KR101264343B1 - Negative Active Material, Manufacturing Method thereof And Lithium Secondary Battery Comprising The Same - Google Patents

Abstract

The present invention relates to a method for producing a tin-based negative electrode active material, which is in the spotlight as a negative electrode active material for a large lithium secondary battery such as an electric vehicle, and more particularly, a tin-based negative electrode active material having a homogeneous chemical composition The present invention provides a method for preparing a composite of Sn-Co-Fe-C, which is a tin-based composite having excellent battery characteristics by preparing a composite, controlling the type and content of the tin-based metal ion composite, applying a reducing agent, and developing heat treatment conditions. do. In addition, the manufacturing method according to the present invention can produce a tin-based composite Sn-Co-Fe-C anode active material in a simple manner and is easy to mass production and economical, Sn-Co-Fe-C anode of the present invention The lithium secondary battery using the active material provides high output, high energy and long life characteristics.

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}

The present invention relates to a negative electrode active material, a method for manufacturing the same, and a lithium secondary battery having the same, and more particularly, a tin-based negative electrode active material including a tin-based composite Sn-Co-Fe-C synthesized by a Sol-Gel method, and It relates to a manufacturing method and a lithium secondary battery having the same.

Lithium secondary batteries, which are being used as a power source for mobile IT such as mobile phones and notebook PCs, have recently been widely applied to power storage devices. Among them, the development of pollution-free transportation means such as electric vehicles is actively being promoted as means for preventing global warming. In order to further improve the performance of existing electric vehicles, it is necessary to develop a battery having high energy and an electrode material constituting the same.

Lithium secondary battery is a broad concept that includes not only secondary battery using lithium metal but also lithium ion secondary battery, and has high voltage and high energy density. It is also divided into a gel polymer battery using a mixture of and a polymer and a solid polymer battery using pure polymers.

The key components of a lithium secondary battery are the positive electrode, the negative electrode, the electrolyte, and the separator.

The lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, a separator, an exterior material, and the like. The anode is constituted by binding a mixture of a cathode active material, a conductive agent and a binder to the current collector. Lithium transition metal compounds such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ are mainly used as the positive electrode active material, and these materials may intercalate / deintercalate lithium ions into the crystal structure.

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 (Poly) in polar organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methylethyl carbonate. A salt containing lithium ions such as SO ₂ C ₂ F ₅ ) ₂ is dissolved and used.

The separator electrically isolates the anode and the cathode and serves as a pathway for the ion, and mainly uses a polyoletine-based polymer such as porous polyethylene.

The exterior material protects the contents of the battery and provides an electrical passage to the outside of the battery, and mainly uses a pouch packaging material composed of a metal can or aluminum and several layers of polymer layers.

Lithium secondary batteries are still the highest performance secondary batteries available, but they require higher performance batteries in terms of electronics. 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.

Sony (http://www.sony.net/SonyInfo/News/Press/200502/05-006E/) developed a Sn-Co-C composite anode active material by mechanical alloying and developed a lithium secondary battery. Reported. The specific capacity of Sn-Co-C composite anode active material of this battery was 450 mAh / g.

Dahn et al. (PP Ferguson, M. Rajora, RA Dunlap, and JR Dahn, Journal of The Electrochemical Society, 156 (3) (2009) A187-A191; PP Ferguson, Peng Liao, RA Dunlap, and JR Dahn, Journal of The Electrochemical Society, 156 (1) (2009) A13-A17), produced alloys by mechanical milling, and reported specific capacity according to carbon content of 400-600 mAh / g.

The results of the alloy composition of Sn ₃₀ (Co _{1 - x} Fe _x ) ₃₀ C ₄₀ show that the relatively high 400 mAh / g of cost can be sustained up to 100 times of charging / discharging at x = 0 and x = 0.5. Respectively.

Wang et al. (Xiuyan Wang, Zhaoyin Wen, Bin Lin, Jiu Lin, Xiangwei, Wu, Xiaogang Xu, Journal of Power Sources, 184 (2008) 508-512) prepared Sn-graphite-Ag composites by mechanical milling, The prepared composite was composed of Sn, Ag ₄ Sn and graphite, and reported that the specific capacity as a lithium secondary battery negative electrode active material was initially 600 mAh / g and 400 mAh / g at 100 charge / discharge cycles.

Yang et al. (Shoufeng Yang, Peter Y. Zavalij, M. Stanley Whittingham, Electrochemistry communications, 5 (2003) 587-590) were found to be charged and discharged as a lithium secondary battery negative electrode using a tin thin film having a thickness of 25 to 30 um. A specific amount of 600 mAh / g may be indicated, but the rapid decrease after about 15 times has been reported.

