KR20170103688A - Negative Electrode Mix for Secondary Battery Comprising CMC-Li Salt and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a negative electrode mixture comprising a negative electrode active material, a thickener, and an aqueous binder, wherein the thickener is a lithium carboxymethyl cellulose (CMC-Li) salt, which has the substitution degree of a hydroxy (-OH) group of 0.7 to 1.3 by a lithium carboxymethyl group (-CH_2COOLi), a molecular weight (Mn) of 300,000 to 1,000,000, viscosity of 2,000 to 15,000 cps, and solubility of 1.0 to 2.0, and to a secondary battery comprising the same. Therefore, lifetime characteristics, discharge characteristics, and cathode efficiency of the secondary battery can be remarkably improved.

Description

[0001] The present invention relates to an anode mixture for a secondary battery including a CMC-Li salt and a lithium secondary battery comprising the same. ≪ RTI ID = 0.0 > [0002] <

The present invention relates to a negative electrode mixture for a secondary battery including a CMC-Li salt and a lithium secondary battery comprising the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

2. Description of the Related Art [0002] Recently, as technology development and demand for portable devices such as portable computers, portable phones, and cameras have increased, the demand for secondary batteries as energy sources has increased sharply. Among such secondary batteries, they exhibit high energy density and operating potential, Many studies have been made on a lithium secondary battery having a long self discharge rate, and it has been commercialized and widely used.

Generally, a lithium secondary battery uses graphite as a negative electrode active material, charging and discharging proceed while repeating the process in which lithium ions in the positive electrode are inserted into the negative electrode and desorbed. The theoretical capacity of the battery varies depending on the kind of the electrode active material, but the charging and discharging capacities decrease with the progress of the cycle.

This phenomenon is most likely to occur between the electrode active material or between the electrode active material and the collector due to the volume change of the electrode caused by the progress of charging and discharging of the battery.

Particularly, in order to increase the discharge capacity, when a material such as silicon, tin, silicon-tin alloy having a large discharging capacity is mixed with natural graphite having a theoretical discharge capacity of 372 mAh / g is used, The volume expansion of the battery is remarkably increased, and the capacity of the battery is rapidly lowered as the charge / discharge cycle progresses.

Therefore, it is possible to prevent separation between the electrode active material or between the electrode active material and the current collector during the production of the electrode with a strong adhesive force, and to control the volume expansion of the electrode active material generated during repetitive charging and discharging with strong physical properties, There is a great demand in the art for a study on a binder and an electrode material capable of improving the performance of the battery due to the above-mentioned problems.

Since polyvinylidene fluoride (PVdF), which is an organic solvent-based binder, does not satisfy the above requirements, recently, an aqueous binder such as styrene-butadiene rubber (SBR) And mixing with a thickener or the like has been proposed and is currently being used commercially. In the case of such a binder, it is environmentally friendly and has an advantage that the battery capacity can be increased by reducing the content of the binder.

Carboxy methyl cellulose is widely used as a thickener because of its high viscosity and stable physical properties. Carboxymethyl cellulose, however, is difficult to increase in the solid content when the electrode slurry is prepared, thus lowering the processability of the battery. Further, the carboxyl group is decomposed at a high temperature, and the overall characteristics of the secondary battery such as lifetime characteristics, discharge characteristics, there is a problem.

Therefore, there is a high need for a stable and eco-friendly anode mixture for a secondary battery while improving the overall characteristics of the secondary battery.

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

As a result of intensive research and various experiments, the present inventors have found that the substitution degree of the hydroxy (-OH) group by the lithium carboxymethyl group (-CH ₂ COOLi) as the thickener is 0.7 to 1.3 , Lithium carbonate (CMC-Li salt) having a molecular weight (Mn) of 300,000 to 1,000,000, a viscosity of 2,000 to 15,000 cps and a solubility of 1.0 to 2.0, is environmentally friendly, The discharge characteristics, and the cathode efficiency were improved, thereby completing the present invention.

Accordingly, the negative electrode material mixture for a secondary battery according to the present invention comprises a negative electrode active material, a thickener, and an aqueous binder; The thickener is a thickener having a degree of substitution of hydroxy (-OH) groups by a lithium carboxymethyl group (-CH ₂ COOLi) of 0.7 to 1.3, a molecular weight (Mn) of 300,000 to 1,000,000, a viscosity of 2,000 to 15,000 cps, Is a lithium carboxymethyl cellulose salt (CMC-Li salt) of 1.0 to 2.0.

