KR20200089208A - Carbon complex anode material based on core shell nanowire - Google Patents

Abstract

The present invention relates to a core-shell nanowire-based carbon composite negative electrode material having excellent energy capacity. More specifically, the present invention relates to a core-shell nanowire-based carbon composite negative electrode material having a high capacity using a silicon-based negative electrode material and having improved capacity retention rate of a lithium secondary battery with a core-shell nanowire structure.

Description

Core shell nanowire-based carbon composite anode material {CARBON COMPLEX ANODE MATERIAL BASED CORE SHELL NANOWIRE}

This specification claims the benefit of priority based on Korean Patent Application No. 10-2019-0005838 filed with the Korean Intellectual Property Office on January 16, 2019, and all contents disclosed in the literature of the Korean patent application are included as part of this specification do.

The present invention relates to a core shell nanowire-based carbon composite anode material having excellent energy capacity, and more specifically, to have a high capacity using a silicon-based anode material, and a core shell nanowire structure to maintain the capacity retention rate of a lithium secondary battery. An improved core shell nanowire-based carbon composite anode material.

Demand for power storage devices is rapidly increasing from small electronic devices such as mobile (IT) devices to medium to large devices such as electric vehicles (EVs) and energy storage devices (ESS). In particular, technology development and demand for lithium secondary batteries are rapidly increasing, and lithium secondary batteries having higher energy densities are required.

In order to increase the energy density, research and development are underway, such as increasing the capacity of the positive electrode material and the negative electrode material, increasing the density of the electrode plate, thinning the separator, and increasing the charge and discharge voltage. In recent years, research and development are focused on increasing the capacity of the cathode and anode materials.

The negative electrode material of a lithium secondary battery discharges electrons upon charging and accepts lithium ions at the same time, and accepts electrons during discharge and simultaneously discharges lithium ions to the positive electrode. In order to be used as a negative electrode material, stability, electrical conductivity, low chemical reactivity, price and storage capacity must be excellent. Natural graphite, artificial graphite, metal-based, carbon-based, and silicon-based materials are used as the negative electrode material, and development of silicon-based materials that are most advantageous for high capacity is being actively conducted. The silicon-based material has a theoretical capacity of 4,200 mAh/g, which is several times higher than the theoretical capacity of the graphite-based negative electrode material, 372 mAh/g, and is attracting attention as a next-generation material to replace the existing negative electrode material.

However, among silicon-based anode materials, silicon oxide-based anode materials having high commercialization potential are irreversible reaction products (Li ₂ O, Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ Li ₄ SiO ₄₎ generated during initial charge/discharge despite high theoretical capacity. ), the electrode is destroyed due to the volume change caused by the lithium secondary battery, the capacity retention rate is very low.

In order to overcome the above-mentioned problems, a method of nano-sizing silicon is used as a physical method. The nano-sized silicon-based negative electrode material has a very low self-weight, which is disadvantageous in handling, and has a very high specific surface area, which is directly applied to the cell production line. There is this difficult problem. Currently, no technology has been provided to solve these problems.

Korean Registered Patent Publication No. 10-1473968

The present invention has been devised to solve the above-described problems, and the object of the present invention is to reduce the volume change of the negative electrode material generated during charging and discharging of a lithium secondary battery, and core shell nanowire-based carbon composite negative electrode material capable of improving capacity retention. Is to provide

In addition, it is an object of the present invention to provide a core shell nanowire-based carbon composite anode material capable of lowering the amount of solid electrolyte (SEI) production through a nanowire having a low specific surface area.

The core shell nanowire according to the present invention includes a core comprising silicon crystal grains; And a silicon oxide shell formed on the surface of the core, wherein the core is formed to a thickness of 1 to 100 nm.

In addition, the core shell nanowires, short diameter; A plurality of branches extending around the short diameter; A plurality of side branches extending around the branch; And a tip formed on the short diameter, the branch, and the end of the side branch. It characterized by including any one or more structures.

