KR101911434B1 - Composite anode active material, anode and lithium battery comprising the material, and preparation method thereof - Google Patents

Abstract

A substrate comprising at least one selected from the group consisting of lithium-alloyable metals and oxides thereof; And a coating layer or an interfacial layer formed on at least a part of or on the surface of the substrate, wherein the coating layer or the interfacial layer comprises a metal silicide compound, a negative electrode and a lithium battery including the composite negative electrode active material, A method for producing a composite negative electrode active material is presented.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite anode active material, a cathode and a lithium battery including the composite anode active material, and a method of manufacturing the anode active material, an anode and a lithium battery,

A negative electrode including the composite negative electrode active material, a lithium battery, and a method of manufacturing the composite negative electrode active material.

Currently, carbon-based materials are widely used as cathode materials for lithium batteries. Examples of such a carbon-based active material include crystalline carbon such as graphite and amorphous carbon such as soft carbon and hard carbon. Although the amorphous carbon has a large capacity, it has high irreversibility in charge and discharge processes, and the crystalline carbon has a somewhat higher theoretical limit capacity, but is still insufficient as a high capacity lithium battery. In order to overcome such a problem, currently active materials are lithium metal-based metal-based or intermetallic compounds-based anode active materials.

Here, the metal that can be alloyed with lithium is Si, Sn, Al, or the like. The lithium-alloyable metal has a very large capacity. For example, the capacity is 10 times higher than that of graphite. Since the metal capable of alloying with lithium is accompanied by volume expansion / contraction at the time of charging and discharging, an active material isolated in the electrode is generated, and the decomposition reaction of the electrolyte due to the increase of the specific surface area is intensified.

Accordingly, there is a need for a composite anode active material having a high capacity of metal capable of alloying with lithium and capable of easily absorbing stress due to the volume expansion of the metal, thereby suppressing deterioration.

One aspect is to provide a composite anode active material having improved capacity and lifetime characteristics.

Another aspect is to provide a negative electrode comprising the composite negative electrode active material.

Another aspect is to provide a lithium battery employing the negative electrode.

Another aspect of the present invention provides a method of manufacturing the composite anode active material.

According to one aspect,

A substrate comprising at least one selected from the group consisting of lithium-alloyable metals and oxides thereof; And

A coating layer or an interfacial layer formed on at least a part of the surface or the periphery of the substrate,

There is provided a composite negative electrode active material in which the coating layer or the interface layer includes a metal silicide compound.

According to another aspect,

There is provided a negative electrode comprising the above composite negative active material.

According to another aspect,

A lithium battery including the negative electrode is provided.

According to another aspect,

There is provided a method for manufacturing a composite negative electrode active material comprising milling a metal silicide particle and particles comprising at least one selected from the group consisting of lithium-alloyable metals and oxides thereof.

According to an aspect of the present invention, there is provided a lithium battery comprising a metal silicide coating layer or an interfacial layer formed on a substrate including at least one selected from the group consisting of lithium-alloyable metals and oxides thereof, The efficiency can be improved.

1 is a cross-sectional view of a composite anode active material according to one embodiment.
2 is a scanning electron microscope (SEM) photograph of the composite negative electrode active material prepared in Example 1. Fig.
FIG. 3A is a transmission electron microscope (TEM) photograph of the composite negative electrode active material prepared in Example 2. FIG.
FIG. 3B is an energy dispersive spectroscopy (EDX) spectrum of the core region of the composite anode active material prepared in Example 2. FIG.
3C is an EDX spectrum of the coating layer region of the composite anode active material prepared in Example 2. FIG.
FIG. 4A is an X-ray diffraction (XRD) spectrum of the CaSi ₂ particles used in Examples 1 to 4. FIG.
FIG. 4B is an X-ray diffraction (XRD) spectrum of the composite anode active material prepared in Example 1. FIG.
4C is an X-ray diffraction (XRD) spectrum of the composite anode active material prepared in Example 2. FIG.
5 is a schematic view of a lithium battery according to one embodiment.
Description of the Related Art
1: Lithium battery 2: cathode
3: anode 4: separator
5: Battery case 6: Cap assembly
10: first core 11: second core
12: Coating layer

Hereinafter, a composite anode active material according to exemplary embodiments, a cathode and a lithium battery including the same, and a method for manufacturing the composite anode active material will be described in detail.

