KR102461948B1 - Negative electrode for rechargeable lithium battery - Google Patents

Abstract

It includes a core and a coating layer surrounding the core, wherein the core includes crystalline carbon, amorphous carbon and silicon nanoparticles, the coating layer includes amorphous carbon, and the adjacent distance between silicon nanoparticles is 100 nm or less, providing a negative active material composite do.

Description

Anode for lithium secondary batteries

It relates to a negative electrode for a lithium secondary battery.

Lithium secondary batteries, which are recently spotlighted as a power source for portable small electronic devices, use an organic electrolyte solution, and thus exhibit a discharge voltage that is twice or more higher than that of a battery using an aqueous alkali solution, resulting in high energy density.

As a cathode active material for a lithium secondary battery, LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ (0 < x < 1) Lithium having a structure that allows intercalation of lithium ions and a transition metal, such as Oxides are mainly used.

Various types of carbon-based materials, including artificial, natural graphite, and hard carbon, which can insert/detach lithium, have been applied as anode active materials. research is in progress.

One embodiment is to provide an anode active material composite with reduced expansion by suppressing side reactions with an electrolyte.

Another embodiment is to provide a method of manufacturing the negative active material composite.

Another embodiment is to provide an anode including the anode active material composite.

Another embodiment is to provide a lithium secondary battery having excellent initial efficiency and cycle life characteristics by including the negative electrode.

One embodiment includes a core and a coating layer surrounding the core, the core includes crystalline carbon, amorphous carbon and silicon nanoparticles, the coating layer includes amorphous carbon, and an adjacent distance between the silicon nanoparticles is 100 nm It provides the following, a negative active material composite.

The silicon nanoparticles may have an average particle diameter (D50) of 50 to 150 nm.

The silicon nanoparticles may have a half width of 0.3° to 7° of an X-ray diffraction angle (2theta) using CuKα on the (111) plane.

The silicon nanoparticles may have an aspect ratio of 2 to 8.

The silicon nanoparticles may be included in an amount of 20 to 80% by weight based on the total weight of the negative active material composite.

The amorphous carbon may be at least one selected from soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and combinations thereof.

The amorphous carbon may be included in an amount of 20 to 80 wt% based on the total weight of the negative active material composite.

The crystalline carbon may be at least one selected from natural graphite, artificial graphite, and combinations thereof.

The crystalline carbon may be included in an amount of 20 to 80 wt% based on the total weight of the negative active material composite.

The negative active material composite may have an average particle diameter (D50) of 2 to 15 μm.

The coating layer may have a thickness of 1 nm to 900 nm.

In the negative active material composite, the total pore volume of pores having a size of 200 nm or less may be 3.0 x 10 ^-2 cm ³ /g or less.

The negative active material composite may have a BET specific surface area of 10 m ² /g or less.

The content of the silicon nanoparticles and the amorphous carbon may be in a weight ratio of 20:80 to 80:20.

Another embodiment is a process for preparing a mixture by mixing and dispersing crystalline carbon, silicon nanoparticles and amorphous carbon; A process of preparing a molded article by spraying and drying the mixture and then compressing; And it provides a method of manufacturing a negative electrode active material composite comprising a step of heat-treating the molded body.

The compression may be performed at a pressure of 50 to 150 MPa.

The heat treatment may be performed at a temperature of 700 to 1100 °C.

Another embodiment is a current collector; and a negative active material layer including a negative active material positioned on the current collector, wherein the negative active material includes the negative active material composite.

The silicon nanoparticles included in the negative active material composite may be included in an amount of 1 to 30% by weight based on the total weight of the negative active material layer.

Another embodiment is a positive electrode comprising a positive electrode active material; the negative electrode; And it provides a lithium secondary battery comprising an electrolyte.

To provide a lithium secondary battery with improved initial efficiency and lifespan characteristics by controlling the volume of pores formed inside the anode active material composite to suppress side reactions between the electrolyte and silicon nanoparticles.

