Positive electrode active material, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

To provide a positive active material, a manufacturing method thereof, and a lithium secondary battery including the same, which are improved in thermal safety.SOLUTION: A positive active material is provided containing lithium metal oxide particles in a secondary particle form including primary particles, where the surface of the secondary particle includes planar primary particles with a narrow angle of 70 to 90° among angles between the c-axis of the primary particles and a straight line connecting a virtual point of a center of the primary particle and a center point of the secondary particle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, the boom in IT mobile devices and small power-driven devices (e-bikes, small EVs, etc.) Driven by a sudden increase in demand and the need for electric vehicles with a driving range of 400km or more, The development of high-capacity, high-energy-density secondary batteries for powering devices is progressing actively worldwide. It is being criticized.

[0003] To manufacture such high-capacity batteries, high-capacity positive electrode active materials must be used. stomach. Among existing layered cathode active materials, the material with the highest capacity is LiNiO2. Although it is rated 2 (275mAh / g), it is prone to structural breakdown during charging and discharging, and there is a problem with oxidized water. Currently, its low thermal stability makes commercialization difficult.

[0004] To solve this problem, other stable transition metals can be added to the unstable Ni site. (Co, Mn, etc.) must be substituted, and for this reason, Co and Mn were substituted. A ternary NCM system was developed. However, in the case of ternary NCMs, thermal safety decreases as the Ni content increases. ru. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Therefore, the present inventors control the structure of primary particles on the surface of layered secondary particles to control the surface of the positive electrode. We propose a method to suppress the decomposition reaction of the electrolyte in the cathode. This will improve the thermal stability of the positive electrode active material. It can improve overall health. [Means for solving the problem]

[0006] In one embodiment of the present invention, lithium metal oxide particles are in the form of secondary particles containing primary particles. The surface of the secondary particle is a child of the primary particle and the virtual center of the primary particle. A plate in which the narrowest angle between the point and the line connecting the point and the center point of the secondary particle is 60 to 90 degrees. The present invention provides a positive electrode active material containing primary particles of a specific shape.

[0007] The surface of the secondary particle refers to the outermost part of the secondary particle that is formed by the primary particle.

[0008] Figure 1 is a schematic diagram of secondary particles according to one embodiment of the present invention.

[0009] As shown in Figure 1, to define the orientation of the primary particle arrangement, a primary particle is defined as plate-shaped if the narrowest angle between the c-axis of the primary particle and the line connecting the imaginary center point of the primary particle and the center point of the secondary particle is between 60 and 90°. More specifically, it may be between 70 and 90°. On the other hand, as can be seen in Figure 1, the c-axis represents the long axis of the primary particle. Furthermore, primary particles with angles of 0° or more and less than 60° are defined as needle-shaped. More specifically, angles of 0° or more and 20° or less may also be defined as needle-shaped.

[0010] The plate-shaped particles on the surface of the secondary particles suppress side reactions with the electrolyte, thereby reducing the positive electrode active material This can improve the thermal stability of the device.

[0011] More specifically, the circle at the center point of the secondary particle, based on 50% of the radius of the secondary particle. For a given area of ​​100% of the total area, the area occupied by the plate-shaped primary particles is 20% or more. It may be present. More specifically, it may be 30% or more of the area.

[0012] Specifically, FIG. 2 is a SEM photograph of secondary particles according to an embodiment of the present invention.

[0013] As shown in FIG. 2, after setting a circle based on the center of the secondary particle, the area of the plate-shaped primary particles inside the circle can be calculated. At this time, as shown in FIG. 2, the area occupied by the plate-shaped primary particles may be 20% or more in area. In this case, as described above, the side reaction with the electrolytic solution can be effectively controlled. More preferably, it may be 50% or more in area, and more preferably, it may be 70% or more in area. The upper limit may be that 100% of the total area is plate-shaped particles, but in reality, a part of needle-shaped particles exists, and the plate-shaped particles can exist at 95% or less in area. With respect to the area of the circle formed by the radius of the secondary particle at 50% of the radius of the secondary particle at the center point of the secondary particle, the average length of the plate-shaped primary particles existing within the area may be 750 nm to 1.2 5 μm.

