Cathode active material and secondary battery including same

Abstract

The present invention provides a cathode active material characterized in that, in a particle size distribution (PSD) graph, at least two peaks are present, and a ratio (A / B) of an area (A) in the 0.1-1 μm region to an area (B) in the region exceeding 1 μm, with 1 μm on the horizontal axis as a reference, is 0.7 to 1.6.

Description

positive electrode active material and secondary battery containing the same

[0001] The present invention relates to a positive electrode active material and a secondary battery comprising the same. More specifically, it relates to a positive electrode active material in which the area ratio of small particles to large particles based on an arbitrary particle size in a particle size distribution graph is within a specific range, and a secondary battery comprising the same.

[0002] Lithium iron phosphate (LFP), whose usage has been increasing recently, offers many advantages in terms of thermal stability, electrochemical stability, eco-friendliness, and cost. On the other hand, it has the disadvantages of low energy density and low electron conductivity.

[0003] Therefore, although improvements such as carbon coating on particle surfaces and particle micronization have been proposed to enhance electronic conductivity, these measures do not solve the problem of low energy density.

[0004] Furthermore, due to the low pellet density (PD) of LFP, the amount of active material that can be packed within the same volume under the same conditions is reduced, which leads to lower energy density.

[0005] In this regard, incorporating large particles or aggregates into the cathode active material increases pellet density through their relationship with small particles, but tends to degrade electrochemical properties. Specifically, while energy density improves with higher pellet density, the aggregation of nano-sized particles as pellet density increases reduces the specific surface area; consequently, this highlights the issue of reduced conductivity and leads to a decrease in overall capacity.

[0006] Therefore, there is a high need in the industry for new technologies that can simultaneously improve energy density and conductivity in LFP cathode active materials.

[0007] The present invention aims to solve the problems of the prior art described above and technical challenges that have been requested over time.

[0008] After conducting in-depth research and various experiments, the inventors of this application confirmed that in a positive electrode active material such as LFP, setting the particle size conditions and their distribution to satisfy specific conditions can lead to both an improvement in energy density and an improvement in electron conductivity, and that this can be achieved by controlling certain process factors during the manufacture of the positive electrode active material, thereby completing the present invention.

[0009] The positive electrode active material of the present invention is characterized by having at least two peaks in a particle size distribution (PSD) graph, and a ratio (A / B) of the area of ​​the region of 0.1 to 1 μm (A) and the area of ​​the region exceeding 1 μm (B) based on the horizontal axis point of 1 μm being 0.7 to 1.6.

[0010] As defined above, when the area of ​​small particles (A) with a relatively small particle size and the area of ​​large particles (B) with a relatively large particle size are distinguished starting from 1 μm and the ratio of their areas (A / B) falls within a specific range as described above, the small particles are efficiently filled into the voids between the large particles, thereby achieving a high pellet density and, consequently, improving the energy density.

[0011] If the area ratio (A / B) falls outside the above range, resulting in an excessive number of small particles or large particles, the pellet density decreases because the spaces between the particles cannot be densely filled.

[0012] In the above, the area can be calculated, for example, in the following way, and V is an example corresponding to the area ratio (A / B). x / V y ratio (V x (0.1~1㎛); V y(>1㎛)) is disclosed in Table 1 of Experimental Example 1, which will be explained later.

[0013] (i) Extract raw data from the Malvern program and aggregate the data into Excel.

[0014] (ii) Verification of vol% for a specific size in raw data

[0015] (iii) The total sum of the vol% recorded in the raw data is 100.

[0016] (iv) V as the sum of vol% in the regions of 1 μm or less and the regions of more than 1 μm, respectively. x and V y Obtaining.

[0017]

[0018] In one preferred example, the positive active material of the present invention may have a composition represented by the following chemical formula 1.

[0019] Li x MP a O b (1)

[0020] In the above formula,

[0021] 0 <x≤2, 0≤a≤2, 0<b≤4;

[0022] M includes Fe and optionally may further include one or more of the following: transition metals of groups 3 to 12 excluding Fe, post-transition metals and metalloids of groups 13 to 15, alkaline earth metals, nonmetals of groups 14 to 16, lanthanides, and actinides.

[0023] In the above,

[0024] "Group 3 to 12 transition metals excluding Fe" may be, for example, Ni, Co, Mn, Sc, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, etc.