Conventional CMCs were generally used as CMC-Na salts containing a sodium carboxymethyl group (-CH ₂ COONa). The CMC-Na salt also has an effect of improving the overall performance of the secondary battery of the binder, but has limitations in lifetime characteristics, discharge characteristics, anode efficiency and solid content in the manufacturing process.

According to the present invention, when the CMC-Li salt is used as a thickener, the lifetime characteristics, the discharge characteristics, the anode efficiency and the solid content of the secondary battery are improved in comparison with the case of using the conventional CMC-Na salt . Particularly, the CMC-Li salt has a substitution degree of the hydroxy (-OH) group of the lithium carboxymethyl group of 0.7 to 1.3, a molecular weight (Mn) of 300,000 to 1,000,000, a viscosity of 2,000 to 15,000 cps and a solubility of 1.0 To 2.0, there is an effect of remarkably improving the overall characteristics of the secondary battery.

In one specific example, the substitution degree of the lithium carboxymethyl group may be from 0.8 to 1.2, and more specifically, from 0.8 to 1.0.

The molecular weight of the CMC-Li salt may be from 350,000 to 900,000, and more specifically, from 500,000 to 900,000.

The viscosity of the CMC-Li salt may be 2,200 cps to 12,000 cps under the conditions of 23 캜 and 12 rpm of a B-type LV type viscometer.

The solubility of the CMC-Li salt may be 1.0 to 1.5 based on weight at 23 ° C. Specifically, the solubility may be a percentage of the weight of CMC-Li relative to the total weight of deionized water and CMC-Li.

The pH of the CMC-Li salt may be 6.8 to 8.0, and more specifically 6.9 to 7.85.

When the CMC-Li salt satisfying both the substitution degree, the molecular weight, the viscosity, the solubility and the pH range is used, the overall performance of the secondary battery can be remarkably improved. The performance of the secondary battery may be deteriorated even if some physical properties out of the physical properties are out of the range. These results can also be confirmed through the following experimental examples. That is, the CMC-Li salt has the best effects when the degree of substitution, the molecular weight, the viscosity, the solubility, and the pH of the CMC-Li salt are both satisfied. All of the physical properties are organically bound and the CMC-Li salt has a microscopic mechanism It can be assumed that they are closely related.

Meanwhile, the aqueous binder may be styrene-butadiene rubber (SBR). As an aqueous binder, SBR can be dispersed in water in the form of an emulsion, so that it is not necessary to use an organic solvent, and the adhesive strength is strong enough to reduce the content of the binder and increase the content of the negative electrode active material, which is advantageous for increasing the capacity of the lithium secondary battery. Particularly, when the CMC-Li salt is used as a thickener together with SBR, the ratio of the active material per unit volume of the negative electrode mixture can be further increased, and the capacity of the negative electrode slurry can be increased. There is an effect that the phenomenon is improved.

When the CMC-Li salt is used as a thickener, the performance of the secondary battery can be further improved when SBR having a particle diameter within a certain range is used. In one specific example, the SBR may have a particle size of 90 nm to 500 nm, and more specifically, 100 nm to 400 nm.

Further, in one specific example, the content ratio of the thickener and the water-based binder may be 1: 2 to 5: 1 by weight, more specifically, 1: 1 to 4: 1, 1: 1 to less than 2: 1.

According to the present invention, the negative electrode active material can be used as an anode active material generally used in a lithium secondary battery without limitation, for example, a carbonaceous material such as non-graphitized carbon or 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 can be used.

However, not all of the negative electrode active materials exhibit the same effect, and among the negative electrode active materials, carbon-based materials can exhibit the most excellent effect. In detail, the carbon-based material may be at least one selected from the group consisting of graphite carbon, coke carbon and hard carbon.

The graphite carbon preferably comprises spherical particles and has an R value of Raman spectrum [R = I ₁₃₅₀ / I ₁₅₈₀ ] (I ₁₃₅₀ is Raman intensity near 1350 cm ^-1 , I ₁₅₈₀ is 1580 cm ^-1 &gt; is a natural graphite having a crystallinity of 0.20 to 1.0.

Such natural graphite can be manufactured into a spherical shape by pulverizing and assembling scaly natural graphite raw materials. The spherical natural graphite thus produced has a minimized specific surface area, so that the decomposition reaction of the electrolyte on the active material surface can be reduced. Therefore, when the spherical granulated natural graphite is mixed with natural graphite in scaly form, the filling density of the electrode increases and the energy density can be improved.

On the other hand, the negative electrode material mixture may further include a conductive material and / or a filler.

The conductive material may be added usually in an amount of 0.1 to 30% by weight based on the total weight of the mixture including the anode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and includes, for example, 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 whiskey 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. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

The present invention also provides a negative electrode for a secondary battery, wherein the negative electrode material mixture is applied on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

In the present invention, the thickness of the anode current collector may be the same within the range of 3 to 201 [mu] m, but may have different values depending on the case.

