Cathode active material for lithium secondary battery and manufacturing method therefor

Abstract

A lithium manganese iron phosphate (LMFP) cathode active material for a lithium secondary battery and a manufacturing method therefor are disclosed. The cathode active material according to the present invention comprises LMFP represented by LiMnaFebPO4 (a + b = 1, a > 0, b > 0), and satisfies relational expression 1. [Relational expression 1] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48 In relational expression 1, CS(101) is a crystal size (nm) of a (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50, nm) of an LMFP slurry as measured by a Malvern particle size analyzer.

Description

Cathode active material for lithium secondary batteries and method for producing the same

[0001] The present invention relates to a lithium manganese iron phosphate (LMFP) cathode active material for a lithium secondary battery and a method for producing the same.

[0002] Lithium iron phosphate (LFP) cathode active material is an olivine structure composed of an octahedral site of FeO6 and a tetrahedral site of PO4, and is a material through which lithium ions are inserted and deintercalated through a one-dimensional pathway.

[0003] LFP cathode active material is a material with a price advantage due to its lower cost of metal minerals compared to NCA or NCM materials that mainly use Ni and Co as Li, Fe, and P.

[0004] In addition, the LFP cathode active material has a stable structure due to strong PO bonds, so it has the advantage of excellent thermal stability as there is no oxygen dissociation at high temperatures during charging.

[0005] In addition, LFP cathode active material has excellent life characteristics, and many electric vehicles using it have been produced in China.

[0006] However, LFP cathode active materials suffer from low energy density. To improve this, research is currently underway on lithium manganese iron phosphate (LMFP) cathode active materials, which substitute manganese (Mn) for the iron (Fe) in LFP cathode active materials.

[0007] LMFP cathode active material has the advantage of increasing energy density by about 15% while increasing operating voltage because it is richer in manganese compared to LFP cathode active material.

[0008] However, LMFP cathode active materials have the disadvantage of lower lithium ion diffusion rate and electrical conductivity compared to LFP cathode active materials, and are being studied from various perspectives by controlling various factors that can affect electrochemical performance.

[0009] The purpose of the present invention is to provide a cathode active material for a lithium secondary battery having excellent initial discharge capacity and a method for producing the same by nano-izing the average particle size (D50) of a slurry after wet bead milling and reducing the crystal size of the (101) plane.

[0010] In addition, an object of the present invention is to provide a cathode active material for a lithium secondary battery and a method for manufacturing the same, which can improve the low electrical conductivity of LMFP by uniformly coating carbon on the surface of LMFP.

[0011] The cathode active material according to the present invention is LiMn a Fe b It is characterized by including an LMFP represented by PO4(a + b = 1, a > 0, b > 0) and satisfying the following relational expression 1.

[0012] [Relationship 1]

[0013] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48

[0014] In the above relational expression 1, CS(101) is the crystal size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50) (nm) of the LMFP slurry measured by a Malvern particle size analyzer.

[0015] The above positive electrode active material may further include 0.5 to 1.5 mol% of a dopant with respect to the total 100 mol%.

[0016] The above dopant may include one or more of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr.

[0017] The LMFP surface further includes a carbon layer coated thereon, and the carbon content of the carbon layer may be 1.5 to 2.3 wt% with respect to the total 100 wt%.

[0018] The average particle size (D50) of the above LMFP slurry may be 200 to 400 nm.

[0019] The crystal size of the above (101) surface can be 80 to 100 nm.

[0020] The lithium ion diffusion path in the above positive electrode active material may be in the direction perpendicular to the (101) plane.

[0021] The a-axis length within the lattice structure of the above-mentioned positive electrode active material may be 10.3 to 10.5 Å, the b-axis length may be 6.0 to 6.1 Å, and the c-axis length may be 4.7 to 4.8 Å.

[0022] In addition, with respect to lithium in the lattice structure of the positive electrode active material, when the bonding distances (Å) with oxygen having different axial directions are referred to as Li-O1, Li-O2, and Li-O3, each of Li-O1, Li-O2, and Li-O3 may be 2.3 Å or less.

[0023]

[0024] In another embodiment, the positive electrode active material according to the present invention is characterized by satisfying the following relationship 1.

[0025] [Relationship 1]

[0026] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48

[0027] In the above relational expression 1, CS(101) is the crystal size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50) (nm) of the lithium manganese iron phosphate (LMFP) slurry measured by a Malvern particle size analyzer.

[0028]

[0029] A lithium secondary battery according to the present invention is characterized by including a positive electrode including the positive electrode active material described above; a negative electrode; and an electrolyte.

[0030]

[0031] The method for manufacturing a positive electrode active material according to the present invention comprises the steps of (a) preparing and grinding an LMFP precursor; (b) spray-drying the slurry obtained by the grinding; and (c) calcining the powder obtained by the spray-drying to manufacture a positive electrode active material; wherein the LMFP is LiMn a Fe b It is expressed as PO4(a + b = 1, a > 0, b > 0) and is characterized by satisfying the following relationship 1.

[0032] [Relationship 1]

[0033] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48

[0034] In the above relational expression 1, CS(101) is the crystal size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50) (nm) of the LMFP slurry measured by a Malvern particle size analyzer.

[0035] In the above step (b), the average particle size (D50) of the slurry obtained by grinding may be 200 to 400 nm.

[0036] The step of preparing and crushing the above (a) LMFP precursor can be performed by mixing and milling a lithium precursor, a phosphorus precursor, an iron precursor, and a manganese precursor for 2 to 5 hours.

[0037] In the above step (a), 1.5 to 2.3 wt% of carbon precursor can be further mixed into the LMFP precursor with respect to the total 100 wt%.