[0025] "Post-transition metals and metalloids in groups 13 to 15" may be, for example, Al, Ga, In, Sn, Tl, Pb, Bi, Po, B, Si, Ge, As, Sb, Te, At, etc., and

[0026] "Alkali earth metals" can be, for example, Be, Mg, Ca, Sr, Ba, Ra, etc., and

[0027] "Nonmetallic elements in groups 14 to 16" may be, for example, C, P, S, Se, etc.

[0028] A preferred cathode active material may be in the form of LiFePO4 or LiFePO4 doped with one or more of post-transition metals, metalloids, alkaline earth metals, nonmetals of groups 14 to 16, lanthanides, and actinides, and additionally, may be in the form coated with carbon, etc. as needed.

[0029] Since LFP cathode active materials address low electronic conductivity and output characteristics by finely grinding particles to the nanoscale, the above conditions can be applied more effectively to increase pellet density and ultimately energy density by classifying them into small and large particles based on 1 μm. Unlike LFP cathode active materials, Ni-based active materials containing Ni as a major transition metal may find it difficult to apply the above conditions because grinding to the nanoscale is inappropriate due to structural instability, which leads to reduced stability such as charge-discharge cycle characteristics.

[0030]

[0031] In one specific example, the positive active material of the present invention comprises Fe2P and Li3PO4, and the content of Fe2P may be greater than that of Li3PO4 on a weight basis.

[0032] Fe2P and Li3PO4 are impurities generated as by-products during the manufacturing process of LFP cathode active materials. The cathode active material of the present invention contains both of these under conditions in which Fe2P has a relatively high content, as shown in the reaction scheme below. Since Fe2P has high electron conductivity and contributes to the improvement of electron conductivity of the cathode active material when it remains in the material, it can be seen that the degradation of properties caused by the presence of Li3PO4 is compensated for under the above conditions.

[0033] 6LiFePO4+ 8C(or 16C) → 2Fe2P + 2Li3PO4+ 2FeP + 8CO2↑ (or 16CO↑)

[0034] → 3Fe2P + 2Li3PO4+ P↑

[0035] The above conditions may be achieved by setting the calcination process for manufacturing the LFP cathode active material to be carried out in a reducing atmosphere. Generally, the calcination process is carried out in an atmosphere of an inert gas such as nitrogen, whereas a reaction as shown in the following reaction equation can proceed by injecting a predetermined amount of a reducing gas, for example, H2 gas, along with this inert gas.

[0036] 6LiFePO4+ 16H2→ 2Fe2P + 2Li3PO4+ 2FeP + 16H2O↑

[0037] → 3Fe2P + 2Li3PO4+ P↑

[0038] However, if the amount of Fe2P produced is excessive, it may act as a resistance or cause a decrease in capacity, so the weight ratio of Fe2P content to Li3PO4 content (Fe2P / Li3PO4) is preferably 1.5 or more, more preferably 1.5 to 4.7, and particularly preferably 2 to 2.4.

[0039] In the above, the content of Fe2P may preferably be 1.3 to 2.9 wt% based on the total weight of the cathode active material, and the content of Li3PO4 may be 0.6 to 1.2 wt%.

[0040] As explained earlier, if the Fe2P content is excessively low, it may be difficult to expect an improvement in electronic conductivity, whereas if it is excessively high, it is undesirable as it can lead to increased resistance and decreased capacitance.

[0041] As can be seen from the reaction equations described above, Li3PO4 has an inevitable relationship with the formation of Fe2P; however, the presence of Fe2P satisfying the above content range can resolve the problem of electrochemical property degradation caused by the presence of Li3PO4.

[0042] Preferably, the content of Fe2P may be 2 to 2.4 wt%, and the content of Li3PO4 may be 0.9 to 1.1 wt%.

[0043] Depending on the amount of H2 gas injected to provide a reducing atmosphere, the Fe2P content and the Fe2P / Li3PO4 content ratio can be determined within the range defined above.

[0044]

[0045] In one specific example, the positive active material of the present invention may have a pellet density (PD) of 2.45 g / cc or more.

[0046] The positive electrode active material of the present invention is characterized by having a significantly higher pellet density compared to conventional positive electrode active materials, and as defined above, it may be at least 2.45 g / cc.

[0047] Such high pellet density can be achieved by controlling process factors during the manufacture of LFP cathode active materials. For example, pellet density can be improved by incorporating polyethylene glycol (PEG) as a carbon source for carbon coating on the particle surface of the LFP cathode active material, or by calcination in a reducing atmosphere as previously described. In the former case, small particles are dispersed by acting as a dispersant, which allows nano-sized particles, which are attracted to each other, to aggregate better during calcination. In the latter case, calcination in a reducing atmosphere not only increases the amount of Fe2P produced but also increases the residual carbon content, which can induce the formation of aggregates.