[0014] The length of the plate-shaped primary particles means the length in the longest direction of the particles. When the average length of the primary particles satisfies the above range, the target battery characteristics can be ensured. % of the area formed by the circle with a radius of 50% of the radius of the secondary particle at the center point of the secondary particle, the average length of the plate-shaped primary particles existing within the area may be 750 nm to 1.2 5 μm.

[0015] The length of the plate-shaped primary particles means the length in the longest direction of the particles. When the average length of the primary particles satisfies the above range, the target battery characteristics can be ensured. When the average length satisfies the above range, the target battery characteristics can be ensured.

[0016] In addition, inside the secondary particle, the c-axis of the primary particle; the narrow angle among the angles between the virtual point at the center of the primary particle and the straight line connecting the center point of the secondary particle is 0 or more and less than 60° It can include needle-shaped primary particles. More specifically, it may be needle-shaped primary particles with an angle of 0 to 20°. It can include needle-shaped primary particles with an angle of 0 to 60°. More specifically, it may be needle-shaped primary particles with an angle of 0 to 20°. It may be needle-shaped primary particles with an angle of 0 to 20°.

[0017] More specifically, inside the secondary particle, the needle-shaped particles are arranged toward the center of the secondary particle It may also be a radial structure.

[0018] A concentration gradient in which the nickel concentration within secondary particles decreases from the interior towards the surface. If present, such an internally oriented structure can be formed.

[0019] In this case as well, the core at the very center of the secondary particle is the center where the nickel concentration is constant. It may contain a portion. This is appropriate when the method of blending raw materials is used during the manufacturing stage of the precursor described later. It can be controlled precisely.

[0020] More specifically, the nickel content in the metal within the secondary particles is 80 mol% or less. It may be higher. Higher than what can be obtained with existing positive electrode active materials containing 50 mol% or less nickel. The nickel concentration can be increased to improve output characteristics.

[0021] In another embodiment of the present invention, a metal precursor is obtained by adding an aqueous solution of a metal salt to a coprecipitation reactor. Steps: and after mixing the metal precursor and lithium raw material, calcining is performed to obtain a positive electrode active material. The step includes adding an aqueous solution of the metal salt in the coprecipitation reactor to obtain a metal precursor. Furthermore, for a total reaction time of 100 hours, the pH at the end of the reaction ranges from 1 to 30 hours. The present invention provides a method for producing a positive electrode active material by changing the conditions.

[0022] More specifically, a method in which the pH at the end of the reaction is changed during the stage in which the precursor is obtained by coprecipitation. This can be provided. At this time, the reaction end time is within 100% of the total reaction time. This can mean 1 to 30 hours from the last end time.

[0023] More specifically, the reaction completion time is the last completion time out of 100% of the total reaction time. The interval can be 1-10 hours or 1-5 hours.

[0024] This is the shape of the plate-like primary particles on the surface of the positive electrode active material, which is the embodiment of the present invention mentioned above. It can influence the outcome and allow for appropriate control to meet the desired specifications. Specifically, in the step of adding an aqueous solution of metal salt to the coprecipitation reactor to obtain a metal precursor, The difference between the reaction start pH and the reaction end pH may be 0.1 to 0.8.

[0025] More specifically, relative to the total reaction time of 100 hours, the reaction completion time is 1 to 30 hours. Within a range of %, the pH condition can be adjusted to be 0.1 to 0.8 higher. As a result, plate-shaped particles can be uniformly formed on the surface of the secondary particles.

[0026] More specifically, the rate of adjustment of the pH conditions is 0.0016 to 0.0133 pH / mil n is also acceptable. More specifically, 0.0066 to 0.0133 pH / min. That's good too.

[0027] These process conditions will be explained in more detail in the examples described later.

[0028] In another embodiment of the present invention, a positive electrode containing a positive electrode active material according to the present embodiment of the present invention described above. ;negative electrode containing negative electrode active material;and electrolyte located between the positive electrode and the negative electrode;containing lithium We provide lithium-ion secondary batteries.

[0029] The description of the positive electrode active material is the same as that of the embodiment of the present invention described above, and is therefore omitted. do.

[0030] The positive electrode active material layer may include a binder and a conductive material.

[0031] The binder ensures that the positive electrode active material particles adhere well to each other and that the positive electrode active material is charged with current. It plays a role in ensuring good adhesion to the electrolytic material.

[0032] The conductive material is used to impart conductivity to the electrode, and the constituent Any electronically conductive material that does not undergo chemical changes can be used in the pond. It is Noh.

