KR20150137946A - Negativ7e electrode active material, methode for synthesis the same, negative electrode including the same, and lithium rechargable battery including the same - Google Patents

Abstract

The present invention relates to: a negative electrode active material comprising carbon-based materials, a silicone coating layer disposed on a surface of the carbon-based materials and a carbon coating layer disposed on the silicone coating layer; a negative electrode plate produced by the negative electrode active material; a producing method of the negative electrode active material; and a lithium secondary battery comprising the negative electrode active material.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material, a method for producing the negative electrode active material, a negative electrode plate containing the same, a lithium secondary battery, and a lithium secondary battery.

A negative electrode plate comprising the negative electrode active material, a method for producing the same, and a lithium secondary battery.

Lithium secondary batteries have attracted attention as power sources for driving electronic devices. Graphite is mainly used as a negative electrode material of a lithium secondary battery, but it is difficult to increase the capacity of a lithium secondary battery because the capacity per unit mass of graphite is as small as 372 mAh / g.

Examples of an anode material exhibiting a higher capacity than graphite include materials forming lithium and intermetallic compounds such as silicon, tin and their oxides. Particularly, materials such as silicon have an advantage of realizing a high capacity and enabling miniaturization of the battery.

However, these materials cause a change in the crystal structure when lithium is absorbed and stored, which causes a problem that the volume expands. In the case of silicon, the volumetric expansion by filling occurs. At room temperature, the volumetric growth rate expands to about 3.7 times that of the volume of silicon before volume expansion. As a result, there is a problem that the life of the battery is rapidly deteriorated. In addition, materials such as silicon have lower electric conductivity than graphite, and thus are difficult to be used alone, and there is a problem in that the resistance between the material and the coating film is large.

Active research is being conducted on a solution to the problems of the negative electrode active material such as silicon.

Provided is a negative electrode active material capable of alleviating the volume expansion of a negative electrode active material, having excellent electrical conductivity and being physically and chemically stable, a method for producing the same, and a lithium secondary battery having high reversibility capacity, high rate characteristics and excellent lifetime characteristics.

According to an embodiment of the present invention, there is provided an anode active material comprising a carbonaceous material, a silicon coating layer disposed on the surface of the carbonaceous material, and a carbon coating layer disposed on the silicon coating layer.

Silicon particles may be included in the carbon-based material.

The thickness of the silicon coating layer may be 15 nm to 30 nm.

The silicon coating layer may be such that silicon particles are present on the surface of the carbonaceous material in the form of an island or a film in which silicon particles are superimposed on each other.

The silicon particles may be in the form of a hemisphere.

The average particle diameter of the silicon particles in the carbon-based material and the silicon coating layer may be 5 nm to 20 nm.

The silicon particles may be uniformly distributed on the surface of the carbon-based material.

The silicon particles in the carbon-based material and in the silicon coating layer may be amorphous or quasi-crystalline silicon.

Wherein the negative electrode active material comprises 92% by weight to 96% by weight of the carbonaceous material, based on the total amount of the negative electrode active material; 3% to 6% by weight of the silicone coating layer; And 0.1% to 2% by weight of the carbon coating layer.

The carbon-based material may be a crystalline carbon-based material.

The carbon-based material may be graphite.

The negative electrode active material may have a capacity of 500 mAh / g to 600 mAh / g.

Another embodiment of the present invention provides a negative electrode plate made of the negative electrode active material.

The negative electrode plate may have an electrode density of 1.0 g / cc to 2.0 g / cc.

The negative electrode plate may have a thickness of the negative electrode plate after 50 cycles / a thickness of the negative electrode plate after one cycle of less than 0.5.

According to another embodiment of the present invention, Coating silicon on the carbonaceous material; And thermally decomposing the hydrocarbon gas to coat the carbon layer on the coated silicon.

The step of coating the carbon-based material with silicon may be a chemical vapor deposition (CVD) method.

The silicon may be amorphous or quasi-crystalline silicon.

The step of coating silicon on the carbonaceous material may include chemical vapor deposition of silicon on the surface of the carbonaceous material using silane gas.

The step of coating the carbon-based material with silicon may be performed at 420 ° C to 650 ° C.

In the step of thermally decomposing the hydrocarbon gas and coating the carbon layer on the coated silicon, the pyrolysis temperature may be 800 ° C to 1000 ° C.

The carbon-based material may be a crystalline carbon-based material.

