KR20170054052A - Positive electrode for lithium secondary battery, preparing method thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery which includes a positive electrode active material layer containing a positive electrode active material, and a polydopamine layer formed on the surface of the positive electrode active material layer; a preparing method thereof; and a lithium secondary battery comprising the positive electrode including the same. The positive electrode according to an embodiment of the present invention has remarkably improved impregnation properties of an electrolyte by having the polydopamine layer. By using the positive electrode, a lithium secondary battery with improved lifespan and rate controlling properties.

Description

[0001] 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 positive electrode,

A positive electrode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

Lithium secondary batteries are used in a variety of applications due to their high voltage and high energy density. For example, when a lithium secondary battery is used in an electric vehicle (HEV, PHEV) or the like, a lithium secondary battery can operate at a high temperature, and a large amount of electricity must be charged or discharged and used for a long time. Life characteristics should be excellent.

As a cathode active material for a lithium secondary battery, lithium cobalt oxide has a very high energy density and is widely used as a cathode active material. However, when such a lithium cobalt oxide is used as a cathode active material, a problem of increased manufacturing cost and difficulty in stable supply due to the ubiquitous nature and scarcity of cobalt is emerging as a problem. To solve this problem, a lot of efforts have been made to develop a substitute for cobalt.

One aspect is to provide a positive electrode for a lithium secondary battery having improved stability. Another aspect is to provide a method of manufacturing the above-described anode for a lithium secondary battery.

Another aspect of the present invention is to provide a lithium secondary battery in which the above-described anode is employed to improve the rate-limiting performance and the life characteristic.

According to one aspect,

There is provided a positive electrode for a lithium secondary battery comprising a positive electrode active material layer and a polypopamine layer formed on the surface of the positive electrode active material layer.

According to another aspect of the present invention, there is provided a method for forming a polypodamine layer on a cathode active material layer comprising a cathode active material, A method for manufacturing a positive electrode for a lithium secondary battery is provided.

According to another aspect, there is provided a lithium secondary battery including the above-described anode.

The anode according to an embodiment has a polypodamine layer, and the impregnability of the electrolyte is greatly improved. By adopting such an anode, it is possible to fabricate a lithium secondary battery with improved rate performance and lifetime characteristics.

1A is a schematic diagram of a lithium secondary battery according to an exemplary embodiment.
FIG. 1B is a conceptual view of a method of manufacturing an exemplary anode.
2 is a scanning electron micrograph of a cathode surface prepared according to Example 1. Fig.
FIGS. 3 and 4 are electron micrographs of the anode surface prepared according to Comparative Examples 1 and 2, respectively.
5 is a graph showing a change in capacity retention rate in a lithium secondary battery produced according to Example 2, Comparative Examples 3 and 4;

Hereinafter, a lithium secondary battery including a cathode active material and a cathode including the cathode active material according to exemplary embodiments will be described in more detail.

There is provided a positive electrode for a lithium secondary battery comprising a positive electrode active material layer and a polypopamine layer formed on the surface of the positive electrode active material layer.

The polydopamine layer has a continuous coating film morphology. As the polypodamine layer has a continuous coating film shape, the property of impregnating (wetting) the electrolyte injected in one direction of the assembled battery can be greatly improved. When the electrolyte impregnating property is improved as described above, the conversion process can be shortened and the output characteristics of the lithium secondary battery can be improved.

The positive electrode for a lithium secondary battery according to an embodiment can realize more stable characteristics by forming a coating layer on the positive electrode than the surface treatment of the positive electrode active material itself, and it is easy to ensure mass productivity by simple process.

The thickness of the poly dopamine layer is 10 to 200 nm, for example, 50 to 150 nm, specifically 80 to 120 nm. When the thickness of the polypodamine layer is in the range described above, the lithium secondary battery having the anode having the polypodamine layer has excellent stability and capacity retention characteristics.

The content of polypodamine in the polypodamine layer is 0.1 to 10 parts by weight, for example, 0.5 to 5 parts by weight, specifically 1 to 3 parts by weight, based on 100 parts by weight of the positive electrode active material. When the content of polypodamine is in the above range, the positive electrode has excellent electrolyte impregnability.

As the cathode active material, at least one selected from the compounds represented by the following formulas (1) to (6) may be used.

