KR102383273B1 - Porous silicon composite comprising a carbon coating layer, preparation of the same and lithium secondary battery using the same - Google Patents

Abstract

In the present specification, as a porous silicon composite, porous silicon particles; and a carbon coating layer formed on the porous silicon particles, wherein the porous silicon particles have pores arranged in three dimensions, and the porous silicon composite has a diameter of 10 to 20 nm, a porous silicon composite, Disclosed are a method for manufacturing the same and a lithium secondary battery including the same.

Description

Porous silicon composite including carbon coating layer, manufacturing method thereof, and lithium secondary battery including same

The present invention relates to a porous silicon composite including a carbon coating layer, a method for manufacturing the same, and a lithium secondary battery including the same. More specifically, the present invention provides a porous silicon composite, comprising: porous silicon particles; and a carbon coating layer formed on the porous silicon particles, wherein the porous silicon particles have pores arranged in three dimensions, and the porous silicon composite has a diameter of 10 to 20 nm, a porous silicon composite, It relates to a method for manufacturing the same and a lithium secondary battery including the same.

With the development of portable IT devices, the demand for a secondary battery having high energy density and stability is increasing, and many studies have been made on the increase in the service life and capacity of the secondary battery. Recently, with the advent of electric vehicles, the use of lithium secondary batteries has been expanded. However, due to the low capacity of the graphite negative electrode used in the existing lithium secondary battery, there is a limit to designing a battery having high energy density and lightness at the same time.

Among materials that can replace the graphite anode, there are silicon, tin, and germanium, which are elements of the same group as carbon constituting graphite. Among them, silicon realizes a high capacity (3580 mAhg ^-1 for Li ₁₅ Si ₄ at room temperature) nearly ten times higher than that of graphite anode, and has a low reaction potential with lithium (<0.4 vs. Li/Li ⁺ ). It is present in a large amount, so it is very advantageous in price compared to other alternative substances and shows non-toxicity. However, the reaction with lithium entails a large volume expansion (>300%, Li _3.75 Si at room temperature), and thus the active material is desorbed from the current collector and the conductive material, resulting in a rapid capacity decrease after the initial several cycles. In addition, due to the low electrical conductivity (10 ^-5 S/cm), a rapid decrease in capacity occurs even during high-rate charging and discharging.

Therefore, in order to use silicon, which is an ultra-high-capacity anode active material, research is mainly conducted in the direction of 1) to alleviate the volume expansion of silicon and 2) to improve the electrical conductivity of silicon. First, in order to alleviate the volume expansion of silicon, bulk silicon particles are pulverized into nanoparticles to reduce the stress applied to the bulk silicon particles during volume expansion, or a porous structure is introduced so that silicon particles break down even during volume expansion. A representative study was carried out to prevent it from falling. Registered Patent No. 0493960 (registered on May 30, 2005) relates to “a method for manufacturing porous silicon and nano-sized silicon particles and their application as anode materials for lithium secondary batteries”, A technique of mixing a silicon precursor and heat-treating it and eluting it with an acid has been proposed. Although these conventional techniques may improve the initial capacity retention rate due to the buffering effect due to the porous structure, since they simply use porous silicon particles with poor conductivity, the conductivity between particles decreases during electrode manufacturing, resulting in lower initial efficiency or capacity retention characteristics. The problem still exists. In addition, a method of using an active/inactive compound or a composite material to which an inactive material capable of buffering a volume change without reacting with lithium is added is being studied. However, when a material other than silicon is used as an alloy material, there is a problem in that the improvement of cycle characteristics and capacity cannot be pursued at the same time because the reduction of the maximum capacity or the limit capacity is caused.

As a study to improve the electrical conductivity of silicon, a study of coating a conductive material on the silicon surface was mainly conducted. Typically, studies have been published to obtain improved cycle and high-speed charge/discharge results by coating carbon with high electrical conductivity on the surface of silicon particles. In addition, metal, graphene, graphene oxide, and reduction treatment Research has been conducted to improve electrical conductivity by coating reduced graphene oxide on the surface of silicon particles. Such surface coating not only improves electrical conductivity, but also serves to improve cycle characteristics by stabilizing the unstable silicon/electrolyte interface, which has become an essential requirement for using silicon as a high-capacity anode active material.

