KR20100059023A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: A lithium secondary battery is provided to improve the discharge rate capacity under the high voltage charge over 4.2V, and to prevent the deterioration during the progress of a rechargeable cycle. CONSTITUTION: A lithium secondary battery comprises the following: a cathode including a positive electrode active material, a conductive material, and a binder in a weight ratio of 90~98:1~5:1~5; an anode including a negative electrode active material with a Sn_aCu_b- graphite composite; and an ionic conductor. The positive electrode active material is selected from the group consisting LiMn_2O_4, LiCoO_2, LiNiO_2, LiFeO_2, V_2O_5, TiS, and MoS. The conductive material is carbon black. The binder is polyvinylidene fluoride.

Description

High Voltage Lithium Secondary Battery

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage lithium secondary battery, and in particular, to develop a positive electrode and a negative electrode suitable for a high voltage environment, and to a high voltage lithium secondary battery having excellent specific capacity even when charged at a voltage higher than 4.2V and having excellent charge and discharge characteristics.

Recently, the development of the electronic and information communication industry is showing rapid growth through the portable, miniaturized, lightweight, and high-performance electronic devices. High-performance lithium secondary batteries are employed as power sources for such 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 have the highest voltage and high energy density. They are the ones that are attracting the most attention. They are liquid-type batteries that use liquids according to electrolytes, gel-type polymer batteries that mix liquids and polymers, and solid polymer batteries that use purely polymers. It can also be distinguished.

In general, a 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 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 polymer layers is mainly used.

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.

On the other hand, in recent years, the battery system has been undergoing a high voltage due to the high capacity of the battery. In the case of the conventional lithium secondary battery was charged at a charge voltage of 3.0V to 4.2V, but the research to seek a higher energy capacity by applying a higher charge voltage (4.2 ~ 4.5V).

However, in the case of using a negative electrode, a positive electrode, and a non-aqueous carbonate-based solvent which is commonly used as an electrolyte, when the battery is charged at a voltage higher than the normal charge potential of 4.2 V, the oxidizing power increases, and as the charge and discharge cycle proceeds, the negative electrode and the positive electrode deteriorate. As the decomposition reaction of the electrolyte proceeds, there is a problem in that the life characteristics rapidly drop.

In recent years, research has been carried out for high voltage application of LiCoO ₂ materials. For example, according to Electrochemistry Communications (Vol. 9, 2007, pp. 149-154), Co ₃ (PO ₄ ) ₂ materials are active as coatings on LiCoO ₂ surfaces. Type LiCoPO ₄ thin film can be formed to improve not only thermal characteristics but also battery operating voltage characteristics.

The present invention is to solve the above problems, by developing a positive electrode and a negative electrode suitable for a high voltage environment, even if the charge at a voltage higher than 4.2V, the cost is excellent, there is no deterioration problem even if the charge and discharge cycle proceeds, the long life It is an object to provide a high voltage lithium secondary battery.

In order to achieve the above object, the present invention, in the lithium secondary battery, a positive electrode active material, a conductive material, and a binder comprising a positive electrode is included in the weight portion within the range of 90 ~ 98: 1 ~ 5: 1-5; _A negative electrode having a negative electrode active material including a Sn _a Cu _b -graphite composite (a: b ratio is in the range of 3: 8 to 8: 3); And an ion conductor; and a high voltage lithium secondary battery characterized by being charged at a charging voltage within a range of 4.2V to 4.5V.

In addition, the cathode active material is preferably at least one selected from LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, MoS.

In addition, it is preferable that TiO 2 is stably coated on the surface of the cathode active material to improve voltage and thermal characteristics.

In addition, the conductive material is carbon black (Super P Black), the binder is preferably polyvinylidene fluoride (PVDF).

The ion conductor may be an electrolyte or a polymer electrolyte, and the ion conductor may be a non-aqueous electrolyte in which LiPF ₆ is dissolved. The non-aqueous electrolyte may include at least one of EC, PC, DEC, and EMC. desirable.

Further, the Sn _a Cu _b - graphite composite is preferably a carbon coating, wherein the carbon is coated Sn _a Cu _b - graphite composite is a sphere, the average particle size is preferably 4 ~ 9㎛.

