Cathode active material for lithium secondary battery, and method for producing same

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, and a method for producing same. More specifically, the present invention relates to a cathode active material for a lithium secondary battery, and a method for producing same, the method comprising applying, to a cathode active material precursor mixture, primary firing at a low temperature of 400°C or lower, thereby increasing production amount and productivity.

Description

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

[0001] The present invention relates to a cathode active material for a lithium secondary battery and a method for producing the same. More specifically, the present invention relates to a cathode active material for a lithium secondary battery and a method for producing the same, which increases production volume and production efficiency by applying low-temperature primary sintering at 400°C or lower to a cathode active material precursor mixture.

[0002]

[0003] Conventional lithium secondary battery cathode active material production processes mainly utilize a one-step secondary sintering process using a roller hearth kiln (RHK). In this conventional one-step process, even if the product is fully loaded into the sintering vessel, the volume decreases from the middle of the process onward, eventually decreasing to less than 50% of the sintering vessel's volume. Specifically, after the initial section in the sintering vessel where moisture in the precursor and lithium hydroxide is removed, the volume begins to decrease as the precursor and lithium react with each other, reducing the volume to less than half of the initial loading volume in the later stages. In other words, since the volume of the sintering vessel cannot be fully utilized, there is a problem of reduced production efficiency.

[0004]

[0005] Another technical problem to be solved by the present invention is to provide a positive electrode active material with improved productivity and moisture content by loading a positive electrode active material precursor, the volume of which has been sufficiently reduced by performing a first firing at a temperature of 400°C or lower, into a firing vessel to the maximum extent and performing a second firing.

[0006] Another technical problem to be solved by the present invention is to provide a method for manufacturing a positive electrode active material having the aforementioned advantages.

[0007]

[0008] A positive electrode active material according to one embodiment of the present invention may satisfy the following equation 1, and the following equation 1 is as follows.

[0009] [Formula 1]

[0010] 3.35 ≤ (grain size / BET) / 100 ≤ 3.65

[0011] A method for producing a cathode active material according to another embodiment of the present invention may include the steps of: producing a mixture by mixing a metal hydroxide precursor and lithium hydroxide; first firing the mixture in a range of 350 to 400°C to obtain a pre-fired product; and second firing the pre-fired product in a range of 700 to 900°C to obtain a lithium metal oxide satisfying the following formula 1, wherein the following formula 1 is as follows.

[0012] [Formula 1]

[0013] 3.35 ≤ (grain size / BET) / 100 ≤ 3.65

[0014]

[0015] According to one embodiment of the present invention, a cathode active material having a low moisture content and high productivity can be obtained by performing a first calcination of the above-described cathode active material precursor at a temperature of 400°C or lower.

[0016] A method for manufacturing a positive electrode active material according to another embodiment of the present invention can provide a positive electrode active material having a low moisture content and high productivity by performing a first calcination of the positive electrode active material precursor described above at a temperature of 400°C or lower.

[0017]

[0018] Figure 1 is a graph showing the change in weight of a cathode material according to a sintering reaction in a manufacturing process of a cathode active material according to one embodiment of the present invention.

[0019] FIG. 2 shows the morphology of a positive electrode active material precursor mixture (IG loss 0% product) according to one embodiment of the present invention.

[0020] FIG. 3 shows the morphology of a 100°C pre-fired product (IG loss 8%) of a positive electrode active material precursor according to one embodiment of the present invention.

[0021] FIG. 4 shows the morphology of a 250°C pre-fired product (IG loss 15%) of a positive electrode active material precursor according to one embodiment of the present invention.

[0022] FIG. 5 shows the morphology of a 350°C pre-fired product (IG loss 22%) of a positive electrode active material precursor according to one embodiment of the present invention.

[0023] FIG. 6 shows the morphology of a 400°C pre-fired product (IG loss 27%) of a positive electrode active material precursor according to one embodiment of the present invention.

[0024] Figure 7 shows the morphology of a 500°C pre-fired product (IG loss 27%) of a positive electrode active material precursor according to one embodiment of the present invention.