In one specific example, the loading amount of the negative electrode mixture may be 10 to 20 mg / cm ² , and more specifically, 14 to 16 mg / cm ² . If the loading amount of the negative electrode mixture is too large, there is a problem that the resistance of the negative electrode increases and the C-rate sharply decreases to lower the charging characteristics. In the case of the negative electrode mixture containing the conventional CMC-Na salt, the maximum loading amount at which an industrially applicable level of charging property can be obtained was about 13 mg / cm ² or less. However, the negative electrode mixture containing the CMC- , It is possible to exhibit an industrially available level of charging property even at a loading amount of up to 16 mg / cm &lt; ² &gt;.

The present invention also provides a secondary battery comprising the negative electrode.

In one specific example, the secondary battery may have a negative electrode efficiency of 93% or more, more specifically 93.5% or more when charging and discharging a coin half cell at a 0.1 C-rate, more specifically, 94 % &Lt; / RTI &gt;

In the case of the secondary battery including the conventional CMC-Na salt, the negative electrode efficiency that can be maximally exhibited under the same conditions was mostly less than about 93%. However, the secondary battery including the CMC-Li salt according to the present invention had 93% Or more.

In one specific example, the secondary battery may have a discharge capacity of 355 mAh / g at a 0.3 C-rate and more specifically 360 mAh / g or more. The discharge capacity was calculated based on the weight of the negative electrode.

In the case of a secondary battery including a conventional CMC-Na salt, the discharge capacity that can be maximally exhibited under the same conditions was less than about 355 mAh / g. However, the secondary battery including the CMC- discharge capacity of mAh / g or more.

In one specific example, the secondary battery may have a capacity retention rate of 75% or more at 300 times charge-discharge and more specifically 80% or more.

In the case of a secondary battery including a conventional CMC-Na salt, the capacity retention ratio that can be exhibited at the maximum under the same conditions was less than about 75%. However, the secondary battery including the CMC-Li salt according to the present invention has a capacity of 75% The capacity retention rate can be obtained.

The secondary battery includes a cathode, a cathode, a separator, and an electrolyte. Other components of the secondary battery will be described below.

The positive electrode may be prepared, for example, by applying a positive electrode mixture mixed with a positive electrode active material, a conductive material and a binder to a positive electrode collector, and if necessary, a filler may further be added to the positive electrode mixture.

The cathode current collector is generally formed to a thickness of 3 to 201 탆 and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium , And a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The binder contained in the positive electrode is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the positive electrode active material, as a component that assists in bonding between the active material and the conductive material and bonding to the current collector. 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-butadiene rubber, fluorine rubber, various copolymers and the like.

In one specific example, the separation membrane may be a polyolefin-based film commonly used in the art, and may be, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyetheretherketone, A sheet made of at least one selected from the group consisting of polyethersulfone, polyphenylene oxide, polyphenylenesulfrode, polyethylene naphthalene, and mixtures thereof.

The separation membrane may be made of the same material but is not limited thereto and may be made of materials different from each other depending on safety, energy density, and overall performance of the battery cell.

The pore size and porosity of the separator or separation film are not particularly limited, but the porosity may be in the range of 10 to 95% and the pore size (diameter) may be in the range of 0.1 to 50 탆. When the pore size and porosity are 0.1 μm or less and 10% or less, respectively, it acts as a resistive layer. If the pore size and porosity are more than 50 μm and 95%, it is difficult to maintain the mechanical properties.

The electrolyte solution may be a non-aqueous electrolyte containing a lithium salt, and the non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. Non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, The present invention is not limited thereto.

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 derivatives, Tetrahydrofuran derivatives, ether, 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 acid 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a substance that is soluble in the nonaqueous electrolyte and includes, 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 ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing nonaqueous electrolyte.

The present invention also provides a battery pack including such a secondary battery as a unit cell, and a device including such a battery pack as a power source.

The device may be, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, MP3, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV) , A plug-in hybrid electric vehicle (PHEV), an electric bike (E-bike), an electric scooter (E-scooter), an electric golf cart, However, the present invention is not limited thereto.

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

As described above, the negative electrode mixture according to the present invention has a substitution degree of the hydroxy (-OH) group of 0.7 to 1.3 with a lithium carboxymethyl group (-CH ₂ COOLi) as a thickener and a molecular weight (Mn) of 300,000 And a CMC-Li salt having a viscosity of 2,000 to 15,000 cps and a solubility of 1.0 to 2.0, thereby significantly improving lifetime characteristics, discharge characteristics, and cathode efficiency of the secondary battery.

