WO2021256716A1 - Positive electrode for secondary battery, method for manufacturing same, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides a positive electrode having good internal short-circuit safety, while having a similar level of capacity and resistance to those of a conventional positive electrode. The present invention relates to a positive electrode for a secondary battery, a method for manufacturing same, and a lithium secondary battery comprising same, the positive electrode including: a positive electrode mixture layer formed on a current collector and including a positive electrode active material; and a coating layer formed on the positive electrode mixture layer and including a compound containing lithium and fluorine, wherein the coating layer has a specific resistance of at least 10⁵ Ω·cm.

Description

Positive electrode for secondary battery, manufacturing method thereof, and lithium secondary battery comprising same

Cross-Citation with Related Applications

This application claims priority based on Korean Patent Application No. 10-2020-0074305 dated June 18, 2020, and all contents disclosed in the documents of the Korean patent application are incorporated as a part of this specification.

technical field

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

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among them, the demand for lithium secondary batteries with high capacity and low resistance and excellent safety is high.

In general, a lithium secondary battery is manufactured by using a material capable of intercalation and deintercalation of lithium ions as a negative electrode and a positive electrode, and charging an electrolyte between the positive electrode and the negative electrode, and lithium ions are the positive electrode and the negative electrode It generates electrical energy by oxidation and reduction reactions when it is inserted and desorbed.

At this time, the negative electrode and the positive electrode include an electrode mixture layer formed on the current collector of each electrode, and for example, a slurry is prepared by mixing and stirring a binder and a solvent, a conductive material, and a dispersing agent, if necessary, in the electrode active material. After that, it is applied to a current collector made of a metal material, compressed and dried to manufacture an electrode.

Such a conventional electrode includes a conductive material at a certain level or more in the electrode mixture layer for securing capacity and low resistance. However, by including the conductive material in the electrode mixture layer, the electrical conductivity of the electrode is increased, and thus, when an internal short circuit occurs due to tearing or folding of the separator, the battery overheats and swells. There is a problem that the stability of the battery is reduced.

Accordingly, there is a need for an electrode having a similar capacity and resistance to that of an existing electrode, but with enhanced internal short-circuit safety.

An object of the present invention is to provide an electrode having a similar level of capacity and resistance as that of a conventional positive electrode, with enhanced internal short-circuit safety, a method for manufacturing the same, and a lithium secondary battery including the same.

The present invention is formed on a current collector, the positive electrode mixture layer comprising a positive electrode active material; and a coating layer formed on the positive electrode mixture layer and including a compound containing lithium and fluorine, wherein the coating layer has a specific resistance of 10 ⁵ Ω·cm or more.

In addition, the present invention comprises the steps of forming a positive electrode mixture layer including a positive electrode active material on a current collector; and forming a coating layer by applying a solution containing lithium salt including lithium and fluorine on the positive electrode mixture layer and then heat-treating it to form a coating layer.

In addition, the present invention provides a lithium secondary battery comprising the positive electrode according to the present invention.

The positive electrode according to the present invention is formed on the positive electrode mixture layer, contains a compound containing lithium and fluorine, ^{and includes a coating layer having a specific resistance of 10 5} Ω·cm or more, and has a capacity and resistance similar to that of a conventional positive electrode while , the internal short circuit safety may be excellent.

1 is a view schematically showing an anode according to the present invention.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the existence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof, is not precluded in advance.

Hereinafter, the present invention will be described in more detail.

Anode for secondary battery

The present invention is formed on a current collector, the positive electrode mixture layer comprising a positive electrode active material; and a coating layer formed on the positive electrode mixture layer and including a compound containing lithium and fluorine, wherein the coating layer has a specific resistance of 10 ⁵ Ω·cm or more.

In the present invention, the specific resistance is measured by placing a probe on the electrode surface using a DC resistance measuring instrument (Hioki, RM3545-20) and allowing the current to flow only to the electrode surface.

1, the positive electrode for a secondary battery according to the present invention is formed on the current collector 100, the positive electrode mixture layer 200 including the positive electrode active material; and a coating layer 300 formed on the positive electrode mixture layer 200 and including a compound containing lithium and fluorine. The coating layer 300 has a resistivity of 10 ⁵ Ω·cm or more.

