Method for preparing cathode active material, cathode active material, and cathode and lithium secondary battery comprising same

Abstract

The present invention relates to a method for preparing a lithium iron phosphate-based cathode active material, a cathode active material obtained by the preparation method, and a cathode and a lithium secondary battery comprising same, the preparation method comprising the steps of: (A) mixing a lithium raw material, a phosphoric acid raw material, and an iron raw material to prepare a mixture; and (B) firing the mixture, wherein the firing involves a temperature raising section in which the temperature is raised from room temperature to 600-800°C; and a maintaining section in which the temperature is maintained at 600-800° C, and comprises a process of introducing water vapor only within a section ranging from room temperature to 450°C during the temperature raising section.

Description

Method for manufacturing a cathode active material, cathode active material, cathode and lithium secondary battery containing the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0072745, filed June 3, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a method for producing a lithium iron phosphate-based cathode active material, a lithium iron phosphate-based cathode active material, a cathode including the same, and a lithium secondary battery.

[0005]

[0006] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0007] Lithium secondary batteries are composed of four major components: a cathode, an anode, a separator, and an electrolyte. Among these, the cathode active material contained in the cathode plays a significant role in determining the battery's capacity, output, and lifespan. Currently used cathode active materials include NCM-based cathode active materials containing nickel, cobalt, manganese, and / or aluminum, and LFP (lithium iron phosphate)-based cathode active materials. Meanwhile, improving the performance of cathode active materials is essential for lithium secondary batteries to achieve high energy density, output, and lifespan. Consequently, extensive research has been conducted recently to develop high-performance cathode active materials.

[0008] Recently, with the increasing use of lithium secondary batteries, active development of NCM cathode active materials with increased nickel content is being actively conducted to increase the energy density of the batteries, especially capacity. However, NCM cathode active materials with increased nickel content suffer from reduced thermal stability due to structural instability caused by high nickel content. On the other hand, LFP cathode active materials, which are olivine-structured cathode active materials, have the advantage of superior thermal stability and price competitiveness, although their capacity is lower than NCM cathode active materials. However, LFP cathode active materials have low electrical conductivity and slow lithium ion diffusion rates, so improvements are being made through carbon coating and particle size control.

[0009] Meanwhile, in order to improve the energy density of LFP-based cathode active materials, simply changing the conditions (e.g., adjusting the firing temperature or time) in the existing LFP-based cathode active material manufacturing method can lead to increased resistance or decreased battery efficiency. In other words, there is a growing need to develop LFP-based cathode active materials with high energy density, but cathode active materials manufactured using existing LFP-based cathode active material manufacturing methods have problems such as low rolling density.

[0010] Accordingly, there is a need to develop a manufacturing method to improve the performance of LFP-based cathode active materials.

[0011]

[0012] An object of the present invention is to provide a method for producing a lithium iron phosphate-based positive electrode active material having improved energy density without deteriorating other performances.

[0013] In addition, an object of the present invention is to provide a positive electrode active material capable of improving the life performance of a lithium secondary battery.

[0014] In addition, an object of the present invention is to provide a positive electrode and a lithium secondary battery including the positive electrode active material.

[0015]

[0016] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

[0017]

[0018] In order to solve the above problem, the present invention provides a method for manufacturing a lithium iron phosphate-based cathode active material, a lithium iron phosphate-based cathode active material, a cathode including the same, and a lithium secondary battery.

[0019]

[0020] (1) The present invention provides a method for producing a lithium iron phosphate-based positive electrode active material, comprising the steps of: (A) mixing a lithium raw material, a phosphate raw material, and an iron raw material to produce a mixture; and (B) calcining the mixture; wherein the calcination comprises a temperature-raising section for raising a temperature from room temperature to 600°C to 800°C, and a maintenance section for maintaining the temperature at 600°C to 800°C, and a process for introducing steam only within a section from room temperature to 450°C among the temperature-raising sections.

[0021] (2) The present invention provides a method for producing a lithium iron phosphate cathode active material, wherein, in the above (1), a carbon coating raw material is further mixed during the preparation of the mixture in step (A).

[0022] (3) The present invention provides a method for manufacturing a lithium iron phosphate cathode active material, wherein, in the above (2), the carbon coating raw material is added in an amount of 5 to 20 wt% relative to the total weight of the lithium raw material, the phosphate raw material, and the iron raw material.