1A is a schematic diagram of an anode active material composite according to an exemplary embodiment.
1B is a schematic diagram of a negative active material composite according to the prior art.
2 is a schematic view showing two adjacent silicon nanoparticles of the negative active material composite according to an embodiment.
3 is an exploded perspective view of a lithium secondary battery according to an embodiment.
4 is a TEM (Transmission Electron Microscopy) photograph showing an adjacent distance between silicon nanoparticles of the negative active material composite prepared in Example 2. FIG.
5 is a graph of measuring the average particle diameter (D50) of the negative active material composite prepared in Example 3;
6 is a scanning electron microscopy (SEM) photograph of the negative active material composite prepared in Example 3. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Unless otherwise specified herein, when a part of a layer, film, region, plate, etc. is said to be "on" or "on" another part, or "surrounding" another part, it means that the other part is "immediately on". "It includes not only the case where it is located, but also the case where there is another part in between.

The negative active material composite according to an embodiment includes a core and a coating layer surrounding the core, the core includes crystalline carbon, amorphous carbon and silicon nanoparticles, the coating layer includes amorphous carbon, and the silicon nanoparticles The adjacent distance between them is less than 100 nm.

Hereinafter, a negative active material composite and silicon nanoparticles according to an embodiment will be described with reference to FIGS. 1A and 2 , and a negative active material composite according to the prior art and a negative active material composite according to an embodiment are compared with reference to FIG. 1B . to explain

Figure 1a is a schematic diagram of a negative active material composite according to an embodiment, Figure 1b is a schematic diagram of a negative active material composite according to the prior art, Figure 2 is a schematic diagram showing two adjacent silicon nanoparticles of the negative electrode active material composite according to an embodiment to be.

The negative active material composite 1 according to an embodiment includes a core 3 and a coating layer 5 surrounding the core, and the core 3 includes crystalline carbon 13, amorphous carbon and silicon nanoparticles 11 ), and the coating layer 5 includes amorphous carbon.

The adjacent distance d between the silicon nanoparticles 11 means the distance between the centers of the silicon nanoparticles 11, and the adjacent distance d between the silicon nanoparticles 11 is 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less.

On the other hand, the adjacent distance (d) between the silicon nanoparticles is 50 to 100% of the total number of silicon nanoparticles included in the negative active material composite core, for example 60 to 100%, 70 to 100%, or 80 to 100% of silicon It may mean that the adjacent distance (d) between nanoparticles is included in the above range.

Meanwhile, comparing FIGS. 1A and 1B , in the negative active material composite 1 according to an exemplary embodiment, since the adjacent distance between the silicon nanoparticles 11 corresponds to the above range, the pores 15 included in the core 3 ), it can be understood that the size and the total pore volume are reduced, while the size of the pores 15a and the total pore volume of the negative active material composite 1a according to the prior art are relatively large. That is, when the adjacent distance between the silicon nanoparticles is within the above range, the volume of pores existing inside the anode active material composite is reduced, and the adjacent distance between the silicon nanoparticles is narrowed so that the electrolyte penetrates into the anode active material composite core during battery operation. it can be prevented As a result, it is possible to improve the battery life characteristics by suppressing the side reaction between the electrolyte and the negative electrode active material composite.

The average particle diameter (D50) of the silicon nanoparticles 11 may be 50 to 150 nm, for example, 50 nm or more, 60 nm or more, 70 nm or more, or 80 nm or more, and 150 nm or less, 140 nm or less, 130 nm or less, or 115 nm or less. When the average particle diameter of the silicon nanoparticles falls within the above range, side reactions with the electrolyte are suppressed, and the expansion of the silicon nanoparticles is reduced, thereby improving the initial efficiency and lifespan characteristics of the battery.

The silicon nanoparticles may have a half width of 0.3° to 7° of an X-ray diffraction angle (2theta) using CuKα on the (111) plane. Accordingly, the lifespan characteristics of the battery can be improved.

The half width of the X-ray diffraction angle (2theta) using CuKα on the (111) plane of the silicon nanoparticles can be achieved by adjusting the size of the silicon particles or changing the silicon nanoparticle manufacturing process.

