Cathode active material and lithium secondary battery using same

Abstract

Disclosed according to an embodiment are: a cathode active material having excellent initial discharge capacity by facilitating the intercalation and deintercalation of Li ions; and a lithium secondary battery using same. Disclosed according to another embodiment are: a cathode active material having excellent initial discharge capacity by controlling the Li+ ion migration distance through the volume and dopant content associated with the (101) and (020) planes and the average particle size (D50) of slurry after raw material pulverization and improving ion conductivity; and a lithium secondary battery using same.

Description

Cathode active material and lithium secondary battery using the same

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery using the same.

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

[0003] LFP cathode active material is Li, Fe, and P, and has a cost advantage as it has lower costs for metal minerals compared to NCA or NCM materials that mainly use Ni and Co.

[0004] In addition, LFP cathode active material has the advantage of excellent thermal stability because its structure is stable due to strong PO bonds, preventing oxygen dissociation at high temperatures during charging.

[0005] In addition, LFP cathode active materials have excellent lifespan characteristics, and there is a history of many electric vehicles being produced in China using them.

[0006] However, LFP cathode active materials have the disadvantage of low energy density. To overcome this drawback, research is currently being conducted on lithium manganese iron phosphate (LMFP) cathode active materials in which manganese (Mn) is substituted for the iron (Fe) sites of LFP cathode active materials.

[0007] Because LMFP cathode active material is rich in manganese compared to LFP cathode active material, it has the advantage of increasing energy density by about 15% as the operating voltage increases.

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

[0009] The technical problem of the present invention is to provide a positive electrode active material with excellent initial discharge capacity and a lithium secondary battery using the same by facilitating the insertion and extraction reactions of Li ions.

[0010] In addition, the technical problem of the present invention is to provide a positive active material that can improve the low electrical conductivity of an LMFP by uniformly coating carbon on the surface of the LMFP, and a lithium secondary battery using the same.

[0011] In addition, the technical problem of the present invention is to provide a positive electrode active material with excellent initial discharge capacity and a lithium secondary battery using the same by controlling the distance traveled by Li ions from the volume and dopant content of the (101) plane and (020) plane and the average particle size (D50) of the slurry after raw material grinding and improving the ion conductivity.

[0012] In addition, the technical problem of the present invention is to provide a positive active material that can improve the low electrical conductivity of an LMFP by uniformly coating carbon on the surface of the LMFP, and a lithium secondary battery using the same.

[0013] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0014] The positive active material according to an embodiment of the present invention is characterized by satisfying the following relationship 1.

[0015] [Relationship 1]

[0016] [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75

[0017] In the above equation 1, CS (101) is the total grating size (nm) of the (101) plane measured by an X-ray diffraction analyzer, d (101) is the interplanar distance (Å) of the (101) plane, CS (020) is the total grating size (nm) of the (020) plane, and d (020) is the interplanar distance (Å) of the (020) plane.

[0018] The above positive active material is LiMn a Fe b It may include lithium manganese iron phosphate (LMFP) represented by PO4(a + b ≤ 1, a > 0, b > 0).

[0019] In the above relationship 1, 18 ≤ [CS(101) / d(101)] ≤ 22 can be satisfied.

[0020] In the above relationship 1, [CS(020) / d(020)] ≤ 28 can be satisfied.

[0021] The average size of the entire crystal can be 50 to 200 nm.

[0022] The above lithium manganese iron phosphate (LMFP) further comprises a dopant, and may further comprise 0.5 to 1.5 mol% of the dopant relative to 100 mol% of the total Mn, Fe, and dopant transition metal.

[0023] The above dopant may include one or more of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr.

[0024] The above LMFP surface further includes a carbon layer coated thereon, and the carbon content of the carbon layer may be 1 to 3 weight percent with respect to 100 weight percent of the total.

[0025] A lithium secondary battery according to an embodiment of the present invention is characterized by comprising: a positive electrode including the aforementioned positive active material; a negative electrode; and an electrolyte.

[0026] A positive active material according to another embodiment of the present invention is characterized by satisfying Equation 2.

[0027] [Relationship 2]

[0028] 3.1 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.1

[0029] In the above equation 2, V (101) is the total volume of the (101) plane where the Li ion is located, V (020) is the total volume of the (020) plane in the direction of movement of the Li ion, D' is the content of the 1+ dopant (mol%), and D50 (WM) is the average particle size (D50) (μm) measured by a Malvern particle size meter after grinding the raw material.

[0030] In the above relationship 2, V(101) = (4 / 3)π Χ (CS(101) / 2) 3 It satisfies the above, and the CS (101) may be the total grating size (nm) of the (101) plane measured by an X-ray diffraction analyzer.

[0031] In the above relationship 2, V(020) = (4 / 3)π Χ (CS(020) / 2) 3 It satisfies the above, and the CS (020) may be the total grating size (nm) of the (020) plane measured by an X-ray diffraction analyzer.

[0032] In the above relationship 2, V(101) = (4 / 3)π Χ (CS(101) / 2) 3 Satisfying, and the above V(020) = (4 / 3)π Χ (CS(020) / 2) 3 It satisfies the condition that CS (101) is greater than CS (020), and the difference between CS (101) and CS (020) is 3 or more.

[0033] The above D50(WM) may be 0.210㎛ or less.

[0034] The cathode active material is LiMn a Fe bIt may include lithium manganese iron phosphate (LMFP) represented by PO4(a + b ≤ 1, a > 0, b > 0).

[0035] The above dopant may include one or more of Ti and Mg.

[0036] The above lithium manganese iron phosphate (LMFP) includes a dopant, and may include 0.1 to 0.5 mol% of the dopant with respect to 100 mol% of the total of the dopant, Mn, and Fe.

[0037] The above-mentioned lithium manganese iron phosphate (LMFP) may further include carbon coated on its surface, and the carbon content may be 1 to 3 weight percent with respect to 100 weight percent of the total.

[0038] A lithium secondary battery according to another embodiment of the present invention is characterized by comprising: a positive electrode including the aforementioned positive electrode active material; a negative electrode; and an electrolyte.

[0039] According to the present invention, by increasing the number of Li ion-filled grids of the positive electrode active material to increase the number of Li ion diffusion channels and reducing the maximum number of grids to which Li ions must move to shorten the distance traveled by Li ions, the insertion and extraction reactions of Li ions can be facilitated.

[0040] If the insertion and extraction reactions of Li ions in the positive electrode active material are facilitated, the initial discharge capacity of the lithium secondary battery is excellent.

[0041] In addition, the positive active material of the present invention can improve the low electrical conductivity of the LMFP by uniformly coating carbon on the surface of the LMFP.

[0042] In addition, according to the present invention, the number of diffusion channels for Li ions in the positive electrode active material is increased, and the space within the crystal plane where Li ions must move is reduced, thereby facilitating the movement of Li ions.

[0043] In addition, according to the present invention, by lowering the average particle size (D50(WM)) of the slurry after grinding the raw material and improving the ion conductivity, the movement of Li ions can be facilitated.

[0044] If the movement of Li ions in the positive electrode active material is facilitated, it has the effect of improving the initial discharge capacity of the lithium secondary battery.

[0045] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below.

[0046] FIG. 1 is a schematic diagram satisfying Equation 1 according to an embodiment of the present invention.

[0047] FIG. 2 is a schematic diagram deviating from Equation 1 according to an embodiment of the present invention.

[0048] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0049] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0050] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0051] Hereinafter, a positive electrode active material according to some embodiments of the present invention and a lithium secondary battery using the same will be described.

[0052] Research is underway on lithium manganese iron phosphate (LMFP) cathode active materials in which manganese (Mn) is substituted for the iron (Fe) in lithium iron phosphate (LFP) cathode active materials.

[0053] LMFP cathode active material has the disadvantage of lower lithium ion diffusion rate and electrical conductivity compared to LFP cathode active material.

[0054] Accordingly, research is being conducted from various perspectives by controlling various factors that can affect the electrochemical performance, such as the electrical conductivity of LMFP cathode active materials.

[0055] After long research, the inventors confirmed that the more the number of grids in the (101) plane within the LMFP structure, the more the number of diffusion channels for Li ions increases, and the fewer the maximum number of grids that Li ions must move in the (020) plane, the shorter the distance Li ions travel, thus having an advantage in the initial discharge capacity of the lithium secondary battery.