Further, the Sn _a Cu _b - the composition ratio of the graphite composite a: b is 5: preferably a 6, the Sn _a Cu _b - mixing weight ratio of the Sn _a Cu _b and graphite from a graphite composite is from 1: preferably 1 Do.

In addition, the weight ratio of the positive electrode active material: conductive material: binder is preferably 92: 4: 4.

As a result of analyzing the physical and electrochemical characteristics of the high voltage lithium secondary battery according to the present invention, the discharge cost is excellent even under a high voltage charge higher than 4.2V, and there is no deterioration problem even when the charge and discharge cycle proceeds. Providing a secondary battery has an industrially useful effect.

The high-voltage lithium secondary battery according to the present invention includes a positive electrode active material, a conductive material, and a binder in which the positive electrode active material, the conductive material, and the binder are included in parts by weight in the range of 90 to 98: 1 to 5: 1, and a Sn _a Cu _b -graphite composite (a: The ratio b is comprised of a negative electrode and an ion conductor having a negative electrode active material, including 3: 8 to 8: 3), and is charged at a charging voltage within the range of 4.2V to 4.5V.

1 is a schematic view showing a high voltage lithium secondary battery 1 according to one embodiment of the present invention. The high voltage lithium secondary battery 1 is impregnated in the negative electrode 2, the 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. It can be comprised with the ion conductor, the battery container 5, and the sealing member 6 which encloses the battery container 5 as a main part. The shape of the lithium secondary battery illustrated in FIG. 1 may be in a cylindrical shape, but in addition, various shapes such as a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like.

The positive electrode 3 is preferably provided with a positive electrode mixture consisting of a positive electrode active material, a conductive material and a binder. As the positive electrode active material, a compound capable of applying a high voltage within a range of 4.2 V to 4.5 V and capable of reversibly intercalating / deintercalating lithium (LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, MoS, etc.) can be used without limitation, and a preferred example is that TiO ₂ is stably coated on the surface of the positive electrode active material, more preferably LiCoO ₂ stably applied to the surface of TiO ₂ . The positive electrode mixture can be bonded to a current collector such as copper.

As a weight ratio of the positive electrode active material, the conductive material, and the binder to be preferably applied to a high voltage, the positive electrode active material, the conductive material, and the binder are preferably in the range of 90 to 98: 1 to 5: 1 to 5. When the positive electrode active material is contained in the above range, problems may occur in cycle characteristics, and when the positive electrode active material is contained in the range below the discharge capacity, the discharge capacity is reduced, which is not preferable. Especially preferably, the positive electrode active material, the conductive material, and the binder have a weight ratio of 95.65: 1.5: 2.85, which is excellent in cycle characteristics and discharge capacity.

The negative electrode 2 includes a negative electrode active material including _a Sn _a Cu _b -graphite composite. In addition, the Sn _a Cu _b -graphite composite may be coated with carbon by mixing with a carbon precursor and carbonizing the carbon precursor. In addition, it may further comprise a negative electrode active material known in the art. That is, although not limited, it may further include lithium metal, carbon or graphite. Activated carbon can also be used.

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. The carbon-coated Sn _a Cu _b -graphite composite is preferably spherical, the average particle size of 4 ~ 9㎛ is preferred.

A method for producing the cathode active material, tin (Sn) and copper to prepare a Sn _a Cu _b complexes by mixing (Cu), the Sn _a Cu _b composites and graphite (graphite) and mixed with Sn _a Cu _b a - Graphite After the composite is prepared, the Sn _a Cu _b -graphite composite is mixed with a carbon precursor and carbonized to form a carbon coated Sn _a Cu _b -graphite composite.

At least one of each manufacturing process is preferably performed in an inert gas atmosphere, the inert gas is preferably argon (Ar) gas. In addition, one or more of the above manufacturing process is preferably to control the particle size by grinding the resulting product. 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.

The method of preparing the Sn _a Cu _b composite is not limited, but an alloying method may be used. In particular, the Sn _a Cu _b composite may be mechanically alloyed 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 preferably 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 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 preferably 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 carbon-coated Sn _a Cu _b -graphite composite is prepared by mixing the Sn _a Cu _b -graphite composite with a carbon precursor and carbonizing the carbon precursor to produce a carbon coated Sn _a Cu _b -graphite composite. Done. 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. Polyvinyl chloride (PVC) is preferable as the carbon precursor.

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.