[0023] (4) The present invention provides a method for producing a lithium iron phosphate cathode active material, wherein, in any one of the above (1) to (3), a manganese raw material is further mixed during the preparation of the mixture in step (A).

[0024] (5) The present invention provides a method for producing a lithium iron phosphate-based positive electrode active material, wherein the calcination is performed under a nitrogen atmosphere in any one of the above (1) to (4).

[0025] (6) The present invention is a lithium iron phosphate cathode active material comprising a lithium iron phosphate compound, wherein the cathode active material powder is 2000 kgf / cm 2 The rolled density measured after pressing with a pressure of 1.95 g / cc to 2.5 g / cc and the BET specific surface area is 15.00 m 2 / g to 17.00m 2 / g, and the lithium iron phosphate-based cathode active material provides a lithium iron phosphate-based cathode active material having a crystal size of 155 nm to 175 nm.

[0026] (7) The present invention provides a lithium iron phosphate-based positive electrode active material, wherein the lithium iron phosphate-based positive electrode active material comprises a coating layer including carbon formed on the lithium iron phosphate-based compound in the above (6).

[0027] (8) The present invention provides a lithium iron phosphate cathode active material, wherein the lithium iron phosphate compound in (6) or (7) has a composition represented by the following chemical formula 1.

[0028] [Chemical Formula 1]

[0029] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0030] In the above chemical formula 1,

[0031] M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y,

[0032] -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0033] (9) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (6) to (8).

[0034] (10) The present invention provides a lithium secondary battery including a positive electrode according to (9).

[0035]

[0036] According to the manufacturing method of the present invention, in the sintering step for manufacturing a lithium iron phosphate cathode active material, a process of introducing steam only within a temperature-elevating section from room temperature to 450°C is included, thereby easily manufacturing a lithium iron phosphate cathode active material having improved energy density without deteriorating other performances.

[0037] The lithium iron phosphate cathode active material according to the present invention has a high rolling density and a small BET specific surface area, and thus can improve the life performance of a lithium secondary battery including the same.

[0038]

[0039] Hereinafter, the present invention will be described in more detail.

[0040] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0041] It should be understood that the terms “include,” “comprising,” or “having” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0042] The term "on" in this specification means not only when a configuration is formed directly on top of another configuration, but also when a third configuration is interposed between these configurations.

[0043]

[0044] Method for manufacturing lithium iron phosphate cathode active material

[0045] The present inventors have discovered that when a process of introducing steam only within a range from room temperature to 450°C is included during the process of calcining a mixture of raw materials during the manufacture of a lithium iron phosphate cathode active material, a cathode active material having high rolling density and low BET specific surface area with excellent performance is manufactured, and have completed the present invention.

[0046]

[0047] Specifically, the method for producing a lithium iron phosphate cathode active material according to the present invention comprises the steps of (A) mixing a lithium raw material, a phosphate raw material, and an iron raw material to produce a mixture; and (B) firing the mixture; wherein the firing includes a temperature-raising section for raising the temperature from room temperature to 600°C to 800°C, and a maintenance section for maintaining the temperature at 600°C to 800°C, and includes a process for introducing steam only within a section from room temperature to 450°C among the temperature-raising sections.

[0048]

[0049] Hereinafter, the method for manufacturing a positive electrode active material according to the present invention will be described in more detail.

[0050]

[0051] (A) Step

[0052] The present invention comprises a step of (A) preparing a mixture by mixing a lithium raw material, a phosphate raw material, and an iron raw material.

[0053] 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, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or the like.

[0054] The above phosphoric acid raw material may be FePO4, H3PO4, NH4H2PO4, (NH4)2HPO4, P2O5, etc.

[0055] The above iron raw material may be an iron-containing phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, etc. Specifically, the above iron raw material may be FePO4, FeSO4, FeC2O4·2H2O, FeCl2, etc.

[0056] The above phosphate raw material and iron raw material may be the same. For example, it may be iron phosphate (FePO4).

[0057]

[0058] According to the present invention, when preparing the mixture in step (A), a carbon coating raw material can be further mixed to produce the mixture. The coating raw material can provide a carbon coating layer through sintering. Accordingly, the electrical conductivity of the lithium iron phosphate-based positive electrode active material can be improved.

