Positive electrode active material, and positive electrode and lithium secondary battery comprising same

Abstract

The present specification relates to: a positive electrode active material for a secondary battery, the positive electrode active material including a lithium iron phosphate manganese-based compound, wherein the voltage at SOC 90% of a lithium secondary battery including a positive electrode including the positive electrode active material is 4.11 V or less, and the value of (a) in Equation 1 indicating the slope between SOC 90% and SOC 100% is 0.014 or more; and a positive electrode and a lithium secondary battery which comprise the positive electrode active material.

Description

Cathode active material, a cathode including the same, and a lithium secondary battery

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0133217 filed September 30, 2024, and all contents disclosed in the literature of said Korean patent applications are incorporated herein as part of this specification.

[0003] This specification relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery.

[0004] Recently, there have been attempts to apply lithium manganese iron phosphate (LMFP) to electric vehicles (EVs), energy storage systems (ESS), portable electronic devices, etc.

[0005] Lithium iron phosphate manganese-based compounds (hereinafter, LMFP-based compounds) are compounds in which manganese is doped into conventional lithium iron phosphate compounds (hereinafter, LFP-based compounds), and have the advantage of having a higher energy density and producing a higher output compared to conventional LFP-based compounds.

[0006] In addition, LMFP-based compounds have a low risk of explosion, can be applied to applications requiring high stability, and have a long lifespan.

[0007] Despite the aforementioned advantages, LMFP-based compounds have inherently low electrical conductivity and low energy density compared to nickel-cobalt-manganese compounds (NCM) or lithium-cobalt oxide (LCO).

[0008] To solve the above problem, there have been attempts to improve the properties, such as coating carbon (C) on LMFP-based compounds, but the problem has not been fundamentally solved.

[0009] In order to solve the inherent problems of LMFP-based compounds, it is expected that further improvement and research on crystal structure and properties will be necessary.

[0010] (Prior Art Literature)

[0011] Patent Document Korean Published Patent Application No. 2008-0100031

[0012] An embodiment of the present invention provides a positive electrode active material having improved charge and discharge efficiency and excellent efficiency in rapid charging when applied to a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery.

[0013] One embodiment of the present invention is a positive electrode active material for a secondary battery comprising a lithium iron phosphate manganese-based compound,

[0014] For a lithium secondary battery comprising a positive electrode containing the above positive electrode active material, the voltage at SOC 90% is 4.11V or less, and

[0015] A positive electrode active material for a secondary battery is provided, wherein the value of (a) of the following mathematical formula 1, which represents a slope between SOC 90% and SOC 100%, is 0.014 or higher.

[0016] [Mathematical Formula 1]

[0017] (a) = [(Voltage at SOC 100%) - (Voltage at SOC 90%)] / 10

[0018] Another embodiment of the present invention provides a positive electrode comprising the positive electrode active material described above.

[0019] Another embodiment of the present invention provides a lithium secondary battery comprising the anode described above.

[0020] When a positive electrode active material according to one embodiment of the present invention is applied to a lithium secondary battery, the charge and discharge efficiency is improved.

[0021] When a positive electrode active material according to one embodiment of the present invention is applied to a lithium secondary battery, it has the effect of excellent efficiency in rapid charging.

[0022] Figure 1 is a graph showing the change in potential during charging and discharging for a lithium secondary battery containing the positive active material prepared in the example and comparative example in Experimental Example 1.

[0023] Figure 2 is a graph of the graph in Figure 1 with the x-axis normalized to represent the State of Charge (SOC).

[0024] Figure 3 is a graph of the graph in Figure 2 enlarged to the range 85% < x < 100% and 3.7V < y < 4.3V.

[0025] Figure 4 is a graph showing the change in potential during charging for a lithium secondary battery containing the positive active material prepared in the example and comparative example in Experimental Example 2.

[0026] According to one embodiment of the present invention,

[0027] A positive electrode active material for a secondary battery comprising a lithium iron phosphate manganese-based compound,

[0028] For a lithium secondary battery comprising a positive electrode containing the above positive electrode active material, the voltage at SOC 90% is 4.11V or less, and

[0029] A positive electrode active material for a secondary battery may be provided, wherein the value of (a) of the following mathematical formula 1, which represents a slope between SOC 90% and SOC 100%, is 0.014 or greater:

[0030] [Mathematical Formula 1]

[0031] (a) = [(Voltage at SOC 100%)-(Voltage at SOC 90%)] / 10.

[0032] According to another embodiment of the present invention, a positive electrode comprising the positive electrode active material may be provided.

[0033] According to another embodiment of the present invention, a lithium secondary battery comprising the positive electrode may be provided.

[0034] Unless otherwise defined in this specification, all technical and scientific terms are used merely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the presence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0035] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0036] The technical terms used in this specification are intended merely to refer to specific embodiments and are not intended to limit the invention. Furthermore, the singular forms used herein include plural forms unless phrases clearly indicate otherwise.

[0037] The present invention will be described in detail below.

[0038] One embodiment of the present invention is a positive electrode active material for a secondary battery comprising a lithium iron phosphate manganese-based compound,

[0039] For a lithium secondary battery comprising a positive electrode containing the above positive electrode active material, the voltage at SOC 90% is 4.11V or less, and

[0040] A positive electrode active material for a secondary battery is provided, wherein the value of (a) of the following mathematical formula 1, which represents a slope between SOC 90% and SOC 100%, is 0.014 or higher.

[0041] [Mathematical Formula 1]

[0042] (a) = [(Voltage at SOC 100%) - (Voltage at SOC 90%)] / 10

[0043] When a positive electrode active material is applied to a lithium secondary battery to perform charging and discharging operations, the range of 90% to 100% SOC shows a distinct difference from other ranges depending on the State of Charge (SOC). The difference in output values ​​in the high SOC range (i.e., the range of 90% to 100% SOC) can serve as an indicator of rapid charging on the battery as an important variable for determining the overvoltage received by the positive electrode active material during the charging process.