2 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.

The separator 4 is not limited, but an olefin porous film such as polyethylene or polypropylene may be used.

The ion conductor is propylene carbonate (hereinafter referred to as PC), ethylene carbonate (hereinafter referred to as EC), butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyl tetrahydrofuran, -butyrolactone and dioxolane as electrolytes. , 4-methyldioxolane, N, N-dimethylformamide, dimethylacetoamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate (hereinafter , DMC), ethylmethyl carbonate (hereinafter referred to as EMC), diethyl carbonate, methylpropyl carbonate, methylisopropyl carbonate, ethylbutyl carbonate, dipropyl carbonate, diisopropylcarbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, and the like. in a non-aqueous electrolytic solution selected at least _{one, LiCF 3 SO 3, Li (} CF 3 SO 2) 2, LiPF 6, LiBF 4, LiClO 4, LiN (SO 2 C 2 F 5) _2, and lithium salts of Added may be used as an electrolyte alone or in combination of two or more. Suitable electrolytes for high voltages include EC, PC, DEC, and EMC in which LiPF6 is dissolved.

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. A gel obtained by adding the solvent and the solute to this polymer can also be used.

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 1>

(a) Preparation of Sn ₅ Cu ₆ Composite

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 ground (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 composites

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 / minute.

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

The crystal structure of the material was measured using Philips 1830's X-ray diffractometer, Ni-filtered Cu Kα radiation (λ = 1.5406 하고), 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 the Sn ₅ Cu ₆ composite, Sn ₅ Cu ₆ -graphite composites, carbon coating Sn ₅ Cu ₆ -graphite composites. Of Figure 3 (a) it can be confirmed that the Cu ₆ Sn ₅ composites are prepared as a 2θ value of as a Cu ₆ Sn ₅ Composition Preparation 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 process is improved to show distinct peaks. 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 applied on the surface of the Sn ₅ Cu ₆ -graphite composite 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.

The peaks of the XRD pattern measured in (c) of FIG. 3 are matched with standard JCPDS values for copper (JCPDS 04-0836) and tin (JCPDS 04-0673), Sn ₅ Cu _6.25 (JCPDS 47-1575) and graphite. It is shown.

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 each material particle was present in spherical shape rather than agglomerated. The average particle size was 4-9 µm.

5A to 5C are graphs showing particle size analysis results for Sn ₅ Cu ₆ composites, Sn ₅ Cu ₆ -graphite composites, and carbon coated Sn ₅ Cu ₆ -graphite composites, 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 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.

<Example 2>

Fabrication of a battery for experimenting with the electrochemical characteristics of a high voltage lithium secondary battery according to the present invention is as follows. A 450 mAh pouch battery was constructed and evaluated. The negative electrode uses 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder based on 90 parts by weight of the carbon-coated Sn ₅ Cu ₆ -graphite composite, which is the electrode active material described above, and N-methyl-2-pyrroli for dispersion of the material. A slurry prepared by using Don (NMP) as a dispersion solvent was applied to a thin copper film, dried and pressed. The positive electrode was prepared by adding LiCoO ₂ as a positive electrode active material, carbon black (super P) as a conductive material, and PVDF as a binder to N-methylpyrrolidone (NMP) at a weight ratio of 95.65: 1.5: 2.85. It was coated on aluminum foil, dried and rolled with a roll press to prepare a positive electrode having a mixture density of 3.6 to 3.2 g / cm ³ . Electrodes and separators prepared and 1.2 M LiPF ₆ / EC (30) + PC (5) + DMC (20) + EMC (45) + VC (1) + PPACA (1.6) + LiBOB (0.5) A pouch battery of 450 mAh class was constructed using the same.

FIG. 6 is a graph showing the results of evaluating the charge upper limit voltages of 4.25 V, 4.35 V, 4.45 V, and 4.55 V under the condition of a charging current of 0.2 C (C = 450 mA) for the lithium secondary battery manufactured in Example 2. . As shown in the drawing, a high voltage lithium secondary battery using LiCoO ₂ stably coated with TiO ₂ was developed.

Table 1 summarizes the manufacturing conditions and characteristics of the batteries corresponding to Examples 2 to 10.