[Chemical Formula 1]

Li _a Ni _x Co _y Mn _z M _c O _{2 - e} A _e

0 <x <1, 0 <x <1, 0 <x <1, 0 <x + y + z + M is at least one element selected from the group consisting of vanadium V, magnesium Mg, gallium Ga, silicon Si, tungsten W, molybdenum Mo, iron Fe, chromium Cr, , Zinc (Zn), titanium (Ti), aluminum (Al) and boron (B)

A is an anion element of F, S, Cl, Br or a combination thereof,

(2)

Li [Co _{1 - x} M _x ] O _{2 - a a a}

Wherein M is at least one metal selected from the group consisting of Mg, Al, Ni, Mn, Zn, Fe, Cr, Ga, Mo, and W,

A is an anion element of F, S, Cl, Br or a combination thereof,

(3)

_{Li 1 + a [Ni 1 -} x M x] O 2- b A b

Wherein M is at least one selected from the group consisting of Mg, Al, Co, Mn, Zn, Fe, Cr, Ga, Mo and W; At least one metal,

A is an anion element of F, S, Cl, Br or a combination thereof,

[Chemical Formula 4]

_{Li 1 + a [Mn 2 -} x M x] O 4- b A b

Wherein M is at least one selected from the group consisting of Co, Ni, Cr, Mg, Al, Zn, Mo and W

[Chemical Formula 5]

LiM _x Fe _{1 - x} PO ₄

In Formula 5, M is at least one metal selected from the group consisting of Co, Ni and Mn, and 0? X? 1.

[Chemical Formula 6]

_{Li 1 + a [Ni 0 .5} Mn 1 .5- x M x] O 4- b A b

Wherein M is at least one metal selected from the group consisting of Co, Ni, Cr, Mg, Al, Zn, Mo, and W; .

The cathode active material includes, for example, a compound represented by the following general formula (7)

have.

(7)

LiNi _x Co _y Mn _{1 -x- y} O ₂

In the above formula (7), 0.5? X? 1.0, 0.0? Y? 0.5.

In the above formula (7), x is, for example, 0.5 to 0.8, and y is 0.1 to 0.35, for example, 0.1 to 0.35.

The compound of formula (7) has a nickel content of at least 50 mol%, which makes it possible to produce a positive electrode having a high energy density. However, if such an anode is used, the electrolyte impregnability may be reduced and the output characteristics may be deteriorated. However, according to one embodiment, if a cathode having a surface coated with a polydodamine layer is employed, a lithium secondary battery having improved energy performance and improved output performance can be produced.

The positive electrode active material, for example, _{LiNi 0 .5 Co 0 .2 Mn 0} .3 O 2, LiNi 0 .6 Co 0 .3 Mn 0 .2 O 2, LiNi 0.7 Co 0.15 Mn 0.15 O 2, or LiNi _{0. 8} is a _{Co 0 .1 Mn 0 .1 O 2} .

The contact angle of the polydopamine layer is 10 to 30 degrees, for example 15 to 25 degrees. Here, the contact angle refers to the contact angle at the anode surface when the electrolyte used in the battery is dropped.

In the case of employing a general anode, the electrolyte impregnation property is not sufficient on the surface of the anode, and the conversion process is required, and the output characteristics can not be satisfied.

Accordingly, the present inventors have improved the impregnability of the electrolyte solution on the anode surface by forming a polypodamine layer on the anode surface. When the polypodamine layer has a continuous coating film form, the impregnation property of the electrolyte injected in one direction of the assembled battery can be further improved.

Hereinafter, a method of manufacturing a positive electrode having a polypodamine layer according to an embodiment will be described.

First, a composition for forming a polypodamine layer containing dopamine, a solvent and a buffer solution is coated on the upper part of the positive electrode active material layer containing the positive electrode active material and dried to form a polypopamine layer on the positive electrode active material layer. An anode can be produced.

Dopamine is a polydodamine through autopolymerization in the pH range of about 8 to 8.8, for example about 8.5.

The pH of the composition for forming a polydodamine layer is from 8.0 to 8.8, for example, about 8.5.

The buffer solution is a solution having a pH of about 8 to 8.8, for example, a buffer solution containing Tris-HCl and water (volume ratio of HCl and H ₂ O is 3: 1), tris borate ethylene diamine tetra-acetic acid (TBE), Tris-buffered saline (TBS) and phosphate-buffered saline (PBS).

As the solvent, for example, an alcohol compound is used as a substance which does not affect the pH of the composition. Examples of the alcohol compound include ethanol, methanol, butanol, and isopropanol. The content of the solvent is, for example, in the range of 100 to 3000 parts by weight based on 100 parts by weight of dopamine.

