KR101723993B1 - Negative electrode for rechargeable lithium battery, method for preparing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

And a negative electrode active material layer formed on the current collector,
Wherein the negative active material layer comprises a carbon-based negative active material and a polyacrylic acid binder,
Wherein the weight ratio of the polyacrylic acid to the carbonaceous anode active material is 0.01 to 0.4, a method for producing the same, and a lithium secondary battery comprising the same.

Description

[0001] The present invention relates to a negative electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the negative electrode. [0002]

The present invention relates to a negative electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

A lithium secondary battery, which has recently been spotlighted as a power source for portable electronic devices, has a discharge voltage twice as high as that of a conventional battery using an alkaline aqueous solution, resulting in high energy density.

Such a lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium and a negative electrode including a negative active material capable of intercalating and deintercalating lithium And the electrolyte solution is injected into the battery cell.

On the other hand, a binder is used for the adhesive force of the active material during the production of the electrode, and a binder material is required to improve the high adhesion force, high electrode density and battery lifetime. In addition, high density of the electrode is required in accordance with the trend of high capacity of the battery, and maintenance of the electrolyte injection property and the thermal stability of the electrode should be improved at high density.

An embodiment of the present invention is to provide a negative electrode for a lithium secondary battery that exhibits safety and excellent lifetime characteristics even in a high-density electrode.

Another embodiment of the present invention is to provide a method for manufacturing the negative electrode for a lithium secondary battery.

Another embodiment of the present invention is to provide a lithium secondary battery including the negative electrode.

One embodiment of the present invention includes a current collector and a negative active material layer formed on the current collector, wherein the negative active material layer includes a carbonaceous negative active material and a polyacrylic acid binder,

The weight ratio of the polyacrylic acid to the carbonaceous anode active material is 0.01 Lt; / RTI > to 0.4 .

The weight average molecular weight (Mw) of the polyacrylic acid binder may be 1,000 to 5,000,000.

The content of the polyacrylic acid binder may be 1 to 30% by weight based on the total amount of the negative electrode active material layer.

The carbon-based negative electrode active material may include natural graphite, artificial graphite, soft carbon, hard carbon or a combination thereof.

The natural graphite may be spherical.

The carbonaceous anode active material may be coated with amorphous carbon.

The amorphous carbon may include petroleum pitch, coal pitch, mesophase pitch, low molecular weight crude oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose or combinations thereof.

The amount of the amorphous carbon may be 0.1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material.

The carbonaceous anode active material may have an average particle diameter of 3 to 30 탆.

The negative electrode active material layer may further include at least one of a carboxymethyl cellulose (CMC) binder, a styrene-butadiene rubber (SBR) binder, or a combination thereof.

The content of at least one of the carboxymethylcellulose (CMC) binder, the styrene-butadiene rubber (SBR) binder, or a combination thereof may be 0.1 to 50 parts by weight based on 100 parts by weight of the polyacrylic acid binder.

The density of the negative electrode for the lithium secondary battery may be 1.6 to 2.0 g / cc.

The negative electrode active material layer may further include a conductive material.

The conductive material may be natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum, metal powder of silver, or metal fiber.

The conductive material may be 0.1 to 30 parts by weight based on 100 parts by weight of the negative electrode active material layer.

According to another embodiment of the present invention, there is provided a negative electrode composition comprising: preparing a negative electrode composition by mixing a carbonaceous anode active material, an aqueous solvent, and a polyacrylic acid binder; Applying the negative electrode composition on a current collector, compressing the current collector coated with the negative electrode composition, and heat treating the compressed current collector. The present invention also provides a method for manufacturing a negative electrode for a lithium secondary battery.

The aqueous solvent may comprise water, alcohol or a combination thereof.

The compression may be performed at a pressure of 1 to 10 kgf / cm < ² >.

The heat treatment may be performed at 100 to 300 ° C.

The weight average molecular weight (Mw) of the polyacrylic acid binder may be 1,000 to 5,000,000.

The content of the polyacrylic acid binder may be 1 to 30% by weight based on the total amount of the electrode material made of the carbonaceous anode active material.

The carbonaceous anode active material may be natural graphite, artificial graphite, soft carbon, hard carbon or a combination thereof.

The natural graphite may be spherical.

The carbonaceous anode active material may be coated with amorphous carbon.

