WO2014092347A1 - Negative electrode active material for lithium secondary battery and secondary battery using same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery and a secondary battery using same, and more specifically provides a negative electrode active material for a lithium secondary battery and a secondary battery using same wherein the active material comprises an alloy represented by chemical formula (1) Si_xNi_yM_z (in the formula 50≤x≤90, 1≤y≤49, 1≤z≤49, x+y+z=100, x, y and z are each atomic percentages, and M is a transition metal), and the amorphization degree of a micro crystal region on the matrix in the alloy is at least 30%.

Description

Anode active material for lithium secondary battery and secondary battery using same

The present invention relates to a negative electrode active material for a lithium secondary battery and a secondary battery using the same, and more particularly, to a negative electrode active material for a lithium secondary battery having a high charge and discharge capacity and an excellent capacity retention rate, and a secondary battery using the same.

Lithium metal is used as a negative electrode active material of a conventional lithium battery. However, when a lithium metal is used, a carbon-based material is used as a negative electrode active material instead of lithium metal because a short circuit of the battery occurs due to dendrite formation. .

Examples of the carbon-based active material include crystalline carbon such as graphite and artificial graphite, and amorphous carbon such as soft carbon and hard carbon. However, although the amorphous carbon has a large capacity, there is a problem in that irreversibility is large in the charging and discharging process. Graphite is typically used as the crystalline carbon, and has a theoretical limit capacity of 372 mAh / g, which has a high capacity, and is used as a negative electrode active material.

However, even if the graphite or carbon-based active material has a rather high theoretical capacity, it is only about 380 mAh / g, and there is a problem in that the above-described negative electrode cannot be used in the development of a high capacity lithium battery in the future.

In order to improve such a problem, a material that is currently being actively researched is a negative electrode active material based on metals or intermetallic compounds. For example, lithium batteries using metals or semimetals such as aluminum, germanium, silicon, tin, zinc, and lead as negative electrode active materials have been studied. Such a material has a high energy density and high energy density, and can absorb and release more lithium ions than a negative electrode active material using a carbon-based material, thereby manufacturing a battery having a high capacity and a high energy density. Pure silicon, for example, is known to have a high theoretical capacity of 4017 mAh / g.

However, when compared with carbon-based materials, the cycle characteristics are deteriorated, and it is still an obstacle to practical use. When the silicon is used as a lithium occlusion and emission material as a negative electrode active material, it is interposed between the active materials due to the volume change in the charging and discharging process. This is because a decrease in conductivity or a phenomenon in which the negative electrode active material peels from the negative electrode current collector occurs. That is, the silicon, etc. included in the negative electrode active material occludes lithium by charging and expands to about 300 to 400% by volume, and when lithium is discharged, the inorganic particles shrink.

Repeating such a charge / discharge cycle may cause electrical insulation due to cracking of the negative electrode active material, and thus has a problem in that it is used in a lithium battery because the life is sharply reduced.

In order to improve such a problem, studies have been made to use nano-sized particles as silicon particles, or to make the silicon porous to have a buffering effect against volume change.

Korean Laid-Open Patent Publication No. 2004-0063802 relates to a "negative active material for lithium secondary batteries, a manufacturing method thereof, and a lithium secondary battery", which uses a method of eluting a metal after alloying another metal such as silicon and nickel. Patent No. 2004-0082876 relates to "Method for Producing Porous Silicon and Nano-Sized Silicon Particles and Application to Cathode Material for Lithium Secondary Battery", and heat treatment by mixing a silicon precursor such as alkali metal or alkaline earth metal in powder state and silicon dioxide. Later, the technique of eluting with an acid was disclosed.

The patents may improve the initial capacity retention rate due to the buffering effect due to the porous structure. However, since only the porous silicon particles having low conductivity are used, if the particles are not nano-sized, the conductivity between the particles may be lowered at the time of manufacturing the electrode. There is a problem that the retention characteristics are lowered.

Therefore, there has been a demand for the preparation of a negative electrode active material which can improve initial efficiency and capacity retention characteristics and at the same time maintain a constant voltage and current amount even after repeatedly charging and discharging.