The aspect ratio (b/a) of the silicon nanoparticles 11 may be 2 to 8, for example, 2 to 6, and the short axis length (a) of the silicon nanoparticles 11 may be 20 to 50 nm, and the long axis The length (b) may be 50 to 300 nm. When the aspect ratio (b/a), major axis length (b), and minor axis length (a) of the silicon nanoparticles 11 fall within the above ranges, side reactions between the negative electrode active material composite and the electrolyte are suppressed, and the silicon nanoparticles expand This can be reduced to improve the initial efficiency and lifespan characteristics of the battery.

The silicon nanoparticles 11 may be included in an amount of 20 to 80% by weight, 30 to 70% by weight, 30 to 60% by weight, or 30 to 50% by weight based on the total weight of the negative active material composite 1 . When the content of the silicon nanoparticles is within the above range, battery capacity may be improved.

The crystalline carbon 13 may be natural graphite, artificial graphite, or a combination thereof, preferably artificial graphite. The crystalline carbon 13 is 20 to 80% by weight, for example, 20 to 70% by weight, 20 to 60% by weight, 20 to 50% by weight or 20 to 40% by weight based on the total weight of the negative electrode active material composite (1). may be included. When the content of the crystalline carbon is within the above range, the expansion of the silicon nanoparticles is reduced to improve the initial efficiency and lifespan characteristics of the battery.

The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof.

When the amorphous carbon is included in the core, a side reaction with the electrolyte may be suppressed by reducing the pore volume of the negative active material composite. In addition, the amorphous carbon can suppress the expansion of the battery by buffering the silicon nanoparticles in the anode active material composite when they expand, and by acting as a binder, the anode active material composite particle can be prevented from breaking and its shape can be well maintained. .

The coating layer 5 includes amorphous carbon. In addition, the coating layer 5 may have a thickness of 1 nm to 900 nm, for example, 5 nm to 800 nm. Accordingly, by reducing the specific surface area of the composite and controlling the penetration of the electrolyte into the anode active material composite core, the side reaction between the electrolyte and the anode active material composite can be minimized, thereby improving the lifespan characteristics of the battery.

Meanwhile, the amorphous carbon included in the coating layer 5 may be the same compound as the amorphous carbon included in the core 3 or a different compound.

The amorphous carbon may be included in an amount of 20 to 80% by weight, for example, 20 to 70% by weight, 20 to 60% by weight, 20 to 50% by weight, or 20 to 40% by weight based on the total weight of the negative active material composite (1). . When the content of the amorphous carbon is within the above range, a side reaction between the negative electrode active material composite and the electrolyte may be suppressed.

The average particle diameter (D50) of the negative active material composite 1 may be 2 to 15 μm, for example, 3 to 13 μm or 5 to 10 μm. When the average particle diameter of the negative active material composite is within the above range, lithium ions may easily diffuse into the negative active material composite, and battery resistance and rate characteristics may be improved. In addition, by suppressing an excessive increase in the specific surface area of the negative active material, side reactions with the electrolyte can be reduced.

On the other hand, the average particle diameter of the anode active material composite can be achieved by appropriately adjusting the pulverization conditions and pulverization conditions during the manufacture of the anode active material composite.

In the negative active material composite 1, the total pore volume of the pores 15 having a size of 200 nm or less is 3.0 x 10 ^-2 cm ³ /g or less, for example, 2.5 x 10 ^-2 cm ³ /g or less, 2.3 x 10 ^-2 cm ³ /g or less, 2.0 x 10 ^-2 cm ³ /g or less, 1.9 x 10 ^-2 cm ³ /g or less, 1.8 x 10 ^-2 cm ³ /g or less, 1.7 x 10 ^-2 cm ³ /g or less g or less, 1.6 x 10 ^-2 cm ³ /g or less, 1.5 x 10 ^-2 cm ³ /g or less, 1.4 x 10 ^-2 cm ³ /g or less, 1.3 x 10 ^-2 cm ³ /g or less, 1.2 x 10 ^-2 cm ³ /g or less, 1.1 x 10 ^-2 cm ³ /g or less, 1.0 x 10 ^-2 cm ³ /g or less, 0.9 x 10 ^-2 cm ³ /g or less, or 0.8 x 10 ^-2 cm ³ /g or less may be below. When the pore volume of the negative active material composite is controlled within the above numerical range, side reactions between the electrolyte and silicon nanoparticles are suppressed, thereby improving initial efficiency and lifespan characteristics.

