KR101637383B1 - lithium secondary battery employing a anode containing silicon quantum dot - Google Patents

Abstract

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including a negative electrode containing a silicon quantum dot polymer.

Description

[0001] The present invention relates to a lithium secondary battery employing a negative electrode containing a silicon quantum dot polymer,

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery employing a silicon quantum dot polymer as a negative electrode.

 The secondary battery is classified into a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen (Ni-MH) battery and a lithium battery according to an anode material and a cathode material. The potential and the energy density are determined. Among them, lithium secondary batteries are widely used as driving power sources for portable electronic devices such as notebook computers, camcorders, and mobile phones because of their high energy density due to the low oxidation / reduction potential and molecular weight of lithium.

In recent years, portable electronic devices have been widespread, and these portable electronic devices have become thinner, smaller, and lighter. As a result, a secondary battery used as a power source of the portable electronic device is small and lightweight and can be charged and discharged for a long time. Efforts are concentrated.

On the other hand, the performance improvement of lithium secondary battery is fundamentally based on the performance improvement of the four core components composed of cathode, anode, separator and electrolyte. Among them, improvement of performance of cathode is focused on capacity increase through development of cathode material It is set.

Conventionally, lithium metal is used as a negative electrode active material of a lithium secondary battery. However, in this case, due to the formation of a dendrite, a short circuit of the battery occurs and a risk of explosion is present. Therefore, carbonaceous anode active material is used instead of lithium metal. Examples of such carbonaceous anode active materials include crystalline carbon such as graphite and artificial graphite, amorphous carbon such as soft carbon and hard carbon, and graphite among crystalline carbon is a typical example .

However, the carbon-based negative electrode active material such as graphite has a limited upper limit of the theoretical capacity, and thus there is a limit to the application of high capacity lithium to secondary batteries.

In order to overcome the above problems, metal-based anode active materials have been actively studied. For example, silicon (Sn), aluminum (Al), germanium (Ge), lead (Pb), zinc ) Has been studied as a negative electrode active material. Such a material mentioned above can absorb and release more lithium ions than the carbon-based anode active material, and is suitable for manufacturing a battery having a high capacity and a high energy density.

In particular, silicon is a material with a high theoretical capacity of up to about 4200 mAh / g.

However, silicone has poor cycle characteristics than the carbon-based negative active material because, when silicon is used as a material for intercalating and deintercalating lithium ions, electrical contact between the active materials is deteriorated due to volume change during charging and discharging, The active material is peeled off from the substrate. That is, the silicon contained in the negative electrode active material expands by 300% or more due to the filling, and the mechanical stress applied at this time causes a crack in the electrode and the surface of the electrode. If the charge / discharge cycle is repeated, the active material may be separated from the current collector, and a space may be formed between the silicon particles and the active material, resulting in electrical insulation. There is a problem.

Korean Patent Laid-Open Publication No. 2013-0138915 discloses a silicon-based anode improved in battery characteristics, but research is still required to solve the above problems.

Korean Patent Laid-Open Publication No. 2013-0138915

Disclosed is a lithium secondary battery employing a silicon quantum dot polymer as an anode material, which does not generate a short circuit during charging and discharging and thus has excellent cycle characteristics.

The present invention provides a lithium secondary battery, wherein the lithium secondary battery of the present invention employs a negative electrode containing a silicon quantum dot polymer in which a polymer linked to each other by a unit represented by the following formula (1) is bonded to the surface of a silicon quantum dot.

[Chemical Formula 1]

(In the formula 1,

Ar is (C6-C12) arylene or (C3-C12) heteroarylene;

R ₁ to R ₄ are independently of each other hydrogen, halogen, hydroxy (C 1 -C 10) alkyl, (C 6 -C 12) aryl or (C 6 -C 12) aryl (C 1 -C 10) alkyl;

n and m are independently an integer of 0 to 5, and when n and m are 2 or more, R ₁ to R ₄ may be mutually different or the same;

The arylene or heteroarylene of Ar may be further substituted with halogen, amino, hydroxy or (C1-C10) alkyl.

Preferably, Ar in formula (1) according to an embodiment of the present invention is (C6-C12) arylene; R ₁ to R ₄ independently of each other may be hydrogen, halogen or (C 1 -C 10) alkyl.

