KR20140120751A - Negative electrode active material and method of manufacturing the same, and electrochemical device having the negative electrode active material - Google Patents

Abstract

The present invention relates to a negative electrode active material, a manufacturing method thereof, and an electrochemical device including the same. The negative electrode active material comprises a material capable of doping and de-doping lithium; a first coating layer formed on the surface of the material capable of doping and de-doping lithium, and including carbon materials; and a second coating layer formed on the outer periphery of the first coating layer, and including chemically crossed polymer.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material, a method for producing the negative electrode active material, and an electrochemical device including the negative electrode active material. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

A negative electrode active material, a method for producing the same, and an electrochemical device including the negative electrode active material.

With the explosive increase in the use of portable electronic devices and the expectation for the development of electric vehicles, the research is being conducted to replace carbon, which is an anode active material of lithium secondary batteries, which are being used.

Substances that can replace carbon include the same family elements silicon, tin, and germanium. Among them, silicon has a capacity 10 times higher than that of carbon (4200 mAh / g), and there is a large amount on the earth as much as carbon, and it is economically more economical than other substitute materials, .

However, despite active research, it has a fatal disadvantage and is not easily commercialized compared to carbon. Instead of implementing high capacity, silicon reacts with lithium as the cycle progresses, expanding more than three times its original volume, losing its original shape, thus reducing its capacity and keeping its initial capacity. In addition, the compound reacts with lithium at the time of charging to form a compound. This material is thermodynamically unstable, and when exposed to a shock or exposure to a high temperature, a large amount of energy is released to cause explosion of the lithium secondary battery, .

Therefore, many researchers are working on various aspects to overcome the disadvantages of silicon. Silicon can be modified to have various forms, or to make various materials and compounds. Among them, the simplest method is to coat the silicon surface with other materials. The most commonly used materials for coating are carbon, carbon inhibits the volume expansion of silicon, improves low electrical conductivity and can improve the performance of lithium secondary batteries. However, carbon also has the disadvantage of reacting with lithium to form an unstable layer between the material and the electrolyte.

One embodiment is to provide a negative active material which is effectively inhibited in volume expansion and is excellent in electric conductivity, ionic conductivity and interfacial stability, and a method for producing the same.

Another embodiment is to provide an electrochemical device excellent in high rate characteristics, life characteristics, and thermal stability.

In one embodiment of the present invention, a material capable of doping and dedoping lithium; A first coating layer formed on a surface of a material capable of doping and dedoping lithium and comprising a carbonaceous material; And a second coating layer formed on the outer surface of the first coating layer and including a chemically crosslinked polymer.

The material capable of doping and dedoping lithium may be selected from the group consisting of carbon-based materials, silicon (Si), SiO _x (0 <x≤2), Si-Y ¹ alloy, silicon-carbon composite material, tin (Sn) (Ge) based materials, and combinations thereof. In the Si-Y ^1, Y ¹ is a metal, alkaline earth metal, a Group 13 to 16 element, transition metal, rare earth element, or a combination of these, silicon is removed from Y ^1.

The material capable of doping and dedoping lithium may be porous.

The surface of the material capable of doping and dedoping lithium may be amorphous, crystalline, or a mixture of crystalline and amorphous.

The chemically crosslinked polymer may be a polymer capable of moving lithium ions.

The chemically crosslinked polymer may be selected from the group consisting of imide, acrylate, urethane, urea, ether, ester, amide, sulfoxide and epoxy epoxy, and the like.

The chemically crosslinked polymer may be, for example, polyimide, polyacrylate, or a combination thereof.

The chemically crosslinked polymer may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium.

The thickness of the second coating layer may be 1 nm to 500 nm.

The surface of the negative electrode active material may be amorphous, crystalline, or a mixture of crystalline and amorphous.

The average particle diameter of the negative electrode active material may be 10 nm to 100 mu m.

In another embodiment of the present invention, there is provided an electrochemical device including a negative electrode, a positive electrode, and an electrolyte solution including the negative active material.

The electrochemical device may be a lithium secondary battery.

According to another embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: forming a first coating layer by coating a carbon material on a surface of a material capable of doping and dedoping lithium; Coating a crosslinkable compound on the outer surface of the first coating layer; And chemically crosslinking the crosslinkable compound to form a second coating layer.

The carbon material may be included in an amount of 1 to 40 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium.

The crosslinkable compound may be contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium.

