KR100743053B1 - Negative electrode active material. The manufacturing method and a lithium secondary battery having the same - Google Patents

Abstract

The present invention provides a negative electrode active material comprising _a Sn _a Cu _b in _a negative electrode active material of a lithium secondary battery. The Sn _a Cu _b may be alloyed with graphite and carbon may be coated. Also, Sn _a Cu _b alloyed with graphite may be coated with carbon. The present invention provides a method for producing the negative electrode active material and provides a lithium secondary battery having the negative electrode active material.

Lithium secondary battery, negative electrode active material, tin

Description

Negative electrode active material. The manufacturing method and a lithium secondary battery having the same {Negative Active Material, Manufacturing Method and And Lithium Secondary Battery Comprising The Same}

1 is a view showing a negative electrode active material manufacturing process according to the present invention,

2 is a block diagram of a lithium secondary battery according to an embodiment of the present invention,

3 is an XRD diffraction analysis of the negative electrode active material according to an embodiment of the present invention,

4A to 4C are SEM images of the negative electrode active material according to one embodiment of the present invention;

5A to 5C are distribution charts related to particle size analysis of an anode active material according to an embodiment of the present invention;

6 is a constant current charge and discharge test results of the lithium secondary battery according to an embodiment of the present invention,

7a and 7b is a result of measuring charge and discharge specific capacity according to the number of cycles of a lithium secondary battery according to an embodiment of the present invention,

8A and 8B are diagrams showing changes in electrode material potential with respect to a change in time of a lithium secondary battery according to one embodiment of the present invention;

** Description of the main symbols in the drawings *

1: lithium secondary battery 2: negative electrode

3: anode 4: separator

5: battery container 6: sealing member

The present invention relates to a negative electrode active material, a method of manufacturing the same, and a lithium secondary battery having the same.

 Recently, the development of the electronic and information communication industry is showing rapid growth through the portable, miniaturized, lightweight, and high-performance electronic devices. Therefore, high-performance lithium secondary batteries are employed as power sources for these portable electronic devices, and demand is increasing rapidly. Secondary batteries used with repeated charging and discharging are essential as power sources for portable electronic devices, electric bicycles, and electric vehicles for information and communication. In particular, since their product performance depends on batteries, which are core components, the demand for high performance batteries is very large. The characteristics required for the battery include various aspects such as charge and discharge characteristics, lifespan, high rate characteristics, and stability at high temperatures, and lithium secondary batteries are most commonly used.

Lithium secondary batteries are the ones that are attracting the most attention because they have high voltage and high energy density. They are liquid type batteries using liquids according to electrolytes, gel polymer batteries using a mixture of liquids and polymers, and solid polymer batteries using pure polymers. It can also be distinguished.

The lithium secondary battery is mainly composed of a positive electrode, a negative electrode, an electrolyte, a separator, a packaging material, and the like. The positive electrode is formed by binding a mixture of a positive electrode active material, a conductive agent, and a binder to a current collector. As the positive electrode active material, lithium transition metal compounds such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ are mainly used. These materials have a high electrochemical reaction potential that proceeds as intercalation / deintercalation of lithium ions into the crystal structure occurs.

Lithium metal, carbon or graphite is mainly used as the negative electrode active material and has a low electrochemical reaction potential as opposed to the positive electrode active material. The electrolyte is mainly composed of LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN ( A salt containing lithium ions such as SO ₂ C ₂ F ₅ ) ₂ is dissolved and used.

As the separator which electrically insulates the positive electrode and the negative electrode and provides a passage of ions, a polyoletin-based polymer such as porous polyethylene is mainly used. As an exterior material that protects the contents of the battery and provides an electrical passage to the outside of the battery, a metal can or a packaging material composed of aluminum and several layers of polymers is mainly used.

Lithium-ion secondary batteries that use liquids as electrolytes present a risk of fire or explosion due to overcharging or other careless use. In order to manufacture such a safety problem and a thinner and free battery, there are many developments of a lithium ion polymer battery using a polymer as an electrolyte. The lithium ion polymer battery is constructed by impregnating a liquid electrolyte in a matrix of polymer materials such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, and the like. Therefore, there is less risk of leakage of the liquid electrolyte, and instead of a metal can, a packaging material composed of aluminum foil and polymer layers can be used, thereby having an advantage of being thin and free of shapes.