Preferably, Formula 1 according to an embodiment of the present invention may be represented by Formula 2 below.

(2)

(In the formula (2)

R ₁₁ independently from each other are hydrogen, halogen, amino, hydroxy or (C 1 -C 10) alkyl;

o is an integer of 1 to 4, and when o is 2 or more, each R < ₁₁ > may be the same or different.)

The silicon quantum dot polymer according to an embodiment of the present invention may be prepared from a silicon quantum dot surface-modified with a compound represented by the following formula (3).

(3)

(3)

Ar is (C6-C12) arylene or (C3-C12) heteroarylene;

R ₁ to R ₄ are independently of each other hydrogen, halogen, hydroxy (C 1 -C 10) alkyl, (C 6 -C 12) aryl or (C 6 -C 12) aryl (C 1 -C 10) alkyl;

R ₅ and R ₆ are hydrogen;

n and m are independently an integer of 0 to 5, and when n and m are 2 or more, R ₁ to R ₄ may be mutually different or the same;

The arylene or heteroarylene of Ar may be further substituted with halogen, amino, hydroxy or (C1-C10) alkyl.

The silicon quantum dot polymer according to an embodiment of the present invention comprises: a) reducing a silicon precursor with a reducing agent in the presence of tetraalkylammonium halide to obtain a silicon quantum dot mixture;

b) quenching the silicon quantum dot mixture to obtain a silicon quantum dot solution;

c) preparing a silicon-modified quantum dots by adding a metal catalyst and the above-described chemical formula 3 to the silicon quantum dot solution;

and d) polymerizing the surface-modified silicon quantum dots to prepare a silicon quantum dot polymer.

The reducing agent may be LiAlH ₄ , NaBH ₄ , Na, sodium naphthalenide, sodium benzophenone, Mg ₂ Si, or KSi. The catalyst may be H ₂ PtCl ₆ or platinum (0) -1,3- divinyl-1,1,3,3-tetramethyldisiloxane complex.

Quenching according to one embodiment of the present invention can be performed with CuSO ₄ .

The lithium secondary battery of the present invention employs the silicon quantum dot polymer as the negative electrode material, so that the battery is not short-circuited at the time of volume expansion during charging and discharging, so that the stability is high and the cycle characteristics are excellent.

In addition, the lithium secondary battery of the present invention employs a silicon quantum dot polymer having a high charge mobility as an anode material, and has a high energy density and thus has excellent output characteristics.

FIG. 1 is a view showing the FT-IR spectra of the surface-modified silicon quantum dots prepared in Example 1 and Comparative Example 1,
FIG. 2 is a view showing ¹ H-NMR of the surface-modified silicon quantum dots prepared in Example 1 and Comparative Example 1. FIG.

Hereinafter, the present invention will be described in more detail. Unless otherwise defined, technical terms and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the following description, And a description of the known function and configuration will be omitted.

[0001] The present invention relates to a lithium secondary battery employing a negative electrode containing a silicon quantum dot polymer, and more particularly to a lithium secondary battery comprising a silicon quantum dot polymer having a polymer bonded to each other by a unit represented by the following formula To provide a lithium secondary battery.

[Chemical Formula 1]

(In the formula 1,

Ar is (C6-C20) arylene or (C3-C20) heteroarylene;

n and m are independently an integer of 0 to 5, and when n and m are 2 or more, each of R ₁ to R ₄ may be mutually different or the same;

The arylene or heteroarylene of Ar may be further substituted with halogen, amino, hydroxy or (C1-C10) alkyl.

Since the lithium secondary battery of the present invention includes the silicon quantum dot polymer unlike the conventional silicon based negative electrode material, the battery is not easily short-circuited to the volume expansion upon charging and discharging, so that the battery has high stability and excellent cycle characteristics.

Meanwhile, the conventional silicon-based anode material is obtained by physically mixing silicon nano-crystals together with a nonconductive binder polymer such as polyvinylidene fluoride (PVdF) or styrene butadiene rubber (SBR), and adding a conductive additive such as carbon black to the electrical conductivity And it is not suitable for a silicon-based negative electrode of a high capacity which has a very large volume change during charging and discharging.