[0033] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active The material layer contains the negative electrode active material.

[0034] The negative electrode active material is a material that can reversibly insert / deinsert lithium ions, lithium Metals, alloys of lithium metals, materials that can be doped and dedoped with lithium, or transition metals Contains genus oxides.

[0035] The material that can reversibly insert / decompress lithium ions is a carbon material, Any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used. Typical examples include using crystalline carbon, amorphous carbon, or a combination of both. It is possible.

[0036] The aforementioned lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn Alloys with metals selected from the group consisting of the above can be used.

[0037] Examples of materials that can be doped and dedoped with lithium include Si and SiO x (0 <x< 2) Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element) Elements selected from the group consisting of elements, transition metals, rare earth elements, and combinations thereof. Yes, not Si), Sn, SnO2, Sn-Y (where Y is an alkali metal, alkali Earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof Examples include elements selected from a group (and not Sn).

[0038] Examples of the aforementioned transition metal oxides include vanadium oxide and lithium vanadium oxide. Furthermore, the negative electrode active material layer contains a binder and selectively further contains a conductive material. That's good too.

[0039] The binder ensures that the negative electrode active material particles adhere well to each other and that the negative electrode active material is charged with current. It plays a role in ensuring good adhesion to the electrolytic material.

[0040] The conductive material is used to impart conductivity to the electrode, and the constituent Any electronically conductive material that does not undergo chemical changes can be used in the pond. It is Noh.

[0041] The current collector may be copper foil, nickel foil, stainless steel foil, titanium foil, or nickel Foam, copper foam, polymer substrate coated with conductive metal, and You can use one selected from the group consisting of these combinations.

[0042] The negative electrode and positive electrode are prepared by mixing an active material, a conductive material, and a binder in a solvent to produce an active material composition. The electrode is manufactured by applying this composition to a current collector. Since this is a widely known topic in the field, a detailed explanation will be omitted in this specification. The solvent is For example, N-methylpyrrolidone can be used, but it is not limited to this. do not have.

[0043] The electrolyte comprises a non-aqueous organic solvent and a lithium salt.

[0044] The non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move. To fulfill one's role.

[0045] The aforementioned lithium salt dissolves in an organic solvent and acts as a source of lithium ions within the battery. This enables the basic operation of a lithium secondary battery, and the transfer of lithium ions between the positive and negative electrodes. It is a substance that plays a role in promoting movement.

[0046] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Examples of separators include polyethylene, polypropylene, and polyvinylidene fluoride. A sid or multilayer film of two or more layers of these materials can be used, and polyethylene / polypropylene Two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, Mixed multilayer films such as polypropylene / polyethylene / polypropylene 3-layer separators. It goes without saying that it can be used.

[0047] Lithium-ion batteries are classified as lithium-ion batteries depending on the type of separator and electrolyte used. They are classified into lithium-ion polymer batteries and lithium polymer batteries, and depending on their form, they are round They are classified into cylindrical, rectangular, coin-shaped, pouch-shaped, etc., and depending on the size, they are available in bulk type and thin film type. They can be divided into two types. The structure and manufacturing methods of these batteries are widely known in this field. I will omit the detailed explanation. [Effects of the Invention]

[0048] In one embodiment of the present invention, the positive electrode active material has a plate-like surface with low reactivity that comes into contact with the electrolyte, This suppresses the decomposition reaction of the electrolyte on the surface of the positive electrode. Reducing these side reactions in the electrolyte improves the thermal safety of the positive electrode active material. More specifically, during DSC analysis, the peak temperature increases and the total heat generation decreases, indicating thermal safety. This allows us to provide a positive electrode active material with improved properties. [Brief explanation of the drawing]

[0049] [Figure 1] This is a schematic diagram of secondary particles according to one embodiment of the present invention. [Figure 2] This shows the shape of primary particles present on the surface of the positive electrode active material in Example 1. [Figure 3] This shows the shape of primary particles present on the surface of the positive electrode active material in Example 3. [Figure 4] This shows the shape of primary particles present on the surface of the positive electrode active material in Comparative Example 1. [Figure 5] This is the cross-sectional shape of the positive electrode active material in Example 1. [Figure 6] This is the cross-sectional shape of the positive electrode active material in Example 3. [Figure 7] This is the cross-sectional shape of the positive electrode active material in Comparative Example 1. [Modes for carrying out the invention]

[0050] The embodiments of the present invention will be described in detail below. However, these are presented as examples only. And by no means is the present invention limited, and the present invention is only within the scope of the claims described below. It is defined.