[0059] The carbon coating raw material may be sucrose, glucose, lactose, starch, oligosaccharide, polyoligosaccharide, fructose, cellulose, vinyl resin, cellulose resin, phenol resin, pitch resin, tar resin, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, citric acid, ammonium citrate, etc. Specifically, the carbon coating raw material may be sucrose.

[0060] According to the present invention, the carbon coating raw material may be added in an amount of 5% to 20% by weight relative to the total weight of the lithium raw material, the phosphate raw material, and the iron raw material.

[0061]

[0062] According to the present invention, when preparing the mixture in step (A), the mixture can be prepared by further mixing in a manganese raw material.

[0063] The above manganese raw material may be a manganese-containing phosphate, iron phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide.

[0064] The above manganese raw material, phosphate raw material and iron raw material may be the same. For example, Mn α Fe (1-α) PO4 (where 0<α<1.0) may be present.

[0065]

[0066] According to the present invention, the lithium raw material, phosphate raw material, iron raw material, manganese raw material, and other doping element raw materials can be mixed in an amount such that the lithium iron phosphate compound included in the resulting lithium iron phosphate cathode active material has a composition represented by the following chemical formula 1.

[0067] [Chemical Formula 1]

[0068] Li 1+x [Fe 1-a-bMn a M 1 b ]PO4

[0069] In the above chemical formula 1,

[0070] M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y,

[0071] -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0072]

[0073] The mixing of the above raw materials may be wet mixing or dry mixing.

[0074] If the above mixing is wet mixing, water may be used as a solvent, and the raw materials may be simply mixed in water, and then the mixed solution may be wet-ground with a bead mill to mix, but is not limited thereto.

[0075] Meanwhile, in the case of wet mixing, a powder (mixture) that has been completely dried can be obtained through spray drying.

[0076]

[0077] According to the present invention, when preparing the mixture in step (A), a doping element-containing material may be additionally mixed in, if necessary. At this time, the doping element may be at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B, and Y.

[0078] The above doping element-containing material may be a phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, oxide, hydroxide or oxyhydroxide containing the doping element.

[0079]

[0080] (B) Step

[0081] The present invention comprises (B) a step of calcining the mixture; wherein the calcination comprises a temperature-raising section for raising the temperature from room temperature to 600°C to 800°C, and a maintenance section for maintaining the temperature at 600°C to 800°C, and is characterized in that it comprises a process for introducing steam only within a section from room temperature to 450°C among the temperature-raising sections.

[0082] According to the present invention, when steam is injected within a range from room temperature to 450°C, no other substance is injected other than an inert gas.

[0083] Specifically, the present invention includes a process of injecting steam only within a section from room temperature to 450°C among the above temperature-elevating sections, and does not include a process of injecting steam in the remaining sections. That is, the temperature-elevating section includes a process of injecting steam in some or all of the section from room temperature to 450°C, and does not inject steam while increasing the temperature from 450°C to 600°C to 800°C.

[0084]

[0085] As in the present invention, in the case where a process of introducing steam is included only within the range from room temperature to 450°C among the above-described temperature-elevating sections, steam is used as a heat transfer medium during the sintering process, thereby increasing the size of the primary particles due to efficient heat transfer, and as a result, the rolling density of the positive electrode active material increases and the BET specific surface area decreases, which is advantageous.

[0086]

[0087] According to the present invention, the sintering includes a temperature raising section for raising the temperature from room temperature to 600°C to 800°C, and a holding section for maintaining the temperature at 600°C to 800°C. On the other hand, if the temperature of the holding section is less than 600°C, there is a problem that a sufficient calcination process does not occur, resulting in the production of an electrochemically inferior cathode active material. On the other hand, if the temperature exceeds 800°C, there is a problem that excessive heat energy transfer causes the production of primary particles that are too large, resulting in the production of an electrochemically inferior cathode active material. Specifically, the sintering may include a temperature raising section for raising the temperature from room temperature to 650°C to 750°C, and a holding section for maintaining the temperature at 650°C to 750°C. More specifically, the sintering may include a temperature raising section for raising the temperature from room temperature to 680°C to 720°C, and a holding section for maintaining the temperature at 680°C to 720°C.

[0088]

[0089] The present invention includes a process of introducing steam only within a temperature-elevating section from room temperature to 450°C. For example, the present invention may introduce steam only during the temperature-elevating section from room temperature to 450°C, or may introduce steam only during the temperature-elevating section from 200°C to 450°C, or may introduce steam only during the temperature-elevating section from 300°C to 450°C.