Do Chil Hoon et al. (Do Chil Hoon et al., A negative electrode active material. A method for manufacturing the same and a lithium secondary battery having the same, Korean Patent No. 10-0743053, July 20, 2007) manufactured Cu ₆ Sn ₅ by a mechanical ball milling method and a lithium secondary battery It was applied as a negative electrode active material. The Cu ₆ Sn ₅ - graphite composite showed a specific capacity of 550 mAh / g, but the cost was rapidly decreased according to the cycle. The carbon coated Cu ₆ Sn ₅ - graphite composite showed a specific capacity of 200 mAh / g, . In both cases, problems of cycle characteristics and non-capacity were shown.

Significant improvements in the specific amount of the anode material have been made. The current graphite material is a material with a theoretical cost of 372 mAh / g and a density of 2.2 g / ml, but in the case of tin under development, it has a remarkably high value of 990 mAh / g and has a density of 7.30 g / ml. Tin exhibits electrochemical reaction potential with lithium as well as graphite-like characteristics. However, tin materials have a problem of volume expansion up to 300% (Li ₂₂ Sn ₅ ) due to lithium insertion.

Conventional method for developing tin-based negative electrode active material is to use a high energy mechanical ball milling method, it is necessary to use a high-speed ball milling device to apply high mechanical energy, using a reduced metal There have been constraints on conditions, such as alloying and difficulty in obtaining a homogeneous chemical composition.

The present invention is relatively simple in the sol-gel method (Sol-Gel method) in order to solve the problems of the tin-based material and the problem of mechanical ball milling as described above, the charge and discharge cost is high using the starting material of the metal ion compound Sn-Co-Fe-C composite anode active material having excellent cycle characteristics was prepared, and a lithium secondary battery using the prepared Sn-Co-Fe-C composite anode active material was developed.

The negative electrode active material in which cobalt (Co), iron (Fe), graphite (C), and tin (Sn) are combined has a characteristic of alleviating the volume expansion caused by the cycle.

The present invention for achieving the above object,

A method of preparing a composition using tin metal salt, cobalt metal salt, ferrous metal salt and graphite in a molar ratio, a metal ion composite gel with a reducing agent and distilled water, and then firing to prepare a Sn-Co-Fe-C composite powder to provide.

In the present invention, the tin metal salts _{(Sn (CH 3 COO) 2} ) tin acetate, tin nitrate _{(Sn (NO 3) 2)} , tin carbonates (SnCO _3), selected from the group consisting of tin sulphate (SnSO ₄₎ and that at least one member characterized in that, with the cobalt salt is cobalt acetate _{(Co (CH 3 COO) 2} ), cobalt nitrate _{(Co (NO 3) 2)} , cobalt carbonate (CoCO _3), cobalt sulfate (CoSO ₄₎ (Fe (CH ₃ COO) ₂ ), iron nitrate (Fe (NO ₃ ) ₂ ), ferric carbonate (FeCO ₃ ), ferrous sulfate FeSO ₄ ). The present invention also provides an anode active material comprising the same.

In addition, the molar ratio of the said tin metal salt, cobalt metal salt, ferrous metal salt, and graphite can be selected freely, and especially 1: 1: 1: 1 is preferable.

The reducing agent is an organic acid, can be selected from the group consisting of citric acid or ascorbic acid (at least one type), the amount of reducing agent is used 1 to 2 times compared to the number of moles of total metal ions. It provides a method for producing a negative electrode active material, characterized in that.

In addition, the metal ion complex aqueous solution is stirred at 70 ~ 90 ℃ to form a reducing agent / metal ion sol with the evaporation of water, the sol is heated in a 100 ~ 120 ℃ oven reducing agent / metal ion complex It provides a method for producing a negative electrode active material, characterized in that to form a gel (metal ion gel), and calcining the gel powder.

In addition, the reducing agent / metal ion composite gel is characterized in that the heat treatment in an inert (Ar) or reducing atmosphere, the heat treatment time and temperature is in the range of 1 to 5 hours and 500 ~ 1000 ℃ and may be a multi-step heat treatment conditions, 300 After sintering at 5 ° C. for 5 hours, heat treatment is further performed at 550˜950 ° C. for 3 hours.

In addition, the negative electrode active material provides a lithium secondary battery, characterized in that the above-described negative electrode active material.

In addition, the anode active material provides a lithium secondary battery, characterized in that further comprises a carbon black (super p. Black) as a conductive material.

In addition, the negative electrode active material provides a lithium secondary battery, further comprising a polyvinylidene fluoride (PVDF) as a binder.

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

The tin-based metal-graphite composite anode active material prepared from the sol-gel method metal ion composite according to the present invention and a lithium secondary battery using the same were analyzed and compared with the negative electrode active material prepared only from tin ions. The charging and discharging characteristics are improved, and excellent cycle characteristics, specific capacity, charge and discharge rate characteristics can be used as a negative electrode active material of a lithium secondary battery.