[0025]

[0026] In this specification, terms such as first, second, and third are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0027] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless specifically stated otherwise.

[0028] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The term "comprising," as used herein, specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0029] In this specification, the term "combination of these" included in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including one or more selected from the group consisting of the components.

[0030] In this specification, when a part is referred to as being "on" or "over" another part, it may be directly on or over the other part, or there may be other parts intervening therebetween. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening therebetween.

[0031] In this specification, D10 means the particle size at 10% by volume in the cumulative size-distribution curve, D50 means the particle size at 50% by volume, D90 means the particle size at 90%, and D99 means the particle size at 99%.

[0032] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0033] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0034] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0035] According to one embodiment, a positive electrode active material for a lithium secondary battery may be a positive electrode active material satisfying the following equation 1.

[0036] [Formula 1]

[0037] 3.35 ≤ (grain size / BET) / 100 ≤ 3.65

[0038] In the above equation 1, the crystal grain size was measured by XRD.

[0039] In the above equation 1, BET means the specific surface area measured by BET.

[0040] In one embodiment, the value of (crystalline size / BET) / 100 of the positive electrode active material may be in the range of 3.35 to 3.65. Specifically, it may be in the range of 3.4 to 3.64. More specifically, it may be in the range of 3.45 to 3.63.

[0041] When the value of (crystalline size / BET) / 100 is within the aforementioned range, the electrochemical discharge capacity increases, which may have the advantage of increasing charging efficiency. On the other hand, when the value of (crystalline size / BET) / 100 is outside the aforementioned range, the total amount of residual lithium increases, which causes the residual lithium to act as an impurity and gel when manufacturing the cathode slurry, making it difficult to form a uniform slurry. In addition, the amount of gas generated during battery operation may increase, which may lower stability and long-term life capability. In addition, the specific surface area of ​​the active material may increase, which may cause a problem of increased side reactions between the residual lithium and the electrolyte.

[0042] In one embodiment, the BET specific surface area of ​​the positive electrode active material is 0.33 m 2 / g or more. Specifically, 0.34 m 2 / g or more. More specifically, 0.34 m 2 / g to 0.40 m 2 / g can be in the range. More specifically, 0.34 m 2 / g to 0.38 m 2 / g can be in the range. More specifically, 0.34 m 2 / g to 0.36 m 2 / g can be in the range.

[0043] When the BET specific surface area of ​​the positive electrode active material falls within the aforementioned range, there may be movement of surface lithium (Li). On the other hand, when the BET specific surface area of ​​the positive electrode active material falls outside the aforementioned range, there may be a problem in that the specific surface area of ​​the active material increases, thereby increasing side reactions between residual lithium and the electrolyte.

[0044] In one embodiment, the crystal grain size of the positive electrode active material may be in the range of 122 nm to 138 nm. Specifically, it may be in the range of 123 nm to 138 nm. More specifically, it may be in the range of 123 nm to 135 nm. More specifically, it may be in the range of 123 nm to 130 nm. More specifically, it may be in the range of 123 nm to 125 nm.

[0045] When the crystal grain size of the positive active material falls within the aforementioned range, the wettability of the positive active material may increase during electrode manufacturing, and lithium ion conductivity may increase. On the other hand, when the crystal grain size of the positive active material falls outside the upper limit of the aforementioned range, the crystal grains may become coarser, which may lead to a problem of decreased lithium ion conductivity. Furthermore, when the crystal grain size falls outside the lower limit of the aforementioned range, the crystal grains may become finer, particle breakage may occur, and unexpected side reactions may occur due to an increase in the specific surface area.

[0046] In one embodiment, the moisture content of the positive electrode active material may be 3700 ppm or less. Specifically, it may be in the range of 1000 ppm to 3700 ppm. More specifically, it may be in the range of 1050 ppm to 3500 ppm.

[0047] When the moisture content of the lithium metal oxide is within the above-mentioned range, the effect of reducing impurities such as oxides of residual lithium on the surface of the active material and reducing the resistance layer on the surface can be achieved.

