JP4069465B2 - Carbonaceous negative electrode material for lithium secondary battery and method for producing the same - Google Patents

Description

【００１９】
表１および図１に示す結果から、本発明による負極材料は、放電容量が大きく、サイクル劣化が少ないことが明らかである。
【図面の簡単な説明】
【図１】実施例および比較例で得られた負極材料のサイクル特性を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbonaceous material and a method for producing the same, a carbonaceous negative electrode material and a negative electrode used for a lithium secondary battery, and a lithium secondary battery.
[0002]
[Prior art]
Lithium secondary batteries that can be charged with high energy density and discharged with high energy density as power source batteries for electronic devices and as backup batteries for electronic devices as electronic devices become smaller, thinner, and lighter Has attracted attention. In addition, since lithium has little impact on the environment and high safety, lithium secondary batteries have been developed as power sources for electric vehicles and further as distributed power storage batteries.
[0003]
A conventional typical lithium secondary battery uses a carbon material as a negative electrode active material, and is charged and discharged by inserting (intercalating) and desorbing (deintercalating) lithium into the carbon material in an ionic state. It is repeating. However, it is difficult to increase the amount of lithium ions inserted into the carbon material, and there is a problem that the charge / discharge capacity of the secondary battery cannot be increased. For example, when graphite is used as the carbonaceous material, the lithium metal has a composition of CLi ₆ and the theoretical charge / discharge capacity of this material is 372 Ah / kg. This is as low as 1/10 or less of the lithium metal theoretical charge / discharge capacity of 3800 Ah / kg (lithium base). In order to improve the charge / discharge capacity, when using a carbon material with a high proportion of amorphous parts, it is said that a charge / discharge capacity of 400 Ah / kg or more is possible. However, since such a carbon material has low conductivity, the overvoltage is large and the initial charge / discharge efficiency is as low as about 80%.
Prior to the use of various carbon materials for the negative electrode, as in today, lithium metal and lithium alloys have been intensively studied. When lithium metal is used as a negative electrode material, there is a problem that dendrites are generated during charging and discharging, and cannot be used as they are. In addition, for lithium alloys, the crystal structure of the alloy changes greatly due to the entry and exit of lithium accompanying charge / discharge, so the electrode performance deteriorates after about 100 charge / discharge cycles due to volume changes associated with expansion / contraction. There is a problem of doing.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and a lithium secondary battery negative electrode material having a low overvoltage, a large discharge capacity, and a small cycle deterioration, a method for producing the same, and a lithium secondary using the negative electrode material The main purpose is to provide a battery.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor has found that (a) at least one metal capable of forming an alloy with lithium in the pores of the activated carbon particles, (b At least one alloy of two or more elements including a metal capable of forming an alloy with lithium, and (c) at least one of oxides, nitrides and other compounds of metals capable of forming an alloy with lithium. The carbonaceous material containing the metal material selected from the seeds has high conductivity and discharge capacity, and the activated carbon pores absorb the volume change due to the change in crystal structure that occurs during the formation of the lithium alloy. The inventors have found that the characteristics are improved and have completed the present invention.
That is, this invention provides the following carbonaceous negative electrode material for lithium secondary batteries, its manufacturing method, a lithium secondary battery negative electrode, and a lithium secondary battery.
1. A carbonaceous negative electrode material for a lithium secondary battery containing at least one of the following metal components (a) to (c) in the pores of the activated carbon particles; (a) forming an alloy with lithium At least one metal that can form an alloy, (b) at least one alloy composed of two or more elements including a metal that can form an alloy with lithium, and (c) an oxide of a metal that can form an alloy with lithium , At least one of nitrides and other compounds.
2. Item 2. The carbonaceous negative electrode material for a lithium secondary battery according to Item 1, wherein the activated carbon particles have an average particle size of 1 to 100 µm.
3. The specific surface area of the activated carbon particles, 50m ² / g~5000m ² / g and a lithium secondary battery carbonaceous negative electrode material according to 1.
4). Metals that can form alloys with lithium are selected from Sn, Ca, Sr, Ba, Ir, Ag, Cd, Hg, B, Al, Ga, In, Ti, Si, Pb, Sb, Bi and Te Item 2. The carbonaceous negative electrode material for a lithium secondary battery according to Item 1, which is a metal.
5. Metal component (b) at least one alloy composed of two or more elements including a metal capable of forming an alloy with lithium, and (c) an oxide, nitride and other metals capable of forming an alloy with lithium Item 2. The carbonaceous negative electrode material for a lithium secondary battery according to Item 1, wherein at least one of the compounds contains at least one of a transition metal and a typical metal.
