Positive electrode active material for lithium secondary batteries

Abstract

The present invention provides a cathode active material that is produced by an environmentally friendly method without the need for a separate precursor synthesis process and has excellent energy density and electron conductivity. The present invention also provides a cathode and a lithium secondary battery that include the cathode active material. [Solution] According to one aspect of the present specification, there is provided a positive electrode active material for a lithium secondary battery, comprising a lithium composite compound capable of lithium intercalation / deintercalation, the lithium composite compound comprising Fe and Mn, the lithium composite compound comprising a plurality of particulate materials, and an FeP phase being present in at least a portion of the particulate materials.

Description

[Technical Field]

[0001] The present specification relates to a positive electrode active material for a lithium secondary battery, and more specifically to a positive electrode active material for a lithium secondary battery that can be produced by an environmentally friendly method and has excellent electrical conductivity and energy density. [Background technology]

[0002] Batteries store electricity by using materials capable of electrochemical reactions at the positive and negative electrodes. A typical example of such batteries is a lithium secondary battery, which stores electrical energy by utilizing the difference in chemical potential when lithium ions are intercalated / deintercalated between the positive and negative electrodes.

[0003] The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte solution or a polymer electrolyte solution between the positive electrode and the negative electrode.

[0004] Various materials are used as the positive electrode active material for lithium secondary batteries, among which lithium metal phosphate, for example, lithium iron phosphate (LiFePO), is widely used in the manufacture of lithium secondary batteries because it has excellent stability, the ability to withstand many charge / discharge cycles, and relatively low manufacturing costs.

[0005] However, lithium iron phosphate has the disadvantage of low operating voltage and energy density. To overcome these drawbacks, lithium manganese iron phosphate (LMFP), in which part of the iron is replaced with manganese, has been proposed. However, lithium manganese iron phosphate has problems with low lithium ion diffusion rate and electronic conductivity.

[0006] Conventional cathode active materials are manufactured by first synthesizing a precursor, then adding lithium and firing it. However, there is a problem with the generation of pollutants such as SOx and NOx due to the components present in the raw materials used to manufacture the precursor. In addition, after synthesizing the precursor, the precursor must be dehydrated and dried before lithium is added, which is disadvantageous in terms of energy and yield. Summary of the Invention [Problem to be solved by the invention]

[0007] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is driving the market, while the demand for positive electrode active materials used in lithium secondary batteries is also continuously changing, and in particular, there is a growing demand to minimize costs when manufacturing positive electrode active materials.

[0008] At the same time, the market is demanding positive electrode active materials with higher energy density and excellent conductivity.

[0009] In order to meet such market demands, an object of the present invention is to provide a positive electrode active material that can be prepared by an environmentally friendly method without a process of synthesizing a separate precursor and has excellent energy density and electron conductivity.

[0010] Another object of the present specification is to provide a lithium secondary battery that uses the positive electrode defined in the present application.

[0011] The objects of the present invention are not limited to the objects mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be easily understood that the objects and advantages of the present invention can be realized by the means set forth in the claims and combinations thereof. [Means for solving the problem]

[0012] According to one aspect of the present specification, there is provided a positive electrode active material for a lithium secondary battery, comprising: a lithium composite compound capable of lithium intercalation / deintercalation, the lithium composite compound comprising Fe and Mn; the lithium composite compound comprising a plurality of particulate materials, wherein an FeP phase is present in at least a partial region of the particulate materials.

[0013] Here, the particulate matter may have an average particle size of 0.01 to 5 μm.

[0014] In addition, 50 wt % or more of the Fe2P phase contained in the positive electrode active material may be located inside the particulate material.

[0015] In one embodiment, the content of the Fe2P phase may be 0.2 to 0.9 wt % based on 100 wt % of the lithium iron manganese phosphate phase contained in the lithium composite compound.

[0016] The particulate matter is obtained by pulverizing a finely pulverized lithium composite compound, which includes a first region in which Fe is present from the center to the surface but Mn is not present, a second region in which a mixed structure of Fe and Mn is present, and a third region in which Mn is present but Fe is not present.

[0017] In this case, in the finely pulverized lithium composite compound, the Fe2P phase may be present in at least a part of the first region and the second region.

[0018] The total thickness of the second and third regions may be 0.5 to 2.0 μm.

[0019] Here, the total content of the Fe2P2O7 phase and the Mn2P2O7 phase in the particulate material may be 2.5 wt % or less based on 100 wt % of the lithium manganese iron phosphate phase contained in the lithium composite compound.

[0020] In addition, the content of the Mn2P2O7 phase in the particulate material may be 2.5 wt % or less based on 100 wt % of the lithium manganese iron phosphate phase contained in the lithium composite compound.

[0021] In one example, the particulate matter may satisfy at least one of the conditions expressed by the following formulas 1 to 3: [Formula 1] 28.10Å 2 ≦A p ≦28.74Å 2 [Formula 2] 62.40Å 2 ≦B p ≦63.10Å 2 [Formula 3] 48.50Å 2 ≦C p ≦49.20Å 2 In the formulas 1 to 3, the A p ~C above p can be calculated using the following formulas 1' to 3': [Formula 1′] A p =V c / l a [Formula 2′] B p =V c / l b [Formula 3′] C p =V c / l c In the formulas 1′ to 3′, the V c is the unit cell volume of the particulate matter, and a , l b , l c may respectively refer to the diameters of the a-axis, b-axis, and c-axis of the particulate matter.

[0022] In another embodiment, the lithium complex compound may be represented by the following Formula 1: [Chemical formula 1] Li p Fe1-x-y Mn x A y A' z P 1-z O w In the formula, A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, A' is at least one selected from the group consisting of C, Si, S, N, B, F, Cl, and I, and 0.5≦p≦1.5, 0 <x<1、0≦y<1、0≦z<1、0<w≦4である。

[0023] At least a portion of the particulate matter may have an amorphous carbon coating layer having a thickness of 1 to 500 nm formed on at least a portion of the surface.

[0024] According to yet another embodiment, there is provided a positive electrode comprising the positive electrode active material.

[0025] According to yet another embodiment, there is provided a lithium secondary battery using the positive electrode. [Effects of the Invention]

[0026] According to the present specification, a positive electrode active material having excellent electrical conductivity and energy density can be obtained.

[0027] Furthermore, according to the present specification, a positive electrode active material can be obtained that is excellent in stability at low temperatures and high currents, and has excellent capacity and life characteristics.

[0028] The specific effects of the present specification, together with the above-mentioned effects, will be described below together with specific matters for implementing the matters described in the specification. [Brief explanation of the drawings]

[0029] [Figure 1]FIG. 1 is a diagram schematically illustrating element concentrations by position in a positive electrode active material according to one embodiment of the present specification. [Figure 2] FIG. 2 is a diagram showing an SEM image of a positive electrode active material according to one embodiment of the present specification. DETAILED DESCRIPTION OF THE INVENTION

[0030] To facilitate understanding of this specification, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used herein have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise specified above, singular terms should be understood to include the plural, and plural terms should be understood to include the singular.

[0031] Hereinafter, a method for manufacturing a cathode active material for a lithium secondary battery according to the present specification, a cathode including the cathode active material manufactured from the cathode active material, and a lithium secondary battery using the cathode will be described in more detail.

[0032] Method for producing positive electrode active material for lithium secondary battery A method for producing a positive electrode active material for a lithium secondary battery according to one embodiment of the present specification may include: (a) reacting an iron source material and a phosphate-based source material to produce a slurry containing an Fe-P composite; (b) reacting a manganese source material and an Fe-P composite to produce a slurry containing an Fe-Mn-P composite; (c) adding a lithium source material and a carbon source material to the slurry, and then drying the mixture to obtain a powder; and (d) heat-treating the powder to obtain a lithium composite compound.

[0033] In a conventional method for manufacturing a phosphate-based lithium composite compound, a phosphate precursor is prepared using sulfate or nitrate as a raw material, and then lithium is added and the precursor is calcined to prepare a positive electrode active material.

