KR20180134615A - Positive electrode for secondary battery, method for preparing the same, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery, a method of producing the same, and a lithium secondary battery comprising the same. The positive electrode for a lithium secondary battery comprises a positive electrode mixing layer formed on a positive electrode assembly, wherein the positive electrode mixing layer includes a positive electrode active material and a radical polymer. The present invention may serve to improve an output of the positive electrode, increase the capacitance, and reduce polarization at boundaries of the positive electrode, thereby achieving high-rate characteristics.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a positive electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the positive electrode,

The present invention relates to a positive electrode for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

2. Description of the Related Art In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, electric vehicles, and the like, the demand for secondary batteries of small size and light weight and relatively high capacity has been rapidly increasing. Particularly, the lithium secondary battery is light in weight and has a high energy density, and is attracting attention as a driving power source for portable devices. Accordingly, research and development efforts for improving the performance of the lithium secondary battery have been actively conducted.

The lithium secondary battery has a structure in which an organic electrolyte or a polymer electrolyte is filled between a positive electrode and a negative electrode, which are made of an active material capable of intercalating and deintercalating lithium ions, and oxidized when lithium ions are inserted / And electrical energy is produced by the reduction reaction.

As the positive electrode active material of the lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compound (LiFePO ₄ ) do. Further, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a method of replacing a part of nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. However, LiNi _{1 - α} Co _α O ₂ (α = 0.1 ~ 0.3) in which a part of nickel is substituted with cobalt exhibits excellent charge / discharge characteristics and life characteristics, but has a low thermal stability. On the other hand, a nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) excellent in thermal stability and a nickel-cobalt manganese-based lithium composite metal oxide in which manganese (Mn) (Hereinafter referred to as " NCM-based lithium oxide ") has an advantage in that it has excellent cycle characteristics and thermal stability.

However, such a cathode active material conventionally used in the art has a limitation in meeting the requirements of high output and high energy density. Therefore, there is a need for a new method for further improving the output of the positive electrode of the lithium secondary battery and increasing the capacity.

Japanese Patent No. 5169181

An object of the present invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode, which further improve the output, further increase the capacity, and have a high rate characteristic.

The present invention provides a positive electrode for a lithium secondary battery comprising a positive electrode mixture layer formed on a positive electrode collector, wherein the positive electrode mixture layer comprises a positive electrode active material and a radical polymer.

The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

The present invention also provides a method for producing a positive electrode for a lithium secondary battery, comprising the step of forming a positive electrode mixture layer containing a positive electrode active material and a radical polymer on a positive electrode collector.

According to the present invention, the output of the anode can be improved, the capacity can be remarkably increased, and the polarization phenomenon at the cathode interface can be reduced to realize excellent high-rate characteristics.

1 is a schematic cross-sectional view of a cathode for a lithium secondary battery according to an embodiment of the present invention.
2 is a schematic cross-sectional view of a portion of an electrode assembly of a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

The positive electrode for a lithium secondary battery of the present invention includes a positive electrode mixture layer formed on a positive electrode collector, and the positive electrode mixture layer includes a positive electrode active material and a radical polymer.

1 is a schematic cross-sectional view of a cathode for a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, an anode 100 for a lithium secondary battery according to an embodiment of the present invention includes a cathode current collector 10 and a cathode mixture layer 20 formed on the cathode current collector 10. The positive electrode material mixture layer 20 includes a positive electrode active material 21 and a radical polymer 22.

In the present invention, by forming the positive electrode material mixture layer 20 such that the radical polymer 22 is mixed with the positive electrode active material 21, the output of the positive electrode can be improved and the capacity can be remarkably increased. The radical polymer 22 refers to a polymer containing a structural unit having radicals, and may be, for example, a polymer having a nitroxide radical, an oxy radical, a nitrogen radical, a nitroylnitroxyl radical, or the like. The radical polymer 22 according to one embodiment of the present invention is characterized by being a material for charging and discharging, and having excellent charge-discharge characteristics even at a high current of about 100 C or so. Therefore, when the cathode mixture layer 20 is formed by using the radical polymer 22 together with the cathode active material 21, the capacity can be increased and a high-rate property can be realized.