In addition, the short diameter is characterized in that the thickness is 10 to 150 nm and the length is 20 to 500 nm.

In addition, the silicon oxide shell is characterized in that it comprises SiOx (0.8≤x≤1.6).

In addition, as a result of X-ray diffraction analysis of the core shell nanowires, the ratio (C/A) of crystalline silicon peak intensity (C) of 28 degrees and amorphous silicon peak intensity (A) of 20 to 23 degrees is 0.1 to 2. .

The core shell nanowire aggregate according to the present invention includes primary particles formed by aggregating the plurality of core shell nanowires of any one of claims 1 to 5; And a carbon layer surrounding the primary particles.

In addition, the carbon layer, a carbon precursor, petroleum-based pitch, coal-based pitch, coal tar, heavy residue oil, phenol resin, PAA, PAT, malic acid, oleic acid, graphite, digraphitizable carbon, or at least one of the hard graphitizable carbon is used It is characterized by carbon composite.

In addition, the core shell nanowire aggregates are characterized by having a carbon content of 10 to 80% by weight, and an average particle diameter (D ₅₀ ) of 0.3 to 5 μm.

The core shell nanowire-based carbon composite anode material according to the present invention is characterized in that the plurality of core shell nanowire aggregates are disposed on a carbon-based substrate.

In addition, the core shell nanowire-based carbon composite anode material has a carbon content of 5 to 80% by weight, the average particle diameter (D ₅₀ ) is 1 to 50 μm, and the specific surface area through BET analysis is 2 to 50 m ² / It is characterized by being g.

According to the present invention, by reducing the volume change of the negative electrode material generated during charging and discharging of the lithium secondary battery, an effect capable of improving the capacity retention rate of the lithium secondary battery occurs.

In addition, by lowering the amount of the solid electrolyte layer (SEI) produced on the lithium secondary battery electrode through the nanowire having a low specific surface area, an effect of improving the initial charge and discharge efficiency of the lithium secondary battery occurs.

1 is a view showing the structure of a core shell nanowire-based carbon composite anode material according to the present invention.
2 is a view showing the structure of the core shell nanowire aggregates according to the present invention.
3 is a view showing the configuration of the core shell nanowires according to the present invention.
4 is a view showing the microscopic structure of the core shell nanowire according to the present invention.
5 is a graph showing X-ray diffraction analysis (XRD) results of the core shell nanowires according to the present invention.
Figure 6 (a) is a SEM analysis of the core shell nanowire 10 according to the invention, Figure 6 (b) is a SEM analysis of the core shell nanowire aggregates 110 according to the invention, Figure 6 ( c) is a SEM analysis of the core shell nanowire-based carbon composite anode material according to the present invention.
7(a) is a SEM analysis photograph of the short diameter of the core shell nanowire, FIG. 7(b) is a SEM analysis photograph of the branch of the core shell nanowire, and FIG. 7(c) is a SEM of the side branch of the core shell nanowire It is an analysis photograph, and FIG. 7(d) is an SEM analysis photograph of the tip of the core shell nanowire.
8 is a graph showing the experimental results of measuring the initial charge/discharge capacity, initial reversible efficiency, and capacity retention rate of Comparative Examples and Examples 1 to 3.

The detailed description of the present invention is intended to completely describe the present invention to those skilled in the art. Throughout the specification, when a part is said to "include" a component or a structure and a shape to be a "feature", it excludes other components or excludes other structures and shapes unless specifically stated otherwise. It does not mean that it can include other components, structures and shapes.

The present invention can be applied to various conversions and can have various embodiments, and thus, specific embodiments will be presented and described in detail in the detailed description. However, this is not intended to limit the content of the invention by examples, it should be understood to include all conversions, equivalents, or substitutes included in the spirit and scope of the present invention.

1 is a view showing the structure of the core shell nanowire-based carbon composite anode material 100 according to the present invention. Referring to Figure 1, the core shell nanowire-based carbon composite anode material 100 according to the present invention may be composed of a core shell nanowire aggregate 110 and a carbon-based substrate 120.