[0044] Specifically, the voltage at 90% SOC is the voltage in the range where the oxidation number of manganese changes. If the voltage at this time exceeds a certain value, a large overvoltage is applied to the redox reaction of manganese, making it impossible to form a sufficiently stable phase. As the charging rate increases, this phenomenon accelerates, and if rapid charging is performed, degradation may be accelerated.

[0045] In addition, the difference in voltage in a specific SOC range (SOC 90% to SOC 100% range), that is, the slope value between SOC 90% and SOC 100%, such as the value of (a) in Equation 1 above, may indicate structural stability during rapid charging, and if the slope value between SOC 90% and SOC 100% is excessively low, it may affect the lithium-ion capacity during high-rate charging, thereby reducing the stability of the crystal structure.

[0046] In summary, the 'voltage at 90% SOC' and the 'slope between 90% SOC and 100% SOC' must be closely balanced to optimize the performance of the lithium secondary battery.

[0047] A positive electrode active material according to one embodiment of the present invention can improve safety while maintaining stable output by adjusting the value of (a) of Equation 1, which represents the slope between SOC 90% and SOC 100%, to 0.014 or higher for a lithium secondary battery including a positive electrode containing the positive electrode active material, such that the voltage at SOC 90% is 4.11V or lower. When the positive electrode active material having the above characteristics is applied to a lithium secondary battery, structural stability is secured during charging of the battery, thereby mitigating overvoltage, and furthermore, charging characteristics can be secured through stable phase change during rapid charging.

[0048] A positive electrode active material in which the voltage at 90% SOC and the slope value between 90% SOC and 100% SOC described above satisfy a predetermined numerical range can be achieved by changing the physical or chemical properties of a lithium iron phosphate manganese-based compound.

[0049] Specifically, this can be achieved by changing the type and content of the carbon source, controlling the average particle size or average crystal grain size, controlling the crystal structure to an olivine structure, or changing the Fe / Mn composition ratio of the lithium iron phosphate manganese-based compound. Alternatively, it can be achieved by doping with elements other than lithium, phosphate, iron, or manganese, changing the calcination temperature or time, performing a pre-calcination step before calcination, or changing the calcination environment.

[0050] In particular, this can be achieved by changing the type and content of the carbon source, changing the Fe / Mn composition ratio of the lithium iron phosphate manganese-based compound, controlling the appropriate particle size and specific surface area, and controlling the calcination temperature and doping elements.

[0051] A positive electrode active material for a secondary battery comprising a lithium iron phosphate manganese-based compound according to one embodiment of the present invention may have a voltage at 90% SOC of 4.11V or less, 4.10V or less, 4.09V or less, 4.08V or less, 4.07V or less, 4.06V or less, or 4.05V or less for a lithium secondary battery comprising a positive electrode comprising the positive electrode active material.

[0052] Within the above numerical range, stable voltage maintenance is possible during charging operation, so when the above positive active material is applied to a lithium secondary battery, the charging overvoltage of the battery is mitigated and excellent charging characteristics can be achieved through stable phase change even during rapid charging.

[0053] The lower limit of the voltage at 90% SOC is not specifically limited, but may be 3.4V or higher, 3.5V or higher, 3.6V or higher, 3.7V or higher, 3.8V or higher, 3.9V or higher, or 4.0V or higher.

[0054] The value of (a) in the following mathematical formula 1, which represents a slope between SOC 90% and SOC 100%, may be 0.014 or higher, 0.015 or higher, 0.016 or higher, 0.017 or higher, or 0.018 or higher.

[0055] [Mathematical Formula 1]

[0056] (a) = [(Voltage at SOC 100%) - (Voltage at SOC 90%)] / 10

[0057] Within the above numerical range, the stability of the crystal structure is increased, so when the above positive active material is applied to a lithium secondary battery, the rapid charging efficiency of the battery is improved and the degradation of battery performance can be prevented.

[0058] The upper limit of the value of (a) in the above mathematical formula 1 is not specifically limited, but may be 0.03 or less, 0.029 or less, 0.028 or less, 0.027 or less, or 0.026 or less.

[0059] The voltage values ​​at SOC 90% and SOC 100% of the present invention are values ​​measured by manufacturing a lithium secondary battery containing a positive electrode containing the positive electrode active material as described in the manufacturing example below.

[0060] In one embodiment of the present invention, the average particle size (D50) of the lithium iron phosphate manganese-based compound may be 0.2 μm or more and 1 μm or less. Specifically, it may be 0.2 μm or more, 0.25 μm or more, or 0.3 μm or more, and 1 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less.

[0061] Within the above numerical range, by maintaining the stress within the lithium iron phosphate manganese-based compound crystal at a constant level, the voltage value at 90% SOC is prevented from becoming excessively large, and the slope value between 90% SOC and 100% SOC can be controlled to a constant level. In addition, the rolling density is improved, which has the effect of improving electrode processability, and the surface area per unit mass is increased, which is advantageous for the insertion / extraction reaction of lithium ions, thereby improving the charge / discharge speed.

[0062] In the present specification, the average particle size (D50) refers to the overall size of individual particles of a lithium iron phosphate manganese-based compound and may include one or more crystal grains. The average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume distribution in the particle size distribution curve (graph curve of the particle size distribution). The average particle size can be measured by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Mastersizer 3000, Malvern), measuring the difference in diffraction patterns according to particle size as the particles pass through a laser beam to calculate the particle size distribution, and calculating the particle diameter at the point where it is 50% of the cumulative volume distribution according to particle size in the measuring device.

[0063] In one embodiment of the present invention, the average grain size of the lithium iron phosphate manganese-based compound may be 100 nm or more and 180 nm or less. Specifically, it may be 100 nm or more, 102 nm or more, or 104 nm or more, and 180 nm or less, 178 nm or less, or 175 nm or less.

