KR20140032836A - Surface-treated si negative electrode active material - Google Patents

Abstract

The present invention relates to a surface-treated Si-based cathode electrode active material and, more specifically, to a Si-based cathode active material facilitated with a secondary surface treatment by surface-treating a SiOx cathode material, which are specifically SiOx nanoscale particles, with polydopamine, to improve dispersibility, and by providing an additional surface treatment reaction site. The present invention relates to the same Si-based cathode material, the method for surface treatment, the cathode material and a lithium secondary battery including the same.

Description

Surface-treated Si-based anode active material {SURFACE-TREATED Si NEGATIVE ELECTRODE ACTIVE MATERIAL}

The present invention relates to a surface-treated Si-based negative electrode 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.

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-based negative electrode active material having a much higher capacity than graphite has been particularly noticed.

However, such a high capacity Si-based negative electrode material is accompanied by a severe volume change during charging and discharging, which results in a breakdown of the particles resulting in poor life characteristics.

In order to overcome this problem, the splitting of particles can be minimized by mixing the active phase (Si) and the inactive phase (SiO ₂ ) or by nanoparticle size. And the number of surface reactors decreases, making the surface treatment difficult.

Therefore, Si-based anode active material, in particular SiO _x By improving the dispersibility of nanoparticles and facilitating additional surface treatment, it is time to develop a technology that can ultimately improve the performance of a battery to which the nanoparticles are applied.

Korean Patent Publication No. 10-2009-0011888

The present invention has been made to solve the above-mentioned requirements and conventional problems, and with SiO _x It is a technical object of the present invention to provide a modified Si-based anode active material capable of improving dispersibility of the same Si-based anode active material and facilitating additional surface treatment.

In order to achieve the above technical problem, the present invention is a Si-based anode active material characterized in that the surface-coated with polydopamine (in detail SiO _x , more specifically, SiO _x Nanoparticles).

In addition, the Si-based negative electrode active material surface-coated with the polydopamine provides a negative electrode active material having a hydrophilic surface.

In addition, the Si-based negative electrode active material provides a negative electrode active material, characterized in that the secondary coating with a second coating material other than polydopamine.

In addition, the polydopamine and the second coating material provides a negative electrode active material, characterized in that the coating by one-pot coating (One-pot coating).

In addition, the secondary coating provides a negative electrode active material, characterized in that performed by polymer grafting.

In addition, the Si-based negative electrode active material provides a negative electrode active material characterized in that the carbon-based conductive material is coated, or that the Si-based negative electrode active material and the carbon-based conductive material is a composite.

In addition, the present invention provides a negative electrode material comprising the Si-based negative electrode active material, and a binder (in detail, an aqueous binder).

In addition, the aqueous binder provides an anode material, characterized in that at least one selected from acrylic binder, urethane resin and styrene-butadiene rubber (SBR).

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

Furthermore, the present invention provides a surface treatment method of a negative electrode active material, characterized in that the mixed Si-based negative active material and dopamine, and coating the poly dopamine on the surface of the Si-based negative active material through the polymerization of the dopamine.

In addition, the polymerization reaction provides a surface treatment method of the negative electrode active material, characterized in that carried out in an atmosphere of pH 8 ~ 9 (details, pH 8.5).

According to the invention SiO _x SiO _x by surface treatment of the anode material with polydopamine Secondary surface treatment can be facilitated by improving the dispersibility of the negative electrode material (specifically, SiO _x nanoparticles) and providing additional surface treatment reaction sites.

In addition, the polydopamine treatment of the present invention can be coated irrespective of the surface properties of the object to be treated, the coating thickness can be easily adjusted, and only water is used in the treatment process.

In addition, according to the present invention, since the aggregation between particles observed in the general wet surface treatment process does not occur, a separate disintegration process is not required after the treatment, and the coating layer may be formed without damaging the surface of the raw material.

1 is SiO _x according to the present invention. It is a schematic diagram which shows the structure in which the polydopamine coating layer was formed in the surface.
Figure 2 is a schematic diagram illustrating a polydopamine surface treatment and a secondary surface treatment according to the present invention.
3 is a schematic diagram illustrating the polydopamine surface treatment and coating thickness over time according to the present invention.

Hereinafter, the present invention will be described in detail.

Surface treatment Si system Anode active material  And its surface treatment method

The negative electrode active material of the present invention is Si-based, the surface of which is coated with polydopamine (Polydopamine).

Si-based negative electrode active material is a material that exhibits a capacity per g up to five times or more of graphite, but when charging and discharging, a severe volume change occurs due to shrinkage and expansion due to insertion, desorption of lithium ions, and thus, particles are cracked or structured. There are disadvantages in that the service life is poor, such as being destroyed.