The core shell nanowire-based carbon composite anode material 100 may be formed by arranging a plurality of core shell nanowire aggregates 110 on a carbon-based substrate 120. Here, the core shell nanowire aggregate 110 may be irregularly arranged on the carbon-based substrate 120, and the surface of the core shell nanowire aggregate 110 may at least partially contact the carbon-based substrate 120. have.

Here, the carbon-based substrate 120 acts as a support for fixing the core shell nanowire aggregate 110 disposed on its surface, thereby suppressing the volume change of the core shell nanowire aggregate 110 during charge and discharge. It can have an effect.

In addition, the core shell nanowire-based carbon composite anode material 100 may include a secondary carbon composite structure as a carbon material substrate 120 and a carbon layer 112 to be described later through a secondary carbon composite step. Through this secondary carbon composite structure, the core shell nanowire-based carbon composite anode material 100 can maximize a volume change suppression effect during charging and discharging to improve capacity retention when applied to a lithium secondary battery.

The core shell nanowire-based carbon composite anode material 100 according to the present invention may have a carbon content of 5 to 80% by weight. Here, when the carbon content of the core shell nanowire-based carbon composite anode material 100 is less than 5% by weight, the effect of preventing the volume change due to silicon and silicon oxide during charging and discharging may be insignificant and exceed 80% by weight. In this case, it is not preferable because the movement of lithium ions inside the electrode can be inhibited.

The average particle diameter (D ₅₀ ) of the core shell nanowire-based carbon composite anode material 100 according to the present invention may be formed from 1 to 50 μm. Here, when the average particle diameter (D ₅₀ ) of the core shell nanowire-based carbon composite anode material 100 exceeds 50 μm, electrode smoothness may be a problem, and when the average particle diameter is less than 1 μm, a binder is introduced. It is undesirable because of the large amount.

The specific surface area of the core shell nanowire-based carbon composite anode material 100 according to the present invention may be 2 to 50 m ² /g as measured by BET analysis. Here, when the specific surface area of the negative electrode material particles is less than 2 m 2 /g, discharge capacity may be lowered and adhesion between electrodes may be lowered, which is not preferable. Further, when the specific surface area of the negative electrode material particles exceeds 50 m 2 /g, it is not preferable because it causes an increase in initial irreversible capacity during charging and discharging.

2 is a view showing the structure of the core shell nanowire aggregate 110 according to the present invention. Referring to FIG. 2, the core shell nanowire aggregate 100 according to the present invention may be formed by aggregating a plurality of core shell nanowire 10 in a network form with each other. Here, the core shell nanowire aggregate 100 may be composed of a primary particle 111 and a carbon layer 112 surrounding the primary particle 111 formed by a plurality of core shell nanowires 10 being aggregated with each other. Can.

The primary particles 111 may be formed by agglomeration of a plurality of core shell nanowires 10 in a spherical shape. Specifically, the primary particle 111 has a plurality of core shell nanowires 10 are supported by each other, and in the state aggregated in a certain spherical shape, between the plurality of core shell nanowires 10 and the outer surface of the carbon layer 112 ).

The carbon layer 112 serves to improve the conductivity of the core shell nanowire-based carbon composite anode material 100. To perform this role, the carbon layer 112 may be coated on the surface of the core shell nanowire 10 and the surface of the primary particles 111.

Here, the carbon layer 112 is at least one of petroleum pitch, coal pitch, coal tar, heavy residue oil, phenol resin, PAA, PAT, malic acid, oleic acid, graphite, digraphitizable carbon, and hard graphitizable carbon, which are carbon precursors. It can be formed by using a carbon composite.