BACKGROUND OF THE INVENTION A lithium secondary battery is used as a battery that stores DC power by repetitive operations of charging and discharging and can supply DC to the outside as needed. Such a secondary battery has a configuration in which a positive electrode and a negative electrode are positioned in the same casing with an electrolyte therebetween, and these electrodes are connected to an external load so that current can flow. To this end, the positive electrode and the negative electrode are coated or cast with a so-called active material which functions as a chemical substance for generating and exporting electrical energy to an external circuit. Since the active material may be uniformly applied to the electrode member to improve the performance of the battery, the application of the active material has a great effect on the performance of the battery and active research is being conducted.

Although lithium secondary batteries are the highest performance secondary batteries in existence, they require higher performance batteries in terms of electronic devices. High performance of lithium secondary batteries plays an important role in improving the characteristics of the positive electrode and the negative electrode, and the development of high performance negative electrode material is an important problem. Existing graphite exhibits a specific capacity of 372 mAh / g, and research is being conducted to develop a new high-performance cathode material that can replace graphite. Research on the improvement of such electrode materials has been in the past, is still in progress, and research for improvement will be required in the future.

As a study to replace graphite with negative electrode active material, studies on metal-metal alloys, transition metal oxides, and metalloids have been conducted. As a result, tin-based composites have high specific capacity and can be developed as important negative electrode candidates. We found a high probability.

In addition, tin-based composites, however, have a large volume expansion during charge and discharge, which causes material particles to break, resulting in poor electrical contact between particles, reduced cost, and reduced cycle life. Nevertheless, it is difficult to be practical.

The present invention aims to provide a negative electrode active material of a tin-copper composite, particularly a tin-copper composite having a specific composition ratio, which can overcome the problems of such a tin-based material.

In addition, in order to reduce the deterioration of performance due to volume expansion by alloying two or more metals, a buffer matrix capable of absorbing expansion is introduced, and the alloyed metal has an electrochemical reaction potential of lithium with tin. Another object of the present invention is to provide a negative electrode active material including a buffer matrix, which is a metal complex which is electrochemically inactive unlike electrochemically active tin in an electrochemical reaction section.

In addition, we have developed _a tin (Sn) -copper (Cu) composite Sn _a Cu _b , _a complex of electrochemically active tin and an electrochemically inert metal complex, and alloying the Sn _a Cu _b composite with graphite. Specific amount and charge and discharge through the development of Sn _a Cu _b -graphite composite or carbon coated Sn _a Cu _b by mixing and carbonizing with carbon precursor and carbon formation on Sn _a Cu _b -graphite composite An object of the present invention is to provide an anode active material having improved characteristics and a lithium secondary battery using the same.

The present invention for achieving the above object,

The negative electrode active material of a lithium secondary battery WHEREIN _{: It} provides the negative electrode active material characterized by including Sn _a Cu _b .

In addition, the Sn _a Cu _b provides a negative electrode active material, characterized in that the alloy with graphite (graphite).

In addition, the Sn _a Cu _b is mixed with a carbon precursor and carbonized carbon precursor to provide a negative electrode active material characterized in that the carbon is applied.

In addition, Sn _a Cu _b alloyed with the graphite provides a negative electrode active material, characterized in that the carbon is coated by mixing the carbon precursor and carbonized.

In addition, the mixed weight ratio of the Sn _a Cu _b composite and graphite provides a negative electrode active material, characterized in that 1: 1.

In addition, the mixed weight ratio of Sn _a Cu _b alloyed with the graphite and the carbon precursor provides a negative electrode active material, characterized in that 3: 7.

In addition, the composition ratio a: _b of the Sn _a Cu _b provides a negative electrode active material, characterized in that 5: 6.

The present invention also comprises the steps of mixing the tin (Sn) and copper (Cu) to prepare a Sn _a Cu _b composite; Preparing a graphite composite - the Sn _a Cu _b composites and graphite (graphite) and mixed with _a Sn Cu _b; And preparing a carbon coated Sn _a Cu _b -graphite composite by mixing the Sn _a Cu _b -graphite composite with a carbon precursor and carbonizing the carbon precursor.

In addition, the composition ratio a: _b of the Sn _a Cu _b provides a method for producing a negative electrode active material, characterized in that 5: 5.

