase in an X-ray diffraction analysis, and the third peak has a peak at 17.3 +/- 0.5 degrees (°), and the third peak may be a diffraction peak due to a crystallographic (001) plane on ferrosilicon (FeSi ₂ ).

In exemplary embodiments, the negative active material further has a fourth peak of 28.5 +/- 0.5 degrees ([deg.]) As indicated by the crystallographic (111) plane of the silicon single phase, (nm) or less.

In the exemplary embodiments, the negative electrode active material may have a specific resistance of 0.2? Cm or less in a state of being compressed with a load of 4 to 20 kN.

In the exemplary embodiments, the electrode made of the negative electrode active material is expanded to a volume of 50% or less of the thickness of the initial electrode plate at the time of single charging, and the volume expansion is 50% or less of the initial electrode plate thickness after repeated charging / can do.

According to another aspect of the present invention, there is provided a method of manufacturing an anode active material for a secondary battery, the method including: forming a first powder containing silicon, a second powder containing iron, and a third powder including a first additive element ≪ / RTI > And forming a negative electrode active material containing silicon, iron and a first additive element by pulverizing and finely grinding the mixture by a mechanical alloying method, wherein the first additive element is selected from the group consisting of boron, carbon, phosphorus, titanium, Wherein the silicon single element is an element selected from the group consisting of chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, and tin, The anode active material including a silicon-metal alloy phase surrounding the silicon single phase is formed.

In the exemplary embodiments, the mechanical alloying method may be performed by any one of vertical attrition milling, horizontal attrition milling, ball milling, planetary milling and Spex milling .

In exemplary embodiments, the step of providing the mixture may comprise providing the mixture by incorporating the first powder, the second powder and the third powder into a pulverizing container in powder form .

In exemplary embodiments, the step of providing the mixture may comprise mixing an intermediate powder comprising silicon and iron formed by melting and cooling the first and second powders and the third powder into a milling vessel And providing the mixture.

In exemplary embodiments, the step of providing the mixture may comprise providing an intermediate powder comprising silicon, iron and a first additive element formed by melting and cooling the first powder, the second powder and the third powder, And providing the mixture by incorporation into a grinding vessel.

The negative electrode active material for a secondary battery according to the present invention can uniformly distribute the silicon single phase in the silicon-metal alloy phase, thereby suppressing the change in volume due to charge / discharge of the negative active material. The secondary battery including the negative electrode active material has excellent lifetime characteristics and excellent electrochemical characteristics.

1 is a flow chart showing a manufacturing process of a negative electrode active material according to exemplary embodiments.
2 is a flowchart showing a manufacturing process of a negative electrode active material according to exemplary embodiments.
3 is a flow chart showing a manufacturing process of the negative electrode active material according to the exemplary embodiments.
4 is a graph showing an X-ray diffraction pattern of the negative electrode active material according to the exemplary embodiments.
5A and 5B are graphs showing the electrical performance of negative electrode active materials according to exemplary embodiments.
6 is a graph showing the electrochemical performance of the negative electrode active material according to the exemplary embodiments.
7A to 7C are scanning electron microscopy (SEM) images of an anode active material according to exemplary embodiments.
FIG. 8 is a transmission electron microscopy (TEM) image of an anode active material according to Exemplary Embodiment 2. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. The scope of technical thought is not limited to the following examples. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The same reference numerals denote the same elements at all times. Further, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing depicted in the accompanying drawings. In the embodiments of the present invention, at% (atomic%) represents the number of atoms occupied by the component in the total atomic number of the whole alloy as a percentage.