That is, when the silicon nanocrystals and the binder polymer and the conductive additive are simply combined physically and used as the negative electrode material, the battery is short-circuited due to a large volume change during charging and discharging, which not only degrades the battery stability but also lowers the cycle characteristics.

On the other hand, the negative electrode material of the present invention has a network structure in which the polymer including the unit of Formula 1 bonded to the silicon quantum dots is connected to the net structure without using a binder and a conductive additive, .

Further, since the polymer comprising the unit represented by Formula 1 is connected to the surface of the silicon quantum dots by a chemical bond of a net structure, the lithium secondary battery of the present invention has high stability at high temperature or low temperature, And the unit represented by the above formula (1) of the silicon quantum dot polymer has a high charge mobility, and the lithium secondary battery employing the negative electrode material has high output characteristics.

The substituents comprising " alkyl ", " alkoxy " and other " alkyl " moieties described in this invention encompass both linear and branched forms. The term " aryl " in the present invention means an organic radical derived from an aromatic hydrocarbon by the removal of one hydrogen, and may be a single or fused ring containing 4 to 7, preferably 5 or 6 ring atoms, A ring system, and a form in which a plurality of aryls are connected by a single bond. Specific examples include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, indenyl, fluorenyl, and the like. "Heteroaryl" in the present invention includes 1 to 4 heteroatoms selected from B, N, O, S, P (= O), Si and P as aromatic ring skeletal atoms and the remaining aromatic ring skeletal atoms are carbon Means a 5 to 6 membered monocyclic heteroaryl and a polycyclic heteroaryl condensed with at least one benzene ring and may be partially saturated. The heteroaryl in the present invention also includes a form in which one or more heteroaryl is connected to a single bond.

In Formula 1 according to an embodiment of the present invention, Ar is (C6-C12) arylene; R ₁ to R ₄ independently of each other may be hydrogen, halogen or (C 1 -C 10) alkyl.

From the viewpoint of having high output characteristics, stability and cycle characteristics, the above-mentioned formula (1) can be represented by the following formula (2).

 (2)

(In the formula (2)

R ₁₁ independently from each other are hydrogen, halogen, amino, hydroxy or (C 1 -C 10) alkyl;

o is an integer of 1 to 4, and when o is 2 or more, each R < ₁₁ > may be the same or different.)

The silicon quantum dot polymer according to an embodiment of the present invention may be prepared from a silicon quantum dot surface-modified with a compound represented by the following formula (3).

(3)

(3)

Ar is (C6-C20) arylene or (C3-C20) heteroarylene;

R ₁ to R ₄ are independently of each other hydrogen, halogen, hydroxy (C 1 -C 10) alkyl, (C 6 -C 12) aryl or (C 6 -C 12) aryl (C 1 -C 10) alkyl;

R ₅ and R ₆ are hydrogen;

n and m are independently an integer of 0 to 5, and when n and m are 2 or more, R ₁ to R ₄ may be mutually different or the same;

The arylene or heteroarylene of Ar may be further substituted with halogen, amino, hydroxy or (C1-C10) alkyl.

The silicon quantum dot polymer according to an embodiment of the present invention may be prepared by polymerization using Ru catalyst or Pd catalyst based Sonogashira coupling from the above formula (3), but is not limited thereto.

More specifically, the silicon quantum dot polymer according to an embodiment of the present invention comprises: a) reducing a silicon precursor with a reducing agent in the presence of tetraalkylammonium halide to obtain a silicon quantum dot mixture;

b) quenching the silicon quantum dot mixture to obtain a silicon quantum dot solution;

c) preparing a silicon-modified quantum dots by adding a metal catalyst and the above-described chemical formula 3 to the silicon quantum dot solution;

and d) polymerizing the surface-modified silicon quantum dots to prepare a silicon quantum dot polymer.

The reducing agent according to an embodiment of the present invention may be LiAlH ₄ , NaBH ₄ , Na, sodium naphthalenide, sodium benzophenone, Mg ₂ Si, or KSi, and may be used in an amount of 2 to 4 moles per mole of the silicon precursor.

