JP2010257982A - Anode active material for lithium secondary battery, and lithium secondary battery including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode active material for a lithium secondary battery and a lithium secondary battery including the same, improving charge/discharge efficiency and cycle characteristics. <P>SOLUTION: The invention relates to the anode active material for a lithium secondary battery and the lithium secondary battery including the same. The anode active material for a lithium secondary battery including carbon anode active material further includes Li<SB>2</SB>SiF<SB>6</SB>. The anode active material for a lithium secondary battery containing Li<SB>2</SB>SiF<SB>6</SB>is used in manufacturing the lithium secondary battery to exhibit the improved charge/discharge efficiency and cycle characteristics. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an anode active material for a lithium secondary battery and a lithium secondary battery including the anode active material. More specifically, the present invention relates to a lithium secondary battery capable of improving the charge / discharge efficiency and cycle characteristics of the battery. The present invention relates to an anode active material and a lithium secondary battery including the anode active material.

  Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook PCs, and electric vehicles, the demand for secondary batteries that are small and light but have a relatively high capacity is rapidly increasing. . In particular, lithium secondary batteries are light and have a high energy density, and are attracting attention as driving power sources for portable devices. As a result, research and development efforts for improving the performance of lithium secondary batteries have been actively conducted.

  In the lithium secondary battery, an organic electrolyte or a polymer electrolyte is filled between an anode and a cathode made of an active material capable of intercalation and deintercalation of lithium ions. And electric energy is produced by oxidation and reduction reaction when inserted / desorbed at the anode.

As the cathode active material of the lithium secondary battery, transition metal compounds such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganese oxide (LiMnO ₂ ) are mainly used.

  The anode active material is generally obtained by carbonizing a crystalline carbon material such as natural graphite or artificial graphite having a large degree of softening, or a hydrocarbon or polymer at a low temperature of 1000 to 1500 ° C. In addition, a low-crystalline carbon material having a pseudo-graphite structure or a turbostratic structure is used.

  However, when such a carbon-based anode active material such as graphite is used, the components of the electrolytic solution are decomposed on the surface of the graphite and a LiF film is formed on the surface of the graphite. It causes the efficiency to decrease. Further, since a thick film is formed on the surface, the impedance is increased and the c-rate characteristic is also decreased.

  In order to solve such a problem, Patent Document 1 (Korea Patent Publication No. 2006-0074808) discloses an anode active material containing silicon. That is, Patent Document 1 discloses an anode active material containing silicon in an amount of about 30% by mass to 70% by mass. When the silicon content is high as described above, an anode reaction to silicon itself is performed. Since it is carried out, there is a disadvantage that the charge / discharge efficiency decreases sharply compared with the carbon material.

  Accordingly, there is a continuing need for new anode active materials that can overcome the disadvantages of carbon materials.

Korean Patent Publication No. 2006-0074808

  Therefore, an object of the present invention is to provide a new anode active material capable of suppressing the generation of LiF and exhibiting excellent battery performance.

  Another object of the present invention is to provide an anode for a lithium secondary battery manufactured using the anode active material and a lithium secondary battery including the anode.

In order to solve the above-described problems, the anode active material for a lithium secondary battery including the carbon-based anode active material according to the present invention further includes Li ₂ SiF ₆ .

In the anode active material of the present invention, Li ₂ SiF ₆ may be included in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the carbon-based anode active material, but is not limited thereto.

  Further, in the anode active material of the present invention, the carbon-based anode active material described above can be formed by coating a carbide layer on a part or all of the edge of the core carbon material, and the core carbon material is a highly crystalline material. Natural spherical graphite, oval, scale, whisker, or crushed natural graphite, artificial graphite, mesocarbon microbeads, mesophase pitch fines, isotropic pitch fines, resin charcoal, and pseudo-graphite structures or It may be any one selected from the group consisting of amorphous carbon fine powder having a turbulent structure or a mixture thereof, but is not limited thereto.

  The carbide layer may be a low crystalline carbide layer formed by coating the core carbon material with pitch, tar or a mixture thereof derived from coal or petroleum and then carbonizing and firing.

  Also, optionally, in the anode active material of the present invention, the carbon-based anode active material may be artificial graphite.