[0090] Meanwhile, among the above temperature-elevating sections, if temperature-elevation in a section other than the section from room temperature to 450°C is performed in an atmosphere containing water vapor, there is a problem that the quality of the carbon coating is poor because it is difficult to maintain a reducing atmosphere in the kiln.

[0091]

[0092] According to the present invention, the heating rate while increasing the temperature from room temperature to 600°C to 800°C can be 1°C / min to 15°C / min. In this case, the heat transfer required for crystal growth can proceed efficiently, thereby improving the crystal size of the positive electrode active material and increasing the rolling density.

[0093]

[0094] According to the present invention, the firing may be performed under an inert atmosphere. Specifically, the firing may be performed under a nitrogen atmosphere. In this case, a reducing atmosphere is maintained during the firing process, which has the advantage of improving the quality of the carbon coating and the degree of formation of the positive electrode active material.

[0095]

[0096] According to the present invention, the maintenance period may be performed for 1 to 20 hours. In this case, high temperatures are sufficiently transmitted, so that impurities are removed and primary particles of the positive electrode active material can grow well.

[0097]

[0098] Meanwhile, the above-mentioned firing may further include a lowering section in which the temperature is lowered from a temperature of 600°C to 800°C to room temperature after the above-mentioned maintenance section.

[0099]

[0100] Lithium iron phosphate cathode active material

[0101] The cathode active material according to the present invention is a lithium iron phosphate cathode active material containing a lithium iron phosphate compound, and the cathode active material powder is 2000 kgf / cm 2 The rolled density measured after pressing with a pressure of 1.95 g / cc to 2.5 g / cc and the BET specific surface area is 15.00 m 2 / g to 17.00m 2 / g, and is characterized by a crystal size of 155 nm to 175 nm. The positive electrode active material according to the present invention can be manufactured by the manufacturing method described above.

[0102] The positive electrode active material according to the present invention has a high rolling density and a small BET specific surface area, and thus can improve the life performance of a lithium secondary battery including the positive electrode active material.

[0103] If the rolling density and / or BET specific surface area do not satisfy the range according to the present invention, the energy density of the electrode / battery including the positive electrode active material may be reduced, or the viscosity of the slurry including the positive electrode active material may increase during the coating process during the process of manufacturing the electrode, which may cause problems.

[0104]

[0105] The lithium iron phosphate-based positive electrode active material according to the present invention may include a coating layer including carbon formed on the lithium iron phosphate-based compound.

[0106]

[0107] The lithium iron phosphate-based cathode active material according to the present invention may have a crystal size of 155 nm to 175 nm. The crystal size is a value obtained from XRD data and can be obtained from the XRD raw data through the Sherrer Equation. When the crystal size of the lithium iron phosphate-based cathode active material is within the above range, it has an appropriate crystal size and may have excellent electrochemical properties. On the other hand, when the crystal size of the lithium iron phosphate-based cathode active material is less than 155 nm, the distribution of too small particles increases and the distribution of relatively large particles decreases, which may lower the rolling density, and when the crystal size exceeds 175 nm, as the particle size increases, the electrical conductivity decreases, which may lower the electrochemical properties.

[0108]

[0109] According to the present invention, the lithium iron phosphate compound may have a composition represented by the following chemical formula 1.

[0110] [Chemical Formula 1]

[0111] Li 1+x[Fe 1-a-b Mn a M 1 b ]PO4

[0112] In the above chemical formula 1,

[0113] M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y,

[0114] -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0115] The above x may be greater than or equal to -0.1, or greater than or equal to -0.05, and may be less than or equal to 0.05, or less than or equal to 0.1.

[0116] The above a may be 0 or more, 0.01 or more, or 0.02 or more, and may be 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, 0.5 or less, 0.6 or less, 0.7 or less, 0.8 or less, or 0.9 or less.

[0117] Above M 1 is a doping element, and b may be 0 or more, 0.01 or more, or 0.02 or more, and 0.04 or less, 0.05 or less, or 0.1 or less.

[0118] When the above x, a, and b satisfy the above ranges, the energy density of a battery including the positive electrode active material according to the present invention can be excellent and the capacity can be high.