The negative electrode active material for a secondary battery according to exemplary embodiments includes a silicon single phase; And a silicon-metal alloy phase which interfaces with the silicon single phase and surrounds the silicon single phase. Wherein the negative active material comprises 0 to 30 atomic% of iron (Fe), 0 to 10 atomic% of a first additive element and 60 to 90 atomic% of silicon, and the first additive element is boron, carbon, , Chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, and tin. Wherein the anode active material has a first peak and a second peak on the silicon-metal alloy phase represented by the silicon-metal alloy phase in an X-ray diffraction analysis, and the first peak has a peak of 49.1 +/- 0.5 degrees ([ And the second peak is 38.0 +/- 0.5 degrees ([deg.]). The diffraction intensity of the first peak is not more than two times the diffraction intensity of the second peak. Wherein the first peak on the silicon-metal alloy is a diffraction peak due to a crystallographic (102) face on ferrosilicon (FeSi2) and the second peak on the silicon-metal alloy is a ferrosilicon (FeSi2) It is the diffraction peak due to the crystallographic (101) plane. Preferably, the diffraction intensity of the first peak relative to the diffraction intensity of the second peak may be 1.8 to 1.9 times.

In exemplary embodiments, the relative sizes of the diffraction intensities of the first and second peaks on the silicon-metal alloy phase are related to the microstructure of the negative active material. For example, in the case of the negative electrode active material containing the first additive element, the silicon single phase can be uniformly distributed in a fine size. In addition, the first additional element is contained in the silicon-metal alloy phase so that stress acts in the lattice of the ferrosilicon crystal structure, and distortion thereof may occur. Further, the lattice of the silicon-metal alloy phase can be deformed (contracted or expanded) by the first additional element. As a result, the intensity of the first peak decreases greatly, while the intensity of the second peak decreases relatively. As the microstructure changes of the silicon-metal alloy phase by the first additive element effectively buffer the volume expansion during charge and discharge, the negative electrode active material has improved electrochemical characteristics (for example, discharge capacity or cycle performance) . The relationship between the microstructure of the negative electrode active material and the relative magnitudes of the diffraction intensities of the first and second peaks will be described later in detail with reference to FIG.

In an exemplary embodiment, the negative active material further comprises a third peak on the silicon-metal alloy phase represented by the silicon-metal alloy phase in an X-ray diffraction analysis, and the third peak has a peak at 17.3 +/- 0.5 degrees ( 0.0 >).≪ / RTI > The third peak may be a diffraction peak due to a crystallographic (001) plane on ferrosilicon (FeSi ₂ ).

Further, in exemplary embodiments, the negative electrode active material may further have a fourth peak of 28.5 +/- 0.5 degrees ([deg.]) As indicated by the crystallographic (111) plane of the silicon single phase. The silicon single phase may have an average crystal grain size of less than 50 nanometers (nm). When the silicon single phase is uniformly distributed within the silicon-metal alloy phase in a fine size, the silicon-metal alloy as a matrix can act as a buffer layer to buffer the volume change of the single phase of silicon due to the insertion / And cracks and damage of the negative electrode active material due to such volume change can be prevented. Therefore, the negative electrode active material can have excellent lifetime characteristics.

The negative electrode active material according to the exemplary embodiments may have a resistivity of 0.2? Cm or less under a compressive load of 4 to 20 kN. Particularly, in the negative electrode active material, since the single stage silicon is dispersed in a fine size in the silicon-metal alloy phase and the lattice constant of the single phase of silicon is less than about 50 nanometers, it has a low specific resistance and excellent electric conduction characteristic have. In addition, the secondary battery using such an anode active material may have a high capacity and a high energy density as the voltage drop (iR drop) due to the electrode resistance is reduced or the electric conductor content to be added is decreased.

The anode active material for a secondary battery according to the exemplary embodiments is subjected to a pulverization and refinement process of a silicon powder using a mechanical alloying method so that the silicon single phase can be uniformly distributed in a fine size inside the silicon-metal alloy phase.

In exemplary embodiments, after a mixture of a first powder comprising silicon, a second powder comprising iron and a third powder comprising the first additive element is provided, the mixture is pulverized by mechanical alloying, Wherein the first additive element can be selected from the group consisting of boron, carbon, phosphorus, titanium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium , Molybdenum, and tin. At this time, the single-phase silicon having a mean crystal grain size of 50 nm or less and the silicon-metal alloy phase surrounding the single-phase silicon are formed by pulverizing and finely grinding the mixture by a mechanical alloying method, Can be formed.