In order to effectively use the high capacity of silicon, a method capable of simultaneously solving the volume expansion and low electrical conductivity of silicon is required. Therefore, it is more preferable to wrap the silicon with a material that can alleviate the volume expansion of silicon while having high electrical conductivity. Typically, many studies have been conducted to introduce conductive carbon to the silicon surface.

However, the existing method is chemical vapor deposition (CVD) or physical vapor deposition (Physical Vapor Deposition) of explosive and harmful gases (CH ₄ , C ₂ H ₄ , C ₇ H ₈ , etc.) under high temperature or high pressure. A carbon coating layer was introduced on the silicon surface through the above method, but these methods are not only dangerous during the process, but also require expensive equipment and processes, so it is difficult to apply to industry through mass production due to problems such as high price. Therefore, there is a demand for the manufacture of a new anode active material capable of improving initial efficiency and capacity retention characteristics and maintaining voltage and current amount almost constant even after repeated charging/discharging.

Patent Publication No. 10-2004-0082876 Patent Publication No. 10-2016-0037334 Registered Patent No. 0493960

One embodiment of the present invention is an anode material for a secondary battery having a high capacity that can replace the existing graphite anode material in a lithium secondary battery used for energy storage for IT devices, electric vehicles, and renewable energy storage. An object of the present invention is to provide an anode material for a secondary battery that is very simple and has a high capacity compared to a method of manufacturing silicon oxide or nano-metal silicon.

In another aspect, an embodiment of the present invention has an object to solve the reactivity problem of silicon by introducing a carbon layer and to make the process more simple, and to improve electrical contact between particles and specific surface area An object of the present invention is to provide an anode active material having a high initial discharge capacity and a high charge capacity by shortening the diffusion path of lithium ions by greatly increasing the (reaction area) and the presence of micropores.

In another aspect, one embodiment of the present invention achieves maximization of cycle characteristics by minimizing the volume expansion and contraction of the anode active material generated during the charging/discharging process, and providing an anode active material capable of high-speed charging/discharging and high output. The purpose of the present invention is to provide a negative electrode for a lithium secondary battery having high mechanical, thermal and electrical stability by greatly increasing the adhesion between the negative electrode active material and the current collector.

In an exemplary embodiment of the present invention, there is provided a porous silicon composite, comprising: porous silicon particles; and a carbon coating layer formed on the porous silicon particles, wherein the porous silicon particles have three-dimensionally arranged pores, and the porous silicon composite has a diameter of 10 to 20 nm. to provide.

Another exemplary embodiment of the present invention provides an anode active material including the above-described porous silicon composite.

Another exemplary embodiment of the present invention provides a lithium secondary battery including the above-described negative active material, a conductive material and a binder.

Another exemplary embodiment of the present invention comprises the steps of obtaining porous silicon particles by selective etching; forming a carbon coating layer on the porous silicon particles using a solution in which the porous silicon particles and a carbon-based polymer are dispersed; and after forming a carbon coating layer on the porous silicon particles, heat-treating the porous silicon particles two or more times; provides a porous silicon composite manufacturing method comprising.

According to an embodiment of the present invention, by forming a carbon coating layer on the surface of the porous silicon particle including a plurality of pores, it can be provided for a negative electrode material for a lithium secondary battery.

In order to suppress volume expansion of silicon having a high capacity, silicon particles are made into nanoparticles to shorten the lithium diffusion distance, enabling rapid insertion and desorption during charging and discharging, and improving electrical contact between particles and particles. high-temperature storage, lifespan, and high-output characteristics can be improved.

In addition, the carbon coating layer covers the entire porous silicon-based particle, so that the electrical conductivity is excellent, and the reaction can be made uniformly during charging and discharging by stabilizing the electrode interface.

In addition, the method for manufacturing a porous silicon composite according to the present invention is a liquid-phase synthesis method, which can be mass-produced, and has a production speed compared to a conventional chemical vapor deposition method or a vapor-liquid-solid (VLS) process. is fast, and it is advantageous in terms of process or safety.