[0048] In one embodiment, the positive electrode active material may satisfy Equation 2.

[0049] [Formula 2]

[0050] 3.35 ≤ (BET / D50)*100 ≤ 3.80

[0051] The value of (BET / D50)*100 of the above positive electrode active material may be in the range of 3.35 to 3.80. Specifically, it may be 3.37 to 3.75. More specifically, it may be 3.40 to 3.70. More specifically, it may be 3.43 to 3.67. More specifically, it may be 3.47 to 3.64.

[0052] In the above equation 2, BET means the specific surface area measured by BET.

[0053] In the above equation 2, D50 means the average particle diameter D50 of the positive electrode active material.

[0054] When the value of (BET / D50)*100 is within the above-mentioned range, the wettability of the active material may increase during electrode manufacturing, and the conductivity of lithium ions may increase. On the other hand, when the value of (BET / D50)*100 is outside the upper limit of the above-mentioned range, unexpected side reactions may occur due to an increase in the specific surface area. In addition, when the value is outside the lower limit of the above-mentioned range, there may be a problem of a decrease in lithium ion conductivity.

[0055] In one embodiment, the total content of residual lithium byproducts of the positive electrode active material may be 0.92 wt% or less based on the total weight of the positive electrode active material, and the positive electrode active material may include LiOH and Li2CO3 as residual lithium byproducts. Specifically, the total content of residual lithium byproducts of the positive electrode active material may be 0.91 wt% to 0.92 wt%.

[0056] When the total content of residual lithium byproducts of the above-mentioned positive electrode active material is within the aforementioned range, there may be an effect of reducing side reactions between residual lithium and the electrolyte while supplementing the amount of lithium that may be insufficient in the parent material.

[0057] In one embodiment, the molar content of nickel among the transition metals included in the positive electrode active material may be 80 mol% or more.

[0058] According to another embodiment, a method for producing a positive electrode active material for a lithium secondary battery may include the steps of: producing a mixture by mixing a metal hydroxide precursor and lithium hydroxide; first firing the mixture in a range of 350 to 400°C to obtain a pre-fired product; and second firing the pre-fired product in a range of 700 to 900°C to obtain a lithium metal oxide satisfying the following formula 1.

[0059] [Formula 1]

[0060] 3.35 ≤ (grain size / BET) / 100 ≤ 3.65

[0061] In the above first calcination step, when the first calcination temperature is within the aforementioned range, the primary particle size may decrease, the BET specific surface area may increase, and thus the rate control characteristics may be improved. In addition, since dehydration of lithium hydroxide as well as dehydration of the metal hydroxide precursor may be promoted, the volume of the precursor mixture may be significantly reduced as the ignition loss increases. Accordingly, the amount of precursor mixture that can be loaded into the calcination vessel may be maximized, thereby improving productivity by maximizing the volume of the calcination vessel.

[0062] On the other hand, if the first calcination temperature is outside the upper limit of the aforementioned range, the specific surface area of ​​the manufactured pre-calcined product decreases, which increases the crystallinity of the positive electrode active material and decreases the specific surface area, which may deteriorate electrochemical performances such as discharge capacity and rate characteristics. In addition, Li2O generated after dehydration of lithium hydroxide reacts with CO2 to generate Li2CO3, a lithium byproduct. As the first calcination temperature increases beyond the upper limit of the aforementioned range, a greater amount of the lithium byproduct may be generated. Therefore, a problem of an increase in the amount of residual lithium byproduct may occur. In addition, if the temperature is outside the lower limit of the aforementioned range, the dehydration of lithium hydroxide may proceed, but the dehydration of the metal hydroxide may not proceed, so the volume of the precursor mixture may not be sufficiently reduced, and as a result, the volume of the calcination vessel may not be utilized to the fullest, which may result in a problem of low productivity.

[0063] The dehydration and weight changes according to the above firing temperature are shown in Fig. 1.