The crosslinkable compound may be a polyamic acid, an acrylate containing monomer, or a combination thereof.

The step of coating the crosslinkable compound includes mixing the crosslinkable compound and a solvent to prepare a polymer solution; Introducing into the polymer solution a substance in which a first coating layer is formed on a surface of a substance capable of doping and dedoping lithium; And removing the solvent.

The solvent may be water, alcohol, acetone, tetrahydrofuran, situhexane, carbon tetrachloride, chloroform, methylene chloride, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N- methylpyrrolidone, .

The step of chemically crosslinking the crosslinkable compound to form the second coating layer may be performed by thermal crosslinking or ultraviolet crosslinking of the crosslinkable compound.

The second coating layer may include at least one selected from the group consisting of imide, acrylate, urethane, urea, ether, ester, amide, sulfoxide, and epoxy epoxy-functional cross-linking polymer.

The thickness of the second coating layer may be 1 nm to 500 nm.

The average particle diameter of the negative electrode active material may be 10 nm to 100 mu m.

According to another embodiment of the present invention, there is provided an electrochemical device including a negative electrode, a positive electrode, and an electrolyte solution including a negative electrode active material prepared according to the above manufacturing method.

The electrochemical device may be a lithium secondary battery.

Other details of the embodiments of the present invention are included in the following detailed description.

The negative electrode active material according to an embodiment has high electrical conductivity and ionic conductivity, and effectively suppresses volume expansion and side reaction with the electrolyte.

The electrochemical device according to another embodiment is excellent in high rate characteristics, life characteristics, and thermal stability.

1 is a schematic view showing a lithium secondary battery according to one embodiment.
2 is a schematic view of an anode active material according to one embodiment.
3 is a schematic view of a negative electrode active material according to another embodiment.
4 is a scanning electron microscope (SEM) photograph of the surface shape of the negative electrode active material of Comparative Example 2. Fig.
5 is a scanning electron microscope (SEM) photograph of the surface shape of the negative electrode active material of Example 1. Fig.
6 is a voltage change curve according to the first capacity of the coin battery manufactured in Example 1, Comparative Example 1 and Comparative Example 2. FIG.
7 is a graph showing the charging / discharging lifetime characteristics of the coin cell manufactured in Example 1, Comparative Example 1, and Comparative Example 2. Fig.
8 is a graph showing charge-discharge lifetime characteristics according to the C-rate of the coin battery manufactured in Example 1, Comparative Example 1 and Comparative Example 2. FIG.
FIG. 9 shows the results of measurement of the differential scanning calorie of the coin cell electrodes of Example 1 and Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In one embodiment of the present invention, a material capable of doping and dedoping lithium; A first coating layer formed on a surface of a material capable of doping and dedoping lithium and comprising a carbonaceous material; And a second coating layer formed on the outer surface of the first coating layer and including a chemically crosslinked polymer.

The negative electrode active material can effectively suppress the expansion of a substance capable of doping and dodoping lithium, and the interfacial amount of the negative electrode active material and the electrolyte generated during charging and discharging can be reduced to improve the thermal stability of the battery.

The negative electrode active material includes a first coating layer containing a carbonaceous material, and is excellent in electronic conductivity and includes a second coating layer containing a chemically crosslinked polymer. Thus, the lithium ion is smoothly transferred, and adhesion, solvent resistance, electrochemical stability And so on.

The electrochemical device including the negative electrode active material is excellent in high rate characteristics, life characteristics, and thermal stability.

The material capable of doping and dedoping lithium may be at least one selected from the group consisting of a carbon-based material, a silicon-based material, a tin-based material, a germanium-based material, Lt; / RTI &gt;

The silicon-based material may be silicon (Si), SiO _x (0 <x? 2), Si-Y ¹ alloy, or silicon-carbon composite. In the Si-Y ^1, Y ¹ is a metal, alkaline earth metal, a Group 13 to 16 element, transition metal, rare earth element, or a combination of these, silicon is removed from Y ^1.

The Y ¹ may be at least ^{one selected} from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr), hafnium (Hf), ruthenium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dibonium (Db), chromium (Cr), molybdenum (Mo), tungsten Rhodium (Rh), rhodium (Rh), ruthenium (Ru), osmium (Os), hydrosium (Hs), rhodium (Rh) (Ir), Pd, Pt, Cu, Ag, Au, Cd, B, Al, , Gallium (Ga), silicon (Si), tin (Sn), indium (In), germanium (Ge), phosphorus (P), arsenic (As), antimony (Sb), bismuth ), Selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

The silicon-based material may be in various forms such as silicon wafer, silicon powder, porous silicon, porous silicon oxide, and the like.