[0056] In other words, the number of diffusion channels for Li ions and the migration distance of Li ions within the crystal had a close influence on the initial discharge capacity of the LMFP cathode material performance.

[0057] First, in order to increase the number of diffusion channels for Li ions, the number of (101) plane lattices must be large.

[0058] FIG. 1 is a schematic diagram satisfying Equation 1 according to an embodiment of the present invention, and FIG. 2 is a schematic diagram deviating from Equation 1.

[0059] As shown in FIGS. 1 and 2, to explain the number of lattices of the (101) plane, CS (101) is defined as the total lattice size of the (101) plane (the total size of the diffusion channel of Li ions).

[0060] When the lattices are repeated and arranged, the total length of the arranged lattices represents the total crystal size, CS (crystal size). d (101) is defined as the interplanar distance of the (101) plane.

[0061] CS (101) / d (101), which represents the number of grids of (101) planes, is defined as the value obtained by dividing the total grid size of (101) planes, CS (101), by the inter-plane distance of (101) planes, d (101).

[0062] Since the number of grids in the (101) plane is obtained by dividing the total grid size of the (101) plane by the inter-plane distance of the (101) plane, the number of grids in the (101) plane increases as the number of grids in the (101) plane increases, so the initial discharge capacity is excellent.

[0063] Secondly, in order to shorten the migration distance of Li ions, the maximum number of lattice points that Li ions must move in the (020) plane must be small.

[0064] To explain the maximum number of lattices that Li ions must move in the (020) plane, CS (020) is defined as the total lattice size of the (020) plane having the same direction as the direction of movement of Li ions (maximum distance that Li ions must move within the lattice when inserted and extracted). d (020) is defined as the interplanar distance of the (020) plane.

[0065] CS (020) / d (020), which represents the maximum number of lattices that Li ions must move in the (020) plane, is defined as the value obtained by dividing the total lattice size of the (020) plane, CS (020), by the interplanar distance of the (020) plane, d (020).

[0066] Since the maximum number of lattices that Li ions must move is obtained by dividing the total lattice size of the (020) plane by the inter-plane distance of the (020) plane, the smaller the number of lattices of the (020) plane, the shorter the movement distance of Li ions, thereby facilitating the movement of Li ions and resulting in excellent initial discharge capacity.

[0067] From these research results, the inventors confirmed that the initial discharge capacity is superior as the number of grids on the (101) plane increases and the number of grids on the (020) plane decreases.

[0068] And it was confirmed that the number of grids in planes (101) and (020) has a greater influence on the initial discharge capacity than the total grid size and inter-plane distance in planes (101) and (020).

[0069] The inventors completed the relationship 1 [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75 by dividing CS(101) / d(101), which represents the number of lattices in the (101) plane, by CS(020) / d(020), which represents the maximum number of lattices that Li ions must move in the (020) plane.

[0070] That is, CS(101) / d(101) was placed in the numerator, and CS(020) / d(020), which is more advantageous for performance the smaller it is, was set as the denominator, and the larger the value of [CS(101) / d(101)] / [CS(020) / d(020)] in relation 1, the more advantageous it was for the insertion and extraction reactions of Li ions.

[0071] Specifically, since the (101) plane and the (020) plane are perpendicular to each other, Equation 1 contains the crystal orientation of the particle. Therefore, the larger the value of Equation 1, the higher the discharge capacity of the LMFP because it has a crystal orientation favorable for ion diffusion.

[0072] Since ion diffusion is influenced by the (101) plane and (020) plane lattice numbers, using the two lattice numbers as a relational equation 1 rather than using each lattice number as an individual indicator better illustrates the trend between the indicator and electrochemical performance.

[0073] The lower limit value (0.75) of Equation 1 was set as a standard satisfying a discharge capacity of 150 mAh / g or more, taking into account the practical aspects of the LMFP.

[0074] In particular, the value of Equation 1 [CS(101) / d(101)] / [CS(020) / d(020)] must be 0.75 or higher for the movement of Li ions to be smooth and for electrochemical performance to be improved, resulting in an initial discharge capacity of 150 mAh / g or higher.

[0075] Conversely, if the value of Equation 1 [CS(101) / d(101)] / [CS(020) / d(020)] is less than 0.75, it means that the number of diffusion channels for Li ions is small or the travel distance of Li ions is long, so it was difficult to secure the initial discharge capacity due to the low mobility of Li ions.

[0076] Therefore, the present invention has technical significance in that it can secure an excellent initial discharge capacity of a lithium secondary battery by satisfying the relationship 1 [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75.

[0077] In addition, instead of using a general parameter called crystal size, a new relationship 1 using the number of grid cells in the (101) plane and (020) plane was used, and a significant result was obtained in the discharge capacity of the lithium secondary battery.

[0078] Cathode active material for lithium secondary batteries

[0079] The positive active material according to an embodiment of the present invention is characterized by satisfying the following relationship 1.

[0080] [Relationship 1]

[0081] [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75

[0082] In equation 1, CS (101) is the total lattice size (nm) of the (101) plane measured by an X-ray diffraction analyzer, and d (101) is the interplanar distance (Å) of the (101) plane.

[0083] CS (020) is the total lattice size (nm) of the (020) plane, and d (020) is the interplanar distance (Å) of the (020) plane.

[0084] In the LMFP, the (101) plane is the plane where the Li ions are located, and the exposure of the (101) plane has a close influence on the performance of the LMFP cathode material.

[0085] When the lattices are arranged in a repeating sequence, the total length of the arranged lattices becomes the total size of the crystal, so the total lattice size of the (101) plane represents the crystal size of the (101) plane, and the crystal growth tendency differs for each crystal plane.

[0086] In relation 1, preferably 0.75 ≤ [CS(101) / d(101)] / [CS(020) / d(020)] ≤ 0.80, and more preferably 0.76 ≤ [CS(101) / d(101)] / [CS(020) / d(020)] ≤ 0.78.

[0087] If [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75 is satisfied, the number of diffusion channels for Li ions increases and the travel distance of Li ions decreases, thereby facilitating the mobility of Li ions and securing an excellent initial discharge capacity.

[0088] In Equation 1, [CS(101) / d(101)] represents the number of lattice points on the (101) plane, which represents the number of diffusion channels for Li ions. As the number of lattice points on the (101) plane increases, the number of diffusion channels for Li ions increases, so the initial discharge capacity development is superior.

[0089] From this perspective, 18 ≤ [CS(101) / d(101)] ≤ 22 can be satisfied, and preferably 19 ≤ [CS(101) / d(101)] ≤ 21 can be satisfied.

[0090] By satisfying 18 ≤ [CS(101) / d(101)] ≤ 22, the number of diffusion channels for Li ions is large, so there is an effect of excellent initial discharge capacity.

[0091] In Equation 1, [CS(020) / d(020)] represents the maximum number of lattices that Li ions must move on the (020) plane, which represents the distance Li ions move.

[0092] (020) As the number of grid cells decreases, the travel distance of Li ions is shortened, so the initial discharge capacity development is superior.

[0093] From this perspective, [CS(020) / d(020)] ≤ 28 can be satisfied, and preferably 24 ≤ [CS(020) / d(020)] ≤ 27 can be satisfied.

[0094] In relation 1, CS(101), d(101), CS(020), and d(020) can be measured as follows.

[0095] After measuring the diffraction pattern using an X-ray diffraction analyzer (Rigaku equipment) with a scan range (10 to 80˚) and scan speed (2.5˚ / min), the peak positions and FWHM of each plane are analyzed by fitting with a Psudo-Voigt function. Then, the total grating size and interplane distance of the (101) plane and (020) plane are calculated using the Scherrer method.

[0096] Immediately after the end of grinding, the crystallization of the positive active material and the average size of the entire crystal can be controlled according to the average particle size (D50) of the slurry.

[0097] The smaller the average particle size of the slurry, the more nano-sized particles are formed, and the formed nano-sized particles constitute secondary particles.

[0098] The smaller the average particle size of the slurry, the higher the surface energy and the more unstable it becomes due to the large surface area. To lower the high surface energy, the slurry easily combines and reacts at lower temperatures.

[0099] The smaller the average particle size of the slurry, the more contact points between nanoparticles increase during the LMFP synthesis process, and the structure synthesis process and crystallization are facilitated by smooth mass transport due to the low radius of curvature of the contact points between nanoparticles.

