KR20140032831A - Si negative electrode active material - Google Patents

Abstract

The present invention relates to a Si negative electrode active material with a reformed surface, and more specifically to: a Si negative electrode active material which remarkably improves the lifetime properties of a battery by forming a stable SEI layer connected with a covalent bond by forming a polymer with an initiation site for producing the SEI layer on the surface of the Si negative electrode active material; a surface reformation method of the Si negative electrode active material; a negative electrode material including the same; and a lithium secondary battery including the same.

Description

Si negative electrode active material {Si NEGATIVE ELECTRODE ACTIVE MATERIAL}

The present invention relates to a Si anode active material.

Recently, interest in energy storage technology is increasing. As the field of application extends to energy sources of mobile phones, camcorders and notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the field that attracts the most attention in this respect, and among them, the development of a secondary battery capable of charging and discharging has become a focus of attention. Recently, in the development of such secondary batteries, research and development on the design of new electrodes and batteries have been conducted in order to improve capacity density and specific energy.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

In general, a method of manufacturing a lithium secondary battery is to apply a slurry including a positive electrode active material and a negative electrode active material to each current collector, and then to prepare and prepare an electrode assembly by winding or laminating together with a separator, which is an insulator, and placing the electrode assembly in a battery case. And inserting and injecting electrolyte into the battery case to seal the battery case, and performing degassing to remove gas generated during initial formation.

Here, lithium ions are transferred to a carbon-based negative electrode, such as graphite, from the lithium metal oxide used as the positive electrode during the initial charging, and intercalated between the layers of the graphite electrode. At this time, since lithium is highly reactive, lithium reacts with an electrolyte solution (non-aqueous organic solvent) on the graphite negative electrode surface, thereby producing compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of passivation layer on the surface of the graphite cathode, which is called a solid electrolyte interface (SEI) layer.

Meanwhile, in order to improve the performance of a lithium secondary battery, it is necessary to use a cathode active material and a cathode active material capable of realizing high capacity. Among them, a carbon-based material such as graphite is mainly used as the negative electrode active material, but recently, a Si negative electrode active material having a much higher capacity than graphite has been particularly attracting attention.

However, these high-capacity Si anode materials are accompanied by extreme volume changes during charging and discharging, which constantly leads to new electrode / electrolyte interface exposures, resulting in irreversible generation of additional SEI layers.

Therefore, when using the Si anode active material, it is time to develop a technology that can greatly improve the life characteristics of the battery by minimizing the new interface exposure even during continuous charge and discharge.

Korean Patent Publication No. 10-2009-0011888

The present invention has been made to solve the above-mentioned demands and conventional problems, and by producing a stable SEI layer on the surface of the Si anode active material and minimizing new interface exposure even during continuous charging and discharging, Si can greatly improve the lifespan characteristics of the battery. It is a technical problem to provide a negative electrode active material.

In order to achieve the above technical problem, the present invention provides a Si anode active material, characterized in that a polymer having a reaction site (initiation site) of the SEI (solid electrolyte interface) generation (hereinafter referred to as SEI layer generation polymer) is formed on the surface do.

In addition, the SEI layer-producing polymer provides a Si anode active material, characterized in that formed by in-situ polymerization (in-situ polymerization).

In addition, the length of the SEI layer generating polymer provides a Si anode active material, characterized in that 5 ~ 10nm.

In addition, the SEI layer generated from the SEI layer generating polymer provides a Si anode active material, characterized in that is covalently connected with the SEI layer generating polymer.

In addition, the SEI layer generating polymer provides a Si anode active material, characterized in that represented by the following formula (1):

[Formula 1]

In addition, the present invention provides a negative electrode material comprising the Si negative electrode active material.

In addition, the present invention provides a lithium secondary battery comprising the negative electrode material.

In addition, the SEI layer-producing polymer provides a lithium secondary battery, characterized in that the same or similar form as the organic solvent of the electrolyte contained in the lithium secondary battery.

In addition, the present invention provides a method for surface modification of a Si anode active material, characterized in that to form an SEI layer generating polymer on the surface of the Si anode active material using in situ polymerization.

