KR20260044559A - Positive electrode active material, and positive electrode and litium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material comprising a lithium iron-manganese phosphate compound and a coating layer formed on the lithium iron-manganese phosphate compound comprising carbon and cobalt, wherein the lithium iron-manganese phosphate compound comprises manganese in an amount greater than 50 mol% and less than 70 mol% relative to the total molar amount of metals excluding lithium, and the coating layer comprises cobalt in an amount greater than 0.5 weight% and less than 1.5 weight%, and a positive electrode comprising the same, and a lithium secondary battery, wherein capacity characteristics and rate characteristics can be improved when the above ranges are satisfied.

Description

Positive electric active material, and positive electric and lithium secondary battery comprising the same

The present invention relates to a positive electrode active material, and a positive electrode and a lithium secondary battery comprising the same.

With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

Lithium secondary batteries consist of four major components: a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the positive electrode active material, which is included in the positive electrode, plays a significant role in determining the battery's capacity, output, and lifespan. Currently used positive electrode active materials include NCM-based positive electrode active materials containing nickel, cobalt, manganese, and/or aluminum, and LFP (lithium iron phosphate)-based positive electrode active materials. Meanwhile, improving the performance of the positive electrode active material is essential for lithium secondary batteries to have high energy density, output, and lifespan; consequently, much research is currently being conducted to develop high-performance positive electrode active materials.

LFP-based cathode active materials, which are olivine-structured cathode active materials, possess high structural stability, excellent thermal stability and lifespan, as well as price competitiveness due to their low cost. However, LFP-based cathode active materials have poor output characteristics due to low electronic and ionic conductivity, and suffer from low energy density due to low rolling density and capacity. To address the issue of low electronic conductivity, research has been conducted on introducing carbon coatings by mixing a cathode active material precursor with a carbon source and calcining it. Additionally, research has been conducted on introducing Mn to solve the problem of low energy density. Meanwhile, for application in automotive batteries, high capacity and output are required under fast charging conditions, making it necessary to develop LFP-based cathode active materials that possess these performance capabilities.

KR 10-2012-0056675 A

The problem to be solved by the present invention is to provide a positive electrode active material with improved capacity and rate characteristics by satisfying a specific range for the manganese content in the lithium iron-manganese phosphate compound and the cobalt content in the coating layer.

The present invention provides a positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

(1) The present invention provides a positive electrode active material comprising a lithium iron-manganese phosphate compound and a coating layer formed on the lithium iron-manganese phosphate compound comprising carbon and cobalt, wherein the lithium iron-manganese phosphate compound comprises manganese in an amount greater than 50 mol% and less than 70 mol% relative to the total molar amount of metals excluding lithium, and the coating layer comprises cobalt in an amount greater than 0.5 weight% and less than 1.5 weight%.

(2) The present invention provides a positive electrode active material according to (1) above, wherein the coating layer contains 0.5% by weight or more and 3% by weight or less of carbon.

(3) The present invention provides a positive electrode active material in which, in (1) or (2) above, the lithium iron manganese phosphate compound has a composition represented by the following chemical formula 1.

[Chemical Formula 1]

Li _a Mn _x Fe _1-x PO ₄

In the above chemical formula 1,

0.8≤a≤1.2, 0.5<x<0.7.

(4) The present invention provides an anode active material in any one of (1) to (3) above, wherein the coating layer is a coating portion containing cobalt on a coating layer containing carbon, in the form of a coating layer, in the form of discontinuously formed islands, or a combination thereof.

(5) The present invention provides a positive active material having an average particle size (D ₅₀ ) of 0.2㎛ to 1.0㎛ in any one of (1) to (4) above.

(6) The present invention provides a positive electrode comprising any one of the positive electrode active materials (1) to (5) above.

(7) The present invention provides a lithium secondary battery comprising the positive electrode of (6) above.

The positive electrode active material according to the present invention comprises a lithium iron-manganese phosphate-based compound and a coating layer formed on the lithium iron-manganese phosphate-based compound comprising carbon and cobalt, wherein the lithium iron-manganese phosphate-based compound comprises manganese in an amount greater than 50 mol% and less than 70 mol% relative to the total molar amount of metals excluding lithium, and the coating layer comprises cobalt in an amount greater than 0.5 wt% and less than 1.5 wt%, thereby improving the capacity characteristics and rate characteristics of a battery comprising the same, so that higher capacity can be exhibited even at higher charging speeds and the output can be improved.

