KR101222292B1 - Organic solvent for making electrode plate slurry and Method of making electrode plate for lithium rechargeable battery - Google Patents

Abstract

The present invention relates to an organic solvent for producing a plate slurry and a method for producing a lithium secondary battery electrode plate using the same, and more particularly, to prevent discoloration and increase of impurities by adding a color change inducing substance control additive during preparation of an organic solvent for preparing a plate slurry. The present invention relates to an organic solvent for producing a cathode plate slurry capable of realizing a battery of the present invention, and a method for manufacturing a cathode plate for a lithium secondary battery using the same.

Lithium Secondary Battery, Organic Solvent, Discoloration Inducing Agent Control Additive, Antioxidant, NMP

Description

Organic solvent for making electrode plate slurry and Method of making electrode plate for lithium rechargeable battery}

1 is a cross-sectional view of a rectangular type lithium secondary battery prepared using an organic solvent for preparing a slurry of the electrode plate of the present invention.

The present invention relates to an organic solvent for producing a plate slurry and a method for producing a lithium secondary battery electrode plate using the same, and more particularly, to prevent discoloration and increase of impurities by adding a color change inducing substance control additive during preparation of an organic solvent for preparing a plate slurry. The present invention relates to an organic solvent for producing a cathode plate slurry capable of realizing a battery of the present invention, and a method for manufacturing a cathode plate for a lithium secondary battery using the same.

2. Description of the Related Art [0002] Portable wireless devices such as video cameras, portable phones, portable computers, and the like are generally made lighter and more sophisticated. Such secondary batteries include, for example, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium secondary batteries. Among them, lithium secondary batteries are rechargeable, compact, and large-capacity, and are widely used in advanced electronic devices because of their high operating voltage and high energy density per unit weight.

Typically, a lithium secondary battery is wound with a separator interposed between a positive electrode plate and a negative electrode plate (hereinafter, referred to as a pole plate) to manufacture an electrode assembly, and after the electrode assembly is accommodated in a case, injecting an electrolyte solution and sealing the case. Are manufactured.

The electrode plate is usually manufactured as follows.

First, a binder is mixed with an organic solvent to prepare a binder solution. Thereafter, an electrode active material and a conductive agent are mixed with the binder solution to prepare an electrode slurry, and the electrode slurry is applied onto an electrode current collector. The applied slurry is dried and rolled to complete the electrode plate.

Since the electrode slurry has to be applied on the electrode current collector, it is essential to impart fluidity. The organic solvent is used to impart fluidity to the electrode slurry. In this case, NMP (N-Methylpyrrolidone) is commonly used as the organic solvent. The NMP is produced from butadiene (butadien) or butanediol (BDO), which is a petroleum intermediate, and is used for washing printed circuit boards (PCBs) or LCD strippers, which are commercial materials for electronic products, in addition to battery slurries.

Controlling foreign substances and moisture in the battery manufacturing process is essential for improving the quality of the battery, and the same applies to the organic solvent. However, commercially available NMP generally has a property of being completely miscible with moisture when contacted with moisture or heat, and easily deteriorated due to an increase in impurities. If the organic solvent is deteriorated in this manner, there is a problem that the performance of the battery may be greatly reduced.

The present invention has been made to solve the above problems, in particular, by adding a color change-causing substance control additive during the manufacture of the organic solvent for the production of the electrode plate slurry to prevent discoloration and increase of impurities to achieve a high-purity battery for the production of organic plate slurry It is an object of the present invention to provide a solvent and a method for manufacturing a cathode plate for a lithium secondary battery using the same.

In order to solve the above problems, the organic solvent of the present invention is characterized in that in the organic solvent for preparing a slurry of a lithium secondary battery, the organic solvent contains a control agent for discoloration inducing substance.

In addition, the organic solvent may be NMP (N-MethylPyrrolidone).

In addition, the discoloration inducing substance control additive may be an antioxidant (antioxidant). In addition, the antioxidant may be 4-tert-butyl-pyrocatechol (TBC) or Butylated HydroxyToluene (BHT) or hydroquinone (hydroquinone).

