KR20130116502A - Anode slurry comprising novel binder and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An anode slurry is provided to increase the energy density and electronic conductivity of a battery, thereby improving the output characteristics of the battery. CONSTITUTION: An anode slurry is an anode active material for the occlusion and tally of lithium ions and is obtained by mixing anode materials including conductive agents and a binder with organic solvents. One or more than 2 kinds are selected from the group of ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and acrylic copolymer for the binder. The content of the lithium oxides and conductive agents is 90 - 99.9 weight%, and the binder is 0.1-10 weight%. The binder is the hydroxypropyl cellulose.

Description

Anode Slurry Comprising Novel Binder and Lithium Secondary Battery Comprising The Same

The present invention relates to a negative electrode slurry including a novel binder and a lithium secondary battery including the same, and more particularly, to a negative electrode active material for a secondary battery that occludes and desorbs lithium ions, including lithium titanium oxide, a conductive material, and a binder. An anode slurry comprising a negative electrode material mixed with an organic solvent, wherein the binder is one or two or more selected from the group consisting of ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and an acrylic copolymer. It relates to a negative electrode slurry and a lithium secondary battery comprising the same.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

In the negative electrode of the conventional lithium secondary battery, a carbon-based compound capable of reversible intercalation and detachment of lithium ions while maintaining structural and electrical properties as a negative electrode active material has been mainly used. A lot of researches on a negative electrode material and lithium titanium oxide by the Li alloy reaction using (Si), tin (Sn).

Lithium titanium oxide is a zero-strain material with extremely low structural changes during charge and discharge, and thus has excellent life characteristics, forms a relatively high voltage range, and does not generate dendrite. It is known to have a very good safety and stability.

However, although the lithium titanium oxide requires a larger amount of binder than the conventional carbon-based negative active material due to its large surface area, the binder acts as an electrical resistance element of the electrode and ultimately deteriorates the overall energy density of the battery. There is a problem that affects.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application do not act as a resistive element when a binder exhibiting a small amount of high electrode adhesion is included in a negative electrode slurry containing lithium titanium oxide as a negative electrode active material. It was confirmed that the overall energy density of the battery can be improved, and the present invention has been completed.

Accordingly, the negative electrode slurry according to the present invention is a negative electrode slurry in which a negative electrode material containing lithium titanium oxide, a conductive material, and a binder is mixed with an organic solvent as a negative electrode active material for secondary batteries that occludes and desorbs lithium ions.

The binder is characterized in that one or more selected from the group consisting of ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, acrylic copolymer.

As described above, the negative electrode slurry according to the present invention is a binder that has not been used in the negative electrode slurry for lithium secondary batteries, and can exhibit an electrode adhesive force of, for example, 20 gf even in a small amount that does not act as a resistance element. Since the polymer binders are used, the electronic conductivity of the electrode may be increased, and the output characteristics of the lithium secondary battery including the same may be improved as compared with the case of using the conventional polyvinylidene fluoride (PVDF).

Therefore, the negative electrode slurry according to the present invention, the content of the lithium titanium oxide and the conductive material of more than 90% to 99.9% by weight relative to the total weight of the negative electrode material and the binder of 0.1% to 10% by weight or less relative to the total weight of the negative electrode material It may have a content. As a result, the content of solids is increased, and the energy density can be greatly improved as compared with the case of using conventional polyvinylidene fluoride (PVDF).

In a specific embodiment of the present invention, the binder is preferably hydroxypropyl cellulose or polyethylene glycol.

In addition, when the content of the binder is less than 0.1% by weight based on the total weight of the negative electrode material, the binding force between the desired negative electrode current collector and the negative electrode active materials cannot be expected, and when the content of the binder is 10% by weight or more, it is not preferable because it acts as a resistance element. . Therefore, for the above reason, the content of the binder is more preferably 0.1 wt% or more and 5 wt% or less.