The mechanical alloying method can form a negative electrode active material having a fine silicon single phase distribution by dry-milling and alloying the first powder, the second powder and the third powder as the powdery mixture. By such a method, a negative electrode active material having a small specific resistance can be formed.

In addition, in the exemplary embodiments, the silicon powder, the iron powder, and the first additive element powder are subjected to a vertical attrition milling, a horizontal attrition milling, a ball milling, a planetary mill and a Spex milling ) To mill and alloy them by a mechanical alloy method to form an anode active material. In particular, the mixture may be provided by incorporating the first powder, the second powder and the third powder in a powder form into a pulverizing vessel. Therefore, for example, after the active material is melted at a high temperature and rapidly cooled to form a primary alloy (for example, a ribbon alloy), the primary alloy is pulverized to form a negative electrode active material powder, So that complicated multi-step processes can be omitted, and the manufacturing cost can be reduced.

However, it is also possible to use the rapid cooling scheme described above in the exemplary embodiments. For example, the first powder containing silicon and the second powder containing iron are melted and cooled to form an intermediate powder containing silicon and iron, and then the intermediate powder containing the intermediate powder and the first additive element The mixture may be provided by mixing and injecting the third powder into a grinding vessel.

Further, the mixture may be provided by injecting an intermediate powder containing silicon, iron and a first additive element formed by melting and cooling the first powder, the second powder and the third powder into a pulverizing vessel.

Hereinafter, the manufacturing process of the negative electrode active material according to the exemplary embodiments will be described in more detail.

1 is a flow chart showing a manufacturing process of a negative electrode active material according to exemplary embodiments.

Referring to FIG. 1, a first powder including silicon, a second powder including iron, and a third powder including a first additive element may be provided (step S10). The first additional element may be at least one element selected from the group consisting of boron, carbon, phosphorus, titanium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, and tin.

The mass of the first to third powders may be weighed so that the negative electrode active material to be formed comprises 60 to 90 atomic percent of silicon, 0 to 30 atomic percent of iron and 0 to 10 atomic percent of the first additive element, respectively. For example, 66.83 grams of silicon, 29.9 grams of iron and 3.27 grams of manganese may be prepared to form a negative active material comprising, for example, 80 atomic percent silicon, 18 atomic percent iron, and 2 atomic percent manganese.

Thereafter, the first to third powders may be pulverized and alloyed by a mechanical alloying method to form a negative active material powder in which a fine silicon single phase is distributed in a silicon-metal alloy phase (step S20).

In an exemplary process, after charging the first powder, the second powder, and the third powder into the pulverizing vessel, the first to third powders may be mixed, pulverized and refined by mechanical alloying.

For example, a mixture of the powders and a milling ball may be drawn into the milling vessel, and the milling energy may pulverize and alloy the powders in a short time. The mixture of the powders can be pulverized into finer powders having a finer size. Particularly, forging, cold pressure welding, and crushing may repeatedly occur between the fine powders ground by the rotation of the milling balls and the impact caused by the collision. As a result, the interfacial energy increase becomes a driving force in the process of mixing the fine powders, so that the solid phase diffusion of the atoms is promoted and microalloying may occur. Therefore, a negative electrode active material powder in which silicon, iron and a first additive element are alloyed can be formed. In the negative electrode active material powder, the silicon single phase may be uniformly distributed in the silicon-metal alloy phase, and the first additive element may be substituted or interstitially contained in the silicon-metal alloy phase, And the silicon single phase.

As the microalloying progresses, the silicon single phase formed in the powder can be changed into a fine silicon single phase, and a fine silicon single phase can evenly be distributed using the silicon-metal alloy phase as a matrix. For example, the anode active material powder formed by the pulverization and alloying process may have a uniform particle size of 50 nm or less in the single phase of the silicon.

In the exemplary embodiments, the mechanical alloying process may be performed by any suitable method, such as vertical attrition milling, horizontal attrition milling, ball milling, planetary milling, and Spex milling. Milling device. For example, the mechanical alloying method may be performed for several tens of minutes to several tens of hours at a speed of about 200 to 1800 rpm using a horizontal-type milling machine.