[0038] In the above step (a), the carbon precursor may include at least one of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite.

[0039] In the above step (a), 0.5 to 1.5 mol% of a dopant may be further mixed with respect to the total 100 wt%.

[0040] In the above step (a), the dopant may include one or more of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr.

[0041] In the above step (c), the calcination can be performed in an inert atmosphere and at 630 to 700°C.

[0042] In the above step (a), one or more dispersants selected from the group consisting of citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutarinc acid, maleic acid, oxalic acid, malonic acid, and ascorbic acid may be further mixed.

[0043]

[0044] In another embodiment, a method for manufacturing a positive electrode active material according to the present invention comprises the steps of (a) preparing and pulverizing a lithium manganese iron phosphate (LMFP) precursor; (b) spray-drying a slurry obtained by the pulverization; and (c) calcining a powder obtained by the spray-drying to manufacture a positive electrode active material, and is characterized in that it satisfies the following relational expression 1.

[0045] [Relationship 1]

[0046] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48

[0047] In the above relational expression 1, CS(101) is the crystal size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50) (nm) of the LMFP slurry measured by a Malvern particle size analyzer.

[0048] According to the positive electrode active material for a lithium secondary battery of the present invention and the method for manufacturing the same, the crystal size can be controlled by controlling at least one of the dopant content, the carbon content, and the firing temperature.

[0049] In particular, in the present invention, the average particle size (D50) of the slurry obtained after wet bead milling is nanosized to improve the crystallinity and reduce the crystal size of the (101) plane, thereby further improving the electrochemical reaction.

[0050] Accordingly, the positive electrode active material of the present invention and the lithium secondary battery using the same have excellent initial discharge capacity.

[0051] In addition, the method for manufacturing a positive electrode active material for a lithium secondary battery of the present invention can improve the low electrical conductivity of LMFP by a carbon layer uniformly coated on the surface of LMFP.

[0052] Figure 1 is a (101) plane within an LMFP lattice structure according to the present invention.

[0053] The above-described objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily practice the technical idea of ​​the present invention. In describing the present invention, if it is determined that a detailed description of known technologies related to the present invention may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0054] Hereinafter, the phrase "any configuration is placed on (or below)" a component or "on (or below)" a component may mean that any configuration is placed in contact with the upper surface (or lower surface) of said component, and that other configurations may be interposed between said component and any configuration placed on (or below) said component.

[0055] Additionally, when it is described that a component is "connected," "coupled," or "connected" to another component, it should be understood that the components may be directly connected or connected to one another, but that other components may also be "interposed" between the components, or that each component may be "connected," "coupled," or "connected" through another component.

[0056] Hereinafter, a cathode active material for a lithium secondary battery and a method for manufacturing the same according to some embodiments of the present invention will be described.

[0057] Research is being conducted on lithium manganese iron phosphate (LMFP) cathode active material, which substitutes manganese (Mn) for the iron (Fe) in lithium iron phosphate (LFP) cathode active material.

[0058] LMFP cathode active materials have the disadvantage of lower lithium ion diffusion rate and electrical conductivity compared to LFP cathode active materials.

[0059] Accordingly, various factors that can affect the electrochemical performance, such as electrical conductivity, of LMFP cathode active materials are being studied from various perspectives.

[0060] After extensive research, the inventors have confirmed that there is a difference in the discharge capacity of a lithium secondary battery depending on the average particle size of the slurry of LMFP after wet bead milling.

[0061] As the average particle size of the slurry decreases, nano-sized particles are formed, and these formed nano-sized particles constitute secondary particles. As the average particle size of the slurry decreases, the surface energy increases and the slurry becomes unstable due to the large surface area.

[0062] The slurry readily combined and reacted at lower temperatures to reduce its high surface energy. During the LMFP synthesis process, contact points between nanoparticles increased, and the low radius of curvature of the contact points between nanoparticles facilitated smooth mass transfer, facilitating the structural synthesis process and crystallization.

[0063] Additionally, as more crystal nuclei were generated to lower the high surface energy of the slurry, growth was suppressed due to the large number of crystal nuclei, allowing the crystal size to be controlled to be small.

[0064] In this way, lowering the average particle size of the slurry improved the crystallinity.

[0065] In the (101) plane where Li ions are located in LMFP, the degree of exposure of the (101) plane closely affected the performance of the LMFP cathode material. A smaller crystal size of the (101) plane meant that more particles of the (101) plane could exist in the same volume of sample, which corresponded to the possibility of more planes being exposed.

[0066] However, if the crystal size becomes too small, the crystal's high surface area can lead to excessive reactivity. This can lead to unwanted side reactions in addition to the desired reaction, potentially rendering the cathode active material structurally unstable.

[0067] Additionally, it is necessary to control the crystal size because an excessively high surface area of ​​the crystal can increase the contact resistance between particles, which can have a negative effect on the conductivity.

[0068] Therefore, the inventor of the present invention completed the parameter [Relational Expression 1] by setting the crystal size, which allows for more active electrochemical reactions due to the high surface area of ​​the crystals while maintaining the structural stability of the positive electrode active material, as a constant, and dividing the average particle size of the slurry, which is advantageous for performance the smaller it is, into a particle size.

[0069] In [Relationship 1] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48 of the present invention, CS(101) is the crystal size (nm) of the (101) plane measured under the conditions of Scan range (10 to 80˚) and Scan speed (2.5˚ / min) of an X-ray diffraction analyzer (Rigaku equipment).

[0070] D50(WM) is the average particle size (D50) (nm) of LMFP slurry measured by a Malvern particle sizer using 0.02 g of LMFP slurry and 1 ml of IGEPAL 1.0 wt.% dispersant.