The catalyst according to an embodiment of the present invention may be H ₂ PtCl ₆ or platinum (0) -1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex, 0.004 mole.

In a tetraalkylammonium halide according to one embodiment of the present invention, the alkyl may be C1-C10 alkyl, and preferred examples thereof may be tetraoctylammonium bromide or tetraoctylammonium chloride.

Quenching according to one embodiment of the present invention can preferably be performed with CuSO ₄ .

The polymerization in step d) according to an embodiment of the present invention may be performed with a dimer (dichloro (p-cymene) ruthenium (II) dimer) or bis (triphenylphosphine) palladium (II) dichloride.

A lithium secondary battery according to an embodiment of the present invention will be described in detail below.

More specifically, the lithium secondary battery of the present invention comprises: a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium; b) a negative electrode comprising a negative electrode active material capable of intercalating and deintercalating lithium; c) the secondary battery electrolyte of the present invention; And d) a separator, wherein the negative electrode active material comprises the silicon quantum dot polymer of the present invention.

The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent, or a mixture thereof for a non-aqueous organic solvent. But it is preferably a linear carbonate-based solvent, a cyclic carbonate-based solvent or a mixed solvent thereof, and most preferably, a linear carbonate-based solvent and a cyclic carbonate-based solvent are mixed and used. The cyclic carbonate solvent has a large polarity, which can sufficiently dissociate lithium ions, but has a disadvantage in that the ion conductivity is low due to the high viscosity. Therefore, by using a linear carbonate solvent having a low polarity but a low viscosity in the cyclic carbonate solvent, the characteristics of the lithium secondary battery can be optimized.

The linear carbonate solvent may be selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) and methyl propyl carbonate And the cyclic carbonate solvent is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2- Terephthalene carbonate, terephthalene carbonate, tilene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), vinylethylene carbonate and fluoroethylene carbonate, and the linear ester solvent is methyl propionate, ethyl propionate Propionate, propyl acetate, butyl acetate, and ethyl acetate. Mixture, and the cyclic ester-based solvent may be alone or a mixture of two or more selected from the group consisting of a lactone with the lactone, caprolactone and ballet as gamma -butyrolactone.

In the electrolyte for a secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent is a mixed solvent of a linear carbonate solvent and a cyclic carbonate solvent, wherein the volume ratio of the linear carbonate solvent to the cyclic carbonate solvent is 1 to 9: 1, preferably in a volume ratio of 2: 8 to 8: 2, in terms of life characteristics and storage characteristics of the battery.

Secondary battery electrolyte according to one embodiment of the present invention comprises a lithium salt, the lithium salt include, but are not in _{limitation, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . _{LiSCN, LiN (C x F 2x} + 1 SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2, One or a mixture of two or more selected from the group consisting of LiF ₂ BC ₂ O ₄ , LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiP (C ₂ O ₄ ) ₃ and LiPO ₂ F ₂ And may preferably be lithium hexafluorophosphate (LiPF ₆ ).

The concentration of the lithium salt is preferably in the range of 0.6 to 2.0 M, and more preferably in the range of 0.8 to 1.5 M, considering the properties related to the electric conductivity and the viscosity associated with the lithium ion mobility. When the concentration of the lithium salt is less than 0.6M, the electric conductivity of the electrolytic solution is lowered, so that the performance of the electrolytic solution which transfers ions at a high speed between the anode and the cathode of the secondary battery decreases. When the concentration exceeds 2.0M, the viscosity of the electrolytic solution increases, There is a problem that the mobility of the mobile terminal is reduced. The lithium salt acts as a source of lithium ions in the battery, thereby enabling operation of a basic lithium secondary battery.

The lithium secondary battery is manufactured by a conventional method, and examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

The positive electrode of the lithium secondary battery according to an embodiment of the present invention includes a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material capable of absorbing and desorbing lithium, a binder, a conductive material, and the like. The positive electrode active material is preferably a composite metal oxide of lithium and at least one element selected from cobalt, manganese, and nickel. In addition to these metals, the employment rate of the metals may be varied. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Sr, V, and a rare earth element. Specific examples of the positive electrode active material may include a compound represented by any one of the following formulas:

Li _a A _1-b B _b D ₂ wherein, in the formula, 0.90? A? 1.8, and 0? B? 0.5; Li _a E _1-b B _b O _{2 -c} D _c wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; 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 wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, 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 ; LiIO 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; B 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; F 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; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

The negative electrode according to an embodiment of the present invention includes a current collector and a negative active material layer formed on the current collector, and the negative active material layer includes the silicon quantum dot polymer of the present invention.