Meanwhile, the total pore volume of pores having a size of 200 nm or less can be quantitatively measured with a Barrett-Joyner-Halenda (BJH) analysis facility.

In addition, the pore size of the negative active material composite 1 may be 200 nm or less, for example, 170 nm or less, 150 nm or less, 130 nm or less, 100 nm or less, or 50 nm or less. When the pore size of the negative active material composite is controlled within the above range, the side reaction between the electrolyte and the silicon nanoparticles can be reduced, and the initial efficiency and lifespan characteristics of the battery can be improved.

The BET specific surface area of the negative active material composite 1 may be 10 m ² /g or less. When the BET specific surface area is within the above range, a side reaction with the electrolyte may be suppressed to improve the efficiency characteristics of the battery.

The content of the silicon nanoparticles 11 and the amorphous carbon is 8:2 to 2:8 by weight, for example, 7:3 to 3:7 by weight, 6:4 to 4:6 by weight, 6:4 to 5:5 by weight. or 4:3 to 3:4 by weight. When the content of the silicon nanoparticles and the amorphous carbon is within the above range, the internal pore volume may be reduced and the amorphous carbon may be uniformly dispersed inside and on the surface of the negative electrode active material composite. As a result, side reactions with the electrolyte can be suppressed and the performance of the negative active material composite can be improved.

Hereinafter, a method of manufacturing a negative active material composite according to another exemplary embodiment will be described.

The method for preparing the negative active material composite includes mixing and dispersing crystalline carbon, silicon nanoparticles, and amorphous carbon to prepare a mixture; A process of preparing a molded article by spraying and drying the mixture and then compressing; and heat-treating the molded body.

First, a mixture is prepared by mixing and dispersing crystalline carbon, silicon nanoparticles and amorphous carbon. The crystalline carbon, the silicon nanoparticles, and the amorphous carbon are the same as described above.

Next, the prepared mixture is sprayed, dried, and compressed to prepare a molded article.

The drying may be performed at 50 to 150° C. using a spray dryer.

The compression may be performed at a pressure of 50 to 150 MPa, for example 75 to 150 MPa or 75 to 125 MPa. When the molded body is compressed within the pressure range, the gap between silicon nanoparticles is properly maintained and the pore volume formed inside the negative active material composite is controlled to suppress side reactions between the electrolyte and silicon nanoparticles, and initial efficiency and lifespan characteristics can be improved

Then, the manufactured molded body is heat-treated to prepare a negative active material composite according to an embodiment.

The heat treatment may be performed at a temperature of 700 to 1100 °C, for example 800 to 1050 °C or 900 to 1000 °C. When the heat treatment is performed in the above temperature range, the strength of the anode active material composite may be strengthened while the amorphous carbon is carbonized. In addition, the conductivity of the negative active material may be improved and the initial efficiency of the battery may be improved.

Meanwhile, the heat treatment may be performed in a nitrogen (N ₂ ) atmosphere in a furnace.

Another embodiment is a current collector; and a negative active material layer including a negative active material positioned on the current collector, wherein the negative active material includes the negative active material composite.

The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with conductive metal, and combinations thereof.

The anode active material layer includes an anode active material, and may optionally further include a binder and a conductive material.

The negative active material includes the negative active material composite according to an embodiment, and selectively reversibly intercalates/deintercalates lithium ions, lithium metal, lithium metal alloy, lithium doping and de-doping It may further comprise at least one of possible materials and transition metal oxides.

The negative active material composite is the same as described above.

As a material capable of reversibly intercalating/deintercalating lithium ions, for example, a carbon material, that is, a carbon-based negative active material generally used in a lithium secondary battery may be used. Representative examples of the carbon-based negative active material include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon. carbon), mesophase pitch carbide, and calcined coke.