A composite anode active material according to an embodiment includes a substrate comprising at least one selected from the group consisting of lithium-alloyable metals and oxides thereof; And a coating layer or an interfacial layer formed on at least a part of the surface or the periphery of the substrate, wherein the coating layer or the interfacial layer includes a metal silicide compound. For example, the composite anode active material includes at least one selected from the group consisting of lithium-alloyable metals and oxides thereof; And a coating layer formed on at least a portion of the core, wherein the coating layer comprises a metal silicide compound.

As shown in FIG. 1, the composite anode active material may have a structure in which the coating layer 12 including the metal silicide covers the cores 10 and 11 including lithium-alloyable metals and / or oxides thereof.

The metal suicide in the composite anode active material is relatively excellent in strength and the like compared with the carbon-based material, so that it can easily absorb the volume expansion of the core during charging and discharging, and has improved conductivity, thereby improving the charging / discharging efficiency, And so on. In addition, the metal silicide can provide enhanced capacity over pure inert metal and carbon-based materials by virtue of the silicon component contained therein.

The core comprising the lithium-metal capable of lithium may simultaneously include a crystalline region and an amorphous region. For example, the core comprising lithium-alloyable metal may comprise a first core comprising a crystalline metal; And a second core comprising amorphous metal formed on the first core. That is, a second core including an amorphous metal may be formed on at least a part of the first core including the crystalline metal. For example, the second core may cover the first core. As shown in Fig. 1, the outer surface of the first core 10, which is a crystalline metal, may be covered with the second core 11, which is amorphous. The above structure can be obtained by amorphizing the outside of the metal particles preferentially while the crystallinity is not completely progressed in the process of milling the metal particles. By including the crystalline region and the amorphous region simultaneously in the core, the high-rate characteristics of the lithium battery including the composite anode active material can be further improved.

The particle size of the core in the composite anode active material may be 5 nm to 100 탆. For example, the particle size of the core in the composite anode active material may be 5 nm to 50 탆.

For example, in the composite anode active material, the particle size of the core may be nanosized to 5 nm to 500 nm. For example, in the composite anode active material, the particle size of the core may be nano-sized from 5 nm to 100 nm.

Alternatively, the particle size of the core in the composite negative electrode active material may be in the range of 1 占 퐉 to 100 占 퐉. For example, in the composite negative electrode active material, the particle size of the core may be in the range of 1 to 50 microns.

The thickness of the coating layer in the composite negative electrode active material may be 1 nm to 500 nm. For example, the thickness of the coating layer in the composite negative electrode active material may be 10 nm to 200 nm. For example, the thickness of the coating layer in the composite negative electrode active material may be 10 nm to 100 nm. If the thickness of the coating layer is too small, it may be difficult to effectively charge and discharge the core. If the thickness of the coating layer is excessively large, the discharge capacity may be excessively reduced.

In the composite negative electrode active material, lithium-alloyable metal may be a Group 14 element of the periodic table of the elements. For example, the lithium-alloyable metal may be Si, Ge, Sn, Pb. In particular, the metal capable of alloying with lithium may be Si.

In the composite negative electrode active material, an oxide of lithium-alloyable metal may be represented by the following formula (1)

≪ Formula 1 >

M _x O _y

Wherein M is at least one selected from the group consisting of Al, Si, Ti, Sn, Ge, and Zr.

For example, the oxide of a metal capable of alloying with lithium may be SiO _z (1? _Z ? 2). For example, the oxide of the lithium-alloyable metal may be SiO.