In addition, the mixed weight ratio of the Sn _a Cu _b composite and graphite (graphite) provides a method for producing a negative electrode active material, characterized in that 1: 1.

In addition, the mixed weight ratio of the Sn _a Cu _b -graphite composite and the carbon precursor provides a method of producing a negative electrode active material, characterized in that 3: 7.

In addition, the method for producing the Sn _a Cu _b complexes provides a cathode hwalmul query method, characterized in that for producing _a Sn _b Cu composite alloy by mechanically using a ball miller (ball miller).

Further, the Sn _a Cu _b - preparing a graphite composite is the Sn _a Cu _b to mechanically mixed using a ball miller (ball miller) - provides a method for producing the negative electrode, characterized in that for producing a graphite composite active material, do.

In addition, at least one of the above steps provides a method for producing a negative electrode active material, characterized in that performed in an inert gas atmosphere.

In addition, the inert gas provides a method for producing a negative electrode active material, characterized in that the argon (Ar) gas.

In addition, the carbon precursor provides a method for producing a negative electrode active material, characterized in that the polyvinyl chloride (PolyVinylChloride).

In addition, the step of preparing the Sn _a Cu _b -graphite composite provides a method for producing a negative electrode active material, characterized in that the carbonization in the range of 800 ~ 1100 ℃ in an electric furnace.

In addition, at least one of the above steps provides a method for producing a negative electrode active material, characterized in that to control the particle size by grinding the resultant.

The present invention also provides a lithium secondary battery having a negative electrode including a negative electrode active material and a positive electrode and an ion conductor including a positive electrode active material, wherein the negative electrode active material comprises a Sn _a Cu _b -graphite composite coated with carbon A lithium secondary battery is provided.

The carbon-coated Sn _a Cu _b -graphite composite is spherical, and provides a lithium secondary battery having an average particle size of 4 to 9 μm.

In addition, the composition ratio a: b of the Sn _a Cu _b -graphite composite coated with carbon provides a lithium secondary battery, characterized in that 5: 6.

In addition, the negative electrode provides a lithium secondary battery, further comprising carbon black (Super P Black) as a conductive material.

In addition, the negative electrode provides a lithium secondary battery, characterized in that the binder further comprises a carboxymethyl cellulose (CMC) and a copper current collector.

In addition, the ion conductor provides a lithium secondary battery, characterized in that the electrolyte or polymer electrolyte.

In addition, the carbon coated Sn _a Cu _b -graphite composite provides a lithium secondary battery, characterized in that prepared according to the above-described manufacturing method.

Hereinafter, the present invention will be described in more detail.

First, the negative electrode active material according to the present invention will be described.

The negative electrode active material according to the present invention is characterized in that it comprises _a Sn _a Cu _b . In addition, the Sn _a Cu _b may be alloyed with graphite. In addition, the Sn _a Cu _b may be carbonized by mixing the carbon precursor and carbonizing the carbon precursor. In addition, Sn _a Cu _b alloyed with the graphite may be carbonized by mixing the carbon precursor and carbonizing the carbon precursor. In addition, a negative electrode active material used in the technical field of the present invention may be mixed and used in the present invention.

The mixing ratio of tin and copper, i.e., the atomic ratio a: b, is not limited but is in the range of 3: 8 to 8: 3, and it is particularly preferable to prepare a composite with a ratio of 5: 6, that is, Sn ₅ Cu ₆ . In addition, the mixed weight ratio of the Sn _a Cu _b composite and graphite is not limited, but is preferably within the range of 5: 1 to 1: 5, and particularly preferably has a mixed weight ratio of 1: 1. The mixed weight ratio of 1: 1 also includes a mixed weight ratio within a range that can be seen as an error range and an equivalent range.

The carbon precursor is not limited as long as it is a material capable of providing carbon so that carbon can be applied to the composite by carbonization, and is particularly preferably a high molecular material. Vinyl-based resins such as polyvinylidene fluoride (PVDF) and polyvinyl chloride (PVC), and conductive polymers such as polyaniline (PAn), polyacetylene, polypyrrole, and polythiophene are selected. The conductive polymer may be a conductive polymer doped with hydrochloric acid or the like. Carbon precursors are particularly preferred polyvinylchloride (PVC). Although the mixing weight ratio of Sn _a Cu _b alloyed with the graphite and the carbon precursor is not limited, it is preferably within the range of 2: 8 to 5: 5, and particularly preferably 3: 7.