Figure 1 is an SEM-EDS image of the positive electrode active material of Example 1.

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

In this case, terms or words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

In this specification, 'D _n ' refers to the particle size at the n% point of the volume cumulative distribution according to particle size. That is, D ₅₀ is the particle size at the 50% point of the volume cumulative distribution according to particle size, D ₉₀ is the particle size at the 90% point of the volume cumulative distribution according to particle size, and D ₁₀ is the particle size at the 10% point of the volume cumulative distribution according to particle size. The above D _n can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern Panalytic, Mastersizer 3000) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution. _D10 , _D50 , and _D90 can be measured by calculating the particle diameter at the points where the volume cumulative distribution according to particle size in the measuring device is 10%, 50%, and 90%.

positive electrode active material

The positive electrode active material according to the present invention comprises a lithium iron-manganese phosphate-based compound and a coating layer formed on the lithium iron-manganese phosphate-based compound comprising carbon and cobalt, wherein the lithium iron-manganese phosphate-based compound comprises manganese in an amount greater than 50 mol% and less than 70 mol% relative to the total molar amount of metals excluding lithium, and the coating layer comprises cobalt in an amount greater than 0.5 weight% and less than 1.5 weight%.

The positive electrode active material according to the present invention satisfies the condition that the manganese content of the lithium iron-manganese-based compound is greater than 50 mol% and less than 70 mol%, and the cobalt content of the coating layer is greater than 0.5 wt% and less than 1.5 wt%, so that a battery containing the positive electrode active material exhibits high capacity and improved rate characteristics, and can exhibit high capacity even under fast charging conditions, thereby showing improved output characteristics. If the manganese content of the compound is less or greater than the above range, or if the cobalt content of the coating layer is less or greater than the above range, the capacity or rate characteristics may be degraded, and the target output improvement effect may not be obtained.

Specifically, the manganese content included in the lithium iron-manganese-based compound may be greater than 50 mol%, 51 mol% or more, 52 mol% or more, 53 mol% or more, 54 mol% or more, 55 mol% or more, 56 mol% or more, 57 mol% or more, 58 mol% or more, 59 mol% or more relative to the total molar amount of metals excluding lithium, and may be less than 70 mol%, 69 mol% or less, 68 mol% or less, 67 mol% or less, 66 mol% or less, 65 mol% or less, 64 mol% or less, 63 mol% or less, 62 mol% or less, 61 mol% or less. In addition, the cobalt content included in the coating layer may be greater than 0.5 wt%, 0.55 wt% or more, 0.6 wt% or more, 0.65 wt% or more, 0.7 wt% or more, 0.75 wt% or more, and less than 0.15 wt%, 0.14 wt% or less, 0.13 wt% or less, 0.12 wt% or less, 0.11 wt% or less.

According to the present invention, the coating layer may contain carbon in an amount of 0.5 wt% or more and 3 wt% or less. When carbon is included within the above content range, the positive electrode active material may have appropriate electronic conductivity due to the carbon layer present on the surface, and the entry and exit of lithium ions may not be hindered. Specifically, the carbon content may be 0.5 wt% or more, 0.6 wt% or more, 0.7 wt% or more, 0.8 wt% or more, 0.9 wt% or more, 1 wt% or more, 1.2 wt% or more, 1.4 wt% or more, 1.6 wt% or more, 1.8 wt% or more, and may be 3 wt% or less, 2.9 wt% or less, 2.8 wt% or less, 2.7 wt% or less, 2.6 wt% or less, 2.5 wt% or less, 2.4 wt% or less, 2.3 wt% or less, 2.2 wt% or less, and 2.1 wt% or less.

According to the present invention, the lithium iron manganese phosphate-based compound may have a composition represented by the following chemical formula 1.

[Chemical Formula 1]

Li _a Mn _x Fe _1-x PO ₄

In the above chemical formula 1,

0.8≤a≤1.2, 0.5<x<0.7.

The above x may be greater than 0.5, 0.52 or more, 0.54 or more, 0.56 or more, or 0.58 or more, and may be less than 0.7, 0.68 or less, 0.66 or less, 0.64 or less, or 0.62 or less.

According to the present invention, the coating layer may have a coating portion containing cobalt on a coating layer containing carbon, in the form of a coating layer, in the form of discontinuously formed islands, or in a combination thereof.