A compound in which the lithium titanium oxide is preferably represented by the following composition formula (1), for example, Li _{0 .8 .2} Ti ₂ O _4, Li ₂ Ti _{.67 1 .33} O _4, LiTi ₂ O _4, Li _{1 .33} Although the like _{Ti 1 .67 O 4, Li 1} .14 Ti 1 .71 O 4, but is not limited to these. More preferably, as having a spinel structure is excellent reversibility small changes in crystal structure during charge and discharge, and may be _{Li 1 .33 Ti 1 .67 O 4} .

Li _x Ti _y O ₄ (0.5≤x≤3; 1≤y≤2.5) (1)

The method for producing the lithium titanium oxide is known in the art, for example, in the atomic ratio of lithium and titanium in a solution in which lithium salts such as lithium hydroxide, lithium oxide, lithium carbonate, and the like are dissolved in water as a lithium source. Accordingly, titanium oxide, or the like, may be added as a titanium source, followed by stirring and drying to prepare a precursor, followed by baking.

In a particular embodiment of the invention, the lithium-titanium oxide is Li _{1 .33 1 .67} Ti O _4, may be a secondary particle with the primary particles are aggregated, the second diameter of the primary particles is 200 nm to 10 μm Can be.

The negative electrode active material according to the present invention is a negative electrode active material capable of occluding and releasing lithium ions in addition to lithium titanium oxide, for example, carbon such as hardly graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like.

At this time, the lithium titanium oxide may be contained in more than 50% by weight to 100% by weight relative to the weight of the entire negative electrode active material. When the content of the lithium titanium oxide is 100% by weight based on the total weight of the negative electrode active material, it means a case in which the negative electrode active material is composed of only lithium titanium oxide.

In addition, the present invention provides an electrode assembly having a structure including a negative electrode including the negative electrode active material and the negative electrode, and a separator between the positive electrode and the negative electrode.

The electrode assembly may include, for example, a jelly-roll (wound) electrode assembly having a structure in which long sheets of positive and negative electrodes are wound with a separator interposed therebetween, and a plurality of positive and negative electrodes cut in units of a predetermined size. A stack-type electrode assembly having a structure in which the layers are sequentially stacked with a separator therebetween, and an electrode assembly having an advanced structure in which the jelly-roll type and the stack type are mixed. The stacked bi-cell or full cells stacked in the interposed state may be a stack / foldable electrode assembly having a structure in which a continuous separator sheet having a long length is wound.

The present invention also provides a lithium secondary battery having a structure in which the electrode assembly is impregnated with an electrolyte and sealed.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

The structure of the battery module and the battery pack and the method of manufacturing the battery module and the battery pack are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the negative electrode slurry according to the present invention is a binder that has not been used in the negative electrode slurry for lithium secondary batteries, and can exhibit an electrode adhesive force of, for example, 20 gf even with a small amount such that it does not act as a resistance element. High molecular weight binders, the content of lithium titanium oxide and conductive material of more than 90% to 99.9% by weight relative to the total weight of the negative electrode material and 0.1 to 10% by weight of the binder of the total weight of the negative electrode material Therefore, compared with the case of using the conventional polyvinylidene fluoride (PVDF), an electronic conductivity and an energy density can be improved significantly.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

The negative electrode may be prepared by applying a slurry prepared by mixing the negative electrode mixture including the negative electrode active material to a solvent such as NMP on a negative electrode current collector, followed by drying and rolling.

The negative electrode mixture may optionally include a conductive material, a binder, a filler, etc. in addition to the negative electrode active material.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. The negative electrode current collector may form fine concavities and convexities on the surface to reinforce the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the negative electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 30 wt% based on the total weight of the mixture including the negative electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component for inhibiting expansion of the negative electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

For example, the positive electrode is manufactured by applying a positive electrode mixture including a positive electrode active material on a positive electrode current collector and then drying the positive electrode mixture. The positive electrode mixture may include components as described above, if necessary.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. Like the negative electrode current collector, fine concavities and convexities may be formed on the surface thereof to increase the adhesion of the positive electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven body may be possible.