The method for producing an anode active material according to the present invention includes, for example, a step of mixing a carbon-based anode active material and Li ₂ SiF ₆ and firing in an inert atmosphere.

  The anode active material of the present invention described above can be used for an anode for a lithium secondary battery and a lithium secondary battery.

The anode active material for a lithium secondary battery according to the present invention is formed by mixing a carbon-based anode active material and Li ₂ SiF ₆ , thereby stabilizing the surface and structure of the anode active material and having an irreversible capacity. It is possible to suppress the decomposition reaction of the organic electrolyte, which is the main cause, and to reduce the influence of the acid generated by oxidation of the electrolyte during charge / discharge, thereby improving the efficiency and cycle characteristics of the battery. .

  The present invention will be described in detail below. Terms and words used in this specification and claims should not be construed to be limited to ordinary or lexicographic meanings, and the inventor should use the terminology concept to best explain his invention. In accordance with the principle that can be appropriately defined, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention.

As described above, the anode active material of the present invention is characterized in that Li ₂ SiF ₆ is further included in the conventional carbon-based anode active material. A typical carbon-based anode active material is natural graphite having an excellent initial capacity. However, since natural graphite has a disadvantage that efficiency and cycle capacity are reduced, in order to overcome this, natural graphite is sometimes coated with low crystalline carbon.

However, since there is a limit to overcome the problems of the carbon material itself, the anode active material of the present invention further contains Li ₂ SiF ₆ . The Li ₂ SiF ₆ contained in the anode active material of the present invention facilitates the movement of lithium ions when charging and discharging are performed, and the Li _x SiF _y form is formed before LiF is formed by the decomposition reaction of the electrolytic solution. Maintaining and suppressing an increase in cell resistance due to the formation of LiF.

According to the present invention, the content of Li ₂ SiF ₆ contained in the anode active material can be variously selected according to the specific type of the carbon material anode active material used together and the use of the lithium secondary battery. For example, 0.1 to 10 parts by weight can be mixed with 100 parts by weight of the carbon-based anode active material, but the present invention is not limited thereto. If the content of Li ₂ SiF ₆ is less than 0.1 parts by weight, the performance improvement due to the use of Li ₂ SiF ₆ is slight, and if it exceeds 10 parts by weight, an increase in resistance may be induced during battery production.

In the anode active material of the present invention, the carbon material anode active material that can be used together with Li ₂ SiF ₆ is not particularly limited as long as it is a carbon material usually used as an anode active material in this field. Examples of the carbon material anode active material include, but are not limited to, a core material carbon material in which a carbide layer is coated on part or all of an edge; or artificial graphite.

  In the carbon material anode active material according to the present invention, the core carbon material may be spherical highly crystalline natural graphite. Optionally, the core carbon material has an elliptical shape, crushed shape, scale shape, whisker shape, etc., natural graphite, mesocarbon microbeads, mesophase pitch fine powder, isotropic pitch fine powder, resin charcoal, and pseudographite structure or It may be any one selected from the group consisting of amorphous carbon fine powder having a turbulent structure or a mixture thereof.

  Preferably, the carbide layer is a low crystalline carbide layer formed by coating the core carbon material with pitch, tar, or a mixture thereof derived from coal or petroleum, and then carbonizing and firing. Here, low crystallinity means that the crystallinity of the carbide layer is lower than that of the core carbon material. If the carbide layer has lower crystallinity than the core carbon material, it is possible to effectively prevent the decomposition reaction of the electrolytic solution from being induced at the edge portion of the core carbon material. Moreover, processability, such as crimping | bonding property, can be improved at the time of an electrode manufacturing process.

The anode active material for a lithium secondary battery of the present invention can be manufactured through a step of mixing Li ₂ SiF ₆ with the above-described carbon material anode active material and firing in an oxidizing atmosphere, a reducing atmosphere or an inert atmosphere.

In the method for producing an anode active material for a lithium secondary battery of the present invention, the carbon material anode active material and Li ₂ SiF ₆ can be mixed by a usual method such as dry or wet.

The firing temperature may be 400 to 700 ° C. If the firing temperature is less than 400 ° C., it is difficult to remove impurities, and if it exceeds 700 ° C., the crystal structure of Li ₂ SiF ₆ may be destroyed.