The amount of the amorphous carbon may be 0.1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material.

The carbonaceous anode active material may have an average particle diameter of 5 to 30 탆.

The density of the negative electrode for the lithium secondary battery may be 1.6 to 2.0 g / cc.

Another embodiment of the present invention provides a lithium secondary battery comprising a cathode, an anode, and an electrolyte.

It is possible to realize an electrode capable of maintaining the shape of the active material and the impregnation path of the electrolyte even in a high-density electrode, and a lithium secondary battery having improved stability and life characteristics including the same.

1 is an exploded perspective view of a lithium secondary battery according to one embodiment.
2 is a SEM photograph showing the surface state of the electrode according to the first embodiment.
3 is an SEM photograph showing the surface state of the electrode according to Example 3. Fig.
4 is an SEM photograph showing the surface state of the electrode according to Example 4. Fig.
5 is an SEM photograph showing the surface state of the electrode according to Comparative Example 1. Fig.
6 is an SEM photograph showing the surface state of the electrode according to Comparative Example 3. Fig.
7 is an SEM photograph showing the surface state of the electrode according to Comparative Example 4. Fig.
8 is an SEM photograph showing the surface state of the electrode according to Comparative Example 5. Fig.
9 is an SEM photograph showing the surface state of the electrode according to Comparative Example 6. Fig.
10 is an SEM photograph showing the surface state of the electrode according to Comparative Example 7. Fig.
11 is a graph showing a capacity retention rate at a high rate of lithium secondary batteries according to Examples 1 to 4;
12 is a graph showing a capacity retention rate at a high rate of a lithium secondary battery according to Comparative Examples 1 to 4.
FIG. 13 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 1 and Comparative Example 1. FIG.
FIG. 14 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 2 and Comparative Example 2. FIG.
FIG. 15 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 3 and Comparative Example 3. FIG.
16 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 4 and Comparative Example 4;
17 shows the results of DSC analysis of the negative electrode for a lithium secondary battery according to Example 1, Comparative Example 1 and Comparative Example 5. Fig.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

The negative electrode for a lithium secondary battery according to an embodiment includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer includes a carbonaceous negative electrode active material and a polyacrylic acid binder. The weight ratio of the polyacrylic acid binder may be 0.01 to 0.4. When the weight ratio is within the above range, the binding effect by the polyacrylic acid binder is improved and the electrical conductivity can be maintained. When the ratio of the polyacrylic acid binder to the carbonaceous anode active material is less than 0.01, the binding effect to the anode active material is insufficient, and when it exceeds 0.4, the electrical conductivity of the electrode is deteriorated.

The polyacrylic acid binder is a polymer binder having a weight average molecular weight (Mw) of 1,000 to 5,000,000, preferably 10,000 to 3,000,000. When the weight average molecular weight (Mw) of the polyacrylic acid is within the above range, the electrode comprising the polyacrylic acid binder exhibits high density characteristics, and the energy density per volume of the battery can be improved.

The weight average molecular weight can be generally measured by a light scattering method. Specifically, the light scattering method can measure the molecular weight, size, shape and thermodynamic properties of the polymer by measuring the scattered light intensity according to the scattering angle as a function of the concentration and temperature of the polymer.

The polyacrylic acid binder may be used in an amount of from 1 to 30% by weight, more preferably from 2 to 10% by weight, based on the total weight of the negative electrode active material layer. When the polyacrylic acid binder is contained within the above range in the negative electrode active material layer, the active material can be stably slurried in the electrode to produce a uniform and stable negative electrode active material slurry, Thereby improving the safety of the lithium secondary battery.

The carbonaceous anode active material may specifically be natural graphite, artificial graphite, soft carbon, hard carbon or a combination thereof. More specifically, the carbonaceous anode active material may be a natural graphite, a crystalline carbonaceous material such as artificial graphite Materials may be mainly used.

Particularly, graphite has a discharge voltage lower than that of lithium of 0.2 V, and a battery using graphite as a negative electrode active material exhibits a high discharge voltage of 3.6 V, thereby providing excellent characteristics in terms of energy density per mass of the lithium secondary battery. In addition, excellent lifetime characteristics of the lithium secondary battery can be ensured due to excellent reversibility. Natural graphite has been converted to a smooth surface shape through post-processing such as sphering to reduce the irreversible reaction and improve the processability of the electrode.