1 is a schematic diagram of a manufacturing process of an anode active material including porous silicon-based particles according to the present invention and a carbon coating layer formed on the surface of the particles.
2A is a scanning microscope (SEM) photograph of Si-Al particles before etching according to the present invention.
2B is a scanning microscope (SEM) photograph of silicon/silicon oxide particles after etching using hydrogen chloride according to the present invention.
2C is a scanning microscope (SEM) photograph of porous silicon particles after etching using hydrogen fluoride according to the present invention.
Figure 2d is a scanning microscope (SEM) photograph showing the structure of the polyacrylamide-coated porous silicone material according to the present invention.
Figure 2e is a scanning microscope (SEM) photograph of the porous silicon material before the formation of the carbon coating layer over the primary heat treatment according to the present invention.
2f is a scanning microscope (SEM) photograph showing the structural change of the carbon layer-coated porous silicon material according to the final heat treatment temperature according to the present invention.
3A is an X-ray diffraction pattern (XRD) graph of porous silicon composite materials according to the present invention.
3B is an infrared spectroscopy (FT-IR) graph of porous silicon composites according to the present invention.
3c is a nitrogen adsorption/desorption isotherm of porous silicon composite materials according to the present invention.
4A is a thermogravimetric analysis (TGA) graph of porous silicon composite materials according to the present invention.
Figure 4b shows the weight ratio of residues after thermogravimetric analysis of the porous silicon composite materials according to the present invention.
5A to 5C are life-time characteristics (5a), rate-rate characteristics graphs (5b), and rate characteristics (5c) according to the secondary heat treatment temperature of the porous silicon composite materials according to the present invention.
6A and 6B are diagrams schematically illustrating changes in the shape of the micro-sized composite active material and the nano-sized composite according to the lithium insertion and desorption processes.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention disclosed in the text are illustrated for the purpose of explanation only, and the embodiments of the present invention may be embodied in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention can make various changes and can have various forms, and the embodiments are not intended to limit the present invention to a specific disclosed form, and all changes, equivalents or substitutes included in the spirit and scope of the present invention should be understood as including

In the present specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

Porous Silicon Composite

In exemplary embodiments of the present invention, there is provided a porous silicon composite comprising: porous silicon particles; and a carbon coating layer formed on the porous silicon particles, wherein the porous silicon particles have three-dimensionally arranged pores, and the porous silicon composite has a diameter of 10 to 20 nm. to provide.

1 shows a conceptual diagram of the porous silicon composite of the present invention. Referring to this, the porous silicon composite according to the present invention forms a carbon coating layer on (surface or inside) porous silicon particles including a plurality of pores, so that a conventional negative electrode As a non-aqueous material, it can be used as an anode active material of a lithium secondary battery as it is possible to improve cycle performance, which is a material problem, and to minimize volume expansion during charging and discharging.

In addition, it is possible to manufacture a nanostructured porous silicon negative electrode active material from an inexpensive raw material without using the existing expensive nanostructure synthesis process, and the lithium diffusion distance can be reduced due to the porous structure, so that lithium ions can be delivered quickly.

In exemplary embodiments, the carbon coating layer may include a carbon-based polymer including an amino group or an amino alkyl group, and silicon nanoparticles functionalized by an amino group having a positive charge suppress aggregation by a repulsive force between positive charges. This can prevent the growth of large particles. In addition, carbon coating may be performed while maintaining the porous structure through heat treatment without additionally introducing a carbon precursor.

As a result, by including a carbon-based polymer including an amino group or an amino alkyl group, the capacity and stability of the lithium ion battery can be further improved by improving electrical conductivity and reducing volume expansion compared to the conventional metal oxide nanocomposite.

When the weight ratio is less than 5:1, the synergistic effect of electrical conductivity is insignificant, and when the negative active material is applied, the reactivity with the electrolyte is high, so there may be a problem of lowering the initial efficiency, and when it is more than 1:1, the thickness of the carbon coating layer increases This may impede the mobility of lithium ions and increase resistance.