[0034] However, this manufacturing method involves losses in energy and yield during the dehydration and drying processes when producing the precursor, and also generates harmful substances such as SOx and NOx.

[0035] The manufacturing method according to one embodiment of the present specification does not generate harmful substances such as SOx and NOx, and by eliminating unnecessary dehydration and drying processes, it is possible to manufacture a positive electrode active material product of the same or better quality while being an environmentally friendly method.

[0036] Furthermore, the manufacturing method according to one aspect of the present specification can suppress the formation of an M2P2O7 (M=Fe or Mn) impurity phase.

[0037] When the Li reactivity is reduced by the unstable MP phase during sintering, an M2P2O7 impurity phase can be formed. The M2P2O7 impurity phase acts as a resistor, reducing the output and capacity characteristics of the positive electrode active material. Furthermore, among the M2P2O7 impurity phases, Mn2P2O7 can cause Mn elution during charge and discharge, reducing the stability of the battery.

[0038] Step (a) is a step of reacting an iron source material with a phosphate-based source material to form an Fe-P complex, where the iron source material and the phosphate-based source material may each be one or more types.

[0039] The iron source material refers to a material containing iron element, and may be, for example, at least one selected from the group consisting of Fe metal, FeOOH, Fe2O3, and Fe3O4.

[0040] In addition, when the source material in step (a) further contains a transition metal M other than Fe, the source material may further contain at least one transition metal source material selected from the group consisting of MSO, HMPO, MPO, M(PO), (CHCOO), M, M(NO), MCO, MCO, and MO.

[0041] The phosphate-based source material includes an anion, salt, functional group, or ester derived from phosphoric acid. For example, the phosphate-based source material may be at least one selected from the group consisting of H3PO4, Li3PO4, NH4H2PO4, and (NH4)2HPO4.

[0042] Here, the iron source material and the phosphate-based source material may be mixed in a ratio of 0.90 to 2.00 moles of phosphorus element per mole of iron element, for example, 0.90 moles, 0.95 moles, 1.00 moles, 1.05 moles, 1.10 moles, 1.15 moles, 1.20 moles, 1.25 moles, 1.30 moles, 1.35 moles, 1.40 moles, 1.45 moles, 1.50 moles, 1.55 moles, 1.60 moles, 1.65 moles, 1.70 moles, 1.75 moles, 1.80 moles, 1.85 moles, 1.90 moles, 1.95 moles, 2.00 moles, or a range between any two of these values.

[0043] In step (a), iron ions and phosphate ions react to form an Fe-P complex. For example, iron ions (Fe 3+ ) and phosphate ions (PO4 3- When the Fe-P complex reacts with FePO₄·nH₂O (0≦n≦9), FePO₄ anhydride, Fe₃(PO₄)₂, Fe₂(HPO₄)₃, etc., various Fe-P complexes can be formed. The Fe-P complexes can also be formed in the form of precipitates in the slurry. Among the Fe-P complexes, FePO₄·2H₂O can have the largest proportion.

[0044] Optionally, in step (a), at least one sub-source material containing an element selected from Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, F, Fe, Ga, Hf, I, In, K, La, Mg, Mo, N, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr may be further added to the slurry.

[0045] The sub-raw material may be introduced to dope the Fe-P composite with a different element, which can control the properties of the composite in subsequent steps or improve the performance of the cathode active material.

[0046] Step (b) is a step of reacting a manganese source material with an Fe-P complex to form an Fe-Mn-P complex, where the manganese source material may be one or more types.

[0047] The manganese source material refers to a material containing elemental manganese, and may be, for example, at least one selected from the group consisting of Mn metal, MnCO3, Mn2O3, and Mn3O4.

[0048] In addition, when the source material in step (b) further contains a transition metal M other than Mn, the source material may further contain at least one transition metal source material selected from the group consisting of MSO4, HMPO4, MPO4, M3(PO4)2, (CH3COO)2M, M(NO3)2, MCO3, M2CO3, and MO2 in addition to the Mn transition metal source material.

[0049] Here, the manganese source material and the Fe-P complex may be mixed in a ratio of 1.00 to 2.00 moles of manganese element per mole of iron element, for example, 1.00 moles, 1.05 moles, 1.10 moles, 1.15 moles, 1.20 moles, 1.25 moles, 1.30 moles, 1.35 moles, 1.40 moles, 1.45 moles, 1.50 moles, 1.55 moles, 1.60 moles, 1.65 moles, 1.70 moles, 1.75 moles, 1.80 moles, 1.85 moles, 1.90 moles, 1.95 moles, 2.00 moles, or a range between any two of these values.

[0050] At least one of the reactions in the step (a) and the step (b) is carried out at a temperature of 50 to 150°C, for example, 50°C, 52.5°C, 55°C, 57.5°C, 60°C, 62.5°C, 65°C, 67.5°C, 70°C, 72.5°C, 75°C, 77.5°C, 80°C, 82.5°C, 85°C, 87.5°C, 90°C, 92.5°C, 95°C, 97.5°C, 10°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 550°C, 57.5°C, 600°C, 62.5°C, 650°C, 6 The heating temperature can be 0°C, 102.5°C, 105°C, 107.5°C, 110°C, 112.5°C, 115°C, 117.5°C, 120°C, 122.5°C, 125°C, 127.5°C, 130°C, 132.5°C, 135°C, 137.5°C, 140°C, 142.5°C, 145°C, 147.5°C, 150°C or a range between any two of these values.

[0051] Here, the reaction can be carried out while stirring the slurry for 4 to 48 hours, for example, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, 48 ​​hours, or a time range between any two of these values.

[0052] In step (b), manganese ions react with the Fe-P complex to form an Fe-Mn-P complex, which acts as a kind of seed and allows the Fe-Mn-P complex to be co-precipitated.

[0053] The Fe-Mn-P complex may be formed so that an Fe-P complex structure exists inside and an Mn-P structure exists on the surface, i.e., the particulate matter may have a structure with a high Fe concentration in the center and a low or no Fe concentration in the surface.

[0054] For example, referring to FIG. 1, from the center (position 0) of the Fe-Mn-P composite toward the surface, there may be a first region where Fe is present but Mn is not present, a second region where a mixed structure of Fe and Mn is present, and a third region where Mn is present but Fe is not present.

[0055] Here, the thickness of the first region may be 3.0 to 5.0 μm, and the thickness of the second region and the third region may be 0.5 to 2.0 μm or more, but is not limited thereto.

[0056] At least a portion of the first region and / or the second region does not come into contact with lithium during firing, and the content of the FeP phase having excellent electronic conductivity can be maintained at an appropriate amount of 0.2 to 0.9 wt %, for example, 0.2 wt %, 0.25 wt %, 0.3 wt %, 0.35 wt %, 0.4 wt %, 0.45 wt %, 0.5 wt %, 0.55 wt %, 0.6 wt %, 0.65 wt %, 0.7 wt %, 0.75 wt %, 0.8 wt %, 0.85 wt %, 0.9 wt %, or a range between two of these values, based on 100 wt % of the lithium manganese iron phosphate phase.

[0057] For example, if the Fe-P composite is exposed to a strongly reducing atmosphere during sintering, excessive Fe2P phases may form, which may aggregate outside the particles and reduce the capacity of the cathode active material. In this case, the unstable MP phase may also form an M2P2O7 impurity phase.

[0058] When the Fe-Mn-P composite is formed so that the Mn-P composite structure exists inside and the Fe-P composite structure exists on the surface, the Fe2P phase is significantly suppressed, but the formation of the M2P2O7 impurity phase increases the resistance, which may result in a decrease in capacity at high current or low temperature.

[0059] Alternatively, if the Fe raw material and oxidant are reacted after the Mn-P composite structure is formed, the oxidant may destabilize the Fe-P composite structure, resulting in the formation of a large amount of Fe2P phase and simultaneously increasing the amount of M2P2O7 impurity phase, which may reduce the stability and capacity of the cathode material.