The positive electrode for a secondary battery according to the present invention contains a compound containing lithium and fluorine, ^{and includes a coating layer having a specific resistance of 10 5} Ω·cm or more, thereby reducing the electrical conductivity of the surface of the positive electrode, a capacity similar to that of a conventional battery and It is possible to provide an anode having good resistance and excellent internal short-circuit safety.

According to the present invention, the specific resistance of the coating layer may be 10 ⁵ Ω·cm or more, specifically, 10 ⁵ Ω·cm to 10 ⁹ Ω·cm, more specifically, 10 ⁵ Ω·cm to 10 ⁷ Ω·cm have. When the resistivity of the coating layer is within the above range, the short-circuit current flowing from the cathode to the anode is reduced due to the high resistivity of the anode surface even if the anode and the cathode contact and an internal short circuit occurs due to the contraction and folding of the separator. By reducing heat generation, the internal short-circuit stability of the positive electrode and, as a result, the internal short-circuit stability of the lithium secondary battery can be improved.

According to the present invention, the compound containing lithium and fluorine may be a compound represented by the following formula (1).

[Formula 1]

Li _x F _y

In Formula 1, 0.9≤x/y≤1.1, and specifically 1≤x/y≤1.1.

When the compound containing lithium and fluorine included in the coating layer is a compound represented by Formula 1, the electrical conductivity of the surface of the positive electrode is reduced due to the high specific resistance of the compounds, and accordingly, the short-circuit current flowing from the negative electrode to the positive electrode is reduced As a result, heat generation due to an internal short circuit is reduced, thereby improving the internal short circuit safety of the positive electrode.

Specifically, the compound containing lithium and fluorine may be at least one selected _{from LiF and Li 0.52} F _0.48. In this case, the internal short-circuit safety of the positive electrode and the internal short-circuit safety of the lithium secondary battery may be further improved due to the remarkably high specific resistance. In terms of further improving internal short-circuit safety, the compound containing lithium and fluorine may be a mixture _{of LiF and Li 0.52} F _0.48.

According to the present invention, the compound containing lithium and fluorine may be included in an amount of 50 wt% to 90 wt% based on the total weight of the coating layer. In this case, the specific resistance of the coating layer ^{can be implemented as 10 5} Ω·cm or more, and thus, the internal short-circuit stability of the positive electrode and the lithium secondary battery can be further improved. On the other hand, when the compound containing lithium and fluorine is a mixture of LiF and Li _0.52 F _0.48 in terms of further improving internal short-circuit safety, the weight ratio of LiF and Li _0.52 F _0.48 is 1:1 to 6:1, specifically , 1.5:1 to 5:1, more specifically 5:3 to 5:1 may be.

According to the present invention, the coating layer may be formed to a thickness of 500nm to 3㎛. Specifically, the thickness of the coating layer may be 1㎛ to 2㎛. When the thickness of the coating layer is within the above range, the reduction in energy density of the lithium secondary battery is insignificant, while the electrical conductivity of the surface of the positive electrode is reduced, so that the internal short circuit stability of the positive electrode may be improved.

According to the present invention, the positive electrode mixture layer may be formed to a thickness of 30㎛ to 150㎛. Specifically, the thickness of the positive electrode mixture layer may be 60㎛ to 100㎛. When the thickness of the positive electrode mixture layer is within the above range, the energy density, capacity, and resistance of the lithium secondary battery may be improved.

A thickness ratio of the coating layer and the positive electrode mixture layer may be 1:300 to 1:15. In this case, due to the thin coating layer compared to the positive electrode mixture layer, the energy density reduction of the lithium secondary battery is insignificant.

The current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium, Those surface-treated with silver or the like may be used. In addition, the current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

The positive electrode mixture layer is formed on the current collector and includes a positive electrode active material, and may further include a conductive material, a binder, etc. in addition to the positive electrode active material.