Hereinafter will be described a method of manufacturing a negative electrode active material according to the present invention. Description of the following manufacturing method also includes a description of the negative electrode active material.

In the manufacturing method of the negative electrode active material according to the present invention, a step of preparing a Sn _a Cu _b composite by mixing tin (Sn) and copper (Cu), by mixing the Sn _a Cu _b composite and graphite (graphite) Sn _a Cu _b - preparing a graphite composite, and the Sn _a Cu _b - that comprises a step for producing a graphite complex-graphite composite is mixed with a carbon precursor and by carbonizing the carbon precursor Sn _a Cu _b a carbon coating It features.

At least one of each of the steps is preferably carried out in an inert gas atmosphere, the inert gas is preferably argon (Ar) gas.

In addition, at least one of the above steps is preferably to control the particle size by grinding the obtained result. Grinding method is well known in the art and accordingly.

The negative electrode active material according to the present invention is not limited as long as it is a battery using an intercalation / deintercalation phenomenon of lithium ions, and may be applied as a negative electrode active material.

Preparing the Sn Cu _{b a} composite is a step for preparing _a Cu _b Sn complex mixture of tin and copper. The mixing ratio of tin and copper, i.e., the atomic ratio a: b, is not limited but is in the range of 3: 8 to 8: 3, and it is particularly preferable to prepare a composite with a ratio of 5: 6, that is, Sn ₅ Cu ₆ . The ratio of 5: 6 is an experimental and practical value rather than a mathematically accurate value, and is included in an experimental or manufacturing error range or an equivalent range.

The method of preparing a Sn _a Cu _b composite by mixing tin and copper is not limited, but an alloying method may be used, and mechanical alloying may be particularly performed while rotating a planetary ball miller. The rotational speed is not limited, but rotates at 50 to 200 rpm, and the time is suitable for 20 to 100 hours, but may be modified as necessary. The ball used in the ball miller may use a kind, but various kinds of balls having different diameters may be used. The alloy container preferably uses a sealed container to prevent oxidation of the material due to the incorporation of oxygen and moisture and is carried out under an inert gas, in particular argon gas atmosphere.

After the preparation of the Sn _a Cu _b composite, the particle size may be adjusted by grinding and sieving the particles.

The Sn _a Cu _b - preparing a graphite composite is _a Sn _b Cu by mixing the Sn _a Cu _b composites and graphite (graphite) - a step for producing a graphite composite. Although the mixing weight ratio of the Sn _a Cu _b composite and graphite is not limited, it is preferably within the range of 5: 1 to 1: 5, and particularly preferably having a mixing weight ratio of 1: 1. The mixed weight ratio of 1: 1 also includes a mixed weight ratio within a range that can be seen as an error range and an equivalent range.

The method of preparing the Sn _a Cu _b -graphite composite is not limited, but the method of the alloy is good, in particular, it is preferable to mechanically alloy while rotating the planetary Ball Miller (Ball Miller). The rotational speed is not limited but rotates at 50 to 200 rpm, and the time is suitable for 10 to 100 hours, but may be modified as necessary. The ball used in the ball miller is omitted because it is the same as the description of the step of producing the Sn _a Cu _b composite described above. The alloy container preferably uses a sealed container to prevent oxidation of the material due to the incorporation of oxygen and moisture and is carried out under an inert gas, in particular argon gas atmosphere.

After the preparation of the Sn _a Cu _b -graphite composite, the particle size may be controlled by grinding and sieving the particles.

The preparing of the Sn _a Cu _b -graphite composite is a step of mixing the Sn _a Cu _b -graphite composite with a carbon precursor and carbonizing the carbon precursor to prepare a Sn _a Cu _b -graphite composite coated with carbon. The carbon precursor is not limited as long as it is a material capable of providing carbon so that carbon can be applied to the composite by carbonization, and is particularly preferably a high molecular material. Vinyl-based resins such as polyvinylidene fluoride (PVDF) and polyvinyl chloride (PVC), and conductive polymers such as polyaniline (PAn), polyacetylene, polypyrrole, and polythiophene are selected. The conductive polymer may be a conductive polymer doped with hydrochloric acid or the like.