The method for producing a negative electrode active material of the metal ion complex can easily produce a material having a homogeneous composition in a large amount compared to a mechanical milling method of high energy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a manufacturing process of a Sn-Co-Fe-C composite according to the present invention.
Fig. 2 shows X-ray diffraction (XRD) results of the Sn-Co-Fe-C composite powder prepared according to the present invention.
3 is an FE-SEM photograph of the Sn-Co-Fe-C composite powder prepared according to the present invention.
4 shows the particle size analysis (PSA) results of the Sn-Co-Fe-C composite powder prepared according to the present invention.
5 is a voltage for the initial charging and discharging of the coin cell prepared by using the Sn-Co-Fe-C composite prepared according to the present invention as a negative electrode active material 1 to 2 times at 0.1 C rate and 3 times at 0.2 C rate The change in overcurrent is shown.
6 shows the results of constant current / constant voltage charge / discharge cycling of a coin-type battery manufactured using a Sn-Co-Fe-C composite anode active material according to the composition ratio of the metal ion material.
FIG. 7 shows the constant current and constant voltage charge / discharge cycles of a coin-type battery prepared using a Sn-Co-Fe-C composite anode active material according to a type of reducing agent such as citric acid and ascorbic acid. The results are shown.
FIG. 8 shows the results of constant current / constant voltage charge / discharge cycling of a coin-type battery manufactured using a Sn-Co-Fe-C composite anode active material with a change in heat treatment temperature.
9 is a schematic cross-sectional view of a lithium secondary battery to which an anode active material according to an embodiment of the present invention is applied.

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

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

The present invention comprises the steps of: (1) mixing a metal salt aqueous solution and a reducing agent prepared by dissolving tin metal salts, cobalt metal salts and ferrous metal salts in distilled water;

(2) stirring the mixture at 70-90 ° C. to form a reducing agent / metal ion sol;

(3) heating the sol at 100-120 ° C. to form a reducing agent / metal ion gel; And (4) calcining the powder; It provides a method for producing a Sn-Co-Fe-C composite anode active material comprising a.

In the present invention, the tin metal salt in the step (1) is tin acetate (Sn (CH ₃ COO) ₂ ), tin nitrate (Sn (NO ₃ ) ₂ ), tin carbonate (SnCO ₃ ), tin sulfate (SnSO ₄ ) Is preferably at least one selected from the group consisting of, the cobalt metal salt is cobalt acetate (Co (CH ₃ COO) ₂ ), cobalt nitrate (Co (NO ₃ ) ₂ ), cobalt carbonate (CoCO ₃ ), cobalt It is preferable that at least one selected from the group consisting of sulfate (CoSO ₄ ), the iron metal salt is iron acetate (Fe (CH ₃ COO) ₂ ), iron nitrate (Fe (NO ₃ ) ₂ ), iron carbonate (FeCO ₃ ), at least one member selected from the group consisting of iron sulfate (FeSO ₄ ).

In addition, the molar ratio of the tin metal salt, cobalt metal salt, ferrous metal salt and graphite can be freely selected. Preferably, the synthesis of tin metal salt, cobalt metal salt, ferrous metal salt and graphite in a molar ratio of (1: 1: 1: 1: 1) is preferred. good.

The reducing agent is an organic acid, is selected from citric acid or ascorbic acid, the amount of the reducing agent is preferably used 1 to 2 times compared to the number of moles of the total metal ions, more preferably It is recommended to use citric acid: total metal ions in a molar ratio of 1: 1.

In addition, in the step (2), it is preferable to prepare a reducing agent / metal ion composite sol by stirring the reducing agent / metal ion complex aqueous solution at 70 to 90 ° C., and more preferably heating to 80 ° C. In the step (3), the sol is preferably heated in an oven at 100 ° C. to 120 ° C. to form a reducing agent / metal ion composite gel, and more preferably at 100 ° C.

In addition, the gel precursor of step (4) is preferably heat-treated in an inert or reducing atmosphere for easy reduction of tin (Sn), cobalt (Co), iron (Fe).

In addition, in the step (4), the heat treatment time and temperature of the gel precursor are preferably sintered at 250-350 ° C. for 3-5 hours, and then heat-treated again at 550 ° C., 750 ° C., and 950 ° C. for 3 hours. This is because when the heat treatment temperature is low, it becomes difficult to form a crystalline material.

The present invention also provides an electrode using the Sn-Co-Fe-C composite prepared by the above method as a negative electrode active material, and a lithium secondary battery comprising the electrode.

In the present invention, the lithium secondary battery is a polyvinylidene fluoride (PVDF) of the tin-based composite Sn-Co-Fe-C as a binder and carbon black (super p. Black) of the conductive material according to a conventional method methylpyrrole An electrode slurry may be prepared by mixing with a donor (NMP, N-methylpyrrolidone) dispersion medium, applying the same to a current collector, drying, and compressing the electrode slurry.

The electrode manufacturing method as described above may use a conventional method known in the art, it is not particularly limited.