The positive active material may _{include a layered compound such as lithium cobalt oxide (LiCoO 2} ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; lithium iron oxides such as LiFe ₃ O _{4 ;} Lithium manganese oxide, such as Formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3) Ni site-type lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO ₈ (herein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) lithium manganese composite oxide represented by; It may be at least one selected _{from LiMn 2} O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples 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 powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used.

The binder serves to improve adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.

Manufacturing method of positive electrode for secondary battery

The present invention provides a first step of forming a positive electrode mixture layer including a positive electrode active material on a current collector; and a second step of forming a coating layer by applying a solution containing a lithium salt including lithium and fluorine on the positive electrode mixture layer and then heat-treating it.

Hereinafter, the manufacturing method of the positive electrode for a secondary battery of the present invention will be described in detail step by step.

(1) Step 1

The first step is a step of forming a positive electrode mixture layer including a positive electrode active material on a current collector.

The forming of the positive electrode mixture layer may be prepared according to a conventional method of forming the positive electrode mixture layer. Specifically, the composition for forming a positive electrode mixture layer prepared by dissolving or dispersing the above-described positive electrode active material and optionally a binder, a conductive material, a dispersing agent, etc. in a solvent as needed is coated on a positive electrode current collector, followed by drying and rolling. can do.

As the solvent, a solvent generally used in the art may be used, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), dimethylformamide ( dimethyl formamide, DMF), acetone, or water may be mentioned, and one type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is to dissolve or disperse the positive electrode active material, the conductive material, the binder, and the dispersing agent in consideration of the application thickness of the slurry and the production yield, and then to have a viscosity that can exhibit excellent thickness uniformity when applied for the production of the positive electrode That's enough.

Alternatively, the positive electrode mixture layer may be prepared by casting the composition for forming the positive electrode mixture layer on a separate support, and then laminating a film obtained by peeling it off the support on the positive electrode current collector.

(2) Step 2

The second step is a step of forming a coating layer by applying a solution containing a lithium salt including lithium and fluorine on the positive electrode mixture layer and performing heat treatment.

The solution application may be performed by one or more methods selected from a spray spray method, an impregnation method, and a blade coating method. Specifically, the solution application may be performed by a spray method. In this case, the solution can be uniformly and thinly applied to the surface of the positive electrode mixture layer by adjusting the nozzle size and the spraying time.

The solution application may be applied so that the coating layer can be formed to a thickness of 500 nm to 3 μm.

The lithium salt containing lithium and fluorine may be at least one selected from among _{LiPF 6} , LiBF ₄ , LiAsF ₆ and LiC ₄ F ₉ SO _{3 .} In this case, lithium salt is decomposed in the heat treatment process after application of the electrolyte, thereby facilitating the formation of a compound containing lithium and fluorine.

The solution may contain a lithium salt in a concentration of 0.8M to 1.4M. In this case, sufficient amounts of lithium and fluorine are included in the solution, so that the compound containing lithium and fluorine can be easily formed.

The heat treatment may be performed at 80°C to 130°C. The heat treatment may be specifically performed at 100°C to 130°C. When the heat treatment temperature is within the above range, the activation energy required for the formation of the generated compound containing lithium and fluorine is reduced, so that it is possible to form a compound containing a large amount of lithium and fluorine in a short time. On the other hand, when the temperature is too high, the crystallinity of the binder in the positive electrode mixture layer may increase, thereby increasing resistance.

lithium secondary battery

The present invention provides a lithium secondary battery including the positive electrode according to the present invention.

The lithium secondary battery includes the positive electrode; cathode; a separator interposed between the anode and the cathode; and electrolyte;

Since the positive electrode is the same as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

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

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

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

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples 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 alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0<β <2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, flaky, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode mixture layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and may be typically added in an amount of 0.1 wt % to 10 wt % based on the total weight of the negative electrode mixture layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro and roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the anode active material, and may be added in an amount of 10 wt% or less, specifically 5 wt% or less, based on the total weight of the anode mixture layer. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The negative electrode mixture layer is prepared by applying and drying a composition for forming a negative electrode mixture layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent on the negative electrode current collector and drying, or for forming the negative electrode mixture layer It can be prepared by casting the composition on a separate support and then laminating a film obtained by peeling it from the support onto a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to respect and an excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte, which can be used in manufacturing a lithium secondary battery.