Hereinafter, the present invention will be described with reference to embodiments thereof, but it should be understood that the scope of the present invention is not limited thereto.

&Lt; Example 1 >

1-1 Preparation of Thickener

LiOH and mono-chlolo acid (MCA) were added to the cellulose to change the degree of substitution of the hydroxy (-OH) group by the lithium carboxymethyl group (-CH ₂ COOLi) to 1.0, the molecular weight (Mn) to 500,000, CMC-Li salt having a solubility of 1, a pH of 7.61 was prepared.

1-2 Cathode manufacturing

As the thickener, CMC-Li salt prepared in 1-1, SBR having a particle size of 200 nm as an aqueous binder, and natural graphite having a crystallinity of 0.2 as a negative electrode active material were mixed in a weight ratio of binder: thickener: negative electrode active material = 1: 1: 98, and water was added as a solvent to prepare an anode mixture slurry. The anode mixture slurry was applied to the copper collector so that the loading amount was 10 mg / cm ² , and then dried in a vacuum oven at 120 캜 for 2 hours or more to prepare a negative electrode.

1-3 Manufacture of secondary battery (coin half cell)

A negative electrode using the negative electrode prepared in 1-2, and using a Li metal as an anode, ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1 as an electrolyte: 1 in the solvent is 1 M LiPF ₆ dissolved , A half-coin cell was prepared.

&Lt; Example 2 >

(OH) group having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 4,300 cps, a solubility of 1.5, and a pH of 7.53 instead of the CMC-Li salt used in Example 1 A secondary battery was prepared in the same manner as in Example 1, except that CMC-Li salt was used.

&Lt; Example 3 >

(-OH) group having a substitution degree of 1.2, a molecular weight (Mn) of 350,000, a viscosity of 3,500 cps, a solubility of 1.5, and a pH of 7.85 instead of the CMC-Li salt used in Example 1 A secondary battery was prepared in the same manner as in Example 1, except that CMC-Li salt was used.

<Example 4>

In Example 1, a CMC-Li salt having a degree of substitution of hydroxy (-OH) group of 0.8, a molecular weight (Mn) of 900,000, a viscosity of 5,400 cps, a solubility of 1.0 and a pH of 7.1 A secondary battery was manufactured in the same manner as in Example 1.

&Lt; Example 5 >

(OH) group having a degree of substitution of 0.8, a molecular weight (Mn) of 900,000, a viscosity of 12,000 cps, a solubility of 1.5, a pH of 6.9 Except that CMC-Li salt was used as the initiator.

&Lt; Comparative Example 1 &

(CMC) having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 3,500 cps, a solubility of 1.0 and a pH of 7.6 instead of the CMC-Li salt used in Example 1 -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 2 &

(CMC) having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight Mn of 500,000, a viscosity of 6,500 cps, a solubility of 1.5 and a pH of 7.5 instead of the CMC-Li salt used in Example 1 -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 3 &

A CMC having a degree of substitution of hydroxy (-OH) group of 1.2, a molecular weight (Mn) of 350,000, a viscosity of 1,500 cps, a solubility of 1.0, and a pH of 7.75 in place of the CMC- -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 4 &

CMC having a degree of substitution of hydroxy (-OH) group of 1.2, a molecular weight (Mn) of 350,000, a viscosity of 4,500 cps, a solubility of 1.5 and a pH of 7.75 in place of the CMC-Li salt used in Example 1 -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 5 &

A CMC-Li salt having a substitution degree of hydroxy (-OH) group of 0.8, a molecular weight (Mn) of 900,000, a viscosity of 7,000 cps, a solubility of 1.0 and a pH of 7.3 instead of the CMC-Li salt used in Example 1 -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 6 >

A CMC having a degree of substitution of hydroxy (-OH) group of 0.8, a molecular weight (Mn) of 900,000, a viscosity of 25,000 cps, a solubility of 1.5, and a pH of 7.1 instead of the CMC-Li salt used in Example 1 -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 7 &

(-OH) group having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 1,100 cps, a solubility of 1.0, and a pH of 7.61 instead of the CMC-Li salt used in Example 1 A secondary battery was prepared in the same manner as in Example 1, except that CMC-Li salt was used.

&Lt; Comparative Example 8 >

(-OH) group having a substitution degree of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 20,000 cps, a solubility of 1.0, and a pH of 7.61 instead of the CMC-Li salt used in Example 1 A secondary battery was prepared in the same manner as in Example 1, except that CMC-Li salt was used.