In addition, the core shell nanowire aggregate 110 according to the present invention may have a carbon content of 10 to 80% by weight. Here, when the carbon content of the core shell nanowire aggregate 110 is less than 10% by weight, the effect of preventing volume change due to silicon and silicon oxide during charging and discharging may be negligible, and when it exceeds 80% by weight, the inside of the electrode It is not preferable because it can inhibit the movement of lithium ions.

The average particle diameter (D ₅₀ ) of the core shell nanowire aggregate 110 according to the present invention may be 0.3 to 5 μm. Here, when the average particle diameter (D ₅₀ ) of the core shell nanowire-based carbon composite anode material 100 exceeds 5 μm, the electrode smoothness may be a problem, and when the average particle diameter is less than 0.3 μm, the role of a binder It is not preferable because the content of the carbon-based substrate 120 is excessively large.

3 is a view showing the configuration of the core shell nanowire 10 according to the present invention. Referring to FIG. 3, the core shell nanowire 10 may be composed of a core 11 located therein and a silicon oxide shell 12 formed on the surface of the core 11.

The core 11 serves to increase the charge and discharge capacity of the core shell nanowire-based carbon composite anode material 100. To perform this role, the core 11 may include silicon grains (Si) having a high theoretical capacity (4,200 mAh/g).

Here, the thickness of the silicon crystal grain may be formed of 1 to 100 nm. If the thickness of the silicon grain is less than 1 nm, the effect of improving the capacity of the negative electrode material may be negligible, and if the thickness exceeds 100 nm, the volume change occurring during charging and discharging becomes very large, which is not preferable because it results in an increase in irreversible capacity per unit weight. not.

The silicon oxide shell 12 serves to suppress the volume change of silicon crystal grains generated during charging and discharging. To perform this role, the silicon oxide shell 12 may include SiOx (0.8≤x≤1.6).

In the general formula SiOx of the silicon oxide shell 12, the x value is in the range of 0.8 to 1.6 as a result of XPS analysis. As a result of XPS analysis, when the x value is lower than 0.8, the amount of silicon is stoichiometrically excessive, so the capacity retention rate is very low when the battery is applied, and when the x value is higher than 1.6, SiO is a stable phase that does not participate in the reaction in the battery. The amount of ₂ may be excessive and the effect of improving the battery capacity may be negligible.

4 is a view showing a microscopic structure of the core shell nanowire 10 according to the present invention. Referring to FIG. 4, the structure of the core shell nanowire 10 may include a structure of a short diameter 10a, a branch 10b, a side branch 10c, and a tip 10d.

Specifically, the core shell nanowire 10 has a plurality of branches (10b) stretched around a plurality of branches (10b) around a relatively thick thick short diameter (10a), a branch (10b), a short diameter (10a), A tip 10d having a round shape may be formed at the ends of the branch 10b and the side branch 10c.

The core shell nanowire 10 may be formed by including any one or more structures of a short diameter 10a, a branch 10b, a side branch 10c, and a tip 10d.

In addition, the short diameter 10a, the branch 10b, the side branch 10c, and the tip 10d of the core shell nanowire 10 may include one or more cores 11 therein. Here, the core 11 may be formed in various shapes such as circular, elliptical, rod-shaped, and branched shapes.

The short diameter 10a of the core shell nanowire 10 has a thickness of 10 to 150 nm and a length of 20 to 500 nm. When the thickness of the short diameter 10a is less than 10 nm and the length is less than 20 nm, economical efficiency is lowered in the synthesis step, the contact resistance is very high, and a high specific surface area may cause a problem that an excessive amount of binder is required during battery manufacturing. In addition, when the thickness of the shorter diameter 10a is more than 150 nm and the length is more than 500 nm, when the battery is applied, destruction of particles occurs and a capacity retention rate may decrease.

