KR20200015992A - Negative electrode active material for rechargeable lithium battery and preparation method of the same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery and a manufacturing method thereof. The negative electrode active material comprises: an amorphous matrix containing Si, Fe, and Al while a crystalline phase is not formed upon heat treatment; and crystalline Si particles dispersed in the amorphous matrix and having a particle size of 50 nm or less. By preventing the coarsening of the crystalline Si particles, a high capacity and excellent lifespan characteristics are realized by the negative electrode active material in which the crystalline Si particles of uniform size are dispersed.

Description

Negative electrode active material for rechargeable lithium battery and preparation method of the same

The present invention relates to a negative electrode active material for a lithium secondary battery using silicon, which has recently been studied as a high capacity negative electrode active material, and a lithium secondary battery including the same.

Silicon (Si) is a negative electrode active material for lithium secondary batteries that requires continuous high capacity, and has been attracting attention as an alternative material of the negative electrode active material based on carbon materials, but its life is abrupt due to excessive volume change due to reaction with lithium during charging and discharging. There is a problem that is degraded. In order to solve this problem, the structure of the composite particles composed of the active Si microparticles and inert intermetallic compounds distributed around the active Si microparticles have attracted attention.

For example, Japanese Patent Application Laid-Open No. 2001-297757 or Japanese Patent Application Laid-open No. Hei 10-312804 proposes a material or method for producing at least a part of a phase such as Si as an intermetallic compound of Si and a metal represented by a transition metal. It is.

Rapidly solidification processes are widely used to construct the above-described structure of the composite particles. The melt-spinning process, which is known to have the highest cooling rate during the quench solidification process, enables phase transformation by rapid cooling at a rate of 10 ⁴ to 10 ⁶ K / s. The hot metal solution coated in a wide and thin direction in the rotational direction in contact with the cooling wheel rotating at a high speed is deprived of heat by the cooling wheel having excellent thermal conductivity, and a phase transformation occurs from the hot metal solution to the metal plate at room temperature. Since phase transformation from the liquid phase to the solid phase is terminated in such a short time, the phase transformation is terminated by forming a plurality of solid phase nuclei rather than growing solid phase nuclei. That is, the size of Si and the intermetallic compound can be finely formed by increasing the nucleus of the solid phase by minimizing the phase transformation time.

However, even when the above-mentioned quenching and coagulation process is used, there exists a region growing coarsely after the formation of the solid-state Si nucleus. This area occurs larger away from the surface in contact with the cooling wheel, differently depending on the composition of the alloy. In particular, as the melting point of Si and the intermetallic compound increases, the range and size of the coarsening region also increase. Such coarsening of Si particles and nonuniformity of microstructures cause a problem of lowering cycle characteristics.

Japanese Patent Laid-Open No. 2001-297757 Japanese Patent Application Laid-Open No. 10-312804

The present invention has been made to solve the problems of the prior art as described above, an object of the present invention to provide a negative active material for a lithium secondary battery showing a high charge and discharge capacity and improved cycle life.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery in which Si fine particles in which coarsening is suppressed as a whole are uniformly formed.

Moreover, an object of this invention is to provide the manufacturing method of the negative electrode active material for lithium secondary batteries which uniformly forms Si microparticles with the coarsening suppressed in a thermally and electrochemically stable amorphous matrix.

The present invention provides a negative electrode active material for a lithium secondary battery, and the negative electrode active material for a lithium secondary battery of the present invention includes an amorphous matrix containing Si, Fe, and Al, wherein a crystal phase is not formed during heat treatment; And crystalline Si particles dispersed in the amorphous matrix and having a particle size of 50 nm or less.

In addition, the negative electrode for a lithium secondary battery of the present invention includes the negative electrode active material according to the present invention.

In addition, the lithium secondary battery of the present invention includes a negative electrode according to the present invention.

In another aspect, the present invention provides a method for producing a negative electrode active material for a lithium secondary battery, the manufacturing method of the present invention, the step of melting a metal material containing Fe and Al together with Si; Quenching the molten material to form a coagulum in which a crystal phase is not precipitated; And heat-treating the coagulated product to precipitate crystalline Si particles having a particle size of 50 nm or less in a matrix including Si, Fe, and Al, wherein the matrix remains amorphous even after the heat treatment.

In one aspect of the invention, the matrix is Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag It may further comprise at least one metal element selected from the group consisting of.