In addition, in the composite negative electrode active material, a lithium-alloyable metal may be coated with a lithium metal oxide. That is, a coating layer containing a lithium metal oxide may be formed on the core containing the lithium-alloyable metal.

For example, the lithium metal oxide covering the metal capable of alloying with lithium may be represented by the following chemical formula 2:

(2)

Li _x M _y O

Where 0.5? X / y? 2, and M is an element selected from the group consisting of Al, Si, Ti, Ge and Zr. For example, the lithium metal oxide may be Li _x Al _y O, Li _x Si _y O, Li _x Ti _y O, Li _x Zr _y O. X / y? 2 in the lithium metal oxide.

The metal suicide included in the coating layer in the composite negative electrode active material may be represented by the following Formula 3:

(3)

M _a Si _b

In the above formula, 1? A? 4, 1? B? 3, and M is a Group 1 to Group 2 metal element or a transition metal of Groups 3 to 12.

For example, the metal of the metal silicide may be an alkali metal other than lithium.
For example, the metal silicide may be at least one selected from the group consisting of CaSi ₂ , Mg ₂ Si, Cu ₃ Si, NiSi, and FeSi.

The metal suicide in the composite anode active material may be amorphous or low-crystalline. Since the metal silicide is amorphous or low crystalline, the life characteristics of the composite anode active material can be further improved.

The content of the metal silicide in the composite anode active material may be 50 wt% or less based on the total weight of the active material. For example, the content of the metal silicide in the composite negative electrode active material may be 50 wt% or less based on the total weight of the active material. For example, the content of the metal silicide in the composite negative electrode active material may be more than 0 to 50% by weight based on the total weight of the active material. For example, the content of the metal silicide in the composite anode active material may be 5 wt% to 45 wt% based on the total weight of the active material. For example, the content of the metal silicide in the composite anode active material may be 10% by weight to 40% by weight based on the total weight of the active material. If the content of the metal suicide in the composite negative electrode active material is too large, the discharge capacity may be greatly reduced. If the content of the metal suicide is too small, the effect may be insignificant.

The composite anode active material may further include a carbon-based material. The carbon-based material may be additionally coated on the coating layer containing the metal silicide, or may be dispersed and compounded in the composite negative electrode active material. The above-mentioned additional carbon-based material is not particularly limited and can be used as long as it can be used as a carbon-based material in the related art. For example, the carbon-based material may be a sintered material of a precursor of a carbon-based material such as a polymer, carbon fiber, carbon nanotube, graphite, amorphous carbon, or the like. The content of the carbon-based material in the composite anode active material may be 1 to 50 wt% of the total weight of the composite anode active material. For example, the content of the carbon-based material in the composite anode active material may be 5 to 40 wt% of the total weight of the composite anode active material. For example, the content of the carbon-based material in the composite anode active material may be 5 to 30 wt% of the total weight of the composite anode active material.

The negative electrode according to another embodiment includes the composite negative electrode active material. The negative electrode may be manufactured, for example, by forming the negative electrode active material composition containing the composite negative electrode active material and the binder in a predetermined shape or by applying the negative electrode active material composition to a current collector such as copper foil .

Specifically, a negative electrode active material composition in which the composite negative electrode active material, the conductive material, the binder, and the solvent are mixed is prepared. The negative electrode active material composition is directly coated on the metal current collector to produce a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then the film peeled off from the support may be laminated on the metal current collector to produce a negative electrode plate. The negative electrode is not limited to the above-described form, but may be in a form other than the above-described form.

The negative electrode active material composition may further include a carbonaceous negative electrode active material in addition to the composite negative electrode active material. For example, the carbonaceous anode active material may be at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, fullerene soot, carbon nanotube, But are not limited to, and can be used in the art.

As the conductive material, metal powders such as acetylene black, Ketjen black, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, copper, nickel, aluminum and silver, metal fibers, In addition, one or more conductive materials such as polyphenylene derivatives may be used in combination, but the present invention is not limited thereto, and any conductive material may be used as long as it can be used as a conductive material in the related art. In addition, the above-described crystalline carbon-based material can be added as a conductive material.