The carbon-containing coating layer may be uniformly coated on the surface of a lithium iron-manganese phosphate-based compound. That is, the coating layer may be in the form of a thin film. The coating layer can improve ion conductivity and electron conductivity during charging and discharging of a battery containing a positive electrode active material. The carbon-containing coating layer may contain trace amounts of impurities such as nitrogen, oxygen, and hydrogen in addition to carbon.

The above-mentioned coating portion containing cobalt may exist on the above-mentioned coating layer containing carbon in the form of a coating layer, in the form of discontinuously formed islands, or a combination thereof.

In the present invention, the fact that the coating portion exists in the form of a coating layer means that it exists in the form of a thin layer on part or all of the surface of the lithium iron-manganese phosphate-based compound particles or the surface of the carbon-containing coating layer. At this time, the area formed in the form of a coating layer may be 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 10% or more, 20% or more, or 30% or more based on the total surface area of the surface of the compound particles or the surface of the coating layer, and may be 100% or less, 90% or less, 80% or less, 70% or less, 60% or less, or 50% or less. Furthermore, the fact that the coating portion exists in the form of discontinuously formed islands means that the coating portion does not cover the entire surface of the lithium iron-manganese phosphate-based compound particles or the surface of the carbon-containing coating layer, but exists dispersed in the form of small particles.

According to the present invention, the average particle size (D ₅₀ ) of the positive active material may be 0.2 μm to 1.0 μm. Specifically, the average particle size (D ₅₀ ) of the positive active material may be 0.2 μm or more, 0.25 μm or more, 0.3 μm or more, and 0.4 μm or less, 0.50 μm or less, 0.6 μm or less, 0.7 μm or less, 0.8 μm or less, 0.9 μm or less, or 1.0 μm or less. When the average particle size of the positive active material satisfies the above range, manganese leaching and capacity characteristics can be further improved.

Method for manufacturing positive electrode active material

The present invention provides a method for manufacturing the above-mentioned positive active material.

The method for manufacturing the above-mentioned positive electrode active material may include: (i) a step of preparing a mixture by mixing a lithium raw material, a phosphate raw material, an iron raw material, and a manganese raw material; (ii) a step of preparing a calcined product by calcining the mixture; and (iii) a step of mixing the calcined product with a cobalt raw material and then calcining it.

The method for manufacturing the above-mentioned positive active material is described in more detail below.

(i) Step

The above manufacturing method may include the step of (i) mixing a lithium raw material, a phosphate raw material, an iron raw material, and a manganese raw material to prepare a mixture.

The above lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide. Specifically, the above lithium raw material may be _Li₂CO₃ , _LiNO₃ , _LiNO₂ , LiOH, LiOH· _H₂O , LiH, LiF, _LiCl , _LiBr , _LiI , CH₃COOLi, _{Li₂O , Li₂SO₄} , _{CH₃COOLi, Li₃C₆H₅O₇ , etc.}

_{The above} phosphoric _acid raw materials may be _FePO4 , _H3PO4 , _NH4H2PO4 , ( _NH4 ) _2HPO4 , _{P2O5 , etc.}

The above iron raw material may be an iron-containing phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide _, or oxyhydroxide. Specifically, the above iron raw material may be _FePO₄ , _FeSO₄ , _FeC₂O₄ · _2H₂O , _FeCl₂ , etc.

The above phosphoric acid raw material and iron raw material may be the same. For example, it may be iron phosphate ( _FePO4 ).

The above manganese-containing raw material may be a manganese-containing phosphate, iron phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide _, or oxyhydroxide. Specifically, the above manganese-containing raw material may be _MnSO₄ , _MnCO₃ , _Mn₂O₃ , _MnO₂ , _Mn₃O₄ , Mn( _NO₃ ) _₂ , manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty _acid salts, oxyhydroxides, and manganese chloride halides.

The above manganese-containing raw material, phosphoric acid raw material, and iron raw material may be the same. For example, it may be Mn _α Fe _(1-α) PO ₄ (wherein 0 < α < 1.0).

When preparing the mixture of step (i) above, additional doping element raw materials may be mixed. At this time, the doping element may be one or more selected from V, Mg, Ti, Co, Ni, Nb, Al, Cu, Ga, Zr, Ce, In, Zn, Na, Si, Ca, B, and Y. The doping element raw materials may be phosphates, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, oxides, hydroxides, or oxyhydroxides containing the doping element.