[0071] In this way, the inventor of the present invention calculated the value obtained by dividing the crystal size of the (101) plane, CS(101), by the average particle size of the slurry, D50(WM), and satisfied [Relationship 1] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48, thereby securing excellent initial discharge capacity of a lithium secondary battery.

[0072] Since the lower limit of CS(101) / D50(WM) satisfies 0.40 and the upper limit satisfies 0.48, the crystal size of the (101) plane could be controlled to less than 100 nm, and the electrochemical reaction was more active due to the high surface area resulting from the small crystal size.

[0073] As a result, it was confirmed that the initial discharge capacity of the lithium secondary battery was 150 mAh / g or more.

[0074] If the value of CS(101) / D50(WM) is less than 0.40, it means that the crystal size is relatively too small or the particle size of the slurry is too large, so it is difficult to smoothly exhibit electrochemical performance due to low ionic conductivity.

[0075] Conversely, when the value of CS(101) / D50(WM) exceeds 0.48, it is difficult to secure excellent initial discharge capacity due to the reduced ionic conductivity caused by the large crystal size.

[0076] Therefore, the present invention has a technical significance in that the initial discharge capacity of a lithium secondary battery can be secured only when [Relationship 1] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48 is satisfied.

[0077] In addition, the inventors of the present invention adjusted at least one of the dopant content, carbon content, and sintering temperature as a method for controlling the crystal size affecting the electrochemical reaction.

[0078] As the dopant content increased, crystal growth was suppressed, resulting in a smaller crystal size. However, excessive dopant content actually hindered the movement of Li ions and electrons, degrading electrochemical performance.

[0079] As carbon content increased, crystal growth was suppressed and conductivity tended to increase. However, if the carbon content increased too much, the specific surface area of ​​the active material became too high, impeding electrical flow.

[0080] As the sintering temperature decreased, crystal growth slowed and crystal size tended to decrease. However, if the sintering temperature was too low, it had a negative effect on LMFP synthesis and crystallization.

[0081] Based on these research results, the inventors of the present invention confirmed that controlling at least one of the dopant content, carbon content, and sintering temperature affects the crystal size.

[0082] <Cathode active material for lithium secondary batteries>

[0083] The cathode active material according to the present invention is LiMn a Fe b It is characterized by including an LMFP represented by PO4(a + b = 1, a > 0, b > 0) and satisfying the following relational expression 1.

[0084] [Relationship 1]

[0085] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48

[0086] More preferably, 0.41 ≤ CS(101) / D50(WM) ≤ 0.46.

[0087] Since the lower limit of CS(101) / D50(WM) satisfies 0.40 and the upper limit satisfies 0.48, the crystal size of the (101) plane can be controlled to less than 100 nm, and the electrochemical reaction can be further improved due to the high surface area resulting from the small crystal size.

[0088] The smaller the average particle size of the raw material slurry, the higher the surface energy and the more unstable it becomes due to the larger surface area. In other words, the slurry readily combines and reacts at lower temperatures to lower surface energy, facilitating structural synthesis.

[0089] In the case of slurry grinding using a bead mill process, the smaller the average particle size (D50) of the slurry becomes, the better the crystallization occurs.

[0090] In this way, the average particle size (D50) of LMFP slurry is a factor that affects the degree of crystallinity.

[0091] From this point of view, the average particle size (D50) of the slurry may be 200 to 400 nm, preferably 200 to 240 nm, and more preferably 200 to 210 nm.

[0092] In LMFP, the (101) plane is the plane where Li ions are located, and the exposure of the (101) plane closely affects the performance of the LMFP cathode material.

[0093] Under identical conditions, a smaller crystal size on the (101) plane means that a larger number of (101)-plane particles can exist within the same volume of sample, thereby exposing more planes. Furthermore, a smaller crystal size leads to a higher surface area, which facilitates more active electrochemical reactions and is advantageous for performance.

[0094] From this point of view, the crystal size of the (101) plane may be 80 to 100 nm, preferably 82 to 94 nm, and more preferably 84 to 93 nm.

[0095] (101) Since the crystal size of the surface satisfies 80 to 100 nm, the electrochemical reaction is improved by the high surface area of ​​the crystal, and the initial discharge capacity can be 150 mAh / g or more.

[0096] Figure 1 is a (101) plane within an LMFP lattice structure according to the present invention.

[0097] As illustrated in Fig. 1, the lithium ion diffusion path in the positive electrode active material may be in the direction perpendicular to the (101) plane.

[0098] The vertical direction of the (101) plane refers to the (010) plane, which indicates the diffusion direction of Li ions. The interplanar distance (d-spacing) of the (101) plane is related to the movement of Li ions, and an increase in the interplanar distance of the (101) plane can facilitate the movement of Li ions.

[0099] The a-axis length within the lattice structure of the positive electrode active material may be 10.3 to 10.5 Å, the b-axis length may be 6.0 to 6.1 Å, and the c-axis length may be 4.7 to 4.8 Å. Preferably, the a-axis length may be 10.39 to 10.40 Å, the b-axis length may be 6.04 to 6.08 Å, and the c-axis length may be 4.71 to 4.75 Å.

[0100] And the lattice volume calculated from the product of the a-axis, b-axis, and c-axis lengths is 297 to 299 Å. 3 It could be.

[0101] Lattice constant (axial length) and lattice volume are factors related to the interatomic distance in the crystal structure, which affect ionic and electronic conductivity and structural stability according to volume changes during charge and discharge.

[0102] If the lattice constant (axial length) is excessively large, the movement path of lithium ions becomes excessively wide, which may have a negative effect on ion conductivity and may also cause structural instability of the positive electrode active material.