In addition, in one aspect of the present invention, the matrix may include one or two or more amorphous phases including any one or more of Si, Fe, and Al.

Also in one aspect of the invention, the matrix may be electrochemically inert with respect to lithium.

In addition, in one embodiment of the present invention, the matrix may have a higher electrical conductivity than the crystalline Si particles.

The negative electrode active material for a lithium secondary battery of the present invention includes crystalline Si microparticles in which coarsening is suppressed, and a matrix distributed around the Si microparticles and stable thermally and electrochemically so that the Si microparticles are uniformly distributed in the matrix, It provides a lithium secondary battery with excellent charge and discharge capacity and cycle life.

In addition, the method for producing a negative electrode active material for a lithium secondary battery of the present invention includes crystalline Si microparticles in which coarsening is suppressed, and a matrix distributed around the Si microparticles and having a thermally and electrochemically stable matrix, wherein the Si microparticles are contained in the matrix. Provided is a method for producing a negative electrode active material uniformly distributed and finely refined evenly over the entire active material under a wide range of process conditions.

1 is a differential scanning calorimetry (DSC) result of a molten metal-containing quench solidified solid according to Example 1;
FIG. 2 is a transmission electron microscopy (TEM) image of a Si-containing molten metal quench solidified product according to Example 1. FIG.
3 is a TEM image of the heat treatment result according to Example 1. FIG.
FIG. 4 is an X-ray diffraction (XRD) result of the molten metal-containing metal quench solidified product and its heat treatment resultant according to Examples 1 and 2. FIG.
5 is a TEM image of the heat treatment result according to Example 2. FIG.
6 is a DSC result of the heat treatment result of Example 2.
7 is a TEM image of the heat treatment result according to Example 3. FIG.
8 is a TEM image of the heat treatment result according to Example 4. FIG.
9 is a TEM image of a Si-containing metal quench solidified product according to a comparative example.
10 is a TEM image of a heat treatment result according to a comparative example.
11 shows charge and discharge results of the lithium secondary battery including the negative active materials prepared in Examples 1 to 4;
12 is a charge and discharge result of the lithium secondary battery including the negative electrode active material prepared in Examples 5 to 8.
13 is a result of charging and discharging of a lithium secondary battery including the negative electrode active materials prepared in Examples 9 to 12.
14 is a charge and discharge result of the lithium secondary battery including the negative electrode active material prepared in Comparative Example.

Hereinafter, the gas generator of the present invention will be described in detail. The embodiments and drawings introduced below are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the embodiments and drawings presented below, but may be embodied in other forms. At this time, if there is no other definitions in the technical terms and scientific terms used, those having ordinary skill in the technical field to which the present invention has a meaning commonly understood, the gist of the present invention in the following description and the accompanying drawings. Descriptions of well-known functions and configurations that may be unnecessarily blurred are omitted.

In the present invention, the negative electrode active material for a lithium secondary battery,

An amorphous matrix containing Si, Fe, and Al, wherein a crystalline phase is not formed upon heat treatment; And

And crystalline Si particles dispersed in the amorphous matrix and having a particle size of 50 nm or less.

In addition, in the present invention, the method for producing a negative electrode active material for a lithium secondary battery,

Melting a metal material including Fe and Al together with Si;

Quenching the molten material to form a coagulum in which a crystal phase is not precipitated; And

Heat treating the coagulated product to precipitate crystalline Si particles having a particle size of 50 nm or less in a matrix comprising Si, Fe, and Al;

The matrix remains amorphous even after the heat treatment.

In one aspect of the present invention, the crystalline Si particles may have a particle size of 50 nm or less, preferably 20 nm or less, more preferably 10 nm or less. Also in one aspect of the invention, the lower limit of the size of the crystalline Si particles may be 10 nm, preferably 5 nm, more preferably 2 nm.

The crystalline Si particles have a high lithium occlusion amount while the crystalline Si particles have a high lithium occlusion amount, and have a small volume change during occlusion and release of lithium ions due to charging and discharging. Is implemented.

The amorphous matrix stably maintains the amorphous phase without forming a crystalline phase even during heat treatment, and stabilizes the structure of the active material according to the volume change during occlusion and release of lithium ions with respect to the crystalline Si particles. While enabling high capacity, good life characteristics can be achieved.

In one aspect of the invention, the melting of the metal material may be carried out in an inert or reducing atmosphere, the atmosphere may be an argon gas atmosphere.