The lithium metal alloy includes lithium and a group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. An alloy of a metal selected from may be used.

Examples of the lithium-doped and de-doped material include a silicon-based material, for example, Si, SiO _x (0<x<2), a Si-Q alloy (wherein Q is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 an element selected from the group consisting of an element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, and not Si), a Si-carbon composite, Sn, SnO ₂ , a Sn-R alloy (the R is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, not Sn), Sn-carbon composite etc. are mentioned, Moreover, at least one _of these and SiO2 can also be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, One selected from the group consisting of Se, Te, Po, and combinations thereof may be used.

Lithium titanium oxide may be used as the transition metal oxide.

Specifically, the negative active material may include the negative active material composite and crystalline carbon. For example, the negative active material may include the negative active material composite, and may further include natural graphite, artificial graphite, or a combination thereof.

In the negative active material, the content of the negative active material composite may be 1 to 50% by weight, 10 to 40% by weight, 10 to 30% by weight, or 10 to 20% by weight based on the total weight of the negative active material.

In the anode active material layer, the content of the anode active material is 95 wt% to 99 wt%, for example 96 wt% to 99 wt%, 97 wt% to 99 wt%, or 97 wt% to 98 wt% based on the total weight of the anode active material layer % by weight.

In the negative active material layer, the negative active material composite is 1 to 90% by weight, such as 1 to 80% by weight, 1 to 70% by weight, 1 to 60% by weight, 1 to 50% by weight, based on the total weight of the negative active material layer, 1 to 40% by weight or 10 to 30% by weight may be included.

In the negative active material layer, the silicon nanoparticles included in the negative active material composite are 1 to 30% by weight, such as 1 to 20% by weight, 1 to 15% by weight, or 1 to 10% by weight based on the total weight of the negative active material layer. may be included as When the content of the silicon nanoparticles is within the above range, the battery capacity may be more effectively improved.

In addition, in the negative active material layer, the crystalline carbon included in the negative active material composite is 1 to 20% by weight, such as 1 to 17% by weight, 1 to 15% by weight, 1 to 10% by weight based on the total weight of the negative active material layer. % or 1 to 8% by weight. When the content of the crystalline carbon is within the above range, the expansion of the silicon nanoparticles may be reduced to improve the initial efficiency and cycle life characteristics of the battery.

In addition, in the negative active material layer, the amorphous carbon included in the negative active material composite is 1 to 20% by weight, such as 1 to 17% by weight, 1 to 15% by weight, 1 to 10% by weight based on the total weight of the negative active material layer. % or 1 to 8% by weight. When the content of the amorphous carbon is within the above range, the occurrence of side reactions may be more effectively suppressed by controlling the pore volume of the negative active material composite.

The anode active material layer may include the anode active material, and optionally further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1 wt% to 5 wt%, respectively, based on the total weight of the anode active material layer.

The binder serves to well adhere the negative active material particles to each other and also to adhere the negative active material well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof may be used.

Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the aqueous binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, polypropylene, ethylene propylene copolymer, and polyepicrohydrin. , polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof can

When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

Another embodiment provides a lithium secondary battery including a positive electrode including a positive electrode active material, the negative electrode, and an electrolyte.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector. As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used. Specifically, at least one of a complex oxide of lithium and a metal 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); Li _a E _1-b X _b O _2-c D _c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a E _2-b X _b O _4-c D _c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤ 2); Li _a Ni _1-bc 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-bc Co _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 _1-bc Mn _b X _c D _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 _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 ≤ e ≤ 0.1); Li _a Ni _b Co _c Al _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 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 Mn _1-b G _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 Mn _1-g G _g PO ₄ (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); 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); Li _a FePO ₄ (0.90 ≤ a ≤ 1.8).

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 mixture of the compound and a compound having a coating layer may be used. The coating layer may contain at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. can The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material (eg, spray coating, dipping method, etc.) by using these elements in the compound. Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

In the positive electrode, the content of the positive active material may be 90 wt% to 98 wt% based on the total weight of the positive active material layer.

In one embodiment of the present invention, the positive active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1 wt% to 5 wt%, respectively, based on the total weight of the positive electrode active material layer.