In the exemplary embodiments, the negative electrode active material may be provided by repeatedly performing two or more milling processes with different rotational speeds. Particularly, the negative electrode active material may be formed by repeatedly performing, for example, a first step of pulverizing at a rotation speed of 1300 rpm for 45 seconds and a second step of pulverizing at a rotation speed of 700 rpm for 15 seconds. The rotation speed and the milling time described above are exemplary and the rotation speed and the milling time may vary depending on the size distribution of the finally obtained negative electrode active material powder particles, the average particle size of a single silicon phase in the negative electrode active material, and the like.

According to the method for manufacturing the negative electrode active material according to the exemplary embodiments, the powders of silicon, iron and the first additive element can be refined or alloyed by the mechanical alloying method, so that the manufacturing process can be facilitated. Also, by the mechanical alloying method, a negative electrode active material in which a fine silicon single phase is uniformly distributed in a silicon-metal alloy phase can be provided.

2 is a flowchart showing a manufacturing process of a negative electrode active material according to exemplary embodiments.

Referring to FIG. 2, the first powder including silicon and the second powder including iron may be melted and cooled to form an intermediate powder in which a single silicon phase is distributed within the silicon-metal alloy phase (step S11a) .

In an exemplary process, a first powder containing silicon and a second powder containing iron are charged in a melting vessel, and then the molten mixture is melted by arc melting, high-frequency melting, The vessel may be heated to form an alloy melt. At this time, in order to prevent the undesired oxidation of the melt, a melt can be formed in a vacuum atmosphere or an inert gas atmosphere such as argon or nitrogen. For example, the heating temperature of the melting vessel can be maintained at a temperature at least 200 ° C above the melting point of the alloy melt, thereby allowing the alloy melt in the melting vessel to be sufficiently melted and mixed.

In an exemplary process, the alloy melt may be quenched and solidified by a melt spinning method or the like to form a ribbon alloy, and the ribbon alloy may be pulverized to form an intermediate powder containing silicon and iron.

For example, in an exemplary process of forming a ribbon alloy using a melt spinner, the alloy melt is discharged from the melt vessel to an upper portion of the rotating roll rotating at a high speed, A ribbon alloy or metal strap can be formed as the alloy melt cools and cools at a rapid rate. For example, the cooling rate of the ribbon alloy may be 10 ³ ° C / sec to 10 ⁷ ° C / sec, and the cooling rate may vary depending on the rotation speed, material, temperature, etc. of the cooling roll. On the other hand, a coarse silicon single phase may be distributed inside the silicon-metal alloy phase when the alloy melt is cooled.

Exemplary processes for rapid quenching of the melt include splat quenching, rotating drum quenching, double-roller quenching, chill block melt spinning, but may include processes such as inside casting, melt extraction method, pendant drop melt extraction method, rotating electrode, electric explosion method, and gas atomization , The quenching and solidifying step is not limited thereto.

Thereafter, the ribbon alloy may be pulverized by a mechanical milling method such as ball milling to form the intermediate powder. The intermediate powder may have a particle size of from about several tens nanometers to about several hundred micrometers.

Thereafter, a third powder containing the intermediate powder and the first additive element may be provided in the crushing vessel (step S11b).

Thereafter, the intermediate powder and the third powder may be pulverized and alloyed by a mechanical alloying method to form a negative electrode active material powder in which a fine silicon single phase is distributed in the silicon-metal alloy phase (S21).

The process of forming the negative electrode active material powder may be similar to the process described with reference to FIG. For example, the intermediate powder and the third powder may be pulverized and alloyed for about several tens to several tens of hours by horizontal attrition milling, vertical attrition milling, ball milling, oil milling, . Fine forging, cold pressing, and fracturing between powders may occur repeatedly due to rotation of the milling balls and impact due to impact, and the first additional element may diffuse into the silicon-metal alloy phase. Further, the single phase of the silicon in the negative electrode active material powder can be made finer.

3 is a flow chart showing a manufacturing process of the negative electrode active material according to the exemplary embodiments.

3, a first powder containing silicon, a second powder containing iron, and a third powder containing the first additional element are melted and cooled to form a coarse silicon single phase in the silicon-metal alloy phase (Step S12).