In addition, the method for manufacturing a lithium secondary battery electrode plate of the present invention is an organic solvent treatment step of adding a color change-causing substance control additive to the organic solvent; A binder solution preparation step of preparing a binder solution by adding a binder to the organic solvent; A slurry manufacturing step of mixing an electrode active material and a conductive agent in the binder solution; A coating step of coating the slurry on an electrode current collector; And a drying / rolling step of drying and rolling the coated slurry.

In the organic solvent treatment step, an antioxidant may be used as a control additive for discoloration inducing substances. In addition, the organic solvent treatment step may use TBC (4-tert-butyl-pyrocatechol) or BHT (Butylated HydroxyToluene) or hydroquinone (hydroquinone) as the antioxidant. In addition, the organic solvent treatment step is preferably made in a vacuum atmosphere at a temperature below the melting point of the antioxidant.

In the organic solvent treatment step, NMP (N-MethylPyrrolidone) may be used as the organic solvent.

Hereinafter, the present invention will be described in more detail.

It describes a lithium secondary battery in which the organic solvent according to the present invention is used for the production of electrode plate slurry. The lithium secondary battery is formed to include a positive electrode, a negative electrode and an electrolyte.

The positive electrode includes a positive electrode active material capable of inserting and detaching lithium ions.

The cathode active material is preferably at least one selected from cobalt, manganese, nickel, and at least one of a composite oxide with lithium, and a lithium-containing compound described below may be preferably used as a representative example.

Li _x Mn _{1 - y} M _y A ₂ (1)

Li _x Mn _{1 - y} MyO _{2 - z} X _z (2)

Li _x Mn ₂ O _{4 - z} X _z (3)

Li _x Mn _{2 - y} M _y M ' _z A ₄ (4)

Li _x Co _{1 - y} M _y A ₂ (5)

Li _x Co _{1 - y} M _y O _{2 - z} X _z (6)

Li _x Ni _{1 - y} M _y A ₂ (7)

Li _x Ni _{1 - y} M _y O _{2 - z} X _z (8)

Li _x Ni _{1 - y} Co _y O _{2 - z} X _z (9)

Li _x Ni _{1 -y- z} Co _y M _z A _α (10)

Li _x Ni _{1 -y- z} Co _y M _z O _{2 -α} X _α (11)

Li _x Ni _{1 -y- z} Mn _y M _z A _α (12)

Li _x Ni _{1 -y- z} Mn _y M _z O _{2 -α} X _α (13)

(Wherein 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M 'are the same or different, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is selected from the group consisting of O, F, S and P And X is selected from the group consisting of F, S and P.)

As the positive electrode current collector, metals such as aluminum, copper, nickel, silver, stainless steel, alloys of these metals, and the like can be used. Typically, aluminum or an aluminum alloy is used as the positive electrode current collector.

The negative electrode includes a negative electrode active material capable of inserting and detaching lithium ions.

The negative electrode active material is made of a carbon-based material or a metal or non-metal material capable of forming a compound with lithium. The metal or nonmetal material may be exemplified by Sn, Si, Al, SnO, SiO, In, Sb, Ag. These metal or nonmetal materials may be used alone or in combination or alloying. In addition, the metal or nonmetallic material may be used as a composite mixed with a carbonaceous material.

Examples of the carbon-based material include natural graphite, artificial graphite, graphitized carbon fiber, graphitized mesocarbon microbead (MCMB), graphitized mesoface pitch-based carbon fiber (MPCFF), fullerene, amorphous carbon, and the like. Can be. Examples of the amorphous carbon include hard carbon, coke, MCMB and MPCF fired at 1500 ° C. or lower. The carbon-based material is preferably a material having an d002 interplanar distance of 3.35 to 3.38 kPa and an Lc (crystallite size) of at least 20 nm by X-ray diffraction.