[0100] As more crystal nuclei are generated to lower the high surface energy of the slurry, growth is inhibited due to the large number of nuclei, thereby allowing control over the average size of the final crystal. In other words, lowering the average particle size of the slurry can improve the degree of crystallinity.

[0101] However, if the average size of the entire crystal becomes too small, reactivity increases excessively due to the high surface area of ​​the crystal. As a result, there is a possibility that undesirable side reactions may occur in addition to the desired reaction, which can lead to structural instability of the cathode active material.

[0102] In addition, since an excessively large surface area of ​​the crystal can increase contact resistance between particles and actually have an adverse effect on conductivity, it is necessary to control the average size of the crystal.

[0103] In this regard, the average particle size (D50) of the LMFP slurry may be 100 to 240 nm, preferably 150 to 230 nm, and more preferably 180 to 210 nm.

[0104] And the average size of the entire crystal of the positive active material can be 50 to 200 nm, preferably 80 to 110 nm, and more preferably 90 to 108 nm.

[0105] By satisfying the average size of the entire crystal of the positive active material to be 50 to 200 nm, the electrochemical reaction is enhanced by the high surface area of ​​the crystal, and the initial discharge capacity can be 150 mAh / g or more.

[0106] If the average size of the entire crystal is less than 50 nm, the contact area between the positive active material and the electrolyte increases, which may lead to increased side reactions, low initial discharge capacity, and deterioration of lifespan.

[0107] In addition, if the average size of the entire crystal exceeds 200 nm, there may be a problem where the resistance inside the positive active material increases and the capacity decreases.

[0108] As such, there is an inflection point of discharge capacity depending on the crystal size.

[0109] When the crystal size corresponding to the peak discharge capacity is exceeded, that is, when the crystal size is less than or greater than the value, the initial discharge capacity is reduced due to the heat deficiency and under-discharge, respectively.

[0110] Therefore, crystal size can be considered a major measure and criterion for finding the initial discharge capacity.

[0111] The positive active material according to the present invention is LiMn a Fe b It includes lithium iron manganese phosphate (LMFP) represented by PO4(a + b ≤ 1, a > 0, b > 0).

[0112] LMFP has a secondary particle form formed by the aggregation of multiple primary particles.

[0113] In the present invention, "primary particle" refers to a minimum particle unit that is distinguished as a single mass when the cross-section of the positive active material is observed through a scanning electron microscope (SEM), and may consist of a single crystal grain or a plurality of crystal grains.

[0114] Here, "grain" refers to a region in which atoms within a primary particle form a lattice structure in a specific direction.

[0115] The above "secondary particles" refer to aggregates formed by the aggregation of tens to hundreds of primary particles through physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles, i.e., secondary structures.

[0116] LiMn a Fe b In the LMFP represented by PO4(a + b ≤ 1), a > 0 and b > 0 may be possible, and preferably a ≥ 0.4 and b ≥ 0.3.

[0117] Here, the molar ratio of Mn to Fe can satisfy approximately 0.5 : 0.5 to 0.8 : 0.2.

[0118] LiMn a Fe b The reason a + b ≤ 1 in PO4 is that the sum is 1, including the molar content of dopants in addition to Mn and Fe. In this case, the molar ratio of dopants can be 0.005 to 0.015.

[0119] By satisfying a molar ratio of Mn to Fe of 0.5 : 0.5 to 0.8 : 0.2, the theoretical energy density is further improved. If the molar ratio of Mn is too low, the energy density is not improved. Conversely, if the molar ratio of Mn is too high, the stability of the lithium secondary battery is reduced and quality problems may occur.

[0120] The positive active material may further include a dopant to control the average size of the entire crystal.

[0121] 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.

[0122] By including additional doping elements in the cathode active material, high-temperature lifespan and thermal stability can be further improved.

[0123] It is desirable to control the dopant content to control the average size of the entire crystal.

[0124] As the dopant content increases, crystal growth is inhibited, which can result in a decrease in crystal size.

[0125] However, if too much is overdoped, even if the growth of the crystal size is suppressed, it may actually block the movement of Li ions and electrons, which can have an adverse effect on performance.

[0126] In this regard, the positive electrode active material of the present invention may further include 0.5 to 1.5 mol% of a dopant with respect to 100 mol% of the total transition metal, and preferably 0.5 to 1.0 mol%.

[0127] By satisfying a dopant content of 0.5 to 1.5 mol%, it has an advantageous effect in exhibiting an initial discharge capacity of 150 mAh / g or more.

[0128] Here, the transition metals include Mn, Fe, and dopants.

[0129] In order to improve the electrical conductivity of the LMFP positive electrode active material, the present invention may further include a carbon layer coated on the surface of the LMFP.

[0130] The carbon to be coated may include one or more of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite, and preferably may include glucose.

[0131] It is desirable to control the carbon content to control the electrical conductivity of the positive active material and the average size of the entire crystal.

[0132] As carbon content increases, crystal growth is inhibited and conductivity tends to increase.

[0133] However, if the carbon content becomes too high, the excessively large specific surface area (BET) can actually become a factor that hinders electrical flow.

[0134] In this regard, the carbon content of the carbon layer may be 1 to 3 weight% with respect to 100 weight% of the total, and preferably 1.5 to 2.0 weight%.

[0135] By satisfying a carbon content of 1 to 3 weight percent in the carbon layer, carbon is dispersed at a uniform concentration in the positive electrode active material, thereby improving the electrical conductivity of the lithium secondary battery, reducing the average crystal size, and further improving the initial discharge capacity at room temperature.

[0136] Method for manufacturing positive electrode active material

[0137] A method for manufacturing a positive electrode active material according to an embodiment of the present invention is characterized by comprising the steps of preparing and grinding an LMFP precursor, spray-drying the slurry obtained by grinding, and calcining the powder obtained by spray-drying to manufacture a positive electrode active material.

[0138] The positive active material manufactured according to the manufacturing method of the present invention comprises an LMFP formed from the precursors, and the LMFP is LiMn a Fe b It is represented as PO4(a + b ≤ 1, a > 0, b > 0).

[0139] Step of preparing and grinding the LMFP precursor

[0140] As LMFP precursors, lithium precursors, phosphorus precursors, iron precursors, and manganese precursors can be mixed and milled for 4 to 6 hours.

[0141]

[0142] The lithium (Li) precursor may include one or more of Li2CO3, Li(OH), Li(OH)·H2O, LiNO3, and LiH2PO4, and preferably may include one or more of Li2CO3 and LiH2PO4.

[0143] The phosphorus (P) precursor may include one or more 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.

[0144] Iron (Fe) precursors may include FePO4, etc.

[0145] Manganese (Mn) precursors may include Mn3O4, etc.

[0146] Grinding can be performed using beads and wet milling methods.

[0147] The bead size may be 0.3 to 0.5 mm, and preferably 0.3 to 0.4 mm.

[0148] The rotational speed can be performed in the range of 3000 to 4000 rpm / min, and preferably in the range of 3100 to 3500 rpm.

[0149] By satisfying the above bead size and rotation speed, the average particle size of the slurry can be controlled, and as a result, there is an advantageous effect in satisfying the total lattice size of the (101) plane where the Li ions are located.

[0150] In addition, lithium secondary batteries containing a positive electrode active material can secure excellent initial discharge capacity.

[0151] In addition, the average particle size of the secondary particles constituting the anode active material and the primary particles constituting the secondary particles can be controlled through grinding using a wet milling method.

[0152] In the present invention, the average particle size (D50) of the LMFP slurry immediately after grinding is a factor that affects the degree of crystallization, and crystallization occurs better as the average particle size (D50) of the slurry becomes nanoscale.

[0153] In this regard, the average particle size (D50) of the slurry obtained by grinding may be 100 to 240 nm. The average size of the entire crystal of the cathode active material may be 50 to 200 nm.

[0154] Matters related to this are the same as those previously mentioned, so they will be omitted.

[0155] For a total of 100 mol% of transition metals including Mn, Fe, and dopants, 0.5 to 1.5 mol% of dopant can be further mixed.

[0156] 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.

[0157] In the process of manufacturing the cathode active material, mixing in additional doping elements is advantageous for controlling the average size of the entire crystal and can further improve high-temperature lifespan and thermal stability.