[0103] Conversely, if the lattice constant (axial length) is too small, the movement path of lithium ions becomes excessively narrow, resulting in low ionic conductivity, and significant volume changes during desorption and insertion of lithium ions may occur, resulting in structural collapse due to deformation.

[0104] In the present invention, by satisfying the a-axis length of 10.3 to 10.5 Å, the b-axis length of 6.0 to 6.1 Å, and the c-axis length of 4.7 to 4.8 Å, an appropriate lithium ion movement path can be formed, and there is an effect of having structural stability by achieving good crystallization.

[0105] The axis length within the lattice structure was precisely analyzed using the Rigaku-SmartLab Studio II program by measuring the X-ray diffraction pattern under the conditions of the scan range (10 to 80˚) and scan speed (2.5˚ / min) of an X-ray diffraction analyzer (Rigaku equipment). For the precise analysis, the FP (Fundamental parameter) method was used as the function model for fitting.

[0106] The crystal structure of LFP cathode materials has strong PO bonds, which ensures structural stability, and Li combines with oxygen within the lattice to form LiO6 octahedra.

[0107] And electrochemical performance is realized through the movement of Li ions between oxygen.

[0108] The electrochemical performance differs because the Li migration rate varies depending on the bonding distance between Li and O.

[0109] The longer the Li-O bond distance, the easier the desorption of Li ions due to the lower binding energy. And the shorter the PO bond distance, the greater the structural stability.

[0110] As explained above, the smaller the average particle size of the slurry, the better the crystallization, so the strong PO bonds are bonded more strongly and the PO bond distance is shortened.

[0111] Assuming the unit cell volume is the same, as crystallization increases, O, which is relatively lighter than P, moves toward P, shortening the bonding distance of PO and increasing the volume of the LiO6 octahedron.

[0112] Therefore, as crystallization increases, the Li-O bond distance becomes longer and the Li-O bond becomes relatively weaker, thus increasing ionic conductivity.

[0113] Regarding lithium in the lattice structure of the positive electrode active material, when the bonding distances (Å) with oxygen in different axial directions are Li-O1, Li-O2, and Li-O3, each of Li-O1, Li-O2, and Li-O3 may be 2.3 Å or less, and preferably 2.09 to 2.2 Å.

[0114] Specifically, Li-O1 can be 2.191 to 2.2 Å, Li-O2 can be 2.093 to 2.102 Å, and Li-O3 can be 2.154 to 2.159 Å.

[0115] The method for measuring the Li-O bond distance is as follows.

[0116] After measuring the diffraction pattern using an X-ray diffractometer (Rigaku), a precise analysis of the crystal structure was performed using the Rigaku-SmartLab Studio II program. The function model for fitting was performed using the FP (Fundamental parameter) method. The distance between Li-O (Li-O1, Li-O2, Li-O3) within the LiO6 octahedron was analyzed through the position of each atom in the analysis results (XRD measurement conditions: Scan range (10-80 o ), Scan speed(2.5 o / min) / Rwp 2.5 or less, S value 2 or less was analyzed with a reliability of 2).

[0117] The cathode active material according to the present invention is LiMn a Fe b Contains lithium manganese iron phosphate (LMFP) represented by PO4(a + b = 1, a > 0, b > 0).

[0118] LMFP has a secondary particle form formed by the agglomeration of multiple primary particles.

[0119] In the present invention, “primary particle” means the smallest particle unit that can be distinguished as a single lump when observing the cross-section of a positive electrode active material through a scanning electron microscope (SEM), and may be composed of a single crystal grain or multiple crystal grains.

[0120] Here, “crystal grain” refers to a region where atoms within a primary particle are distinguished in the form of a lattice structure with a certain direction.

[0121] The above “secondary particle” refers to an aggregate, i.e., a secondary structure, in which tens to hundreds of primary particles are aggregated together by physical or chemical bonding between the primary particles without any intentional aggregation or assembly process for the primary particles.

[0122] LiMn a Fe b In LMFP represented by PO4(a + b = 1), a > 0, b > 0 may be present, and preferably a ≥ 0.4, b ≥ 0.4 may be present.

[0123] Here, the molar ratio of Mn and Fe can be approximately 0.5:0.5 to 0.6:0.4.

[0124] By ensuring that the molar ratio of Mn to Fe is approximately 0.5:0.5 to 0.6:0.4, the theoretical energy density is further improved. If the molar ratio of Mn is too low, energy density will not improve. Conversely, if the molar ratio of Mn is too high, the stability of the lithium secondary battery will be reduced, potentially leading to quality issues.

[0125] The cathode active material may further include a dopant to control the crystal size.

[0126] The above dopant may include one or more of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr, and preferably may further include a Ti doping element.

[0127] By including more doping elements in the positive electrode active material, high-temperature life and thermal stability can be further improved.

[0128] It is desirable to adjust the dopant content to control the crystal size.

[0129] As dopant content increases, crystal growth can be suppressed, resulting in a smaller crystal size. However, excessive doping with excessive amounts of dopant can actually hinder the movement of Li ions and electrons, negatively impacting performance, even if crystal growth is suppressed.

[0130] From this point of view, the positive electrode active material of the present invention may contain 0.5 to 1.5 mol% of the dopant, and preferably 0.5 to 1.0 mol%, based on 100 mol% of the total.

[0131] By satisfying the dopant content of 0.5 to 1.5 mol%, there is a favorable effect in showing an initial discharge capacity of 150 mAh / g or more.

[0132] In the present invention, in order to improve the electrical conductivity of the LMFP positive electrode active material, a carbon layer coated on the surface of the LMFP may be further included.