Examples of the negative electrode current collector may include a punching metal, an punching metal, a gold foil, a foamed metal, a sintered mesh fiber, nickel foil, and copper foil.

The positive electrode or negative electrode is formed by dispersing an active material, a binder and a conductive material, if necessary, a thickener in a solvent to prepare a slurry composition, applying the slurry composition to an electrode current collector, and drying and rolling it. As the solvent, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

At this time, the non-aqueous solvent including the NMP is added a control agent for discoloration causing material. An antioxidant may be used as the discoloration inducing substance control additive. Antioxidants may be commercialized enough to be used in food, and by oxidizing itself instead of NMP to slow the oxidation of the NMP to prevent discoloration, flavor and the like. In addition, since the antioxidant is mostly oxidized by the oxygen contained in the NMP according to the type and content, it is almost disappeared or extremely small after a certain time. The antioxidant may be exemplified by 4-tert-butyl-pyrocatechol (TBC) or Butylated HydroxyToluene (BHT) or hydroquinone. However, the type of the antioxidant is not limited thereto. The antioxidant prevents discoloration and oxidation of the non-aqueous solvent, thereby suppressing formation of organic impurities, thereby obtaining a high purity positive electrode plate and a negative electrode plate. Therefore, the performance of the battery can be improved by adding the oxidant to a nonaqueous solvent including NMP.

The binder is a material that serves to paste the active material, the mutual adhesion of the active material, the adhesion with the current collector, the buffering effect on the expansion and contraction of the active material, for example, polyvinylidene fluoride (PVdF), polyhexafluorine Copolymer of ropropylene-polyvinylidene fluoride (P (VdF / HFP)), poly (vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (Methyl methacrylate), poly (ethyl acrylate), polytetrafluoroethylene, polyvinylchloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber and the like can be used. The content of the binder is preferably 1 to 10% by weight based on the electrode active material. When the content of the binder is less than 1% by weight, the content of the binder is too small, so that the adhesion between the electrode active material and the current collector is insufficient. When the content of the binder exceeds 10% by weight, the adhesion is improved, but the content of the electrode active material decreases by that amount, thereby increasing the battery capacity. It is disadvantageous to

As the conductive agent, at least one selected from the group consisting of a graphite-based conductive agent, a carbon black-based conductive agent, a metal or a metal compound-based conductive agent may be used as a material for improving electronic conductivity. Examples of the graphite conductive agent include artificial graphite and natural graphite, and examples of the carbon black conductive agent include acetylene black, ketjen black, denka black, thermal black, and channel. Channel black and the like, and examples of the metal or metal compound conductive agent include perovskite such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , and LaSrMnO _3. ) There is a substance. However, it is not limited to the conductive agents listed above. 0.1-10 weight% is preferable with respect to an electrode active material, and, as for the addition amount of a electrically conductive material, it is more preferable that it is 1-5 weight%. When the content of the conductive material is less than 0.1% by weight, the electrochemical properties are lowered, and when the content of the conductive material is more than 10% by weight, the energy density per weight is reduced.

The thickener is not particularly limited as long as it can play a role of controlling the viscosity of the active material slurry, for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like.

The non-aqueous electrolyte may include a lithium salt and a non-aqueous organic solvent, and may further include additives for improving charge and discharge characteristics, preventing overcharge, and the like. The lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium battery, and the non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ It may be used in combination of one or two or more selected from the group consisting of. The concentration of the lithium salt is preferably used in the range of 0.6 to 2.0M, more preferably in the range of 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, and if it exceeds 2.0M, the viscosity of the electrolyte is increased, there is a problem that the mobility of lithium ions decreases.

As the non-aqueous organic solvent, carbonate, ester, ether or ketone may be used alone or in combination. The carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and as the ester, γ-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like may be used. As the ether, dibutyl ether may be used, but is not limited thereto.

In the case of the carbonate-based solvent in the non-aqueous organic solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, it is preferable to use the cyclic carbonate and the chain carbonate by mixing in a volume ratio of 1: 1 to 1: 9. The performance of the electrolyte is preferable when mixed in the above volume ratio.