The anode active material layer according to an embodiment of the present invention may be formed of only the silicon quantum dot polymer of the present invention. However, in addition to the silicon quantum dot polymer of the present invention, a carbon active material, a binder, a conductive material, . As the carbon-based active material, a carbon material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber can be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500 ° C. or lower, and mesophase pitch-based carbon fiber (MPCF). The crystalline carbon is a graphite-based material, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbonaceous material is preferably a material having an interplanar distance of 3.35 to 3.38 angstroms and a crystallite size (Lc) of at least 20 nm by X-ray diffraction.

The anode and / or the cathode according to an embodiment of the present invention may be manufactured by dispersing an electrode active material, a binder and a conductive material, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector have. As the positive electrode current collector, aluminum or an aluminum alloy may be commonly used, and copper or a copper alloy may be used as the negative electrode current collector. The anode current collector and the anode current collector may be in the form of a foil or a mesh.

The binder according to one embodiment of the present invention acts as a paste for the active material, mutual adhesion of the active material, adhesion to the current collector, buffering effect on expansion and contraction of the active material, and the like. Anything is possible. For example, there may be mentioned polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, Polyvinylidene fluoride (PVdF), copolymers of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP), poly (vinyl acetate), alkylated polyethylene oxide, polyvinyl ether , Poly (methyl methacrylate), poly (ethyl acrylate), polyacrylonitrile, polyvinylpyridine, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile- Epoxy resin, nylon, and the like can be used, but the present invention is not limited thereto. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesive force between the electrode active material and the current collector is insufficient. If the content of the binder is too large, the adhesive force is improved but the content of the electrode active material is reduced accordingly.

The conductive material according to one embodiment of the present invention is used for imparting conductivity to an electrode, and any material can be used as an electron conductive material without causing any chemical change in the battery. As the conductive material, at least one selected from the group consisting of a graphite-based conductive material, a carbon black-based conductive material, and a metal or metal compound-based conductive material may be used. Examples of the black graphite conductive material include artificial graphite and natural graphite. Examples of the carbon black conductive material include acetylene black, ketjen black, denkablack, thermal black, channel black black or the like. Examples of metal or metal compound conductive agents include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ and LaSrMnO ₃ have. However, the present invention is not limited to the above-mentioned conductive materials. The content of the conductive material is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive material is less than 0.1% by weight, the electrochemical characteristics are deteriorated, and when it exceeds 10% by weight, the energy density per weight is decreased.

The thickening agent according to an embodiment of the present invention is not particularly limited as long as it can control the viscosity of the active material slurry. For example, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and the like are used .

As the solvent in which the electrode active material, the binder, the conductive material and the like are dispersed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The secondary battery of the present invention may include a separator to prevent a short circuit between the positive electrode and the negative electrode and to provide a path for the lithium ion. The separator may be a polypropylene, a polyethylene, a polyethylene / polypropylene, a polyethylene / polypropylene / , Polyolefin-based polymer membranes such as polypropylene / polyethylene / polypropylene, or multi-membranes thereof, microporous films, woven fabrics and nonwoven fabrics. Further, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

The lithium secondary battery of the present invention may have other shapes such as a cylindrical shape, a pouch shape, and the like.

The present invention will be described in detail with reference to the following examples. However, the following examples are only illustrative of the present invention and the scope of the present invention is not limited thereby.