[0119]

[0120] anode

[0121] In addition, the present invention provides a positive electrode comprising the positive electrode active material described above. The positive electrode may be a positive electrode for a lithium secondary battery.

[0122] Specifically, the positive electrode includes a positive electrode current collector, and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector and including the positive electrode active material described above.

[0123] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0124]

[0125] The above positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0126] At this time, the positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98 wt%, based on the total weight of the positive electrode active material layer. When included in the above content range, excellent capacity characteristics can be exhibited.

[0127] At this time, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0128]

[0129] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0130]

[0131] The above-mentioned positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above-mentioned positive electrode active material is used. Specifically, the positive electrode slurry, prepared by dissolving or dispersing the above-mentioned positive electrode active material and optionally a binder and a conductive agent in a solvent, is applied onto a positive electrode current collector, and then dried and rolled. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0132]

[0133] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the positive electrode slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for positive electrode manufacturing.

[0134]

[0135] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry onto a separate support, then peeling the film from the support and laminating the resulting film onto a positive electrode current collector.

[0136]

[0137] lithium secondary battery

[0138] In addition, the present invention can manufacture an electrochemical device including the positive electrode. The electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0139] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. 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.

[0140] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0141]

[0142] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0143] The negative electrode 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0144]

[0145] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0146] As the 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 alloy, Sn alloy, or Al alloy; SiO β (0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, 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.

[0147] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0148]

[0149] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0150] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include 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 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; and conductive materials such as polyphenylene derivatives.

[0151]

[0152] The above negative electrode active material layer can be manufactured by applying and drying a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry on a separate support and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0153]

[0154] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, 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, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0155]

[0156] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0157] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0158] As the organic solvent, any solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol, isopropyl alcohol, etc.; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc. can be used. Among these, carbonate solvents are preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable.

[0159] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1 to 4.0 M, and preferably, 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0160]

[0161] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte.

[0162]

[0163] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0164] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0165] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0166] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0167] 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 be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0168]

[0169] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0170]

[0171] Examples and Comparative Examples

[0172] Example 1

[0173] Li2CO3 and FePO4 were mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.05:1 (the total content of Li2CO3 and FePO4 was mixed to be 40 wt% of the solution), and sucrose was added in an amount of 12 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. The mixed solution was wet-ground with a bead mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0174] Afterwards, the dried powder (hereinafter, the mixture) was fed into a kiln, and steam was fed into the kiln at a rate of 500 g / h, and the temperature was increased from room temperature to 450°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the steam input was stopped, and the temperature was increased from 450°C to 700°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the kiln was fired at 700°C for 10 hours under a nitrogen atmosphere, thereby manufacturing a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0175]

[0176] Example 2

[0177] Li2CO3 and FePO4 were mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.05:1 (the total content of Li2CO3 and FePO4 was mixed to be 40 wt% of the solution), and sucrose was added in an amount of 12 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. The mixed solution was wet-ground with a bead mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0178] Afterwards, the dried powder (hereinafter, the mixture) was put into a sintering furnace, and the temperature was increased from room temperature to 200°C at a rate of 4°C / min under a nitrogen atmosphere, and then steam was introduced at a rate of 500 g / h, and the temperature was increased from 200°C to 450°C at a rate of 4°C / min under a nitrogen atmosphere, and then the steam introduction was stopped, and the temperature was increased from 450°C to 700°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the sintering was performed at 700°C for 10 hours under a nitrogen atmosphere, thereby manufacturing a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0179]

[0180] Example 3

[0181] Li2CO3 and FePO4 were mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.05:1 (the total content of Li2CO3 and FePO4 was mixed to be 40 wt% of the solution), and sucrose was added in an amount of 12 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. The mixed solution was wet-ground with a bead mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0182] Thereafter, the dried powder (hereinafter, the mixture) was placed in a kiln, and the temperature was increased from room temperature to 300°C at a rate of 4°C / min under a nitrogen atmosphere, and then steam was introduced into the kiln at a rate of 500 g / h, and the temperature was increased from 300°C to 450°C at a rate of 4°C / min under a nitrogen atmosphere, and then the steam introduction was stopped, and the temperature was increased from 450°C to 700°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the kiln was fired at 700°C for 10 hours under a nitrogen atmosphere, thereby manufacturing a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0183]