[0051] (Example 1) Production of a positive electrode active material with 88 mol% Ni 1) Preparation of metal salt solutions First, the nickel raw material is NiSO4·6H2O, and the cobalt raw material is C Using oSO4·7H2O, and MnSO4·H2O as the manganese raw material, Ni, C Two metal salt aqueous solutions were prepared with different concentrations of o and Mn. The first metal salt aqueous solution for core formation is prepared by dipping (Ni) in distilled water. 0.98 Co 0.01 Mn 0.01 The above-mentioned raw materials were mixed to satisfy the stoichiometric molar ratio of (OH)2. Independently, the second metal salt aqueous solution for shell formation is prepared in distilled water (Ni 0. 64 Co 0.23 Mn 0.13 Each of the above ingredients satisfies the stoichiometric molar ratio of (OH)2. The ingredients were mixed together.

[0052] 2) Co-precipitation process A coprecipitation reactor is prepared in which two metal salt aqueous solution supply tanks are connected in series, and each gold The first metal salt aqueous solution and the second metal salt aqueous solution were charged into the metal salt aqueous solution supply tank. After adding distilled water to the coprecipitation reactor, the reactor was stirred while maintaining a constant temperature. Furthermore, NH4(OH) is used as a chelating agent, and NaOH solution is used as a pH adjuster. did. At this time, the initial pH inside the reactor during the reaction was set to 11.2.

[0053] In this way, the reactor, in which the pH is kept constant and the chelating agent is supplied, is connected in series with the following: The timing and amount of each metal salt solution added from two separate metal salt aqueous solution supply tanks were adjusted. Specifically, while adding the first metal salt aqueous solution at a rate of 0.4 liters / hour, the precipitate The coprecipitation reaction was carried out until the diameter reached about 11.1 μm. At this time, the flow rate was adjusted so that the average residence time in the solution reactor was about 10 hours. After the reaction reached a steady state, a steady-state duration was given to the reactants to obtain a coprecipitate compound with a higher density.

[0054] Next, while changing the mixing ratio of the first metal salt aqueous solution and the second metal salt aqueous solution, the total supply solution was introduced at 0.4 liters / hour. The supply rate of the first metal salt aqueous solution was gradually decreased at 0. 05 liters / hour, and the supply rate of the second metal salt aqueous solution was gradually increased at 0.35 liters / hour. At this time, the flow rate was adjusted so that the average residence time in the solution reactor was within 20 hours, and finally, the coprecipitation reaction was carried out until the diameter of the precipitate reached 16.0 μm. At this time, the pH was adjusted high to the range of 12.0 one hour before the end of the reaction. The pH adjustment rate was 0.0133 pH / min.

[0055] [[ID=-28]]3) Post-treatment process The precipitate obtained by the series of coprecipitation processes was filtered, washed with water, and then dried in an oven at 100 °C for 24 hours to produce a precursor of active material with a composition of (Ni Co 0.88 0. 095 Mn 0.025 )(OH)2 and an average particle size of 16.0 μm.

[0056] 4) Calcination process There is a core-shell concentration gradient, and a precursor having a composition of Ni 0.88 Co 0.095 Mn 0.025 (OH)2 and ZrO2 (Aldrich, 4N, Zr concentration 3,400 pp​​​​​​ (Based on m), Al(OH)3 (Aldrich, 4N, Al concentration standard 140 ppm) Mix first, then add LiOH·H2O (Samchun Chemical, batt After mixing the ery grade again in a molar ratio of 1:1.05, in a furnace... It was placed in a chamber and fired while oxygen was introduced.

[0057] Subsequently, the material was allowed to cool naturally, and the positive electrode active material was produced by pulverization and classification.

[0058] (Example 2) Production of a positive electrode active material with 88 mol% Ni When preparing raw materials, (Ni 0.88 Co 0.095 Mn 0.025 )(OH)2 In addition to preparing the mixture to satisfy the molar ratio, the reaction start pH during the coprecipitation step was adjusted to 11.2. The pH was adjusted to a high level of 11.8 one hour before the end of the reaction, and pH adjustment The positive electrode active material was manufactured in the same manner as in Example 1, except that the rate was adjusted to 0.01 pH / min. did.