When preparing the mixture in step (i) above, the mixture may be prepared by further mixing carbon coating raw materials. The coating raw materials may provide a carbon coating layer through calcination. Accordingly, the electrical conductivity of the lithium iron manganese phosphate-based cathode active material may be improved.

The above carbon coating raw material may be sucrose, glucose, lactose, starch, oligosaccharide, polyoligosaccharide, fructose, cellulose, vinyl resin, cellulose-based resin, phenolic resin, pitch-based resin, tar-based resin, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, citric acid, ammonium citrate, etc. Specifically, the above carbon coating raw material may be sucrose.

The carbon coating raw material may be added in an amount of 1% to 10% relative to the total weight of the lithium raw material, phosphoric acid raw material, iron raw material, and manganese raw material. More specifically, it may be added in an amount of 1% to 8%, 2% to 7%, or 3% to 6%.

In step (i) above, the lithium raw material, the phosphate raw material, the iron raw material, the manganese raw material, and other doping element raw materials may be mixed in an amount such that the lithium iron-manganese phosphate compound included in the resulting cathode active material has a composition represented by Formula 1 below.

[Chemical Formula 1]

Li _a Mn _x Fe _1-x PO ₄

In the above chemical formula 1,

0.8≤a≤1.2, 0.5<x<0.7, and x may be within the aforementioned range.

The mixing of the above raw materials may be wet mixing or dry mixing.

In the case where the above mixture is a wet mixture, water may be used as a solvent, and the raw materials may be simply mixed in water, and then the mixture solution may be wet-ground with a bead mill to be mixed, but is not limited thereto. Meanwhile, in the case of wet mixing, a dried powder (mixture) can be obtained by finally spray drying.

(ii) Step

The above manufacturing method may include (ii) a step of manufacturing a sintered product by sintering the above mixture.

The above-mentioned firing may be performed in a nitrogen atmosphere. The firing temperature may be performed at 500°C or higher and 1000°C or lower, and specifically, it may be 500°C or higher, 550°C or higher, 600°C or higher, 650°C or higher, and 750°C or lower, 800°C or lower, 850°C or lower, 900°C or lower, 950°C or lower, and 1000°C or lower. The firing time may be 5 hours or more and 20 hours or less, and specifically, it may be 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, and 12 hours or less, 14 hours or less, 16 hours or less, 18 hours or less, and 20 hours or less.

The positive active material manufactured according to the above method for manufacturing a positive active material may have a composition represented by the aforementioned chemical formula 1.

(iii) Step

The above manufacturing method may include (iii) a step of mixing the above-mentioned product with a cobalt raw material and then firing it.

The above cobalt raw material may be a cobalt-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, _halide , hydroxide, or oxyhydroxide. Specifically, the above cobalt raw material may be one or more selected from the group consisting of _Co₂O₃ , CoO, _Co₃O₄ , _{and CoCO₃} .

The above cobalt raw material can be introduced in an amount such that the cobalt content in the coating layer of the finally manufactured cathode active material is greater than 0.5 weight% and less than 1.5 weight%. Specifically, it may be introduced in an amount of 0.5% to 5% relative to the total weight of the lithium raw material, phosphoric acid raw material, iron raw material, and manganese raw material, preferably in an amount of 1% to 4%, and more preferably in an amount of 2% to 4%.

The above-mentioned firing may be performed in a nitrogen atmosphere. The firing temperature may be performed at 400°C or higher and 800°C or lower, and specifically, it may be 400°C or higher, 450°C or higher, 500°C or higher, 550°C or higher, and 650°C or lower, 700°C or lower, 750°C or lower, and 800°C or lower. The firing time may be 1 hour or higher and 5 hours or lower, and specifically, it may be 1 hour or higher, 1.5 hours or higher, 2 hours or higher, 2.5 hours or higher, and 3.5 hours or lower, 4 hours or lower, 4.5 hours or lower, and 5 hours or lower.

The positive active material manufactured according to the above method for manufacturing a positive active material may include a coating layer containing carbon and cobalt.

anode

The present invention provides a positive electrode comprising the above positive electrode active material.

The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The positive active material layer may include, together with the positive active material, a conductive material and a binder as needed. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity characteristics within this range.

The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive active material layer.

The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, the above-described anode may be manufactured by applying a composition for forming an anode active material layer (anode slurry), prepared by dissolving or dispersing the above-described anode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, onto an anode current collector, followed by drying and rolling, or by casting the composition for forming an anode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for anode manufacturing thereafter.

lithium secondary battery

The present invention provides a lithium secondary battery comprising the above positive electrode.