Hereinafter, a cathode 100 for a lithium secondary battery according to an embodiment of the present invention will be described in detail.

The positive electrode current collector 10 is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, the positive electrode current collector 10 may be made of stainless steel, aluminum, nickel, titanium, Nickel, titanium, silver, or the like may be used. In addition, the cathode current collector 10 may have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the cathode current collector 10 to increase the adhesion of the cathode active material 21. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The cathode active material may be a lithium transition metal oxide generally used as a cathode active material and more preferably at least one transition metal cation selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn) A lithium transition metal oxide may be used. For example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a layered compound such as Li _{1 + x 1} Mn _{2 - x 1} O ₄ (where x 1 is 0 to 0.33), LiMnO ₃ , LiMn ₂ O _3, LiMnO _2, such as lithium manganese oxide, the general formula LiNi ₁ of _{- x2} M1 _x2 O ₂ (wherein, M1 = Co, and Mn, Al, Cu, Fe, Mg, B or Ga, x2 = 0.01 ~ 0.3) with formula Ni site type lithium nickel oxide, which is represented _{LiMn 2 - x3 M2 x3 O 2} ( where, M2 = Co, Ni, Fe, Cr, and Zn, or Ta, x3 = 0.01 ~ 0.1) or Li ₂ Mn ₃ M3O ₈ ( where M3 = Fe, Co, Ni, Cu or Zn) lithium-manganese composite oxide, LiNi _x4 Mn _2, which is represented by _{- x4} O ₄ (here, lithium-manganese composite oxide of a spinel structure represented by x4 = 0.01 ~ 1), Lithium iron phosphate (LiFePO ₄ ), and the like. However, the present invention is not limited thereto.

Alternatively, the cathode active material may include a lithium-transition metal composite oxide represented by the following general formula (1).

[Chemical Formula 1]

Li _a Ni _{1 -x- y} Co _x Mn _y M _z O ₂

Wherein M is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9? A? 1.5, 0? X? 0.5, 0? Z? 0.1. More preferably 0? X + y? 0.7.

More preferably, the cathode active material is lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium iron phosphate compound (LiFePO ₄ ) Complex oxides, and combinations thereof.

The positive electrode active material 21 may be contained in an amount of 80 to 98% by weight, more specifically 85 to 98% by weight based on the total weight of the positive electrode material mixture layer 20. When included in the above content range, excellent capacity characteristics can be exhibited.

The radical polymer (22) may be coated on the surface of the cathode active material (21). The radical polymer 22 may be coated on part or all of the surface of the cathode active material 21. The radical polymer 22 may be mixed with the cathode mixture layer 20 together with the cathode active material 21 in the form coated on the cathode active material 21.

The radical polymer 22 can be used as long as it is a stable material that can be charged and discharged and exhibits excellent charge / discharge characteristics even at high currents. For example, the radical polymer 22 may be a material including a nitroxide radical, an oxy radical, a nitrogen radical, and a nitronylnitroxyl radical Lt; / RTI > and at least one polymer selected from the group consisting of polymers. More preferably a polymer having a nitroxide radical, and most preferably a (2,2,6,6-tetramethylpiperidin-1-yl) oxyl ((2,2,6,6-Tetramethylpiperidin -1-yl) oxyl, TEMPO) in the structural unit.

The main chain of the radical polymer (22) is a polymer composed of (meth) acrylate, acetylene, norbornene, styrene, ethylene glycol, methylsiloxane, vinyl ether, (meth) acrylamide and styrene sulfotate ≪ / RTI > may be polymers or copolymers of selected monomers.

The radical polymer 22 is most preferably a poly ((2,2,6,6-tetramethylpiperidin-1-yl) oxyl) methacrylate-styrenesulfonate copolymer.

By forming the positive electrode mixture layer 20 in which the radical polymer 22 is mixed with the positive electrode active material 21 as described above, high output, high capacity and excellent high-rate characteristics can be exhibited.

The positive electrode active material 21 and the radical polymer 22 may be included in the positive electrode material mixture layer 20 at a weight ratio of 9: 1 to 7: 3. More preferably from 9: 1 to 8: 2, and most preferably from 8.5: 1.5 to 8: 2. When included in the above weight ratio, the capacity can be further increased, and the polarization of the anode interface can be lowered to further improve the high-rate characteristics.