In order to solve the above problems, there is provided a negative electrode active material for a lithium secondary battery in which the electrical change does not easily occur due to a small volume change during charge and discharge.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery excellent in initial efficiency and capacity retention characteristics.

In order to achieve the above object, the present invention provides an anode active material for a lithium secondary battery, characterized in that the amorphous crystallinity of the microcrystalline region of the matrix (Matrix) in the alloy is 30% or more as an alloy consisting of the formula (1).

[Formula 1]

Si _x Ni _y M _z

(Where 50≤x≤90, 1≤y≤49, 1≤z≤49, x + y + z = 100, x, y, z are atomic% and M is a transition metal)

In another aspect, the present invention provides a negative electrode active material for a lithium secondary battery, characterized in that the transition metal is selected from the group consisting of Al, Cu, Ti and Fe.

In another aspect, the present invention provides an anode active material for a lithium secondary battery, characterized in that the degree of amorphousness in the XRD pattern diffraction angle 2θ = 20 ° ~ 100 ° of the alloy is 30% or more.

The present invention also provides a secondary battery comprising a cathode and an electrolyte including a cathode and an anode active material according to the present invention.

In another aspect, the present invention provides a secondary battery in which the positive electrode comprises a thiolated intercalation compound, an inorganic sulfur or a sulfur compound.

The present invention also provides a secondary battery in which the electrolyte contains a non-aqueous organic solvent and a lithium salt.

The present invention also provides a secondary battery having a cylindrical shape, a horn shape, a coin shape, or a pouch shape.

The negative electrode active material for a lithium secondary battery according to the present invention has an effect of extending the service life because the electrical change does not occur because the volume change is small during charge and discharge when used in the secondary battery.

The negative electrode active material for a lithium secondary battery according to the present invention has an excellent initial efficiency and capacity retention characteristics when used in a secondary battery.

The negative electrode active material for a lithium secondary battery according to the present invention has an effect that the amount of voltage and current is maintained substantially constant even when repeated charging and discharging when used in the secondary battery.

Figure 1 shows the SEM measurement results of the negative electrode active material according to an embodiment of the present invention.

Figure 2 shows the XRD measurement results of the negative electrode active material according to an embodiment of the present invention.

Figure 3 shows the amorphousness measurement of the negative electrode active material according to an embodiment of the present invention.

Figure 4 shows the charge and discharge capacity of the negative electrode active material according to an embodiment of the present invention.

5 is a charge and discharge cycle repeated up to 50 times at 0.5C of a battery manufactured using a negative electrode active material according to an embodiment of the present invention, the capacity change according to the cycle is measured.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. First, it should be noted that in the drawings, the same components or parts denote the same reference numerals as much as possible. In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the subject matter of the present invention.

As used herein, the terms “about”, “substantially”, and the like, are used at, or in close proximity to, numerical values when manufacturing and material tolerances inherent in the meanings indicated are intended to aid the understanding of the invention. Accurate or absolute figures are used to assist in the prevention of unfair use by unscrupulous infringers.

The unit "%" used in the present specification means "atomic%" unless otherwise specified.

The present invention provides an anode active material for a secondary battery, characterized in that the amorphous crystallinity is 30% or more in the microcrystalline region of the matrix (Matrix) in the alloy as an alloy of the formula (1).

[Formula 1]

Si _x Ni _y M _z

(Where 50≤x≤90, 1≤y≤49, 1≤z≤49, x + y + z = 100, x, y, z are atomic% and M is a transition metal)

The microcrystalline region is present on the matrix of the alloy, and the presence of the microcrystalline region allows lithium to be diffused more easily than the crystalline region mainly. The ratio of the presence of the microcrystalline region may be represented through the degree of amorphousness, and when the amorphous region is formed on the matrix, it may be suppressed in the volume expansion during charging of the secondary battery in applying it as a negative electrode active material of the secondary battery.

Characterized by the presence of Ni in the alloy of the present invention, there is an advantage in the high-strength matrix as the strength is excellent due to the presence of Ni.