The binder serves to well adhere the positive active material particles to each other and also to adhere the positive active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including ethylene oxide, polyvinyl pyrrol Money, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto. .

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

Al may be used as the current collector, but is not limited thereto.

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.

As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used.

Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, and caprolactone. etc. may be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used. In addition, cyclohexanone and the like may be used as the ketone-based solvent. In addition, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, nitriles such as nitriles (which may contain double bond aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

The organic solvents may be used alone or in mixture of one or more, and when one or more of the organic solvents are mixed and used, the mixing ratio may be appropriately adjusted according to the desired battery performance, which can be widely understood by those in the art. have.

In addition, 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 1:1 to 1:9, the electrolyte performance may be excellent.

The organic solvent may further include an 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 1:1 to 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 1 may be used.

[Formula 1]

(In Formula 1, R ₁ to R ₆ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.)

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 ,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rottoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3 ,5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of Chemical Formula 2 as a lifespan improving additive to improve battery life.

[Formula 2]

(In Formula 2, R ₇ and R ₈ are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, , wherein at least one of R ₇ and R ₈ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R ₇ and R ₈ are both not hydrogen.)

Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. can When such a life-enhancing additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent, serves as a source of lithium ions in the battery, enables the basic operation of a lithium secondary battery, and serves to promote movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , 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, for example It is an integer from 1 to 20), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB) one or more selected from the group consisting of supporting (supporting) It is included as an electrolyte salt.It is recommended that the concentration of the lithium salt be used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited; Lithium ions can move effectively.

A separator may exist between the positive electrode and the negative electrode depending on the type of the lithium secondary battery. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used. A polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and polypropylene/polyethylene/poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator or the like can be used.

3 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. Although the lithium secondary battery according to an embodiment is described as an example of a prismatic shape, the present invention is not limited thereto, and may be applied to various types of batteries such as a cylindrical shape and a pouch type.

Referring to FIG. 3 , a lithium secondary battery 100 according to an exemplary embodiment includes an electrode assembly 50 wound with a separator 40 interposed between the positive electrode 20 and the negative electrode 30 , and the electrode assembly 50 . ) may include a built-in battery case (60). The positive electrode 20 , the negative electrode 30 , and the separator 40 may be impregnated with an electrolyte.

Hereinafter, Examples and Comparative Examples of the present invention will be described. However, the following examples are only examples of the present invention, and the present invention is not limited to the following examples.

Example

Example 1

Silicon nanoparticles (aspect ratio: 5, average particle diameter: about 100 nm), artificial graphite and petroleum pitch (amorphous carbon) are mixed in an alcohol solvent in a weight ratio of 40: 30: 30 and dispersed using a homogenizer to obtain a dispersion (mixture) prepared. The prepared dispersion was sprayed at 120° C. using a spray dryer. The obtained spray-dried product (precursor) is pressurized to 50 MPa using Powder Pressure and then heat-treated at 1000° C. in a furnace of N ₂ atmosphere. A core containing artificial graphite, amorphous carbon and silicon nanoparticles, and the core A reaction product was prepared in which a coating layer containing amorphous carbon was formed on the surface of the. The obtained reaction product was pulverized and classified using a 325 mesh to prepare a negative electrode active material composite powder.

Example 2

A negative active material composite was prepared in the same manner as in Example 1 except that the precursor was pressurized to 75 MPa.

Example 3

A negative active material composite was prepared in the same manner as in Example 1 except that the precursor was pressurized to 120 MPa.

Example 4

A negative active material composite was prepared in the same manner as in Example 1 except that the precursor was pressurized to 150 MPa.

Comparative Example 1

A negative active material composite was prepared in the same manner as in Example 1 except that the precursor was pressurized to 20 MPa.

Comparative Example 2

A negative active material composite was prepared in the same manner as in Example 1 except that the precursor was not pressurized.

evaluation example

Evaluation Example 1: Measurement of the adjacent distance between silicon nanoparticles and the average particle diameter (D50) of the anode active material composite

Cross-sections of the anode active material composite powders prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were analyzed by transmission electron microscopy (TEM) to measure adjacent distances between silicon nanoparticles. The measurement results are shown in Table 1 below, and a TEM photograph showing the adjacent distance between silicon nanoparticles of the negative active material composite prepared in Example 2 is shown in FIG. 4 .