The positive electrode material mixture layer 20 includes the positive electrode active material 21 and the radical polymer 22, and may further include a conductive material and a binder.

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture layer 20.

The binder serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof. One kind or a mixture of two or more kinds of them may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture layer 20.

A method for producing the positive electrode for a lithium secondary battery according to the present invention will be described.

The method for producing a positive electrode for a lithium secondary battery according to the present invention comprises forming a positive electrode mixture layer containing a positive electrode active material and a radical polymer on a positive electrode collector.

The method of forming the positive electrode mixture layer containing the positive electrode active material and the radical polymer is not particularly limited as long as it is a method capable of forming a positive electrode mixture layer in which the positive electrode active material and the radical polymer are mixed. According to an embodiment of the present invention, the step of forming the positive electrode material mixture layer may include coating the positive electrode active material with a radical polymer, Mixing a cathode active material coated with the radical polymer with a conductive material and a binder to form a composition for forming an anode; And applying the composition for forming an anode onto the positive electrode current collector.

In the step of coating the cathode active material with the radical polymer, the cathode active material may be immersed in a solution containing the radical polymer to perform liquid coating. At this time, the radical polymer may be coated so that the cathode active material and the radical polymer satisfy a weight ratio of 9: 1 to 7: 3.

Next, the cathode active material coated with the radical polymer, the conductive material, and the binder may be dissolved or dispersed in a solvent to prepare a composition for forming an anode. The types and contents of the radical polymer, the cathode active material, the conductive material and the binder are as described above.

Meanwhile, the solvent for forming the positive electrode composition may be a solvent commonly used in the art, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and either one of them or a mixture of two or more of them may be used. The amount of the solvent to be used is determined by dissolving or dispersing the cathode active material coated with the radical polymer, the conductive material and the binder in consideration of the coating thickness of the slurry and the production yield, It is enough to have it.

Next, the positive electrode may be prepared by applying the composition for forming an anode to the positive electrode current collector, followed by drying and rolling.

Alternatively, the anode may be produced by casting the composition for forming an anode on a separate support, then peeling the support from the support, and laminating the obtained film on the cathode current collector.

According to another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, it may be a lithium secondary battery.

2 is a schematic cross-sectional view of a portion of an electrode assembly of a lithium secondary battery according to an embodiment of the present invention.

2, the lithium secondary battery includes a positive electrode 100, a negative electrode 200 facing the positive electrode 100, a separator 300 interposed between the positive electrode 100 and the negative electrode 200, ) And an electrolyte. At this time, the anode 100 is as described above. The lithium secondary battery may further include a battery container that accommodates the positive electrode 100, the negative electrode 200, the electrode assembly 500 of the separator 300, and a sealing member that seals the battery container. have.

In the lithium secondary battery, the negative electrode includes a negative electrode collector and a negative electrode mixture layer disposed on the negative electrode collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes 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, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material mixture layer may optionally include a binder and a conductive material together with the negative electrode active material.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; _{SiO β (0 <β <2} ), SnO 2, vanadium oxide, lithium titanium oxide, which can dope and de-dope a lithium metal oxide such as lithium vanadium oxide; Or a composite containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

In addition, the binder and the conductive material may be the same as those described above for the anode.

The negative electrode material mixture layer may be formed by applying and drying a negative electrode composition prepared by dissolving or dispersing a negative electrode active material on the negative electrode collector, and optionally a binder and a conductive material in a solvent, or by drying the composition for negative electrode, Casting on a support, and then peeling the support from the support to laminate a film on the negative electrode collector.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions. The separator can be used without any particular limitation as long as it is used as a separator in a lithium secondary battery. Particularly, It is preferable to have a low resistance and an excellent ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. It is not.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium _{salt, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAl0 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2 _{, LiN (C 2 F 5 SO} 2) 2, LiN (CF 3 SO 2) 2. LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ may be used. 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 above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