[0064] Within the above numerical range, by maintaining the stress within the lithium iron phosphate manganese-based compound crystal at a constant level, the voltage value at SOC 90% is prevented from becoming excessively large, and the slope value between SOC 90% and SOC 100% can be controlled to a constant level. In addition, the mechanical strength of the material is improved, thereby maintaining the stability of the electrode structure even during repeated charging and discharging processes.

[0065] In this specification, the average grain size refers to the size of a region having a well-aligned atomic arrangement within a single crystal. This region is named as a single grain and forms a boundary with other grains. The average grain size can be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays. Specifically, XRD data of the synthesized cathode active material can be obtained using a Bruker D8 XRD instrument (Cu-target, voltage: 45kV, current: 40mA, 2θ: 10° to 80°), and structural analysis of the obtained data can be performed using the Rietveld refining method, a general structural analysis method, using Malvern Panalytical's Highscore software.

[0066] The aforementioned Rietveld refining method is a technique that obtains a diffraction pattern calculated from an initial structural model of the crystal structure of the materials and compares it with the measured diffraction pattern of the actual synthesized material. It involves introducing various structure-related factors and iteratively adjusting their values ​​until the two patterns match well. This method assesses validity based on the difference between the calculated and measured patterns and repeats the process until the difference between the two patterns is minimized. Among the structure-related factors that can be introduced in this process, crystal size can be derived using the full width at half maximum (FWHM) of the peaks of each crystal plane appearing in the measured diffraction pattern.

[0067] In one embodiment of the present invention, the lithium iron phosphate manganese-based compound may include an olivine structure. In this case, since it has strong PO bonds, it can prevent the crystal structure from collapsing during the charging and discharging process, thereby improving high-temperature stability. The olivine structure can be confirmed using X-ray diffraction (XRD) analysis.

[0068] The above lithium iron phosphate manganese-based compound can be represented by the following chemical formula 1.

[0069] [Chemical Formula 1]

[0070] Li 1+y1 Fe a Mn b M1 c (PO4)

[0071] In the above chemical formula 1,

[0072] The above M1 is one or more elements selected from the group consisting of Ni, Co, Mg, Nb, Mo, W, Ti, Sr, V, Zr, and Zn, and

[0073] -0.1≤y1<0.1, 0 <a<1, 0<b≤0.8, 0≤c≤0.5 및 a+b+c=1이다.

[0074] In the present specification, a, b, and c of Chemical Formula 1 may represent the molar content of each component. Specifically, they may represent the molar content of the elements other than lithium (Li) and phosphoric acid (PO4) in the lithium iron phosphate manganese compound represented by Chemical Formula 1. For example, if a and b are 0.5 and c is 0, the molar content of Fe and Mn, respectively, and the molar content of M1 may be 50 mol% and 0 mol%, based on the total moles of the elements (Fe, Mn, M1) other than lithium (Li) and phosphoric acid (PO4) in the lithium iron phosphate manganese compound represented by Chemical Formula 1. Meanwhile, if M1 is two or more elements, c may be the molar content calculated based on the total moles of the two or more elements.

[0075] The above y1 may be 0≤y1≤0.1 or 0≤y1≤0.03. When y1 satisfies the above range, structural stability may be improved.

[0076] The above a may be 0.1 or more and 0.9 or less, 0.15 or more and 0.85 or less, or 0.2 or more and 0.8 or less. In particular, it may be 0.3 or more and 0.4 or less, or 0.6 or more and 0.8 or less. Crystal structure stability may be improved within the above numerical range.

[0077] The above b may be 0.8 or less, less than 0.7, less than 0.6, or less than 0.5.

[0078] Preferably, it may be 0.1 or more and less than 0.5, 0.25 or more and less than 0.45, or 0.3 or more and less than 0.4. Within the above numerical range, the ionic conductivity of the electrode is not reduced and high kinetics are maintained, so that the crystal structure can be stably maintained during the operation of the battery.

[0079] The above c may be 0 or more and 0.5 or less, 0 or more and 0.1 or less, or 0 or more and 0.01 or less. By improving electrical conductivity within the above numerical range, charge and discharge efficiency can be improved when applied to a battery, and the lattice structure can be stabilized so that the movement of lithium ions can be smooth.

[0080] The ratio of b to a may be 10:90 to 80:20. Preferably, it may be 10:90 to 50:50, or 20:80 to 40:60. Within the above numerical range, stability and high charge / discharge capacity can be secured through iron, and the formation of unstable phases through manganese can be suppressed.

[0081] The above M1 refers to an element doped into a lithium iron phosphate manganese-based compound and can be used to obtain effects such as electrical conductivity and structural stability.

[0082] The above M1 may be one or more elements selected from the group consisting of Ni, Co, Mg, Nb, Mo, W, Ti, Sr, V, Zr, and Zn. Meanwhile, other elements may be included in addition to the elements described above to improve chemical or physical performance, and non-metallic elements such as F, S, and N may also be included to improve electrochemical performance.

[0083] The above M1 may be Mg, Ti, V, or a combination thereof. The above elements are elements that are highly effective in improving lithium ion mobility characteristics or ensuring structural stability, and the effect can be further enhanced depending on the combination used. Specifically, the above M1 may be one or more selected from the group consisting of Mg, Ti, and V.

[0084] When Mg is used as the above M1, the charge / discharge efficiency can be improved by enhancing the lithium ion mobility characteristics, and stability can be improved by facilitating the control of particle growth of the lithium iron phosphate manganese-based compound.

[0085] When using Ti as the above M1, thermal stability can be improved by improving structural stability.

[0086] When using V as the above M1, electrical conductivity is improved, which can improve power density when applied to a lithium secondary battery.

[0087] A carbon coating layer containing carbon may be provided on the above-mentioned lithium iron phosphate manganese-based compound. By including carbon in the carbon coating layer, the electrical conductivity of the positive electrode active material can be improved.