The negative electrode for a lithium secondary battery according to one embodiment may include graphite and a polyacrylic acid binder simultaneously, which are carbon-based negative electrode active materials. In this case, since the negative electrode increases not only the energy density per mass but also the energy density per volume, even if the density of the electrode is increased to 1.7 g / cc or more, the shape of the graphite particles is not deformed and the pores contained in the electrode are maintained And the penetration rate of the electrolytic solution can also be maintained. In addition, a polyacrylic acid binder may be coated on the negative electrode active material to suppress the reactivity between the negative active material and the organic electrolyte at high temperature, thereby improving the thermal stability of the lithium secondary battery.

The carbonaceous anode active material may include, in addition to the carbonaceous material, a material capable of reversibly intercalating / deintercalating lithium ions, an alloy of lithium metal and lithium metal, a material capable of doping and dedoping lithium, Oxides or combinations thereof. .

As a material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium ion secondary batteries can be used as the carbonaceous material. Typical examples thereof include crystalline carbon , Amorphous carbon, or a combination thereof.

As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used.

As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-Y alloy (Y is an alkali metal, an alkali earth metal, a Group 13 element, a Group 14 element, A rare earth element or a combination thereof, but not Si), a Si-C composite, or a combination thereof; A Sn-based compound of Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element or a combination thereof, Or a combination thereof.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

According to one embodiment, the carbonaceous anode active material of the negative electrode may be coated with amorphous carbon. By covering the surface of the carbon-based anode active material with an appropriate amount of amorphous carbon, it is possible to prevent destruction by the electrolyte and reduce the irreversible reaction. More specifically, it is preferable that 0.1 to 50 parts by weight, more specifically 1 to 20 parts by weight, of amorphous carbon per 100 parts by weight of the negative electrode active material The above-mentioned effect can be achieved. The carbonaceous anode active material may be spherical particles and may have an average particle diameter of 3 to 30 mu m, preferably 5 to 25 mu m. When the average particle diameter is within the above range, it is possible to produce a stable negative electrode slurry at the time of producing the electrode, thereby making it possible to manufacture a high density electrode. In addition, a lithium secondary battery including a high-density electrode can exhibit excellent lifetime characteristics and safety. Here, the average particle diameter may include both the average particle diameter before and after the carbon-based negative active material is coated with the amorphous carbon. At this time, the thickness of the coating layer may be about 0.1 to 1.0 mu m.

The amorphous carbon may be a petroleum pitch, coal pitch, mesophase pitch, low molecular weight crude oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose or a combination thereof.

The negative electrode active material layer may include only a polyacrylic acid binder, but is not limited thereto, and may further include an aqueous binder containing water as a solvent or a dispersion medium. Specific examples thereof include polyvinyl alcohol, carboxymethylcellulose (CMC), hydroxypropylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane , Styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like can be used, and preferably carboxymethylcellulose ( CMC), styrene-butadiene rubber (SBR), or a combination thereof.

The content of the aqueous binder contained in the negative electrode active material layer may be 0.1 to 50 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the polyacrylic acid. When the content of the aqueous binder is within the above range, the binding effect by the binder and the electrode characteristics can be improved.

The negative electrode for a lithium secondary battery may exhibit an electrode density of 1.6 to 2.0 g / cc.

The electrode density Can be calculated by dividing the weight of the electrode applied on the current collector by the volume. Specifically, the electrode density can be obtained by dividing the weight per unit area (g) of the electrode coated on the current collector by the unit volume (cm ³ ) multiplied by the unit area.

The negative electrode active material layer may further include a conductive material.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, or metal fibers may be used, and conductive materials such as polyphenylene derivatives may be mixed and used. In particular, when the conductive material is contained in an amount of 0.1 to 30 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer, the electrical conductivity of the electrode is improved.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

According to another embodiment of the present invention, there is provided a negative electrode composition comprising: preparing a negative electrode composition by mixing a carbonaceous anode active material, an aqueous solvent and a polyacrylic acid binder; applying the negative electrode composition onto a current collector; Compressing the compressed current collector, and heat-treating the compressed current collector. The present invention also provides a method of manufacturing a negative electrode for a lithium secondary battery.