Carbon precursors are particularly preferred polyvinylchloride (PVC).

Although the mixing weight ratio of the Sn _a Cu _b -graphite composite and the carbon precursor is not limited, it is preferably in the range of 2: 8 to 5: 5, and particularly preferably 3: 7. PVC is good to use powder. The mixed material is placed in a carbonization furnace or an electric furnace and carbonized to produce a carbon coated Sn _a Cu _b -graphite composite. It is preferable to carry out in the atmosphere of an inert gas, and it is especially preferable to use argon gas as an inert gas. In addition, the carbonization time is not limited, but is preferably 1 to 3 hours, the carbonization temperature is preferably carried out at 800 ~ 1100 ℃.

After the carbonization step, the obtained carbon-coated Sn _a Cu _b -graphite composite may be finely ground using a mortar.

1 shows a process for producing graphite alloying and carbon coating material from Sn and Cu powders.

Physical properties of the carbon-coated Sn _a Cu _b -graphite composite according to an embodiment of the present invention prepared by the above process were measured and the measurement results will be described in more detail in Examples and Experimental Examples to be described below.

Hereinafter, a lithium secondary battery having a negative electrode active material according to an embodiment of the present invention will be described in detail.

A lithium secondary battery having a negative electrode active material according to the present invention is a lithium secondary battery having a negative electrode including a negative electrode active material, a positive electrode containing a positive electrode active material and an ion conductor, wherein the negative electrode active material is carbon coated Sn _a Cu _It is characterized by comprising a _b -graphite composite. The carbon-coated Sn _a Cu _b -graphite composite is preferably spherical, characterized in that the average particle size is 4 ~ 9 ㎛. The carbon coated Sn _a Cu _b -graphite composite may be prepared according to the above-described manufacturing method. Although the composition ratio a: b is not limited, the composition ratio mentioned above in a manufacturing method is preferable, and 5: 6 is especially preferable.

Sn _a Cu _b of the coating of the spherical carbon-graphite composite Sn Cu _{b a} a a _b Sn _a Cu alloy composites and graphite-form a carbon coating on graphite-like composite.

Except for the carbon-coated Sn _a Cu _b -graphite composite, the other configurations can be selected and applied without limitation to those known in the art. Preferably, the negative electrode may further include carbon black (Super P Black) as a conductive material, and the negative electrode may further include a carboxymethyl cellulose (CMC) and a copper current collector as a binder. In addition, the ion conductor may be an electrolyte solution or a polymer electrolyte.

The lithium secondary battery according to an embodiment of the present invention may further include a negative electrode active material known in the art, in addition to the above-described negative electrode active material. That is, although not limited, it may further include lithium metal, carbon or graphite. It is also possible to further use activated carbon.

2 shows a lithium secondary battery 1 which is an embodiment of the present invention. The lithium secondary battery 1 includes a negative electrode 2, an electrode 3, a separator 4 disposed between the negative electrode 2 and the positive electrode 3, the negative electrode 2, the positive electrode 3, and the separator 4. ), The ion conductor impregnated in the ()), the battery container (5), and the sealing member (6) for sealing the battery container (5) as a main portion. The shape of the lithium secondary battery illustrated in FIG. 2 may be in the form of a cylinder, in addition to various shapes such as a cylinder, a square, a coin, or a sheet.

The positive electrode 3 is provided with a positive electrode mixture composed of a positive electrode active material, a conductive material and a binder. The positive electrode active material is a compound capable of reversibly intercalating / deintercalating lithium, including LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, MoS, and the like.

As the separator, an olefin porous film such as polyethylene or polypropylene can be used.

The ion conductor may be propylene carbonate (hereinafter referred to as PC), ethylene carbonate (hereinafter referred to as EC), butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyl tetrahydrofuran, γ-butyrolactone, dioxane, and the like. Solan, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetoamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate ( Hereinafter, DMC), ethyl methyl carbonate (hereinafter EMC), diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN () in an aprotic solvent such as or a mixed solvent in which two or more of these solvents are mixed. SO ₂ C ₂ F ₅₎ may be used that prepared by dissolving a mixture of the electrolyte alone or in combination of two or more made of a lithium salt of _2, and so on.