The present invention provides a stable SEI layer covalently linked by forming a polymer having an reaction site for generating an SEI layer on the surface of the Si anode active material, thereby greatly improving the lifespan characteristics of the battery.

1 is a schematic diagram showing a polymer having a reaction site (initiation site) of the formation of the SEI layer formed on the surface of the Si anode active material and the SEI layer is covalently connected.

Hereinafter, the present invention will be described in detail.

Si Anode active material  And Surface modification  Way

The negative electrode active material of the present invention is a Si negative electrode active material, on which a polymer having a reaction site (initiation site) for generating a solid electrolyte interface (hereinafter referred to as "SEI layer generating polymer") is formed.

Si anode active materials (including Si, SiO, SiO ₂ , composites and mixtures thereof; in particular, Si) are materials that exhibit a capacity per gram of up to five times or more of graphite, but include lithium ion insertion during repeated charge and discharge, Severe volume change occurs due to shrinkage and expansion due to desorption, which in turn causes a new electrode / electrolyte interface exposure, resulting in irreversible generation of additional SEI layers.

Thus, in the present invention, by forming a polymer (red solid line in Fig. 1) having a reaction site of the SEI layer formation by the electrolyte reduction / decomposition reaction on the surface of the Si anode active material, the SEI layer (cloud shape in Fig. 1) ) Is connected to the polymer by a stable covalent bond to provide a Si anode active material that greatly improves the life characteristics of the battery (see Figure 1).

In addition, the SEI layer generating polymer is not particularly limited as long as it has a reaction site for SEI layer formation, and can form stable covalent bonds with the generated SEI layer.

In one embodiment, the SEI layer generating polymer may be represented by the following formula (1).

[Formula 1]

In Formula 1,

R is a hydrogen atom, a halogen atom (e.g., Cl or Br), a hydroxy group, an alkyl group (e.g., an alkyl group having 1 to 13 carbon atoms; specifically a methyl group, an ethyl group or a propyl group), an alkoxy group (e.g., alkoxy having 1 to 13 carbon atoms) Specifically, a methoxy group, an ethoxy group or a propoxy group) or an aryl group (for example, an aryl group having 6 to 10 carbon atoms; specifically, a phenyl group, a chlorophenyl group or a tolyl group). It may be a hydrogen atom.

n represents an integer of 2 to 1000 as a repeating unit.

In the SEI layer-forming polymer of Chemical Formula 1, the reaction site (starting site) of SEI generation becomes a CO ₃ portion of a cyclic carbonate.

The present invention introduces a reaction site through the surface treatment of the Si anode active material, and proceeds to form the SEI material therefrom. The SEI layer thus formed is connected by covalent bonds to maintain a stable structure even during continuous charge and discharge. (See FIG. 1).

The method of surface modifying the Si anode active material by forming the SEI layer generating polymer on the surface of the Si anode active material is not particularly limited.

In one embodiment, the SEI layer generating polymer may be formed by in-situ polymerization, thereby efficiently generating a stable SEI layer covalently linked.

In detail, surface treatment may be performed by introducing a radical polymerization site for growing the SEI layer generating polymer on the surface of the Si anode active material in the manner as shown in [Figure 1].

[Figure 1]

는 Si 음극활물질 표면에 존재하는 히드록시기(-OH)의 산소 원자(O)를 매개로 서로 연결됨과 동시에 직접 Si 음극활물질 표면에 부착된다. 또한 Si 음극활물질 표면에 도입된 상기 중합 개시제(initiator)에는 반응성이 높은 Cl이 포함되어 있어 이후 SEI층 생성 폴리머를 효율적으로 성장시킬 수 있다. In Figure 1 above,

Are directly connected to the surface of the Si anode active material while being connected to each other through an oxygen atom (O) of a hydroxyl group (—OH) present on the surface of the Si anode active material. In addition, the polymerization initiator (Initiator) introduced to the surface of the Si anode active material (Cl) contains a highly reactive Cl can subsequently grow the SEI layer generating polymer efficiently.