In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, the step of preparing the negative electrode composition may be performed in an aqueous solvent. The polyacrylic acid binder is an aqueous binder usable in an aqueous solvent, The lithium secondary battery is not dissolved in an electrolyte having a high polarity such as a carbonate-based organic solvent, so that the binding force can be maintained even during the temperature rise or charging / discharging of the electrode, and thus the safety of the battery can be improved. Specifically, it may be water, an alcohol system, or a combination thereof.

The step of compressing the current collector may be performed by, for example, a high-pressure press, a hot press, or a roll press, but is not limited thereto.

The production of the negative electrode may be performed at a pressure of 1 to 10 kgf / cm &lt; ² &gt;. The pressure range may be a suitable range for producing a negative electrode having a density of 1.6 to 2.0 g / cc. More specifically, the density of the cathode may be 1.7 to 1.9 g / cc. When the density of the cathode is within the above range, the energy density per volume of the electrode is increased, and thus it is possible to manufacture a battery having a high energy density.

The current collector compressed by the press can be dried by a heat treatment step. The heat treatment is performed in a vacuum state, and may be performed at 100 to 400 ° C, specifically at 120 to 280 ° C, and may be performed for about 1 to 24 hours, specifically, for 1 to 20 hours. The negative electrode subjected to vacuum drying at the above temperature and time range can be made into a high-density electrode.

Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte as described above. Optionally, a separator may be present between the anode and the cathode.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the type of the separator and electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

1 is an exploded perspective view of a lithium secondary battery according to one embodiment. 1, the lithium secondary battery 100 has a cylindrical shape and includes a cathode 112, a cathode 114, a separator 113 disposed between the cathode 112 and the anode 114, An electrolyte 114 (not shown), an electrolyte (not shown) impregnated into the separator 113, a battery container 120, and a sealing member 140 for sealing the battery container 120. The lithium secondary battery 100 is constructed by laminating a cathode 112, a separator 113 and an anode 114 in this order and then winding them in a spiral wound state in the battery container 120.

The negative electrode is as described above.

The anode 114 includes a current collector and a cathode active material layer formed on the current collector. The cathode active material layer includes a cathode active material and a binder.

Al may be used as the current collector, but the present invention is not limited thereto.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, it is possible to use at least one of complex oxides of cobalt, manganese, nickel or a combination of metals and lithium, and specific examples thereof include compounds represented by any one of the following formulas. Li _a A _{1 - b} R _b D ₂ wherein, in the formula, 0.90? A? 1.8 and 0? B? 0.5; Li _a E _{1 - b} R _b O _{2 - c} D _c , wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05; LiE _{2 - b} R _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -b- c} Co _b R _c D _{α where} 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2; Li _a Ni _{1 - b - c} Co _b R _c O _{2 - ?} Z _{? Wherein} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -bc} Co _b R _c O _2-α Z ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 <α <2; Li _a Ni _{1 -b- c} Mn _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z _{? Where the} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -bc} Mn _b R _c O _2-α Z ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a MnG _b O ₂ wherein, in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1; Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise, as a coating element compound, an oxide, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be carried out by any of coating methods such as spray coating, dipping, and the like without adversely affecting the physical properties of the cathode active material by using these elements in the above compound. It is a content that can be well understood by people engaged in the field, so detailed explanation will be omitted.

The binder may be an aqueous binder containing water as a solvent or a dispersion medium, or a combination thereof.

The binder may be selected from the group consisting of polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, and ethylene oxide. Polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon or the like may be used But is not limited thereto.

The cathode active material layer may further include a conductive material.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The cathode 112 and the anode 114 are each prepared by mixing an active material, a conductive material or a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein. As the solvent, N-methylpyrrolidone or the like can be used, but it is not limited thereto.

The electrolytic solution includes a lithium salt and a non-aqueous organic solvent.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the cell to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the anode and the cathode.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO _{2 , LiAlCl 4, LiN (C x} F 2x +1 SO 2) (C y F 2y +1 SO 2) ( where, x and y are natural numbers), LiCl, LiI, and _{LiB (C 2 O 4) 2} ( lithium Lithium bis (oxalato) borate (LiBOB), etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the range The electrolyte can exhibit excellent electrolyte performance because of its appropriate conductivity and viscosity, and lithium ions can effectively migrate.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate , BC) and the like can be used.