6). The carbonaceous negative electrode material for a lithium secondary battery according to Item 1, wherein the ratio of at least one of the metal components (a) to (c) to the weight of the activated carbon particles is 1 to 80% by weight.
7). (I) a step of obtaining an activated carbon-metal composite by impregnating and supporting at least one of the following metal components (a) to (c) in activated carbon particles in a solvent; and (II) the obtained activated carbon A method for producing a carbonaceous material for a lithium secondary battery, comprising a step of heat-treating a metal composite; (a) at least one metal capable of forming an alloy with lithium; (b) lithium And (c) at least one of metal oxides, nitrides and other compounds capable of forming an alloy with lithium.
8). Item 8. The above item 7, wherein at least one of the metal components (a) to (c) is supported in the pores of the activated carbon and then heat-treated in an inert atmosphere at 2800 ° C. or lower, in a nitrogen atmosphere or in an oxidizing atmosphere. A method for producing a carbonaceous negative electrode material for a lithium secondary battery.
9. A lithium secondary battery using a nonaqueous electrolyte, a positive electrode, and a negative electrode that occludes / releases lithium, wherein the carbonaceous negative electrode material described in the above item 1 is used as a negative electrode material.
10. Item 10. The lithium secondary battery according to Item 9, wherein a negative electrode formed by adding 1 to 30% by weight of a carbonaceous material as a conductive material to the metal-containing carbonaceous negative electrode material according to Item 1 is used.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Negative electrode material In the present invention, in the pores of activated carbon, (a) at least one metal capable of forming an alloy with lithium and (b) two or more metals including a metal capable of forming an alloy with lithium. And at least one metal alloy selected from at least one metal oxide, nitride and other compound capable of forming an alloy with lithium. The carbonaceous material to be used is used as a carbonaceous negative electrode material for a lithium secondary battery.
As the activated carbon particles, those having an average particle diameter of 1 to 100 μm and a specific surface area of 50 to 5000 m ² / g can be used. Although the raw material, a manufacturing method, etc. are not specifically limited, For example, according to a conventional method, it obtains by activating treatment of the carbonaceous material etc. which prepared wood, coconut shell, coal, sugar charcoal, pitch, etc. as a raw material be able to. The conditions for the activation treatment are not particularly limited as long as the specific surface area of the carbonaceous material can be increased, and the carbonaceous material is inert such as water vapor, carbon dioxide, oxygen or a mixture thereof, or these gases are inert such as nitrogen. Examples thereof include a method of holding at 800 to 1200 ° C. in an atmosphere such as a gas diluted with a gas; a method of mixing a carbonaceous material with an alkali hydroxide and performing a heat treatment at an activation temperature. Further, the activated carbon particles need not be in the form of particles before activation. For example, the activated carbon particles may be used after being pulverized after activating the carbonaceous material prepared in a fibrous form by spinning such as petroleum or coal-based pitch. it can.
In the present specification, the average particle size of the activated carbon particles means the center particle size in the volume particle size distribution obtained by the dry laser diffraction measurement method. The specific surface area is a numerical value measured by the BET method.
[0007]
Examples of the metal that forms an alloy with lithium include a group IIA element (for example, Ca, Sr, Ba), a group VIIIB element (for example, Ir), a group IB element (for example, Ag), a group IIB element (for example, Cd, Hg), Examples include IIIB group elements (for example, B, Al, Ga, In, Ti), IVB group elements (Sn), VB group elements (for example, Sb, Bi), and VIB group elements (for example, Te). These elements can be used alone or in combination of two or more. These elements may be in the form of compounds. Specifically, it can be used as a carbide, nitride, organic acid salt (for example, acetate), inorganic acid salt (for example, chloride, carbonate, nitrate) of a metal that forms an alloy with lithium. In the present specification, the above elements and compounds are sometimes referred to as “metal components”. In addition, the “group” designation of elements in this specification is based on “periodic table of elements (short-period type)” in “Iwanami Dictionary of Chemical Sciences; Fifth Edition”.
By adjusting the amount of the metal component used with respect to the activated carbon particles, the content of elements forming an alloy with lithium in the pores of the activated carbon can be controlled. Considering the final yield, the ratio of the metal component forming an alloy with lithium can be adjusted to 1 to 80% by weight with respect to the weight of the activated carbon. As an ordinary preparation method, activated carbon having an appropriate specific surface area, a metal capable of forming an alloy with lithium alone, an alloy composed of two or more elements containing the metal, or a compound of these metals in an appropriate solvent. The carbon material carrying these metal components is prepared by impregnating with. For example, when Sn is selected as a metal that forms an alloy with lithium, a predetermined amount of activated carbon and Sn (CH ₂ CO ₂ ) ₂ can be impregnated and supported in ethanol.