[0158] To improve the electrical conductivity of the lithium secondary battery and to control the average size of the entire crystal, 10% or less of a carbon precursor can be further mixed into the LMFP precursor with respect to 100% by weight of the total.

[0159] When the carbon precursor is mixed at 10% by weight or less, the carbon content of the carbon layer can satisfy 3% by weight or less.

[0160] The carbon precursor may include one or more of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite, and preferably may include glucose.

[0161] In addition, one or more dispersants selected from citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, maleic acid, oxalic acid, malonic acid, and ascorbic acid may be further mixed, and preferably, citric acid may be further mixed.

[0162] In the process of manufacturing the positive electrode active material, by further mixing in a dispersant, the precursors in the slurry are uniformly dispersed, which is advantageous for manufacturing high-quality olivine-based LMFP positive electrode active materials for lithium secondary batteries.

[0163] With respect to 100% by weight of the total, 5% by weight or less of a dispersant may be mixed, but is not limited thereto.

[0164] Step of spray-drying the slurry obtained by grinding

[0165] In the step of spray-drying the slurry obtained by grinding, spray drying can be performed using a spray dryer.

[0166] The spray pressure of the spray dryer can be 0.5 to 2 bar, and preferably 1 to 1.5 bar.

[0167] The temperature of the main chamber may be 200 to 300°C, and preferably 220 to 260°C.

[0168] The discharge temperature of the spray dryer can be set to 80 to 160°C, and preferably to 100 to 130°C.

[0169] By setting the spray pressure, main chamber temperature, and outlet temperature of the spray dryer as described above, spherical powder can be obtained from the slurry through spray drying.

[0170] The above spherical powder may be a secondary particle constituting the LMFP.

[0171] Step of manufacturing an anode active material by calcining powder obtained by spray drying

[0172] The powder obtained by spray drying is loaded into a kiln. Then, by firing under high temperature conditions for a predetermined time in an atmosphere where an inert gas is continuously supplied, a positive electrode active material for a lithium secondary battery with a carbon layer coated on the surface of the LMFP can be manufactured.

[0173] The lower the calcination temperature, the slower the crystal growth and the smaller the crystal size. However, since low calcination temperatures adversely affect the synthesis and crystallization of the cathode active material, it is important to control the average size of the entire crystal by adjusting the calcination temperature.

[0174] Calcination can be performed in an inert atmosphere at 630 to 700°C for 1 to 10 hours, and preferably at 650 to 690°C for 3 to 8 hours.

[0175] By satisfying a calcination temperature and calcination time of 630 to 700°C for 1 to 10 hours, the average size of the entire crystal can be controlled to 50 to 200 nm, which is advantageous for demonstrating the performance of the cathode active material.

[0176] Cathode active material for lithium secondary batteries

[0177] According to another embodiment, after long research, the inventors confirmed that the larger the volume of the (101) plane in which the Li ions are located within the LMFP structure, the greater the number of diffusion channels for Li ions within the particle, and the smaller the volume of the (020) plane in which the Li ions are in the diffusion direction, the smaller the space for Li ions to move within the crystal plane, thus having an advantage in the development of the initial discharge capacity of the lithium secondary battery.

[0178] In other words, the number of diffusion channels for Li ions and the distance traveled by Li ions within the crystal are related to the volume of the crystal plane (the three-dimensional Li ion diffusion space), and had a close influence on the initial discharge capacity of the LMFP cathode material performance.

[0179] First, in order to increase the number of diffusion channels for Li ions, the total volume of the (101) plane must be large.

[0180] (101) Since the total volume of the plane is spherical, corresponding to the 3-dimensional Li ion diffusion space, V(101) = (4 / 3)π Χ (CS(101) / 2) 3 It was defined as.

[0181] (101) To explain the total volume of the plane, CS (101) is defined as the total lattice size of the plane (101) (the total size of the diffusion channel of the Li ion).

[0182] When lattices are arranged in a repeating sequence, the total length of the arranged lattices represents the crystal size (CS).

[0183] The inventor determined that CS (101) has a significant effect on V (101), so (CS (101) / 2) 3As shown, the cube was used as a weight, and V (101) was assumed to be a spherical volume and calculated by multiplying by (4 / 3)π. In addition, to apply the value corresponding to the radius in the spherical volume formula, CS (101), which corresponds to the concept of the diameter of the sphere, was divided by 2.

[0184] Secondly, in order to shorten the movement distance of Li ions within the crystal, the total volume of the (020) plane, which is the direction of diffusion of Li ions, must be small. The (101) plane and the (020) plane have directions perpendicular to each other.

[0185] Since the total volume of the (020) plane is spherical and corresponds to the 3-dimensional Li ion diffusion space, V(020) = (4 / 3)π Χ (CS(020) / 2) 3 It was defined as.

[0186] To explain the volume of the (020) plane, CS (020) is defined as the total lattice size of the (020) plane having the same direction as the movement direction of the Li ion (maximum movement distance that Li ions must travel within the lattice when inserted and extracted).

[0187] (020) As the total lattice size of the plane becomes smaller, the travel distance of Li ions is shortened, thereby facilitating the movement of Li ions and exhibiting excellent initial discharge capacity.

[0188] From these research results, the inventors confirmed that the initial discharge capacity is superior as the volume of the (101) plane increases and the volume of the (020) plane decreases.

[0189] And it was confirmed that the volume containing the maximum and shortest travel distances of Li ions in the (101) plane and (020) plane, rather than the total grid size in the (101) plane and (020) plane, has a significant effect on the initial discharge capacity.

[0190] Accordingly, the inventors completed V (101) / V (020) by placing V (101), which represents the total volume of the (101) plane, in the numerator and setting V (020), which is more advantageous for performance when smaller, as the denominator, and the larger the value of V (101) / V (020), the more advantageous it is for the initial discharge capacity.

[0191] Furthermore, ionic conductivity, as well as the distance traveled by Li ions, influences the speed at which Li ions move from within the particle to the electrolyte and from the electrolyte to the particle.

[0192] Since the concentration (content) of the dopant that improves ion conductivity also has a significant effect on the discharge capacity, D' was reflected in parameter relationship 2 as 1 + the content (mol%) of the dopant.

[0193] As a result of including 0.1 to 0.5 mol% of dopant relative to 100 mol% of total dopant, Mn, and Fe, it exhibited an excellent discharge capacity compared to a positive electrode active material that did not include a dopant or had a dopant content outside the above range.

[0194] Cation doping showed an effect of improving the structural stability and ion conductivity of the positive electrode active material.

[0195] However, when the dopant content exceeded the above range, the doping element acted as a defect within the lattice, thereby reducing the surface reactivity of the positive electrode active material and showing a tendency for discharge capacity to decrease.

[0196] Therefore, the parameter D' (1 + dopant content (mol%)) related to the dopant content was added to the parameter related to the volume above.

[0197] In addition, since the dopant content is located in the denominator of Equation 2, it was determined that it is difficult to quantify it in the non-doped state D', so a minimum constant 1 was introduced.

[0198] Furthermore, it was confirmed that ion conductivity affects the discharge capacity, and that the smaller the average particle size (D50) (㎛) of the slurry after grinding the raw material as measured by a Malvern particle size meter, the more the uniformity of the atomic arrangement of Fe and Mn is improved, thereby enhancing the ion conductivity within the particles.

[0199] The result of improved ionic conductivity facilitated the movement of Li ions.

[0200] Therefore, the average particle size of the slurry after grinding the raw material (D50(WM)), which is more advantageous for performance the smaller it is, and the value multiplied by D' were set as the denominator.

[0201] The lower limit value (3.1) of Equation 2 was set as a standard satisfying a discharge capacity of 150 mAh / g or more, taking into account the practical aspects of the LMFP.

[0202] In particular, the value of [V(101) / V(020)] / [D'ΧD50(WM)] in Equation 2 must be 3.1 or higher and 5.1 or lower for the movement of Li ions to be smooth and for electrochemical performance to be improved, resulting in an initial discharge capacity of 150 mAh / g or higher.

[0203] Conversely, when the value of [V(101) / V(020)] / [D'ΧD50(WM)] in Equation 2 is less than 3.1 or greater than 5.1, it means that the number of diffusion channels for Li ions is small, the travel distance of Li ions is long, the doping content is too high, or the average particle size of the slurry is large, so it was difficult to secure the initial discharge capacity due to the low mobility of Li ions.