  The anode active material of the present invention thus manufactured is mixed with a conductive material, a binder and an organic solvent to produce an active material paste according to a normal anode manufacturing method, and then used as a commonly used anode current collector such as a copper foil. After being applied to the body, it can be dried, heat-treated and pressure-bonded to be used for producing an anode for a lithium secondary battery.

  In addition, as described above, the anode manufactured according to the present invention and the cathode manufactured by coating the cathode current collector with a predetermined thickness on the cathode current collector are made to face each other by inserting the separator, and then the lithium is applied to the separator. If the secondary battery electrolyte is impregnated, it is possible to manufacture a lithium secondary battery that can be repeatedly charged and discharged. Such a method of manufacturing a lithium secondary battery is widely known to those having ordinary knowledge in the technical field to which the present invention belongs, and thus detailed description thereof is omitted.

Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified in many forms, and the scope of the present invention should not be construed to be limited to the embodiments described later. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.
Example 1
A spherical natural graphite is dry-mixed at a high speed for about 10 minutes with a pitch of 10 parts by weight with respect to 100 parts by weight of natural graphite to produce a mixture. Subsequent firing, fine powder was removed through a classification step, and an anode active material for a lithium secondary battery made of natural graphite coated with a carbide layer was manufactured. After mixing 2 parts by weight of Li ₂ SiF ₆ with respect to 100 parts by weight of the carbon material anode active material thus produced, the carbon material anode active material was mixed with 5 parts at a temperature of 600 ° C. in an inert atmosphere of nitrogen gas. The anode active material for a lithium secondary battery of the present invention was manufactured by time calcination.

100 g of the anode active material thus produced was put into a 500 ml reactor, and a small amount of N-methylpyrrolidone (NMP) and PVDF (binder) were added, and then mixed using a mixer to produce a slurry. . The slurry was uniformly applied to a 12 μm thick copper foil and vacuum dried at 120 ° C. to produce an anode for a lithium secondary battery. The prepared anode, a cathode manufactured using LiCoO ₂ as a cathode active material, Celgard 2400 (manufactured by Celgard) as a separator, and 1M LiPF ₆ solution (EC: DEC = 3: 7) as a non-aqueous electrolyte. A coin cell was manufactured using the solvent used.
Example 2
An anode active material, an anode, and a coin-type battery were manufactured in the same manner as in Example 1 except that Li ₂ SiF ₆ was changed to 4 parts by weight with respect to 100 parts by weight of the carbon material anode active material.
Example 3
An anode active material, an anode, and a coin-type battery were manufactured in the same manner as in Example 1 except that Li ₂ SiF ₆ was changed to 6 parts by weight with respect to 100 parts by weight of the carbon material anode active material.
Example 4
An anode active material, an anode, and a coin-type battery were manufactured in the same manner as in Example 1 except that Li ₂ SiF ₆ was changed to 8 parts by weight with respect to 100 parts by weight of the carbon material anode active material.
Example 5
An anode active material, an anode, and a coin-type battery were manufactured in the same manner as in Example 1 except that Li ₂ SiF ₆ was changed to 10 parts by weight with respect to 100 parts by weight of the carbon material anode active material.
Example 6
Coke was baked at 3000 ° C. for 24 hours, classified to remove fine powder, and artificial graphite as an anode active material for a lithium secondary battery was produced. After mixing 2 parts by weight of Li ₂ SiF ₆ with the carbon material anode active material with respect to 100 parts by weight of the artificial graphite thus produced, the mixture was calcined at 600 ° C. for 5 hours in an inert atmosphere of nitrogen gas. Thus, an anode active material for a lithium secondary battery of the present invention was produced.

The manufacture of the anode and coin-type battery is the same as in Example 1.
Example 7
An anode active material, an anode, and a coin-type battery were manufactured in the same manner as in Example 6 except that 4 parts by weight of Li ₂ SiF ₆ was used with respect to 100 parts by weight of the carbon material anode active material.
Comparative Example 1
A spherical natural graphite is dry-mixed at a high speed for about 10 minutes with a pitch of 10 parts by weight with respect to 100 parts by weight of natural graphite to produce a mixture. Subsequent firing, fine powder was removed through a classification step, and an anode active material for a lithium secondary battery made of natural graphite coated with a carbide layer was manufactured.