[0048] However, while a higher pellet density is advantageous for improving energy density, if it is too high, it may lead to a decrease in battery characteristics, so a desirable pellet density may be 2.45 to 2.52 g / cc.

[0049]

[0050] In one specific example, the peaks of the two peaks may be located in the 0.1 to 1 μm region and the greater than 1 μm region, respectively.

[0051] The first peak located on area (A) can be seen as representing small particles, and the second peak located on area (B) as representing large particles.

[0052] Generally, Ni-based cathode active materials have a fine region of less than 1 μm, which leads to a deterioration in lifespan characteristics, so the particle size is made much larger. On the other hand, as explained above, LFP cathode active materials may be advantageous to produce nano-sized fine particles due to characteristic limitations, so the above peak condition may be suitable for LFP cathode active materials where the presence of particles with a particle size of less than 1 μm may be required.

[0053] In this case, the second peak peak may be equal in height to or greater than the first peak peak.

[0054] Preferably, the height of the second peak peak is greater than the height of the first peak peak, so that the volume percentage of large particles represented by the first peak is slightly higher, which can further help improve pellet density.

[0055] For reference, the "peak" in the PSD graph defined in the present invention refers to the highest point of each peak rising high on the graph, which mathematically means the point where the slope becomes zero, and may exist as a single peak or multiple peaks on the graph.

[0056]

[0057] The present invention also relates to a secondary battery characterized by comprising the above-mentioned positive active material.

[0058] Since the composition and manufacturing method of secondary batteries are known in the art, a detailed description thereof is omitted in this specification.

[0059] As explained above, the positive electrode active material of the present invention can be configured such that particle size conditions and their distribution satisfy specific conditions by controlling some process factors during the manufacture of the positive electrode active material, and the positive electrode active material satisfying these conditions can bring about both an improvement in energy density and an improvement in electron conductivity.

[0060] FIG. 1a is an FE-SEM image of the positive electrode active material of Example 2 in Experimental Example 1;

[0061] FIG. 1b is EDS data for the positive electrode active material of Example 2 in Experimental Example 1;

[0062] FIG. 2a is an FE-SEM image of the positive electrode active material from Experimental Example 1 to Comparative Example 3;

[0063] FIG. 2b is EDS data for the positive electrode active materials of Experimental Example 1 to Comparative Example 3;

[0064] Figure 3 is a graph showing the rate characteristic retention of Example 2 and Comparative Example 3 in Experimental Example 2.

[0065] The present invention will be described further below with reference to embodiments thereof, but the scope of the invention is not limited by them.

[0066]

[0067] [Comparative Example 1]

[0068] A mixture of Li2CO3 as a lithium raw material and FePO4 as a precursor (Li / Me molar ratio = 1.040) was mixed with a mixture of glucose and PEG as a carbon source (Glucose : PEG weight ratio = 2 : 8) at approximately 10 wt% relative to the combined weight of the lithium raw material and the precursor, added to distilled water as a solvent so that the solid content was approximately 40%, and stirred for 1 hour to prepare a wet raw material.

[0069] For the wet raw material prepared above, wet coarse grinding was performed using an Attrition mill (Nanointec Co.) equipped with Beads size Φ2.0mm as a coarse grinding device, with the pump pressure set to 300 rpm and the grinding speed to 1000 rpm, thereby adjusting the wet solution particle size D50 to 1.0 ~ 2.0 μm.

[0070] Then, using a fine mill (Daehwa Tech Co.) as the fine grinding equipment, wet fine grinding was performed with the pump pressure set to 300 rpm and the grinding pressure set to 2200 ppm, and the wet solution D50 was adjusted to 0.3 ~ 0.5 μm.

[0071] A wet fine grinding solution prepared in this way was used with a Spray dry Atomizer type TS-Minor, M02 / 4 (Ain System Co., Ltd.), with the spray pressure set to approximately 1.5 to 2.0 bar, the Atomizer spray rotation set to 17,000 to 36,000 rpm, the Atomizer spray inlet temperature set to approximately 300℃, and the outlet temperature set to approximately 100℃, and then spray drying was performed to produce a dried product.