[0060] In step (b), various Fe-Mn-P complexes can be formed. These Fe-Mn-P complexes include FePO4·nH2O (0≦n≦9), FePO4 anhydride, Fe3(PO4)2, Fe2(HPO4)3, H10 MnO 20 The Fe-Mn-P complex may be formed in the form of a precipitate in the slurry.

[0061] Optionally, in step (b), at least one sub-source material containing an element selected from Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, F, Fe, Ga, Hf, I, In, K, La, Mg, Mo, N, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr may be further added to the slurry.

[0062] The sub-raw material may be introduced to dope the Fe-Mn-P composite with a different element, which may control the reaction between the Fe-P composite and Mn or adjust the properties of the resulting cathode active material.

[0063] In particular, the reaction in step (b) can be carried out in the presence of an oxidizing agent, examples of which include, but are not limited to, at least one selected from the group consisting of hydrogen peroxide, potassium permanganate, acetic peroxide, perbenzoic acid, sodium perborate, periodic acid, sodium percarbonate, potassium percarbonate, vanadium trioxide, ammonium chloride, ammonium phosphate, ferric chloride, hypochlorous acid, sodium hypochlorite, and dissolved ozone.

[0064] Here, the oxidizing agent may be added after step (a) is completed. Referring to Reaction Scheme 1 below, in step (a), it may be difficult to form an Fe-P complex in the presence of an oxidizing agent.

[0065] [Reaction Scheme 1] (1) 2FeOOH + 2H2O2 → 2Fe(OH)3 + O2 (2)Fe(OH)3→FeOOH(200℃ dehydration) Additionally, step (c) may be a step of adding a lithium source material and a carbon source material to the slurry containing the Fe—Mn—P composite without a separate dehydration or drying process.

[0066] In addition, when the dehydration and drying processes are simply omitted in the manufacturing method of the lithium manganese iron phosphate compound using the conventional precursor, sulfur (S) and nitrogen (N) compounds may be contained as impurities in the slurry. These impurities are generated by SO x , NO x These impurities not only generate harmful substances such as nitriding agents, but also hinder the carbonization of the carbon raw material and the growth of olivine crystals. Furthermore, if these impurity-derived components remain in the positive electrode active material, gas may be generated inside the battery, reducing stability.

[0067] The lithium source material may be used to introduce lithium into the Fe—Mn—P composite so that the composite can function as a lithium positive electrode active material.

[0068] The lithium source material in step (c) may be added so that the ratio (Li / Metal) of the number of lithium atoms (Li) to the total number of atoms of metal elements other than lithium in the slurry is 0.50 to 1.50, for example, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, or a range between any two of these values, but is not limited thereto.

[0069] The carbon source material added in step (c) may be used to form a carbon coating that improves the conductivity of the positive electrode active material. Minimizing the thickness and increasing the uniformity of the carbon coating layer can minimize the decrease in flowability due to amorphous carbon and improve the conductivity of the positive electrode active material.

[0070] For example, lithium manganese iron phosphate compounds, which are olivine-based cathode materials, are PO4 3- The strong covalent bond between Li and Li2 results in a relatively low electrical conductivity. + is known to have one-dimensional diffusion and low ionic conductivity.

[0071] To overcome these drawbacks, we have developed a technology to improve conductivity by forming a carbon coating and a technology to improve conductivity by nanoparticle formation. + Techniques have been proposed to improve diffusion.

[0072] However, the coated carbon in conventional positive electrode active materials exists in an amorphous phase, which can reduce the density of the positive electrode active material.

[0073] Furthermore, conventional nano-sized particulate materials grow into angular particles due to aggregation during the firing process.

[0074] As a result, the poor flowability and angular particle shape of the amorphous carbon can reduce the density of the positive electrode active material and lower the energy density of the final product.

[0075] Meanwhile, the carbon coating layer formed by this method may have a uniform and thin thickness, and the carbon source material may induce the lithium complex compound to grow into a spherical shape.

[0076] The carbon source material may be a compound having a C element ratio of 30 to 60% by weight in its molecular structure, for example, 30% by weight, 31% by weight, 32% by weight, 33% by weight, 34% by weight, 35% by weight, 36% by weight, 37% by weight, 38% by weight, 39% by weight, 40% by weight, 41% by weight, 42% by weight, 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, or a range between any two of these values.

[0077] When a carbon source material having a C element ratio within the above range is used, a product with excellent yield and uniformity of carbon coating can be produced even when a compound with the same content is used.

[0078] Examples of the carbon source material include, but are not limited to, sucrose, glucose, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), colloidal carbon, citric acid, tartaric acid, glycolic acid, polyacrylic acid, adipic acid, glycine, and aminobenzoic acid.

[0079] Furthermore, the properties of the carbon coating layer formed can be controlled by adjusting the properties of the carbon source material.

[0080] For example, minimizing the thickness of the carbon coating layer in the positive electrode active material and increasing its uniformity can minimize the decrease in flowability caused by amorphous carbon and improve the conductivity of the positive electrode active material.

[0081] For example, the thickness of the carbon coating layer formed in step (c) may be 1 to 500 nm, for example, 1 nm, 2.5 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range between two of these values, but is not limited thereto.

[0082] In one embodiment, the carbon source material in step (c) has a ratio (C / Metal) of the number of carbon atoms (C) to the total number of atoms of metal elements other than lithium (Metal) in the slurry of 0.25 to 0.75, for example, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0. 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or a range between any two of these values.

[0083] Optionally, in step (c), at least one sub-source material containing an element selected from Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, F, Fe, Ga, Hf, I, In, K, La, Mg, Mo, N, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr may be further added to the slurry.

[0084] The sub-raw material may be introduced to dope the lithium composite compound with a different element, which may improve the stability or conductivity of the positive electrode active material.

[0085] During the preparation of the Fe—Mn—P composite, some solid particles may aggregate with each other. If at least some of these particles are over-aggregated, it may be difficult to sufficiently react with the lithium source material or the carbon source material.

[0086] Therefore, if necessary, the solid content of the slurry can be pulverized before or after step (c) to break down over-agglomerated particles.

[0087] The pulverization can be carried out under conditions that do not damage the Fe-Mn-P composite including the first region, the second region, and the third region, and that allow over-agglomerated particles to be crushed. In this specification, the terms "finely pulverized lithium composite compound" and "finely pulverized state" do not simply mean only a lithium composite compound that has not undergone a pulverization step, but may also include a lithium composite compound that has undergone a pulverization step but has only undergone the crushing of over-agglomerated particles under conditions that do not damage the Fe-Mn-P composite including the first region, the second region, and the third region.

[0088] The slurry may have a solids content of 20 to 50%, for example, but not limited to, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, or a range between any two of these values.

[0089] The average particle size (D50) of the pulverized particles may be 1.0 μm or less, for example, 1.0 μm, 0.95 μm, 0.90 μm, 0.85 μm, 0.80 μm, 0.75 μm, 0.70 μm, 0.65 μm, 0.60 μm, 0.55 μm, 0.50 μm, 0.45 μm, 0.40 μm, 0.35 μm, 0.30 μm, 0.25 μm, 0.20 μm, 0.15 μm, 0.10 μm, 0.05 μm, or a range between any two of these values, but is not limited thereto.

[0090] To pulverize the particles, a dry or wet dispersion mill such as a ball mill, a bead mill (beads typically used for pulverizing metallic raw materials, such as Al beads, Fe beads, or Zr beads, can be used), a vibratory mill, an attritor mill, an air jet mill, a disk mill, or an air classifier mill can be used.

[0091] For example, the grinding step may be performed in a mill containing beads ranging in size from 0.1 to 1.5 mm, e.g., 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1 mm, 1.05 mm, 1.1 mm, 1.15 mm, 1.2 mm, 1.25 mm, 1.3 mm, 1.35 mm, 1.4 mm, 1.45 mm, 1.5 mm, or any range between any two of these values. Here, the size may refer to the diameter of the beads. If the beads are not spherical, the diameter may refer to the diameter of the major axis.