[0088] The carbon content included in the carbon coating layer may be 1% by weight or more and 3% by weight or less based on the total weight of the positive electrode active material. Preferably, it may be 1% by weight or more, 1.1% by weight or more, 1.2% by weight or more, 1.3% by weight or more, 1.4% by weight or more, 1.5% by weight or more, 1.6% by weight or more, 1.7% by weight or more, 1.8% by weight or more, 1.9% by weight or more, or 2% by weight or more, and 2.1% by weight or less, 2.2% by weight or less, 2.3% by weight or less, 2.4% by weight or less, 2.5% by weight or less, 2.6% by weight or less, 2.7% by weight or less, 2.8% by weight or less, 2.9% by weight or less, or 3% by weight or less. Within the above numerical range, the carbon coating layer may not act as a resistor while improving the electron conductivity of the positive electrode active material.

[0089] The thickness of the carbon coating layer may be 10 nm or more and 50 nm or less. Preferably, it may be 10 nm or more and 40 nm or less, or 10 nm or more and 30 nm or less. Within the above numerical range, the carbon coating layer may not act as a resistor while improving the electronic conductivity of the positive electrode active material.

[0090] For a lithium secondary battery including a positive electrode containing the above positive electrode active material, the 0.1C discharge capacity may be 130 mAh / g or more, 131 mAh / g or more, or 132 mAh / g or more. Within the above numerical range, it can be determined that crystals of the olivine structure have formed, stable charge and discharge capacity is exhibited, and the olivine crystal structure can be stably maintained even during the rapid charging process.

[0091] The upper limit of the above 0.1C discharge capacity is not specifically limited, but may be 170 mAh / g or less, 168 mAh / g or less, 165 mAh / g or less, 163 mAh / g or less, 162 mAh / g or less, 161 mAh / g or less, or 160 mAh / g or less.

[0092] For a lithium secondary battery containing a cathode containing the above-mentioned cathode active material, the 0.1C charge capacity is expressed by dividing it into the total charge capacity and the CC (Constant Current) charge capacity. The larger the CC charge capacity, the lower the capacity secured through CV (Constant Voltage) charging, which is a relatively unstable charging state. A cathode active material with a higher proportion of CC capacity can be judged as a cathode active material in which the movement path of lithium ions is sufficiently secured. Therefore, it has the effect of ensuring the stability of the battery by maintaining a relatively stable structure even in the charged state.

[0093] For a lithium secondary battery comprising a positive electrode containing the above positive electrode active material, the 0.1C charge capacity may be 150 mAh / g or more, 151 mAh / g or more, or 152 mAh / g or more. The upper limit is not specifically limited, but may be 170 mAh / g or less, 168 mAh / g or less, 165 mAh / g or less, 163 mAh / g or less, 162 mAh / g or less, 161 mAh / g or less, or 160 mAh / g or less.

[0094] For a lithium secondary battery comprising a positive electrode containing the above positive electrode active material, the 0.1C CC charge capacity may be 145 mAh / g or more, 147 mAh / g or more, or 150 mAh / g or more. The upper limit is not specifically limited, but may be 170 mAh / g or less, 168 mAh / g or less, 165 mAh / g or less, 163 mAh / g or less, 162 mAh / g or less, 161 mAh / g or less, or 160 mAh / g or less.

[0095] For a lithium secondary battery including a cathode containing the above-mentioned cathode active material, the 2C CC charging capacity may be 120 mAh / g or more, 122 mAh / g or more, or 125 mAh / g or more. The above-mentioned cathode active material having a high 2C CC charging capacity means that it is a cathode active material with a structure having high lithium ion conductivity and a well-secured lithium ion transport pathway. This means that such a cathode active material is capable of operating stably in rapid charging, which is the most important factor in actual battery operation, as it can be charged while maintaining structural stability even at high rates.

[0096] The upper limit of the above 2C CC charging capacity is not specifically limited, but may be 150 mAh / g or less, 148 mAh / g or less, 145 mAh / g or less, 143 mAh / g or less, 142 mAh / g or less, 141 mAh / g or less, or 140 mAh / g or less.

[0097] The above charging capacity and discharging capacity may be values ​​measured and calculated when the above positive active material is applied to a half-cell.

[0098] The above half-cell is an electrochemical cell used to evaluate the electrochemical performance of electrode materials.

[0099] The above half cell may include an electrode; a reference electrode; an electrolyte; and a separator.

[0100] The electrode of the above half-cell may be an anode or a cathode. The electrode is determined by the type of material to be evaluated according to the purpose of the half-cell, and in the present invention, it may be an anode.

[0101] The reference electrode of the above half-cell may include lithium metal. The lithium metal acts as a source of lithium ions.

[0102] One embodiment of the present invention provides a method for manufacturing the anode active material described above.

[0103] The above method for manufacturing the positive electrode active material includes the step of mixing raw materials to prepare a mixture; and the step of calcining the mixture.

[0104] The method for manufacturing the above positive active material includes the step of grinding the mixture; the step of drying the mixture or a combination thereof.

[0105] The step of preparing the above mixture may include the step of mixing the cathode material raw materials.

[0106] The above-mentioned cathode material raw materials may include lithium-containing raw materials, manganese-containing raw materials, iron-containing raw materials, and phosphoric acid-containing raw materials.

[0107] The above lithium-containing raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH2PO4), and lithium nitrate (LiNO3). , It may be lithium acetate (CH3COOLi) and Li2(COO)2 or a combination thereof. Specifically, it may be lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH2PO4), or a combination thereof.

[0108] The above manganese-containing raw material may be at least one selected from the group consisting of MnSO4, MnPO3, MnPO4, MnCO3, MnFeO, Mn2O3, MnO2, Mn3O4, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citric acid, manganese fatty acid salts, oxyhydroxides, and manganese chloride halides, and one or more of these may be used.