[0064] In the above-mentioned second firing step, the second firing temperature may be specifically 750 to 900°C. More specifically, it may be 750 to 790°C. Even more specifically, it may be 770 to 790°C.

[0065] When the secondary sintering temperature is within the above-mentioned range, the sintering of the layered cathode active material including the above-mentioned nickel content range can proceed appropriately. On the other hand, when the secondary sintering temperature exceeds the upper limit of the above-mentioned range, structural instability may occur due to Li / Ni mixing caused by over-sintering, and when it exceeds the lower limit of the above-mentioned range, the formation of the layered structure is not sufficiently achieved, making it impossible to obtain the desired electrochemical performance.

[0066] In another embodiment, the value of (crystalline size / BET) / 100 of the positive electrode active material may be in the range of 3.35 to 3.65. Specifically, it may be in the range of 3.4 to 3.64. More specifically, it may be in the range of 3.45 to 3.63.

[0067] When the value of (crystalline size / BET) / 100 is within the aforementioned range, the electrochemical discharge capacity increases, which may have the advantage of increasing charging efficiency. On the other hand, when the value of (crystalline size / BET) / 100 is outside the aforementioned range, the total amount of residual lithium increases, which causes the residual lithium to act as an impurity and gel when manufacturing the cathode slurry, making it difficult to form a uniform slurry. In addition, the amount of gas generated during battery operation may increase, which may lower stability and long-term life capability. In addition, the specific surface area of ​​the active material may increase, which may cause a problem of increased side reactions between the residual lithium and the electrolyte.

[0068] In another embodiment, the positive electrode active material may satisfy Equation 2.

[0069] [Formula 2]

[0070] 3.35 ≤ (BET / D50)*100 ≤ 3.80

[0071] The value of (BET / D50)*100 of the above positive electrode active material may be in the range of 3.35 to 3.80. Specifically, it may be 3.37 to 3.75. More specifically, it may be 3.40 to 3.70. More specifically, it may be 3.43 to 3.67. More specifically, it may be 3.47 to 3.64.

[0072] In the above equation 2, BET means the specific surface area measured by BET.

[0073] In the above equation 2, D50 means the average particle diameter D50 of the positive electrode active material.

[0074] When the value of (BET / D50)*100 is within the above-mentioned range, the wettability of the active material may increase during electrode manufacturing, and the conductivity of lithium ions may increase. On the other hand, when the value of (BET / D50)*100 is outside the upper limit of the above-mentioned range, unexpected side reactions may occur due to an increase in the specific surface area. In addition, when the value is outside the lower limit of the above-mentioned range, there may be a problem of a decrease in lithium ion conductivity.

[0075] In another embodiment, the ignition loss after the first firing may comprise a range of 22% to 27%. Specifically, it may be 25% to 27%.

[0076] Ignition loss can be defined as the rate of weight loss of the active material before and after firing.

[0077] If the ignition loss is within the above-mentioned range, it can be confirmed that the sintering has sufficiently progressed within an appropriate range, and at this time, as in the above-mentioned Equations 1 and 2, the values ​​of (crystal grain size / BET) / 100 and (BET / D50)*100 can be within the above-mentioned range. On the other hand, if the ignition loss is outside the upper limit of the above-mentioned range, the structure may become structurally unstable due to Li / Ni mixing due to oversintering, and if it is outside the lower limit of the above-mentioned range, the formation of a layered structure is not sufficiently achieved, so that the desired electrochemical performance cannot be obtained.

[0078] In another embodiment, the BET specific surface area of ​​the pre-fired product formed after the first firing is 20.5 m 2 / g may be higher. Specifically, 22.0 m 2 / g may be higher. More specifically, 24.0 m 2 / g or more. More specifically, 24.5 to 30.0 m 2 / g can be more specifically 24.5 to 27.5 m 2 / g can be more specifically 24.5 to 25.5 m 2 / g could be.