&Lt; Comparative Example 9 &

(-OH) group having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 2,200 cps, a solubility of 0.5, a pH of 7.61 A secondary battery was prepared in the same manner as in Example 1, except that CMC-Li salt was used.

&Lt; Comparative Example 10 &

(OH) group having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 2,200 cps, a solubility of 2.5, a pH of 7.61 A secondary battery was prepared in the same manner as in Example 1, except that CMC-Li salt was used.

&Lt; Example 6 >

2-1 Cathode manufacturing

As the thickener, CMC-Li salt prepared as 1-1, an aqueous binder of SBR having a particle diameter of 100 nm and a natural graphite having a crystallinity of 0.2 were used as a negative electrode active material, and the weight ratio of the binder to the negative active material was 1: 1: 98, and water was added as a solvent to prepare an anode mixture slurry. The anode mixture slurry was applied to the copper collector so that the loading amount was 10 mg / cm ² , and then dried in a vacuum oven at 120 캜 for 2 hours or more to prepare a negative electrode.

2-2 Manufacture of secondary battery (coin-full cell)

LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material, natural graphite as a conductive material, and PVdF as a binder were mixed in a ratio of 96: 2: 2, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to the aluminum foil so that the loading amount was 10 mg / cm ² , and then dried in a vacuum oven at 120 캜 for 2 hours or more to prepare a positive electrode.

(EC) and dimethyl carbonate (DMC) were dissolved in a solvent of 1: 1 by volume in a concentration of 1 M in which LiPF ₆ was dissolved as an electrolyte, and the coin A coin full cell was prepared.

&Lt; Example 7 >

A secondary battery was prepared in the same manner as in Example 6, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the binder: thickener: negative active material = 1.33: 0.66: 98 in Example 6.

&Lt; Example 8 >

A secondary battery was prepared in the same manner as in Example 6, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the binder: thickener: negative active material = 1.6: 0.4: 98 in Example 6.

&Lt; Example 9 >

A secondary battery was prepared in the same manner as in Example 6 except that SBR having a particle diameter of 200 nm was used instead of the SBR used in Example 6.

&Lt; Example 10 >

A secondary battery was prepared in the same manner as in Example 9, except that the negative electrode mixture slurry was prepared by mixing the negative electrode active material in a ratio of binder: thickener: negative active material = 1.33: 0.66: 98 in Example 9.

&Lt; Example 11 >

A secondary battery was prepared in the same manner as in Example 9 except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the binder: the thickener: the negative electrode active material = 1.6: 0.4: 98 in Example 9.

&Lt; Example 12 >

A secondary battery was prepared in the same manner as in Example 6, except that SBR having a particle diameter of 400 nm was used instead of the SBR used in Example 6.

&Lt; Example 13 >

A secondary battery was prepared in the same manner as in Example 12, except that the negative electrode mixture slurry was prepared by mixing the negative electrode active material in a ratio of binder: thickener: negative electrode active material = 1.33: 0.66: 98 in Example 12.

&Lt; Example 14 >

A secondary battery was prepared in the same manner as in Example 12, except that the negative electrode mixture slurry was prepared by mixing the negative electrode active material in a ratio of binder: thickener: negative active material = 1.6: 0.4: 98 in Example 12.

&Lt; Example 15 >

A secondary battery was manufactured in the same manner as in Example 9, except that the negative electrode mixture slurry was applied to the copper current collector so that the loading amount was 14 mg / cm ² in Example 9.

&Lt; Example 16 >

A secondary battery was manufactured in the same manner as in Example 9, except that the anode current collector slurry was applied to the copper current collector so that the loading amount was 16 mg / cm ² in Example 9.

&Lt; Comparative Example 11 &

CMC having a degree of substitution of hydroxy (-OH) group of 1.0, a molecular weight (Mn) of 500,000, a viscosity of 3,500 cps, a solubility of 1.0 and a pH of 7.6 instead of the CMC-Li salt used in Example 6 -Na salt was used as a negative electrode active material.

&Lt; Comparative Example 12 >

In Comparative Example 11, a secondary battery was manufactured in the same manner as in Comparative Example 11, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the thickener: negative electrode active material = 1.33: 0.66: 98.

&Lt; Comparative Example 13 &

In Comparative Example 11, a secondary battery was manufactured in the same manner as in Comparative Example 11, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the thickener: the negative electrode active material = 1.6: 0.4: 98.

&Lt; Comparative Example 14 >

A secondary battery was manufactured in the same manner as in Comparative Example 11, except that SBR having a particle diameter of 200 nm was used instead of the SBR used in Comparative Example 11.