[0109] The iron-containing raw material mentioned above may be iron sulfate (FeSO4), iron oxide (FeO), iron oxalate (FeC2O4), iron phosphate (FePO4), ferric phosphate {Fe3(PO4)2}, or a combination thereof. Preferably, iron phosphate may be used. In this case, chemical stability is high, and since the compound itself contains phosphoric acid, the use of additional phosphates can be reduced.

[0110] The above-mentioned phosphoric acid-containing raw materials may include lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), ammonium dihydrogen phosphate ((NH4)2HPO4), ammonium monohydrogen phosphate (NH4H2PO4), phosphoric acid (H3PO4), etc., and these may be used alone or in a mixture of two or more. Preferably, lithium dihydrogen phosphate (LiH2PO4) or ammonium monohydrogen phosphate (NH4H2PO4) may be used. In this case, chemical reaction byproducts can be reduced and the pH of the reaction system can be stabilized.

[0111] The above mixture may include raw materials containing doping elements.

[0112] The above-mentioned raw material containing doping elements may include one or more doping elements (M1) selected from the group consisting of Ni, Co, Mg, Nb, Mo, W, Ti, Sr, V, Zr, and Zn. Meanwhile, to improve chemical or physical performance, other elements other than those described above may be included, and to improve electrochemical performance, non-metallic elements such as F, S, and N may also be included.

[0113] The above-mentioned raw material containing the doping element may be an oxide, chloride, nitrate, sulfate compound, oxalate compound, or a combination thereof of the doping element.

[0114] When the doping element is vanadium (V), the raw material containing the doping element may be vanadium oxide. The vanadium oxide may be VO2, V2O3, V2O5, or a combination thereof. Preferably, it may be V2O5. V2O5 has high reactivity, which can improve doping efficiency, and since it has excellent heat resistance, it has the effect of stably maintaining the crystal structure of the lithium iron phosphate manganese-based compound during the calcination process.

[0115] When the doping element is magnesium (Mg), the raw material containing the doping element may be magnesium oxide (MgO), magnesium hydroxide {Mg(OH)2}, magnesium chloride (MgCl2), or a combination thereof. Preferably, magnesium oxide may be used. Magnesium oxide has excellent thermal stability, so it is maintained without decomposing even during high-temperature heat treatment, and has excellent dispersibility, which has the effect of excellent doping efficiency.

[0116] When the doping element is zirconium (Zr), the raw material containing the doping element may be zirconium oxide (ZrO2), zirconium chloride (ZrCl4), or a combination thereof. Preferably, zirconium oxide may be used. Zirconium oxide has excellent thermal stability, so it is maintained without decomposing even during high-temperature heat treatment, and it has excellent reactivity and doping efficiency.

[0117] When the above doping element is titanium (Ti), the raw material containing the above doping element may be titanium oxide (TiO2). Titanium oxide has excellent thermal stability, so it is maintained without decomposing even during high-temperature heat treatment, and has the effect of excellent reactivity.

[0118] The above mixture may include a carbon source. The carbon source may form a carbon coating layer by being carbonized during the calcination step of the mixture.

[0119] The carbon source may be sucrose, glucose, polyethylene glycol, polyvinyl alcohol, polyvinyl acetate, or a combination thereof. Preferably, it may be sucrose, glucose, or polyethylene glycol. In this case, it has the effect of easily thermally decomposing even at low temperatures, thereby facilitating the formation of a carbon coating layer. Additionally, since sucrose is uniformly carbonized upon heat treatment and glucose is well soluble in water and easily adsorbed onto a lithium iron-manganese phosphate compound, the carbon coating is uniformly formed and the microstructure is easy to control.

[0120] The content of the carbon source may be 3 to 15 parts by weight per 100 parts by weight of the total amount of the cathode material raw materials. Preferably, it may be 5 to 10 parts by weight. Within the above numerical range, a uniform carbon coating is possible, and the energy density of the cathode material can be improved.

[0121] The solid content of the above mixture may be 10 wt% to 40 wt%. Preferably, it may be 15 wt% to 35 wt% or 25 wt% to 35 wt%. Within the above numerical range, the processability can be improved by preventing an increase in viscosity, and a uniform carbon coating can be achieved. The solid content of the above mixture can be achieved by adding a solvent such as water (H2O).

[0122] The calcination temperature of the step of calcining the above mixture may be 500°C to 850°C. Preferably, it may be 600°C to 830°C or 680°C to 780°C. Within the above numerical range, the raw materials can react sufficiently to stably form a crystal structure, and excessive particle growth can be prevented. That is, under the above temperature conditions, the electrochemical properties and crystallinity of the positive active material can be improved.

[0123] The firing time of the step of firing the above mixture may be 1 hour to 50 hours. Preferably, it may be 2 hours to 20 hours or 5 hours to 10 hours. Within the above numerical range, the effect of controlling the firing temperature described above can be secured without setting the firing temperature excessively.

[0124] The step of calcining the above mixture can be performed in a reducing atmosphere. In this case, the oxidation state of the iron ions can be easily controlled to secure electrochemical properties due to the iron ions.

[0125] The step of calcining the mixture may be performed under inert gas conditions. The inert gas may be argon (Ar), nitrogen (N2), or a combination thereof. The inert gas conditions may mean that the molar content of the inert gas in the space where the mixture is calcined is 70 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more. The remainder of the gas may be hydrogen (H2).

[0126] The step of calcining the above mixture can be performed under pressure conditions.

[0127] The step of calcining the above mixture can be performed in a furnace.

[0128] The method for manufacturing the above-described positive active material may include a pre-calcination step of the mixture prior to the step of calcining the mixture. The calcination temperature of the pre-calcination step may be lower than the calcination temperature of the calcination step. The pre-calcination step has the effect of promoting the reaction of precursors, removing impurities, and helping a clear crystalline phase to appear in the calcination step by allowing a basic crystalline phase to be formed in advance.