In addition, the present invention is characterized in that at least 30% of the degree of amorphousness of the microcrystalline region on the matrix (Matrix). The amorphousness of the microcrystalline region is 30% or more, thereby facilitating the diffusion of lithium.

When the amorphous phase on the matrix is 30% or more, when the secondary battery is used as a negative electrode active material, it can be seen that volume expansion is suppressed during charging.

In addition, in the present invention, the transition metal is preferably selected from one or more from the group consisting of Al, Cu, Ti and Fe.

Figure 1 shows the SEM measurement results of the negative electrode active material according to an embodiment of the present invention, Figure 2 shows the XRD measurement results of the negative electrode active material according to an embodiment of the present invention.

1 is an alloy _{consisting of} Si _65.40 Ni _25.69 Cu _8.91 , Si _65.41 Ni _25.69 Ti _8.90 , Si _65.40 Ni _25.69 Fe _8.91 and Si _65.40 Ni _25.70 Al _8.90 , which are embodiments of the present invention. Amorphization degree of the microcrystals in the range of ° ~ 100 ° to 30 to 45%, thereby having an effect that the volume expansion is suppressed when the alloy is charged in the secondary battery.

In the negative electrode active material according to the embodiment of the present invention, it is preferable that the amorphous degree is 30 to 45% in the XRD pattern diffraction angle 2θ = 20 ° to 100 ° of the alloy. When the amorphousness is 30 to 45%, volume expansion is suppressed so that electrical insulation is hardly generated.

Calculation of the degree of amorphousness used in the present invention is as follows, the expression can be obtained by looking at the area to measure the degree of amorphousness of FIG.

% Crystallization = ((Total Area-Crystallization Area) ÷ Total Area) × 100

The high degree of amorphousness may be interpreted to mean that there are many microcrystalline regions, and thus, a buffering function may be performed in the microcrystalline region during charging to block a factor in which lithium ions may accumulate and expand in volume. It becomes possible.

The method for preparing the negative electrode active material of the present invention is not particularly limited, and for example, various fine powder production techniques known in the art (gas atomizer method, centrifugal gas atomizer method, plasma atomizer method, rotary electrode method, Mechanical alignment, etc.) may be used. In the present invention, for example, Si and the components constituting the matrix may be mixed, the mixture may be melted by an arc melting method or the like, and then applied to a single roll quench solidification method in which the melt is sprayed onto a rotating copper roll to prepare an active material. have. However, the method applied in the present invention is not limited to the above method, and if a sufficient quenching speed can be obtained in addition to the single-roll quenching solidification method, the fine powder production technique (gas atomizer method, centrifugal gas atomizer method) presented above. , Plasma atomizer method, rotary electrode method, mechanical aligning method, and the like.

In addition, a secondary battery may be manufactured using a negative electrode active material according to an embodiment of the present invention, and the positive electrode of the secondary battery may include a ritated intercalation compound, and also inorganic sulfur (S8). Also, elemental sulfur and sulfur compounds may be used. The sulfur compounds include Li ₂ S _n (n ≧ 1), Li ₂ S _n (n ≧ 1) dissolved in catholyte, An organic sulfur compound or a carbon-sulfur polymer ((C ₂ S _f ) _n : f = 2.5 to 50, n ≧ 2) and the like can be exemplified.

In addition, the kind of electrolyte included in the secondary battery of the present invention is not particularly limited either, and general means known in the art may be employed. In one example of the present invention, the electrolyte may include a non-aqueous organic solvent and a lithium salt. In the above, the lithium salt may be dissolved in an organic solvent to serve as a source of lithium ions in the battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts that can be used in the present invention include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), where x and y are natural numbers, LiCl, LiI, and lithium It includes the one or more kinds of bisoxalate borate (lithium bisoxalate borate) or the like as a supporting electrolyte salt. The concentration of lithium salt in the electrolyte, which can vary depending on the application, is typically used within the range of 0.1M to 2.0M.