[Example 1] Production of surface-modified silicon quantum dots with 1,4-diethynylbenzene

SiCl ₄ (1.33 g, 7.8 mmol) and tetraoctylammonium bromide (TOAB, 13.5 g) were added to anhydrous toluene (900 mL) and sonicated for 90 minutes. Here _{LiAlH 4 (2M in THF, 27mmol} ) was added and the reduction of SiCl ₄ by ultrasonic treatment for three hours to remove the excess of LiAlH ₄ CuSO ₄ (21 g, 84.6 mmol) was quenched to prepare a silicon quantum dot solution. To the silicon quantum dot solution prepared above in an argon atmosphere, 1,4-diethynylbenzene 30 mL of anhydrous toluene containing 1.5 g and 0.9 mL of a 0.05 MH ₂ PtCl ₆ methanol solution were added, and the mixture was stirred at room temperature for 48 hours. The reaction mixture was distilled under reduced pressure at 40 ° C to remove the solvent. The solvent was separated and purified by column chromatography to prepare a silicon quantum dot that was surface-modified with 1,4-diethynylbenzene as a yellow solid.

The FT-IR spectrum of the surface-modified silicon quantum dots produced is shown in FIG. 1, and FIG. 2 shows ¹ H-NMR.

From FIGS. 1 and 2, it can be seen that a silicon quantum dot surface-modified with 1,4-diethynylbenzene was produced.

[Comparative Example 1] Production of silicon quantum dot surface-modified with 1-octene

1-octene-modified silicon quantum dots were prepared in the same manner as in Example 1, except that 1-octene was used instead of 1,4-diethynylbenzene in Example 1.

1 shows the FT-IR spectra of 1-octene-modified silicon quantum dots, and FIG. 2 shows ¹ H-NMR.

[Example 2] Production of silicon quantum dot polymer

300 mg of the surface modified silicon quantum dots with 1,4-diethynylbenzene and 30.6 mg (0.05 mmol, Sigma Aldrich) of dichloro (p-cymene) ruthenium (II) dimer as a Ru metal catalyst were added to a 100 mL three- The vacuum / argon (Ar) cycle was then repeated three times to remove oxygen and moisture in the flask. 50 mg of the acetic acid / THF solvent prepared in a volume ratio of 3: 2 was separately prepared and the vacuum / argon (Ar) cycle was repeated three times. The silicon quantum dots and 1,4-diethynylbenzene- -cymene) ruthenium (II) dimer in a prepared flask. The reaction mixture was stirred in an argon atmosphere at room temperature for 24 hours. The silicon quantum dot polymer product was precipitated and the solvent was removed and filtered. Washed with methanol and dried in air and vacuum, respectively, to produce pure silicon quantum dot polymer.

[Example 3] Production of silicon quantum dot polymer

4.2 mL of bis (triphenylphosphine) palladium (II) dichloride [Pd (PPh ₃ ) ₂ Cl ₂ ], 1.1 mg of copper (I) iodide (CuI) and 8 mL of triethylamine (TEA) were placed in 200 mL of toluene, After stirring for 1 hour and dispersing, 80 mg of surface modified silicon quantum dots with 1,4-diethynylbenzene and 40 mg of 1,4-diidobenzene were added. The solution was heated at 100 ^° C for 48 hours to complete the reaction, and then all solvents were first removed using a rotary evaporator for purification. The dried solid was washed with acetone, methanol, and methyl chloride, respectively, and dried in a vacuum for one day to prepare a silicon quantum dot polymer.

[Example 4] Production of a lithium secondary battery containing a silicon quantum dot polymer as an anode material.

The silicon quantum dot polymer prepared in Example 3 was mixed with water (H ₂ O) as a solvent to prepare a uniform negative electrode slurry. The prepared negative electrode slurry was coated on one side of the copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a required size to prepare a negative electrode.

LiPF ₆ was added to the non-aqueous electrolyte solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, to prepare a 1 M LiPF ₆ nonaqueous electrolyte solution.

A lithium metal foil was used as a counter electrode, that is, an anode. A polyolefin separator was interposed between both electrodes, and then the electrolyte was injected to prepare a coin type lithium secondary battery.

[Comparative Example 2] Production of a lithium secondary battery comprising a silicon quantum dot surface-modified with 1-octene as an anode material.

(SBR) as a binder, carboxy methylcellulose (CMC) as a thickener, and acetylene black as a conductive material at a weight ratio of 95: 2: 2: 1 prepared in Comparative Example 1 to 1-octene- , And they were mixed together with water (H ₂ O) as a solvent to prepare a uniform negative electrode slurry. The prepared negative electrode slurry was coated on one side of the copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a required size to produce a negative electrode. A battery was prepared.