In addition, a polymer solid electrolyte may be used instead of the electrolyte solution. In this case, it is preferable to use a polymer having high ion conductivity with respect to lithium ions, and polyethylene oxide, polypropylene oxide, polyethyleneimine and the like can be used. The solvent and the solute may be added to the polymer of to form a gel.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

<Example>

(a) Sn ₅ Cu ₆ Preparation of the complex

Tin and copper powder (99.9% pure, Sigma Aldrich) were prepared by mechanically alloying at 120 rpm for 60 hours in a Planetary Ball Miller at an atomic ratio of 5: 6. The balls used were two different sizes, 5 mm in diameter and 10 mm in diameter, and used in a weight ratio of 2: 4. As the vessel, a sealed vessel was used to prevent oxidation of the material by incorporation of oxygen and moisture, and argon gas was substituted for about 30 minutes. After the production was ground (grinding) and sieving (sieving) to adjust the particle size of the material.

(b) Preparation of Sn ₅ Cu ₆ -graphite composite

The prepared Sn ₅ Cu ₆ composite was prepared by mechanically alloying the graphite (DAG-68s, SODIFF) in a weight ratio of 1: 1 with a planetary Ball Miller at 160 rpm for 18 hours. After the prepared alloy material was prepared (grinding) and sieving (sieving) to control the particle size of the material.

(c) Preparation of carbon coated Sn ₅ Cu ₆ or carbon coated Sn ₅ Cu ₆ -graphite composite

Carbon coating on the prepared Sn ₅ Cu ₆ or Sn ₅ Cu ₆ -graphite composite was prepared using PVC (PolyVinylChloride) powder as a carbon precursor. The weight ratio of Sn ₅ Cu ₆ or Sn ₅ Cu ₆ -graphite composite to PVC was 3: 7. The mixed material was prepared by carbonization in an electric furnace at 800-1000 ° C. under an argon stream. The temperature increase rate of an electric furnace was 10 degreeC / minute.

Experimental Example 1 Material Properties Analysis of Carbon Coated Sn ₅ Cu ₆ -Graphite Composite

The crystal structure of the material was measured by Philips 1830's X-ray diffractometer, Ni-filtered Cu Kα radiation (λ = 1.5406 Å), scanning rate of 0.04 ° / sec. The range was 10 ° to 120 °. Surface shape of the material was used SEM (Scanning Electron Microscope, Jeol S-300 H). Particle size analysis was performed using a Malvern easy particle size analyzer.

The experimental results are as follows.

Figure 3 is a graph showing the PXRD tendency of Sn ₅ Cu ₆ composite, Sn ₅ Cu ₆ -graphite composite, carbon coating Sn ₅ Cu ₆ -graphite composite. Of Figure 3 (a) it can be confirmed that the Cu ₆ Sn ₅ composite is obtained as a value of 2θ as a Cu ₆ Sn ₅ composites prepared 29 ° and 42 °. 3 (b) shows that the XRD pattern for the Sn ₅ Cu ₆ -graphite composite is low in crystallinity as the peak is not intensive. 3 (c) is an XRD pattern for the carbon-coated Sn ₅ Cu ₆ -graphite composite, which shows that the crystallinity of the alloy material having low crystallinity during the heat treatment is improved, and thus the peaks are clearly distinguishable. Can be.

Carbonization of carbon precursors such as PVC proceeds at 500 ° C. or higher, and when the heat treatment is performed at 1000 ° C. or higher, the crystal size (La) of the carbon material increases and the H / C element ratio decreases. During this process, the position of the d002 peak of the XRD, which represents the interplanar spacing, does not change significantly, indicating that the amorphous carbon material does not improve to the crystalline form. For this reason, the peak corresponding to d002 of graphite does not appear in the produced material. Therefore, the carbon material coated on the Sn ₅ Cu ₆ -graphite composite surface has an amorphous structure.

The well known d002 peak of graphite in the 26 ° region of Figure 3 (b) can be seen. As can be seen, unnecessary XRD peaks do not appear in the material, indicating that a high purity composite was obtained.

Peaks of the XRD pattern measurement in Fig. 3 (c) copper (JCPDS 04-0836) and tin (JCPDS 04-0673), Cu ₆ Sn _{5 .25} (JCPDS 47-1575) and JCPDS standard value with respect to the graphite It is shown by matching.