[0204] Therefore, the present invention has technical significance in that it can secure an excellent initial discharge capacity of a lithium secondary battery by satisfying the relationship 2 of 3.1 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.1.

[0205] In addition, a new relationship 2 was used in combination with the total lattice size (CS) of the crystal planes, the volume of the (101) plane and the (020) plane, the dopant content, and the average particle size of the slurry, and significant results were obtained in the discharge capacity of the lithium secondary battery.

[0206] A positive electrode active material according to another embodiment of the present invention is characterized by satisfying the following relationship 2.

[0207] [Relationship 2]

[0208] 3.1 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.1

[0209] In the above equation 2, V (101) is the total volume of the (101) plane where the Li ion is located, and V (020) is the total volume of the (020) plane in the direction in which the Li ion moves.

[0210] D' is the content of 1+ dopant (mol%), and D50 (WM) is the average particle size (D50) (㎛) measured by a Malvern particle size meter after grinding the raw material.

[0211] In the above Equation 2, V(101) = (4 / 3)π Χ (CS(101) / 2) 3 It can satisfy.

[0212] The above CS (101) is the total grating size (nm) of the (101) plane measured by an X-ray diffraction analyzer.

[0213] In the LMFP constituting the positive electrode active material, the (101) plane is the plane where the Li ions are located, and the exposure of the (101) plane has a close influence on the performance of the LMFP positive electrode material.

[0214] When the lattices are arranged in a repeating sequence, the total length of the arranged lattices becomes the total size of the crystal, so the total lattice size of the (101) plane represents the crystal size of the (101) plane, and the crystal growth tendency differs for each crystal plane.

[0215] In the above Equation 2, V(020) = (4 / 3)π Χ (CS(020) / 2) 3 It can satisfy.

[0216] The above CS (020) is the total grating size (nm) of the (020) plane measured by an X-ray diffraction analyzer.

[0217] In relation 2, preferably 3.5 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.0, and more preferably 3.8 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.0.

[0218] By satisfying the above range, as the number of diffusion channels for Li ions increases and the space for Li ion movement decreases, the mobility of Li ions becomes smooth, and an excellent initial discharge capacity can be secured.

[0219] In the above relationship 2, CS (101), which is the total grid size of plane (101), is larger than CS (020), which is the total grid size of plane (020), and the difference between CS (101) and CS (020) can be 3 or more.

[0220] In LMFP, the fact that the crystal size (total lattice size) of the (101) plane is small means that there may be more particles of the (101) plane in the same volume of sample, which is consistent with the fact that more planes may be exposed.

[0221] However, if the crystal size of the (101) plane becomes too small, the reactivity increases excessively due to the high surface area of ​​the crystal. As a result, there is a possibility that side reactions that should not occur may occur in addition to the desired reaction, which can make the cathode active material structurally unstable.

[0222] In addition, it is necessary to control the crystal size because an excessively high surface area of ​​the (101) plane crystal can increase contact resistance between particles and have an adverse effect on conductivity.

[0223] In this regard, the total lattice size of the plane (101), CS (101), can be 70 to 100 nm, preferably 75 to 98 nm, and more preferably 79 to 97 nm.

[0224] Since CS (101) satisfies 70 to 100 nm, the electrochemical reaction is enhanced by the high surface area of ​​the crystal, and the initial discharge capacity is 150 mAh / g or more, which has an advantageous effect.

[0225] CS (020) is the total lattice size of the (020) plane having the same direction as the movement direction of the Li ion (maximum movement distance that Li ions must travel within the lattice when inserted and extracted), and the smaller the total lattice size of the (020) plane, the shorter the movement distance of the Li ion, so the initial discharge capacity development is superior.

[0226] In this regard, the total lattice size of the (020) plane, CS (020), can be 70 to 100 nm, preferably 72 to 95 nm, and more preferably 75 to 92 nm.

[0227] At this time, CS (101) is greater than CS (020), and the difference (nm) between CS (101) and CS (020) can satisfy 3 or more, and preferably the difference between CS (101) and CS (020) can satisfy 3 to 8.

[0228] In Equation 2, CS (101) and CS (020) can be measured under the Scan range (10 ~ 80˚) and Scan speed (2.5˚ / min) conditions of an X-ray diffraction analyzer (Rigaku equipment), and since the specific details are the same as those previously described, they will be omitted.

[0229] Immediately after grinding, the crystallization and crystal size of the positive active material can be controlled according to the average particle size (D50(WM)) of the slurry.

[0230] The smaller the average particle size of the slurry, the more nano-sized particles are formed, and the formed nano-sized particles constitute secondary particles.

[0231] The smaller the average particle size of the slurry, the higher the surface energy and the more unstable it becomes due to the large surface area. To lower the high surface energy, the slurry easily combines and reacts at lower temperatures.

[0232] The explanation regarding the degree of crystallization and crystal size according to the average particle size of the slurry is the same as previously described, so it will be omitted.

[0233] Since an excessively large surface area of ​​the crystal can increase contact resistance between particles and actually have an adverse effect on conductivity, it is necessary to control the crystal size.

[0234] In this regard, the average particle size (D50(WM)) of the slurry may be 0.210 μm or less, preferably 0.150 to 0.208 μm, and more preferably 0.180 to 0.206 μm.

[0235] The positive active material according to the present invention is LiMn a Fe b It includes lithium iron manganese phosphate (LMFP) represented by PO4(a + b ≤ 1, a > 0, b > 0).

[0236] LMFP has a secondary particle form formed by the aggregation of multiple primary particles.

[0237] Details regarding primary and secondary particles are the same as those previously mentioned, so they will be omitted.

[0238] LiMn a Fe b In the LMFP represented by PO4(a + b ≤ 1), a > 0 and b > 0 may be possible, and preferably a ≥ 0.4 and b ≥ 0.3.

[0239] Here, the molar ratio of Mn to Fe can satisfy approximately 0.5 : 0.5 to 0.8 : 0.2.

[0240] LiMn a Fe b The reason a + b ≤ 1 in PO4 is that the sum is 1, including the molar content of dopants in addition to Mn and Fe. In this case, the molar ratio of dopants can be 0.001 to 0.005.

[0241] By satisfying a molar ratio of Mn to Fe of 0.5 : 0.5 to 0.8 : 0.2, the theoretical energy density is further improved. If the molar ratio of Mn is too low, the energy density is not improved. Conversely, if the molar ratio of Mn is too high, the stability of the lithium secondary battery is reduced and quality problems may occur.

[0242] The positive electrode active material may further include a dopant to ensure structural stability and improved ion conductivity.

[0243] The above dopant may include one or more of Ti and Mg.

[0244] By including one or more doping elements among Ti and Mg in the positive electrode active material, the high-temperature lifespan and thermal stability can be further improved, and the structural stability and ion conductivity can be improved.

[0245] The dopant content can affect the development of discharge capacity.

[0246] As the dopant content increases, crystal growth is inhibited, which can result in a decrease in crystal size.

[0247] However, if too much is overdoped, even if the growth of the crystal size is inhibited, it may reduce the surface reactivity of the positive active material and decrease the discharge capacity.

[0248] In this regard, the positive electrode active material of the present invention may contain 0.1 to 0.5 mol% of a dopant with respect to 100 mol% of the total dopant, Mn, and Fe.

[0249] By satisfying a dopant content of 0.1 to 0.5 mol%, it has an advantageous effect in exhibiting an initial discharge capacity of 150 mAh / g or more.

[0250] In order to improve the electrical conductivity of the LMFP positive electrode active material, the present invention may further include carbon coated on the surface of the LMFP.

[0251] The type of carbon to be coated is the same as previously mentioned, so it will be omitted.

[0252] It is desirable to control the carbon content to control the electrical conductivity of the positive electrode active material.

[0253] As carbon content increases, crystal growth is inhibited, and conductivity tends to increase.

[0254] However, if the carbon content becomes too high, the excessively large specific surface area (BET) can actually become a factor that hinders electrical flow.

[0255] In this regard, the coated carbon content may be 1 to 3 weight% with respect to 100 weight% of the total, and preferably 1.5 to 2.0 weight%.

[0256] By satisfying a coated carbon content of 1 to 3 weight percent, carbon is dispersed at a uniform concentration 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.