[0133] The carbon to be coated may include at least one of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite, and preferably may include glucose.

[0134] It is desirable to adjust the carbon content to control the electrical conductivity and crystal size of the positive electrode active material.

[0135] As carbon content increases, crystal growth is inhibited and conductivity tends to increase.

[0136] However, if the carbon content is too high, it can actually hinder electrical flow due to the large specific surface area (BET).

[0137] From this point of view, the carbon content of the carbon layer may be 1.5 to 2.3 wt%, and preferably 1.6 to 2.0 wt%, with respect to the total 100 wt%.

[0138] Since the carbon content of the carbon layer satisfies 1.5 to 2.3 wt%, the carbon is uniformly dispersed in the positive electrode active material, thereby improving the electrical conductivity of the lithium secondary battery and further improving the initial discharge capacity at room temperature.

[0139] <Method for producing positive electrode active material for lithium secondary batteries>

[0140] A method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention is characterized by including the steps of preparing and pulverizing an LMFP precursor, spray-drying a slurry obtained by the pulverization, and calcining the powder obtained by the spray-drying to manufacture a positive electrode active material.

[0141] Step of preparing and crushing LMFP precursor

[0142] As an LMFP precursor, a lithium precursor, a phosphorus precursor, an iron precursor, and a manganese precursor can be mixed and milled and pulverized for 2 to 5 hours, preferably pulverized for 3 to 5 hours.

[0143] Grinding can be performed at a rotation speed of 500 to 4000 rpm, preferably 1000 to 3000 rpm, using beads and wet milling methods.

[0144] Additionally, 0.3 to 0.5 mm zirconia beads may be used, but are not limited thereto.

[0145] In the present invention, there is an advantageous effect in controlling the average particle diameter of the secondary particles constituting the positive electrode active material and the primary particles constituting the secondary particles through grinding using a wet milling method.

[0146] The lithium (Li) precursor may include at least one of Li2CO3, Li(OH), Li(OH)·H2O, LiNO3, and LiH2PO4, and preferably may include at least one of Li2CO3 and LiH2PO4.

[0147] The phosphorus (P) precursor may include at least one of lithium dihydrogen phosphate (LiH2PO4) and FePO4. The lithium dihydrogen phosphate (LiH2PO4) can be obtained by reacting lithium phosphate (Li3PO4), an intermediate product, with a phosphoric acid (H3PO4) solution during the process of producing lithium carbonate or lithium hydroxide in a salt lake.

[0148] The iron (Fe) precursor may include FePO4, etc.

[0149] The manganese (Mn) precursor may include Mn3O4, etc.

[0150] In order to improve the electrical conductivity of a lithium secondary battery and control the crystal size, 1.5 to 2.3 wt% of a carbon precursor can be further mixed into the LMFP precursor with respect to the total 100 wt%, and preferably 1.6 to 2.0 wt% can be further mixed.

[0151] By satisfying the content of the carbon precursor of 1.5 to 2.3 wt%, carbon is uniformly dispersed in the positive electrode active material, thereby improving the electrical conductivity of the lithium secondary battery and further improving the initial discharge capacity at room temperature.

[0152] The carbon precursor may include at least one of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite, and preferably may include glucose.

[0153] Additionally, dopants can be further mixed into the LMFP precursor.

[0154] The dopant may include one or more of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr, and preferably may include Ti.

[0155] In the process of manufacturing a cathode active material, by further mixing in a doping element, it is advantageous to control the crystal size, and high-temperature life and thermal stability can be further improved.

[0156] In particular, it is desirable to adjust the dopant content to control the crystal size.

[0157] As dopant content increases, crystal growth can be suppressed, resulting in a smaller crystal size. However, excessive doping with excessive amounts of dopant can actually hinder the movement of Li ions and electrons, negatively impacting performance, even if crystal growth is suppressed.

[0158] From this point of view, 0.5 to 1.5 mol% of dopant can be further mixed with respect to the total 100 wt%, and preferably 0.5 to 1.0 mol% can be included.

[0159] By satisfying the dopant content of 0.5 to 1.5 mol%, there is a favorable effect in showing an initial discharge capacity of 150 mAh / g or more.

[0160] In addition, one or more dispersants selected from citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutarinc acid, maleic acid, oxalic acid, malonic acid, and ascorbic acid may be further mixed, and citric acid may be further mixed, preferably.

[0161] In the process of manufacturing a cathode active material, by further mixing a dispersant, the precursors in the slurry are uniformly dispersed, which is advantageous in manufacturing an olivine-based LMFP cathode active material for lithium secondary batteries of excellent quality.

[0162] The cathode active material of the present invention comprises LMFP formed from the precursors, and the LMFP is LiMn a Fe b It is expressed as PO4(a + b = 1, a > 0, b > 0).

[0163] In the present invention, it is preferable to satisfy the following relational expression 1 using the average particle size (D50) and the crystal size (CS) of the (101) plane of the slurry obtained by the above grinding.

[0164] [Relationship 1]

[0165] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48

[0166] In the above equation 1, CS(101) is the crystal size (nm) of the (101) plane measured under the conditions of scan range (10 to 80˚) and scan speed (2.5˚ / min) of an X-ray diffraction analyzer (Rigaku equipment), and D50(WM) is the average particle size (D50) (nm) of LMFP slurry measured using a Malvern particle sizer using 0.02 g of LMFP slurry and 1 ml of IGEPAL 1.0 wt.% dispersant.