In addition, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. Specific examples of the aromatic hydrocarbon organic solvent may include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, and the like. It may be used alone or in combination. It is preferable that the volume ratio of the carbonate solvent / aromatic hydrocarbon-based organic solvent in the electrolyte solution containing the aromatic hydrocarbon-based organic solvent is 1: 1 to 30: 1. The performance of the electrolyte solution may be desirable to be mixed in the volume ratio.

The lithium secondary battery may include a separator that prevents a short circuit between the positive electrode and the negative electrode and provides a passage for lithium ions, and such separators include polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, poly Polyolefin type polymer membranes, such as propylene / polyethylene / polypropylene, or a well-known thing, such as a multilayer of these, a microporous film, a woven fabric, and a nonwoven fabric, can be used. Further, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

1 is a cross-sectional view of a rectangular type lithium secondary battery manufactured using the organic solvent for preparing a slurry of the electrode plate of the present invention.

Referring to FIG. 1, a lithium secondary battery accommodates an electrode assembly 12 including a positive electrode 13, a negative electrode 15, and a separator 14 in a can 10 together with an electrolyte, It is formed by sealing the upper end with the cap assembly 20. The cap assembly 20 includes a cap plate 40, an insulating plate 50, a terminal plate 60, and an electrode terminal 30. The cap assembly 20 is combined with the insulating case 70 to seal the can 10.

The electrode terminal 30 is inserted into the terminal through-hole 41 formed in the center of the cap plate 40. When the electrode terminal 30 is inserted into the terminal through-hole 41, the tubular gasket 46 is coupled to the outer surface of the electrode terminal 30 and inserted together to insulate the electrode terminal 30 and the cap plate 40. . After the cap assembly 20 is assembled to the upper end of the can 10, the electrolyte is injected through the electrolyte injection hole 42 and the electrolyte injection hole 42 is closed by a stopper 43.

The electrode terminal 30 is connected to the negative electrode tab 17 of the negative electrode 15 or the positive electrode tab 16 of the positive electrode 13 to act as a negative electrode terminal or a positive electrode terminal.

The lithium secondary battery of the present invention is not limited to the above shape, and any shape such as a cylindrical shape, a pouch, etc., including the negative electrode of the present invention and capable of operating as a battery, is possible.

Next, the manufacturing method of the lithium secondary battery pole plate of this invention is demonstrated easily.

The manufacturing method of the lithium secondary battery electrode plate of the present invention comprises an organic solvent treatment step, binder solution production step, slurry (slurry) production step, coating step and drying / rolling step.

The organic solvent treatment step is a step of adding a color change causing substance control additive to the organic solvent. In the organic solvent treatment step, an antioxidant may be used as a control additive for discoloration inducing substances. In addition, the antioxidant may be used TBC (4-tert-butyl-pyrocatechol) or BHT (Butylated HydroxyToluene) or hydroquinone (hydroquinone). In addition, the organic solvent treatment step is preferably made in a vacuum atmosphere at a temperature below the melting point of the antioxidant. If the organic solvent treatment step is performed at a temperature higher than the melting point temperature of the antioxidant, there is a problem that the organic solvents, including NMP can be thermally oxidized by heat to generate impurities. In addition, when the organic solvent treatment step is performed in the air with high humidity, there is a problem that the organic solvent may be in contact with moisture, oxygen to generate foreign substances.

The binder solution manufacturing step is a step of preparing a binder solution by adding a binder to the organic solvent. Examples of the binder include polyvinylidene fluoride (PVdF), copolymers of polyhexafluoropropylene-polyvinylidene fluoride (P (VdF / HFP)), poly (vinylacetate), polyvinyl alcohol, polyethylene oxide, Polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), poly (ethylacrylate), polytetrafluoroethylene, polyvinylchloride, polyacrylonitrile, polyvinylpyridine, Styrene-butadiene rubber, acrylonitrile-butadiene rubber and the like can be used.