The carbon-based material may be graphite.

In another embodiment of the present invention, there is provided a lithium secondary battery including the negative electrode, the positive electrode, and the electrolyte including the negative active material.

The negative electrode active material according to one embodiment alleviates the problem of volume expansion, is excellent in electric conductivity, and is physically and chemically stable. The lithium secondary battery according to another embodiment has a high reversible capacity, and has excellent output characteristics and life characteristics.

1 is a graph showing changes in initial capacities of a half cell to which a negative electrode active material according to Example 1 and Comparative Examples 1 to 3 is applied.
FIG. 2 is a graph showing cycle retention of a half cell to which the negative electrode active material according to Example 1 and Comparative Examples 1 to 3 is applied.
3 is a graph showing the cycle efficiency of a half cell to which the negative electrode active material according to Example 1 and Comparative Examples 1 to 3 is applied.
4 is a scanning electron microscope (SEM) photograph of the surface of the negative electrode active material according to Example 1. Fig.
5 is a transmission electron microscope (HRTEM) photograph of a cut surface of the negative electrode active material according to Example 1. Fig.
FIG. 6 is a scanning electron microscope (SEM) image and EDX data obtained by analyzing components of the surface of the negative electrode active material according to Example 1. FIG.
FIGS. 7 to 9 are EDX data obtained by analyzing the components of the cut surface of the negative electrode active material according to Example 1. FIG.
10 is a scanning electron microscope (SEM) image of a section of an anode plate showing the initial cycle of the anode plate made from the anode active material according to Example 1 and the thickness change after 50 cycles.
11 is a scanning electron micrograph showing the initial cycle of the negative electrode plate made of the negative electrode active material according to Example 1 and the surface change of the negative electrode plate after 50 cycles.
12 is an XRD graph of the negative electrode active material according to Example 1 and Comparative Examples 1 to 3. 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.

According to an embodiment of the present invention, there is provided an anode active material comprising a carbonaceous material, a silicon coating layer disposed on the surface of the carbonaceous material, and a carbon coating layer disposed on the silicon coating layer.

The carbonaceous material has a low capacity and has a problem that the output characteristic is remarkably lowered at the time of fast charging. In addition, since silicon is a material that undergoes considerable volume expansion during charging and discharging, it can not only lead to serious electrode damage, but also results in a rapid decrease in capacity.

However, the negative electrode active material according to an embodiment of the present invention may have a capacity of 500 mAh / g or more, for example, 500 mAh / g to 600 mAh / g or more, by coating silicon on the surface of the carbonaceous material in the form of a salt or thin film. And the output characteristics and life characteristics can be improved while securing up to 50% of the expansion rate of the electrode plate on the basis of the electrode thickness over 50 cycles at the time of battery evaluation.

Furthermore, the carbon coating layer located at the outermost portion can improve the electrical conductivity by providing an electron transfer path, and can control the volume change of metal such as silicon during charging and discharging, thereby greatly improving the stability of the electrode plate. In addition, the carbon coating layer can prevent interfacial reaction that may occur when the metal coating layer comes into direct contact with the electrolyte, improve the electrical conductivity of the interface, and control the volume expansion of the electrode.

In addition, the carbon-based material plays a role of supporting the silicon so as not to be separated from the silicon, and can sufficiently transfer electrons and control the volume expansion during charging and discharging.

The silicon coating layer may have a thickness of 15 nm to 30 nm. When the silicon coating layer has a thickness in the above range, it becomes a very thin film form, which can greatly control the volume expansion of the metal during charging and discharging, and the rate of increase is also greatly increased. Furthermore, when preparing a negative electrode active material for general lithium secondary batteries, different materials are mixed to prepare a slurry. In this case, layer separation occurs. However, since the silicon coating layer is combined with the carbon-based material in the form of a very thin film, it is possible to solve the problem of layer separation as described above. That is, the anode active material according to one embodiment can be rapidly charged and discharged while having stability against volume expansion.

Specifically, the silicon coating layer may be formed such that silicon particles are present on the surface of the carbon-based material in the form of an island or a film in which silicon particles are superimposed on each other. Accordingly, the anode active material according to one embodiment can alleviate the expansion problem of silicon such as silicon due to charging and discharging, and can use the physical and electrical characteristics of the carbon-based material as it is.

The carbon-based material may be a porous carbon-based material. That is, the anode active material according to one embodiment may include silicon particles in the porous carbonaceous material.