&Lt; Comparative Example 15 &

In Comparative Example 14, a secondary battery was manufactured in the same manner as in Comparative Example 14, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the thickener: negative electrode active material = 1.33: 0.66: 98.

&Lt; Comparative Example 16 >

In Comparative Example 14, a secondary battery was manufactured in the same manner as in Comparative Example 14, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the thickener: the negative electrode active material = 1.6: 0.4: 98.

&Lt; Comparative Example 17 >

A secondary battery was manufactured in the same manner as in Comparative Example 11, except that SBR having a particle diameter of 400 nm was used instead of the SBR used in Comparative Example 11.

&Lt; Comparative Example 18 >

In Comparative Example 17, a secondary battery was manufactured in the same manner as in Comparative Example 17 except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the thickener: the negative electrode active material = 1.33: 0.66: 98.

&Lt; Comparative Example 19 >

In Comparative Example 17, a secondary battery was manufactured in the same manner as in Comparative Example 17, except that the negative electrode mixture slurry was prepared by mixing the binder in the ratio of the thickener: the negative electrode active material = 1.6: 0.4: 98.

&Lt; Comparative Example 20 &

A secondary battery was manufactured in the same manner as in Comparative Example 14, except that the anode current collector slurry was applied to the copper current collector so that the loading amount was 14 mg / cm ² in Comparative Example 14.

&Lt; Comparative Example 21 &

A secondary battery was manufactured in the same manner as in Comparative Example 14, except that the anode current collector slurry was applied to the copper current collector so that the loading amount was 16 mg / cm ² in Comparative Example 14.

<Experimental Example 1>

The secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 10 were charged at 0.1 C-rate (0.1 C constant current charging, 0.05 V constant voltage charging and 0.005 C cut off) and discharged at 0.1 C-rate Constant current discharge, 1.5 V cut off) to measure the initial discharge capacity and the negative electrode efficiency (Coulomb efficiency) at this time. The discharge capacity was calculated based on the weight of the negative electrode active material, and the results are shown in Table 1 below.

<Experimental Example 2>

The secondary batteries prepared in Examples 6 to 16 and Comparative Examples 11 to 21 were charged at 0.3 C-rate (0.3 C constant current charging, 4.2 V constant voltage charging, 0.005 C cut off) and discharged at 0.3 C-rate Constant current discharge, 3.0 V cut off) was performed once. Then, the coin half cell was fabricated using the cathode and Li metal obtained by dissolving the coin pull cell. The thus prepared coin half cell was charged at 0.1 C-rate (0.1 C constant current charging, 0.05 V constant voltage charging and 0.005 C cut off ), Discharged at 0.1 C-rate (0.1 C constant current discharge, 1.5 V cut off), and the initial discharge capacity and the negative electrode efficiency (Coulomb efficiency) at that time were measured. Discharge capacity was calculated based on the weight of the negative electrode active material, and the results are shown in Table 2 below.

<Experimental Example 3>

The secondary batteries prepared according to the methods of Examples 6 to 16 and Comparative Examples 11 to 21 were charged at 0.3 C-rate (0.3 C constant current charging, 4.2 V constant voltage charging, 0.005 C cut off) at room temperature (23 캜) The process of discharging at 0.3 C-rate (0.3 C constant current discharge, 3.0 V cut off) was repeated 300 times to measure the capacity retention rate. The results are shown in Table 2 below.

<Experimental Example 4>

The films were prepared using the mixture of the binder and the thickener used in Examples 6 to 16 and Comparative Examples 11 to 21, and then the tensile strength of the film was measured. Specifically, CMC aqueous solution and SBR aqueous solution were put into a 500 ml beaker together and stirred at 500 rpm for 1 hour to prepare a CMC / SBR mixture. The thus prepared CMC / SBR mixture was put into a weighing dish of a Teflon material having a diameter of 200 mm and a height of 20 mm and dried naturally at room temperature to prepare a CMC / SBR film having a thickness of 200 μm. The thus prepared CMC / SBR film was used to measure the tensile strength by a universal tension measurement (UTM) method. The results are shown in Table 2 below.

<Experimental Example 5>

The volumetric expansion ratios of the negative electrodes used in Examples 6 to 16 and Comparative Examples 11 to 21 were measured. Specifically, after one cycle, the secondary battery of the fully charged state (4.2 V) was disassembled to measure the thickness of the negative electrode. After 300 cycles, the secondary battery of the full charge state (4.2 V) was disassembled to measure the thickness of the negative electrode. The rate of change in the thickness of the negative electrode after 300 cycles was calculated based on the thickness of the negative electrode after one cycle. The results are shown in Table 2 below.