The drying is carried out, for example, in the range of 20 to 25 占 폚.

The coating may be applied by dipping, spray coating, bar coating, die casting, comma coating,

Screen printing, and the like. It is also possible to bond the anode to the anode by a pressing or laminating method after forming on a separate substrate. The coating according to one embodiment refers to a spray coating method.

The use of the anode having the surface-coated polydopamine layer can improve the output characteristics and the life characteristics.

The positive electrode having the positive electrode active material layer containing the positive electrode active material may be produced according to the following procedure.

A cathode active material composition in which a cathode active material, a binder and a solvent are mixed is prepared.

A conductive agent may further be added to the cathode active material composition.

The positive electrode active material composition is directly coated on a current collector and dried to produce a positive electrode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then the film peeled from the support may be laminated on the metal current collector to produce a cathode plate.

As the conductive agent, binder and solvent in the positive electrode active material composition, the same materials as those for the negative electrode active material composition may be used. It is also possible to add a plasticizer to the cathode active material composition and / or the anode active material composition to form pores inside the electrode plate.

Examples of the conductive agent include carbon black, graphite fine particle natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fiber; Metal powders or metal fibers or metal tubes such as carbon nanotubes, copper, nickel, aluminum, and silver; Conductive polymers such as polyphenylene derivatives, and the like can be used, but the present invention is not limited thereto, and any conductive polymer may be used as the conductive polymer in the art.

Examples of the binder include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyimide, polyethylene, polyester, polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene (PTFE) Carboxymethyl cellulose-styrene-butadiene rubber (CMC / SBR) copolymer, styrene-butadiene rubber-based polymer, or a mixture thereof.

As the solvent, N-methylpyrrolidone, acetone or water may be used.

But not limited to, all of those which can be used in the technical field.

As the cathode active material, at least one selected from the compounds represented by the formulas (1) to (6) may be used.

The content of the cathode active material, the conductive agent, the binder, and the solvent is a level commonly used in a lithium battery. At least one of the conductive agent, the binder and the solvent may be omitted depending on the use and configuration of the lithium battery.

The negative electrode can be obtained by substantially the same method except that the negative electrode active material is used in place of the positive electrode active material in the positive electrode manufacturing process described above.

As the negative electrode active material, a carbon-based material, silicon, a silicon oxide, a silicon-based alloy, a silicon-carbon-based material composite, a tin, a tin alloy, a tin-carbon composite or a metal oxide or a combination thereof is used.

The carbon-based material may be crystalline carbon, amorphous carbon or a mixture thereof. The crystalline carbon may be graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type, and the amorphous carbon may be soft carbon or hard carbon carbon fiber, carbon fiber, mesophase pitch carbide, fired cokes, graphene, carbon black, fullerene soot, carbon nanotubes, and carbon fiber, and the like, Anything that can be used is possible.

The negative electrode active material may be selected from the group consisting of Si, SiOx (0 <x <2, for example, 0.5 to 1.5), Sn, SnO ₂ or a silicon-containing metal alloy and mixtures thereof. At least one of Al, Sn, Ag, Fe, Bi, Mg, Zn, In, Ge, Pb and Ti may be used as the metal for forming the silicon alloy.

The negative electrode active material may include a metal / metalloid alloy that is alloyable with lithium, an alloy thereof, or an oxide thereof. For example, the metal / metalloid capable of alloying with lithium may be at least one selected from the group consisting of Si, Sn, Al, Ge, Pb, Bi, SbSi-Y alloy (Y is an alkali metal, an alkaline earth metal, a Group 13 element, , A rare earth element or a combination element thereof and not Si), an Sn-Y alloy (Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, , MnOx (0 < x? 2), and the like. The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, or a combination thereof. For example, the oxide of the metal / metalloid capable of alloying with lithium may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, SnO ₂ , SiO _x (0 <x <2) and the like.

For example, the negative electrode active material may include one or more elements selected from the group consisting of Group 13 elements, Group 14 elements, and Group 15 elements of the Periodic Table of the Elements.

For example, the negative electrode active material may include at least one element selected from the group consisting of Si, Ge, and Sn.

The content of the negative electrode active material, the conductive agent, the binder and the solvent is a level commonly used in a lithium battery.

The current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. The positive electrode current collector may be formed into various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like by forming fine irregularities on the surface to enhance the bonding force of the positive electrode active material. Specifically, the cathode current collector may be a metal current collector including aluminum, and the anode current collector may be a metal current collector including copper. The current collector may be a metal foil, or may be aluminum (Al) foil or copper (Cu) foil.