As described above, by first introducing a radical polymerization site for growing the SEI layer-forming polymer on the surface of the Si anode active material, the monomer and other additives represented by the following formula (2) are added and subjected to radical polymerization, thereby forming the surface of the formula (1) on the surface of the Si anode active material. The polymer of can finally be formed. Subsequently, an SEI layer is formed through radical polymerization from an reaction site, such as a CO ₃ moiety, on the polymer of Formula 1, and the SEI layer thus formed is stably connected to the polymer by covalent bonds.

(2)

In Formula 2,

R is as defined above in formula (1).

In addition, in terms of minimizing the increase in resistance, the length of the SEI layer generating polymer may be formed in the range of 5 ~ 10nm.

Anode material

According to another aspect of the present invention, a negative electrode material including the Si negative electrode active material of the present invention as described above is provided.

The negative electrode material may include a binder, a conductive material, etc. in addition to the Si negative electrode active material of the present invention.

The binder is a component that assists the bonding between the active material and the conductive material and the current collector, and includes polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), Polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE), poly Vinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene Rubber, fluororubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, and mixtures thereof But it can be used at least one member selected from the group, is not limited thereto consisting of.

The conductive material is not particularly limited as long as it has excellent electrical conductivity without causing side reactions in the internal environment of the lithium secondary battery and without causing chemical changes to the battery. Typically, graphite or conductive carbon may be used.

For example, graphite, such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, denca black, thermal black, channel black, furnace black, lamp black and summer black; Carbon-based materials whose crystal structure is graphene or graphite; Conductive fibers such as carbon fiber and metal fiber; Carbon fluoride; Metal powders such as aluminum and nickel powders; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And conductive polymers such as polyphenylene derivatives; may be used alone or in combination of two or more thereof, but is not necessarily limited thereto.

Filler may be selectively added to the negative electrode material of the present invention as a component that suppresses the expansion of the electrode.

The filler is not particularly limited as long as it can suppress the swelling of the electrode without causing chemical change in the battery, for example, olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers; Etc. may be used.

Lithium secondary battery

According to another aspect of the present invention, there is provided a lithium secondary battery comprising the negative electrode material of the present invention as described above.

The lithium secondary battery of the present invention includes a positive electrode and a negative electrode, and the negative electrode includes a Si negative electrode active material in which an SEI layer-forming polymer is formed on a surface thereof.

In general, a lithium secondary battery includes a positive electrode composed of a positive electrode material and a current collector, a negative electrode composed of a negative electrode material and a current collector, and a separator that blocks electrical contact between the positive electrode and the negative electrode and moves lithium ions. Void contains electrolyte for conduction of lithium ion.

The positive electrode and the negative electrode may be prepared according to conventional methods known in the art. For example, at least one positive electrode active material and the Si negative electrode active material, the conductive material, the binder, and the filler (if necessary) of the present invention are dispersed and mixed in a dispersion medium (solvent) to form a slurry and coated on the current collector. It can be dried and rolled to produce a positive electrode and a negative electrode.

As the cathode active material, conventional active materials used for the cathode of a lithium secondary battery may be used without particular limitation. For example, at least one selected from the group consisting of lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt oxide, and lithium-nickel-manganese-cobalt oxide may be used as the lithium metal oxide. Can be.

The dispersant may be N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof, but is not limited thereto.

The current collector may be platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al) , Copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and These alloys, and the surface treatment of carbon (C), nickel (Ni), titanium (Ti) or silver (Ag) on the surface of aluminum (Al), copper (Cu) or stainless steel can be used, It is not necessarily limited thereto. Specifically, aluminum is used as the positive electrode current collector and copper is used as the negative electrode current collector. The shape of the current collector may be in the form of a foil, film, sheet, punched, porous body, foam or the like.

The separator is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and serves to provide a movement passage of lithium ions.

The separator may be an olefin-based polymer such as polyethylene or polypropylene, glass fiber, or the like, in the form of a sheet, a multilayer, a microporous film, a woven fabric, a nonwoven fabric, but is not limited thereto. On the other hand, when a solid electrolyte such as a polymer (eg, an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 ~ 10㎛, the thickness may generally range from 5 ~ 300㎛.