Particularly, in the case where the material capable of doping and dedoping lithium is silicon, the lithium ion is reacted with lithium as the cycle progresses, thereby expanding three times or more than the existing volume, thereby losing the existing shape. The volume expansion due to the progress of the cycle can be effectively suppressed.

The tin-based material may be tin, tin oxide, tin alloy, tin-carbon composite, or the like. The germanium-based material may be germanium, germanium oxide, germanium alloy, germanium-carbon composite, or the like. The tin-based material and germanium-based material may also be porous.

The porous material can be used as a material capable of doping and dedoping lithium. In this case, interfacial stability between the negative electrode active material and the electrolyte can be improved and the volume expansion can be effectively suppressed.

The surface of the material capable of doping and dedoping lithium may be amorphous, crystalline, or a mixture of crystalline and amorphous.

The carbon material may specifically be natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or the like. The carbon material may be formed by, for example, pyrolysis of acetylene.

The negative electrode active material includes a first coating layer containing the carbonaceous material, so that excellent electrical conductivity can be realized.

The chemically crosslinked polymer may be any polymer capable of moving lithium ions. The chemically crosslinked polymer may be one formed by thermal crosslinking or ultraviolet (UV) crosslinking.

  Specifically, the chemically crosslinked polymer may be an imide, an acrylate, a urethane, a urea, an ether, an ester, an amide, a sulfoxide, An epoxy, and the like.

For example, the chemically crosslinked polymer may be polyimide, polyacrylate, or a combination thereof.

For example, the chemically crosslinked polymer may be a polyimide formed through thermal crosslinking of a polyamic acid.

As another example, the chemically crosslinked polymer may be a polyacrylate crosslinked from a monomer containing an acrylate. Specifically, it may be poly (tri-acrylate) or poly (trimethylopropane ethoxylate triacrylate) (poly (trimethylpropane ethoxylate triacrylate)).

The chemically crosslinked polymer may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium. Specifically, it may be 0.01 to 3 parts by weight, 0.01 to 1 part by weight, 0.1 to 5 parts by weight, 0.1 to 1 part by weight, 0.3 to 5 parts by weight, and 0.4 to 5 parts by weight. When the above-mentioned chemically crosslinked polymer is included in the above range, the negative electrode active material can effectively suppress the volume expansion while maintaining excellent electrochemical characteristics, and improve the conductivity of lithium ion.

The thickness of the second coating layer may be 1 nm to 500 nm. Specifically, 1 nm to 400 nm, and 1 nm to 300 nm. When the thickness of the second coating layer satisfies the above range, the negative electrode active material can effectively suppress the volume expansion while maintaining excellent electrochemical characteristics and improve the conductivity of lithium ions.

The average particle diameter of the negative electrode active material may be 10 nm to 100 mu m. Specifically, it may be 50 nm to 100 탆, 100 nm to 100 탆, 500 nm to 100 탆, and 1000 nm to 100 탆. When the average particle diameter of the negative electrode active material satisfies the above range, the battery including the negative electrode active material can exhibit excellent high rate characteristics, life characteristics, and thermal stability.

According to another embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: forming a first coating layer by coating a carbon material on a surface of a material capable of doping and dedoping lithium; Coating a crosslinkable compound on the outer surface of the first coating layer; And chemically crosslinking the crosslinkable compound to form a second coating layer.

2 is a schematic view of a negative electrode active material prepared by the above method. 2, the shape of a negative electrode active material into which a first coating layer containing a carbon material and a second coating layer including a chemically crosslinked polymer are sequentially introduced on the surface of a material capable of doping and dedoping lithium can be confirmed .

FIG. 3 is a schematic view of a negative electrode active material prepared according to another embodiment, in which a first coating layer and a second coating layer are sequentially introduced onto the surface of a porous material.

A description of the material capable of doping and dedoping lithium is as described above.

The carbon material may specifically be natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or the like. The step of forming the first coating layer may be performed, for example, by thermal decomposition of acetylene or the like.