The activated carbon-supported metal composite material prepared at a predetermined weight ratio as described above is subjected to heat treatment in an inert atmosphere, a nitrogen atmosphere or an oxidizing atmosphere, whereby lithium and an alloy are formed in the pores of the activated carbon. A metal that can be formed, an alloy composed of two or more elements containing the metal, or a metal compound (oxide, nitride, etc.) can be formed. The heat treatment temperature can be carried out, for example, by heating to about 800 to 1500 ° C, more preferably about 1000 to 1300 ° C.
Even when activated carbon particles having the same specific surface area are used, the particle size of the metal component contained in the pores of the activated carbon particles can be controlled by changing the weight ratio between the activated carbon and the metal component. For example, after impregnating and supporting Sn (CH ₂ CO ₂ ) ₂ in an ethanol solvent using activated carbon having a specific surface area of 700 m ² / g, treatment in an inert atmosphere at 1000 ° C. In the case where Sn metal is supported on Sn, the crystallite size of Sn can be controlled such as 30 nm when the Sn amount is 14 wt%, 40 nm when 33 wt%, and 50 nm when 45 wt%.
Negative electrode for lithium secondary battery The carbonaceous negative electrode material of the present invention can be used as a constituent material of a negative electrode for a lithium secondary battery by a conventional method. The material for a carbonaceous negative electrode of the present invention can be formed into a negative electrode for a lithium secondary battery having an arbitrary shape by molding in combination with a terminal as necessary according to a conventional method.
[0008]
The carbonaceous negative electrode material of the present invention can also be used as a paste by mixing with a dispersion of a resin such as polyvinylidene fluoride or polytetrafluoroethylene. The mixing amount of the resin is not particularly limited, and is usually 3 parts by weight or more, preferably 5 parts by weight or more, and preferably 30 parts by weight or less, preferably the lower limit with respect to 100 parts by weight of the carbonaceous negative electrode material. Can be 20 parts by weight or less. As a solvent for the dispersion, for example, an organic solvent such as N-methylpyrrolidone can be used. In addition, by using a negative electrode made by adding 1 to 30% by weight of a carbonaceous material as a conductive material to the negative electrode material, it is possible to improve the conductivity as an electrode, and further improve the discharge capacity and cycle characteristics. Can be made. Examples of such added carbonaceous materials include carbon blacks such as acetylene black, thermal black, and furnace black. These may be used alone or in combination of two or more.
Lithium secondary battery By using the negative electrode for a lithium secondary battery of the present invention as a constituent element, a lithium secondary battery having a large charge / discharge capacity and a high initial efficiency can be produced. Specifically, a lithium secondary battery can be produced by a conventional method using the negative electrode of the present invention obtained by the above method as a constituent element, in combination with a positive electrode, an electrolyte (electrolyte), and the like.
[0009]
For example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, etc. can be used as the positive electrode binding material.
[0010]
By using an electrolytic solution in which an electrolyte is dissolved in an organic solvent, a non-aqueous lithium secondary battery can be manufactured. As the electrolyte, for example, it can be a salt which generates a _{LiPF 6, LiClO 4, LiBF 4} , LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiCl, hardly solvated such LiI anion.
[0011]
Examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, gamma butyl lactone, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, sulfolane, 1,2-dimethoxyethane, dimethyl sulfoxide, acetonitrile, N , N-dimethylformamide, diethylene glycol, dimethyl ether and other aprotic solvents can be used alone or as a mixture of two or more.
When manufacturing a lithium secondary battery, together with the above negative electrode material, positive electrode material, and electrolytic solution, separators and collectors of polyolefin-based porous membranes including commonly used porous non-woven fabrics Using a battery component such as a gasket, a sealing plate, and a case, a lithium secondary battery in any form such as a cylindrical shape, a square shape, or a button shape can be produced according to a conventional method.
[0012]
【The invention's effect】
According to the present invention, it is possible to produce a carbonaceous material in which metal particles forming an alloy with lithium are uniformly dispersed in the pores of activated carbon particles. Such a carbonaceous material has excellent characteristics as a carbonaceous negative electrode material for a lithium secondary battery. Therefore, according to the present invention, a lithium secondary battery having a large charge / discharge capacity and high initial efficiency can be provided.