In order to enhance the durability of the Si-based anode active material, the particle size may be nanoscaled to minimize the cleavage of the particles, but in this case, aggregation occurs between the nanoparticles, thereby reducing the number of surface reactors. Surface treatment of the particles to be performed becomes difficult.

Accordingly, in the present invention, the surface of the Si-based negative electrode active material for the purpose of improving the characteristics, by coating the surface with polydopamine, to improve the dispersibility and to facilitate additional surface treatment to improve the performance of the negative electrode and the battery applied thereto It provides a modified Si-based negative electrode active material. The polydopamine is a non-toxic chemical component that mimics a mussel adhesive, and refers to a polymer polymerized using dopamine (following formula) as a monomer.

Dopamine

Specifically, the Si-based negative electrode active material is SiO _x , that is, an oxide of Si (SiO, SiO _2, etc.), or an active phase (Si) and an inactive phase (SiO ₂ ) are mixed (SiO _x ). Nano-sized SiO _x May be particles.

In one embodiment, the surface of the Si-based negative electrode active material (eg, SiO _x nanoparticles) of the present invention surface-coated (surface modified) with polydopamine exhibits hydrophilicity (see FIG. 1). For this reason, the dispersibility at the time of electrode manufacturing (especially at the time of manufacturing an aqueous electrode) is improved significantly and the aggregation between particle | grains can be efficiently minimized.

In addition, the Si-based negative electrode active material may be coated with a carbon-based conductive material, or a composite of the Si-based negative electrode active material and the carbon-based conductive material. The Si-based negative electrode active material may be insufficient in conductivity alone. To compensate for this, the Si-based negative electrode active material is coated with a material having excellent conductivity or a composite thereof is formed before surface modification with polydopamine.

The carbon-based 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, and for example, natural graphite, artificial graphite, and the like. black smoke; Carbon blacks such as carbon black, acetylene black, ketjen black, denca black, thermal black, channel black, furnace black, lamp black and summer black; Graphite, graphite-based carbonaceous material, or the like can be used.

The negative electrode active material according to the present invention is capable of further surface treatment (surface modification) after polydopamine coating. That is, when the Si-based anode active material is surface-modified with polydopamine, an additional surface treatment reaction site is provided, and thus secondary coating may be easily performed with a second coating material other than polydopamine.

In addition, the polydopamine coating has the property of forming a coating layer without damaging the surface of the raw material on any surface, so that additional surface treatment can be more easily performed (see FIG. 2).

The purpose and specific coating method of the secondary coating that can be used for the polydopamine coating followed by additional surface treatment is not particularly limited.

In one embodiment, the polydopamine and the second coating material may be coated by one-pot coating. That is, polydopamine can be coated on the negative electrode active material along with other materials (functional groups) having desired properties through the method of one-pot coating, from which secondary surface modification is possible.

Here, the one-pot coating (or one-pot reaction) means that in the case of synthesizing the target compound by two or more reaction processes, the product (intermediate product) of each stage is isolated in one reaction vessel without isolation and purification. It refers to a synthetic operation in which the method of adding a reactant in the step is continued to obtain a target compound. One-pot coatings avoid the loss of material from the isolation purification of the intermediate product, so all yields are compared to the process of isolating and purification of the intermediate product one by one, as long as the by-products do not interfere with the reaction of the next step. Can be improved.

In another embodiment, the secondary coating may be performed by polymer grafting. That is, secondary surface modification can be performed by copolymerizing linear polydopamine formed on the surface of the negative electrode active material in a state of having a different polymer.

The method of coating the surface of the Si-based negative electrode active material such as SiO _x nanoparticles with polydopamine is not particularly limited. In one embodiment, the Si-based negative electrode active material and dopamine may be mixed, and polydopamine may be coated on the surface of the Si-based negative electrode active material through polymerization of the dopamine (see FIG. 3). Here, the polymerization of dopamine may be performed in an atmosphere of pH 8-9, more specifically in an atmosphere of pH 8.5.

Anode material

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

The binder is a component that assists the bonding between the active material and the conductive material and the bonding to the current collector, and includes polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), and poly Vinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE), polyvinyl 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 Luer binary, but it can be used at least one member selected from the group, is not limited thereto.

The surface-modified Si-based negative electrode active material of the present invention may be applied to both the non-aqueous binder and the aqueous binder, and there is no particular limitation on the type of binder.

In one embodiment, the surface-modified Si-based negative electrode active material of the present invention can be applied to an aqueous binder. Since the surface of the Si-based negative electrode active material (eg, SiO _x nanoparticles) of the present invention coated with polydopamine exhibits hydrophilicity, its dispersibility is greatly improved when manufacturing an aqueous electrode, thereby minimizing aggregation between particles.

In addition, the aqueous binder is economical and environmentally friendly, unlike the solvent-based (non-aqueous) binder, and has the advantage of harmless to the health of the worker, and has a high binding effect compared to the solvent-based binder, so that the ratio of the active material per volume can be increased to increase the capacity Make it possible.