In addition, the negative electrode active material according to the present invention may be applied to the negative electrode active material without limitation as long as it is a battery using an insertion / desertion phenomenon of ions.

Physical properties of the material prepared according to the embodiment of the present invention manufactured by the above process was 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.

In a lithium secondary battery having a negative electrode active material according to the present invention, 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, the negative electrode active material is tin (Sn), cobalt ( Co), iron (Fe), characterized in that it comprises a composite of graphite (C).

Except for the tin-based composite Sn-Co-Fe-C, 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 polyvinylidene fluoride (PVDF) as a binder and a current collector. 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. But not limited to, lithium metal, non-graphitizable carbon, graphitizable carbon, natural graphite, artificial graphite, and the like. Further, activated carbon may be further used.

9 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. ) And the sealing member 6 which encloses the battery container 5 and the battery container 5 as a main part is comprised. The shape of the lithium secondary battery illustrated in FIG. 6 may be in various shapes such as cylindrical, square, square, coin, or sheet.

The anode (3) is provided with a cathode mixture composed of a cathode active material, a conductive material and a binder. The positive electrode active material is a compound capable of reversibly intercalating / deintercalating lithium. LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiFeO ₄ , LiNiVO ₄ , the _{LiNi 1/2 Mn 1/2} O 2 , etc. are not limited.

As the separator, an olefin porous film such as polyethylene or polypropylene can 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), 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, etc. To an aprotic solvent or a mixed solvent in which two or more of these solvents are mixed, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ C ₂ F ₅ ) _{2 A} mixture of one or two or more electrolytes composed of lithium salts may be used.

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

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

≪ Example 1 >

(a) Preparation of Sn-Co-Fe-C (1115) -550-CA Composite Cathode Active Material

Tin acetate (4.7360 g, 0.02 mole), cobalt acetate (4.9816 g, 0.02 mole), iron acetate (3.4786 g, 0.02 mole) and graphite (1.2011 g, 0.1 mole, graphite material for lithium secondary battery) : 1: 1: 5) Determine the molar ratio and dissolve in a small amount of distilled water, and then mix the citric acid with 1 mole ratio (11.5272 g, 0.06 mole) to the total metal ions. 20 ml and then stirred slowly at 80 ° C. for 30 minutes to form a sol, concentrated at 100 ° C. to prepare a reducing agent / metal ion complex gel, and the gel was sintered at 300 ° C. for 5 hours in an argon atmosphere tubular kiln. Thereafter, heat treatment was performed again at 550 ° C. for 3 hours to prepare a tin composite Sn-Co-Fe-C (1115) -550-CA anode active material (see FIG. 1).
Here, referring to the meaning of Sn-Co-Fe-C (1115) -550-CA, the meaning of '(1115)' means that the molar ratio of Sn, Co, Fe, C is 1: 1: 1: 5, '55O' means that the heat treatment temperature is carried out at 550 ℃, 'CA' means that 'Citric Acid' is used as the reducing agent. In the embodiments to be described later it will be used in the same sense as above, 'AA' means that 'Ascobic Acid' is used as the reducing agent.

(b) Fabrication of lithium secondary battery using Sn-Co-Fe-C (1115) -550-CA material

1.4 g of Sn-Co-Fe-C (1115) -550-CA anode active material, a tin composite prepared in Example 1a as a negative electrode active material, 0.3 g of polyvinylidene fluoride (PVDF) as a binder, and carbon black as a conductive material (super p. black) 0.3 g was mixed with a methylpyrrolidone (NMP, 10 ml) dispersion medium to prepare a battery negative electrode slurry. Each composition was made into the active material: conductive material: binder = 70: 15: 15 weight ratio.

The prepared negative electrode mixture slurry was applied to a 10 μm thick Cu foil and dried at 100 ° C. for 4 hours or more to prepare a negative electrode active material electrode.

In order to examine the charge and discharge characteristics of the synthesized material, a coin cell using a lithium foil as a counter electrode was fabricated. The separator was made of porous polypropylene film (Celgard 3501) and the electrolyte was 1.2M LiPF _{6 from} Techno Semichem. + EC / EMC (1/1 vol.%) + VC 2%.

<Example 2>

(a) Preparation of Sn-Co-Fe-C (1110) -550-CA Composite Cathode Active Material

Same as Example 1a except that the molar ratio of tin acetate, cobalt acetate, iron acetate and graphite was changed from (1: 1: 1: 1: 5) to (1: 1: 1: 1) and no graphite was used. Sn-Co-Fe-C (1110) -550-CA was prepared.

(b) Fabrication of lithium secondary battery using Sn-Co-Fe-C (1110) -550-CA material

It is the same as Example 1b except having replaced the Sn-Co-Fe-C (1115) -550-CA with Sn-Co-Fe-C (1110) -550-CA, and manufactured the lithium secondary battery.