[0129] The pre-calcination temperature of the step of pre-calcining the above mixture may be 100°C to 490°C. Preferably, it may be 200°C to 400°C or 300°C to 450°C. Within the above numerical range, the precursor may start the reaction, but prevent the formation of a complete crystalline phase.

[0130] The pre-calcination time of the step of pre-calcining the above mixture may be 1 hour to 20 hours. Preferably, it may be 2 hours to 10 hours or 2 hours to 5 hours. Within the above numerical range, the precursor may be induced to start a reaction while sufficiently removing impurities.

[0131] The step of pre-calcining the mixture may be performed under inert gas conditions. The inert gas may be argon (Ar), nitrogen (N2), or a combination thereof. The inert gas conditions may have a molar content of inert gas in the space where the mixture is calcined of 90 mol% or more, 95 mol% or more, 99 mol% or more, or 100 mol%. In this case, unnecessary oxidation reactions can be prevented.

[0132] The step of grinding the above mixture is a step that breaks up inter-particle necking and controls particle size. In addition, it can maintain a uniform particle size distribution and prevent particles from aggregating with each other.

[0133] The step of grinding the above mixture may use bead milling, ball milling, jet milling, ultrasonic milling, or vibratory milling, or a combination thereof.

[0134] The step of grinding the mixture can be performed prior to the step of calcining the mixture. By controlling the particle size through grinding before calcination, the reaction rate for calcination is increased, thereby allowing the formation and growth of the crystal structure to be performed stably.

[0135] After the step of calcining the above mixture, a step of secondary grinding the mixture can be performed. At this time, the particle size of the final product can be finely controlled.

[0136] The step of drying the above mixture is a step that removes moisture present in the mixture to ensure excellent quality in subsequent processes such as grinding or calcination.

[0137] The step of drying the mixture may be performed before the step of grinding the mixture; after the step of grinding the mixture; before the step of calcining the mixture; or in a combination thereof.

[0138] If the step of drying the mixture is performed before the step of grinding the mixture, the mixture is easily broken down, which has the effect of improving grinding efficiency.

[0139] If the step of drying the mixture is performed after the step of grinding the mixture, moisture introduced during the grinding step can be removed.

[0140] If the step of drying the mixture is performed prior to the step of calcining the mixture, moisture or impurities within the material are removed, thereby improving reactivity during the calcination process and enhancing crystallinity. If moisture or impurities are not sufficiently removed before calcination, pores formed by them may occur, resulting in defects in the crystal structure.

[0141] The step of drying the above mixture can be performed in a temperature range of 50°C to 300°C. Preferably, it can be performed in a temperature range of 80°C to 250°C or 90°C to 230°C. In the above numerical ranges, moisture can be sufficiently removed and thermal deformation of the material can be prevented.

[0142] The step of drying the above mixture can be performed for 10 minutes to 10 hours. Preferably, it can be performed for 30 minutes to 8 hours or 1 hour to 5 hours. Within the above numerical ranges, moisture can be sufficiently removed and thermal deformation of the material can be prevented.

[0143] The step of drying the above mixture may be oven drying, vacuum drying, spray drying, or a combination thereof. Preferably, spray drying can be used to enable simple and mass production.

[0144] One embodiment of the present invention provides a positive electrode comprising the positive electrode active material described above.

[0145] The above-described positive electrode comprises a positive electrode active material layer containing the positive electrode active material described above. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material. Since the positive electrode active material has been described above, a detailed explanation is omitted, and only the remaining components are described in detail below.

[0146] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0147] The above positive active material layer may include a conductive material and a binder together with the positive active material. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity characteristics within this range.

[0148] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0149] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1% to 15% by weight based on the total weight of the positive active material layer.

[0150] The above binder may have a molecular weight (Mw) of 20,000 g / mol or more and 1,200,000 g / mol or less.

[0151] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the above-described anode active material and, optionally, a binder and a conductive material in a solvent, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above. Alternatively, the above-described anode may be manufactured by casting the composition for forming an anode active material layer onto a separate support, and then laminating the film obtained by peeling from the support onto an anode current collector.

[0152] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0153] One embodiment of the present invention may manufacture an electrochemical device including the anode. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0154] One embodiment of the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte,

[0155] The above-mentioned positive electrode comprises a positive electrode active material for a secondary battery comprising a lithium iron phosphate manganese-based compound, and

[0156] The voltage at 90% SOC is 4.11V or less, and

[0157] A lithium secondary battery is provided in which the value of (a) of the following mathematical formula 1, which represents a slope between SOC 90% and SOC 100%, is 0.014 or higher.

[0158] [Mathematical Formula 1]

[0159] (a) = [(Voltage at SOC 100%) - (Voltage at SOC 90%)] / 10

[0160] One embodiment of the present invention provides a lithium secondary battery comprising the anode described above.

[0161] Specifically, the above lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is identical to the one described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0162] In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0163] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0164] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0165] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0166] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ β Examples include metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum and coal tar pitch-derived cokes.

[0167] The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0168] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0169] The above 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% by weight or less, specifically 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0170] The above-mentioned cathode active material layer may be manufactured by applying a composition for forming a cathode active material layer, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector and drying it, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto a cathode current collector.

[0171] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is commonly used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0172] Examples of the above electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0173] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0174] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0175] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt 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. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, specifically 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0176] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10 weight%, specifically 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0177] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent lifespan and capacity characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0178] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0179] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0180] There are no specific restrictions on the external shape of the above lithium secondary battery, but it may be a cylindrical type using a can, a prismatic type, a pouch type, or a coin type.

[0181] The above lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0182] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0183] <Examples and Comparative Examples>

[0184] Example 1

[0185] Raw material mixing and particle size control step

[0186] Li2CO3, MnCO3, FePO4, NH4H2PO4, and V2O3 were mixed so that the molar ratio of Li:Mn:Fe:V:PO4 was 1.02:0.297:0.693:0.01:1. Subsequently, Li2CO3, MnCO3, FePO4, NH4H2PO 4, 6 parts by weight of sucrose and 2 parts by weight of polyethylene glycol were mixed as carbon sources for 100 parts by weight of V2O3. Water was mixed to make an aqueous solution with a solid content concentration of 30 wt%, and then a slurry (D50: 500 nm) was prepared by wet mixing and grinding in a bead mill for 2.5 hours.