The average particle diameter of the silicon particles in the carbon-based material may be the same as the silicon particles in the silicon coating layer. In addition, the silicon particles in the carbon-based material may be amorphous or quasi-crystalline silicon particles.

The silicon particles may be, for example, in the form of a hemisphere.

The average particle diameter of the silicon particles may be 5 nm to 20 nm, for example, 10 nm to 20 nm, and 5 nm to 15 nm.

The silicon particles may be uniformly distributed on the surface of the carbon-based material.

The silicon in the silicon coating layer may be amorphous or quasi-crystalline silicon. In this case, the silicon coating layer is less likely to break crystals due to volume expansion and can maintain a stable structure. Unlike crystalline silicon, amorphous or quasi-crystalline silicon does not have the directionality in which lithium is absorbed, and uniformly expands in volume and has a high lithium migration rate. Amorphous or quasi-crystalline silicon can be stably structured because it has less stress or strain in lithium absorption and desorption than crystalline silicon. In addition, the conventional silicon powder has a problem that dispersion is not uniform, but the anode active material according to one embodiment can distribute the silicon particles on the surface of the carbon-based material very uniformly. Furthermore, the silicon particles are present on the surface of the carbonaceous material in the form of an island or a thin film, so that the physical and electrical characteristics of the carbonaceous material can be maximized without being disturbed by silicon. In this case, the first cycle efficiency (Coloumbic efficiency) reaches about 90%.

Wherein the negative electrode active material comprises 92% by weight to 96% by weight of the carbonaceous material, based on the total amount of the negative electrode active material; 3% to 6% by weight of the silicone coating layer; And 0.1% to 2% by weight of the carbon coating layer.

The carbon-based material may be a crystalline carbon-based material such as graphite.

The carbonaceous material may be porous. For example, the carbon-based material may be a porous graphite.

The negative electrode active material may have a capacity of 500 mAh / g or more, for example, 500 mAh / g to 600 mAh / g.

Another embodiment of the present invention provides a negative electrode plate made of the negative electrode active material.

The negative electrode plate may have an electrode density of 1.0 g / cc to 2.0 g / cc.

The negative electrode plate may have a volume (thickness) of the negative electrode plate after 50 cycles / a volume (thickness) of the negative electrode plate after one cycle of less than 0.5, based on the electrode thickness. That is, the negative electrode plate may have a volume expansion rate of less than 50% after 50 cycles based on the electrode thickness.

According to another embodiment of the present invention, Coating silicon on the carbonaceous material; And thermally decomposing the hydrocarbon gas to coat the carbon layer on the coated silicon.

The above-described negative electrode active material can be produced through the above-described production method.

The silicon may be amorphous or quasi-crystalline silicon.

The step of coating the carbon-based material with silicon may be a chemical vapor deposition (CVD) method. Specifically, the step of coating silicon on the surface of the carbonaceous material may include chemical vapor deposition of silicon on the surface of the carbonaceous material using silane gas.

Conventional silicon powders have a problem of low dispersion, but when silicon is deposited on the surface of the carbonaceous material by chemical vapor deposition, silicon particles can be deposited very uniformly. In addition, when the chemical vapor deposition method is used, silicon particles may be coated on the surface of the carbon-based material in the form of an island or an overlapping silicon particles.

Further, since silicon is chemically vapor-deposited using silane gas, not only a silicon coating layer is formed on the surface of the carbon-based material, but silicon can also be contained in the carbon-based material.

The step of coating the carbon-based material with silicon may be performed at 420 ° C to 650 ° C. In this case, high purity silicon, such as amorphous or quasi-crystalline silicon, can be deposited in large quantities.

Silane gas decomposition does not occur at a temperature lower than 420 DEG C and crystalline silicon is formed at a temperature higher than 650 DEG C. The crystalline silicon is more susceptible to stress or strain than amorphous or quasi-crystalline silicon, The speed is relatively low.

In the step of thermally decomposing the hydrocarbon gas and coating the carbon layer on the coated silicon, the pyrolysis temperature may be 800 ° C. to 1000 ° C., for example, 850 ° C. to 950 ° C., and the pyrolysis time may vary depending on the amount of the filler .

The carbon-based material may be a crystalline carbon-based material such as graphite.