The adjacent distance between silicon nanoparticles is a measure of the distance between the centers of silicon nanoparticles.

The average particle diameter (D50) of the negative active material composites prepared in Examples 1 to 4 and Comparative Examples 1 to 2 was measured using a particle size analysis_Beckman coulter (PSA) facility, and the measurement results are shown in Table 1 below, A graph of measuring the average particle diameter (D50) of the negative active material composite prepared in Example 3 is shown in FIG. 5 .

Adjacent distance between silicon nanoparticles (nm) Average particle diameter (D50) (㎛) of the negative electrode active material composite Example 1 65 14.5 Example 2 50 14.4 Example 3 35 13.6 Example 4 30 13.3 Comparative Example 1 115 14.9 Comparative Example 2 200 15.5

Referring to Tables 1 and 4, the negative active material composites prepared in Examples 1 to 4 had an adjacent distance between silicon nanoparticles of 65 nm or less to 30 nm or less, and compared to the negative active material composites of Comparative Examples 1 and 2, silicon compared to the negative active material composites of Comparative Examples 1 and 2 It can be seen that the adjacent distance between nanoparticles is reduced. In addition, referring to Table 1 and FIG. 5 , it can be confirmed that the average particle diameter (D50) of the negative active material composite prepared in Examples is 13 μm to 15 μm.

Evaluation Example 2: Scanning Electron Microscopy (SEM) Image Analysis of Anode Active Material Composite

The SEM image of the negative active material composite prepared in Example 3 was analyzed, and the results are shown in FIG. 6 .

Referring to FIG. 6 , it can be seen that artificial graphite (Gr) and silicon nanoparticles (Si) are mixed and distributed in the interior (core) of the anode active material composite. In addition, it can be seen that the amorphous carbon contained in the core and the coating layer of the anode active material composite is present in the form of a thin film, so it is difficult to confirm it with an SEM photograph.

Evaluation Example 3 : Evaluation of specific capacity, initial efficiency, and room temperature cycle life characteristics of lithium secondary batteries

97.5% by weight of a mixture of the negative active material composite prepared according to Examples 1 to 4 and Comparative Examples 1 to 2 and natural graphite in a 20:80 weight ratio, carboxymethylcellulose 1.0% by weight, and styrene-butadiene rubber 1.5% by weight A negative active material slurry was prepared by mixing in a water solvent.

This negative electrode active material slurry was applied to a copper foil current collector, dried and rolled to prepare a negative electrode.

The positive electrode was prepared by mixing 97.3% by weight of lithium cobalt oxide (LiCoO ₂ ) as a positive active material, 1.4% by weight of polyvinylidene fluoride as a binder, and 1.3% by weight of Ketjen Black as a conductive material in N-methyl pyrrolidone to prepare a positive electrode active material slurry. prepared.

This positive electrode active material slurry was applied to Al foil, dried and rolled to prepare a positive electrode.

A lithium secondary battery was manufactured using this negative electrode, positive electrode, and electrolyte.

A mixed solvent (3:7 volume ratio) of ethylene carbonate and dimethyl carbonate in which 1M LiPF ₆ was dissolved was used as the electrolyte.

The prepared lithium secondary battery was charged and discharged once at 0.1 C to evaluate specific capacity and initial charge/discharge efficiency, and the results are shown in Table 2 below.

The prepared lithium secondary battery was charged and discharged 100 times at 25°C at 0.5C. The ratio of the 100 discharge capacity to the single discharge capacity was calculated, and the results are shown in Table 2 below.