[0059] (Example 3) Production of a positive electrode active material with 88 mol% Ni During the coprecipitation step, the reaction start pH was adjusted to 11.2, and the p 1 hour before the end of the reaction was measured. The points where H was adjusted to the range of 11.6, and the pH adjustment rate was adjusted to 0.0066 pH / min. Except for the adjustments made, the positive electrode active material was manufactured in the same manner as in Example 2.

[0060] (Example 4) Production of 88 mol% Ni cathode active material During the coprecipitation step, the reaction start pH was adjusted to 11.2, and the p 1 hour before the end of the reaction was measured. The points where H was adjusted to the range of 11.4, and the pH adjustment rate was adjusted to 0.0033 pH / min. Except for the adjustments made, the positive electrode active material was manufactured in the same manner as in Example 2.

[0061] (Comparative Example 1) Production of a positive electrode active material with 88 mol% Ni Except for the fact that the pH was maintained at 11.0 during the reaction in the coprecipitation step, Example 2 is the same. The positive electrode active material was manufactured in the same manner.

[0062] [Table 1]

[0063] (Experimental Example 1) Surface shape analysis of the positive electrode active material (SEM) SEM analysis was performed on the positive electrode active materials of Example 1, Example 3, and Comparative Example 1. The shape of primary particles present on the surface was observed.

[0064] Figure 2 shows the shape of primary particles present on the surface of the positive electrode active material in Example 1, which are plate-shaped. It was confirmed that the secondary particles uniformly surrounded the entire surface of the positive electrode active material. The surface (c-axis surface) is a surface where Li desorption / insertion reactions do not occur, therefore, the surface of the positive electrode is electrically charged. It is presumed that the decomposition reaction of the dissolution was suppressed.

[0065] Figure 3 shows the shape of primary particles present on the surface of the positive electrode active material in Example 3, which are plate-shaped. Subatomic particles and needle-shaped particles are mixed on the surface of the positive electrode active material.

[0066] Figure 4 shows the shape of primary particles present on the surface of the positive electrode active material of Comparative Example 1, which are needle-shaped. The particles are uniformly distributed. This is the shape typically observed when manufacturing positive electrode active materials. It is similar to that.

[0067] (Experimental Example 2) Shape analysis of the cross-section of the positive electrode active material (TEM) The positive electrode active materials of Example 1, Example 3, and Comparative Example 1 were cut crosswise using FIB, and TEM was used. The shape distribution of primary particles in the cross-section of the cathode material was observed using an analytical instrument.

[0068] Figure 5 shows the cross-sectional shape of the positive electrode active material of Example 1, and Figure 6 shows the cross-sectional shape of the positive electrode active material of Example 3. Figure 7 shows the cross-sectional shape of the positive electrode active material of Comparative Example 1. In all three examples (Example 1, Example 3, and Comparative Example 1), the arrangement of primary particles within the positive electrode active material consisted of needle-shaped particles. Numerous needle-shaped particles are observed, and they exhibit a radial morphology, arranged toward the center of the secondary particles.

[0069] However, in the case of the arrangement of primary particles on the surface of the positive electrode active material, Comparative Example 1 is similar to the interior and has needles. The shape is shown, but in the case of Example 3, primary particles showing a plate-like shape and needle-like shape are shown. It can be confirmed that primary particles and other particles are present together. It can be confirmed that the positive electrode active material in Example 1 contains a greater proportion of plate-shaped particles.

[0070] In Examples 1-4 and Comparative Example 1, primary particles having a plate-like shape are found on the surface of the positive electrode active material. We examined how much of the surface area it occupied. This was confirmed using the following method.

[0071] As shown in Figure 2, the SEM image of the secondary particle is used as a reference, and the two points at the center of the secondary particle The area occupied by the plate-shaped particle relative to 100% of the area of ​​a circle based on 50% of the radius of the next particle. The product was calculated.

[0072] [Table 2]

[0073] (Experimental Example 3) Differential Scanning Calorimetry in Charged State Calorimetry, DSC) The positive electrode active materials of Examples 1-4 and Comparative Example 1 were used in the manufacturing and charging of coin cells. The device was disassembled, and the thermal safety of the positive electrode active material was analyzed using DSC.