100 g of the anode active material thus prepared was put into a 500 ml reactor, a small amount of N-methylpyrrolidone (NMP) and PVDF (binder) were added, and then mixed using a mixer to prepare a slurry. . The slurry was uniformly applied to a 12 μm thick copper foil and vacuum dried at 120 ° C. to produce an anode for a lithium secondary battery. The prepared anode, a cathode manufactured using LiCoO ₂ as a cathode active material, Celgard 2400 (manufactured by Celgard) as a separator, and 1M LiPF ₆ solution (EC: DEC = 3: 7) as a non-aqueous electrolyte. A coin-type battery was manufactured using the above-mentioned solvent use).
Comparative Example 2
The coke was baked at 3000 ° C. for 24 hours, and then classified to remove fine powder to produce artificial graphite as an anode active material for a lithium secondary battery. A battery anode and a coin-type battery were produced.
Experimental Example The following experiment was carried out on the examples and comparative examples to evaluate the characteristics. The evaluation results are as shown in Table 1 below.
(1) Battery characteristics In the charge / discharge test, the battery is charged to 0.01 V at a charging current of 0.5 mA / cm ² while regulating the potential within a range of 0.01 to 1.5 V, and a voltage of 0.01 V is used. The charging was continued until the charging current reached 0.02 mA / cm ² . A discharge current of 0.5 mA / cm ² was discharged up to 1.5 V.

  In the table below, the charge / discharge efficiency indicates the ratio of the discharged electric capacity to the charged electric capacity.

  As shown in Table 1, it can be seen that Examples 1 to 7 according to the present invention have better overall battery characteristics than the comparative battery. In the case of Example 6, the discharge capacity is somewhat lower than that of Comparative Example 2, but the cycle efficiency and capacity retention rate are superior to that of Comparative Example 2, so that the battery characteristics improved as compared with Comparative Example 2 as a whole are exhibited. I understand.

Claims (13)

In an anode active material for a lithium secondary battery including a carbon-based anode active material,
The anode active material for a lithium secondary battery, wherein the anode active material further includes Li ₂ SiF ₆ . The anode active material for a lithium secondary battery according to claim 1, wherein the Li ₂ SiF ₆ is included in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the carbon-based anode active material. 2. The anode active material for a lithium secondary battery according to claim 1, wherein the carbon-based anode active material is formed by coating a carbide layer on a part or all of an edge of a core carbon material. The anode active material for a lithium secondary battery according to claim 3, wherein the core carbon material is highly crystalline spherical natural graphite. The core carbon material is composed of oval, scale, whisker, or crushed natural graphite, mesocarbon microbeads, mesophase pitch fine powder, isotropic pitch fine powder, resin charcoal, and pseudo-graphite structure or 4. The anode active for a lithium secondary battery according to claim 3, wherein the anode active material is any one selected from the group consisting of amorphous carbon fine powder having a disordered layer structure or a mixture thereof. material. The anode active material for a lithium secondary battery according to claim 3, wherein the crystallinity of the carbide layer is lower than the crystallinity of the core carbon material. The lithium carbide layer according to claim 3, wherein the carbide layer is a low crystalline carbide layer formed by coating a pitch, tar, or a mixture thereof derived from a coal-based or petroleum-based material and then carbonizing and firing. Anode active material for secondary batteries. The anode active material for a lithium secondary battery according to claim 1, wherein the carbon-based anode active material is artificial graphite. A method for producing an anode active material for a lithium secondary battery, comprising mixing a carbon-based anode active material and Li ₂ SiF ₆ and firing the mixture in an oxidizing atmosphere, a reducing atmosphere, or an inert atmosphere. The anode active material for a lithium secondary battery according to claim 9, wherein the Li ₂ SiF ₆ is mixed in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the carbon-based anode active material. Production method. The method for producing an anode active material for a lithium secondary battery according to claim 9, wherein the firing temperature is 400 to 700 ° C. In an anode for a lithium secondary battery formed by coating an anode active material and a binder on an anode current collector,
The anode for a lithium secondary battery, wherein the anode active material is the anode active material according to any one of claims 1 to 8. In a lithium secondary battery comprising an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte solution,
The lithium secondary battery according to claim 12, wherein the anode is an anode according to claim 12.