The above lithium secondary battery may comprise the positive electrode; the negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. Additionally, the lithium secondary battery may optionally further comprise a battery container housing an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

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

The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material.

As the above-mentioned negative electrode 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; metallic 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; metal oxides capable of doping and dedoping lithium, such as _SiO₂β (0<β<2), _SnO₂ , vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as the carbon material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. The above-mentioned cathode active material may be included in an amount of 80% to 99% by weight based on the total weight of the cathode active material layer.

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

The conductive material of the above-mentioned negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

The above cathode may be manufactured by applying a composition for forming a cathode active material layer (cathode slurry), prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector and drying it, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto a cathode current collector.

The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special limitations as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

Examples of the above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these. As a specific example, the above electrolyte may include an organic solvent and a lithium salt.

The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion _of the lithium salt may be at least one _selected from _the group consisting of F- ^{, Cl-} , ^{Br- , I-} , _NO3- ^, N( ^CN ) _2- ^, _BF4- , _CF3CF2SO3- , ( _CF3SO2 ) _2N- , ( _FSO2 ) ^2N- _{, CF3CF2} ( _CF3 ) _2CO- ^, ( _CF3SO2 ) _2CH- , ( _{SF5 ) 3C-} ^{, (} _{CF3SO2 )} ^3C- _{, CF3 ( CF2 )} ^{7SO3- , CF3CO2-} , _CH3CO2- ^, _SCN- ^, and ( _{CF3CF2SO2 ) 2N- ,} and the _lithium salt may be ^LiPF6 _{, LiClO4 , LiAsF Li6} , _LiBF4 , _LiSbF6 , LiAlO4, _LiAlCl4 , _{LiCF3SO3 ,} LiC4F9SO3, _{LiN (C2F5SO3)2 , LiN ( C2F5SO2} ) ₂ , LiN( _CF3SO2 ) ₂ , LiCl, LiI, or LiB( _C2O4 ) ₂ may be used. It is preferable to use the lithium salt within the range of _0.1 M _{to 2.0 M.} When the concentration _of the lithium salt falls within _the above range, the electrolyte has appropriate conductivity and viscosity _, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. 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.

Since the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent capacity and rate characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in electric vehicle fields such as hybrid electric vehicles (HEV) and electric vehicles (EV).

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

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

Accordingly, a battery module including the above-mentioned lithium secondary battery as a unit cell and a battery pack including the same are provided.

The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle, including an electric vehicle, a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

Examples

The present invention will be explained in more detail below through examples. However, the following examples are intended to illustrate the present invention and do not limit the scope of the present invention.

Example 1

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.6:0.4, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ with a coating layer containing carbon and cobalt.

LiMn _0.6 Fe _0.4 PO ₄ with the above-mentioned carbon-containing coating layer and Co ₂ O ₃ were mixed to be 3% by weight relative to the total weight of LiMn _0.6 Fe _0.4 PO ₄ , and then heat-treated at 600°C for 3 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ (average particle size (D ₅₀ ): 0.35 μm) with a coating layer containing carbon and cobalt.

Example 2

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.6:0.4, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ with a coating layer containing carbon and cobalt.

LiMn _0.6 Fe _0.4 PO ₄ with the above-mentioned carbon-containing coating layer and Co ₂ O ₃ were mixed to a ratio of 3.5 wt% relative to the total weight of LiMn _0.6 Fe _0.4 PO ₄ , and then heat-treated at 600°C for 3 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ (average particle size (D ₅₀ ): 0.35 μm) with a coating layer containing carbon and cobalt.

Comparative Example 1

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.6:0.4, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ (average particle size (D ₅₀ ): 0.3㎛) with a coating layer containing carbon and cobalt formed.

Comparative Example 2

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.6:0.4, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ with a coating layer containing carbon and cobalt.

LiMn _0.6 Fe _0.4 PO ₄ with the above-mentioned carbon-containing coating layer and Co ₂ O ₃ were mixed to a ratio of 1.5 wt% relative to the total weight of LiMn _0.6 Fe _0.4 PO ₄ , and then heat-treated at 600°C for 3 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ (average particle size (D ₅₀ ): 0.35 μm) with a coating layer containing carbon and cobalt.