In particular, when a mixture of a chain carbonate compound and a cyclic carbonate compound is used, the solvent may be prepared from a solvent having a high viscosity and a high dielectric constant. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed in a volume ratio of about 1: 1 to 1: 9.

Examples of the ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate, methyl propionate, ethyl propionate, butyrolactone, decanolide, valerolactone, mevalonolactone mevalonolactone, caprolactone, and the like may be used. Examples of the ether-based solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. As the ketone solvent, cyclohexanone and the like can be used. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, An amide such as nitriles such as dimethylformamide, and dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

The non-aqueous organic solvent may be used alone or in admixture of one or more. If the non-aqueous organic solvent is used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired cell. .

The non-aqueous electrolytic solution may further contain additives such as an overcharge inhibitor such as ethylene carbonate, pyrocarbonate and the like.

The separator 113 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene double layer separator, a polyethylene / polypropylene / polyethylene triple layer separator, a polypropylene / polyethylene / Polypropylene three-layer separator, or the like can be used.

Hereinafter, specific examples of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

Example  One

(Negative active material and Polyacrylic acid  Preparation of electrode mixed with binder)

Spherical natural graphite having an average particle diameter (D ₅₀ ) of 10 μm and a polyacrylic acid binder (K-702 Polymer, Lubrizol) were mixed at a weight ratio of 95: 5 and then dispersed in water to prepare a slurry composition for forming an anode active material layer .

The composition was applied to a Cu-foil current collector and dried in air to prepare an anode precursor.

The negative electrode precursor was compressed at a pressure of 2 kgf / cm ² using a roll press, then placed in a vacuum oven and dried at 180 ° C. for 12 hours or more to prepare a negative electrode for a lithium secondary battery.

(Production of lithium secondary battery)

A coin-type half-cell was fabricated by using the negative electrode as a working electrode and metal lithium as a counter electrode. At this time, a separator made of a porous polypropylene film was inserted between the working electrode and the counter electrode, and a 1: 1 mixed solution of diethyl carbonate (DEC) and ethylene carbonate (EC) ₆ was dissolved.

Example  2 to 4

In Example 1, instead of the roll press pressure of 2 kgf / cm ² ,

Except that the negative electrode was produced by compressing the negative electrode at a pressure of 3 kgf / cm ² (Example 2), 4 kgf / cm ² (Example 3) and 6 kgf / cm ² (Example 4) .

Comparative Example  One

In Example 1, instead of the polyacrylic acid binder,

A negative electrode was prepared in the same manner as in Example 1 except that a mixture of carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) was used.

Comparative Example  2 to 4

In Comparative Example 1, instead of the roll press pressure of 2 kgf / cm ² ,

3 kgf / cm ² (Comparative Example ^{2), 4 kgf / cm 2} ( Comparative Example 3) and 6 kgf / cm ² (Comparative Example 4) the negative electrode is compressed to a pressure as in the Comparative Example 1 except that the preparation of .

Comparative Example  5

In the first embodiment,

The procedure of Example 1 was repeated, except that a negative electrode was prepared using a polyvinylidene fluoride (PVDF) binder instead of a polyacrylic acid binder.

Comparative Example  6 and 7

In Comparative Example 5, instead of the roll press pressure of 2 kgf / cm ² ,

4 kgf / cm ² (Comparative Example 6) and 6 kgf / cm ² (Comparative Example 7) to produce a negative electrode.

Evaluation 1: Scanning electron microscope ( Scanning Electron Microscope , SEM ) Picture

2 is a SEM photograph showing the surface state of the electrode according to the first embodiment.

3 is an SEM photograph showing the surface state of the electrode according to Example 3. Fig.

4 is an SEM photograph showing the surface state of the electrode according to Example 4. Fig.

5 is an SEM photograph showing the surface state of the electrode according to Comparative Example 1. Fig.

6 is an SEM photograph showing the surface state of the electrode according to Comparative Example 3. Fig.

7 is an SEM photograph showing the surface state of the electrode according to Comparative Example 4. Fig.

8 is an SEM photograph showing the surface state of the electrode according to Comparative Example 5. Fig.

9 is an SEM photograph showing the surface state of the electrode according to Comparative Example 6. Fig.

10 is an SEM photograph showing the surface state of the electrode according to Comparative Example 7. Fig.