Examples of the binder include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyacrylic liquid seed, polyamideimide, polytetrafluoro Ethylene and mixtures thereof, styrene butadiene rubber-based polymers, and the like can be used, but not limited thereto, and any of them can be used as long as they can be used as a bonding agent in the technical field.

As the solvent, N-methylpyrrolidone, acetone, water or the like may be used, but not limited thereto, and any solvent which can be used in the technical field can be used.

The content of the composite anode active material, the conductive material, the binder, and the solvent is a level commonly used in a lithium battery. At least one of the conductive material, the binder and the solvent may be omitted depending on the use and configuration of the lithium battery.

A lithium battery according to another embodiment employs a negative electrode comprising the above negative electrode active material. The lithium battery can be produced by the following method.

First, a negative electrode is prepared according to the negative electrode manufacturing method.

Next, a cathode active material composition in which a cathode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated on the metal current collector and dried to produce a positive electrode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then the film peeled from the support may be laminated on the metal current collector to produce a cathode plate.

The positive electrode active material may include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide. However, May be used.

For example, Li _a A _1-b B _b D ₂ , wherein 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); In the formula of LiFePO ₄ may be used a compound represented by any one:

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 combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise an oxide, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a coating element compound of the hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method that does not adversely affect 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.

For example, LiNiO ₂ , LiCoO ₂ , LiMn _x O ₂ x (x = 1, 2), LiNi _1-x Mn _x O ₂ (0 <x <1), LiNi _1-xy Co _x Mn _y O ₂ ? 0.5, 0? Y? 0.5), LiFeO ₂ , V ₂ O ₅ , TiS, MoS and the like can be used.

As the conductive material, binder and solvent in the positive electrode active material composition, the same materials as those of the negative electrode active material composition may be used. It is also possible to add a plasticizer to the cathode active material composition and / or the anode active material composition to form pores inside the electrode plate.

The content of the cathode active material, the conductive material, the binder, and the solvent is a level commonly used in a lithium battery. Depending on the application and configuration of the lithium battery, one or more of the conductive material, the binder, and the solvent may be omitted.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared. The separator can be used as long as it is commonly used in a lithium battery. A material having low resistance against the ion movement of the electrolyte and excellent in the ability to impregnate the electrolyte may be used. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a rewindable separator such as polyethylene, polypropylene, or the like is used for the lithium ion battery, and a separator having excellent organic electrolyte impregnation capability can be used for the lithium ion polymer battery. For example, the separator may be produced according to the following method.

A polymer resin, a filler and a solvent are mixed to prepare a separator composition. The separator composition may be coated directly on the electrode and dried to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled from the support may be laminated on the electrode to form a separator.

The polymer resin used in the production of the separator is not particularly limited, and any material used for the binder of the electrode plate may be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate or mixtures thereof may be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, boron oxide, lithium oxynitride, and the like, but not limited thereto, and any of them can be used as long as they can be used as solid electrolytes in the art. The solid electrolyte may be formed on the cathode by a method such as sputtering.

For example, an organic electrolytic solution can be prepared. The organic electrolytic solution can be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be any organic solvent which can be used in the art. Examples of the solvent include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , Fluoroethylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, gamma -butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide , Dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or mixtures thereof.

The lithium salt may also be used as long as it can be used in the art as a lithium salt. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 5, the lithium battery 1 includes an anode 3, a cathode 2, and a separator 4. The anode 3, the cathode 2 and the separator 4 described above are wound or folded and housed in the battery case 5. Then, an organic electrolytic solution is injected into the battery case 5 and is sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may have a cylindrical shape, a rectangular shape, a thin film shape, or the like. For example, the lithium battery may be a thin film battery. The lithium battery may be a lithium ion battery.