The carbon material may be included in an amount of 1 to 40 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium. Specifically 1 to 30 parts by weight, 1 to 20 parts by weight, 10 to 40 parts by weight, and 10 to 30 parts by weight. When the carbon material is included in the above range, excellent electrical conductivity of the negative electrode active material can be realized.

The crosslinkable compound is not particularly limited, but is preferably a polyamide acid, an acrylate-containing monomer, a urethane-containing monomer, a urea-containing monomer, an ether-containing monomer, an ester- Monomers, sulfoxide-containing monomers and epoxy-containing monomers, or combinations thereof. As an example, it may be a polyamic acid, an acrylate-containing monomer.

The crosslinkable compound may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium. Specifically 0.01 to 1 part by weight, 0.1 to 5 parts by weight, and 0.1 to 1 part by weight. When the cross-linkable compound is included in the above range, the negative electrode active material can effectively suppress the volume expansion while maintaining excellent electrochemical characteristics, and improve the conductivity of lithium ion.

Specifically, the step of coating the crosslinkable compound includes: preparing a polymer solution by mixing the crosslinkable compound and a solvent; Introducing into the polymer solution a substance in which a first coating layer is formed on a surface of a substance capable of doping and dedoping lithium; And removing the solvent.

The solvent may be, for example, water, an alcohol, acetone, tetrahydrofuran, situhexane, carbon tetrachloride, chloroform, methylene chloride, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, Lt; / RTI &gt;

The step of chemically crosslinking the crosslinkable compound to form the second coating layer may be performed by thermal crosslinking or ultraviolet crosslinking of the crosslinkable compound.

The second coating layer formed by the above method comprises a chemically crosslinked polymer. The chemically crosslinked polymer is a polymer capable of transferring lithium ions.

The negative electrode active material comprising the second coating layer prepared according to the above method is excellent in adhesion, solvent resistance, electrochemical stability, and the like.

The second coating layer may be formed of, for example, an imide, an acrylate, a urethane, a urea, an ether, an ester, an amide, a sulfoxide And a functional group formed of an epoxy. The term &quot; functional group &quot; Specifically, the chemically crosslinked polymer may be a polyimide, a polyacrylate, or a combination thereof.

The chemically crosslinked polymer may be, for example, polyimide formed through thermal crosslinking of polyamic acid.

As another example, the chemically crosslinked polymer may be poly (tri-acrylate), and specifically may be poly (trimethylopropane ethoxylate triacrylate) (poly (trimethylpropane ethoxylate triacrylate) have.

The thickness of the second coating layer may be 1 nm to 500 nm. Specifically, 1 nm to 400 nm, and 1 nm to 300 nm. When the thickness of the second coating layer satisfies the above range, the negative electrode active material can effectively suppress the volume expansion while maintaining excellent electrochemical characteristics and improve the conductivity of lithium ions.

The surface of the negative electrode active material may be amorphous, crystalline, or a mixture of crystalline and amorphous.

The average particle diameter of the negative electrode active material may be 10 nm to 100 mu m. Specifically, it may be 50 nm to 100 탆, 100 nm to 100 탆, 500 nm to 100 탆, and 1000 nm to 100 탆. When the average particle diameter of the negative electrode active material satisfies the above range, the battery including the negative electrode active material can exhibit excellent high rate characteristics, life characteristics, and thermal stability.

According to another embodiment of the present invention, there is provided an electrochemical device including a negative electrode, a positive electrode, and an electrolyte including the negative active material.

The electrochemical device may be a battery, a capacitor, or the like, and may be specifically a lithium secondary battery.

A lithium secondary battery according to one embodiment will be described with reference to FIG. 1 is a schematic view showing a lithium secondary battery according to one embodiment. 1, a lithium secondary battery 100 according to an embodiment includes a cathode 114, a cathode 112 opposed to the anode 114, a separator 112 disposed between the anode 114 and the cathode 112, An electrode assembly including an electrode assembly 113 and an electrolyte solution (not shown) for impregnating the anode 114, the cathode 112 and the separator 113; and a battery container 120 containing the electrode assembly, And a sealing member 140 sealing the sealing member 120.

The negative electrode 112 includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes a negative electrode active material.

The negative electrode active material is as described above.