In addition to the electrolyte components, the electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like, pyridine, triethanolamine, or the like for the purpose of improving lifetime characteristics of the battery, Ethyl phosphite, triethanol amine, cyclic ether, ethylenediamine, glyme, hexametriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, At least one additive such as benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, The additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles hybrid electric vehicle (HEV)).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

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

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  One

200 g of a poly ((2,2,6,6-tetramethylpiperidin-1-yl) oxyl) -methacrylate-styrenesulfonate copolymer as a radical polymer was dissolved in solvent NMP to prepare a radical polymer solution. 800 g of LiCoO ₂ was immersed in the radical polymer solution to coat the surface of the LiCoO ₂ with a radical polymer. At this time, the weight ratio of LiCoO ₂ to the coated radical polymer was 8: 2.

A radical polymer-coated LiCoO ₂ , carbon black, and a PVDF binder were mixed in a N-methylpyrrolidone solvent in a weight ratio of 95: 2.5: 2.5 to prepare a composition for forming a positive electrode, After drying at 130 DEG C, the anode was rolled to prepare a positive electrode.

Example  2

LiCoO ₂ as a cathode active material Instead, LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ was used as the cathode active material, a positive electrode was prepared.

Comparative Example  One

Radical polymer-free LiCoO ₂ of The positive electrode was prepared in the same manner as in Example 1, except that it was used.

Comparative Example  2

LiNi ₀ without radical polymer coating _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ was used as the cathode active material, a positive electrode was prepared.

Comparative Example  3

(2,2,6,6-tetramethylpiperidin-1-yl) oxyl) -methacrylate-styrene sulfonate copolymer, carbon black, and PVDF binder in a solvent of N-methylpyrrolidone At a weight ratio of 95: 2.5: 2.5 to prepare a composition for forming an anode. This composition was coated on one side of an aluminum current collector, dried at 130 캜, and rolled to prepare a positive electrode.

[ Experimental Example  1: Evaluation of capacity and cycle characteristics]

The positive electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were charged to a coin half cell at 25 DEG C in a CCCV mode until the voltage reached 0.1 C and 4.3 V and a constant current of 0.1 C To 2.5 V, and the charge / discharge test was performed 1000 times. The results are shown in Table 1 below.

Charging capacity (mAh / g) Discharge capacity (mAh / g) Capacity Density (Wh / L) Capacity retention rate
(@ 1000th cycle) Example 1 190 175 600 85 Example 2 250 230 660 85 Comparative Example 1 160 148 550 60 Comparative Example 2 210 195 600 70 Comparative Example 3 150 145 300 90

* Capacity retention rate = 1000th cycle capacity / 1st cycle capacity

As shown in Table 1, in Examples 1 and 2, in which a cathode in which a cathode active material and a radical polymer were mixed was coated with a radical polymer on a cathode active material, the capacity was increased compared to Comparative Examples 1 and 2 in which the radical polymer was not coated It was significantly increased by about 15% or more, and cycle characteristics were also remarkably improved. On the other hand, in Comparative Example 3 in which the radical polymer itself was used as the cathode active material without coating the cathode active material with the radical polymer, the energy density per volume was remarkably decreased.

[ Experimental Example  2: Evaluation of high rate property]

The high-rate characteristics were evaluated by dividing the positive electrode prepared in Examples 1 and 2 and Comparative Examples 1 and 2 into a charge of 0.1 C and a discharge of 1 C, 3 C, 5 C and 10 C, respectively. The results are shown in Table 2 below

Capacity retention rate (%)
(@ 1C) Capacity retention rate (%)
(@ 3C) Capacity retention rate (%)
(@ 5C) Capacity retention rate (%)
(@ 10C) Example 1 98 95 92 85 Example 2 98 95 92 80 Comparative Example 1 95 90 80 60 Comparative Example 2 95 85 75 50

* Capacity maintenance rate = expression capacity @ 1C, 3C, 5C, 10C / expression capacity @ 0.1C

As shown in Table 2, in Examples 1 and 2 in which a cathode in which a cathode active material and a radical polymer were mixed was coated with a radical polymer on a cathode active material, a high rate characteristic Can be confirmed.