In an exemplary process, the melting and cooling process may be a process similar to that of S11a described above with reference to FIG.

Thereafter, the intermediate powder is pulverized and alloyed by a mechanical alloying method to form an anode active material powder in which a fine silicon single phase is distributed within the silicon-metal alloy phase (S22).

Hereinafter, an experimental example of the anode active material powder for a secondary battery manufactured by the method of manufacturing the anode active material according to the exemplary embodiments will be described.

Table 1 below shows the parent alloy forming conditions and the crushing conditions of the negative electrode active material for a secondary battery according to the exemplary embodiments.

The negative electrode active materials according to the first embodiment were prepared so as to contain 18 atomic% of iron, 80 atomic% of silicon and 2% of manganese (Si ₈₀ Fe ₁₈ Mn ₂ ), and the negative electrode active materials according to the second and third embodiments include iron 16 at.%, silicon 80 at.% and manganese of 4%, and _{(Si 80 Fe 16 Mn 4)} , iron 14 at.%, (Si ₈₀ Fe ₁₄ Mn ₆₎ to include silicon of 80 at.% and manganese 6% Ready. Specifically, in order to produce the negative electrode active material according to the first embodiment, 66.83 g of the first powder containing silicon, 29.9 g of the second powder containing iron and 3.27 g of manganese were weighed, and the powders were inductively melted After forming the mother alloy melt, the solids were quenched and solidified to produce a ribbon alloy. The produced ribbon alloy was pulverized into powder having a particle size of about 100 micrometers or less using a mortar bowl. Then, it was milled and alloyed for 10 hours using a horizontal attrition milling machine (Simoloyer CM01 from Zoz-GmbH). 15 kg of chromium steel balls having a diameter of 4.7 mm were used in the pulverization and alloying process, and the first step of pulverizing for 45 seconds at a rotation speed of 1300 rpm and the second step of pulverizing for 15 seconds at a rotation speed of 700 rpm The powder was milled for 10 hours. 66.87 g of silicon, 26.59 g of iron and 6.54 g of manganese were weighed to produce the negative electrode active material according to the second embodiment. To manufacture the negative active material according to the third embodiment, 66.9 g of silicon, 23.28 g of iron, 9.82 g of manganese And the negative electrode active materials were prepared by performing the same process as the method of manufacturing the negative active material according to the first embodiment.

The negative electrode active material according to the comparative example was prepared so as to contain 20 atomic% of iron and 80 atomic% of silicon (Si ₈₀ Fe ₂₀ ). The powder was arc-dissolved and rapidly solidified to prepare a ribbon alloy. Thereafter, the produced ribbon alloy was pulverized into a powder having a particle size of about 100 micrometers or less using a mortar, and the powder was subjected to a milling process for about 8 hours using a horizontal attrition milling apparatus .

Furtherance Method of providing powder Milling conditions Comparative Example Si80Fe20 After induction melting, master alloys were prepared and mechanically pulverized (using a mortar bowl) Horizontal type milling, 8hr (1300rpm-45sec, 700rpm-15sec) Example 1 Si80Fe18Mn2 Arc-melting to produce parent alloy, followed by mechanical grinding (using a mortar bowl) Horizontal attrition milling, 10 hr (1300 rpm-45 sec, 700 rpm-15 sec) Example 2 Si80Fe18Mn2 Arc-melting to produce parent alloy, followed by mechanical grinding (using a mortar bowl) Horizontal attrition milling, 10 hr (1300 rpm-45 sec, 700 rpm-15 sec) Example 3 Si80Fe14Mn6 Arc melting to produce parent alloy and mechanical grinding (using a mortar bowl) Horizontal attrition milling, 10 hr (1300 rpm-45 sec, 700 rpm-15 sec)

4 is a graph showing an X-ray diffraction pattern of the negative electrode active material according to the exemplary embodiments. Using a CuKα (1.5406 Å) target at 40 kV, 40 mA using an X-ray diffraction spectrometer (Bruker, D8 focus), the 2 theta range of 10-60 degrees (˚) was measured at a scanning speed of 0.5 degree (˚) Ray diffraction pattern. The position and diffraction intensity of the diffraction peaks shown in the graph of FIG. 4 are shown in Table 2 below.