Specific capacity (mAh/g) Initial charge/discharge efficiency (%) room temperature cycle life
(25℃, 0.5C, 100 times) (%) Example 1 500 90.1 81.5 Example 2 501 90.9 82.7 Example 3 504 91.1 83.7 Example 4 503 90.8 83.0 Comparative Example 1 495 85.8 65.4 Comparative Example 2 482 84.2 60.2

Referring to Table 2, it can be confirmed that the lithium secondary batteries including the negative active material composite prepared in Examples 1 to 4 have improved specific capacity, initial charge/discharge efficiency, and cycle life compared to Comparative Examples 1 and 2.

Evaluation Example 4: pore volume measurement

In Evaluation Example 3, the electrode plate portion of the non-reacted region of the lithium secondary battery charged and discharged once at 0.1C was collected, and it was put into a pore measuring equipment (equipment name: ASAP series, manufacturer: Micromeritics Instrument Corp), and 10K After raising the temperature to 623K at /min, it was pre-treated by holding for 2 to 10 hours (vacuum 100 mmHg or less). In this case, the temperature and time may be appropriately adjusted according to the anode active material composite powder.

Thereafter, the pore volume was measured in liquid nitrogen controlled to a relative pressure (P/P _o ) of 0.01 or less. Specifically, it was measured by nitrogen adsorption at 32 points up to a relative pressure of 0.01 to 0.995, and nitrogen desorption at 24 points up to a relative pressure of 0.14. At this time, in general, the relative pressure (P/P _o ) can also be calculated as BET up to the point where it is 0.1. The total pore volume measurement results of pores having a size of 200 nm or less are shown in Table 3 below.

pore volume ( x 10 ^-2 cm ³ /g) Example 1 2.0 Example 2 1.1 Example 3 0.5 Example 4 0.3 Comparative Example 1 4.2 Comparative Example 2 5.5

Referring to Table 3, in the negative active material composites prepared in Examples 1 to 4, the total pore volume of pores having a size of 200 nm or less was 2.0 x 10 ^-2 cm ³ /g or less, compared to Comparative Examples 1 and 2 Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications by those skilled in the art using the basic concept of the present invention as defined in the appended claims. and improved forms also fall within the scope of the present invention.

1: Anode active material composite
1a: negative active material composite prepared by the prior art
3: Core 5: Coating layer
11: silicon nanoparticles 13: crystalline carbon
15: Qigong
15a: pores of the negative active material composite prepared in the prior art
20: positive electrode 30: negative electrode
40: separator 50: electrode assembly
60: battery case 100: lithium secondary battery

Claims (11)

Comprising a core and an amorphous carbon coating layer surrounding the core,
The core comprises crystalline carbon and silicon nanoparticles,
The silicon nanoparticles include a negative active material composite having an aspect ratio of 2 to 8,
The negative active material composite is a negative electrode for a lithium secondary battery having a total pore volume of 3.0 x 10 ^-2 cm ³ /g or less of pores having a size of 200 nm or less. According to claim 1,
The silicon nanoparticles have an average particle diameter (D50) of 50 to 150 nm, a negative electrode for a lithium secondary battery. According to claim 1,
The silicon nanoparticles have a half width of 0.3° to 7° of an X-ray diffraction angle (2theta) using CuKα on the (111) plane, a negative electrode for a lithium secondary battery. According to claim 1,
The silicon nanoparticles have an adjacent distance between lithium of 100 nm or less, a negative electrode for a lithium secondary battery. According to claim 1,
The silicon nanoparticles are included in an amount of 20 to 80% by weight based on the total weight of the anode active material composite, a negative electrode for a lithium secondary battery. According to claim 1,
The crystalline carbon is at least one selected from natural graphite, artificial graphite, and combinations thereof, a negative electrode for a lithium secondary battery. According to claim 1,
The crystalline carbon is contained in an amount of 20 to 80% by weight based on the total weight of the negative active material composite, a negative electrode for a lithium secondary battery. According to claim 1,
The negative electrode active material composite has an average particle diameter (D50) of 2 to 15 ㎛, a negative electrode for a lithium secondary battery. According to claim 1,
The coating layer has a thickness of 1nm to 900nm, a lithium secondary battery negative electrode. delete According to claim 1,
The negative active material composite has a BET specific surface area of 10 m ² /g or less, a negative electrode for a lithium secondary battery.

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