[0092] The mill machine may also contain beads in an amount of 30 to 50% by volume, for example, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, or a range between any two of these values.

[0093] In step (c), the slurry may be dried to obtain a powder form. For example, the slurry may be dried by spray drying. That is, the powder in step (d) may be obtained by spray drying the slurry in step (c).

[0094] Spray drying, which is one example of the drying, can be performed in a spray dryer. The spray dryer is not particularly limited as long as it is a spray drying device that can spray-dry the slurry containing particles to produce dried particles having a nearly spherical shape. Examples of the spray dryer that can be used include an ultrasonic atomizer, a single-fluid jet nozzle atomizer, a two-fluid jet nozzle atomizer, an ultrasonic nozzle atomizer, a filter expansion droplet generator (FEAG), and a disk-type droplet generator.

[0095] The spray dryer may include a spray nozzle and a drying chamber, and the slurry is atomized into droplets of a predetermined size through the spray nozzle and sprayed into the drying chamber in the presence of a relatively high temperature gas flow.

[0096] The droplets of raw material sprayed into the drying chamber can be dried into particles having a nearly spherical shape under the temperature environment in the drying chamber.

[0097] Furthermore, when the slurry contains a specific carbon source material, unwanted aggregation of the particles can be suppressed during spray drying, resulting in particles with a nearly spherical shape.

[0098] For example, moisture loss during drying can reduce particle density and form pores, resulting in reduced particle strength and insufficient stability of the positive electrode active material.

[0099] Here, adjusting the viscosity of the slurry before drying can shorten the condensation time during drying and minimize the decrease in density due to moisture loss during drying. If the viscosity of the slurry is too high, the fluidity during drying decreases, resulting in insufficient process efficiency and difficulty in obtaining spherical particles. One method for adjusting the viscosity of the slurry is to add a binder.

[0100] Next, step (d) may be a step of heat-treating the powder dried in step (c) to form a lithium composite compound.

[0101] During the heat treatment in step (d), the carbon source material may be carbonized to form a carbon coating layer. Therefore, the carbon source material must be carbonized within the heat treatment temperature in step (d). If uncarbonized carbon-based compounds remain in the positive electrode active material, the conductivity may not be improved sufficiently or unexpected side effects may occur.

[0102] The heat treatment in step (d) can be performed in an inert atmosphere at a maximum temperature of 500 to 950° C. for 5 to 15 hours, where the maximum temperature can vary depending on the composition of the target positive electrode active material.

[0103] For example, the heat treatment can be performed at a maximum temperature of 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C, 775°C, 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, or a range between any two of these values. Such heat treatment can be performed while maintaining the maximum temperature for, but is not limited to, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours, 15 hours, or a range between any two of these values.

[0104] When the heat treatment is performed at a temperature that satisfies the above range, the density of the lithium composite compound is excellent.

[0105] Meanwhile, if the heat treatment temperature in step (d) is insufficient, the precursor may not be sufficiently calcined, resulting in insufficient crystal growth of the lithium composite compound or difficulty in forming a carbon coating layer, which may result in a decrease in density of the lithium composite compound.

[0106] If the heat treatment temperature in step (d) is too high, the lithium composite compound may be thermally decomposed, resulting in a decrease in particle strength or particle collapse.

[0107] The heat treatment can be carried out by increasing the temperature by 1 to 10°C per minute, for example, 1°C, 1.5°C, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C, 5°C, 5.5°C, 6°C, 6.5°C, 7°C, 7.5°C, 8°C, 8.5°C, 9°C, 9.5°C, 10°C, or a range between any two of these values, until the maximum temperature is reached.

[0108] Here, the inert atmosphere may be constructed by replacing air with at least one inert gas selected from the group consisting of, for example, N2, Ar, He, Rn, Ne, and Xe, but is not limited thereto.

[0109] The majority of the Fe-Mn-P composite formed in step (b) may be in the form of a hydrate. The Fe-Mn-P composite in the form of a hydrate may have its crystal water removed and re-established during the calcination in step (d). This re-establishment process generates moisture and consumes heat energy. As a result, the carbon source material is carbonized at a relatively high temperature, resulting in a more uniform carbon coating and improved conductivity.

[0110] After the heat treatment in the step (d), the material can be cooled while maintaining an inert atmosphere at a temperature of 150° C. or less. For example, the heat-treated lithium composite compound can be obtained by furnace cooling.

[0111] For example, the lithium composite compound obtained in step (d) may include a first region in which Fe is present from the center to the surface and Mn is not present, a second region in which a mixed structure of Fe and Mn is present, and a third region in which Mn is present and Fe is not present. In the lithium composite compound in a finely pulverized state, the FeP phase may be present in at least a part of the first region and / or the second region.

[0112] Here, the thickness of the first region may be 3.0 to 5.0 μm, for example, 3 μm, 3.25 μm, 3.5 μm, 3.75 μm, 4 μm, 4.25 μm, 4.5 μm, 4.75 μm, 5 μm, or a range between any two of these values, and the thicknesses of the second and third regions may be 0.5 to 2.0 μm or more, for example, 0.5 μm, 0.75 μm, 1.0 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2.0 μm, a range between any two of these values, or 2.0 μm or more, but are not limited to these.

[0113] When the Fe-Mn-P composite including the first, second, and third regions is heat-treated with a lithium source material, the FeP phase is significantly suppressed or excessive formation is minimized, and a lithium composite compound can be produced. In addition, the first, second, and third regions may be present in the heat-treated lithium composite compound.

[0114] Furthermore, before or after performing step (d), the lithium composite compound may be subjected to disintegration, distribution, and / or water washing.

[0115] In one example, after step (d), the method may further include step (e) of pulverizing the lithium composite compound to an average particle size of 1.0 μm or less. The lithium composite compound having an appropriate amount of FeP phase distributed therein obtained by the above method may be pulverized to obtain a particulate material having a controlled particle size.

[0116] In step (e), the particulate material may be pulverized to have an average particle size of 1.0 μm or less, for example, 1.0 μm, 0.9 μm, 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm, 0.2 μm, 0.1 μm, or a range between any two of these values.

[0117] In another example, the average particle size (D50) of the milled particulate material may be 0.5 to 0.7 μm, for example, 0.5 μm, 0.51 μm, 0.52 μm, 0.53 μm, 0.54 μm, 0.55 μm, 0.56 μm, 0.57 μm, 0.58 μm, 0.59 μm, 0.6 μm, 0.61 μm, 0.62 μm, 0.63 μm, 0.64 μm, 0.65 μm, 0.66 μm, 0.67 μm, 0.68 μm, 0.69 μm, 0.7 μm, or a range between any two of these values.

[0118] The particulate material milled to have an average particle size within the above range can be appropriately aggregated by surface energy, thereby improving the density characteristics of the positive electrode active material.

[0119] To pulverize the particles, a dry or wet dispersion mill such as a ball mill, a bead mill (beads typically used for pulverizing metallic raw materials, such as Al beads, Fe beads, or Zr beads, can be used), a vibratory mill, an attritor mill, an air jet mill, a disk mill, or an air classifier mill can be used.

[0120] Positive electrode active material for lithium secondary batteries According to another embodiment of the present specification, there is provided a positive electrode active material for a lithium secondary battery, the positive electrode active material including a lithium composite compound capable of lithium intercalation / deintercalation, the lithium composite compound including Fe and Mn, the lithium composite compound including a plurality of particulate materials, and an FeP phase may be present in at least a partial region of the particulate materials.

[0121] The positive electrode active material may include a particulate material made of a lithium composite compound capable of lithium intercalation / deintercalation. Here, the particulate material may be a compound containing Fe and Mn as constituent elements. The particulate material may include a lithium manganese iron phosphate phase.

[0122] In one embodiment, the particulate material may exist without forming separate aggregates. In this case, the particulate material may have a spherical shape. In addition, since the lithium composite compound is a particulate material having a smooth surface, the positive electrode active material may have excellent compaction density.