In exemplary embodiments, the specific surface area of the porous silicon composite including the carbon coating layer may be 60 m ² /g or more.

Anode active material and lithium secondary battery containing porous silicon composite

In exemplary embodiments of the present invention, an anode active material including the above-described porous silicon composite is provided.

In an exemplary embodiment, the negative active material is one or more metals selected from the group consisting of Sn, Al, Ge, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag and Au, or alloys and oxides thereof. may include

In exemplary embodiments of the present invention, a lithium secondary battery including the above-described negative active material, a conductive material and a binder is provided.

Method for manufacturing porous silicon composite

In exemplary embodiments of the present invention, the method includes the steps of: obtaining porous silicon particles by selective etching; forming a carbon coating layer on the porous silicon particles using a solution in which the porous silicon particles and a carbon-based polymer are dispersed; and after forming a carbon coating layer on the porous silicon particles, heat-treating the porous silicon particles two or more times; provides a porous silicon composite manufacturing method comprising.

1 is a flowchart illustrating a method for manufacturing a porous silicon composite according to an embodiment of the present invention. Referring to this, it is possible to prepare porous silicon particles having micropores by performing selective etching with an alloy powder made of silicon and an alkali metal. Thereafter, a carbon coating layer can be formed on the porous silicon particles without a complicated process by using a liquid phase synthesis method. After that, by heat-treating the porous silicon particles having the carbon coating layer formed thereon twice or more, it is possible to suppress the rapid volatilization of the polymer and increase the carbonization yield.

In an exemplary embodiment, the carbon-based polymer may include a carbon-based polymer including an amino group or an amino alkyl group, and the silicon nanoparticles functionalized by the amino group having a positive charge are too large due to the repulsive force between the positive charges. It can prevent them from growing large or agglomerated to become large particles.

In an exemplary embodiment, the weight ratio of the porous silicon particles and the carbon-based polymer may be 5:1 to 1:1, or 4:1 to 2:1. When the weight ratio is less than 5:1, the synergistic effect of electrical conductivity is insignificant, and when the negative active material is applied, the reactivity with the electrolyte is high, so there may be a problem of lowering the initial efficiency, and when it is more than 1:1, the thickness of the carbon coating layer increases This may impede the mobility of lithium ions and increase resistance.

In an exemplary embodiment, the heat treatment may be performed continuously two or more times, suppressing the rapid volatilization of the polymer, and increasing the carbonization yield.

In an exemplary embodiment, the heat treatment may include primary heat treatment at 200 to 350 °C; and secondary heat treatment at 700 to 900 °C. Crosslinking is achieved through heat treatment at a low temperature, and a nano-sized carbonized film with an increased carbon content is formed through high temperature heat treatment, which is thermally stable to increase conductivity.

In an exemplary embodiment, the first heat treatment and the second heat treatment may be performed for 30 minutes to 2 hours, respectively.

In an exemplary embodiment, the step of obtaining the porous silicon particles by the selective etching may be performed by etching the Al-Si microparticles with hydrogen chloride.

The present invention will be described in more detail through the following practice. However, the examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

Example

[Example 1: Preparation of porous silicon composite including carbon coating layer]

Porous Silicone Manufacturing

Al-Si (8.8:1.2) alloy powder was immersed in 100 ml of 3 M hydrogen chloride solution, mixed, and etched for 24 hours by stirring, then sufficiently washed and filtered. The filtered resultant was dried in a drying furnace at 100° C. for 2 hours to obtain porous silicon/silicon oxide (PSi/SiOx) particles.

Thereafter, the porous silicon/silicon oxide particles were immersed in a 5% hydrogen fluoride 100 ml solution, mixed, and etched for 5 hours by stirring, followed by sufficient washing and filtration. The filtered resultant was dried in a drying furnace at 100° C. for 2 hours to obtain porous silicon (PSi) particles.