In addition, the organic solvent serves as a medium to move ions involved in the electrochemical reaction of the battery, for example, benzene, toluene, fluorobenzene, 1,2-difluorobenzene, 1, 3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1, 3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiobenzene, 1, 3-diiobenzene, 1,4-diiobenzene, 1,2,3-triiobenzene, 1,2,4-triiobenzene, fluorotoluene, 1,2-difluorotoluene , 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene , 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4-tri Chlorotoluene, iodotoluene, 1,2-dioodotoluene, 1,3-dioodotoluene, 1,4-dioodotoluene, 1,2,3-triiodotoluene, 1,2,4 -Triiodotoluene, R-CN (wherein R is a linear, branched or cyclic hydrocarbon group having 2 to 50 carbon atoms, the hydrocarbon group may include a double bond, an aromatic ring or an ether bond, etc. Dimethylformamide, dimethylacetate, xylene, cyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl Carbonate, propylene carbonate, methyl propionate, ethyl propionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxyethane, 1,3-dioxolane, diglyme, tetraglyme, ethylene carbo Sites, but are propylene carbonate, -butyrolactone γ- lactone, sulfolane (sulfolane), valerolactone, big surprise grade or type of mevalolactone or two kinds or more, without being limited thereto.

In addition to the above elements, the secondary battery of the present invention may further include conventional elements such as a separator, a can, a battery case or a gasket, and the specific types thereof are not particularly limited.

In addition, the secondary battery of the present invention may be manufactured in a conventional manner and shape in the art, including such elements. Examples of the shape that the secondary battery of the present invention may have include a cylindrical shape, a horn shape, a coin shape, or a pouch shape, but are not limited thereto.

Hereinafter, the present invention will be described in more detail through examples according to the present invention, but the scope of the present invention is not limited to the following examples.

Example 1

The method for preparing the negative electrode active material of the present invention is not particularly limited, and for example, various fine powder production techniques known in the art (gas atomizer method, centrifugal gas atomizer method, plasma atomizer method, rotary electrode method, Mechanical alignment, etc.) may be used. In Example 1, Si and the components constituting the matrix were mixed, the mixture was melted by an arc melting method or the like, and then applied to a single roll quench solidification method in which the melt was sprayed onto a rotating copper roll to prepare an active material.

The method applied in the present invention is not limited to the above method, and if a sufficient quenching speed can be obtained in addition to the single-roll quenching solidification method, the fine powder manufacturing technique (gas atomizer method, centrifugal gas atomizer method, plasma method) presented above. It can also be manufactured by the atomizer method, the rotating electrode method, the mechanical etching method and the like.

A composite alloy was prepared in which the transition metal was Cu _65.40 Ni _25.69 Cu _8.91 in the Si _x Ni _y M _z alloy, and the degree of amorphousness of the alloy was measured. In preparing, it was used as a negative electrode active material.

Example 2

It carried out similarly to Example 1 except having set the transition metal as Ti in Si _x Ni _y M _z alloy, and set it as Si _65.41 Ni _25.69 Ti _8.90 .

Example 3

It carried out similarly to Example 1 except having set the transition metal to Fe in the alloy of Si _x Ni _y M _z to Si _65.40 Ni _25.69 Fe _8.91 .

Example 4

It carried out similarly to Example 1 except having set the transition metal to Al in Si _x Ni _y M _z alloy, and set it as Si _65.40 Ni _25.70 Al _8.90 .

Comparative Example 1

An alloy of Si ₆₀ Fe ₁₄ Al ₂₆ was prepared. At this time, Si ₆₀ Fe ₁₄ Al ₂₆ was prepared and used as a negative electrode active material.

Comparative Example 2

Si _x Ni _y M _z in the alloy of the transition metals of Ti and except that the Si ₄₀ Ni ₂₀ Ti ₄₀ was performed in the same manner as in Example 1.

Comparative Example 3

Si _x Ni _y M _z of a transition in the alloy and the metal of Fe was carried out in the same manner as in Example 1 except that Si ₄₅ Ni ₂₅ Fe _30.

Comparative Example 4

The same procedure as in Example 1 was carried out except that Si ₄₈ Ni ₃₀ Al ₂₂ was prepared using Al as a transition metal in the alloy of Si _x Ni _y M _z .