5 is a graph showing the results of X-ray diffraction analysis (XRD) of the core shell nanowire 10 according to the present invention. Referring to FIG. 5, the core shell nanowire 10 has a ratio (C/A) of crystalline silicon peak intensity (C) of 28 degrees and amorphous silicon peak intensity (A) of 20 to 23 degrees as X-ray diffraction analysis results of 0.1 to It may be formed of two. Here, when the crystalline silicon peak intensity (C) of 28 degrees is too high to form a ratio (C/A) of more than 2 with the amorphous silicon peak intensity (A), the silicon crystal grains included in the core shell nanowire 10 are formed. As the size increases, a volume change of the negative electrode material occurs during charging and discharging of the battery, and as a result, a capacity retention rate may decrease.

And, when the ratio (C/A) of the crystalline silicon peak intensity (C) of 28 degrees and the amorphous silicon peak intensity (A) of 20 to 23 degrees is less than 0.1, silicon crystal grains are well formed in the core shell nanowire 10. The capacity-enhancing effect may be insignificant because it is not formed or the grain growth is lowered.

Figure 6 (a) is a SEM analysis of the core shell nanowire 10 according to the invention, Figure 6 (b) is a SEM analysis of the core shell nanowire aggregates 110 according to the invention, Figure 6 ( c) is a SEM analysis of the core shell nanowire-based carbon composite anode material 100 according to the present invention.

Referring to FIG. 6(a), it can be seen that the core 11 made of Si of the core shell nanowire 10 and the silicon oxide shell 12 made of SiOx. Referring to FIG. 6(b), it can be seen that a plurality of core shell nanowires 10 are supported and agglomerated with each other to form a circular sphere based on the carbon layer 20. And, referring to Figure 6 (c), a plurality of core shell nanowire aggregates 110 are irregularly arranged and supported on the carbon material substrate 120, the carbon layer 20 and the carbon material substrate 120 The secondary carbon composite core shell nanowire-based carbon composite anode material 100 can be confirmed.

FIG. 7(a) is a SEM analysis photograph of the short diameter 10a of the core shell nanowire 10, and FIG. 7(b) is a SEM analysis photograph of the branches 10b of the core shell nanowire 10, and FIG. 7 (c) is a SEM analysis picture of the side branches 10c of the core shell nanowire 10, and FIG. 7(d) is a SEM analysis picture of the tip 10d of the core shell nanowire 10. 7(a) to 7(d), cores formed in various shapes inside the short diameter 10a, branch 10b, side branch 10c, and tip 10d of the core shell nanowire 10 (11) can be confirmed. For example, inside the short diameter 10a, a pillar, rod, or a plurality of spherical cores 11 may be formed, and the cores 11 may be branched 10b and branches 10b and 10c. It may be formed in a split shape corresponding to the side branches (10c).

<Comparative Example>

The comparative example is an experimental result of measuring the capacity, initial reversible efficiency and capacity retention rate during charging and discharging using Si-SiOx nanoparticles.

<Example 1>

Example 1 is an experimental result of measuring the capacity, initial reversible efficiency and capacity retention rate during charging and discharging using Si-SiOx core shell nanowires.

<Example 2>

Example 2 uses the Si-SiOx-C composite anode material in which Si-SiOx core-shell nanowires, graphite, and pitch precursors are compounded at a mass ratio of 6:3:1, respectively, during charging and discharging capacity, initial reversible efficiency, and capacity It is the result of the experiment that measured the retention rate.

<Example 3>

Example 3 uses a Si-SiOx-C composite anode material in which Si-SiOx core-shell nanowires, graphite, and pitch precursors are combined at a mass ratio of 2:7:1, respectively, during charging and discharging capacity, initial reversible efficiency, and capacity It is the result of the experiment that measured the retention rate.

Initial charge capacity (mAh/g) Initial discharge capacity (mAh/g) Initial reversible efficiency
(%) Capacity retention rate
(3~50 cycle, %) Comparative example 2464.5 712.5 28.9 79.6 Example 1 2552.5 1505.5 58.9 95.7 Example 2 1679 1202 71.6 100.2 Example 3 901 664 73.7 102.3

Tables 1 and 8 are comparative examples, tables and graphs showing experimental results of measuring the initial charge/discharge capacity, initial reversible efficiency, and capacity retention rate of Examples 1 to 3. Referring to Table 1 and FIG. 8, the comparative example composed of nanoparticles has a very large specific surface area, and thus, due to high SEI (solid electrolyte membrane) production, initial reversible efficiency (28.9%) is significantly lower than Examples 1 to 3. You can confirm that.