4A to 4C are SEM photographs of Sn ₅ Cu ₆ composites, Sn ₅ Cu ₆ -graphite composites, and carbon coated Sn ₅ Cu ₆ -graphite composites, respectively. There was no big difference in the apparent shape, and the common point was that the material particles were not agglomerated but exist in spherical shape. The average particle size was 4-9 μm.

5A to 5C are graphs showing particle size analysis results for Sn ₅ Cu ₆ composite, Sn ₅ Cu ₆ -graphite composite, and carbon coated Sn ₅ Cu ₆ -graphite composite, respectively. As shown, the average particle size was 4-9 μm, and the particle size increased with the application of graphite and carbon to the material. The average particle size of the Sn ₅ Cu ₆ composite was 4.8 μm, but the average particle size of the Sn ₅ Cu ₆ -graphite composite, which is a composite material with graphite, increased to 5.6 μm. The carbon coated Sn ₅ Cu ₆ -graphite composite had an average particle size of 8.9 μm. This increase is a result of doubling the Sn ₅ Cu ₆ composite. This increase is the result of the deposition of carbon on the surface of the Sn ₅ Cu ₆ -graphite composite, which sufficiently covers the material surface.

Experimental Example 2

Preparation of a battery for experimenting the electrochemical characteristics of the carbon-coated Sn ₅ Cu ₆ -graphite composite according to the present invention to the lithium secondary battery negative electrode active material is as follows. A 2025-type coin cell was constructed and evaluated. The test electrode uses 10% by weight of polyvinylidene fluoride (PVDF) as a binder relative to 90% by weight of the carbon-coated Sn ₅ Cu ₆ -graphite composite, which is the electrode active material described above, and N-methyl-2- for dispersing the material. Pyrrolidone (NMP) was used as the dispersion solvent. The prepared slurry was applied to a thin copper film, dried and pressed to prepare an electrode. A 2025 disc battery was constructed using the prepared electrode, lithium metal foil, separator, and electrolyte solution. As the electrolyte solution, 1.0M LiPF 6 EC / DMC / EMC / PC 4/3/3/1 (Cheil Industries Ltd, South Korea) was used.

Fig. 6 shows the results of the constant current charge / discharge test of the (Sn ₅ Cu ₆ -graphite composite) ┃Li battery and the (carbon coated Sn ₅ Cu ₆ -graphite composite) ┃Li battery. (Sn ₅ Cu ₆ -graphite composite) ┃The primary charging specific capacity of Li battery was about 564 mAh / g, and (Carbon-coated Sn ₅ Cu ₆ -graphite composite) 충전 Li battery was about 303 mAh / g is shown. (Carbon coated Sn ₅ Cu ₆ -graphite composite) The low specific capacity of Li batteries appears to be due to the fact that carbon materials with low lithium storage capacity used twice as much weight as Sn ₅ Cu ₆ materials.

7A and 7B show charge and discharge specific capacities according to the number of cycles for the (Sn ₅ Cu ₆ -graphite composite) ┃Li battery and the (carbon coated Sn ₅ Cu ₆ -graphite composite) ┃Li battery, respectively. As shown, when the carbon material is used a lot, the specific capacity is low but the charge and discharge cycle characteristics are better. The application of the Sn ₅ Cu ₆ -graphite composite by the carbon material increases the buffer capacity to absorb the expansion of the electrode material, resulting in improved cycle characteristics.

By controlling the content of the carbon material, it is possible to improve the specific capacity of the electrode material with good cycle characteristics. As charging and discharging progressed, the specific capacity decreased, which is believed to be the result of the electrode material being detached from the electron conduction path between the genuine and the material due to the volume expansion of the alloy material.

8A and 8B show the change in electrode material potential over time. The Sn ₅ Cu ₆ -graphite composite exhibited dislocation planar regions due to the formation of Li ₇ Sn ₃ at 400 mV, while the carbon coated Sn ₅ Cu ₆ -graphite composite did not exhibit such dislocation planar regions.

Application of the carbon material to the Sn ₅ Cu ₆ -graphite composite can reduce the volume expansion of the alloying material while facilitating the electronic conductivity, and can be used as a high-capacity long-life electrode material by optimizing the carbon material coating content. Sn ₅ Cu ₆ -graphite composites showed a specific capacity of about 564 mAh / g, it can be seen that the volume expansion can be reduced by the introduction of carbon.