[0187] drying stage

[0188] The moisture was removed from the above mixture by spray drying (inlet temperature 230℃, outlet temperature 90℃, for 1 hour).

[0189] firing stage

[0190] Calcined for 10 hours under a vacuum atmosphere and a calcination temperature of 780℃, Li 1.02 Mn 0.297 Fe 0.693 V 0.01 A lithium iron phosphate manganese-based compound having a composition represented by PO4 was prepared.

[0191] Grinding step

[0192] Grinding was performed using a 2-inch jet mill at a pressure of 2 bar to obtain D50 0.5㎛.

[0193] <Example 2>

[0194] Li2CO3, MnCO3, FePO4, NH4H2PO 4, V2O3 and MgO were mixed such that the molar ratio of Li:Mn:Fe:V:Mg:PO4 was 1.02:0.297:0.693:0.005:0.005:1.

[0195] A lithium iron phosphate manganese-based compound was prepared in the same manner as in Example 1, except that the remaining process conditions were changed to the conditions in Table 1 below.

[0196] <Example 3>

[0197] Li2CO3, MnCO3, FePO4, and NH4H2PO4 were mixed such that the molar ratio of Li:Mn:Fe:PO4 was 1.02:0.3:0.7:1. Subsequently, 10 parts by weight of sucrose was mixed as a carbon source with respect to 100 parts by weight of the total weight of Li2CO3, MnCO3, FePO4, and NH4H2PO4. Water was added to prepare a mixture with a solid content concentration of 30 wt%.

[0198] A lithium iron phosphate manganese-based compound was prepared in the same manner as in Example 1, except that the remaining process conditions were changed to the conditions in Table 1 below.

[0199] <Example 4>

[0200] LiH2PO4 was used as the phosphoric acid-containing raw material instead of NH4H2PO4.

[0201] Li2CO3, MnCO3, FePO4, LiH2PO4, and TiO2 were mixed such that the molar ratio of Li:Mn:Fe:Ti:PO4 was 1.02:0.297:0.693:0.01:1. Subsequently, 8 parts by weight of glucose and 2 parts by weight of polyethylene glycol were mixed as carbon sources with respect to 100 parts by weight of the total weight of Li2CO3, MnCO3, FePO4, LiH2PO4, and TiO2.

[0202] A lithium iron phosphate manganese-based compound was prepared in the same manner as in Example 1, except that the remaining process conditions were changed to the conditions in Table 1 below.

[0203] <Comparative Example 1>

[0204] Li2CO3, MnCO3, FePO4, and LiH2PO4 were mixed such that the molar ratio of Li:Mn:Fe:PO4 was 1.03:0.6:0.4:1.

[0205] A lithium iron phosphate manganese-based compound was prepared in the same manner as in Example 1, except that the remaining process conditions were changed to the conditions in Table 1 below.

[0206] <Comparative Example 2>

[0207] Li2CO3, MnCO3, FePO4, and NH4H2PO4 were mixed such that the molar ratio of Li:Mn:Fe:PO4 was 1.03:0.6:0.4:1.

[0208] A lithium iron phosphate manganese-based compound was prepared in the same manner as in Example 1, except that the remaining process conditions were changed to the conditions in Table 1 below.

[0209] <Comparative Example 3>

[0210] Li2CO3, MnCO3, FePO4, LiH2PO4, and TiO2 were mixed such that the molar ratio of Li:Mn:Fe:Ti:PO4 was 1.02:0.297:0.693:0.01:1. Subsequently, 8 parts by weight of glucose and 2 parts by weight of polyethylene glycol were mixed as carbon sources with respect to 100 parts by weight of the total weight of Li2CO3, MnCO3, FePO4, LiH2PO4, and TiO2.

[0211] A lithium iron phosphate manganese-based compound was prepared in the same manner as in Example 1, except that the remaining process conditions were changed to the conditions in Table 1 below.

[0212]

[0213] The above average particle size was measured by dispersing the powder to be measured in a dispersion medium, introducing it into a laser diffraction particle size measuring device (Mastersizer 3000, Malvern), measuring the difference in diffraction patterns according to particle size as the particles pass through a laser beam to calculate the particle size distribution, and calculating the particle diameter at the point where the cumulative volume distribution according to particle size in the measuring device is 50%, and the above average crystal grain size was analyzed using a Bruker D8 XRD instrument (Cu-target, voltage: 45kV, current: 40mA, 2θ: 10° to 80°).

[0214] Preparation Example 1: Preparation of anode

[0215] An electrode was prepared by mixing the respective positive active material, conductive material, and binder prepared in the examples and comparative examples.

[0216] As a conductive material, the specific surface area is 62 m² 2 Polyvinylidene Fluoride (PVDF) with a molecular weight (Mw) of 63,000 g / mol was used as a binder for carbon black (super-C65) with a molecular weight of 63,000 g / mol.

[0217] A positive electrode composite was prepared by mixing the positive electrode active material, conductive material, and binder prepared in the above examples and comparative examples in a weight ratio of 90:5:5, and a slurry was prepared by adjusting the solid content to between 30% and 60% using an N-methylpyrrolidone solvent. The slurry was then applied to one side of an aluminum current collector, dried at 130°C, and rolled to achieve a porosity of 30% to produce a positive electrode.

[0218] Preparation Example 2: Preparation of a lithium coin half cell

[0219] A lithium secondary battery was manufactured using the wellcos 2032 product, each using the anode prepared in Manufacturing Example 1 above.