The separator is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used.

The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 20 mu m. As such a separator, for example, an olefin-based polymer such as polypropylene; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte may also serve as a separator.

Among the separators, specific examples of the olefin-based polymer include 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 multi-layered film such as a polypropylene / polyethylene / polypropylene three-layer separator or the like may be used.

The lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and a lithium salt.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte is used.

The nonaqueous electrolytic solution includes an organic oil. These organic solvents may be used as long as they can be used as organic solvents in the art. Examples of the solvent include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate N, N-dimethylformamide, N, N-dimethylformamide, tetrahydrofuran, tetrahydrofuran, Dimethylacetamide, N, N-dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or mixtures thereof.

Examples of the organic solid electrolyte include a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a polyelectrolytic lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene chloride, And the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI- ₃ PO ₄ -Li ₂ S-SiS _2, and the like can be used.

The lithium salt is a substance which can be dissolved in the non-aqueous electrolyte, for example,

_{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiClO 4, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, Li (FSO 2) 2 N, LiC 4 F 9 SO 3, 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 or mixtures thereof. For the purpose of improving the charge-discharge characteristics and the flame retardancy, non-aqueous electrolytes include, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexamethylphosphoamide hexamethyl phosphoramide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, Etc. may be added. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability.

As shown in FIG. 1A, the lithium battery 11 includes an anode 13, a cathode 12, and a separator 14. The positive electrode 13, the negative electrode 12 and the separator 14 described above are wound or folded and accommodated in the battery case 15. Then, an organic electrolytic solution is injected into the battery case 15 and the cap assembly 16 is sealed to complete the lithium secondary battery 11. The battery case may have a cylindrical shape, a rectangular shape, a thin film shape, or the like. For example, the lithium battery may be a thin film battery. The lithium battery may be a lithium ion battery.

A separator may be disposed between the anode and the cathode to form a battery structure. The cell structure is laminated in a bi-cell structure, then impregnated with an organic electrolyte solution, and the obtained result is received in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery assemblies may be stacked to form a battery pack, and such battery pack may be used for all devices requiring high capacity and high output. For example, a notebook, a smart phone, an electric vehicle, and the like.

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

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

The present invention will be described in more detail by way of the following examples and comparative examples. However, the examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example  1: Preparation of positive electrode

The positive electrode active material _{(LiNi 0 .5 Co 0 .2 Mn} 0 .3 O 2), a mixture of polyvinylidene fluoride and a conductive agent of carbon black mixture to prepare a slurry for forming a positive electrode active material layer. N-methyl pyrrolidone as a solvent was added to the slurry, and the mixing ratio of the cathode active material, polyvinylidene fluoride, and carbon black was 94: 3: 3 by weight.

The slurry thus prepared was coated on an aluminum foil using a doctor blade to form a thin electrode plate, which was then dried at 135 ° C for 3 hours or more, followed by rolling and vacuum drying to prepare a cathode.

And 50 ml of a buffer solution having a pH of 8.5 per 0.1 g of dopamine to prepare a composition for forming a polypodamine layer. Ethanol was further diluted to improve the viscosity and drying characteristics without affecting the pH in the process.

As shown in Fig. 1B, the composition was applied to a collector 22 and a positive electrode active material

A nozzle (24) is provided on the upper surface of the anode (20) having a structure in which the layer (21)

And dried at about 25 캜 to form a poly dopamine layer 23 having a thickness of about 100 nm on the cathode active material layer 22.

Example  2: The lithium secondary battery (coin cell)  Produce

A 2032 type coin cell was prepared using the anode prepared in Example 1 and the lithium metal counter electrode as a counter electrode. A coin cell was produced between the positive electrode and the lithium metal counter electrode by injecting an electrolyte through a separator (thickness: about 16 μm) made of a porous polyethylene (PE) film.

The electrolyte used was a solution containing 1.1 M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3: 4: 3.

Example  3: Preparation of positive electrode

A positive electrode was prepared in the same manner as in Example 1 except that the content of dopamine was changed to 1 g in the composition for forming a polydodamine layer.

Example  4: Manufacture of anode

A positive electrode was prepared in the same manner as in Example 1 except that the spray coating process was controlled so that the thickness of the polypodamine layer was about 50 nm.

Example  5-6: The lithium secondary battery  Produce

A lithium secondary battery was produced in the same manner as in Example 2 except that the positive electrodes prepared in accordance with Examples 3 and 4 were used in place of the positive electrodes prepared in Example 1, respectively.