Comparative Example 3

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.6:0.4, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ with a coating layer containing carbon and cobalt.

LiMn _0.6 Fe _0.4 PO ₄ with the above-mentioned carbon-containing coating layer and Co ₂ O ₃ were mixed to a ratio of 4.5 wt% relative to the total weight of LiMn _0.6 Fe _0.4 PO ₄ , and then heat-treated at 600°C for 3 hours under a nitrogen atmosphere to produce LiMn _0.6 Fe _0.4 PO ₄ (average particle size (D ₅₀ ): 0.35 μm) with a coating layer containing carbon and cobalt.

Comparative Example 4

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.7:0.3, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.7 Fe _0.3 PO ₄ with a carbon-containing coating layer formed.

LiMn _0.7 Fe _0.3 PO ₄ with the carbon-containing coating layer formed above and Co ₂ O ₃ were mixed to be 3% by weight relative to the total weight of LiMn _0.7 Fe _0.3 PO ₄ , and then heat-treated at 600°C for 3 hours under a nitrogen atmosphere to produce LiMn _0.7 Fe _0.3 PO ₄ (average particle size (D ₅₀ ): 0.35 μm) with a coating layer containing carbon and cobalt.

Comparative Example 5

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.7:0.3, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.7 Fe _0.3 PO ₄ (average particle size (D ₅₀ ): 0.3㎛) with a carbon-containing coating layer formed.

Comparative Example 6

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.5:0.5, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.5 Fe _0.5 PO ₄ with a coating layer containing carbon and cobalt.

LiMn _0.5 Fe _0.5 PO ₄ with the above-mentioned carbon-containing coating layer and Co ₂ O ₃ were mixed to be 3% by weight relative to the total weight of LiMn _0.5 Fe _0.5 PO ₄ , and then heat-treated at 600°C for 3 hours under a nitrogen atmosphere to produce LiMn _0.5 Fe _0.5 PO ₄ (average particle size (D ₅₀ ): 0.35 μm) with a coating layer containing carbon and cobalt.

Comparative Example 7

_Li₂CO₃ , _{MnCO₃ ,} and _FePO₄ were mixed such that the molar ratio of Li:Mn:Fe was 1.02:0.5:0.5, and then sucrose was additionally mixed to be 5% by weight relative to the total weight of the Li material, Mn material, and _FePO₄ to prepare a mixture. The mixture was wet-milled using a bead mill to obtain a slurry. At this time, the average particle size ( _D₀ ) of all raw materials (Li material, Mn material, _FePO₄ , sucrose) present in the slurry was 300 nm.

After drying the above slurry by spray drying (inlet temperature: 170 ℃, outlet temperature: 95 ℃), the dried powder was heat-treated at 700 ℃ for 10 hours under a nitrogen atmosphere to produce LiMn _0.5 Fe _0.5 PO ₄ (average particle size (D ₅₀ ): 0.3㎛) with a coating layer containing carbon and cobalt formed.

Experimental Example

Experimental Example 1: Confirmation of Carbon (C) and Cobalt (Co) Content in Anode Active Material

The carbon content present in the coating layer formed on the cathode active materials of Examples 1 to 2 and Comparative Examples 1 to 7 was measured using a carbon-sulfur analyzer (LECO, CS844), and the cobalt content was measured using a ThermoScientific ICAP PRO ICP-OES, and the results are shown in Table 1 below.

division Carbon content (weight%) Cobalt content (weight%) Example 1 2 1 Example 2 2 1.2 Comparative Example 1 2 0 Comparative Example 2 2 0.5 Comparative Example 3 2 1.5 Comparative Example 4 2 1 Comparative Example 5 2 0 Comparative Example 6 2 1 Comparative Example 7 2 0

Experimental Example 2: Confirmation of the morphology of the positive electrode active material coating layer

SEM-EDS images were obtained for the positive electrode active material of Example 1 using a scanning electron microscope and are shown in Figure 1.

Through Figure 1, it can be seen that a coating portion containing Co is distributed in the form of islands on the positive active material of Example 1.

Experimental Example 3: Battery Performance Evaluation

For each of Examples 1 to 2 and Comparative Examples 1 to 7, a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 90:5:5 in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

An electrode assembly was manufactured by using a lithium metal electrode (thickness: 300 μm) as the negative electrode and interposing a porous polyethylene separator (thickness: 20 μm) between the positive electrode and the negative electrode. This was placed inside a battery case, and a coin half-cell was manufactured by injecting an electrolyte solution in which 1.0 M LiPF6 was dissolved in an organic solvent mixed with ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) in a volume ratio of 1:2:1.