[0123] Here, the average particle size of the particulate matter (here, the average particle size of the particulate matter may be the length of the average major axis of the particulate matter) is 0.01 to 5 μm, for example, 0.01 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, , 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, or within a range between two of these values, thereby enabling the optimal density of a positive electrode manufactured using the positive electrode active materials according to various embodiments to be realized.

[0124] As another example, the particulate material may exist as primary particles, and a plurality of the primary particles may aggregate to form secondary particles. Here, the primary particle refers to a single crystal grain (grain or crystallite), and the secondary particle refers to an aggregate formed by the aggregation of a plurality of primary particles. In this case, the primary particle may have a spherical shape. Since the lithium composite compound is a particle having a smooth surface, the positive electrode active material may have excellent compaction density.

[0125] The particulate material may have an Fe2P phase present in at least a portion thereof. The Fe2P phase has excellent electrical conductivity and can improve the performance of the positive electrode active material. In particular, when the Fe2P phase is uniformly distributed within the particulate material, the above-mentioned effects are even more pronounced.

[0126] For example, 50 wt% or more of the total FeP phase contained in the positive electrode active material, for example, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 99 wt%, 100 wt%, or a range between any two of these values, may be located inside the particulate material. Here, when the particulate material is formed by agglomeration of a plurality of primary particles to form secondary particles, the "interior of the particulate material" refers to the interior of the primary particles.

[0127] The Fe2P phase may be formed under excessively reducing or over-firing conditions during the synthesis of a positive electrode active material. The Fe2P phase formed in this manner may be unevenly distributed or located outside the particles, and may cause excessive growth of crystal grains of the lithium composite compound or may even inhibit crystal growth during the synthesis process.

[0128] In addition, the particulate material has a high conductivity because the Fe2P phase is uniformly distributed inside the primary particles, and as a result, the capacity and rate characteristics of the positive electrode active material can be improved.

[0129] The Fe2P phase can be confirmed using XRD Rietveld refinement. For example, the lithium manganese iron phosphate phase can be confirmed using a JCPDS No. 74-0375 card having an orthorhombic Pnma space group, and the Fe2P phase can be confirmed using a JCPDS No. 01-1200 card, but these are not limited to these. The lithium manganese iron phosphate phase can refer to a compound phase containing Li, Fe, Mn, P, and O simultaneously.

[0130] The content of the FeP phase may be 0.2 to 0.9 wt% based on 100 wt% of the lithium manganese iron phosphate phase contained in the lithium composite compound, for example, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%, 0.8 wt%, 0.85 wt%, 0.9 wt%, or a range between any two of these values. When the content of the FeP phase is within this range, the positive electrode active material has excellent conductivity and sufficient capacity.

[0131] For example, the particulate material may be a finely pulverized lithium composite compound including a first region in which Fe is present from the center to the surface but Mn is not present, a second region in which a mixed structure of Fe and Mn is present, and a third region in which Mn is present but Fe is not present, or may be obtained by pulverizing the finely pulverized lithium composite compound. The particulate material may be obtained by pulverizing a finely pulverized lithium composite compound in which the FeP phase is present in at least a portion of the first region and / or the second region. The particulate material may be, but is not limited to, a lithium composite compound including the first region, the second region, and the third region without undergoing a separate pulverization process.

[0132] Here, the thickness of the first region may be 3.0 to 5.0 μm, for example, 3 μm, 3.25 μm, 3.5 μm, 3.75 μm, 4 μm, 4.25 μm, 4.5 μm, 4.75 μm, 5 μm, or a range between any two of these values, but is not limited thereto.

[0133] The thickness of the second and third regions may be 0.5 to 2.0 μm or more, for example, 0.5 μm, 0.75 μm, 1.0 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2.0 μm, a range between two of these values, or 2.0 μm or more, but is not limited to these.

[0134] For example, when the thicknesses of the first region, the second region, and the third region satisfy the above ranges, the particulate material obtained through pulverization can have an appropriate amount of uniformly dispersed FeP phase, thereby improving performance by increasing conductivity and capacity, and minimizing performance degradation due to impurity phases.

[0135] As a non-limiting example, the total content of the Fe2P2O7 phase and the Mn2P2O7 phase in the particulate material may be 2.5 wt% or less, for example, 2.5 wt%, 2.25 wt%, 2 wt%, 1.75 wt%, 1.5 wt%, 1.25 wt%, 1 wt%, 0.75 wt%, 0.5 wt%, 0.25 wt%, 0.15 wt%, 0.05 wt%, an immeasurable amount (nd), or a range between any two of these values, based on 100 wt% of the lithium manganese iron phosphate phase contained in the lithium composite compound. The Fe2P2O7 and Mn2P2O7 phases can be confirmed using the XRD Rietveld method.

[0136] The content of the Mn2P2O7 phase in the particulate material may be 2.5 wt% or less, for example, 2.5 wt%, 2.25 wt%, 2 wt%, 1.75 wt%, 1.5 wt%, 1.25 wt%, 1 wt%, 0.75 wt%, 0.5 wt%, 0.25 wt%, 0.15 wt%, 0.05 wt%, an unmeasurable amount (nd), or a range between two of these values, based on 100 wt% of the lithium manganese iron phosphate phase contained in the lithium composite compound. The Mn2P2O7 phase can be confirmed using the XRD Rietveld method.

[0137] The Fe2P2O7 and Mn2P2O7 phases act as resistors, reducing the output and capacity characteristics of the positive electrode active material. Among them, Mn2P2O7 causes Mn elution during charge and discharge, reducing the stability of the battery.

[0138] As an example, the particulate matter may satisfy at least one of the conditions expressed by the following formulas 1 to 3, but is not limited thereto.

[0139] [Formula 1] 28.10Å 2 ≦A p ≦28.74Å 2 [Formula 2] 62.40Å 2 ≦B p ≦63.10Å 2 [Formula 3] 48.50Å 2 ≦C p ≦49.20Å 2 Here, the A p ~C above p can be calculated using the following formulas 1' to 3'.

[0140] [Formula 1′] A p =V c / l a [Formula 2′] B p =V c / l b [Formula 3′] C p =V c / l c In the formula, V c is the unit cell volume of the particulate matter, and a , l b , l c respectively mean the diameters of the a-axis, b-axis, and c-axis of the particulate material.

[0141] Formulas 1 to 3 are cell characteristic values ​​that indicate the atomic arrangement of Fe and Mn in the particulate material. When Fe-Mn is homogeneous, or when it is a Mn-rich phase or an Fe-rich phase, different cell characteristic values ​​can be exhibited. When the A' to C' characteristic values ​​satisfy the above ranges, the rate characteristics, life characteristics, and low-temperature characteristics of the positive electrode active material are more excellent. However, these values ​​are merely examples and may vary depending on the characteristics of the positive electrode active material.

[0142] The lithium composite compound may be represented by the following Chemical Formula 1:

[0143] [Chemical formula 1] Li p Fe 1-x-y Mn x A y A' z P 1-z O w In the formula, A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, A' is at least one selected from the group consisting of C, Si, S, N, B, F, Cl, and I, and 0.5≦p≦1.5, 0 <x<1、0≦y<1、0≦z<1、0<w≦4である。

[0144] The formula 1 represents a lithium complex compound capable of lithium intercalation / deintercalation, and may include lithium, metal, and phosphate.

[0145] For example, p can be, but is not limited to, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or a range between any two of these values.

[0146] Additionally, x, y, and z may each be, but are not limited to, 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.99, or a range between any two of these values.

[0147] Furthermore, the w can be, but is not limited to, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, or a range between any two of these values.

[0148] That is, LiFe 0.8 Mn 0.2 PO4, LiFe 0.5 Mn 0.5 PO4, etc., can be represented by Chemical Formula 1. The lithium composite compound may further include a dopant, where the dopant can be represented by A and / or A'.

[0149] Here, the formula 1 may represent an average composition of the lithium composite compound.