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

The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as 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 ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of 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 electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as an anion of the lithium salt ^{, F -} , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be at least one selected from the group consisting of, The lithium salt is, 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 ,} etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, 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 positive electrode according to the present invention exhibits excellent capacity, low resistance and excellent safety, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles, HEV) and the like are useful in the field of electric vehicles.

Accordingly, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same can be provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium-to-large devices in a system for power storage.

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

The lithium secondary battery may not only be used in a battery cell used as a power source for a small device, but may also be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

Examples of the medium-large device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

Hereinafter, examples will be given to describe the present invention in detail. However, the embodiment according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiment described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Examples and Comparative Examples

Example 1

Ni _1/3 Co _1/3 Mn _1/3 O _{2 A} positive electrode active material, PVdF binder, and carbon black conductive material were mixed in NMP in a weight ratio of 90:5:5 to prepare a composition for forming a positive electrode mixture layer.

The composition for forming the positive electrode mixture layer was applied on an aluminum current collector (Al foil) having a thickness of 20 μm, and then dried (130° C.) to form a positive electrode mixture layer having a thickness of 80 μm.

_{A solution containing 1.0M LiPF 6} in a solvent having an EC/EMC mixing volume ratio = 30/70 by spraying on the positive electrode mixture layer was applied so that the final thickness of the coating layer was 1 μm, and then at 100° C. 5 Heat-treated for minutes _{to contain LiF and Li 0.52} F _0.48 . Using a DC resistance measuring instrument (Hioki, RM3545-20), the probe was placed on the surface of the electrode to allow current to flow only through the surface of the electrode, and the measured resistivity was 10 ⁶ Ω A coating layer of cm was formed. The content of LiF included in the coating layer was 50 wt% based on the total weight of the coating layer, and the content of _{Li 0.52} F _{0.48 was 10 wt% based on the total weight of the coating layer.}

As a result, a positive electrode having a structure of a current collector/anode mixture layer/coating layer was manufactured.

Example 2

_{In Example 1, a solution containing 1.0M LiPF 6} in a solvent having an EC/EMC mixing volume ratio = 30/70 by spraying on the positive electrode mixture layer was applied so that the final thickness of the coating layer was 2 μm, It was heat treated at 130° C. for 10 minutes _{to include LiF and Li 0.52} F _0.48 (the content of LiF included in the coating layer was 50% by weight based on the total weight of the coating layer, and _{the content of Li 0.52} F _0.48 was based on the total weight of the coating layer. It was 30% by weight) and a DC resistance measuring device (Hioki, RM3545-20) was used to place a probe on the surface of the electrode to allow current to flow only to the surface of the electrode, and a coating layer having ^{a measured specific resistance of 10 7 Ω·cm was formed.} Except that, in the same manner as in Example 1, a positive electrode having a structure of a current collector/anode mixture layer/coating layer was manufactured.

Comparative Example 1

Ni _1/3 Co _1/3 Mn _1/3 O _{2 A} positive electrode active material, PVdF binder, and carbon black conductive material were mixed in NMP in a weight ratio of 90:5:5 to prepare a composition for forming a positive electrode mixture layer.

The composition for forming the positive electrode mixture layer was applied on an aluminum current collector (Al foil) having a thickness of 20 μm, and then dried (130° C.) to form a positive electrode mixture layer having a thickness of 80 μm.

As a result, a positive electrode having a structure of a current collector/positive mixture layer was manufactured.