In another embodiment of the present invention, there is provided a lithium secondary battery including the negative electrode, the positive electrode, and the electrolyte including the negative active material.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the type of the separator and electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

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

The description of the anode active material is omitted since it is as described above.

The negative electrode active material layer also includes a binder, and may further include 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. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and olefin copolymers having 2 to 8 carbon atoms, (meth) acrylic acid and (meth) Copolymers or combinations thereof.

When a water-soluble binder is used as the negative electrode binder, it may further include a cellulose-based compound capable of imparting viscosity. As the cellulose-based compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, alkali metal salts thereof or the like may be used in combination. As the alkali metal, Na, K or Li can be used. The content of the thickener may be 0.1 to 3 parts by weight based on 100 parts by weight of the binder.

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, Carbon-based materials such as black and carbon fiber; 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 collector may be selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foil, a polymer substrate coated with a conductive metal, and a combination thereof.

The anode includes a current collector and a cathode active material layer formed on the current collector. As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, at least one of complex oxides of metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used. As a more specific example, a compound represented by any one of the following formulas may be used.

Li _a A _{1 - b} X _b D ₂ (0.90? A? 1.8, 0? B? 0.5); Li _a A _{1 - b} X _b O _{2 - c} D _c (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05); LiE _{1 - b} X _b O _{2 - c} D _c (0? B? 0.5, 0? C? 0.05); LiE _{2 - b} X _b O _{4 - c} D _c (0? B? 0.5, 0? C? 0.05); Li _a Ni _{1 -b- c} Co _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <?? 2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 -α} T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 - ?} T ₂ (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? <2); Li _a Ni _{1 -b- c} Mn _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <?? 2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2- α} T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -bc} Mn _b X _c O _2-α T ₂ (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 (0.90? A? 1.8, 0? B? 0.9, 0? C? 0.5, 0.001? D? 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a CoG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a MnG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (0.90? A? 1.8, 0.001? B? 0.1); Li _a MnG _b PO ₄ (0.90? A? 1.8, 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO 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); LiFePO ₄

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations 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 at least one coating element compound selected from the group consisting of oxides, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. 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 any coating method as long as it can coat the above compound by a method which does not adversely affect the physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

The cathode active material layer also includes a binder and a conductive material.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl Polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-acrylonitrile, styrene-butadiene rubber, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

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 conductive material and a binder in a solvent to prepare an active material composition and applying the composition to an electric 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.

In the non-aqueous liquid electrolyte secondary battery according to an embodiment of the present invention, the electrolyte 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.

Depending on the type of the lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. The separator may be a polyethylene / polypropylene double layer separator, a polyethylene / polypropylene / polyethylene triple layer separator, a polypropylene / polyethylene / poly It is needless to say that a mixed multilayer film such as a propylene three-layer separator and the like can be used.

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

(Preparation of negative electrode active material)

Comparative Example  One

Bare Graphite (BTR, SG-17), which is uncoated, was used as the negative electrode active material.

Comparative Example  2

50 g of the graphite of Comparative Example 1 was chemically vapor-deposited at a rate of 50 sccm / 60 min at a temperature of 550 캜 under the condition of SiH ₄ (g) to prepare a negative electrode active material having a silicon coating layer formed on the graphite.

Comparative Example  3

The negative electrode active material of Comparative Example 2 was heat-treated at 900 캜.

Example  One

Under the temperature conditions of the comparative negative electrode active material of Example 2 900 ℃, by thermal decomposition of C ₂ H ₂ (g) at a rate of 1.5L / min, to thereby prepare a negative active material coated with the carbon layer on the silicon coating layer. At this time, graphite is contained in an amount of 95% by weight, silicon is 4% by weight, and outermost carbon is 1% by weight based on the total amount of the negative electrode active material.

( Negative plate  Produce)

A slurry was prepared in the ratio of the negative electrode active material: conductive material: binder of 95.8: 1: 3.2. The conductive material used was super-P, and the binder was a mixture of styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) at a weight ratio of 1.5: 1.7.

The slurry was uniformly applied to a copper foil, dried in an oven at 80 캜 for about 2 hours, rolled and further dried in a vacuum oven at 110 캜 for about 12 hours to prepare a negative electrode plate.