[0150] The positive electrode active material may include a coating layer that covers at least a portion of the surface of the particulate matter (e.g., the interface between the particulate matter) and / or the surface of the aggregates formed by aggregation of the particulate matter.

[0151] Here, the coating layer may include a carbon layer and / or an oxide layer to improve the stability and conductivity of the particulate matter.

[0152] For example, the coating layer may be present so as to cover at least a portion of the exposed surface of the particulate matter. When the particulate matter aggregates to form secondary particles, the coating layer may be present so as to cover at least a portion of the exposed surface of the primary particles present at the outermost portion of the secondary particles.

[0153] Thus, the coating layer may exist as a layer that continuously or discontinuously coats the surface of the particulate material and / or the secondary particles formed by aggregation of the particulate material. When the coating layer exists discontinuously, it may exist in the form of islands.

[0154] Furthermore, when the particulate matter forms an aggregate, the coating layer may be present not only at the interface between the particulate matter and at least a portion of the surface of the secondary particles, but also in internal voids formed inside the secondary particles.

[0155] The coating layer thus present can contribute to improving the electrochemical properties and stability of the positive electrode active material.

[0156] In this case, the coating layer may exist in the form of a solid solution that does not form a boundary with the particulate material and / or the secondary particles formed by aggregation of the particulate material, but this is not necessarily the case.

[0157] The thickness of the amorphous carbon coating layer formed on at least a portion of the surface of at least a portion of the particulate matter may be 1 to 500 nm, for example, 1 nm, 2.5 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range between any two of these values.

[0158] Here, the thickness of the carbon coating layer can be adjusted depending on the balance between the fluidity and conductivity of the lithium composite compound.

[0159] In particular, the carbon coating layer has little variation in thickness, and the positive electrode active material has excellent balance of fluidity and conductivity, which are complementary to each other.

[0160] The thickness of the carbon coating layer can be measured by various known methods. For example, it can be measured from a TEM or SEM image, or confirmed from a line scan of carbon in a specific direction in EDX analysis results. The thickness can be an average value obtained by measuring at least three times.

[0161] Furthermore, the carbon coating layer may be uniformly formed on the surface of the lithium composite compound particles, providing a smooth surface texture, thereby increasing the compaction density of the positive electrode active material.

[0162] Olivine cathode materials are PO4 3- It is known that the electrical conductivity is low due to the strong covalent bond of Li. + To solve this problem, it has been proposed to form a carbon coating layer and produce a nano-sized positive electrode active material.

[0163] However, the amorphous carbon coating layer reduces the density of the positive electrode active material. Nanoparticles aggregate and grow into angular shapes during firing, reducing flowability and also reducing the density of the positive electrode active material. This results in a problem of reduced energy density per unit volume.

[0164] Meanwhile, the particulate material including the lithium composite compound according to the present invention includes a uniform carbon coating layer. Furthermore, under conditions for forming such a carbon coating layer, the lithium composite compound grows into a spherical particulate material, thereby minimizing density reduction.

[0165] Even if a coating layer of the compound is present on at least a portion of the surface of the particulate matter, it is preferable that the particulate matter maintains a spherical shape.

[0166] Lithium secondary battery According to yet another aspect, a positive electrode may be provided, including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include a positive electrode active material manufactured by the manufacturing method according to any of the various embodiments described above.

[0167] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance 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 material, foam, or nonwoven fabric.

[0168] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0169] In this case, the positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically, 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0170] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0171] The binder serves to improve adhesion between positive electrode active material particles and 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination. The binder may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0172] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, coating the composition on a positive electrode current collector, and then drying and rolling the composition.

[0173] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0174] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the positive electrode slurry composition from the support, and laminating the resulting film on a positive electrode current collector.

[0175] According to yet another aspect, there may be provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0176] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

[0177] The lithium secondary battery may also be provided as an anode-free secondary battery. Here, since the positive electrode is as described above, detailed description thereof will be omitted for brevity's sake, and only the remaining components not described above will be described in detail below. Furthermore, the following description of the negative electrode should be understood to be based on the assumption that the lithium secondary battery includes a negative electrode.

[0178] The lithium secondary battery may have a separator replaced with a solid electrolyte. In this case, an electrode slurry composition containing a solid electrolyte may be used when preparing the positive and negative electrodes.

[0179] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0180] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0181] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0182] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0183] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0184] The negative electrode active material may be contained in an amount of 80 to 99 wt % based on the total weight of the negative electrode active material layer.

[0185] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may typically be added in an amount of 0.1 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0186] The conductive material 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. Such a conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of such a conductive material include graphite such as natural graphite and 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 and metal fiber, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives.

[0187] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition 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 and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and the resulting film may be laminated on the negative electrode current collector.

[0188] In another embodiment, the negative electrode active material layer may be fabricated by coating a negative electrode slurry composition 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 and drying the coating; or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0189] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without limitation. It is particularly preferable that the separator has low resistance to ion migration and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0190] Examples of the electrolyte used in the lithium secondary battery include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used when manufacturing a lithium secondary battery.

[0191] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0192] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether solvents such as dibutyl ether and tetrahydrofuran, ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as benzene and fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0193] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0194] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt.% based on the total weight of the electrolyte.

[0195] The electrolyte may include a solid electrolyte such as a solid polymer electrolyte, a gel polymer electrolyte, or a solid inorganic electrolyte.

[0196] In lithium secondary batteries containing a solid electrolyte, the separator can be omitted. However, since the electrolyte is difficult to penetrate into the cathode and anode, the solid electrolyte can be mixed into the cathode and anode during the manufacturing process to form the electrodes.

[0197] The solid polymer electrolyte or gel polymer electrolyte may be a composite of a salt of a metal ion of Group 1 or Group 2 of the periodic table used in secondary batteries and a polymer resin, such as a solvated lithium salt to which a polymer resin is added.

[0198] The salt of the metal ion may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2.

[0199] Examples of the polymer resin include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives such as polyethylene oxide, phosphate ester polymers, polyazitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociating groups, branched copolymers in which amorphous polymers such as PMMA, polycarbonate, polysiloxane (PDMS) or phosphazene are copolymerized with a comonomer on a PEO (polyethylene oxide) main chain, comb-like polymers, and crosslinked polymer resins.

[0200] The solid inorganic electrolyte can be broadly classified into sulfide-based solid electrolytes and oxide-based solid electrolytes.

[0201] The sulfide-based solid electrolyte may be a material containing sulfur (S) and having conductivity of metal ions of Group 1 or Group 2 of the periodic table used in secondary batteries, such as Li-PS glass or Li-PS glass ceramic, which has lithium ion conductivity.

[0202] An example of the sulfide-based solid electrolyte may be at least one selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2OP2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS.

[0203] The oxide-based solid electrolyte may be a material containing oxygen (O) and having the conductivity of metal ions from Group 1 or Group 2 of the periodic table used in secondary batteries. For example, LLTO-based compounds, Li6La2CaTa2O 12 , Li6La2ACaNb2O 12 , Li6La2ASrNb2O 12 , Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP-based compounds, LATP-based compounds, LISICON-based compounds, LIPON-based compounds, perovskite-based compounds, NASICO-based compounds, and LLZO-based compounds.

[0204] As described above, a lithium secondary battery including the positive electrode active material stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0205] The external shape of the lithium secondary battery is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0206] According to yet another aspect, a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same may be provided.

[0207] The battery module or the 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.

[0208] The above-mentioned matters will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and are not to be construed as limiting the scope of the present specification.

[0209] Production Example 1. Production of positive electrode active material (1) Example 1 FeOOH and 85 wt% H3PO4 were mixed in a reactor so that the molar ratio of Fe to P was 1:2.55. Distilled water was then added so that the FeOOH and H3PO4 in the slurry accounted for 40 wt% of the total weight. The mixture was then stirred at 60°C for 8 hours to obtain a slurry containing an Fe-P complex. An example of the reaction by which the Fe-P complex is formed can be seen in the following reaction formula 2.