The negative electrode active material layer may further include a binder and / or a conductive material.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any material can be used as long as it does not cause any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, , Carbon-based materials such as carbon fibers; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The positive electrode 114 includes a current collector and a positive electrode active material layer formed on the current collector, and the positive electrode active material layer includes a positive electrode active material.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, it is possible to use at least one of complex oxides of cobalt, manganese, nickel or a combination of metals and lithium, and specific examples thereof include compounds represented by any one of the following formulas. Li _a A _{1 - b} R _b D ₂ wherein, in the formula, 0.90? A? 1.8 and 0? B? 0.5; Li _a E _{1 - b} R _b O _{2 - c} D _c , wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05; LiE _{2 - b} R _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -bc} Co _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 - b - c} Co _b R _c O _{2 - ?} Z _{? Wherein} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Co _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z _{? Where the} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a MnG _b O ₂ wherein, in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1; Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise, as a coating element compound, an oxide, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be carried out by any of coating methods such as spray coating, dipping, and the like without adversely affecting the physical properties of the cathode active material by using these elements in the above compound. It is a content that can be well understood by people engaged in the field, so detailed explanation will be omitted.

The cathode active material layer may also include a binder and a conductive material.

The binder serves to adhere the positive electrode active materials to each other and to adhere the positive electrode active material to the current collector. Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinyl pyrrolidone But are not limited to, polyurethane, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

As the current collector, Al may be used, but the present invention is not limited thereto.

The negative electrode and the positive electrode are prepared by mixing an active material, a binder and a conductive material in a solvent to prepare an active material composition, and applying the composition to a current collector. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein. As the solvent, N-methylpyrrolidone or the like can be used, but it is not limited thereto.

The electrolytic solution includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate , Ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like can be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, An amide such as dimethylformamide in which nitriles such as methylene chloride or dimethylformamide may be used, and dioxolanes such as 1,3-dioxolane, sulfolane, and the like can be used.

The non-aqueous organic solvent may be used alone or in admixture of one or more. If the non-aqueous organic solvent is used in combination, the mixing ratio may be appropriately adjusted according to the desired cell performance. .

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The non-aqueous organic solvent may further include the aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

The non-aqueous electrolyte may further include a vinylene carbonate or an ethylene carbonate-based compound to improve battery life.

Representative examples of the ethylene carbonate-based compound include, for example, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, vinylene Ethylene carbonate, and the like. When the vinylene carbonate or the ethylene carbonate compound is further used, the amount of the vinylene carbonate or the ethylene carbonate compound can be appropriately controlled to improve the life.

The lithium salt is dissolved in the non-aqueous organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery, and a material capable of promoting the movement of lithium ions between the positive electrode and the negative electrode to be. The lithium salt Representative examples are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y ₊₁ SO ₂₎ (where, x and y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2 ( lithium bis oxalate reyito borate (lithium bis (oxalato) borate; LiBOB) , or in a combination thereof The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity Can exhibit excellent electrolyte performance, and lithium ions can effectively migrate.

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ion, and any separator can be used as long as it is commonly used in a lithium battery. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a polyolefin-based polymer separator such as polyethylene, polypropylene and the like is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer substance may be used for heat resistance or mechanical strength, Structure.

Hereinafter, examples and comparative examples of the present invention will be described. The following embodiments are only examples of the present invention and the present invention is not limited to the following embodiments.

( Example  One)

Production of negative electrode active material

The porous silicon powder is put into a tube-shaped heat treatment apparatus and acetylene gas (C ₂ H ₂ ) is flowed at 900 ° C. for about 10 minutes to coat about 10 to 15 parts by weight of carbon on the surface of the porous silicon powder.

(4) reacted with monomers of p-phenylenediamine (PDA), oxydianiline (ODA), pyromellitic dianhydride PDMA, and biphenyl dianhydride Component polyamic acid is diluted with a solvent of dimethyl acetamide to a concentration of 0.5% by weight to prepare a polymer solution.

The porous silicon powder coated with carbon is put into the prepared polymer solution and stirred sufficiently. A filter process is performed to remove the unreacted polyamic acid on the powder surface. Thereafter, the resultant was vacuum-dried at room temperature, and the temperature was gradually raised to 400 DEG C in a heat treatment apparatus of nitrogen atmosphere in order to convert polyamic acid into polyimide. Specifically, the imidization reaction proceeds while raising the temperature of the powder coated with the polyamic acid to 60 ° C, 120 ° C, 200 ° C, 300 ° C, and 400 ° C. The polyimide is coated on the surface of the powder in a stable form at 400 DEG C since the temperature at which the polyimide is carbonized is 550 DEG C or higher.