Thickener OH group
Degree of substitution Molecular Weight Viscosity (cps) Solubility pH Discharge capacity (mAh / g) Cathode efficiency (%) Example 1 CMC-Li One 500,000 2,200 One 7.61 360 94.1 Example 2 CMC-Li One 500,000 4,300 1.5 7.53 361 94.5 Example 3 CMC-Li 1.2 350,000 3,500 1.5 7.85 360 93.5 Example 4 CMC-Li 0.8 900,000 5,400 One 7.1 363 94.1 Example 5 CMC-Li 0.8 900,000 12,000 1.5 6.9 362 94.3 Comparative Example 1 CMC-Na One 500,000 3,500 One 7.6 354 92.5 Comparative Example 2 CMC-Na One 500,000 6,500 1.5 7.5 353 93.1 Comparative Example 3 CMC-Na 1.2 350,000 1,500 One 7.75 355 92.1 Comparative Example 4 CMC-Na 1.2 350,000 4,500 1.5 7.75 353 92.3 Comparative Example 5 CMC-Na 0.8 900,000 7,000 One 7.3 355 93.1 Comparative Example 6 CMC-Na 0.8 900,000 25,000 1.5 7.1 355 93.5 Comparative Example 7 CMC-Li One 500,000 1,100 One 7.61 356 93.4 Comparative Example 8 CMC-Li One 500,000 20,000 One 7.61 357 93.4 Comparative Example 9 CMC-Li One 500,000 2.200 0.5 7.61 357 93.3 Comparative Example 10 CMC-Li One 500,000 2.200 2.5 7.61 358 93.2

Comparing Examples 1 to 5 and Comparative Examples 1 to 10 with reference to Table 1, the degree of substitution of hydroxy (-OH) groups is 0.7 to 1.3, the molecular weight (Mn) is 300,000 to 1,000,000, and the viscosity is 2,000 When the CMC-Li salt having a solubility of 1.0 to 2.0 is used as a thickener, the discharge capacity and the cathode efficiency of the secondary battery are remarkably improved.

In particular, referring to Examples 1, 2, 4, and 5, particularly when the OH group substitution degree of CMC-Li is 0.8 to 1.0, the molecular weight is 500,000 to 900,000, and the pH is 6.9 to 7.61, Is remarkably improved.

On the other hand, referring to Comparative Examples 7 to 10, it can be confirmed that even if one of the above parameters is out of the scope of the present invention, the same effect as the present invention can not be exerted even if the same thickener is used.

Thickener SBR Particle Size
(nm) SBR: CMC weight ratio Cathode loading amount Discharge capacity (mAh / g) Capacity retention rate (%) Cathode efficiency (%) SBR: CMC Film Tensile Strength (kgf) Cathode Volume Expansion Rate (%) Example 6 CMC-Li 100 1: 1 10 358 81 93.2 340 22.3 Example 7 CMC-Li 100 2: 1 10 358 79 93.1 230 25.4 Example 8 CMC-Li 100 4: 1 10 357 78 92.8 150 31.8 Example 9 CMC-Li 200 1: 1 10 359 81 94.1 432 22 Example 10 CMC-Li 200 2: 1 10 358 78 93.2 340 22.5 Example 11 CMC-Li 200 4: 1 10 353 75 92.8 310 24.6 Example 12 CMC-Li 400 1: 1 10 360 78 93.2 230 22.6 Example 13 CMC-Li 400 2: 1 10 356 75 92.8 220 22.6 Example 14 CMC-Li 400 4: 1 10 352 73 91 87 26.5 Example 15 CMC-Li 200 2: 1 14 358 80 93.5 340 28.6 Example 16 CMC-Li 200 2: 1 16 358 80 93.2 340 36 Comparative Example 11 CMC-Na 100 1: 1 10 356 74 92.7 285 25.4 Comparative Example 12 CMC-Na 100 2: 1 10 355 73 92.5 154 30.2 Comparative Example 13 CMC-Na 100 4: 1 10 354 71 92.3 56 36.6 Comparative Example 14 CMC-Na 200 1: 1 10 354 73 92.5 340 23.6 Comparative Example 15 CMC-Na 200 2: 1 10 354 70 92.1 260 31.6 Comparative Example 16 CMC-Na 200 4: 1 10 347 65 92 164 33.1 Comparative Example 17 CMC-Na 400 1: 1 10 353 73 92.6 115 28.1 Comparative Example 18 CMC-Na 400 2: 1 10 351 72 91.5 76 28.9 Comparative Example 19 CMC-Na 400 4: 1 10 347 70 90.2 35 28.8 Comparative Example 20 CMC-Na 200 2: 1 14 350 65 91.2 260 34.1 Comparative Example 21 CMC-Na 200 2: 1 16 348 55 90.5 260 38.7

Comparing Examples 6 to 16 and Comparative Examples 11 to 21 with reference to Table 2, when SRB and a CMC-Li salt having a particle size of 180 nm to 220 nm were mixed, discharge capacity, capacity retention, cathode efficiency and tensile strength Is significantly improved, and the volume expansion rate is remarkably reduced.