<Cycle characteristics>

The charge and discharge characteristics of the lithium secondary batteries of Example 4 and Comparative Example 2 were evaluated using a charge-discharge device (WBCS 3000, WON A TECH).

The lithium secondary battery (battery capacity: 3.4 mAh) manufactured in Example 4 and Comparative Example 2 was charged until the constant current (CC) 2 V of 0.1 C was reached and then charged to the constant voltage (CV), and when the charging current reached 0.17 mAh The first charging was performed. Thereafter, the battery was allowed to stand for 10 minutes, and discharged at a constant current of 0.1 C until it reached 10 mV, and the discharge capacity at the first cycle was measured. Subsequently, the batteries of Example 4 and Comparative Example 2 were repeatedly charged and discharged for up to 100 cycles, and the discharge capacity was measured for each cycle. The results are shown in Table 1.

Discharge capacity (mAh / g) Initial efficiency (%) Life characteristics (%) Example 4 1615 76.2% 97% Comparative Example 2 1641 74.9% 86%

- Initial efficiency: (first cycle discharge capacity / first cycle charge capacity) ㅧ 100

- Life characteristics: (49th cycle discharge capacity / first cycle discharge capacity) 100

As shown in Table 1, the lithium secondary battery including the silicon quantum dot polymer of the present invention as the negative electrode material of the present invention had better cycle characteristics than the lithium secondary battery employing the silicon quantum dot surface-modified with 1-octene of Comparative Example 1 as an active material And the lifetime characteristics are remarkably improved.

It is understood that the silicon quantum dot polymer of the present invention has a structure in which the π-organic molecular network is connected to the net, and therefore, the battery does not short-circuit due to the volume expansion during charging and discharging.

That is, since the silicon quantum dot polymer of the present invention is connected to the silicon quantum dot and the conductive polymer by a chemical bond network structure, it has high stability and excellent cycle characteristics without using any conventional binder or conductive additive.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. And various modifications may be made to the invention. Therefore, modifications of the embodiments of the present invention will not depart from the scope of the present invention.

Claims (8)

In the lithium secondary battery,
A lithium secondary battery employing a negative electrode comprising a silicon quantum dot polymer in which a polymer linked to each other by a unit represented by the following formula (2) is bonded to the surface of a silicon quantum dot.
(2)

(In the formula (2)
R ₁₁ independently from each other are hydrogen, halogen, amino, hydroxy or (C 1 -C 10) alkyl;
o is an integer of 1 to 4, and when o is 2 or more, each R &lt; ₁₁ &gt; may be the same or different.) delete delete The method according to claim 1,
Wherein the silicon quantum dot polymer is prepared from a silicon quantum dot surface-modified with a compound represented by the following formula (3).
(3)

(3)
Ar is (C6-C12) arylene;
R ₁ to R ₄ are independently of each other hydrogen, halogen, hydroxy (C 1 -C 10) alkyl, (C 6 -C 12) aryl or (C 6 -C 12) aryl (C 1 -C 10) alkyl;
R ₅ and R ₆ are hydrogen;
n and m are 0.) 5. The method of claim 4,
The silicon quantum dot polymer
a) reducing the silicon precursor with a reducing agent in the presence of tetraalkylammonium halide to obtain a silicon quantum dot mixture;
b) quenching the silicon quantum dot mixture to obtain a silicon quantum dot solution;
c) preparing a silicon-modified quantum dots by adding a metal catalyst and the above-described chemical formula 3 to the silicon quantum dot solution;
d) polymerizing the surface-modified silicon quantum dots to produce a silicon quantum dot polymer. 6. The method of claim 5,
Wherein the reducing agent is LiAlH ₄ , NaBH ₄ , Na, sodium naphthalenide, sodium benzophenone, Mg ₂ Si, or KSi. 6. The method of claim 5,
Wherein the catalyst is H ₂ PtCl ₆ or a platinum (0) -1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. 6. The method of claim 5,
The quenching cell of the lithium secondary one to be performed with CuSO _4.

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