The polyimide synthesized by crosslinking the four-component polyamic acid can be represented by the following formula (1).

[Chemical Formula 1]

In the above formula (1), k, l, m and n represent the number of moles of each repeating unit, and 1? K? 10000, 1? L? 10000, 1? M? 10000 and 1?

In this way, a negative electrode active material in which a carbon layer and a polyimide layer are sequentially introduced on the porous silicon surface was prepared.

The prepared negative electrode active material was confirmed by a scanning electron microscope (SEM). FIG. 4 is a photograph of a porous silicon powder coated with carbon, and FIG. 5 is a photograph of a negative electrode active material into which a polyimide layer is introduced after carbon coating.

Lithium secondary battery ( Half - cell )

Super P was mixed with the water used as a solvent at a weight ratio of 1: 1, and poly (acrylic acid) (PAA) / cellulose (CMC) To prepare a negative electrode active material slurry. This was uniformly coated on a copper foil and vacuum dried to produce a negative electrode.

Lithium metal foil was used as a counter electrode, and polypropylene (PP) was used as a separator. A coin cell was prepared using EC: DEC (volume ratio 3: 7) with LiPF ₆ added to contain 5 wt% of the additive FEC as the electrolyte and 1.3 M.

( Comparative Example  One)

A coin cell was prepared in the same manner as in Example 1, except that the porous silicon powder itself was used as the negative electrode active material.

( Comparative Example  2)

A coin cell was prepared in the same manner as in Example 1, except that only the carbon layer was introduced into the porous silicon powder in Example 1 and the polyimide layer was not introduced into the negative electrode active material.

Evaluation example  1: Charging and discharging  Evaluation of life characteristics

The coin cells prepared in Example 1, Comparative Example 1 and Comparative Example 2 were subjected to a constant current test using a charging / discharging device capable of constant current / constant potential control at 25 ° C. The results are shown in FIGS. 6 and 7.

Of capacity with the respective coin cells C / 5 (lithiation, charge) C / 2 (Delithiation, discharge) was applied to a constant current that corresponds to the rate, the discharge (delithiation) end voltage is ^{1.2 V (vs. Li / Li +} ) And the termination of the lithiation was fixed at 0.005 V (vs. Li / Li ⁺ ), respectively.

FIG. 6 is a voltage variation curve according to the one cycle capacity, and FIG. 7 is a capacity variation curve when charge and discharge are performed up to 80 times.

6 and 7, in Comparative Example 1 using porous silicon itself as a negative electrode active material, no coating layer was introduced, which indicates that the initial irreversibility is very large due to the low electrical conductivity of silicon. On the other hand, in the case of Comparative Example 2 and Example 1 in which carbon was coated, the initial irreversibility was greatly reduced by increasing the electric conductivity.

The capacity of Example 1 was higher than that of Comparative Example 2. This is because the polyimide coating layer has a high ionic conductivity to facilitate the passage of lithium ions.

Evaluation example  2: C- rate In accordance Charging and discharging  Evaluation of life characteristics

Experiments were carried out by varying the constant current rate of the coin cell manufactured in Example 1, Comparative Example 1 and Comparative Example 2 using a charging / discharging device capable of constant current / constant potential control at 25 ?.

The experimental conditions were as follows: 0.2 - 0.5 - 1 - 3 - 5 - 10 - 15 C - rate based on the capacity of each coin cell, and the delithiation termination voltage was 1.2 V (vs. Li / Li &lt; + &gt;) and the end-of-lithiation voltage was fixed to 0.005 V (vs. Li / Li ⁺ ).

The experimental results are shown in Fig. Referring to FIG. 8, in Comparative Example 2 in which polyimide was not coated, the performance was only 13% at 10 C compared with the condition at 0.2 C, whereas in Example 1 using 0.5 wt% , The performance was maintained at 75% at 10 C compared with 0.2 C. As a result, it can be seen that the high-rate lifetime characteristics of the examples are significantly superior to those of the comparative examples.

Evaluation example  3: Thermal safety evaluation

A constant current was applied to the coin cell prepared in Example 1 and Comparative Example 2 using a charge / discharge device capable of constant current / constant potential control at 25 ?. The delithiation termination voltage was 1.2 V (vs. Li / Li ⁺ ), And the ending voltage of the lithiation was fixed to 0.005 V (vs. Li / Li +), respectively.