[0072] Then, 35 g of the dried product was placed into a small graphite sagger and introduced into a tuber furnace made of quartz, SH-FU-100LTG-3 (Samheung Energy Co.). At this time, the firing temperature was set to a range of 750 to 800°C, the heating rate was set to 2 to 5°C / min, and the firing time was set to 10 hours or less, and N2 gas (99.999% purity) was injected at a rate of 5 L / min or more as a gas to maintain an inert atmosphere.

[0073] The calcined product prepared in this way was ground using an air jet mill, JM-LB (KM Tech Co., Ltd.), while maintaining a grinding pressure of 0.05 to 0.3 MPa and a conveying pressure of 0.3 to 0.5 MPa to produce a LiFePO4 cathode active material.

[0074]

[0075] [Comparative Example 2]

[0076] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 1, except that a mixture of glucose and PEG (glucose:PEG weight ratio = 4:6) was used as the carbon source.

[0077]

[0078] [Comparative Example 3]

[0079] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 1, except that only glucose was used as the carbon source and an N2 / H2 mixed gas (H2: 5 vol%) was used to maintain a reducing atmosphere.

[0080]

[0081] [Example 1]

[0082] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 2, except that an N2 / H2 mixed gas (H2: 5 vol%) was used to maintain a reducing atmosphere.

[0083]

[0084] [Example 2]

[0085] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 3, except that a mixture of glucose and PEG (glucose:PEG weight ratio = 6:4) was used as the carbon source.

[0086]

[0087] [Example 3]

[0088] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 3, except that a mixture of glucose and PEG (glucose:PEG weight ratio = 8:2) was used as the carbon source.

[0089]

[0090] [Example 4]

[0091] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 3, except that a mixture of glucose and PEG (glucose:PEG weight ratio = 9:1) was used as the carbon source.

[0092]

[0093] [Comparative Example 4]

[0094] A LiFePO4 cathode active material was prepared in the same manner as Comparative Example 1, except that a mixture of glucose and PEG (glucose:PEG weight ratio = 5:5) was used as the carbon source and an N2 / H2 mixed gas (H2: 15 vol%) was used to maintain a reducing atmosphere.

[0095]

[0096] [Example 5]

[0097] LiFe was prepared in the same manner as Comparative Example 3, except that FeTiPO4 was used as the precursor and a mixture of glucose and PEG (glucose:PEG weight ratio = 7:3) was used as the carbon source. 1-x Ti x A PO4 (x = 0.001 ~ 0.005) cathode active material was prepared.

[0098]

[0099] [Example 6]

[0100] Except for using FeMnPO4 as the precursor and a mixture of glucose and PEG (glucose:PEG weight ratio = 7:3) as the carbon source, LiFe was prepared in the same manner as Comparative Example 3. 1-x Mn x A PO4 (x = 0.001 ~ 0.005) cathode active material was prepared.

[0101]

[0102] [Example 7]

[0103] Except for using FeMnPO4 as a precursor, a mixture of glucose and PEG (glucose:PEG weight ratio = 6:4) as a carbon source, and using an N2 / H2 mixed gas (H2: 10 vol%) to maintain a reducing atmosphere, LiFe was prepared in the same manner as in Comparative Example 3. 1-x Mn x A PO4 (x = 0.001 ~ 0.005) cathode active material was prepared.

[0104]

[0105] [Example 8]

[0106] Except for using FeMnPO4 as a precursor, a mixture of glucose and PEG (glucose:PEG weight ratio = 4:6) as a carbon source, and using an N2 / H2 mixed gas (H2: 15 vol%) to maintain a reducing atmosphere, LiFe was prepared in the same manner as in Comparative Example 3. 1-x Mn x A PO4 (x = 0.001 ~ 0.005) cathode active material was prepared.

[0107]

[0108] [Experimental Example 1]

[0109] Measurements were performed on the cathode active materials prepared in Comparative Examples 1 to 4 and Examples 1 to 8, respectively, by the following methods, and the results are shown together in Table 1.

[0110]

[0111] Measurement method of PSD (Particle Size Distribution)

[0112] Mastersizer 3000 equipment (Malvern Panalytical) was used, and the measurement conditions are as follows.

[0113] - Sample amount: 0.45 g

[0114] - Sample Addition Dispersant: 10% Sodium Hexamethaphosphate 1ml

[0115] - Sample input solvent: 40 ml distilled water

[0116] - Sample ultrasonic dispersion: 40 kHz, 3 min

[0117] - Refraction Index: 1.692

[0118]

[0119] FE-SEM / EDS Measurement Method

[0120] JSM-IT800 (Jeol) was used as the SEM measurement device. A sample was sampled onto carbon tape, and after Pt coating was performed in a vacuum atmosphere, it was placed into the FE-SEM device for measurement. The acceleration voltage was set to a range of 10 to 30 kV, and the magnification during measurement was changed to x5000, x10000, x30000, and x50000, respectively.