Comparative Example 2

_{A solution containing 1.0M LiPF 6} in a solvent having an EC/EMC mixing volume ratio = 30/70 by spraying on the positive electrode mixture layer was applied so that the final thickness of the coating layer was 0.1 μm, and then at 50° C. 5 It was heat treated for minutes to contain _{Li 0.25} F _0.75 and Li _0.52 F _{0.48 (the content of Li 0.25} F _0.75 contained in the coating layer was 30 wt % based on the total weight of the coating layer, and _{the content of Li 0.52} F _0.48 was the total amount of the coating layer. It has been a 10% by weight), based on the weight, the DC resistance meter (Hi of coating Oki社, RM3545-20) using the electrodes to place the probe on the surface of the electrode surface current to flow in only one resistivity of 10 ³ Ω · cm measured in A positive electrode having a structure of a current collector/anode mixture layer/coating layer was manufactured in the same manner as in Example 1, except that it was formed.

Preparation Example: Preparation of Lithium Secondary Battery

The positive electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 were cut into 3 cm × 4 cm sizes, respectively, and a porous separator having ^{a polypropylene/polyethylene/polypropylene structure with a size of 3.5 cm × 4.5 cm and a thickness of 20 μm and a 1 cm 2 area perforated.} is placed in contact with one side of the porous membrane, and a porous membrane having a thickness of 20 μm of a polypropylene structure having a size of 2 cm × 6 cm is placed on the perforated porous membrane to cover the perforated area. After that, the other surface of the porous separator was brought into contact with the graphite anode, and then 1M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70 by injection. A lithium secondary battery was manufactured.

Experimental example

Experimental Example 1: Evaluation of the electrical conductivity of the positive electrode

The anodes of Examples 1 and 2 and Comparative Examples 1 and 2 were cut into pieces of 5 cm × 5 cm, respectively, and placed on a vertical resistor, and then the resistance was measured by applying a current in the vertical direction. The results are shown in Table 1 below.

On the other hand, electrical conductivity and electrical resistance are inversely related.

	vertical resistance (Ω)
Example 1	0.45
Example 2	0.51
Comparative Example 1	0.21
Comparative Example 2	0.23

Referring to Table 1, the positive electrode of Examples 1 and 2 including a coating layer having a ^{specific resistance of 10 5 Ω·cm or more has a specific resistance and a specific resistance of less than 10 5} Ω·cm with the positive electrode of Comparative Example 1 not including a coating layer. It can be seen that the vertical resistance is higher than that of the anode of Fig. 2. This is because the anodes of Examples 1 and 2 ^{include a coating layer having a specific resistance of 10 5} Ω·cm or more, so that the electrical conductivity of the surface of the anode is reduced. , As a result, there is an advantageous effect in that the internal short-circuit stability of the lithium secondary battery can be improved.

Experimental Example 2: Capacity evaluation of lithium hetero battery

0.2C discharge capacity was measured at 25°C using the lithium secondary batteries prepared using the positive electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 (voltage range 3V to 4.2V). The results are shown in Table 2 below.

	0.2C discharge capacity (mAh)
Example 1	75.3
Example 2	75.3
Comparative Example 1	75.3
Comparative Example 2	75.3

Referring to Table 2, ^{the secondary batteries including the positive electrodes of Examples 1 and 2 including the coating layer having a specific resistance of 10 5} Ω·cm or more have a level similar to that of the secondary battery including the positive electrode of Comparative Example 1 not including the coating layer. It can be seen that the discharge capacity of This is because a thin coating layer is formed only on the surface of the positive electrode, so that the positive electrode as a whole reacts during actual charging and discharging.

Experimental Example 3: Resistance evaluation of lithium hetero battery

Using the lithium secondary batteries manufactured using the positive electrodes of Examples 1 and 2 and Comparative Examples 1 and 2, a 2.5C discharge current was applied for 30 seconds at 25° C. and SOC 50 to measure resistance. The results are shown in Table 3 below.

	Resistance (Ω)
Example 1	1.51
Example 2	1.52
Comparative Example 1	1.50
Comparative Example 2	1.50

Referring to Table 3, ^{the secondary batteries including the positive electrodes of Examples 1 and 2 including the coating layer having a specific resistance of 10 5} Ω·cm or more have a level similar to that of the secondary battery including the positive electrode of Comparative Example 1 not including the coating layer. It can be seen that the resistance of This is because, since a thin coating layer is formed only on the surface of the anode, the degree of increase in resistance is insignificant.