(Preparation of half cell)

The prepared negative electrode plate and the lithium foil were used as counter electrodes and the porous polyethylene membrane was used as a separator and diethyl carbonate (DEC) and fluoro-ethylene carbonate (FEC) were mixed at a volume ratio of 7: 3 a CR2016 coin-type half-cells in accordance with the manufacturing process in using a liquid electrolyte with a LiPF ₆ dissolved to a concentration of 1.0M to the mixed solvent was prepared by conventionally known.

Test Example  1: Analysis of shape of anode active material

4 is a scanning electron microscopic photograph of the surface of the negative electrode active material according to Example 1. Fig. 4A, 4B, 4C and 4D are scanning electron micrographs from low magnification to high magnification.

FIG. 6A is a graph showing the EDX data obtained by analyzing the element composition of the surface of the negative electrode active material according to Example 1, and FIG. 6B is a mapping image of the surface of the negative active material according to the EDX data.

Meanwhile, FIG. 5 is a scanning electron microscope photograph of the cut surface of the negative electrode active material according to Example 1. 5A and 5B are scanning electron micrographs from a low magnification to a high magnification.

FIG. 7 (a) is a photograph showing the element composition of the cut surface of the negative electrode active material according to Example 1 in different colors, and FIG. 7 (b)

8 (a) is a transmission electron microscope (SEM) image of the cut surface of the negative electrode active material according to Example 1, and b is EDX data obtained by analyzing elemental components of the yellow line portion of a.

9 (a) is a transmission electron microscope photograph of the cut surface of the negative electrode active material according to Example 1, and b is a photograph in which element components of the photograph portion of a are mapped by different colors.

4 to 9, amorphous silicon of less than about 20 nm is uniformly distributed on the graphite surface, and carbon is coated thereon. It can also be seen from Figs. 7 and 9 that the silicon particles are contained in the graphite.

Test Example  2: Tap density  And Non-face-to-face  analysis

The particle size of the negative electrode active material according to Example 1 and Comparative Examples 1 to 3 was measured using a particle size analyzer (MICROTRAC, S3500), tap density was measured using a density meter (Micromeritics, GeoPyc 1360) , And a specific surface area was measured using a powder surface area meter (Micromeritics, Inc., TriStar II).

Particle diameter (占 퐉) of the negative electrode active material Tap density (g / cc) Specific surface area (m ² / g) D- _min D ₁₀ D ₅₀ D ₉₀ D _max Example 1 7.78 13.37 18.93 27.39 57.06 1.07 3.69 Comparative Example 1 7.78 12.71 18.30 27.00 57.06 1.02 5.28 Comparative Example 2 7.78 12.88 18.29 26.53 57.06 0.96 2.73 Comparative Example 3 7.78 13.28 18.64 26.86 57.06 0.93 3.36

It can be seen from Table 1 that the negative electrode active material of Example 1 has a higher tap density than the negative active materials of Comparative Examples 1 to 3, and thus has excellent capacity characteristics. The negative electrode active material of Example 1 and the negative electrode active materials of Comparative Examples 1 to 3 largely differ in specific surface area. The negative electrode active material of Example 1 exhibits the capacity characteristics Can be greatly improved.

Test Example  3: On charge and discharge  Following Negative plate  Change analysis

10 is a scanning electron microscope (SEM) image of a section of an anode plate prepared using the anode active material according to Example 1. FIG.

10 is a scanning electron microscope (SEM) image of a section of the first negative electrode plate to which the negative electrode active material of Example 1 is applied, and a, b and c are scanning electron micrographs from a low magnification to a high magnification.

10 is a scanning electron micrograph of a cathode plate after 50 cycles of an anode plate cross section using the anode active material of Example 1, and d, e and f are scanning electron micrographs from a low magnification to a high magnification.

It can be seen from FIG. 10 that the negative electrode plate using the negative electrode active material according to one embodiment has a small volume expansion rate.

11 is a scanning electron microscope (SEM) image of the surface of a negative electrode plate prepared using the negative electrode active material according to Example 1. FIG.

11 is a scanning electron microscope photograph of the surface of the first negative electrode plate to which the negative electrode active material of Example 1 is applied, and a, b and c are scanning electron microscope photographs from a low magnification to a high magnification.

11 is a scanning electron micrograph of the negative electrode plate after 50 cycles of the surface of the negative electrode plate to which the negative electrode active material of Example 1 is applied, and d, e and f are scanning electron micrographs from low magnification to high magnification.

From FIG. 11, it can be seen that the negative electrode plate using the negative electrode active material according to an embodiment has a small volume expansion ratio.