<Example 3>

(a) Preparation of Sn-Co-Fe-C (3000) -550-CA Composite Cathode Active Material

Example 1- (a) except that the molar ratio of tin acetate, cobalt acetate, iron acetate and graphite was changed from (1: 1: 1: 1: 5) to (3: 10: 0: 0) and only tin was used. In the same manner as in Sn-Co-Fe-C (3000) -550-CA was prepared.

(b) Fabrication of lithium secondary battery using Sn-Co-Fe-C (3000) -550-CA material

It is the same as Example 1b except having manufactured the lithium secondary battery by changing Sn-Co-Fe-C (1115) -550-CA into Sn-Co-Fe-C (3000) -550-CA.

<Example 4>

(a) Preparation of Sn-Co-Fe-C (1115) -550-AA Composite Cathode Active Material

Tin acetate (4.7360 g, 0.02 mole), cobalt acetate (4.9816 g, 0.02 mole), iron acetate (3.4786 g, 0.02 mole) and graphite (1.2011 g, 0.1 mole, graphite material for lithium secondary battery) : 1: 1: 5) Determine the molar ratio and dissolve it in a small amount of distilled water. Then, ascorbic acid is mixed with 2 mole ratio (21.1344 g, 0.12 mole) to the total metal ions. 20 ml and then stirred at 80 ° C. for 30 minutes to form a sol, concentrated at 100 ° C. to prepare a reducing agent / metal ion complex gel, and the gel was sintered at 300 ° C. for 5 hours in an argon atmosphere tubular kiln. Thereafter, heat treatment was performed again at 550 ° C. for 3 hours to prepare a tin composite Sn-Co-Fe-C (1115) -550-AA anode active material (see FIG. 1).

(b) Fabrication of lithium secondary battery using Sn-Co-Fe-C (1115) -550-AA material

1.4 g of Sn-Co-Fe-C (1115) -550-AA anode active material, a tin composite prepared in Example 4a, 0.3 g of polyvinylidene fluoride (PVDF) as a binder, and carbon black as a negative electrode active material (super p. black) 0.3 g was mixed with a methylpyrrolidone (NMP, 10ml) dispersion medium to prepare a battery negative electrode slurry. Each composition was made into the active material: conductive material: binder = 70: 15: 15 weight ratio.

The prepared negative electrode mixture slurry was applied to a 10 μm thick Cu foil and dried at 100 ° C. for at least 4 hours to prepare a negative electrode active material electrode.

In order to examine the charge and discharge behavior of the synthesized material, a coin cell was fabricated using lithium foil as a counter electrode. The separator was made of porous polypropylene film (Celgard 3501) and the electrolyte was 1.2M LiPF _{6 from} Techno Semichem. + EC / EMC (1/1 vol.%) + VC 2%.

<Example 5>

(a) Preparation of Sn-Co-Fe-C (1115) -750-AA Composite Cathode Active Material

Tin acetate (4.7360 g, 0.02 mole), cobalt acetate (4.9816 g, 0.02 mole), iron acetate (3.4786 g, 0.02 mole) and graphite (1.2011 g, 0.1 mole, graphite material for lithium secondary battery) : 1: 1: 5) Determine the molar ratio and dissolve it in a small amount of distilled water. Then, ascorbic acid is mixed with 2 mole ratio (21.1344 g, 0.12 mole) to the total metal ions. 20 ml of the mixture was then stirred slowly at 80 ° C. for 30 minutes to form a sol, and concentrated at 100 ° C. to prepare a reducing agent / metal ion complex gel, and the gel was sintered at 300 ° C. for 5 hours in an argon atmosphere tubular kiln. Thereafter, heat treatment was further performed at 750 ° C. for 3 hours to prepare a tin composite Sn-Co-Fe-C (1115) -750-AA anode active material (see FIG. 1).

(b) Fabrication of Lithium Secondary Battery Using Sn-Co-Fe-C (1115) -750-AA Material

It is the same as Example 4b except having manufactured the lithium secondary battery by changing the heat processing temperature to 750 degreeC.

<Example 6>

(a) Preparation of Sn-Co-Fe-C (1115) -950-AA Composite Cathode Active Material

Tin acetate (4.7360 g, 0.02 mole), cobalt acetate (4.9816 g, 0.02 mole), iron acetate (3.4786 g, 0.02 mole) and graphite (1.2011 g, 0.1 mole, graphite material for lithium secondary battery) : 1: 1: 5) Determine the molar ratio and dissolve in a small amount of distilled water, and then mix ascorbic acid with 2 mole ratio (21.1344 g, 0.12 mole) to the total metal ions. 20 ml and then stirred slowly at 80 ° C. for 30 minutes to form a sol, concentrated at 100 ° C. to prepare a reducing agent / metal ion complex gel, and the gel was sintered at 300 ° C. for 5 hours in an argon atmosphere tubular kiln. Thereafter, heat treatment was performed again at 950 ° C. for 3 hours to prepare a tin composite Sn-Co-Fe-C (1115) -950-AA anode active material (see FIG. 1).