The first peak The second peak First Peak: Second Peak
Intensity ratio Location (degree) Diffraction intensity (a.u.) Location (degree) Diffraction intensity (a.u.) Comparative Example 49.27 1922 38.19 851 2.26: 1 Example 1 49.12 1467 37.98 787 1.86: 1 Example 2 49.29 1315 38.04 729 1.80: 1 Example 3 49.08 1307 37.86 687 1.90: 1

Referring to FIG. 4 and Table 2, the comparative example 40 and the first to third embodiments 41, 42 and 43 show the first to third peaks (?,?,?). Silicon single-phase diamond cubic crystal structure (space group (space group): Fd3 (227 )) having an, ferrosilicon (ferrosilicon, FeSi ₂₎ phase is a tetragonal crystal structure (tetragonal crystal structure) (Space group: P4 / mmm ( 123). In Figure 4, the first peak (■) is a diffraction peak by a surface crystallographic 102 on ferrosilicon (FeSi _2), the second peak (●) is ferrosilicon (FeSi ₂₎ crystallographic 101 on the surface . The third peak (?) Is the diffraction peak due to the crystallographic (001) plane on the ferrosilicon (FeSi ₂ ).

On the other hand, as can be seen from Table 2, in the comparative example (40), the diffraction intensities of the first and second peaks were 1922 and 851, respectively, whereas in the case of the first embodiment (41) Of diffraction intensity of 1467 and 787, respectively. In addition, the second embodiment 42 has diffraction intensities of 1315 and 729, respectively, and the third embodiment 43 has diffraction intensities of 1307 and 687, respectively. Therefore, it can be confirmed that the first to third embodiments 41, 42 and 43 have significantly lower diffraction intensity than the comparative example 40. [ This is because the first to third embodiments 41, 42 and 43 include a first addition element (specifically, manganese) of 2 to 6 atomic%, and thus the first addition element is a silicon single phase, It may be possible to refine the silicon-metal alloy phase surrounding the silicon single phase. Specifically, the smaller the particle size, the broader the width of the diffraction peak (for example, the full width at half maximum (FWHM)) and thus the intensity of the diffraction peak can be reduced. The strength of the diffraction peak was remarkably reduced in the first to third embodiments 41, 42 and 43 of the comparative example 40 compared to the comparative example 40 because the first additive element had a grain size of the silicon single phase and the silicon- It is thought that it makes fine.

In the first embodiment 41, the diffraction intensity of the first peak relative to the second peak is 1.86 times, and in the second and fourth embodiments 42 and 43, the diffraction intensity is 1.8 times and 1.9 times, respectively, It shows strength. On the other hand, in the case of the comparative example (40), it can be confirmed that the first peak diffraction intensity with respect to the second peak is 2.26 times. When such a difference in diffraction intensity occurs, in the case of the negative active material according to the first to third embodiments 41, 42, and 43, the diffraction intensity of the first peak is lowered while the diffraction intensity of the second peak is higher Or the degree of reduction of the diffraction intensity of the first peak is large while the degree of decrease of the diffraction intensity of the second peak is small. This, in the case of the first additional element the first to the third embodiments 41, 42 and 43 including the first additional element is a silicon-metal alloy phase (specifically, ferrosilicon (FeSi ₂₎ silicon or in the (For example, an interstitial dopant or a substitutional dopant) in such a manner that iron is substituted or intruded, whereby stress acts in the lattice of the ferrosilicon crystal structure, thereby causing distortion As shown in Fig.