In addition, an organic / inorganic composite porous separator prepared from a slurry including inorganic particles, a binder polymer, and a solvent having greatly enhanced safety may be used as the separator.

The electrolyte may be used alone or as a mixture of two or more kinds of carbonate, ester, ether or ketone as a non-aqueous electrolyte (non-aqueous organic solvent), but is not limited thereto.

For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, gamma- butyrolactone, n-methyl acetate, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid triesters, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran Tetrahydrofuran derivatives, dimethyl sulfoxide, formamide, dimethylformamide, dioxolon and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxy methane, sulfolane, methyl sulfolane, 1,3 Aprotic organic solvents such as dimethyl-2-imidazolidinone, methyl propionate and ethyl propionate may be used, but are not limited thereto. It is not.

Lithium salt may be further added to the electrolyte solution (so-called lithium salt-containing non-aqueous electrolyte solution), and the lithium salt may be well-known in the non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, and LiClO _4. , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₃ (CF ₂ CF ₃ ) _3, LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carbonate, lithium 4-phenylborate, imide, and the like, but are not necessarily limited thereto.

In the (non-aqueous) electrolyte, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, for the purpose of improving charge and discharge characteristics, flame retardancy, and the like. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to impart nonflammability, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

In the lithium secondary battery of the present invention, the SEI layer-forming polymer formed on the surface of the Si anode active material may be the same as or similar to the organic solvent of the electrolyte contained in the lithium secondary battery. By introducing a polymer of the same or similar form as the organic solvent of the electrolytic solution participating in the reduction / decomposition reaction to the surface of the Si anode active material, the SEI layer formation reaction may occur smoothly.

Here, the 'same or similar form' means that the organic solvent of the SEI layer-forming polymer and the electrolyte belongs to the organic compound of the same classification, for example, carbonate-based and carbonate-based, ester-based and ester-based, ether-based, ether-based, ketone It means the case of organic compounds, such as a system and a ketone system.

The lithium secondary battery of the present invention can be manufactured according to a conventional method in the art. For example, it can be prepared by putting a porous separator between the prepared positive and negative electrodes, respectively, and adding a nonaqueous electrolyte.

The lithium secondary battery of the present invention uses a Si anode active material including a stable SEI layer generating site, and the lifespan characteristics of the battery are greatly improved compared to the case of using a conventional surface-modified Si anode active material.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. The scope of the present invention should be interpreted based on the scope of the following claims, and all technical ideas within the scope of equivalents thereof should be interpreted in accordance with the following claims: It is to be understood that the invention is not limited thereto.

Claims (10)

Si anode active material characterized in that a polymer having a reaction site (initiation site) of the SEI layer (solid electrolyte interface) generation (hereinafter referred to as SEI layer generation polymer) formed on the surface.
The method of claim 1,
The SEI layer generating polymer is Si anode active material, characterized in that formed by in-situ polymerization (in-situ polymerization).
The method of claim 1,
Si anode active material, characterized in that the length of the polymer produced SEI layer is 5 ~ 10nm.
The method of claim 1,
And a SEI layer formed from the SEI layer generating polymer is covalently connected to the SEI layer generating polymer.
The method of claim 1,
The SEI layer generating polymer is Si anode active material, characterized in that represented by the formula (1):
[Chemical Formula 1]

In Formula 1,
R represents a hydrogen atom, a halogen atom, a hydroxy group, an alkyl group, an alkoxy group or an aryl group,
n is an integer of 2 to 1000 as a repeating unit.
6. The method of claim 5,
In Formula 1,
R is a Si anode active material, characterized in that a hydrogen atom.
A negative electrode material comprising the Si negative electrode active material according to any one of claims 1 to 6.
A lithium secondary battery comprising the negative electrode material according to claim 7.
9. The method of claim 8,
The SEI layer generating polymer is a lithium secondary battery, characterized in that the same or similar form as the organic solvent of the electrolyte contained in the lithium secondary battery.
A method for surface modification of an Si anode active material, comprising forming an SEI layer-forming polymer on the surface of the Si anode active material using in situ polymerization.

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