[0079] When the BET specific surface area of ​​the pre-sintered material falls within the aforementioned range, the wettability of the active material may increase and the conductivity of lithium ions may increase during electrode manufacturing. On the other hand, when the BET specific surface area of ​​the pre-sintered material falls outside the aforementioned range, side reactions with the electrolyte may increase excessively or, conversely, reactivity may be significantly reduced.

[0080] In another embodiment, the primary firing may be performed in an atmosphere having an oxygen concentration of 21% and a carbon dioxide (CO2) concentration of 10 ppm or less.

[0081] When the above first firing is performed in an atmosphere with an oxygen (O2) concentration of 21% and a carbon dioxide (CO2) concentration of 400 ppm or less, the reaction between residual lithium and CO2 is suppressed, thereby increasing safety during the process while appropriately oxidizing the active material and allowing the active material to satisfy the above moisture content range.

[0082] In another embodiment, the first firing step may be performed for a period of time ranging from 8 hours to 12 hours. Specifically, it may be performed for a period of time ranging from 8 hours to 10 hours. More specifically, it may be performed for a period of time ranging from 8 hours to 9 hours.

[0083] When the above first firing time is within the above-mentioned range, the moisture content of the active material can be economically reduced and the loading amount can be increased.

[0084] In another embodiment, the secondary firing step may be performed for a period of time ranging from 15 hours to 22 hours. Specifically, it may be performed for a period of time ranging from 16 hours to 20 hours. More specifically, it may be performed for a period of time ranging from 17 hours to 19 hours. Even more specifically, it may be performed for a period of time ranging from 17 hours to 18 hours.

[0085] In another embodiment, the molar content of nickel among the transition metals included in the metal hydroxide precursor may be 80 mol% or more.

[0086]

[0087] Hereinafter, preferred manufacturing examples, examples, comparative examples, and experimental examples according to the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0088] Example 1 - Preparation of positive electrode active material with primary sintering temperature of 400°C

[0089] Ni 0.88 Co 0.05 Mn 0.07 After preparing a precursor with a composition of (OH)2, a mixture was prepared by uniformly mixing LiOH·H2O (Samsung Chemical, battery grade) as a lithium raw material into the precursor.

[0090] At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.07.

[0091] The above mixture was placed in a kiln in an atmosphere of 21% oxygen and 5 ppm or less of carbon dioxide, and calcined at 400°C for 10 hours to produce a preliminary calcined material, and then the preliminary calcined material was subjected to a second calcination at 770°C for 18 hours to produce a positive electrode active material.

[0092] The morphology of the preliminary calcined product (precursor) derived in Example 1 is shown in Fig. 6.

[0093] Example 2 - Preparation of positive electrode active material with primary sintering temperature of 350°C

[0094] A positive electrode active material for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the primary sintering temperature was set to 350°C.

[0095] The morphology of the preliminary calcined product (precursor) derived in Example 2 is shown in Fig. 5.

[0096] Comparative Example 1 - Preparation of positive electrode active material with primary sintering temperature of 500°C

[0097] A positive electrode active material for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the primary sintering temperature was set to 500°C.

[0098] The morphology of the preliminary sintered product (precursor) derived from Comparative Example 1 is shown in Fig. 7.

[0099] Comparative Example 2 - Manufacturing of positive electrode active material with primary sintering temperature of 250°C

[0100] A positive electrode active material for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the primary sintering temperature was set to 250°C.

[0101] The morphology of the preliminary sintered product (precursor) derived from Comparative Example 2 is shown in Fig. 4.

[0102] Comparative Example 3 - Manufacturing of positive electrode active material with primary sintering temperature set to 100°C

[0103] A positive electrode active material for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the primary sintering temperature was set to 100°C.

[0104] The morphology of the preliminary sintered product (precursor) derived from Comparative Example 3 is shown in Fig. 3.

[0105] Comparative Example 4 - Manufacturing of positive electrode active material by performing only secondary firing without performing primary firing.

[0106] A positive electrode active material for a lithium secondary battery was manufactured under the same conditions as Example 1, except that only the secondary firing was performed without performing the primary firing.