Further, the performance of the secondary battery is remarkably improved when the mixing ratio of SBR and CMC-Li salt is from 1: 1 or more to less than 2: 1.

Further, Examples 10, 15, 16 and Comparative Examples 15 and 20, as compared to 21, compared to the case where the loading of the amount of 10 mg / cm ^2, in the case of 14 mg / cm ² to 16 mg / cm ² CMC-Li It is confirmed that the salt further improves the performance of the secondary battery as compared with the CMC-Na salt. From this, it can be seen that the CMC-Li salt is more effective in a high capacity battery having a high loading amount.

It is also confirmed that when CMC-Li is used instead of CMC-Na when the mixing ratio of SBR: CMC is constant, the tensile strength of the SBR: CMC film remarkably increases and the volume expansion rate of the negative electrode is remarkably reduced . When the volume expansion rate of the negative electrode is reduced, the change in the volume during the use of the secondary battery is reduced, and the lifetime characteristics can be remarkably improved.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (21)

A negative electrode active material, a thickener, and an aqueous binder;
The thickener is a thickener having a degree of substitution of hydroxy (-OH) groups by a lithium carboxymethyl group (-CH ₂ COOLi) of 0.7 to 1.3, a molecular weight (Mn) of 300,000 to 1,000,000, a viscosity of 2,000 to 15,000 cps, Is a lithium carboxymethyl cellulose salt (CMC-Li salt) having a molecular weight of from 1.0 to 2.0. The negative electrode material mixture according to claim 1, wherein the substitution degree of the lithium carboxymethyl group is 0.8 to 1.2. The negative electrode material mixture according to claim 1, wherein the CMC-Li salt has a molecular weight of 350,000 to 900,000. The negative electrode material mixture according to claim 1, wherein the viscosity of the CMC-Li salt is from 2,200 cps to 12,000 cps under the conditions of 23 ° C and 12 rpm of a B type LV type viscometer. The negative electrode material mixture according to claim 1, wherein the solubility of the CMC-Li salt is 1.0 to 1.5 based on weight at 23 ° C. The negative electrode mix according to claim 1, wherein the pH of the CMC-Li salt is 6.8 to 8.0. The negative electrode material mixture according to claim 1, wherein the aqueous binder is styrene-butadiene rubber (SBR). The negative electrode material mixture according to claim 7, wherein the SBR has a particle diameter of 90 nm to 500 nm. The negative electrode material mixture according to claim 1, wherein the content ratio of the thickener and the aqueous binder is 1: 2 to 5: 1 by weight. The negative electrode material mixture according to claim 1, wherein the negative electrode active material is a carbon-based material, and the carbon-based material is at least one selected from the group consisting of graphite carbon, coke carbon and hard carbon. [Claim 11] The method of claim 10, wherein the graphite carbon is spherical particles and the R value of the Raman spectrum [R = I ₁₃₅₀ / I ₁₅₈₀ ] (I ₁₃₅₀ is Raman intensity near 1350 cm ^-1 , I ₁₅₈₀ is 1580 cm &lt; ^-1 &gt;) is in the range of 0.20 to 1.0. The negative electrode material mixture according to claim 1, wherein the negative electrode material mixture further comprises a conductive material, a filler, or a conductive material and a filler. An anode for a secondary battery, characterized in that the anode mixture according to claim 1 is applied on the anode current collector. The negative electrode for a secondary battery according to claim 13, wherein the loading amount of the negative electrode mixture is 10 to 20 mg / cm ² . The negative electrode for a secondary battery according to claim 13, wherein the loading amount of the negative electrode mixture is 14 to 16 mg / cm ² . A secondary battery comprising a negative electrode according to claim 13. The secondary battery according to claim 16, wherein the secondary battery has a discharge capacity of 350 mAh / g or more at 0.3 C-rate. 17. The secondary battery according to claim 16, wherein the secondary battery has a capacity retention rate of 75% or more at 300 cycles of charging and discharging. 17. The secondary battery according to claim 16, wherein the secondary battery has a negative electrode efficiency of 93% or more when the coin half cell is charged / discharged at 0.1 C-rate. A battery pack comprising the secondary battery according to claim 16 as a unit cell. A device comprising the battery pack according to claim 20 as a power source.