The negative electrode active material and the lithium secondary battery according to the present invention, as a result of analyzing the physical and electrochemical properties, the charge and discharge characteristics were improved, exhibited better charge and discharge cycle characteristics, has an excellent specific capacity and shows excellent performance and industrially useful Do.

Claims (25)

delete In the negative electrode active material of a lithium secondary battery, Sn _a Cu _b (a: b ratio is in the range of 3: 8 ~ 8: 3), and the Sn _a Cu _b is an anode active material, characterized in that alloyed with graphite (graphite). In the negative electrode active material of a lithium secondary battery, Sn _a Cu _b (the ratio of a: b is in the range of 3: 8 ~ 8: 3), and the Sn _a Cu _b is characterized in that the carbon is coated by carbonizing the carbon precursor after mixing with the carbon precursor A negative electrode active material. The method of claim 2, Sn _a Cu _b alloyed with the graphite is mixed with a carbon precursor and carbonized carbon precursor is coated with a negative electrode active material. The negative active material of claim 2, wherein the mixed weight ratio of the Sn _a Cu _b composite to graphite is 1: 1. The negative active material of claim 4, wherein a mixed weight ratio of Sn _a Cu _b alloyed with graphite and _a carbon precursor is 3: 7. Claim 2 according to sixth to any one of items, wherein the composition ratio of _a Sn Cu _b a: b is 5: 6, in the negative electrode active material according to claim. Mixing tin (Sn) and copper (Cu) to produce a Sn _a Cu _b composite (a: b ratio is in the range of 3: 8 to 8: 3); Preparing a graphite composite - the Sn _a Cu _b composites and graphite (graphite) and mixed with _a Sn Cu _b; And And mixing the Sn _a Cu _b -graphite composite with a carbon precursor and carbonizing the carbon precursor to prepare a Sn _a Cu _b -graphite composite coated with carbon. The method of claim 8, wherein the composition ratio of the Sn _a Cu _b a: b is 5: The method of producing a cathode active material according to claim 6 in. The method of claim 8, wherein the mixing weight ratio of the Sn _a Cu _b composite and graphite is 1: 1. The method of claim 8, wherein the mixing weight ratio of the Sn _a Cu _b -graphite composite and the carbon precursor is 3: 7. 9. The method of claim 8, wherein the manufacturing of the Sn _a Cu _b composite comprises mechanically alloying a ball miller to produce a Sn _a Cu _b composite. The method of claim 8, wherein the step of preparing the Sn _a Cu _b -graphite composite is mechanically mixed using a ball miller (ball miller) to produce the Sn _a Cu _b -graphite composite of the negative electrode active material Manufacturing method. The method of claim 8, wherein at least one of the steps is performed in an inert gas atmosphere. The method of claim 8, wherein the inert gas is argon (Ar) gas. The method of claim 8, wherein the carbon precursor is polyvinyl chloride (PolyVinylChloride). The method of claim 8, wherein the preparing the Sn _a Cu _b -graphite composite is carbonized in an electric furnace in the range of 800 to 1100 ° C. 10. The method of claim 8, wherein at least one of each of the steps comprises grinding the resultant to adjust the particle size. In a lithium secondary battery provided with a negative electrode containing a negative electrode active material and a positive electrode containing a positive electrode active material and an ion conductor, The negative electrode active material is a lithium secondary battery, characterized in that made of carbon-coated Sn _a Cu _b -graphite composite (a: b ratio is in the range of 3: 8 ~ 8: 3). 20. The lithium secondary battery of claim 19, wherein the carbonaceous Sn _a Cu _b -graphite composite is spherical and has an average particle size of 4 to 9 µm. The lithium secondary battery according to claim 19, wherein the composition ratio a: b of the Sn _a Cu _b -graphite composite coated with carbon is 5: 6. The lithium secondary battery of claim 19, wherein the negative electrode further comprises carbon black (Super P Black) as a conductive material. The lithium secondary battery according to claim 19, wherein the negative electrode further comprises a carboxymethyl cellulose (CMC) and a copper current collector as a binder. 20. The lithium secondary battery of claim 19, wherein the ion conductor is an electrolyte or a polymer electrolyte. The lithium secondary battery according to claim 19, wherein the carbon-coated Sn _a Cu _b -graphite composite is manufactured according to any one of claims 8 to 18.

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