(1) Capacity evaluation

Each coin half-cell manufactured as described above was charged to 4.25V in CC (0.1C)-CV (cut-off current: 0.05C) mode at 25℃, and then discharged to 2.5V at 0.1C to measure the charging capacity and discharging capacity, which are shown in Table 2 below.

division Charging capacity
(mAh/g) Discharge capacity
(mAh/g) Example 1 153.1 151.3 Example 2 152.9 150.9 Comparative Example 1 152.4 150.4 Comparative Example 2 152.8 150.7 Comparative Example 3 152.5 150.2 Comparative Example 4 150.2 148.3 Comparative Example 5 150.5 148.9 Comparative Example 6 153.0 151.7 Comparative Example 7 153.5 152.3

(2) Evaluation of rate characteristics

Using each coin half-cell manufactured as described above, charging was performed in CC/CV mode at 25°C with a constant current of 0.5 C to 4.25 V (ending current 0.05 C), and then the discharge capacity was measured while discharging in CC mode with a constant current of 0.2 C until it reached 2.5 V.

In addition, the discharge capacity was measured while charging in CC/CV mode with a constant current of 0.5 C at 25°C to 4.25 V (ending current 0.05 C), and then discharging in CC mode with a constant current of 1.0 C until it reached 2.5 V. Then, the discharge capacity was measured while charging in CC/CV mode with a constant current of 0.5 C at 25°C to 4.25 V (ending current 0.05 C), and then discharging in CC mode with a constant current of 4.0 C until it reached 2.5 V. The percentage of the discharge capacity at 0.2 C discharge after 0.5 C charging is shown in Table 3 below.

division Percentage (%) of 1C discharge capacity to 0.2C discharge capacity Percentage (%) of 4C discharge capacity to 0.2C discharge capacity Example 1 92.4 87.5 Example 2 92.2 85.3 Comparative Example 1 91.3 83.4 Comparative Example 2 91.4 83.7 Comparative Example 3 91.5 83.2 Comparative Example 4 90.3 81.2 Comparative Example 5 90.2 82.1 Comparative Example 6 91.5 84.2 Comparative Example 7 91.7 84.8

Referring to Tables 2 and 3 above, it can be seen that in the case of the battery containing the positive electrode active material of Examples 1 and 2, the charge and discharge capacity is higher and the output is improved due to superior rate characteristics compared to the battery containing the positive electrode active material of Comparative Examples 1 to 3, which has the same lithium iron-manganese phosphate compound composition but has a low or high cobalt content in the coating layer, and the battery containing the positive electrode active material of Comparative Examples 4 and 5, which has a composition with a high manganese content. It can also be seen that compared to the battery containing the positive electrode active material of Comparative Examples 6 and 7, which has a composition with a low manganese content compared to Examples 1 and 2, the charge and discharge capacity is in a similar range, but the output is improved due to superior rate characteristics.

Claims (7)

It comprises a lithium iron-manganese phosphate-based compound and a coating layer comprising carbon and cobalt formed on the lithium iron-manganese phosphate-based compound, and
The above lithium iron-manganese phosphate-based compound contains manganese in an amount greater than 50 mol% and less than 70 mol% relative to the total molar amount of metals excluding lithium, and
The above coating layer is a positive active material containing more than 0.5 weight% and less than 1.5 weight% of cobalt.
In claim 1,
The above coating layer is a positive active material containing 0.5 weight% or more and 3 weight% or less of carbon.
In claim 1,
The above lithium iron-manganese phosphate-based compound is a positive electrode active material having a composition represented by the following chemical formula 1:
[Chemical Formula 1]
Li _a Mn _x Fe _1-x PO ₄
In the above chemical formula 1,
0.8≤a≤1.2, 0.5<x<0.7.
In claim 1,
The above coating layer is a positive active material in which a coating portion containing cobalt exists on a coating layer containing carbon in the form of a coating layer, in the form of discontinuously formed islands, or a combination thereof.
In claim 1,
The above positive active material is a positive active material having an average particle size (D ₅₀ ) of 0.2㎛ to 1.0㎛.
A positive electrode comprising the positive electrode active material of any one of claims 1 to 5.
A lithium secondary battery comprising the positive electrode of claim 6.