[0167] Since the lower limit of the above CS(101) / D50(WM) satisfies 0.40 and the upper limit satisfies 0.48, the crystal size of the (101) plane can be controlled to 100 nm or less, and the electrochemical reaction can be further improved due to the high surface area resulting from the small crystal size.

[0168] The smaller the average particle size of the raw material slurry, the higher the surface energy and the more unstable it becomes due to the larger surface area. In other words, the slurry readily combines and reacts at lower temperatures to lower surface energy, facilitating structural synthesis.

[0169] In the case of slurry grinding using a bead mill process, the smaller the average particle size (D50) of the slurry becomes, the better the crystallization occurs.

[0170] In this way, the average particle size (D50) of LMFP slurry is a factor that affects the degree of crystallinity.

[0171] From this point of view, the average particle size (D50) of the slurry obtained by grinding may be 200 to 400 nm, preferably 200 to 240 nm, and more preferably 200 to 210 nm.

[0172] Step of spray drying the slurry obtained by grinding

[0173] In the spray drying step of the slurry obtained by grinding, spray drying can be performed using a spray dryer.

[0174] The injection pressure of the spray dryer may be 0.5 to 2 bar, preferably 1 to 1.5 bar. The temperature of the main chamber may be 200 to 300°C, preferably 220 to 260°C. In addition, the outlet temperature of the spray dryer may be set to 80 to 160°C, preferably 100 to 130°C.

[0175] By setting the spray pressure, main chamber temperature, and outlet temperature of the spray dryer as described above, a spherical powder can be obtained from the slurry through spray drying. The spherical powder can be a secondary particle constituting LMFP.

[0176] A step of manufacturing a positive electrode active material by calcining the powder obtained by spray drying.

[0177] The powder obtained by spray drying is loaded into a sintering furnace. Thereafter, by sintering at high temperatures for a predetermined period of time in an atmosphere continuously supplied with inert gas, a positive electrode active material for a lithium secondary battery having a carbon layer coated on the surface of the LMFP can be manufactured.

[0178] The lower the sintering temperature, the slower the crystal growth and the smaller the crystal size. However, because an excessively low sintering temperature adversely affects the synthesis and crystallization of the positive electrode active material, it is important to control the crystal size by adjusting the sintering temperature.

[0179] The calcination can be performed in an inert atmosphere at 630 to 700°C for 1 to 10 hours, preferably 3 to 8 hours.

[0180] By satisfying the sintering temperature and sintering time of 630 to 700°C for 1 to 10 hours, the crystal size can be controlled to 80 to 100 nm, which is advantageous for demonstrating the performance of the positive electrode active material.

[0181] Lithium secondary battery

[0182] A lithium secondary battery according to the present invention is characterized by including a positive electrode, a negative electrode, and an electrolyte including the positive electrode active material described above.

[0183] The 0.1C discharge capacity of the lithium secondary battery may be 150 mAh / g or more, preferably 151 mAh / g or more, and more preferably 152 to 160 mAh / g.

[0184] anode

[0185] A lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator, among which the positive electrode includes a positive electrode material including a positive electrode active material, a conductive material, and a binder, and a current collector.

[0186] The positive electrode according to the present invention comprises a current collector, and a positive electrode material disposed on at least one surface of the current collector and including the positive electrode active material described above.

[0187] Therefore, a detailed description of the positive electrode active material will be omitted.

[0188] Cathode materials serve as a lithium source in lithium secondary batteries and are a key material that determines battery capacity and average voltage.

[0189] The cathode material may include a binder and a conductive material.

[0190] The above binder serves to attach the positive electrode active material particles well to each other and also to attach the positive electrode active material well to the current collector.

[0191] Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0192] The above conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery to be constructed. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0193] The above positive electrode is manufactured by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector.

[0194] Since such electrode manufacturing methods are widely known in the art, a detailed description thereof will be omitted herein. Examples of the solvent used include, but are not limited to, N-methylpyrrolidone.

[0195] The above-mentioned collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0196] cathode

[0197] The above negative electrode includes a current collector and a negative electrode material formed on the current collector, and the negative electrode material may include a negative electrode active material.

[0198] The above negative active material may include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0199] The material capable of reversibly intercalating / deintercalating the lithium ions may be, for example, a carbon material, and any carbon-based negative electrode active material generally used in the lithium secondary battery may be used.

[0200] For example, the carbon-based negative electrode active material may be crystalline carbon, amorphous carbon, or a combination thereof.

[0201] As the above lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0202] Examples of materials capable of doping and dedoping the lithium include Si, SiOx (0 < x < 2), Si-Y alloy (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn).

[0203] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, etc.

[0204] The above cathode material also includes a binder and may optionally further include a conductive material.

[0205] The above binder can play a role in attaching the negative electrode active material particles well to each other and also attaching the negative electrode active material well to the current collector.

[0206] The above conductive material is used to provide conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed.

[0207] The above-mentioned current collector may be selected from the group consisting of, for example, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof.

[0208] The above negative and positive electrodes can be manufactured by mixing an active material, a conductive material, and a binder in a solvent to manufacture an active material composition, and applying the composition to a current collector. The present invention does not limit the method for manufacturing the electrodes.

[0209] The above solvent may include, but is not limited to, N-methylpyrrolidone.

[0210] electrolyte

[0211] The above electrolyte may be a non-aqueous electrolyte or a solid electrolyte, and one in which a lithium salt is dissolved is used.

[0212] The non-aqueous electrolyte may include an organic solvent, and the non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0213] Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; and amides such as dimethylformamide. These may be used singly or in combination.

[0214] In particular, a mixed solvent of a cyclic carbonate and a chain carbonate can be preferably used.

[0215] Additionally, as an electrolyte, a gel polymer electrolyte impregnated with an electrolyte solution in a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N may be used.