Experimental Example 4: Internal short-circuit test of lithium hetero battery

After charging the lithium secondary battery prepared using the positive electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 at SOC 100 at 25° C., cut the pouch and remove the porous separator covered on the perforated porous separator . Next, 1 MPa was applied from the outside to short-circuit the anode and the cathode, and the maximum temperature was measured while maintaining for 30 minutes. The results are shown in Table 4 below.

	Maximum temperature (℃)
Example 1	47.1
Example 2	45.7
Comparative Example 1	91.2
Comparative Example 2	91.0

Referring to Table 4, ^{the secondary battery including the positive electrode of Examples 1 and 2 including the coating layer having a specific resistance of 10 5} Ω·cm or more, the secondary battery including the positive electrode of Comparative Example 1 not including the coating layer, and the specific resistance It can be seen that the maximum temperature measured in the internal short circuit test is significantly lower than that of the secondary battery including the positive electrode of Comparative Example 2 including a coating layer having a specific resistance of ^{less than 10 5 Ω·cm.} This is because current flows through the anode and cathode interface during an internal short circuit, and the resistance of the coating layer on the anode surface is very high, so that the short circuit current is reduced.

As a result, the positive electrode according to the present invention is formed on the positive electrode mixture layer, contains a compound containing lithium and fluorine, ^{and includes a coating layer having a specific resistance of 10 5} Ω·cm or more, and has a capacity similar to that of a conventional positive electrode and It can be seen that while having resistance, the internal short circuit safety is excellent.

[Explanation of code]

100: current collector

200: positive electrode mixture layer

300: coating layer

Claims (13)

1. a positive electrode mixture layer formed on the current collector and including a positive electrode active material; and

   and a coating layer formed on the positive electrode mixture layer and comprising a compound containing lithium and fluorine;

   The coating layer is a positive electrode for a secondary battery having a ^{specific resistance of 10 5 Ω·cm or more.}
2. According to claim 1,

   The coating layer has a specific resistance of 10 ⁵ Ω·cm to 10 ⁹ Ω·cm for a secondary battery positive electrode.
3. According to claim 1,

   The compound containing lithium and fluorine is a positive electrode for a secondary battery, which is a compound represented by the following Chemical Formula 1:

   [Formula 1]

   Li _x F _y

   In Formula 1, 0.9≤x/y≤1.1.
4. According to claim 1,

   The compound containing lithium and fluorine is a positive electrode for a secondary battery comprising at least one selected _{from LiF and Li 0.52} F _0.48.
5. According to claim 1,

   The positive electrode for a secondary battery of which the compound containing lithium and fluorine is included in an amount of 50% to 90% by weight based on the total weight of the coating layer.
6. According to claim 1,

   The coating layer is a positive electrode for a secondary battery formed to a thickness of 500nm to 3㎛.
7. According to claim 1,

   The positive electrode mixture layer is a secondary battery positive electrode formed to a thickness of 30㎛ to 150㎛.
8. forming a positive electrode mixture layer including a positive electrode active material on a current collector; and

   A method of manufacturing a positive electrode for a secondary battery according to claim 1, comprising: coating a solution containing a lithium salt containing lithium and fluorine on the positive electrode mixture layer and then heat-treating to form a coating layer.
9. 9. The method of claim 8,

   The method of manufacturing a positive electrode for a secondary battery, wherein the solution application is performed by at least one method selected from a spray spraying method, an impregnation method, and a blade coating method.
10. 9. The method of claim 8,

    The lithium salt containing lithium and fluorine is LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiC ₄ F ₉ SO _{3 A} method of manufacturing a positive electrode for a secondary battery at least one selected from the group consisting of.
11. 9. The method of claim 8,

    The method of manufacturing a positive electrode for a secondary battery, wherein the heat treatment is performed at 80 °C to 130 °C.
12. 9. The method of claim 8,

    A method of manufacturing a positive electrode for a secondary battery in which the coating layer is formed to a thickness of 500 nm to 3 μm.
13. A lithium secondary battery comprising the positive electrode according to any one of claims 1 to 7.

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