A separator may be disposed between the anode and the cathode to form a battery structure. The cell structure is laminated in a bi-cell structure, then impregnated with an organic electrolyte solution, and the obtained result is received in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery assemblies may be stacked to form a battery pack, and such battery pack may be used for all devices requiring high capacity and high output. For example, a notebook, a smart phone, an electric vehicle, and the like.

Particularly, the lithium battery is suitable for an electric vehicle (EV) because it has a high rate characteristic and a good life characteristic. For example, it is suitable for a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV).

According to another embodiment of the present invention, a method for manufacturing a composite negative electrode active material includes milling particles and metal silicide particles containing at least one selected from the group consisting of lithium-alloyable metals and oxides thereof.

In the above manufacturing method, milling can be performed for 4 hours or more. If the milling time is too short, the degree of milling is low so that the particles can not be mixed together and only simple mixing can be achieved. The pore-forming material may be a material that is pyrolyzed at a temperature below 1500 ° C. For example, milling may be carried out for 4 to 10 hours in the above manufacturing method.

The apparatus used for the milling is not particularly limited and can be any milling apparatus that can be used in the art. For example, a spes mill, a planetary mill, or the like may be used.

Further, the gravitational acceleration, which is a force applied to the material at the time of milling, may be 10 G or more. If the gravitational acceleration applied to the material at the time of milling is less than 10G, the particles can not be mixed with each other and only simple mixing can be performed.

The metal particles that can be alloyed with lithium may be Si nanoparticles, Si microparticles, Ge nanoparticles, Ge microparticles, Sn nanoparticles, Sn microparticles, Pb nanoparticles, Pb microparticles, As long as it can be used as particles of lithium-alloyable metal in the technical field. In addition, the lithium-alloyable metal particles may be coated with a lithium metal oxide. The lithium metal oxide may be lithium titanium oxide.

The particle diameter of the nanoparticles may be 10 nm to 500 nm. For example, the particle size of the nanoparticles may be between 10 nm and 100 nm. On the other hand, the particle size of the microparticles may be 1 탆 to 100 탆. For example, the particle size of the microparticles may be between 1 탆 and 50 탆.

The oxide particles of the lithium-alloyable metal may be SiO ₂ particles, SiO _1.5 particles, a complex of Si and SiO ₂ , and the like, but are not limited thereto. If they can be used as oxide particles of lithium-alloyable metals in the related art Everything is possible.

The metal silicide particles may be at least one particle selected from the group consisting of CaSi ₂ , Mg ₂ Si, Cu ₃ Si, NiSi, and FeSi, but is not limited thereto. The metal silicide particles may be nanoparticles or microparticles. The particle size of the metal silicide nanoparticles may be 10 nm to 500 nm. The particle diameter of the metal silicide microparticles may be 1 탆 to 100 탆.

In the milling step, a carbon-based material may be further included. The carbon-based material is not particularly limited, and carbon fiber, carbon nanotube, graphite, amorphous carbon and the like can be used.

Further, it may further include a step of mixing the precursor of the carbon-based material after the milling step and firing in an inert atmosphere. In the firing step, the carbon-based precursor may be carbonized to form a coating layer containing a carbon-based material.

The present invention will be described in more detail by way of the following examples and comparative examples. However, the examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

(Preparation of negative electrode)

Example 1

6 g of silicon nanoparticles (Aldrich) having a particle diameter of about 50 nm and 3.3 g of CaSi ₂ microparticles (~ 325 mesh, Aldrich) having a particle diameter of about 40 μm were milled for 5 hours with a high energy mechanical milling machine (SPEX CertiPrep, 8000M) Si / CaSi ₂ composites were prepared.

Example 2

Milled for 7 hours to a particle size of about 20㎛ silicon microparticles (~ 325mesh, Aldrich) CaSi ₂ 24.2g of the microparticles with diameter 40 ㎛ (~ 325mesh, Aldrich) 13.2g of a the planetray mill filled with Ar Si / CaSi ₂ Complex.