The slurry manufacturing step is a step of mixing an electrode active material and a conductive agent in the binder solution. As the conductive agent, a graphite conductive agent, a carbon black conductive agent, a metal or metal compound based conductive agent, or the like may be used.

The coating step is a step of coating the prepared slurry on the electrode current collector.

The drying / rolling step is a step of drying and rolling the coated slurry. The drying / rolling step may be made by a dryer and a roller.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

Comparative example

N-methyl-2-pi after mixing LiCoO ₂ (average particle diameter: 10 mu m) as a positive electrode active material, a carbon conductive material (super P) and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 94: 3: 3 Slurries were prepared by dispersing in Ralidone (NMP). The slurry was applied on an aluminum foil having a thickness of 20 µm, dried, and rolled by a roll press to prepare a positive electrode plate.

Synthetic graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96: 2: 2, and then dispersed in water to prepare a slurry. The negative electrode plate was prepared by coating onto a copper foil of μm, drying and rolling in a roll press.

A separator made of a polyethylene (PE) porous film (thickness: 25 μm) was inserted between the positive electrode plate and the negative electrode plate, wound, compressed, placed in a square can, and an electrolyte was injected to prepare a lithium secondary battery. At this time, an ethylene carbonate (EC) / diethyl carbonate (DEC) mixed solution (1: 1 volume ratio) in which LiPF ₆ was dissolved in 1.0 M was used.

Example

After adding a small amount of TBC to N-methyl-2-pyrrolidone (NMP), LiCoO ₂ (average particle size: 10 µm) as a positive electrode active material, a carbon conductive material (super P), and polyvinylidene fluoride as a binder ( A slurry was prepared by dispersing the mixture of PVdF) in a weight ratio of 94: 3: 3. The remaining conditions are the same as in the comparative example.

<Experimental Results>

The color and the degree of foreign matter generation of NMPs of the Comparative Examples and Examples were observed through the naked eye and a microscope. As a result, in the case of the comparative example, NMP discolored with time and a large number of foreign substances were observed in the microstructure. On the other hand, the color of the NMP did not change even in the case of the above example, and the formation of foreign matters was little when the microstructure was observed. Therefore, discoloration and oxidation are prevented when the electrode plate slurry is prepared after the antioxidant is treated to the organic solvent for preparing the electrode plate slurry.

As described above, the present invention is not limited to the above-described specific preferred embodiments, and any person skilled in the art may apply the present invention without departing from the gist of the present invention. It is to be understood that various changes and modifications may be practiced within the scope of the appended claims.

According to the organic solvent and electrode plate manufacturing method for producing a cathode plate slurry of a lithium secondary battery according to the present invention, by using an organic solvent to which a color change-inducing substance control additive is added to prevent discoloration of the organic solvent and the generation of foreign substances to improve the purity of the electrode plate There is an effect that can improve the performance of.

Claims (9)

delete delete delete delete An organic solvent treatment step of adding a discoloration causing substance control additive to the organic solvent; A binder solution preparation step of preparing a binder solution by adding a binder to the organic solvent; A slurry manufacturing step of mixing an electrode active material and a conductive agent in the binder solution; A coating step of coating the slurry on an electrode current collector; And A drying / rolling step of drying and rolling the coated slurry, The organic solvent treatment step uses an antioxidant as a control additive for discoloration causing material, The organic solvent treatment step is a lithium secondary battery electrode plate manufacturing method characterized in that the vacuum atmosphere at a temperature below the melting point of the antioxidant. delete 6. The method of claim 5, The organic solvent treatment step is a lithium secondary battery electrode plate manufacturing method characterized in that using TBC (4-tert-butyl-pyrocatechol) or BHT (Butylated HydroxyToluene) or hydroquinone (hydroquinone) as the antioxidant. delete 6. The method of claim 5, The organic solvent treatment step is a lithium secondary battery electrode plate manufacturing method characterized in that using NMP (N-MethylPyrrolidone) as the organic solvent.

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