[0074] The electrode plate slurry consists of: Positive electrode: conductive material (denka black): binder (PVDF) The ratio of KF1100 is 92.5:3.5:4 wt%, and the solid content is approximately 30%. Adding NMP (N-Methyl-2-pyrrolidone) to the slurry viscosity I made adjustments. The manufactured slurry is coated onto a 15μm thick aluminum foil using a doctor blade method. After processing, it was dried and then rolled. The electrode loading amount is 14.6 mg / cm³. 2 The rolling density is 3.1 g / cm³. 3 in Yes, it was there. The electrolyte was 1M LiPF6in ethylene carbonate:dimethyl carbonate. Using ethyl methyl carbonate = 3:4:3 (vol%), a polypropylene separation membrane A coin cell was manufactured using a lithium anode (200um, Honzo metal). The charging conditions are CC / CV 2.5~4.25V, 1 / 20C cut-off. there were. Afterward, the coin cell was disassembled in a dry room, and 10 mg of positive electrode active material was collected and DSC was used. An analysis was conducted.

[0075] DSC analysis involves heating from 25°C to 400°C at a rate of 5°C / min while the exothermic reaction begins. After analyzing the set temperature, the peak temperature at which heat generation is maximum, and the total heat generation, the results are shown in the table below. I summarized it in section 3.

[0076] (Experimental Example 4) Evaluation of electrochemical properties The positive electrode active materials of Examples 1-4 and Comparative Example 1 were prepared in the same manner as in Experimental Example 3 for a 2032 coin-type electrode. After manufacturing the half-cells, they are aged at room temperature (25°C) for 10 hours, followed by charging and discharging. They went on strike.

[0077] Capacity evaluation was based on a reference capacity of 215 mAh / g, with charge / discharge conditions of CC / CV 2.5~4.2. A 5V, 1 / 20C cutoff was applied. The initial capacity was 0.2C charge / 0.2C discharge. It was done under certain conditions.

[0078] [Table 3]

[0079] From Table 3 above, the active material in the examples shows an increase in peak temperature and a decrease in total heat generation, resulting in thermal stability. It can be seen that overall quality has improved.

[0080] [Table 4]

[0081] As can be seen from Table 4 above, the positive electrode active material according to the embodiment of this application has thermal stability as shown in Table 3. Despite significant improvements, it exhibits charge / discharge capacity and efficiency at a level equivalent to Comparative Example 1. This can be understood.

[0082] The present invention is not limited to the above embodiments and can be manufactured in a variety of different forms. It is possible, and a person with ordinary skill in the art to which the present invention belongs will understand the technical concept of the present invention. It is understood that it can be implemented in other specific forms without changing the original concept or essential features. Therefore, the examples described above are illustrative in all respects and are not limited to... You must understand that it does not exist.

Claims

1. A method for producing a positive electrode active material, The step of adding an aqueous solution of metal salt to a coprecipitation reactor to obtain a metal precursor; and The step of mixing the metal precursor and lithium raw material and then calcining to obtain a positive electrode active material; In the step of adding an aqueous metal salt solution to the coprecipitation reactor to obtain a metal precursor, For a total reaction time of 100 hours, the pH condition was adjusted to be 0.1 to 0.8 higher for a range of 1 to 30 hours after the end of the reaction. The positive electrode active material is These are lithium metal oxide particles, which are in the form of secondary particles containing primary particles. The surface of the secondary particle includes plate-shaped primary particles such that the narrowest angle between the c-axis of the primary particle and the line connecting a virtual point at the center of the primary particle and the center point of the secondary particle is 60 to 90°. With respect to 100% of the area of ​​a circle based on 50% of the radius of the secondary particle at the center point of the secondary particle, The area occupied by the plate-shaped primary particles is 20% or more. A method for producing a positive electrode active material, wherein the interior of the secondary particles contains needle-shaped primary particles in which the narrow angle between the c-axis of the primary particles and the straight line connecting a virtual point at the center of the primary particles and the center point of the secondary particles is 0° or more and less than 60°.

2. The method for producing a positive electrode active material according to claim 1, wherein the difference between the reaction start pH and the reaction end pH in the step of adding the metal salt aqueous solution in the coprecipitation reactor to obtain a metal precursor is 0.1 to 0.

8.

3. The method for producing a positive electrode active material according to claim 1, wherein the rate of adjustment of the pH conditions is 0.0016 to 0.0133 pH / min.

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