Porous silicon composite including carbon coating layer (PSiPAM-280/800)

The porous silicone particles and the polyacrylamide (Polyacrylamide) solution are mixed in 75:25 parts by weight, the porous silicone particles are dispersed in the polyacrylamide solution, and dried in a drying furnace at 100° C. for 2 hours. The polymer-coated porous silicone A complex (PSiPAM) was prepared.

The prepared polymer-coated porous silicon composite is supplied with compressed air at a flow rate of 5 to 20 ml per minute, and the primary heat treatment is performed at 280 ° C. for 1 hour at a temperature increase rate of 1 ° C. per minute, followed by an inert gas (N ₂ , Ar gas), a porous silicon composite (PSiPAM-280/800) including a carbon coating layer was prepared by performing secondary heat treatment at a temperature of 800 °C for 1 hour at a temperature increase rate of 5 °C per minute.

Comparative Example 1. Preparation of porous silicon composite excluding carbon coating layer (PSi280/800)

The porous silicon composite (PSi280/800) except for the carbon coating layer according to the present invention used the same Al-Si particles as the porous silicon source, and the same except for the polymer polyacrylamide coating in the PSiPAM-280/800 production. prepared by the process.

Comparative Example 2. Preparation of porous silicon composite except for primary heat treatment (PSiPAM-800)

To compare the higher lithium ion storage capacity of the porous silicon composite (PSiPAM-280/800) including the carbon coating layer according to the present invention, PSiPAM-800 was prepared. PSiPAM-800 used the same Al-Si particles as the porous silicon source, and polyacrylamide was also used for the polymer.

Comparative Example 3. Composite preparation according to secondary heat treatment temperature

A porous silicon composite was prepared according to the secondary heat treatment temperature (600, 700, 900, 1000 ° C.), and Comparative Examples (PSiPAM-280/600, PSiPAM-280) were prepared in the same manner as in Example 1 except for the secondary heat treatment temperature condition. /700, PSiPAM-280/900, PSiPAM-280/1000) were prepared.

Experimental Example 1. Evaluation of Surface and Structural Characteristics

(1) SEM analysis result

As shown in FIGS. 2A-2F , it can be confirmed that the surface of the porous silicon composite according to an embodiment of the present invention and a plurality of pores are formed. As shown in FIG. 2a (indicated by Al-Si), it can be seen that the Al-Si microparticles have a spherical shape in which Si and Al are evenly mixed with each other with a size of ~10 nm.

As shown in FIG. 2b (PSi/SiOx), it can be confirmed that, while aluminum is selectively removed by hydrogen chloride etching, fine pores are generated on the surface together with silicon/silicon oxide crystal particles having a size of several hundred nm.

As shown in FIG. 2c (PSi), it can be confirmed that silicon oxide is selectively removed by hydrogen fluoride etching, and fine pores are generated on the surface together with silicon crystal particles having a size of several hundred nm.

As shown in FIG. 2d (PSiPAM), it can be confirmed that the polymer surrounds the porous silicon particles. As shown in FIGS. 2e (PSiPAM-280) and 2f (PSiPAM-280/800), the carbon layer-coated porous silicon material obtained by continuous heat treatment (primary, secondary) of polyacrylamide on the porous silicon surface is 10 It was confirmed that it has a diameter of ~ 20 nm and also has fine pores.

Specifically, it can be seen that after the secondary heat treatment, as the polymer around the silicon is formed into a carbonized film, pores are partially created, and thus more branched microstructures are observed.

(2) XRD analysis characteristics

Figure 3a is a graph showing the XRD pattern of the porous silicon composite material prepared in Example 1 and Comparative Example 2. Referring to FIG. 3a, silicon's main peaks of 2θ°, 47.3°, 56.1°, 69.1°, 76.4°, and 88.1° were shown, and each of the peaks was (111), (002), (101), ( 220) was shown.

(3) FT-IR analysis characteristics

Figure 3b was analyzed using an infrared spectrometer to confirm the coating layer of the polymer and carbon of the samples of Example 1 and Comparative Example 2. In the case of the material obtained through heat treatment, the spectrum showed a C=O peak at 1663 cm ^-1 , confirming that the polyacrylamide on the porous silicon surface was made into a carbon layer during the heat treatment process.