[0257] Method for manufacturing positive electrode active material

[0258] A method for manufacturing a positive electrode active material according to another embodiment of the present invention is characterized by comprising the steps of preparing and grinding an LMFP precursor, spray-drying the slurry obtained by grinding, and calcining the powder obtained by spray-drying to manufacture a positive electrode active material.

[0259] The positive active material manufactured according to the manufacturing method of the present invention comprises an LMFP formed from the precursors, and the LMFP is LiMn a Fe b It is represented as PO4(a + b ≤ 1, a > 0, b > 0).

[0260] Step of preparing and grinding the LMFP precursor

[0261] As LMFP precursors, lithium precursors, phosphorus precursors, iron precursors, and manganese precursors can be mixed and milled for 4 to 6 hours.

[0262] Details regarding lithium (Li) precursors, phosphorus (P) precursors, iron (Fe) precursors, and manganese (Mn) precursors are the same as those previously mentioned, so they will be omitted.

[0263] Details regarding bead size, rotation speed, and wet milling method related to grinding are the same as those previously mentioned, so they will be omitted.

[0264] In the present invention, the average particle size (D50(WM)) of the slurry immediately after grinding is a factor that affects the degree of crystallinity.

[0265] As the average particle size (D50(WM)) of the slurry becomes nanoscale, crystallization occurs more effectively, which is advantageous for satisfying Equation 2.

[0266] In this regard, the average particle size (D50(WM)) of the slurry obtained by grinding may be 0.210 μm or less.

[0267] Matters related to this are the same as those previously mentioned, so they will be omitted.

[0268] 0.1 to 0.5 mol% of dopant may be mixed with respect to 100 mol% of the total of Mn, Fe, and dopant. The dopant may include one or more of Ti and Mg.

[0269] To improve the electrical conductivity of the lithium secondary battery, 10% by weight or less of a carbon precursor may be further mixed into the LMFP precursor with respect to 100% by weight of the total.

[0270] If the carbon precursor is mixed at 10% by weight or less, the coated carbon content can satisfy 3% by weight or less.

[0271] Details regarding carbon precursors are the same as those previously mentioned, so they will be omitted.

[0272] In addition, 5% by weight or less of a dispersant may be further mixed into the LMFP precursor, and details regarding the type and content of the dispersant are the same as those previously described and will be omitted.

[0273] Step of spray-drying the slurry obtained by grinding

[0274] In the step of spray-drying the slurry obtained by grinding, spray drying can be performed using a spray dryer.

[0275] Details regarding the spray pressure of the spray dryer, the temperature of the main chamber, the temperature of the spray dryer outlet, and the spherical powder are the same as previously described and will therefore be omitted.

[0276] Step of manufacturing an anode active material by calcining powder obtained by spray drying

[0277] The powder obtained by spray drying is loaded into a kiln. Then, by firing under high temperature conditions for a predetermined time in an atmosphere where an inert gas is continuously supplied, a positive electrode active material for a lithium secondary battery with carbon coated on the surface of the LMFP can be manufactured.

[0278] The lower the calcination temperature, the slower the crystal growth and the smaller the crystal size. However, since low calcination temperatures adversely affect the synthesis and crystallization of the cathode active material, it is important to control the calcination temperature.

[0279] Calcination can be performed in an inert atmosphere at 630 to 700°C for 1 to 10 hours, and preferably at 650 to 690°C for 3 to 8 hours.

[0280] By satisfying a calcination temperature and calcination time of 630 to 700°C for 1 to 10 hours, it is advantageous to demonstrate the performance of the cathode active material.

[0281] Lithium secondary battery

[0282] A lithium secondary battery according to an embodiment of the present invention is characterized by comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode active material (satisfying Equation 1) described above is included.

[0283] The 0.1C discharge capacity of the lithium secondary battery may be 150 mAh / g or more, and preferably 150 to 160 mAh / g.

[0284] A lithium secondary battery according to another embodiment of the present invention is characterized by comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode active material (satisfying Equation 2) described above is included.

[0285] The 0.1C discharge capacity of the lithium secondary battery may be 150 mAh / g or more, and preferably 152 to 160 mAh / g.

[0286] anode

[0287] A lithium secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator, and among these, the positive electrode includes a positive electrode material comprising a positive electrode active material, a conductive material, and a binder, and a current collector.

[0288] The anode according to the present invention comprises a current collector and an anode material disposed on at least one surface of the current collector and comprising the aforementioned anode active material.

[0289] A detailed explanation regarding the positive electrode active material will be omitted.

[0290] The cathode material acts as a lithium source in lithium-ion batteries and is a key material that determines battery capacity and average voltage.

[0291] The cathode material may include a binder and a conductive material.

[0292] The above binder serves to effectively bond the positive active material particles to each other and also to effectively bond the positive active material to the current collector.

[0293] Representative examples of binders include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0294] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials comprising mixtures thereof.

[0295] The above anode is manufactured by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and applying this composition to a current collector.

[0296] Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted in this specification. The solvent may include N-methylpyrrolidone, but is not limited thereto.

[0297] The above current collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.

[0298] cathode

[0299] The above cathode includes a current collector and a cathode material formed on the current collector, and the cathode material may include a cathode active material.

[0300] The above negative electrode 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.

[0301] The material capable of reversibly intercalating / deintercalating the above lithium ions may be, for example, a carbon material, and any carbon-based negative electrode active material generally used in the above lithium secondary battery may be used.

[0302] For example, carbon-based cathode active materials can use crystalline carbon, amorphous carbon, or a combination thereof.

[0303] As the above lithium metal alloy, an alloy of a metal selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0304] Examples of materials capable of doping and dedoping the above 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).

[0305] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, etc.

[0306] The above cathode material also includes a binder and may optionally further include a conductive material.

[0307] The above binder can serve to effectively attach the negative electrode active material particles to each other and also effectively attach the negative electrode active material to the current collector.

[0308] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any electronically conductive material that does not cause chemical changes can be used.

[0309] For example, the above current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0310] The above-mentioned cathode and anode may be manufactured by preparing an active material composition by mixing an active material, a conductive material, and a binder in a solvent, and applying the composition to a current collector, and the present invention does not limit the method of manufacturing the electrodes.

[0311] The above solvent may include N-methylpyrrolidone, but is not limited thereto.

[0312] electrolytes

[0313] The above electrolyte may be a non-aqueous electrolyte or a solid electrolyte, and may be used in which a lithium salt is dissolved.

[0314] The above-mentioned non-aqueous electrolyte may include an organic solvent, and the above-mentioned non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0315] The above organic solvent may be, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide. These may be used individually or in combination.

[0316] In particular, a mixed solvent of cyclic carbonates and chain carbonates can be preferably used.

[0317] In addition, as an electrolyte, a gel-type polymer electrolyte in which an electrolyte solution is impregnated into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N, is possible.

[0318] The above lithium salt is a material 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 facilitating the movement of lithium ions between the positive and negative electrodes.

[0319] The above lithium salt may be applied without limitation to any commonly used in the art, provided that it does not impede the purpose of the present invention.

[0320] 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.

[0321] Depending on the type of the above lithium secondary battery, a separator may be present between the positive and negative electrodes.

[0322] As such separators, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof may be used, and of course, mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators may be used.

[0323] 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; they can be classified into cylindrical, prismatic, coin, and pouch types depending on their shape; and they can be divided into bulk and thin-film types depending on their size.

[0324] The present invention does not limit the structure and manufacturing method of the battery.

[0325] As such, specific embodiments of the positive electrode active material and the lithium secondary battery using it are as follows.

[0326] 1. Preparation of a positive electrode active material according to an example

[0327] Manufacturing method of Example 1 in [Table 1] below

[0328] Wet Bead Mill (WM): 314 g of a mixture of FePO4, Mn3O4, LiH2PO4, Li2CO3, and TiO2 as a dopant in a molar ratio of Li:Mn:Fe:Ti:P = 1.03:0.597:0.398:0.005:1 and glucose (C6H2) as a carbon source 12 24g (7 wt%) of O6 and 5g of citric acid (C6H8O7) as a dispersant were mixed with 700g of ultrapure water, and the raw material (D50) was ground to approximately 202nm in a bead mill at 3500 rpm / min. (0.3mm zirconia beads used. NETZSCH MINISERIES model)

[0329] Spray Drying (SD): The mixed slurry obtained after wet bead milling was spray-dried using a spray dryer (Spray pressure: 1.5 bar, Main chamber temperature: 250℃, Outlet temperature: 110℃)

[0330] Calcination (High-temperature heat treatment): 30g of SD products were placed in a graphite saga and calcined under a nitrogen atmosphere (calcination temperature: 680°C, calcination holding time: 6 hours, heating rate: 5°C / min, nitrogen flow rate: 1.0 L / min).