On the other hand, as can be seen in Table 2, the comparative example 40 shows the first peak at about 49.27 degrees and the second peak at 38.19 degrees, while the first embodiment 41 shows the first peak at about 49.12 degrees, And a second peak at about 37.98 °. In addition, the third embodiment 43 also shows the first peak at about 49.08 degrees and the second peak at about 37.86 degrees. As such, the position of the diffraction peak can be increased or decreased by about 0.5 degrees at the maximum. Since the position of the diffraction peak in the X-ray diffraction pattern is related to the interplanar distance (i.e., lattice constant), the shift of the diffraction peak may be due to lattice strain (e.g., shrinkage or expansion) have. For example, the first embodiment 41 is shifted in the direction of decreasing the position of the first peak by 0.15 degrees and the position of the second peak by 0.21 degrees (shifted to the left with respect to the X axis) as compared with the comparative example 40, , Which may be due to the shrinkage of the lattice of the silicon-metal alloy phase by the first additional element.

5A and 5B are graphs showing the electrical performance of negative electrode active materials according to exemplary embodiments. Specifically, FIG. 5A and FIG. 5B show the measured resistivity of the negative electrode active materials according to the exemplary embodiments, and particularly show the resistivity values of the first to third embodiments 51, 52 and 53 shown in FIG. 5A Are enlarged and shown again in FIG. 5B. Also, the resistivity values according to the compression load are shown in Table 3 below.

Resistivity according to compressive load 4kN 8kN 12kN 16kN 20 kN Comparative Example 16.8 4.4 2.47 1.69 1.29 Example 1 0.15 0.08 0.05 0.04 0.04 Example 2 0.16 0.08 0.06 0.05 0.04 Example 3 0.20 0.10 0.07 0.06 0.05

Referring to FIGS. 5A, 5B, and 3, the first through third embodiments 51, 52, and 53 exhibit a resistivity of about 0.20? Cm or less under a compressive load of 4 to 20 kN. On the other hand, the comparative example (50) shows a resistivity of 16.8? Cm when a compressive load of 4 kN is applied. In particular, the first to third embodiments 51, 52 and 53 exhibit a significantly reduced resistivity, which means that as the first additional element atomizes the silicon single phase and the silicon-metal alloy phase, the electrical conductivity in the anode active material As shown in FIG. Furthermore, it is believed that the first additional element can contribute to the increase in electrical conductivity as it is contained in the silicon-metal alloy phase or as an interstitial or substitutional dopant at the interface between the silicon single phase and the silicon-metal alloy phase.

Generally, in the case of a silicon anode active material, a voltage drop (i.e., iR drop) due to a current flow during charging and discharging may be increased due to a high specific resistance value, thereby lowering the energy density. However, the first to third embodiments 51, 52, and 53 can minimize the above-described voltage drop by having a significantly reduced resistivity value, and accordingly, a negative electrode active material having a high energy density can be realized .

In addition, a negative electrode is generally manufactured by mixing a negative electrode active material and a conductor including an electrically conductive material such as an organic binder and applying the mixture onto a negative electrode foil. At this time, when the content of the conductive material mixed in the negative electrode increases due to the low resistivity of the conventional silicon negative electrode active material, the capacity of the secondary battery including the negative electrode may be reduced. However, the negative electrode active material according to the exemplary embodiments has a significantly reduced resistivity value, so that the conductor content can also be reduced, so that the secondary battery having a high capacity can be provided.

6 is a graph showing the electrochemical performance of the negative electrode active material according to the exemplary embodiments. 6, the discharge capacity according to the number of cycles of the negative electrode active materials according to the exemplary embodiments is measured and shown. The initial efficiency (%), the initial discharge capacity (or the discharge capacity in two cycles) g), 100 times discharge capacity (mAh / g) and life retention rate (%) are shown in Table 4 below.

Specifically, using the negative electrode active material according to the comparative example and the first to third embodiments, a coin type half cell having a lithium metal as a reference electrode was manufactured. The first cycle had a current density of 0.1 C, The cycle was repeatedly charged and discharged at a current density of 0.2 C, and the third cycle to the 100th cycle at a current density of 1C.