Example 3

Silicon monoxide (SiO) (~ 325 mesh, Aldrich) particles were milled for 135 minutes in a 2-butanol solvent using Bead mill equipment (Kotobuki, model name: UAM05), and the solvent was vacuum dried to obtain SiO 2 particles .

4.52 g of the SiO ₂ particles and 2.44 g of CaSi ₂ microparticles (~ 325 mesh, Aldrich) having a particle diameter of 40 μm were milled for 5 hours with a high energy mechanical milling machine (SPEX CertiPrep, 8000M) as Ar to prepare a SiO ₂ / CaSi ₂ composite.

Example 4

1.6 g of silicon nanoparticles (Aldrich) having a particle diameter of about 50 nm and 0.4 g of Lithium Titanium Oxide (LTO) (Ishihara) particles having a particle diameter of about 10 탆 were sprayed for 5 hours with a high energy mechanical milling machine (SPEX CertiPrep, 8000M) After milling, Si / LTO composites were prepared by annealing under 850 ㅀ C nitrogen atmosphere.

4.52 g of the Si / LTO composite and 1.22 g of CaSi ₂ microparticles (~ 325 mesh, Aldrich) having a particle diameter of about 40 μm were milled for 5 hours in a high energy mechanical milling machine (SPEX CertiPrep, 8000M) CaSi ₂ complex was prepared

Comparative Example 1

5 g of silicon microparticles (~ 325 mesh, Aldrich) having a particle diameter of about 20 탆 were milled for 5 hours with a high energy mechanical milling machine (SPEX CertiPrep, 8000 M) filled with Ar to prepare a Si negative electrode active material.

Comparative Example 2

Silicon monoxide (SiO) (~ 325 mesh, Aldrich) particles were milled for 135 minutes in a 2-butanol solvent using Bead mill equipment (Kotobuki, model name: UAM05), and the solvent was vacuum dried to obtain SiO 2 particles .

(Preparation of negative electrode and lithium battery)

Example 5

0.057 g of the composite anode active material powder synthesized in Example 1 and 0.276 g of graphite (ICG10H) were mixed in a mortar and then mixed with 6.5 wt% N-methyl (meth) acrylate of a polyamide-imide 0.369 g of pyrrolidone solution was added and mixed again to prepare a negative electrode active material slurry.

The anode active material slurry was coated on a Cu foil having a thickness of 15 탆, dried in an oven at 80 캜 for 1 hour, rolled, dried in a vacuum oven at 200 캜 for 2 hours, .

(Ethylene carbonate): DEC (diethylene carbonate): FEC (fluoroethylene carbonate) was used as a separator, while a polyethylene separator (Tonnen Co., Ltd.) was used as a separator. (5/70/25 by volume ratio) mixed solvent and 1.5 M LiPF ₆ dissolved therein.

Example 6

A coin cell was prepared in the same manner as in Example 5, except that the composite negative electrode active material prepared in Example 2 was used.

Comparative Example 3

0.032 g of the Si powder prepared in Comparative Example 1 and 0.152 g of graphite (ICG10H) were mixed in a mortar. Then, 6.5 wt% of N-methylpyrrole (PAI) of a polyamide- A coin cell was prepared in the same manner as in Example 5, except that 0.246 g of a Don solution was added and mixed again to prepare a negative electrode active material slurry.

Example 7

0.07 g of the composite anode active material powder prepared in Example 3 and 0.114 g of graphite (ICG10H) were mixed in a mortar. Then, 6.5 wt% of a mixture of 6.5 wt% of a polyamide-imide (Torlon) And 0.246 g of methyl pyrrolidone solution were added and mixed again to prepare a negative electrode active material slurry.

Example 8

0.051 g of the composite anode active material powder prepared in Example 4 and 0.134 g of graphite (ICG10H) were mixed in a mortar and then mixed with 6.5 wt% of a polyamide-imide (Toridon) And 0.246 g of methyl pyrrolidone solution were added and mixed again to prepare a negative electrode active material slurry.