In one aspect of the invention, the metal material may be melted by arc melting, but there is no particular limitation on the melting method.

In one aspect of the invention the quench rate may be 10 ⁴ to 10 ⁸ K / s, preferably 10 ⁶ to 10 ⁸ K / s, more preferably 10 ⁷ to 10 ⁸ K / s Can be. In one aspect of the present invention, the melt spinning method may be used as a quenching method, but there is no particular limitation on the method as long as a sufficient cooling rate can be realized. In one aspect of the invention, the cooling wheel rotational speed during the melt spinning method may be 20 to 60 m / s, preferably 30 to 50 m / s.

As the amorphous matrix includes Fe and Al, the amorphous matrix maintains an amorphous phase in which no additional crystal phase is formed not only at the time of quenching but also at a temperature above the temperature at which the crystalline Si particles are precipitated. In one embodiment of the present invention, the heat treatment temperature at which the crystal phase of the matrix is not formed may be 900 K or less.

In one aspect of the present invention, the crystalline Si particles may be single crystal or polycrystal, and the polycrystalline particles are polycrystalline particles in consideration of the influence of the cycle characteristics due to expansion because they are advantageous for expansion inhibition and acceptance during charge and discharge. It is preferable.

In one aspect of the present invention, the crystalline Si particles may have an average particle diameter of 40 nm or less, preferably 20 nm or less, more preferably 10 nm or less.

In addition, unlike the general case in which the crystalline Si particles are precipitated upon cooling and grow during the heat treatment process, the crystalline Si particles are dispersed in a uniform size throughout the active material, and have a relative standard deviation of the particle diameter, that is, the particle diameter. The standard deviation divided by the average particle diameter may be 20% or less, preferably 15% or less, more preferably 10% or less, even more preferably 5% or less.

In one aspect of the invention, the matrix is Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag It may further comprise at least one metal element selected from the group consisting of. The metal element, which may be further included, is more conductive than Si and forms a flexible intermetallic compound to surround the crystalline Si particles, thereby relieving stress caused by volume expansion when lithium is occluded and released into Si and This prevents desorption of electrodes and electrical isolation of Si.

In one embodiment of the present invention, the negative electrode active material may be an alloy having a composition of Formula 1.

[Equation 1]

Si _x Fe _y Al _z M _a

Wherein M is selected from the group consisting of Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag It is at least one metal element, 40≤x≤80, 1≤y≤25, 10≤z≤40, 0≤a≤20, x + y + z + a = 100, preferably 45≤x≤70 , 5 ≦ y ≦ 20, 15 ≦ z ≦ 30, 1 ≦ a ≦ 15, x + y + z + a = 100, more preferably 50 ≦ x ≦ 60, 10 ≦ y ≦ 15, 20 ≦ z ≦ 25, 1 ≦ a ≦ 10, and x + y + z + a = 100.

In one aspect of the invention, the matrix may comprise one or two or more amorphous phases comprising any one or more of Si, Fe, and Al.

In one aspect of the invention, the matrix comprises a phase comprising Si and Fe, a phase comprising Si and Al, a phase comprising Si, Fe, and Al, a phase comprising Fe and Al, and the like. can do. As described above, when the raw metal material including Si is solidified by cooling from a high temperature liquid phase, the phases help to form fine particles with a pinning effect that suppresses grain growth of crystalline Si particles.

In one aspect of the invention, it may be desirable for the matrix to include two or more phases in terms of control of the microstructure.

In one aspect of the present invention, the matrix may be electrochemically inactive with respect to lithium, but may not be limited, even if it is electrochemically active with respect to lithium, provided that it does not deteriorate the characteristics of the secondary battery.

In one aspect of the invention, the matrix may have an electrical conductivity equal to or greater than that of the crystalline Si particles. Such conductivity characteristics may be realized by including metals such as Fe, Al, M, etc. in the matrix in addition to Si, and in one aspect of the present invention, may further include an element capable of improving electrical conductivity. Any one or two or more of B, P, As, Sb, Ge, N, Au, and Pt may be used as the element. In one aspect of the present invention, the element that may be further included to improve conductivity may be included in 1 at% or less, preferably 0.5 at% or less, more preferably 0.1 at% or less.

Moreover, in this invention, the negative electrode for lithium secondary batteries contains the negative electrode active material of this invention. In one aspect of the invention, the negative electrode for a lithium secondary battery may further comprise a current collector.