(b) Fabrication of Lithium Secondary Battery Using Sn-Co-Fe-C (1115) -950-AA Material

It is the same as Example 4b except having manufactured the lithium secondary battery by changing the heat processing temperature to 950 degreeC.

<Experimental Example>

The crystal structure and surface morphology of the synthesized Sn-Co-Fe-C anode active material were confirmed by XRD and FE-SEM. XRD analysis was performed using X`pert PRO MPD Philips, and FE-SEM analysis was performed using Hitachi S-4800.

The prepared coin cell was subjected to a charge-discharge test using a Toscat-3000 series manufactured by Toyo Co., Ltd.

In the actual lithium secondary battery, the negative electrode active material is in a direction in which the potential decreases in the initial charging, and accordingly, in the present invention, charging is described as a process of charging electricity as a negative electrode due to a decrease in potential.

The following charge / discharge method was used to demonstrate the capacity, charge rate, and discharge rate characteristics of the lithium secondary battery according to the cycle.

One to two times of charging was performed at a constant current up to 0.005 V at a current of 0.1 C rate, and at a constant voltage from 0.005 V to 0.01 C at a current. Discharged.

The charging process of 3 ~ 30 times was charged with constant current up to 0.005 V at a current of 0.2 C rate, and was charged with constant voltage from a current of 0.005 V to 0.02 C rate, and the discharge was carried out by constant current method up to 1.5 V at a current of 0.2 C rate. Discharged.

The 31 ~ 35 cycles of charging were performed at a constant current up to 0.005 V at a current of 0.5 C, and at a constant voltage from 0.005 V to 0.05 C at a constant current. Discharged.

36-40 cycles of charging were performed at a constant current up to 0.005 V at a current of 1 C rate, and at a constant voltage from 0.005 V to 0.1 C at a current. Discharged.

The 41 ~ 45 cycles of charging were performed at a constant current up to 0.005 V at a current of 2 C, and at a constant voltage up to 0.2 C at a current of 0.005 V. Discharged.

The charge of 46 ~ 50 times was charged with constant current up to 0.005 V at 3 C current, and was charged with constant voltage from 0.005 V to 0.3 C current, and the discharge was carried out with constant current up to 1.5 V at 3 C current. Discharged.

The 51 ~ 55 cycles of charging were performed at a constant current up to 0.005 V at a current of 5 C, and at a constant voltage from 0.005 V to 0.5 C at a constant current. Discharged.

The 56 ~ 60 cycles of charging were performed at constant current up to 0.005 V at a current of 10 C, and at a constant voltage from 0.005 V to 1 C at a constant current. Discharged.

The 61 ~ 65 cycles were charged with a constant current up to 0.005 V at a current of 0.2 C rate, and were charged with a constant voltage from a current of 0.005 V to 0.02 C at a constant voltage. Discharged.

The evaluation results of charge / discharge characteristics are as follows.

As described above, despite the high theoretical capacity of tin (Sn), it is not commercialized because the lithium ion is inserted and desorbed with the progress of charging and discharging accompanied by the volume expansion and the cycle characteristics are deteriorated. In order to solve this problem, Sn-Co-Fe-C anode active material having a high charge / discharge capacity and excellent cycle characteristics was prepared by sol-gel method.

FIG. 2 shows Sn-Co-Fe-C (1115) -550-AA and Sn-Co-Fe-C (1115)-prepared using ascorbic acid at a heat treatment temperature of 550 ° C, 750 ° C, and 950 ° C. XRD patterns of 750-AA and Sn-Co-Fe-C (1115) -950-AA composite anode active materials are shown.
JCPDS analysis confirmed that the tin composite Sn-Co-Fe-C (1115) -550-AA, which was heat treated at 550 ° C, coexisted with CoSn, Fe, and graphite (C), and the tin composite Sn- heat treated at 750 ° C. Co-Fe-C (1115) -750-AA confirmed the presence of Fe ₃ SnC, and in the case of Sn-Co-Fe-C (1115) -950-AA heat-treated at 950 ° C, the presence of Fe ₃ SnC was confirmed. However, the crystallinity was higher than that of Sn-Co-Fe-C (1115) -750-AA. Table 1 below shows the crystal phases of Sn-Co-Fe-C (1115) -AA materials according to heat treatment temperatures.

Example Anode active material Crystal phase in anode active material Example 4 Sn-Co-Fe-C (1115) -550-AA Fe, C, CoSn, etc. Example 5 Sn-Co-Fe-C (1115) -750-AA Fe3SnC, C, etc. Example 6 Sn-Co-Fe-C (1115) -950-AA Fe3SnC, C, etc.

Figure 3 shows the FE-SEM picture of the Sn-Co-Fe-C composite according to the heat treatment temperature. The particle size of the synthesized tin composite Sn-Co-Fe-C is about 20 to 30 um, and a small amount of about 70 to 80 um is included.