Comparative Example  1: Preparation of positive electrode

It carried the positive electrode active material obtained according to Example _{1 (LiNi 0 .5 Co 0 .2} Mn 0 .3 O 2), a polyvinylidene fluoride, and a conductive agent of carbon black mixture by using a mixer to remove the air bubbles are uniformly distributed Thereby preparing a slurry for forming the positive electrode active material layer. N-methylpyrrolidone as a solvent was added to the mixture, and the mixing ratio of the cathode active material, polyvinylidene fluoride, and carbon black was 92: 4: 4 by weight.

The slurry thus prepared was coated on an aluminum foil using a doctor blade to form a thin electrode plate, which was then dried at 135 ° C for 3 hours or more, followed by rolling and vacuum drying to prepare a cathode.

Comparative Example  2: Preparation of anode

First, a cathode active material having a polypodamine layer formed on the surface thereof was obtained according to the following procedure.

And 50 ml of a buffer solution having a pH of 8.5 per 0.1 g of dopamine to prepare a composition for forming a polypodamine layer. Ethanol was further diluted to improve the viscosity and drying characteristics without affecting the pH in the process.

The positive electrode active material _{(LiNi 0 .5 Co 0 .2 Mn} 0 .3 O 2) into the powder was washed with distilled water and then stirred for 2 hours. And dried at 130 DEG C for 5 days to prepare a cathode active material surface-modified with a polypodamine layer.

The mixture of the cathode active material surface-modified with the polypodamine layer, polyvinylidene fluoride, and carbon black as a conductive agent was removed using a blender to prepare a slurry for forming a uniformly dispersed cathode active material layer. N-methyl pyrrolidone as a solvent was added to the mixture, and the mixing ratio of the cathode active material, polyvinylidene fluoride, and carbon black was 94: 3: 3.

The slurry thus prepared was coated on an aluminum foil using a doctor blade to form a thin electrode plate, which was then dried at 135 ° C for 3 hours or more, followed by rolling and vacuum drying to prepare a cathode.

Comparative Example  3-4: The lithium secondary battery  Produce

A lithium secondary battery was fabricated in the same manner as in Example 2 except that the anode obtained in Comparative Example 1-2 was used instead of the anode obtained in Example 1.

Evaluation example  One: Contact angle  characteristic

The contact angles were evaluated on the anode surface prepared according to Example 1, Comparative Example 1, and Comparative Example 2. The contact angle was measured using a contact angle measuring instrument (manufacturer: SEO, Model: Phoenix 300).

 After dropping the electrolyte solution on the surface of the anode, the contact angle was evaluated. The results are shown in Table 1 and FIGS. 2 to 4.

2 to 4 are scanning electron microscope (SEM) photographs of the anode surface prepared according to Example 1, Comparative Example 1 and Comparative Example 2.

division Contact angle (°) Example 1 23 Comparative Example 1 79 Comparative Example 2 54

As shown in Table 1 and Figs. 2 to 4, it was found that the contact angle of the anode prepared according to Example 1 was smaller than that of the anode prepared according to Comparative Examples 1 and 2. The reason why the contact angle was reduced in this manner is that a continuous coating film is formed because the anode of Comparative Example 2 is discontinuously coated on the surface of the cathode active material as shown in Fig. 4, In the prepared anode, as shown in FIG. 3, the polydopamine layer is continuously and uniformly coated so that the wettability of the anode is greatly improved.

Evaluation example  One: Charging and discharging  characteristic

Charge-discharge characteristics and the like of the lithium secondary batteries fabricated according to Examples 2, 5-6 and Comparative Example 3-4 were evaluated under the following conditions with a charge-discharge machine (TOYO, model: TOYO-3100).

The coin cells prepared in Examples 2, 5-6, and Comparative Example 3 were first charged and discharged once at 0.1 C to proceed formation, and then the initial charge / discharge characteristics were confirmed at 0.2 C charge / And cycling characteristics were examined while repeating charge and discharge, and the results are shown in FIG.

The constant current mode is set to CC (constant current) at the time of charging and then set to cut off at 0.05C by changing to CV (constant voltage) and set to cut off at 4.3V in CC (constant current) mode. The discharge rate (C-rate) was changed to 0.2C, 0.5C, 1C, 2C, 5C, or 10C or 0, 2C, respectively, as shown in Fig.