[0107] The morphology of the preliminary sintered product (precursor) derived from Comparative Example 4 is shown in Fig. 2.

[0108] Experimental Example 1 - SEM Analysis

[0109] SEM analysis was performed on the negative active materials according to Examples 1 and 2 and Comparative Examples 1 to 3, and the results are shown in FIGS. 2 to 7.

[0110] Referring to FIGS. 2 to 7, in the case of the active materials of FIGS. 5 to 6, the distance between the primary particles is increased, so that the pores are clearly visible, and through this, the specific surface area of ​​the active material satisfies the above-described range, thereby affecting the improvement of the electrochemical performance of the active material.

[0111] Experimental Example 2 - Electrochemical Evaluation

[0112] (1) Manufacturing of coin-type half-cells

[0113] A CR2032 coin cell was manufactured using the positive electrode active material manufactured from the above examples and comparative examples using the following method.

[0114] Specifically, a positive electrode active material, a conductive agent (acetylene black FX35, Denka), and a polyvinylidene fluoride binder (trade name: KF9709) were mixed in a weight ratio of 95:2:3, and the mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 65 to 69 wt% to prepare a positive electrode active material slurry.

[0115] The above slurry was coated on an aluminum foil (Al foil, thickness: 20 μm), which is a positive electrode collector, using a doctor blade, dried, and rolled to manufacture a positive electrode. The loading amount of the positive electrode was about 14-15 mg / cm2, and the rolling density was about 3.5 g / cm 3 It was.

[0116] A 2032 coin-type half-cell was manufactured using the above positive electrode, lithium metal negative electrode (400 μm thick, NEBA), electrolyte, and polypropylene polyethylene separator in a conventional manner. The electrolyte was manufactured by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mixing ratio EC:DMC:DEC=1:2:1 vol%) to prepare a mixed solution, to which 2 wt% of vinylene carbonate (VC) was added.

[0117] (2) Evaluation of charge and discharge characteristics

[0118] After aging the coin-shaped half-cell manufactured in the above (1) at room temperature (25°C) for 24 hours, a charge / discharge test was conducted.

[0119] Capacity evaluation was conducted with 200 mAh / g as the standard capacity, and charge / discharge conditions were constant current (CC) / constant voltage (CV) 2.5 V to 4.45 V, 1 / 20 C cut-off.

[0120] The initial capacity was measured by measuring the discharge capacity after 0.1C charge / 0.1C discharge, and the initial efficiency was calculated, and the results are shown in Table 1 below.

[0121] The properties of the pre-fired product (precursor) and the secondary fired product (positive electrode active material) manufactured according to Examples 1 and 2 and Comparative Examples 1, 2, and 4 are shown in Table 1 below.

[0122] Classification 1st firing temperature (℃) Preliminary firing product (precursor) Main firing product (positive electrode active material) Ignition loss (%) BET specific surface area (m 2 / g)Moisture content (ppm)Particle size (D50, ㎛)BET specific surface area (m 2 / g)LiOH(wt%)Li2CO3(wt%)Crystal grain size(nm)(crystal grain Size / BET) / 100(BET / D50)*100Example 14002725.410449.90.360.380.541253.473.64Example 23502224.536509.80.340.360.551233.623.47Comparative Example 15002720.298710.60.310.360.611394.482.92Comparative Example 22501510.252009.60.320.380.551213.663.33Comparative Example 4005.013690009.50.270.410.671124.152.84

[0123] The pre-fired products (precursors) of Examples 1 and 2 showed higher BET specific surface areas compared to the pre-fired products of Comparative Examples 1, 2, and 4. Although the first firing temperature of Comparative Example 1 was higher than that of Example 1, the BET specific surface area actually decreased.