Test Example  4: Electrochemical Characterization of Half Cells

The electrochemical characteristics of the half cells to which the negative electrode active materials of Example 1 and Comparative Examples 1 to 3 were applied were evaluated and the results are shown in FIGS. At this time, the discharge was set to 1/10 C (CCCV methode), the cutoff voltage was set to 0.005 V to 1.5 V, the discharge was set to 0.5 C (CCCV methode), and the cutoff voltage was set to 0.005 V to 1.0 V.

1 is a graph showing the initial capacity change of a half cell. It can be confirmed that the half cells to which the negative electrode active materials of Example 1, Comparative Example 2 and Comparative Example 3 were applied had a high capacity characteristic of 500 mAh / g or more, as compared with the half cell to which the negative electrode active material of Comparative Example 1 was applied.

 FIG. 2 is a graph showing a change in cycle retension of a half cell. As the cycle progresses, the half cell to which the negative active material of Example 1 is applied has a better capacity characteristic than the half cell to which the negative active material of Comparative Example 1 to Comparative Example 3 is applied can confirm.

FIG. 3 is a graph showing a change in cycle efficiency of a half cell. As the cycle progresses, the half cell to which the negative active material of Example 1 is applied has better cycle efficiency than the half cell to which the negative active material of Comparative Example 1 to Comparative Example 3 is applied Can be confirmed.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (25)

Carbon-based materials,
A silicon coating layer positioned on the surface of the carbonaceous material; and
And a carbon coating layer disposed on the silicon coating layer. The method of claim 1,
Wherein the carbon-based material contains silicon particles. The method of claim 1,
Wherein the silicon coating layer has a thickness of 15 nm to 30 nm. The method of claim 1,
Wherein the silicon coating layer contains silicon particles in the form of a thin film in which islands or silicon particles are superimposed on each other on the surface of the carbonaceous material. 5. The method of claim 4,
Wherein the silicon particles are in a hemisphere form. 3. The method of claim 2,
Wherein the average particle diameter of the silicon particles is 5 nm to 20 nm. 5. The method of claim 4,
Wherein the average particle diameter of the silicon particles is 5 nm to 20 nm. 5. The method of claim 4,
Wherein the silicon particles are uniformly distributed on a surface of the carbonaceous material. The method of claim 1,
Wherein the silicon particles in the silicon coating layer are amorphous or semi-crystalline silicon particles. 3. The method of claim 2,
Wherein the silicon particles in the carbonaceous material are amorphous or quasi-crystalline silicon particles. The method of claim 1,
The negative electrode active material,
With respect to the total amount of the negative electrode active material,
92% by weight to 96% by weight of the carbonaceous material;
3% to 6% by weight of the silicone coating layer; And
Wherein the carbon coating layer comprises 0.1 wt% to 2 wt% of the carbon coating layer. The method of claim 1,
Wherein the carbon-based material is a crystalline carbon-based material. The method of claim 1,
Wherein the carbon-based material is graphite. An anode plate made from the anode active material of any one of claims 1 to 13. The method of claim 14,
Wherein an electrode density of the negative electrode plate is 1.0 g / cc to 2.0 g / cc. The method of claim 14,
The negative electrode plate has a thickness of the negative electrode plate after 50 cycles / a thickness of the negative electrode plate after one cycle of less than 0.5. Preparing a carbonaceous material;
Coating silicon on the carbonaceous material; And
And thermally decomposing the hydrocarbon gas to coat the carbon layer on the coated silicon. The method of claim 17,
Wherein the step of coating the carbon-based material with silicon is performed by chemical vapor deposition (CVD). The method of claim 17,
Wherein the silicon is amorphous or quasi-crystalline silicon. The method of claim 18,
The step of coating silicon on the carbonaceous material
And silicon is chemically vapor-deposited on the surface of the carbon-based material by using silane gas. The method of claim 17,
Wherein the step of coating the carbon-based material with silicon is performed at a temperature of 420 ° C to 650 ° C. The method of claim 17,
In the step of thermally decomposing the hydrocarbon gas to coat the carbon layer on the coated silicon,
Wherein the thermal decomposition temperature is 800 ° C to 1000 ° C. The method of claim 17,
Wherein the carbon-based material is a crystalline carbon-based material. The method of claim 17,
Wherein the carbon-based material is graphite. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 13,
Anode, and
A lithium secondary battery comprising an electrolyte.

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