(4) BET analysis characteristics

3C is an isotherm shown through a nitrogen adsorption/desorption test of the samples of Example 1 and Comparative Example 2, and the calculated specific surface area of the sample is shown in Table 1 below.

Specific surface area of porous silicon composites Sample PSIPAM PSiPAM-280 PSiPAM-280/800 PSiPAM-800 specific surface area (m ² /g) 29 34 61 52

Referring to Table 1, it can be seen that there is a difference in the specific surface area of the manufactured material according to the heat treatment process. The highest specific surface area of 61 m ² /g in PSiPAM-280/800 particles through pore distribution analysis is interpreted as the formation of a porous structure with uniformly sized pores. The specific surface area of PSiPAM-280/800 by the final heat treatment has been increased by about 2 times, which shortens the diffusion distance of lithium ions, enabling fast insertion and desorption during charging and discharging, and improving lifespan and high output characteristics.

(5) TGA analysis characteristics

Thermogravimetric analysis was performed to investigate the content of silicon and materials other than silicon, and the results are shown in FIGS. 4A and 4B. As a result of measuring up to ~1000 °C while heating the temperature increase rate at 5 °C/min in an air atmosphere, it was observed that a rapid change in weight occurred near 400 to 600 °C. In the case of PSiPAM-280/800, the thermal decomposition in the vicinity of over 600°C appears to be due to the thermal stability of the composite material.

In addition, it was confirmed that the weight ratio of the residue was 5.7 wt% and 2.6 wt% in Example 1 (PSiPAM-280/800) and Comparative Example 2 (PSiPAM-800), respectively. It can be confirmed that the carbonization yield is increased by suppressing the rapid volatilization process of the polymer by performing the first heat treatment.

Specifically, in general, only high-temperature heat treatment (carbonization) is carried out, and the added heat treatment at low temperature cross-links to form a nano-sized carbonized film with increased carbon content, which is thermally stable in high-temperature heat treatment, thereby increasing conductivity. . It can be said to be a continuous process because only the temperature variable can be controlled in one equipment without changing the equipment and process method.

Preparation Example 1. Preparation of electrodes and configuration of lithium ion secondary battery cells

The porous silicon composite material obtained in Example 1 and Comparative Examples 1, 2, and 3 was prepared as an electrode in order to examine the difference between using each as an anode of a lithium secondary battery, and the composition of the electrode was 80 wt% of a negative electrode active material, and a conductive material 10 wt%, the binder was mixed in a ratio of 10 wt%.

A coin cell composed of the prepared negative electrode and positive electrode lithium hexafluorophosphate (Lithium Hexafluorophosphate, LiPF ₆ ) and 1:1 vol% ethylene carbonate (Ethylene Carbonate, EC) / dimethyl carbonate (Dimethyl Carbonate, DMC) liquid electrolyte was prepared And the charge-discharge capacity and cycle characteristics were investigated as a negative electrode of a lithium secondary battery prepared by conducting a charge-discharge experiment using a charge/discharger for the coin cell.

Using the lithium secondary battery negative electrode prepared by using the composite of Example 1 and Comparative Examples 1, 2, and 3, a charge/discharge experiment was conducted using a WBCS3000L charge/discharge device manufactured by Won-A tech. Charging and discharging was performed in a voltage range of 0.005 to 2.0 V with a current of 200 mAh/g.

Experimental Example 2. Evaluation of electrochemical properties

The charging and discharging results of the lithium secondary batteries according to Example 1 and Comparative Examples 1 and 2 are shown in FIG. 5A . As shown in Fig. 5a, PSiPAM-280/800 of Example 1 showed an initial negative electrode capacity of 2107 mAh/g, while PSi280/800 and PSiPAM800 of Comparative Examples 1 and 2 had 2018 mAh/g and 1469 mAh/g. The initial capacity of the negative electrode is shown respectively. In the case of initial coulombic efficiency, PSiPAM-280/800 shows 74%, PSi280/800 shows 56%, and PSiPAM800 shows 63%. Therefore, it can be seen that the initial capacity and initial coulombic efficiency of PSiPAM-280/800 are high. In addition, as can be seen from the cycle characteristics of the electrodes, the electrodes of Comparative Examples 1 and 2, PSi280/800 and PSiPAM800, showed unstable cycle characteristics and low capacity in 100 charge/discharge results. On the other hand, the PSiPAM-280/800 electrode maintains 1400 mAh/g, which is about 3.5 times higher than graphite with a theoretical capacity of 372 mAh/g, and shows a stable capacity decrease as the cycle increases.