[0184] Comparative Example 1

[0185] Li2CO3 and FePO4 were mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.05:1 (the total content of Li2CO3 and FePO4 was mixed to be 40 wt% of the solution), and sucrose was added in an amount of 12 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. The mixed solution was wet-ground with a bead mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0186] Afterwards, the dried powder (hereinafter, the mixture) was placed in a sintering furnace and heated from room temperature to 700°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the sintering was performed at 700°C for 10 hours under a nitrogen atmosphere to manufacture a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0187]

[0188] Comparative Example 2

[0189] Li2CO3 and FePO4 were mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.05:1 (the total content of Li2CO3 and FePO4 was mixed to be 40 wt% of the solution), and sucrose was added in an amount of 12 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. The mixed solution was wet-ground with a bead mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0190] Afterwards, the dried powder (hereinafter, the mixture) was put into a kiln, and the temperature was increased from room temperature to 300°C at a rate of 4°C / min under a nitrogen atmosphere, and then steam was injected into the kiln at a rate of 500 g / h, and the temperature was increased from 300°C to 600°C at a rate of 4°C / min under a nitrogen atmosphere, and then the steam injection was stopped, and the temperature was increased from 600°C to 700°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the kiln was fired at 700°C for 10 hours under a nitrogen atmosphere, thereby manufacturing a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0191]

[0192] Comparative Example 3

[0193] Li2CO3 and FePO4 were mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.05:1 (the total content of Li2CO3 and FePO4 was mixed to be 40 wt% of the solution), and sucrose was added in an amount of 12 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. The mixed solution was wet-ground with a bead mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0194] Thereafter, the dried powder (hereinafter, the mixture) was placed in a kiln, and the temperature was increased from room temperature to 450°C at a rate of 4°C / min under a nitrogen atmosphere, and then steam was introduced into the kiln at a rate of 500 g / h, and the temperature was increased from 450°C to 600°C at a rate of 4°C / min under a nitrogen atmosphere, and then the steam introduction was stopped, and the temperature was increased from 600°C to 700°C at a rate of 4°C / min under a nitrogen atmosphere. Then, the kiln was fired at 700°C for 10 hours under a nitrogen atmosphere, thereby manufacturing a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0195]

[0196] Classification Steam injection status Steam injection section Example 1○25~450℃ Example 2○200~450℃ Example 3○300~450℃ Comparative example 1Ⅹ-Comparative example 2○300~600℃ Comparative example 3○450~600℃

[0197]

[0198] Experimental example

[0199] Experimental Example 1: Rolling Density Measurement

[0200] Each of the positive electrode active material powders of Examples 1 to 3 and Comparative Examples 1 to 3 was weighed at 5 g and placed in a 4-pin probe mold, and 2000 kgf / cm 2 After pressing with a pressure of (2 tons), the rolling density was measured, and the results are shown in Table 2 below.

[0201]

[0202] Experimental Example 2: BET Surface Area Measurement

[0203] Using a BET measuring device (Micromeritics, Tristar II 3020), the BET specific surface area of ​​each of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 was measured by a gas adsorption method using nitrogen gas, and the results are shown in Table 2 below.

[0204]

[0205] Experimental Example 3: Crystal Size Measurement

[0206] Using XRD (Bruker, D8 ENDEAVOR), XRD raw data of each of the positive electrode active material powders of Examples 1 to 3 and Comparative Examples 1 to 3 were obtained, and the crystal size of the positive electrode active material was derived using the Sherrer Equation, and the results are shown in Table 2 below.

[0207]

[0208] Rolled density (g / cc)BET specific surface area (m 2 / g) Crystal size Example 11.98616.55163.47 Example 22.00115.03173.61 Example 32.01216.39158.58 Comparative Example 11.90617.87114.58 Comparative Example 21.93118.24158.67 Comparative Example 31.92518.83165.91

[0209]

[0210] Experimental Example 4: Battery Performance Evaluation

[0211] Each of the positive electrode active materials, carbon black conductive agent, and polyvinylidene fluoride (PVdF) binder manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 was mixed in a weight ratio of 95:2:3 in an N-methylpyrrolidone (NMP) solvent to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture a positive electrode.

[0212] Lithium metal was used as the cathode.

[0213] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. The electrode assembly was placed inside a battery case and an electrolyte was injected to manufacture a lithium secondary battery (half cell). At this time, the electrolyte was a solution of 1.0 M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:4:3.