Claims (19)

And a positive electrode mixture layer formed on the positive electrode collector,
Wherein the positive electrode material mixture layer comprises a positive electrode active material and a radical polymer.
The method according to claim 1,
Wherein the radical polymer is coated on the surface of the positive electrode active material.
The method according to claim 1,
Wherein the radical polymer is a polymer comprising at least one member selected from the group consisting of a nitroxide radical, an oxy radical, a nitrogen radical, and a nitroyl nitroxyl radical.
The method according to claim 1,
The radical polymer can be prepared by reacting (2,2,6,6-tetramethylpiperidin-1-yl) oxyl, TEMPO) with (2,2,6,6-tetramethylpiperidin- Anode for a lithium secondary battery which is a polymer.
The method according to claim 1,
The main chain of the radical polymer may be a monomer selected from the group consisting of (meth) acrylate, acetylene, novolene, styrene, ethylene glycol, methylsiloxane, vinyl ether, (meth) acrylamide and styrene sulfotate &Lt; / RTI &gt; wherein the polymer is a polymer or copolymer thereof.
The method according to claim 1,
Wherein the radical polymer is a poly ((2,2,6,6-tetramethylpiperidin-1-yl) oxyl) methacrylate-styrene sulfonate copolymer.
The method according to claim 1,
Wherein the positive electrode active material is a lithium transition metal oxide comprising at least one transition metal cation selected from the group consisting of cobalt (Co), nickel (Ni), and manganese (Mn).
The method according to claim 1,
Wherein the cathode active material is at least one selected from the group consisting of lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium iron phosphate compound (LiFePO ₄ ) And at least one of the positive electrode and the negative electrode.
[Chemical Formula 1]
Li _a Ni _{1 -x- y} Co _x Mn _y M _z O ₂
Wherein M is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9? A? 1.5, 0? X? 0.5, 0? Z? 0.1.
The method according to claim 1,
Wherein the positive electrode active material and the radical polymer are contained in the positive electrode material mixture layer at a weight ratio of 9: 1 to 7: 3.
The method according to claim 1,
Wherein the positive electrode material mixture layer further comprises a conductive material and a binder.
A positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
The positive electrode is a positive electrode for a secondary battery according to any one of claims 1 to 10.
And forming a positive electrode mixture layer containing a positive electrode active material and a radical polymer on the positive electrode collector.
13. The method of claim 12,
Wherein forming the positive electrode material mixture layer comprises:
Coating the cathode active material with a radical polymer;
Mixing a cathode active material coated with the radical polymer with a conductive material and a binder to form a composition for forming an anode; And
Applying the composition for forming an anode onto a positive electrode current collector;
Wherein the positive electrode is a positive electrode.
13. The method of claim 12,
The radical polymer is a polymer comprising lithium (2,2,6,6-tetramethylpiperidin-1-yl) oxyl, (TEMPO) (Method for manufacturing positive electrode for secondary battery).
13. The method of claim 12,
The main chain of the radical polymer may be a monomer selected from the group consisting of (meth) acrylate, acetylene, novolene, styrene, ethylene glycol, methylsiloxane, vinyl ether, (meth) acrylamide and styrene sulfotate &Lt; / RTI &gt; wherein the polymer is a polymer or copolymer of the lithium salt.
13. The method of claim 12,
Wherein the radical polymer is a poly ((2,2,6,6-tetramethylpiperidin-1-yl) oxyl) -methacrylate-styrene sulfonate copolymer.
13. The method of claim 12,
Wherein the cathode active material is a lithium transition metal oxide containing at least one transition metal cation selected from the group consisting of cobalt (Co), nickel (Ni), and manganese (Mn).
13. The method of claim 12,
The cathode active material is composed of lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium iron phosphate compound (LiFePO ₄ ) Wherein the positive electrode and the negative electrode are made of the same material.
[Chemical Formula 1]
Li _a Ni _1-xy Co _x Mn _y M _z O ₂
Wherein M is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9? A? 1.5, 0? X? 0.5, 0? Z? 0.1.
13. The method of claim 12,
Wherein the positive electrode active material and the radical polymer are contained in the positive electrode material mixture layer in a weight ratio of 9: 1 to 7: 3.

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