4 is a result of analyzing the particle size of each material. Table 2 below shows particle sizes of Sn-Co-Fe-C (1115) -AA materials according to heat treatment temperature.

(Unit: um)     Furtherance D (10) d (50) d (90) Example 4 SnCoFeC (1115) -550-AA 5.9 21.1 61.9 Example 5 SnCoFeC (1115) -750-AA 7.3 22.7 58.2 Example 6 SnCoFeC (1115) -950-AA 7.7 27.2 90.7

The overall particle size ranges from about 25 μm for D (50) and about 7 μm and 80 μm for D (10) and D (90), respectively.

5 to 8 are views showing charge and discharge characteristics of the lithium secondary battery manufactured according to the above invention.

Since the results of the embodiments presented in the present invention are not optimized, improvements in performance due to technical improvements within the scope of the present invention can be seen as falling within the scope of the present invention.

FIG. 5 shows a battery using a Sn-Co-Fe-C (1115) -550-CA anode active material having a molar ratio of citric acid / metal ion composite sol of 1: 1 and heat-treated at 550 ° C. (Example 1 ) Shows the voltage and current.
The initial charge specific capacity of Sn-Co-Fe-C (1115) -550-CA anode active material was 1503 mAh / g, and the initial discharge specific capacity was 642 mAh / g.

FIG. 6 shows Sn-Co-Fe-C (3000) -550-CA (Example 3) and Sn-Co-Fe-C prepared by using a citric acid and heat-treated at 550 ° C. by varying the composition of the metal ion complex. (1115) -550-CA (Example 1) and Sn-Co-Fe-C (1110) -550-CA (Example 2) Charge and Discharge of Anode Active Materials of Lithium Secondary Batteries Prepared Using Three Cathode Active Materials As a characteristic, the specific amount of the charging and discharging process is shown with respect to the number of cycles.

The primary discharge specific capacity is 640 mAh / g for Sn-Co-Fe-C (3000) -550-CA (Example 3) and Sn-Co-Fe-C (1115) -550-CA (Example 1) Sn-Co-Fe-C (1110) -550-CA (Example 2) showed 430 mAh / g. Sn-Co-Fe-C (1115) -550-CA (Example 1) and Sn-Co-Fe-C (1110) -550-CA (Example 2) have no difference in graphite presence at the same metal composition ratio. In the case of Sn-Co-Fe-C (1115) -550-CA with graphite, the specific specific amount was higher than that of Sn-Co-Fe-C (1115) -550-CA, but the cycle characteristics were similar and the charge and discharge rate characteristics were almost the same. . Discharge capacities of 3C rate were 268 for Sn-Co-Fe-C (1115) -550-CA (Example 1) and Sn-Co-Fe-C (1110) -550-CA (Example 2), respectively. mAh / g and 189 mAh / g, and the discharge capacity after the rate characteristic test of 0.2 C rate was 403 mAh / g and 295 mAh / g, respectively, and the ratio of discharge capacity of 3 C rate to 0.2 C rate was Sn-Co- For Fe-C (1115) -550-CA (Example 1) and Sn-Co-Fe-C (1110) -550-CA (Example 2), they were similar at 67% and 64%, respectively.

Sn-Co-Fe-C (3000) -550-CA (Example 3) and Sn-Co-Fe-C (1115) -550-CA (Example 1) are the differences between pure tin and metal-graphite composites. Sn-Co-Fe-C (1115) -550-CA (Example 1) has better cycle characteristics than Sn-Co-Fe-C (3000) -550-CA (Example 3), and The specific capacity of the Co-Fe-C (1115) -550-CA (Example 1) up to 65 cycles was 400 mAh / g, and the Sn-Co-Fe-C (3000) -550-CA (Example 3) showed specific capacity of about 300 mAh / g.

7 shows Sn-Co-Fe-C (1115) -550-CA and Sn-Co-Fe-C (1115) -550-AA prepared by applying an organic acid to citric acid and ascorbic acid in the sol-gel method. It shows the charge and discharge specific capacity according to the number of cycles.

The use of ascorbic acid showed a relatively low specific capacity compared to the case of using citric acid, and cycle characteristics and charge and discharge rate characteristics showed the same results. The discharge specific capacities of Sn-Co-Fe-C (1115) -550-CA and Sn-Co-Fe-C (1115) -550-AA at 65 charge / discharge cycles are 400 mAh / g and 300 mAh / g. It was.

FIG. 8 shows Sn-Co-Fe-C (1115) -550-AA and Sn-Co-Fe-C prepared by changing the same metal ion composite by heat treatment at 550 ° C., 750 ° C., and 950 ° C. under ascorbic acid conditions. (1115) -750-AA, Sn-Co-Fe-C (1115) -950-AA The discharge specific amount and the Ah efficiency are shown as the number of cycles as charge / discharge characteristics of the negative electrode active material.