[0013]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
* Manufacture of carbonaceous materials Impregnation / supporting treatment by stirring 1.1 g of pitch-based activated carbon fiber (specific surface area 700 m ² / g) and 1 g of SnSO _{4 in} 500 mL of 0.01N dilute sulfuric acid for 2 hours and evaporating the solvent. Went.
[0014]
Next, after drying the impregnated / supported sample, in a normal heat treatment furnace, the temperature was increased to 1000 ° C. at a temperature increase rate of 10 ° C./min in an argon stream, and held at that temperature for 1 hour, Processed. The weight after firing was 1.2 g, and the ratio of Sn supported on activated carbon was determined to be 33% by weight in consideration of the yield of activated carbon fibers.
[0015]
The electrode was prepared by adding an NMP solution of binder (PVDF) to the heat-treated sample, adding 15% by weight of acetylene black based on the weight of the sample, and then applying it on the copper foil.
[0016]
The charge / discharge test uses a 1M solution of LiPF ₆ / EC: DMC = 1: 1 as the counter electrode and the prepared electrode, LiPF ₆ / EC: DMC = 1: 1, low current method (current density 0.5 mA / cm ² ), voltage range 0 Performed using a bipolar closed cell at ~ 1.5V.
[0017]
The results are shown in Table 1 and FIG. Table 1 shows the results obtained in Example 2 and Comparative Examples 1 and 2 together. FIG. 1 shows the results obtained in Example 2 and Comparative Example 1 together.
Example 2
After obtaining a carbonaceous material in the same manner as in Example 1, an electrode coating was prepared in the same manner as in Example 1 except that acetylene black was not added, and an electrode evaluation test was conducted.
Comparative Example 1
After obtaining a carbonaceous material in the same manner as in Example 1 except that powdered Sn and pitch-based activated carbon fibers (specific surface area 700 m ² / g) were mixed in a mortar, Example 1 except that acetylene black was not added. Similarly, an electrode coating was prepared and an electrode evaluation test was performed.
Comparative Example 2
Heat treatment and electrode coating preparation were performed in the same manner as in Example 1 except that pitch-based activated carbon fibers (specific surface area 700 m ² / g) not supporting metal were used, and an electrode evaluation test was performed.
[0018]
[Table 1]

[0019]
From the results shown in Table 1 and FIG. 1, it is clear that the negative electrode material according to the present invention has a large discharge capacity and little cycle deterioration.
[Brief description of the drawings]
FIG. 1 is a graph showing cycle characteristics of negative electrode materials obtained in Examples and Comparative Examples.

Claims (7)

(I) a step of obtaining an activated carbon-metal composite by impregnating and supporting at least one of the following metal components (a) to (c) in activated carbon particles in a solvent; and (II) the obtained activated carbon -A method for producing a carbonaceous material for a lithium secondary battery, comprising a step of heat-treating a metal composite at 800 to 1500 ° C ;
(a) at least one metal capable of forming an alloy with lithium;
(b) at least one alloy of two or more elements including a metal capable of forming an alloy with lithium, and
(c) At least one of metal oxides, nitrides and other compounds capable of forming an alloy with lithium. In the pores of the activated carbon, after carrying at least one metal component (a) ~ (c), 2800 ℃ following in an inert atmosphere, according to claim 1, wherein the heat treatment in a nitrogen atmosphere or in an oxidizing atmosphere A method for producing a carbonaceous negative electrode material for a lithium secondary battery. The method for producing a carbonaceous negative electrode material for a lithium secondary battery according to claim 1 or 2, wherein the activated carbon particles have an average particle size of 1 to 100 µm. The specific surface area of the activated carbon particles, 50 m ² / g or more 5000 m ² / g or less manufacturing method of the carbonaceous negative electrode material for lithium secondary battery according to any of claims 1 to 3. Metals that can form alloys with lithium are selected from Sn, Ca, Sr, Ba, Ir, Ag, Cd, Hg, B, Al, Ga, In, Ti, Si, Pb, Sb, Bi and Te The method for producing a carbonaceous negative electrode material for a lithium secondary battery according to any one of claims 1 to 4 . Metal component (b) at least one alloy composed of two or more elements including a metal capable of forming an alloy with lithium, and (c) an oxide, nitride and other metals capable of forming an alloy with lithium The method for producing a carbonaceous negative electrode material for a lithium secondary battery according to any one of claims 1 to 5 , wherein at least one of the compounds contains at least one of a transition metal and a typical metal. The ratio of at least one of the metal components (a) to (c) to the weight of the activated carbon particles is 1 to 80% by weight. The production of the carbonaceous negative electrode material for a lithium secondary battery according to any one of claims 1 to 6. Way .

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