Comparative Example 4

0.07 g of the SiO powder prepared in Example 3 and 0.114 g of graphite (ICG10H) were mixed in a mortar, and then 6.5 wt% of N-methylpyrrole (PAI) of a polyamide-imide A coin cell was prepared in the same manner as in Example 5, except that 0.246 g of a Don solution was added and mixed again to prepare a negative electrode active material slurry.

Evaluation Example 1: Measurement of SEM, TEM, EDX, and XRD

A cross-sectional SEM image of the composite negative electrode active material prepared in Example 1 is shown in FIG. It can be seen that CaSi ₂ is uniformly distributed around the Si particles.

A TEM image of the composite anode active material prepared in Example 2 is shown in FIG. 3A, and EDX spectra for the coating layer region 1 and the core region 2 in the composite are shown in 3b to 3c.

3B shows a composite structure in which a core and a coating layer are formed as shown in FIG. 3A. As shown in FIG. 3B, the coating layer region includes Ca atoms, and the core region shown in FIG. 3C does not substantially contain Ca atoms , It was confirmed that a CaSi ₂ coating layer was formed on the Si core.

FIG. 4A is an X-ray diffraction (XRD) spectrum of CaSi ₂ particles used in Examples, and XRD spectra of composite anode active materials prepared in Examples 1 and 2 are shown in FIGS. 4B and 4C. As shown in FIGS. 4B and 4C, almost no peak related to the CaSi ₂ particles is observed, and the core and coating layers of the composite anode active material are mostly amorphized and have partial crystallinity because the Si peak intensity is very low. have.

4B, which is an XRD spectrum of the composite anode active material prepared using the silicon nanoparticles of Example 1, shows that the peak is broader than the XRD spectrum of the composite anode active material prepared using silicon microparticles, ), It can be seen that the amorphization has proceeded much more. That is, it is shown that the composite negative electrode active material of Example 2 contains more regions having crystallinity than the composite negative active material of Example 1.

Since the amorphization of the metal is performed by milling, the center portion of the silicon particle corresponds to the crystalline region and the surface portion corresponds to the amorphous region.

Evaluation Example 2: Evaluation of charge / discharge characteristics

The coin cells prepared in Examples 5 to 8 and Comparative Examples 3 to 4 were subjected to constant current charging at a current of 0.1 C rate at 25 DEG C until the voltage reached 0.01 V (vs. Li), and while maintaining 0.01 V And the cells were subjected to constant-voltage charging until the current reached 0.01C. After the charged coin cell was stopped for 10 minutes, it was discharged at a constant current of 0.1 C until the voltage reached 1.5 V (vs. Li) at the time of discharging.

Then, the battery was charged at a constant current of 0.2 C at a constant current until the voltage reached 0.01 V (vs. Li), and charged at a constant voltage until the current became 0.01 C while maintaining the voltage at 0.01 V. After the charged coin cell was stopped for 10 minutes, the battery was discharged at a constant current of 0.2 C until the voltage reached 1.5 V (vs. Li) at the time of discharging (Mars phase).

The coin cell having undergone the above conversion step was subjected to constant current charging at a current of 1.0 C rate at 25 DEG C until the voltage reached 0.01 V (vs. Li), and the battery was charged at a constant voltage until the current became 0.01 C while maintaining the voltage at 0.01 V . After the charged coin cell was stopped for 10 minutes, a cycle of discharging at a constant current of 1.0 C was repeated 30 times until the voltage reached 1.5 V (vs. Li) at the time of discharging. Part of the charge-discharge test results are shown in Table 1 below.

The initial efficiency and the capacity retention rate were calculated from the following equations (1) and (2), respectively.