2 to 10, compared with the electrodes according to Comparative Examples 1, 3 and 4 using CMC / SBR as a binder and the electrodes according to Comparative Examples 5 to 7 using PVDF as a binder, the use of polyacrylic acid as a binder It was confirmed that the electrodes according to Examples 1, 3 and 4 showed less pressing phenomenon of graphite particles as the pressure of the press increased, and that electrode pores were easily maintained even at high density.

Evaluation 2: Evaluation of high lifetime characteristics of lithium secondary battery

The high-rate lifetime characteristics of the lithium secondary batteries fabricated according to Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated, and the results are shown in Table 1, Fig. 11, and Fig.

Each of the lithium secondary batteries manufactured according to Examples 1 to 4 and Comparative Examples 1 to 4 was subjected to constant current charging at a current of 70 mA / g, and after completion of charging at a battery voltage of 0.005 V, a current of 70 mA / The capacity retention ratio when discharged from 1C, 2C and 5C to 2 V with respect to the capacity when discharged from 0.2C to 2V was measured. The results are shown in Fig. 11 and Fig. 12, respectively. In addition, V, compared to the capacity at discharge, V are shown in Table 1 below

11 is a graph showing a capacity retention rate at a high rate of lithium secondary batteries according to Examples 1 to 4;

12 is a graph showing a capacity retention rate at a high rate of a lithium secondary battery according to Comparative Examples 1 to 4.

Referring to FIGS. 11 and 12, it can be seen that the lithium secondary batteries according to Examples 1 to 4 are superior in the high-rate characteristics to the lithium secondary batteries according to Comparative Examples 1 to 4.

Evaluation 3: Evaluation of cycle life characteristics of lithium secondary battery

The cycle life characteristics of the lithium secondary batteries manufactured according to Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated, and the results are shown in Table 1 and Figs. 13 to 16, respectively.

Each of the lithium secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was charged from 0.2 C to 0.005 V and then discharged from 0.2 C to 2 V for 50 times, And the results are shown in FIGS. 13 to 16. FIG. The remaining capacity (%) represents the percentage at the 40th discharge capacity relative to the initial discharge capacity. Particularly, the percentages at the 40th discharge capacity as compared to the initial discharge capacity are shown in Table 1.

FIG. 13 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 1 and Comparative Example 1. FIG.

FIG. 14 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 2 and Comparative Example 2. FIG.

FIG. 15 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 3 and Comparative Example 3. FIG.

16 is a graph showing the capacity retention rate according to the number of cycles of the lithium secondary battery according to Example 4 and Comparative Example 4;

Referring to FIGS. 13 to 16, it can be seen that the capacity retention ratio of the lithium secondary battery according to Examples 1 to 4 is maintained higher than that of the lithium secondary batteries according to Comparative Examples 1 to 4 according to cyclic repetition.

bookbinder Press
pressure
(Kgf / cm ² ) Electrode density
(g / cc) High rate discharge characteristic
[5C / 0.2C]
(%) Life characteristics
(40 times / initial)
(%) Example 1 Polyacrylic acid 2 1.74 95.6 99.4 Example 2 Polyacrylic acid 3 1.75 90.7 99.1 Example 3 Polyacrylic acid 4 1.80 65.7 99.1 Example 4 Polyacrylic acid 6 1.92 49.0 98.7 Comparative Example 1 CMC / SBR 2 1.72 84.4 96.2 Comparative Example 2 CMC / SBR 3 1.85 48.6 89.0 Comparative Example 3 CMC / SBR 4 1.9 39.1 85.0 Comparative Example 4 CMC / SBR 6 1.98 29.6 41.0

Evaluation 4: Thermal analysis of cathode

The results of thermal analysis of the negative electrode prepared according to Example 1 and Comparative Examples 1 and 5 are shown in Table 2 and FIG.

The negative electrode for a lithium secondary battery manufactured according to Example 1 and Comparative Examples 1 and 5 was charged and discharged three times, and the electrode in a lithium-charged state (0.005 V) was heated at a rate of 5 ° C per minute using a differential scanning calorimeter (DSC) RTI ID = 0.0 &gt; 200 C &lt; / RTI &gt; The results are shown in Table 2 and Fig.

17 shows the results of DSC analysis of the negative electrode for a lithium secondary battery according to Example 1, Comparative Example 1 and Comparative Example 5. Fig.