Initial efficiency (%) Initial discharge capacity (mAh / g) 100 discharge capacity (mAh / g) Life Retention Rate (%) Comparative Example 86.0 945.7 634.2 67.1 Example 1 80.8 672.8 574.8 85.4 Example 2 83.6 782.7 606.5 77.5 Example 3 83.3 783.4 584.5 74.6

Referring to FIGS. 6 and 4, it can be seen that the first through third embodiments 61, 62 and 63 exhibit excellent cycle performance as compared with the comparative example 60. Specifically, 85.4% of the first to third embodiments 61, 62, and 63 are. 77.5% and 74.6%, respectively, while the comparative example 60 shows a life retention rate of 67.1%. As described above, when the first additional element is included in the first to third embodiments 61, 62 and 63, the silicon-metal alloy phase surrounding the silicon single phase and the silicon single phase can be refined, This is because the silicon-metal alloy phase can effectively buffer the volume expansion of the single phase of silicon that occurs as lithium ions are inserted or removed from the single phase of silicon. Therefore, it can be seen that the first to third embodiments 61, 62 and 63 including the first additional element have excellent lifetime characteristics.

On the other hand, it can be seen that the first to third embodiments 61, 62 and 63 show a somewhat lower initial efficiency and initial discharge capacity as compared with the comparative example 60. [ This is because the first to third embodiments 61, 62, and 63 include the first additive element, so that it acts as an active region in which lithium ions can be inserted / desorbed by charging / discharging the negative active material It can be considered that the content of silicon and iron is somewhat reduced.

7A to 7C are scanning electron microscopy (SEM) images of an anode active material according to exemplary embodiments. Specifically, FIGS. 7A to 7C show SEM images of the electrodes using the negative electrode active material before the cycle test, after the first charge, and after the 50th discharge.

7A to 7C, the negative electrode active material electrode before the cycle test showed an electrode thickness of about 22 micrometers, while the electrode thickness after about one time of charging was about 31.4 micrometers, and the negative active material electrode Of the initial thickness is less than 50% of the initial thickness. Compared to a conventional silicon anode active material, which has a volume expansion of about 400% at the time of charging (i.e., when lithium ions are inserted), the negative electrode active material according to the exemplary embodiments can be significantly reduced in volume expansion Able to know. This is because, as described above, the first additional element included in the exemplary embodiments finely and uniformly distributes the single-phase silicon so that the silicon-metal alloy phase acting as the matrix can effectively buffer the volume expansion of the single- As shown in FIG. Referring to FIG. 7C, according to the exemplary embodiments, no cracks or undifferentiated state occurred on the surface of the negative electrode active material after the 50th cycle, and the electrode thickness was 31.8 micrometers. Can be confirmed.

FIG. 8 is a transmission electron microscopy (TEM) image of an anode active material according to Exemplary Embodiment 2. FIG. And a silicon-metal alloy phase surrounding the silicon single phase and the silicon single phase having an average crystal grain size of 50 nm or less.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. Will be apparent to those of ordinary skill in the art.

Claims (5)

Providing a mixture of a first powder comprising silicon, a second powder comprising iron and a third powder comprising a first additive element; And
Pulverizing and finely grinding the mixture by a mechanical alloying method to form a negative electrode active material containing silicon, iron and a first additive element,
Wherein the first additive element is an element selected from the group consisting of boron, carbon, phosphorus, titanium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum,
Wherein the negative electrode active material is formed by the mechanical alloying method, the negative active material including a silicon single phase having an average crystal grain size of 50 nm or less and a silicon-metal alloy phase surrounding the single silicon phase . The method according to claim 1,
Wherein the mechanical alloying method is performed by any one of vertical attrition milling, horizontal attrition milling, ball milling, planetary milling and Spex milling. Way. The method according to claim 1,
Wherein providing the mixture comprises:
Providing the mixture by mixing the first powder, the second powder and the third powder in a powder form into the pulverizing vessel. The method according to claim 1,
Wherein providing the mixture comprises:
Providing an intermediate powder comprising silicon and iron formed by melting and cooling the first powder and the second powder and mixing the third powder into a pulverizing vessel to provide the mixture. Gt; The method according to claim 1,
Wherein providing the mixture comprises:
Providing the mixture by mixing an intermediate powder comprising silicon, iron and a first additive element formed by melting and cooling the first powder, the second powder and the third powder into a pulverizing vessel By weight based on the total weight of the negative electrode active material.

Images