[0216] The above lithium salt is a substance that is dissolved in an organic solvent and acts as a source of lithium ions within the battery, enabling the operation of a basic lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes.

[0217] The lithium salt mentioned above can be applied without limitation to those commonly used in the art as long as they do not hinder the purpose of the present invention.

[0218] For example, the lithium salt may be one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiSbF6, LiAlO4, LiAlCl4, LiCl, and LiI.

[0219] Depending on the type of the lithium secondary battery, a separator may exist between the positive and negative electrodes.

[0220] As such separators, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc. may be used.

[0221] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and can be classified into cylindrical, square, coin, and pouch types depending on the shape, and can be divided into bulk type and thin film type depending on the size.

[0222] The structure and manufacturing method of the battery are not limited in the present invention.

[0223] Specific examples of positive electrode active materials and lithium secondary batteries using the same are as follows.

[0224] 1. Manufacturing of positive electrode active material

[0225] Manufacturing method of each sample in [Table 1] below

[0226] Wet bead mill (WM): Lithium source, iron source, manganese source, and phosphorus were ground in a molar ratio of 1.03:0.4:0.6:1 with 800 g of ultrapure water in a bead mill at a maximum of 3500 rpm for a maximum of 5 hours.

[0227] At this time, the lithium source is Li2CO3, LiH2PO4, the iron source is FePO4, the manganese source is Mn3O4, and the phosphorus source is FePO4.

[0228] As described in Table 1, glucose (C6H) was used as a carbon source. 12 O6) was added in an amount of about 10 wt% or less of the total weight of the active material, and TiO2 was added as a dopant in an amount of 1.5 mol% or less.

[0229] Citric acid (C6H8O7) was added as a dispersant in an amount of about 2 wt% or less (0.3-0.5 mm zirconia beads were used. NETZSCH MINISERIES model).

[0230] Spray drying (SD): The mixed slurry obtained after wet bead milling was spray dried using a spray dryer (injection pressure: 1.5 bar, main chamber temperature: 250℃, outlet temperature: 110℃).

[0231] Firing (high-temperature heat treatment): 30 g of SD product was placed in a graphite saga and sintered under a nitrogen atmosphere (sintering temperature: 630–700°C (Table 1), sintering maintenance time: 6 hours, heating rate: 5°C / min, nitrogen flow rate: 1.0 L / min, nitrogen flow rate in the sintering furnace before sintering: 1.5 L / min, nitrogen replacement for 1 hour and 30 minutes (for oxygen removal)).

[0232] [Table 1]

[0233]

[0234] 2. Physical property evaluation method and results

[0235] 1) Electrochemical (coin half-cell) electrode coating: 4.5 g of LMFP, 0.25 g of SuperP, 8 wt.% of PVDF (KF7208, a solution of binder dissolved in NMP) and 4.3 g of NMP were added to prepare an electrode slurry. After electrode coating was performed using a doctor blade, it was dried at 130°C for 2 hours and rolled to a height of 0.2 mm (manufactured coin half-cell electrode specifications: mass loading - 10~11 mg / cm 2 ).

[0236] 2) Electrochemical C-rate capacity evaluation conditions: 24-hour aging immediately after cell manufacturing (temperature 25℃), 1 formation cycle (2.5-4.4V) with 0.1C charge / discharge, fixed charge rate 0.1C, 1 measurement each at 0.1, 0.33, 1, 2, 5, and 10 C discharge rates (2.5-4.4V), CC-CV charge mode used (Charge step condition: fixed at 0.1 C, 0.05 C cut-off current). 20 minutes of rest was performed immediately after the charge and discharge steps.

[0237] 3) The axis lengths in Table 2 were precisely analyzed using the Rigaku-SmartLab Studio II program for the X-ray diffraction patterns measured under the conditions of the scan range (10 to 80˚) and scan speed (2.5˚ / min) of an X-ray diffraction analyzer (Rigaku equipment). For the precise analysis, the FP (Fundamental parameter) method was used as the function model for fitting.

[0238] 4) The method for measuring the Li-O bond distance in Table 3 is as follows.

[0239] After measuring the diffraction pattern using an X-ray diffractometer (Rigaku), a precise analysis of the crystal structure was performed using the Rigaku-SmartLab Studio II program. The function model for fitting was performed using the FP (Fundamental parameter) method. The distance between Li-O (Li-O1, Li-O2, Li-O3) within the LiO6 octahedron was analyzed through the position of each atom in the analysis results (XRD measurement conditions: Scan range (10-80 o ), Scan speed(2.5 o / min) / Rwp 2.5 or less, S value 2 or less was analyzed with a reliability of 2).

[0240] 5) Crystal size of each facet: After measuring the diffraction pattern of the sample using an X-ray diffractometer (Rigaku), the exact peak position and FWHM of each facet were analyzed by fitting with the Psudo-Voigt function.

[0241] And the crystal size of the (101) plane was calculated using the Scherrer method (XRD measurement conditions: Scan range (10-80°), Scan speed (2.5° / min)).

[0242] 6) Measurement of slurry particle size (D50(WM)): 0.02 g of LMFP slurry after wet bead milling was measured using a Malvern particle sizer using 1 ml of IGEPAL 1.0 wt.% dispersant.

[0243] [Table 2]

[0244]

[0245] [Table 3]

[0246]

[0247] [Table 4]

[0248]

[0249] Comparative Examples 1 to 3 showed that the content of Ti dopant was controlled, and the average particle size of the LMFP slurry after wet bead milling exceeded 270 nm, and the CS(101) / D50(WM) value of equation 1 was less than 0.40 nm.