Figure 5b is a graph showing the rate capability (Rate Capabilities) of the battery for the lithium secondary battery included as a negative active material according to Example 1 and Comparative Example 2, current density at the time of charging in the range of 0.005 V ~ 2 V is fixed at 0.1 C (100 mAhg ^-1 ), and the storage capacity of the secondary battery is measured as the current density during discharge is changed in the range of 0.1, 0.2, 0.5, 1, 3, 0.2 C. According to FIG. 5B , when the negative active material of Example 1 is applied, it can be confirmed that the output characteristics are excellent.

5c is a graph showing the cycle characteristics of the lithium secondary battery including the negative active material according to Example 1 and Comparative Example 3, and in the case of PSiPAM-280/800, excellent performance of 64% even after 100 times of charging and discharging Capacity retention was shown. On the other hand, in the case of the PSiPAM-280/600, PSiPAM-280/700, PSiPAM-280/900, and PSiPAM-280/1000 materials of Comparative Example 3, 289, 478, 585, and 98 mAh/g were low after 100 times of charging and discharging. It can be seen that the capacity retention rate and unstable cycle characteristics are exhibited.

6a and 6b are views schematically showing the change in shape of the negative electrode composite active material according to the lithium insertion and desorption process, FIG. 6a is a schematic diagram of a micro-sized composite active material electrode, and FIG. 6b is a porous silicon composite including a carbon coating layer ( Example 1 It is a schematic diagram of the electrode of PSiPAM-280/800).

Example PSiPAM-280/800 prepared by the above method has a nanoscale size (~15 - 20 nm) and a plurality of internal nanocavities inside the particle. Nanoporous silicon particles have excellent cycle stability and high reversible capacity as an anode material for lithium ion batteries, and the nanoporous structure with a large surface area can reduce the lithium diffusion distance. A large amount of expansion can be alleviated. In addition, the carbon coating layer covers the entire porous silicon-based particle to provide excellent electrical conductivity and uniform reaction during charging and discharging by stabilizing the electrode interface, thereby improving high-temperature storage, lifespan and high-output characteristics of the secondary battery.

As described above in detail a specific part of the content of the present invention, for those of ordinary skill in the art, it is clear that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Accordingly, it is intended that the substantial scope of the present invention be defined by the appended claims and their equivalents.

Claims (6)

obtaining porous silicon particles by performing selective etching with an alloy powder consisting of silicon and an alkali metal;
using a solution in which the porous silicon particles and a carbon-based polymer are dispersed, forming a carbon coating layer on the surface or inside the porous silicon particles by a liquid phase synthesis method; and
After forming a carbon coating layer on the porous silicon particles, heat-treating the porous silicon particles two or more times; includes,
The heat treatment step is
First heat treatment at 200 to 350 ℃; and
Secondary heat treatment at 700 to 900 ℃; Method for producing a porous silicon composite comprising the. According to claim 1,
The carbon-based polymer is a method for producing a porous silicone composite, characterized in that it comprises a carbon-based polymer including an amino group or an amino alkyl group. According to claim 1,
The weight ratio of the porous silicon particles and the carbon-based polymer is 5:1 to 1:1, characterized in that the porous silicon composite manufacturing method. According to claim 1,
The heat-treating step is a method for producing a porous silicon composite, characterized in that made two or more consecutively. According to claim 1,
The first heat treatment step and the second heat treatment step are each performed for 30 minutes to 2 hours, the method for producing a porous silicon composite. According to claim 1,
The step of obtaining the porous silicon particles,
A method for producing a porous silicon composite, characterized in that the Al-Si micro-particles are etched with hydrogen chloride.

Images