As shown in FIG. 5, the lithium secondary battery produced according to Example 2 improved the capacity retention ratio as compared with the lithium secondary battery produced according to Comparative Example 3-4. In particular, the lithium secondary battery produced according to Example 2 The capacity difference between the battery and the lithium secondary battery produced according to Comparative Example 3 was increased. The reason why the capacity characteristics was improved as described above is that the lithium secondary battery of Example 2 formed a polypodamine layer on the surface of the positive electrode and the wettability of the electrolyte solution was improved.

The lithium secondary battery manufactured according to Example 5 and Example 6 exhibited a capacity retention characteristic equivalent to that of the lithium secondary battery produced according to Example 2 above.

It will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit or scope of the following claims.

11: lithium secondary battery 13: anode
12: cathode 14: separator
15: battery case 16: cap assembly

Claims (12)

A positive electrode for a lithium secondary battery comprising a positive electrode active material layer containing a positive electrode active material and a polypopamine layer formed on the surface of the positive electrode active material layer. The method according to claim 1,
Wherein the polypodamine layer is a continuous coating film. The method according to claim 1,
Wherein the cathode active material is at least one selected from the group consisting of compounds represented by Chemical Formulas 1 to 6:
[Chemical Formula 1]
Li _a Ni _x Co _y Mn _z M _c O _{2 - e} A _e
0 <x <1, 0 <x <1, 0 <x <1, 0 <x + y + z + M is at least one element selected from the group consisting of vanadium V, magnesium Mg, gallium Ga, silicon Si, tungsten W, molybdenum Mo, iron Fe, chromium Cr, , Zinc (Zn), titanium (Ti), aluminum (Al) and boron (B)
A is an anion element of F, S, Cl, Br or a combination thereof,
(2)
Li [Co _{1 - x} M _x ] O _{2 - a a a}
Wherein M is at least one metal selected from the group consisting of Mg, Al, Ni, Mn, Zn, Fe, Cr, Ga, Mo, and W,
A is an anion element of F, S, Cl, Br or a combination thereof,
(3)
_{Li 1 + a [Ni 1 -} x M x] O 2- b A b
Wherein M is at least one selected from the group consisting of Mg, Al, Co, Mn, Zn, Fe, Cr, Ga, Mo and W; At least one metal,
A is an anion element of F, S, Cl, Br or a combination thereof,
[Chemical Formula 4]
_{Li 1 + a [Mn 2 -} x M x] O 4- b A b
Wherein M is at least one selected from the group consisting of Co, Ni, Cr, Mg, Al, Zn, Mo and W
[Chemical Formula 5]
LiM _x Fe _{1 - x} PO ₄
In Formula 5, M is at least one metal selected from the group consisting of Co, Ni and Mn, and 0? X? 1.
[Chemical Formula 6]
_{Li 1 + a [Ni 0 .5} Mn 1 .5- x M x] O 4- b A b
Wherein M is at least one metal selected from the group consisting of Co, Ni, Cr, Mg, Al, Zn, Mo, and W; . The method according to claim 1,
Wherein the positive electrode active material comprises a compound represented by Formula 7:
(7)
LiNi _x Co _y Mn _{1 -x- y} O ₂
In the above formula (7), 0.5? X? 1.0, 0.0? Y? 0.5. The method according to claim 1,
The positive electrode active material layer was _{LiNi 0 .5 Co 0 .2 Mn 0} .3 O 2, LiNi 0 .6 Co 0 .3 Mn 0 .2 O 2, LiNi 0.7 Co 0.15 Mn 0.15 O 2, or LiNi _{0 .8} Co _{0 .1} Mn _{0 .1} O ₂ for a lithium secondary battery positive electrode comprising a. The method according to claim 1,
Wherein the polypodamine layer has a contact angle of 10 to 30 DEG. The method according to claim 1,
Wherein the thickness of the polypodamine layer is 10 to 200 nm. The method according to claim 1,
The content of polypodamine in the polypodamine layer is 100 parts by weight of the cathode active material
By weight based on the total weight of the positive electrode for a lithium secondary battery. A step of coating a composition for forming a polypodamine layer containing dopamine, a solvent and a buffer solution on the cathode active material layer containing the cathode active material and drying the same to form a polypodamine layer on the cathode active material layer; A method of manufacturing an anode. 10. The method of claim 9,
Wherein the pH of the composition for forming a polydodamine layer is 8 to 8.8. 10. The method of claim 9,
Wherein the coating is carried out by a spray coating method. 9. A lithium secondary battery comprising a positive electrode according to any one of claims 1 to 8.

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