1. SEM analysis

Scanning Electron Microscopy (SEM) analysis was performed on the prepared anode active material. 1 is an enlarged SEM photograph of the negative electrode active material of Examples 1 to 4.

In the negative electrode active material, it was confirmed that the Si phase was uniformly dispersed and precipitated on the matrix.

2. XRD Analysis

Cu kα-ray XRD measurements were performed on the negative active materials prepared in Examples 1 to 4, and the results are shown in FIG. 2. In the analysis, the measurement angle was set at 20 degrees to 100 degrees, and the measurement speed was set at 5.7 degrees per minute.

3. Charge and discharge capacity

Coin-shaped secondary batteries were prepared using the negative electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4, and after the charge and discharge evaluations, the results are shown in FIG. 4. In the manufacture of the coin-shaped electrode plate, the mixing ratio of the active material, the conductive agent (Super P-based conductive agent), and the binder (PI-based binder) is 77: 15: 2: 6 (active material: additive: conductive agent: binder). It was prepared as possible. Charged and discharged after performing once at 0.5C for the prepared electrode plate was measured, as shown in Table 1 below.

4. Determination of amorphousness

The amorphousness measurement can be obtained by using the formula of the amorphousness degree using the XRD pattern of the alloy.

% Crystallization = ((Total Area-Crystallization Area) ÷ Total Area) × 100

The higher the degree of amorphousness, the larger the number of fine crystal regions, and thus, the volume expansion factor may be reduced.

Examples 1 to 4 and Comparative Examples 1 to 4, the amorphous degree is shown in Table 1 below.

Table 1

division	Electrode characteristics			Amorphous Degree (%)
	Charge capacity (mAh / g)	Discharge Capacity (mAh / g)	efficiency(%)
Example 1	1162	969	83	32
Example 2	873	706	81	43
Example 3	617	498	81	42
Example 4	1394	1198	86	45
Comparative Example 1	1241	986	79	29.5
Comparative Example 2	598	468	78	29
Comparative Example 3	605	472	78	28
Comparative Example 4	602	462	77	28

When the negative electrode active material was prepared using the alloys of Comparative Examples 1 to 4, the degree of amorphousness was less than 30%, and thus, it is judged that the volume expansion is higher than that of the Examples.

5. Cycle life characteristics measurement

Charge and discharge was repeated 50 times at 0.5C and measured, and the result is as shown in FIG. In the above, the charge and discharge method was performed according to the charge and discharge method for the active material for a lithium secondary battery generally known in the art.

As shown in FIG. 5, even after repeated charging and discharging, the voltage and current amount are almost constant, and thus, reversible charging and discharging is possible. After repeated charging and discharging up to 50 times at 0.5 C with respect to the negative electrode active material of the present invention, the capacity change according to the cycle was measured, it can be seen that there is no sudden decrease in the discharge capacity even after repeated charging and discharging.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

Claims (7)

1. An alloy composed of the following formula (1), characterized in that the amorphous degree of the amorphous state of the crystal phase in the alloy (Matrix) in the alloy is 30% or more.

   [Formula 1]

   Si _x Ni _y M _z

   (Where 50≤x≤90, 1≤y≤49, 1≤z≤49, x + y + z = 100, x, y, z are atomic% and M is a transition metal)
2. The method of claim 1,

   The transition metal is an anode active material for a lithium secondary battery, characterized in that at least one selected from the group consisting of Al, Cu, Ti and Fe.
3. The method of claim 1,

   XRD pattern diffraction angle 2θ = 20 ° ~ 100 ° of the alloy in the range between the amorphous degree of the negative electrode active material for lithium secondary battery, characterized in that 30 to 45%.
4. A secondary battery comprising a negative electrode and an electrolyte comprising a positive electrode and the active material according to any one of claims 1 to 3.
5. The method of claim 4, wherein

   The cathode includes a secondary intercalation compound, an inorganic sulfur or sulfur compound.
6. The method of claim 4, wherein

   The electrolyte comprises a non-aqueous organic solvent and a lithium salt.
7. The method of claim 4, wherein

   A secondary battery having a cylindrical shape, a horn shape, a coin shape, or a pouch shape.

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