The aqueous binder may be used without particular limitation, those commonly used in the art, including an acrylic binder. For example, at least one selected from an acrylic binder, a urethane resin, and styrene-butadiene rubber (SBR) may be used. In one embodiment, SBR can be used.

When using an aqueous binder, the negative electrode material of the present invention may further include a cellulose-based dispersant. Aqueous binders, in particular SBR, are prepared in a form in which fine particles are dispersed by suspension in water, and the viscosity of the slurry is very low at the time of manufacture, so that mixing and coating may not proceed smoothly. It is preferable to add additional. The cellulose-based dispersant may be used at least one selected from the group consisting of carboxy methyl cellulose (CMC), hydroxy methyl cellulose, hydroxy ethyl cellulose and hydroxy propyl cellulose, but is not necessarily limited thereto.

The binder is typically added in an amount of 1 to 50 parts by weight, more specifically 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the negative electrode material including the active material. When the content of the binder is less than 1 part by weight, the adhesion between the active material and the current collector may be insufficient. When the content of the binder exceeds 50 parts by weight, the adhesion may be improved, but the content of the active material may be reduced, thereby lowering the battery capacity.

The negative electrode material of the present invention may further include a conductive material to improve electrical conductivity.

The conductive material is not particularly limited as long as the conductive material 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 powder; Conductive whiskey 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.

The conductive material is typically added in an amount of 0.5 to 50 parts by weight, specifically 1 to 15 parts by weight, and more specifically 3 to 10 parts by weight, based on 100 parts by weight of the total weight of the negative electrode material including the active material. If the content of the conductive material is too small, less than 0.5 parts by weight, it is difficult to expect the effect of improving electrical conductivity or the electrochemical properties of the battery may be lowered. If the content of the conductive material is more than 50 parts by weight, the amount of the active material is relatively small. Capacity and energy density can be lowered.

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 inhibit the swelling of the electrode without causing chemical change in the battery, and examples thereof include olefinic 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 cathode including a cathode and an Si-based anode active material surface-coated with polydopamine.

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, one or more active materials, conductive materials, binders, fillers (if necessary), and the like are dispersed and mixed in a dispersion medium (solvent) to form a slurry, and then coated on a current collector, followed by drying and rolling to form a positive electrode and a negative electrode. It can manufacture.

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.

As the separator, an olefin polymer such as polyethylene or polypropylene, glass fiber, or the like may be used in the form of a sheet, a multilayer, a microporous film, a woven fabric, and 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.

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-based negative electrode active material that is greatly improved in dispersibility by polydopamine surface coating and is suitable for additional surface treatment, compared to the case of using a conventional unmodified Si-based negative electrode active material. The performance of the battery is greatly improved.

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 (15)

Si-based negative electrode active material, characterized in that the surface coating with polydopamine.
The method of claim 1,
The Si-based anode active material is a cathode active material, characterized in that SiO _x .
3. The method of claim 2,
The Si-based negative electrode active material is SiO _x Cathode active material, characterized in that the nanoparticles.
The method of claim 1,
Si-based negative electrode active material surface-coated with the polydopamine is characterized in that it has a hydrophilic surface.
The method of claim 1,
The Si-based negative electrode active material is a negative electrode active material, characterized in that the secondary coating with a second coating material other than polydopamine.
6. The method of claim 5,
The polydopamine and the second coating material is a negative electrode active material, characterized in that the coating by one-pot coating (One-pot coating).
6. The method of claim 5,
The secondary coating is a negative electrode active material, characterized in that performed by polymer grafting (Polymer grafting).
The method of claim 1,
The Si-based negative electrode active material is a negative electrode active material, characterized in that the carbon-based conductive material is coated, or that the Si-based negative electrode active material and the carbon-based conductive material is a composite.
A negative electrode material comprising a Si-based negative electrode active material according to any one of claims 1 to 8, and a binder.
10. The method of claim 9,
The binder is an anode material, characterized in that the aqueous binder.
11. The method of claim 10,
The aqueous binder is an anode material, characterized in that at least one selected from acrylic binder, urethane resin and styrene-butadiene rubber (SBR).
A lithium secondary battery comprising the negative electrode material according to claim 9.
A method of treating a surface of a negative electrode active material comprising mixing a Si-based negative active material and dopamine and coating polydopamine on the surface of the Si-based negative active material through a polymerization reaction of the dopamine.
14. The method of claim 13,
The polymerization reaction surface treatment method of the negative electrode active material, characterized in that carried out in an atmosphere of pH 8 ~ 9.
15. The method of claim 14,
The polymerization reaction surface treatment method of the negative electrode active material, characterized in that carried out in an atmosphere of pH 8.5.

Images