TABLE 1

Example Type of anode Electrode density
(g / cc) Cathode / anode
Capacity ratio Mars Specific Capacity
(mAh / cell, 4.2V) Initial charge and discharge capacity (mAh / cell) and efficiency (%) 4.25V 4.35V 4.45V 4.55 V charge Discharge efficiency charge Discharge efficiency charge Discharge efficiency charge Discharge Example 2 LiCoO2
D50 = 17.65 um
3.6 1.12 520 532.9 535.8 100.6 560.5 562.8 100.4 606.4 610.1 100.6 529.1 539.0 Example 3 TiO2 thin film coating LiCoO2 (TiO2 0.16 wt%, D50 = 18.10 um) 3.6 1.07 413 429.2 430.8 100.4 472.8 466.9 98.8 503.7 437.8 86.9 536.0 399.5 Example 4 1.12 397 387.0 386.8 99.9 454.3 433.2 95.3 490.5 397.8 81.1 525.4 415.2 Example 5 1.17 375 416.9 417.4 100.1 511.7 499.5 97.6 470.0 369.1 78.5 503.4 394.2 Example 6 TiO2 thick film coating LiCoO2 (TiO2, 0.8 wt%,
50 = 18.83 um) 3.6 1.07 414 436.4 436.8 100.1 470.2 451.0 95.9 492.8 374.3 80.0 526.7 447.7 Example 7 3.39 1.12 397 412.7 411.8 99.8 449.7 429.3 95.5 471.7 390.6 82.8 507.4 384.4 Example 8 1.17 377 426.4 423.2 99.3 463.4 386.2 83.4 509.9 362.4 71.1 395.3 397.5 Example 9 3.21 3.39 420 426.7 428.7 100.5 478.2 474.2 99.2 501.1 443.8 88.6 544.9 432.7 Example 10 3.21 418 433.3 434.3 100.2 465.7 466.2 100.1 504.4 462.9 91.8 536.2 420.7

The battery manufactured according to each example was evaluated at different charge upper limit voltages of 4.25 V, 4.35 V, 4.45 V and 4.55 V to evaluate the characteristics of the battery and the results are shown separately.

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

2 is a view showing a negative electrode active material manufacturing process according to 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 charge and discharge characteristics test results of the lithium secondary battery according to an 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

Claims (13)

In a lithium secondary battery, A positive electrode comprising a positive electrode active material, a conductive material, and a binder in an amount of 90 to 98 parts by weight in a range of 1 to 5: 1 to 5; _A negative electrode having a negative electrode active material including a Sn _a Cu _b -graphite composite (a: b ratio is in the range of 3: 8 to 8: 3); And an ion conductor; wherein the high voltage lithium secondary battery is charged at a charging voltage within a range of 4.2V to 4.5V. The high voltage lithium secondary battery of claim 1, wherein the cathode active material is at least one selected from LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, and MoS. The high voltage lithium secondary battery according to claim 2, wherein TiO ₂ is coated on the surface of the positive electrode active material. The high voltage lithium secondary battery of claim 1, wherein the conductive material is carbon black (Super P Black). The high voltage lithium secondary battery of claim 1, wherein the binder is polyvinylidene fluoride (PVDF). The high voltage lithium secondary battery according to claim 1, wherein the ion conductor is an electrolyte solution or a polymer electrolyte. The high voltage lithium secondary battery according to claim 1, wherein the ion conductor is a non-aqueous electrolyte in which LiPF ₆ is dissolved. The high voltage lithium secondary battery of claim 7, wherein the non-aqueous electrolyte comprises at least one of EC, PC, DEC, and EMC. The high voltage lithium secondary battery according to claim 1, wherein the Sn _a Cu _b -graphite composite is coated with carbon. 10. The high voltage lithium secondary battery of claim 9, wherein the carbonaceous Sn _a Cu _b -graphite composite is spherical and has an average particle size of 4 to 9 µm. The high voltage lithium secondary battery according to claim 1, wherein the composition ratio a: b of the Sn _a Cu _b -graphite composite is 5: 6. 2. The method of claim 1, wherein _a Sn Cu _b - mixing weight ratio of the Sn _a Cu _b and graphite from a graphite composite is from 1: high-voltage lithium secondary battery according to claim 1. The high voltage lithium secondary battery according to claim 1, wherein the weight ratio of the positive electrode active material: the conductive material: the binder is 95.65: 1.5: 2.85.

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