[0121] For EDS calculation, the measured atomic % was verified using the Aztec program, and based on this, the amount of byproducts was determined using the following calculation method.

[0122]

[0123]

[0124] XRD measurement method

[0125] The D8 ENDEAVO instrument (Bruker) was used, and the measurement conditions are as follows.

[0126] - Sample preparation: Flatten approximately 2 g of the sample in the sample holder.

[0127] - Measurement range: 10 ~ 80°

[0128] - Scan rate: 2.0° / min

[0129] Phase fractions were calculated by performing 'Rietveld Refinement' using the 'Topas' program.

[0130]

[0131] Method for measuring pellet density (PD)

[0132] PD used the Auto 3887NE (Carver) press machine and conducted measurements using equipment equipped with a modified vernier caliper to measure the stage height, and the measurement method is as follows.

[0133] - Place a blank Φ13mm molding press mold in the center of the stage inside the press equipment and apply 0.5 tons of pressure.

[0134] - Record the initial stage height 30 seconds after reaching 0.5 ton.

[0135] - Weigh 1 g of the sample and place it into a press mold.

[0136] - Place the press mold containing the sample in the center of the stage and apply 2.5 tons of pressure.

[0137] - Record the later stage height 30 seconds after reaching 2.5 tons.

[0138] - Calculate PD using the following calculation method based on the measured stage height and sample weight after 30 seconds of 0.5 ton / 2.5 ton.

[0139]

[0140]

[0141] From the results of Table 1 above, the following facts can be confirmed.

[0142]

[0143] First, it can be seen that under the calcination conditions of Comparative Examples 1 and 2, which are not in a reducing atmosphere, only trace amounts of Fe2P are formed, and when the amount of H2 gas introduced to provide a reducing atmosphere increases, the amount of Fe2P produced increases in proportion to the amount of H2 gas introduced, as in Examples 6 to 8. On the other hand, it can be seen that if only the amount of H2 gas introduced is increased without considering the conditions of other process factors, Fe2P is produced excessively as in Comparative Example 4, and even more Li3PO4 is produced, failing to satisfy the conditions set in the present invention.

[0144]

[0145] Second, in the case of Comparative Example 3, in which PEG was not added as a carbon source, particle aggregation did not occur properly during calcination, so a PSD graph with many small particles was formed, and accordingly, it can be confirmed that the pellet density (PD) decreased.

[0146]

[0147] Third, Examples 1 to 8, in which the calcination process was performed in a reducing atmosphere with a certain amount of H2 gas introduced and a certain amount of PEG was used as a carbon source, V x / V y It can be seen that all of the conditions are satisfied, including a ratio of 0.7 to 1.6, a weight ratio of Fe2P content to Li3PO4 content of 1.5 or higher, a Fe2P content of 1.3 to 2.9 wt%, a Li3PO4 content of 0.6 to 1.2 wt%, and a pellet density (PD) of 2.45 g / cc or higher.

[0148]

[0149] In addition, FE-SEM images and EDS data for the cathode active material of Example 2 are disclosed in FIGS. 1a and 1b, and FE-SEM images and EDS data for the cathode active material of Comparative Example 3 are disclosed in FIGS. 2a and 2b. As such, the cathode active material of the example can be expected to have a high pellet density due to an appropriate combination of large and small particles when compared to the comparative example, and it can be confirmed that Fe2P is present in an appropriate content.

[0150]

[0151] [Experimental Example 2]

[0152] The positive active materials prepared in Comparative Examples 1 to 4 and Examples 1 to 8, respectively, were mixed with PVdF (KF1100) as a binder and Super-P as a conductive material in a weight ratio of 95:2:3, and added to an NMP solvent to prepare a positive active material slurry. The slurry was coated onto an aluminum foil (Al foil, thickness: 20 μm) serving as a positive current collector, dried at 120°C, and then rolled to produce a positive electrode plate. The loading level of the rolled positive was 12 mg / cm². 2 The rolled density is 2.40 g / cm³ 3 The above positive electrode plate was stamped to 13.8Φ, and a 2032 coin-type half cell was fabricated using a 15Φ lithium metal negative electrode and an electrolyte (1M LiPF6 in EC / DMC / DEC 1:2:1).