&Quot; (1) &quot;

The initial efficiency (%) = [discharge capacity / charge capacity at 1 ^st cycle at 1 ^st cycle] × 100

&Quot; (2) &quot;

Capacity retention rate [%] = [Discharge capacity of 33 ^rd cycle / Discharge capacity of 3 ^rd cycle] × 100

Initial efficiency
[%] Capacity retention rate
[%] Comparative Example 3 85 88 Example 5 82 94 Example 6 84 93 Comparative Example 4 63 95 Example 7 74 99 Example 8 79 98

As shown in Table 1, the coin cells of Examples 5 to 6 including the metal silicide showed an increase in the capacity retention ratio as compared with Comparative Example 3.

Further, in Comparative Examples 4, 7 and 8 including the metal oxide, the initial efficiency and the capacity retention rate of Examples 7 to 8 including the metal silicide were improved as compared with Comparative Example 4.

Evaluation Example 3: Evaluation of output characteristics

The coin cells prepared in Comparative Example 4 and Examples 7 to 8 were subjected to a chemical conversion step as in Evaluation Example 2 and the coin cells were subjected to a voltage of 0.01 V (vs. Li) at a current of 0.5 C rate at 25 캜, And the battery was charged at a constant voltage until the current became 0.05 C while maintaining the voltage at 0.01 V. [ After the charged coin cell was stopped for 10 minutes, a cycle of discharging at a constant current of 1.0 C and 3 C was performed until the voltage reached 1.5 V (vs. Li) at the time of discharging. Respectively. The output characteristic was calculated from the following equation (3).

&Quot; (3) &quot;

Output characteristic [%] = [Discharge capacity at 3C rate / Discharge capacity at 0.2C rate] × 100

Output characteristics [%] Comparative Example 4 75 Example 7 87 Example 8 92

As shown in Table 2, the output characteristics of the coin cells of Examples 7 to 8 were improved compared to the lithium battery of Comparative Example 4.

Claims (19)

A substrate comprising lithium and an alloyable metal; And
A coating layer or an interfacial layer formed on at least a part of the surface or the periphery of the substrate,
Wherein the coating or interfacial layer comprises a metal silicide compound,
Wherein the substrate comprising the metal capable of alloying with lithium,
A first core comprising a crystalline metal; And
And a second core comprising an amorphous metal formed on the first core,
And the second core covers the first core. delete delete delete The composite negative electrode active material according to claim 1, wherein the metal capable of alloying with lithium is an element belonging to Group 14 of the Periodic Table of Elements. The composite negative electrode active material according to claim 1, wherein the lithium-alloyable metal is Si. delete delete The composite negative electrode active material according to claim 1, wherein the lithium-alloyable metal is coated or compounded with a lithium metal oxide. The composite negative electrode active material according to claim 9, wherein the lithium metal oxide is represented by the following formula (2)
(2)
Li _x M _y O
Where 0.5? X / y? 2, and M is an element selected from the group consisting of Al, Si, Ti, Ge and Zr. The composite negative electrode active material according to claim 1, wherein the metal silicide is represented by the following formula (3)
(3)
M _a Si _b
In the above formula, 1? A? 4, 1? B? 3, and M is a Group 1 to Group 2 metal element or a Group 3 to Group 12 transition metal. The composite negative electrode active material according to claim 1, wherein the metal of the metal silicide is an alkali metal other than lithium. The composite anode active material according to claim 1, wherein the metal silicide is at least one selected from the group consisting of CaSi ₂ , Mg ₂ Si, Cu ₃ Si, NiSi, and FeSi. The composite anode active material according to claim 1, wherein the metal silicide is amorphous or low crystalline. The composite anode active material according to claim 1, wherein the content of the metal silicide is 50 wt% or less based on the total weight of the active material. The composite negative electrode active material according to claim 1, wherein the composite negative electrode active material further comprises a carbon-based material. A negative electrode comprising the composite negative electrode active material according to any one of claims 1, 5, 6, and 9 to 16. 18. A lithium battery comprising a negative electrode according to claim 17. 17. A method of manufacturing a composite negative electrode active material according to any one of claims 1, 5, 6, and 9 to 16,
And milling the metal silicide particles and particles comprising lithium-alloyable metal.

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