[0250] Comparative Examples 1 to 3 showed that the room temperature initial discharge capacity of the lithium secondary battery was considerably low.

[0251] Comparative Examples 4 to 6 showed that the C content was controlled, and the average particle size of the LMFP slurry after wet bead milling exceeded 270 nm, and the CS(101) / D50(WM) value of equation 1 was less than 0.40 nm.

[0252] Comparative Examples 4 to 6 showed that the room temperature initial discharge capacity of the lithium secondary battery was considerably low.

[0253] Comparative Examples 7 to 9 showed that the average particle size of the LMFP slurry after wet bead milling exceeded 240 nm, and the CS(101) / D50(WM) value of equation 1 was less than 0.40 nm.

[0254] Comparative Examples 7 to 9 showed that the room temperature initial discharge capacity of the lithium secondary battery was considerably low.

[0255] Examples 1 to 4 satisfy the dopant and carbon content, sintering temperature and average particle size of the slurry of the present invention, and the CS(101) / D50(WM) value of equation 1 satisfies 0.41 to 0.46, thereby showing a room temperature initial discharge capacity of 150 mAh / g or more of the lithium secondary battery.

[0256] From these results, it can be seen that the average particle size of the slurry of the LMFP cathode active material and the crystal size controlled by the dopant content and carbon coating amount have a great influence on the room temperature initial discharge capacity of a lithium secondary battery.

[0257] Although the present invention has been described with reference to the drawings exemplified above, it is to be understood that the present invention is not limited to the embodiments and drawings disclosed herein, and that various modifications may be made by those skilled in the art within the scope of the technical idea of ​​the present invention. Furthermore, even if the operational effects according to the configuration of the present invention have not been explicitly described while describing the embodiments of the present invention, it is natural that the effects predictable by the corresponding configuration should also be acknowledged.

Claims

1. LiMn a Fe b Contains LMFP represented by PO4(a + b = 1, a > 0, b > 0), A positive electrode active material satisfying the following relational expression 1. [Relationship 1] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48 In the above relational expression 1, CS(101) is the crystal size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50) (nm) of the LMFP slurry measured by a Malvern particle size analyzer.

2. In paragraph 1, A cathode active material further comprising 0.5 to 1.5 mol% of a dopant relative to the total 100 mol%.

3. In paragraph 2, The above dopant is a cathode active material including at least one of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr.

4. In paragraph 1, Further comprising a carbon layer coated on the surface of the LMFP, The carbon content of the above carbon layer is 1.5 to 2.3 wt% based on 100 wt% of the total positive electrode active material.

5. In paragraph 1, The average particle size (D50) of the above LMFP slurry is 200 to 400 nm, which is a positive electrode active material.

6. In paragraph 1, A cathode active material having a crystal size of 80 to 100 nm on the above (101) surface.

7. In paragraph 1, The lithium ion diffusion path in the above positive electrode active material is in the direction perpendicular to the (101) plane.

8. In paragraph 1, The a-axis length within the lattice structure is 10.3 to 10.5 Å, The b-axis length is 6.0 to 6.1 Å, A cathode active material with a c-axis length of 4.7 to 4.8 Å.

9. In paragraph 1, For lithium within the lattice structure, when the bonding distances (Å) with oxygen in different axial directions are Li-O1, Li-O2, and Li-O3, Li-O1, Li-O2, and Li-O3 are each positive active materials with a thickness of 2.3 Å or less.

10. A positive electrode comprising the positive electrode active material of any one of claims 1 to 9; cathode; and A lithium secondary battery comprising an electrolyte. 11.(a) Step of preparing and crushing an LMFP precursor; (b) a step of spray drying the slurry obtained by the above grinding; and (c) a step of manufacturing a positive electrode active material by calcining the powder obtained by the above spray drying; The above LMFP is LiMn a Fe b It is expressed as PO4(a + b = 1, a > 0, b > 0), A method for manufacturing a positive electrode active material satisfying the following relational expression 1. [Relationship 1] 0.40 ≤ CS(101) / D50(WM) ≤ 0.48 In the above relational expression 1, CS(101) is the crystal size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and D50(WM) is the average particle size (D50) (nm) of the LMFP slurry measured by a Malvern particle size analyzer.

12. In paragraph 11, A method for manufacturing a positive electrode active material, wherein the average particle size (D50) of the slurry obtained by grinding in the above step (b) is 200 to 400 nm.

13. In paragraph 11, The step of preparing and crushing the above (a) LMFP precursor is A method for producing a cathode active material by mixing and milling a lithium precursor, a phosphorus precursor, an iron precursor, and a manganese precursor for 2 to 5 hours.

14. In paragraph 11, A method for producing a cathode active material, wherein in step (a), 1.5 to 2.3 wt% of a carbon precursor is further mixed into the LMFP precursor with respect to the total 100 wt%.

15. In paragraph 14, A method for producing a cathode active material, wherein in the step (a), the carbon precursor comprises at least one of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite.

16. In paragraph 11, A method for producing a positive electrode active material, wherein in the above step (a), 0.5 to 1.5 mol% of a dopant is further mixed with respect to the total 100 wt%.

17. In paragraph 16, A method for producing a cathode active material, wherein in the step (a), the dopant includes at least one of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr.

18. In paragraph 11, A method for producing a positive electrode active material, wherein in the step (c) above, calcination is performed in an inert atmosphere and at 630 to 700°C.

19. In paragraph 11, A method for producing a positive electrode active material, wherein in the step (a), at least one dispersant selected from the group consisting of citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutarinc acid, maleic acid, oxailic acid, malonic acid, and ascorbic acid is further mixed.

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