[0331] Example 2

[0332] A positive electrode active material was prepared under the same conditions as in Example 1, except that the calcination temperature was 650℃.

[0333] Example 3

[0334] A positive electrode active material was prepared under the same conditions as in Example 1, except that the average particle size (D50) of the slurry was 187 nm and the calcination temperature was 670°C.

[0335] Comparative Example 1

[0336] A positive electrode active material was prepared under the same conditions as in Example 1, except that the average particle size (D50) of the slurry was 394 nm and the calcination temperature was 700°C.

[0337] Comparative Example 2

[0338] A positive electrode active material was prepared under the same conditions as in Example 1, except that 1 mol% of MgO was added (molar ratio of Li:Mn:Fe:Ti:Mg:P = 1.03:0.591:0.394:0.005:0.01:1), the average particle size (D50) of the slurry was 287 nm, and the calcination temperature was 700°C.

[0339] In Table 1 below, "C (weight%) after firing" is the carbon content (weight%) of the carbon coating layer after firing.

[0340] [Table 1]

[0341]

[0342] 2. Method for evaluating physical properties and results

[0343] 1) Electrochemical (coin half-cell) electrode coating: An electrode slurry was prepared by adding 4.3g of NMP to 4.5g of LMFP, 0.25g of SuperP (conductive carbon black), and 3.125g of PVDF 8wt.% (KF7208, a solution of binder dissolved in NMP). After electrode coating using a doctor blade, the electrodes were dried at 130°C for 2 hours and rolled to a height of 0.2 mm. (Specifications of fabricated coin half-cell electrodes: mass loading - 10~11 mg / cm² 2 ).

[0344] 2. Electrochemical C-rate capacity evaluation conditions: 24 hours of aging immediately after cell fabrication (temperature 25℃), one formation cycle (2.5-4.4V) with 0.1 C charge / discharge, a fixed charge rate of 0.1C, and one measurement each at discharge rates of 0.1, 0.33, 1, 2, 5, and 10 C (2.5-4.4V), using CC-CV charge mode (Charge step condition: fixed at 0.1C, 0.05 C cut-off current). A 20-minute rest was performed immediately after the charge and discharge steps.

[0345] 3. Measurement of average particle size of slurry (D50(WM)): 0.02 g of LMFP slurry after wet bead milling was measured using a Malvern particle size meter with 1 ml of IGEPAL 1.0 wt.% dispersant.

[0346] 4. Average Crystal Size (CS): 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. To analyze the crystal information regarding the entire diffraction pattern, the Fundamental Parameter (FP) method was used as the functional model, and the average crystal size was calculated by assuming spherical particles. (XRD measurement conditions: Scan range (10⁻⁸⁰) o ), Scan speed(2.5 o / min) / Analysis was performed with a reliability of Rwp 2.5 or less and an S value 2 or less).

[0347] 5. CS(101), d(101), CS(020), d(020): After measuring the diffraction pattern using an X-ray diffraction analyzer (Rigaku equipment) with a Scan range (10 ~ 80˚) and Scan speed (2.5˚ / min), the peak positions and FWHM of each plane were analyzed by fitting with a Psudo-Voigt function. Then, the total grating size (nm) and interplane distance (Å) of the (101) plane and the (020) plane were calculated using the Scherrer method.

[0348] [Table 2]

[0349]

[0350] Examples 1 to 3 showed an average crystal size of 110 nm or less.

[0351] Examples 1 to 3 showed a lattice number of (101) planes of 19 or more, so the number of diffusion channels for Li ions was large, and a lattice number of (020) planes of 28 or less, so the travel distance of Li ions was shortened.

[0352] Examples 1 to 3 satisfied [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75 of Equation 1, thereby showing an initial discharge capacity of the lithium secondary battery at room temperature of 150 mAh / g or more.

[0353] Comparative Examples 1 and 2 showed an average crystal size of 120 nm or more.

[0354] Comparative Examples 1 and 2 had a large number of diffusion channels for Li ions, with 19 or more lattice points of the (101) plane, but compared to Examples 1 to 3, the number of lattice points of the (020) plane was large, so the travel distance of Li ions increased.

[0355] The results of Comparative Examples 1 and 2 indicate that the Li insertion and extraction reactions were not smooth, and did not satisfy [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75 of Equation 1. Accordingly, the initial discharge capacity of the lithium secondary battery at room temperature in Comparative Examples 1 and 2 was significantly low.

[0356] From these results, it can be seen that Equation 1, which uses the number of grids of the (101) plane calculated from the total grid size of the (101) plane of the LMFP positive electrode active material and the number of grids of the (020) plane calculated from the total grid size of the (020) plane and the number of grids of the (020) plane calculated from the distance between the (020) planes, has a significant effect on the room temperature initial discharge capacity of the lithium secondary battery.

[0357] 3. Preparation of a positive electrode active material according to another embodiment

[0358] Manufacturing method of Example 4 in [Table 3] below

[0359] Wet Bead Mill (WM): 314 g of a mixture of FePO4, Mn3O4, LiH2PO4, Li2CO3, and MgO as a dopant in a molar ratio of Li:Mn:Fe:Mg:P = 1.03:0.597:0.398:0.005:1, and glucose (C6H2) as a carbon source 12 24g (7 wt%) of O6 and 5g of citric acid (C6H8O7) as a dispersant were mixed with 700g of ultrapure water, and the raw material (D50(WM)) was ground to approximately 0.194㎛ in a bead mill at 3500rpm. (0.3mm zirconia beads used. NETZSCH MINISERIES model)

[0360] Spray Drying (SD): The mixed slurry obtained after wet bead milling was spray-dried using a spray dryer (Spray pressure: 1.5 bar, Main chamber temperature: 250℃, Outlet temperature: 110℃)

[0361] Calcination (High-temperature heat treatment): 30g of SD products were placed in a graphite saga and calcined under a nitrogen atmosphere (calcination temperature: 670°C, calcination holding time: 6 hours, heating rate: 5°C / min, nitrogen flow rate: 1.0 L / min).

[0362] Example 5

[0363] A cathode active material was prepared under the same conditions as in Example 4, except that it was doped with 0.1 mol% TiO2 and 0.1 mol% MgO as dopants (Li:Mn:Fe:Ti:Mg:P = 1.03:0.5988:0.3992:0.001:0.001:1 molar ratio) and the average particle size (D50(WM)) of the slurry was 0.206 μm.

[0364] Example 6

[0365] A cathode active material was prepared under the same conditions as in Example 4, except that 0.5 mol% of TiO2 was doped as a dopant (Li:Mn:Fe:Ti:P = 1.03:0.597:0.398:0.005:1 molar ratio) and the average particle size (D50(WM)) of the slurry was 0.187 μm.

[0366] Comparative Example 3

[0367] A positive electrode active material was prepared under the same conditions as in Example 4, except that it was cation-undoped (Li:Mn:Fe:P = 1.03:0.6:0.4:1 molar ratio) and the calcination temperature was 700℃.

[0368] Comparative Example 4

[0369] A positive electrode active material was prepared under the same conditions as in Example 4, except that 0.3 mol% of TiO2 and 0.3 mol% of MgO were doped as dopants (Li:Mn:Fe:Ti:Mg:P = 1.03:0.5964:0.3976:0.003:0.003:1 molar ratio) and the calcination temperature was 730℃.

[0370] Comparative Example 5

[0371] A positive electrode active material was prepared under the same conditions as in Example 4, except that 0.5 mol% of TiO2 and 1 mol% of MgO were doped as dopants (Li:Mn:Fe:Ti:Mg:P = 1.03:0.591:0.394:0.005:0.01:1 molar ratio), the raw material (D50(WM)) was ground to about 0.287 μm, and the calcination temperature was 700°C.