[0210] [Reaction Scheme 2] xFeOOH+yH3PO4→Fe x (PO4) y nH2O Mn3O4 and H2O2 were added to the slurry so that the molar ratio of Fe, Mn, and H2O2 was 4:6:5. The mixture was then stirred at 60°C for an additional 8 hours to obtain a slurry containing an Fe-Mn-P complex. Reaction Scheme 3 below can be used as an example of the reaction that forms the Fe-Mn-P complex.

[0211] [Reaction Scheme 3] xMn3O4+yH3PO4+H2O2→Mn 3x (PO4) z (HPO4) y-z nH2O To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1 to obtain a precipitate. The slurry was then dried using a spray dryer (Toshin Giken, DJE003R).

[0212] The temperature of the furnace in a N2 atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 10 hours while maintaining the temperature at 650°C. After the heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then furnace-cooled and classified to obtain a positive electrode active material containing lithium manganese iron phosphate.

[0213] (2) Example 2 FeOOH and 85 wt% H3PO4 were mixed in a reactor so that the molar ratio of Fe to P was 1:2.55. Distilled water was then added so that the FeOOH and H3PO4 in the slurry were 40 wt% of the total weight. The mixture was then stirred at 60°C for 8 hours to obtain a slurry containing an Fe-P complex.

[0214] Mn3O4 and H2O2 were added to the slurry so that the molar ratio of Fe, Mn, and H2O2 was 4:6:5. After that, the mixture was stirred at 60°C for an additional 8 hours to obtain a slurry containing an Fe-Mn-P complex.

[0215] To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1, and TiO2 as a dopant was added so that Ti was 0.4 mol% based on the total moles of the positive electrode active material, to obtain a precipitate. The slurry was then dried using a spray dryer.

[0216] The mixture was heated in a furnace in a N2 atmosphere at a rate of 2°C / min, and then heat-treated for 10 hours while maintaining the temperature at 650°C. After heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a cathode active material containing lithium manganese iron phosphate.

[0217] (3) Example 3 FeOOH and 85 wt% H3PO4 were mixed in a reactor so that the molar ratio of Fe to P was 1:2.55, and TiO2 was added as a dopant so that Ti was 0.4 mol% based on the total moles of the positive electrode active material. Next, distilled water was added so that the FeOOH and H3PO4 in the slurry were 40 wt% of the total weight. The mixture was then stirred at 60°C for 8 hours to obtain a slurry containing an Fe-P complex.

[0218] Mn3O4 and H2O2 were added to the slurry so that the molar ratio of Fe, Mn, and H2O2 was 4:6:5. After that, the mixture was stirred at 60°C for an additional 8 hours to obtain a slurry containing an Fe-Mn-P complex.

[0219] To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1 to obtain a precipitate, and then the slurry was dried using a spray dryer.

[0220] The mixture was heated in a furnace in a N2 atmosphere at a rate of 2°C / min, and then heat-treated for 10 hours while maintaining the temperature at 650°C. After heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a cathode active material containing lithium manganese iron phosphate.

[0221] (4) Example 4 FeOOH and 85 wt% H3PO4 were mixed in a reactor so that the molar ratio of Fe to P was 1:2.55. Distilled water was then added so that the FeOOH and H3PO4 in the slurry were 40 wt% of the total weight. The mixture was then stirred at 60°C for 8 hours to obtain a slurry containing an Fe-P complex.

[0222] Mn3O4 and H2O2 were added to the slurry so that the molar ratio of Fe, Mn, and H2O2 was 4:6:5, and TiO2 was added as a dopant so that Ti was 0.4 mol% based on the total moles of the positive electrode active material.Then, the mixture was stirred at 60°C for an additional 8 hours to obtain a slurry containing an Fe-Mn-P composite.

[0223] To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1, to obtain a precipitate, which was then dried using a spray dryer.

[0224] The mixture was heated in a furnace in a N2 atmosphere at a rate of 2°C / min, and then heat-treated for 10 hours while maintaining the temperature at 650°C. After heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a cathode active material containing lithium manganese iron phosphate.

[0225] (5) Comparative Example 1 FeOOH was mixed with 85 wt% H3PO4, Mn3O4, and H2O2 in a reactor so that the molar ratio of Fe, P, Mn, and H2O2 was 1:2.55:1.5:1.25. Distilled water was then added so that the concentration of the aforementioned raw materials in the slurry was 40 wt% of the total weight. The mixture was then stirred at 60°C for 24 hours to obtain a slurry.

[0226] To the slurry, Li2CO3 as a lithium source material and sucrose as a carbon source material were added so that the atomic ratio of Fe to Li and C was 1:2.55:1 to obtain a precipitate, which was then dried using a spray dryer.

[0227] The temperature of the furnace in a N2 atmosphere was increased at a rate of 2°C / min, and the mixture was then heat-treated for 10 hours while maintaining the temperature at 650°C. After the heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a positive electrode active material.

[0228] (6) Comparative Example 2 FeOOH and 85 wt% H3PO4 were mixed in a reactor so that the molar ratio of Fe to P was 1:2.55. Next, distilled water was added so that the FeOOH and H3PO4 in the slurry became 40 wt% of the total weight. After that, the mixture was stirred at 60°C for 8 hours to obtain a slurry.

[0229] Mn3O4 was added to the slurry so that the molar ratio of Fe to Mn was 2: 3. After that, the mixture was further stirred at 60°C for 8 hours to obtain a slurry.

[0230] To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1 to obtain a precipitate, and then the slurry was dried using a spray dryer.

[0231] The temperature of the furnace in a N2 atmosphere was increased at a rate of 2°C / min, and the mixture was then heat-treated for 10 hours while maintaining the temperature at 650°C. After the heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a positive electrode active material.

[0232] (7) Comparative Example 3 Mn3O4, 85 wt% H3PO4, and H2O2 were added to a reactor so that the molar ratio of Mn, P, and H2O2 was 1:1.55:1.25. Next, distilled water was added so that the Mn3O4, H3PO4, and H2O2 in the slurry were 40 wt% of the total weight. The mixture was then stirred at 60°C for 8 hours to obtain a slurry.

[0233] To the slurry, FeOOH was added so that the molar ratio of Mn to Fe was 3: 2. After that, the mixture was further stirred at 60°C for 8 hours to obtain a slurry.

[0234] To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1, to obtain a precipitate, which was then dried using a spray dryer.

[0235] The temperature of the furnace in a N2 atmosphere was increased at a rate of 2°C / min, and the mixture was then heat-treated for 10 hours while maintaining the temperature at 650°C. After the heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a positive electrode active material.

[0236] (8) Comparative Example 4 FeOOH, 85 wt% H3PO4, and Li2CO3 as a lithium source were mixed in a reactor so that the molar ratio of Fe, P, and Li was 1:2.55:2.55. Next, distilled water was added so that the FeOOH, H3PO4, and Li2CO3 in the slurry were 40 wt% of the total weight. The mixture was then stirred at 60°C for 8 hours to obtain a slurry containing an Fe-P complex.

[0237] Mn3O4 and H2O2 were added to the slurry so that the molar ratio of Fe, Mn, and H2O2 was 4:6:5. After that, the mixture was further stirred at 60°C for 8 hours to obtain a slurry.

[0238] Glucose as a carbon source material was added to the slurry so that the molar ratio of Fe to C was 1:1 to obtain a precipitate, and then the slurry was dried using a spray dryer.

[0239] The temperature of the furnace in a N2 atmosphere was increased at a rate of 2°C / min, and the mixture was then heat-treated for 10 hours while maintaining the temperature at 650°C. After the heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a positive electrode active material.

[0240] (9) Comparative Example 5 Mn3O4 and 85 wt% H3PO4 were mixed in a reactor so that the molar ratio of Mn to P was 1:1.55. Next, distilled water was added so that the Mn3O4 and H3PO4 in the slurry were 40 wt% of the total weight. After that, the mixture was stirred at 60°C for 8 hours to obtain a slurry.