Referring to FIG. 17, in the case of the negative electrode for a lithium secondary battery according to Example 1, the amount of heat generation is significantly small over a temperature range of 25 (normal temperature) to 200 ° C, compared with the negative electrode for lithium secondary battery according to Comparative Example 1 and Comparative Example 5 .

From this, it can be seen that a more stable lithium secondary battery can be realized at a high temperature by using an electrode manufactured using a polyacrylic acid binder.

bookbinder DSC (room temperature to 200 ° C)
(J / g) Example 1 PAA 365 Comparative Example 1 CMC / SBR 470 Comparative Example 5 PVDF 635

100: lithium secondary battery 112: cathode
113: separator 114: positive electrode
120: battery container 140: sealing member

Claims (28)

Collecting house; And a negative electrode active material layer formed on the current collector, wherein the negative electrode has a density of 1.7 to 2.0 / cc,
The negative electrode active material layer may include a carbon-based negative electrode active material; And a polyacrylic acid binder coated on the carbonaceous anode active material,
The weight ratio of the polyacrylic acid binder to the carbonaceous anode active material is 0.01 to 0.4,
The carbonaceous anode active material is a spherical natural graphite having an average particle size of 3 to 30 um,
Negative electrode for lithium secondary battery. The method according to claim 1,
Wherein the polyacrylic acid binder has a weight average molecular weight (Mw) of 1,000 to 5,000,000. The method according to claim 1,
The content of the polyacrylic acid binder
And 1 to 30% by weight based on the total amount of the negative electrode active material layer. delete delete The method according to claim 1,
Wherein the carbonaceous anode active material is coated on the surface with amorphous carbon. The method according to claim 6,
Wherein the amorphous carbon is a petroleum pitch, coal pitch, mesophase pitch, low molecular weight crude oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose or a combination thereof. The method according to claim 6,
Wherein the amount of the amorphous carbon is 0.1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. delete The method according to claim 1,
Wherein the negative electrode active material layer further comprises at least one of a carboxymethyl cellulose (CMC) binder, a styrene-butadiene rubber (SBR) binder, or a combination thereof. 11. The method of claim 10,
Wherein the content of at least one of the carboxymethyl cellulose (CMC) binder, the styrene-butadiene rubber (SBR) binder, or a combination thereof is 0.1 to 50 parts by weight based on 100 parts by weight of the polyacrylic acid. delete The method according to claim 1,
Wherein the negative electrode active material layer further comprises a conductive material. 14. The method of claim 13,
Wherein the conductive material is natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum, silver metal powder, or metal fiber. 14. The method of claim 13,
Wherein the conductive material is 0.1 to 30 parts by weight based on 100 parts by weight of the negative electrode active material layer. Preparing a negative electrode composition by mixing a carbonaceous anode active material, an aqueous solvent, and a polyacrylic acid binder;
Applying the negative electrode composition onto a current collector;
Compressing the current collector coated with the negative electrode composition; And
And heat treating the compressed current collector,
The carbonaceous anode active material is a spherical natural graphite having an average particle diameter of 3 to 30 μm,
Compressing the current collector to which the negative electrode composition is applied, the compression is performed at a pressure of 1 to 10 kgf / cm &lt; ² &
Heat-treating the compressed current collector; And a negative electrode active material layer formed on the current collector, wherein a density of 1.7 to 2.0 / cc is obtained.
(Method for manufacturing negative electrode for lithium secondary battery). 17. The method of claim 16,
Wherein the aqueous solvent comprises water, an alcohol-based solvent, or a combination thereof. delete 17. The method of claim 16,
Wherein the heat treatment is performed at 100 to 300 ° C. 17. The method of claim 16,
Wherein the weight average molecular weight (Mw) of the polyacrylic acid binder is 1,000 to 5,000,000. 17. The method of claim 16,
The content of the polyacrylic acid binder
Based on the total amount of the carbon-based anode active material layer, is 1 to 30 wt%. delete delete 17. The method of claim 16,
Wherein the carbonaceous anode active material is coated on the surface of the amorphous carbon. 25. The method of claim 24,
Wherein the amount of the amorphous carbon is 0.1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. delete delete anode;
A cathode according to any one of claims 1 to 3, 6 to 8, 10, 11, and 13 to 15; And
A lithium secondary battery comprising an electrolytic solution.

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