[0214]

[0215] For each lithium secondary battery (half cell) manufactured as described above, the initial charge / discharge capacity was measured by charging to 3.65 V in CC (0.1 C)-CV (Cut-off current: 0.1 C) mode at 25°C and then discharging to 2.5 V at 0.1 C.

[0216] In addition, for each lithium secondary battery (half cell) manufactured as described above, the discharge capacity was measured by performing 30 cycles in which one cycle was charged to 3.65 V in CC (0.1 C)-CV (Cut-off current: 0.1 C) mode at 25°C and then discharged to 2.5 V at 0.1 C. At this time, the percentage of the discharge capacity of the 30th cycle to the discharge capacity of the first cycle was defined as the capacity retention rate (%), and is shown in Table 3 below.

[0217]

[0218] Classification Charge capacity (mAh / g) Discharge capacity (mAh / g) Capacity retention rate (%) Example 1 162.3 159.199 Example 2 162.3 159.898 Example 3 162.1 160.299 Comparative example 1 162.5 159.696 Comparative example 2 161.5 157.893 Comparative example 3 160.8 157.594

[0219]

[0220] Referring to Table 2 above, it can be confirmed that the positive electrode active materials of Examples 1 to 3, in which steam was introduced only to a specific section during the firing for manufacturing the positive electrode active material, have a higher rolling density and a smaller BET specific surface area compared to the positive electrode active materials of Comparative Examples 1 to 3.

[0221] Additionally, in the case of the positive electrode active materials of Examples 1 to 3, it can be confirmed that the crystal size is larger compared to Comparative Example 1 in which no steam was added during the firing for manufacturing the positive electrode active material.

[0222] And, referring to Table 3 above, it can be confirmed that the lithium secondary battery including the positive electrode active material of Examples 1 to 3 has a large charge / discharge capacity and, in particular, a remarkably excellent capacity retention rate.

[0223] This is because, only when the manufacturing method of the present invention includes a process of introducing steam (no substance other than steam is introduced) only within the temperature-raising section from room temperature to 450°C, the rolling density of the lithium iron phosphate-based positive electrode active material increases and the BET specific surface area decreases.

[0224] In conclusion, it can be seen that the quality of the positive electrode active material manufactured according to the manufacturing method of the present invention is improved, and the life characteristics of a battery including the positive electrode active material are significantly improved.

Claims

1. (A) A step of preparing a mixture by mixing a lithium raw material, a phosphate raw material, and an iron raw material; and (B) a step of calcining the mixture; The above firing includes a temperature raising section in which the temperature is raised from room temperature to 600°C to 800°C, and a holding section in which the temperature is maintained at 600°C to 800°C. A method for manufacturing a lithium iron phosphate-based positive electrode active material, comprising a process of introducing steam only within a range from room temperature to 450°C among the above-mentioned temperature-raising ranges.

2. In claim 1, A method for producing a lithium iron phosphate-based positive electrode active material, wherein a carbon coating raw material is further mixed during the preparation of the mixture in step (A).

3. In claim 2, A method for producing a lithium iron phosphate cathode active material, wherein the carbon coating raw material is added in an amount of 5 to 20 wt% relative to the total weight of the lithium raw material, the phosphate raw material, and the iron raw material.

4. In claim 1, A method for producing a lithium iron phosphate-based positive electrode active material, wherein a manganese raw material is further mixed in when producing the mixture in step (A).

5. In claim 1, A method for producing a lithium iron phosphate-based positive electrode active material, wherein the above-mentioned calcination is performed under an inert atmosphere.

6. A lithium iron phosphate cathode active material comprising a lithium iron phosphate compound, 2000kgf / cm of positive electrode active material powder 2 The rolled density measured after pressing with a pressure of 1.95 g / cc to 2.5 g / cc, BET surface area is 15.00m 2 / g to 17.00m 2 / g, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material having a crystal size of 155 nm to 175 nm.

7. In claim 6, The lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material comprising a coating layer including carbon formed on the lithium iron phosphate-based compound.

8. In claim 6, The lithium iron phosphate compound is a lithium iron phosphate cathode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4 In the above chemical formula 1, M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y, -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.

1.

9. A cathode comprising a lithium iron phosphate cathode active material according to claim 6.

10. A lithium secondary battery comprising a positive electrode according to claim 9.