[0220] Each of the anodes prepared above was placed at the bottom, 40 μm of electrolyte was injected, a separator was placed on top of it, an additional 40 μm of electrolyte was injected, a lithium anode was inserted, and a coin half-cell was fabricated in the order of Gasket, Spacer, Spring, and Cap. At this time, the electrolyte was prepared by dissolving 1.0 M concentration lithium hexafluorophosphate (LiPF6) and 2 wt% vinylene carbonate (VC) in an organic solvent composed of ethylene carbonate / dimethyl carbonate / diethyl carbonate (mixed volume ratio of EC / DMC / DEC = 1 / 2 / 1).

[0221] Experimental Example 1: Evaluation of Initial Charge / Discharge Characteristics

[0222] The change in potential during charging and discharging was observed for a lithium coin half cell containing the positive electrode active material prepared in the above examples and comparative examples.

[0223] Specifically, under constant current / constant voltage (CC / CV) conditions, it was charged to 4.25V at 0.1C (0.05C cut off), and then discharged to 2.5V at 0.1C under constant current (CC) conditions, and the potential change, initial charge capacity, and discharge capacity were checked.

[0224] The results are shown in Figure 1 below.

[0225] In addition, the result of standardizing the x-axis of the graph in Fig. 1 and expressing it as SOC is shown in Fig. 2.

[0226] In addition, the results of the graph in Fig. 2 were enlarged to an x-axis range of 85%-100% and a y-axis range of 3.7-4.3V and shown in Fig. 3.

[0227] Experimental Example 2: Measurement of Charging Rate

[0228] A lithium coin half cell containing the positive electrode active material prepared in the above examples and comparative examples was measured using the method of Experimental Example 1, and then charged at 2C in CCCV mode (Constant Current, Constant Voltage) until it reached 4.25V, and the charging rate (2C / 0.1C) was measured by dividing the capacity charged in CC mode by the capacity charged in 0.1C CC mode in Experimental Example 1.

[0229] The results are shown in Figure 4 below.

[0230] Classification SOC 100% Voltage SOC 90% Voltage (a) 0.1C Charging Capacity (mAh / g) 0.1C CC Charging Capacity (mAh / g) 0.1C Discharging Capacity (mAh / g) 2C CC Charging Capacity (mAh / g) Charging Rate (%, 2C / 0.1C) Mn:Fe Ratio Example 1 4.25 4.03 0.02 215 7.9 15 6.9 15 7.3 136.18 6.73:7 Example 2 4.25 4.03 90.02 111 56.7 15 4.9 15 5.1 129.48 3.53:7 Example 3 4.25 4.03 80.02 1215 3.9 15 3.3 15 3.01 32.08 6.13:7 Example 44.254.0500.020153.3151.5148.6139.492.13:7 Comparative Example 14.254.1230.0127153.2151.1148.372.047.66:4 Comparative Example 24.254.1230.0127152.7150.7148.2116.477.36:4 Comparative Example 34.254.1120.0138140.0133.5128.2100.975.63:7(a) = [(Voltage at SOC 100%)-(Voltage at SOC 90%)] / 10

[0231] From the above results, it was confirmed that for a lithium secondary battery containing a positive electrode containing a positive electrode active material, when the voltage at SOC 90% is 4.11V or less and the value of (a) is adjusted to 0.014 or more, the charge / discharge efficiency is improved and the efficiency in rapid charging is excellent.

[0232] The present invention is applicable to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, and a lithium secondary battery.

Claims

1. A positive electrode active material for a secondary battery comprising a lithium iron phosphate manganese-based compound, For a lithium secondary battery comprising a positive electrode containing the above positive electrode active material, the voltage at SOC 90% is 4.11V or less, and A positive electrode active material for a secondary battery, wherein the value of (a) of the following mathematical formula 1, representing a slope between SOC 90% and SOC 100%, is 0.014 or greater: [Mathematical Formula 1] (a) = [(Voltage at SOC 100%)-(Voltage at SOC 90%)] / 10.

2. In Paragraph 1, A positive electrode active material for a secondary battery, wherein the average particle size (D50) of the above lithium iron phosphate manganese-based compound is 0.2㎛ or more and 1㎛ or less.

3. In Paragraph 1, A positive electrode active material for a secondary battery, wherein the average crystal grain size of the above lithium iron phosphate manganese-based compound is 100 nm or more and 180 nm or less.

4. In Paragraph 1, The above lithium iron phosphate manganese-based compound is a positive electrode active material for a secondary battery comprising an olivine structure.

5. In Paragraph 1, The above lithium iron phosphate manganese-based compound is a positive electrode active material for a secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li 1+y1 Fe a Mn b M1 c (PO4) In the above chemical formula 1, The above M1 is one or more elements selected from the group consisting of Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn, and -0.1≤y1<0.1, 0 <a<1, 0<b≤0.8, 0≤c≤0.5 및 a+b+c=1이다.

6. In Paragraph 5, A positive electrode active material for a secondary battery, wherein b is less than 0.

5.

7. In Paragraph 1, A positive electrode active material for a secondary battery, further comprising a coating layer formed on the surface of the above-mentioned lithium composite transition metal oxide and containing carbon (C).

8. In Paragraph 1, A positive electrode active material for a secondary battery comprising a positive electrode including the above positive electrode active material, wherein the 0.1C discharge capacity is 130 mAh / g or more.

9. In Paragraph 1, A positive electrode active material for a secondary battery comprising a positive electrode including the above positive electrode active material, wherein the 0.1C charge capacity is 150 mAh / g or more.

10. In Paragraph 1, A positive electrode active material for a secondary battery comprising a positive electrode including the above positive electrode active material, wherein the 0.1C CC charging capacity is 145 mAh / g or more.

11. In Paragraph 1, A positive electrode active material for a secondary battery comprising a positive electrode including the above positive electrode active material, wherein the 2C CC charging capacity is 120 mAh / g or more.

12. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 11.

13. A lithium secondary battery comprising a positive electrode according to paragraph 12.

Images