In addition, in the present invention, the lithium secondary battery includes the anode for lithium secondary battery of the present invention. In one aspect of the present invention, a lithium secondary battery includes a positive electrode including a positive electrode active material; A negative electrode including the negative electrode active material of the present invention; And an electrolyte solution. In addition, in one aspect of the present invention, the lithium secondary battery may include a separator disposed between the positive electrode and the negative electrode.

 In the lithium secondary battery of the present invention, the cell forms of the component and the lithium secondary battery except for the negative electrode active material included in the negative electrode may be used without limitation, those known in the art, further description thereof will be omitted.

Example 1

Si, Al, and Fe master alloys were melted by an arc melting method under an argon gas atmosphere to have a composition of Si 56 at.%, Al 25 at.%, Fe 16 at.% Cu 1 at% Ni 2%, and this was 40 m / It was quenched using the melt spinning method under the squeeze rate (rotational speed of the cooling wheel) of s to prepare a coagulated product in which no precipitated crystal phase was present. The heat entry and exit of the coagulated product with temperature was investigated, and the DSC result is shown in FIG. 1. An exothermic peak is observed at the temperature at which the coagulum is heated to form crystal phases.

The solidified product prepared by quenching was heat-treated at 723 K for 60 minutes in an electric furnace which is a reducing atmosphere of argon atmosphere.

TEM images of the prepared coagulum and the negative electrode active material are shown in FIGS. 2 and 3, respectively. Immediately after quenching, no precipitated crystals were seen (FIG. 2), and after heat treatment, it was confirmed that particles smaller than 20 nm were precipitated (FIG. 3). It can be confirmed that the precipitated particles are crystalline Si particles through the XRD results before (FIG. 4 (a)) and after (FIG. 4 (b)).

[Examples 2 to 4]

The same coagulum as in Example 1 was prepared. This was heat-treated at 773 K (Example 2), 823 K (Example 3), and 873 K (Example 4) for 60 minutes in an electric furnace which is a reducing atmosphere of argon atmosphere. After the heat treatment of 773 K, the growth of the particles was limited, and it was confirmed that fine particles were still precipitated (FIG. 5). In addition, it can be confirmed that the precipitated particles are crystalline Si particles (FIG. 4 (c)).

The heat-treated product at 773 K was examined for the exothermic and endothermic reactions according to temperature, and the DSC results are shown in FIG. 6. As a result of the heat treatment at the temperature, no exothermic / endothermic peaks due to the crystallization reaction were observed at higher temperatures, and thus, it was confirmed that a stable material was formed in terms of thermally and crystalline phases.

In addition, it was confirmed that even after the heat treatment of 823 K and 873 K, fine particles were still precipitated (FIGS. 7 and 8).

[Examples 5 to 8]

Except that the Si, Al, and Fe master alloys were melted by an arc melting method under an argon gas atmosphere to have a composition of Si 54 at.%, Al 27 at.%, Fe 16 at.% Cu 1 at% Ni 2%. In the same manner as in Example 1, a coagulum was prepared in which no precipitated crystal phase was present.

The solidified product prepared by quenching was 60 into 723 K (Example 5), 773 K (Example 6), 823 K (Example 7), and 873 K (Example 8) in an electric furnace which is a reducing atmosphere of argon atmosphere. Heat treatment was performed for a minute. Even after the heat treatment, the growth of the particles was limited, and still fine crystalline Si particles were precipitated.

[Examples 9 to 12]

Except that the Si, Al, and Fe mother alloys were melted by an arc melting method under an argon gas atmosphere to have a composition of Si 51 at.%, Al 29 at.%, Fe 17 at.% Cu 1 at% Ni 2%. In the same manner as in Example 1, a coagulum was prepared in which no precipitated crystal phase was present.

The solidified product prepared by quenching was 60 into 723 K (Example 9), 773 K (Example 10), 823 K (Example 11), and 873 K (Example 12) in an electric furnace which is a reducing atmosphere of argon atmosphere. Heat treatment was performed for a minute. Even after the heat treatment, the growth of the particles was limited, and still fine crystalline Si particles were precipitated.