[0241] To the slurry, FeOOH and H2O2 were added so that the molar ratio of Fe, Mn, and H2O2 was 4:6:5. After that, the mixture was further stirred at 60°C for 8 hours to obtain a slurry.

[0242] To the slurry, Li2CO3 as a lithium source material and glucose as a carbon source material were added so that the molar ratio of Fe, Li, and C was 1:2.55:1, to obtain a precipitate, which was then dried using a spray dryer.

[0243] The temperature of the furnace in a N2 atmosphere was increased at a rate of 2°C / min, and the mixture was then heat-treated for 10 hours while maintaining the temperature at 650°C. After the heat treatment, the mixture was pulverized in a jet mill to a D50 of 1.0 μm or less. The mixture was then cooled and classified to obtain a positive electrode active material.

[0244] Experimental Example 1: Characterization of Positive Electrode Active Material Each of the positive electrode active materials prepared in Preparation Example 1 was subjected to XRD analysis by the Rietveld method to determine the proportions of the lithium manganese iron phosphate (LMFP) phase, Fe2P phase, and Mn2P2O7 phase, and the results are shown in Table 1. SEM images of Example 1 and Comparative Example 4 are shown in Figure 2.

[0245] [Table 1]

[0246] Furthermore, from the XRD results of each positive electrode active material manufactured in Manufacturing Example 1, the unit cell volume (Vc), the length of the a-axis (l a ), the length of the b axis (l b ), the length of the c-axis (l c ) was measured, and A was calculated using the following formulas 1' to 3'. p ~C p After calculating the cell characteristic values, the results are shown in Table 2 below.

[0247] [Formula 1′] A p =V c / l a [Formula 2′] B p =V c / l b [Formula 3′] C p =V c / l c

[0248] [Table 2]

[0249] Referring to Tables 1 and 2, when over-reduced by carbon at high temperatures, Fe2P can be produced.

[0250] Furthermore, when the MP phase is unstable, as in the comparative example, a M2P2O7 phase (M = Fe or Mn) may be generated during sintering due to a decrease in Li reactivity. The M2P2O7 phase acts as a resistor, reducing output characteristics and capacity. Among these, Mn2P2O7 causes Mn elution during charge and discharge, reducing battery stability.

[0251] The cell characteristics can vary depending on the atomic arrangement of Fe and Mn. For example, when the Fe-Mn is homogeneous, or when it is in a Mn-rich phase or an Fe-rich phase, different cell characteristics can be exhibited.

[0252] The positive electrode active material prepared in the example had a thickness of 28.10 Å. 2 ≦A p ≦28.74Å 2 , 62.40Å 2 ≦B p ≦63.10Å 2 , 48.50Å 2 ≦C p ≦49.20Å 2 It can be confirmed that the range is:

[0253] Manufacturing Example 2: Manufacturing of lithium secondary batteries A positive electrode slurry was prepared by dispersing 94 wt% of each positive electrode active material prepared in Preparation Example 1, 3 wt% of artificial graphite, and 3 wt% of PVDF binder in 3.5 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was applied to a 20 μm-thick aluminum (Al) thin film as a positive electrode current collector, dried, and roll-pressed to prepare a positive electrode.

[0254] A coin battery was fabricated according to a commonly known manufacturing process using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and a liquid electrolyte of 1.15 M LiPF in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0255] Experimental Example 2: Evaluation of the characteristics of the positive electrode active material In Production Example 2, a charge-discharge experiment was conducted on the coin battery using an electrochemical analyzer (Toyo, Toscat 3100) at 25°C, a voltage range of 2.0 to 3.65V, and a discharge rate of 0.1 to 5.0C, and the discharge capacity was measured. Charge-discharge was repeated 100 times at a voltage range of 2.0 to 3.65V and a current of 1.0C, and the life characteristics were evaluated as the ratio of the 100th discharge capacity to the initial capacity. A charge-discharge experiment was also conducted at -20°C, a voltage range of 2.0 to 3.65V, and a discharge rate of 0.1C, and the analysis results are shown in Table 3 below.

[0256] [Table 3]

[0257] Referring to Tables 1 to 3 and Figure 2, it can be seen that the positive electrode active materials according to the examples have a uniform distribution of the Fe2P phase, which has excellent electrical and ionic conductivity, and thus have high conductivity and sufficient capacity. On the other hand, the positive electrode active materials according to the comparative examples have a very small amount of the Fe2P phase, which does not improve performance, or as can be seen from Figure 2, the Fe2P phase aggregates outside the particles or is present in an excessive amount, resulting in reduced conductivity and capacity.

[0258] The above describes the examples of this specification, but a person having ordinary knowledge in the technical field may modify and change this specification in various ways by adding, changing, deleting or adding elements, within the scope of the gist of this specification as set forth in the claims, and this can also be said to be included in the scope of rights of this specification.

Claims

1. Contains a lithium complex compound capable of lithium intercalation / deintercalation, the lithium composite compound contains Fe and Mn; the lithium composite compound includes a plurality of particulate materials, Fe in at least a portion of the particulate matter ２ A positive electrode active material for a lithium secondary battery, in which a P phase exists.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the particulate matter has an average particle size of 0.01 to 5 μm.

3. The total Fe contained in the positive electrode active material ２ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein 50% by weight or more of the P phase is located inside the particulate matter.

4. The Fe ２ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the P phase is 0.2 to 0.9 wt % based on 100 wt % of the lithium manganese iron phosphate phase contained in the lithium composite compound.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the particulate matter is obtained by pulverizing a finely pulverized lithium composite compound including: a first region in which Fe is present from a center to a surface region but Mn is not present; a second region in which a mixed structure of Fe and Mn is present; and a third region in which Mn is present but Fe is not present.

6. In the finely pulverized lithium composite compound, the Fe ２ The positive electrode active material for a lithium secondary battery according to claim 5 , wherein a P phase is present in at least a part of the first region and the second region.

7. 6. The positive electrode active material for a lithium secondary battery according to claim 5, wherein the total thickness of the second region and the third region is 0.5 to 2.0 μm.

8. In the particulate matter, Fe ２ P ２ O ７ phase and Mn ２ P ２ O ７ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the total content of the phases is 2.5% by weight or less based on 100% by weight of the lithium manganese iron phosphate phase contained in the lithium composite compound.

9. In the particulate matter, Mn ２ P ２ O ７ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the phase is 2.5% by weight or less based on 100% by weight of the lithium manganese iron phosphate phase contained in the lithium composite compound.

10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the particulate matter satisfies at least one of the conditions represented by the following formulas 1 to 3: [Formula 1] 28.10 years ２ ≦A ｐ ≦28.74Å ２ [Formula 2] 62.40A ２ ≦B ｐ ≦63.10Å ２ [Formula 3] 48.50Å ２ ≦C ｐ ≦49.20Å ２ In the formulas 1 to 3, the A ｐ ~ Said C ｐ can be calculated using the following formulas 1' to 3': [Formula 1′] A ｐ =V ｃ / l ａ [Formula 2′] B ｐ =V ｃ / l ｂ [Formula 3'] C ｐ =V ｃ / l ｃ In the formulas 1' to 3', The V ｃ is the unit cell volume of the particulate matter, Said l ａ , l ｂ , l ｃ respectively mean the diameters of the a-axis, b-axis, and c-axis of the particulate material.

11. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium composite compound is represented by the following Chemical Formula 1: [Chemical formula 1] Li ｐ Fe １－ｘ－ｙ Mn ｘ A ｙ A′ ｚ P １－ｚ O ｗ In the above formula, A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn and Zr; A' is at least one selected from the group consisting of C, Si, S, N, B, F, Cl and I, and 0.5≦p≦1.5, 0<x<1, 0≦y<1, 0≦z<1, 0<w≦4.

12. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein at least a portion of the particulate material has an amorphous carbon coating layer having a thickness of 1 to 500 nm formed on at least a portion of the surface thereof.

13. A positive electrode comprising the positive electrode active material according to claim 1 .

14. A lithium secondary battery using the positive electrode according to claim 13.

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