The initial specific capacity of Sn-Co-Fe-C (1115) -550-AA is 500 mAh / g, 65 times of specific capacity is 290 mAh / g, and the discharge capacity at 10 C rate is 130 mAh / g. It was 44% of the 0.2 C discharge capacity after the test.

Sn-Co-Fe-C (1115) -750-AA had an initial specific capacity of 290 mAh / g and 130 mAh / g at 10 C, which was 59% of the 65-time 0.2 C discharge capacity of 220 mAh / g.

Sn-Co-Fe-C (1115) -950-AA had an initial specific capacity of 360 mAh / g and 180 mAh / g at 10 C, which was 62% of the 65-time 0.2C discharge capacity of 290 mAh / g.

From the above results, Sn-Co-Fe-C (1115) -950-AA showed the best result by combining specific capacity, cycle characteristics, charge and discharge rate characteristics.

The first discharging process of the Sn-Co-Fe-C (1115) -550-CA anode active material of Example 1 using graphite and a metal composite composition among six tin-based metal ion composites shown in Examples 1 to 6 The specific capacity was 640 mAh / g at, and the specific capacity was 400 mAh / g at the charge and discharge of 0.2 C at 60 to 65 times, and 200 mAh / g at 10 C at 55 to 60 times.

** Description of the major symbols in the drawings **
1: lithium secondary battery 2: negative electrode
3: anode 4: separator
5: Battery container 6: Sealing member

Claims (15)

(1) mixing a metal salt aqueous solution prepared by dissolving tin metal salt, cobalt metal salt, ferrous metal salt and graphite in distilled water and a reducing agent;
(2) stirring the mixture at 70-90 ° C. to form a reducing agent / metal ion sol;
(3) heating the sol at 100-120 ° C. to form a reducing agent / metal ion gel; And
(4) a method of producing a Sn-Co-Fe-C composite anode active material comprising a; heat-treating the reducing agent / metal ion composite. The tin metal salt according to claim 1, wherein the tin metal salt is tin acetate (Sn (CH ₃ COO) ₂ ), tin nitrate (Sn (NO ₃ ) ₂ ), tin carbonate (SnCO ₃ ), tin sulfate (SnSO ₄ ) The production method, characterized in that at least one member selected from the group consisting of. The cobalt metal salt of claim 1, wherein the cobalt metal salt is cobalt acetate (Co (CH ₃ COO) ₂ ), cobalt nitrate (Co (NO ₃ ) ₂ ), cobalt carbonate (CoCO ₃ ), cobalt sulfate (CoSO ₄ ) The production method, characterized in that at least one member selected from the group consisting of. According to claim 1, wherein in the step (1), the ferrous metal salt is iron acetate (Fe (CH ₃ COO) ₂ ), iron nitrate (Fe (NO ₃ ) ₂ ), iron carbonate (FeCO ₃ ), iron sulfate (FeSO ₄ ) The production method, characterized in that at least one member selected from the group consisting of. The method of claim 1, wherein the graphite is at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, carbon black, carbon nanotube (CNT), and fullerene. The method according to claim 1, wherein in the step (1), the molar ratio of the tin metal salt, the cobalt metal salt, the ferrous metal salt, and graphite is 1: 1: 1: 1. The method of claim 1, wherein the reducing agent of the process is selected from citric acid or ascorbic acid. The method according to claim 1, wherein the amount of reducing agent used in the step (1) is 1 to 2 times the number of moles of the total metal ions. The method according to claim 1, wherein the gel precursor in the step (4) is heat-treated under an argon gas atmosphere. The method of claim 1,
In the step (4), the reducing agent / metal ion composite gel is sintered at 250 to 350 ° C. for 3-5 hours, and then heat-treated again at 550 to 950 ° C. for 3 hours. In the negative electrode active material used in the lithium secondary battery,
Sn-Co-Fe-C composite, including the Sn-Co-Fe-C composite is uniformly mixed by the sol-gel chemical method, and then sintered at 250 ~ 350 ℃ for 3-5 hours and again 550 ~ Cathode active material, characterized in that the heat treatment for 3 hours at 950 ℃. delete In a lithium secondary battery provided with a negative electrode including a negative electrode active material and a positive electrode and a positive electrode containing a positive electrode active material,
Sn-Co-Fe-C composites as a negative electrode active material, the Sn-Co-Fe-C composites are uniformly mixed by a sol-gel chemical method, and then sintered at 250 ~ 350 ℃ for 3-5 hours Lithium secondary battery characterized in that the heat treatment again at 550 ~ 950 ℃ for 3 hours. The lithium secondary battery according to claim 13, wherein the negative electrode uses carbon black as a conductive material. The lithium secondary battery of claim 13, wherein the negative electrode comprises polyvinylidene fluoride (PVDF) as a binder.

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