The cathode active material is a material capable of causing an electrochemical reaction. Examples of the lithium transition metal oxide include lithium cobalt oxide (LiCoO ₂ ) containing two or more transition metals and substituted with one or more transition metals, lithium Layered compounds such as nickel oxide (LiNiO ₂ ); Lithium manganese oxide substituted with one or more transition metals; Formula _{LiNi 1-y M y O 2} ( where, M = Co, Mn, Al , Cu, Fe, Mg, B, Cr, Zn or Ga and Lim, 0.01≤y≤0.7 include one or more elements of the element) A lithium nickel-based oxide represented by the following formula: _{Li 1 + z Ni 1/3 Co 1/3} Mn 1/3 O 2, Li 1 + z Ni 0.4 Mn 0.4 Co 0.2 O 2 , such as _{Li 1 + z Ni b Mn c} Co 1- (b + c + d _{) M d O (2-e} ) A e ( where, -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2 , 0≤e≤0.2, b + c + d <1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl; lithium nickel cobalt manganese composite oxide; And the formula _{Li 1 + x M 1-y} M 'y PO 4-z X z ( wherein, M = a transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, and -0.5? X? +0.5, 0? Y? 0.5, and 0? Z? 0.1), but the present invention is not limited thereto.

The binder, the conductive material, and the components added as necessary are the same as those in the negative electrode.

The separator is an insulating thin film interposed between the anode and the cathode and having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, glass fiber, polyethylene or the like is used.

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative of such gel polymers are polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and the like. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. carbonate), PRS (propene sultone), FPC (Fluoro-Propylene carbonate) may be further included.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (16)

As a negative electrode active material for storing and detaching lithium ions as a negative electrode slurry containing a negative electrode material containing lithium titanium oxide, a conductive material and a binder in an organic solvent,
The binder is a negative electrode slurry, characterized in that one or more selected from the group consisting of ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, acrylic copolymer. The negative electrode slurry of claim 1, wherein the lithium titanium oxide and the conductive material are present in an amount of 90 wt% or more and 99.9 wt% or more, and the binder is 0.1 wt% or more and 10 wt% or less. The negative electrode slurry according to claim 1, wherein the binder is hydroxypropyl cellulose. The negative electrode slurry according to claim 1, wherein the binder is polyethylene glycol. The negative electrode slurry of claim 1, wherein the binder is present in an amount of 0.1 wt% to 5 wt% based on the total weight of the negative electrode material. The negative electrode slurry according to claim 1, wherein the lithium titanium oxide is a compound represented by the following formula (1).
Li _x Ti _y O ₄ (0.5≤x≤3; 1≤y≤2.5) (1) Claim 1, wherein the lithium titanium oxide is Li ₁ Ti _{.33 1 .67} O ₄ in Cathode slurry, characterized in that. The negative electrode slurry of claim 1, wherein the lithium titanium oxide is a secondary particle in which primary particles are aggregated. The negative electrode slurry of claim 8, wherein the secondary particles have a particle diameter of 200 nm to 10 m. The negative active material of claim 1, wherein the lithium titanium oxide is contained in an amount of 50 wt% to 100 wt% based on the weight of the entire negative active material. The negative electrode in which the negative electrode slurry in any one of Claims 1-10 is apply | coated to the negative electrode electrical power collector. An electrode assembly comprising a cathode according to claim 11 and having a separator interposed between the anode and the cathode. A lithium secondary battery having a structure in which the electrode assembly according to claim 12 is impregnated with an electrolyte and sealed. A battery module comprising the lithium secondary battery according to claim 13 as a unit cell. A battery pack comprising the battery module according to claim 14. A device comprising the battery pack according to claim 15 as a power source.