[0124] The secondary fired products (positive active materials) of Examples 1 and 2 showed reduced moisture content compared to Comparative Examples 2 and 4, which had relatively low primary firing temperatures. According to Table 1, as the primary firing temperature increased, the particle size (D50) of the positive active material slightly increased. The BET specific surface area of ​​the positive active materials of Examples 1 and 2, in which the primary firing temperature ranged from 350 to 400°C, critically increased, while in Comparative Example 1, in which the primary firing was performed at a higher temperature of 500°C, the BET specific surface area actually decreased. In addition, the total weight fraction of lithium byproducts in Examples 1 and 2 also showed a tendency to critically decrease.

[0125] The electrochemical properties of the positive electrode active materials according to Examples 1 and 2 and Comparative Examples 1, 2, and 4 are shown in Table 2 below.

[0126] Classification 0.1C charge capacity (mAh / g) 0.1C discharge capacity (mAh / g) 2.0C / 0.1C rate characteristics (%) Example 1 226.2 198.8 8.7 Example 2 2225.5 198.3 8.5 Comparative Example 1 227.8 196.1 86.5 Comparative Example 2 2225.2 197.9 86.4 Comparative Example 4 2225.1 197.1 84.0

[0127] The positive electrode active materials of Examples 1 and 2 exhibited a critical increase in 0.1C discharge capacity and 2.0C / 0.1C rate characteristics compared to the positive electrode active materials of Comparative Examples 1 to 4. It can be judged that the electrochemical characteristics are improved as described above as the moisture content of the positive electrode active material decreases and the specific surface area increases.

Claims

1. A positive electrode active material for a lithium secondary battery, satisfying the following equation 1. [Formula 1] 3.35 ≤ (grain size / BET) / 100 ≤ 3.65 Cathode active material for lithium secondary batteries.

2. In paragraph 1, The BET specific surface area of ​​the above positive electrode active material is 0.33 m 2 / g or more, Cathode active material for lithium secondary batteries.

3. In paragraph 1, The crystal grain size of the above positive electrode active material is in the range of 122 nm to 138 nm. Cathode active material for lithium secondary batteries.

4. In paragraph 1, The above positive electrode active material has a moisture content of 3700 ppm or less, Cathode active material for lithium secondary batteries.

5. In paragraph 1, The above positive electrode active material is a positive electrode active material for a lithium secondary battery that satisfies Equation 2. [Formula 2] 3.35 ≤ (BET / D50)*100 ≤ 3.80 6. In paragraph 1, The total content of residual lithium byproducts of the above positive electrode active material is 0.92 wt% or less based on the total weight of the positive electrode active material, The above positive electrode active material contains LiOH and Li2CO3 as residual lithium byproducts. Cathode active material for lithium secondary batteries.

7. In paragraph 1, The molar content of nickel among the metals included in the above positive electrode active material is 80 mol% or more, Cathode active material for lithium secondary batteries.

8. A step of first firing the above mixture in the range of 350 to 400°C to obtain a pre-fired product; and A step of obtaining a lithium metal oxide satisfying the following formula 1 by performing a second firing of the above-mentioned preliminary firing material in the range of 700 to 900°C; Method for manufacturing a cathode active material for a lithium secondary battery. [Formula 1] 3.35 ≤ (grain size / BET) / 100 ≤ 3.65 9. In paragraph 8, The ignition loss of the above preliminary fired product is in the range of 22% to 27%. Method for manufacturing a cathode active material for a lithium secondary battery.

10. In paragraph 8, The BET specific surface area of ​​the above pre-calcined material is 20.5 m 2 / g or more, Method for manufacturing a cathode active material for a lithium secondary battery.

11. In paragraph 8, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above first firing is performed in an atmosphere having an oxygen (O2) concentration of 21% and a carbon dioxide (CO2) concentration of 10 ppm or less.

12. In paragraph 8, The above first firing is performed in the range of 8 to 12 hours, Method for manufacturing a cathode active material for a lithium secondary battery.

13. In paragraph 8, The above secondary firing is performed in the range of 15 to 22 hours. Method for manufacturing a cathode active material for a lithium secondary battery.

14. In paragraph 8, The molar content of nickel among the metals included in the above metal hydroxide precursor is 80 mol% or more. Method for manufacturing a cathode active material for a lithium secondary battery.

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