[0372] Example 6 of Tables 3 and 4 is a positive active material prepared under the same conditions as Example 3 of Tables 1 and 2.

[0373] Comparative Example 5 in Tables 3 and 4 is a positive active material prepared under the same conditions as Comparative Example 2 in Tables 1 and 2.

[0374] [Table 3]

[0375]

[0376] 4. Method for evaluating physical properties and results

[0377] The evaluation methods for 1) electrochemical (coin half-cell) electrode coating, 2) electrochemical C-rate capacity evaluation conditions, 3) slurry average particle size (D50(WM)) measurement after raw material grinding, and 4) CS (101) and CS (020) (total grid size of the (101) plane and (020) plane) in Tables 3 and 4 were conducted in the same manner as the evaluation methods in Tables 1 and 2 above.

[0378] [Table 4]

[0379]

[0380] Examples 4 to 6 contained 0.1 to 0.5 mol% of one or more dopants among Ti and Mg, and D50(WM) was 0.21 μm or less.

[0381] In addition, Examples 4 to 6 satisfy V (101) from CS (101) and V (020) from CS (020), so the number of diffusion channels for Li ions was large and the travel distance of Li ions was shortened.

[0382] Examples 4 to 6 satisfied 3.1 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.1 of Equation 2, thereby showing an initial discharge capacity of the lithium secondary battery at room temperature of 150 mAh / g or more.

[0383] Comparative Examples 3 to 5 do not contain one or more of Ti and Mg dopants, or the dopant content deviates from 0.1 to 0.5 mol%, or deviates from at least one of the ranges of D50 (WM), CS (101) and CS (020).

[0384] Specifically, Comparative Example 3 is an example that does not contain a dopant, and it appears that there is no improvement effect on the structural stability and ion conductivity of the positive electrode active material, and the value of Equation 2 exceeded 5.1.

[0385] In addition, Comparative Example 3 showed that CS (101) and CS (020) were 94 nm or larger, and the difference between CS (101) and CS (020) was small, less than 2.

[0386] From these results, it can be seen that V(020) is large, and since the space for Li ion movement is wide, it is disadvantageous for the development of the initial discharge capacity.

[0387] Comparative Example 3 showed an initial discharge capacity of less than 150 mAh / g at room temperature for the lithium secondary battery.

[0388] Comparative Example 4 is an example in which the dopant content exceeded 0.5 mol%, and the surface reactivity of the cathode active material was reduced, resulting in a value of Equation 2 of less than 3.1.

[0389] In addition, Comparative Example 4 could not expect an improvement in ion conductivity within the particle because the uniformity of the arrangement of Fe and Mn atoms was not sufficiently improved as D50(WM) exceeded 0.210 μm.

[0390] In addition, Comparative Example 4 showed that CS (101) and CS (020) were 94 nm or larger, and the difference between CS (101) and CS (020) was small, less than 2.

[0391] From these results, it can be seen that Comparative Example 4 is disadvantageous for the initial discharge capacity development because V (020) is large and the space for the movement of Li ions is wide.

[0392] Comparative Example 5 is an example in which the dopant content exceeded 0.5 mol%, and the surface reactivity of the cathode active material was reduced, resulting in a value of Equation 2 of less than 3.1.

[0393] In addition, Comparative Example 5 could not expect an improvement in ion conductivity within the particle because the uniformity of the arrangement of Fe and Mn atoms was not sufficiently improved as D50(WM) exceeded 0.210 μm.

[0394] The results of Comparative Examples 3 to 5 indicate that the movement of Li ions is not smooth depending on the movement speed and distance of the Li ions, and the relationship 3.1 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.1 of Equation 2 was not satisfied.

[0395] Accordingly, Comparative Examples 3 to 5 had significantly low initial discharge capacities at room temperature for lithium secondary batteries.

[0396] From these results, it can be seen that Equation 2, which combines the volume of the (101) plane calculated from the total lattice size of the (101) plane of the LMFP positive electrode active material, the volume of the (020) plane calculated from the total lattice size of the (020) plane, the dopant content, and the average particle size (D50) of the slurry, has a significant effect on the initial discharge capacity of the lithium secondary battery at room temperature.

[0397] Although the present invention has been described above with reference to the illustrated drawings, the present invention is not limited by the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration according to the present invention were not explicitly described while explaining the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized.

Claims

1. A positive active material satisfying the following relationship 1. [Relationship 1] [CS(101) / d(101)] / [CS(020) / d(020)] ≥ 0.75 In the above equation 1, CS (101) is the total grating size (nm) of the (101) plane measured by an X-ray diffraction analyzer, d (101) is the interplanar distance (Å) of the (101) plane, CS (020) is the total grating size (nm) of the (020) plane, and d (020) is the interplanar distance (Å) of the (020) plane.

2. In Paragraph 1, LiMn a Fe b A positive electrode active material comprising lithium manganese iron phosphate (LMFP) represented by PO4(a + b ≤ 1, a > 0, b > 0).

3. In Paragraph 1, In the above relationship 1, A positive active material satisfying 18 ≤ [CS(101) / d(101)] ≤ 22.

4. In Paragraph 1, In the above relationship 1, A positive active material satisfying [CS(020) / d(020)] ≤ 28.

5. In Paragraph 1, A positive active material having an average crystal size of 50 to 200 nm.

6. In Paragraph 2, The above lithium manganese iron phosphate (LMFP) further includes a dopant, and A positive electrode active material comprising 0.5 to 1.5 mol% of a dopant with respect to 100 mol% of the total transition metals of the above Mn, Fe, and dopants.

7. In Paragraph 6, The above dopant comprises one or more of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, Y, P, V, and Sr, making it an anode active material.

8. In Paragraph 2, The above-mentioned lithium manganese iron phosphate (LMFP) surface further comprises a carbon layer coated thereon, A positive electrode active material having a carbon content of 1 to 3 weight percent based on 100 weight percent of the total carbon layer.

9. Anode comprising the positive active material of any one of claims 1 to 8; cathode; and A lithium secondary battery containing an electrolyte.

10. A positive active material satisfying the following relationship Equation 2. [Relationship 2] 3.1 ≤ [V(101) / V(020)] / [D'ΧD50(WM)] ≤ 5.1 In the above equation 2, V (101) is the total volume of the (101) plane where the Li ion is located, V (020) is the total volume of the (020) plane in the direction of movement of the Li ion, D' is the content of the 1+ dopant (mol%), and D50 (WM) is the average particle size (D50) (μm) measured by a Malvern particle size meter after grinding the raw material.

11. In Paragraph 10, In the above relationship 2, The above V(101) = (4 / 3)π Χ (CS(101) / 2) 3 Satisfying, The above CS (101) is a positive active material with a total lattice size (nm) of the (101) plane measured by an X-ray diffraction analyzer.

12. In Paragraph 10, In the above relationship 2, The above V(020) = (4 / 3)π Χ (CS(020) / 2) 3 Satisfying, The above CS (020) is a positive active material with a total lattice size (nm) of the (020) plane measured by an X-ray diffraction analyzer.

13. In Paragraph 10, In the above relationship 2, The above V(101) = (4 / 3)π Χ (CS(101) / 2) 3 Satisfying, The above V(020) = (4 / 3)π Χ (CS(020) / 2) 3 Satisfying, The above CS (101) is larger than CS (020), and The difference between the above CS (101) and CS (020) is 3 or more, and the positive active material satisfies this.

14. In Paragraph 10, The above D50(WM) is a positive active material having a thickness of 0.210㎛ or less.

15. In Paragraph 10, LiMn a Fe b A positive electrode active material comprising lithium manganese iron phosphate (LMFP) represented by PO4(a + b ≤ 1, a > 0, b > 0).

16. In Paragraph 10, The above dopant is a positive active material comprising one or more of Ti and Mg.

17. In Paragraph 15, The above lithium manganese iron phosphate (LMFP) includes a dopant, and A positive electrode active material comprising 0.1 to 0.5 mol% of a dopant with respect to 100 mol% of the total of the above dopants, Mn, and Fe.

18. In Paragraph 15, The above includes carbon coated on the surface of the lithium manganese iron phosphate (LMFP), and A positive electrode active material having a carbon content of 1 to 3 weight percent based on 100 weight percent of the total.

19. Anode comprising the positive active material of any one of claims 10 to 18; cathode; and A lithium secondary battery containing an electrolyte.

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