Example 1 composed of nanowires has a higher capacity than graphite of crystalline silicon, and thus initial charge capacity (2552.5 mAh/g) and initial discharge capacity (1505.5 mAh) than Examples 2 and 3 composed of a Si-SiOx-C composite anode material. /g) is high.

However, in Examples 2 and 3, it is confirmed that the low conductivity of silicon-based is supplemented through graphite, so that the initial reversible efficiency (71.6%, 73.7%) is higher than in Example 1.

The difference between the experimental results of Examples 2 and 3 is due to the difference in the content of graphite and silicon contained in the negative electrode material, and when the mass ratio of the Si-SiOx core-shell nanowire is high (Example 2), the negative electrode due to the high content of silicon The initial capacity of ash is relatively high. And when the mass ratio of graphite is high (Example 3), the initial capacity of the negative electrode material is relatively low due to the high content of graphite.

Although described above with reference to preferred embodiments of the present invention, those skilled in the art variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You can understand that you can.

100: core shell nanowire-based carbon composite anode material
110: core shell nanowire aggregate
120: carbon-based substrate
111: primary particle
112: carbon layer
10: core shell nanowires
11: core
12: Silicon oxide shell
10a: Short diameter
10b: eggplant
10c: side branches
10d: Tips

Claims (10)

A core comprising silicon crystal grains; And
It includes; a silicon oxide shell formed on the surface of the core,
The silicon crystal grain,
Characterized in that formed to a thickness of 1 to 100 nm,
Core shell nanowires.
According to claim 1,
The core shell nanowire,
Short diameter;
A plurality of branches extending around the short diameter;
A plurality of side branches extending around the branch; And
A tip formed on the short diameter, the branch, and the end of the side branch; Characterized in that it comprises a structure of any one or more of
Core shell nanowires.
According to claim 2,
The short diameter,
Characterized in that the thickness is 10 to 150 nm and the length is 20 to 500 nm.
Core shell nanowires.
According to claim 1,
The silicon oxide shell,
Comprising SiOx (0.8≤x≤1.6),
Core shell nanowires.
According to claim 1,
As a result of X-ray diffraction analysis of the core shell nanowires, the ratio (C/A) of crystalline silicon peak intensity (C) of 28 degrees and amorphous silicon peak intensity (A) of 20 to 23 degrees is 0.1 to 2,
Core shell nanowires.
The primary particles formed by aggregating the plurality of core shell nanowires of any one of claims 1 to 5; And
A carbon layer surrounding the primary particles; containing,
Core shell nanowire aggregates.
The method of claim 6,
The carbon layer,
It is characterized by carbon composite using at least one of petroleum pitch, coal pitch, coal tar, heavy residue oil, phenol resin, PAA, PAT, malic acid, oleic acid, graphite, digraphitizable carbon, and hard graphitizable carbon. doing,
Core shell nanowire aggregates.
The method of claim 6,
The core shell nanowire aggregate,
Carbon content has 10 to 80% by weight,
The average particle diameter (D ₅₀ ) is characterized in that 0.3 to 5 μm,
Core shell nanowire aggregates.
The method of claim 6,
Characterized in that the plurality of core shell nanowire aggregates are disposed on a carbon-based substrate,
Core shell nanowire-based carbon composite anode material.
The method of claim 9,
The core shell nanowire-based carbon composite anode material,
Carbon content of 5 to 80% by weight,
The average particle diameter (D ₅₀ ) is 1 to 50 μm,
Characterized in that the specific surface area through BET analysis is 2 to 50 m ² /g,
Core shell nanowire-based carbon composite anode material.

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