Comparative Example 1

A coagulated product was prepared and heat-treated in the same manner as in Example 1 except that the Si, Ni, and Al mother alloys had a composition of Si 40at.%, Ni 25at.%, And Al 35at.%. The prepared coagulum was obtained in a state in which Si microparticles were already formed unlike in Example 1 (FIG. 9). Further, the Si particles formed were also prepared the negative electrode active material containing a significant growth (Fig. 10), Si particle finally did roughness is not suppressed as compared with the embodiments after heat treatment.

Experimental Example: Fabrication of Lithium Secondary Battery

10 wt% of polyimide (based on the total amount of the negative electrode active material) was added to the negative electrode active material for lithium secondary batteries prepared in Examples 1 to 12 and Comparative Examples, respectively, and N-methylpyrrolidone was mixed to prepare a slurry for forming a negative electrode active material layer. It was. Each of the slurries was coated on a copper foil having a thickness of 15 μm, and the electrodes were press-molded by a roller press and vacuum dried at 110 ° C. for 2 hours. The dried negative electrode plate was cut to a size of 1.33 cm ² to prepare a negative electrode.

A 2032 coin cell was fabricated by using LiPF6 as a 1.0 M solution in a solvent having a lithium metal as an anode, a Celgard 2500 as a separator, and an electrolytic solution with an EC: EMC of 3: 7 by volume.

PNE was used as a charging and discharging device, and the initial three cycles were applied at 0.1 C and the fourth cycle at 0.5 C.

Cycle characteristics of the battery including the negative electrode active materials prepared in Examples 1 to 4, 5 to 8, 9 to 12, and Comparative Examples, respectively, are shown in FIGS. 11 to 14, respectively. The battery including the negative electrode active material of Examples 1 to 12 according to an aspect of the present invention shows a significantly superior capacity retention rate and coulombic efficiency compared to the case of the comparative example, the lithium secondary battery according to the present invention has a high capacity and excellent It can be seen that it has a life characteristic.

Claims (14)

An amorphous matrix containing Si, Fe, and Al, wherein a crystalline phase is not formed upon heat treatment; And
Crystalline Si particles dispersed in the amorphous matrix and having a particle size of 50 nm or less;
Anode active material for a lithium secondary battery comprising a.
The method of claim 1, wherein the matrix is Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag. A negative electrode active material for lithium secondary batteries, further comprising at least one metal element selected from the group consisting of:
The negative electrode active material for lithium secondary batteries of Claim 1 which has a composition of the said Formula 1.
[Equation 1]
Si _x Fe _y Al _z M _a
Wherein M is selected from the group consisting of Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag It is at least one metal element, 40≤x≤80, 1≤y≤25, 10≤z≤40, 0≤a≤20, and x + y + z + a = 100.
The negative active material of claim 1, wherein the matrix comprises one or two or more amorphous phases including at least one of Si, Fe, and Al.
The negative active material of claim 1, wherein the matrix is electrochemically inactive with respect to lithium.
The negative active material of claim 1, wherein the matrix has higher electrical conductivity than the crystalline Si particles.
The negative electrode for lithium secondary batteries containing the negative electrode active material of any one of Claims 1-6.
A lithium secondary battery comprising the negative electrode of claim 7.
Melting a metal material including Fe and Al together with Si;
Quenching the molten material to form a coagulum in which a crystal phase is not precipitated; And
And heat-treating the coagulated product to precipitate crystalline Si particles having a particle size of 50 nm or less in a matrix including Si, Fe, and Al.
The matrix is maintained even after the heat treatment, the method of manufacturing a negative electrode active material for a lithium secondary battery.
The method of claim 9, wherein the metal material is Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag A method for producing a negative electrode active material for a lithium secondary battery, further comprising at least one metal selected from the group consisting of:
The negative electrode active material manufacturing method for lithium secondary batteries of Claim 9 which has a composition of the said Formula 1.
[Equation 1]
Si _x Fe _y Al _z M _a
Wherein M is selected from the group consisting of Cr, Cu, Mn, Mo, Ni, Nb, Ti, V, Co, Zr, Mg, Se, Te, Sn, In, Ga, Pb, Bi, Zn, and Ag It is at least one metal element, 40≤x≤80, 1≤y≤25, 10≤z≤40, 0≤a≤20, and x + y + z + a = 100.
The method of claim 9, wherein the matrix comprises one or two or more amorphous phases including any one or more of Si, Fe, and Al.
The method of claim 9, wherein the matrix is electrochemically inactive with respect to lithium.
The method of claim 9, wherein the matrix has a higher electrical conductivity than the crystalline Si particles.

Images