[0153] After aging the above coin-type half cell at room temperature for 10 hours, charge-discharge tests were performed, and the results are shown in Table 2 below. Capacity evaluation was based on a standard of 150 mAh / g at a 0.1C rate, and charge-discharge conditions were executed under constant current (CC) / constant voltage (CV) within a voltage range of 3.7 to 2.5.

[0154]

[0155] As shown in Table 2 above, it can be confirmed that the secondary batteries of the examples all have a larger battery capacity and excellent rate retention compared to the comparative examples.

[0156] Specifically, Comparative Examples 1 and 2 show that only a small amount of Fe2P was generated due to the inert atmosphere composition during calcination, and more Li3PO4 was generated than Fe2P, so the effect of improving electronic conductivity was not realized, and as a result, the capacity was reduced compared to the example.

[0157] In Comparative Example 3, Fe2P was generated more through the creation of a reducing atmosphere, but because PEG was not added as a carbon source, less particle aggregation occurred, resulting in a form with a high proportion of small particles in the PSD. Consequently, the desired pellet density was not achieved.

[0158] In Comparative Example 4, PEG was introduced as a carbon source, but the H2 gas content was excessive during calcination, resulting in the formation of an over-reducing atmosphere and the excessive production of Fe2P and Li3PO4. Consequently, the amount of LiFePO4 decomposition was high, and the capacity was significantly lower compared to the example.

[0159] Examples 1 to 4 show changes in PSD according to the PEG ratio, and show that as PEG increases, particles aggregate and the large particle content increases. In addition, Examples 5 to 8 show that the same characteristics are observed regardless of the core composition, and Examples 6 to 8 show that the Fe2P content increases according to the H2 gas content.

[0160]

[0161] In relation to the above rate characteristic retention, FIG. 3 discloses a graph showing the degree of rate characteristic retention when the charge / discharge speed is increased for the secondary batteries of Example 2 and Comparative Example 3. Referring to FIG. 3, it can be seen that as the charge / discharge speed is increased, particularly as the discharge speed is increased, the retention rate decreases, and in the case of Comparative Example 3, a relatively more rapid decline is observed.

[0162]

[0163] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. At least two peaks exist in the particle size distribution (PSD) graph, and A positive electrode active material characterized by a ratio (A / B) of the area (A) of the 0.1 to 1 µm region and the area (B) of the region exceeding 1 µm being 0.7 to 1.6 based on a point of 1 µm on the horizontal axis.

2. The positive active material according to claim 1, characterized in that the positive active material has a composition represented by the following chemical formula 1: There x MP a OR b (1) In the above formula, 0 <x≤2, 0≤a≤2, 0<b≤4; M includes Fe and optionally may further include one or more of the following: transition metals of groups 3 to 12 excluding Fe, post-transition metals and metalloids of groups 13 to 15, alkaline earth metals, nonmetals of groups 14 to 16, lanthanides, and actinides.

3. A positive electrode active material according to claim 2, comprising Fe2P and Li3PO4, wherein the content of Fe2P is greater than that of Li3PO4 on a weight basis.

4. A positive electrode active material according to claim 3, characterized in that the calcination process for manufacturing the LFP positive electrode active material is set to be carried out in a reducing atmosphere.

5. A positive active material according to claim 4, characterized in that the reducing atmosphere is achieved by adding hydrogen gas to an inert gas.

6. A positive electrode active material according to claim 3, characterized in that the weight ratio of Fe2P content to Li3PO4 content is 1.5 or higher.

7. A positive electrode active material according to claim 3, characterized in that the content of Fe2P is 1.3 to 2.9 wt%.

8. A positive electrode active material according to claim 3, characterized in that the content of Li3PO4 is 0.6 to 1.2 wt%.

9. The positive active material according to claim 1, characterized in that the pellet density (PD) is 2.45 g / cc or higher.

10. The positive electrode active material according to claim 9, characterized in that the pellet density is achieved by including polyethylene glycol (PEG) as a carbon source for carbon coating on the particle surface of the positive electrode active material.

11. The positive active material according to claim 9, characterized in that the pellet density is achieved by calcination in a reducing atmosphere.

12. The positive active material according to claim 1, characterized in that the highest points of the two peaks are located in the 0.1 to 1 μm region and the greater than 1 μm region, respectively.

13. The positive active material according to claim 12, characterized in that the highest point of the second peak located on area (B) has a height equal to or greater than the highest point of the first peak located on area (A).

14. A secondary battery characterized by including a positive electrode active material according to claim 1.

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