(Li _x Si _y ) was prepared by differential scanning calorimetry (DSC). The results are shown in Fig.

9 shows the results of differential scanning calorimetry. In Comparative Example 2, the polyimide coating is not the entire amount of heat generated is 924 Jg ^-1 On the other hand, 525 Jg in Example 1 of 0.5 wt% polyimide is coated on a ^surface to determine that it has the overall heating value reduced by ^a factor have.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

Claims (25)

A material capable of doping and dedoping lithium;
A first coating layer formed on a surface of a material capable of doping and dedoping lithium and comprising a carbonaceous material; And
A second coating layer formed on the outer surface of the first coating layer and including a chemically crosslinked polymer;
/ RTI &gt; The method of claim 1,
The material capable of doping and dedoping lithium may be selected from the group consisting of carbon-based materials, silicon (Si), SiO _x (0 <x≤2), Si-Y ¹ alloy, silicon-carbon composite material, tin (Sn) (Ge) based material, and a combination thereof.
In the Si-Y ^1, Y ¹ is a metal, alkaline earth metal, a Group 13 to 16 element, transition metal, rare earth element, or a combination of these, silicon is removed from Y ^1. The method of claim 1,
Wherein the material capable of doping and dedoping lithium is porous. The method of claim 1,
Wherein the surface of the material capable of doping and dedoping lithium is amorphous, crystalline, or a mixture of crystalline and amorphous. The method of claim 1,
Wherein the chemically crosslinked polymer is a polymer capable of moving lithium ions. The method of claim 1,
The chemically crosslinked polymer may be selected from the group consisting of imide, acrylate, urethane, urea, ether, ester, amide, sulfoxide and epoxy wherein the negative active material is a polymer comprising at least one of a functional group consisting of an epoxy functional group. The method of claim 1,
Wherein the chemically crosslinked polymer is polyimide, polyacrylate, or a combination thereof. The method of claim 1,
Wherein the chemically crosslinked polymer is contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium. The method of claim 1,
And the second coating layer has a thickness of 1 nm to 500 nm. The method of claim 1,
Wherein the average particle diameter of the negative electrode active material is 10 nm to 100 탆. The method of claim 1,
Wherein the negative electrode active material is porous. A negative electrode comprising the negative active material according to any one of claims 1 to 11,
Anode, and
An electrochemical device comprising an electrolytic solution. The method of claim 12,
Wherein the electrochemical device is a lithium secondary battery. Coating a surface of a material capable of doping and dedoping lithium with a carbon material to form a first coating layer;
Coating a crosslinkable compound on the outer surface of the first coating layer; And
Chemically crosslinking the crosslinkable compound to form a second coating layer;
And a negative electrode active material. The method of claim 14,
Wherein the carbon material is included in an amount of 1 to 40 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium. The method of claim 14,
Wherein the crosslinkable compound is contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the material capable of doping and dedoping the lithium. The method of claim 14,
Wherein the crosslinkable compound is a polyamic acid, an acrylate-containing monomer, or a combination thereof. The method of claim 14,
The step of coating the crosslinkable compound
Mixing the crosslinkable compound and a solvent to prepare a polymer solution;
Introducing a substance in which a first coating layer is formed on the surface of a substance capable of doping and dedoping lithium into the polymer solution; and
And removing the solvent. The method of claim 18,
Wherein the solvent is at least one selected from the group consisting of water, alcohols, acetone, tetrahydrofuran, situhexane, carbon tetrachloride, chloroform, methylene chloride, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, &Lt; / RTI &gt; The method of claim 14,
The step of chemically crosslinking the crosslinkable compound to form a second coating layer
Wherein said crosslinking is performed through thermal crosslinking or ultraviolet crosslinking of said crosslinkable compound. The method of claim 14,
The second coating layer may include at least one selected from the group consisting of imide, acrylate, urethane, urea, ether, ester, amide, sulfoxide, and epoxy wherein the chemical crosslinking polymer comprises at least one functional group selected from the group consisting of epoxy, The method of claim 14,
And the thickness of the second coating layer is 1 nm to 500 nm. The method of claim 14,
Wherein the average particle diameter of the negative electrode active material is 10 nm to 100 mu m. A negative electrode comprising a negative electrode active material produced by the method of any one of claims 14 to 23,
Anode, and
An electrochemical device comprising an electrolytic solution. 25. The method of claim 24,
Wherein the electrochemical device is a lithium secondary battery.

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